Green Chemistry and Sustainabiity Pulp & Paper

Pratima
Bajpai
Green
Chemistry and
Sustainability
in Pulp and
Paper Industry
Green Chemistry and Sustainability in Pulp
and Paper Industry
Pratima Bajpai
Green Chemistry
and Sustainability in Pulp
and Paper Industry
Pratima Bajpai
C-103 Thapar Centre for Industrial R&D
Consultant (Pulp and Paper)
Patiala, India
ISBN 978-3-319-18743-3 ISBN 978-3-319-18744-0 (eBook)

DOI 10.1007/978-3-319-18744-0
Library of Congress Control Number: 2015942906
Springer Cham Heidelberg New York Dordrecht London

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Preface
Rising raw material prices, increasing waste disposal costs and expanding legislation
are the major drivers behind the rise of sustainable technologies. Producers around
the world are forced to evaluate their production processes and to search for alterna-
tive technologies with lower environmental impact. A comprehensive technology
mapping can help producers to compare sustainable technologies and to select via-
ble alternatives.
With increasing regulatory pressure and growing market demand for better prod-
ucts, the pulp and paper industry faces many challenges and must find new ways to
improve environmental and process performance and reduce operating costs. There
has been a growing demand in the pulp and paper industry to adopt waste minimiza-
tion strategies in order to create a minimum impact mill. A minimum impact mill
does not strictly mean a zero-discharge mill, but rather one which either has no
discharge or whose effluent discharge has a minimum or no impact on the environ-
ment. The goal of minimum impact mills is to minimize natural resource consump-
tion (wood, water, energy) and minimize the quantity and maximize the quality of
releases to air, water and land taking into account economic aspects and working
environments. The minimum impact mill makes optimal use of its raw materials;
reduces air emissions, water usage, and waste generation; and is a net producer of
electricity. The vision of minimum impact manufacturing has captured the imagina-
tions of industry leaders and the environmental community alike. This book gives
updated information on minimum impact mill technologies which can meet the
environmental challenges of the pulp and paper industry and describes some of the
newest twenty first-century fibre lines.
Patiala, India Pratima Bajpai
v
Contents
1 General Background ................................................................................. 1

References ................................................................................................... 8
2 Basic Overview of Pulp and Paper Manufacturing Process ................. 11
2.1 Raw Material Preparation ................................................................ 14
2.2 Pulping ............................................................................................. 15
2.2.1 Chemical Pulping ................................................................. 15
2.2.2 Mechanical Pulping.............................................................. 17
2.2.3 Semi-chemical Pulping ........................................................ 18
2.2.4 Secondary Fibre Pulping ...................................................... 19
2.2.5 Dissolving Kraft and Sulphite Pulping Processes ................ 20
2.2.6 Non-wood Pulping ............................................................... 20
2.3 Pulp Washing.................................................................................... 21
2.4 Pulp Screening, Cleaning and Fractionation .................................... 23
2.5 Bleaching.......................................................................................... 23
2.6 Chemical Recovery .......................................................................... 26
2.6.1 Black Liquor Concentration ................................................. 26
2.6.2 Recovery Furnace................................................................. 26
2.6.3 Causticizing and Calcining .................................................. 27
2.7 Stock Preparation and Papermaking ................................................ 27
References ................................................................................................... 37
3 Environmental Consequences of Pulp and Paper Manufacture ........... 41
3.1 Water Pollution................................................................................. 46
3.2 Atmospheric Pollution ..................................................................... 51
3.3 Sludge and Solid Waste .................................................................... 56
References ................................................................................................... 59
4 Minimum Impact Mill Technologies........................................................ 65
4.1 Emission Reduced Wood Handling.................................................. 66
4.2 Dry Debarking.................................................................................. 69
4.3 High Yield Pulping ........................................................................... 71
vii
viii Contents
4.4 Extended or Modified Cooking ........................................................ 73

4.4.1 Batch Cooking.................................................................... 74
4.4.2 Continuous Cooking........................................................... 76
4.4.3 Modifying Kraft Pulping with Additives ........................... 80
4.5 Efficient Brownstock Washing/Improved Pulp Washing ................. 84
4.6 Oxygen Delignification .................................................................... 87
4.7 Ozone Bleaching of Chemical Pulps................................................ 96
4.8 Ozone for High Yield Pulping .......................................................... 106
4.9 Elemental Chlorine-Free Bleaching (ECF) Bleaching..................... 108
4.9.1 Modified ECF Sequences ................................................... 116
4.10 Totally Chlorine-Free (TCF) Bleaching ........................................... 119
4.11 Fortification of Extraction Stages with Oxygen
and Hydrogen Peroxide .................................................................... 126
4.12 Removal of Hexenuronic Acids ....................................................... 128
4.12.1 Hot Acid Stage (Ahot) or Combined
Hot Acid and Chlorine Dioxide Stage (AD)hot ................. 129
4.12.2 High Temperature Chlorine Dioxide Stage (DHT) ............ 131
4.13 Liquor Loss Management ................................................................ 132
4.14 Condensate Stripping and Recovery ................................................ 134
4.15 Reduction of Sulphur Oxides and Nitrogen Oxides Emissions ....... 139
4.16 Electrostatic Precipitators................................................................. 142
4.17 Installation of Scrubbers on Recovery Boiler .................................. 146
4.18 Increase in the Dry Solids Content of Black Liquor ........................ 148
4.19 Incineration of Odorous Gases in the Lime Kiln ............................. 151
4.20 Installation of Low NOx Technology
in Auxiliary Boilers and the Lime Kiln ............................................ 154
4.21 Selective Non-Catalytic Reduction on Bark Boilers ........................ 156
4.22 Over Fire Air Technique on Recovery Boilers ................................. 160
4.23 Installation of Improved Washing
and Filtration of Lime Mud in Recausticizing ................................. 161
4.24 Technologies That can Help Achieve Practical
Minimum Energy Consumption ....................................................... 163
4.24.1 Impulse Technology for Dewatering of Paper.................... 163
4.24.2 Energy Efficient Thermo-Mechanical
Pulping (TMP) Processes ................................................... 165
4.24.3 New Energy Efficient Bleached Chemi-Thermo
Mechanical Pulping Processes ........................................... 166
4.24.4 Use of Enzymes During the Refining of TMP ................... 167
4.24.5 Condebelt Process .............................................................. 168
4.24.6 High Consistency Forming................................................. 170
4.24.7 Black Liquor and Hog Fuel Gasification ........................... 172
4.24.8 Partial Borate Autocaustising ............................................. 177
4.24.9 Biorefinery.......................................................................... 179
4.25 Partial System Closure ..................................................................... 180
4.25.1 Control of NPE with Partial Closure .................................. 183
Contents ix
4.26 Water Recycling/Reuse .................................................................... 187

4.27 Primary, Secondary and Tertiary Waste Treatment .......................... 192
4.27.1 Primary Treatment.............................................................. 192
4.27.2 Secondary Waste Water Treatment ..................................... 193
4.27.3 Tertiary Treatment .............................................................. 196
References ................................................................................................... 197
5 State-of-the-Art Pulp Mills ....................................................................... 217
5.1 Celulosa Arauco y Constitución S.A. Nueva Aldea, Chile .............. 219
5.2 Veracel Celulose ............................................................................... 221
5.3 Hainan Jinhai Pulp mill .................................................................... 223
5.4 Cellulosa Arauco Valdivia ................................................................ 226
5.5 APRIL/SSYMB Rizhao Greenfield Mill ......................................... 228
5.6 Aracruz, Line C, Brazil .................................................................... 230
5.7 Mercal Stendal, Germany................................................................. 231
5.8 Bowater, Catawba SC, USA ............................................................. 233
5.9 Zhanjiang Chenming Greenfield Pulp Mill, China .......................... 236
5.10 Eldorado Celulose e Papel S.A.’s
New Greenfield Pulp Mill in Três Lagoas, Brazil ............................ 236
5.11 Montes del Plata Mill in Uruguay .................................................... 237
5.12 Oji Holdings Nantong Pulp Mill Jiangsu Province, China .............. 238
5.13 Aracruz’s Pulp Line, at Their Guaiba Mill
in Rio Grande do Sul, Brazil ............................................................ 238
5.14 Ilim Group’s New Kraft Pulp Mill,
in Bratsk, Irkutsk Oblast, Russia ...................................................... 239
5.15 Metsa-Botnia, Rauma Mill ............................................................... 240
5.16 Metsa-Botnia Joutseno Mill ............................................................. 240
5.17 Stora Enso’s Nymölla Mill ............................................................... 241
5.18 UPM Fray Bentos Pulp Mill ............................................................ 242
5.19 New Projects .................................................................................... 243
References ................................................................................................... 245
6 The Future ................................................................................................. 247
References ................................................................................................... 250
Index ................................................................................................................. 251

Abbreviations
AOX Adsorbable organic halides

APMP Alkaline peroxide mechanical pulp
BCTMP Bleached chemi-thermo-mechanical pulp
BFR Bleach filtrate recovery
BLS Black liquor solids
BOD Biochemical oxygen demand
CBC Continuous batch cooking
CLB Closed loop bleaching
COD Chemical oxygen demand
CTMP Chem-thermo-mechanical pulp/pulping
DD Drum displacer
DIP Deinked pulp
DS Dry solids
DSC Dry solids content
DTPA Diethylene triamine pentaacetic acid
EDTA Ethylenediaminetetraacetic acid
EGSB Expanded granular sludge blanket
EPA Environment protection agency
ESP Electrostatic precipitator
GHG Greenhouse gas
HAPs Hazardous air pollutants
HYP High-yield pulp
IC Internal circulation reactor
MBBR Moving bed biofilm reactor
MCC Modified continuous cooking
MIM The minimum-impact mill; minimum-impact manufacturing
NSSC Neutral sulfite semi-chemical
PCDDS Polychlorinated dibenzodioxins
PCDFS Polychlorinated dibenzofurans
P-RC APMP preconditioning refiner chemical-treatment alkaline peroxide
mechanical pulp
xi
xii Abbreviations
RDH Rapid displacement heating

SS Suspended solids
TCDD Tetrachlorodibenzodioxin
TCDF Tetrachlorodibenzofuran
TEF Totally effluent-free
TMP Thermomechanical pulp/pulping
TRI Toxics release inventory
TRS Total reduced sulphur
TSS Total suspended solids
UASB Upflow anaerobic sludge blanket
VOC Volatile organic compounds
List of Figures
Fig. 2.1 Overview of kraft pulping mill with papermaking system ............. 13
Fig. 2.2 A flow diagram for a typical papermaking process ........................ 30
Fig. 2.3 Details of papermaking process...................................................... 31
Fig. 2.4 Schematic of Fourdrinier paper machine........................................ 32
Fig. 3.1 Polychlorinated dibenzodioxins (PCDD)
and polychlorinated dibenzofurans (PCDF) .................................. 49
Fig. 4.1 AQ catalytic cycle........................................................................... 80
Fig. 4.2 Benefits of using anthraquinone and surfactants ............................ 84
Fig. 4.3 Incorporation of the oxygen delignification stage
in brownstock washing and cooking liquor recovery cycle ............ 89
Fig. 4.4 Flowsheet of typical medium-consistency
oxygen delignification .................................................................... 90
Fig. 4.5 Equipment of medium-consistency oxygen delignification ........... 90
Fig. 4.6 Flowsheet of typical high-consistency oxygen delignification....... 91
Fig. 4.7 High-consistency oxygen delignification reactor ........................... 91
Fig. 4.8 Two-stage oxygen delignification ................................................... 92
Fig. 4.9 Typical OxyTrac system set up....................................................... 93
Fig. 4.10 Typical configuration of medium-consistency ozone stage ............ 100
Fig. 4.11 HC Ozone bleaching in 1990s and today........................................ 101
Fig. 4.12 Oxygen-reinforced alkaline extraction (EOP) stage ....................... 126
Fig. 4.13 Schematic of Condebelt drying process ......................................... 169
Fig. 4.14 Integrated gasification and combined cycle (IGCC) ...................... 173
Fig. 4.15 The CHEMREC DP-1 plant ........................................................... 175
Fig. 5.1 Nueva Aldea, Pulp Mill, Chile ........................................................ 220
Fig. 5.2 Veracel fibre line. ............................................................................ 222
Fig. 5.3 Hainan Jinhai pulp mill .................................................................. 224
Fig. 5.4 Celulosa Arauco y Constitucion’s new facility
in Valdivia Province, Chile ............................................................. 226
Fig. 5.5 Arauco Valdivia fibre line ............................................................... 227
xiii
xiv List of Figures
Fig. 5.6 Super batch digesters at Cellulosa Arauco Valdivia ....................... 228
Fig. 5.7 Twin roll presses at Cellulosa Arauco Valdivia .............................. 229
Fig. 5.8 The twin-wire pulp machine at Aracruz Celulose
S.A.’s new C line at its Barra do Riacho mill ................................. 231
Fig. 5.9 Recausticizing plant at Aracruz Celulose
S.A.’s new C line at its Barra do Riacho mill ................................. 232
Fig. 5.10 Evaporation plant at Stendal ........................................................... 232
Fig. 5.11 Fibre line at Catawba ...................................................................... 234
Fig. 5.12 Continuous digester, Catawba’s new fibre line,
uses low solids cooking for lowest kappa
number and highest fibre quality .................................................... 235
Fig. 5.13 Fray Bentos Pulp mill fibre line...................................................... 243
List of Tables
Table 1.1 Goals in pursuit of an environmentally

and socially sustainable paper production
and consumption system .............................................................. 5
Table 2.1 Steps involved in the manufacturing of pulp and paper ............... 13
Table 2.2 Types of pulping ........................................................................... 16
Table 2.3 Unit processes in stock preparation.............................................. 28
Table 2.4 Common pulp stock additives ...................................................... 30
Table 3.1 Important parameters followed in order to demonstrate
improvements towards a minimum impact mill ........................... 43
Table 3.2 Chlorinated organic compounds in bleach plant effluents ........... 47
Table 3.3 Regulated chlorophenols .............................................................. 47
Table 3.4 Solid waste generated in pulp and paper mills ............................. 56
Table 3.5 Generation of waste in a kraft mill ............................................... 56
Table 4.1 Measures to reduce environmental impacts
from wood handling ..................................................................... 68
Table 4.2 Important feature of HYP............................................................. 72
Table 4.3 Modified cooking principles ........................................................ 74
Table 4.4 Modified continuous cooking systems ......................................... 78
Table 4.5 World market share of modified cooking processes..................... 79
Table 4.6 Typical operating data ranges for oxygen
delignification process.................................................................. 92
Table 4.7 Effect of different delignification technologies
on kappa number and effluent COD............................................. 95
Table 4.8 Mills using ozone bleaching......................................................... 97
Table 4.9 Mills using ZeTrac technology .................................................... 102
Table 4.10 World bleached chemical pulp production: 1990–2012............... 110
Table 4.11 Modern ECF bleaching sequences ............................................... 112
Table 4.12 Chemical consumption in bleaching of softwood
kraft pulp in D(EOP)D(ED) sequence – mill results ................... 113
xv
xvi List of Tables
Table 4.13 Brightness development in different

chlorine dioxide bleaching sequences .......................................... 114
Table 4.14 Brightness development in a sequence replacing
the first D-stage with a Z-stage .................................................... 114
Table 4.15 Effect of peroxide use in a chlorine
dioxide bleaching sequence.......................................................... 114
Table 4.16 Modern bleaching sequences of eucalyptus-based
kraft pulp mills ............................................................................. 115
Table 4.17 (DZ) and (ZD) treatments of an unbleached
softwood kraft pulp ...................................................................... 117
Table 4.18 Environmental aspects of ECF and TCF – effluent quality.......... 118
Table 4.19 Environmental aspects of ECF – pulp properties ......................... 118
Table 4.20 Bleaching sequences for TCF bleaching ...................................... 120
Table 4.21 Chemical consumption in bleaching
of softwood kraft pulp in Q(OP)(ZQ)(PO) sequence ................... 120
Table 4.22 A comparison of some oxygen chemical
bleaching sequences applied to a softwood
kraft pulp when the ozone charge is 5 kg/adt ............................... 121
Table 4.23 Effect of kappa number after ozone delignification
when bleaching softwood kraft pulp
in a Q(ZQ)(PO) sequence............................................................. 121
Table 4.24 BKP mills using TCF bleaching .................................................. 122
Table 4.25 Mills using both ECF and TCF bleaching.................................... 122
Table 4.26 Advantages with oxygen-reinforced alkaline extraction .............. 126
Table 4.27 Conditions in an EOP stage.......................................................... 128
Table 4.28 Undesirable effects of HexA in bleaching ................................... 129
Table 4.29 Typical conditions for (A) hot and (AD) hot stages ..................... 130
Table 4.30 Benefits of using hot acid stage in bleached
eucalyptus kraft mills ................................................................... 131
Table 4.31 Typical pollutant loads in foul condensates
in bleached kraft mill (softwood) ................................................. 135
Table 4.32 Heat value of pollutants................................................................ 135
Table 4.33 Prominent Pulp and Paper Industry
sources of SOx and NOx (103 tons) ............................................. 140
Table 4.34 Range of observed emissions of SOx
and NOx from recovery furnace and lime kiln ............................ 141
Table 4.35 Typical noncondensable gas analysis
by volume % of an NCG gas stream ............................................ 152
Table 4.36 NOx emission from fluidised bed boilers
of paper mills using primary and/or secondary
measures for NOx reduction ........................................................ 158
Table 4.37 Kraft mills (paper grade) practising
bleach plant filtrate recovery ........................................................ 182
Table 4.38 Advantages of waste water recycling ........................................... 188
Table 4.39 Water conservation measures adopted in the pulp mill ................ 188
Chapter 1
General Background
Abstract The pulp and paper industry is one of the most important industries in the
world. The global demand for paper products is significant, evidenced by the more
than 400 million tons produced annually. In today’s world of scarce raw materials,
increasing energy costs and talent shortages, managing resources more sustainably
is becoming a potential game changer for all sectors. Pulp and paper companies
today are highly motivated to operate sustainably and there has been a growing
demand to adopt waste minimization strategies in order to create a minimum impact
mill which means a concept with a broader range of issues and challenges covering
minimisation of resource and emissions, minimising cross-media effects, taking
into account economic aspects and working environments. The general background
on Green Chemistry and Sustainability in Pulp and Paper Industry is presented.
Keywords Pulp and paper industry • Sustainability • Minimum impact mill • Waste
minimization • Emission
The pulp and paper industry is highly diversified in terms of products, raw materi-
als, product qualities, distribution channels, and end uses. RISI (2014) reports that
despite the continuous decline in North America and Europe, global paper and
board production advanced 0.8 % to reach a new record level of 403 million tonnes
in 2013. It has been predicted that global production in the pulp, paper and publish-
ing sector will increase to 500 million tonnes by 2020. Positive growth in tissue and
packaging grades continued to offset the retreat in global graphic paper production.
China has maintained the top spot for both demand and production of total paper
and board over the last 5 years, with the United States remaining in second place.
China accounted for 25 % of world demand and 26 % of global production of total
paper and board in 2013. In terms of pulp production, the United States remained
the top producing country in the world with 49.4 million tonnes in 2013. Canada
stood second, producing 17.3 million tonnes, with China a close third at 17.1 mil-
lion tonnes.
The world’s largest paper and paperboard producers are China, United States,
Japan, Germany, Canada, Finland, Republic of Korea, Indonesia, Sweden and
Brazil, whereas the largest pulp producers are United States, China, Canada, Brazil,
Sweden, Finland, Japan, Russian Federation, Indonesia and Chile.
© Springer International Publishing Switzerland 2015 1

P. Bajpai, Green Chemistry and Sustainability in Pulp and Paper Industry,
DOI 10.1007/978-3-319-18744-0_1
2 1 General Background
Inspite of the advancement of digital technology paper consumption is increasing

and growth is set to increase as demand in Asia and emerging nations increases.
New technology has resulted in a decrease in consumption of newsprint in the
United States and Western Europe. But less than half of the wood pulp produced in
2013 was made into printing, writing and newsprint paper. The rest was made into
other products including cardboard packaging, toilet tissue and paper towels.
Demand for these products is continuously increasing in emerging markets. China
has led the increase in demand. China accounted for about 15 % of global paper
demand ten years ago. Currently, it accounts for around 25 %, making it the largest
consumer of paper in the world ahead of the United States and Western Europe at 18
and 17 % respectively. Worldwide paper use has grown an average 1.7 % each year
over the past decade. Inspite of this, China’s paper use per person is still only a one
third of that in the United States (74 kg against 228 kg). Consumption is expected
to increase further as China and other emerging markets continue to grow, with an
estimated 650 million people set to join Asia’s urban population in the next 20 years.
Urbanisation tends to be associated with an increasing demand for hygiene and
consumer products containing paper, such as toilet tissue, hand towels and cleaning
wipes. Globally paper use has grown an average 1.7 % each year over the past
decade. Consumption is expected to grow at an annual rate of 2.4 % over the next
5 years, driven by emerging market demand. Recycled paper accounts for around
55–60 % of global production. However, paper can be recycled only a handful of
times before the fibres break down and become unusable. Some countries mandate
the use of non-recycled paper in certain types of packaging, for example, when it
comes into contact with food. This means that increasing demand for paper also
drives up demand for wood pulp, the main raw ingredient for new paper. The United
States is the world’s largest producer of wood pulp, followed by China and Canada.
However, global patterns of production are changing. Improved cultivation tech-
niques have significantly increased the potential yield per hectare of some species
of tree. Eucalyptus, originally from Australia, has become popular, and grows well
in Latin America – a region that is increasingly important in pulp production. Brazil,
for example, has more than doubled pulp production in the last two decades, over-
taking countries such as Sweden, Finland and Russia. Eucalyptus can grow all year
round in Brazil and reach maturity within 6–7 years. Trees in North America or
Scandinavia, where growth stops during winter, can take 25 years to be ready for
harvest. Brazil currently produces 40 % of the hardwood pulp sold worldwide. This
could increase to 60 % over the next 10 years. Though China is a significant pro-
ducer of pulp, domestic demand continues to outstrip domestic supply. Around
30 % of Brazil’s pulp exports go to China. With China’s demand for paper likely to
continue to increase, Brazil’s pulp exports to China are set to grow in the coming
years. Paper is another sector demonstrating the south-south trade flows that are
increasingly important to the global economy.
Pulp and paper production, consumption and wasting have several negative envi-
ronmental and social impacts. The pulp and paper industry is among the world’s
largest producers of air and water pollutants, waste products, and the gases that
cause climate change. It is also one of the largest users of raw materials, including
1 General Background 3
fresh water, energy, and forest fibers. Forests that are essential for clean air and
water, wildlife habitat, climate protection, spirituality, recreation and indigenous
peoples’ cultural survival – including old-growth and other ecologically important
forests – are being logged for fiber; in many places they also are being cleared for
replacement by plantations that have reduced ecological value and employ toxic
chemical herbicides and fertilizers. The pulp and paper industry also has negative
effects on the health, well-being and stability of local communities. In North
America the majority of paper products are buried in landfills or burned in incinera-
tors which result in significant pollution, forest destruction and major climate
change impacts. Industrialized nations, with 20 % of the world’s population, con-
sume 87 % of the world’s printing and writing papers (Toepfer 2002). Global pro-
duction in the pulp, paper and publishing sector is expected to increase significantly
(OECD 2001). While paper and paper products yield many benefits, due to society’s
growing demand for paper and the industry’s unacceptably large ecological foot-
print on the planet, it is necessary to transform global paper production and con-
sumption towards processes that are ecologically and socially responsible and
sustainable (Environmental Paper Network 2002). The pulp and paper industry has
undergone some important changes in environmental performance in the last three
decades. According to some observers, this is quite surprising for an industry that
has often been taken as an example of a mature sector with a low rate of innovation
(Reinstaller 2005).
Inspite of the development of information and communication technology,
paper production still remains one of the industrial activities regarded as a pointer
to industrialization and educational development worldwide, and, without any
doubt, pulp and paper production capacity is increasing (Ogunwusi and Ibrahim
2014). It is one of the high demand sectors in the world of industrial production
(Sridach 2010). In the light of this, and also in view of the increasing protectionism
of the environment, research and development in the sector have concentrated on
overcoming environmental problems associated with pulp and paper manufactur-
ing activities globally. For example pulp and paper production is regarded as the
fourth highest consumer of energy globally (Gielen and Tam 2006). It is also a
major cause of deforestation, effluent discharge, air and water pollution (Anslem
and Oluighbo 2012).
There is no single definition for sustainability, perhaps because it is a process
or journey, rather than a state or endpoint. In the academic literature there are
hundreds of definitions (Lélé 1991; Low and Gleeson 2005; Marcuse 1998;
Mawhinney 2002). Therefore the term ‘sustainable’ or ‘sustainability’ is difficult
to define and context dependant. A preferred definition of environmental sustain-
ability is “the ability to maintain things or qualities that are valued in the physical
environment” (physical environment includes the natural and biological environ-
ments) (Sutton 2004). A commonly referenced definition is from the Brundtland
Report (UN General Assembly 1987) which defines sustainable development as
“…development that meets the needs of the present without compromising the
ability of future generations to meet their own needs”. The United States
Department of Commerce defines sustainable manufacturing as “the creation of
manufactured products that use processes that minimize negative environmental

impacts, conserve energy and natural resources, are safe for employees, commu-
nities, and consumers and are economically sound.” Another organization defines
sustainable manufacturers as those who “use world-class manufacturing and envi-
ronmentally friendly practices to improve the profitability of their business and
reduce their impact on the environment.” The Organisation for Economic
Co-operation and Development (OECD) defines the general principle of sustain-
able manufacturing “to reduce the intensity of materials use, energy consumption,
emissions, and the creation of unwanted by-products while maintaining, or
improving, the value of products to society and to organizations.” The OECD also
relates the term ‘sustainable manufacturing’ to ‘eco-innovation’. The latter is
described as the trigger to developing a green economy and thus assisting manu-
facturing to become, sustainable (Sustainable Manufacturing Initiative 2011).
A sustainability issue arises whenever a valued system, object, process or attri-
bute is under threat. The existence of the valued system, object, process or attribute
could be threatened or its quality could be threatened with serious decline. In other
words there is a sustainability issue whenever there is something that is valued that
faces the risk of not being maintained. Whenever there is a strong sense of urgency,
there is always a sustainability issue involved. This urgency could relate to some-
thing that already exists or to an understood potential.
Pulp and paper companies have faced environmental issues for many years
because of the resource-intensive nature of their industry contributing to several
environmental problems which include global warming, human toxicity, eco-
toxicity, photochemical oxidation, acidification, nutrification, and solid wastes
(Blazejczak and Edler 2000). Most noticeable have been allegations from NGOs
against companies running logging activities in primary forest to supply fiber for
their chemical or mechanical pulping operations. These allegations and the com-
plaints from other civil society groups against the industry, have led governments to
strengthen environmental regulations, initially in the developed world, but currently
the regulatory trend is global. Frequently changing regulations have thus shaped the
pulp and paper industry for decades and are continuing to shape it globally. This has
resulted in many innovations – a new form of raw material, recycled fiber, to name
just one. For obvious commercial reasons, Pulp and paper companies today are also,
intrinsically highly motivated to operate sustainably, for example, to ensure a suf-
ficient flow of fiber into their mills from nearby forests or plantations.
In today’s world of scarce raw materials, increasing energy costs and talent
shortages, managing resources more sustainably will become a potential game
changer for all sectors. This is particularly true for resource intensive sectors like
the forest product industry. If pulp and paper companies address this new reality
proactively, they will both avoid unnecessary costs and capture opportunities to
create significant value. The key to success is to embed sustainability – environ-
mental, operational and even social sustainability- as an objective into every man-
agement decision, at every level of the organization. Table 1.1 shows goals in
pursuit of an environmentally and socially sustainable paper production and con-
sumption system.
Table 1.1 Goals in pursuit of an environmentally and socially sustainable paper production and
consumption system
Minimize paper consumption
Eliminate excessive and unnecessary paper consumption
Clean production
Minimize the combined impacts of water, energy, wood, and chemical usage, air, water, solid
waste, and thermal pollution across the entire paper production system including: fiber
production/sourcing, pulping, production, transportation, use, and disposal.
Eliminate harmful pulp and paper mill discharges and the use of chlorine and chlorine
compounds for bleaching.
Responsible fiber sourcing
End the use of wood fiber that threatens endangered forests.
End the clearing of natural forest ecosystems and their conversion into plantations for paper
fiber.
Source any remaining virgin wood fibers for paper from independent, third–party certified forest
managers that employ the most environmentally and socially responsible forest management and
restoration practices (Forest Stewardship Council is the only acceptable international
certification program that comes close to meeting this objective).
Use alternative crops for paper if comprehensive and credible analysis indicates that they are
environmentally and socially preferable to other virgin fiber sources.
Eliminate widespread industrial use of pesticides, herbicides and fertilizers in plantations and
fiber production.
Stop the introduction of paper fiber from genetically modified organisms
Maximize recycled content
Eliminate paper manufactured solely of virgin fiber and fundamentally reduce reliance on virgin
tree fibers.
Maximize post-consumer recycled fiber content in all paper and paper products.
Increase the use of other recovered materials example agricultural residues and pre-consumer
recycled as a fiber source in paper.
Based on www.greenamerica.org/PDF/PaperVision.pdf
Paper mills vary significantly in their environmental performance, depending on

their age, efficiency and how they are run. Minimum-impact mills are those that
minimize resource inputs (wood, water, energy and chemicals) and minimize the
quantity and maximize the quality of releases to air, water and land (Axegard et al.
1997; Pryke 2008). Paper mills can optimize their environmental performance by
implementing the
– most advanced manufacturing technologies,
– most efficient mill operations
– most effective environmental management systems.
The vision of Minimum Impact-Manufacturing has captured the imaginations of
industry and the environmental community alike (Axegard et al. 1997; Pryke 2008).
Minimum Impact-Mill is:
“A completely ecocyclic system for high quality pulp and paper production which
efficiently utilizes the energy potential of the biomass”
“An ecologically sound industry, producing recyclable products from renewable
resources”
“An industry we are so proud of we encourage our grand children to join”
There is an opportunity to move public perception from “the pulp and paper
industry is the largest water consumer and biggest polluter” to “the pulp and paper
industry is ecologically sound, while producing recyclable products from renewable
resources.” However, public trust must be earned through addressing local issues
like odor, plumes and other aesthetic issues. Elimination of elementary chlorine free
bleaching (ECF) or totally chlorine free bleaching (TCF) bleaching effluent is not
necessary for environmental protection, nor is it necessarily the place to start.
Process development toward the minimum-impact mill should begin by concentrat-
ing on minimizing releases from the pulping and recovery processes. Presently,
there are no kraft mills operating full time which completely recover all bleach plant
effluent. In other words there are no “zero” effluent kraft mill bleach plants. The
minimum-impact mill does not mean “no bleach plant effluent,” or “zero effluent,”
nor is it exclusive to one bleaching technology. It is a much bigger concept (Hanninen
1996; Elo 1995). The minimum-impact mill is one which:
– Maximizes pulp yield and produces high quality products which can be easily
recycled, and/or safely combustible
– Minimizes water consumption
– Minimizes wastes – gaseous, liquid and solid – and disposes of them optimally
– Maximizes the energy potential of the biomass
– Optimizes capital investment
– Creates sustainable value to shareholders, customers, employees and to local,
regional, and national communities
The industry’s environmental progress over the last few decades, while maintaining
economic viability provides confidence that the minimum-impact mill of the future
will be realized. Several strategies have been proposed (Erickson 1995; Paper Task
Force 1995; Maples et al. 1994; Ahlenius et al. 1994; Kinell et al. 1996; Wearing
1994; Albert 1993; Gleadow et al. 1996; Basta et al. 1996). These are:
– The Minimum-Impact Mill – MIM
– Minimum-Impact Manufacturing – MIM
– Bleach Filtrate Recovery – BFR®
– Closed Loop Bleaching – CLB
– The Eco-Balanced Pulp Mill
– Progressive Systems Closure
– Effluent Free
– Closed Cycle Technology
– Ecocyclic Pulp Mill
– Partial Mill Closure
A strong thrust within many of these process technology developments is toward

recovery and elimination of bleach plant effluent. However, a direct link between
bleaching processes and environmental responses of concern has not been demon-
strated. Furthermore, current environmental research is pointing toward other pro-
cesses within the mill, rather than bleaching, as the sources of substances causing
environmental responses. In light of such information, some have questioned the
wisdom of placing virtually exclusive emphasis on reduction or elimination of
bleach plant effluent. They ask the following questions:
Where is the evidence that these technological developments will lead to reduced
environmental impact?
Will new bleaching sequences complicate process chemistry?
Will demand for wood increase due to lower process yields?
Will energy consumption increase?
Will complicated and expensive control and back-up systems be required?
Finally there has been considerable debate as to compatibility and the merits of both
ECF and TCF based bleaching strategies within minimum-impact manufacturing
processes incorporating recycle and recovery of bleaching effluent.
Pressures to maximise energy efficiency, improve product quality, reduce envi-
ronmental impact, and optimise capital and operating costs have significantly
shaped the design of recent mills. Producers have responded to these demands by
adopting efficient, low impact designs on economies of scale that far surpass most
existing mills. Modern mills have less equipment, but are of much larger capacity
than twentieth century mills (Johnson et al. 2009). New fibrelines have been built
mainly in Asia and South America where access to fast growing raw material,
other production cost advantages, stable politics and economies, and surging
demand from the East give favourable levels of cost and return. India’s non wood
and hardwood market pulp segment must compete in the longer term with these
new fibrelines.
Minimum environmental impact is not only to have nice quality control figures.
It means a continuous effort in the direction of the zero impact. It is more difficult
to achieve the objectives when you are closer to zero. However, this must be a phi-
losophy, a conceptual way of working. With the rise in environmental awareness
due to the lobbying by environmental organizations and with increased government
regulation there is now a trend towards sustainability in the pulp and paper industry.
During the last decade, there have been revolutionary technical developments in
pulping, bleaching and chemical recovery technology. These developments have
made it possible to further reduce loads in effluents and airborne emissions. Thus,
there has been a strong progress towards minimum impact mills in the pulp and
paper industry. The minimum-impact mill is a holistic manufacturing concept that
encompasses environmental management systems, compliance with environmental
laws and regulations and manufacturing technologies. The minimum impact mill is
a much bigger concept which means that significant progress must be made in the
following areas:
– Water Management
– Internal Chemical Management
– Energy Management
– Control and Discharge of Non-Process Elements
– Removal of Hazardous Pollutants
Sustainable pulp and paper manufacturing requires a holistic view of the manu-
facturing process. This concept begins with a vision and commitment to a long-term
goal that should guide all decisions about the direction of both the mill operations
and the selection of manufacturing technologies. Investing in manufacturing pro-
cesses that prevent pollution and practicing good environmental management go
hand-in-hand. A poorly run mill may not be able to reap the environmental benefits
that result from installing advance pollution prevention technologies. Outdated
manufacturing technologies, however, will limit the ability of a well run mill to
achieve continuous environmental improvement. Adopting the long-term goal of
operating minimum impact mills allows suppliers to develop measurable and cost
effective investment strategies that provide environmental benefits and improve
economic competitiveness. Pulp and paper mills routinely make investments in
individual pieces of equipment and periodically undergo more costly renovations
and expansions. The strategic application of the minimum impact mill concept will
allow manufacturers to integrate decisions that affect manufacturing costs, produc-
tivity, quality and environmental impacts.
The minimum-impact mill is a dynamic and long-term goal that will require an
evolution of technology in some cases. Many factors will affect the specific technol-
ogy pathway and the rate at which individual mills will progress toward this goal.
These factors include the products manufactured at the mill, the types of wood that
are available, the mill’s location, the age and configuration of equipment, operator
expertise, the availability of capital and the stages a mill has reached in its capital
investment cycle. Some mills, for example, will install the most advanced current
technologies with a relatively low capital investment within the next 5 years.
Responsible pulp and paper operations can bring many benefits to forests, local
economies and people, particularly in rural areas. Many pulp and paper companies
are demonstrating leadership in responsible forestry and plantation management as
well as in clean manufacturing processes and recycled content.
References
Ahlenius L, Alfthan CJ, Wikberg E (1994) Closing up a TCF bleach plant. In: CPPA 1994 interna-
tional pulp bleaching conference proceedings, Vancouver, Canada, June 1994
Albert R (1993) Technical and economic feasibility of the effluent-free bleached kraft pulp mill.
In: 1993 international non chlorine bleaching conference proceedings, Hilton Head, SC, USA,
Mar 1993
Anslem EO, Oluighbo SN (2012) Mitigating the impact of climate change through waste recy-
cling. Res J Environ Earth Sci 4(8):776–781
References 9
Axegard P, Carey J, Folke J, Gleadow P, Gullichsen J, Pryke DC, Reeve DW, Swan B, Uloth V
(1997) Minimum-impact mills: issues and challenges. In: Proceedings of the minimum effluent
mills symposium. Tappi Press, Atlanta, pp 529–541
Basta J, Wäne G, Herstad-Svärd S, Lundgren P, Johansson NG, Edwards L, Gu Y (1996) Partial
closure in modern bleaching sequences. In: Tappi 1996 international pulp bleaching conference
proceedings, Washington, DC, USA
Blazejczak J, Edler D (2000) Elements of innovation-friendly policy regimes – an international
comparative study for the paper industry. In: Hemmelskamp J, Rennings K, Leone F (eds)
Innovation-oriented environmental regulation: theoretical approaches and empirical analysis,
vol 10, ZEW economic studies. Physica Verlag, Heidelberg/New York, pp 175–192
Elo A (1995) Minimum impact mill. In: Third global conference on paper and the environment,
London, 26–28 March 1995, pp 105–110
Environmental Paper Network (2002) A common vision for transforming the paper industry: striv-
ing for environmental and social sustainability. 20 November 2002
Erickson D (1995) Closing up the bleach plant: striving for a minimum-impact mill. In: Tappi/NC
state emerging pulping & bleaching technologies workshop, Raleigh, NC, USA, May 1995
Gielen D, Tam C (2006) Energy use, technologies and CO2 emissions in the pulp and paper indus-
try. In: Energy efficient technologies and CO2 reduction potentials in the pulp and paper indus-
try in collaboration with WBCSD, IEA, Paris, 9 October 2006
Gleadow P, Vice K, Johnson A, Sorenson D, Hastings C (1996) Mill applications of closed-
cycle technology. In: Proceedings, 1996 international non-chlorine bleaching conference,
March 1996
Hanninen E (1996) Minimum impact mill. Pap Asia 12(1):24–29
Johnson T, Johnson B, Gleadow P, Araneda H, Silva F, Aquilar R, Hsiang C (2009) 21st century
fibrelines. Pulp Pap-Can 110(9):26–31
Kinell P, Ström K, Swan B (1996) Sustainable development in Stora pulp mills. In: Proceedings,
1996 international non-chlorine bleaching conference, March 1996
Lélé S (1991) Sustainable development: a critical review. World Dev 19(6):607–621
Low N, Gleeson B (2005) If sustainability is everything, maybe it’s nothing? In: State of
Australian cities conference, Griffith University, Brisbane, 30 November–2 December
2005, pp 01-1–01-10
Maples G, Ambady R, Caron JR, Stratton S, Vega Canovas R (1994) BFR: a new process toward
bleach plant closure. TAPPI J 77(11):71–80
Marcuse P (1998) Sustainability is not enough. Environ Urban 10(2):103–111
Mawhinney M (2002) Sustainable development: understanding the green debates. Blackwell
Publishing, Oxford
OECD (2001) Environmental outlook. OECD, Paris, p 215
Ogunwusi AA, Ibrahim HD (2014) Advances in pulp and paper technology and the implication for
the paper industry in Nigeria. Ind Eng Lett 4(10):17–29. ISSN 2224–6096 (Paper), ISSN
2225–0581
Paper Task Force (1995) Paper task force recommendations for purchasing and using environmen-
tally preferable paper, Environmental Defense Fund, 15 December 1995
Pryke D (2008) Perspectives on the pulp and paper industry. Digital Presentation
Reinstaller A (2005) Policy entrepreneurship in the co-evolution of institutions, preferences, and
technology. Comparing the diffusion of totally chlorine free pulp bleaching technologies in the
US and Sweden. Res Policy 34(9):1366–1384
RISI (2014) Global paper and board production hits record levels in 2013. In: Annual review of pulp
and paper statistics. www.risiinfo.com/…/news/…/Global-paper-and-board-production-hits-re
Sridach W (2010) The environmentally benign pulping process of non wood fibres. Suranaree J Sci
Technol 17(2):105–123
Sustainable Manufacturing Initiative (2011) www.csiro.au/…/CSIROau/…/What%20is%20
Sustainable%20Manufactur
Sutton P (2004) A perspective on environmental sustainability? Victorian Commissioner for

Environmental Sustainability, Melbourne
Toepfer K (2002) Keynote address. In: UNEP’s 7th international high level seminar on cleaner
production, 29–30 April 2002
UN General Assembly (1987) Towards sustainable development, Annex to document A/42/427,
Environment: our common future. In: Report of the World commission on environment and
development: our common future. Available at http://www.un-documents.net/ocf-02.htm
Wearing J (1994) Closed cycle design in the pulp and paper industry: current technology and
needs for future research. In: Presentation to France-Canada exchange on the paper industry
and the environment. Niagara-on-the-Lake, ON, October 1994. www.greenamerica.org/PDF/
PaperVision.pdf
Chapter 2
Basic Overview of Pulp and Paper
Manufacturing Process
Abstract Pulp and paper mills are highly complex and integrate many different
process areas including wood preparation, pulping, chemical recovery, bleaching,
and papermaking to convert wood to the final product. Processing options and the
type of wood processed are often determined by the final product.
The pulp for papermaking may be produced from virgin fibre by chemical or
mechanical means or may be produced by the repulping of paper for recycling.
Wood is the main original raw material. Paper for recycling accounts for about 50 %
of the fibres used – but in a few cases straw, hemp, grass, cotton and other cellulose-
bearing material can be used. Paper production is basically a two-step process in
which a fibrous raw material is first converted into pulp, and then the pulp is con-
verted into paper. The harvested wood is first processed so that the fibres are sepa-
rated from the unusable fraction of the wood, the lignin. Pulp making can be done
mechanically or chemically. The pulp is then bleached and further processed,
depending on the type and grade of paper that is to be produced. In the paper fac-
tory, the pulp is dried and pressed to produce paper sheets. Post-use, an increasing
fraction of paper and paper products is recycled. Non recycled paper is either land-
filled or incinerated.
Keywords Pulp and Paper industry • Pulping • Bleaching • Papermaking •

Recycling • Chemical recovery
The pulp and paper industry is one of the most important industries in the world. It
supplies paper to over 5 billion people worldwide. Originally, papermaking was a
slow and labour-intensive process. Today pulping and papermaking are driven by
capital-intensive technical equipment and high-tech and high-speed paper machines
that produce rolls of paper at a speed that may reach 2000 m/min. and with a web
width that may exceed 8 m. Paper is essentially a sheet of cellulose fibres with a
number of added constituents, when necessary, to affect the quality of the sheet and
its fitness for the intended end use. The two terms paper and board generally refer
to the weight of the product sheet (grammage) with paper ranging up to about 160
or 220 g/m2 and a heavier sheet regarded as board (cartonboard). The grammage
above which papers are called board however vary slightly between countries.
AD 105 is often cited as the year in which papermaking was invented. In that
year, historical records show that the invention of paper was reported to the Chinese
Emperor by Ts’ai Lun, an official of the Imperial Court. The modem manufacture

DOI 10.1007/978-3-319-18744-0_2
12 2 Basic Overview of Pulp and Paper Manufacturing Process
of paper evolved from an ancient art first developed in China. Although the modern
product differs considerably from its ancestral materials, papermaking retains dis-
tinct similarities to the processes developed by Ts’ai Lun. In principle, paper is
made by:
– Pulping, to separate and clean the fibres
– Beating and refining the fibres
– Diluting to form a thin fibre slurry
– Suspended in solution
– Forming a web of fibres on a thin screen
– Pressing the web to increase the density of the material
– Drying to remove the remaining moisture
– Finishing, to provide a suitable surface for the intended end use.
Pulp and paper are made from cellulosic fibres and other plant materials, although
some synthetic materials may be used to impart special qualities to the finished
product. Most paper is made from wood fibres, but rags, flax, cotton linters, and
bagasse which is a sugar cane residue are also used in some papers. Used paper is
also recycled, and after purifying and sometimes deinking, it is often mixed with
virgin fibres and reformed again into paper. Other products made from wood pulp
(cellulose) include diapers, rayon, cellulose acetate, and cellulose esters, which are
used for cloth, packaging films, and explosives. Wood is composed of cellulose,
lignin, hemicellulose, and extractives. Cellulose, comprises about 50 % of wood by
oven dry weight. This constituent is of primary interest in papermaking. Lignin
cements the wood fibres together. It is a complex organic chemical. Its structure and
properties are not fully understood. It is largely burned for the generation of energy
used in pulp and paper mills. As the chemistry of lignin becomes better understood,
what is now mostly a waste product used for fuel (some is converted to chemical
products), it could become a valuable feed stock for new chemical products. The
objective of pulping process is to remove as much lignin as possible without sacri-
ficing fibre strength, thereby freeing the fibres and removing impurities which cause
discoloration and possible future disintegration of the paper. Hemicellulose plays an
important role in fibre-to-fibre bonding in papermaking. Several extractives (exam-
ple, oleoresins and waxes) are contained in wood but do not contribute to its strength
properties; these too are removed during the pulping process. The fibre from nearly
any plant or tree can be used for paper. However, the strength and quality of fibre,
and other factors that can complicate the pulping process, varies among tree species.
In general, the softwoods (example, pines, firs, and spruces) yield long and strong
fibres that impart strength to paper and are used for boxes and packaging. Hardwoods,
on the other hand, generally have shorter fibres and therefore produce a weaker
paper, but one that is smoother, more opaque, and better suited for printing. Both
softwoods and hardwoods are used for papermaking and are sometimes mixed to
provide both strength and printability to the finished product. Figure 2.1 shows an
overview of the pulping and papermaking process.
The manufacturing of paper or paperboard can be divided into several process
areas (Table 2.1). Paper production is mainly a two-step process in which a fibrous
2 Basic Overview of Pulp and Paper Manufacturing Process 13
Chemical recovery
Wood chips 11
Screening system
Digester system Evaporator 10
1 System 4
Turpentine
Recovery 4
Oxygen delignification
System
Pulp washing 4 system
system Decker
Knotter system system
5 6
2 3
Weal black liquor

storage system
Paper making system Refiners/Cleaners Bleaching system
9 8 7
Fig. 2.1 Overview of kraft pulping mill with papermaking system. Based on USEPA (1998)
Table 2.1 Steps involved in the manufacturing of pulp and paper

Operation Processes
Raw material preparation Debarking
Chipping and conveying
Pulping Chemical pulping
Semichemical pulping
Mechanical pulping
Recycled paper pulping
Chemical recovery Evaporation
Recovery Boiler
Recausticizing
Calcining
Bleaching Mechanical or chemical pulp bleaching
Stock preparation and papermaking Preparation of stock
Dewatering
Pressing and drying
Finishing
raw material is first converted into pulp, and then the pulp is converted into paper.
The harvested wood is first processed so that the fibres are separated from the unus-
able fraction of the wood, the lignin. Pulp making can be done mechanically or
chemically. The pulp is then bleached and further processed, depending on the type
and grade of paper that is to be produced. In the paper factory, the pulp is dried and
pressed to produce paper sheets. Post-use, an increasing fraction of paper and paper
products is recycled. Nonrecycled paper is either landfilled or incinerated.
Some integrated pulp and paper mills perform multiple operations (example,
chemical pulping, bleaching, and papermaking; pulping and unbleached papermak-
ing etc.). Nonintegrated mills may perform either pulping (with or without bleach-
ing), or papermaking (with or without bleaching).
2.1 Raw Material Preparation
Wood is the primary raw material used to manufacture pulp, although other raw
materials can be used. Pulp manufacturing starts with raw material preparation,
which includes debarking (when wood is used as raw material), chipping, chip
screening, chip handling and storage and other processes such as depithing (for
example, when bagasse is used as the raw material) (Biermann 1996; Gullichsen
2000; Ressel 2006). Wood typically enters a pulp and paper mill as logs or chips and
is processed in the wood preparation area, referred to as the woodyard. In general,
woodyard operations are independent of the type of pulping process. If the wood
enters the woodyard as logs, a series of operations converts the logs into a form suit-
able for pulping, usually wood chips. Logs are transported to the slasher, where they
are cut into desired lengths, followed by debarking, chipping, chip screening, and
conveyance to storage. The chips produced from logs or purchased chips are usually
stored on-site in large storage piles. Chips are screened for size, cleaned, and tem-
porarily stored for further processing (Smook 1992).
Certain mechanical pulping processes, such as stone groundwood pulping, use
roundwood; however, the majority of pulping operations require wood chips. A uni-
form chip size (typically 20 mm long in the grain direction and 4 mm thick) is
necessary for the efficiency of the processes and for the quality of the pulp. The
chips are then put on a set of vibrating screens to remove those that are too large or
small. Large chips stay on the top screens and are sent to be re-cut, while the smaller
chips are usually burned with the bark or may be sold for other purposes. Non-wood
fibres are handled in ways specific to their composition in order to minimize degra-
dation of the fibres and thus maximize pulp yield. Non-wood raw materials are
usually managed in bales.
Two main products derive from debarking process, the chips which are the main
product and the bark that can be characterized as by-product. Bark can be used as a
fuel or it can be sold off-site for other purposes. Bark is typically used as a fuel in
burners for energy production. Other debarking methods that are being used are the
following (Ressel 2006):
– Rotary or cradle debarker
– Ring debarker
– Flail debarker
– Rosser head debarker
– Mobile debarker
2.2 Pulping 15
After the logs have been debarked, the chipping of the logs occurs in order to reduce
logs size and produce chips; a typical option for chipping is the use of a radial chip-
per. The quality of the chips is of high importance, since if the chips produced are
not homogeneous, raw material consumption will increase. Furthermore, a homog-
enized chip distribution will improve the energy performance of the system. The
next process is the screening of the produced chips in order to separate long size
chips that are not properly chipped; the screening process also contributes by remov-
ing sawdust. The recovered sawdust is also a by-product that can be burnt while the
long size chips can be re-chipped in a crusher or re-chipper. The screening process
can affect the plant’s performance. Optimizing the screening process can lead to the
production of high-quality pulp and can improve the environmental performance of
the mill by reducing pollution. In order to achieve the optimum screening perfor-
mance however, raw material consumption should be increased. Chips produced
can now be transported to the next step which is pulping. Chips transportation is
made using conveyors. Various types of conveyors exist (Ressel 2006) which are
listed below:
– Chain conveyor
– Roller conveyor
– Steel plate conveyor
– Vibrating conveyor
– Belt conveyor
– Scraper conveyor
– Screw conveyor
Storage facilities may be required for storing materials or products in some cases;
both raw material (wood) and chips produced may demand storage. Storage condi-
tions are very much important in cases where the material needs to be transported.
2.2 Pulping
During the pulping process, wood chips are separated into individual cellulose
fibres by removing the lignin from the wood (Smook 1992; Biermann 1996; Ince
2004). Table 2.2 shows the main types of pulping processes.
2.2.1 Chemical Pulping
Chemical pulping (i.e., kraft, soda, and sulphite) involves “cooking” of raw materi-
als (example, wood chips) using aqueous chemical solutions and elevated tempera-
ture and pressure to extract pulp fibres. Chemical pulps are made by cooking the
raw materials, using the kraft (sulphate) and sulphite processes (Casey 1983a).
Table 2.2 Types of pulping

Pulp grades Raw material End product use
Chemical pulps
Sulfite pulp Softwoods Fine and printing papers
and hardwoods
Kraft sulfate pulp Softwoods Bleached-printing and writing papers,
and hardwoods paperboard, unbleached-heavy packaging
papers, paperboard
Dissolving pulp Softwoods Viscose rayon, cellophane, acetate fibers,
and hardwoods and film
Semichemical pulps
Cold-caustic process Softwoods Newsprint and groundwood printing papers
and hardwoods
Neutral sulfite process Hardwoods Newsprint and groundwood printing papers
Mechanical pulps
Stone groundwood Mainly softwoods Corrugating medium
Refiner mechanical (RMP) Mainly softwoods Newsprint and groundwood printing papers
Thermomechanical (TMP) Mainly softwoods Newsprint and groundwood printing papers
Chemi-mechanical (CTMP) Mainly softwoods Newsprint, Fine Papers
Kraft pulping is by far the most common pulping process used by plants in the
United States for virgin fibre, accounting for more than 80 % of total United States
pulp production.
2.2.1.1 Kraft Pulping Process
Kraft process produces a variety of pulps. These pulps are used mainly for packag-
ing and high-strength papers and board. The Kraft process dominates the industry
because of advantages in chemical recovery and pulp strength. It represents 91 % of
chemical pulping and 75 % of all pulp produced. The kraft pulping process uses an
alkaline cooking liquor of sodium hydroxide and sodium sulphide to digest the
wood, while the similar soda process uses only sodium hydroxide. This cooking
liquor (white liquor) is mixed with the wood chips in a reaction vessel (digester).
After the wood chips have been “cooked,” the contents of the digester are discharged
under pressure into a blow tank. As the mass of softened, cooked chips impacts on
the tangential entry of the blow tank, the chips disintegrate into fibres or “pulp.” The
pulp and spent cooking liquor (black liquor) are subsequently separated in a series
of brown stock washers (EPA 2001a). A number of pulp grades are commonly pro-
duced, and the yield depends on the grade of product. Unbleached pulp grades are
characterized by a dark brown color. These are generally used for packaging prod-
ucts and are cooked to a higher yield and retain more of the original lignin. Bleached
pulp grades are used to produce white papers. Nearly half of the Kraft production is
in bleached grades, which have the lowest yields. The superiority of kraft pulping
has further extended since the introduction of modified cooking technology in the
2.2 Pulping 17
early 1980s. In the meantime, three generations of modified kraft pulping processes
(MCC, ITC and Compact Cooking as examples for continuous cooking and Cold-
blow, Superbatch/RDH and Continuous Batch Cooking, CBC, for batch cooking
technology) have emerged through continuous research and development (Annergren
and Lundqvist 2008; Marcoccia et al. 2000).
2.2.1.2 Sulphite Process
The cooking liquor in the sulphite pulping process is an acidic mixture of sulfurous
acid and bisulphite ion. In preparing sulphite cooking liquors, cooled sulfur dioxide
gas is absorbed in water containing one of four chemical bases – magnesium,
ammonia, sodium, or calcium. The sulphite pulping process uses the acid solution
in the cooking liquor to degrade the lignin bonds between wood fibres. Sulphite
pulps have less color than kraft pulps and can be bleached more easily, but are not
as strong. The efficiency and effectiveness of the sulphite process is also dependent
on the type of wood furnish and the absence of bark. Due to these reasons, the use
of sulphite pulping has declined in comparison to kraft pulping over time (EPA
2001a). This process uses different chemicals to attack and remove lignin. Sulphite
pulps are produced in several grades but bleached grades dominate production
(Sixta 2006). Yields are generally in the range of 40–50 %, but tend toward the
lower end of this range in bleached grades. Compared to the Kraft process, this
operation has the disadvantage of being more sensitive to species characteristics.
The sulphite process is usually intolerant of resinous softwoods, tannin-containing
hardwoods, and any furnish containing bark. Sulphite Process produces bright pulp
which is easy to bleach to full brightness and produces higher yield of bleached pulp
which is easier to refine for papermaking applications.
The sulphite process is characterised by its high flexibility compared to the kraft
process, which is a very uniform method, which can be carried out only with highly
alkaline cooking liquor. The dominating sulphite pulping process in Europe is the
magnesium sulphite pulping with some mills using sodium as base. Both magne-
sium and sodium bases allow chemical recovery. The lignosulphonates generated in
the cooking liquour can be used as a raw material for producing different chemical
products.
2.2.2 Mechanical Pulping
There are three main categories of mechanical pulp: groundwood pulp, refining
pulp, and chemi-mechanical pulp. In both the grinding and refining processes, the
temperature is increased to soften the lignin. This breaks the bonds between the
fibres (Gullichsen 2000; Casey 1983b). Groundwood pulp shows favorable proper-
ties with respect to brightness (≥85 % ISO after bleaching), light scattering and
bulk, which allows the production of papers with low grammages. Moreover, the
groundwood process also offers the possibility of using hardwood (example, aspen)
to achieve even higher levels of brightness and smoothness. Groundwood pulp has
been the quality leader in magazine papers, and it is predicted that this situation will
remain (Arppe 2001). The most important refiner mechanical pulping process today
is thermomechanical pulping (TMP). This involves high-temperature steaming
before refining; this softens the inter-fibre lignin and causes partial removal of the
outer layers of the fibres, thereby baring cellulosic surfaces for inter-fibre bonding.
TMP pulps are generally stronger than groundwood pulps, thus enabling a lower
furnish of reinforcing chemical pulp for newsprint and magazine papers. TMP is
also used as a furnish in printing papers, paperboard and tissue paper. Softwoods are
the main raw material used for TMP, because hardwoods give rather poor pulp
strength properties. This can be explained by the fact that hardwood fibres do not
form fibrils during refining but separate into short rigid debris. Thus, hardwood
TMP pulps, characterized by a high-cleanness, high-scattering coefficient, are
mainly used as filler-grade pulp. The application of chemicals such as hydrogen
sulphite prior to refining causes partial sulfonation of middle lamella lignin. The
better swelling properties and the lower glass transition temperature of lignin results
in easier liberation of the fibres in subsequent refining. The chemithermomechani-
cal pulp (CTMP) show good strength properties, even when using hardwood as a
fibre source, and provided that the reaction conditions are appropriate to result in
high degrees of sulfonation. Mechanical pulps are weaker than chemical pulps, but
cheaper to produce (about 50 % of the costs of chemical pulp) and are generally
obtained in the yield range of 85–95 %. Currently, mechanical pulps account for
20 % of all virgin fibre material. It is anticipated that mechanical paper will consoli-
date its position as one major fibre supply for high-end graphic papers. The growing
demand on pulp quality in the future can only be achieved by the parallel use of
softwood and hardwood as a raw material.
The largest threat to the future of mechanical pulp is its high specific energy
consumption. In this respect, TMP processes are most affected due to their consid-
erably higher energy demand than groundwood processes. Moreover, the increasing
use of recovered fibre will put pressure on the growth in mechanical pulp volumes.
2.2.3 Semi-chemical Pulping
Semi-chemical pulping uses a combination of chemical and mechanical (i.e., grind-

ing) energy to extract pulp fibres. Wood chips first are partially softened in a digester
with chemicals, steam, and heat. Once chips are softened, mechanical methods
complete the pulping process. The pulp is washed after digestion to remove cooking
liquor chemicals and organic compounds dissolved from the wood chips. This vir-
gin pulp is then mixed with 20–35 % recovered fibre (example, double-lined kraft
clippings) or repulped secondary fibre (example, old corrugated containers) to
enhance machinability. The chemical portion (example, cooking liquors, process
equipment) of the pulping process and pulp washing steps are very similar to kraft
2.2 Pulping 19
and sulphite processes. At currently operating mills, the chemical portion of the
semi-chemical pulping process uses either a nonsulfur or neutral sulphite semi-
chemical (NSSC) process. The nonsulfur process uses either sodium carbonate only
or mixtures of sodium carbonate and sodium hydroxide for cooking the wood chips,
while the NSSC process uses a sodium-based sulphite cooking liquor (EPA 2001a).
Semichemical pulps, which apply to the category of chemical pulps, are obtained
mainly from hardwoods in yields of between 65 and 85 % (average ca. 75 %). The
most important semichemical process is the NSSC process, in which chips undergo
partial chemical pulping using a buffered sodium sulphite solution, and are then
treated in disc refiners to complete the fibre separation. The sulfonation of mainly
middle lamella lignin causes a partial dissolution so that the fibres are weakened for
the subsequent mechanical defibration. NSSC pulp is used for unbleached products
where good strength and stiffness are particularly important; examples include cor-
rugating medium, as well as grease-proof papers and bond papers. NSSC pulping is
often integrated into a kraft mill to facilitate chemical recovery by a so-called cross-
recovery, where the sulphite spent liquor is processed together with the kraft liquor.
The sulphite spent liquor then provides the necessary make-up (Na, S) for the kraft
process. However, with the greatly improving recovery efficiency of modern kraft
mills, the NSCC make-up is no longer needed so that high-yield kraft pulping devel-
ops as a serious alternative to NSCC cooking. Semichemical pulps is still an impor-
tant product category, however, and account for 3.9 % of all virgin fibre material.
2.2.4 Secondary Fibre Pulping
Recovered paper has become an increasingly important source of fibre for paper-
making (Bajpai 2013). Currently, nearly 50 % of the fibre raw material for paper-
making is based on recycled fibre. In the recycling process, recycled paper or
paperboard is rewetted and reduced to pulp, principally by mechanical means. Inks,
adhesives, and other contaminants may be removed by chemical deinking and
mechanical separation. Because the fibres in recycled paper and paperboard have
been fully dried and then rewetted, they generally have different physical properties
than virgin wood pulp fibres. In some cases, mills using recycled paper, without
deinking, can operate without any effluent discharge due to the use of closed water
cycles together with small anaerobic or aerobic biological treatment systems to
remove some dissolved organics from the recycled waters. The closed cycle pro-
cesses are practical where the product can tolerate a certain degree of dirt and con-
tamination, as in some packaging and construction paper grades. In some recycle
plants, approximately 30–40 % of the raw material processed results in sludge that
requires management as a solid waste. Processing of recovered paper without deink-
ing is sufficient for applications that do not require high brightness, such as corru-
gated board, carton board, and some tissue. Deinking processes are used to remove
ink to make the pulp brighter and cleaner. Sometimes bleaching is also applied after
deinking. Recycled fibre with deinking is used for applications requiring higher
brightness, such as newsprint, magazine paper, and tissue. Process waters are simi-
lar to those from systems without deinking. However, deinking results in lower
yields and requires additional internal treatment. The pulp yield may be as low as
60–70 % of the recovered paper entering the process; therefore, as much as 30–40 %
of the entering material may enter the white water and need to be treated and
removed before discharge of the wastewater.
2.2.5 Dissolving Kraft and Sulphite Pulping Processes
Dissolving kraft and sulphite pulping processes are used to produce highly bleached
and purified wood pulp suitable for conversion into products such as rayon, viscose,
acetate, and cellophane (EPA 2002).
2.2.6 Non-wood Pulping
Worldwide, non-wood sources make up about 6 % of the total fibre supply for
papermaking. Non-wood fibres are derived from agricultural fibres such as straw
and other plant fibres such as bamboo, bagasse, and annual fibre crops such as kenaf
(Ince 2004). In general, non-wood plant fibres are more costly to collect and process
than wood fibre in regions of the world where wood supplies are adequate, and thus
pulp is produced almost exclusively from wood fibre in most regions of the world.
However, substantial quantities of nonwood pulp are produced, especially in regions
of Asia and Africa where wood fibre is relatively less abundant and non-wood fibres
are available. Most non-wood fibres are relatively short, similar to fibres derived
from hardwood, and therefore are suited to similar applications, such as writing
paper. However, non-wood fibres are often used for other grades as well, such as
newsprint and corrugated board, simply because local wood is not available for
pulping. Non-wood species normally cook more readily than wood chips. Thus,
Kraft cooking is normally replaced with soda cooking (sodium hydroxide only), and
the charge is usually less. The spent liquors usually have lower concentrations of
dissolved organics and process chemicals compared with chemical pulping of wood,
thus increasing the cost of chemical recovery. In addition, non-wood pulping plants
are normally small, typically producing less than 100,000 t/year of pulp, and there-
fore lack the economies of scale that make environmental investments economical
at larger facilities. As a result, many non-wood mills have limited or no recovery of
chemicals and have substantially higher waste emissions per ton of product than
modern Kraft mills. Non-wood plants normally contain higher amounts of silica
than wood. Silica causes problems in chemical recovery and also adversely affects
paper quality. In particular, silica increases scaling in the liquor evaporators and
reduces the efficiency of both the causticizing operation and conversion of lime mud
(calcium carbonate) to calcium oxide (burnt lime) in the lime kiln. To counter these
2.3 Pulp Washing 21
affects, non-wood pulping facilities generally discharge higher proportions of lime

mud and purchase higher amounts of lime or limestone as make-up. In the United
States, non-wood fibre pulp production is not common (EPA 2001b).
2.3 Pulp Washing
The purpose of pulp washing is to obtain pulp that is free of unwanted solubles. In
the most basic case, this can be done by replacement of the contaminated liquor
accompanying the pulp fibres by clean water. In a modern pulp mill, washing opera-
tions include also displacement of one type of liquor by another type of liquor.
Aside from its washing function, washing equipment must at times also allow the
effective separation of chemical regimes or temperature levels between single fibre-
line process steps (Krotscheck 2006). Various benefits result from pulp washing,
such as:
– Minimizing the chemical loss from the cooking liquor cycle
– Maximizing recovery of organic substances for further processing or incineration
– Reducing the environmental impact of fibreline operations
– Limiting the carry-over between process stages
– Maximizing the re-use of chemicals and the energy conservation within a single
bleaching stage
– Obtaining a clean final pulp product
Ideally, pulp washing is carried out with the minimum amount of wash water in
order to conserve fresh water resources and to take capacity burden from down-
stream areas which process the wash filtrate. Very often, pulp washing is a compro-
mise between the cleanness of the pulp and the amount of wash water to be used. In
the mill, pulp washing operations can be found in brownstock washing, in the bleach
plant and, as the case may be, also in digesting and on the dewatering machine
(Smook 1992; Krotscheck 2006).
After pulp production, pulp is processed to remove impurities, such as uncooked
chips, and recycles any residual cooking liquor via the pulp washing process (Smook
1992). Pulps are processed in a wide variety of ways, depending on the method that
generated them (e.g., chemical, sulphite). Some pulp processing steps that remove
pulp impurities include screening, defibering, and deknotting. Pulp may also be
thickened by removing a portion of the water. At additional cost, pulp may be
blended to ensure product uniformity. If pulp is to be stored for long periods of time,
drying steps are necessary to prevent fungal or bacterial growth. Residual spent
cooking liquor from chemical pulping is washed from the pulp using pulp washers,
called brown stock washers for Kraft and red stock washers for sulphite. Efficient
washing is very important to maximize return of cooking liquor to chemical recov-
ery and to minimize carryover of cooking liquor (known as washing loss) into
the bleach plant, because excess cooking liquor increases consumption of bleach-
ing chemicals. Specifically, the dissolved organic compounds (lignins and
hemicelluloses) contained in the liquor will bind to bleaching chemicals and thus
increase bleach chemical consumption. In addition, these organic compounds func-
tion as precursors to chlorinated organic compounds (example, dioxins, furans),
increasing the probability of their formation.
The most common washing technology is rotary vacuum washing, carried out
sequentially in two, three, or four washing units. Other washing technologies
include diffusion washers, rotary pressure washers, horizontal belt filters, wash
presses, and dilution/extraction washers. Pulp screening removes remaining over-
sized particles such as bark fragments, oversized chips, and uncooked chips. In open
screen rooms, wastewater from the screening process goes to wastewater treatment
prior to discharge. In closed loop screen rooms, wastewater from the process is
reused in other pulping operations and ultimately enters the mill’s chemical recov-
ery system. Centrifugal cleaning (also known as liquid cyclone, hydro-cyclone, or
centri-cleaning) is used after screening to remove relatively dense contaminants
such as sand and dirt. Rejects from the screening process are either repulped or
disposed of as solid waste (Gullichsen 2000).
The objective of brown stock washing, is to remove the maximum amount of
liquor dissolved solids from the pulp while using as little wash water as possible.
The dissolved solids left in the pulp after washing will interfere with later bleaching
and papermaking and will increase costs for these processes. The loss of liquor
solids due to solids left in the pulp means that less heat can be recovered in the
recovery furnace. Also, makeup chemicals must be added to the liquor system to
account for lost chemicals (Gullichsen 2000).
It would be easy to obtain very high washing efficiencies if one could use unlim-
ited amounts of wash water. As it is, one has to compromise between high washing
efficiency and a low amount of added wash water. The water added to the liquor
during washing must be removed in the evaporators before to burning the liquor in
the recovery furnace. This is a costly process and often the bottleneck in pulp mill
operations. Reducing the use of wash water will therefore reduce the steam cost for
evaporation. In dilution/extraction washing, the pulp slurry is diluted and mixed
with weak wash liquor or fresh water. Then the liquor is extracted by thickening the
pulp, either by filtering or pressing. This procedure must be repeated many times in
order to sufficiently wash the pulp.
In displacement washing, the liquor in the pulp is displaced with weaker wash
liquor or clean water. Ideally, no mixing takes place at the interface of the two
liquors. In practice, however, it is impossible to avoid a certain degree of mixing.
Some of the original liquor will remain with the pulp and some of the wash liquor
will channel through the pulp mass. The efficiency of displacement washing then
depends on this degree of mixing and also on the rate of desorption and diffusion of
dissolved solids and chemicals from the pulp fibres.
All pulp washing equipment is based on one of both of these basic principles.
Displacement washing is utilized in a digester washing zone. A rotary vacuum
washer utilizes both dilution/extraction and displacement washing, while a series of
wash presses utilizes dilution\extraction. Most pulp washing systems consist of
more than one washing stage. The highest washing efficiency would be achieved if
2.5 Bleaching 23
fresh water were applied in each stage. However, this approach would require large
quantities of water and is, therefore, not used. Countercurrent washing is the gener-
ally used system design. In counter-current washing, the pulp in the final stage is
washed with the cleanest available wash water or fresh water before leaving the
system. The drained water from this stage is then sent backwards through each of
the previous stages in a direction opposite to the pulp flow (Smook 1992).
2.4 Pulp Screening, Cleaning and Fractionation
Screening of the pulp is done to remove oversized and unwanted particles from
good papermaking fibres so that the screened pulp is more suitable for the paper or
board product in which it will be used (Biermann 1996; Ljokkoi 2000; Krotscheck
2006). The biggest oversized particles in pulp are knots. Knots can be defined as
uncooked wood particles. The knots are removed before washing and fine screen-
ing. In low-yield pulps they are broken down in refiners and/or fiberizers. In low-
yield pulps they are removed in special coarse screens called knotters.
The main purpose of fine screening is to remove shives. Shives are small fibre
bundles that have not been separated by chemical pulping or mechanical action.
Chop is another kind of oversize wood particle removed in screening. It is more of
a problem when pulping hardwoods, since it originates mostly from irregularly
shaped hardwood vessels and cells. Chop particles are shorter and more rigid than
shives. Debris is the name for shives, chop, and any other material that would have
any sort of bad effect on the papermaking process or on the properties of the paper
produced.
2.5 Bleaching
Bleaching of pulp is done to achieve a number of objectives. The most important of

these is to increase the brightness of the pulp so that it can be used in paper products
such as printing grades and tissue papers (Bajpai 2012). Bleaching is any process
that chemically alters pulp to increase its brightness. Bleached pulps create papers
that are whiter, brighter, softer, and more absorbent than unbleached pulps. Bleached
pulps are used for products where high purity is required and yellowing is not
desired (example printing and writing papers). Unbleached pulp is typically used to
produce boxboard, linerboard, and grocery bags. Any type of pulp may be bleached,
but the type(s) of fibre and pulping processes used, as well as the desired qualities
and end use of the final product, greatly affect the type and degree of pulp bleaching
possible. The lignin content of a pulp is the major determinant of its bleaching
potential. Pulps with high lignin content (example, mechanical or semi-chemical)
are difficult to bleach fully and require heavy chemical inputs. Excessive bleaching
of mechanical and semi-chemical pulps results in loss of pulp yield due to fibre
destruction. Chemical pulps can be bleached to a greater extent due to their low
(10 %) lignin content. Whereas delignification can be carried out within closed
water systems, bleach plants tend to discharge effluent to external treatment.
Effluents from the bleach plant cannot easily be recirculated into the chemicals
recovery mainly because they would increase the build-up of chlorides and other
unwanted inorganic elements in the chemical recovery system, which can cause
corrosion, scaling, and other problems.
For chemical pulps an important benefit is the reduction of fibre bundles and
shives as well as the removal of bark fragments. This improves the cleanliness of the
pulp. Bleaching also eliminates the problem of yellowing of paper in light, as it
removes the residual lignin in the unbleached pulp. Resin and other extractives pres-
ent in unbleached chemical pulps are also removed during bleaching, and this
improves the absorbency, which is an important property for tissue paper grades. In
the manufacture of pulp for reconstituted cellulose such as rayon and for cellulose
derivatives such as cellulose acetate, all wood components other than cellulose must
be removed. In this situation, bleaching is an effective purification process for
removing hemicelluloses and wood extractives as well as lignin. To achieve some of
these product improvements, it is often necessary to bleach to high brightness. Thus,
high brightness may in fact be a secondary characteristic of the final product and not
the primary benefit. It is therefore simplistic to suggest that bleaching to lower
brightness should be practiced based on the reasoning that not all products require
high brightness.
The papermaking properties of chemical pulps are changed after bleaching.
Removal of the residual lignin in the pulp increases fibre flexibility and strength. On
the other hand, a lowered hemicellulose content results in a lower swelling potential
of the fibres and a reduced bonding ability of the fibre surfaces. If bleaching condi-
tions are too severe there will be fibre damage, leading to a lower strength of the
paper. The purpose of bleaching is to dissolve and remove the lignin from wood to
bring the pulp to a desired brightness level (Reeve 1989, 1996a; Farr et al. 1992;
Fredette 1996; McDonough 1992). Bleaching is carried out in a multi-stage process
that alternate delignification and dissolved material extracting stages. Additional
oxygen- or hydrogen peroxide-based delignification may be added to reinforce the
extracting operation. Since its introduction at the turn of the century, chemical Kraft
bleaching has been refined into a stepwise progression of chemical reaction, evolv-
ing from a single-stage hypochlorite (H) treatment to a multi-stage process, involv-
ing chlorine (CI2), chlorine dioxide (CIO2), hydrogen peroxide and ozone (O3).
Bleaching operations have continuously evolved since the conventional CEHDED
sequence and now involve different combinations with or without chlorine contain-
ing chemicals (Rapson and Strumila 1979; Reeve 1989, 1996a, b).
The introduction of chlorine and chlorine dioxide in the 1930s and early 1940s,
respectively, increased markedly the efficiency of the bleaching process (Rapson
and Strumila 1979; Reeve 1996a; Fredette 1996). Being much more reactive and
selective than hypochlorite, chlorine had less tendency to attack the cellulose and
other carbohydrate components of wood, producing much higher pulp strength.
Although it did not brighten the pulp as hypochlorite, it extensively degraded the
lignin, allowing much of it to be washed out and removed with the spent liquor by
2.5 Bleaching 25
subsequent alkaline extraction. The resulting brownish Kraft pulp eventually

required additional bleaching stages to increase brightness, which led to the devel-
opment of the multi-stage process. Chlorine dioxide, a more powerful brightening
agent than hypochlorite, brought the Kraft process efficiency one step further
(Rapson and Strumila 1979; Reeve 1996a). Between the 1970s and 1990s, a series
of incremental and radical innovations increased again the efficiency of the process,
while reducing its environmental impacts (Reeve 1996b). Development of oxygen
delignification, modified and extended cooking, improved operation controls,
example improved pulp and chemical mixing, multiple splitted chlorine additions,
and pH adjustments increased the economics of the process and led to significant
reduction of wastewater (McDonough 1992, 1995; Malinen and Fuhrmann 1995).
In addition, higher chlorine dioxide substitution, brought down significantly the
generation and release of harmful chlorinated organic compounds.
Concerns over chlorinated compounds such as dioxins, furans, and chloroform
have resulted in a shift away from the use of chlorinated compounds in the bleach-
ing process. Bleaching chemicals are added to the pulp in stages in the bleaching
towers. Spent bleaching chemicals are removed between each stage in the washers.
Washer effluent is collected in the seal tanks and either re-used in other stages as
wash water or sent to wastewater treatment.
Bleaching of mechanical pulp is based on lignin-saving methods and is funda-
mentally different from bleaching of chemical pulps, which is based on removal of
lignin. The bleaching of mechanical pulp changes chromophoric groups of lignin
polymers into a colorless form. Thus, the bleaching of mechanical pulp increases
primarily the brightness of the pulp with minimum losses of dry solids and overall
yield. The effect is not permanent, and the paper yellows with time. As it does not
result in permanent brightness gain, bleached mechanical pulp is more suitable for
newsprint and magazine paper than for books or archive papers. The lignin- saving
bleaching is carried out in one to two stages, depending on the final brightness
requirements of the pulp. The bleaching stages are distinguished according to the
bleaching agent applied. Reductive bleaching uses sodium dithionite, which does
not dissolve organic material from the pulp, and therefore results in only a minimal
reduction in yield. Residual dithionite in the pulp can cause corrosion of metallic
components downstream in the process. In most mills a metal chelating agent
(example Ethylenediaminetetraacetic acid (EDTA), diethylene triamine pentaacetic
acid (DTPA)) is used to prevent degradation of the dithionite. Oxidative bleaching
uses hydrogen peroxide. Peroxide bleaching results in an approximately 2 % reduc-
tion in yield, mainly due to the alkalinity during the bleaching that results in some
dissolution of organic substances in the wood (and in an increase of pollution load).
Peroxide bleaching also improves the strength and water uptake capacity of the
pulp. The bleaching process results in lower brightness in the presence of heavy
metal ions; therefore, chelating agents (example EDTA, DTPA) are usually added
before bleaching to form complexes with heavy metals (example Fe, Mn, Cu, Cr),
which prevents the pulp from discoloring and the peroxide from decomposing.
EDTA and DTPA contain nitrogen, which enters the wastewater. Introduction of a
washing stage between pulping and bleaching is effective in reducing the problem-
atic metals and can thus reduce the amount of chelating agent needed and improve
the effectiveness of the applied peroxide. The bleached pulp is acidified with sulfu-
ric acid or sulfur dioxide to a pH of 5–6.
2.6 Chemical Recovery
For economic and environmental reasons, chemical and semi-chemical pulp mills
employ chemical recovery processes to reclaim spent cooking chemicals from the
pulping process (Vakkilainen 2000; Tran 2007; Reeve 2002). At Kraft and soda pulp
mills, spent cooking liquor, referred to as “weak black liquor,” from the brown stock
washers is routed to the chemical recovery area at kraft and soda pulp mills (Bajpai
2008). The chemical recovery process involves concentrating weak black liquor,
combusting organic compounds, reducing inorganic compounds, and reconstituting
the cooking liquor. The typical kraft chemical recovery process consists of the gen-
eral steps described in the following paragraphs (EPA 2001a).
2.6.1 Black Liquor Concentration
Residual weak black liquor from the pulping process is a dilute solution (approxi-
mately 12–15 % solids) of wood lignins, organic materials, oxidized inorganic com-
pounds (sodium sulphate, sodium carbonate), and white liquor (sodium sulphide
and sodium hydroxide). The weak black liquor is first directed through a series of
multiple-effect evaporators to increase the solids content to about 50 % to form
“strong black liquor.” The strong black liquor from the multiple-effect evaporators
system is either oxidized in the black liquor oxidation system if it is further concen-
trated in a direct contact evaporator or routed directly to a nondirect contact evapo-
rator, also called a concentrator. Oxidation of the black liquor before evaporation in
a direct contact evaporator reduces emissions of odorous total reduced sulfur com-
pounds, which are stripped from the black liquor in the direct contact evaporator
when it contacts hot flue gases from the recovery furnace. The solids content of the
black liquor following the final evaporator/ concentrator typically averages 65–68 %.
The soda chemical recovery process is similar to the kraft process, except that the
soda process does not require black liquor oxidation systems, since it is a nonsulfur
process that does not result in total reduced sulfur emissions.
2.6.2 Recovery Furnace
The concentrated black liquor is then sprayed into the recovery furnace, where
organic compounds are combusted, and the sodium sulphate is reduced to sodium
sulphide (Vakkilainen 2000; Tran 2007). The black liquor burned in the recovery
furnace has a high energy content (5,800–6,600 British thermal units per pound
2.7 Stock Preparation and Papermaking 27
[Btu/lb] of dry solids), which is recovered as steam for process requirements, such
as cooking wood chips, heating and evaporating black liquor, preheating combus-
tion air, and drying the pulp or paper products. The process steam from the recovery
furnace is often supplemented with fossil fuel-fired and/or wood-fired power boil-
ers. Particulate matter (primarily sodium sulphate) exiting the furnace with the hot
flue gases is collected in an electrostatic precipitator (ESP) and added to the black
liquor to be fired in the recovery furnace. Additional makeup sodium sulphate, or
“saltcake,” may also be added to the black liquor prior to firing. Molten inorganic
salts, referred to as “smelt,” collect in a char bed at the bottom of the furnace. Smelt
is drawn off and dissolved in weak wash water in the smelt dissolving tank to form
a solution of carbonate salts called “green liquor,” which is primarily sodium sul-
phide and sodium carbonate. Green liquor also contains insoluble unburned carbon
and inorganic impurities, called dregs, which are removed in a series of clarification
tanks.
2.6.3 Causticizing and Calcining
Decanted green liquor is transferred to the causticizing area, where the sodium car-
bonate is converted to sodium hydroxide by the addition of lime (calcium oxide).
The green liquor is first transferred to a slaker tank, where calcium oxide from the
lime kiln reacts with water to form calcium hydroxide (Biermann 1996; Adams
1992; Venkatesh 1992). From the slaker, liquor flows through a series of agitated
tanks, referred to as causticizers, that allow the causticizing reaction to go to com-
pletion (i.e., calcium hydroxide reacts with sodium carbonate to form sodium
hydroxide and calcium carbonate). The causticizing product is then routed to the
white liquor clarifier, which removes calcium carbonate precipitate, referred to as
“lime mud.” The lime mud is washed in the mud washer to remove the last traces of
sodium. The mud from the mud washer is then dried and calcined in a lime kiln to
produce “reburned” lime, which is reintroduced to the slaker. The mud washer fil-
trate, known as weak wash, is used in the SDT to dissolve recovery furnace smelt.
The white liquor from the clarifier is recycled to the digesters in the pulping area of
the mill (Arpalahti et al. 2000).
2.7 Stock Preparation and Papermaking
Stock preparation involves a series of operations by which pulp properties are tai-
lored to fit the product produced. To balance the efficiency and reliability of the
papermaking process against end-product quality is a crucial factor in stock prepa-
ration optimization. The objective of fibre stock preparation systems is to modify
the different ingoing raw materials in such a way that the finished stock finally sup-
plied to the paper machine suits the requirements of the paper machine and of the
quality demands put on the produced paper or board. The raw stocks used are the
Table 2.3 Unit processes in stock preparation

Unit process Objective
Slushing and deflaking To break down the fiber raw material into a suspension of individual
fibers. Slushing should at least result in a pumpable suspension
enabling coarse separation and deflaking if required
In the case of recovered paper, ink particles and other nonpaper
particles should be detached from the fibers
Screening To separate particles from the suspension which differ in size, shape
and deformability from the fibers
Fractionation To separate fiber fractions from each other according to defined
criteria such as size or deformability of the fibers
Centrifugal cleaning To separate particles from the suspension which differ in specific
gravity, size and shape from the fibers
Refining To modify the morphology and surface characteristics of the fibers
Selective flotation To separate particles from the suspension which differ in surface
properties (hydrophobicity) from the fibers
Nonselective flotation To separate fine and dissolved solids from water
Bleaching To impart yellowed or brown fibers with the required brightness and
luminance
Washing To separate fine solid particles from suspension (solid/solid separation)
Dewatering To separate water and solids
Dispersing To reduce the size of dirt specks and stickies (visibility, floatability), to
detach ink particles from fibers
Based on Holik (2006)
various types of virgin pulps as well as recovered paper grades (Biermann 1996;
Paulapuro 2000). They are available in the form of bales, loose material or, in the
case of integrated mills, as suspensions. The finished stock is a suspension of defined
quality as far as the mixture and characteristics of the fibres, additives, and impuri-
ties are concerned. This quality essentially determines paper machine runnability
and is the basis for the final paper and board quality. Stock preparation consists of
several process steps (Table 2.3). These systems differ considerably depending on
the raw stock used and on the quality of furnish required. For instance, in the case
of pulp being pumped directly from the pulp mill, the slushing and deflaking stages
are omitted. The operations are practiced in the paper mills are Dispersion; Refining
and Metering and blending of fibre and additive. A number of new concepts have
been introduced by Kadant Lamort with regard to virgin pulp stock preparation.
Pulpers are used to disperse dry pulp into water to form a slush or a slurry. The
stock in the pulper is accelerated and decelerated repeatedly, and hydrodynamic
shear forces are produced by the severe velocity gradients. The resulting forces
serve to loosen fibres and reduce any flakes into individual fibres.
Pulp produced in a mill without mechanical treatment is unsuitable for most
paper grades. Paper made from unbeaten virgin pulp has a low strength, is bulky and
has a rough surface. In good quality paper, the fibres must be matted into a uniform
sheet and must develop strong bonds at the points of contact. Beating and refining
are the processes by which the undesirable characteristics are changed (Baker
2000). Mechanical treatment is one of the most important operations when prepar-
ing papermaking fibres. The term beating is applied to the batch treatment of stock
in a Hollander beater or one of its modifications. The term refining is used when the
pulps are passed continuously through one or more refiners, whether in series or in
parallel. Refining develops different fibre properties in different ways for specific
grades of paper. Usually, it aims to develop the bonding ability of the fibres without
reducing their individual strength by damaging them too much, while minimising
the development of drainage resistance. So the refining process is based on the prop-
erties required in the final paper. Different types of fibre react differently because of
differences in their morphological properties (Baker 2000, 2005). The refining pro-
cess must take into account the type of fibres.
Most of the strength properties of paper increase with pulp refining, since they
rely on fibre-fibre bonding. However, the tear strength, which depends highly on the
strength of the individual fibres, decreases with refining. After a certain point the
factor limiting the strength is not the fibre-fibre bonding, but the strength of the
individual fibres. Refining beyond this causes a decrease in other strength properties
besides tear. Refining a pulp increases the fibres’ flexibility and results in denser
paper which means that bulk, opacity and porosity values decrease during the pro-
cess (Lumiainen 2000). Mechanical and hydraulic forces are employed to alter the
fibre characteristics. Shear stresses are imposed by the rolling, twisting, and ten-
sional actions occurring between the bars and in the grooves and channels of the
refiner. Normal stresses (either tensional or compressive) are imposed by the bend-
ing, crushing, and pulling/pushing actions on the fibre clumps caught between the
bar-to-bar surfaces. During beating and refining, fibres randomly and repeatedly
undergo tensile, compressive, shear and bending forces. They respond in three ways
(Bajpai 2005; Baker 2000, 2005; Stevens 1992):
– Fibres develop new surfaces externally through fibrillation and internally through
fibre wall delamination.
– Fibres deform, resulting in changes in their geometric shape and the fibrillar
alignment along their length. Overall, the fibres flatten or collapse. Fibre curl
changes and kinks are induced or straightened. On the small scale, dislocations,
crimps, and microcompressions are induced or diminished.
– Fibres break, resulting in changes in length distribution and a decrease in mean-
fibre length. A small amount of fibre wall material also dissolves.
All these changes occur simultaneously and are primarily irreversible. The extent
of the changes depends on the morphology of the fibres, the temperature, the chemi-
cal environment and the treatment conditions. The conditions depend on the design
of the equipment and its operating variables such as the consistency, intensity and
amount of treatment. Each pulp responds differently to a given set of conditions and
not all fibres within it receive the same treatment. The furnish (as it is now referred
to) can also be treated with chemical additives. These include resins to improve the
wet strength of the paper, dyes and pigments to affect the color of the sheet, fillers
such as talc and clay to improve optical qualities, and sizing agents to control
Table 2.4 Common pulp Acids and bases:

stock additives
Control of pH
Sizing agents:
Water repellent
Dry strength additives:
Strength and stiffness (starch)
Wet strength additives:
Linking of fibers (polymers)
Fillers:
Gloss, brightness, and opacity
(kaolin, TiO2)
Defoamers:
Reduce foam and entrained
air (surfactants)
Fig. 2.2 A flow diagram for a typical papermaking process
penetration of liquids and to improve printing properties (Krogerus 2007; Bajpai

2004; Hodgson 1997; Davison 1992; Neimo 2000; Roberts 1996, 1997). The com-
monly used additives are shown in Table 2.4.
After stock preparation, the next step is to form the slurry into the desired type of
paper at the paper machine. A flow diagram for a typical papermaking process is shown
in Fig. 2.2. The actual papermaking process consists of two primary processes:
Wet end operation:
In wet end operations, the cleaned and bleached pulp is formed into wet paper
sheets.
Dry end operations:
In the dry end operations, those wet sheets are dried and various surface treat-
ments are applied to the paper.
The traditional Fourdrinier machine is still widely used but for many paper
grades has been replaced with twin wire machines or gap formers and hybrid
formers (Ishiguro 1987; Buck 2006; Atkins 2005; Lund 1999 and Malashenko and
Karlsson 2000). Twin wire formers have become the state-of-the-art design
(Malashenko and Karlsson 2000). In twin wire formers, the fibre suspension is led
between two wires operating at the same speed, and is drained through one or both
sides. There are different types of twin wire formers (e.g. gap formers. In gap
formers, the diluted stock is injected directly into the gap between the two wires)
and combinations of Fourdrinier and twin wires (hybrid formers). Multiply papers
can be made on a variety of formers but recently two and three ply papers and
liners are being made on multi-fourdrinier wet ends. Whatever the forming device,
the wet paper web is passed through presses to remove as much water as possible
by mechanical means. More moisture is removed by evaporation on multiple dry-
ing cylinders.
The Fourdrinier paper making machine is composed of three main sections: the
forming section, the press section, and the dryer section. A paper slurry consisting
of around 0.5–1.0 % fibre, is pumped into a box where it flows out through a slot
onto a moving wire belt. Once on the belt the water is removed by draining and suc-
tion, leaving the fibres to form a very wet, and weak paper. The paper is then pressed,
heated, dried, resulting in a continuous roll or “web” which can be further finished
as desired or required (Biermann 1996; Smook 1992). Figure 2.3 shows the details
of the papermaking process; Fig. 2.4 shows Schematic of Fourdrinier paper machine.
The forming section of the Fourdrinier constitutes what is called the wet end of the
machine. This section consists of the head box, the forming wire, foils, suction
boxes, couch roller, breast roller and dandy roll (Buck 2006; Smook 1992). Pulp is
pumped from the machine box through the screens and cleaners to the head box.
The purpose of the head box is to deliver a uniform slurry to the forming wire. There
are several different designs, but all incorporate a method to induce turbulence
(deflocculation), while preventing cross currents, which would inhibit the unifor-
mity of the stock. The simplest design is the gravity fed head box. It uses height/
weight level difference to force the pulp through several baffles and a through a
perforated rotating cylinder, before flowing through the apron and slice. A gravity-
fed head box can deliver an eight-inch stock depth at a rate of 400 ft/min. If faster
Fig. 2.3 Details of papermaking process

Headbox Slice Dolly Roller Felt Felt Dryer Heated dryer Top felt Felt dryer
Suction box
Breast roller Couch roller Pickup roller Bottom felt, Felt Dryer
Wet End Wet Press Section Dryer Section Calender Section
Fig. 2.4 Schematic of Fourdrinier paper machine
production speeds are required the stock must be fed under pressure. These machines
can operate at speeds greater than 4,000 ft/min. The pressurized head boxes are
usually hydraulic and the stock is forced through conical injectors, through a perfo-
rated plate and through a horizontally split apron and the slice. The apron height and
the slice height, which control the jet of pulp can be independently adjusted by
hydraulics.
The pulp flowing onto the forming wire is approximately 0.5–1.0 % fibres, with
the make-up consisting of water. As the water is removed from the slurry, the fibres
settle onto the surface of a traveling wire, forming a wet mat of paper. Therefore, the
main objective of the forming section is the controlled removal of water. Originally
gravity allowed the water to drain through a brass forming wire 60–70 mesh per
inch, 40–50 ft length and 70–90 in. in width. But as production speeds increased,
more efficient methods were developed. The forming wire, now a fine polymer
screen with about 65 meshes per inch, carries the paper slurry over table rolls, foils
and suction boxes, providing precise control over drainage and agitation control. As
the slurry exits the slice onto the wire, the water starts draining from the suspension.
Water jets are positioned over the edges of the forming wire to control the width of
web, creating what is called the deckle edge. The first fibres forming the mat on the
wire are oriented in the direction of the machine; this is the wire side of the paper.
If the rest of the fibres in the slurry were allowed to orient themselves in the same
direction, the paper would have poor tear resistance and surface properties. If grav-
ity was the main method of dehydration, the machine would have to be run at low
speeds to overcome the orientation problem, the alternative is to remove the water
quickly while the fibres are still agitated from the effects of the headbox.
The first set of de-watering elements is a bank of table rolls. In earlier designs,
table rolls were a series of small solid rollers. Now, they are much larger and are
used as only the first water removal step. The rotation of the roll in contact with the
covered wire causes a vacuum to form between the two, which pulls the water from
the web.
With increasing speeds the table rolls cause problems with paper uniformity and
are not able to remove enough water before the presses. Foils have replaced most, if
not all of the table rolls. Foils remove water using a doctor blade on the bottom of
the forming wire. The blade causes a difference in pressures, which draws water
from the web behind the blade. This method allows for more control over the
removal process and is not significantly affected by machine speeds.
Water removal can be further increased by placing a vacuum on the foil drain-
age system. After the foils, water is further removed using flat suction boxes. The
suction boxes remove the majority of the water, changing the stock consistency
from 2 to 20 % fibre content. Above the first couple of suction boxes a skeleton roll
covered with wire may ride on the top of the paper mat. This roll called a “dandy
roll” compresses the paper, releasing any trapped air and improving the surface.
The dandy roll can be covered with various wire patterns, which may simulate the
forming wire and may have recessed or raised elements-designs imparting a water-
mark onto the paper. In areas where the watermark elements, usually a wire design,
are above the surface of the dandy roll, fewer fibres are allowed to settle, and the
paper appears light. If the watermark elements are below the dandy roll surface,
more fibres are allowed to settle than in the rest of the paper, and the paper appears
darker in these areas. An alternative to using a dandy roll to create watermarks is
the Molette. The Molette is a rubber stamp roll located before the wet press of the
machine. This type of watermark actually embosses the paper and squeezes the
fibres to the edges of the stamp.
A variation on the Fourdrinier was developed in the 1960s and employed the
use of two forming wire, allowing the paper mat to be dried from both sides simul-
taneously. The First Twin Wire machines were constructed so that the headbox
sprayed a vertical stream between the forming wires at the nip of twin breast rolls
(Malashenko and Karlsson 2000). The paper web was then further drawn vertically,
while vacuum boxes operate from both sides. Newer designs returned to a horizon-
tal feed system with both forming wires traveling horizontally and vacuum boxes
drawing suction from below and above the web. Another variation is the use of a
de-watering mat above the suction boxes on a Fourdrinier; this is referred to as a
Hybrid Twin Wire Machine.
In 1809, in England, John Dickinson invented another mechanical method of
manufacturing paper, the cylinder mold machine (Smook 1992). Instead of pouring
fibres through the forming wire, his machine dipped the forming wire into a vat,
much in the same manner as hand made paper. This allowed him to create water
marks and four-sided deckled edges comparable to hand couched paper. The mod-
ern cylinder mold machine, also known as “cylinder vat” or “mold made,” is used to
make fine bond paper with shadowed watermarks, currency and security papers, art
papers, extremely heavy stock, corrugated cardboards, and multi-ply papers. The
key to the cylinder mold machine is the use of a cylinder wire covered by the form-
ing wire (now called the cylinder blanket or cover), partially submerged in a vat full
of pulp. As the cylinder rotates into the paper stock, the slurry flows onto the surface
of the cylinder, and the water flows through the wire cover to the inside of the cyl-
inder where it is discharged. The fibre mat that accumulates onto the cylinder sur-
face is removed or “couched” by a traveling felt belt. This traveling felt “the cylinder
felt” is sometimes referred to as the forming wire, even though the paper is already
formed by the cylinder. If multiple layer paper is desired, several vats and cylinders
can be placed in series with the paper web acting as the cylinder felt for the addi-
tional paper mat. There are two main cylinder vat designs, contraflow and direct
flow; and the cylinder felt can be above or below the drying stock.
When the paper leaves the couch roll it contains 80–85 % of water, is very easily
damaged, and will support its own weight for only a very short distance. It is there-
fore transferred to a traveling woolen felt which supports it through the first of a
series of presses whose function is to remove more water by squeezing and at the
same time make the sheet denser and smoother. Two or three presses are used in
series, and the paper may go directly through, or it may pass under one press and be
reversed through its rolls so that the two sides of the sheet may be more nearly alike.
The top roll of the press stands vertically over the lower roll and it is connected with
compound levers and weights which allows regulation of the pressure applied and a
maximum pressure much greater than that supplied merely by the weight of the top
roll. Each press has a separate felt to carry the web, and just before the web reaches
each set of rolls the felt often passes over a suction box to aid in water removal. All
felts are kept taut by a series of stretch rolls as they return to the point at which they
picked up the paper web. Transferring the web from the couch to the first felt is done
when starting by cutting a narrow strip by means of the squirt on the wire and blow-
ing it onto the felt by an air blast; in slow machines it may be done by picking it off
the couch by hand and lifting it onto the felt. At each press the web sticks to the top
roll and has to be transferred to the next felt by hand or air blast. After leaving the
last press to go to the driers the sheet will still contain about 71–74 % of water, but
it has gained enough in strength so that it can be handled to the driers without dif-
ficulty (Biermann 1996).
Many modern machines are equipped with a smoothing press whose function is
not to remove water, but to smooth and flatten the sheet after it comes from the true
presses and before it goes to the driers. This aids in removing wire and felt marks
and produces a superior paper, both for smoothness and strength.
The felts used on the wet end of the paper machine are not true felts, which are
made without weaving, but are actually heavy blankets woven from very high grade
woolen yarns. They must be strong to withstand the pull of the machine, but also of
a texture loose enough to pass water readily. They are made in great variety to suit
the speed of the paper machine and the grade of paper being made, and the surface
of the paper is significantly affected by the length of nap and the fineness of weave
of the felt. Felts are easily damaged and must be handled carefully both off and on
the machine.
After leaving the presses the paper goes to the dry section of the machine, the
purpose of which is the removal of the water which cannot be taken out by pressing
and which amounts to about 70 % of the weight of the wet paper at this point
(Biermann 1996). A paper machine drier is a cast iron drum with closed ends, very
carefully made so that it may be in good running balance and supplied with a steam
inlet and a device to remove condensed water continuously and without loss of pres-
sure. The outer surface is turned and polished as smooth as possible. Driers are
usually mounted in two rows, one above the other, but staggered, so that an upper
drier is over the space between its two neighbours in the bottom row. At the back
end of each drier is a gear which meshes with the gears on two driers in the row
above or below, so that all turn at the same speed. A row of driers is usually broken
into two banks with approximately an equal number of drums, and each bank is
driven independently of the other. In some machines the driers are driven by an end-
less roller chain instead of gears; this is simpler in some respects and is desirable on
high-speed news and kraft machines.
When the driers are arranged in two rows, each row usually has a long felt
which covers about one half of the surface of each drier and is kept tight by means
of stretch rolls. These felts also are not true felts, and most of them are not wool,
but a kind of heavy cotton duck; some are made of cotton and asbestos to withstand
better the deterioration caused by the heat of the driers, which gradually rots the
cotton. The purpose of the felts is to hold the paper firmly against the surface of the
driers, except where it passes from one drum to the next, and thus produce a smooth
sheet with-out cockles. The wet web is carried from the last press to the first drier
and then in turn to the others until it emerges in a dry condition at the end of the
two banks.
In passing the driers, about two pounds of water must be evaporated for each
pound of paper made. In cold climates if this is allowed to escape directly into the
room it causes condensation on the ceiling and water drops all over the machine, so
it is customary to cover the drier section with a hood from which the vapors are
removed by fans.
From the driers the paper generally goes through calenders which consist of rolls
of cast iron, chilled on the surface to make them hard, and ground and polished to a
very smooth surface. A machine calender stack may have as many as eleven rolls,
all mounted in a housing at each end of the rolls, and all driven from the bottom roll
by friction. The paper is fed in at the top, passes down through the stack and out at
the bottom to the reel, where it is wound into large rolls, which are then rewound at
full width or through slitter knives which allow the preparation of rolls of other
desired sheet widths. The machine calender is designed to compact the sheet and
give it a better finish. If this is not desired, the sheet coming from the driers may
by-pass the calender and go directly to the reel. Some paper machines use two cal-
ender stacks set so that the sheet passes first one and then the other.
There are various modified paper machines for special purposes and products,
but these need only brief mention:
– The “Yankee machine” dries the paper against a highly polished, single-drum
drier, and this may be combined with the wet part of either a fourdrinier or a
cylinder. This produces the paper sometimes called “machine glazed.”
– A modified fourdrinier, known as the Harper machine, was built to handle very
thin tissues which were too light to be passed from the couch to the wet felt.
Other modifications combine portions of the fourdrinier and cylinder machines
into various assemblies.
After the drying section, the web is subjected to several finishing steps prior
to shipping it as a final product. The web can be sized, giving the paper surface
resistance, or if other properties are needed, the web can be surface coated. The web
can also be supercalendered giving the surface a very smooth the uniform surface.
In the final stages the web is rewound and slit into two or more rolls and if needed
sheeted.
Sizing imparts resistance to liquids on the paper surface, a property necessary for
paper used for writing or printing. Without external sizing, ink would bleed and
feather. External or Surface sizing can either be performed on the paper machine or
on a stand alone unit (Smook 1992; Latta 1997). Machine sizing can be performed
either by running the web through a size vat or by running the web through a size
press. In the case of the size vat, the web, after exiting the dryer section, is directed
down into a vat and through another set of drying cans. Size presses are located after
the between two dryer sections and applies a coat of sizing by transference from
rollers and the metering is accomplished by the nip. The most common types of siz-
ing consist of pigments and starches, although animal glue and glycerin can also be
used (art and banknote papers).
Coating paper may be desirable or necessary to improve optical, printing/writ-
ing, and/or functional properties. Functional properties can be for protection from
liquids, oils, gases, chemicals, improve adhesion characteristics, improve wear, or
some other property. Coatings can be classified as aqueous, solvent, high solids, or
extrusion, coatings. Aqueous coatings, used for commodity papers, contain water
soluble binders and are applied as a liquid. Common aqueous binders are Casein,
Starch, Protein, Acrylics and Polyvinyl Acetates. Solvent Coatings are used in situ-
ations where the binders are not soluble in water and are used with specialty papers.
High solid and Extrusion coatings are used for specialized papers, where chemical,
gas or liquid resistance is necessary. High solid coatings are applied as a coating of
monomers and are polymerized by UV or electron curing. Extrusion coatings are
applied as a molten film of wax or polymer.
After the chemical processes have been completed, physical processes, like
super calendering, cockling, and embossing, can be used to create the desired sur-
face texture to the paper (Smook 1992). Super calendering uses friction and pres-
sure to create a very smooth and glossy paper surface. The super calender consists
of a stack of rollers having surfaces alternating between steel and cotton in con-
struction. There is enough pressure between the steel and cotton rollers to slightly
compress the cotton surface causing a drag. The difference in surface speed on
either side of the nip creates friction, which polishes the paper surface. The cockle
finish on many bond writing papers is created by vat sizing the web then subjecting
it to high velocity air dryers under high tension, then under low tension. The fin-
ished paper is usually heavily sized and has the characteristic rattle associated with
high quality bond paper. Embossing is achieved by running the web through an off-
line press, where it is subjected to an engraved cylinder. The concept is similar to the
dandy roll, but since the paper fibres cannot be redistributed the surface of the paper
is raised or depressed.
Once the paper roll (machine log) is reeled from the paper machine it is removed
and transferred to a rereeler or a machine winder (Biermann 1996). A rereeler
unreels the web from the mandrels to create a full log. During this process any
References 37
defects can be removed and the web spliced. A machine winder is similar to the
rereeler, but is able to slit the web into multiple, narrower rolls. These rolls can be
further finished by super calendering, embossing, etc., sheeted, or wrapped and
shipped. If the finished product is sheeted paper, the rewound rolls are transferred to
machines known as cutters. The cutters can slit the web to form multiple narrower
webs and cut across the web creating sheets. The paper rolls are placed onto a stand
at one end of the machine. As the web unwinds it can be slit either adjusting the web
width or creating several parallel webs. After the slitters, the web travels under a
revolving knife, which cuts the web into sheets. After being cut the sheets are jogged
through an on-line inspection system which checks caliper and dimensions. If the
sheet does not conform it drops down into a sheeter for recycling as broke. After the
cutters, the paper stacks are placed into guillotine trimmers, where the edges receive
their final trim.
After trimming, paper rolls have inner headers (circular disks) applied to the
ends, are wrapped with a heavy moisture resistant paper or plastic and sealed with
outer headers. The sealed rolls are then placed flat, to prevent flat spots from form-
ing, and shipped. Sheeted paper can be prepared for shipping in various ways
depending on the size of the finished product. If the finished sheets are small, such
as 8 1/2″ × 11″, the sheets are stacked in junior cartons, cross stacked on pallets,
strapped and wrapped. Similarly larger sheets can also be carton packaged, strapped
and wrapped. Large orders, such as those for printers, can be bulk packed on skids
(slightly different dimensions and design than a pallet), wrapped, and strapped.
References
Adams TN (1992) Lime reburning. In: Kocurek MJ (ed) Pulp and paper manufacture, vol 5, 3rd
edn. TAPPI/CPPA, Atlanta/Montreal, p 590
Annergren G, Lundqvist F (2008) Continuous kraft cooking: research and applications. STFI-
Packforsk, Stockholm, 82 pp
Arpalahti O, Engdahl H, Jantti J, Kiiskila E, Liiri O, Pekkinen J, Puumalainen R, Sankala H,
Vehmaan-Kreula J (2000) Chapter 14: White liquor preparation. In: Gullichsen J, Paulapuro H
(eds) Papermaking science and technology, vol 6B. Fapet Oy, Helsinki, p 135
Arppe M (2001) Mechanical pulp: has it got a future or will it be discontinued? Int Papwirtsch
10:45–50
Atkins J (2005) The forming section: beyond the fourdrinier. Solutions! :28–30
Bajpai P (2004) Emerging technologies in sizing. PIRA International, Leatherhead, 159 pp
Bajpai P (2005) Technological developments in refining. PIRA International, Leatherhead, 140 pp
Bajpai P (2008) Chemical recovery in pulp and paper making. PIRA International, Leatherhead,
166 pp
Bajpai P (2012) Environmentally benign approaches for pulp bleaching, 2nd edn. Elsevier,
Amsterdam
Bajpai P (2013) Recycling and deinking of recovered paper. Elsevier Science, Amsterdam
Baker C (2000) In: Baker C (ed) Refining technology. Pira International, Leatherhead, 197 pp
Baker CF (2005) Advances in the practicalities of refining. In: Scientific and technical advances in
refining and mechanical pulping, 8th Pira International refining conference, Pira International,
Barcelona, 28 February–March 2005
Biermann CJ (1996) Handbook of pulping and papermaking, 2nd edn. Academic, San Diego,
p 754
Buck RJ (2006) Fourdrinier: principles and practices, 2006 In: TAPPI papermakers conference,
Atlanta, 24–28 April 2006, Session 15, 13pp
Casey JP (1983a) Chemical pulping: a perspective. Tappi J 66(1):155–156
Casey JP (1983b) Mechanical and chemi-mechanical pulping: a perspective. Tappi J 66(6):95–96
Davison RW (1992) Internal sizing. In: Hagemeyer RW, Manson DW (eds) Pulp and paper manu-
facture, vol 6. TAPPI/CPPA, Atlanta/Montreal, p 39
EPA (2001a) Pulp and paper combustion sources national emission standards for hazardous air
pollutants: a plain English description. U.S. Environmental Protection Agency.
EPA-456/R-01-003. September 2001. http://www.epa.gov/ttn/atw/pulp/chapters1-6pdf.zip
EPA (2001b) Pulping and bleaching system NESHAP for the pulp and paper industry: a plain
English description. U.S. Environmental Protection Agency. EPA-456/R-01-002. September
2001. http://www.epa.gov/ttn/atw/pulp/guidance.pdf
EPA (2002) Profile of the pulp and paper industry, 2nd edn. EPA Office of Compliance
Sector Notebook Project. U.S. Environmental Protection Agency. EPA/310-R-02-002.
November 2002
Farr JP, Smith WL, Steichen DS (1992) Bleaching agents (survey). In: Grayson M (ed) Kirk-
Othmer encyclopedia of chemical technology, vol 4, 4th edn. Wiley, New York, p 271
Fredette MC (1996) Section 2, Chapter 2: Pulp bleaching: principles and practice. In: Dence CW,
Reeve DW (eds) Bleaching chemicals: chlorine dioxide. Tappi Press, Atlanta, p 59
Gullichsen J (2000) Fibre line operations. In: Gullichsen J, Fogelholm CJ (eds) Chemical pulp-
ing – papermaking science and technology. Book 6A. Fapet Oy, Helsinki, p A19
Hodgson KT (1997) Overview of sizing. In: Tappi sizing short course, Session 1. TAPPI, Nashville
(April 14–16, 1997)
Holik H (2006) Stock preparation. In: Sixta H (ed) Handbook of paper and board. WILEY-VCH,
Weinheim, pp 150–206
Ince PJ (2004) Pulping – fibre resources. In: Burley J, Evans J, Youngquist JA (eds) Encyclopedia
of forest sciences. Elsevier, Oxford, pp 877–883
Ishiguro K (1987) Paper machine. Jpn Tappi 41(10):44–50
Krogerus B (2007) Chapter 3: Papermaking additives. In: Alen R (ed) Papermaking chemistry:
papermaking science and technology, vol 4, 2nd edn. Finnish Paper Engineers’ Association,
Helsinki, pp 54–121, 255 pp
Krotscheck AW (2006) In: Sixta H (ed) Handbook of pulp. WILEY-VCH, Weinheim,
pp 512–605
Latta JL (1997) Surface sizing I: overview and chemistry. In: Tappi sizing short course, Session 5.
TAPPI, Nashville (April 14–16, 1997)
Ljokkoi R (2000) Pulp screening applications. In: Gullichsen J, Fogelholm C-J (eds) Chemical
pulping. Papermaking science and technology, vol 6A. Fapet Oy, Helsinki, pp A603–A616
Lumiainen J (2000) Chapter 4: Refining of chemical pulp. In: Papermaking science and technol-
ogy, vol 8, Papermaking part 1: Stock preparation and wet end. Fapet Oy, Helsinki, p 86
Lund A (1999) The paper machine 200 years Nord. Pappershistorisk Tidskr 27(2):9–16
Malashenko A, Karlsson M, (2000) Twin wire forming – An overview. In: 86th annual meeting,
Montreal, Que, Canada, 1–3 February. 2000, Preprints A, pp A189–A201
Malinen, Fuhrmann A (1995) Recent trends in bleaching of chemical pulp. Paperi ja puu
77(3):78–83
Marcoccia B, Prough JR, Engstrom J, Gullichsen J (2000) Chapter 6: Continuous cooking applica-
tions. In: Gullichsen J, Fogelholm C-J (eds) Papermaking science and technology, vol 6A,
Chemical pulping., pp A512–A570
McDonough T (1992) Bleaching agents (pulp and paper). In: Grayson M (ed) Kirk-Othmer ency-
clopedia of chemical technology, vol 4. Wiley, New York, p 301
McDonough TJ (1995) Recent advances in bleached chemical pulp manufacturing technology.
Part 1: extended delignification, oxygen delignification, enzyme applications, and ECF and
TCF bleaching. Tappi J 78(3):55–62
References 39
Neimo L (2000) Internal sizing of paper. In: Neimo L (ed) Papermaking chemistry. Tappi Press/
Fapet Oy, Atlanta/Helsinki, p 150
Paulapuro H (2000) Stock and water systems of the paper machine. In: Gullichsen J, Fogelholm
C-J (eds) Papermaking science and technology, vol 8, Papermaking part 1, Stock preparation
and wet end. Fapet Oy, Helsinki, p 125
Rapson WH, Strumila GB (1979) The bleaching of pulp. In: Singh RP (ed) Chlorine dioxide
bleaching, 3rd edn. Tappi Press, Atlanta, p 113
Reeve DW (1989) Bleaching chemicals. In: Kocurek MJ (ed) Pulp and paper manufacture, vol 5,
Alkaline pulping. TAPPI/CPPA, Atlanta/Montreal, p 425
Reeve DW (1996a) Section 1, Chapter 1: Introduction to the principles and practice of pulp bleach-
ing. In: Dence CW, Reeve DW (eds) Pulp bleaching: principles and practice. Tappi Press,
Atlanta, p 1
Reeve DW (1996b) Section 4, Chapter 8: Pulp bleaching: principles and practice. In: Dence CW,
Reeve DW (eds) Chlorine dioxide in bleaching stages. Tappi Press, Atlanta, p 379
Reeve DW (2002) The kraft recovery cycle, Tappi kraft recovery operations short course. Tappi
Press, Atlanta
Ressel JB (2006) In: Sixta H (ed) Handbook of pulp. WILEY-VCH, Weinheim, pp 69–105
Roberts JC (1996) Neutral and alkaline sizing. In: Roberts JC (ed) Paper chemistry, 2nd edn.
Chapman and Hall, London, p 140
Roberts JC (1997) A Review of Advances in Internal Sizing of Paper. In: Baker CF (ed) The fun-
damentals of paper making materials: transactions, 11th fundamental research symposium
(Cambridge), vol 1. PIRA International, Leatherhead, p 209
Sixta H (2006) In: Sixta H (ed) Handbook of pulp. WILEY-VCH, Weinheim, pp 2–19
Smook GA (1992) Handbook for pulp and paper technologists. Angus Wilde Publications, Inc,
Vancouver, 425p
Stevens WV (1992) Refining. In: Kocurek MJ (ed) Pulp and paper manufacture, vol 6, 3rd edn.
TAPPI/CPPA, Atlanta, p 187
Tran H (2007) Advances in the kraft chemical recovery process, Source 3rd ICEP international
colloquium on eucalyptus pulp, 4–7 March, Belo Horizonte, Brazil, 7pp
USEPA (1998) Pulp and paper NESHAP: a plain English description www.epa.gov/ttnatw01/pulp/
guidance.pdf
Vakkilainen EK (2000) Chapter 1: Chemical recovery. In: Gullichsen J, Paulapuro H (eds)
Papermaking science and technology, vol 6B. Fapet Oy, Helsinki, p 7
Venkatesh V (1992) Chapter 8: Lime reburning. In: Greenand RP, Hough G (eds) Chemical recov-
ery in the alkaline pulping process, vol 6B. Tappi Press, Atlanta, p 153
Chapter 3
Environmental Consequences of Pulp
and Paper Manufacture
Abstract Pulp and paper companies have faced environmental issues for many
years because of the resource-intensive nature of their industry. The pulp and paper
mills represent a major source of polluting materials which are very different regard-
ing their characteristics and quantities. The most significant environmental impacts
of the pulp and paper manufacture result from the pulping and bleaching processes:
some pollutants are emitted to the air, others are discharged to the wastewaters, and
solid wastes are generated as well. The environmental consequences of pulp and
paper manufacture are presented in this chapter. A special attention is focused on the
pulp bleaching as the most pollution process of the chemical pulp manufacturing.
Keywords Kraft pulping • Pulp bleaching • Environment • Wastewaters • Air emis-

sions • Liquid • Discharges • Solid wastes
The pulp and paper industry has been considered a major consumer of natural
resources, energy and water and is a significant contributor of pollutant discharges
and emissions to the environment. It ranks fourth among industrial sectors in emis-
sions of Toxics Release Inventory (TRI) chemicals to water, and third in such
releases to air. Technological changes, the use of environmental and energy man-
agement systems, investments in environmental measures and continuous improve-
ments, the increased recycling of paper, the employment of highly trained and
committed personnel have allowed for a stepwise reduction in the environmental
footprint, and have reduced emissions by 80–90 % or more on a product-specific
basis (per tonne of product) since about 1980. In the United States, the paper indus-
try is the largest user of industrial process water (per tonne of product) (US EPA
2002) and the third largest industrial consumer of energy (US DOE) (Papercutz:
PlanetArk 2008).
Paper’s impact on the environment continues even after it has been thrown away.
As at early 2008 in the United States, paper and paperboard accounted for the larg-
est portion (34 %) of the municipal waste stream, and 25 % of discards after recovery
of materials for recycling and composting. The problem with all this paper being
Some excerpts taken from Bajpai Pratima, “Environmentally Friendly Production of Pulp and
Paper” John Wiley & Sons, (2010) with kind permission from John Wiley & Sons Inc., Hoboken,
NJ, USA, Copyright © 2010 John Wiley & Sons, Inc.

DOI 10.1007/978-3-319-18744-0_3
42 3 Environmental Consequences of Pulp and Paper Manufacture
thrown away is not just about landfill space. Once in a landfill, paper has the poten-
tial to decompose and produce methane which is, a greenhouse gas (GHG). It has
21 times the heat-trapping power of carbon dioxide. Finally, transportation through-
out the system also has considerable environmental impacts. Harvested trees or
recovered paper are transported to pulp mills, rolls of paper are transported to con-
verters, and finished paper products are transported to wholesale distributors and
then on to their retail point of sale. Transportation at each of these stages consumes
energy and results in emission of GHGs.
There is a strong drive to improve the impact of the pulp and paper industry upon
the environment. This includes moves to sustainable forest management with
Forestry Stewardship Certification and removal of harmful bleaching technologies.
Impacts on the environment can potentially come from toxic and hazardous chemi-
cals in water and air emissions, odor-causing chemicals, thermal loading to natural
waterways, air pollutants from combustion, and solid wastes. The industry is taking
steps to reduce environmental impacts by increasing the use of recycled paper,
improving energy efficiency, and making capital investments for effective compli-
ance with regulations.
A pulp mill influences the water and air near the mill, and the emissions are fol-
lowed by measurements and there are emission limits set by authorities. Disposal of
solid waste, recycling of fibres and use of land and forest are gaining attention.
Other effects of a pulp mill on the nearby society are smell, noise and influence of
traffic related to the transport of raw materials and products. Table 3.1 shows param-
eters important to demonstrating continuous improvements towards a minimum
impact mill.
The environmental impacts of kraft pulp production mainly result from the
chemicals used for both cooking and bleaching. Some of which are: sulphur, chlo-
rine, chlorinated compounds, remaining organic and inorganic materials, lignin and
undissolved fibre material, typically mixed up in the black liquor, and eventually
sodium and magnesium salts, chelating agents and heavy metals such as manganese
or iron. Thus, the main environmental problems of kraft pulp production are water
consumption, wastewater loads and gaseous emissions, including malodorous sul-
fur compounds and carbon dioxide (European Commission 2001, 2013).
The most significant environmental impacts of the pulp and paper manufacture
result from the pulping and bleaching processes. Some pollutants are released to the
air, others are discharged to the wastewaters, and solid wastes are also generated
(Bajpai 2001). Much research has focused upon the bleaching technology employed
because this component of the production process has historically been associated
with the formation of chlorinated dioxins and other chlorinated organic chemicals.
These pollutants are toxic, non biodegradable and have the tendency to contaminate
food chains through bioaccumulation. The dioxins are known for their extreme tox-
icity and are believed to be carcinogenic. Bleaching technology is also a key deter-
minant of the potential for the closure of mill process circuits to achieve zero effluent
operation (Bajpai and Bajpai 1996; Bajpai 2001).
The impact of pulp effluent has been studied in some detail in Scandinavia,
where significant efforts have been made to reduce pulp mill discharges. A three-
3 Environmental Consequences of Pulp and Paper Manufacture 43
Table 3.1 Important parameters followed in order to demonstrate improvements towards a

minimum impact mill
Water Air Solid Waste Other
Water usage Particulates Solid waste Accidental releases
generated
Bleach plant Total reduced sulfur Solid waste Accidental releases
effluent disposal Non-compliant events
Final effluent Methanol Landfill SARA 313 releases
BOD Chloroform Recycled Energy use/energy export
COD Chlorine Energy Transportation effects
aesthetics
Suspended solids Chlorine dioxide Hazardous waste Site appearance
AOX
Dioxins and furans CO/CO2 Elimination Odor
Color NOX Noise
Biological tests SO2
Nutrients VOC
Heavy metals Dioxins and furans
Safety Opacity
Hazardous air
pollutants
year study of pulp mill effluents in the Baltic Sea showed that near the effluent
outflow fish biomass was low, and species composition had changed with perch
(Perca fluviatilis) showing reduced reproduction, changes in physiology and dam-
age to the spinal column. Presence of a pulp mills affected recruitment to fish popu-
lations over an area of several square kilometres, thus having an economic impact
on fisheries. In the case of perch reproductive losses of 30–70 % were made in the
affected area. The effluent also affected the diversity, biomass and distribution of
invertebrates and plants, including the crustacean Pontoreia affinis and the bivalve
mollusc Macoma baltica (Södergren 1989). Further research revealed that the distri-
bution of the seaweed bladder wrack (Fucus vesiculosus) was affected by pulp mill
effluent, with the algae disappearing from the most polluted areas. Pollution also
decreased the numbers of mussels and increased the frequency of malformed larvae.
Bleached pulp mill effluents also apparently increased the prevalence of three fish
diseases (Södergren 1993):
– Fin erosion in perch and goldfish (Carassius auratus studied in New Zealand),
– Jaw deformity in pike
– Gill cover deformity in perch
A series of studies in Scandinavia found that chronic effects of pulp mill efflu-
ents could include:
– Changes in reproductive and life cycles, deformities in embryos, stunted growth
and higher egg mortalities;
– Deformities in bones and gill erosion in fish;

– Biochemical and physiological disturbances, including reduced ability of mus-
cles to store carbohydrates, impaired stamina and increased susceptibility to pre-
dation and disease;
– Changes in habitat and community structure (Abel 1993).
Inspite of that, the relationships between specific effluent compounds and toxic
effects is poorly understood, and sublethal biological effects occur even when dilu-
tion of waste is quite high. Synergistic and/or antagonistic effects amongst chemical
compounds are probably important in some cases (Priha 1991). Toxicity is affected
by the type of wood used and the procedures used for processing (Fandry et al.
1989). Research funded by the Department of Fisheries and Oceans, Canada, and
the Ontario Ministry of Environment Research Advisory Council found that several
species of fish exhibited damage from pulp mill effluents at Jackfish Bay, Lake
Superior. The white sucker (Catostomus commersoni) showed a variety of responses
listed below when exposed to kraft pulp mill effluent:
– Reduction in body size
– Delayed sexual maturity
– Smaller gonads
– Increased liver size
Similar effects were observed in lake whitefish (Coregonus clupeaformis) and
longnose sucker (Catostomus catostomus). The mill discharge into Jackfish Bay
was reduced by installation of an aerated stabilisation basin in 1989. Studies in 1993
showed no evidence of recovery in reproductive function, but did find limited
improvement in liver size. Further research on white sucker fish found that loss of
reproductive capability occurred near pulp mills with and without chlorine bleach-
ing, and at sites with secondary effluent treatment (Munkittrick and van der Kraak
1994). Researchers now believe that some effects on fish are caused by non-
chlorinated compounds, probably coming from the wood itself. One of these com-
pounds has been positively identified as a steroid (Cockram and Richard 1994).
Dioxins were found in the effluent of two thirds of Japanese pulp and paper mills.
In October 1990, research by Ehime University revealed that fish caught in sea
water near pulp mills in lyo-Mishima contained 9.4 parts per thousand of dioxin.
The Ministry of International Trade and Industry called for the 32 mills producing
bleached kraft pulp by chlorine gas to change to oxygen or chlorine dioxide. There
are now no mills in Japan using chlorine gas bleaching (Kondo 1993). Other by-
products of the process include ‘non-filterable material’ consisting of bark and
wood fibres. These materials can also be of threat to aquatic organisms forming
fibre mats on ocean bottoms, eliminating or altering bottom-dwelling organisms
(IIED 1994). Toxic effects can extend to other groups of animals as well. In North
America, both peregrine falcon. and blue herons have suffered reproductive failure
through accumulation of organochlorines from pulp mill effluent.
There is a development to close up water circuits in pulp and paper mills and a
further reduction of discharges can be expected (towards effluent free mills).
3 Environmental Consequences of Pulp and Paper Manufacture 45
However, today there are no kraft mills operating full time, which completely
recover all bleach plant effluent. Few CTMP mills, sodium-based sulphite pulp
mills and a few producers of corrugating medium and testliner using recycled fibre
have realised zero effluents to water.
There is a debate about minimum-impact pulp manufacturing in the recent past
(Axegard et al. 1997; Hanninen 1996; Elo 1995). This minimum-impact mill stands
for a concept with a broader range of issues and challenges covering minimisation
of resource consumption and emissions, minimising crossmedia effects, taking into
account economic aspects and working environment.
The pulp mills caused serious emissions of sulphur in the past but in the recent
years especially the sulphur air emissions has been reduced significantly which
could be attributed to advancement of process technology. In most of the countries,
the recycling of fibres of used paper has reached a quite advanced level and for some
paper grades a further increase may be expected. The recovery of energy from
wastes from pulp and paper manufacturing processes (rejects, sludge) is possible
thereby avoiding a waste disposal problem. But in this respect there is still a high
potential for increased use of efficient on-site techniques. For chemical pulping no
external energy is needed but the total demand of process energy is still on a high
level. Mechanical pulping is the most energy-intensive process because of the elec-
tricity demand of the refiners. Also recovered paper processing and papermaking
are energy-intensive processes. This is caused by the fact that for papermaking the
solid content of a dilute suspension of fibres and possibly fillers has to be brought to
about 95 % solids as a typical dry solid content in finished papers by means of press-
ing and drying.
During the period before the 1970s, the pulp and paper industry caused substan-
tial wastewater discharges into receiving waters. The effects observed were some-
times of dramatic character with oxygen depletion and fish kills. From the end of the
1970s until recently, the main emphasis was put on the role of chlorinated sub-
stances formed in the bleach plant. Dioxins and Furans had been detected in some
effluents of pulp mills and the public discussion focussed on the harmful effects of
chlorine bleaching. The public concern about the potential environmental hazard
imposed by the use of chlorine in the bleach plants has brought about a drastic
decrease in the use of molecular chlorine as a bleaching chemical during the last
decade (Bajpai 2001).
Increasing awareness of environmental consequences of bleach effluent has lead
to stringent environmental regulations. Prior to 1985, there were prescribed limits
for only conventional parameters such as chemical oxygen demand (COD), biologi-
cal oxygen demand (BOD), total suspended solids (TSS) etc. But now, most nations
have imposed limits on adsorbable organic halides (AOX) of the effluents. In some
nations, limits have also been set on individual chlorinated organic compounds of
bleach effluents viz. 2,3,7,8-tetrachlorodibenzodioxin (2,3,7,8-TCDD), and
2,3,7,8-tetrachlorodibenzofuran (2,3,7,8-TCDF). A reduction of AOX has been
achieved by a combination of several measures. The use of molecular chlorine has
been largely replaced by chlorine dioxide and introduction of other oxygen-
containing chemicals such as molecular oxygen, peroxide and ozone. Due to the
strong reduction of the chloride content of the effluents a closure of the mill system
and recycling of the bleach plant effluent back to the chemical recovery system of
the mill has been made possible. The reduction of both chlorinated and non-
chlorinated organic substances in the effluents of pulp mills has been achieved to a
large extent by in-process measures as for example: increased delignification before
the bleach plant by extended or modified cooking and additional oxygen stages,
spill collection systems, efficient washing, and stripping and reuse of condensates.
Another contributing factor to the decreased emissions of AOX and unchlorinated
toxic organic compounds into receiving waters, was the installation of external
treatment plants of different designs (Bajpai and Bajpai 1996).
There has been a development to close up water circuits in pulp and paper mills
(McDonough 1995; Chirat and Lachenal 1997; Pryke 2003; Bajpai and Bajpai
1999; Bajpai 2012). And in regions with scarce water resources or dry climate, fur-
ther reduction of water use per tonne of product will be essential in order to keep the
capital-intensive production sites. Those sites will probably be the first movers that
develop new techniques and management methods toward water-saving solutions.
Other driving forces for developing less water using techniques will probably be the
regional costs of raw and waste water. However, there is a trend not to push too
much further the closure of water circuits in normal pulp and paper mills because of
the often involved technical drawbacks such as scaling, increased corrosion, accu-
mulation of salts or non-process elements in process waters, etc. Today there are no
kraft mills operating full time, which completely recover all bleach plant effluent.
One CTMP mill, a sodium-based bleach plant of a sulphite pulp mill and a few
producers of corrugating media and Testliner using recycled fibre have realised zero
effluents to water (European Commission 2013). Under an integrated perspective,
the aim is to move towards the minimum impact pulp and paper manufacturing. In
a few paper mills, an increased reuse of treated process waters by implementing
production-integrated advanced waste water treatment systems can be observed.
However, water use is not to be seen separately from the other main elements for
production which are energy, fibres and chemical additives and proper functioning
of all technical devices. Energy consumption, use of chemical additives, runnability
of the paper machines and product quality are closely linked to the water used per
tonne of pulp or paper and should be assessed in an integrated way.
In paper mills an increased reuse of treated process waters by implementing
production integrated advanced wastewater treatment systems will be allowed.
Wastewater discharges, environmentally friendly handling of wastes, energy saving
and recovery and locally smell from kraft pulp mills are expected to remain also
future priorities of environmental actions in pulp and paper industry.
3.1 Water Pollution
Of the different wastewaters generated by the pulp and paper industry, bleach plant
effluents are considered to be the most polluting. About 300 different compounds in
bleached pulp mill effluents have been identified. About 200 of them are chlorinated
3.1 Water Pollution 47
organic compounds which include chlorinated resin acids, chlorinated phenolics

and dioxins. The main compounds, by general type, are listed in Table 3.2. Pollutants
such as chlorinated phenolics and dioxins are toxic, non biodegradable and have the
tendency to contaminate food chains through bioaccumulation. The dioxins are
known for their extreme toxicity and are believed to be carcinogenic (Bajpai 2001).
Table 3.3 shows the list of 12 polychlorinated phenolics selected by EPA for
regulation.
The most common chlorinated phenolics in bleached kraft pulp mill effluents are
tri- and tetra chloroguaiacols (Liebergott et al. 1990). The substitution of chlorine
dioxide for chlorine in the bleaching stage also alters effluent composition. For
example, catechols and guaiacols together include 77 % of the total chlorinated
phenolic content when chlorine alone was used in the bleaching stage. When a
70:30 chlorine dioxide:chlorine ratio was used in the first stage, the catechol and
guaiacol portion decreased to 46 %, and at 100 % chlorine dioxide substitution, only
Table 3.2 Chlorinated Variations

organic compounds in bleach Types of chlorinated compounds (numbers)
plant effluents Acids, esters, aldehydes, furans, 77
pyrenes
Phenols and phenol ethers 52
Aldehydes and ketones 66
Hydrocarbons 75
Alcohols 25
Dioxins and furans 20
Miscellaneous 15
Total 330
Based on McKague and Carlberg (1996)
Table 3.3 Regulated 2,3,4,6-Tetrachlorophenol

chlorophenols
2,4,5-Trichlorophenol
2,4,6-Trichlorophenol
Pentachlorophenol
3,4,5-Trichloroguaiacol
3,4,5-Trichlosyringal
3,4,5,6, Tetrachlorocatechol
3,4,6-Trichlorocatechol
3,4,5-Tetrachlorocatechol
3,4,5,6-Tetrachloroguaiacol
Based on Vice and Carrol
(1998)
10 % of the chlorinated phenolics were of the catechol and guaiacol type (Liebergott
et al. 1989).
Bleach kraft mill effluent is a complex mixture of chlorinated and non-chlorinated
products of lignin and/or extractives of wood that imparts dark colour to the efflu-
ent. Coloured effluent may result in the following adverse effects upon the receiving
water body:
(a) Colour reduces the visual appeal and recreational value of the water.
(b) Colour, derived from lignin, is an indicator of the presence of potentially inhib-
iting compounds.
(c) Colour affects downstream municipal and industrial water uses, and increases
the cost and difficulty of pre-treatment for industrial processes.
(d) Colour retards sunlight transmission, thus reducing the productivity of the
aquatic community by interfering with photosynthesis.
(e) Colour-imparting substances form complexes with metal ions, such as iron, or
copper, and form tar like residues. These residues may have direct inhibitory
effects on some of the lower organisms in the food chain.
(f) Colour bodies exert long term BOD (20–100 days) that cannot be measured in
terms of 5-day BOD.
Bleached kraft mill effluent can effect the biological quality of the receiving
water. Disappearance of benthic invertebrates, high incidence of fish diseases, and
mutagenic effects on the aquatic fauna are some of the consequences of the disposal
of bleach effluents into surface waters (Sundelin 1988; Sodergren et al. 1993).
Bleached kraft and bleached sulphite mill effluents have been demonstrated to
impair the functions of liver, enzyme systems, and metabolic cycles in the exposed
fish. Furthermore, such exposures have been demonstrated to increase the incidence
of spinal deformities and reduced gonad development. The low molecular weight
fraction of bleach effluent contains potentially problematic (toxic) compounds.
These have the ability to penetrate cell membranes and a tendency to bioaccumu-
late. Low molecular weight chlorinated organic compounds significantly affect the
biology of aquatic ecosystems.
A major part of the organically bound chlorine (80 %) is believed to be heteroge-
neous material of relatively high molecular weight compounds. These compounds
apparently contribute little to the effluent BOD and acute toxicity. Their major con-
tribution is towards colour, COD, and chronic toxicity. Ecological/natural processes,
such as sedimentation, biodegradation, and bioaccumulation, are apparently corre-
lated with the molecular size and hydrophobicity of the compounds. Highly polar
and high molecular mass constituents are responsible for the toxicity of the bleach
effluents during early life stages of marine animals and plants (Higachi et al. 1992).
Chlorocymenes and chlorocymenenes in the bleach effluent have been reported to
bio-accumulate in fish and mussels (Suntio et al. 1988).
Chlorinated dioxins, which are present in very low concentrations in the bleach
plant effluent (usually in ppt levels), account to a 10 billionth of the total AOX dis-
charged. About 210 different dioxins, belonging to the two families, namely, poly-
chlorinated dibenzodioxins (PCDDs), and polychlorinated dibenzofurans (PCDFs),
3.1 Water Pollution 49
have been reported in the bleach effluents. 2,3,7,8-TCDF, and 2,3,7,8-TCDD are
especially toxic, carcinogenic, and bio-accumulable. The structures of the most
toxic forms of dioxin and furan molecules are shown in Fig. 3.1. A dioxin molecule
is bonded by two oxygen atoms and a furan molecule by a single oxygen atom and
a direct bond (Rappe and Wagman 1995). Under standard atmospheric conditions,
all dioxins are solid and are characterised by low vapour pressure and limited solu-
bility in water. Polychlorinated dioxins toxicity depends on the location and the
number of additional chlorine atoms attached to the benzene rings. PCDD/F that
have four chlorine atoms substituted in positions 2, 3, 7, and 8 are considered to be
the most toxic (Rappe and Wagman 1995). The major source of dioxins in the pulp
and paper industry is the bleaching process in which chlorine is used as reagent. It
was found that pulp chlorination stage is the first point where dioxins are generated
(McKague and Carlberg 1996). The chlorinated pulp contains largest concentration
of dioxins that are solubilized in the next alkaline extraction stage. The quantity of
dioxins in the bleaching effluents is very low; normally these compounds cannot be
determined even with the best analytical techniques.
Dioxins are almost insoluble in water. They tend to enter the food chains and
accumulate in high concentrations in predators, such as fish-eating birds (McCubbin
1989; McCubbin et al. 1990). Adverse effects of dioxins have been observed in
almost all species tested. According to an Environmental Protection Agency (EPA)
report (Anonymous 1994), human beings lie somewhere in the middle of the sensi-
tivity range (from extremely responsive to extremely resistant) for dioxins. Even in
trace amounts, dioxins may cause a wide range of adverse health conditions, such
as disruption of regulatory hormones, reproductive and immune system disorders
and abnormal fetal development (Bajpai and Bajpai 1996).
Fig. 3.1 Polychlorinated PCDD

dibenzodioxins (PCDD) and
polychlorinated O
dibenzofurans (PCDF) 7 2
8 3
O
CI CI
PCDF
7 2
8 3
O
CI CI
Some data suggest that the toxicity of treated effluent from advanced ECF mills
can be similar to treated TCF effluent (Verta et al. 1996). The most advanced TCF
effluents generally show the lowest toxic effects for effluents tested using stan-
dardised techniques. Moreover, many studies continue to suggest that even the most
advanced ECF mills produce effluent with a higher toxicity than TCF mills (Vidal
et al. 1997; Cates et al 1995; Kovacs et al. 1995; Rappe and Wagman 1995;
Rosenberg et al. 1994). Some of these studies also suggest that formation of bioac-
cumulative dioxins and furans, while indeed greatly reduced in mills using ECF
processes, continues to occur. This is most probably due to the partial dissociation
of chlorine dioxide to produce elemental chlorine, throwing some doubt on the
accuracy of the term ECF (Johnston et al. 1996). Research has been conducted on
ecosystem integrity and biodiversity in waters which receive treated effluent from
ECF mills in British Columbia, Canada. These mills meet some of the strictest
existing standards in the world. The data continue to show a strong correlation
between exposure to the effluent and severe ecosystem disturbance (Bard 1998).
In general, treatment of effluent reduces toxicity in the case of all effluents (Verta
et al. 1996), although toxicity of the effluent can itself influence the effectiveness of
biological treatment processes. There are indications that TCF effluents may be
simpler to treat. For example, reduction of AOX and chlorate, which are only gener-
ated in ECF, but not TCF, bleaching (Germgard et al. 1981), requires anaerobic
conditions, while COD and BOD, produced in both ECF and TCF mills, are most
effectively removed in aerobic conditions (Duncan et al. 1995). Because TCF mills
do not produce AOX and chlorate, the treatment systems needed are, therefore,
likely to be less complex. A study, which contradicts assertions that ECF and TCF
effluents have a similar toxicity, demonstrates that ECF effluents are more toxic to
methanogenic organisms than TCF effluents. A greater potential for anaerobic bio-
degradation was also demonstrated for TCF effluent (Vidal et al. 1997) as might
have been expected from these results. Nonetheless, certain types of chronic toxic-
ity do appear in both the treated ECF and TCF effluents (Stauber et al. 1995).
Despite the general reductions in toxicity which have been achieved for pulp
effluents, certain biologically active chemicals present in the wood furnish can pass
through treatment plants without being degraded. Hence, impacts on fish popula-
tions have been detected following exposure to a wide variety of mill effluents
employing various bleaching processes (Johnston et al. 1996). Research from
British Columbia has shown that dilute concentrations as low as 2 % of treated
bleach effluent from kraft mills with 100 % chlorine dioxide substitution can cause
actual, physical genetic damage to salmon (Easton et al. 1997). This research needs
to be replicated for the effluents of the most advanced ECF mills, as well as TCF
mills. Indeed, these observations have provided a compelling argument for develop-
ing Totally Effluent Free mills.
In addition to the identified problems of chemicals in the wood furnish, alterna-
tive bleaching processes require changes in process chemicals. One group of
chemicals which has given rise to concerns are the chelating agents
(Ethylenediaminetetraacetic acid (EDTA), diethylene triamine pentaacetic acid
(DTPA) are examples). Such agents are used to remove metallic contaminants in
3.2 Atmospheric Pollution 51
the pulp before bleaching with peroxide and are employed in most currently oper-
ating TCF mills as well as in some ECF mills with peroxide stages. Metallic con-
taminants would otherwise reduce the efficiency of the peroxide (Södra-Cell 1996).
These chelating agents are currently discharged to effluent treatment and appear to
be relatively resistant to degradation. At present, there does not appear to be an
efficient decomposition pathway for the chelants EDTA and DTPA and their pres-
ence may initially inhibit the efficiency of activated sludge secondary treatment
(Larisch and Duff 1997). However, treatment with aluminum sulphate can result in
a 65 % EDTA reduction in treated effluent, and photochemical degradation is
known to be a possibility (Saunamaki 1995). While most toxicity studies seem to
support the claim that any chelants and metals coming through to treatment and/or
the final effluent are not a significant environmental problem (Saunamaki 1995),
this issue needs to be more specifically studied in relation to aspects other than
direct toxicity. In particular, the ability of chelating agents to mobilise metals after
discharge, and the potential consequences of this for natural systems requires com-
prehensive evaluation.
Some studies suggest that efficient acid washing of the pulp before bleaching can
eliminate the need for chelating agents (Bouchard et al. 1995), but this may be very
dependent on furnish. Moreover, acid wash strategies that can fully eliminate the
need for chelants may cause unacceptable viscosity loss in the pulp. Metal removal
treatments using acid washing need to be further developed into processes which
avoid degradation of the final product quality (Lapierre et al. 1997). Alternative
chelants are being investigated. Hydroxycarbolates (glycolate and galactarate) have
been shown to act as effective complexing agents in closed TCF process simulations
(Gevert and Lohmander 1997). Moreover, research has led to the identification of
chelants that may be used to control process metals and which appear to be readily
biodegradable (Lockie 1996). While these initiatives show promise, the usefulness,
degradability and toxicity of such alternative chelating compounds requires exhaus-
tive evaluation. It is inevitable that some of these chemicals will be purged from
pulp production systems as a result of the need to control the build up of non-
process elements, particularly in the bleach lines. The purging of non-process ele-
ments from pulp production systems is, therefore, an issue of some importance in
relation to the potential for full mill closure and zero-effluent operation in both TCF
and ECF systems.
3.2 Atmospheric Pollution
Although atmospheric pollution is generally reckoned to be less important than dis-

charges to water it remains important in some areas. Sulphur dioxide is the most
important component of acid rain on a global basis, and chlorinated solvents
released by chemical pulping contribute to both global warming and the breakdown
of the ozone layer. Hydrogen sulphide, chloroform and carbon tetrachloride can all
be released from mills and result in significant health risks to workers and nearby
residents. The US Environmental Protection Agency has recently added the pulp
and paper industry to its category of “major sources of hazardous air pollutants” due
to the presence of chlorine, other volatile organic compounds and chloroform in
waste gases. In addition, sulphuric acid fumes, released from some pulp factories,
can damage the bronchial tract. In Russia, the area round Bratsk in the east Siberian
taiga, was declared a disaster area in 1992, as a result of air pollution from the local
pulp and board producer.
The US Environmental Protection Agency estimates that people regularly eating
fish caught near pulp mills have 1,000 times the chance of developing certain can-
cers. In 1989, a study by the Canadian Department of Health and Welfare reported
that residents of British Columbia had the highest average levels of dioxin in body
tissue in the country. Several areas of British Columbia, have subsequently banned
shellfish collection due to mill pollution (Greenpeace 1990). Although the impacts
of dioxins remain controversial, some are now regarded as carcinogens by most
regulatory authorities. Dioxin pollution problems have been addressed by many
pulp mills, other effects, less clearly understood, have been identified in fish popula-
tions near pulp mills in Scandinavia and Canada (Carey et al. 1993). Workers at pulp
and paper mills appear to face some direct and long term risks from pollution. A
study by the International Labour Office found wide differences in accident rates
between countries and some industry-specific diseases occurred. In Finland, a num-
ber of cancers were recorded at high incidence levels amongst workers in pulp mills,
probably as a result of chemicals used in the pulp process and biological agents
(International Labour Organisation 1992). Concern about dioxins has extended
beyond the pulp-making process to the risks from residues remaining in paper and
sanitary products, particularly in Europe where scares about the impact of dioxins
in coffee filters, disposable nappies and tampons has been the subject of much con-
sumer concern. In Sweden, regulations have been tightened as a result of findings
about dioxins in paper waste effluent and alternative oxygen bleaching processes
have been encouraged, so that by 1993 TCF paper was available (Women’s
Environmental Network 1989). In North America, where anxiety about chlorine
residues has not been as high, the industry has chosen to use chlorine dioxide as the
primary bleaching agent, resulting in discharge which is elemental chlorine free.
These developments are not without their own controversy, and questions remain
about the pollution from TCF plants. Some campaign groups, including notably
Greenpeace, remain totally opposed to use of chlorine in any form. In a further
development, several plant in North America and Scandinavia are now attempting
to develop completely closed loop systems, where there would be zero discharge of
any effluent.
In the past, chemical pulp mills have caused serious emissions of sulphur (acidifi-
cation) but in recent years, sulphur air emissions have especially been reduced by
substantial progress in process technology. Recovery boilers and lime kilns are still
important sources of air pollutants such as particulate matter, NOX, SO2, CO and H2S
in some cases. Because of the need for heat and power, most pulp and paper mills
operate on-site power plants, auxiliary boilers, steam blocs or combined heat and
power plants. These plants contribute significantly to total industrial emissions-despite
high efficiency combustion and efficient flue gas cleaning. The key air emissions con-
nected to the combustion of fuels for energy production (NOX, SO2, dust) will thus
remain an issue for the sector as Directive 2001/81/EC of the European Parliament
and of the Council on national emission ceilings for certain atmospheric pollutants
(NEC Directive) aims at limiting emissions of acidifying and eutrophying pollutants
and ozone precursors. The objective to move towards the long-term objectives of not
exceeding critical levels and loads and of effective protection of all people against
recognised health risks from air pollution will also demand some additional efforts
from a number of mills that still have potential for improvement.
Air emissions from chemical pulp mills are primarily made up of particulates,
hydrogen sulphide, oxides of sulphur and oxides of nitrogen. Micro-pollutants
include chloroform, dioxins and furans, other organochlorines and other volatile
organics. As with liquid effluent discharges, the levels of emissions are highly
dependent upon the type of process technology employed and individual mill prac-
tice. Another important factor is the fuel type and quality. Whilst older mills caused
severe air pollution, mitigating technology now exists to eliminate most harmful gas
and particulate emissions. Whether this technology is utilised depends on local fac-
tors such as legislation, company and mill policy and proximity to populated areas.
The contribution of the paper industry to global warming has been an ongoing
debate for several years, with some suggesting that the absorption of carbon dioxide
by plantation forestry more than offsets the emissions of (GHGs) caused during the
production, transportation and disposal of pulp and paper products. A study by the
International Institute for Environment and Development dismisses this argument,
concluding that the paper cycle results in the net addition of some 450 million car-
bon dioxide equivalent units per year.
While the advantages of in-mill process changes with respect to the use of water
resources and concomitant impacts upon receiving aquatic systems are well docu-
mented, the implications for changes in air emissions (principally from recovery
boiler systems) as a result of closed-loop operation have been less well explored
(Caron and Delaney 1998).
Södra Cell has reported occasional increases in NOx emissions at its low-flow
TCF plants located at Värö and Mörrum, but these have been reduced and attributed
to the numerous mill start ups and shutdowns as the various processes were refined
(Södra Cell 1996). The company is considering additional technological controls to
reduce NOx emissions to 1 kg/tonne of pulp or less. The increased quantity of
organic matter reaching the recovery boiler from recycling of effluent has increased
the amount of electricity the mill is capable of generating for itself. As a source of
energy from combustion, recovery boilers are regarded as preferable to hog fuel
boilers in terms of the relative amount of air pollutants generated (Luthe et al. 1997).
Information contained in the annual environmental reports from mills in Scandinavia
producing both advanced ECF and TCF pulp suggest that overall releases of NOx,
total reduced sulphur (TRS), sulphur dioxide and particulate matter are similar for
both production processes (Södra Cell 1996). While NOx, carbon dioxide, TRS/
sulphur dioxide and particulate matter continue to be important, there are other
emissions which must be considered.
The potential for products of incomplete combustion and other hazardous com-
pounds, including chemicals such as the chlorinated dioxins, from ECF mills is an
obvious area of concern (Environment Canada 1998). PCBs, dioxins and furans
have been found in fly ash from the burning of sludge from kraft mills (Kopponen
et al. 1994) raising concerns that substantial quantities may be released to atmo-
sphere. One study from British Columbia, Canada suggests that the flue gas from
recovery boilers with high chloride loading due to salt-laden wood does not repre-
sent a major source of dioxin/furan emission to air, however, levels of these persis-
tent organic pollutants have been observed in other recovery boiler emissions (Luthe
et al. 1997).
In addition, some of the hazardous air pollutants, or trace air contaminants and
total reduced sulphur compounds such as methyl mercaptan, chlorine dioxide,
formaldehyde and chloroform are a priority for individual regulation and control,
particularly with respect to their potential to compromise mill worker health and
safety. Accordingly, one mill has installed a “light stripper” for cleaning the less
polluted condensates in the evaporator stage. The aim is to eliminate emissions of
polluted condensates and reuse them in the process. This company has also installed
the first weak gas system in Sweden (Södra Cell 1996). The weak gas system is able
to collect malodorous gases and combust them in the recovery boiler. This limits
malodorous discharges and aerial emissions of process sulphur (Södra Cell 1996).
Both of these systems were added at the Värö Bruk mill. This mill already used TCF
bleaching, and generates bleach plant effluent of between 10 and 15 m3/ADT.
Hydrogen chloride and methanol are other major air pollutants of concern pro-
duced in recovery boilers (Andrews et al. 1996). Older, direct contact evaporator
recovery boilers emit greater quantities of these pollutants, as well as generating
significant sulphur emissions. Accordingly, upgrading of mills to closed loop opera-
tion should ideally include installation of non-direct contact, low odour recovery
boilers (Simons 1994). This type of recovery boiler should be fitted at newly con-
structed mills. In addition to reducing environmentally significant air emissions
these recovery boilers also allow the firing of black liquor solids (BLS) at greater
concentrations (up to 80 % BLS) than direct contact units. In turn, this increases
recovery boiler capacity and generally reduces emissions of TRS and sulphur diox-
ide (McCubbin 1996).
Methanol and a wide range of other hazardous air pollutants and volatile organic
compounds are also generated in the process lines and vented from oxygen deligni-
fication systems and white liquor oxidation systems (Crawford et al 1995; NCASI
1994). Methanol, especially, may be generated in large quantities. Reducing the
methanol content of the final post-oxygen washer shower water is likely to have a
significant positive impact on emissions of methanol from oxygen delignification
systems (Crawford et al. 1995). It is not clear from the literature if this measure will
also lower the concentrations of the other hazardous air pollutants (HAPs) and vola-
tile organic carbon (VOC) compounds present. Hence, the US EPA Cluster Rules
outline techniques for these gaseous streams to be collected and introduced into the
fire zone of the recovery boiler (USEPA 1998). It has also been pointed out
(Crawford et al. 1995) that there is a need to routinely monitor the areas around the
oxygen delignification system for HAPs and VOCs.
The question of precisely what to monitor in the way of air emissions from
pulping operations is an important one. The US EPA suggests that methanol is an
acceptable surrogate target compound for monitoring and regulation of gas phase
HAP compounds. This assertion is, however, somewhat difficult to verify. A wide
range of HAPs and VOCs have been detected in studies of pulp mill air emissions
(NCASI 1994). Moreover, it appears that no direct correlation exists between reduc-
tion in emissions of methanol and reduced emissions of other pollutants such as
methyl mercaptan and chlorobenzene among the variety found in actual working
mill environments. Phenols, as well, do not appear to be reduced proportionally to
methanol (Simons 1994). This is of significance in terms of potential long term, low
level worker and community exposure to the other compounds. It implies that moni-
toring needs to be extended in scope and should encompass not only recovery and
power boiler stacks but also cooling towers, process vents from oxygen delignifica-
tion, washers and chemical generation processes. Additionally, internal mill work-
ing areas need to be subjected to monitoring as well as external environments. In
bleaching operations, TCF mills emit no chlorinated compounds, which are gener-
ated in ECF mills by bleaching or chlorine dioxide manufacture. Chloroform,
dichloroacetic acid methyl ester, 2,5-dichlorothiophane and other volatile organo-
chlorine compounds have been found in the vent gases of mills using 100 % chlo-
rine dioxide substitution. These compounds have also been found to volatilise from
the treatment ponds of these mills, but were almost non-existent when investigated
in a TCF mill (Juuti et al. 1996). Side reactions during chlorine dioxide bleaching
lead to the formation of chloroform, chlorinated phenolics and other chlorinated
organics, as well as phenol and methanol (Simons 1994). The precursors for the
chlorinated organic chemicals are not present in TCF bleach plants. While the con-
centrations of chlorinated compounds have decreased markedly from levels gener-
ated by mills employing elemental chlorine as a bleaching agent, they have not been
eliminated by the use of chlorine dioxide. These chemicals are of environmental
significance because they are released into the local environment and may also be
transported over large distances from the mill (Juuti et al. 1996; Calamari et al.
1994). Chlorine dioxide itself is an air pollutant of great concern, especially in rela-
tion to the possibility of leaks and fugitive emissions in the plant (Simons 1994).
The US EPA has recognised the major benefit that TCF systems are not expected to
produce HAPs in the bleach plant (USEPA 1998). For the most part there are overall
positive environmental benefits in relation to air emissions from the use of modern
mill technology and additional benefits for non-chlorine chemical bleach sequences.
Nonetheless, the implications of technology and process change upon this aspect of
pulp mill operations have not been exhaustively explored. There is a need to gener-
ate comparative information from advanced mill operations in order to assess the
nature and scale of likely atmospheric emissions under closed loop mill operations
in order to establish, as a minimum, that improvement in effluent quality is not at the
expense of air quality.
3.3 Sludge and Solid Waste
Different types of sludge and solid wastes are generated in the Pulp and Paper
Industry at different production processes. Treatment of wastewater generated at
pulping, papermaking, and deinking processes is the main source of wastewater
treatment sludge and deinking sludge (Monte et al. 2009; Gavrilescu 2004, 2005;
Abubakr et al. 1995). Table 3.4 shows solid waste generated in Pulp and Paper mills.
Table 3.5 shows generation of Waste in a Kraft mill (Gavrilescu 2004).
About 300 kg of sludge is produced for each one ton of recycled paper (Balwaik
and Raut 2011). The amount of waste generated in paper production varies greatly
within different regions, because of different recycling rates. In Finland, the ratio of
recycled fibre production to paper production can be expected to be smaller than
example in central Europe (Kujala 2012). This is due to the reason that most of the
paper produced in Finland is exported to other countries and so the amount of recov-
ered paper is relatively low. According to WRAP (2010), over 5 million tons of
paper and board was produced in 2007. At the same time, the production of paper
mill sludge from Recycled fibre production was approximately 1 million tons
(Rothwell and Éclair-Heath 2007).
The generation of wastewater treatment sludge vary widely among mills (Monte
et al. 2009; Abubakr et al. 1995). Not much data is available on total waste genera-
tion. This is due to the fact that most of the pulp and paper mills already have pro-
cesses applied to internally treat the wastes which reduce the generation of solid
Table 3.4 Solid waste generated in pulp and paper mills

Pulp mill Paper mill
Rejects Rejects
Green liquor sludge, dregs and lime mud Deinking sludge
Wastewater treatment sludge Primary sludge
Chemical flocculation sludge Secondary sludge or biological sludge
Table 3.5 Generation Waste

of waste in a kraft mill
Wood wastes:
Sawdust coming from the slasher deck
Bark falling from the debarking drum
Pins and fines from chip screening
Wood waste from woodyard
Knots from pulp deknotting
Sodium salts from recovery boiler
Dregs from causticizing
Grit from causticizing
Based on Gavrilescu (2004)
3.3 Sludge and Solid Waste 57
waste. This applies to bark residues from debarking which are incinerated in the
bark boiler and, as a result, only ashes remain as waste. The same can apply to
sludge incineration. The amount of waste generated when virgin fibres are used as
raw material depends mainly on the pulping process used. European Commission
(2001) reports that in Europe, 65 % of total pulp production is kraft pulp which
produces about 100 kg/Adt of wastes. Semi-chemical and mechanical processes
produce about 60 kg/Adt.
CEPI (2006) has reported that in 2005, the total production of paper in Europe
was 99.3 million tonnes. This generated 11 million tonnes of waste, representing
about 11 % in relation to the total paper production. The production of recycled
paper, during the same period, was 47.3 million tonnes generating 7.7 million
tonnes of solid waste (about 70 % of total generated waste in papermaking) which
represents 16 % of the total production from this raw material.
The amount of waste sludges generated from a mill using secondary fibre differ
from a mill using virgin materials. Also, the composition is different. A greater
amount of rejects is produced when processing recycled fibre, because of the unre-
cyclable filler proportion in the raw material. This problem is especially conspicu-
ous in mills producing recycled paper from office waste, using highly filled grades
as the raw material. Deinking mill sludge generally has a higher ash content; the
kraft pulp mill sludge is found to be high on sulfur. Obviously, great variations
occur within both plant types, depending on the processes and raw materials (Glenn
1997). The amount of wastes produced in paper mills based on recycled fibre
depends mainly on the quality of recovered paper used as raw material. It also
depends on the effort and expenses made in preparation of secondary fibres for cer-
tain product and process requirements.
Disposal of solid waste is usually to landfill, although incineration is becoming
increasingly widespread. Other experimental disposal techniques include using the
waste as a soil improver but, as with all disposal options, there is some concern
about possible dioxin and heavy metal contamination. Solid waste disposal issues
significantly decrease in a perfect closed loop mill (Ritchlin and Johnston 1998).
However, the need to control the nonprocess elements will require purge points to
prevent upsets in bleaching and recovery chemistry, and reduce corrosion of mill
equipment (Gleadow et al. 1997a, b). Given that there will continue to be some
sludge and solid waste produced, the quality of these wastes becomes of consider-
able concern. This is particularly the case since, increasingly, land spreading is
being promoted as a means of disposing of these wastes. Uncontaminated sludge
could prove to be a beneficial resource. Composting of properly treated sludge
could facilitate the reuse of otherwise un-recyclable wastes. Use of pulping and
bleaching wastes as raw materials for other processes may also be a desirable goal.
However, there is a need to carry out long-term studies on the feasibility and
safety of composting and re-using waste solids from either ECF or TCF mills. In
practice, sludge is increasingly being fed into mill recovery boilers. While current
evidence suggests that both ECF and TCF mills increasing their burn volume in the
recovery boiler are maintaining compliance with air quality regulations, this must
be continuously monitored as the move to full effluent loop closure proceeds. As
noted above, current air monitoring obligations are demonstrably deficient.

Increased combustion of sludge provides a further imperative for developing the
scale and scope of air monitoring programmes.
Sludge from bleach kraft pulp mills contains a wide variety of chemicals of
both natural origin and originating de novo from pulping and bleaching activities.
The commonly tested regulatory chemical parameters include chlorinated dioxin
congeners and heavy metals, together with agriculturally orientated parameters
such as carbon nitrogen ratio and salt content (O’Connor 1995; Rabert and
Zeeman 1992). While all of these parameters continue to be important, improve-
ments to secondary treatment and the move towards complete chlorine dioxide
substitution have revealed new compounds that need to be addressed. Plant ste-
rols, resin acids, phthalates, chlorinated and non-chlorinated alcohols (phenols,
guiacols, catechols), terpenes and benzene have been detected in ECF kraft mill
secondary sludge (Martin et al. 1995; Fitzsimons et al. 1990; O’Connor and Voss
1992; Brezny et al. 1993; Kookana and Rogers 1995). These studies primarily
address sludge from mills at, or approaching 100 % chlorine dioxide substitution.
The concentrations of chlorinated, bioaccumulative compounds found in these
studies vary. Some debate has taken place concerning the best sampling and test-
ing methods for low levels of these compounds, as well as on their origin: from
the breakdown of chlorolignin or through a sorption – desorption pathway (Martin
et al 1995; O’Connor and Voss 1992).
Regardless of the origin of such substances in mill sludge, it is clear that long-
term studies under realistic conditions, backed by comprehensive chemical analysis
are necessary before large scale land-spreading of kraft mill sludge can be justified
(Kookana and Rogers 1995). Additionally, the extreme variability in sludge indi-
cates a need for continuous testing at each mill before sludge can be spread on land
(Aitken 1995). This has been emphasised by the New Hampshire Department of
Environmental Services following experiences in New Hampshire, United States.
This body consider that the inherent variability in sludge composition necessitates
extensive testing and monitoring prior to spreading on land. This followed the dis-
covery of VOCs during post application testing in landfill groundwater where short
paper fibre sludge had been used for remediation purposes. The potential for this
problem was not identified through pre application tests.
The process changes adopted by the industry are known to have resulted in quali-
tative changes in the sludge. For ECF sludge, closing the loop is resulting in
increased disposal of sulphur chemicals from the chlorine dioxide generator
(Paleologou et al. 1997) due to the fact that sulphate compounds are by-products of
chlorine dioxide generator and often used as make-up chemicals in bleaching and
pulping. Increased chlorine dioxide production for ECF, and increased filtrate recy-
cling heighten concentration of sulphur chemicals in process circuits. Because
increased sulphur becomes a concern for non-process element control in closed
loop designs, this increase necessitates disposal of excess sulphates. These eventu-
ally end up in effluent treatment in many current mills. Under anaerobic conditions,
certain bacteria can reduce sulphate, leading to increased bacterial growth, corro-
sion problems, and increase in treated effluent toxicity. TCF sludge has not been
References 59
commonly tested. Because many of the TCF mills in the world are in the forefront
of effluent recycling technology, it is likely that issue of waste fibre sludge disposal
will progressively diminish in importance. The impacts of burning this material
must be continuously evaluated, and opportunities for more beneficial re-use
sought out.
Assertions that increased effluent recycling will lead to an eventual doubling of
lime muds, dregs, precipitator ash and other purge streams must be viewed with
some concern (Ryynänen and Nelson 1996). On an average, grits, dregs and ash
currently comprise about 3 % of the dissolved material resulting from pulping and
bleaching operations. While closed loop operations may double that figure to 6 %,
this must be weighed against the complete elimination of liquid effluent discharge
and of dissolved waste fibre and spent liquors going to aquatic or land-based dis-
charge. Processes that allow for a maximum of non-polluting and worker-safe re-
use of pulping and bleaching by-products are needed.
Many companies choose to implement integrated waste management plans that
seek to minimise residues to be sent to landfill and to further increase the share of
residues that are reused, recycled or recovered (including energy recovery). The
goals for the management of residues in the pulp and paper sector include their use
as renewable fuels, as soil improvers or as raw materials for other industries or their
conversion into added value products for other users. New concepts in the sector
aim at a best possible usage and energetic recovery of most residues generated on-
site, if possible recycling also the ashes, example in the construction or cement
industry or using ash for soil stabilisation. The general target is minimising the
amount of waste to be sent to landfills. These solutions aim to achieve waste reduc-
tion, resource recovery and energy efficiency at reasonable costs. Locally odour and
noise nuisances from pulp or paper mills are expected to remain future priorities for
environmental actions in the pulp and paper industry.
References
Abel, K (1993) Pulp mill effluents national pulp mills research program, CSIRO, Dickson
Abubakr S, Smith A, Scott G (1995) Sludge characteristics and disposal alternatives for the pulp
and paper industry. In: Proceedings of the 1995 international environmental conference,
Atlanta, GA, Tappi Press, 7–10 May 1995, pp 269–279
Aitken M (1995) Effects on soil fertility from applying paper mill sludge to agricultural land. Soil
Use Manag 11:152–153
Andrews RS, Paisley MA, Smith M, Young RJ (1996) Formation and release of methanol and
hydrogen chloride from DCE recovery boiler systems. Tappi J 79(8):55–160
Anonymous (1994) EPA report thrusts dioxins back into the spot light. ENDS Ref. No. 236,
pp 21–24
mills Symposium. Tappi Press, Atlanta, pp 529–541
Bajpai P (2001) Microbial degradation of pollutants in pulp mill effluents in advances in applied
microbiology, vol 48. Neidleman S, Laskin A (eds), Academic, New York, pp 79–134
Bajpai P (2012) Environmentally benign approaches for pulp bleaching, 2nd edn. Elsevier,
Amsterdam
Bajpai P, Bajpai PK (1996) Organochlorine compounds in bleach plant effluents – genesis and
control. PIRA International, Leatherhead
Bajpai P, Bajpai PK (1999) Recycling of process water for closed mill systems. PIRA International,
Leatherhead
Balwaik SA, Raut SP (2011) Utilization of waste paper pulp by partial replacement of cement in
concrete. Int J Eng Res Appl 1(2):300–309. Available at: http://ijera.com/pages/v1no2.html
Bard S (1998) A biological index to predict pulp mill pollution levels. Water Environ Res
70(11):108–122
Bouchard J, Nugent HM, Berry RM (1995) A comparison between acid treatment and chelation
prior to hydrogen peroxide bleaching of kraft pulps. J Pulp Pap Sci 21(6):203–208
Brezny R, Joyce T, González B, Slimak M (1993) Biotransformations and toxicity changes of
chlorolignins in soil. Environ Sci Tech 27:1880–1884
Calamari D, Tremolada P, Guardo AD (1994) Chlorinated hydrocarbons in pine needles in Europe:
fingerprint for the past and recent use. Environ Sci Tech 28:429–434
Carey JH, Hodson PV, Munkittrick KR, Servos MR (1993) Recent Canadian studies on the physi-
ological effects of pulp effluent on fish. Environment Canada, Ottawa
Caron JR and Delaney G (1998) Initial learning from the BFR demonstrations. In: 84th annual
meeting, technical section Canadian pulp & paper association. 27–30 January 1998, Preprints
A, pp A379–A384
Cates DH, Eggert C, Yang JL, Eriksson K-E L (1995) Comparison of effluents from TCF and
ECF. TAPPI J 78(12):93–98
Chirat C, Lachenal D (1997) Pulp producers race to keep up with technology. Pulp Pap Int
39(10):29–32
Cockram, Richard (1994) Are they doing their best for the environment? Eur Papermak 2(3), April
1994, Sweden
Confederation of European Paper Industry (2006) Special recycling 2005 statistics, (http://www.
cepi.org)
Crawford RJ, Rovell-Rixx DC, Jett SW, Jain AK, Dillard DS (1995) Emissions of volatile organic
compounds and hazardous air pollutants from oxygen delignification systems. In: 1995 inter-
national environmental conference, Atlanta, 7–10 May, Book 1, pp 575–587
Duncan A, Thia BC, Jelbart J, Donlon PJ (1995) Factors influencing the treatment of Australian
pulp mill effluent. Appita J 48(4):295–298
Easton MDL, Kruzynski GM, Solar II, Dye HM (1997) Genetic toxicity of pulp mill effluent on
Juvenile Chinook Salmon (Onchorhynchus Tshawytscha) using flow cytometry. Water Sci
Technol 35(2):347–355
Elo A (1995) Minimum impact mill. In: Third global conference on paper and the environment,
London, 26–28 March 1995, pp 105–110
Environment Canada (1998) Dioxins and furans and hexachlorobenzene inventory. environment
Canada and the federal/provincial task force on dioxins and furans for the federal-provincial
advisory committee for the Canadian environmental protection act draft 4. April, 1998
European Commission (2001) Reference document on best available techniques in the pulp and
paper industry, Institute for prospective technological studies. Integrated Pollution Prevention
and Control (IPPC), Seville
European commission (2013) Best Available Techniques (BAT) Reference document for the pro-
duction of pulp, paper and board. Industrial Emissions Directive 2010/75/EU (Integrated
Pollution Prevention and Control). Joint Research Centre, Institute for Prospective
Technological Studies Sustainable Production and Consumption Unit European IPPC Bureau
Fandry, CB, Johannes RE, Nelson PJ (1989) Pulp mills: modern technology and environmental
protection: report to Senator the Hon. John Button, Minister for Industry, Technology and
Commerce, Commonwealth of Australia, Commonwealth Scientific and Industrial Research
Organisation, June 1989
References 61
Fitzsimons R, Ek M, EL Eriksson K (1990) Anaerobic dechlorination/degradation of chlorinated

organic compounds of different molecular masses in bleach plant effluents. Environ Sci Tech
24(11):1744–1748
Gavrilescu D (2004) Solid waste generation in kraft pulp mills. Environ Eng Manag J 3:399–404
Gavrilescu D (2005) Sources of solid wastes in pulp mills. Bull Polytechnic Inst Iasi (Buletinul
Institutului Politehnic din Iasi) LI(LV):99–105
Germgard U, Teder A, Tormund D (1981) Chlorate formation during chlorine dioxide bleaching of
softwood kraft pulp. Paperi Ja Puu 63(3):127–133
Gevert BS, Lohmander SF (1997) Influence of sulfur compounds, manganese, and magnesium of
oxygen bleaching of kraft pulp. TAPPI J 80(10):263–268
Gleadow P, Hastings C, Warnqvist B, Barynin J, Schroderus S (1997a) Towards closed-cycle
kraft – ECF vs TCF case studies. In: 1996 CPPA annual meeting, Montreal (winner of 1996
CPPA Douglas Jones Award for Best Environmental Paper)
Gleadow P, Hastings C, Richardsdon B, Towers M, Uloth V (1997b) Towards closed cycle kraft
pulping: Canadian mill studies. PAPRICAN miscellaneous report 353. Pulp and Paper Research
Institute of Canada
Glenn J (1997) Paper mill sludge: feedstock for tomorrow. BioCycle [magazine] 38(11). Available
through: ABI/INFORM Global database. Accessed 20 October 2011
Greenpeace (1990) No time to waste, broadsheet produced by Greenpeace Canada, Vancouver
Hanninen E (1996) Minimum impact mill. Pap Asia 12(1):24–29
Higachi R, Cherr G, Shenker J, Macdonald J, Crosby D (1992) A polar high molecular mass con-
stituent of bleached kraft mill effluent is toxic to marine organisms. Environ Sci Technol
26(12):2413–2420
IIED (1994) The sustainable paper cycle. IIED, London
International Labour Organisation (1992) Social and labour issues in the pulp and paper industry.
ILO, Geneva
Johnston P, Stringer R, Santillo D, Stephenson A, Labounskia I, McCartney H (1996) Towards zero
effluent pulp and paper production: the pivotal role of TCF bleaching. Technical Report 7/96
Greenpeace Research Laboratories, Earth Resources Centre, University of Exeter, Exeter, UK
Greenpeace International, Amsterdam
Juuti S, Vartiainen T, Joutsenoja P, Ruuskanen J (1996) Volatile organochlorine compounds formed
in the bleaching of pulp. Chemosphere 33(3):437–448
Kondo, Tadahiro (1993) Japan’s pulp and paper industry faces dramatic changes. Paper &
Packaging Analyst, No 15, November 1993, Pira International, UK
Kookana R, Rogers S (1995) Effects of pulp mill effluent disposal on soil. Rev Environ Contam
Toxicol 142:13–64
Kopponen P, Välttilä O, Talka E, Törrönen R, Tarhanen J, Ruuskanen J, Kärenlampi S (1994)
Chemical and biological 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin equivalents in fly ash from
combustion of bleached kraft pulp mill sludge. Environ Toxicol Chem 13:143–148
Kovacs TG, Tana J, Lehtinen KJ, Sangfars O (1995) A comparison of the environmental quality of
ECF and TCF bleached plant effluent. In: Proceedings of the annual international non-chlorine
bleaching conference, Amelia Island, 5–9 March 1995, paper 5-3, 26pp
Kujala A (2012). Papermaking sludges and possibilities of utilization as material, Lappeenranta
University of Technology, Bachelor seminar of environmental technology
Lapierre L, Paleologou M, Berry RM, Bouchard J (1997) The limits of metal removal from kraft
pulp by acid treatment. J Pulp Pap Sci 23(11):J539–J542
Larisch B, Duff S (1997) Effect of H2O2 and DTPA on the characteristics and treatment of TCF
(Totally Chlorine-Free) and ECF (Elementally Chlorine-Free) kraft pulping effluents. Water
Sci Technol 35:2–3
Liebergott N, van Lierop B, Nolin A, Faubert M, Laflamme J (1989) Modifying the bleaching
process to decrease AOX formation, report. Pulp and Paper Research Institute of Canada,
Pointe-Claire
Liebergott N, van Lierop B, Kovacs T, Nolin A (1990) Comparison of the order of addition of
chlorine and chlorine dioxide in the chlorination stage. Tappi J 73:207–213
Lockie M (1996) Pulp producers: losing metal or resolve? Pulp Pap Int 39(10):44–46
Luthe CE, Uloth V, Karidio I, Wearing J (1997) Are salt-laden recovery boilers a significant source
of dioxins? TAPPI J 80(2):165–169
Martin VJJ, Burnison BK, Lee H, Hewitt LM (1995) Chlorophenolics from high molecular weight
chlorinated organics isolated from bleach kraft mill effluents. Holzforschung 49(5):453–461
McCubbin N (1989) Dioxin’89: a bit like the adventures in Alice and wonderland. Pulp Pap Can
90(11):17–19
McCubbin N (1996) Numerous recovery options offer solutions for mill effluent closure. Pulp Pap
70(3):181–193
McCubbin N, Sprague JB, Bonsor N (1990) Kraft mill effluents in Ontario. Pulp Pap Can
91(3):T112–T114
Part 1: extended delignification, oxygen delignification, enzyme applications, and ECF and
TCF bleaching. Tappi J 78(3):55–62
Mckague AB, Carlberg G (1996) Pulp bleaching and the environment. In: Dence CW, Reeve DW
(eds) Pulp bleaching – principles and practice. Tappi Press, Atlanta, pp 746–820
Monte MC, Fuente E, Blanco A, Negro C (2009) Waste management from pulp and paper produc-
tion in the European Union. Waste Manag, 29(1):293–308
Munkittrick, KR, van der Kraak GJ (1994) Receiving water environmental effects associated with
discharges from Ontario pulp mills, Pulp Pap, 95(5), Canada
NCASI (National Council of the Pulp and Paper Industry on Air and Stream Improvement) (1994)
Technical bulletin #684. NCASI, New York
O’Connor B (1995) Review of guidelines pertaining to the land application of municipal of indus-
trial solid residues in Canada. Miscellaneous Report 314, PAPRICAN
O’Connor B, Voss R (1992) A new perspective (Sorption/Desorption) on the question of chloro-
lignin degradation to chlorinated phenolics. Environ Sci Tech 26:556–560
Paleologou M, Thibault A, Wong PY (1997) Enhancement of the current efficiency for sodium
hydroxide production from sodium sulphate in a two-compartment bipolar membrane electro-
dialysis system. Sep Purif Technol 11:159–171
Papercutz: PlanetArk (2008) The environmental impact of paper production. http://papercutz.plan-
etark.org/paper/impact.cfm
Priha M (1991) Toxic characteristics of effluents from bleached Kraft pulp mills. In: Crossland
Chris (ed) International conference on bleached kraft pulp mills: Technical and environmental
issues, 4–7 February 1991, World Congress Centre, Melbourne, National Pulp Mills Research
Program, CSIRO, Dickson
Pryke D (2003) ECF is on a roll: it dominates world bleached pulp production. Pulp Pap Int
45(8):27–29
Rabert W, Zeeman M (1992) Dioxins/furans: U.S. EPA ecological risk assessment for land appli-
cation and disposal methods for paper pulp sludge. Chemosphere 25:7–10
Rappe C, Wagman N (1995) Trace analysis of PCDDs and PCDFs in unbleached and bleached
pulp samples. Organohalogen Compd 23:377–382
Ritchlin J, Johnston P (1998) Zero discharge: technological progress towards eliminating Kraft
pulp mill liquid effluent, minimising remaining waste streams and advancing worker safety.
Reach for Unbleached Foundation, Comox, 51 pp. ISBN 0-9680431-2-7
Rosenberg C, Kontsas H, Jäppinen P, Tornaeus J, Hesso A, Vainio H (1994) Airborne chlorinated
dioxins and furans in a pulp and paper mill. Chemosphere 29:9–11
Rothwell A, Éclair-Heath G (2007) A new approach to paper mill sludge. Waste & Resources
Action Programme, Oxon
Ryynänen H, Nelson P (1996) Environmental life cycle assessment of some new methods for
producing bleached pulps from Australian eucalypt woods. Appita 49(3):167–172
References 63
Saunamaki R (1995) Treatability of wastewaters from totally chlorine-free bleaching. TAPPI J

78(8):185–192
Simons HA (1994) Technical background information document on pulp and paper mill air emis-
sions. H.A. Simons Ltd., p 5517A
Södergren A (1989) Biological effects of bleached pulp mill effluents, National Swedish
Environmental Protection Board Report 3558, Solna, Sweden
Södergren A (1993) Bleached pulp mill effluents: composition, fate and effects in the Baltic Sea,
Swedish Environmental Protection Agency, Report 4047, Solna, Sweden
Sodergren A, Adolfsson-Erici M, Bengtsson BE, Jonsson P, Lagergren, S, Rahm R, Wulff F (1993)
Environmental impact of bleached pulp mill effluent – bleached pulp mill effluent composition,
fate and effects in baltic sea. Environmental Protection Agency Report 4047. Sodergren A (ed)
Arlow, p 26–46
Södra Cell (1996) Annual environmental report, Södra Cell, Sweden
Stauber J Gunthorpe L Deavin J Munday B Krassoi R Simon J (1995) Comparative toxicity of
effluents from ECF and TCF bleaching of eucalypt kraft pulps. In: 49th APPITA annual general
conference, 3–7 April 1995, Hobart, pp 483–490
Sundelin B (1988) Effects of sulphate pulp mill effluents on soft bottom organisms – a microcosm
study. Water Sci Technol 20(2):175–177
Suntio LR, Shiu WY, Mackay DA (1988) A review of the nature and properties of chemicals pres-
ent in pulp mill effluents. Chemosphere 17(7):1249–1299
USEPA (1998) Maximum Achievable Control Technology (MACT) I & II. Title 40, Chapter 1,
CFR, Part 63
United States Environmental Protection Agency (U.S. EPA) (2002) Chemical releases and trans-
fers: pulp and paper industry. Sector notebook. http://www.epa.gov/compliance/resources/pub-
lications/assistance/sectors/notebooks/pulppasnp2.pdf
Verta M, Ahtiainen J, Nakari T, Langi A, Talka E, Servos MR, Munkittrick KR, Carey JH, van der
Kraak GJ (1996) The effect of waste constituents on the toxicity of TCF and ECF pulp bleach-
ing effluents. In: Servos M, Munkittrick K, Carey J, Van der Kraak G (eds) Environmental fate
and effects of pulp and paper mill effluents. St. Lucie Press, Delray Beach
Vice K, Carrol R (1998) The cluster rule: a summary of phase I. Tappi J 81(2):91–98
Vidal J, Soto M, Field J, Mendez-Pampin R, Lema JM (1997) Anaerobic biodegradability and
toxicity of wastewaters from chlorine and total chlorine-free bleaching of eucalyptus kraft
pulps. Water Res 31(10):2487–2494
Women’s Environmental Network (1989) The sanitary protection scandal, London; and National
Swedish Environmental Protection Board (1989); Dioxins: A Programme for Research and
Action, Stockholm, Sweden
WRAP (2010) Environmental benefits of recycling 2010 update – SAP097 http://www.wrap.org.
uk/downloads/Environmental_benefits_of_recycling_2010_update53016551.8816.pdf
Chapter 4
Minimum Impact Mill Technologies
Abstract The Minimum Impact Mill Technologies which can meet the

environmental challenges of the pulp and paper industry are discussed in this chap-
ter. These include Optimised wood handling; Dry Debarking; High Yield Pulping
Process; Extended Modified cooking; Efficient Brownstock Washing/Improved
Pulp Washing; Oxygen Delignification; Ozone bleaching; ECF and TCF bleaching;
Fortification of extraction stages with oxygen and hydrogen peroxide; HexA
Removal; Condensate Stripping and Recovery; Minimum SO2 and NOx Emissions;
Electrostatic Precipitators; Increase in the dry solids content of black liquor;
Installation of scrubbers on the recovery boiler; Incineration of odorous gases in the
lime kiln; Installation of low NOx technology in auxiliary boilers and the lime kiln;
SNCR on bark boilers; Over Fire Air Technique on recovery boilers; Installation of
improved washing of lime mud in recausticizing; Efficient Primary, Secondary and
Tertiary Waste Treatment (in some special cases); Partial system closure; Minimum
Power Consumption; Waste water Recycling and reuse.
Keywords Pulp and paper industry • Minimum impact mill • Wood handling • Dry
debarking • High yield pulping • Extended modified cooking • Oxygen delignifica-
tion • Ozone • ECF • TCF • HexA • Emission • SO2 • NOx electrostatic precipitator
• Black liquor • Scrubber • Recovery boiler • Odorous gases • Lime Kiln • SNCR •
Over fire air technique • Lime mud • Recausticizing • Partial system closure • Waste
water treatment • Recycling
Paper mills vary widely in their environmental performance, depending on their

age, efficiency and how they are run. Minimum-impact mills are those that min-
imize resource inputs and minimize the quantity and maximize the quality of
releases to air, water and land. Pulp and Paper industry can optimize their envi-
ronmental performance by implementing the most advanced manufacturing
technologies, the most efficient mill operations, and the most effective environ-
mental management systems.
Some excerpts taken from Bajpai Pratima, “Environmentally Friendly Production of Pulp and
Paper” John Wiley & Sons, (2010) with kind permission from John Wiley & Sons Inc., Hoboken,
NJ, USA, Copyright © 2010 John Wiley & Sons, Inc.

DOI 10.1007/978-3-319-18744-0_4
66 4 Minimum Impact Mill Technologies
A number of research programs focusing on minimum impact, sustainable,

energy-efficient pulp and paper manufacturing have been undertaken, some of
which continue today. Many of these where funded at national levels, and typically
involved national pulp and paper research institutes. With the use of clean technol-
ogy, the manufacturing processes can minimize pulp and paper products’ impacts
on climate change and water (European Commission 2001; Nilsson et al. 2007;
Vasara et al. 2001; Gavrilescu 2005; Hitchens et al. 2001; RPDC 2004; Suhr 2000;
Woodman 1993; Beca AMC 2004, 2006). Carbon dioxide emissions from the man-
ufacturing process can be reduced by investing in new plants, retrofitting existing
plants, heat recovery and increased paper recycling.
The American Forest & Paper Association has announced an ambitious set of
sustainability goals for its member organizations to aim for by 2020. The goals for
the industry cover several areas listed below:
–– Including improved recycling rates
–– Reducing greenhouse gases
–– Increasing the amount of fibre procured from certified forest lands
–– Better use of energy
–– Lowering the number of injuries in the industry
Among the goals, the industry hopes to improve the rate of paper recovery for
recycling by pushing the rate to 70 % or more. According to the American Forest &
Paper Association, 63.5 % of paper in the United States was recovered in 2010.
The Minimum Impact Mill Technologies which can meet the environmental
challenges of the pulp and paper industry are presented below:
4.1 Emission Reduced Wood Handling
Wood is one of the nature’s valuable raw materials and is an indispensable source of
pulp, paper and panel board. Wood handling is the very start of the processing chain
in the mills. Trains or trucks are used to transport the wood in the mills. Logs are
usually cut in the forests to a free length of 2–6 m. The incoming raw material is
weighed at the mill gate, and the volume is also measured in some cases. The logs
are discharged to the mill yard for intermediate storage or directly into the process
by truck loaders. Some process layouts contain slashing decks, which enable the
logs to be cut to certain lengths. Logs then are lifted towards the drum by the infeed
conveyor. During cold periods hot water or steam is used in the infeed conveyor to
de-ice the logs. This results in weakening of the bond strength between the bark and
the wood, making the logs easier to debark (Hatton 1987). Then the logs enter the
debarking drum. The drum is usually from 5 to 6 m in diameter and from 25 to 35 m
long in tumble debarking. The logs are debarked in a drum, where they hit against
the drum and each other causing the separation of the bark from the logs (Scheriau
1972). The bark and some wood material exit usually through bark slots in the side
of the drum. Finally, the logs leave the drum through the closing gate at the
4.1 Emission Reduced Wood Handling 67
discharge end. The position of closing gate mostly affects the filling degree of the
drum, which means the proportion of the drum volume which is occupied by the
logs. After that the logs are typically sprayed with water at the washing station. This
is done to remove the remaining loose bark and other impurities. Stones are removed
from the main material flow at the stone trap and metal detector stops the conveyor
if fragments of metal are found, which are removed manually. The logs are then cut
into chips by either a gravity or horizontal feed chipper. In some plants the short
logs are separated from the main stream and chipped with a short wood chipper. The
chips are transported by a conveyor belt first to chip piles and then to a screening
device. In some cases it is performed in the opposite order.
Some chemical pulp mills store wood chips in piles for 45 days or more. During
this period the resinous compounds (extractives) within the wood degrade by oxida-
tive and enzymatic mechanisms. The pile of wood chips can become quite warm
during the storage period. Storage for longer periods may reduce the pulp yield and
also the pulp strength.
Chip uniformity is very much important for proper circulation and penetration of
the pulping chemicals. Therefore, significant attention is paid to operational control
and maintenance of the chipper. Chips between 10 and 30 mm in length, and
2–5 mm in thickness, are generally considered acceptable for pulping. The chipped
wood is passed over a vibrating screen that removes undersized particles (fines) and
the oversized chips are routed for rechipping. Usually, the fines are burned with bark
as hogged fuel. But they can also be pulped separately in specialized “sawdust”
digesters. Most mills, segregate the chips according to the chip length. Chip thick-
ness screening has become important as mills realize the need to extend delignifica-
tion and reduce bleach plant chemical demands. Since the kraft cooking liquor can
only penetrate the chip to a certain thickness, both absolute chip thickness and
thickness uniformity have a significant effect on delignification (Tikka et al. 1992).
Thin chips can be easily cooked to lower kappa numbers. Uncooked cores from
over-thick chips will lower the average kappa reduction of a cook. This will contrib-
ute to higher bleaching chemical demands. Many mills are now using screening
equipment that separates chips according to thickness in order to improve thickness
uniformity (Strakes and Bielgus 1992). The overall optimum can sometimes be
reached by sacrificing some raw material to secure stable processing conditions,
which, in turn, promote better pulp quality and less pollution. The material removed
in the screening operation may be sold for other purposes or can also be burned in a
power boiler with heat recovery (USEPA 1992). Table 4.1 shows the measures to
reduce environmental impacts from wood handling.
The effluents to water from wood handling originate from the debarking drum
and from any spraying of wood piles with water. By the use of dry debarking, efflu-
ent from debarking can be minimised. In spraying piles the amount of water should
be minimised by control versus ambient temperature and humidity to match the
evaporation of water from the piles. Contamination of soil and groundwater should
be avoided by paving the wood yard area particularly the surfaces used for storage
of chips and by using water collection systems. Further treatment of polluted water
might be required, whereas nonpolluted water may not require any treatment. Some
Table 4.1 Measures to reduce environmental impacts from wood handling

Effluents to water
Minimise the generation of effluents by using dry debarking; Recycle bark press filtrate to the
kraft process; Organise separation of solids in wood yard effluent before bringing it to secondary
treatment or flocculation
When sprinkling wood piles with water, the flow should be controlled to minimise run off; for
sprinkled wood piles water collection systems in the wood yard avoid discharge of organic
substances (COD, toxicity)
Air emissions
Prevention of dust formation and wind drift from the wood yard area and from the chip piles
Solid waste
Bark and wood residues are contaminated by sand and stones. Minimise their amount by clean
handling. Recover bark and fines
Energy use
Use bark and wood fragments as fuel or prepare their use for energy recovery. Strive for high
dry content by pressing and drying for increasing the calorific value
Noise
Suitable layout and location of wood yard. Locate debarking drums, chippers and chip screens
indoors if possible. Use of low noise trucks and band conveyors
Based on European Commission (2013)
dusting of wood fragments from the chips and chip piles will occur and also from
the wood yard area itself. This is normally a very local issue and seldom of any
consequence outside the mill site. Wood and chip piles release volatile organic
compounds (VOCs) originating from the extractives. No control measures for VOC
reduction are applied in practice. Bark and any wood residues from the wood yard
should be collected in a as dry and uncontaminated form as possible to use them as
a fuel either in a bark or biofuel boiler at the mill or at a boiler with heat recovery
outside the mill. In spite of the careful handling it is unavoidable that some of the
material gets contaminated with sand and stones. Such material can often be used
for soil improvement. The most important energy aspect in wood handling is to as
efficiently as possible use the available residual biomass (bark, wood residue) to
generate energy. Power use in the wood yard is commonly about 10 kWh per m3
solid under bark of wood processed. This means about 25 kWh/tonne pulp for a
mechanical pulp mill and below 60 kWh per tonne for a chemical pulp mill. Suitable
dimensioning of the electric motors and motor controls should be used to keep
power use low. Band conveyors provide a low power use alternative for chip trans-
portation within the wood yard. There are many sources of quite high noise levels in
the wood yard area such as from the debarking drum and the chippers. Ways to
reduce the noise is primarily to locate this equipment in buildings or to construct
noise protections. Trucks used in unloading and handling logs and chips are noisy
in themselves. Noise in the form of impulse sounds is in addition created when logs
are dropped onto piles or receiving tables. Purchase of low noise trucks and training
in ‘soft’ driving are measures that should be applied. Noise protections may also be
considered to shield receiving tables.
4.2 Dry Debarking 69
Since the wood raw material varies greatly depending on the location of the mill,
the main challenge is how to handle these various species of wood in the right way.
That means treating the raw material as gently as possible to make it perfect for further
processing and to get the best possible yield. For this purpose, Metso Paper has devel-
oped a unique solution called ChipWay (www.ceeindustrial.com/public/data/compa-
nyCatalogue1224056297.pdf). This is their concept of wood handling, which
incorporates all process stages and results in high quality chips in a way that saves
wood. ChipWay features in-depth process know-how based on their wide experience,
cutting-edge machine technology and embedded automation solutions. Besides being
gentle to the raw material, ChipWay also pays special attention to the environment.
4.2 Dry Debarking
Debarking of the logs is usually the first process stage in pulp and paper mills.
Debarking is required to separate the bark from wood, due to many adverse effects
at the following process stages. The debarking drum does not operate in an ideal
manner, and wood loss always occurs (Niiranen 1985). Wood loss depends mainly
on the end product and the quality of the raw material which are mentioned below:
–– Wood species
–– Temperature (particularly below zero degrees)
–– Cutting season
–– Log freshness
–– Dimensions of the logs
Koskinen (1999) has reported that normal wood loss may vary in the range 1–3 %
whereas Agin and Svensson (1990) have reported that a wood loss of 5–6 % is nor-
mal. The end product mainly determines the requirements for the bark removal,
which is usually measured by log cleanliness measurement system. Log cleanliness
is defined as the percentage of the log surface that is bark-free after debarking. For
groundwood pulp or thermo mechanical pulp (TMP) a log cleanliness of 98–99 % is
usually required, but if the mill produces bleached softwood kraft pulp, then about
85–92 % log cleanliness is acceptable (Koskinen 1999). High bark removal requires
a long residence time of logs in the drum and wood loss may become high. On the
other hand, insufficient bark removal, saves raw material but it starts to increase the
chemical consumption in chemical pulp making and detracts from the quality of the
end product, particularly in the production of mechanical pulp. The debarking result
is therefore a compromise between bark removal and wood loss. In the Finnish
chemical pulp industry, the log cleanliness for softwood in particular is normally
above 85–92 %, which is acceptable (Koskinen 1999). It is possible to reduce wood
loss by aiming at a lower bark removal. This is emphasised when bark removal is
already high and it is almost impossible to remove all the bark. However, if the pro-
cessing is continued, wood loss will continue to increase. Moreover, a prolonged
residence time of the logs in the drum increases the probability of their breaking.
The bark of the tree comprises about 10 % of the weight of the tree trunk. Bark
is resistant to pulping, contains a high percentage of extractives, and retains dirt.
Therefore it does not yield good papermaking material. In most pulping processes,
bark is removed from the logs before they undergo chipping. Debarking drum is
most commonly used, which removes bark by tumbling the logs together in a large
cylinder. Slots in the outside of the drum allow the removed bark to fall through.
The bark collected from these operations is usually fed to the hogged fuel boiler for
generating process heat or steam. Wet debarkers rotate logs in a pool of water and
remove bark by knocking the log against the side of a drum by using large volumes
of water. The water used in this process is recycled but a certain amount is lost as
overflow to carry away the removed bark. In wet debarking, 3–10 m3 of water per
tonne of pulp are discharged. Organic compounds like resin acids, fatty acids etc.
and highly coloured materials leach out of the bark and go into this wastewater
stream. This effluent stream is collected and routed to the wastewater treatment
system, where the pollutants are normally removed quite effectively by using the
biological processes that take place there. Dry debarking methods such as dry drum
debarkers eliminate the water stream and the pollutants associated with it. Dry
debarking has gradually taken over wet debarking. In the dry debarking, the con-
sumption of water, and hence the emissions of organic substances, are much lower.
It is possible to eliminate emissions. In dry debarking, the bark that is used for
energy production has a lower water content, enabling better energy balance (Nordic
Council of Ministers 1993). Effluent from debarking is treated biologically. Use of
biotechnically produced enzymes in debarking is under research (Bajpai 2012a).
Process water is used only for log washing and de-icing (in cold climates water
or steam is used for thawing of wood) and is recirculated effectively with minimum
generation of wastewater and water pollutants. Dry debarking creates bark with a
lower water content, which will result in a better energy balance for the mill. Less
water is needed in the debarking and the dissolved amount of organic substances is
reduced (Jaakko Pöyry 1997; Finnish BAT Report 1997; SEPA-Report 4712-4
1997a). Although the process may increase the energy consumption, it results in
better energy balance for the mill due to reduced water content of the barks, which
are used for energy recovery. Effluent amounts and COD and BOD load is signifi-
cantly reduced compared to wet barking – and this is often the main driver for
installing dry debarking. Dry debarking can be applied in both new and existing
mills and for most debarking purposes (softwoods, hardwoods) and for all pulping
processes – mechanical pulping, chemical pulping etc. However, when producing
high brightness TCF bleached sulphite pulps, wet debarking may be necessary
because of quality reasons.
Raw effluents from a debarking plant are toxic to aquatic life. Biological treat-
ment has proven to be very efficient in eliminating toxicity. The dry debarking or
one with low wastewater discharges can be applied at both new and existing mills.
New mills almost exclusively and an increasing number of existing mills are using
dry debarking.
With dry debarking, the wood handling wastewater volume is usually in the
range of 0.5–2.5 m3/ADt. Decrease in wastewater amount is obtained by increased
4.3 High Yield Pulping 71
internal water circulation. By changing from wet debarking to dry debarking, the
wastewater amount would decrease often by 5–10 m3/ADt. With dry debarking the
total COD loading can be reduced up to 10 % (Salo 1999). The higher bark dryness
in the boiler feed improves the energy efficiency. Energy consumption in debarking
may increase due to the operation of the debarking drum in dry debarking mode. On
the other hand, substantial amount of energy may be gained, if the bark is used as an
auxiliary fuel at lower water content.
Where wet debarking is used, improved water recirculation coupled with grit and
solids removal systems for water has been applied with success. Dry debarking usu-
ally requires fresh wood in order to obtain good debarking results. The costs of dry
drum debarkers should not differ significantly from a wet system. Typical invest-
ment cost of a completely new dry debarking system is about 15 MEuros for a
capacity of 1500 ADt/d pulp (European Commission 2001). Dry debarkers already
dominate the industry, and wet systems have been in the process of being phased out
since the 1970s (Smook 1992).
The conversion of an existing wet debarking system to a dry debarking system
costs 4–6 MEuros. These costs include equipment and installation. Driving force for
implementing this technique are that dry debarking decreases TSS, BOD and COD
load as well as organic compounds like resin acids, fatty acids leaching out of the
bark and into this wastewater stream. Some of these substances are regarded as
toxic to aquatic life. The measure also increases energy yield. Dry debarking is
being used in several mills around the world.
4.3 High Yield Pulping
For the production of various paper products, pulp fibres liberated from woody or
non-woody biomass are used as raw materials. Two main concepts are adopted for
fibre liberation. One is related to chemical action, which dissolves the native lignin
that naturally binds fibres together. The dominant process of this type is known as
the “kraft” process. The pulp yield for a typical kraft process is about 45 %. Another
approach is mainly based on mechanical action to liberate the fibres; it is known as
the high-yield pulping process, and its pulp yield typically is within the range
85–95 %. Bleached chemi-thermo-mechanical pulp (BCTMP), alkaline peroxide
mechanical pulp (APMP), and preconditioning refiner chemical-treatment alkaline
peroxide mechanical pulp (P-RC APMP) are referred to as high yield pulps (HYP)
(Cannell and Cockram 2000; Zhou et al. 2005; Zhou 2004; Xu 2001; Reis 2001).
The properties of HYP produced from the three different pulping processes are in
general similar, depending on wood species, brightness levels and physical strength
properties. Table 4.2 shows important feature of HYP.
HYP is in fact a cost-effective replacement for hardwood bleached kraft pulp in
the manufacturing of printing and writing paper products. Hardwood HYP can
impart fine papers higher bulk, stiffness, opacity, and better printability (Cannell
and Cockram 2000; Zhou et al. 2005; Zhou 2004; Xu 2001; Reis 2001; Levlin 1990;
Table 4.2 Important feature of HYP

The production cost of high yield pulp is generally lower than that of chemical pulp
High-yield pulp is superior to chemical pulp in terms of light scattering, opacity, bending
stiffness, and bulk. The presence of large amounts of fines also contributes to good sheet
formation and surface smoothness, which can yield good printability
High-yield pulp has better recyclability than chemical pulp, due to less fiber hornification of the
pulp
The fast-growing hardwood species such as popular are most suitable for the BCTMP and
PRC-APMP processes
Due to wood shortage, a yield of about 90 % is indeed a considerable advantage
Ford and Sharman 1996; Johnson and Bird 1991). Use of high-bulk HYP allows
papermakers to make paper with the same caliper and stiffness with less pulp.
Presently, papermakers are using about 10 % HYP pulp in wood-free paper grades.
Potentially, up to 50 % HYP pulp can be used in most printing and writing paper
grades, for both coated and uncoated papers. In addition to having high pulping
yield and low cost, HYP has clearly different characteristics in comparison with
bleached kraft pulp (BKP). Most of the lignin from wood remains in HYP pulp
fibres causing the fibres to be relatively stiff and resistant to lumen collapse. On the
other hand kraft pulp, being essentially lignin-free, contains very flexible, collapsed
fibres. The rigid tube-like structure of HYP pulp fibres results in a higher bulk and
generally lower bonding characteristics than BKP fibres. The refining process in
HYP pulping produces a broad distribution of fibre sizes due to peeling and delami-
nation along the length of fibres and due to some fibre breakage. Fibre fragments,
fibre fibrils and fibrillated fibres give HYP pulp significantly higher specific area
than BKP, which may influence certain papermaking operations like, filler reten-
tion, internal sizing and polymer adsorption. Furthermore, the physical and chemi-
cal properties of fibres (increased bonding, decreased bulk and opacity) are
significantly modified in the alkaline hydrogen peroxide bleaching process in HYP
pulp production (Holmbom et al. 1991; Gullichsen et al. 2000; Pan 2001; He et al.
2004a, 2006a). HYP contains much more anionic groups such as sulfonic and car-
boxylic groups and thus has a higher fibre charge density than BKP (Thornton et al.
1993; He et al. 2004b, 2006b). Also, the anionic trash content of HYP is signifi-
cantly higher than that of BKP. These unique physical and chemical properties of
HYP may affect the wet-end chemistry of the papermaking process when HYP is
substituted for BKP.
Today, kraft pulping is the dominant pulping process around the globe. However,
in China, there has been a rapid increase in the production of high-yield pulp. For
example, during the years 2000 to 2010, China’s high-yield pulp production
increased from about 500,000 to 4,500,000 t/a (Bräuer et al. 2012). This marked
increase was caused by the huge domestic expansion in paper production/consump-
tion and the enormous demand for pulp (Jerschefske 2012). In China, the hard-
woods (poplar and eucalyptus), are the main raw materials for producing high-yield
pulp. To date, China has become the largest producer of high-yield hardwood pulp,
using both the BCTMP and the PRC-APMP processes, with the newly installed
4.4 Extended or Modified Cooking 73
production lines being predominately based on the PRC-APMP process (Bräuer

et al. 2012). The production of high-yield pulp in China has increased considerably
in the recent years. The well-known advantages of this type of pulp include low
production cost, high opacity, and good paper formation. In the context of state-of-
the-art technologies, China’s high-yield pulping, which is dominated by the PRC-
APMP process, has a much higher energy input but a significantly lower wood
consumption as compared to the kraft pulping process (Yanhong et al. 2015). If the
saved wood in the forest or plantation is considered as an increment of carbon stor-
age, then the carbon dioxide emission from the production of high-yield pulp can be
regarded as much lower than that of kraft pulp. High-yield pulp can offer a signifi-
cant environmental advantage of having a lower carbon footprint than kraft pulp,
based on the assumption that wood saving from high-yield pulping (over kraft pulp-
ing) is considered as a repository of carbon storage.
A bilateral research team, bringing together scientists from FP Innovations with
their industrial and academic partners from Canada and China, leveraged more than
$1 million to develop a new HYP destined to meet this objective. The team’s labora-
tory and mill trials have so far shown that current market high-yield pulp substitution
levels can be increased up to 40 % in paper furnish without any significant negative
effect on paper quality such as paper physical strength properties and printability.
Concerns over end product quality and paper machine operations have been lim-
iting the use of HYP for the last three decades. HYP is gaining increasing interest
for the production of high-quality wood-free paper grades as it is now known that
HYP provides lower furnish cost, better printability and improved paper bulk and
opacity. HYP is also environmental friendly due to its higher yield and lower carbon
footprint in manufacturing process as compared to kraft pulp. This translates into
less trees and chemicals per ton of paper, meaning a more cost competitive product
and overall reduced environmental footprint. Researchers are now exploring to
improve some of HYP properties, develop better paper coating and calendaring
strategies, and reduce/eliminate the negative effect of HYP on wet-end chemistry.
4.4 Extended or Modified Cooking
Extended delignification addresses environmental issues and improve mill energy

efficiency and has received wide use in the pulp and paper industry. Extended del-
ignification is performed before the bleach plant to reduce the lignin content in the
pulp entering the bleach plant in order to reduce the use of the bleaching chemicals.
Reduction in the use of bleaching chemicals reduces the amount of pollutants dis-
charged and increase the amount of organic substances going to the recovery boiler.
New cooking methods have been developed which allow more selective delignifica-
tion and provide mills with new pulping options. Mills are able to cook to lower
kappa numbers, allowing less bleach chemical usage or permitting alternative
bleaching methods. Mills can also maintain kappa numbers while improving yield
and physical strength properties.
Table 4.3 Modified cooking High initial hydrosulfide ion

principles (HS-) concentration
Even alkali (OH-) profile
Low concentration of dissolved
solids in the liquor
Low initial and final temperature
High initial ratio of HS- to OH
In the late 1980s modified cooking was introduced and all new fibreline mill
p rojects applied it. Modified cooking refers to a variety of techniques that have been
developed in the last two decades to modify the conditions in kraft digesters so that the
kappa number can be reduced while minimising loss of strength properties and yield.
The extended delignification through modified cooking uses the principle of alkali
concentration profiling. The alkali concentration is kept lower at the beginning of the
cooking (in impregnation) and is increased towards the end of the cook. This allows
cooking to reduce the residual lignin contents without undue degradation of carbohy-
drates or excessive loss of pulp strength thus reducing the delignification demand in
the bleaching plant and its environmental load. Table 4.3 shows modified cooking
principles. These principles are applied in different ways and to various degrees in
case of both modified continuous cooking (MCC) and modified batch cooking (MBC).
4.4.1 Batch Cooking
There are different types of batch extended delignification systems available:

–– Rapid Displacement Heating (RDH)
–– SuperBatch
–– Enerbatch.
In the RDH and Superbatch processes, impregnation with black liquor is per-
formed to decrease the heat consumption and at the same time to increase the initial
sulphide concentration and decrease the effective alkali charge (Bowen 1990;
Barratt 1990). Developments in SuperBatch® cooking have focused on the cooking
technology and chemistry that yield the highest possible strength. The SuperBatch
system allows the extension of cooking to very low lignin contents without any
process modifications and without losing pulp strength. Today, we are able to pro-
duce pulps that not only meet stringent pulp requirements, but also due to effective
impregnation stages and high chip quality improve the operation of the following
stage, i.e. the knotting and screening process. SuperBatch cooked pulps can also
improve profitability in papermaking process by enabling higher machine speeds.
There are several installations of SuperBatch cooking plant world wide.
In the Enerbatch process, a pretreatment with white liquor followed by a pre-
treatment with black liquor is performed. All these displacement cooking processes
show significant energy saving and an improved pulp quality. The lignin content is
usually measured as the kappa number with a standardised method. In all these
modified batch cooking methods, chips are impregnated in the digester before the
bulk delignification that is proceeded by an alkali concentration profile. In displace-
ment batch cooking the heat in the spent cooking liquor is recovered by displacing
it from the digester with a washing liquid and using it to preheat chips in the next
cooking batch (impregnation).
There are limitations in case of conventional cooking regarding how low the
kappa number can be brought without affecting the pulp quality. This kappa number
is around 30–32 for softwood and 18–20 for hardwood. By use of several cooking
modifications, the kappa from the cooking of softwood can be reduced to a level of
18–22 for softwood and 14–16 for hardwood, while maintaining the yield and
strength properties. The kappa reduction depends beside others on the modified
cooking technology applied and whether a retrofitted or new installation is used.
Several mills in the world with conventional batch cooking installations have
rebuilt their conventional batch cooking plants to modified batch cooking systems.
Modified batch cooking includes liquor displacement stages in the cooking cycle.
Most new batch cooking installations are modified batch cooking installations. The
advantages of the modified systems are better heat economy, improved pulp quality
and less rejects. The modified batch cooking system consists of several batch digest-
ers and a tank farm. The production rate determines the number and size of digest-
ers. The tank farm consists of hot liquor (black and white) accumulators, tanks for
impregnation and displacement liquors and soap separation, and a pulp discharge
tank. Intermediate black and white liquor accumulators are essential for balancing
the flows between different cooking stages. Several heat exchangers recover heat
from the hot liquors.
In the modified system, after cooking, the digester is cooled by displacement
with cold wash liquor. The hot displaced liquor is taken to a pressurized tank. After
cooling, the pulp suspension is pumped, out of the digester at a low consistency. The
hot liquor is reused in the cooking cycle to heat up the digester after impregnation
liquor fill. White liquor can be added both to the impregnation fill and the hot liquor
fill. Compared to conventional batch cooking, a tank farm is needed in the modified
system to store the different liquors between the digesters. Depending on the dis-
placement batch process (RDH, SuperBatch, Cold Blow or Enerbatch), there are
some differences in the cooking cycles, displacement liquors and tank farm configu-
rations, but the principles are similar. The digesters are heated at the beginning after
filling by using hot displacement liquors, and the cook is ended with a cold displace-
ment before discharging by pumping. In a conventional cooking system, more time
is needed to heat the digester than in modified cooking. In displacement cooking,
the cook is brought to a high temperature in the relatively short hot liquor fill or
displacement stage. The digester is at a high temperature for a longer period and a
lower cooking temperature can be used. Furthermore, the alkali profile can be
adjusted and controlled in the different stages of cooking in the modified system. A
higher residual alkali can be used at the end of the cook as the displaced cooking
liquor containing considerable amounts of alkali is reused in the next cook as hot
liquor fill. The longer cooking time at a lower temperature and the higher residual
alkali level at the end of the cook give several advantages with respect to pulp qual-
ity. The chips are cooked more homogenously, the kappa number deviations inside
the digester are reduced and less reject is produced. The strength properties of pulp
produced by displacement batch cooking as compared to conventional batch cook-
ing is improved. There are several reasons for this improvement in pulp quality, the
main reasons being gentler blowing after cooking, more uniform cooking, high
residual alkali at the end of cook and lower cooking temperature. There is sufficient
automation in the modern displacement cooking plants and a computer system con-
trols the entire operation. The control system includes controls at basic (distributed
control system) and supervisory levels.
4.4.2 Continuous Cooking
Continuous digesters are being used in modern kraft pulping. Continuous kraft
cooking was the standard until the 1980s, but in the middle of the 1980s, the break-
through of modified continuous kraft cooking occurred and the technology has
since been developed further. The major principles of modified kraft cooking that
distinguish it from conventional kraft cooking are: the split white liquor charge,
prolonged delignification by using the washing zone for delignification and the use
of counter-current cooking at the later part of the cook because it was thought at that
time that the concentration of dissolved lignin and sodium ions in the liquor should
be as low as possible, particularly in the final phase of the kraft cook (Axegård et al.
1978; Nordén and Teder 1979; Teder and Olm 1981; Kubes et al. 1983; Sjöblom
et al. 1983; Johansson et al. 1984). The introduction of split alkali charge actually
reduces the hydroxide ion concentration at the beginning of the cooking process,
which reduces the carbohydrate loss and increases the hydroxide ion concentration
at the end of the kraft cooking process. This in turn enables the transformation of the
slowly reacting residual-phase lignin to react like the faster bulk-phase lignin
(Lindgren and Lindström 1996). The use of the modified kraft cooking principles
made it possible to reduce the temperature of both continuous kraft cooking and
batch cooking systems. The major benefits of modified kraft cooking are improved
yield and selectivity (drop in limiting viscosity number versus reduction in kappa
number) (Andbacka and Svanberg 1997). The first continuous cooking application
on the market that adapted split white liquor charge and counter-current cooking
was named Modified Continuous Cooking (MCC) and developed by Kamyr. Later,
similar industrial continuous cooking concepts were established, such as Extended
Modified Continuous Cooking (EMCC) by Alström, Iso Thermal Cooking (ITC) by
Kvaerner Pulping and Lo-Solids by (Alström/Andritz) (Kubes et al. 1983; Sjöblom
et al. 1983; Johansson et al. 1984; Andbacka 1991). Modified continuous kraft
cooking was later improved by black liquor impregnation, where black liquor was
withdrawn from a later part of the digester and charged into the impregnation phase
at the start of the cooking process. The idea of using black liquor recirculation
during continuous cooking was adapted from the batch cooking systems. The initial
sulfide ion concentration thus increased significantly, which led to faster degrada-
tion of the initial-, bulk- and residual-phase lignin. Although high sulfidity is advan-
tageous from a chemical delignification point of view, the sulfidity charge is also
regulated in practice by discharge limits. Black liquor contains organic matter which
when present during the impregnation phase have been shown to have a rate-
increasing effect on bulk-phase delignification but a rate-decreasing effect when the
final residual delignification phase dominates (Wedin 2012). To avoid severe carbo-
hydrate loss, the kraft cook should thus be terminated before the even slower resid-
ual phase begins to dominate, example by terminating the cook at a higher kappa
number. The positive effect on the bulk phase has been related to lignin structures
having free phenolic groups (Sjödahl et al. 2006).
At the end of the 1990s, a new application called Compact Cooking, was mar-
keted and supplied by Kvaerner. Compact Cooking used black liquor recirculation
in a continuous cooking system, It was carried out using a significantly simplified
digester compared to that used in ITC consisting of two cooking zones used con-
currently and two sieves for black liquor extraction. A separate impregnation ves-
sel also became a standard in the Compact Cooking concept. This made it easier to
decrease the temperature during impregnation. The alkali charge was split between
two positions, as black liquor (adjusted with white liquor to the right concentra-
tion) to the impregnation vessel and as white liquor to the first cooking zone of the
digester. After the first cooking zone, the black liquor was extracted and transferred
to the impregnation. The recirculation of the black liquor made it possible to reduce
the cooking temperature (without increasing the size of the digester) because it
allowed for a higher hydroxide ion concentration through the entire cooking pro-
cess. This resulted in an increased delignification rate and reduced amount of resid-
ual phase lignin (Lindgren and Lindström 1996). The implementation of
black-liquor recirculation allowed for a decrease in temperature of approximately
10 °C for softwood and 5 °C for hardwood, which improved the yield and selectiv-
ity in comparison to ITC cooking. Another improvement in the Compact Cooking
was the use of a higher liquor-to-wood ratio during impregnation. This was able to
remove one of the most harmful alkali peaks for hemicellulose dissolution and
degradation during kraft cooking. Table 4.4 shows modified continuous cooking
systems.
The MCC process is based on two main principles. As compared with conven-
tional cooking, the cook starts at a reduced concentration of effective alkali and
ends at a higher concentration of effective alkali. The lignin concentration is reduced
at the end of the cook. This is performed by splitting the alkali charge into different
insertion points and by ending the cook in the counter-current zone, where the
liquor flows in an opposite direction to the chips. In a typical MCC digester, cook-
ing is divided into two zones. The impregnation vessel has a 30 min retention. The
con-current zone has a 60 min, and the counter-current zone has a 60 min. The white
liquor charge is split into three zones. Approximately 65 % is added to the impreg-
nation vessel, 15 % to the transfer circulation line, and 20 % to the counter-current
zone. Two benefits are achieved by adding white liquor to the counter-current zone.
Table 4.4 Modified MCC – Modified continuous

continuous cooking systems Cooking (Kamyr)
EMCC – Extended modified
continuous cooking (Kamyr Inc/
Ahlstrom)
ITC – Iso thermal cooking
(Kværner Pulping)
BLI – Black liquor
impregnation (Kværner Pulping)
Lo Solids – Lo solids cooking
Ahlstrom/Andritz
CC – Compact cooking
Based on Headley (1996), Bowen
(1990), and Andbacka (1991)
The initial hydroxide concentration is lowered. Some cooking is performed in the

counter-current zone, where the dissolved solids are lower.
EMCC was a further development in extended cooking. The EMCC process fur-
ther decreases the initial hydroxide concentration and increases the amount of cook-
ing in the counter-current zone. A fourth white liquor addition point is added to the
high heat circulation, and the temperature in the high heat zone is increased from
approximately 290–300 degF. Iso-Thermal Cooking (ITC) (developed by Kvaerner)
expands on EMCC with an additional circulation loop and fifth white liquor addi-
tion point (Engstrom 1996). The ITC circulation is a very high volume
(2100 gal/b.d.st) and requires a special type of screen to handle the flow. The screens
are equipped with back flushing valves which reduce blinding. The high circulation
rates result in even more cooking in the counter-current zone. As compared with
EMCC, the initial hydroxide concentration is reduced. The temperature in the
digester is lower and nearly uniform throughout the digester. The amount of cook-
ing in the counter-current zone is increased. Existing digesters can be retrofitted to
ITC provided an upflow exists in the digester. The downtime required is 10–14
days. The cost of a retrofit is approximately $3 million. To date, several digesters in
Europe and Japan have been converted to ITC. One retrofit has been installed in
North America in a southern kraft mill.
Black liquor impregnation, also developed by Kvaerner, takes extraction liquor
from the digester back to the impregnation vessel. This liquor has a relatively low
hydroxide concentration and comparatively high hydrogen sulfide concentration.
Black liquor impregnation is only applicable for new digester installations, or when
replacing the impregnation vessel due to corrosion or other problems. Existing
impregnation vessels cannot be converted to black liquor impregnation unless oper-
ated well below design capacity. The retention time required is approximately
40 min compared with 30 min for a conventional impregnation vessel. The major
benefit observed with black liquor impregnation is a 10 % increase in tear.
Table 4.5 World market Compact cooking 12

share of modified cooking (%)
processes
Lo solids (%) 34
ITC (%) 12
MCC (%) 19
EMCC (%) 4
RDH (%) 7
SuperBatch (%) 10
Heat recovery (%) 1
Kobudomari (%) 1
Based on data from Beca
AMEC (2004)
A number of continuous digesters have been retrofitted to ITC without having to

sacrifice production. However, this possibility has to be evaluated in each individual
case. This has to do with the dimensions of the pressure vessel in relation to the
capacity. Some other continuous digesters have been rebuilt to MCC. To achieve
this, white liquor is pumped into the digester at several points. With MCC and ITC
it is possible to cook the pulp to lower Kappa number, without losses in quality
(Kappa number 20–24 for softwoods and 14–18 for hardwoods). In continuous
cooking systems, the capacity of the plant would decrease with extended cooking
and imply higher cost burden to the pulp mill. In batch cooking, extended delignifi-
cation is carried out by means of displacement and black liquor recycling tech-
niques. The process is possible to install as retrofit in conventional plants, if the
digester capacity is large enough. In a new installation the kappa number from the
cook may be kept at 15–16 for softwoods and at about 12 for hardwoods. In prac-
tice, the modifications of an existing batch cooking system are possible to carry out
with additional batch digesters and additional investment costs without losing the
capacity of the cooking plant.
The most recent cooking development concerns the extension of the impregna-
tion process. A longer impregnation process at lower temperature improves the uni-
formity of the pulp and reduces the reject content of softwood (Karlström 2009).
The Compact Cooking concept has adapted prolonged impregnation; it is marketed
as Compact Cooking Generation 2 and supplied by Metso (CoC-G2).
Currently there are several continuous and batch digester systems with modified
cooking worldwide, capable of producing about several thousand ADt/d of pulp.
Modified cooking capacity increased more than fivefold during the 1990s, but has
tapered off in recent years. Table 4.5 shows the market share of the various systems
offered, based on system capacity.
4.4.3 Modifying Kraft Pulping with Additives
The era of modified kraft pulping originally called extended delignification which
began in the 1980s was founded on chemical principles intended to make kraft
pulping more selective for delignification over polysaccharide degradation. At
present, available pulping technologies like MCC, EMCC, RDH, Superbatch
require extensive retrofitting or digester replacements. So, their usefulness is lim-
ited if capital investment is a constraint. An ideal alternative process to achieve
extended delignification should be one with less extensive and/or expensive modi-
fications. Nowadays, applications of anthraquinone as a pulping additive has
become a simple and practical approach to overcome the above concerns. Other
chemicals like polysulfides and surfactants are also becoming strong candidates to
be considered as pulping additives during kraft pulping (Borchardt et al. 1997;
Bajpai et al. 2005). Digester modifications and pulping additives do not work
antagonistically but are complementary.
4.4.3.1 Anthraquinone
Anthraquinone (AQ) and a few closely related compounds can act as redox
(reduction-oxidation) catalysts for alkaline pulping (Fig. 4.1). Very small amounts
of AQ are enough. AQ, increases the delignification rate in a soda cook and also to
a smaller extent in a kraft cook (Holton 1977; Fleming et al. 1978; Löwendahl and
Samuelsson 1978; Fullerton and Wright 1984; Dimmel 1995; Quinde et al. 2004).
AQ stabilises the carbohydrates by oxidising their reducing end groups (Obst et al.
1979) and thereby protecting them against the peeling reactions which lead to a
decrease in pulp yield. In this reaction, AQ is itself reduced to anthrahydroquinone
(AHQ), which can cleave β-O-4 linkages in the lignin. Different reaction mecha-
nisms have been suggested for the lignin degradation caused by AHQ. Both an ionic
mechanism (Aminoff 1979; Obst et al. 1979; Gratzl 1980) and a radical mechanism
Carbohydrate
reaction
O O O (-)
(-)
O HO OH
Anthraquinone Anthrahydroquinone
Lignin reaction
Fig. 4.1 AQ catalytic cycle

(Dimmel and Schuller 1986) for the β-arylether cleavage have been reported. The
AQ acts almost like a catalyst during the kraft cook, as about 20 % of the AQ can be
found in the black liquor after the kraft cook (Laubach 1998; Goyal 1997; Ahluwalia
et al. 1992). AQ can be used in the soda-AQ process, but its main use today is as an
additive in the kraft process, mainly in countries with high raw material costs such
as Japan. A major disadvantage of the addition of AQ, apart from the price, is that
the bleachability i.e. the amount of bleaching chemicals required to reach a given
brightness for a given lignin content of the unbleached pulp, decreases when AQ is
added to kraft or soda cooks (Håkansdotter and Olm 2002).
The addition of 0.5–1 kg AQ/t wood to a standard kraft cook results in a 4–6
kappa number reduction while increasing pulp yield by 1–2 %, at constant pulp
strength (McDonough and Herro 1997). The yield can vary significantly with wood
species and cooking conditions. Since AQ increases the pulping reaction rate, white
liquor requirements can typically be reduced by 8–10 %. This can eliminate or
reduce black liquor shipments, increase washing efficiencies, and reduce consump-
tion of makeup chemicals. If a mill suffers from total reduced sulfur (TRS) emission
problems, AQ can reduce the amount of sodium sulfide required since AQ and
sodium sulfide compete with each other to prevent carbohydrate dissolution. A
bleached pulp mill may choose to take the benefit of the lower kappa number that
resulted from extended delignification by reducing the bleaching chemical demand.
4.4.3.2 Polysulfide
Polysulphide is another additive that has been examined by several researchers

(Kleppe, and Kringstad 1963; Teder 1968). The polysulphide has a positive effect
both on the delignification rate (Lindström and Teder 1995) and on the carbohydrate
stability, as it oxidises the carbohydrates, reducing the end groups to alkali-stable
aldonic acid end groups (Teder 1968; Pekkala 1982, 1986; Jiang 1993, 1995; Katz
1993). The positive effect of polysulphide on the delignification rate is evident at
concentrations of 0.02 mol/dm3 and higher (Berthold and Lindström 1997). Even
though polysulphide is formed during the kraft cook, most of it rapidly decomposes
at temperatures higher than 110 °C. Without polysulphide addition, the concentra-
tion of polysulphide is lower than required to achieve the positive effect on the
delignification rate (Gellerstedt 2003). Because of this, polysulphide has to be
added to the cooking liquor. The drawback of polysulphide addition is that the
amount of sulphur in the system is increased, and this disturbs the sodium-sulphur
balance in the mill, thereby generating higher emissions to the atmosphere.
Polysulfide pulping is a variant of kraft pulping in which half or more of the
sodium sulfide of kraft white liquor is first oxidised. This orange liquor has the abil-
ity to preferentially oxidize end-groups of hemicelluloses, making them more stable
to alkaline attack and resulting in higher yields of pulp from wood. Laboratory stud-
ies have shown that the addition of polysulfide to modified cooking makes it possi-
ble to produce a fully bleached pulp from softwood brown stock in the 15–18 kappa
range with final yield and strength properties comparable to those from conventional
kraft brown stock at about 30 kappa number (Jiang 1995). Kraft polysulfide pulps
have different papermaking characteristics due to the retention of hemicelluloses,
and may be undesirable in some paper grades. However, the use of polysulfide has
achieved limited commercial acceptance due to the instability of the polysulfide ion
at normal kraft cooking temperatures, thus requiring extended impregnation time at
low temperature and a slow heating rate to cooking temperature.
Mead Corporation has patented MOXY polysulfide process. It is being used in
few mills. The pulp yield is generally about 1–3 % higher (from wood) than that of
kraft pulp at the same kappa number. The Pulp and Paper Research Institute of
Canada (Paprican) has also developed a polysulfide generation system that has been
used in one Canadian mill up to July 2003.
4.4.3.3 Sodium Borohydride
A preliminary report on the use of sodium borohydride in kraft pulping was pub-
lished by Hartler in 1959. The results of this study revealed that sodium borohydride
increases the pulp yield. Subsequently, investigations in the 1960s and 1970s
showed similarity with the results of Hartler (Pettersson and Rydholm 1961; Meller
1963; Aurell and Hartler 1963; Annergren et al. 1963; Meller and Ritman 1964;
Gabir and Khristov 1973; Diaconescu and Petrovan 1976). In the last decades, some
investigations focused on feasibility of using boron compounds with different spe-
cies and additive ratios in pulp and paper industry (Istek and Gonteki 2009; Tutus
2005). Sodium borohydride, has a reducing effect on the carbohydrate end groups
and makes them alkali-resistant (Hartler 1959). This gives an increase of 3 percent-
age points in the softwood pulp yield. It is mainly glucomannan that accounts for
this yield increase. At the same time, the amount of xylan in the pulp decreases. This
is probably due to a decrease in the xylan adsorption onto the fibres as a result of the
higher amount of glucomannan. Sodium borohydride is today not used commer-
cially, as it is too expensive. Adding of sodium borohydride to cooking liquor
increases pulp yield through greater retention of hemicelluloses. Sodium borohy-
dride causes reduction of the carbonyl group located on the end group of cellulose
to a hydroxyl group during the cooking and stops the probable peeling reaction
because it is a powerful reducing agent. Thus, a decrease in yield during cooking
can be prevented. This reaction can occur in both cellulose and hemicellulose
(Courchene 1998). The peeling reaction initiated in carbonyl groups in the end units
is prevented by the conversion of carbonyls to hydroxyls by borohydride. The major
effect of borohydride is to prevent the acceleration of glucomannan removal that
otherwise occurs at 100 °C (Tutus and Usta 2004).
4.4.3.4 Surfactants
The first patent on the use of non-ionic surfactants as additives on pulping dates
from 1975 (Parker and Lundsted 1975). Surfactants help the penetration of the
cooking liquor by wetting and emulsifying the wood extractives. However, it should
also be considered the wetting effect on the chip surface and improved penetration
of the liquor into the interstices of the chip. This action will allow to have a more
efficient and faster delignification with the resulting effects of lowering the kappa
numbers and/or reducing the rejects (yield increase) (Chen 1990, 1994). Anionic
surfactant carries no charge and its hydrophilic portion contains several polar ether
linkages derived from the polymerization of ethylene oxide and/or propylene oxide
with the hydrophobe.
Surfactants as surface active chemicals are very effective at very low concentra-
tions. Usually they are applied at 0.025–0.06 % based on o.d. wood. The dosage
will depend on the degree of delignification and the target kappa number must be
based on the capacity of rejects processing equipment in the mill. Additional ben-
efits of surfactants are their ability to keep both lignin and wood extractives in
solution in the black liquor. The later benefit was already envisioned by Mutton
(1958) who stated that application of surfactants would help the deresination in the
hot alkaline extraction stage. Full utilization of aspen in western Canada has been
slow to develop because of problems associated with excessive pitch and subse-
quently poor quality pulp. Due to the low ratio of saponifiables-to unsaponifiables
in its extractives composition, attempts have been made to favorably alter this ratio
during pulping. A common operation when pulping hardwoods (they lack of resin
acids) is the addition of ‘tall oil’ which is composed mainly of sodium salts of
resin- and fatty acids. This acid fraction is able to aid in the dissolution and emul-
sification of the neutral unsaponifiables present during pulping. Even though this is
a very common practice not all mills have quoted effective results. Some mills
reports favorable results upon addition of tall oil at a rate of 1.5–2.5 % of o.d.
wood. In the case of softwoods (presence of resin acids) even though they contain
higher amount of total extractives they have less problems related to pitch than
hardwoods. This phenomenon can be explained because of the emulsifying action
of the resin acids (Quinde 1994).
4.4.3.5 Combination of AQ/Surfactant
There has been growing interest in combining AQ and surfactant- based digester for
gaining additional benefits. The surfactant, when used in conjunction with AQ,
improves AQ selectivity by transporting the AQ to more reaction sites. This can
result in a 20 % AQ reduction while maintaining the same AQ benefits. The ability
to reduce the total quantity of AQ in the system results in reduced downstream prob-
lems such as evaporator and economizer fouling and residual AQ in the crude tall
oil. As mills continue to run their systems beyond designed capacity, the need for a
digester additive program will increase. Digester additives can provide an alterna-
tive to expensive capital expenditures and allow the mill more operational flexibility
as illustrated in Fig. 4.2.
AQ Surfactants
• Reduces peeling • Increase yield • Reduce rejects
reaction • Decrease kappa • improve deresignation
• Lower sulfidity number • Improve brownstock
• Reduce white liquor washing
• Reduce bleaching • Maximize AQ benefits
chemicals
Fig. 4.2 Benefits of using anthraquinone and surfactants
4.4.3.6 Combination of AQ-Polysulfide
It has been proved that the combination of anthraquinone and polysulfide give more
yield gains than the sum of respective yield increase. This augmentation is called
the synergistic yield increasing effect of polysulfide and anthraquinone (Jiang 1993;
Malkov 1990; Yamaguchi 1983). This synergistic effect decreases at low kappa
number. Strategies for implementing AQ and AQ-Polysulfide extended digester del-
ignification are site-specific.
4.5 Efficient Brownstock Washing/Improved Pulp Washing
About half of the wood is dissolved in the digester. The pulp coming from the
digester contains both fibres and spent cooking liquor (black liquor). The black
liquor contains inorganic chemicals and a large amount of organic compounds con-
tributing to BOD, COD, colour and conductivity in the effluent. The black liquor
from the pulp is removed in the subsequent washing stages and fed to the chemical
recovery system, where cooking chemicals and energy are recovered (Bajpai 2008a).
The dissolved organic compounds together with the spent cooking chemicals are
separated from the cellulose fibres in the brown stock washing stages. The main
objectives in brown stock washing are to achieve:
–– The cleanest pulp while using the minimum amount of water.
–– A high solids concentration in the weak black liquor fed to the evaporators.
In chemical pulping, the main reason for brown stock washing is to remove
soluble impurities using a minimal amount of water (as this water must be evapo-
rated later on). Pulp is also washed to recover valuable cooking chemicals and
organic chemicals, which are recovered for their heating value (Crotogino et al.
1987). Efficient washing improves the recovery of spent chemicals, reduces the
4.5 Efficient Brownstock Washing/Improved Pulp Washing 85
consumption of reagents in the subsequent bleaching and limits effluent load from
the plant (Tervola and Gullichsen 2007). It also has a positive effect on pulp qual-
ity and prevents deposition problems (Wilson 1993). The brown stock washing
system is always mill dependent. It starts with cooking (Hi-Heat) and is followed,
mainly in series, by various equipments such as a Drum Displacer (DD), a vac-
uum filter, a diffuser, a press filter, which use either dilution/thickening or dis-
placement washing principles or their combination. The target is to connect these
different washing equipments in a series and obtain as good a washing result as
possible with a minimum amount of used wash water (Crotogino et al. 1987).
Brown stock washing also plays a key role in oxygen delignification performance.
Washing before oxygen delignification is important, because a high incoming
wash loss into the oxygen delignification reduces pulp strength and consumes
oxygen and alkali. Washing after oxygen delignification is also very important, as
it reduces the amount of detrimental organic wash loss and cooking chemicals
entering bleaching. When the amount of washing loss is high in the bleaching
feed, more bleaching chemicals are consumed. With washing after oxygen delig-
nification the economy and the environmental friendliness of the whole fibreline
is improved (Andbacka 1998).
Examples of washers with excellent washing efficiency at low dilution factor
(ratio of wash water used to pulp washed) are:
–– Compaction baffle filter
–– Atmospheric diffusion washers
–– Pressure diffusion washers
–– Pressure drum washers
–– Displacement (twin roll) wash presses
–– Drum displacement (DD) washer (multi-stage)
The discharge consistency is highest for wash presses. Wash presses and diffu-
sion washers are especially effective in the removal of dissolved organic com-
pounds. Wash presses have become more common, especially as the last washing
stage before bleaching.
The pulp is then screened with pressure screens. The screen room may be located
before or after the oxygen delignification stage. Most mills screen the pulp before
oxygen delignification, but there are many mills where the screen room being
located after the oxygen delignification stage. Modern screen rooms are closed
operations, i.e. without a continuous process effluent discharge during normal oper-
ating conditions. In practice there typically is a small discharge due to, for example,
pump seal water, drainage from screening rejects, and minor leakage from piping
and equipment. A key principle in such an operation is that any water entering the
process must leave either with the unbleached pulp or with the weak black liquor
fed to the chemical recovery system. Closed fibreline operation requires that the
volume of water entering the system be as small as possible to reduce both capital
cost and operating cost (as steam) for evaporation. Key components of the closed
fibreline include adequate brown stock washing capacity, closed screening, control
of water inputs and effective process controls (Stratton and Gleadow 2003).
Most of the modern systems normally recover at least 99 % of the dissolved
wood solids and pulping chemicals applied in the digester. In today’s batch as well
as continuous cooking fibrelines, washing already starts in the digester by displac-
ing hot black liquor with cold wash liquor. Subsequent washing is carried out in
various types of washing equipment mentioned above. Efficient washing reduces
the carry-over of black liquor with the pulp resulting in a decreased consumption of
chemicals in oxygen delignification and bleaching and reduced discharges from the
bleach plant.
In most mills in Europe, the water system in the brown stock screening plant is
completely closed. With modern wood handling and cooking, less than 0.5 % knots
and shives are left in the pulp after cooking. The closing contributes to the reduction
of organic compounds in the effluents and they are then recovered and incinerated
in the recovery boiler. The idea is to bring the clean counter-currently through the
fibreline, which gradually increases the dry solid content of the liquor.
The closing of the washing and screening may require supplementation or
replacement of existing equipment with new units to reach lower wash water con-
sumption and to have better materials to resist corrosion. In a few existing mills the
capacity of the evaporation plant or the recovery boiler may need to be increased in
order to cope with the improved closure of the washing and screening departments.
The closing contributes to the significant reduction of organic compounds in the
effluents. They are then recovered and incinerated in the recovery boiler. Thus, the
screening plant has no discharges to water. Energy consumption increases due to
increased need for evaporation. The measure has been applied since 1980s with
good experiences. In Europe and North America, closed screening and brown stock
washing is reality in almost all mills.
In many pulp mills the washers are equipped with basic instrumentation and the
individual control loops are supervised by a DCS system. In most cases, the coordi-
nation of these individual control loops is done manually by the operators. In any
manual operation the results vary with the individual, so the stability of the whole
operation suffers. The transition periods during fibre species and production rate
changes can be particularly troublesome. Many mills are now realizing that poor
performance in the washing line can have a significant effect on the stability of
operation and the production costs in other related processes pulping or recovery
process. For example, poor washing of the pulp can result in higher bleaching chem-
ical consumption. Organic materials that are not washed out of the pulp are a lost
source of energy for the recovery boiler. On the other hand, if the filtrate liquor is
too dilute, evaporation costs will be higher. In some cases this may result in a pro-
duction bottleneck for the whole pulp mill. Also, if outlet consistency is not regu-
lated and becomes too high the washer operation may be halted. The operation of
the brown stock washing operation is therefore a delicate balancing act, with the
operators trying to achieve the best removal of soluble impurities, the highest
possible outlet consistency and the highest solids content in the dilute liquor sent to
the evaporation plant. But operating practices vary from operator to operator and, in
some mills, the wood species and production rates change on a regular basis, thereby
destabilizing the washing process. Because the washing line is a sequential,
4.6 Oxygen Delignification 87
c ountercurrent operation, the stability of the whole line can be upset. It may take
only a few minutes to destabilize, but the recovery may take several hours. To
address these issues Metso Automation has introduced a whole-line optimization
control called DNAwash, which controls first the individual washing units and then
balances the distribution of washing liquors and manages filtrate tank levels through-
out the entire line (Kapanen and Kuusisto 2002). Most importantly, this control
manages the washing operation through transitions between fibre species and dur-
ing the usual production rate changes. The benefits of improved washing line con-
trol and optimization include: optimized washer load distribution; consistent
operation; no human errors; lower more stable washing losses; steam savings in
evaporation plant; more even pulp quality and reduced bleaching chemical use; alle-
viation of bottlenecks and higher production rates; more pulp with the same equip-
ment. Stora Enso Fine Paper’s Veitsiluoto mill, in Kemi, Finland invested in Metso
Automation’s DNAwash, implemented in their metso DNA control system to real-
ize many of these goals (Williamsson and Kapanen, 2005).
4.6 Oxygen Delignification
Oxygen delignification of pulp is a proven technology which has been in use for
more than four decades. In most cases, the term is used synonymously with oxy-
gen bleaching. The use of oxygen delignification systems is increasing throughout
the world (Genco et al. 2012). Oxygen was recognized as a potential bleaching
agent as early as 1867, at which time a process was patented to improve pulp
bleaching by running “heated air through an agitated pulp suspension”. Because
of the trend in the industry towards ECF bleaching combined with minimal emis-
sion of chlorinated organic compounds, oxygen delignification has emerged as a
very important process. Oxygen delignification can be used successfully to delig-
nify kraft softwood and hardwood pulps, sulphite softwood and hardwood pulps,
and nonwood pulps. These pulps are used in a wide variety of products, including
printing and writing papers, copy paper, newsprint, grease proof paper, paper
board, tissue, and diapers.
The ‘oxygen stage’ was developed in the late 1960s when serious concerns
about bleach plant effluent discharges, pollution control and energy consumption
began to surface. These concerns were originally directed at reductions in BOD,
COD and colour. The major areas of growth for oxygen delignification initially
were Sweden in the 1970s and Japan in the 1980s, in order to save bleaching
chemical costs. The late 1980s saw a widespread growth due to the chlorinated
organics issue. For TCF production, oxygen is essential to obtain a major decrease
in lignin prior to the bleach plant. The choice of oxygen delignification is based on
economical, technical and environmental needs at a particular mill. The worldwide
installed capacity of oxygen delignified kraft pulp in 2010 was estimated (Genco
et al. 2012) at about 300,000 metric tons/day, representing most of the world’s
bleachable grade pulp.
Oxygen delignification involves an extension of the delignification started in the

cooking process and provides the bleaching plant with a pulp that has a significantly
reduced kappa number. The primary advantages of oxygen delignification coupled
with modified bleaching over conventional bleaching include:
–– Partial replacement of chlorine based chemicals (especially chlorine gas) for
ECF pulp production
–– Elimination of all chlorine based chemicals in TCF sequences
–– Retainment and the recycling of the extracted organics and chemicals applied in
the oxygen stage
–– Incineration of the recycled organics to generate energy;
–– Energy savings
Oxygen production requires only 12.5 % the energy of chlorine dioxide expressed
as equivalent chlorine (McDonough 1990, 1995; McDonough and Herro 1997;
Simons and AF-IPK 1992; Nelson 1998; Jones 1983; Gullichsen 2000; Pikka et al.
2000; Tench and Harper 1987). Most American and Canadian mills apply oxygen
delignification to assist in the economics of bleach plant modernization or expan-
sion, although more and more interest is being placed on the reduction of environ-
mental pollutants (Tatsuishi et al. 1987; Enz and Emmerling 1987). In Scandinavia,
the main purpose of oxygen delignification is the reduction in the formation of
chlorinated organics, especially chlorinated phenolics, to minimize the biological
impact of the bleaching effluent on the environment. Oxygen delignification signifi-
cantly improves bleach process efficiency and can shorten a bleaching sequence
provided that effective washing is used after the oxygen stage. Because less lignin
enters the bleach plant, there is a significant decrease in consumption of bleaching
chemicals and a reduction in cost because oxygen is less expensive than chlorine
dioxide and hydrogen peroxide.
Oxygen delignification, is done as the first bleaching stage after kraft cooking to
reduce the kappa number by 45–65 %. The effluent from the oxygen stage can be
recovered and taken to the recovery boiler by integrating the oxygen stage into the
brown stock washing system. The oxygen delignification stage is a more selective
way to delignify the pulp than to extend the cooking to low kappa numbers. There
are, however, viscosity and pulp strength losses also related to oxygen delignifica-
tion, which is why the oxygen stage cannot be extended to too low kappa numbers.
Figure 4.3 shows how the oxygen stage is integrated into the brown stock counter-
current washing system. The pulp is washed after cooking to reduce the amount of
dissolved material from cooking entering the oxygen stage. The pulp is mixed with
alkali and oxygen. Steam is added to increase the temperature to 90–110 °C. After
delignification and bleaching in the pressurized reactor, the pulp is discharged to a
blow tank where gases are separated out. After oxygen delignification and gas sepa-
ration, the pulp is washed to recover the used chemicals and the dissolved organic
material, corresponding to a yield loss of 2–4 % of the pulp flow.
Oxygen may be classified as an oxidizing agent with low reactivity, moderate
selectivity, and low efficiency. It has moderate ability to bleach shives and other
particulate matter and most significantly has low impact on the environment. The
NaOH
Steam
Wash
O2 Water
Vent Gases
(CO2 & Steam)
Unbleached Pulp to Further

Pulp
Pump, mixers Bleaching
Reactors Blow Washers
tank
Filtrate to Brown
Stock Washing
and Recovery
System
Fig. 4.3 Incorporation of the oxygen delignification stage in brownstock washing and cooking
liquor recovery cycle (Based on McDonough 1996; Gullichsen 2000)
low reactivity necessitates elevated temperatures (85–115 °C) and pressures (4–8

bars) for oxygen delignification reactions to proceed. Oxygen’s moderate selectivity
can sometimes lead to appreciable loss in pulp viscosity and may necessitate adding
a viscosity protector such as magnesium sulphate to the pulp in the case of soft-
wood. Low efficiency means that appreciable quantities of the reagent must be
added to the oxygen delignification system (15–25 kg O2 per tonne of pulp).
Two types of systems are used commercially for oxygen delignification; these
are generally characterized as high- and medium-consistency systems. Figures 4.4
and 4.5 show flowsheet and equipment of typical medium consistency oxygen del-
ignification; Fig. 4.6 shows flowsheet of typical high consistency oxygen delignifi-
cation and Fig. 4.7 shows the reactor for high consistency oxygen delignification.
Because of better selectivity and lower investment costs, the medium consistency
(MC, 10–15 % consistency) system has dominated mill installations since the early
1990s (European Commission 2001) but high consistency installations (HC,
25–30 % consistency) are in use as well. Table 4.6 shows typical operating data
ranges for Oxygen Delignification Process. Figure 4.8 shows the flow sheet of a
typical two-stage oxygen-delignification installation.
The OXYTRAC system (Bokström and Nordén 1998) is an example of a modern
two-stage oxygen delignification process system. The first installation of this design
was at SCA’s Östrand mill in Sweden. Very high delignification degrees, approxi-
mately 70 %, have been achieved through optimization of the system. It is claimed
that chemical consumption has been reduced and pulp quality improved with better
selectivity than with the single-stage oxygen delignification this system replaced.
The OXYTRAC design utilizes two reactor stages (Fig. 4.9) (Alejandro and Saldivia
2003). The first operates at high chemical charge and pressure (8–10 Bar) but at
relatively low temperature (85 °C) and with a short retention (20–30 min). The high
Fig. 4.4 Flowsheet of typical medium-consistency oxygen delignification
PULP FROM
WASHING
WASH WATER
NaOH
O, STEAM
HD-TOWER
BROWN STOCK
WASHING
Fig. 4.5 Equipment of medium consistency oxygen delignification

Fig. 4.6 Flowsheet of typical high-consistency oxygen delignification
Fig. 4.7 High consistency

oxygen delignification reactor
Table 4.6 Typical operating data ranges for oxygen delignification process
Variable Medium consistency High consistency
Consistency (%) 10–14 25–30
Alkali consumption (Kg/Tonne) 15–35 (1.5–3.5 %) 15–25 (1.5–2.5 %)
Temperature (°C) 85–105 100–115
Pressure (Bars) In (7–8); In (4–6);
Out (4.5–6.0) Out (4–6)
Retention time (Minutes) 50–60 (1 Stage); 25–35
20/60 (2 Stage)
Oxygen Consumption (Kg/Tonne) 20–24 (2.0–2.4 %) 15–24 (1.5–2.4 %)
Magnesium sulphate (%) (When required) 0–0.02 0–0.02
Fig. 4.8 Two-stage oxygen delignification
pressure is used to keep the concentration of dispersed oxygen high. The second
reactor operates at lower chemical concentration and pressure but with higher tem-
perature (100 °C) and a longer retention (60 min). Only direct steam to heat the
stock is added between the reactors. Other variations on the two-stage oxygen del-
ignification include systems in which washing is carried out between the two oxy-
gen reactors. Studies have shown that interstage washing improves the delignification
power of the system (lower kappa out) and reduces the alkali charge required to
maintain satisfactory pH levels due to the buffering characteristics of the lignin
dissolved in the first stage (Allison and Wrathall 1998). It does not appear that dis-
solved solids carried over from the first reactor have any adverse impact on the
selectivity of the system.
The choice between one-stage and two-stage systems will be dictated by the
selected starting kappa number, i.e. the kappa number from cooking, and the
selected kappa number from the oxygen stage. The higher the kappa drop in the
Fig. 4.9 Typical Oxytrac system set up (Alejandro and Saldivia 2003, Reproduced with
permission)
oxygen stage, the greater the need for a two-stage system. The kappa number
range before the oxygen stage of eucalypt kraft pulp is typically 15–18, while the
target kappa number range after the oxygen stage is typically 9–12. While two-
stage oxygen delignification is a safer and better choice for softwood due to their
higher kappa number at the end of cooking, it is optional for hardwood. Since
1995, the changes to oxygen delignification have been minor and have consisted
of changes in process conditions which distinguish the systems provided by the
different vendors. The trend towards medium consistency, two-stage installations
has strengthened.
In order to maximize pulp yield, the trend is to target a higher digester kappa
and a high kappa reduction in the oxygen stage. Most new installations of oxygen
delignification favour a medium consistency two-stage process, over a single
stage, with or without intermediate washing. Recent improvements in oxygen del-
ignification have been focused on improving the effectiveness and selectivity of
the stage (Johnson et al. 2008). For example, the Veracel bleached eucalyptus
kraft mill in Brazil is typical of optimal systems that operate the first reactor at
lower temperatures (92–96 °C) and higher pressure (6–8 bar) than the second
stage (98–100 °C and 3–5 bar).
Oxygen delignification is more selective than most extended delignification pro-
cesses, but may require significant capital investment to implement (Gullichsen
2000; McDonough 1996; Tench and Harper 1987; Kiviaho 1995). The major
b enefits of oxygen delignification are decrease of the amount of chemicals, p ollution

load and the total costs for bleaching chemicals. The chemicals applied to the pulp
and the materials removed from the pulp are compatible with the kraft chemical
recovery system. This enables the recycling of oxygen- stage effluent to the recov-
ery system by way of the brown stock washers, decreasing the potential environ-
mental impact of the bleach plant. The decrease is roughly proportional to the
amount of delignification achieved in the oxygen stage. This applies not only to
chlorinated organic by-products, but also to other environmental parameters associ-
ated with bleach plant effluents, including BOD, COD, and colour. The decrease in
colour, however, is larger than expected on the basis of the lignin removed in the
oxygen stage. Oxygen delignification decreases the kappa number prior to chlorina-
tion and therefore the effluent load emanating from the bleach plants is reduced.
The industrial application of oxygen bleaching has expanded very rapidly in
recent years. Today, North American mills are showing greater interest for the tech-
nology, principally because of increased environmental concerns, and also because
the application of medium-consistency equipment now provides more process
options. Ozone, although possesses certain advantages over oxygen, will probably
see application only in conjunction with oxygen.
Oxygen will be used to predelignify pulp to the point where the necessary ozone
charge becomes small enough to be economical and selective. Typically, it is pos-
sible to reduce the lignin content by up to 50 % in the oxygen delignification stage;
further delignification would cause excessive cellulose degradation. A commensu-
rate reduction in the discharge of pollutants is achieved by washing the dissolved
solids from the oxygen-delignified stock and recycling them to the pulp mill recov-
ery system. As a result, the total solids load to the recovery boiler will increase
significantly, by about 3 % with softwood pulp and 2 % with hardwood pulp. Since
these solids are already partially oxidized, steam generation will increase by only
1–2 %. Most kraft mills employing oxygen delignification systems use oxidized
white liquor as the source of the alkali in order to maintain the sodium/sulphur bal-
ance in the chemical cycle (Colodette et al. 1990). In most instances, air systems are
used for white liquor oxidation because they are more economical to operate, even
though the initial capital cost is higher than for oxygen systems. The use of oxidized
white liquor increases the load on the causticizing plant and lime kiln by 3–5 %.
Oxygen delignification can be adopted in new and existing kraft mills but not in
the same way and at the same costs. The installation of oxygen delignification phase
in the existing kraft mill may decreases the fibreline production, if there is not
enough spare capacity in the whole recovery system. The additional evaporator
steam requirements are from 0 to 4 % for high consistency system and from 4 to
10 % for medium consistency system. The total additional solids load is about
70 kg/t for softwood and 45 kg/t with hardwood. The steam generation of the excess
solids is about 1.5–2.5 % less than the increasing of solids load because of a lower
heating value of the black liquor from oxygen stage.
Modern mills are always designed for a combination of modified cooking and
oxygen delignification and for the effect on the environment (discharges of COD
and AOX) both techniques have to be considered together.
Table 4.7 Effect of different delignification technologies on kappa number and effluent COD
Conventional Extended
Delignification Conventional cooking + oxygen Extended/modified cooking + oxygen
technologies cooking delignification cooking delignification
Kappa number 14–22 13–15 14–16 8–10
(Hardwood)
Kappa number 30–35 18–20 18–22 8–12
(Softwood)
COD load (kg/t) 28–44 26–30 28–32 16–20
(Hardwood)
COD load (kg/t) 60–70 36–40 36–44 16–24
(Softwood)
Based on data from European Commission (2001)
Table 4.7 presents kappa numbers currently achieved with different d elignification

technologies and gives a rough comparison of the effluent loads to be expected with
and without extended delignification.
The highest oxygen delignification while maintaining pulp quality and yield is
obtained when the overall delignification-cellulose degradation selectivity is maxi-
mized (Van Heiningen and Ji 2012). This is achieved at low alkali concentrations
and temperatures of about 100 °C or less. Oxygen pressure has little effect on the
selectivity. If the DP of cellulose is optimal, then the pulp yield loss is also mini-
mized because the reduction in cellulose DP is mainly caused by radicals gener-
ated by phenolic delignification, and to a much smaller extent by random alkaline
hydrolysis. Since the newly generated reducing ends in both cellulose and hemicel-
luloses undergo peeling reaction, the carbohydrate yield loss is linearly correlated
with cellulose degradation. Hexenuronic acids are not removed during optimal
oxygen delignification, and must be removed in a subsequent bleaching stage.
Although radicals have a negative effect on pulp viscosity and yield, they are also
needed for removal of non-lignin and non-HexA oxidizable structures, which con-
tribute to kappa number. This means that for a very high degree of oxygen deligni-
fication, the generation of radicals may be essential. In order to increase
delignification beyond about 60 % for softwood pulp, the oxygen system design
should be changed so that alkali concentration and charge are decoupled, as is
similarly done in modern cooking systems, to create a more uniform delignifica-
tion rate throughout the reactor. The reduction of kappa, organic substances and the
consumption of chemicals in oxygen delignification are strongly related to the effi-
ciency of washing between stages. The mentioned environmental performance is
not reached without efficient washing.
The strength properties of oxygen bleached pulp and conventionally bleached
pulp are very similar although oxygen bleached pulp has lower average viscosity.
No significant differences are seen in burst factor and tear factor at given breaking
length. The chemical reactions involved in this process are complex, as the oxygen
reacts not only with lignin, but with the other material within the pulp to produce
many byproducts and trace elements which can affect the procedure. When higher
rates of delignification are required, the two-reactor procedure, which uses differing
pressures and temperatures in the separate reactors, is employed. The degree of
delignification is dependent upon many separate factors such as pulp consistency,
presence/absence of additives/catalysts, pulp initial kappa index, temperature,
ambient pH, quantity of alkali and the presence of transitional metals. The greatest
single advantage of oxygen delignification is the reduced pollutant output it offers.
The technology is compatible with new developments aimed at reducing the dis-
charge of bleach plant effluents. Post-oxygen washing must provide a well washed
pulp to the bleach plant to avoid dissolved organic and inorganic carry-over. Post-
oxygen washing assumes greater importance as the kappa number is reduced and
carry-over becomes a larger component of the bleach plant infeed kappa number.
New lines tend to have high efficiency washers such as the drum displacement
washers or displacement wash presses as final washing devices.
Investment cost for an oxygen delignification system is typically 35–40 MEuros
for 1500 ADt/d bleached pulp production. Its operating costs are 2.5–3.0 MEuro/a.
(European Commission 2001). However, the oxygen delignification will decrease
the chemical consumption in bleaching. The net effect is a cost saving which
depends on the wood species. At existing mills, additional dry solids loads to recov-
ery boiler have been reported up to 10 % and more general it is at least 4–6 % addi-
tionally, and 4–6 % more capacity would be required in recausticising and lime kiln.
Should this capacity not be readily available, it normally results to a corresponding
loss in production capacity of the whole mill.
The reduction of emissions to water (effluent treatment plant and recipient) is
major reason to implement the method. Oxygen delignification is an essential part
of any modern, low environmental impact fibreline. Virtually all new fibrelines
incorporate oxygen delignification.
4.7 Ozone Bleaching of Chemical Pulps
Significant progress has been made in the use of ozone for emerging green bleach-
ing practice, favouring on-site chemicals production, including complete reuse of
byproducts, minimising the ecological footprint and reducing operating costs.
Ozone can be used in both chemical and mechanical pulping and has enabled many
pulp mills to improve product quality, environmental and process performance
(Hostachy and Serfass 2009; Hostachy 2010a, b, c). It is now a state-of-the-art
bleaching process; More than 8 million tons per year of chemical pulps are now
being bleached with ozone accounting for 8 % of the worldwide bleached chemical
pulp capacity. Table 4.8 shows the list of mill using ozone in their bleaching process
(Hostachy 2009). Promising growth is also expected in the market segments of dis-
solving pulps and non-wood fibres. Ozone for pulp bleaching was born at Lenzing
in Austria and Union Camp in United States in the 1990s.
Nowadays, ozone is considered as one of the Best Available Technology (BAT)
for pulp bleaching. With increasing regulatory pressure and growing market demand
4.7 Ozone Bleaching of Chemical Pulps 97
Table 4.8 Mills using ozone bleaching

Mill Pulp type Year
Lenzing AG, Lenzing Austria Birch 1992 1992
IP Franklin (Union C), USA Mixed hardwood 1992
Kymmene (Wisaforest), Finland Hardwood/softwood 1993
MoDo Husum Sweden Hardwood/softwood 1993
Metsä-Botnia Kaskinen, Finland Softwood 1993
Peterson Säffle, Sweden Hardwood/softwood 1994
SCA Pulp Sundsvall, Sweden Hardwood/softwood 1994
Bacell Salvador/Bahia Brazil Eucalyptus 1995
Sappi Kraft Ngodwana, South Africa Mixed hardwood 1995
Stora Enso (Consolidated) WI, USA Hardwood/softwood 1995
Votorantim Jacarei, Brazil Eucalyptus 1995
Votorantim Luis Antonio Brazil Eucalyptus 1995
Domtar EB Espanola, Ontario, Canada Mixed hardwood 1999
Rosenthal Blankenstein, Germany Hardwood/softwood 1999
Burgo Ardennnes. Belgium Mixed hardwood 2000
Nippon Paper Yufutsu mill,Japan Mixed hardwood 2000
OJI Paper Nichinan mill, Japan Mixed Hardwood 2002
Votorantim,Jaccarei Brazil Eucalyptus 2002
Nippon Paper Yatsushiro Japan Mixed hardwood 2003
Lenzing Lenzing Austria Birch 2003
SCP/Mondi Ruzumberock Slovakia Hardwood/softwood 2004
OJI Paper, Tomioka Japan Mixed hardwood 2005
Marusumi Mishima, Japan Mixed hardwood 2006
Daio Mishima, Japan Mixed hardwood 2006
SNIACE Cantabria, Spain Eucalyptus 2007
Paperlinx Maryvale, Australia Mixed hardwood 2007
ITC Hyderabad, India Eucalyptus 2008
Celtejo Vila Velha de Rodao, Portugal Eucalyp/Pine 2008
for better products, the pulp and paper industry faces many challenges and must find
new ways to improve environmental and process performance, and reduce operating
costs. By choosing ozone in their bleaching process, many pulp mills in various part
of the world have already obtained these benefits.
Ozone occupies a very unique position in the whole chemistry involved in Pulp
and Paper manufacture. As a gas, produced only from oxygen, and reverting back to
oxygen as the final by-product, ozone is an eco-efficient “super oxidant” that needs
to be used straight after generation. Ozone can react in seconds to minutes on many
of the substances found in pulping and papermaking. The use of ozone has been
investigated on many materials such as virgin and recycled fibres, sludge, process
waters and wastewaters. Ozone bleaching has already been industrially imple-
mented, experienced and improved from the past 25 years. It is a well proven and
safe process, currently used by some reference pulp mills among the most modern
in the world. It has advantages in terms of bleaching cost savings, effluent load
reduction and usage simplicity. It is applicable to all kind of pulps and has no nega-
tive impact on their mechanical properties when the process design is correctly
performed. As a result of continuous improvements of the equipment and process
automation as well as tuning of the operating conditions for almost 25 years, mod-
ern ozone bleaching is recognized today as a state-of-the-art technology for both
hardwood and softwood pulps.
Ozone is a powerful oxidizing agent for ligno-cellulosic material (Rice and
Netzer 1982). To achieve brightness comparative to chlorine and extraction stages,
low lignin pulp from extended pulping or oxygen delignification must be used for
ozone bleaching. Ozone is found to efficiently delignify all types of chemical pulps.
It is used either at medium or high pulp consistency in ECF and TCF bleaching
sequences (van Lierop et al. 1996; Gullichsen 2000; Nelson 1998; Pikka et al. 2000;
Lindstrom 2003; Lindstrom et al. 2007; Lindström and Larsson 2003; Vehmaa and
Pikka 2007). The typically used charges of ozone are lower than 6–7 kg/t of pulp.
As ozone is a very efficient delignifying agent, it can partially or totally replace
chlorine dioxide in an economical way (1 kg of ozone replaces about 2 kg of pure
chlorine dioxide). The effluent from ozone prebleaching can be used in brown stock
counter-current washing and taken to the chemical recovery system, provided its
acidic nature is taken into account.
When compared with the industrial development of oxygen delignification, the
implementation of ozone for pulp bleaching has grown quite rapidly (Govers et al.
1995). The main reason underlying this evolution is the necessity to respond to
growing environmental awareness, reflected both in regulatory restrictions and mar-
ket demands. The fact that ozone is finding growing acceptance as a bleaching
chemical compatible with these requirements results from a combination of
advances with regard to the bleaching process and associated equipment on the one
hand, and ozone production and handling on the other. Recent advances in ozone
generation, and in particular the development of Ozonia’s AT95 technology, as well
as the lowering of oxygen cost by means of on-site production, have established
ozone as a highly competitive bleaching chemical.
It is not surprising that TCF sequences combining ozone and hydrogen peroxide
are significantly less costly than those employing hydrogen peroxide only, it should
be stressed that ECF sequences that combine ozone with chlorine dioxide are more
cost effective than ECF sequences using only chlorine dioxide. Ozone is today
about 1.5 times less expensive than chlorine dioxide, when compared on the basis
of the same costing structure, i.e. allowing for operating expenses and investment
costs in both cases, and at equal bleaching power.
Ozone is manufactured by passing air or oxygen through a corona discharge. The
electrical potential used to maintain the discharge is usually in excess of
10,000 V. When oxygen is used, it is possible to produce a mixture of ozone and
oxygen containing up to about 14 % of ozone by weight. The manufacture of ozone
requires a relatively large amount of electricity. At the Lenzing mill in Austria,
about half of the operating cost of ozone generation is for energy and the other half
is for the oxygen.
Ozone is less selective towards lignin than are chlorine and chlorine dioxide and
low charges are required to prevent strength loss. Unwanted reactions with cellulose
leading to a deterioration in pulp quality occur when large doses are applied (van
Lierop et al. 1996). A highly selective ozone treatment remains elusive in spite of
the substantial efforts directed towards elucidating the mechanisms of ozone and
carbohydrate reactions and the conditions required to minimize these reactions.
Ozone has very high investment costs due to the high costs of ozone generators
and auxiliary equipment for ozone generation (van Lierop et al. 1996). Since the
ozone concentration will be only about 14–16 % in oxygen, fairly large volumes of
oxygen are required. Thus, the operating cost is rather high due to a relatively high
cost of oxygen required for ozone generation and also the high power consumption.
A modern ozone generator may consume 10–15 kWh/kg ozone when feeding it
with oxygen. The measure can be adopted in new and existing kraft mills. In ECF
bleaching replacement for chlorine dioxide further reduces the discharges of AOX
(“ECF light”). In TCF bleaching ozone is a common bleaching stage. In TCF mills
the use of ozone and other chlorine free bleaching chemicals makes possible to
close up the filtrate streams from washing stages. A pressurised (PO)-stage at the
end of the bleaching sequence is another option to reduce the charge of chlorine
dioxide. In TCF pulp mills, a PO stage is mostly used. Ozone with ECF bleaching
plant normally results in pulp with the same papermaking properties.
The commercial ozone bleaching installations around the world are operated at
medium (about 10 %) and high (about 35–40 %) pulp consistencies, with the major-
ity using medium consistency. Each of these systems has advantages and disadvan-
tages, and there is no general agreement as to which is superior. A higher degree of
delignification is obtained in high consistency conditions because a greater charge
of ozone (about 0.8 %, pulp basis) can be applied to the pulp. In case of medium
consistency, it is difficult to apply more than about 0.5 % ozone (pulp basis). Ozone
is used under pressure (0.8–1 MPa) with medium consistency technology to obtain
sufficient ozone consumption by the pulp, and mixing is critical. High consistency
ozone bleaching uses a gas pressure slightly above atmospheric pressure, and this
low pressure minimizes the chance and severity of a gas leak. High pulp consistency
involves prior removal of a larger proportion of the liquor in the pulp. The advantage
is that there are lower amounts of dissolved organics and heavy metals remaining in
the pulp. Medium consistency technology is better suited for a retrofit of a fibreline
as existing equipment can be used in many cases. However, the costs for ozone
generation and compression in this case are higher (Kappel et al. 1994).
Improvements in medium consistency (MC) ozone bleaching consist in fact of
alterations to the ozone mixers. This is no wonder since the ozone mixer is the core
of the MC Z-stage and the quality of the final pulp depends on its efficiency. It is
worth remembering that the very few mills which faced quality issues are those
where the first MC ozone bleaching technique was implemented. This was mainly
due to a non homogenous mixing and a mixer which mechanically affected the
fibres. Andritz, GL&V and Lenzing Technik are the three suppliers of MC ozone
mixers and all MC Z-stages are designed according to the same principles. Industrial
practice has shown that Andritz technology requires two mixers in series for a
Gas
7
5 8
1
Ozone
O3 Acid
2 3 4 9
1. Dropleg
2. MC pump
3. AZ-FS Ozone mixer - 1
4. AZ-FS Ozone mixer - 2
5. Ozone reactor 10-180s
6. Flow discharger with gas removal
7. Scrubber
8. MC blow tube
9. MC-pump
Fig. 4.10 Typical configuration of medium consistency ozone stage (Based on Germer et al. 2011;
Vehmaa and Pikka 2007)
3–6 kg/tonne ozone dose to obtain the optimal bleaching efficiency while Lenzing
Technik considers that one single mixer of its own is sufficient for a 4–5 kg/tonne
ozone charge. Because of the larger amount of filtrate around the fibres at 12 % pulp
consistency, the reaction must take place in a pressurized (7–8 bar) reactor and con-
sequently the total gas flow (oxygen and ozone) must be compressed accordingly. In
medium consistency systems, the high content of water prevents the effective use of
ozone. Figure 4.10 shows typical configuration of medium consistency ozone stage.
The first commercial High consistency (HC) ozone bleaching started in 1992 at
the Union Camp mill in Franklin, VA. According to the C-Free® process imple-
mented there, the pulp was pH adjusted, pressed to high consistency, fluffed and
transferred to the ozone paddle reactor operating at atmospheric pressure. The
C-Free® was provided by Sunds Defibrator until the late 1990s in the United States,
Sweden, South Africa and Germany. Modern HC ozone bleaching uses the
ZeTracTM technology provided by Metso which is a much simplified version of the
C-Free. The experience gained from the first industrial installations showed that
ozone requires very short contacting time around 1 min with the pulp and that a
5–10 min extraction stage after the Z-stage is in most cases sufficient. These obser-
vations allowed the size of reactors to be reduced, which lowered investment costs.
Then the plug screw feeder, the refiner fluffer and the washing stage prior to the
extraction stage could all be eliminated. These drastic simplifications led to signifi-
cant reduction of the capital expenditure, energy requirements, maintenance costs
as well as effluent volume. Figure 4.11 shows the principle of the modern ZeTrac
Fig. 4.11 HC Ozone bleaching in 1990s and today (Based on Chirat 2007; Germer et al. 2011)
system. The pulp is acidified and then pressed to high consistency (38–42 %). Such
a high consistency is a prerequisite to facilitate the rapid contact between ozone gas
and well fluffed pulp and so preserves the reaction efficiency. Once dewatered, the
pulp is fluffed in a shredder screw on the top of the press and fed by gravity into the
reactor. Ozone is added to the reactor which is operated at a pressure slightly below
atmospheric. After the reactor, the pulp is diluted with alkaline liquor (Lindstrom
2003; Lindstrom et al. 2007). In the ozone reactor, the virtually dry fibres whirl
around like flakes in a snowstorm allowing the ozone/oxygen mixture to effectively
react with the fibres. Another advantage is that in high consistency system the con-
centration of ozone used can be low, which means lower investment costs in ozone
production. ZeTrac enables to build a more closed system with a lower effluent
discharge. The system can be closed without mixing acid and alkaline washing fil-
trates that could lead to troublesome precipitation. Although ozone bleaching is an
acidic process, there is no need for washing before alkali is added due to the high
pulp consistency. When using ozone in mill operations, the safety aspect is very
much important. The ZeTrac process has been designed in such a way that the reac-
tor works at a slight under pressure and thus ensures that no gas can escape to the
ambient air. In today’s bleaching technology, ZeTrac represents by far the most
intelligent way to combine high brightness with care for the environment. The
ZeTrac process features the latest development in ozone bleaching technology and
the first system was taken into operation at the Burgo Ardennes mill in Belgium.
Table 4.9 shows the list of mills using ZeTrac technology. Several ZeTrac projects
are under construction in different parts of the world. ZeTrac process allows to com-
bine high brightness and strength with cost efficiency and represents a modern and
intelligent way, in which caring for the environment is compatible with quality and
production goals.
Depending on the bleaching strategy to be implemented, different bleaching
technologies are proposed to mix ozone with the pulp. High consistency ozone
bleaching systems represents one of the most efficient solutions. Such high consis-
tency ozone installations have been made for both softwood and hardwood where
the ozone charge varies between 2 and 9 kg ozone/adt for the different installations.
VCP Jacarei mill in Brazil is using ozone bleaching. In that mill the bleaching
Table 4.9 Mills using IP Franklin, USA

ZeTrac technology
SCA Östrand, Sweden
SENA, Wisconsin Rapids, USA
ZPR Rosenthal, Germany
Burgo Ardennes, Belgium
Oji Nichinan, Japan
VCP Jacarei, Brasil
Ruzomberok1, Slovakia
ITC Bhadrachalam, India
sequence is (Ze)DP. The designed production is 2200 adt/d of bleached eucalyptus

pulp and the mill is running up to 2500 adt/d (Carre and Wennerström 2005). The
ozone system shows very high efficiency over (Ze) stage since kappa/kg ozone is
generally 1.2 with an ozone charge of 5 kg/adt.
Today, when designing a bleach plant for hardwood pulps or eucalyptus pulp, the
amount of hexenuronic acids responsible for brightness reversion has to be consid-
ered. Ozone bleaching is very effective for removing HexA in a cost-effective way
and can be compared to other bleaching alternatives (Wennerström 2002). For
example, an ozone bleaching sequence (Ze)DD can be compared with the DHT(OP)
DD bleaching sequence including a hot chlorine dioxide stage (DHT), and a refer-
ence bleaching sequence D(OP)DD with respect to brightness ceiling and reversion,
bleaching chemical cost, mechanical properties and environmental load (Carre and
Wennerström 2005). The powerful delignification and brightening capability of
ozone allows for a significant reduction of total chlorine dioxide use for an ECF
bleach plant, e.g. (OO)(Ze)D, (OO)(Ze)DD or (OO)(Ze)DP, and peroxide in a TCF
plant, e.g. (OO)(Zq)P or (OO)ZQ(PO). As an example of that, chlorine dioxide
consumption was lowest for the ozone-bleached pulp for reaching a certain bright-
ness and reverted brightness. Furthermore, ozone made it possible to reach higher
brightness and reverted brightness targets compared with the reference (Carre and
Wennerström 2005). The use of ozone provided the lowest chemical costs for reach-
ing a certain brightness and reverted brightness.
Ozone sequences offer the best options for environmentally sound bleaching.
By using ozone in a (Ze)DD ECF sequence, the filtrate from the (Ze) stage can be
recovered. The washing after ozone bleaching is alkaline as the ozone treatment is
followed directly by an alkaline extraction. This makes it possible to recycle the
filtrate after ozone bleaching. This is a unique possibility for the HC ozone system,
as the dilution with alkali gives a rapid pH change and thereby precipitation of
calcium oxalate is avoided. With presses as washers, the total effluent volume will
be 7 m3/t including 2 m3/t taken out from the acidification stage ahead of the ozone
stage. Comparing the water consumption and effluent load for the light ECF ozone
sequence and the DHT bleaching sequence applied on a hardwood pulp, the efflu-
ent volume is reduced by 30 % and the COD load by 40 %. As a consequence of
the low effluent volume, also the fresh water consumption is low (Carre and
Wennerström 2005).
During full bleaching of chemical pulp the last points of brightness are usually
difficult to achieve, which is reflected in the relatively high chemical charges
needed, and in the rather drastic conditions (temperature and time) required by com-
parison with those used in the first stages of the bleaching sequence. Moreover,
obtaining a constant level of brightness is still an issue in many pulp mills. A new
development concerns the use of ozone as a brightening agent applied at the end of
a bleaching sequence, where these last points of brightness are usually difficult to
gain (Kuligowski et al. 2005; Pipon et al. 2005). One to two kg ozone per ton of pulp
is sufficient to produce an instantaneous bleaching effect, increasing the brightness
by several points (Pipon et al. 2005). No cellulose degradation takes place under
these conditions, and the strength properties of the ozonated pulps are not affected.
The process is working equally well at acidic or neutral pH. The efficiency of a last
ozone stage depends on the bleaching sequence applied and on the nature of the
pulp. In terms of chemical saving, the results obtained in the best cases indicated
that 1 kg ozone could replace 2 kg hydrogen peroxide or chlorine dioxide. No cel-
lulose degradation takes place under these conditions, and the strength properties of
the ozonated pulps are not affected. The process is working equally well at acidic or
neutral pH. The efficiency of a last ozone stage depends on the bleaching sequence
applied and on the nature of the pulp.
Different possibilities have been considered to implement ozone as a last bleach-
ing stage. The first consists to transfer ozone into water before mixing the ozonated
water to the pulp. The use of dissolved ozone reduces the transfer problems and
bleaching occurs in a very short time (few seconds) without any significant ozone
loss. However, water quality remains the limiting factor for the process implementa-
tion. The best ways to apply ozone consist to use conventional bleaching systems
where ozone is introduced into low or medium consistency mixers. Industrial vali-
dation of the use of ozone as a last bleaching stage is in progress.
Several studies have been devoted to the increase in pulp yield to improve the
overall economy of the production of kraft pulps. Among those, it was demon-
strated that by stopping the cooking at a higher kappa number and then applying
oxygen delignification, a higher final pulp yield was observed (Kleppe et al. 1972;
Jamieson and Fossum 1976; Magnotta et al. 1998). This was explained by the fact
that the last phase of a cooking step is less selective than oxygen delignification.
Indeed, ozone is a more efficient delignification agent than oxygen. Moreover the
presence of a high quantity of lignin protects cellulose from degradation. First
experiments have shown promising results which were confirmed on both soft-
wood and hardwood pulps. Chirat et al. (2005) reported that with eucalyptus kraft
pulp, ozone treatment applied to the high kappa pulps led to a better overall yield
(cooking yield × Z treatment yield) than for the control kraft. For a kappa of 17, the
yield gain was 2.3 on wood when applying ozone to the 28 kappa pulp. A better
refining ability of the ozonated high kappa pulp was observed and the strength
properties were significantly better especially the tear index (Chirat et al. 2005).
Applying ozone on high kappa pulps is an attractive way to increase the pulp yield
more extensively than the other known alternatives. The high kappa pulps treated
by ozone and then fully bleached by an ECF sequence appeared easier to refine
than the control kraft pulp, both for softwood and hardwood. Equal or better
strength properties than the control pulps were obtained.
In India Metso installed high consistency (HC) ozone bleaching at ITC’s
Paperboards and Specialty Papers division in Bhadrachalam, India (Sheats 2010).
When compared with other technologies, HC ozone bleaching results in lower efflu-
ent load and less OX in bleached pulp, lower water consumption, and lower opera-
tional costs. ITC is the first company in India to use ozone bleaching (Oinonen
2010). Using ozone has helped to increase the brightness stability and runnability
on the paper machine. The pulp mill has a design capacity of 800 tpd blown pulp
from Super Batch Cooking Plant. Fibreline one, commissioned in 2002, processes
300 tpd of bleached pulp, while fibreline two, commissioned in 2008, processes
400 tpd of bleached pulp. Fibreline one was originally built with ECF sequence of
Do-EOP-D1, but was retrofitted with ozone bleaching in 2008, while fibreline two
has a bleaching sequence of Ze-DP. Technically, the production of ozone is by elec-
tric discharge of oxygen rich feed gas using a special generator and the generator at
ITC has a capacity to produce 200 kg/h ozone at 12 % concentration and can reach
up to 230 kg/h at 10 % concentration. Parameters that affect the bleaching process
include consistency, temperature, pH and retention time. The ozone bleaching tech-
nology has provided reduction in chlorine dioxide and hydrogen peroxide consump-
tion, together with better pulp quality, improved strength properties and reduction in
AOX generation (Sharma 2010). This technology is technically, environmentally
and commercially superior to conventional ECF technology and that the runnability
of paper machines improves with ozone bleached pulp.
The Oji Paper Co Ltd’s Nichinan Mill, Japan has moved to ECF operation using
a Ze-Trac system from Metso Paper introduced into the Z stage for the first time in
Japan. Operating experience has highlighted the four most important areas in ozone
reaction efficiency: pulp pH; pulp consistency; gas flow in the ozone reactor; and
pulp retention in the ozone reactor. Following optimisation of these four parameters,
pulp strength as measured by burst index and tear index were unchanged, except for
slightly lower viscosity. There was no effect on machine runnability. The cost of
ozone ECF bleaching is particularly sensitive to the price of electricity. This is of
particular significance in Japan, where electricity costs are particularly high.
Discharges of adsorbable organic halogen AOX and COD have fallen and hypoha-
lite (OX) in bleached pulp has been reduced by approximately 30 %.
At Ruzomberok, Slovakia, an existing D(EOP)DED bleaching sequence with
two alkaline extraction (E) stages was converted to HC ozone bleaching, with a
resulting bleaching sequence of Z(EO)(DnD). The results obtained at the
Ruzomberok mill with Metso’s ZeTrac HC ozone bleaching process showed only
minor differences in pulp properties before and after the installation of ozone
bleaching, and the effluent load and organic chloride compounds were significantly
reduced.
For a while many mills looked at ozone bleaching to produce TCF pulps
because of tightening environmental regulations. Today ozone is seen as a
c omplement to produce ECF at a lower cost than standard ECF pulp without
ozone. With replacement ratios of chlorine dioxide by ozone in the range of 2.0–
3.5, savings of 6–8 US$/mT of pulp net can be achieved. Whenever chlorine bleach-
ing chemicals are replaced by non-chlorine chemicals, a reduction in AOX is
seen. When ozone completely substitutes the first chlorination stage (C/D), then
the extract from the washers following the ozone stage can be recycled to the
chemical recovery system leading them closer to closing the mill water loop. If
an extraction stage follows the ozone stage, the extract from this washer can also
be recycled. This is greatly desired since most of the COD and BOD, are con-
tained in this extract.
From an economics point of view, ozone is a highly competitive bleaching chem-
ical which when compared at equal bleaching power, is typically 1.2–1.5 times less
costly than chlorine dioxide. It can be purchased on an “over-the-fence” basis,
enabling the mill to benefit from the most appropriate oxygen + ozone supply solu-
tion without detracting capital- and human resources from its core activities.
ECF sequences combining ozone and chlorine dioxide are economically com-
petitive with sequences using chlorine dioxide only, even when capital expenses
for modifying process equipment are taken into consideration. They have the
advantage of improved performance and added flexibility in regard to effluent
characteristics, and position the mill on the pathway to (nearly) effluent-free
bleaching. In combination with (pressurized) hydrogen peroxide, ozone makes it
possible to produce fully bleached TCF pulp while maintaining expenditures in
bleaching chemicals at levels that are comparable, if not lower, than those pertain-
ing to ECF bleaching. Bleaching lines equipped with oxygen delignification can be
retrofitted to ozone-based TCF production with a full bleaching cost, including
capital charges on process equipment, only about 10 USD higher than that for ECF
sequences. Mills that are considering modifying or expanding their effluent treat-
ment facilities may well find that opting for TCF bleaching instead is economically
more advantageous.
Bleaching plants that do not yet have oxygen delignification can achieve AOX
levels of the order of 0.3 kg/tonne pulp after effluent treatment by combining “wise
man’s” delignification with D/Z-based ECF bleaching. The cost of such sequences,
capital charges for process equipment included, is comparable or lower than that of
standard ECF solutions whose AOX levels are nearly twice as high. By adopting
D/Z-based bleaching, the mill will be in a position to gradually upgrade its sequence
to meet evolving effluent standards or market demands, while minimizing the risks
of making soon-obsolete investments. Whether it concerns greenfield mills, new
bleach lines or retrofit projects, whether the mill wishes to adopt ECF or TCF
sequences, oxygen and ozone are today the most cost effective bleaching chemicals
available to the Pulp and Paper Industry. Investment costs for a 1500 Adt/d ozone
bleaching system are 12–15 MEuro. Corresponding operating costs are 1.8–
2.1 MEuro/a (European Commission 2001). The reduction of AOX emission to
water is the main reason to use this technology.
4.8 Ozone for High Yield Pulping
Continuous investigation has brought major gains in the mechanical pulping

industry regarding reduction of the energy consumption and improvement of pulp
and paper quality. However, a more energy efficient pulping process producing bet-
ter quality pulp and paper is always the major focus for maintaining competitive-
ness inspite of the continuous increase of manufacturing costs, including fibrous
materials and energy costs. For mechanical pulp fibres, one of the main reasons for
low inter-fibre bonding is the presence of lignin, although the hydrophobic lignin
needs to be retained to give the high yield and high bulk property to mechanical pulp
(Li et al. 2010). Using a chemical agent to modify the lignin-rich material on the
fibre surface can improve the bonding ability of mechanical pulp fibres while pre-
serving the high yield. Ozone is known to be a powerful oxidizing agent that has
already been used in industrial pulp bleaching (Germer et al. 2011; Cloutier et al.
2009; Cloutier et al. 2010). It has a positive effect on both energy savings (Lecourt
et al. 2007; Petit-Conil 2003) and on pulp qualities (Katz and Scallan 1983). Several
practical studies have been conducted on the use of ozone during high yield pulping.
Ozone was initially investigated on thermo-mechanical pulp (TMP) collected from
the main or reject line to reduce energy requirement and to improve pulp strength
properties (Allison 1979, 1980; Soteland 1977, 1982; Lindholm 1977a, b).
Ozone was used for the first time in a mechanical pulping process in 1964
(Ruffini 1966). It was mainly applied on SGW, RMP or TMP pulps after secondary
refining to increase pulp strength properties. The efficiency could be classified as
such: TMP > RMP > SGW. It was also studied between defibering and refining
stages of TMP or CTMP processes in order to reduce energy consumption and to
improve the pulp quality (Allison 1979; de Choudens and Monzie 1978; Eriksson
and Sjöström 1968; Lindholm 1977a, b, c; Lindholm and Gummerus 1983; Soteland
and Loras 1974; Vasudevan et al. 1987).
During pulp refining, ozone plays the role of a “chemical” refining agent com-
plementing mechanical energy normally provided by refiners. The softening action
of ozone facilitates fibre separation. During the last decade, efforts were made to
clarify the remaining limitations to achieve the full-scale implementation (Hostachy
2010a, b, c). The main points were the identification of the best application point to
maximize energy reduction and the build-up of the full scale mixing equipment
regarding practical aspects (mixing, safety etc.). In a thermo-mechanical process in
order to achieve the same final freeness, about 0.65 MWh per ton of pulp can be
saved using 20 kg/t ozone on both Spruce or Pine TMP pulps. The net saving is
about 0.4 MWh per ton of pulp, considering energy for oxygen and ozone produc-
tion (Soteland and Loras 1974; Lindholm 1977a, b, c). In case of softwood species,
decrease in brightness was observed whereas the inverse was observed for hard-
wood species. This showed that the lignin structure was an important parameter in
ozone reaction. The energy consumption reduced by 45 %, the tensile and tear prop-
erties increased by about 90 % when a charge of 2.5 % in ozone was applied on
birch primary-refined CTMP in alkaline medium as an interstage (Soteland 1982).
4.8 Ozone for High Yield Pulping 107
However, brightness and pulp yield reduced by three points. Oxidation of lignin by
ozone modified the fibre surface (Kojima et al. 1988; Kojima and Yoon 1991). Petit-
Conil et al. (1998) conducted detailed study on the effect of inter-stage ozone treat-
ment. Up to 40 % energy saving was achieved for an ozone charge of 3 %, and pulp
quality improved with softwoods and hardwoods without adverse effect on bright-
ness and pulp bleachability. Ozone reacted with fibre wall components at the fibre
surface (Kibblewhite et al. 1980; Rothenberg et al. 1981). Ozone reacted with lignin
by oxidizing the lateral chains associated with a depolymerisation of the macromol-
ecule, by opening the aromatic ring and by forming water-soluble organic acids.
This delignification occurred in the composite lamella modifying the fibre flexibil-
ity. With polysaccharides, an oxidation of terminal hemiacetal groups was found to
produce some aldonic acids. The oxidation of primary and secondary alcohol groups
produced some carbonyl and carboxyl groups by opening the pyranosidic ring. In
case of mechanical pulps, the hemicelluloses were found to be affected and the cel-
lulose was generally protected by the lignin (Magara et al. 1998). All these chemical
reactions modified the hydrophilicity of the fibre surface. This increased the interfi-
bre bonding potential. Also, ozone could act as a chemical refining agent. It was
found to increase fibre wall hydration and facilitated microfibril separation. This
resulted in a decrease in pulp freeness after ozonation (Petit-Conil 1995; Petit-Conil
et al. 1997; Petit-Conil and de Choudens 1994). The lignin of ozonated softwood
TMP was analysed by 13C NMR (Robert et al. 1999). The carbon skeleton pre-
sented far fewer structural modifications than the lignin extracted from the chemical
pulps. No correlation was observed between the strength improvement and the
increase in carbonyl groups in lignin. Ozone did not degrade the polymeric structure
of lignin in mechanical pulp. The improvement in pulp strength properties was
explained by the increase in fibre flexibility. Ozone was an efficient bleaching agent
for TMP if charges between 0.1 and 1 % were used (Hsieh et al. 2000). Saharinen
and Nurminen (2001) reported that bulk and the internal cohesion of multilayer
board can be enhanced by ozonating mechanical pulp. A charge of ozone lower than
3 % at low consistency increased the Scott bond of long fibres by 250 % without
decrease in bulk.
Ozone has been found to be a selective agent for removing resin and fatty acids
in CTMP effluents (Roy-Arcand and Archibald 1996). Small charges of ozone are
found to be sufficient for degrading these harmful components in effluents and
reducing effluent toxicity. Now a days, mechanical pulp producers are faced with a
significant increase in energy costs. Even if ozone production consumes electricity,
its application in the process is an alternative to be considered not only to decrease
specific energy but also to improve pulp quality, pulp bleachability, runnability on
the paper machine and the pulping effluent.
Lecourt et al. (2007) investigated ozone in the main line (directly in refiners) or
in the reject line to reduce energy consumption in TMP pulping. The experiments
were conducted with spruce chips at pilot plant scale (ozone in refiners) and at labo-
ratory scale (reject treatment). The use of ozone in primary or secondary refiners
modified the fibre separation mechanisms and reduced electrical energy consump-
tion by 10–20 %. Ozone was shown to mainly oxidise the wood extractives and
consequently modified the fibre surface chemistry and the final pulp quality. Ozone
treatment of TMP rejects appears a very promising technology. An ozone charge of
1–2 % saved energy by 10–20 %. It also resulted in degradation of wood extractives
and modification of lignin at the fibre surface. The reintroduction of these ozonated-
refined reject fibres in the TMP accepts improved the strength properties and the
peroxide bleachability of the final pulp. These effects could quite easily compensate
the costs of ozone generation and use.
Sun et al. (2013), found that the presence of sodium hydroxide is important in the
ozone treatment of mechanical pulp. Ozone has a good performance when the reac-
tion pH is between 5.4 and 6.15 and the reaction is carried out with whole primary
pulp. Short fibres and fines have much larger specific surfaces and more contact
with chemical components than do long fibres (Han et al. 2008). The effect of selec-
tive refining of the primary long-fibre fraction combined with an inter-stage ozone
treatment on energy consumption and pulp qualities has been recently studied (Sun
et al. 2014a, b). Secondary pulp was recombined with the primary short-fibre frac-
tion to form the initial pulp for comparison with a traditional TMP process. Selective
refining shows a significant advantage with respect to refining energy. About 15 %
total refining energy could be saved when obtaining a pulp of 100 mL freeness,
compared with the control TMP trial. With use of 1.5 % ozone, another 13.8 %
energy savings can be achieved. Selective refining does not greatly change the phys-
ical properties of the handsheet, and an increase of the light scattering coefficient
can be observed. Treatment of primary long fibres with ozone can modify the sec-
ondary pulp properties compared with selective refining only. But, this improve-
ment could disappear when secondary pulp is recombined with primary short fibres.
This is mainly due to the poor bonding ability of the primary fines. For the optical
properties, the same phenomenon does not exist. Recombination of long fibres and
fines results in an augmentation of the handsheet brightness, opacity and light scat-
tering coefficient.
Concerning the use of ozone in high pulping processes, a promising field of new
applications is just opening. Sustainability in raw material supply and better control
of energy requirement are of major interest for many pulp and paper companies.
4.9 Elemental Chlorine-Free Bleaching (ECF) Bleaching
The realization that chlorine-based pulp bleaching sequences exhibited a signifi-

cant and potentially negative impact on the environment, and the promulgation of
the “Cluster Rules” in the United States (USEPA 1997) and similar regulations in
several other countries led to a virtual explosion of research examining alternative
bleaching chemistries during the late 1980s and early 1990s (Department of Justice
2012; Environment Canada 1992a, b; Rajotte 2000; Shrinath and Bowen 1993).
Several alternative chemicals – peroxide, peroxyacetic acid, peroxyformic acid,
potassium peroxymonosulfate (Oxone), dimethyldioxirane (which is generated in
situ from acetone and potassium peroxymonosulfate), peroxymono-phosphoric
4.9 Elemental Chlorine-Free Bleaching (ECF) Bleaching 109
acid, various enzymes, polyoxomolybdates, Monox-L, dithionite, ozone, chlorine

dioxide, and oxygen have been investigated (Brogdon and Hart 2012; Ragauskas
et al. 1993; Bouchard et al. 1996; Springer 1997; Harazono et al. 1996; Katsoulis
2002;. Heimburger et al. 2002; Yant, and Hurst 1991; Carreira et al. 2012; Peter
1993; Nutt et al. 1993; Gotlieb et al. 1994; Helander et al. 1994; Homer et al. 1996;
Reeve 1996; Rapson and Anderson 1978; Ni et al. 1992; Berry 1996; Parthasarathy
1997). Research into the formation of adsorbable organic halogens (AOX), chloro-
form, and other bleach plant pollutants showed that higher kappa number pulps
entering the bleach plant tended to increase the amount of these pollutants being
formed (Dallons et al. 1990; Knutson et al. 1992). As a result of these findings, a
significant amount of research effort was expended on developing methods that
could be used to reduce the kappa number of pulp entering the bleach plant. Some
of these efforts included cooking modifications to extend delignification in the
digesters (Jameel et al. 1995; Sezgi et al. 1994; Walkush, and Gustafson 2002;
Buchert et al. 2001; Goyal et al. 1994). Other methods of lowering the entering
kappa number included the use of oxygen bleaching (Carter et al. 1997; Croon and
Andrews 1971) and enhancements to oxygen delignification, including pretreat-
ment with nitrogen dioxide (Prenox) (Brännland et al. 1990) and the use of nitrosyl
sulfuric acid (NSA) (Ku et al. 1992). By the end of the 1990s, commercial bleach-
ing sequences had evolved to virtually eliminate chlorine and hypochlorite as via-
ble bleaching chemistries (Reeve 1996). Most of the kraft pulp industry had now
settled on ECF bleaching as the sequence of choice (Pryke et al. 1995, 1997, 2003;
Govers et al. 1995; Moldenius 1995, 1997). ECF bleaching sequences tend to use
chlorine dioxide, caustic, oxygen, and peroxide as the main bleaching chemistries
(AET 2008b).
The science, a proven environmental track record, and strong market demand
demonstrate that ECF is without rival in terms of pollution prevention, resource
conservation, and product quality. According to Dr. Robert Huggett, former
United States. EPA Assistant Administrator, Research & Development “Chlorine
dioxide is a solution to dioxin and other persistent, bio-accumulative, toxic sub-
stances in mill waste water” and according to Professor Don Mackay, former mem-
ber of the International Joint Commission, the Great Lakes Science Advisory Board
and its Virtual Elimination Task Force “ECF is an excellent example of enlightened
industrial response to an environmental concern and should be embraced by the
environmental community”. ECF technology is the ‘best available technology’
selected for the paper grade kraft mills.
ECF pulp, bleached with chlorine dioxide, continues to grow and now dominates
the world-bleached chemical pulp market (Pryke 2003; AET 2002a, 2007, 2008a, b,
2013). ECF pulp, bleached with chlorine dioxide, continues to dominate the world
bleached chemical pulp market. In 2012, ECF pulp production reached ~94 million
tonnes, totaling more than 93 % of world market share (Table 4.10). Totally
Chlorine-Free (TCF) production declined modestly, while sustaining a small niche
market at less than 5 % of world bleached chemical pulp production. Moreover,
since the market downturn in 2008 and 2009, ECF pulp production has rebounded
both with restarts of previously idled production and new greenfield pulp mills.
Table 4.10 World bleached chemical pulp production: 1990–2012

ECF TCF Others
1990 4.4 0.2 64.0
1991 9.6 0.5 59.4
1992 17.2 1.4 53.1
1993 22.4 3.0 48.1
1994 29.2 4.7 42.1
1995 34.6 5.5 38.0
1996 38.0 5.3 36.3
1997 42.3 5.9 33.2
1998 45.9 5.8 30.5
1999 50.3 5.8 25.4
2000 56.0 6.0 21.2
2001 66.1 5.2 15.4
2002 67.7 6.1 15.3
2003 70.3 6.1 13.2
2004 72.0 6.1 11.5
2005 75.6 5.9 9.9
2006 79.7 5.5 8.3
2007 88.2 4.8 5.7
2010 88.3 4.8 2.4
2012 93.9 4.7 2.4
In Scandinavia, ECF accounts for over 80 % of bleached chemical pulp produc-
tion. Japan produces approximately 8.5 million tonnes of bleached chemical pulp
and began converting production to ECF in 1996. During the period 2005–2007,
over 2 million tonnes of pulp converted to ECF which represents 88 % of Japanese
bleached chemical pulp production. Continued growth is consistent with the com-
mitment made by the major bleached pulp producers in Japan to eliminate chlorine,
and convert to ECF.
In North America, ECF production now represents ~99 % of bleached chemical
pulp production. The transition to ECF was essentially completed in 2001 as the
balance of United States production came into compliance with the United States
Environmental Protection Agency’s Cluster Rule. The Cluster Rule is based, in part,
on ECF as Best Available Technology (BAT) for bleached paper grade kraft and
soda mills. Total production in North America declined by approximately 4 million
tonnes over the period 2005–2010. However, since then, a number of idled bleached
mills restarted, adding back approximately 1.6 million tonnes to North American
ECF pulp production. Moreover, an additional 0.5 million tonnes are expected to
restart in 2014. In South America, ECF production continues to grow rapidly. An
additional 2 million tonnes of new ECF production was added in the region since
2010. In 2012 ECF represented over 97 % of bleached chemical pulp production.
Production of ECF pulp is also growing in the South East Asia region (AET 2013).
Significant ECF capacity was added in Indonesia and China in the recent years.
In China where small mills are being shutdown, new larger mills are coming on
stream and utilizing ECF bleaching technology. China’s ECF production increased
from 1.1 million tonnes in 2005 to 2.6 million tonnes in 2007 (AET 2007).
Over the next five years, bleached chemical pulp production is set to increase
dramatically with significant expansions and new investments totaling more than 13
million tonnes planned for China, Uruguay, and Brazil. All of this new production
is expected to be ECF. ECF’s market share will continue to grow due to it’s acknowl-
edged environmental compatibility, cost-competitiveness, and high quality desired
by producers and users alike.
Different kinds of ECF bleaching processes have been reported. Traditional ECF
processes replace elemental chlorine with chlorine dioxide. Enhanced ECF pro-
cesses use oxygen delignification and/or extended delignification to remove more
lignin during the pulping process before bleaching the pulp with an ECF process.
Low-effluent ECF processes have modified an enhanced ECF process to send addi-
tional organic waste generated in the bleach plant back to the chemical recovery
system. In a low-effluent ozone ECF process, ozone replaces chlorine dioxide in the
first bleaching stage of an enhanced ECF process. A second approach uses an
enhanced ECF process but installs additional technologies in other parts of the mill
to remove chlorides from the bleach plant filtrates.
Examples of typical modern ECF bleaching sequences are shown in Table 4.11.
Sequences including only D and E stages are called “straight ECF” whereas those
including D in combination with P and (PO) are called “ECF light” and “ECF super
light” (Bergnor-Gidnert 2006). These sequences are also sometimes called “low-
impact ECF”, “low-AOX ECF” (e.g. Aracruz Barrado Riacho, Brazil) and “low-OX
ECF” (e.g. Line C at Votorantim Celulose e Papel Jacareí, Brazil.
Generally, to reach a certain brightness target, hardwood requires fewer chemi-
cals than softwood, which usually means that the number of bleaching stages can be
shorter. Over the years, the use of chlorine dioxide has substantially decreased in
bleaching and has been replaced by oxygen based chemicals. ECF light and ECF
super light sequences can be applied for both hardwood and softwood, depending
on the brightness target (UNEP 2006).
Recent studies comparing ECF and TCF have reiterated ECF’s overwhelming
product and yield advantages and ECF’s environmental compatibility with aquatic
ecosystems (Beca AMEC 2006). ECF’s market share will continue to grow due to
its acknowledged environmental compatibility, cost-competitiveness, and high
quality desired by producers and users alike. Field studies and research have dem-
onstrated that treated wastewater from well-managed pulp and paper mills using
ECF bleaching is virtually free of dioxin and persistent bioaccumulative toxic sub-
stances. The remaining chlorine containing organic substances resulting from ECF
bleaching have a composition similar to those found in nature, degrade naturally
and do not persist in the environment. Research shows that they present a negligible
environmental risk to aquatic ecosystems (Bright et al. 2003). This research has
been confirmed in ecosystem simulations by comparing wastewaters from ECF
bleaching with other nonchlorine bleaching concepts, including TCF. These inves-
tigations have reached a common conclusion (Hamm and Gottshing 2002; Tana and
Table 4.11 Modern ECF O/ODEDP

bleaching sequences
O/OADPZP
O/OADED
O(OPDQ(PO)
O/ODED
O/OZEDD
OQ(PO)(DQ)(PO)
O/O(Q)OP(Paa/Q)PO
O/ODEDD
OQXOP/ODEPDPaa
O/OADEDP
O/OZDP
O/O(Q)OPDPO
A Acid wash to remove metal element
from pulp, D Chlorine dioxide, E Alkaline
extraction, EO Alkali extraction reinforced
with oxygen, EP Alkali extraction rein-
forced with hydrogen peroxide, EOP
Alkali extraction reinforced with oxygen
and hydrogen peroxide, mP Modified per-
oxide, O Oxygen, P Peroxide hydrogen
peroxide (H2O2), Paa Peracetic acid, Q
Chelating agent, X Xylanase, Z Ozone, ZD
Ozone and chlorine dioxide added sequen-
tially in same stage
Lehtinen 1996). Studies comparing ECF and TCF effluents confirmed the absence
of significant differences in biological effects in the aquatic environment.
ECF bleaching is practiced on both conventional and reduced kappa pulps
(Chirat and Lachenal 1997). Few examples of commonly used ECF bleaching
sequences are OD(EOP)D, D(EO)DD, D(EOP)D, AD(EO)DOD (EO)DD, O(AD)
(EOP)D, (EOP)D(PO)D (Pikka et al. 2000). The oxygen delignification stage can
include one or two stages. An acid hydrolysis stage is especially suitable for hard-
wood pulps. Chemical consumption varies with wood species and mill and is espe-
cially connected to kappa number. The chemical consumption (kg/ADT) of a mill
using D(EO)DD bleaching of oxygen-delignified softwood pulp from kappa num-
ber 12–90 % ISO brightness are: chlorine dioxide (as equivalent chlorine), 44;
sodium hydroxide, 15; oxygen, 4; and sulphur dioxide, 1.5. Another typical ECF
bleaching sequence is D(EOP)D(ED). The first D stage has a retention time of less
than 1 h and a temperature of about 60 °C. The alkaline stage is preferably pressur-
ized, and oxygen and hydrogen peroxide are added to boost the delignification in
this stage to reduce subsequent chlorine dioxide consumption. The two final D
stages normally have a retention time of 3 h each, and the temperature is
70–75 °C. Diffusers on top of the chlorine dioxide bleaching towers do the washing
after each stage. Wash press is generally used after the EOP stage. The wash press
in this position gives a higher degree of flexibility for filtrate circulations and reduction
Table 4.12 Chemical Brightness, % ISO 89.5

consumption in bleaching of
ClO2, kg acl/adt 42
softwood kraft pulpa in
D(EOP)D(ED) sequence – H2O2, kg/adt 2
mill results COD, kg/adt before secondary 30
treatment
AOX, kg/adt before secondary 0.25
treatment
Based on data from Pikka et al. (2000)
a
Kappa No. 12
of effluent volumes. Table 4.12 shows typical mill data in case of DEOPDED

sequence with softwood Kraft pulp of 12 kappa number. Brightness vs. consump-
tion of active chlorine for pulps bleached in three, four and five bleaching stages is
presented in Table 4.13. In this example, the three-stage sequence can reach a
brightness target of 88 % ISO. The four-stage sequence can go upto 90 % ISO and
the five-stage sequence upto 92 % ISO.
Besides the number of bleaching stages, the amount of bleaching chemical added
to the first stage (the kappa factor) also affects the brightness development.
Introduction of an ozone stage in a chlorine dioxide bleaching sequence means that
the consumption of chlorine dioxide required to reach a certain brightness can be
reduced considerably. Table 4.14 shows brightness vs. active chlorine charge for the
sequences D(EOP)DD and Z(EO)D(ED). In the ozone sequence, filtrate from the
prebleaching Z(EO) treatment can be used as wash water in oxygen delignification
washing. Replacing the last (ED) stage of a chlorine dioxide bleaching sequence
with a pressurized peroxide stage reduces the need for chlorine dioxide. The effect
of peroxide use in a chlorine dioxide bleaching sequence is presented in Table 4.15.
Chlorine dioxide demand can also be reduced by using ozone synergistically with
chlorine dioxide.
Table 4.16 shows the bleaching sequences implemented in the latest designs of
eucalyptus-based pulp mills.
Parthasarathy et al. (1993) have reported that conversion of a (C + D)(EOP)D
sequence into ECF is technically feasible for full bleaching of both softwood and
hardwood pulps. There are potentially large increases in bleaching chemical cost,
however. Certain changes could minimize the cost increase which are listed below:
–– Increase the first stage consistency from 3 to 12 %
–– Increase the extraction stage temperature from 75 to 95 °C
–– Operate the final d stage at high temperature
–– Add a peroxide stage at the end of the sequence
Another short sequence, OD(EP)P, can bleach softwood kraft pulp to a bright-
ness of 89 if chelants are added at several stages and the peroxide stage operates
under severe conditions (2 % hydrogen dioxide, 30 % consistency and 4 h at 90 °C)
(Desprez et al. 1993). A similar, forcing, final peroxide stage can allow full bleach-
ing of softwood kraft pulp in the OQPDP sequence (Q – chelation stage) (Devenyns
et al. 1993). This is one step further along the road to TCF bleaching than the
Table 4.13 Brightness development in different chlorine dioxide bleaching sequences

Brightness (% ISO)
Chemical consumption (kg act Cl/odt) D(EO)DED D(EO)DD D(EO)D
20 81.0 –
30 89.0 87.0 86.0
40 91.0 89.5 88.0
50 92.0 90.0 –
Table 4.14 Brightness Brightness, % ISO

Kg active Cl/
development in a sequence
ton D(EOP)DD Z(EO)DnD
replacing the first D-stage
with a Z-stage 15 87.0 –
20 89.2 –
27 90.0 –
35 – 84.2
40 – 86.2
47 – 88.5
52 – 89.2
O2 delignified pulp, Kappa No. 11.1
Table 4.15 Effect of peroxide use in a chlorine dioxide bleaching sequence

D(EOP)D(PO)
Chlorine dioxide consumption (kg Cons. in PO stage Cons. in PO stage D(EOP)
act Cl/ADMT) (5.5 kg) (3.0 kg) D(ED)
36 91.0 91.9 –
41 – – 90.2
53 – – 90.5
64 – – 90.6
Lab ITCTM, O2 delignified pulp; Kappa No. 12.0; Viscosity 1017 dm3/kg
OQPD(EP)D sequence that has the same performance. A western Canadian mill
uses the sequences DE(EO)DED and OD(EP)(EOP)DED. In another mill, using
ozone in the OA(EOP)D(EP)D sequence has given fully bleached pulp with proper-
ties similar to the ECF reference sequence without the ozone stage (Helander et al.
1994). Cost is similar. Market pulp quality from ECF bleaching is excellent
(Moldenius 1995, 1997). Mill studies in Canada and the United States have shown
high brightness, 89–90 % ISO and high strength (burst, tear, tensile and viscosity)
pulps are produced with ECF (Pryke et al. 1995). ECF production does not require
low lignin content of unbleached pulps and therefore has higher yield than today’s
TCF pulping and bleaching processes.
Table 4.16 Modern Eucalyptus-based kraft pulp mills Bleaching sequence

bleaching sequences of
VERACEL AD0 EOP D1 P
eucalyptus-based kraft pulp
mills ARACRUZ C AD0 EOP D1 D2
RIPASA Dhot PO D1
UPM FRAY BENTOS AD EOP D P
ENCE-NAVIA D0 EOP D1
VALDIVIA ARAUCO D0 EOP D1 D2
NUEVA ALDEA Dhot EOP D1 D2
SANTA FE CMPC AD0 EOP D1 D2
For existing mills, conversion to ECF has been relatively easy for the following
reasons:
–– Many mills had existing chlorine dioxide generators that could be upgraded to
the required production for relatively low capital cost
–– Existing bleach plants were totally compatible
–– Bleaching cost increased modestly by 5–10 %.
ECF is integral to achieving the vision of minimum impact (Haller 1996; Axegård
et al. 2003; European Commission 2001; Pryke 2003). Pulping and bleaching strate-
gies incorporating ECF produce strong softwood fibres, minimizing the reinforcing
fibre requirements for many paper grades such as lightweight coated (LWC). It has
also been recognized that in combination with enhanced pulping, ECF manufacturing
has a higher yield, using the least amount of wood compared with other pulping and
bleaching techniques. Finally, ECF is compatible with, and at the leading edge of, so-
called ‘closed-loop’ strategies for minimizing wastewater from bleaching (Pryke
2003). Along with efficient wastewater treatment, closed-loop strategies are providing
optimal solutions for protecting and sustaining the receiving water ecosystem (Stratton
and Gleadow 2003; Anonymous 1997).
During the 1990s, governments, responding to the environmental concerns posed
by persistent, bio-accumulative, and toxic compounds, developed new regulations
for their respective pulp and paper industries. A common feature of many of these
regulations and guidelines is the concept of ‘best available technology’ (BAT).
Recognizing excellent performance, the United States and the European Commission
developed pulp and paper guidelines and regulations based on ECF bleaching as a
core component of BAT (European Commission 2001). These regulations and
guidelines ensure compliance with the International Stockholm Convention on
Persistent Organic Pollutants, the so-called POPs Treaty. The virtual elimination of
dioxin has been a key contributor to the sustainable recovery of affected aquatic
ecosystems throughout the world. Fish consumption advisories downstream of pulp
and paper mills are rapidly disappearing (AET 2002b). Since 1990, state authorities
in the United States have lifted dioxin advisories from 25 ecosystems downstream
of pulp mills, representing 83 % of the 30 such advisories in effect in 1990. In 2003,
only 10 ecosystems remained with a dioxin advisory downstream of a bleached pulp
and paper mill in the United States. The Environmental Protection Agency predicts
that over time all remaining dioxin advisories downstream of mills in United States
should be lifted following conversion to ECF bleaching. Conversion of existing mill
to ECF mill has been possible but require often considerable modifications in the
fibreline and chlorine dioxide production: Chlorine dioxide generators have to be
upgraded to meet the increased demand of this bleaching chemical. Existing bleach
plants have to be retrofitted with different chemical mixing etc. systems. Bleaching
chemical cost will increase.
4.9.1 Modified ECF Sequences
One promising trend today is the use of modified ECF sequences, i.e., sequences
which still use chlorine dioxide, but not in the traditional manner of DEDED or
ODED sequences (Chirat and Lachenal 1997). The key here is to make them as
efficient as chlorine-containing sequences (Andrew et al. 2008). The use of chlorine
dioxide and ozone in combination – in (DZ) or (ZD) stages—has started to appear
in the recent years. Indeed, basic chemistry tells us that the reactions of these two
chemicals on lignin complement each other, for example as with the case of chlo-
rine and chlorine dioxide combinations (DC). It makes the process more efficient
than DO or Z alone. The other interest in combining the use of ozone and chlorine
dioxide lies in the fact that the required operating conditions (temperature, pH) are
similar for the two chemicals, making it possible to run (DZ) or (ZD) stages with no
intermediate washing. The criterion in the process is the replacement ratio, i.e. the
amount of chlorine dioxide replaced by 1.0 kg of ozone. Ozone and chlorine dioxide
(as pure chlorine dioxide) being of the same order of cost today, a replacement ratio
higher than one means a reduction in chemical cost.
Table 4.17 shows an example of the (ZD) and (DZ) processes applied to a soft-
wood kraft pulp. This type of combination has been thoroughly studied in France,
both in the laboratory and at pilot scale to optimize the process. The (ZD) process is
already in use in a few mills and several other projects announced recently intend to
utilize it. This process provides a good example of how a relatively simple retrofit
in an existing mill can meet most of the requirements described earlier.
ECF bleaching eliminates 2,3,7,8-TCDD and 2,3,7,8-TCDF to non-detectable
levels. However, the complete elimination of dioxins in ECF bleached effluents is a
question of kappa-number and purity of chlorine dioxide. With high kappa and
impure chlorine dioxide (i.e. high concentration of chlorine) the probability of
forming dioxins increase. ECF bleaching eliminates the priority chlorophenols pro-
posed by the United States Environmental Protection Agency (EPA) for regulation
to non-detectable levels. It decreases chloroform formation and decreases AOX for-
mation to a level of 0.2–1.0 kg/ADt prior to external effluent treatment. Usually
AOX levels <0.3 kg AOX/ADT can easily be achieved by ECF bleaching.
Implementation of ECF has required the pulp and paper industry to increase
the use of substituting bleaching chemicals which require considerable amounts
Table 4.17 (DZ) and (ZD) treatments of an unbleached softwood kraft pulpa
Bleaching sequence DEDED (DZ)EDED (ZD)EDED
ClO2 (kg/ODT of pulp) 35 27 29
O3 (kg/ODT of pulp) – 3.7 3.6
Brightness (% ISO) 90.0 90.5 90.3
Viscosity (mPa.s) 15.1 13.2 13.7
Replacement ratio (kgClO2/kg.O3) – 20.1 1.7
AOX (kg/ODT of pulp) 1.5 0.65 0.61
AOX measured on the combined effluent
Based on data from Chirat and Lachenal (1997)
a
Kappa number 24
of energy in manufacturing of chlorine dioxide, oxygen and hydrogen peroxide.

The production of ECF has been tested and practised in full-scale pulp lines for
several years.
ECF bleaching based on chlorine dioxide is a technology choice for sustain-
able pulp and paper manufacturing. Papermakers and paper users alike desire
ECF’s excellent product quality, resource conservation attributes, and compati-
bility with sustainable minimum impact-manufacturing. Government organiza-
tions increasingly recognize and document ECF’s proven pollution prevention
record, its contribution to sustainable ecosystem recovery and its position as a
core component of BAT. Fueled by continued strong government support and
proven environmental integrity, new paper mills throughout the world are incor-
porating ECF-based bleaching to produce quality products with sustainable man-
ufacturing technologies.
In the United States, the ECF process is regarded as BAT and in Europe, the
Commission has decided that there is no significant difference between TCF and
ECF and, therefore, both are regarded as BAT. Tables 4.18 and 4.19 show environ-
mental aspects of ECF and TCF bleaching processes.
In the last decades the ECF technology has developed remarkably, and the mod-
ern ECF bleaching provides pulp with same or even lower environmental impacts
than TCF. ECF bleaching, in combination with oxygen delignification, provides –
with lower energy consumption – higher yield and produces stronger fibres com-
pared to TCF bleaching. This, in turn, enhances the ability to recycle the products
made out of the pulp and contributes to more efficient use of wood resources. ECF
pulp also has higher brightness than TCF pulp. Studies by the International joint
Commission, the European Commission, the Darmstadt Technical Institute for
Papermaking in Germany and documented reports from industry sources support
the efficacy of ECF. The modern ECF pulp mills use bio-activated sludge in
wastewater treatment, so the water released back to the watercourses is virtually
free of toxic substances.
ECF manufacturing produces the strongest fibres, while conserving forest resources
and enhancing recyclability. In combination with enhanced pulping strategies, ECF
manufacturing has a higher yield, using the least amount of wood compared to other
Table 4.18 Environmental aspects of ECF and TCF – effluent quality

ECF TCF
AOX (adsorbable organic Some AOX content from bleaching none
halides) process but substances are different to
those produced by chlorine gas and are
non persistent. Modern effluent plants
reduce this content to a level which is
insignificant
Molecular weight of Generally high molecular weight (and Low molecular weight
compounds in effluent therefore less toxic) compounds compounds such as
detected glyoxal and vanillin
Short-term single species TCF and ECF equal TCF and ECF equal
toxicity
Chronic single species Slightly lower and below toxicity level Slightly lower and below
toxicity of natural peat bog water and toxicity level of natural
municipal effluent peat bog water and
municipal effluent
Overall environmental TCF and ECF equal and below toxicity TCF and ECF equal and
watercourse impact level of natural peat bog water and below toxicity level of
municipal effluent natural peat bog water
and municipal effluent
Results of biological tests TCF and ECF equal TCF and ECF equal
on effluent of mills having
both TCF and ECF plants
Endocrine disruption There is some evidence of endocrine disrupting substances in the
effluent of both processes but these are believed to originate from
wood or naturally-occurring chemicals and the impact from the
two processes is indistinguishable
Table 4.19 Environmental Aspects of ECF – Pulp properties

Brightness Bleaching reduces pulp strength. At the same level of reduction,
ECF produces pulp having approximately 2 ISO points brighter
than TCF
Yield (i.e.) how much pulp For hardwoods, ECF has an approx. 2 % higher yield than TCF
can be made from the trees and for softwood, this advantage rises to around 4 %
bleaching processes. And finally, ECF is compatible with, and at the leading edge of,
closed loop strategies for minimizing wastewater from bleaching. Along with efficient
wastewater treatment, closed loop strategies are providing optimal solutions for pro-
tecting and sustaining the receiving water ecosystem.
The measure can be adopted in new and existing kraft mills. Conversion of exist-
ing mill to ECF mill has been possible but require often considerable modifications
in the fibreline and chlorine dioxide production: Chlorine dioxide generators have
to be upgraded to meet the increased demand of this bleaching chemical. Existing
bleach plants have to be retrofitted with different chemical mixing etc. systems.
Bleaching chemical cost will increase.
4.10 Totally Chlorine-Free (TCF) Bleaching 119
The investment costs for a 1500 ADt/d ECF bleaching system are 8–10 MEuros
at new mills and 3–5 MEuros at existing mills. The operating costs are 10–12
MEuro/a (European Commission 2001). These costs are based on the assumption
that an existing bleach plant can be used and the investment costs include then the
necessary increase in chlorine dioxide production. The operating costs also contain
thus the additional cost of using chlorine dioxide instead of elementary chlorine for
bleaching.
The world’s papermakers desire for ECF’s superior product quality remains
unabated. With such strong attributes, new bleached chemical production will come
to the market using ECF based bleaching technology. The future remains bright for
ECP pulp production.
4.10 Totally Chlorine-Free (TCF) Bleaching
Bleaching sequences that use no chlorine chemicals are termed as TCF. TCF is the
culmination of several technologies involving oxygen, ozone, hydrogen peroxide,
and various other peroxygens.
TCF bleaching processes significantly reduce the effluent loadings and allow
total closure. TCF bleaching began to be practiced on a commercial scale basis in
the paper industry beginning in the late 1980s. However, developments leading up
to the various TCF technologies began much earlier in the twentieth century.
In TCF bleaching, unpressurized (P) and pressurized (PO) peroxide stages, the
slightly acid peracetic acid stage (Paa), and ozone stages (Z) are used. Transition
metals contained in the pulp are first removed in a chelating stage (Q). Alternatively,
acid hydrolysis can remove metals without the conventional chelating agent, and in
a broad pH range. Oxygen delignification (often multistage) always precedes TCF
bleaching. Examples for different TCF bleaching sequences are listed in Table 4.20
(European Commission 2013). A high final brightness is also possible with
sequences containing only alkaline bleaching stages, but these stages are most suit-
able as oxygen chemical sequences in fibrelines that also bleach pulp with the use
of chlorine chemicals. Typical chemical consumption (kg/ADT) in oxygen chemical
bleaching of softwood kraft pulp of kappa number 10–88 % ISO brightness are:
hydrogen peroxide, 20; sodium hydroxide 32; oxygen, 6; ozone, 5; sulphuric acid
20; and EDTA, 2. Peroxide and oxygen are not sufficient to delignify the pulp fur-
ther when the kappa number of the pulps is low. Ozone or peracids are more effi-
cient delignifying chemicals, and can be used to reduce the kappa number to a low
level before the final brightness increase in the pressurized peroxide stage. Chemical
consumption for bleaching softwood kraft pulp of kappa number 11–89 % ISO
brightness in Q(OP)(ZQ)(PO) sequence is shown in Table 4.21. The chemical
charges and process conditions will obviously vary depending on wood species,
degree of system closure, etc. The brightness development in TCF sequence depends
on the proportions of various chemicals used. Table 4.22 compares the sequences
(QZ)Q(PO), QpaaQ(PO), and Q(PO) for a Scandinavian softwood kraft pulp of
Table 4.20 Bleaching Softwood kraft pulp

sequences for TCF bleaching
Q(EP)(EP)(EP)
Q(OP)(ZQ)(PO)
Q(EOP)Q(PO)
Q(OP)ZQ(PO)
Q-OP-(Q + Paa)-PO
O/O(Q)OP(Paa/Q)PO
Hardwood kraft pulp
QPZP
Q(OP)(ZQ)(PO)
Q(EOP)Q(PO)
Q(OP)ZQ(PO)
O/OZPZP
OPZPZP
Based on European Commission
(2013)
Q Acid stage where the chelating agent
EDTA or DTPA has been used for the
removal of metals, EP Extraction stage
using sodium hydroxide with the sub-
sequent addition of hydrogen peroxide
solution as a reinforcing agent, EOP
Alkaline extraction bleaching stage
using sodium hydroxide with the sub-
sequent addition of oxygen and hydro-
gen peroxide solution as a reinforcing
agent, EO Extraction stage using
sodium hydroxide with subsequent
addition of gaseous oxygen as a rein-
forcing agent, P Alkaline stage with
hydrogen peroxide as liquid, Z Ozone
bleaching using gaseous ozone, PO
Pressurised peroxide bleaching
Table 4.21 Chemical Brightness, % ISO 89.0

consumption in bleaching of
DTPA 2.5
softwood kraft pulpa in
Q(OP)(ZQ)(PO) sequence H2SO4 20.0
NaOH 34.0
H2O2 20.0
MgSO4 2.0
O2 10.0
O3 5.0
Based on data from Pikka
et al. (2000)
a
Kappa No. 11
Table 4.22 A comparison of some oxygen chemical bleaching sequences applied to a softwood
kraft pulpa when the ozone charge is 5 kg/adt
Brightness, % ISO
Peroxide charge (kg/odt) Q(PO) QpaaQ(PO) (QZ)Q(PO)
10 – – 86.5
20 82.0 84.2 90.0
30 – – –
40 84.2 88.0 –
Kappa number 12.0
a
Table 4.23 Effect of kappa number after ozone delignification when bleaching softwood kraft
pulpa in a Q(ZQ)(PO) sequence
Brightness after (PO), % ISO
Kappa Peroxide charge Peroxide charge Peroxide charge
No. after Z (5 kg/odt) (10 kg/odt) (20 kg/odt)
2.0 88.0 91.0 92.0
2.8 86.0 89.0 90.5
3.8 80.5 84.0 87.0
a
Kappa number 12.0
kappa number 12. The ozone charge is 5 kg/ADT. The effect of kappa number after
ozone delignification when bleaching softwood kraft pulp of kappa number 12 in a
Q(ZQ)(PO) sequence is shown in Table 4.23.
TCF bleaching was first used for sulphite pulps, which are much easier to bleach
than kraft pulps. When in the early 1990s the Scandinavian kraft mills started
employing TCF bleaching, the main driver was the possibility to take advantage of
the developing market for chlorine-free bleached pulp and paper primarily in
Germany but also Sweden, the Netherlands, Switzerland and Austria. Initially TCF
pulps were also paid a premium compared to conventionally bleached kraft pulp. An
additional driver was the expectation that it would be feasible to recycle bleach
plant effluents to the chemical recovery system for incineration thereby reducing the
effluent load. TCF pulps are produced in a few BKP mills in Brazil, Europe and
United States. The following Table 4.24 lists the BKP mills that are employing TCF
bleaching. The “fully integrated” mills in Brazil and Sweden bleach only part of the
production. Furthermore they may not bleach to full brightness since the entire
amount of bleached pulp is directly used in the linerboard/board product. A few
BKP mills have the capability to produce both ECF pulps and TCF pulps (Table 4.25).
TCF sequences today are less selective than ECF and consequently have been
unable to retain high strength values at full brightness (Panchapakeshan and Hickman
1997). A number of studies have shown that TCF tear strength at high brightness is
10 % lower than ECF and the pulps have lower fibre strength (Ek et al. 1994;
Moldenius 1995, 1997). The lower strength has implications for paper machine
Table 4.24 BKP mills using TCF bleaching

Mill Wood type Sequence or bleaching agents used
Smurfit Piteå, Sweden HW Fully integrated
Södra Cell Värö, Sweden SW O, P, Q
Södra Cell Mönsterås, Sweden HW, SW O, Z, P, Q
Korsnäs Frövi, Sweden HW Fully integrated
SCA Munksund, Sweden HW Fully integrated
SCA Östrand, Sweden SW OOQ(OP)(ZQ)(PO)
ENCE Pontevedra, Spain HW OOQPQP
Klabin Bacell Camacari, Brazil HW OOAhotZP/Fully integrated
Klabin Telêmaco Borba, Brazil HW OOQ(PO)(EO)P/Fully integrated
Metsä-Botnia Rauma, Finland SW O(ZQ)(PO)(ZQ)(PO/PO)
Evergreen Pulp Samoa, CA, USA SW OQQPQ(PO)
Based on Beca AMC (2006)
Table 4.25 Mills using both ECF and TCF bleaching

Mill Wood/bleaching sequence
Kymmene Pietarsaari, Finland, Line 1 HW OA(Z/D)(OP/P)Z/DP
OA(Z/Q)(OP)(Z/Q)P
Votorantim Celulose e Papel Jacareí, Brazil, Line Ba HW (O/O)AhotZD(PO)1/
O(OP)Z(PO)
Smurfit Munksjö Aspa Bruk, Sweden SW OQ(PO) OQ(PO)DD
Mercer Rosenthal, Germany SW OQOPQZ(PO)P
Mercer Stendal, Germany SW O(OP)DD(PO)
a
VCP also uses Votorantim Chlorine Free (VCF) bleaching. This is a low-OX ECF with small charge
of ClO2 under controlled conditions (ECF pulp OX = 80–120 g/ADt – VCF pulp OX = 30 g/ADt)
productivity and virgin fibre requirements in recycled grades and recyclability. TCF
production requires low lignin content of unbleached pulp and therefore has lower
yield than today’s ECF pulping and bleaching processes. Studies show that TCF
bleaching of 8 kappa number pulp increases overall wood consumption up to 10 %
when compared to an ECF bleaching of 30 kappa number pulp (Steffes and Germgard
1995). In a tour of Scandinavian mills, mill experience confirmed the yield loss.
Wisaforest (Finland) claims it requires 6 % more wood to make a ton of TCF pulp
than ECF pulp. This was confirmed at the Enocell (Finland) mill. All the mills that
produced any TCF pulp noted its lower strength properties. In North America, if the
industry converted to TCF, an additional harvest of 100 million trees would be neces-
sary to produce the same amount of pulp.
Conversion to TCF is relatively difficult for most existing mills for the following
reasons (Lancaster et al. 1992):
–– Capital cost to convert ranges from US$40–$190 million;
–– Operating costs increase US$20–$75 per tonne

–– Existing bleach plants have insufficient retention time for efficient hydrogen
peroxide bleaching.
These estimates in operating cost increases have been by mills that produce
both ECF and TCF. An Austrian mill, which modernized its bleach plant to pro-
duce ECF, determined that the incremental bleaching cost for TCF would be
US$60/t (Haller 1996). The superiority of TCF over ECF bleaching in terms of
environmental impact is questionable.
There are some significant disadvantages in TCF bleaching, which explains the
lack of interest still being expressed by most of the pulp producers (Chirat and
Lachenal 1997). The most important of these is that bleaching a kraft pulp to high
brightnesses (90 % ISO) is not possible without sacrificing some strength proper-
ties. The problem of cellulose degradation during TCF bleaching has been exten-
sively studied. Taking an OPZ(EO)P sequence for example, it was shown that each
stage might contribute to some cellulose depolymerization. One critical factor is the
amount of ozone introduced in the sequence. For charges higher than 5–6 kg/t, the
cellulose may be slightly depolymerized and oxidized. This last effect makes the
pulp sensitive to any alkaline environment such as (EO)P, which leads to further
chain cleavage by a mechanism that has already been well documented.
Consequently, despite the fact that such a sequence was close to optimum efficiency
in terms of delignification (ozone is ranked in the same category as chlorine) and
bleaching power, it is penalized by the occurrence of several degradation mecha-
nisms taking place on cellulose in a synergistic way. One possible solution to the
problem of cellulose degradation during TCF bleaching to 90 % ISO, is to limit the
charge of ozone and to introduce some non degrading bleaching agents in the
sequence. The only reagents that demonstrate this property so far are the peroxyac-
ids (peroxyacetic, peroxymonosulphuric acids). But more research is needed to
reduce the chemical cost to acceptable levels when peroxyacids are used.
TCF pulps differ qualitatively from ECF pulps (Panchpakeshan and Hickman,
1997). TCF bleaching tends to dissolve more of the hemicellulose fraction, as indi-
cated by the higher concentrations of the monomeric sugar units. The different pro-
portions of functional groups, derived from cellulose and hemicellulose degradation,
are responsible for some of the differences in chemical and physical properties
between TCF and ECF pulps. The proportion of hemicelluloses retained is less in
kraft pulps compared with sulphite pulps. The viscosity and degree of polymeriza-
tion (DP) of TCF kraft pulps is based on the type of bleaching sequence and the
operating conditions. For achieving the same brightness, TCFz pulp (OZED
sequence) had a lower viscosity compared with conventional bleaching (CEDED
sequence). TCFz pulps tend to have lower brightness and reduced strength proper-
ties compared with ECF pulps. The correlation between the chemical characteristics
of TCF pulps and the lower strength properties is not well established.
The refining energy (hpd/t) applied depends on the type of bleaching sequence
and viscosity of pulps. The degree of refining is generally less for TCFz pulps
(Panchapakeshan and Hickman 1997). This is due to the increased water-holding
capacity of the pulps due to the higher proportion of carboxyl end groups. Higher
viscosity in TCF pulps means a higher degree of polymerization (DP) and less
number of end groups. Lower hemicellulose retention in TCF pulps also decreases
the number of end groups. Reduction in the number of end groups decreases the
number of active sites available for intermolecular hydrogen bonding and can result
in an overall reduction in the relative bonded area. But this has to be confirmed by
further experimental work. Malinen et al. (1994) have reported that softwood TCF
pulps tend to show more significant loss in strength properties compared with the
hardwood TCF pulps. High consistency ozone-bleached pulps tend to have lower
strength properties compared with medium-consistency pulps due to the loss in
selectivity of attack by ozone and possible degradation of cellulose at higher concen-
trations in high-consistency bleaching. The increase in yield from extended deligni-
fication is attributed to higher retention of alpha cellulose in RDH pulps. When
extended delignification is followed by a TCF bleaching sequence, the yield advan-
tage from higher retention of cellulose is maintained through the bleaching process.
Starting from the same kappa number levels, the bleaching yield in TCFz is generally
lower by 0.5–1 % compared with ECF bleaching processes (Panchapakeshan and
Hickman 1997).
Decrease in strength properties is generally compensated by increasing the pro-
portion of the softwood pulp in the furnish. However, the pulp mill capacity and the
high cost of softwood pulp may constrain some situations. The loss in brightness
and strength properties are generally less for hardwoods than for softwoods. Lower
loss in strength properties for hardwoods may be due to fewer hydrophilic groups in
hardwood pulps compared with softwood pulps, lower swelling ability and higher
possibility of strength development by refining without losing freeness
(Panchapakeshan and Hickman 1997). This must be confirmed by further experi-
mental work. The behaviour of TCF pulps towards heat- and light-induced degrada-
tion is different than that of ECF pulps. The higher proportion of carbonyl and
carboxyl groups (photoreceptors) account for the accelerated brightness reversion
characteristics of TCF pulps. Higher losses in hemicelluloses during extended del-
ignification and TCF bleaching processes are expected to result in a pulp with lower
hydrophilicity. Also, with the increased proportion of cellulosic fraction, the pulp is
expected to be harder to beat. The beatability of TCF pulps is dictated by the type of
bleaching sequence used and the bleached pulp viscosity.
TCFz pulps tend to be more hydrophilic and easier to beat than TCFp pulps.
The higher proportion of acidic functional groups is responsible for the higher
affinity to water (Panchapakeshan and Hickman 1997). This results in a higher
water retention value for TCFz pulps. Increase in the acidic groups results in an
increase in the swelling capability and decreases beating energy required for TCF
pulps as compared with ECF pulps. The differences are always more significant
for softwood than for hardwood pulps. Refiner plate designs may need some mod-
ifications to promote fibrillation. Wide bars may be required in place of low-width
bars. The effectiveness of wet strength additives and the affinity of dye stuff also
differs when changing from ECF to TCF pulps. This is due to the changes in the
functional groups of TCF pulps (Panchapakeshan and Hickman 1997). The zeta
potential may have been altered due to the changes in functional groups in cellu-
lose and hemicellulose fractions. This can affect the effectiveness of chemicals,
first- pass retention and some sheer characteristics. Higher swelling capacity of
TCFz pulps means increased drainage resistance and water retention value. These
different properties particularly affect the production of printing papers, wood-
free uncoated and coated grades. Higher water retention value may be a problem
in situations where forming section drainage capacity is limited. The drainage
elements in such situations may need to be rearranged or additional vacuum ele-
ments may be required. In some cases, major modifications such as increasing the
forming table length or providing additional top wire dewatering may be required.
First-pass retention is generally expected to increase for TCFZ pulps due to less
refining, better fibre swelling ability and, hence, lowest production of fines. Due
to the increased hydrophilicity of the pulp, problems may be encountered in the
saveall, especially if the saveall is hydraulically limited (Panchapakeshan and
Hickman 1997). Optimizing furnish refining and adjusting drainage elements in
the forming section will help improve first-pass retention and also lower the
amount of fines circulating in the white-water system. Decreasing the fines con-
tent helps improve the filtration rate in the saveall and also reduces the sweetener
requirement. Increased swelling capacity of fibre results in an increase in the
amount of bound water. This can limit water removal in the press section.
Modifications required in the press section may include increased press loadings,
upgrading the vacuum systems and major changes in press section configuration.
Higher press loads may also be necessary to control sheet bulk. Lower strength
properties may mean increased sheet breaks in situations where significant open
draw exists between the dryer sections. This may require modifications to support
the control sheet caliper. However, no significant changes should normally be
required in the calendar section.
The measure can be adopted in new and existing kraft mills. In existing mills,
using chelating stage, a new oxygen stage and washer is usually needed to convert
the ECF bleaching sequence to TCF. If hydrogen peroxide or ozone stages are used,
two new bleaching towers are used and reconstruction of bleaching filters. Ozone
bleaching needs ozone generators and reactor. For peracetic acid one bleaching
tower is needed. In new greenfield mills, less modifications and investment costs are
required but operating costs are likely to be the same order of magnitude.
The investment costs for peroxide bleaching at new mills with 1500 ADt/d pro-
duction rate are 7–8 MEuros, with existing pulp mills the costs are 2–5 MEuros
depending on the materials of the existing bleaching equipment. If the materials
tolerate hydrogen peroxide the costs are 2–3 MEuros. Operating costs with peroxide
bleaching are considerably higher, 18–21 MEuro/a, than with ECF bleaching due to
the higher chemical costs. If both ozone and peroxide bleaching are applied, the
investment costs are higher (European Commission 2001).
4.11 F
ortification of Extraction Stages with Oxygen
and Hydrogen Peroxide
Addition of oxygen to the pulp in alkaline extraction is an efficient method for

increasing the bleaching effect and decreasing the consumption of chlorine chemi-
cals and hence the pollution load. Oxygen improves the dissolution of lignin. An
oxygen-reinforced extraction stage is designated EO. Table 4.26 shows the advantages
with oxygen reinforced alkaline extraction. When peroxide is added, it is designated
EOP. Figure 4.12 shows the oxygen reinforced extraction stage with hydrogen per-
oxide (EOP stage). The extraction process reinforced with atmospheric peroxide has
gained notability due to its good effectiveness and low capital requirement for imple-
mentation. Hydrogen peroxide in alkaline extractions allows a reduction in the use of
chlorinated compounds as well as giving a number of quality improvements to the
pulp and the bleach plant effluents (Walsh et al. 1991; Anderson 1992; Anderson and
Amini 1996). Significant reduction in effluent colour is the greatest benefits of
hydrogen peroxide addition in the extraction stage. Other advantages of alkaline
extraction with peroxide include improvement of environmental parameters such as
COD, BOD and AOX. It is common to use the alkaline extraction reinforced with
oxygen (EO) or hydrogen peroxide (EP) or both (EOP, PO), to compensate for lower
chlorine dioxide availability and also to make possible the bleaching in short
Table 4.26 Advantages with Large savings of chlorine dioxide

oxygen-reinforced alkaline with a low charge of oxygen
extraction
Freedom of process conditions:
65–90 °C (149–194 °F) in
atmospheric systems
Option: pressurizing and/or
addition of peroxide for further
reinforcement
Applicable in all types of
sequences, classic chlorine
bleaching, ECF and TCF
Fig. 4.12 Oxygen-reinforced alkaline extraction (EOP) stage

4.11 Fortification of Extraction Stages with Oxygen and Hydrogen Peroxide 127
sequences. When hydrogen peroxide is applied to reinforce the oxidative extraction

stage of an ECF sequence, the brightness reversion can also be slightly improved
(Young et al. 1992). Hydrogen peroxide can also be used in the second alkaline
extraction stage to counteract pulp darkening to reduce chlorine dioxide consump-
tion. Mills also use peroxide to reduce the total applied chlorine dioxide in the final
chlorine dioxidestage. The oxidative extraction stages are currently being designed
to operate at temperatures of 90 °C or higher and at pressures more than 75 psig in
order to obtain the maximum effect from oxygen and added peroxide (Bajpai 2012b).
However, peroxide reinforcement can be more effective when pressurized in the
so-called PHT -stage technology (Pereira et al. 1995; Breed et al. 1995). The most
common types of alkaline extractions now a days are those reinforced with oxygen
and peroxide, partially pressurized (EOP) or pressurized all the way, the so-called
(PO)-stage. For a softwood kraft pulp (kappa factor 0.18), the use of oxygen and
hydrogen peroxide in the extraction stage (EOP) results in reduction on kappa
number after extraction from 3.5 to 2.5. Bleach plants that have a low availability
of chlorine dioxide and require high peroxide dosages (0.8–1.0 %) needs more
severe conditions for peroxide consumption. In these cases, pressurized peroxide
stages such as (PO) or PHT are recommended, because they allow use of high
temperatures. A very significant increase in brightness is achieved when peroxide
is applied to the alkaline extraction for eucalyptus kraft pulp (Boman et al. 1995;
Süss 2000). Another positive effect is the peroxide effectiveness to bleach shives;
even when they are not completely bleached they are lighter and less visible
(Anderson and Amini 1996).
A more powerful oxygen extraction stage is accomplished by raising the tem-
perature in the stage, increasing the oxygen charge, pressurizing the pre-retention
tube and adding hydrogen peroxide. The most important factor is temperature. Use
of pressurized peroxide stages (PO) makes possible to achieve a high final bright-
ness in totally chlorine free (TCF) bleaching (Anderson and Amini 1996; Bajpai
2012b; Suss et al. 2000). In sequences with chlorine dioxide (ECF bleaching), a
powerful peroxide stage will reduce the consumption of chlorine dioxide or even
replace one chlorine dioxide stage. A hot, pressurized peroxide stage operates at
temperatures above 100 °C with a small amount of oxygen added. A prerequisite for
successful peroxide bleaching is that the content of metal ions, e.g. manganese, cop-
per and iron, is low. Several mills around the world are using oxygen-peroxide rein-
forced extraction stage.
For first extraction stage, the dose of hydrogen peroxide is 0.25–0.75 % on oven-
dry pulp whereas for second extraction stage, the dose is 0.05–0.20 % on oven-dry
pulp. Anderson (1992) has reported that by limiting the peroxide charge in the sec-
ond extraction stage, any harmful effect that peroxide may have on pulp viscosity is
minimized. When the kappa factor of the first bleaching stage is less than 0.13,
hydrogen peroxide charge of >1 % can be used in the first extraction stage. However,
higher pH and temperature must be used to efficiently consume the higher dose of
hydrogen peroxide and to increase the rate of reaction. Control of pH in the initial
chlorine dioxide stage is an important feature of this application (Andrews and
Singh 1979). A two-stage hydrogen peroxide treatment with an intermediate washing
Table 4.27 Conditions in an Pulp consistency % 10–15

EOP stagea
Temperature °C 60–70
Charge of NaOH kg/Adt 0.8–1.2
x
Kappa
No.
Charge of O2 kg/Adt 3–5 (7)
Charge of H2O2 kg/Adt 0–3
Pressure bar 1.5
(3–4)
Oxygen treatment min 5–15
(30–60)
Total retention min 30–90
time
pH (final) 10–11
a
Conditions given in parenthesis refer to
a more powerful extraction stage
stage can improve the brightness and delignification for a particular level of hydrogen
peroxide (Troughton and Sarot 1992). Process conditions in extraction stage in most
pulp mills are generally sufficient to efficiently utilize the added hydrogen peroxide.
Table 4.27 shows conditions in a EOP stage.
4.12 Removal of Hexenuronic Acids
This method is becoming a standard feature at bleaching plants using hardwoods.

Hexenuronic acids (HexA) have attracted great attention recently because of their
effect on bleaching operations (Jiang et al., 2000; Vuorinen et al. 1996, 1997).
During kraft pulping, polysaccharides undergo some undesirable reactions and
lead to the formation of HexA by the elimination of methanol from the
4-O-methylglucuronic acids, which are the side groups linked to the xylan back-
bone (Buchert et al. 1995). Hexenuronic acids are detrimental to kraft bleaching
systems in the paper making process; they reduce bleaching efficiency by con-
suming a disproportionate amount of bleaching chemicals. When the bleaching
chemicals are being consumed in non-essential reactions, there is a decrease in the
efficiency of the chemicals, as well as the cost efficiency of an operation (Chai
et al. 2001; Vuorinen et al. 1996; Bergnor and Dahlman 1998). Some studies have
shown that the consumption of bleaching chemicals correlates with the amount of
HexA groups in hardwood kraft pulps. Approximately 35–55 % of elemental
chlorine-free (ECF) bleaching chemical costs may be due to the presence of these
acids. In addition, these groups are also a principal component impacting the
retention of non-process elements, which can cause loss of efficiency and acceler-
ate deposit buildup on process equipment (Laine et al. 1996). It also binds
4.12 Removal of Hexenuronic Acids 129
Table 4.28 Undesirable effects of HexA in bleaching

Increased consumption of bleaching agents to reach target brightness and consequently
increased contribution to AOX and calcium oxalate in effluent
Increased brightness reversion
May increase binding of transition metal ions, thus may increase the use of chelating agents in
hydrogen peroxide bleaching
May contribute to the formation and deposition of oxalates on bleaching equipment
Based on Bajpai (2012b) and Vuorinen et al. (1999)
transition metal ions, intensifying the use of expensive complexing agents in

hydrogen peroxide bleaching (Devenyns and Chauveheid 1997). In addition, the
presence of HexA not only increases the difficulty of reaching a high degree of
brightness, but also increases brightness reversion (Vuorinen et al. 1996). It has
been also found that HexA groups contribute to the pulp kappa number and lin-
early correlates with kappa reduction, as these groups consume part of the potas-
sium permanganate used in this determination (Li and Gellerstedt 1997a, b; Chai
et al. 2001). Since kappa number is widely used for the evaluation of delignifica-
tion efficiency in cooking and bleaching process, the presence of HexA affects the
results of this analysis and thus give erroneous information about the amount of
residual lignin in the pulp (Tenkanen et al. 1999). These problems are more pro-
nounced in the case of hardwood pulps because of their higher xylan content
(Chai et al. 2001). Table 4.28 shows the undesirable effects of HexA in
bleaching.
Low HexA pulps are likely to provide a cleaner production opportunity, likely to
be cost effective due to lesser consumption of bleach chemicals and pollution.
Following methods have been examined for selective removal of HexA:
• Hot acid stage (Ahot) (Henricson 1997; Van Jiang et al. 2000)
• Combined hot acid and hot D stage (AD)hot (Ragnar 2002)
• High temperature D stage also called hot D stage (designated DHT or Dhot)
(Lachenal et al. 2000; Eiras and Colodette 2003; Lindstrom 2003)
4.12.1 H
ot Acid Stage (Ahot) or Combined Hot Acid
and Chlorine Dioxide Stage (AD)hot
HexA can be removed through mild acid hydrolysis which results in bleaching
chemical savings. The extent of savings and economical viability of adopting this
process (new tower and washer stage) is dependent of the HexA content of the
pulp and effective chemicals reduction verified without yield loss and degradation
of pulp quality (Pikka et al. 2000; Furtado et al. 2001; Marechal 1993; Lachenal
and Papadopoulos 1988; Vuorinen et al. 1996; Hosoya et al. 1993; Fatehi et al.
2009). The conditions for mild hydrolysis are: pH 3–3.5, temperature 85–95 °C
Table 4.29 Typical Parameter

conditions for (A) hot and (Unit) (A) hot (AD) hot
(AD) hot stages
pH 3–4 3–3.5 (A), 2.5–3 (D)
Temperature 90–110 90–95 (A), 80–85 (D)
(°C)
Time (minutes) 60–180 120 (A), 15–30 (D)
and time 120–180 min. The first whole bleaching sequence where an A-stage was
combined with bleaching was applied at Aracruz Pulp Mill in 2002 (Brazil). Later,
it was applied in other South American mills using high HexA content eucalyptus
pulps. The A –stage is applied without interstage washing before the chlorine
dioxide stage (D0) or the initial ozone stage (Z) but in this last configuration also
with an interstage washing. Table 4.29 lists the typical conditions for these types
of hot acid stages.
A hot acid stage (Ahot) usually precedes a first dioxide stage (D0) or a ZMC
stage. The objectives are to reduce the charge of chlorine dioxide or ozone and to
decrease brightness reversion of the fully bleached pulps. A hot acid stage (Ahot) is
a fully equipped stage within a bleaching sequence. In other words the pulp is
washed after the acid treatment before heading for the next stage. In (AD)hot two
stages have been combined in one stage. The procedure is: acid treatment, no inter-
mediate washing, chlorine dioxide bleaching, washing. Hence, one washing unit
has been omitted. The reported savings in chlorine dioxide vary considerably (1–2
and up to 3 kg/ADt as chlorine dioxide), when complementing a conventional D0
stage with an Ahot stage or replacing a conventional D0 stage with an (AD)hot stage
in ECF bleaching of eucalyptus kraft pulp. These are actual mill data. In general,
AOX decreases with a decreasing charge of chlorine dioxide. When (AD)hot is
introduced, the observed decrease in AOX formation is due to lower chlorine diox-
ide consumption, but may also be due to lower AOX formation as such. A conse-
quence of the severe process conditions (time, temperature and pH) in Ahot and
(AD)hot stages is a strong acid hydrolysis, which effectively removes not only
HexA but also hemicelluloses and degrades the cellulose. It is, therefore, likely that
the total yield will decrease (wood consumption will increase) and also that the
formation of COD will increase. With regard to pulp quality, the major benefit of
replacing a conventional D0 stage with Ahot and (AD)hot stages is a decrease in
brightness reversion. Pulp strength and pulp refinability may decrease or remain the
same. Some mills have been retrofitted with hot acid stages, Ahot or (AD)hot. A few
examples are: the Aracruz, Guaiba, Brazil BEKP mill in 1999 – ECF sequence (AD)
EDEDW (Ratnieks et al. 2001) and Votorantim Celulose e Papel (VCP), Jacareí,
Brazil BEKP mill, Line B in 2000 – ECF sequence (O/O)AZD(PO) (Rodrigues da
Silva et al. 2002). Table 4.30 lists the benefits reported by these mills which could
be attributed exclusively to the installation of the hot acid stage.
4.12 Removal of Hexenuronic Acids 131
Table 4.30 Benefits of using hot acid stage in bleached eucalyptus kraft mills
Reduced consumption of chlorine dioxide (active chlorine)
Reduced oxalate scaling
Reduced brightness reversion
Increased level of metal ions in the digester washing zone with closure of the A stage
Good performance of the recovery boiler despite the increased level of chloride with closure of
the last bleaching stage
A hot acid stage is also operating at the Klabin Bacell, Camacari, Brazil, BEKP
mill – TCF sequence OOAZP and has been trialled at the VCP, Luiz Antonio, Brazil
BEKP mill – ECF sequences (O/O)A(ZD)(EOP)D and (O/O)AD(EOP)(ZD) and
CENIBRA, Bel Oriente, Brazil BEKP mill – ECF sequence OADEDED (Gomes da
Silva et al. 2002; Costa and Colodette 2002; Beca AMC 2004). During 2002/2003 a
new kraft eucalyptus fibreline was started up at Aracruz, Barra do Riacho, Brazil
with a bleach plant including a hot acid stage, (AD)hot(EOP)(DD). Experience so
far supports around 15–20 % savings in chlorine dioxide consumption, somewhat
reduced AOX formation, higher COD formation and less brightness reversion, when
compared to an initial D0 stage. Hot acid stages do not brighten the pulp although
efficient in removing HexA, and thus reducing the consumption of chlorine dioxide
and decreasing the brightness reversion. In addition such stages may decrease pulp
yield, strength and refinability and also require significant capital for installation.
The savings in chlorine dioxide vary considerably and depend on eucalyptus spe-
cies, number of bleaching stages, bleachability of the pulp and process conditions in
pulping. Thus, despite a few application in the Brazilian BEKP mills, adoption of
acid hydrolysis as a standalone stage, Ahot or (AD)hot, has not been widespread
(Eiras and Colodette 2003) and is debatable as an environmental measure.
4.12.2 High Temperature Chlorine Dioxide Stage (DHT)
This technique is similar to (AD)hot (acid hydrolysis followed by chlorine dioxide

without interstage washing) technology, except that the addition of chlorine dioxide
occurs at the beginning of the stage. The DHT stage is based on the principle that
the reaction rate of chlorine dioxide with lignin is faster than that with HexA. Hence,
the majority of the chlorine dioxide is consumed by lignin at the beginning of the
reaction, while the HexA are eliminated later through acid hydrolysis at high tem-
perature and long exposure (Eiras and Colodette 2003). The main motivations for
applying the DHT stage in ECF bleaching of eucalyptus kraft pulps are potential
reductions in capital costs (shorter sequences), operating costs and increased pulp
brightness stability ((Eiras and Colodette 2003). The DHT stage is more efficient
than a conventional first D stage (D0). It decreases bleaching chemical costs and the
formation of AOX in ECF bleaching. This is particularly true for three-stage

sequence bleaching, which requires an extracted kappa number of ~3.5. However,
the DHT stage usually negatively affect the pulp yield, viscosity/strength, and refin-
ability, which can offset the economic gains. Moreover, the filtrate, rich in metal
ions and organic matter (increased COD formation), may be difficult to manage. For
long sequences, 4–5 stages, the gains due to a DHT stage can be negligible and,
probably, do not justify its implementation. However, it must be considered, that
this technology can be a unique alternative in bleaching eucalyptus pulp to 90 %
ISO brightness, with acceptable chemical consumption, in a three-stage bleaching
sequence (Eiras and Colodette 2003). Shorter sequences are being used to reduce
the capital costs (Ragnar and Dahllöf 2002; Süss and Del Grosso 2002; Eiras and
Colodette 2003; Leporini Filho et al. 2003). There are some kraft eucalyptus mills
operating or coming into operation with bleach plants including a DHT stage, e. g.
CENIBRA, Bel Oriente, Brazil, DHT(EO)DED (2002); Ripasa, Limeira, Brazil,
DHT(OP)D (2003); CMPC, Santa Fé, Chile, DHT(EOP)D (2003/2004); Suzano,
Mucuri (Bahia Sul) DHT(EOP)D(PO) (2004) and Mondi, Richards Bay, South
Africa, DHT(OP)DD (2005).
Despite the positive effects of Ahot, (AD)hot and DHT, possible drawbacks are :
increased yield loss (increased wood consumption), decreased pulp viscosity/
strength and refinability and increased COD in bleach plant effluents The positive
and negative effects of the three modes of ‘hot acid’ or hot D stages vary consider-
ably depending on the eucalyptus species, the number of bleaching stages, the
bleachability of the pulp and the process conditions in pulping and bleaching.
Usually both the advantages and drawbacks are more accentuated for Ahot and
(AD)hot than for DHT. There are a number of ‘hot acid’ or hot D in operation or
coming into operation in BEKP mills. The rationale for, and effects from, the imple-
mentation of any of the stages must be evaluated from case to case.
4.13 Liquor Loss Management
Black liquor may be lost from the kraft mill at several locations in the fibreline and
recovery areas. Due to the organic matter present in black liquor, losses of black
liquor are of much greater concern than losses of green or white liquors. The organic
fraction of black liquor is composed of degraded lignin; wood sugars; carboxylic
and hydroxy acids; extractives consisting of resin acids, fatty acids, and neutral
compounds such as sterols and a variety of other compounds. The composition of a
black liquor depends on the wood species from which it was generated. The various
types of compounds are removed to different degrees in biological treatment sys-
tems. Wood sugars, formic and acetic acids are readily biodegradable, exerting a
BOD load on treatment systems. Lignin degradation compounds are not readily
biodegraded; they pass through treatment into the effluent, contributing COD and
colour. The extractives are somewhat biodegradable but may produce toxic effects
in treatment systems and final effluents (Stratton and Gleadow 2003). In almost all
4.13 Liquor Loss Management 133
kraft mills, leakage from seals on pumps, agitators, and other rotating equipment
occurs. Certain events may generate wastewaters containing black liquor, including
startups, shutdowns, and cleanings of storage and process vessels. Most black liquor
evaporators do not have continuous losses, although carryover of liquor into evapo-
rator condensates may occur, particularly in older rising-film design units, units
with poor mist eliminators, or units that are heavily loaded. Evaporator boilouts
may result in losses of dilute black liquor. Boilouts are initiated every few days or
weeks to remove water-soluble scales that reduce heat transfer performance. A
boilout involves shutting off the liquor feed and purging the system with clean water
or thin liquor while maintaining steam flow. As the product liquor becomes more
dilute, the boilout liquor is diverted to a tank for later recovery. Few mills recover
all of the boilout stream, while others divert the most dilute portions to the wastewa-
ter system. Factors which may affect specific practices at mills include value of the
recovered chemicals and energy, treatment cost and capacity, evaporation cost and
capacity, effluent discharge limitations, or other constraints. A review of mill spill
management practices shows that, in the absence of such constraints and using
assumptions to represent a typical ECF bleached kraft mill, recovery of dilute black
liquor directly to the evaporators becomes uneconomic at concentrations below
about 4 % black liquor solids (Amendola et al. 1996). However, recovery of black
liquor is often practiced down to a concentration of 0.5 % solids (McCubbin 2001a).
The recovery of tall oil and turpentine byproducts are activities with potential to
generate potent wastewaters that can affect treatment performance and effluent
quality. In most of the mills these byproduct recovery areas are isolated from the
mill wastewater collection system so that any spills can be recovered. These materi-
als contain high levels of BOD and COD and are found to be toxic to treatment plant
biota and effluent bioassay test organisms. EPA in its Cluster Rule regulation pro-
mulgated in 1998 included best management practices (BMPs) for spent pulping
liquors, tall oil soaps, and turpentine (USEPA 1998a). Bleached chemical, soda, and
stand-alone semi-chemical pulp mills are required to comply with the BMPs.
Inclusion of BMPs indicates an increasing focus on the importance of fibreline and
recovery area wastewaters from chemical pulp mills.
The chemical recovery area should be designed according to the spill manage-
ment concepts. Spill and buffer tank capacity needs to be determined as part of an
engineered system (USEPA 1998b). Tanks should be large enough so that process
changes can be made to avoid unplanned overflows, but not so large as to enable
unbalanced operating conditions to continue without corrective action being taken.
Their use needs to be integrated into normal operating strategies, since very large
buffer and spill tanks often operate at full capacity and their contents may not be
recycled back into production as part of normal operation. Spill control can be one
of the most cost-effective method by which a mill can reduce effluent loads. It can
be especially effective at reducing colour loads, since black liquor losses can repre-
sent a significant contribution to colour and conventional effluent treatments do not
remove colour efficiently. Managing liquor losses involves both behavioural and
equipment aspects. A review of mill spill management practices showed that mills
achieving the lowest levels of liquor loss emphasised preventive measures to avoid
the need for spill recovery (Amendola et al. 1996). Conventional bleached kraft
mills with untreated effluent COD of roughly 40 kg/ADt would be considered to
have good spill control. Mills with oxygen delignification would be expected to be
at about 30 kg COD/ADt. However, many other factors could influence these values
(McCubbin 2001a). To increase preventive measures, mills typically have spill
recovery sump pumps in critical areas that are automatically activated when a
stream monitoring parameter, usually conductivity, exceeds a set point value.
Design of sumps should be appropriate for the size and type of spills likely to be
encountered. The objective is to recover the spilled material and return it to the
black liquor system with minimal contamination. Water is a contaminant, as it must
be subsequently removed from the recovered spill. Some mills isolate clean water
streams (example seal water) by running them into separate pipes laid on the bottom
of floor drains (McCubbin 2001b).
4.14 Condensate Stripping and Recovery
In-plant treatment of waste condensate has become an accepted method for the
removal of odorous gases and BOD (Stratton and Gleadow 2003). This treatment is
required for environmental reasons as the pollution control regulations have become
increasingly stringent (Burgess 1993). Weak black liquor from brownstock washing
contains about 15 % dissolved solids (85 % water) by weight. Before firing the
liquor in a recovery furnace, it is concentrated to 60–85 % dry solids. Therefore, for
each kilogram of black liquor solids (BLS), about five kilograms of water must be
removed. The majority of this water removal is performed in multiple effect evapo-
rator sets, each consisting of a series of vessels equipped with heat exchangers.
Fresh steam enters the first effect, which operates above atmospheric pressure to
evaporate water from the most concentrated liquor. The resulting water vapor (low
pressure steam) passes to the next effect, which operates under a lower pressure, to
evaporate additional water, and so on. The final effects of the evaporator train are
under vacuum. Condensates are generated in each effect as the vapors transfer heat
to the liquor (Stratton and Gleadow 2003). The initial vapors from boiling the weak
black liquor, typically condensed in the final effects and surface condenser, contain
most of the volatile components of the liquor. The volumes of evaporator conden-
sates generated are substantial. A mill with an evaporator load of 5 kg water/kg BLS
and 1500 kg BLS/ADMTP would produce at least 7.5 m3/ADMTP of evaporator
condensates. Actual volumes generated may be substantially higher in evaporator
sets equipped with barometric condensers, which can add from 2 to 45 m3 cooling
water per ADMTP (Blackwell et al. 1979). Table 4.31 shows typical pollutant loads
in foul condensates (bleached kraft mill) and Table 4.32 shows the heat value of
pollutants.
Modern evaporator systems use non-contact surface condensers to condense
the final vapors. Additional condensate volumes are generated by using vacuum
pumps or steam ejectors used to provide vacuum. Evaporator condensates contain
4.14 Condensate Stripping and Recovery 135
Table 4.31 Typical pollutant loads in foul condensates in bleached kraft milla (softwood)
Total reduced
Total flow Methanol Turpentine sulphur
Source kg/tonne kg/t b/t kg/t kg/tt
Batch digester mill
Digester accumulator overflow 1125 4.0 0.50 0.20
Turpentine decanter underflow 250 1.5 0.50 0.15
Total evaporator condensate 7000 4.2 0.25 1.00
Continuous Digester Mill
Turpentine decanter underflow 450 2.5 0.50 0.12
Total evaporator condensate 8000 7.5 0.50 1.20
Based on Lin (2008)
Based on unbleached digester production
a
Table 4.32 Heat value of Net heat of

pollutants combustion
Pollutant (kgcal/kg)
Methyl akcohal 5037
Alpha-pinene 9547
Hydrogen sulphide 3647
Methyl sulphide 6229
Dimethyl sulphide 7371
Dimethyl disulphide 5638
Based on Lin (2008)
the volatile low molecular weight compounds present in black liquor, including
alcohols, ketones, terpenes, phenolics, organic acids, reduced sulphur compounds,
and others. Methanol is the primary constituent, accounting for up to 95 % of the
total organic content of condensates. Methanol is easily biodegraded. Each
kilogram exert about 1 kg BOD5. The total BOD5 load from condensates has
been reported to be about 8 to 12 kg/ADMT pulp (Blackwell et al. 1979).
Evaporator condensates are typically segregated according to their level of con-
tamination, with the goal of reusing the cleaner fractions and reducing the volume
requiring treatment. There are many different segregation schemes in use at mills.
A simple scheme involves collection of the most contaminated condensates from
the sixth effect and final surface condenser in one stream, and all the remaining
condensates in a second, larger, combined stream. The evaporator foul condensate
stream would then typically be combined with other foul condensate streams from
the digester area before treatment in a steam stripper or biological treatment plant
to reduce the release of hazardous air pollutants (HAPs). The combined conden-
sates and stripped foul condensates are often used as wash water on the final
brownstock or post-oxygen washer, and sometimes for mud washing in the caus-
ticizing plant. In most mills, the available volume of condensates exceeds the total
requirement of these two areas, and the excess becomes wastewater. There are
other process areas such as the bleach plant where there is a need for clean hot
water. Because condensates are hot and have very low concentrations of metals,
they are potentially attractive hot water sources, particularly in peroxide-based
bleach plants where transition metal ions have harmful impact. Condensates also
have very low hardness (calcium and magnesium) levels and may reduce scaling
in mills with hard process water. Due to their COD and reduced sulphur com-
pound content, additional treatment may be required before reuse in the bleach
plant would be considered in many mills. However, it has been shown that even
highly contaminated condensates (COD of 6218 mg/L) had only minor effects on
peroxide or ozone bleaching performance or pulp quality, and the bleached pulps
were free from unpleasant odors (Annola et al. 1995).
In Sweden, Sodra Cell’s Varo mill reported on its operation of a second conden-
sate stripper to clean evaporator condensates having a COD of 2000 mg/L. The unit
was installed with and is integrated into a new evaporator set. Performance was
reported to be 90 % removal of COD and greater than 95 % removal of reduced
sulphur compounds. The unit has enabled the mill to reuse all its condensates and
eliminate fresh water use in the bleach plant during normal operation. Bleaching is
done with a peroxide-based TCF sequence. Benefits from lower peroxide use for
bleaching and better pulp strength, presumably due to lower metals concentrations,
were also reported (Emilsson et al. 1997). Improvement in effluent toxicity response
resulting from the use of a reverse osmosis (RO) treatment for “clean” (COD of
1067 mg/L) condensate from the fifth effect of the evaporators at the Irving Pulp &
Paper mill in St. John, New Brunswick, Canada has been reported (Dubé et al.
2000). The RO unit uses a three layer composite membrane and concentrates at least
88 % of the BOD and COD in a volume representing 1 % of the feed volume. The
concentrate is burned in the bark boiler or with the black liquor in the recovery fur-
nace. The treated condensate is used for brownstock washing. Mill effluent, which
is not biologically treated, produced a much lower toxicity test response when the
RO unit was operating.
Other methods have been suggested for cleaning condensates before reuse. These
are aerobic biological treatment using a high temperature membrane bioreactor
(Bérubé and Hall 2000). The advantages of reusing the condensate streams are:
–– Reduction in energy
–– Reduction in water use
–– Reduction in effluent flow
The chemical constituents in evaporator condensates are usually removed to a
high degree in mill effluent treatment plants anyway, so unless the treatment plant is
heavily loaded, few benefits are expected in treated effluent quality due to separate
treatment of condensates. Combustion of methanol, in a boiler or incinerator con-
verts all of the carbon to carbon dioxide and water. Methanol has a fuel value of
21 MJ/kg, and this has the potential to offset a substantial portion of the energy
required for steam to strip the condensates. Biological treatment, in a mill’s effluent
treatment plant or a dedicated unit, will convert a portion of the organic carbon into
biological solids, which requires dewatering and disposal.
4.14 Condensate Stripping and Recovery 137
These strong condensates are generally treated in a stripper where the removal
efficiency for most compounds is more than 90 % depending on the pH. Stripping
systems usually remove malodorous gases and COD-contributing substances at the
same time. Stripped condensates after treatment can be 1–1.5 kg COD/m3 of con-
densate. The stripped gases can be inserted to CNCG system and handled appropri-
ately. These gases can be incinerated in a dedicated burner, the recovery boiler or
the lime kiln. About 7–9 m3 of weaker condensates with medium and low contami-
nation are produced with COD ranging from 0.5 to 2 kg COD/m3 containing a total
of about 8–12 kg of COD/t of pulp. Moderately-contaminated condensates can also
be stripped in a system linked to the evaporation plant thus effecting treatment with-
out any substantial additional use of energy. In this way the total COD load before
any reuse is reduced by about 50 % compared to only treating the most contami-
nated condensates. The stripping column can be a separate piece of equipment or it
can be an integrated part of the evaporation plant. The condensates are fed to the top
of the stripping column. Steam or vaporised condensate rises from the bottom of the
column in a countercurrent manner to the foul condensate. The overhead vapour
from the stripping column is sent to a reflux condenser where it is partly condensed.
The purpose of the reflux condenser is to condense some of the water and to increase
the concentration of volatile material in the gases leaving the condenser. The non-
condensable gases (NCGs) from the condenser contain the majority of the volatile
compounds that are stripped in the stripping column. They are led to incineration
where the organic and TRS compounds are destroyed by thermal oxidation. Cleaned
condensates are free of metals and therefore are particularly useful for washing in
the bleach plant when aiming at closing up this part of the process. They can also be
reused in brown stock washing, in the causticising area (mud washing and dilution,
mud filter showers), as TRS scrubbing liquor for lime kilns or as white liquor make-
up water. This means that some condensates will be used in closed parts of the
process and will not be discharged to waste. Other condensates will be used in open
parts, example the bleach plant, and end up in the effluent together with those con-
densates, which are not reused but discharged directly to waste.
When steam stripping is used, the NCGs have to be incinerated separately in
order to avoid release of concentrated TRS gases into the atmosphere. When the
stripping of concentrated, contaminated condensates is used, the load to the waste
water plant will be reduced and if there are difficulties to meet the permit, new
investments in the effluent treatment plant may be avoided. This also means that less
energy is required for aeration and less energy and chemicals in the sludge treat-
ment. When combining the recovery of clean condensates and stripped condensates,
fresh water consumption may be decreased by 6 m3/ADt. Because the condensates
are hot, part of the energy used in the stripping column can be saved. Fugitive TRS
emissions from waste water treatment plants can be reduced by the steam stripping
of condensates which removes TRS compounds from foul condensates. As the strip-
per off-gases contain 8–12 kg/ADt methanol, there is the potential to save fuel oil or
natural gas, provided that the stripper gas can replace the fuel.
The stripping of contaminated condensate is common in most mills. When the
stripping system is used for high methanol removals, the condensates from the
stripping column are relatively clean and can be reused in the pulp mill for applications
such as brown stock washing. The basis for the design should be the minimisation
of the flow to the stripping system by segregating the condensates in order to
reduce the required investment. In the evaporation plant, the first liquor vapour
condensate can be split into two fractions. Surface condenser can be split into two
units or two condensing steps. The blow vapour from a batch digester can be con-
densed in two steps. Secondary steam can be used as the main steam source to the
stripping column. The best place to reuse the condensates is pulp washing either on
the last washer or on the decker in a mill with a closed screen-room water system.
The typical wash water demand is 10–13 m3/ADt. The evaporator-area and digester-
area condensate available for reuse can amount to 6–9 m3/ADt, which is the amount
of potential water savings. In total the stripping of only the heavily polluted con-
densates would result in 4–6 kg COD/ADt while with stripping of the condensates
with medium contamination, about 3–5 kg COD/ADt can be obtained. However,
condensates discharged to effluent treatment are mostly readily biodegradable.
TRS removal is about 97 % from the condensate, methanol removal about 92 %
(European Commission 2013).
Steam stripping can be applied at both new and existing kraft mills. The conden-
sate stripping column can be separate or it can be integrated into the evaporation
plant. In the former case, live steam would be required whereas in the latter case,
secondary steam from evaporator effects can be used. However, thermal oxidation
of the vapours from the stripper system is needed. Lime kilns, power boilers and
separate TRS incinerators can be used for this purpose.
The investment required for the stripper system at a 1500 ADt/d kraft pulp mill
is about EUR 2.0 million – 2.5 million (European Commission 2013). Additional
investment may be required to increase the capacity of the evaporation plant of the
mill, but this depends very much on the existing evaporation plant configuration.
Retrofitting costs can vary between EUR 1 million and 4 million. The operating
costs of condensate stripping consist mainly of the cost of steam used in stripping
and maintenance. If the stripper is operated separately from the evaporation plant,
the operating costs are significantly higher due to the demand of fresh steam. The
costs are about EUR 0.6 million – 0.7 million/year. If the stripper is connected
between the evaporation stages, the operating costs are lower. The operating costs in
the latter case are EUR 0.3 million – 0.4 million/year.
The majority of kraft pulp mills in Europe carry out the steam stripping of con-
taminated condensates from the cooking and evaporation plant. The stripping of
contaminated condensates efficiently removes its odorous components (Urbanski
et al. 1998). Stripped condensates may be reused in unbleached and bleached pulp
washing and in causticising processes thus achieving a reduced water consumption.
Numerous mills in Europe are using this approach (Sebbas 1988).
Catalytic oxidation has been developed for treatment of condensates and odor-
ous gases (Norvall et al. 2001). The use of catalytic oxidation provides a low capi-
tal cost option for treatment of condensates and odorous gases. ODORGARD™ is
best described as catalytically enhanced wet scrubbing. Wet scrubbing, using
sodium hypochlorite, has been used to treat TRS gases generated at sewage
4.15 Reduction of Sulphur Oxides and Nitrogen Oxides Emissions 139
treatment works, and meat rendering plants (Stitt and Fakley 1995). The Domtar
Papers mill in Cornwall, ON, has long used a hypochlorite scrubber to treat odors
from the batch digesters (Bonsu et al. 1986). The ODORGARD® Process, mar-
keted in Australia and New Zealand by Orica Watercare under licence from Johnson
Matthey PLC, offers catalytically enhanced odour and low-level VOC destruction,
using a heterogeneous supported catalyst in a fixed-bed reactor. With patents for
both the catalyst and process applied for or granted around the world, the
ODORGARD® Process is recognised as a unique and practical solution to a high
profile environmental problem. Based on conventional alkaline bleach scrubbing
the ODORGARD® Process utilises a catalyst to convert the sodium hypochlorite
molecule into brine and a highly reactive oxygen atom held on the surface of the
catalyst. The reaction which takes place over the catalyst can be summarised thus:
It is this oxygen species which is responsible for the enhancement in scrubbing
efficiency both in the level to which particular compounds are oxidised and the
range of compounds that can be oxidised.
4.15 R
eduction of Sulphur Oxides and Nitrogen
Oxides Emissions
Forest products manufacturing is one of many industrial sources of sulphur oxides

(SOx) and nitrogen oxides (NOx) emissions (NCASI 2013). They originate as prod-
ucts of combustion that accompany steam and power generation, processing of
pulping chemicals, and wood drying. In the United States, electric utilities are by far
the dominant sector for SOx and NOx emissions. In Canada, smelting (for SOx) and
upstream oil and gas (for NOx) sectors dominate these releases. Since the 1980s,
measures have been taken in North America to reduce atmospheric emissions of
SOx and NOx where levels contributed to impaired environmental quality, as well
as in response to government mandated performance standards. Considered together,
these substances have been implicated in adverse respiratory effects where certain
thresholds are exceeded, as well as acidic deposition thought to be of consequence
to vegetation, soils, and surface waters. NOx emissions are also known to contribute
to ozone formation and deposition-related eutrophication of surface waters. Most
recently, SOx and NOx emissions are being scrutinized because of their role in the
formation of fine particulate matter, which is an emerging health concern and a
contributor to visibility impairment in certain geographic settings (USEPA 2007).
SOx and NOx emissions are both largely the result of combustion processes. In the
United States, SOx emissions are dominated by stationary sources, foremost among
them electric utilities. The fuel combustion-related emissions from utilities are
about five times those associated with industrial fuel combustion, the second largest
source. NOx emissions are dominated by mobile sources, which are nearly three
times as great as those from utility and industrial fuel combustion combined.
Emissions reductions since the 1980s have been dramatic. Ambient air quality
Table 4.33 Prominent Pulp Source SOx NOx

and Paper Industry sources of
Power boilers 205 124
SOx and NOx (103 tons)
Kraft recovery furnaces 29 55
Kraft lime kilns 2 8
Kraft thermal oxidizers 1 1
Based on NCASI (2013)
standards for NO2 are universally met across the United States, and the new more
stringent short-term sulphur dioxide standards are exceeded in just four limited
areas in the nation (USEPA 2011). Further reductions in ambient concentrations
will occur due to revision of performance standards, declining use of coal by elec-
tric utilities and industrial sources, and requirements that utilities and industry
address emissions that contribute to regional haze and ozone.
The most prominent source of SOx and NOx emissions at a pulp and paper mill
is the power boilers that generate steam and electrical energy for the manufacturing
process. Both SOx and NOx are the result of the combustion of sulphur- or nitrogen-
containing fossil fuels and non-fossil fuels, respectively. Emission levels are driven
largely by the choice of fuels, principally fossil fuels fired alone or in combination
with wood-derived fuels, along with the facility’s approach for controlling these
emissions either in situ or post combustion. The magnitude of boiler emissions in
2010 relative to those from process sources is illustrated in Table 4.33. In the pulp
and paper industry, SOx is typically measured as SO2. NOx is made up of NO and
NO2, and all the NO is reported as though it were NO2 (NCASI 2012).
Kraft recovery furnaces are the second largest source after power boilers.
Together, boilers and recovery furnaces constitute approximately 98 and 92 % of the
pulp and paper sector’s SOx and NOx emissions, respectively. The pulp and paper
industry has a history of reducing emission levels of SOx and NOx. Practices that
have been applied or have potential application include
–– Increased energy efficiency
–– Use of alternative fuels with low nitrogen and sulphur content or lower emission
potential
–– Decreasing the moisture content and increasing the heat value of pulping liquors
fired in recovery furnaces
–– Optimization of combustion conditions
–– Growing use of add-on control technologies
For its part, the pulp and paper industry has had a sustained reduction in emis-
sions of SOx and NOx since the 1980s. In the United States, sulphur dioxide emis-
sions have declined over 70 % from 1980 levels despite increases in production.
NOx emissions in 2010 were 30 % lower than in 1980. In Canada, sulphur dioxide
emissions decreased by 51 % between 2001 and 2010, from 2.29 kg/tonne to
1.13 kg/tonne (production-weighted mean). NOx emissions in Canada were more
consistent during this period of time, but were reduced by 11 %, from 1.42 kg/tonne
4.15 Reduction of Sulphur Oxides and Nitrogen Oxides Emissions 141
Table 4.34 Range of observed emissions of SOx and NOx from recovery furnace and lime kiln
Emission source SOX NOX
Recovery boiler Observed emission levels ~0 to 300 ppm 40–130 ppm
Best available control technology 50–300 ppm 75–150 ppm
Lime Kiln Observed emission levels ~0 to 20 ppm 30–350 ppm
Best available control technology 30–80 ppm 30–300 ppm
Based on NCASI (2013)
to 1.27 kg/tonne (production-weighted mean). These reductions, in part, reflect a

response to technology-driven regulatory standards, equipment modernization,
improved operating and energy efficiency, alternative fuel selection, and industry
restructuring. Table 4.34 illustrates the range of observed SOx and NOx emissions
from various pulp and paper mill sources, along with emission levels derived on the
basis of control technology benchmarks (NESCAUM 2005; European Commission
2001; NCASI. 2013).
Flue gas treatment (FGT) is more effective in reducing NOx emissions than are
combustion controls, although at higher cost. FGT is also useful where combustion
controls are not applicable. Pollution prevention measures, such as using a high-
pressure process in nitric acid plants, is more cost-effective in controlling NOx
emissions (World Bank 1998). FGT technologies have been primarily developed
and are most widely used in Japan and other OECD countries. The techniques can
be classified as selective catalytic reduction, selective noncatalytic reduction, and
adsorption. Selective catalytic reduction (SCR) is currently the most developed and
widely applied FGT technology.
SCR is the most advanced and effective method for reducing NOx emissions and
can do so by up to 80–90 %. SCR entails the reaction of NOx with ammonia within
a heterogeneous catalytic bed in the presence of oxygen at temperatures normally in
the range of 523–673 K. The predominant reactions are (Radojevic 1998):
4 NO + 4 NH 3 + O2 → 4 N 2 + 6H 2 O
6 NO2 + 8NH 3 → 7N 2 + 12H 2 O

NH3 is chemisorbed on a catalyst and reacts with NOx in the gas phase. Many cata-
lysts with varying operating temperature windows may be used. The performance of
SCR is affected by temperature, NH3/NOx ratio, oxygen concentration, catalyst
loading and the type of catalyst support used (Radojevic 1998). Depending on the
process parameters, various catalysts have been studied for NH3-SCR including
noble metals, metal oxides and zeolites. The catalyst is usually a mixture of titanium
dioxide, vanadium pentoxide, and tungsten trioxide (Bounicore and Wayne 1992).
No catalysts have been reported to be active at temperatures above 873 K or below
523 K. It is also possible to achieve SCR by using hydrocarbons as a reducing agent
(HC-SCR). However, at temperatures above 773 K all of the hydrocarbons are con-
sumed by combustion reactions. Overall the application of SCR to CFBC is
problematic due to high risks of poisoning by sulphur dioxide and vapours of

volatile metals, alternating oxidising and reducing atmospheres, and the low operat-
ing temperatures of 150–180 °C after the boiler and de-dusting (Tran et al. 2008).
Unfortunately, the process is very expensive (US$40–$80/kW), and the associated
ammonia injection results in an ammonia slipstream in the exhaust. In addition,
there are some concerns associated with anhydrous ammonia storage. SCR can
remove 60–90 % of NOx from flue gases.
Selective noncatalytic reduction (SNCR) using ammonia- or urea-based com-
pounds is still in the developmental stage. Early results indicate that SNCR systems
can reduce NOx emissions by 30–70 %. Capital costs for SNCR are expected to be
much lower than for SCR processes, ranging between US$10 and US$20 per kilo-
watt (Bounicore and Wayne 1992). Several dry adsorption techniques are available
for simultaneous control of NOx and sulphur oxides (SOx). One type of system uses
activated carbon with ammonia injection to simultaneously reduce the NOx to nitro-
gen and oxidize the sulphur dioxide to sulphuric acid. If there is no sulphur in the
fuel, the carbon acts as a catalyst for NOx reduction only. Another adsorption system
uses a copper oxide catalyst that adsorbs sulphur dioxide to form copper sulphate.
Both copper oxide and copper sulphate are reasonably good catalysts for the selec-
tive reduction of NOx with ammonia. This process, which has been installed on a
40-MW oil-fired boiler in Japan, can remove about 70 % of NOx and 90 % of SOx
from flue gases (Cooper and Alley 1986).
The most cost-effective methods of reducing emissions of NOx are the use of
low-NOx burners and the use of low nitrogen fuels such as natural gas. Natural gas
has the added advantage of emitting almost no particulate matter or sulphur dioxide
when used as fuel. Other cost-effective approaches to emissions control include
combustion modifications. These can reduce NOx emissions by up to 50 % at rea-
sonable cost. Flue gas treatment systems can achieve greater emissions reductions,
but at a much higher cost. New recovery boilers are designed to reduce the forma-
tion of NOx within the combustion process primarily as a result of the correct air
register and geometrical design of the boiler.
4.16 Electrostatic Precipitators
Electrostatic precipitators (ESPs) are one of the most widely used highly efficient
particulate pollution control equipments used mainly for the treatment of gaseous
effluents at high flow rates (REHVA 2005). It removes particles from a flowing
gaseous stream such as air using the force of an induced electrostatic charge. ESPs
are filtration devices that minimally impede the flow of gases through the device,
and can easily remove fine particulate matter such as dust and smoke from the air
stream. Consequently electrostatic precipitators are widely used in thermal power
plants, cement plants and pulp mills. Apart from a high efficiency, other advantages
are related with the fact that this type of equipment has a considerable low payback
time in industrial plants where the particulate recovered from the gases has
4.16 Electrostatic Precipitators 143
commercial value and can be recycled within the industrial process itself or even
sold to other industrial c ompanies. Where Kraft pulp mills are concerned, an elec-
trostatic precipitator or a set of these equipments, is used to achieve treatment of
waste gases from recovery boilers by collecting the load of particulate which is
mainly formed of sodium sulphate, a chemical compound that is recycled back to
the production process. ESPs remove particles in much the same way that static
electricity in clothing picks up small pieces of lint. Transformers are used to develop
extremely high voltage drops between charging electrodes and collecting plates.
The electrical field produced in the gas stream as it passes through the high voltage
discharge introduces a charge on the particles, which is then attracted to the collect-
ing plates. Periodically the collected dust is removed from the collecting plates by a
hammer device striking the top of the plates (rapping) dislodging the particulate,
which falls to a bottom hopper for removal. Electrostatic precipitators are often
configured as a series of collecting plates to improve overall collection efficiency.
Efficiencies exceeding 99 % can be achieved. In some applications water is used to
remove the collected particulates. ESPs using this cleaning mechanism are referred
to as “wet ESPs” and are often used to remove fumes such as sulphuric acid mist.
ESP can be operated at high temperature and pressures, and its power requirement
is low. For these reasons the electrostatic precipitation is often the preferred method
of collection where high efficiency is required with small particles. In the electro-
static precipitation process the basic force which acts to separate the particles from
the gas is electrostatic attraction. The particles are given an electrical charge by
forcing them to pass through a corona, a region in which gaseous ions flow. The
electrical field that forces the charged particles to the walls comes from electrodes
maintained at high voltage in the center of the flow lane (Theodore 2008).
Electrostatic precipitators are a demonstrated control technique for reducing PM
emissions from kraft recovery furnaces and lime kilns. The PM emissions from over
98 % of kraft recovery furnaces and approximately 10 % of kraft lime kilns are
controlled with ESP’s. Paper mills face some unique challenges when it comes to
optimizing the performance of electrostatic precipitators. Resistivity, for example,
is a key issue for power boilers fired by wood waste (bark burners) because often the
ash is high in calcium. Carbon carryover (loss on ignition, LOI) and heavy inlet ash
loading can also limit ESP performance. For recovery boilers, dust resistivity is
typically not a problem, but collection is made difficult because the recovered
chemical compounds tend to consist of very fine particles and the dust loading can
also be relatively high, leading to significant suppression of inlet field current levels.
Proper operating temperature, good gas-flow distribution, good mechanical align-
ment and optimized rapping are needed to comply with emission limits on a consis-
tent basis.
Recovery boiler precipitators tend to suffer from corrosion of both the casing/
shell and internal components, because the flue gas is high in acid and moisture
content. Wet bottom precipitators are especially susceptible to this problem. For
example, because of baffles between fields, there is typically little or no flow just
above the liquor level. In these locations, shell wall temperatures fall below the acid
dew point, and sometimes even below the moisture dew point. Corrosion occurs in
these areas and other spots where flow and temperature are both low. Ensuring that
flue gas and shell temperatures are well above the acid dew point is the key to mini-
mizing corrosion. To do that, it’s necessary to find and fix sources of air in-leakage
(cold outside air getting in), and maintain good insulation. In some cases, it may be
necessary to add heat tracing for parts of the shell.
Because of these challenges, it’s not uncommon for a paper mill to meet emis-
sion requirements with relative ease, yet still have trouble complying with opacity
limits. This is especially prevalent with recovery boilers. Routinely meeting emis-
sion limits requires optimizing boiler operation (not exceeding boiler firing by more
than 5–10 % of design) and gas flow distribution into and out of the precipitator. It’s
also necessary to perform regular ESP maintenance, including minimizing air
in-leakage.
ESPs are very efficient devices for collecting ultrafine particles (<0.5 Zm), pro-
viding the particles have the ability to agglomerate, as e.g. recovery boiler dust
(European Commission 2013). In kraft pulp recovery boilers, the particle size
allows a good separation efficiency of the ESP. No aerosols are formed during
combustion. There are a number of special considerations to be addressed when
designing and operating an ESP for use after the recovery boilers. Some of the key
recommendations are:
–– Avoid flat surfaces in the gas path from the boiler to the ESP to prevent dust
build-up; each gas path should be designed to allow a portion of the gas cleaning
system to be taken out of service for maintenance while the boiler is operating at
a reduced load (i.e. design for 70 % of total flow through one ESP system);
–– With an increase in DS in the liquor, there is often an increase in the dust loading
to the ESP
–– The pH of the dust must be kept above 8.5 to avoid sticky dust that will be diffi-
cult to remove from surfaces
–– Gas flow distribution into each ESP must be kept as stable as possible (standard
deviation of the gas flow after the first collection field should be 20 % or less)
–– Due to the difficulties in removing collected dust from the collecting electrodes
the electrode height, length and total area of collecting surface per rapper must
be sized appropriately
–– The dust removal system from the bottom of the ESP must be very robust, reli-
able, efficient and must not contribute to dust re-entrainment.
The performance of existing ESP installations can often be improved without the
need for total replacement thereby limiting costs. Improvements of ESPs can be
done by fitting more modern electrodes, installing automatic voltage controllers or
upgrade of the rapping systems. In addition, it may be possible to improve the gas
passage through the ESP (improved gas flow distribution) or add supplementary
stages. The performance of an existing ESP can be improved through improving the
alignment of emitting electrodes with the collecting electrodes, eliminate gas sneak-
age around the electrodes, improve the collecting plate cleaning and ensure that
electrical power supply is optimised. The latter may need to have the T/R set and
controls changed. However, there are times when the increase in gas and dust load
4.16 Electrostatic Precipitators 145
to the ESP or reduced allowable emissions from the plant are such that making
changes to power supplies and controls will not be sufficient. In these cases, the
existing ESP size would need to be increased. Only after a thorough evaluation of
the existing ESP size, past performance and new performance requirements, the
determination of the correct approach to upgrade the existing plant be determined.
The black liquor composition may change the ESP performance. The dust may
adhere stronger to the collecting plate. Cleaning the electrodes may need adjust-
ment of the rapping. Modern control systems can detect this and alter the rapping
for optimal performance. Also the electrical power input will adapt to such a chang-
ing situation.
The size and electrical power consumption of ESPs increases exponentially with
the decreasing of clean gas dust content. An ESP depends on defined raw gas condi-
tions, such as temperature and humidity, for optimum operation. The lifetime of an
ESP can be several decades, providing all recommended maintenance is properly
carried out. Some parts, such as hammers and bearings, need regular replacement
after a few years of operation as part of routine maintenance.
Many times the ESP performance is affected by dust composition, gas flow dis-
tribution and gas volume, sneakage around the charging/collection systems,
improper rapping system design, not having advanced power supplies and controls,
and general and poor maintenance of the ESP over time. Keeping the internals of the
ESP clean, properly aligned and powered with the latest type of control system is
needed to achieve best performance. Routine inspections and scheduled mainte-
nance of the ESP internals will result in reliable operation.
Monitoring the power input to each section of the ESP and reacting to large
variations will help to keep the unit performing well: the dust collection efficiency
of the ESP is maximised when the charging of the dust particles is optimised and
the T/Rs that are used to convert the plant alternating current to high voltage direct
current are operating at peak levels. Closely monitoring the secondary voltage
(kV), current (mA) and the sparks per minute (spark rate) from each T/R and
addressing variations by boiler operation are needed to achieve the best possible
collection of the dust. Higher levels of secondary current and lower amounts of
sparking are key factors in maximising ESP collection efficiency. For the overall
performance of ESPs, it is important to avoid CO trips. Because of their high effi-
ciency, low pressure loss, high availability and energy efficiency, electrostatic pre-
cipitators became successfully established for dust collection from recovery boiler
exhaust gas. The major disadvantages of ESPs are their decreased efficiency with
an insulating layer and the possible build-up of material on the collection plates.
No bag filters applications for recovery boilers have been reported. The nature of
the dust and flue-gas composition from recovery boilers are not well suited for the
bag materials used in fabric filters. The gas temperature and moisture content are
higher than most filter bags can accept. The dust is small in size and is often very
sticky. This type of dust composition would be difficult to clean from the bags
resulting in a very high pressure drop across the filter. Boiler upset conditions
could also result in bag damage that would require an outage to repair (Stubenvoll
et al. 2007; EIPPCB 2011).
The ESP’s used to control PM emissions from kraft recovery furnaces and lime
kilns are generally classified as plate-wire ESP’s. In plate-wire ESP’s, the flue gas
flows between parallel sheet metal plates and high voltage electrodes. The flue gas
passes between collecting plates into a field of ions that have been negatively
charged by the high-voltage electrodes located between the plates. Each paired set
of electrodes and plates forms a separate electrostatic field within the
ESP. Electrostatic precipitators used to control PM emissions from kraft recovery
furnaces typically have two parallel precipitator chambers (i.e., flue gas passages)
with three or four electrostatic fields per chamber. Lime kiln ESP’s typically have
one chamber with two or three electrostatic fields. As the flue gas passes through
each electrostatic field, the particles suspended in the flue gas are bombarded by the
ions, imparting a negative charge to the particles. The negatively charged particles
then migrate towards the positively charged or grounded “collecting” plates, where
the particles transfer a portion of their charge, depending upon their resistivity. The
particles are kept on the collecting plates by the electrostatic field and the remaining
charge. At periodic intervals, the collection plates are knocked and the accumulated
PM falls into the bottom of the ESP. The recovered PM is subsequently recycled to
the black liquor in recovery furnace applications or, in lime kiln applications, fed
back to the kiln. The ESP’s used on recovery furnaces may be designed with either
a wet or dry bottom. In wet-bottom ESP’s, the collected PM falls directly into a pool
of liquid, which may be black liquor or water, in the bottom of the ESP. In dry-
bottom ESP’s, the collected PM falls to the (dry) bottom of the ESP and is trans-
ferred from the ESP bottom to a mix tank (containing black liquor) via drag-chain
or screw conveyors.
Electrostatic precipitators of many mills achieve dust emissions from reburning
lime kilns of between 5 and 25 mg/Nm3 determined as annual average value (at 6 %
O2) or 0.02 kg dust/ADt. An example for achieved dust emissions over a complete
year show that the dust emissions from the lime kiln are <25 mg/Nm3 as a daily
average (dry gas, 273 K, 5–6 % O2), or less than 20 mg/Nm3 as annual average. The
data are taken from the on-line transfer of emission data of the competent authority.
In a 1500 ADt/d kraft mill, the investment required for an electrostatic precipitator
at the lime kiln is EUR 5 million – 6 million. The operating costs are less than EUR
0.3 million/year (European Commission 2013).
4.17 Installation of Scrubbers on Recovery Boiler
The recovery boiler can be equipped with a flue gas scrubber in order to reduce the
emissions of sulphur dioxide. A Kraft recovery boiler scrubber of the wet type may
include three process stages. Chloride is absorbed by cold water introduced in the
flue gas inlet. The chloride efficiency is normally 60–70 %. In the washing zone,
SO2 and particulates are removed. Scrubbing takes places at a pH of 6–7. The pH
value is controlled with addition of sodium hydroxide, weak liquor or oxidised
white liquor. SO2 reacts with the scrubbing liquor and Na2SO3 and also some Na2SO4
4.17 Installation of Scrubbers on Recovery Boiler 147
is formed. TRS in the form of H2S can be removed together with SO2. However, to
remove hydrogen sulphide from the flue gases, a high pH of the scrubbing liquor
would be required. At such a high pH, also carbon dioxide would be absorbed,
which is unrealistic due to the relatively large amounts of carbon dioxide being
formed in the combustion. Surplus liquor from the scrubber is recycled to the pro-
cess, normally to the white liquor preparation.
Installation of a scrubber is preferably done at the same time as a new boiler is
installed, although at much higher cost also existing boilers can be equipped with
scrubbers. Recovery boilers burning high dry solids black liquor normally give rise
to low sulphur emission which makes the installation of scrubber less interesting.
The removal efficiency for SO2 is typically >90 %. A scrubber on the recovery
boiler can reduce the sulphur emissions from 0.5 to 2 kg/Adt down to 0.1–0.3 kg S/
ADt or concentrations from 50 to 200 mg/Nm3 down to 10–50 mg/Nm3. Continuous
SO2 measurement prior to and after the scrubber is needed to control the operation
of the scrubber.
By introduction of fresh water in top of the scrubber, hot water can be produced
(if there is a need). The water is normally clean enough to be used as wash water in
the bleach plant. The scrubber needs alkali in the form of oxidised white liquor,
weak liquor or sodium hydroxide, which can increase the capacity demands on the
recovery department.
Wet scrubbers are used at about one third of the recovery boilers. However, if
utilized, the reason is often also heat recovery. The removal efficiency of wet scrub-
bers for SO2 is typically >90 %. According to the data gathered, the same perfor-
mance for SO2 reduction can be achieved by using high dry solid content firing and
by using wet scrubbing of the flue-gas.
For those mills that even though running the recovery boiler at high dry solid
content have higher SO2 emissions (e.g. because of boiler overload), a scrubber can
be a measure to reduce these emissions.
Scrubbers on recovery boilers can be operated without problems. The equipment
comes usually as a package from the supplier. The investment costs for a bleached
kraft mill with a production capacity of 250,000 and 500,000 t/a amount to
7.2 MEuros and 10.4 MEuros respectively. They include scrubber, scrubber liquor
pumps, circulation pumps, electrification and instrumentation. Operating cost
amount to 580,000 Euro/a and 920,000 Euros respectively. Scrubbers have been
installed on numerous recovery boilers in the last decades (SEPA-Report 4713-2
1997b; Pöyry 1992).
Benefits of this technology are reduction of SO2 emissions; heat recovery; dust
removal in some cases. In pulp mills that run the recovery boiler with a high DS
content, the SO2 emission can be substantially reduced and for such mills, there is
not much of a need to install scrubbers. The internal energy situation of the mill
might or might not motivate warm water production in the scrubber. In a modern
kraft recovery boiler, especially if it operates on high DS, the H2S is normally not a
problem that needs scrubbing to resolve. Scrubbers can also be used as a second part
of a two-stage dust removal facility (ESPs and wet scrubbers). Scrubbers have been
installed on numerous recovery boilers in Europe.
4.18 Increase in the Dry Solids Content of Black Liquor
The inorganic substances are reduced in the recovery boiler and separated as a smelt
from the bottom. The organic substances are oxidised and generate heat. In a con-
ventional recovery boiler, there is an oxidizing zone in the upper part and a reducing
part in the lower part. The strong black liquor is introduced through one or several
liquor nozzles into the reducing zone. Combustion air is usually supplied at three
different levels as primary, secondary and tertiary air (from the bottom up-wards).
Emissions generated from the recovery boiler mainly consist of particulates, nitro-
gen oxides and sulphur dioxide. The emission levels are kept low by optimising the
combustion parameters – temperature, air supply, black liquor dry solids content
and the chemical balance. The objective of improved evaporation is to obtain as
high content of dry solids (DS) as possible in the strong black liquor. The DS con-
tent in the strong black liquor is about 65 % after a conventional evaporation. DS
content up to 80 % can be obtained by installing a superconcentrator. However, the
achievable DS-content depends on the type of wood. A target for optimal dry solid
content of thick liquor in a balanced mill could be 72–73 % after evaporation but
measured before the recovery boiler mixer.
The most effective way to reduce both TRS and sulphur dioxide emissions from
kraft pulp mills is to run the recovery boiler with high dry solid content. The sulphur
content of CNCG and the fuel oil burnt in the recovery boiler are less significant for
the reduction of sulphur dioxide emissions.
Sulphur dioxide emissions are formed mainly through the oxidation of hydrogen
sulphide and carbonyl sulphide in the lower furnace. The major source of gaseous
sulphur emissions is the black liquor and the sulphur content in additional fired
streams such as CNCG. The emission levels are kept low by operating the boiler
with high black liquor dry solids content (higher temperature) and by optimising the
combustion parameters such as air supply and mixing of air and fuel. The emission
of sulphur from the recovery boiler is affected by the following operating
variables:
–– Temperature in the different zones which is affected by the dry solids content
(heating value) of the strong black liquor and the amount of combustion air. With
higher DS feedstock, the combustion temperature increases and causes more
sodium to be vaporized. This then takes up the sulphur dioxide and form sodium
sulphate, thus reducing sulphur dioxide emissions from the recovery boiler. On
the other hand, the fact that more sulphur is driven of in the evaporation when the
dry solids content of the black liquor is raised, could reduce the sulphur reaching
the recovery boiler if the sulphur-containing odorous gases from evaporation are
not burnt in the recovery boiler. However, at high temperature, emission of NOx
may increase.
–– At higher sulphidity levels, the release of sodium in the furnace in relation to the
sulphur amount may not be enough to bind all the sulphur emitted and thus a
4.18 Increase in the Dry Solids Content of Black Liquor 149
share of the sulphur may leave the furnace as sulphur dioxide instead of sodium
sulphate. High dry solids contents of the black liquor may compensate this effect.
–– Excess air supply, primary air temperature and distribution of combustion air.
–– Operating a recovery boiler in an overloaded mode has a harmful effect on the
emission characteristics of sulphur dioxide. The load of the furnace is directly
proportional to the temperature in the furnace. When the load of the furnace is
changed, the temperature changes accordingly. In some boilers, the sulphur diox-
ide emissions are sensitive to changes in load i.e. sulphur dioxide emissions may
change due to the temperature changes in the furnace. Sulphur dioxide emissions
may also increase when the boiler load is reduced. Sulphur dioxide emissions
from other boilers with very high DS do not react to changes in the boiler load.
Increasing the firing concentration of the black liquor has been shown to be fea-
sible and to increase the capacity of the boiler (AFPA 1988; EPA, NCASI 1995;
Hyoty and Ojala 1988; Huber et al. 1995; Ibach 1995). Several boilers fire black
liquor at concentrations between 75 and 79 %. Many evaporator installations since
about 1989 have been designed to produce 80 % concentration black liquor
(McCubbin 1996). Huber et al. (1995) described a project that resulted in increasing
the concentration from 68 to 75 % of the liquor fired in the boiler at Pope & Talbot’s
Halsey, Ore., mill. This increased the boiler capacity from 806 tpd of black liquor
solids to 1020 tpd (approximately 16 % increase). It was later on reported, that the
boiler was successfully fired at up to 1180 tpd, representing an increase of 28 % in
capacity. This project also included the installation of a liquor heat treatment sys-
tem, which reduces the calorific value of the liquor by about 5 %. Some of the
increase in capacity can be attributed to this. Lefebvre and Santyr (1989) stated that
calculations using Combustion Engineering Inc. (ABB) boiler simulation software
indicate that where the capacity of a boiler is limited by plugging, increased solids
throughput could be achieved by increasing the liquor firing consistency. Increase of
several percent in capacity due to reduced temperatures in the boiler bank and
reduced gas flow. The higher flame temperatures resulting from the high-
concentration liquors increases heat transfer to the water walls in the lower furnace,
which leads to lower temperatures in the critical boiler bank, thus reducing the
tendency to plug the passages within the boiler (AFPA 1988). Imelainen et al.
(1989) reported modifications to a recovery boiler at the Kemi mill in Finland,
where they attributed an increase of 15 % in boiler capacity to raising liquor firing
consistency from the low 60 % to the low 70 %. It was found that increasing consis-
tency from 65 to 75 % reduced sulphur dioxide emissions substantially and increased
the thermal efficiency from 55 to 60 % while improving reduction efficiency from
95 to 97 %. The same change in firing conditions increased the dust emissions from
the boiler itself by 30 %, but resulted in lower stack particulate emissions due to an
improvement in the electrostatic precipitator’s performance resulting from the lower
gas flows and temperatures. Hyoty and Ojala (1988) described three years’ experi-
ence of operating a “super concentrator” to evaporate black liquor to 78–82 % and
fire it in a recovery boiler at a mill in Pori, Finland. The authors concluded that
boiler operations had improved in a number of ways, with the only difficulty being
the extra operator attention required by the high-solids evaporator. It was reported
that the effective increase in boiler capacity was 15 % when increasing firing con-
sistency from 65 to 80 %. The boiler reportedly fired routinely with 78 % consis-
tency liquor, since this provides sufficient capacity for the mill’s requirements.
Increasing the black liquor firing consistency generally involves installing an addi-
tional black liquor evaporator, usually known as a concentrator, to raise the concen-
tration to the desired level, which may be up to 80 % dry solids. In most cases, the
viscosity of the thick black liquor is the limiting factor. This can be readily reduced
by heat treatment, but the capital cost of the necessary equipment (typically a few
million dollars) may be unacceptable. Several mills use a heat treatment process to
lower the viscosity of high-concentration black liquor. Ryham and Nikkanen (1992)
described a system where the black liquor was heated to 180 °C near the end of the
evaporator set, permanently reducing viscosity by a factor of about 5 (Ryham and
Nikkanen 1992). The absolute reduction was most pronounced at high-liquor con-
centrations (65–80 %). The equipment used to treat the liquor is effectively a multi-
flash evaporator, and it raised the concentration of the liquor by about 5 %. It also
caused sufficient emission of reduced sulphur gases to replace 12 % of the fuel
burned in the mill’s lime kiln. This corresponds to about a 4 % drop in the calorific
value of the black liquor, which in itself increases the boiler’s capacity to burn black
liquor solids. Ryham and Nikkanen (1992) reported an improvement in reduction
efficiency from 93 to 96 %. This is marginally beneficial to recovery boiler capacity.
Huber et al. (1995) described a comparable installation at the Halsey, Ore., mill.
Heating value of the black liquor was lowered by 4 to 5 % by the heat treatment, due
to evolution of sulphur gases that are burned in the lime kiln. The increase in boiler
capacity was 28 %, as mentioned above. This was attributed to a combination of
lowered calorific value of the black liquor, increased liquor firing concentration
(from 68 to 75 %+), and a cleaner burning liquor.
The emission of total reduced sulphur (TRS) from the recovery boiler is influ-
enced by almost the same operating variables as the sulphur dioxide emissions.
–– Due to firing high dry solid content black liquor, there is enough sodium in the
flue-gases to bind almost all sulphur formed in black liquor combustion. Sulphur
emissions are found to be extremely low during full load and stable operated
boilers. If there is enough sodium to bind all the sulphur, virtually there is no
sulphur dioxide emissions (Tamminen et al. 2002).
–– The load of the furnace is directly proportional to the temperature in the furnace.
Operating a recovery boiler in an overloaded mode may have a negative effect on
the emissions characteristics, particularly the quantity of hydrogen sulphide pro-
duced. Rapid changes in the operation mode may generate some momentary
TRS peaks. TRS emissions from boilers with very high dry solid content do not
react to changes in the boiler load.
–– The main controlling factor for the TRS emissions from recovery boiler furnace
is mixing of oxygen and sulphur containing gases. If the gases are well mixed
they are converted to sulphur dioxide. Modern air systems help in obtaining suf-
ficient mixing.
4.19 Incineration of Odorous Gases in the Lime Kiln 151
Increasing dry solids reduces sulphur emissions but increases NOX emissions if
no counter measure is taken. Running recovery boilers at high dry solids and high
furnace temperatures maximises the electricity production from the boilers (high
pressures and temperatures). The reduction of sulphur emissions by high DS con-
tent increases the emissions of particulates prior to flue-gas cleaning. To compen-
sate for this, a more efficient and expensive electrostatic precipitator has to be
installed. At very high DS content (DS >80 %) there is a significant release of sul-
phur compounds from the last evaporator stage, which have to be collected and
incinerated.
The process can be applied at both new and existing kraft mills. A superconcen-
trator can be implemented as a separate phase also to existing evaporation plants.
Viscosity problems can be handled with pressurised storage or heat treatment before
the last concentrator. In existing mills the cost of improved evaporation and concen-
tration of strong black liquor is tied to the target concentration. At existing mills
with 1500 ADt/d kraft pulp production the investment required for increased black
liquor concentration from 63 % upward are as follows (European Commission
2013):
–– concentration from 63 to 70 %, EUR 1.7 million – 2.0 million
Increasing the dry solids content does not increase operating costs, and indeed
significant savings are possible. The measure increases the energy economy of the
mill and leads to gains in recovery boiler capacity. Driving force for implementation
are increased process efficiency. The Finnish recovery boilers are on average firing
close to 80 % dry solids; Swedish recovery boilers are on average firing close to
70 % dry solids (FRBC 2010; Finnish BAT Report 1997).
4.19 Incineration of Odorous Gases in the Lime Kiln
Disposal of malodorous gases from the kraft process is a difficult waste stream
problem in the Pulp and Paper industry. The human detection threshold is as low as
1 part per billion (ppb) for reduced sulphur gases (USEPA 1976). Non-condensible
gases (NCG’s) containing reduced sulphur gases are not only noxious but also very
hazardous. NCG’s are highly corrosive due to the sulphur compounds and chlorides
with water vapor, and volatile enough to be explosive. Disposal of various NCG’s in
Pulp and Paper mills is always a concern if present and future environmental regula-
tions are to be met. The primary sources of NCG’s in a kraft mill are digesters,
evaporators and turpentine recovery systems. Kraft mill odor can be attributed to
four reduced sulphur gases namely:
Hydrogen Sulphide (H2S)
Methyl Mercaptan (CH3SH)
Table 4.35 Typical Hydrogen sulphide 1.7

noncondensable gas analysis
Methyl sulphide 2.1
by volume % of an NCG gas
stream Dimethyl sulphide 2.1
Dimethyl disulphide 1.7
Turpentine 0.1
Methanol 0.2
Water Vapor 6.0
Nitrogen 77.2
Oxygen 8.9
Based on Santos and Backlund
(1992)
Dimethyl they Sulphide (CH3SCH3)

Dimethyl Disulphide (CH3SSCH3)
These gases are collectively referred to as total reduced sulphur (TRS) gases.
Volatile organic compounds (VOC) other than those containing sulphur are also
emitted during digester relief. Typical constituents are alcohols, terpenes, and phe-
nols. Table 4.35 shows a typical analysis of an NCG gas stream.
Incineration (or thermal destruction) has been well recognized in the paper mill
industry as the preferred method of disposal. Firing NCGs in the power or recovery
boilers is often more troublesome because of high capital and maintenance costs
plus, the increased emissions of sulphur dioxide in the stack.
Incineration of concentrated NCG is conducted in the lime kiln or in a separate
NCG incinerator having sulphur dioxide -scrubber. The concentrated NCGs contain
over 90 % of all TRS compounds generated in the cooking of pulp. Efficient
odourous gas collection from all sources and effective treatment reduces sulphur
emissions and annoying smell in the neighbourhood
High concentrated and low volume gases are produced in:
–– Turpentine recovery system

–– Continuous digester flash steam condensers
–– Foul condensate storage tanks
–– Evaporator non-condensable gas relief and hotwells
–– Batch cooking blow heat recovery system instead of continuous digester flash
steam condensates
The actual composition varies greatly from case by case. The major sources of
lean malodorous gases are:
–– Washing and screening equipment of unbleached pulp
–– Several tanks of pulp and washing liquor in the washing and screening
–– Storage tanks of black liquor in the evaporation plant
–– Storage tanks of white liquor in the recausticising plant
The collection is carried out through gas pipelines, ejectors and blowers for gas
transfer. The collected lean malodorous gases can be incinerated as secondary air of
4.19 Incineration of Odorous Gases in the Lime Kiln 153
lime kiln or in a separate NCG incinerator, in a bark boiler or other auxiliary boiler
or as secondary or tertiary air of the recovery boiler. Depending on the volume of
diluted NCGs and the lay out of the pulp mill, there can be several TRS-destruction
systems for different departments.
The measures can be adopted in the existing and new kraft mills. In the existing
pulp mills it may be difficult to retrofit a collection and treatment of diluted NCGs.
The TRS emissions of the kraft mill can be reduced by more than 90 % by only col-
lecting and burning the concentrated TRS-compounds. The advantage of burning
the malodorous gas in the lime kiln is that no extra furnace is needed. Also, the
sulphur in the gas can be absorbed in the lime, which decrease the emission of sul-
phur dioxide. However, only a limited amount of sulphur can be absorbed in the
lime kiln by gaseous sodium forming sodium sulphate. The main sulphur absorbing
compound is sodium carbonate in the lime mud. When this capacity is exhausted,
sulphur dioxide is released. This effect is increased when malodorous NCGs are
incinerated in a kiln. So, sulphur dioxide emissions are usually a clear function of
the amount of malodorous gas flow. To reduce the formation of sulphur dioxide
either the sulphur content in the fuel can be reduced or if malodorous NCGs are to
be burnt in the lime kiln, sulphur compounds can be scrubbed out of these gases
before burning in the lime kiln.
TRS-control can also decrease the malodorous constituents released in the
wastewater treatment. An average 10–15 % of the fuel used in a lime kiln can be
replaced by the heat value of the concentrated malodorous gases. However, the
variation of the amount of energy of the gas may make it difficult to hold a lime of
good and uniform quality. Condensation of methanol after the stripper column can
reduce the problem with varying gas quality. However, it would require additional
investment costs.
Investment costs of collection and incineration of both strong and weak gases are
typically 4–5 MEuros at new mills and 5–8 MEuros at existing mills with a capacity
of 1500 ADt/d (European Commission 2001). No major increase in operating cost,
if the heat value of recovered methanol can be utilised. Otherwise, an increase of
0.3–0.5 MEuros/a is expected. The reduction of TRS emissions of the kraft mill is a
major reason to implement this technique (Hupa 2005; EIPPCB 2011; Botnia
Rauma 2009; FRBC 2010; DeMartini 2010; Malmström 2010; European
Commission 2001).
Though the lime kiln is the first choice for most plants, but mill production can
be affected by any downtime in the kiln. Potlatch Corporation at their Cypress
Bend facility near McGehee, Arkansas realized that an alternative stand-by system
was necessary to keep production at near 100 % and meet the strict environmental
regulations. The modular incinerator concept can accommodate different high per-
formance burners for different composition and volumes of waste streams. If there
are space constraints, a modular incinerator can operate in different configurations
(i.e vertically or horizontally). Modular systems allows future retrofit at minimal
cost. A stand alone incinerator can reduce problems associated with incinerating
NCG’s in the lime kiln, power boiler or recovery boiler. Ringing problems in lime
kilns have been attributed to incineration of concentrated NCG’s. Corrosion prob-
lems in boiler tubes and reduction of boiler efficiency have been blamed on NCG
firing. With more stringent environmental regulations requiring tighter closure of

all industrial processes and pressure to reduce odorous emissions, stand alone
incinerators become a more feasible and attractive means of NCG disposal in the
pulp and paper industry.
4.20 I nstallation of Low NOx Technology in Auxiliary

Boilers and the Lime Kiln
The formation of nitrogen oxide emissions from pulp mills is significantly more
complicated than was perceived before. Detailed studies on the formation of nitro-
gen oxides in the burning of black liquor started in the 1990s. However, a complete
picture of the cycle of nitrogen compounds at pulp mills has only been clarified now.
In particular, the sodium cyanate (NaOCN) forming in the recovery boiler smelt and
the ammonia generated through it in the chemical recovery cycle are the major fac-
tors, the importance of which has only been understood in the last few years.
Nitrogen is mainly introduced into the mill with wood chips, but other nitrogen
sources are also available, including defoamers, anti-scaling agents, chelating
agents, etc. Their contribution has been considered to be negligible, but they may,
however, have an effect on the black liquor nitrogen content in the future. The recy-
cling of fibreline filtrates back to the recovery cycle in a mill with a high degree of
closure may increase the nitrogen content of black liquor significantly (Telkkinen
1997). Raw wood material contains organic nitrogen compounds as natural con-
stituents, typically 0.05–0.50 % of dry matter (Martius 1992; Nichols et al. 1993;
Verveka et al. 1993; Kymäläinen 2001). In normal cooking, nitrogen compounds in
the wood dissolve more or less completely in the alkaline cooking liquor and are
transferred as part of the black liquor to the evaporation plant and further to the
recovery boiler.
The lime kiln is an important part of the kraft process chemical recovery cycle.
Emissions of NOx from the lime kiln are relatively low. They are influenced by the
following parameters:
–– Composition of materials fed to the kiln
–– Fuel choice
–– Chemical reactions that accompany lime mud calcinations
–– Choice of external control approaches for particulate emissions
Combustion process modifications may be useful, but are limited by site-specific
considerations and product quality impact.
Though the mechanisms differ, NOx produced in the kraft lime kiln originates
from the combustion of fossil fuels, such as natural gas and residual fuel oil. The
range of emissions is wide, and data are equivocal as to whether gas or oil is associ-
ated with the greater level. The introduction of other fuels and reduced sulphur
compound bearing process gas streams such as stripper off-gases (SOGs), which are
4.20 Installation of Low NOx Technology in Auxiliary Boilers and the Lime Kiln 155
relatively rich in nitrogen content, increases the potential. Combustion modifications

are the best prospect for altering NOx emissions. The opportunities are extremely
limited, however, due to the temperature and combustion conditions that must be
sustained to efficiently produce an end product (calcium oxide) of consistently
acceptable quality. The NOx control strategies for each kiln have to be evaluated
on a case-by-case basis since mechanisms of formation and control are not well
understood (NESCAUM 2005). To illustrate, techniques to minimize the hot end
temperatures in gas-fired kilns, while potentially helpful in reducing NOx emissions,
must be balanced with the simultaneous need to address emission levels of total
reduced sulphur compounds and to sustain the necessary calcining capacity.
Reducing available oxygen in the kiln combustion zone may be useful for NOx
reduction in oil-fired kilns, but effects on emissions of carbon monoxide and TRS
emissions would have to be considered. Whatever combustion modifications are
made may be limited by kiln configuration and geometry, and also by impacts on
process performance, stability, and control.
In the Kraft mills, several types of fossil fuels – bark, coal, lignite, oil or natural
gas – can be used for supplemental steam production, typically coupled with
turbines for electric power production. In burning of these fuels environment

friendly incineration techniques are used to reduce particulate, sulphur dioxide and
NOX emissions. Coal and lignite suit well to be burned as major or support fuel in
fluidised bed systems, which by careful operation control promotes low NOx
formation. In conventional oil or natural gas fuelled boilers, the burners feeding the
fuel-air mixture, must apply designs that maintain low NOx burning conditions.
Also coal or peat is often burned as finely ground dust in conventional boilers, fed
through burners that with proper designs provide low NOx burning. The primary
burning air is brought through the burner in the fuel-air mix. Secondary and tertiary
air is fed in separately to maintain an appropriate primary: secondary: tertiary air
balance in the flame area to maintain low NOx combustion. Some air may still be
fed, if necessary above the main flame area to complete the fuel combustion. The
reason of the multi-phase air feed is to burn the fuel without excess air and actually
even under reducing conditions, meaning that there is not enough oxygen to
promote strong NOx formation; the flame temperature is lower than in conventional
burners which further decreases NOX formation. Part of the NOx formed will
reduce back to elementary nitrogen for example when a residual amount of the fuel
is burned in the outer flame area or outside it.
Low NOx burners can be used both in the new and existing boilers. When
powdered solid fuels are used it is important that they are pre-dried if they have high
humidity to support fast and efficient burning. It is also required that the burning air
is preheated to assure quick ignition and complete burning. Generally, emissions
vary with the fuel. In comparison to conventional burners with 250–500 mg/MJ
NOx emissions, the low NOx burners can reach 120–140 mg/MJ level in stack
emissions.
With online NOx meters, emission monitoring can be carried out. Also oxygen
meters can help to determine that low NOx burning conditions are maintained. Low
NOx burners have been applied successfully in the retrofit of existing boilers and
construction of new ones. The investment costs are typically 0.5–0.8 MEuros. No

major increase in the operating costs is anticipated. Low NOx burners are mainly
used to reduce NOx emissions from auxiliary boilers (Rentz et al. 1996; Pöyry
1997, Finnish BAT Report 1997).
4.21 Selective Non-Catalytic Reduction on Bark Boilers
In Selective Non-Catalytic Reduction (SNCR) systems, ammonia or urea is

injected into the furnace within a suitable temperature window. Emissions of NOX
can be reduced by 30–70 % by the reaction between NO and the reducing agent to
form nitrogen and water. The most common reagents used in SNCR processes are
given below:
–– Anhydrous ammonia
–– Aqueuos ammonia
–– Urea solution
SNCR is a simple process, referred to as “thermal deNOx”, and involves the
reduction of NOx to nitrogen in the presence of oxygen by reaction with amine-
based reagents, either ammonia (NH3) or urea, CO(NH2)2 at 1073–1273 K, the
higher temperature being needed for urea. Exxon developed the SNCR process and
first applied it in 1974 (Lyon 1987).
With NH3 as the reagent the reaction scheme is shown below (Lyon 1979):
4 NH 3 + 6 NO → 5N 2 + 6H 2 O

4 NH 3 + 4 NO + O2 → 4 N 2 + 6H 2 O

8NH 3 + 6 NO2 → 7N 2 + 12H 2 O

With urea as the reagent the reaction scheme is as follows:
H 2 NCONH 2 + 2 NO + ½ O2 → 2 N 2 + CO2 + H 2 O

The reagent ammonia or urea can be injected directly into the fluidized bed or riser.
The SNCR process efficiency depends upon the following (Teixeira et al. 1991):
–– Temperature
–– Reagent/flue gas mixing
–– Reagent/NOX ratio
–– Reaction time
SNCR systems reduce NOx emissions by 30–90 % but the performance is highly
variable for different applications. A typical SNCR system involves reagent storage,
multi-level reagent-injection equipment, and associated control instrumentation.
4.21 Selective Non-Catalytic Reduction on Bark Boilers 157
The SNCR reagent storage and handling systems are similar to those for SCR
systems. However, because of higher stoichiometric ratios required at equivalent
efficiency, both ammonia and urea SNCR processes require larger quantities of
reagent than SCR systems to obtain similar NOx reductions. The capital cost of
SNCR is low compared to that of SCR systems since there is no catalyst, and overall
operating costs are similar (Mahmoudi et al. 2010). The addition of aluminium-
based catalysts has been suggested for the full and rapid decomposition of urea.
In the SNCR process, it is the ammonia molecule that is the active reducing
agent. When using urea solution in such a deNOX process, the urea will be first
converted into ammonia prior to the deNOX process. The dominating reaction in the
SNCR processes in combustion processes where NO is the main NOX species is:
4 NO + 4 NH 3 + O2 f 4 N 2 + 6H 2 O

In the more efficient SCR process about 1 mole of ammonia is required per mole
of NOX reduced or about 0.5 mole urea per mole NOX reduced. The SNCR process
is not as efficient as SCR when it comes to reagent utilisation. In this process, the
reagents needs to be dosed in an over-stoichiometric ratio. For SNCR it can be in
the range of 1.5–2 (or even higher in some cases). The approximated reagent
consumption for SCR and SNCR process is:
SCR: 1 kg NOX reduction require 0.37 kg NH3 or 0.653 kg urea.
SNCR: 1 kg NOX reduction require 1.2–1.9 kg NH3 or 2.2–3.3 kg urea.
The temperature window for efficient SNCR operation is typically between 800
and 1050 °C. When the reaction temperature increases over 1000 °C, the NOX
removal rate decreases due to thermal decomposition of ammonia. Below 800 °C,
the NOX reduction rate decreases and ammonia slip may increase. The longer the
reagent is in the optimum temperature window, the better the NOX reduction.
Residence times in excess of one second yield optimum NOX reductions. Ammonia
slip from the SNCR systems occurs either from injection at temperatures too low for
effective reaction with NOX or from over-injection of reagent. Controlling ammo-
nia slip in SNCR systems is difficult since there is no opportunity for effective
feedback to control reagent injection. Another difficulty is that the reagent should be
placed where it is most effective and the NOX distribution varies within the boiler
cross section. Distribution of the reagent needs to be particularly controlled in larger
boilers because of the long distance required to cover the cross-section of the boiler.
Multiple points of injection are commonly used to follow the temperature changes
caused by boiler load changes. In well controlled SNCR systems, ammonia emis-
sions are in the range of 1–10 mg/Nm3.
Injected urea or ammonia does not react completely but a small share of the
reagent escapes in the flue-gas. The benefit of reduced NO should be weight against
increased ammonia emissions and ammonia slip controlled and kept as low as
possible. Depending on the stoichiometry the urea is added, a slight increase of
ammonia (slip) may be determined but measurements demonstrate the risk to be
marginal. A potential danger is unreacted ammonia combining with SO3 to form
ammonium bisulphate. Ammonium bisulphate will precipitate at air heater operating

temperatures and can ultimately lead to air heater fouling and plugging. If not prop-
erly controlled, there is a certain risk that an SNCR process may produce nitrous
oxide, which contributes to the greenhouse effect. However, nitrous oxide emissions
are more likely to occur at coal-fired boilers than at biomass-fired ones. Carbon
dioxide emissions associated with the use of urea and ammonia for NOX reduction
are relatively small to negligible compared to overall generation of carbon dioxide
in pulp and paper production; on the other hand, reduction of NOX emissions is
required for health reasons and to protect environment from adverse effects such as:
–– Euthrophication,
–– Acidification
–– Ozone formation
For SNCR, a reduction of 30–70 % is reported (European Commission 2013).
The result of the application of SNCR is very sensitive to variations in the operational
conditions of the boiler and urea/ammonia dosing needs to be controlled perma-
nently. Continuous NOX measurement should be carried out and experience shows
reliable results. The total NOX reduction achievable in a bark boiler is about
30–50 % by changing the combustions techniques and/or by applying an SCNR
process. The NOX emissions would then amount to 40–60 mg/MJ equal to about
100–200 mg/Nm3. Achieved emission data for SNCR applications in fluidised bed
boilers can also be seen in Table 4.36.
Bark boilers give relatively low NOx emissions because of the low combustion
temperature. When only bark is fired, emissions are typically 70–100 mg NOx/MJ
and when oil is used in the bark boiler, NOx increases to about 100–150 mg NOx/
MJ. NOx formation is affected by excess oxygen and should be avoided. Too low
excess oxygen increases the risk for emissions of carbon monoxide and VOC. Primary
NO is formed in furnaces either through reaction with nitrogen in air (thermal NO)
Table 4.36 NOx emission from fluidised bed boilers of paper mills using primary and/or
secondary measures for NOX reduction
Rated
thermal Flue gas
input Year of cleaning NOX CO (mg/ O2
(MW) commissioning Fuels system (mg/Nm3) Nm3) (%) Observation
48 1994 Bark, Primary 90–220 3–20 11 Corg <2 mg/
sludge, measures (DAV) (DAV) Nm3
paper, 142–187 4–9
waste (MAV) (MAV)
wood 165 (YAV) 6.4 (YAV)
4.8 2003 Waste Primary 161–171 2.3–2.8 11 Corg <1 mg/
wood, measures, (YAV) (YAV) Nm3
rejects, SNCR
sludge
Based on European Commission (2013)
4.21 Selective Non-Catalytic Reduction on Bark Boilers 159
or through oxidation of nitrogen in fuel (fuel NO). Formation of thermal NO

increases with increasing temperature of the flame. A part of the NO is further oxidised
to NO2. In the SNCR process, NO is reduced by urea to nitrogen, carbon dioxide
and water according to the reaction
2 NO + ( NH 2 ) 2CO + ½ O2 → N 2 + CO2 + 2H 2 O. The reaction occurs

around 1, 000 °C.
Equipment to inject urea or ammonia can be installed in both existing and new
boilers. The optimal reaction conditions can be difficult to obtain in existing boilers,
thus reducing the potential NOx reduction to about 40 %. The total NOx-reduction
achievable in a bark boiler is about 30–50 % by making change in the combustions
techniques and/or by applying an SCNR process. The NOx emissions would then
amount to 40–60 mg/MJ equal to about 100–200 mg/Nm3. Emissions of gaseous
sulphur are low or about 10–20 mg/MJ when burning bark. Continuous NOx
measurement can be installed and experience shows reliable results.
This technique is being used since the early 1990s. Good availability is normally
reported, but a number of incidents have occurred where the injection of urea
solution has caused damages inside the boiler. SNCR technique is difficult to control
because of relatively fast changes of load might happen in bark boilers. This results
in variations in NOx reductions achieved by these techniques. The process can be a
potential source of emission of N2O or ammonia but measurements demonstrate the
risk to be marginal.
Full scale trials both with urea and ammonia have been carried out in Sweden.
The trials showed NOx emission reductions of 10.30 %, with one test up to 60 %.
The efficiency depends on many factors, e.g. the boiler furnace configuration. In
practice, this method also generates secondary ammonia emissions, or ammonia
slip. The injection of urea or ammonia into the boiler may damage the furnace and
boiler tubes. For safety reasons, the Swedish Recovery Boiler Committee has
advised against the installation of SNCR on recovery boilers.
The investment costs for adding SNCR to the bark boiler for a bleached kraft mill
with a production capacity of 250,000 and 500,000 t/a amount to 690,000 Euros and
1.15 MEuros respectively (European Commission 2001). The investment costs
include injection equipment, pipes, pumps, tanks and rebuild/adoption of the boiler.
The operating costs are mainly urea. About 1–2 kg urea is required per kg NOx
removed.
NOx has an acidifying potential and may increase eutrophication. In some
sensitive lake areas in Europe a further reduction of NOX emissions by secondary
measures as SNCR technique is therefore regarded as necessary. A fee on NOx
emissions in Sweden may also give an incentive for further NOx reduction (SEPA-
Report 4713-2 1997b).
4.22 Over Fire Air Technique on Recovery Boilers
The formation of NOx in the Kraft recovery boiler is lower as compared to other
furnaces because it operates with a reducing atmosphere in the bottom. Modifications
to the air feed system have been found successful with respect to NOx reductions.
By limiting the amount of air in the combustion zone, thermal NOx by fixation of
nitrogen in the combustion air can be reduced. A reduced NOx formation can be
obtained in a kraft recovery boiler by modification of the air feed system such as
introducing a fourth air inlet in the upper part of the boiler (European Commission
2001). The reduction of NOx emissions attributable to the use of this technique is
variable. It depends on the boiler type and design and the method of Over Fire air
(OFA) application, and will normally be 10–25 %.
OFA is a NOx reduction technique that removes a portion of the combustion air
from the burner wind box. This air is introduced to OFA ports located above the
burners. This technique provides an additional layer of air staging to the furnace
zone. When the diverted air is introduced above the burners, the combustion is com-
pleted and the remaining CO is burned out. OFA has been incorporated in multi-
burner units since the 1970s. Older OFA port designs are not as effective as current
generation of OFA ports. In some cases, original OFA ports have been removed
because they were ineffective or caused boiler performance and maintenance issues.
Using CFD modeling, current generation OFA systems are found to be capable of
25 % NOx reduction with minimal impact to the unit operation. An alternative to
dedicated OFA ports is a tuning technique known as burners out of service (BOOS).
BOOS is implemented by taking one burner or row of burners out of service. Out-
of-service burners act as OFA ports by permitting the remaining burners to run lean.
The remaining required combustion air is supplied through the BOOS to complete
combustion. BOOS reduces boiler efficiency by increasing the excess oxygen
requirement by about 1 %.
Furnace OFA requires combustion air to be separated into primary and secondary
air to achieve complete burnout and to formation of nitrogen rather than NOX. The
primary air (70–90 %) is mixed with the fuel producing a relatively low-temperature,
oxygen deficient, fuel-rich zone and moderate amounts of fuel NOX are formed.
The secondary (10–30 %) combustion air is injected above the combustion zone.
The relatively low-temperature secondary-stage limits the production of thermal
NOX. The location of the injection ports and mixing of overfire air are critical to
maintain efficient combustion.
B&W pioneered the development and application of NOx ports and air staging
as a NOx emissions control technique. Combined with B&W’s other low NOx
technologies, such as burners and selective catalytic reduction systems, overfire air
systems are part of an overall NOx reduction strategy. Their combustion and OFA
systems can be installed on all wall-fired and corner-fired steam generators.
Air staging involves removing a portion of the air from the burners to reduce o xygen
availability early in the combustion process and reintroducing it later in the combus-
tion process. Often the physical arrangement dictates replacing the staged air
4.23 Installation of Improved Washing and Filtration of Lime Mud in Recausticizing 161
through ports located above the combustion zone; hence the name OFA is commonly
applied to such systems. The layout of a combustion system and furnace, however,
may necessitate supplying staged air at the same elevation or below the burner zone,
such that OFA is something of a misnomer. OFA is used here, in its generic sense,
to refer to any air staged system. The ports through which the OFA is injected are
called OFA ports or NOx ports.
It is applicable to both existing and new mills. The achieved NOx-reduction
appears to be different from recovery boiler to recovery boiler. Following experiences
have been reported in some Swedish kraft pulp mills (European Commission 2001):
1. Installation and use of OFA-technique on an existing recovery boiler and

operation since 1990: 30 % NOx-reduction achieved.
2. Installation of the OFA technique on an existing recovery boiler. The new air
feed system is not any more used because of the increase of temperature in the
overheater.
3. Installation of the OFA technique on an existing recovery boiler in 1995: 20 %
NOx reduction achieved and in operation since the beginning of 1997.
4. First new recovery boiler with OFA technique in 1996.
The reduction of NOx emissions with the use of this technique is variable. It
depends on the boiler type and design and the method of OFA application. It has to
be adapted to the specific conditions of recovery boilers. The application of this
technique which is widely used in other combustion processes may result in
increases in carbon monoxide and unburned carbon emissions if not well controlled.
The investment costs for modifying the air introduction to the recovery for a
bleached kraft mill with a production capacity of 250,000 and 500,000 t/a amount
to 1.7 MEuros and 2.3 MEuros respectively (European Commission 2001). The
investment costs include new air inlets to the recovery boiler, instrumentation, pipes
and fans. There is no change in operating costs.
NOx has an acidifying potential and may increase eutrophication. In some
sensitive lake areas, a further reduction of NOx emissions by secondary measures is
therefore regarded as necessary (SEPA-Report 4713-2 1997b).
4.23 I nstallation of Improved Washing and Filtration

of Lime Mud in Recausticizing
The recausticizing plant is a very important part of chemical recovery at the pulp
mill. It uses dissolved smelt from the recovery boiler as a raw material and consumes
lime to produce white liquor, which is an active chemical used in pulping. It also
produces lime mud, which mainly consists of precipitated calcium carbonate
particles, as a byproduct. The purpose of the lime reburning process is to convert the
lime mud back into reburned lime for reuse in the causticizing process. The primary
method used for the required high temperature treatment of the lime mud has been,
and is still today even, a rotary lime kiln (Mehra 1979; Schroderus et al. 2000). The
lime mud recovered from the white liquor clarification, which is the last stage in the
causticizing process, contains substantial amounts of residual white liquor and
therefore also large quantities of sodium hydroxide and sodium sulphide. These
compounds must be removed from the mud because excessive amounts of sodium
and/or sulphide in the mud will impair the operation of the kiln process. According
to Prakash and Murray (1973), Steen and Stijnen (1984), the amount of sodium
sulphide fed into the kiln is also directly related to the TRS emissions. Furthermore,
according to Tran and Barham (1991) and Tran et al. (1993), ring formation in the
kiln is associated with a high residual sodium content of the mud. Furthermore,
these sodium compounds are valuable chemicals, and need to be recycled back to
the process. In order to avoid these problems, the lime mud must be washed and
dewatered before it is fed into the kiln. Efficient washing and filtration of the lime
mud reduces the concentration of sodium sulphide in the lime mud, thus reducing
the formation of hydrogen sulphide entering the kiln during the reburning process.
Insufficient lime mud dry solids content and purity may also cause hydrogen
sulphide formation. With modern LMD-filters a TRS content of 10 ppm can easily
be achieved. Vacuum filters are mainly used for lime mud washing. Lime is used to
causticise green liquor (Na2S + Na2CO3) into white liquor (Na2S + NaOH). After
causticising, lime mud (CaCO3) is formed. Normally lime mud is recycled in a lime
kiln, where lime mud is reburnt and new lime is created. Before the lime is sent to
the kiln it must be washed in order to remove residual sodium hydroxide, sodium
sulphide and other sodium salts. The equipment used for lime mud washing are
usually press filters. Single-stage lime mud washing in pressure filters are dominant
(Arpalahti et al. 2000).
Improved lime mud washing can reduce the residual content of white liquor in
the mud from 100 mg/L to 0–30 mg/L. The lime mud dryness in older mills is
typically 60–65 %, while modern mills using filters with a larger specific area and
better dewatering capacity typically perform at 70–80 % dryness. The more
efficient filters reduce the concentration of sodium sulphide in the lime mud through
both washing and oxidation. Sodium sulphide is oxidized to sodium thiosulphate by
passing air through the mud mat on the filter. The lower concentration of sodium
sulphide in the lime mud reduces the formation of hydrogen sulphide in the lime
kiln during the mud drying process. Improved washing of lime mud has been
practiced since the late 1980s in kraft pulp mills. Monitoring of residual sodium
hydroxide is required to avoid plugging of the lime kiln (SEPA-Report 4713-2 1997b).
Improved lime mud washing and filtration (LMD-filter) can reduce the residual
content of white liquor in the mud from 100 mg/l to 0–30 mg/l in modern filters. The
lime mud dryness can be increased to 70–80 %. In addition to energy savings the
operation of the kiln becomes more stable. The LMD-Filter keeps the remaining
sodium content in the lime mud at a low level, which also prevents process distur-
bancies like ring formation. Operational data Improved washing of lime mud is
common practice in pulp mills in Europe. Monitoring of residual sodium hydroxide
is required to avoid the damming of the lime kiln. No specific data concerning the
effectiveness of this measure have been provided.
4.24 Technologies That can Help Achieve Practical Minimum Energy Consumption 163
The main achieved environmental performance is possible reduction of hydrogen

sulphide in the lime kiln, which depends mainly on the availability of sodium in the
lime and the sulphur content of all fuels fed to the lime kiln. At the lowest sulphur
input a small reduction can be achieved but with higher sulphur inputs the effect can
be non-existent or detrimental. If washed to a too low sodium content, the emissions
of TRS and also particulate emissions from the lime kiln tend to increase. Improved
washing of lime mud has been practiced in several pulp mills in Europe. Investment
costs are typically 1–1.5 MEuros (European Commission 2001). Driving force for
implementing this technique is the reduction of hydrogen sulphide (TRS) and
odours from the flue gases of the lime kiln (SEPA-Report 4713-2 1997b).
4.24 T
echnologies That can Help Achieve Practical
Minimum Energy Consumption
Current pulp and paper facilities in many countries are nearing the end of their
operating life and will need to be replaced over the next 10–15 years. This presents
an excellent opportunity for new technology deployment to have an impact on
energy savings in the sector in the medium term. This section describes few
technologies which can help achieve minimum energy consumption.
4.24.1 Impulse Technology for Dewatering of Paper
Impulse technology is a high-intensity web consolidation technique in which water

is removed from a wet paper web by the combined action of mechanical pressure
and intense heat. Impulse technology implements the positive effect of increased
web temperature on both dewatering rate and web consolidation. The basic c oncepts
of impulse technology stem from Douglas Wahren’s invention and vision of com-
bining pressing and dewatering of paper by exposing the sheet to a heated pressing
surface. Later, it was realised that high temperatures have the potential to modify
and improve the paper surface. In its present form, the process is a direct evolution
of the idea originally proposed by Wahren (1978) and later named “Impulse Drying”
(Arenander and Wahren 1983). The wet pressing and drying operations can be
combined into a single event by pressing the sheet in a nip formed between a
felt-covered shoe and a solid roll. The latter is heated externally to temperatures
exceeding 200 °C.
Impulse technology is aimed at decreasing the investment costs and reducing the
operational costs of a paper machine (Stenström 1989; Persson 1994; Nilsson
1998). Although impulse pressing of paper uses high-grade energy for dewatering
the sheet, it has generally been postulated to be economically advantageous for the
following reasons:
–– Uses less energy than conventional drying because all water may not need to be
evaporated
–– Permits substantially higher speeds and drying rates than conventional design
–– Eliminates or strongly reduces capital costs for bulky drier sections, and associ-
ated peripheral equipment
This technology has the potential for energy saving and may provide opportunities
to achieve high solids content after the impulse unit and thus saving heat energy for
subsequent drying. The paper web reaches a dryness of about 40 % in an ordinary
press section. In extended nip presses the web may reach dryness levels of about
50 %. From impulse drying, some reports have stated dryness levels of 55–65 %
before the drying section, which gives a possibility to decrease the heat
consumption. Higher dryness levels means that less water has to be evaporated in
the drying section by means of steam, and the drying section could be made smaller
(shorter). The technology is also expected to provide a smooth paper surface with a
high mechanical integrity and a sheet that retains a high bending stiffness.
This combination of properties is of great value both in packaging materials and in
printing papers.
As stated earlier, impulse technology tries to combine pressing and drying into a
single compact process. The wet paper web is exposed to an intense impulse of heat
energy under pressure between a press element and a heated element in a paper
machine. This induces a sudden increase of the surface temperature of the paper to
considerably higher temperatures than employed in traditional technology. When
the paper web gets into contact with the hot surface, generated steam starts to
displace water in the paper web. The hot side of the web will be compressed due to
thermal softening and may be subject to chemical modification. The web enters a
second impulse stage immediately after the first unit. In the second stage, which acts
from the reverse side, water is displaced in the reverse direction. The two impulse
steps must be properly balanced to produce a symmetrical sheet.
By increasing the dryness of the paper sheet from 50 to 51 %, there will be
about 35 kg less water/t of paper to evaporate. Thus, the impulse drying technology
has the potential of reducing the amount of water to evaporate by 175–350 kg/t
of paper. This would simply save the amount of steam consumption by 175–
350 kg/t or about 0.44–0.9 GJ/t of paper (assuming 2.5 MJ/kg steam), correspond-
ing to about 10–25 % of present steam consumption in papermaking. However,
when calculating the energy saving, the energy needed for the impulse drying
itself must be taken into account. While for impulse drying high temperatures are
required, steam cannot be utilised. On the other hand, paper mills normally have
excess amount of steam available which is also a less expensive energy. Thus,
the need for high value energy, like electricity decreases the possible benefits for
environment and the potential for profitability (Talja et al. 1998; SEPA Report
4712-4 1997a).
4.24.2 E
nergy Efficient Thermo-Mechanical
Pulping (TMP) Processes
The TMP process is a heavy energy user. It consumes large amounts of electrical
energy in the range of 1600–3200 kWh/ADt. The process shows a great flexibility
in many respects and it is not likely that the industry would switch the existing TMP
processes to PGW (apart from some cases), which consumes less power (about
600–1200 kWh/ADt less) than TMP production for the same grades (SEPA-Report
4712-4 1997a; European Commission 2001). Therefore, a lot of development work
has been focusing on reduction of the power consumption in the TMP process.
There have been promising pilot trials such as the KCL multistage process, which
show that significant power reductions of about 10–15 % (200–450 kWh/t) are
possible by changing the refining strategy. This claim cannot be fully verified at
present stage. However, since the mid-1990s, there are also a few mill-scale applica-
tions of new energy efficient TMP processes like RTS ThermopulpR. RTS process
combines conditions of a low residence time [R] at a temperature [T] exceeding the
glass transition temperature of lignin and elevated disc speed [S]. These processes
consume substantially less energy than “normal” TMP processes. Few examples for
energy efficient development in TMP pulping are presented below:
4.24.2.1 High-Speed and High-Intensity TMP Refining
An example is the RTS refiner. It usually operates up to 2300 revolutions per minute
and 5.5 bar over pressure. References are e.g. Norske Skog Walsum (DE), Norske Skog
Golbey (FR), Holmen Halstavik (SE), Iggesund Paperboard, UK), UPM-Kymmene
Stracel (FR), Norske Skog Follum (NO) (European Commission 2013). Several lines
of the ThermopulpR process went into operation both in Europe and North America in
the mid-1990s. The first RTS installation was at Perlen Papier AG, Switzerland, in
1996. Both system can be considered as available techniques but would normally only
be installed at new mills or when existing equipment is replaced. The first full-
scale experience suggests that an energy reduction in the order of 15 % compared to
conventional TMP is possible with acceptable pulp quality using this system.
4.24.2.2 Chip Pretreatment
Andritz has developed the RT Pressafiner pretreatment for chips to be treated before
main-line refining (European Commission 2013). In the RT TMP process, the chips
are first macerated in a pressurised RT Pressafiner chip press before entering the
main-line refiners. RT treatment is being used at Holmen Braviken, SE, before
single-stage DD refining, and in North America combined with RTS Twin SD-refiners.
The reduction in specific energy consumption is about 10 %, i.e. 100–180 kWh/t.
TMP mills that use this chip pretreatment may reduce their waste water load by
using a washing stage (plug screw) before refining and bleaching. This reduces
COD and the extractives content measured as DCM in the pulp by around 30 %. The
low volume but highly concentrated pressate may undergo a specific waste water
treatment (Gorski et al. 2009).
The objective of the RTS conditions, according to Andritz, is to thermally shock
the wood fibre while in chip form, subjecting it to higher temperatures for a shorter
period of time and thus making it more receptive to initial defibreization during the
primary refining operation. RTS also differs from a standard TMP process in that
the rotational speed of the primary refiner is much higher.
The concept of reduced energy consumption by increasing the disc speed of
refining has been established using single disc and double disc refiners in both pilot
plant and mill applications. The speed increase for this process typically comes
from installation of a speed increaser between the refiner motor and the refiner. RTS
is designed to avoid the shortcomings of the TMP process that produces stronger
fibres but darkens the pulp. By exposing fibres to high temperatures while still in
chip form, the heating occurs mainly through the lumina cavities, which means that
the cellulose wall layers are heated first, while the middle lamella of the fibre has the
least exposure to heat. The low-retention time at elevated temperature reduces
thermal darkening reactions of the colour bodies associated with the middle lamella
lignin. The result is a brighter and more easily bleached pulp. As for strength, most
fractured fibres that are produced by a conventional TMP process occurs during
primary refining. Since RTS softens chips by increasing fibre wall temperature prior
to primary refining, fibre cutting is reduced, and fibre development is improved.
Thus RTS can reduce or eliminate the requirement for kraft pulp in some paper
grades. Also, RTS operation at high refiner disc speed reduces the residence time
between refiner plates and increases specific refining power. This produces an
improved pulp “fingerprint” that establishes potential pulp quality.
High-speed refining, is the key to improved operator efficiency. By subjecting
thermally softened chips to higher refiner speeds for extremely short periods, high-
speed refining can improve pulp quality while using 10–25 % less electrical power.
RTS system can produce equivalent pulp strength at lower energy. Conversely, RTS
will produce pulp with dramatic increases in tear and bonding strength at specific
energy levels comparable to conventional TMP.
Energy savings must be balanced with investment cost. It can be expected that
the new technology will only be implemented gradually due to the remaining
lifetime of present equipment and plants (Lönnberg 2009).
4.24.3 N
ew Energy Efficient Bleached Chemi-Thermo
Mechanical Pulping Processes
For chemi-thermo mechanical pulping (CTMP) also, the main research work
focused on energy reduction in refining. The production of conventional aspen
chemi-thermo mechanical pulp at 250 ml CSF still requires 1350–1500 kWh/ADt.
Caustic application ahead of the primary refiner, decreases the applied specific
refining energy and develops the strength properties. Different to the conventional
CTMP, the P-RC APMP process (mild Preconditioning of the chips, Refiner
Chemical Alkaline Peroxide Mechanical Pulping) uses alkaline peroxide solutions
ahead of refining, which allows higher alkali charges before refining resulting in a
decrease of refining energy down to 1050–1200 kWh/ADt at the same freeness. In
addition, the efficient chip pretreatment yields well impregnated flexible fibres
which can be refined to the required freeness level with low consistency refiners in
the second stage and in reject, which drops the specific energy consumption by
another 100–150 kWh/ADt without compromising strength properties. Most of the
recent hardwood bleached CTMP installations apply the P-RC-APMP technology,
which show the energy savings potential. Also low consistency refining in the
second stage and in reject has been implemented in industrial operation with the
desired results (Hill et al. 2009; Sabourin 2007; Sabourin et al. 2003).
4.24.4 Use of Enzymes During the Refining of TMP
The addition of enzymes to the wood chips between the first and secondary refiner
can hydrolyze the hemicellulose and improve the fibre freeness of the cellulose
fibres. This would allow to reduce the necessary time in the secondary refiner. The
treatment with Novozym 476 (Cellulase) shows a significant saving of electricity in
the second stage of refining and in the reject refiner by softening cellulose fibres
(−160 kWh/t pulp). Kazymov (2010) studied the effects of pectinase, endoglucanase
and a mixture of enzymes on three different size raw materials – normal size chip,
crushed chip and water impregnated, instantly preheated, pressed and then fibreized
at 400 kWh/t chip further named fibreized pulp showed that 5 kg/t of endoglucanase
reduced the energy consumption by 20 % while the use of 1.5 kg/t of the mixture
of enzymes produced a reduction of about 15 % of energy consumption during
refining. Pectinase at different dosages to a maximum of 5 kg/t and different
treatment times did not show significant effect on energy consumption. These
results differ from those obtained by Sabourin and Hart (2010) who applied two
pectinase treatments to TMP of black spruce (Picea mariana) wood chips and
allowed to react for a period of 2.5 h. The average temperature during the reaction
period was 47–48 °C. Enzymatic effects were studied on two refined pulps (1800
PFI revolutions). Pectinex 3XL® is a polygalacturonase, the enzyme protein used
was separated and purified from Aspergillus aculeatus and Aspergillus niger. The
application dosage was 720 g/t wood. The Novozyme 863® was a more aggressive
enzyme preparation produced by a selected strain of Aspergillus aculeatus. This
enzyme preparation contains polygalacturonase, other pectolytic activities, and a
range of hemicellulolytic activities. It has the ability to disintegrate wood fibre
cell wall material and works well in the temperature range of 25–50 °C. The application
dosage was 830 g/t wood. The specific energy consumption was reduced by 9 % and
9.6 % respectively. The Pectinex 3XL® enzyme treatment successfully improved the
tensile and tears indexes of the resulting pulp through specific surface activity in a
desirable way while Novozyme 863® was somewhat harmful toward some of the
desired pulp properties (Sabourin and Hart 2010). So far, this technique has been
tested in several laboratory tests and on pilot plant scale. Also, short-term tests
(1.2 weeks) have been carried out in the TMP line of UPMK Kymmene/Rauma
mill. Main environmental benefit derived from the application of the technique
would be the reduction of electricity consumption in the second refiner, due to
shorter refining time. Trials made so far point out that energy savings in the reject
refiners of up to 10–15 % could be possible.
4.24.5 Condebelt Process
The Condebelt drying process is a new paper drying technology that is based on the
condensing belt principle. Metso developed the CondeBeltTM drying system in the
early 1990s. It is being used in several mills in Europe and Korea. The system was
originally designed as an alternative to a Yankee Dryer for high speed coated board
machines. The process conditions experienced by the web during Condebelt drying
are essentially similar to those prevailing in the so–called press drying experiments.
Condebelt drying has been studied over a span of many years by means of several
static units, as well as a pilot stage dynamic device. Based on these experiences, as
well as several theoretical studies, designs have been developed for doing Condebelt
drying as a production process. Condebelt drying is versatile, in that the process
conditions can be changed to produce optimum quality for most paper and board
grades. In this capability the Condebelt process is much superior to conventional
cylinder drying.
In Condebelt drying, the paper is dried in a drying chamber by contact with a
continuous hot steel band which is heated either by steam or hot gas. The water from
the band is evaporated due to the heat from the band. This drying technology has the
potential to replace the drying section of paper machine entirely, with drying rate 5
to 15 times higher than the conventional steam drying. However, condebelt drying
is not suited for high basis weight papers. Although the technology is in use in
Europe and Korea, it has found limited application in the United States.
The Condebelt process offers several advantages over conventional cylinder
drying. In the Condebelt drying concept a wet web (sheet of paper) is carried
between two steel bands, one hot band and one cold band, and subjected to high
pressure (max. 10 bar) and temperature (max. 180 °C) (Fig. 4.13). Heat is trans-
ferred from the hot band to the sheet, moisture evaporates and traverses through
two wire screens to the cold band, where it condenses. The condensate is carried
away by the thickest of the two wire screens. The sheet is dried in absence of air. In
contrast with conventional pressing technologies and impulse drying the pressure is
maintained for several seconds, resulting in good paper qualities. Drying rates are
5–15 times as high as in conventional drying. Condensing belt drying can dry paper
from 44 % (exit conventional pressing section) to 94 %. The technical life of paper
Fig. 4.13 Schematic of Condebelt drying process (Based on Lee et al. 2000)
machines is approximately 20 years and investment costs are extremely high

(Retulainen et al. 1998; Ojala 1999). This drying process offers opportunities for
–– Reducing the grammage of board
–– Reducing the weight of corrugated boxes,
–– Increasing the use of recycled furnishes and high-yield pulps
It is best suited to board grades, but also can be used for paper grades. In this
process drying shrinkage of the web is eliminated, and even stiff fibres can effec-
tively be plasticized and bonded to each other. Compared to cylinder drying, this
results in improved strength properties, particularly in the cross-machine direction.
Condebelt drying improves strength properties (20–60 %), surface smoothness,
dimensional stability and resistance against humidity. In Condebelt drying, with
recycled fibres it is possible to obtain the same strength values as with virgin fibres
in conventional drying.
The disintegration of condensing belt dried board requires slightly more energy
than cylinder-dried board. However, the recyclability of the board is good, espe-
cially when the re-made web is dried using the condensing belt process. The
worsening of board properties after multiple recycling and condensing belt drying
is quite moderate. This shows that condensing belt drying can form part of a
ecologically sustainable paper cycle.
Presently, there are few Condebelt drying processes in commercial operation.
Few mills have installed this technology (Retulainen 2001). One installation is
2.5 m wide with a machine speed of 200 m/min and has been running since 1996 at
Stora Enso’s Pankakoski board mill in Finland (Retulainen and Hamalainen 2000;
Retulainen 2001). The other one is 4.5 m wide with a machine speed of 650 m/min
and began operation in 1999 at Dong II Paper Mfg. in South Korea, producing
linerboard and fluting (Lee et al. 2000; Retulainen 2001). This technology can save
an estimated 15 % in steam consumption (1.6 GJ/tonne paper) and can slightly
reduce electricity consumption (20 kWh/tonne paper), with investment costs of
$28/t paper for a retrofit and $110/t for new construction (Martin et al. 2000a).
O&M costs are not expected to be significantly different from current practice (Xu
et al. 2010). As a promising drying technology, Condebelt drying could be widely
applied in the paper industry.
The use of this new drying technology does not result in significant direct energy
savings. However, the strength improvements give the potential for savings through
reduced basic weight. That means, more square meters from the same amount of
fibres can be manufactured without sacrificing product quality. Moreover, because
of the improved paper sheet properties with Condebelt drying, it seems to be
possible to use lower grade fibre material or high yield pulp (e.g. 10 % less wood
per tonne of liner). Higher strength and better protection against adverse moisture
effects can have the effect that surface sizing could often be dispensed with, although
normally they would be used. Although the specific consumption of electric energy
and primary steam roughly equals that of traditional drying, there are greater oppor-
tunities to save heat energy. This is because almost all of the evaporated water and
its latent heat can be recovered from the cooling water at a fairly high temperature
normally about 80 °C. This energy can be used in other parts of the process
also using heat pumping. The environmental benefits are potential savings of raw
material (fibres, sizing agents) and a somewhat higher potential for energy recovery
(Retulainen, 1998; Ojala 1999). Reductions in steam consumption are estimated to
be 15 %, or 1.6 GJ/t-paper, with a slight reduction (~20 kWh/t-paper) in electricity
consumption (Martin et al. 2000a). Capital costs are high. Investment cost of $28/
ton paper has been estimated for retrofit installations, and $110/t for greenfield
plants (1998 dollars) (Martin et al. 2000a).
4.24.6 High Consistency Forming
In the state-of-the-art papermaking process, paper products are formed from a low
consistency water suspension approximately 0.6–1.0 % made up of fibres, fillers
and chemicals. This suspension is pumped through a head-box that spreads it on a
plastic wire. With the complex design of the head-box, sufficient turbulent flow
conditions are created to control the homogeneity of the papermaking suspension
through the subsequent drainage process. Due to low consistency, chemicals have to
be used to increase the retention of furnish components on paper. The recovery of
un-retained material and water consumes a lot of energy and requires numerous unit
operations and pieces of process equipment. Thus increasing consistency would be
a technological step forward for papermaking.
High consistency (HC) forming was first introduced in the late 1960s when the
industry was concerned about the cost of wastewater treatment. In high consistency
forming, the furnish which enters at the forming stage has more than double the
consistency (3 %) than normal furnish. This measure increases forming speed, and
reduces dewatering and vacuum power requirements (Maleshenko et al. 2008;
Gullichsen et al. 2009; Elaahi and Lowitt 1988). Application of this technology is
limited to specific paper grades, especially low-basis weight grades such as tissue,
toweling, and newsprint. Electricity savings are estimated at 8 % that is about
41 kWh/t of paper (Elaahi and Lowitt 1988; de Beer 1998). High consistency form-
ers are expected to cost $70/t of paper with an additional maintenance cost of $0.72/t
(Jaccard and Willis Enterprises Associates 1996), also assuming that new paper
machine wet ends are similarly costly. This measure is applied to 20 % of current
paper production with exclusion to light grade. HC forming will give a strong
advantage to the pulp and paper industry as such a system can reduce not only
energy but also the use of chemical additives. HC forming integrates well with
closed water circulations and with new heat recovery techniques, and surface
treatment methods. Furthermore, new types of products can be manufactured. HC
papermaking will reduce pumping costs, increase the retention of fibres with fewer
chemicals, and simplify the wet end process. Together with closed water circulation
and higher process temperature, high-consistency forming may lead to a dramati-
cally reduced energy consumption of the production line. The HC system creates a
new platform for the production of many different paper and board products which
will form a paradigm shift in paper production.
It is expected that HC short circulation process will consume 50 % less energy
and 30 % less vacuum energy, and that the capital intensity of the process will be
reduced by 30 %. Due to improved retention, the consumption of chemicals and the
environmental load of the process will also be reduced. Increasing the consistency
in forming was initially studied already in the 1980s, e.g. in Finland but with little
success. The early studies resulted in unacceptable sheet quality due to the difficulties
in maintaining sufficient turbulence during web drainage. However, during recent
years, substantial progress has been obtained through the integration of head-box
and drainage. The operation window of current machines can most likely be w idened
by optimising the whole process, e.g. raw-materials, machinery, clothing and
chemicals. This can however lead to difficulties in dewatering or runnability of the
paper machine. The control of fluidisation and the screening of high-consistency
stock together with product quality, have been found to be major difficulties to
overcome. A breakthrough in HC papermaking would require new technology
where current unit operations, i.e. head-box, drainage and pressing are integrated
together in a compact way, resulting in desired paper structures from high-consistency
furnish. The HC papermaking process would require that the approach and
short circulation systems, fluidisation and dewatering processes take place at high
consistency. Progress is needed in the mixing of fibres and chemicals and in screening,
air removal, fluidisation, dewatering of furnish, and in process control. The develop-
ment of reliable measurement system for the process including web properties is
one of the key tasks for process control. Modeling is needed in dimensioning the
process and in analysing and determining the optimal process concept. Stability of
the process is one of the major concerns. With regard to raw material control, soft
sensors and new measurement techniques will make it possible to identify incoming
material properties, and thus make it possible to take the optimisation and control
further in a proper way. Overall dynamic energy system analysis using simulation
and optimisation will provide solutions that reduce energy losses compared to what
is obtainable with state-of-the-art steady state analysis, e.g. the pinch method. By
orchestrating the production entities dynamically, the intermediate buffers can be
radically reduced. This leads to major energy savings in production systems due
to, e.g. less pumping, and both energy and capital savings in new and rebuilt pro-
duction systems.
Fresh water is introduced to the HC process as shower water and as dilution
water of the chemicals just like in modern processes. To reduce the use of fresh
water, the output streams from screening and fibre recovery should be low in vol-
ume and the combination of former and fibre recovery units should result in high
quality circulation water that has a very low concentration of solids and dissolved
and colloidal substances.
High-consistency forming of paper products requires new innovative process
solutions that will significantly reduce the energy and water consumption in paper-
making processes. Pilot scale studies aimed towards HC papermaking are under
way. Modelling and simulation tools will be an integral part of the development
work both at the unit process level and in analysing how mill concepts will be
changed as a result of HC forming. New measurement techniques will be used in the
development of models and control methods of the forming process.
4.24.7 Black Liquor and Hog Fuel Gasification
Black liquor gasification (BLG) is an emerging technology with a long research and
development history. BLG entails pyrolyzing concentrated black liquor into an
inorganic phase and a gas phase through reactions with oxygen or air at high
temperatures. BLG technology can be an alternative to using a recovery boiler to
produce electricity, chemicals, or fuels such as dimethyl ether (DME), synthetic gas
(syngas), methanol, hydrogen, or synthetic diesel (Naqvi et al. 2010, 2012). BLG
can also be integrated with combined-cycle (CC) technology (BLGCC), which has
potential to produce significantly more electricity than current boiler/steam turbine
systems and could even make the mill an electricity exporter (Martin et al. 2000b).
Alternatively, the syngas can be used as a feedstock to produce chemicals, thereby
using the pulp mill as a biorefinery (Worrell et al. 2004, 2010).
There have been several demonstration and commercial units built for both black
liquor and hog fuel gasification. All existing units in the United States have been
atmospheric units. Gasification is a promising technique for pulp mills for the
generation of surplus of electrical energy but yet to achieve widespread acceptance.
Production of a combustible gas from various fuels – coal, wood residues,
black liquor – is possible through different gasification technologies. The
principle of the gasification of black liquor is to pyrolyse concentrated black
liquor into an inorganic phase and a gas phase through reactions with oxygen (air)
at high temperatures.
Fig. 4.14 Integrated gasification and combined cycle (IGCC) (Based on Sricharoenchaikul 2001)
Gasification may become part of integrated gasification and combined cycle

(IGCC) operation, or lead to pulp mills becoming biorefineries (Larsen et al. 2003).
Figure 4.14 shows a schematic for the black liquor IGCC. In the gasifier, the organic
matter in black liquor is partially oxidized with an oxidizing agent to form syngas,
and the condensed phase is left behind. The syngas is cleaned in order to remove
particulates and tars and to absorb inorganic species which are alkali vapour s pecies,
sulphur dioxide, and hydrogen sulphide. This is performed to prevent damage to the
gas turbine and to reduce emissions of the pollutants. The clean syngas is burned in
gas turbines coupled with generators to produce electricity. Gas turbines are
inherently more efficient than the steam turbines of recovery boilers because of their
high overall air fuel ratios (Nilsson et al. 1995). The hot exhaust gas is then passed
through a heat exchanger typically a waste-heat boiler to produce high-pressure
steam for a steam turbine and/or process steam. The condensed phase continuously
leaves the bottom of the gasifier and must be processed further in the lime cycle for
recovering pulping chemicals.
In recovery boilers, virtually all of the alkali and sulphur species leave in the
smelt mostly as sodium sulphide and sodium carbonate, but in gasifiers, there is a
natural partitioning of sulphur to the gas phase (mainly hydrogen sulphide) and
alkali species to the condensed phase after the black liquor is gasified. Because of
this inherent separation, it is possible to use alternative pulping chemistries that
would result in higher amounts of pulp per unit of wood consumed (Larsen et al.
1998, 2003). Gasification at low temperatures thermodynamically favours a higher
sodium/sulphur split than gasification at high temperatures. This actually results in
higher amounts of sulphur gases at low temperatures. A large amount of the black
liquor sulphur species leaves the low-temperature process as hydrogen sulphide.
It may be recovered via absorption to facilitate alternative pulping chemistries.
Compared to the current technology, the partitioning of sodium and sulphur in

black liquor gasification requires a higher capacity for the lime cycle. The sodium/
sulphur split results in a higher amount of sodium carbonate in the green liquor. This
is because less sulphur is available in the smelt to form sodium sulphide. For each
mole of sulphur that goes into the gas phase, one more mole of sodium carbonate is
produced in the condensed phase (Larsen et al. 2003). The increase in sodium
carbonate results in higher causticization loads, increases in lime kiln capacity, and
increases in fossil fuel consumption to run the lime kiln. This leads to higher raw
material and operating costs, which must be reduced in order to make the gasification
process economically favorable.
Black liquor gasification can be conducted at low temperatures and also at high
temperatures, based on whether the process is conducted above or below the melting
temperature range (650–800 °C) of the spent pulping chemicals (Sricharoenchaikul
2001). In low temperature gasification, the alkali salts in the condensed phase
remain as solid products while molten salts are produced in high-temperature
gasification. Low temperature gasification is advantageous over high-temperature
gasification because gasification at low temperatures yields improved sodium and
sulphur separation. Additionally, low-temperature gasification requires fewer con-
straints for materials of construction because of the solid product. However, the
syngas of low-temperature gasification may contain larger amounts of tars, which
can contaminate gas clean-up operations in addition to contaminating gas turbines
upstream of the gasifier. These contamination problems may result in a loss of fuel
product from the gasifier (Sricharoenchaikul 2001). Low temperature gasification
processes work below 715 °C and the inorganic salts are removed as dry solids.
High temperature processes operate above 900 °C and an inorganic salt smelt is
obtained.
Several companies conducted trials to develop a commercially feasible process
for black liquor gasification (Whitty and Baxter 2001; Whitty and Verrill 2004).
However, currently only two technologies are being commercially pursued:
MTCI (low temperature) (Durai-Swamy et al. 1991; Mansour et al. 1992, 1993,
1997; Rockvam 2001; Whitty and Verrill 2004)
MTCI has two projects running today, both in mills with a sodium carbonate semi-
chemical cooking process. The first project is for Georgia Pacific Corporation’s
Big Island mill in Virginia. This system is a full-scale gasifier, designed to
process 200 ton dry solids per day and is fully integrated with the mill (DeCarrera
2006). The second project is for the Norampac Trenton mill, Ontario, Canada
which had no chemical recovery before the steam reformer commission began
2003 (Middleton 2006; Newport et al. 2004; Vakkilainen et al. 2008). This
gasifier has a processing rate of 115 ton DS/day.
Chemrec (high temperature) (Brown and Landälv 2001; Kignell 1989; Stigsson
1998; Whitty and Nilsson 2001; Whitty and Verrill 2004).
Chemrec is working on both an atmospheric version and a pressurized version of a
high temperature downflow entrained flow reactor. The atmospheric versions
mainly considered as a booster to give additional black liquor processing capacity.
The pressurized version is more advanced and would replace a recovery boiler or
function as a booster. Chemrec has built and operated a black liquor gasification
plant in Piteå in northern Sweden and later together with partners added a bio-
DME synthesis plant on the same site. The subsidiary owning this development
plant is now sold to Luleå University of Technology for the plant to be used in
continued R&D work. The pressurized, oxygen-blown gasifier of this plant has
till date been operated more than 18 000 h, consistently producing syngas of very
good quality. The system includes the processes of gasification and quenching,
gas cooling and gas cleaning. The produced gas has been determined to contain
the following gases (Lindblom 2006):
–– 41 % hydrogen
–– 31 % carbon dioxide
–– 25 % carbon monooxide
–– 2 % methane
–– 1.4 % hydrogen sulphide
The aim of the program is a verified process that will be ready for scale up (15
times) as well as an optimized integration of the process with the pulping cycle.
Figure 4.15 shows the CHEMREC DP-1 plant.
Since 2011 the syngas produced has been used for synthesis of bio-methanol and
bio-DME (dimethyl ether). The bio-DME produced has been used in very successful
heavy truck fleet trials conducted by Volvo Trucks within the pan-European
BioDME project. Overall, this extended period of operation has validated the
Chemrec gasification concept and provided all information required for commercial-
scale implementation. Effective from Dec 31, 2012 these plants have been transferred
Black liquor White liquor

Short time
Atomizing Gasification Cooling contactors
medium water
Boiled
Oxygen feed
water
Reactor LP steam*
Separation of
gas and smelt Raw gas Gas cooler
MP steam*
Sulphur removal
Quench
Purified and
Particulate cooled syngas
removal and (to flare)
Green liquor gas cooling
Condensate
*Cooling water in DP1
Weak wash
Fig. 4.15 The CHEMREC DP-1 plant (Source: www.chemrec.se/admin/UploadFile.aspx?path=/

UserUploadFiles/2005%20DP-1%20brochure.pdf. Reproduced with permission)
to Luleå University of Technology (LTU). Also the operating and development

personnel at the plant are now employed by LTU. In December 2012, the Swedish
Energy Agency approved funding supporting the continued operation of the plants
to make it available for new research and development programs. Chemrec actively
participates in these programs and has retained the right of access to the plant
for future trials, e.g. with feedstock of specific customers. Chemrec in its new form
will thus for further development work rely largely on this new network structure
and the core organization will be heavily focused on the commercialization of
the technology.
The CHEMREC BLGCC system has several advantages over recovery boilers;
the most significant being dramatically improved electricity yield. The CHEMREC
BLGMF system combines black liquor gasification with a chemical synthesis plant
for production of green automotive fuels such as Methanol or DME (Di Methyl
Ether). The new combined pulp and chemicals production facility requires a dditional
energy to compensate the pulp mill for the withdrawal of the new green automotive
fuels. The efficiency of the CHEMREC BLGMF system for generating the new
green automotive fuels is very high and the cost of these fuels from a full scale unit
is competitive with petroleum based alternatives. The CHEMREC BLGH2 system
utilizes the syngas from the black liquor gasifier as feedstock for novel green
hydrogen production.
The investment cost for a full-scaled PBLG unit is estimated to be slightly higher
than for a new conventional recovery boiler (Warnqvist et al. 2000). However,
pressurized black liquor gasification with an integrated combined cycle (BLGCC)
has the potential to double the amount of net electrical energy for a kraft pulp mill
compared to a modern recovery boiler with a steam turbine (Axegård 1999). For
more closed systems with less need of steam, this increase in electrical energy will
be even higher. Another advantage with the PBLG process is the increased control
of the fate of sulphur and sodium in the process that can be used to improve the pulp
yield and the quality for the mill. This control is very important for the green liquor
quality and is quite limited with a conventional recovery boiler. A disadvantage with
gasification is that it will increase the causticizing load. However, BLG has a lower
requirement for make-up salt cake compared to the recovery boiler. Even though
the PBLG process might have a lot of advantages compared to the recovery boiler
there are still a number of uncertainties for this technology.
Black liquor gasification is still a developing technology. Only small (100–
350 tds/d) commercial atmospheric units have been built (Bajpai 2010; Naqvi et al.
2010). Similar size pressurized demonstration units do not yet exist. It will take
some time before reliable large units are available. Black liquor gasification can
produce more electricity (Vakkilainen et al. 2008). Current commercial atmospheric
processes are not as energy efficient as the kraft recovery boiler process (Grace and
Timmer 1995; Mckeough 2003). The black liquor gasifier needs to operate under
pressure to have an electricity advantage.
The following benefits and costs have been identified for BLG (Worrell et al.
2004; Gebart 2006; IEA 2009; Cheremisinoff and Rosenfeld 2010; Program 2011;
Chemrec 2012):
–– Increases pulping process energy recovery by 10 %
–– Increases power production by two to three times at the pulp mills that exported
electricity sold to power grid
–– BLGCC system has investment 60–90 % higher than for standard boiler system,
ranging from $200–400 million
–– Increases pulp yield by about 5–7% if done in conjunction with significant
changes in pulping conditions
Even though there are significant gains to be made, there still remain many
unresolved issues (Tucker 2002 and Katofsky et al. 2003) listed below:
–– Finding materials that survive in a gasifier
–– Mitigating increased causticizing load
–– How to startup and shutdown
–– Tar destruction
–– Alkali removal
–– Achieving high reliability
The full impact of the black liquor gasification on recovery cycle chemistry
needs to be carefully studied with commercial units. The first large demonstration
units will cost 2–3 times more than a conventional recovery boiler. Although this
will improve with time, price will hinder the progress of black liquor gasification. A
small BLG with a commercial gas turbine size of 70 MWe requires a mill size of
over 500,000 ADt/a. Commercial gasifiers probably need to be over 250 MWe in
size. It is therefore expected that full size black liquor gasifiers will be built in new
greenfield mills, and not as replacement units of old recovery boilers.
4.24.8 Partial Borate Autocaustising
This technique makes it possible to produce caustic (sodium hydroxide) directly in

the recovery boiler and improves the lime kiln and recausticisation operations by
reducing causticising loads and the amount of lime processed through the system.
The partial borate autocausticising process occurs when sodium borates are added
to the kraft liquor at sub-stoichiometric levels (Björk et al. 2005). A portion of the
sodium carbonate is causticised in the recovery boiler. The causticisation of the
remaining sodium carbonate is completed in a conventional recausticising plant of
the pulp mill with a reduced quantity of lime. The technology may appear as an
attractive option particularly for kraft pulp mills where incremental causticising and
lime kiln capacity are required. Mill-scale trials have shown that there are no major
side effects on the mill operations. The major findings of the studies suggest that
borate present in cooking liquor presents the following advantages (Bujanovic et al.
2003; Eckert et al. 2005):
–– Increases pulp yield

–– May decrease rejects
–– Improves the selectivity of lignin removal
–– Can increase pulp viscosity at the same kappa number
–– Does not require capital investment since the autocausticising reaction occurs in
the existing recovery boiler
The principal autocausticising reaction that takes place in the recovery boiler
furnace occurs between sodium metaborate and sodium carbonate in the molten
smelt to form trisodium borate. The critical parameters of the process are the tem-
perature and Na/B ratio in the black liquor. Trisodium borate reacts with water in the
smelt dissolving tank to form sodium hydroxide and regenerate NaBO2 (Tran et al.
2001; Bujanovic et al. 2003; Michniewicz and Janiqa 2010). The partial borate
autocausticising process occurs when sodium borates are added to the kraft liquor
at sub-stoichiometric levels (Björk et al. 2005). A portion of the sodium carbonate
is causticised in the recovery boiler. The causticisation of the remaining sodium
carbonate is completed in a conventional recausticising plant of the pulp mill with a
reduced quantity of lime. The technology may appear as an attractive option
particularly for kraft pulp mills where incremental causticising and lime kiln capacity
are required. Mill trials have shown that there are no major side effects on the mill
operations. The success of the technology depends greatly on whether the boron-
containing black liquor can be effectively processed in a recovery boiler, and on the
degree of completion of the reactions that produce trisodium borate in the boiler.
Promising environmental benefits are connected with a reduction of the emissions
from the lime kiln and a reduced consumption of energy or fuel by a lime kiln.
Several mill trials with partial borate autocausticisation have been conducted and
the problems encountered have been resolved. The technology is now being used at
several mills in Sweden, Brazil, Indonesia and the United States. The results show
that the technology works. It allows the lime consumption to be reduced by an
amount proportional to the level of autocausticisation (depending on the Na/B molar
ratio in the liquor cycle). No negative effect has been found on pulp properties,
equipment corrosion, digester operations, pulp washing, black liquor evaporation,
recausticizing and lime kiln operations. For a greenfield kraft pulp mill, with proper
equipment design and operation, the technology has the potential to eliminate com-
pletely the causticisation plant and lime kiln, making the kraft process much simpler
(Hoddenbagh et al. 2001; Kochesfahani and Bair 2002; Kochesfahani et al. 2006).
Six mill trials are reported by Kochesfahani and Bair (2002), who carried out
short-term trials to evaluate the effect of the technology on specific parts of the mill,
and long-term trials to demonstrate the overall effects of the technology on the mill
operations. At autocausticisation levels up to 25 %, no undesired effects could be
observed on digesters, pulp quality, brownstock washing, black liquor evaporation,
lime recausticisation or kiln operations. The most apparent effect of autocausticisation
on the liquor cycle is the increase in total inorganic salts in the system. This leads to
an increase in the throughput of solids for evaporators, concentrators and recovery
boilers. Because of the endothermic nature of the autocausticisation reaction, the
black liquor heating value decreases. The evaporation load is not affected, however,
and so the temperature may decrease in the recovery boiler. Even though
Kochesfahani and Bair (2002) report the conversion of autocausticisation to be
sensitive to operation conditions, especially temperature, they claim that the overall
impacts on the recovery boiler are manageable.
Partial borate autocausticizing may offer cost savings and environmental benefits
to kraft pulp mills that are recausticising-limited by relieving production bottle-
necks in the liquor cycle without costs for the capacity growth of the conventional
causticisation plant and lime kiln. The benefits are obtained through decreasing
the lime kiln load and fuel usage or reducing fresh lime purchases and lime mud
disposal. Some benefits also result from the increase in pulp yield at the digester
and/or potential decrease in alkali charge. However, addition of borate increases the
solids content in fired black liquor, especially at high levels of autocausticising and
may result in a decrease in black liquor heating value and in steam production (Mao
et al. 2006; Tran et al. 2001; Bujanovic et al. 2003; Michniewicz and Janiqa 2010;
Björk et al. 2005;Eckert et al. 2005).
4.24.9 Biorefinery
Much has been discussed about biorefinery concept in recent years (Bajpai 2012a).
It was a subject mentioned in President Bush’s 2006 State of the Union Address. It
is a component of AF&PA’s Agenda 2020. Extracting hydrogen, and other chemical
feed stock, from wood chips prior to pulping has the potential for a significant
change in the way pulp mills utilize/produce energy. Net energy efficiency impact
of a biorefinery is currently being investigated . The development of an integrated
forest biorefinery (IFBR) would enable the industry to increase its revenue by
producing bioenergy and new biomaterials in addition to traditional wood, pulp and
paper products. The IFBR concept also addresses the societal need to use renewable
resources rather than fossil fuels to produce commodity products, liquid fuels and
electricity. The initial visualised IFBR would be based on sulphur-free, alkaline
pulping of hardwood with an alkaline hemicellulose extraction step prior to pulping
and spent pulping liquor gasification and lignin precipitation after pulping. New
products from an IFBR based on alkaline pulping include electric power, new wood
composites, liquid fuel, ethanol, chemicals and polymers. Pre-extraction generates
a feed stream for new bioproducts, while decreasing alkali consumption, increasing
delignification rate and reducing black liquor load (Jönsson et al. 2011; Mäkinen
et al. 2011; Wang et al. 2012; CEPI 2009). Black liquor gasification and/or lignin
precipitation are an integral part of the IFBR, with the synthesis gas and precipitated
lignin being the feed for liquid fuel and carbon fibres, respectively. The additional
energy requirements of the IFBR would be met by gasification/combustion of waste
biomass. The key to the successful implementation of the forest biorefinery is to
identify possible products that can be economically produced by a pulp and paper mill.
Process integration tools can be used to identify these products. A roadmap can be
developed once the products have been identified. The successful implementation of
the forest biorefinery will likely be mill specific, and will in many cases require
strategic collaborations with experts.
4.25 Partial System Closure
The pulp and paper industry is faced with mounting environmental, political and
economic pressures to reduce the volume and toxicity of its industrial waste water.
During the last few years, the concept of system closure has been gaining popularity
in the forest products industry. Bleach plant closure, through filtrate recycle, to the
recovery cycle, is becoming attractive in light of the stringent environmental regula-
tions (Johnson et al. 1996; Gleadow and Hastings 1995; Gleadow et al. 1996; Albert
1995, 1997; Bajpai and Bajpai 1999). Complete closure, however, is difficult with
chlorine-based sequences, because the resulting bleach liquor chloride level is a
threat to the recovery boiler. No bleach plants at papergrade bleached kraft mills
are known to be operating effluent-free on a continuous basis. Mills with oxygen
delignification and a low chlorine dioxide charge may be able to close the bleach
plant if chloride levels in the recovery cycle are monitored carefully. Fibreline and
bleach plant process changes that reduce elemental chlorine demand, such as
extended cooking, oxygen delignification and high chlorine dioxide substitution,
have been used for several years; but lower AOX limits, changing markets surround-
ing the use of chlorine chemicals, and the drive for bleach plant closure to reduce
COD emissions have focused interest on TCF bleaching. The TCF bleach plant uses
no chlorine-based bleaching chemicals, eliminating concerns about dioxins and
furans and the more general measurement of chlorinated organic compounds. An
added benefit of TCF processes is the high potential for complete reuse of bleach
plant filtrates in the recovery cycle.
Partial closure of the bleach plant and other mill systems, leads to increased
concentrations of organics (dissolved wood compounds) and inorganics, often
called non-process elements (NPE). Consequences of this are listed below:
–– Increased corrosion in digesters, evaporators and recovery boilers
–– Depression of recovery boiler capacity and efficiency
–– Scaling and deposits in bleach plants, digesters and evaporators
–– Increased consumption of chemicals
–– Variable pulp quality.
–– Efficiency of a Q stage in removing transition metal ions is reduced by extensive
system closure due to the inhibition created by the Donnan effect (KAM Report
A100 2003).
Therefore, before implementing a closure strategy, the consequences for mill
operations listed below have to be analysed:
–– Mill uptime
–– Construction materials
4.25 Partial System Closure 181
–– Mill personnel safety

–– Pulp quality
Kraft mill bleach plant effluent flows usually range from 10 to 30 m3/ADt in
modern mills. Many European mills have flows between 15 and 25 m3/ADt. Few
mills have bleach plant effluent flows under 10 m3/ADt. There are still many mills
having bleach plant effluent flows above 30 m3/ADt. The two main strategies for
bleach plant closure are presented below (Beca AMEC 2004):
Increased recycle of filtrates within the bleach plant –
This results in reduced fresh water consumption and bleach plant effluent flows.
However, it does not lead to a reduction of specific emissions like AOX and COD on
a mass basis (example kg/ADt)
Recycle of bleach plant filtrates to the recovery system –
Only alkaline bleach plant filtrate is recycled generally, but a few mills also
recycle acidic filtrate. The filtrate can be used as partial replacement of wash liquid
in the fibreline brown stock washing, or directly recycled to the recovery area. Any
of these two methods reduces the emissions in terms of AOX, COD and other
environmental parameters on a mass basis (example kg/ADt). The fresh water
consumption and effluent flow may also decrease, but not necessarily.
Currently, ECF effluents cannot be easily recycled to chemical recovery due to
the build-up of chloride ions and in some cases potassium, and scaling/deposition of
organic and inorganic compounds. The COD loads of BEKP mill bleach plant
effluents are about 20–30 kg/ADt for ECF bleaching and 20–35 kg/ADt for TCF
bleaching at a kappa number of 8–12 to the bleach plant and with no recovery of
bleach plant filtrates. Partial recovery of bleach plant filtrates has the potential to
reduce COD emissions by up to 30 %. The adverse effects of partial bleach plant
closure are presented below:
–– Partial closure of the bleach plant and other mill systems leads to increased
concentrations of organic and inorganic compounds, also including NPE, resulting
in increased corrosion, scaling and deposition within the bleach plant and other
mill areas
–– The accumulation of dissolved solids causes a considerable increase in the
consumption of bleaching chemicals
–– Difficulty in reaching target brightness
–– Variable pulp quality
–– pH adjustments with sulphuric acid and sodium hydroxide may be costly because
of the considerable buffer capacity of the pulp. The sodium-sulphur balance of
the mill may, therefore, be disrupted.
–– Large buffer storage capacity for filtrates is necessary to absorb transient and
upset conditions, whose frequency increases with the degree of closure.
–– Precipitation of calcium oxalate, calcium carbonate and barium sulphate.
Precipitates of calcium oxalate are dominant at pH values lower than 8 while
calcium carbonate precipitates at pH 8–12. Barium sulphate precipitates over the
entire technically interesting pH range (2–12) (KAM Report A100 2003)
Table 4.37 Kraft mills (paper grade) practising bleach plant filtrate recovery
Filtrates
Mills Bleaching agents/sequence recovered
Södra Cell – Mörrum, Sweden O, P, Q, D Alkaline
Södra Cell – Värö, Sweden O, P, Q Alkaline
M-Real Sverige AB Husum, Sweden O, D, E, P Acid, alkaline
O, Z, E, P, D All – part time
Aspa Bruk – Munksjo, Sweden OQ(PO) Q, PO
OQ(PO)DD O, PO
SCA – Östrand, Sweden OOQ(OP)(ZQ)(PO) Alkaline
Stora Enso – Skoghall, Sweden O(PO)DQ(PO) PO
Metsä-Botnia – Rauma, Finland O(ZQ)(PO)(ZQ)(PO/PO) PO
UPM-Kymmene Wisaforest- Pietarsaari, Finland O(ZD)(O/EO)(ZD)EP Z/D, OP
O(ZQ)(OP)ZP Z/D, EOP, D, P
OW(Z/D)(EOP)DP
Blue Ridge Paper – Canton, NC OD(EOP)D D, EOP
OD(EO)D EO
International Paper – Franklin, OZED Z, E
Samoa-Pacific – Samoa, CA OQQPQ(PO) P, PO
Based on Beca AMC (2004, 2006)
–– A control strategy for water management in the plant has to be developed and
implemented.
–– Additional evaporation plant capacity and additional recovery boiler capacity
may have to be installed
A number of mills are currently practicing of bleaching filtrate recovery.
Table 4.37 shows the list of paper grade Kraft mills practicing recovery of bleach
plant filtrate (Beca AMEC, 2004). In all cases the filtrates are recovered via the pulp
washing line. Filtrates are recovered from both ECF and TCF bleach plants, and the
challenges of closure are to a great degree the same for all bleach plants. Apart from
the mills, shown in the table, there may be other mills practicing filtrate recovery
(Stratton and Gleadow 2003). The original intent for many of these mills was to
completely eliminate bleach plant effluents. Mills have generally found that as the
degree of closure increases, incremental benefits decrease and technical challenges
increase. Complete closure appears to be significantly more difficult to achieve than
expected. Most mills have found that operations can be sustained only under partially
closed conditions. Furthermore, several of the mills in Sweden have concluded
that partial closure coupled with secondary treatment of the remaining effluent
represents a more optimal solution than full closure. In order to reduce operating
problems, several mills have decided to decrease the degree of bleach plant
closure.
There are three essentially closed-cycle bleach plants in operation in Swedish
mills that bleach a portion of their total pulp production in addition to the mills
presented in Table 4.37. In these mills, a small bleach plant was added to an existing
brown paper and board mill in order to produce white top liner. Alkaline filtrates
from bleaching are recycled countercurrently to brown stock washing. The neutral
or acidic filtrate is returned for washing brown stock in two of the mills, and in the
third mill it is concentrated in a low temperature evaporation stage; the concentrate
is added to the black liquor concentrators. The bleached pulp production represents
only 20 % of production in SCA Munksund and Kappa Kraftliner Piteå (formerly
AssiDomän Lövholmen) mill and in AssiDomän Frövi, 40 % of production is
bleached. The small capacity of these bleach plants relative to the total capacity of
the brown stock system and chemical recovery facilities provides conducive condi-
tions for recovering of bleaching filtrates compared with papergrade bleached kraft
mills where all of the pulp is bleached.
There are no bleach plants at paper grade bleached kraft mills that operate fully
closed on a continuous basis. A number of relatively ‘closed’ new bleaching
lines using presses have been built or are under construction. Some perform with
bleaching effluent flows from 6 to 9 m3/ADt, including Advance Agro in Thailand,
Stora Enso Skoghall and SCA Östrand in Sweden, and ZP Rosenthal in Germany.
Several mills practice recovery of alkaline filtrates via the post-oxygen or
brown stock washers. A few mills are recovering acidic bleaching filtrates, and few
linerboard mills have small bleach plants for top liner production from which all of
the filtrates are recycled to associated base liner brown stock systems (Beca AMC
2006; Ernerfeldt et al. 1999).
4.25.1 Control of NPE with Partial Closure
Process closure in general and particularly bleaching wastewater recovery, can lead
to increased concentrations of so-called non-process elements (NPEs). NPEs can
cause several problems as mentioned before if allowed to accumulate in mill p rocess
streams. The degree to which filtrate recovery can be practiced is limited by the
availability of means to effectively manage these and other impacts (Stratton and
Gleadow 2003). Important sources of NPEs are raw materials, especially wood,
water, and makeup chemicals. NPEs can be classified according to the kinds and
locations of impacts they have.
–– Chlorine which exists almost exclusively as chloride ion in mill liquor streams
and potassium have adverse impacts on recovery furnace operation
–– Calcium and barium can form scale deposits in the bleach plant and at locations
where acidic bleaching filtrates are recovered
–– Manganese, iron, and copper consume certain bleaching chemicals and the
subsequent degradation products can cause pulp strength losses
–– Silicon and aluminum form scale deposits on heat transfer surfaces
Several technologies are available to manage the impacts of NPEs (Stratton et al.
2003). There are potentially significant impacts associated with certain transition
metal ions, including Mn + 2, Fe + 3, and Cu + 2, that catalyze the decomposition of
peroxide. In ozone bleaching, Fe + 3 and Cu + 2 can result in significant degradation
of cellulose. This can be attributed to free radical species produced by reactions
involving these ions (Chirat and Lachenal 1994). In order to limit the impact of
transition metals in ozone and peroxide stages, provisions are made to sequester
and/or remove these ions. Chelating agents, especially EDTA, are used in a Q stage
just before the peroxide stage. The chelating agent affect their removal from the
pulp and chemically isolates them in a dissolved state; they are subsequently washed
from the pulp and discharged with the Q stage filtrate. In ozone bleaching, the
unbleached pulp is treated with acid at a pH of about 2 to remove the transition
metals, followed by washing to remove the dissolved metals ions. The acid treat-
ment also provides the optimum pH for ozone treatment (van Lierop et al. 1996).
Transition metal ions do not appear to influence chlorine dioxide bleaching. In addi-
tion to the transition metals, kraft pulps contain alkaline earth metals, particularly
calcium and barium. These metals originate in the wood and as lime mud particles
in the white liquor. They remain chemically or physically bound to the pulp through
the fibreline, dissolving in the first acidic stage of the bleach plant, typically the first
D stage, Q stage, or Z stage. The acid filtrate discharge serves as a purge for metals
in a conventional open bleach plant. As closure is practiced, a purge of these metals
must be maintained, as they will precipitate onto the pulp if acidic filtrate is recycled
to the alkaline brownstock or post-oxygen washing systems. The precipitated metals
would then be carried forward into the bleach plant where they would be re-
dissolved. Finally, the concentration in this loop would build until scale deposits
formed, plugging washer drums and causing downtime to remove the offending
material. This phenomenon has been referred to as an acid/base trap or, specifically,
a metals trap. Closure of a bleach plant, whether ECF or TCF, cannot be achieved
without new provisions for purging or stabilizing metals from acidic filtrates.
Aluminum and silicon are two other elements that can cause problems in a kraft
mill. These elements combine with each other and various anions to create scale
deposits on heat transfer surfaces particularly in the black liquor evaporators.
Although they are not removed as efficiently as other metals such as manganese and
iron, aluminum and silicon are co-precipitated as double or triple salts and removed
with the green liquor dregs. One method to purging metals from the acid bleaching
filtrate is to install an auxiliary system to remove the metal ions from the acid
filtrate. Chemical precipitation and ion exchange have been examined as metal
removal schemes. By addition of sodium hydroxide and sodium carbonate, or by
adding green liquor, precipitation of metal hydroxides and carbonates can be
obtained (Lindberg et al. 1994). The BFR process developed by Champion
International includes a treatment of acid filtrate such as chemical precipitation or
ion exchange (Maples et al. 1994). Another method for purging metals is to operate
an acid wash stage with a low volume purge. Sulphuric or other acid is added to
control the pH below a value of 4, and the pulp is washed to limit metals carryover
into the first bleaching stage. Some of the acid filtrate can be recycled to the fi
breline,
as long as a sufficient purge stream is maintained. This purge will contain some
organic compounds. However, some of the organics, particularly high molecular
weight lignin fragments, will tend to partition onto the pulp under acidic conditions
(Joseph and White 1996). This scheme is practiced on the OZED bleaching line at
the bleached kraft mill in Franklin, Virginia. The oxygen delignified pulp is treated
with acid and dewatered before the ozone (Z) stage. A purge is maintained to c ontrol
metals, and the Z and E stage filtrates are recovered via the post-oxygen washers.
Control of aluminium and silicon is difficult because they are relatively soluble in
alkaline liquors compared to other metals. Reducing inputs by utilizing makeup
lime with low levels of these elements may be an effective approach. They are more
soluble in white liquor than in green, so efficient dregs removal can reduce buildup
of these elements. Addition of magnesium salts to green liquor can remove aluminum
and silicon by precipitation of minerals and subsequent removal with the dregs
(Wannenmacher et al. 1998).
Phosphorus is introduced into the mill primarily with the wood supply (Ulmgren
and Rådeström 1997). The primary purges for phosphorus include the bleaching
filtrates or unbleached pulp, grits, dregs, and lime mud losses. Recovery of bleach-
ing filtrates can reduce or eliminate an important purge point for phosphorus. Its
primary impact is that it can accumulate in the lime cycle as calcium phosphate
thereby reducing the chemical availability of the lime and increasing lime require-
ments. Increased purging of lime mud has been suggested as a corrective action,
although the increased fresh lime makeup could bring additional aluminum and
silica into the liquor cycle (Ulmgren and Rådeström 1997). Dissolved organic
matter consumes bleaching chemicals.
Closure of the bleaching process increases the concentrations of dissolved organ-
ics. Therefore, increase in the usage of bleaching chemicals usage is expected. The
source of the organic compounds is a key variable in determining the amount of
bleaching chemicals consumed (Stratton et al. 2003). The organics from cooking
(black liquor) consume more chlorine or chlorine dioxide than solids generated in
oxygen delignification. This in turn consume more chemicals than bleach plant
extraction stage organics (Canovas and Maples 1995). Generally, organics produced
in chlorine dioxide stages are well oxidized and consume only minor amounts of
chlorine dioxide. The primary means of mitigating the effect of organic matter on
bleach chemical use is efficient washing, particularly after oxygen delignification.
In this regard, the performance of pulp washing equipment is the most important
consideration. Organic compounds in the wood termed as extractives, can result in
pitch deposits on process equipment and in the product. Pitch is of special concern
in acid or neutral sulfite mills, as the resinous material is not saponified as in case of
most alkaline pulping systems. Traditional methods of controlling pitch are through
the use of dispersants, fixation agents and talc. Process closure at mills is likely to
increase pitch accumulations. Kemira Chemicals Oy has developed a process
to remove extractives from process filtrates. This process utilizes polyethylene
oxide flocculant and flotation separation. The process was first implemented at the
Domsjö Fabriker sulfite mill in Sweden. This enabled closure of its TCF bleach
plant. The process appears to be also effective on kraft mill filtrates. The resulting
pitch-containing residue may be suitable for burning in a wood waste fired boiler
(Rampotas et al. 1996).
The elemental chlorine enters a kraft mill as the chloride ion with the wood and
the makeup chemicals such as sodium hydroxide. Chloride is extremely soluble in
the alkaline liquors of the kraft cycle, and accumulates there. The typical chloride
purge points in a mill are:
–– Recovery boiler stack emissions
–– Washing losses from brownstock or post-oxygen washing into the bleach plant
–– Losses of green, white and black liquor
Because process closure reduces such losses, chloride and potassium concentra-
tions will increase unless alternative purge means are provided. There are several
ways to manage Cl and K impacts. Coastal mills in British Columbia, Canada, are
designed to cope with very high Cl levels due to seaborne wood. In particular, the
recovery boilers at these mills are designed with larger superheater sections so that
the upper furnace temperatures are somewhat lower than in units of more common,
inland designs. The lower temperatures reduce the potential for the condensed fume
particles to accumulate in areas where the flue gas passages are narrow and easily
plugged.
A few techniques are being used by mills to control Cl and K levels in their liquor
systems. These techniques generally have limited effectiveness, and so are not gen-
erally sufficient where recovery of ECF bleaching filtrates is practiced. A relatively
simple measure is to use only makeup chemicals, especially caustic, with very low
Cl content. Another commonly used technique is to periodically purge some of the
recovery boiler precipitator catch (the condensed fume from the furnace), which is
enriched with Cl and K compounds. Normally, this chemical ash collected by the
electrostatic precipitator is returned to the black liquor just before firing. The purged
ash may be dissolved in water and discharged as a low volume brine wastewater.
This technique is generally ineffective because the ash, while enriched in Cl and K,
consists mostly of sodium sulphate, and any loss of sodium and sulphur represents
a loss of pulping chemicals. Higher Cl and K purge amounts can be obtained by
separating the Cl and K from the ESP catch so that most of the sodium and sulphur
is returned to the liquor cycle. The simplest process to achieve this is to leach the Cl
and K from the ESP catch, taking benefit of the higher solubility of NaCl and KCl
compared to Na2SO4. The liquid phase is then sewered and the saltcake (Na2SO4) is
returned to the black liquor. This method is being used at International Paper’s Mogi
Guaçu mill in Brazil. Higher Cl and K removals and saltcake recovery efficiencies
can be achieved by completely dissolving the ESP catch and crystallising the
Na2SO4 by evaporation or cooling. The crystals are separated by filtration or
centrifugation and returned to the black liquor. Two basic versions of this process
have been developed. One version generates Na2SO4 decahydrate, Glauber’s salt,
and the other generates anhydrous Na2SO4. The first version, developed by
Mitsubishi, involves acidifying the dissolved material to remove carbonates by
purging carbon dioxide, and concentrating the solution by evaporative crystallisa-
tion. Glauber’s salt is returned to the black liquor and a concentrated Cl and K
solution is purged. Fujisaki et al. (2001) reported on results for the sixth mill (the
Oji.s Kasugai mill in Japan) to adopt this patented technology, known as Potassium
4.26 Water Recycling/Reuse 187
Removal Equipment. The system removes 90 % of Cl and 75 % of K, and has
obtained 96.6 % recovery of Na2SO4. ERCO Worldwide developed a process based
on evaporative crystallisation known as the chloride removal process (CRP). The
first CRP unit was installed as part of the bleach filtrate recycle (BFR) technology
demonstration facilities in Canton, North Carolina. CRP uses forced circulation
evaporation to concentrate the dissolved ESP catch. Sodium sulphate crystallises at
saturation, is removed by filtration and returned to the black liquor. Cl and K are
purged as a low-volume brine wastewater. Other CRP units have since been installed
at mills to improve recovery boiler performance where no bleaching filtrate
recovery is practiced. CRP units or developments of this system have been installed
at Visy Tumut, NSW, International Paper Eastover, SC, USA and Smurfit-Stone,
Hopewell, VA, USA.
Kværner has developed a leaching system. In this system, a centrifuge is used to
separate Na2SO4. Aracruz, Brazil BEKP mill is using this leaching system. Also this
system has been installed in Chile and China.
Other processes for removing Cl and K from the ESP catch have been developed
(Stratton et al. 2003). An example is the Precipitator Dust Purification process that
was jointly developed by Paprican and ProSep Technologies, Inc. of Canada. This
process uses ion exchange technology to generate a purged stream rich in NaCl and
a recovered stream rich in Na2CO3 and Na2SO4. Precipitator dust is dissolved in
water and filtered prior to the ion exchange step. Water is used to regenerate the ion
exchange resin. Studies using precipitator dust from two mills showed efficiencies
of more than 95 % for Cl removal and 85 % for Na recovery, however, K removal
efficiency was insignificant. The recovered stream would be directed to the black
liquor evaporators (Jemaa et al. 1999).
Another method to Cl purging is to promote the formation of hydrogen chloride
gas which will pass through the ESP where it can be scrubbed from the flue gas.
Sulphur dioxide reacts with NaCl in the flue gas to give HCl gas. Sulphur dioxide
concentrations generally limit the amount of NaCl converted to HCl, but mills that
operate at high liquor sulphidity may have most of the Cl load in HCl form. A
number of Scandinavian mills operate in this manner, utilising scrubbers for SO2
control. In these mills, the scrubber wastewater may serve as a significant Cl purge.
4.26 Water Recycling/Reuse
In recent years, there have been considerable incentives to reduce the amount of
water used by the pulp and paper industry, stemming from the need to reduce or
eliminate the discharge of liquid effluents into the environment and regulations
introduced to control the amount of suspended solids, oxygen consuming wastes
and chemicals toxic to marine life.
The driving forces responsible for waste water recycling in pulp and paper indus-
try are the high cost of fresh water, inclination of the industry towards environment
friendly process, discharge norms lay down by regulatory authorities, community
Table 4.38 Advantages of waste water recycling

Less water requirement depending on degree of back water recycling in the various mill operations
Savings in energy
Reduced waste water discharge
Simultaneous reduction in effluent treatment cost due to lower effluent discharges
Table 4.39 Water conservation measures adopted in the pulp mill

Use of treated effluent for raw material washing
Improving washing efficiency of pulp washers
Use of paper machine back water in the pulp dilution in the unbleached tower
Use of back water in centricleaning of pulp and vacuum pump sealing
Recycling of bleach plant filtrate for pulp dilution in tower and vats and shower sprays in the
preceding stage
Based on Bajpai (2008b)
perception and high cost of secondary effluent treatment process (Bajpai 2008b).
The advantages of waste water recycling are shown in Table 4.38.
Industry has several options with respect to minimizing the use of fresh water.
These options can be spill control, process modification, water reuse, partial
treatment and reuse and full treatment and recycling. Optimal water management
involves developing an understanding of where detrimental substances are generated
as well as which ones are critical to the process and how they impact on mill operation.
Optimal solutions always require an integrated approach where product and process
quality, novel treatment technologies and economical factors are involved. Water
conservation options also depend upon the category and scale of operations.
The water consumption can be reduced to a great extent by making minor
modifications in the process which may also involve recycling or reuse of process
water in the system.
An effluent free pulp mill is the dream of the environmentalists and of many
engineers and scientists. Research towards this goal has been going on for more
than three decades. Some of the simple water conservation measures in the pulp mill
are shown in Table 4.39.
Recycle of bleach plant filtrate from the last D-stage to other acid stages and
from the second alkaline stage to the first alkaline stage is practiced to reduce the
effluent volume from the bleach plant. The concepts of jump stage and split flow
countercurrent washing have been practiced in Scandinavian and North American
mills for many years. Equipment parameters, metallurgy, and operating costs are the
main considerations in choosing the degree of closure in an existing bleach plant.
With bleach plant filtrate recycle, the water and heat consumption decreases while
chemical consumption and corrosion increase. In a three-stage bleach plant shower,
water usage can be reduced by 60–70 % with fully countercurrent filtrate flow. An
intermediate level of recycling can be chosen to suit the plant conditions by c hoosing
a jump stage configuration. The savings in water usage will obviously be lower.
Effluent reduction and steam savings for a three-stage bleach plant with various
closure options has been estimated to be 26.8 and 40.4 % respectively by D-stage
jump, 52.6 and 56.9 % respectively by D/Eo stage jump and 70.7 and 80.7 %
respectively by following fully counter current configuration (Chandra 1997). The
assumptions for these estimates include a brown high-density consistency of 12 %,
a washer feed consistency of 1.5 %, a dilution factor of 1.0, and a displacement ratio
of 0.81. The consistencies of the CD, Eop, and D stages are assumed to be 10.5, 9.5,
and 12 %, respectively.
A closed loop bleaching system developed by Swedish company MoDo uses
oxygen in the first stage, then hydrogen peroxide, ozone and small amounts of
chlorine dioxide are used in subsequent stages. Twelve washing stages are included,
with clean water being added only at the final stage (Anon 1997). The water is
passed back through the pulp not into the drains and is then evaporated into steam.
The MoDo Husum mill has a capacity of 690,000 t/year of bleached sulphate pulp.
The Wisaforest pulp mill of UPM-Kymmene Corporation has started to use bleach
plant filtrate for post-oxygen washing on fibre line 1 (Siltala and Winberg 1999).
Recycle loops observed in market bleached Kraft mills are described below:
–– Blow gas condenser cooling water is used as a hot water source for bleach
washing and machining showers (stock heating).
–– Liquor evaporator condensates are utilized for brownstock washing.
–– Chlorine dioxide plant cooling water is recycled to process freshwater supply.
–– Chlorination effluents are used for unbleached stock dilution.
–– Machine white water is utilized for final bleach stage shower and dilution water.
–– Machine white water is utilized for all dilution/shower water in stock preparation.
–– Press effluents are reused for machine white water make-up.
–– Liquor evaporator condensates are utilized for boiler feed water make-up (clean
condensates), causticizing mud washers, lime-kiln scrubbers, dreg washing, and
wood yard requirements.
In addition, fresh water usage is to be eliminated in the following areas of the mills:
Wood preparation: All wood flumes utilize recycled waters. Wet debarking has
typically been eliminated. Remaining water requirements are met with process
wastewater.
Washing: Brown stock washing is typically accomplished entirely with waste water
from the evaporators and turpentine decanter underflow from pulping.
Screening: Stock screening is typically relocated immediately upstream of washing
with screening dilution coming from weak black liquor. In the absence of this
approach, stock screening typically retains its place in the process stream (after
washing) with high levels of water recycle and water makeup from the Decker
filtrate. Decker filtrate shower water is principally supplied from evaporator
condensates.
Cleaning/Refining: Stock preparation waters are met primarily with machine and/or
press section white water.
Drying: Cooling water for drum bearing lubrication system, air conditioning, etc. is
either recycled via an evaporative cooler or is returned to freshwater reservoirs.
Liquor Evaporation: Condenser cooling water is either recycled via an evaporative

cooler or returned to freshwater reservoirs.
Causticizing: Water requirements for mud washing, dregs filter showers, and lime
kiln scrubbe rs are supplied by other sub process waste streams. Cooling water is
returned to freshwater reservoirs.
The kappa number of the pulp going to the bleach plant can be reduced by using
chemical additives, such as anthraquinone and polysulphides, or by using modified
cooking techniques such as modified continuous cooking (MCC) and extended
MCC, isothermal cooking (ITCTM), black liquor impregnation (BLI), LoSolidsTM
cooking, use of oxygen delignification following low-kappa cooking (Chandra
1997). This will result in lower quantities of pollutants going to the bleach filtrate,
improving its suitability for recycling and reuse. It may also be easier with low
kappa pulp to use non-chlorine bleaching agents such as ozone, peroxide and
peracids, to enable recycle of bleach effluents in liquor cycle. These technologies
have reduced the bleach plant effluent considerably.
The chemicals applied to pulp in the oxygen delignification and ozone stages and
the material removed from the pulp in the brown stock washing area, are compatible
with the black liquor recovery system. Therefore, filtrate from the wash press after
the ozone stage is utilized as full counter-current washing through the post-oxygen
wash press and brown stock washers, and sent to the recovery area to be evaporated
and burnt in the recovery boiler.
Campo and Marques (2009) reported in a retrofitted bleach plant that is designed
to process bleached softwood pulp or, alternatively, bleached hardwood pulp with
low effluent flow and load, the total bleaching plant effluent volume is maintained
at a very low level, approximately 6–8 m3/ADt in ECF and 4–6 m3/ADt in TCF, with
COD about 17 and 18 kg/ADt, respectively. A modern ECF-bleaching plant with
countercurrent washing system normally uses a waste water flow in the order of
magnitude of 15–20 m3/ADt. Further closure of the bleach plant filtrates should be
based on the balances of ‘non process elements’ (NPE) including chloride and
potassium, the sodium/sulphur balance and the energy balance of the mill.
The extent of closing water circuits in the bleach plant depends also on the
quality of the fresh water source, the type, number and capacity of washing equip-
ment, designed existing bleaching sequence and due to its cross-media effects in
other process areas, also in the capacity of the recovery boiler part of the mill to deal
with possible problems (example K and Cl accumulation in the recovery boiler). A
prerequisite for partial bleach plant closure is a sufficient capacity in evaporators
and recovery boiler. It should be noted that the evaporation of bleach plant effluents
is easier to apply in case of TCF bleaching. For safety reasons, in ECF bleaching
there is an elevated risk of chloride corrosion in the recovery boiler with the level of
development.
Södra Cell mills in Mönsterås, Mörrum and Värö (SE), Celtejo mill, (PT), Mercer
Stendal and Rosenthal kraft pulp mill (DE), many others are practicing process
water recycling (European Commission 2001).
A new strategy (change of pulping from soda to organosolv process) of reduction

of water consumption and effluent discharge was applied to the pulp and paper
mill of Damuji at Cienfuegos, Cuba (European Commission 2013). After a careful
analysis of the water flows in the mill, and with the help of mathematical optimization
through use of the LINGO software, internal reuse of water was improved for
each step of processes. As a result, freshwater consumption decreased by 88 % and
effluent discharge by 87 %. Moreover fibre recovery was better. Furthermore, on
changing from soda to organosolv pulping to reduce environmental impact, a good
quality paper could be obtained by using 35 % of organosolv pulp and 65 % of
recycled pulp. Economic analysis shows that the payback time would be 1 year.
Using wash presses at the brown stock increases the pulp consistency to more
than 30 % and the filtrate can be taken into the liquor cycle for recovery. It will also
require less water to wash the brown stock. In fact, use of wash presses compared to
filters in bleach plants can reduce effluent by about 50 % without any closure
(Germguard and Steffes 1996). For example, the Advance Agro mill in Thailand
uses presses in a three-stage bleach plant. The bleach plant effluent volume is
reported to be 8–9 m3 per tonne compared to 20–25 m3 per tonne in similar plants
using vacuum washers. Wash presses have a further benefit in that they use a limited
amount of wash water, which increases the potential to reduce effluents. In addition,
a press can restrict the amount of heat carryover between stages, which would
significantly improve process conditions for a following ozone stage, which requires
low temperatures.
As water is used, collected and reused in the papermaking process, the concen-
tration through filtration of suspended solids increases. This can be detrimental to
the paper product or process of papermaking. Filtration, or the physical separation
of the unwanted particles from the water, is necessary if the water is to be reused in
the paper mill. Various filtration components allow papermakers to use filtration to
conserve water through the reuse of waters used in the papermaking process. The
choice of filter type (strainers, pressure filters, gravity filters, save-all), filter media,
filter location and filter maintenance programmes are critical to successful water
reuse (Walter 1996). Machine backwater can be reused in high-pressure paper
machine showers. The choice of showers to use clarified white water must take into
account the payback risks of plugging nozzles and of the ‘plating out’ of solids on
machine surfaces. Barrier filtration technology is limited to removing particles
larger than 75 μm while dissolved air flotation (DAF) clarifiers are prone to upset by
fluctuations in the flow rate and the suspended solids load. This tends to restrict the
use of clarified white water to low-risk showers. In a linerboard mill, using white
water in low risk and medium risk showers could achieve 33 % and 48 % in savings,
respectively (McGowan 2002). Using the Petax fine filtration system developed by
Kadant, fines and high solids can be removed in a single stage. Inlet concentrations
of up to 2000 parts per million (ppm) can be treated without chemicals, without a
vacuum drop leg and without fibre sweetener stock. Filtrate passes through disk
filter media into a hollow shaft, which directs the filtrate to a hollow screen. Fines
and solids are trapped on the exterior of the filter screen. Trapped debris is removed
in three cleaning stages, with contaminants drawn out of the system by two positive
displacement pumps. The recovered clear water is used in machine showers.
4.27 Primary, Secondary and Tertiary Waste Treatment
4.27.1 Primary Treatment
For most paper mills, this measure is not considered as a standalone technique but
as a pretreatment. Pretreatment is usually carried out ahead of biological treatment
in order to facilitate and improve the treatment process. In some special cases where
the organic load is too low for efficient biological treatment, primary treatment may
be the only waste water treatment.
Primary treatment primarily aims at:
–– Avoiding peaks in pollution load, temperature or flows of the influent of a waste
water treatment plant, thus protecting the later biological treatment
–– Initially reducing the pollution load allowing for a more efficient biological
treatment with generation of less sludge
Primary waste water treatment consists of physical-chemical treatment. It
consists of:
–– Equalisation,
–– neutralization
–– Sedimentation
–– Flotation
–– Filtration
In equalisation tank, the inflow is collected, mixed and intermediately stored and
thus peaks are leveled. Suspended solids – fibres, bark particles, and organic material
such as fillers – are removed by mechanical means (sedimentation, flotation and
filtration). Coagulants or flocculants can be added in order to enhance the clarifica-
tion and separation of some suspended solids, colloidals and certain dissolved
substances,. Achieved environmental benefits are reduction of pollution load, espe-
cially total suspended solids (TSS). Primary waste water treatment methods are
described below:
–– Coarse screening is carried out for removing larger objects and sand, which may
cause damage to the subsequent equipment
–– Equalisation and spill collection are required for effluents with large variations
as regards flow and content of pollutants. Such variations may disturb the func-
tion of the subsequent treatment processes, especially biological processes. A
retention time of 4 h in the equalisation basin can be taken as an indication for
appropriate design. However, the appropriate retention time of the equalisation
tank depends on fluctuations in water quality.
4.27 Primary, Secondary and Tertiary Waste Treatment 193
–– Primary or mechanical treatment: Sedimentation is carried out for the removal of

suspended solids (SS), such as fibres, bark particles and inorganic particles (fillers,
lime particles, etc.). A certain minimum size of the particles is required. The finer
particles will settle too slowly for practical use or not settle at all. Also, microfilters
as a first stage before the clarifier are used, which allow for recovering of some
fibres. Microflotation can also be used for primary clarification. Some smaller mills
use primary treatment by means of filtration as the only waste water treatment. The
particles, settling to the bottom of the primary clarifier form a sludge, which has to
be removed. This is obtained by pumping in circular c larifiers in combination with
bottom scraping. The sludge is usually low in dry solid (DS) content, approximately
1–2 %, and has to be thickened and dewatered before final disposal.
4.27.2 Secondary Waste Water Treatment
4.27.2.1 Aerobic Treatment
Pulp and paper mill effluents are mostly treated with aerobic methods. The
commonly used aerobic treatment methods are aerated lagoon and activated sludge
process (Nesaratnam 1998). Biofilm systems (such as moving bed biofilm reactors
(MBBR) or membrane bioreactors (MBR) are also being used. Aerobic biological
waste water treatment consumes energy (example for aerators and pumps) and
generates sludge that normally requires treatment before utilisation or disposal.
Some biological treatment plants in the pulp industry have detected Legionella
bacteria. The issue should be taken care of by operators in cooperation with the
competent authorities in order to reduce and control the dispersion of these bacteria.
The environmental benefits achieved are reduction of emissions of organic matter
(COD, BOD), AOX, phosphorus, nitrogen and chelating agents to water.
Aerated lagoons have been used for a long time in many pulp and paper mills for
medium level removal of effluent contaminants. An aerated lagoon or aerated basin
is a holding and/or treatment pond provided with artificial aeration to promote the
biological oxidation of wastewaters. In aerated lagoon, the reduction of pollutants is
lesser. Currently many of the existing lagoons in the industry have been closed
down or retrofitted into a high-efficiency activated sludge process or supplementary
effluent treatment basins. Aerated lagoons have a large volume; the residence times
for the effluent is 3–20 days. The micro-organisms grow in suspension in the bulk
of liquid, reaching in the lagoon relatively low solids concentration, 100–300 mg/l.
The growth of micro-organisms requires oxygen, which is provided almost exclu-
sively by mechanical aeration equipment. Surface turbine aerators are the most
common aeration units. However, in deep lagoons also bottom aerators with self-
induced or compressed air feed are also used. Aeration equipment provides also
mixing required to keep solids in suspension and enhance microbial action. Aerated
lagoons require large area and volume and are constructed as earth basins and can
be constructed with or without a settling zone. In the first case the end of the lagoon
is left without aeration and mixing, thus allowing solids to settle. In the latter case
this settling is carried out in a separate pond. The biological process does not involve
recirculation of biomass from the end to the beginning of the basin. The settled
sludge is removed seldom, once in 1–10 years.
Activated sludge plants are widely used in the pulp and paper industry. As a
rough estimate, the activated sludge process is used in 60–75 % of all the biological
effluent treatment plants in this industry and is also the most common waste water
treatment used in recently built plants. Generally, the activated sludge process – or
comparable techniques such as moving bed biofilm reactors – achieve high treatment
efficiencies. However, the biomass is vulnerable to disturbances and operational
instability. Therefore, operators usually make provisions that peak loads or flows or
some toxic waste water streams be kept away from the biomass of the aerated basin.
The activated sludge plant consists of aeration basin and the secondary clarifier
-sedimentation basin. The effluent is treated in the aeration basin, with a culture of
micro-organisms (the activated sludge), which are present in a high concentration.
The sludge is separated from the water in the clarifier. The main part of the sludge
is recycled to the aeration basin, which is important for keeping the high sludge
concentration. A small part of the sludge, corresponding to the net growth, is
removed from the system as the excess sludge. Oxygen and mixing is provided to
the aeration basin by mechanical aeration equipment. Various types of aerators
listed below are in use:
–– Surface aerators
–– Submerged turbine aerators
–– Fine bubble aerators
–– Jet aerators
The last three aerators require compressed air from blowers or compressors. A
large number of process and plant designs exist for the activated sludge process.
These alternatives may vary in design of the aeration basin, the number of stages,
the clarifier, the aeration equipment, and also the sludge recycling.
The basis of the moving bed biofilm reactor (MBBR) process is the biofilm
carrier elements that are made from polyethylene. The elements provide a large
protected surface area for the biofilm and optimal conditions for the bacteria culture
to grow. The bacterial cultures digest the soluble organics, gradually mature, and
slough from the media. The cultures form a natural floc that can be easily separated
from the water.
Compact biological treatment effluent plants were developed during the last
decade in order to reduce volumes and decrease energy consumption. This c ombines
moving bed carriers with activated sludge (BAS). The advantage of the biofilm
carrier is that a large amount of biomass is staying on the carrier and does not have
to be circulated via a sedimentation chamber. The advantage of this reactor compared
with fixed beds is that there is no risk of plugging. This technology reduces the
retention time by at least 50 % compared with traditional activated sludge plants.
4.27 Primary, Secondary and Tertiary Waste Treatment 195
The smaller volume makes it possible to build the biological treatment plants closer
to the production line thus saving energy and costs. The reduction of COD is similar
in all different types of treatment plants with activated sludge, but the sludge pro-
duction is lower than in activated sludge plants when sludge is decomposed in the
last stage of the BAS plant (example BAS 0.15 kg SS compared to long term acti-
vated sludge treatment plant (LAS) 0.3 kg SS/kg reduced COD (reference Södra
mills)) (European Commission 2013). Due to anoxic conditions in the growing
biomass, reduction of chlorate is high, 95–100 % and due to the compact volume
(BAS 23 kWh/ADT compared to LAS 0.33 kWh/ADt), BAS treatment plants use
less energy than other treatment plants. However, these compact systems are sensi-
tive to lack of nutrients as the retention time is short. Therefore, these systems are
operated with a nutrient surplus, leading to higher emissions of phosphorus and
nitrogen.
Membrane bioreactor (MBR) generally consists of an aerated bioreactor, similar
to activated sludge process, combined with a membrane process to separate the
biomass from the effluent. Two basic MBR configurations exist:
–– Membranes are immersed in the reactor and are an integral part of the biological
reactor (internal/submerged)
–– Membranes are a separate unit process following the biological reactor (external/
sidestream).
The cleared filtrate from the membrane stage can be reused in the process and the
separated biomass is recirculated to the bioreactor. The high quality of the filtrate
makes the MBR technology best suited for use as internal water circuit treatment.
To avoid solids accumulation on the membrane surface, the membrane system
requires in defined time intervals a mechanical or chemical cleaning. This is nor-
mally done fully automatic and carried out directly in the MBR basin (no removal
of membranes is necessary).
4.27.2.2 Anaerobic Treatment
In anaerobic biological waste water treatment, the biologically degradable load is

reduced in absence of oxygen by digestion by microorganisms mainly generating
methane and carbon dioxide. Anaerobic pretreatment reduces the organic pollution
load of waste water, reduces the excess sludge generated in comparison to stand-
alone aerobic treatment and utilises the energetic content inherent in the organic
pollution load (biogas production) (Bajpai 2000). The volume of biogas produced
during anaerobic degradation ranges from 400 to 600 m3/tonne COD removed and
consists of methane (60–75 %), carbon dioxide (20–35 %) and small amounts of
hydrogen sulphide. Before being used as fuel in in-mill power plants as substitution
of fossil fuels, the biogas is desulphurised. Otherwise, corrosion problems and
higher sulphur dioxide emission in the power plant occur.
The main reactor types used are (Bajpai 2000):
–– Fixed-bed reactor
–– Sludge contact process
–– Anaerobic upflow sludge blanket (UASB)
–– Expanded granular sludge blanket (EGSB)
–– Internal circulation (IC) reactors.
Sludge particles are kept fluidised by the up-flowing influent in UASB and EGSB
reactors whereas in IC reactors, the gas produced in the system drives the circulation
and mixing of liquid and solids in the reactor. The purpose of the different reactor
concepts is to ensure a high concentration of biomass within the reactors. This is
accomplished either by recycling washed out biomass after settling in an external
separator (contact reactor system), by attaching the biomass to a supporting media
within the reactor (fixed-bed reactor) or through auto-immobilisation producing
granular biomass (UASB and EGSB reactor). The reactors can be operated as single
units or as modular combined units.
Combined anaerobic/aerobic treatment plants have proved themselves to be
more stable systems with respect to changing COD loads and toxic or inhibiting
substances in the process water as compared to standalone aerobic treatment plants.
For an economic application of anaerobic techniques as a first stage of biological
waste water treatment, the COD concentration of the process water should not be
less than 1000–2000 mg/l. Depending on the design of the anaerobic reactor
suspended solids in concentrations above 200–500 mg/l could cause problems in
anaerobic systems, particularly in fixed-bed reactors. In some UASB reactors a slow
disintegration of the biomass pellets was observed. In this case, the biomass can be
replaced with new pellets from other UASB reactors in order to keep the reactor in
effective operation. The anaerobic pretreatment significantly reduces the tendency
for developing bulky sludge in the subsequent aerobic stage. In standalone and well
designed aerobic plants, the energy demand for 1 tonne COD removed amounts to
500–600 kWh whereas in combined anaerobic/aerobic treatment plants, the energy
demand related to 1 tonne COD removed (mainly used for pumping and aeration) is
about 200–300 kWh (European Commission 2013).
4.27.3 Tertiary Treatment
Tertiary treatment is performed to reduce the emissions of suspended solids, partly

non-biodegradable dissolved COD matter and phosphorus. It is used when further
removal of organic substances, nitrogen or phosphorus is required. The reduction of
suspended matter emissions also reduces the nutrient emissions bound thereto. A
rather high amount of chemical sludge is produced. This sludge is more difficult to
dewater and handle than biosludge. Aluminium or iron residues can be measured in
low concentrations in the treated effluents after chemical precipitation. This treat-
ment can be a reasonable solution when the waste water load changes significantly
during different seasons and the performance of the secondary treatment (example.
References 197
an aerated lagoon) is lower compared with a well designed and operated activated
sludge plant. It is also used to improve the efficiency of waste water treatment
(example in case of aerated lagoons). Low reduction efficiencies for phosphorus and
COD of aerated lagoons in wintertime can be improved (PARCOM 1994; SEPA-
Report 4713-2 1997b).
SE Varkaus mill, tertiary treatment achieved the following reductions
(Nurmesniemi 2010): TSS 55 %; COD 35 %; Phosphorus 60 %; Nitrogen 50 %. At
the Varkaus Mill, all sludges are mixed before being dewatered with a screw press
and the dried sludge is incinerated at the mill’s own power plant. At the SE Varkaus
mill, investment cost of tertiary treatment after the aerated lagoon was lower com-
pared with the upgrading of the aerated lagoon to the activated sludge plant
(Nurmesniemi 2010).
Biological treatment plus chemical flotation of waste water from the manufactur-
ing of kraft pulp is used at some plants in Sweden, example, Skoghall, Billingfors,
Bäckhammar or Iggesund. Several mills in Finland also use tertiary treatment with
chemical flotation (example. SE Varkaus).
References
Agin SA, Svensson Å (1990) Fibre losses – economic consequences for the wood yard processes.
In: Proceedings of the 24th Eucepa conference, Stockholm, pp 47–55
Ahluwalia MR, Coffey JM, Norris A (1992) Emerging technology in kraft pulping with digester
additives. In: CPPA Spring conference proceedings, Canada, p 1
Albert RJ (1995) Worldwide status of effluent-free technology for bleached kraft pulp production.
In: Proceedings if the international non-chlorine bleaching conference, Amelia Island, FL,
March, Paper 9–2
Albert RJ (1997) Effluent-free pulp mill possible with existing fiberline equipment. In: Advances
in bleaching technology. Miller Freeman Books, San Francisco, p 133
Alejandro M, Saldivia G (2003) Two-stage O2 delignification system cuts mill’s chemical use.
Boosts Pulp Qual January/February, PaperAge, pp 18–24
Alliance for Environmental Technology (AET) (2002a) Trends in world bleached chemical pulp
production: 1990–2001
Alliance for Environmental Technology (AET) (2002b) Eco-system recovery: lifting of fish
consumption advisories for dioxin downstream of US Pulp Mills – 2002. Update
Alliance for Environmental Technology (AET) (2007) Trends in world bleached chemical pulp
production: 1990–2007. Alliance for Environmental Technology, Washington, DC
Alliance for Environmental Technology (AET) (2008a) ECF: the sustainable technology, quality
paper clean environment. Alliance for Environmental Technology, Washington, DC, 2008.
Available online at http://www.aet.org/epp/brochure_0806.pdf
Alliance for Environmental Technology (AET) (2008b) Trends in world bleached chemical pulp
production, 1990–2007, Alliance for Environmental Technology, Washington, DC, 2008.
Available online at http://www.aet.org/science_of_ecf/eco_risk/2008_pulp.html
Alliance for Environmental Technology (AET) (2013) Trends in World Bleached Chemical Pulp
Production: 1990–2012 www.aet.org/science_of_ecf/eco_risk/2013_pulp.html
Allison RW (1979) Effect of ozone on high-temperature thermo-mechanical pulp. Appita J
32(4):279–284
Allison RW (1980) Low energy pulping through ozone modification. Appita J 34(3):197–204
Amendola GA, Vice K, McCubbin N (1996) Design considerations for cost effective kraft and
sulfite pulping liquor spill control systems. In: 1996 Tappi minimum effluent mills symposium
proceedings. Tappi Press, Atlanta.
American Forest & Paper Assn (AFPA) (1988) Kraft recovery boiler physical and chemical
processes, 1988, Textbook sponsored and published by AF&PA. Washington, DC
Aminoff H (1979) A mechanism for the delignifying effect of the anthraquinone in soda pulping.
Pap Puu 61(6):29
Andbacka S (1991) Experiences of modified continuous cooking. Presentation at the Kamyr
symposium in Portugal, April 1991
Andbacka S (1998) The importance of washing in oxygen delignification and TCF bleaching. Pulp
Pap Can 99(3):57–60
Andbacka S, Svanberg J (1997) Isothermal cooking and pulp washing in a modern fiber line. In:
51th Appita general conference, proceedings 1, Melbourne, Australia
Anderson JR (1992) Hydrogen peroxide use in chemical pulp bleaching. In: Tappi bleach plant
operations short course notes. Tappi Press, Atlanta, p 123
Anderson JR, Amini B (1996) Hydrogen peroxide bleaching. In: Dence CW, Reeve DW (eds) Pulp
bleaching – principles and practice. Tappi Press, Atlanta, p 411
Andrew J, Chirat C, Mortha G, Grzeskowiak V (2008) Modified ECF bleaching sequences for
South African hardwood kraft pulps. In: International pulp bleaching conference, Quebec City,
QC, Canada, 2–5 June 2008, pp 55–60
Andrews DH, Singh RP (1979) Peroxide bleaching. In: Singh RP (ed) The bleaching of pulp, 3rd
edn. Tappi Press, Atlanta, pp 211–253
Annergren G, Rydholm SA, Vardheim S (1963) Influence of raw material and pulping process on
the chemical composition and physical properties of paper pulps. Sven Pap 66(6):196–210
Annola A, Hynninen P, Henricson K (1995) Effect of condensate use on bleaching. Pap Ja Puu 77(3)
Anonymous (1997) Closed loop bleaching’. UpTimes no. 1, 1997, p 8
Arenander S, Wahren D (1983) Impulse drying adds new dimension to water removal. Tappi J
66(9):123–126
Arpalahti O, Engdahl H, Jäntti J, Kiiskilä E, Liiri O, Pekkinen J, Puumalainen R, Sankala H,
Vehmaan-Kreula J (2000) Chemical pulping, white liquor preparation. In: Gullichsen
J. Fogelholm C-J (ed) Papermaking science and technology, book 6B. Gummerus Printing,
Jyväskylä, pp B178–B202
Aurell R, Hartler N (1963) Sulphate cooking with the addition of reducing agents. Part III. The
effect of sodium borohydride. Tappi 46(4):209–215
Axegård P (1999) Kretsloppsanpassad massafabrik-Slutrapport, KAM 1 1996–1999, KAMrapport
A31, Stiftelsen för Miljöstrategisk forskning
Axegård P, Norden S, Teder A (1978) Production of pulp for bleaching – some principles. Sven
Pap 81(4):97–100, 104
Axegård P, Carey J, Folke J, Gleadow P, Gullichsen J, Pryke DC, Reeve DW, Swan B, Uloth V (2003)
Minimum -impact mills: issues and challenges. In: Stuthridge T, van den Hueval MR (eds)
Bajpai P (2000) Treatment of pulp and paper mill effluents with anaerobic technology. Pira
International, Leatherhead
Bajpai P (2008a) Chemical recovery in pulp and paper making. PIRA International, Leatherhead,
166 pages
Bajpai P (2008b) Water recovery in pulp and paper making. PIRA International, Leatherhead
Bajpai (2010) Environmentally friendly production of pulp and paper. Wiley, New York
Bajpai P (2012a) Biotechnology in pulp and paper processing. Springer, New York, 412 pp
Bajpai P (2012b) Environmentally benign approaches for pulp bleaching, 2nd edn, Elsevier, London
Bajpai P, Bajpai PK (1999) Recycling of process water in a closed mill systems – an introduction.
ISBN 1 85802 277 0, Pira International UK, 104 pages
Bajpai P, Kumar S, Mishra SP, Mishra OP, Bajpai PK (2005) Improving digester performance
through the use of surfactants and AQ. IPPTA Conv Issue 43–53
Barratt KB (1990) Kraft pulping for the 90s environment. Paper presented at Tappi 90 conference
held 5–8 March, 1990 at Atlanta, GA, USA, pp 95–102
References 199
Beca AMEC (2004) Study report: independent advice on the development of environmental guide-
lines for any new Bleached Eucalypt Kraft Pulp Mill in Tasmania, prepared for the Resource
Planning and Development Commission, Tasmania, Australia
Beca AMEC (2006) Review of ECF and TCF bleaching processes and specific issues raised in the
WWF report on Arauco Valdivia. Prepared for Resource Planning and Development
Commission, Tasmania, Australia. May 2006
Bergnor G, Dahlman O (1998) Influence on pulp quality during the removal of hexenuronic acids
In: Proceedings international pulp bleaching conference, Helsinki, Finland, p 185
Bergnor-Gidnert E (2006) STFI Pac kforsk report, February, 2006 (in Swedish)
Berry R (1996) Oxidative alkaline extraction. In: Dence CW, Reeve DW (eds) Pulp bleaching –
principles and practice. Tappi Press, Atlanta, pp 291–320
Berthold F, Lindström ME (1997) Polysulfide addition as a means to increase delignification in
kraft pulping. Nord Pulp Pap Res J 12(4):230
Bérubé PR, Hall ER (2000) Removal of methanol from evaporator condensate using a high
temperature membrane bioreactor: determination of optimal operating temperature and system
costs. Pulp Pap Can 101(3):54–58
Björk M, Sjögren, Tomas, Lundin T Rickards H, Kochesfahani, SH (2005) Partial borate autocaus-
ticizing trial increases capacity at Swedish mill, Tappi J 4(9):15–19
Blackwell BR, MacKay WB, Murray FE, Oldham WK (1979) Review of kraft foul condensates,
sources, quantities, chemical composition, and environmental effects. Tappi J 62(10):33–37
Bokström M, Nordén S (1998) Extended oxygen delignification. In: Proceedings of the 1998 inter-
national pulp bleaching conference, Helsinki, Finland
Boman R, Reeves R, Nordgren B (1995) Mills improve bleach results with pressurized peroxide.
Pulp Pap 69(10):121–125
Bonsu AK, Marois J, Rowbottom RS (1986) Standby wet scrubber for kraft digester blow and
relief gases. Pulp Paper Can 87(8):T318-T323 (August 1986)
Borchardt JK, Biancalana RP, Mahoney CL (1997) Improved deresination agents: laboratory and
mill results, In: Proceedings of the 1997 Tappi pulping conference, TAPPI Press, Atlanta,
pp 395–413
Botnia Rauma (2009) Air emissions – Botnia Rauma mill. Presentation given during a mission to
Finland, 23.02.2009,
Bouchard J, Maine C, Berry RM (1996) Kraft pulp bleaching using dimethyldioxirane: stability of
the oxidants. Can J Chem 74(2):232
Bounicore A, Wayne TD (1992) Air pollution engineering manual. Van Nostrand Reinhold, New York
Bowen IJ (1990) Overview of emerging technologies in pulping and bleaching. Tappi J
73(9):205–217
Brännland R, Nordén S, Lindström LA (1990) Implementation in full scale – the next step for
prenox. Tappi I 73(5):231–237
Bräuer P, Großalber J, Münster H, Zhang X, Nagalla RN (2012) China is steaming ahead with
high-yield pulping, Success story of Chinese paper and board industry with the use of
mechanical pulping, What can Asia learn from this, http://papermart.in/2012/09/28/
china-is-steaming-ahead-with-high-yield-pulping-success-story-of-chinese-paper-and-
board-industry-with-the-use-of-mechanical-pulping-what-can-asia-learn-from-this
Breed D, Shackford LD, Pereira ER, Colodette JL (1995) Cost-effective retrofit of existing bleach
plants to ECF and TCF bleached pulp production using a novel peroxide bleaching process. In:
1995 pulping conference, Chicago, IL, USA, 1–5 October, 1995, Book 2, pp 779–788
Bright D, Hodson P, Lehtinen, K-J, Mckague B, Rodgers J, Solomon K (2003) Evaluation of
ecological risks associated with the use of chlorine dioxide for the bleaching of pulp: scientific
progress since 1993. In: T Stuthridge, van den Hueval MR, Marvin NA, Slade AH, Gifford J
(eds) Environmental impacts of pulp and paper waste streams, SETAC Press, Pensacola
Brogdon BN, Hart PW (2012) Chapter 10: Peroxide bleaching. In: Hart PW, Rudie AW (eds)
Bleaching of pulp, 5th edn. Tappi Press, Atlanta, pp 273–308
Brown C, Landälv I (2001) The chemrec black liquor recovery technology – a status report. In:
International chemical recovery conference, Whistler, Canada, 11–14 June 2001
Buchert J, Teleman A, Harjunpaa V, Tenkanen M, Viikari L, Vuorinen T (1995) Effect of cooking

and bleaching on the structure of xylan in conventional pine kraft pulp. Tappi J 78(11):125
Buchert J, Tenkanen M, Tamminen T (2001) Characterization of carboxylic acids during kraft and
Superbatch pulping. Tappi J 84(4):1
Bujanovic B, Cameron J, Yilgor N (2003) Comparative studies of kraft and kraft-borate pulping of
black spruce. J Pulp Pap Sci 29(6):190–196
Burgess T (1993) The basics of foul condensate stripping. In: Proceedings of the 1993 kraft recovery
operations short course. Tappi J 137–146
Campo R, Marques P (2009) Celtejo plays in the top division. Results Pulp Pap 3:32–34
Cannell E, Cockram R (2000) The future of BCTMP. Pulp Pap 74(5):61–76
Canovas RV, Maples GE (1995) Bleach plant closure with the BFR™ process. In: 1995 nonchlorine
bleaching conference proceedings. Orlando, Florida
Carre G, Wennerström M (2005) Ozone bleaching – an established technology. IPBC, Stockholm,
pp 144–149
Carreira HJM, Loureiro PEG, Graca M, Carvalho MGVS, Evtuguinet DV (2012) Reductive
degradation of residual chromophores in kraft pulp with sodium dithionite. Tappi J

11(3):59–67
Carter DN, McKenzie DG, Johnson AP, Idner K (1997) Performance parameters of oxygen
delignification. TAPPI J 80(10):111–117
Chai XS, Luo Q, Yoon SH, Zhu JY (2001) The fate of hexanuronic acid groups during kraft pulping
of hardwoods. J Pulp Pap Sci 27(12):403
Chandra B (1997) Effluent minimization – a little water goes a long way. Tappi J 80(12):37–42
Chemrec (2012) A gasification technology inherently more efficient. Retrieved on April 10, 2012.
Available at: http://www.chemrec.se/
Chen CI (1990) Process for producing kraft pulp for paper using nonionic surface active agents to
improve pulp yield, U.S. Patent 4,952,277
Chen GC (1994) Application of a surfactant as a kraft pulping additive. Tappi 77(2):125–128
Cheremisinoff NP, Rosenfeld PE (2010) Handbook of pollution prevention and cleaner production
vol. 2: best practices in the wood and paper industries, 1st edn. Elsevier, New York
Chirat C, Lachenal D (1994) Minimizing pulp degradation during totally chlorine free bleaching
sequences including an ozone stage. In: 1994 international pulp bleaching conference papers.
Canadian Pulp and Paper Association, Montreal
Chirat C, Lachenal D (1997) Pulp producers race to keep up with technology. In: Pate KL (ed)
Advances in bleaching technology. Miller Freeman Books, San Francisco, p 20
Chirat C, Nyangiro D, Struga B, Lachenal D (2005) The use of ozone on high kappa softwood and
hardwood kraft pulps to improve pulp yield. IPBC, Stockholm, pp 74–80
Chirat С (2007). Proceedings of the EFPG days 2007, Grenoble, France
Cloutier JN, Lecourt M, Petit-Conil M (2009) Ozonisation of TMP – Part I – direct ozone injection
in the eye of the secondary refiner In: PACWEST conference, Kamloops, BC, Canada, 10 pages
Cloutier JN, Lecourt, M, Petit-Conil M (2010) Ozonation of TMP – Part II – interstage treatment of
primary TMP in a dedicated reactor In: PACWEST conference, Kamloops, BC, Canada, 9 pages
Colodette JL, Campos AS, Gomide JL (1990) Attempts to use white liquor as the source of alkali
in the oxygen delignification of eucalypt kraft pulp. In: 1990 Tappi oxygen delignification
symposium notes. Tappi Press, Atlanta, p 145
Confederation of European Paper Industries (CEPI) (2009) CEPI Europe’s pulp and paper industry
in 2020 and beyond. Carta & Cartiere 14–18
Cooper CD, Alley FC (1986) Air pollution control: a design approach. Waveland Press, Prospect
Heights
Costa MM, Colodette JL (2002) The effect of kraft pulp composition on its bleachability. In:
TAPPI international pulp bleaching conference, 2002. Ortland, Oregon, USA
Courchene CE (1998) The tried, the true and the new – getting more pulp from chips – modifications
to the kraft process for increased yield. In: Proceedings of the breaking the pulp yield barrier
symposium, 1998. Tappi Press, Atlanta, pp 11–20
References 201
Croon I, Andrews DH (1971) Advances in oxygen bleaching, Part I. Demonstration of its feasibility
and scope. Tappi 54(11):1892–1898
Crotogino RH, Poirier NA, Trinh DT (1987) The principles of pulp washing. Tappi J 70(6):95–103
Dallons VJ, Hoy DR, Messmer RA, Crawford RJ (1990) Chloroform formation and release from
pulp bleaching. Results of field measurements. Tappi J 73(6):91–95
De Beer JG (1998) Potential for industrial energy efficiency Improvement in the long term. PhD
thesis Utrecht University, Department of Science, Technology, and Society
de Choudens C, Monzie P (1978) Pâtes TMP. Traitement par l’ozone, Atip 32(9):350–359
DeCarrera R (2006) Quaterly technical progress report 20 demonstration of black liquor gasifi-
cation at Big Island. Report 40850R20 http://www.gp.com/containerboard/mills/big/pdf/
rpt40850R20.pdf (06-04-28)
DeMartini Nl (2010) Final summary report on nitrogen oxide emissions from Finnish pulp mills.
Finnish Recovery Boiler Committee, 2010
Department of Justice (2012) Pulp and paper effluent regulations (SOR/92-269). Department of
Justice, Government of Canada, Ottawa, ON, Canada, 2012. Available online at http://laws.
justice.gc.ca/eng/SOR-92-269
Desprez F, Devenyns J, Troughton N (1993) One stage hydrogen peroxide full bleaching of previ-
ously delignified soft wood kraft pulp. In: Tappi pulping conference proceedings. Tappi Press,
Atlanta, p. 443
Devenyns J, Chauveheid E (1997) Uronic acid and metal control. In: 9th international symposium
on wood and pulping chemistry. Montreal, QC, Canada, pp M5-1
Devenyns J, Desprez FS, Troughton N (1993) Peroxygen bleaching and prebleaching technologies
for step wise conversion from conventional chlorine bleaching via ECF to TCF. In: Tappi
pulping conference proceedings. Tappi Press, Atlanta, p 341
Diaconescu V, Petrovan S (1976) Kinetics of sulfate pulping with addition of sodium borohydride.
Cellul Chem Technol 10(3):357–378
Dimmel DR (1995) Electron-transfer reactions in pulping systems. (1). Theory and applicability to
anthraquinone pulping, Institute of Paper Chemistry. J Wood Chem Technol 5(1):1–14
Dimmel DR, Schuller LF (1986) Structural/reactivity studies (II): reactions of lignin model
compounds with pulping additives. J Wood Chem Technol 6(4):565
Dubé M, McLean R, MacLatchy D, Savage P (2000) Reverse osmosis treatment: effects on
effluent quality. Pulp Pap Can 101:8
Durai-Swamy K, Mansour MN, Warren DW (1991) Pulsed combustion process for black liquor
gasification, U.S. DOE report DOE/CE/40893-T1 (DE92003672)
Eckert B, Turpin D, Dunn J (2005) Improving fiber yield through borate autocausticizing,
Improving fiber yield through borate autocausticizing, Tappi/Solut April 2005, pp 33–34
EIPPCB (2011) Assessment of the data collection on air emissions from European kraft pulp mills,
February – April 2011, 2011. European Commission, Spain
Eiras KMM, Colodette JL (2003) Eucalyptus kraft pulp bleaching with chlorine dioxide at high
temperature. JPPS 29(2):62–64
Ek M, Axegård P, Bergnor E, Ekholm U (1994) The role of metal ions in TCF-bleaching of
softwood pulps. In: Tappi pulping conference proceedings. Tappi Press, Atlanta
Elaahi A, Lowitt HE (1988) The U.S. pulp and paper industry: an energy perspective.
U.S. Department of Energy, Washington, DC
Emilsson K, Håkansson M, Danielsson G (1997) Extended stripping and usage of evaporator
condensates at Varo Mill, Sweden. In: 1997 Tappi minimum effluent mills symposium
proceedings. Tappi Press, Atlanta
Engstrom JH (1996) Black liquor impregnation and iso thermal cooking. Pap Asia 12(2):18–21
Environment Canada (1992a) Aquatic effects monitoring requirements. Report EPS 1/RM/18,
Environment Canada, Ottawa, ON, Canada, 1992
Environment Canada (1992b) Reference method for the determination of polychlorinated
dibenzo-para-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) in pulp and paper
mill effluents, Report EPS 1/RM/19, Environment Canada, Ottawa, ON, Canada, 1992
Enz SM, Emmerling F (1987) North America’s first fully integrated, medium. consistency oxygen
delignification stage. Tappi J 70(6):105–112
EPA, NCASI (1995) Survey of recovery furnaces in the kraft pulp sector, carried out by NCASI in
cooperation with EPA in 1994–1995
Eriksson E, Sjöström E (1968) The influence of acid groups on the physical properties of high-
yield pulps. Tappi J 51(1):56
Ernerfeldt B, Södersten PA, Eriksson HO, Näsholm AS (1999) Bleach plant presses reduce chemical
consumption. In: 6th international conference on newly available technologies, Stockholm
European Commission (2001) Integrated Pollution Prevention and Control (IPPC). Reference
document on best available techniques in the pulp and paper industry. Institute for Prospective
Technological Studies, Seville
European Commission (2013) Best Available Techniques (BAT) reference document for the production
of pulp, paper and board. Industrial Emissions Directive 2010/75/EU (Integrated Pollution
Prevention and Control). JOINT RESEARCH CENTRE, Institute for Prospective Technological
Studies Sustainable Production and Consumption Unit European IPPC Bureau
Fatehi P, Malinen RO, Ni Y (2009) Removal of hexenuronic acid from eucalyptus kraft pulps
during chlorine dioxide- and ozone-based ECF bleaching sequences. Appita 62(3):212–218
Finnish BAT Report (1997) The Finnish background report for the EC documentation of best
available techniques for pulp and paper industry. The Finnsih environment 96, Ministry of
Environment in Finland, Helsinki 1997, ISBN 952-11-0123-7
Fleming BI, Kubes GJ, MacLeod JM, Bolker HI (1978) Soda pulping with anthraquinone. A
mechanism. Tappi 61(6):43
Ford M, Sharman P (1996) Performance of high yield hardwood pulp is investigated as it should
be the choice of the future. Pulp Pap Int 38(10):29
FRBC (2010) NOx emissions from recovery boilers – why discrepancy between Finnish and
Swedish values, Finnish Recovery Boiler Committee, 22.12.2010, 2010, p 12
Fujisaki A, Tateishi M, Baba Y, Arakawa Y (2001) Plugging prevention of recovery boiler by char-
acter improvement of the ash which used potassium removal equipment (part II). In: Proceedings
of the international chemical recovery conference, Pulp and Paper Technical Association of
Canada, Tampa
Fullerton TJ, Wright LJ (1984) Redox catalysis of alkaline pulping by organometallic complexes.
Wood Chem Technol 4(1):61–74
Furtado FP, Evtugin DV, Gomes TM (2001) Effect of the acid stage in ECF bleaching of eucalyptus
globulus kraft pulp bleachability and strength. Pulp Pap Can 102(12):93
Gabir S, Khristov T (1973) Kraft cooks of papyrus (Cyperus papyrus L.) stalks in the presence of
sodium borohydride. Tselul Khartiya 4(6):12–18
Gavrilescu D (2005) Best practices in kraft pulping – benefits and costs. Environ Eng Manag J
4:29–46
Gebart R (2006) Improvement Potential in chemical pulping: black liquor gasification. In: Paper
presented at the IEA-WBCSD workshop on energy efficient technologies and CO2 reduction
potentials in the pulp and paper industry, Paris, France
Gellerstedt G (2003) Condensation in kraft pulping. A reality?. In: 12th International Symposium
on Wood and Pulping Chemistry (ISWPC) Madison, USA, June 9–12, 2004, Vol I, 1
Genco JM, van Heiningen A, Miller W (2012) Chapter 2: Oxygen delignification, the bleaching of
pulp. In: Hart P, Rudie A (eds) TAPPI Press, Atlanta
Germer E, Metais A, Hostachy JC (2011) State-of-the-art industrial ozone bleaching. Tappsa J
6:30–37
Germguard U, Steffes F (1996) Pulp washing in a closed bleached plant. In: Proceedings of the
Tappi 1996 minimum effluent mills symposium. Tappi Press, Atlanta, pp 115–118
Gleadow PL, Hastings C (1995) Closed cycle kraft ECF vs. TCF. In: Proceedings international
non-chlorine bleaching conference, Amelia Island, FL, March, Paper 9–1
Gleadow PL,Vice K, Johnson AP, Sorenson DR, Hastings CR (1996) Mill applications of closed
cycle technology. In: Proceedings international non-chlorine bleaching conference, Orlando,
FL, March, Paper 11–3
References 203
Gomes da Silva Jr F, Duarte FA, Saco VM, dos Santos JT, Bassa A (2002) Ozone based ECF
bleaching sequence for eucalyptus pulp: optimization studies. In: TAPPI International pulp
bleaching conference. Portland, OR, USA
Gorski D, Engstrand P, Hill J, Johansson L (2009) Review: reduction of energy consumption in
refining through mechanical pretreatment of wood chips. In: International mechanical pulping
conference, Sundsvall
Gotlieb PM, Nutt WE, Miller SR, Macas TS (1994) Mill experience in high-consistency ozone
bleaching of southern pine pulp. Tappi J 77(6):117–124
Govers T, Homer G, Scheeff D (1995) The cost of ozone-based ECF and TCF bleaching. In: AIR
LIQUIDE/OZONIA ozone symposium, Helsingör, Denmark. http://perso.wanadoo.fr/govers/
aecono/pulp_bleaching. (28–29 September 1995)
Goyal GC (ed) (1997) Anthraquinone pulping: a Tappi Press anthology of published papers, 1977–
1996. Tappi Press, Atlanta
Goyal G, Jokela V, Munro FC (1994) Low kappa number pulping – mill experiences, In: 1994,
Tappi pulping conference. Tappi Press, Atlanta, p 305
Grace TM, Timmer WM (1995) A comparison of alternative black liquor recovery technologies.
In: Proceedings of the international chemical recovery conference, Toronto, pp B269 – 275
Gratzl JS (1980) The action mechanism of anthraquinone in alkaline pulping. EUCEPA s ymposium
“The delignification methods of the future”, Helsinki, paper 12
Gullichsen J (2000) Fiber line operations. In: Gullichsen J, Fogelholm C-J (eds) Chemical pulp-
ing – papermaking science and technology, Book 6A. Fapet Oy, Helsinki, Finland, p A19
Gullichsen J, Paulapuro H, Sundholm J (2000) (book editor), Papermaking science and technology,
Book 5. Mechanical pulping, Fapet Oy, Helsinki, Finland
Gullichsen J, Ilmoniemi E, Kaasalainen H, Manninen TA (2009) Method for feeding high-
consistency pulp to a formation support and high-consistency Headbox, WO 2009063135 (A1)
Håkansdotter L, Olm L (2002) Soda-AQ pulping of softwood, the influence of cooking parameters
on the properties and bleachability. Pap Puu 84(1):43
Haller KH (1996) A decision in favor of ECF: what a decision in the German speaking area. In:
Proceedings International Non-Chlorine Bleaching Conference, Orlando, FL
Hamm U, Gottshing L (2002) ECF and TCF bleached pulps: a comparison of their environmental
impact. German Pulp and Paper Association VDP—INFOR project (No. 19)
Han Y, Law KN, Lanouette R (2008) Modification of jack pine TMP long fibers by alkaline peroxide
–Part 1. Chemical characteristics of fibers and spent liquor. BioResources 3(3):870–880
Harazono K, Kondo R, Sakai K (1996) Bleaching of hardwood kraft pulp with manganese
peroxidase from Phanerochaete sordida YK-624 without addition of MnSO4. Appl Environ
Microbiol 62(3):913–917
Hartler N (1959) Sulfate cooking with the addition of reducing agents. I. Preliminary report on the
addition of sodium borohydride. Sven Pap 62:467
Hatton J (1987) Debarking of frozen wood. Tappi J 70(2):61–66
He Z, Wekesa M, Ni Y (2004a) Pulp properties and effluent characteristics from the Mg(OH)(2)-
based peroxide bleaching process. Tappi J 3(12):27–31
He Z, Ni Y, Zhang E (2004b) Further understanding on the cationic demand of dissolved substances
during peroxide bleaching of a spruce TMP. J Wood Chem Technol 24(2):153–168
He Z, Qian X, Ni Y (2006a) The tensile strength of bleached mechanical pulps from the Mg(OH)2-
based and NaOH-based peroxide bleaching processes. J Pulp Pap Sci 32(1):47–52
He Z, Wekesa M, Ni Y (2006b) A comparative study of Mg(OH)(2)-based and NaOH-based
peroxide bleaching of TMP: anionic trash formation and its impact on filler retention. Pulp
Paper Can 107(3):29–32
Headley RL (1996) Pulp cooking developments focus on fiber yield, lower chemical use. Pulp Pap
70(10):49–57
Heimburger S, Thireault D, Boechler T (2002) International pulp bleaching conference. Tappi
Press, Atlanta, p 271
Helander R, Nilsson B, Bohman G (1994) Developments and progress in ozone bleaching at the
Skoghall mill. In: CPPA international pulp bleaching conference papers, CPPA, Montreal, p 289
Henricson K (1997) Ahlstrom machinery, AHLTM-stage. A new bleaching stage for kappa
reduction and metal profile control, In: Emerging new technologies conference (March 1997),
Orlando, USA
Hill J, Sabourn M, Johansson L, Aichinger J (2009) Enhancing fibre development at reduced
energy consumption using TMP subprocesses and targeted chemcial application – pilot and
commercial scale results, International Mechanical Pulping Conference, Sundsvall, Sweden,
May 31–June 4
Hitchens D, Farrell F, Lindblom J, Triebswetter U (2001) The impact of Best Available Techniques
(BAT) in the competitiveness of European industry. European Comission, report EUR 20133
EN. 120 pp
Hoddenbagh JA, Wilfing K, Miller K, Hardman D, Tran H, Bair C (2001) Borate autocausticizing –
a cost effective technology. In: International chemical recovery conference, Whistler, Canada,
11–14 June 2001, pp 345–53
Holmbom B, Ekman R, Sjoholm R, Eckerman C, Thornton J (1991) Chemical-changes in peroxide
bleaching of mechanical pulps. Papier 45(10A):16–22
Holton H (1977) Soda additive softwood pulping: a major new process. Pulp Pap Can 78(10):19
Homer G, Muguet M, Epiney M, Johnson S (1996) Oxygen, ozone, and chlorine dioxide. In: 82nd
annual meeting, technical section, CPPA, Montréal, 1996
Hosoya S, Tomimura Y, Shimada K (1993) Acid treatment as one stage of non chlorine bleaching,
In: 7th international symposium on wood and pulping chemistry, vol 1, Beijing, China, p 206
Hostachy JC (2009) Bagasse pulp bleaching with ozone: it’s time to implement green bleaching
practice paperex. In: 2009 – international technical conference 4-6th December 2009, New
Delhi, India
Hostachy JC (2010a) Ozone-enhanced bleaching of softwood kraft pulp, Tappi J 9(8):16–23
Hostachy JC (2010b) Softwood pulp bleaching with ozone: a new concept to reduce the bleaching
chemical cost by 25%, Appita 63(2):92–97
Hostachy JC (2010c) Use of ozone in chemical and high yield pulping processes: latest innova-
tions maximizing efficiency and environmental performance. In: 64th Appita annual confer-
ence and exhibition, 18–21 April 2010, Melbourne, Australia, pp 349–354
Hostachy JC, Serfass R (2009) Ozone bleaching – state of the art and new developments www.
otsil.net/…/ozone%20bleaching%20State%20of%20Art%20TECHNOLOGY%2…A.
Wedeco report
Hsieh JS, Long PX, BaOsman A (2000) Kinetic study of ozone treatment on mechanical pulp. In:
Proceedings from the 2000 Tappi pulping/process & product quality conference, Boston, DF
MA, Paper 46
Huber E, Rank P, Rauscher JW, Williamson DF (1995) High black liquor solids firing at pope and
talbot. In: Proceedings of the 1995 international chemical recovery pulping conference. TAPPI
Press, Toronto.
Hupa (2005). Nitrogen oxide emissions from pulp mills and the factors affecting them – a sum-
mary of the current knowledge, Report for the Finnish Recovery Boiler Committee, 2005, p. 15
Hyoty PA, Ojala ST (1988) High solids black liquor combustion. Tappi J 71(1):108–111
Ibach S (1995). Conversion to High Solids Firing, Proceedings of the International Chemical
Recovery Conference, TAPPI Press, Toronto, Ont., Apr. 1995
Imelainen K, Ekholm J, Kukkanen K, Pasola I (1989) A computer controlled recovery boiler burn-
ing high dry solids. Pulp Pap Can 90(4):15–20
International Energy Agency (IEA) (2009) Energy technology transitions for industry – strategies
for the next industrial revolution. International Energy Agency (IEA), Paris
Istek A, Gonteki E (2009) Utilization of sodium borohydride (NaBH4) in kraft pulping process. J
Environ Biol 30(6):5–6
Jaakko Pöyry Consulting AB (1997) Energy conservation in the pulp and paper industry
Jaccard M, Willis Enterprises Associates (1996) Energy conservation potential in six Canadian
industries. Natural Resources Canada, Ottawa
Jameel H, Gratzl J, Prasad DY, Chivikula S (1995) Extending delignification with AQ/polysulfide.
Tappi J 78(9):151–160
References 205
Jamieson AG, Fossum G (1976) Influence of oxygen delignification on pulp yields. Appita
29(4):253–256
Jemaa N, Paleologou M, Thompson R, Richardson B, Brown C, Sheedy M (1999) Chloride
removal from the kraft recovery boiler ESP dust using the precipitator dust purification (PDP)
system. Pulp Pap Can 100:T219–T226
Jerschefske D (2012) China invests to meet booming paper demand. http://www.labelsandlabeling.
com/news/features/china-invests-meet-booming-paper-demand
Jiang JE (1993) Extended delignification of Southern Pine with polysulfide and anthraquinone. In:
Tappi pulping conference proceedings, Atlanta, November 14–18, pp 313–321
Jiang JE (1995) Extended delignification of southern pine with anthraquinone and polysulfide,
Tappi J 78/2:126
Johansson B, Mjöberg J, Sandström P, Teder A (1984) Modified continuous kraft pulping – now a
reality. Sven Pap 87(10):30–35
Johnson RW, Bird A (1991). CTMP in Fine Papers: Impact of CTMP on Permanence of Alkaline
Papers, 1991 Papermakers conference proceedings, TAPPI Press: 267–273.
Johnson T, Gleadow P, Hastings C (1996) Pulping technologies for the 21st century – a North
American view. Part 4 emerging technologies and mill closure. Appita 49(2):76–82
Johnson AP, Johnson BI, Gleadow P, Silva FA, Aquilar RM, Hsiang CJ, Araneda H (2008) 21st
century fibrelines. In: Proceedings of the international bleaching conference, Quebec City, 2008
Jones AR (1983) How bleaching hardwood kraft pulp with oxygen affects the environment. Tappi
J 66(12):42–43
Jönsson J (2011) Analysing different technology pathways for the pulp and paper industry in a
European energy systems perspective. PhD thesis, Department of Energy and Environment,
Chalmers University of Technology, Göteborg, Sweden
Jönsson J, Ruohonen P, Michel G, Berntsson T (2011) The potential for steam savings and imple-
mentation of different biorefinery concepts in Scandinavian integrated TMP and paper mills.
Appl Therm Eng 31(13):2107–2114
Joseph JC, White DE (1996) The use of modeling in mill closure activities. In: 1996 Tappi mini-
mum effluent mills symposium proceedings. Tappi Press, Atlanta
KAM Report A100 (2003) Ecocyclic pulp mill – “KAM”. Final report 1996–2002
Kapanen J, Kuusisto L (2002) A new brown stock washing optimization method for economical
pulp production, TAPPSA APPW, 2002
Kappel J, Bräuer P, Kittel FP (1994) High consistency ozone bleaching technology. Tappi J
77(6):109
Karlström K (2009) Extended impregnation kraft cooking of softwood: effects on reject, yield,
pulping uniformity and physical properties, Lic. thesis, Royal Institute of Technology (KTH),
Stockholm, Sweden
Katofsky R, Consonni S, Larson ED (2003) A cost-benefit analysis of black liquor gasification
combined cycle systems. In: Proceedings of the Tappi fall technical conference: engineering,
pulping & PCE&I, Chicago, 22 p
Katsoulis DE (2002) A survey of applications of polyoxometalates. Chem Rev 98(1):359
Katz G (1993) Anthraquinone and anthraquinone-polysulfide pulping for extended delignification.
In: Tappi pulping conference proceedings, Atlanta, November 14–18, pp 323–331
Katz S, Scallan AM (1983) Ozone and caustic soda treatments of mechanical pulp. TAPPI J
66(1):85–87
Kazymov D (2010) Biochemical modification of thermomechanical pulp fibers. Master’s degree
program in chemical and process engineering. Lappeenranta University of Technology
Kibblewhite RP, Brookes D, Allison RW (1980) Effect of ozone on the fiber characteristics of
thermomechanical pulps. Tappi J 63(4):133–136
Kignell JE (1989) Process for chemicals and energy recovery from waste liquors, U.S. Patent no.
4,808,264
Kiviaho I (1995) Optimizing oxygen delignification. In: Proceedings of the international non-
chlorine bleaching conference, Amelia Island, FL, paper 2–2, p 12
Kleppe PJ, Kringstad K (1963) Sulfate pulping by the polysulfide process. II. Birch. Norsk Skogind
18(1):13
Kleppe PJ, Hm C, Eckert RC (1972) Delignification of high yield pulp with oxygen and alkali, I,
preliminary studies on southern pines. Pulp Pap Mag Can 73(12):T400–T404
Knutson I, Lovblad R, Malmström J, De Sousa F, Kringstad KP (1992) Minimizing dioxin formation
in mill-scale bleaching of softwood kraft pulp. Tappi J 75(6):112
Kochesfahani SH, Bair C (2002) Overcoming recausticizing limitations; mill experiences with
borate autocausticization. In: 7th international conference on new available technologies,
Stockholm, Sweden, 4–6 June 2002, pp 87–90
Kochesfahani SH, Bair CM, Kirk M (2006) Partial borate autocausticizing, a new technology in
chemical recovery. Appita J 59(2):130–135
Kojima, Y, Yoon, SL (1991) Distribution of lignin in the cell wall of ozonized CTMP fibres. In:
Proceedings from the 1991 6th international symposium on wood and pulp chemistry,
Melbourne, Australia, p 109
Kojima Y, Yoon SL, Kayama T (1988) A study of production of CTMP from hardwood. Part B :
characterization of pulp produced by CTMP-O3 process, Japan Tappi J 42(10): 953–962
Koskinen K (1999) Wood handling applications. In: Gullichsen J, Fogelholm C-J (eds) Papermaking
science and technology, Book 6A. Chemical pulping. Fapet Oy, Helsinki, pp 331–491
Ku PWC, Hsieh JS, Jayawant MD, Houle L (1992) Chlorination stage elimination by using
nitrosation pretreatment before oxygen delignification/oxygen reinforced extraction. Tappi J
75(10):146–151
Kubes GJ, Fleming BI, Macleod JM, Bolker HI, Werthemann DP (1983) Viscosities of unbleached
alkaline pulps.2. The G-factor. J Wood Chem Technol 3(3):313–333
Kuligowski C, Brochier B, Petit-Conil M (2005) New ways to use ozone in bleaching sequences:
ozonated water as a last bleaching stage. In: 2005 international pulp bleaching conference,
Stockholm, Sweden, 14–16 June 2005, pp 284–287
Kymäläinen M (2001) Fate of nitrogen in the chemical recovery cycle of a kraft pulp mill. PhD
thesis, Åbo Akademi University, Turku, Finland
Lachenal D, Papadopoulos J (1988) Improvement of hydrogen peroxide delignification. J Cellul
Chem Technol 22(5):537
Lachenal D, Chirat C, Viardin MT (2000) High temperature chorine dioxide delignification. A
breakthrough in ECF bleaching of hardwood kraft pulps. Tappi J 83(8):96
Laine J, Stenius P, Carlsson G, Storm G (1996) The effect of ECF and TCF bleaching on the
surface chemical composition of kraft pulp as determined by ESCA. Nord Pulp Pap Res J
11(3):201
Lancaster L,Yin C, Renard J, Phillips RB (1992) The effects of alternative pulping and bleaching
processes on product performance – economic and environmental concerns. In: Proceedings,
EPA international symposium on pollution prevention in the manufacture of pulp and paper.
Washington, USA
Larsen E, Kreutz T, Consonni S (1998) Performance and preliminary economics of black liquor
gasification combined cycles for a range of kraft pulp mill sizes. In: International chemical
recovery conference, vol 2, Tampa, FL, USA, 1–4 June 1998, pp 675–692
Larsen E, Consonni S, Katofsky R (2003) A cost-benefit assessment of biomass gasification power
generation in the pulp and paper industry. Final report. Princeton Environmental Institute,
October 8, 2003. Princeton University Princeton, NJ, USA
Laubach GD (1998) 1997 TAPPI survey of pulping additives – AQ and chip penetrants, In: TAPPI
proceedings: breaking the pulp yield barrier symposium. TAPPI Press, Atlanta, pp 103–111
Lecourt M, Struga B, Delagoutte T, Petit-Conil M (2007) Saving energy by application of ozone in
the thermomechanical pulping process. IMPC, Minneapolis, pp 494–507
Lee HL, Yuon HJ, Jung TM (2000) Improvement of linerboard properties by Condebelt drying.
TAPPI 83(7)
Lefebvre BE, Santyr GM (1989) Effect of operating variables on kraft recovery boiler performance.
Pulp Pap Can 90(12):145–152
References 207
Leporini Filho C, Süss HU, Rodrigues da Silva M, Lopes Peixoto MA (2003) Addition of hydrogen
peroxide to ozonation for improved bleaching results., ABTCP-TAPPI 2003, 36° Congresso
Internacional de Celulose e Papel, São Paulo, Brazil
Levlin JE (1990) On the use of chemi-mechanical pulps in fine papers. Pap Ja Puu-Pap Timber
72(4):301–308
Li J, Gellerstedt G (1997a) On the structural significance of kappa number measurement. In: Preprints
9th international symposium, wood pulping chemistry, vol 1, Montreal, QC, Canada, GI-I
Li J, Gellerstedt G (1997b) The contribution to kappa number from hexenuronic acid groups in
pulp xylan. Carbohydr Res 302(3–4):213
Li K, Lei X, Lu L, Camm C (2010) Surface characterization and surface modification of mechanical
pulp fibers. Pulp Pap Can 111(1):28–33
Lin B (2008) The basics of foul condensate stripping. Krat recovery short course, Florida, USA
Lindberg H, Engdahl, H, Puumalinen R (1994) Strategies for metal removal control in closed cycle
mills. In: 1994 proceedings of the international pulp bleaching conference. CPPA, Montreal
Lindblom M (2006) Chemrec pressurized black liquor gasification – status and future plans. In: 7th
international colloquium on black liquor combustion and gasification, Jyväskylä, Finland, 31
July – 2 August 2006
Lindgren CT, Lindström ME (1996) The kinetics of residual delignification and factors affecting
the amount of residual lignin during kraft pulping. J Pulp Pap Sci 22(8):J290–J295
Lindholm CA (1977a) Ozone treatment of mechanical pulp. Part 2: influence on strength properties,
Pap Ja Puu 59(2):47–50, 53–58, 60, 62
Lindholm CA (1977b) Ozone treatment of mechanical pulp. Part 3: influence on optical properties,
Pap Ja Puu 59(4a):217–218, 221–224, 227–232
Lindholm CA (1977c) Ozone treatment of mechanical pulps. Pap Ja Puu (Special No. 4a):217–231.
Lindholm CA, Gummerus M (1983) Comparison of alkaline sulphite and ozone treatment of
SGW, PGW and TMP fibre’s. Pap Ja Puu 65(8):467–473
Lindstrom LA (2003) Impact on bleachability and pulp properties by environmentally friendly bleach-
ing concepts. In: Metso paper pulping technology seminar, Hyderabad, India, November 2003
Lindström LÅ, Larsson, PE (2003) Fiber lines for bleached eucalyptus kraft pulps. Impact on
bleachability and paper properties. In: Conference in Vicosa, Brasil, 4–5 September 2003
Lindström ME, Teder A (1995) The effect of polysulfide pretreatment when kraft pulping to very
low kappa numbers. Nord Pulp Pap Res J 10(1):8
Lindstrom LA, Norden S, Wennerstrom M (2007) High consistency ozone bleaching: present sta-
tus and future. IPPTA 19(1):83–86
Lönnberg B (2009) Papermaking science and technology, Book 5, mechanical pulping, Chapter 7,
Thermomechanical Pulping, pp 214–221, Paperi ja Puu Oy
Löwendahl L, Samuelsson O (1978) Carbohydrate stabilization during soda pulping with addition
of antraquinone. Tappi 61(17):566
Lyon RK (1979) Thermal DeNOx: How it works. In: Hydrocarbon processing, October. Gulf
Publishing Co., Houston, Texas
Lyon RK (1987) Thermal DeNO: controlling nitrogen oxides emissions by a noncatalytic process,
Environ Sci Technol 21(3):231
Magara K, Ikeda I, Tomimura Y, Hosoya S (1998) Accelerated degradation of cellulose in the pres-
ence of lignin during ozone bleaching. J Pulp Pap Sci 24(8):264
Magnotta V, Kirkman A, Jameel H, Gratzl J (1998) High kappa pulping and extended oxygen
delignification to increase yield, Breaking the pulp yield barrier symposium, Atlanta, February
17–18 1998, Tappi Press, Atlanta, pp 165–182
Mahmoudi S, Baeyens J, Seville JPK (2010) NOx formation and selective non-catalytic reduction
(SNCR) in a fluidized bed combustor of biomass. Biomass Bioenergy 34:1393–1409
Mäkinen T, Alakangas E, Kauppi M (2011) BioRefinery yearbook 2011. Tekes, Helsinki
Maleshenko A, Ilmoniemi E, Kaasalainen H (2008) Web-forming unit of a paper or board machine.
WO 2006120294 (A1)
Malinen R, Rantanen T, Rautonen R, Toikkanen L (1994) TCF bleaching to high brightness – bleaching
sequences and pulp properties. In: Paper presented at 1994 international pulp bleaching confer-
ence held at Vancouver, Canada, 13–16 June 1994, Paper presentations, pp 187–194
Malkov Y (1990) A polysulfide liquor regeneration process with the use of an MT catalyst. Pap Ja
Puu 72(10):961–966
Malmström J (2010) NOx emissions from Swedish recovery boilers. Swedish Forest Industries
Federation, Sweden
Mansour MN, Steedman, WG, Durai-Swamy K, Kazares, RE, Raman TV (1992) Chemical and
energy recovery from black liquor by steam reforming. In: International chemical recovery
conference, Seattle, WA, USA, 7–11 June 1992
Mansour MN, Durai-Swamy K, Aghamohammadi B (1993). Pulsed combustion process for black
liquor gasification. Second annual report U.S. DOE report DOE/CE/40893-T2 (DE94002668)
Mansour MN, Durai-Swamy K, Warren DW (1997) Endothermic spent liquor recovery process,
U.S. Patent no 5,637, 192
Mao X, Kim J, Tran H, Kochesfahani SH (2006) Effect of chloride and potassium on borate
autocausticizing reactions during black liquor combustion, Pulp Pap Can 107(10):T201–T204
Maples GM, Ambady R, Caron JR, Stratton SC, Vega Canovas RE (1994) BFR™: a new process
toward bleach plant closure. Tappi J 77(11)
Marechal AJ (1993) Acid extraction of alkaline wood pulps before or during bleaching: reason and
opportunity, Wood Chem Technol 13(2):261
Martin N, Anglani N, Einstein D, Khrushch M, Worrell E, Price L (2000a) Opportunities to
improve energy efficiency and reduce greenhouse gas emissions in the U.S. Pulp and Paper
Industry. Lawrence Berkeley National Laboratory, LBNL-46141, Berkeley
Martin N, Worrell E, Ruth M, Price L, Elliott RN, Shipley AM, Thorne J (2000b) Emerging
energy-efficient industrial technologies. Lawrence Berkeley National Laboratory, LBNL-
46990, Berkeley
Martius C (1992) Density, humidity, and nitrogen content of dominant wood species of floodplain
forests (várzea) in Amazonia. Holz Roh Werkst 50:300–303
McCubbin N (1996) Numerous recovery options offer solutions for mill effluent closure. Pulp Pap Mag
March 1996. Available online. www.risiinfo.com/db_area/archive/p_p_mag/1996/9603/96030131.htm
McCubbin N (2001a) Spill control: assessing your situation. Solutions 84(11):49–50
McCubbin N (2001b) Spill control. Part II: Reducing spills. Solutions 84(12):36–37
McDonough TJ (1990) Oxygen delignification. In: Tappi bleach plant operations short course,
Hilton Head, Tappi press
Tappi J 78:55–62
McDonough TJ (1996) Oxygen delignification. In: Dence CW, Reeve DW (eds) Pulp bleaching –
principles and practice. Tappi Press, Atlanta, p 213
McDonough T, Herro J (1997) Influence of low-lignin pulping conditions on bleachability; effects
of anthraquinone and effective alkali charge, anthraquinone pulping: TAPPI Press Anthology
of Published Papers 1977–1996 (Goyal G. ed.) Chapter 1, pp 129–133
McGowan D R (2002) White water reuse in high-pressure paper machine showers. Preprints 88th
PAPTAC annual meeting, Montreal, QC, Canada, 29–31 January 2002 [Pulp and Paper
Technical Association of Canada, Montreal, Canada: 2002), pp B125–B128
Mckeough P (2003) Evaluation of potential improvements to BLG technology. Colloquium of
black liquor combustion and gasification. Utah, Park City, 12 p
Mehra NK (1979) Recausticizing and lime mud reburning, Tappi 62(9):47–51
Meller A (1963) Retention of polysaccharides in kraft pulping. Part 1. The effect of borohydride
treatment of Pinus radiata wood on its alkali stability. Tappi 46(5):317–319
Meller A, Ritman BL (1964) Retention of polysaccharides in kraft pulping. Part II. The effect of
borohydride addition to kraft liquor on pulp yield, chemical characteristics and papermaking
properties of Pinus radiata pulps. Tappi 47(1):55–64
Michniewicz M, Janiqa M (2010) The technique for sodium carbonate autocausticization with
sodium metaborate. Polish Pap Rev 66(5):263–268
References 209
Middleton T (2006) Steam reforming technology at the norampac trenton mil. Presentation at IEA
meeting, annex XV black liquor gasification, Washington, DC, USA, 20–22 February 2006.
Moldenius S (1995) Pulp quality and economics of ECF vs. TCF. In: Presentation, international
non-chlorine bleaching conference. Amelia Island, Florida
Moldenius S (1997) Mill experience with ECF and TCF bleaching facts vs. fiction. In: Proceedings
of the international emerging technologies conference, Orlando, FL
Mutton DB (1958) Hardwood resin. Tappi 41(11):632–643
Naqvi M, Yan J, Dahlquist E (2010) Black liquor gasification integrated in pulp and paper mills: a
critical review. Bioresour Technol 101:8001–8015
Naqvi M, Yan J, Dahlquist E (2012) Bio-refinery system in a pulp mill for methanol production
with comparison of pressurized black liquor gasification and dry gasification using direct caus-
ticization. Appl Energy 90(1):24–31
National Council for Air and Stream Improvement (NCASI) (2012) Pulp and paper mill emissions
of SO2, NOx, and particulate matter in 2010. Special report no. 12–03. National Council for Air
and Stream Improvement Inc, Research Triangle Park
National Council for Air and Stream Improvement (NCASI) (2013) Overview of effects of
decreased SOx and NOx emissions. www.paperenvironment.org/PDF/SOxNOx/SOxNOx
Nelson PJ (1998) Elemental chlorine free (ECF) and totally chlorine free (TCF) bleaching of
pulps. In: Young RA, Akhtar M (eds) Environmentally friendly technologies for the pulp and
paper industry. Wiley, New York, p 215
Nesaratnam S (1998) Effluent treatment. Pira environment guide series, Pira International,
Leatherhead, p 72
Newport DG, Rockvam 1, Rowbotton R (2004) Black liquor steam reformer start-up at Norainpac.
In: Proceedings of TAPPI international chemical recovery conference, South Carolina
Ni Y, Kubes GJ, van Heiningen ARP (1992) Rate processes of chlorine dioxide distribution during
prebleaching of kraft pulp. Nord Pulp Pap Res J 7(4):200–204
Nichols KM, Thompson, LM, Empie HJ (1993) A review of NOx formation mechanisms in
recovery furnaces. Tappi J 76(1):119–124
Niiranen M (1985) Study of debarking drum process dimensioning. Doctoral thesis. Helsinki
University of Technology
Nilsson J (1998) A literature survey of impulse drying, 1994–1998. Technical report. LUTKDH/
(TKKA-7004)/1-36/1998. Lund University
Nilsson LJ, Larson ED, Gilbreath KR, Gupta A (1995) Energy efficiency and the pulp and paper
industry. ACEEE, Washington, DC/Berkeley
Nilsson P, Puurunen K, Vasara P,Jouttijarvi T (2007) Continuum – rethinking BAT emissions of the
pulp and paper industry in the European Union, Finnish environment report 12/2007. 41 pp
Nordén S, Teder A (1979) Modified kraft processes for softwood bleached-grade pulp. Tappi
62(7):49–51
Nordic Council of Ministers (1993) Study on nordic pulp and paper industry and the environment.
Nordic Council of Ministers, Copenhagen
Northeast States for Coordinated Air Use Management (NESCAUM) (2005) Assessment of
control options for BART-eligible sources. Steam electric boilers, industrial boilers, cement
plants and paper and pulp facilities. Northeast States for Coordinated Air Use Management In
Partnership with The Mid-Atlantic/Northeast Visibility Union. www.nescaum.org/documents/
bart-controlassessment.pdf/
Norvall G, Burton T, Kanters C (2001) The removal of pulp mill odors by novel catalytic environ-
mental technology. Pulp Pap Can 102(4):T111–T113
Nurmesniemi H (2010) Tertiary treatment of biologically treated waste water from the pulp and
paper mill – internal report assessing findings of the WWF report on the Celco pulp mill in
Valdivia, Chile, Sora Enso Oyj, Environmental affairs, 2010, p 2
Nutt WE, Griggs BF, Eachus SW, Pikulin MA (1993) Developing an ozone bleaching process.
Tappi J 76(3):115–213
Obst JR, Landucci LL, Sanyer N (1979) Quinons in alkaline pulping. Tappi 62:1, 55
Oinonen H (2010) Ozone bleached pulp and fine papers. Results Pulp Pap (2):35–38
Ojala T (1999) Condebelt drying process benefiting paper- and boardmanufacturing and convert-
ing. In: Presentation at Aticelca/ATI Convention in Milan, April 19, 1999, Energetic evolution
in the paper sector
Pan GX (2001) An insight into the behaviour of aspen CTMP in peroxide bleaching – alkalinity’s
influence is greater than that of peroxide charge. Pulp Pap Can 102(11):41–45
Panchapakeshan B, Hickman E (1997) Fiberline advancements spur papermaking process changes. In:
Patrick KL (ed) Advances in bleaching technology. Miller Freeman Books, San Francisco, p 82
PARCOM (1994) BAT and BEP for the Sulphite and Kraft Pulp Industry, PARCOM, ISBN 0946
56 367
Parker ET, Lundsted LG (1975) U.S.A. Patent 3,909,345
Parthasarathy VR (1997) Oxidative extraction of hardwood and softwood kraft pulps with sodium
carbonate-sodium hydroxide mixtures or oxidized white liquor during multistage bleaching.
Tappi J 80(10):253–261
Parthasarathy VR, Rudie GF, Detty AE (1993) Total chlorine dioxide substitution in short sequence
bleaching and it’s effect on pulp brightness and effluent characteristics. In: Tappi pulping
conference proceedings. Tappi Press, Atlanta, p 933
Pekkala O (1982) On the extended delignification using polysulfide or anthraquinone in kraft
pulping. Pap Ja Puu 64(11):735–744
Pekkala O (1986) Prolonged kraft cooking modified by anthraquinone and polysulfide. Pap Ja Puu
68(5):385–400
Pereira ER, Colodette JL, Barna J (1995) Peroxide bleaching in pressurised equipment: influence
of temperature and consistency. Papel 56(12):61–67
Persson H (1994) A literature review of impulse drying, 1988–1994. Technical report LUTKDH/
(TKKA-7005)/1-42/1994. Lund University
Peter W (1993) First experience with mill-scale ozone bleaching, non-chlorine bleaching conference,
Miller Freeman, San Francisco, CA, USA, 1993, Paper 22
Petit-Conil, M (1995) Principes de préparation des pâtes CTMP de bois résineux et feuillus. Application
à la mise au point de procédés, Thèse de l’Institut National Polytechnique de Grenoble
Petit-Conil M (2003) Use of ozone in mechanical pulping processes. ATIP 57(2):17–26
Petit-Conil M, de Choudens C (1994) A new chemithermomechanical process : use of oxygen in
the primary refining stage. Part 1: oxidative sulfonation for hardwood and softwood CTMP
pulping. Das Pap 48(10):628–634
Petit-Conil M, Robert A, Pierrard JM (1997) Fundamental principles of mechanical pulping from
softwoods and hardwoods. Part 1: theoretical aspects. Cellul Chem Technol 31(1/2):93–104
Petit-Conil M, de Choudens C, Espilit T (1998) Ozone in the production of softwood and hardwood
high-yield pulps to save energy and improve quality. Nord Pulp Pap Res J 13(1):16–22
Pettersson SE, Rydholm SA (1961) Hemicelluloses and paper properties of birch pulps, Part 3.
Sven Pap 64(1):4–17
Pikka O, Vessala R, Vilpponen A, Dahllof H, Germgard U, Norden S, Bokstrom M, Steffes F,
Gullichsen J (2000) Bleaching applications. In: Gullichsen J, Fogelholm C-J (eds) Chemical
pulping –papermaking science and technology. Fapet Oy, Helsinki, Finland, Book 6A, p A19
Pipon G, Chirat C, Lachenal D (2005) Final bleaching with ozone – basic and applied aspects.
IPBC, Stockholm, pp 138–143
Pöyry J (1992) Reduction of atmospheric emissions from pulp industry, on behalf of Swedish EPA
Pöyry J (1997) A compilation of BAT techniques in Pulp and Paper Industry. Jaakko Pöyry Oyj, 1997,
Finland
Prakash CB, Murray FE (1973). Studies on H2S emission during calcining, Pulp Pap Mag Can
74(5):99–102
Program SNB (2011) Gasification of black liquor, popolar scientific summary of the BLG II – program
2007–2010. Retrieved on March 15, 2012. Available at: http://www.etcpitea.se/pdf/BLG_eng.pdf
Pryke DC (1997) Elemental Chlorine-Free (ECF): pollution prevention for the pulp and paper
industry. http://www.ecfpaper.org/science/science.html (April 1997)
Pryke DC (2003) ECF is on a roll: it dominates world bleached pulp production. Pulp Pap Int
45(8):27–29
References 211
Pryke DC, Farley B, Wolf A (1995) Implementation of ECF bleaching at Mead Paper Co.,
Chillicothe, Ohio. In: Tappi pulping conference proceedings. TAPPI PRESS, Atlanta
Quinde A (1994) Pulping additives in kraft pulping: past, present and future. In: 1994 Spring
conference, Canadian Pulp and Paper Association. Jasper, Alberta. May 19–2
Quinde A, Brogdon, B, Fowler L, Lee C (2004) A decade of AQ benefits at Canfor’s Northwood
Mill (1994–2004). In: 2004 TAPPI Fall technical conference. Atlanta, GA, USA, October 31–
November 3, 2004
Radojevic M (1998) Reduction of nitrogen oxides in flue gases. Environ Pollut 102:685–689
Ragauskas AJ, Poll KM, Cesternino AJ (1993) Effect of xylanase pretreatment procedures for non-
chlorine bleaching. IPST technical paper series, no. 482, Institute of Paper Science, Atlanta, 1993
Ragnar M (2002) Modification of the D0 stage into D* makes 2-stage bleach plant for HW kraft
pulp a reality. TAPPI international pulp bleaching conference. Portland, OR. Tappi Press,
Atlanta
Ragnar M, Dahllöf H (2002) Kvaerner pulping, ECF bleaching of eucalypt kraft pulp bleaching
chemical needs and yellowing characteristics of different sequences. Nord Pulp Pap Res J 17:3,
228–233
Rajotte A (2000) Technology and environmental policy: case study on chlorine policies in the P&P
sector in Finland, France, and Sweden, School of Business and Economics, University of
Jyväskylä, Finland. In: 4th framework programme of DG XII of the European Commission,
Contract ENV4-CT97-0604, 2000.
Rampotas C, Terelius H, Jansson K (1996) The netfloc system – the tool to remove extractives and
NPE. In: Proceedings of the 1996 minimum effluent mills symposium, Atlanta
Rapson WH, Anderson CB (1978) Kraft pulp bleaching with chlorine and chlorine dioxide. Tappi
J 61(10):97
Ratnieks E, Ventura JW, Mensch MR, Zanchin RA (2001) Acid stage improves production in
eucalyptus fibreline. P&P Can 102:12
Reeve DW (1996) In: Dence CW, Reeve DW (eds) Pulp bleaching – principles and practice. Tappi
Press, Atlanta, pp 263–287
REHVA (2005) Electrostatic precipitators for industrial applications. REHVA guidebook,
REHVA – Federation of European Heating and Air-conditioning Assosiations. REHVA,
Brussels, p 117
Reis R (2001) The increased use of hardwood high yield pulps for functional advantages in paper-
making. In: Proceedings of the 2001 papermakers conference, Cincinnati, OH, USA, pp 87–108
Rentz O, Schleef, HJ, Dorn R, Sasse H, Karl U (1996) Emission control at stationary sources in the
Federal Republic of Germany, Volume I, Sulphur oxide and Nitrogen oxide emission control,
French-German Institute for Environmental Research University of Karlsruhe (TH), Karlsruhe,
August 1996
Retulainen E (2001) Key development phases of condebelt: long journey from idea to commercial
product. Dry Technol 19(10):2451–2467
Retulainen E, Hamalainen A (2000) Three years of condebelt drying at stora enso’s pankakoski
mill. TAPPI 83(5):1–8
Retulainen E, Merisalo N, Lehtinen J, Paulapuro H (1998) Effect of condebelt press drying in sheet
structure and properties. Pulp Pap Can 99(1):53–58
Rice RC, Netzer A (1982) Handbook of ozone technology and applications. Ann Arbor Science,
Ann Arbor
Robert DR, Szadeczki M, Lachenal D (1999) Chemical characteristics of lignins extracted from softwood
TMP after O3 and ClO2 treatment. In: Proceedings from the 215th national ACS meeting, Lignin:
historical, biological and materials perspectives, Dallas, Texas, USA, chapter 27, pp 520–531
Rockvam LN (2001) Black liquor steam reforming and recovery commercialization. In:
International chemical recovery conference, Whistler, Canada, 11–14 June 2001
Rodrigues da Silva M, Peixoto MAL, Colodette JL (2002) Mill experience using a hot acid stage
for eucalyptus kraft pulp bleaching. In: TAPPI international pulp bleaching conference.
Portland, OR. Tappi Press, Atlanta
Rothenberg S, Shaw J, Durst WB (1981) Effect of chemical modification on the properties of

lignin-containing fibres. Pap Ja Puu 63(3):111–114, 117–119
Roy-Arcand L, Archibald F (1996) Selective removal of resin and fatty acids from mechanical pulp
effluents by ozone. Water Res 30(5):1269–1279
RPDC (2004) Development of new environmental emission limit guidelines for any new bleached
eucalypt Kraft pulp mill in Tasmania- volume 1. Resource Planning and Development
Commission, Tasmania
Ruffini G (1966) Improvement of bonding in wood pulps by the presence of acidic groups, Svensk
Papperstding 69(3):72
Ryham R, Nikkanen S (1992) Liquor heat treatment and its impact on chemical recovery. In:
Proceedings of the 1992 European pulp & paper week, Bologna, Italy, May 1992
Sabourin M (2007) Minimizing TMP energy consumption using a combination of chip pre-
treatment, RTS and multiple stage low consistency refining. In: 25th international mechanical
pulping conference, Minneapolis, MN, USA, May 6–9, Tappi, Atlanta, GA, USA, 8 pp
Sabourin MJ, Hart PW (2010) Enhanced fiber quality of black spruce (Picea mariana) thermome-
chanical pulp fiber through selective enzyme application. Ind Eng Chem Res 49:5945–5951
Sabourin M, Aichinger J, Wiseman N (2003) Effect of increasing wood chip defibration on
thermomechanical and chemi-thermomechanical refining efficiency, In: International mechanical
pulping conference, Quebec City, pp 163–170
Saharinen E, Nurminen I (2001) Improving internal bonding strength and bulk for folding b oxboard
middle layer by ozone treatment. In: Proceedings from the 2001 international mechanical
pulping conference, Helsinki, Finland, pp 119–124
Salo M (1999) Environmental best practices in the forest cluster, Interim Report IR-00-015,
International Institute for Applied Systems Analysis, Vienna, Austria
Santos RE, Backlund JC (1992) Firing of non-condensible waste gas streams in stand alone
modular incineration systems. In: Presented at the 1992 incineration conference, Albuquerque,
New Mexico, Session XXI
Scheriau R (1972) Theorie der trommelentrindung unter besonderen berücksichtigung der
trockenentrindung . Dissertation an der Technischen Hochschule Graz
Schroderus S, Carter D, Brumme H (2000) Upgrade of lime kiln and causticizing plant in kraft
mill. Pulp Pap Can 101(1):74–78
Sebbas E (1988) Reuse of Kraft Mill secondary condensates. Tappi J 71(7):53–58
SEPA-Report 4712-4 (1997a) Energy conservation in the pulp and paper industry. Jaakko Pöyry
Consulting AB, Scotland, 1997
SEPA-Report 4713-2 (1997b) Aspects on energy and environment costs in connection with
production of kraft pulp, Recycled fibre and TMP. Jaakko Pöyry Consulting AB, Scotland,
1997
Sezgi US, Kirkman AG, Jameel H, Chang H, Morrison JJ, Bianchini CA, Wilson JRA (1994)
Combined discrete-continuous simulation model of an RDH tank farm. Tappi J 77(7):213–220
Sharma KD (2010) ITC’s experience with light ECF bleaching (ozone). IPPTA 22(1):131–133
Sheats A (2010) Ozone bleaching: environmental, production, and cost benefits. Pap Asia
26(3):24–26, 28
Shrinath SA, Bowen I.J (1993) An overview of AOX regulations and reduction strategies, In: Tappi
pulping conference proceedings, Atlanta 14–18.11.1993, pp 1–15
Siltala M, Winberg K (1999) The use of bleach plant filtrate for post-oxygen washing: a way to save
money and the environment. In: Proceedings of the 27th EUCEPA conference – crossing the mil-
lennium frontier, emerging technical and scientific challenges, Grenoble, France, pp 11–14
Simons HA, AF-IPK (1992) Multi-client study. In: Towards kraft mill 2000, Vancouver, Canada,
Book 2, p 54
Sjöblom K, Mjöberg J, Hartler N (1983) Extended delignification in kraft cooking through
improved selectivity .1. The effects of the inorganic composition of the cooking liquor. Pap Puu
65(4):227–240
Sjödahl RG, Axelsson P, Lindström ME (2006) Addition of dissolved wood components to improve
the delignification rate and pulp yield in hardwood kraft pulping. Appita J 59(4):317–320
References 213
Smook GA (1992) Handbook for pulp & paper technologists, 2nd edn. Angus Wilde Publications,
Vancouver, p 36
Soteland N (1977) The effect of ozone on mechanical pulps, Pulp Pap Can 78(7):45–48
Soteland N (1982) Interstage ozone treatment of hardwood high yield pulp. Pap Ja Puu 64(11):707–
708, 710, 712–714
Soteland N, Loras V (1974) The effect of ozone on mechanical pulps. Norsk Skogind
28(6):165–169
Springer EL (1997) Delignification of wood and kraft pulp with peroxomonophosphoric acid. J
Pulp Pap Sci 23(12):582
Sricharoenchaikul V (2001) Fate of carbon-containing compounds from gasification of kraft black
liquor with subsequent catalytic conditioning of condensable organics. Ph.D dissertation,
Georgia Institute of Technology, 2001
Steen B, Stijnen T (1984) Hydrogen sulfide formation in a lime kiln at a kraft mill, Svensk
Papperstidning 87(3):R14–R17
Steffes F, Germgard U (1995) ECF, TCF upgrade choices key on world market, environmental
forces. Pulp Pap 69(6):83–92
Stenström S (1989) Impulstorkning av papper. STU projekt 742-88-02837. Lunds Tekniska
Högskolan, (in Swedish)
Stigsson L (1998) Chemrec black liquor gasification. In: International chemical recovery conference,
Tampa, Florida, USA, 1–4 June 1998
Stitt, EH, Fakley ME (1995) New process for the abatement of odors and low level VOCs. preprints.
AIChE Spring meeting, Houston, TX, March, 1995
Strakes G, Bielgus J (1992) New chip thickness screening system boosts efficiency, extends wear
life. Pulp Pap, July, p 93
Stratton S, Gleadow P (2003) Pulp mill process closure: a review of global technology developments
and mill experiences in the 1990s. Technical bulletin no. 860. Research. National Council for
Air and Stream Improvement, Inc., Triangle Park
Stratton S, Gleadow P, Johnson A (2003) Pulp mill process closure: a review of global technology
developments and mill experiences. In: The 1990s international Water Association conference,
Seattle, USA
Stubenvoll J, Holzerbauer, E, Böhmer, S (2007) Overview of NOx and dust emissions of the
Austrian pulp and paper industry, Unweltbundesamt, 2007
Suhr M (2000) The BREF in the pulp and paper industry. BAT for an industry with a large variety
of raw materials and products. In: European conference on the seville process: a driver for
environmental performance in industry, April, 6–7, Stuttgart, Germany
Sun, Y, Lanouette R, Pelletier E, Cloutier JN, Epiney M (2013) Impact of pH during an interstage
ozone treatment of thermomechanical pulp. In: PACWEST conference, Kamloops, BC,
Canada, 6 pages
Sun Y, Lanouette R, Pelletier E, Cloutier JN, Epiney M (2014a) Fibre performance of mechanical
pulp after selective refining combined with interstage ozone treatment. In: IMPC conference,
Helsinki, Finland, 10 pages
Sun Y, Lanouette R, Cloutier JN, Pelletier E, Épiney M (2014b) Impact of selective refining combined
with inter-stage ozone treatment on thermomechanical pulp. BioResources 9(1):1225–1235
Süss HU, Del Grosso M (2002) Bleaching of eucalyptus kraft pulp to market pulp brightness in
only 2 stages. In: Appita Conference, Rotorua, New Zealand
Suss HU, Schmidt K, Del Grosso M, Mahagaonkar M (2000) Peroxide application in ECF
sequences: a description of the state-of-the-art. Appita 53(2):116–121
Talja R, Bäckström, M, Kilian M (1998) Impulse technology – a paper making process for
tomorrow, EcoPaperTech, 1998. KCL, Helsinki
Tamminen T, Forssen M, Hupa M (2002) Dust and flue gas chemistry during rapid changes in the
operation of black liquor recovery boilers: Part 3 – gaseous emissions. Tappi J 1(7):25–29
Tana J, Lehtinen KJ (1996) The aquatic environmental impact of pulping and bleaching operations –
an overview. Finnish Environmental Agency, Helsinki
Tatsuishi H, Hatano T, Iwai T, Kovasin K (1987) Practical experiences of medium consistency

oxygen delignification by Rauma-Repola and Sumitomo heavy industries. In: Tappi interna-
tional oxygen delignification conference proceedings. Tappi Press, Atlanta, p 209
Teder A (1968) Redox potential of polysulphide solutions and carbohydrate stabilisations. Sven
Pap 71(5):149
Teder A, Olm L (1981) Extended delignification by combination of modified kraft pulping and
oxygen bleaching. Pap Puu 63(4a):315–326
Teixeira DP, Muzio LJ, Montgomery TA (1991) Effect of trace combustion species on SNCR per-
formance. In: International conference on environmental control of combustion processes, joint
meeting of the American Flame Research Committee and the Japanese Flame Research
Committee, Honolulu, HI. October, 1991
Telkkinen, UT (1997) Typen määrä ja vaikutukset sulfaattisellutehtaan kemikaalikierrossa
johdettaessa valkaisun vedet kemikaalien talteenottoon. Lic. Tech. thesis. Helsinki University
of Technology, Espoo, Finland. (in Finnish)
Tench L, Harper S (1987) Oxygen bleaching practices and benefits – an overview. In: Tappi
international oxygen delignification conference proceedings. Tappi Press, Atlanta, p 1
Tenkanen M, Gellerstedt G, Vuorinen T, Teleman A, Perttula M, Li J, Buchert J (1999)
Determination of hexenuronic acid in softwood kraft pulps by three different methods. J Pulp
Pap Sci 25(9):306
Tervola P, Gullichsen J (2007) Confidence limits in mass balances with application to calculation
of pulp washing efficiency. Appita J 60(6):474–481
Theodore L (2008) Electrostatic precipitators in air pollution control equipment calculations,
Wiley, 2008
Thornton J, Ekman R, Holmbom B, Eckerman C (1993) Release of potential anionic trash in
peroxide bleaching of mechanical pulp. Pap Ja Puu-Pap Timber 75(6):426–431
Tikka PO, Tahkenen H, Korasin KK (1992) Chip thickness vs. kraft pulping performance, Part I:
experiments by multiple hanging baskets. In: Proceedings, 1992 Tappi pulping conference,
Boston MA, November 1992, p 555
Tran HN, Barham D (1991) An overview of ring formation in lime kilns. Tappi J 74(1):131–136
Tran HN, Mao X, Barham D (1993) Mechanisms of ring formation in lime kilns, J Pulp Pap Sci
19(4):167–174
Tran H, Bair CM, McBroom RB, Strang W, Morgan B (2001) Partial autocausticizing of kraft
smelt with sodium borates. Tappi/Solutions! 84(9):1–16
Tran KQ, Kilpinen P, Kuma N (2008) In-situ catalytic abatement of NOx during fluidized bed
combustionda literature study. Appl Catal B Environ 78:129–138
Troughton N, Sarot P (1992) The efficient use of hydrogen peroxide as a chemical pulp delignifica-
tion agent: the macrox system. In: Proceedings Tappi pulping conference. TAPPI PRESS,
Atlanta, GA, USA, p 519
Tucker P (2002) Changing the balance of power. Solutions 85(2):34–38
Tutus A (2005) The utilization of the boron compounds in pulping and bleaching. In: National
boron symposium proceedings, Ankara, 2005, pp 399–404
Tutus A, Usta M (2004) Bleaching of chemithermomechanical pulp (CTMP) using environmen-
tally friendly chemicals. J Environ Biol 25:141–145
Ulmgren P, Rådeström R (1997) The build-up of phosphorus in a kraft pulp mill and the precipita-
tion of calcium phosphate from green and white liquors. J Pulp Pap Sci 23(2):J52–J58
United Nations Environment Programme (UNEP) (2006) Draft guidelines on best available tech-
niques and provisional guidance on best environmental practices relevant to Article 5 and
Annex C of the Stockholm convention on persistent organic pollutants, revised working draft
version 25 April 2006 www.chem.unep.ch/pops/
Urbanski R, Lister S, Raoul D (1998) Development of an effective TRS and odor reduction pro-
gram. Pulp Pap Can 99(8):T278–T281
USEPA (1992) Model pollution prevention plan for the kraft segment of the pulp and paper indus-
try. Region 10, Seattle, WA. EPA 910/9-92-030, September, 1992
References 215
USEPA (1976) Technology transfer, environmental pollution control, pulp and paper industry, Part
1: Air, EPA 625/7-76-001.
USEPA (1997) Supplemental technical development document for effluent limitations guidelines
and standards for the pulp and paperboard category – subpart B and subpart E. U.S. Environmental
Protection Agency, Washington, DC, USA, October 1997. Available online at http://water.epa.
gov/scitech/wastetech/guide/pulppaper/upload/1997_12_12_guide_pulppaper_jd_stdd-v4.pdf
USEPA (1998a) Federal register notices for final air and water rules, (63 FR 18504–18751, April
15, 1998 and 63 FR 42238–42240, August 7, 1998) www.epa.gov/OST/pulppaper/cluster.html
USEPA (1998b) Pulp and paper NESHAP: a plain English description www.epa.gov/ttnatw01/
pulp/guidance.pdf
USEPA (2007) Fact sheet – final amendments to the regional haze rule and guidelines for Best
Available Retrofit Technology (BART) determinations. United States Environmental Protection
Agency, Washington, DC. http://www.epa.gov/visibility/fs_2005_6_15.html
USEPA (2011) Sulfur dioxide designations and EPA response. United States Environmental Protection
Agency, Washington, DC. http://www.epa.gov/air/sulfurdioxide/designations/state.htm
Vakkilainen EK, Kankkonen S, Suutela J (2008) Advanced efficiency options: increasing electricity
generating potential from pulp mills. Pulp Pap Can 109(4):14–18
Van heiningen A, Ji Y (2012) Southern pine oxygen delignified pulps produced in a Berty throughflow
reactor: how to obtain the highest degree of delignification while maintaining pulp yield and
quality. Tappi J 11(3):9–17
Van Jiang Z-H, Lierop B, Berry R (2000) Hexenuronic acid groups in pulping and bleaching chemistry.
TAPPI J 83:1
Van Lierop B, Skothos A, Liebergott N (1996) Section IV: the technology of pulp bleaching,
Chapter 5: ozone delignification. In: Dence CW, Reeve DW (eds) Pulp bleaching principles and
practices. Tappi Press. Atlanta
Vasara P, Jappinen H, Lobbas P (2001) A strategic concepts for best available techniques in the
forest industry. Finnish Environment Institute, Oy Edita Ab, Helsinki, p 73.
Vasudevan B, Panchapakesan B, Gratzl, JS, Holmbom B (1987) The effect of ozone on strength
development and brightness reversion characteristics of high yield pulps. In: Proceedings from
the 1987 Tappi pulping conference, proceedings, Washington, DC, pp 517–523
Vehmaa J, Pikka O (2007) Proceedings of the paperex 2007, New Delhi, India
Verveka P, Nichols KM, Horton RR, Adams TN (1993) The form of nitrogen in wood and its fate
during kraft pulping. In: Proceedings of the Tappi 1993 environmental conference, Tappi Press,
Atlanta, pp 777–780
Vuorinen T, Taleman A, Fagerstrom P, Buchert J, Tenkanen M (1996) Selective hydrolysis of
hexenuronic acid gr oups and its application in ECF and TCF bleaching of kraft pulps. In:
International pulping bleaching conference, Washington DC, USA, Book 1, p 43
Vuorinen T, Fagerstrom P, Rasanen E, Vikkula A, Henrisson K, Teleman A (1997) Selective hydro-
lysis of hexenuronic acid groups opens new possibilities for development of bleaching pro-
cesses. In: 9th international symposium on wood and pulping chemistry, Montreal, QC,
Canada, p M4-1
Vuorinen T, Fagerstrom P, Buchert J, Tenkanen M, Teleman A (1999) Selective hydrolysis of hex-
enuronic acid groups and its application in ECF and TCF bleaching of kraft pulps. JPPS 25:5
Wahren D (1978) Förfarande och anordning för konsolidering och torkning av en fuktig porös
bana. Swedish patent no. 7803672-0
Walkush K, Gustafson RR (2002) Application of pulping models to investigate the. Performance
of commercial continuous digesters. Tappi J 1(5):13–19
Walsh PB, Secombe RC, Hoyos M (1991) Practical mill experience with the use of hydrogen per-
oxide reinforced extraction stages to reduce and/or eliminate the use of elemental chlorine in
hardwood kraft Pulps for AOX reduction. In: Paper presented at pulping Conference held 3–7
November at Orlando, FL, USA: Book 1, p 35
Walter JC (1996) Water reuse through filtration. In: Proceedings of the 1996 Tappi engineering
conference (Electronic, available at Tappi website). TAPPI, Atlanta, GA
Wang L, Templer R, Murphy RJ (2012) High-solids loading enzymatic hydrolysis of waste papers
for biofuel production. Appl Energy 99:23–31
Wannenmacher PN, Frederick WJ, Hendrickson KA, Holman KL (1998) The solubility of
aluminosilicates in kraft green and white liquors. In: Proceedings of the 1998 international
chemical recovery conference. Tappi Press, Atlanta
Warnqvist B, Delin L, Theliander H, Nohlgren I (2000) Teknisk ekonomisk utvärdering avsvartlut-
förgasningsprocesser. Värmeforsk Service AB, Stockholm
Wedin H (2012) Aspects of extended impregnation kraft cooking for high-yield pulping of hard-
wood. Ph.D thesis, KTH Royal Institute of Technology, Stockholm, Sweden
Wennerström M (2002) Decreasing brightness reversion with powerful ozone bleaching, at IPBC,
Portland, Oregon, USA, p 265
Whitty K, Baxter L (2001) State of the art in black liquor gasification technology. In: Joint
international combustion symposium, Kauai, Hawaii, 9–12 September 2001
Whitty K, Nilsson A (2001) Experience from a high temperature, pressurized black liquor gasifica-
tion pilot plant. In: International chemical recovery conference, Whistler, Canada, 11–14 June
2001
Whitty K, Verrill CL (2004) A historical look at the development of alternative black liquor recov-
ery technologies and the evolution of black liquor gasifier designs. In: International chemical
recovery conference, Charleston, SC, USA, 6–10 June 2004
Wilson J (1993) Results from improved brown stock washing. In: TAPPI pulping conference,
proceedings. Atlanta, GA, USA, pp 155–157
Woodman J (1993) Pollution prevention technologies for the bleached kraft segment of the U.S
pulp and paper industry. US EPA, Washington, DC
World Bank (1998) Nitrogen oxides: pollution prevention and control pollution prevention and
abatement handbook. World Bank Group, Washington, DC, pp 245–249
Worrell E, Price L, Galitsky C (2004) Emerging energy-efficient technologies in industry: case stud-
ies of selected technologies. Lawrence Berkeley National Laboratory, LBNL-54828, Berkeley
Worrell E, Blinde P, Neelis M, Blomen E, Masanet E (2010) Energy efficiency improvement and
cost saving opportunities for the U.S. Iron and Steel Industry: an ENERGY STAR guide for
energy and plant managers. www.energystar.gov/ia/business/industry/Iron_Steel_Guide.pdf,
www.ceeindustrial.com/public/data/companyCatalogue1224056297.pdf
Xu EC (2001) P-RC alkaline peroxide mechanical pulping of hardwood, part 1: aspen, beech,
birch, cottonwood and maple. Pulp Paper Can 102(2):44–47
Xu T, Slaa JW, Sathaye J (2010) Characterizing costs, savings and benefits of a selection of energy
efficient emerging technologies in the United States. California, p 101
Yamaguchi A (1983) Operating experiences with the moxy process and quinoid compounds. In:
Tappi pulping conference proceedings, Houston, October 24–26, pp 544–548
Yanhong G, Jing S, Qun L (2015) China’s high-yield pulp sector and its carbon dioxide emission:
considering the saved standing wood as an increase of carbon storage. BioResources
10(1):10–13
Yant R, Hurst MM (1991) Mill optimization using Monox-L as a replacement for chlorine dioxide.
Tappi J 74(4):165–168
Young J, Start G, Lazorek J (1992) Utilization of an Eop stage during 100 % ClO2 bleaching at
Weldwood Hinton. In: CPPA Pacific and Western Branch annual meeting preprints, Technical
section, CPPA, Montreal: Section 4A, paper No. 3
Zhou Y (2004) Overview of High Yield Pulps (HYP) in paper and board. In: PAPTAC 90th annual
meeting, 2004, pp B143–B148 (Montreal, Canada)
Zhou Y, Zhang D, Li G (2005) An overview of BCTMP: process, development, pulp quality and
utilization. China Pulp Pap 24(5):51–60
Chapter 5
State-of-the-Art Pulp Mills
Abstract Fiberlines that encompass “State-of-the-Art” technology and management

practices are discussed. These include: Celulosa Arauco y Constitución S.A. Nueva
Aldea, Chile; Veracel Celulose; Hainan Jinhai Pulp mill; Cellulosa Arauco Valdivia;
Aracruz, Line C, Brazil; Mercal Stendal, Germany; Bowater, Catawba SC, USA;
Zhanjiang Chenming Greenfield pulp mill, China; Eldorado Celulose e Papel S.A.’s
new greenfield pulp mill in Três Lagoas, Brazil; Montes del Plata mill in Uruguay;
Oji Holdings Nantong pulp mill Jiangsu Province, China; Aracruz’s pulp line, at
their Guaiba mill in Rio Grande do Sul, Brazil; Ilim Group’s new kraft pulp mill, in
Bratsk, Irkutsk Oblast, Russia; Metsa-Botnia, Rauma Mill; Metsa-Botnia Joutseno
mil; Stora Enso’s Nymölla Mill. Today’s State-of-the-Art mills use less wood; are
energy self sufficient; less polluting and provide sustainable value to society.
Keywords Pulp and paper industry • Pulp mill • Fibreline • Energy efficiency
• Environmental impact • Productivity • State-of-the-art mills • State-of-the-art
technology
Pulp and Paper industry is facing continuous pressure to improve energy effi-
ciency, raise product quality, reduce environmental impact and maximize pro-
ductivity. This has notably shaped bleaching and pulp production methods.
Producers have responded to these demands by adopting efficient, low impact
designs on economies of scale that far surpass most existing mills. Modern mills
have less equipment, but are of significantly larger capacity than 20th century
mills (Johnson et al. 2008, 2009a, b; Andrede 2011). New fibrelines have been
built especially in Asia and South America. In these countries, access to fast
growing raw material, other production cost advantages, stable politics and econ-
omies, and surging demand from the East give favourable levels of cost and
return. Several mills and fibrelines that encompass “State-of-the-Art” technology
and management practices have been started. Today’s State-of-the-Art mills use
less wood; are energy self sufficient; less polluting and provide sustainable value
to society (www.aet.org).
State-of-the-art cooking includes both batch and continuous processes using low
cooking temperatures and optimised alkali profiles (Gullichsen and Fogelholm
2000). Continuous cooking has been mostly used over the last decade. It typically
consists of two-vessels for softwood and one- or two-vessels for hardwoods.

DOI 10.1007/978-3-319-18744-0_5
218 5 State-of-the-Art Pulp Mills
The chip feed is of uniform quality. This results in reduced processing upsets. Lower
cooking temperatures (145–153 °C) are typically used. Kappa numbers are in the
range 17–22 for birch, 15–18 for eucalyptus and 26–35 for softwoods. Good
impregnation is a key factor in obtaining good yield. The washing equipment and
configuration are different for most mills. Compared with the previous generation
of mills, atmospheric diffusion washers and drum washers have been replaced in
modern mills by presses, CB filters and multi-stage DD washers that achieve high
Equivalent Displacement Ratios (EDRs). Employing efficient wash equipment is
very much important if a mill wants to achieve sustained bleach plant closure and
filtrate recycling. This type of equipment ensures high dissolved solids recovery,
minimum filtrate volume and minimum fibre content in the filtrate. To avoid calcium
oxalate scaling and control bleaching chemical (particularly peroxide) consump-
tion, pH control and metal ion management is required. Deknotting and primary
screening can be performed in a single stage with knot separation and return to the
digester chip bin via a blower system. Alternatively, recovered knots can be directly
injected into the digesters. Deknotting and screening can be carried out before or
after oxygen delignification. Screening after oxygen delignification has the follow-
ing advantages:
– Less foaming
– Making the pulp easier to screen
– Higher yields due to breakdown of shives
– Smaller and cleaner rejects
– Heat balance advantages between the cooking and oxygen stages
Screening can be performed in either 3-stages or 4-stages. Rejects can be taken out
of the system or recycled by washing and return to the oxygen delignification stage.
Oxygen delignification is typically carried out at medium consistency and in two
stages (Lindstrom 2003; Hart and Rudie 2012). In the previous decade, oxygen
delignification was mostly conducted in one stage. The bulk of the delignification
occurs in the first tower, which is typically run at lower temperature and higher
pressure than the second reactor. The first reactor temperature is typically in the
range 85–95 °C, at a pressure of 6–8 bar, and with addition of around 60–70 % of
the alkali and oxygen charge. Some mills add all chemicals to the first reactor.
Typically, the retention time in the first tower is around half that of the second tower.
The second reactor temperature is 95–100 °C at a pressure of 3–5 bar (McDonough
1996; Lindstrom 1990). Temperatures and chemical charges are lower for hardwoods,
reflecting the generally lower incoming kappa number compared with softwoods.
The degree of delignification varies between 50–60 % for softwood, and 40–50 %
for hardwoods. A significant portion of the hardwood “kappa number” is hexeneuronic
acid which lowers the overall degree of delignification compared with softwoods
(Vuorinen et al. 1999; Jiang et al. 2000). Kappa targets are set to preserve pulp
strength and pulp yield. Magnesium sulphate is often added to preserve strength,
5.1 Celulosa Arauco y Constitución S.A. Nueva Aldea, Chile 219
particularly for softwood pulps (McDonough 1996). To conserve water, condensate

from evaporation is sometimes used in the last stage of oxygen delignification for
washing.
In the modern mills, elemental chlorine free (ECF) bleaching sequences are the
standard for bleaching (Pikka et al. 2000; Johnson et al. 1996; Beca AMEC 2006;
AET 2007; Nelson 1998; Nelson et al. 1995; Pryke 2003; NCASI 2003). Bleaching
is performed in four stages. Modern bleach plants commonly operate with upflow
towers in all stages, with interstage washing using drum displacer (DD) washers or
presses. The washing is typically counter current with white water from the pulp
machine being used for washing on the final stage washer. Variations to true counter
current washing have been developed to reduce pH transitions and to create alkaline
and acid purge streams to manage metals, extractives and scaling. The excess
filtrates, both acid and alkaline, are often filtered to recover fibre before they are
sewered. To reduce emissions of COD, BOD5 and colour from the bleach plant, it
is possible to recycle the alkaline filtrate from the Eop stage (oxidative alkaline
extraction using hydrogen peroxide) and use it for washing prior to the first bleaching
stage (NCSU 2003; Beca AMC 2004; Chandra 1997). All mills have on-line analysers
and optimisation controls. The control of final brightness is very accurate and
quality downgrades are almost non-existent. Standard deviation of the final bright-
ness is typically less than +0.5 % ISO. The bleach plants have a high level of on-line
instrumentation that allows tracking, analysis and optimal control of the bleaching
process to achieve consistent quality and cost efficiency.
The information on few state-of-the art mills – Celulosa Arauco y Constitución
S.A. Nueva Aldea, Chile; Veracel Celulose; Hainan Jinhai Pulp mill; Cellulosa
Arauco Valdivia; Aracruz, Line C, Brazil; Mercal Stendal, Germany; Bowater,
Catawba SC, USA; Zhanjiang Chenming Greenfield pulp mill, China; Eldorado
Celulose e Papel S.A.’s new greenfield pulp mill in Três Lagoas, Brazil; Montes del
Plata mill in Uruguay; Oji Holdings Nantong pulp mill Jiangsu Province, China;
Aracruz’s pulp line, at their Guaiba mill in Rio Grande do Sul, Brazil; Ilim Group’s
new kraft pulp mill, in Bratsk, Irkutsk Oblast, Russia; Metsa-Botnia, Rauma Mill;
Metsa-Botnia Joutseno mil; Stora Enso’s Nymölla Mill – are presented below:
5.1 Celulosa Arauco y Constitución S.A. Nueva Aldea, Chile
Nueva Aldea is a model for environment-friendly operation and is a gleaming exam-

ple of a modern pulp mill (Rodden 2007) (Fig. 5.1). This mill started in mid-
September 2006, and has an annual production of 856,000 tonnes of kraft pulp
(Wold 2008). The mill consists of two continuous fibre lines. One is for production
from eucalyptus nitens and eucalyptus globulus and another is for production from
radiata pine. 50 % of the production is hardwood and 50 % softwood. Both qualities
are fully bleached. Metso Paper supplied the mill with two parallel pulp drying lines
with three complete baling lines. Pulp drying line included rescreening, wet end,
Fig. 5.1 Nueva Aldea, Pulp Mill, Chile (Rodden 2007. Reproduced with permission)
airborne dryer, cutter lay boy and pulp baling systems and designed to minimize
consumption of water, steam and electrical energy. The machinery operates in a
closed system, returning all of its emissions back to other processes in the fibre
lines. Metso Paper supplied two complete fibre lines featuring the latest technology
in continuous digesting, Compact Cooking G2 process. This process uses a high
liquor to wood ratio, which produces a much more uniform pulp. The liquor to
wood ratio in Nueva Aldea’s digesters is 4–5:1 compared with the normal 2.7:1.
Pulp quality is high at an average brightness of 92 ISO. In terms of production, each
line produces the guaranteed 1,300 ADT/day. Except for a small amount of
purchased chips, all of the wood used comes from Arauco’s own plantations. The
pine and eucalyptus are separated in the woodyard. However, the two species of
eucalyptus are mixed after chipping. Hardwood yield is 53–54 %, softwood, about
48 %. Hardwood and softwood lines are separated in the woodyard. Only the recov-
ery area is common. Kvaerner Pulping supplied both fibrelines while Kvaerner
Power supplied the power and recovery boilers. Both units are now part of Metso
Paper, which additionally supplied the two parallel pulp dryers as well as three
baling lines. Andritz supplied the woodyard, limekiln and causticizing unit. Emerson
provided the Delta V distributed control system, while Metso Automation supplied
the pulp analyzers and valves. On the chemical side, Aga supplied the oxygen
system while Akzo Nobel chlorine provided the chlorine dioxide plant. The eucalyptus
bleaching sequence features hot chlorine dioxide in the first stage. The sequence is
D0EOPD1D2. There is a GL&V (formerly Kvaerner Pulping) Compact Press
between the D1 and D2 stages. Pulp enters the dryer at 53 % dryness and exits at
90 %. Nominal speed of the dryers is 250 m/min. As with most kraft pulps, Nueva
Aldea is energy self-sufficient and is able to sell 35 MW back to the grid. Water
5.2 Veracel Celulose 221
consumption is running about 30 m3/tonne. The mill’s efficiency goal is 93. Recently,
Nueva Aldea pulp mill has upgraded their bleach plant by two Valmet TwinRoll
wash presses. One press is placed between the first stages of the bleaching sequence,
between the D0 and EOP stages, while the other one is installed after the D1 stage.
The presses are designed for a production of up to 1,580 tonnes/day and a pulp feed
consistency of 7 %. The main advantages of the new presses are the high availability,
the high output consistency and the low consumption of chemicals.
5.2 Veracel Celulose
Veracel Celulose S.A. engages in the forestry and pulp mill businesses in Brazil. Its
forestry operations comprise interests in approximately 164,600 ha of land distrib-
uted in ten municipalities in the south of the state of Bahia. It primarily focuses on
eucalyptus plantations. The company also operates pulp mills; and produces pulp
and paper. The company was formerly known as Veracruz Florestal Ltd. and changed
its name to Veracel Celulose S.A. in 1998 (www.veracel.com). Veracel Celulose
S.A. was founded in 1991 and is based in Eunapolis, Brazil. The company is a sub-
sidiary of Stora Enso Corp. and Fibria Celulose SA. Veracel is considered to be one
of the top performing bleached hardwood kraft mills in the world. Investment for
the mill $US 860 million Started up May 2005. Veracel Celulose is located in the
extreme southern portion of the Brazilian state of Bahia. The area, rich in eucalyp-
tus, is one of the largest and productive plantations in the world. Andritz, supplied
fibre line, drying machine, causticising plant, rotary lime kiln. Chemical plant was
supplied by EKA Chemicals; Confab supplied falling-film type evaporation in six
stages, Aker Kvaerner supplied recovery boiler and auxiliary boiler using bubbling
fluidizer bed technology, Mitsubishi supplied turbine-generator and ABB supplied
electrical power distribution system.
Veracel Celulose, eucalyptus mill uses 2-vessel vapour-phase Lo-Solids® con-
tinuous cooking, and a hot chlorine dioxide ECF bleach sequence (Johnson et al.
2008, 2009a, b) (Fig. 5.2). The mill has a design capacity of 900,000 adt per annum
but actual production has consistently exceeded this target. Eucalyptus urograndis
is the main species used. Production in 2007 was in excess of 1,050,000 adt.
Veracel operate continuous pulping systems. Veracel’s low level – Lo-Solids
cooking system consists of an hydraulic impregnation vessel and a steam-phase
digester. The main objective of the Lo-solids cooking is to increase the selectivity of
the cook through low and uniform radial cooking temperatures and a uniform alkali
profile. Cellulose dissolution is minimised in the principal and residual delignification
phases, and relatively high yields of around 55 % OD are achieved. Veracel has two
parallel pressurized diffusers after the digester followed by 2-stage DD washers
prior to oxygen delignification. Deknotting and screening can be carried out
either before oxygen delignification, or after. Veracel claims advantages in screen-
ing after oxygen delignification. Deknotting and primary screening occur in a
single stage. Veracel operates two parallel ModuScreen units for knots separation
Fig. 5.2 Veracel fibre line (Johnson et al. 2009b. Reproduced with permission)
and primary screening, followed by washing and return of knots to the digester.
Screening is 3-stage and the options with rejects are to recycle; they are cleaned,
washed and returned to the oxygen delignification stage, or landfill them. Veracel is
using two stage oxygen delignification. It runs its first reactor at a temperature of
92–96 °C, a pressure of 6–8 bar, with the addition of 60–70 % of the alkali and
oxygen charge. Veracel operates the second reactor at a temperature of 98–100 °C
and a pressure of 3–5 bar. The degree of delignification varies between 60 % for
softwood, and 40 % for hardwoods. Veracal is using 4-stage bleaching sequence.
The original bleach sequence of Veracel was A/D0 (Eop) D P which was modified
after start up to Dhot (Eop) D P. This resulted in a significant reduction in chemical
consumption. Veracel’s bleach plant operates with upflow towers in all stages fol-
lowed by a DD washer after each tower. The washing is counter current with filtrate
from the pulp machine being used for washing on the final DD washer. Veracel, has
very low bleach chemical consumption. The two first stages have displacement
presses and the last two stages have simpler dewatering presses. Hot water is used
for Eop washing, and pulp machine filtrate is used before the last D stage press. A
minor amount of cold water may be added to the dilution before the first D stage for
temperature control. The excess filtrates, both acid and alkaline, are filtered before
they are sewered. To decrease emissions of COD, BOD and colour from the bleach
plant, it is possible to recycle the alkaline filtrate from the Eop stage and use it for
5.3 Hainan Jinhai Pulp mill 223
washing prior to the first bleaching stage. This mill claims to have the lowest
chlorine dioxide consumption in the world. It is using online Kajaani analyzers and
bleach plant optimization controls provided by Metso Automation. The low level of
chemical usage means lower costs of production. Moreover, the control of final
product brightness is so precise that quality downgrades are virtually non-existent.
To ensure this consistent quality and cost efficiency, the mill uses a high level of
online bleach plant instrumentation that allows it to track, analyze and optimally
control the bleaching process. Veracel Celulose is using HPD® black liquor evapora-
tion system, designed by Veolia Water Technologies and installed by Confab
Equipamentos S.A. (www.veoliawaterstna.com/news-resources/…/veracelhp-
devaporators.htm). The system has achieved and maintained the specified rates and
capacity since commissioning. The condensate segregation system has produced the
quality of water required for optimal reuse in the mill.
The environmental performance for the Veracel mill has been well within the
internal targets and the Best Available Technology (BAT) references. Veracel is
probably the only mill that discharges its effluent upstream of its intake, which is a
requirement of the mill’s operating licence. Effluent is treated in an activated sludge
process and solid wastes are used to produce organic compost. The mill is believed
to be amongst the best in the world in terms of effluent and air emissions, operating
at approximately 50–75 % of the legal limits. Water consumption is in the range of
22–24 m3/tonne of pulp, with BOD and COD limits set at 0.3–0.4 kg/tonne and
5 kg/tonne, respectively. Atmospheric emissions are permanently monitored. There
is one common stack for all air emissions. Emission control technology includes
high efficiency electrostatic precipitators, an odorous gases collection system, and
stripping of foul condensates which are collected and burnt in the boilers.
5.3 Hainan Jinhai Pulp mill
Hainan Jinhai Pulp mill is located on Hainan Island in southern China. It produces
1 million tonnes/year of bleached hardwood kraft pulp. It is the world’s largest
single-line pulp mill and is China’s first large-scale fibre line (Rodden 2006; Johnson
et al. 2009a, b). Its recovery boiler can handle 6,000 tonnes/day of dry solids.
Environmental standards for the mill are strict as Hainan Island is a popular tourist
destination. The mill is aiming to keep effluent emission levels below the imposed
standards. Hainan Jinhai produced its first pulp in November 2004. The mill’s
fibre supply is Eucalyptus grandis and Acacia crassicarpa, in approximately
equal volume and is sourced internally from plantation forests. The mill’s fibre is
eucalyptus and acacia, split about evenly. Presently, about 20 % of the mill’s fibre
is purchased; the rest comes from APP’s plantations. About half of the wood is
delivered as chips. The mill’s production is used to supply pulp to the several APP
paper machines in China.
Major suppliers to the project included Kvaerner Pulping and Kvaerner Power,
ABB, Siemens, Andritz, Foster Wheeler, BTG, Veolia Water-unit HPD (six-effect,
Fig. 5.3 Hainan Jinhai pulp mill (Johnson et al. 2009b. Reproduced with permission)
falling film evaporators), FL Schmidt (lime kiln), Rexroth (digester motor),

Hagglunds (motors), Sulzer Pumps and Aker Kvaerner Chemetics (chlorine dioxide
generator). Andritz supplied woodyard/wood processing and pulp dryer/baler. The
woodyard is the world’s largest. It can handle 1,160 m3/h of solid wood. There are
four wood receiving and chipping lines (Rodden 2006). Each line has a feeder deck,
conveyors and gravity-fed HQ-Chipper (Fig. 5.3). The feeder deck operates without
conventional chains, making maintenance easier. The chippers are designed to pro-
duce high quality chips even with the small diameter logs the mill has available.
Stone traps, metal detectors and other devices ensure that clean chips are sent to the
fibre line. The chips are stored in two open piles, each containing 150,000 m3. Four
CantiScrews under each pile reclaim the chips and send them to screening: this is
the JetScreen system in which dust, fines, oversize and overthick chips are separated
from accept chips with air impulses. The oversize and overthick chips are sent to an
HQ-Sizer for reprocessing prior to cooking. Rejects are used as fuel in the power
boiler (Rodden 2006). The pulping process uses Compact Cooking from Kvaerner
Pulping. Following the steam bin, the chips go through a high-pressure feeder
5.3 Hainan Jinhai Pulp mill 225
(Compact Feed). The system does not break the chips but feeds them into the liquor
impregnation vessel which is as big as a conventional digester. The digester is one
of the largest pressure vessels of its type with a bottom diameter of 12.5 m. It is
71 m high and the retention time is 6 h. Both the impregnator and digester are
downflow. The digester takes about 30 m3 of chips per minute. After cooking the
pulp is sent to a blow tank. After that it is pumped to a high-pressure screening sys-
tem to remove any knots. The system is set up for two-stage screening but the mill
generally needs to run only one stage. APP China has made extensive use of
Kvaerner Pulping’s Compact Press technology with nine units in place. In the
brownstock line, the presses help reduce COD carryover and soda loss into the
bleach plant. The advantage of the presses in the bleaching process is low water
consumption. The first two Compact Presses are in parallel, after the screening
stage. Pulp enters the press with 3.5 % consistency. It is the only place where there
are two parallel presses. The pulp then passes to a third Compact Press. This mill is
using Dualox process (two-stage oxygen delignification). The retention time in the
second stage is 1 h. The pulp is then washed and sent to a medium consistency
(10 %) tower (7,000 m3 capacity). Following the fifth Compact Press, the pulp is
ready for bleaching. The process is the DualD using hot chlorine dioxide. There are
upflow/downflow towers in each D stage. Retention time can be controlled making
the process easier to operate. There are Compact Presses for washing after each
stage. Brightness is up to 89 ISO. The bleached pulp is sent to one of two high-
consistency storage tanks, each with a capacity of 11,000 m3. The pulp dryer at
Hainan Jinhai is the world’s largest. Prior to the pulp machine, there is an
ModuScreen screening system, arranged in a closed cascade design to achieve high
efficiency. The pulp dryer uses twin-wire forming technology. A three-roll Combi-
Press followed by a double-felted shoe press results in good dewatering. In the Flakt
air dryer, there are no moving mechanical parts inside the drying chamber except for
turning rolls at either end of the machine. After the cutter/layboy, there are four
automated baling lines. The mill makes its own wrapping. Approximately $250 million
was spent on environmental protection. There is a three-stage effluent treatment
plant: primary, secondary and biological. Sludge from the treatment plant is dried
and pressed to about 70 % moisture and then burned in the power boiler. All non-
condensible gases from the fibre line are collected in a closed system and burned in
the recovery boiler. The gases from the bleach plant are collected, passed through a
scrubber and released. Dust from the boiler and limekiln is treated in an electrostatic
precipitator before being released. The mill is energy self-sufficient. Although it is
connected to the national grid, it operates as an island. Its self-sufficiency is helped
by the world’s largest recovery boiler, which can produce 204 kg/s of steam at
84 bar and 480 °C. The Kvaerner Power unit has a multi-level air system to ensure
consistent combustion. It is also designed to give low emissions of carbon monoxide,
total reduced sulfur and NOx. The Foster Wheeler power boiler burns coal, bark, pin
chips and other waste. The mill can produce 1,000 tonnes of steam/h, 30 % of which
comes from the power boiler, the rest from the recovery boiler. Siemens supplied
the three steam turbine generators and also the complete electrical engineering
system for the mill.
5.4 Cellulosa Arauco Valdivia
Valdivia Cellulose Pulp Plant is located in San Pedro de La Mariquina 56 km north-

west of Valdivia in southern Chile (Fig. 5.4). It started in February 2004. The mill is
owned by Cellulosa Arauco y Constitucion S.A. (CELCO-Arauco) and produces
550,000 tonnes pulp per year for international exportation. Valdivia is a ‘swing’ mill
producing both radiata pine (60 % of production) and eucalyptus pulp. The mill
design and vendor equipment packages are based on a maximum capacity rate of
1,700 ad tpd for pine and 1,900 ad tpd for eucalyptus. E. nitens (70 %) and E. globu-
lus (30 %) are the eucalyptus species pulped (Johnson et al. 2008, 2009a, b). The
mill is located in an environmentally sensitive area, especially with respect to air
and water emissions. Very low loadings to the recipient waters are a key require-
ment, which are achieved by a combination of process selection and operational
control. Concentrated and dilute non-condensible gases from the fibreline, evapora-
tion and causticizing plants are collected, treated and incinerated in the recovery
boiler. Effluent treatment consists of primary, secondary and tertiary treatment
stages followed by disk filtration to minimise suspended solids prior to discharge.
Arauco Valdivia’s bleaching sequence is a conventional ECF sequence, D (Eop) D
D. The first bleaching tower is upflow, with a top scraper and a dropleg to the MC
pump standpipe (Fig. 5.5). The three other towers are upflow-downflow, with MC
bottom. The upflow section of the Eop tower is a pressure vessel. Mixers are all
dynamic type SMD-300 in all stages. Washing is with wash presses. The two first
stages have displacement presses and the last two stages have simpler dewatering
presses. Hot water is used for Eop washing, and pulp machine filtrate is used before
the last D stage press. A minor amount of cold water may be added to the dilution
before the first D stage for temperature control. The excess filtrates, both acid and
Fig. 5.4 Celulosa Arauco y Constitucion’s new facility in Valdivia Province, Chile (Rodden 2005.
Reproduced with permission)
5.4 Cellulosa Arauco Valdivia 227
Fig. 5.5 Arauco Valdivia fibre line (Johnson et al. 2009b. Reproduced with permission)
alkaline, are filtered before they are sewered. To decrease emissions of COD, BOD
and colour from the bleach plant, it is possible to recycle the alkaline filtrate from
the Eop stage and use it for washing prior to the first bleaching stage. Figures 5.6
and 5.7 show Super Batch digesters and TwinRoll Presses Valdivia mill respectively.
The Arauco Valdivia mill is located in an environmentally sensitive area, and
based on some benchmarking of its permit, have some of the most stringent effluent
limits for bleached kraft pulp mills anywhere. Valdivia has three permits that cover
all parameters. The mill is in compliance with its permit targets. The Valdivia efflu-
ent treatment system treats three main mill streams: the low solid sewer which
includes bleach plant effluents and excess evaporator condensates; the general mill
sewer including effluent from landfill and the woodyard; the storm water system.
The main features of the treatment system include:
– A spill pond with spill pumps (130,000 m3)
– Primary treatment for the main sewer including an automatic screen, primary
clarifier, scraper, and fibre sludge pump
– Neutralisation stage, and cooling towers (two chambers)
– Secondary treatment (two parallel lines)
– Aerated basins, nutrient addition, secondary clarifiers, scrapers, and fibre sludge
pumps
Fig. 5.6 Super batch digesters at Cellulosa Arauco Valdivia (Rodden 2005. Reproduced with
permission)
– Tertiary treatment (parallel lines) – flocculation chambers, chemical addition

(alum, polymer, peroxide), scrapers, and sludge pumps
– Disc filters (three) in parallel, to reduce hansuspended solids
– Cooling towers to control the final effluent temperature
– Sludge handling system including two belt filter presses for sludge dewatering.
Toxicological studies of acute toxicity and chronic toxicity have showed no impact in
the recipient (river) environment. No lethal effects were detected for the species H.
gracilicornis, D. obtusa, G.. affinis. y O. mykiis, nor any chronic toxicity in L. valdiviana,
S. capricornotum, G. affinis y O. mykiis. Arauco Valdivia both use a tertiary floccula-
tion stage to remove additional organic material. This results in very low COD and
AOX levels in discharged effluent in comparison to biological treatment alone, but
incurs the expense of additional chemicals, and sludge handling and disposal. Sludge
disposal options include land application or incineration. The use of additional
chemicals may also increase the discharge of inorganic salts in the final effluent.
Tertiary treatment is considered in cases where receiving waters are of poor assimila-
tive capacity, or otherwise restricted, and, as such, is identified as a supplemental or
optional technology in recent BKP best technology reviews (Beca AMC 2004).
5.5 APRIL/SSYMB Rizhao Greenfield Mill
APRIL SSYMB Rizhao mill, is situated in the heart of Rizhao city. The mill is a
joint venture between APRIL (Asia Pacific Resources International) and local
government. All main processes for kraft pulp production and chemical recovery
was supplied by Valmet. Valmet also provided supervision services for erection and
5.5 APRIL/SSYMB Rizhao Greenfield Mill 229
Fig. 5.7 Twin roll presses at Cellulosa Arauco Valdivia (Rodden 2005. Reproduced with permission)
start-up, as well as training of mill staff. On June 30, 2010, the mill produced it’s
first pulp sheet. The mill has a state of the art ecofriendly and odorless production.
The Rizhao mill is designed for very low energy, water and chemical consumption
(www.valmet.com/en/products/pulping…/WTB-110628-2256F-F0632?).
Compared to any other pulp mill built in recent times, it has the lowest impact on
the environment. The target is to eliminate solid waste from the mill. The mill has
invested in the best available technologies to eliminate smell and reduce the colour
of effluent, and minimize solid waste. “This mill is the new benchmark in size and
performance for the pulping industry,” says APRIL COO A. J. Devanesan. Acacia
and eucalyptus wood are the raw material for pulp production. The chips are stored
in five GentleStore circular chip storage systems, each designed for a capacity of
190,000 m3. The fibre line comprises equipment and processes for cooking, pulp
screening, brownstock washing, oxygen delignification and bleaching. The selected
technology features Valmet’s continuous CompactCooking, Delta screening and
TwinRoll wash presses installed for each stage of pulp washing. An ECF sequence
O-DHT–EOP–D-D/P was selected for pulp delignification and bleaching. The new
CompactCooking method produces pulp with higher yield, better bleachability and
lower energy consumption than other cooking methods. Pulp drying is carried out
using Valmet’s energy-saving DryWay concept. The process at the APRIL/SSYMB

mill consists of two parallel drying lines. The trim width of the drying machines is
eight meters. The delivery encompasses all necessary process systems from re-
screening, drying and cutting through to ready-made bales. Valmet’s twin-wire
DryWay concept furnished with two shoe presses enables high web dryness prior to
the airborne dryer and thereby remarkable energy savings. After pulp drying and
cutting, the sheets are baled in three baling lines installed for both lines. Valmet’s
Robobaling technology is used for pulp baling. Both baling systems share two
unitizers from where the bale units are transported to storage.
Black liquor from the pulping system is evaporated in Valmet’s EVAPS plant
including two parallel evaporation lines, each dimensioned for evaporation of
1,000 tonnes of water per hour. The liquor at approximately 80 % dry solids content
is burned in Valmet’s RECOX boiler which is designed for a maximum capacity of
7,000 tonnes of dry solids per day. Strong and weak odorous gases are burnt in the
recovery boiler. During June 2010, the boiler was run for few days with 7,550 tDS/
day – the record firing capacity in the world. APRIL is the largest tree planter in the
world. It is also the largest hardwood market pulp supplier in Asia and the second
largest globally. The company produces paper under the brand name PaperOne,
which is sold as a premium product in over 60 countries.
5.6 Aracruz, Line C, Brazil
Fibreline C was started in 2002 which increased the Aracruz’s production from
1.3 million to two million tonnes of pulp per year. Andritz was a major supplier of
process technology and systems for the Fibreline C project. Andritz supplied
Woodyard, Fibreline (excluding digester), Recausticizing/Kiln, Pulp Dryer (with
Voith Paper/ ABB/Moura Schwark), Automated Baling Lines. Fibreline C has the
capacity to produce special ECF pulps for printing/writing, hygienic, photographic,
and papers for digital printing. Kvaerner Pulping supplied cooking and washing
equipment. Compact CookingTM is used which provides greater strength and
higher yield while reducing chemical consumption (Knight 2002). The strength of
the pulp is higher in comparison to the pulp of other lines. Part of the strength
improvements are achieved in the cooking process and part in the bleaching process.
The processes include oxygen delignification, ECF bleaching, closing the effluent
loops in the second and fourth bleaching stages, reusing water from the dryer in
bleaching, and a system of collection and recovery of spillage in all areas. The
bleaching sequence used is ADO-Eop-DnD sequence. Design capacity is 2,200 admt/
day. Pulp can be bleached to 92 ISO brightness. Patented AhlStage technology
is used to lower bleach plant chemical consumption. The new line gives Aracruz
flexibility to produce pulps for various paper grades. Aracruz is reducing water
consumption through new equipment and processes. Fibreline C will consume
about 18 m3/t of pulp produced. The fibreline equipment contributes significantly to
reduced water consumption. Odorous gas emissions will be around 2 ppm of
5.7 Mercal Stendal, Germany 231
Fig. 5.8 The twin-wire pulp machine at Aracruz Celulose S.A.’s new C line at its Barra do Riacho
mill (Knight 2002. Reproduced with permission)
total reduced sulfur (TRS). Fibreline C also has a latest generation system of gas
incineration for the entire complex. This system prevents emissions of odorous
gases which, after being treated, are burned in the recovery boiler. About half of line
C’s output will be used to make tissue. The rest will be split evenly between
specialty papers and printing and writing grades.
Figures 5.8 and 5.9 show the Twin-wire pulp machine and the Recausticizing
plant respectively.
5.7 Mercal Stendal, Germany
The Stendal mill is a state-of-the-art, single-line NBSK pulp mill situated near the
town of Stendal, Germany with a current annual pulp production capacity of
approximately 645,000 ADMTs. Metso supplied the complete fibreline, from wood
handling to finished bales, as well as a millwide automation system (Toland 2004).
The black liquor evaporation plant (670 tonnes/h), recovery boiler (3,250 tonnes dry
solids/day) and recausticizing plant (8,000 m3/day) was supplied by Andritz. Other
key suppliers included Purac (biological water treatment), Sulzer Pumps (pumps
and agitators) and Wiessner (air engineering). Stendal Fibre line system has Twin
roll wash presses in each washing stage. Figure 5.10 shows the Evaporation plant.
Stendal is PEFC-certified and sources wood exclusively from sustainable forests
within a 300 km radius of the mill, as well as using chips from sawmills. The mill
aims to use 70 % own-produced chips and 30 % from outside. There is three weeks
roundwood storage space on site.
Fig. 5.9 Recausticizing plant

at Aracruz Celulose S.A.’s
new C line at its Barra do
Riacho mill (Knight 2002.
Reproduced with permission)
Fig. 5.10 Evaporation plant at Stendal (Toland 2004. Reproduced with permission)
5.8 Bowater, Catawba SC, USA 233
Stendal’s pulp is produced from 70 to 80 % pine, 20 to 30 % spruce. ZS Holz

which is a subsidiary company is responsible for wood procurement. ZS Transport,
a second daughter company is responsible for both internal logistics and wood chip
transport and product shipments to all markets. The logs are processed using Metso
ChipWay technology, consisting of two debarking and chipping lines. Each line can
handle up to 300 m3 solid wood/h. The wood infeed system – GentleFeed – conveys
the logs into the debarking drum on top of moving lamellas, rather than using chains
or sprockets, the aim being to eliminate wood breakages and improve yield and chip
quality, thereby decreasing the need for bleaching chemicals. Together with the
infeed system, the Easy Tyre debarking drums and Camura GS chippers are designed
to minimize wood losses and maximize the uniformity of chips destined for the
digester. The mill also has a bark press that is used in winter when the bark is less
dry. Unused bark is stored and then burnt in the bark boiler to generate energy.
Stendal’s bark and recovery boilers between them generate 90 MW energy. Since
the mill needs only 55 MW, the remainder is sold to electricity suppliers. The mill
is an “industry leader” in terms of efficient production and good environmental
performance. Only chips of the right size and quality are made into pulp; those that
are too large are rechipped, while fines go to the bark storage area prior to being
burnt in the bark boiler. Chips produced on-site and those brought in from sawmills
are stored in separate 60,000 m3 chip piles for quality control reasons. Stendal
employs Metso’s SuperBatch pulp digesting process, including eight 400 m3 digesters,
together with pressurized accumulators and tanks for black, white and displacement
liquor. After cooking, knots and shives are separated using four-stage DeltaCombi
screening. The pulp is then further delignified in a two-stage OxyTrac oxygen
delignification process. Bleaching is in four stages with washing by Twin Roll wash
presses after each stage: the sequence for ECF pulp is Q-OP-D-PO; for TCF it is
Q-OP-PAA-PO (Metso 2005). Stendal was initially conceived as a TCF-only mill,
but they are producing both ECF and TCF pulp, with more of a focus on ECF. The
storage area at Stendal can hold around 20,000 tonnes at any one time, or approxi-
mately 12 days’ storage once the mill hits its target output of 1,700 tonnes/day. All
the pulp Stendal is producing is basically the same. End-uses for Stendal’s NBSK
include printing papers, tissue papers and white packaging grades.
5.8 Bowater, Catawba SC, USA
State-of-the- art Bowater’s Fibreline at the Catawba site was started in 2003, This
Fibreline offers top-tier quality, environmental performance for bowater (Shaw
2004). It is designed to produce 1,500 tpd of bleached pine pulp for use in lightweight
coated papers. Figure 5.11 shows the Catawba mill’s fibre line design. The new fibre
line can provide pulp that has improved optical and strength properties, using the
latest technologies advantageous to the environment. This allows Bowater to compete
more effectively in the North American and European tissue and towel and food
packaging segments. In late 1999, the Catawba mill was faced with eliminating
Lo-Solids Cooking Oxygen Delignification Knotting & Screening

Chips In and BS Washing
To Black Liquor Cooler

DD 3070 1.5 MCV DD 3070 1.5 MCV DD 3070.1 LC
Co
O2 O2
nd
en
20 min 60 min
sa
te
Lo-Level
Food
Bleaching
3070.1.5 MCV 3070.1.5 MCV 3070.1.5 MCV
White Water
D0 EOP D1 D2
30 min 60 min 180 min 180 min Hot Water
To Existing #3
Bleached HD
Storage Tank
To Existing #6
HD Storage
To Existing #7
HD Storage Tank
To Existing #8
HD Storage Tank
Bleached HD
Booster MC Pump
Fig. 5.11 Fibre line at Catawba (Shaw 2004. Reproduced with permission)
elemental chlorine and reducing AOX emissions from its bleached kraft fibre line.
A major modification to the existing line might have met Cluster Rule compliance,
but Bowater preferred to explore the long-term advantages of a completely new
fibreline that would guarantee compliance. From an environmental point of view, a
new fibreline would require less water and steam for the process resulting in reduced
operating costs. The advanced technology has given Bowater Tier I Cluster Rule
status with very low AOX discharge. Also, the new fibre line allows the use of less
wood fibre and chemicals and provides a better quality pulp. Higher strength prop-
erties were important to Bowater’s expanded emphasis on coated paper grades
within the Coated and Specialty Papers Division especially with the conversion of
the No. 3 paper machine from newsprint to coated paper. A turnkey EPC project was
awarded to a consortium of three companies (AMEC/Andritz/Kamt) in December
2000. The fibre line design included a continuous digester (Fig. 5.12) featuring a
low solids cooking method and brownstock washing to replace ten existing batch
digesters. After the continuous digester comes a pressure diffuser, followed by two
stages of oxygen delignification, each of which is succeeded by washing in a new,
multi-stage drum displacement pressurized washer. Next, brownstock is screened,
knotted, and washed again prior to bleaching. The selected bleaching equipment
included a ECF, four-stage bleach plant that features a D0-Eop-D1-D2 sequence
with the capability for n-stage bleaching between stages D1 and D2. Each bleaching
stage is followed by washing in new, multi-stage pressurized washers. After bleaching,
pulp is sent to one of four existing high-density storage tanks. Andritz DD washers
are used from pre-oxygen to the end of the bleach plant. In addition, the project
included a new chip conveyor leading to the fibreline that would be built around
existing lines. Also included was a new, state-of-the art control room featuring a
5.8 Bowater, Catawba SC, USA 235
Fig. 5.12 Continuous

digester, Catawba’s new fibre
line, uses low solids cooking
for lowest kappa number and
highest fibre quality (Shaw
2004. Reproduced with
permission)
new distributed control system. Presently, the new kraft pulp line consistently
produces bleached kraft pulp at brightness levels of 89–90, with TAPPI dirt count of
1 or less. Pulp strength is good, as evidenced by record paper production, and it is
improving all the time. The combined strength parameter has improved about 10 %
already and continues to increase. In addition, water use and steam use have been
reduced by about 25 %. Due to oxygen delignification, chemical consumption in
the bleach plant is much less. The kappa number going into the bleach plant signifi-
cantly reduced from around 30–14 with the use of two-stage oxygen delignification
stage and low solids cooking in the continuous digester, along with advanced washing
technologies. With no increased chlorine dioxide requirement in the new DEOPDD
bleach plant, the mill was able to use its existing chlorine dioxide generation
capacity. It could also retain its existing chemical recovery island with a few minor
upgrades. Because oxidized white liquor was to be used in the two-stage oxygen
delignification towers, about 30 % more was needed than before. A new burner was
fitted in the lime kiln to achieve this and automated causticizing efficiency controls
were installed in order to ensure sufficient white liquor production and a correct
sulphidity balance in the mill. Because the new pulp mill and bleach plant operate
considerably more “closed” than its predecessor, a new cooling tower was also
installed. Overall, the new fibreline uses about 2 million gal of water/day less than
the old pulp mill (20 % reduction/tonne of pulp). The effluent colour also improved.
Among the water reduction measures implemented in the project was use of paper
machine white water for washing in the bleach plant EOP stage. The mill has an
effluent colour removal plant on site that ran all the time with the old pulp mill. But
since startup of the new fibreline, it has not been used at all. Effluent colour has been
more of a discharge limitation than anything else. AOX has been well within the
limits since startup of the new fibreline.
5.9 Zhanjiang Chenming Greenfield Pulp Mill, China
Zhanjiang Chenming pulp mill is located in China’s Guangdong Province. It reached

the nominal production capacity of 700,000 tonnes/a in world record time – only
121 days from start-up. It has also produced 100 % of the design capacity during
the first full operating year, thus achieving another world record (PPI mills and
technology 2012). All key production technologies and start-up supervision were
provided by international technology Group Andritz. Zhanjiang Chenming Pulp &
Paper is a subsidiary of Shandong Chenming Paper, one of the largest pulp and
paper producers in China. Andritz was awarded the contract to deliver all process
technologies for the bleached hardwood kraft pulp mill located in Guangdong
Province. The mill was started up in September 2011 and reached its nominal average
production capacity only four months later (measured as a 30-day moving average).
This represents a new “world record” based upon officially available figures of
greenfield pulp mills. This extremely fast start-up has an important economic
element in that it greatly enhances a mill’s return on investment. Andritz supplied
included the wood handling system, the fibreline (cooking, washing, screening,
bleaching, pulp dryer, and bale finishing), and the recovery island (evaporation,
recovery boiler, and white liquor plant) (Andritz 2012).
5.10 Eldorado Celulose e Papel S.A.’s New Greenfield

Pulp Mill in Três Lagoas, Brazil
Eldorado Celulose e Papel pulp mill is based in the city of Três Lagoas, in the state
Mato Grosso do Sul. This is the largest single-line pulp mill in the world, with
capacity to produce 1.5 million tonnes of bleached pulp per year (www.valmet.com/
valmet/products/…nsf/…/Results313Eldorado.pdf). The mill has been designed to
optimize the energy balance and maximize electricity produced from biomass. The
pulp is delivered to customers in Brazil and also exported to paper producing
markets in South America, North America, Europe, and Asia. The recovery boiler
combusts 6,800 tonnes of black-liquor dry solids per day and generates 1,109 tonnes
of steam an hour. Andritz supplied woodyard, complete fibreline – cooking, washing,
screening, and bleaching systems, pulp drying equipment and baling lines, as well
as the white liquor plant with recausticizing and lime kiln and Metso supplied
5.11 Montes del Plata Mill in Uruguay 237
recovery boiler and evaporation plant. The mill will produce 1,600,000 tonnes/a
bleached eucalyptus. The recovery boiler has a capacity of 6.800 tonnes of dry
solids per day (tDS/day) and steam generation of 308 kg/s. The evaporation plant
has six thermal stages and capacity of 1,600 tonnes per hour.
5.11 Montes del Plata Mill in Uruguay
Montes del Plata, the pulping company owned jointly by Stora Enso and Arauco,
officially inaugurated its greenfield mill near Punta Pereira, Uruguay on September 8,
2014 (www.storaenso.com/…/inauguration-of-stora-enso’s-joint-operation-pulp..).
The design capacity for the mill is 1.3 million tonnes of bleached eucalyptus pulp
per year. Andritz delivered key production lines for the mill. Andritz was also
responsible for the civil construction, erection, commissioning, and start-up of these
production lines (Andritz 2014). The pulp will be produced using ECF bleaching
with low chlorine dioxide consumption (ECF-Light) from plantation grown
eucalyptus trees. The main processing units of the pulp mill will include the following:
wood yard; digester; oxygen delignification; ECF bleach plant; pulp dryers; evapo-
rators; recovery boiler, turbogenerators and recausticizing (i.e. chemical regenera-
tion), water supply; and effluent treatment. Andritz supplied technology for log
receiving, two chipping lines, bark processing, chip storing and reclaiming (shown
here), chip screening, and chip conveying to the cooking plant. The total processed
wood amount is 4,800,000 m3 sub per year. The fibreline includes a DownFlow
Lo-Solids digester with TurboFeed chip feeding, brownstock washing, screening,
postoxygen washing, and bleaching. In total, there are eight DD washers in the
fibreline. Daily design capacity is 4,090 admt/day at 92 % ISO brightness. Design
capacity of the recovery boiler is 5,710 tds/day at 495 ° C and a pressure of 96.8 bar.
The recausticizing plant is designed to product 13,370 m3/day of white liquor. The
Lime Kiln has a capacity of 1,100 tonnes/day of burnt lime. The pulp drying plant
consists of two parallel lines including pulp screening/ cleaning, TwinWire pulp
machines, airborne sheet dryers, and cutter/layboys. The seven-effect evaporation
plant has a capacity of 1,466 tonnes/h. Integrated in the design are systems for
stripping and methanol liquefaction, processing of bio-sludge and chlorine dioxide
plant brine, and removal of chlorine and potassium from the black liquor. A Duct
Stripper is utilized to improve condensate quality. Three automated lines produce
baled, wrapped, and palletized units ready for shipment to Montes del Plata’s global
customers. Andritz was responsible for the automation, electrification, and
instrumentation in each process area with the exception of the DCS. Included in the
delivery were Advanced Control (ACE) optimization software, web-based training
tools for operators and maintenance personnel, and the IDEAS Simulator for DCS
checkout and operating “virtual” training. Andritz delivered all the centrifugal
process pumps including medium consistency as well as fan pumps.
The mill is proposing to utilize the water resource of the Rio de la Plata for process
and cooling. The mill will be supported by its own energy generation plant, which
will run on energetic rating of black liqueur and bark recovered from incoming tree
trunks and other combustibles produced at the plant. The biomass power plant has a
potential to generate 170 MW, 90 MW will be used in the plant and up to 80 MW
could be sold to the Uruguayan national grid. The power plant will be located in the
plant area and will include the following sub-components: a recovery boiler and a
biomass boiler for the production of steam; turbine generator; substations, electrical
rooms and interconnection with the national grid; and storage facilities for heavy
fuel oil reserves to be used for starting up the mill and for backup purposes.
5.12 Oji Holdings Nantong Pulp Mill Jiangsu

Province, China
Oji Holdings has started a 700,000 tonne/year BHK pulp line at Nantong mill Jiangsu
Province, in the southern part of China. Metso has supplied a greenfield kraft pulp
mill; scope of supply covers all main process equipment for the new mill, including
chip screens and storage systems, a continuous cooking system, a fibreline including
wash presses, ozone bleaching, a wet lap machine, a recovery boiler, an evaporation
system, a white liquor plant and a gas handling system. The state-of-the-art technol-
ogy delivered by Metso ensures environmentally friendly and efficient production.
The mill is beginning trial runs and will make BHK pulp at a rate of 500,000 tonnes/a
when commercial production begins (KSH Consulting 2014). The BHK line has a
design capacity of 700,000 tonnes/a. More than a half of the output on the line will
be integrated with the Nantong mill’s sole 400,000 tonne/a coated fine paper machine,
PM 1, with some tonnage likely to be shipped to the company’s 20,000 tonne/a tis-
suemill in Suzhou city, also in Jiangsu province. The remaining BHK pulp from the
line, amounting to 240,000 tonnes/a, will be sold on the Chinese market. The market
pulp will be in slurry form, with a moisture content of 50 %.
5.13 Aracruz’s Pulp Line, at Their Guaiba

Mill in Rio Grande do Sul, Brazil
Aracruz’s has set up new 1.5-million-tonnes/year bleached hardwood kraft (BHK)

pulp line, at their Guaiba mill in Rio Grande do Sul, Brazil. The expansion will raise
the mill’s total annual capacity to almost 2 million tonnes (www.bloomberg.com/
apps/news?pid=newsarchive&sid.). The production is expected to start in 2015.
Metso will supply the entire fibre line comprising pulp cooking, screening and
washing, bleaching, drying and baling, as well as the recovery boiler and white liquor
preparation systems. Metso will also provide process control systems, including the
necessary analyzers and special equipment for quality and runnability management.
5.14 Ilim Group’s New Kraft Pulp Mill, in Bratsk, Irkutsk Oblast, Russia 239
The fibre line process features the latest evolution of cooking and washing technolo-
gies. The continuous digester is designed for a daily capacity of 5,030 tonnes. The
drying machine will have a trim width of 9.99 m and is designed for 4,970 tonnes
daily production. Metso will supply for black liquor burning has a design capacity
of 6,130 tonnes dry solids per day. The boiler employs technology to maximize
power generation from bioenergy. The nominal capacity of the white liquor plant
will be 14,300 m3 of white liquor per day. Aracruz is the world’s leading producer
of bleached eucalyptus pulp. Total production today is the equivalent of 3.2 million
tonnes a year, produced by three pulp mills: Barra do Riacho (2.3 million tonnes),
Guaiba (450,000 tonnes) and Veracel (450,000 tonnes, or 50 % of the unit’s
total capacity).
5.14 Ilim Group’s New Kraft Pulp Mill, in Bratsk,

Irkutsk Oblast, Russia
Ilim Group’s has started a new kraft pulp mill, in Bratsk, Irkutsk Oblast, Russia.
Ilim Group on June 19, 2013 officially inaugurated its new pulp mill at its Bratsk
pulp and containerboard mill (Irkutsk Oblast) in Russia. The annual capacity of
the new fibreline after ramp-up will reach 720,000 tonnes of bleached softwood
market pulp, with the total annual pulp and paper products output of the Bratsk
Mill exceeding 1 million tonnes per year www.paperage.com/2013news/06_28_
2013ilim_bratsk_pulp_mill.html. Metso’s delivery to Ilim Group represents state-
of-the-art pulping technology. Metso will supply a complete fibre line comprising a
CompactCooking G2 digester, a screen room with DeltaScreen screens, an OxyTrac
oxygen delignification system, brown stock washing and bleaching plants with
TwinRoll Evolution wash presses and a DryWay drying line with a Fourdrinier wet
end and two Robobaling lines. Integral to the Bratsk reconstruction program are a
new Metso recovery boiler and an upgrade of the evaporation plant. Metso will also
deliver a metsoDNA CR automation system for all process areas, and necessary
analyzers and special equipment for quality and runnability management. The new
pulp mill will produce 720,000 tonnes of bleached softwood market pulp a year,
bringing the overall annual pulp production at Bratsk to over 1 million tonnes.
When in operation, the Bratsk mill will be one of the world’s largest and most
modern softwood pulp production facilities. Ilim Group is a leading Russian pulp
and paper producer, headquartered in St. Petersburg. The strategic partner of Ilim
Group is International Paper, a global leader in the paper and packaging industry.
The total annual pulp and paper production volume of Ilim Group is more than
2.3 million tones.
5.15 Metsa-Botnia, Rauma Mill
Metsa-Botnia, Rauma Mill of Finland came on stream in 1996 as the world’s first
mill built solely for producing chlorine-free TCF pulp. The Rauma mill changed its
bleaching system from TCF to ECF in summer 2007 (www.metsafibre.com/
Company/ProductionUnits/Pages/raumamill.aspx). It produces 650,000 tonnes/a of
ECF bleached softwood pulp in a single line. Metso supplied wood room with two
debarking-chipping line and fibreline and the main machinery for brown stock
washing, comprising TwinRoll™ displacement presses. A baling line for this new
fibreline was also included in the Metso Paper delivery. The equipment was delivered
during 1994–1995 and the start-up of the SuperBatch cooking system took place in
January, 1996. The cooking process was updated to SuperBatch-K in September
2000. Metso Paper supplied Metsa-Botnia, Rauma Mill with a wood room to handle
abt. 2.5 million solid m3 softwood annually. The softwood raw material is 20–30 %
spruce and the rest is pine. The wood room has two debarking-chipping lines each
with a capacity of 350 solid m3/h. Uniform, high quality chips for Rauma Mill’s
reinforcement pulp are produced with the following machinery: Two GentleFeed™
log feed systems, 72 m Two EasyTyre™ debarking drums, 5.5 × 35 m Two
GentleSlice™ chippers, 0 3.3 m, providing an optimum yield of raw material. The
SuperBatch cooking system is designed for 1,700 adt/day production for softwood,
mainly domestic pine and spruce as raw material. The design kappa was 18 for
softwood pulp. The cooking system comprises ten 400 m3 digesters made of SS
2273 duplex steel. A 500 m3 chip silo and all the chip conveying screws from silo to
digesters were also included in the delivery. The cooking process was updated to
SuperBatch-K in September 2000. Two TwinRoll™ A-1872 displacement presses
were installed for brown stock washing. The designed production is 1,700 adt/day
bleached softwood pulp. The TwinRoll presses installed are the biggest units in the
world. The order also included the main equipment, basic engineering, training and
start-up supervision. Metso Paper also supplied two additional presses to Metsa-
Botnia, Rauma Mill. The first one, a TwinRoll A-1572 was installed as the first
washing stage in the bleaching plant. The second, a TwinRoll W-1255S dewatering
press, was installed for the pulp prior to entering the paper mill. Baling systems The
Metso Paper baling system comprises two baling lines, known as the domestic line
and the export line. The latter also has an additional wrapper storage line. Capacity
per line is 250 bales/h.
5.16 Metsa-Botnia Joutseno Mill
The Joutseno mill was completely modernised at the turn of the twenty first century.
The Joutseno mill has the capacity to produce 670,000 tonnes per year of ECF
bleached softwood pulp (www.metsafibre.com/Company/ProductionUnits/Pages/
Joutseno.aspx). The mill is a world leader in efficiency and environmental
5.17 Stora Enso’s Nymölla Mill 241
management and a pioneer in renewable energy utilization. The mill produces more
bio energy than it needs. This mill is a carbon neutral pulp mill during normal
operation. It specialises in manufacturing pulp for wood-fibre printing papers (SC
and LWC) and for high-quality coated printing and speciality papers. Wood
consumption is 3.5 million m3 annually. Metsä Fibre has introduced polysulfide
cooking in their Joutseno mill in the year 2013. The technology for the preparation
of polysulfide, and the digester modifications to enable production of the improved
softwood pulp, were supplied by Andritz. According to Joutseno Mill Manager
Risto Joronen, the use of polysulfide cooking liquor enables the mill to improve
certain pulp qualities that benefits papermakers. One of those benefits is a reduction
in specific energy to refine the pulp, resulting in lower operating costs for paper-
makers. There are also some enhancements to the fibre bonding due to the retention
of certain hemicellulose materials in the pulp. The Joutseno mill is also increasing
its fibre yield, which makes the investment economically beneficial. As a result, the
mill is able to reduce the loading of its recovery boiler which allows it to improve
production capacity. According to Andritz, the polysulfide process modifies conven-
tional white cooking liquor to “orange liquor” (named due to the characteristic
colour of the modified liquor) by oxidizing sodium sulfide in the liquor to polysulfide.
The plant provided is based on the proven MOXY process (white liquor sulfide-to-
polysulfide conversion), already installed in several mills around the world. Andritz
also modified Joutseno’s cooking plant to optimize the new process.
5.17 Stora Enso’s Nymölla Mill
Nymölla Mill – part of the Stora Enso Group’s Printing and Reading business area –
is a modern pulp and fine papers mill. Annual production capacity is 340,000
metric tonnes of pulp and 470,000 metric tonnes of paper. Nymölla Mill is located
on the coast, in Bromölla Municipality, about 20 km east of Kristianstad. The
Skräbe River, with excellent fishing waters, flows past the plant area and is the
source of the mill’s process water (assets.storaenso.com/…/printingandreading/…/
Environmental%20stateme). The wood raw material consists of roundwood mostly
spruce, pine, beech, aspen and sawmill chips. In the wood room, the wood is
debarked and chipped. The bark is collected, dewatered and burned in the boiler
house. All the softwood chips are stored for about 6 weeks in chip piles to reduce
the pitch content and other extractive matter in the chips through the activity of
microorganisms. The chips are transported to the digester after storage. Cooking is
done with magnesium bisulfate. Cooking is done in batches. The cooking is done
for about 8 h. After that the pulp is screened and washed. The digester liquid known
as weak liquor is then separated from the pulp. The recovery process for digester
chemicals consists of (1) the evaporation of the weak liquor to thick liquor, (2) com-
bustion of the thick liquor in two recovery boilers and (3) the preparation of new
cooking liquor from the recovered chemicals. The recovery rate for digester chemi-
cals is at least 95 %. There is also a solid fuel boiler, in which bark, twigs, screening
rejects, fuel chips, ultrafiltration concentrate and sludge from the wastewater
treatment plant, and also oil and LPG, are burned. The steam from the boilers is
transported to two back-pressure turbines that produce approximately 30 MW of
electrical power. The pulp is bleached after screening and washing. Nymölla is not
using chlorine-based chemicals for bleaching. It is using oxygen, sodium hydrox-
ide, hydrogen peroxide and peracetic acid as bleaching chemicals, and EDTA is
used as a chelating agent. The bleaching process takes about 8–12 h. After bleaching,
the pulp is again screened. Following bleaching and screening, the pulp is pumped
to the paper mill for production of fine papers. A small portion of the pulp is dried
and stored for subsequent use. Fine papers are produced on two paper machines
(PM1 and PM2). Softwood and hardwood pulp from the pulp plant are used as the
fibre raw material, together with a certain amount of purchased pulp from other pulp
plants. The paper machines produce uncoated fine papers in grammages ranging
from 70 to 160 g/m2. The paper is trimmed into rolls or sheets of various sizes, and
then packaged. The packaged products are then loaded for transport to the customers.
Wastewater is treated first in primary clarifiers and biologically in an activated-
sludge plant. A significant portion of the bleach plant wastewater also receives
preliminary treatment in an ultrafiltration plant, where substances that are difficult
to break down in the activated-sludge plant are separated out. Small molecular size
substances pass through the membrane and are transported onward to the external
wastewater treatment plant. The larger molecules that remain, are burned in the
solid fuel boiler. Small molecular size substances pass through the membrane and
are transported onward to the external wastewater treatment plant.
Electrical filters and special flue gas scrubbers are used to clean air flue gases
from the boilers primarily to remove sulfur dioxide and dust from the flue gases.
Urea is also injected into the boilers to reduce emissions of nitrogen oxides. A
portion of the flue gases is transported to a plant for producing filler (precipitated
chalk) adjacent to the paper mill and used there as process gas. Gas flows in the pulp
plant that contain odorous substances are channeled to one of the boilers, where
these odorous substances are burned.
5.18 UPM Fray Bentos Pulp Mill
UPM Fray Bentos pulp mill was started up in November 2007. The Fray Bentos
pulp mill is one of the most modern pulp mills in the world. It has a capacity of
1 million tonnes/a of fully bleached eucalyptus market pulp. The entire process and
all the areas of the pulp mill have been designed and implemented according to the
IPPC BREF to comply the Best Available Techniques for chemical pulp manufac-
turing. Basically the entire raw material supply of the mill comes from the eucalyp-
tus plantations of Forestal Oriental from usually within the maximum distance of
200 km from the mill. When having reached the full capacity, the mill will use more
than 3 million solid cubic meters of eucalyptus, mainly Eucalyptus Grandis. The
cooking of eucalyptus is performed using two-vessel downflow Lo-Solids cooking
5.19 New Projects 243
Fig. 5.13 Fray Bentos Pulp mill fibre line (Saarela et al. 2007. Reproduced with permission)
process (Saarela et al. 2007). The pulp is cooked to kappa number 18. The mill is
using oxygen delignification which is performed in two stages. The kappa number
is brought down to the level of 10. Pulp is then bleached to the full market pulp
brightness of 91 % ISO. The bleaching sequence is A/D-EOP-D-P. The black liquor
evaporation is performed in seven effects to reach the dissolved solids concentration
of 80 %. The recovery boiler has the combustion capacity of 4,450 tonnes solids/day
and the steam values are 94 bar (g) and 490 °C. Andritz is the main supplier of the
fibreline and recovery island. Figure 5.13 shows the Fray Bentos Pulp mill fibre
line.
5.19 New Projects
Several new projects have been announced (Forest Industry News 2014 www.ksh.
ca/2014PDF/Forest%20Industry%20News%20Jun%20Jul%20). Few are mentioned
below:
Metsä Fibre, part of Metsä Group, is planning to build a next generation bio-
product mill in the existing mill area in Äänekoski, Finland (www.metsafibre.
com/…/Bio-product%20mill/Bio-product-mill-press-con). When materialized, the
approximately EUR 1.1 billion investment would be the largest ever investment in
the forest industry in Finland. The new mill with an annual pulp production capacity
of 1.3 million tonnes is planned to be operational in 2017. The new mill will be the
world’s first next-generation bio-product mill that can convert wood raw material
into a diverse range of products. In addition to high-quality pulp, the mill will
produce bio-energy and various bio-materials in a resource-efficient way. A unique

bio-economy ecosystem of companies will be built around pulp production. This
new mill will be the most efficient and modern bio-product mill in the world. The
global increase in the demand for high-quality softwood pulp is the most important
driver for the investment. The investment will support Metsä Fibre’s growth and
improve profitability in the long term. The bio-product mill will contribute to
achieving renewable energy targets in Finland through increasing the share of
renewable energy by approximately two percentage points. Furthermore, the mill
will not use any fossil-based fuels; all of the energy required for it will be generated
from wood. The wood raw material and side streams will be utilised 100 % as prod-
ucts and bio-energy. The mill will increase the consumption of fibre wood in Finland
by approximately 4 million m3 (some 10 %) per year. The annual harvesting of soft-
wood can be increased sustainably by approximately 7 million m3, and birch fibre
by 4 million m3. The fibre wood will be procured mainly in Finland. Metsä Fibre
will launch the EIA and environmental permit processes immediately with the aim
to have them completed during the first quarter of 2015. The final investment deci-
sion is planned to be made in early 2015, in which case the new mill would become
operational during 2017.
Södra Cell, Sweden is expanding the capacity of their Värö pulp mill (www.
paperage.com/…/06_03_2014sodra_varo_pulp_mill_valmet.html). The pulp pro-
duction capacity will increase from 425,000 tonnes to 700,000 tonnes/year. Valmet
has received a major rebuild and new equipment order. Valmet’s delivery will con-
tribute to Södra’s performance by significantly increasing the Värö mill’s pulp pro-
duction capacity and energy efficiency. The order consists of a new continuous
cooking plant and upgrades of wood handling, fibre line, evaporation plant, recov-
ery boiler, recausticizing, flash dryer, pulp dryer and baling. On completion of the
project, Värö will be one of the world’s largest softwood sulphate pulp mills. The
start-up of the renewed pulp mill is scheduled in the third quarter of 2016. A large
part of the order will be delivered from Valmet’s operations in Sweden: the cooking
plant and recausticizing from Karlstad, fibre line, flash dryer and baling from
Sundsvall, and evaporation and recovery boiler from Gothenburg. The wood han-
dling and pulp dryer delivery will come from Finland.
Klabin, the largest integrated pulp and paper company in Brazil, has planned a
new pulp mill in Ortigueira, Paraná, Brazil. Start-up is scheduled for the first quarter
of 2016 (www.forstwirtschaft.com/de/aggregator/sources/). ANDRITZ has received
major order. The scope of supply of the Andritz covers the woodyard, the complete
fibreline (for softwood and hardwood), and the white liquor plant. The pulp mill
will have an annual production capacity of 1.5 million tonnes, 1.1 million tonnes
thereof in short fibre and 400,000 tonnes in long fibre. Klabin operates 16 plants
(15 in Brazil and one in Argentina), targeting markets such as packaging paper and
board, corrugated packaging, and industrial bags producers. The new pulp project in
Brazil is the largest investment in Klabin’s history and will double the company’s
production capacities.
OKI Pulp and Paper Mills has planned a pulp mill project in South Sumatra,
Indonesia (www.pulpandpaperonline.com/…/valmet-oki-pulp-paper-mills-
References 245
supplying). Valmet supplies a part of pulp mill equipment and systems with a value
of approximately EUR 340 million. The new mill is expected to produce approxi-
mately 2 million ADT (air dry tonne) of pulp annually. The commercial production
is expected to begin in 2016. Valmet’s delivery includes the following parts of the
pulp mill: two biomass gasifiers, two biomass boilers, an evaporation system, two
lime kilns and two pulp dryers.
References
Alliance for Environmental Technology (AET) (2007) Trends in world bleached chemical pulp
production: 1990–2007
Andrede M (2011) The fibre line of the future for eucalyptus kraft pulp, Keynote presentation. In:
5th international colloquium on eucalyptus pulp, Porto Seguro, Brazil, 9–11 May 2011
Andritz (2012) World records after start-up of greenfield pulp mill of Zhanjiang Chenming, China.
www.andritz.com/group/gr-news/gr-news-detail.htm?id
Andritz (2014) Greenfield Montes del Plata mill inaugurated in Uruguay. Spectrum – Andritz
magazine of Pulp and Paper, Issue 30 – No. 2. spectrum.andritz.com/ru/index/iss_30.htm
Beca AMEC (2004) Independent advice on the development of environmental guidelines for any new
bleached eucalypt kraft pulp mill in Tasmania for resource planning and development commission,
Tasmania. http://www.rpdc.tas.gov.au/__data/assets/pdf_file/0005/66335/Study_Report.pdf
Beca AMEC (2006) Review of ECF and TCF bleaching processes and specific issues raised in the
WWF report on Arauco Valdivia. Prepared for resource planning and development commis-
sion. Tasmania, Australia. May 2006
Chandra B (1997) Effluent minimization – a little water goes a long way. Tappi J 80(12):37–42
KSH Consulting (2014) www.ksh.ca/2014PDF/Forest%20Industry%20News%20Jun%20Jul%20
Forest Industry News (2014) www.ksh.ca/2014PDF/Forest%20Industry%20News%20Jun%20
Jul%20
Gullichsen J, Fogelholm CJ (2000) Chemical pulping—papermaking science and technology.
Book 6A. Fapet Oy, Helsinki, p A19
Hart PW, Rudie AW (2012) The bleaching of pulp, 5th edn. Tappi press, Atlanta
Jiang ZH, Van Lierop B, Berry R (2000) Hexenuronic acid groups in pulping and bleaching chem-
istry. Tappi J 83(1):167
Johnson T, Santos CA, Herschmiller D, Palmiere M, Trepte R, Purdie D (1996) APP, AlPac and
Bahia Sul – current design and environmental performance for ECF in the Americas. In:
International pulp bleaching conference, Washington
Johnson AP, Johnson BI, Gleadow P, Silva FA, Aquilar RM, Hsiang CJ, Araneda H (2008) 21st
century fibre lines. In: Proceedings of international pulp bleaching conference, Quebec City, p. 1
Johnson T, Johnson B, Gleadow P (2009a) The fibreline of the future, pulp and paper international,
PPI magazine, March 2009. www.risiinfo.com/magazines/march/2009/ppi/the-fibreline-of-
the-future.html
Johnson T, Johnson B, Gleadow P, Araneda H, Silva F, Aquilar R, Hsiang C (2009b) 21st century
fibrelines. Pulp Pap Can 110(9):26–31
Knight P (2002) Aracruz concept pays off. Pulp & Paper International, www.risiinfo.com/maga-
zines/September/2002/PPI/pulp-paper
Lindstrom LA (1990) Oxygen stage design and performance. In: Tappi bleach plant operations
short course notes. Tappi Press, Atlanta, p 89
Lindstrom LA (2003) Impact on bleach ability and pulp properties by environmentally friendly
bleaching concepts. In: Metso paper pulping technology seminar, Hyderabad, November 2003
McDonough TJ (1996) Oxygen delignification. In: Dence CW, Reeve DW (eds) Pulp bleaching –
principles and practice. Tappi Press, Atlanta, p 213
Metso (2005) Zellstoff Stendal. Fiber Pap 7(1):12–17

National Council for Air and Stream Improvement Inc (NCASI) (2003) Pulp mill process closure: a
review of global technology developments and mill experiences in the 1990s. Technical Bulletin
No. 860. National Council for Air and Stream Improvement, Inc, Research Triangle Park
Nelson PJ (1998) Elemental Chlorine Free (ECF) and Totally Chlorine Free (TCF) bleaching of
pulps. In: Young RA, Akhtar M (eds) Environmentally friendly technologies for the pulp and
paper industry. Wiley, New York, p 215
Nelson PJ, Chin, CWJ, Grover SG, Ryynänen H (1995) Elemental Chlorine-Free (ECF) and
Totally Chlorine-Free (TCF) bleaching of eucalyptus kraft pulps. In: Appita annual general
conference proceedings, p 179
Pikka O, Vessala R, Vilpponen A, Dahllof H, Germgard U, Norden S, Bokstrom M, Steffes F,
Gullichsen J (2000) Bleaching applications. In: Gullichsen J, Fogelholm C-J (eds) Chemical
pulping—papermaking science and technology. Book 6A. Fapet Oy, Helsinki, p A19
PPI mills and technology (2012) ppimagazine.com/mills/asia-pacific/zhanjiang-chenming-sets-
record-pulp-production-700000-tyr-andritz-supplied-process-technologies-greenfield-pulp-
mill-china
Pryke DC (2003) ECF is on a roll: it dominates world bleached pulp production. Pulp Pap Int
45(8):27–29
Rodden G (2005) Greenfield mill. PPI Magazine (Pulp & Paper International) www.risiinfo.com/
db_area/archive/ppi_mag/2005/01/01.html
Rodden G (2006) The birth of a giant. Pulp Pap Int 48(4):13–17
Rodden G (2007) Nueva Aldea starts up smoothly. PPI Magazine (Pulp & Paper International)
http://www.risiinfo.com/magazines/February/2007/PPI/4380.html
Saarela S, Garcia E, Eluen I, Fernandez, V (2007) The first year of operation of the Botnia Fray
Bentos pulp mill in Uruguay, Ruta Puente Puerto, Botnia
Shaw M (2004) New fibre line offers top-tier quality, environmental performance for bowater. Pulp
and Paper magazine www.risiinfo.com/…/New-Fibre-Line-Offers-Top-Tier-Quality-Environ
Toland J (2004) Stendal starts up. Pulp & Paper International, www.risiinfo.com/magazines/
December/2004/PPI/Stendal-starts-up
Vuorinen T, Fagerström P, Buchert J, Tenkanen M, Teleman A (1999) Selective hydrolysis of hex-
enuronic acid groups and its application in ECF and TCF bleaching of kraft pulps. J Pulp Pap
Sci 25(5):155–162
Wold D (2008) Nueva Aldea: a gleaming example of a modern pulp mill. Fibre & Paper & Power,
www.valmet.com/…nsf/…/Pages4-7from108Fibre&Paper&Power.pdf?
www.aet.org
www.forstwirtschaft.com/de/aggregator/sources/
www.metsafibre.com/…/Bio-product%20mill/Bio-product-mill-press-con
www.metsafibre.com/Company/ProductionUnits/Pages/Joutseno.aspx
www.metsafibre.com/Company/ProductionUnits/Pages/raumamill.aspx
www.paperage.com/…/06_03_2014sodra_varo_pulp_mill_valmet.html
www.paperage.com/2013news/06_28_2013ilim_bratsk_pulp_mill.html
www.pulpandpaperonline.com/…/valmet-oki-pulp-paper-mills-supplying
www.valmet.com/en/products/pulping…/WTB-110628-2256F-F0632
www.valmet.com/valmet/products/…nsf/…/Results313Eldorado.pdf
www.veoliawaterstna.com/news-resources/…/veracelhpdevaporators.htm
Chapter 6
The Future
Abstract Minimum Impact Manufacturing has and will continue to be the vision
of the pulp and paper industry. The vision of the forest products industry as an eco-
cyclic industry is becoming firmly established. This vision is aimed at sustainable
development, resource utilization, efficient internal conversion and recycling of
fibers, chemicals and energy. The large majority of companies are now taking steps
toward implementing ecocyclic processes at their plants. Future technologies may
emerge that make additional progress toward the minimum-impact mill. The pace
of research and development of new technologies has quickened dramatically in the
last decade, giving manufacturers more options to consider. Pulp mills have been
identifying new pathways to go beyond the production of pulp and electricity. One
widely discussed approach is the integration of multi-products biorefineries, providing
an opportunity to contribute to the future demands for energy, fuels and chemicals.
Keywords Pulp and paper industry • Pulp mill • Minimum impact manufacturing •
Minimum-impact mill • Sustainable development • Resource utilization • Recycling
• Energy • Electricity • Biorefinery • Energy • Fuel • Chemical
The future of the paper industry will be the minimum-impact mill. Closed loop, and
minimum impact concepts continue to be intensively researched and implementation
of process improvements is ongoing. The vision of the forest products industry as
an ecocyclic industry is becoming firmly established in the minds of many people
(STFI 2003). This vision involves much more than simple environmental compliance.
It is aimed at following (Warnqvist 1999):
– Sustainable development
– Resource utilization
– Efficient internal conversion and recycling of fibers
– Chemicals and energy
At the mill level, ecocyclic principles require closed cycle compatible process
technology. But this does not necessarily mean that mills are ‘totally effluent-
free’ or TEF. Instead, the process could be considered as MEM (minimum efflu-
ent mill), MIM (minimum impact mill), or even ‘minimum input mill’ in view of
the elemental input/output mass balance equation Sustainable development can-
not be achieved without continuous innovation, improvement, and use of clean

DOI 10.1007/978-3-319-18744-0_6
248 6 The Future
technologies and “green” chemistry to make fundamental process changes to

reduce pollution levels and resource consumption. According to Colin L. Powell
United States Secretary of State “Sustainable development is a compelling moral
and humanitarian issue. But sustainable development is also a security impera-
tive.” The large majority of companies are now taking steps toward implement-
ing ecocyclic processes at their plants, but the concept also goes beyond the mill
itself (STFI 2003). The idea also encompasses the flow and delivery of recycled
resources to other industries, society and markets. In Sweden, the main driving
force behind the introduction of MIM or MEM mills comes from the Swedish
environmental protection agency, the Naturvårdsverket (Warnqvist 1999). The
organization is calling for effluent COD targets of 10–15 kg/ADT. This will typi-
cally require a comparatively small total effluent volume at a mill – about 20 m/
ADT or less – of which bleach effluent accounts for 5–10 m/ADT. In many cases,
the optimum solution in both technical and economic terms would be to combine
internal process measures and efficient external treatment. Within the global
closed cycle vision, the future of kraft pulp mills is likely to center more and
more on the MIM concept. Both meanings – minimum impact mill and minimum
input mill – are likely to play an important part in the process. Introducing this
new concept will involve challenges for the mill’s process technology, manage-
ment, operation and control. Equally, the MIM concept poses significant chal-
lenges on the technical research and development side for both suppliers and
consultants in the industry.
Chemical pulping technology has changed and developed rapidly in the past
decade. The pressure to develop comes primarily from two directions: concern
about the environment, and increased global competitiveness in the pulp and paper
business. Environmental organizations throughout the world are educating both
consumers and pulp and paper producers to accept the philosophy that no effluents
with unknown environmental consequences should be allowed. Meanwhile, global
competition has subjected all producers to strong price and quality competition.
Therefore, equipment/technology suppliers are continually seeking to improve and
optimize the processes and deliveries to obtain the best possible quality and economy
for the customers.
Pulp and paper mills have presently the appearance of largest water consumer
and biggest polluter because of residual odor and visual aesthetic disturbances
from water vapor. Until some of these very real community impacts are taken care
of, the industry will continue to have trouble building public credibility in spite of
strong technical arguments demonstrating “absence of harm”. The vision of
minimum-impact manufacturing, be it “a completely ecocyclic system for high
quality paper production which efficiently utilizes the energy potential of the bio-
mass” has captured the imaginations of the industry’s leaders (Axegard et al.
1997). Opportunity exists to move public view point to “the pulp and paper indus-
try is ecologically sound, while producing recyclable products from renewable
resources.” However, local issues and other aesthetic issues should be addressed
6 The Future 249
to earn public trust. Efforts should be made to minimize releases from the pulping
and recovery processes. Currently there are no “zero” effluent kraft mill bleach
plants (NCASI 2003; Stratton et al. 2005).
There has been marked reductions in key pollutants such as sulfur oxides, nitro-
gen oxides, chlorinated organics, BOD and COD. It is also important to note that the
industry’s emissions of carbon dioxide per ton of product has dropped by almost
80–90 % in the developing countries. Ecocyclic visions and sustainable industrial
production methods have also become the main focus of the high profile environ-
mental policies formulated by many European and some North American compa-
nies. A quick glance at the web sites of these companies confirms this trend.
Mills that recirculate the filtrates from the first bleaching and extraction stages of
the bleach plant make additional progress toward the minimum-impact mill. These
low-effluent processes represent the most advanced current technologies.
Future technologies may emerge that make additional progress toward the
minimum-impact mill. The pace of research and development of new technologies
has quickened dramatically in the last five years, giving manufacturers more options
to consider. Agenda 2020, a research agenda proposed by the American Forest &
Paper Association, provides an indication of the trends in research on future techno-
logical advances. Chloride removal technologies are currently undergoing a mill-scale
demonstration. Other potential future technologies are being tested at the laboratory
and the pilot plant scale. These technologies include novel bleaching agents and
other process modifications. These new technologies are in different phases of
development, and it is difficult to predict when they will become commercially
available. Purchasers should recognize that new technologies in pulp and paper
manufacturing do not provide benefits to the environment until they are actually
running at a commercial scale. In the paper industry, technologies usually require a
minimum of 5–10 years of laboratory and pilot plant testing before they reach
mill-scale demonstration. Technologies such as oxygen delignification and ozone
bleaching took about 20 years from initial laboratory demonstration to successful
commercial application, for example.
Today’s State-of-the-Art mills compared to 1975 use less wood to make a piece
of paper; are energy self sufficient and export green power to the grid; use 70 % less
water, discharge less solid waste, and emit 96 % less SO2 and 90 % less odorous
compounds; protect the ecosystem with advanced wastewater treatment in discharg-
ing 95 % less BOD, 90 % less suspended solids, discharging no POP (Persistent
Organic Pollutants), creates high quality recyclable products while providing sus-
tainable value to society (www.aet.org/science_of_ecf/ecf_closed…/metafore_pre-
sentation.pdf). Minimum Impact Manufacturing has and will continue to be the
vision of the pulp and paper industry (Axegard et al. 1997; Erickson 1995; Broman
and Lindberg 1997; Pryke 2008). Pulp mills have been identifying new pathways to
go beyond the production of pulp and electricity. One widely discussed approach is
the integration of multi-products biorefineries, providing, therefore, an opportunity
to contribute to the future demands for energy, fuels and chemicals. The potential is
250 6 The Future
vast, considering that the sector is already engaged with the development of tree
seedlings, forest management and transportation of logs to the industrial facilities.
In addition, pulp mills have the competence to process wood chips and residues in
a very effective way. On the other hand, achieving profitable growth through the
introduction of new sellable products might be challenging and has to be carefully
evaluated (Bajpai 2012, 2013).
References
mills symposium. Tappi Press, Atlanta, pp 529–541
Bajpai P (2012) Biotechnology in pulp and paper processing. Springer US New York Inc, 412 pp
Bajpai P (2013) Biorefinery in the pulp and paper industry. Academic/Elsevier Inc, Burlington
Broman PG, Lindberg H (1997) Working toward ecobalance. In: 1997 Tappi minimum effluent
mills symposium proceedings. Tappi Press, Atlanta
Erickson D (1995) Closing up the bleach plant: striving for a minimum-impact mill. Tappi/NC
State emerging pulping & bleaching technologies workshop, May 1995
National Council for Air and Stream Improvement Inc (NCASI) (2003) Pulp mill process closure: a
review of global technology developments and mill experiences in the 1990s. Technical Bulletin
No. 860. National Council for Air and Stream Improvement, Inc, Research Triangle Park
Pryke D (2008) Perspectives on the pulp and paper industry. Digital Presentation, 2008
Pryke D The Minimum-impact mill: “State-of-the-Art” manufacturing. AEt alliance for. Environmental
Technology. www.aet.org/science_of_ecf/ecf_closed…/metafore_presentation.pdf
Stratton S, Gleadow P, Johnson A (2005) Pulp mill process closure: a review of global technology
developments and mill experiences in the 1990s. Water Sci Technol 50(3):183–194
Swedish Pulp and Paper Research Institute (STFI) (2003) Ecocyclic pulp mill – “KAM” – final
report 1996–2002. KAM Report A100. Swedish Pulp and Paper Research Institute, Stockholm
Warnqvist B (1999) Closing in on the bleached kraft pulp mills. Pulp Paper International. www.
risiinfo.com/magazines/october/1999/ppi/pulp-paper/magazine/international/october/1999/
closing-in-on-the-bleached-kraft-pulp-mills.html
Index
A Bark boiler, 57, 136, 153, 156–159, 233

Acacia, 223, 229 Batch cooking, 17, 74–77, 79, 104, 152
Acid hydrolysis, 112, 119, 129–131 Beating, 12, 28, 29, 124
Acidification, 4, 52, 102, 158 Belt conveyor, 15
Activated sludge, 51, 193–195, 197, 223, 242 Best Available Technology (BAT), 70, 96, 109,
Acute toxicity, 48, 228 110, 115, 117, 223
Adsorbable organic halides (AOX), 43, 45, 46, Best management practice (BMPs), 133
48, 50, 94, 99, 104, 105, 109, 113, Biogas, 195
116–118, 126, 129–132, 180, 181, 193, Biological oxygen demand (BOD), 43, 45, 48,
228, 234, 236 50, 70, 71, 84, 87, 94, 105, 126,
Aerated basin, 193, 194, 227 132–134, 136, 193, 222, 223,
Aerated lagoon, 193, 197 227, 249
Aeration basin, 194 Biological reactor, 195
Aerobic treatment, 19, 193–196 Biomass, 6, 43, 68, 71, 179, 194–196, 236,
Air emission, 42, 45, 52–55, 68, 223 238, 248
Air pollution, 52, 53 boiler, 238, 245
Alkaline peroxide mechanical pulp (APMP), gasifier, 245
71, 167 Biorefinery, 172, 179–180
Anaerobic, 19, 50, 58, 195–196 Black liquor, 16, 26, 27, 42, 74, 76–79,
Anaerobic upflow sludge blanket, 196 81, 83–86, 94, 132–136, 145–152,
Animal glue, 36 154, 172–179, 183–187, 189, 190,
Annual fibre crops, 20 223, 230, 231, 236, 237, 239, 243
Anthrahydroquinone, 80 Black liquor oxidation, 26
Anthraquinone, 80–81, 84, 190 Bleachability, 81, 107, 108, 131, 132, 229
Aspen, 18, 83, 166, 241 Bleached chemi-thermo-mechanical pulp
Aspergillus aculeatus, 167 (BCTMP), 71, 72
Aspergillus niger, 167 Bleach Filtrate Recovery (BFR), 6, 184
Autocaustising, 177–179 Bleaching, 6, 7, 50, 54, 87, 96–105, 108–132,
Automotive fuel, 176 136, 180, 181, 184, 186, 190, 219, 230,
Auxiliary boiler, 52, 153–156, 221 237, 238, 249
Bleaching chemical demand, 67, 81
Bleach plant, 6, 21, 24, 45, 46, 55, 67, 73,
B 86–88, 94, 96, 102, 109, 111, 115, 116,
Bacteria, 58, 193, 194 118, 119, 123, 127, 131, 132, 136, 137,
Bagasse, 12, 14, 20 147, 180–186, 188–191, 219, 221–223,
Bamboo, 20 225, 227, 230, 234–237, 242, 249

DOI 10.1007/978-3-319-18744-0
252 Index
Bleach plant closure, 180–182, 190, 218 Chemical pulp, 13, 15, 16, 18, 19, 24, 25,
Bleach plant effluent, 6, 7, 43, 45–48, 54, 87, 52, 53, 67–69, 72, 96–105, 107,
94, 96, 121, 126, 132, 181, 182, 190, 109–111, 133, 242
191, 227 Chemical pulping, 13–17, 19–21, 23, 45, 51,
Board, 1, 11, 16, 19, 20, 23, 27, 28, 70, 84, 248
52, 56, 66, 87, 107, 121, 168, Chemical recovery, 7, 13, 16, 17, 19–22, 24,
169, 171, 183, 244 26, 46, 84, 85, 94, 98, 105, 111, 121,
Brightness, 17–20, 23–25, 28, 30, 70, 71, 81, 133, 154, 161, 174, 181, 183, 228, 235
98, 101–104, 106–108, 111–114, Chemicals, 5, 8–86, 88, 94–96, 99, 105, 108,
117–121, 123, 124, 127–129, 111, 116, 119, 125, 126, 128, 129, 133,
132, 181, 219, 220, 223, 225, 230, 137, 139, 162, 170–174, 176, 179–181,
235, 237, 243 183, 185–187, 190, 191, 218, 221, 228,
Brightness reversion, 102, 124, 127, 129–131 233, 234, 241, 242, 247, 249
Brown stock washer, 16, 21, 26, 94, 183, 190 Chemi-mechanical pulp, 17
Brownstock washing, 21, 22, 84–89, 134, Chipping, 13–15, 70, 220, 224, 233, 237, 240
136–138, 178, 181, 183, 189, 190, 229, Chlorinated compounds, 25, 42, 47, 55, 126
234, 237, 239, 240 Chlorinated phenolics, 47, 48, 55, 88
Bulk, 17, 29, 37, 71–73, 75–77, 106, Chlorine, 5, 24, 25, 42–45, 47–50, 52, 55, 88,
107, 125, 193, 218 98, 99, 105, 109, 111–113, 116, 118,
119, 123, 126, 131, 183, 185, 186, 220,
234, 237
C Chlorine dioxide, 24, 25, 43–45, 47, 50, 52,
Calcining, 13, 27, 155 54, 55, 58, 88, 98, 99, 102–105, 109,
Calcium carbonate, 20, 27, 161, 181 111–119, 126, 127, 129–132, 180, 184,
Calcium hydroxide, 27 185, 189, 220, 221, 223–225, 235, 237
Calcium oxalate, 102, 129, 181, 218 Chlorine dioxide generator, 58, 115, 116,
Calcium oxide, 20, 27, 155 118, 224
Calender, 35, 36 Chlorine dioxide substitution, 25, 47, 50,
Carbon footprint, 73 55, 58, 180
Carbon tetrachloride, 51 Chlorocymenenes, 48
Carcinogenic, 42, 47, 49 Chlorocymenes, 48
Casein, 36 Chloroform, 25, 43, 51–55, 109, 116
Catalyst, 80, 81, 96, 139, 141, 142, 157 Chronic toxicity, 48, 50, 228
Catalytic oxidation, 138 Clarification, 27, 162, 192, 193
Catechol, 47, 48, 58 Cleaning, 2, 22, 23, 28, 53, 54, 133, 136,
Causticizers, 27 143–145, 151, 158, 175, 189,
Causticizing, 20, 27, 56, 94, 135, 161, 192, 195, 237
162, 176, 177, 189, 190, 220, Cleanliness, 24, 69
226, 235 Clean manufacturing, 8
Cellulase, 167 Closed Cycle Technology, 6
Cellulose, 11, 12, 15, 24, 82, 84, 94, 95, Closed loop, 22, 52–55, 57–59, 115,
99, 103, 107, 123–125, 130, 166, 167, 118, 189, 247
184, 221 Closed screening, 85, 86
acetate, 12, 24 Cluster rule, 54, 108, 110, 133, 234
ester, 12 Coagulant, 192
Centrifugal cleaning, 22, 28 Coarse screening, 23, 192
Chemical additives, 29, 46, 171, 190 Coating, 36, 73
Chemical oxygen demand (COD), 43, 45, 48, Cockling, 36
50, 68, 70, 71, 84, 87, 94, 95, 102, Cold Blow, 17, 75
104, 105, 113, 126, 130–134, Compact cooking, 17, 77–79, 220, 224, 230
136–138, 166, 180, 181, 190, 193, Condensate, 46, 54, 133–139, 152, 168, 189,
195–197, 219, 222, 223, 225, 227, 219, 223, 227, 237
228, 248, 249 Contaminant, 19, 22, 50, 51, 54, 134, 192, 193
Index 253
Continuous cooking, 17, 76–79, 86, 217, Donnan effect, 180

221, 238, 244 Double-lined kraft clippings, 18
Conveyor, 15, 66–68, 146, 224, 234 Dregs, 27, 56, 59, 184, 185, 189, 190
Cooking liquor, 16–19, 21, 26, 67, 75, 81, Drum displacement (DD) washer, 85, 96,
82, 84, 89, 154, 177, 241 218, 219, 221, 222, 234, 237
Cooling tower, 55, 227, 228, 235 Drum washer, 218
Corrosion, 24, 25, 46, 57, 58, 78, 86, 143, 144, Dry debarking, 67–71
153, 178, 180, 181, 188, 190, 195 Dryer section, 31, 36, 125
Corrugating media, 46 Dry solid (DS), 25, 27, 45, 86, 96, 134,
Cotton linter, 12 144, 147–151, 162, 174, 193, 223,
Countercurrent washing, 23, 88, 188, 190 230, 231, 236, 237, 239
Cradle debarker, 14 DTPA. See Diethylene triamine pentaacetic
Cylinder mold machine, 33 acid (DTPA)
Cylinder vat, 33, 34
E
D ECF. See Elementary chlorine free (ECF)
Dandy roll, 31, 33, 36 Ecocyclic Pulp Mill, 6
Debarking, 13, 14, 57, 66–71, 233 EDTA. See Ethylenediaminetetraacetic
Debarking drum, 56, 66–71, 233, 240 acid (EDTA)
Defibering, 21, 106 Effluent, 3, 6, 7, 19, 42–48, 54, 67, 87, 94,
Deflaking, 28 96, 105, 121, 126, 132, 180–182,
Deforestation, 3 188, 190, 191, 223, 227, 247, 249
Deinking, 12, 19, 20, 56, 57 Effluent Free, 6, 44, 50, 105, 180, 188
Deknotting, 21, 56, 218, 221 Electricity, 45, 53, 98, 104, 107, 143, 151,
Delignification, 24, 46, 67, 73–77, 80, 81, 164, 167, 168, 170–173, 176, 177,
83, 84, 88, 89, 92, 94–96, 99, 102, 179, 233, 236, 249
103, 105, 107, 112, 123, 128, 129, Electrostatic precipitators (ESPs), 27,
179, 218, 221, 222, 229 142–147, 149, 151, 186,
Depithing, 14 187, 223, 225
Diethylene triamine pentaacetic acid Elementary chlorine free (ECF)
(DTPA), 25, 50, 51, 120 bleaching, 6, 87, 99, 104, 105, 108–119,
Diffuser, 85, 112, 221, 234 122–125, 127, 128, 130–132, 181,
Diffusion washer, 22, 85, 218 186, 190, 219, 230, 237
Digester, 16, 18, 22, 27, 67, 74–80, 83, 84, 86, light, 99, 102, 111, 237
93, 109, 131, 135, 138, 139, 151, 152, super light, 111
178–180, 218, 220–222, 224, 225, 227, Embossing, 36, 37
228, 230, 233–235, 237, 239–241 Emission, 4, 7, 20, 26, 41, 42, 45, 46, 52–55,
Digester additives, 83 66–70, 73, 81, 87, 96, 105, 137,
Dimethyldioxirane, 108 139–163, 173, 178, 180, 181, 186,
Dimethyl disulphide, 135, 152 193, 195, 196, 219, 220, 222, 223,
Dimethyl ether (DME), 172, 175, 176 225–227, 231, 234, 242, 249
Dimethyl sulphide, 135, 152 Endoglucanase, 167
Dioxin, 22, 25, 42–45, 47–50, 52–54, 57, Enerbatch, 74, 75
58, 109, 111, 115, 116, 180 Energy, 3, 12, 41, 66, 217, 241, 244, 247
Direct contact evaporator, 26, 54 Energy efficiency, 7, 42, 59, 71, 73, 140,
Dispersion, 28, 193 141, 145, 179, 217, 244
Displacement cooking, 74–76 Environment, 3, 4, 29, 41, 42, 44, 45, 53–55,
Displacement washing, 22, 85 69, 88, 94, 101, 108, 111, 112, 123,
Displacement wash press, 96 155, 158, 164, 187, 219, 228, 229,
Dissolved air flotation (DAF), 191 233, 248, 249
Dissolving pulp, 16, 96 Environmental impact, 4, 7, 8, 21, 25, 42, 67,
Dithionite, 25, 109 68, 94, 96, 117, 123, 191, 217
254 Index
Environmental management, 5, 7, 8, 65 Fuel, 12, 14, 53, 59, 67, 68, 70, 71, 136,
Environment-friendly operation, 219 137, 139–142, 148, 150, 153–155,
Equalisation, 192 158–160, 163, 172–179, 195, 224,
Equivalent Displacement Ratio (EDRs), 218 238, 241, 242, 244, 249
Ethylenediaminetetraacetic acid Furan, 22, 25, 43, 45, 47, 49, 50, 53, 54, 180
(EDTA), 25, 50, 51, 119, 120,
184, 242
Eucalyptus, 2, 72, 93, 97, 102, 103, 113, G
115, 127, 130–132, 218–221, 223, Gap former, 31
226, 229, 237, 239, 242 Gasifier, 173–177, 245
Evaporation plant, 86, 87, 137, 138, 151, Glucomannan, 82
152, 154, 182, 231, 232, 237, 239, 244 Grammage, 11, 17, 169, 242
Expanded granular sludge blanket Graphic paper, 1, 18
(EGSB), 196 Grease proof paper, 19, 87
Explosive, 12, 151 Greenhouse gas (GHG), 42, 53, 66
Extended cooking, 25, 78, 79, 95, 180 Green liquor, 27, 56, 162, 174, 176, 184, 185
Extended delignification, 73, 74, 79–81, Groundwood pulp, 14, 17, 18, 69
93, 95, 111, 124 Guaiacol, 47, 48
Extended modified continuous cooking
(EMCC), 76, 78–80
Extended modified cooking, 95 H
Extraction stage, 49, 83, 98, 100, 105, 113, Hardwood, 2, 7, 12, 16–20, 23, 70–72, 75,
120, 126–128, 185, 249 77, 79, 83, 87, 93–95, 97, 98,
Extractives, 12, 24, 48, 67, 68, 70, 82, 83, 101–104, 106, 107, 111–113, 118,
107, 108, 132, 166, 185, 219, 241 120, 124, 128, 129, 167, 179, 190,
217–223, 230, 236, 238, 242, 244
Hazardous air pollutants (HAPs), 43, 52,
F 54, 55, 135
Fatty acid, 70, 71, 83, 107, 132 Head-box, 170, 171
Felt, 33–35, 163 Heat recovery, 66–68, 79, 147, 152, 171
Fibre bundle, 23, 24 Hemicellulose, 12, 22, 24, 77, 81, 82, 95, 107,
Fibreline, 7, 21, 74, 85, 86, 94, 96, 99, 104, 123–125, 130, 167, 179, 241
116, 118, 119, 131–133, 154, Hexenuronic acid, 95, 102, 128–132
180, 181, 184, 217, 220, 226, High yield pulp (HYP), 71–73, 169, 170
230, 231, 233–240, 243, 244 High yield pulping, 71–73, 106–108
Filtrate recycle, 180, 188 Horizontal belt filters, 22
Fine paper, 16, 71, 238, 241, 242 Hot acid stage, 129–132
Fir, 12 Hybrid former, 31
Fish, 43–45, 48–50, 52, 115 Hydrogen, 172, 175, 176, 179
Fixed-bed reactor, 139, 196 Hydrogen peroxide, 24, 25, 72, 88, 98,
Flail debarker, 14 103–105, 112, 117, 119, 120, 123,
Flax, 12 125–129, 189, 219, 242
Flocculant, 185, 192 Hydrogen sulphide, 51, 53, 135, 147, 148,
Flue gas, 26, 27, 53, 54, 141–147, 150, 151, 150–152, 162, 163, 173, 175, 195
156–158, 163, 186, 187, 242 Hydrophilicity, 107, 124, 125
Flue gas treatment (FGT), 141, 142 Hydrophobicity, 28, 48
Forestry, 8, 53, 221 Hydroxycarbolates, 51
Forming section, 31, 32, 125 Hypochlorite, 24, 25, 109, 138, 139
Fortification, 126–128
Fossil fuel, 27, 140, 154, 155, 174, 179, 195
Foul condensate, 134, 135, 137, 152, 223 I
Fourdrinier machine, 31, 32, 35 Impregnation, 74–79, 82, 218
Fractionation, 23, 28 Impregnation vessel, 77, 78, 221, 225
Index 255
Impulse technology, 163–164 M

Incineration, 21, 57, 88, 121, 137, 151–155, Malodorous gas, 54, 137, 151–153
228, 231 Market pulp, 7, 114, 230, 238, 239,
Incinerator, 3, 136, 138, 152–154 242, 243
Integrated mill, 28, 121 Mechanical pulping, 4, 13, 14, 17–18,
Internal circulation (IC) reactor, 196 45, 70, 96, 106
Iso Thermal Cooking (ITC), 17, 76–79, Membrane, 48, 136, 193, 195, 242
97, 102, 104 Membrane bioreactor (MBR),
136, 193, 195
Metering, 28, 36
K Methanol, 43, 54, 55, 128, 135–138, 152,
Kappa number, 67, 73–77, 79, 153, 172, 175, 176, 237
81–84, 88, 92–96, 103, 109, Methyl mercaptan, 54, 55, 151
112, 113, 116, 119, 121, 122, Microflotation, 193
124, 127, 129, 132, 178, 181, Minimum impact manufacturing, 5–7, 117,
190, 218, 235, 243 248, 249
Knot, 23, 56, 86, 218, 221, 222, 225, 233 Minimum impact mill, 5–8, 42, 43, 45, 65,
Kraft pulp, 25, 42, 44, 46, 47, 57, 247–249
58, 69, 71–73, 82, 87, 93, 103, Minimum Impact Mill Technologies, 65–197
104, 109, 113, 115, 116, Mobile debarker, 14
119–121, 123, 127, 130, 138, 143, Modified cooking, 16, 46, 73–84,
144, 148, 151, 161, 162, 166, 94, 95, 190
176–179, 190, 197, 219, 223, 227, Modified kraft pulping, 17, 80
228, 235, 236, 238, 239, 248 Molette, 33
Kraft pulping, 13, 16–17, 19, 72, 73, 76, Monox-L, 109
80–84, 128 Moving bed biofilm reactor
(MBBR), 193, 194
Multiple-effect evaporator, 26, 134
L Mussel, 43, 48
Landfills, 3, 42, 43, 57–59, 222, 227
Lethal effect, 228
Light ECF, 102 N
Light scattering, 17, 72, 108 Neutral sulphite semi-chemical
Lightweight coated (LWC), 115, 233, 241 (NSSC), 19
Lignin, 12, 13, 15–19, 21, 23–26, 42, 48, Newsprint paper, 2
58, 71–77, 80, 81, 83, 87, 88, 92, 94, Nitrogen dioxide, 109
95, 98, 99, 103, 106–108, 111, 114, Nitrosyl sulfuric acid (NSA), 109
116, 122, 126, 129, 131, 132, 165, Noise, 42, 43, 59, 68
166, 178, 179, 184 Nonchlorine bleaching, 111, 190
Lignosulphonates, 17 Non-condensible gases (NCG's),
Lime kiln, 20, 27, 52, 94, 96, 137, 138, 140, 137, 151–154, 225, 226
141, 143, 146, 150–156, 162, 163, Non-integrated mill, 14
174, 177–179, 189, 190, 221, 224, Non process element (NPE), 8, 46, 51, 58,
235, 237, 245 128, 180, 181, 183–187, 190
Lime mud, 20, 21, 27, 56, 59, 153, 154, Non-wood plant fibres, 20
161–163, 179, 184, 185 Non-wood pulping, 20–21
Limestone, 21 NOX, 43, 52, 53, 139–142, 148, 151,
Linerboard, 23, 121, 170, 183, 191 154–161, 225
Lo-Solids, 76, 221, 237
Lo-Solids cooking, 221, 242
Low-AOX ECF, 111 O
Low-impact ECF, 111 ODORGARD, 138, 139
Low Nox burner, 142, 155, 156 Odorous gases, 134, 138, 148, 151–154,
Low-OX ECF, 111 223, 230, 231
256 Index
Odour, 54, 59, 139, 163 Pollutants, 2, 8, 41–43, 47, 52–55, 70, 73, 88,
Old corrugated containers, 18 94, 96, 109, 115, 134, 135, 173, 190,
Oleoresin, 12 192, 193, 249
Opacity, 29, 30, 43, 71–73, 108, 144 Pollution, 3, 8, 15, 25, 43, 46–53,
Open screen room, 22 67, 87, 94, 126, 129, 134, 142,
Organochlorines, 44, 53, 55 192, 195, 248
Over Fire Air Technique, 160–161 Pollution prevention, 8, 109, 117, 141
Oxidative extraction, 127 Polychlorinated dibenzodioxins
Oxidized white liquor, 94, 235 (PCDDs), 48, 49
Oxygen Polychlorinated dibenzofurans
delignification, 25, 54, 55, 85–96, 98, (PCDFs), 48, 49
103, 105, 109, 111–113, 117, 119, Polygalacturonase, 167
134, 180, 185, 190, 218, 219, 221, Polyoxomolybdates, 109
222, 225, 229, 230, 233–235, 237, Polysulfide, 80–82, 84, 241
239, 243, 249 Polyvinyl acetate, 36
reinforced alkaline extraction, 126 Potassium permanganate, 129
OxyTrac system, 89, 93 Potassium peroxymonosulfate, 108
Ozone, 24, 45, 51, 53, 94, 106–109, Potassium peroxymonosulfate (Oxone), 108
111–114, 116, 119–121, Power consumption, 99, 145, 165
123–125, 130, 139, 140, 158, Precipitated calcium carbonate, 161
184, 185, 189–191 Precipitator ash, 59
bleaching, 96–105, 120, 125, 136, 184, Prenox, 109
238, 249 Press filter, 85, 162
generator, 99, 125 Press section, 31, 125, 164, 189
Pressure screen, 85
Pressurized peroxide stage, 113, 119, 127
P Primary clarifier, 193, 227, 242
Packaging film, 12 Primary screening, 218, 221, 222
Packaging paper, 16, 244 Primary treatment, 192–193, 227
Paper machine, 11, 27, 28, 30–32, 34–36, Printability, 12, 71–73
46, 73, 104, 107, 121, 163, 164, 168, Printing paper, 16, 18, 125, 164,
171, 188, 191, 223, 234, 233, 241
236, 238, 242 Productivity, 8, 48, 122, 217
Papermaking, 11–14, 17, 19, 20, 22–24, Protein, 36, 167
27–37, 45, 56, 57, 70, 72, 74, 82, 97, Pulp and paper industry, 1–4, 6, 7, 11,
99, 117, 164, 170–172, 191 41, 42, 45, 46, 49, 52, 56, 59,
Paper towel, 2 65, 66, 73, 82, 97, 105, 116,
Partial closure, 180–187 140, 151, 154, 171, 180, 187,
Partial system closure, 180–187 194, 217, 248, 249
Pectinase, 167 Pulp dryer, 220, 224, 225, 230, 236,
Peracetic acid, 112, 119, 125, 242 237, 244, 245
Peroxyacetic acid, 108 Pulping, 4, 11, 15–21, 41, 65, 165–167,
Peroxyformic acid, 108 220, 239, 248
Peroxygen, 119 Pulping additive, 80
Peroxymono-phosphoric Pulp mill, 21, 22, 25, 26, 28, 42–47, 52, 53,
enzyme, 108–109 55–58, 67, 68, 79, 81, 86, 94, 96, 97,
Persistent organic pollutants, 54, 115, 249 99, 103, 104, 109, 113, 115, 117,
Pigment, 29, 36 124, 125, 128, 130, 133, 138, 142,
Pine, 12, 97, 106, 219, 220, 226, 233, 240, 241 143, 147, 148, 153, 154, 161–163,
Plantation, 3–5, 8, 53, 73, 220, 221, 172, 173, 176–179, 188–190, 197,
223, 237, 242 217–245, 248–250
Index 257
Pulp screening, 22, 23, 229, 237 Screening, 14, 15, 21–23, 28, 56, 67, 74, 85,
Pulp washing, 18, 21–23, 84–87, 138, 178, 86, 152, 171, 172, 189, 192, 218, 219,
182, 185, 229 221, 222, 224, 225, 229, 230, 233,
Pulp yield, 6, 14, 20, 23, 67, 71, 80–82, 236–238, 241, 242
93, 95, 103, 107, 131, 132, Screw conveyor, 15, 146
176–179, 218 Scrubber, 139, 146–147, 152, 187,
189, 225, 242
Secondary clarifier, 194, 227
R Secondary fiber, 18, 57
Radiata pine, 219, 226 Secondary fiber pulping, 19–20
Rapid Displacement Heating (RDH), 17, 74, Secondary refining, 106
75, 79, 80, 124 Secondary treatment, 51, 58, 68, 113, 182,
Rayon, 12, 16, 20, 24 196, 227
RDH. See Rapid Displacement Sedimentation basin, 194
Heating (RDH) Selective catalytic reduction (SCR),
Reaction vessel, 16 141, 142, 157, 160
Recausticizing, 13, 161–163, 178, 230–232, Selective noncatalytic reduction
237, 244 (SNCR), 141, 142, 156–159
Recovered fibre, 18 Selective refining, 108
Recovery Selectivity, 76, 77, 83, 88, 89, 92, 93,
chemical, 7, 13, 16, 17, 19–22, 24, 95, 124, 178, 221
26, 46, 84, 85, 94, 98, 105, 111, Semi-chemical pulping, 13, 18–19
121, 133, 154, 161, 174, 181, Separation, 19, 21, 28, 66, 68, 75, 88,
183, 228, 235 106, 107, 144, 173, 174, 185,
furnace, 22, 26–27, 134, 136, 140, 141, 191, 192, 218, 222
143, 146, 183 Shive, 23, 24, 86, 88, 127, 218, 233
heat, 66–68, 79, 147, 152, 171 Sizing, 29, 30, 36, 72, 170
Recycling, 19, 37, 41, 42, 45, 46, 53, 56, 58, Sludge contact process, 196
59, 66, 79, 88, 94, 154, 169, 187–192, Sludge handling, 228
194, 196, 218, 247 Sludge recycling, 194
Refining, 12, 17, 18, 28, 29, 72, 103, Slushing, 28
106–108, 123–125, 165–168, 189 Smoothness, 18, 34, 72, 169
Refining pulp, 17 Soda pulping, 15
Renewable energy, 241, 244 Sodium borohydride, 82
Resin, 24, 29, 187 Sodium carbonate, 19, 26, 27, 153, 173,
Resin acid, 47, 58, 70, 71, 83, 107, 132 174, 177, 178, 184
Resource utilization, 247 Sodium cyanate, 154
Retention time, 78, 92, 104, 112, 123, 128, Sodium hydroxide, 16, 19, 20, 26, 27, 108,
166, 192, 194, 195, 218, 225 112, 119, 120, 146, 147, 162, 177,
Ring debarker, 14 178, 181, 184, 186, 242
Roller conveyor, 15 Sodium sulfate, 26, 27, 143, 148, 149,
Rotary pressure washer, 22 153, 186, 187
Rotary vacuum washing, 22 Sodium sulphide, 16, 26, 27, 162, 173, 174
Runnability, 28, 46, 104, 107, Softwood, 12, 16–18, 69, 70, 75, 77, 79,
171, 239 81–83, 87, 89, 93–95, 97, 98, 101,
103, 104, 106, 107, 111–113,
115–121, 124, 127, 135, 190,
S 217–220, 222, 239–242, 244
Salt cake, 176 Solid waste, 4, 5, 19, 22, 42, 43, 56–59, 68,
Saponifiable, 83 223, 229, 249
Scaling, 20, 24, 46, 131, 136, 180, 181, Spent cooking liquor, 16, 21, 26, 75, 84
218, 219 Spill collection, 46, 192
Scraper conveyor, 15 Spruce, 12, 106, 107, 167, 233, 240, 241
258 Index
Starch, 30, 36 U
Steel plate conveyor, 15 Ultrafiltration, 242
Sterol, 58, 132 Unpressurized peroxide stage, 119
Stiffness, 19, 30, 71, 72, 164 Unsaponifiable, 83
Stock preparation, 13, 27–37, 189
Stone groundwood pulping, 14
Straight ECF, 111 V
Straw, 20 Vanadium pentoxide, 141
Strength properties, 12, 18, 29, 71, 73–76, Vibrating conveyor, 15
81, 95, 103, 104, 106–108, 122–125, Viscosity, 51, 76, 88, 89, 95, 104, 114, 117,
167, 169, 233, 234 123, 124, 127, 132, 150, 151, 178
Stripping, 46, 134–139, 223, 237 Volatile organics, 52–54, 68, 152
Strong black liquor, 26, 148, 151
Sulphate pulp, 189, 244
Sulphidity, 148, 187, 235 W
Sulphite pulp, 17, 45, 46, 70, 121, 123 Washing equipment, 21, 22, 85, 86, 185,
Sulphite pulping, 17, 20 190, 218, 230
Sulphur oxide, 139–142 Wash presses, 22, 85, 96, 112, 190, 191,
Superbatch, 17, 74, 75, 79, 80, 233, 240 221, 226, 229, 231, 233, 238, 239
Super calendering, 36, 37 Waste management, 59
Super concentrator, 149 Waste minimization, 6, 229
Surfactants, 30, 80, 82–84 Wastewater, 20, 22, 25, 42, 45, 46, 56, 70, 71,
Sustainability, 3, 4, 7, 66, 108 97, 111, 115, 117, 118, 133, 135, 153,
Sustainable development, 3, 247, 248 170, 183, 186, 187, 189, 193, 242, 249
Synthetic diesel, 172 Waste water recycling, 187, 188
Synthetic gas, 172 Water pollution, 3, 46–51
Weak black liquor, 26, 84, 85, 134, 189
Web consolidation, 163
T Wet debarking, 70, 71, 189
Tannin, 17 Wet scrubbing, 138, 147
Tear strength, 29, 121 White liquor, 16, 26, 27, 54, 74–79, 81, 94,
Tertiary treatment, 196–197, 226, 228 132, 137, 146, 147, 152, 161, 162, 184,
Tertiary waste treatment, 192–197 185, 235, 237, 239, 241
Testliner, 45, 46 White liquor plant, 236–239, 244
2,3,7,8-Tetrachlorodibenzodioxin, 45 Wood
2,3,7,8-Tetrachlorodibenzofuran, 45 handling, 66–70, 86, 231, 236, 244
Tetra chloroguaiacols, 47 processing, 224
Thermal oxidation, 137, 138 Wood yard, 14, 56, 67, 68, 189, 220, 224,
Tissue paper, 18, 23, 24, 233 227, 230, 236, 237, 244
Titanium dioxide, 141 Writing paper, 3, 16, 20, 23, 36, 71, 72, 87
Totally chlorine free (TCF) bleaching, 6, 7,
50, 54, 98, 99, 105, 113, 117,
119–125, 127, 180, 181, 190 X
Total reduced sulfur (TRS), 26, 43, 53, 54, Xylan, 82, 128, 129
81, 135, 137, 138, 147, 148, 150, 152,
153, 155, 162, 163, 225, 231
Total suspended solids (TSS), 45, 71, 192, 197 Y
Toxicity, 4, 42, 44, 47–51, 58, 68, 70, 107, Yankee machine, 35
118, 136, 180, 228
Transition metal, 119, 129, 136, 180, 183, 184
Trichloroguaiacols, 47 Z
Tungsten trioxide, 141 Zero effluent kraft mill, 6, 249
Twin wire machine, 31, 33 ZeTrac process, 101

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Pratima

ISBN 978-3-319-18743-3 ISBN 978-3-319-18744-0 (eBook)

Library of Congress Control Number: 2015942906

Springer Cham Heidelberg New York Dordrecht London

Printed on acid-free paper

Springer International Publishing AG Switzerland is part of Springer Science+Business Media (www.

Patiala, India Pratima Bajpai

1 General Background ................................................................................. 1

4.4 Extended or Modified Cooking ........................................................ 73

4.26 Water Recycling/Reuse .................................................................... 187

Index ................................................................................................................. 251

AOX Adsorbable organic halides

RDH Rapid displacement heating

Table 1.1 Goals in pursuit of an environmentally

Table 4.13 Brightness development in different

© Springer International Publishing Switzerland 2015 1

Inspite of the advancement of digital technology paper consumption is increasing

manufactured products that use processes that minimize negative environmental

Paper mills vary significantly in their environmental performance, depending on

A strong thrust within many of these process technology developments is toward

Sutton P (2004) A perspective on environmental sustainability? Victorian Commissioner for

Keywords Pulp and Paper industry • Pulping • Bleaching • Papermaking •

© Springer International Publishing Switzerland 2015 11

Weal black liquor

Table 2.1 Steps involved in the manufacturing of pulp and paper

2.1 Raw Material Preparation

2.2.1 Chemical Pulping

Table 2.2 Types of pulping

2.2.1.1 Kraft Pulping Process

2.2.1.2 Sulphite Process

2.2.2 Mechanical Pulping

2.2.3 Semi-chemical Pulping

Semi-chemical pulping uses a combination of chemical and mechanical (i.e., grind-

2.2.4 Secondary Fibre Pulping

2.2.5 Dissolving Kraft and Sulphite Pulping Processes

2.2.6 Non-wood Pulping

affects, non-wood pulping facilities generally discharge higher proportions of lime

2.3 Pulp Washing

2.4 Pulp Screening, Cleaning and Fractionation

Bleaching of pulp is done to achieve a number of objectives. The most important of

subsequent alkaline extraction. The resulting brownish Kraft pulp eventually

2.6 Chemical Recovery

2.6.1 Black Liquor Concentration

2.6.2 Recovery Furnace

2.6.3 Causticizing and Calcining

2.7 Stock Preparation and Papermaking

Table 2.3 Unit processes in stock preparation

Table 2.4 Common pulp Acids and bases:

Fig. 2.2 A flow diagram for a typical papermaking process

penetration of liquids and to improve printing properties (Krogerus 2007; Bajpai

Fig. 2.3 Details of papermaking process

Wet End Wet Press Section Dryer Section Calender Section

Fig. 2.4 Schematic of Fourdrinier paper machine

Keywords Kraft pulping • Pulp bleaching • Environment • Wastewaters • Air emis-

© Springer International Publishing Switzerland 2015 41

Table 3.1 Important parameters followed in order to demonstrate improvements towards a

– Deformities in bones and gill erosion in fish;

3.1 Water Pollution

organic compounds which include chlorinated resin acids, chlorinated phenolics

Table 3.2 Chlorinated Variations

4.1 Emission Reduced Wood Handling

4.2 Dry Debarking

4.3 High Yield Pulping

4.4 Extended or Modified Cooking

4.4.1 Batch Cooking

4.4.2 Continuous Cooking

4.4.3 Modifying Kraft Pulping with Additives

4.4.3.3 Sodium Borohydride

4.4.3.5 Combination of AQ/Surfactant

4.4.3.6 Combination of AQ-Polysulfide

4.5 Efficient Brownstock Washing/Improved Pulp Washing

4.6 Oxygen Delignification

b enefits of oxygen delignification are decrease of the amount of chemicals, p ollution

Table 4.7 presents kappa numbers currently achieved with different d elignification

4.7 Ozone Bleaching of Chemical Pulps

4.8 Ozone for High Yield Pulping

4.9 Elemental Chlorine-Free Bleaching (ECF) Bleaching

4.9.1 Modified ECF Sequences