Bioresource Technology 100 (2009) 310–315
Contents lists available at ScienceDirect
Bioresource Technology
journal homepage: www.elsevier.com/locate/biortech
The reuse of spent mushroom compost and coal tailings for energy recovery:
Comparison of thermal treatment technologies
Karen N. Finney *, Changkook Ryu, Vida N. Sharifi, Jim Swithenbank
Department of Chemical and Process Engineering, University of Sheffield, Mappin Street, Sheffield S1 3JD, UK
a r t i c l e
i n f o
Article history:
Received 7 January 2008
Received in revised form 21 May 2008
Accepted 23 May 2008
Available online 14 July 2008
Keywords:
Energy recovery
Spent mushroom compost
Coal tailings
Thermal treatment technologies
a b s t r a c t
Thermal treatment technologies were compared to determine an appropriate method of recovering
energy from two wastes – spent mushroom compost and coal tailings. The raw compost and pellets of
these wastes were combusted in a fluidised-bed and a packed-bed, and contrasted to pyrolysis and gasification. Quantitative combustion parameters were compared to assess the differences in efficiency
between the technologies. Fluidised-bed combustion was more efficient than the packed-bed in both
instances and pellet combustion was superior to that of the compost alone. Acid gas emissions (NOx,
SOx and HCl) were minimal for the fluidised-bed, thus little gas cleaning would be required. The fuels’
high ash content (34%) also suggests fluidised-bed combustion would be preferred. The Alkali Index of
the ash indicates the possibility of fouling/slagging within the system, caused by the presence of alkali
metal oxides. Pyrolysis produced a range of low-calorific value-products, while gasification was not
successful.
Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction
To mitigate the impacts of our growing demand for energy and
the increase in waste production, it is possible to use many wastes
as fuel resources – two of these wastes include spent mushroom
compost, hereinafter SMC, and coal tailings.
The formation of the mushroom compost substrate takes place
in stages: (i) pre-wetting and mixing of straw, gypsum, horse manure, poultry litter, peat, lime and activators; (ii) phase 1 composting in windrows and bunkers; and (iii) phase 2 composting
involving pasteurisation and conditioning. After this, a peat casing
layer is added to the surface for mushroom cultivation (spawning,
casing, pinning and cropping), after which it is cooked out and discarded (DEFRA, 2006; Iiyama et al., 1994). Disposal is problematic,
unsustainable and harmful to the environment, since the majority
goes to landfill or is used as agricultural fertilisers, where leaching
can be a serious issue for local water courses from both sources, as
phosphorous and nitrates cause eutrophication. For every 1 kg of
mushrooms grown, approximately 5 kg of SMC is produced. The
generation rate of SMC is about 200,000 tonnes/annum in UK
alone. The lack of sustainable waste management solution for
SMC is the most significant barrier to the future development of
this industry.
Previous studies into the use of SMC as a renewable fuel propose that SMC can be combusted in a bubbling fluidised-bed to
generate power with high efficiency (McCahey et al., 2003; Wil* Corresponding author. Tel: +44 114 2227578; fax: +44 114 2227501.
E-mail address: cpp06knf@sheffield.ac.uk (K.N. Finney).
0960-8524/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.biortech.2008.05.054
liams, 2001; Williams et al., 2001; BioMatNet, 2004). The calorific
value (CV) is comparable to other fuels, though drying or mixing
with drier materials is needed. ‘Auxiliary fuels’, such as natural
gas, can be co-fried with SMC to promote drying and enable greater
energy recovery. Combustion of SMC leads to the production of
ash, usually about 10% of its original volume, in addition to what
it already contains. A preliminary investigation has been completed into the reuse of this ash as a chemical activator to enhance
the pozzolanic reactivity of pulverised fuel ash (PFA) in the cement
industry (Russell et al., 2005). SMC ash and PFA mixtures ensure
rapid early improvements in the strength, although it is too soon
to investigate the long-term implications of its use.
There are also many potential agricultural, horticultural and
industrial uses of SMC including: An agricultural fertiliser (Gent
et al., 1998; McCahey et al., 2003; Rhoads and Olson, 1995); a
ruminant feed for sheep (Fazaeli and Masoodi, 2006); environmental enrichment in intensive pig farms (Beattie et al., 2001); treatment for coal mine drainage (Stark et al., 1994); bioremediation
(Lau et al., 2003); enzyme extraction (Ball and Jackson, 1995);
and a novel biosorbent (Chen et al., 2005).
Coal tailings are formed from coal cleaning processes, where
coal is separated from its impurities. It has a significant proportion
of moisture, although dewatering takes place in the lagoons where
it is deposited, usually located in close proximity to the mining
area. Lagoon management is vitally important, as mismanagement
of these sites can result in contamination or lagoon failure, thus
removing coal tailing deposits will eliminate these risks (Thompson, 1982). There are currently few uses of coal tailings. Noble
and Dobrovin-Pennington (2005) investigated how it replace some
311
K.N. Finney et al. / Bioresource Technology 100 (2009) 310–315
Nomenclature
1
2
AI
BR
Cb
Cl
CV
FB
IFS
IR
Mp
NOx
P
PB
Pc
PFA
RDF
SMC-coal tailing pellets
raw SMC
Alkali Index
burning rate
cardboard
chlorides
calorific value
fluidised-bed
ignition front speed
ignition rate
Miscanthus pellets
oxides of nitrogen
pyrolysis
packed-bed
pine cubes
pulverised fuel ash
refuse-derived fuel
of the peat in the casing layer added to the mushroom substrate,
whereas Tiwari et al. (2004) focussed on its reuse for aggregates
or the production of concrete blocks for construction. Only a few
have examined its potential as a fuel, such as Chugh and Patwardhan (2004) and Radloff et al. (2004). The latter considered the processes of turning 70,000 tonnes/annum of waste from the
Wallerawang colliery into fuel for a power station. This could be
the greatest potential use of this waste, where 50 mm-diameter
pellets were formed with a binding agent, followed by drying
and then combustion with coarse waste from the coal mining
industry.
There is a clear potential to combine these wastes, for energy
recovery through use in thermal treatment technologies. Combustion, gasification and pyrolysis have been utilised with both conventional and renewable fuels to produce heat, energy and
subsequent fuel products. These three treatments were compared
herein, with the aim of determining the most appropriate technology for the reuse of SMC and coal tailings. Consequently, it is hoped
that this will provide a renewable fuel for industry, divert SMC
from landfill and aid the cleaning and reclamation of land contaminated by coal tailings. Furthermore, this may partially mitigate the
impacts of environmental issues associated with present energy
production and waste management strategies.
2. Methods
SMC
Sp
Sr
SOx
SO24
Ww
spent mushroom compost
switchgrass pellets
raw switchgrass
oxides of sulphur
sulphates
willow wood
Greek symbols
DM
mass loss
gCE
combustion efficiency
k
equivalence ratio
q
density
Subscripts
C
char combustion stage
I
ignition propagation stage
Table 1
Material characterisation of the coal tailings and the two layers of the SMC
Analysis
Constituent
Moisture (%)
Basis
Coal
tailings
SMC
substrate
SMC
casing
ar
40
65.70
68.56
Proximate analysis
(%)
Ash
Volatile
Fixed
Carbon
dry
41.25
20.51
38.24
26.89
61.80
11.31
28.87
60.18
10.95
Ultimate analysis
(%)
Carbon
Hydrogen
Nitrogen
Chlorine
Sulphur
dry
47.87
2.90
1.01
–
1.38
35.13
3.59
2.85
0.51
2.95
35.72
3.01
1.11
0.70
2.16
CV (MJ/kg)
GCV
GCV
NCV
NCV
dry
ar
dry
ar
19.85
11.91
19.22
10.55
14.11
4.94
13.33
3.08
12.37
4.33
11.71
2.51
Table 2 shows the full elemental analyses. In addition to the potential pollutants described above, other issues may arise due to
the presence of specific elements. Slagging/fouling may occur due
to the alkali metals present, specifically potassium and sodium.
The large proportion of calcium, particularly in the SMC casing
may be beneficial, however, as this could reduce SOx compounds
2.1. Characterisation of spent mushroom compost and coal tailings
Table 1 shows the material characterisation. The results for the
SMC were comparable to those previously reported in the literature (Williams et al., 2001). The two SMC layers were quite analogous and the volatile and fixed carbon contents were similar to
other types of biomass used for energy recovery. The nitrogen
and sulphur contents were high, however it has been found from
previous literature that these are mainly bound in inorganic forms
(nitrates and sulphates), and thus fluidised-bed combustion will
minimise the risks of forming NOx and SOx (Williams et al.,
2001). All three substances have significant quantities of moisture
and ash, which have detrimental implications on the CVs, as shown
in Table 1. These were comparable to other wastes currently used
as fuels, such as MSW and sewage sludge. Coal tailings have a
comparable CV to sub-bituminous C coal and the other coal tailing
samples (Radloff et al., 2004).
Table 2
Selected results from the full elemental analyses
Element (mg/kg)
Coal tailings
SMC substrate
SMC casing
Al
As
Ca
Cr
Cu
Fe
K
Mg
Mo
Na
P
Pb
Si
Zn
4360.0
14.8
2940.0
13.0
19.0
9700.0
1070.0
2420.0
2.3
450.0
74.3
12.9
1380.0
34.6
441.5
<1
40900.0
3.8
46.1
1240.0
18650.0
4620.0
4.1
2095.0
6655.0
2.6
1620.0
194.5
1435.0
<1
118500.0
6.2
11.7
2580.0
3685.0
4265.0
0.3
600.0
4220.0
5.1
1485.0
44.1
312
K.N. Finney et al. / Bioresource Technology 100 (2009) 310–315
in a similar manner to scrubbing processes – the sulphur content of
all three components was quite significant. This sulphur can inhibit
de Novo Synthesis, preventing the formation of dioxins and furans,
as chlorine was also present in the SMC layers (Fielder, 1998). Iron
and phosphorus were found in significant quantities, although heavy metals were not prevalent.
2.2. Spent mushroom compost and coal tailing pelletisation
Optimum values were experimentally-determined for a number
of key pelletisation variables. The parameters included the moisture content (10–11%) followed by air-drying, compaction pressure
(up to 6000 psi) and pellet composition (50:50 SMC:coal tailings
wt% ratio). Pellet quality was based on their density, tensile
strength, durability and maximum pellet pile heights (Table 3).
The methods and results for these are presented in a previous publication (Ryu et al., 2008).
Table 4
Thermal treatment conditions and results for key parameters for the combustion tests
Parameter
FB1
FB2
PB1
PB2
Material
Small
pellets
4.6
240–610
60–90
SMC
SMC
3.0
190–770
90
Large
pellets
6.26
720–1200
480
13.50
4.22
1.22
12.91
4.04
1.38
17.28
0.49
1.85
17.19
2.76
5.22
Amount of material (kg)
Primary air (kg/m2h)
Secondary air (kg/m2h)
Average gas
Concentration
CO2 (%)
O2 (%)
CO (%)
4.34
720
0–480
Combustion efficiency, gCE (%)
91.7
90.3
90.3
76.7
Average Temperature
(°C)
816
813
799
797
1139
1117
1133
728
509
443
1055
735
Bed
Above
bed
Freeboard
2.3. Methods for thermal treatments
2.3.1. Fluidised-bed for combustion
A small-scale fluidised-bed was used to combust the pellets
(FB1) and the raw SMC (FB2). The fuel was placed in the sealed
hopper of the calibrated pneumatic screw feeder. The sand on
the perforated distributor plate 200 mm from the base of the reactor forms the fluidised-bed within the 2.3 m 0.15 m stainless
steel combustion chamber. This was heated with propane until
the temperatures were stable, monitored using K-type mineral
insulated thermocouples. Once this was achieved, the fuel was
gradually fed in and the feedrate increased as the propane flowrate
decreased. Table 4 shows the conditions for these and the subsequent tests. The exhaust produced passed through the cyclone to
remove and collect particulate matter and the remaining gas was
analysed for CO2, CO and O2 with an ADC MGA300 gas analyser,
and NOx (NO and NO2) using a Signal Series 4000 NOx analyser before being discharged to the atmosphere. Chlorides (Cl ) and sulphate (SO24 ) species were collected by a wet chemical method,
to indicate the presence of HCl and SOx.
the reaction. The emissions passed through a probe to the cooling
tower, where the moisture was condensed out before CO2, CO and
O2 concentrations were established.
2.3.3. Pyrolyser
Pyrolysis (P) was performed in an electrically-heated, insulated
130 mm 320 mm stainless steel chamber, where the SMC was
placed in the primary fixed-bed at the top of the cylinder. During
the reaction, char was formed, which remained inside the reactor.
This was fed with nitrogen at the base to prevent oxidation and to
force the volatiles into the subsequent analysing equipment. These
volatiles passed through a heated tube and were condensed to collect pyrolytic liquids. The gases were fed through a condensing
tower, where samples were taken to assess the changing syngas
(gaseous fuel product) composition with temperature. These were
analysed with a Varian CP 3000 gas chromatograph. The exhaust
then entered the CO2 and CO analyser. The solid, liquid and gaseous
fuels were analysed for composition and CV, as appropriate.
2.4. Further data analysis
2.3.2. Packed-bed for combustion and gasification
A packed-bed was also used to combust the pellets (PB1) and
SMC (PB2), as well as perform the gasification of the SMC. The fuel
was placed onto the perforated grate at the bottom of the
1.5 m 0.2 m reactor chamber and ignited using a gas burner. Primary and secondary air was fed from the bottom and top, respectively. Table 4 shows the operating conditions. The reactor was
suspended from a weighing beam to monitor weight-loss during
Table 3
Results of pellet density, tensile and compressive strengths and pellet pile-up
Variables and parameters
Optimum 1
2
3
4
5
Initial moisture content
(%)
Drying
Pressure (psi)
Composition (SMC:coal
tailings)
Pellet diameter (mm)
Pellet length (mm)
Density (kg/m3)
Tensile strength (kPa)
Compressive strength (N)
Weight (kg)
Number of pellets
15
16.3
16.0
10
15
15
Yes
2700
50:50
No
2700
0:100
Yes
2700
0:100
Yes
6000
0:100
Yes
Yes
2700 2700
100:0 Substrate
26.8
43.0
1083.7
116.4
134.3
11.9
451.7
26.8
31.8
1483.3
69.4
59.1
7.1
266.1
26.8
32.0
1371.0
108.7
93.2
9.5
384.4
26.8
4.3
1367.9
364.1
421.7
43.0
1290.4
26.8
56.7
661.4
60.8
92.5
9.4
445.9
Height of pellet pile (m)
12.10
7.13
10.30
34.58
11.95 33.73
26.8
5.8
689.7
179.1
277.1
28.3
1258.7
1: wet coal tailings; 2: dried coal tailings; 3: coal tailings at high pressure; 4: SMC
and 5: SMC substrate.
Based on the CO and CO2 concentrations, the combustion efficiency (gCE) was calculated for the combustion cases. A number
of other quantitative combustion parameters, namely mass loss
(DM), ignition front speed (IFS), ignition rate (IR), burning rates
for ignition propagation and char combustion (BRI and BRC) and
equivalence ratio (k) were determined for the packed-bed cases
to evaluate their performance (Ryu et al., 2006, 2007a; Ryu et al.,
2007b). The Alkali Index (AI) was computed to assess the potential
for slagging/fouling. Values above 0.34 suggest fouling is certain
(Jenkins et al., 1998). Full elemental analyses of the ash aided the
determination of this parameter.
3. Results and discussion
The operating conditions used in the fluidised-bed and packedbed cases and the key results are shown in Table 4. gCE in the fluidised-bed was superior in the both cases and pellet combustion
efficiency was also notably higher compared to the SMC alone.
SMC pyrolysis produced a variety of low-CV fuels. These results
are discussed below, although as SMC gasification was not successful, it is not considered further.
3.1. Combustion in the fluidised-bed
The combustion of the SMC-coal tailing pellets in the fluidisedbed (FB1) achieved the highest gCE (91.7%) and was superior to the
313
K.N. Finney et al. / Bioresource Technology 100 (2009) 310–315
combustion of SMC (FB2). The gas concentrations were similar for
both tests, although there was slightly more oxygen for SMC combustion, indicating fuel lean conditions, which resulted in a slightly
lower efficiency (90.3%). The average NOx concentration during
pellet combustion was low (8.8 ppm ± 0.76), thus little gas cleaning, for example selective catalytic or non-catalytic reduction,
would be required. Furthermore, SO24 and Cl concentrations were
0.52 and 0.61 ppm, respectively, indicating the presence of SOx and
HCl species were also minimal. The Ca present in the SMC may
have reduced some SOx species, via the mechanism described
above. Previous thermal treatments of SMC have shown that NOx
and SOx will be negligible if it is combusted in a fluidised-bed,
due to the inorganic origin of the majority of nitrogen and sulphur
(Williams et al., 2001). It was also reported that though some HCl
may form, most Cl should remain as chlorides in the ash (Williams
et al., 2001; Williams, 2001). Additionally, it has been suggested
that NOx and SOx emissions from coal tailing combustion would
also be minimal (Chugh and Patwardhan, 2004). These findings
were corroborated here. Temperatures for FB2 were somewhat
lower than that for FB1, due to the inferior CV of the SMC. Temperatures in and just above the bed were higher than those in the freeboard in both cases.
3.2. Combustion in the packed-bed
The temperatures achieved during combustion in the packedbed were higher than those in the fluidised-bed. The temperatures
in the bed for PB2 were similar to those for PB1, although the freeboard was appreciably cooler. As the temperatures were significantly lower, there was less sintering off the ash for PB2. The O2
concentration decreased to lower levels than that in the fluidised-bed and consequently, the combustion products (CO and
CO2) were more abundant, particularly CO, indicating less efficient
combustion. gCE for PB1 and PB2 were 90.3% and 76.7%, respectively, where the latter was severely affected by the high CO. It
was found that the air flowrates were crucial in determining
whether or not the fuel would burn, particularly for the SMC. If
the air flowrates were too high, this caused dramatic cooling of
the reaction and combustion ceased, whereas when the flowrates
were too low, there was insufficient oxygen for the reaction to
continue.
A range of quantitative combustion parameters were calculated
(Table 5) and compared to those from the literature for miscanthus
pellets (Mp), pine cubes (Pc), willow wood (Ww) and refuse-derived fuel pellets (RDF) (Ryu et al., 2006), cardboard (Cb) (Ryu et
al., 2007b), switchgrass pellets (Sp) and raw switchgrass (Sr) (Gilbert et al., 2006). In general, these results corroborate well with
other biomass combustion tests. DMI was greater for the pellets
compared to the SMC, and as such, the BR during this phase was
much higher. By contrast, the BR during char combustion was more
rapid for the SMC, although the overall BR was faster for the pellets. The IFS and IR for the pellets were both significantly lower
than that for the SMC, due to the differential densities. Variations
between the pelletised and non-pelletised fuels in this study have
been confirmed by the differences between pelletised and nonpelletised switchgrass, namely DMI, IFS and IR (Gilbert et al.,
2006). DMI was significantly lower for these tests, where the
majority of mass loss occurred during the char combustion phase,
particularly for PB2. Char formation, rather than combustion, was
the significant process occurring during the initial stages of these
reactions. As previously suggested, BRI was lower than IR in all
cases, thus char remained after volatile combustion. The IFS were
similar for all the cases shown, except for the raw switchgrass,
due to its very low density (Gilbert et al., 2006). Although the range
of IR was vast in previous literature, the results gained were within
the range shown in Table 5. The BR was also comparable, except
the switchgrass, which showed significantly higher overall BR,
although the results for Sp and Sr were very similar. The equivalence ratio at the ignition propagation stage (kI) was also calculated. The values for these were significantly lower than those
reported in Table 5. The Alkali Index was calculated from the full
elemental analyses of the ash samples, assuming that all K and
Na present were in oxide form. Probable fouling will occur with
the combustion of these pellets. The combustion of the SMC still
had the potential to foul, as there were noteworthy amounts of
potassium and sodium in the ash.
3.3. Pyrolysis
Three hundred grams of non-pelletised SMC was pyrolysed for
1 h at 500 °C with 2 l/min of nitrogen. The temperature profiles
and gas concentrations are shown in Fig. 1. Despite the lack of oxygen in the system, CO2 was still produced in significant quantities,
due to the oxygen present in the feed material. As expected, CO
was much higher than combustion, as pyrolysis is a thermal
decomposition, not an oxidation, process. In addition to these,
other gases were also analysed (Table 6). Towards the end of the
reaction, the proportion of hydrocarbon fuels increased, where
methane (CH4), ethane (C2H4) and propane (C3H8) became more
abundant as the temperatures became higher.
In addition to these gases, solid and liquid fuels were produced
(Table 7). The char was similar in appearance, in terms of particle
size and shape, to the original material, although once pyrolysed,
the material became dark and uniform in colour. The liquids separated out, where the heavier, paler pyrolysis liquid settled towards
the bottom, with the darker, aqueous phase on top. CV tests revealed large differences between their energy values. The paler
pyrolysis liquid had a reasonable CV of 5.85 MJ/kg, whereas the
Table 5
Comparison of quantitative parameters for the combustion in the packed-bed
Test
PB1
PB2
Mpa
Pca
Wwa
RDFa
Cbb
Spc
Src
a
b
c
Parameter
DMI (%)
IFS (m/h)
IR (kg/m 2h)
BRI (kg/m 2h)
BRC (kg/m 2h)
x BR (kg/m2 h)
kI
AI (kg-alkali/GJ)
q (kg/m3)
51.4
19.4
75–81
84–86
68–82
73–75
68–90
90
65.6
0.7
1.3
0.36
0.7–0.8
1.1–1.2
0.2–0.3
–
0.76
8.9
296.4
376.8
–
–
–
–
190–300
280
508
152.5
72.9
–
–
–
–
135–310
312
385
75.9
120.4
–
–
–
–
55–115
–
–
109.8
93.7
94–148
123–134
104–141
97–112
–
252
253
1.27
0.45
2.1–2.3
2.1–2.3
2.9–4.1
2.2–2.4
2.0–2.5
2.39
2.40
0.17
0.13
0.34
<0.1
<0.1
>0.2
–
–
–
442.8
300.3
660
272–295
181
715
76
370
57
Ryu et al. (2006).
Ryu et al. (2007a,b).
Gilbert et al. (2006).
314
K.N. Finney et al. / Bioresource Technology 100 (2009) 310–315
600
20
T1, y = 300mm
Temperature (˚C)
15
400
300
10
200
5
Gas Concentration (%)
500
T2, y = 250mm
T3, y = 200mm
T4, before condenser
T5, after condenser
Carbon Dioxide
100
Carbon Monoxide
0
0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Time (hrs)
Fig. 1. The temperature profiles and gas concentrations during SMC pyrolysis.
Table 6
Analysis of the changing composition of gaseous fuel products with temperature from
SMC pyrolysis
Gas
CO2
CO
CH4
H2
C2H4
C3H10
Gas concentration (%) with temperature
350 °C
400 °C
450 °C
500 °C
13.02
8.96
0.11
0.04
0.14
0.06
16.61
9.40
0.54
0.08
0.08
0.05
14.44
6.67
0.78
0.22
0.13
0.07
8.19
7.69
1.26
1.34
0.18
0.08
Table 7
Analysis of the solid and liquid fuel products from SMC pyrolysis
Analysis
Constituent
Char
Liquid
Yield
%g
43.33
130
34.71
104
Ultimate analysis (%)
Carbon
Hydrogen
Nitrogen
Oxygen
34.2
1.2
1.4
63.2
5
11.8
1.5
81.8
CV (MJ/kg)
GCV
NCV
7.95
7.68
2.98
–
darker, aqueous phase had a low CV of just 2.16 MJ/kg. The lower
CV product was found in greater abundance, however, which was
why the overall CV for the liquid phase was low. Separation of
these two phases may be beneficial and further processing, as
refining may be required.
temperatures could be generated for the production of useful and
moreover saleable heat and/or power. Pellet combustion achieved
the greatest efficiency, as the bulk and energy densities were increased by drying and pelletisation, thus pre-processing these
wastes is integral to their successful use as a fuel. This was seen
particularly in the fluidised-bed, which had the highest overall efficiency. Fluidised-bed combustors usually have higher carbonburnout efficiencies due to their superior fluid-particle contacting,
clearly shown in the comparison between the two combustion
methods. Pelletised fuels also generally have better combustion
efficiencies than non-pelletised fuels, especially in fluidised-beds
where the densified fuel can burn within the bed. The ash produced from pellet combustion has the potential to be utilised as
an activator for PFA, eliminating the need for landfilling, as discussed previously (Russell et al., 2005).
The use of SMC-coal tailing pellets clearly has a wide variety of
benefits, on the pelletisation of these substances, the combustion
process and the overall environmental considerations. The SMC ensures that lower net CO2 emissions are produced than for conventional fuels, mitigating environmental issues, whereas the coal
tailings enhance the CV and thus the energy which can be recovered. Improving the overall CV of the fuel increases the combustion
efficiency and the greater bulk and energy densities ensure that
combustion takes place within the bed at greater efficiency than
the SMC alone. The reuse of both of these wastes also means less
land is taken up by landfill sites and coal tailing lagoons; even
the ash can be used in an environmental manner.
Pyrolysis did produce a combination of solid, liquid and gaseous
fuels and although the CVs of these products were reasonable, they
were not necessarily sufficiently high to necessitate the wide-scale
use of this technology. Other biomass materials could be used in
this process to greater effect. Gasification of the material in a
small-scale fixed-bed gasifier was not successful.
3.4. Discussion of results
4. Conclusions
Three technologies were compared, where combustion was
most successful and thus deemed the best thermal treatment for
SMC and coal tailings, particularly in pellet form. The combustion
of both the pellets and SMC were self-sustaining and sufficient
The main conclusions from this comparison of thermal treatments technologies for the reuse of SMC and coal tailings are as
follows:
K.N. Finney et al. / Bioresource Technology 100 (2009) 310–315
SMC-coal tailing pellet combustion in a fluidised-bed was most
efficient (91.7%), when compared to packed-bed combustion or
the use of unpelletised SMC.
This produced minimal acid gas emissions (NOx, SOx and HCl),
although the alkali metal oxide content of the flyash was sufficient to cause possible slagging/fouling in the system.
Using these wastes for energy recovery provides a sustainable
management solution to divert SMC from landfill and aid the
reclamation of contaminated land, and is therefore both practical and environmentally-sound.
Acknowledgements
The authors would like to thank the Engineering and Physical
Science Research Council (EPSRC) and Veolia Environmental Trust
(Grant reference RES/C/6046/TP) for their financial support of this
project. Thanks also go to Maltby Colliery, Dr. John Burden and
Monaghan Mushrooms Ltd. for providing SMC and coal tailing
samples.
References
Ball, A.S., Jackson, A.M., 1995. The recovery of lignocellulose-degrading enzymes
from spent mushroom compost. Bioresource Technology 54 (3), 311–314.
Beattie, V.E., Sneddon, I.A., Walker, N., Weatherup, R.N., 2001. Environmental
enrichment of intensive pig housing using spent mushroom compost. Animal
Science 72 (Part 1), 35–42.
BioMatNet, 2004. NNE5-1999-20229 MON – CHP: Optimised Biomass CHP Plant for
Monaghan Integrating Condensing Economiser Technology. Available from:
<http://www.biomatnet.org/secure/FP5/F1730.htm>.
Chen, G.Q., Zeng, G.M., Tu, X., Huang, G.H., Chen, Y.N., 2005. A novel biosorbent:
characterisation of the spent mushroom compost and its application for
removal of heavy metals. Journal of Environmental Sciences – China 17 (5),
756–760.
Chugh, Y.P., Patwardhan, A., 2004. Mine-mouth power and process steam
generation using fine coal waste fuel. Resources, Conservation and Recycling
40, 225–243.
DEFRA, Department for Environment, Food and Rural Affairs, 2006.
Process Guidance Note 6/30(06): Secretary of State’s Guidance for
Mushroom Substrate Manufacture. Available from: <http://www.defra.gov.uk/
environment/airquality/lapc/pgnotes/pdf/pg6-30.pdf>.
Fazaeli, H., Masoodi, A.R.T., 2006. Spent wheat straw compost of Agaricus bisporus
mushroom as ruminant feed. Asian-Australasian Journal of Animal Sciences 19
(6), 845–851.
Fielder, H., 1998. Thermal formation of PCDD/PCDF: a survey. Environmental
Engineering Science 15, 49–58.
315
Gent, M.P.N., Elmer, W.H., Stoner, K.A., Ferrandino, F.J., La Mondia, J.A., 1998.
Growth, yield and nutrition of potato in fumigated or nonfumigated soil
amended with spent mushroom compost and straw mulch. Compost Science
and Utilization 6 (4), 45–56.
Gilbert, P., Ryu, C., Sharifi, V.N., Swithenbank, J., 2006. Pelletisation of Herbaceous
Crops. Departmental Internal Report, Department of Chemical and Process
Engineering, University of Sheffield.
Iiyama, K., Stone, B.A., Macauley, B.J., 1994. Compositional changes in compost
during composting and growth of Agaricus bisporus. Applied and Environmental
Microbiology 60 (5), 1538–1546.
Jenkins, B.M., Baxter, L.L., Miles Jr., T.R., Miles, T.R., 1998. Combustion properties of
biomass. Fuel Processing Technology 54, 17–46.
Lau, K.L., Tsang, Y.Y., Chiu, S.W., 2003. Use of spent mushroom compost to
bioremediate PAH-contaminated samples. Chemosphere 52 (9), 1539–1546.
McCahey, S., McMullan, J.T., Williams, B.C., 2003. Consideration of spent mushroom
compost as a source of energy. Developments in Chemical Engineering and
Mineral Processing 11 (1–2), 43–53.
Noble, R., Dobrovin-Pennington, A., 2005. Partial substitution of peat in mushroom
casing with fine particle coal tailings. Scientia Horticulturae 104, 351–367.
Radloff, B., Kirsten, M., Anderson, R., 2004. Wallerawang colliery rehabilitation: the
coal tailings briquetting process. Minerals Engineering 17, 153–157.
Rhoads, F.M., Olson, S.M., 1995. Crop production with mushroom compost. Soil and
Crop Science Society of Florida Proceedings 54, 53–57.
Russell, M., Basheer, P.A.M., Rao, R.J., 2005. Potential use of spent mushroom
compost ash as an activator for pulverised fuel ash. Construction and Building
Materials 19, 698–702.
Ryu, C., Yang, Y.B., Khor, A., Yates, N.E., Sharifi, V.N., Swithenbank, J., 2006. Effect of
fuel properties on biomass combustion: part I. Experiments–fuel type,
equivalence ratio and particle size. Fuel 85, 1039–1046.
Ryu, C., Phan, A.N., Yang, Y.B., Sharifi, V.N., Swithenbank, J., 2007a. Ignition and
burning rates of segregated waste combustion in packed beds. Waste
Management 27, 802–810.
Ryu, C., Phan, A.N., Yang, Y.B., Sharifi, V.N., Swithenbank, J., 2007b. Co-combustion of
textile residues with cardboard and waste wood in a packed bed. Experimental
and Thermal Fluid Science 32, 450–458.
Ryu, C., Finney, K., Sharifi, V.N., Swithenbank, J., 2008. Pelletised fuel production
from coal tailings and spent mushroom compost–part I. Effect of pelletisation
parameters. Fuel Processing Technology 89, 269–275.
Stark, L.R., Wenerick, W.R., Williams, F.M., Stevens, S.E., Wuest, P.J., 1994. Restoring
the capacity of spent mushroom compost to treat coal-mine drainage by
reducing the inflow rate – a microcosm experiment. Water, Air and Soil
Pollution 75 (3–4), 405–420.
Thompson, M.J., 1982. Spoil disposal. Environmental Geochemistry and Health 4 (2–
3), 87–90.
Tiwari, K.K., Basu, S.K., Bit, K.C., Banerjee, S., Mishra, K.K., 2004. High-concentration
coal-water slurry from Indian coals using newly developed additives. Fuel
Processing Technology 85 (1), 31–42.
Williams, B.C., 2001. Energy from Spent Mushroom Compost, The Mushroom
People, IPP Limited, Wilmslow, UK. 3a (120) 18. Available from: <http://
www.engj.ulst.ac.uk/NICERT/mushroom_compost.htm>.
Williams, B.C., McMullan, J.T., McCahey, S., 2001. An initial assessment of spent
mushroom compost as a potential energy feedstock. Bioresource Technology
79, 227–230.