VP3.1.24 Paper Hamburg
VP3.1.24 Paper Hamburg
VP3.1.24 Paper Hamburg
ABSTRACT: Since 1995, Cameroon has been witnessing energy crisis due to demographic and industrial growth. This is
portrayed in the electricity sector by several power cuts in towns. Electrification rate is estimated at 25% at the national
level, 46% in towns and less than 1% in the rural areas. The valorization of fossilized primary sources contributes to
environmental destruction through the abundant emission of greenhouse gases. Wood remains the main source of energy
in this country. Consequently, this contributes to deforestation. The current study addresses the issue of energy recovery
from palm nut fibres and shells produced by oil mills. Mixed with binders like starch, ash, clay or lime, this
biodegradable waste is conditioned in the form of briquettes. Their density, specific heat and lower calorific capacities
are estimated. A comparative study of the various binders used shows a ratio of lower calorific power on the cost of the
binder, which varies from 14,538 kJ.m-3/(CFA franc) for starch to 55,736 kJ.m-3/(CFA franc) for ash. An improved
cooking hearth is designed and produced to supply a clean and economic energy solution. Concerning environmental
impact, the substitution of charcoal with this combustible material enables us to save 784,100 tons of wood each year and
to reduce the emission of methane into the environment by limiting the degradation of this waste product emitted
carelessly into the open air.
Keywords: valorization of waste, energy, palm nut, fuel briquette, environment, fibres and shells.
1 INTRODUCTION Wood Energy) shows that although oil mills are major
producers of huge quantities of fuel wastes, they hardly
In Cameroon, biomass is available everywhere but is valorise the wastes. Less than 10 % of these wastes available
rather poorly valorized. Only carpenter workshops based in are used in cooking nuts [5]. All oil mills produce wastes
towns manage to get the most from their wastes by selling (stalks, fibres and shells) which some valorise partially. In
them to households who use them for cooking. However, in Cameroon, an average of 484,000 tons of oil is produced
many countries, heat, vapour and electricity are produced each year. Oil represents approximately 20 % of the mass of
from the combustion of waste because of the tariff bunches which contain on average about 12.5 % fibres [6]. It
incentives attached to the repurchase of cogenerated is therefore estimated in this country that 290,400 tons of
electricity [1] [2]. For example, Guadeloupe and Reunion fibres are produced on average yearly by oil mills.
Islands exploit extensively in cogeneration factories the Most of these biodegradable wastes are therefore
combustion of bagasse whose energy efficiency is abandoned without carelessly in open air. Under these
approximately 2.2 kWh.kg-1 [3]. Similarly, the incineration conditions, they undergo the process of methanisation which
of one ton of household refuse in industrialized countries releases, inter alia, methane, one of the most harmful
enables to produce 300 to 500 kWh and many rubbish greenhouse gases in the air. In addition, the lack of
dumps use this energy to produce electricity and heat [3]. At knowledge on the energy properties does not permit to
the global level, it was estimated in 1998 that 155.109 kWh consider a rational valorisation of these wastes.
of electricity was generated from biomass and waste [4]. In Europe, the fuel briquettes derived from the
The valorization of primary fossilized sources compaction of sawmill wastes, wood and dead leaves, fruit
contributes towards environmental destruction through the cores, barks and roots of trees replace wood by presenting
abundant emission of greenhouse gases. Moreover, in rural some advantages to users such as zero dust, easy storage,
areas where more than 50 % of the Cameroonian easy conditioning and easy upkeep of fire [7].
populations live, less than 1 % of the inhabitants have access The main aim of this work is to attempt the first
to this form of energy and barely 46 % in towns. Wood is solutions to this problem. It will involve determining the
therefore presented as the main source of energy in this essential characteristics of oil mill wastes in particular the
country, its consequence being extensive deforestation. water content, the specific heat, the lower calorific capacity,
Agro-industrial fuel wastes are however capable of the density and rate of mineral matter, on the one hand, and
restoring greater energy than the amount necessary for conditioning them in the form of fuel briquettes for easier
industrial needs. In a boiler which recovers heat and transportation and use, on the other hand.
produces steam, hot water or electricity, agro-industrial fuel A prototype of improved furnace, intended for cooking
wastes are all the more interesting to burn given that their food, is proposed to provide a first clean and efficient energy
calorific power is relatively high. solution to the user.
A study carried out in Cameroon by Institut Technique
Européen du Bois Énergie (European Technical Institute for
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(X f + 100 )
e0 initial state of water with ρf = and ρ s = (4)
ec hot water Vf
ef cold water
em average state of water where mf: mass of the fuel briquette (kg),
er remaining water Vf: volume of the fuel briquette (m 3),
s0 initial state of the solid ρf: density of the water content of the fuel
briquette Xf (kg.m-3),
ρs density of dry fuel briquette (kg.m-3),
3 THEORETICAL ANALYSIS ρe density of water (kg.m-3),
The characteristics of the fuel briquettes studied are 3.4 Specific heat dry fuel
given using experimental results coupled with mathematical Specific heat represents the amount of energy necessary
simulation models. to raise one kilogramme of matter by one degree Celsius.
The importance of this parameter resides in the evaluation of
3.1 Water Content heat exchanges in connection with the variation of
Water content X in dry base is one of the major temperature. Although specific heat does not contribute to
properties of a fuel, given that it determines the other the classification of fuels in a combustion process, it
parameters. It represents the quantity of water contained in a contributes towards energy balance in a process which
sample by its anhydrous mass unit. A zero water content fuel emphasizes the energy value contained in these fuels.
is desirable to provide the best energy properties. However, The measurement of the specific heat of the fuel
it is difficult, in practice, to have a solid fuel whose mass is residues studied is obtained through the calorimetric
equivalent to its dry mass. The dry base water content Xt at method. The heat balance carried out on the calorimeter
the time t is given by the relation: enables to show, in equilibrium between water and fuel, that
( )
mt specific heat cs can be evaluated by the relation:
Xt = X f +100 − 100 (1)
( θ e − θ e0
me ce + ρ aVa ca ) θ s 0 − θ e
1
mf cs =
ms
where Xf is the final water content of the fuel briquette (in
% kge.kgms-1) t
mt and mf respectively represent the wet mass at +
KS
(
∫ θ em − θ a dt ) (5)
the time t and the final mass of the sample (in (θ s 0 − θe 0)
kg). With ce: specific heat of water (J.°C-1 kg-1)
ca: specific heat of air (J.°C-1 m-3)
3.2 Rate of Mineral Matter
The water value µc of the colorimeter is deduced through
The mineral matter of a fuel briquette (ash after total
experiments by applying the relation obtained hereafter
combustion) is that part of the fuel which remains unburnt
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through the energy balance of the mixture of a certain - a ventilated drying oven whose temperature is
quantity of cold water and hot water: regulated to determine the anhydrous mass of the
fuel,
θ
ec − θ e
µc = m − m - a precision balance of 0.001 g to measure fuel
(6)
θe − θ ec ef masses,
ef - a calorimetric bomb containing the test-tubes to be
Similarly, the total coefficient of the thermal losses on tested,
the walls of the calorimeter is obtained by experiments, - type K thermocouples connected to a computer
thanks to the heat balance, by applying the relation: through a data acquisition device (ALMEMO 2390-
5) intended to measure the temperatures in the
K = − mce p (7) calorimeter,
where p is the slope straight line: - a graduated burette intended to measure the volume
of water allowed in the calorimeter,
θ e (t ) − θ a K
ln - a brazier used to test the combustion of the fuel
θ −θ = pt = − t (8)
briquettes produced,
e0 a mce
- a stop watch to control, if necessary, the duration of
a test,
3.5 Specific heat of wet fuel - a calliper rule used to measure the test-tube
The knowledge of the specific heat cs of dry fuel dimensions of fuel briquettes.
enables to deduce the specific heat of the fuel having known
water content. By neglecting the heat exchanges due to the
presence of air and water vapour in the fuel in front of the 4.2 Experimental Protocol
calorific exchanges of the liquid and solid phases, the
• Water Content
specific heat of the wet fuel ch of water content X is
The palm nut wastes are densified and dried in the open
estimated by the relation:
air until equilibium with the environment. The state of
100 c s + X ce equilibrium is recorded when the mass of the products stops
ch = (9)
100 + X decreasing. A sample of wet mass mf is then taken and
introduced into the ventilated drying oven where the
with X: Water content of the sample (kge.kgms -1)
temperature is maintained at 103 °C. After approximately 48
hours, the mass of the sample is stabilized at the value ms
3.6 Lower Calorific Capacity of Fuel Briquettes which corresponds to its anhydrous mass. The application of
The densification of palm nut fibres and shells studied the relation (1) then enables us to deduce the final water
is ensured by a manual press designed and produced for that content of the fuel.
purpose. This press enables easy operation and strong
compression. The shape and dimensions of the briquettes are • Rate of Mineral Matter
chosen to adapt to the hearths commonly used in households To determine the rate of mineral matter, we do dry
or the improved systems to be proposed. extract of a sample taken on a dried briquette until its final
The experimental estimation of lower calorific capacity water content. The anhydrous mass ms of this sample is
(PCI) of the fuel briquettes studied is based on a combustion subjected to complete combustion. The mass mc of the fuel
test on a brazier with water used as test body to be heated. residue is then measured using a precision balance and
The heat balance resulting from this test enables us to enables to deduce the rate of mineral matter by applying the
deduce this parameter using the expression: relation (2).
PCI =
1
[me0 ce (θ eb − θ ie ) + Lv (me0 − mer )] (10) • Density
mcη To determine the density of fuel briquettes, their mass is
with η : hearth output measured thanks to a precision balance and their volume
Lv: latent heat of water vaporization (J.kg-1) calculated based on the geometrical dimensions measured
using a calliper rule. These measurements enable to deduce
the density of the briquettes by applying the relation (3).
The density of palm nut fibres is estimated by
4 MATERIALS USED AND EXPERIMENTAL densifying, without a binder, the mass of the sample taken
PROTOCOL then by evaluating the volume occupied by these residues.
The required density is equally deduced as before. This size,
4.1 Materials used in this particular case, depends on the densification pressure.
The testing device is made up of: As regards the density of the palm nut shells, a sample
- a manual metal press illustrated by figure 1 and made with a known mass is taken and introduced in a burette
up of a cylinder 9 cm in diameter and 10 cm high, of containing water. The measurement of the water volume
a screw 80 cm long, an arm 70 cm long and a nut of moved by this test-tube enables to deduce the density of the
2 cm. This press is designed and produced for the palm nut shells.
densification of the fibres and palm nut shells
studied,
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• Choice of Binders
The binder is the substance which stabilizes palm nut
fibres and shells in the form of fuel briquettes. Accessibility
and the moderate cost of acquisition are the selection criteria
for the binders to be tested. Hence, we retained for that
purpose starch, lime, clay and ash.
Starch refers to a white and odourless compound which
is marketed for other purposes (clothes treatment), in the
granulated or powder form. It is a complex glucide of
formula (C6H10O5)X, abundant in the grains of cereals, bulbs
and cassava tubers in particular. The starch used in our
work is extracted from cassava tubers, accessible in several Figure 1: Diagram of the designed press and its main
localities across the country. Its retail price, on average, is components
900 CFA francs for a bottle of 1.5 l (600 g) on the
Cameroonian market.
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5 RESULTS AND DISCUSSIONS shells, an average density of 744 kg.m-3 for fibres and 1277
kg.m-3 for shells. As one could have anticipated, the density
5.1 Densification of Fuel Briquettes of fibres for example is far greater than that of briquettes
Using binders described earlier and measured out in whose fibres are densified using binders (at rupture at the
various proportions, we produced fuel briquettes with palm withdrawal, of 220 kg.m-3 for starch at 469 kg.m-3 for lime
nut fibres and shells. Figure 2 shows a sample of approximately). An explanation would be the low porosity
manufactured briquettes. of fibres compressed without binders compared to fuel
briquettes.
800
However, it does not suffice to determine previous major
characteristics to propose a suitable and economic way of
600 conditioning these wastes. To get there, it is necessary to
consider the lower calorific capacity and evaluate the cost of
conditioned briquettes.
400
Starch
Clay
Lime
200
Ash
0
0 100 200 300 400 500
Mass binder (g)
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30
accessories. The energy efficiency in the hearth of this
29 device is estimated at 30 % [9]. Figure 5 illustrates, as an
example, the variation in temperature of water heated using
28
fuel briquettes conditioned with lime during a combustion
27 test intended to determine the lower calorific capacity. This
approach is in conformity with the experimental protocol
26 and the application of the theoretical correlations developed
25 earlier. During the test, the atmospheric pressure is
maintained on the water surface. Figure 5 shows the rise in
0
200
400
600
800
1000
1200
1400
1600
1800
2000
2200
2400
2600
2800
3000
3200
3400
3600 water temperature up to 100°C, corresponding to the boiling
Duration (s) point at the atmospheric pressure. This temperature is then
maintained constant for some time before it starts dropping;
Figure 4: Example of curve showing the variation in water which implies the end of the combustion.
temperature depending on the time for fuel briquettes As concerns the cost of the conditioned fuel briquettes,
conditioned with clay we took into account labour cost and the cost of the binder.
We suppose that the worker is paid as manufacturers of
120
Test of combustion of briquette conditioned with lime
earth bricks in Cameroon, i.e. 2 000 CFA francs on average
per day of 9 working hours. In addition, the manufacture of
100
a fuel briquette requires 15 minutes on average i.e. 56 CFA
francs. This cost could reduce considerably by developing a
Temperature (°C)
80
more effective densification technique. As for the cost of the
60
binder, it is mainly made up of transport charges and the
purchase cost itself. All the binders tested within the
40
framework of this work are accessible near the densification
unit (Ferme Suisse, palm oil industry used as sample for our
20 studies); ash is taken from one of the boilers of this oil mill.
Transportation cost under these conditions is minimal.
0 Retailed starch is bought at 1 077 CFA francs per
0 500 1000 1500 2000 2500 3000 3500 4000 kilogramme and lime at 500 CFA francs for the same mass.
Duration (s)
Taking into account, for each type of binder, the
concentration likely to guarantee better stability of fuel
Figure 5: Example of variation according to the
briquettes, we record in Table II the characteristic
time of the temperature of the water heated with a fuel
properties resulting from the combustion test.
briquette conditioned with lime
Based on the ratio of the lower calorific capacity on the
cost of the fuel briquette, preference would be given to ash-
Table I: Some thermo physical parameters of fuel conditioned briquette. However, there could be inadequate
briquettes produced with palm nut fibres supply of such a binder in case of large scale manufacturing
of briquettes. Due to this potential disadvantage, we
Nature of the binder advocate the production of fuel briquettes conditioned with
Fibres Shells lime as binder with a concentration of 75 g for 300 g of palm
Ash Clay Lime Starch nut wastes.
Water content 15.00 17.23 31.12 20.16 20.05 15.40
In addition, we noted through the combustion tests that
(% kge.kgms -1) 300 g of briquettes with 75 g of lime could replace 80 g of
Rate of
mineral 61.14 58.65 49.30 9.72 9.24 38.31
coal sold on the Cameroonian market at 100 francs per kg.
matter (%) The average lower calorific capacity of this fuel is estimated
Density 426.25 447.23 569.90 455.30 743.42 1277.18
at 33,700 kJ.kg-1 [10]. However, 300 g of briquettes with
(kg. m -3) 75 g of lime contain about 154 g of fibres. In other words 1
Anhydrous kg of densified palm nut fibres containing lime could replace
Density 370.65 381.5 0 434.64 379.02 619.32 1107.00
(kg. m -3) approximately 0.54 kg of charcoal.
Specific heat
1374.63 1455.26 1794.85 1497.90 1357.25 1493.64
(J. kg -1 °C -1)
Specific heat
anhydrous 979.42 980.05 1113.50 964.04 810.50 1067.70
(J. kg -1 °C -1)
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