BRIQUETTING-MACHINE

CONTENTS
S. No.
Title
Abstract
List of Figures
List of tables
Page No.
1.
Introduction
Background of the study
Objectives
Literature Review
Briquetting Process
Historical Background of Briquetting Process
Advantages of briquette production:
Bio-Coal Briquettes
Characteristics of Bio-Coal Briquettes
Advantages of bio-coal briquettes:
Production Process of Bio-Coal Briquette
Preparation of other types of Briquettes
Coal
Biomass Resources of Nigeria
Bio-coal briquette
Charcoal
Starches as a Binder
Binders used in the production of bio-coal briquettes
Calcium Hydroxide
Environmental issues.
Groundnut shell as an appropriate residue for the production
of bio-coal briquette.
Analysis of groundnut shell
Uses of groundnut shell.
MATERIALS AND METHODS
Use Of Agricultural Waste Instead Of Petroleum In A Lime
Kiln
Technical description
Solid fuel from the fields: coal from agricultural waste
Binder preparations and mixing
Design considerations
Operation and Cost of the Machine
1-8
1
8
9-20
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10
10
11
12
13
14
15
15
16
16
16
17
17
18
18
19
1.1.
1.2.
2.
2.1.
2.2.
2.3.
2.3.1.
2.3.2.
2.3.3.
2.3.4.
2.3.5.
2.4.
2.5.
2.5.1.
2.5.2.
2.6.
2.6.1.
2.6.2.
2.6.3.
2.6.4.
2.6.5.
2.6.6.
3.
3.1.
3.1.1.
3.1.2.
3.2.
3.3.
3.4.
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20
21-30
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21
22
23
24
27
3.5.
4.
5.
6.
Performance Evaluation
3.5.1. Physical Properties Determination
3.5.2. Combustion Properties Determination
3.6.
Environmental considerations
RESULTS AND DISCUSSIONS
4.1.
Physical and Combustion Properties of Sawdust Briquette
4.2.
Optimum Sawdust-Binder Blend
Conclusion
REFERENCES
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3132
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ABSTRACT
Deforestation and firewood shortage are growing problems in many countries of the South.
The energy and fuel shortage in these countries is not only a problem of the rural areas but also
of the densely populated poor margins of medium and large cities. While the traditional types
of fuel (fire wood and charcoal) become more and more exhausted, modern fuels (paraffin,
coal, mineral oil, electricity) are not affordable for the majority of the poor. At the same time,
the generation of organic waste in urban areas poses a growing challenge to the local waste
management system. Organic waste (30-50% of the total waste) is not only a problem because
of its large volume but also because it causes bio-chemical reactions on landfill sites leading to
the formation of landfill gas (methane) and leachates that pollute atmosphere and groundwater.
In rural areas, agricultural residues (straw, rice and coffee husks, coconut and groundnut shells,
bagasse, coir dust, etc.) are generated in large volumes and often not utilised at all. Both urban
and rural organic residues and wastes could be used as alternative domestic fuel if offered in
an acceptable form and at a reasonable price. Briquetting and carbonisation are common
processes to transfer the organic waste into appropriate domestic fuel.
In this study, an appropriate commercial biomass briquetting machine suitable for use in rural
communities was designed and constructed, and the performance evaluation carried out using
sawdust. The physical and combustion properties of the briquette were determined at varying
biomass-binder ratios of 100:15, 100:25, 100:35 and 100:45 using cassava starch as the binding
agent. Both the physical and combustion properties of the briquette were significantly affected
by the binder level (P < 0.05). The optimum biomass-binder ratio on the basis of the
compressed density was attained at the 100:25 blending ratio having a compressed density of
0.7269g/cm3 and a heating value of 27.17MJKg-1 while the optimum blending ratio on the basis
of the heating value was attained at the 100:35 blending ratio with a compressed density of
0.7028g/cm3. It was concluded that the heating values at the optimum biomass-binder ratios
were sufficient to produce heat required for household cooking and small scale industrial
cottage applications. The biomass briquetting machine had a production capacity of about
43kg/hr.
Agro waste manual briquetting machine have been designed and fabricated using locally
available materials. The machine principal parts are made of frame, compaction chamber and
base plate. Compaction chamber contains nine (9) moulding dies each having transmission rod,
piston and ejector. The machine can produce nine (9) briquettes at a time of about 50mm length
and 28mm diameter. The compaction pressure and force was determined to be 17.5 KN/m2
and 215.3N respectively. It is hoped that machine will be very useful for small and medium
scale briquette manufacturers.
List of Figures
S. No.
Figure 1.
Figure 2.
Figure 3.
Figure 4.
Figure 5.
Figure 6.
Figure details
The basic flow process for Bio-Coal production
Modelled design in Auto CAD Isometric view of Briquetting machine
Briquette Moulding Machine
Inserting raw material in Briquetting machine
Some produced Briquette
Expansion in the height of sawdust briquette with time
Page no.
14
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26
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30
33
List of Tables
S. No.
Table 1.
Table 2.
Table Details
Chemical composition of groundnut shell.
Production time components of the briquetting machine
Page No.
20
31
CHAPTER 1
Introduction
1.1 Background of the study
Biomass, particularly agricultural residues seem to be one of the most promising energy
resources for developing countries (Patomsok, 2008). Rural households and minority of urban
dwellers depend solely on fuel woods (charcoal, firewood and sawdust) as their primary
sources of energy for the past decades (Onuegbu, 2010). Of all the available energy resources
in Nigeria, coal and coal derivatives such as smokeless coal briquettes, bio-coal briquettes, and
biomass briquettes have been shown to have the highest potential for use as suitable alternative
to coal/ fuel wood in industrial boiler and brick kiln for thermal application and domestic
purposes. Global warming has become an international concern. Global warming is caused by
green house gasses which carbon dioxide is among the major contributors. It was shown that
increased emissions of CO2 have been drastically reduced owing to the fact that the rate of
deforestation is higher than the afforestation effort in the country.
The use of fuel wood for cooking has health implications especially on women and children
who are disproportionately exposed to the smoke apart from environmental effects. Women in
rural areas frequently with young children carried on their back or staying around them, spend
one to six hours each day cooking with fuel wood. In some areas, the exposure is even higher
especially when the cooking is done in an unventilated place or where fuel wood is used for
heating of rooms. Generally, biomass smoke contains a large number of pollutants which at
varying concentrations pose substantial risk to human health. Among hundreds of the pollutants
and irritants are particulate matters, 1, 2-butadiene and benzene (Schirnding and Bruce, 2002).
Studies showed that indoor air pollution levels from combustion of bio fuels in Africa are
extremely high, and it is often many times above the standard set by US Environment
Protection Agency (US- EPA) for ambient level of these pollutants (USEPA, 1997). Exposure
to biomass smoke increases the risk of range of common diseases both in children and in adult.
The smoke causes acute lower respiratory infection (ALRI) particularly pneumonia in children
(Smith and Samet, 2000; Ezzati and Kammen, 2001).
Agro waste is the most promising energy resource for developing countries like ours. The
decreasing availability of fuel woods has necessitated that efforts be made towards efficient
utilization of agricultural wastes. These wastes have acquired considerably importance as fuels
for many purposes, for instance, domestic cooking and industrial heating. Some of these
1
agricultural wastes for example, coconut shell, wood pulp and wood waste can be utilized
directly as fuels.
Fortunately, researches have shown that a cleaner, affordable fuel source which is a substitute
to fuel wood can be produced by blending biomass (agricultural residues and wastes) with coal.
Nigeria has large coal deposit which has remained ntapped since 1950’s, following the
discovery of petroleum in the country. Also, millions of tons of agricultural wastes are
generated in Nigeria annually. But it is unfortunate that farmers still practice “slash-and-burn”
agriculture.
These agricultural wastes they encounter during clearing of land for farming or during
processing of agricultural produce are usually burnt off. By this practice, not only that the
useful raw materials are wasted, it further pollutes the environment and reduces soil fertility.
On the other hand, the majority of the huge materials are not suitable to be used directly as fuel
without undergoing some processes. This is probably as a result of inappropriate density and
high moisture contents and these factors may cause problems in transportation, handling and
storage. Most of these wastes are left to decompose or when they are burnt, there would be
environmental pollution and degradation (Jekayinfa, and Omisakin, 2005). Researchers have
shown that lots of potential energies are abounding in these residues (Fapetu, 2000). Hence,
there is a need to convert these wastes into forms that can alleviate the problems they pose
when use directly. An assessment of the potential availability of selected residues from maize,
cassava, millet, plantain, groundnuts, sorghum, oil palm, palm kernel, and cowpeas for possible
conversion to renewable energy in Nigeria has been made (Jekayinfa and Scholz, 2009).
However, these health hazard faced by people from the use of fuel wood, along with the
agricultural wastes management and reduction of pressure mounted on the forest can be
mitigated if Nigeria will switch over to production and utilization of bio-coal briquette; a
cleaner, and environmental friendly fuel wood substitute made from agricultural wastes and
coal. Moreover, this will offer a good potential for utilization of a large coal reserve in Nigeria
for economic diversification and employment generation through bio-coal briquette.
In countries like Japan, China and India, it was observed that agricultural waste (agro residues)
can also be briquetted and used as substitute for wood fuel. Every year, millions of tonnes of
2
agricultural waste are generated. These are either not used or burnt inefficiently in their loose
form causing air pollution to the environment. The major residues are rice husk, corn cob,
coconut shell, jute stick, groundnut shell, cotton stalk, etc. These wastes provide energy by
converting into high-density fuel briquettes. These briquettes are very cheap, even cheaper than
coal briquettes. Adoption of briquette technology will not only create a safe and hygienic way
of disposing the waste, but turn into a cash rich venture by converting waste into energy and
also contributing towards a better environment.
Coal can be blended with a small quantity of these agricultural waste (agro residues) to produce
briquettes (bio-coal briquettes) which ignites fast, burn efficiently, producing little or no smoke
and are cheaper than coal briquettes.
Briquetting is a technology for densification of agricultural residues/wastes to increase their
bulk density, lower their moisture contents and make briquettes of uniform sizes and shapes
for easy handling, transport and storage. Briquettes can be defined as a product formed from
physic-mechanical conversion of loose and tiny particle size materials with or without binder
in different shapes and sizes. Osarenwinda and Ihenyen (2012) stated that F.P Veshinakov (a
Russian inventor) developed a method of producing briquettes from waste wood, charcoal and
hard coal. Briquettes have high specific densities ranging from 1100-1200kg/m3 and bulk
densities of 800kg/m3 as compared to lose agricultural residues which have bulk densities that
range from 80kg/m3 – 120kg/m3 (Srivastra, 2009). This implies that briquetting can reduce
the volume of materials by about 10 times. Briquettes are made using briquetting machine of
either manual, screw and hydraulic types (Chinyere, 2014, Osarenwinda and Ihenyen, 2012
and Ramesh, 2005). Briquettes have high calorific value up to 60Mkal/kg depending on the
material compared to loose materials (Chinyere, 2014). In Nigeria, as in other developing
countries, the prevelenceof sawdust hills around sawmills constitute an unsightedful problem
to the local environment and a breeding ground for wood decaying organisms.But these
sawdust hills could be compacted into briquettes for fuel energy supply. Also, the direct
burning of loose agro waste residues like rice husk, palm kernel shells, groundnut shells in
conventional manner is associated with very low thermal efficiency, loss of fuel and
widespread air pollution (Osarenwinda and Ihenyen, 2012). When compressed into briquettes,
these problems are mitigated, transportation and storage cost are reduced and energy
production by improving their net calorific value per unit is enhanced (Grover et al, 1996). This
work is focussed on the Preliminary Production of Briquettes from sawdust and corn starch.
3
Briquetting of biomass is a relatively new technology in most African countries but there exist
a number of different commercial briquetting technologies in Asia, America and Europe. The
expansion of the use of biomass as an alternative source of energy for heating applications
depends basically on three factors: residue availability for briquetting, adequate technologies
and the market for briquettes reported that although the importance of biomass briquette as a
substitute fuel for wood is widely recognized, the numerous failures of briquetting machines
in almost all developing countries have inhibited their extensive exploitation. The constraint in
the advancement of biomass briquetting in Africa and in developing nations generally, is the
development of appropriate briquetting technology that suits the local condition; both in terms
of the briquetting press itself for local manufacture and the briquettes. The failure of these
machines have been attributed to some factors which include inappropriate or mis-match of
technology; technical difficulty and lack of knowledge to adapt the technology to suit local
conditions; excessive initial and operating cost of the machines; and the low local prices of
wood fuel and charcoal.
The more replicable, appropriate, cost effective, locally available, easy to make,
environment friendly and culturally fitting a technology is for the briquetting of biomass, the
higher its chance of success. There currently exist a number of machines developed for the
production of biomass briquettes in developing nations. Some of the existing machines in the
rural areas are either gender unfriendly, or having poor production capacity and briquette
quality, and depends on direct human strength for densification. The need at the moment in the
densification of biomass in developing countries is the development of an appropriate
briquetting machine suitable to the local communities. For biomass to make a significant
impact as fuel for rural communities, it is imperative that an efficient, cost effective and easy
to duplicate technology is developed specifically for rural communities. The general objective
of the study was to develop a biomass briquetting machine appropriate for rural communities
of developing countries; in terms of its operating technicalities and socio-economic
requirements.
Many of the developing countries produce huge quantities of agro residues but they are
used inefficiently causing extensive pollution to the environment. The major residues are rice
husk, coffee husk, coirpith, jute sticks, bagasse, groundnut shells, mustard stalks and cotton
stalks. Sawdust, a milling residue is also available in huge quantity. Apart from the problems
of transportation, storage, and handling, the direct burning of loose biomass in conventional
grates is associated with very low thermal efficiency and widespread air pollution. The
4
conversion efficiencies are as low as 40% with particulate emissions in the flue gases in excess
of 3000 mg/Nm³In addition, a large percentage of unburnt carbonaceous ash has to be disposed
of. In the case of rice husk, this amounts to more than 40% of the feed burnt. As a typical
example, about 800 tonnes of rice husk ash are generated every day in Ludhiana (Punjab) as a
result of burning 2000 tonnes of husk. Briquetting of the husk could mitigate these pollution
problems while at the same time making use of this important industrial/domestic energy
resource.
Historically, biomass briquetting technology has been developed in two distinct directions.
Europe and the United States has pursued and perfected the reciprocating ram/piston press
while Japan has independently invented and developed the screw press technology. Although
both technologies have their merits and demerits, it is universally accepted that the screw
pressed briquettes are far superior to the ram pressed solid briquettes in terms of their storability
and combustibility. Japanese machines are now being manufactured in Europe under licensing
agreement but no information has been reported about the manufacturing of European
machines in Japan.
Worldwide, both technologies are being used for briquetting of sawdust and locally available
agro-residues. Although the importance of biomass briquettes as substitute fuel for wood, coal
and lignite is well recognized, the numerous failures of briquetting machines in almost all
developing countries have inhibited their extensive exploitation.
Briquetting technology is yet to get a strong foothold in many developing countries because of
the technical constraints involved and the lack of knowledge to adapt the technology to suit
local conditions. Overcoming the many operational problems associated with this technology
and ensuring the quality of the raw material used are crucial factors in determining its
commercial success. In addition to this commercial aspect, the importance of this technology
lies in conserving wood, a commodity extensively used in developing countries and leading to
the widespread destruction of forests.
Biomass densification, which is also known as briquetting of sawdust and other agro residues,
has been practicedfor many years in several countries. Screw extrusion briquetting technology
was invented and developed in Japan in 1945. As of April 1969, there were 638 plants in Japan
engaged in manufacturing sawdust briquettes, known as ‘Ogalite’, amounting to a production
of 0.81 MTY. The fact that the production of briquettes quadrupled from 1964 to 1969 in Japan
speaks for the success of this technology. This technology should be differentialed from such
5
processes as the ‘Prest-o-log’ technology of the United States, the ‘Glomera’ method in
Switzerland and the ‘Compress’ method in West Germany.
At present two main high pressure technologies: ram or piston press and screw extrusion
machines, are used for briquetting. While the briquettes produced by a piston press are
completely solid, screw press briquettes on the other hand have a concentric hole which gives
better combustion characteristics due to a larger specific area. The screw press briquettes are
also homogeneous and do not disintegrate easily. Having a high combustion rate, these can
substitute for coal in most applications and in boilers. Briquettes can be produced with a density
of 1.2 g/cm³from loose biomass of bulk density 0.1 to 0.2 g/cm³These can be burnt clean and
therefore are eco-friendly arid also those advantages that are associated with the use of biomass
are present in the briquettes. With a view to improving the briquetting scene in India, the Indian
Renewable Energy Development Agency (IREDA) -a finance granting agency -has financed
many briquetting projects, all of which are using piston presses for briquetting purposes. But
the fact remains that these are not being used efficiently because of their technical flaws and
also due to a lack of understanding of biomass characteristics. Holding meetings with
entrepreneurs at different levels, providing technical back-up shells and educating
entrepreneurs have to some extent helped some plants to achieve profitability and holds out
hope of reviving the briquetting sector. In other Asian countries although briquetting has not
created the necessary impact to create confidence among entrepreneurs, recent developments
in technology have begun to stimulate their interest. In Indonesia, research and development
works (R&D) have been undertaken by various universities, the national energy agency and
various research institutes since the mid-seventies. So far, these have mainly focussed on
biomass conversion technologies. R&D works on biomass densification development are
relatively rare. There are a number of export-oriented sawdust and coconut shell charcoal
briquette producers. At present, densified biomass, particularly that which is not carbonized,is
not a popular fuel in the country. A limited amount of smokeless charcoal briquettes, mostly
imported, are consumed in some households of big cities. However, the prospects for the
densified biomass industry in Indonesia, particularly where it is export oriented, seems to be
good. The Phillipine Department of Energy is currently promoting the development and
widespread use of biomass resources by way of encouraging the pilot-testing, demonstration
and commercial use of biomass combustion systems, as well as gasification and other systems
for power, steam and heat generation. There is a limited commercial production of biomass
briquettes in the country. At present nine commercial firms produce amounts ranging from 1
6
ton/day to 50 tons/day. Four pilot briquetting plants have stopped operation. Briquettes are
produced from sawdust, charcoal fines and/or rice husk. In the Philippines the conversion cost
from biomass to briquette is very high.
In Sri Lanka no briquetting projects have been implemented because of lack of exposure to the
technology. But the prospects for substituting wood are high because the traditional sector
relies heavily on fuel wood. The tea industry is the largest firewood consumer and it is supplied
mainly from nearby rubber plantations or forests.
In Vietnam people have been involved in briquetting, but for limited uses. The briquettes are
used basically for heating/cooking purposes and this is limited to households. The present noncommercial energy, mainly from biomass fuel, shares a great part of the total energy supply.
R&D efforts should be undertaken to make briquetting technology economically profitable and
socially acceptable to the public so that it might be widly adopted.
Briquetting plants with both small and high production capacities can be found in Thailand
and, in general, plant performance in terms of profitability and management is encouraging.
They have been successful in briquetting rice husk commercially. In other countries bottlenecks
in the technology are the major reasons why briquetting is not popular. In Nepal small
production capacity briquetting machines are currently operating and these can pave the way
for large commercial production of briquettes which could make use of the huge quantity of
agro-residues available in the country. In Bangladesh and Pakistan, although agro-residues are
abundantly available, they are not used in briquetting.
Efforts have been made in Myanmar to reduce pressure on fuel wood and charcoal production.
The government is providing support to state-run and private organizations to promote
briquetting. The entrepreneurs, especially, are very much interested in briquetting of agroresidues and their utilisation.
India is the only country where the briquetting sector is growing gradually in spite of some
failures. As a result of a few successes and IREDA’s promotional efforts, a number of
entrepreneurs are confidently investing in biomass briquetting. These entrepreneurs are also
making strenuous efforts to improve both the production process and the technology.
Both national and international agencies have funded projects to improve the existing
briquetting technology in India. Recently, the Indian Institute of Technology, Delhi in
collaboration with the University of Twente, the Netherlands carried out research to adapt the
7
European screw press for use with Indian biomass. The two major impediments for the smooth
working of the screw press -- the high wear of the screw and the comparatively large specific
power consumption required --were overcome by incorporating biomass feet preheating into
the production process.
The recent successes in briquetting technology and the growing number of entrepreneurs in the
briquetting sector, are evidence that biomass briquetting will emerge as a promising option for
the new entrepreneurs and other users of biomass.
1.2.OBJECTIVES
The specific objectives of the study were:

To design and construct a biomass briquetting machine;

To undertake a performance evaluation of the briquetting machine using sawdust at
varying binder levels and

To determine the physical and combustion properties of the sawdust briquette.
8
CHAPTER II
LITERATURE REVIEW
2.1 Briquetting Process
A briquette is a block of compressed coal, biomass or charcoal dust that is used as fuel to start
and maintain fire (Grainger et al, 1981). Briquetting is a mechanical compaction process for
increasing the density of bulky materials. This process is used for forming fine particles into a
designed shape. It can be regarded as a waste control measure in the case of production of
briquettes from agricultural wastes. However, depending on the material of interest, briquetting
can be used to provide fuel source as a preventive measure to many ecological problems.
Briquetting is a high-pressure process which can be done at elevated temperature (Zhanbin,
2003) or at ambient temperature (Mohammad, 2005) depending on the technology one wants
to employ.
During this process, fine material is compacted into regular shape and size which does not
separate during transportation, storage or combustion. In some briquetting techniques, the
materials are simply compressed without addition of adhesive (binderless briquettes) (Mangena
and Cann, 2007) while in some, adhesive material is added to assist in holding the particles of
the material together.
Generally, briquetting process has focused more on the production of smokeless solid fuels
from coal and agricultural wastes. There are various techniques which have been used to
produce smokeless solid fuel from coal fine. The most common technique is the use of roller
press using only moderate pressure and binder. Note that the machines employed for this
process are also used to make other kind of 5 non-fuel briquettes from inorganic materials such
as metal ores. However, briquetting of organic materials (agricultural wastes) requires
significantly higher pressure as additional force is needed to overcome the natural springiness
of these materials. Essentially, this involves the destruction of the cell walls through some
combination of pressure and heat. High pressure involved in this process suggests that organic
briquetting is costlier than coal briquettes.
Various briquetting machines have been designed, ranging from very simple types which are
manually operated to more complex ones mechanically or electrically powered. Generally,
briquetting operations have developed in two directions, mechanically compression (hydraulic
or pistons) and worm screw pressing types.
9
2.2 Historical Background of Briquetting Process
Although, compaction of loose combustible materials for fuel making purposes is a technique
which has been in existence thousands of years ago but industrial method of briquetting seems
to be dated back to eighteenth century. In 1865, report was made on machines used for making
fuel briquettes from peats and are recognized as the predecessors of the present briquetting
machines. Since then, there has been a wide spread use of briquettes made from brown coal
and peat etc.
The use of organic briquettes (biomass briquettes) started more recently compared to coal
briquette. It seems to have been common during world war and during the 1930s depression.
The modern mechanical piston briquetting machine was developed in Switzerland based upon
German development in the 1930s.
Briquetting of saw dust are widespread in many countries in Europe and America during World
War 11 because of fuel shortages. However, after the World War, briquettes were gradually
phased out of the market because of availability and cheapness of hydrocarbon fuels.
Common types of briquettes so far in use are coal briquettes, peat briquettes, charcoal
briquettes, and biomass briquettes, etc. Most recently, researchers have studied the effect of
blending of coal and biomass such as enhancing the properties of coal briquettes using spear
grass (Onuegbu et al, 2010a), enhancing the Efficiency of coal Briquette in Rural Nigeria using
pennisetumpurpurem (Onuegbu et al, 2010b). Onuegbu et al, (2012)
2.3. Advantages of briquette production:
Briquette production will:
i.
Provide a cheap source of fuel for domestic purposes, which will be affordable by all
Nigerians.
ii.
Provide a good means of converting coal fines, low rank coal, and waste agro residue
into a resourceful substance of economic value.
iii.
Help to conserve some of natural resources since it is a good substitute for fire wood.
Therefore, it will help to reduce the quantity of firewood, oil and gas that is used in the
production of energy for domestic uses and generating plants.
iv.
Help to develop the demand for coal. Coal is used in making bio-coal and coal briquette.
This will in turn promote coal mining which seems dormant for some time.
10
v.
Create employment opportunities for people since people will be needed to operate the
briquette machine, get the raw materials (i.e. coal and agro-residue, etc.), sell the
briquettes produced, etc (Bhattacharya, 1985).
2.3.1. Bio-Coal Briquettes
Bio-coal briquette is a type of solid fuel prepared by blending coal, biomass, binder, and
sulphur fixation agent. Other additives may also be added. A research showed that bio-coal
briquettes may be prepared by blending the following (Mohammad, 2005):
● Biomass (25% to 50%)
● Coal (75% to 50%)
● Sulphur fixation agent (up to 5%)
● Binder (up to 5%)
In this process, Ca(OH)2 acts as both sulphur fixation agent and the binder.
The high pressure involved in the process ensures that the coal particles and the fibrous biomass
material interlace and adhere to each other as a result, do not separate from each other during
combustion, transportation and storage. During combustion, the low ignition temperature of
the biomass simultaneously combusts with the coal. The combined combustion of both gives a
favourable ignition and fire properties; emits little dust and soot, generates sandy combustion
ash. Also, the desulphurizing agent such as Ca(OH)2 in the briquette effectively reacts with the
sulphur
content
of
the
coal
to
fix
about
60-80%
of
it
into
the
ash
(http:www.nedo.go.jp/sekitan/cc.eng-pdf/2-3c3pdf). It was showed that lime (CaO) as a
desulphurizing agent was able to capture up to 90-95% of the total sulphur in the coal, leaving
only 5-10% emitted as sulphur oxides.
The equation of the reaction is as follows:
1
2
→
Evidence also showed that lime when used as desulphurizer also acts as a binder. Also clay has
been reported to be a good desulphurizing agent. Clay contains CaO and MgO which acts as
desulphurizing agents. Also it contains Fe2O3 which has been shown to have a catalytic effect
on the sulfation reaction (Somchai et al.,1988).
11
There are various biomass resources available for production of biomass briquettes. Some of
them are straw, sugar bagasse (fibrous residue of processed ugar cane), corn stalk, groundnut
– shell, wheat straw, palm husk, rice husks, corn cob, forest wastes, and other agricultural
wastes. Several researches on bio-coal briquette have been carried out using some of these
biomass resources.
Furthermore, it has been shown that many grades of coal can be used for bio-coal production,
even low grade coal containing high sulphur contents (Patomsok, (2008). This implies that, by
this technology, extra cost of carbonizing low grade coal before briquetting is saved. Binder is
an adhesive material which helps to hold the particles of the material together in the briquette.
Apart from its function to hold the particle from separation, it also protects the briquette against
moisture in case of long storage. There are several binders that can be used some of them are
starch (from various starchy root such as cassava, and cereals), molasses, clay and tree gum
etc. some chemical substances have also been used as binding agent for production of
briquettes. Some of them are asphalt, magnesia and pitch. Though, the use of starch as binder
is satisfactory in every respect, it disintegrates under moist or tropical condition. However, the
use of small additional hydrocarbon binder such as pitch or bitumen has been reported to
improve the water resisting property (Wilfred and Martin, 1980). Moreover, the nature of the
binder has influence in the combustibility of the briquette produced. For instance, briquette
produced using clay takes longer time to ignite than the one produced using starch.
2.3.2. Characteristics of Bio-Coal Briquettes
(1) Bio-coal briquette decreases the generation of dust and soot up to one-tenth that of direct
combustion of coal (http:www.nedo.go.jp/sekitan/cc.eng-pdf/2-3c3pdf). Combustion of coal
generates dust and soot because, during the combustion, the volatile components of the coal
are released at low temperature (200-400oC) as incomplete combusted volatile matter.
(2) Bio-coal briquette has a significant shorter ignition time when compared with coal or
conventional coal briquette Biomass has low ignition time.
(3) Bio-coal briquette has superior combustion-sustaining properties. Because of low
expansibility and caking properties of bio-coal briquette, sufficient air flow is maintained
between the briquettes during combustion in a fire-place. Hence it has very good combustionsustaining properties and does not die out in a fireplace or other heater even when the air supply
is decreased. This property offers the opportunity of adjusting the combustion rate of the biocoal briquette easily.
12
(4) Bio-coal briquette emits less SO2. It contains desulphurizing agent and the high reassure
involved in the process enables the coal particles to adhere strongly to the desulphurizing agent.
During combustion, the desulphurizing agent effectively reacts with the sulphur content of the
coal to form a solid compound instead of being released as oxides of sulphur to the atmosphere.
However, it is widely accepted that bio-coal briquette technology is one of the most promising
technologies for the reduction of SO2 emission associated with burning of coal (Patomsok,
2008).
(5) Bio-coal briquette has high breaking strength for easy transportation. The high pressure
involved in the process coupled with the binder, compressed the raw material into a rigid mass
which does not break easily, hence can be stored and transported safely
(6) Bio-coal briquette generates sandy ash which can be utilizes in agriculture for soil
improvement. In the briquette, since the fibrous biomass interwined with the coal particles, the
resulted ash after combustion does not adhere or form clinch-lump; therefore, the ash is always
sandy.
(7) Bio-mass briquette burns nearly perfect; therefore the flame has significant higher
temperature than simple biomass burning or coal (Hayami, 2001).
2.3.3. Advantages of bio-coal briquettes:
1. Briquette from biomass and coal are cheaper than briquette from coal. This is so, since some
of the biomass materials used are of less economic importance and are always left to waste,
except in cases where they are to be used, which is rare.
2. High sulphur content of oil and coal when burnt pollutes the environment. In bio-coal
briquettes, part of the coal is substituted with biomass; hence the sulphur content is reduced
(Bhattacharya, 1985).
3. Bio-coal briquettes have a consistent quality high burning efficiency, and are ideally sized
for complete combustion.
4. Combustion of bio-coal briquettes produces ashes which can be added to soil to improve soil
fertility.
5. Bio-coal briquettes are usually produced near the consumption centers and supplies do not
depend on erratic transportation from long distance.
13
Based on these facts, bio-coal can replace the following conventional fuels that are used in
mass quantities: diesel, kerosene, furnace oil, fire wood, coal, lignite, etc.
2.3.4. Production Process of Bio-Coal Briquette
The production process of bio-coal briquette is very simple and cost effective. The raw
materials; coal and biomass are pulverized to a size of approximately 3mm, and then dried.
Research showed that 0-5mm is the optimum particle size of the raw materials for a briquette.
The dried pulverized materials, a desulphurizing agent and binder are mixed together in
appropriate proportions and are compressed with briquette machine into a designed shape. The
type of briquetting machine determines the shape and size of the briquette. Some briquette
machines have small mould while some have relatively larger mould. For a large mould, there
is always a facility which creates holes in the briquettes when formed. These holes are
necessary for efficient combustion of the briquette. It allows for proper flowing of air needed
to maintain the combustion.
In this production process, high temperature is not required. The process is simple, safe and
does not require skilled operating technique. Hence the process can easily be adopted and
sustained in Nigeria. Fig.1 shows the basic process flow for bio-coal production.
Fig 1: The basic flow process for Bio-Coal production
14
2.3.5. Preparation of other types of Briquettes
As it has been mentioned earlier, briquette is a kind of solid smokeless fuel produced by
compressing pulverized raw materials under high pressure at ambient or elevated temperature.
The raw materials are generally coal and biomass of various forms. The name given to any fuel
briquette depends on the materials of which it was made. For instance, common briquettes:
charcoal briquettes, biomass briquettes and coal briquettes are prepared as follows:
Charcoal briquettes: Charcoal briquette is a common type of briquette made by compressing
pulverized wood charcoal with a binder. However, other activator such as sodium nitrate is
added as an accelerant.
Biomass briquettes: Biomass briquette is made from agricultural wastes. It is a renewable
source of energy. Lignin and cellulose are the two major compounds of biomass. The lignin
distributed among cellulose determines the structural strength of biomass. Lignin is a noncrystallized aromatic polymer with no fixed melting oint. When heated to 200-300oC, lignin
melts and liquefies. When pressure is applied in this case, the method lignin glues the cellulose
together; hence the biomass is briquetted when cooled. This method of production of biomass
briquette is based on lignin plasticization mechanism. However, biomass briquette can also be
produced at room temperature by the application of another briquetting technique; in that case
binder is used.
Coal briquette: Coal briquettes are made by compressing finely divided coal particles. The coal
is dried, crushed into appropriate particle sizes. Binder desulphurizing agents are added, and
then the material is compressed into briquette. Also, coal briquette can be produced by first
carbonizing the coal before it is used. During the carbonization, some of the volatile
components of the coal are driven off.
2.4. Coal
Coal was formed by the remains of vegetable that were buried under ground millions of years
ago under great pressure and temperature in the absence of air. Coal is a complex mixture of
compounds composed mainly of carbon, hydrogen and oxygen with small amounts of sulphur,
nitrogen, and phosphorus as impurities.
15
2.5. Biomass Resources of Nigeria
Biomass is organic non-fossil material of biological origin. The biomass resources of Nigeria
can be identified as wood, forage, grasses and shrubs, animal waste, and waste arising from
forest, agricultural, municipal and industrial activities as well as aquatic biomass. Generally,
biomass can be converted into energy either by thermal or biological process.
Biomass energy resources base in Nigeria is estimated to be about 144 million tonnes per year.
Nigeria has about 71.9 million hectares of land considered to be arable and grasses of different
kinds are among the major agricultural purposes. The potential for the use of biomass as energy
source in Nigeria is very high. This can be explained from the fact that about 80% of Nigerians
are rural or semi-urban dwellers and they depend solely on biomass for their energy source.
Biomass may be used directly as energy source for heating or are better converted to a cleaner
fuel source. For-instance, conversion of wood into charcoal and biomass based briquettes is
always encouraged. Other energy sources that are got from biomass include: biogas, biodiesel
and bio-ethanol etc. All these energy sources have been shown to have better combustion
performance and are more environmental friendly than direct combustion of biomass.
However, owing to the fact that firewood is the energy choice of the rural dwellers and the
urban poor, pressure is mounted on the forest in search of fuel wood while on the other hand,
vast majority of other biomass resources in form of agricultural wastes are wasted either
deliberately or inadvertently. Meanwhile, researches have proved that this category of biomass
resources can be converted to better fuel sources compared to fire wood, and at the same time,
act as pollution control measures.
2.5.1. Bio-coal briquette
They are briquettes formed by blending coal with vegetable matter (biomass), and then treating
with desulphurizing agent (Ca(OH)2), using an amount corresponding to the sulphur content in
the coal. When high pressure is applied in the briquetting process, the coal particles and fibrous
vegetable matter in the bio-briquette strongly intertwined and adhere to each other, and do not
separate from each other during combustion.
2.5.2. Charcoal
Types of charcoal are: wood charcoal, sugar charcoal, and animal charcoal. They are produced
by burning wood, sugar and animal refuse (blood, bones), respectively in limited supply of
oxygen. Wood charcoal is a common fuel source used by some people. It is a cleaner fuel
16
source than fuel wood. In fact, analysis shows that transition from fuel wood to charcoal would
have been a best option for reducing exposure to indoor pollution but such transition could lead
to even more severe environmental degradation and fuel scarcity as more wood is needed per
meal using charcoal compared to fuel wood.
2.6. Starches as a Binder
Starch is a white granule organic chemical compound that occurs naturally in all green plants.
The percentage of occurrence varies with plant and in different parts of the same plant. The
natural function of the starch is to provide a reserve food supply for the plant. Starch can be
extracted from many kinds of plants, only a few plants can yield starch in commercial
quantities. Such plants are maize, potato, rice, sorghum and cassava, etc.
Cassava plants are the major source of starch. The plant thrives in the equatorial region between
the tropics of capricom, and as well it thrives very well in Nigeria. There are many varieties of
cassava plants of which two varieties-bitter and sweet varieties are widely grown for the
purpose of manufacturing of starch. They contain high content of starch which ranges from 1233%. A typical composition of the cassava root is moisture (70%), starch (24%), fiber (2%),
protein (1%) and other substance including materials (3%).
When starch is cooked, it gelatinizes to form viscous solution with water. The starch granules
begin to swell as they are heated in water until they absorb most of the water and starch paste
which differs in clarity, texture and gelling strength is formed. Cassava starch has numerous
industrial uses. They are used as an additive in cement to improve the setting time. It is used to
improve the viscosity of drilling moulds in oil wells. It is used to seal the walls of bore holes
and prevent fluid loss. It is used in the main raw material in glue and adhesive industries. In
briquetting industries, it is widely used as a binder. Briquette produced using starch as the
binder is easily ignitable and burns with less ash deposit.
2.6.1. Binders used in the production of bio-coal briquettes
Binders are substances, organic or inorganic, natural or synthetic, that can hold (bind) two
things or something together. Two types are combustible and non-combustible binders.
Combustible binders are binders that support combustion and can burn. Examples are starch,
petroleum residues, molasses, cottonseed oil etc. Non-combustible binders are binders that
cannot support combustion examples are clay, cement, limestone, etc. Starches have proved
very satisfactory as binders.
17
2.6.2. Calcium Hydroxide
Calcium hydroxide is also known as slaked lime, hydrated lime, slake lime or picking lime. It
is a chemical compound with the formula, Ca(OH)2. It is a white powder or colourless crystal.
Commercially, it is produced when calcium oxide (CaO) (also known as quick lime or lime) is
mixed with water. This process is known as slaking of lime.
CaO(s) + H2OCa(OH)2(S)
Naturally, calcium hydroxide occurs in mineral form called portlandite. Portlandite is a
relatively rare mineral known from some volcanic, plutonic, and metamorphic rocks. It has
also been known to arise in burning of coal dumps.
Quicklime is a white solid obtained when limestone (calcium trioxocarbonate (iv)) is heated to
a very high temperature, about 900o C.
⇄
In Nigeria, calcium hydroxide is expected to be very cheap and available in abundance because
there is large deposit of limestone in the country and besides, the production of calcium
hydroxide is a simple process. Many investigations have shown that calcium hydroxide is an
effective sulphur fixation agent (Desulphurizing agent) for production of briquettes.
2.6.3. Environmental issues
Coal contains carbon, hydrogen, sulphur, and other minerals. When coal is burnt, carbon,
hydrogen and sulphur react with oxygen in the atmosphere to form carbon (iv) oxide, water
and sulphur (iv) oxide. The sulphurdioxide can react with more oxygen to form sulphur
trioxide, SO3.
2SO2 (g) + O2 (g)  2SO3 (g)
The SO3 dissolves readily in water droplets in the atmosphere to form an aerosol of sulphuric
acid which falls as rain.
H2O(l) + SO3(g) H2SO4
When inhaled, the sulphuric acid aerosol is small enough to be trapped in the lung tissues,
were they cause severe damage. Acid rain destroys vegetation and forest as well as life in the
sea, lake, ocean, streams, etc. Also, CO2 is produced when coal is burnt. The total quantity of
18
CO2 released by the human activities of deforestation and burning of fossil fuel is 6-7 billion
metric tonnes per year. Carbon (iv) oxide causes global warming and depletes the ozone layer.
Bio-coal briquette contains less percentage of coal than in coal briquette (since there is partial
substitution of coal with biomass). Hence, there will be lesser emission of carbon, sulphur,
dust, etc, into the environment. In order to reduce the emission of these gases into the
environment, lime based products such as Ca(OH)2 can be incorporated into the mixture to fix
the pollutants to the sandy ash, or the coal can be carbonized.
Since the use of bio-coal briquettes will reduce cutting down of trees for the purpose of using
them as fire wood, briquette technology can serve as global warming countermeasure by
conserving forest resources which absorbs CO2, through provision of bio-coal briquettes.
2.6.4. Groundnut shell as an appropriate residue for the production of bio-coal briquette.
Groundnuts, Arachius hypogeal, are legumes whose fruits are formed underground; each fruit
or nut usually contains two or three seeds, enclosed by the shell. It is one of most important
annual cash crops grown in West Africa. In Nigeria, the crop is grown mainly in Kano State,
but also in the Sokoto, Bornu and Kaduna States.
Groundnuts require rich, light, sandy loam soils, since such light soils allow the ovary to push
easily into the soil, making harvesting easier. It requires annual rainfall of 80-120cm, abundant
sunshine and fairly high temperatures. These conditions are obtained in the savanna areas.
Groundnuts are propagated by seed. Planting is done with the early rains in March-April in
South, and May-June in the North. Groundnuts reach maturity in 4-5 months. In wetter areas,
groundnuts are harvested in August, while in the dries savannah, harvesting is done in OctoberNovember. Harvested pods are spread on concrete floors or plat forms to dry. They are beaten
with sticks or pounded or using threshing machine to remove the shells. This is called shelling
or decortications machine to remove the shells. The seeds are separated from the shells by
winnowing or using a shelling machine. The seeds are further dried and packed in jute bags,
while the shells are dried and kept (Akinyosoye, 1993).
Groundnuts are normally baked before eating. Groundnut oil is used in cooking and also in the
manufacture of margarine and soap. It is also used in canning sardines. The solid portion which
remains after the oil is extracted is used in the manufacture of biscuits and for animal feed in
the form of groundnut cake. This cake is richer in protein than other cake such as palm kernel
and coconut cakes.
19
Groundnuts may be crushed and used as a fodder crop or ploughed into the soil as organic
manure. It is a most useful rotational crop since it enriches the soil with nitrogenous material.
Groundnut shell is obtained after the groundnut seeds have been removed from the pod. Hence,
it is an agro residue.
2.6.5. Analysis of groundnut shell
Table 1: Chemical composition of groundnut shell.
Constituent
Percentage
Cellulose
65.7
Carbohydrate
21.2
Protein
7.3
Mineral
4.5
Lipids
1.2
2.6.6. Uses of groundnut shell.
Groundnut shell is used as fuel, for manufacturing coarse boards, cork substitutes, etc.
Groundnut shell can also be grounded and mixed with feed, to be used in feeding livestocks. A
recent experiment carried out, showed that groundnut shell can be used as partial replacement
of ordinary Portland cement. In the experiment, the ash analysis of the groundnut shell was
carried out, and it was observed that the constituents in groundnut shell (which was given in
the table above) have cement properties that would be beneficial to the concrete. Groundnut
shell, when ground is an appropriate agro waste for the production of bio-coal briquettes, since
it burns smoothly and very fast when it is dried.
20
CHAPTER III
3. MATERIALS AND METHODS
3.1. USE OF AGRICULTURAL WASTE INSTEAD OF PETROLEUM IN A LIME
KILN
The project is concerned with the modification of a traditional vertical type lime kiln in order
to substitute the fuel oil with agricultural waste and to achieve significant energy saving by
recycling the exhaust gases from the kiln. The recovery of the waste heat can increase the
productivity and the quality of the lime. In addition, the modifications facilitate the working
conditions for the operators and have significant reduction of emissions offering better
environmental protection. The majority of the traditional lime industries uses fuel oil. Most of
the kilns modified to run on biomass or other solid fuels are equipped with open burners which
result in high surface area requirements in the kiln, defective loading and unloading equipment
and no recycling of the flue gases for energy savings. This results in energy waste, low quality
lime, low efficiency and high production cost.
3.1.1. Technical description
The Vertical kiln is in steel construction with refractory bricks lining, charging and discharging
systems that work automatically, and 2 rows of burners in order to have a better temperature
distribution in the kiln. The flue gases are removed from the top of the kiln, and after
particulates removal in a cyclone the flue gases are supplied to the heat exchanger, in order to
transfer the heat to the fresh combustion air. Additional particulates removal is achieved in a
bag filter before the flue gases are emitted to the atmosphere. In order to improve the
temperature distribution in the kiln and eliminate any cold spots. The biomass burners are of
the closed type without any contact with the atmosphere. This combustion system provides for
more accurate and better control of the pressure and temperature in the kiln. One part of the
exhaust gases (with very low oxygen concentration) is sent by a fan to the burners in order to
protect them (by providing local cooling) and to facilitate the burning process, together with
the mixture of fuel biomass and fresh air.
The operation of the kiln is very simple, the calcium carbonate stone (CaCO3) is loaded from
the top by a conveyor and a charging system which works automatically. Discharging of the
quick lime (CaO) is from the bottom with a feeder and a conveyor. During the process, the
stone is moving slowly downwards, passing from-the preheating zone, to the burning zone and
21
finally to the cooling zone. The burners are situated at about 1/3 of the kiln in two rows. Every
burner is provided with an independent feeding system and for every two burners there is one
blower and one silo. The fresh air is preheated in the heat exchanger increasing its temperature
from about 20 °C to about 100 - 120 °C. This process is very innovative comparing to
traditional kilns, as it provides for excellent mixture of fuel biomass with air in the burners,
and eliminates the possibility that the biomass will burn in the calcium carbonate bed. The
utilization of the closed biomass burners resulted in a 40% decrease in the internal diameter of
the kiln without any compromise in its output. The ideal biomass fuel is the residue from the
olive oil industry of Peloponnese. It has the advantage that the material has a relative small size
(< 10mm) which makes it ideal for pneumatic feeding. In addition, the high surface area of the
fuel and the still relatively high concentration of oil components result in very good combustion
behaviour in the kiln. However since it is not possible to guarantee the supply of olive oil
residues throughout the year other types of biomass residues (such as olive tree pruning) must
be used. For these fuels size reduction must be carried out by a chipper. The biomass is stored
under a shed as shown in Figure-2. The shed covers an area of 2,500 m2 and has a storage
capacity of 15,000 tons. The construction of the shed was necessary in order to provide big
storage capacity, natural drying and storage of different types of biomass.
3.1.2. SOLID FUEL FROM THE FIELDS: COAL FROM AGRICULTURAL WASTE
2.4 billion people use solid fuels like wood, coal as their cooking fuel on daily basis worldwide.
Biomass may account over 70% of cooking fuel in many developing countries. But, burning
of biomass in raw form has created many health and environmental hazards. For example,
burning of unprocessed biomass leads to indoor air pollution, and it is estimated that over 1.6
million people die each year due to such kind of air pollution; especially women and children
are highly prone to it. A team called „Fuel from the Fields‟ (FftF) effectively developed a
method of generating charcoal from unused agricultural wastes. Charcoal thus provides many
advantages over raw biomass fuels, because the process of carbonization lessens the particulate
emissions, and lowers the risk of emerging respiratory infections. Another advantage is that,
people does not require to buy new stoves or change the way they cook, unlike liquefied
petroleum gas (LPG) or compressed natural gas (CNG).Charcoal making is very traditional
across the world–charcoal is an energy dense fuel that can be easily transported from rural to
urban environments. It also helps generating employment, for example, in a charcoal industry
22
near Haiti, more than 1,50,000 people are employed. Three conditions should be satisfied to
make charcoal:
• A carbon-rich material
• Heat
• Anaerobic fermentation or anaerobic conditions
3.2. Binder preparations and mixing
A binder is used for strengthening the briquettes. The carbonized char powder can be mixed
with different binders such as commercial starch, rice powder, rice starch (rice boiled water)
and other cost effective materials like clay soil and mixed in different proportions and shaped
with the help of briquetting machine.
For preparation of binding material add starch to water in the ratio of 10:1 and al-low it
to disperse without any clumps. Then heat the solution for 10 minutes and do not allow it
to boil (the final stage can be identified by the stickiness of the solution). After boiling,
pour the liquid solution onto the char powder and mix to ensure that every particle of
carbonized char is coated with the binder. This process enhances charcoal adhesion and
produce identical briquettes.
Briquetting is defined as the densification (agglomeration) of an aggregate of loose particles
into a rigid monolith. (Mordi, 2007).A briquette can thus be defined as a product formed from
the physico-mechanical conversion of dry, loose and tiny particle size material with or without
the addition of an additive into a solid state characterized by a regular shape.
Briquetting was first proposed in Russia by a Russian inventor F.P Veshniakov (Prokhorov,
1982). Veshniakov developed a method of producing briquettes from waste wood, charcoal
and hard coal. The most important advawntages of briquette are its low sulphur content, relative
freedom from dust, ease of handling and high calorific value (Osarenmwinda and Imoebe,
2006).
Briquette machines have been in existence and used for sawdust and waste materials in
Europe,Asia, and America(Kishimoto,1969;ASTM,1951).Saglam et al.(1990) reported that a
briquette machine was designed and used for the briquetting of lignites using calcium
ammonium
sulphite
and
liquor. Afonja(1975) had earlier reported on a specially designed
23
briquette machine for briquetting sub–bituminous coal. Ilechie et al, 2001, designed a moulding
machine to produce briquettes from palm waste. Inegbenebor, 2002, developed a five (5) tones
capacity briquetting machine for compressing agricultural and wood waste that can produce
six briquette at a time. This work focuses on preliminary design and fabrication of a ten (10)
tonnes manual briquetting machine capable of producing twenty (20) briquettes at time which
is of higher capacity than of the produced by Inegbenebor (2002).
In developing countries like Nigeria, the direct burning of loose agro waste residues like rice
husk, palm kernel shells, and groundnut shells in a conventional manner is associated with very
low thermal efficiency, loss of fuel and widespread air pollution. When they are made into
briquettes, these problems are mitigated, transportation and storage cost are reduced and energy
production by improving their net calorific values per unit is enhanced (Grover et al, 1996).The
briquetting machine we seek to produce will help minimize the environmental hazard from
agro waste. This machine it is hoped will be useful to small and medium scale briquette
manufacturers.
3.3. DESIGN CONSIDERATIONS
The manual briquetting machine was designed to produce twenty (20) briquettes at a time.
Total area which pressure act = number of mould die x cross sectional area of die
20
4
Where d = diameter of moulding die = 28mm = 0.028m, number of mould die=20, π=3.142
20
3.142
0.028
4
0.0123
Mass of one pressure transmission rod used = 450grams.
Number of pressure transmission rods = 20.
Total mass of 20 transmission rods = 450x20 = 9000g = 9kg.
Mass of ejecting piston = 100g.
Total mass of 20 ejection piston= 100x10 = 2000g = 2kg
Mass of the base plate = 4.5kg
Maximum mass of one wet briquette sample = 50g
24
Thus, Total mass of briquette samples = number of briquette sample x mass of one sample
= 20 x 50=1000g = 1kg
Total mass to be lifted by hydraulic jack is = total mass of transmission rod + mass of base
plate + total mass of ejection piston + total mass of briquette samples
9
2
4.5
1
16.5
Assume g (acceleration due to gravity) = 9.81
16.5 9.81
161.87
A 10 tonnes (10,0000N) hydraulic jack was used to lift the machine components and compress
the briquettes.
The hydraulic jack used was obtained as a bought out item. The compaction force was
calculated using the pressure. Pressure read from the pressure gauge connected to hydraulic
jack (Compaction Pressure)=17.5KN/ m2 (Ihenyen,2010).
Let FC = Compaction Force, and
PC = Compaction Pressure and
AC = Total Compacted Area.
Thus FC = PC + AC
Where AC = Number of Briquette produced at a time x cross sectional Area of briquette sample
Thus,
20
Where d = diameter of briquette sample = 28mm = 0.028m, π=3.142
20
3.142
0.028
4
0.0123
FC = 17.5x0.0123 = 0.2153KN = 215.3 N
25
Fig 2: Modelled design in Auto CAD Isometric view of Briquetting machine
The briquetting machine fabricated is shown in Fig.2 & Fig. 3, shows the isometric view of the
briquetting machine. The Parts of the manual briquetting machines produced are the main
frame, the compaction chamber and base plate. The Main Frame: The main frame houses and
support the other parts of the machine. The main frame was made from mild steel angular iron
bars. The Compaction Chamber: The compaction chamber was made with mild steel block.
Base Plate: The base plate of the machine is made from mild steel and is housed within the
frame of the machine just beneath the compaction chamber. Twenty pressure transmitting mild
steel rods are welded to the base plate of the machine, and these rods go into holes rods made
at the base of the machine to support the ejection piston.
Fig 3: Briquette Moulding Machine
26
Fig 4: Inserting raw material in Briquetting machine
3.4. Operation and Cost of the Machine
The palm kernel (other agro waste can be used) granules was mixed with starch binder and
feed into the dies in the compaction chamber and rammed until they are full. The lid of the
machine was then closed and screwed to position. The ten tonnes (10 ton) hydraulic jack which
was under the base plate was used to lift the plate assembly carrying the transmission rods,
which then pushes the piston against the mixture inside the various dies of the compaction
chamber. The mix is thus compacted against the lid of the machine, and the reading on a
pressure gauge attached to hydraulic jack is recorded. The mix was then left to set for about
five minutes after which the lid of the machine is opened and the briquettes were then ejected
.Some of the produced briquette are shown in Fig.4.The briquetting machine performance was
found to be satisfactory.
3.5. Performance Evaluation
For the performance evaluation, six briquette samples were randomly selected from the
sawdust briquette for evaluation. During the process of densification, the following statistic:
time for loading biomass into moulds, t1, sec, time for compressing the biomass, t2, sec, and
27
time for ejecting the biomass briquettes, t3, sec, were observed and recorded following after.
The production capacity of the machine in kg/hr was also recorded. On ejection of the
briquettes from the moulds, the mass and the dimensions of the briquettes were taken to
determine the density in g/cm3 using a digital weighing balance and a digital caliper. The
compressed density, relaxed density, relaxation ratio and dimensional stability of the sawdust
briquette were determined in accordance with the methods described by. Figure 3 shows the
sawdust briquette from the briquetting machine.
3.5.1. Physical Properties Determination
The bulk density of the loose biomass sample was determined by weighing an empty
cylindrical container of known volume and mass, and then carefully filled with the biomass
sample. After filling every third portion of the container with the sample, it was tapped on a
wooden table for approximately 10 times to allow the material to settle down.
After completely filling the container, excess material at the top was removed by moving a
steel roller in a zig-zag pattern over the container. The mass of the containing sample was
determined.
The compressed density (density immediately after compression) of the briquette was
determined immediately after ejection from the moulds as the ratio of measured weight to the
calculated volume. The relaxed density (density determined when dried) and relaxation ratio
(ratio of compressed density to relaxed density) of the briquette were determined in the dry
condition of the briquette after about 27 days of sun drying to a constant weight at an ambient
temperature of 34 ± 4o C and relative humidity of 68 ± 5% respectively. The relaxed density
was calculated as the ratio of the briquette weight (g) to the new volume (cm3). This gave an
indication of the relative stability of the briquette after compression. The compaction ratio was
obtained from the ratio of the maximum density and the initial density of the sawdust sample.
Briquette stability was measured in terms of its dimensional changes when exposed to the
atmosphere. To determine the dimensional stability of the briquette, the height was measured
at 0, 30, 60, 1440 and 10,080 min intervals. Durability represents the measure of shear and
impact forces a briquette could withstand during handling, storage and transportation
processes. The durability of the briquette was determined in accordance with the chartered
index described by after sun drying to a constant weight. The briquette was dropped repeatedly
from a height of 1.5m onto a metal base. The fraction of the briquette that remained unshattered
28
was used as an index of briquette durability. The durability rating of the briquette was expressed
as a percentage of the initial mass of the material remaining on the metal plate and this gave an
indication of the ability of the briquette to withstand mechanical handling. Water resistance of
the briquette was tested by immersing the briquette in a container filled with cold tap water and
measuring the time required for the onset of dispersion in water. The higher the water resistance
time, the more stable the briquette is in terms of weathering resistance.
3.5.2. Combustion Properties Determination
Proximate analysis was carried out to determine the percentage volatile matter, fixed carbon
and ash content of the sawdust briquette. The proximate analysis was determined based on
ASTM Standard. For the percentage volatile matter, 1g of the sawdust briquette was placed in
a crucible of known weight and oven dried (ELE Limited – Serial no: S80F185 – Hemel
Hempstead Hertfordshire, England) to a constant weight after which it was heated in a furnace
(Isotemp Muffle Furnace Model 186A – Fisher Scientific) at a temperature of 600o C for 10
minutes. The percentage volatile matter was then expressed as the percentage of loss in weight
to the oven dried weight of the original sample. The percentage of ash content followed the
same procedure as the volatile matter except that the sample was heated in the furnace for 3
hours. The ash content obtained after cooling in a desiccator was then expressed as a percentage
of the original sample. The percentage of fixed carbon was calculated using the equation below:
%
100
%
%
The heating value for the sawdust briquette produced was calculated using the Gouthal
formula:
2.326 147.6
144
Where, HV is the heating value (MJ·kg-1), C is the percentage fixed carbon, and V is the
percentage volatile matter.
29
Fig.5: Some produced Briquette
3.6. Environmental considerations
Carbonisation takes place under absence or restriction of oxygen. Apart from the emission of
CO2, NOX and dust, products of incomplete combustion (PIC), such as CO, vaporous and liquid
CXHY, soot and acids like formic and acetic acid are released. So-called polycyclic aromatic
hydrocarbons (PACs) are emitted, which are known to be highly carcinogenic. The best
protection of the environment is offered by afterburning systems, which transform all
incomplete combustion products (CO, CXHY, soot, PAC) into CO2 and H2O. Modern designs
even use the calorific energy of the off-gas to generate the necessary heat for the carbonisation
process itself. In India, pyrolysis gas burners have been tested, which burn the off-gas of
carbonisation (pyrolysis) processes (see figure 5).
30
Chapter IV
4. RESULTS AND DISCUSSIONS
Sometimes the briquetting material does not have suitable composition from good adhesion
binding. Then mixing the binding agent into the shredded MSW can be used. If the binder is
cheap or unnecessary material, it is an advantage. According to this reason the following
additives: cartoon paper, cement, and wood sawdust were used. Of course from gasification
point of view, a binder should be combustible. The briquette density value is influenced not
only by material composition but also by type of briquetting press. Briquettes produced on
mechanical press have higher density than briquettes produced on hydraulic press. Positive
aspect is also the usage of a binder: paper, wood sawdust, or cement. Adding more binder leads
to better briquette density. Fig. 6 presents a comparison of produced samples –briquettes from
clear softwoods, hardwoods, and straw. Briquettes from these materials are produced as highgrade solid biofuels. The Standards for these solid biofuels determine that briquettes should
have density over 1.12kg dm-3.The Standards also define the material composition; high-grade
solid biofuels can be produced only from clear wood. For gasification it is not necessary to
achieve high grade of briquette density. Briquettes from municipal waste will be gasifying in
furnace. An advantage will be more effective gasifying process, decreasing the transportation
costs and simplifying the storage process.
The mean biomass loading time, t1, mean biomass compaction time, t2, and the mean
briquette ejection time, t3 as well as their percentages of the total production time were recorded
as shown in Table 1.
Table 2: Production time components of the briquetting machine
Mean production time components
Time (Sec)
% of Total production time
Biomass loading time, t1
45
32.14
Biomass compaction time t2
58
41.43
Briquette ejection time t3
37
26.43
Total
140
100
In comparison to 74.8% of the total production time attributed to briquette ejection as reported
by, 48.37% of the time was saved on briquette ejection using the developed briquetting
machine. The mean total production time of 140 seconds (2.33 minutes) was lesser than the
31
mean total production time of 868.1 seconds (14.47 minutes) reported by. The production
capacity of the machine was about 43 kg/hr.
4.1. Physical and Combustion Properties of Sawdust Briquette
The influence of binder level was significant on the physical properties of the briquette (P<
0.05). The compressed density ranged from 0.6125 to 0.7269 g/cm3 on the addition of 15 to
45% cassava starch. The maximum compressed density of 0.7269 g/cm3 was reached at the
25% binder level and it was significantly different from the value obtained at 15, 35 and 45%
binder levels. This was reflected in the compaction ratio at this binder level which was recorded
as 2.9:1 showing that the particles were well compacted compared to the briquettes with 15,
35 and 45% binder having compaction ratios of 2.4:1, 2.8:1 and 2.7:1 respectively. A direct
relationship was observed between the compressed density and the relaxation ratio: the higher
the compressed density, the higher the relaxation ratio. This shows that the sawdust briquettes
became more unstable with increasing compressed density. The durability rating of the sawdust
briquette ranged from 37.75 – 91.43%. The durability rating was observed to vary directly with
the compressed density. A durability rating of 91.43% was recorded for sawdust briquette with
25% binder having the highest compressed density while 37.75% was recorded for the briquette
with 15% binder having the least compressed density. This shows that the durability of sawdust
briquettes is dependent on the compressed density. The resistance of the briquette to weathering
effect measured in terms of the length of time it takes just for the onset of dispersion in water
was observed to vary directly with the compressed density and the durability rating of the
briquette.
The dimensional stability of the briquette which was measured in terms of its dimensional
changes when exposed to atmosphere is shown in Figure 4. From the figure, briquette produced
with 35% of the binder appeared to be most stable between 30 – 1440 minutes, hence it can be
inferred that it produced the most stabilizing effect when exposed to the atmosphere compared
to briquettes at other binder levels.
32
Fig 6. Expansion in the height of sawdust briquette with time
The different binder levels had a significant effect on the combustion properties of the briquette
(P < 0.05). The volatile matter recorded ranged from 67.08% to 91.63%. These values fell
outside the range of smokeless fuel which is known to contain no more than 20% volatile
matters. The highest volatile matter content was recorded at the 35% binder level. The ash
content ranged from 0.56% to 19.21%. Ash content in briquettes normally causes increase in
combustion remnant in the form of ash which lowers the heating value of briquettes; the lowest
value was recorded at the 35% binder level. The calculated fixed carbon was highest at the
25% binder level with a value of 13.71%.
The heating value is the most important combustion property for determining the suitability of
a material as fuel. It gives the indication of the quantity of fuel required to generate a specific
amount of energy. The heating value ranged from 27.17 MJ.Kg-1 to 33.37 MJ.Kg-1. The highest
value was recorded at the 35% binder level and the lowest at the 25% binder level; and they
were all significantly different from one another. The low heating value at the 25% binder level
could be due to the high ash content recorded at that binder level. The highest heating value of
33.37 MJ.Kg-1 was found to be higher than 18.89 MJ·kg-1 obtained in banana peel briquette and
14.1 MJ·kg-1 obtained in maize cob briquette, 24–27 MJ·kg-1 for lignite with bio-binder, 12.60
MJ.kg-1 for groundnut shell briquette and 33.08 MJ·kg-1 obtained by for sawdust briquette. This
makes the sawdust briquette a good potential fuel for domestic cooking. In the production of
the sawdust briquette, 3700cm3 of water per kilogram of sawdust was in producing a good
biomass-binder mix for briquetting.
33
4.2. Optimum Sawdust-Binder Blend
The optimum blend of biomass-binder ratio was assessed on the basis of the briquette
compressed density and heating value since they are two of the major indices for assessing the
combustion, handling characteristics and ignition behaviour of briquettes as reported by a blend
of sawdust and cassava starch in the ratio of 100:25 gave the optimum compressed density of
0.7269 g/cm3 with a heating value of 27.17 MJ.Kg-1 while a blending ratio of 100:35 gave the
highest heating value of 33.37 MJ.Kg-1 with a compressed density of 0.7028 g/cm3. The heating
values were higher than those reported by some researchers for some biomass briquettes. In
terms of quality specification of briquettes, excellent briquette can be produced from sawdust
using the developed biomass briquetting machine.
34
Chapter V
5. Conclusion
Generally, biomass can be defined as renewable organic materials that contain energy in a
chemical form that can be converted to fuel. It includes the residues from agricultural
operations, food processing, forest residues, municipal solid wastes and energy plantations.
The use of biomass residues and wastes (for chemical and energy production) was first
seriously investigated during the oil embargo of the 1970s.
In recent years, the use of biomass as a sourceof energy became of great interest world-wide
because of its environmental advantages. The use of biomass for energy production (biofuels)
has been increasingly proposed as a substitute for fossil fuels. Biomass can also offer an
immediate solution for the reduction of the CO2 content in the atmosphere. It has three other
main advantages: firstly its availability can be nearly unlimited, secondly it is locally produced
and thirdly it can be used essentially without damage to the environment. In addition to its
positive global effect in comparison with other sources of energy, it presents no risk of major
accidents, as do nuclear and oil energy.
Due to their heterogeneous nature, biomass materials possess inherently low bulk densities,
and thus it is difficult to efficiently handle large quantities of most feed stocks. Therefore, large
expenses are incurred during material handling (transportation, storage, etc.). Agro-processing
residues, for example bagasse and to some extent groundnut shells, may already have a more
convenient use as fuel. In the sugar industry, bagasse is principally used for processes
generating heat and power. In other circumstances the agricultural residues are important
sources of domestic fuel. For example, cotton stalk is an important domestic fuel in the rural
areas of central Sudan. Generally field crop residues have an inherent characteristic of being
spatially scattered. The production areas may as well be located in remote areas, such as
mechanized farms in Sudan.
Under such circumstances the cost of collection and transportation to central processing points
may be prohibitive. Forest residues are also classified under this category. A variety of
technologies can convert solid biomass into cleaner, more convenient energy forms such as
briquettes, gases, liquids and electricity. The economic use of biomass residues and wastes
implies the development of cost-effective, safe and sustainable feedstock supply technologies.
These technologies should address the following inherent characteristics of biomass residues
35
and wastes: (a) low bulk density, (b) variable and often high moisture content, (c)
combustibility, (d) affinity to spoilage and infestation (e) geographically dispersed and varied
material, (f) seasonal variations in yield and maturity, (g) a short window of opportunity for
harvest and demands on labor and machines that often conflict with the main crops (grain), and
finally (i) local regulations that put limits on storage size and transportation loads.
Biomass densification represents a set of technologies for the conversion of biomass residues
into a convenient fuel. The technology is also known as briquetting or agglomeration.
Depending on the types of equipment used, it can be categorized into five main types:

Piston press densification

Screw press densification

Roll press densification

Pelletizing

Low pressure or manual presses
The preliminary design and fabrication of manual briquetting machine that can produce 9
briquettes at a time using locally available material have been achieved. Different agro waste
can be used to produce briquette using this machine. It is hoped that this produced manually
operated briquetting machine will be useful to small and medium scale briquette manufacturers
.Further studies is recommended in other to introduce heating elements in the machine to
enhance drying of the produced briquette and make it electrically operated.
Municipal waste can be briquetted by using pre-treatment technology (drying, shredding, and
mixing with the binder). Material composition has great influence on the final quality of the
produced briquettes (the density and strength of the briquettes). Therefore it is strongly
recommended to mix municipal waste with organic binder (paper, wood, sawdust) before
briquetting. From mechanical indicators from the point of view of the quality of the briquettes
(density, strength) we recommend to use the mechanical press for producing the briquettes.
Continuous running pressing in ‘open’ chamber has positive impact on the creation of binding’s
mechanisms between particles of materials which influences the final quality of the briquettes.
From the point of view of dimension and shape precision requirements it is recommended to
use hydraulic press for producing briquettes. Briquettes produced on hydraulic press have equal
diameter and the same length. An advantage of briquetting in ‘closed’ chamber is the stability
of dimension and precision of shape of the briquettes. Briquettes produced on mechanical press
36
do not have equal heads; moreover, the length of the briquettes is slightly different. This
disadvantage of mechanical presses can be eliminated by a dividing saw.
The study on the development of a biomass briquetting machine is of great importance to poor
and developing countries as it addresses the issues surrounding the efficient utilization of
abundant quantities of agricultural wastes and residues which provide an enormous untapped
fuel resource. The following conclusions were arrived at from the study:
1. A biomass briquetting machine suitable for the production of biomass briquettes on a small
scale with a production capacity of 43kg/hr was developed and successfully used in the
production of biomass briquette using sawdust.
2.
The physical and combustion properties of the sawdust briquette were found to be
significantly affected by the binder level.
3. Briquette with satisfactory qualities was produced using the developed briquetting machine.
However for optimum sawdust briquette quality on the basis of compressed density, a blending
ratio of 100:25 should be used while on the basis of the heating value, a blending ratio of 100:35
should be used.
4. The heating value calculated at the optimum biomass-binder ratios were sufficient to
produce heat required for household cooking in rural communities and small scale industrial
cottage applications.
The domestic use of sawdust briquettes in low-income families constitutes an important
alternative that should be further developed as it allows for the economic revaluation of wood
waste and the mitigation of greenhouse gas emissions. The sawdust briquette has positive
results compared to the bio-fuel materials currently used, with a higher bulk density, similar
levels of calorific power, less moisture, and low levels of fixed carbon, chlorine and sulphur,
promoting a healthier environment for the consumer and the environment. The energy content
of sawdust briquettes is considered sufficient for domestic use in low-income sectors. Including
different traditional fuels in sawdust briquettes would increase its calorific power butwould
also increase costs that the resident is unable to pay. The different bio-fuel materials used in
the comparison have high energy potential such as sugarcane bagasse, which has a low bulk
density level indicating an opportunity that could be evaluated to produce briquettes from this
material. The use of sawdust briquettes was very well received by the target families, not only
for the cost savings involved but also for the higher performance, ease of use and health care
37
issues. Communication and awareness workshops played a very important awareness role in
using sawdust briquettes as substitute for traditional fuel materials. The dimensions of the
briquettes facilitated their use in product testing, but different lengths and sliced portions could
be considered in the future to facilitate the regulation of their consumption.
38
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