CONTENTS

S. No. Title Page No. Abstract List of Figures List of tables 1. Introduction 1-8 1.1. Background of the study 1 1.2. Objectives 8 2. Literature Review 9-20 2.1. Briquetting Process 9 2.2. Historical Background of Briquetting Process 10 2.3. Advantages of briquette production: 10 2.3.1. Bio-Coal Briquettes 11 2.3.2. Characteristics of Bio-Coal Briquettes 12 2.3.3. Advantages of bio-coal briquettes: 13 2.3.4. Production Process of Bio-Coal Briquette 14 2.3.5. Preparation of other types of Briquettes 15 2.4. Coal 15 2.5. Biomass Resources of Nigeria 16 2.5.1. Bio-coal briquette 16 2.5.2. Charcoal 16 2.6. Starches as a Binder 17 2.6.1. Binders used in the production of bio-coal briquettes 17 2.6.2. Calcium Hydroxide 18 2.6.3. Environmental issues. 18 2.6.4. Groundnut shell as an appropriate residue for the production

of bio-coal briquette. 19

2.6.5. Analysis of groundnut shell 20 2.6.6. Uses of groundnut shell. 20 3. MATERIALS AND METHODS 21-30 3.1. Use Of Agricultural Waste Instead Of Petroleum In A Lime

Kiln 21

3.1.1. Technical description 21 3.1.2. Solid fuel from the fields: coal from agricultural waste 22 3.2. Binder preparations and mixing 23 3.3. Design considerations 24 3.4. Operation and Cost of the Machine 27

3.5. Performance Evaluation 27 3.5.1. Physical Properties Determination 28 3.5.2. Combustion Properties Determination 29 3.6. Environmental considerations 30 4. RESULTS AND DISCUSSIONS 31- 4.1. Physical and Combustion Properties of Sawdust Briquette 32 4.2. Optimum Sawdust-Binder Blend 34 5. Conclusion 35 6. REFERENCES 39

  

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 details Page no. Figure 1. The basic flow process for Bio-Coal production 14 Figure 2. Modelled design in Auto CAD Isometric view of Briquetting machine 26 Figure 3. Briquette Moulding Machine 26 Figure 4. Inserting raw material in Briquetting machine 27 Figure 5. Some produced Briquette 30 Figure 6. Expansion in the height of sawdust briquette with time 33

 

List of Tables S. No. Table Details Page No. Table 1. Chemical composition of groundnut shell. 20 Table 2. Production time components of the briquetting machine 31

 

1  

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

2  

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

3  

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.

4  

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

5  

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

6  

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

7  

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 non-

commercial 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 agro-

residues 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

8  

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.

9  

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.

10  

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.

11  

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).

12  

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 combustion-

sustaining 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 bio-

coal briquette easily.

13  

(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.

14  

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

15  

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 non-

crystallized 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.

16  

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

17  

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 12-

33%. 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.

18  

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) + H2OCa(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

19  

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 October-

November. 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.

20  

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.

 

 

21   

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

22   

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

23   

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 and

ammonium sulphite liquor. Afonja(1975) had earlier reported on a specially designed

24   

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

204

Where d = diameter of moulding die = 28mm = 0.028m, number of mould die=20, π=3.142

  203.142

40.028 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

25   

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

203.142

40.028 0.0123

FC = 17.5x0.0123 = 0.2153KN = 215.3 N

26   

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

27   

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

Fig 4: Inserting raw material in Briquetting machine

28   

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

29   

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.

30   

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).

Fig.5: Some produced Briquette 

31   

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 high-

grade 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

32   

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.  

33   

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.

34   

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.

35   

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

36   

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

37   

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

38   

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.

39   

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