BRIQUETTING OF BIOMASS

5

BRIQUETTING OF BIOMASS

Introduction 7<^_Λ

Briquetting is one of several tech­ niques which are broadly characterized as densification technologies. Ag­ glomerating residues and making them more dense can expand their use in energy production since such measures improve the calorific value of fuel, reduce the cost of transport to urban areas and may also improve the fuel situation in rural areas. Raw materials for briquetting are commonly available and include resi­ dues and waste products from the wood industries, loose biomass, rub­ bish and other combustible waste products (see Chapter 3 ) . Many of these waste products create problems and using them as an energy resource can solve some disposal difficulties. When using agricultural residues the ecological consequences must be considered. In many areas of the Third World, soil quality and the productivity of agriculture are being undermined as more people turn to organic wastes for fuel.

Biomass briquette

from screw

extruder.

The briquetting technologies can be divided by scale and compacting method. The division according to scale can be taken as:

However, certain amounts of selected agricultural and processing plant residues, such as groundnut, coffee or rice husk, are available in large quantities and can be used for fuel without major implications for soil productivity. If technologies are used for agglomerating the residue or making it more dense, its handling can be considerably facilitated. At the same time the energy content is raised to a level approximately equivalent to that of fuel wood.

1

large scale, done by motor on an industrial or regional basis

2

medium scale, done by bullock or motor on a village basis

3

small scale, done manually, on a family basis.

The compacting methods can be divided into:

Another example is the conversion of charcoal fines (small fragments, powder etc.) , into charcoal briquettes so that the fines are used and not wasted.

a)

high pressure compaction

b)

medium pressure compaction with a heating device

c)

low pressure compaction with a binder or string.

Some raw materials, like straw or charcoal, do not remain together with high pressure alone so a binder has to be added.

a. b. C. «I. «.

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Hfl— „ I Diagram of briquetting

43

) ,, I

plant.

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=t

44

Biomass briquettes

from piston

extruder.

Briquettes vary a lot in size and form, but usually they are of a cylin­ drical shape with a diameter of be­ tween 25 and 100 mm and lengths rang­ ing from 10 to 400 mm. Square or rectangular briquettes also exist. Pellets are smaller and more suitable for large-scale, high-technology production and are therefore, not so well suited to developing coun­ tries.

Large-scale Briquetting Where large amounts of residues are concentrated as in the wood industry (at sawmills) or in cash crop agri­ culture (at harvest time) another approach to briquettes has to be taken. The industrial presses for briquettes currently available are capable of exerting a pressure of about 1000 kg/cm 2 . The combination of high pressure and the heat gene-

rated during the compression process breaks down the elasticity of the materials used and enables hard, solid briquettes to be produced without the need for a binder which would only hinder the functioning of the machine. The capacity of industrial presses ranges from 2503000 kg/hr. The press is only one element in a complete production chain which will include: collection of waste, storage, drying, grinding, pressing, cooling, storing and tran­ sporting to user. The more stages that can be avoided, the more econom­ ical will be the briquetting. But the investment cost is high (about US$ 100 000). So in order to make it more economical when used for seasonal agri-wastes, it could be made movable so that it could be used at different times and places, according to the availability of raw materials. For a briquetting press with a capacity of 1000 kg/hr the power consumption is approximately 20-30 kW. To this must be added the power needed for the grinder and other auxiliary equipment. At present there are three different briquetting technologies used: rind dye or roller head pelletizing machines, piston extruder and screw extruder devices. Traditionally, briquettes were pro­ duced in rolling presses consisting of two drums with half impressions which line up at the moment of com­ paction. Much work is going on to find better compacting methods and other methods will soon be available.

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Biomass briquetting

plant

in Sweden,

with a capacity

of 120

ton/day.

45

Principle

of piston extruder hriquetting

machine,

The pelletizing machines consist of a circular die with holes where the pellets are formed (the die can be stationary or rotating) and edge runners (wheels) which press the material through the die while rotat­ ing inside it. This kind of equipment is expensive and complicated and economical only on a fairly large scale. It will usually not be suit­ able in a developing country. The piston extruder is the most fre­ quently used hriquetting equipment and is available from many producers around the world. It consists of a fly-wheel that operates a piston, which presses the material through a die where the briquette is formed like a long log and is later broken into convenient lengths. The screw extruder consists of an extrusion screw and a die; the screw compresses the material and forces it through the die where the briquette is formed. Sometimes the material is pre-heated to enble the power to be reduced on the screw, and often the die is water cooled. Briquetting is being used more and more in developed countries and some projects are also operating in devel­ oping countries. Intermediate Briquetting Technology A small inexpensive machine and simple press that could convert small quanti-

Principle machine.

of rotary

pelletizing

(JOO&L &ΙΟΜΛ«4

Principle of screw extruder machine.

hriquetting

46 ties of residues to briquettes econ­ omically would be very useful (espec­ ially if portable) for places where available waste is not sufficient to warrant the installation of the large-capacity machines now avail­ able. The capacity of this kind of village equipment should be some­ where between 25 and 250 kg/hr. Several different methods are avail­ able but each seems to have its prob­ lems. Bullock-operated machines. Briquetting machines, with dies and punches, driven by a single bullock, have been developed by the School of Applied Research in Maharashtra, India. They cost about US$ 2400 each. The machine is very sturdy but the problem is the limited maximum production 25 kg/hr and the price of the equipment. Power-operated machines. The same school has also developed a briquetting machine with two plungers driven by a 3 horse powermotor. The maximum capacity is 100 kg/hr and the price about US$ 4000. However, the pres­ sure on the briquettes is not very high and it is necessary either to use a binder or to handle the bri­ quettes with great care. GAKO-Spezialmaschenen in West Germany produces briquetting equipment that uses the piston extruder compacting method and produces good quality b r i q u e t t e s because of the high pressure - although this results in higher prices and power consump­ tion. A 150 kg/hr machine costs about US$ 12 900 and a 60 kg/hr machine about US$ 8800 and requires a power

load of 8.5 kW. T & P Intertrade Corporation Ltd in Thailand markets a press-screw system briquetter that heats the agro-waste before compression. This means that good briquettes can be produced without needing a binder and at lower pressure, resulting in cheaper equipment. Their "Ecofumac" has a capacity of about 150 kg/hr, needs a 15 hp motor and three 2000 watt heaters and costs about US$ 5850. The grinder needs a 5 hp motor. Unfortunately a lot of energy is used by the heaters and there have also been some problems with other components. It can be seen, therefore, that even if equipment does exist, the problems are not totally solved. Either equip­ ment is too expensive with little capacity and too high an energy use, or poor quality briquettes result. There is still a need for a mediumsize briquetting machine that is in­ expensive, easy to operate, repairable using local tools and commonsense, energy efficient, reliable and which can handle different types of raw material. The advantage of mediumsized equipment is that capital in­ vestment is low and mechanized drying and special storage space is not required. In addition it would be practical for use in villages and in places with small wood industries or small agro-industries like ground­ nut oil mills, sugar mills, saw mills and paper mills. The briquettes could be used locally in bakeries, brickworks, potteries, curing houses, breweries, drieries or simply for cooking.

V)

w4


operated

compaction

machine.

Hand-made Briquettes In many rural areas there are vast amounts of agricultural residues available, at least seasonally, to­ gether with biomass materials such as shrubs, twigs, bark, straw, hay, weeds, dry leaves, etc. However, in many such places there are great difficulties in obtaining firewood for cooking needs. The major drawback with the above-mentioned materials is that they all burn too quickly to be used for cooking purposes but this difficulty can be overcome if they are made into bundles or small faggots. Such a process diminishes the access of air and thereby slows combustion. Efficiency can be further enhanced if each bundle or faggot contains a piece of wood in the centre. Bundles may be fashioned, very simply, by hand, but their heat value increases if they are pressed using simple devices, eg presses made from rope, wood or metal. Bundles and faggots should not be looked upon merely as a poor wood substitute. Indeed, for many uses they are even more suitable than larger pieces of wood. Bakers, for example, traditionally use faggots composed of branches of between 3 and 5 cm in diameter to heat bread ovens.

Simple press.

hand

Materials such as dry weeds, husks, cotton waste, coconut fibre, olive residue, fish waste, wood sawdust and municipal rubbish - can be con­ verted into briquettes. This kind of material can be compressed quite adequately with the aid of simple hand operated presses. The pressure exerted varies from 10-1000 kg/cm^ depending on the design of the press, and with such low pressures a binder is needed in order to prevent the briquette from falling apart. The higher the pressure that can be ex­ erted by the press, the higher the density and heat value of the result­ ing briquettes. Thus, wherever poss­ ible, it is desirable to use equipment capable of producing high pressure. The first operation in producing briquettes is the chopping of the chosen material for which a machete, broad axe or a hand-operated straw chopper may be employed. The next step is to blend it with a suitable binding material which can be done in a cement mixer or a specially made cylinder drum mixer. Next it is necessary to compress the material in some kind of press. Manual bri­ quette presses have been designed by The Bellerive Foundation and VITA and prototypes have been made and tried. They consist of a mould and a piston. The piston can be operated through the hitting power of a hammer or by the pressing power of a lever.

RET-C

A "baker"

operated

briquetting

Tying the

bundle.

press

larger

A small

for

metal

press.

bundles.

48

Lever press for briquette

making.

An earth block press (like the Cinva Ram) is a manually-operated piston press for making building blocks, but can be readily converted to pro­ duce excellent briquettes. The press can also be adapted to produce several briquettes in one movement. This design is called the TERSTRAM and is produced in Belgium by Fernand Platbrood. The limitation of a hand-operated briquetting press is the low produc­ tion of about 5 kg/hr or 50 kg in a 10-hour day. The advantage is the relatively low cost (an Indian hand press costs US$ 360). Storage is no problem because of the small amount of briquettes, but drying might be necessary depending on the moisture content of the raw material, and can be done outdoors in the sun.

Mould for briquette the lever press.

making use in

quent loss of fine pieces through the grate. Finally, the briquette should not produce much smoke, gummy deposits, an objectionable odour or dust during burning, storage or handling. Added binders should be combustible and preferably have a heat value at least as high as wood. The majority of binders most suitable from a physical standpoint are too expensive to use in the proportions necessary for good briquetting. Inorganic materials such as cement, clay and silicate of soda are some­ times used but are objectionable because of increased ash, decreased combustibility, and disintegration during combustion. Organic binders usually increase the heat value, do not add to the ash content and do not disintegrate during combus­ tion. Consequently, these are the ones most commonly used.

Binders Binders are needed when the pressure produced by the compacting equipment is too low for "self-bonding", or when materials are compacted that do not self-bond such as straw, rice husk and charcoal. In simple and cheap briquetting equipment, binders could be a solution to producing good quality briquettes. Some raw materials have internal binders and can be compacted with low pressure like bitumen in soft coal, gums in southern pines and tars in partially carbonized wood. If satisfactory briquettes are to be produced economically, binders must meet a number of stringent re­ quirements. Overall cost is the primary consideration in which cost of material, cost of application and effect on production must be considered. Availability is a second consideration where relative quantity required, transport needed and com­ petitive use of binder material must be considered. Thirdly, the binder must produce a briquette of sufficient toughness to withstand exposure to weather, must not cause crumbling or excessive softening and during combustion exposure to heat must not cause disintegration and conse-

Commonly used binding agents include starches from corn, wheat or cassava, sugar cane molasses, tars, pitch, resins, glues, fibre, fish waste and certain plants like algae. Dung is also widely used, but this is unsatisfactory as its combustion is a major cause of lung and eye disease and it has other important uses as a fertilizer. Of non-combustible binders, ash, clay or mud are the most widely used. Adding used motor oil increases heat value, but actually acts as an antibinder and makes the briquette crumble. Another way to make good briquettes is to use mixtures of several raw materials, e.g. hay, dry leaves, wood shavings, charcoal dust, sawdust and some binder. One of the most interesting oppor­ tunities for utilizing waste products like sawdust, bark, agricultural residues of fine structure and grass­ es, is afforded by carbonizing and briquetting. Many kinds of neglected biomass e.g. lalang grass, water hyacinth, reed, lantan, etc. can be converted into char and char bri­ quettes. Charcoal briquettes may

49 be produced by preparing the charcoal first and then pressing it, by car­ bonizing wood briquettes after forma­ tion, or by heating the material under pressure so that semi-charcoal briquettes are formed.

Economy Economy of briquetting is very sitespecific. It depends on the cost of collecting the residues, the scale of production and transport require­ ments to the end-users. A better idea of the costs involved can be gained by considering some examples. The UNSO/DANIDA project in Gambia. The plant capacity is 5.52 t/hr. The annual production period is 5.5 months. The raw material is groundnut shells which have no other value. The work is carried out by one shift of 8 hours for two months, and two shifts the rest of the time. This means 1360 effective hours of opera­ tion and a total production of 7510 tons of briquettes (160 000 bags of 47 kg each). The economic data assumed for this plant are the following (in US$ 1981 prices), estimated production is 7.507 tonnes per year. See Table below. The price of fuelwood varied between 57 $/ton-62 $/ton. It should be pointed out that in this case transport costs are un­ usually high. In spite of that, the cost of briquettes on an energy basis (i.e. per energy value) is, however, somewhat cheaper than the cost of commercial fuelwood with a similar calorific value of 4000 kcal/kg. It

is also about one third of the corre­ sponding cost for oil fuels. In addition to this plant, a similar plant of equal capacity is also now being planned for the Senegal, again sponsored by Denmark. Very briefly, the comparable indicative economic data given for that plant are very similar to the Gambian plant and results in a retail price of 46.75

Raw material costs are also taken as zero in this case. The high labour costs in this case are based on offic­ ial fixed minimum wages, although actual market wages are about one third of those. Labour costs may therefore be significantly overcalculated. However, in the high wage case, commercial fuelwood is also much more expensive. Similar cost calculations for a Swe­ dish sponsored plant in Nicaragua based on cotton waste with no compet­ ing value, gives a considerable chea­ per cost, mainly due to smaller plant (1 ton/hour), more continuous usage pattern, and lower transport costs due to local use in small indust­ ry. Plant and interest costs are USD 7/ton, and maintenance, elec­ tricity, labour and transport costs amount to USD 2/ton each, adding up to a total of only USD 15/ton. Going down the scale to still smaller plants of the village level size, calculations concern a plant with an output of 250 tons/year. Again costs do not include any charge for the raw material, but includes only plant etc., interests, energy, main­ tenance and labour costs, divided as follows (see Table on the next page).

Annual Cost of the Gawbla briquettes project. Plant Planthouse Storage Interest

399 000 (10 years depreciation) 69 825 -"83 125 (20 years depreciation) (10*)

39 6 4 34

900 $/year 983 156 865

5.31 $/ton 0.93 0.55 4.64

Maintenance of plant and generator Labour Energy (dieseI) Bags (for distribution) Transport

25 28 28 15 71

365 215 262 152 345

3.38 3.76 3.76 2.01 9.50

Administration 10* of total cost

25 460

3.39

279 917 $/year

Wholesale price Transport Retailers cost and profit Margin

37.29 1.82

9.8 Grand total

Source: DanIda (1981)

37.29 $/ton

48.91 S/fon

The price of fuelwood varied between 57 S/ton - 62 $/ton.

50 in projects with somewhat larger end-users. This would solve several problems as it would be easier to get briquettes accepted as a fuel, it would be simpler to get a combus­ tion process that reduces the problems of smoke and it would make it possible to minimize transport and to organize the whole briquetting chain in a more efficient way. In a more indust­ rial application, it would also be easier to run and maintain the process machinery.

Annual Cost of a Village Scale Plant Plant machinery 4500 US$ Plant bulIdlng 1000 US$ Depreciation 5 years 900 US$ Interest 20$ 540/year 350/year Energy Ma Intenance 200/year Labour 2000/year Total annual cost, abt 4000/year Total annual output 250 tons 16 US$/ton Tota1 cost/ton Source: Di1Iner et al . (1983).

This would mean that briquetting could be introduced at sawmills, paper mills, rice mills and in other factories that produce agroindustrial waste. Other bigger end-users could be bakeries, brickworks, potteries, curing houses, breweries and drying processes for agro-industries (e.g. tea, tobacco, coffee, spices, veget­ ables and cereals).

Briquette Technology Dissemination The dissemination of the use of bri­ quettes is dependent on a whole series of circumstances. There has to be knowledge that such a possibility does exist, there has to be an ade­ quate raw material that does not have competing end-uses, there has to be a way to get the right equip­ ment, there has to be knowledge of how to run and maintain it and finally, there has to be an accepted end-use for the briquettes.

Another dissemination possibility would be locally on a village scale. Here the whole briquetting chain would be in one place, the trans­ portation would be easier and the obvious advantages of briquettes in areas with fuelwood shortages should be incentive enough for the end-users. But here the machinery still needs to be perfected. The small scale equipment now available is too expensive, unreliable, uses too much energy or produces briquettes of too poor a quality. When these technical problems are solved it should be worthwhile to try production on this smaller scale. Other problems are the need for organizing finance at a village scale and until this happens, larger scale industrially orientated briquetting seems to be the most viable solution. Problems to be solved involve the training of workers to operate and maintain the equipment, and the eventual pro­ duction of complete machines or spare parts in the country. Even if lowcost densification technologies such as briquetting were perfected, they would add value to previously "free" goods which would have effects on the distribution of income and serious consequences for the poor.

The main problem experienced in the Danish project in Gambia seems to be that people do not want to use the briquettes for cooking purposes because they give off too much smoke. The same was experienced by the Aeroglide Corporation in Chile, Ecuador and Mexico; people were reluctant to use briquettes. However, recent experiments with improved briquette stoves in the Gambia have given a clear indication that those problems might be overcome in the near future. Although the Danish plant shows that the briquettes can compete economi­ cally with firewood and charcoal, the transportation cost is very high when one has to distribute the bri­ quettes to many small end-users. They also had problems with the run­ ning of the briquetting equipment, with the feeding of raw material and with the electric motors. Conclusions In summary, all this indicates that it would probably be much easier to introduce briquettes as a fuel For* AND

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Principle

for briquetting

plant,

producing its

own fuel,

51

Agrowaste Compaction Machine (1982) School of Applied Research, Vishrambag, Sangli, 416 415, Maharashtra, India. Danida (1981) The Gambia. Improving the Production of Fuel Briquettes in Kaur Plant and the Use of Agricul­ tural Waste Products for Fuel. Project no. UNSO/DES/GAM/81/006. United Nations Sudano-Sahelian Office. Dillner, P. & Saask, A. (1983) Bri­ quetting of Agro-waste in Villages. SCARAB, Gärdesvägen 11, S-183 30 Täby, Sweden. Hall, D.O. & Barnard, G.W. & Moss, P.A. (1982) Biomass for Energy in the Developing Countries. Pergamon Press. Ltd., Headington Hill Hall, Oxford, 0X3 OBW, U.K. Hausmann, F. Briquetting Wood Waste by the Hausmann Method. Fred Hausmann Ltd., Basel, Switzer­ land. Janczak, J. (1980) Compendium of simple Technologies for Agglomerating and/or Densifying Wood, Crop and Animal Residues. FAO Forestry Dept., Rome, Italy.

Joseph, S. &Hislop,D. (1984) Residue Briquetting in Developing Countries. Intermediate Technology Development Group, 9, King Street, London WC2E 8HW, U.K. Journey, T. (1981) Charcoal Briquett­ ing Experiment at Kilifi Plantations Ltd. Kilifi, Kenya. A.T. International, 1709 N. Street, N.W., Washington, D.C., U.S.A 20036. Lichtman, R. Briquetting Agricul­ tural, Animal and Forest Residues. Energy Division, The World Bank. Mandley,E. Briquettes the Alternative Fuel. Bogma Maskin A . B . , Ulricehamn, Sweden. McChesney, I . ( 1 9 8 5 ) Briquetting Wastes and Residues for Fuel. A r t i c l e i n Appropriate Technology Vol. 12, No. 2 , September 1985. Intermediate Technology Development G r o u p , 9 . King S t r e e t , London, WC2E 8HW, U.K. Pinson, G.S. (1983) Report on I n i t i a l Commissioning T r i a l s for V.S. Extruder/Briquetting Machine at TPI, Culham. Tropical Products Institute, Culham, Abingdon, Oxfordshire 0X14 JDA, U.K.

Reed, T. & Bryant, B. (1978) "Densified Biomass: A new form of solid fuel". SERI, 1536 Cole Boulevard, Golden, Colorado 8401, U.S.A. R e i n e c k e , L.H. ( 1 9 6 4 ) B r i q u e t t e s from Wood Residue. F o r e s t product l a b o r a t o r y , f o r e s t s e r v i c e . U.S. Department of Agricul­ ture. UNS0 ( 1 9 8 1 ) S e n e g a l . Development of New and Renewable Energy Sources and Strengthening of Energy Conserva­ tion A c t i v i t i e s . UNSO/DES/81/001. United Nations Sudano-/Sahelian Office.