Part 1.An overview of briquetting
Contents - Previous - Next
Chapter 2.The residue base
Chapter 3.The markets for briquettes
Chapter 4.Technical aspects of briquetting
Chapter 5.Economics of briquetting
Chapter 1.Main issues
In this part we want to address the main issues of briquetting without going into detail of later chapters. These issues are conveniently contained under four broad headings:
the residue base
the market for briquettes
the technology of briquetting
A discussion of technology and associated matters, such as operational and capital costs and the characteristics of the briquettes made by various techniques, sometimes dominates a study of briquetting. Yet in looking at the overall picture such a concentration may be misleading
Briquetting can be regarded as an attempt to link up two large and complex worlds: that of agriculture and that of fuel supply and use. Briquetting will never have the impact of a major new fuel such as oil, which can change entire patterns of consumer behaviour in the energy world, nor will it ever become the equivalent of an important new crop in agriculture. This means that the technology of briquetting must fit in with the existing agricultural context rather than the other way round.
This is a problem faced by many attempts to utilise natural resources in a way which is less wasteful. It is often convenient to divide human needs into neat compartments and then to provide for these needs in separate ways. But the price of convenience is often waste. It is usually necessary to examine the issues involved from a number of angles, not just technological, if ways to provide sustainable resource use are to be found.
First, we look at the residue base from which briquetting draws its raw material and consider the general circumstances in which briquetting might become established drawing upon particular types of residue. Then we look at the fuel markets in which briquettes might be used and how the nature of those markets effects the briquetting process.
It is often convenient to divide human needs into neat compartments and then to provide for these needs in separate ways. But the price of convenience is often waste.
We then summarise the technology in terms of its technical features and its costs. Finally, we try to make some generalizations about the total cost of briquettes in different circurnstances and how these costs compare with alternative fuels. In Parts 2 and 4, the technology and its economics are considered in much greater detail Here we are concerned to place the technology into a wider context to give some idea as to what role briquetting might play in fuel supply in developing countries.
Chapter 2.The residue base
Biomass densification means the use of some form of mechanical pressure to reduce the volume of vegetable matter and its conversion to a solid form which is easier to handle and store than the original material. There are a number of different densification techniques, which will be discussed in some detail later on; for convenience, they will all be called "briquetting" although, as will be discussed, they may produce final products which are very different.
The briquetting of agro-residues is one of a number of ways which have been developed to solve a problem: how to put the huge volume of wastes from agriculture and agro-processing to some useful purpose. (This presupposes, of course, that disposal of agro-residues is a problem. In fact, in many places, no such problem exists and residues are already absorbed in the local economy in a useful way). We are concerned with only one aspect of briquetting: its use for fuel production. Other applications of briquetting include the production of animal feed and, in general, any reduction of material volume to reduce transport of handling costs.
In aggregate, the numbers look very attractive. There is certainly a huge volume of residues which are associated with agriculture and with wood processing and, probably, most of these are not fully utilised. One of the major world crops, rice, has about 25% of the crop in the form of husk which amounts to about 100 million tonnes of residue. On a smaller scale, world production of groundnuts is about 10 million tonnes of which about 45% is shell. In general although there are crops with both higher and lower residue yields, it is reasonable to assume that about 25% of any dry agricultural feedstock is a residue.
In general , although there are crops with both higher and lower residue yields,it is reasonable to assume that about 25% of any dry agricultural feedstok is a residue.
Barnard and Kristoferson (Barnard&Kristoferson, 1985) have surveyed the whole field of agro-residues and whilst wide variations exist between crops, they show that commonly between 1 and 2 tonnes of residue will arise from every tonne of cereal crops. Other crops produce residue ratios which are both higher and lower.
The actual volume of residues which arise in any place will depend upon the cropping patterns and yields in use. There are such big variations in these that any generalization is impossible. However, even in the most under-developed agricultural area, it is possible to produce aggregate numbers which are impressive. In Figure 1, we reproduce a calculation of Barnard and Kristoferson which shows the per capita residue production from cereal crops alone in various countries.
Table 1: Agricultural Residues in the Sudan (1978/79)
The residues concerned will have an average heat content of 12-20 GJ/tonne. This means that even in the least productive countries and including only cereal crops, it is possible, in theory, to envisage household fuel needs being satisfied very largely from residues in some form or other. As residues in rural areas arise close to the communities, the existence of such a resource-base has aroused hopes that a fuller use of agroresidues could provide a partial solution to fuelwood shortages and increasing fuel costs.
In Table 1, an estimate made for the fuel value of residues in one country, the Sudan, is shown. It can be seen from this that, in principle, the utilisation of residues could have an appreciable impact in a country which is suffering badly from fuelwood shortages.
The potential for utilisation of woodwastes is also, in principle, very great though there are no good data on the general arisings of such wastes. However, one survey has suggested that in 1979, worldwide, "about 250 million tonnes of sawdust, close to 200 million tonnes of bar and over 400 million tonnes of other wood residues were produced" (TDRI, 1983). The report also notes that about 60% of this material arose in developing countries and, whereas in the USA up to 80% of this waste was utilised, in developing countries large quantities remained unused. This comment might well be applied to other residues derived from agriculture as there are a number of factors which make the utilisation of residues easier in industrial countries. These include the presence of large combustors which can handle difficult fuels, and a greater access to investment capital and technical know-how. Additionally, fuel costs are higher in many industrial countries than in many developing countries so there may be greater immediate incentives towards conservation.
Although these numbers are interesting in setting a general perspective, they have to be immediately and heavily qualified for any practical assessment of the likely importance of any technology based upon residues. The issue is that agro-residues (hereafter wood-wastes are included in this general term) arise as a small part of a very complex economic and social process - the growing, marketing and consumption of crops. This process is, in most parts of the world, the key underpinning to almost all activities and it has a dynamic which is likely to be particular not just to a country but to the regions within a country or even to the immediate area of a community.
Agriculture is changing in most parts of the world and the disposition of residues is likely to be incidental to the main dynamics of such change. Any method of utilising residues has to follow the trends within agriculture; it cannot hope to influence them in any significant way. New crops or varieties of crops; new processing methods at new locations; new markets and routes to market; all these things are likely to alter more or less significantly the volume and location of residues. However, in making the decision to use any new procedure, the effect on residues will be considered, if at all, as a very secondary matter The reason for this is simple: the economic value of the crop is always much greater than any possible value placed upon the residue.
However attractive a residue-conversion technology may seem in terms of its efficiency or cost-effectiveness in producing fuel, it must conform to the existing local dynamics of agriculture or it will not be adopted.
Figure 1: Per Capita Cereal Residue Production (tonnes/year)
However attractive a residue
conversion technology may seem in terms of its
efficiency or cost:
effectiveness in producing fuel, must conform to the local dynamics of agriculture or it will not be adopted.
It is likely that many of the trends at work in agriculture in developing countries, for better or worse in the overall sphere, will act to make the introduction of new techniques for residue use more attractive. Amongst these are the greater centralisation of processing to serve urban or export markets and the use of chemical fertilisers to raise yields and decrease dependence upon organic fertilisers, themselves very often based upon residues. However, this may be offset by other changes; for example the use of high-yielding varieties with a lower ratio of residue to crop or changes in landholding away from large farms to smaller units. In all situations, the introduction of any new technology has to fit in with these trends.
An example of such a change which has occurred in most Asian countries is the shift towards mechanised rice-milling. This occurs in a number of stages away from hand-milling in the household and towards centralised large mills. In the process of centralization, the residue ricehusk becomes a waste product which cannot be utilised in the immediate environs of the mill as, once, rice-husk could be used around a rural household. Thus in India, where central rice-milling is common, rice-husk exists as a waste product in large volumes whereas in Bangladesh, where smallscale milling remains normal, rice-husk is largely utilised by households. Such patterns of change are repeated, though in different ways, for most crops. The applicability of briquetting will depend very much on the particular form of agricultural practice in the region of interest. Huge volumes of residue can be swallowed up in some forms of agriculture and never be available for reprocessing.
It is sometimes assumed that residues are wastes and therefore "free" almost by definition. In practice, it is unwise to assume that any residue is "free" in the sense that it has no alternative use of some value. This is most obvious in the case of fully commercial briquetting plants based upon processing residues or wood-wastes. It is difficult to find examples of operating briquetting plants which do not have to pay something for the residues they use. Such payments may arise because there are competing uses for the "waste" but it may also arise simply because a residue provider is unwilling to allow someone else to make a profit from their wastes without asking for a share in the form of payment for the raw material.
Some plants operate using their own internally-generated wastes, particularly wood-wastes. These residues may seem "free" particularly if there are costs associated with waste disposal. However, in a country with a developed briquette industry, such as is beginning in Brazil, an alternative use may be the sale of the waste outside the plant to independent briquettors. Thus inevitably in a monetised economy, everything which has a use acquires a monetary value.
Even when this is not true, the wastes may, in practice, have various uses in the local community despite being given no monetary value. Such situations are likely to be well understood within the community even when they are not so apparent to the outside observer. Attempts to utilise the residue without offering any compensation are unlikely to be successful. Even when compensation is made, it may be that payment is made to someone other than the person to whom the original benefit so the result may be social disruption of some kind.
In general, it is probably unwise to assume that any "waster has no alternative use without careful investigation.
The broadest classification that can be made of residues is into field residues and processing residues, that is residues which remain in the fields after harvesting and those which arise during some further processing of the crop.
In order to analyse the conditions under which briquetting of field residues may be applicable it is convenient to start with the volume of residues produced per unit area of cultivation. Barnard and Kristoferson show the data of Fig 2 which summarises the residue production of six common crops in terms of high, medium and low yields.
It can be seen from this that, whilst highyielding maize can give as much as 11 t/hectare annually, a more likely yield in most developing countries would be 25 t/ha with rice being the highest yielder. Other crops could be added to this list, some with rather higher rates of residue production. For example, cotton grown in Nicaragua is reported to produce 4-20 tonnes/ha annually with a mean of 8 tonnes (Svenningsson 1985), though this is high in comparison with figures quoted for the Sudan of 2.1-3.6 t/ha (Biomass Technology Croup 1987). However, the broad figure of 2-5 t/ha seems acceptable for a general analysis.
Only a fraction of this would be practically recoverable though under conditions of highly mechanised harvesting with associated straw baling, the fraction could be close to one. However, mechanised baling is likely to be uncommon in developing countries and a more realistic recoverable fraction might be closer to 50%. In any practical evaluation of a field-residue briquetting plant, the likely recovery rate would be a critical factor.
The recovery rate would be lowered by alternative uses for the residue particularly informal, though important, uses by local people. These could include animal feed and bedding, direct use as fuel and various building applications in thatch or mudbricks. In addition, the ploughing in or burning of residues may play a part in promoting soil fertility. Field residues seldom have significant commercial applications; that is why they are left behind. However, these informal uses may be of great significance locally.
It is unlikely that briquetting would deny local people access to residues. The very nature of field residues makes them difficult to secure against systematic informal gathering. A more likely consequence is that where a number of other uses existed for the residues, the practical recovery rates would be low compared with theoretical yields. The impact on soil fertility, particularly trace elements, if the residues are usually burned in the fields, might be more significant and, in this situation, deleterious effects might not be immediately noticed.
It is unlikely that briquetting would: deny local people access to field residues. Their very nature makes them difficult to secure against systematic informal gathering.
The issue of soil fertility and the recycling of residues is not well understood. There seems to be little nutritional value in the direct restoration of uncomposted residues to the soil. However, they may play a part in maintaining the quality of the soil by keeping up its organic content. It is also possible that the burning of residues in the fields plays an important role in supplying trace elements. Certainly there is no generalisation which can be made; the importance of any one of these factors will depend critically upon specific local circumstances. The difficulty is that, in any specific situation, there is likely to be very little local knowledge about what impact a sudden change in residue recycling patterns would have on the soil. In principle, monitoring of agricultural yields after the change should indicate whether any adverse effects have resulted. In practice, such monitoring would be complex and expensive whilst changes could easily be hidden in the normal fluctuations of agriculture.
Briquetting machines have size ranges upwards from 0.1 t/h of input material. (Nominal size ratings are usually for woodwaste; a plant using straw would be substantially aerated over such figures.) If it is assumed that the smallest machine which would be commercially sustainable on its own would be 0.5 t/h then, at a recovered residue value of 1.5 t/ha, such a plant, working 6 months in the year, would require about 600 ha of land to supply its residue.
Figure 2: Residue Yields of Major Crops (tonnes/hectare)
The technical needs of a briquetting machine are best suited to a continuous homogeneous feed though not necessarily one based upon a single residue. The problem of maintaining a standard mix of different residues might be large however and a plant would probably be best served by a single type of residue input. This means that the plant assumed above would need over 600 ha growing a single crop, most of whose residues could be devoted to briquetting.
This area of land would comprise a very large farm unit in most parts of the world apart from those devoted to cattle rearing. This means that to be feasible, a field residue plant would usually have to draw upon several farms and be confident that their cropping patterns would not switch so as to leave the plant without adequate residue supply. This means, in turn, that local agriculture should be extensively based upon a single crop. Such conditions would be met in the rice-growing areas of Asia and maize areas of Africa but might be less easy to meet elsewhere.
Field residues are bulky; baled wheat straw has been put at 90 kg/m³ (World Bank 1986) and stacked cotton residues at 55 kg/m³. Even when chipped, cotton residues only have a bulk density of 130 kg/m³ (Svenningsson 1985). By contrast, stacked wood has a bulk density above 500 kg/m³. This means that the transport of residues to a briquetting plant can become increasingly expensive as the distance from the site of the residues to the plant increases.
A survey of straw-briquetting plants in Germany (KTBL 1983) contains costs which suggest that as the distance from field to plant increases from 1 km to 10 km, the cost of the briquettes increases by between 16-22 DM/t (10-14 US$/t). Field collection and baling costs are also high: 29 DM/t for collection in a 0.5 ha field though this could drop to 11 DM/t in a big 10 ha field making use of large baling machinery.
These German costs are likely to be rather higher than would be incurred in a developing country because of comparative labour costs. However, it is unrealistic to expect residues to be transported without mechanisation in any country and the capital costs alone of the necessary equipment can be high.
In a feasibility study for a wheat-straw plant in Ethiopia (World Bank 1986), it has been estimated that, even working under near-ideal circumstances of a large statefarm producing the 5 000 tonnes/year of residue required by the project, 6 tractors, 5 trailers and 3 balers would be required to cope with residue collection and transport. The capital cost of this equipment is put at US$107 000 . This may be an overmechanised plant for other circumstances but clearly the costs are high for any plant based upon a residue supply which is at all remote from the briquetter.
...the plant assumed above would need over 600 ha growing a single crop, most of whose residues could be devoted to briquetting.
These simple sums suggest the residue context in which briquetting could be applied; a fairly large area of monoculture in which a uniform residue arises in the fields within a distance of ready transport to a central processing point. What exactly constitutes "ready transport" will, of course, vary widely but even under the most ideal circumstances it would be necessary to transport the residues a few kilometres. (A circle with area 2 000 ha has a radius of 2.52 km and this is the ideal geometric configuration.) This means that mechanical transportation is certainly required with the consequent capital costs.
A context such as this possesses many associated advantages; notably that such a large area of monoculture is likely to use chemical fertilizers, which means that soil fertility issues may be minimal, and is less likely to have a significant part of its residues used for other, informal needs. However, it is also clear that such situations are fairly rare and remote from the conditions of mixed, subsistence agriculture which characterises the rural conditions of many countries.
There are numerous examples of this type of briquetting operation based upon maize cultivation in the USA and, rather less common, on wheat straw in Europe. Until recently examples in developing countries have been rare. However, some recent projects suggest that such plants may be developed more often in the future.
In Ethiopia, there are plans to build pilot plants based upon wheat, maize and cotton residues under just such circumstances of large state farms devoted mainly to a single crop (World Bank 1986). In the Sudan, a semi-mobile briquetting plant has been installed to utilise cotton-wastes from the huge cotton-growing areas of the Gezira (the plant is mobile as wastes cannot be removed from the fields to avoid infestation), whilst in Nicaragua, a fixed plant is fed by chipped wastes from the cotton fields (Svenningsson 1985). All these are based upon conventional piston-briquetters. A more unusual plant based upon cotton-residues, using a lower cost technology and producing charcoal briquettes for the domestic market is also under investigation in the Sudan (Biomass Technology Group 1987).
It is difficult to make any clear rules about the minimum land area required, in practice, to operate a briquetting plant. In Germany, a plant has been reported operating on as little as 45 ha though using a small machine and with high residue yields. A much more common size would be 500 ha and in developing countries with lower yields, a level of 1000 ha would seem more appropriate.
The most likely sites for briquetting plants based upon field residues would be on land growing maize or cotton in single land parcels of at least 1000 ha and, for preference, rather more. Other cereals, such as wheat, might also be attractive but would require rather larger areas. It is possible that plants based upon rice-straw could be developed but the logistics of transportation in paddy-fields plus the common occurrence of multiple cropping would probably make the plant impossible to run. There are no known examples of plants based upon rice-straw.
The most likely sites for briquetting plants based upon field residues would be on land growing maize or cotton in single land parcels of at least 1000 ha and, for preference, rather more.
This land requirement is onerous though it is not necessary that the land should be under single ownership or control. In Europe, one form in which briquetting of cereal residue has developed is the purchase of a single machine by a cooperative of farmers. However, this is in a context where cooperative ownership and operation of machinery is quite well established.
No mention has been made of the equivalent to field residues in forestry, that is the branches, tops and even leaves, left behind in forest logging operations. The reason for this omission is essentially pragmatic: no briquetting operation based upon such residues has been located and it may be therefore assumed that its economic viability is very limited.
This is not to suggest that forest-residue recovery is not undertaken; in Sweden, for example, there is a considerable business in such recovery in the form of wood chips. However, the logistics of the operation with a very high degree of mechanisation in areas remote from the consumer seems to point towards the bulk use of wood-chips in large, centralised combustion-plants. The inherent moisture of forestry residues, at around 40%, is too high for immediate briquetting and forest drying is impractical. The bulk density of wood-chips, about 300 kg/m³, is quite high so there is little potential saving in transport costs available after briquetting.
Although these conditions might not be precisely reproduced in developing countries, there does not seem any evidence yet that briquetting has any role to play in the utilisation of forestry residues. This is not true of sawmill and other wood-wastes from processing; these are considered below.
In this category, we include all residues obtained from the processing of a crop or wood including, for example, bagasse from sugar-cane, coffee husks, groundnut shells, rice husks, coir dust, sawdust, furniture wastes, in fact a very long list indeed as nearly all crops produce some kind of residue. Virtually all of these residues appear to have been briquetted, particularly if one believes the lengthy citations contained in manufacturers' brochures. In principle, these claims may well be true as the briquetting process works quite well for a wide range of feedstocks provided they are homogeneous and contain below 15% moisture. "If you can shovel it then
If you can shovel it then you can briquette it" would be a reasonably sound motto for a briquettor. "If you can shovel it then you can briquette it" would seem to be a reasonably sound motto for a briquettor.
This means that evaluation of a plant based upon process residues is, in principle, less complex than for one based on field wastes. The main problem is to establish the quantitative availability of material from a limited number of point sources, possibly only one. This is inherently simpler than to establish the potential residue yields from shifting agricultural patterns of several outside farms. Factories do not easily shift the nature of their operations.
The scale of operation of briquetting machines is quite well suited to most processing plants in developing countries. Rice-milling in Thailand, for example, is undertaken in mechanised plants which commonly process between 25 and 500 tonnes/day. The proportion of husk in this is about 25% so between 8 and 125 tonnes/day of residue will be produced. These quantities could be absorbed by single briquetting units using either one or two larger piston machines or four or five screw presses. The former set-up is used in India, the latter has been adopted in Thailand.
Similar calculations suggest that a single briquetting unit could be adequately fed by the sawdust from a few sawmills with a combined throughput of about 100 tonnes daily. This grouping of small processing units of the same kind in a single area is quite common for most of the main crops and suggests that the feed basis for briquetting may exist in a number of countries.
The relationship between one briquetting plant and one or more small agro-processing units may well be the most favourable for the establishment of briquetting. Although larger processing units may offer a super-abundance of supply for a single machine and offer visions of large multimachine briquetting operations, such schemes do not seem, in practice, to develop. (Large multi-unit plants are planned in Brazil and Argentina but based upon a number of saw-mills rather than a single processor). The reasons for this are not clear; it is always difficult to explain a negative. However, the most likely explanation is that large plants are set up with built-in methods of waste disposal, usually in their own boilers possibly using specially designed combustion equipment.
This issue of alternative uses is the one which lies at the heart of all application of briquetting to process residues. Once the residue has been centralised then a range of applications may emerge...
This situation is most obvious with respect to sugar cane processing which is probably the biggest bulk agro-processing operation commonly found in developing countries. World production of sugarcane amounts to several hundred million tonnes mostly in developing countries. As about 25-30% of cane is residue, bagasse, this amounts to a very large volume indeed of residues, larger even than rice-husk of which there was about 50 million tonnes produced in 1984. However, very little bagasse ever emerges as a waste for it is consumed internally to generate steam and power in the sugar-mill. It has been suggested that much more efficient use could be made of this bagasse by optimising its combustion and selling power externally. However, even in the most prolific producer, Brazil, no briquetting based upon bagasse has yet emerged even though surplus bagasse amounting to tens of millions of tonnes emerges and there is an established briquetting industry, based upon other residues.
Part of the reason for this lack of interest lies in the high moisture content of bagasse, about 50%, which necessitates a separate drying stage. However, this problem has been accepted in the briquetting of sawdust and presents no technical difficulty. The major reason appears to be that the scale of bagasse production encourages the installation of special combustion systems at a few larger plants able to cope with the residue directly without any intermediate treatment. In this situation, the extra costs of briquetting can only be justified on a transport-saving basis which may not be a strong enough incentive.
This issue of alternative uses is the one which lies at the heart of all applications of briquetting to process residues. Once the residue has been centralised then a range of applications may emerge both as a fuel and in other sectors which were not apparent when the crop was processed locally either manually or in small units. In effect, the transport costs of gathering, which are the main barrier to utilization of crop residues, have been absorbed by the transport of the valuable food-component of the crop.
Direct combustion is usually the one option of most relevance in the energy field whilst other uses may include animal feed-stuffs and bedding or such, at first sight unlikely, uses as additions to cement making (rice-husk) or packing for car-doors (bagasse). In all these applications, the users will compete for the residue and the briquettor may have to pay high prices for a residue once considered "free".
At the other extreme, a briquettor tied to a particular process residue from a single plant may find itself stranded if the supply of residues fails to meet expectations as the plant itself fails to find any raw material. There are a number of plants, particularly in Africa, where changes in agricultural practice or simple miscalculation have meant that the feed-plants have simply not delivered enough residues. The small value of the briquettes relative to the total value of the crop meant that the issue of providing briquetting raw-material was irrelevant to the wider agricultural changes going on.
Some reasonably successful briquetting operations have been set up attached to a single processing unit with no alternative source of supply, but they are rare. The most prolific conditions for operation, and this applies to plants based upon field residues as well, are units based upon small-scale processing of a crop or wood which is quite widely based. The obvious examples are rice-husk and wood-processing if the latter is taken to mean small sawmills and furniture plants.
Chapter 3.The markets for briquettes
Energy markets like agriculture are complex and changing entities with many national and local peculiarities. If one has to attempt to characterise the role of briquettes in these markets it would be in terms of the answers to two key questions:
The form of the first question is important for it suggests an implicit answer to another question: Will consumers alter their normal combustion appliances to suit briquettes? The answer to this is almost invariably: No. The reasons for this definite answer are twofold. First, in terms of quality of combustion, briquettes do not offer any significant advantages that might persuade consumers to spend money on new appliances. They are neither very convenient nor smoke-free; in contrast to electricity or LPG, both fuels for which consumers have shown themselves ready to switch appliances. They are essentially a small variation on a basic and not particularly attractive theme of solid fuels.
Some industrial consumers may be prepared to make adjustments to their boilers and domestic consumers may shift their fuel-feeding patterns if, in both cases, they can see a financial advantage. But it is difficult to envisage - and impossible to find in practice - any situation where consumers are prepared to shift to new appliances.
There is a crucial difference to testing new appliances for a fuel which has wide existing circulation and attempting to introduce new appliances for a novel: and minor fuel.
Second, the likely size of briquette supply relative to the total fuel supply even to a particular market sector is going to be small. Even the most optimistic view could hardly suppose that briquettes will ever supply more than 5-10% of, say, the total household market in any particular region of industrial demand. At these kind of penetrations with no prospect of the proportion increasing, consumers will always be aware of the need to give themselves an alternative source of fuel. This will certainly be true in the early stages of marketing briquettes whether or not, at a later stage, some consumers would have the confidence to commit themselves wholly to briquettes. Thus briquettes have to be compatible with existing appliances if they are to have any chance of achieving initial market penetration.
Of course, it is always possible to persuade some consumers to use new appliances if they are given them as part of a testing programme and then supplied with free or subsidised fuel. Such testing is a necessary part of any appliance programme, for example, to introduce more efficient wood-stoves. However, there is a crucial difference to testing new appliances for a fuel which has wide existing circulation and attempting to introduce new appliances for a novel and minor fuel.
Briquettes must therefore be compatible with existing appliances with little or no modification if they are to have any chance of successful marketing. The range of appliances can be divided, broadly, into three:
Appliances based on oil or gas-burning are almost invariably unsuited for briquettes.
Briquettes must therefore be compatible with existing appliances with little or no modification if they are to have any chance of successful marketing.
The household market
In the household sector there is relatively little data about the acceptability of briquettes as a wood substitute. Ordinary briquettes cannot substitute for charcoal; for this various kinds of carbonised briquette have been developed which have met with variable success. Rather few projects have ever attempted to sell ordinary briquettes direct to households and virtually all of these have met with commercial failure usually connected with problems of residue supply, machine failure or price uncompetitiveness.
The only systematic market study, which we have located (Association Bois de Feu 1985), which looked at domestic consumer response to briquettes gave quite optimistic results. Briquettes were burnt on ordinary stoves mixed with fuelwood and the specially modified stoves which were distributed were not required. Indeed it was claimed that briquettes could even acquire a cachet of modernity (though it was not reported whether this would imply acceptance of a price differential making briquettes more expensive).
This result is encouraging and does refute totally negative views about the potential use of briquettes in the household sector. But a single, limited survey cannot be used to prove universal acceptability. The Niger project failed because the supply of residues proved inadequate and briquettes could not compete in price with firewood so no extended market tests were made.
The only situation where uncarbonised briquettes appear to be sold commercially to households is in Thailand where sawdust and, to a limited extent, rice-husk briquettes are sold to refugee camps. However, this is a rather negative recommendation as sales to other types of households have proved unsuccessful and the refugee camps are forbidden to use fuelwood. The reason for the failure in other sectors is largely price-based; fuelwood remains rather cheap in Thailand. Rice-husk briquettes are also disliked because of their high ash content (over 20%), something which would probably prove an insuperable barrier for this material in normal household use.
Nevertheless, technically there does not seem to be any major problem about using briquettes in the existing appliances. Certainly no new or modified appliances have been developed though it is possible that the performance of briquettes is inferior to wood were it to be available.
There have been efforts to sell carbonised briquettes to households, mainly in India but also in Thailand and some places in Africa. The Indian efforts have not been very successful, though again this was using rice-husk as the base material. Carbonised wood-briquettes are largely indistinguishable from ordinary charcoal and are quite acceptable. Test marketing of carbonised briquettes in the Sudan is claimed to have been successful.
Laboratory tests are not a good substitute for genuine consumer use as they cannot reproduce all the complexities of practical application. But, such as they are, most tests suggest that, although the combustion characteristics of briquettes are somewhat different to wood, they are not so different as to require device modification.
The issue of household acceptability of briquettes made from materials other than rice-husk must remain open as no full commercial marketing has yet been undertaken. The preliminary results of test marketing offer reasonable grounds for optimism however.
It is probable that at least the smaller diameter briquettes, in particular the hollow examples from screw-presses, would find acceptance, possibly used with wood for initial ignition and heat-raising. It would probably be more difficult to sell
The issue of household acceptability of briquettes made from materials other than rice-husk must remain open as no full commercial marketing has yet been undertaken the bigger sizes, say about 8 cm diameter, simply because the physical dimensions of household stoves are limited. Large logs would be similarly rejected. Piston briquettes can be readily split into disks but this causes losses and may not be liked by consumers.
Industrial and commercial furnaces and kilns
In the other markets, for example, industries based on wood or coal, brick-kilns, bakeries, commercial establishments such as hotels, restaurants and other places with heavy hot-water demand, the issue is rather simpler than in households. There are many examples of briquettes being burnt in various enclosed stoves and kilns with very few problems.
The only practical difficulty found is the very high ash content of rice-husk briquettes. Whilst there does not seem any other comparable material, ash-contents of 510% are quite common and ash problems might arise with other materials.
Rice-husk briquettes have been sold fairly readily in India in industrial establishments with coal-burning boilers. However Indian coal is high-ash and so industries are prepared to cope with the problem. However, even in coal-burning boilers, most sales go to particular designs of boiler, notably step furnaces, in which the rice-ash moves out of the combustion zone. Rice-ash is almost entirely silica and it can fuse together into a clogging mass if the temperature is too high. This has been a problem in marketing rice-husk briquettes in Brazil to customers used to burning wood in their boilers.
Problems of ash-fusion could occur using lower-ash materials, though this has not been reported. In general, small wood-burning boilers may run at lower temperatures than coal units and, in wood units, most types of briquettes burn very well.
In Brazil, industrial consumers are actually prepared to pay a premium over the wood price for briquettes (these are mainly wood-based) of up to 50%. This is because briquettes are of uniform size and quality, are dry, and are purchased by weight. This last is important in Brazil, and possibly elsewhere, as wood is purchased by volume from a lorry and there are constant reports of suppliers cheating by packing the interior of the load with inferior material stacked randomly.
A recent study of a Ghanaian plant has also reported (World Bank 1987) a readiness by bakeries to pay a premium price for briquettes.
In most places, the market for briquettes in industry is large enough to absorb all the present and the likely future output of briquettes. Because of this and the ready acceptability of briquettes in industrial use, it is an obvious marketing strategy to focus on this market to the exclusion of household consumers.
In Tanzania, a project set up to produce carbonised briquettes for households has taken this line of marketing and is, in practice, selling all its output, uncarbonised, to small industry and commercial users.
There may be reasons of social policy to focus on household use, something which is reflected in various projects to produce carbonised briquettes as a charcoal substitute. There are also continuing efforts to produce low-cost briquetting machines which can operate on a small scale at the village level to produce a household wood substitute. Even in this area, it is worth noting that the only semimanual briquetting plant, known to operate on a commercial basis, sells its output to local brick-kilos. This plant operates in the east of the Sudan using semi-rotted bagasse as its raw material.
It must be acknowledged that, in virtually all situations, the industrial market has proved the easiest for briquettes to penetrate.
It must be acknowledged than, in virtually all situations, the industrial market has proved the easiest for briquettes to penetrate.
Can briquettes compete?
The second question concerning the price competitiveness of briquettes can only be adequately answered by reference to specific local conditions. In general, however, the level of current wood-fuel prices in large parts of Africa, Asia and Latin America are too low to allow briquettes much competitive room. In order to compete, briquettes often have to be sold without any capital charge component and, even then, may not cover their operational costs.
The failures of briquettes to compete with fuelwood prices is repeated from Niger to Thailand and at many places en route; it is without doubt an international conclusion. To appreciate the circumstances in which briquetting may be economic, it is useful to review, briefly, the two countries, Brazil and India, where an infant briquetting business has been established.
In India, the main residue used is rice-husk which, despite its drawback of high ash content, is very widely available and can be readily briquetted without any drying or chipping. This last point means that capital costs of the total plant can be kept down, something which is aided by local manufacture of machines.
The existing fuel at which briquettes are aimed is coal, which is often of poor quality and whose supply, particularly to smaller industries, may be irregular. It is also expensive; the price varies by region: in Delhi it may cost over 80 US$/t while fuelwood was reported to be 50-70 US$/t.
The failures of briquettes to compete with fuelwood prices is repeated from Niger to Thailand and at many places en route; it is without doubt an international conclusion.
The rice-residues are not free as, over the past few years, a number of industries in rice-producing areas have converted to direct firing of husk. This means that the rice-mills have become able to charge up to 250 Rupees/tonne (20 US$/t) though a more usual price is 100150 R/t. The direct use of rice-husk close to the mills mean that the best markets for the briquettes are often rather far from the point of production. In effect, briquettors are taking advantage of the fact that the unit transport costs of briquettes are lower than those for loose rice husk.
Briquettors in India estimated that they could break even at a factory-gate price of 550-600 R/t which implies a price of about 3040 US$/t net of the cost of rice-husk. Such prices were achievable but did not allow for any large profit.
In Brazil, although some use has been made of rice-husk, most of the briquetting plants utilise wood-wastes which require preliminary chipping and, sometimes, drying. The use of wood-waste means that the throughput of machines is quite high whilst the local plant manufacturer offers very cheap machines. These two factors lower capital costs considerably.
The residues are cheaply available, perhaps 35 US$/t, where they are not actually free as there are almost no alternative uses. Most wood-waste is dumped.
The target fuel with which briquettes compete is wood used in industry, an area of fuel use which has grown considerably in the last few years as the Brazilian government has supported a major biofuel programme. The wood supply is not of consistent quality however, in particular it may contain up to 50% moisture. There is also a good deal of cheating by wood fuel suppliers.
Wood prices are regionally variable but are still not high even in the higher price areas. In Sao Paula, wood prices of 13-16 US$/t were quoted. Briquettes are sold at 25-40 US$/t; prices which at the upper end seem to offer a reasonable profit. Briquettes can be sold at a premium over wood because of their lower moisture and consistent quality.
Three conclusions emerge from the case-studies in Brazil and India despite the big national differences.
First, it is necessary to keep capital costs down to a minimum by purchasing cheap, though obviously reliable, machines and not over-engineering the rest of the plant. Capital costs are also minimised by working the machine for at least eight months in a year even with a seasonal crop like rice. Large stocks of husk may have to be kept.
Second, it helps to have a fuel against which to compete which may be of unreliable quality and suffers from irregular delivery. ibis may enable a premium to be charged for briquettes.
Third, in order to break even, a factory gate price of 30-40 US$/t not including residue costs, is required to make a small profit even if capital costs have been minimised. Additional capital cost items, such as a dryer, and any costs associated with collection, storage and handling of residues can raise this by 50-100%.
It is this conclusion which shows why, to take a single example in Nairobi, a plant which possesses a briquetting machine has reverted to burning wood as its main fuel burning wood as its main fuel It helps to have a fuel to compete
It helps to have a fuel to compete which is of unreliable quality and suffers from irregular delivery.This may enable a premium to be charged for briquettes after considerable trials with coffee-husk briquettes. Industrial fuelwood costs under 20 US$/t, at which price it is difficult to cover the operating costs of briquettes. It is not possible to charge a premium for briquettes as wood is usually of reasonable quality. Clearly the incentives for setting up a new plant are small in such circumstances.
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