| Boiling Point No. 25 - August 1991 |
Research Project of University of Twente,
Technology and Development Group.
Summary of report of Phase One, 1990. (Ed note: descriptions of briquetting processes and equipment were given in BP No. 14, Dec 1987 and the Special Edition of 1989.)
Biomass densification represents a set of technologies for the conversion of residues of plant origin into a fuel. The technology is also known as briquetting, and it essentially improves the handling characteristics of the materials for transport, storage, etc. Briquetting has been applied for many years in several developing countries. As yet, the technology suffers from technical problems, such as fast wear of components.
Apart from technical constraints, the viability of briquetting depends on a number of key factors, such as: the markets for briquettes (ea. costs as compared to other fuels), the acceptance of briquettes by potential users, the availability of raw materials as a resource, and the modes of production.
This report reviews recent experiences in densification and briquetting in Thailand, India, Nepal, Sri Lanka, Malaysia and The Philippines.
In the countries surveyed, private investments in briquette production exceeded US$ 15 million over the last ten years (mainly in India and Thailand). Such ventures showed limited success because of:
- mismatch of technology, raw material supply and prospective markets;
- unsuitability of the briquettes for the intended market;
- technical difficulties;
- excessive operating costs (mainly electricity and maintenance).
2. In South and South-East Asia, a focal point is lacking for the accumulation and exchange of experiences in briquette production in conjunction with advances in briquetting technology.
3. Briquetting can only compete in a monetized fuel economy. Uncarbonised briquettes have to compete with fuelwood, coal or lignite, whereas carbonized briquettes compete with lump charcoal.
4. Today, the most likely market for uncarbonized briquettes is in energy-intensive, fuelwood-using industries, where fuel costs are substantial as compared to product value (ea. in brickmaking, potteries, lime kilns). This sector is a major employer and currently faces problems of wood shortages and high fuel bills. Further markets for both carbonized and uncarbonized briquettes are in institutional kitchens (restaurants, schools, hospitals, barracks, camps).
5. Users of briquettes have a marked preference for a mixture of their traditional fuel and briquettes. This allows the smooth switching from the one fuel to the other and vice versa.
6. In most regions, briquettes have not penetrated and, most likely, will not penetrate the household market. People either don't pay for their present fuel or, when they are able to pay, switch to more convenient fuels such as kerosene or electricity.
On Resources and Environment
7. South and South-East Asia have a large potential of residue sources for briquetting.
8. The most promising residues for briquetting are: sawdust, cotton stalks, groundnut shells, rice husk and coconut pith. In some places, these residues have little or no alternative use.
9. The direct impact of briquetting on the process of deforestation will be negligible.
10. Direct combustion of certain loose biomass residues in imperfect furnaces and stoves results in low conversion efficiencies. The incomplete combustion can cause considerable disposal problems of large quantities of ash containing particulate products. Briquetting can offer solutions to these problems.
On Technology and Production
11. Various residues can be either combusted directly or first briquctted and then combusted. The value added by briquetting must yield a return in increased efficiency, improved handling and storage characteristics, increased convenience, or reduced health hazards. This value added must outweigh the costs of briquetting. Otherwise briquetting should not be promoted.
12. The nature and morphology of the raw material is of utmost importance for technology selection. Sawdust and other materials with a low ash content can be briquetted without much difficulty. However, the use of equipment that operates successfully on sawdust does not guarantee success for other raw materials. Materials with a high ash content, such as rice husk and groundnut shells, result in excessive wear and high operating costs.
13. Briquette production is very site specific. It is extremely difficult to prepare a cross-evaluation of the performance of the different technologies, since no two operate under identical conditions.
14. There appears to be very little information exchange on briquetting experiences amongst the countries surveyed. Large differences showed with respect to technologies and types of briquettes. The differences cannot be explained by market demand, but are more likely the result of random technology selection and insufficient information on alternative production processes.
On Social Aspects
15. The availability of briquettes can reduce the pressure on scarce fuelwood resources. This would relieve poor households which are suffering from the fuelwood crisis.
16. Briquetting technology can be indigenised, mastered and controlled by local manufacturers and engineering workshops, thus enhancing appropriate technological advancements.
17.Briquette production creates employment in rural areas in post-harvest seasons.
18. The utilization of briquettes for fuelwood can support the viability of energy-intensive industries in rural areas.
19. Briquetting technology and briquette production can fit well in government policies towards the promotion of small scale and rural industries.
Present Use of Briquettes
Three markets for briquettes can be identified:
- 'domestic' use - cooking - space heating - institutional kitchens and restaurants
- industrial use
- export (mainly as barbecue fuel)
This type of cooking requires certain properties of the cooking fuel. In Thailand, the main dishes are stir-fried, requiring a high power output for a short time. In India, many dishes are simmered thus requiring a fuel with a low power output. Also in India, people are used to cooking with wood and other residues that are smoky, while in Thailand, 98% of the cooking fuel is supplied by charcoal, which is smokeless.
The present domestic utilization of briquettes in the countries surveyed can be briefly summarised as negligible. The only noticeable household consumption is of carbonised sawdust briquettes, uncarbonized rice husk and sawdust briquettes in Thailand, and char briquettes in India, Nepal and the Philippines.
In all countries, entrepreneurs have tried to capture the domestic market, but invariably encountered the following contraints:
- the present domestic cooking fuel is gathered for free (rural areas) or almost for free.
- those who can afford to switch from fuelwood or residues turn to more convenient fuels such as electricity, LPG or kerosene.
- briquettes are inconvenient, difficult to ignite, and smoke too much.
Acceptable Biomass Resources
It is important to distinguish between crop residues and agro-processing residues. Crop residues are the plant materials remaining in the field after the removal of the main crop produce. Agro-processing residues are the byproducts of the industrial processing of crop raw materials.
Crop residues are of a variety of shapes and densities straw, stalks, sticks, leaves, haulms, fibrous material, roots, etc. The amounts available vary from area to area, with crop type and crop variety, also with season and method of cultivation. The residues are diffuse which makes the process of collection, which is unmechanised, time consuming and expensive, thus rendering them unsuitable for briquetting. Moreover, they should not be regarded as a free waste material since they form an important source of materials for many village applications, for example, animal fodder and supplementary domestic fuels. The situation with regard to straws could change, however, if a project in India for the development of suitable equipment for the collection and baling of rice straw proves successful. Mechanization of collection could substantially alter the economics of utilization of straws.
With regard to briquetting, agro-processing residues would appear to have a greater potential, since they are produced at a central site and their accumulation represents a disposal problem with an environmental cost. However, some agro-processing residues have a potential for making high value products, for example, oil seed shells can be made into cattle cake. Therefore, for briquetting it is better to consider those residues with the lowest opportunity costs. These appear to be rice husk (although in India this may be changing), groundnut shells, bagasse, cotton ginning waste, cotton hulls, coconut shell, husk and pith, sawdust, and woodchips. The amount of residues available depends upon the type of industry and most importantly upon the type of process employed. The type and variety of crop also affects the quantity of residue produced.
The present commercial production of briquettes has utilized two main residues: rice husk and sawdust. There are examples of the commercial use of other residues and many different materials are currently undergoing experimental trials throughout South and Southeast Asia.
Rice husk has been extensively used throughout India and in Thailand as the main feedstock for briquettes. The material is extremely abrasive, due to its high silica content, and causes severe wear problems in the die. Domestic users of rice husk briquettes complain about the smoke and ash. Industrial users complain about the ash build up blocking grates and the need for frequent cleaning of boiler tubes. An improvement in production has been reported in India when the rice husk is mixed with sawdust and coir dust. It is difficult to understand why this material is so popular other than the large amounts are produced. Also rice husk is being increasingly used in India for direct combustion in industrial furnaces and other high value purposes, such as amorphous silica and furfural production. This competition is causing the price of the residue to rise.
The experiences with sawdust briquettes, in terms of both production and utilization, are much more positive. Users report much less smoke than with rice husk and a good heat output. Carbonized sawdust briquettes are produced primarily for the export market, and so prove too expensive for local use. However, substandard briquettes are utilized by restaurants, who are positive about the combustion characteristics.
Coconuts are a major crop throughout the region and a considerable amount of development work is being done with coconut residues, such as coir dust. Half a million tonnes of coir dust are produced in Sri Lanka annually, and approximately one million tonnes in India. A briquetting process using coir dust and lime as the binder has been developed in Sri Lanka and export to India is being considered in the near future.
Coconut shell is converted into activated charcoal and the fines from this process are used to make high quality briquettes in the Philippines. However, producers are keen to reduce the amount of fines, since this represents a substantial income loss.
Other processing residues reported to be in use, primarily in India, to make briquettes, include groundnut shells, bagasse and decaffeinated tea waste. Groundnut shells are also abrasive, although improvements are said to occur when the shells are mixed with coffee husk. There is considerable competition for bagasse as a feedstock in paper and board manufacture. Decaffeinated tea waste mixed with bamboo dust and lime has also been successfully briquetted.
Green fuel briquettes produced in Thailand use aquatic plants, such as water hyacinth and salvinia, that are causing major environmental problems in waterways. Usually these plants are cleared and left to rot on the river banks. The briquettes, however, have a number of serious problems which need to be resolved to increase their user acceptability.
Municipal solid waste is a major disposal problem in many developing countries. In India, where this material is hand sorted to remove any metal, thereby reducing its abrasive nature and potential damage to briquetting machines, a plant has recently opened in Bangalore using MSW as a feedstock.
Molasses would appear to be the most popular binder material, although in the Philippines tests have been carried out using a number of binder materials with wood charcoal fines. Cassava is regarded favourably, while lime, cement and clay were found to have low crushing strength.
As one step towards increasing the feasibility of briquette production, the report states that it is essential to make a comparative study of the micro- and macro- economic aspects of briquetting in a number of countries and to design a methodology that warrants a uniform system of reporting and evaluation. An economic analysis of briquetting has been beyond the scope of the present study. Such an analysis could throw more light on the potential competitiveness of briquetted biomass fuels as compared to internationally traded fossil fuels. This information is crucial for any strategic decision on large scale introduction of briquetted fuels. Of particular interest is the position in the Philippines, India, Sri Lanka and Nepal.
Note: The University of Twente has also produced a report 'Stoves for Biomass Briquettes' (40 pages) which will be summarized in our next edition.