BIO-MASS BRIQUETTES MANUFACTURING
INTRODUCTION & MARKET PROSPECTS OF BIOMASS BRIQUETTES
Biomass briquettes are manufactured mainly from agro residues. 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, coir pith, jute sticks, bagasse, groundnut shells, mustard stalks, and cotton stalks. Sawdust, a milling residue is also available in huge quantities. 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 conversion efficiencies are as low as 40% with particulate emissions in the flue gases in excess of 3000 mg/Nm³ In addition, a large percentage of un-burnt 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 tones of rice husk ash are generated every day in Ludhiana (Punjab) as a result of burning 2000 tones 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 have pursued and perfected the reciprocating ram/piston press while Japan has independently invented and developed the screw press technology.
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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 a 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.
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Biomass densification, which is also known as briquetting of sawdust and other agro residues, has been practiced for 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 the 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 differentiated from such processes as the ‘Presto-o-log’ technology of the United States, the ‘Glom era’ 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/cm³ from loose biomass of bulk density 0.1 to 0.2 g /cm³ These 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 midseventies. So far, these have mainly focused 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, dandified 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 dandified biomass industry in Indonesia, particularly where it is export-oriented, seem to be good. The Philippine 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 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.
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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 utilization. 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 Twenty, the Netherlands carried out research to adapt the 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.
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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.
POTENTIAL AGRO-RESIDUES AND THEIR CHARACTERISTICS
Potential Agri-residues FOR BIOMASS BRIQUETTES
The potential agro-residues which do not pose collection and drying problems, normally associated with biomass are rice husk, groundnut shells, coffee husk, and coir waste (obtained by the dry process). At present, loose rice husk, groundnut shells, and other agro-residues are being used mostly by small scale boilers in process industries. Apart from being inefficient, these boilers do not have provision to capture fly ash and un-burnt carbon, with the result that extensive air pollution is being created. In Ludhiana, one of the industrialized cities of Punjab (India), about 2,000 tones of rice husk is burnt every day.
This pollution problem has become so acute that the State Government of Punjab has banned the burning of loose husk in such boilers. It is very likely that other States in India will soon follow this policy. The users have been advised to use husk either as briquette fuel or in fluidized bed boilers with proper pollution control measures.
As the number of industries is growing day by day, the energy required is also increasing proportionately and the present power supply is unable to meet the energy demand. To combat this energy shortage, developed as well as developing countries are putting more efforts into R&D to tap alternative energy sources. State policies are also being formulated to encourage alternative sources of energy. In India alone, it is proposed that 17,000 MW should be produced from biomass. Although other options like gasification can be used for power generation, briquetting of biomass can be considered for its economics, reliability, and ease of operation. Briquettes of small size can be used in gasifiers for power generation. If the plant sites are chosen properly for easy availability of raw material, the agro-residues can be briquettes to reduce further transportation costs and associated pollution. This also improves the handling characteristics of biomass. The briquettes so obtained are very good fuels for local small scale industries and domestic purposes. The basic use can be to substitute wood and coal thereby conserving natural wealth.
Appropriate Biomass Residues for Briquetting.
There are many factors to consider before biomass qualifies for use as feedstock for briquetting. Apart from its availability in large quantities, it should have the following characteristics:
Low moisture content
Moisture content should be as low as possible, generally in the range of 10-15 percent. High moisture content will pose problems in grinding and excessive energy is required for drying.
Ash content and composition FOR BIOMASS BRIQUETTES
Biomass residues normally have much lower ash content (except for rice husk with 20% ash) but their ashes have a higher percentage of alkaline minerals, especially potash. These constituents have a tendency to volatilize during combustion and condense on tubes, especially those of superheaters. These constituents also lower the sintering temperature of ash, leading to ash deposition on the boiler’s exposed surfaces.
The ash content of different types of biomass is an indicator of the slugging behavior of the biomass. Generally, the greater the ash content, the greater the slugging behavior. But this does not mean that biomass with lower ash content will not show any slugging behavior. The temperature of operation, the mineral compositions of ash, and their percentage combined determine the slugging behavior. If conditions are favorable, then the degree of slugging will be greater. Minerals like SiO2 Na2O and K2O are more troublesome. Many authors have tried to determine the sagging temperature of ash but they have not been successful because of the complexity involved. Usually slagging takes place with biomass fuels containing more than 4% ash and non-slagging fuels with ash content less than 4%. According to the melting compositions, they can be termed as fuels with a severe or moderate degree of slagging.
Flow characteristics OF BIOMASS BRIQUETTES
The material should be granular and uniform so that it can flow easily in bunkers and storage silos. Some of the appropriate agro-residues are described below. Rice husk When compared to sawdust, agro residues have a higher ash content, higher potash content, and have poor flow characteristics. However, rice husk is exceptional biomass. It has good flowability, normally available with 10 percent moisture and the ash contains fewer alkaline minerals, thereby it has a high ash sintering temperature. In fact, it makes an excellent fuel although its calorific value is less than wood and other agro-residues. Other biomass materials. Groundnut shell: Because of low ash (2-3%) and moisture content of less than 10%, it is also an excellent material for briquetting. Cotton sticks: This material is required to be chopped and then stored in dry form. It has a tendency to degrade during storage. Also, it has a higher content of alkaline minerals and needs to be used with caution.
Bagasse/bagasse pith FOR BIOMASS BRIQUETTES
These residues have a high moisture content of 50% after milling, hence drying is energy-intensive. They have low ash content and a correspondingly high heating value of the order of 4400 kcal/kg. Pith is the small fibrous material that has to be removed from bagasse before bagasse is used as feedstock for making paper. Due to shortages of wood and increasing demand for paper and pulp, an ever-increasing number of paper units are switching over to bagasse as feed material. The amount of pith available is almost equal to the tonnage of paper produced by a paper mill. For example, a 60 TPD mill will generate 60 TPD of bagasse pith. This material does not require milling before it is briquetted. At present, this pith is available from sugar mills at much lower costs. This is a potential material for briquetting.
Excellent material for briquetting having low ash and available with 10 percent moisture content. The material is available in the coffee-growing areas of Karnataka and Kerala.
Like cotton sticks, it is also an appropriate material for briquetting.
Other potential biomass residues suitable for briquetting are lentil stalks, sawdust, lantana camera in hilly areas, tea wastes, and coir pith.
LOCATION OF THE UNIT FOR BIOMASS BRIQUETTES
The proposed unit be set up on such land that justifies the following basic considerations:-
- Availability of raw materials & consumables.
- Availability of Power, Fuel, Water.
- Banking facility.
- Marketing prospectus.
- Good communications.
- Labor facility.
RAW MATERIALS AND CONSUMABLES FOR BIOMASS BRIQUETTES
- All varieties of bio-agro waste.
- Packing bags.
ITEMS TO BE PRODUCED
- Biomass Briquettes.
– 12 MT briquettes per day of 8 hours running.
– 300 MT briquettes.
– 3600 MT paddy per annum.
WORKING HOURS FOR BIOMASS BRIQUETTES
- 8 hours per day.
- 25 days per month.
- 300 days per annum.
MANUFACTURING PROCESS OF BIOMASS BRIQUETTES
Manufacturing of bio-mass briquettes is mainly the high compaction to bind the agro and other waste materials together. High compaction technology or binder less technology consists of the piston press and the screw press. Most of the units currently installed in India are the reciprocating type where the biomass is pressed in a die by a reciprocating ram at very high pressure. In a screw extruder press, the biomass is extruded continuously by a screw through a heated taper die. In a piston press the wear of the contact parts e.g., the ram and die is less compared to the wear of the screw and die in a screw extruder press. The power consumption in the former is less than that of the latter. But in terms of briquette quality and production procedure screw press is definitely superior to the piston press technology. The central hole incorporated into the briquettes produced by a screw extruder helps to achieve a uniform and efficient combustion and, also, these briquettes can be carbonized.
The piston presses which are currently operating in India are also known as ram and die technology. In this case, the biomass is punched into a die by a reciprocating ram with a very high pressure thereby compressing the mass to obtain a briquette. The briquette produced is 60 mm in external diameter. This machine has a 700 kg/hr capacity and the power requirement is 25 kW. The ram moves approximately 270 times per minute in this process.
Depending upon the type of biomass, three processes are generally required involving the following steps.
- Sieving – Drying – Preheating – Densification – Cooling – Packing
- Sieving – Crushing – Preheating – Densification – Cooling – Packing
3. Drying – Crushing – Preheating – Densification – Cooling – Packing