Biomass Briquettes as Fuel

Although agricultural and forestry processing residues such as rice husk, rice straw, jute stick, sawdust, bagasse, and other residues account for a significant share in the total energy consumption in Bangladesh, the major limitation in utilizing them for energy is their low bulk densities and high moisture content. Biomass briquetting technology can transform these lose biomass into dry, solid briquettes of regular shape, usually cylindrical with a diameter of 5-10 cm, which can be easily stored and transported.

Use of briquettes as a substitute for firewood helps to reduce deforestation. It will also help the rural women who spend considerable time and energy collecting firewood. However, traditional Bangladesh stoves are not the best burners for briquettes. Improvements to stoves are also necessary for harnessing the full benefit of briquetting technology. Briquettes can also be easily substituted for coal or firewood in industrial burners and kilns.

Briquetting Technology in Bangladesh

Briquetting machines used in Bangladesh are practically all of heated-die screw-press type. This type of briquetting machines produce briquettes in a continuous fashion using an extruder and a barrel. The briquettes have a partly carbonized outer surface, and a hole at the center.

 At the onset of RETs in Asia program, Bangladesh and the other participating countries had only limited experience in briquetting technology. Briquetting activities of the program attempted to address the following needs:  

Development of improved biomass briquetting systems and briquette stoves appropriate for local raw material, conditions, and practices;

Local capacity building for designing, fabricating and maintaining biomass briquetting systems; and

Demonstration and dissemination of improved briquetting systems and stoves.

Heated-Die screw-Press Biomass Briquetting System

In heated-die screw-press briquetting machine, the raw material (e.g.: ricehusk) fed into the briquetting machine is forced by a screw through a heated die. The die is maintained at a temperature of about 300°C by an electrical coil heater fixed around it. The screw is driven by an electric motor.

The briquettes often get partially pyrolysed at the surface and cause a lot of smoking. The briquettes formed are of 50-100 mm in diameter, and have a central circular hole that facilitates better combustion The heated-die screw press briquetting process produces denser ana stronger briquettes compared to other methods.

The technology seems to offer an ideal business opportunity for small entrepreneurs in rural Bangladesh. However, electricity is required for running the motor and heating the die. The amount of electrical energy input is a concern, as electricity is expensive and scarce in Bangladesh. The short lifetime 01 screw is another worrying factor .

Technology Improvement through Adaptive Research

BIT -Khulna, the institution involved in briquetting research in Bangladesh initiated its activities with a countrywide survey on briquetting machines The survey found that there were about 900 briquetting machines in use 98% of which were manufactured in Bangladesh. Most of these were smal machines which can densify 75-120 kg of biomass per hour. They were operated with 15, 20 or 25 horsepower electric motors. The only ra", material used was rice husk. Major problems faced by local entrepreneurs were the short screw life and high specific electricity consumption. These machines cannot be used in areas without electricity supply. BIT gave higt" priority to research for addressing these problems.

Enhancing the Screw Life

Field surveys and laboratory tests indicated that screw life is as short as two hours in some cases. Worn out screws can be repaired by welding using filler metals and reused several times. Screw wear can be reduced by applying a hard-facing on the screw. BIT carried out extensive work on the selection of filler material and hard-facing alloys by carefully testing a large number of screws. Many other local institutions such as Metallurgical Department of Bangladesh University of Engineering Technology, surface- hardening section of Bangladesh Industrial Technical Assistance Center, and private companies such as Jameer Engineering Industries Limited were associated with this work. As a result of these efforts, the life of screw could be extended from 2-3 hours oer run to 22 hours.

Improved Low-Cost Briquetting Machines

Initial survey showed that the average cost of a briquetting machine was about US$ 2500, which is quite high for small investors in Bangladesh. BIT's efforts in improving design and fabrication methods have brought down the cost of briquetting machine of similar production capacity to about US$ 800. In addition to cost reductions, BIT also developed anew mechanism for changing the worn out screws in a shorter time, thus reducing the machine downtime during screw replacement significantly. A smoke removal system was also tried out with limited success.

Reducing Electrical Energy Consumption

Heating loose biomass before feeding into the briquetting machine reduces the power required for the motor, and gives an added benefit of longer screw life. Research at AIT has shown that preheating can save up to 10% of the total electrical energy required for briquetting ricehusk in conventional electric motor-driven briquetting machines. BIT developed prototypes of two different raw material pre-heaters, which used biomass briquettes as fuel. BIT also developed several models of briquette and kerosene stoves to heat the die. to replace electrical coil heaters. ,

Another development very relevant to Bangladesh was a briquetting machine that can be run without electricity, using alternate means. In this machine, the electrical motor was replaced with a diesel engine, and the electrical coil heaters were replaced with kerosene stoves. The machine is attractive even at locations where electricity is available: the cost of fuel for  running the engine (diesel) is only 50% of the cost of electricity  required for the motor, and the cost of fuel used for the die heating stove (kerosene) is only 33% of that consumed by the electrical heater.

Alternate Raw Materials

Almost all briquetting machines operating in Bangladesh use rice huskas raw material. Availability of new potential raw materials such as wheat husk and wheat straw were discovered during the survey. BIT experimented with different raw materials such as bagasse, wheat husk, rice straw and sawdust and studied variations necessary in the screw design for using these raw materials. However, rice husk was found to be the best raw material, while a combination of rice husk and rice straw or wheat straw could also be used successfully with the existing designs of briquetting machines, screws and dies.

Stoves for Biomass Briquettes

Biomass briquettes have different density and combustion characteristics compared to other biomass fuels such as wood. Therefore, it is essential to develop suitable low-cost briquette stoves to popularize biomass briquettes as a domestic fuel. Under RETs in Asia, BIT developed five different briquette-fired stoves for domestic use and tested them for their efficiency and user acceptance. Over 400 of these stoves were distributed to a local village community with whom the stoves became very popular. In addition, BIT carried out research on a gasifier-stove design (which is more efficient and less polluting) developed by AIT.

Capacity Building, Technology Transfer and Training

Junior researchers of BIT participated in several academic and training programmes on renewable energy in general, and briquetting technology in particular, at Air, which possesses considerable expertise in the fields. The knowledge thus gained was used by BIT in the development of improved biomass briquetting systems and efficient briquette-fueled stoves. Experimental results and design details were also shared between Air, BIT and other institutions participating in the programme. A biomass briquetting laboratory with fabricating and testing facilities was established at BIT. RETs in Asia helped BIT to achieve significant expertise in the area within the short span of five-years.

Training programmes and workshops were conducted as part of the capacity building and technology transfer activities. BIT organised a regional training program on fabricating briquetting systems for researchers from Vietnam and Nepal. Later, in a reciprocating visit to Vietnam, researchers from Bangladesh learned about an improved briquetting machine and anew screw fabrication method developed at the Institute of Energy, Vietnam, which is another NRI participating in RETs in Asia. The above training programs point to the clear benefits of south-south collaboration in capacity building and technology transfer.

BIT also developed a month-long intensive training program on briquetting technology for locals. BIT organised three such training programs where 68 local technicians were trained in fabricating, operating and repairing of briquetting systems.

Under the special student program, two researchers from BIT got the opportunity of studying at AIT, where they followed advanced courses in biomass energy and participated in briquetting research. BIT also participated in the RETs in Asia Annual Progress Review Workshops held at AIT, which provided an opportunity for networking with other national research institutes, exchange of experiences and discussion of problems encountered.

Dissemination and Demonstration

BIT organized a series of events such as seminars, workshops and exhibitions with the aim of disseminating the improved biomass briquetting technology . Several national workshops with more technical contents were  organized, targeting the participants such as briquetting machine owners and operators, technicians, and teachers of engineering institutes. Other dissemination activities such as demonstration of briquetting machines and distribution of improved biomass briquette-fired stoves were also car(ied out concurrent with these workshops.  

Briquetting Technology Dissemination Activities in Bangladesh   

Briquette stoves disseminated in a local workshop

Several demonstration biomass briquetting systems were set up at BIT briquetting laboratory. Briquetting machine owners, operators and potential investors were encouraged to visit BIT laboratory and examine these systems. Several other means of information dissemination such as distribution of brochures, calendars, diaries, and other information materials were undertaken on a regular basis to increase the awareness of this technology among the potential entrepreneurs and briquette users.