Electrification Through Biogas
Abdullah Al-muyeed and A. M. Shadullah argue the case for boigas
Bangladesh still remains an agrarian country. Because of increasing population growth, the amount of per capita cultivable land is dwindling very fast. In order to survive as a nation, and to prosper in the 21st century, Bangladesh will have to shift from an agrarian economy to an industrial one. Consequently, power generation will have to increase substantially to achieve that goal and measures to achieve country-wide transmission coverage should be initiated on a priority basis. Electricity is an essential pre-requisite for technological progress and economic growth. Bangladesh has been facing a severe power crisis for about a decade. Currently, power generation in the country is almost entirely dependent on natural gas (i.e. 84.5% of total electricity generation installed capacity). At the current 10% annual rate of growth of consumption, the proven reserve of natural gas may not last more than the next 10-15 years. Electrification of villages in remote areas usually requires large investment and leads to power losses associated with transmission and distribution networks.
One of the great promises of renewable energy technologies is the potential to provide electricity in areas not served by national power grids. The Renewable Energy Policy of Bangladesh, published in 2008, stated that renewable energy could play a vital role for off-grid electrification in the country. The main renewable energy resources in Bangladesh are biomass, solar, wind and hydropower. The hydropower potential of Bangladesh is limited due to the relatively flat topography of the country. Most of the potential sites for wind power utilisation are situated in the coastal regions. Wind power generation in Bangladesh has certain limitations due to the lack of reliable wind speed data and the remarkable seasonal variation of wind speed. Another potential source is solar energy (utilising solar photovoltaic (PV) systems) but the high capital investment cost of solar PV is a big barrier. Biomass is the major energy source in Bangladesh and biomass utilisation systems represent a proven option for small to medium- scale decentralised electricity generation.
Bangladesh's per capita energy consumption is very low, the lowest within the Indian subcontinent. The 2008 energy consumption value stands at about 250 kgOE which is quite low compared to 550 kgOE for India, 515 kgOE for Pakistan, 430 kgOE for Sri Lanka, 475 kgOE (average) for South Asia and far below the world average of 1680 kgOE. Total primary energy consumption in 2008 was 33.50 MTOE and the energy consumption mix was estimated as: indigenous biomass 62%, indigenous natural gas 25%, imported oil 12% and imported coal and hydro combined about 1%. Two-thirds of the country's total population livel in rural areas, meeting most of their energy needs (domestic, commercial and industrial) from traditional biomass fuels. Various marketing companies under the Bangladesh Petroleum Corporation (BPC) distribute kerosene and diesel throughout the country at a uniform tariff rate set by the government. Around 32% have access to electricity, while in rural areas the availability of electricity is only 22%.
But the quality of service in rural areas is very poor: frequent outages, voltage fluctuations and unreliable and erratic supply. Only 34% of the households have natural gas connection for cooking purposes. Only about 23% households use kerosene for cooking and the rest (over 90%) depend on biomass. Contribution of biomass in total primary energy consumption of Bangladesh is around 60%. The major sources of traditional biomass are agricultural residues (45%), wood and wood wastes (35%) and animal dung (20%). Industrial and commercial use of biomass accounts for 14% of total energy consumption. 63% of energy required in the industrial sector comes from biomass fuel.
Primarily biomass and kerosene are used by a majority of households. Natural gas, liquefied petroleum gas (LPG), electricity, kerosene and biomass fuels are mainly used for cooking. In areas without natural gas and electricity, biomass is used to meet household cooking needs. A good amount of bio energy is used for parboiling and space heating. A recent urban household survey estimated that consumption of biomass fuel is 319 kg per capita per year. Natural gas is currently the only indigenous non-renewable energy resource of the country and this has been continuously produced and consumed in significant quantities since 1970. Gas, the main source of commercial energy, plays a vital role in the economic growth of Bangladesh. The major consumers of gas are the power and fertiliser (using gas as feedstock) sectors, which account for 46.65% and 21.71% respectively. The cumulative efforts for exploration of oil and gas resources in Bangladesh have resulted in the discovery of 22 gas fields of various sizes. According to the 2008 BP Statistical Energy Survey, Bangladesh had, in 2007, proven natural gas reserves of 0.39 trillion cubic meters (0.21% of the world total) with production for the year totaling 16.27 billion cubic meters (0.55% of the world total). Although the remaining recoverable gas reserve is enough for the time being, it is understood that there is significant field growth potential, as most of the state-owned gas fields have not yet been fully appraised. Therefore, among the various renewable energy options, biomass energy might be the best choice for the electrification of rural Bangladesh.
The economy of Bangladesh depends principally on agriculture. The main crops produced are rice, sugar cane, vegetables, wheat, jute, pulses, coconuts, maize, millet, cotton and groundnuts. Agricultural crops generate large quantities of residues. Such residues represent an important source of energy both for domestic and industrial use. Other sources of biomass are farm-animal wastes and poultry droppings, fire-wood, tree residues and saw dust from the forestry industry. The 138.1 million citizens of Bangladesh produce huge amounts of human waste and municipal solid waste (MSW) annually.
Agricultural residues: There are two types of agricultural crop residues: field residues and processing residues. Studies in some neighbouring Asian countries produced useful residue-to-yield ratios for several agricultural crops. Crop residues can be collected, mostly by bailing, either at the same time or after the primary crop has been harvested. Not all field residues are recoverable. The percentage of field residues of a crop to be recycled onto the land depends upon the specific local climatic and soil conditions. No specific data is available concerning the common practices in Bangladesh or the neighbouring Asian countries. However, in developed countries, it has been established that only about 35% of field crop residues can be removed without adverse effects on future yields. Crop processing residues, on the other hand, have a 100% recovery factor. Accordingly, it is estimated that the total annual amount of recoverable agricultural-crop residues in Bangladesh is about 42 MT of which 63% are field residues and 37% are process residues.
Animal wastes and poultry droppings: Manure from cattle, goats, buffaloes and sheep are the common animal wastes in Bangladesh. The quantity of waste produced per animal per day varies depending on body size, type of feed and level of nutrition. The average amount of droppings (on air dry basis) produced by broilers and layers are 0.02 and 0.03 kg/bird/day respectively. The recovery/collection factors for animal waste and poultry droppings were reported in several studies to be 60% and 50% respectively. Accordingly, it is estimated that the total annual amount of recoverable animal wastes and poultry droppings in Bangladesh is 20.619 MT.
Human waste and MSW: The total quantity of human waste generated in Bangladesh has been estimated as 4.537 MT of dry matter/year (corresponding to 0.09 kg/capita/day). The rate of generation of MSW in the urban areas of Bangladesh is 0.4 kg/capita/day whereas the rate varies between 0.4 to 0.5 in Indian cities. In rural areas of Bangladesh, the generation rate is only 0.15 kg/capita/day. Considering that human waste and MSW are 100% recoverable, the total annual amount of the biomass available from these two sources in Bangladesh is 14.793 MT.
Forests and wood-processing industry: Forest biomass includes tree components such as trunks, branches, foliage and roots. Tree trunks and main branches are the sources of fuel wood. Twigs, leaves, bark and roots are tree residues. Total fuel wood production in Bangladesh in 2003 was 6.932 MT. Both wood processing residues (e.g. sawmill off-cuts and sawdust) and recycled wood (derived from the demolition of buildings, pallets and packing crates) are important sources of energy. The annual availability of such recycled wood, on a sustainable basis, is, however, not known. It has been estimated that only about 20% of a tree, initially harvested for timber, is recoverable for use in furniture and fittings. The remaining 80% is discarded, in equal proportions, as forest residues and process residues (i.e. bark, slabs, sawdust, trimmings and planer shavings). Plywood mills produce about the same amount of residues as sawmills. In 2004, 0.123 MT of sawdust was available for energy purposes. Considering 100% recovery rate, the annual amount of recoverable biomass from forests and forestry industry in Bangladesh is 8.871 MT.
Availability of biomass for electricit generation
The total annual generation and recoverable amounts of biomass in Bangladesh are about 165 and 9 MT/year respectively. Agricultural residues represent 48% of the total recoverable biomass followed by 23.9% from animal wastes and poultry droppings. In 2006, the biomass consumption for energy in Bangladesh was about 350 pico-Joules (PJ). At an average annual growth rate of 1.3%, the consumption in 2010 will be about 370 PJ. The total recoverable biomass energy of the country in 2006 was about 1250 PJ from which about 820 PJ of biomass energy was available for electricity generation. On the other hand, the total biomass energy consumption in 2006 was about 473 PJ. Assuming the same average annual growth rate of 1.3%, the biomass consumption in 2010 will be about 286 PJ. Therefore, the amount of biomass energy available in 2006 was 777 PJ, which is equivalent to 216 terawatt-hours (TWh). According to these two estimates and considering that the consumption of biomass for non-energy purposes is negligible, the annual available biomass energy potential for electricity generation in Bangladesh is in the range of 216- 250 TWh.
Data regarding availability of biomass resources in individual districts is needed for planning off-grid decentralised sustainable biomass electricity generation in Bangladesh. In many developing countries, the efficiency of utilisation of biomass in traditional systems is very low. A large amount of biomass can be saved annually in Bangladesh by employing improved (i.e. more efficient) cooking stoves, furnaces, boilers and other devices consuming biomass fuels. Overall efficiencies of the traditional mud cooking stoves used in Bangladesh vary from 5% to 10%. A number of improved stoves have been developed by the Bangladesh Council of Scientific and Industrial Research (BCSIR). These have been classified as:
-improved stoves without chimney which consume 50-55% less fuel than traditional stoves;
-stoves with chimney with fuel savings of 60-65%; and
-stoves with waste heat recovery system.
The Institute for Fuel Research and Development (IFRD) has been engaged in a pilot-scale dissemination of improved model biomass-fired stoves, capable of saving 50-70% of fuel compared with traditional stoves, all over the country. These improved stoves are gradually gaining popularity. Biomass briquettes have the advantages of easy transportation, better handling, cleaner and more efficient combustion and higher volumetric calorific value of the fuel. It also produces a fuel that is suitable for a variety of applications. Briquetting of sawdust and other agro residues has been practiced for many years in several countries. Briquettes can be produced with a density of 12001400 kg/m3 whereas the corresponding value for common wood is 500-700 kg/m3. Accordingly, savings of diesel fuel during the transportation of residues or wood are substantial: a 10 ton truck can transport 34 times more weight of briquette than loose biomass fuel. There are two types of machines used for briquetting the biomass: piston presses (also known as die and punch machines) and screw extruders. The screw extruder technology has proved successful in briquetting rice husk and saw dust in Europe, Japan, Malaysia, Taiwan and Thailand. The machines operating in Bangladesh are of heated-die type and there are currently 906 of these machines in operation.
Prospects of utilising biogas for electrification
Biogas has huge potential for electricity generation in Bangladesh provided proper research is carried out in this field. According to Infrastructure Development Company Limited (IDCOL) sources, Bangladesh has 215,000 poultry farms and 15,000 cattle farms where electricity could be generated by establishing biogas plants. So far, 35,000 biogas plants have been established for the production of gas for cooking purposes in the rural areas. IDCOL has set a target of establishing 60,000 biogas plants by 2012, each of which could produce, on average, 94.22 square feet of gas. At present, 3.3 million square feet biogas is being produced in the country daily. If this generated gas can be utilised properly, about 1,000MW electricity could be generated which could be used for the electrification of rural areas. This would go a long way in solving the problem of electricity shortage in this power-starved country of ours.
Different implementing agencies in Bangladesh, which are active in promoting biogasification technology, are not paying sufficient attention to effective and focused group-collaborative R&D aimed at renovating, optimising and improving the design for adaptation to local conditions. Limited R&D facilities and capabilities and lack of co-ordination among the researchers and implementing authorities may well pose a major stumbling-block towards the success of this endeavor. Moreover, the follow-up action program is also very limited. Sometimes, the plant-owners do not get proper technical guidance for the operation and maintenance of their plants.
Thus, the successful application and extension of this option depends on:
-institutional measures and close collaboration between sectors involved. This should include, among others, provision for soft loans and/or subsidy;
-availability of standard prototype for design and construction and site-specific maintenance guidelines;
-meaningful public involvement which should aim at passing relevant information of this technology to the community to increase awareness and promote acceptability of this technology; and,
-accurate calculation of the benefits of this technology.
Dr. Abdullah Al-Muyeed and Dr. A. M. Shadullah are faculty members of the Civil and Environmental Engineering Departments of Ahsanullah University of Science and Technology.