Bangladesh is an agriculture based country where more than 65 percent of the people live in rural areas and over 70% of total primary energy consumption is covered by biomass, mainly agricultural waste and wood. Only about 6% of the entire population has access to natural gas, primarily in urban areas. Electricity production in Bangladesh largely depends on fossil fuel whose reserve is now under threat and the government is now focusing on the alternating sources to harness electricity to meet the continuous increasing demand. To reduce the dependency on fossil fuels, biomass to electricity could play a vital role in this regard. This paper explores the biomass based power generation potential of Bangladesh through gasification technology—an efficient thermochemical process for distributed power generation. It has been estimated that the total power generation from the agricultural residue is about 1178 MWe. Among them, the generation potential from rice husk, and bagasses is 1010 MWe, and 50 MWe, respectively. On the other hand, wheat straw, jute stalks, maize residues, lentil straw, and coconut shell are also the promising biomass resources for power generation which counted around 118 MWe. The forest residue and municipal solid waste could also contribute to the total power generation 250 MWe and 100 MWe, respectively.
Bangladesh is one of the world’s most densely (1142.29/km2 in 2010) populated nations with an area of 147,570 km2 and a population of about 150 million [
In Bangladesh, agricultural residues vastly meet the household energy demands in rural and semiurban areas. This is practiced mainly because of the fact that around 65 percent of our economic activities are based on agriculture. The rain fed ecosystem of Bangladesh produces huge amounts of biomass resources, for example, agriculture residues (crop/tree residue, rice husk, and jute stick), animal waste (cow dung and human excreta), wood/tree leaves, municipal waste, vegetation, sugarcane bagasse, water hyacinth, poultry droppings, garbage, and so forth. Due to the lack of electricity supply in rural areas, the rural population depends mainly on biomass as a source of energy. Only about 6% of the entire population has access to natural gas, primarily in urban areas. Biomass fuels, such as wood, cow dung, and agricultural residues, are collected mainly from the local environment and have become a traded commodity as cooking fuel. Most Bangladeshi households in rural areas (99%) as well as urban areas (66%) use biomass such as wood, cow dung, jute sticks, or other agricultural wastes for cooking and Table
Source of cooking fuels (in %).
Fuel type | 2011 | 2004 | 1991 |
---|---|---|---|
Wood | 34.80 | 31.76 | 44.27 |
Kerosene | 1.00 | 1.79 | 0.57 |
Gas/LPG | 12.60 | 9.09 | 2.36 |
Electricity | 0.40 | 0.76 | 0.88 |
Straw/leaf/dried cow dung | 51.20 | 55.91 | — |
Biogas | 0.10 | — | — |
Source of lights (in %).
Source | 2011 | 2004 | 1991 |
---|---|---|---|
Grid electricity | 56.60 | 39.77 | 14.37 |
Solar energy | 3.30 | — | — |
Kerosene | 39.50 | 59.93 | 84.73 |
Biogas | 0.10 | — | — |
Others | 0.50 | 0.31 | 0.89 |
Power generation in Bangladesh largely depends on natural gas considering its apparent huge availability. Maximum share of generated power comes from natural gas and the rest is from liquid fuel, coal, and hydropower. The present share of renewable energy is only 0.5% [
The biggest renewable energy program in Bangladesh is solar home system (SHS). In Bangladesh, SHS project has been implemented under Infrastructure Development Company Limited (IDCOL) and so far installed 900,000 units and still increasing due to an integrated program undertaken by the government through its financial institution, IDCOL. IDCOL’s program is considered as a successful model for installation of SHSs in the world. Till now, national capacity of renewable energy based power is approximately 50 MWe [
Total area of Bangladesh is about 147,570 km², where the total agricultural land is about 90500 km² which is 62.8% of the total area. Total arable land is 79700 km² which is 55.3% of the total area. Approximately 52.54% of the country’s land is used for agricultural practices and 17.50% for forest [
Table
Total residue production with percentage of fractions of some selected agricultural crops.
Crops | Production in 2011 (million tons) | Fractions | Amount of fractions | Crop residue (million tons) |
---|---|---|---|---|
Rice | 50.63 | Straw | 50.00 | 25.31 |
Husk | 20.00 | 10.13 | ||
Maize | 1.02 | Stalks | 200.00 | 2.04 |
Cobs | 30.00 | 0.31 | ||
Wheat | 0.97 | Straw | 65.00 | 0.63 |
Jute | 1.52 | Stalk | 58.84 | 0.90 |
Leaves | 13.91 | 0.21 | ||
Sugarcane (trimmed) | 4.67 | Bagasse | 36.00 | 1.68 |
Mustard | 0.23 | Straw | 75.00 | 0.17 |
Coconut | 0.08 | Husk | 31.00 | 0.024 |
Shell | 24.40 | 0.019 | ||
Lentil | 0.081 | Straw | 72.46 | 0.058 |
|
||||
Total residue production in 2011 (million tons) | 41.66 |
The energy content or caloric value of the husks varies somewhat with the crops variety, the amount of bran mixed with the husks, and the moisture content of the husks (usually 8 to 10%). According to the report, the energy in 3 kg of husk approximately equals that in 1 kg of fuel oil or 1.5 kg of coal [
Proximate and ultimate analysis of some selected agricultural residues [
Crops residue | Fixed carbon (%) | Volatile matter (%) | Ash |
C (%) | H (%) | O (%) | N (%) | S (%) | HHV MJ/kg |
---|---|---|---|---|---|---|---|---|---|
Rice straw | 14.01 | 61.2 | 20.49 | 39.99 | 3.94 | 30.26 | 0.79 | 0.2 | |
Rice husk | 16.22 | 63.52 | 20.26 | 38.83 | 4.75 | 35.47 | 0.52 | 0.05 | 15–17 |
Wheat straw | 19.80 | 71.30 | 8.90 | 43.20 | 5.00 | 39.40 | 0.61 | 0.11 | |
Maize stalks | 16.03 | 70.31 | 5.25 | 44.20 | 5.80 | 43.5 | 1.30 | 0.01 | 14.66 |
Maize cobs | 16.67 | 64.32 | 19.00 | 39.60 | 5.17 | 34.06 | 1.78 | 0.38 | 15.65 |
Jute stalk | 21.00 | 76.05 | 0.62 | 49.79 | 6.02 | 41.37 | 0.19 | 0.05 | 19.70 |
Sugarcane bagasse | 14.95 | 73.78 | 11.27 | 44.80 | 5.35 | 39.55 | 0.38 | 0.01 | 18.10 |
Mustard straw | 17.66 | 68.36 | 6.34 | 46.48 | 5.08 | 33.36 | 0.74 | 0.36 | |
Coconut shell | 22.01 | 71.84 | 0.47 | 49.41 | 6.20 | 37.29 | 0.28 | 0.75 | 20.58 |
Lentil straw | 24.00 | 72.00 | 4.00 | 46.60 | 5.60 | 42.80 | 0.70 | 0.01 | 15.20 |
The typical HHV of agricultural residue ranges between 15 MJ/kg and 17 MJ/kg [
According to Bangladesh Bureau of Statistics and Department of Forest, a total of 2.52 million hectares area which is nearly 17.4 percent of the land mass is forests, of which 1.52 million hectares are under direct control of the department. Homestead Trees supplies a significant amount of fuelwood which mainly consists of firewood, twigs, and leaves. The trees are supplied as timber to urban and semiurban areas sawmill and to wood processing industries. The data concerning wood residues from different types of timber logs, that is, sawlogs and veneer logs, plywood and split logs, pulpwood and particle board, and production of fuelwood in 2011, were gathered from Food and Agriculture Organization (FAO) FAOSTAT Statistics Database 2011 [
Forests products in Bangladesh.
Forest products | Production in 2011 |
---|---|
Sawlogs and veneer logs | 174000 m3 |
Plywood | 1000 m3 |
Sawnwood | 388000 m3 |
Wood fuel | 27286834 m3 |
Industrial roundwood | 282000 m3 |
Pulpwood round and splits | 18000 m3 |
Particle board | 2200 m3 |
Hardboard | 5100 m3 |
Wood charcoal | 326684 tons |
Paper and paperboard | 8000 tons |
Writing and printing paper | 30000 tons |
Fiber pulp | 18000 tons |
Newsprint | 20000 tones |
Municipal solid waste (MSW) is the heterogeneous composition of wastes that are organic and inorganic, rapidly and slowly biodegradable, fresh and putrescible, and hazardous and nonhazardous, generated in various sources in urban areas due to human activities [
MSW generation in six major districts of Bangladesh.
MSW generation | Dhaka | Chittagong | Khulna | Rajshahi | Barisal | Sylhet |
---|---|---|---|---|---|---|
Population (millions)4 | 11.9 | 7.5 | 2.3 | 2.6 | 2.3 | 3.4 |
MSW generation (tons/day) | 5770 | 2700 | 796 | 1042 | 748 | 1462 |
MSW generation rate (kg/capita/day) | 0.485 | 0.360 | 0.346 | 0.401 | 0.325 | 0.430 |
The major physical characteristics measured in waste are (1) density, (2) size distribution of components, and (3) moisture content. Other characteristics which may be used in making decision about solid waste management are (1) colour, (2) voids, (3) shape of components, (4) optical property, (5) magnetic properties, and (6) electric properties [
There are many bioenergy routes which can be used to convert raw biomass feedstock into a final energy product. Several conversion technologies have been developed that are adapted to the different physical nature and chemical composition of the feedstock and to the energy required (heat, power, and transport fuel) [ direct combustion of biomass; thermochemical processing to upgrade the biofuel: processes in this category include pyrolysis, gasification, and liquefaction; biological processing: natural processes such as anaerobic digestion and fermentation, encouraged by the provision of suitable conditions, again lead to a useful gaseous or liquid fuel.
Incineration is a common technique and the earliest one for producing heat and power from biomass. For a more energy efficient use of the biomass resource, modern, large-scale heat applications are often combined with electricity production in combined heat and power (CHP) systems. Cocombustion (also called cofiring) in coal-based power plants is the most cost-effective use of biomass for power generation. Dedicated biomass combustion plants are also in successful commercial operation and many are industrial or district heating CHP facilities. Plant efficiency is around 30% depending on plant size. This technology is used to dispose of large amounts of residues and wastes (e.g., bagasse). Using high-quality wood chips in modern CHP plants with maximum steam temperature of 540°C, electrical efficiency can reach 33-34% (LHV) and up to 40% if operated in electricity-only mode. Fossil energy consumed for biopower production using forestry and agriculture products can be as low as 2–5% of the final energy produced. Based on life-cycle assessment, net carbon emissions per unit of electricity are below 10% of the emissions from fossil fuel-based electricity. Incineration of biomass is a mature technology. During operation of biomass to energy, emission control is very important and its major effluents are flue gas, ash, and wastewater. Dioxins emission from biomass thermal treatment has been a major issue that concerns people. To secure dioxins emission, further treatment for flue gas can be applied with activated carbon injection before dust collection or SCR (catalyst) after dust collection. This recent development of the preventive technologies has made it possible to reduce the amount of dioxins to the level of public acceptance emissions of pollutants and dioxin can be effectively controlled, but in many countries, incinerators face public acceptance issues and are seen as competing with waste recycling [
In the absence of air, organic matter such as animal manures, organic wastes, and green energy crops (e.g., grass) can be converted by bacteria-induced fermentation into biogas (a 40–75% methane-rich gas with CO2 and a small amount of hydrogen sulphide and ammonia). Anaerobic digestion is also the basic process for landfill gas production from municipal green waste. It has significant potential, but it is characterised by relatively small plant size. Anaerobic digestion is increasingly used in small-size, rural, and off-grid applications at the domestic and farm-scale. In general, 50% of such gas can be recovered and used for power and heat generation. After purification and upgrading, biogas can be used in heat plants and stationary engines, fed into the natural gas grid, or used as a transport fuel (compressed natural gas). Large-size plants using MSW, agricultural wastes, and industrial organic wastes (large-scale codigestion) need 8000–9000 tons MSW per year per MW of installed capacity.
Pyrolysis is a thermochemical decomposition of organic material at elevated temperatures without the participation of oxygen. Conventional pyrolysis involves heating the original material in the near absence of air, typically at 300–500°C, until the volatile matter has been driven off. The residue is then the char more commonly known as charcoal, a fuel which has about twice the energy density of the original and burns at a much higher temperature. With more sophisticated pyrolysis techniques, the volatiles can be collected, and careful choice of the temperature at which the process takes place allows controlling their composition. The liquid products have potential as fuel oil but are contaminated with acids and must be treated before use. Fast pyrolysis of plant material, such as wood and nutshells, at temperatures of 800–900°C leaves as little as 10% of the material as solid char and converts 60% into a gas rich in hydrogen and carbon monoxide. At present, the preferred technology is fast or flash pyrolysis at high temperatures with very short residence time [
During a gasification process, biomass is directly converted to synthesis gas (syngas) in a gasifier under a controlled amount of air. Syngas can be used in internal combustion (IC) engine to produce power or in a cogeneration system to produce heat and electricity. Previously, Kapur et al. calculated the unit cost of electricity of using rice husk gasifier based power generation system and evaluated its financial feasibility with utility supplier and diesel generated electricity [
Biomass gasification is a multistep process. The chemistry of biomass gasification is similar to that of coal gasification in the sense that thermal decomposition of both solids occurs to yield a mixture of essentially the same gases [
The reaction mechanism of biomass gasification process [
Classification of biomass gasifiers based on the density factor (ratio of dense biomass phase to total reactor volume) is a simple and effective method of classification. In this way the gasifiers can be classified into (a) dense phase gasifiers and (b) lean phase gasifiers. In lean phase gasifiers, for example, fluidized bed, the biomass occupies very little reactor volume, that is, 0.05−0.2. Most of the gasifiers employed for decentralized applications in developing countries are dense phase reactors, mostly fixed bed reactors; they have typical density factor of 0.3−0.08 [
In this type of reactor, air is taken in at the bottom, and the gas leaves at the top. The biomass moves counter to the gas flow and passes successively through drying, pyrolization, reduction, and hearth zones. Gases follow a natural upward movement as the increasing temperature reduces their density. Updraft gasifier can be designed to work under a natural or forced draft. With this configuration, the air or oxidizing agent entering gets in contact with the chars creating the combustion zone. The gases coming out of the combustion zone have to pass through the layer of chars above them created by the heat of the combustion zone. Here, CO2 and H2O are reduced into CO and H2. The reduced gases still contain enough energy to pyrolyze the descending biomass along a range 200 to 500°C, thus creating the chars that feed the combustion zone. In a reaction chain, pyrolysis gases also have sufficient temperature to dry the wet biomass entering above them. However, during pyrolysis, chemicals, tars, and oils are released and they become part of the producer gases. This drawback restrains the application of the updraft gasifier, because these products released from pyrolysis would be detrimental in a heat engine; however, it could be used for heating applications [
In the downdraft gasifier, air enters at the middle level of the gasifier above the grate, and the resultant mixture of air and gas flows down into the gasifier reactor through the high temperature oxidation zone resulting in thermal cracking of volatiles resulting in a gas which has relatively lower tar content and is better suited for use in engines. This type of gasifier is cheap and easy to make. Such systems have shorter contact times and therefore are more responsive than updraught gasifiers to surge in gas demands that are experienced when fuelling engines [
Fluidized-bed gasification was initially developed to overcome operational problems of fixed bed gasification of fuels with high ash content but is suitable for large capacities (more than 10 MW) in general [
A 250 kW rice husk gasifier based power plant has been installed and commissioned in Kapasia, Bangladesh, in October 2007 (Figure
Plant technical details [
Parameters | Description |
---|---|
Gasifier type | Downdraft (250 kW) |
Rated gas flow | 625 Nm3/hr (up to total 250 kW capacity) |
Rated biomass consumption | Up to 300 kg/hr (for total 250 kW capacity) |
Gasification temperature | 1050°C–1100°C |
Gasification efficiency | Up to 75% |
Temperature of gas at gasifier outlet | 250 to 400°C |
Biomass feeding | Manual |
Desired operation | Continuous (minimum 300 days/yr) |
Typical auxiliary power consumption | Up to 11 kW |
Typical gas composition | CO-20.62%, H2-10.62%, CO2-13.61%, CH4-Up to 4%, N2-52.62% |
Gas purifications unit | Coarse filter, sawdust fine filters, fabric safety filter (5 micron particulate size), wet scrubbers |
Engine | 300 kW capacity dual fuel generator (producer gas to diesel ratio is 70 : 30) |
Rice husk fired 250 kW gasifier power plant at Kapasia, Bangladesh [
The choice of one type of gasifiers over another is dictated by fuel, its final available form, size, moisture content, and ash content. Fixed bed gasifiers are more suitable for small-scale power generation and industrial heating applications [
Downdraft gasifier system can be chosen for Bangladesh’s perspective due to its simplicity in construction and cost competitiveness. Downdraft gasifier produces very small amount of tar and with little treatment it can be used directly in the internal combustion engine. Also, the technologies of these systems are quite matured in the world. Based on the above comparative discussions, however, a downdraft gasifier is better than an updraft gasifier system in many aspects. This gasifier has some unique advantages like suitability to small- scale production (50–150 kW), minimum operating labor required, exhaust type (particularly % of tar content), and easy as well as less maintenance required.
The producer gas so obtained is a low calorific value gas with typical higher heating value in the range of 5.4–5.7 MJ/m3 [
The combustible producer gas from biomass gasification either can be used in a diesel engine together with a small fraction of diesel in dual fuel mode [
In recent years, biomass gasifiers have been used for electrification of remote villages. The size of such systems can vary from 10 kWe to 500 kWe. In India, several of the smaller size (10–20 kWe) biomass gasifier systems have been established under two government of India schemes called Remote Village Electrification (RVE) and Village Energy Security Programme (VESP) [
Amongst the bioenergy technologies, the biomass gasification option for meeting the rural electricity needs of domestic, irrigation, and rural small and cottage industrial as well as thermal activities is shown to have a large potential. Gasification is the technology capable of producing fuel gas from conversion of biomass, which can serve the need of energy in various forms. In recent years, biomass gasification technology seems to have given concerns around the world. It is an efficient way to utilize waste biomass and the gas produced from gasification can be used for generating electricity. Gasification produces less harmful exhaust as biomass is very low in sulfur, chlorine, or heavy metals, which are detrimental to the environment. The biggest advantage of gasification is the use of variety of feedstock and products, as the syngas can also be used for chemical industry along with power generation.
Being an agricultural country, Bangladesh has strong potential for power generation from agricultural residues. Bangladesh is among the top five rice producing countries in the world. Rice is the main crop of the country in terms of arable area and production. The production of rice husk and rice straw was 10.12 million tons and 25.31 million tons, respectively, in 2011 [
Bangladesh, having about 15 sugar mills, produces around 1.68 million tons of bagasse in 2011 which is sufficient to produce power. In the north-western region, which is starved for energy, the sugar mills would be a great energy resource. This is also an advantage as all the 15 sugar-producing units were installed in the region. The bagasse has the potential to produce power around 50 MWe which would be able to consume the mills itself and the rest of the power can be supplied to the nearby areas or to the national grid as well. Government of Bangladesh would need to amend energy policy so that the gasification plants can run to their full capacity and can sell the surplus electricity to the grid.
Wheat straw, jute stalks, maize residues, lentil straw, and coconut shell are also the promising biomass resources for power generation as well. Counting all the agricultural residues about 41.26 million tons as stated in Table
Bangladesh has very limited forest resources. Broadly speaking, Bangladesh’s forests can be divided into four types: (1) mangrove forests in the coastal delta, (2) hill forests in the interior, (3) sal (Shorea robusta) forests in smaller areas inland, and (4) social forests. The bioenergy potential from wood residues is not high but it has significant importance to different level of consumers in rural areas. Nevertheless, fuelwood is the major sources of supplying wood energy in the country. Most of the household uses fuelwood for cooking purposes in the rural areas. However, efficient use of forest residues could be a renewable source of energy in any given part of Bangladesh. Forest residue comprises small branches, leaves, corn stove, and so forth. Bangladesh has good potential of harvesting bioenergy from forest residues by setting up biomass gasifier in forest regions to produce power. On the basis of the forests residue available in Bangladesh and assuming that a small fraction (~30% availability) of residues is available from the forests, the possible power potential is about 250 MWe.
Main parameters determining the potential of energy recovery from wastes (including MSW) are quantity of waste and physical and chemical characteristics (quality) of the waste. The actual production of energy will depend upon specific treatment process in use, the selection of which is also significantly dependent upon the above two parameters. The important physical parameters requiring consideration include constituent’s size, density, and moisture content. Smaller size of the constituents helps in faster decomposition of the waste [
Biomass gasification can offer an attractive alternative renewable energy system especially in rural areas where biomass fuel is readily available. These resources could provide community based small-scale independent power plants. Rice husk and straw can be ranked the top of the available biomass types in Bangladesh and have power generation potential of around 1010 MWe. The power plant could be installed near the larger rice mills’ “cluster areas” in Dinajpur, Bogra, Naogaon, Chapainawabganj, and Ishwardi with the surplus rice husk. However, establishment of bagasse based power plants in sugar industries will lead to an enormous change in the sugar production and the rest of power will be supplied to national grid and to the local communities. However, other types of biomass such as rind of pulses saw dust should also be considered for gasification. Bangladesh has a significant potential form of power generation from biomass gasification and has estimated around 1500 MWe. Provision of government subsidies need to overcome the barriers for the installation of such gasification power plants. Government can seek funds from different foreign aids. Also carbon trade can be an option. Installation of biomass based power plants in rural areas will lead to an enormous change in the lifestyle of the local communities. Increased lighting would also indirectly help the community by increasing the business hours in the market area, improving health conditions, and encouraging new business developments.
Megawatt of electricity
Megawatt
Kilowatt
Kilowatt of electricity
Kilowatt hour
Kilograms of oil equivalent
Heavy fuel oil
Nongovernmental organizations
Metric tonne.
The authors declare that there is no conflict of interests regarding the publication of this paper.