Biomass energy: Sustainable solution for greenhouse gas emission

Biomass energy: Sustainable solution for greenhouse gas emission A. K. M. Sadrul Islam and M. Ahiduzzaman Citation: AIP Conf. Proc. 1440, 23 (2012); doi: 10.1063/1.4704200 View online: http://dx.doi.org/10.1063/1.4704200 View Table of Contents: http://proceedings.aip.org/dbt/dbt.jsp?key=apcpcs&volume=1440&issue=1 Published by the American Institute of Physics. Additional information on AIP Conf. Proc. Journal Homepage: http://proceedings.aip.org/ Journal Information: http://proceedings.aip.org/about/about_the_proceedings Top downloads: http://proceedings.aip.org/dbt/most_downloaded.jsp?key=apcpcs Information for Authors: http://proceedings.aip.org/authors/information_for_authors

Biomass Energy: Sustainable Solution for Greenhouse Gas Emission A.K.M. Sadrul Islam a* and M. Ahiduzzaman b ab Mechanical & Chemical Engineering Department, Islamic University of Technology, Board Bazar, Gazipur-1704, Bangladesh * Corresponding Author: Email- sadrul05@gmail.com Abstract. Biomass is part of the carbon cycle. Carbon dioxide is produced after combustion of biomass. Over a relatively short timescale, carbon dioxide is renewed from atmosphere during next generation of new growth of green vegetation. Contribution of renewable energy including hydropower, solar, biomass and biofuel in total primary energy consumption in world is about 19%. Traditional biomass alone contributes about 13% of total primary energy consumption in the world. The number of traditional biomass energy users expected to rise from 2.5 billion in 2004 to 2.6 billion in 2015 and to 2.7 billion in 2030 for cooking in developing countries. Residential biomass demand in developing countries is projected to rise from 771 Mtoe in 2004 to 818 Mtoe in 2030. The main sources of biomass are wood residues, bagasse, rice husk, agro-residues, animal manure, municipal and industrial waste etc. Dedicated energy crops such as short-rotation coppice, grasses, sugar crops, starch crops and oil crops are gaining importance and market share as source of biomass energy. Global trade in biomass feedstocks and processed bioenergy carriers are growing rapidly. There are some drawbacks of biomass energy utilization compared to fossil fuels viz: heterogeneous and uneven composition, lower calorific value and quality deterioration due to uncontrolled biodegradation. Loose biomass also is not viable for transportation. Pelletization, briquetting, liquefaction and gasification of biomass energy are some options to solve these problems. Wood fuel production is very much steady and little bit increase in trend, however, the forest land is decreasing, means the deforestation is progressive. There is a big challenge for sustainability of biomass resource and environment. Biomass energy can be used to reduce greenhouse emissions. Woody biomass such as briquette and pellet from un-organized biomass waste and residues could be used for alternative to wood fuel, as a result, forest will be saved and sustainable carbon sink will be developed. Clean energy production from biomass (such as ethanol, biodiesel, producer gas, bio-methane) could be viable option to reduce fossil fuel consumption. Electricity generation from biomass is increasing throughout the world. Co-firing of biomass with coal and biomass combustion in power plant and CHP would be a viable option for clean energy development. Biomass can produce less emission in the range of 14% to 90% compared to emission from fossil for electricity generation. Therefore, biomass could play a vital role for generation of clean energy by reducing fossil energy to reduce greenhouse gas emissions. The main barriers to expansion of power generation from biomass are cost, low conversion efficiency and availability of feedstock. Internationalization of external cost in power generation and effective policies to improve energy security and carbon dioxide reduction is important to boost up the bio-power. In the long run, bio-power will depend on technological development and on competition for feedstock with food production and arable land use. Keywords: Biomass energy, agro-waste and residues, energy crops, biomass conversion, bio-power, carbon cycle, greenhouse gas emission. PACS: 88.20.-j;88.05.Np INTRODUCTION Energy consumption varies dramatically in different parts of the world. World average annual per-capita consumption of modern energy is 1,519 kilograms of oil equivalent (kgoe).while the average per capita energy consumption in high-income countries is 5,228 kgoe, in low-income countries it is only 250 kgoe [1, 2]. Traditional biomass is the only source of energy for the people of low income countries. The biomass includes fuel wood, crop residues, and animal wastes [3]. However, world energy demand is increasing due to the rapid economic development of the developing countries. Fossil fuel is used to meet the energy demand for such development. Due to use of fossil fuel green house gas emissions are rising rapidly. The supply of sustainable energy is one of the main challenges that mankind will face over the coming decades, particularly because of the need to address climate change. Biomass can make a substantial contribution to supplying future energy demand in a sustainable way [4]. It is presently the largest global contributor of renewable energy, and has significant potential to expand in the production of heat, electricity, and fuels for transport. Biomass is The 4th International Meeting of Advances in Thermofluids (IMAT 2011) AIP Conf. Proc. 1440, 23-32 (2012); doi: 10.1063/1.4704200 2012 American Institute of Physics 978-0-7354-1032-9/$30.00 23

produced by capturing carbon dioxide from air by plant during photosynthesis process. By combustion process of biomass the carbon dioxide is released into air that can be captured by the plant during next growing season. Therefore, biomass can be renewed after combustion within a very short time scale. If carefully managed, the bioenergy could provide an even larger contribution to global primary energy supply, significant reductions in greenhouse gas emissions and potentially other environmental benefits. Bioenergy could provide opportunities for economic and social development in rural areas. Moreover, there is scope for using wastes and residues, reducing waste disposal problems and making better use of resources. Biomass, derived from forestry, agricultural, and municipal residues as well as from a small share of crops grown specifically as fuel, is available as straw or wood chips, vegetable oils and animal slurries that can be converted to biogas. It is commonly used to generate both power and heat, generally through combustion, and some biomass can be converted to biofuels for transport. Biogas, a byproduct of fermenting solid and liquid biomass, can be converted by a combustion engine to heat and power. Recent increases in biomass use for power production have been seen in a number of European countries and in some developing countries. Global Bioenergy Scenario At present, the main biomass feedstocks are forestry, agricultural and municipal residues and wastes for the generation of electricity and heat. In addition, liquid biofuels are produced from a very small shares of sugar, grain, and vegetable oil crops. The share of renewable energy in global final energy comsumption is 19 percent [5] (Fig. 1). This renewable energy includes traditional biomass, large hydropower, and new renewables (small hydro, modern biomass, wind, solar, geothermal, and biofuels). Of this 19 percent, traditional biomass, used primarily for cooking and heating, accounts for approximately 13 percent and is growing slowly or even declining in some regions as biomass is used more efficiently or is replaced by more modern energy forms. FIGURE 1. Renewable energy share of global final energy consumption in 2008 [5] The predominant use of fuel wood in non-commercial applications, in simple inefficient stoves for domestic heating and cooking in developing countries. This traditional use of biomass is expected to grow with increasing world population. Among the different source of biomass energy wood fuel contribute 67% of total biomass supply (Fig. 2). Wood fuel production is very much steady and little bit increase in trend, however, the forest land is decreasing, means the deforestation is progressive accounted 8.3 million hectare per year [6]. Woody biomass such as briquette and pellet from un-organized biomass waste and residues could be used for alternative to wood fuel, as a result, forest will be saved and sustainable carbon sink will be developed [7]. Clean energy production from biomass (such as ethanol, biodiesel, producer gas, bio-methane) could be another viable option to reduce fossil fuel consumption. There is significant scope to improve its efficiency and environmental performance and thereby help reduce biomass consumption and related impacts. The biomass supplies some 50 EJ globally, which represents 10% of global annual primary energy consumption. This is mostly traditional biomass used for cooking and heating [8,14]. There is significant potential to expand biomass use by tapping the large volumes of unused residues and wastes. The use of conventional crops for energy use can also be expanded, with careful consideration of land availability and food demand. In the medium term, lignocellulosic crops (both herbaceous and woody) could be produced on marginal, degraded and surplus agricultural lands and provide the bulk of the biomass resource. In the longer 24

term, aquatic biomass (algae) could also make a significant contribution. Based on this diverse range of feedstocks, the technical potential for biomass is estimated in the literature to be possibly as high as 1500 EJ/yr by 2050, although most biomass supply scenarios that take into account sustainability constraints indicate an annual potential of between 200 and 500 EJ/yr (excluding aquatic biomass). Forestry and agricultural residues and other organic wastes (including municipal solid waste) would provide between 50 and 150 EJ/yr, while the remainder would come from energy crops, surplus forest growth, and increased agricultural productivity [4]. FIGURE 2. Share of biomass sources in primary bioenergy mix [4,8] Without strong new policies to expand access to cleaner fuels and technologies, the number of people in developing countries relying on traditional biomass as their main fuel for cooking will continue to increase as the global population increases. According to the estimates of World Energy Outlook (WEO) [14] in the Reference Scenario, in which no new policies are introduced, the number rises from 2.5 billion in 2004 to 2.6 billion in 2015 and to 2.7 billion in 2030 (Table 1). Residential biomass demand in developing countries is projected to rise from 771 Mtoe in 2004 to 818 Mtoe in 2030. These projections take into account the fuel substitution and the market penetration of more efficient technologies that would occur as a result of rising percapita incomes, fuel availability and other factors. TABLE (1). People relying on traditional biomass (million) [14] Region Year 2004 2015 2030 Sub-Saharan Africa 575 627 720 North Africa 4 5 5 India 740 777 782 China 480 453 394 Indonesia 156 171 180 Rest of Asia 489 521 561 Brazil 23 26 27 Rest of Latin America 60 60 58 Total 2528 2640 2727 Biomass Power Around The World Existing global renewable power capacity reached an estimated 1,230 gigawatts (GW) in 2009. Renewable energy now comprises about a quarter of global power-generating capacity (estimated at 4,800 GW in 2009) and supplies some 18 percent of global electricity production. When large-scale hydropower is not included, renewables reached a total of 305 GW. Among all renewables, global wind power capacity increased the most in 2009, by 38 GW. Hydropower has been growing annually by about 30 GW in recent years, and solar PV 25

capacity increased by more than 7 GW in 2009. Share of biomass electricity is 52 GW in 2009 (Fig. 3 and Fig. 4). An estimated 52 GW of biomass power capacity was in place by the end of 2009. As of 2007, the United States accounted for more than 34 percent of electricity from solid biomass generated in Organization of Economic Cooperation and Development (OECD) countries, with a total of 42 Terawatt-hours (TWh). Japan was the OECD s second largest producer, at 16 TWh, and Germany ranked third, with 10 TWh [9]. Although the U.S. market is less developed than Europe s, by late 2009 some 80 operating biomass projects in 20 states provided approximately 8.5 GW of power capacity, making the United States the leading country for total capacity [10]. Many U.S. coal- and gas-fired power plants are undergoing partial or even full conversion to biomass by co-firing fuels in conventional power plants [11]. Germany and the United Kingdom also generate increasing amounts of electricity with solid biomass through co-firing, and the capacity of biomass-only plants is rising rapidly across Europe [12]. The region s gross electricity production from solid biomass has tripled since 2001 [13]. By early 2010, some 800 solid biomass power plants were operating in Europe burning wood, black liquor, or other biomass to generate electricity representing an estimated 7 GW of capacity. The largest scale and number of such plants are in the heavily wooded countries of Scandinavia, but Germany and Austria have also experienced significant growth in recent years. Most of this increase in biomass capacity has resulted from the development of combined heat-and-power (CHP) plants. Just over half of the electricity produced in the European Union from solid biomass in 2008 was generated in Germany, Finland, and Sweden. Biomass accounts for about 20 percent of Finland s electricity consumption, and Germany is Europe s top producer. Germany increased its generation of electricity with solid biomass 20-fold between 2002 and 2008, to 10 TWh, and had about 1,200 MW installed by the end of 2008. By early 2010, bioenergy accounted for 5.3 percent of Germany s electricity consumption, making it the country s second largest renewable generating source after wind power. Biomass power has also grown significantly in several developing countries, including Brazil, Costa Rica, India, Mexico, Tanzania, Thailand, and Uruguay. China s capacity rose 14 percent in 2009 to 3.2 GW, and the country plans to install up to 30 GW by 2020. India generated 1.9 TWh of electricity with solid biomass in 2008. By the end of 2009, it had installed 835 MW of solid biomass capacity fueled by agricultural residues (up about 130 MW in 2009) and more than 1.5 GW of bagasse cogeneration plants (up nearly 300 MW in 2009, including off-grid and distributed systems); it aimed for 1.7 GW of capacity by 2012. Brazil has over 4.8 GW of biomass cogeneration plants at sugar mills, which generated more than 14 TWh of electricity in 2009; nearly 6 TWh of this total was excess that was fed into the grid. FIGURE 3. Share of global electricity from renewable source in 2008 [5] The use of biogas to generate electricity is on the rise as well, with production increasing an estimated 7 percent during 2008. Biogas is used for electricity generation mainly in OECD countries, with some 30 TWh produced in the OECD in 2008. But a number of developing countries also produce electricity with biogas, including Thailand, which nearly doubled its capacity in 2009 to 51 MW, and Malaysia, which is also seeing significant biogas power expansion. Germany passed the United States in biogas-generated electricity in 2007 and remained the largest producer in 2009; it is also the world s largest generator of electricity from liquid biomass, at 2.9 TWh in 2007. The number of German biogas plants increased by 570 in 2009, to nearly 4,700, 26

and associated capacity rose by 280 MW to 1.7 GW; total domestic production was an estimated 9 12 TWh of electricity. In 2008, the most recent year for which data are available, the United States generated some 7 TWh with biogas, followed by the United Kingdom at 6 TWh and Italy at 2 TWh (Table 2). FIGURE 4. Capacity of world renewable electricity generation in 2009 [5] TABLE (2). Biomass power generation at different locations of the world [5] Type of biomass Electricity generation and capacity Year Country MW TWh Solid biomass 42 2007 USA Solid biomass 16 2007 Japan Solid biomass 10 2007 Germany Solid biomass 3200 2009 China Solid biomass 30000 by 2020 China Bagasse 1500 2009 India Bagasse 1700 by 2012 India Bagasse 4800 14 2009 Brazil Bagasse 30 2008 OECD countries Biogas 51 2009 Developing countries Biogas 280 12 2009 Germany Biogas 7 2008 USA Biogas 6 2008 UK Biogas 2 2008 Biomass Conversion Technologies The use of biomass to produce energy is becoming more and more frequent as it helps to achieve a sustainable environmental scenario. However the exploitation of this fuel source does have drawbacks that need to be solved. There are some drawbacks of biomass energy utilization compared to fossil fuels viz: heterogeneous and uneven composition, lower calorific value and quality deterioration due to biodegradation. Pelletization, briquetting, liquefaction and gasification of biomass energy are the few options to solve some of those problems. 27

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 service required (heat, power, transport fuel). Upgrading technologies for biomass feedstocks (e.g. pelletisation, torrefaction and pyrolysis) are being developed to convert bulky raw biomass into denser and more practical energy carriers for more efficient transport, storage and convenient use in subsequent conversion processes. The production of heat by the direct combustion of biomass is the leading bioenergy application throughout the world, and is often cost-competitive with fossil fuel alternatives. Technologies range from rudimentary stoves to sophisticated modern appliances. 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. Different technologies exist or are being developed to produce electricity from biomass. Co-combustion (also called co-firing) in coal-based power plants is the most cost-effective use of biomass for power generation. Dedicated biomass combustion plants, including municipal solid waste (MSW) combustion plants, are also in successful commercial operation and many are industrial or district heating CHP facilities. For sludges, liquids and wet organic materials, anaerobic digestion is currently the best-suited option for producing electricity and/or heat from biomass, although its economic case relies heavily on the availability of low-cost feedstock. All these technologies are well established and commercially available. At present, biomass co-firing in modern coal power plants with efficiencies up to 45% is the most costeffective biomass use for power generation. Due to feedstock availability issues, dedicated biomass plants for combined heat & power (CHP), are typically of smaller size and lower electrical efficiency compared to coal plants (30%-34% using dry biomass, and around 22% for municipal solid waste). In cogeneration mode the total efficiency may reach 85%-90%. Biomass integrated gasification in gas-turbine plants (BIG/GT) is not yet commercial, but integrated gasification combined cycles (IGCC) using black-liquor (a by-product from the pulp & paper industry) are already in use. Anaerobic digestion to produce biogas is expanding in small, off-grid applications. Bio-refineries may open the door to combined, cost-effective production of bio-chemicals, electricity and biofuels. There are few examples of commercial gasification plants, and the deployment of this technology is affected by its complexity and cost. In the longer term, if reliable and cost-effective operation can be more widely demonstrated, gasification promises greater efficiency, better economics at both small and large-scale and lower emissions compared with other biomass-based power generation options. Other technologies (such as Organic Rankine Cycle and Stirling engines) are currently in the demonstration stage and could prove economically viable in a range of small-scale applications, especially for CHP. In the transport sector, first-generation biofuels are widely deployed in several countries, mainly bioethanol from starch and sugar crops and biodiesel from oil crops and residual oils and fats. Production costs of current biofuels vary significantly depending on the feedstock used (and their volatile prices) and on the scale of the plant. The potential for further deploying these first generation technologies is high, subject to sustainable landuse criteria being met. First-generation biofuels face both social and environmental challenges, largely because they use food crops which could lead to food price increases and possibly indirect land-use change. While such risks can be mitigated by regulation and sustainability assurance and certification, technology development is also advancing for next generation processes that rely on non-food biomass (e.g. lignocellulosic feedstocks such as organic wastes, forestry residues, high-yielding woody or grass energy crops and algae). The use of these feedstocks for second-generation biofuel production would significantly decrease the potential pressure on land use, improve greenhouse gas emission reductions when compared to some first-generation biofuels, and result in lower environmental and social risk. Second-generation technologies, mainly using lignocellulosic feedstocks for the production of ethanol, synthetic diesel and aviation fuels, are still immature and need further development and investment to demonstrate reliable operation at commercial scale and to achieve cost reductions through scale-up and replication. The current level of activity in the area indicates that these routes are likely to become commercial over the next decade. Future generations of biofuels, such as oils produced from algae, are at the applied R&D stage, and require considerable development before they can become competitive contributors to the energy markets. 28

TABLE (3): Typical Costs of different Renewable Energy Technologies [5] Technology Typical Energy Costs (U.S. cents/kwh) Technology Typical Energy Costs (U.S. cents/kwh) Power Generation Large hydro Small hydro Biofuels On-shore wind 5 9 Rural Energy 3 5 Ethanol 30 50 cents/liter (sugar) 60 80(gasoline equivalent) 5 12 Biodiesel 40 80 cents/liter (diesel equivalent) Off shore wind 10 14 Mini-hydro 5 12 Biomass power 5 12 Micro-hydro 7 30 Geothermal power 4 7 Pico-hydro 20 40 Solar PV (module) Rooftop solar PV Utility-scale solar PV Concentrating solar thermal power (CSP) Hot Water/ Heating/Cooling Biomass heat 1 6 Biogas digester n/a 20 50 Biomass gasifier 8 12 15 30 Small wind turbine 15 25 14 18 Household wind turbine Village-scale minigrid Solar home system 15 35 25 100 40 60 Solar hot water/heating 2 20 (household) 1 15 (medium) Geothermal heating/cooling 0.5 2 Further development of bioenergy technologies is needed, mainly to improve the efficiency, reliability and sustainability of bioenergy chains. The use of domestic biomass resources can make a contribution to energy security, depending on which energy source it is replacing. Biomass imports from widely distributed international sources generally also contribute to the diversification of the energy mix. However, supply security can be affected by natural variations in biomass outputs and by supply-demand imbalances in the food and forest product sectors, potentially leading to shortages. Finally, the cost of different renewable energy technologies is given in Table 3 [5]. For electricity generation and heating the biomass is a very competitive source. The production of bioenergy can also result in other (positive and negative) environmental and socioeconomic effects. Most of the environmental effects are linked to biomass feedstock production, many of which can be mitigated through best practices and appropriate regulation. Technical solutions are available for mitigating most environmental impacts from bioenergy conversion facilities and their vehicle fleets such as city buses have historically been diesel powered but are very suitable for the introduction of new fuels, e.g. biogas or ethanol. 29

Environmental Issues: Global Carbon Emissions The history and projection of world energy-related carbon dioxide emissions are given in Table 4 [15]. It rises from 29.7 billion metric tons in 2007 to 33.8 billion metric tons in 2020 and 42.4 billion metric tons in 2035 an increase of 43 percent over the projection period. With strong economic growth and continued heavy reliance on fossil fuels expected for most non-oecd economies under current policies, much of the projected increase in carbon dioxide emissions occurs among the developing non-oecd nations. In 2007, non-oecd emissions exceeded OECD emissions by 17 percent; in 2035, they are projected to be double OECD emissions. A significant degree of uncertainty surrounds any long term projection of energy-related carbon dioxide emissions. Major sources of uncertainty include estimates of energy consumption in total and by fuel source. TABLE (4). World energy-related carbon dioxide emissions by region, 1990-2035 [15] (billion metric tons) History Projections Average annual percentage change Region 1990 2007 2015 2020 2025 2030 2035 1990-2007 2007-2035 OECD 11.5 13.7 13.0 13.1 13.5 13.8 14.2 1.0 0.1 North America 5.8 7.0 6.7 6.9 7.2 7.4 7.7 1.1 0.3 Europe 4.2 4.4 4.1 4.0 4.0 4.1 4.1 0.3-0.2 Asia 1.6 2.3 2.1 2.2 2.3 2.3 2.4 2.1 0.2 Non-OECD 10.0 16.0 18.5 20.7 23.0 25.5 28.2 2.8 2.0 Europe and Eurasia 4.2 2.9 2.9 2.9 3.0 3.0 3.2-2.2 0.3 Asia 3.7 9.4 11.2 13.0 14.9 16.9 19.0 5.7 2.5 Middle East 0.7 1.5 1.9 2.1 2.3 2.5 2.7 4.6 2.1 Africa 0.7 1.0 1.2 1.2 1.3 1.5 1.6 2.6 1.7 Central and South 0.7 1.2 1.3 1.4 1.5 1.6 1.7 3.1 1.4 America Total World 21.5 29.7 31.5 33.8 36.5 39.3 42.4 1.9 1.3 Reduction of Ghg Emission by Bioenergy Bioenergy cycles reduce the carbon emissions by replacing the fossil fuels energy. The reduction of carbon emissions depend on how efficient the generation technology is and how much fossil fuel is used to produce the biomass. Table 5 gives an approximate values for the carbon emissions of selected technologies [16]. Biomass sources produce much less emissions than fossil fuels. Among the vast area of biomass sources, a few are discussed below. TABLE (5). Approximate Carbon Emissions from Sample Biomass and Conventional Technologies [16] Fuel and Technology Generation Grams of CO 2 per kwh Efficiency diesel generator 20 % 1320 coal steam cycle 33% 1000 natural gas combined cycle 45% 410 biogas digester and diesel generator 18% 220 (with 15% diesel pilot fuel ) biomass steam cycle 22% 100 (biomass energy ratio*= 12) biomass gasifier and gas turbine (biomass energy ratio*= 12) 35% 60 *The energy of the biomass produced divided by the energy of the fossil fuel consumed to produce the biomass. Production of ethanol from sugar cane is energy-efficient since the crop produces high yields per hectare and the sugar is relatively easy to extract. If bagasse is used to provide the heat and power for the process, and 30

ethanol and biodiesel are used for crop production and transport, the fossil energy input needed for each ethanol energy unit can be very low compared with 60%-80% for ethanol from grains. As a consequence, ethanol wellto wheels CO 2 emissions can be as low as 0.2-0.3 kgco 2 /litre ethanol compared with 2.8 kg CO 2 /litre for conventional gasoline (90% reduction). Ethanol from sugar beet requires more energy input and provides 50%- 60% emission reduction compared with gasoline. Ethanol production from cereals and corn (maize) can be even more energy-intensive and debate exists on the net energy gain. Estimates, which are very sensitive to the process used, suggest that ethanol from maize may displace petroleum use by up to 95%, but total fossil energy input currently amounts to some 60%-80% of the energy contained in the final fuel (20% diesel fuel, the rest being coal and natural gas) and hence the CO 2 emissions reduction may be as low as 15%-25% vs. gasoline. Ethanol from ligno-cellulosic feedstock At present, the total energy input needed for the production process may be even higher as compared to bioethanol from corn, but in some cases most of such energy can be provided by the biomass feedstock itself. Net CO 2 emissions reduction from ligno-cellulosic ethanol can therefore be close to 70% vs. gasoline, and could approach 100% if electricity co-generation displaced gas or coal-fired electricity. Current R&D aims to exploit the large potential from improving efficiency in enzymatic hydrolysis. Energy input and overall emissions for biodiesel production also depend on feedstock and process. Typical values are fossil fuel inputs of 30% and CO 2 emission reductions of 40%-60% vs. diesel. Using recycled oils and animal fats reduces the CO 2 emissions. Municipal solid waste (MSW) also offers net reduction of CO 2 emissions. MSW can generate some 600 kwh of electricity per tonne and emit net 220-440 kg CO 2 from the combustion of the fossil-derived materials (20-40% of MSW). The CO 2 emitted to generate 600 kwh from coal would be some 590 kg. Methane emissions from MSW in modern landfills would be between 50-100 kg/t (equivalent to 1150-2300 kg CO 2 ), 50% of which is collected and 50% is released in the atmosphere. Thus, electricity production from MSW offers a net emission saving between 725 and 1520 kg CO 2 /t MSW. Saving is even higher for CHP. Rice husk, a milling by-product of rice, is used as a source of thermal energy to produce steam for parboiling of raw rice. The rice is mostly dried on a concrete floor under the sunshine. In mechanical drying, rice husks are used as a source of primary energy. In Bangladesh, the annual estimated energy used in 2000 for the drying of rice by sunshine was 10.7 million GJ and for drying and parboiling by rice husks it was 48.2 million GJ. These amounts will increase to 20.5 and 92.5 million GJ in 2030, respectively. Electrical energy consumption for mechanical drying and milling of rice was calculated as 1.83 million GJe and 3.51 million GJe in 2000 and in 2030, respectively. Biogenic carbon dioxide emission from burning of rice husk is renewed every year by the rice plant. Both the biogenic and non-biogenic carbon dioxide emissions in 2000 were calculated as 5.7 and 0.4 million tonnes, respectively, which will increase to 10.9 and 0.7 million tonnes in 2030. The demand of energy for rice processing increases every year, therefore, energy conservation in rice processing industries would be a viable option to reduce the intensity of energy by increasing the efficiency of rice processing systems which leads to a reduction in emissions and an increased supply of rice husk energy to other sectors as well [17]. The net GHG impact of various biofuels is given in Table 6 [18]. Cellulosic ethanol and sugarcane ethanol are more effective at displacing GHG emissions ( 90% reduction) than soy or rape biodiesel ( 50% reduction), which are in turn more effective at displacing GHG emissions than corn ethanol, which is itself only marginally lower in GHGemissions than gasoline (<20% reduction). TABLE (6). Estimates of net GHG reductions and land requirements for various biofuel options [18] GHG reductions relative to gasoline/ diesel vehicle Yield per hectare (liters fuel/ha) Hectares required to fuel one car (ha/car) Ethanol (corn) 14% 3463 1.1 Ethanol 88% 5135 0.7 (cellulosic) Ethanol 91% 6307 0.6 (sugarcane) Biodiesel (soya) 40% 5444 4.3 Biodiesel (rape) 50% 1200 2.0 31

Land suitable for producing biomass for energy can also be used for the creation of biospheric carbon sinks. Several factors determine the relative attractiveness of these two options, in particular land productivity, including co-products, and fossil fuel replacement efficiency. Also, possible direct and indirect emissions from converting land to another use can substantially reduce the climate benefit of both bioenergy and carbon sink projects, and need to be taken into careful consideration. A further influencing factor is the time scale that is used for the evaluation of the carbon reduction potential: a short time scale tends to favour the sink option, while a longer time scale offers larger savings as biomass production is not limited by saturation but can repeatedly (from harvest to harvest) deliver greenhouse gas emission reductions by substituting for fossil fuels. Mature forests that have ceased to serve as carbon sinks can in principle be managed in a conventional manner to produce timber and other forest products, offering a relatively low GHG reduction per hectare. Alternatively, they could be converted to higher yielding energy plantations (or to food production) but this would involve the release of at least part of the carbon store created. Conclusions The bioenergy plays a dominant role in the developing countries that needs to be modernized in terms of efficiency, emission and cost. The modern bioenergy has rapidly expanded over the past decade and is poised to become a major contributor to global commercial energy supplies. As with other potentially attractive renewable energy sources, biomass energy has a definite contribution to make a sustainable development especially in terms of GHG emission. The ability of this energy depends on how it is produced, converted, and used. Among the OECD (developed) countries Germany, UK, Japan, USA have emphasized on the use of bioenergy in place of fossil fuel and thus targeted to reduce GHG emission. Among the non-oecd counties notable initiative is taken by China, India, Brazil and Thailand. As of 2009, the biomass electricity generation was 52 GW among the total renewable energy power of 1,230 GW which is about 25% of global power generating capacity. The main barriers to widespread use of biomass for power generation are cost, low conversion efficiency and feedstock availability. Several bioenergy options have great potential in terms of reduction of GHG emission. Biofuel, MSW, rice husk, agro-residues etc can contribute in the commercial energy sector and thus reduce the GHG emission. REFERENCES 1. REN21 Energy for Development. The Potential Role of Renewable Energy in Meeting the Millennium Development Goals. 2010. 2. World Bank, The Little Green Data Book (Washington, DC: 2005). 3. Doug Barnes et al., The Urban Household Transition: Social and Environmental Impacts in the Developing World. (Washington, DC: Resources for the Future (RFF), 2005), pp. 58-61. 4. World Energy Council. 2010 Survey of Energy Resources. Regency House 1-4 Warwick Street, London W1B 5LT United Kingdom. 5. REN21. Renewable Energy Policy Network for 21 st Century. Renewable 2010 Global Status Report. 6. FAOSTAT 2009. www.fao.org. 7. A.K.M. Sadrul Islam and M. Ahiduzzaman, Rational Use of Waste Biomass Energy: Potential of Carbon Sink Development, Keynote paper presented in the Conference on Engineering Research, Innovation and Education 2011, Jan 11-13, 2011, Sylhet, Bangladesh. 8. IPCC, 2007. Mitigation of Climate Change, Working Group III, Chapter 4 of the 4th Assessment Report. 9. IEA, Development of Renewables and Waste in OECD Countries, in Renewables Information, op. cit. note 42. 10. Lee Clair, Biomass An Emerging Fuel for Power Generation, Renewable Energy World North America Magazine, January/February 2010. 11. Ron Pernick, C. Wilder, D. Gauntlett and T Winnie, Clean Energy Trends 2010 (San Francisco/Portland: Clean Edge, March 2010), p. 12. 12. Uwe Fritsche, Öko-Institut, Germany, REN21, March 2010. 13. EurObserv ER, Solid Biomass Barometer, December 2009, p. 9. 14. World Energy Outlook (WEO) 2006. 15. International Energy Outlook 2010. U.S. Energy Information Administration, Office of Integrated Analysis and Forecasting, U.S. Department of Energy, Washington, DC 20585. 16. Sivan Kartha and E.D. Larson, Bioenergy Primer: Modernised Biomass Energy for Sustainable Development, UNDP,2000. 17. Mohammed Ahiduzzaman and A. K. M. Sadrul Islam, Energy Utilization and Environmental Aspects of Rice Processing Industries in Bangladesh Energies 2009, 2(1), pp. 134-149. 18. A.D. Sagar and S. Kartha, Bioenergy and Sustainable Development?, Annu. Rev. Environ. Resourc. 2007.32:131-167. 32