Biomass is the material derived from plants that use sunlight to grow which include plant and animal material such as wood from forests, material left over from agricultural and forestry processes, and organic industrial, human and animal wastes. Biomass comes from a variety of sources which include:
Wood from natural forests and woodlands
Agricultural residues such as straw, stover, cane trash and green agricultural wastes
Agro-industrial wastes, such as sugarcane bagasse and rice husk
Industrial wastes, such as black liquor from paper manufacturing
Municipal solid wastes (MSW)
Food processing wastes
In nature, if biomass is left lying around on the ground it will break down over a long period of time, releasing carbon dioxide and its store of energy slowly. By burning biomass its store of energy is released quickly and often in a useful way. So converting biomass into useful energy imitates the natural processes but at a faster rate.
Biomass can be transformed into clean energy and/or fuels by a variety of technologies, ranging from conventional combustion process to advanced biofuels technology. Besides recovery of substantial energy, these technologies can lead to a substantial reduction in the overall biomass waste quantities requiring final disposal, which can be better managed for safe disposal in a controlled manner while meeting the pollution control standards.
Biomass conversion systems reduces greenhouse gas emissions in two ways. Heat and electrical energy is generated which reduces the dependence on power plants based on fossil fuels. The greenhouse gas emissions are significantly reduced by preventing methane emissions from decaying biomass. Moreover, biomass energy plants are highly efficient in harnessing the untapped sources of energy from biomass resources and helpful in development of rural areas.
With Indonesia’s recovery from the Asian financial crisis of 1998, energy consumption has grown rapidly in past decade. The priority of the Indonesian energy policy is to reduce oil consumption and to use renewable energy. For power generation, it is important to increase electricity power in order to meet national demand and to change fossil fuel consumption by utilization of biomass wastes. The development of renewable energy is one of priority targets in Indonesia.
It is estimated that Indonesia produces 146.7 million tons of biomass per year, equivalent to about 470 GJ/y. Sources of biomass energy in Indonesia are scattered all over the country, but the biggest potential in concentrated scale can be found in the Island of Kalimantan, Sumatera, Irian Jaya and Sulawesi. Studies estimate the electricity generation potential from the roughly 150 Mt of biomass residues produced per year to be about 50 GW or equivalent to roughly 470 GJ/year. These studies assume that the main source of biomass energy in Indonesia will be rice residues with a technical energy potential of 150 GJ/year. Other potential biomass sources are rubber wood residues (120 GJ/year), sugar mill residues (78 GJ/year), palm oil residues (67 GJ/year), and less than 20 GJ/year in total from plywood and veneer residues, logging residues, sawn timber residues, coconut residues, and other agricultural wastes.
Sustainable and renewable natural resources such as biomass can supply potential raw materials for energy conversion. In Indonesia, they comprise variable-sized wood from forests (i.e. natural forests, plantations and community forests that commonly produce small-diameter logs used as firewood by local people), woody residues from logging and wood industries, oil-palm shell waste from crude palm oil factories, coconut shell wastes from coconut plantations, as well as skimmed coconut oil and straw from rice cultivation.
The major crop residues to be considered for power generation in Indonesia are palm oil sugar processing and rice processing residues. Currently, 67 sugar mills are in operation in Indonesia and eight more are under construction or planned. The mills range in size of milling capacity from less than 1,000 tons of cane per day to 12,000 tons of cane per day. Current sugar processing in Indonesia produces 8 millions MT bagasse and 11.5 millions MT canes top and leaves. There are 39 palm oil plantations and mills currently operating in Indonesia, and at least eight new plantations are under construction. Most palm oil mills generate combined heat and power from fibres and shells, making the operations energy self –efficient. However, the use of palm oil residues can still be optimized in more energy efficient systems.
Other potential source of biomass energy can also come from municipal wastes. The quantity of city or municipal wastes in Indonesia is comparable with other big cities of the world. Most of these wastes are originated from household in the form of organic wastes from the kitchen. At present the wastes are either burned at each household or collected by the municipalities and later to be dumped into a designated dumping ground or landfill. Although the government is providing facilities to collect and clean all these wastes, however, due to the increasing number of populations coupled with inadequate number of waste treatment facilities in addition to inadequate amount of allocated budget for waste management, most of big cities in Indonesia had been suffering from the increasing problem of waste disposals.
The current pressure for cost savings and competitiveness in Indonesia’s most important biomass-based industries, along with the continually growing power demands of the country signal opportunities for increased exploitation of biomass wastes for power generation.
Being an agricultural economy, biomass energy potential in Pakistan is highly promising. Pakistan is experiencing a severe energy crisis these days which is resulting in adverse long term economic and social problems. The electricity and gas shortages have directly impacted the common man, industry and commercial activities.
The high cost of energy mix is the main underlying reason behind the power crisis. The main fuel for the local power industry is natural gas however due to the continued depletion of this source and demands elsewhere the power generation companies are now dependent on furnace oil which is relatively expensive.
The way out of this crisis is to look for fuel sources which are cheap and abundantly available within the country. This description and requirement is fulfilled by biomass resources which have been largely ignored in the past and are also available in sufficient quantities to tackle the energy crisis prevailing in the country.
Biomass Energy in Pakistan
The potential to produce power from biomass resources is very promising in Pakistan. Being an agrarian economy, more than 60% of the population is involved in agricultural activities in the country. As per World Bank statistics, around 26,280,000 hectares of land is under cultivation in Pakistan. The major sources of biomass energy are crop residues, animal manure and municipal solid wastes
Wheat straw, rice husk, rice straw, cane trash, bagasse, cotton sticks are some of the major crop residues in Pakistan. Sugar cane is a major crop in the country and grown on a wide scale throughout Pakistan. During 2010-2011, the area under sugarcane cultivation was 1,029,000 hectares which is 4% of the total cropped area.
Sugarcane trash which constitutes 10% of the sugar cane is currently burned in the fields. During the year 2010-11, around 63,920,000 metric tons of sugarcane was grown in Pakistan which resulted in trash generation of around 5,752,800 metric tons. As per conservation estimates, the bioenergy potential of cane trash is around 9,475 GWh per year.
Cotton is another major cash crop in Pakistan and is the main source of raw material to the local textile industry. Cotton is grown on around 11% of the total cropped area in the country. The major residue from cotton crop is cotton sticks which is he material left after cotton picking and constitute as much as 3 times of the cotton produced.
Majority of the cotton sticks are used as domestic fuel in rural areas so only one-fourth of the total may be considered as biomass energy resource. The production of cotton sticks during 2010-2011 was approximately 1,474,693 metric tons which is equivalent to power generation potential of around 3,071 GWh.
Cotton sticks constitute as much as 3 times of the cotton produced.
Pakistan is the world’s fourth largest producer of milk. The cattle and dairy population is around 67,294,000 while the animal manure generation is estimated at 368,434,650 metric tons. Biogas generation from animal manure is a very good proposition for Pakistan as the country has the potential to produce electrical energy equivalent to 23,654 GWh
Municipal Solid Waste
The generation or solid wastes in 9 major urban centers is around 7.12 million tons per annum which is increasing by 2.5% per year due to rapid increase in population and high rate of industrialization. The average calorific value of MSW in Pakistan is 6.89 MJ/kg which implies power generation potential of around 13,900 GWh per annum.
Southeast Asia, with its abundant bioenergy resources, holds a strategic position in the global biomass energy atlas. There is immense bioenergy potential in Southeast Asian countries due to plentiful supply of diverse forms of biomass wastes such as agricultural residues, woody biomass, animal wastes, municipal solid waste, etc. The rapid economic growth and industrialization in the region has accelerated the drive to implement the latest waste-to-energy technologies to tap the unharnessed potential of biomass resources.
Southeast Asia is a big producer of agricultural and wood products which, when processed in industries, produces large amounts of biomass residues. According to conservative estimates, the amount of biomass residues generated from sugar, rice and palm oil mills is more than 200-230 million tons per year which corresponds to cogeneration potential of 16-19 GW.
Rice mills in the region produce 38 million tonnes of rice husk as solid residue which is a good fuel for producing heat and power. Sugar industry is an integral part of the industrial scenario in Southeast Asia accounting for 7% of sugar production worldwide. Sugar mills in Thailand, Indonesia, Philippines and Vietnam generate 34 million tonnes of bagasse every year. Malaysia, Indonesia and Thailand account for 90% of global palm oil production leading to the generation of 27 million tonnes of waste per annum in the form of empty fruit bunches (EFBs), fibers and shells, as well as liquid effluent.
Woody biomass is a good energy resource due to presence of large number of forests in Southeast Asia. Apart from natural forests, non-industrial plantations of different types (e.g. coconut, rubber and oil palm plantations, fruit orchards, and trees in homesteads and gardens) have gained recognition as important sources of biomass. In addition, the presence of a large number of wood processing industries also generates significant quantity of wood wastes. The annual production of wood wastes in the region is estimated to be more than 30 million m3.
The prospects of biogas power generation are also high in the region thanks to presence of well-established food-processing and dairy industries. Another important biomass resource is contributed by municipal solid wastes in heavily populated urban areas. In addition, there are increasing efforts both commercially and promoted by governments to develop biomass energy systems for efficient biofuel production, e.g. bio-diesel from palm oil.
Biomass resources, particularly residues from forests, wood processing, agricultural crops and agro-processing, are under-utilised in Southeast Asian countries. There is an urgent need to utilize biomass wastes for commercial electricity and heat production to cater to the needs of the industries as well as urban and rural communities.
Southeast Asian countries are yet to make optimum use of the additional power generation potential from biomass waste resources which could help them to partially overcome the long-term problem of energy supply. Technologies for biomass utilization which are at present widely used in Southeast counties need to be improved towards best practice by making use of the latest trends in the biomass energy sector.
Malaysia is blessed with abundant renewable sources of energy, especially biomass and solar. Under the Eighth Malaysian Plan, renewable energy was added in the energy mix to unveil a Five-Fuel Strategy to achieve 5 percent contribution by 2005.
Among the various sources of renewable energy, bioenergy seems to be the most promising option for Malaysia. The National Biofuel Policy, launched in 2006 encourages the use of environmentally friendly, sustainable and viable sources of biomass energy. Under the Five Fuel Policy, the government of Malaysia has identified biomass as one of the potential renewable energy. Malaysia produces atleast 168 million tonnes of biomass, including timber and oil palm waste, rice husks, coconut trunk fibres, municipal waste and sugar cane waste annually. Being a major agricultural commodity producer in the region Malaysia is well positioned amongst the ASEAN countries to promote the use of biomass as a renewable energy source.
Malaysia has been one of the world’s largest producers and exporters of palm oil for the last forty years. The Palm Oil industry, besides producing Crude Palm Oil (CPO) and Palm Kernel Oil, produces Palm Shell, Press Fibre, Empty Fruit Bunches (EFB), Palm Oil Mill Effluent (POME), Palm Trunk (during replanting) and Palm Fronds (during pruning).
Malaysia has approximately 4 million hectares of land under oil palm plantation. Over 75% of total area planted is located in just four states, Sabah, Johor, Pahang and Sarawak, each of which has over half a million hectares under cultivation. The total amount of processed FFB (Fresh Fruit Bunches) was estimated to be 75 million tons while the total amount of EFB produced was estimated to be 16.6 million tons. Around 58 million tons of POME is produced in Malaysia annually, which has the potential to produce an estimated 15 billion m3 of biogas can be produced each year.
Malaysia is the world’s second largest producer of crude palm oil. Almost 70% of the volume from the processing of fresh fruit bunch is removed as wastes in the form of empty fruit bunches, palm kernel shells, palm oil mill effluent etc. With more than 423 mills in Malaysia, this palm oil industry generated around 80 million dry tonnes of biomass in 2010. Malaysia has more than 2400 MW of biomass and 410 MW of biogas potential, out of which only 773MW has been harnessed until 2011.
Rice husk is another important agricultural biomass resource in Malaysia with good potential for power cogeneration. An example of its attractive energy potential is biomass power plant in the state of Perlis which uses rice husk as the main source of fuel and generates 10 MW power to meet the requirements of 30,000 households. The US$15 million project has been undertaken by Bio-Renewable Power Sdn Bhd in collaboration with the Perlis state government, while technology provider is Finland’s Foster Wheeler Energia Oy.
Under the EC-ASEAN Cogeneration Program, there are three ongoing Full Scale Demonstration Projects (FSDPs) – Titi Serong, Sungai Dingin Palm Oil Mill and TSH Bioenergy – to promote biomass energy systems in Malaysia. The 1.5MW Titi Serong power plant, located at Parit Buntar (Perak), is based on rice husk while the 2MW Sungai Dingin Palm Oil Mill project make use of palm kernel shell and fibre to generate steam and electricity. The 14MW TSH Bioenergy Sdn Bhd, located at Tawau (Sabah), is the biggest biomass power plant in Malaysia and utilizes empty fruit bunches, palm oil fibre and palm kernel shell as fuel resources.
Sugarcane is one of the most promising agricultural sources of biomass energy in the world. Sugarcane produces mainly two types of biomass, Cane Trash and Bagasse. Cane Trash is the field residue remaining after harvesting the Cane stalk while bagasse is the fibrous residue left over after milling of the Cane, with 45-50% moisture content and consisting of a mixture of hard fibre, with soft and smooth parenchymatous (pith) tissue with high hygroscopic property. Bagasse contains mainly cellulose, hemi cellulose, pentosans, lignin, Sugars, wax, and minerals. The quantity obtained varies from 22 to 36% on Cane and is mainly due to the fibre portion in Cane and the cleanliness of Cane supplied, which, in turn, depends on harvesting practices.
The composition of Bagasse depends on the variety and maturity of Sugarcane as well as harvesting methods applied and efficiency of the Sugar processing. Bagasse is usually combusted in furnaces to produce steam for power generation. Bagasse is also emerging as an attractive feedstock for bioethanol production. It is also utilized as the raw material for production of paper and as feedstock for cattle. The value of Bagasse as a fuel depends largely on its calorific value, which in turn is affected by its composition, especially with respect to its water content and to the calorific value of the Sugarcane crop, which depends mainly on its sucrose content.
Moisture contents is the main determinant of calorific value i.e. the lower the moisture content, the higher the calorific value. A good milling process will result in low moisture of 45% whereas 52% moisture would indicate poor milling efficiency. Most mills produce Bagasse of 48% moisture content, and most boilers are designed to burn Bagasse at around 50% moisture. Bagasse also contains approximately equal proportion of fibre (cellulose), the components of which are carbon, hydrogen and oxygen, some sucrose (1-2 %), and ash originating from extraneous matter. Extraneous matter content is higher with mechanical harvesting and subsequently results in lower calorific value.
For every 100 tons of Sugarcane crushed, a Sugar factory produces nearly 30 tons of wet Bagasse. Bagasse is often used as a primary fuel source for Sugar mills; when burned in quantity, it produces sufficient heat and electrical energy to supply all the needs of a typical Sugar mill, with energy to spare. The resulting CO2 emissions are equal to the amount of CO2 that the Sugarcane plant absorbed from the atmosphere during its growing phase, which makes the process of cogeneration greenhouse gas-neutral.
35MW Bagasse and Coal CHP Plant in Mauritius
Cogeneration of Bagasse is one of the most attractive and successful energy projects that have already been demonstrated in many Sugarcane producing countries such as Mauritius, Reunion Island, India and Brazil. Combined heat and power from Sugarcane in the form of power generation offers renewable energy options that promote sustainable development, take advantage of domestic resources, increase profitability and competitiveness in the industry, and cost-effectively address climate mitigation and other environmental goals.
India has a tremendous biomass potential which could easily be relied upon to fulfil most of our energy needs. An estimated 50 MMT (million metric tonnes) of liquid fuels are consumed annually in India, but with the actual biomass potential and its full utilization, India is capable of generating almost double that amount per annum. These biomass estimates only constitute the crop residues available in the country and essentially the second-generation fuels since the use of first-generation crop bases fuels in such food-starved nations is a criminal thought.
Currently, there are various technologies available to process such crop residues and generate value products from them. However, essentially, they all revolve around two main kinds of processes, either biochemical or thermal.
The biochemical process involves application of aerobic/anaerobic digestion for the production of biogas; or fermentation, which results in the generation of ethanol. Both these products could be subsequently treated chemically and through trans-esterification process, leading to production of biodiesel.
Alternatively, the thermochemical processes involve either the combustion, gasification or pyrolysis techniques, which produces heat, energy-rich gas and liquid fuels respectively. These products can be used as such, or could be further processed to generate high quality biofuels or chemicals.
The estimated organized energy breakup for India is 40 percent each for domestic and transport sectors and 20 percent for the industrial sectors. The current share of crude oil and gases is nearly 90 percent for the primary and transport sectors and the remaining 10 percent for the generation of industrial chemicals. The escalating prices of crude oil in the international market and the resulting concern over energy security, has lead developing nations to explore alternative and cheap sources of energy to meet the growing energy demand. One of the promising solution for agrarian economies is Biorefinery.
Biorefinery is analogous to the traditional petroleum refineries employing fractional distillation process for obtaining different fractions or components from the same raw material, i.e. the crude oil. Biorefinery involve the integration of different biomass treatment and processing methods into one system, which results in the production of different components from the same biomass. This makes the entire chain more viable economically and also reduces the waste generated.
Typical Model of a Biorefinery
The outcome ranges from high-volume, low-energy content liquid fuels, which could serve the transportation industry needs, to the low-volume but high-value chemicals, which could add to the feasibility of such a project. Steam and heat generated in the process could be utilized for meeting process heat requirements. By-products like chemicals, fertilizers, pharmaceuticals, polymers etc are also obtained which provide additional revenue streams.
Biorefineries can help in utilizing the optimum energy potential of organic wastes and may also resolve the problems of waste management and GHGs emissions. Wastes can be converted, through appropriate enzymatic/chemical treatment, into either gaseous or liquid fuels. The pre-treatment processes involved in biorefining generate products like paper-pulp, HFCS, solvents, acetate, resins, laminates, adhesives, flavour chemicals, activated carbon, fuel enhancers, undigested sugars etc. which generally remain untapped in the traditional processes. The suitability of this process is further enhanced from the fact that it can utilize a variety of biomass resources, whether plant-derived or animal-derived.
The concept of biorefinery is still in early stages at most places in the world. Problems like raw material availability, feasibility in product supply chain, scalability of the model are hampering its development at commercial-scales. The National Renewable Energy Laboratory (NREL) of USA is leading the front in biorefinery research with path-breaking discoveries and inventions. Although the technology is still in nascent stages, but it holds the key to the optimum utilization of wastes and natural resources that humans have always tried to achieve. The onus now lies on governments and corporate to incentivize or finance the research and development in this field.
The Middle East and North Africa (MENA) region offers almost 45 percent of the world’s total energy potential from all renewable sources that can generate more than three times the world’s total power demand. Apart from solar and wind, MENA also has abundant biomass energy resources which have remained unexplored to a great extent.
According to conservative estimates, the potential of biomass energy in the Euro Mediterranean region is about 400TWh per year. Around the region, pollution of the air and water from municipal, industrial and agricultural operations continues to grow. The technological advancements in the biomass energy industry, coupled with the tremendous regional potential, promises to usher in a new era of energy as well as environmental security for the region.
The major biomass producing countries are Egypt, Yemen, Iraq, Syria and Jordan. Traditionally, biomass energy has been widely used in rural areas for domestic purposes in the MENA region, especially in Egypt, Yemen and Jordan. Since most of the region is arid or semi-arid, the biomass energy potential is mainly contributed by municipal solid wastes, agricultural residues and industrial wastes.
Municipal solid wastes represent the best source of biomass in Middle East countries. Bahrain, Saudi Arabia, UAE, Qatar and Kuwait rank in the top-ten worldwide in terms of per capita solid waste generation. The gross urban waste generation quantity from Middle East countries is estimated at more than 150 million tons annually. Food waste is the third-largest component of generated waste by weight which mostly ends up rotting in landfill and releasing greenhouse gases into the atmosphere. The mushrooming of hotels, restaurants, fast-food joints and cafeterias in the region has resulted in the generation of huge quantities of food wastes.
In Middle East countries, huge quantity of sewage sludge is produced on daily basis which presents a serious problem due to its high treatment costs and risk to environment and human health. On an average, the rate of wastewater generation is 80-200 litres per person each day and sewage output is rising by 25 percent every year. According to estimates from the Drainage and Irrigation Department of Dubai Municipality, sewage generation in the Dubai increased from 50,000 m3 per day in 1981 to 400,000 m3 per day in 2006.
The food processing industry in MENA produces a large number of organic residues and by-products that can be used as biomass energy sources. In recent decades, the fast-growing food and beverage processing industry has remarkably increased in importance in major countries of the region. Since the early 1990s, the increased agricultural output stimulated an increase in fruit and vegetable canning as well as juice, beverage, and oil processing in countries like Egypt, Syria, Lebanon and Saudi Arabia.
The MENA countries have strong animal population. The livestock sector, in particular sheep, goats and camels, plays an important role in the national economy of respective countries. Many millions of live ruminants are imported each year from around the world. In addition, the region has witnessed very rapid growth in the poultry sector. The biogas potential of animal manure can be harnessed both at small- and community-scale.
The Philippines is mainly an agricultural country with a land area of 30 million hectares, 47 percent of which is agricultural. The total area devoted to agricultural crops is 13 million hectares distributed among food grains, food crops and non-food crops.Among the crops grown, rice, coconut and sugarcane are major contributors to biomass energy resources.
The most common agricultural wastes in the Philippines are rice husk, rice straw, coconut husk, coconut shell and bagasse. The country has good potential for biomass power plants as one-third of the country’s agricultural land produces rice, and consequently large volumes of rice straw and hulls are generated.
Rice is the staple food in the Philippines. The Filipinos are among the world’s biggest rice consumers. The average Filipino consumes about 100 kilograms per year of rice. Though rice is produced throughout the country, the Central Luzon and Cagayan Valley are the major rice growing regions. With more than 1.2 million hectares of rain-fed rice-producing areas, the country produced around 16 million tons of rice in 2007. The estimated production of rice hull in the Philippines is more than 2 million tons per annum which is equivalent to approximately 5 million BOE (barrels of oil equivalent) in terms of energy. Rice straw is another important biomass resource with potential availability exceeding 5 million tons per year across the country.
With the passing of Biofuels Act of 2006, the sugar industry in the Philippines which is the major source of ethanol and domestic sugar will become a major thriving industry. Around 380,000 hectares of land is devoted to sugarcane cultivation. It is estimated that 1.17 million tonnes of sugarcane trash is recoverable as a biomass resource in the Philippines. In addition, 6.4 million tonnes of surplus bagasse is available from sugar mills. There are 29 operating sugar mills in the country with an average capacity of 6,900 tonnes of cane per day. Majority is located in Negros Island which provides about 46% of the country’s annual sugar production.
The Philippines has the largest number of coconut trees in the world as it produces most of the world market for coconut oil and copra meal. The major coconut wastes include coconut shell, coconut husks and coconut coir dust. Coconut shell is the most widely utilized but the reported utilization rate is very low. Approximately 500 million coconut trees in the Philippines produce tremendous amounts of biomass as husk (4.1 million tonnes), shell (1.8 million tonnes), and frond (4.5 million tonnes annually).
Maize is a major crop in the Philippines that generates large amounts of agricultural residues. It is estimated that 4 million tonnes of grain maize and 0.96 million tonnes of maize cobs produced yearly in the Philippines. Maize cob burning is the main energy application of the crop, and is widely practiced by small farmers to supplement fuelwood for cooking.
A wide range of technologies are available for realizing the energy potential of biomass wastes, ranging from very simple systems for disposing of dry waste to more complex technologies capable of dealing with large amounts of industrial waste. Conversion routes for biomass wastes are generally thermo-chemical or bio-chemical, but may also include chemical and physical.
The three principal methods of thermo-chemical conversion corresponding to each of these energy carriers are combustion in excess air, gasification in reduced air, and pyrolysis in the absence of air. Direct combustion is the best established and most commonly used technology for converting wastes to heat. During combustion, biomass is burnt in excess air to produce heat. The first stage of combustion involves the evolution of combustible vapours from wastes, which burn as flames. Steam is expanded through a conventional turbo-alternator to produce electricity. The residual material, in the form of charcoal, is burnt in a forced air supply to give more heat.
Co-firing or co-combustion of biomass wastes with coal and other fossil fuels can provide a short-term, low-risk, low-cost option for producing renewable energy while simultaneously reducing the use of fossil fuels. Co-firing involves utilizing existing power generating plants that are fired with fossil fuel (generally coal), and displacing a small proportion of the fossil fuel with renewable biomass fuels. Co-firing has the major advantage of avoiding the construction of new, dedicated, waste-to-energy power plant. An existing power station is modified to accept the waste resource and utilize it to produce a minor proportion of its electricity.
Gasification systems operate by heating biomass wastes in an environment where the solid waste breaks down to form a flammable gas. The gasification of biomass takes place in a restricted supply of air or oxygen at temperatures up to 1200–1300°C. The gas produced—synthesis gas, or syngas—can be cleaned, filtered, and then burned in a gas turbine in simple or combined-cycle mode, comparable to LFG or biogas produced from an anaerobic digester. The final fuel gas consists principally of carbon monoxide, hydrogen and methane with small amounts of higher hydrocarbons. This fuel gas may be burnt to generate heat; alternatively it may be processed and then used as fuel for gas-fired engines or gas turbines to drive generators. In smaller systems, the syngas can be fired in reciprocating engines, micro-turbines, Stirling engines, or fuel cells.
Pyrolysis is thermal decomposition occurring in the absence of oxygen. During the pyrolysis process, biomass waste is heated either in the absence of air (i.e. indirectly), or by the partial combustion of some of the waste in a restricted air or oxygen supply. This results in the thermal decomposition of the waste to form a combination of a solid char, gas, and liquid bio-oil, which can be used as a liquid fuel or upgraded and further processed to value-added products.
Biochemical processes, like anaerobic digestion, can also produce clean energy in the form of biogas which can be converted to power and heat using a gas engine. Anaerobic digestion is a series of chemical reactions during which organic material is decomposed through the metabolic pathways of naturally occurring microorganisms in an oxygen depleted environment. In addition, wastes can also yield liquid fuels, such as cellulosic ethanol and biodiesel, which can be used to replace petroleum-based fuels.
Anaerobic digestion is the natural biological process which stabilizes organic waste in the absence of air and transforms it into biogas and biofertilizer. Almost any organic material can be processed with anaerobic digestion. This includes biodegradable waste materials such as municipal solid waste, animal manure, poultry litter, food wastes, sewage and industrial wastes. An anaerobic digestion plant produces two outputs, biogas and digestate, both can be further processed or utilized to produce secondary outputs. Biogas can be used for producing electricity and heat, as a natural gas substitute and also a transportation fuel. Digestate can be further processed to produce liquor and a fibrous material. The fiber, which can be processed into compost, is a bulky material with low levels of nutrients and can be used as a soil conditioner or a low level fertilizer.
A variety of fuels can be produced from biomass wastes including liquid fuels, such as ethanol, methanol, biodiesel, Fischer-Tropsch diesel, and gaseous fuels, such as hydrogen and methane. The resource base for biofuel production is composed of a wide variety of forestry and agricultural resources, industrial processing residues, and municipal solid and urban wood residues. The largest potential feedstock for ethanol is lignocellulosic biomass wastes, which includes materials such as agricultural residues (corn stover, crop straws and bagasse), herbaceous crops (alfalfa, switchgrass), short rotation woody crops, forestry residues, waste paper and other wastes (municipal and industrial). The three major steps involved in cellulosic ethanol production are pretreatment, enzymatic hydrolysis, and fermentation. Biomass is pretreated to improve the accessibility of enzymes. After pretreatment, biomass undergoes enzymatic hydrolysis for conversion of polysaccharides into monomer sugars, such as glucose and xylose. Subsequently, sugars are fermented to ethanol by the use of different microorganisms. Bioethanol production from these feedstocks could be an attractive alternative for disposal of these residues. Importantly, lignocellulosic feedstocks do not interfere with food security.
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