The Earth is warming due to the accumulation of greenhouse gases (GHGs) from the intensive use of fossil fuels and other natural resources. GHGs include carbon dioxide (CO2), methane, nitrogen oxides, water vapor, ozone and others, but CO2 is responsible for more than half of the anthropogenic greenhouse effects. These GHGs are trapping heat over the Earth's surface, resulting in changes in temperature and other climatic processes. Biomass is a unique source of renewable energy as it can be provided as solid, gaseous or liquid fuel and can be used for generating electricity, transport fuels, as well as heat - in particular, high-temperature heat for industry purposes. Bioenergy can be stored at times of low demand and provide energy when needed. Depending on the type of conversion plant, bioenergy can thus play a role in balancing the rising share of variable renewable electricity from wind and solar in the power system. In addition, the possibility to store biomass allows for generation of biomass derived heat to meet seasonal demand.
Biomass provided about 10.2% of the annual global primary energy supply in 2008, from a wide variety of biomass sources feeding numerous sectors of society. The biomass feedstock's used for energy, and more than 80% are derived from wood (trees, branches, residues) and shrubs. The remaining bioenergy feedstock's came from the agricultural sector (energy crops, residues and by-products) and from various commercial and post-consumer wastes and by-product streams biomass product recycling and processing or the organic biogenic fraction of municipal solid waste. Low-efficiency traditional biomass such as wood, straws, dung and other manures are used for cooking, lighting and space heating, generally by the poorer populations in developing countries. This biomass is mostly combusted, creating serious negative impacts on health and living conditions. Increasingly, charcoal is becoming a secondary energy carrier in rural areas. High-efficiency modern bioenergy uses more convenient solids, liquids and gases as secondary energy carriers to generate heat, electricity, combined heat and power (CHP) and transport fuels for various sectors. Many entities in the process industry, municipalities, districts and cooperatives generate these energy products, in some cases for their own use, but also for sale to national and international markets in the increasingly global trade. Liquid Biofuels, such as ethanol and biodiesel, are used for global road transport and some industrial uses. Biomass-derived gases, primarily methane from anaerobic digestion of agricultural residues and waste treatment streams, are used to generate electricity, heat or CHP for multiple sectors. The most important contribution to these energy services is, however, based on solids, such as chips, pellets, recovered wood previously used etc.
Agricultural energy crops
Several traditional crops that are grown for food and other uses can also be used to produce bioenergy, primarily as Biofuels. Crops currently used as biomass feedstocks include
Corn is the primary biomass feedstock currently used in the United States to produce ethanol. Rapeseed is the primary feedstock used in Europe to produce biodiesel. Sorghum is used in the United States as an alternative to corn for ethanol production. As of 2008, 15 percent of U.S. grain sorghum is being used for ethanol production at eight plants (Biomass Research and Development Initiative, 2008). Soybeans are the primary biomass feedstock currently used in the United States to produce biodiesel from soybean oil. Sugarcane. Brazil uses sugarcane to produce ethanol and uses the sugarcane residue for process heat. Some of the microbial species are also used like the oil in microalgae can be converted into jet fuel or diesel fuel National Renewable Energy Laboratory (NREL), 2006. Microalgae with high lipid content are best suited to production of liquid fuel.
Biomass feedstocks from waste materials are often referred to as "opportunity" fuels because they would otherwise go unused or be disposed of; bioenergy production is an opportunity to use these materials productively. Common opportunity fuels include: Biogas. Biogas, consisting primarily of methane, is released during anaerobic decomposition of organic matter. Facilities that deal with large quantities of organic waste can employ anaerobic digesters and/or gas collection systems to capture biogas, which can be used as a source of on-site bioheat and/or biopower. Major sources of biogas include: Wastewater treatment plants (WWTPs). Anaerobic digesters can be used during treatment of wastewater to break down effluent and release biogas, which can then be collected for subsequent use as a source of bioenergy.
Food processing wastes.
Food processing wastes include nut shells, rice hulls, fruit pits, cotton gin trash, meat processing residues, and cheese whey, among others. Because these residues can be difficult to use as a fuel source due to the varying characteristics of different waste streams, the latter two of these food processing wastes are often disposed of as industrial wastewater. Work is under way in the food processing industry to evaluate the bioenergy potential of these residues, including collection and processing methods to allow more effective use as biomass feedstocks. Utilities and universities have used food wastes such as peanut hulls and rice hulls for biopower. Many anaerobic digester operators are currently adding agricultural and food wastes to their digesters to provide enhanced Waste management and increased biogas generation.
Residues from silviculture (wood harvesting) include logging residues such as limbs and tops, excess small pole trees, and dead or dying trees. Trees have been harvested from a forest for timber; forest residues are typically either left in the forest or disposed of via open burning through forest management programs because only timber of a certain quality can be used in lumber mills and other processing facilities. An advantage of using forest residues from silviculture for bioenergy production is that a collection infrastructure is already in place to harvest the wood. Approximately 2.3 tons of forest residues are available for every 1,000 cubic feet of harvested timber.
Biomass Feedstock's: Current Status and 2020 Estimation
The large majority of NREAPs indicate that solid biomass and forestry biomass in particular will continue to be the major source for bioenergy within the European Union and this raises issues about the sustainability of biomass usage. Several NREAPs, such as that for the UK estimate large local potentials for woody energy crops derived from sustainable forestry. However, the NREAPs don't provide details on how this forestry resource will be collected or the forests managed and there is not enough evidence to evaluate the potential impacts of increased use of forestry products for energy generation. Other plans estimate that domestic resources will not be sufficient and thus anticipate imports of solid biomass or biofuels. Estimates of generation costs for electricity today and in 2030 are based on a wide range of sources. Generation costs for different scales of operation and different biomass feedstock compared to levelised cost of electricity generated from coal and natural gas. The analysis indicates that there is a strong scale effect, but the lower capital costs and higher power generation efficiencies are to some extent offset by increased fuel prices likely to be required for large scale operation. In favorable circumstances, co firing of internationally traded fuels can be close to competitive with coal-based electricity generation. Electricity generation in dedicated biomass plants is currently competitive with fossil-based electricity only at a higher carbon price, meaning that at present financial support is needed to make these options commercially attractive.
• Commonwealth of Massachusetts, 2008. Advanced Biofuels Task Force Report. Boston, 2008.
• U.S. DOE (Department of Energy), 2003. Industrial Bioproducts: Today and Tomorrow. U.S. DOE, Washington, DC, July 2003.
• Lal, R. (2003). Offsetting global CO2 emissions by restoration of degraded soils and intensi?cation of world agriculture and forestry. Land Degradation & Development,
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