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Biomass

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This article is about biomass as a renewable energy source. For the use of the term in ecology, see Biomass (ecology).
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Biomass, as a renewable energy source, is biological material from living, or recently living organisms.[1] As an energy source, biomass can either be used directly, or converted into other energy products such as biofuel.

In the first sense, biomass is plant matter used to generate electricity with steam turbines & gasifiers or produce heat, usually by direct combustion. Examples include forest residues (such as dead trees, branches and tree stumps), yard clippings, wood chips and even municipal solid waste. In the second sense, biomass includes plant or animal matter that can be converted into fibers or other industrial chemicals, including biofuels. Industrial biomass can be grown from numerous types of plants, including miscanthus, switchgrass, hemp, corn, poplar, willow, sorghum, sugarcane,[2] and a variety of tree species, ranging from eucalyptus to oil palm (palm oil).

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[edit] Biomass sources

Wood is a typical source of biomass

Biomass is carbon, hydrogen and oxygen based. Biomass energy is derived from five distinct energy sources: garbage, wood, waste, landfill gases, and alcohol fuels. Wood energy is derived both from direct use of harvested wood as a fuel and from wood waste streams. The largest source of energy from wood is pulping liquor or “black liquor,” a waste product from processes of the pulp, paper and paperboard industry. Waste energy is the second-largest source of biomass energy. The main contributors of waste energy are municipal solid waste (MSW), manufacturing waste, and landfill gas. Biomass alcohol fuel, or ethanol, is derived primarily from sugarcane and corn. It can be used directly as a fuel or as an additive to gasoline.[3]

Biomass can be converted to other usable forms of energy like methane gas or transportation fuels like ethanol and biodiesel. Rotting garbage, and agricultural and human waste, release methane gas – also called “landfill gas” or “biogas.” Crops like corn and sugar cane can be fermented to produce the transportation fuel, ethanol. Biodiesel, another transportation fuel, can be produced from left-over food products like vegetable oils and animal fats.[4] Also, Biomass to liquids (BTLs) and cellulosic ethanol are still under research.[5][6]

The biomass used for electricity production ranges by region.[7] Forest by products, such as wood residues, are popular in the United States.[7] Agricultural waste is common in Mauritius (sugar cane residue) and Southeast Asia (rice husks).[7] Animal husbandry residues, such as poultry litter, is popular in the UK.[7]

[edit] Biomass conversion process to useful energy

This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (November 2010)

There are a number of technological options available to make use of a wide variety of biomass types as a renewable energy source. Conversion technologies may release the energy directly, in the form of heat or electricity, or may convert it to another form, such as liquid biofuel or combustible biogas. While for some classes of biomass resource there may be a number of usage options, for others there may be only one appropriate technology.

[edit] Thermal conversion

These are processes in which heat is the dominant mechanism to convert the biomass into another chemical form. The basic alternatives of combustion, torrefaction, pyrolysis, and gasification are separated principally by the extent to which the chemical reactions involved are allowed to proceed (mainly controlled by the availability of oxygen and conversion temperature).

There are a number of other less common, more experimental or proprietary thermal processes that may offer benefits such as hydrothermal upgrading (HTU) and hydroprocessing. Some have been developed for use on high moisture content biomass, including aqueous slurries, and allow them to be converted into more convenient forms. Some of the applications of thermal conversion are combined heat and power (CHP) and co-firing. In a typical biomass power plant, efficiencies range from 20–27%.[8]

[edit] Chemical conversion

A range of chemical processes may be used to convert biomass into other forms, such as to produce a fuel that is more conveniently used, transported or stored, or to exploit some property of the process itself.

[edit] Biochemical conversion

A microbial electrolysis cell can be used to directly make hydrogen gas from plant matter

As biomass is a natural material, many highly efficient biochemical processes have developed in nature to break down the molecules of which biomass is composed, and many of these biochemical conversion processes can be harnessed.

Biochemical conversion makes use of the enzymes of bacteria and other micro-organisms to break down biomass. In most cases micro-organisms are used to perform the conversion process: anaerobic digestion, fermentation and composting. Other chemical processes such as converting straight and waste vegetable oils into biodiesel is transesterification.[9] Another way of breaking down biomass is by breaking down the carbohydrates and simple sugars to make alcohol. However, this process has not been perfected yet. Scientists are still researching the effects of converting biomass.

[edit] Environmental impact

The existing biomass power generating industry in the United States, which consists of approximately 11,000 MW of summer operating capacity actively supplying power to the grid, produces about 1.4 percent of the U.S. electricity supply.[10]

Currently, the New Hope Power Partnership is the largest biomass power plant in North America. The 140 MW facility uses sugar cane fiber (bagasse) and recycled urban wood as fuel to generate enough power for its large milling and refining operations as well as to supply renewable electricity for nearly 60,000 homes. The facility reduces dependence on oil by more than one million barrels per year, and by recycling sugar cane and wood waste, preserves landfill space in urban communities in Florida.[11][12]

Using biomass as a fuel produces air pollution in the form of carbon monoxide, NOx (nitrogen oxides), VOCs (volatile organic compounds), particulates and other pollutants, in some cases at levels above those from traditional fuel sources such as coal or natural gas.[13][14][15] Black carbon – a pollutant created by incomplete combustion of fossil fuels, biofuels, and biomass – is possibly the second largest contributor to global warming.[16] In 2009 a Swedish study of the giant brown haze that periodically covers large areas in South Asia determined that it had been principally produced by biomass burning, and to a lesser extent by fossil-fuel burning.[17] Researchers measured a significant concentration of 14C, which is associated with recent plant life rather than with fossil fuels.[18]

Biomass power plant size is often driven by biomass availability in close proximity as transport costs of the (bulky) fuel play a key factor in the plant’s economics. It has to be noted, however, that rail and especially shipping on waterways can reduce transport costs significantly, which has led to a global biomass market.[19] To make small plants of 1 MWel economically profitable those power plants have need to be equipped with technology that is able to convert biomass to useful electricity with high efficiency such as ORC technology, a cycle similar to the water steam power process just with an organic working medium. Such small power plants can be found in Europe.[20] [21][22][23]

On combustion, the carbon from biomass is released into the atmosphere as carbon dioxide (CO2). The amount of carbon stored in dry wood is approximately 50% by weight.[24] When from agricultural sources, plant matter used as a fuel can be replaced by planting for new growth. When the biomass is from forests, the time to recapture the carbon stored is generally longer, and the carbon storage capacity of the forest may be reduced overall if destructive forestry techniques are employed.[25][26][27][28]

Despite harvesting, biomass crops may sequester carbon. So for example soil organic carbon has been observed to be greater in switchgrass stands than in cultivated cropland soil, especially at depths below 12 inches.[29] The grass sequesters the carbon in its increased root biomass. Typically, perennial crops sequester much more carbon than annual crops due to much greater non-harvested living biomass, both living and dead, built up over years, and much less soil disruption in cultivation.

The biomass-is-carbon-neutral proposal put forward in the early 1990s has been superseded by more recent science that recognizes that mature, intact forests sequester carbon more effectively than cut-over areas. When a tree’s carbon is released into the atmosphere in a single pulse, it contributes to climate change much more than woodland timber rotting slowly over decades. Current studies indicate that “even after 50 years the forest has not recovered to its initial carbon storage” and “the optimal strategy is likely to be protection of the standing forest”.[30][not in citation given][31][32]

[edit] See also

[edit] References

  1. ^ Biomass Energy Center
  2. ^ T.A. Volk, L.P. Abrahamson, E.H. White, E. Neuhauser, E. Gray, C. Demeter, C. Lindsey, J. Jarnefeld, D.J. Aneshansley, R. Pellerin and S. Edick (October 15–19, 2000). “Developing a Willow Biomass Crop Enterprise for Bioenergy and Bioproducts in the United States”. Proceedings of Bioenergy 2000. Adam’s Mark Hotel, Buffalo, New York, USA: North East Regional Biomass Program. OCLC 45275154.
  3. ^ Energy Information Administration
  4. ^ Energy Kids
  5. ^ “Fuel Ethanol Production: GSP Systems Biology Research”. U.S. Department of Energy Office of Science. April 19, 2010. http://genomicscience.energy.gov/biofuels/ethanolproduction.shtml. Retrieved 2010-08-02.
  6. ^ “Breaking the Biological Barriers to Cellulosic Ethanol: A Joint Research Agenda”. June 2006. http://genomicscience.energy.gov/biofuels/2005workshop/2005low_lignocellulosic.pdf. Retrieved 2010-08-02.
  7. ^ a b c d Frauke Urban and Tom Mitchell 2011. Climate change, disasters and electricity generation. London: Overseas Development Institute and Institute for Development Studies
  8. ^ Owning and Operating Costs of Waste and Biomass Power Plants
  9. ^ http://www.biomassenergycentre.org.uk/portal/page?_pageid=75,15179&_dad=portal&_schema=PORTAL
  10. ^ “U.S. Electric Net Summer Capacity”. U.S. Energy Information Administration. July 2009. http://www.eia.doe.gov/cneaf/alternate/page/renew_energy_consump/table4.html. Retrieved 2010-01-25.
  11. ^ Agreement for Generating Balancing Service
  12. ^ Biomass: Can Renewable Power Grow on Trees?
  13. ^ Eartha Jane Melzer (January 26, 2010). “Proposed biomass plant: Better than coal?”. The Michigan Messenger. http://michiganmessenger.com/33868/proposed-biomass-plant-better-than-coal.
  14. ^ Zhang, J.; Smith, K. R. (2007). “Household Air Pollution from Coal and Biomass Fuels in China: Measurements, Health Impacts, and Interventions”. Environmental Health Perspectives 115 (6): 848–855. doi:10.1289/ehp.9479. PMC 1892127. PMID 17589590. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1892127.
  15. ^ http://www.springerlink.com/index/M36715RK56PTL772.pdf
  16. ^ 2009 State Of The World, Into a Warming World, Worldwatch Institute, 56-57, ISBN 978-0-393-33418-0
  17. ^ Science, 2009, 323, 495
  18. ^ Biomass burning leads to Asian brown cloud, Chemical & Engineering News, 87, 4, 31
  19. ^ Production and trading of biomass for energy – An overview of the global status
  20. ^ Use of biomass by help of the ORC process
  21. ^ How False Solutions to Climate Change Will Worsen Global Warming
  22. ^ Biofuel crops may worsen global warming: study
  23. ^ Biodiesel Will Not Drive Down Global Warming
  24. ^ Forest volume-to-biomass models and estimates of mass for live and standing dead trees of U.S. forests
  25. ^ Prasad, Ram. “SUSTAINABLE FOREST MANAGEMENT FOR DRY FORESTS OF SOUTH ASIA”. Food and Agriculture Organization of the United Nations. http://www.fao.org/DOCREP/003/X6895E/x6895e04.htm. Retrieved 11 August 2010.
  26. ^ “Treetrouble: Testimonies on the Negative Impact of Large-scale Tree Plantations prepared for the sixth Conference of the Parties of the Framework Convention on Climate Change”. Friends of the Earth International. http://www.foei.org/en/resources/forests/treetrouble.html. Retrieved 11 August 2010.
  27. ^ Laiho, Raija; Sanchez, Felipe; Tiarks, Allan; Dougherty, Phillip M.; Trettin, Carl C.. “Impacts of intensive forestry on early rotation trends in site carbon pools in the southeastern US”. United States Department of Agriculture. http://www.srs.fs.usda.gov/pubs/5295. Retrieved 11 August 2010.
  28. ^ “THE FINANCIAL AND INSTITUTIONAL FEASIBILITY OF SUSTAINABLE FOREST MANAGEMENT”. Food and Agriculture Organization of the United Nations. http://www.fao.org/DOCREP/003/X4107E/X4107E04.htm#P866_112288. Retrieved 11 August 2010.
  29. ^ Soil Carbon under Switchgrass Stands and Cultivated Cropland (Interpretive Summary and Technical Abstract). USDA Agricultural Research Service, April 1, 2005
  30. ^ Jobs and Energy
  31. ^ Edmunds, Joe; Richard Richets; Marshall Wise, “Future Fossil Fuel Carbon Emissions without Policy Intervention: A Review”. In T. M. L. Wigley, David Steven Schimel, The carbon cycle. Cambridge University Press, 2000, pp.171-189
  32. ^ Luyssaert, Sebastiaan; -Detlef Schulze, E.; Börner, Annett; Knohl, Alexander; Hessenmöller, Dominik; Law, Beverly E.; Ciais, Philippe; Grace, John (11 September 2008). “Old-growth forests as global carbon sinks”. Nature 455 (7210): 213–215. doi:10.1038/nature07276. PMID 18784722.

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