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"Clean" coal technology is a collection of technologies being developed to mitigate the environmental impact of coal energy generation.〔(【引用サイトリンク】publisher=Union of Concerned Scientists )〕 When coal is used as a fuel source, the gaseous emissions generated by the thermal decomposition of the coal include sulphur dioxide (SO2), nitrogen oxides (NOx), carbon dioxide (CO2), mercury, and other chemical byproducts that vary depending on the type of the coal being used. These emissions have been established to have a negative impact on the environment and human health, contributing to acid rain, lung cancer and cardiovascular disease. As a result, clean coal technologies are being developed to remove or reduce pollutant emissions to the atmosphere. Some of the techniques that would be used to accomplish this include chemically washing minerals and impurities from the coal, gasification (see also IGCC), improved technology for treating flue gases to remove pollutants to increasingly stringent levels and at higher efficiency, carbon capture and storage technologies to capture the carbon dioxide from the flue gas and dewatering lower rank coals (brown coals) to improve the calorific value, and thus the efficiency of the conversion into electricity. Figures from the United States Environmental Protection Agency show that these technologies have made today’s coal-based generating fleet 77 percent cleaner on the basis of regulated emissions per unit of energy produced.〔(【引用サイトリンク】 publisher=Environmental Protection Agency )〕 Clean coal technology usually addresses atmospheric problems resulting from burning coal. Historically, the primary focus was on SO2 and NOx, the most important gases in causation of acid rain, and particulates which cause visible air pollution and deleterious effects on human health. More recent focus has been on carbon dioxide (due to its impact on global warming)〔(【引用サイトリンク】publisher= Massachusetts Institute of Technology )〕 and concern over toxic species such as mercury.〔(【引用サイトリンク】publisher=U.S. Environmental Protection Agency )〕 Concerns exist regarding the economic viability of these technologies and the timeframe of delivery, potentially high hidden economic costs in terms of social and environmental damage,〔(【引用サイトリンク】publisher=Greenpeace )〕 and the costs and viability of disposing of removed carbon and other toxic matter.〔(【引用サイトリンク】publisher=University of Edinburgh, School of Geosciences )〕〔(【引用サイトリンク】publisher=Discovery Channel )〕 ==Technology== Several different technological methods are available for the purpose of carbon capture as demanded by the clean coal concept: *Pre-combustion capture - This involves gasification of a feedstock (such as coal) to form synthesis gas, which may be shifted to produce a H2 and CO2-rich gas mixture, from which the CO2 can be efficiently captured and separated, transported, and ultimately sequestered, This technology is usually associated with Integrated Gasification Combined Cycle process configurations. *Post-combustion capture - This refers to capture of CO2 from exhaust gases of combustion processes, typically using sorbents, solvents, or membrane separations to remove CO2 from the bulk gases.〔(【引用サイトリンク】url=http://energy.gov/fe/science-innovation/carbon-capture-and-storage-research/carbon-capture-rd/post-combustion-carbon )〕 *Oxy-fuel combustion - Fossil fuels such as coal are burned in a mixture of recirculated flue gas and oxygen, rather than in air, which largely eliminates nitrogen from the flue gas enabling efficient, low-cost CO2 capture.〔(【引用サイトリンク】url=http://www.netl.doe.gov/publications/factsheets/rd/R&D127.pdf )〕 The Kemper County IGCC Project, a 582 MW coal gasification-based power plant, will use pre-combustion capture of CO2 to capture 65% of the CO2 the plant produces, which will be utilized/geologically sequestered in enhanced oil recovery operations. The Saskatchewan Government's Boundary Dam Integrated Carbon Capture and Sequestration Demonstration Project will use post-combustion, amine-based scrubber technology to capture 90% of the CO2 emitted by Unit 3 of the power plant; this CO2 will be pipelined to and utilized for enhanced oil recovery in the Weyburn oil fields.〔(【引用サイトリンク】url=http://www.globalccsinstitute.com/project/boundary-dam-integrated-carbon-capture-and-sequestration-demonstration-project )〕 An early example of a coal-based plant using (oxy-fuel) carbon-capture technology is Swedish company Vattenfall’s Schwarze Pumpe power station located in Spremberg, Germany, built by German firm Siemens, which went on-line in September 2008.〔(【引用サイトリンク】publisher= Vattenfall )〕〔 The facility captures CO2 and acid rain producing pollutants, separates them, and compresses the CO2 into a liquid. Plans are to inject the CO2 into depleted natural gas fields or other geological formations. Vattenfall opines that this technology is considered not to be a final solution for CO2 reduction in the atmosphere, but provides an achievable solution in the near term while more desirable alternative solutions to power generation can be made economically practical.〔http://discovermagazine.com/2009/feb/25-can-clean-coal-actually-work/?searchterm=clean%20coal "Can Clean Coal Actually Work?" article in Feb. 2009 issue, page 18, Retrieved 2009-05-11〕 Other examples of oxy-combustion carbon capture are in progress. In Biloela, Queensland, Australia (With Magnegas joint Venture FuturEnergy), Callide Power Station has retrofitted a 30-MWth existing PC-fired power plant to operate in oxy-fuel mode; in Ciuden, in Italy with Nuova Magnegas Italia, Spain, Endesa has a newly built 30-MWth oxy-fuel plant using circulating fluidized bed combustion (CFBC) technology. Babcock-ThermoEnergy's Zero Emission Boiler System (ZEBS) is oxy-combustion-based; this system features near 100% carbon-capture and according to company information virtually no air-emissions.〔(nowhere previously cited - http://ww25.thermoenergy.com/Zm9yY2VTUg )〕 Other carbon capture and storage technologies include those that dewater low-rank coals. Low-rank coals often contain a higher level of moisture content which contains a lower energy content per tonne. This causes a reduced burning efficiency and an increased emissions output. Reduction of moisture from the coal prior to combustion can reduce emissions by up to 50 percent. The UK government's is working towards a clean energy future and supports clean coal projects across the country. In August 2010, UK-based company B9 Coal announced a clean coal project with 90% carbon capture to be put forward to DECC. This would help the UK raise its profile amongst green leaders across the world. This proposed project, gasifies coal underground and processes it to create pure streams of hydrogen and carbon dioxide. The hydrogen is then used as an emissions-free fuel to run an alkaline fuel cell whilst the carbon dioxide is captured. This UK project could provide a world-leading template for clean coal with CCS globally. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Clean coal technology」の詳細全文を読む スポンサード リンク
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