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Carbon capture and storage (CCS) (or carbon capture and sequestration) is the process of capturing waste carbon dioxide () from large point sources, such as fossil fuel power plants, transporting it to a storage site, and depositing it where it will not enter the atmosphere, normally an underground geological formation. The aim is to prevent the release of large quantities of into the atmosphere (from fossil fuel use in power generation and other industries). It is a potential means of mitigating the contribution of fossil fuel emissions to global warming〔(【引用サイトリンク】title=IPCC Special Report Carbon Dioxide Capture and Storage Summary for Policymakers )〕 and ocean acidification.〔(【引用サイトリンク】title=Introduction to Carbon Capture and Storage - Carbon storage and ocean acidification activity )〕 Although has been injected into geological formations for several decades for various purposes, including enhanced oil recovery, the long term storage of is a relatively new concept. The first commercial example was the Weyburn-Midale Carbon Dioxide Project in 2000.〔(Burying the problem. ), ''Canadian Geographic Magazine''〕 Other examples include SaskPower's Boundary Dam and Mississippi Power's Kemper Project. 'CCS' can also be used to describe the scrubbing of from ambient air as a climate engineering technique. An integrated pilot-scale CCS power plant was to begin operating in September 2008 in the eastern German power plant Schwarze Pumpe run by utility Vattenfall, to test the technological feasibility and economic efficiency. CCS applied to a modern conventional power plant could reduce emissions to the atmosphere by approximately 80–90% compared to a plant without CCS.〔(2005 ) ''IPCC special report on Carbon Dioxide Capture and Storage''. Prepared by working group III of the Intergovernmental Panel on Climate Change. Metz, B., O. Davidson, H. C. de Coninck, M. Loos, and L.A. Meyer (eds.). Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 442 pp. Available in full at (www.ipcc.ch ) (PDF - 22.8MB)〕 The IPCC estimates that the economic potential of CCS could be between 10% and 55% of the total carbon mitigation effort until year 2100.〔 Capturing and compressing may increase the fuel needs of a coal-fired CCS plant by 25–40%.〔 These and other system costs are estimated to increase the cost of the energy produced by 21–91% for purpose built plants.〔 Applying the technology to existing plants would be more expensive especially if they are far from a sequestration site. Recent industry reports suggest that with successful research, development and deployment (RD&D), sequestered coal-based electricity generation in 2025 may cost less than unsequestered coal-based electricity generation today.〔(Coal Utilization Research Council (CURC) Technology Roadmap ), 2005〕 Storage of the is envisaged either in deep geological formations, or in the form of mineral carbonates. Deep ocean storage is no longer considered feasible because it greatly increases the problem of ocean acidification.〔(Scientific Facts on CO2 Capture and Storage ), 2012〕 Geological formations are currently considered the most promising sequestration sites. The National Energy Technology Laboratory (NETL) reported that North America has enough storage capacity for more than 900 years worth of carbon dioxide at current production rates.〔(NETL 2007 Carbon Sequestration Atlas ), 2007〕 A general problem is that long term predictions about submarine or underground storage security are very difficult and uncertain, and there is still the risk that might leak into the atmosphere. == Capture == Capturing is most effective at point sources, such as large fossil fuel or biomass energy facilities, industries with major emissions, natural gas processing, synthetic fuel plants and fossil fuel-based hydrogen production plants. Extracting from air is also possible, but not very practical because the is not concentrated.〔(【引用サイトリンク】title=Capturing Carbon Dioxide From Air )〕 Concentrated from the combustion of coal in oxygen is relatively pure, and could be directly processed. Impurities in streams could have a significant effect on their phase behaviour and could pose a significant threat of increased corrosion of pipeline and well materials.〔(【引用サイトリンク】title=Effects of Impurities on Geological Storage of CO2 )〕 In instances where impurities exist and especially with air capture, a scrubbing process would be needed.〔(【引用サイトリンク】title=Good plant design and operation for onshore carbon capture installations and onshore pipelines - 5 Carbon dioxide plant design )〕 According to the Wallula Energy Resource Center in Washington state, by gasifying coal, it is possible to capture approximately 65% of carbon dioxide embedded in it and sequester it in a solid form. Organisms that produce ethanol by fermentation generate cool, essentially pure that can be pumped underground.〔(【引用サイトリンク】title=News for the Business of Energy )〕 Fermentation produces slightly less than ethanol by weight. Broadly, three different types of technologies for scrubbing exist: post-combustion, pre-combustion, and oxyfuel combustion: *In ''post combustion capture'', the is removed after combustion of the fossil fuel — this is the scheme that would be applied to fossil-fuel burning power plants. Here, carbon dioxide is captured from flue gases at power stations or other large point sources. The technology is well understood and is currently used in other industrial applications, although not at the same scale as might be required in a commercial scale power station. *The technology for ''pre-combustion'' is widely applied in fertilizer, chemical, gaseous fuel (H2, CH4), and power production.〔(【引用サイトリンク】title=Gasification Body )〕 In these cases, the fossil fuel is partially oxidized, for instance in a gasifier. The resulting syngas (CO and H2) is shifted into and H2. The resulting can be captured from a relatively pure exhaust stream. The H2 can now be used as fuel; the carbon dioxide is removed before combustion takes place. There are several advantages and disadvantages when compared to conventional post combustion carbon dioxide capture.〔(integrated gasification combined cycle for carbon capture storage ) Claverton Energy Group conference 24th October Bath.〕〔(Energy Futures Laboratory and the Grantham Institute for Climate Change )〕 The is removed after combustion of fossil fuels, but before the flue gas is expanded to atmospheric pressure. This scheme is applied to new fossil fuel burning power plants, or to existing plants where re-powering is an option. The capture before expansion, i.e. from pressurized gas, is standard in almost all industrial capture processes, at the same scale as will be required for utility power plants. *In ''oxy-fuel combustion'' the fuel is burned in oxygen instead of air. To limit the resulting flame temperatures to levels common during conventional combustion, cooled flue gas is recirculated and injected into the combustion chamber. The flue gas consists of mainly carbon dioxide and water vapour, the latter of which is condensed through cooling. The result is an almost pure carbon dioxide stream that can be transported to the sequestration site and stored. Power plant processes based on oxyfuel combustion are sometimes referred to as "zero emission" cycles, because the stored is not a fraction removed from the flue gas stream (as in the cases of pre- and post-combustion capture) but the flue gas stream itself. A certain fraction of the generated during combustion will inevitably end up in the condensed water. To warrant the label "zero emission" the water would thus have to be treated or disposed of appropriately. The technique is promising, but the initial air separation step demands a lot of energy. An alternate method under development is chemical looping combustion (CLC). Chemical looping uses a metal oxide as a solid oxygen carrier. Metal oxide particles react with a solid, liquid or gaseous fuel in a fluidized bed combustor, producing solid metal particles and a mixture of carbon dioxide and water vapor. The water vapor is condensed, leaving pure carbon dioxide, which can then be sequestered. The solid metal particles are circulated to another fluidized bed where they react with air, producing heat and regenerating metal oxide particles that are recirculated to the fluidized bed combustor. A variant of chemical looping is calcium looping, which uses the alternating carbonation and then calcination of a calcium oxide based carrier as a means of capturing .〔(【引用サイトリンク】title=The Global Status of CCS: 2011 - Capture )〕 A few engineering proposals have been made for the more difficult task of removing from the atmosphere – a form of climate engineering – but work in this area is still in its infancy. Capture costs are estimated to be higher than from point sources, but may be feasible for dealing with emissions from diffuse sources such as automobiles and aircraft. The theoretically required energy for air capture is only slightly more than for capture from point sources. The additional costs come from the devices that use the natural air flow. Global Research Technologies demonstrated a pre-prototype of air capture technology in 2007.〔(【引用サイトリンク】title=First Successful Demonstration of Carbon Dioxide Air Capture Technology Achieved by Columbia University Scientist and Private Company )〕 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「Carbon capture and storage」の詳細全文を読む スポンサード リンク
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