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Clean Coal: A New Fossil Fuel Technology?There has been a lot of talk in the media of recent times about introducing Clean Coal technology to combat CO2 emissions from coal fired power stations. Indeed, the former Liberal government of Australia was strongly favouring this approach in combination with nuclear energy rather than turning to solar power or other alternatives in a meaningful way. The present left wing Australian government has also hinted at pursuing this technology. Give the fact that the International Energy Agency expects a 43% increase in coal use from 2000 to 2020 it would seem that the need to reduce CO2 emissions from the burning of this fossil fuel is essential.
Clean Coal…What Is It?
This is an experimental technology aimed at removing carbon dioxide from the emissions of coal fired power stations. The ultimate goal of this process is to have no CO2 emissions from coal fired power stations. Despite the talk this is still in the testing stage and is not yet commercially viable on a large scale. The Australian CSIRO Chief of Energy Technology Division, David Brockway, has estimated that the technology will not be commercially viable until between 2020 and 2025 (Crikey.com.au February 2007).Given that the majority of climate scientists are now saying that immediate reductions in greenhouse gas emissions are needed, the value of clean coal technology seems questionable. How it works.The current way of removing CO2 from a gas stream is with a process called amine scrubbing. This involves passing the gas stream through a cool amine solution, which then absorbs the CO2. Amines are the building blocks for proteins. The amine solution is then moved to another part of the processing plant. Since gases are less soluble at higher temperatures, the solution then is heated to release the CO2. This process produces very high purity CO2 gas.At present this technology is used mainly for obtaining high purity CO2 gas for industrial processes and is not applied in a widespread manner to power station emissions. It is also an expensive process and has an energy cost associated with it which reduces the environmental efficiency of the process. CO2 emissions from coal fired power stations contain approximately 14% CO2 which makes the amine scrubbing method of its removal expensive. Methods are being researched to increase the concentration of CO2 in the emission stream in order to improve capture rates via processes such as amine scrubbing. One such method is the Integrated Coal Gasification Combined Cycle, or IGCC for short. Technical details aside, this process aims to increase the purity of CO2 in the emission stream from the power plant while increasing efficiency. Coal is pulverised into a gas, then this happens: This process provides excellent thermal efficiency, up to 60% for the overall process. It also provides a high percentage purity of CO2 in the emissions, which increases the efficiency of CO2 capture processes. Commercial uses of CO2The CO2 extracted from power station emissions has several commercial uses. A major use is in the enhanced recovery of oil, where it is pumped underground beneath oil bodies in order to force the oil out of the porous rocks it is lodged in. CO2 is ideal for this job since it is very stable and does not readily dissolve in liquids.There is also the possibility to inject CO2 into deep, unmineable deposits of coal. This forces methane gas, CH4, to be broken off the coal molecules and rise upwards, potentially providing a source of natural gas which would then be burnt as fuel. Disposal of excess CO2Current commercial uses of CO2 are massively outweighed by our production of this gas, so finding ways to store the excess are essential. If we are to pursue clean coal as an energy source, disposing of the greenhouse gas CO2 will become a critical issue.GeosequestrationThis is the term for storing CO2 underground. Potential sites for this storage include deep saline aquifers and depleted oil and gas fields. CO2 can be injected in liquid form (requiring lots of cooling and pressure to achieve) and stored there indefinitely. This does not seem to be an ideal situation though given the stability and non-reactivity of CO2. Should these storage locations be compromised from, say, geological activity, the effect will be a greenhouse gas release of large proportions.
References for Clean Coal: Uranium Information Centre Ltd, Australia: Briefing Paper # 83 Return from Clean Coal to Fossil Future or return to the Green Planet home page for more Solar Power Facts.
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