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Possible ways of capturing the carbon
Oxyfuel combustion, the method being used in Germany by Vattenfall, burns fossil fuels in 95 per cent pure oxygen instead of air. This results in a flue gas with high CO2 concentrations that can be compressed for transport and storage.
Pre-combustion capture systems remove CO2 before combustion by gasifying the fossil fuel. This produces a mix of carbon monoxide, methane and hydrogen which is then reacted with steam. The carbon in the methane and in the carbon monoxide grabs the oxygen atom from the steam (H2O) to leave just hydrogen and CO2. The CO2 is separated out and the hydrogen is burned. China and Australia are building plants which use this technique.
Post-combustion techniques treat power station flue gas. Flue gas typically contains up to 14 per cent CO2, which can be separated out by chemical or physical absorption, cryogenics or the use of membranes. Chemical absorption with amines is currently preferred. Once recovered, the CO2 is cooled, dried and compressed for transport. Existing coal power stations will have to use this post-combustion technique but it is costly to install - perhaps $1600/kWe – and takes a lot of energy to operate. One estimate is that it would reduce the output of an existing 500MW subcritical pulverized coal power plant by over 40 per cent to 294MW.
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Richard Douthwaite |
| About the author: |
| Richard Douthwaite is an economist and writer with a special interest in climate and energy issues and local economic development.
He is a co-founder of Feasta, the Foundation for the Economis of Sustainability, the Dublin-based international network of people who believe that the world's sustainability problems are due to the use of dysfunctional systems and are trying to develop better ones. He is co-editor of the Feasta Review, which carries cutting-edge thinking on sustainability issues. He led a recently-completed research project which was commissioned from Feasta by the Irish Government’s Environmental Protection Agency into the effects that very much higher energy prices might have on the various sectors of Irish life..
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