Removing CO₂ from combustion gases in production of electricity from coal

Carbon dioxide (CO₂) is a product of combustion of all carbonaceous materials, not excepting coal. It is the only pollutant that nature is able to process and recycle completely - plants, seaweed, coral, zooplankton and other organisms incorporate it in the formation of their structure. Sedimentary complexes of limestone and other carbonate rocks of kilometre thickness as well as coal seams, oil and natural gas deposits are nothing else than carbon dioxide converted to stone by actions of live creatures.

In the present, however, a hitherto insufficiently examined theory prevails according to which the production of CO₂ in the course of human activity causes the changes in climate. Although no-one has clarified so far why there were even greater climatic deviations in the past than those we can observe nowadays, political measures against emissions of carbon dioxide are being adopted. As production of electricity in coal-burning plants has approximately a one-third share of worldwide emissions of CO₂, there is a strong pressure on the part of politicians (EU in particular) and environmental groups to reduce this share.

CCS – storing of CO₂ into underground tanks

Removal of CO₂ emissions from combustion gases in coal-burning plants is easier than from any other sources. At present, it is expected that the CCS method - Carbon Capture and Geological Storage - will be applied primarily. Geological formations from which oil and natural gas has been exploited, unworkable coal strata, salt domes and similar formations with overlying confining seams appear to be suitable for capturing of CO₂. It is a technology similar to that which is used in underground containers of natural gas for creation of reserves. As a matter of fact, this concerns artificial repetition of biological processes in the course of which in the distant geological past carbon dioxide was bound into rocks.

Risks

Storing of CO₂ into underground tanks also produces certain problems. In particular, it increases the costs of electricity production. Also, the process has to be safe enough so that the gas does not leak over the period of many thousands of years. Some experts thus reason that a closed cycle of carbon utilization would be more appropriate than underground storage.

Pilot project

The Air Liquid company is preparing a CCS pilot project in France. The storage will be carried out in the Lacq site in the south-east of the country into geological strata from which natural gas was exploited. The technology is based on the principle of air replacement during combustion by oxygen. The result is a high concentration of CO₂ in combustion gases, which improves the efficiency of capturing. The project is due to start in 2008. In the course of two years 150,000 t of CO₂ is to be stored underground.