Letter: Carbon capture caveats

From Luc Gagnon

Recent articles have discussed the future potential of carbon dioxide capture and storage: for example, your editorial on 17 March (p 5). They focus mainly on two questions: Is it possible to capture CO₂? Will the storage be reliable in the long term? The answers are “yes”, and “don’t know”.

There are in addition major issues that these discussions neglect. CO₂ capture is energy intensive. On a life-cycle basis, it will reduce the effective output of a coal-fired power plant by 25 to 40 per cent, depending on the distance to the storage area. Capturing sulphur dioxide, to mitigate acid rain, reduces output by about 10 per cent.

CO₂ capture imposes a huge waste-management challenge. The volume and weight of wastes is greater than the volume and weight of the coal being burned. This issue is unavoidable, because of the carbon content of coal: 70 to 80 per cent, compared with 1 to 2 per cent sulphur.

Very few of the world’s coal-fired plants are scrubbing SO₂ emissions, because of the efficiency penalty and waste-management challenge, so how many would be prepared to take on the much greater burden imposed by CO₂ capture?

Assume, however, that CO₂ capture technologies will become affordable and that reliable long-term storage proves possible. We will then have to recognise that the life-cycle emissions factor of a “clean coal” plant will remain high. A realistic CO₂ capture rate will be about 85 per cent, not 100 per cent. Moreover, emissions due to extraction, processing and transportation of coal would not be captured. If the energy penalty of CO₂ capture is 30 per cent, 30 per cent more coal will have to be extracted, processed and transported to provide the same final service.

These factors have been reported in numerous life-cycle assessments of CO₂ capture. The key is to put them together to give a complete picture of what the options are.

The editor writes:

• This letter expresses a personal view, but Gagnon points out that he is Senior Advisor, Climate Change, for Quebec-Hydro.

Montreal, Canada