Mercurial powers

Simple, inexpensive modifications could have important implications for the environment by drastically reducing mercury emissions from coal-fired boilers, according to recent research.

The findings, from the Energy Research Centre (ERC) of Lehigh University in Pennsylvania, could cut flue-gas treatment costs at coal-fired power stations. This is good news for countries such as China which, with the fastest growing electricity generating market in the world, is almost totally dependent on coal.

Coal-fired power stations are one of the largest single sources of mercury emissions. It is generally emitted as a vapour, and if it enters the atmosphere, can fall to Earth as rain. Mercury is a neurotoxin, and once it enters the body of a living organism, it accumulates. If it enters the food chain, for example if it is ingested by fish, it can be dangerous to humans.

To remove gaseous mercury, power stations use systems such as filters made of activated carbon, which absorb the vapour. However, this is not a cheap process, as a large amount of carbon is needed — some 120kg/hour for a 250MW boiler. It is also expensive to verify levels of mercury emissions, because the toxic levels are very low, in the parts per billion range.