Most coals contain a small amount of mercury and this can easily end up being discharged in the flue gas from a coal-fired power plant. In the United States the emission of mercury is to be regulated and proposals have also been put forward in the EU. This will necessitate the introduction of effective capture methodologies.
Dust removal systems in power plants will remove around 25% of the mercury released during combustion. When a wet scrubbing sulfur removal system is installed too this can increase to 40–60%. Adding SCR can lead to 95% removal with bituminous coals. However, sub-bituminous coals and lignites do not respond well so alternative measures may be needed to reduce mercury emissions to below regulatory limits.
The injection of activated carbon particles has been used to remove impurities such as mercury in waste incineration plants, and this appears to offer the best solution where further mercury capture is necessary. The carbon particles will then be removed in the dust removal system through which the flue gases pass at a later stage. It is expected that plants will eventually need to remove 90% or more of the mercury released during combustion.