Development of dry control technology for emissions of mercury in flue gas

In flue gases from coal-combustion systems, mercury in either the elemental state or its chloride form (HgCl2) can be predominant among all the possible mercury species present; this predominance largely depends on the chlorine-to-mercury ratio in the coal feeds. Conventional flue-gas cleanup technologies are moderately effective in controlling HgCl2 but are very poor at controlling elemental mercury. Experiments were conducted on the removal of elemental mercury vapor by means of a number of different types of sorbents, using a fixed-bed adsorption system. Of the four commercial activated carbons evaluated, the sulfur-treated carbon sample gives the best removal performance, with good mercury-sorption capacities. Promising removal results also have been obtained with low-cost minerals after chemical treatments. These inorganic sorbents could potentially be developed into a cost-effective alternative to activated carbons for mercury removal.