Mercury

Mercury in flue gas exists as gas-phase elemental mercury (HgO) and oxidized or ionic form of mercury, such as mercuric chloride, HgCl2 (HgII+) or mercuric oxide (HgO). Speciation (oxidation state) of the mercury influences the effectiveness of various control technologies and whether the mercury is deposited locally or transported over long distances. Emissions of elemental mercury, for example, can remain in the atmosphere for about a year and be transported over thousands of miles before being deposited.

Oxidized forms of mercury that are water soluble can be scrubbed out of the flue gas via scrubber, a cost-effective option if a FGD scrubber already exists. Alternatively, carbon injection followed by a fabric filter is an option to capture mercury. However, carbon injection contaminates any fly ash preventing its resale and creates a hazardous waste disposable problem once captured on the fabric filter.