Mercury Vapor Pressure
of Flue Gas Desulfurization
Scrubber Suspensions: Effects of pH Level, Gypsum, and Iron
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Abstract
Calcium-based scrubbers designed to absorb HCl and SO<sub>2</sub> from flue gases can also remove oxidized mercury. Dissolved
mercury
halides may have an appreciable partial vapor pressure. Chemical reduction
of the dissolved mercury may increase the Hg emission, thereby limiting
the coremoval of mercury in the wet scrubbing process. In this paper
we evaluate the effects of the pH level, different gypsum qualities,
and iron in flue gas desulfurization (FGD) scrubber suspensions. The
impact of these parameters on mercury vapor pressure was studied under
controlled laboratory conditions in model scrubber suspensions. A
major influence is exerted by pH values above 7, considerably amplifying
the mercury concentration in the vapor phase above the FGD scrubber
suspension. Gypsum also increases the mercury re-emission. Fe(III)
decreases and Fe(II) increases the vapor pressure significantly. The
consequences of the findings for a reliable coremoval of mercury in
FGD scrubbers are discussed. It is shown that there is an increased
risk of poor mercury capture in lime-based FGD scrubbers in comparison
to limestone FGD scrubbers