Citation:

CHANG, J. C., B. GHORISHI, AND Y. ZHAO. PREVENTION OF ELEMENTAL MERCURY REEMISSIONS FROM ILLINOIS COAL WET SCRUBBERS. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-05/075 (NTIS PB2006-102387), 2005.

Description:

This research conducted pilot plant tests to investigate techniques for controlling and reducing Hg⁰ re-emissions. A pilot-scale (0.01MW) wet scrubber was designed to simulate the wet limestone flue gas desulfurization system. Hg⁰ re-emissions, manifested by an increase of flue gas Hg⁰ concentrations across the scrubber, were detected when sufficient amount of Hg²⁺ was accumulated in the slurry. Experimental results indicated that the higher the slurry pH was, the more Hg⁰ re-emitted. Hg⁰ re-emissions decreased with temperature decline. However, no significant change of Hg⁰0 re-emissions was observed with temperature increase. Two potential additives, trimercapto-s-triazine tri-sodium (TMT) and sodium hydrosufide (NaHS) were tested for their effects on the Hg⁰ re-emission rate in flue-gas desulfurization systems. Pilot plant data showed both TMT and NaHS capable of inhibiting Hg⁰ from re-emission in a wet scrubber. When used as additives, the TMT and NaHS concentrations in the slurry need to be higher than 0.1 ppm and 0.01 ppm, respectively, to induce sustainable inhibitory effects. Based on the pilot plant test results, it was recommended that limestone wet scrubbers should be operated with pH and temperature as low as possible to minimize Hg⁰ re-emissions. Both TMT and NaHS are viable options as additives to suppress Hg⁰ re-emissions in wet scrubbers.

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