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EVALUATION OF SCR CATALYSTS FOR COMBINED CONTROL OF NOX AND MERCURY
Citation:
Srivastava*, R K., C W. Lee*, S. B. Ghorishi, W. Jozewicz, AND T. W. Hastings. EVALUATION OF SCR CATALYSTS FOR COMBINED CONTROL OF NOX AND MERCURY. U.S. Environmental Protection Agency, Washington, DC, EPA600/R-04/130, 2004.
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Description:
The report documents two-task, bench- and pilot-scale research on the effect of selective catalytic reduction (SCR) catalysts on mercury speciation in Illinois and Powder River Basin (PRB) coal combustion flue gases. In task I, a bench-scale reactor was used to study the oxidation of elemental mercury (Hg0) in simulated Illinois and PRB coal flue gases by a vanadium/titanium SCR catalyst. Elemental mercury oxidation on the order of 90% was observed in all the simulated coal flue gases. It was shown that hydrogen chloride (HCl) may be the critical flue gas component that causes the conversion of Hg0 to oxidized mercury (Hg2+) under SCR reaction conditions. Since high HCl concentrations are expected during combustion of all Illinois coals, firing these coals should result in significant Hg0 oxidation occurring across SCR reactors. Based on bench-scale results, an appropriate SCR catalyst was produced in pilot-scale and installed in a pilot-scale combustor for Task II studies. Three different Illinois coals (from high to low sulfur and chlorine) and one PRB coal were combusted in the pilot-scale unit. For the high sulfur/low chlorine Illinois coals, about 68% 84% Hg0 was measured at the inlet of the pilot-scale SCR reactor and below 16% Hg0 at the outlet of the SCR. Flue gas from the combustion of low sulfur/high chlorine Illinois coal had 21% Hg2+ at the inlet of the SCR, and the Hg0 content was decreased from about 73% at the inlet of the SCR reactor to about 4% at the outlet. For the PRB coal tests, the percentage of Hg0 decreased from about 96% at the inlet of the SCR reactor to about 80% at the outlet.