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EVALUATION OF MERCURY SPECIATION AT POWER PLANTS USING SCR AND SNCR NOX CONTROL TECHNOLOGIES
Citation:
Laudal, D. L., J. S. Thompson, J. H. Pavlish, L. A. Brickett, P. Chu, R K. Srivastava*, C W. Lee*, AND J D. Kilgroe*. EVALUATION OF MERCURY SPECIATION AT POWER PLANTS USING SCR AND SNCR NOX CONTROL TECHNOLOGIES. Presented at International Air Quality Conference III, Arlington, VA, 9-12 Septmber 2002.
Description:
The paper describes the impact that selective catalytic reduction (SCR), selective noncatalytic reduction (SNCR), and flue gas-conditioning systems have on total mercury emissions and on the speciation of mercury. If SCR and/or SNCR systems enhance mercury conversion/capture, then they could be thought of as multipollutant technologies. Previous pilot-scale tests investigated the role that coal type plays in mercury speciation with the addition of ammonia (NH3) and the use of SCR. The results indicated that SCR and NH3 may enhance mercury capture, although it appeared that the impact was highly coal-specific. To validate pilot-scale results, sampling was conducted at the full scale, and seven power plants were chosen for full-scale sampling. Over a 10-12 day period, sampling was conducted at locations both before and after the SCR unit or NH3 injection point using both the wet-chemistry Ontario Hydro method and near-real-time continuous mercury monitors. Mercury variability, speciation, and concentration were evaluated. Additional sampling involved the use of EPA Method 26A to test for chlorides, a selective condensation method to measure SO3, and EPA Method 27 for NH3 slip. Fly ash and coal samples were also collected to obtain the mercury balance across the control devices. Although laboratory analyses and data interpretation are still ongoing, preliminary results indicate that SCRs can assist in converting elemental mercury to oxidized mercury. However, the effect appears to be coal-specific and possibly catalyst-specific. NH3 injection, whether directly as a gas or indirectly as urea, did not appear to have an effect on mercury speciation and removal.