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EVALUATION OF THE EFFECT OF SCR ON MERCURY SPECIATION AND EMISSIONS
Citation:
Laudal, D. L., C. A. Wocken, P. Chu, L. A. Brickett, AND C W. Lee*. EVALUATION OF THE EFFECT OF SCR ON MERCURY SPECIATION AND EMISSIONS. Presented at International Conference on Air Quality IV, Arlington, VA, 22-24 Sept 2003.
Description:
The paper presents the results of an investigation on the impact that selective catalytic reduction (SCR) has on both the total emissions and the speciation of mercury (Hg). SCR systems can be used as multipollutant technologies if they enhance Hg conversion/capture. Previous pilot-scale tests investigated the role that coal type plays in Hg speciation with the addition of ammonia (NH3) and the use of SCR. The results indicated that SCR and NH3 may enhance Hg oxidation although the impact appeared to be highly coal-specific, which raised concerns regarding the applicability of the pilot-scale results to full-scale power plants. To investigate the role of SCR in mercury speciation at full-scale power plants, Hg was measured at seven different power plants equipped with SCR, four sets of measurements in the year 2001, two in 2002, and one in 2003. In addition, two of the plants tested in 2001 were retested in 2002 for a total of nine data sets. Sampling was conducted to evaluate the effect of SCR operation by testing both with and without the SCR in operation. Hg sampling was conducted using both the manual Ontario Hydro (OH) method and Hg semicontinuous emission monitors (Hg SCEMS). OH samples were taken at the SCR inlet and outlet, ESP venturi scrubber inlet and outlet, and at the stack. The Hg SCEMs were used to measure Hg speciation primarily at the outlet of the particulate control device. Fly ash and coal samples were also collected to obtain the Hg balance across the control devices. For plants firing eastern bituminous coals, there was an increase in Hg oxidization across the SCR catalysts. The effect SCR has on Hg speciation (i.e., extent of additional oxidation that occurs) is apparently dependent upon the coal characteristics and catalyst properties.