Study of elemental mercury oxidation over an SCR catalyst with calcium chloride addition

Elemental mercury in the flue gas of coal combustion is challenging to remove. A new method is introduced of adding calcium chloride to a commercial SCR catalyst in a fixed bed to evaluate the effect on elemental mercury oxidation. In simulated coal combustion flue gas at 350 degrees C, the calcium chloride addition dramatically enhanced the Hg-0 oxidation activity over the catalyst. By adding 1.0 wt.% calcium chloride to the catalyst, the Hg-0 oxidation efficiency rose from 7.7% to 78.8%. With a temperature increase from 100 degrees C to 400 degrees C, the catalytic oxidation efficiency of elemental mercury considerably increased, and mercury capture by the catalyst dropped. Both oxygen and sulfur dioxide exhibited promotional effects on Hg oxidation, whereas water vapor inhibited it. No apparent difference was observed by varying the nitric oxide concentration. The positive function of calcium chloride addition on elemental mercury oxidation is due to two reasons: hydrogen chloride formed through the hydrolysis process of calcium chloride and active chlorine species generated by calcium chloride. Experimental study showed that no significant effect of calcium chloride addition on NOx reduction and SO2-SO3 conversion has been observed. Because oxidized mercury can be easily removed by traditional pollutant control equipment and because calcium chloride is enriched in the wastewater of the wet flue gas desulfurization system in power plants, this method shows a reasonable simultaneous mercury reduction method. (C) 2014 Elsevier B.V. All rights reserved.