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

• Hg0 could be oxidized over CaCl2.
• Adding CaCl2 to the SCR catalyst dramatically enhanced the Hg0 oxidation activity.
• Key factors on mercury oxidation over the catalyst added with CaCl2 were Optimized.
• Mercury oxidation was due to the combined action of HCl and Cl∗ generated by CaCl2.

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 °C, the calcium chloride addition dramatically enhanced the Hg0 oxidation activity over the catalyst. By adding 1.0 wt.% calcium chloride to the catalyst, the Hg0 oxidation efficiency rose from 7.7% to 78.8%. With a temperature increase from 100 °C to 400 °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 Hg0 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.