Co-effects of sulfur dioxide load and oxidation air on mercury re-emission in forced-oxidation limestone flue gas desulfurization wet scrubber

Re-emission of Hg0 refers to the reduction of oxidized mercury (Hg2+) to the elemental mercury (Hg0) in a wet flue gas desulfurization process (WFGD), resulting Hg0 re-emits to the flue gas and increasing mercury emission for a coal combustion power plant. The correlations between re-emission of Hg0 and operation parameters of WFGD process, i.e., sulfur dioxide removal, oxidation air flow, and pH of FGD slurry, were investigated with mercury field data collected from two coal combustion power plants (Plant C and Plant O). At Units 31/32 of Plant C, Coupling mercury results and the plant information (PI) data suggested that an increase of the oxidation air flow in the WFGD effectively inhibited the re-emission of Hg0, and consequently increased the flue gas mercury removal efficiency from 63% to over 92%. But at Plant O, the increase of the oxidation air flow can sometimes increase Hg0 re-emission. It was further found that the re-emission of Hg0 at Plant O was strongly correlated not only to the flow rate of the oxidation air in the forced-oxidation operation conditions, but also to the amount of sulfur dioxide removed from the flue gas by the FGD scrubber (i.e., the sulfur dioxide load in the scrubber). Possible mechanisms were proposed.