Abstract
The elemental mercury (Hg0) removal performance of wet electrostatic precipitator (WESP) was studied on a lab-scale experimental device. Increasing voltage in WESP promoted the Hg0 oxidation because higher-energy electrons in the electric field accelerated the discharge of O2 and H2O to form free radicals like O, O3 and OH. The oxidation of Hg0 by O2-ionized products was the dominant pathway for Hg0 removal in WESP. H2O played an inhibitive role in Hg0 removal. The presence of H2O competed with O2 for electron energy to form OH, thus inhibiting the generation of O and/or O3. The OH could oxidize Hg0 into HgOH; however, HgOH tended to decompose and release as Hg0. The wash-down effect of water film could collect part of Hg0, which could partly offset the inhibitive effect of H2O on Hg0 removal. As Hg0 is insoluble, the Hg0 removal by wash-down of the water film was insignificant in WESP. Mercury re-emission existed in WESP because of the water-insolubility of Hg0 and the instability of HgOH. The findings indicate that oxidizing Hg0 by radicals in the electric field of WESP might be a feasible method for removing Hg0 from power plants.
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