Mass Flow Analysis of Mercury Transformation and Effect of Seawater Flue Gas Desulfurization on Mercury Removal in a Full-Scale Coal-Fired Power Plant

To understand the mercury speciation and mass flow in a full-scale bituminous coal-fired power plant equipped with a selective catalytic reduction (SCR) unit, an electrostatic precipitator (ESP), and a seawater flue gas desulfurization (SWFGD) scrubber, the evolution and emission of mercury was systematically measured and analyzed. The results showed that the elemental mercury (Hg-0) was oxidized mainly through heterogeneous oxidation, especially in SCR, which transformed 57-64% of elemental mercury (Hg-0) to oxidized mercury (Hg2+). It changed the concentrations of different mercury species and then increased the Hg2+ removal efficiencies of SWFGD, which ranged from 67 to 82%. A total of 8.24-11.54% of mercury was adsorbed by fly ash to form particulate-bound mercury (Hg-P) and subsequently removed by the ESP. Mass flow and mass distribution of mercury indicated that most mercury was removed and retained in the SWFGD. The heterogeneous oxidation of Hg-0 in SCR and then absorption of Hg2+ by SWFGD significantly enhanced the mercury removal in the studied coal-fired power plant, although a part of Hg2+ absorbed in SWFGD was reduced and released back to the flue gas. Hg2+ was a little more than Hg-0 in the flue gas emitted to the atmosphere. In addition, the SWFGD system without limestone addition may be beneficial for decreasing the re-emission of Hg-0. The mercury emission factor at the power plant is 4.098 g/TJ, which is lower than that at other power plants without SCR. The configuration of SCR + ESP + SWFGD enhances the co-benefit mercury control.