Effect of the existing air pollutant control devices on mercury emission in coal-fired power plants

Ontario-Hydro method (OHM) and semi-continuous mercury emission (SCEM) were used to study the effects of the existing air pollutant control devices on mercury emission in coal-fired power plants. The results indicate that more than 50% of Hg0 is oxidized into Hg2+ by selective catalytic (V2O5/TiO2) reduction (SCR), but SCR itself couldn't control mercury emission. The collection of fly ash by electrostatic precipitator (ESP) directly lowers the proportion of particle mercury in the flue gas. For water soluble Hg2+, wet flue gas desulphurization (FGD) could control mercury emission by absorbing Hg2+ in flue gas. Most of Hg2+ is reduced into Hg0 by reacting with SO32– and HSO3− in FGD slurry, which results in the decrease in mercury control efficiency. At the same time, it leads to the secondary emission of mercury, and it is more serious when SCR is in service.