Experimental study on mercury transformation and removal in coal-fired boiler flue gases

This paper reported mercury speciation and emissions from five coal-fired power stations in China. The standard Ontario Hydro Method (OHM) was used into the flue gas mercury sampling before and after fabric filter (FF)/electrostatic precipitator (ESP) locations in these coal-fired power stations, and then various mercury speciation such as Hg0, Hg2+ and HgP in flue gas, was analyzed by using EPA method. The solid samples such as coal, bottom ash and ESP ash, were analyzed by DMA 80 based on EPA Method 7473. Through analysis the mercury speciation varied greatly when flue gas went through FF/ESP. Of the total mercury in flue gas, the concentration of Hg2+ is in the range of 0.11–14.76 μg/N m3 before FF/ESP and 0.02–21.20 μg/N m3 after FF/ESP; the concentration of Hg0 ranges in 1.18–33.63 μg/N m3 before FF/ESP and 0.77–13.57 μg/N m3 after FF/ESP, and that of HgP is in the scope of 0–12.11 μg/N m3 before FF/ESP and 0–0.54 μg/N m3 after FF/ESP. The proportion of Hg2+ ranges from 4.87%–50.93% before FF/ESP and 2.02%–75.55% after FF/ESP, while that of Hg0 is between 13.81% – 94.79% before FF/ESP and 15.69%–98% after FF/ESP, with that of HgP is in the range of 0%–45.13% before FF/ESP and 0%–11.03% after FF/ESP. The mercury in flue gas mainly existed in the forms of Hg0 and Hg2+. The concentrations of chlorine and sulfur in coal and flue gas influence the species of Hg that are formed in the flue gas entering air pollution control devices. The concentrations of chlorine, sulfur and mercury in coal and the compositions of fly ash had significant effects on mercury emissions.