环境地球化学国家重点实验室知识库

Mercury (Hg) emitted from two circulating fluidized bed (CFB) utility boilers (150 MW, P#1 and 300 MW, P#2) in Guizhou province, Southwest China, was characterized. P#1 used anthracite coal and was equipped with in-furnace desulfurization (IFD) and electrostatic precipitator (ESP). P#2 co-burned gangue and coal slime and was equipped with selective non-catalytic reduction (SNCR), ESP, fabric filter (FF) and limestone gypsum wet flue gas desulfurization (WFGD). Flue gas samples from the inlets and outlets of air pollution control devices (APCDs) in the two plants were analyzed using the Ontario Hydro Method (OHM). Solid samples including feed coal, limestone, bottom ash, fly ash and gypsum were also collected and analyzed. Hg removal efficiency by the APCDs and Hg emission factors (MEFs) were estimated. Total Hg (THg) in the flue gas at the inlet of ESP are 32.3 µg·m⁻³ and 15.3 µg·m⁻³ for P#1 and P#2, respectively, both dominated (95.11–99.26%) by the particulate form (Hg^p). THg decreased significantly to 0.19–0.24 µg·m⁻³ at the final APCDs outlets of these two power plants, yielding an overall Hg removal efficiency of 98.53–99.41% for THg. Mass balance analysis indicated that >97% of Hg in coals ended up in captured fly ash. MEFs of the two tested power plants are relatively lower than the values typically found in CFB and pulverized coal (PC) utility boiler power plants. The emission data of Hg from CFB coal-fired power plants should be updated and attention should be directed to the secondary emission/release of Hg from the captured fly ash.