Mercury transformation across various air pollution control devices in a 200 MW coal-fired boiler of China

An onsite investigation of the mercury emission from a Chinese 200 MW pulverized coal (PC) boiler equipped with various air pollution control devices (APCDs) was conducted by using the Ontario Hydro method (OHM). The mercury mass balance was +4.6% of the input coal mercury for the whole system. Small amounts of mercury were detected in the bottom ash; nearly 90% of the mercury in PC was removed by the existing APCDs, i.e. selective catalytic reduction unit (SCR) and electrostatic precipitator (ESP) followed by fabric filters (FFs) baghouse, and flue gas desulfurization system (FGD). The concentration of oxidized mercury (converted from the elemental form) in the flue gas increased from 14% before SCR to 75% after SCR. Hence, the mercury removal efficiency of ESP and FGD was significantly improved when compared to the removal rates found in previous field measurement. This study demonstrates that the conversion of elemental mercury into the oxidized forms significantly improves the overall mercury removal efficiency of conventional APCDs, and most of the mercury emitted after FGD was in the elemental form. (C) 2009 Curtin University of Technology and John Wiley & Sons, Ltd.