Abstract
Abstract. Comprehensive field measurements are needed to understand the mercury emissions from Chinese power plants and to improve the accuracy of emission inventories. Characterization of mercury emissions and their behavior were measured in six typical coal-fired power plants in China. During the tests, the flue gas was sampled simultaneously at inlet and outlet of Selective Catalytic Reduction (SCR), electrostatic precipitators (ESP), and flue gas desulfurization (FGD) using the Ontario Hydro Method (OHM). The pulverized coal, bottom ash, fly ash and gypsum were also sampled in the field. Mercury concentrations in coal burned in the measured power plants ranged from 17 to 385 μg/kg. The mercury mass balances for the six power plants varied from 87 to 116% of the input coal mercury for the whole system. The total mercury concentrations in the flue gas from boilers were at the range of 1.92–27.15 μg/m3, which were significantly related to the mercury contents in burned coal. The mercury speciation in flue gas right after the boiler is influenced by the contents of halogen, mercury, and ash in the burned coal. The average mercury removal efficiencies of ESP, ESP plus wet FGD, and ESP plus dry FGD-FF systems were 24%, 73% and 66%, respectively, which were similar to the average removal efficiencies of pollution control device systems in other countries such as US, Japan and South Korea. The SCR system oxidized 16% elemental mercury and reduced about 32% of total mercury. Elemental mercury, accounting for 66–94% of total mercury, was the dominant species emitted to the atmosphere. The mercury emission factor was also calculated for each power plant.
Highlights
Mercury (Hg) is one of the most important environmental contaminants that has aroused a global concern due to its toxicity, long range transport, persistence and bioaccumulation in the environment
The six selected plants are located in different parts of China, and the coal collected from each plant has different qualities
Differences in coals quality may lead to a different behavior of mercury species in the flue gas
Summary
Mercury (Hg) is one of the most important environmental contaminants that has aroused a global concern due to its toxicity, long range transport, persistence and bioaccumulation in the environment. At the high temperatures in combustion zone of boilers, combustion releases the Hg in coal into the exhaust gas as elemental mercury (Hg0). This vapor may be oxidized by HCl, SO2, and fly ash in flue gas due to thermo-chemical processes (Meij et al, 2002; Niksa et al, 2004; Lee et al, 2006; Park et al, 2008). Emissions of Hg2+, may be efficiently controlled by typical air pollution control devices (APCD), such as electrostatic precipitators (ESP), fabric filter (FF), and flue gas desulfurization (FGD) systems (US EPA, 1997, 2000b, 2002a). Emission speciation is an important source of uncertainty when assessing the atmospheric fate
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