| Mercury has long been identified as a hazard to human health and the environment. Since coal-fired power plants represent a significant fraction of the anthropogenic emissions of mercury into the atmosphere, the speciation and control of mercury in coal-fired power plants is currently an active topic of research.First, the physical and chemical properties, the distribution and occurrence characteristics of Chinese coal were presented in the paper. The information of mercury measurement and control in coal-fired power plants was introduced systematically. Based on Ontario-Hydro method, the method of the mercury sampling, disposal and analysis method (CVAFs) was established.The coal sample was heated in heating oven, the mercury content of the residual after coal combustion or pyrolysis was investigated with different temperature and heating time. The results indicate that mercury in coal during coal combustion discharge faster than during coal pyrolysis. Nearly all of the mercury in coal samples discharge rapidly in gaseous state at high temperature (above 700℃) during coal combustion or pyrolysis.The studies of the mercury transformation mechanism with different coal combustion mode were performed. Coal of grate firing, suspension firing and fluidi/ed bed firing experiments were carried out respectively in a quartz tube furnace, a bench-scale pulverized coal furnace and a pilot-scale CFB system. The experimental data showed that the speciation of mercury occurring under the above three systems were similar, however mercury behave differently because of the difference of the combustion conditions and coal species etc.The data of coal grate firing and suspension firing shows that the gaseous mercury concentrations in the flue gas range from 10 and 15 (μg/Nm3, emissions of mercury are approximately 40% divalent mercury (Hgg2+) in the flue gas, and mercury in the ash was below 20%, which suggested that most of the mercury went into the flue gas in gaseous state. In addition, the cooling rate of hot flue gas is considered to be an important factor tending to increase the conversion ratio of elemental mercury (Hgg0) to divalent mercury (Hgg2+) with slower cooling rate.Stone coal mixed with bituminous coal combustion in fluidized bed System showed that the gas phase concentration of mercury in the flue gases is 6.8-9.3 μg/Nm3, the content of mercury in ash and flue gas is about 90%, and in bottom ash, the content is very low. The effect of limestone as the additive into stone coal is obvious, it increases the content of mercury in ash and decreases the mercury content in flue gas.The mechanisms and rate of elemental mercury (Hg0) capture by activated carbons andother sorbents such as fly ash, lime, zeolite, roseite and bentonite, have been studied using a bench-scale fixed-bed apparatus. The effects of inlet mercury concentration, flue gas composition, and adsorption temperature were investigated to determine the abilities to remove mercury in simulated flue gas streams. The amount of mercury adsorbed increased with increasing carbon content. Temperature had a tremendous impact on the adsorbed-phase mercury concentration, the adsorption capacities increased as the temperature decreased. These data are consistent with a physical adsorption mechanism. However the adsorption capacities were also affected by flue gas composition, SO2 HC1 and other flue gases, which suggested the mechanism is not purely physical, may be a combination of physisorption and chemisorption. Sorbents modified chemically resulted an increase of mercury removal capacity. Activated carbon were impregnated with chloride, The chloride content of chloride-impregnated AC increased slightly, which resulted an increase of mercury removal capacity.A Theoretical model was developed to predict mercury removal based on sorbents characteristics as determined in laboratory fixed-bed reactor tests at different conditions. The simulation results indicated that the model is capable of describing the te...
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