Experimental Study And Field Test On The Emission And Control Of Fine Particulates And Trace Element From Coal Combustion

Coal-fired power generation is now the main power generation method in China. Many kinds of air pollutants can generate in the process of coal combustion, in which the particulate matter and trace element have drawn increasing attention of the society. In recent years, the development and application of a number of new technologies can impose many effects on the emission and control characteristics of particulate matter and trace element. In view of this situation, at first the effects of high concentration H2O, SO2and HCI on the emission and control characteristics of particulate matter and trace element under oxy-fuel combustion were studied through the laboratory experiments, and then, the variation characteristics of particulate matter and trace element in flue gas duct and the effect of low temperature economizer on the reduction of the two pollutants by electrostatic precipitator (ESP) were researched by the way of field test.The detailed experimental methods and main conclusions are shown as follows:(1) The coal combustion experiment under oxy-fuel combustion was conducted in the high temperature drop tube furnace, to investgate the effect of high concentration CO2, H2O and SO2on the generation characteristics of particulate matter and distribution characteristics of trace element under oxy-fuel combustion. From the experimental results, compared to the air combustion, oxy-fuel combustion can significantly reduce the generation of particulate matter and the volatility of trace element, but can increase the trace element concentration in particulate matter. Under oxy-fuel combustion, the high concentration H2O can obviously enhance the yield of particulate matter and the migration of trace element to particulate matter, however, decrease the trace element concentration in particulate matter. High concentration SO2has nearly no effect on the generation of particulate matter, but can decrease the total amount and concentration of trace element in the particulate matter to some extend under oxy-fuel combustion.(2) The reduction of PM0.2(particle with aerodynamic diameter less than0.2μm) and adsorption of Na vapor by kaolinite under oxy-fuel combustion was carried out in the high temperature dorp tube furnace. The effect of H2O and HCl on the efficiency of kaolinite was clarified by the particulate matter experiment, and the influence of H2O and HCl on the action mechanisms of kaolinite was detailedly interpreted through the Na vapor experiment and thermal equilibrium calculation. The experimental results indicate that, H2O can improve the migration rate of Na vapor and the reaction rate between Na vapor and kaolinite, and hence enhance the adsorption of Na vapor by kaolinite. The addition of high concentration H2O can increase the reduction absolute value of PM0.2, but decrease the reduction ratio of PMo.2-HC1can promote the volatilities of alkali metal and alkaline earth metal, and inhibit the reaction between these metals and kaolinite, then decrease the efficiency of kaolinite. The action mechanisms mentioned above are also adequate for the adsorption of trace element such as Pb and Cd by kaolinite.(3) The particulate matters from the inlet of selective catalytic reduction (SCR), ESP and flue gas desulfurization (FGD) in a220MW power plant in China were sampled by the DGI system, to study the variation characteristics of the mass size distribution and main chemical composition of particulate matter along the flue gas duct, and to investigate the migration characteristics of trace element along the flue gas duct. The experimental results reveal that, compared to the inlet of SCR, the yield of supermicron particulate matter at the inlet of ESP decreases. The S content in particulate matter increases along the flue gas duct, but in contrast, the concentration of Al and Si in the particulate matter decrease along the flue gas duct. When the flue gas go from the inlet of SCR to the inlet of ESP, the masses of As, Cd, Cr and Pb which converting from vapor phase to solid phase account for26%,16%,12%and11%of the total mass respectively. Most of the trace elements remain in the ESP fly ash, and the part escaped from ESP is very little. The masses of As, Cd, Cr and Pb in the each size segment of PM10(particle with aerodynamic diameter less than10μm) at the inlet of FGD increase with the decreasing particle size, however, the mass size distribution of Mn corresponds to that of particulate matter. (4) To investigate the effect of low temperature economizer on the removal of particulate matter and trace element by ESP, the low pressure impactor (LPI) and gravimetric impactor (DGI) system were applied to the particulate matter sampling in a660MW power plant in China. From the results, the low temperature economizer can significantly enhance the efficiency of the ESP, and can obviously decrease the mass of the particulate matter at the outlet of ESP. The low temperature economizer can enhace the collection efficiency of minor element by ESP, and the enhacement becomes weaker with the volatility of minor element becomes higher, in the meantime, the low temperature economizer can also reduce the emission of trace element at the outlet of ESP. The low temperature economizer can decrease the relative enrichment factors of As, Cd, Cr and Pb in PM0.2-0.5(particle with aerodynamic diameter in0.2-0.5μm) to some extend.