DISTRIBUTION OF MERCURY SPECIATION IN COAL-FIRED PLANTS

摘要

Two 200MW, pulverized bituminous coal-fired electric utility boiler equipped with a five-field cold-side electrostatic precipitator (ESP) as the only air pollution control device (APCD) were investigated into mercury distribution and speciation under various conditions. Both facilities consume same fuel and are in the same configuration except for the different burner type, low-NOx burners versus conventional ones. Sampling points of gaseous mercury and chlorine species were selected at both the inlet and outlet of the ESP. The mercury concentration in various solid samples such as parent coal, bottom slag, economizer bottom ash, fly ash in different hoppers of ESP, was sampled and analyzed. The Ontario Hydro Method (ASTM D6784) was employed to detect mercury in flue gas as well as the EPA method 26 was carried out to detect HCl and Cl2. A series of tests were conducted on the boiler with low-NOx burners under various load (70, 85 and 100% of full load) and on the other boiler with conventional burners under full load. Results showed that, under all experimental conditions, small amount of mercury were remained in the solid combustion product and most of mercury were released into atmosphere. Among the released mercury, major proportion was in oxidized form. Burner type and load variation had effects on Cl species concentration in flue gas, particle diameter and carbon content and specific surface area of fly ash, in further, affected speciation and distribution of mercury and mercury removal efficiency of ESP.