Mercury adsorption characteristics of Cl-impregnated activated carbons in simulated flue gases

Abstract

Activated carbon injection upstream of a particulate matter control device is a general method to control mercury in a coal-fired flue gas. Nitrogen oxides (NOx) and hydrogen chloride (HCl) in flue gas have been reported to increase the efficiency of activated carbon for mercury removal. In a coal-fired power plant, a NOx control device is generally located upstream of a particulate matter control device. In addition, if coal with a low chloride (Cl) content is burned, the concentrations of NOx and HCl may be low in the flue gas upstream of a particulate matter control device. Under these conditions, chemically promoted activated carbon is necessary to effectively control mercury. This study was designed to suggest the best chloride compound impregnated on activated carbon depending on the flue gas composition. HCl, ferric chloride (FeCl3) and cupric chloride (CuCl2) were impregnated with an identical concentration of Cl on activated carbon. Then, each sorbent was tested using a fixed-bed reactor system at 140 °C. CuCl2-impregnated activated carbon (CuCl2-AC) was tolerant of SO2 gas. The mercury adsorption efficiency was higher in the order of CuCl2-AC, FeCl3-impregnated activated carbon (FeCl3-AC) and HCl-impregnated activated carbon (HCl-AC) with 1% Cl for all three sorbents for the tests with a simulated flue gas of 12% CO2, 5% O2, 7% H2O, 60–70 µg/m3 Hg0, 500 ppm SO2, 20 ppm NO and N2 balance gas. However, the mercury adsorption efficiencies among the Cl-impregnated activated carbon sorbents became more similar with the increase in Cl concentration on activated carbon.