Simultaneous Removal of SO2 and NOx From Flue Gas by Low-temperature Adsorption Over Activated Carbon

Abstract An exceptional phenomenon has been observed that nitrogen monoxide can be effectively adsorbed over activated carbon at cold temperatures with the presence of oxygen. Based on this finding, a novel low temperature adsorption process is developed to simultaneously remove SO2 and NOx from flue gas with a target of near-zero emission. In this study, the adsorption characteristics of NO and SO2 over activated carbon at various temperatures (-20, 0, 20 and 80℃) are experimentally investigated. For NO-O2 co-adsorption, NO-NO2 equilibriums with increasing NO2 concentration along the the adsorption bed are established due to the catalytic oxidation of NO over activated carbon. Co-adsorption of NO-NO2 occurs at each cross section of the adsorption bed and the adsorption capability increases along the adsorption bed with increasing NO2 concentrations. The oxidation rate of NO can be significantly enhanced at cold temperatures, which leads to an extraordinary improvement of NO adsorption. At a space velocity of 5000h-1 and an initial NO concentration of 200 ppmv, the breakthrough time increases from 3.49 to 1591.75 minutes when the temperature decreases from 80 to -20℃. In addition, the adsorption capacity of SO2 is also dramatically increased at cold temperatures. At a space velocity of 5000h-1 and an initial SO2 concentration of 1000 ppmv, the breakthrough time increase from 20 to 265 minutes when the temperature decreases from 80 to -20℃. A pilot-scale testing platform with a flue gas flowrate of 3600 Nm3/h is developed to validate this novel adsorption process for simultaneous desulfurization and denitrification. Emission of both SO2 and NOx is less than 1mg/Nm3, and the predicted energy penalty is about 3% of the net generation.