Study on the influence mechanism of mineral Ca on NO reduction in the high temperature oxygen-lean zone of ammonia-coal co-combustion

Abstract

Ammonia-coal co-combustion can effectively reduce CO2 emissions in power plant. However, ammonia, as an N source, will increase NOx foamation path when it is co-fired with coal. It is very necessary to explore the NO reduction mechanism in ammonia-coal co-combustion to realize low-nitrogen emissions. In this study, the mechanism of NO reduction in the high temperature oxygen-lean zone of ammonia-coal co-combustion is explored through experiment and quantum chemical theory calculation, and the influence mechanism of Calcium, an important mineral in coal, on the reduction of NO by NH3 and char is further explored. The experimental results show that mineral Ca in char inhibits NO reduction by char and ammonia. Under the same temperature and NSR, the efficiency of NO heterogeneous reduction by char impregnated with Ca is lower than that by demineralized char. Theoretical calculation results have shown that amino/char in the high-temperature lean-oxygen area can reduce NO to N2 through the formation of important transition intermediates such as NNH and N2O, and the participation of Ca inhibits the reduction of NO by NH3 and char. Ca enhances the binding energy between the NNH group and the char surface, so that under the participation of top-Ca, the energy barrier of the rate-determining step is 197.92 kJ/mol higher than that of the NH/char/NO system. The participation of face-centered Ca has a stronger inhibitory effect on NH/char/NO system than that of top-Ca. The kinetic results show that the reduction rate of NO by NH on the char surface in the presence of Ca is lower than that in the absence of Ca.