Studying the mechanism and impact of H2O-rich atmosphere on N oxidation during ammonia combustion and ammonia-coal co-combustion

Abstract

Carbon-free fuel ammonia and coal co-combustion, an effective way to reduce thermal power CO2 emissions, has attracted more and more attention in recent years. Due to the hydrogen-rich property of ammonia, more H2O is generated during combustion, and the high H2O atmosphere significantly affects the NOx formation. Therefore, it is necessary to explore the oxidation path of N in the combustion of ammonia and its coupling coal in the H2O atmosphere. In this study, quantum chemistry theory and transition state theory are used to investigate the influence mechanism of H2O atmosphere on the oxidation of ammonia and fuel-N in the ammonia-coal co-combustion. The results show that the presence of OH in the H2O atmosphere promotes the formation of NH2 and NH, which is conducive to their oxidation to HNO and NO. The condition without OH is conducive to the oxidation of ammonia to HNO, and the presence of OH promotes the further oxidation of HNO to NO in the co-combustion of ammonia and coal. The H2O atmosphere reduces the energy barrier value of rate-determing step for ammonia and coal char oxidation during co-combustion, and increases the oxidation rate of ammonia-N and char-N. This work reveals the molecular mechanism by which H2O atmosphere promotes the combination of OH and O2 to generate HO2, and discovers the temperature conditions for HO2 formation. This study provides theoretical support for the development of N oxidation mechanism in the ammonia-coal co-combustion.