Mechanistic study on the effect of ammonia co-firing with pulverized coal on NO formation and reduction

In this study, the heterogeneous formation and reduction mechanisms of NO by ammonia (NH3) were determined to evaluate the performance of NH3 co-firing with coal in NO emissions by density functional theory and canonical variational transition-state theory. NO formation is initialized by the dissociative adsorption of O-2 on the char, and the subsequent dehydrogenation reactions after NH3 adsorption are prioritized. NO reduction via char synergism with NH3 are also elucidated by the NNH dissociation or ONNH conversion. Thermodynamic and kinetic results indicate that introducing NH3 has the advantage of promoting heterogeneous NO reduction, which is characteristic of the synergistic effect afforded by the properties of char and reducing agent NH3. The reduction effect of NH3 on NO is more significant than its oxidation effect for NO formation at elevated temperatures, which provides theoretical evidence for the potential advantages of NH3 co-firing on NO emissions in coal-fired boilers.