Simplified Mechanisms of Nitrogen Migration Paths for Ammonia-Coal Co-Combustion Reactions

Ammonia–coal co-combustion has emerged as a promising strategy for reducing carbon emissions from coal utilization, although its underlying reaction mechanisms remain insufficiently understood. The Chemkin simulation of zero-dimensional homogeneous reaction model and entrained flow reaction model was employed here, and the ROP (rate of production) and sensitivity analysis was performed for analyzing in-depth reaction mechanisms. The nitrogen conversion pathways were revealed, and the mechanisms were simplified. Based on simplified mechanisms, molecular-level reaction pathways and thermochemical conversion networks of nitrogen-containing precursors were established. The results indicate that NO emissions peak at a 30% co-firing ratio, while N2O formation increases steadily. The NH radical facilitates NO reduction to N2O, with NH + NO → N2O + H identified as the dominant pathway. Enhancing NNH formation and suppressing NCO intermediates are key to improving nitrogen conversion to N2. This paper quantifies the correlation between NOx precursors such as HCN and NH3 and intermediates such as NCO and NNH during ammonia–coal co-firing and emphasizes the important role of N2O. These insights offer a molecular-level foundation for designing advanced ammonia–coal co-combustion systems aimed at minimizing NOx emissions.