Reaction Analysis and Migration Path of Nitrogen under Ammonia/Coal Cofiring Condition

Cofiring ammonia with coal is gaining attention as a potential strategy to conserve coal and reduce the level of CO2 emissions. However, the mechanisms for ammonia/coal cofiring remain incomplete, with limited studies on key pollutant formation pathways like NO and CO. This study developed a reduced mechanism with 29 species and 49 reactions by direct relation graph (DRG), directed relation graph with error propagation (DRGEP), full species sensitivity analysis (FSSA), and sensitivity analysis, to simulate cofiring conditions, demonstrating good agreement with experimental data. The effects of temperature, ammonia blending ratio, and equivalence ratio on NO and CO concentrations were examined. NO levels increased rapidly during combustion before stabilizing, while the level of CO initially rose and then oxidized to CO2, resulting in low CO concentrations in most cases. Reaction pathway analyses showed that most NO is formed via the oxidation of HNO, which is generated from NH3, with smaller contributions from char and volatile combustion. CO primarily comes from coal’s incomplete combustion, with minor contributions from char and soot oxidation by NO. NO can be reduced by soot and char, with soot showing a better performance. Nitrogen migration was categorized into ammonia-nitrogen, coal-nitrogen, and ammonia/coal-nitrogen interactions. Higher temperature enhanced nitrogen reactions, more ammonia intensified ammonia-related reactions, and a higher equivalence ratio favored ammonia/coal interactions, while reducing coal-nitrogen reactions. These findings provide insights into the reaction pathways and nitrogen migration during ammonia/coal cofiring.