NO Reduction during Pressurized Coal/NH ₃ Reburning

A pressurized drop tube furnace experiment combined with ReaxFF molecular dynamics simulations was conducted to systematically investigate the NO reduction characteristics during coal/NH3 cocombustion under reburning conditions. The effects of equivalence ratio, temperature, ammonia blending ratio, and pressure on NO reduction behavior were comprehensively analyzed. The results indicate that the NO reduction efficiency decreases with increasing excess air ratio and temperature, whereas it is significantly enhanced by elevated ammonia blending ratios and pressures. Under fuel-rich conditions, the thermal decomposition of NH3 produces abundant NH2 and NH radicals, which promote the conversion of NO to N2 through homogeneous gas-phase reactions. However, elevated temperatures promote the formation of oxidative radicals such as O and OH, thereby inhibiting both homogeneous reduction reactions and heterogeneous char–NO interactions. Increasing the ammonia blending ratio enhances the reducing environment, while higher pressures increase molecular collision frequency and extend NO residence time, thus reinforcing the NHx–NO reaction pathway. ReaxFF simulations provide insights into the influence of equivalence ratio, temperature, ammonia blending ratio, and pressure on the NHx–NO reduction network by modulating the radical pool composition, reaction pathway competition, and temporal evolution of intermediate species. Atomistic-level analysis of reaction sequences reveals that the primary NO reduction pathways proceed via NO → HON2 → N2H → N2 and NO → HON2 → N2. Elevated pressure enhances these pathways by increasing the collision frequency and stabilizing key reactive intermediates. By combining pressurized drop-tube-furnace experiments with ReaxFF simulations, this study establishes experimental and mechanistic benchmarks for NO reburning under elevated pressure, linking macroscopic reburning performance to microscopic nitrogen reaction pathways.