Combustion and NO Emission During Different Ammonia-Coal Blending Mode: The Effect of Oxygen Concentration and Temperatures

Ammonia-coal co-combustion is a promising approach for coal decarbonization. However, the introduction of NH₃ tends to increase NO emissions. Therefore, understanding the formation characteristics and the associated reaction mechanisms of NO in ammonia-coal co-combustion mode is essential for its industrialized development. In this study, a high-temperature tubular furnace and CHEMKIN simulation are employed to investigate NO formation and its underlying mechanisms over a wide range of ammonia blending ratios, O₂ concentrations, and temperatures. Experimental results show that during the co-combustion of ammonia with either volatiles or char, NO peak values increase with rising O₂ concentration at low ammonia blending ratios (R = 10). However, at higher blending ratios (R ≥ 20), a reduction in NO peaks is observed in the high-temperature region. CHEMKIN simulations further reveal that at low temperature (1100°C), increasing O₂ concentration suppresses the reaction of NH2 with NO at a low blending ratio (R = 10). In contrast, at a high blending ratio (R = 40), the conversion of HNO to NO is enhanced, and the reduction of NO by HO₂ radicals is also promoted. At high temperature (1400°C), increasing O₂ concentration at R = 10 mainly intensifies the competition between NO₂ reduction to NO and NO oxidation to NO₂. Under high blending conditions (R = 40), the conversion of HNO to NO is weakened, while multiple competing pathways between NO and NO₂ emerge.