Experimental study of pollutant generation characteristics of ammonia-coal co-combustion and local atmosphere regulation mechanism

While existing studies on ammonia-coal co-combustion have primarily focused on NO_x emissions, there has been limited attention to the generation mechanisms of corrosive pollutants such as SO₂. Researchers have also noted the inhibitory effect of CO₂ on NO_x formation during ammonia-coal co-combustion, but relevant studies have mostly focused on oxygen-enriched combustion atmospheres. Under air combustion conditions, the mechanism by which CO₂ in the local combustion atmosphere regulates pollutant formation during ammonia-coal co-combustion remains unclear. In this study, a drop-tube furnace experimental system for ammonia-coal-CO-combustion was established to investigate the Influence mechanism of the local combustion atmosphere. The effects of premixed/non-premixed co-combustion methods on pollutant generation were also focused on. The main influencing factors include the co-firing ratio of ammonia, excess air coefficient, combustion temperature, local combustion atmosphere, and co-combustion methods. The combustion products were characterized via FTIR online monitoring and fly ash elemental analysis to reveal the multiphase reaction mechanism of pollutants such as NO_x, SO₂. The results showed that the NO concentration increased with a higher NH₃-fuel ratio, but the ammonia-coal co-combustion still reduced the NO_x emission compared to pure ammonia combustion. A synergistic effect between the NH₃-fuel ratio and excess air coefficient was observed, with the lowest NO concentration occurring at a 30% NH₃-fuel ratio and an excess air coefficient of 1.2. The optimal excess air coefficient decreased with a lower NH₃-fuel ratio. Introducing CO₂ into the local atmosphere initially reduced NO concentration significantly, which then gradually increased as the CO₂ concentration rose to 15%, accompanied by a sharp rise in residual carbon in fly ash. Compared to the non-premixed mode, the premixed co-combustion resulted in higher NO concentrations due to more complete mixing. Meanwhile, SO₂ emissions were lower in the non-premixed mode, where more sulfur was retained as elemental sulfur in the ash. Under non-premixed co-combustion, after delayed injection of NH₃, the NO concentration increased; the fraction of S in ash increased slightly, while the N content doubled.