Investigation of the effect of ammonia on coal pyrolysis based on TG-FTIR

NH3/coal co-combustion has recently emerged as a novel pathway for reducing carbon emissions in coal-fired power plants. Investigating the effects of NH3 on coal pyrolysis is critical for better understanding the NH3/coal combustion process. In this study, thermogravimetric experiments and kinetic analysis were performed to examine the co-pyrolysis behavior, gas emissions, char structure evolution, and reaction kinetics of coal samples under an NH3 atmosphere. Results indicate that the NH3 atmosphere enhances the coal pyrolysis process by raising the decomposition temperature threshold, increasing the cracking peak (286.48 % max.), accelerating volatile release, and significantly increasing char fragmentation. This enhancement is associated with increased NH3 adsorption on the char surface, which improves secondary reaction efficiency. Meanwhile, it is found that at a higher NH3 co-pyrolysis ratio, char yield decreases, and surface disorder intensifies, inducing lower graphitization and greater surface defects, especially for medium-rank coals. In addition, during the devolatilization stage, the NH3 atmosphere inhibits the release of H2O and itself from coal while increasing that of HCN and CH4, leading to increased secondary reactions at higher temperatures. Moreover, kinetic studies reveal that NH3 significantly reduces activation energy (38.58 %∼43.72 %) in the fast condensation stage due to intensified secondary reaction, char breakdown, and enhanced reaction efficiency. Overall, this work aims to enhance the understanding of NH3's impact on coal pyrolysis.