Experimental and kinetic investigation of coal char combustion behavior in ammonia atmosphere using TG-FTIR

Green ammonia/coal co-firing represents an effective strategy for carbon reduction at the source in the thermal power sector, and a thorough understanding of its combustion characteristics and kinetic mechanisms is crucial for optimizing co-firing strategies. In this study, thermogravimetric-Fourier transform infrared (TG-FTIR) analysis was employed to systematically investigate the combustion behavior and kinetic mechanisms of coal char in NH 3 atmospheres under both isothermal and non-isothermal conditions. The results indicate that increasing the heating rate shifts NH 3 -doped char combustion toward higher temperatures and induces pronounced thermal lag. NH 3 addition elevates ignition and burnout temperatures, reduces the combustion rate, and prolongs combustion duration, with the inhibitory effect intensifying at higher NH 3 concentrations. Lignite char is more strongly affected than anthracite char. Gas product analysis reveals CO 2 and unburned NH 3 as the primary products. NH 3 addition enhances late-stage CO 2 formation and increases residual NH 3 . Ash analysis shows that NH 3 significantly alters the structure and composition of coal ash. Soluble alkaline components on particle surfaces dissolve, disrupting the integrity of the glassy shell, resulting in a fragmented ash morphology, increased porosity, migration of alkali metals, and enrichment of hydroxyl and amine functional groups. Kinetic analysis indicates that NH 3 addition increases the activation energy of char combustion and alters the reaction mechanism, predominantly following Nucleation Growth and Reaction Order models. The activation energy under isothermal conditions is significantly lower than under non-isothermal conditions, and a pronounced kinetic compensation effect is observed. This study elucidates the coupled mechanisms and temperature-dependent responses of NH 3 /char co-firing, providing a theoretical foundation for combustion optimization and kinetic modeling. • First coupled TG-FTIR reveals multi-stage combustion and NH 3 /char interactions. • NH 3 addition raises T i / T b , lowers rate; inhibition intensifies with concentration. • Multi-model kinetics show higher E , dominant NG/RO mechanisms, compensation effect.