Behavior and kinetic analysis of coal combustion under ammonia atmosphere based on thermogravimetric experiment

• First TGA investigation of NH 3 /coal co-firing behavior and the kinetic mechanism. • Exploring NH 3 /coal co-firing initial process and measuring its basic parameters. • NH 3 has a greater effect on the char combustion of coal than volatile combustion. • Inhibition of coal combustion by NH 3 increased from 24.18 to 78.23% in co-firing. • A computational model of the NH 3 /coal co-firing mechanism is proposed & validated. Ammonia/coal co-firing is an efficient strategy in the thermal power industry for source-based carbon reduction. Its ignition and combustion are critical for maintaining flame stability and boiler operational safety, but the co-firing characteristics and kinetic mechanism remain unclear. In this paper, based on thermogravimetric conditions and kinetic model analysis, the combustion behavior and kinetic mechanisms of typical coal samples were systematically investigated under ammonia co-firing conditions, considering different heating rates and co-firing ratios. The effects of different conditions on the characteristics of co-firing (characteristic temperature, reactivity, ignition, burnout, stabilization and integrated combustion index, etc.) were revealed. It is found that the effects of co-firing mainly occur in the char combustion stage. The addition of ammonia significantly prolongs the reaction time of coal combustion , increasing the characteristic temperature (9.89–55.78 %), and significantly decreasing the reaction rate and combustion characteristic parameters. Furthermore, the kinetic parameters of co-firing are investigated by combining model-free and model-based methods, and the two models show highly consistent results: the average activation energy of the coal samples increases significantly (24.18–78.23 %) under co-firing and further intensified with the increase of the co-firing ratio. Meanwhile, the mechanism models applicable to ammonia/coal co-firing are selected from 40 commonly used models, and the Nucleation growth and Reaction order models show good applicability. This paper reveals the behavior and combustion mechanism of ammonia/coal co-firing under varying conditions. It proposes a reliable ammonia/coal combustion mechanism model, which is of great significance for developing and applying ammonia/coal co-firing.