Mechanisms and quantitative characterization of surrounding coal combustion driven by thermal radiation from a high-temperature source

To investigate the mechanism by which thermal radiation from high-temperature sources influences the combustion of surrounding coal and to quantitatively characterize its impact, a combined approach integrating quantitative thermal radiation experiments, theoretical modeling, and numerical simulations are employed. Thermal radiation-driven coal combustion is systematically revealed as the dominant driving process, exhibiting cascading amplification effects. The results indicate that thermal radiation flux is a crucial external factor governing the coal combustion process. It influences not only the oxidation reaction pathways but also significantly accelerates the evolution across all stages of coal oxidation and combustion. The coal combustion process under thermal radiation is divided into four consecutive stages: moisture evaporation (Ⅰ), self-sustained oxidation (Ⅱ), thermal decomposition and intense oxidation (Ⅲ), and carbon oxidation (Ⅳ). Under low thermal radiation flux conditions, oxidation reactions primarily depend on coal-oxygen self-heating, with smaller particle sizes enhancing heat accumulation during the self-sustained oxidation stage (Ⅱ) due to their larger specific surface area and denser packing. In contrast, under higher thermal radiation flux conditions, external thermal radiation directly drives complete oxidation on the coal surface, markedly accelerating the critical transitions from the moisture evaporation stage (Ⅰ) to the self-sustained oxidation stage (Ⅱ) and subsequently to the thermal decomposition and intense oxidation stage (Ⅲ). Based on the principle of energy conservation and the temperature at the point of abrupt change in CO, a model for calculating the critical thermal radiation flux was established. This model demonstrates that the critical thermal radiation flux q_cri significantly decreases as particle size diminishes, further confirming that coal with smaller particle sizes can more easily navigate the key transition points of each oxidation combustion stage under thermal radiation. Through simulations of CH₄/CO mixed gas combustion and from the perspective of reaction kinetics, the influence of a high-temperature source on the combustion of coal-derived gases is attributed to its quantitative modulation of the radical pool and the rates of elementary reactions. High temperatures significantly promote the generation of chain-branching radicals, such as H and O, shifting the CH₄ consumption pathway toward H radical-dominated dehydrogenation while suppressing the conversion of CO to CO₂. This redistribution of reaction rates at the micro-scale effectively accelerates fuel consumption and intermediate product accumulation, resulting in a forward shift of the combustion center and a notable enhancement in overall reaction intensity, thereby driving the transition from stage (Ⅲ) to a more intense combustion state.