Borehole-based coal seam enhanced combustion: Kinetics and exhaust gas explosion risk control under varying airflow rates

To operationalize the extraction of thermal energy from underground coal enhanced combustion (UCEC), safe and efficient deployment hinges on optimizing air injection combustion and controlling exhaust gas explosion hazards. Using a pilot-scale system integrated with TG-FTIR and DSC, this study established an integrated framework coupling temperature field dynamics with mass-loss kinetics and exhaust gas hazard criteria, thereby elucidating how injection rate governs thermo-mass coupling and risk evolution. Results showed that the airflow driven competition between oxygen supply and convective heat removal controls the global response, yielding combustion characteristics that initially improve but then deteriorate as flow rate increases. The borehole channel exhibited the optimal heat extraction potential. At an air injection rate of 80 L·min −1 , optimal enhanced combustion was achieved, manifested by the shortest total combustion period, fastest one-dimensional thermal propagation speed, and broadest high-temperature zone coverage. However, when borehole channel temperature dropped below 100 °C, the enhanced combustion efficiency was notably attenuated. Exhaust gas composition exhibited the most significant fluctuations within the initial ∼150 min, and the lower explosive limit (LEL) was substantially influenced by the phase-dependent regulatory effects of hydrocarbon gases (CH 4 ), CO, and H 2 . An engineering scheme integrating dynamic flow regulation, zoned heat extraction, and phase-specific explosion prevention was proposed. This research provides a quantitative theoretical basis for enhancing UCEC efficiency and ensuring safety control.