Enhanced reaction kinetics of subsurface coalseam in-situ combustion: Moisture content effects

Gas injection-enhanced underground coal combustion for heat extraction represents a disruptive chemical fluidized extraction method of coal resources. Coal seam combustion dynamics provide crucial underpinnings for engineering realization. This study establishes an experimental system for monitoring temperature field evolution during gas-assisted combustion in cylindrical coal cores, investigating the influence of moisture content (0 %, 16 %, 24 %) on gas-assisted combustion kinetics. Results showed moisture content significantly influences combustion: higher levels (16 %-24 %) delay high-temperature expansion (0–1 h) due to evaporation energy absorption, but subsequently enhance efficiency through pore formation and oxygen diffusion, achieving 1120–1230°C peaks. Dry coal exhibits rapid initial combustion (peak temperature of 1130°C within 1 h) but weaker sustained reactions. The temperature field evolves from localized hotspots to an elliptical high-temperature zone, with axial expansion rates surpassing radial rates, driven by thermal buoyancy and convective heat transfer. Moisture’s dual role is revealed: initially as a thermodynamic inhibitor and later as a promoter by increasing pore diameter and oxygen diffusion coefficients. An optimal moisture content of 16 % balances initial heat loss with enhanced reactivity, offering practical insights for optimizing gas injection and thermal recovery in underground coal combustion.