Spontaneous combustion of coal in the active goaf area has been reported in several Australian underground coal mines during normal production cycles. The onset of spontaneous heating in underground goaf areas is dictated by many operational and environmental parameters, including proactive inertisation and geologic variations. Based on site-specific conditions of an Australian underground coal mine where seam gas is predominantly composed of carbon dioxide (80%) with a total emission rate of 2 m³/s, extensive computational fluid dynamics (CFD) simulations were conducted. The simulation results revealed that seam orientation played a significant role in gas distribution in the goaf area and the determination of proactive goaf inertisation strategies. Regardless of seam orientations investigated in the simulation, nitrogen performed better than boiler gas and carbon dioxide in shrinking the oxidation zone area and reducing the likelihood of spontaneous combustion. In addition, a total inert gas injection rate of 1.5 m³/s was recommended to effectively manage spontaneous heating, and the ratio of oxidation zone area to goaf area was approximately 10%, which dropped by approximately 15% compared to scenarios without inert gas injection.
 

Spontaneous combustion, CFD modelling, seam orientations, proactive goaf inertisation