Studies on the Impact of Seam Gas Composition on Proactive Goaf Inertization Strategies for Spontaneous Combustion Management—a Computational Modeling Approach

Spontaneous heating of coal continues to present a health and safety hazard in underground coal mines. The influence of seam gas composition on gas flow dynamics and distribution characteristics in the active longwall goaf has not been studied in-depth, and corresponding effective proactive goaf inertization strategies for preventing potential spontaneous heating from occurring have limited investigation. To advance this knowledge, an 80-m-height goaf model was constructed and developed based on specific conditions of an Australian underground coal mine, and onsite gas monitoring data was collated to verify base model results, which allowed for various scenarios of seam gas composition to be simulated and investigated with confidence. This study involved modeling five different gas composition scenarios for the goaf atmosphere, namely, 100% CO 2 (case 1), 80% CO 2 and 20% CH 4 (case 2), 50% CO 2 and 50% CH 4 (case 3), 20% CO 2 and 80% CH 4 (case 4), and 100% CH 4 (case 5). Simulation results show that O 2 is primarily distributed at the middle and upper part of the CO 2 -dominant goaf model, while it is mainly layered at the floor level of the CH 4 -dominant goaf model. N 2 is superior to CO 2 in the goaf inertization for the CO 2 -dominant goaf model, whereas CO 2 performs better than N 2 for the CH 4 -dominant goaf model. The optimal inert gas flowrates for case 1 to case 5 are 1.5, 1.75, 0.75, 0.5, and 1.0 m 3 /s, and the oxidation zone area is reduced by 55.76%, 67.21%, 58.04%, 78.17%, and 81.82%, respectively. The simulation results allow for increased insight and understanding of the gas distribution patterns in the active goaf with different seam gas composition and the development of corresponding proactive goaf inertization practices, thus minimizing potential spontaneous-heating-related hazards and improving mining safety.