Ventilation arrangement evaluation and proactive goaf inertisation for spontaneous combustion and gas explosion management during longwall panel sealing-off process

When a longwall face approaches the finish-off line, 1 month is normally required to relocate the longwall equipment and seal the longwall panel, during which time the goaf gas atmosphere changes and the risk of spontaneous combustion and gas explosion considerably increases. To minimise the occurrence of these hazards, an improved insight into gas flow dynamics within the longwall panel is essential during the panel sealing-off process. Based on mining conditions of an Australian underground coal mine, three-dimensional computational models were developed and calibrated with onsite gas monitoring data, allowing for evaluating ventilation arrangements and understanding methane dispersion in the longwall workings during the six-stage panel sealing-off process with confidence. The simulation results indicate that nitrogen should be injected on the travel road side at a distance of 120 m behind the longwall face at a rate of 0.75 m3/s and the rear of the travel road should be tightly sealed at the final sealing-off stage, resulting in oxygen levels lowering than 5% in the longwall workings and producing desired panel sealing-off performance. In addition, gas sensors should be employed and positioned at the appropriate locations to reliably monitor goaf atmosphere change. This study sheds improved insights into evaluating ventilation arrangements and understanding gas flow dynamics during the panel sealing-off process and provides critical knowledge of effective proactive goaf inertisation strategies, thus minimising the risk of spontaneous heating and gas explosion and reducing environmental pollution induced by these hazards.