Dynamic evolution of spontaneous combustion of coal in longwall gobs during mining-stopped period

Abstract

Mining-stopped period is a high-risk stage owing to spontaneous combustion of coal in longwall gobs, but there have been few studies in this regard. To address this issue, a multi-physical coupling transient model was developed to characterize the evolution of coal self-ignition in longwall gobs during mining-stopped period. The initial condition of the model had used the temperature distribution of the gob at the moment when coal mining ends. The boundary of the solid temperature field, which was exchanging heat with airflow across working face, was set as the convective heat transfer condition. These improvements ensured that the calculative model was more realistic. The hazards due to spontaneous heating during stoppage period that were associated with some extrinsic mining parameters had been clearly evaluated. The results show that the high-temperature zones in the stoppage period are still located on the windward side of the gob, and the calculated spontaneous combustion period of the gob is consistent with the scenario on-site. Furthermore, the mining parameters can be optimized to effectively increase the time required for spontaneous combustion in the stoppage state by increasing the longwall advance rate or reducing the thickness of crushed coal in the coal mining process, and by further reducing the ventilation flux during the stoppage period. This work can provide suggestions on how to extend the spontaneous combustion period for safely dismantling and moving machines and equipment away from the working face.