Numerical investigation of coal self-heating in longwall goaf considering airflow leakage from mining induced crack

Abstract

Self-heating of coal is a long-standing hazard and pollution source in longwall goaf and abnormal air leakage into goaf is a key yet complex drive to the hazard. To investigate such a problem with more insights, a numerical model without considering coal moisture is established based on a Shendong longwall. Abnormal air leakage into goaf mainly sources from the edge cracks resulting in presence of high level oxygen (8 %∼13 %) in start-off area of the longwall. Two heating liable regimes were identified: one is behind longwall face and another one locates in the start-off zone. Heating in the start-off zone develops more quickly than that in heating regime one. On day 25 the maximum temperature of regime two can rise to 500K while it can only increase to approximately 340K in regime one. The heating spot behind longwall face tends to be self-suppressed with longwall advancing while the heating in the start-off zone can develop to a spontaneous combustion incident due to constant airflow leakage from the mining induced cracks. A wide range of inertisation plans including different locations, strategies, and flowrates of nitrogen injection were conducted. An optimum inertisation plan is to proactively inject inert gas with a low flowrate (e.g. 122m3/h) from a seal along the start-off line. A high flowrate of nitrogen stream is preferable to suppress an on-going heating and the reactive inertisation should be maintained for a long run otherwise the heating is very likely to re-develop.