Determination on the hazard zone of spontaneous coal combustion in the adjacent gob of different mining stages

Abstract Coal seam mining, especially during roadway driving with narrow coal pillars, can cause air leakage along the gob side and increase the risk of spontaneous coal combustion. To explore the oxygen distribution and spontaneous coal combustion risk zone in an adjacent gob of a fully mechanized mining face, a temperature-programmed experiment, a secondary oxidation experiment, gas monitoring, and numerical simulation were conducted. The oxygen consumption rates of the coal sample in primary and secondary oxidation processes were compared, and the oxygen concentration at the inner coal pillar of an adjacent gob was monitored. The oxygen concentration distribution in the adjacent gob was simulated, and the spontaneous coal combustion risk zone in the adjacent gob was determined. The results show that secondary coal oxidation was stronger than primary oxidation below 90 °C, and primary coal oxidation was stronger than secondary oxidation above 90 °C. The oxygen consumption rate ratio (i.e., the oxidation size) of the coal sample during primary and secondary oxidation processes below 90 °C was fitted to obtain the relationship. During roadway driving of the 2202 working face along the gob, the air leakage intensity of the coal pillar was between 0.0335–0.0365 cm3/(s∙cm2). The area 23 m from the coal pillar to the depth of the adjacent gob behind the heading face was found to be at risk of spontaneous coal combustion. During normal and end mining of the 2202 working face, the air leakage intensity of the coal pillar along the gob was between 0.005–0.024 cm3/(s∙cm2). The residual coal in a narrow area, 87 m long in the adjacent gob was in an oxidizing environment. When the working face advanced slowly, the residual coal in this area was prone to oxidation and at risk of spontaneous combustion.