Numerical investigation of gas emission and extraction under the action of coal-oxygen recombination in longwall gobs

The emission and migration of gas in the longwall gobs are closely linked to the temperature field formed by the oxidation and exothermic behavior of coal. This work conducted gas adsorption and desorption experiments on coal particles and obtained the relationship between gas desorption rate and temperature. Additionally, the coupling relationship between multi-physical fields, including the air flow, gas and oxygen concentration, air and solid temperature has been improved. On this basis, a coupled model for gas and coal spontaneous combustion was constructed. The distribution characteristics of the gas concentration field and solid temperature field before and after extraction in gob were simulated. The optimal extraction point position was determined at 38 m from the working face, 25 m on the return air side, and a height of 11 m with an extraction negative pressure of -6 kPa. The results show that: The gas desorption rate exhibits an exponential relationship with temperature, and the coefficient and exponential factor in the exponential equation are AT and BT. The gas concentration in the gob and upper corner before extraction is high, and there is also a high-temperature area on the air intake side. After extraction, the gas concentration in the upper corner decreased from 2.94% to 0.366%, which is lower than the critical value of 0.8%. At the meanwhile, the maximum temperature only increased by 3.36 degrees C. Based on the field's verification, the monitoring value of gas concentration in the upper corner is 0.253%, which reduces the danger of gas in the upper corner while controlling the heating of residual coal. This work can provide basic support for the prevention and control of gas disasters in gobs.