Modeling and simulation of coal spontaneous combustion in a gob of shallow buried coal seams

The pore and fracture are the path of energy, mass and momentum transfer and conduction in the gob, determine its reasonable distribution is the basis for studying the coal spontaneous combustion hazardous area and migration law of gas products. A discrete fracture-pore model of gob in shallow buried coal seams is being proposed, which is based on the periodic pressure of the overburden, the key strata theory and the compression deformation of the broken rock mass. The model consists of a porous medium media and a discrete fracture network, and calculation equation for the porous medium and the crack width is granted. Taking the Bulianta mine as the background, the model was introduced into FLUENT to simulate the oxygen concentration field, the carbon monoxide concentration field and wind velocity field in the gob. The simulation results agreed well with the measured oxygen concentrations in the field. The spontaneous combustion danger zone and the law of carbon monoxide accumulation in gob are obtained by simulation. In the lower coal seam gob, the maximum width of the spontaneous combustion hazard zone is 108.67m, and the maximum width is 104.94m from the return air side of the gob, and its area is calculated to be 14,645 m2. In the upper coal seam gob, there is basically no spontaneous combustion danger zone that simultaneously meets wind speed and oxygen concentration. However, the oxygen concentration in most areas of the upper gob is between 8% and 18%. In order to prevent the formation of spontaneous combustion danger zone, it is necessary to take corresponding measures for the location with large surface cracks. The concentration of carbon monoxide in the lower gob is greater than the concentration of carbon monoxide in the upper gob. For upper gob, the distribution of carbon monoxide concentration is mainly affected by ground air leakage; for the lower gob, the distribution of carbon monoxide concentration is mainly affected by air leakage of working face.