Coal spontaneous combustion and N2 suppression in triple goafs: A numerical simulation and experimental study

Coal pillar fragmentation caused by mining stress will cause multiple goafs in series on the isolated island's small coal pillar working face. Due to the unclear rule of air leakage in the mined-out area and coal pillar, once the spontaneous combustion occurs, it will threaten the safety of the mine, causing a large number of Waste of resources. To examine this problem, taking a coal mine in Shaanxi Province as an example, this study analyses the air leakage laws and areas prone to coal spontaneous combustion (CSC) in the series goafs through experimental tests, field observations, and numerical simulations and use the inert goaf method to prevent and control CSC. The results indicate that there is a large air leakage in the goaf of the isolated island small coal pillar working face, particularly on the air inlet side of the goaf. The three series goafs have the hidden danger of spontaneous combustion. The relationship between the air leakage intensity and the buried depth in coal pillar is determined. The ideal inert gas injection position for controlling the spontaneous combustion of the coal seam lies in the transition area between the heat dissipation zone and the oxidation zone. After the injection of inert gas, the area of the oxidation zone in the goaf decreased by 25%. The research results are of scientific guiding significance for the control of air leakage in the triple goafs and the prevention of coal seam fire.