Study on the effect of nitrogen injection fire prevention and extinguishing on the pore fracture structure of coal body

To study the effect of nitrogen injection and liquid nitrogen injection on the spontaneous combustion of coal, SEM and LTN were used to analyze the pores and cracks of coal samples under five different treatment conditions, the pore and fissure structure of the coal body is analyzed from micro and multi-angle. The results show that the evolution of pore and fissure structures of coal samples under different treatment conditions is different with the increase of temperature, and the effect of 300 ℃ heat-treated coal samples under air atmosphere treated with liquid nitrogen on the pore and fissure structure is the most significant, under the action of hot and cold stress, the coal sample treated by air atmosphere heat treatment produces more strip cracks and coal fragments, and the specific surface area and pore volume of coal body are reduced by 82.5% and 85.7% respectively compared with the raw coal. Both nitrogen injection and liquid nitrogen injection inhibit the development of the pore structure of coal, thus reducing the gas adsorption site, and delaying the coal-oxygen reaction, which is beneficial to inhibit the oxidation and spontaneous combustion of residual coal.