Research on the evolution of pore and fracture structures during spontaneous combustion of coal based on CT 3D reconstruction

To study the evolution law of the pore and fracture structures during the spontaneous combustion of coal, a self-built high-temperature tube furnace was used in the experiment to heat the coal samples at different temperatures and gas atmospheres. The coal samples were scanned by Xray-CT technology, and the three-dimensional (3D) pore structure and equivalent pore network model of coal samples were extracted by CT 3D reconstruction technology. In the process of heating at 25–200 °C, the porosity and fractal dimension were more significantly developed for coal samples heat-treated in an air atmosphere than those for the coal samples heat-treated in nitrogen atmosphere. The connectivity and permeability of coal samples were investigated, and it was found that the connectivity of pore and fracture structures of coal samples heated in the air atmosphere was better. However, the coal samples heated after nitrogen injection had weak connectivity and permeability. At this temperature stage, the nitrogen injection into the goaf will have a stronger inhibitory ability to develop coal sample pore and fracture structures and a more obvious weakening of the permeability. Therefore, oxygen circulation inside the coal sample may be suppressed, which is more conducive to preventing and controlling coal spontaneous combustion.