Experimental and numerical simulation analyses of selective fragmentation of coal samples by plasma

To reveal the principles of fracture extension within coal under the impact of plasma, the fracture and mineral phase of Hongliu bituminous coal were experimentally extracted through 3D visual software Dragonfly. Besides, the principles of fracture extension within coal in different directions were further analyzed under the impact of plasma. The results show that fractures on axial and horizontal surfaces both extend along minerals, which indicates that the distortion of electrical field on the boundaries between minerals and coal leads to the concentration of stress. The distribution of minerals serves to lead fracture extension, and plasma forms a spatial network fracture structure within the coal. The results indicate that electrical field intensity can be distorted among dielectrics with various dielectric constants. The intensity of electric filed is low when passing through the dielectric with a large dielectric constant, whereas it is high when passing through the dielectric with a small dielectric constant. Furthermore, aiming at investigating selective fragmentation of coal sample by plasma path, an experiment was performed by drilling boreholes and infusing iron powder in coal samples before electric breakdown. The results show that fractures extend along the drilling boreholes and run through some drilling boreholes, suggesting that the iron powder that has infused in the boreholes disturbs the plasma path. Besides, plasma paths are also influenced by the location and amount of drilling boreholes, as well as their distances to the electrode center. The results of experiment and numerical simulation are mutually validated.