Abstract:

In order to explore the critical conditions of coal breaking by submerged jet in the hydraulic pressure relief and permeability enhancement operation of coal mines, the stress model of submerged jet impinging on coal body was established by using the theories of turbulent jet, contact mechanics and momentum theorem. The distribution of surface stress on coal body under the submerged jet impinging was studied through discrete numerical solutions for the established stress model. Then, the critical conditions of coal breaking by submerged jets were determined according to the maximum normal stress criterion. Finally, the correctness of the above theory was verified through on-site tests of submerged jet coal breaking at Jinjia mine in Guizhou. The results show that the maximum principal stress of coal is axial compressive stress in the impact zone, while it is radial tensile stress outside the impact zone. Whether inside or outside the impact zone, the maximum principal stress on the coal surface, central symmetry, decreases with the radial distance. The critical pressure and nozzle diameter of submerged jet coal breaking increase with the coal strength and impact target distance. The larger the target distance is, the greater the impact of coal strength on critical conditions. A submerged jet is only suitable for crushing soft coal seams, while a non-submerged jet or accompanying jet can be used for crushing hard coal.

Key words: submerged jet, stress model, jet impinging, coal fragmentation, critical condition, gas control