Erosion model of abrasive air jet used in coal breaking

Induced by the hydraulic improving permeability technology in coal seam,the borehole collapses easily. This paper developed a new technology of improving permeability with abrasive air jet. To clarify the coal breaking parame- ters of abrasive air jet,using ANSYS Fluent software in a discrete phase model(DPM),the accelerating effect of abra- sive particle in the nozzle was calculated,and the influence of air pressure,abrasive density and particle size on the ac- celeration of abrasive was analyzed. Based on the finite element( FEM) and smooth particle method( SPH),the LS- DYNA software was used to simulate the abrasive gas jet erosion target under certain energy conditions. Using the ex-periment system with air high pressure abrasive jet,and the Laval nozzle,under the condition of different gas pres- sures,the abrasive jet air erosion experiments on coal,sandstone,limestone and granite were conducted using standard 180 microns garnet abrasive,and obtained the parameters of crushing energy per unit volume,then the equation of ab- rasive air jet erosion energy conversion rate was established. Using the control variable method,the influence of differ- ent influencing factors on the erosion effect was corrected by the experimental data of abrasive air jet erosion of lime- stone. The abrasive air jet impact coal experiment was carried out to verify the accuracy of the erosion model. The volu- metric model of abrasive air jet erosion media was analyzed. The results show that the weights of the factors affecting the erosion effect are:air pressure>diffusion angle>abrasive density>abrasive particle size>abrasive shape. The opti- mum jet parameters of the abrasive air jet breaking coal are 180 μm garnet,air pressure 15 MPa,and diffusion angle 10. 52°. In the process of model building,the compression conditions are not put into the model. In the future,some relevant experiments will be carried out to take the com-pression conditions as the correction coefficient to further im- prove the erosion model.