Study On The Flow Law Of Borehole Gas Discharged In Closed Roadway Area Under Electrothermal High Temperature Field

In view of the difficulty of gas drainage in low-permeability coal seams in deep mines in my country,based on the principle that temperature rise can promote coal seam gas desorption and increase coal seam permeability,it is proposed to use the electric heating high temperature field generated in the coal seam by heating cables to promote coal seam gas desorption.It is discharged into the closed roadway area,and finally a new method of extracting the gas from the roadway with a drainage pipeline.In this paper,a combination of theoretical analysis and numerical simulation is used.Based on porous media elasticity,seepage mechanics,thermodynamics,and fluid mechanics,the multi-field coupling mathematical model of gas flow in a borehole under electrothermal high temperature field is established and the mathematical model of gas flow in closed tunnels is established.The mathematical model of gas drainage.Taking the K15 coal seam working face transportation roadway of a mine in Guizhou Province as the engineering background,COMSOL Multiphysics 5.5 software was used to systematically study the flow law of gas discharged from boreholes in closed roadways under electric heating and high temperature fields.The main research results are as follows:(1)According to the characteristics of the fracture-pore structure of coal,the dynamic control equations of porosity and permeability considering the temperature effect are derived,and on this basis,the control equations of coal stress field,gas seepage field and temperature field are established.Combining the above equations,a multi-field coupling mathematical model of gas flow in the discharge borehole under the electric heating high temperature field including coal deformation,gas seepage and temperature effects is obtained.(2)According to the characteristics of gas distribution and migration,combined with the law of conservation of fluid mass,the law of conservation of momentum,the law of conservation of energy and the law of conservation of composition,the basic control equations for gas migration in closed tunnels are deduced,and the drainage in closed tunnels is established.Mathematical model of gas migration.(3)Based on the multi-field coupling mathematical model of gas flow in the discharge boreholes under the electric heating high temperature field,numerical simulation experiments under different heating temperatures,different apertures and different borehole spacing conditions were carried out,revealing the propagation of electric heating high temperature in the coal body.Mechanism,explored the change law of coal seam gas pressure,coal seam permeability and gas emissions from boreholes in the process of gas discharge,and the influence of the above parameters on their effects,and gave the best borehole layout parameters.(4)Based on the mathematical model of gas migration in closed roadways,numerical simulation studies under different suction pressure and different pipe diameters were carried out,and the gas concentration and flow in closed roadways were explored during the process of gas drainage.The distribution of the field,the change law of gas concentration and pure gas flow in the drainage pipe,and the best pipeline layout parameters are given.