Analysis of coal particles passing screen pipe and test of gas drainage effect in underground coal mine

The completion of screen pipe after coal seam drilling has become an effective hole protection measure for gas drainage in broken and soft coal seam. In order to study the influence of the slitting parameters of conventional round-hole screen pipe and slotted screen pipe on the gas drainage effect,this paper built the particle flow model of coal particles passing through screen pipe with PFC3D software on the basis of discrete element method,and analyzed the ability of coal particles passing through screen pipe,as well as the influence of parameters,including the diameter of round-hole,the width of the slotting and the length of the slotting by simulating the coal particles passing through screen pipe under confining pressure. According to the simulation result,the gas drainage tests of the round-hole screen pipe and three kinds of the slotted screen pipe with different slotting parameters were carried out in the coal seam of 864 working face at Tongting coal mine in Huaibei,China. The results of numerical simulation show that the passing volume of coal particles increases linearly with the increase of round-hole diameter or slotted width and length under the same flow area,the passing volume of coal particles is basically the same under the same round-hole diameter and slit width,and the influence of round-hole diameter and slit width on the volume of coal particles passing through is far greater than the slit length. The gas drainage test shows that the net volume of gas drainage of three groups of slotted screen pipes is 60. 0% ,43. 3% and 33. 4% higher than that of round-hole screen pipes,and the gas mixing flow and net volume after 51 days of drainage are about 4 times,2. 5 times and 1. 5 times of the round-hole screen pipes. Combined with the fact that the volume of coal particles passing through the ϕ10 mm round hole screen pipe is 22,6 and 3. 3 times of the slit width of 2 mm,3 mm and 4 mm slotted screen pipe respectively,it can be found that reducing the volume of coal particles passing through the screen pipe can effectively improve the drainage mixing flow and gas net volume during the whole drainage process.