Study On Dust Prevention Technology By Water Injection In Extremely Soft Coal Seam Of Xin’an Coal Mine

The main coal seam of Xin ’ an Coal Mine is very soft coal seam,which is easy to be powdered under the influence of mining,and the dust production is large in the mining process.The dust production can be effectively reduced by water injection in advance of the coal seam,but the hydrophilicity of the coal seam is poor and the water injection is difficult.It is particularly important to study the dust prevention technology of water injection in such coal seam.According to the coal seam conditions of Xin ’ an Coal Mine,it is urgent to put forward the coal dust control method suitable for the site.Based on this,according to the development of coal pores and cracks in 11240 working face of Xin ’ an Coal Mine,this thesis puts forward the method of water injection and dust prevention in dusty coal seam.The parameters and mechanism of coal seam permeability are studied by laboratory test,numerical simulation and theoretical analysis,and the parameters and process of coal seam water injection are optimized.The main research results are as follows :(1)According to the characteristics of loose coal body in Xin ’ an Coal Mine,the molded coal samples were obtained by pressing method,and the permeability of coal samples under different confining pressures and permeability pressures was tested.Under the condition of constant confining pressure,with the increase of water injection pressure,the permeability of coal samples gradually increased,and the increase rate was faster and faster.Under the condition of constant water injection pressure,the permeability of coal samples gradually decreases with the increase of confining pressure.The change rate of coal sample permeability has a typical nonlinear correlation with the change rate of confining pressure and the change rate of water injection pressure.When the change rate of confining pressure is constant,the change rate of coal sample permeability decreases gradually,and the decrease rate decreases gradually.When the change rate of water injection pressure is constant,the change rate of coal permeability increases gradually,and the increase rate increases gradually.(2)Using FLAC3D numerical simulation software,the numerical simulation of coal seam water injection was established,and the influence of water injection pressure and injection time on water pressure around water injection borehole was analyzed.Under the same injection time,the injection radius increases linearly with the increase of injection pressure.Under the same injection pressure,when the injection time exceeds 20 min,the injection radius increases significantly with time.(3)Three main factors affecting the effect of coal seam water injection are briefly analyzed,namely geological factors(coal seam burial depth,ground pressure concentration),coal factors(fracture and pore development degree,gas pressure)and water injection factors(liquid properties,water injection parameters).On the basis of the above analysis,11240 fully mechanized working face in Xin ’ an Coal Mine was selected to test the water injection parameters of static pressure water injection and dynamic pressure water injection,so as to achieve the purpose of optimizing the water injection parameters of soft coal seam.The results show that the closer to the water injection borehole,the higher the water content of the coal body,the better the water injection effect.With the increase of the distance from the water injection borehole,the water injection effect gradually decreases,and the permeability radius of the coal body under dynamic pressure water injection is 11.8 % higher than that under static pressure water injection.The effect of dynamic pressure water injection is significantly better than that of static pressure water injection.(4)Industrial Test of Water Injection and Dust Reduction in 11240 Fully Mechanized Mining Face of Xin ’ an Coal Mine,and the water injection dust reduction process was optimized.The effect of water injection dust reduction was measured.The results show that the dust reduction efficiency of the proposed water injection dust reduction process reaches40.4 % – 44.1 %.