Theories And Tests Of Stereo Gas Drainage For Outburst Prevention Under Closed Distance Seam Group With Protection Layer Mining

The gas stereo drainage theoretical system for outburst prevention of mining of closed distance coal seam group with Protection Layer Mining was set up, based on The coal seams characteristics of Rongguang Coal Mine, such as: high gas content, many coal seams, short distance between seams, coal and gas outburst, low permeability of coal seam, small drainage radius, short time of drainage, complex structure and bad gas drainage influenced by water. The authentication equations of stereo gas drainage for outburst prevention under closed distance seam group with protection layer mining and stereo gas drainage for outburst prevention in the Rongguang Coal Mine were derived. Authentication experiment of stereo outburst prevention was established, measures for stereo outburst prevention were presented as follow: drainage in current seam with horizontal borehole, drainage with high location strike drilling hole, goaf drainage with"T"type tube, drainage with drilling holes from floor. The drainage method was changed from drainage in a single horizontal plane to multi-direction that could solve the deficiency of old method and outburst problems. The hole protection technology with PE mine plastic guiding pulley pipeline during gas drainage was developed, improving the gas drainage rate in a drilling field. The dynamic development of overlying strata collapse with short distance upper protective layers method was simulated by UDEC, the rules of strata and floor movement, coal bed stress and strain of protected seam were obtained. The significance of it for drainage drilling holes optimization. Gas reservoir of short distance coal seams, movement of mining strata and fracture evolvement were analyzed together. Quantitative research on permeability of crushing rock mass in falling zone was carried out, and then the semi-theoretical permeability equations of falling zone were described, and applied to stereo gas drainage. The every process of gas stereo outburst prevention and drainage was simulated with FLUENT. The rules of gas flow and methane contribution with short distance upper protective layers method were found; Drainage with high location strike drilling hole could enhance methane drainage and reduce methane emission of upper corner; The methane pressure of drilling holes becomes larger from the center to outer circle, and the methane flow velocity gets smaller.It was set up that the safety management measures of gas stereo drainage and outburst prevention for short distance coal seams. The tests with gas stereo drainage and outburst prevention method indicate that the gas content and pressure of C5 coal seam were reduced to 5.83m³/t and 0.28Mpa, and the gas content and pressure of C₆, C₈ to 3.04m³/t,3.22m³/t and 0.35MPa, 0.42Mpa respectively, as the same time, the increment of permeability of C₆, C₈ achieved 250times and 284 times. The parameters of outburst prevention were below the critical value. The methane concentration of return was changed from 1.5% to 0.3% and the methane flow rate of return became below 4.50m³/min to below 24.33m³/min. There were no coal and gas outburst accident in the whole mining process and daily yield was 2000t, annual output value exceeding 0.24 billion. The effects of gas stereo drainage and outburst prevention was obvious, the method was proved that it was worth for extension.