Closed gas drainage technique by extra large diameter pipeline connected with goaf transversely in tailing roadway

The problem of gas concentration often seriously beyond the allowed level in upper corner of coal face and tail roadway existed when mining the soft coal seams with highly gas content and low permeability.Based on gas emission characters of fully mechanized coal face in test area and both advantages and limitations of gas tail roadway in "U+L" type ventilation system,closed gas drainage technique by extra large diameter pipeline connected with goaf transversely in tailing road way was put forward,besides,the gas drainage principle of controlling seepage field of gas in goaf was described.CFD model of three-dimensional seepage in gob was established according to the governing equation of gas mixture in goaf,and through studying the CFD model,obtained the relation between gas concentration in upper corner,seepage field in goaf and the distance from coal face to gas drainage location,then the key parameters of gas drainage technique were determined.The experimental results show that this technique is very effective to control coal gas and not only keeping gas concentration less than 0.9% in upper corner,but also decreasing gas concentration from 6.0% to less than 1.7% in tailing roadway,thereby the safe and high-efficient exploitation of coal is achieved under complex gas geological conditions.