"Sectional Gas Drainage" Technology in Goaf for High Level Borehole of Diameter Variation

Aim at the problems that closed distance seam group is influenced during No.19 coal seam mining, a large amount of pressure relief gas poured into the goaf which causes serious gas exceeding at the upper corner and behind the support. High level borehole of diameter variation is proposed based on basic form of gas flow in goaf and movement laws of overlying strata. The gas released from the upper adjacent layer is passively removed by using high level borehole-thin diameter section and the gas released from the lower adjacent layer and rest of coal in goaf is passivity drainage by using high level borehole-enlarge diameter section, which realizes the pattern about sectional gas drainage in goaf. The test is carried out at 31906 working face. The result shows that high level borehole of diameter variation is compared with the traditional high level borehole, the mixed gas flow increases more than 10 times. The extraction concentration increased 251.58%. The average of gas extraction scalar increased 36 times. The average of gas extraction concentration increases 4 to 6 times compared with the same diameter of the pipe drainage technology. The gas concentration at the upper corner and behind the support is controlled between 0.5% and 0.7%, and between 0.6% and 0.9%, respectively, which ensures continuous progress of coal mining.