Research on gas extraction technology in goaf across working face

The Y-shaped ventilation continuous working face adopts the technology of gob-side entry retaining to improve the coal recovery rate. As the working face recovers, the goaf area will expand and connect. The air flow in the return corner and gangue rack is not smooth. Gas not only accumulates easily, but is also difficult to dilute and blow away. This leads to frequent exceeding limit alarms. At present, solutions of the gas accumulation in the return corner and gangue rack is unable to achieve continuous extraction of goaf. The extraction capacity is relatively scattered, making it difficult to ensure the effectiveness of governance. In order to solve the difficult problem of gas control in the goaf of the Y-shaped ventilation continuous working face, a gas extraction technology in cross working face is proposed based on the engineering background of the 3202 working face of Dongfeng Coal Mine. The directional long boreholes are constructed in the return air roadway of adjacent working faces to the roof crack zone of the goaf. The directional long borehole extraction pipeline does not need to be removed after the mining of the working face. The pipeline can continuously extract gas from the goaf, minimizing the gas storage in the goaf and its roof crack zone, forming a cross working face for gas extraction in the goaf. This reduces the accumulation of gas in adjacent goaf areas, and effectively prevents gas disasters caused by sudden gas gushing out of goaf during large-scale roof collapse. The test results show that the distance between the cross working face drilling and the roadway roof is 30-40 meters. The extraction effect is ideal when the final position of the directional long borehole across the working face is 20 to 40 meters horizontally from the track roadway. The directional long boreholes are carried out to the roof crack zone of the goaf, and the gas in the goaf is continuously extracted. The gas volume fraction in the gangue rack decreases from 0.67% to 0.22%. The gas volume fraction in the return air flow decreases from 0.47% to 0.18%. During the mining period, the gas volume fraction in the 3202 working face remaines below 0.6%. The gas extraction technology in the goaf cross working face provides a new approach for gas extraction methods in goaf areas.