Abstract
This study introduced gas control technology in goaf using adjacent roadway large-diameter (550 mm) boreholes to control gas accumulation in the upper corner of a fully mechanized working face in high-gas coal seams. The gas control process in the upper corner and gas interception in goaf by large-diameter boreholes was analyzed using the CFD model of the gas flow in goaf. The latter considered the control equation of gas flow, the established permeability model of goaf, and the gas emission law in goaf. Using the 2-105 working face of the Tenghui Coal Mine, Shanxi Province, China, as a case study, the distribution patterns of gas concentration and flow field in the goaf for various extraction flow parameters and different positions of boreholes were numerically simulated. The dependences between various locations, drainage flows, and the gas concentration in the upper corner were determined and fitted by engineering equations. The evolution pattern of the spontaneous combustion zone in the goaf under the drainage conditions was also analyzed. The optimal borehole configuration parameters ensuring the extraction flow rate exceeding 3 m·s−1 and the effective gas control in the upper corner of the working face at a distance of 5 m–15 m behind the working face were identified. The engineering practice proved the feasibility of gas control in the goaf using the adjacent roadway large-diameter borehole. The gas concentrations in the return airflow and the upper corner of the working face were kept below 0.65 and 0.8%, respectively, to ensure production safety and improve the gas utilization efficiency.
Highlights
Despite the global trend of green energy promotion, coal resources remain vital to industrial development, accounting for over half of China’s power production
Based on the available theoretical achievements, this paper proposes the gas control in the goaf using a large-diameter borehole constructed in the adjacent roadway of the working face. is technology, characterized by high flexibility and productivity, adopts an improved geological drilling machine, producing a largediameter (550 mm) extraction borehole. e drilling parameters can be adjusted, according to particular geological conditions, changes in airflow, and abnormal gas emission
Under the “U-shaped” ventilation mode, the upper corner of the fully mechanized working face in the high-gas coal seam is close to the coal wall and the goaf side; the airflow velocity is very low, and some areas are in the eddy current state. e gas emitted from the goaf circulates near the upper corner and accumulates in the eddy current area
Summary
Despite the global trend of green energy promotion, coal resources remain vital to industrial development, accounting for over half of China’s power production. E large-diameter gas extraction boreholes of adjacent roadway construction at the air-return side of the working face shown in Figure 1 can change the eddy current formed at the upper corner of the working face into the original flow field of the goaf, introduce new disturbance, extract the goaf gas in the form of large flow and low negative pressure, and intercept the gas from the goaf due to the air leakage of the working face to solve the problem of local gas overrun.
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