Field investigation of using water injection through inseam gas drainage boreholes to control coal dust from the longwall face during the influence of abutment pressure

Abstract

Coal dust is a primary contributor to underground coal-mining disasters and is also a major factor in adversely affecting the occupational health of mine workers. Pre-wetting the coal seam with water injection is widely considered as one of the effective means of mitigating coal dust generation during mining. Injecting water through inseam long boreholes parallel to the working face is a commonly used technique. However, for most fully-mechanised top-coal caving working faces, inseam gas drainage boreholes are drilled to extract gas from the gassy seam prior to mining. Therefore, there is neither enough time nor space at the working site for an elaborated water injection process. Based on the mining conditions at Panel 9801 of the Yangquan coalfield, this study designed a water injection system through the inseam gas drainage boreholes to control dust arising from the longwall face. Under the influence of abutment pressure, water injection through a set of inseam gas drainage boreholes was experimentally investigated to offset the conflict between water injection and gas drainage in terms of the time and space availability. The relations between the amount of injected water, the injection rate, the seam moisture content and the coal dust level at the working space were investigated. The effect of water injection for dust control at different distances ahead of working face was assessed. With the change of abutment pressure, the effect of water injection to inseam gas drainage and gas emission at working face was revealed and a space-time balance between gas drainage and dust control by water injection was established. The results indicate that under the influence of abutment pressure, water injection through inseam gas drainage boreholes wetted the seam and decreased the dust level at the working face. Water injection only has marginal influence on inseam borehole drainage and has a negligible impact on the gas level produced at the working face. Under the influence of abutment pressure, the optimum area for water injection through the inseam boreholes was the primary fracture opening zone and the secondary fracture development zone.

Keywords:

• abutment pressure influence period
• inseam gas drainage boreholes
• coal seam water injection
• dust control at working space
• gas drainage

Additional information

Funding

Funding. This work was supported by the National Natural Science Foundation of China [grant number 51104155]; Natural Science Foundation of Jiangsu Province of China [grant number BK20141131]; the Fundamental Research Funds for the Central Universities [grant number 2012QNA34]; a Project Funded by the Priority Academic Programme Development of Jiangsu Higher Education Institutions [grant number SZBF2011-6-B35]. The authors are grateful to Yangquan Coal Industry (Group) Co., LTD for their great support.