No abstract

Coal seam pores are the major places for coalbed methane storage, diffusion, and seepage, and changes in the pore structure cause changes in the porosity. The porosity of coal seams can be effectively improved by applying strongly corrosive and oxidative chemical reagents to coal seam pores, but these reagents may pose threats to coal workers, corrode mining equipment, and pollute the environment. In this study, coal samples were treated with solutions compounded by acetic acid and anionic, cationic, and non-ionic surfactants. The variations of pores in coal samples after the compound modification of surfactants and acetic acid were investigated. Experimental methods of SEM, MIP, LTNA, PAC, and FTIR and fractal theory are applied in this work. The results reveal that the compound modification of surfactants and acetic acid conduces to the transformation of pore shape and affects a wider pore size range. The anionic and cationic surfactants can increase the hydrophilicity and can promote the connection of larger pores. The non-ionic surfactant reduces the hydrophilicity and capillary effect yet increases the porosity. Thus, it promotes the connection of pores and makes the pore surface smooth and the pore structure simple. Comparing the three kinds of surfactants, non-ionic surfactants are more conducive to coal seam pore reconstruction.

This paper explores the effectiveness of drilling ventilation in a semi-enclosed mine during the long-distance tunneling. Firstly, a resistance-pressure energy balance equation was established. Then, the drilling ventilation effect was analyzed at different borehole lengths and borehole diameters. After that, the drilling conditions were determined for the effective drilling ventilation of longdistance tunneling. The relationships between borehole diameter, borehole length, borehole position and effective airflow on the heading face were discussed in details. The results show that the effective airflow increases with the borehole length and the borehole diameter. However, the increase ceases when the airflow reaches the saturation point. Beyond this point, the maximum airflow depends on the fan capacity. The ventilation effect can be improved by increasing the borehole length between 0~200m. When the length falls between 100~650m, the ventilation effect can be enhanced by expanding the borehole diameter. When the auxiliary fan had a power of 2×30kW and the borehole diameter was 665mm, the transfer distance fell between 50~250m and the effective airflow was enough to prevent the circulation of foul air. The research findings shed important new light on downhole air management.