Effect of high voltage pulse on micro-pore structure of bituminous coal 高压电脉冲对烟煤微观孔隙结构的影响作用

The micro-pore structure of coal is vital for gas desorption flow. The high voltage electrical coal-breaking experimental system was used to break down bituminous coal samples from Hongliu coalmine in Shanxi province. Along with scanning electron microscopy (SEM) and liquid nitrogen adsorption experiments, surface morphology and pore structure distribution characteristics of pore fissures before and after breakdown of the coal samples were analyzed. Meanwhile, on the basis of fractal theory, fractal characteristics of SEM images were analyzed through box-counting dimension, and fractal dimension of coal samples before and after electrical breakdown was calculated by means of Frenkel-Halsey-Hill (FHH) equation. The results have shown that a new network of fractures is formed in the surface of coal samples subject to breakdown with high voltage electric pulses. The fractal characteristics of SEM images confirm the improvement of surface roughness. Compared with that before electric pulse breakdown, the adsorption hysteresis of coal samples after the breakdown is more obvious, the pore volume and pore area are increasing, and the pore structure, especially those in the micro-pore area, is greatly improved. Coal samples before and after breakdown have fractal characteristics, and fractal dimension of coal samples in low pressure section decreases after the electric pulse breakdown, which indicates that the surface of coal samples becomes smoother after the electric pulse breakdown. The fractal dimension of coal samples in high pressure section increases after the electric pulse breakdown, which indicates that some closed holes develop into semi-closed holes under the electric pulse breakdown, facilitating coal gas desorption flow.