高压电脉冲对烟煤微观孔隙结构的影响作用

Effect of high voltage pulse on micro-pore structure of bituminous coal

煤体微观孔隙结构特征对瓦斯解吸流动至关重要,本文利用高压脉冲放电碎煤实验系统,对山西红柳煤矿的烟煤进行高压电脉冲击穿实验,结合扫描电镜和液氮吸附法分析煤样击穿前后孔裂隙的表面形态特征和孔结构的分布特征。同时在分形理论的基础上,应用盒子覆盖法分析了扫描电镜图像的分形特征,结合FHH方程计算了击穿前后煤样孔隙的液氮吸附分形维数值。研究表明:经过高压电脉冲的击穿,煤样表面形成新生裂隙并构成裂隙网络,扫描电镜图像分形特征证实了表面粗糙度提高;与电脉冲击穿前相比,击穿后煤样的吸附滞后现象更明显,孔容和孔面积有一定程度的增加,孔隙结构特别是微孔区域的孔结构得到较大改善;击穿前后的煤样都具有分形特征,煤样低压段的分形维数值在电脉冲击穿后降低,击穿后煤样的表面变得更加光滑,煤样高压段的分形维数值在电脉冲击穿后升高,说明部分封闭孔在电脉冲击穿下发展成半封闭孔,促进煤体瓦斯解吸流动。

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.