Experimental investigation on anthracite coal fragmentation by high-voltage electrical pulses in the air condition: Effect of breakdown voltage

Coalbed methane (CBM) reservoirs in China are characterized by extremely low aperture and natural fractures density, which seriously affects the efficient CBM exploitation. In this paper, we have developed an experimental system for crushing coal by high-voltage electrical pulses (HVEP) to improve the pore structure. The coal samples collected were crushed under different breakdown voltages. It can be observed that under the action of HVEP, the coal sample is broken down into multiple small pieces, and the degree of coal fragmentation increases with the increase of breakdown voltage. Furthermore, we adopt three tests including Scanning electron microscopy (SEM), low-pressure nitrogen gas adsorption (LP-N2G) and mercury intrusion porosimetry (MIP) to gain a clearer insight into the variations in pore structure. SEM images demonstrate that the higher breakdown voltage attributes to the generation of more pores and fractures in coal samples. Adsorption analysis reveals that the micropores of the coal samples crushed by HVEP present an increasing trend compared with the micropores of raw coal sample. Besides, a normal distribution correlation is observed between cumulative micropore volume and breakdown voltage. MIP test shows that the macropore is dominant for all the fragmented coal samples and the effect of high voltage on macropores is more remarkable than other types of pores. (C) 2016 Elsevier Ltd. All rights reserved.