Effect of temperature on structural evolution and breakdown electrical characteristics of bituminous coal subjected to plasma breakage

Plasma breakage (PB) is a promising technology in enhancing coal seam permeability, but the effect of temperature on it has not been revealed yet. In this study, a self-developed coal rock PB system was established. With the aid of this system, the breakdown voltages of coal samples were tested at different temperatures, and a general functional relationship between breakdown field and temperature was established. Besides, the pore structures of broken-down coal samples at different temperatures were analyzed through scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) tests. Furthermore, the effects of temperature on breakdown delay, peak current, effective energy and energy conversion efficiency were discussed by collecting voltage and current waveforms in the breakdown process. The results show that the porosities, total pore volumes and average pore diameters of broken-down coal samples exceed those of the raw coal sample. Under the action of PB, the volumes of micropores and ascopores pores barely change with temperature, while the volumes of mesopores and macropores increase as the temperature goes up. Under the same discharge voltage, the voltage and current waveforms differ when the coal samples are broken down at different temperatures. With the rise of temperature, the peak current soars first and then tends to level off, and the breakdown delay falls continuously, reaching 0 μs at 60 °C. The effective energy and energy conversion efficiency of PB both increase with the increase of temperature.