| Summary: | Abstract High‐voltage electrical pulse (HVEP) technology, a potential method for degassing coal seam in the future, has made great progress in field application. However, the previous studies mainly concentrated on the coal‐crushing effect of the action of single pulse, ignoring the influence of cyclic single pulse on the fracture structure of coal. In this paper, Huaibei anthracite coal and Inner Mongolia bituminous coal were taken as the experimental objects to study the effect of cyclic single pulse on the fracture structure of coal. The results show that the uneven distribution of electric field in the coal causes the crack to break along the interface between the mineral and the coal. Besides, the characteristics of cracks and functional groups of coal before and after electrical breakdown were investigated through scanning electron microscope and Fourier transform infrared spectroscopy. The results suggest that the relative contents of oxygen‐containing functional groups are reduced after electrical breakdown, which promotes the gas desorption from the surfaces of coal samples. Moreover, changes in CH4 adsorption capacity of HVEP‐treated coal were studied through a high‐pressure adsorption instrument, with the adsorption temperature set from 40 to 120°C. The results show that the adsorption amount of electrically broken coal is smaller than that of raw coal, which proves that temperature and current exert similar influences on the adsorption capacity of coal sample. Additionally, current waveforms indicate that the peak current increases with the number of cycle, whereas the breakdown time decreases with it. However, the peak current and breakdown time will eventually become stable as the number of cycles grows, demonstrating that electrical properties of coal are changed in the process of breakdown, which thus affects the next discharge.
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