Study on the influence of different-voltage plasma breakdowns on functional group structures in coal

Promoting gas desorption is the key to improving gas extraction efficiency, physical discharge-based plasma carries massive joule heat, and inevitably affects the structures of functional groups in coal, which has a certain impact on the adsorption and desorption of gas, but existing literature lacks in-depth research on this. This study explores the changes of functional groups on GHS high metamorphic anthracite and HL low metamorphic bituminous coal samples under different breakdown voltages (BVs), from 15.3 kV to 17.3 kV, which serves as the key to determining the amount of energy injected into plasma channels. This study also explains the influence of BV on functional groups in coal from the perspective of electrical parameters such as voltage, current waveform and deposited energy. For two kinds of coal samples, the results reveal the following: (1) With the breakdown voltage increases, the coal is more likely to be polarized and the pre-breakdown period is shorter; accordingly, the coal can be broken down more easily. (2) The peak current increases linearly with the rise of BV, and the energy conversion efficiency jumps first and then tends to stabilize; (3) The plasma-induced oxidation reaction degree of the coal surface gradually strengthens as the BV rises, because more energy is used for reactions on the coal surface. Specifically, the higher the BV is, the faster the contents of hydroxyl and oxygen-containing functional groups decline, and the faster the aliphatic hydrocarbons in the coal decompose.