Study on gas production mechanism of medium- and low-rank coals excited by the external DC electric field

Abstract

This study aims to further explain abnormal phenomena occurring during coal and gas outbursts and grasp the gas production effect of the micro-structure on outburst coal surface under the action of the electric field. To this end, in this study, an experimental system for gas production of coal excited by the external DC electric field was established. Then, gas production experiments were performed on medium- and low-rank coals excited by the different-strength electric fields to reveal the relationships between gas production and coal rank and excitation voltage. Subsequently, the variations of functional groups and chemical bonds on coal sample surface after the external DC electric field excitation (EFE) were measured and analyzed through Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). According to the results of the gas production experiment, gases produced by medium- and low-rank coals under EFE include CH4, CO and CO2, and the gas production volume rises with the increase in excitation voltage. The results of FTIR analysis show that the contents of hydroxyl, aliphatic hydrocarbons and oxygen-containing functional groups of medium- and low-rank coals decrease to varying extents after EFE. The results of XPS analysis disclose that the structure of C element on the surface of medium- and low-rank coals changes after EFE. Therefore, the CO, CH4 and CO2 produced by medium- and low-rank coals during EFE come from the breakage of chemical bonds and the falling-off of functional groups. The research results provide theoretical support for revealing the mechanism of coal rock dynamic disasters and exploring methods for the monitoring and pre-warning of these disasters.