| Coal and gas outburst is one of the main disaster forms of coal mine gas disaster.In the process of coal and gas outburst,there will be a phenomenon of"abnormal gas production",that is,the amount of gas outburst is often much higher than the actual gas content in outburst coal.The related coal deformation experiments at sub high temperature and high pressure show that the coal will produce gas due to the mechanochemical effect in the loading process,but there are still some limitations.When the coal is fractured,the electric field of microstructure will be generated between the crack wall and the microcrack,and the intensification of the electric field may be one of the reasons to promote the gas production of coal.Therefore,this paper analyzes the gas production effect of coal in the electric field and expounds the gas production mechanism of coal excited by the external electric field through the investigation of the experiment of coal gas production excited by the external DC electric field.In this paper,after testing the breakdown voltage of three kinds of metamorphic coal,the change of coal porosity before and after breakdown is analyzed by using low-field nuclear magnetic resonance equipment,and it is proved that the electric field energy will not be released in the coal pore structure when the coal is not broken down.The internal and surface temperature of coal is simulated and tested by infrared thermal imager and COMSOL Multiphysics software,and the maximum temperature of coal in the process of external DC electric field excitation is obtained,which excludes the thermal effect of electric field causing coal pyrolysis to produce gas.With the help of gc-4000a gas chromatograph,the gas produced by different coal samples under DC electric field excitation was detected,and the gas produced by coal under breakdown condition and constant temperature 95°C without electric field loading condition was compared.The results show that no gas is produced in the coal under constant temperature;the gas production of CH4,CO2 and CO is large at the moment of breakdown,and a small amount of C2H6,C2H4 and C3H8 hydrocarbon gas is produced at the same time;under the excitation of DC electric field,the gas produced by coal is CH4,CO2 and CO,and the cumulative gas production in 8h is smaller than that at the moment of breakdown,which indicates that the gas production behavior of coal under breakdown voltage is stable CH4 concentration increases with time,CO2 concentration decreases with time,and CO concentration increases first and then decreases with time.Under the theoretical conditions,the energy required to stimulate coal gas production by DC electric field is the difference between the energy input by electric field and the cumulative heat production by Joule heat effect.X-ray photoelectron spectroscopy（XPS）and Fourier transform infrared spectroscopy（FTIR）were used to analyze the effect of electric field on chemical bonds and functional groups in coal.The results show that the relative contents of C-C/C-H and C-O bonds of C element in coal decrease,and the contents of oxygen-containing functional groups and aliphatic hydrocarbons decrease after DC electric field stimulation.During the experiment,CH4 gas is generated from the shedding of methyl functional groups in coal after electric field stimulation,and CO gas is generated from the fracture of C-O bond.CO2 gas is generated from the cross-linking reaction between C=O fracture and COOH. |
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