Study On Gas Adsorption And Diffusion Behavior In Guizhou Low-permeability Coal Under Slow Acid Actio

The long-term dominant position of coal in energy consumption is controlled by the energy characteristics of rich coal,poor oil and less gas in China.Guizhou Province is rich in coal resources,but the geological structure is complex.Most coal mines are high gas mines or coal and gas outburst mines.Coal seams have the characteristics of high gas content,low permeability and difficult desorption,resulting in serious gas disasters.The production of gas in coal must undergo adsorption,desorption,seepage,and diffusion,all of which are closely related to the safe production of coal mines.Due to the constraints of the roof and floor conditions of coal seams,the field application of traditional coal seam physical antireflection technology in Guizhou mining area is limited.Based on the theory of chemical permeability enhancement of coal seam,according to the characteristics of low permeability anthracite rich in silicate minerals in Guizhou mining area,the main acid solution of acidification experiment was determined by the combination of laboratory measurement and theoretical analysis,and the optimum acidification retarder and concentration were optimized.Through conducting acidification experiments,the corresponding laws of the physical and chemical structures of experimental coal samples under the action of slow acid were explored.The mechanism of the influence of retarded acid action on the adsorption characteristics and diffusion behavior of gas in coal was revealed.Through this study,The main achievements and understandings are as follows:(1)According to the mineral analysis results of the experimental coal samples,the main acid solution for the acidification experiment is determined.The acidification retarder was preliminarily selected by using the retarding principle of various retarders.The static corrosion experiment was carried out to optimize the best retarder.The determination of hydrogen ion concentration was carried out to further determine the optimal concentration of the preferred retarder.Retarding acids were prepared and acidification experiments were conducted.(2)X-ray diffraction experiments,low-temperature liquid nitrogen adsorption experiments,high-pressure mercury intrusion experiments,and scanning electron microscopy experiments were carried out on experimental coal samples before and after acidification to clarify the impact of slow acid on the stacking structure,pore structure,and surface morphology of experimental coal samples.According to fractal theory,combined with the physical structure test results of experimental coal samples,the fractal dimensions of experimental coal samples are characterized from different dimensions.(3)Fourier transform infrared spectroscopy(FTIR)and Raman spectroscopy(Raman)experiments were conducted on experimental coal samples before and after acidification.Combined with the results of X-ray diffraction experiments,the evolution laws of slow acid action on the surface functional groups,chemical bonds,and chemical structural parameters of experimental coal samples were explored.(4)Isothermal adsorption experiments and initial velocity of gas emission of coal samples before and after acidification were conducted to analyze the influence of slow acid action on the gas adsorption characteristics in coal,and clarify the impact mechanism based on the structural change characteristics of coal samples.(5)Based on the viewpoint of molecular motion theory,combined with the gas diffusion model in porous media,a gas diffusion model in coal is constructed.The experimental data of isothermal adsorption and pore structure of coal samples were used to calculate the effective diffusion coefficient of gas in coal,and the evolution law and mechanism of gas diffusion behavior in coal by retarded acid were revealed.