Study On Gas Adsorption Law Of Coal Under Different Stresses And Application

Gas is one of the main factors leading to the frequent occurrence of coal mine disasters and accidents.The level of gas content in the coal seam determines the likelihood of gas accidents during the underground mining process.With the increase of mining depth,the influence of stress on the gas adsorption characteristics of coal has gradually become significant.However,most of the current research on the gas adsorption characteristics of coal ignores the influence of stress factors.Therefore,this thesis uses a self-built "gas adsorption experimental platform for coal under stress" to study the influence of different stress（axial pressure and confining pressure）loading on the gas adsorption of coal through laboratory tests,numerical analysis,theoretical analysis,etc.It explores the changes in pore structure characteristics and gas adsorption laws in coal,constructs a gas adsorption characteristic model for coal under stress,optimizes the indirect calculation method of coal seam gas content,and verifies it through field measurements.Taking the 15#coal seam anthracite of Yangquan Minmetals as the research object,this thesis tested the pore structure of coal before and after stress by mercury injection method and low-temperature nitrogen adsorption method.The fractal dimension D₁ of the coal samples decreased by 1.9%after the stress,and the pore surface was smoother,while the fractal dimension D₂ increased by 1.2%,and the non-homogeneity of the pore structure was enhanced,which was unfavorable to the gas adsorption of coal.Based on the constructed experimental platform for gas adsorption,the trend of the relationship between the volumetric stress Θ and the porosity φ of coal was studied under the conditions of different circumferential and axial pressures,and the function was fitted to find that the average relative error of the calculated value of the secondorder function was the smallest,and the relationship could be expressed asφ=φ₀(0.9940-0.0197Θ+1.805×10^-4Θ²).The isothermal adsorption experimental data of coal under different stresses were fitted using Langmuir equation,D-A equation,and Freundlich empirical equation,and it was found that the average relative error of the gas adsorption results calculated by Langmuir equation is the smallest,which can better describe the gas adsorption law of coal under different stresses,where the relationship between the value of Langmuir adsorption constant a、b and volumetric stress can be characterized as a function of a=43.50-0.88Θ+0.0085Θ² and b=0.78e^-0.017Θ.Finally,the equations of free gas and adsorbed gas content were corrected to optimize the indirect calculation method of coal seam gas content.The average relative error between the measured data in the field and the calculated value of the optimized model was 6.65%,which shows that the optimized model is more accurate in predicting the gas content of coal seams with different burial depths.