CO₂ Dynamic Diffusion Model And Test Based On Coal Grain Size Classification And Non-isothermal Conditions

Coal serves as a porous medium,and its internal complex pore structure and huge specific surface area provide broad places for the storage and transport of the gas in its interior.The adsorption-desorption-diffusion characteristics of the adsorption gas in the coal matrix is closely related to the engineering practice.Researching the adsorption-desorption-diffusion mechanism of the gas inside the coal mass and proposing a reasonable numerical model will help to better solve the practical engineering problems such as CO2 sealing,coal seam gas yield prediction and prominent disaster control.According to previous experimental studies,the researchers have not agreed on the relationship between diffusion coefficient and gas pressure;although the study of diffusion model has been derived many models are produced and the experimental data are well fitted,but the universal applicability of the model needs further research.Based on this,the main research contents of this paper include:(1)Taking anthracite Coal of Wangpo Mine in Shanxi Province and bitumite of Dongsheng Coal Mine in Inner Mongolia,a series of industrial analysis,element analysis and pore structure analysis were analyzed.(2)The isothermal adsorption tests with temperature 303 K、308K、313K、318K、323K,pressure 0-5MPa were carried out with CO2 as the gas medium.The results were analyzed and the adsorption heat was calculated.(3)The constant isothermal/adiabatic desorption-diffusion tests with equilibrium pressures of 1.0 MPa、1.5 MPa、2.0 MPa and 2.5 MPa at temperatures 313K and 323K were carried out with self-made test equipment to analyze the characteristics of cumulative diffusion curves under different conditions.(4)Based on the pore structure and previous studies,a gas-heat-solid coupling model based on the variable diffusion coefficient was established for CO2 desorption-diffusion process in coal particles under variable temperature;according to the results of adiabatic desorption-diffusion test,the coupling model is verified and the related parameters are analyzed.