Experiment On CO₂ Diffusion In Coal Particles With Different Sizes And Correction Of Diffusion Coefficient

The exploitation of underground coalbed methane,the use of coal seams to seal carbon dioxide and the prevention of gas outburst accidents are all related to the characteristics of gas adsorption,desorption and diffusion in coal seams.Outburst process will destroy the coal seam,and it is also accompanied by the generation of coal particles with different particle sizes.It is of great significance to study the migration law of gas in coal particles with different particle sizes for understanding the coal powder outburst process.There are many pores in coal particles,which are different in pore size,shape and connectivity,and also show different parameters such as porosity of coal particles.The change of coal particle size will lead to the change of pore structure.Under different temperature,pressure and geological conditions,the metamorphic degree of coal changes,which will also affect the microstructure of coal.The size and metamorphic degree of coal particles will affect the diffusion ability of gas in pores.Therefore,this paper has done the following research work:(1)Bituminous coal and anthracite coal are selected and crushed to suitable particle size,and the desorption and diffusion experiment scheme is designed for these coal samples.(2)Measure the basic parameters of coal particles,carry out constant temperature experiments at 30℃ and different pressures,and carry out adiabatic experiments at 30℃and 1 MPa adsorption equilibrium.meanwhile,measure the temperature changes during the experiments.On the basis of obtaining more accurate experimental data,the influence mechanism of particle size on gas diffusion law under different metamorphic conditions was studied.(3)The influence of coal pore structure on gas diffusion is expressed by diffusion factor,and the diffusion factor is used to modify the diffusion coefficient changing with temperature and pressure.The mathematical model considering diffusion factor is established from microscopic aspect,and the laws of diffusion factor and diffusion coefficient changing with coal particle size under different metamorphic degrees are studied.(4)Based on data processing and numerical simulation,analyze the variation law of gas diffusion coefficient with particle size under different conditions,and according to the diffusion factor model,invert the diffusion coefficient under different particle sizes,compare with the experimental data,verify the accuracy of the model,and analyze the possible problems in the experiment and model.