Theoretical model and numerical solution of CO adsorption diffusion flow in coal particles

In order to explore the theoretical model of CO adsorption and diffusion flow in coal,based on the theory of density gradient diffusion,a mathematical model of CO adsorption in spherical coal particles was established. Finite difference and nondimensionalization methods were used to solve and simplify the model,and a new method of diffusion coefficient inversion was proposed to verify the method and model. Then,the CO pressure evolution process of different coal samples and particle sizes was simulated,and the differences of adsorption properties and diffusion coefficients of CH₄,CO and CO₂ were discussed. The results show that the simulation curve of CO adsorption is consistent with the experimental data,which proves the reliability of the model and the inversion method. The diffusion coefficient is proportional to the particle size and is a power function. The adsorption process of CO is gradually diffused from the surface to the inside. The nondimensionalization pressure on the outer surface of coal particles decreases with the increase of nondimensionalization time. Under the same nondimensionalization time, the nondimensionalization pressure near the center of coal particle is inversely proportional to the particle size. The diffusion coefficient and adsorption capacity of CO₂ with smaller molecular dynamics diameter are much greater than that of CO and CH₄. The diffusion coefficient and adsorption property of CO and CH₄ are similar.