Abstract: In order to investigate the variation characteristics of gas instantaneous diffusion coefficient through coal particles under different conditions, based on the similarity theory and diffusion equation, a method was worked out for calculating methane diffusion coefficient, and a coal gas particle diffusion determination system was developed. Then the instantaneous diffusion coefficients of methane through coal particles under different conditions involving coal structure, methane gas pressure and coal particle size were determined via experiments, and the variation characteristics of instantaneous diffusion coefficients under different conditions were analyzed. The results indicate that at the some methane pressure, the instantaneous diffusion coefficient for methane in coal dropps by power function with time, that the instantaneous diffusion coefficient of methane in tectonic coal is much larger than that of methane in the primary structure coal within the initial time, that there is a positive correlation between the instantaneous diffusion coefficient of methane in the primary structure coal or tectonic coal and the particle size, and that with the increase of particle size, the instantaneous effective diffusion coefficient of methane in the primary structure coal has an increasing tendency but the instantaneous effective diffusion coefficient of methane in the tectonic coal reduces obviously.

Key words: methane, diffusion coefficient, law of Fick, coal structure, equilibrium pressure, coal particles size