Correlation between Gas Permeability and Macropore Structure of Coal

Abstract

This paper deals with the basic data on gas permeability and diffusion coefficients of coal and its correlation with the characteristics of the macropore such as Klinkenberg's constant, mean pore-radius, effective pore-area and porosity. Numerical researches on the flow and diffusion of gas in the coal seam have been extensively studies, however many numerical constants determined by experiments are necessary. This paper aims at stating the possibility of reduction the number of numerical constants of the numerical analysis by means of several relationship equations between the numerical parameters.
Two kinds of test pieces, made of lump coal and compressed fine coals, were prepared. Measurements were performed by flowing methane, nitrogen and other gases through the test pieces. On the basis of experimental results for compressed finecoals, the empirical equations between gas permeability and characteristics of macropore were obtained. For lump coal, thef actors were determined to express its heterogeneity in comparison with the equations for compressed fine-coals. Permeability flowing methane was less by 10-15% than that of nitrogen. This amount of reduction can be explained on the basis of the difference inmean free-pass of molecule. The effect of adsorption on macropore surfaces of coal was not evident for gas per-meability.