Study On Diffusion Of Coal With Different Metamorphic Degree

China has large reserves of coal resources with different metamorphic degrees,and the breakthrough of coalbed methane production has been achieved successively over the years.Combined with the mechanism of coalbed methane production,it is of great theoretical and practical significance to study the influence of metamorphic degree and gas pressure on methane diffusion coefficient in coal.Hence 6 kinds of coal samples with different degrees of metamorphism(R_o,ran=0.68%⁵.82%)were collected.The pore structural characteristics of these coals were studied by scanning electron microscope and low temperature nitrogen adsorption experiment.The influence of degree of metamorphism on diffusion coefficient was studied by particle diffusion method and inverse diffusion method,respectively.The influence of gas pressure on diffusion coefficient was studied by inverse diffusion method.The main results are as follows:?1?When the Langmuir equation is used to determine the adsorption constants a and b,the linear regression method does not satisfy the minimum of the sum of squares of the residuals of the dependent variables of corresponding curve.Linear regression method for the number of variables from the irrational number to a finite number of rounding is the cause of the rounding error.Based on the nonlinear regression method,in which the measured data has the characteristic that the residual sum of squares is smaller.When applying the Langmuir equation to find the parameters,a nonlinear regression method is recommended.?2?In the particle diffusion experiment,with the degree of metamorphism increasing,the diffusion coefficient first decreases,then increases and finally decreases.In the inverse diffusion experiment,the diffusion coefficient decreases with the increase of the degree of metamorphism.In the inverse diffusion experiment,the diffusion coefficient increases with the increase of gas pressure.