Study On The Variation Law Of Diffusion Coefficient Of Methane From Coal Particle With Diffusion Time

Engineering application shows that there was a large deviation when computing the gas loss quantity,predicting parameters of gas outburst and gas reserves.One of the main reasons was that diffusion coefficient was regarded as a constant in the model.It was a great significance to improve the accuracy and adaptability of gas diffusion theory from coal particle in engineering application,in particular of whether or how diffusion coefficient changed with time.By means of physical simulation experiment,theoretical calculation and comparative analysis,the paper studied the variation law of diffusion coefficient of methane from coal particle and diffusion time,the influence of different factors was also studied,the accuracy and adaptability of the law was analyzed.First of all,the physical simulating experiment about diffusion coefficient from coal particle was conducted,Different factors including pressure,temperature,moisture and particle size,damage degree and rank were taken into account.Secondly,based on the computing method of diffusion coefficient between Nie Baisheng and Yang Qiluan,the variation law of diffusion coefficient with time was fitted.Finally,The pore structure of typical soft and hard coal with different metamorphic degree was determined by mercury injection and Liquid nitrogen adsorption method.The mechanism of diffusion coefficient with time was studied,the difference of diffusion coefficient from soft and hard coal was also analyzed.Research results show that the computation method of Nie Baisheng is better than Yang Qiluan,when calculating diffusion coefficient with the time section.Diffusion coefficient with time was power function type,which showed a better consistency with experimental data than exponential type.Equilibrium pressure had a little effect on diffusion coefficient,the other five influencing factors have a great influence,but it is consistent that the variation law of diffusion coefficient of methane from coal particle and diffusion time.Based on pore structure,gas adsorption and migration theory,the location of gas from coal particles distribution were different,It was also different that the path,resistance and aperture of gas from coal particles in inner surface diffused to outside,this was why apparent diffusion coefficient of gas from coal particle decreased gradually with diffusion time.Because the volume of mesopores and macropores was increased obviously,the diffusion coefficient of soft coal was larger than hard coal.