Research On The Methane Adsorption /Desorption/Diffusion Characteristics Of Tectonic Coal

High adsorption structure of coal, rapid desorption, low strength and low permeability characteristics are one of the main factors of coal and gas outburst, which is a major cause of coal mine gas content calculation allowed highlighting predict cuttings gas desorption index measurement error, and the direct cause is difficult to construct coal bed methane development. In view of this, this paper, different rank coal rank native structure and its symbiotic constructed experimental coal core samples for the study of the adsorption of nitrogen by cryogenic methane adsorption isotherm and desorption experiments, combined with previous research results from different differences pore structure of coal, different adsorption and desorption characteristics of coal particles and gas diffusion angle model, for construction of the adsorption, desorption experiments and model of conduct and diffusion theory. Mainly made the following understanding:(1) Reveals the low molecular weight compounds in coal is an important factor affecting the pore structure of coal. In the process of forming the structure of coal to generate and save a lot of low molecular weight compounds, as compared to the native structure of coal, the coal structure of saturated hydrocarbon content lower, much higher content of polar aromatic compounds, low-molecular compound content of large, intermolecular force is small, resulting in specificity of the molecular structure of coal structure. It was found that with the increase of fixed carbon from fat coal to coke, pore specific surface area and pore volume ratio ratio has decreased, while the hole contrast, the hole than the specific surface area and pore volume ratio declined first increased. low molecular weight compounds in the free state, adsorbed and solution-state structure confined to the coal macromolecular structure, the transformation of the morphological structure of the pore structure of coal pore size distribution. The presence of low molecular weight compounds of the transformation of coal to some extent, the pore structure of coal, thereby affecting the adsorption properties of coal in methane.(2) States that the coal structure has an important influence on the pore structure and adsorption and desorption of coal. Predecessors have pointed to the pore structure of coal structure has some reworking, based on the different coal structure cryogenic nitrogen adsorption trial found that pore volume ratio of each segment and the specific surface area of the aperture ratio does not correspond, in particular, microporous pore volume is small, but large specific surface area. Compared with the original structure of coal, coal increased symbiotic structure at various stages of the pore volume and specific surface area are. Coal reservoirs porosity is the main gathering place for the gas, but also its migration pathway; pore structure not only restricts the gas content of coal, but also have a significant impact on the desorption and diffusion.(3) Verify the adsorption constant tectonic coal compared with the native coal has a significantly different structure. Predecessors have pointed coal structure is an important factor affecting the adsorption properties of coal, the paper was found tectonic coal isothermal adsorption constants a, b values significantly greater than symbiotic native structure of coal. Temperature adsorption capacity for coal plays a negative role in the adsorption capacity of coal decreases with increasing temperature; different coal structure at different temperatures have different adsorption characteristics, the native structure of coal compared with the performance of the more obvious symbiotic structure of coal. Construction of coal a limit adsorption amount than the limit value of the native structure of coal adsorption capacity of symbiotic larger, indicating that construction of coal should be larger than the specific surface area of symbiotic native structure of coal, has a stronger adsorption capacity. different coal structure, under isothermal conditions, the construction of coal coal sample b is greater than the native structure of coal.(4) That the coal diffusion coefficient is not constant, it reveals the structure of coal gas diffusion coefficient of dynamic attenuation characteristic diffusion coefficient as the native structure of coal and coal structure are quite different. Many scholars of coal gas diffusion law aspects of the research work carried out, but more classic diffusion model based on coal particles still can not accurately describe the whole gas diffusion process. In this paper, a new model to calculate the variation of initial diffusion coefficient D0 and translational diffusion coefficient attenuation coefficient ?, and explore the different ranks, different sizes, different coal structure on coal sample of D0 and ?, obtained tectonic coal the initial diffusion coefficient D0 is greater than the native structure of coal, the overall size of the coal samples of initial diffusion coefficient D0 is greater than the size of 0.5-1.0mm coal 0.25-0.5mm, the overall degree of fat coal metamorphism of Pingdingshan coal initial diffusion coefficient D0 is greater than the lean coal rank coal samples conclusions Hebi. This determination and development of coalbed methane gas content of great significance.