Research On Influence Factors Of Methane Desorption Hysteresis And Its Mechanism

Gas stored in the coal is a kind of potential unconventional energy, at the same time, is one of the hidden trouble of coal mine safety production. Considering from two aspects of energy utilization and prevention and control of coal mine disasters, the importance of the gas extraction is getting more and more attention. Rule of gas adsorption desorption is widely studied, a large number of adsorption desorption experiment and gas extraction data show that gas desorption process lags behind the adsorption process, but the current study on the gas desorption hysteresis effect is less. This paper analyzed the current problems existing in the research area of gas adsorption desorption, on the basis of summarizing the research status at home and abroad,determines the gas desorption hysteresis effect mechanism as the research target, the main achievements are as follows:Firstly, on the basis of summing up the experience formula of soil, polymers, organic materials, and other porous media to quantitative describe desorption hysteresis effect, this paper proposed a method to quantitative analyze the gas desorption hysteresis effect. This method use the Langmuir adsorption model and gas desorption model respectively to simulate the adsorption desorption data fitting precisely, according to the fitting curve, use the proposed lag coefficient calculation method based on hysteresis area ratio to calculate the hysteresis coefficient. According to the size of desorption hysteresis coefficient to quantitatively describe the strength of desorption hysteresis effect.Secondly, according to the physical characteristics of coal are analyzed, studied the coal composition characteristic, the pore and surface characteristics. To carry out industrial analysis, coal maceral identification, mercury injection experiment, nitrogen adsorption experiment etc., test of coal type,coal maceral, porosity, entrance, pore size distribution, pore types and forms, the specific surface area and physical characteristics of coal related parameters. Summed up the composition characteristics and pore surface characteristics of different degree of metamorphic coal.Thirdly, carrying out the adsorption and desorption experiment of coal in coal rank, different temperature, moisture content, studying on the gas adsorption and desorption, and hysteresis characteristics on the condition of different coal rank, temperature, water content etc. Calculate desorption hysteresis coefficient under the different conditions. It reduces along with the coal rank, coal to gas adsorption capacity gradually decreased, the gas desorption hysteresis is more and more small, With increasing temperature, the adsorption capacity of coal for gas decreased, the gas desorption capacity is gradually increased, the gas desorption hysteresis is more and more small, With the increase of water content in coal, gas adsorption and desorption capacity of coal gas are reduced, the gas desorption hysteresis is more and more.Finally, the influence of coal quality, pore configuration, temperature, moisture and other factors on gas desorption hysteresis were analyzed on the basis of related experiments on physical characteristics and adsorption and desorption characteristics of coal. It is a positive correlativity between gas desorption hysteresis coefficient and ash content, mineral content, moisture content, porosity, number of pores, specific surface area. And, the greater the values of these parameters, the larger the gas desorption hysteresis coefficient. The number of ink bottle shape pore and thin neck bottle pore has a significant effect on gas desorption hysteresis. With the increase of methane molecular kinetic energy because of temperature rise, the adsorption-desorption equilibrium is partial to desorption, therefore, the degree of desorption hysteresis gradually reduces. In addition, the enhancement of water lock effect with the increase of moisture content of coal result in the degree of desorption hysteresis gradually strengthens. Based on the summary of various factors, a reasonable mechanism of gas desorption hysteresis was concluded, and the influence on local gas extraction was also analyzed, these regulars will provide theoretical guidance for practice.