Study On Gas Adsorption Characteristics Of Coking Coal In High Temperature And High Pressure Environment

In order to study the gas adsorption characteristics of coking coal in deep mining areas,this paper selects coking coal samples from two high-quality coking coal mining areas,Pingdingshan,Henan province,and Liulin,Shanxi province,and uses the Hsorb-2600high-temperature and high-pressure gas adsorption instrument to simulate the ground temperature and gas pressure in deep coal seam,confirm the experiment temperature is30℃ ～ 80℃,the pressure is 0 ～ 11 MPa.By testing the gas adsorption isotherm,the high-temperature and high-pressure gas adsorption characteristics of coking coal were studied;The low-temperature liquid nitrogen adsorption method and mercury intrusion method were used to test and analyze the pore size distribution,pore volume and specific surface area of coking coal samples from the two mining areas,and to analyze the differences in coal pore structure before and after the high temperature and high pressure test.The test and analysis were carried out to analyze the difference of pore structure under high temperature and high pressure environment.On the basis of the above studies,the relationship between the pore structure of coking coal under high temperature and high pressure environment and the gas adsorption characteristics was qualitatively analyzed.The research has achieved the following main research results:(1)High temperature and high pressure adsorption experiments show that the adsorption curve can be divided into three stages with increasing pressure.The first stage is the rapid adsorption stage,and the adsorption amount increases roughly linearly with the increase of pressure;the second stage is the slow adsorption stage,the adsorption capacity increases gradually with the increase of the adsorption pressure,but the increase rate decreases with the increase of the pressure;the third stage is the adsorption saturation stage,the adsorption capacity changes little with the increase of the pressure and gradually approaches the limit adsorption capacity.At the same pressure,the amount of methane adsorption gradually decreases with increasing temperature.The temperature is negatively correlated with the adsorption capacity of coal.When the temperature and pressure are relatively small,the growth rate of gas adsorption capacity is fast,and the difference in gas adsorption capacity at the same pressure and different temperatures is small;as the temperature and pressure increase,the temperature increase makes the decrease in adsorption capacity greater than the pressure increase the amount of adsorption.(2)The methane adsorption of coking coal under high temperature and high pressure environment still conforms to the Langmuir adsorption model,the isothermal adsorption curve still belongs to the type I adsorption curve,and the correlation coefficient reaches above0.99.(3)After the high temperature and high pressure adsorption test,the pore structure of coal is more complex,including a wide range of pore types.Differences in pore structure characteristics of coal samples before and after high temperature and high pressure adsorption tests were analyzed by mercury intrusion method.After the high-temperature and high-pressure adsorption test,the cumulative mercury input into the coal is lower than that before the high-temperature and high-pressure coal samples.Pore connectivity becomes poor;analysis of coal pore changes through a combination of mercury injection experiments and liquid nitrogen adsorption experiments: found that the pores in the coal are moving in a more dense direction,and coal samples contain a large number of semi-closed micropores and pinholes,the connectivity of coal becomes worse.(4)The difference in the pore structure characteristic values of coal samples before and after the high temperature and high pressure test were analyzed using the low temperature liquid nitrogen adsorption method.After the high temperature and high pressure adsorption test,the coal sample’s absorption-desorption loop is higher than before the high temperature and high pressure.(5)At the same temperature and pressure,the hard coal gas adsorption capacity and the adsorption constant a value of the same coal sample are less than the corresponding soft coal;when the pressure is constant,the higher the temperature,the coal’s adsorption constant a does not change.Larger,the b value decreases.Different coal samples have different adsorption characteristics of soft and hard coal.The adsorption capacity of Liulin hard coal and soft coal is greater than that of Pingdingshan hard coal and soft coal,respectively.