Study On Gas Adsorption And Desorption Characteristics Of Coal At Low Temperature Fracturing Process

The low-temperature cracking-promoting extraction technology of coal bodies is widely used in coal mine gas management and coalbed methane extraction,but during the low-temperature cracking process,the original equilibrium state of adsorption/desorption of gas-containing coal is bound to be broken.In this paper,an improved adsorption/desorption device is used to study the adsorption/Desorption amount,adsorption/desorption rate,adsorption constants a and b values,and temperature and energy changes during the adsorption/desorption process of gas-containing coal under the combined action of low temperature environment（-45℃～30℃）and pressure（1MPa～3MPa）,the main conclusions are as follows:（1）The low temperature environment effectively promotes the adsorption of methane by the coal body,but the ambient temperature has no significant effect on desorption;when the ambient temperature is constant,the adsorption amount and desorption amount are positively related to the gas pressure;when the gas pressure is constant,the ambient temperature and the adsorption amount are negatively correlated,And its correlation with the desorption amount is small.（2）When the gas pressure is constant,as the ambient temperature decreases,the coal sample’s adsorption rate of methane increases,but its desorption rate has no significant effect;when the ambient temperature is constant,as the gas pressure increases,the coal body adsorbs methane/The desorption rate is increasing.During the process of coal adsorption/desorption gas,the rate of change of adsorption/desorption amount is generally declining.The rate of change of adsorption/desorption amount is steep in the early stage,and the change in the later period is gradually flat,indicating that with the As adsorption/desorption continues,the rate of change of adsorption/desorption amount becomes slower.（3）With the continuous decrease of the ambient temperature,the values of the adsorption parameters a and b show an increasing trend;the value of the saturated adsorption amount a changes with a negative exponential law as the temperature increases,and the value of the limit adsorption pressure b varies with temperature The increase changes in a negative exponential pattern.（4）When the ambient temperature is constant,the maximum value of the temperature change(（35）T_max)in the adsorption/desorption process also increases with the continuous increase of the gas pressure,and the change trend is approximately a linear relationship;when the gas pressure is constant,as the ambient temperature increases,（35）T_max Continuously decreasing,the adsorption process is increasing,while the change trend of the desorption process（35）T_max is not significant.（5）The calculation formula of coal surface free energy in the adsorption process is deduced,and the changes of free energy and heat are analyzed,and it is obtained:1)The coal sample at the same temperature value increases with the equilibrium pressure Large,the free energy and heat per unit mass of coal samples gradually increase during the adsorption process,and the change trend is approximately a linear relationship;2)As the temperature of coal samples under the same equilibrium pressure continues to decrease,their adsorption In the process,the free energy and heat of a unit mass of coal sample also increase;there is a physical phenomenon that free energy is converted into heat during the adsorption process;3)coal samples at the same temperature value desorb as the equilibrium pressure increases During the process,the heat of the unit mass of coal sample also gradually increased;4)For coal samples under the same equilibrium pressure,the correlation between ambient temperature and heat change during desorption is small.