Study on the Effect of Pore Structure on Desorption Hysteresis of Deep Coking Coal under High-Temperature and High-Pressure Conditions

Abstract

Pore space is the main desorption space for methane in coal; to study the effect of changes in pore structure on the desorption hysteresis effect of methane in coal under high-temperature and high-pressure conditions, the coking coal from Pingdingshan Twelve Mine was taken as the research object, and the isothermal adsorption and desorption curves were obtained and quantitatively analyzed at different temperatures and pressures by the help of isothermal adsorption and desorption experiments, combined with the pressed mercury experiments and the low-temperature liquid nitrogen adsorption experiments to test the pore structure of the coal samples before and after the adsorption and desorption tests. The pore structure of coal samples before and after the adsorption and desorption tests was tested by combining the mercury pressure test and the low-temperature liquid nitrogen adsorption test, and the influence of the change in the pore structure of coal samples after the high-temperature and high-pressure adsorption and desorption tests on the hysteresis effect of methane desorption was studied. The results showed that under the same pressure, the pore volume of coal samples increased with the increase in temperature, the pore-specific surface area showed a tendency to decrease, and the fractal dimension could well characterize the relationship between the pore structure and the pore surface of coal, in which the fractal dimension of the pores in the large pore size section gradually increased with the increase of temperature, and the fractal dimension in the small pore size section gradually decreased; there was a good correlation between the pore structure of the coal samples after the high-temperature and high-pressure adsorption and desorption tests and the hysteresis coefficient of desorption. The structural characteristics of the coal samples after adsorption and desorption hysteresis coefficient at high temperature and high pressure showed good correlation, i.e., the pore volume, the fractal dimension of the large pore size section, and the desorption hysteresis effect were negatively correlated, while the specific surface area, the fractal dimension of the small pore size section, and the desorption hysteresis effect were positively correlated.