Experimental investigation on gas adsorption characteristics and microstructural features of coking coal under temperature–pressure coupling

Abstract

Gas adsorption characteristics are significantly affected by coal pore structure and temperature and pressure conditions. In this paper, we investigated the adsorption characteristics and microstructural changes of coal samples through gas adsorption experiments, combined with scanning electron microscopy (SEM) and low-temperature liquid nitrogen adsorption experiments. The results show that the adsorption capacity increases with pressure and decreases with temperature; moreover, it under high and low pressures and high temperatures exhibits complex non-linear characteristics. For example, at 25 ℃, the adsorption capacity increases significantly with pressure; at 120 ℃, it is extremely low in the low-pressure zone but increases significantly in the high-pressure zone. This reflects that changes in pore structure enhance the adsorption capacity under high temperature and high pressure. Scanning electron microscopy (SEM) and low-temperature liquid nitrogen adsorption experiments show that an increase in temperature causes micropore collapse and consolidation, as well as a decrease in specific surface area; furthermore, pretreatment at 80 ℃/2.5 MPa could optimise the pore structure. This paper has also established application models applicable to three aspects: goaf gas control, goaf spontaneous combustion prevention and control, and goaf stability evaluation. These models provide theoretical support for the exploration and development of deep coalbed methane, as well as the condition optimization and technical improvement in the process of coalbed methane extraction.