The characteristics of pore structure and gas adsorption for water-immersion coal after drying

In order to investigate the characteristics of pore structure and methane adsorption for water-immersion coal after drying, two coal samples with different ranks were soaked in distilled water for a long time(60 d). Then, the low-temperature N₂ adsorption experiments and CO₂ adsorption experiments were carried out to investigate the changing rules of pore structure for coal before and after water immersion, and the high-pressure capacity method was used to test the characteristics of methane adsorption. Results showed that the pore volume and specific surface area of coal decreased after water immersion. According to the results of low-temperature N₂ adsorption, the specific surface area of mesopore and macropore can be reduced by up to 48.9%. CO₂ adsorption experiments shows that the pore volume and specific area of micropore decrease in varying degrees. The changes of pore structure consists of three stages, namely, the "pore increase" stage of mineral dissolution, the "shrinkage" of local expansion of coal matrix, and the "pore expansion" of overall swelling of coal matrix. In addition, the adsorption capacity of coal decreases after water immersion due to the interconnection of micropores caused by coal expansion and deformation, which reduces the pore volume and specific surface area of coal micropores. The research results have a guiding significance for gas drainage in water-rich coal measures and coal seam after hydraulic measures.