Effect of water immersion on pore structure of bituminous coal with different metamorphic degrees

It is important to understand the disaster-causing mechanism of dried water-immersed coal by investigating the influence of water immersion on the coal pore structure. In this study, low-temperature nitrogen adsorption experiments of eight bituminous coals with different metamorphic degrees and their dried water-immersed coals were carried out to analyze the adsorption/desorption mechanism and investigate the effects of water immersion on the pore shape, pore-structure parameters, and fractal dimension of coal. The results showed that adsorption of nitrogen on coal mainly includes micropore filling, monolayer adsorption, multilayer adsorption, and capillary condensation. The pores of coal were a continuous system from nanometer pores to relatively unlimited size pores. Water immersion did not significantly affect the pore shape of the coal, decreased the specific surface area and adsorption capacity, and increased the total pore volume and average pore diameter. It had the greatest effect on the average pore size of moderately metamorphosed coals, which may accelerate the oxidation process of coal and aggravate gas emission. The fractal results showed that water immersion reduced the surface fractal dimension of higher and lower metamorphic coal, while it increased that of moderately metamorphic coal, and it had the opposite effect on the structural fractal dimension.

Automated summary

It is crucial to understand the mechanism of disaster caused by dried water-immersed coal by studying its influence on coal pore structure. This study conducted low-temperature nitrogen adsorption experiments on eight different metamorphic bituminous coals and their dried water-immersed coals to analyze the adsorption/desorption mechanism and investigate the effects on pore shape, pore-structure parameters, and fractal dimension. The results showed that water immersion had minimal effect on the pore shape of the coal, but decreased specific surface area and adsorption capacity while increasing total pore volume and average pore diameter. It had the greatest impact on the average pore size of moderately metamorphosed coals, which could accelerate coal oxidation and worsen gas emission. The fractal results revealed that water immersion reduced the surface fractal dimension of higher and lower metamorphic coal, while it increased that of moderately metamorphic coal, with the opposite effect on the structural fractal dimension.