Experimental investigation on the effect of multiscale pore characteristics of tectonic coal on gas adsorption/desorption and diffusion characteristics

In the paper, the findings demonstrated that the pore volume and specific surface area within tectonic coals increase as the particle size decreases. The pores consisted of different proportions of bottleneck pores, cylindrical pores, and slit-/plate-like pores. The ultimate gas desorption volume and initial gas desorption rate of tectonic coals varied exponentially and quadratically with macropore volume, respectively. The variation law of gas desorption rate states that when the particle size is below the limiting particle size, the coal matrix sustains significant damage. This results in a shortened gas diffusion length and reduces the gas diffusion resistance, leading to an extremely rapid increase in the initial gas desorption rate. Due to the limitation of pore scale in coals, the gas diffusion coefficient of tectonic coal rises with particle size. The effective diffusion coefficient increases with a decrease in coal particle size, providing an intuitive representation of the fundamental diffusion behavior.