Experimental Investigation of Pore Structure Damage in Pulverized Coal: Implications for Methane Adsorption and Diffusion Characteristics

To study the effect of pulverization on coal's pore structure and the implications for methane adsorption and diffusion properties, three kinds of high volatile bituminous coals were sampled and crushed into six kinds of particle sizes to conduct the experiments using a combination of proximate analysis, N-2 (77 K)/CO2 (273 K) adsorption pore structure characterization, and high-pressure methane adsorption and diffusion properties determination. Results indicate that the pulverization process has no remarkable influence on the proximate properties of the coal, while the pore structures are evidently modified. The pulverization process significantly increases the specific surface area and pore volume (measured by N-2 adsorption) of the coal, which favors gas adsorption and diffusion. However, its effects on <2 nm micropore structure (measured by CO2 adsorption) are variable. The high-pressure methane adsorption and diffusion tests demonstrate that the adsorption volume and diffusion quantities both increase with the decrease of coal particle size. The adsorption experiments also indicate that because of the complex adsorption mechanism, the high-pressure adsorption capacities of the coal are comprehensively influenced by the <2 nm micropore (measured by CO2 adsorption) as well as the additional BET specific surface area and pore volume (diameter below 10 nm, measured by N-2 adsorption) that are generated during the pulverization process. Moreover, methane desorption experiments reveal the existence of coal rank -dependent extremity particle size, which can significantly affect the diffusion performance of methane within coal.