Thermal Evolution Characteristics of the Pore Structure in Coal and Its Dominant Factor Conversion

This study analyzed the pore characteristics of coal after heat treatment under air and vacuum conditions using low-temperature gas adsorption (LTGA) measurements. The removal of moisture significantly increases the micropore and mesopore volumes and results in a reduction in surface fractal dimension D-1 and an increase in structure fractal dimension D-2 in the mesopore. Volatile emission leads to the formation of ultramicropores and has a pore-expanding effect on ultramicropores and small mesopores. The enlarged mesopores result in a rougher surface and better connectivity. Thermal expansion decreases pore volume and is the dominant factor of pore evolution at a lower temperature. However, more drastic volatile emission with increasing temperature gradually dominates pore evolution. The heating condition also affects the dominant factor conversion. Volatile emission under the air condition dominates pore evolution under higher temperatures, and pore volume has a tremendous increment.