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

Abstract

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)/CO 2 (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 CO 2 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 CO 2 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.

Experimental Investigation of the Adsorption Characteristics of Mixed Coal and Variations of Specific Surface Areas before and after CH4 Adsorption

“…The gas enters the micro pores of coal rock by adsorption [13]. Buss [14], Talu [15], Cowlard [16], and Jin [17] investigated the distribution of pore structures of coal and obtained the same results as those presented in Reference [12] by gas isothermal adsorption. Manasi [18] and Qi [19] studied the pore characterization of different types of coal from coal.…”

Investigation of the fractal characteristics of adsorption‐pores and their impact on the methane adsorption capacity of various rank coals via N2 and H2O adsorption methods

“…35 Moreover, the hysteresis loop of the anthracite sample WLH8 and low-rank coal sample YZG2, which can be classified as the L4 type, is not mentioned in the above classification but appears in many published reports. 2,[57][58][59] Its main characteristic is that the adsorption and desorption curves do not coincide, even in a very low relative pressure range (P/P 0 < 0.35). The low-pressure hysteresis may be related to the change in the volume of the adsorbent, for example, the sorption-swelling effect of the coal.…”

Coal permeability evolution characteristics: Analysis under different loading conditions

“…Coal is a complex porous medium that contains an extremely uneven distribution of pores and fractures 20–24 . Coal permeability is affected not only by scale effect and stratification but also by ground stress, gas pressure, matrix sorption‐induced deformation, and temperature.…”