Work

An experimental study on pore complexity in single-particle coal and its impact on CH₄ diffusion kinetics

Year: 2025

Type: article

Abstract: CH₄ diffusion kinetics in coal are critical for coal mine gas disaster control. Conventional qualitative analyses of coal gas diffusion, based on unit-mass pore parameters, neglect its fundamental origin within individual particles. In this study, a medium-volatile bituminous coal sample was gradually crushed by a jaw crusher and screened with a sample sieve into six particle size ranges: 0.3–0.5, 0.2–0.3, 0.125–0.2, 0.074–0.125, 0.045–0.075, and < 0.045 mm. The coal particle was modeled as homogeneous spheres and quantitatively characterized the full-scale pore structure (micropores: <2 nm, mesopores: 2–50 nm, macropores: 50–300 nm) using low-pressure N₂ (77 K) and CO₂ (273 K) adsorption. By integrating particle density and median size ( D 50), unit-mass pore parameters were converted into single-particle parameters. Results show that as the particle size decreased from 0.3 to 0.5 mm to <0.045 mm, the total pore volume within a single particle decreased exponentially by nearly four orders of magnitude. In addition, the initial CH 4 desorption rate ( V 0 – 1 ) increased rapidly (5.5 times) as the particle size decreased, while the initial CH 4 diffusion coefficient ( D 0 ) decreased linearly from 1.47 × 10 −13 m 2 /s to 4.29 × 10 −15 m 2 /s (34.3 times). The attenuation coefficient ( β ) increased exponentially from 8.97 × 10 −5 to 1.401 × 10 −3 s −1 (15.6 times). Analysis from the single-particle perspective reveals that smaller coal particles have simpler pores, accelerating initial CH₄ desorption but hastening decay. This contradicts unit-mass perspective suggesting finer coal has richer porosity, indicating that mass-averaging in traditional methods obscures the true impact of particle size on diffusion kinetics.

Source: Fuel Processing Technology

DOI: 10.1016/j.fuproc.2025.108355