Understanding gas transport mechanisms within the coal matrix is crucial for optimizing coalbed methane extraction and preventing gas-related accidents. However, current academic research often ignores the release characteristics and transport behaviors of gas stored within rocks. This study first determined the adsorption constants of coal and rock particles for different gases and conducted isothermal desorption experiments for both carbon dioxide and methane under constant-volume conditions. Based on the free gas density gradient diffusion theory, a mathematical model for gas transport was developed and solved numerically using the finite difference method. Furthermore, a novel method integrating dimensionless analysis criteria with an empirical desorption formula was proposed to determine the micropore diffusion coefficient. The results demonstrate that (1) for both rock and coal particles, and for both carbon dioxide and methane desorption, the simulation curves based on the density gradient diffusion model show fundamental consistency with the experimental data, verifying the model's correctness; (2) within the same coal/rock particle, the micropore diffusion coefficient of carbon dioxide is greater than that of methane. For anthracite under 2 MPa, the methane diffusion coefficient is 6.3 × 10−8 cm2/s, while the carbon dioxide diffusion coefficient is 4.9 × 10−7 cm2/s. For the same gas, the micropore diffusion coefficient is greater in coal particles than in rock particles; (3) although the total gas content stored in the rock matrix is less compared to coal particles, it is not negligible. Subsequent research should pay greater attention to the storage and transport behaviors of gas within rocks.

Conventional standard oxygen-consumption-rate models can retain an apparent dependence on reactor height and gas flow rate when outlet oxygen concentrations become low. To examine this issue, programmed-temperature oxidation experiments were conducted using gas-fat coal from the Zhuxianzhuang Coal Mine. Two packed coal-bed configurations were used: a full bed (coal-bed height, 20 cm; packed-coal volume, 250 cm³) and a half bed (coal-bed height, 10 cm; packed-coal volume, 125 cm³); both were operated at inlet flow rates of 80, 100, and 120 mL min⁻¹. Outlet O₂, CO, and CO₂ samples were collected near the end of each isothermal hold and analysed by gas chromatography. An empirical effective oxygen-concentration correction parameter was introduced to revise the conventional standard oxygen-consumption-rate model, and corresponding standard CO and CO₂ generation-rate and calculated heat-release-intensity models were derived. The outlet oxygen concentration exhibited four apparent stages with increasing temperature: slow decrease, rapid decrease, renewed slow decrease, and stabilization. Above approximately 195 °C, the outlet oxygen concentration approached a nonzero plateau. On the basis of this plateau and the consistency of results obtained under the tested conditions, a value of 1.21 vol.% was selected as an empirical correction parameter for the present system. The conventional model produced increasingly separated oxygen-consumption-rate curves at high temperatures and yielded R² = 0.930. After introducing the correction parameter, the curves obtained under the tested conditions showed improved convergence and R² increased to 0.993. The revised standard CO and CO₂ generation rates and calculated heat-release intensities likewise showed reduced dependence on reactor height and flow rate within the present dataset and increased exponentially with temperature. These empirical correlations describe the tested coal under the specified reactor and heating conditions. Independent validation is required before extending them to other coals or operating conditions.