Effects of particle mixing on characteristics of gas desorption and non-constant dynamic diffusion in coal

ABSTRACT

Gas drainage technology is closely related to the flow of methane in coal. Desorption and diffusion of gas in coal is an important basic research area, and particle size is one of the influencing factors. In this study, the desorption and diffusion characteristics of coal samples mixed with different particle sizes over time were measured under constant temperature and pressure. The results show that in the initial stage, the desorption volume and desorption rate of coal samples are relatively large. The improved desorption model can well fit the data and the order of desorption volume is negatively correlated to the mean particle size of coal samples. The single small particle coal sample has the largest desorption volume which reached 3.77ml/g. Both the unipore model and the constructed unsteady dynamic diffusion model can well describe the diffusion of gas in coal, the diffusion coefficient of coal sample decreases with time, and the decay rate decreases gradually with time until it remains unchanged. The calculation results of the two models show that the diffusion coefficient ranges of gas in coal between 10⁻¹⁰m²/s and 10⁻¹²m²/s. For single-particle coal samples, the diffusion coefficient is positively correlated with particle size. The diffusion coefficient D is affected by the particle size and the degree of compaction between coal particles. These observations indicate that coal samples with different particle sizes will affect the desorption and diffusion of gas, and it has a positive impact on methane recovery.

KEYWORDS:

• Mixing of different particle sizes
• gas desorption
• unipore model
• non-constant dynamic diffusion
• diffusion coefficient

Conflict of interest

The authors declare that there are no conflicts of interest.

Additional information

Funding

This work was supported by the National Natural Science Foundation of China (No. 51274206, 51404277).