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Bidisperse pore-diffusion model seeking to linearise the extended Langmuir equation in a piece-wise manner in the temporal dimension

The pore structure of coal matrix is highly heterogeneous, with the pore size varying from a few Angstroms to frequently over a micrometer in size. Many coal exhibit a bidisperse pore structure, with significant fractions of the total pore volume being found in size greater than 30nm and less than 1.2nm. Gas diffusion in micropores (<2nm) is controlled by a distinctively different mechanism from those identified in macropores (molecular diffusion, Knudsen diffusion and surface diffusion).

A bidisperse pore-diffusion model that accounts for competitive gas adsorption/desorption is developed. A solution procedure that is more suitable for coal due to its low micropore diffusivity is proposed. This procedure seeks to linearise the extended Langmuir equation in a piece-wise manner in the temporal dimension. It dose not directly enforce the parabolic concentration profile within a particle. In other words, the parabolic concentration profile assumption is used to evaluate the concentration gradient at the particle surface only and no explicit assumption is made regarding to the concentration profile within the particle.

When applied to a laboratory core flush test, an excellent match to the test data was achieved using sorbate concentration dependent apparent micropore diffusivity.

Reported by

Imperial College London
Department of Environmental Science and Technology, South Kensington Campus
SW7 2AZ London
United Kingdom
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