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Diffusion models for gas production from coal: Determination of diffusion parameters

✍ Scribed by Douglas M. Smith; Frank L. Williams

Publisher
Elsevier Science
Year
1984
Tongue
English
Weight
672 KB
Volume
63
Category
Article
ISSN
0016-2361

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✦ Synopsis

A method for the laboratory measurement of transient diff usivity parameters for methane in coal has been developed. Previously described chromatographic techniques for measurement of single diffusivity parameters have been modified for the bi-disperse pore diffusion model. This model, which is necessary to describe methane diffusion and desorption in coal for both short and long times, requires the determination of three parameters to characterize a particular coal sample. The experimental technique uses a pulse of methane gas which is introduced into a helium stream flowing through a long tube containing the coal sample. The three desired parameters are determined by matching the experimental and theoretical elution curves. Further refinement of the technique accounts for tracer pulse duration thus allowing operation over a greater flow rate and sample size range. This technique has been applied to anthracite, bituminous and subbituminous coals. For all three coal types, the macropore diffusivity (z 1 Oe5 s) was about two orders of magnitude higher than the micropore diffusivity. The anthracite adsorbs more methane in the micropores than the other coals. These results showed the expected trends taking the known change of pore structure with rank into account.

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