Geologica Belgica

1374-8505 2034-1954

 

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Nikolai SIEMONS, Hans BRUINING & Bernhard M. KROOSS

UPSCALED DIFFUSION IN COAL PARTICLES

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Mots-clés : Coal, upscaling, homogenisation, diffusion, adsorption.

Abstract

We use homogenisation to derive two types of upscaled diffusion adsorption model equations for carbon dioxide in small coal particles. The coal particles are considered to be composed of aromatic crystallites embedded in amorphous coal. The type of model equations depends on the ratio between the effective diffusion coefficients in the crystallites Db and the amorphous background Da with respect to the ratio of the square of their respective radii �?�2. In one model it is assumed that D~Da and in the other that D~�?�2Da . Effectively, both models lead to a single characteristic time for the adsorption rate. We assert, however, that two characteristic times would have been observed if D~�?�3Da . The model equations are used for the interpretation of CO2 high-pressure adsorption experiments (<20 MPa) on a dry Pennsylvanian coal sample. The experiments determine the total excess sorption capacity for CO2 and the rate at which the adsorption equilibrium is attained. Our preliminary experiment indicates that the adsorption rate is determined by a single characteristic time. Comparison to the modelling results leads to an estimated diffusion coefficient of the order of 10-11 m2/s. Additional adsorption rate experiments are needed to confirm our preliminary results.

To cite this article

Nikolai SIEMONS, Hans BRUINING & Bernhard M. KROOSS, «UPSCALED DIFFUSION IN COAL PARTICLES», Geologica Belgica [En ligne], volume 7 (2004), number 3-4 - Proceedings of the 5th European Coal Conference, 129-136 URL : http://popups.ulg.ac.be/1374-8505/index.php?id=272.

About: Nikolai SIEMONS

Faculty of Civil Engineering & Applied Earth Sciences, Technical University of Delft, Mijnbouwstraat 120, 2628 RX Delft, Netherlands. E-mail: N.Siemons@citg.tudelft.nl

About: Hans BRUINING

Faculty of Civil Engineering & Applied Earth Sciences, Technical University of Delft, Mijnbouwstraat 120, 2628 RX Delft, Netherlands.

About: Bernhard M. KROOSS

Institute of Geology and Geochemistry of Petroleum and Coal, Rheinisch-Westfälische Technische Hochschule Aachen, Lochnerstrasse 4-20, 52056 Aachen, Germany