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  • Author or Editor: Aleksandra Marecka x
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Abstract  

The present paper contains theoretical analysis and a thorough discussion of the applicability of Fick’s approach to modelling CO2 and CH4 diffusion in heterogeneous coal, especially with regard to the estimation of a single diffusion coefficient from the dependence defined by a number series. The computations were performed for high rank coal depending on the grain size of coal samples and within a narrow range of temperature − 293 and 303 K. The results of the model’s application to the experimental data show that the method of estimation of the diffusion coefficient is very important. Our results also show that the diffusion coefficient changes are closely related with the one-parameter analysis of coal grain size distribution. It was shown that for the investigated grain size distribution the diffusion coefficient as expressed by Fick’s law may only be determined as a value which is directly proportional to the diffusion parameter. Hence, the estimation of D/r 2 is recommended.

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Abstract  

Using the earlier theoretical achievements, it was possible to elaborate a full description of adequate transport properties, including the determination of activation energy for the sorption of such gases as CO2 and CH4 on coal, as well as the formulation of model solutions. The interrelation of the kinetic-diffusion parameters was also demonstrated. We then analyse the experimental kinetic curve over the entire time range with a constant of a kinetic character and with the application of two typical solutions of Fick’s law, for fast and slow processes. These three constants may be compared with one another, since they are expressed using the same unit, and, in effect, may be used to determine the isokinetic effect. Finally, we suggest a new approach to the estimation of the activation energy, despite the fact that the measurements were performed at two close temperatures, 293 and 303 K. In the presented investigations, the isokinetic effect for sorption process has been found to be statistically less significant when compared with that of chemical reactions/processes.

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