Evaluation of the Classical Reaction Engineering models in terms of mass transport and reaction rate distribution for low tube-to-particle diameter ratio beds.

Allain, Florent

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Evaluation of the Classical Reaction Engineering models in terms of mass transport and reaction rate distribution for low tube-to-particle diameter ratio beds.

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Packed bed reactors are widely used in the chemicals industry and have been studied carefully in the last century. Several reaction engineering models have been developed in order to predict the behavior of such reactors under specified conditions, in order to assist in the sizing during an industrial process conception. These reactors can be categorized using different parameters, and the bed-to- particle diameter ratio - N - is one of them. It has been shown that this parameter influences greatly the transfer phenomena that occur in the bed, and that for ratios under 10, particular attention is needed when considering the wall effects. An impor- tant point that has to be evaluated is the accuracy of the actual chemical reaction engineering models when simulating such beds as it is valid to question the hypoth- esis of a pseudo-continuum model when considering a low bed-to-particle diameter ratio bed. Through high precision Computational Fluid Dynamics calculations, several beds of particles are modeled and studied in term of mass dispersion and reaction rate distribution. Two reaction engineering models - a simple pseudo-continuum model with effectiveness factor, and a model we refer to as Ã‚â€Single pelletÃ‚â€ model - and several correlations regarding Peclet numbers are then evaluated under the same conditions in order to determine their accuracy and reliability for that particular kind of bed. Two beds of N = 5.96 and N = 7.99 are studied for dispersion phenomena, and the bed of N = 5.96 is studied for reaction rate distribution. It is shown that the pseudo- continuum model of dispersion stands valid for the higher N, but that none of the correlations we used were able to correctly predict the behavior of the N = 5.96 bed at any of the Reynolds number we considered, only giving close behaviors. We were confronted with some difficulties regarding the reaction simulation under Fluent, but some comparisons were successfully made regarding species and reaction rate distribution in the bed.

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