Fluidized bed catalytic reactor modeling across the flow regimes

Fluidized bed reactor models are generally specific to a single flow regime resulting in ambiguities and discontinuities at the regime boundaries. In practice, only the bubbling, turbulent and fast fluidization regimes are of industrial significance for catalytic reactions. The turbulent fluidization regime is especially advantageous because of improved interphase mass transfer, resulting in improved selectivities and conversions. It is shown that some of the difficulties in modeling can be resolved by means of the probabilistic-averaging model, recently published by Thompson et al. (1999). This model interpolates between the Grace (1984) two-phase bubbling bed model at low velocities and single phase axially dispersed flow for fully established turbulent fluidization conditions, leading to improved predictions of conversion and selectivity for catalytic fluidized bed reactors operated at flow rates covering the full range between bubbling and fully turbulent fluidization. An analogous approach should be useful for beds operated at higher gas velocities as fast fluidization conditions are approached. Les modevles de reacteur a lit fluidise sont generalement specifiques a un regime d'ecoulement, resultant en ambiguites et en discontinuites aux limites des regimes. En pratique, seules les regimes bouillonnants, turbulents et fluidisation rapide ont une importance industrielle pour les reactions catalytiques. Le regime de fluidisation turbulent est particulierement avantageux en raison du transfert de matiere interphasique ameliore, d— a de meilleures selectivites et conversions. On montre que certaines des difficultes de modelisation peuvent etre resolues au moyen du modele de moyennes proba-biliste, recemment publie par Thompson et al. (1999). Ce modele fait l'interpolation entre le modele a lit bouillonnant biphasique de Grace (1984) a de faibles vitesses et l'ecoulement disperse axialement a phase unique pour des conditions de fluidisation turbulentes pleinement etablies, ce qui permet de meilleures predictions de conversion et de selectivite pour des reacteurs a lits fluidises catalytiques fonctionnant a des debits couvrant la gamme complete entre la fluidisation bouillonnante et la fluidisation pleinement turbulente. Une approche analogue devrait etre utile pour des lits fonctionnant a des vitesses de gaz elevees lorsqu'on s'approche des conditions de fluidisation rapide.