Mass transfer around freely moving active particles in the dense phase of a gas fluidized bed of inert particles

Mass Transfer in Fluidized Bed Drying of Moist Particulate

“…The above correlation was found to be independent of the fluidization velocity or regime change from bubbling to slugging. Accordingly, Scala (2007) concluded that in a dense bubbling bed the active particle only reside in the dense phase and never enters the bubble phase, hence it has no direct contribution to the bubble-dense phase interchanges. This contradicts the observation noted by Kunii and Levenspiel (1991) and others (e.g.…”

“…Recently, Scala (2007) experimentally studied the mass transfer around a freely active particle in a dense fluidized bed of inert particles. The results suggested that the mass transfer coefficient for a single particle is best correlated by a modified Foressling ( .…”

Mass Transfer around Active Particles in Fluidized Beds

“…4) the active particle density is explicitly present. In the experiments performed by Scala (2007) this variable was varied in a relatively limited range (1050 < ρ a < 1950 kg/m 3 ), and within this range it appeared not to influence significantly Sh. It is our opinion that if particle segregation is avoided, the active particle density has no importance on mass transfer, but this speculation needs further experimental confirmation.…”

“…In addition, if high CO concentrations are used the heat balance must be solved together with the mass balance (or the particle temperature must be measured during the experiments) as a consequence of the appreciable heat effects of combustion. Scala (2007) applied this technique to measure the mass transfer coefficient around freely moving active particles under bubbling/slugging fluidized bed conditions in a lab-scale reactor. In this work the mass transfer coefficient around one or few attrition-resistant Pt catalyst spheres immersed in an inert bed of sand was measured by following the CO oxidation reaction at 450°C at different fluidization velocities, catalyst sphere sizes and inert bed particle sizes.…”

“…The available empirical/theoretical correlations reported in the previous sections were checked for their accuracy in predicting the experimental mass transfer data of Scala (2007), which we consider to be the most complete and accurate reported in the literature to date. As a preliminary screening, all the correlations which predict a (direct or indirect) influence of the total fluidization velocity on Sh were discarded (Eqs 8-13, 17-19), as they are incompatible with the experimental data.…”