TRAJECTORY LENGTH AND RESIDENCE-TIME DISTRIBUTIONS OF THE SOLIDS IN 3-PHASE FLUIDIZED-BEDS

The novel concept of trajectory length distribution (TLD), recently in troduced by Villermaux (1996, Chem. Engng Sci. 51, 1939) for character izing the macromixing of fluid elements in flow systems, is used to de scribe solids mixing in the fully developed zone (FDZ) of three-phase fluidized beds. Tests with monodispersed and binary mixtures of solids of different sizes and densities were performed in the dispersed and the coalesced bubble flow regimes. The Lagrangian trajectories of sing le traced particle were measured non-invasively via radioactive partic le tracking (RPT). A macromixing index was derived from the experiment al TLDs for describing solids mixing in both upward and downward secti ons of the FDZ. Residence-time distributions (RTDs) of the solid parti cles, moving upwards in the column core section and downwards in the s idewall section of the FDZ, were generated from the RPT-measured traje ctories. Based on the observed physical features of the solids flow, t hese RTDs were modeled using a two-zone one-dimensional cross-flow mul tistage stirred reactors (CFMSR) model. Part of the CFMSR input parame ters were obtained taking advantage of the exhaustive three-dimensiona l trajectories measured from RPT. The model is shown to compare well w ith the experimental RTDs in both ascending and descending sections. ( C) 1997 Elsevier Science Ltd.