Influence of horizontal tube banks on the behavior of bubbling fluidized beds 2. Mixing of solids

Video image analysis techniques were used to investigate the solids mixing behavior in a two-dimensional (thin) fluidized bed containing "simulated" h orizontal tube banks. Colored glass beads were used as the tracer, and the image intensity was used to deduce the variation of axial concentration pro files with time. A three-phase counter-current back-mixing model was develo ped for data interpretation. The model accounted for the axial variations i n bubble properties and in flow (of gas and solids) in the presence of tube s. These variations induce cross-flow of material between phases (for volum e conservation). Mathematical form for the cross-flow term for inclusion in the conservation equations was deduced. The model equations were solved us ing finite difference techniques; bubble parameters for use in the model ha ve been described in a previous paper, part 1 in this series. Calculations compare favorably with experimental data. The results also show that both t ube position and tracer feed location have significant effects on the mixin g time. Tubes located in the top and the bottom of the bed lead to smaller mixing times; tracer fed in the middle of the bed provides the fastest mixi ng rate. (C) 2000 Elsevier Science S.A. All rights reserved.