Continuous Fluidized Bed Drying With and Without Internals: Kinetic Model

C. Srinivasakannan, A. Al Shoaibi and N. Balasubramanian

Abstract
Spirals as internals are utilized to reduce the axial mixing of solids in fluidized beds, by routing the solids flow in a predetermined route or by localizing the solids mixing. The drying kinetics of continuous fluidized bed with and without internals has been compared and modeled using batch drying kinetics and residence time distribution analysis. The batch drying experiments were conducted to establish the drying kinetics of ragi mimicking the conditions in the continuous fluidized bed. The batch drying kinetic data was modeled using a number of semi empirical models to identify the appropriate model and establish the kinetic parameters. Among the models tested, the Page model was found to match the experimental data, with minimum error. The kinetic parameter (k) was found to increase with temperature. The activation energy (E) was estimated to be 30.5kJ mol–1, while the Arrhenius constant was 0.03 s–1. The drying rate in the continuous bed was found to increase with increase in temperature of the heating medium and height of the downcomer. The rate of drying in a continuous fluidized bed is lower than the rate of drying in batch fluidized bed, while the drying rate in a continuous fluidized bed with internals approximates drying rate in batch fluidized bed.

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Keywords
fluidized bed, drying kinetics, spiral internals, food grain drying