A contribution to the scale-up of fluidized bed driers and conversion from batchwise to continuous operation

Abstract

Fluidized bed driers are used in many large-scale processes. In process selection, an estimate of size and operating parameters on the basis of laboratory data is desirable, in order to obtain a cost estimate for the production plant as soon as possible. A model of fluidized bed drying has therefore been developed. This model allows for the influence of bubbles in fluid dynamics. Heat and mass transfer coefficients between particles and suspending gas are determined from a simple discontinuous laboratory experiment. The transport coefficients between suspending gas and bubbles can be calculated by means of correlations from the literature. This procedure is used for scaling up the discontinuous operation. In a further step, the behavior of continuously operating fluidized bed driers was modeled. The core piece of this modeling is the calculation of the distribution function which indicates, as a function of the moisture content, how the quantity of product is distributed in a continuously operated stirred vessel. As in scaling up, only easily determined laboratory data are required for the entire calculation of the continuous operating behavior. Starting from simple discontinuous laboratory experiments, a fairly accurate cost estimate for discontinuously and continuously operated fluidized bed drying processes can be made by means of the method described in this paper.