From Single Particle to Fluid Bed Drying Kinetics

The concept of a normalized single particle drying curve has been integrated into a generic, heterogeneous fluid bed model in order to describe batch fluid bed drying. Drying curves have been measured for both single particles and fluid beds. Two different coarse-grained materials, aluminum silicate and a technical product, have been used. In general, fluid bed drying curves appear to be predictible on the basis of single particle data and with the help of the model. Dificulties may arise mainly with particles of low sphericity and a large initial moisture content. Model parameters are in the range indicated by general fluidization literature. However, Sherwood numbers for particle-to-fluid mass transfer in the- fluid bed are significantly lower than the values for single particles. This can hardly be attributed to bubbling and bypassing, since these effects have been explicitly accounted for in the model.