Drying of baker's yeast in batch fluidized bed

A drying model was developed for production scale fluid bed drying of granular baker's yeast. In the model, heat capacity of the dryer and the product entrained through cyclone and heat transfer from the dryer to environment were also taken into account to improve the predictive capacity of the model. Kinetic model based on the assumption that the resistances to mass transfer during drying lie not inside but liquid film around the granules was integrated into material and energy balances. Drying rate constant was determined from experimental results at constant air inlet flow rate and temperature but at varying dryer loadings. Its magnitude was found as function of amount of product loaded into the dryer. Simulations were performed for two different granule sizes and good correspondence was found between model predictions and experimental measurements for small granule sizes. For larger granules, deviations between simulations and measurements were observed and this was attributed to diffusive transport limitation of moisture inside granules, which requires mathematical description of spatial distribution of moisture and temperature inside the particles. The model can be used for design, optimization and control of drying processes for various applications.