Investigation of fluidized bed drying

Throughout history, there has always been a significant need for food. This need has played an important role in terms of the processes for preserving food for a long time and drying food is one of those processes. In the early days, mainly natural resources were utilized to dry food, however along with the advancements in technology; various systems have been developed to serve the same purpose. In the process of drying food, the temperature as well as the rate of drying may vary according to the type of material. During the process, depending on the type of material, temperatures exceeding a particular value can not be applied. The temperature is desired to remain under a certain critical value. For this reason, the duration of the drying process varies depending on the drying rate rather than the temperature itself. Therefore, to shorten the duration of the drying process significantly, drying air should completely penetrate into the material. However, the energy supplied to heat the air in the system during the drying process is one of the main problems. Due to energy saving policies, the utilization of fluidized beds gained a great importance in food drying processes recently. Fluidized bed systems are used in a wide range of activities such as fuel burning systems, nuclear research, medical systems and food drying systems. Especially, use of fluidized beds has increased to a large extent recently. Fluidized bed drying systems from general research are adapted to large systems after extrapolation. The main problem encountered during the research is the simulation of the pressure drop that emerges due to fluidization. In fluidized bed systems, the highest pressure drop takes place within the bed. To estimate this pressure drop in the fluidized bed, the minimum fluidization velocity should be calculated. There are various correlations for the minimum fluidization velocity in literature and these are empirical statements achieved through experiments. The pressure drop can be calculated after the minimum fluidization velocity is determined. In this study, separate calculations with correlations in literature for the minimum fluidization velocity are carried out and subsequently the fluidization process is examined in a fluidized bed for materials with known physical properties. The minimum fluidization velocity values calculated for these materials are compared with the values calculated based on mathematical correlations, to predict real minimum fluidization values. The necessary equipment and their characteristics for a fluidized bed drying system are explained in detail. Keywords: Fluidized Bed Drying, Ergun Equation, Minimum Fluidization Velocity