Drying of Cohesive Powders in a Pilot Plant Scale Vibrated Fluidized Bed

Hindrance of fluidization of fine particles in form of agglomeration, channeling or complete de-fluidization is caused by cohesive forces. Mechanical vibration may be applied to fluidized bed equipment in processing of fine or sticky powders to improve or enable fluidization by counter acting cohesive effects. Vibrated fluidized beds are widely applied in industrial scale in the pharmaceutical and food industries.

However, almost all research in the field of vibrating fluidized beds is conducted with lab-scale apparatuses. Within the current project a pilot scale unit with a cross section of 250 x 500 mm² and a total height of 3 m was built. The experimental equipment allows comprehensive parameter studies of hydrodynamics and drying kinetics.

The drying kinetics of cohesive powders has been investigated via parameter studies with regard to different drying air conditions and vibration states. Temperature and humidity of drying air at inlet and outlet were measured online as well as the vibration parameters. Furthermore, powder samples were taken during operation for further analysis. Additionally, visual observations can be made through one transparent wall of the apparatus.

Heat and mass transfer as well as drying curves were calculated to evaluate the influence of vibration on drying kinetics. Based on the experimental results a flow sheet simulation model for vibrated fluidized bed dryers was developed and validated.