(130d) Investigation and Analysis of Particle Drying in a Pilot Plant Scale Vibrated Fluidized Bed

Mechanical vibration is often applied in industrial scale fluidized bed dryers in food and pharmaceutical processes. However, the understanding of the underlying physical process is still insufficient regarding detailed modelling, apparatus design, up-scaling and process optimization.

Almost all of the experimental research in the field of vibrating fluidized beds is conducted with lab-scale apparatuses. Within the current project a pilot plant scale unit with a cross section of 250 x 500 mm² and a total height of 3 m was built. As a first step cohesive food powders and well-studied model substances (glass beads) were investigated regarding their fluidization behavior under varying process parameters.

The experimental equipment allows comprehensive parameter studies: frequency, amplitude and direction of vibration; air temperature, air velocity and air humidity as well as the bed masses during the experiment can be varied individually.

Temperature and humidity of drying air are measured online as well as the vibration parameters. Furthermore, the extensive measurement equipment inside the fluidized bed consists of temperature and pressure sensors as well as capacitance probes. Hence, a detailed investigation of the fluidization behavior of the product can be conducted. Additionally, visual observations can be made through one transparent wall of the apparatus.

In the next step, the drying kinetics of cohesive food powders was investigated. Parameter studies were conducted for different drying air conditions and vibration states. Heat and mass transfer as well as drying curves were calculated to evaluate the influence on drying kinetics.

The experimental results will be used to develop and validate a flow sheet simulation model for vibrating fluidized bed dryers.

Experimental results regarding fluidization characteristics in dependence of superficial gas velocity, product type, bed height, vibration and moisture content of the product are presented and discussed.