Impact of Process Conditions on Fluidized Bed Drying: Experiments and Model Predictions

Fluidized bed drying is an essential unit operation in the manufacturing of supported catalysts. Heated gas flows through a bed of wet catalyst supports which promotes fluidization, allowing for high rates of heat and mass transfer between the gas and solids. Although many studies have been conducted in fluidized bed dryers, general prediction equations for fluidized bed drying of catalysts are lacking, as drying depends on the fluidization conditions and support properties. Several phenomena, including heat and mass transfer, drying and fluidization, makes it difficult to choose the operating conditions to optimize the drying process. In general, one would like to have sufficient understanding of the process so that laboratory scale experiments can be used to predict behavior at the pilot and manufacturing scales.

Experiments were carried out in a Glatt GPCG-1 fluidized bed dryer. Water impregnated catalyst supports were used as the experimental material. The change in moisture content of the bed over time was measured along with the bed temperature and the rate of drying was calculated. Different bed loading, inlet air temperature, initial moisture content, and gas flowrate were tested. Using experimental reference drying curves, model equations for predicting the moisture content of the bed were implemented. For a large range of process conditions, we found that the model worked best when the drying rate was roughly constant, which correlates to the unhindered or constant rate drying period. However, the model was still able to make reasonably good predictions, even when drying started in the hindered or falling rate drying period. For high bed loadings, where the number of transfer units was large, the experiments and model showed the best agreement. This work provides quantitative findings on how process conditions affect the rate of drying for a bed of catalyst supports with corresponding prediction equations.