Evaluation of Hydrodynamic Behavior of a Fluidized Bed Dryer by Analysis of Pressure Fluctuation

During drying, hydrodynamics of fluidized beds can vary due to moisture evaporation. It is of practical importance to quantify the fluidized bed hydrodynamics by analysis of pressure fluctuations, especially when drying cohesive materials. In this study, spent liquor from a fermentation process for the production of yeast was mixed with corn bran at different mass ratios, and used as the fluidizing material of various stickiness levels. Local bed pressure fluctuations and the dryer exhaust air temperature as well as relative humidity were monitored over the course of drying. The pressure fluctuation data were analyzed using statistical methods. The bed hydrodynamic behavior was interpreted in terms of the time-averaged bed-pressure drop and its standard deviation. The transition from channeling to uniform fluidization occurs when both the average pressure drop and the standard deviation vary little with time. Also, the average values of the bed-pressure drop within short periods in reference to the ideal bed-pressure drop (the weight of the bed per unit cross-sectional area) is considered a potentially useful criterion to evaluate fluidization quality. Parametric studies show that fluidized bed behavior during the drying process can be improved by adjusting the operating conditions.