Experimental investigation and modelling of continuous fluidized bed drying under steady-state and dynamic conditions

Abstract

In a lab-scale device, continuous fluidized bed drying has been investigated experimentally under both steady-state and dynamic conditions. The mixing behaviour and residence time distribution of particles in the dryer have been shown to be that of a continuous stirred tank reactor. Particle mass flow rate and inlet moisture content, gas mass flow rate, air heater capacity and gas inlet temperature have been varied systematically. The average moisture content of outlet solids has been determined by means of microwave absorption. In the course of the work, close reference to a previous investigation of batch fluidized bed drying has been kept by using an adapted version of the same equipment and the same material (water-moist γ-Al 2O 3 with an average particle diameter of 1.8 mm ). Furthermore, the model previously developed and successfully validated for batch operation has been the starting point of the actual theoretical analysis. This model has been extended in order to account for continuous and dynamic conditions. Additionally, population balances have been introduced. In spite of the fact that no other adaptations have been undertaken, and though the extended model does not contain adjustable parameters, a very satisfactory agreement between calculated and measured results could be achieved. In this way, it could be demonstrated that it is possible to treat all different modi of fluidized bed drying (batch, steady continuous, dynamic continuous) in a unified, successful and applicable manner. Two aspects are considered essential for the good final performance: The use of separately determined, product-specific single-particle drying kinetics as a basis for every scale-up duty, and a stepwise methodology of model development with detailed experimental validation of every individual step.