CFD analysis of air distribution in fluidised bed equipment

Abstract

The unique features of the fluidised bed—excellent mixing capacity and high heat and mass transfer rates—are highly dependent on the quality of fluidisation resulting from the bubble characteristics of the fluidising gas, which to a large extent depend on the distributor design. In order to understand the fluidisation hydrodynamics of a fluidised bed operation, it is essential to assess how airflow is distributed through the equipment. This paper reports on the use of Computational Fluid Dynamics (CFD) as a numerical tool to enlarge this understanding. CFD simulations were performed for a Glatt GPCG-1 fluidised bed coater in which stainless steel woven wire mesh distributors are used as the standard distributor plates. Firstly, an experiment was set up in which the permeability and the inertial resistance of the investigated distributors were determined. Using these inputs, two types of boundary conditions, available in the CFD software Fluent, to model a porous medium such as a distributor, were compared. Furthermore, the CFD simulations were verified in the lab-scale fluidised bed unit using air mass flow rate, pressure drop and inner wall temperature recordings. As an unequal airflow inside the plenum of the GPCG-1 was found to occur, CFD was used as a design tool to investigate reactor configuration changes in order to obtain a more homogeneous airflow towards the distributor.