(320d) Computational Fluid Dynamics Simulations of Adsorption Columns Based on Computed Tomography Experiments

It is well known that the efficiency of adsorption columns with extremely high aspect ratios of column to particle diameter (e.g. chromatographic columns) is strongly determined by the homogeneity of the packed bed. For the reason that the separation takes place inside closed columns, the measurement of local system parameters related to the column efficiency cannot be achieved easily without the deterioration of the flow field. On the other hand, x-ray computed tomography (CT) as a non invasive measurement technique renders the measurement of local packing properties possible. In our study, axial compression columns made of glass which is opaque for x-rays were investigated with a CT-Scanner at several monitoring positions while Potassium Iodide (KI) solutions in Methanol were conveyed through the column. The high x-ray attenuation of KI allowed to determine spatially resolved ?intra-column breakthrough curves?. The experimental findings suggested that the column packing is heterogeneous in the radial direction. The packing can be divided into a homogeneous core region where porosity and efficiency vary only slightly and into a wall region with decreasing porosity and efficiency, respectively. By deducing local packing properties like e.g. the permeability from the monitored data it was possible to develop column models by the use of the commercial computational fluid dynamics code StarCD. For this purpose the original features of the code had to be extended via user coding to allow the consideration of adsorption. The simulations were performed assuming a rotational symmetry (2D-Model) of the flow field in order to keep the computational effort reasonable. The breakthrough curves calculated with the CFD-Models matched the experimental results better than commonly used one dimensional models.