(98d) Investigation of Hydrodynamic Effects in Separation Columns Using X-Ray Computed Tomography

In the chemical industry packed columns are widely-used for different unit operations as for instance distillation, extraction or chromatography. To increase the separation efficiency of these processes it is necessary to determine relevant parameters like the packing structure or geometry and the wettability of the internals, without influencing the fluid flow through the measurement. Therefore we used a common medical X-ray computer tomograph as a non‑invasive measuring technique. With this device a flow through horizontal separation columns can be investigated.

Due to the fact that in nearly every technical application the fluid flow proceeds in vertical direction we put a customized computed tomograph into operation at our institute. In this computer tomograph the detector and X-ray source are rotating around the column during the measurement and they can be moved in vertical direction which enables scanning of vertical objects. As at our institute the column is not moved the fluid flow is not influenced by centrifugal forces and based on a high spatial (83 μm) and temporal resolution (1000 projections per second), dynamic processes inside separation columns can be analyzed with a high precision.

We have shown that X-ray computed tomography is a well suited method for the measurement of local parameters, like the porosity and axial dispersion coefficient in chromatographic columns without influencing the fluid flow. With this technique it is possible to observe the fluid flow along the column in axial and radial direction. In a further step the measured parameters are used to establish and validate a CFD‑model for the simulation of chromatographic separation processes and selection of a stationary phase for a specific separation problem.

Hence to the good applicability of computed tomography as measurement method we want to transfer this technique to three-phase rectification to determine the liquid distribution on column internals, the liquid hold-up and the entrainment of liquid droplets due to the gas flow.