(292d) Application of X-Ray Computed Tomography for Flow Visualization in Packed Extraction Columns

Hydrodynamic parameters such as drop size distributions and dispersed phase holdup have been studied extensively with various optical measuring techniques. Non-invasive optical measuring techniques however are limited to non-opaque systems mostly at low disperse holdup. Industrial extraction columns however are often operated close to the flooding point at high disperse hold-up. Until now there is no optical measuring technique to evaluate flow conditions in random or structured packings used for extraction columns. Computed tomography allows non-invasive observations of fluid dynamics in such systems and is not limited to low disperse hold-up conditions. The measuring technique is established for investigations on hydrodynamics in opaque packed distillation columns.

In this work X-ray computed tomography as a non-invasive measuring technique is applied to investigations in packed extraction columns. The tomographic setup allows high spatial (80 µm) and temporal resolution (1 fps) tomographic measurements of the packed column. It has been designed for process technology applications and is mounted on a gantry system. Therefore the packed column is not exerted to any centrifugal forces during the measurement.

The technique allows for the determination of drop shapes, drop size distributions and local holdup measurements inside the packed section, which are hardly accessible with common optical measuring techniques such as particle video microscopy.

This work presents a suitable test-system for tomographic studies in packed extraction columns and methods for the investigation of bubble flow inside the packed section. The experiments are conducted in a glass column with internal diameter of 50 mm and packing length of 600 mm.

The local dispersed phase hold-up is measured non-invasively over packing height and at the intersection between two packing segments for varying liquid loads. The tomographic images enable qualitative measurements of the evolving drop-size distribution over the full packing height. An algorithm was developed for the qualitative processing of the tomographic images. It includes automatic image segmentation, bubble detection and bubble size measurements.

Beside quantitative measurements of drop size distributions and local holdup, we are able to qualitatively visualize drop deformation and breakage phenomena inside the channels of the structured packing. Multiple measurements at different packing heights reveal preferred bubble paths inside the structured packing.