Analysis of Flow Patterns in Structured Zickzack-Packings for Rotating Packed Beds using Gamma-Ray Computed Tomography

Rotating Packed Beds (RPBs) are increasingly used in academia and industry for separation processes, but a lack of knowledge about fluid dynamics and liquid maldistribution still limits understanding the mass transfer inside. Recently, structured Zickzack packings (ZZ packings) were designed that promise to provide homogeneous liquid distribution throughout the packing volume. In this study, the fluid dynamics of a water-air system in ZZ packings were characterized at atmospheric pressure and 20°C. For decreasing rotational speeds, a strongly increasing wet pressure drop was observed below 500 rpm due to a formation of a liquid wreath in front of the inner packing edge, and flooding of the rotor eye was visually detected at rotational speeds lower than 300 rpm. At rotational speeds greater than the flooding limit, the fluid dynamics of a single ZZ packing were found to be equal to a stacked two-level ZZ packing. In addition, gamma-ray computed tomography (CT) was used to non-invasively study the liquid distribution inside the rotating packing at multiple scanning planes along the packing height for selected operating conditions. The scans revealed that liquid maldistribution occurred at rotational speeds lower than 1200 rpm, while the liquid was perfectly distributed throughout the packing volume at rotational speeds greater than 1200 rpm.