Assessment of column tray flow patterns and separation efficiencies on large-scale distillation trays

Thorough characterization of mixing behavior and separation efficiencies of large-scale distillation trays is important especially in their design phase. A precise account of the tray operation would allow modifying their mixing and mass-transfer characteristics (via design modifications) for better separation efficiencies (see design strategy in Fig. 1, left).
Fig. 1. Design strategy for distillation trays (left), and relevant data on the distributions of liquid holdup, residence time, RTD variance, and species concentration (right).
The existing literature lacks a thorough hydrodynamic description of large-scale distillation trays. Thus, the CFD studies have relied either on trivial measurements (such as those of pressure drop, liquid weeping and entrainment, visual froth height, etc.) or the available low-resolution residence time data for model validation rather than on refined data on flow path and local mixing.
Meanwhile, an extensive description of the tray hydrodynamics can be made available using the recently proposed flow profiler.1 Based on recent developments in that regard, the distributions of liquid holdup, residence time and mixing are obtained over the entire deck (see Fig. 1, right) for several gas and liquid loadings at high resolution.
The acquired data permits to predict the tray efficiency by applying models that relate liquid flow patterns with the tray performance, such as the recently proposed ‘Refined RTD (RRTD) model’ that considers the mixing behavior at intermediary tray locations.2
Eventually, experimental data on air stripping of isobutyl acetate from the aqueous solution at tray loadings same as those during the hydrodynamic experiments can be applied to validate the proposed efficiency model. An example of species concentration distribution (i.e., examined using UV spectroscopy) over the tray deck is also shown in Fig. 1 (right).

[1] Vishwakarma, V., Schleicher, E., Schubert, M., Tschofen, M. and Löschau, M., 2020. Sensor zur Vermessung von Strömungsprofilen in großen Kolonnen und Apparaten. Deutsches Patent und Markenamt, DE 10 2018 124 501.
[2] Vishwakarma, V., Schubert, M. and Hampel, U., 2019. Development of a refined RTD-based efficiency prediction model for cross-flow trays. Ind. Eng. Chem. Res., 58(8), pp.3258-3268.