Effect of flow non-idealities on tray efficiency

Cross-flow trays are highly reputed among vapour-liquid contacting devices in distillation columns. Their ability to perform in various operating conditions, low fouling sensitivity, low cost and access for inspections make them potential nominee for column internals. Tray separation efficiency as well as overall performance of the column is strongly dictated by evolving flow patterns on the tray. Liquid plug flow is considered ‘ideal’ at which the maximum tray efficiency can be expected. On the other hand, liquid channelling, bypassing, retrograde flow and stagnant zones are known to be detrimental to tray efficiency. Schubert et. al. (2016) established the wire-mesh sensor as a novel technique to extract liquid flow patterns on trays and presented the effect of variable liquid load and weir design on the flow patterns.
As a follow up, the most common mathematical models, which were recently revisited by Vishwakarma et al. (2016), are applied to associate flow and mixing patterns with tray efficiency. They indicate serious loss in efficiency for the tray with largest stagnant regions. The location of dead zones is also important as most of the mass transfer on large trays happens in their first half. Any stagnant liquid in these areas is highly disadvantageous for the tray to fractionate as per expectations. This contribution will stimulate to develop a new practicable model that can account for the effect of location and type of non-ideality on the tray efficiency.

(1) M. Schubert, M. Piechotta, M. Beyer, E. Schleicher, U. Hampel and J. Paschold, ‘An imaging technique for characterization of fluid flow pattern on industrial-scale column sieve trays’, Chemical Engineering Research and Design, vol. 111, pp.138–146, 2016.
(2) V. Vishwakarma, M. Schubert and U. Hampel, ‘Distillation tray efficiency modelling: a forgotten chapter’, Jahrestreffen der ProcessNet-Fachgruppe Fluidverfahrenstechnik, 16-17 March 2016, Garmisch-Partenkirchen.