(62b) Droplet Entrainment and Separation in Distillation and Absorption Columns

Both Gas-Carry-Under and Liquid-Carry-Over negatively affect the performance of columns with counter current gas and liquid flow. Especially liquid entrainment in the form of fine droplets often leads to a reduction in stage efficiency, product purity and to hydraulic instabilities such as tray blowing or unsealed downcomers. Insufficient vapor-liquid separation at the column head can result in expensive solvent loss (e.g. methanol or amine) for absorption or wash columns and may even cause damage to downstream equipment, such as adsorbers or compressors. The consequences of insufficient vapor-liquid separation are undesirable both from an economic and ecological point of view. Hence, an optimized column does not only consist of well-designed mass-transfer sections but also requires properly selected and sized phase separation areas and internals.

This presentation covers the basics of vapor-liquid separation in columns such as the Souders-Brown-Equation [1], internals selection, and droplet separation at low surface tensions as encountered in natural gas plants at high pressures [2] or other cryogenic processes. Similarities between capacity limits of wire mesh mist eliminators and tower packings will be discussed. Lastly, some examples from the extensive Linde Engineering plant portfolio will be presented.

References:
[1] M. Souders, G. G. Brown, Ind. Eng. Chem. 1934, 2, 98-103
[2] F. Flegiel, C. Windmeier, M. Wiezorek, A. Döß, M. Schubert, U. Hampel, E. Schleicher, Chemie Ingenieur Technik 2021, 93: 1166-1177