A column is used in process engineering for mass transfer and energy/heat transfer between gases, vapours and liquids flowing in the opposite direction. The gases, vapours and liquids come into direct contact with each other. Columns are usually vertical cylinders where the length is a multiple of the diameter.

For mass transfer and heat transfer, columns are fitted inside with structured packings or trays and often with demisters/swirl droplet separators for better gas-liquid separation. Columns are used in process engineering for gas scrubbing, gas cooling/quenching, heat recovery, absorption, adsorption, extraction, rectification/distillation and crystallisation.

Columns used as gas scrubbers are often fitted as a second stage downstream of a jet scrubber to increase absorption and gas cooling/quenching of the process as a whole. Columns used for absorption and gas cooling/quenching virtually always have a pressure loss on the gas side that shouldn’t be underestimated, but which an upstream jet scrubber can easily compensate for.