Pressure drop of internals for packed columns

Because of their low pressure drop per equilibrium stage, random and particularly structured packings are frequently used in vacuum distillation. For applications requiring operation at absolute pressures below 100 mbar usually the total allowable pressure drop is specified. Demanding separations require frequent collection and redistribution of liquid. This means dealing with an additional source of pressure drop which is usually ignored, taking into account the pressure drop of the irrigated packed bed only. Unfortunately only scarce data on the pressure drop of liquid and vapour redistribution sections can be found in open literature. In this paper, the available pressure drop data for liquid collectors and distributors are evaluated. A simple first principles pressure drop model for liquid collectors and distributors is derived and validated by comparison with experimental data. Open area is the key variable in the design of low pressure drop internals, however all internals investigated exhibited certain liquid loading effect, which is accounted for by corresponding pressure drop enhancement factor. The pressure drop model presented offers a practical guideline for the evaluation of internals for packed columns.