When one packed tower handles multiple process campaigns, each duty should be evaluated separately. The controlling case for material compatibility, gas capacity, liquid turndown, mass transfer, demister loading, and cleaning may be different. Packing should be selected for the full defined operating envelope rather than a single average condition.

Low-surface-tension liquids can change packing wetting, liquid holdup, foaming behavior, pressure drop, and flooding characteristics. Standard air-water performance data remain useful references, but actual liquid density, viscosity, surface tension, foaming tendency, and packing material should be considered for unusual process systems.

When inlet gas already contains liquid droplets, the packed bed may experience additional and uneven liquid loading, higher pressure drop, fouling, and reduced flooding margin. Droplet quantity, size, composition, inlet gas distribution, and the need for upstream separation should be reviewed before finalizing the tower design.

Intermittently operated packed towers can develop dry-out, crystallization, poor restart wetting, stagnant corrosion, thermal cycling, and drainage problems that are not obvious from steady-state design data. Shutdown and restart conditions should therefore be included in packing and internal-system design.

Tower-packing material selection should include CIP and cleaning conditions as well as normal process chemistry. Strong acids, alkalis, oxidizers, solvents, hot water, or steam may create more severe material exposure than normal operation and can affect packing, distributors, supports, demisters, fasteners, and gaskets.