Why Low-Surface-Tension Liquids Can Behave Differently from Water in a Packed Tower

Many packing comparisons and hydraulic checks are based on data obtained using air and water.

Industrial process liquids may behave very differently.

One important property is surface tension.

Liquids containing:

• solvents;
• surfactants;
• organic compounds;

may have much lower surface tension than water.

This can change both wetting and hydraulic behavior.

Surface Tension Affects Wetting

A liquid with lower surface tension may spread more easily across certain surfaces.

This can improve apparent wetting.

However, the relationship between wetting and overall tower performance is not always simple.

Other properties still matter, including:

• viscosity;
• density;
• chemistry.

Foaming Tendency May Change

Some low-surface-tension systems also have strong foaming behavior.

Foam can occupy void space inside packing and significantly increase apparent liquid holdup.

The tower can then show unexpectedly high pressure drop even when normal water-based hydraulic expectations suggest adequate capacity.

Published Capacity Data Has Limits

Manufacturer data are valuable for comparing packings.

But a hydraulic curve measured with air and water is not a guarantee that a different liquid will behave identically.

Process-property corrections or additional engineering evaluation may be required.

Surface Chemistry of the Packing Matters

A liquid does not wet every material equally.

The same process liquid may behave differently on:

• metal;
• ceramic;
• plastic.

Therefore, material selection can influence not only corrosion resistance but also wetting behavior.

Very Easy Wetting Does Not Eliminate Distribution Requirements

Even a highly wetting liquid still requires suitable initial distribution.

A good material cannot compensate for a distributor that sends most liquid to only part of the tower.

Foaming Can Be Mistaken for Conventional Flooding

Operators may observe:

• pressure-drop increase;
• liquid backup;
• carryover.

The first conclusion may be that packing is too small.

But if the process liquid foams strongly, changing packing alone may not solve the problem.

Process chemistry should be investigated.

Anti-Foam Addition Can Change the System Again

If antifoam is used, it may alter:

• surface behavior;
• mass transfer;
• downstream contamination.

It should therefore be treated as a process change rather than an invisible operating aid.

Laboratory Testing Can Be Valuable

For unusual liquids, small-scale testing may help reveal:

• wetting;
• foaming;
• drainage behavior.

The results should still be interpreted carefully when scaling to the industrial tower.

Ask for Real Liquid Properties

Important data may include:

• density;
• viscosity;
• surface tension;
• foaming tendency;
• solids content.

Using water properties for every scrubber liquid can produce misleading conclusions.

Final Engineering Principle

Packing hydraulics are controlled by the actual gas-liquid system, not the name of the packing alone.

Low-surface-tension and foaming liquids may require different interpretation from standard air-water data.