Engineering Evaluation Case: Oil Mist from a Steel Pickling Line Coats HCl Scrubber Packing and Reduces Water Wetting

Pickling-line scrubbers are normally designed around:

• HCl gas;
• acid droplets;
• corrosion resistance.

Steel strip and upstream equipment can also introduce oil mist.

That creates a very different type of packing contamination.

Instead of blocking the packing immediately, oil can form a hydrophobic film that prevents the aqueous scrubbing liquid from spreading normally.

Project Situation

Consider an HCl scrubber serving a steel pickling line.

The packing remains:

• structurally intact;
• largely free of hard scale.

Yet removal efficiency gradually declines.

Inspection finds an oily film on the packing surface.

Wetting Is Essential to Mass Transfer

Plastic packing may be chemically resistant to HCl.

Its effective area still depends on water or scrubbing solution spreading over the surface.

Oil contamination can cause the liquid to:

• bead;
• channel;
• bypass portions of the packing.

Pressure Drop May Remain Normal

This is what makes the problem easy to misdiagnose.

Unlike heavy solids fouling, a thin oil film may not reduce void space significantly.

The tower can show:

• normal pressure drop;
• poor gas removal.

Oil Can Enter as Fine Aerosol

Possible sources include:

• strip oil;
• lubricants;
• upstream mist.

The tower may capture these droplets and concentrate the oil in the circulation system.

Recirculation Spreads the Contamination

Once oil reaches the sump, the pump can redistribute it across the whole bed.

A local inlet problem becomes a full-tower wetting problem.

Upstream Oil-Mist Control May Be Needed

If oil loading is significant, controlling it before the HCl absorber may protect:

• packing;
• distributor;
• demister.

Cleaning Must Remove the Film

A water rinse may leave hydrophobic residue.

The cleaning method should remove the actual contaminant while remaining compatible with:

• polymer packing;
• FRP;
• gaskets.

Engineering Takeaway

Not all fouling works by blocking passages.

Surface contamination alone can destroy the effective wetting area of a packed absorber.