How to Select a Mist Eliminator for Chlor-Alkali and Wet Chlorine Service

Chlor-alkali and wet chlorine processes create a difficult combination for mist eliminators.

The separator may be exposed to:

• chlorine-containing gas;
• brine droplets;
• caustic solution;
• dissolved salts;
• highly corrosive condensate.

The design problem is therefore not only removing droplets.

The mist eliminator must also remain chemically stable, maintain drainage, and avoid rapid salt deposition or mechanical degradation.

A separator that performs well in a conventional water scrubber cannot automatically be transferred into wet chlorine service.

Why Wet Chlorine Is Different

Dry chlorine and wet chlorine do not create the same material environment.

The presence of moisture can dramatically change corrosion behavior.

Condensed liquid may contain:

• chlorine;
• chlorides;
• acidic species.

This liquid can be much more aggressive than the nominal gas description suggests.

The mist eliminator therefore needs to be evaluated based on the actual wet phase contacting it.

This includes:

• active media;
• support grid;
• frame;
• fasteners.

Brine Droplets Add a Salt-Fouling Problem

In chlor-alkali systems, entrained liquid may contain concentrated brine.

When these droplets are captured by the demister, water can:

• drain;
• evaporate.

Dissolved salt remains.

Crystals can gradually accumulate on:

• wire surfaces;
• vane blades;
• support structures.

This reduces flow area and interferes with drainage.

The separator can therefore face corrosion and crystallization at the same time.

Fine Mesh May Capture Well but Plug Quickly

A dense wire mesh provides a large surface area.

This can improve fine-droplet capture.

But in brine-containing service, the same large surface area provides many nucleation sites for salt.

As deposits grow:

• void fraction decreases;
• differential pressure increases;
• drainage becomes more difficult.

The separator may then flood at a lower gas load.

This creates a classic design tradeoff:

fine droplet removal versus long-term salt tolerance.

Plastic Materials Can Be Attractive

Materials such as:

• PP;
• PVDF

may offer useful corrosion resistance in some chlor-alkali applications.

However, material selection should not be made from chemical resistance alone.

The actual operating temperature matters.

Plastic separators also require review of:

• stiffness;
• creep;
• support spacing;
• thermal expansion.

A chemically compatible polymer can still fail mechanically if the structure deforms under long-term load.

Metallic Materials Need Project-Specific Review

Conventional stainless steels are not universally suitable for wet chlorine or concentrated chloride conditions.

Corrosion behavior depends on:

• concentration;
• temperature;
• water content;
• contaminants.

Therefore, a specification such as:

“SS316L demister for chlorine”

should not be accepted automatically without reviewing the real service.

The weakest component may be a:

• fastener;
• clip;
• support member

rather than the active mesh itself.

Droplet Source Must Be Identified

Mist can originate from:

• brine handling;
• caustic spray;
• scrubber entrainment;
• condensation;
• process flashing.

Each mechanism can create different droplet sizes and liquid load.

If the separator receives heavy coarse entrainment, drainage capacity may dominate.

If fine condensed droplets are present, collection efficiency may become more difficult.

The correct separator type depends on which mechanism controls the duty.

Condensation Can Change the Chemistry Locally

Gas cooling near the mist eliminator can create new liquid.

This liquid may have a composition different from the bulk process liquid.

For example, condensation may create highly corrosive wet regions around:

• vessel wall;
• support members.

Localized corrosion can therefore appear even where the general process chemistry seems acceptable.

Temperature profile should be considered together with corrosion compatibility.

Salt Deposits Can Concentrate at Drainage Restrictions

If liquid drains poorly, brine remains on the separator longer.

More water evaporates.

Salt concentration rises.

Crystallization begins.

This makes drainage quality especially important.

Avoid locations where liquid can collect:

• low spots;
• compressed mesh;
• blocked vane pockets.

Good drainage can significantly reduce the rate at which deposits form.

Washing May Be Necessary

If salt deposition is expected, a wash system may be needed.

The washing strategy should consider:

• salt solubility;
• wash-water quality;
• coverage;
• drainage.

Using saline or contaminated wash water may simply add more dissolved material.

Fresh-water rinsing may be valuable in some systems.

The objective is not only to wet the separator but to dissolve and remove accumulated salt.

Differential Pressure Provides Early Warning

Salt deposition gradually reduces open area.

A rising demister DP under comparable gas load can indicate developing fouling.

The trend should be interpreted together with:

• gas flow;
• temperature;
• liquid loading.

Cleaning before severe plugging generally provides easier recovery than waiting for large crystalline deposits to develop.

Vane Separators Can Offer Better Fouling Tolerance

Where droplet size allows, an open vane system may provide:

• larger passages;
• better drainage;
• easier washing.

For finer droplets, a second polishing stage may be considered.

A staged design can reduce the burden on the fine separator.

However, each additional stage creates:

• pressure drop;
• maintenance requirements.

The process duty should justify the complexity.

What Should Be Included in an RFQ?

Useful information includes:

• gas composition;
• chlorine concentration;
• temperature;
• pressure;
• liquid composition;
• chloride or salt concentration;
• gas flow;
• liquid loading;
• fouling history;
• allowable DP;
• material requirements.

If exact droplet size is unknown, the source of the entrainment should at least be described.

Final Engineering Perspective

Wet chlorine and chlor-alkali mist elimination is a combined separation, corrosion, and salt-deposition problem.

The separator must remove the required droplets while surviving the actual wet chemistry and remaining hydraulically open.

Reliable design therefore requires balancing material compatibility, droplet capture, drainage, salt tolerance, washing, and mechanical stability.