How to Retrofit a Mist Eliminator When Liquid Loading Increases but Gas Flow Does Not

A process change can increase the amount of entrained liquid reaching a mist eliminator without materially changing gas flow.

Examples include higher spray rate, greater liquid circulation, increased condensation, or more vigorous upstream contacting.

Because face velocity remains similar, the separator may appear hydraulically unchanged.

In reality, its drainage and liquid-handling duty can increase dramatically.

Distinguish Gas Load from Liquid Load

Mist-eliminator performance depends on both.

A separator selected only from gas velocity may become overloaded by liquid even when velocity remains within the original range.

The retrofit should estimate the new entrained-liquid load.

Look for Drainage Symptoms

Possible signs include:

• intermittent carryover;
• liquid accumulation inside the separator;
• rising pressure drop;
• heavy drainage from one region.

These can indicate that the separator captures liquid but cannot remove it quickly enough.

Check Upstream Droplet Generation

A higher liquid flow may also change droplet size.

More liquid is not necessarily the only difference.

If upstream atomization becomes stronger, both droplet quantity and fineness may change.

Review Mesh Liquid Capacity

Dense mesh can retain more liquid.

At high liquid load, gas can re-entrain the accumulated liquid.

A different mesh structure or thickness may be needed.

Review Vane Drainage

Vane packs often include directional drainage channels.

These should be checked for capacity and fouling.

Inspect Support Obstruction

Support grids can interfere with downward drainage.

At low liquid load this may not matter.

At higher load, trapped liquid above support bars can become significant.

Check Tower Levelness

A small slope can concentrate drainage on one side.

The effect becomes more serious as liquid load increases.

Consider Pre-Separation

If upstream conditions generate very large droplets or bulk liquid, removing some liquid before it reaches a fine mist separator can reduce load.

Whether a separate first stage is practical depends on space and pressure-drop allowance.

Check Disengagement Space

Allowing larger droplets to settle before reaching the demister can reduce separator load.

Insufficient free space can send more liquid directly into the element.

Define Carryover Requirement

The retrofit should balance liquid-handling capacity and outlet performance.

An overly open separator may tolerate more liquid but allow too much carryover.

Verify at Maximum Liquid Condition

Testing only at maximum gas flow is insufficient.

The limiting point may be a high-liquid operating case with normal gas flow.