How to Retrofit a Mist Eliminator with Poor Liquid Drainage

A mist eliminator removes droplets by capturing them on mesh, vanes, or other separating surfaces.

Capture is only half of the job.

The collected liquid must then drain away.

If drainage is poor, liquid accumulates inside the separator until gas re-entrains it. The tower can show high carryover even though the separation medium itself is capable of capturing the droplets.

A retrofit should therefore evaluate drainage as part of mist-eliminator performance.

Recognize Drainage Problems

Possible signs include:

• intermittent bursts of liquid carryover;
• increasing pressure drop;
• large liquid inventory in the separator;
• uneven drainage after shutdown;
• sections of mesh heavily saturated.

Carryover that becomes worse at high liquid load can strongly suggest drainage limitation.

Check Separator Orientation

Vane packs and some mesh arrangements depend on correct orientation.

If a separator was installed incorrectly, collected liquid may have no efficient path toward drains.

Verify installation against the intended flow direction.

Inspect the Support Frame

Support bars can unintentionally block liquid drainage.

This is particularly important with mesh pads resting directly on dense grids.

Liquid trapped above support members can accumulate and then re-entrain.

Check Tower Levelness

A separator installed in a tilted tower may drain toward one side.

If the drainage system assumes a level surface, liquid can accumulate at the high or low edge.

Field level measurement can help diagnose the problem.

Evaluate Liquid Load

A process change may increase droplet load without changing gas flow.

The existing drainage system may simply be overwhelmed.

The retrofit should estimate how much liquid the separator must remove under maximum conditions.

Inspect Drain Channels

Some vane separators include dedicated liquid channels.

These can plug with:

• solids;
• scale;
• corrosion products.

Cleaning may restore performance if geometry remains adequate.

Avoid Creating Gas Bypass Through Drainage Features

A large drain opening can become a gas path.

Drainage improvements should therefore control both phases.

In some designs, liquid seals or directional geometry are required.

Check Re-Entrainment Velocity

Even with good drainage, gas velocity may be high enough to strip collected liquid back into the gas stream.

The retrofit should distinguish drainage failure from excessive separator velocity.

Improve Access for Cleaning

If drainage passages repeatedly foul, redesign may include removable or accessible sections.

A drain that cannot be inspected will eventually recreate the same problem.

Check Corrosion

Localized corrosion often develops where liquid remains stagnant.

Poor drainage can therefore cause both performance loss and structural damage.

Replacement material should be reviewed if corrosion is significant.

Verify After Retrofit

Useful indicators include:

• more stable pressure drop;
• consistent drain flow;
• reduced downstream carryover.

Performance should be checked at the liquid-load condition that previously caused the problem.