How to Retrofit a Mist Eliminator Installed Too Close to the Gas Outlet Nozzle

A mist eliminator can be correctly selected and installed yet still show uneven performance if the gas outlet nozzle is located too close above or beside it.

The outlet creates a strong local suction path.

Gas velocity becomes higher near the nozzle and lower elsewhere across the separator.

This nonuniform face velocity can cause local re-entrainment or bypass even when the average tower velocity appears acceptable.

Why Outlet Proximity Matters

Separator calculations often use total gas flow divided by tower cross-sectional area.

This assumes reasonably uniform flow.

A nearby side outlet can violate that assumption.

Gas accelerates toward the nozzle, producing a local high-velocity zone.

Look for Localized Damage or Carryover

Evidence may include:

• one separator region repeatedly fouled or damaged;
• stronger liquid movement near the outlet side;
• asymmetric support wear;
• carryover increasing at high load.

These signs can point to nonuniform gas draw.

Measure Available Disengagement Space

The distance between separator and outlet influences how much the gas flow can redistribute after leaving the demister.

Very small clearance allows the nozzle to affect the separator directly.

Consider Moving the Separator

If tower geometry allows, changing separator elevation may increase disengagement distance.

However, this can reduce space above the packed bed or interfere with manways.

The complete top-tower layout should be checked.

Consider a Flow-Equalizing Space or Device

In some cases, a suitable flow-distribution arrangement can reduce local acceleration.

Any added device must avoid excessive pressure drop and should not create new liquid-collection problems.

Check Separator Area Near the Nozzle

Increasing local structural support is not the same as correcting velocity distribution.

The objective should be more uniform gas flow through the separator.

Review Peripheral Sealing

A nearby side outlet increases the driving force for gas to use any perimeter gap.

Wall bypass should therefore be inspected particularly carefully on the outlet side.

Check Drainage

Higher local velocity can re-entrain collected liquid before it drains.

Drainage near the high-velocity region should be unobstructed.

Consider Outlet-Nozzle Limitation

If the gas outlet itself is undersized, the local acceleration may be unavoidable without vessel modification.

The nozzle can become part of the capacity bottleneck.

Use Flow Modeling Where Necessary

Large or critical towers with complex top geometry may benefit from more detailed flow analysis.

Simple average velocity may not capture the local condition.

Verify After Modification

Carryover and pressure drop should be checked at the highest gas rate.

A successful retrofit should reduce local overload without introducing significant new resistance.