Why Mist Eliminator Performance Can Become Worse After Cleaning

Cleaning a mist eliminator is supposed to restore performance.

Deposits are removed.

Open area is recovered.

Pressure drop should decrease.

Drainage should improve.

Yet some plants find that a demister performs worse after maintenance.

Possible symptoms include:

• higher carryover;
• higher pressure drop;
• unstable operation;
• new bypass.

This does not necessarily mean cleaning was a mistake.

It means something changed during cleaning, removal, or reinstallation.

A post-cleaning problem should therefore be investigated as a maintenance-induced geometry or surface-condition change, not automatically as proof that the separator is unsuitable.

Cleaning Can Damage Fine Wire Mesh

Wire mesh can be mechanically delicate.

Aggressive cleaning methods may:

• stretch wire;
• crush mesh;
• break strands;
• change pad thickness.

High-pressure water jets are particularly important.

A jet concentrated on one region can deform the knitted structure.

The pad may look clean afterward but no longer have the original density and voidage.

Hydraulic behavior changes.

Excessive Handling Can Distort Segments

Demister sections are often removed through a manway for cleaning.

Workers may:

• bend;
• compress;
• drag

the segments during removal and reinstallation.

If the pad does not return to its intended shape, neighboring sections may no longer fit correctly.

Possible consequences include:

• edge gaps;
• segment-joint gaps;
• uneven compression.

The separator becomes cleaner but hydraulically less uniform.

Reinstallation Can Create Bypass

Before cleaning, the old demister may have been tightly fitted.

After removal, the segments are reinstalled in a different sequence or orientation.

Small gaps remain.

Gas now has an easier path around or between the segments.

Outlet carryover increases immediately after maintenance.

This pattern is a strong clue.

If performance deteriorates directly after shutdown work, inspect installation before changing mesh grade.

The Hold-Down May Be Reinstalled Too Tightly

Maintenance teams naturally want the demister to be secure.

Fasteners may be tightened more aggressively than before.

The upper grid compresses the mesh.

Effective density increases.

Voidage falls.

Pressure drop rises.

Drainage becomes more difficult.

The clean pad may therefore show more resistance than the dirty pad did immediately after earlier installation.

Hold-down systems should restrain the separator without crushing it.

Supports Can Be Reassembled Incorrectly

Support bars or frames may be removed during maintenance.

If they are reinstalled incorrectly, they can:

• obstruct drainage;
• leave unsupported spans;
• change segment elevation.

One section may sag.

Another may become compressed.

Gas distribution changes.

Mechanical maintenance quality directly influences separation performance.

Cleaning May Not Remove Internal Deposits

A pad can look clean on its external faces while deposits remain deep inside.

This is especially common with:

• dense mesh;
• hardened salt;
• polymeric material;
• oily solids.

If cleaning removes only surface deposits, the internal hydraulic restriction remains.

The plant may expect pressure drop to return to the original baseline but see little improvement.

This is not a new failure.

The cleaning was incomplete.

Deposit Removal Can Expose Corrosion Damage

Fouling sometimes hides severely corroded wire.

After cleaning, the deposit is removed and weak wire loses structural support.

Sections may:

• break;
• collapse;
• become loose.

The operator may believe cleaning damaged the demister.

In reality, the underlying corrosion already existed.

Cleaning simply revealed the remaining mechanical condition.

This is why the separator should be inspected carefully after deposits are removed.

Cleaning Chemicals Can Change Surface Behavior

Chemical cleaning may leave residues.

Surfactants, solvents, or detergents can change how the process liquid wets the wire.

Immediately after restart, the separator may exhibit different:

• film formation;
• coalescence;
• drainage.

In some cases, this effect is temporary.

The pad may return to normal after the cleaning chemical is fully displaced.

Performance should therefore be judged after stable process conditions are restored.

Improper Rinsing Can Introduce New Deposits

If cleaning chemicals are not removed fully, they may:

• react with process liquid;
• form salts;
• create sticky residue.

The clean separator begins a new operating cycle already contaminated.

Cleaning procedure should therefore include suitable rinsing and drainage where required.

Wrong Segment Orientation Can Matter

For ordinary homogeneous wire mesh, orientation may appear unimportant.

But some pads use:

• graded-density layers;
• different upstream/downstream structures.

Reversing the segment can change hydraulic behavior.

For vane packs, orientation is even more critical.

Installing a module backwards can disrupt drainage immediately.

Maintenance records should preserve intended orientation.

A Lower Pressure Drop Is Not Always Proof of Better Performance

Suppose cleaning creates a gap between segments.

Overall differential pressure may fall.

At first this appears positive.

But the lower resistance is partly caused by gas bypass.

Carryover rises.

Therefore, after cleaning, both should be checked:

• differential pressure;
• separation performance.

One number alone cannot prove successful maintenance.

Establish a Post-Maintenance Baseline

After cleaning and reinstallation, record:

• gas flow;
• liquid load;
• differential pressure;
• outlet condition.

Compare these with the original clean baseline where available.

Large differences deserve investigation while the maintenance details are still known.

Waiting several months makes it much harder to determine what changed.

Photograph the Assembly Before Vessel Closure

Useful photographs include:

• segment layout;
• edge fit;
• support arrangement;
• hold-down grid.

These records provide evidence if performance changes after restart.

They are especially useful in large systems where reopening the vessel requires another shutdown.

When Replacement Is Better Than Repeated Cleaning

If cleaning repeatedly causes:

• damage;
• incomplete recovery;
• shorter run life,

the separator may no longer be maintainable economically.

A replacement with:

• more open geometry;
• easier-removal segments;
• better washability

may provide better lifecycle performance.

Final Engineering Perspective

Cleaning does not automatically restore a mist eliminator to its original condition.

The separator must remain mechanically and hydraulically correct after:

• cleaning;
• handling;
• reassembly.

Post-maintenance performance problems often come from deformation, incomplete cleaning, incorrect reinstallation, bypass, excessive compression, or chemical residue.

Cleaning quality should therefore be judged by restored operating performance—not simply by visual cleanliness.