Why Foaming and Hydrocarbon Contamination Matter in Amine and Glycol Mist Separation

Gas-treatment systems using amine or glycol solutions often require effective liquid separation.

Carryover can create:

• solvent loss;
• downstream contamination;
• compressor problems;
• reduced process efficiency.

At first, the mist eliminator duty may appear straightforward:

remove liquid droplets from the gas.

In practice, amine and glycol systems can be strongly affected by:

• foaming;
• hydrocarbon contamination;
• solids;
• degradation products;
• changing liquid properties.

These factors change both the amount of entrainment reaching the demister and the way captured liquid drains.

A separator selected only from vessel diameter and gas flow may therefore perform poorly.

Normal Solvent Carryover Is Only One Part of the Duty

Under stable operation, gas can entrain small amounts of:

• amine;
• glycol solution.

The mist eliminator captures these droplets and returns the liquid to the vessel.

This reduces solvent loss.

But the separator operating condition can change significantly if the process begins to foam.

The inlet liquid loading may rise rapidly.

Fine droplets may also become more important.

The same demister now faces a much more difficult duty.

Foaming Creates Unstable Entrainment

Foam can form because of:

• hydrocarbons;
• degradation products;
• solids;
• contaminants.

When bubbles burst, they generate droplets.

Foam can also physically rise toward the separator.

This creates:

• high instantaneous liquid loading;
• pressure-drop fluctuations;
• outlet carryover.

The separator may appear to “fail intermittently” even though the root cause lies in changing liquid chemistry below it.

Hydrocarbon Contamination Changes Surface Behavior

Liquid hydrocarbons can alter:

• surface tension;
• viscosity;
• wetting.

This affects how droplets form and how captured liquid behaves on the demister surface.

A mesh pad designed around relatively clean aqueous solvent may hold contaminated liquid differently.

Hydrocarbon films may drain more slowly or create sticky surfaces that trap solids.

The process becomes both a mist-separation and fouling problem.

Solids Can Turn the Wet Demister Into a Filter

Amine and glycol systems may contain:

• corrosion products;
• iron sulfide;
• degradation solids;
• particulates.

When these particles reach a wet mesh pad, they can stick to the liquid-coated wire.

The separator gradually captures solids as well as droplets.

Pressure drop rises.

Drainage passages narrow.

The mist eliminator starts functioning like an unintended filter.

This can shorten operating life significantly.

Fine Mesh Can Become a Maintenance Problem

A dense mesh provides strong collecting surface.

In clean service, that may improve fine-droplet separation.

In contaminated amine or glycol service, the same fine structure can accumulate:

• sticky liquid;
• solids.

The pad becomes difficult to clean.

This illustrates a recurring separator tradeoff:

maximum clean efficiency versus long-term fouling tolerance.

The best separator is not always the finest one available.

Liquid Loss Can Be an Important Performance Indicator

In solvent systems, demister performance may be reflected in:

• amine makeup rate;
• glycol makeup rate;
• downstream contamination.

If solvent consumption rises without another obvious cause, entrainment should be investigated.

This does not automatically prove demister failure.

Possible causes include:

• foaming;
• high gas velocity;
• liquid level;
• damaged separator.

Solvent-loss trend is therefore a useful process clue.

High Liquid Level Can Intensify Carryover

Separator vessels and contactors require adequate disengagement space.

If liquid level rises, the distance between the liquid surface and mist eliminator decreases.

Foam can further reduce effective clearance.

Bulk liquid can then reach the separator.

The demister is exposed to much higher liquid load.

Level behavior should therefore be reviewed whenever carryover increases.

Gas Velocity Still Matters

As gas throughput rises, the separator experiences greater aerodynamic load.

The same contaminated liquid that drains adequately at lower gas velocity may become re-entrained at higher load.

This can explain why a system operates well under normal production but loses solvent at peak throughput.

A debottlenecked gas plant should include mist eliminator review.

Anti-Foam Treatment Can Help—but Changes Chemistry

Anti-foam chemicals may reduce entrainment by suppressing foam.

However, they can also change:

• surface tension;
• wetting;
• liquid film behavior.

The separator should therefore be monitored after anti-foam changes.

The process may improve overall while the demister experiences a different wetting condition.

Cleaning Method Must Match the Deposit

Water flushing may not remove:

• hydrocarbon-rich deposits;
• hardened degradation material.

A suitable cleaning strategy should consider:

• deposit chemistry;
• separator material;
• process safety.

If removal is difficult, the segmentation and access design become important.

Maintenance should be considered during initial separator selection.

Vane or Mesh?

There is no universal answer.

Wire mesh may be attractive where:

• droplets are relatively fine;
• service is clean.

A vane separator may be more robust where:

• liquid loading is high;
• solids or contamination are significant.

Some duties may benefit from staged separation.

The decision should reflect actual process cleanliness and outlet requirements.

What Data Should Be Collected?

Useful inputs include:

• gas flow;
• pressure;
• temperature;
• solvent type and concentration;
• foaming history;
• hydrocarbon contamination;
• solids content;
• liquid level;
• required outlet carryover.

Existing solvent-loss and demister DP history can also be valuable.

Final Engineering Perspective

Amine and glycol mist separation is not just a conventional clean-droplet problem.

Foaming, hydrocarbons, solids, degradation products, and liquid-level behavior can all change the separator duty.

The best design balances droplet capture, drainage, fouling tolerance, solvent recovery, and maintainability.