Engineering Evaluation Case: A TEG Gas-Dehydration Contactor Starts Carrying Glycol After Hydrocarbon Condensate Enters the Circulation Loop

A glycol contactor removes water vapor from natural gas by contacting the gas with lean glycol.

Packed contactors can provide efficient gas-liquid contact at relatively low pressure drop.

Performance can deteriorate when the glycol becomes contaminated with hydrocarbon liquid.

The symptoms can appear to be a packing or demister problem even when the contamination originates upstream.

Project Situation

Consider a packed TEG contactor.

The unit originally operates with:

• stable differential pressure;
• acceptable water removal;
• low glycol carryover.

After an upstream operating change, small amounts of hydrocarbon condensate begin entering the gas stream.

Operators later observe:

• foaming;
• increased glycol losses;
• unstable differential pressure;
• wet-gas outlet performance deterioration.

The tower internals should be inspected.

The entire glycol loop should also be investigated.

Hydrocarbon Liquid Can Change Glycol Behavior

TEG is intended to circulate as the absorbing liquid.

Hydrocarbon contamination can alter:

• surface tension;
• foam stability;
• phase behavior.

A contaminated glycol may therefore behave differently inside the same packing geometry.

Foaming Increases Apparent Liquid Holdup

Stable foam occupies void space in the bed.

This can lead to:

• increased differential pressure;
• earlier loading;
• greater entrainment.

The tower may appear hydraulically overloaded even though nominal gas and glycol flow rates remain unchanged.

Hydrocarbon Condensate Can Enter from Upstream Separation Problems

Potential sources include:

• ineffective inlet separation;
• changing gas temperature;
• liquid slugging;
• upstream separator upset.

If hydrocarbon enters continuously, cleaning the contactor without correcting the source will not provide a durable solution.

The Top Separator Becomes Important

A glycol contactor often relies on effective mist separation to reduce glycol losses.

During foaming or entrainment, droplet load can increase dramatically.

The existing mist eliminator may then be asked to handle a duty far above normal design.

High glycol carryover does not automatically mean the separator itself is defective.

Packing Surface Can Become Contaminated

Hydrocarbon films can alter glycol wetting on the packing.

This may reduce effective gas-liquid contact.

The tower can therefore suffer from both:

• hydraulic foam;
• reduced effective mass-transfer area.

Pressure drop and dehydration performance should be reviewed together.

Lean Glycol Quality Matters

The contactor receives glycol from regeneration.

Important liquid properties can include:

• glycol concentration;
• contamination;
• solids;
• degradation products.

Even perfect packing cannot compensate for poor lean-glycol quality.

High Gas Velocity Can Amplify the Problem

A contactor operating close to its hydraulic limit is more sensitive to increased foam and liquid holdup.

A process expansion that increases gas flow may therefore reveal contamination problems that were previously tolerable.

The design should distinguish:

• clean-solvent capacity;
• real operating capacity.

Do Not Increase Glycol Rate Blindly

When dehydration worsens, operators may increase circulation.

That can provide more absorbent.

It also increases liquid load in the packing.

If the underlying problem is foaming, additional circulation may worsen hydraulic instability.

The process should identify the limiting mechanism first.

Inspect the Inlet Zone

If liquid hydrocarbon enters with the gas, the lower part of the contactor may show the strongest evidence.

Inspection can look for:

• oily deposits;
• unusual liquid films;
• localized fouling.

The inlet separator and gas-entry arrangement should be included in the investigation.

What Data Helps?

Trend:

• gas rate;
• gas temperature and pressure;
• TEG circulation;
• lean glycol concentration;
• bed differential pressure;
• glycol loss;
• hydrocarbon contamination.

The relationship between these parameters often reveals when the problem began.

Packing Replacement Is a Late Decision

If packing is physically damaged or irreversibly contaminated, replacement may eventually be required.

But replacing clean packing before controlling the hydrocarbon source can waste both time and money.

Engineering Takeaway

A packed TEG contactor is part of a complete dehydration loop.

Upstream liquid separation and glycol condition can control tower performance as strongly as the packing itself.