Glycol Dehydration Tower Packing: When to Use Metal Pall Ring Instead of Structured Packing

Natural gas dehydration systems remove water vapor from gas before transmission, compression, cryogenic processing, LNG treatment, or downstream use.

One of the most common processes uses glycol, particularly triethylene glycol (TEG).

Inside a glycol contactor, wet gas flows upward while lean glycol flows downward. Water vapor transfers from the gas into the glycol, producing dry gas and water-rich glycol.

Many modern glycol contactors use trays or structured packing, but Metal Pall Ring random packing is still relevant in certain small towers, retrofit units, packaged systems, and installations where simple and robust random packing is preferred.

The practical engineering question is:

When does Metal Pall Ring make sense in a glycol dehydration tower, and when is structured packing the better choice?

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1. What the Packing Does in a TEG Contactor

The packing does not chemically remove water.

Its function is to create gas-liquid contact between:

• upward-flowing wet natural gas
• downward-flowing lean glycol

The glycol absorbs water vapor from the gas.

Packing therefore needs to provide:

• sufficient effective contact area
• good glycol distribution
• open gas passages
• low-to-moderate pressure drop
• stable liquid drainage
• resistance to process temperature and chemistry

Actual dehydration performance also depends on:

• lean glycol purity
• glycol circulation rate
• operating pressure
• gas temperature
• inlet water content
• required outlet water content
• contactor height

Packing is only one part of the dehydration system.

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2. Why Metal Pall Ring Can Be Used

Metal Pall Ring is an open random packing geometry with wall windows and internal structural surfaces.

Compared with an old-style Raschig Ring, it generally provides:

• greater open flow area
• improved access to internal surfaces
• better liquid redistribution
• more effective use of packing volume
• lower hydraulic restriction than simple closed rings

For glycol dehydration, this provides a practical compromise between:

gas capacity + liquid contact + mechanical robustness.

Random packing can also be attractive where simple installation and maintenance are important.

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3. Gas Capacity Is Important in Natural Gas Service

Gas contactors may handle substantial gas throughput.

As gas velocity rises:

• pressure drop increases
• glycol drainage becomes more difficult
• liquid holdup increases
• the tower approaches flooding

The packing therefore needs enough open area to handle the required gas volume.

Metal Pall Ring can provide useful hydraulic capacity, particularly compared with older random ring designs.

However, actual capacity depends strongly on:

• gas density
• operating pressure
• packing size
• glycol circulation rate
• tower diameter
• packed height

A high-pressure gas flow must always be evaluated using actual operating conditions rather than standard volumetric flow alone.

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4. Pressure Drop Matters

Pressure loss through a gas dehydration contactor is normally undesirable.

Excessive packed-bed pressure drop can:

• reduce available process pressure
• limit gas throughput
• increase upstream compression burden
• reduce hydraulic margin
• indicate fouling or flooding

For high-pressure gas service, tower pressure drop should be considered as part of the complete process pressure balance.

This is one reason engineers sometimes consider higher-capacity random packing or structured packing when upgrading an existing contactor.

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5. Glycol Distribution Is Critical

A random packing bed performs properly only when lean glycol is distributed across the full tower cross-section.

Poor distribution can create:

• dry packing regions
• gas channeling
• reduced effective contact
• locally overloaded zones
• poor dehydration performance

This is particularly important because glycol circulation rates can be relatively low compared with many wet scrubber liquid loads.

At low irrigation rates, inadequate distribution can leave large areas of the packing underused.

Therefore:

good packing + poor distributor = poor contactor performance.

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6. Low Liquid Rate Can Favor Structured Packing

This is one reason structured packing may outperform random packing in some glycol dehydration services.

Structured packing offers an ordered flow geometry and can provide:

• high effective mass-transfer area
• relatively low pressure drop
• controlled liquid spreading
• strong performance at suitable liquid loads

Where very low glycol circulation and high dehydration efficiency are required, structured packing may provide a more predictable solution.

Random Pall Ring should therefore not automatically be selected just because it is cheaper or easier to install.

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7. Why Random Pall Ring Still Has a Place

Despite the advantages of structured packing, Metal Pall Ring can remain attractive when the project values:

• simple installation
• easy replacement
• robust mechanical construction
• tolerance of less-than-perfect installation
• lower initial packing cost
• compatibility with existing random-packing supports
• straightforward retrofit

For small or medium packaged contactors, these practical factors can matter.

Not every tower requires the highest-performance structured packing solution.

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8. Packing Size Matters

Metal Pall Rings are available in multiple nominal sizes.

Smaller Pall Ring

Generally provides:

• more pieces per unit volume
• greater available surface
• more frequent glycol redistribution

But may also create:

• higher pressure drop
• lower gas capacity
• greater fouling sensitivity

Larger Pall Ring

Generally provides:

• lower pressure drop
• larger gas passages
• higher hydraulic capacity
• better tolerance to contamination

But lower surface area per cubic meter.

The correct size should therefore balance:

dehydration performance + gas capacity + allowable pressure drop.

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9. Natural Gas Pressure Changes the Hydraulic Picture

A common mistake is evaluating packing only from the stated gas flow in Nm³/h or SCFD.

The actual gas volume inside the contactor depends strongly on:

• pressure
• temperature
• gas composition

At higher pressure, gas density increases and actual volumetric flow decreases compared with standard conditions.

This changes:

• superficial gas velocity
• pressure drop
• flooding behavior

Therefore, a meaningful packing evaluation requires:

operating pressure and temperature, not simply standard gas flow.

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10. Hydrocarbon Condensation Can Affect the Bed

Natural gas may contain heavier hydrocarbons.

Under some process conditions, hydrocarbon liquids can enter or form inside the contactor.

These liquids may:

• change wetting behavior
• contaminate glycol
• promote foaming
• alter mass transfer
• increase liquid holdup

If an existing tower experiences unstable differential pressure or poor dehydration, contamination should be investigated before blaming the random packing.

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11. Glycol Foaming Can Mimic a Packing Problem

Foaming is a known operational issue in glycol systems.

Potential causes include:

• hydrocarbons
• corrosion products
• solids
• degradation products
• chemical contaminants

Foaming can cause:

• increased liquid holdup
• glycol entrainment
• higher differential pressure
• unstable tower operation
• reduced dehydration efficiency

A fouled or foaming glycol system may make an otherwise adequate packing bed appear hydraulically undersized.

Replacing the packing without correcting the glycol contamination may not solve the problem.

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12. Packing Fouling Should Be Considered

Natural gas treatment systems may carry:

• compressor oil
• corrosion products
• fine solids
• hydrocarbon condensate
• glycol degradation products

These contaminants can accumulate inside the packed bed.

Over time this may reduce:

• open area
• liquid distribution
• effective mass transfer

and increase:

• pressure drop
• liquid holdup
• cleaning frequency

Where contamination is significant, a more open Pall Ring size may provide better operating tolerance than a very small packing.

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13. Metallurgy Must Match the Gas and Glycol System

Metal Pall Ring may be manufactured from:

• carbon steel
• SS304
• SS316
• SS316L
• other alloys

The correct material depends on:

• gas composition
• CO₂
• H₂S
• chlorides
• water content
• glycol chemistry
• operating temperature
• plant corrosion specification

A gas stream containing acid gases can create a substantially different corrosion environment from clean dry natural gas.

Therefore, “Metal Pall Ring” is not a complete RFQ specification.

The required alloy must be stated or evaluated.

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14. Metal Pall Ring vs Plastic Packing

Plastic random packing may be used in some gas-liquid systems, but metallic packing is generally more attractive where the process requires:

• higher temperature capability
• mechanical strength
• dimensional stability
• high-pressure equipment compatibility
• plant-standard metallic internals

Plastic may still be suitable in some special low-temperature or non-hydrocarbon service.

But material selection should be based on the entire contactor environment rather than packing cost alone.

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15. Metal Pall Ring vs Metal Raschig Ring

Older glycol or gas-contacting equipment may contain Metal Raschig Rings.

Pall Ring can offer a more hydraulically open geometry.

A Pall Ring retrofit may therefore be evaluated when the existing Raschig Ring tower suffers from:

• excessive pressure drop
• limited gas capacity
• inefficient use of packing volume

However, changing packing geometry affects:

• surface area
• void fraction
• packing factor
• bed weight
• mass-transfer behavior

It should therefore be treated as an engineering retrofit rather than a simple one-for-one substitution.

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16. Metal Pall Ring vs Structured Packing

This is the more important modern comparison.

Neither is universally better.

The correct choice depends on the specific contactor objective.

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17. When Metal Pall Ring Is the Better Starting Point

Metal Pall Ring may be more logical when:

Existing Tower Already Uses Random Packing

The support and tower geometry are already designed around dumped packing.

Retrofit Simplicity Is Important

The plant wants to avoid a major internal redesign.

Moderate Dehydration Duty Is Required

The existing process does not demand extreme separation performance per meter.

Mechanical Robustness Matters

The tower operates in demanding industrial service.

Cost and Replacement Availability Matter

Standard Pall Ring sizes and alloys may be relatively easy to source.

In these situations, random packing remains a practical solution.

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18. When Structured Packing Deserves Strong Consideration

Structured packing becomes especially attractive when:

• pressure drop must be minimized
• higher gas throughput is required
• packed height is limited
• low glycol rates must still achieve good effective wetting
• dehydration performance must be improved significantly
• a major tower revamp is already planned

If the project objective is a substantial capacity or efficiency upgrade, simply installing another random packing may not be enough.

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19. Do Not Replace Packing Before Checking Glycol Quality

If a TEG contactor is not meeting the dry-gas specification, investigate:

• lean glycol concentration
• glycol circulation rate
• glycol temperature
• reboiler/regeneration performance
• contamination
• foaming
• liquid distribution

before concluding that the packing is inadequate.

For example, low lean-glycol purity can reduce dehydration performance even if the packed bed is in excellent condition.

The entire TEG system must be reviewed.

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20. Packing Support and Bed Limiter

Random Metal Pall Rings need an appropriate support.

The support must:

• retain the packing
• carry the wet packing load
• provide sufficient open gas area
• resist corrosion
• withstand equipment conditions

A bed limiter may also be required to prevent packing movement under high gas velocity.

Both components should provide high open area so they do not become hydraulic restrictions.

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21. Retrofit Projects Need a Clear Objective

Before changing packing, define whether the project needs to:

• increase gas throughput
• reduce pressure drop
• improve dehydration
• replace damaged packing
• solve fouling
• reduce glycol carryover
• modernize an older Raschig Ring bed

These are different engineering problems.

The correct packing response may therefore be different for each case.

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22. Data Needed for a Glycol Contactor Packing RFQ

Useful information includes:

• tower internal diameter
• operating pressure
• gas flow rate
• gas temperature
• gas composition
• inlet water content
• required outlet water content
• glycol type
• lean glycol concentration
• glycol circulation rate
• glycol temperature
• current packing type
• current packing size
• packed-bed height
• current pressure drop
• foaming history
• fouling history
• required metallurgy
• liquid distributor information
• packing support details

For retrofit projects, current dry-gas performance should also be provided.

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Final Selection Principle

Metal Pall Ring remains a useful random packing option for glycol dehydration towers where the process values:

robust construction + open gas passages + simple installation + retrofit flexibility + economical random packing.

Structured packing may provide advantages when very low pressure drop, high efficiency, high capacity, or strong low-liquid-rate performance are required.

The practical decision is therefore not:

“Is Pall Ring outdated?”

It is:

“Does this glycol contactor actually require the performance benefit of structured packing, or will a properly sized Metal Pall Ring satisfy the dehydration duty with simpler installation and lower retrofit complexity?”

That distinction is particularly important in existing towers.