Boiler Feedwater Deaerator Packing: When to Use Stainless Steel Pall Ring

Boiler feedwater deaeration removes dissolved oxygen and other non-condensable gases from water before the water enters a boiler or steam system.

This is important because dissolved oxygen can contribute to corrosion in:

• boilers
• economizers
• condensate systems
• feedwater piping
• downstream heat-transfer equipment

Many deaeration systems use direct contact between water and steam.

Packing can be used to increase the contact area between the two phases, helping dissolved gases transfer from the liquid into the stripping vapor.

For packed deaeration equipment, stainless steel Pall Ring is one random packing option worth evaluating where the process requires:

• metallic construction
• elevated-temperature capability
• open gas-flow passages
• effective water redistribution
• mechanical durability
• economical random packing

The engineering question is not simply:

“Can Pall Ring remove oxygen?”

A more useful question is:

“When does stainless steel Pall Ring provide the right hydraulic and mechanical characteristics for a packed feedwater deaerator?”

---

Why Feedwater Must Be Deaerated

Water entering a boiler may contain dissolved gases, particularly oxygen and carbon dioxide.

If these gases remain in the system, they can contribute to corrosion.

Dissolved oxygen is especially important because it can promote localized corrosion and pitting in metal equipment.

A deaerator reduces these gases by combining several effects:

• heating the water
• reducing gas solubility
• providing intimate steam-water contact
• venting released non-condensable gases

Packing can increase the available contact between water and stripping steam.

But packing is only one part of the deaeration system.

Performance also depends on:

• water temperature
• steam rate
• operating pressure
• venting
• distributor design
• residence time
• equipment configuration

---

1. What Role Does Packing Play?

Inside a packed deaeration section, water flows over the packing while steam or stripping vapor moves through the bed.

The packing helps:

• spread the water
• renew liquid surfaces
• increase vapor-liquid contact
• reduce large liquid streams
• promote gas release from the water

The purpose is not to “filter” oxygen.

Instead, packing provides a physical contact environment in which dissolved gases can leave the liquid phase.

This distinction is important.

Deaeration efficiency comes from mass transfer and thermodynamic conditions, not from chemical adsorption by the packing.

---

2. Why Pall Ring Is a Practical Random Packing Geometry

Pall Ring was developed as a more open alternative to the traditional Raschig Ring.

Its cylindrical wall contains windows and internal structural elements.

This produces:

• high void fraction
• multiple gas-flow passages
• exposed liquid-contact surfaces
• reduced flow obstruction compared with simple solid-wall rings
• repeated liquid redistribution

For deaerator service, these characteristics can help maintain contact between hot water and steam without creating unnecessarily high hydraulic resistance.

That is particularly useful when the equipment must handle significant steam or vapor flow.

---

3. Why Stainless Steel Is Often Considered

Plastic random packing can be useful in many scrubbers and water-treatment towers, but boiler feedwater deaerators frequently operate at temperatures where metallic construction is more appropriate.

Stainless steel packing can provide:

• high temperature resistance
• good mechanical strength
• dimensional stability
• long service life
• resistance to many water-service corrosion environments

Common stainless steel selections may include grades such as:

• SS304
• SS316
• SS316L

The correct metallurgy depends on the actual feedwater chemistry, chlorides, temperature, treatment chemicals, and equipment specification.

Packing material should therefore match the broader metallurgy philosophy of the deaerator.

---

4. Temperature Is Central to Deaeration

Gas solubility in water generally decreases as temperature rises.

This is one reason thermal deaeration uses steam to heat the feedwater.

As the water approaches the appropriate saturation condition, dissolved gases become easier to release.

Packing can help by exposing the liquid repeatedly to the stripping vapor.

But a larger packing surface cannot compensate for inadequate thermal conditions.

If:

• water temperature is too low
• steam distribution is poor
• venting is inadequate

then simply installing more packing will not solve the problem.

Packing works as part of the deaeration process, not independently from it.

---

5. Steam Distribution Matters

A packed bed should receive reasonably uniform upward vapor flow.

If steam enters only one area of the tower or channels through the bed, part of the packing may receive limited vapor contact.

This can reduce effective deaeration.

Important considerations include:

• steam inlet arrangement
• vapor distribution
• tower diameter
• packing support openness
• packing depth
• water distribution

A good random packing geometry helps redistribute flow, but it cannot correct a fundamentally poor inlet design.

---

6. Water Distribution Is Equally Important

The incoming feedwater should spread across the packing bed rather than flowing down a limited number of paths.

Poor distribution can create:

• locally overloaded zones
• poorly wetted regions
• vapor channeling
• reduced effective contact area
• inconsistent deaeration performance

For larger diameter equipment, the water distributor becomes particularly important.

Therefore, a packed deaerator should be treated as:

water distributor + packing + support + vapor flow path

rather than treating Pall Ring as an isolated component.

---

7. Why Pressure Drop Still Matters

Deaerators are not usually selected with the same deep-vacuum sensitivity as vacuum distillation towers, but excessive pressure drop is still undesirable.

Packed-bed resistance can affect:

• steam distribution
• vapor flow
• equipment operating stability
• required pressure differential
• hydraulic capacity

A relatively open packing geometry can help limit unnecessary resistance.

This is one reason Pall Ring may be preferred over older, more restrictive ring geometries.

However, actual pressure drop depends on:

• ring size
• vapor rate
• liquid rate
• tower diameter
• bed height
• packing condition

---

8. Pall Ring Size Must Be Selected Carefully

Stainless steel Pall Rings are available in different nominal sizes.

The size influences both mass transfer and hydraulic performance.

Smaller Pall Ring

Generally provides:

• more elements per unit volume
• more available contact surface
• more frequent liquid redistribution

But it may also create:

• higher pressure drop
• smaller flow passages
• greater sensitivity to deposits

Larger Pall Ring

Generally provides:

• larger vapor passages
• lower hydraulic resistance
• higher vapor capacity
• lower number of elements per cubic meter

But potentially less contact area per unit packed volume.

Therefore, selecting the smallest ring simply to maximize surface area is not always the best deaerator design.

The packing size must balance:

contact efficiency + vapor capacity + allowable pressure drop.

---

9. Packing Size Must Match Tower Diameter

Large random packing used in a small-diameter column can create strong wall effects.

The packing arrangement near the vessel wall differs from the arrangement in the center of the bed.

This can lead to:

• uneven flow
• reduced effective contact
• preferential vapor paths

Therefore, packing size should always be reviewed relative to the deaerator diameter.

A ring that is perfectly suitable for a large industrial vessel may be too large for a small packaged deaerator.

---

10. What About Metal Raschig Ring?

Older deaeration equipment may contain simple metallic Raschig Rings.

Raschig Ring is mechanically simple and still usable in some applications.

However, Pall Ring geometry provides more open wall area and internal structure.

For a retrofit, Pall Ring may therefore be considered where the objective is to obtain:

• more open vapor flow
• improved water spreading
• reduced hydraulic restriction
• better utilization of packing volume

But this should not automatically be treated as a direct replacement.

The new packing may differ in:

• packing factor
• surface area
• bulk density
• pressure drop
• bed weight

A retrofit should be checked rather than simply replacing equal cubic meters without review.

---

11. When Stainless Steel Pall Ring Is a Strong Candidate

Stainless steel Pall Ring is particularly worth considering when:

Elevated Temperature Rules Out Ordinary Plastic

The thermal environment favors metallic packing.

Random Packing Is Preferred

The equipment design does not require highly engineered structured packing.

Mechanical Durability Is Important

The packing may undergo maintenance, handling, or long service.

Steam/Vapor Capacity Matters

An open ring geometry helps maintain usable vapor passages.

Existing Equipment Already Uses Random Metal Packing

A Pall Ring retrofit may be relatively straightforward to evaluate.

---

12. When Structured Packing May Be Better

Pall Ring is not automatically the best packing for every deaerator.

Structured packing may be worth evaluating when the project requires:

• highly controlled liquid distribution
• very low pressure drop
• predictable mass-transfer performance
• specific proprietary deaeration designs

Structured packing generally requires more deliberate engineering and installation.

For many conventional industrial packed sections, however, random metallic packing can remain attractive because of simplicity, availability, and robustness.

---

13. Fouling and Deposits Still Matter

Boiler feedwater is normally cleaner than many wastewater streams, but deposits can still occur if water treatment or operating conditions are poor.

Possible issues include:

• mineral deposits
• iron oxides
• suspended solids
• treatment-chemical residues

Deposits can reduce:

• packing openness
• liquid distribution
• vapor flow area

If an existing deaerator develops increasing pressure drop or declining performance, the bed should be inspected before assuming the packing geometry is inadequate.

The real issue may be contamination or upstream water treatment.

---

14. The Packing Support Must Remain Open

Packing support design is especially important because both liquid and vapor must pass through it.

The support must:

• carry the wet packing load
• retain the Pall Rings
• provide sufficient open area
• withstand operating temperature
• resist corrosion

A restrictive or partially blocked support can become a larger hydraulic bottleneck than the packing itself.

Therefore, replacing packing without inspecting the support may fail to correct an existing capacity problem.

---

15. Retrofit Projects Need Operating Data

For an existing feedwater deaerator, the replacement decision should begin with the actual operating issue.

Examples include:

• dissolved oxygen remains too high
• packing is damaged
• existing rings are heavily corroded
• vapor flow is restricted
• capacity must increase
• water distribution is uneven

Each problem suggests a different solution.

For example:

High residual oxygen does not automatically mean the packing is wrong.

The cause may instead be:

• insufficient heating
• poor steam distribution
• poor venting
• inadequate water distribution

This should be diagnosed before changing the packing.

---

16. Stainless Steel Pall Ring vs Plastic Pall Ring

In low-temperature water treatment, plastic Pall Ring may be economically attractive.

For thermal deaeration, the decision changes.

The material decision should follow actual operating temperature and water chemistry.

---

17. What Data Are Needed for an RFQ?

For preliminary selection of stainless steel Pall Ring for a boiler feedwater deaerator, useful information includes:

• deaerator internal diameter
• operating pressure
• water flow rate
• steam flow rate
• feedwater temperature
• outlet water temperature
• current dissolved oxygen level
• required dissolved oxygen level
• packed-bed height
• current packing type
• current packing size
• existing material
• chloride concentration where relevant
• water-treatment chemistry
• packing support details
• available drawings

For retrofit projects, the current operating problem should also be clearly described.

---

Final Selection Principle

Stainless steel Pall Ring can be a practical random packing for packed boiler feedwater deaerators because it provides:

metallic temperature resistance + mechanical strength + open vapor passages + water redistribution.

But deaeration performance cannot be determined from the packing alone.

The complete process depends on:

• water temperature
• steam rate
• operating pressure
• water and vapor distribution
• venting
• packing size
• packed height
• tower geometry

The correct engineering question is therefore:

Does the selected stainless steel Pall Ring provide sufficient steam-water contact without creating unnecessary hydraulic resistance under the actual deaerator operating conditions?

That is the basis for a reliable packing specification.