PVDF Raschig Ring Packing: 25 vs 38 vs 50 mm Selection, Material Position and Limits

PVDF Raschig Ring is a fluoropolymer random packing used when a packed tower needs the simple cylindrical geometry of Raschig Rings together with stronger chemical and temperature capability than many conventional plastic materials can provide.

DAIER's engineering database contains three PVDF Raschig Ring size nodes:

• 25 mm;
• 38 mm;
• 50 mm. 

The main engineering decision is not simply:

“Is PVDF better than PP?”

It is:

Does the actual process require PVDF, and if so, should 25, 38 or 50 mm Raschig Ring be used to balance mass-transfer intensity, hydraulic openness, fouling tolerance and tower geometry?

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1. What Is PVDF Raschig Ring?

PVDF Raschig Ring is a plastic random packing made from polyvinylidene fluoride.

Its geometry is intentionally simple:

• cylindrical wall;
• open center;
• open top and bottom.

Individual rings are randomly loaded into the packed bed.

Unlike Pall Ring, the Raschig Ring does not use:

• side-wall windows;
• internal tongues;
• complicated molded flow structures.

Its engineering identity is therefore:

Simple Ring Geometry + PVDF Material Capability

This simplicity can be useful where engineers value predictable geometry, chemical compatibility and straightforward replacement.

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2. Why Choose PVDF Instead of Standard Plastic Packing?

Many packed towers operate successfully with conventional plastics such as PP.

PVDF becomes more relevant when the process conditions place stronger demands on:

• chemical compatibility;
• temperature resistance;
• long-term material stability.

This can occur in selected:

• chemical absorbers;
• corrosive scrubbers;
• specialty chemical processes;
• stripping systems.

However:

PVDF should not automatically replace PP whenever the process is described as corrosive.

If PP provides adequate compatibility and temperature margin, it may remain the more economical solution.

PVDF should solve a documented material problem.

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3. Verified DAIER Size Range

DAIER's Engineering Assistant separately lists:

• PVDF Raschig Ring 25 mm
• PVDF Raschig Ring 38 mm
• PVDF Raschig Ring 50 mm. 

The same database treats them as distinct random-packing selection nodes, meaning size is part of the engineering decision rather than simply a purchasing preference.

The general size direction is:

25 mm → Greater Contacting Intensity

38 mm → Intermediate Balance

50 mm → Greater Hydraulic Openness

Final performance still depends on actual operating conditions.

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4. Why Size Matters Even with the Same Material

Changing nominal ring size changes the packed bed.

Smaller elements generally create:

• more pieces per cubic meter;
• greater geometric surface density;
• more frequent gas-liquid contact points.

Larger elements generally create:

• fewer packing pieces;
• larger characteristic void spaces;
• stronger hydraulic openness.

Therefore:

Material selection and packing-size selection are two different decisions.

Choosing PVDF does not tell you whether the correct ring size is 25, 38 or 50 mm.

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5. When Should 25 mm PVDF Raschig Ring Be Considered?

The 25 mm size moves selection toward the finer end of this PVDF series.

It may deserve stronger consideration when:

• mass-transfer intensity is important;
• the process is relatively clean;
• tower diameter is relatively small;
• hydraulic loading is moderate.

A smaller packing bed can provide more frequent gas-liquid contacting opportunities.

But the trade-off can include:

• higher pressure-drop tendency;
• greater sensitivity to solids;
• increased plugging risk.

Therefore:

25 mm should not be selected only because smaller packing usually provides greater surface area.

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6. When Should 38 mm PVDF Raschig Ring Be Considered?

The 38 mm class occupies the middle of the verified DAIER series.

It may provide a useful compromise where:

• 25 mm appears unnecessarily fine;
• 50 mm sacrifices too much contacting intensity;
• hydraulic capacity and mass transfer both matter.

This can make 38 mm worth evaluating for many medium-size packed towers.

Its engineering position can be summarized as:

Balanced Size / Balanced Contacting and Openness

rather than an extreme efficiency or capacity choice.

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7. When Should 50 mm PVDF Raschig Ring Be Considered?

The 50 mm size moves the family toward a more open packed-bed structure.

It may deserve stronger consideration when:

• gas throughput is higher;
• allowable pressure drop is tighter;
• moderate fouling exists;
• tower diameter is sufficiently large.

The trade-off is reduced geometric surface density compared with smaller rings.

Therefore, 50 mm becomes stronger when:

Hydraulic margin matters more than maximizing contacting surface.

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8. 25 vs 38 vs 50 mm: Preliminary Decision Table

This is a selection direction, not a final hydraulic-performance guarantee.

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9. PVDF Raschig Ring vs PP Raschig Ring

This is primarily a material decision because the basic geometry can remain similar.

PP Raschig Ring

May be preferable when:

• process chemistry is compatible;
• operating temperature is moderate;
• project cost is important;
• large packing volume is required.

PVDF Raschig Ring

May deserve stronger consideration when:

• PP chemical resistance is insufficient;
• temperature margin is inadequate;
• longer-term material reliability requires a stronger fluoropolymer option.

The correct principle is:

Do not pay for PVDF unless the process requires PVDF.

Using a more expensive polymer does not automatically improve mass-transfer efficiency.

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10. PVDF Raschig Ring vs PTFE Raschig Ring

S130 covered PTFE Raschig Ring as a separate material node.

The distinction is important.

PVDF

Can occupy a middle fluoropolymer position where:

• conventional plastics are inadequate;
• PTFE may be unnecessary;
• process temperature and chemistry fit PVDF.

PTFE

May move higher when:

• chemistry becomes more demanding;
• higher material margin is required;
• PVDF does not provide sufficient compatibility.

Therefore, the material decision should usually be:

Use the lowest-cost compatible material with adequate engineering margin.

Not:

Always choose the chemically strongest polymer available.

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11. PVDF Raschig Ring vs PVDF Pall Ring

Both can use PVDF but have different geometries.

PVDF Raschig Ring

Uses:

• simple cylindrical wall;
• open central passage;
• no side-wall windows.

PVDF Pall Ring

Uses:

• wall openings;
• internal formed surfaces;
• more multidirectional flow.

DAIER's database separately lists PVDF Pall Ring and PVDF Raschig Ring in 25, 38 and 50 mm classes.

PVDF Pall Ring may deserve stronger consideration where:

• more open side flow;
• better internal volume utilization

are desired.

PVDF Raschig Ring may remain preferable where:

• simple geometry;
• replacement compatibility;
• process robustness

matter more.

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12. PVDF Raschig Ring vs Ceramic Raschig Ring

Both can be candidates for corrosive service, but their material behavior differs substantially.

Ceramic

May provide:

• strong temperature capability;
• useful resistance in many chemical environments.

But it is:

• heavy;
• brittle;
• chemically unsuitable for some services.

PVDF

Can provide:

• fluoropolymer chemical resistance;
• lower bed weight than many ceramic packings;
• easier handling.

But it has:

• polymer temperature limitations;
• material-specific chemical boundaries.

The choice should therefore begin with:

Chemistry + Temperature

before considering packing geometry.

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13. PVDF Raschig Ring vs Metal Raschig Ring

Metal Raschig Ring can offer:

• thin walls;
• high mechanical strength;
• strong hydraulic openness.

PVDF may become preferable where:

• metal corrosion is unacceptable;
• alloy cost is excessive;
• non-metallic construction is preferred.

If a suitable stainless steel or alloy performs reliably, metal may still provide advantages.

So the decision is not:

Plastic vs Metal

in the abstract.

It is:

Material Compatibility + Hydraulic Requirement + Mechanical Requirement + Cost

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14. Chemical Compatibility Must Use the Actual Chemical Stream

PVDF has strong resistance to many chemical environments, but no engineering polymer should be selected from a generic statement such as:

“The process is acidic.”

Material review should identify:

• exact chemicals;
• concentrations;
• temperature;
• solvents;
• oxidizers;
• cleaning chemicals;
• process upsets.

Two acidic streams can behave very differently toward the same polymer.

Therefore:

pH alone is not a PVDF compatibility specification.

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15. Temperature Must Also Be Project-Specific

DAIER's engineering-tool database places the PVDF family above conventional PP in its internal preliminary temperature screening, but those values are engineering-screening data rather than a universal production guarantee.

Final procurement should confirm:

• actual PVDF grade;
• continuous operating temperature;
• short-term upset temperature;
• chemical exposure at temperature.

This distinction is important because polymer performance depends on both:

Temperature + Chemical Environment

not temperature alone.

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16. Fouling Changes the Size Decision

PVDF material does not prevent packing fouling.

Deposits can still accumulate:

• inside Raschig Rings;
• between neighboring elements;
• at contact points.

Possible foulants include:

• salts;
• solids;
• scale;
• biological deposits;
• crystallized material.

As fouling severity increases, selection may move from:

25 mm

toward:

38 or 50 mm

to create a more open bed.

However, severe fouling may justify moving to a different packing geometry entirely.

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17. Why Simple Raschig Geometry Can Still Be Useful

Modern random packing often uses more complicated structures.

But more complicated does not always mean better.

The simple Raschig Ring has:

• straightforward flow passages;
• easily understood geometry;
• limited internal structural features.

That can be useful when the process values:

• simplicity;
• established replacement;
• predictable mechanical shape.

A project should select modern complex geometry only when it solves a real process requirement.

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18. Scrubber Applications

PVDF Raschig Ring may be evaluated in compatible scrubbers where:

• chemical resistance is important;
• conventional plastics provide insufficient material margin;
• simple random packing is acceptable.

Possible applications may include suitable:

• chemical exhaust treatment;
• acid-gas scrubbing;
• specialty process-gas treatment.

But the word “scrubber” alone cannot determine:

• size;
• material;
• packed height.

Actual operating conditions are required.

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19. Absorption Applications

PVDF Raschig Ring can also be considered for absorption systems.

Smaller sizes may provide stronger contacting intensity.

Larger sizes may provide stronger hydraulic margin.

Selection should consider:

• gas flow;
• liquid flow;
• required absorption duty;
• tower ID;
• bed height;
• fouling;
• pressure-drop limit.

The correct size depends on the limiting condition of the absorber.

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20. Stripping Applications

For compatible stripping service, the packing needs to provide:

• gas or air passage;
• liquid drainage;
• sufficient interfacial contact.

A 25 mm model may be more attractive where mass-transfer intensity dominates.

A 50 mm model may move higher when:

• gas load is larger;
• hydraulic openness becomes more important.

Again, size selection should follow process duty rather than habit.

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21. Tower Diameter Can Eliminate a Size

Packing should not be excessively large relative to tower diameter.

A 50 mm Raschig Ring in a relatively small tower may create:

• strong wall effects;
• too few packing elements across the tower;
• uneven random-bed behavior.

Likewise, 25 mm packing can be unnecessarily fine in a large high-throughput column.

Therefore:

Tower ID must be part of every final PVDF Raschig Ring RFQ.

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22. Retrofit Applications

PVDF Raschig Ring may be considered when replacing:

• PP Raschig Rings that have insufficient material resistance;
• existing PVDF rings;
• corroded metal packing;
• chemically unsuitable ceramic packing.

Before conversion, identify why the current packing is being replaced.

Was the problem:

• corrosion?
• temperature?
• fouling?
• pressure drop?
• poor mass transfer?
• mechanical damage?

If the real problem is hydraulic or liquid distribution, changing to PVDF alone will not solve it.

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23. Support Grid Review

When changing:

• packing size;
• packing material;

the support system should be checked.

Confirm:

• support opening size;
• support load;
• packed volume;
• wet operating load.

A smaller new Raschig Ring must not be able to pass through the existing support openings.

For retrofit work, support compatibility should be confirmed before procurement.

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24. What Should Be Included in an RFQ?

A useful PVDF Raschig Ring RFQ should include:

• required packing type;
• nominal size;
• required quantity;
• tower ID;
• bed height;
• process chemicals;
• chemical concentrations;
• operating temperature;
• pressure;
• gas load;
• liquid load;
• fouling or solids information.

Also request confirmation of:

• PVDF grade;
• element dimensions;
• bulk density;
• void fraction;
• specific surface area if available;
• packing quantity per cubic meter;
• temperature limitation;
• packing method;
• net and gross weight.

For replacement projects, include details of the existing packing.

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Common Selection Mistakes

Choosing PVDF Simply Because It Is More Chemical-Resistant Than PP

PVDF should solve an actual compatibility requirement.

Assuming PVDF Automatically Improves Tower Efficiency

Material and geometry are separate decisions.

Selecting 25 mm Only Because It Is Smaller

Hydraulic margin and fouling still matter.

Selecting 50 mm Only for More Openness

Mass-transfer requirements may favor a smaller size.

Treating PVDF Raschig Ring and PVDF Pall Ring as the Same Product

They use different geometries.

Assuming PVDF Is Equivalent to PTFE

They are different fluoropolymers with different engineering and commercial positions.

Using a Generic Temperature Number as a Guarantee

Final limits should come from the actual supplied PVDF grade and operating environment.

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Frequently Asked Questions

What is PVDF Raschig Ring?

PVDF Raschig Ring is a cylindrical fluoropolymer random packing used in gas-liquid contacting towers where PVDF provides the required material compatibility.

What sizes are represented in DAIER's engineering database?

The database includes 25, 38 and 50 mm PVDF Raschig Ring models.

Which size should be selected?

25 mm generally favors contacting intensity, 38 mm provides an intermediate balance, and 50 mm favors hydraulic openness.

Is PVDF better than PP for Raschig Rings?

Only when the chemistry or temperature requires PVDF. If PP is fully suitable, PVDF may add unnecessary cost.

Is PVDF better than PTFE?

Not universally. PTFE may be needed for more demanding conditions, while PVDF can provide a useful intermediate material solution.

Is PVDF Raschig Ring the same as PVDF Pall Ring?

No. Raschig Ring has a simple cylindrical structure; Pall Ring includes side-wall openings and additional internal surfaces.

Is PVDF Raschig Ring suitable for fouling service?

Larger sizes may provide better tolerance for moderate fouling, but severe fouling can still restrict the packed bed.

Can PVDF Raschig Ring replace PP Raschig Ring?

Potentially. Material compatibility, packing size, bed weight, hydraulics, support-grid compatibility and tower performance should all be reviewed.

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Selection Takeaway

PVDF Raschig Ring occupies an important material position between conventional plastic random packing and more specialized fluoropolymer solutions such as PTFE.

Its engineering logic is two-stage:

First: Does the process genuinely require PVDF?

Then:

Second: Which size gives the correct mass-transfer/hydraulic balance?

The general size direction is:

25 mm → Greater Contacting Intensity

38 mm → Balanced Position

50 mm → Greater Hydraulic Openness

The correct selection sequence is:

Chemistry → Temperature → PVDF Justification → Mass-Transfer Requirement → Gas/Liquid Load → Fouling → 25/38/50 mm → Tower Diameter → Support Review

The key principle is:

Use PVDF Raschig Ring when PVDF provides a real compatibility advantage and the simple Raschig geometry matches the tower duty—not simply because PVDF is a higher-grade plastic.