Plastic Raschig Ring Replacement: What Must Be Matched Before Ordering?

Replacing Plastic Raschig Rings should not be handled by ordering “the same nominal size” alone. A correct replacement specification should identify the existing polymer, nominal size, actual element dimensions, packed volume, physical properties, tower diameter, support-grid compatibility and the reason for replacement.

DAIER's catalog-confirmed Plastic Raschig Ring series includes nominal sizes of approximately 16, 25, 38, 50 and 80 mm, but their specific surface area, void fraction, bulk density, packing population and dry packing factor change substantially across the series.

The central procurement rule is:

Nominal size identifies only one part of the packing. It does not fully define the replacement product.

For routine maintenance, the safest target is usually:

same packing family + same polymer + same verified geometry + same physical specification

unless the project intentionally wants an engineering retrofit.

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1. Direct Answer

Before ordering replacement Plastic Raschig Rings, confirm:

• existing packing family;
• nominal size;
• actual outside diameter;
• actual height;
• wall thickness;
• polymer grade;
• packed-bed volume;
• specific surface area;
• void fraction;
• bulk density;
• pieces per cubic meter;
• dry packing factor where available;
• tower internal diameter;
• support-grid opening;
• hold-down arrangement;
• reason for replacement.

If the existing packing has operated successfully and the objective is only maintenance replacement:

Do not change geometry, material or size without a defined engineering reason.

That keeps the project closest to known operating performance.

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2. Why “Plastic Raschig Ring 50 mm” Is Not a Complete Specification

A buyer may send an RFQ saying:

Plastic Raschig Ring, 50 mm

This tells the supplier:

• product family;
• approximate nominal size.

But it does not confirm:

• polymer;
• exact dimensions;
• wall thickness;
• supplier-specific construction;
• physical bed properties.

Two products sold under the same nominal description may not necessarily produce identical:

• kg/m³;
• surface area;
• free volume;
• hydraulic characteristics.

Therefore:

nominal size should be treated as an identification field—not the entire technical specification.

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3. DAIER Plastic Raschig Ring Catalog Range

DAIER's catalog-confirmed data include:

These data show immediately why:

“Raschig Ring” alone is not enough.

A 16 mm bed and an 80 mm bed are completely different engineering systems.

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4. First Determine Whether This Is Replacement or Retrofit

There are two very different projects.

Like-for-Like Replacement

The objective is:

• restore the existing tower;
• preserve known operating behavior.

Normally keep:

• product family;
• polymer;
• size;
• physical specification.

Engineering Retrofit

The objective is to change:

• capacity;
• pressure drop;
• fouling behavior;
• mass-transfer performance;
• material compatibility.

Then a different:

• size;
• material;
• packing geometry

may be justified.

Do not confuse the two.

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5. Routine Replacement Should Minimize Variables

If the existing Plastic Raschig Ring tower has:

• acceptable capacity;
• acceptable pressure drop;
• required process performance;
• no serious fouling problem;

then replacement procurement should normally aim to reproduce the existing bed as closely as practical.

Changing several variables simultaneously can make it difficult to know why tower behavior changed after startup.

Therefore:

Maintenance replacement is primarily an identification problem.

Retrofit is an engineering-selection problem.

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6. Confirm the Existing Polymer

“Plastic” is not a complete material specification.

Possible polymer families can include, depending on product availability:

• PP;
• PVC;
• CPVC;
• PVDF;
• PTFE;
• other project-specific polymers.

The correct polymer matters because chemical and temperature compatibility depend on:

• exact chemical species;
• concentration;
• operating temperature;
• peak temperature;
• solvents;
• oxidizing conditions.

Do not specify replacement material from:

color

or:

appearance

alone.

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7. Why Polymer Identification Matters Even for the Same Geometry

Two Raschig Rings can have the same nominal geometry but use different polymers.

That can change:

• density;
• mechanical behavior;
• thermal limits;
• chemical resistance;
• product weight.

So an RFQ such as:

“same white plastic Raschig Ring”

is not sufficiently controlled.

The polymer should be confirmed from:

• historical purchase records;
• supplier documentation;
• material certificate;
• known operating specification.

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8. Do Not Identify Polymer Only by Visual Appearance

White, natural, gray or black appearance does not reliably establish:

• PP;
• PVDF;
• PVC;
• another polymer.

Fillers, pigments and production differences can also change appearance.

If material is uncertain:

state that the existing polymer is unknown rather than guessing.

Then provide:

• process chemistry;
• temperature;
• old packing sample if practical.

The supplier can evaluate the candidate material separately.

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9. Confirm Actual Piece Dimensions

Nominal size is a commercial designation.

For replacement procurement, confirm as much as possible about:

• outside diameter;
• element height;
• wall thickness.

This is especially important when:

• the original supplier is unknown;
• the packing is old;
• the tower has been operating for many years.

DAIER's current verified Raschig Ring catalog dataset provides nominal size and physical bed properties, but does not provide a complete actual-dimension field for every listed Plastic Raschig Ring model.

Therefore:

exact replacement dimensions should be physically confirmed rather than invented from nominal size.

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10. A Physical Sample Can Be Extremely Valuable

If drawings and historical records are unavailable, remove several undamaged pieces and measure:

• outside diameter;
• height;
• wall thickness.

Photograph the sample next to:

• ruler;
• caliper.

Also record:

• color;
• approximate rigidity;
• any markings.

For old towers:

one actual piece can sometimes prevent a much larger procurement error.

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11. Do Not Measure a Deformed Piece

Plastic packing may change after long service due to:

• heat;
• mechanical loading;
• chemical attack.

A distorted piece may no longer represent the original manufacturing dimensions.

Therefore use:

• several intact pieces;
• preferably from different tower locations.

If measurements vary significantly:

record the range instead of forcing one number.

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12. Specific Surface Area Should Be Confirmed

Specific surface area varies strongly with size.

DAIER's verified values fall from:

260 m²/m³ at 16 mm

to:

90 m²/m³ at 80 mm.

The 25 mm model provides:

205 m²/m³

while 50 mm provides:

93 m²/m³.

That is less than half.

Therefore accidentally replacing a smaller model with a substantially larger one can materially change the bed's geometric contacting area.

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13. Void Fraction Should Also Be Matched

The verified DAIER series shows:

• 16 mm — 91%;
• 25 mm — 90%;
• 38 mm — 89%;
• 50 mm — 90%;
• 80 mm — 95%. 

Notice something important:

void fraction is not monotonic.

It decreases from 16 to 38 mm, then rises again.

So a buyer should not assume:

larger size always means proportionally higher voidage.

Use the actual model data.

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14. Bulk Density Is Important for Quantity Verification

The catalog bulk densities are:

• 16 mm — 94 kg/m³;
• 25 mm — 112 kg/m³;
• 38 mm — 70 kg/m³;
• 50 mm — 68 kg/m³;
• 80 mm — 66 kg/m³. 

Notice another non-monotonic result:

25 mm is heavier per cubic meter than 16 mm.

Therefore:

do not estimate packing weight from nominal diameter alone.

Actual supplier bulk density should be used.

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15. Why Bulk Density Matters During Procurement

Suppose a tower needs:

12 m³ of replacement packing.

For 50 mm Plastic Raschig Ring using the catalog value:

12 × 68 ≈

816 kg

of theoretical dry packing.

For 25 mm:

12 × 112 ≈

1,344 kg.

Both fill the same theoretical bed volume.

But shipment mass differs by more than:

500 kg.

That affects:

• freight;
• handling;
• delivery verification.

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16. Order Quantity Should Normally Be Based on Packed Volume

Random packing replacement is usually specified primarily by:

• m³ of packing;

rather than simply:

• number of pieces.

Why?

A tower requires a physical packed volume based on:

• tower cross-sectional area;
• packed height.

The basic theoretical bed volume is:

Tower Cross-Sectional Area × Packed Height

Purchase allowance is a separate commercial/project decision.

Do not replace bed-volume specification with only:

“X pieces.”

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17. Pieces per Cubic Meter Are Still Valuable

Packing population is useful for:

• product identification;
• checking whether supplier data are comparable.

DAIER's series changes dramatically:

• 16 mm — 241,000 pcs/m³;
• 25 mm — 50,000;
• 38 mm — 19,000;
• 50 mm — 6,500;
• 80 mm — 1,820. 

This illustrates how dramatically the packed bed changes with nominal size.

But:

piece count should not replace volume as the primary tower-fill quantity.

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18. Packing Factor Is Another Useful Identification Field

DAIER's dry packing factors are:

• 16 mm — 490 m⁻¹;
• 25 mm — 400;
• 38 mm — 305;
• 50 mm — 177;
• 80 mm — 130. 

These values provide another way to detect whether two proposed products really occupy the same geometric position.

If the old and new supplier quote:

• same nominal size;

but very different:

• surface area;
• void fraction;
• packing factor;

the products should not automatically be treated as equivalent.

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19. Packing Factor Is Not Actual Tower Pressure Drop

A dry packing factor is useful in hydraulic characterization.

But actual pressure drop depends on:

• gas flow;
• liquid flow;
• fluid properties;
• tower diameter;
• bed height.

Therefore do not demand:

“same packing factor = guaranteed same pressure drop.”

It is an important comparison parameter—not a performance guarantee.

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20. Confirm Tower Internal Diameter

Tower ID matters even in a replacement project.

Why?

It helps confirm whether:

• the stated packing size is plausible;
• the old packing identification makes engineering sense;
• wall effects could be significant.

If someone reports:

80 mm Raschig Ring in a very small column

that deserves verification.

The replacement supplier should know the tower ID before making a final engineering confirmation.

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21. Confirm Existing Packed Height

Replacement quantity depends on actual packed height.

Do not rely only on:

• old purchase quantity.

Previous purchase quantities may have included:

• spare material;
• installation allowance;
• multiple beds.

Record:

• number of beds;
• height of each bed;
• tower diameter.

This creates a much more reliable replacement basis.

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22. Multi-Bed Towers Need Bed-by-Bed Confirmation

A tower may contain:

• several packed sections;
• redistributors between beds.

Do not assume every bed contains:

• the same packing;
• the same size;
• the same height.

During shutdown inspection, record each bed separately:

Bed 1 / Bed 2 / Bed 3

with:

• packing type;
• size;
• material;
• height.

This prevents procurement from treating the whole tower as one uniform bed when it is not.

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23. Support Grid Must Be Checked

The packing support must retain the smallest relevant dimension of the packing without creating excessive blockage.

When replacement geometry is truly like-for-like, support compatibility is usually easier.

But if the supplier proposes:

• smaller size;
• different shape;

the existing support may no longer be suitable.

Therefore include:

• support-grid photo;
• opening dimension

in a retrofit RFQ.

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24. Hold-Down Arrangement Should Be Recorded

Plastic random packing is lightweight.

At sufficiently high gas velocities, packing movement can become a concern.

The existing tower may use:

• hold-down grid;
• bed limiter;
• other restraint.

When replacing the packing, confirm whether the existing device:

• remains intact;
• matches the proposed packing.

A hold-down should:

restrain movement

rather than:

compress the bed.

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25. Why the Existing Packing Is Being Replaced Matters

The supplier needs to know whether the reason is:

• normal age;
• contamination;
• deformation;
• chemical attack;
• pressure-drop increase;
• fouling;
• capacity limitation;
• mechanical damage.

These are very different problems.

If old packing failed because of:

chemical attack

simply supplying the same polymer again may repeat the failure.

If it is only:

routine shutdown replacement

changing geometry may be unnecessary.

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26. Fouled Packing Should Not Be Used to Estimate Original Bulk Density

Used packing may contain:

• solids;
• salts;
• deposits;
• retained liquid.

Its measured field weight can therefore be much higher than clean catalog bulk density.

So:

do not identify the original product from used-bed kg/m³ alone.

Use:

• dimensions;
• product geometry;
• historical documentation;
• clean supplier data.

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27. Replacement Due to Fouling May Justify a Size Review

If the old tower repeatedly plugs or fouls, like-for-like replacement may reproduce the same maintenance problem.

Then the project may evaluate:

• larger Raschig Ring;
• another more open packing geometry;
• process-side fouling mitigation.

At that point:

the project is no longer simple replacement.

It becomes an engineered retrofit.

Hydraulic and mass-transfer effects must be reviewed.

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28. Do Not Increase Size Only Because Fouling Exists

For example, moving from 25 to 50 mm changes DAIER's catalog data from:

25 mm

• 205 m²/m³;
• 90% void;
• 400 m⁻¹.

to:

50 mm

• 93 m²/m³;
• 90% void;
• 177 m⁻¹. 

The packing factor falls substantially.

But geometric surface area also falls by more than half.

Therefore:

a fouling-driven size increase can create a mass-transfer trade-off.

Do not change size without reviewing required duty.

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29. 38 mm vs 50 mm Is Another Good Example

Moving from 38 to 50 mm changes:

• surface area: 130 → 93 m²/m³;
• void fraction: 89 → 90%;
• bulk density: 70 → 68 kg/m³;
• packing factor: 305 → 177 m⁻¹. 

Notice:

• bulk density barely changes;
• voidage barely changes;

while:

• surface area;
• packing factor

change significantly.

This shows again why replacement decisions cannot rely on:

weight and nominal size alone.

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30. 50 mm vs 80 mm Is Not a Simple “Bigger Is Better” Choice

DAIER data show:

50 mm

• 93 m²/m³;
• 90% void;
• 68 kg/m³;
• 6,500 pcs/m³;
• 177 m⁻¹.

80 mm

• 90 m²/m³;
• 95% void;
• 66 kg/m³;
• 1,820 pcs/m³;
• 130 m⁻¹. 

Interestingly, surface area changes only:

93 → 90 m²/m³

while void fraction increases and packing population falls dramatically.

This may make 80 mm attractive in some large-tower retrofit cases.

But tower diameter must be suitable for such a large packing element.

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31. Do Not Substitute a Different Packing Family Without Approval

A supplier may propose:

• Pall Ring;
• saddle-type packing;
• another open plastic packing

as an alternative.

That may be technically reasonable.

But it is no longer:

Plastic Raschig Ring replacement.

It is:

packing-family conversion.

That requires review of:

• geometry;
• surface area;
• hydraulics;
• packed height;
• support compatibility.

Alternative packing should therefore be shown clearly as:

Alternative Proposal

rather than silently replacing the requested product.

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32. Supplier Quotations Should Be Compared Parameter by Parameter

When comparing two offers, do not compare only:

• USD/m³.

Compare:

A lower price for a physically different product is not necessarily a comparable quotation.

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33. Ask the Supplier to State Missing Data Clearly

A good quotation does not need to invent every field.

If a parameter is:

• unavailable;
• not measured;
• not part of the product datasheet;

it should be marked accordingly.

That is better than copying an approximate value from another supplier.

For replacement procurement:

unknown data should remain unknown until verified.

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34. Packaging Method Matters for Plastic Random Packing

Plastic Raschig Rings are relatively light but occupy substantial volume.

Commercial shipment may be affected more by:

• cubic volume

than by:

• net weight.

The RFQ should therefore request:

• packing method;
• package dimensions;
• number of packages;
• gross volume;
• net/gross weight.

This is particularly useful for:

• sea freight;
• LCL shipments.

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35. Confirm Manway Size Before Replacement Installation

Packing must physically enter the tower.

For maintenance projects, confirm:

• manway size;
• access route.

This is less problematic for small individual Raschig Rings than for large modular internals, but access still affects:

• unloading method;
• removal logistics;
• installation sequence.

Do not separate procurement completely from field installation conditions.

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Plastic Raschig Ring Replacement Checklist

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36. Quick Procurement Logic

If the existing bed works well:

Specify:

same Plastic Raschig Ring family + same polymer + same size + matched physical properties.

If the old packing is chemically damaged:

Re-evaluate:

polymer compatibility.

If the old packing is thermally deformed:

Re-evaluate:

polymer + temperature capability.

If the old bed repeatedly fouls:

Re-evaluate:

size / geometry / process conditions.

If pressure drop is too high:

Do not simply buy larger packing.

Review:

hydraulics + required mass transfer + tower diameter.

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Common Replacement Mistakes

Ordering Only by Nominal Size

“50 mm Plastic Raschig Ring” is not a complete replacement specification.

Guessing the Polymer

Visual appearance does not reliably identify material.

Measuring Only One Used Piece

Old plastic can be deformed.

Comparing Supplier Price Without Comparing Physical Data

Different products can share the same commercial name.

Calculating Quantity Only from Old Shipment Weight

Packing quantity should be tied to actual bed volume.

Assuming Larger Size Always Has Higher Voidage

The catalog trends are not perfectly monotonic.

Assuming Larger Size Is Always Lighter

25 mm has higher bulk density than the 16 mm model in the verified series.

Changing Size Without Reviewing Mass Transfer

Surface area can change substantially.

Changing Polymer Without Chemical Review

Material compatibility is project-specific.

Accepting an Alternative Geometry as “Equivalent” Automatically

A different packing family is a retrofit.

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Frequently Asked Questions

What information is required to replace Plastic Raschig Rings?

At minimum, confirm packing family, polymer, nominal size, actual dimensions where possible, tower diameter, packed height and required quantity. Physical parameters such as surface area, void fraction, bulk density and packing factor should also be compared.

Is nominal size enough?

No. Nominal size does not fully define supplier-specific element geometry or packed-bed properties.

What sizes are shown in DAIER's Plastic Raschig Ring catalog data?

Approximately 16, 25, 38, 50 and 80 mm.

What is the 25 mm specification?

Approximately:

• 205 m²/m³ surface area;
• 90% void fraction;
• 112 kg/m³ bulk density;
• 50,000 pcs/m³;
• 400 m⁻¹ dry packing factor. 

What is the 50 mm specification?

Approximately:

• 93 m²/m³;
• 90% void;
• 68 kg/m³;
• 6,500 pcs/m³;
• 177 m⁻¹.

Should replacement packing always use the same size?

For routine maintenance, matching the proven existing size is usually the lowest-change starting point. If the project is trying to solve fouling, pressure-drop or capacity problems, size may be re-evaluated as an engineered retrofit.

Can a supplier substitute Pall Ring for Raschig Ring?

It can be offered as an alternative, but it should not be treated as a silent like-for-like substitution because the geometry and bed properties differ.

How should replacement quantity be specified?

Normally by required packed volume, supported by tower diameter and packed height.

Should used packing weight be used to identify bulk density?

Not by itself. Deposits and retained material can make used packing substantially heavier.

What if the existing polymer is unknown?

State that clearly and provide process chemistry, concentration, temperature and preferably an intact packing sample for evaluation.

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Selection Takeaway

Plastic Raschig Ring replacement is primarily a specification-control problem.

DAIER's verified product series shows why exact model identification matters:

16 mm → 260 m²/m³ / 91% void / 94 kg/m³ / 241,000 pcs/m³ / 490 m⁻¹

25 mm → 205 m²/m³ / 90% void / 112 kg/m³ / 50,000 pcs/m³ / 400 m⁻¹

38 mm → 130 m²/m³ / 89% void / 70 kg/m³ / 19,000 pcs/m³ / 305 m⁻¹

50 mm → 93 m²/m³ / 90% void / 68 kg/m³ / 6,500 pcs/m³ / 177 m⁻¹

80 mm → 90 m²/m³ / 95% void / 66 kg/m³ / 1,820 pcs/m³ / 130 m⁻¹.

These properties do not follow one simple rule.

For example:

• 25 mm is heavier per cubic meter than 16 mm;
• void fraction falls through 38 mm before rising;
• 50 → 80 mm changes packing population dramatically while surface area changes only slightly.

Therefore the replacement workflow should be:

Identify Existing Packing → Confirm Polymer → Measure Actual Element → Confirm Tower ID and Bed Height → Compare Supplier Physical Data → Check Support / Hold-Down → Define Replacement Quantity → Decide Whether This Is Truly Like-for-Like or an Engineering Retrofit

The key principle is:

Do not purchase an old tower's Plastic Raschig Ring replacement from the product name alone. Match the physical specification that created the proven packed bed—or clearly treat any change as a retrofit requiring engineering review.