Plastic Raschig Ring vs Plastic Ralu Ring: Which Random Packing Should You Select?

Plastic Raschig Ring and Plastic Ralu Ring are both lightweight plastic random packings, but their relative engineering positions change significantly with size. DAIER's comparable product data show that Plastic Raschig Ring has the stronger surface-area and void-fraction position at 25 mm, while 38 and 50 mm Ralu Ring provides both higher geometric surface area and higher void fraction. At the larger 80–90 mm class, the relationship changes again.

This means there is no valid universal rule such as:

Ralu Ring is always more open than Raschig Ring.

or:

Rasching Ring always provides less contacting area.

The correct question is:

At the required size class, which exact geometry provides the better balance of surface area, void fraction, packed-bed weight, element population and hydraulic requirements?

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1. Direct Answer

Choose Plastic Raschig Ring more readily when:

• simple cylindrical geometry is preferred;
• existing Raschig Ring operation is already proven;
• like-for-like replacement is important;
• the selected Raschig size has a favorable verified hydraulic position;
• simpler flow paths are desirable for fouling-sensitive service.

Evaluate Plastic Ralu Ring more strongly when:

• the 38 or 50 mm size class is being considered;
• higher catalog void fraction is attractive;
• maintaining or increasing geometric surface area is useful;
• reducing dry packed-bed weight matters;
• a more developed ring geometry is desired.

The important point is:

The answer changes with size.

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2. Comparable DAIER Product Data

The strongest exact comparisons are at:

• 25 mm;
• 38 mm;
• 50 mm.

A larger near-size comparison is also possible between:

• 80 mm Plastic Raschig Ring;
• 90 mm Plastic Ralu Ring.

The 80/90 mm pair is a near-size-class comparison, not an exact same-size comparison.

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3. The 25 mm Result Favors Raschig Ring Geometrically

At 25 mm:

Plastic Raschig Ring

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

Plastic Ralu Ring

• 190 m²/m³ surface area;
• 88% void fraction;
• 46.8 kg/m³ bulk density;
• 36,000 pcs/m³.

At this size, Plastic Raschig Ring provides:

• more geometric surface area;
• higher void fraction.

Ralu Ring provides:

• much lower dry bed weight;
• fewer packing elements.

So 25 mm already shows a real engineering trade-off.

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4. 25 mm Ralu Ring Is Not Simply an “Improved Raschig Ring”

The 25 mm data are important because a buyer may assume that the more developed Ralu geometry must automatically provide:

• more surface area;
• more voidage.

It does not.

At this exact size:

Raschig Ring → 205 m²/m³ / 90% void

versus:

Ralu Ring → 190 m²/m³ / 88% void.

Therefore:

a more complex packing geometry does not automatically improve every physical property.

Exact supplier data are more useful than product reputation.

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5. But Ralu Ring Is Dramatically Lighter at 25 mm

Dry bulk density changes from:

Raschig Ring

112 kg/m³

to:

Ralu Ring

46.8 kg/m³.

That is approximately:

65 kg/m³ lower dry packing weight.

For a 20 m³ packed bed:

Raschig Ring

20 × 112 = 2,240 kg

Ralu Ring

20 × 46.8 ≈ 936 kg

Difference:

approximately 1.3 tonnes of dry packing.

This can matter for:

• tower-support loading;
• lightweight vessels;
• shipping;
• installation handling.

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6. Lower Weight Does Not Mean Better Process Performance

A lower bulk density tells us about:

• material mass per packed volume.

It does not directly establish:

• mass-transfer efficiency;
• operating pressure drop;
• tower capacity.

Therefore the 25 mm choice is not:

lighter = better.

It is:

Raschig → More Area + More Voidage

versus:

Ralu → Much Lighter + Fewer Elements.

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7. 38 mm Completely Reverses the Main Ranking

At 38 mm:

Plastic Raschig Ring

• 130 m²/m³;
• 89% void;
• 70 kg/m³;
• 19,000 pcs/m³;
• 305 m⁻¹ packing factor.

Plastic Ralu Ring

• 150 m²/m³;
• 95% void;
• 65 kg/m³;
• 13,500 pcs/m³.

Now Ralu Ring provides:

• more surface area;
• substantially higher void fraction;
• lower bulk density;
• fewer packing elements.

This is very different from the 25 mm comparison.

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8. Why the 38 mm Comparison Is So Important

Surface area changes from:

130 → 150 m²/m³

while void fraction rises from:

89% → 95%.

Normally, engineers expect a trade-off between:

• more contacting area;
• more open bed volume.

But in this exact comparison, Ralu Ring improves both catalog parameters.

That makes 38 mm Ralu Ring a strong candidate when the design wants:

higher geometric area without sacrificing catalog voidage.

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9. But We Still Cannot Claim Lower Ralu Pressure Drop

DAIER's verified Plastic Raschig Ring dataset provides:

305 m⁻¹

dry packing factor at 38 mm.

The current verified Ralu Ring dataset does not provide a corresponding dry packing factor.

Therefore it would be incorrect to write:

38 mm Ralu Ring definitely has lower pressure drop.

Higher void fraction is favorable for hydraulic screening.

But actual pressure drop still requires:

• gas flow;
• liquid flow;
• fluid properties;
• tower diameter;
• packed height;
• suitable hydraulic data.

Missing packing-factor data should remain missing.

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10. 38 mm Ralu Ring Also Has Fewer Elements

Packing populations are:

Raschig Ring

19,000 pcs/m³.

Ralu Ring

13,500 pcs/m³.

So Ralu Ring achieves:

• higher surface area;
• higher voidage;

with:

• fewer individual packing pieces.

This tells us something important:

the individual Ralu element makes more efficient use of its geometry than the simple cylindrical ring at this size.

That is a genuine product-level distinction.

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11. 50 mm Strengthens the Ralu Position

At 50 mm:

Plastic Raschig Ring

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

Plastic Ralu Ring

• 110 m²/m³;
• 95% void;
• 53.5 kg/m³;
• 6,300 pcs/m³.

Here the packing population is almost identical.

Yet Ralu Ring provides:

• more surface area;
• higher void fraction;
• lower dry bed weight.

That makes 50 mm one of the strongest direct Ralu Ring screening cases.

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12. The 50 mm Packing Count Is Almost the Same

Raschig Ring

6,500 pcs/m³.

Ralu Ring

6,300 pcs/m³.

Difference:

only about 200 elements/m³.

Yet:

Surface Area

93 → 110 m²/m³.

Void Fraction

90 → 95%.

Bulk Density

68 → 53.5 kg/m³.

This is an excellent example of why:

pieces per cubic meter alone tells very little about packed-bed performance.

Individual geometry matters much more.

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13. What Does 50 mm Ralu Ring Actually Gain?

Compared with 50 mm Raschig Ring, Ralu provides approximately:

Surface Area

17 m²/m³ more.

Void Fraction

5 percentage points more.

Dry Bed Weight

14.5 kg/m³ less.

Packing Population

Almost unchanged.

So if all catalog values are confirmed for the exact proposed product:

50 mm Ralu Ring deserves serious consideration as an alternative to 50 mm Plastic Raschig Ring.

But actual process performance still needs project conditions.

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14. This Does Not Mean Ralu Ring Is Universally Better

The 25 mm comparison already disproves that.

At 25 mm:

Raschig has more area and more voidage.

At 38 and 50 mm:

Ralu has more area and more voidage.

Therefore:

the relative engineering position of the two packing families reverses with size.

That is the central reason this comparison needs its own page.

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15. Surface-Area Ranking Changes with Size

So there is no valid general statement:

Ralu always provides higher surface area.

Nor:

Raschig always provides higher surface area.

The answer depends on exact size.

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16. Void-Fraction Ranking Also Changes

Again, the 25 mm model behaves differently.

This is another reason why:

a family-level statement should never replace supplier-specific size data.

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17. Bulk Density Gives Ralu Ring a Consistent Advantage in These Sizes

At the directly matched sizes:

25 mm

112 vs 46.8 kg/m³

38 mm

70 vs 65 kg/m³

50 mm

68 vs 53.5 kg/m³

Ralu Ring is lighter in all three comparisons.

But the magnitude of the advantage varies strongly.

At 25 mm:

very large.

At 38 mm:

relatively small.

At 50 mm:

moderate.

So even this advantage is size-dependent in importance.

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18. Around 80–90 mm, the Relationship Changes Again

The closest large-size comparison is:

Plastic Raschig Ring 80 mm

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

Plastic Ralu Ring 90 mm

• 75 m²/m³;
• 90% void;
• 40 kg/m³;
• 1,000 pcs/m³.

These are not exact same-size products.

But they show another important large-size trend.

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19. Large Raschig Ring Regains the Surface-Area Advantage

At approximately the 80–90 mm class:

Raschig

90 m²/m³.

Ralu

75 m²/m³.

The Raschig Ring has approximately:

20% greater geometric surface area

in this near-size comparison.

So the 38/50 mm Ralu advantage does not simply continue indefinitely into larger sizes.

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20. Large Raschig Ring Also Has Higher Void Fraction Here

At this near-size class:

Raschig 80 mm

95%.

Ralu 90 mm

90%.

So the ranking reverses again.

This reinforces the core principle:

Do not extrapolate a packing family's 38 or 50 mm behavior to its 80–90 mm models.

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21. But 90 mm Ralu Ring Remains Much Lighter

Bulk density:

Raschig 80 mm

66 kg/m³.

Ralu 90 mm

40 kg/m³.

Ralu also has:

• only 1,000 pcs/m³

compared with:

• 1,820 pcs/m³

for the 80 mm Raschig Ring.

So the large Ralu model remains the:

lighter / coarser element-population option

in this near-size comparison.

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22. Why Large-Size Comparison Requires Extra Caution

80 mm and 90 mm are not identical nominal dimensions.

Therefore the data should be used to understand:

product positioning

rather than to claim a strict same-size performance advantage.

For final engineering selection:

compare the exact commercially available model that fits the tower diameter and project duty.

Never hide a near-size comparison as if it were exact.

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23. Which Is Better for High Contacting-Area Priority?

The answer depends on size.

At 25 mm

Raschig Ring has more catalog area.

At 38–50 mm

Ralu Ring has more area.

At the large ~80–90 mm class

Raschig Ring again has more area in the available near-size comparison.

Therefore:

contact-area selection is model-specific, not family-specific.

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24. Which Is Better for High Void Fraction?

Same answer:

25 mm

Raschig.

38 mm

Ralu.

50 mm

Ralu.

~80–90 mm

Raschig in the current near-size comparison.

This is one of the clearest examples in the DAIER random-packing database of why:

“Which product is more open?” is incomplete without a size.

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25. Which Is Better for Low Bed Weight?

Ralu Ring has a strong advantage across the directly compared sizes.

This can be useful for:

• FRP scrubbers;
• lightweight towers;
• older support structures;
• retrofit projects;
• freight-sensitive export shipments.

But tower design must still account for:

• liquid holdup;
• support weight;
• operating loads.

Dry bulk density is not the total operating load.

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26. Which Is Better for Fouling?

There is no universal winner, but geometry gives some preliminary clues.

Raschig Ring

has:

• simple cylindrical passages;
• fewer internal geometric features.

Ralu Ring

uses a more developed open-ring geometry.

At 38 and 50 mm, Ralu also has:

• higher verified void fraction.

This may make it attractive in certain moderate-fouling applications.

However:

simple Raschig geometry can still be valuable where deposits are sticky, crystalline or difficult to remove.

Fouling mechanism matters more than product marketing.

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27. Do Not Use Void Fraction Alone to Select for Fouling

A bed can have high void fraction and still foul because deposits occur on:

• surfaces;
• element contacts;
• support grids.

Fouling selection should consider:

• particle size;
• crystal growth;
• solids concentration;
• biological activity;
• cleaning method.

Neither packing is:

• self-cleaning;
• non-clogging.

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28. Which Is Better for High Gas Throughput?

38 and 50 mm Ralu Ring deserve strong hydraulic screening because they provide:

• 95% verified voidage.

But the absence of verified dry packing factor means we should not automatically conclude:

lower pressure drop than Raschig Ring.

Raschig Ring has known dry packing factors:

• 38 mm — 305 m⁻¹;
• 50 mm — 177 m⁻¹;
• 80 mm — 130 m⁻¹.

Actual hydraulic selection requires operating data.

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29. Which Is Better for Scrubbers?

Both can be used in suitable scrubber systems.

Raschig Ring may move higher when:

• simple geometry is preferred;
• service history is proven;
• larger open rings are used;
• fouling simplicity matters.

Ralu Ring may move higher when:

• 38–50 mm high voidage is useful;
• lighter packing is valuable;
• higher geometric area in those size classes is attractive.

But:

“scrubber” is not enough information to select a packing.

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30. Required Scrubber Data

A meaningful comparison requires:

• tower ID;
• gas flow;
• liquid circulation rate;
• gas composition;
• liquid chemistry;
• required removal;
• temperature;
• fouling/solids information;
• available packed height;
• allowable pressure drop.

Without these inputs:

the article can identify candidate positions but cannot guarantee the final packing choice.

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31. Existing Raschig Ring Tower: Should You Change to Ralu Ring?

A Ralu retrofit may deserve evaluation when:

• bed weight should be reduced;
• 38 or 50 mm is the relevant size class;
• more verified surface area is useful;
• higher void fraction is attractive.

For example, at 50 mm:

Raschig

93 m²/m³90% void68 kg/m³

Ralu

110 m²/m³95% void53.5 kg/m³.

That creates a legitimate engineering reason to evaluate conversion.

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32. But Do Not Convert a Successful Tower Without a Reason

If the Raschig Ring tower already has:

• acceptable pressure drop;
• sufficient capacity;
• required removal;
• manageable fouling;

then like-for-like Raschig replacement may remain the lowest-risk option.

Existing operating history has real value.

A theoretically attractive alternative should solve a specific problem.

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33. Existing Ralu Ring Tower: Should You Change to Raschig Ring?

Possible reasons include:

• supplier availability;
• desire for simpler geometry;
• specific fouling experience;
• a large-size Raschig model better fits the new operating condition.

But the geometry change may alter:

• area;
• voidage;
• bed weight;
• hydraulic behavior.

Therefore:

Ralu → Raschig is an engineering retrofit, not a simple substitution.

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34. Same Nominal Size Does Not Mean Equivalent Packing

The 25 mm comparison proves this.

Both are called:

25 mm.

But one has:

• 205 m²/m³;
• 90% void;
• 112 kg/m³;

and the other:

• 190 m²/m³;
• 88% void;
• 46.8 kg/m³.

Therefore nominal size is only one specification field.

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35. Do Not Automatically Keep the Same Packed Height

Changing packing geometry can change:

• geometric area;
• wetting;
• voidage;
• element distribution.

Therefore:

same nominal size + same bed height does not guarantee equivalent process performance.

Any Raschig ↔ Ralu conversion should review:

• mass-transfer duty;
• hydraulics;
• packed height.

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36. Tower Diameter Must Be Considered Before Size

A 90 mm Ralu Ring or 80 mm Raschig Ring requires sufficient tower diameter.

Large packing in a narrow column can create:

• wall effects;
• insufficient elements across the cross-section.

Therefore the selection sequence should normally be:

Tower Diameter → Appropriate Size Class → Compare Raschig / Ralu Geometry

rather than selecting the product family first.

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37. Polymer Compatibility Is a Separate Decision

Both are plastic random packings.

But:

plastic is not a material grade.

Actual material selection can depend on available products and may include:

• PP;
• other project-suitable polymers.

Compatibility depends on:

• exact chemical;
• concentration;
• temperature;
• solvent exposure;
• oxidizing conditions.

Do not select geometry correctly and then assume the polymer is automatically suitable.

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38. Support Grid Compatibility

Changing geometry or size should trigger a check of:

• support-grid opening;
• packing retention;
• structural load;
• open area.

This is especially important when changing between:

• large Ralu;
• smaller Raschig;

or the reverse.

A packing can only work correctly if the tower internals support it properly.

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39. Hold-Down Review

Both products are relatively light.

At high gas velocities, lightweight random packing can move.

Review:

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

The restraint should:

prevent excessive packing movement

rather than compress the bed.

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Decision Table

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40. Quick Selection Guide

At 25 mm

Raschig Ring has the stronger:

• surface area;
• voidage

position.

Ralu Ring is much lighter.

At 38 mm

Ralu Ring has the stronger:

• surface area;
• voidage;
• dry weight

position.

At 50 mm

Ralu Ring again provides:

• higher surface area;
• higher voidage;
• lower dry bulk density.

At the large ~80–90 mm class

Available data show:

• Raschig has higher area and voidage;
• Ralu remains lighter and coarser.

Therefore:

always compare the exact size—not just the product family.

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Common Selection Mistakes

Saying Ralu Ring Always Has More Surface Area

False at 25 mm and in the available large near-size comparison.

Saying Ralu Ring Always Has Higher Voidage

False at 25 mm.

Saying Raschig Ring Is Always the Simpler but Lower-Performance Packing

The actual physical ranking changes with size.

Claiming Ralu Ring Has Lower Pressure Drop Without Verified Data

Its current dry packing factor is not available in the verified dataset.

Using Bulk Density as a Performance Metric

Lower weight does not automatically mean better separation.

Assuming Same Nominal Size Means Same Bed

The 25 mm example clearly disproves this.

Treating 80 vs 90 mm as Exact Same-Size Data

It is only a near-size comparison.

Changing Packing Family Without Reviewing Bed Height

That is an engineered retrofit.

Ignoring Polymer Compatibility

Geometry and material selection are separate decisions.

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Frequently Asked Questions

Which is better: Plastic Raschig Ring or Plastic Ralu Ring?

Neither is universally better. Their relative surface area and void fraction change with size.

What is the 25 mm comparison?

Plastic Raschig Ring:

• 205 m²/m³;
• 90% void;
• 112 kg/m³;
• 50,000 pcs/m³;
• 400 m⁻¹.

Plastic Ralu Ring:

• 190 m²/m³;
• 88% void;
• 46.8 kg/m³;
• 36,000 pcs/m³.

Which has higher surface area at 38 mm?

Ralu Ring:

150 vs 130 m²/m³.

Which has higher void fraction at 38 mm?

Ralu Ring:

95% vs 89%.

What is the 50 mm comparison?

Raschig Ring:

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

Ralu Ring:

• 110 m²/m³;
• 95% void;
• 53.5 kg/m³;
• 6,300 pcs/m³.

Which is lighter?

Ralu Ring is lighter in all directly matched 25, 38 and 50 mm examples.

Does Ralu Ring always have lower pressure drop?

That cannot be concluded from the current verified data because matching dry packing-factor data are not available for Ralu Ring.

Which is better for fouling?

The answer depends on fouling mechanism and exact size. Raschig offers very simple passages, while some Ralu sizes provide very high voidage and fewer elements.

Can Ralu Ring directly replace Raschig Ring?

Do not treat it as like-for-like. Geometry and physical bed properties change.

Which is better for a scrubber?

Selection requires tower diameter, gas/liquid loads, removal duty, fouling and polymer compatibility.

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Selection Takeaway

Plastic Raschig Ring vs Plastic Ralu Ring is a strongly size-dependent comparison.

At 25 mm:

Raschig → 205 m²/m³ / 90% void / 112 kg/m³ / 50,000 pcs/m³

versus:

Ralu → 190 m²/m³ / 88% void / 46.8 kg/m³ / 36,000 pcs/m³.

Here Raschig provides more area and voidage, while Ralu is dramatically lighter.

At 38 mm:

Raschig → 130 m²/m³ / 89% void / 70 kg/m³

versus:

Ralu → 150 m²/m³ / 95% void / 65 kg/m³.

At 50 mm:

Raschig → 93 m²/m³ / 90% void / 68 kg/m³ / 6,500 pcs/m³

versus:

Ralu → 110 m²/m³ / 95% void / 53.5 kg/m³ / 6,300 pcs/m³.

So the engineering relationship reverses:

25 mm → Raschig has stronger area/voidage

while:

38–50 mm → Ralu has stronger area/voidage and lower dry weight.

At the larger ~80–90 mm class, the available near-size data show another reversal, with Raschig again providing higher surface area and void fraction while Ralu remains substantially lighter.

The correct selection sequence is:

Process Duty → Tower Diameter → Size Class → Required Contacting Area → Hydraulic Constraint → Fouling → Compare Exact Raschig/Ralu Product Data → Polymer Compatibility → Internals Review

The key principle is:

Never ask whether Ralu Ring is generally better than Raschig Ring. The useful engineering question is which exact size and geometry solves the tower's limiting condition—and the answer can reverse as the packing size changes.