When Should Ceramic Raschig Rings Be Replaced with Plastic Raschig Rings?

Replacing Ceramic Raschig Rings with Plastic Raschig Rings can dramatically reduce packed-bed weight and change void fraction, packing factor and hydraulic behavior without necessarily sacrificing geometric surface area. However, the conversion is only appropriate when the selected polymer can safely tolerate the actual chemical system and operating temperature.

In DAIER's comparable 25, 38 and 50 mm catalog data, Plastic Raschig Ring provides similar or slightly higher specific surface area than Ceramic Raschig Ring while providing much higher void fraction and dramatically lower dry bulk density.

At 80 mm, the difference becomes even larger.

The real retrofit question is therefore:

Can the existing ceramic bed be replaced by a much lighter and more open plastic bed without losing the temperature, chemical-resistance or mechanical properties that made ceramic necessary in the first place?

That is the decision this article addresses.

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1. Direct Answer

Consider replacing Ceramic Raschig Rings with Plastic Raschig Rings when:

• the process temperature is within the verified limit of the selected polymer;
• the polymer is chemically compatible with the actual process stream;
• reducing packed-bed weight is valuable;
• lower packing-factor geometry is desirable;
• the existing ceramic bed has breakage or handling problems;
• a lighter retrofit can reduce support loading;
• the process does not specifically require ceramic temperature resistance.

Keep Ceramic Raschig Rings when:

• operating temperature exceeds the safe range of available polymers;
• ceramic compatibility with the process is proven while polymer compatibility is uncertain;
• the service involves conditions for which ceramic is specifically required;
• existing ceramic performance is satisfactory and there is no defined retrofit objective.

The governing rule is:

Do not replace ceramic merely because plastic is lighter. Replace it only when the polymer is technically suitable and the lighter, more open bed solves a real project constraint.

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2. DAIER Plastic vs Ceramic Raschig Ring Data

The strongest direct comparisons occur at:

• 25 mm;
• 38 mm;
• 50 mm;
• 80 mm.

These are supplier-specific physical data. Final procurement should confirm the exact selected model and material grade.

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3. The Biggest Retrofit Difference Is Bed Weight

Ceramic Raschig Rings are heavy.

Plastic Raschig Rings are dramatically lighter.

At 25 mm:

112 vs 650 kg/m³

At 38 mm:

70 vs 650 kg/m³

At 50 mm:

68 vs 600 kg/m³

At 80 mm:

66 vs 660 kg/m³

The difference can reach almost:

one order of magnitude.

This makes packed-bed load one of the strongest reasons to investigate a ceramic-to-plastic retrofit.

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4. What Does This Mean in a Real Packed Bed?

Consider a 20 m³ packed volume.

Using catalog dry bulk density:

50 mm Ceramic Raschig Ring

20 × 600 =

12,000 kg

of dry packing.

50 mm Plastic Raschig Ring

20 × 68 =

1,360 kg.

The difference is approximately:

10.64 tonnes of dry packing weight.

That is enormous from a mechanical-retrofit perspective.

Final structural calculations must also include:

• liquid holdup;
• deposits;
• support structure;
• operating loads.

But even dry packing alone shows why material conversion can transform tower loading.

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5. Why Lower Bed Weight Matters

A lighter random-packing bed can reduce load on:

• packing support grids;
• support beams;
• tower attachments;
• vessel structure.

It can also simplify:

• removal;
• installation;
• maintenance handling;
• transportation.

This can be especially valuable in:

• old towers;
• retrofit projects;
• towers with questionable support margins.

However:

weight reduction alone cannot override material compatibility.

A light packing that softens, swells or chemically degrades is not an improvement.

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6. Plastic Also Provides Much Higher Void Fraction

At every matched size, Plastic Raschig Ring has the higher catalog void fraction.

This difference is substantial.

The plastic bed contains much more free volume for:

• gas flow;
• liquid drainage.

That creates a strong reason to evaluate plastic where hydraulic capacity matters.

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7. Why Plastic Raschig Rings Can Be More Open

Plastic rings can be manufactured with relatively thin walls while remaining sufficiently robust for suitable service.

Ceramic packing requires:

• thicker ceramic walls

to maintain element integrity.

That additional solid volume reduces bed void fraction.

Therefore:

same nominal 50 mm diameter does not mean the plastic and ceramic beds occupy the same amount of solid volume.

Material and wall construction matter.

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8. Does Higher Void Fraction Guarantee Lower Pressure Drop?

No.

Actual tower pressure drop depends on:

• gas velocity;
• liquid flow;
• gas density;
• viscosity;
• packed height;
• liquid holdup.

Void fraction is important, but it is only one hydraulic descriptor.

That is why packing factor also needs to be considered.

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9. Packing Factor Generally Favors Plastic

The verified comparisons are:

25 mm

Plastic:

400 m⁻¹

Ceramic:

508 m⁻¹

38 mm

305 vs 312 m⁻¹

50 mm

177 vs 213 m⁻¹

80 mm

130 vs 280 m⁻¹

Plastic has the lower dry packing factor at all four directly matched sizes.

But the magnitude of the difference changes substantially.

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10. 38 mm Shows Why Generalizations Are Dangerous

At 38 mm:

• Plastic packing factor = 305 m⁻¹;
• Ceramic = 312 m⁻¹.

The difference is very small.

Yet void fraction differs dramatically:

• Plastic = 89%;
• Ceramic = 73%.

So even though one physical parameter changes strongly, another changes only slightly.

Therefore:

do not predict actual hydraulic improvement from void fraction or packing factor alone.

The tower operating point must be checked.

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11. 80 mm Is Completely Different

At 80 mm:

Plastic Raschig Ring

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

Ceramic Raschig Ring

• 46 m²/m³ surface area;
• 80% void;
• 660 kg/m³;
• 1,953 pcs/m³;
• 280 m⁻¹ packing factor.

At this particular size, Plastic Raschig Ring has:

• almost twice the geometric area;
• substantially higher void fraction;
• one-tenth the dry bulk density;
• less than half the dry packing factor.

This makes 80 mm a particularly strong candidate for engineering review when polymer compatibility allows it.

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12. Why the 80 mm Comparison Is So Valuable

Look at packing population:

Plastic

1,820 pcs/m³.

Ceramic

1,953 pcs/m³.

The number of individual elements is almost the same.

Yet surface area is:

90 vs 46 m²/m³.

So the difference cannot be explained simply by:

more pieces.

It comes from:

• individual element dimensions;
• wall geometry;
• material construction.

Again:

pieces per cubic meter is not a substitute for physical packing data.

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13. Surface Area Is Surprisingly Similar at 25–50 mm

Many engineers might assume that switching from ceramic to plastic drastically reduces contacting area.

DAIER's matched data do not support that assumption.

25 mm

Plastic:

205 m²/m³

Ceramic:

190 m²/m³.

38 mm

130 vs 121.

50 mm

93 vs 92.

At 50 mm they are almost identical.

That makes the retrofit question much more interesting.

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14. What Does the 50 mm Comparison Really Mean?

At 50 mm:

Geometric Surface Area

Almost unchanged:

93 vs 92 m²/m³.

Void Fraction

Plastic rises from:

74% → 90%.

Bulk Density

Falls from:

600 → 68 kg/m³.

Packing Factor

Falls from:

213 → 177 m⁻¹.

This is a very compelling preliminary retrofit position.

But only if the selected polymer survives the process environment.

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15. Ceramic's Main Advantage Is Not Geometric Surface Area

The comparison shows that ceramic does not automatically provide more geometric area.

Ceramic is instead selected because of material characteristics that may be valuable in suitable services, including:

• temperature capability;
• chemical resistance in appropriate environments;
• dimensional stability under heat.

Therefore:

The reason to retain ceramic should come from material requirements—not from assuming ceramic necessarily provides a better geometric packed bed.

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16. Temperature Is the First Major Retrofit Boundary

Plastic materials have temperature limitations.

And:

there is no single temperature limit for “plastic Raschig Ring.”

The actual polymer matters.

Possible materials can include:

• PP;
• PVC;
• CPVC;
• PVDF;
• PTFE;

depending on product availability and project requirements.

Each has a different:

• continuous-temperature capability;
• chemical-resistance envelope;
• mechanical behavior.

Therefore the ceramic-to-plastic evaluation starts with:

What polymer is being proposed?

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17. High Temperature Can Immediately Eliminate Plastic

If process temperature exceeds the confirmed safe limit of the available polymer:

Plastic Raschig Ring should not be selected.

This is especially important in:

• hot gas treatment;
• high-temperature absorption;
• thermal process applications.

Ceramic may remain the correct material even if:

• it is heavier;
• its void fraction is lower.

Material survival comes first.

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18. Chemical Compatibility Is the Second Major Boundary

Plastic may offer excellent corrosion resistance in many services.

But:

no plastic should be described as universally corrosion-resistant.

Compatibility depends on:

• chemical species;
• concentration;
• temperature;
• oxidizers;
• solvents.

Likewise ceramic compatibility depends on its:

• composition;
• chemical-resistance characteristics.

Do not choose from pH alone.

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19. Strong Alkali Requires Special Attention

“Ceramic” is not automatically compatible with every corrosive environment.

Depending on ceramic composition, alkaline resistance can differ significantly from acid resistance.

The same is true for polymers:

• one polymer may tolerate the stream;
• another may not.

Therefore the material decision should be based on:

actual chemical + concentration + temperature + verified material data

rather than simply:

acid = ceramic

or:

corrosive = plastic.

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20. Breakage Can Be a Strong Reason to Move Away from Ceramic

Ceramic random packing is inherently brittle.

During:

• unloading;
• installation;
• maintenance;
• repeated tower entry;

elements can break if handled improperly.

Broken packing can create:

• fragments;
• fines;
• altered bed geometry.

Where recurring mechanical breakage is a serious maintenance problem and the process is compatible with plastic:

Plastic Raschig Ring may deserve strong retrofit consideration.

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21. Plastic Does Not Have the Same Failure Mode

Plastic is less brittle than ceramic.

But it can experience different problems, such as:

• thermal deformation;
• chemical attack;
• long-term mechanical distortion.

So the trade-off is not:

fragile ceramic vs indestructible plastic.

It is:

different materials with different failure mechanisms.

The process determines which failure mode matters more.

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22. Installation Can Become Much Easier with Plastic

Compare 50 mm dry bulk density:

• Ceramic — 600 kg/m³;
• Plastic — 68 kg/m³.

Handling a large plastic packing volume can therefore be much easier than handling the equivalent ceramic mass.

This can reduce:

• lifting requirements;
• manpower;
• physical handling difficulty.

But installation procedures should still avoid:

• excessive impact;
• poor distribution;
• damage to internals.

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23. Existing Support Grid May Be More Than Strong Enough

Unlike a Plastic → Metal retrofit, a Ceramic → Plastic conversion reduces dry support load dramatically.

This generally moves structural loading in a favorable direction.

However, support compatibility still requires review because:

• element geometry;
• characteristic dimensions

may differ.

Check:

• support-grid opening;
• packing retention;
• hold-down arrangement.

A lighter bed can actually make restraint more important under high gas velocities.

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24. Hold-Down Requirements Can Change

Ceramic packing is very heavy.

Plastic packing is much lighter.

A high upward gas load can move lightweight plastic packing more readily.

Therefore a ceramic-to-plastic retrofit may require renewed review of:

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

The purpose is to:

restrain packing movement.

It should not compress the bed.

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25. Why Packing Weight Can Change Tower Dynamics

A heavy ceramic bed has substantial gravitational stability.

A plastic bed may weigh only a fraction as much.

Changing material can therefore affect:

• bed movement;
• startup behavior;
• upset response.

This is another reason why:

ceramic → plastic is an engineered retrofit, not merely a purchasing substitution.

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26. Existing Ceramic Tower: When Is Plastic Especially Attractive?

Plastic deserves strong review when all of the following are true:

• temperature is moderate;
• compatible polymer exists;
• ceramic breakage is problematic;
• tower support load is a concern;
• hydraulic capacity needs improvement;
• high-temperature ceramic capability is not actually needed.

In that case the retrofit can solve several constraints simultaneously.

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27. When Should You Keep the Existing Ceramic Packing?

Keep Ceramic Raschig Ring when:

• it is chemically proven;
• temperature requires ceramic;
• tower performance is satisfactory;
• breakage is not a problem;
• there is no capacity constraint.

A working packed tower has valuable operating history.

Replacing it simply because:

plastic has better catalog voidage

is not enough.

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28. Retrofit to Plastic Should Solve a Specific Problem

Good reasons include:

Problem 1: Excessive Dead Load

Plastic dramatically reduces dry packed-bed weight.

Problem 2: Ceramic Breakage

Plastic eliminates brittle ceramic fracture as the dominant handling failure mode.

Problem 3: Hydraulic Constraint

Higher void fraction and lower packing factor may create an attractive alternative.

Problem 4: Maintenance Difficulty

Much lower packing weight can simplify replacement handling.

But every benefit is conditional on:

material compatibility.

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29. Which Size Should Be Used After Conversion?

Do not automatically specify:

same nominal size.

Same-size replacement may be a useful starting point because it simplifies comparison.

But the project should review:

• tower diameter;
• gas flow;
• liquid flow;
• required mass transfer;
• allowable pressure drop;
• fouling.

Sometimes a different Plastic Raschig Ring size may better solve the actual problem.

At that point the project becomes:

material + size retrofit

rather than only a material retrofit.

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30. Do Not Automatically Keep the Same Packed Height

Even at the same nominal size, the bed characteristics change.

At 50 mm:

• surface area is almost identical;
• void fraction is very different;
• packing factor changes;
• surface wetting behavior changes.

Therefore:

same size + same height should not automatically be treated as guaranteed equivalent process performance.

Review the actual process duty.

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31. Fouling Can Influence the Decision

Plastic provides higher verified void fraction in all directly matched sizes.

That can be useful where bed openness matters.

However fouling behavior also depends on:

• solids;
• crystals;
• sticky deposits;
• biological growth;
• surface chemistry.

Neither Ceramic nor Plastic Raschig Ring should be called:

• self-cleaning;
• non-clogging.

For severe fouling, another packing geometry may be more appropriate.

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32. Do Not Choose Plastic Only Because It Is Cheaper

Purchase price may favor plastic in some projects.

But the correct comparison is:

technical suitability + installed lifecycle cost.

Consider:

• packing cost;
• freight;
• installation;
• support modifications;
• replacement frequency;
• shutdown labor;
• expected service life.

A cheaper material that must be replaced frequently may be more expensive over the tower lifecycle.

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Ceramic-to-Plastic Retrofit Decision Table

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33. Quick Retrofit Logic

Keep Ceramic Raschig Ring when:

• temperature requires it;
• material compatibility is proven;
• existing performance is good;
• mechanical load is acceptable.

Evaluate Plastic Raschig Ring when:

• operating temperature permits polymer use;
• chemical compatibility is confirmed;
• reducing bed weight has high value;
• breakage is a maintenance issue;
• hydraulic margin needs improvement.

Stop the plastic retrofit if:

• polymer compatibility is uncertain;
• temperature exceeds its confirmed limit;
• solvent/oxidizer exposure creates unacceptable material risk.

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34. What Information Is Required Before Conversion?

Provide:

• existing Ceramic Raschig Ring size;
• tower internal diameter;
• packed height;
• process application;
• gas composition;
• liquid composition;
• concentration;
• operating temperature;
• maximum temperature;
• operating pressure;
• gas flow;
• liquid flow;
• existing pressure drop;
• required process performance;
• fouling condition;
• reason for considering replacement.

Also provide:

• support-grid opening;
• hold-down arrangement;
• manway size;
• packing-bed volume.

For plastic selection, specify or request confirmation of:

• polymer type;
• chemical compatibility;
• project-specific temperature capability.

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35. What Should the Supplier Confirm?

For the proposed Plastic Raschig Ring:

• polymer grade;
• nominal size;
• actual dimensions;
• wall thickness;
• surface area;
• void fraction;
• bulk density;
• pieces per cubic meter;
• dry packing factor;
• chemical compatibility;
• temperature limits applicable to the exact polymer grade.

For the existing ceramic packing, confirm as much as possible about:

• size;
• wall thickness;
• physical properties;
• ceramic composition.

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Common Retrofit Mistakes

Assuming Plastic Is Always Better Because It Is Lighter

Temperature and chemical compatibility come first.

Assuming Ceramic Has More Surface Area

DAIER's matched 25–50 mm data do not support that assumption.

Ignoring the Huge Weight Difference

A ceramic bed can weigh many tonnes more.

Assuming Higher Voidage Guarantees a Specific Pressure-Drop Reduction

Actual operating conditions are required.

Using One Universal “Plastic Temperature Limit”

Different polymers have different limits.

Choosing Polymer from pH Alone

Chemical identity, concentration and temperature matter.

Assuming Plastic Cannot Break or Fail

Plastic has different failure modes including deformation and chemical degradation.

Forgetting Hold-Down Review

The new bed may be dramatically lighter.

Keeping the Same Bed Height Without Process Review

Material and hydraulic behavior change.

Choosing the Same Nominal Size Automatically

The retrofit objective may justify a different size.

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Frequently Asked Questions

Can Ceramic Raschig Rings be replaced with Plastic Raschig Rings?

Yes, when the selected polymer is compatible with the process chemistry and operating temperature and the retrofit meets the required hydraulic and mass-transfer duty.

Which is lighter?

Plastic Raschig Ring by a very large margin in the DAIER matched-size data.

What is the 50 mm comparison?

Plastic:

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

Ceramic:

• 92 m²/m³;
• 74% void;
• 600 kg/m³;
• 213 m⁻¹.

Does plastic provide less surface area?

Not necessarily. At 25, 38 and 50 mm, DAIER's Plastic Raschig Ring surface area is similar to or slightly higher than the comparable ceramic product.

Which has higher void fraction?

Plastic in all four matched 25, 38, 50 and 80 mm examples.

Which has lower packing factor?

Plastic in the matched DAIER data used here.

Does that mean Plastic Raschig Ring always has lower operating pressure drop?

No. Actual pressure drop requires gas and liquid operating conditions.

Why keep ceramic if the plastic physical data look better?

Ceramic may be required because of temperature, chemical compatibility or proven service conditions that the proposed polymer cannot safely tolerate.

Is plastic better for maintenance?

Its much lower mass and non-brittle behavior can simplify handling, but actual maintenance suitability depends on the process.

Does a plastic retrofit need a hold-down grid?

Possibly. Because the bed is much lighter, packing movement under gas flow should be reviewed.

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Selection Takeaway

Replacing Ceramic Raschig Ring with Plastic Raschig Ring can create one of the largest packed-bed weight reductions available without necessarily sacrificing geometric surface area—but material suitability determines whether the retrofit is technically possible.

At 25 mm:

Plastic → 205 m²/m³ / 90% void / 112 kg/m³ / 400 m⁻¹

versus:

Ceramic → 190 m²/m³ / 74% void / 650 kg/m³ / 508 m⁻¹.

At 50 mm:

Plastic → 93 m²/m³ / 90% void / 68 kg/m³ / 177 m⁻¹

versus:

Ceramic → 92 m²/m³ / 74% void / 600 kg/m³ / 213 m⁻¹.

At 80 mm:

Plastic → 90 m²/m³ / 95% void / 66 kg/m³ / 130 m⁻¹

versus:

Ceramic → 46 m²/m³ / 80% void / 660 kg/m³ / 280 m⁻¹.

The physical case for plastic can therefore be strong:

• far lower dry bed weight;
• higher verified void fraction;
• lower catalog packing factor;
• comparable or higher geometric surface area.

But the material boundary is absolute:

If the proposed polymer cannot tolerate the actual temperature and chemistry, none of those geometric advantages matter.

The correct retrofit sequence is:

Why Replace the Ceramic Bed? → Process Chemistry → Operating / Peak Temperature → Polymer Compatibility → Compare Exact Raschig Ring Data → Hydraulic Review → Tower Diameter / Size → Support & Hold-Down Review → Process Performance Verification

The key principle is:

Do not ask whether Plastic Raschig Ring is generally better than Ceramic Raschig Ring. Ask whether the process still needs ceramic—and if it does not, whether a compatible polymer can deliver the required duty with a much lighter and more open packed bed.