Ammonia Stripping Tower Packing: When to Use Plastic Pall Ring

Ammonia stripping towers are widely used to remove dissolved ammonia from industrial wastewater, landfill leachate, fertilizer wastewater, chemical process water, and other high-ammonia liquid streams.

Unlike conventional gas absorption, ammonia stripping transfers ammonia in the opposite direction:

NH₃ in the liquid phase → gas phase

The packed bed increases the contact area between wastewater flowing downward and stripping air moving upward.

For this service, Plastic Pall Ring is one of the most practical random packing options because it combines:

• corrosion resistance
• relatively low weight
• open gas-flow passages
• good liquid spreading
• broad industrial availability
• economical replacement cost

However, ammonia stripping can also create scaling, fouling, high-pH conditions, and substantial airflow requirements.

Therefore, selecting Pall Ring only by nominal size is not enough.

The real question is:

When does Plastic Pall Ring provide the right balance of mass transfer, pressure drop, fouling tolerance, and material compatibility for an ammonia stripping tower?

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Why Ammonia Stripping Requires a Packed Tower

Ammonia in water exists mainly as two forms:

NH₄⁺ — ammonium ionNH₃ — dissolved ammonia

Only the un-ionized NH₃ form is readily transferred into the gas phase.

The equilibrium between these two forms depends strongly on:

• pH
• temperature

Increasing pH shifts more ammonium toward gaseous ammonia.

For this reason, ammonia stripping systems commonly operate under alkaline conditions.

Once sufficient NH₃ is available in the liquid, air flowing through the packing carries it out of the wastewater.

The packing helps by creating a large and continuously renewed gas-liquid contact surface.

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1. Why Plastic Pall Ring Is Commonly Considered

Plastic Pall Ring is a second-generation ring-type random packing developed from the simpler Raschig Ring geometry.

Its cylindrical body contains open windows and internal structural elements that create more accessible surface area and gas-liquid flow paths.

For ammonia stripping towers, this geometry provides several practical advantages:

• relatively high void space
• low-to-moderate pressure drop
• good liquid redistribution
• reasonable mass-transfer area
• lightweight packed bed
• corrosion-resistant polymer construction

This makes Pall Ring a useful general-purpose starting point when the process does not require a more specialized packing geometry.

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2. Airflow Capacity Is Important

Ammonia stripping often requires substantial airflow.

The gas phase must continuously remove ammonia from the tower so that a driving force for further mass transfer is maintained.

As airflow increases, however:

• gas velocity rises
• packed-bed pressure drop increases
• liquid drainage becomes more difficult
• liquid holdup increases
• the tower approaches loading and flooding

Therefore, the packing must provide sufficient open area for upward airflow.

Plastic Pall Ring offers considerably more open flow paths than older solid-wall Raschig Ring designs.

This is one reason it remains common in gas stripping applications.

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3. Pressure Drop Affects Blower Size and Operating Cost

The stripping air is normally supplied by a blower or fan.

That equipment must overcome pressure losses from:

• air inlet
• packing support
• packed bed
• liquid distributor interaction
• mist eliminator
• outlet ducting

If the packing creates excessive resistance, the system may require:

• higher blower pressure
• larger motor size
• higher electricity consumption
• reduced maximum treatment capacity

For continuously operating wastewater treatment equipment, blower energy can become a significant lifecycle cost.

Packing selection should therefore consider not just purchase price, but also hydraulic resistance over the operating life of the tower.

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4. Pall Ring Size Creates an Efficiency–Capacity Trade-Off

Plastic Pall Rings are available in multiple nominal sizes.

Packing size has a major influence on ammonia stripper performance.

Smaller Pall Ring

Typically provides:

• more packing elements per cubic meter
• greater available contact area
• more frequent liquid redistribution

But may also produce:

• higher pressure drop
• smaller open passages
• greater fouling sensitivity

Larger Pall Ring

Typically provides:

• larger gas and liquid passages
• lower hydraulic resistance
• higher fouling tolerance
• greater airflow capacity

But provides less surface area per unit packed volume.

Therefore:

smaller is not automatically better.

The correct Pall Ring size should balance the required ammonia removal efficiency with allowable pressure drop and wastewater cleanliness.

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5. Scaling Can Be a Major Problem in Ammonia Stripping

One of the most important differences between ammonia stripping and clean-water air stripping is the chemical environment.

Because ammonia stripping frequently uses elevated pH, the wastewater chemistry may promote precipitation or mineral scaling.

Possible deposits can accumulate on:

• packing surfaces
• distributor holes
• packing support
• tower walls

As deposits build up:

• packing void space decreases
• airflow resistance rises
• liquid distribution deteriorates
• treatment performance becomes unstable

This means the packing should not be selected only for maximum theoretical surface area.

In scaling-prone wastewater, a somewhat larger and more open Pall Ring may provide better long-term operation than a smaller, tighter packing.

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6. Fouling History Should Influence Packing Selection

For retrofit projects, the existing tower can provide valuable evidence.

If the existing packed bed experiences:

• rapid pressure-drop increase
• repeated blockage
• heavy scale
• frequent shutdown for cleaning

then simply reinstalling the same small packing may reproduce the same problem.

The engineering review should ask:

Is the packing itself too restrictive for the wastewater quality?

Possible responses may include:

• increasing packing size
• improving pretreatment
• increasing washing frequency
• redesigning liquid distribution
• changing packing geometry

The best solution may involve more than the packing alone.

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7. Liquid Distribution Is Essential

Plastic Pall Ring only performs effectively when wastewater reaches the bed uniformly.

Poor liquid distribution can create:

• dry packing regions
• localized over-irrigation
• gas channeling
• reduced effective mass-transfer area
• premature fouling

For larger stripping towers, the liquid distributor should provide sufficient distribution points across the tower cross-section.

Distributor problems are especially serious when wastewater contains suspended solids or precipitates because small orifices may gradually block.

A retrofit should therefore inspect both:

packing condition + distributor condition.

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8. High pH Makes Material Selection Important

Ammonia stripping wastewater may operate under strongly alkaline conditions.

Plastic packing is often attractive because suitable polymers can provide good corrosion resistance without the weight or corrosion concerns associated with many metallic materials.

Common plastic random packing materials may include PP and other polymers depending on the application.

Material selection should consider:

• wastewater pH
• chemical additives
• operating temperature
• oxidants
• solvents
• cleaning chemicals
• long-term exposure

The correct polymer should be confirmed from the actual wastewater chemistry.

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9. Temperature Also Influences the Stripping Process

Temperature affects ammonia equilibrium and mass-transfer behavior.

Warmer wastewater generally favors ammonia volatilization compared with colder water under otherwise similar conditions.

But increasing temperature also affects:

• polymer material limits
• gas density
• liquid properties
• tower hydraulics
• evaporation losses

Therefore, packing selection should use both:

normal operating temperatureandmaximum possible temperature.

A packing that is chemically resistant but thermally unsuitable can deform or lose mechanical stability.

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10. Tower Diameter and Packing Size Must Match

Large packing elements used in a very small column can create wall effects.

Near the tower wall, random packing cannot arrange itself in the same way as it does in the central bed.

This may produce:

• preferential gas paths
• uneven liquid flow
• reduced mass-transfer efficiency

Therefore, selecting a very large Pall Ring simply to minimize pressure drop can be counterproductive in a small tower.

Packing size should be selected relative to the actual tower diameter.

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11. Packed Height Is Part of the Selection

Ammonia removal performance depends not only on packing type but also on the amount of packing installed.

A taller packed bed generally provides more opportunity for gas-liquid contact.

But increasing bed height also increases:

• total pressure drop
• tower height
• structural cost
• packing volume

Therefore, packing size and packed height should be optimized together.

A larger packing with lower pressure drop may require a different bed height than a smaller packing with greater effective contact area.

This is a process-design decision rather than a simple product substitution.

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12. Do Not Forget the Packing Support

Plastic Pall Ring is relatively lightweight, but the packing support still plays an important hydraulic role.

The support must:

• retain the packing
• carry the wet bed load
• provide sufficient free area
• resist process chemicals

If support openings become blocked by scale or solids, tower pressure drop can increase even if the packing itself remains relatively clean.

Therefore, an apparent “packing pressure-drop problem” may actually originate at the support plate.

This should be checked during tower maintenance.

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13. Mist Elimination May Be Required

High airflow through a wet packed tower can entrain liquid droplets.

An outlet mist eliminator may therefore be used to reduce droplet carryover.

This becomes important because alkaline or contaminated wastewater droplets may:

• corrode downstream equipment
• create emissions problems
• contaminate ductwork
• increase chemical loss

The mist eliminator is not a substitute for packing.

Its function is different:

Packing → mass transfer

Mist eliminator → droplet removal

Both may be required for stable tower operation.

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14. Plastic Pall Ring vs Tri-Pack for Ammonia Stripping

Both Pall Ring and Tri-Pack may be considered for stripping towers.

A simplified comparison is:

Tri-Pack may become attractive where hydraulic openness is a dominant requirement.

Pall Ring remains a practical choice where the process needs a conventional, economical and widely available random packing.

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15. When Plastic Pall Ring Is a Strong Choice

Plastic Pall Ring is particularly worth considering when:

The Wastewater Is Moderately Clean

Severe plugging is not expected.

Conventional Random Packing Is Preferred

The plant wants a mature and widely available product.

Corrosion Resistance Is Required

Plastic material is compatible with the alkaline wastewater.

Airflow Is Significant but Manageable

The tower needs reasonable hydraulic capacity without moving to a more specialized geometry.

Replacement Simplicity Matters

The existing tower already uses Pall Ring or similar random packing.

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16. When Another Packing Should Be Evaluated

Another random packing may be more appropriate when:

• scaling is severe
• suspended solids are high
• very low pressure drop is critical
• extremely high airflow is required
• existing small Pall Rings repeatedly plug
• the tower has unusual diameter constraints

In these situations, more open geometries or larger packing sizes may provide better long-term operation.

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17. Retrofit Projects Should Start With the Real Operating Problem

Before replacing packing in an existing ammonia stripper, record:

• current ammonia removal
• current pressure drop
• cleaning frequency
• scale condition
• gas flow
• liquid flow
• tower flooding history

Then define the retrofit objective.

For example:

Reduce packing blockage and cleaning frequency.

or:

Increase wastewater treatment capacity without increasing tower diameter.

These are meaningful engineering goals.

Simply asking for “better Pall Rings” is not enough to determine the correct replacement.

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18. Data Needed for an Ammonia Stripping Tower RFQ

For preliminary packing selection, provide:

• tower internal diameter
• wastewater flow rate
• air flow rate
• inlet ammonia concentration
• target outlet ammonia concentration
• operating pH
• operating temperature
• maximum temperature
• wastewater composition
• suspended solids
• scaling tendency
• available packed height
• allowable pressure drop
• existing packing type and size
• distributor type
• support details

For retrofit projects, photos of fouled packing can be especially useful.

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Final Selection Principle

Plastic Pall Ring remains a practical random packing option for ammonia stripping towers because it provides a balanced combination of:

mass-transfer area + open gas flow + corrosion resistance + low weight + economical procurement.

However, ammonia stripping frequently involves high pH, scaling, fouling and substantial airflow.

This means packing selection cannot be based only on nominal surface area.

The correct decision must balance:

• ammonia removal requirement
• gas and liquid load
• packing size
• pressure drop
• fouling tendency
• wastewater chemistry
• tower diameter
• distributor quality

The practical engineering question is:

Can the selected Pall Ring provide enough gas-liquid contact to achieve the required ammonia removal while remaining hydraulically open and maintainable under the actual wastewater conditions?

That is the basis for a reliable ammonia stripping tower packing specification.