Engineering Evaluation Case: A Seawater Packed Tower Suffers Biological Growth Even Though the Packing Is Chemically Compatible

Seawater applications often favor plastic packing because polymers can provide good resistance to chloride-rich water.

Chemical compatibility, however, does not guarantee a clean bed.

Natural seawater contains:

• microorganisms;
• suspended matter;
• nutrients;
• biological larvae.

Over time, the packed tower may develop biological fouling even though the packing material itself shows no corrosion.

Project Situation

Consider a packed tower using seawater for:

• gas scrubbing;
• degassing;
• aeration;
• water treatment.

PP or another compatible plastic packing is installed.

Initial operation is stable.

After months of service, operators notice:

• higher bed pressure drop;
• uneven water flow;
• biological film;
• shell or debris attached to the packing.

The resin is still physically intact.

The failure mechanism is biological rather than chemical.

Biofilm Changes the Packing Surface

A thin biological layer can initially increase apparent wetting.

As growth continues, it can become thick and irregular.

This can:

• reduce open area;
• capture suspended solids;
• increase liquid holdup.

The bed gradually becomes a biological filter.

Marine Growth Can Bridge Openings

Larger organisms or accumulated organic material can bridge packing passages.

The risk depends on:

• seawater source;
• screening;
• temperature;
• nutrient level;
• operating season.

A tower operating well in winter may foul faster in warm months.

Packing Geometry Influences Fouling Tolerance

More open random packing generally provides larger passages for:

• water;
• gas;
• debris.

Fine high-area packing may offer better theoretical transfer performance but can lose capacity faster when biological growth is significant.

Selection should therefore consider required cleaning interval.

Upstream Screening Is Important

Large debris should ideally be removed before entering the circulation system.

The tower should not be expected to retain:

• seaweed;
• shell fragments;
• large marine organisms.

Upstream screening can reduce the load on:

• pump;
• distributor;
• packing.

Distributor Openings Can Plug First

Marine debris and biological material can collect in small distributor holes.

The bed then develops maldistribution before serious packing blockage occurs.

For seawater service, distributor maintainability should be considered together with packing geometry.

Continuous and Intermittent Operation Differ

A continuously flowing seawater system may remain more stable than a tower that sits stagnant for long periods.

During shutdown:

• warm stagnant water;
• oxygen availability;
• retained nutrients

may create different biological conditions.

Startup after long idle periods can release accumulated material into the packing.

Water Treatment Can Influence Material Choice

Plants may use biological-control methods such as:

• chlorination;
• other approved treatment.

The packing and other internals must remain compatible with both:

• normal seawater;
• treatment chemicals.

A material selected only from chloride resistance may not cover the complete operating chemistry.

Support and Demister Need the Same Fouling Review

Biological material can accumulate on:

• support grid;
• demister;
• drains.

A clean packing bed does not help if the support becomes blocked.

The whole water and gas path should be accessible for inspection.

Cleaning Strategy Should Be Designed In

Depending on tower size, practical options may include:

• water flushing;
• removable packing sections;
• access manways;
• mechanical cleaning.

The planned method should influence the equipment layout before fabrication.

Monitor More Than Differential Pressure

Useful operating trends can include:

• pressure drop;
• seawater flow;
• distributor pressure;
• biological growth observations;
• seasonal temperature.

A gradually increasing differential pressure may confirm fouling progression, but visual inspections can identify the mechanism.

Chemical Resistance Is Still Necessary

The existence of biological fouling does not reduce the importance of corrosion compatibility.

The material must survive:

• seawater chloride;
• temperature;
• cleaning chemistry.

The engineering problem contains both:

material durability and fouling tolerance.

Engineering Takeaway

For seawater packed towers, “non-corroding” is not the same as “maintenance-free.”

A chemically resistant plastic packing can still lose hydraulic capacity because the seawater ecosystem grows on and around it.