All About Biofouling in Heat Exchangers

Technical Introduction – The Real Impact of Biofouling

Biofouling is not only a microbiological contamination issue. It is a thermal resistance problem.

When biofilm develops on heat exchange surfaces, it creates:

• An additional thermal barrier
• Localized oxygen concentration cells
• Under-deposit corrosion risk
• Increased friction losses

From a heat transfer perspective: Biofilm has a lower thermal conductivity than mineral scale like CaCO3. This means:

• A thin biological layer can reduce heat transfer more severely than a thicker calcium carbonate deposit.
• The insulating effect increases energy consumption.
• Steam demand rises to compensate for reduced exchanger efficiency.
• Cooling efficiency drops due to surface passivation.

Operational consequences:

• Higher fuel consumption
• Rising approach temperatures in cooling towers
• Condenser inefficiency
• Increased blowdown rates
• Escalating chemical demand

Biofouling becomes a systemic performance amplifier.

The Complex Scenario : When Steam & Cooling Interact

The situation becomes significantly more complex in interconnected systems where:

• A portion of steam condensate is diverted to the cooling tower
• and/or
• Cooling water contaminates the boiler circuit through process interaction

This creates a cross-contamination dynamic:

• Organic carryover from process vapors enriches the cooling tower with nutrients.
• Cooling tower microbiology impacts downstream heat exchangers.
• Condensate contamination destabilizes boiler chemistry.
• Standard treatment programs become chemically incompatible.

In these hybrid systems:

• Oxidizing biocides from cooling water may interfere with boiler treatments.
• High organic load increases biological oxygen demand.
• Deposits become a mixed matrix of scale, sludge and bacterial polymers.

The result is not isolated fouling.
It is an integrated surface degradation mechanism.

Strategic Surface Management – Why FFA’s Matter

This customer is a leader in the manufacturing of synthetic resins, specializing in the production of emulsion polymers. The system included:

• Steam boiler (150 HP)
• Cooling tower (16,000 gal / 60 m3)

In this specific process configuration, steam and cooling water are not fully segregated. To initiate the chemical reaction, process components are first heated using steam. Once the target temperature is reached, manual valve switching redirects cooling water into the system to trigger the flash reaction. This operational transition — from steam heating to rapid cooling — creates a temporary hydraulic overlap, allowing steam condensates and cooling water to mix.

The exchanger was initially saturated with:

• Scale
• Sludge
• Bacterial deposits

The treatment protocol integrated:

Steam side:

• Film Forming Amines + Neutralizing amines

Cooling side:

• Polymers + FFAs
• pH regulation
• Continuous oxidizing biocide
• Non-oxidizing biocide shock

Key technical effect:

Filming amines created a hydrophobic molecular layer that:

• Reduced bacterial adhesion
• Limited under-deposit corrosion
• Facilitated progressive detachment of biofilm
• Restored metal surface wettability characteristics

Bellow: at the start of the treatment system (left), and the system after 9 months of treatment (right).

After nine months:

• Heat exchangers were fully restored
• 100% condensate recovery achieved

No mechanical dismantling.
No aggressive acid descaling.
Controlled in-line surface recovery.

Discussion

In complex hybrid systems, the question is not: “How strong is your biocide?”

The real question is: “Is your surface chemistry stabilized across interconnected loops?”