Why do heat exchangers lose their efficiency over time?

Introduction

Imagine an industrial boiler or chiller system in your factory that was previously operating at high efficiency suddenly consumes a significant amount of fuel or electricity and its outlet temperature is no longer as expected. These symptoms are often a sign of reduced heat exchanger efficiency. But why does this equipment “wear out” over time? Is this wear and tear normal or can it be prevented?

In this article, we take a practical look at the three main enemies of heat exchangers: scaling, corrosion, and biofouling, based on industry data. We also provide statistics on efficiency declines in various industries and explain practical solutions for identifying, preventing, and resolving these problems. If you are a facility manager, maintenance engineer, or decision maker in an industrial unit, this article could save years of useful life for your equipment.

How do heat exchangers work?

Before we get into the problems, it is better to understand why heat exchangers are so important in the first place.

Heat exchangers are equipment that transfers heat between two or more fluids (liquids or gases) without their direct mixing. These equipment play a vital role in various industries from power plants and refineries to food and pharmaceutical factories.

Common types of heat exchangers

• Shell and Tube exchangers: The most common type in heavy industries.
• Plate Heat Exchangers: For applications with limited space and high efficiency requirements.
• Double Pipe Heat Exchangers: Simple and for small capacities.
• Air Cooled Exchangers: In areas where water is scarce.

The efficiency of these equipment directly depends on the cleanliness of the heat transfer surfaces. Any layer that forms on these surfaces acts as an insulator and disrupts heat transfer.

The Three Main Enemies of Heat Exchangers

Over time and with continuous use, three physical-chemical phenomena cause a sharp decrease in the efficiency of exchangers:

1. Scaling

2. Corrosion

3. Biofouling

These three phenomena sometimes occur separately and sometimes in combination and are collectively known as Fouling.

Scaling — Unwanted Insulation on Pipes

What is Scaling and How Does It Form?

Scaling is a hard, mineral layer that forms when water-soluble substances such as calcium carbonate (CaCO₃), calcium sulfate (CaSO₄), or silica (SiO₂) come out of solution due to changes in temperature, pressure, or pH and deposit on the inner surfaces of the tubes or plates of the exchanger.

This phenomenon occurs most often in systems where:

• Hard water (high hardness) is used.
• The water temperature in the exchanger rises (e.g. in boilers or thermal desalination plants).
• The system operates without proper chemical control.

Plate exchanger with deposits

Plate heat exchanger after scale removal

The Impact of Scale on Heat Exchanger Efficiency — Shocking Statistics

According to industry reports:

• Just 1 mm of scale can reduce heat exchanger efficiency by 10%.
• In systems with 5 mm of scale, energy consumption increases by 40%.
• In thermal power plants, scale in boilers can increase fuel costs by millions of dollars annually.

These statistics show that scale is not just a “cleaning” problem, but an economic crisis.

Corrosion — The Hidden Wear That Costs

How Does Corrosion Occur in Heat Exchangers?

Corrosion is the chemical or electrochemical degradation of metals due to reaction with the surrounding environment (usually water or steam). In heat exchangers, corrosion can manifest itself in several forms:

• Uniform Corrosion: A reduction in the thickness of the entire metal surface.
• Pitting: The formation of tiny but deep holes that are more dangerous.
• Galvanic corrosion: When two dissimilar metals come into contact.
• Stress Corrosion Cracking: Cracks caused by a combination of mechanical stress and a corrosive environment.

Corrosion consequences in industrial systems

• Leaks in pipes and fittings
• Contamination of process fluid (e.g. in the food or pharmaceutical industries)
• Need for premature replacement of equipment
• Unplanned downtime and reduced productivity

According to NACE (now AMPP), the global cost of corrosion is over $2.5 trillion annually, equivalent to about 3.4% of global GDP!

Biofouling — Algae, Bacteria, and Biodegradation

What is biofouling?

Biofouling is the accumulation of microorganisms (such as iron-removing bacteria, algae, fungi, and biofilms) on wet surfaces. This phenomenon is most commonly seen in systems with circulating water, such as cooling towers or seawater systems.

Biofilms are sticky layers where microbes live and protect themselves from disinfectants.

Why is biofouling dangerous?

• Reduced water flow due to clogged channels
• Increased Microbiologically Influenced Corrosion (MIC)
• Spread of pathogenic bacteria
• Reduced heat transfer due to bio-insulation layer

In an industrial study, it was found that the presence of a 0.5 mm biofilm can reduce the efficiency of the exchanger by up to 15%.

Industry statistics: How much efficiency is lost?

Here are some real data from various industries:

These statistics show that without regular chemical maintenance, no water circulation system can maintain its efficiency.

How do we know if our exchanger is fouled?

Early detection of the problem is half the solution. Warning signs include:

• Increased inlet pressure or reduced outlet flow
• Abnormal temperature difference between inlet and outlet
• Increased energy consumption without a change in workload
• Unexpected leaks or unpleasant odors from the system
• Detection of solid particles or sticky layers in water samples

At this stage, water and internal surface tests are essential.

Practical solutions to prevent and eliminate fouling

With more than two decades of experience in this field, Abrizan Industrial Research Company offers specialized and test-based solutions.

Accurate analysis of the type of sediment or contamination

Before taking any action, we must know what type of problem we are facing. Using advanced laboratories, Abrizan performs the following types of tests:

• XRD (X-ray diffraction):To accurately identify the mineral composition of the deposit
• SEM-EDS:To examine the corrosion surface and its chemical composition
• Microbiology tests:To identify biofouling bacteria
• Process water analysis:pH, hardness, TDS, iron, silica, etc.

These tests help us to understand exactly what type of scale remover or anti-corrosion agent is needed.

Specialized Chemical Cleaning with Mitreh Products

Abrizan Company, under the Mitreh brand, produces a full range of specialized chemical solutions:

• Acidic and non-acidic scale removers: for carbonate, sulfate and silica scale deposits
• Post-rinse corrosion inhibitors: to protect metal surfaces
• Specialized biocides and biodispersants: to remove biofilms without damaging the equipment
• Circulation Cleaning: without the need to open the equipment

All of these products are customized based on the type of metal, type of scale and operating conditions.

Preventive Maintenance Planning

The best solution is prevention. Abrizan designs periodic chemical maintenance programs for various industries, including:

• Continuous injection of scale inhibitors
• Control of pH and water hardness
• Use of filtration and antimicrobial systems
• Periodic inspections with non-destructive testing (NDT)

These programs can increase the useful life of equipment by up to 2 times.

Case study: Restoring 15% efficiency to an industrial chiller

In a chemical manufacturing plant in southern Iran, a plate chiller had significantly lost its efficiency after 18 months of operation. Electricity consumption had increased by 22% and the cooling water outlet temperature was 6°C higher than normal.

Steps taken by the abrizan

1. Sampling of internal sediment and circulating water

2. XRD analysis: Identification of the main sediment as calcium carbonate and silica

3. Design of a non-acidic scale removal solution (to prevent corrosion of stainless steel)

4. Conducting a circulating wash for 8 hours

5. Anti-corrosion injection after washing

Results:

• Full return of outlet temperature to nominal value
• 19% reduction in electricity consumption
• 15% increase in system efficiency
• Avoidance of expensive chiller replacement (savings of approximately $120,000)

This example shows that a specialized wash can save years of economic life of an equipment.

Frequently Asked Questions (FAQ)

Can the exchanger be cleaned without opening it?

Yes. With the Circulation Cleaning method, the chemical solution is circulated through the system through special pumps and disassembly is not required.

Do scale removers damage the equipment?

If used professionally and with the appropriate formulation, no. Mitreh products contain corrosion inhibitors that protect metals.

When should washing be performed?

The best time is before the critical threshold is reached. It is usually recommended every 6 to 18 months (depending on water quality and type of industry).

Do thermal desalination plants suffer from these problems?

Yes, even more often! Because in these systems, water evaporates at high temperatures and deposits accumulate quickly.

Conclusion: Investing in cleanliness is an investment in profitability

The reduction in the efficiency of heat exchangers is a predictable and controllable problem, not an inevitable fate. By understanding the contributing factors (sedimentation, corrosion, biofouling) and using scientific and expert solutions, you can:

• Reduce energy consumption
• Extend the life of equipment
• Avoid costly downtime
• Ensure the safety and hygiene of the system

If you operate in an industry that uses water circulation systems, whether boilers, chillers, desalination plants or cooling towers, free expert advice and detailed testing are the first step towards restoring efficiency.

Abrizan Industrial Research Company, with more than 20 years of experience, is ready to provide free consultation, sample analysis, and custom solution design for your industrial unit.