Over time in service, deposits typically build up on the surface of tubes in a heat exchanger.
This is known as fouling, and it can occur on the inside, outside or both sides of the tubes. Fouling refers to the accumulation of unwanted deposits or substances on the heat transfer surfaces of a heat exchanger, resulting in reduced heat transfer efficiency. These deposits can include scales, corrosion products, sediment, organic matter and other contaminants present in the fluid being heated or cooled.
Fouling can occur in shell and tube exchangers, plate heat exchangers, finned tube heat exchangers and in others. The presence of fouling layers on the heat transfer surfaces reduces the overall heat transfer coefficient, increases pressure drop and leads to higher energy consumption. Unchecked fouling can reduce flow rates, causing uneven heating and major damage to the exchanger.
Since the fouling layers usually have a lower thermal conductivity than the tube material, this process will also reduce the amount of heat that the exchanger can transfer. Some amount of fouling can be accounted for in the initial thermal design of the exchanger, by using a standardized fouling factor for the expected service.
Several factors contribute to heat exchanger fouling:
- Nature of the fluid: The composition of the fluid being processed in the heat exchanger plays a significant role in fouling. Fluids with high mineral content, suspended solids or dissolved impurities are more prone to fouling.
- Temperature and pressure: Higher temperatures and pressures can promote fouling by accelerating chemical reactions or causing the precipitation of dissolved substances.
- Flow velocity: Low flow velocities can lead to sedimentation and settling of particles, resulting in fouling. High flow velocities can cause erosion and increase the chances of fouling.
- Heat exchanger design: The design and geometry of the heat exchanger can influence fouling. Dead spots, low-velocity areas and spaces with poor fluid distribution are more susceptible to fouling.
- Fluid turbulence: Turbulent flow can help prevent fouling by promoting the removal of deposits from the heat transfer surfaces. Laminar flow is more prone to fouling.
- To mitigate heat exchanger fouling and maintain optimal performance, several preventive and corrective measures can be implemented:
- Exchanger design: Can be designed to minimize fouling by promoting increased fluid velocities and reducing dead zones and areas with poor circulation. Access for cleaning both sides can also be a design consideration.
- Regular maintenance and cleaning: Recurring cleaning can help reduce or remove accumulated deposits and prevent excessive fouling. Cleaning techniques, such as chemical cleaning, mechanical cleaning and hydro blasting, can be employed.
- Fluid treatment: Treating the fluid before it enters the heat exchanger can help minimize fouling. Filtration, coagulation and chemical additives can be used to remove or inhibit fouling substances.
- Surface modifications: Applying anti-fouling coatings or using special materials with low fouling tendencies on heat transfer surfaces can reduce the adherence of deposits.
- Operating conditions: Optimizing operating parameters like flow rate, temperature and pressure can help reduce fouling. Higher flow velocities and proper fluid mixing can prevent the settling of particles and enhance self-cleaning effects.
- Monitoring and fouling detection: Implementing monitoring systems to regularly assess heat exchanger performance and detect fouling at an early stage can enable initiative-taking maintenance and cleaning.
It is important to note that specific fouling mechanisms and mitigation strategies can vary depending on the type of heat exchanger, the nature of the fluid and the operating conditions. It is recommended to consult experts or refer to industry-specific guidelines such as the TEMA Standard for detailed information on managing fouling in specific heat exchanger applications.
Ward Vessel & Exchanger offers design and fabrication of custom shell and tube heat exchangers and pressure vessels, manufactured in accordance with ASME Code: Section VIII, Division 1.
For more information, visit wardve.com or call (704) 568-3001.
