Navigating the Depths of Marine Condenser Fouling: Challenges and Solutions
Example of biological and manmade material found inside a titanium chiller.
Keeping your condenser clean is necessary to maintain the efficiency of your system and prolong the life of your equipment. Fouling occurs when materials, such as algae or silt, accumulate on the heat-exchange surface.
Fouling has various negative effects on your system:
Poor heat transfer: Fouling is a layer of insulation on the heat exchanger surface which will inhibit the transfer of heat from the refrigerant to the seawater. This will cause reduced cooling capacity and higher condensing temperatures - which means a decrease in system efficiency and increased fuel consumption.
Increased pressure-drop: Fouling can restrict the flow of seawater through the condenser which will increase pump-load and reduce efficiency of the system.
Shortened lifespan: Fouling can accelerate corrosion and wear on the surfaces of the condenser.
Maintenance time: A heavily fouled condenser will be more difficult to clean. A condenser fouled to the point of system shut-down due to high discharge pressure will require the system to be secured to clean the condenser.
There are different types of fouling:
Biological fouling: Organisms in seawater can attach to the surfaces of the condenser forming a film that reduces heat transfer efficiency. These can be microorganisms such as algae, or larger organisms such as barnacles and mussels.
Scale fouling: Seawater contains minerals which can precipitate out and form a scale deposit on the surfaces of the condenser.
Corrosion fouling: Corrosion of the condenser materials can lead to the formation of deposits on the surfaces. Corrosion decreases efficiency and the life of the condenser.
Particulate fouling: Sediment from corrosion products, silt, sand, algae, and pieces of man-made materials such as twine or plastic can form an insulating layer on the heat exchange surfaces or even completely block the water flow through a tube.
Factors that affect fouling:
Water temperature: Warmer water promotes the growth of marine organisms in the condenser.
Water salinity: Higher salinity levels can contribute to scale formation since there are more minerals present with a higher likelihood of precipitation out of the water.
Flow rate: Low flow rates can allow organisms to attach to the surfaces and grow more easily. Adequate flow can mitigate this by preventing the buildup of layers. Excessive flow rate can increase corrosion and can erode the surfaces of the condenser.
Location: Areas with high levels of microorganisms or particulates, such as coastal waters, can cause fouling more quickly than open-ocean areas.
Materials used: Certain materials are more resistant to fouling in seawater due to corrosion resistance and biofouling resistance. IMS uses copper-nickel condensers for marine applications to mitigate corrosion and biological fouling.
Design and Operation: Finding a condenser of the proper size and material is important to maintain efficiency and maximize the life of the condenser. Use of strainers or filters can help mitigate particulate build-up. Monitoring the seawater pressure drop across the condenser and the discharge pressure of the refrigerant will keep the operator informed of the state of the condenser.
Maintenance: Regular cleaning prevents excessive fouling. Regularly changing zinc anodes prevents corrosion of the condenser materials.
Other factors: This includes seasonal water variations, nutrient and pollution levels in water, types of organisms present, and the chemical composition of the water.
How should I maintain my condenser?
Monitor it! An increase in the pressure-drop across the water side of the condenser indicates fouling. As does an increase in refrigerant discharge pressure during normal operation. It’s best practice to clean the condenser before these signs arise by implementing a cleaning schedule that works for your application.
Clean it! Generally, at the end of each season, or a couple of times a year, open your condenser for inspection (more often in tropical climates). Any large objects will usually get caught at the water inlet tube-sheet. Determining the level of fouling on the tube surfaces is more difficult. One way is to measure the buildup by comparing the ID of the tube at its current state with the ID when it is clean.
Change your zincs! Zinc anodes prevent corrosion of the materials in the condenser. Check your zincs regularly to understand their rate of corrosion and change them before they are gone!
Check your flow! Do not continuously increase your water flow to keep your head pressure down. Rather, clean your condenser if the head pressure is rising. Excessive flow can cause erosion and increase corrosion in the condenser. Keep the flow rate within the recommended limits.
What is the proper condenser cleaning procedure?
Remove condenser heads. We recommend having spare gaskets handy.
Remove any large objects by hand.
Using clean water to flush as you go, carefully brush the tubes using a nylon brush. This will remove any soft deposits like algae or silt.
Rinse well.
Remove scale deposits using either (or both) of the following methods:
Brush the tubes using a copper brush. Rinse.
Fill condenser tubes with 25% citric acid/water solution. Allow it to soak for 24 hours with occasional circulation. Flush out the vessel.
Be sure to dispose of all contaminants according to regulations.
Go ahead and open your condenser and have a look before there is a problem. Be sure to have gaskets and zinc anodes on-hand. If needed, clean it to keep your system operating efficiently for years to come.