A clean slate for your heat exchanger
Maintenance can go a long way to avoiding long-term complications
Author: Jamie Zachary
A new year means a clean slate, right? How about one for your heat exchanger, too?
Depending on your plant’s production process, now might be the best time to put your New Year’s resolutions into action by performing preventive maintenance on processing equipment, says Peter Menchenton, Vice President of Operations for Solex Thermal Science.
“A little can go a long way in extending the life of your heat exchanger,” he says. “Simple tasks such as cleaning plates and inspecting connections can minimize longer-term issues such as fouling, corrosion and, in extreme cases, even equipment failure.”
The good news, says Menchenton, is indirect heat exchangers are designed to include minimal moving parts when compared to other methods of heating, cooling or drying bulk solids. In fact, many of the exchangers Solex has installed decades ago are still in service and have required minimal maintenance.
“That being said, good design must consider and allow for the possibilities that can happen over the life of the equipment,” says Menchenton.
Focusing on the stainless-steel plates used in Solex’s heat exchangers, Menchenton recommends annual cleaning to mitigate corrosion that can be caused by cooling water. Higher chloride concentrations than anticipated in cooling water can lead to stress corrosion cracking or pitting, potentially resulting in leaks.
Likewise, corrosion can occur on the outside of the plates, more likely in chloride-containing bulk solids such as NPK fertilizer or potash and if free moisture is present.
“Instances of corrosion of the exchanger plates have been rare and limited to conditions where chlorides are present,” says Menchenton, noting every plate is fully welded and thoroughly tested during the manufacturing process (which includes being hydraulically inflated at more than 40 bar pressure) to meet strict internal quality and all pressure vessel code requirements.
The following steps provide a simple way to clean your heat exchanger plates.
1. Prepare a 6% citric acid solution. This solution is an effective and environmentally friendly way to remove corrosion and contaminants from the interior of the plates. Nitric acid can be used as an alternative, but is often a more problematic solution to manage safely.
2. Close the valves to the inlet and outlet manifolds of the heat exchanger to isolate the unit from the plant piping system.
3. Open the vent on the top heat exchanger manifold.
4. Drain all process fluid (to a safe location) from the plates by opening the drain on the bottom heat exchanger manifold. Once the fluid is completely removed, close the drain.
5. Fill the plates completely with the citric acid solution by pouring it through the vent on the top heat exchanger manifold.
6. Let the solution stand in the heat exchanger for two hours.
7. Drain the solution (to a safe location) from the plates by opening the drain on the bottom heat exchanger manifold.
8. Flush the heat exchanger with clean water for 30 minutes or until no solids appear in the flushed water.
9. Close the drain and the vent on the upper manifold.
10. Reconnect the heat exchanger manifolds to plant piping.
Indirect heat exchangers, like any heat exchanger, can also suffer from fouling caused by microorganisms, deposition of solids, or scaling from calcium found in the heat transfer fluid. Fouling can decrease thermal efficiency and increase pressure drop, both of which can hamper heat exchanger performance.
One of the clearest signs of fouling is a gradual increase in pressure drop. This indicates the flow of heat transfer fluid in the exchanger plates is becoming restricted and therefore the plates need to be cleaned using the above procedure.
“By monitoring pressure drop across your Solex heat exchanger, you can identify instances of fouling and incorporate cleaning and flushing of the exchanger plates into your preventative maintenance planning to avoid costly decreases in heat exchanger performance,” says Menchenton.
Still have questions?
Solex’s technical services team is available to answer any questions regarding maintenance, parts, training, equipment optimization and more. Email us to consult with a member of the Technical Services team, or request service today.
This entry was last updated on January 15, 2021
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