Similar to cars or computers, regular maintenance is necessary to ensure that a heat exchanger operates at its peak performance. Fortunately, plate heat exchangers (PHE) are generally easier to maintain compared to other types of heat exchangers, and problems are relatively easier to diagnose.
In the absence of regular maintenance, the efficiency of a PHE naturally declines. The main reason for this is plate fouling – as debris accumulates in the grooves of a plate, the heat transfer capacity decreases because the fouling is less thermally conductive than the plate itself. The more scaling there is on a plate, the faster fouling occurs. Therefore, it is important to identify and address this issue early on in order to avoid extended downtime and excessive maintenance costs.
While less likely, other parts of a plate heat exchanger can also fail. It is important to visually inspect the gaskets, frame, and bars whenever the heat exchanger is opened for maintenance. Conducting regular visual examinations can save a significant amount of time and money in the long run.
To ensure proper maintenance of your plate heat exchanger, it is essential to keep basic records. These records should include the make and model number of the unit, details of the performed maintenance, inventory of available spare parts, and the number of plates and gaskets in the unit. You should also be aware of the dimensions of the plate pack as specified by the manufacturer (PHEs are not tightened to a torque specification, but rather to the width of the plate pack) so that you can periodically check for tightness and return it to its original state after scheduled maintenance. Additionally, when tightening the PHE, it is a good time to lubricate the carrying and guide bars to facilitate easier opening of the PHE during the next maintenance cycle.
The most important type of maintenance is regular scheduled maintenance, even if the unit appears to be functioning properly. This is equivalent to going to the dentist for a check-up, even if you do not have cavities (i.e., it should be done!). Perform this maintenance at least once every six months.
As mentioned earlier, regular visual examinations are important. Ensure that the plate pack is tightened according to specifications, the carrying and guide bars are lubricated, and the gaskets are undamaged. Additionally, check the pressure gauges at each end of the plate heat exchanger to ensure that the pressure drop is within the expected limits.
If, after performing the regular maintenance tasks mentioned above, the pressure drop is excessive, it indicates a fouling issue that requires unscheduled maintenance, resulting in downtime. It is also possible that the problem lies elsewhere in the process. Make sure the pipes are in good condition and all pumps are functioning properly. If everything else appears to be in order, it is time to clean the PHE.
Periodic cleaning is the most effective form of maintenance and should be the primary focus of your maintenance efforts. Most PHEs can be cleaned using a clean-in-place (CIP) process, which eliminates the need to open the plate pack. The main goal of cleaning is to flush out any debris that accumulates in the PHE over time, which will vary depending on your specific process.
To clean your plate heat exchanger, start by draining both sides and isolating it from your system fluid using isolation valves. Then, flush water through both sides until it runs clear. For optimal results, flush the fluids in the opposite direction of their usual flow during operation. If a significant amount of debris is flushed out, you are on the right track! However, if the excessive pressure drop persists even after returning the PHE to service or if only a small amount of debris is observed, a more aggressive cleaning agent than water will be required.
The next step is to circulate a cleaning agent through the PHE using a circular pump and solution tank. It is crucial to ensure that the cleaning agent is compatible with the plates and gaskets of your PHE. For example, chloride will likely corrode stainless steel plates (which most PHEs are made of). After circulating the cleaning agent, flush the PHE with water again until both sides discharge clear. If the PHE still underperforms after returning to service, it will be necessary to open the plate pack and manually clean it.
It is preferable to clean the plates without removing them from the frame, which is one of the reasons why it is recommended to install a PHE in a location with ample space for maneuvering around it.
Next, apply the cleaning agent manually to each plate to loosen any accumulated debris. Then, rinse off the agent using a soft bristle brush and a high-pressure washer. Avoid using wire brushes or metal pads as they may damage the plates. Take care not to directly hit the gaskets with the high-pressure washer, as it may loosen or dislodge them. After thoroughly rinsing the plates, reassemble the PHE and put it back into service – everything should be as good as new!
While this cleaning process does require significant effort, it should not take longer than 24 hours. Scheduled maintenance tasks take much less time and can save your maintenance crew both time and money.