Due to the particularity of the application, shell and tube exchangers are used because brazed plate exchangers have a working temperature limit of 200° C. There are in fact also models that can work at higher temperatures, but they have costs and limitations in terms of cleaning and fouling that would compromise their use with diathermic oil in these extreme high-temperature conditions.

To ensure full control over the construction standards and the ready availability of these special TCFT HT shell and tube exchangers for high temperature oil, we have therefore decided to bring their construction in-house, and to market them to make available to the market a device that is difficult to find when the working conditions become so extreme.

The TCFT HT exchangers exist in a full stainless steel version and with the possibility of making the casing in carbon steel. The brochure below contains all the technical characteristics of these exchangers.

L'articolo Special Tempco shell and tube exchangers for high temperature oil proviene da Tempco Blog.

This happened because the user had committed a serious imprudence: following the intervention of the high temperature safety thermostat, he had in fact ignored the alarm ‘bypassing’ it. The alarm was caused by poor oil circulation, for reasons related to fouling of the plant.

The scarce oil circulation therefore caused the intervention of the maximum temperature thermostat. By bypassing it, the customer caused the electrical resistances to break. Fortunately, everything was resolved with a shutdown of the thermoregulator, but the imprudence could have had even more serious consequences, for example if the oil had caught fire…

Preventive maintenance, evaluation of the manufacturer’s alarms, requesting the intervention of the service or telephone assistance, would have prevented everything.

L'articolo Preventive maintenance and the importance of alarms in thermoregulation proviene da Tempco Blog.

However, with time and continuous use, the plates can accumulate deposits and the seals can deteriorate, compromising the performance and integrity of the entire system.

One of the key aspects of maintaining the transfer efficiency of plate heat exchangers is the replacement of gaskets. Gaskets are essential components that guarantee the tightness of the system. There are two main types of gaskets: glued and clip-on.

Glued gaskets: these gaskets are permanently attached to the plates with an adhesive. They allow for easier on-site plate washing operations, but replacing them can be more laborious and requires careful cleaning of the surfaces before applying the new gaskets.
Clip gaskets: these gaskets are designed to be easily removable and replaceable without need of adhesives. Clip-on seals are more convenient for periodic maintenance as they can be quickly removed and replaced, reducing system downtime.

The market is now dominated by clip seals.

It is essential to carry out regular inspections to detect any signs of wear or damage to the seals, such as cracks, swelling or loss of elasticity. A compromised seal can lead to fluid leaks, contamination and heat transfer inefficiency.

In conclusion, preventive maintenance and timely replacement of gaskets in plate heat exchangers are essential to maintain optimal performance and extend the useful life of the system. Investing time and resources in regular maintenance not only prevents costly breakdowns, but also ensures efficiency and safety of industrial operations.

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Clearly it depends on the kind of fluids that flow inside it: having heat exchangers employed with clean fluids there are obviously no fouling issues and. Thus, it is possible to size the exchanger very precisely on the project working conditions, not considering too much the possible fouling effect and therefore a possible reduction of the thermal transfer surface.

Instead, when fluids involved can be dirty then it is mandatory to carefully consider the fouling factor. The fouling level depends on the kind of fluids employed. There are several kinds of fouling: there is fouling involving a scaling effect, when there are fluids that get stuck onto thermal transfer surfaces. And this is probably the worst example. Otherwise, there can be fouling due to solid particles on the fluids circulating inside the exchanger. When fluids with suspended solid particles are involved there is a series of strategies to carry out in order to avoid fouling. On top of them there is filtration. Clearly, filters represent a bottleneck for thermal transfer because they reduce the flow rate of water, they involve pressure drops and thus requiring a higher pumping pressure, but they surely protect the exchanger from the fouling.

Obviously, there are even suspended solid particles that can be very small that are challenging even for a good filter. For example when using a kind of water with quite heavy suspended solid particles, such as sand, metallic swarf or fine dust. What is possible to do is to try to reduce the internal fouling of the exchanger, and we are speaking about plate heat exchangers, letting the fluid in from the bottom. In this way, the heavy particles tend to deposit on the bottom of the nozzle, and therefore not fouling all the plate, allowing to extend the maintenance periods.

Otherwise, fouling can be due to scaling, and let’s think about limestone, for example, or resins, as well about greasy products getting stuck on thermal transfer surfaces of plates. In this case, the only possible solution is a washing intervention that can be done in different ways: for example with a cleaning in place, or even dismantling the exchanger for a more accurate cleaning using a pressure washer, a brush or some washing cleansers.

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The occasion to go back on it was given by a recent experience for an application made for a customer, who requested a fouling factor with a value usually related to shell and tube exchangers. The results were utterly deadly, because sizing the exchanger using fouling factor values suitable for a shell and tube exchanger led to a slowdown of the speeds of fluids inside the exchanger and therefore to an increase of the fouling, drastically reducing the efficiency of the thermal transfer rate.

The solution to the problem has been to remove 30% of the plates from the exchanger, getting back to a fouling factor value more suitable for a plate heat exchanger.

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In this tiny video here, we can see a shell and plate exchanger designed for low flow rates and to achieve a crossing of temperatures and heat recovery. As you can see, the exchanger is very long, with tubes with a length of 6 meters. This length is required due to the fact that, having a low flow rate, we want to achieve a temperature crossing and obtain a heat recovery, which is a very hard task for a shell and tube exchanger.

In fact there was no valid alternative, due to a problem of fouling because the customer works with a very dirty fluid, rich in suspended particles. That’s why a shell and plate exchanger has been chosen with very long tubes, allowing a pipe cleaner to be inserted to clean the tubes internally. A plate heat exchanger would have required very intensive maintenance operations with close intervention times.

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• Anti-corrosion coating cycles (such as for C5 M environments)
• Stainless steel nameplates and data plates
• Line connections made in AISI 316
• Thermal security coefficients increased (suitable fouling factor rate)
• Earthing systems
• Declaration of conformity for ATEX area installation
• Certifications of materials

These features are referred to the construction and selection of constructive materials of the plate heat exchanger, but also to all the engineering evaluations and the technical documentation required to ensure the exchanger is suitable to cope with the challenging conditions of the harsh industrial environment.

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Brazed plate exchangers are employed in chillers in function of condensers, in case of water condensation, or as evaporators, which means they function as exchangers between the evaporating refrigerant and the fluid to be cooled, being it water, non-freezing solutions or oil.

The reduction of the environmental impact of industrial refrigeration is possible thanks to the use of micro channel exchangers, plate heat exchangers having a plate design with small pressing depth, approximately 2 mm, or 2,5, 3 mm depending on the type of fluid employed by the heat exchanger.

The challenge is then to create a machine able to ensure the same thermal efficiency but using a reduced amount of refrigerants. The aim is to have less amounts of freon or refrigerant gases in case of release in the environment. Having smaller and tiny passages between the plates of the exchanger allows therefore to have reduced amount of refrigerant flowing, achieving the same thermal work.

Usually, the size of these channels in exchangers must have a certain diameter, in order to avoid fouling and scaling effects, depending on the type of application. In case of chillers, the water flows within the exchangers in a closed-loop circuit and gets filtrated at the beginning, then remaining always the same re-circulated. So that it barely contains particles that can cause fouling or scaling. Furthermore, the exchanger/evaporator works at very low temperature levels, surely lower than temperatures causing carbonates precipitation, thus a further reason why these exchangers are not prone to fouling.

For all of the above reasons, that’s why it’s possible to employ much smaller passages, in fact reducing the amount of refrigerant that flows within the exchanger creating refrigerating groups characterized with a much lower carbon footprint.

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In case of plate heat exchangers, preventive maintenance can in addition ensure relevant advantages in terms of energy saving, because it ensures to leverage the thermal transfer at its maximum efficiency, as it was originally designed.

The monitoring of some key parameters allows in fact to evaluate the most suitable moment to proceed with a maintenance intervention:

• increasing values of flow rate pressure drop, compared to design values
• diminished performances in terms of output temperature levels, compared to design values

These are two main KPI to check in order to determine if the exchanger need a cleaning and washing service. These two parameters are a key indicator for each kind of heat exchanger: at same capacity, is in fact clear that fouling and scaling on thermal transfer surfaces cause an increase of the pressure drop, being it the pressure difference between inlet and outlet of the fluid. In addition, the thickness of the scaling generates a sort of isolating effect, decreasing the thermal transfer efficiency rate of the exchanger.

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After the cleaning of the plates, with the removal of limescale, we proceeded with the test with penetrating liquids, represented here in these pictures with plates under a blu-purple light. This is a crucial step in order to identify all the cracks along the plates (appearing in brighter light).

The regeneration then also involved the frames of the exchangers, with the renewal of nozzles and related coatings.

The intervention had to be done in a very narrow time span. The customer, indeed, after a slowdown of the production during the lockdown period, had to be ready for the restart. We succeeded in respecting his requests, and all the maintenance and regeneration work has been made during two weeks in August. Everything was then ready for the restart of the production, which has been hectic.

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