Like all equipment, tubular heat exchangers can encounter problems during their lifetime. Leaks can occur, but what is most critical is if your end product becomes contaminated. We examine some typical problems, and what you can do to avoid them.
The last thing you want is a problem with a heat exchanger that holds up operations or affects product quality. Proper maintenance and cleaning can prevent many typical problems.
“Respect the recommended procedures!” is the best advice for customers from Jimmy Moons, Cluster Product Manager for Heat Transfer in Cluster Europe and Central Asia for Tetra Pak. He sometimes observes how service engineers at the customer carry out the services themselves and make critical mistakes, such as fitting the wrong gasket. And sometimes services are not carried out on time or shortcuts are introduced for the recommended cleaning-in-place procedures. “Shortcuts can jeopardize food quality,” he says.
Sometimes he sees tubular heat exchangers used for applications they were not designed for. “Whenever you change the recipe or product, it is always a good idea to seek our advice to hear if this is possible,” Moons recommends.
Based on his experience, he has identified five typical problems with installed tubular heat exchangers – and has advice on how to avoid them.
1. Leakages due to poor service. Tubular heat exchangers typically have a service interval of 6,000 running hours, or two years. The service should be carried out regularly at this interval by a qualified service engineer. Using trained service engineers helps avoid mistakes like incorrectly replacing old gaskets, which can lead to leakages.
2. Leakages due to incorrect gaskets. A Tetra Pak tubular heat exchanger has a large number of gaskets or O-rings. Different types are used for different places, but they may look almost identical. Some are made to resist high temperatures and some are not. It is important to use original gaskets with the right rubber quality and marked with a product label and number for easy identification. Then follow the instructions carefully. The right gasket has to be placed in the right section of the unit for a heat exchanger to function properly without leakage.
3. Leakages due to corrosion. Though this problem is fairly uncommon, it does happen, and when it does it can be very serious. For most food and beverage applications without salt, a heat exchanger made of high-grade 316 stainless steel is sufficient. But suppose you decide later to use the same heat exchanger for processing products with certain concentrations of salt. The salty solution can attack this form of stainless steel, especially in higher concentrations and at high temperatures. The result can be disastrous if a hole forms and incoming product on the shell side becomes mixed with outgoing product on the tube side. Always inform the manufacturer if you are planning to process salty solutions such as sport drinks, salty types of yoghurt drinks or sauces containing salts. In that case, an alloy of stainless steel containing a higher content of molybdenum (SMO) is recommended.
4. Contamination due to poor cleaning. Proper cleaning according to the recommendations ensures the sterility of heat exchangers. If you have a cleaning detergent and cleaning regime that works well, don’t change it! Just by changing the cleaning agent or cutting the cleaning time, you may be able to save money – but the cleaning could become less efficient, resulting in the build-up of residues. That means unwanted bacteria can multiply and that you are not sterilizing the equipment properly. Likewise, you can run into problems if the cleaning is not performed at regular intervals. Therefore to avoid problems, cleaning of the heat exchanger should always be performed according to the manufacturer’s recommended programme for cleaning-in-place. Poor cleaning can jeopardize food quality.
5. Pressure drop is too high. There can be a number of reasons for an increase in the pressure drop. Perhaps one ingredient, such as a starch derivative, has been replaced by starch from another supplier, and the viscosity of the product has changed. Ask the manufacturer for advice when you change the product recipe and they should be able to upgrade or modify the heat exchanger to handle a more viscous product. Whenever selecting a suitable tubular heat exchanger, it is important for the manufacturer to know the exact physical properties of the product. Tetra Pak can often do specific tests in its labs to arrive at the exact viscosity properties of a customer’s product before designing a heat exchanger to handle it. In this way, the flow rate can be maintained without unexpected increases in pressure drop.