Product-to-product (P2P) heat exchangers rely on clever design and maintenance to ensure rigorous food safety. Unlike a conventional heat exchanger, where piped water heats and cools the food or beverage to the desired temperature, a P2P unit exploits the product’s own heat to achieve the desired temperature.
Using product instead of water on the heat exchanger’s “shell side”, meaning around the tubes, makes it imperative to have good design and effective cleaning-in-place to avert bacterial blind spots and to combat fouling.
“At Tetra Pak we’ve been making product-to-product heat exchangers for 20 years. That experience really counts when it comes to avoiding issues with hygiene,” says Jaana Mathisson, Tetra Pak Heat Transfer Technology Specialist.
One way to achieve the food safety gold standard is to weld the tubes of a P2P heat exchanger from the inside using protective gas. This innovative and patented technique eliminates any theoretical hygiene blind spots where product could potentially lodge and cause bacterial build-up. A smart weld can also be combined with internal baffles that are electro-polished to create an ultra-smooth surface for maximum hygiene.
Customers seeking to process fibrous products may consider replacing baffles with an optional spring box. This is an external tube divider whose angled discs create a force that, when compressed, separates the heat exchanger tubes.
“The spring box takes hygiene to the next level because removing baffles takes away a flow obstruction inside the unit, which makes cleaning that much easier,” says Tetra Pak’s Mathisson.
All of Tetra Pak Tubular Heat Exchangers are fitted with a floating protection system that allows the unit to be easily opened for inspection and cleaning.
“To perform a hygienic evaluation, you need to have direct contact with the surface you’re going to test. Many tube heat exchangers don’t allow this, but a floating protection system makes this very easy,” Mathisson says.
Some manufacturers use cameras to allow internal inspection, but true hygiene can only be guaranteed by being able to see and touch the surface.
“It really makes a difference – it’s a critical part of a hygienic design and being able to guarantee food safety depends on it,” Mathisson explains.
Over time, the thermal pressure inside a heat exchanger can cause wear and metal fatigue that leads to parts to crack. This creates hygiene and maintenance issues and, inevitably, costs money to fix.
Floating protection allows the heat exchanger tubes to move horizontally during production and thus absorb thermal pressure. This considerably prolongs the life of the heat exchanger and also eliminates the potential hygiene risk from pressure-induced metal fatigue.
Effective cleaning-in-place (CIP) is another key parameter. Here, the supplier’s experience is critical.
The most advanced P2P heat exchangers can require less frequent cleaning, with weekly intervals not uncommon among leading models, depending on the type of food or beverage being processed.
The key thing is to choose a supplier with extensive familiarity with the various issues that arise with different kinds of product.
Mathisson advises buyers to see this a specialist competence area and to seek out a supplier with high-level CIP expertise and experience.
“Milk, say, fouls in one way and then you need a balance in terms of flow, cleaning time, temperature and detergent concentration to get optimal CIP,” she says. “Juice fouls differently, so it’s important you use different parameters.”