Plate heat exchangers for energy conservation

Paul Boughton

With energy conservation becoming a major focus for manufacturers, the demand for plate heat exchangers is booming.

As fundamental parts of many production processes, plate heat exchangers allow the use of what otherwise would be wasted heat.

With energy conservation becoming a major focus for manufacturers, the demand for plate heat exchangers is booming. As fundamental parts of many production processes, they allow the use of what otherwise would be wasted heat.

"Heat is generated in all types of processing," says Jon Cutler, Trelleborg Sealing Solutions Material Development Manager for Plate Heat Exchanger gaskets. "In less environmentally aware times heat was just pumped out of the processing system and wasted. That wasn't good for energy conservation or the atmosphere."

Diverting energy

Now this is happening less and less. Plate heat exchangers (PHEs) are key to capturing processing heat and effectively reusing it, either within the processing system itself or by diverting the energy elsewhere.

They ensure efficient energy use for heating and cooling, minimising overall heat loss and helping protect the environment.

The applications for PHEs are countless. Originally they were used in the sterilisation and pasteurisation of dairy products, mainly milk. Now, however they are used on ships, to feed heating systems for buildings and in almost every processing plant.

Driven by a desire to manage energy better, in the past 10 years the market for PHEs has doubled.

"In power stations PHEs make it possible for the steam used for energy production to be diverted into heating offices and homes," continues Cutler.

"On a ship, PHEs mean heat from its combustion engine can be used for air-conditioning and heating. In processing plants, PHEs ensure efficient energy use by recycling heat. When they are employed within a system, the overall heat loss can be extremely low," he added.

Leak prevention

The plates within a PHE are sealed with rubber gaskets, preventing the two liquids within a PHE from leaking out or mixing.

"Gaskets are critical elements within a PHE and potentially their weakest link," says Cutler. "Sealing in PHEs is not easy. Temperatures are at extremes, while chemicals are some of the most aggressive processed and pressures are also high."

Trelleborg has been making plat heat exchangers gaskets for more than 25 years, and customers rely on its material expertise.

The company has invested research and development resources into maximising gasket life and optimising design.

"If there is one thing we pride ourselves on more than any other," Cutler says, "it is the initial fit of our gaskets. Probably better than any other manufacturer we are able to guarantee meeting the original equipment manufacturers' tight tolerances in gasket length control."

An emerging trend is that the PHE original equipment manufacturers, who have predominantly manufactured in Europe up until now, are expanding production globally.

"That's where our global reach becomes important," explains Cutler. "In Europe we manufacture in Poland, and demand from the Americas is fulfilled from Trelleborg's facility in Tijuana, Mexico. With manufacturing in Asia increasing, we have now transferred gasket technology to our plant in Shanghai, China."

Sealing in an aggressive environment

"Wander around a processing plant and you'll see PHEs up to five metres in height," says Jonas Jerleus, Trelleborg Sealing Solutions Global PHE Co-ordinator.

"The largest plate width is 1.5 metres. They will range from this size down to about 280 millimetres long and 100 millimetres wide. Gasket thickness is from 20 millimetres down to just two.

"Sealing conditions are very demanding in PHEs. Temperatures are at extremes, from -45°C to 200°C, while chemicals are extremely aggressive.

"As the liquids are pushed through a large PHE with maybe 200 plates, pressures are also high."

Heat and cooling

The design concept of all PHEs is the same. Between two metal end plates there is a series of thin metal plates close to each other. The liquid to be processed is pumped into one side of the plates while the liquid facilitating heating and cooling is pumped into the other.

The key to the process is that both liquids come into contact with the maximum plate surface area to rapidly exchange heat from one liquid to the other.

In processing plants PHEs can be up to five metres/16feet in height. The largest length is four metres/13feet and plate width is one and a half metres/five feet which is the maximum size that strip steel can be produced.

Plates will range from this size down to about 280 millimetres/11inches long and 100 millimetres/4inches wide.

The plate heat exchanger gaskets have to match the size of the plates with thicknesses which range from two millimetres/0.08 inches up to 20 millimetres/0.8 inches.

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