Rotary Heat Exchangers

The rotary regenerative heat exchanger, commonly known as the air preheater or gas reheater was invented by the Swedish engineer Frederick Ljungstrom in 1922. Shortly after, Howden and Ljungstrom worked together to commercialize the technology for use in the power generation industry.

In a rotary heat exchanger heat is transferred from a hot gas to a cold one via a rotating cylinder of densely packed metal sheets, called elements. These elements are packed in containers and slowly rotate through one gas stream and into the other.

A hot gas flows over the surface of the metallic elements, raising their temperature. As the rotor turns, at around 1RPM, the heated elements move into the cool gas stream, increasing its temperature accordingly.

Rotary heat exchangers are produced in various sizes dependent on the application, but can be as large as 20 meters in diameter, weighing over 800 tones.

Different elements are designed specifically for particular fuels or applications, with performance reflecting a balance between resistance to erosion or fouling and efficiency of heat transfer.

In a rotary air preheater some leakage of higher pressure gas into the lower pressure gas stream is inevitable as small running clearances are required between the rotor and the housing.

When handling large quantities of gas or air, regenerative heat exchangers are an extremely efficient and compact solution. The reason for this is that both surfaces of each element plate are used simultaneously for heat transfer as they rotate through both the gas and air side of the heat exchanger.

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