Air preheater

An air preheater is any device designed to heat air before another process (for example, combustion in a boiler), with the primary objective of increasing the thermal efficiency of the process. They may be used alone or to replace a recuperative heat system or to replace a steam coil.

In particular, this article describes the combustion air preheaters used in large boilers found in thermal power stations producing electric power from e.g. fossil fuels, biomass or waste.^[1]^[2]^[3]^[4]^[5] For instance, as the Ljungström air preheater has been attributed worldwide fuel savings estimated to 4,960,000,000 tons of oil, "few inventions have been as successful in saving fuel as the Ljungström Air Preheater", marked as the 44th International Historic Mechanical Engineering Landmark by the American Society of Mechanical Engineers.^[6]

The purpose of the air preheater is to recover the heat from the boiler flue gas which increases the thermal efficiency of the boiler by reducing the useful heat lost in the flue gas. As a consequence, the flue gases are also conveyed to the flue gas stack (or chimney) at a lower temperature, allowing simplified design of the conveyance system and the flue gas stack. It also allows control over the temperature of gases leaving the stack (to meet emissions regulations, for example). It is installed between the economizer and chimney.

^ Sadik Kakaç; Hongtan Liu (2002). Heat Exchangers: Selection, Rating and Thermal Design (2nd ed.). CRC Press. ISBN 0-8493-0902-6.
^ Babcock & Wilcox Co. (2005). Steam: Its Generation and Use (41st ed.). ISBN 0-9634570-0-4.
^ Sadik Kakaç, ed. (April 1991). Boilers. Evaporators and Condensers. Wiley Interscience. ISBN 0-471-62170-6. (See Chapter 8 by Z.H. Lin)
^ British Electricity International (1991). Modern Power Station Practice: incorporating modern power system practice (3rd Edition (12 volume set) ed.). Pergamon. ISBN 0-08-040510-X.
^ Thomas C. Elliott; Kao Chen; Robert Swanekamp (1997). Standard Handbook of Powerplant Engineering (2nd ed.). McGraw-Hill Professional. ISBN 0-07-019435-1.
^ "The Ljungström Air Preheater 1920". asme.org. American Society of Mechanical Engineers. June 21, 1995. Archived from the original on October 20, 2016. Retrieved April 5, 2019.

[Liu-1] Sadik Kakaç; Hongtan Liu (2002). Heat Exchangers: Selection, Rating and Thermal Design (2nd ed.). CRC Press. ISBN 0-8493-0902-6.

[BW-2] Babcock & Wilcox Co. (2005). Steam: Its Generation and Use (41st ed.). ISBN 0-9634570-0-4.

[Sadik-3] Sadik Kakaç, ed. (April 1991). Boilers. Evaporators and Condensers. Wiley Interscience. ISBN 0-471-62170-6. (See Chapter 8 by Z.H. Lin)

[4] British Electricity International (1991). Modern Power Station Practice: incorporating modern power system practice (3rd Edition (12 volume set) ed.). Pergamon. ISBN 0-08-040510-X.

[5] Thomas C. Elliott; Kao Chen; Robert Swanekamp (1997). Standard Handbook of Powerplant Engineering (2nd ed.). McGraw-Hill Professional. ISBN 0-07-019435-1.

[6] "The Ljungström Air Preheater 1920". asme.org. American Society of Mechanical Engineers. June 21, 1995. Archived from the original on October 20, 2016. Retrieved April 5, 2019.

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