Water shortage and increasing costs, together with more recent concerns about water pollution and cooling tower plumes, have greatly reduced industry's use of water cooled heat exchangers. A large proportion of the process cooling in refineries and chemical plants takes place in Air Cooled Heat Exchangers (AC-HEs).
AC-HEs for process plants are normally just called Aircoolers, but should not be confused with devices for cooling air (best described as Air Chillers).
The design of an AC-HE is more complex than for a Shell and Tube Heat Exchanger, as there are many more components and variables.
Air-cooled heat exchangers are used extensively throughout the oil and gas industry, from upstream production to refineries and petrochemical plants, under high pressure and high temperature conditions, as well as corrosive fluids and environments.
Typically, an air-cooled exchanger for process use consists of a finned-tube bundle with rectangular box headers on both ends of the tubes. Cooling air is provided by one or more fans. Usually, the air blows upwards through a horizontal tube bundle.
The fans can be either forced or induced draft, depending on whether the air is pushed or pulled through the tube bundle. The space between the fan(s) and the tube bundle is enclosed by a plenum chamber which directs the air. The whole assembly is usually mounted on legs or a pipe rack.
The fans are usually driven be electric motors through some type of speed reducer. The speed reducers are usually either V-belts, HTD drives, or right angle gears. The fan drive assembly is supported by a steel mechanical drive support system. They usually include a vibration switch on each fan to automatically shut down a fan which has become imbalanced for some reason.
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