Air-cooled heat exchangers are designed to operate over a wide range of environmental
conditions, including ambient temperatures from −600F to 1300F. Special design features are
employed for operation in cold climates in order to prevent freezing of the process fluid. If
the wall temperature of a tube carrying a hydrocarbon stream reaches the pour point of the
hydrocarbon, the liquid will congeal around the wall, thereby reducing the flow area and
increasing the tube-side pressure drop. If water is present in the process stream, ice can
form around the tube wall with similar effect. Likewise, methane hydrates can form on the
tube walls of natural gas coolers.
The standard method for preventing freezing is to intentionally recirculate some of the
warm air leaving the unit in order to raise the temperature of the intake air. This can be
accomplished in a number of ways, depending on whether forced-draft or induced-draft operation is employed and the severity of the winter climate