3.2.6 Refrigeration
Refrigeration is needed for processes that require temperatures below those that can be economically
obtained with cooling water, i.e., below about 40 ºC. For temperatures down to around 10 °C, chilled
water can be used. For lower temperatures, down to −30 °C, salt brines (NaCl and CaCl2) are sometimes
used to distribute the “refrigeration” around the site from a central refrigeration machine. Large
refrigeration duties are usually supplied by a standalone packaged refrigeration system.
Vapor compression refrigeration machines are normally used, as illustrated in Figure 3.5. The
working fluid (refrigerant) is compressed as a vapor, and then cooled and condensed at high pressure,
allowing heat rejection at high temperature in an exchanger known as a condenser. Heat is
usually rejected to a coolant such as cooling water or ambient air. The liquid refrigerant is then
expanded across a valve to a lower pressure, where it is vaporized in an exchanger known as an
evaporator, taking up heat at low temperature. The vapor is then returned to the compressor, completing
the cycle.