Page 529 - Mechanical Engineers' Handbook (Volume 4)

518 Cryogenic Systems

these plants are located in remote areas where energy is cheap but repair facilities expensive
or nonexistent. Thus, only two types of processes have been used: the classic cascade cycle
and the mixed refrigerant cascade. Of these the mixed refrigerant cascade has gradually
become dominant because of its mechanical simplicity and reliability.
Figure 40 shows a simplified process flow sheet of a mixed refrigerant cascade liquefier
for natural gas. Here the natural gas passes through a succession of heat exchangers, or of
bundles in a single heat exchanger, until liquified. The necessary refrigeration is supplied by
a multicomponent refrigeration loop, which is essentially a Joule-Thomson cycle with suc-
cessive phase separators to remove liquids as they are formed. These liquid streams are
subcooled, expanded to low pressure, and used to supply the refrigeration required both by
the natural gas and by the refrigerant mixture.

Figure 40 Mixed refrigerant LNG process flow sheet. (Courtesy Plenum Press.)