For this kind of natural gas liquefaction plant, the liquefaction unit usually adopts step-by-step liquefaction process and mixed refrigerant liquefaction process. The natural gas liquefaction plant, which was first built in 1960s, adopted the step-by-step liquefaction process with mature technology at that time. In 1970s, it became a simplified mixed refrigerant liquefaction process. After the 1980s, almost all newly built or expanded basic load liquefaction plants adopted propane precooling mixed refrigerant liquefaction process. The advantages of cascade liquefaction process are low energy consumption, independent refrigeration cycle and natural gas liquefaction system, less mutual restriction and stable operation. Its disadvantages are complex technology, many units and equipment for producing and storing various refrigerants, no infiltration between refrigeration circulation systems and inconvenient maintenance.
The world's first large-scale basic load liquefaction plant (CAMEL) was built in Algeria, which adopted a cascade liquefaction process consisting of propane, ethylene and methane. It was delivered in Arzew, Algeria on 1964. Liquefaction device * * has three identical liquefaction devices, each with a liquefaction capacity of1.42m3/d. In order to reduce the energy consumption of the mixed refrigerant liquefaction process, many improved mixed refrigerant liquefaction processes appeared in the late 1960s. In 1970s, APCI (American Air Liquefaction Company) developed the propane precooling mixed refrigerant liquefaction process, and obtained the patent of 1973, which was widely used in large LNG plants. It is a combination of cascade cycle and mixed refrigerant cycle, and propane is used to cool natural gas from 40 degrees Celsius to -30 degrees Celsius. The mixed refrigerant cycle cools the natural gas from -30℃ to-160℃.