Generally, there are three types of expanders, namely, low-pressure expander, medium pressure expander and liquid expander. For a certain type of gas expander, the greater the volume flow of working medium, the higher the efficiency. Generally, the efficiency of the low-pressure expander with a flow of more than 8000nm is 85 ∽ 88%, and the efficiency of the expander with a flow of less than 3000 ∽ 8000nm will be as low as 70 ∽ 80%.

The air cooling tower of precooling system has two forms: closed circulation (the air cooling tower is divided into upper and lower sections, and the chilled water circulates between the upper section of the air cooling tower and the water cooling tower) and open circulation (into the circulating water system). The closed circulation is mainly used in chemical plants with poor water quality, which needs to supplement fresh water and chemicals