The technology of air separation with the help of cryogenic temperatures is by far not new. The principle of cryogenic plants operation is based on the air liquefaction and its subsequent separation with the recovery of nitrogen, oxygen, and argon.
This method of gas production is called deep air freezing. The feed air is initially compressed, and, after passing though the heat exchangers, is expanded in the turbine expander or on the expansion valve with the resulting temperature decrease down to the 93 °K point, where it is turned into liquid.
Subsequent separation of liquefied air, which mainly consists of liquid nitrogen and liquid oxygen, is based on the difference in the boiling points of its components: oxygen — 90.18 °K, nitrogen — 77.36 °K. By gradual evaporation of liquid air, nitrogen is being preferentially evaporated, while the residual liquid is becoming increasingly saturated with oxygen. The process is then multiply repeated at the air separation rectifying tray with the production of liquid oxygen, nitrogen, and argon of the required purity.