Air separation unit is a kind of unit which takes air as raw material, turns air into liquid by compression cycle deep freezing method, and then gradually separates and produces inert gases such as oxygen, nitrogen and argon from liquid air after rectification. Air separation unit is widely used in metallurgy, new coal chemical industry, large-scale nitrogen fertilizer, refining and chemical integration, professional gas supply and other fields. The demand for liquid oxygen and liquid nitrogen air separation unit is also increasing.