Small scale ASU consists of air compressor, pre-cooling unit, purification system, turbo expander, fractionation tower, liquid oxygen pump and connecting pipelines. Small scale ASU is a plant that uses cryogenic technology to extract oxygen from the air. It mainly relies on the turbo expander to provide cooling capacity to liquefy the air. Then use the different boiling points of liquid oxygen and nitrogen to separate oxygen and nitrogen in the fractionation tower. Then obtain high-purity oxygen and high-purity nitrogen. Application scope of small scale ASU: hospital oxygen, steel smelting, non-ferrous smelting industry, chemical industry, paper industry, laser cutting, small gas factory.