Dust and mechanical impurities in air are removed by air Bai filter Du and compressed to < 0.7MPa in oil-free air compressor. The hot knife generated by compression is taken away by cooling water after heat exchange by water cooler, and then enters the precooling unit for precooling to (2 ~ 10) ℃. In this stage, part of the free water is separated and then goes to the Molecular Sieve Purifier (ms1201 or ms1202) for switching. The residual water vapor, carbon dioxide, acetylene and other hydrocarbons in the air are adsorbed. The two adsorption cylinders of the molecular sieve purifier are used alternately, one working and the other regenerating. The two groups of purifier adsorption cylinders are controlled by the program controller and automatically switched on time.

The purified dry air temperature of the purifier rises to ~ 15 ℃. It is divided into two parts: most of the air enters into the air separation cooling box and exchanges heat with the reflux cold air flow (pure oxygen, pure nitrogen, sewage nitrogen and pressure nitrogen) in the main plate fin heat exchanger. The temperature drops to close to the liquefying temperature and enters the lower tower after throttling by V1 valve.

After the other part of the air enters the supercharger for pressurization, about 100m3 / h gas is used as the gas bearing gas of the turbo expander unit, and the rest goes into the cold box to exchange heat with the reflux cold air flow (pure oxygen, pure nitrogen, sewage nitrogen, etc.) in the main plate fin heat exchanger, and then is pumped out through the intermediate extraction valve V5 or bottom suction valve V6, and enters the expansion refrigeration of the expander. The expansion air enters into the tower through V12 valve or enters sewage nitrogen pipeline through V11 valve bypass, and is discharged into cold box after reheating by main heat exchanger.

In the lower tower, the air is initially divided into liquid nitrogen and oxygen enriched liquid air. The rising nitrogen in the condensing evaporator exchanges heat with the low-pressure liquid oxygen at the bottom of the upper tower, and the low-pressure liquid oxygen is liquefied and vaporized at the same time. The liquid nitrogen is divided into two routes, one of which enters the lower tower as reflux through valve V4, and the other enters the upper part of upper tower through V3 valve after heat exchange with pure nitrogen and sewage nitrogen through cooler. The oxygen rich liquid gas in the lower tower is drawn out from the bottom of the tower, subcooled with pure nitrogen and waste nitrogen by the cooler, and then sent to the upper tower as reflux liquid through V2 valve throttling.

After further distillation, high purity nitrogen was obtained at the top of the upper column and oxygen was obtained at the bottom of the upper column. The pure nitrogen is extracted from the top of the upper tower, reheated by the cooler and the main heat exchanger, and then sent to the cold box for compression filling or liquefaction; the polluted nitrogen is extracted from the upper part of the upper tower, reheated by the cooler and the main heat exchanger, and then out of the cold box of the main heat exchanger. One part is used as regeneration gas of purifier and the other part is discharged. After the oxygen is reheated by the main heat exchanger, it is sent out by the cold box for compression filling or liquefaction, and then heated and pressurized. The nitrogen is forced to pass through the main heat exchanger, and the heater is sent out from the cold box.