1. Raw air comes from air, goes through air filter for removal of dust and other mechanical particle and enters non-lub air compressor to becompressed by two stage compressor to approx. 0.65MPa(g).It goes through cooler and enters precooling unit to be cooled to 5~10℃.

Then it goes to switch-over MS purifier for removal of moisture, CO2, carbon hydrogen.  Purifier consists of two molecular sieve filled vessels.One is in use while anther is under regeneration by waste nitrogen from the cold box and through heater heating.

2.After purified, small part of it is used as bearing gas for turbine expander, other enters cold box to be cooled by reflux(pure oxygen, pure nitrogen and waste nitrogen) in main heat exchanger. Part of air is abstracted from the middle part of main heat exchanger and goes to expansion turbine for production of cold. Most of expanded air goes through subcooler which is cooled by oxygen from upper column to be delivered to upper column. Small part of it goes through bypass to waste nitrogen pipe directly and is reheated to go out of the cold box. The other part of air continues to be cooled to near liquid air tempt to lower column.

3.In lower column air,air is separated and liquified as liquid nitrogen and liquid air. Part of liquid nitrogen s abstracted from the top of the lower column. Liquid air after subcooled and throttled is delivered to the middle part of upper column as reflux.

4. Product oxygen is abstracted from the lower part of upper column and reheated by expanded air subcooler, main heat exchange. Then it is delivered out of column. Waste nitrogen is abstracted from the upper part of upper column and is reheated in subcooler and main heat exchanger to go out of column. Part of it is used as regeneration gas for MS purifier. Pure nitrogen is abstracted from the top of the upper column and is reheated in liquid air , liquid nitrogen subcooler and main heat exchanger to be delivered out of the column.

5.  Oxygen out of the distillation column is compressed to customer.