The feed air from the purification system is rectified in the lower column and then nitrogen is obtained at its top. Small part of the gained nitrogen is used as the heat source for the fine argon column while the rest is condensed in the main condenser/evaporator. Part of the condensed liquid from the main condenser/evaporator is used as the reflux of the lower column and the rest is throttled and delivered to the upper column as the reflux after being cooled in the sub-cooler. The oxygen-enriched liquid air obtained at the bottom of the lower column is throttled to the middle of the upper column for rectification after being cooled in the sub-cooler.
After being rectified in the upper column, the product nitrogen is gained at the top of the upper column while the waste nitrogen is obtained at the upper section of the upper column. The nitrogen gas and waste nitrogen are reheated in the sub-cooler and main heat exchanger. After being reheated, part of the nitrogen gas is delivered to the pipe network of the user while the rest is sent to the water cooling tower for refrigeration; part of the waste nitrogen is used as the regenerating gas while the rest is also transferred to the water cooling tower for refrigeration. The oxygen obtained at the bottom of the upper column is delivered to the piping network of the user after being heated in the main heat exchanger.
The liquid oxygen is sent to the storage system of the user after being extracted from the bottom of the main condenser/evaporator and the liquid nitrogen is extracted to the storage system of the user after being sub-cooled.