Air separation unit

An air separation unit comprising:

• a main heat exchanger in which feed air is introduced from a warm end and drawn out from a cold end;
• an intermediate-pressure rectification column into which feed air drawn out from the main heat exchanger is introduced;
• a nitrogen condenser in which a vapor stream is introduced from the intermediate-pressure rectification column, and is condensed and drawn out as a reflux liquid;
• a low-pressure rectification column into which an oxygen-rich liquid drawn out from the intermediate-pressure rectification column is introduced;
• an oxygen turbine, which expands and cools oxygen gas drawn out from a bottom section of the low-pressure rectification column or a gas phase in a refrigerant storage section of the nitrogen condenser, after the oxygen gas has undergone heat exchange in the main heat exchanger;
• an oxygen turbine inlet pipe for feeding the oxygen gas to the oxygen turbine via the main heat exchanger, and feeding the oxygen gas to the main heat exchanger again;
• an oxygen bypass pipe which branches from the oxygen turbine inlet pipe;
• and
• a dilution stream pipe for drawing out a nitrogen-containing gas, in which the oxygen concentration is lower than the oxygen concentration in the oxygen gas drawn out from the bottom section of the low-pressure rectification column or the gas phase in the refrigerant storage section, as a dilution stream, and introducing the dilution stream into the oxygen turbine inlet pipe.