Air separation device and air separation method

An air separation device, comprising:

• a high-pressure column which distills high-pressure raw material air at a low temperature and separates it into high-pressure nitrogen gas and high-pressure oxygen-enriched liquefied air;
• a low-pressure column which distills the high-pressure oxygen-enriched liquefied air at a low temperature and separates it into low-pressure nitrogen gas, low-pressure liquefied oxygen, and argon-enriched liquefied oxygen;
• an argon column which distills the argon-enriched liquefied oxygen having a pressure higher than the pressure of the low-pressure column at a low temperature and separates it into argon gas and medium-pressure liquefied oxygen;
• a first indirect heat-exchanger which indirectly heat-exchanges between the argon gas and the low-pressure liquefied oxygen, liquefies the argon gas to generate liquefied argon, and vaporizes the low-pressure liquefied oxygen to generate low-pressure oxygen gas;
• a second indirect heat-exchanger which indirectly heat-exchanges between the high-pressure nitrogen gas and the medium-pressure liquefied oxygen, liquefies the high-pressure nitrogen gas to generate high-pressure liquefied nitrogen, and vaporizes the medium-pressure liquefied oxygen to generate medium-pressure oxygen gas;
• a first gas-liquid separation chamber which separates the low-pressure oxygen gas which has been vaporized by the first indirect heat-exchanger and the low-pressure liquefied oxygen which has not been vaporized by the first indirect heat-exchanger into a gas phase and a liquid phase;
• a second gas-liquid separation chamber which separates the medium-pressure oxygen gas which has been vaporized by the second indirect heat-exchanger and the medium-pressure liquefied oxygen which has not been vaporized by the second indirect heat-exchanger into a gas phase and a liquid phase;
• a first passage which communicates the gas phase of the low-pressure column and the gas phase of the second gas-liquid separation chamber;
• a second passage which communicates the liquid phase of the low-pressure column and the second gas-liquid separation chamber;
• a first opening/closing mechanism located on the first passage;
• and
• a second opening/closing mechanism located on the second passage.