Air separation device and air separation method

An air separation device, comprising:

• a high-pressure column configured to distill high-pressure raw material air at a low temperature and separate it into high-pressure nitrogen gas and high-pressure oxygen-enriched liquefied air;
• a low-pressure column configured to distill the high-pressure oxygen-enriched liquefied air at a low temperature and separate it into low-pressure nitrogen gas, low-pressure liquefied oxygen, and argon-enriched liquefied oxygen;
• an argon column configured to distill the argon-enriched liquefied oxygen having a pressure higher than the pressure of the low-pressure column at a low temperature and separate it into argon gas and medium-pressure liquefied oxygen;
• a first indirect heat-exchanger configured to indirectly heat-exchange between the argon gas and the low-pressure liquefied oxygen, liquefy the argon gas to generate liquefied argon, and vaporize the low-pressure liquefied oxygen to generate low-pressure oxygen gas;
• a second indirect heat-exchanger configured to indirectly heat-exchange between the high-pressure nitrogen gas and the medium-pressure liquefied oxygen, liquefy the high-pressure nitrogen gas to generate high-pressure liquefied nitrogen, and vaporize the medium-pressure liquefied oxygen to generate medium-pressure oxygen gas;
• a first gas-liquid separation chamber configured to separate 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 configured to separate 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 configured to communicate the gas phase of the low-pressure column and the gas phase of the second gas-liquid separation chamber;
• a second passage configured to communicate the liquid phase of the low-pressure column and the second gas-liquid separation chamber;
• a movable first opening/closing mechanism located on the first passage;
• and
• a movable second opening/closing mechanism located on the second passage.