Air separation method and apparatus

An air separation method for cryogenically liquefying and separating feed air to collect product oxygen comprising:

• a first separation step in which compressed, purified and cooled feed air is cryogenically distilled to be separated into high pressure nitrogen gas and high pressure oxygen-enriched liquid air;
• a second separation step in which the high pressure oxygen-enriched liquid air is cryogenically distilled after reducing pressure to be separated into medium pressure nitrogen gas, and medium pressure oxygen-enriched liquid air;
• a third separation step in which low pressure oxygen-enriched liquid air which is the medium pressure oxygen-enriched liquid air whose pressure is reduced is cryogenically distilled to be separated into low pressure nitrogen gas and low pressure liquid oxygen;
• a first indirect heat exchange step in which indirect heat exchange is performed between the medium pressure nitrogen gas, and low pressure oxygen-enriched refluxed liquid air in an intermediate stage in the third separation step, and the medium pressure nitrogen gas is condensed to obtain a medium pressure liquid nitrogen, and at the same time, the low pressure oxygen-enriched refluxed liquid air is vaporized to obtain low pressure oxygen-enriched vaporized air;
• a second indirect heat exchange step in which indirect heat exchange is performed between the high pressure nitrogen gas and the low pressure liquid oxygen, and the high pressure nitrogen gas is condensed to obtain high pressure liquid nitrogen, and at the same time, the low pressure liquid oxygen is vaporized to obtain low pressure oxygen gas;
• a third indirect heat exchange step in which indirect heat exchange is performed between high pressure nitrogen-enriched air in an intermediate stage in the first separation step and the medium pressure oxygen-enriched liquid air, and the high pressure nitrogen-enriched air is condensed to obtain high pressure nitrogen-enriched liquid air, and at the same time, the medium pressure oxygen-enriched liquid air is vaporized to obtain medium pressure oxygen-enriched air;
• and
• a product gas collecting step in which the low pressure oxygen gas and/or the low pressure liquid oxygen is/are collected as a product oxygen gas after heat recovery.

An air separation apparatus for cryogenically liquefying and separating feed air to collect product oxygen comprising:

• a high pressure column in which compressed, purified and cooled feed air is cryogenically distilled to be separated into high pressure nitrogen gas and high pressure oxygen-enriched liquid air;
• a medium pressure column in which the high pressure oxygen-enriched liquid air is cryogenically distilled after reducing pressure to be separated into medium pressure nitrogen gas, and medium pressure oxygen-enriched liquid air;
• a medium pressure column condenser in which indirect heat exchange is performed between low pressure oxygen-enriched liquid air which is the medium pressure oxygen-enriched liquid air whose pressure is reduced and the medium pressure nitrogen gas, and the medium pressure nitrogen gas is condensed to obtain a medium pressure liquid nitrogen, and at the same time, the low pressure oxygen-enriched liquid air is vaporized to obtain low pressure oxygen-enriched air;
• a low pressure column in which the low pressure oxygen-enriched air is cryogenically distilled to be separated into low pressure nitrogen gas and low pressure liquid oxygen;
• a main condenser reboiler in which indirect heat exchange is performed between the high pressure nitrogen gas and the low pressure liquid oxygen, and the high pressure nitrogen gas is condensed to obtain high pressure liquid nitrogen, and at the same time, the low pressure liquid oxygen is vaporized to obtain low pressure oxygen gas;
• a medium pressure column reboiler in which indirect heat exchange is performed between high pressure nitrogen-enriched air taken out from an intermediate portion in the high pressure column and the medium pressure oxygen-enriched liquid air, and the high pressure nitrogen-enriched air is condensed to obtain high pressure nitrogen-enriched liquid air, and at the same time, the medium pressure oxygen-enriched liquid air is vaporized to obtain medium pressure oxygen-enriched air;
• and
• a product oxygen gas collecting path in which the low pressure oxygen gas and/or the low pressure liquid oxygen is/are collected as a product oxygen gas after heat recovery.

An air separation apparatus for cryogenically liquefying and separating feed air to collect product oxygen comprising:

• a high pressure column in which compressed, purified and cooled feed air is cryogenically distilled to be separated into high pressure nitrogen gas and high pressure oxygen-enriched liquid air;
• a medium pressure column in which the high pressure oxygen-enriched liquid air is cryogenically distilled after reducing pressure to be separated into medium pressure nitrogen gas, and medium pressure oxygen-enriched liquid air;
• a low pressure column in which low pressure oxygen-enriched liquid air which is the medium pressure oxygen-enriched liquid air whose pressure is reduced is cryogenically distilled to be separated into low pressure nitrogen gas and low pressure liquid oxygen;
• a medium pressure nitrogen condenser in which indirect heat exchange is performed between the medium pressure nitrogen gas, and low pressure oxygen-enriched refluxed liquid air descending at an intermediate portion of the low pressure column, and the medium pressure nitrogen gas is condensed to obtain medium pressure liquid nitrogen, and at the same time, the low pressure oxygen-enriched refluxed liquid air is vaporized to obtain low pressure oxygen-enriched vaporized air;
• a main condenser reboiler in which indirect heat exchange is performed between the high pressure nitrogen gas and the low pressure liquid oxygen, and the high pressure nitrogen gas is condensed to obtain high pressure liquid nitrogen, and at the same time, the low pressure liquid oxygen is vaporized to obtain low pressure oxygen gas;
• a medium pressure column reboiler in which indirect heat exchange is performed between high pressure nitrogen-enriched air taken out from an intermediate portion of the high pressure column and the medium pressure oxygen-enriched liquid air, and the high pressure nitrogen-enriched air is condensed to obtain high pressure nitrogen-enriched liquid air, and at the same time, the medium pressure oxygen-enriched liquid air is vaporized to obtain medium pressure oxygen-enriched air;
• and
• a product gas collecting path in which the low pressure oxygen gas and/or the low pressure liquid oxygen is/are collected as a product oxygen gas after heat recovery.