Method and device for producing air product based on cryogenic rectification

A method for producing an air product on the basis of cryogenic rectification, the method comprising the steps of:

• a. providing a first tower and a second tower, the top of the first tower being in communication by heat exchange with the bottom of the second tower by means of a main condensing evaporator, and an operating pressure of the first tower being higher than an operating pressure of the second tower;
• b. providing a main air compressor, an air pre-cooling system, an air purification system, a main heat exchanger, at least one nitrogen gas compressor, a supercooler, and at least one nitrogen gas expander;
• c. subjecting an air feed gas, which has been pressurized via the main air compressor, to further pre-cooling and purification, then cooling said air feed gas in the main heat exchanger before introducing into the first tower to undergo rectification;
• d. extracting a first nitrogen gas at the top of the first tower or second tower, reheating the first nitrogen gas via the main heat exchanger, then pressurizing the first nitrogen gas via the at least one nitrogen gas compressor to form a second nitrogen gas;
• at least a portion of the second nitrogen gas being cooled in the main heat exchanger to form a first liquid nitrogen, which is depressurized via a depressurization device to form a second liquid nitrogen which is sent into the top of the first tower and/or the second tower;
• at least another portion of the second nitrogen gas being partially cooled in the main heat exchanger to form a third nitrogen gas, which is expanded via a first nitrogen gas expander and then sent into the top of the first tower and/or the second tower;
• e. extracting a first oxygen-rich liquid air from the first tower, supercooling the first oxygen-rich liquid air via the supercooler, and then sending into the second tower as reflux liquid;
• wherein a second oxygen-rich liquid air or liquid air is extracted from the first tower and pressurized via a first pump, then undergoes heat exchange with the second nitrogen gas in the main heat exchanger, and an air product is then outputted.