US 11,988,446 B2
Method and apparatus for producing high-purity nitrogen and low-purity oxygen
Alain Briglia, Hangzhou (CN); Huali Xie, Hangzhou (CN); and Yongshun Zhang, Hangzhou (CN)
Assigned to L'Air Liquide, Societe Anonyme Pour L'Etude Et L'Exploitation Des Procedes Georges Claude, Paris (FR)
Filed by L'Air Liquide, Societe Anonyme pour l'Etude et l'Exploitation des Procedes Georges Claude, Paris (FR)
Filed on Sep. 8, 2021, as Appl. No. 17/469,823.
Claims priority of application No. 202010985907.3 (CN), filed on Sep. 18, 2020.
Prior Publication US 2022/0090855 A1, Mar. 24, 2022
Int. Cl. F25J 3/04 (2006.01)
CPC F25J 3/04448 (2013.01) [F25J 3/04084 (2013.01); F25J 3/0409 (2013.01); F25J 3/0423 (2013.01); F25J 3/04436 (2013.01); F25J 3/04454 (2013.01); F25J 2200/08 (2013.01); F25J 2210/40 (2013.01); F25J 2215/42 (2013.01); F25J 2215/50 (2013.01); F25J 2235/02 (2013.01); F25J 2235/42 (2013.01); F25J 2235/50 (2013.01)] 10 Claims
OG exemplary drawing
 
1. A method for producing high-purity nitrogen and low-purity oxygen, the method comprising the steps of:
cooling feedstock air in a main heat exchanger and then introducing the feedstock air into a rectification system for nitrogen/oxygen separation, the rectification system having at least a high-pressure column and a low-pressure column;
collecting an oxygen stream from a lower region of the low-pressure column, heating the oxygen stream in the main heat exchanger, and then obtaining the oxygen stream as a pressurized oxygen product;
collecting a first nitrogen stream from a top region of the high-pressure column, heating the first nitrogen stream in the main heat exchanger, and obtaining the first nitrogen stream as a pressurized nitrogen product;
collecting waste nitrogen in a gaseous state from a top region of the low-pressure column and heating the waste nitrogen in the main heat exchanger, before using as regenerated gas or venting; and
providing a medium-pressure column between the high-pressure column and low-pressure column, with an operating pressure of the medium-pressure column being between that of the high-pressure column and that of the low-pressure column,
wherein the lower region of the low-pressure column has a low-pressure condensing evaporator,
wherein a lower region of the medium-pressure column has a medium-pressure condensing evaporator,
wherein the rectification system comprises a high-pressure subcooler and a low-pressure subcooler,
wherein the feedstock air passing through a first pressurizer is pressurized to a first pressure air, and then a first portion of the first pressure air is cooled in the main heat exchanger and led into a lower region of the high-pressure column, and a second portion of the first pressure air is pressurized in a second pressurizer to a second pressure air;
wherein a first portion of the second pressure air is cooled in the main heat exchanger and collected from a middle position of the main heat exchanger, and then passes through an expander to obtain a third pressure air which is led into the lower region of the medium-pressure column, and a second portion of the second pressure air is liquefied or undergoes pseudo-liquefaction in the main heat exchanger,
wherein one portion of the second portion of the second pressure air which has been liquefied or has undergone pseudo-liquefaction is led into the lower region of the high-pressure column,
wherein another portion of the second portion of the second pressure air which has been liquefied or has undergone pseudo-liquefaction passes through the high-pressure subcooler and is led into a middle region of the low-pressure column,
wherein high-pressure oxygen-rich liquid air is collected from the bottom of the high-pressure column, passes through the low-pressure subcooler and is then throttled and led into a middle region of the medium-pressure column; medium-pressure oxygen-rich liquid air is collected from the medium-pressure condensing evaporator, passes through the low-pressure subcooler and is then throttled and led into the lower region of the low-pressure column; lean liquid nitrogen is collected from the middle region of the medium-pressure column, passes through the low-pressure subcooler and is then throttled and led into an upper region of the low-pressure column, and
wherein a second nitrogen stream is collected from an upper region of the medium-pressure column, undergoes a pressure increase in the liquid state, passes through the high-pressure subcooler and is led into the top region of the high-pressure column.