Cryogenic air separation system for enhanced liquid production

• US 20070209389A1
• Filed: 03/10/2006
• Published: 09/13/2007
• Est. Priority Date: 03/10/2006
• Status: Active Grant

• Current Assignee: Praxair Technology Incorporated (Linde Plc)
• Original Assignee: Praxair Technology Incorporated (Linde Plc)
• Inventors: Prosser, Neil
• Granted Patent: US 7,533,540 B2
• Time in Patent Office: Days
• US Class Current: 62/643
• CPC Class Codes: F25J 2240/10 the fluid being air
• CPC Class Codes: F25J 2290/10 Mathematical formulae, modeling, plot or curves; Design methods
• CPC Class Codes: F25J 3/0409 of oxygen
• CPC Class Codes: F25J 3/042 having an intermediate feed connection
• CPC Class Codes: F25J 3/04296 Claude expansion, i.e. expanded into the main or high pressure column
• CPC Class Codes: F25J 3/04303 Lachmann expansion, i.e. expanded into oxygen producing or low pressure column
• CPC Class Codes: F25J 3/04387 using liquid or hydraulic turbine expansion
• CPC Class Codes: F25J 3/04393 using multiple or multistage gas work expansion
• CPC Class Codes: F25J 3/04412 in a classical double column flowsheet, i.e. with thermal coupling by a main reboiler-condenser in the bottom of low pressure respectively top of high pressure column
• CPC Class Codes: F25J 3/04678 cooled by oxygen enriched liquid from high pressure column bottoms
• CPC Class Codes: F25J 3/04969 Retrofitting or revamping of an existing air fractionation unit

Abstract

A system for separating air by cryogenic rectification whereby liquid production is increased by employing two separate turboexpanders, one which exhausts at a pressure no higher than that sufficient to feed the lower pressure column, the other which exhausts at a pressure no lower than that sufficient to feed the higher pressure column, and wherein one of the turboexpanders is fed with ambient temperature or modestly cooled feed air and preferably operates intermittently depending upon whether greater or lesser amounts of liquid product are desired.

Claims

1. A method for operating a cryogenic air separation plant employing a double column having a higher pressure column and a lower pressure column comprising:

(A) passing a first gas stream having a temperature within the range of from 125K to 200K to a cold turbine, turboexpanding the first gas stream in the cold turbine to a pressure no greater than 3 psi higher than the operating pressure of the lower pressure column, and passing the turboexpanded first gas stream into at least one of the lower pressure column, the atmosphere, and a product stream; and

(B) passing a second gas stream having a temperature within the range of from 200K to 320K to a warm turbine, turboexpanding the second gas stream in the warm turbine to a pressure no lower than the operating pressure of the higher pressure column, and passing the turboexpanded second gas stream into at least one of the higher pressure column and the cold turbine.

2. The method of claim 1 wherein at least some oxygen product is recovered as liquid from the cryogenic air separation plant.

3. The method of claim 1 wherein at least some nitrogen product is recovered as liquid from the cryogenic air separation plant.

4. The method of claim 1 further comprising an argon column, passing fluid from the lower pressure column to the argon column, and recovering argon product from the argon column.

5. The method of claim 4 wherein at least some of the recovered argon product is recovered as liquid.

6. The method of claim 1 wherein the first gas stream comprises feed air.

7. The method of claim 1 wherein the first gas stream comprises nitrogen-enriched vapor.

8. The method of claim 1 wherein the turboexpanded first gas stream is passed into the lower pressure column.

9. The method of claim 1 wherein the turboexpanded first gas stream is recovered as product.

10. The method of claim 1 wherein the second gas stream comprises feed air.

11. The method of claim 1 wherein the second gas stream has a temperature within the range of from 280K to 320K.

12. The method of claim 1 wherein the turboexpanded second gas stream is passed into the higher pressure column.

13. The method of claim 1 wherein the turboexpanded second gas stream is passed into the cold turbine.

14. The method of claim 1 wherein the operation of the warm turbine is turned on and off during the time the cold turbine is operating.

15. The method of claim 14 wherein more liquid product is produced during the time the warm turbine is operating than during the time the warm turbine is not operating.