Liquid products using an air and a nitrogen recycle liquefier

• US 4,705,548 A
• Filed: 04/25/1986
• Issued: 11/10/1987
• Est. Priority Date: 04/25/1986
• Status: Expired due to Fees

• Current Assignee: Air Products and Chemicals Incorporated (Linde Plc)
• Original Assignee: Air Products and Chemicals Incorporated (Linde Plc)
• Inventors: Agrawal, Rakesh, Auvil, Steven R.
• Primary Examiner(s): Capossela, Ronald C.
• Application Number:
  US06/856,087
• Time in Patent Office: 564 Days
• Field of Search: 62/18, 62/26, 62/28, 62/33, 62/38, 62/22
• US Class Current: 62/645
• CPC Class Codes: F25J 2200/20 in an elevated pressure multiple column system wherein the lowest pressure column is at a pressure well above the minimum pressure needed to overcome pressure drop to reject the products to atmosphere
• CPC Class Codes: F25J 2200/50 using multiple (re-)boiler-condensers at different heights of the column
• CPC Class Codes: F25J 2200/54 in the low pressure column of a double pressure main column system
• CPC Class Codes: F25J 2205/02 using simple phase separation in a vessel or drum
• CPC Class Codes: F25J 2245/40 the recycled stream being air
• CPC Class Codes: F25J 2245/42 the recycled stream being nitrogen
• CPC Class Codes: F25J 2250/40 One fluid being air
• CPC Class Codes: F25J 2250/42 One fluid being nitrogen
• CPC Class Codes: F25J 2270/02 Internal refrigeration with liquid vaporising loop
• CPC Class Codes: F25J 2270/08 Internal refrigeration by flash gas recovery loop
• CPC Class Codes: F25J 3/0406 of nitrogen
• CPC Class Codes: F25J 3/04175 at a pressure of substantially more than the highest pressure column
• CPC Class Codes: F25J 3/0423 Subcooling of liquid process streams
• CPC Class Codes: F25J 3/04296 Claude expansion, i.e. expanded into the main or high pressure column
• CPC Class Codes: F25J 3/04345 and comprising a gas work expansion loop
• CPC Class Codes: F25J 3/04351 of nitrogen
• CPC Class Codes: F25J 3/04393 using multiple or multistage gas work expansion
• CPC Class Codes: F25J 3/044 using a single pressure main column system only F25J3/0446, F25J3/04624, F25J3/04636 take precedence
• 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: Y10S 62/924 : Argon

Abstract

Liquid nitrogen, oxygen and/or argon are produced from a cryogenic distillative separation efficiently and economically using a combination of air recycle and nitrogen recycle to produce a liquid product.

Claims

1. In a process for the cryogenic distillative separation of air by fractionation in a distillation column to produce at least one liquid product stream selected from the group consisting of liquid nitrogen, liquid oxygen and/or liquid argon, the improvement comprising:

(a) cooling a feed air stream by appropriate refrigeration to produce at least a portion of the feed air stream as a liquid air stream;

(b) introducing at least a portion of the liquid air stream to the distillation column as feed;

(c) producing a gaseous nitrogen stream from the distillation column and recycling at least a portion of said nitrogen stream to the process;

(d) compressing the recycled nitrogen stream and reboiling a process stream with the recycle nitrogen stream to produce boil-up for the process and a condensed nitrogen stream, and

(e) recovering at least a portion of the condensed recycle nitrogen as liquid nitrogen product.

2. The process of claim 1 wherein a portion of the condensed recycle nitrogen is introduced into the distillation column as reflux.

3. The process of claim 1 wherein the compressed recycle nitrogen stream provides boil-up for a portion of the distillation column.

4. The process of claim 1 wherein the compressed recycle nitrogen stream boils a liquid feed air to the distillation column.

5. The process of claim 1 wherein at least a portion of the nitrogen streams of step (c) is recycled to provide refrigeration for the feed stream(s) before compressing it.

6. A process for the cryogenic distillative separation of air to produce at least a liquid nitrogen product, comprising the steps of:

(a) compressing feed air to an elevated pressure and removing water, carbon dioxide and condensibles from the feed air;

(b) splitting the feed air into a first split feed stream and a second split feed stream;

(c) cooling each split feed stream to a lower temperature by indirect heat exchange against process streams;

(d) expanding a first portion of the first split feed stream through a warm expander and recycling at least a part of the expanded stream to the feed air while providing refrigeration to the feed air by indirect heat exchange;

(e) expanding the second split feed stream through a cold expander and using at least a first portion of the expanded stream for a distillation step;

(f) recycling a second portion of the expanded second split stream to the feed air while providing refrigeration to the feed air by indirect heat exchange;

(g) removing an oxygen-enriched stream from the base of the distillation column;

(h) removing a gaseous nitrogen stream from the distillation column and condensing at least a first portion of the gaseous nitrogen stream against a fluid of the distillation column to form a liquid nitrogen stream;

(i) removing a second gaseous nitrogen stream from the distillation column and recycling said stream in heat exchange against process streams;

(j) recompressing the second gaseous nitrogen stream and liquefying said stream against process fluid of the distillation column to form a second liquid nitrogen stream; and

(k) recovering at least a portion of the liquid nitrogen of step (h) and/or step (j) as a liquid nitrogen product.

7. The process of claim 6 wherein the distillation column has a high pressure stage and a low pressure stage.

8. The process of claim 7 wherein nitrogen gas from the high pressure stage is condensed against oxygen-enriched fluid in the low pressure stage by indirect heat exchange.

9. The process of claim 7 wherein a gaseous nitrogen product is recovered from the low pressure stage of the distillation column.

10. The process of claim 7 wherein an oxygen enriched stream from the sump of the low pressure stage of the distillation column is indirectly heat exchanged against gaseous nitrogen from said low pressure stage in a boiler-condenser to produce liquid nitrogen and a gaseous oxygen-enriched stream.

11. The process of claim 7 wherein an oxygen-enriched stream is removed from the base of the high pressure stage of the distillation column and is boiled in a boiler-condenser of a side-arm column to provide reflux in said column which produces argon from a fluid feed from the low pressure stage of the distillation column.

12. The process of claim 6 wherein the liquid nitrogen stream of step (h) and the second liquid nitrogen stream of step (j) are combined, phase separated and at least a portion of the liquid phase is recovered as liquid nitrogen product.

13. The process of claim 6 wherein the recompressed second gaseous nitrogen stream of step (j) is liquefied in a boiler-condenser in the low pressure stage of a two pressure stage distillation column.

14. The process of claim 6 wherein the recompressed second gaseous nitrogen stream of step (j) is liquefied in a side boiler-condenser by heat exchange against a part of the second portion of the first split stream of the feed air.

15. The process of claim 6 wherein an oxygen enriched stream is removed from the low pressure stage of the distillation column.

16. The process of claim 15 wherein a liquid oxygen product is recovered from the sump of the low pressure stage of the distillation column as the oxygen enriched stream.

17. The process of claim 6 wherein a part of the second portion of the first split stream is expanded and rewarmed in a subcooling heat exchanger and combined with the first portion of the second split stream and the combined streams are introduced into the distillation column.

18. The process of claim 6 wherein at least a portion of the liquid nitrogen from the distillation column is subcooled in a subcooling heat exchanger against a part of the second portion of the first split stream, the subcooled nitrogen stream is reduced in pressure and at least a portion of the stream is recovered as liquid nitrogen product.

19. The process of claim 6 wherein the recompressed second gaseous nitrogen stream of step (j) is liquefied in a boiler-condenser in the sump of a single stage distillation column.