System and method for high recovery of nitrogen and argon from a moderate pressure cryogenic air separation unit

Patent metadata

Field	Value
Publication number	US-10816263-B2
Application number	US-201815962358-A
Country	US
Kind code	B2
Filing date	Apr 25, 2018
Priority date	Apr 25, 2018
Publication date	Oct 27, 2020
Grant date	Oct 27, 2020

Abstract

A moderate pressure air separation unit and air separation cycle is disclosed that provides for up to about 96% recovery of argon and an overall nitrogen recovery of 98% or greater. The air separation is configured to produce a high purity oxygen enriched stream which is used as the refrigerant to condense the argon in the argon condenser, with the resulting vaporized oxygen stream used to regenerate the temperature swing adsorption prepurifier unit. Argon recovery is facilitated with the use of an argon superstaged column.

First claim

What is claimed is:

1. An air separation unit comprising:
a main air compression system configured for receiving a stream of incoming feed air and producing a compressed air stream;
an adsorption based pre-purifier unit configured for removing water vapor, carbon dioxide, nitrous oxide, and hydrocarbons from the compressed air stream and producing a compressed and purified air stream, wherein the compressed and purified air stream is split into at least a first part of the compressed and purified air stream and a second part of the compressed and purified air stream;
a main heat exchange system configured to cool the first part of the compressed and purified air stream to produce a vapor air stream and to partially cool the second part of the compressed and purified air stream;
a turboexpander arrangement configured to expand the partially cooled second part of the compressed and purified air stream to form an exhaust stream that imparts refrigeration to the air separation unit;
a distillation column system having a higher pressure column having an operating pressure between 6.0 bar and 10.0 bar and a lower pressure column having an operating pressure between 1.5 bar and 2.8 bar linked in a heat transfer relationship via a condenser reboiler;
the distillation column system further includes an argon column arrangement operatively coupled with the lower pressure column, the argon column arrangement having at least one argon column and an argon condenser;
the distillation column system is configured to receive all or a portion of the vapor air stream in the higher pressure column and to receive the exhaust stream in the lower pressure column or the higher pressure column and to produce one or more oxygen enriched streams from the lower pressure column and a nitrogen overhead stream from the lower pressure column;
wherein the argon column is configured to receive an argon-oxygen enriched stream from the lower pressure column and to produce an oxygen enriched bottoms stream that is returned to or released into the lower pressure column and an argon-enriched overhead that is directed to the argon condenser;
a subcooler arrangement operatively coupled with the distillation column system and configured to subcool a kettle oxygen stream from the higher pressure column and a nitrogen stream from the condenser-reboiler via indirect heat exchange with the nitrogen overhead stream from the lower pressure column;
wherein the subcooler arrangement is further configured to subcool an oxygen enriched stream extracted from a lower section of the lower pressure column via indirect heat exchange with an oxygen enriched waste stream to produce a subcooled oxygen enriched stream;
wherein the argon condenser is configured to condense the argon-enriched overhead against the subcooled oxygen enriched stream extracted from the lower section of the lower pressure column to produce a crude argon stream or a product argon stream, an argon reflux stream, the oxygen enriched waste stream, and a liquid oxygen-rich stream; and
wherein the air separation unit is configured to produce one or more high purity nitrogen products and has a nitrogen recovery of 98 percent or greater.

2. The air separation unit of claim 1 , wherein the adsorption based pre-purifier unit is a multi-bed temperature swing adsorption unit configured for purifying the compressed air stream, the multi-bed temperature swing adsorption unit is further configured such that each bed alternates between an on-line operating phase adsorbing the water vapor, carbon dioxide, and hydrocarbons from the compressed air stream and an off-line operating phase where the bed is being regenerated with a purge gas taken from the air separation unit and having greater than 90.0 percent oxygen content.

3. The air separation unit of claim 2 , wherein the purge gas is the oxygen enriched waste stream.

4. The air separation unit of claim 3 , further comprising a regeneration blower configured to raise the pressure of the waste stream by about 0.1 bar(a) to 0.3 bar(a).

5. The air separation unit of claim 3 , wherein the adsorption based pre-purifier unit further comprises a steam heater, electric heater, or other non-fired heater configured to heat the oxygen enriched waste stream to a temperature less than or equal to about 450° F. for use in regenerating the adsorbent beds in the temperature swing adsorption unit.

6. The air separation unit of claim 1 , wherein the oxygen enriched stream extracted from the lower section of the lower pressure column is a high purity oxygen enriched stream taken from a sump where the oxygen-rich liquid column bottoms are located and has oxygen concentration of greater than 99.5%.

7. The air separation unit of claim 1 , wherein the oxygen enriched stream extracted from the lower section of the lower pressure column is a lower purity oxygen enriched stream taken several stages above a sump where the oxygen-rich liquid column bottoms are located and has oxygen concentration of between about 93% and 99.7%.

8. The air separation unit of claim 1 , further comprising a booster compressor configured to further compress the second part of the compressed and purified air stream.

9. The air separation unit of claim 8 , wherein a portion of the further compressed second part of purified air stream is fully or partially condensed in main heat exchanger and fed to an intermediate location of the higher pressure column.

10. The air separation unit of claim 8 , wherein the turboexpander arrangement further comprises a booster loaded turbine configured to expand the further compressed, partially cooled second part of the compressed and purified air stream to form the exhaust stream and the booster loaded turbine is operatively coupled to drive the booster compressor.

11. The air separation unit of claim 8 , wherein the subcooler arrangement is further configured to subcool the exhaust stream via indirect heat exchange with the waste oxygen enriched stream.

12. The air separation unit of claim 1 , wherein the argon column is configured to operate at a pressure of between about 1.3 bar and 2.8 bar.

13. The air separation unit of claim 12 , wherein the argon column in the argon column arrangement is a superstaged column having between 180 and 260 stages of separation.

14. The air separation unit of claim 12 wherein the argon column arrangement further comprises a first argon column configured as a superstaged argon column, and a second argon column configured as a high ratio argon column.

15. The air separation unit of claim 12 wherein the argon column in the argon column arrangement further comprises an ultra-superstaged column having between 185 and 270 stages of separation.

16. The air separation unit of claim 13 , wherein the air separation unit is configured to produce argon product and has an argon recovery of 30 percent or greater.

17. The air separation unit of claim 1 , wherein the one or more nitrogen products further comprise a high purity gaseous nitrogen product stream produced by warming the nitrogen overhead stream in the subcooler arrangement and the main heat exchanger system and a high purity liquid nitrogen product stream produced by diverting a portion of the subcooled nitrogen from the condenser-reboiler.

18. The air separation unit of claim 1 , further comprising:
an argon refining system disposed downstream of the argon condenser, the argon refining system configured to refine the crude argon stream to produce a high purity argon product stream;
wherein the argon refining system is an argon liquid adsorpti

Assignees

• Prosser Neil M
• Handley James R
• Kromer Brian R
• Praxair Technology Inc

Inventors

• Prosser Neil M
• Handley James R
• Kromer Brian R

Classifications

• F25J2200/20

  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 title

• F25J3/0486

  of vaporisers for oxygen enriched liquids, e.g. purging of liquids · CPC title

• F25J2235/50

  the fluid being oxygen · CPC title

• F25J3/04412

  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 title

• F25J3/0409 Primary

  of oxygen · CPC title