System and method for enhanced recovery of argon and oxygen from a nitrogen producing cryogenic air separation unit

Patent metadata

Field	Value
Publication number	US-10663223-B2
Application number	US-201815962297-A
Country	US
Kind code	B2
Filing date	Apr 25, 2018
Priority date	Apr 25, 2018
Publication date	May 26, 2020
Grant date	May 26, 2020

Abstract

A moderate pressure air separation unit and air separation cycle is disclosed that provides for up to about 96% recovery of argon, an overall nitrogen recovery of 98% or greater and limited gaseous oxygen production. The air separation is configured to produce a first high purity oxygen enriched stream and a second lower purity oxygen enriched stream from the lower pressure column, one of 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 pre-purifier unit. All or a portion of the first high purity oxygen enriched stream is vaporized in the main heat exchanger to produce the gaseous oxygen products.

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(a) and 10.0 bar(a) and a lower pressure column having an operating pressure between 1.5 bar(a) and 2.8 bar(a) 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 and to produce a first oxygen enriched stream from the lower pressure column having a first oxygen concentration greater than or equal to 99.5 percent oxygen, a second oxygen enriched stream from the lower pressure column having a second oxygen concentration greater than or equal to 93.0 percent oxygen and less than the oxygen concentration of the first oxygen enriched stream, and a nitrogen overhead stream from the lower pressure column;
wherein the first oxygen enriched stream is split into a first portion of the oxygen enriched stream and a second portion of oxygen enriched stream;
wherein the argon column is configured to receive an argon-oxygen enriched stream from the lower pressure column and to produce a 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;
wherein the argon condenser is configured to condense the argon-enriched overhead against either: (i) the first portion of the first oxygen enriched stream; or (ii) the second oxygen enriched stream, to produce a crude argon stream or product argon stream, an argon reflux stream and an oxygen enriched waste stream;
a subcooler arrangement operatively coupled with the distillation column system and configured to subcool a oxygen enriched kettle 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; and
wherein the air separation unit is configured to produce one or more high purity nitrogen products; and
wherein the air separation unit is configured to produce one or more oxygen products including a high purity pumped oxygen stream from the second portion of the oxygen enriched stream at a pressure greater than or equal to 3.4 bar(a).

2. The air separation unit of claim 1 , wherein the subcooler arrangement is further configured to subcool the first portion of the first oxygen enriched stream or the second oxygen enriched stream via indirect heat exchange with the oxygen enriched waste stream and to subcool the exhaust stream via indirect heat exchange with the waste oxygen enriched stream.

3. 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, nitrous oxide, 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; and
wherein the air separation unit is configured to produce one or more high purity nitrogen products and is configured to recover greater than or equal to 98 percent of the nitrogen contained in the compressed air stream.

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

5. The air separation unit of claim 4 , 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 second part of the compressed and purified air stream is less than about 15 percent of the total compressed and purified air stream.

7. The air separation unit of claim 1 , wherein the lower pressure column of the distillation column system are configured to receive predominately liquid streams collectively having less than 15 percent vapor.

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 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.

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

11. The air separation unit of claim 10 , wherein the argon column in the argon column arrangement is a superstaged column having between 180 and 260 stages of separation or an ultrasuperstaged column having between 185 and 270 stages of separation.

12. The air separation unit of claim 10 wherein the argon column arrangement further comprises a first argon column configured as a superstaged argon column, a second argon column configured as a high ratio argon column.

13. The air separation unit of claim 1 , further comprising:
a boosted air compressor circuit coupled to the main heat exchange system;
wherein the compressed and purified air stream is split into the first part of the compressed and purified air stream, the second part of the compressed and purified air stream, and a third part of the compressed and purified air stream; and
wherein boosted air compressor circuit is configured to further compress the third part of the compressed and purified air stream to a pressure exceeding the pressure of the pumped oxygen product stream in the main heat exchange system.

14. The air separation unit of claim 1 , wherein the one or more oxygen products further comprise a gaseous oxygen product stream from the vaporized pumped oxygen stream exiting the main heat exchange system and a liquid oxygen stream diverted from the first oxygen enriched stream from the lower pressure column.

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Assignees

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

Inventors

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

Classifications

• F25J2200/08

  in a triple pressure main column system · CPC title

• F25J2245/50

  the recycled stream being oxygen · CPC title

• F25J2230/42

  the fluid being nitrogen · CPC title

• F25J3/04303

  Lachmann expansion, i.e. expanded into oxygen producing or low pressure column · CPC title

• F25J3/04193

  Division of the main heat exchange line in consecutive sections having different functions · CPC title