SYSTEM AND METHOD FOR ENHANCED RECOVERY OF ARGON AND OXYGEN FROM A NITROGEN PRODUCING CRYOGENIC AIR SEPARATION UNIT

• US 20190331417A1
• Filed: 04/25/2018
• Published: 10/31/2019
• Est. Priority Date: 04/25/2018
• Status: Active Grant

• Current Assignee: Praxair Technology Incorporated (Linde Plc)
• Original Assignee: Praxair Technology Incorporated (Linde Plc)
• Inventors: Kromer, Brian R., Handley, James R., Prosser, Neil M.
• Granted Patent: US 10,663,222 B2
• Time in Patent Office: Days
• 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 2200/94 Details relating to the withdrawal point
• CPC Class Codes: F25J 2205/60 using adsorption on solid adsorbents, e.g. by temperature-swing adsorption [TSA] at the hot or cold end
• CPC Class Codes: F25J 2210/06 Splitting of the feed stream, e.g. for treating or cooling in different ways
• CPC Class Codes: F25J 2210/40 Air or oxygen enriched air, i.e. generally less than 30mol% of O2
• CPC Class Codes: F25J 2210/42 Nitrogen
• CPC Class Codes: F25J 2215/40 Air or oxygen enriched air, i.e. generally less than 30mol% of O2
• CPC Class Codes: F25J 2215/42 Nitrogen or special cases, e.g. multiple or low purity N2
• CPC Class Codes: F25J 2220/40 Separating high boiling, i.e. less volatile components from air, e.g. CO2, hydrocarbons
• CPC Class Codes: F25J 2230/30 Compression of the feed stream
• CPC Class Codes: F25J 2230/40 the fluid being air
• CPC Class Codes: F25J 2230/42 the fluid being nitrogen
• CPC Class Codes: F25J 2230/52 the fluid being oxygen enriched compared to air, e.g. "crude oxygen"
• CPC Class Codes: F25J 2235/50 the fluid being oxygen
• CPC Class Codes: F25J 2240/40 Expansion without extracting work, i.e. isenthalpic throttling, e.g. JT valve, regulating valve or venturi, or isentropic nozzle, e.g. Laval
• CPC Class Codes: F25J 2245/50 the recycled stream being oxygen
• CPC Class Codes: F25J 2270/14 External refrigeration with work-producing gas expansion loop
• CPC Class Codes: F25J 3/04024 of purified feed air, so-called boosted air
• CPC Class Codes: F25J 3/0409 of oxygen
• CPC Class Codes: F25J 3/04169 by adsorption of the impurities adsorption in general B01D53/02
• CPC Class Codes: F25J 3/04181 : Regenerating the adsorbents
• CPC Class Codes: F25J 3/04187 : Cooling of the purified feed air by recuperative heat-exchange; Heat-exchange with product streams arrangements of cold exchangers F25J5/002
• CPC Class Codes: F25J 3/04193 : Division of the main heat exchange line in consecutive sections having different functions
• CPC Class Codes: F25J 3/04212 : and simultaneously condensing vapor from a column serving as reflux within the or another column
• CPC Class Codes: F25J 3/0423 : Subcooling of liquid process streams
• CPC Class Codes: F25J 3/0426 : The cryogenic component does not participate in the fractionation
• CPC Class Codes: F25J 3/04303 : Lachmann expansion, i.e. expanded into oxygen producing or low pressure column
• CPC Class Codes: F25J 3/04406 : using a dual pressure main column system F25J3/0446, F25J3/04624, F25J3/04636 and F25J3/04715 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 3/04672 : having a top condenser
• CPC Class Codes: F25J 3/04684 : and a bottom re-boiler F25J3/04696 takes precedence
• CPC Class Codes: F25J 3/04727 : using an auxiliary pure argon column for nitrogen rejection F25J3/04739 takes precedence
• CPC Class Codes: F25J 3/048 : Argon recovery
• CPC Class Codes: F25J 3/0486 : of vaporisers for oxygen enriched liquids, e.g. purging of liquids

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 percent 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.

Claims

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 or higher 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 93.0 percent and lower than the first oxygen concentration 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 a third 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 the first oxygen enriched stream or second oxygen enriched stream to produce a crude argon stream or a 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 fourth 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;

wherein the air separation unit is configured to recover greater than 75 percent argon if the argon is condensed against the first oxygen enriched stream and configured to recover greater than 30 percent argon if the argon is condensed against the second oxygen enriched stream; and

wherein the air separation unit is configured to produce one or more oxygen products including a high purity pumped oxygen stream from the lower pressure column 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 second oxygen enriched stream from the lower pressure column via indirect heat exchange with the oxygen enriched waste 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 have a nitrogen recovery of 98 percent or greater.

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 8, wherein the subcooler arrangement is further configured to subcool the exhaust stream via indirect heat exchange with the waste oxygen enriched stream.

11. 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).

12. The air separation unit of claim 11, 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.

13. The air separation unit of claim 11 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.

14. The air separation unit of claim 1, further comprising:

a boosted air compressor circuit coupled to the main heat exchanger;

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 exchanger.

15. 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 exchanger and a liquid oxygen stream diverted from the first oxygen enriched stream from the lower pressure column.

16. 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.

17. The air separation unit of claim 1 further comprising:

a recirculating circuit disposed between the argon condenser and the lower pressure column and configured for directing a liquid oxygen-rich stream from the argon condenser to the lower pressure column;

a gel trap disposed in operative association with the a recirculating circuit and configured to receive the liquid oxygen-rich stream and removing carbon dioxide, nitrous oxide, or other contaminants from the liquid oxygen-rich stream.

18. 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).

19. A method of separating air to produce one or more high purity nitrogen products in a cryogenic air separation unit with a total nitrogen recovery of 98 percent or greater, the method comprising the steps of:

compressing a stream of incoming feed air to produce a compressed air stream;

purifying the compressed air stream in an adsorption based prepurification unit configured to removing water vapor, carbon dioxide, nitrous oxide, and hydrocarbons from the compressed air stream to producing a compressed and purified air stream splitting 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;

cooling the first part of the compressed and purified air stream to a vapor air stream at a temperature suitable for rectification in a cryogenic distillation system and partially cooling the second part of the compressed and purified air stream;

expanding the partially cooled second part of the compressed and purified air stream in a turbine to form an exhaust stream;

rectifying the liquid air stream and exhaust stream in a cryogenic 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), the higher pressure column and the lower pressure column being linked in a heat transfer relationship via a condenser reboiler, wherein the rectifying step produces 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 93 percent and lower than the first oxygen concentration, a nitrogen overhead stream from the lower pressure column; and

a condensed nitrogen stream from the condenser-reboiler;

rectifying an oxygen-argon stream extracted from the lower pressure column in an argon column arrangement, the argon column arrangement having at least one argon column and an argon condenser and wherein the argon column is configured to produce a third oxygen enriched bottoms stream and an argon-enriched overhead;

subcooling a fourth oxygen enriched kettle stream from the higher pressure column and the condensed nitrogen stream from the condenser-reboiler via indirect heat exchange with the nitrogen overhead stream from the lower pressure column;

returning the third oxygen enriched bottoms stream from the argon column to the lower pressure column;

directing the argon-enriched overhead from the argon column to an argon condenser;

condensing the argon-enriched overhead in the argon condenser against the second oxygen enriched stream from the lower pressure column to produce a crude argon stream or a product argon stream, an argon reflux stream and an oxygen enriched waste stream;

wherein the method produces one or more high purity nitrogen products;

wherein the method recovers greater than 75 percent of the argon in the feed air stream if the argon is condensed against the first oxygen enriched stream and recover greater than 30 percent of the argon in the feed air stream if the argon is condensed against the second oxygen enriched stream; and

wherein the method recovers greater than 98 percent of the nitrogen in the feed air stream and produces one or more high purity oxygen products including a high purity pumped oxygen stream from the lower pressure column at a pressure greater than or equal to 3.4 bar(a).

20. The method of claim 19 wherein the adsorption based pre-purifier unit is a multi-bed temperature swing adsorption unit configured to purifying the compressed air stream, the multi-bed temperature swing adsorption unit is 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 regenerated with the oxygen enriched waste stream having greater than 90.0 percent oxygen content;

wherein the air separation unit is configured to produce one or more high purity nitrogen products and have a nitrogen recovery of 98 percent or greater.

21. The method of claim 19, further comprising the step of subcooling the second oxygen enriched stream from the lower pressure column via indirect heat exchange with the oxygen enriched waste stream.