METHOD AND APPARATUS FOR AIR SEPARATION BY CRYOGENIC DISTILLATION

• US 20200132367A1
• Filed: 05/18/2018
• Published: 04/30/2020
• Est. Priority Date: 05/24/2017
• Status: Active Application

• Current Assignee: L'Air Liquide Societe Anonyme Pour L'Etude et L'Exploitation Des Procedes Georges Claude (L'Air Liquide SA)
• Original Assignee: L'Air Liquide Societe Anonyme Pour L'Etude et L'Exploitation Des Procedes Georges Claude (L'Air Liquide SA)
• Inventors: TRANIER, Jean-Pierre
• Application Number:
  US16/615,978
• Publication Number:
  US 20200132367A1
• Time in Patent Office: Days
• CPC Class Codes: F25J 1/0012 Primary atmospheric gases, e.g. air
• CPC Class Codes: F25J 1/0015 Nitrogen
• CPC Class Codes: F25J 1/0037 of a return stream
• CPC Class Codes: F25J 1/0045 by vaporising a liquid return stream
• CPC Class Codes: F25J 1/0224 in combination with an internal quasi-closed refrigeration loop F25J1/0208, F25J1/0219 take precedence
• CPC Class Codes: F25J 1/0234 Integration with a cryogenic air separation unit cryogenic separation of air F25J3/04
• CPC Class Codes: F25J 2200/06 in a classical double column flow-sheet, 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 2205/66 Regenerating the adsorption vessel, e.g. kind of reactivation gas
• CPC Class Codes: F25J 2210/42 Nitrogen
• CPC Class Codes: F25J 2210/50 Oxygen
• CPC Class Codes: F25J 2240/10 the fluid being air
• CPC Class Codes: F25J 2245/58 the recycled stream being argon or crude argon
• CPC Class Codes: F25J 2250/42 One fluid being nitrogen
• CPC Class Codes: F25J 2250/58 One fluid being argon or crude argon
• CPC Class Codes: F25J 2270/02 Internal refrigeration with liquid vaporising loop
• CPC Class Codes: F25J 2270/90 External refrigeration, e.g. conventional closed-loop mechanical refrigeration unit using Freon or NH3, unspecified external refrigeration
• CPC Class Codes: F25J 3/04054 of air
• CPC Class Codes: F25J 3/0406 of nitrogen
• CPC Class Codes: F25J 3/04084 of nitrogen
• CPC Class Codes: F25J 3/0409 of oxygen
• CPC Class Codes: F25J 3/04181 : Regenerating the adsorbents
• CPC Class Codes: F25J 3/04224 : Cores associated with a liquefaction or refrigeration cycle
• CPC Class Codes: F25J 3/04278 : using external refrigeration units, e.g. closed mechanical or regenerative refrigeration units
• CPC Class Codes: F25J 3/04303 : Lachmann expansion, i.e. expanded into oxygen producing or low pressure column
• CPC Class Codes: F25J 3/04339 : of air
• 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 3/04357 : and comprising a gas work expansion loop
• 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 3/04509 : within the cold part of the air fractionation, i.e. exchanging "cold" within the fractionation and/or main heat exchange line
• CPC Class Codes: F25J 3/04515 : Simultaneously changing air feed and products output
• CPC Class Codes: F25J 3/04678 : cooled by oxygen enriched liquid from high pressure column bottoms
• CPC Class Codes: F25J 3/04727 : using an auxiliary pure argon column for nitrogen rejection F25J3/04739 takes precedence

Abstract

A method for separating air by cryogenic distillation in a system of columns comprising a first column and a second column operating at a lower pressure than the first column, comprising the steps of compressing all of the feed air in a first compressor to a first output pressure of at least 1 bar greater than the pressure of the first column, sending a first portion of the air under the first output pressure to the second compressor, and compressing the air to a second output pressure, cooling and condensing at least a portion of the air under the second output pressure in a heat exchanger, withdrawal of a liquid from a column of the system of columns, pressurising the liquid and evaporating the liquid by heat exchange in the heat exchanger, and pressure reduction of a portion of the compressed air to a second output pressure, at least partially evaporating said air in the heat exchanger, optionally additional heating of said air in the heat exchanger, and sending at least a portion of this air to the second compressor.

Claims

1-15. -15. (canceled)

16. A process for the separation of air by cryogenic distillation in a system of columns comprising a first column and a second column operating at a lower pressure than the first column, the process comprising the steps of:

i) compressing all of the feed air in a first compressor up to a first outlet pressure of at most one bar greater than and preferably substantially equal to the pressure of the first column;

ii) sending a first part of the air under the first outlet pressure to a second compressor, and compression of the air to a second outlet pressure;

iii) cooling and condensation of at least a part of the air under the second outlet pressure in the heat exchanger;

iv) sending an air gas flow under the first outlet pressure to the system of columns, without more forceful compression, and separation of the air in the system of columns;

v) withdrawing the liquid from the system of columns, pressurizing the liquid and vaporizing the liquid by heat exchange in the heat exchanger; and

vi) reducing a pressure of at least a fraction of the cooled and condensed air, from the second outlet pressure to at least a third pressure, at least partial vaporizing of said air in the heat exchanger under the at least a third pressure, the third pressure being intermediate between the first outlet pressure and the second outlet pressure, wherein at least a vaporized part of this air is sent to the second compressor in order to be compressed up to the second outlet pressure.

17. The process as claimed in claim 16, wherein the reduction in pressure is carried out in at least one valve.

18. The process as claimed in claim 16, wherein the reduction in pressure is carried out in at least one turbine and produces work.

19. The process as claimed in claim 16, wherein step vi) further comprises heating of said at least partially vaporized air in the heat exchanger.

20. The process as claimed in claim 16, wherein the temperature of the at least a fraction before reduction in pressure is less than the sum of the temperature of the vaporization of the liquid and the minimum temperature approach in the heat exchanger.

21. The process as claimed in claim 16, wherein the second compressor is a multistage compressor.

22. The process as claimed in claim 21, wherein said at least a third pressure is at least the inlet pressure of one of the stages of the second compressor.

23. The process as claimed in claim 16, wherein a stage of the second compressor is driven by a device for the reduction in pressure with regard to a fluid of the process.

24. The process as claimed in claim 23, wherein the inlet temperature of the device for the reduction in pressure is less than ambient temperature.

25. The process as claimed in claim 16, wherein at least one stage of the second compressor has a suction temperature which is less than ambient temperature.

26. The process as claimed in claim 25, wherein the suction temperature is greater than the vaporization temperature of the liquid, but is close to it,

27. The process as claimed in claim 16, wherein the liquid is a flow enriched in oxygen.

28. The process as claimed in claim 16, wherein the liquid is a flow enriched in nitrogen.

29. The process as claimed in claim 16, wherein the production flow of the final liquid product or products is not greater than 10% of the feed air.

30. The process as claimed in claim 16, wherein the production flow of the final liquid product or products is not greater than 5% of the feed air.

31. An apparatus for separating air by cryogenic distillation in a system of columns comprising a first column and a second column operating at a lower pressure than the first column, additionally comprising:

i) a first compressor configured to compress the feed air to a first outlet pressure of at most one bar greater than the pressure of the first column;

ii) means for sending purified and cooled air from the first compressor at the first pressure to the system of columns in order to be separated therein;

ii) a second compressor and a means for sending a first part of the air under the first outlet pressure from the first compressor to the second compressor, in order to compress the air to a second outlet pressure;

iii) a heat exchanger, in which at least a part of the air under the second outlet pressure is cooled and condensed;

iv) a means for removing the liquid from a column of the system of columns, a means for pressurizing the liquid, a means for sending the pressurized liquid to the heat exchanger and a means for removing the vaporized liquid from the heat exchanger; and

v) a means for reducing in pressure a fraction of the air cooled and condensed under the second outlet pressure, a means for sending said pressure-reduced air to the heat exchanger and a means for sending at least a part of said pressure-reduced air, which has been vaporized in the heat exchanger under at least a third pressure, intermediate between the first and second outlet pressures, from the heat exchanger to the second compressor, in order to compress said pressure-reduced air to the second outlet pressure.

32. The apparatus as claimed in claim 31, where the means for reducing in pressure is a valve or a turbine.