Process for the generation of gaseous and/or liquid nitrogen

• US 4,595,405 A
• Filed: 12/21/1984
• Issued: 06/17/1986
• Est. Priority Date: 12/21/1984
• 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): Sever, Frank
• Application Number:
  US06/684,655
• Time in Patent Office: 543 Days
• Field of Search: 62/23-33, 62/38, 62/39, 62/18, 62/19, 55/68, 55/73
• US Class Current: 62/646
• CPC Class Codes: B01D 53/229 Integrated processes (Diffusion and at least one other process, e.g. adsorption, absorption)
• CPC Class Codes: C01B 23/00 Noble gases; Compounds thereof liquefying F25J ; noble gases obtained by rectification F25J3/028
• CPC Class Codes: F25J 2200/02 in a single pressure main column system
• CPC Class Codes: F25J 2200/72 Refluxing the column with at least a part of the totally condensed overhead gas
• CPC Class Codes: F25J 2205/02 using simple phase separation in a vessel or drum
• 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 2205/80 using membrane, i.e. including a permeation step
• CPC Class Codes: F25J 2205/82 using a reactor with combustion or catalytic reaction
• CPC Class Codes: F25J 2210/50 Oxygen
• CPC Class Codes: F25J 2215/42 Nitrogen or special cases, e.g. multiple or low purity N2
• CPC Class Codes: F25J 2230/52 the fluid being oxygen enriched compared to air, e.g. "crude oxygen"
• CPC Class Codes: F25J 2245/02 Recycle of a stream in general, e.g. a by-pass stream
• CPC Class Codes: F25J 2245/42 the recycled stream being nitrogen
• CPC Class Codes: F25J 2245/90 the recycled stream being boil-off gas from storage
• CPC Class Codes: F25J 2270/02 Internal refrigeration with liquid vaporising loop
• CPC Class Codes: F25J 2290/10 Mathematical formulae, modeling, plot or curves; Design methods
• CPC Class Codes: F25J 3/04193 Division of the main heat exchange line in consecutive sections having different functions
• CPC Class Codes: F25J 3/042 having an intermediate feed connection
• CPC Class Codes: F25J 3/04218 Parallel arrangement of the main heat exchange line in cores having different functions, e.g. in low pressure and high pressure cores F25J3/04503 takes precedence
• 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 3/04636 : using a hybrid air separation unit, e.g. combined process by cryogenic separation and non-cryogenic separation techniques F25J3/04733 and F25J3/04757 take precedence
• CPC Class Codes: Y02P 20/129 : Energy recovery, e.g. by cogeneration, H2recovery or pressure recovery turbines
• CPC Class Codes: Y10S 62/939 : Partial feed stream expansion, air

Abstract

The present invention involves an efficient process for separating components of a gas stream by integrating a cryogenic separation unit and a membrane separation unit. One embodiment provides for the generation of one or more nitrogen-rich streams in the gas or liquid phase, or both, from a stream comprising oxygen and nitrogen; e.g., air.

Claims

1. A process for the production of gaseous and/or liquid nitrogen from a feed gas stream comprising nitrogen and oxygen, said process comprising providing an additional degree of freedom for adjusting the process parameters by:

(a) feeding said feed gas stream comprising nitrogen and oxygen to a cryogenic separation unit to treat said gas stream;

(b) withdrawing at least a portion of the treated gas stream from the cryogenic separation unit;

(c) feeding said portion of the treated gas stream to a membrane unit wherein said stream is separated to form a nitrogen-rich stream and an oxygen-rich stream;

(d) returning said nitrogen-rich stream to the cryogenic separation unit for further treatment and separation; and

(e) subsequently recovering a purified liquid and/or gaseous nitrogen-rich product stream.

2. The process in accordance with claim 1 wherein at least a portion of said oxygen-rich stream is returned to the cryogenic separation unit for further processing.

3. The process in accordance with claim 2 wherein said oxygen-rich stream is passed through a compressor prior to being returned to the cryogenic separation unit.

4. The process in accordance with claim 1 wherein the feed gas stream comprising nitrogen and oxygen is air.

5. The process in accordance with claim 4 wherein the feed gas stream is passed through an H₂ O and CO₂ removal unit prior to being fed to the cryogenic separation unit.

6. The process in accordance with claim 5 wherein said H₂ O and CO₂ removal unit contains one or more molecular sieve beds.

7. The process in accordance with claim 6 wherein a portion of said oxygen-rich stream is used to regenerate the molecular sieve beds.

8. The process in accordance with claim 7 wherein said feed gas stream is passed through a compressor prior to entering the H₂ O and CO₂ removal unit.

9. The process in accordance with claim 1 wherein said treated gas stream which is withdrawn from the cryogenic separation unit is passed through a compressor prior to entering the membrane unit.

10. The process in accordance with claim 1 wherein said nitrogen-rich stream from the membrane unit is passed through a compressor prior to being returned to the cryogenic separation unit.

11. The process in accordance with claim 1 wherein the total nitrogen recovery, based on the feed stream, is at least 75%.

12. The process in accordance with claim 1 wherein the nitrogen product has a purity of at least 99.7%.

13. The process in accordance with claim 1 wherein the oxygen-rich stream is recovered as product.

14. A process for the production of liquid nitrogen from an air feed stream, said process comprising providing an additional degree of freedom for adjusting the process parameters by:

(a) passing said air feed stream through a molecular sieve bed to remove water and carbon dioxide, thereby producing a nitrogen/oxygen-rich gas stream;

(b) condensing at least a portion of the nitrogen/oxygen-rich gas stream in a cryogenic processing unit to produce a liquid nitrogen/oxygen stream;

(c) passing said liquid nitrogen/oxygen stream to a distillation column where it is treated to form an oxygen-rich liquid stream and a gaseous nitrogen stream;

(d) condensing said gaseous nitrogen stream to produce a liquid nitrogen stream;

(e) reducing the pressure of said liquid nitrogen stream to produce a nitrogen product stream;

(f) vaporizing said oxygen-rich liquid stream in step (c) to form a gaseous oxygen-rich stream;

(g) passing said gaseous oxygen-rich stream to a membrane unit for separation into a oxygen-rich permeate stream and a nitrogen-containing reject stream; and

(h) passing said nitrogen-containing reject stream back through the cryogenic processing unit.

15. The process in accordance with claim 14 wherein the pressure of the gaseous oxygen-rich stream passed to the membrane unit is chosen such that the pressure of the nitrogen-containing reject stream from the membrane unit is about the same as the pressure of the nitrogen/oxygen-rich gas stream leaving the molecular sieve bed.

16. The process in accordance with claim 14 wherein the pressure of the gaseous oxygen-rich stream passed to the membrane unit is chosen such that the pressure of the nitrogen-containing reject stream from the membrane unit is significantly higher than the pressure of the nitrogen/oxygen-rich gas stream leaving the molecular sieve bed.

17. A process for the production of gaseous nitrogen from an air feed stream, said process comprising providing an additional degree of freedom for adjusting the process parameters by:

(a) passing said air feed stream through a molecular sieve bed to remove water and carbon dioxide, thereby producing a nitrogen/oxygen-rich gas stream;

(b) cooling said nitrogen/oxygen-rich gas stream;

(c) treating said cooled nitrogen/oxygen-rich gas stream in a distillation column to remove nitrogen thereby forming an oxygen-rich stream;

(d) passing said oxygen-rich stream to a membrane unit where it is separated to form a permeate stream and a reject stream;

(e) returning said reject stream to the distillation column where it is treated along with the nitrogen/oxygen-rich gas stream of step (c) to form a nitrogen-rich stream;

(f) withdrawing said nitrogen-rich stream from the distillation column; and

(g) heating said nitrogen-rich stream in a series of heat exchangers to produce a gaseous nitrogen product stream.

18. A process for separating components of a gas stream containing at least two components having different permeability through a given membrane, process provides an additional degree of freedom for optimizing said process comprising providing an additional degree of freedom for adjusting the process parameters by:

(a) feeding said gas stream to a cryogenic separation unit to treat said gas stream;

(b) withdrawing at least a portion of the treated gas stream from the cryogenic separation unit;

(c) feeding said portion of the treated gas stream to a membrane unit to form a premeate stream and a reject steam;

(d) returning at least one of the streams from the membrane unit to the cryogenic separation unit for further treatment and separation to form a purified stream; and

(e) subsequently recovering said purified stream as a gaseous and/or liquid product.