System and method for enhanced argon recovery from a feed stream comprising hydrogen, methane, nitrogen and argon

Patent metadata

Field	Value
Publication number	US-10072890-B2
Application number	US-201715453942-A
Country	US
Kind code	B2
Filing date	Mar 9, 2017
Priority date	Mar 21, 2016
Publication date	Sep 11, 2018
Grant date	Sep 11, 2018

Abstract

A system and method for argon and nitrogen extraction from a feed stream comprising hydrogen, methane, nitrogen and argon, such as tail gas of an ammonia production plant is provided. The disclosed system and method provides for nitrogen-argon rectification and the methane rejection within a column system comprised of at least one distillation column. Nitrogen and argon are further separated and to produce liquid products. An argon stripping column arrangement is disclosed where residual argon is further removed from the methane-rich fuel gas and recycled back to the feed stream.

First claim

What is claimed is:

1. A method for separating a feed stream comprised primarily of hydrogen, nitrogen, methane and argon, the method comprising the steps of:
conditioning the feed stream to a temperature suitable for distillation at pressure less than 400 psia;
directing the conditioned feed stream to a rectification system which is comprised of at least one rectifying column;
separating the conditioned feed stream in the rectification system to produce an argon depleted nitrogen enriched vapor stream, an argon enriched stream, and a methane-rich liquid stream;
directing the methane rich liquid stream into an argon stripping column configured to strip argon from the methane rich liquid stream using an argon-depleted, nitrogen rich vapor stream having an argon concentration less than the argon concentration of the methane-rich liquid stream;
directing the argon-depleted, nitrogen rich vapor stream into the argon stripping column at a feed point below a feed point of the methane rich liquid stream such that mass transfer of argon is effected between the methane rich liquid stream and the argon-depleted, nitrogen rich vapor stream;
extracting an argon depleted methane rich liquid from the bottom of the argon stripping column;
extracting an argon containing overhead gas from the top of the argon stripping column; and
recovering purified argon from the argon containing overhead gas or recycling the argon containing overhead gas to be recombined with the feed stream.

2. The method of claim 1 wherein the feed stream is a feed synthesis gas stream.

3. The method of claim 1 wherein the step of conditioning the feed stream to a temperature suitable for distillation at pressure less than 400 psia further comprises one or more of the following steps: compression of the feed stream, prepurification of the feed stream, expansion of the feed stream, cooling of the feed stream, or heating of the feed stream.

4. The method of claim 1 wherein the feed stream is a two phase stream comprising a fraction of liquid and a fraction of vapor.

5. The method of claim 1 wherein the argon-depleted, nitrogen rich vapor stream comprises primarily nitrogen and hydrogen and the method further comprises a step of conditioning the argon-depleted, nitrogen rich vapor stream prior to the step of directing the argon-depleted, nitrogen rich vapor stream into the argon stripping column.

6. The method of claim 1 wherein the argon enriched stream is a two phase stream comprising a fraction of liquid argon and a fraction of gaseous argon.

7. The method of claim 1 wherein the argon enriched stream is an argon enriched liquid stream.

8. The method of claim 1 wherein the argon enriched stream is an argon enriched gaseous stream.

9. The method of claim 1 wherein the argon-depleted, nitrogen rich vapor stream further comprises a first portion of the argon depleted nitrogen enriched vapor stream.

10. The method of claim 1 wherein at least a portion of the argon containing overhead gas is recycled and recombined with the feed stream, and the method further comprises the steps of warming the recycled argon containing overhead gas and optionally compressing the argon containing overhead gas prior to recombining the argon containing overhead gas with the feed stream.

11. The method of claim 1 wherein the argon depleted, nitrogen enriched vapor is split into at least two portions with a first portion being directed into the argon stripping column and a second portion being combined with the argon depleted, methane rich liquid stream.

12. The method of claim 11 further comprising the step of subcooling the argon depleted methane rich liquid stream and combining the subcooled argon depleted, methane rich liquid stream with the second portion of the argon depleted, nitrogen enriched vapor.

13. The method of claim 11 further comprising the steps of vaporizing the argon depleted methane rich liquid stream and combining the vaporized argon depleted, methane rich liquid stream with the second portion of the argon depleted nitrogen enriched vapor or combining the argon depleted, methane rich liquid stream with the second portion of the argon depleted nitrogen enriched vapor and then vaporizing the combined stream.

14. The method of claim 1 further comprising the steps of:
directing the argon enriched stream to an auxiliary rectification column; and
separating the argon enriched stream in the auxiliary rectification column to produce a high purity argon stream and a high purity nitrogen stream.

15. The method of claim 14 wherein the auxiliary rectification column employs nitrogen as a working fluid.

16. The method of claim 1 further comprising the steps of:
removing trace hydrogen from the argon enriched stream using an evaporator, a phase separator or a hydrogen stripping column to produce a hydrogen-free argon enriched stream;
directing the hydrogen-free argon enriched stream to an auxiliary rectification system comprised of at least one distillation column and
separating the hydrogen-free argon enriched stream in the auxiliary rectification column to produce a high purity argon stream and a high purity nitrogen stream.

17. The method of claim 1 further comprising the steps of pumping the methane rich liquid stream or expanding the methane rich liquid stream to condition the methane rich liquid stream to a prescribed pressure prior to the step directing the methane rich liquid stream into the argon stripping column.

18. The method of claim 1 further comprising the steps of compressing the argon-depleted, nitrogen rich vapor stream or cooling the argon-depleted, nitrogen rich vapor stream or both prior to the step of directing the argon-depleted, nitrogen rich vapor stream into the argon stripping column.

19. The method of claim 1 wherein the feed stream is a tail gas from an ammonia plant and the argon depleted methane rich liquid is suitable for use as a fuel gas in the ammonia plant.

20. The method of claim 1 wherein the feed stream contains greater than about 50% nitrogen by mole fraction.

21. The method of claim 1 wherein the conditioned feed stream is at a pressure of less than or equal to about 150 psia.

22. A system for separating a feed stream comprising hydrogen, nitrogen, methane and argon, the system comprising:
a conditioning circuit configured for conditioning the feed stream gas to a temperature suitable for rectification and at pressure less than or equal to about 400 psia;
at least one rectifying column configured to receive the conditioned feed stream and produce an argon depleted, nitrogen rich vapor stream, an argon enriched stream, and a methane-rich liquid stream;
an argon stripping column configured to receive the methane rich liquid stream and strip argon from the methane rich liquid stream using the argon depleted, nitrogen rich vapor stream and produce an argon depleted methane rich liquid from the bottom of the argon stripping column and an argon containing overhead gas from the top of the argon stripping column; and
a recycle circuit configured for extracting the argon containing overhead gas from the argon stripping column and mixing the argon containing overhead gas with the feed stream;
an auxiliary rectification column configured to rectify the argon enriched stream to produce a high purity argon stream and a high purity nitrogen stream.

Assignees

• Howard Henry E
• Praxair Technology Inc

Inventors

• Howard Henry E

Classifications

• F25J2270/04

  Internal refrigeration with work-producing gas expansion loop · CPC title

• F25J2270/02

  Internal refrigeration with liquid vaporising loop · CPC title

• F25J2245/02

  Recycle of a stream in general, e.g. a by-pass stream · CPC title

• F25J2240/02

  Expansion of a process fluid in a work-extracting turbine (i.e. isentropic expansion), e.g. of the feed stream · CPC title

• F25J2235/60

  the fluid being (a mixture of) hydrocarbons · CPC title