Nitrogen removal with ISO-pressure open refrigeration natural gas liquids recovery

Patent metadata

Field	Value
Publication number	US-9534837-B2
Application number	US-201514751562-A
Country	US
Kind code	B2
Filing date	Jun 26, 2015
Priority date	Mar 4, 2009
Publication date	Jan 3, 2017
Grant date	Jan 3, 2017

Abstract

A process for recovery of natural gas liquids is disclosed, the process including: fractionating a gas stream comprising nitrogen, methane, ethane, and propane and other C 3+ hydrocarbons into at least two fractions including a light fraction comprising nitrogen, methane, ethane, and propane, and a heavy fraction comprising propane and other C 3+ hydrocarbons; separating the light fraction into at least two fractions including a nitrogen-enriched fraction and a nitrogen-depleted fraction in a first separator; separating the nitrogen-depleted fraction into a propane-enriched fraction and a propane-depleted fraction in a second separator; feeding at least a portion of the propane-enriched fraction to the fractionating as a reflux; recycling at least a portion of the propane-depleted fraction to the first separator. In some embodiments, the nitrogen-enriched fraction may be separated in a nitrogen removal unit to produce a nitrogen-depleted natural gas stream and a nitrogen-enriched natural gas stream.

First claim

What is claimed:

1. A process for recovery of natural gas liquids, comprising:
fractionating a gas stream comprising nitrogen, methane, ethane, and propane and other C 3+ hydrocarbons in a fractionator into at least two fractions including a light fraction comprising nitrogen, methane, ethane, and propane, and a heavy fraction comprising propane and other C 3+ hydrocarbons;
separating the light fraction into at least three fractions including a nitrogen-enriched fraction, an intermediate nitrogen-content fraction, and a nitrogen-depleted fraction in a first separator;
compressing and cooling the nitrogen-depleted fraction;
separating the compressed and cooled nitrogen-depleted fraction into a propane-enriched fraction and a propane-depleted fraction in a second separator;
feeding at least a portion of the propane-enriched fraction to the fractionator as a reflux;
recycling at least a portion of the propane-depleted fraction to the first separator;
exchanging heat between two or more of the gas stream, the light fraction, a portion of the propane-depleted fraction, the nitrogen-enriched fraction, the nitrogen-depleted fraction, the compressed and cooled nitrogen-depleted fraction, the intermediate nitrogen-content fraction, and a refrigerant;
separating the nitrogen-enriched fraction in a nitrogen removal unit to produce a first nitrogen-depleted natural gas stream, a first nitrogen-enriched natural gas stream, and a recycle stream; and
feeding the recycle stream to at least one of the first separator and an upstream end of the nitrogen removal unit.

2. The process of claim 1 , wherein the first separator is an absorber column.

3. The process of claim 1 , further comprising admixing the first nitrogen-depleted natural gas stream and the intermediate nitrogen-content fraction to form a natural gas product stream.

4. The process of claim 3 , wherein the natural gas product stream Comprises 4 mole % or less nitrogen.

5. The process of claim 1 , further including exchanging heat between the intermediate nitrogen-content fraction and the recycle stream to the first separator.

6. The process of claim 5 , wherein the first separator is an absorber column.

7. The process of claim 1 , wherein the recycle stream is fed to the first separator.

8. The process of claim 1 , wherein the recycle stream is fed to the first separator at a location above a point of removal of the intermediate nitrogen-content fraction.

9. The process of claim 4 , wherein the recycle stream is fed to the first separator at a location above a point of removal of the intermediate nitrogen-content fraction.

10. The process of claim 1 , wherein the nitrogen removal unit comprises at least a first membrane separation stage.

11. The process of claim 10 , wherein the first nitrogen-depleted natural gas stream is formed in the first membrane separation stage.

12. The process of claim 1 , wherein the nitrogen removal unit comprises at least first and second membrane separation stages.

13. The process of claim 12 , wherein the recycle stream and the first nitrogen-enriched natural gas stream are formed in the second membrane separation stage.

14. The process of claim 1 , wherein the recycle stream is fed to the upstream end of the nitrogen removal unit.

15. The process of claim 13 , wherein the recycle stream is fed to the upstream end of the nitrogen removal unit.

16. The process of claim 15 , further comprising admixing the first nitrogen depleted natural gas stream and the first nitrogen-enriched natural gas stream to form a natural gas product stream.

17. The process of claim 16 , wherein the natural gas liquids product stream comprises 4 mole % or less nitrogen.

Assignees

• Lummus Technology Inc

Inventors

• Malsam Michael

Classifications

• F25J2205/80

  using membrane, i.e. including a permeation step · CPC title

• F25J1/0022

  Hydrocarbons, e.g. natural gas · CPC title

• F25J2200/94

  Details relating to the withdrawal point · CPC title

• F25J2215/62

  Ethane or ethylene · CPC title

• F25J2205/40

  using hybrid system, i.e. combining cryogenic and non-cryogenic separation techniques · CPC title