Twin reflux process and configurations for improved natural gas liquids recovery

• US 20040261452A1
• Filed: 08/09/2004
• Published: 12/30/2004
• Est. Priority Date: 05/20/2002
• Status: Active Grant

• Current Assignee: Fluor Enterprises Incorporated (Fluor Corporation)
• Original Assignee: Fluor Enterprises Incorporated (Fluor Corporation)
• Inventors: Mak, John, Graham, Curt, Chung, Chengwen Wayne
• Granted Patent: US 7,051,553 B2
• Time in Patent Office: Days
• US Class Current: 62/620
• CPC Class Codes: F25J 2200/04 in a dual pressure main column system
• CPC Class Codes: F25J 2200/74 Refluxing the column with at least a part of the partially condensed overhead gas
• CPC Class Codes: F25J 2200/78 Refluxing the column with a liquid stream originating from an upstream or downstream fractionator column
• CPC Class Codes: F25J 2205/04 in the feed line, i.e. upstream of the fractionation step
• CPC Class Codes: F25J 2235/60 the fluid being (a mixture of) hydrocarbons
• CPC Class Codes: F25J 2240/02 Expansion of a process fluid in a work-extracting turbine (i.e. isentropic expansion), e.g. of the feed stream
• 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 2280/02 Control in general, load changes, different modes ("runs"), measurements
• CPC Class Codes: F25J 3/0209 Natural gas or substitute natural gas
• CPC Class Codes: F25J 3/0233 separation of CnHm with 1 carbon atom or more
• CPC Class Codes: F25J 3/0238 separation of CnHm with 2 carbon atoms or more
• CPC Class Codes: F25J 3/0242 separation of CnHm with 3 carbon atoms or more

Abstract

A two-column NGL recovery plant includes an absorber (110) and a distillation column (140) in which the absorber (110) receives two cooled reflux streams, wherein one reflux stream (107) comprises a vapor portion of the NGL and wherein the other reflux stream (146) comprises a lean reflux provided by the overhead (144) of the distillation column (140). Contemplated configurations are especially advantageous in a upgrade of an existing NGL plant and typically exhibit C₃ recovery of at least 99% and C2 recovery of at least 90%.

Claims

1. A plant comprising an absorber that receives a first reflux stream and that further receives a second reflux stream, the first reflux stream comprising a cooled lean overhead product from a distillation column, and the second reflux stream comprising a cooled vapor portion of a natural gas feed that is reduced in pressure via a device other than a turbo expander.

2. The plant of claim 1 wherein the absorber further receives a liquid portion of the natural gas feed and a second vapor portion of the natural gas feed wherein the second portion is reduced in pressure via a turbo expander.

3. The plant of claim 1 wherein the absorber produces a bottom product that cools at least one of the first and second reflux streams.

4. The plant of claim 3 wherein at least a portion of the bottom product is fed into the distillation column.

5. The plant of claim 1 wherein the absorber produces an overhead product that cools at least one of the first and second reflux streams.

6. The plant of claim 5 wherein the overhead product further cools at least one of the natural gas feed and a vapor portion of the natural gas feed.

7. The plant of claim 1 wherein the device other than the turbo expander comprises a Joule-Thomson valve.

8. The plant of claim 1 wherein the distillation column comprises a demethanizer.

9. The plant of claim 1 wherein the first lean reflux stream is fed into the absorber as a vapor/liquid or liquid feed, and wherein the distillation column comprises a deethanizer.

10. A method of operating a plant comprising:

providing an absorber and a distillation column;

feeding a cooled lean overhead product from the distillation column to the absorber as a first reflux stream;

reducing pressure of a cooled vapor portion of a natural gas feed via a device other than a turbo expander; and

feeding the cooled vapor portion that is reduced in pressure to the absorber as a second reflux stream in addition to the first reflux stream.

11. The method of claim 10 further comprising feeding a liquid portion of the natural gas feed and a second vapor portion of the natural gas feed into the absorber, wherein the second portion is reduced in pressure via a turbo expander.

12. The method of claim 10 further comprising providing a heat exchanger in which at least one of a bottom product and an overhead product of the absorber cool at least one of the first and second reflux streams.

13. The method of claim 10 further comprising feeding at least part of the bottom product from the absorber into the distillation column.

14. The method of claim 10 wherein the device other than the turbo expander comprises a Joule-Thomson valve.

15. The method of claim 10 wherein the first lean reflux stream is fed into the absorber as a vapor/liquid feed, and wherein the distillation column comprises a deethanizer.

22. The method of any one of claim 10 or 16 wherein the absorber is operated at a pressure higher than a pressure in the distillation column, and wherein a compressor is provided on the distillation column overhead that compresses overhead vapor to the absorber.

16. A method of increasing throughput in a natural gas recovery plant having an absorber and a distillation column, comprising:

providing a first reflux stream to the absorber, wherein the first reflux stream comprises an overhead product from the distillation column;

providing a bypass upstream of a turbo expander, wherein the bypass receives a vapor portion of a cooled natural gas liquid and provides the vapor portion to the absorber;

reducing pressure of the vapor portion before the vapor portion enters the absorber as a second reflux stream; and

providing a heat exchanger that cools at least one of the first reflux stream and the second reflux stream using at least one of an absorber bottom product and an absorber overhead product.

17. The method of claim 16 wherein a second vapor portion of the cooled natural gas liquid is expanded in a turbo expander and fed into the absorber, and wherein a liquid portion of the cooled natural gas liquid is fed into the absorber.

18. The method of claim 16 wherein the absorber overhead product further cools at least one of the natural gas liquid and a vapor portion of the natural gas liquid.

19. The method of claim 16 wherein the first reflux stream is fed into the absorber as a vapor/liquid or liquid feed and wherein the distillation column comprises a deethanizer.

20. The method of claim 16 wherein the distillation column comprises a demethanizer.

21. The method of claim 20 wherein the absorber is first refluxed by a cooled separator gas, and wherein overhead vapor from the demethanizer is fed to a bottom of the absorber for ethane recovery.