Configurations and methods for improved natural gas liquids recovery

• US 9,103,585 B2
• Filed: 08/13/2008
• Issued: 08/11/2015
• Est. Priority Date: 08/14/2007
• Status: Active Grant

• Current Assignee: Fluor Technologies Corporation (Fluor Corporation)
• Original Assignee: Fluor Technologies Corporation (Fluor Corporation)
• Inventors: Mak, John
• Primary Examiner(s): Pettitt, John F
• Assistant Examiner(s): Mengesha, Webeshet
• Application Number:
  US12/669,025
• Publication Number:
  US 20100206003A1
• Time in Patent Office: 2,554 Days
• Field of Search: 626/20, 626/30, 626/32, 626/57, 626/11, 626/13, 626/17, 626/18, 626/22
• US Class Current: 1/1
• CPC Class Codes: C10G 2400/28 Propane and butane
• CPC Class Codes: C10G 5/06 by cooling or compressing
• CPC Class Codes: F25J 2200/04 in a dual pressure main column system
• CPC Class Codes: F25J 2200/70 Refluxing the column with a condensed part of the feed stream, i.e. fractionator top is stripped or self-rectified
• CPC Class Codes: F25J 2200/74 Refluxing the column with at least a part of the partially condensed overhead gas
• CPC Class Codes: F25J 2200/76 Refluxing the column with condensed overhead gas being cycled in a quasi-closed loop refrigeration cycle
• 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 2210/06 Splitting of the feed stream, e.g. for treating or cooling in different ways
• 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 2245/02 Recycle of a stream in general, e.g. a by-pass stream
• CPC Class Codes: F25J 2270/02 Internal refrigeration with liquid vaporising loop
• CPC Class Codes: F25J 2270/88 Quasi-closed internal refrigeration or heat pump cycle, if not otherwise provided
• 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

Contemplated plants for recovery of NGL from natural gas employ alternate reflux streams in a first column and a residue gas bypass stream, wherein expansion of various process streams provides substantially all of the refrigeration duty in the plant. Contemplated plants not only have flexible recovery of ethane between 2% and 90% while recovering at least 99% of propane, but also reduce and more typically eliminate the need for external refrigeration.

Claims

1. A method of recovering natural gas liquids from natural gas, the method comprising:

feeding a vapor portion of a cooled feed gas in a first column to thereby form a first column bottom product and a first column overhead product, and configuring the first column to allow feeding of alternate first and second reflux streams to the first column such that the first column receives the first reflux stream during ethane recovery, and such that the first column receives the second reflux stream during propane recovery;

feeding the first column bottom product and a liquid portion of the cooled feed gas to a second column to thereby produce a second column overhead and a second column bottom product;

wherein the first column bottom product is used as a reflux for the second column during ethane recovery and as a refrigerant for an overhead condenser of the second column and second column feed during propane recovery;

compressing the first column overhead product and (a) expanding a portion of the compressed first column overhead product in a first expansion device to thereby form the first reflux stream during ethane recovery, and (b) expanding the portion of the compressed first column overhead product in a second expansion device to thereby provide cooling to the feed gas by combing with the first column overhead product when a portion of the second column overhead is used as the second reflux stream during propane recovery.

2. The method of claim 1 wherein the step of compressing comprises compressing the first column overhead product to pipeline pressure.

3. The method of claim 1 wherein the portion of the compressed first column overhead product is between 10% and 50% of the compressed first column overhead product.

4. The method of claim 1 wherein the cooled feed gas is cooled using refrigeration content of at least one of the first column overhead product and a second column reboiler stream.

5. The method of claim 1 wherein further cooling is provided to the first column by expansion of the vapor portion.

6. The method of claim 1 wherein further cooling is provided to the second column by expansion of a liquid portion of the cooled feed gas.

7. The method of claim 1 wherein the second column is operated at a pressure that is at least 50 psi higher than an operating pressure of the first column.

8. The method of claim 1 wherein the second column bottom product comprises at least 99% of the propane contained in the feed gas and at least 80% of the ethane contained in the feed gas.

9. The method of claim 1 wherein ethane recovery in the second column bottom product is variable between 2% and 90% of the ethane contained in the feed gas.

10. The method of claim 1 wherein the second column bottom product comprises at least 99% of the propane contained in the feed gas, and wherein ethane recovery in the second column bottom product is variable between 2% and 90% of the ethane contained in the feed gas.

11. A natural gas liquids recovery plant comprising:

a first column fluidly coupled to a second column such that a first column bottom product is provided to the second column, wherein the first column is configured to receive a vapor portion of a cooled feed gas and a first reflux stream during ethane recovery and a second reflux stream during propane recovery, and

wherein the second column is configured to receive a liquid portion of the cooled feed gas;

a separator that is fluidly coupled to the first column and configured such that the separator produces the vapor portion of the feed gas and the liquid portion of the feed pas;

a first bottom liquid conduit for providing a portion of the first column bottom product to the second column as reflux during ethane recovery and a second bottom liquid conduit for providing a portion of the first column bottom product to an overhead condenser of the second column during propane recovery;

a compressor that is fluidly coupled to the first column and configured to compress a first column overhead;

a bypass conduit that includes a first expansion device and that is configured to provide a portion of expanded compressed first column overhead to a feed exchanger during propane recovery, and a reflux conduit with a second expansion device that is configured to provide a portion of expanded compressed first column overhead to the first column as the first reflux stream during ethane recovery; and

a second conduit that is configured to provide a second column overhead to the first column as (a) a column feed when the portion of the expanded compressed first column overhead is provided to the first column as the first reflux or (b) the second reflux stream when the portion of the expanded compressed first column overhead is provided to the feed exchanger.

12. The plant of claim 11 further comprising a side reboiler that is thermally coupled to a feed gas conduit such as to allow cooling of a feed gas.

13. The plant of claim 11 further comprising an expansion device fluidly coupled between the separator and the first column and configured to reduce pressure in at least one of the vapor portion and the liquid portion.

14. The plant of claim 11 wherein the compressor is configured to allow compression of the first column overhead to pipeline pressure.

15. The plant of claim 11 further comprising a second exchanger that further cools a feed gas using refrigeration content of the first column overhead.

16. The plant of claim 11 wherein the first column is configured to operate at a first pressure, wherein the second column is configured to operate at a second pressure, and wherein the second pressure is higher than the first pressure.

17. The plant of claim 11 wherein the bypass conduit is configured to allow conveying of between 10% and 50% of the compressed first column overhead product.

18. The plant of claim 11 wherein the plant is configured to allow variable recovery of between 2% and 90% of the ethane contained in the feed gas.