Configurations and methods for rich gas conditioning for NGL recovery

• US 8,677,780 B2
• Filed: 07/09/2007
• Issued: 03/25/2014
• Est. Priority Date: 07/10/2006
• Status: Active Grant

• Current Assignee: Fluor Technologies Corporation (Fluor Corporation)
• Original Assignee: Fluor Technologies Corporation (Fluor Corporation)
• Inventors: Mak, John
• Primary Examiner(s): Jules, Frantz
• Assistant Examiner(s): KING, BRIAN M
• Application Number:
  US12/304,734
• Publication Number:
  US 20090165498A1
• Time in Patent Office: 2,451 Days
• Field of Search: 626/20, 626/26, 626/30, 626/11, 626/18
• US Class Current: 62/620
• CPC Class Codes: C10L 3/12 Liquefied petroleum gas liquefying by pressure and cold treatment F25J

Abstract

Contemplated gas treatment plants for recovery of NGL from rich feed gas include an upstream conditioning unit in which heavier hydrocarbons, and most typically C5 and heavier are removed prior to feeding the processed feed gas to an NGL recovery plant, thus avoiding the need to process the heavier hydrocarbons in the NGL recovery plant. Such conditioning units advantageously reduce energy demand for dehydration otherwise required and allow for production of C2-C4, and C5+ streams that can be sold as valuable products.

Claims

1. A method of conditioning a rich feed gas containing C1, C2 to C4, and C5+ in a conditioning unit, comprising:

cooling and separating the rich feed gas into a liquid portion and a vapor portion;

further cooling a first fraction of the vapor portion and separating the cooled vapor portion into a C5+ depleted vapor stream and a C5+ enriched liquid stream;

separating the C5+ enriched liquid stream and the liquid portion in a refluxed fractionator into a C2-C5 enriched bottom product and an overhead product;

compressing and cooling the overhead product and separating the compressed and cooled overhead product into a reflux liquid for the fractionator and a lean vapor;

wherein the step of cooling the overhead product to obtain the reflux liquid is performed by reducing pressure of the C5+ enriched liquid stream and using refrigeration obtained from the step of reducing pressure in the step of cooling the overhead product; and

combining a second fraction of the vapor portion, the lean vapor, and the C5+ depleted vapor stream to form a C2 to C4-containing combined stream, and feeding the combined stream to a downstream NGL recovery plant for separation of C2 to C4 from C1.

2. The method of claim 1 wherein the rich feed gas is cooled to a temperature of 1-20°

F. above a hydrate point of the rich feed gas, and wherein water is removed from the cooled rich feed gas.

3. The method of claim 2 further comprising a step of further drying the liquid portion and the vapor portion.

4. The method of claim 1 further comprising a step of feeding the C5++ enriched liquid stream to the fractionator after the step of reducing pressure of the C5++ enriched liquid stream.

5. The method of claim 1, further comprising a step of expanding the reflux liquid prior to feeding the reflux liquid into the fractionator.

6. The method of claim 1 further comprising a step of separating in a debutanizer the C2-C5 bottom product into a C5+ fraction and a C2-C4 NGL product.

7. The method of claim 6 further comprising a step of using one portion of the C2-C4 NGL product as reflux to the debutanizer.

8. The method of claim 7 further comprising a step of combining another portion of the C2-C4 NGL product with an NGL product of the NGL recovery plant.

9. The method of claim 1 wherein the conditioning unit is provided as a retrofit to the NGL recovery plant.

10. The method of claim 1 wherein the rich feed gas comprises at least 20 mol % C2+ components with at least 2.5 mol % C5+ components.

11. A gas conditioning unit for operation upstream of a natural gas liquid (NGL) recovery plant and configured to process a rich feed gas containing C1, C2 to C4, and C5+, comprising:

a first separator configured to separate a cooled and dehydrated first portion of a vapor phase of a cooled rich feed gas in a C5+ depleted vapor stream and in a C5+ enriched liquid stream;

an expansion device configured to receive and at least partially depressurize the C5+ enriched liquid stream and coupled to a refluxed fractionator via a heat exchanger, wherein the fractionator is configured to receive the at least partially depressurized C5+ enriched liquid stream;

wherein the refluxed fractionator is coupled to a compressor, and wherein the refluxed fractionator and compressor are further configured to provide a compressed overhead product to a reflux separator downstream of the heat exchanger, and wherein the heat exchanger is configured to provide refrigeration content of the at least partially depressurized C5+ enriched liquid stream to the overhead product;

conduits coupled to the first separator and the reflux separator, wherein the conduits are configured such as to allow combining a second portion of the vapor phase of the cooled rich feed gas, the C5+ depleted vapor stream, and a lean vapor to form a C2 to C4-containing combined stream, and to allow feeding the combined stream to the NGL recovery plant for separation of C2 to C4 from C1; and

wherein the refluxed fractionator is configured to receive a cooled and dehydrated liquid phase of the cooled rich feed gas and to produce a C2-C5 bottom product.

12. The gas conditioning unit of claim 11 further comprising a second separator that is configured to separate the cooled rich feed gas into a feed gas vapor and a feed gas liquid, wherein the second separator is fluidly coupled to the fractionator to allow delivery of the feed gas liquid to the fractionator and wherein the second separator is fluidly coupled to a dryer unit that is configured to dry the feed gas vapor to thereby produce the dehydrated vapor phase of the rich feed gas.

13. The gas conditioning unit of claim 12 wherein the second separator is further configured to allow removal of water from the cooled rich feed gas.

14. The gas conditioning unit of claim 12 further comprising a rich feed gas cooler that is configured to cool the rich feed gas to a temperature of 1-20°

F. above a hydrate point of the rich feed gas, and wherein the rich feed gas cooler is fluidly coupled to the second separator.

15. The gas conditioning unit of claim 11 wherein the expansion device is a JT valve or expansion turbine.

16. The gas conditioning unit of claim 11 wherein the reflux separator is configured to produce a reflux liquid.

17. The gas conditioning unit of claim 15 further comprising a second expansion device configured to reduce pressure of the reflux liquid.

18. The gas conditioning unit of claim 11 further comprising a debutanizer that is fluidly coupled to the fractionator, and that is further configured to receive the C2-C5 bottom product and to produce a C2-C4 NGL debutanizer overhead product and a C5+ bottom product.

19. The gas conditioning unit of claim 18 further comprising a conduit that is fluidly coupled between the NGL, recovery plant and the debutanizer to allow combination of the C2-C4 NGL debutanizer overhead product and an NGL product of the NGL recovery plant.

20. The gas conditioning unit of claim 18 wherein the debutanizer is a refluxed debutanizer.