Method of Extracting Ethane from Liquefied Natural Gas

• US 20080087041A1
• Filed: 08/17/2005
• Published: 04/17/2008
• Est. Priority Date: 09/14/2004
• Status: Active Grant

• Current Assignee: Allen Brimm, Robert Denton, Russell Oelfke
• Original Assignee: Allen Brimm, Robert Denton, Russell Oelfke
• Inventors: Denton, Robert, Brimm, Allen, Oelfke, Russell
• Granted Patent: US 8,156,758 B2
• Time in Patent Office: Days
• US Class Current: 62/618
• CPC Class Codes: F25J 2200/02 in a single 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 2205/02 using simple phase separation in a vessel or drum
• 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 2215/02 Mixing or blending of fluids to yield a certain product
• CPC Class Codes: F25J 2230/08 Cold compressor, i.e. suction of the gas at cryogenic temperature and generally without afterstage-cooler
• CPC Class Codes: F25J 2230/60 the fluid being hydrocarbons or a mixture of hydrocarbons
• CPC Class Codes: F25J 2235/60 the fluid being (a mixture of) hydrocarbons
• CPC Class Codes: F25J 2245/02 Recycle of a stream in general, e.g. a by-pass stream
• CPC Class Codes: F25J 2245/90 the recycled stream being boil-off gas from storage
• CPC Class Codes: F25J 2280/02 Control in general, load changes, different modes ("runs"), measurements
• CPC Class Codes: F25J 2290/34 Details about subcooling of liquids
• CPC Class Codes: F25J 3/0214 Liquefied 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

Abstract

Methods and systems for recovery of natural gas liquids (NGL) and a pressurized methane-rich sales gas from liquefied natural gas (LNG) are disclosed. In certain embodiments, LNG passes through a heat exchanger, thereby heating and vaporizing at least a portion of the LNG. The partially vaporized LNG passes to a fractionation column where a liquid stream enriched with ethane plus and a methane-rich vapor stream are withdrawn. The withdrawn methane-rich vapor stream passes through the heat exchanger to condense the vapor and produce a two phase stream, which is separated in a separator into at least a methane-rich liquid portion and a methane-rich gas portion. A pump pressurizes the methane-rich liquid portion prior to vaporization and delivery to a pipeline. The methane-rich gas portion may be compressed and combined with the vaporized methane-rich liquid portion or used as plant site fuel.

Claims

1. A method of processing liquefied natural gas (LNG), comprising:

passing LNG through a heat exchanger to provide heated LNG;

fractionating the heated LNG into a methane-rich vapor stream and a natural gas liquids (NOL) stream;

passing the methane-rich vapor stream through the heat exchanger to transfer heat from the methane-rich vapor stream to the LNG passing through the heat exchanger and to provide a two-phase stream that includes a methane-rich liquid phase and a methane-rich vapor phase;

separating the two-phase stream into at least a methane-rich liquid portion and a methane-rich gas portion;

increasing the pressure of the methane-rich liquid portion to provide a sendout liquid stream;

recovering the sendout liquid stream to provide a sales gas for delivery to a pipeline; and

diverting the LNG at a predetermined time to a diverted flow path that bypasses the fractionating to provide sales gas that includes methane and ethane plus for delivery to the pipeline.

3. The method of claim 1, wherein the methane concentration of the sales gas is substantially the same as the methane concentration of the methane-rich liquid portion.

4. The method of claim 1, wherein fractionating the heated LNG occurs in a fractionating tower, which produces the methane-rich vapor stream at a tower output pressure, and wherein the pressure of the methane-rich vapor stream entering the heat exchanger is substantially the same pressure as the tower output pressure.

5. The method of claim 1, wherein passing the methane-rich vapor stream through the heat exchanger occurs substantially without increasing the pressure of the methane-rich vapor stream.

6. The method of claim 1, further comprising increasing the pressure of the LNG before passing the LNG through the heat exchanger.

7. The method of claim 1, further comprising:

mixing a compressed boil-off vapor stream from an LNG tank with an LNG liquid stream from the LNG tank increased to a first pressure, wherein the mixing provides an LNG feed stream; and

increasing the pressure of the LNG feed stream to a second pressure to provide the LNG for passing through the heat exchanger.

8. The method of claim 1, wherein the methane-rich liquid phase constitutes at least 85 weight percent of the two-phase stream.

9. The method of claim 1, wherein the methane-rich liquid phase constitutes at least 95 weight percent of the two-phase stream.

10. The method of claim 1, wherein passing the methane-rich vapor stream through the heat exchanger occurs without increasing the pressure of the methane-rich vapor stream, and wherein the methane-rich liquid phase occupies at least 85 weight percent of the two-phase stream.

11. The method of claim 1, wherein the sendout liquid stream is at a pressure of at least 1000 psia.

12. The method of claim 1, wherein delivery of sales gas to a pipeline includes transporting methane-rich gas at a pressure of at least 800 psia via the pipeline.

13. The method of claim 1, wherein the methane-rich vapor stream and the sendout liquid stream each has a methane concentration of at least 98 mole percent.

14. The method of claim 1, wherein the NGL stream has an ethane plus concentration of at least 98 mole percent.

15. The method of claim 1, further comprising utilizing at least part of the methane-rich gas portion as a plant site fuel.

16. The method of claim 1, further comprising boosting the pressure of at least part of the methane-rich gas portion for delivery to the pipeline.

17. The method of claim 1, further comprising heat exchanging the NGL stream with the heated LNG to chill the NGL stream.

21. The method of claim 1, further comprising splitting a part of the methane-rich liquid portion into a reflux stream that provides a reflux for fractionating the heated LNG.

22. The method of claim 1, further comprising:

splitting a part of the methane-rich liquid portion into a reflux stream; and

chilling the reflux stream against the heated LNG to provide a reflux for fractionating the heated LNG.

2. (canceled)

18. A method of processing liquefied natural gas (LNG), comprising:

passing LNG through a heat exchanger to provide heated LNG;

fractionating the heated LNG into a methane-rich vapor stream and a natural gas liquids (NGL) stream;

passing the methane-rich vapor stream through the heat exchanger to transfer heat from the methane-rich vapor stream to the LNG passing through the heat exchanger and to provide a two-phase stream that includes a methane-rich liquid phase and a methane-rich vapor phase;

separating the two-phase stream into at least a methane-rich liquid portion and a methane-rich gas portion;

increasing the pressure of the methane-rich liquid portion to provide a sendout liquid stream;

recovering the sendout liquid stream to provide a sales gas for delivery to a pipeline;

heat exchanging the NGL stream with the heated LNG to provide a chilled NGL stream; and

flashing the chilled NGL stream to substantially atmospheric pressure to provide a flashed NGL stream.

19. The method of claim 18, further comprising:

passing the flashed NGL stream to storage.

20. A method of processing liquefied natural gas (LNG), comprising:

passing LNG through a heat exchanger to provide heated LNG;

fractionating the heated LNG into a methane-rich vapor stream and a natural gas liquids (NGL) stream;

passing the methane-rich vapor stream through the heat exchanger to transfer heat from the methane-rich vapor stream to the LNG passing through the heat exchanger and to provide a two-phase stream that includes a methane-rich liquid phase and a methane-rich vapor phase;

separating the two-phase stream into at least a methane-rich liquid portion and a methane-rich gas portion;

increasing the pressure of the methane-rich liquid portion to provide a sendout liquid stream;

recovering the sendout liquid stream to provide a sales gas for delivery to a pipeline; and

splitting a portion of the LNG into a reflux stream that bypasses the heat exchanger and provides a reflux for fractionating the heated LNG.

23. A method of processing liquefied natural gas (LNG), comprising:

(a) providing LNG containing natural gas liquids (NGL);

(b) increasing the pressure of the LNG to a first pressure to provide pressurized LNG;

(c) passing the pressurized LNG through a heat exchanger to heat the LNG and provide heated LNG;

(d) passing the heated LNG to a fractionation system that produces a methane-rich vapor stream and an NGL stream;

(e) passing the methane-rich vapor stream produced by the separation system through the heat exchanger, to provide a two-phase stream that includes a liquid phase and a vapor phase;

(f) separating the two-phase stream into at least a liquid portion and a gas portion;

(g) increasing the pressure of the liquid portion to a second pressure which is higher than the first pressure to provide a pressurized liquid portion;

(h) vaporizing at least a portion of the pressurized liquid portion without further removal of an ethane plus component to produce a high-pressure, methane-rich gas; and

(i) providing at least part of a refrigeration duty for the fractionation system by withdrawing a fraction of the LNG before being heated and passing the withdrawn fraction to the fractionation system.

25. The process of claim 23, further comprising providing at least part of a refrigeration duty for the fractionation system by passing at least a portion of the methane-rich vapor stream produced by the fractionation system in heat exchange with the LNG to effect cooling of the methane-rich vapor stream, and passing at least a portion of the cooled stream to the fractionation system.

26. The process of claim 23, further comprising providing at least part of a refrigeration duty for the fractionation system by withdrawing a fraction of the LNG before being heated and passing the withdrawn fraction to the fractionation system and passing at least a portion of the methane-rich vapor stream produced by the fractionation system in heat exchange with the LNG to effect cooling of the methane-rich vapor stream and passing at least a portion of the cooled stream to the fractionation system.

27. The process of claim 23, wherein the NGL stream has ethane as a predominant component.

28. The process of claim 23, wherein the pressure of LNG of step (a) is at or near atmospheric pressure.

29. The process of claim 23, wherein the first pressure ranges from 400 psia to 600 psia.

30. The process of claim 23, wherein the second pressure ranges from 1000 psia to 1300 psia.

24. (canceled)

31. A system for processing liquefied natural gas (LNG), comprising:

a heat exchanger;

an LNG inlet line in fluid communication with an LNG source and the heat exchanger, configured such that LNG is capable of passing through the LNG inlet line and the heat exchanger;

a fractionation system in fluid communication with the heat exchanger, the fractionation system having a first outlet for a methane-rich vapor stream and a second outlet for a natural gas liquids (NGL) stream, wherein the fractionation system comprises a reflux input in fluid communication with a portion of the LNG inlet line;

a vapor-liquid separator;

a condensation line fluidly connecting the first outlet of the fractionation system to the vapor-liquid separator, the condensation line passing though the heat exchanger, configured such that heat from the methane-rich vapor stream is transferred to any LNG passing through the heat exchanger;

a pump having an inlet in fluid communication with a liquid recovered in the vapor-liquid separator; and

a vaporizer in fluid communication with an outlet of the pump and a pipeline for delivery of sales gas.

32. The system of claim 31, wherein the condensation line connects the first outlet of the fractionation system to the heat exchanger without providing an increase in pressure to the methane-rich vapor stream.

33. The system of claim 31, further comprising an NGL heat exchanger in fluid communication with the second outlet of the fractionation system for chilling the NGL against the LNG while the LNG passes through the NGL heat exchanger.

34. The system of claim 31, further comprising a condenser for the fractionation system that provides reflux thereto, wherein the condenser provides heat exchange against the LNG while the LNG passes through the condensor.

35. The system of claim 31, wherein the vapor-liquid separator further includes a vapor outlet in fluid communication with the pipeline.

36. The system of claim 31, wherein the vapor-liquid separator further includes a vapor outlet in fluid communication with the pipeline and a plant site fuel line.

37. The system of claim 31, wherein the fractionation system comprises a reflux input in fluid communication with a portion of the liquid recovered in the vapor-liquid separator.

38. (canceled)