Process for making pressurized liquefied natural gas from pressured natural gas using expansion cooling

• US 6,378,330 B1
• Filed: 12/07/2000
• Issued: 04/30/2002
• Est. Priority Date: 12/17/1999
• Status: Expired due to Fees

• Current Assignee: Exxonmobil Upstream Research Company (Exxon Mobil Corporation)
• Original Assignee: Exxonmobil Upstream Research Company (Exxon Mobil Corporation)
• Inventors: Minta, Moses, Bowen, Ronald R., Stone, John B.
• Primary Examiner(s): CAPOSSELA, RONALD C
• Application Number:
  US09/731,874
• Time in Patent Office: 509 Days
• Field of Search: 626/13, 626/19
• US Class Current: 62/613
• CPC Class Codes: F17C 2265/017 different phases of a same fluid
• CPC Class Codes: F25J 1/0022 Hydrocarbons, e.g. natural gas
• CPC Class Codes: F25J 1/0035 by gas expansion with extraction of work
• CPC Class Codes: F25J 1/0037 of a return stream
• CPC Class Codes: F25J 1/004 by flash gas recovery F25J1/0267 takes precedence
• CPC Class Codes: F25J 1/0042 by liquid expansion with extraction of work
• CPC Class Codes: F25J 1/0202 in a quasi-closed internal refrigeration loop F25J1/0208, F25J1/0219, F25J1/0224 take precedence
• CPC Class Codes: F25J 1/0208 in combination with an internal quasi-closed refrigeration loop, e.g. with deep flash recycle loop F25J1/021 takes precedence
• CPC Class Codes: F25J 1/0219 in combination with an internal quasi-closed refrigeration loop, e.g. using a deep flash recycle loop
• CPC Class Codes: F25J 1/0254 controlling particular process parameter, e.g. pressure, temperature
• CPC Class Codes: F25J 2205/02 using simple phase separation in a vessel or drum
• CPC Class Codes: F25J 2210/04 Mixing or blending of fluids with the feed stream
• CPC Class Codes: F25J 2210/06 Splitting of the feed stream, e.g. for treating or cooling in different ways
• CPC Class Codes: F25J 2220/62 Separating low boiling components, e.g. He, H2, N2, Air
• CPC Class Codes: F25J 2230/30 Compression 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 2245/90 the recycled stream being boil-off gas from storage
• CPC Class Codes: F25J 2270/06 with multiple gas expansion loops
• 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 2290/62 Details of storing a fluid in a tank

Abstract

This invention relates to process for liquefying a pressurized gas stream rich in methane. In a first step of the process, a first fraction of a pressurized feed stream, preferably at a pressure above 11,000 kPa, is withdrawn and entropically expanded to a lower pressure to cool and at least partially liquefy the withdrawn first fraction. A second fraction of the feed stream is cooled by indirect heat exchange with the expanded first fraction. The second fraction is subsequently expanded to a lower pressure, thereby at least partially liquefying the second fraction of the pressurized gas stream. The liquefied second fraction is withdrawn from the process as a pressurized product stream having a temperature above −112° C. and a pressure at or above its bubble point pressure.

Claims

1. A process for liquefying a pressurized gas stream rich in methane, which comprises the steps of:

(a) withdrawing a first fraction of the pressured gas stream and entropically expanding the withdrawn first fraction to a lower pressure to cool and at least partially liquefy the withdrawn first fraction;

(b) cooling a second fraction of the pressurized gas stream by indirect heat exchange with the expanded first fraction;

(c) expanding the second fraction of the pressurized gas stream to a lower pressure, thereby at least partially liquefying the second fraction of the pressurized gas stream; and

(d) removing the liquefied second fraction from the process as a pressurized product stream having a temperature above −

112°

C. (−

170°

F.) and a pressure at or above its bubble point pressure.

2. The process of claim 1 wherein the pressurized gas stream has a pressure above 11,032 kPa (1,600 psia).

3. The process of claim 1 wherein the cooling of the second fraction against the first fraction is in one or more heat exchangers.

4. The process of claim 1 wherein further comprising before step (a) the additional steps of withdrawing a fraction of the pressured gas stream and entropically expanding the withdrawn fraction to a lower pressure to cool the withdrawn fraction and cooling the remaining fraction of the pressurized gas stream by indirect heat exchange with the expanded fraction.

5. The process of claim 4 wherein the steps of withdrawing and expanding a fraction of the pressurized gas stream are repeated in two separate, sequential stages before step (a) of claim 1.

6. The process of claim 5 wherein the first stage of indirect cooling of the second fraction is in a first heat exchanger and the second stage of indirect cooling of the second fraction is in a second heat exchanger.

7. The process of claim 1 further comprises, after the expanded first fraction cools the second fraction, the additional steps of compressing and cooling the expanded first fraction, and thereafter recycling the compressed first fraction by combining it with the pressurized gas stream at a point in the process before step (b).

8. The process of claim 1 further comprising the step of passing the expanded second fraction of step (c) to a phase separator to produce a vapor phase and a liquid phase, said liquid phase being the product stream of step (d).

9. The process of claim 1 wherein the pressure of the expanded first fraction exceeds 1,380 kPa (200 psia).

10. The process of claim 1 further comprising the additional steps of controlling the pressure of the expanded first fraction to obtain substantial matching of the warming curve of expanded first fraction and the cooling curve of the second fraction as the expanded first fraction cools by indirect heat exchange the second fraction.

11. The process of claim 1 wherein substantially all of cooling and liquefaction of the pressurized gas is by at least two work expansions of the pressurized gas.

12. The process of claim 1 further comprising, before step (a), the additional step of pre-cooling the pressurized gas stream against a refrigerant of a closed-loop refrigeration system.

13. The process of claim 12 wherein the refrigerant is propane.

14. A process for liquefying a pressurized gas stream rich in methane, which comprises the steps of:

(a) withdrawing a first fraction of the pressurized gas stream and expanding the withdrawn first fraction to a lower pressure to cool the withdrawn first fraction;

(b) cooling a second fraction of the pressurized gas stream in a first heat exchanger by indirect heat exchange against the expanded first fraction;

(c) withdrawing from the second fraction a third fraction, thereby leaving a fourth fraction of the pressurized gas stream, and expanding the withdrawn third fraction to a lower pressure to cool and at least partially liquefy the withdrawn third fraction;

(d) cooling the fourth fraction of the pressurized gas stream in a second heat exchanger by indirect heat exchange with the at least partially-liquefied third fraction;

(e) further cooling the fourth fraction of step (d) in a third heat exchanger;

(f) pressure expanding the fourth fraction to a lower pressure, thereby at least partially liquefying the fourth fraction of the pressurized gas stream;

(g) passing the expanded fourth fraction of step (f) to a phase separator which separates vapor produced by the expansion of step (f) from liquid produced by such expansion;

(h) removing vapor from the phase separator and passing the vapor in succession through the third heat exchanger, the second heat exchanger and the first heat exchanger;

(i) compressing and cooling the vapor exiting the first heat exchanger and returning the compressed, cooled vapor to the pressurized stream for recycling; and

(j) removing from the phase separator the liquefied fourth fraction as a pressurized product stream having a temperature above −

112°

C. (−

170°

F.) and a pressure at or above its bubble point pressure.

15. The process of claim 14 wherein the process further comprises the step of introducing boil-off vapor to the vapor stream removed from the phase separator before the vapor stream is passed through the third heat exchanger.

16. The process of claim 14 further comprises, after the expanded first fraction cools the second fraction, the additional steps of compressing and cooling the expanded first fraction, and thereafter recycling the compressed first fraction by combining it with the pressurized gas stream at a point in the process before step (b).

17. The process of claim 14 wherein the process further comprises, after the third fraction is passed through the second heat exchanger, the additional steps of passing the third fraction through the first heat exchanger, thereafter compressing and cooling the third fraction, and introducing the compressed and cooled third fraction to the pressurized gas stream for recycling.

18. The process of claim 14 wherein the pressurized gas stream has a pressure above 11,032 kPa (1,600 psia).

19. A process for liquefying a pressurized gas stream rich in methane, which comprises the steps of:

(a) withdrawing from the pressured gas stream a first fraction and passing the withdrawn first fraction through a first heat exchanger to cool the first fraction;

(b) withdrawing from the pressured gas stream a second fraction, thereby leaving a third fraction of the pressurized gas stream, and expanding the withdrawn second fraction to a lower pressure to cool the withdrawn second fraction;

(c) cooling the third fraction of the pressurized gas stream in a second heat exchanger by indirect heat exchange with the cooled second fraction;

(d) withdrawing from the cooled third fraction a fourth fraction, thereby leaving a fifth fraction of the pressurized gas stream, and expanding the withdrawn fourth fraction to a lower pressure to cool and at least partially liquefy the withdrawn fourth fraction;

(e) cooling the fifth fraction of the pressurized gas stream in a third heat exchanger by indirect heat exchange with the expanded fourth fraction;

(f) pressure expanding the cooled first fraction and the cooled fifth fraction to a lower pressure, thereby at least partially liquefying the cooled first fraction and the cooled fifth fraction, and passing the expanded first and fifth fractions to a phase separator which separates vapor produced by such expansion from liquid produced by such expansion;

(g) removing vapor from the phase separator and passing the vapor through the first heat exchanger to provide cooling of the first withdrawn fraction; and

(h) removing liquid from the phase separator as a product stream having a temperature above −

112°

C. (−

170°

F.) and a pressure at or above its bubble point pressure.

20. A process for liquefying a pressurized gas stream rich in methane, which comprises the steps of:

(a) withdrawing from the pressured gas stream a first fraction and passing the withdrawn first fraction through a first heat exchanger to cool the first fraction;

(b) withdrawing from the pressured gas stream a second fraction, thereby leaving a third fraction of the pressurized gas stream, and expanding the withdrawn second fraction to a lower pressure to cool the withdrawn second fraction;

(c) cooling the third fraction of the pressurized gas stream in a second heat exchanger by indirect heat exchange with the cooled second fraction;

(d) withdrawing from the cooled third fraction a fourth fraction, thereby leaving a fifth fraction of the pressurized gas stream, and expanding the withdrawn fourth fraction to a lower pressure to cool and at least partially liquefy the withdrawn fourth fraction;

(e) cooling the fifth fraction of the pressurized gas stream in a third heat exchanger by indirect heat exchange with the expanded fourth fraction;

(f) combining the cooled first fraction and the cooled fifth fraction to form a combined stream;

(g) pressure expanding the combined stream to a lower pressure, thereby at least partially liquefying the combined stream, and passing the expanded combined stream to a phase separator which separates vapor produced by the expansion from liquid produced by the expansion;

(h) removing vapor from the phase separator and passing the vapor through the first heat exchanger to provide cooling of the first withdrawn fraction; and

(i) removing liquid from the phase separator as a product stream having a temperature above −

112°

C. (−

170°

F.) and a pressure at or above its bubble point pressure.

21. The process of claim 20 which further comprises the steps of, after the expanded second fraction cools the third fraction in the second heat exchanger, compressing and cooling the second fraction and thereafter introducing the second fraction to the pressurized gas stream for recycling.

22. The process of claim 20 which further comprises the steps of, after the expanded fourth fraction cools the fifth fraction in the third heat exchanger, passing the fourth fraction through the second heat exchanger, thereafter compressing and cooling the fourth fraction, and then introducing the fourth fraction to the pressurized gas stream for recycling.

23. The process of claim 20 which further comprises the steps of introducing boil-off vapor to the vapor stream withdrawn from the phase separator before the vapor stream is passed through the first heat exchanger.

24. The process of claim 20 wherein the pressurized gas stream has a pressure above 13,790 kPa (2,000 psia).