Hybrid cycle for the production of liquefied natural gas

• US 6,308,531 B1
• Filed: 10/12/1999
• Issued: 10/30/2001
• Est. Priority Date: 10/12/1999
• Status: Expired

• Current Assignee: Air Products and Chemicals Incorporated (Linde Plc)
• Original Assignee: Air Products and Chemicals Incorporated (Linde Plc)
• Inventors: Roberts, Mark Julian, Agrawal, Rakesh
• Primary Examiner(s): DOERRLER, WILLIAM CHARLES
• Application Number:
  US09/416,042
• Time in Patent Office: 749 Days
• Field of Search: 626/06, 626/11, 626/12, 629/12, 623/35
• US Class Current: 62/611
• CPC Class Codes: F25J 1/0022 Hydrocarbons, e.g. natural gas
• 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 1/005 by expansion of a gaseous refrigerant stream with extraction of work
• CPC Class Codes: F25J 1/0052 by vaporising a liquid refrigerant stream
• CPC Class Codes: F25J 1/0055 originating from an incorporated cascade
• CPC Class Codes: F25J 1/0057 after expansion of the liquid refrigerant stream with extraction of work
• CPC Class Codes: F25J 1/0072 Nitrogen
• CPC Class Codes: F25J 1/0097 Others, e.g. F-, Cl-, HF-, HClF-, HCl-hydrocarbons etc. or mixtures thereof
• CPC Class Codes: F25J 1/0207 as at least a three level SCR refrigeration cascade
• CPC Class Codes: F25J 1/0214 as a dual level refrigeration cascade with at least one MCR cycle
• CPC Class Codes: F25J 1/0215 with one SCR cycle
• CPC Class Codes: F25J 1/0216 using a C3 pre-cooling cycle
• CPC Class Codes: F25J 1/0217 as at least a three level refrigeration cascade with at least one MCR cycle
• CPC Class Codes: F25J 1/0218 with one or more SCR cycles, e.g. with a C3 pre-cooling cycle
• 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 1/0267 using flash gas as heat sink
• CPC Class Codes: F25J 1/0274 Retrofitting or revamping of an existing liquefaction unit
• CPC Class Codes: F25J 1/0288 using work extraction by mechanical coupling of compression and expansion of the refrigerant, so-called companders
• CPC Class Codes: F25J 1/0291 : Refrigerant compression by combined gas compression and liquid pumping
• CPC Class Codes: F25J 1/0292 : Refrigerant compression by cold or cryogenic suction of the refrigerant gas
• CPC Class Codes: F25J 2220/62 : Separating low boiling components, e.g. He, H2, N2, Air
• CPC Class Codes: F25J 2220/64 : Separating heavy hydrocarbons, e.g. NGL, LPG, C4+ hydrocarbons or heavy condensates in general
• CPC Class Codes: F25J 2245/02 : Recycle of a stream in general, e.g. a by-pass stream

Abstract

Refrigeration process for gas liquefaction which utilizes one or more vaporizing refrigerant cycles to provide refrigeration below about −40° C. and a gas expander cycle to provide refrigeration below about −100° C. Each of these two types of refrigerant systems is utilized in an optimum temperature range which maximizes the efficiency of the particular system. A significant fraction of the total refrigeration power required to liquefy the feed gas (typically more than 5% and often more than 10% of the total) can be consumed by the vaporizing refrigerant cycles. The invention can be implemented in the design of a new liquefaction plant or can be utilized as a retrofit or expansion of an existing plant by adding gas expander refrigeration circuit to the existing plant refrigeration system.

Claims

1. A method for the liquefaction of a feed gas which comprises providing at least a portion of the total refrigeration required to cool and condense the feed gas by utilizing

(a) a first refrigeration system comprising at least one recirculating refrigeration circuit, wherein the first refrigeration system utilizes two or more refrigerant components and provides refrigeration in a first temperature range;

and

(b) a second refrigeration system which provides refrigeration in a second temperature range by work expanding a pressurized gaseous refrigerant stream.

2. The method of claim 1 wherein the lowest temperature in the second temperature range is less than the lowest temperature in the first temperature range.

3. The method of claim 1 wherein at least 5% of the total refrigeration power required to liquefy the feed gas is consumed by the first refrigeration system.

4. The method of claim 1 wherein the feed gas is natural gas.

5. The method of claim 1 wherein the refrigerant in the first recirculating refrigeration circuit comprises two or more components selected from the group consisting of nitrogen, hydrocarbons containing one or more carbon atoms, and halocarbons containing one or more carbon atoms.

6. The method of claim 1 wherein the pressurized gaseous refrigerant stream comprises nitrogen.

7. The method of claim 1 wherein at least a portion of the first temperature range is between about −

40°

C. and about −

100°

C.

8. The method of claim 7 wherein at least a portion of the first temperature range is between about −

60°

C. and about −

100°

C.

9. The method of claim 1 wherein at least a portion of the second temperature range is below about −

100°

C.

10. The method of claim 1 wherein at least 10% of the total refrigeration power required to liquefy the feed gas is consumed by the first recirculating refrigeration system.

11. The method of claim 1 wherein the first recirculating refrigeration system is operated by

(1) compressing a first gaseous refrigerant;

(2) cooling and at least partially condensing the resulting compressed refrigerant;

(3) reducing the pressure of the resulting at least partially condensed compressed refrigerant;

(4) vaporizing the resulting reduced-pressure refrigerant to provide refrigeration in the first temperature range and yield a vaporized refrigerant; and

(5) recirculating the vaporized refrigerant to provide the first gaseous refrigerant of (1).

12. The method of claim 11 wherein at least a portion of the cooling of the resulting compressed refrigerant in (2) is provided by indirect heat exchange with vaporizing reduced-pressure refrigerant in (4).

13. The method of claim 11 wherein at least a portion of the cooling in (2) is provided by indirect heat exchange with one or more additional vaporizing refrigerant streams provided by a third recirculating refrigeration circuit.

14. The method of claim 13 wherein the third recirculating refrigeration circuit utilizes a single component refrigerant.

15. The method of claim 13 wherein the third recirculating refrigeration circuit utilizes a mixed refrigerant comprising two or more components.

16. The method of claim 1 wherein the second refrigeration system is operated by

(1) compressing a second gaseous refrigerant to provide the pressurized gaseous refrigerant in (b);

(2) cooling the pressurized gaseous refrigerant to yield a cooled gaseous refrigerant;

(3) work expanding the cooled gaseous refrigerant to provide the cold refrigerant in (b);

(4) warming the cold refrigerant to provide refrigeration in the second temperature range; and

(5) recirculating the resulting warmed refrigerant to provide the second gaseous refrigerant of (1).

17. The method of claim 16 wherein at least a portion of the cooling in (2) is provided by indirect heat exchange by warming the cold refrigerant stream in (4).

18. The method of claim 16 wherein at least a portion of the cooling in (2) is provided by indirect heat exchange with the vaporizing refrigerant of (a).

19. The method of claim 16 wherein at least a portion of the cooling in (2) is provided by indirect heat exchange with one or more additional vaporizing refrigerants provided by a third recirculating refrigeration circuit.

20. The method of claim 19 wherein the third recirculating refrigeration circuit utilizes a single component refrigerant.

21. The method of claim 19 wherein the third recirculating refrigeration circuit utilizes a mixed refrigerant which comprises two or more components.

22. The method of claim 1 wherein the first refrigeration system and the second refrigeration system provide in a single heat exchanger a portion of the total refrigeration required to liquefy the feed gas.

23. The method of claim 1 wherein the first refrigerant system is operated by

(1) compressing a first gaseous refrigerant;

(2) cooling and partially condensing the resulting compressed refrigerant to yield a vapor refrigerant fraction and a liquid refrigerant fraction;

(3) further cooling and reducing the pressure of the liquid refrigerant fraction, and vaporizing the resulting liquid refrigerant fraction to provide refrigeration in the first temperature range and yield a first vaporized refrigerant;

(4) cooling and condensing the vapor refrigerant fraction, reducing the pressure of at least a portion of the resulting liquid, and vaporizing the resulting liquid refrigerant fraction to provide additional refrigeration in the first temperature range and yield a second vaporized refrigerant; and

(5) combining the first and second vaporized refrigerants to provide the first gaseous refrigerant of (1).

24. The method of claim 23 wherein vaporization of the resulting liquid in (4) is effected at a pressure lower than the vaporization of the resulting liquid refrigerant fraction in (3), and wherein the second vaporized refrigerant is compressed before combining with the first vaporized refrigerant.

25. The method of claim 16 wherein work from work expanding the cooled gaseous refrigerant in (3) provides a portion of the work required for compressing the second gaseous refrigerant in (1).

26. The method of claim 16 wherein the feed gas is natural gas, the resulting liquefied natural gas stream is flashed to lower pressure to yield a light flash vapor and a final liquid product, and the light flash vapor is used to provide the second gaseous refrigerant in the second refrigerant circuit.