METHOD FOR PRODUCING LIQUEFIED NATURAL GAS

• US 20090084132A1
• Filed: 09/28/2007
• Published: 04/02/2009
• Est. Priority Date: 09/28/2007
• Status: Abandoned Application

• Current Assignee: Praxair Technology Incorporated (Linde Plc)
• Original Assignee: Praxair Technology Incorporated (Linde Plc)
• Inventors: Dragomir, Ramona Manuela, Shah, Minish Mahendra, Howard, Henry Edward
• Application Number:
  US11/864,316
• Publication Number:
  US 20090084132A1
• Time in Patent Office: Days
• US Class Current: 62/613
• 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 1/0045 by vaporising a liquid return stream
• 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 1/0232 integration within a pressure letdown station of a high pressure pipeline system
• CPC Class Codes: F25J 1/0264 Arrangement of heat exchanger cores in parallel with different functions, e.g. different cooling streams F25J1/0272 takes precedence
• CPC Class Codes: F25J 1/0267 using flash gas as heat sink
• 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 2205/66 Regenerating the adsorption vessel, e.g. kind of reactivation gas
• 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 2220/64 Separating heavy hydrocarbons, e.g. NGL, LPG, C4+ hydrocarbons or heavy condensates in general
• CPC Class Codes: F25J 2240/40 Expansion without extracting work, i.e. isenthalpic throttling, e.g. JT valve, regulating valve or venturi, or isentropic nozzle, e.g. Laval
• CPC Class Codes: F25J 2270/06 with multiple gas expansion loops

Abstract

A method for liquefying natural gas using the pressure energy of the natural gas, wherein flash vapor from natural gas depressurization is employed in a refrigeration cycle for subcooling high pressure natural gas prior to flashing.

Claims

1. A method for producing liquefied natural gas comprising:

(A) compressing a first portion of a high pressure natural gas, bringing it to a temperature above its dew point and turbo-expanding such first portion to produce at least a part of the refrigeration required to liquefy the remaining second portion of the natural gas;

(B) liquefying the remaining second portion of the natural gas and subcooling said liquefied second portion and flashing the subcooled natural gas to produce flash vapor and liquefied natural gas at low pressure;

(C) compressing a refrigeration gas and turbo-expanding the compressed refrigeration gas to produce cooled refrigeration gas; and

(D) warming the flash vapor and the cooled refrigeration gas by indirect heat exchange with the high pressure natural gas to produce subcooled liquified natural gas.

2. The method of claim 1 wherein the compressed first portion of the natural gas is cooled to bring it to a temperature above its dew point.

3. The method of claim 1 wherein the compressed first portion is cooled and expanded in a first expansion to produce at least a part of the refrigeration required to liquefy the remaining second portion of the natural gas, and heating such first portion to bring it to a temperature above its dew point.

4. The method of claim 1 wherein the high pressure natural gas is purified in a first purification system.

5. The method of claim 4 wherein a part of the first portion of the natural gas is used as regeneration gas for the first purification system.

6. The method of claim 1 wherein the second portion of natural gas is purified in a second purification system and said purified second portion is cooled.

7. The method of claim 6 wherein a part of the second portion of natural gas is flashed to a pressure marginally above letdown pressure and such part of the second portion is used as regeneration gas for the second purification system, after recovering the contained refrigeration by indirect heat exchange with incoming streams.

8. The method of claim 1 wherein the flash vapor and the cooled refrigeration gas are combined prior to warming by indirect heat exchange with the subcooling liquid natural gas.

9. The method of claim 1 wherein a portion of the refrigeration gas is withdrawn prior to turbo-expansion.

10. The method of claim 1 wherein the flash vapor and the cooled refrigeration gas, after the said warming, are compressed to form the said compressed refrigeration gas.

11. The method of claim 1 wherein the subcooled liquid natural gas has a pressure within the range of from 400 to 1500 psia, and the flash vapor and liquefied natural gas resulting from the flashing of the subcooled natural gas have a pressure within the range of from 14.7 to 40 psia.

12. A method for producing liquefied natural gas comprising:

(A) purifying a high pressure natural gas in a first purification system;

(B) compressing a first portion of a high pressure natural gas, cooling it to a temperature above its dew point and turbo-expanding such first portion to produce at least a part of the refrigeration required to liquefy the remaining second portion of the natural gas;

(C) using a part of the first portion as regeneration gas for the first purification system;

(D) purifying the second portion of natural gas in a second purification system and cooling said purified second portion;

(E) flashing a first part of the second portion of natural gas to a pressure marginally above letdown pressure and using it as regeneration gas for the second purification system;

(F) recovering contained refrigeration of such first part of the second portion by indirect heat exchange with the remaining second portion;

(G) compressing a refrigeration gas and turbo-expanding the compressed refrigeration gas to produce cooled refrigeration gas; and

(H) warming the flash vapor and the cooled refrigeration gas by indirect heat exchange with the liquefied natural gas to effect the sub-cooling of the liquefied natural gas.

13. The method of claim 12 wherein the flash vapor and the cooled refrigeration gas are combined prior to warming by indirect heat exchange with the subcooled liquefied natural gas.

14. The method of claim 12 wherein a portion of the refrigeration gas is withdrawn prior to turbo-expansion.

15. The method of claim 12 wherein the flash vapor and the cooled refrigeration gas, after the said warming, are compressed to form the said compressed refrigeration gas.

16. The method of claim 12 wherein the subcooled liquefied natural gas has a pressure within the range of from 400 to 1500 psia, and the flash vapor and liquefied natural gas resulting from the flashing of the subcooled natural gas have a pressure within the range of from 14.7 to 40 psia.

17. A method for producing liquefied natural gas comprising:

(A) purifying a high pressure natural gas in a first purification system;

(B) compressing and cooling a first portion of a natural gas and expanding such first portion in a first expansion to produce at least a part of the refrigeration required to liquefy the remaining second portion of the natural gas;

(C) heating such first portion to bring it to a temperature above its dew point and turbo-expanding such heated first portion;

(D) using a part of the first portion as regeneration gas for the first purification system;

(E) purifying the second portion of natural gas in a second purification system and cooling said purified second portion;

(F) flashing a first part of the second portion of natural gas to a pressure marginally above letdown pressure and using it as regeneration gas for the second purification system;

(G) recovering contained refrigeration of such first part of the second portion by indirect heat exchange with the remaining second portion;

(H) compressing a refrigeration gas and turbo-expanding the compressed refrigeration gas to produce cooled refrigeration gas; and

(I) warming the flash vapor and the cooled refrigeration gas by indirect heat exchange with the cooled second portion of natural gas to produce sub-cooled liquefied natural gas.

18. The method of claim 17 wherein the flash vapor and the cooled refrigeration gas are combined prior to warming by indirect heat exchange with the subcooled liquefied natural gas.

19. The method of claim 17 wherein a portion of the refrigeration gas is withdrawn prior to turbo-expansion.

20. The method of claim 17 wherein the flash vapor and the cooled refrigeration gas, after the said warming, are compressed to form the said compressed refrigeration gas.

21. The method of claim 17 wherein the subcooled liquefied natural gas has a pressure within the range of from 400 to 1500 psia, and the flash vapor and liquefied natural gas resulting from the flashing of the subcooled natural gas have a pressure within the range of from 14.7 to 40 psia.