Natural gas liquefaction system

• US 7,228,714 B2
• Filed: 10/28/2004
• Issued: 06/12/2007
• Est. Priority Date: 10/28/2004
• Status: Active Grant

• Current Assignee: Praxair Technology Incorporated (Linde Plc)
• Original Assignee: Praxair Technology Incorporated (Linde Plc)
• Inventors: Howard, Henry Edward
• Primary Examiner(s): DOERRLER, WILLIAM CHARLES
• Application Number:
  US10/975,077
• Publication Number:
  US 20060090508A1
• Time in Patent Office: 957 Days
• Field of Search: 626/11, 626/12, 626/13
• 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 1/0265 comprising cores associated exclusively with the cooling of a refrigerant stream, e.g. for auto-refrigeration or economizer
• 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 2205/02 using simple phase separation in a vessel or drum
• 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

Abstract

A method for producing liquefied natural gas wherein high pressure liquid natural gas is subcooled and then flashed to form flash vapor and liquefied natural gas product, and the flash vapor is employed in a refrigeration cycle to generate refrigeration for subcooling the liquid natural gas.

Claims

1. A method for producing liquefied natural gas comprising:

(A) compressing a refrigeration gas and turboexpanding the compressed refrigeration gas to produce cooled refrigeration gas;

(B)(1) cooling natural gas to form a two phase stream comprising said natural gas in liquid and vapor phases;

(2) withdrawing vapor phase natural gas from said two phase stream;

(3) cooling said vapor phase natural gas to form liquid natural gas;

(4) subcooling said liquid natural gas and flashing the subcooled natural gas to produce flash vapor and liquefied natural gas; and

(C) warming the flash vapor and the cooled refrigeration gas by indirect heat exchange with the liquid natural gas to effect the subcooling of the liquid natural gas

wherein the subcooled liquid natural gas has a pressure within the range of from 700 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.

3. The method of claim 1 wherein a portion of the refrigeration gas is withdrawn prior to turboexpansion.

2. A method for producing liquefied natural gas comprising:

(A) compressing a refrigeration gas and turboexpanding the compressed refrigeration gas to produce cooled refrigeration gas;

(B)(1) cooling natural gas to form a two phase stream comprising said natural gas in liquid and vapor phases;

(2) withdrawing vapor phase natural gas from said two phase stream;

(3) cooling said vapor phase natural gas to form liquid natural gas;

(4) subcooling said liquid natural gas and flashing the subcooled natural gas to produce flash vapor and liquefied natural gas; and

(c) warming the flash vapor and the cooled refrigeration gas by indirect heat exchange with the liquid natural gas to effect the subcooling of the liquid natural gas

wherein all of the flash vapor and the cooled refrigeration gas are combined prior to warming by indirect heat exchange with the subcooling liquid natural gas.

4. The method of claim 2 wherein the combined flash vapor and cooled refrigeration gas, after the said warming, are compressed to form the said compressed refrigeration gas.

5. The method of claim 4 wherein the combined flash vapor and cooled refrigeration gas, after the said warming, are compressed to form the said compressed refrigeration gas.

16. The method of claim 2 wherein a portion of the refrigeration gas is withdrawn prior to turboexpansion.

6. A method for producing liquefied natural gas comprising:

(A) compressing a refrigeration gas and turboexpanding the compressed refrigeration gas to produce cooled refrigeration gas;

(B) subcooling liquid natural gas and flashing the subcooled natural gas to produce flash vapor and liquefied natural gas; and

(C) warming the flash vapor and the cooled refrigeration gas by indirect heat exchange with the liquid natural gas to effect the subcooling of the liquid natural gas;

wherein all of the flash vapor and the cooled refrigeration gas are combined prior to warming by indirect heat exchange with the subcooling liquid natural gas.

7. The method of claim 6 wherein a portion of the refrigeration gas is withdrawn prior to turboexpansion.

8. The method of claim 6 wherein the combined flash vapor and cooled refrigeration gas, after the said warming, are compressed to form the said compressed refrigeration gas.

9. The method of claim 8 wherein the subcooled liquid natural gas has a pressure within the range of from 700 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.

10. A method for producing liquefied natural gas comprising:

(A) compressing a refrigeration gas and turboexpanding the compressed refrigeration gas to produce cooled refrigeration gas;

(B) subcooling liquid natural gas and flashing the subcooled natural gas to produce flash vapor and liquefied natural gas; and

(C) warming the flash vapor and the cooled refrigeration gas by indirect heat exchange with the liquid natural gas to effect the subcooling of the liquid natural gas;

wherein the subcooled liquid natural gas has a pressure within the range of from 700 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.

11. The method of claim 10 wherein the flash vapor and the cooled refrigeration gas are combined prior to warming by indirect heat exchange with the subcooling liquid natural gas.

12. The method of claim 10 wherein a portion of the refrigeration gas is withdrawn prior to turboexpansion.

13. The method of claim 11 wherein the combined flash vapor and cooled refrigeration gas, after the said warming, are compressed to form the said compressed refrigeration gas.

14. The method of claim 10 wherein all of the flash vapor and the cooled refrigeration gas are combined prior to warming by indirect heat exchange with the subcooling liquid natural gas.

15. The method of claim 14 wherein the combined flash vapor and cooled refrigeration gas, after the said warming, are compressed to form the said compressed refrigeration gas.