Methods and configurations of boil-off gas handling in LNG regasification terminals

• US 8,893,515 B2
• Filed: 04/07/2009
• Issued: 11/25/2014
• Est. Priority Date: 04/11/2008
• Status: Expired due to Fees

• Current Assignee: Fluor Technologies Corporation (Fluor Corporation)
• Original Assignee: Fluor Technologies Corporation (Fluor Corporation)
• Inventors: Mak, John
• Primary Examiner(s): Jules, Frantz
• Assistant Examiner(s): RAYMOND, KEITH MICHAEL
• Application Number:
  US12/936,070
• Publication Number:
  US 20110056238A1
• Time in Patent Office: 2,058 Days
• Field of Search: 626/13, 626/14, 62/481, 62/482, 62/483, 62/501, 62/502, 62/503
• US Class Current: 62/48.2
• CPC Class Codes: F17C 2221/014 Nitrogen
• CPC Class Codes: F17C 2221/033 Methane, e.g. natural gas, CNG, LNG, GNL, GNC, PLNG
• CPC Class Codes: F17C 2223/0161 cryogenic, e.g. LNG, GNL, PLNG
• CPC Class Codes: F17C 2223/033 Small pressure, e.g. for liquefied gas
• CPC Class Codes: F17C 2227/0135 Pumps
• CPC Class Codes: F17C 2227/0157 Compressors
• CPC Class Codes: F17C 2227/0185 comprising several pumps or compressors
• CPC Class Codes: F17C 2227/0344 Air cooling
• CPC Class Codes: F17C 2227/0348 Water cooling
• CPC Class Codes: F17C 2227/036 "Joule-Thompson" effect
• CPC Class Codes: F17C 2227/0362 in a turbine
• CPC Class Codes: F17C 2227/0393 using a vaporiser
• CPC Class Codes: F17C 2260/046 Enhancing energy recovery
• CPC Class Codes: F17C 2265/015 by separating
• CPC Class Codes: F17C 2265/034 with condensing the gas phase
• CPC Class Codes: F17C 2265/036 with heating
• CPC Class Codes: F17C 2265/037 with pressurising
• CPC Class Codes: F17C 2265/05 Regasification
• CPC Class Codes: F17C 2265/07 Generating electrical power as side effect
• CPC Class Codes: F17C 2270/0136 Terminals
• CPC Class Codes: F17C 9/02 : with change of state, e.g. vaporisation
• CPC Class Codes: F17C 9/04 : Recovery of thermal energy
• CPC Class Codes: F25J 1/0025 : Boil-off gases "BOG" from storages
• 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 1/005 : by expansion of a gaseous refrigerant stream with extraction of work
• CPC Class Codes: F25J 1/0072 : Nitrogen
• CPC Class Codes: F25J 1/0204 : as a single flow SCR cycle
• CPC Class Codes: F25J 1/0221 : using the cold stored in an external cryogenic component in an open refrigeration loop
• CPC Class Codes: F25J 1/0222 : in combination with an intermediate heat exchange fluid between the cryogenic component and the fluid to be liquefied F25J1/0224 takes precedence
• CPC Class Codes: F25J 1/023 : for the combustion as fuels, i.e. integration with the fuel gas system
• CPC Class Codes: F25J 1/0255 : controlling the composition of the feed or liquefied gas, e.g. to achieve a particular heating value of natural gas
• 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 2205/90 : Mixing of components
• CPC Class Codes: F25J 2210/62 : Liquefied natural gas [LNG]; Natural gas liquids [NGL]; Liquefied petroleum gas [LPG]
• CPC Class Codes: F25J 2215/02 : Mixing or blending of fluids to yield a certain product

Abstract

A LNG storage and regasification plant includes a reliquefaction unit in which boil-off vapors from the storage tanks are re liquefied and recycled back to the LNG storage tanks for tank pressure and Wobbe index control. Preferably, LNG cold is used for reliquefaction and operational flexibility is achieved by feeding a portion of the pressurized boil-off gas to a fuel gas header and/or to be recondensed by the sendout LNG.

Claims

1. A method of Wobbe index control of LNG in an LNG storage tank, comprising:

fluidly coupling an LNG storage tank to a regasification unit such that the tank provides LNG to the regasification unit;

fluidly coupling a compression unit to the LNG storage tank such that the tank provides cold boil-off gas to the compression unit, wherein the compression unit forms a compressed boil-off gas;

heat-exchanging a first stream of the compressed boil-off gas using the cold boil-off gas to form cooled compressed boil-off gas, and combining a first portion of the cooled compressed boil-off gas with the LNG that is fed to the regasification unit;

reliquefying a second portion of the cooled compressed boil-off gas to form a reliquefied boil-off gas;

separating nitrogen from the reliquefied boil-off gas to produce a lean reliquefied boil-off gas; and

feeding the lean reliquefied boil-off gas into the LNG storage tank.

2. The method of claim 1 further comprising a step of feeding the combined cooled compressed boil-off gas and LNG into a recondenser upstream of the regasification unit.

3. The method of claim 1 wherein LNG provides refrigeration content for the step of reliquefying.

4. The method of claim 3 wherein the step of reliquefying comprises use of a cold box.

5. The method of claim 1 wherein the step of reliquefying comprises use of a cold box.

6. The method of claim 1 wherein the step of separating nitrogen from the reliquefied boil-off gas comprises a step of expanding the reliquefied boil-off gas in a JT valve or an expander and separating the expanded reliquefied boil-off gas in a phase separator.

7. The method of claim 4 wherein the nitrogen is combined with the cold boil-off gas.

8. The method of claim 1 further comprising a step of compressing a second stream of the compressed boil-off gas.

9. The method of claim 8 wherein the second stream of the compressed boil-off gas is fed to a combustor or utilized as fuel gas.

10. The method of claim 1 further comprising a step of increasing a ratio between first and second portion when flow of the LNG to the regasification unit increases.

11. A LNG storage and regasification plant comprising:

a LNG storage tank fluidly coupled to a regasification unit to allow providing LNG from the tank to the regasification unit;

a compression unit fluidly coupled to the LNG storage tank to allow providing cold boil-off gas from the tank to the compression unit, wherein the compression unit is configured to form a compressed boil-off gas;

a heat exchanger configured to allow cooling of a first stream of the compressed boil-off gas using the cold boil-off gas to so form a cooled compressed boil-off gas;

a first conduit configured to allow combination of a first portion of the cooled compressed boil-off gas with the LNG that is provided to the regasification unit;

a cooler configured to allow reliquefaction of a second portion of the cooled compressed boil-off gas to form a reliquefied boil-off gas;

a separator configured to allow separation of nitrogen from the reliquefied boil-off gas to so produce a lean reliquefied boil-off gas; and

a second conduit configured to allow feeding the lean reliquefied boil-off gas into the LNG storage tank.

12. The storage and regasification plant of claim 11 further comprising a recondenser upstream of the regasification unit hath is configured to receive the cooled compressed boil-off gas and the LNG.

13. The storage and regasification plant of claim 11 wherein the cooler is configured to employ refrigeration content from the LNG for the reliquefaction.

14. The storage and regasification plant of claim 13 wherein the cooler is a cold box.

15. The storage and regasification plant of claim 11 wherein the cooler is a cold box.

16. The storage and regasification plant of claim 11 further comprising an expansion device upstream of the separator and configured to at least partially expand the reliquefied boil-off gas.

17. The storage and regasification plant of claim 14 further comprising a third conduit that is configured to allow combination of the nitrogen with the cold boil-off gas.

18. The storage and regasification plant of claim 11 further comprising a compressor that is configured to allow compression of a second stream of the compressed boil-off gas.

19. The storage and regasification plant of claim 18 wherein the compressor is fluidly coupled to a combustor to allow feeding of the second stream from the compressor to the combustor.

20. The storage and regasification plant of claim 11 further comprising a flow control unit that is configured to allow increasing a ratio between the first and second portion when flow of the LNG to the regasification unit increases.