Method for utilization of lean boil-off gas stream as a refrigerant source

Patent metadata

Field	Value
Publication number	US-9989304-B2
Application number	US-69110010-A
Country	US
Kind code	B2
Filing date	Jan 21, 2010
Priority date	Jan 21, 2009
Publication date	Jun 5, 2018
Grant date	Jun 5, 2018

Abstract

This invention relates to a system and method for liquefying natural gas. In another aspect, the invention concerns an improved liquefied natural gas facility employing a closed loop methane refrigeration cycle. In another aspect, the invention concerns the utilization of lean boil-off gas.

First claim

The invention claimed is:

1. A process for liquefying natural gas, said process comprising the steps of:
a. cooling a natural gas stream in a first refrigeration cycle employing a first refrigerant, wherein the first refrigerant cycle includes a plurality of first refrigerant cooling stages, wherein the natural gas stream comprises a plurality of heavy components;
b. downstream of the first refrigerant cycle, further cooling the natural gas stream in a final refrigeration cycle employing a final refrigerant, wherein the final refrigeration cycle is a closed loop methane final refrigerant cycle, wherein the final refrigerant predominately comprises less than 10 mole percent nitrogen, wherein the final refrigeration cycle includes a plurality of final refrigerant cooling stages, wherein the plurality of final refrigerant cooling stages includes a first cooling stage and a final cooling stage, wherein the temperature of the final refrigeration cycle operates at a lower temperature than the temperature of the first refrigeration cycle;
c. delivering the natural gas stream to a natural gas product storage tank, wherein evaporation of a portion of the natural gas stream occurs within the natural gas product storage tank resulting in boil-off gas;
d. compressing as least a portion of the boil-off gas; and
e. delivering at least a portion of the compressed boil-off gas from the natural gas product storage tank to the final cooling stage of the closed loop methane final refrigeration cycle, wherein at least a portion of the compressed boil-off gas serves as the final refrigerant in the final cooling stage of the closed loop methane refrigerant final refrigerant cycle.

2. The process according to claim 1 , wherein the plurality of first refrigerant cooling stages in the first refrigeration cycle comprises 2 to 4 cooling stages.

3. The process according to claim 2 , wherein the plurality of first refrigerant cooling stages in the first refrigeration cycle comprises 3 cooling stages.

4. The process according to claim 1 , wherein the first refrigerant comprises at least 75 mole percent propane, propylene or mixtures thereof.

5. The process according to claim 4 , wherein the first refrigerant comprises at least 90 mole percent propane.

6. The process according to claim 5 , wherein the first refrigerant consists essentially of propane.

7. The process according to claim 1 , wherein the first refrigerant comprises at least 75 mole percent ethane, ethylene or mixtures thereof.

8. The process according to claim 7 , wherein the first refrigerant comprises at least 90 mole percent ethane, ethylene or mixtures thereof.

9. The process according to claim 8 , wherein the first refrigerant consists essentially of ethylene.

10. The process according to claim 1 , wherein the final refrigerant is predominately methane comprising less than 5 mole percent nitrogen.

11. A process for liquefying natural gas, said process comprising the steps of:
a. cooling a natural gas stream in a first refrigeration cycle employing a first refrigerant, wherein the first refrigeration cycle includes a plurality of first refrigerant cooling stages wherein the natural gas stream comprises a plurality of heavy components;
b. downstream of the first refrigeration cycle, further cooling the natural gas stream in a final refrigeration cycle employing a final refrigerant, wherein the final refrigeration cycle is a closed loop methane refrigeration cycle, wherein the final refrigeration cycle includes a plurality of final refrigerant cooling stages;
c. delivering the natural gas stream to a natural gas product storage tank, wherein evaporation of a portion of the natural gas stream occurs within the natural gas product storage tank resulting in a boil-off gas;
d. compressing at least of portion of the boil-off gas; and
e. delivering at least a portion of the compressed boil-off gas from the natural gas product storage tank to the final cooling stage of the closed loop methane refrigerant final refrigeration cycle, wherein at least a portion of the compressed boil-off gas serves as the final refrigerant in the final cooling stage of the closed loop methane refrigerant final refrigeration cycle.

12. The process according to claim 11 , wherein the final refrigeration cycle operates at a lower temperature than the first refrigeration cycle.

13. The process according to claim 11 , wherein the plurality of first refrigerant cooling stages in the first refrigeration cycle comprises 2 to 4 cooling stages.

14. The process according to claim 13 , wherein the plurality of first refrigerant cooling stages in the first refrigeration cycle comprise 3 cooling stages.

15. The process according to claim 11 , wherein the first refrigerant comprises at least 75 mole percent propane, propylene or mixtures thereof.

16. The process according to claim 15 , wherein the first refrigerant comprises at least 90 mole percent propane.

17. The process according to claim 16 , wherein the first refrigerant consists essentially of propane.

18. The process according to claim 11 , wherein the first refrigerant comprises at least 75 mole percent ethane, ethylene or combinations thereof.

19. The process according to claim 18 , wherein the first refrigerant comprises at least 90 mole percent ethane, ethylene or combinations thereof.

20. The process according to claim 19 , wherein the first refrigerant consists essentially of ethylene.

21. The process according to claim 11 , wherein the final refrigerant is predominately methane comprising less than 10 mole percent nitrogen.

22. The process according to claim 21 , wherein the final refrigerant is predominately methane comprising less than 5 mole percent nitrogen.

23. The process according to claim 11 , wherein the plurality of final refrigerant cooling stages in the final refrigeration cycle comprises 2 to 4 cooling stages.

24. The process according to claim 23 , wherein the plurality of final refrigerant cooling stages in the final refrigeration cycle comprises 3 cooling stages.

Assignees

• Evans Megan V
• Praderio Attilio J
• Strassle Lisa M
• Conocophillips Co

Inventors

• Evans Megan V
• Praderio Attilio J
• Strassle Lisa M

Classifications

• F25J1/0022

  Hydrocarbons, e.g. natural gas · CPC title

• F25J1/025

  Details related to the refrigerant production or treatment, e.g. make-up supply from feed gas itself · CPC title

• F25J1/0052

  by vaporising a liquid refrigerant stream · CPC title

• F25J1/0045

  by vaporising a liquid return stream · CPC title

• F25J1/0087

  Propane; Propylene · CPC title