METHOD AND SYSTEM FOR OPTIMIZED LNG PRODUCTION

• US 20110203312A1
• Filed: 08/27/2009
• Published: 08/25/2011
• Est. Priority Date: 08/29/2008
• Status: Active Grant

• Current Assignee: Wartsila Oil and Gas Systems
• Original Assignee: Hamworthy Oil & Gas Systems AS (Wartsila Oyj Abp)
• Inventors: Jakobsen, Arne, Rummelhoff, Carl J., Haukedal, Bjorn H.
• Granted Patent: US 9,163,873 B2
• 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 1/0025 Boil-off gases "BOG" from storages
• 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 1/0205 as a dual level SCR refrigeration cascade
• CPC Class Codes: F25J 1/0207 as at least a three level SCR refrigeration cascade
• CPC Class Codes: F25J 1/0249 Controlling refrigerant inventory, i.e. composition or quantity charging or discharging refrigerants in cooling systems F25B45/00
• CPC Class Codes: F25J 1/0279 Compression of refrigerant or internal recycle fluid, e.g. kind of compressor, accumulator, suction drum etc.
• 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 1/0298 Safety aspects and control of the refrigerant compression system, e.g. anti-surge control
• CPC Class Codes: F25J 2270/16 with mutliple gas expansion loops of the same refrigerant
• CPC Class Codes: F25J 2270/60 Closed external refrigeration cycle with single component refrigerant [SCR], e.g. C1-, C2- or C3-hydrocarbons
• CPC Class Codes: F25J 2270/902 Details about the refrigeration cycle used, e.g. composition of refrigerant, arrangement of compressors or cascade, make up sources, use of reflux exchangers etc.

Abstract

A method and system for producing liquefied and sub-cooled natural gas by means of a refrigeration assembly using a single phase gaseous refrigerant comprising: at least two expanders (1-3); a compressor assembly (5-7); a heat exchanger assembly (8) for heat absorption from natural gas; and a heat rejection assembly (10-12). The novel features according to the present invention are arranging the expanders (1-3) in expander loops; using only one and the same refrigerant in all loops; passing an expanded refrigerant flow from the respective expander into the heat exchanger assembly (8), each being at a mass flow and temperature level adapted to de-superheating, condensation or cooling of dense phase and/or sub-cooling of natural gas; and serving the refrigerant to the respective expander in a compressed flow by means of the compressor assembly having compressors or compressor stages enabling adapted inlet and outlet pressures for the respective expander.

Claims

1. A method for producing liquefied and sub-cooled natural gas by means of a refrigeration assembly using a single phase gaseous refrigerant comprising:

at least two expanders (1-3;

2-3);

a compressor assembly (5-7;

13-18;

5-7;

14-18);

a heat exchanger assembly (8) for heat absorption from natural gas; and

a heat rejection assembly (10-12;

19-24;

10-12;

20-24), characterized in that;

arranging the expanders (1-3;

2-3) in expander loops;

using only one and the same refrigerant in all loops;

passing an expanded refrigerant flow from the respective expander (1-3;

2-3) into the heat exchanger assembly (8), each being at a mass flow and temperature level adapted to de-superheating, condensation or cooling of dense phase and/or sub-cooling of natural gas; and

serving the refrigerant to the respective expander (1-3;

2-3) in a compressed flow by means of the compressor assembly (5-7;

13- 18;

5-7;

14-18) having compressors or compressor stages enabling adapted inlet and outlet pressures for the respective expander.

2. A method according to claim 1, characterized in that using nitrogen as the refrigerant.

3. A method according to claim 1 and claim 2, characterized in that connecting the expanders (1-3;

2-3) to the compressor assembly (5-7) as to fluidly form an integrated refrigeration assembly with separate expander loops (52, 51, 56, 55, 60, 59;

56, 55, 60, 59).

4. A method according to claim 1 and claim 2, characterized in that connecting the expanders (1-3;

2-3) to the compressor assembly (5-7) as to fluidly form an integrated refrigeration assembly with merging of cold streams in loops the expander loops (52, 56) in connection with the heat exchanger assembly (8).

5. A method according to claim 1 and claim 2, characterized in that connecting the expanders (1-3;

2-3) to the compressor assembly (5-7) as to fluidly form an integrated refrigeration assembly with splitting of warm streams in the expander loops (51, 56) in connection with the heat exchanger assembly (8) upstream from the expanders (1-3;

2-3).

6. A method according to claim 1 and claim 2, characterized in that connecting the expanders (1-3;

2-3) to the compressor assembly (5-7) as to fluidly form an integrated refrigeration assembly with splitting of warm streams (51, 55) upstream of the expanders (1-3;

2-3) and merging of cold streams (52, 56) in connection with the heat exchanger assembly (8).

7. A method according to claim 1 and claim 2, characterized in that connecting each expander (1-3;

2-3) to the compressor assembly (13- 18;

14-18) as to fluidly form separate refrigeration cycles.

8. A method according to claims 1, claim 2, claim 3 and claim 4, characterized in that controlling refrigeration capacities by varying a refrigerant inventory.

9. A method according to claims 1, claim 2 and claim 5, characterized in that independently varying the refrigeration capacities in each cycle by separate inventory control.

10. A method according to any preceding claims, characterized in that controlling the refrigeration capacities by compressor speed control.

11. A method according to any preceding claims, characterized in that replacing any of the expanders by two or more expanders connected in series with intermediate cooling between expander stages.

21. A system according to any of the preceding claims, characterized in that the refrigeration capacities are controlled by compressor speed control.

22. A system according to any of the preceding claims, characterized in that any of the expanders are replaced by two or more expanders connected in series with intermediate cooling between expander stages.

12. A system for producing liquefied and sub-cooled natural gas by means of a refrigeration assembly using a single phase gaseous refrigerant comprising:

at least two expanders (1-3;

2-3);

a compressor assembly (5-7;

13- 18;

5-7;

14-18);

a heat exchanger assembly (8) for heat absorption from natural gas; and

a heat rejection assembly (10-12;

19-24;

10-12;

20-24), characterized in that;

the expanders (1-3;

2-3) are arranged in expander loops;

only one and the same refrigerant is used in all loops;

an expanded refrigerant flow from the respective expander (1-3;

2-3) is passed into the heat exchanger assembly (8), each being at a mass flow and temperature level adapted to de-superheating, condensation or cooling of dense phase and/or sub-cooling of natural gas; and

the refrigerant to the respective expander (1-3;

2-3) is served in a compressed flow by means of the compressor assembly (5-7;

13-18;

5-7;

14-18) having compressors or compressor stages enabling adapted inlet and outlet pressures for the respective expander.

13. A system according to claim 12, characterized in that nitrogen is used as the refrigerant.

14. A system according to claim 12 and claim 13, characterized in that the expanders (1-3;

2-3) are connected to the compressor assembly (5-7) as to fluidly form an integrated refrigeration assembly with separate expander loops (52, 51, 56, 55, 60, 59;

56, 55, 60, 59).

15. A system according to claim 12 and claim 13, characterized in that the expanders (1-3;

2-3) are connected to the compressor assembly (5-7) as to fluidly form an integrated refrigeration assembly with merging of cold streams in the expander loops (52, 56) in connection with the heat exchanger assembly (8).

16. A system according to claim 12 and claim 13, characterized in that the expanders (1-3;

2-3) are connected to the compressor assembly (5-7) as to fluidly form an integrated refrigeration assembly with splitting of warm streams in the expander loops (51, 56) in connection with the heat exchanger assembly (8) upstream of the expanders (1-3;

2-3).

17. A system according to claim 12 and claim 13, characterized in that the expanders (1-3;

2-3) are connected to the compressor assembly (5-7) as to fluidly form an integrated refrigeration assembly with splitting of warm streams (51, 55) upstream of the expanders (1-3;

2-3) and merging of cold streams (52, 56) in connection with the heat exchanger assembly (8).

18. A system according to claim 12 and claim 13, characterized in that each expander (1-3;

2-3) are connected to the compressor assembly (13- 18;

14-18) as to fluidly form separate refrigeration cycles.

19. A system according to claim 12, claim 13, claim 14 and claim 15, characterized in that controlling refrigeration capacities by varying a refrigerant inventory.

20. A system according to claim 12, claim 13 and claim 16, characterized in that the refrigeration capacities are independently varied in each cycle by separate inventory control.