METHOD FOR START-UP OF A LIQUEFIED NATURAL GAS (LNG) PLANT

• US 20130036763A1
• Filed: 02/25/2011
• Published: 02/14/2013
• Est. Priority Date: 02/26/2010
• Status: Active Grant

• Current Assignee: Equinor Energy AS (Asa Equinor)
• Original Assignee: Statoil Petroleum As (Asa Equinor)
• Inventors: Vist, Sivert, Lland, Tore, Svenning, Morten, Glyseth, Silja Eriksson
• Granted Patent: US 10,527,346 B2
• Time in Patent Office: Days
• US Class Current: 62/611
• CPC Class Codes: F25J 1/0022 Hydrocarbons, e.g. natural gas
• CPC Class Codes: F25J 1/0245 Different modes, i.e. 'runs', of operation; Process control
• CPC Class Codes: F25J 1/0247 start-up of the process
• CPC Class Codes: F25J 1/0248 Stopping of the process, e.g. defrosting or deriming, maintenance; Back-up mode or systems
• CPC Class Codes: F25J 2210/04 Mixing or blending of fluids with the feed stream
• CPC Class Codes: F25J 2210/62 Liquefied natural gas [LNG]; Natural gas liquids [NGL]; Liquefied petroleum gas [LPG]
• CPC Class Codes: F25J 2220/62 Separating low boiling components, e.g. He, H2, N2, Air
• CPC Class Codes: F25J 2245/02 Recycle of a stream in general, e.g. a by-pass stream

Abstract

A method for start-up of a liquefied natural gas (LNG) plant, the plant including a liquefaction unit arranged in a flow path of the plant, including removing LNG from a first location in the flow path downstream of the liquefaction unit; vaporizing the removed LNG, or heating the removed LNG so that the removed LNG is transformed to gas phase; and re-admitting the vaporized or transformed LNG to the flow path at a second location upstream of the liquefaction unit. A corresponding LNG plant is also provided.

Claims

1. A method for start-up of a liquefied natural gas (LNG) plant, the plant including a liquefaction unit arranged in a flow path of the plant, wherein the method comprises:

removing LNG from a first location in the flow path downstream of the liquefaction unit;

vaporizing the removed LNG, or heating the removed LNG so that the removed LNG is transformed to gas phase; and

re-admitting the vaporized or transformed LNG to the flow path at a second location upstream of the liquefaction unit.

2. A method according to claim 1, further comprising:

increasing the pressure of the removed LNG.

3. A method according to claim 2, wherein the pressure of the removed LNG is increased by pumping the removed LNG to a pressure of about 5-10 MPa before vaporizing or transforming the removed LNG.

4. A method according to claim 1, wherein the vaporized or transformed LNG is re-admitted at a rate less than the plant'"'"'s full production rate.

5. A method according to claim 1, performed during start-up of the plant.

6. A method according to claim 5, wherein the LNG is removed from an LNG storage tank of the plant or from a rundown line to the storage tank of the plant.

7. A method according to claim 5, wherein the vaporized or transformed LNG is re-admitted to the flow path upstream of a pre-cooling unit of the plant, but downstream of a gas pre-treatment unit of the plant.

8. A method according to claim 5, wherein the vaporized or transformed LNG is re-admitted at a rate that corresponds to about 1-10% of the plant'"'"'s full production rate.

9. A method according to claim 5, wherein the re-admitted vaporized or transformed LNG is used as a heat sink for heat exchangers in the liquefaction unit.

12. A method according to claim 2, wherein the vaporized or transformed LNG is re-admitted at a rate less than the plant'"'"'s full production rate.

13. A method according to claim 3, wherein the vaporized or transformed LNG is re-admitted at a rate less than the plant'"'"'s full production rate.

14. A method according to claim 2, performed during start-up of the plant.

15. A method according to claim 3, performed during start-up of the plant.

16. A method according to claim 4, performed during start-up of the plant.

17. A method according to claim 6, wherein the vaporized or transformed LNG is re-admitted to the flow path upstream of a pre-cooling unit of the plant, but downstream of a gas pre-treatment unit of the plant.

18. A method according to claim 6, wherein the vaporized or transformed LNG is re-admitted at a rate that corresponds to about 1-10% of the plant'"'"'s full production rate.

19. A method according to claim 7, wherein the vaporized or transformed LNG is re-admitted at a rate that corresponds to about 1-10% of the plant'"'"'s full production rate.

20. A method according to claim 6, wherein the re-admitted vaporized or transformed LNG is used as a heat sink for heat exchangers in the liquefaction unit.

10. A liquefied natural gas (LNG) plant, comprising:

a liquefaction unit arranged in a flow path of the plant;

first means for removing LNG from a first location in the flow path downstream of the liquefaction unit;

one of a vaporizer adapted to vaporize the removed LNG and a heater adapted to heat the removed LNG so that the removed LNG is transformed to gas phase; and

second means for re-admitting the vaporized or transformed LNG to the flow path at a second location upstream of the liquefaction unit.

11. An LNG plant according to claim 10, further comprising control means adapted to control at least one of said first means, the vaporizer or heater, and the second means during start-up of the LNG plant.