VESSEL FOR THE TRANSPORT OF LIQUEFIED GAS AND METHOD OF OPERATING THE VESSEL

• US 20190323659A1
• Filed: 12/19/2017
• Published: 10/24/2019
• Est. Priority Date: 12/23/2016
• Status: Active Grant

• Current Assignee: Shell USA Incorporated (Shell Plc)
• Original Assignee: Shell Oil Company (Shell Plc)
• Inventors: HODGSON, Mark Andrew, BROWN, Stephen Andrew
• Granted Patent: US 11,698,169 B2
• Time in Patent Office: Days
• CPC Class Codes: F17C 1/002 Storage in barges or on ships
• CPC Class Codes: F17C 13/00 Details of vessels or of the filling or discharging of vessels
• CPC Class Codes: F17C 13/002 for vessels under pressure F17C13/008 and F17C13/02 - F17C13/12 take precedence
• CPC Class Codes: F17C 2201/052 large (>1000 m3)
• CPC Class Codes: F17C 2221/033 Methane, e.g. natural gas, CNG, LNG, GNL, GNC, PLNG
• CPC Class Codes: F17C 2223/0123 gaseous, e.g. CNG, GNC
• 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 2223/043 in the gas
• CPC Class Codes: F17C 2223/046 in the liquid
• CPC Class Codes: F17C 2225/0161 cryogenic, e.g. LNG, GNL, PLNG
• CPC Class Codes: F17C 2225/033 Small pressure, e.g. for liquefied gas
• CPC Class Codes: F17C 2225/035 High pressure, i.e. between 10 and 80 bars
• CPC Class Codes: F17C 2225/044 at several points, e.g. with a device for recondensing gas
• CPC Class Codes: F17C 2225/046 in the liquid
• CPC Class Codes: F17C 2227/0135 Pumps
• CPC Class Codes: F17C 2227/0157 Compressors
• CPC Class Codes: F17C 2227/0339 using the same fluid
• CPC Class Codes: F17C 2227/039 on the pipes
• CPC Class Codes: F17C 2250/01 Intermediate tanks
• CPC Class Codes: F17C 2265/034 : with condensing the gas phase
• CPC Class Codes: F17C 2265/066 : for feeding engines for propulsion
• CPC Class Codes: F17C 2270/0105 : Ships
• CPC Class Codes: F25J 1/0025 : Boil-off gases "BOG" from storages

Abstract

A vessel for the transport of liquefied gas has a hull, a cargo storage tank arranged in the hull for storing liquefied gas and an engine to propel the ship. A compressor has a compressor inlet connected to a vapour space of the at least one cargo storage tank for receiving boil-off gas at a first pressure and a compressor outlet for supplying pressurized boil-off gas to the at least one engine at a second pressure exceeding the first pressure. A boil-off gas recovery system is provided for recovery of boil off gas. The boil-off gas recovery system has a cooling section with a cooling section inlet connected to the compressor outlet to recondense at least part of the pressurized boil-off gas and a boil-off gas storage tank having a boil-off gas storage tank inlet connected to the cooling section outlet for storing the recondensed pressurized boil-off gas.

Claims

1. A vessel for the transport of liquefied gas, comprising:

a hull;

at least one cargo storage tank arranged in the hull for storing liquefied gas;

at least one engine to propel the vessel;

at least one compressor having a compressor inlet connected to a vapour space of the at least one cargo storage tank for receiving boil-off gas at a first pressure (P₁) and a compressor outlet for supplying pressurized boil-off gas to the at least one engine at a second pressure (P₂) exceeding the first pressure; and

boil-off gas recovery system for recovery of boil-off gas, the BOG recovery system comprising;

a cooling section having a cooling section inlet connected to the compressor outlet to recondense at least part of the pressurized boil-off gas and a cooling section outlet for providing recondensed pressurized boil-off gas; and

at least one recovery tank having a recovery tank inlet connected to the cooling section outlet for storing the recondensed pressurized boil-off gas.

2. The system of claim 1, the boil-off gas as recovery system comprising a first pump arranged between the cooling section outlet and the recovery tank inlet.

3. The system of claim 1, the cooling section comprising a recondenser having a recondenser inlet and a recondenser outlet for providing the recondensed pressurized boil-off gas.

4. The system of claim 3, the cooling section comprising a pre-cooler section having a pre-cooler inlet connected to the compressor outlet and a pre-cooler outlet to provide pre-cooled pressurized boil-off gas to the recondenser inlet.

5. The system of claim 3, the recondenser being adapted to operate at a third pressure (P₃) being substantially the same or lower than the second pressure (P₂).

6. The system of claim 3, the first pump being connected to the recondenser outlet, and the first pump having a first pump outlet for providing the recondensed pressurized boil-off gas at a fourth pressure (P₄), the fourth pressure exceeding the third pressure (P₃), to a secondary pre-cooler inlet for heat exchange of the recondensed pressurized boil-off gas against the pressurized boil-off gas.

7. The system of claim 6, a secondary pre-cooler outlet being connected to the recovery tank inlet.

8. The system of claim 1, the cooling section comprising a recondenser heat exchanger for heat exchanging the pressurized boil-off gas with part of the liquefied gas stored in the at least one cargo storage tank.

9. The system of claim 8, the recondenser heat exchanger being arranged inside the recondenser.

10. The system of claim 3, the reconderser being provided with spray headers to spray liquefied gas from the at least one cargo storage tank into the recondenser.

11. The system of claim 1, the recovery tan being provided with a first spray header connected to the at least one cargo storage tank, the first spray header being adapted to spray liquefied gas into the recovery tank.

12. The system of claim 1, the cooling section being provided with a second spray header connected to the at least one cargo storage tank, the second spray header being adapted to spray liquefied gas into the cooling section.

13. The system of claim 1, the recovery tank having a first outlet connected to the at least one engine.

14. The system of claim 1, the recovery tank having a second outlet connected to a second pump for pumping the recondensed pressurized boil-off gas to the at least one cargo storage tank.

15. The system of claim 1, the liquefied gas being liquefied natural gas.

16. The system of claim 1, the recovery tank being a C-type cryogenic storage tank.

17. The system of claim 1, the recovery tank having a total volume for storing the recondensed pressurized boil-off gas being in the order of about 0.5% to 5% of the total volume of the at least one cargo tank.

18. A method for the transport of liquefied gas, comprising:

transporting liquefied gas in a vessel, the vessel comprising;

a hull,

at least one cargo storage tank arranged in the hull for storing liquefied gas,

at least one engine to propel the vessel;

receiving boil-off gas at a compressor inlet of at least one compressor, the compressor inlet connected to a vapour space of the at least one cargo storage tank, at a first pressure (P₁);

using the compressor to supply pressurized boil-off gas to the at least one engine at a second pressure (P₂) exceeding the first pressure;

diverting at least part of the pressurized boil-off gas to a boil-off gas recovery system for recovery of boil-off gas;

recondensing the at least part of the pressurized boil-off gas in a cooling section of the BOG recovery system to provide recondensed pressurized boil-off gas;

storing the recondensed pressurized boil-off gas in at least one recovery tank (32).

19. The method of claim 18, comprising the further step of:

providing vaporized boil-off gas from the at least one recovery tank to the at least one engine.