Vessel for the transport of liquefied gas and method of operating the vessel
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.
1. 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 (P 1 );
using the compressor to supply pressurized boil-off gas to the at least one engine at a second pressure (P 2 ) 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, wherein 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.
2. The method of claim 1 , comprising the further step of:
providing vaporized boil-off gas from the at least one recovery tank to the at least one engine.
3. The method of claim 1 , further comprising:
operating the recondenser at a third pressure (P 3 ) being substantially the same or lower than the second pressure (P 2 ).
4. The method of claim 3 , further comprising:
providing the recondensed pressurized boil-off gas at a fourth pressure (P 4 ), the fourth pressure exceeding the third pressure (P 3 ), to a secondary pre-cooler inlet for heat exchange of the recondensed pressurized boil-off gas against the pressurized boil-off gas.
5. The method of claim 1 , wherein the storing step comprises: storing the recondensed pressurized boil-off gas in the at least one recovery tank at a storage pressure in a range from 6 bar and up to 25 bar.
6. The method of claim 1 , wherein the storing step comprises: storing the recondensed pressurized boil-off gas in at least one recovery tank for a period of at least one day.
7. The method of claim 6 , wherein the storing step comprises: storing the recondensed pressurized boil-off gas in at least one recovery tank for a period of at least 9 days.
8. The method of claim 7 , wherein the storing step comprises: storing the recondensed pressurized boil-off gas in at least one recovery tank for a period of at least 10 days.
9. The method of claim 8 , wherein a secondary pre-cooler outlet being connected to the recovery tank inlet.