LNG fuel tank system for at least one gas engine used for ship propulsion
An LNG fuel tank system for at least one gas engine used for ship propulsion is comprising at least one LNG fuel tank ( 4 ) and a gas vessel ( 8 ), the LNG fuel tank to be-bunkered from an onshore LNG pressure tank filling facility by means of an LNG filling line ( 1 ). According to the present invention the LNG fuel tank ( 4 ) is a ship low pressure controlled atmospheric pressure LNG tank, and the gas vessel ( 8 ) is a single shell non-insulated pressure vessel arranged to accumulate flashed and boil-off gas during LNG bunkering and pressure relieving the LNG fuel tank, respectively, and the gas engines are fuelled from either the gas vessel ( 8 ) or the LNG fuel tank ( 4 ), dependent on a predefined gas vessel pressure.
1. A liquefied natural gas (LNG) fuel tank system for at least one gas engine used for ship propulsion, comprising at least one LNG fuel tank and a gas vessel, the LNG fuel tank configured to be bunkered from an onshore LNG pressure tank filling facility utilizing an LNG filling line, wherein the LNG fuel tank is a ship low pressure controlled atmospheric pressure LNG tank, and the gas vessel is a single shell non-insulated pressure vessel arranged to accumulate flashed and boil-off gas during LNG bunkering and pressure relieving the LNG fuel tank, respectively, and that the gas engines are fuelled from either the gas vessel or the LNG fuel tank, dependent on a predefined gas vessel pressure.
2. The LNG fuel tank system according to claim 1 , wherein the LNG fuel tank is pressure controlled using a Joule-Thompson valve arranged in the LNG filling line.
3. The LNG fuel tank system according to claim 1 , wherein the vapor pressure within the LNG fuel tank is controlled to be below about 0.7 bar gauge.
4. The LNG fuel tank system according to claim 1 , wherein a compressor which is situated in a suction and compression line extending between the LNG fuel tank and gas vessel is used as to limit the LNG fuel tank pressure during bunkering and pressure relieving the LNG fuel tank.
5. The LNG fuel tank system according to claim 1 , wherein the gas engine is configured to be fuelled from the gas vessel until the pressure approaches about 5-7 bar gauge, whereafter the fuelling is effected from the LNG fuel tank.
6. The LNG fuel tank system according to claim 5 , wherein propulsion gas from the gas vessel is supplied via a gas line passing a heater.
7. The LNG fuel tank system according to claim 6 , wherein the gas flow pressure is reduced using a Joule-Thompson valve arranged upstream the heater.
8. The LNG fuel tank system according to claim 5 , wherein propulsion gas from the LNG fuel tank is supplied via a liquid and vapor line having a mainly vertical riser equipped with a centrifugal pump situated near a lower portion of the LNG fuel tank, the LNG being evaporized in a vaporizer.
9. The LNG fuel tank system according to claim 8 , wherein vapor from the vaporizer is flowed through the vapor line via a check valve into the gas line upstream of the heater.
10. The LNG fuel tank system according to claim 8 , wherein propulsion gas is supplied from both the gas vessel and vaporizer when extra fuel is needed for propulsion of the ship.
11. The LNG fuel tank system according to claim 8 , wherein the riser is provided with a spray line extending into the gas vessel as to reduce the gas temperature when needed, the spray line including a normally closed valve.
12. The LNG fuel tank system according to claim 1 , wherein the LNG fuel tank system is configured to allow for filling from atmospheric pressure LNG tanks as well, a vapor return line is added between the top of the LNG fuel tanks and LNG onshore filling facility.