Fuel supply system and method for ship engine
Disclosed are a fuel supply system and method for a ship engine. The fuel supply system for a ship engine of the present invention comprises: a submersible pump which is provided to an LNG storage tank of a ship for supplying LNG to the engine of the ship; a high-pressure pump which has the LNG supplied thereto from the submersible pump and pressurizes the same under high pressure; and a return flow channel which, at the upstream of the high-pressure pump, returns the LNG to the LNG storage tank, wherein the flow of the LNG returning through the return flow channel is controlled, and the temperature of the LNG is controlled at the front end of the high-pressure pump.
1. A system of a ship, comprising;
a liquefied natural gas (LNG) storage tank configured to contain LNG;
a discharge pump located inside the LNG storage tank and configured to discharge LNG contained in the LNG storage tank;
a high-pressure pump configured to pressurize LNG from the LNG storage tank;
an LNG transfer line between the discharge pump and the high-pressure pump;
a LNG return line branched off the LNG transfer line and configured to return LNG to the LNG storage tank from a branch location of the LNG transfer line, wherein the branch location is located outside the LNG storage tank;
a flow control valve provided on the LNG return line and configured to regulate a flow rate of LNG in the LNG return line; and
one or more controllers configured to control the discharge pump and the flow control valve for discharging LNG from the LNG storage tank, returning a first portion of LNG flowing in the LNG transfer line to the LNG storage tank, and supplying a second portion of LNG flowing in the LNG transfer line to the high-pressure pump,
wherein, when the second portion supplied to the high-pressure pump is at a temperature higher than a predetermined temperature, the one or more controllers are configured:
to control the discharge pump to increase a discharge flow rate of LNG discharged at the discharge pump to inhibit the temperature of the LNG flowing in the LNG transfer line from increasing to the boiling point of LNG for minimizing boil-off gas generation in the LNG transfer line and further for avoiding a supply of boil-off gas to the high-pressure pump, and
to control the flow control valve to increase a return flow rate of the first portion of LNG returning to the LNG storage tank in view of the increased discharge flow rate.
2. A method of operating a system of a ship, the method comprising:
discharging LNG from an LNG storage tank by a discharge pump located inside the LNG storage tank;
supplying LNG discharged from the LNG storage tank to a high-pressure pump via an LNG transfer line;
branching off LNG from the LNG transfer line and returning LNG to the LNG storage tank via an LNG return line;
controlling the discharge pump and a flow control valve located at the LNG return line for discharging LNG from the LNG storage tank, returning a first portion of LNG flowing in the LNG transfer line to the LNG storage tank, and supplying a second portion of LNG flowing in the LNG transfer line to the high-pressure pump,
wherein, when the second portion supplied to the high-pressure pump is at a temperature higher than a predetermined temperature, the discharge pump is controlled to increase a discharge flow rate of LNG discharged at the discharge pump to inhibit the temperature of the LNG flowing in the LNG transfer line from increasing to the boiling point of LNG for minimizing boil-off gas generation in the LNG transfer line and further for avoiding a supply of boil-off gas to the high-pressure pump, and further the flow control valve is controlled to increase a return flow rate of the first portion of LNG returning to the LNG storage tank in view of the increased discharge flow rate.
3. The method of claim 2 , wherein the LNG return line is branched off at a branch location of the LNG transfer line which is closer to the high-pressure pump than the discharge pump.
4. The method of claim 3 , further comprising detecting the temperature of the second portion of LNG at a point between the branch location and the high-pressure pump.
5. The method of claim 2 , wherein the predetermined temperature is lower than the boiling point of LNG.
6. The method of claim 2 , wherein the high-pressure pump pressurizes the second portion of LNG to generate pressurized LNG having a pressure of 150 bar to 400 bar.
7. The method of claim 6 , further comprising heating the pressurized LNG to generate supercritical state LNG for supplying the supercritical state LNG to an engine of the ship.
8. The system of claim 1 , wherein the branch location is located closer to the high-pressure pump than the discharge pump.
9. The system of claim 8 , further comprising a temperature detector configured to detect the temperature of the second portion of LNG at a point between the branch location and the high-pressure pump.
10. The system of claim 1 , wherein the predetermined temperature is lower than the boiling point of LNG.
11. The system of claim 1 , wherein the high-pressure pump is configured to pressurize the second portion of LNG to generate pressurized LNG having a pressure of 150 bar to 400 bar.
12. The system of claim 11 , further comprising a heater configured to heat the pressurized LNG to generate supercritical state LNG for supplying the supercritical state LNG to an engine of the ship.