WO2016163332A1

WO2016163332A1 - Fuel gas supply system for liquefied gas transport vessel

Info

Publication number: WO2016163332A1
Application number: PCT/JP2016/060999
Authority: WO
Inventors: 伸哉湯浅; 貴士渡邉; 林　弘能; 康之辻
Original assignee: 三井造船株式会社
Priority date: 2015-04-10
Filing date: 2016-04-04
Publication date: 2016-10-13
Also published as: JP2016200068A; CN107614858A; CN107614858B; JP6541059B2; KR20170142167A; KR102562868B1

Abstract

A fuel gas supply system for liquefied gas transport vessel is provided with a first fuel gas supply line 14, which supplies boil-off gas (BOG) in a cargo tank 11 as fuel gas to a main engine 12 via a high-pressure gas compressor 13, and a second fuel gas supply line 21, which draws in liquefied gas in the cargo tank 11 with a pump 22, and uses a high-pressure liquid pump 24 and a gas heater 25 to generate high-pressure gas. During travel while carrying liquefied gas, if the amount of fuel gas is sufficient using only the BOG, only the first fuel gas supply line 14 is used, and if the amount is not sufficient, the second fuel gas supply line 21 also is used. During travel when there is no liquefied gas load and a spraying operation is not being performed, only the second fuel gas supply line 21 is used.

Description

Fuel gas supply system for liquefied gas carrier

The present invention relates to a fuel gas supply system applied to a liquefied gas carrier ship equipped with a low-speed diesel engine capable of gas burning as a main engine.

In recent years, from the viewpoint of reducing environmental impact and improving energy consumption, a gas-fired low-speed diesel engine has been adopted as the main engine of the LNG carrier, and boil-off gas (NATUREL BOG) that is naturally generated in the LNG cargo tank is used as the main engine fuel. The configuration to be used is known. However, it is necessary to supply fuel gas having a pressure of about 30 MPa to the gas-fired low-speed diesel engine. Therefore, when boil-off gas is used as fuel, it is necessary to compress this boil-off gas to about 30 MPa with a high-pressure gas compressor. However, the method using a high-pressure gas compressor has a problem that power consumption is large. On the other hand, as a method for generating high-pressure fuel gas with low power consumption, a configuration in which liquefied natural gas is pressurized with a high-pressure liquid pump and heated to a high-pressure gas of about 30 MPa is known (Patent Document 1).

JP 2012-177333 A

When the liquefied gas in the cargo tank is changed to a high-pressure gas through the high-pressure liquid pump, the boil-off gas is not consumed as fuel, so the boil-off gas is forcibly burned to prevent an increase in the cargo tank pressure due to the generation of the boil-off gas. It is necessary to prepare a gas combustion device and a reliquefaction device for returning boil-off gas to liquid. However, burning boil-off gas increases the environmental load and reduces the energy efficiency of the entire liquefied gas carrier. Also, the operation of the reliquefaction device generally requires more energy than the operation of the high pressure gas compressor.

The present invention aims to optimize boil-off gas processing and energy consumption in a liquefied gas carrier using a high-pressure gas compressor and a high-pressure liquid pump in combination with the operating state of the liquefied gas carrier.

A fuel gas supply system for a liquefied gas carrier of the present invention includes a low-speed diesel engine that can be used as a main engine, a tank that stores liquefied gas, a high-pressure gas compressor that compresses boil-off gas generated in the tank, A high-pressure liquid pump that pressurizes liquefied gas from the tank, a first fuel gas supply line that supplies fuel gas from the tank to the low-speed diesel engine through the high-pressure gas compressor, and fuel gas from the tank to the low-speed diesel engine through the high-pressure liquid pump A second fuel gas supply line for supplying, and a first operation mode for supplying fuel gas to the low-speed diesel engine through the first fuel gas supply line and the second fuel gas supply line. The fuel gas supply amount by the gas supply line is controlled based on the tank pressure, and the second It is characterized by controlling on the basis of the amount of fuel gas supplied by the material gas supply line to the fuel gas required pressure of the low-speed diesel engine.

In operation when loading liquefied gas, when the fuel consumption of the low-speed diesel engine is larger than the amount of boil-off gas generated, the first operation mode is selected, and the boil-off gas is supplied to the low-speed diesel engine as fuel gas through the first fuel gas supply line. The liquefied gas in the tank is supplied to the low-speed diesel engine through the second fuel gas supply line as a shortage of fuel gas. In addition, when the liquefied gas is loaded, when the fuel consumption of the low-speed diesel engine is less than the boil-off gas generation amount, the second operation mode for supplying the fuel gas to the low-speed diesel engine only through the first fuel gas supply line is selected. The amount of fuel gas supplied from the high pressure gas compressor is controlled based on the required fuel gas pressure of the low speed diesel engine.

During operation when liquefied gas is empty, spray work (when liquefied gas is received in the cargo tank, the liquefied gas left in the cargo tank is put into the cargo tank to prevent damage to the cargo tank due to a sudden temperature difference. If the cargo tank is not precooled by the heat of vaporization of the liquefied gas, the third operation mode is selected to supply the liquefied gas in the cargo tank as fuel gas to the low-speed diesel engine only through the second fuel gas supply line. The discharge pressure of the high-pressure liquid pump is controlled based on the required fuel gas pressure of the low-speed diesel engine. Further, when the spray operation is performed in the operation when the liquefied gas is empty, either the first or the second operation mode is selected from the relationship between the fuel consumption amount of the low speed diesel engine and the boil-off gas generation amount.

Further, the final stage of the high-pressure gas compressor is preferably provided with a first circulation line for circulating the fuel gas from the discharge side to the suction side so that the pressure of the cargo tank is kept constant in the first operation mode. It is preferable to control the amount of fuel gas circulated by controlling the first valve provided in the first circulation line. Further, it is preferable that a second circulation line for circulating the liquefied gas from the discharge side to the upstream side of the high pressure liquid pump is provided. In the third operation mode, when the load of the low speed diesel engine is low, the high pressure liquid pump is minimized. It is preferable that the liquefied gas can be circulated upstream by controlling the second valve provided in the second circulation line while being driven by the capacity.

The second fuel gas supply line includes a suction drum provided on the upstream side of the high-pressure liquid pump and a gas heater provided on the downstream side. The high-pressure gas compressor is a multi-stage compressor including a low-pressure stage and a final stage, and preferably includes a branch line for sending surplus gas from the low-pressure stage to the boil-off gas processing device.

The liquefied gas carrier ship of the present invention is characterized by including the fuel gas supply system for the liquefied gas carrier ship.

According to the present invention, in the liquefied gas carrier ship, the high pressure gas compressor and the high pressure liquid pump can be used in combination to optimize the boil-off gas processing and energy consumption according to the operating state of the liquefied gas carrier ship.

It is a block diagram which shows the structure of the fuel gas supply system which is one Embodiment of this invention. Operation speed and use in (a) liquefied gas loading, (b) liquefied gas empty (with spray operation), (c) liquefied gas empty (no spray operation) in one embodiment of the present invention It is a graph which shows the relationship of fuel consumption.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
FIG. 1 is a block diagram showing a configuration of a fuel gas supply system according to an embodiment of the present invention.

The fuel gas supply system 10 of this embodiment is applied to a ship that transports a liquefied gas such as natural gas, and the liquefied gas (LNG in this embodiment) is loaded on a cargo tank 11 provided in the hull. The main engine 12 is a low-speed diesel engine that can be gas-fired. The main engine 12 is supplied with boil-off gas (NATUREL BOG) that is naturally generated in the cargo tank 11 through a first fuel gas supply line 14 including a high-pressure gas compressor 13. Is possible.

The boil-off gas generated in the cargo tank 11 is sent to the high-pressure gas compressor 13 through the upstream line of the first fuel gas supply line 14 and is compressed in the high-pressure gas compressor 13. The compressed boil-off gas is sent as “high pressure gas” to the main engine 12 through the first fuel gas supply line 14 on the downstream side. The high-pressure gas compressor 13 is, for example, a multistage compressor, and includes an upstream-side low-pressure stage 13A and a downstream-side final stage 13B. For example, from the low pressure stage 13A, the fuel gas can be sent out as “low pressure gas” having a relatively low pressure through the branch line 15, and the fuel gas can be supplied to the gas-fired generator engine. Further, surplus BOG that cannot be consumed by the main engine 12 or the generator engine is also supplied as fuel gas to the BOG processing device (boiler, gas combustion device, reliquefaction device) through the branch line 15. Further, the line for sending the surplus gas to the BOG processing device may be configured to supply the decompressed gas from the discharge side of the final stage 13B of the high pressure gas compressor 13 to the required pressure of the BOG processing device. In the present embodiment, the low-pressure stage to the high-pressure stage are described as one multi-stage high-pressure gas compressor, but the low-pressure stage may be another compressor and the low-pressure gas compressor and the high-pressure gas compressor may be installed in series.

In the high-pressure gas compressor 13, a first circulation line 16 for returning the fuel gas to the suction side of the final stage 13B is provided on the discharge side of the final stage 13B. The first circulation line 16 is provided with a first valve 16V for controlling the flow rate of the recirculated gas, and the opening degree of the first valve 16V is controlled by the first controller 17. A pressure sensor 18 is provided on the discharge side of the final stage 13B, and the pressure value PV1 on the discharge side of the fuel gas supplied to the main engine 12 is measured. On the other hand, a pressure sensor 19 for measuring the pressure PV2 of the boil-off gas in the cargo tank 11 is provided on the upstream side of the first fuel gas supply line 14. Although a plurality of cargo tanks 11 are provided in the hull, in this embodiment, the pressure PV2 is measured at one point in a common pipe of the plurality of cargo tanks 11. However, the pressure may be measured at a plurality of locations and the average may be set as the pressure PV2.

The measured pressure values PV1 and PV2 are input to the first controller 17, the fuel gas request pressure SP1 of the main engine 12 from the main engine controller 20, and the pressure in the cargo tank 11 set by the operator. A set value SP2 or the like is input. As will be described later, the first controller 17 adjusts the opening degree of the first valve 16V of the first circulation line 16 based on these values, and boil-off gas supplied from the first fuel gas supply line 14 to the main engine 12. Control the amount of supply.

The fuel gas supply system 10 of this embodiment further includes a second fuel gas supply line 21. The second fuel gas supply line 21 includes a pump 22 disposed near the bottom in the cargo tank 11, and liquefied gas in the cargo tank 11 is pumped up by the pump 22 in accordance with an operation mode to be described later. In the second fuel gas supply line 21, the pumped liquefied gas is temporarily stored in the suction drum 23. A high pressure liquid pump 24 is connected to the downstream side of the suction drum 23, and the liquefied gas in the suction drum 23 is pressurized and sent to the gas heater 25. In the gas heater 25, the liquefied gas pressurized by the high-pressure liquid pump 24 is heated and vaporized and supplied to the main engine 12 as a high-pressure gas. Even when the first fuel gas supply line 14 is not used, a line for supplying fuel gas to the gas-fired generator engine downstream of the gas heater 25 in order to use the liquefied gas as fuel for the gas-fired generator engine. Alternatively, a line for supplying gas to the gas-fired generator engine from the front of the suction drum 23 may be branched.

The high-pressure liquid pump 24 is driven by a motor 26, and the motor 26 is driven and controlled by a second controller 28 through an inverter 27. A second circulation line 29 for returning the liquefied gas to the suction drum 23 is provided on the downstream side of the high-pressure liquid pump 24, and a second circulation line 29 for controlling the flow rate of the returned liquefied gas is provided in the second circulation line 29. A valve 29V is provided. The second controller 28 receives the fuel gas required pressure SP1 from the main engine controller 20 and is measured by a pressure sensor 30 provided between the high pressure liquid pump 24 and the gas heater 25 in the second fuel gas supply line 21. The pressure value PV3 is input. As will be described later, the second controller 28 adjusts the opening degree of the second valve 29V and controls the driving of the motor 26 in accordance with the operation mode and the operation state. The motor 26 may be a hydraulic drive motor. In that case, the drive of the hydraulic drive motor is controlled not through the inverter 27 but through a hydraulic drive source. In the present embodiment, the second circulation line 29 is guided to the suction drum 23, but may be guided to the cargo tank 11.

The suction drum 23 is provided with a third circulation line 31 for returning the boil-off gas in the drum to the upstream side (cargo tank 11 side) of the first fuel gas supply line 14. Is provided with a third valve 31V. A fourth valve 21V for keeping the load of the pump constant is provided immediately after leaving the cargo tank 11 of the second fuel gas supply line 21, and a high pressure liquid pump 24 is provided immediately downstream thereof. A branch line 32 for adjusting the supply pressure of the liquefied gas to be supplied to is provided, and the branch line 32 includes a fifth valve 32V.

Further, the NPSH (effective suction head) of the high-pressure liquid pump 24 can be sufficiently secured without installing the suction drum 23, and the suction drum 23 that degass the gas vaporized between the cargo tank 11 and the high-pressure liquid pump 24. When an alternative means is provided, the suction drum 23 is not necessarily provided. In this case, the third circulation line 31 is not provided, and the second circulation line 29 is guided to the cargo tank 11.

In the present embodiment, surplus BOG through the branch line 15 is supplied to the BOG processing device (boiler, gas combustion device, reliquefaction device) by opening the opening of the sixth valve 15V provided in the branch line 15. It is controlled by adjusting with the third controller 33. The third controller 33 receives the cargo tank pressure value PV2 and the pressure set value SP2 set by the operator, adjusts the opening of the sixth valve 15V based on these values, and converts the surplus BOG to the BOG processing device. To supply.

Next, referring to FIG. 1 and FIG. 2, to the main engine 12 in the first to third operation modes using the first and second fuel

gas supply lines

14 and 21 of the fuel gas supply system 10 of the present embodiment. A mode of fuel gas supply will be described.

Figures 2 (a) to 2 (c) show (a) the relationship between operating speed and fuel consumption when liquefied gas is loaded, and (b) when spray work is performed when liquefied gas is empty. It is a graph which shows the relationship between the operation speed and use fuel consumption of (c), and the relationship between the operation speed and use fuel consumption when the spray operation | work is not performed in the operation at the time of (c) liquefied gas empty load. In FIGS. 2 (a) to 2 (c), the horizontal axis represents the ship operating speed, and the vertical axis represents the fuel consumption.

2 (a) to 2 (c), a curve S is a curve showing the relationship between the ship speed and the fuel consumption (fuel gas supply amount / unit time), and the fuel consumption is approximately the cube of the ship speed. Is proportional to A straight line L (NATURAL BOG) in FIG. 2A is an amount per unit time at which the liquefied gas (natural gas) in the cargo tank 11 spontaneously evaporates and becomes boil-off gas.

That is, in FIG. 2A, when only boil-off gas and all of it is used as fuel for the main engine 12 and the gas-fired generator engine, a boat speed corresponding to the intersection P between the curve S and the straight line L is obtained. On the other hand, on the higher speed side than the operating point P, the difference between the curve S and the straight line L is the amount of fuel that needs to be added, and on the lower speed side than the operating point P, the difference between the straight line L and the curve S is the surplus boil-off gas. Become.

In the present embodiment, the first operation mode (hybrid mode) is selected when the vehicle is operated on the higher speed side (high speed operation region) than the operation point P (NATURER BOG 100% speed) in a state where the liquefied gas is loaded. In the first operation mode, the boil-off gas compressed by the high pressure gas compressor 13 is supplied to the main engine 12 through the first fuel gas supply line 14, and an insufficient amount of fuel is supplied through the second fuel gas supply line 21. That is, in the first operation mode, the pump 22, the high pressure liquid pump 24, and the gas heater 25 are driven to generate high pressure gas from the liquefied gas in the cargo tank 11, and together with the boil-off gas compressed by the high pressure gas compressor 13, the main engine 12. To supply.

In the first operation mode, the first controller 17 controls the first valve 16V of the high-pressure gas compressor 13 so that the measured pressure value PV2 on the cargo tank 11 side becomes the pressure SP2 set by the operator. The second controller 28 monitors the discharge-side pressure value PV3 of the high-pressure liquid pump 24 so that the discharge pressure of the second fuel gas supply line 21 becomes the fuel gas required pressure SP1 of the main engine 12, and the high-pressure liquid The drive of the pump 24 is controlled.

When the liquefied gas is loaded and operated at the operation point P or at a lower speed side (deceleration operation region) than the operation point P, the second operation mode (compressor mode) is selected, and the high-pressure gas compressor 13 is operated. Only the first fuel gas supply line 14 to be used is used. That is, the operation of the main engine 12 is performed using only the boil-off gas, and when there is surplus gas, the gas is supplied to the BOG processing device (boiler, gas combustion device, reliquefaction device) through the branch line 15.

In the second operation mode, the first controller 17 monitors the pressure value PV1 on the discharge side so that the discharge pressure of the first fuel gas supply line 14 becomes the fuel gas required pressure SP1 of the main engine 12, thereby increasing the pressure. The first valve 16V of the gas compressor 13 is controlled.

FIG. 2 (b) shows the operation mode when the spray operation is performed in the operation when the liquefied gas is empty. In FIG. 2B, a straight line Ls is the amount of boil-off gas per unit time generated in the spray operation, and varies up and down depending on the amount of liquid used in the spray operation. The intersection point Ps between the curve S and the straight line Ls is a point where the amount of boil-off gas generated by the spray work and the boat speed are balanced. As in FIG. 2A, the first operation mode (hybrid mode) is selected on the higher speed side than the operation point Ps, and the second operation mode (hybrid mode) is selected on the lower speed side than the operation point Ps or the operation point Ps. Compressor mode) is selected. That is, either the first or second operation mode is selected from the relationship between the fuel consumption of the low speed diesel engine and the boil-off gas generation amount.

Further, when the amount of boil-off gas generated by the spraying operation exceeds the consumption by the main engine 12 and the generator engine, the surplus boil-off gas is removed from the BOG treatment device (boiler) through the branch line 15 as in FIG. , Gas combustion device, reliquefaction device). Even when the liquefied gas is empty, some liquefied gas is stored in order to use the liquefied gas as a spray liquid for cooling the cargo tank and as fuel for the main engine. The cargo tank 11 is not completely emptied.

FIG. 2 (c) is a graph corresponding to the operation mode when the spray operation is not performed in the operation when the liquefied gas is empty. In this mode of operation, the third operation mode (pump mode) is selected, and fuel gas is supplied to the main engine 12 only through the second fuel gas supply line. That is, high pressure gas is generated from the liquefied gas in the cargo tank 11 using the pump 22, the high pressure liquid pump 24, and the gas heater 25, and supplied to the main engine 12. The first fuel gas supply line 14 is not used, and the high-pressure gas compressor 13 is turned off.

In the third operation mode, the second controller 28 increases the pressure so that the discharge pressure of the second fuel gas supply line 21 becomes the fuel gas required pressure SP1 of the main engine 12 as in the first operation mode. The discharge side pressure value PV3 of the liquid pump 24 is monitored to control the driving of the high-pressure liquid pump 24. Further, in the third operation mode, when it is necessary to supply the fuel gas to the main engine 12 with a supply amount lower than the fuel gas supply amount at the minimum capacity (the minimum rotation speed of the motor 26) at which the high-pressure liquid pump 24 can operate. The second controller 28 drives the high-pressure liquid pump 24 with the minimum capacity that can be operated, and opens the second valve 29V to discharge the surplus fuel discharged from the high-pressure liquid pump 24 to the suction drum 23 in the second circulation line. Reflux through 29.

It should be noted that the cruise speed of the ship is set to the operating point P or a slightly lower speed, and the ship navigates at the cruise speed most of the time, so for example near the operating point P in FIG. Driven. That is, when the liquefied gas is loaded, only the substantially high-pressure gas compressor 13 is driven, and most of the boil-off gas is consumed as fuel for the main engine 12. Only when the operation in the high-speed operation region is necessary, the high-pressure liquid pump 24 is driven to generate high-pressure gas directly from the liquefied gas. Further, since most of the time during the operation when the liquefied gas is empty is not sprayed, the operation mode of FIG. 2 (c) is almost taken without operating the high-pressure gas compressor 13, Fuel gas is supplied by the high-pressure liquid pump 24. On the other hand, when a spray operation is performed and boil-off gas is generated, the high-pressure gas compressor 13 is driven, and almost all of the boil-off gas is used as fuel for the main engine 12.

As described above, according to the present embodiment, boil-off gas processing and energy consumption can be optimized in accordance with the operating state of the liquefied gas carrier ship by using the high-pressure gas compressor and the high-pressure liquid pump together.

In this embodiment, in the first operation mode in which the high pressure gas compressor of the first fuel gas supply line and the high pressure liquid pump of the second fuel gas supply line are simultaneously driven, the discharge amount from the high pressure gas compressor is the cargo tank pressure. Is controlled so that only the discharge amount from the high-pressure liquid pump becomes the required pressure of the main engine, so the parameters to be controlled differ between the high-pressure gas compressor and the high-pressure liquid pump. The discharge amount of the high pressure gas compressor is supplied with priority (consumption of boil-off gas is given priority), and the control of both is prevented from interfering with each other. Only the shortage is supplied by the high-pressure liquid pump.

The main engine may be a gas-only low-speed diesel engine, but it may be a dual-fuel low-speed diesel engine with oil fuel. In this case, for example, oil is used as an additional fuel in a high-speed operation region. May be used. In this embodiment, the liquefied gas carrier ship carrying LNG mainly composed of methane is described, but the present invention is also applicable to a liquefied gas carrier ship carrying cargo other than LNG. The gas pressure at the engine inlet required by the low-speed diesel engine varies depending on the properties of the fuel gas used (for example, ethane), and may require a higher pressure than when LNG is used as the fuel (for example, 40 MPa). ~ 60 MPa) can be applied in the same manner as the embodiment mainly composed of methane.

DESCRIPTION OF SYMBOLS 10 Fuel gas supply system 11 Cargo tank 12 Main engine 13 High pressure gas compressor 13A Low pressure stage 13B Final stage 14 1st fuel gas supply line 16 1st circulation line 16V 1st valve 17

1st controller

18, 19, 30 Pressure sensor 20 Main controller 21 Second fuel gas supply line 22 Pump 23 Suction drum 24 High pressure liquid pump 25 Gas heater 28 Second controller 29 Second circulation line 29V Second valve

Claims

A gas-fired low-speed diesel engine used as the main engine;
A tank for storing liquefied gas;
A high-pressure gas compressor for compressing boil-off gas generated in the tank;
A high-pressure liquid pump for pressurizing the liquefied gas from the tank;
A first fuel gas supply line for supplying fuel gas from the tank to the low-speed diesel engine through the high-pressure gas compressor;
A second fuel gas supply line for supplying fuel gas from the tank to the low-speed diesel engine through the high-pressure liquid pump;
A first operation mode for supplying fuel gas to the low-speed diesel engine through the first fuel gas supply line and the second fuel gas supply line;
In the first operation mode, the amount of fuel gas supplied from the first fuel gas supply line is controlled based on the pressure of the tank, and the amount of fuel gas supplied from the second fuel gas supply line is controlled by the low-speed diesel engine. A fuel gas supply system for a liquefied gas carrier ship, which is controlled based on a required fuel gas pressure.
In operation when loading liquefied gas, when the fuel consumption of the low-speed diesel engine is larger than the boil-off gas generation amount, the first operation mode is selected, and the boil-off gas is supplied to the low-speed diesel engine through the first fuel gas supply line. 2. The liquefied gas carrier according to claim 1, wherein the liquefied gas in the tank is supplied to the low-speed diesel engine through the second fuel gas supply line as a shortage of fuel gas. Fuel gas supply system.
In operation when loading liquefied gas, when the fuel consumption of the low-speed diesel engine is less than the boil-off gas generation amount, the second operation mode for supplying fuel gas to the low-speed diesel engine only through the first fuel gas supply line is selected 3. The fuel gas for a liquefied gas carrier according to claim 1, wherein a fuel gas supply amount from the high-pressure gas compressor is controlled based on a fuel gas demand pressure of the low-speed diesel engine. Supply system.
In the operation when the liquefied gas is empty, when the spray operation is not performed, the third operation mode is selected in which the liquefied gas in the tank is supplied as fuel gas to the low-speed diesel engine only through the second fuel gas supply line. The fuel gas supply system for a liquefied gas carrier ship according to any one of claims 1 to 3, wherein a discharge pressure of the high-pressure liquid pump is controlled based on a required fuel gas pressure of the low-speed diesel engine. .
In the operation when the liquefied gas is empty, when performing the spray operation, either the first or second operation mode is selected from the relationship between the fuel consumption of the low-speed diesel engine and the boil-off gas generation amount. The fuel gas supply system for a liquefied gas carrier ship according to claim 3.
The final stage of the high-pressure gas compressor is provided with a first circulation line for circulating fuel gas from the discharge side to the suction side, and the first pressure is set to maintain the tank pressure constant in the first operation mode. The fuel gas supply system for a liquefied gas carrier ship according to any one of claims 1 to 5, wherein the amount of fuel gas circulated is controlled by controlling a first valve provided in one circulation line.
A second circulation line for circulating the liquefied gas from the discharge side to the upstream side of the high pressure liquid pump is provided, and in the third operation mode, the second circulation is performed while driving the high pressure liquid pump with a minimum capacity that can be operated. The fuel gas supply system for a liquefied gas carrier ship according to claim 4, wherein a liquefied gas can be circulated to the upstream side by controlling a second valve provided in the line.
The liquefaction according to any one of claims 1 to 7, wherein the second fuel gas supply line includes a suction drum provided on the upstream side of the high-pressure liquid pump and a gas heater provided on the downstream side. Fuel gas supply system for gas carriers.
9. The high-pressure gas compressor is a multi-stage compressor including a low-pressure stage and a final stage, and includes a branch line for sending surplus gas from the low-pressure stage to a boil-off gas processing device. A fuel gas supply system for a liquefied gas carrier according to claim 1.
A liquefied gas carrier comprising the fuel gas supply system for a liquefied gas carrier according to any one of claims 1 to 9.