Ship and inboard power generation method

Abstract

This ship comprises: a hull having a propeller; a main engine which is provided to the hull and which drives the propeller; a shaft power generator which is driven with the rotation of the main engine to generate inboard power; a tank which is provided to the hull and which can store liquefied gas; a main supply line in which it is possible to gasify the liquified gas stored in the tank and supply the gas to the main engine; and a boil-off gas line in which it is possible to supply boil-off gas generated in the tank to the main engine.

Description

Ships and onboard power generation methods

[0001] This application claims priority to Japanese Patent Application No. 2023-208378, filed on December 11, 2023, the contents of which are incorporated herein by reference.

[0002] Patent Document 1 discloses a configuration in which boil-off gas generated in a storage tank that stores liquefied natural gas as fuel is compressed and re-liquefied, and then supplied to an engine. This configuration makes effective use of the boil-off gas generated in the tank and reduces fuel consumption.

[0003] Japanese Patent No. 5926748

[0004] Incidentally, some ships such as those described in Patent Document 1 are equipped with an engine for driving a generator, separate from the main engine, to generate electricity for onboard use. The engine for driving the generator has lower fuel efficiency than the main engine. For this reason, it is desirable to improve fuel efficiency while effectively utilizing boil-off gas.

[0005] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a ship and an onboard power generation method that can effectively utilize boil-off gas and improve fuel efficiency.

[0006] In order to solve the above problems, a ship according to the present disclosure includes a hull, a main engine, a shaft generator, a tank, a main supply line, and a boil-off gas line. The hull has a propeller. The main engine is mounted on the hull and drives the propeller. The shaft generator is driven in conjunction with the rotation of the main engine to generate onboard electricity. The tank is mounted on the hull and is capable of storing liquefied gas. The main supply line is capable of vaporizing the liquefied gas stored in the tank and supplying it to the main engine. The boil-off gas line is capable of supplying boil-off gas generated in the tank to the main engine.

[0007] An onboard electric power generation method according to the present disclosure is a method for generating electric power on a ship as described above. The onboard electric power generation method switches between a first mode and a second mode. In the first mode, boil-off gas is supplied to the main engine while the ship is sailing, and onboard electric power is generated by the shaft generator. In the second mode, the boil-off gas is supplied to the auxiliary engine while the ship is at anchor, and onboard electric power is generated by the auxiliary engine.

[0008] According to the ship and onboard power generation method disclosed herein, boil-off gas can be effectively utilized to improve fuel efficiency.

[0009] 1 is a side view of a marine vessel according to an embodiment of the present disclosure. FIG. 2 is a diagram showing a fuel supply system from a tank to a main engine and an auxiliary engine in a marine vessel according to a first embodiment of the present disclosure. FIG. 3 is a diagram showing a state in which power is generated using the main engine in a marine vessel according to an embodiment of the present disclosure. FIG. 4 is a diagram showing a state in which power is generated using the auxiliary engine in a marine vessel according to an embodiment of the present disclosure. FIG. 5 is a diagram showing a fuel supply system from a tank to a main engine and an auxiliary engine in a marine vessel according to a second embodiment of the present disclosure. FIG. 6 is a diagram showing a flow of boil-off gas when a first mode is being executed in an onboard electric power generation method according to a second embodiment of the present disclosure. FIG. 7 is a diagram showing a flow of boil-off gas when a second mode is being executed in an onboard electric power generation method according to a second embodiment of the present disclosure. FIG. 8 is a diagram showing a fuel supply system from a tank to a main engine and an auxiliary engine in a marine vessel according to a third embodiment of the present disclosure. FIG. 9 is a diagram showing a flow of boil-off gas when a first mode is being executed in an onboard electric power generation method according to a third embodiment of the present disclosure. FIG. 10 is a diagram showing a flow of boil-off gas when a second mode is being executed in an onboard electric power generation method according to a third embodiment of the present disclosure. FIG. 10 is a diagram showing the flow of boil-off gas when a first mode is being executed in the onboard electric power generation method according to the fourth embodiment of the present disclosure. FIG. 11 is a diagram showing the flow of boil-off gas when a second mode is being executed in the onboard electric power generation method according to the fourth embodiment of the present disclosure. FIG. 12 is a diagram showing the flow of boil-off gas when a fuel supply system from a tank to a main engine and an auxiliary engine in a marine vessel according to a fifth embodiment of the present disclosure. FIG. 13 is a diagram showing the flow of boil-off gas when a first mode is being executed in the onboard electric power generation method according to the fifth embodiment of the present disclosure. FIG. 14 is a diagram showing the flow of boil-off gas when a second mode is being executed in the onboard electric power generation method according to the fifth embodiment of the present disclosure.

[0010] A ship and an onboard power generation method according to embodiments of the present disclosure will be described below with reference to Figures 1 to 16. <First embodiment> (Overall configuration of ship) As shown in Figure 1, a ship 1 according to this first embodiment mainly comprises a hull 2, a main engine 20, a shaft generator 25, auxiliary machinery 30, and a tank 10. The type of ship 1 is not limited to a specific one. Examples of the type of ship 1 include a carrier of liquefied gas such as liquefied natural gas (LNG), carbon dioxide, or ammonia, a ferry, a roll-on / roll-off ship (RORO ship), a pure car and truck carrier (PCTC), and a passenger ship.

[0011] The hull 2 ​​has a pair of side walls 3A, 3B, a bottom wall 4, and an upper deck 5 that form its outer shell. The side walls 3A, 3B are made up of a pair of side wall shell plates that form the port and starboard sides, respectively. The bottom wall 4 is made up of a bottom wall shell plate that connects the side walls 3A, 3B. The upper deck 5 is a full-length deck that is exposed to the outside. The hull 2 ​​has a superstructure 7 with accommodation areas formed on the upper deck 5, for example, on the stern 2b side.

[0012] (Configuration of main engine, shaft generator, and auxiliary engine) The main engine 20 and the auxiliary engine 30 are provided inside the hull 2. The main engine 20 and the auxiliary engine 30 use liquefied gas stored in the tank 10 as fuel. In this first embodiment, the main engine 20 and the auxiliary engine 30 use LNG, for example, as fuel. The liquefied gas used as fuel for the main engine 20 and the auxiliary engine 30 is not limited to LNG, and may be LPG (liquefied petroleum gas), ammonia, hydrogen, etc.

[0013] The main engine 20 is an engine (internal combustion engine) that burns, for example, liquefied gas as fuel. In this first embodiment, the main engine 20 is a direct injection two-stroke engine that directly injects fuel into the combustion chamber. The main engine 20 uses fuel at a higher pressure than the auxiliary engine 30. The pressure of the fuel (fuel gas) used by the main engine 20 is high, for example, at least 20 MPa and not more than 35 MPa. The pressure of the fuel supplied to the main engine 20 is preferably, for example, at least 25 MPa and not more than 30 MPa.

[0014] The main engine 20 drives the propeller 9. The propeller 9 is provided outside the stern 2b of the hull 2. The main engine 20 and the propeller 9 are connected via a propeller shaft 8 extending in a bow-to-stern direction FA. The main engine 20 rotates the propeller shaft 8 about its axis, thereby driving the propeller 9 to rotate. The propeller 9, driven to rotate by the main engine 20, generates a propulsive force that causes the ship 1 to sail.

[0015] The shaft generator 25 is provided inside the hull 2 ​​and generates onboard electricity used inside the vessel 1. The shaft generator 25 is driven in conjunction with the rotation of the main engine 20. In this first embodiment, the shaft generator 25 is connected to the propeller shaft 8. The shaft generator 25 converts the rotational energy of the propeller shaft 8, which is rotationally driven by the main engine 20, into electrical energy. The shaft generator 25 may be directly connected to the propeller shaft 8, or may be connected to the propeller shaft 8 via a speed increaser, a clutch, or the like.

[0016] The auxiliary machinery 30 illustrated in this first embodiment is a generator engine for driving a generator (not shown) for generating onboard electricity used within the vessel 1. The auxiliary machinery 30 uses fuel with a lower pressure than the main engine 20. The pressure of the fuel (fuel gas) used by the auxiliary machinery 30 is, for example, 0.5 MPa or more and 1.0 MPa or less. For example, a gas turbine or a reciprocating engine can be used as the auxiliary machinery 30. The rotational energy generated by the auxiliary machinery 30 is converted into electrical energy by the generator and can be supplied to various parts within the hull 2.

[0017] (Configuration of Tank) The tank 10 is installed in the hull 2. The tank 10 in this first embodiment is provided, for example, on the upper deck 5. The tank 10 may also be provided inside the hull 2. In this first embodiment, the tank 10 stores LNG as a liquefied gas that serves as fuel for the main engine 20 and the auxiliary engine 30.

[0018] (Configuration of main supply line and boil-off gas line) Figure 2 is a diagram showing a fuel supply system from a tank to a main engine and an auxiliary engine in a ship according to a first embodiment of the present disclosure. As shown in Figure 2, the ship 1 is equipped with a main supply line 100, an auxiliary engine supply line 200, and a boil-off gas line 300A to supply liquefied gas stored in a tank 10 as fuel to the main engine 20 and the auxiliary engine 30.

[0019] The main supply line 100 connects the tank 10 and the main engine 20. The main supply line 100 vaporizes the liquefied gas LG in the tank 10 and supplies it to the main engine 20. The main supply line 100 is provided with a pump 11, a pressure pump 12, and a high-pressure vaporizer 13.

[0020] The pump 11 is provided in the main supply line 100. The pump 11 sucks out the liquefied gas LG in the tank 10. The pump 11 pumps out the sucked out liquefied gas LG toward the main engine 20.

[0021] The pressure pump 12 is provided on the main supply line 100 downstream of the pump 11 in the flow direction of the liquefied gas LG on the main supply line 100. The pressure pump 12 increases the pressure of the liquefied gas LG to a higher pressure than the pressure of the pump 11.

[0022] The high-pressure vaporizer 13 is provided in the main supply line 100 downstream of the pressure pump 12 in the flow direction of the liquefied gas LG in the main supply line 100. The high-pressure vaporizer 13 vaporizes the liquefied gas LG pressurized by the pressure pump 12. The high-pressure vaporizer 13 vaporizes the liquefied gas LG at a pressure higher than that of an auxiliary equipment vaporizer 31 described below, to generate fuel gas FG. In this first embodiment, the pressure of the fuel gas FG generated via the pressure pump 12 and the high-pressure vaporizer 13 is, for example, about 30 MPa. The fuel gas FG generated via the high-pressure vaporizer 13 is supplied to the main engine 20 through the main supply line 100.

[0023] The auxiliary equipment supply line 200 vaporizes the liquefied gas LG in the tank 10 and supplies it to the auxiliary equipment 30. An upstream end 201 of the auxiliary equipment supply line 200 is connected to the main supply line 100 between the pump 11 and the pressure pump 12. A downstream end 202 of the auxiliary equipment supply line 200 is connected to the auxiliary equipment 30.

[0024] The auxiliary equipment supply line 200 is equipped with an auxiliary equipment vaporizer 31. The auxiliary equipment vaporizer 31 vaporizes the liquefied gas LG pressure-fed by the pump 11. The auxiliary equipment vaporizer 31 vaporizes the liquefied gas LG at a pressure lower than that of the high-pressure vaporizer 13 to generate auxiliary equipment fuel gas FG2. The pressure of the auxiliary equipment fuel gas FG2 generated through the pump 11 and the auxiliary equipment vaporizer 31 is, for example, approximately 0.6 MPa. The auxiliary equipment fuel gas FG2 generated by the auxiliary equipment vaporizer 31 is supplied to the auxiliary equipment 30 through the auxiliary equipment supply line 200.

[0025] The boil-off gas line 300A can supply the boil-off gas BOG generated in the tank 10 to the main engine 20. An upstream end 301 of the boil-off gas line 300A is connected to the tank 10 so as to communicate with the gas phase portion in the tank 10. A downstream end 302 of the boil-off gas line 300A is connected to the main supply line 100 downstream of the high-pressure vaporizer 13.

[0026] In the tank 10, the liquefied gas LG in a liquid state is vaporized by natural heat input from the outside, etc., and boil-off gas BOG is generated. In this first embodiment, the boil-off gas line 300A introduces the boil-off gas BOG generated in the tank 10 into the main engine 20.

[0027] The boil-off gas line 300A is equipped with a high-pressure gas compressor (gas compressor) 51 that pressurizes the boil-off gas supplied to the main engine 20 through the boil-off gas line 300A. The high-pressure gas compressor 51 is capable of pressurizing the boil-off gas BOG to a pressure equal to or higher than that of the fuel gas FG supplied to the main engine 20. The high-pressure gas compressor 51 of this first embodiment pressurizes the boil-off gas BOG in a gaseous state to a pressure equivalent to that of the fuel gas FG that has passed through the pump 11, the booster pump 12, and the high-pressure vaporizer 13. The boil-off gas line 300A of this first embodiment is configured to allow the boil-off gas BOG pressurized by the high-pressure gas compressor 51 to merge with the main supply line 100 downstream of the high-pressure vaporizer 13. In other words, the boil-off gas line 300A mixes the boil-off gas BOG with the fuel gas FG vaporized in the high-pressure vaporizer 13, and supplies the mixture to the main engine 20.

[0028] (Onboard Electric Power Generation Method) Next, an onboard electric power generation method for the ship 1 will be described. FIG. 3 is a diagram showing a state in which power is generated using the main engine in the ship according to the first embodiment of the present disclosure. As shown in FIG. 3 , in this first embodiment, when the ship 1 is sailing by driving the propeller 9 using the main engine 20, the main engine 20 drives the shaft generator 25, and the shaft generator 25 generates onboard electric power. In this case, boil-off gas BOG in the tanks 10 is pressurized by a high-pressure gas compressor 51 and supplied to the main engine 20 through a boil-off gas line 300A. Furthermore, fuel gas FG (gas obtained by vaporizing liquefied gas LG) that has passed through a pressure pump 12 and a high-pressure vaporizer 13 from the tanks 10 may be supplied to the main engine 20 through a main supply line 100, depending on the amount of boil-off gas BOG produced in the tanks 10. Alternatively, the fuel gas FG from the main supply line 100 may be mainly supplied to the main engine 20, and any shortfall may be supplemented with boil-off gas BOG through the boil-off gas line 300A. In this first embodiment, when the shaft generator 25 is driven by the main engine 20 in this manner, the auxiliary engine 30 is stopped. To do this, the supply of liquefied gas LG to the auxiliary engine 30 is stopped by, for example, closing the valve 205 provided in the auxiliary engine supply line 200. In this way, while the ship 1 is sailing, onboard electricity is generated by the shaft generator 25 using the main engine 20, which has better fuel efficiency than the auxiliary engine 30.

[0029] FIG. 4 is a diagram illustrating a state in which power is generated using auxiliary machinery in a vessel according to an embodiment of the present disclosure. As shown in FIG. 4 , when the vessel 1 is at anchor and the main engine 20 is stopped, the auxiliary machinery 30 drives a generator (not shown) to supply onboard electricity. To do this, the auxiliary machinery supply line 200 vaporizes the liquefied gas LG in the tank 10 through the auxiliary machinery vaporizer 31 to generate auxiliary machinery fuel gas FG. The auxiliary machinery supply line 200 supplies the generated auxiliary machinery fuel gas FG2 to the auxiliary machinery 30. In this case, the supply of liquefied gas LG to the main machinery 20 is prevented by, for example, closing the valve 105 provided in the main supply line 100. Furthermore, the supply of boil-off gas BOG to the main machinery 20 is also prevented by, for example, closing the valve 305 provided in the boil-off gas line 300A. In the first embodiment described above, the auxiliary machinery 30 is not driven while the ship 1 is sailing. However, if there is a shortage of onboard power when only the shaft generator 25 is driven, the auxiliary machinery 30 may be driven to make up for this shortage.

[0030] (Operation and Effect) The ship 1 of the first embodiment is equipped with a main supply line 100 capable of supplying the liquefied gas LG in the tanks 10 to the main engine 20, and a boil-off gas line 300A capable of supplying the boil-off gas BOG in the tanks 10 to the main engine 20. This allows the main engine 20 to use, as fuel, both the liquefied gas LG in the tanks 10 and the boil-off gas BOG generated by vaporizing the liquefied gas LG in the tanks 10. By driving the shaft generator 25 in accordance with the rotation of the main engine 20 when driving the propeller 9 with such a main engine 20, it is possible to generate onboard electricity using the main engine 20 with high fuel efficiency. Therefore, the boil-off gas BOG can be effectively utilized, and fuel efficiency can be improved.

[0031] Furthermore, in the first embodiment, the pressure pump 12 and the high-pressure vaporizer 13 provided in the main supply line 100 generate high-pressure fuel gas from the liquefied gas LG in the tank 10 to serve as fuel for the main engine 20. In the boil-off gas line 300A, the high-pressure gas compressor 51 pressurizes the boil-off gas BOG to the pressure of the fuel gas supplied to the main engine 20, making it possible to use the boil-off gas BOG as high-pressure fuel gas FG to be supplied to the main engine 20. This makes it possible to effectively utilize the boil-off gas BOG and improve fuel efficiency even when the main engine 20 requires high-pressure gas as fuel.

[0032] Second Embodiment Next, a second embodiment of a ship and onboard electric power generation method according to the present disclosure will be described. In the second embodiment described below, only the configuration of the boil-off gas line differs from the first embodiment. Therefore, the same parts as in the first embodiment will be denoted by the same reference numerals and will not be described again. Figure 5 is a diagram showing a fuel supply system from a tank to a main engine and auxiliary engines in a ship according to the second embodiment of the present disclosure. As shown in Figure 5, the ship 1 of the second embodiment includes a main supply line 100, an auxiliary engine supply line 200, and a boil-off gas line 300B to supply liquefied gas stored in a tank 10 as fuel to the main engine 20 and auxiliary engine 30.

[0033] The boil-off gas line 300B can supply the boil-off gas BOG generated in the tank 10 to the main engine 20. An upstream end 301 of the boil-off gas line 300B is connected to the tank 10 so as to communicate with the gas phase portion in the tank 10. A downstream end 302 of the boil-off gas line 300B is connected to the main supply line 100 downstream of the high-pressure vaporizer 13.

[0034] The boil-off gas line 300B includes a gas compressor 52 that pressurizes the boil-off gas BOG supplied to the main engine 20 through the boil-off gas line 300B. The gas compressor 52 is capable of pressurizing the boil-off gas BOG to a pressure equal to or higher than the pressure of the fuel gas FG supplied to the main engine 20. The boil-off gas line 300B of the second embodiment includes a first gas compressor 53 and a second gas compressor 54 as the multiple gas compressors 52.

[0035] The first gas compressor 53 increases the pressure of the boil-off gas BOG from the tank 10 supplied through the boil-off gas line 300B to a first pressure (e.g., 0.6 MPa) required as fuel for the auxiliary equipment 30 (the pressure of the auxiliary equipment fuel gas FG2).

[0036] The second gas compressor 54 is disposed in the boil-off gas line 300B between the first gas compressor 53 and the main supply line 100 to which the downstream end 302 is connected. The second gas compressor 54 further increases the boil-off gas BOG, which has been pressurized to the first pressure via the first gas compressor 53, to a second pressure (e.g., 30 MPa) required as fuel for the main engine 20. This second pressure is preferably set to a pressure equivalent to that of the fuel gas FG which has passed through the pump 11, the booster pump 12, and the high-pressure vaporizer 13. Here, the second gas compressor 54 only needs to increase the boil-off gas BOG, which has been pressurized to the first pressure via the first gas compressor 53, to the second pressure, and therefore can have a lower capacity than the high-pressure gas compressor 51 shown in the first embodiment.

[0037] The boil-off gas line 300B allows the boil-off gas BOG, which has been pressurized through the first gas compressor 53 and the second gas compressor 54, to flow into the main supply line 100 downstream of the high-pressure vaporizer 13. In other words, the boil-off gas line 300B mixes the boil-off gas BOG with the fuel gas FG vaporized in the high-pressure vaporizer 13, and supplies the mixture to the main engine 20.

[0038] In addition, an auxiliary boil-off gas supply line 400 is branched off and connected to the boil-off gas line 300B. The upstream end of the auxiliary boil-off gas supply line 400 is connected to the boil-off gas line 300B between the first gas compressor 53 and the second gas compressor 54. The downstream end of the auxiliary boil-off gas supply line 400 is connected to the auxiliary 30. This auxiliary boil-off gas supply line 400 supplies the boil-off gas BOG, which has been pressurized to a first pressure through the first gas compressor 53, to the auxiliary 30 as auxiliary fuel gas FG2 for the auxiliary 30.

[0039] (Configuration of the switching unit) The ship 1 of the second embodiment includes a switching unit 70. The switching unit 70 can selectively switch the supply destination of the boil-off gas BOG through the boil-off gas line 300B between the main engine 20 and the auxiliary engine 30. The switching unit 70 includes a first valve 71 and a second valve 72. The first valve 71 is provided in the boil-off gas line 300B between the first gas compressor 53 and the second gas compressor 54. The first valve 71 is provided in the boil-off gas line 300B downstream of the position where the upstream end of the auxiliary engine boil-off gas supply line 400 is connected. The first valve 71 is capable of opening and closing the flow path in the boil-off gas line 300B. The second valve 72 is provided midway along the auxiliary engine boil-off gas supply line 400. The second valve 72 is capable of opening and closing the flow path in the auxiliary engine boil-off gas supply line 400.

[0040] When the first valve 71 is opened and the second valve 72 is closed, the boil-off gas BOG passes through the first gas compressor 53 and the second gas compressor 54, is pressurized to the second pressure, and is supplied to the main machinery 20. When the first valve 71 is closed and the second valve 72 is opened, the boil-off gas BOG passes only through the first gas compressor 53, is pressurized to the first pressure, and is supplied to the auxiliary machinery 30 as auxiliary machinery fuel gas FG2. The first valve 71 and the second valve 72 can be opened and closed manually by an operator, by remote operation by an operator, or the like.

[0041] (Onboard Electric Power Generation Method) Next, an onboard electric power generation method for the ship 1 described above will be described. Fig. 6 is a diagram showing the flow of boil-off gas when a first mode is being executed in the onboard electric power generation method according to the second embodiment of the present disclosure. Fig. 7 is a diagram showing the flow of boil-off gas when a second mode is being executed in the onboard electric power generation method according to the second embodiment of the present disclosure. The ship 1 switches the supply destination of the boil-off gas BOG between the main engine 20 and the auxiliary engine 30 depending on its navigation state, specifically, whether or not the main engine 20 is operating for navigation. For this reason, the ship 1 is configured to be able to switch between a first mode M1 executed while sailing and a second mode M2 ​​executed while berthing.

[0042] As shown in Fig. 6 , in the second embodiment, when the ship 1 is sailing with the propeller 9 driven by the main engine 20, the ship 1 executes a first mode M1. In the first mode M1, the main engine 20 drives the shaft generator 25, and onboard electricity is generated by the shaft generator 25. In this case, the first valve 71 is opened and the second valve 72 is closed. As a result, boil-off gas BOG from the tank 10 passes through the first gas compressor 53 and the second gas compressor 54, is pressurized to the second pressure, and is supplied to the main engine 20. In the first mode M1, when the ship 1 is sailing, boil-off gas BOG is supplied to the main engine 20, and onboard electricity is generated by the shaft generator 25. At this time, depending on the amount of boil-off gas BOG generated in the tank 10 and the shortfall in the supply capacity of the second gas compressor 54 relative to the amount of fuel gas required by the main engine 20, fuel gas FG (gas vaporized from liquefied gas LG) that has passed through the pressure pump 12 and high-pressure vaporizer 13 from the tank 10 may be supplied to the main engine 20 through the main supply line 100.

[0043] 7 , in the second embodiment, when the vessel 1 is at anchor and the propeller 9 is not driven by the main engine 20, the vessel 1 executes a second mode M2. In the second mode M2, the first valve 71 is closed and the second valve 72 is opened. As a result, the boil-off gas BOG from the tank 10 passes only through the first gas compressor 53, is pressurized to a first pressure, and is supplied as auxiliary fuel gas FG2 to the auxiliary machinery 30 through the auxiliary machinery boil-off gas supply line 400. In the second mode M2, when the vessel 1 is at anchor, the boil-off gas BOG is supplied to the auxiliary machinery 30, and the auxiliary machinery 30 generates onboard electricity. At this time, depending on the amount of boil-off gas BOG generated in the tank 10 and the shortage of the supply capacity of the first gas compressor 53 relative to the amount of fuel gas required by the auxiliary equipment 30, fuel gas FG (gas obtained by vaporizing liquefied gas LG) that has passed through the pump 11 and the auxiliary equipment vaporizer 31 from the tank 10 may be supplied to the auxiliary equipment 30 through the auxiliary equipment supply line 200. Note that in the above second embodiment, a case has been described in which the auxiliary equipment 30 is not driven while the ship 1 is sailing, but as in the first embodiment, if there is a shortage of onboard power when only the shaft generator 25 is driven, boil-off gas BOG may be supplied from the first gas compressor 53 to both the auxiliary equipment 30 and the second gas compressor 54, and the auxiliary equipment 30 may be driven to make up for the shortage of onboard power.

[0044] (Operation and Effect) In the ship 1 of the second embodiment, the supply destination of the boil-off gas BOG through the boil-off gas line 300B can be selectively switched between the main engine 20 and the auxiliary engine 30 by the switching unit 70. As a result, when the main engine 20 is operating, the boil-off gas BOG can be supplied to the main engine 20, and when the auxiliary engine 30 is operating, the boil-off gas BOG can be supplied to the auxiliary engine 30. Therefore, the boil-off gas BOG generated in the tank 10 can be effectively consumed by the main engine 20 and the auxiliary engine 30 without being wasted.

[0045] In the second embodiment, the pressure pump 12 and the high-pressure vaporizer 13 provided in the main supply line 100 generate high-pressure fuel gas from the liquefied gas LG in the tank 10 to serve as fuel for the main engine 20. In the boil-off gas line 300B, the gas compressor 52 pressurizes the boil-off gas BOG to the pressure of the fuel gas supplied to the main engine 20, making it possible to use the boil-off gas BOG as high-pressure fuel gas supplied to the main engine 20. This makes it possible to effectively use the boil-off gas BOG and improve fuel efficiency even when the main engine 20 requires high-pressure gas as fuel.

[0046] In the second embodiment, the gas compressor 52 includes a first gas compressor 53 and a second gas compressor 54. The first gas compressor 53 pressurizes the boil-off gas BOG to a first pressure, and the pressurized boil-off gas BOG can be supplied to the auxiliary machinery 30 as the auxiliary machinery fuel gas FG2. The second gas compressor 54 further pressurizes the boil-off gas that has been pressurized to the first pressure via the first gas compressor 53 to a second pressure, and the pressurized boil-off gas BOG can be supplied to the main machinery 20 as the fuel gas FG. In this way, when supplying the boil-off gas BOG to the main machinery 20, the boil-off gas BOG is pressurized in two stages by the first gas compressor 53 and the second gas compressor 54, and when supplying the boil-off gas BOG to the auxiliary machinery 30, the boil-off gas BOG is pressurized only by the first gas compressor 53. Such a boil-off gas line 300B makes it possible to realize a configuration in which the supply destination of the boil-off gas BOG can be switched between the main engine 20 and the auxiliary engine 30.

[0047] In the onboard electric power generation method of the second embodiment, switching is performed between a first mode M1 in which boil-off gas (BOG) is supplied to the main engine 20 while the ship 1 is sailing, and the shaft generator 25 generates onboard electric power, and a second mode M2 ​​in which boil-off gas (BOG) is supplied to the auxiliary engine 30 while the ship 1 is at anchor, and the auxiliary engine 30 generates onboard electric power. As a result, when the main engine 20 is operating while the ship 1 is sailing, onboard electric power is generated by the main engine 20, and when the auxiliary engine 30 is operating while the ship 1 is at anchor, onboard electric power is generated by the auxiliary engine 30. Therefore, boil-off gas (BOG) generated in the tank 10 can be effectively used to generate onboard electric power by the main engine 20 and the auxiliary engine 30, without wasting it. As a result, even when the ship is equipped with a main engine 20 that requires high-pressure gas as fuel, boil-off gas can be effectively used, and fuel efficiency can be improved.

[0048] Furthermore, in the second embodiment, similarly to the first embodiment, the main supply line 100 is provided which can supply the liquefied gas LG in the tank 10 to the main engine 20, and the boil-off gas line 300B is provided which can supply the boil-off gas BOG in the tank 10 to the main engine 20. This allows the boil-off gas BOG to be used effectively, and fuel efficiency can be improved.

[0049] In the second embodiment, the pressure pump 12 and the high-pressure vaporizer 13 provided in the main supply line 100 generate high-pressure fuel gas FG from the liquefied gas LG in the tank 10 to serve as fuel for the main engine 20. In the boil-off gas line 300B, the high-pressure gas compressor 51 pressurizes the boil-off gas BOG to a pressure corresponding to the fuel gas FG supplied to the main engine 20, making it possible to use the boil-off gas BOG as high-pressure fuel gas FG supplied to the main engine 20. This makes it possible to effectively utilize the boil-off gas and improve fuel efficiency even when the main engine 20 requires high-pressure gas as fuel.

[0050] In the second embodiment, the switching unit 70 includes the first valve 71 and the second valve 72, but this is not limited thereto. Instead of using the first valve 71 as the switching unit 70, the supply and stop of boil-off gas BOG through the boil-off gas line 300B may be switched on and off by switching the second gas compressor 54 on and off. That is, when onboard electricity is generated by the shaft generator 25, the second gas compressor 54 is operated, and boil-off gas BOG from the tanks 10 is supplied to the main engine 20 via the first gas compressor 53 and the second gas compressor 54. When onboard electricity is generated by the auxiliary machinery 30, the operation of the second gas compressor 54 is stopped. As a result, the boil-off gas BOG from the tanks 10 passes only through the first gas compressor 53 and is supplied to the auxiliary machinery 30 as auxiliary machinery fuel gas FG2.

[0051] <Third Embodiment> Next, a third embodiment of a ship and onboard electric power generation method according to the present disclosure will be described. In the third embodiment described below, only the configuration of the boil-off gas line differs from the first embodiment. Therefore, the same parts as those in the first and second embodiments will be denoted by the same reference numerals and will not be described again. Figure 8 is a diagram showing a fuel supply system from a tank to a main engine and auxiliary engines in a ship according to the third embodiment of the present disclosure. As shown in Figure 8, the ship 1 of the third embodiment includes a main supply line 100, an auxiliary engine supply line 200, and a boil-off gas line 300C to supply liquefied gas stored in a tank 10 as fuel to the main engine 20 and auxiliary engine 30.

[0052] The boil-off gas line 300C can supply boil-off gas BOG generated in the tank 10 to the main engine 20. An upstream end 301 of the boil-off gas line 300C is connected to the tank 10 so as to communicate with the gas phase portion in the tank 10. A downstream end 303 of the boil-off gas line 300C is connected to the main supply line 100 between the pump 11 and the pressure pump 12. The downstream end 303 of the boil-off gas line 300C is connected to the main supply line 100 downstream of the upstream end 201 of the auxiliary equipment supply line 200.

[0053] The boil-off gas line 300C is provided with a gas compressor 55 that pressurizes the boil-off gas supplied through the boil-off gas line 300C to the main engine 20. In this third embodiment, the gas compressor 55 increases the pressure of the boil-off gas BOG from the tank 10 that is supplied through the boil-off gas line 300C to a pressure (e.g., 0.6 MPa) required as fuel for the auxiliary engine 30 (auxiliary engine fuel gas FG2).

[0054] The boil-off gas line 300C mixes the boil-off gas BOG pressurized through the gas compressor 55 with the liquefied gas LG flowing through the main supply line 100. In this third embodiment, the boil-off gas line 300C mixes the boil-off gas BOG pressurized through the gas compressor 55 with the liquefied gas LG flowing through the main supply line 100 upstream of the pressure pump 12. As a result, the boil-off gas BOG mixed with the liquefied gas LG is cooled by the liquefied gas LG, thereby promoting re-liquefaction of the boil-off gas BOG. ​​Therefore, the boil-off gas BOG pressurized through the gas compressor 55 is further pressurized by the pressure pump 12 together with the liquefied gas LG from the tank 10, and then vaporized in the high-pressure vaporizer 13 and sent to the main engine 20.

[0055] In addition, an auxiliary boil-off gas supply line 400 is connected to the boil-off gas line 300C. The upstream end of the auxiliary boil-off gas supply line 400 is connected to the boil-off gas line 300C between the gas compressor 55 and the downstream end 303 of the boil-off gas line 300C. The downstream end of the auxiliary boil-off gas supply line 400 is connected to the auxiliary equipment 30. This auxiliary boil-off gas supply line 400 supplies the boil-off gas BOG, which has been pressurized through the gas compressor 55, to the auxiliary equipment 30 as auxiliary equipment fuel gas FG2 for the auxiliary equipment 30.

[0056] (Configuration of Switching Unit) The ship 1 of the third embodiment includes a switching unit 70B. The switching unit 70B selectively switches the supply destination of the boil-off gas BOG through the boil-off gas line 300C between the main engine 20 and the auxiliary engine 30. The switching unit 70B includes a first valve 73 and a second valve 74.

[0057] The first valve 73 is provided in the boil-off gas line 300C between the gas compressor 55 and the downstream end 303 of the boil-off gas line 300C. The first valve 73 is provided in the boil-off gas line 300C downstream of the position where the upstream end of the auxiliary equipment boil-off gas supply line 400 is connected. The first valve 73 is capable of opening and closing the flow path in the boil-off gas line 300C. The second valve 74 is provided midway along the auxiliary equipment boil-off gas supply line 400. The second valve 74 is capable of opening and closing the flow path in the auxiliary equipment boil-off gas supply line 400.

[0058] When the first valve 73 is opened and the second valve 74 is closed, the boil-off gas BOG is pressurized through the gas compressor 55, the pressure pump 12, and the high-pressure vaporizer 13, and is supplied as fuel gas FG to the main machinery 20. When the first valve 73 is closed and the second valve 74 is opened, the boil-off gas BOG is pressurized only through the gas compressor 55, and is supplied to the auxiliary machinery 30 as auxiliary machinery fuel gas FG2.

[0059] (Onboard electric power generation method) Next, an onboard electric power generation method for the ship 1 as described above will be described. Fig. 9 is a diagram showing the flow of boil-off gas when the first mode is being executed in the onboard electric power generation method according to the third embodiment of the present disclosure. Fig. 10 is a diagram showing the flow of boil-off gas when the second mode is being executed in the onboard electric power generation method according to the third embodiment of the present disclosure.

[0060] As shown in Fig. 9 , when the vessel 1 is sailing with the propeller 9 driven by the main engine 20, the vessel 1 executes a first mode M11. In the first mode M11, the main engine 20 drives the shaft generator 25, and the shaft generator 25 generates onboard electricity. In this case, the first valve 73 is opened and the second valve 74 is closed. As a result, boil-off gas BOG from the tank 10 passes through the gas compressor 55, the pressure pump 12, and the high-pressure vaporizer 13 and is supplied to the main engine 20 as fuel gas FG. In the first mode M11, when the vessel 1 is sailing, boil-off gas BOG is supplied to the main engine 20, and the shaft generator 25 generates onboard electricity.

[0061] 10 , when the vessel 1 is at anchor and the propeller 9 is not driven by the main engine 20, the vessel 1 executes a second mode M12. In the second mode M12, the first valve 73 is closed and the second valve 74 is opened. As a result, the boil-off gas BOG from the tank 10 is pressurized only through the gas compressor 55 and supplied as auxiliary fuel gas FG2 to the auxiliary machinery 30 through the auxiliary boil-off gas supply line 400. In the second mode M12, when the vessel 1 is at anchor, the boil-off gas BOG is supplied to the auxiliary machinery 30, and the auxiliary machinery 30 generates onboard electricity.

[0062] (Operation and Effect) In the ship 1 of the third embodiment, high-pressure fuel gas that serves as fuel for the main engine 20 is generated from the liquefied gas LG in the tank 10 by the pressure pump 12 and the high-pressure vaporizer 13 provided in the main supply line 100. By mixing boil-off gas BOG with the pressurized liquefied gas LG flowing through the main supply line 100, the liquefied gas LG can be supplied as fuel for the main engine 20. In this way, by vaporizing the boil-off gas BOG together with the liquefied gas LG flowing through the main supply line 100, fuel gas FG can be efficiently generated and supplied to the main engine 20.

[0063] Furthermore, in the third embodiment, similarly to the second embodiment, the switching unit 70B can selectively switch the supply destination of the boil-off gas BOG through the boil-off gas line 300C between the main engine 20 and the auxiliary engine 30. As a result, when the main engine 20 is operating, the boil-off gas BOG can be supplied to the main engine 20, and when the auxiliary engine 30 is operating, the boil-off gas BOG can be supplied to the auxiliary engine 30. Therefore, the boil-off gas BOG generated in the tank 10 can be effectively consumed by the main engine 20 and the auxiliary engine 30 without being wasted.

[0064] In the onboard electric power generation method of the third embodiment, switching is performed between a first mode M11 in which boil-off gas (BOG) is supplied to the main engine 20 while the ship 1 is sailing, and the shaft generator 25 generates onboard electric power, and a second mode M12 in which boil-off gas (BOG) is supplied to the auxiliary engine 30 while the ship 1 is at anchor, and the auxiliary engine 30 generates onboard electric power. As a result, when the main engine 20 is operating while the ship 1 is sailing, onboard electric power is generated by the main engine 20, and when the auxiliary engine 30 is operating while the ship 1 is at anchor, onboard electric power is generated by the auxiliary engine 30. Therefore, boil-off gas (BOG) generated in the tank 10 can be effectively used to generate onboard electric power by the main engine 20 and the auxiliary engine 30, without wasting it. As a result, boil-off gas can be effectively used, and fuel efficiency can be improved.

[0065] Furthermore, in the third embodiment, similarly to the first embodiment, the main supply line 100 is provided which can supply the liquefied gas LG in the tank 10 to the main engine 20, and the boil-off gas line 300C is provided which can supply the boil-off gas BOG in the tank 10 to the main engine 20. This allows the boil-off gas BOG to be used effectively, and fuel efficiency can be improved.

[0066] Fourth Embodiment Next, a fourth embodiment of a ship and an onboard electric power generation method according to the present disclosure will be described. In the fourth embodiment described below, only the configuration of the boil-off gas line differs from the first to third embodiments. Therefore, the same parts as those in the first to third embodiments will be denoted by the same reference numerals and will not be described again. FIG. 11 is a diagram showing a fuel supply system from a tank to a main engine and auxiliary engines in a ship according to the fourth embodiment of the present disclosure. As shown in FIG. 11 , the ship 1 of the fourth embodiment includes a main supply line 100, an auxiliary engine supply line 200, and a boil-off gas line 300D to supply liquefied gas stored in a tank 10 as fuel to the main engine 20 and auxiliary engine 30.

[0067] The boil-off gas line 300D can supply the boil-off gas BOG generated in the tank 10 to the main engine 20. An upstream end 301 of the boil-off gas line 300D is connected to the tank 10. A downstream end 304 of the boil-off gas line 300D is connected to the main supply line 100 between the pump 11 and the booster pump 12. The downstream end 304 of the boil-off gas line 300D is connected to the main supply line 100 downstream of the upstream end 201 of the auxiliary equipment supply line 200.

[0068] The boil-off gas line 300D is provided with a gas compressor 55 and a heat exchanger 56. The gas compressor 55 pressurizes the boil-off gas BOG supplied to the main engine 20 through the boil-off gas line 300D. The heat exchanger 56 is provided in the main supply line 100 between the pressure pump 12 and the high-pressure vaporizer 13. The heat exchanger 56 exchanges heat between the boil-off gas BOG flowing through the boil-off gas line 300D and the liquefied gas LG that has passed through the pressure pump 12 of the main supply line 100.

[0069] The boil-off gas line 300D cools the boil-off gas BOG pressurized through the gas compressor 55 by heat exchange with the liquefied gas LG in the heat exchanger 56, and then mixes the boil-off gas BOG with the liquefied gas LG flowing through the main supply line 100. In an embodiment of the present disclosure, the boil-off gas line 300D mixes the boil-off gas BOG pressurized through the gas compressor 55 with the liquefied gas LG flowing through the main supply line 100 upstream of the pressure pump 12. As a result, the boil-off gas BOG pressurized and cooled through the gas compressor 55 and the heat exchanger 56 is further pressurized by the pressure pump 12 together with the liquefied gas LG from the tank 10, and then vaporized in the high-pressure vaporizer 13 and sent to the main engine 20.

[0070] (Onboard electric power generation method) Next, an onboard electric power generation method for the ship 1 as described above will be described. Fig. 12 is a diagram showing the flow of boil-off gas when the first mode is being executed in the onboard electric power generation method according to the fourth embodiment of the present disclosure. Fig. 13 is a diagram showing the flow of boil-off gas when the second mode is being executed in the onboard electric power generation method according to the fourth embodiment of the present disclosure.

[0071] 12 , when the vessel 1 is sailing with the propeller 9 driven by the main engine 20, the vessel 1 executes a first mode M21. In the first mode M21, the main engine 20 drives the shaft generator 25, and the shaft generator 25 generates onboard electricity. In this case, the first valve 73 is opened and the second valve 74 is closed. As a result, boil-off gas BOG from the tank 10 passes through the gas compressor 55, the heat exchanger 56, the pressure pump 12, and the high-pressure vaporizer 13, and is supplied to the main engine 20 as fuel gas FG. In the first mode M21, the boil-off gas BOG generated while the vessel 1 is sailing is supplied to the main engine 20, and the shaft generator 25 generates onboard electricity.

[0072] 13 , when the vessel 1 is at anchor and the propeller 9 is not driven by the main engine 20, the vessel 1 executes a second mode M22. In the second mode M22, the boil-off gas BOG from the tank 10 is pressurized only through the gas compressor 55 and supplied as auxiliary fuel gas FG2 to the auxiliary equipment 30 through the auxiliary equipment boil-off gas supply line 400. In the second mode M22, the boil-off gas BOG generated when the vessel 1 is at anchor is supplied to the auxiliary equipment 30, and the auxiliary equipment 30 generates onboard electricity.

[0073] (Operation and Effect) The ship 1 of the fourth embodiment is provided with the heat exchanger 56. The boil-off gas BOG is cooled by heat exchange in the heat exchanger 56 between the boil-off gas BOG flowing through the boil-off gas line 300D and the liquefied gas LG that has passed through the pressure pump 12. The boil-off gas BOG cooled in the heat exchanger 56 is mixed with the liquefied gas LG flowing through the main supply line 100, thereby increasing the amount of boil-off gas BOG that can be reliquefied, and enabling efficient consumption of the boil-off gas BOG.

[0074] Furthermore, in the fourth embodiment, similarly to the third embodiment, the boil-off gas BOG is mixed with the pressurized liquefied gas LG flowing through the main supply line 100, thereby increasing the pressure of the boil-off gas BOG and making it more likely to vaporize when supplied as fuel to the main engine 20. In this way, by vaporizing the boil-off gas BOG together with the liquefied gas LG flowing through the main supply line 100, it is possible to efficiently generate fuel gas FG and supply it to the main engine 20.

[0075] Furthermore, in the fourth embodiment, similarly to the first embodiment, the main supply line 100 capable of supplying the liquefied gas LG in the tank 10 to the main engine 20 and the boil-off gas line 300D capable of supplying the boil-off gas BOG in the tank 10 to the main engine 20 are provided. This makes it possible to effectively utilize the boil-off gas BOG and improve fuel efficiency.

[0076] Fifth Embodiment Next, a fifth embodiment of a ship and an onboard electric power generation method according to the present disclosure will be described. The fifth embodiment described below differs from the first to fourth embodiments only in the configuration of the boil-off gas line. Therefore, the same components as those in the first to fourth embodiments will be denoted by the same reference numerals and will not be described again. FIG. 14 is a diagram showing a fuel supply system from a tank to a main engine and auxiliary engines in a ship according to the fifth embodiment of the present disclosure. As shown in FIG. 14 , the ship 1 of the fifth embodiment includes a main supply line 100, an auxiliary engine supply line 200, and a boil-off gas line 300E to supply liquefied gas stored in a tank 10 as fuel to the main engine 20 and auxiliary engine 30.

[0077] The boil-off gas line 300E can supply the boil-off gas BOG generated in the tank 10 to the main engine 20. An upstream end 301 of the boil-off gas line 300E is connected to the tank 10. The boil-off gas line 300E branches into a first line 310 and a second line 320 midway. A downstream end 312 of the first line 310 is connected to the main supply line 100 downstream of the high-pressure vaporizer 13. A downstream end 322 of the second line 320 is connected to the main supply line 100 between the pump 11 and the booster pump 12. The downstream end 322 of the second line 320 is connected to the main supply line 100 downstream of the upstream end 201 of the auxiliary equipment supply line 200.

[0078] The boil-off gas line 300E is provided with a first gas compressor 53 and a second gas compressor 54 as gas compressors 52, and a heat exchanger 56. The first gas compressor 53 is disposed in the boil-off gas line 300E between the tank 10 and the second gas compressor 54. The first gas compressor 53 pressurizes the boil-off gas BOG from the tank 10 and supplied through the boil-off gas line 300E to a first pressure (e.g., 0.6 MPa) required as fuel for the auxiliary equipment 30 (the pressure of the auxiliary equipment fuel gas FG2).

[0079] The second gas compressor 54 is provided in the boil-off gas line 300E, midway through the first line 310. The second gas compressor 54 further pressurizes the boil-off gas BOG, which has been pressurized to the first pressure via the first gas compressor 53, to a second pressure (e.g., 30 MPa) required as fuel for the main engine 20. The boil-off gas line 300E mixes the boil-off gas BOG, which has been pressurized via the first gas compressor 53 and the second gas compressor 54, into the main supply line 100 downstream of the high-pressure vaporizer 13. The boil-off gas line 300E mixes a portion of the boil-off gas BOG to be supplied to the main engine 20 with the fuel gas FG vaporized in the high-pressure vaporizer 13 in the main supply line 100.

[0080] The heat exchanger 56 is provided in the second line 320. The heat exchanger 56 exchanges heat between the boil-off gas BOG, which flows through the boil-off gas line 300E and is pressurized through the first gas compressor 53, and the liquefied gas LG, which has passed through the pressure pump 12 of the main supply line 100.

[0081] The boil-off gas line 300E cools a portion of the boil-off gas BOG pressurized through the first gas compressor 53 by heat exchange with the liquefied gas LG in the heat exchanger 56, and then mixes the cooled portion with the liquefied gas LG flowing through the main supply line 100. In the fifth embodiment, the boil-off gas line 300E mixes the boil-off gas BOG pressurized through the first gas compressor 53 with the liquefied gas LG flowing through the main supply line 100 upstream of the pressure pump 12. As a result, the boil-off gas BOG pressurized and cooled through the first gas compressor 53 and the heat exchanger 56 is further pressurized by the pressure pump 12 together with the liquefied gas LG from the tank 10, and then vaporized in the high-pressure vaporizer 13 and sent to the main engine 20.

[0082] Each of the first line 310 and the second line 320 may be provided with an on-off valve, a flow rate control valve, or the like, to adjust the balance in flow rate between the boil-off gas BOG supplied to the second gas compressor 54 and the boil-off gas BOG supplied to the heat exchanger 56. Also, the heat exchanger 56 in this fifth embodiment may be omitted.

[0083] (Onboard electric power generation method) Next, an onboard electric power generation method for the ship 1 as described above will be described. Fig. 15 is a diagram showing the flow of boil-off gas when the first mode is being executed in the onboard electric power generation method according to the fifth embodiment of the present disclosure. Fig. 16 is a diagram showing the flow of boil-off gas when the second mode is being executed in the onboard electric power generation method according to the fifth embodiment of the present disclosure.

[0084] As shown in FIG. 15 , when the ship 1 is sailing with the propeller 9 driven by the main engine 20, the ship 1 executes a first mode M31. In the first mode M31, the main engine 20 drives the shaft generator 25, and onboard electricity is generated by the shaft generator 25. In this case, the first valve 71 is opened and the second valve 72 is closed. As a result, a portion of the boil-off gas BOG from the tanks 10 is sent to the main supply line 100 via the first gas compressor 53 and the second gas compressor 54. The remaining portion of the boil-off gas BOG from the tanks 10 is supplied to the main engine 20 as fuel gas FG via the first gas compressor 53, the heat exchanger 56, the booster pump 12, and the high-pressure vaporizer 13. In this way, in the first mode M31, the boil-off gas BOG generated while the ship 1 is sailing is supplied to the main engine 20, and onboard electricity is generated by the shaft generator 25.

[0085] 16 , when the vessel 1 is at anchor and the propeller 9 is not driven by the main engine 20, the vessel 1 executes a second mode M32. In the second mode M32, the boil-off gas BOG from the tank 10 is pressurized only through the first gas compressor 53 and supplied as auxiliary fuel gas FG2 to the auxiliary equipment 30 through the auxiliary equipment boil-off gas supply line 400. In the second mode M32, the boil-off gas BOG generated when the vessel 1 is at anchor is supplied to the auxiliary equipment 30, and the auxiliary equipment 30 generates onboard electricity.

[0086] (Action and effect) In the ship 1 of the above-mentioned fifth embodiment, the boil-off gas BOG, which has been pressurized in two stages by the first gas compressor 53 and the second gas compressor 54, is mixed with the liquefied gas LG circulating in the main supply line 100, so that the boil-off gas BOG can be supplied to the main engine 20 as fuel for the main engine 20 together with the liquefied gas LG circulating in the main supply line 100.

[0087] In the fifth embodiment, the boil-off gas BOG is cooled by heat exchange in the heat exchanger 56 between the boil-off gas BOG flowing through the boil-off gas line 300E and the liquefied gas LG that has passed through the pressure pump 12. By mixing the boil-off gas BOG cooled in the heat exchanger 56 with the liquefied gas LG flowing through the main supply line 100, the boil-off gas BOG can be more easily reliquefied, the amount of boil-off gas BOG that can be reliquefied is increased, and the boil-off gas BOG can be consumed efficiently.

[0088] Furthermore, in the fifth embodiment, similarly to the first embodiment, the main supply line 100 is provided which can supply the liquefied gas LG in the tank 10 to the main engine 20, and the boil-off gas line 300E is provided which can supply the boil-off gas BOG in the tank 10 to the main engine 20. This makes it possible to effectively utilize the boil-off gas BOG and improve fuel efficiency.

[0089] <Additional Notes> The ship 1 and the onboard electric power generating method described in each embodiment can be understood, for example, as follows.

[0090] (1) A ship 1 according to a first aspect comprises a hull 2 ​​having a propeller 9, a main engine 20 mounted on the hull 2 ​​and driving the propeller 9, a shaft generator 25 that generates onboard electricity when driven by the rotation of the main engine 20, a tank 10 mounted on the hull 2 ​​and capable of storing liquefied gas LG, a main supply line 100 that vaporizes the liquefied gas LG in the tank 10 and supplies it to the main engine 20, and boil-off gas lines 300A to 300E that can supply boil-off gas BOG from the tank 10 to the main engine 20.

[0091] This allows the main engine 20 to use, as fuel, both the liquefied gas LG in the tanks 10 and the boil-off gas BOG generated within the tanks 10. By driving the shaft generator 25 in conjunction with the rotation of the main engine 20 when driving the propeller 9 with such a main engine 20, it is possible to generate onboard electricity using the fuel-efficient main engine 20. Therefore, even when the ship is equipped with a main engine 20 that requires high-pressure gas as fuel, it is possible to effectively use the boil-off gas BOG and improve fuel efficiency.

[0092] (2) The ship 1 according to the second aspect is the ship 1 of (1), further comprising an auxiliary machine 30 that generates onboard electricity by fuel supply, and the boil-off gas line 300B is capable of supplying the boil-off gas BOG to the auxiliary machine 30 in addition to the main machine 20, and is equipped with a switching unit 70 that can selectively switch the supply destination of the boil-off gas BOG by the boil-off gas line 300B between the main machine 20 and the auxiliary machine 30.

[0093] As a result, when the main engine 20 is operating, boil-off gas BOG can be supplied to the main engine 20, and when the auxiliary engine 30 is operating, boil-off gas BOG can be supplied to the auxiliary engine 30. Therefore, the boil-off gas BOG generated in the tank 10 can be effectively consumed by the main engine 20 and the auxiliary engine 30 without being wasted.

[0094] (3) The ship 1 according to the third aspect is the ship 1 of (1) or (2), wherein the main supply line 100 is provided with a pressure pump 12 that pressurizes the liquefied gas LG and a vaporizer 13 that vaporizes the liquefied gas LG pressurized by the pressure pump 12 to generate fuel gas that serves as fuel for the main engine 20, and the boil-off gas lines 300A, 300B are provided with gas compressors 51, 52 that can pressurize the boil-off gas BOG to the pressure of the fuel gas supplied to the main engine 20.

[0095] This allows the boil-off gas BOG to be used as high-pressure fuel gas supplied to the main engine 20. Therefore, the boil-off gas BOG can be effectively used, and fuel efficiency can be improved.

[0096] (4) The ship 1 according to a fourth aspect is the ship 1 of (2), wherein the boil-off gas lines 300B, 300E are provided with a first gas compressor 53 that pressurizes the boil-off gas BOG to a first pressure required as fuel for the auxiliary machinery 30, and a second gas compressor 54 that further pressurizes the boil-off gas BOG, which has been pressurized to the first pressure via the first gas compressor 53, to a second pressure required as fuel for the main machinery 20.

[0097] As a result, the boil-off gas BOG can be pressurized in two stages by the first gas compressor 53 and the second gas compressor 54. Therefore, the boil-off gas BOG can be supplied to the auxiliary machinery 30 as fuel for the auxiliary machinery 30, and the pressurized boil-off gas BOG can be supplied to the main machinery 20 as fuel for the main machinery 20.

[0098] (5) The ship 1 according to the fifth aspect is the ship 1 of (4), in which the boil-off gas line 300E mixes the boil-off gas BOG pressurized by the first gas compressor 53 with the liquefied gas LG circulating in the main supply line 100.

[0099] This allows the boil-off gas BOG pressurized by the first gas compressor 53 to be mixed with the liquefied gas LG circulating in the main supply line 100, so that the boil-off gas BOG can be supplied to the main engine 20 as fuel for the main engine 20 together with the liquefied gas LG circulating in the main supply line 100.

[0100] (6) The ship 1 according to the sixth aspect is the ship 1 of (5), wherein the main supply line 100 is provided with a pressure pump 12 that pressurizes the liquefied gas LG and a vaporizer 13 that vaporizes the liquefied gas LG pressurized by the pressure pump 12 to generate fuel gas that serves as fuel for the main engine 20, and further includes a heat exchanger 56 that exchanges heat between the boil-off gas BOG pressurized by a first gas compressor and the liquefied gas LG that has passed through the pressure pump 12 of the main supply line 100.

[0101] This cools the boil-off gas BOG before it is mixed with the liquefied gas LG. Therefore, by mixing the boil-off gas BOG cooled in the heat exchanger 56 with the liquefied gas LG flowing through the main supply line 100, the boil-off gas BOG is more easily re-liquefied.

[0102] (7) The ship 1 according to the seventh aspect is any one of the ships 1 of (1) to (6), wherein the main supply line 100 is provided with a pressure pump 12 that pressurizes the liquefied gas LG and a vaporizer 13 that evaporates the liquefied gas LG pressurized by the pressure pump 12 to generate fuel gas that serves as fuel for the main engine 20, and the boil-off gas lines 300C, 300D mix the boil-off gas BOG to be supplied to the main engine 20 with the liquefied gas LG circulating in the main supply line 100.

[0103] As a result, the boil-off gas BOG is cooled and re-liquefied by the liquefied gas LG flowing through the main supply line 100, and can be efficiently supplied to the main engine 20 as fuel for the main engine 20.

[0104] (8) The ship 1 according to the eighth aspect is the ship 1 of (7), further comprising a heat exchanger 56 that exchanges heat between the boil-off gas BOG flowing through the boil-off gas line 300D and the liquefied gas LG that has passed through the pressure pump 12 of the main supply line 100.

[0105] This allows the boil-off gas BOG cooled in the heat exchanger 56 to be mixed with the liquefied gas LG flowing through the main supply line 100, making it even easier for the boil-off gas BOG to be re-liquefied.

[0106] (9) The onboard electricity generation method according to the ninth aspect is an onboard electricity generation method for the ship 1 of (2), which switches between a first mode M1, M11, M21, M31 in which boil-off gas BOG is supplied to the main engine 20 when the ship 1 is sailing and onboard electricity is generated by the shaft generator 25, and a second mode M2, M12, M22, M32 in which the boil-off gas BOG is supplied to the auxiliary engine 30 when the ship 1 is at anchor and onboard electricity is generated by the auxiliary engine 30.

[0107] As a result, when the main engine 20 is operating while the vessel 1 is sailing, the main engine 20 generates onboard electricity, and when the auxiliary engine 30 is operating while the vessel 1 is at anchor, the auxiliary engine 30 generates onboard electricity. Therefore, the boil-off gas BOG generated in the tanks 10 can be effectively used to generate onboard electricity by the main engine 20 and the auxiliary engine 30, without wasting it. As a result, the boil-off gas can be effectively used, and fuel efficiency can be improved.

[0108] According to the ship and onboard power generation method disclosed herein, boil-off gas can be effectively utilized to improve fuel efficiency.

[0109] DESCRIPTION OF SYMBOLS 1 Ship 2 Hull 2b Stern 3A, 3B Side 4 Ship bottom 5 Upper deck 7 Superstructure 8 Propeller shaft 9 Propeller 10 Tank 11 Pump 12 Pressure pump 13 Vaporizer 13 High-pressure vaporizer 20 Main engine 25 Shaft generator 30 Auxiliary engine 31 Auxiliary engine vaporizer 51 High-pressure gas compressor (gas compressor) 51, 52, 55 Gas compressor 53 First gas compressor 54 Second gas compressor 56 Heat exchanger 70, 70B Switching unit 71, 73 First valve 72, 74 Second valve 100 Main supply line 105, 205, 305 Valve 200 Auxiliary engine supply line 201, 301 Upstream end 202, 302, 303, 304, 312, 322 Downstream end 300A to 300E Boil-off gas line 310 First line 320 Second line 400 Auxiliary boil-off gas supply line M1, M11, M21, M31 First mode M2, M12, M22, M32 Second mode

Claims

1. A ship comprising: a hull having a propeller; a main engine mounted on the hull for driving the propeller; a shaft generator driven by the rotation of the main engine to generate onboard electricity; a tank mounted on the hull for storing liquefied gas; a main supply line for vaporizing the liquefied gas stored in the tank and supplying it to the main engine; and a boil-off gas line for supplying boil-off gas generated in the tank to the main engine.

2. The ship described in claim 1, further comprising auxiliary machinery that generates onboard electricity by fuel supply, the boil-off gas line being capable of supplying the boil-off gas to the auxiliary machinery in addition to the main engine, and a switching unit capable of selectively switching the supply destination of the boil-off gas by the boil-off gas line between the main engine and the auxiliary machinery.

3. The ship according to claim 1 or 2, wherein the main supply line is provided with a pressure booster pump which pressurizes the liquefied gas and a vaporizer which vaporizes the liquefied gas pressurized by the pressure booster pump to generate fuel gas to be used as fuel for the main engine, and the boil-off gas line is provided with a gas compressor capable of pressurizing the boil-off gas to the pressure of the fuel gas to be supplied to the main engine.

4. The ship according to claim 2, wherein the boil-off gas line comprises: a first gas compressor which pressurizes the boil-off gas to a first pressure required as fuel for the auxiliary machinery; and a second gas compressor which further pressurizes the boil-off gas, which has been pressurized to the first pressure through the first gas compressor, to a second pressure required as fuel for the main engine.

5. The ship according to claim 4, wherein the boil-off gas line mixes the boil-off gas pressurized by the first gas compressor with the liquefied gas circulating in the main supply line.

6. The ship according to claim 5, further comprising: a pressure pump for pressurizing the liquefied gas; a vaporizer for vaporizing the liquefied gas pressurized by the pressure pump to generate fuel gas to be used as fuel for the main engine; and a heat exchanger for exchanging heat between the boil-off gas pressurized by the first gas compressor and the liquefied gas that has passed through the pressure pump of the main supply line.

7. The ship described in claim 1 or 2, wherein the main supply line is equipped with a pressure pump which pressurizes the liquefied gas and a vaporizer which vaporizes the liquefied gas pressurized by the pressure pump to generate fuel gas which serves as fuel for the main engine, and the boil-off gas line mixes the boil-off gas to be supplied to the main engine with the liquefied gas circulating in the main supply line.

8. The ship according to claim 7, further comprising a heat exchanger for exchanging heat between the boil-off gas flowing through the boil-off gas line and the liquefied gas that has passed through the pressure pump of the main supply line.

9. An onboard electric power generation method for a ship as described in claim 2, which switches between a first mode in which boil-off gas is supplied to the main engine while the ship is sailing and onboard electric power is generated by the shaft generator, and a second mode in which the boil-off gas is supplied to the auxiliary engine while the ship is anchored and onboard electric power is generated by the auxiliary engine.

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