JP2017110621A - Marine vessel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a marine vessel capable of supplying a sufficient amount of fuel gas to a main gas engine and a sub-gas engine without using a high pressure pump.SOLUTION: A marine vessel comprises: a main gas engine for propulsion; a tank for accumulating a LNG; a gas supply line for introducing a BOG produced in the tank to a compressor; a first supply line for introducing the BOG discharged from the compressor to the main gas engine; a sub-gas engine for electric power generation; a liquid supply line for introducing the LNG discharged from a pump disposed in the tank to a forced carburetor; a second supply line for introducing the VG produced in the forced carburetor to the sub-gas engine; a bridge line having a first adjusting valve changeable the opening degree for introducing the VG to the gas supply line from the second supply line; a return line having a second adjusting valve changeable the opening degree for connecting to the tank from the second supply line; and a control device for controlling the first adjusting valve and the second adjusting valve.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a ship including a main gas engine for propulsion and a sub gas engine for power generation.

  Conventionally, a ship including a main gas engine for propulsion and a sub gas engine for power generation is known. For example, Patent Document 1 discloses a ship 100 as shown in FIG.

  Specifically, the ship 100 includes a tank 110 that stores liquefied natural gas, a main gas engine 130 for propulsion, and a sub gas engine 140 for power generation. The main gas engine 130 is a diesel cycle type engine with a high fuel gas injection pressure, and the sub gas engine 140 is a dual fuel engine with a low fuel gas injection pressure.

  The tank 110 is connected to the high-pressure compressor 120 via the air supply line 101, and the high-pressure compressor 120 is connected to the main gas engine 130 via the first supply line 102. The air supply line 101 guides the boil-off gas generated in the tank 110 to the high-pressure compressor 120, and the high-pressure compressor 120 compresses the boil-off gas to a high pressure (for example, about 30 MPa). The first supply line 102 guides high-pressure boil-off gas discharged from the high-pressure compressor 120 to the main gas engine 130.

  Further, the second supply line 103 is connected to the auxiliary gas engine 140 from the middle of the high-pressure compressor 120. When the amount of boil-off gas generated is larger than the fuel gas consumption of the main gas engine 130, surplus gas is supplied to the sub gas engine 140 through the second supply line 103.

  Further, the ship 100 shown in FIG. 4 has a configuration for supplying a sufficient amount of fuel gas to the main gas engine 130 even when the amount of boil-off gas generated is smaller than the fuel gas consumption of the main gas engine 130. It has been adopted. Specifically, a pump 150 is disposed in the tank 110, and the pump 150 is connected to the suction drum 160 through the first supply line 104. The suction drum 160 is connected to the high-pressure pump 170 through the second supply line 105, the high-pressure pump 170 is connected to the gas heater 180 through the third supply line 106, and the fourth supply line 107 is connected to the first supply line 102 from the gas heater 180. ing.

  Further, a connection line 190 is branched from the first supply line 102 at a downstream side of a position where the fourth supply line 107 is connected, and the connection line 190 is connected to the second supply line 103. The communication line 190 is provided with a check valve 191 with a pressure adjustment function. That is, the high-pressure gas in the first supply line 102 can be supplied to the auxiliary gas engine 140 after the pressure is reduced.

Japanese Patent Laying-Open No. 2015-145243

  However, in the ship 100 shown in FIG. 4, when the amount of boil-off gas generated is less than the consumption of the main gas engine 130, it is necessary to operate the high-pressure pump 170 in addition to the high-pressure compressor 120. From the viewpoint of preventing air pollution, it is desirable to reduce the amount of fuel oil consumed in the secondary gas engine 140, which is a dual fuel engine, as much as possible. It is necessary to let

  Accordingly, an object of the present invention is to provide a ship that can supply a sufficient amount of fuel gas to a main gas engine and a sub gas engine without using a high-pressure pump.

  In order to solve the above problems, a ship of the present invention includes a main gas engine for propulsion, a tank for storing liquefied natural gas, an air supply line for guiding boil-off gas generated in the tank to a compressor, A first supply line for guiding boil-off gas discharged from the compressor to the main gas engine, a sub-gas engine for power generation, and liquefied natural gas discharged from a pump disposed in the tank are guided to a forced vaporizer. An opening degree change that leads the liquid supply line, the second supply line that leads the vaporized gas generated in the forced vaporizer to the sub-gas engine, and the vaporized gas from the second supply line to the air supply line. A bridge line provided with a first adjustable valve, a return line connected to the tank from the second supply line and provided with a second adjustable valve capable of changing the opening, and the first adjustable valve And a control unit for controlling the fine said second regulating valve, characterized in that.

  According to the above configuration, since the liquefied natural gas is forcibly vaporized by the forced vaporizer and the vaporized gas is supplied to the secondary gas engine, a sufficient amount of fuel is supplied to the secondary gas engine without using a high-pressure pump. Gas can be supplied. Thereby, combustion of the fuel oil in a subgas engine becomes unnecessary, or the consumption of fuel oil can be suppressed. Moreover, when the boil-off gas is insufficient with respect to the fuel gas consumption of the main gas engine, the vaporized gas generated by the forced vaporizer is merged with the boil-off gas sucked into the compressor through the bridge line. Can do. Therefore, a sufficient amount of fuel gas can be supplied to the main gas engine without using a high-pressure pump. Note that the phrase “without using a high-pressure pump” does not exclude the provision of a high-pressure pump on a ship as an alternative means in the event of a compressor failure.

  By the way, while the vaporized gas flows through the bridge line, in other words, while the first adjustment valve provided in the bridge line is opened, the vaporized gas supplied to the auxiliary gas engine through the second supply line is excessive. Sometimes. In this case, if the second regulating valve provided in the return line is opened, excess vaporized gas can be returned to the tank.

  The ship includes a first pressure gauge that detects a pressure of the boil-off gas in the tank or the boil-off gas that flows through the air supply line, and a second pressure gauge that detects the pressure of the vaporized gas that flows through the second supply line. The control device calculates an available amount of boil-off gas from the amount of liquefied natural gas in the tank and the pressure of the boil-off gas detected by the first pressure gauge, and the boil-off gas can be used. When the amount is smaller than the fuel gas consumption of the main gas engine, the first adjustment valve is opened to a predetermined opening, and the second adjustment valve is opened while the first adjustment valve is opened to the predetermined opening. When the pressure of the vaporized gas detected by the pressure gauge exceeds a threshold value, the second adjustment valve may be opened from a fully closed state to a predetermined opening. According to this configuration, it is possible to follow the pressure change of the second supply line without being affected by the response delay of the forced vaporizer, that is, the excess or deficiency of the amount of vaporized gas to be generated. In addition, even if the fuel gas consumption of the auxiliary gas engine is reduced, the minimum flow rate of the forced carburetor can be maintained.

  The ship includes a first pressure gauge that detects a pressure of the boil-off gas in the tank or the boil-off gas that flows through the air supply line, and a second pressure gauge that detects the pressure of the vaporized gas that flows through the second supply line. The control device calculates an available amount of boil-off gas from the amount of liquefied natural gas in the tank and the pressure of the boil-off gas detected by the first pressure gauge, and the boil-off gas can be used. When the amount is smaller than the fuel gas consumption of the main gas engine, the first adjustment valve is opened to a predetermined opening, and the second adjustment valve is opened while the first adjustment valve is opened to the predetermined opening. When the pressure of the vaporized gas detected by the pressure gauge exceeds a threshold value, the opening of the first adjustment valve may be further increased from the predetermined opening. According to this configuration, in addition to the effect of following the pressure change of the second supply line without being affected by the response delay of the forced vaporizer described above and the effect of maintaining the minimum flow rate of the forced vaporizer, The effect that the amount of heat input to the tank can be suppressed as compared with the case where the surplus vaporized gas is returned to the tank can be obtained.

  The control device fully closes the second adjustment valve when the pressure of the vaporized gas detected by the second pressure gauge exceeds a threshold value while keeping the first adjustment valve in the fully closed state. You may open from a state to a predetermined opening degree. According to this configuration, when the vaporized gas is not flowing through the bridge line, even if the vaporized gas supplied to the auxiliary gas engine through the second supply line is excessive, the surplus vaporized gas can be returned to the tank. it can.

  According to the present invention, a sufficient amount of fuel gas can be supplied to the main gas engine and the auxiliary gas engine without using a high-pressure pump.

It is a schematic structure figure of a ship concerning one embodiment of the present invention. It is a graph which shows the relationship between the deviation of the pressure of the boil-off gas in a tank, and a setting pressure, and the available amount of boil-off gas. It is a schematic block diagram of the ship of a modification. It is a schematic block diagram of the conventional ship.

  FIG. 1 shows a ship 1A according to an embodiment of the present invention. The ship 1A includes a tank 11 for storing liquefied natural gas (hereinafter referred to as LNG), a main gas engine 13 for propulsion, and a sub gas engine 16 for power generation (that is, for onboard power).

  In the illustrated example, only one tank 11 is provided, but a plurality of tanks 11 may be provided. In the present embodiment, the ship 1A is an LNG carrier, and the ship 1A is equipped with a plurality of cargo tanks. That is, the tank 11 shown in FIG. 1 is each of a plurality of cargo tanks. In the illustrated example, one main gas engine 13 and one sub gas engine 16 are provided, but a plurality of main gas engines 13 may be provided, or a plurality of sub gas engines 16 may be provided. Good.

  In this embodiment, the ship 1A is a mechanical propulsion type, and the main gas engine 13 directly rotates and drives a screw propeller (not shown). However, the ship 1A may be an electric propulsion type, and the main gas engine 13 may rotationally drive the screw propeller via a generator and a motor.

  The main gas engine 13 is a diesel cycle type two-stroke engine having a high fuel gas injection pressure of about 20 to 35 MPa, for example. However, the main gas engine 13 may be an Otto cycle type two-stroke engine whose fuel gas injection pressure is an intermediate pressure of about 1 to 2 MPa, for example. Alternatively, in the case of electric propulsion, the main gas engine 13 may be an Otto cycle type four-stroke engine having a low fuel gas injection pressure of, for example, about 0.5 to 1 MPa. The main gas engine 13 may be a gas-only combustion engine that burns only fuel gas, or may be a dual fuel engine that burns one or both of fuel gas and fuel oil (binary fuel engine). In this case, the fuel gas may be burned by the Otto cycle, and the fuel oil may be burned by the diesel cycle).

  The auxiliary gas engine 16 is an Otto cycle type four-stroke engine having a low fuel gas injection pressure of, for example, about 0.5 to 1 MPa, and is connected to a generator (not shown). The auxiliary gas engine 16 may be a gas combustion engine that burns only fuel gas, or may be a dual fuel engine that burns one or both of fuel gas and fuel oil.

  The fuel gas of the main gas engine 13 is mainly boil-off gas (hereinafter referred to as BOG) generated in the tank 11 by natural heat input, and the fuel gas of the auxiliary gas engine 16 is mainly forced by LNG. The vaporized gas (hereinafter referred to as VG).

  Specifically, the tank 11 is connected to the compressor 12 by an air supply line 21, and the compressor 12 is connected to the main gas engine 13 by a first supply line 31. Further, a pump 14 is disposed in the tank 11, and the pump 14 is connected to the forced vaporizer 15 by a liquid feed line 41. The forced vaporizer 15 is connected to the auxiliary gas engine 16 by the second supply line 51.

  The air supply line 21 guides BOG generated in the tank to the compressor 12. In the present embodiment, the compressor 12 is a multistage high pressure compressor. The compressor 12 compresses the BOG to a high pressure. The first supply line 31 guides the high-pressure BOG discharged from the compressor 12 to the main gas engine 13. However, the compressor 12 may be a low-pressure compressor, for example, when the fuel gas injection pressure of the main gas engine 13 is low.

  The liquid feed line 41 guides LNG discharged from the pump 14 to the forced vaporizer 15. The liquid feed line 41 is provided with an adjustment valve 42 capable of changing the opening degree. The forced vaporizer 15 uses, for example, steam generated in a boiler as a heat source, and forcibly vaporizes LNG to generate VG. The second supply line 51 guides VG generated by the forced vaporizer 15 to the sub gas engine 16.

  In the present embodiment, the second supply line 51 is provided with a cooler 52, a gas-liquid separator 53, and a heater 54 in order from the upstream side. The cooler 52 cools the VG generated by the forced vaporizer 15 and generates a liquid component whose main component is a component other than methane. The produced liquid component is collected by the gas-liquid separator 53. As a result, most of the heavy components (for example, ethane, propane, butane, etc.) are removed from the VG, so that VG having a high methane number can be supplied to the auxiliary gas engine 16. The liquid component collected by the gas-liquid separator 53 is returned to the tank 11 through the drain line. The VG that has passed through the gas-liquid separator 53 is heated by the heater 54. As a result, VG having an appropriate temperature can be supplied to the auxiliary gas engine 16.

  More specifically, regarding the cooler 52, an extraction line 44 is connected to the cooler 52. The extraction line 44 branches from the liquid supply line 41 on the upstream side of the regulating valve 42. The extraction line 44 is provided with an adjustment valve 45 whose opening degree can be changed. The cooler 52 cools the VG by injecting LNG supplied from the extraction line 44 into the VG.

  Further, a first bridge line 61 is connected to the air supply line 21 from the second supply line 51. In the present embodiment, the upstream end of the first bridge line 61 is connected to the second supply line 51 between the cooler 52 and the gas-liquid separator 53, but the upstream end of the first bridge line 61 is connected to the cooler. It may be connected to the second supply line 51 upstream of 52, between the gas-liquid separator 53 and the heater 54, or downstream of the heater 54. The first bridge line 61 guides VG from the second supply line 51 to the air supply line 21 when the BOG is insufficient with respect to the fuel gas consumption Q1 of the main gas engine 13. As a result, BOG and VG are supplied to the main gas engine 13 as fuel gas.

  From the middle of the compressor 12, the second bridge line 63 is connected to the second supply line 51. In the present embodiment, the downstream end of the second bridge line 63 is connected to the second supply line 51 on the downstream side of the heater 54, but the downstream end of the second bridge line 63 is on the upstream side of the heater 54. It may be connected to the second supply line 51. The second bridge line 63 guides the BOG from the compressor 12 to the second supply line 51 when the BOG is surplus with respect to the fuel gas consumption Q1 of the main gas engine 13. As a result, VG and BOG (in some cases, only BOG) are supplied to the auxiliary gas engine 16 as fuel gas.

  The first bridge line 61 is provided with an adjustment valve 62 capable of changing the opening (corresponding to the first adjustment valve of the present invention), and the second bridge line 63 has an adjustment valve capable of changing the opening. 64 is provided. In this embodiment, each of the regulating valves 62 and 64 plays a role of opening or closing the bridge line (61 or 63). However, each of the first bridge line 61 and the second bridge line 63 may be provided with an open / close valve separately from the adjustment valve (62 or 64).

  In the present embodiment, the pump 14 causes the pressure of the VG generated by the forced vaporizer 15 (in other words, the outlet pressure of the forced vaporizer 15) to be higher than the fuel gas supply pressure of the auxiliary gas engine 16. , LNG is discharged. That is, the pressure of VG flowing through the second supply line 51 is higher than the pressure of BOG in the tank 11. For this reason, the regulating valve 62 reduces the pressure of VG to the same level as the pressure of BOG in the tank 11 when opening the first bridge line 61. The air supply line 21 is provided with a check valve 22 on the upstream side of the position where the first bridge line 61 is connected. This prevents VG from the first bridge line 61 from flowing into the tank 11.

  Furthermore, in this embodiment, a return line 71 is connected from the second supply line 51 to the tank 11. In the present embodiment, the upstream end of the return line 71 is connected to the second supply line 51 between the gas-liquid separator 53 and the heater 54, but the upstream end of the return line 71 is connected to the cooler 52 and the gas-liquid. The separator 53 may be connected to the second supply line 51. The downstream end of the return line 71 may be located above the liquid level of LNG in the tank 11 or may be located below the liquid level.

  The return line 71 is provided with an adjustment valve 72 (corresponding to the second adjustment valve of the present invention) whose opening degree can be changed. In the present embodiment, the regulating valve 72 plays a role of opening or closing the return line 71. However, the return line 71 may be provided with an open / close valve separately from the regulating valve 72.

  The regulating valves 42, 45, 62, 64, 72 described above are controlled by the control device 8. In FIG. 1, only some signal lines are drawn for the sake of simplicity. The control device 8 includes a first pressure gauge 81 provided in the air supply line 21, a second pressure gauge 82 provided in the second supply line 51, a flow meter 83 provided in the first bridge line 61, and A thermometer 84 provided in the second supply line 51 is connected.

  The first pressure gauge 81 detects the pressure Pb of the BOG flowing through the air supply line 21. The first pressure gauge 81 may be provided on either the upstream side or the downstream side of the check valve 22 as long as the first pressure gauge 81 is located upstream of the position where the first bridge line 61 is connected in the air supply line 21. . However, the first pressure gauge 81 may be provided in the tank 11 to detect the pressure Pt of the BOG in the tank 11.

  The second pressure gauge 82 detects the pressure Pv of VG flowing through the second supply line 51. The second pressure gauge 82 is located on the downstream side of the position where the second bridge line 63 is connected in the second supply line 51. However, when the second pressure gauge 82 is used only for controlling the regulating valve 72 provided in the return line 71 described later, the second pressure gauge 82 is connected to the second bridge line 63 in the second supply line 51. It may be located on the upstream side. The flow meter 83 detects the flow rate Fv of VG flowing through the first bridge line 61. The thermometer 84 detects the outlet temperature of the cooler 52.

  The control device 8 includes a first gas engine controller (not shown) for controlling the fuel gas injection timing of the main gas engine 13 and a second gas engine controller for controlling the fuel gas injection timing of the auxiliary gas engine 16. Various signals are transmitted from (not shown). Then, the control device 8 calculates the fuel gas consumption Q1 of the main gas engine 13 from the signal transmitted from the first gas engine controller, and the auxiliary gas engine 16 from the signal transmitted from the second gas engine controller. The fuel gas consumption Q2 is calculated. However, the control device 8 may acquire the fuel gas consumption Q1 directly from the first gas engine controller or may acquire the fuel gas consumption Q2 directly from the second gas engine controller. Good.

  The control device 8 first calculates the available amount Qa of BOG from the amount of LNG in the tank 11 and the BOG pressure Pb detected by the first pressure gauge 81. Specifically, the control device 8 adds the pressure loss from the upstream end of the air supply line 21 to the position of the first pressure gauge 81 to the pressure Pb of the BOG detected by the first pressure gauge 81, and the tank 11 The pressure Pt of the BOG inside is calculated. As shown in FIG. 2, the usable amount Qa of BOG increases as the deviation ΔP (= Pt−Ps) between the BOG pressure Pt in the tank 11 and the set pressure Ps increases. Here, the set pressure Ps is a pressure at which the BOG usable amount Qa becomes equal to the BOG generation amount Qn. Note that the BOG generation amount Qn varies depending on the pressure of the BOG in the tank 11, but substantially depends on the amount of LNG in the tank 11. Further, since the capacity of the tank 11 which is a cargo tank is very large, even when BOG and / or LNG is used as the fuel gas, the height of the liquid level of the LNG in the tank 11 does not change so much. For this reason, in this embodiment, the amount of LNG in the tank 11 is not a variable but is treated as a constant value (different between full load and empty load). Then, the control device 8 calculates the available amount Qa of BOG from the amount of LNG in the tank 11 and the deviation ΔP between the calculated pressure Pt of the BOG in the tank 11 and the set pressure Ps. However, when the capacity of the tank 11 is small, a level meter that detects the amount of LNG in the tank 11 may be provided in the tank 11 and the amount of LNG in the tank 11 may be treated as a variable.

  The control device 8 has a deficient amount of LNG obtained by subtracting the BOG usable amount Qa from the total fuel gas consumption Qt, which is the sum of the fuel gas consumption Q1 of the main gas engine 13 and the fuel gas consumption Q2 of the auxiliary gas engine 16. Is supplied to the forced vaporizer 15 through the liquid feed line 41, and the adjustment valve 42 provided in the liquid feed line 41 is controlled. A return line 43 is branched from the liquid supply line 41 on the upstream side of the adjustment valve 42, and the portion of the LNG discharged from the pump 14 that is limited by the adjustment valve 42 is in the tank 11 through the return line 43. Will be returned. Further, the control device 8 controls the regulating valve 45 provided in the extraction line 44 based on the outlet temperature of the cooler 52 detected by the thermometer 84.

  Further, the control device 8 determines that the BOG usable amount Qa is larger than the fuel gas consumption Q1 of the main gas engine 13 (when the BOG is greater than the fuel gas consumption Q1 of the main gas engine 13). The adjustment valve 62 provided in the bridge line 61 is fully closed, and the adjustment valve 64 provided in the second bridge line 63 is opened to a predetermined opening.

  Conversely, when the available amount Qa of BOG is smaller than the fuel gas consumption Q1 of the main gas engine 13 (when BOG is insufficient with respect to the fuel gas consumption Q1 of the main gas engine 13), the control device 8 The adjustment valve 64 provided in the second bridge line 63 is fully closed, and the adjustment valve 62 provided in the first bridge line 61 is opened to a predetermined opening. At this time, the controller 8 causes the flow rate Qv of the VG detected by the flow meter 83 to be a deviation ΔA (= Q1−Qa) between the fuel gas consumption amount Q1 of the main gas engine 13 and the BOG usable amount Qa. In addition, the control valve 62 is controlled.

  As described above, in the marine vessel 1A of the present embodiment, LNG is forcibly vaporized by the forced vaporizer 15 and the VG is supplied to the secondary gas engine 16, so that the secondary gas engine is not used without using a high-pressure pump. A sufficient amount of fuel gas can be supplied to 16. Thereby, combustion of the fuel oil in the auxiliary gas engine 16 becomes unnecessary or the consumption amount of the fuel oil can be suppressed. In addition, when the BOG is insufficient with respect to the fuel gas consumption Q 1 of the main gas engine 13, the VG generated in the forced vaporizer 15 is taken into the BOG through the first bridge line 61 into the compressor 12. Can be joined. Therefore, a sufficient amount of fuel gas can be supplied to the main gas engine 13 without using a high-pressure pump.

  By the way, while the VG is flowing through the first bridge line 61, in other words, while the regulating valve 62 provided in the first bridge line 61 is opened, the supply is performed to the sub gas engine 16 through the second supply line 51. VG may be left behind. On the other hand, since the return line 71 is provided in this embodiment, when such a VG is left, if the adjustment valve 72 provided in the return line 71 is opened, the excess VG is returned to the tank 11. be able to.

  In particular, when the forced vaporizer 15 uses steam as a heat source and the cooler 52 is provided on the downstream side of the forced vaporizer 15, the forced vaporization is performed in order to ensure controllability of the outlet temperature of the cooler 52. It is necessary to supply a certain amount of LNG to the vessel 15. In other words, the forced vaporizer 15 has a minimum flow rate. In such a configuration, not only temporarily VG is temporarily generated as the load of the auxiliary gas engine 16 is reduced, but also when the fuel gas consumption of the auxiliary gas engine 16 is lower than the minimum flow rate of the forced carburetor 15. Surplus VG is constantly generated. Accordingly, the return line 71 is particularly useful for such a configuration.

  Specifically, in the present embodiment, when the control device 8 opens the regulating valve 62 at a predetermined opening, and the pressure Pv of the VG detected by the second pressure gauge 82 exceeds the threshold value α, The adjustment valve 72 provided in the return line 71 is opened from the fully closed state to a predetermined opening degree. With such control, it is possible to follow the pressure change of the second supply line 51 without being affected by the response delay of the forced vaporizer 15, that is, the excess or deficiency of the generated VG amount. In addition, even if the fuel gas consumption of the auxiliary gas engine 16 is reduced, the minimum flow rate of the forced vaporizer 15 can be maintained.

  Alternatively, the control device 8 fully closes the adjustment valve 72 when the pressure Pv of the VG detected by the second pressure gauge 82 exceeds the threshold value α while the adjustment valve 62 is opened to a predetermined opening degree. Instead of opening from the predetermined opening to the predetermined opening, the opening of the regulating valve 62 may be further increased from the predetermined opening. With such control, it is possible to follow the pressure change of the second supply line 51 without being affected by the response delay of the forced vaporizer 15 described above, and to maintain the minimum flow rate of the forced vaporizer 15. In addition, it is possible to obtain an effect that the amount of heat input to the tank 11 can be suppressed as compared with the case where surplus VG is returned to the tank 11 through the return line 71.

  Further, the control device 8 fully closes the adjustment valve 72 when the pressure Pv of the VG detected by the second pressure gauge 82 exceeds the threshold value α while the adjustment valve 62 is kept in the fully closed state. You may open from a state to a predetermined opening degree. In this way, even when VG is not flowing through the first bridge line 61 and the VG supplied to the secondary gas engine 16 through the second supply line 51 is surplus, the surplus VG is returned to the tank 11. can do.

(Modification)
The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the gist of the present invention.

  For example, the pump 14 may have a function of pumping up LNG up to the forced vaporizer 15, and a compressor may be provided in the second supply line 51. However, if the fuel gas injection pressure of the auxiliary gas engine 16 is ensured by the pump 14 as in the above embodiment, it is not necessary to provide a compressor in the second supply line 51, and the cost can be reduced.

  3, the return line 91 may be branched from the first supply line 31, and the return line 91 may be connected to the tank 11. The tip of the return line 91 may be located above the liquid level of LNG in the tank 11 or may be located below the liquid level. The return line 91 is provided with an expansion device 92 such as an expansion valve. When the return line 91 is employed, the second bridge line 63 may be omitted.

  Further, the return line 91 and the liquid supply line 41 are provided with a heat exchanger 93. The heat exchanger 93 cools the BOG flowing in the return line 91 upstream of the expansion device 92 (BOG returned to the tank 11) with LNG flowing in the liquid supply line 41. By being expanded after this cooling, the BOG returned to the tank 11 is partially reliquefied. On the other hand, the LNG flowing in the liquid feeding line 41 may be partially vaporized by taking heat from the BOG.

  Further, the regulating valve 62 provided in the first bridge line 61 is not necessarily controlled based on the flow rate Qv of VG detected by the flow meter 83. For example, a flow meter (not shown) is provided in the air supply line 21 on the upstream side of the position where the first bridge line 61 is connected, and the BOG flow rate detected by this flow meter becomes the BOG usable amount Qa. As described above, the regulating valve 62 may be controlled.

  Alternatively, the first bridge line 61 is provided with a third pressure gauge (not shown) for detecting the pressure of the first bridge line 61 on the downstream side of the regulating valve 62, and the BOG detected by the first pressure gauge 81 is provided. The adjustment valve 62 may be controlled so that the deviation between the pressure Pb and the pressure of the first bridge line 61 detected by the third pressure gauge becomes a predetermined value.

  Further, the first bridge line 61 may be provided with a pressure reducing valve that outputs a constant secondary pressure even when the primary pressure fluctuates, and a check valve, instead of the regulating valve 62. According to this configuration, VG is automatically replenished when the pressure of the BOG flowing through the air supply line 21 falls below the secondary pressure of the pressure reducing valve.

  Further, when the auxiliary gas engine 16 is not restricted by the methane number, the second supply line 51 may not include the cooler 52, the gas-liquid separator 53, and the heater 54.

  Further, one or both of the main gas engine 13 and the auxiliary gas engine 16 are not necessarily a reciprocating engine, and may be a gas turbine engine.

1A, 1B Ship 12 Compressor 13 Main gas engine 14 Pump 15 Forced vaporizer 16 Sub gas engine 21 Air supply line 31 First supply line 41 Liquid supply line 44 Extraction line 51 Second supply line 52 Cooler 53 Gas-liquid separator 61 First bridge line 62 Control valve (first control valve)
71 Return line 72 Adjustment valve (second adjustment valve)
8 control device 81 first pressure gauge 82 second pressure gauge

Claims (4)

A main gas engine for propulsion,
A tank for storing liquefied natural gas;
An air supply line for guiding boil-off gas generated in the tank to the compressor;
A first supply line for guiding boil-off gas discharged from the compressor to the main gas engine;
A sub-gas engine for power generation,
A liquid feed line for guiding liquefied natural gas discharged from a pump disposed in the tank to a forced vaporizer;
A second supply line that leads the vaporized gas generated in the forced vaporizer to the sub-gas engine;
A bridge line provided with a first adjustment valve capable of changing an opening degree, which guides the vaporized gas from the second supply line to the air supply line;
A return line provided with a second regulating valve capable of changing an opening degree, connected to the tank from the second supply line;
A control device for controlling the first regulating valve and the second regulating valve;
A ship equipped with. A first pressure gauge for detecting the pressure of the boil-off gas in the tank or the boil-off gas flowing in the air supply line;
A second pressure gauge for detecting the pressure of the vaporized gas flowing in the second supply line,
The control device calculates an available amount of boil-off gas from the amount of liquefied natural gas in the tank and the pressure of the boil-off gas detected by the first pressure gauge, and the available amount of the boil-off gas is the main gas. When the fuel gas consumption of the engine is smaller, the first adjustment valve is opened to a predetermined opening,
When the pressure of the vaporized gas detected by the second pressure gauge exceeds a threshold value while the first adjustment valve is opened to a predetermined opening, the second adjustment valve is opened from the fully closed state to the predetermined opening. The ship according to claim 1, which opens up to. A first pressure gauge for detecting the pressure of the boil-off gas in the tank or the boil-off gas flowing in the air supply line;
A second pressure gauge for detecting the pressure of the vaporized gas flowing in the second supply line,
The control device calculates an available amount of boil-off gas from the amount of liquefied natural gas in the tank and the pressure of the boil-off gas detected by the first pressure gauge, and the available amount of the boil-off gas is the main gas. When the fuel gas consumption of the engine is smaller, the first adjustment valve is opened to a predetermined opening,
When the pressure of the vaporized gas detected by the second pressure gauge exceeds a threshold value while the first adjustment valve is opened to a predetermined opening, the opening of the first adjustment valve is set to the predetermined opening. The ship according to claim 1, wherein the ship is further enlarged. The control device fully closes the second adjustment valve when the pressure of the vaporized gas detected by the second pressure gauge exceeds a threshold value while keeping the first adjustment valve in the fully closed state. The ship according to claim 2 or 3, which opens from a state to a predetermined opening degree.

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