CN108368796B

CN108368796B - Ship with a detachable cover

Info

Publication number: CN108368796B
Application number: CN201680073009.2A
Authority: CN
Inventors: 安藤明洋; 武田宏之; 印藤尚子; 安部崇嗣; 成岛直树; 桥本康平
Original assignee: Kawasaki Heavy Industries Ltd
Current assignee: Kawasaki Heavy Industries Ltd
Priority date: 2015-12-18
Filing date: 2016-12-13
Publication date: 2020-10-02
Anticipated expiration: 2036-12-13
Also published as: JP2017110621A; KR102100435B1; WO2017104633A1; JP6600248B2; KR20180090368A; CN108368796A

Abstract

A ship is provided with: a main gas engine for propulsion; a storage tank for storing LNG; a gas supply line for guiding the BOG generated in the storage tank to the compressor; a first supply line for guiding the BOG discharged from the compressor to the main gas engine; a secondary gas engine for power generation; a liquid feed line for guiding the LNG discharged from the pump disposed in the storage tank to the forced vaporizer; a second supply line for guiding VG generated by the forced gasifier to the secondary gas engine; a bridge pipeline provided with a first regulating valve with changeable opening degree, which guides VG from the second supply pipeline to the air supply pipeline; a return line provided with a second regulating valve whose opening degree can be changed, and connected from the second supply line to the storage tank; and a control device for controlling the first regulating valve and the second regulating valve.

Description

Ship with a detachable cover

Technical Field

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

Background

Conventionally, there is known a ship including a main gas engine for propulsion and a sub gas engine for power generation. For example, patent document 1 discloses a ship 100 as shown in fig. 4.

Specifically, the ship 100 includes a tank 110 for storing 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 an engine of a diesel cycle type in which the fuel gas injection pressure is high, and the sub gas engine 140 is a binary fuel engine in which the fuel gas injection pressure is low.

The storage tank 110 is connected to a high-pressure compressor 120 through a feed gas line 101, and the high-pressure compressor 120 is connected to a main gas engine 130 through a first feed line 102. The gas delivery line 101 guides the boil-off gas generated in the storage tank 110 to the high-pressure compressor 120, and the high-pressure compressor 120 compresses the boil-off gas to a high pressure (e.g., about 30 MPa). The first supply line 102 guides the high-pressure boil-off gas discharged from the high-pressure compressor 120 to the main gas engine 130.

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

In the ship 100 shown in fig. 4, a sufficient amount of fuel gas can be supplied to the main gas engine 130 even when the amount of boil-off gas generated is less than the fuel gas consumption of the main gas engine 130. Specifically, a pump 150 is disposed in the storage tank 110, and the pump 150 is connected to a Suction tank (Suction) 160 through a first supply line 104. The suction tank 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 a fourth supply line 107 from the gas heater 180 is connected to the first supply line 102.

A connection line 190 branches off from the first supply line 102 on the downstream side of the position where the fourth supply line 107 is connected, and the second supply line 103 is connected to the connection line 190. The connecting pipe 190 is provided with a check valve 191 having a pressure adjusting function. That is, the high-pressure gas in the first supply line 102 can be depressurized and supplied to the sub-gas engine 140.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2015-145243.

Disclosure of Invention

The problems to be solved by the invention are as follows:

however, in the ship 100 shown in fig. 4, when the amount of boil-off gas generated is less than the consumption amount of the main gas engine 130, the high-pressure pump 170 needs to be operated 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 by the sub-gas engine 140, which is a two-fuel engine, as much as possible, but the high-pressure pump 170 must be operated to achieve this.

Accordingly, an object of the present invention is to provide a ship 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.

Means for solving the problems:

to solve the above problem, a ship according to the present invention includes: a main gas engine for propulsion; a tank for storing liquefied natural gas; a gas supply line for guiding the boil-off gas generated in the storage tank to a compressor; a first supply line for guiding the evaporated gas discharged from the compressor to the main gas engine; a secondary gas engine for power generation; a liquid feed line for guiding liquefied natural gas discharged from a pump disposed in the storage tank to a forced gasifier; a second supply line for guiding the gasified gas generated by the forced gasifier to the secondary gas engine; a bridge pipeline provided with a first regulating valve with changeable opening degree, wherein the bridge pipeline guides the gasified gas from the second supply pipeline to the gas supply pipeline; a return line provided with a second regulating valve whose opening degree can be changed, the return line being connected from the second supply line to the storage tank; and a control device that controls the first regulating valve and the second regulating valve.

According to the above configuration, since the liquefied natural gas is forcibly gasified by the forced gasifier and the gasified gas is supplied to the sub gas engine, a sufficient amount of fuel gas can be supplied to the sub gas engine without using a high-pressure pump. Thus, it is possible to eliminate the need for burning fuel oil or to suppress the fuel oil consumption in the sub-gas engine. In addition, when the consumption of the evaporated gas with respect to the fuel gas of the main gas engine is insufficient, the evaporated gas generated by the forced gasifier can be joined to the evaporated gas sucked into the compressor through the bridge pipe. Therefore, a sufficient amount of fuel gas can be supplied to the main gas engine without using a high-pressure pump. In addition, the term "without using the high-pressure pump" does not mean that the high-pressure pump cannot be equipped on the ship as a substitute means in the case of a compressor failure.

While the gasified gas flows through the bridge line, in other words, while the first regulator valve provided in the bridge line is open, the gasified gas supplied to the sub-gas engine through the second supply line may be excessive. At this time, the excess vaporized gas can be returned to the storage tank by opening the second regulating valve provided in the return line.

The ship may further include: a first pressure gauge that detects a pressure of the boil-off gas in the storage tank or the boil-off gas flowing through the gas supply line; and a second pressure gauge that detects a pressure of the vaporized gas flowing through the second supply line; the controller calculates an available amount of boil-off gas from an amount of liquefied natural gas in the tank and a pressure of the boil-off gas measured by the first pressure gauge, opens the first regulating valve to a predetermined opening degree when the available amount of boil-off gas is less than a fuel gas consumption amount of the main gas engine, and opens the second regulating valve from a fully closed state to the predetermined opening degree when a pressure of the boil-off gas measured by the second pressure gauge is higher than a threshold value while the first regulating valve is opened at the predetermined opening degree. According to this configuration, the pressure change in the second supply line can be followed without being affected by a response delay of the forced gasifier, that is, without being affected by an excess or deficiency in the amount of the generated gasification gas. Further, even if the fuel gas consumption of the sub-gas engine is reduced, the minimum flow rate of the forced gasifier can be maintained.

The ship may further include: a first pressure gauge that detects a pressure of the boil-off gas in the storage tank or the boil-off gas flowing through the gas supply line; and a second pressure gauge that detects a pressure of the vaporized gas flowing through the second supply line; the controller calculates an available amount of boil-off gas from an amount of liquefied natural gas in the tank and a pressure of the boil-off gas measured by the first pressure gauge, opens the first regulating valve to a predetermined opening degree when the available amount of boil-off gas is less than a fuel gas consumption amount of the main gas engine, and changes the opening degree of the first regulating valve from the predetermined opening degree to a larger opening degree when a pressure of the boil-off gas measured by the second pressure gauge is higher than a threshold value while the first regulating valve is opened at the predetermined opening degree. According to this configuration, in addition to the effect of being able to follow the pressure change in the second supply line without being affected by the response delay of the forced gasifier and the effect of being able to maintain the minimum flow rate of the forced gasifier, the effect of being able to suppress the amount of heat input to the storage tank is obtained as compared with the case where the excessive gasified gas is returned to the storage tank through the return line.

The controller may open the second regulating valve from the fully closed state to a predetermined opening degree when the pressure of the boil-off gas measured by the second pressure gauge is higher than a threshold value while the first regulating valve is kept in the fully closed state. According to this configuration, even when the gasified gas supplied to the sub-gas engine through the second supply pipe is excessive when the gasified gas is not circulated in the bridge pipe, the excessive gasified gas can be returned to the storage tank.

The invention has the following effects:

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

Drawings

Fig. 1 is a schematic configuration diagram of a ship according to an embodiment of the present invention;

FIG. 2 is a graph showing the relationship between the difference in pressure of boil-off gas in the storage tank from the set pressure and the available amount of boil-off gas;

fig. 3 is a schematic configuration diagram of a ship according to a modification;

fig. 4 is a schematic configuration diagram of a conventional ship.

Detailed Description

Fig. 1 shows a ship 1A according to an embodiment of the 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 (i.e., for an onboard power supply).

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 (cargo tank). That is, the tank 11 shown in fig. 1 is one of a plurality of cargo tanks. In the illustrated example, the main gas engine 13 and the sub gas engine 16 are provided separately, but a plurality of main gas engines 13 may be provided, or a plurality of sub gas engines 16 may be provided.

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

The main gas engine 13 is a two-stroke engine of a diesel cycle type having a high fuel gas injection pressure of, for example, about 20 to 35 MPa. However, the main gas engine 13 may be an otto cycle type two-stroke engine having a fuel gas injection pressure of about 1 to 2MPa, for example, as a medium pressure. 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 engine that burns only fuel gas, or may be a binary fuel engine that burns one or both of fuel gas and fuel oil (in the case of a binary fuel engine, an otto cycle may be used when fuel gas is burned, and a diesel cycle may be used when fuel oil is burned).

The sub-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 1MPa, and is connected to a generator (not shown). The sub-gas engine 16 may be a gas-only engine that burns only the fuel gas, or may be a binary fuel engine that burns one or both of the fuel gas and the fuel oil.

The fuel Gas of the main Gas engine 13 is mainly Boil-Off Gas (hereinafter referred to as BOG) generated by natural heat input of LNG in the storage tank 11, and the fuel Gas of the sub Gas engine 16 is mainly gasified Gas (hereinafter referred to as VG) obtained by forcibly gasifying LNG.

Specifically, the accumulator 11 is connected to the compressor 12 through the air supply line 21, and the compressor 12 is connected to the main gas engine 13 through the first supply line 31. A pump 14 is disposed in the tank 11, and the pump 14 is connected to the forced vaporizer 15 through a liquid feed line 41. The forced gasifier 15 is connected to the secondary gas engine 16 via a second supply line 51.

The supply line 21 leads the BOG generated in the storage tank to the compressor 12. In the present embodiment, the compressor 12 is a multi-stage 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 when the fuel gas injection pressure of the main gas engine 13 is low, for example.

The liquid feed line 41 guides the LNG discharged from the pump 14 to the forced vaporizer 15. The liquid feed line 41 is provided with an adjustment valve 42 whose opening degree can be changed. The forced gasifier 15 forcibly gasifies the LNG using, for example, boiler generated steam as a heat source and generates VG. The second supply line 51 guides VG generated by the forced gasifier 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 this order from the upstream side. The cooler 52 cools the VGs generated by the forced gasifier 15 and generates a liquid component having a component other than methane as a main component. The resultant liquid component is collected by the gas-liquid separator 53. Thereby, since most of the heavy components (for example, ethane, propane, butane, etc.) are removed from the VGs, the VGs having a high methane value can be supplied to the secondary gas engine 16. The liquid component collected by the gas-liquid separator 53 is returned to the storage tank 11 through a drain line. VG passing through the gas-liquid separator 53 is heated by the heater 54. Thereby, VG having an appropriate temperature can be supplied to the sub gas engine 16.

With respect to the cooler 52, more specifically, the cooler 52 is connected to the extraction line 44. The drawing line 44 branches off from the liquid sending line 41 on the upstream side of the regulating valve 42. The suction line 44 is provided with an adjustable valve 45 having an adjustable opening. The cooler 52 cools the VGs by injecting LNG supplied from the extraction line 44 into the VGs.

Further, a first bridge pipe 61 is connected to the air supply pipe 21 from the second supply pipe 51. In the present embodiment, the upstream end of the first bridge conduit 61 connects the second supply conduit 51 between the cooler 52 and the gas-liquid separator 53, but the upstream end of the first bridge conduit 61 may connect the second supply conduit 51 on the upstream side of the cooler 52, between the gas-liquid separator 53 and the heater 54, or on the downstream side of the heater 54. When the BOG is insufficient for the fuel gas consumption Q1 of the main gas engine 13, the first bridge pipe 61 guides VG from the second supply pipe 51 to the air supply pipe 21. As a result, the BOG and VG are supplied to the main gas engine 13 as the fuel gas.

From the middle of the compressor 12 there is a second bridge line 63 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 may be connected to the second supply line 51 on the upstream side of the heater 54. The second bridge line 63 leads the BOG from the compressor 12 to the second supply line 51 when the BOG is excessive with respect to the fuel gas consumption Q1 of the main gas engine 13. As a result, VG and BOG (only BOG may be supplied) as fuel gas to the sub gas engine 16.

The first bridge line 61 is provided with a variable opening degree adjustment valve 62 (corresponding to a first adjustment valve of the present invention), and the second bridge line 63 is provided with a variable opening degree adjustment valve 64. In the present embodiment, the regulating

valves

62 and 64 each function to open and close the bridge line (61 or 63). However, an on-off valve may be provided in addition to the regulator valve (62 or 64) in each of the first bridge line 61 and the second bridge line 63.

In the present embodiment, the pump 14 discharges LNG so that the pressure of VG generated by the forced gasifier 15 (in other words, the outlet pressure of the forced gasifier 15) becomes higher than the fuel gas supply pressure of the sub-gas engine 16. That is, the pressure of VG flowing through the second supply line 51 is higher than the pressure of BOG in the tank 11. Therefore, the regulator 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 pipe 21 is provided with a check valve 22 on the upstream side of the position where the first bridge pipe 61 is connected. Thereby, VG from the first bridge line 61 is prevented from flowing into the storage tank 11.

In the present 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 connects the second supply line 51 between the gas-liquid separator 53 and the heater 54, but the upstream end of the return line 71 may connect the second supply line 51 between the cooler 52 and the gas-liquid separator 53. The downstream end of the return line 71 may be located above the liquid level of the LNG in the tank 11 or below the liquid level.

The return line 71 is provided with an adjustment valve 72 (corresponding to a second adjustment valve of the present invention) whose opening degree can be changed. In the present embodiment, the regulating valve 72 functions to open and close the return line 71. However, the return line 71 may be provided with an on-off valve in addition to the control valve 72.

The control device 8 controls the

control valves

42, 45, 62, 64, 72. In fig. 1, only a part of the signal lines is shown for simplicity. The control device 8 is connected to 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.

The first pressure gauge 81 detects the pressure Pb of the BOG flowing through the air supply pipe 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 it is located on the upstream side of the position of the air supply pipe 21 to which the first bridge pipe 61 is connected. 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 the VG flowing through the second supply line 51. The second pressure gauge 82 is located on the downstream side of the position of the second supply line 51 to which the second bridge line 63 is connected. However, when the second pressure gauge 82 is used only for controlling the regulator valve 72 provided in the return line 71 described later, the second pressure gauge 82 may be located upstream of the position where the second bridge line 63 is connected to the second supply line 51. The flow meter 83 detects a flow rate Fv of VG flowing through the first bridge line 61. The thermometer 84 detects the outlet temperature of the cooler 52.

Various signals are transmitted to the control device 8 from a first gas engine controller (not shown) that controls the fuel gas injection timing and the like of the main gas engine 13 and a second gas engine controller (not shown) that controls the fuel gas injection timing and the like of the sub gas engine 16. Then, the controller 8 calculates a fuel gas consumption Q1 of the main gas engine 13 from the signal transmitted from the first gas engine controller, and calculates a fuel gas consumption Q2 of the sub gas engine 16 from the signal transmitted from the second gas engine controller. However, the controller 8 may directly obtain the fuel gas consumption Q1 from the first gas engine controller, or may directly obtain the fuel gas consumption Q2 from the second gas engine controller.

The controller 8 first calculates the amount Qa of the BOG available from the amount of LNG in the tank 11 and the pressure Pb of the BOG measured by the first pressure gauge 81. Specifically, the controller 8 calculates the pressure Pt of the BOG in the tank 11 by adding the pressure Pb of the BOG measured by the first pressure gauge 81 to the pressure loss from the upstream end of the air supply pipe 21 to the position of the first pressure gauge 81. As shown in fig. 2, the usable amount Qa of the BOG increases as the difference Δ P (Pt — Ps) between the pressure Pt of the BOG in the tank 11 and the set pressure Ps increases. Here, the set pressure Ps is a pressure at which the available amount Qa of the BOG is equal to the generated amount Qn of the BOG. The amount Qn of BOG generation varies depending on the pressure of BOG in the tank 11, but generally depends on the amount of LNG in the tank 11. Since the tank 11 as the cargo tank has a very large capacity, the height of the LNG liquid level in the tank 11 does not change even when BOG and/or LNG is used as the fuel gas. Therefore, in the present embodiment, the amount of LNG in the tank 11 is treated as a constant value (different between the full load time and the empty load time) instead of a variable. Then, the controller 8 calculates the usable amount Qa of BOG from the amount of LNG in the tank 11 and the difference Δ P between the calculated pressure Pt of BOG in the tank 11 and the set pressure Ps. However, when the capacity of the tank 11 is small, a level meter for detecting 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 controls the regulating valve 42 provided in the liquid feed line 41 so that an insufficient amount of LNG obtained by subtracting the available BOG 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 sub gas engine 16, is supplied to the forced gasifier 15 through the liquid feed line 41. Further, a return line 43 branches off from the liquid supply line 41 on the upstream side of the regulating valve 42, and the LNG discharged from the pump 14 is returned to the tank 11 through the return line 43 by an amount limited to the regulating valve 42. The control device 8 controls the regulating valve 45 provided in the extraction line 44 based on the outlet temperature of the cooler 52 measured by the thermometer 84.

When the available BOG amount Qa is larger than the fuel gas consumption Q1 of the main gas engine 13 (when the BOG is excessive with respect to the fuel gas consumption Q1 of the main gas engine 13), the controller 8 completely closes the regulating valve 62 provided in the first bridge pipe 61 and opens the regulating valve 64 provided in the second bridge pipe 63 to a predetermined opening degree.

Conversely, when the available BOG amount Qa is smaller than the fuel gas consumption Q1 of the main gas engine 13 (when the BOG is insufficient for the fuel gas consumption Q1 of the main gas engine 13), the controller 8 completely closes the regulating valve 64 provided in the second bridge pipe 63 and opens the regulating valve 62 provided in the first bridge pipe 61 to a predetermined opening degree. At this time, the controller 8 controls the regulating valve 62 so that the flow rate Qv of VG measured by the flowmeter 83 becomes the difference Δ a (Q1-Qa) between the fuel gas consumption Q1 of the main gas engine 13 and the available amount Qa of BOG.

As described above, in the ship 1A of the present embodiment, since the LNG is forcibly vaporized by the forced vaporizer 15 and VG thereof is supplied to the sub gas engine 16, a sufficient amount of fuel gas can be supplied to the sub gas engine 16 without using a high-pressure pump. This eliminates the need to burn fuel oil or reduces the fuel oil consumption in the sub-gas engine 16. When the BOG is insufficient for the fuel gas consumption Q1 of the main gas engine 13, VG generated by the forced gasifier 15 can be merged with the BOG drawn into the compressor 12 through the first bridge pipe 61. Therefore, a sufficient amount of fuel gas can be supplied to the main gas engine 13 without using a high-pressure pump.

While VG flows through the first bridge line 61, in other words, while the regulator valve 62 provided in the first bridge line 61 is open, VG supplied to the sub-gas engine 16 through the second supply line 51 may be excessive. On the other hand, since the return line 71 is provided in the present embodiment, when VG of this kind is excessive, the excessive VG can be returned to the storage tank 11 by opening the regulating valve 72 provided in the return line 71.

In particular, when the forced gasifier 15 uses steam as a heat source and the cooler 52 is provided downstream of the forced gasifier 15, LNG needs to be supplied to the forced gasifier 15 at a certain flow rate in order to ensure controllability of the outlet temperature of the cooler 52. In other words, there is a minimum flow across the forced gasifier 15. In such a configuration, excessive VGs are generated not only temporarily as the load of the slave gas engine 16 decreases but also constantly when the fuel gas consumption of the slave gas engine 16 is lower than the minimum flow rate of the forced gasifier 15. Therefore, the return line 71 is particularly useful for the above-described structure.

Specifically, in the present embodiment, the control device 8 opens the regulating valve 72 provided in the return line 71 from the fully closed state to the predetermined opening degree when the pressure Pv of the VG measured by the second pressure gauge 82 is higher than the threshold value α while the regulating valve 62 is opened at the predetermined opening degree. With such control, the pressure change in the second supply line 51 can be followed without being affected by a response delay of the forced gasifier 15, that is, without being affected by an excess or deficiency of the generated VG amount. Further, even if the fuel gas consumption of the sub-gas engine 16 is reduced, the minimum flow rate of the forced induction vaporizer 15 can be maintained.

Alternatively, the control device 8 may change the opening degree of the regulating valve 62 from the predetermined opening degree to a larger value instead of opening the regulating valve 72 from the fully closed state to the predetermined opening degree when the pressure Pv of the VG measured by the second pressure gauge 82 is higher than the threshold value α while the regulating valve 62 is opened at the predetermined opening degree. Such control has the effect of being able to follow the pressure change in the second supply line 51 without being affected by the response delay of the forced gasifier 15, and the effect of being able to maintain the minimum flow rate of the forced gasifier 15, and also has the effect of being able to suppress the amount of heat input to the storage tank 11 compared to the case where excess VG is returned to the storage tank 11 through the return line 71.

While the control valve 62 is maintained in the fully closed state, the control device 8 may open the control valve 72 from the fully closed state to a predetermined opening degree when the pressure Pv of VG measured by the second pressure gauge 82 is higher than the threshold value α. In this way, when no VG flows through the first bridge line 61, even when there is an excess of VG supplied to the slave gas engine 16 through the second supply line 51, the excess VG can be returned to the storage tank 11.

(modification example)

The present invention is not limited to the above-described embodiments, and various modifications are possible within a range not departing from the gist of the present invention.

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

As shown in fig. 3, the ship 1B according to the modification may be configured such that a return line 91 branches off from the first supply line 31, and the tank 11 is connected to the return line 91. The tip end of the return line 91 may be located above the liquid level of the LNG in the tank 11 or below the liquid level. An expansion device 92 such as an expansion valve is provided in the return line 91. When the return line 91 is used, the second bridge line 63 may be omitted.

The return line 91 and the liquid feed line 41 are provided with a heat exchanger 93. The heat exchanger 93 cools the BOG (BOG returned to the storage tank 11) flowing through the return line 91 on the upstream side of the expansion device 92 by the LNG flowing through the liquid supply line 41. The BOG portion returned to the storage tank 11 is reliquefied by expansion after the cooling. On the other hand, LNG flowing through the liquid delivery line 41 may be partially vaporized by extracting heat from BOG.

The regulating valve 62 provided in the first bridge line 61 is not necessarily controlled based on the flow rate Qv of VG measured by the flow meter 83. For example, the supply pipe 21 may be provided with a flow meter (not shown) on the upstream side of the position connected to the first bridge pipe 61, and the control valve 62 may be controlled so that the flow rate of BOG measured by the flow meter becomes the usable amount Qa of BOG.

Alternatively, a third pressure gauge (not shown) for detecting the pressure of the first bridge pipe 61 may be provided on the first bridge pipe 61 downstream of the regulating valve 62, and the regulating valve 62 may be controlled so that the difference between the pressure Pb of the BOG measured by the first pressure gauge 81 and the pressure of the first bridge pipe 61 measured by the third pressure gauge becomes a predetermined value.

Instead of the regulator valve 62, the first bridge conduit 61 may be provided with a pressure reducing valve and a check valve that can output a constant secondary pressure even if the primary pressure changes. According to this configuration, VG is automatically supplied when the pressure of BOG flowing through the air supply line 21 is lower than the secondary pressure of the pressure reducing valve.

When the sub-gas engine 16 is not limited by the methane value, the cooler 52, the gas-liquid separator 53, and the heater 54 may not be provided in the second supply line 51.

One or both of the main gas engine 13 and the sub gas engine 16 are not necessarily reciprocating engines, and may be gas turbine engines.

Description of the symbols:

1A, 1B vessel;

12 a compressor;

13 a main gas engine;

14 a pump;

15 forced gasifier;

16 pairs of gas engines;

21 an air supply pipeline;

31 a first supply line;

41 liquid conveying pipeline;

44 a draw line;

51 a second supply line;

a cooler 52;

53 gas-liquid separator;

61 a first bridge conduit;

62 regulating valve (first regulating valve);

71 a return line;

72 regulating valve (second regulating valve);

8 a control device;

81 a first pressure gauge;

82 second pressure gauge.

Claims

1. A ship is characterized by comprising:

a main gas engine for propulsion;

a tank for storing liquefied natural gas;

a gas supply line for guiding the boil-off gas generated in the storage tank to a compressor;

a first supply line for guiding the evaporated gas discharged from the compressor to the main gas engine;

a secondary gas engine for power generation;

a liquid feed line for guiding liquefied natural gas discharged from a pump disposed in the storage tank to a forced gasifier;

a second supply line for guiding the gasified gas generated by the forced gasifier to the secondary gas engine;

a bridge pipeline provided with a first regulating valve capable of changing the opening degree, the bridge pipeline guiding the gasified gas from the second supply pipeline to the gas supply pipeline;

a return line provided with a second regulating valve capable of changing the opening degree, the return line being connected from the second supply line to the storage tank; and

a control device that controls the first regulating valve and the second regulating valve;

further provided with:

a first pressure gauge that detects a pressure of the boil-off gas in the storage tank or the boil-off gas flowing through the gas supply line; and

a second pressure gauge that detects a pressure of the gasification gas flowing through the second supply line;

the controller calculates an available amount of boil-off gas from an amount of liquefied natural gas in the storage tank and a pressure of the boil-off gas measured by the first pressure gauge, and opens the first regulating valve to a predetermined opening degree when the available amount of boil-off gas is less than a fuel gas consumption amount of the main gas engine, and the controller opens the first regulating valve to a predetermined opening degree when the available amount of boil-off gas is less than the fuel gas consumption amount of the main gas engine

And a second pressure gauge for measuring a pressure of the vaporized gas, the second pressure gauge being configured to measure a pressure of the vaporized gas, and the second pressure gauge being configured to open the second regulating valve from a fully closed state to a predetermined opening degree while the first regulating valve is opened at the predetermined opening degree.

2. The vessel according to claim 1,

the controller opens the second regulating valve from the fully closed state to a predetermined opening degree when the pressure of the boil-off gas measured by the second pressure gauge is higher than a threshold value while the first regulating valve is kept in the fully closed state.

3. A ship is characterized by comprising:

a main gas engine for propulsion;

a tank for storing liquefied natural gas;

a secondary gas engine for power generation;

further provided with:

While the first regulating valve is opened at a predetermined opening degree, the opening degree of the first regulating valve is changed from the predetermined opening degree to a larger opening degree when the pressure of the boil-off gas measured by the second pressure gauge is higher than a threshold value.

4. The vessel according to claim 3,