CN111065576B

CN111065576B - Ship and liquefied petroleum gas temperature/pressure management method

Info

Publication number: CN111065576B
Application number: CN201880056759.8A
Authority: CN
Inventors: 野崎拓海; 高木俊宏; 武田宏之; 印藤尚子; 萩原和也; 宍粟雄辉; 安部崇嗣; 成岛直树
Original assignee: Kawasaki Jukogyo KK
Current assignee: Kawasaki Motors Ltd
Priority date: 2017-09-08
Filing date: 2018-09-07
Publication date: 2022-05-17
Anticipated expiration: 2038-09-07
Also published as: JP6959804B2; CN111065576A; SG11202001766UA; KR102316444B1; KR20200047640A; WO2019050004A1; JP2019048507A

Abstract

The ship has a fuel tank, a propulsion engine, a fuel supply line, a pump, a fuel recovery line, a bypass line, a pressure gauge, and a control device. When the pressure of the gas layer in the fuel tank detected by the pressure gauge is equal to or lower than a predetermined value while the LPG is not used as fuel, the control device operates the pump to circulate the LPG in the fuel tank to the fuel tank via the engine and/or the bypass line.

Description

Ship and liquefied petroleum gas temperature/pressure management method

Technical Field

The present invention relates to a ship including an LPG-fueled propulsion engine.

Background

In a conventional ship, a fuel of a propulsion engine is generally a fuel oil such as heavy oil or light oil, or LNG (Liquefied Natural Gas). In recent years, it has been proposed to use LPG (Liquefied Petroleum Gas) as a fuel for a propulsion engine. For example, patent document 1 discloses a ship that supplies LPG from a fuel tank to a propulsion engine in a liquid state.

Documents of the prior art

Patent document

Patent document 1: korea laid-open patent publication No. 2012-0113398

Disclosure of Invention

Problems to be solved by the invention

In the case of using LPG as fuel, it is conceivable to connect a fuel tank and a propulsion engine via a fuel supply line and a fuel recovery line, and use LPG in the engine in a required amount while circulating between the fuel tank and the engine.

However, as described above, when the LPG is circulated between the fuel tank and the engine, it is preferable to supply a slightly larger amount of fuel to the engine than the fuel consumption of the engine. To achieve this, it is considered to adjust the rotation speed of a pump provided in a fuel supply line according to the fuel consumption of the engine. In order to properly inject fuel into the engine, it is necessary to keep the fuel supply pressure to the engine at a certain value or more. Therefore, it is preferable to set the minimum rotation speed for the pump.

For example, in order to keep LPG containing propane gas as a main component as a liquid under atmospheric pressure, it is necessary to keep the fuel tank at-42 ℃ or lower. Therefore, it is considered that the temperature of the LPG in the fuel tank changes following the atmospheric temperature by using the fuel tank as a pressure vessel. That is, the equilibrium state of the LPG is maintained by the high pressure in the fuel tank. However, in such a case, the pressure of the gas layer in the fuel tank (saturated vapor pressure in the case where the gas layer component is only vaporized PG) greatly changes depending on the temperature of LPG in the fuel tank. When the temperature of LPG in the fuel tank is low, the pressure to be boosted by the pump is large, and when the temperature of LPG in the fuel tank is high, the pressure to be boosted by the pump is small.

Therefore, when the temperature of the LPG in the fuel tank is low (when the pressure of the gas layer is low and the pressure range to be boosted by the pump is large), the supply pressure of the LPG may not be boosted to the pressure required by the engine when the LPG is used as fuel, and the engine may not be operated smoothly.

Accordingly, an object of the present invention is to provide a ship capable of smoothly operating a propulsion engine when starting to use LPG.

Means for solving the problems

A ship according to one embodiment of the present invention includes: a fuel tank that stores liquefied petroleum gas so that the temperature of the liquefied petroleum gas changes in accordance with the atmospheric temperature; a propulsion engine using liquefied petroleum gas as fuel; a fuel supply line that supplies liquefied petroleum gas from the fuel tank to the engine; a pump provided to the fuel supply line; a fuel recovery line that recovers unused liquefied petroleum gas from the engine to the fuel tank; a pressure gauge that detects a pressure of a gas layer in the fuel tank; and a control device that controls a rotation speed of the pump, wherein the control device operates the pump to circulate the liquefied petroleum gas in the fuel tank to the fuel tank via the engine when a pressure detected by the pressure gauge is equal to or lower than a predetermined value while the liquefied petroleum gas is not used as fuel.

Another aspect of the present invention provides a ship comprising: a fuel tank that stores liquefied petroleum gas so that the temperature of the liquefied petroleum gas changes in accordance with the atmospheric temperature; a propulsion engine using liquefied petroleum gas as fuel; a fuel supply line that supplies liquefied petroleum gas from the fuel tank to the engine; a pump provided to the fuel supply line; a fuel recovery line that recovers unused liquefied petroleum gas from the engine to the fuel tank; a bypass line branching from the fuel supply line on a downstream side of the pump and connected to the fuel recovery line or the fuel tank; a pressure gauge that detects a pressure of a gas layer in the fuel tank; and a control device that controls a rotation speed of the pump, wherein the control device operates the pump to circulate the liquefied petroleum gas in the fuel tank to the fuel tank via the engine and/or the bypass line when a pressure detected by the pressure gauge is equal to or lower than a predetermined value while the liquefied petroleum gas is not used as fuel.

An LPG temperature/pressure management method according to an aspect of the present invention is applied to a ship having: a fuel tank that stores liquefied petroleum gas so that the temperature of the liquefied petroleum gas changes in accordance with the atmospheric temperature; a propulsion engine using liquefied petroleum gas as fuel; a fuel supply line that supplies liquefied petroleum gas from the fuel tank to the engine; a pump provided to the fuel supply line; and a fuel recovery line that recovers unused liquefied petroleum gas from the engine to the fuel tank, wherein the pump is operated to circulate the liquefied petroleum gas in the fuel tank to the fuel tank via the engine when a condition that a pressure of a gas layer in the fuel tank is lower than a predetermined value, a condition that a temperature of the liquefied petroleum gas in the fuel tank is lower than a predetermined value, and/or a condition that a pump operation command member is operated by a crew member are satisfied during a period in which the liquefied petroleum gas is not used as a fuel.

According to this configuration, if the pressure of the inner gas layer is low during a period in which LPG is not used as fuel, the pump operates to circulate LPG. The temperature of the LPG rises as it passes through the pump due to the incoming heat from the pump. In addition, the temperature of the engine can be raised by heat from the engine. By returning the LPG whose temperature has been raised during the circulation to the fuel tank in this way, the temperature of the LPG in the fuel tank can be raised, and the pressure of the gas layer can also be raised. Therefore, when starting to use the LPG, the supply pressure of the LPG can be increased to the pressure required by the engine by the pump, and the engine can be smoothly operated.

Effects of the invention

According to the present invention, it is possible to provide a ship capable of smoothly operating a propulsion engine at the start of using LPG.

Drawings

Fig. 1 is a schematic configuration diagram of a ship according to embodiment 1.

Fig. 2 is a schematic configuration diagram of a ship according to embodiment 2.

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

Detailed Description

Hereinafter, embodiments will be described with reference to the drawings. Throughout the drawings, the same or corresponding elements are denoted by the same reference numerals, and overlapping detailed description is omitted.

(embodiment 1)

Fig. 1 shows a ship of embodiment 1. The ship 1 includes a fuel tank 2 for storing LPG so that the temperature of the LPG changes in accordance with the atmospheric temperature, and a propulsion engine 11 using LPG as fuel. The main component of LPG may be propane (propane gas) or butane (butane gas).

In the present embodiment, the fuel tank 2 is composed of a large-volume storage tank 21 and a small-volume service tank 22. The storage tank 21 and the service tank 22 are pressure vessels having a pressure higher than atmospheric pressure. The storage tank 21 and the service tank 22 are connected to each other by a trunk line 26.

LPG is introduced from an LPG supply source into the storage tank 21 through a fuel introduction line 23. The LPG supply source may be a cargo tank mounted on the vessel 1, or may be an LPG supply facility or an LPG fuel supply ship on the land.

A pump 25 is provided inside the storage tank 21. The number of the pumps 25 may be 1 or more. The upstream end of the trunk line 26 is connected to the pump 25. The downstream end of the trunk line 26 opens into the service tank 22. LPG is supplied from the storage tank 21 to the service tank 22 via a trunk line 26 by a pump 25. However, the pump 25 may be provided outside the storage tank 21 on the way of the line 26.

In the present embodiment, no means (e.g., a heat insulating material) for maintaining the LPG at a low temperature is provided in the storage tank 21, and the temperature of the LPG in the storage tank 21 changes in accordance with the atmospheric temperature. On the other hand, LPG introduced from the LPG supply source is often about-42 ℃ when LPG is propane gas. Therefore, a heater 24 for heating LPG to, for example, -5 ℃ or higher is provided in the fuel introduction line 23. However, if a heater is installed on an onshore LPG supply facility or an LPG fuel supply ship as an LPG supply source and the temperature of LPG transferred to the ship 1 is set to-5 ℃ or higher, the heater 24 is not required.

When the component of the gas layer in the storage tank 21 is only vaporized PG, the pressure of the gas layer in the storage tank 21 is the saturation vapor pressure of LPG. For example, in the case where the temperature in the storage tank 21 is 25 ℃, the pressure of the gas layer (saturated vapor pressure) in the storage tank 21 is about 0.9MPa under gauge pressure. Hereinafter, the pressure is shown as a gauge pressure. Since the saturated vapor pressure of LPG is about 1.7MPa at 50 ℃, the storage tank 21 is configured to be able to withstand up to 1.8MPa, for example. For reference, the saturated vapor pressure of LPG is about 0.4MPa at 0 deg.C.

As in the storage tank 21, the service tank 22 is not provided with a mechanism for maintaining the LPG at a low temperature, and the temperature of the LPG in the service tank 22 changes in accordance with the atmospheric temperature. In the case where the composition of the gas layer in the service tank 22 is only vaporized PG, the pressure of the gas layer in the service tank 22 is the saturated vapor pressure of LPG.

In the circulation of LPG between the engine 11 and the service tank 22 as described later, the temperature of LPG in the service tank 22 may be higher than the atmospheric temperature. For example, in the case where the temperature of LPG in the service tank 22 is 60 ℃, the pressure of the gas layer (saturated vapor pressure) in the service tank 22 is about 2.1 MPa. The service tank 22 is configured to be able to withstand, for example, 2.2 MPa.

The service tank 22 is connected to the propulsion engine 11 through a fuel supply line 31 and a fuel recovery line 41. LPG is supplied from the service tank 22 to the engine 11 through the fuel supply line 31, and unused LPG is recovered from the engine 11 to the service tank 22 through the fuel recovery line 41. In other words, LPG circulates between the service tank 22 and the engine 11 through the fuel supply line 31 and the fuel recovery line 41.

An upstream end of the fuel supply line 31 is connected to a lower portion of the service tank 22. The downstream end of the fuel recovery line 41 opens in the service tank 22.

The engine 11 is, for example, a reciprocating engine of a diesel cycle or an otto cycle. Although not shown, the engine 11 includes: a main flow path connecting a downstream end of the fuel supply line 31 and an upstream end of the fuel recovery line 41; and a plurality of fuel injection valves connected in parallel with the main flow path.

The fuel supply line 31 is provided with a pump 32, a heater 33, and a shutoff valve 34 in this order from the upstream side. The heater 33 heats the LPG to a required temperature (e.g., 45 ℃) of the engine 11.

The junction line 26 is provided with a heater 27 for heating the LPG supplied from the storage tank 21 to the service tank 22. During operation of the engine 11, LPG in an amount corresponding to the fuel consumption Qe of the engine 11 is supplied from the storage tank 21 to the service tank 22. The heater 27 is used when it is difficult to heat the engine 11 to the required temperature only by the heater 33. In addition, the heater 27 may be omitted.

The 1 st pressure regulating valve 42, the shutoff valve 43, the cooler 44, and the 2 nd pressure regulating valve 45 are provided in this order from the upstream side in the fuel recovery line 41. The cooler 44 cools the LPG to a prescribed temperature (e.g., 40 ℃). In addition, the cooler 44 may be omitted.

In the present embodiment, the fuel supply line 31 and the fuel recovery line 41 are connected by the 1 st bypass line 51. The 1 st bypass line 51 branches from the fuel supply line 31 between the heater 33 and the shutoff valve 34, and is connected to the fuel recovery line 41 between the shutoff valve 43 and the cooler 44. A flow control valve 52 is provided in the 1 st bypass line 51.

In the present embodiment, the 2 nd bypass line 53 is also used. The 2 nd bypass line 53 branches from the fuel supply line 31 between the pump 32 and the heater 33, and is connected to the service tank 22. A flow control valve 54 is provided in the 2 nd bypass line 53. However, either one of the 1 st bypass line 51 and the 2 nd bypass line 53 may be omitted.

The pump 32, the

shutoff valves

34 and 43, the

pressure regulating valves

42 and 45, and the flow

rate control valves

52 and 54 are controlled by the control device 6. However, in fig. 1, only a part of the signal lines is depicted for simplification of the drawing. The control device 6 is a computer having a memory such as a ROM or a RAM and a CPU, and a program stored in the ROM is executed by the CPU. The control device 6 may be a single device or may be divided into a plurality of devices (for example, an engine control device and a fuel supply control device).

The control device 6 is electrically connected to the 1 st to 3 rd pressure gauges 71 to 73 and the flow meter 81. The 1 st pressure gauge 71 and the flow meter 81 are used for controlling the pump 32 and the flow

rate control valves

52 and 54, the 2 nd pressure gauge 72 is used for controlling the 1 st pressure regulating valve 42, and the 3 rd pressure gauge 73 is used for controlling the 2 nd pressure regulating valve 45.

Here, the engine 11 may be an engine using only LPG as fuel, or may be a dual-fuel engine using LPG and fuel oil such as heavy oil or light oil as fuel.

In the case of an engine using only LPG as fuel, the timing to start using LPG as fuel corresponds to the timing to start the operation of the engine 11. The period during which the LPG is stopped corresponds to the period during which the engine 11 is stopped.

In the case of a dual-fuel engine, the timing to start using LPG as fuel includes a timing to start the operation of the engine 11 and a timing to switch the fuel used by the engine 11 to LPG or add LPG to the fuel used by the engine 11 while the engine 11 is in operation. The period in which the use of LPG is stopped includes a period in which the engine 11 is stopped and a period in which the engine 11 is operated using only fuel oil as fuel.

The control device 6 closes the

shutoff valves

34 and 43 while the supply of LPG to the engine 11 is stopped, with respect to the

shutoff valves

34 and 43. While the LPG is being supplied to the engine 11, the control device 6 opens the

shutoff valves

34, 43. While the engine 11 is stopped, the flow path between the shutoff valves 34 and 43 (the downstream side portion of the fuel supply line 31, the main flow path of the engine 11, and the upstream side portion of the fuel recovery line 41) is purged with the inert gas.

When LPG is used as fuel in the engine 11, pressure control, flow control, and temperature management of LPG are performed as follows.

The 1 st pressure gauge 71 is provided in the service tank 22, and detects the pressure of the gas layer in the service tank 22. The flow meter 81 is provided on the fuel supply line 31 downstream of the branch point of the 1 st bypass line 51, and detects the supply flow rate Qi of the LPG flowing into the engine 11 through the fuel supply line 31. As long as the rotation speed of the pump 32 is not the lowest rotation speed, the control device 6 maintains the flow rate control valve 52 fully closed. The control device 6 controls the pump 32 so that the supply flow rate Qi detected by the flow meter 81 becomes a predetermined value V corresponding to the fuel consumption Qe of the engine 11. In the present embodiment, the predetermined value V is a value obtained by multiplying the fuel consumption Qe of the engine 11 by a coefficient C (V — Qe × C). For example, the coefficient C is usually 1.1 to 1.50. The coefficient C may be a fixed value set within the numerical range, or may be variably set within the numerical range.

For example, the control device 6 may determine the fuel consumption Qe of the engine 11 based on the operation amount of the telescopic link operated by the boat operator. Alternatively, when the control device 6 is divided into an engine control device that controls the engine 11 and a fuel supply control device that controls the pump 32 and various valves, the fuel supply control device determines the fuel consumption Qe of the engine 11 from a value related to the fuel consumption calculated by the engine control device.

As a result of the control based on the supply flow rate Qi detected by the flow meter 81, when the rotation speed of the pump 32 is the lowest rotation speed, the control device 6 controls one of the flow

rate control valves

52 and 54 so that the supply flow rate Qi detected by the flow meter 81 becomes the predetermined value V. Specifically, the controller 6 increases the opening degree of either one of the flow

rate control valves

52 and 54 as the fuel consumption Qe of the engine 11 decreases.

The 2 nd pressure gauge 72 is provided on the fuel supply line 31 on the downstream side of the heater 33, and detects the pressure of the LPG supplied to the engine 11. In the present embodiment, the 2 nd pressure gauge 72 is located on the downstream side of the stop valve 34, but may be located on the upstream side of the stop valve 34. The controller 6 controls the 1 st pressure regulating valve 42 so that the pressure detected by the 2 nd pressure gauge 72 becomes the required pressure (for example, 5.0 to 6.0MPa) of the engine 11.

The 3 rd pressure gauge 73 is provided in the fuel recovery line 41 between the 1 st pressure regulating valve 42 and the 2 nd pressure regulating valve 45, and detects the pressure of the LPG decompressed by the 1 st pressure regulating valve 42. In the present embodiment, the 3 rd pressure gauge 73 is located upstream of the cooler 44, but may be located downstream of the cooler 44.

The temperature of the LPG slightly increases (e.g., 55 c) due to the passage of the LPG through the engine 11. Therefore, in order to prevent vaporization of the LPG decompressed by the 1 st pressure regulating valve 42, the controller 6 controls the 2 nd pressure regulating valve 45 so that the pressure detected by the 3 rd pressure gauge 73 is a set value (for example, 2.0MPa) higher than the saturated vapor pressure at the assumed maximum temperature.

Even when the LPG is not used, temperature management and pressure control of the LPG are performed. In particular, temperature management of LPG in the fuel tank 2 and control of the pressure of the gas layer in the fuel tank 2 are performed.

Specifically, the control device 6 operates the pump 32 when the pressure of the gas layer in the service tank 22 detected by the 1 st pressure gauge 71 is equal to or lower than a predetermined value or when the pump operation command means 61 is operated by a crew member while LPG is not used as fuel. At this time, either one of the

shutoff valves

34 and 43 and/or the flow

rate control valves

52 and 54 is opened. When the

shutoff valves

34, 43 are opened, the LPG in the service tank 22 circulates to the service tank 22 via the fuel supply line 31 and the engine 11 (particularly, the main flow path thereof). When the flow control valve 52 is opened, LPG in the service tank 22 circulates to the service tank 22 via the fuel supply line 31 and the 1 st bypass line 51. When the flow control valve 54 is opened, LPG in the service tank 22 circulates to the service tank 22 via the fuel supply line 31 and the 2 nd bypass line 53. When any one of the

shutoff valves

34, 43 and the

flow control valves

52, 54 is opened, the LPG in the service tank 22 circulates to the service tank 22 via the engine 11 and the fuel recovery line 41 and/or the 1 st bypass line 51 or the 2 nd bypass line 53.

As described above, the pressure of the gas layer of the service tank 22 (the saturated vapor pressure of LPG) when the temperature of LPG in the service tank 22 is 0 ℃ is about 0.4MPa, whereas the required pressure of the engine 11 when LPG is used as fuel is 5.0MPa to 6.0 MPa. When the pressure of the gas layer in the service tank 22 is lower than a predetermined value, even when the engine 11 is desired to be operated using LPG as fuel, the supply pressure of LPG cannot be raised to the required pressure by the pump 32, and therefore the engine 11 cannot be operated using LPG. Since the engine 11 cannot be operated using LPG until the required pressure is reached (until the pressure of the gas layer becomes equal to or higher than the predetermined value), the start of the operation of the engine 11 using LPG is delayed accordingly.

As described above, when the control device 6 circulates LPG via the engine 11 and/or the 1 st bypass line 51 or the 2 nd bypass line 53 during a period in which LPG is not used as fuel, the temperature of the LPG rises at least due to heat input from the pump 32. In the case of a dual fuel engine, if the engine 11 is operated using fuel oil, the LPG circulates through the engine 11, and therefore heat is also taken from the engine 11, and the temperature of the LPG is likely to rise. In the present embodiment, the heater 33 is disposed on the fuel supply line 31 between the pump 32 and the branch point of the 1 st bypass line 51, and therefore, even when the LPG circulates through the 1 st bypass line 51, the temperature of the LPG can be increased by the heater 33. Since the cooler 44 is a thermostat that regulates the temperature of the LPG to a lower temperature than the heater 33, the temperature of the LPG is lower than the regulation temperature of the cooler 44 when the LPG circulates due to low pressure. Therefore, the "cooler 44" can function as a heater.

The circulation of LPG increases the temperature of LPG in the service tank 22, and the pressure of the gas layer in the service tank 22 (the saturated vapor pressure of LPG) also increases accordingly. If the pressure of the gas layer is higher than a predetermined value, the pump 32 is stopped to stop the circulation of LPG. In order to suppress frequent repetition of the operation and stop of the pump 32, the threshold value for the cycle stop determination may be set to a value (high pressure value) larger than the threshold value for the cycle start determination.

The rotation speed of the pump 32 is not particularly limited, and may be constant at the lowest rotation speed or variable depending on the detected pressure of the gas layer. By increasing the rotation speed of the pump 32 when the pressure of the gas layer is low, the temperature can be increased at an early stage.

Since the pressure of the gas layer in the service tank 22 is maintained at a predetermined value or more when the use of LPG is stopped, the supply pressure of LPG can be increased by the pump 32 to the pressure required by the engine 11 when the use of LPG as fuel is started, and the operation of the engine using LPG can be started smoothly and quickly.

(embodiment 2)

Fig. 2 is a schematic configuration diagram of a ship 101 according to embodiment 2. As shown in fig. 2, the bypass lines 51, 53 and

flow control valves

52, 54 may also be omitted. In this case, when the LPG is not used, the controller 6 operates the pump 32 to circulate the LPG in the service tank 22 to the service tank 22 via the engine 11 when the pressure of the gas layer in the service tank 22 detected by the 1 st pressure gauge 71 is equal to or lower than a predetermined value. In the present embodiment, as in embodiment 1, when starting to use LPG as fuel, the supply pressure of LPG can be increased by the pump 32 to the pressure required by the engine 11, and the operation of the engine using LPG can be started smoothly and quickly.

(modification example)

Fig. 3 is a schematic configuration diagram of a ship 201 according to a modification. As shown in fig. 3, the flow meter 81 may be provided in the fuel recovery line 41 on the upstream side of the shutoff valve 43 to detect the flow rate Qo of the LPG from the engine 11. That is, the control device 6 may control the pump 32 and the flow rate control valve 52 so that the outflow rate Qo detected by the flow meter 81 becomes the predetermined value V' corresponding to the fuel consumption Qe of the engine 11. In this case, the predetermined value V' is, for example, a value obtained by multiplying the fuel consumption Qe of the engine 11 by a coefficient C of usually 0.1 to 0.50. In this case, the coefficient C may be a fixed value set within the numerical range, or may be variably set within the numerical range.

The predetermined value V, V 'does not necessarily have to be constant, and the controller 6 may increase the predetermined value V, V' when the rotation speed of the pump 32 is the minimum rotation speed. For example, in the configuration shown in fig. 1, the prescribed value V may also be increased to a flow rate in the range of 1.1 × Qe to 11.0 × Qe. Alternatively, in the configuration shown in fig. 3, the predetermined value V' may be increased to a flow rate in the range of 0.1 × Qe to 10.0 × Qe.

When the rotation speed of the pump 32 is the lowest rotation speed, the predetermined value V, V 'is constant, and when the flow rate control valve 54 provided on the 2 nd bypass line 53 is opened, the remaining portion obtained by subtracting the predetermined value V, V' from the discharge flow rate Q of the pump 32 passes through the 2 nd bypass line 53 and is returned to the service tank 22. Since this remaining portion is heated in the pump 32, the temperature of the LPG in the service tank 22 rises. In contrast, if the predetermined value V, V' is increased when the rotation speed of the pump 32 is the lowest rotation speed, the LPG returned to the service tank 22 through the 2 nd bypass line 53 can be reduced. On the other hand, as the predetermined value V, V' increases, the amount of LPG passing through the engine 11 also increases, but this increase is cooled by the cooler 44 provided in the fuel recovery line 41. Therefore, the temperature of the LPG in the service tank 22 can be suppressed from rising.

In the above embodiment, the fuel tank 2 is constituted by the reserve tank 21 and the service tank 22, but the reserve tank 21 may be omitted and the fuel tank 2 may be constituted by only the service tank 22. That is, the LPG may be directly introduced into the service tank 22 from the LPG supply source. However, if the configuration is as in the above embodiment, the fuel tank 2 can be divided into the storage tank 21 for LPG introduction and the service tank 22 for LPG circulation.

Since the pressure of the gas layer (saturated vapor pressure) in the service tank 22 depends on the temperature in the service tank 22, a thermometer for detecting the temperature in the service tank 22 (which may be the temperature of the gas layer or the temperature of the liquid layer) may be provided instead of the 1 st pressure gauge 71, and whether or not the pump 32 needs to be operated may be determined based on the temperature detected by the thermometer.

Description of the reference symbols

1. 101, 201: a vessel; 11: a propulsion engine; 2: a fuel tank; 6: a control device; 31: a fuel supply line; 32: a pump; 41: a fuel recovery line; 51. 53: a bypass line; 61: a pump operation command unit; 71: 1 st pressure gauge.

Claims

1. A marine vessel having:

a fuel tank that stores liquefied petroleum gas so that the temperature of the liquefied petroleum gas changes in accordance with the atmospheric temperature;

a propulsion engine using liquefied petroleum gas as fuel;

a fuel supply line that supplies liquefied petroleum gas from the fuel tank to the engine;

a pump provided to the fuel supply line;

a fuel recovery line that recovers unused liquefied petroleum gas from the engine to the fuel tank;

a pressure gauge that detects a pressure of a gas layer in the fuel tank; and

a control device that controls a rotational speed of the pump,

when the pressure detected by the pressure gauge is equal to or lower than a predetermined value while the liquefied petroleum gas is not used as fuel, the control device operates the pump to circulate the liquefied petroleum gas in the fuel tank to the fuel tank via the engine, thereby increasing the temperature of the liquefied petroleum gas in the fuel tank, and accompanying this, the pressure of the gas layer in the fuel tank also increases.

2. A marine vessel, having:

a propulsion engine using liquefied petroleum gas as fuel;

a pump provided to the fuel supply line;

a bypass line branching from the fuel supply line on a downstream side of the pump and connected to the fuel recovery line or the fuel tank;

a pressure gauge that detects a pressure of a gas layer in the fuel tank; and

a control device that controls a rotational speed of the pump,

when the pressure detected by the pressure gauge is equal to or lower than a predetermined value while the liquefied petroleum gas is not used as fuel, the control device activates the pump to circulate the liquefied petroleum gas in the fuel tank to the fuel tank via the engine and/or the bypass line, thereby increasing the temperature of the liquefied petroleum gas in the fuel tank, and accompanying this, the pressure of the gas layer in the fuel tank also increases.

3. A liquefied petroleum gas temperature/pressure management method, which is applied to a ship having:

a propulsion engine using liquefied petroleum gas as fuel;

a pump provided to the fuel supply line; and

a fuel recovery line that recovers unused liquefied petroleum gas from the engine to the fuel tank,

wherein the content of the first and second substances,

when a condition that the pressure of the gas layer in the fuel tank is lower than a predetermined value, a condition that the temperature of the liquefied petroleum gas in the fuel tank is lower than a predetermined value, and/or a condition that a crew member operates a pump operation command member are satisfied while the liquefied petroleum gas is not used as fuel, the pump is operated to circulate the liquefied petroleum gas in the fuel tank to the fuel tank via the engine, thereby increasing the temperature of the liquefied petroleum gas in the fuel tank, and the pressure of the gas layer in the fuel tank is also increased accordingly.