Liquefied gas fuel tank equipment, and method for inerting and gas-freeing liquefied gas fuel tank

Abstract

A liquefied gas fuel tank equipment (50) comprises: a liquefied gas fuel tank (1) that accommodates a fuel including a fuel gas (G) and a liquefied fuel gas (LG); a heat exchanger (2) that is positioned below the liquefied gas fuel tank (1) and heats the fuel; and a circulation line (3) that has a low-temperature-side fuel line (31) that connects the liquefied gas fuel tank (1) and the heat exchanger (2) and in which flows fuel flowing out from the liquefied gas fuel tank (1) and into the heat exchanger (2), and a high-temperature-side fuel line (32) that connects the heat exchanger (2) and the liquefied gas fuel tank (1) and in which flows fuel flowing out from the heat exchanger (2) and into the liquefied gas fuel tank (1).

Description

Liquefied gas fuel tank equipment, and method for inerting and gas-freeing a liquefied gas fuel tank

[0001] The present disclosure relates to liquefied gas fuel tank installations and methods for inerting and gas-freeing liquefied gas fuel tanks.

[0002] BACKGROUND ART Ships equipped with equipment capable of inerting liquefied gas fuel tanks have been known for some time (see, for example, Patent Document 1).

[0003] The vessel is equipped with multiple gas fuel tanks that store liquefied petroleum gas. Some of the gas fuel tanks are filled with inert gas at a pressure higher than atmospheric pressure, and after inspection of the other gas fuel tanks is completed, inert gas is supplied from the gas fuel tanks filled with high-pressure inert gas to the other gas fuel tanks that are filled with air, thereby performing inerting.

[0004] Japanese Patent Application Laid-Open No. 2018-176886

[0005] However, the ship described in Patent Document 1 has a problem in that when the gas fuel tank is at a low temperature, the fluidity of the liquefied gas decreases, and it takes a long time to discharge the liquefied gas from the tank.

[0006] In order to solve the above problems, a liquefied gas fuel tank facility according to an embodiment of the present disclosure includes a liquefied gas fuel tank that stores fuel including fuel gas and liquefied fuel gas, a heat exchanger located below the liquefied gas fuel tank that heats the fuel, a circulation line that connects the liquefied gas fuel tank to the heat exchanger and has a low-temperature side fuel line through which the fuel flows out of the liquefied gas fuel tank and into the heat exchanger, and a high-temperature side fuel line that connects the heat exchanger to the liquefied gas fuel tank and through which the fuel flows out of the heat exchanger and into the liquefied gas fuel tank.

[0007] According to this configuration, the temperature of the fuel in the liquefied gas fuel tank and the fuel tank itself can be increased. This improves the fluidity of the fuel in the liquefied gas fuel tank and allows the liquefied gas to be efficiently discharged from the liquefied gas fuel tank. In addition, a natural circulation path for the fuel can be formed between the liquefied gas fuel tank and the heat exchanger, allowing the equipment for increasing the temperature of the fuel in the liquefied gas fuel tank and the liquefied gas fuel tank to be made compact.

[0008] The present disclosure provides an effect of improving the fluidity of fuel in a liquefied gas fuel tank and enabling efficient discharge of liquefied gas from the liquefied gas fuel tank.

[0009] Fig. 1 is a diagram showing an example of the configuration of a ship equipped with a liquefied gas fuel tank facility according to Embodiment 1. Fig. 2 is a block diagram showing an example of the configuration of the liquefied gas fuel tank facility of Fig. 1. Fig. 3 is a flowchart showing an example of the operation of the liquefied gas fuel tank facility of Fig. 1. Fig. 4 is a flowchart showing an example of the operation of the liquefied gas fuel tank facility of Fig. 1. Fig. 5 is a flowchart showing an example of the operation of the liquefied gas fuel tank facility of Fig. 1. Fig. 6 is a flowchart showing an example of the operation of the liquefied gas fuel tank facility according to Embodiment 2.

[0010] Hereinafter, embodiments will be described with reference to the drawings. Note that the present invention is not limited to the following embodiments. In addition, the same or corresponding elements will be denoted by the same reference numerals throughout the drawings, and redundant description will be omitted.

[0011] The functions of the elements disclosed herein can be performed using circuits or processing circuits, including general-purpose processors, special-purpose processors, integrated circuits, application-specific integrated circuits (ASICs), conventional circuits, and / or combinations thereof, configured or programmed to perform the disclosed functions. A processor is considered a processing circuit or circuit because it includes transistors and other circuitry. In this disclosure, a circuit, unit, or means is hardware that performs the recited functions or hardware that is programmed to perform the recited functions. The hardware may be hardware disclosed herein or other known hardware that is programmed or configured to perform the recited functions. Where the hardware is a processor, which is considered a type of circuit, the circuit, means, or unit is a combination of hardware and software, and the software is used to configure the hardware and / or processor.

[0012] (First Embodiment) FIG. 1 is a diagram showing an example of the configuration of a ship 100 equipped with a liquefied gas fuel tank facility 50 according to a first embodiment. The ship 100 is a ship that uses hydrogen gas G as a fuel for propulsion and power generation, and is equipped with a liquefied gas fuel tank that stores liquefied hydrogen LG. Note that the liquefied gas fuel is not limited to hydrogen gas G, and may be, for example, LNG (Liquefied Natural Gas). The ship 100 includes a hull 51 and a liquefied gas fuel tank facility 50 installed on the ship 100. The ship 100 may be a pure car carrier or a tanker.

[0013] Incidentally, in a ship fueled by liquefied gas, it is necessary to perform inerting and gas-freeing, which involves replacing the fuel remaining in a liquefied gas fuel tank 1 with an inert gas or air, before docking for a periodic inspection. A fuel tank equipment 50 is equipment that can perform inerting and gas-freeing on board the ship. FIG. 2 is a block diagram showing an example configuration of the fuel tank equipment 50. As shown in FIG. 2, the liquefied gas fuel tank equipment 50 includes one or more liquefied gas fuel tanks 1 that store hydrogen gas G and liquefied hydrogen LG, a first heat exchanger 2, a circulation line 3, a fuel discharge line 4, a second heat exchanger 5, a fuel gas consumption device 6, an inert gas supply device 7, an inert gas supply line 8, an analyzer 11, and a controller 12. The fuel tank equipment 50 may have multiple fuel tanks 1 arranged in one or more rows longitudinally or transversely. In the following description, the liquefied gas fuel tank facility 50 and the liquefied gas fuel tank 1 may be simply referred to as the fuel tank facility 50 and the fuel tank 1, respectively.

[0014] The fuel tank 1 is a tank that contains and stores fuel. The fuel tank equipment 50 including the fuel tank 1 is a vacuum insulated tank equipment, and a vacuum space 63 is provided between the fuel tank 1 and an outer tank 62 that surrounds the fuel tank 1. Note that the fuel tank equipment 50 is not limited to the vacuum insulated type. The fuel tank 1 is also a pressure vessel, and the maximum operating pressure is, for example, 0.6 MPaG.

[0015] The fuel tank 1 includes a pressure gauge 15 that detects the pressure inside the fuel tank 1 and a thermometer 16 that detects the temperature of the fuel tank 1. The pressure gauge 15 transmits the detected pressure of the fuel tank 1. The thermometer 16 transmits the detected temperature of the fuel tank 1. A plurality of pressure gauges 15 and a plurality of thermometers 16 may be provided.

[0016] Liquefied hydrogen LG is loaded at the bunkering site through a fuel gas loading line 21. The fuel gas loading line 21 is connected to a fuel gas supply facility 110 provided, for example, on a quay. When liquefied hydrogen LG is loaded into the fuel tank 1, the liquefied hydrogen LG is supplied from the fuel gas supply facility 110, passes through the fuel gas loading line 21, and is stored in the fuel tank 1. A fuel gas loading line valve 22 that opens and closes the fuel gas loading line 21 is provided on the fuel gas loading line 21. The fuel gas loading line valve 22 is normally closed and is opened when liquefied hydrogen LG is loaded.

[0017] The first heat exchanger 2 is a heat exchanger that uses a heat source such as glycol water or other antifreeze as a heat medium, and heats the cryogenic hydrogen gas G and liquefied hydrogen LG. In this embodiment, the first heat exchanger 2 functions to raise the temperature of the cryogenic hydrogen gas G and liquefied hydrogen LG to a temperature range where nitrogen gas does not condense. Note that the first heat exchanger 2 is not limited to a dedicated heat exchanger, and may be another heat exchanger used to pressurize the fuel tank 1 or to evaporate the liquefied hydrogen LG inside the fuel tank 1. As shown in FIG. 1 , the first heat exchanger 2 is located below the fuel tank 1. More specifically, the first heat exchanger 2 is located below the bottom of the fuel tank 1.

[0018] The circulation line 3 is a pipeline for circulating fuel between the fuel tank 1 and the first heat exchanger 2, and includes a low-temperature side fuel line 31, a high-temperature side fuel line 32, and a circulation line valve 33. The low-temperature side fuel line 31 connects the fuel tank 1 and the first heat exchanger 2, and is a pipeline through which hydrogen gas G and liquefied hydrogen LG flow, flowing from the fuel tank 1 and flowing into the first heat exchanger 2. The low-temperature side fuel line 31 opens at or near the bottom of the fuel tank 1. The high-temperature side fuel line 32 connects the first heat exchanger 2 and the fuel tank 1, and is a pipeline through which hydrogen gas G flows, flowing from the first heat exchanger 2 and flowing into the fuel tank 1. The high-temperature side fuel line 32 opens at or near the top of the fuel tank 1. The circulation line valve 33 is a flow rate adjustment valve that can open and close the circulation line 3. The circulation line valve 33 is provided in the high-temperature side fuel line 32. Alternatively, the circulation line valve 33 may be provided in the low temperature side fuel line 31 .

[0019] The fuel gas consuming device 6 is a device that consumes hydrogen gas G. The fuel gas consuming device 6 includes one or more devices selected from the group consisting of a gas combustion unit that incinerates hydrogen gas G and releases the combustion gas into the atmosphere, a hydrogen fuel engine that drives the ship 100, a fuel cell that uses hydrogen as fuel to generate electrical energy used in the ship 100, and a hydrogen-fired boiler installed on the ship 100.

[0020] The fuel discharge line 4 is connected to the fuel tank 1 and is a pipe through which hydrogen gas G discharged from the fuel tank 1 flows. More specifically, the fuel discharge line 4 connects the fuel tank 1 and the fuel gas consumption device 6 and is a pipe through which hydrogen gas G flows out of the fuel tank 1 and into the fuel gas consumption device 6. The fuel discharge line 4 opens at or near the top of the fuel tank 1.

[0021] The fuel discharge line 4 includes a fuel discharge line valve 42. The fuel discharge line valve 42 is a flow rate control valve that partially opens the fuel discharge line 4 to an arbitrary degree and functions to adjust the flow rate of the hydrogen gas G flowing into the fuel gas consumption device 6.

[0022] The fuel discharge line 4 also branches and is connected to an analyzer 11. The analyzer 11 is a device that detects the concentration of hydrogen gas G contained in the mixed gas of hydrogen gas G and nitrogen flowing through the fuel discharge line 4. The analyzer 11 transmits the detected concentration of hydrogen gas G.

[0023] The second heat exchanger 5 is a heat exchanger that uses an antifreeze such as glycol water as a medium, and functions to heat the low-temperature hydrogen gas G discharged from the fuel tank 1 to a temperature range required for the normal operation of the fuel gas consuming device 6. The temperature range required for the normal operation of the fuel gas consuming device 6 is, for example, room temperature.

[0024] The inert gas supply device 7 is a device that supplies an inert gas to the inert gas supply line 8. In this embodiment, the inert gas supplied by the inert gas supply device 7 is nitrogen. The inert gas supply device 7 supplies compressed nitrogen to the inert gas supply line 8 at a pressure that is equal to or less than the maximum operating pressure of the fuel tank 1. The inert gas supply device 7 is a device that can supply compressed nitrogen to the inert gas supply line 8 at a pressure of, for example, 0.5 MPaG.

[0025] The inert gas supply line 8 connects the inert gas supply device 7 and the fuel tank 1, and is a pipeline through which the inert gas supplied from the inert gas supply device 7 flows into the fuel tank 1. The inert gas supply line 8 includes an inert gas supply line valve 81. The inert gas supply line valve 81 is a valve that can open and close the inert gas supply line 8.

[0026] The controller 12 includes, for example, a control unit having a computing unit such as a CPU, and a storage unit having memories such as ROM and RAM. The controller 12 may be configured as a single controller for centralized control, or may be configured as a plurality of controllers for distributed control in cooperation with each other. The controller 12 outputs control signals that control the open / close states of the valves of the fuel tank equipment 50, namely, the fuel gas loading line valve 22, the circulation line valve 33, the fuel discharge line valve 42, and the inert gas supply line valve 81. The fuel gas loading line valve 22, the circulation line valve 33, the fuel discharge line valve 42, and the inert gas supply line valve 81 open or close the corresponding lines in response to the control signals output from the controller 12. The opening and closing of the corresponding lines is not limited to fully opening or fully closing, but also includes partial opening.

[0027] Furthermore, the controller 12 outputs a control signal for controlling the operation of the inert gas supply device 7. The inert gas supply device 7 operates in response to the control signal output from the controller 12, and starts and stops supplying the inert gas and air, respectively.

[0028] Furthermore, the controller 12 receives the pressure inside the fuel tank 1, the temperature of the fuel tank 1, and the concentration of hydrogen gas G contained in the mixed gas of hydrogen gas G and nitrogen flowing through the fuel discharge line 4, all of which are transmitted from the pressure gauge 15, the thermometer 16, and the analyzer 11. Note that a plurality of pressure gauges 15 may be provided. In this case, the controller 12 may treat the average value of the pressures detected by the plurality of pressure gauges 15 as the pressure inside the fuel tank 1. Similarly, a plurality of thermometers 16 may be provided. In this case, the controller 12 may treat the average value of the temperatures detected by the plurality of thermometers 16 as the temperature of the fuel tank 1.

[0029] Next, an operation example will be described when performing an inerting and gas-free process for the fuel tank 1, which replaces the liquefied hydrogen LG and hydrogen gas G remaining in the fuel tank 1 of the fuel tank equipment 50 with an inert gas or air. Figures 3 to 5 are flowcharts showing an operation example of the fuel tank equipment 50 in this embodiment.

[0030] When inerting and gas-freeing the fuel tank 1, usually, most or all of the liquefied hydrogen LG in the fuel tank 1 is consumed as fuel for the ship 100. A small amount of liquefied hydrogen LG remains at the bottom of the fuel tank 1, and hydrogen gas G vaporized from the liquefied hydrogen LG remains in other spaces in the fuel tank 1. Alternatively, hydrogen gas G vaporized from the liquefied hydrogen LG remains in all spaces in the fuel tank 1. In addition, the temperature of the fuel tank 1, which is insulated by a vacuum insulation system, is an extremely low temperature close to the temperature of the liquefied hydrogen LG and is below the temperature at which nitrogen, the inert gas used for inerting, condenses. In the initial state, all valves of the fuel tank equipment 50 are closed. The boiling point of liquefied hydrogen LG at atmospheric pressure is −253°C, and the boiling point of nitrogen at atmospheric pressure is −196°C.

[0031] As shown in FIG. 3, the controller 12 executes a warm-up process shown in step S1, and after the warm-up process is completed, executes an inerting and gas-free process shown in step S2.

[0032] As shown in FIG. 4 , the controller 12 executes the process of step S11 during the warm-up process. That is, the controller 12 opens the circulation line valve 33 to open the circulation line 3. When the circulation line 3 is opened, the liquefied hydrogen LG and hydrogen gas G, which are low-temperature and have high density in the fuel tank 1, flow from the fuel tank 1 into the low-temperature side fuel line 31, flow through the low-temperature side fuel line 31 toward the first heat exchanger 2 located below the fuel tank 1, and flow into the first heat exchanger 2. The liquefied hydrogen LG and hydrogen gas G that flow into the first heat exchanger 2 are heated in the first heat exchanger 2. When heated, the liquefied hydrogen LG vaporizes and becomes hydrogen gas G, and its density decreases. Furthermore, when heated, the hydrogen gas G expands and its density decreases. The heated hydrogen gas G, whose density has been reduced, then flows from the first heat exchanger 2 into the high-temperature side fuel line 32, flows from the high-temperature side fuel line 32 toward the fuel tank 1, flows into the fuel tank 1, and is returned. The hydrogen gas G returned to the fuel tank 1 spreads into the space above the fuel tank 1 due to the density difference with the lower temperature liquefied hydrogen LG or hydrogen gas G located in the space below the fuel tank 1 .

[0033] In this way, the low-temperature liquefied hydrogen LG and hydrogen gas G stored in the fuel tank 1 are heated by the first heat exchanger 2 located below the fuel tank 1, and a static pressure difference occurs due to the density difference between the fluids present at each location in the closed loop formed by the fuel tank 1, the low-temperature side fuel line 31, the first heat exchanger 2, and the high-temperature side fuel line 32. The static pressure difference serves as a driving force for natural circulation between the fuel tank 1 and the first heat exchanger 2, and the liquefied hydrogen LG and hydrogen gas G, starting with the relatively low temperature liquefied hydrogen LG and hydrogen gas G, are heated sequentially by the first heat exchanger 2. In order to increase the static pressure difference that serves as the driving force for natural circulation of the low-temperature liquefied hydrogen LG and hydrogen gas G, it is preferable to position the first heat exchanger 2 below the bottom of the fuel tank 1. Furthermore, as the liquefied hydrogen LG and hydrogen gas G are heated, after all the liquefied hydrogen LG in the fuel tank 1 is vaporized, the temperature of the hydrogen gas G increases, and the temperature of the fuel tank 1 also gradually increases.

[0034] Next, the controller 12 executes the determination process of step S12. That is, the controller 12 determines whether the pressure in the fuel tank 1 detected by the pressure gauge 15 is equal to or greater than the upper limit reference pressure. The upper limit reference pressure is a preset target value at which the fuel tank 1 does not become overpressurized, and is, for example, a value between 0.4 MPaG and 0.55 MPaG. Then, if the controller 12 determines Yes in step S12, i.e., that the pressure in the fuel tank 1 detected by the pressure gauge 15 is equal to or greater than the upper limit reference pressure, the controller 12 executes the process of step S13. That is, the controller 12 opens the fuel discharge line valve 42 to open the fuel discharge line 4. Note that, if the fuel discharge line valve 42 is already open, the controller 12 maintains the open state of the fuel discharge line valve 42. This prevents hydrogen gas G, which expands due to a temperature rise, from being discharged to the outside of the fuel tank 1, thereby preventing the fuel tank 1 from becoming overpressurized. The hydrogen gas G discharged from the fuel tank 1 and flowing into the fuel discharge line 4 flows through the fuel discharge line 4 toward the fuel gas consuming device 6, and is heated in the second heat exchanger 5 to a predetermined room temperature range required by the fuel gas consuming device 6. The hydrogen gas G heated to the predetermined room temperature range then flows through the fuel discharge line 4 into the fuel gas consuming device 6 and is consumed by the fuel gas consuming device 6. In step S13, the hydrogen gas G supplied to the fuel gas consuming device 6 is highly pure and can be effectively used as fuel for an engine or a fuel cell, so it is preferable that the hydrogen gas G be supplied to the engine or the fuel cell of the fuel gas consuming device 6 and used as fuel.

[0035] After executing step S13, or if the controller 12 determines No in step S12, i.e., if it determines that the pressure in the fuel tank 1 detected by the pressure gauge 15 is less than the upper limit reference pressure, the controller 12 then executes the determination process of step S14. That is, the controller 12 determines whether the pressure in the fuel tank 1 detected by the pressure gauge 15 is equal to or less than the lower limit reference pressure. The lower limit reference pressure is a pressure less than the upper limit reference pressure and is within the pressure range required by at least one of the fuel gas consumption devices 6 to which hydrogen gas G is supplied. Then, if the controller 12 determines Yes in step S14, i.e., if it determines that the pressure in the fuel tank 1 detected by the pressure gauge 15 is equal to or less than the lower limit reference pressure, the controller 12 executes the process of step S15. That is, the controller 12 closes the fuel discharge line 4 by closing the fuel discharge line valve 42. Note that if the fuel discharge line valve 42 is already closed, the controller 12 maintains the closed state of the fuel discharge line valve 42. As a result, the controller 12 stops discharging the hydrogen gas G from the fuel tank 1 .

[0036] After executing step S15, or if the controller 12 determines that the pressure in the fuel tank 1 detected by the pressure gauge 15 is greater than the lower-limit reference pressure in step S14, the controller 12 then executes the determination process of step S16. That is, the controller 12 determines whether the temperature detected by the thermometer 16 is equal to or greater than a reference temperature. The reference temperature is a predetermined target value that is higher than the condensation temperature of nitrogen gas. Then, if the controller 12 determines that the temperature detected by the thermometer 16 is less than the reference temperature in step S16, the controller 12 executes step S12 and the process following step S12 again.

[0037] If the controller 12 determines "Yes" in step S16, i.e., that the temperature detected by the thermometer 16 is equal to or higher than a reference temperature that is higher than the condensation temperature of nitrogen gas, the controller 12 executes the process of step S17. That is, the controller 12 closes the circulation line 3 by closing the circulation line valve 33. This stops the heating of the hydrogen gas G in the fuel tank 1 by the first heat exchanger 2. The controller 12 then ends the warm-up process.

[0038] Next, the controller 12 executes the inerting and gas-freeing process of step S2. First, in the inerting and gas-freeing process, the controller 12 executes the initial discharge process of step S20. The initial discharge process is a process for reducing the amount of hydrogen gas G in the fuel tank 1 in advance. In the initial discharge process, the controller 12 first opens the fuel discharge line valve 42 to open the fuel discharge line 4. This causes the hydrogen gas G in the fuel tank 1 to be discharged to the outside of the fuel tank 1 through the fuel discharge line 4, and the pressure in the fuel tank 1 gradually decreases toward atmospheric pressure. The controller 12 then repeatedly determines whether the pressure detected by the pressure gauge 15 is equal to or lower than the initial discharge reference pressure, and waits until the pressure detected by the pressure gauge 15 is equal to or lower than the initial discharge reference pressure. The initial discharge reference pressure is a target value set in advance to reduce the amount of hydrogen gas G in the fuel tank 1, and is a value between 0 MPaG and 0.2 MPaG. Furthermore, it is preferable that the initial discharge reference pressure be set in accordance with the minimum pressure at which any one of the fuel gas consuming devices 6 can consume the fuel gas.

[0039] Next, when the controller 12 determines that the pressure detected by the pressure gauge 15 is equal to or lower than the initial discharge reference pressure, it executes the first process of step S21. That is, the controller 12 closes the fuel discharge line 4 by closing the fuel discharge line valve 42, thereby stopping the discharge of hydrogen gas G from the fuel tank 1. Furthermore, the controller 12 opens the inert gas supply line valve 81 to open the inert gas supply line 8. Then, the controller 12 activates the inert gas supply device 7. As a result, compressed nitrogen is supplied into the fuel tank 1 through the inert gas supply line 8, and the pressure in the fuel tank 1 increases again. Furthermore, as compressed nitrogen in the room temperature range is supplied into the fuel tank 1, the temperatures of the hydrogen gas G and the fuel tank 1 increase. When step S21 is executed, the temperature in the fuel tank 1 is equal to or higher than the reference temperature, which is higher than the condensation temperature of nitrogen gas, and therefore, condensation of nitrogen gas in the fuel tank 1 can be prevented.

[0040] Next, the controller 12 performs the determination process of step S22. That is, the controller 12 determines whether the pressure detected by the pressure gauge 15 is equal to or greater than the reference pressure during inert gas supply. The reference pressure during inert gas supply is a preset target value that prevents the fuel tank 1 from becoming overpressurized, and is, for example, a value of 0.3 MPaG or greater and 0.4 MPaG or less. Then, if the controller 12 determines No in step S22, that is, the pressure detected by the pressure gauge 15 is less than the reference pressure during inert gas supply, the controller 12 performs the determination process of step S22 again. That is, the controller 12 waits until the pressure detected by the pressure gauge 15 becomes equal to or greater than the reference pressure during inert gas supply.

[0041] If the controller 12 determines "Yes" in step S22, i.e., that the pressure detected by the pressure gauge 15 is equal to or greater than the reference pressure during inert gas supply, the controller 12 executes a second process in step S23. Specifically, the controller 12 closes the inert gas supply line 8 by closing the inert gas supply line valve 81, thereby stopping the supply of nitrogen to the fuel tank 1. Furthermore, the controller 12 opens the fuel discharge line valve 42 to open the fuel discharge line 4. As a result, the mixed gas, which is a mixture of hydrogen gas G and nitrogen in the fuel tank 1, is discharged to the outside of the fuel tank 1 through the fuel discharge line 4, and the pressure of the fuel tank 1 gradually decreases toward atmospheric pressure. The mixed gas discharged to the outside of the fuel tank 1 is consumed by the fuel gas consumption device 6. Because an engine or a fuel cell cannot consume a mixed gas containing nitrogen, the controller 12 consumes hydrogen gas G using a combustion device (GCU) or a boiler as the fuel gas consumption device 6 to reduce the pressure to near atmospheric pressure.

[0042] Next, the controller 12 performs the determination process of step S24. That is, the controller 12 determines whether the pressure detected by the pressure gauge 15 is equal to or less than the reference pressure when the mixed gas is discharged. The reference pressure when the mixed gas is discharged is a predetermined target value that is lower than the reference pressure when the inert gas is supplied, for example, atmospheric pressure or a pressure close to atmospheric pressure, and is, for example, a value within a range of 0 MPaG to 0.2 MPaG. Then, if the controller 12 determines No in step S90, that is, the pressure detected by the pressure gauge 15 is higher than the reference pressure when the mixed gas is discharged, the controller 12 again performs the determination process of step S24. That is, the controller 12 waits until the pressure detected by the pressure gauge 15 becomes equal to or less than the reference pressure when the mixed gas is discharged.

[0043] If the controller 12 determines "Yes" in step S24, i.e., that the pressure detected by the pressure gauge 15 is equal to or lower than the reference pressure for discharging the mixed gas, the controller 12 then performs the determination process of step S25. That is, the controller 12 determines whether the concentration of hydrogen gas G contained in the mixed gas of hydrogen gas G and nitrogen flowing through the fuel discharge line 4, detected by the analyzer 11, is equal to or lower than a predetermined concentration. The predetermined concentration is, for example, a concentration lower than 4 percent, which is the lower explosion limit of hydrogen gas.

[0044] If the controller 12 determines No in step S25, that is, that the concentration of hydrogen gas G contained in the mixed gas of hydrogen gas G and nitrogen detected by the analyzer 11 is greater than the predetermined concentration, the controller 12 executes step S21 and the process following step S21 again. That is, the controller 12 executes the first process and the second process from step S21 to step S24 again. As a result, the first process and the second process from step S21 to step S24 are alternately repeated until the concentration of hydrogen gas G contained in the mixed gas of hydrogen gas G and nitrogen detected by the analyzer 11 becomes equal to or less than the predetermined concentration. As a result, the concentration of hydrogen gas G contained in the mixed gas of hydrogen gas G and nitrogen in the fuel tank 1 gradually decreases.

[0045] Then, when the controller 12 determines that the concentration of hydrogen gas G detected by the analyzer 11 is equal to or lower than the predetermined concentration, the controller 12 next executes the process of step S26. That is, the controller 12 closes the fuel discharge line 4 by closing the fuel discharge line valve 42. Then, the controller 12 ends the inerting and gas-free process of the fuel tank 1. Note that, after executing step S26, the controller 12 may execute a process of replacing the nitrogen gas in the fuel tank 1 with air.

[0046] As described above, the fuel tank equipment 50 circulates the hydrogen gas G and liquefied hydrogen LG in the fuel tank 1 between the fuel tank 1 and the first heat exchanger 2, thereby raising the temperature of the hydrogen gas G, liquefied hydrogen LG, and the fuel tank 1 in the fuel tank 1. This improves the fluidity of the fuel in the fuel tank 1 and allows the hydrogen gas G to be efficiently discharged from the fuel tank 1. It also prevents condensation of nitrogen gas in the fuel tank 1. Furthermore, by utilizing the density difference between the hydrogen gas G and liquefied hydrogen LG before and after heating, a natural circulation path for the hydrogen gas G and liquefied hydrogen LG can be formed between the fuel tank 1 and the first heat exchanger 2, eliminating the need for a gas compressor and a blower, which require large installation space. This allows the equipment for raising the temperature of the hydrogen gas G, liquefied hydrogen LG, and the fuel tank 1 in the fuel tank 1 to be compact. Furthermore, the fuel tank equipment 50 is simple in configuration and can perform inerting and gas-freeing of the fuel tank 1.

[0047] Furthermore, since the first heat exchanger 2 is located below the bottom of the fuel tank 1, natural circulation of the hydrogen gas G and the liquefied hydrogen LG can be efficiently performed by utilizing the density difference.

[0048] The fuel tank equipment 50 is equipment installed on the ship 100, and can inertize and gas-free the fuel tank 1 on board the ship without the aid of external equipment, thereby shortening the berthing period at the bunkering site.

[0049] (Embodiment 2) Fig. 6 is a flowchart showing an example of operation of the liquefied gas fuel tank facility 50 according to embodiment 2. The present embodiment differs from embodiment 1 in the inerting and gas-free processing in step S2 of the operation example.

[0050] As shown in FIG. 6 , in an operation example of this embodiment, the controller 12 first executes the process shown in step S221 in the inerting and gas-free process. That is, the controller 12 opens the inert gas supply line valve 81 to open the inert gas supply line 8. Then, the controller 12 activates the inert gas supply device 7. As a result, nitrogen is supplied into the fuel tank 1 through the inert gas supply line 8. Furthermore, the controller 12 opens the fuel discharge line valve 42 to open the fuel discharge line 4. As a result, the mixed gas of hydrogen gas G and nitrogen in the fuel tank 1 is discharged to the outside of the fuel tank 1 through the fuel discharge line 4. The mixed gas discharged to the outside of the fuel tank 1 is consumed and incinerated by the fuel gas consumption device 6. As a result, the concentration of hydrogen gas G flowing through the fuel tank 1 and the fuel discharge line 4 gradually decreases over time.

[0051] Next, the controller 12 performs the determination process of step S222. That is, the controller 12 determines whether the concentration of the hydrogen gas G flowing through the fuel discharge line 4 detected by the analyzer 11 is equal to or lower than a predetermined concentration. The predetermined concentration is, for example, a concentration lower than 4 percent, which is the lower explosion limit of hydrogen gas.

[0052] If the determination in step S222 is No, i.e., if the controller 12 determines that the concentration of hydrogen gas G detected by the analyzer 11 is greater than the predetermined concentration, the controller 12 executes the determination in step S222 again. That is, the controller 12 waits until the concentration of hydrogen gas G detected by the analyzer 11 becomes equal to or less than the predetermined concentration.

[0053] Then, when the controller 12 determines that the concentration of hydrogen gas G detected by the analyzer 11 is equal to or lower than the predetermined concentration, the controller 12 executes the process of step S223. That is, the controller 12 closes the fuel discharge line 4 by closing the fuel discharge line valve 42. Furthermore, the controller 12 closes the inert gas supply line 8 by closing the inert gas supply line valve 81.

[0054] Then, the controller 12 ends the inerting and gas-freeing process of the fuel tank 1.

[0055] (Embodiment 3) In the above-described embodiments 1 and 2, the controller 12 controls the open / closed state of the valve of the fuel tank equipment 50. Alternatively, an operator may operate the valve of the fuel tank equipment 50. When an operator operates the valve of the fuel tank equipment 50, the controller 12 in the operation examples of the above-described embodiments 1 and 2 can be read as the operator.

[0056] From the above description, many modifications and other embodiments of the present invention will be apparent to those skilled in the art. Therefore, the above description should be construed as illustrative only and is provided for the purpose of teaching those skilled in the art the best mode for carrying out the present invention. Details of the structure and / or function thereof may be substantially changed without departing from the spirit of the present invention.

[0057] (List of embodiments)

[0058] (Mode 1) A liquefied gas fuel tank facility comprising: a liquefied gas fuel tank that stores fuel including fuel gas and liquefied fuel gas; a heat exchanger located below the liquefied gas fuel tank that heats the fuel; and a circulation line that connects the liquefied gas fuel tank to the heat exchanger, the circulation line having: a low-temperature side fuel line through which the fuel flows out of the liquefied gas fuel tank and into the heat exchanger; and a high-temperature side fuel line that connects the heat exchanger to the liquefied gas fuel tank, the circulation line through which the fuel flows out of the heat exchanger and into the liquefied gas fuel tank.

[0059] According to this configuration, the fuel in the liquefied gas fuel tank and the liquefied gas fuel tank can be heated. This improves the fluidity of the fuel in the liquefied gas fuel tank and enables efficient discharge of the liquefied gas from the liquefied gas fuel tank. In addition, a natural circulation path for the fuel can be formed between the liquefied gas fuel tank and the heat exchanger, making it possible to make the equipment for heating the fuel in the liquefied gas fuel tank and the liquefied gas fuel tank more compact.

[0060] (Mode 2) The liquefied gas fuel tank facility according to Mode 1, wherein the heat exchanger is located below the bottom of the liquefied gas fuel tank.

[0061] According to this configuration, a natural circulation path for fuel can be effectively formed between the liquefied gas fuel tank and the heat exchanger, and the temperature of the fuel in the liquefied gas fuel tank and the liquefied gas fuel tank can be effectively raised.

[0062] (Mode 3) A liquefied gas fuel tank facility according to Mode 3, further comprising: a thermometer that detects the temperature of the liquefied gas fuel tank; an inert gas supply device that supplies an inert gas; an inert gas supply line that connects the inert gas supply device and the liquefied gas fuel tank and through which the inert gas supplied from the inert gas supply device flows into the liquefied gas fuel tank; a circulation line valve that opens and closes the circulation line; an inert gas supply line valve that opens and closes the inert gas supply line; and a controller that controls the circulation line valve and the inert gas supply line valve, wherein after opening the circulation line, the controller closes the circulation line, and after closing the circulation line, opens the inert gas supply line when it determines that the temperature detected by the thermometer is equal to or higher than a reference temperature that is equal to or higher than the condensation temperature of the inert gas.

[0063] This configuration makes it possible to prevent the inert gas from condensing inside the liquefied gas fuel tank.

[0064] (Mode 4) The liquefied gas fuel tank facility according to Mode 3, further comprising: a pressure gauge that detects the pressure inside the liquefied gas fuel tank; a fuel discharge line that is connected to the liquefied gas fuel tank and through which the fuel gas discharged from the liquefied gas fuel tank flows; and a fuel discharge line valve that opens and closes the fuel discharge line, wherein the controller controls the fuel discharge line valve to open the fuel discharge line when it determines that the pressure inside the liquefied gas fuel tank detected by the pressure gauge is equal to or higher than a predetermined upper reference pressure during a period from when the circulation line is opened to when the inert gas supply line is opened, and closes the fuel discharge line when it determines that the pressure inside the liquefied gas fuel tank detected by the pressure gauge is equal to or lower than a predetermined lower reference pressure that is lower than the upper reference pressure.

[0065] This configuration can prevent the liquefied gas fuel tank from becoming overpressurized due to expansion of the fuel.

[0066] (Mode 5) The liquefied gas fuel tank facility according to Mode 4, further comprising a fuel gas consumption device connected to the fuel discharge line and configured to consume the fuel gas.

[0067] According to this configuration, the fuel gas can be consumed.

[0068] (Mode 6) The liquefied gas fuel tank facility according to Mode 4, further comprising an analyzer that detects the concentration of the fuel gas flowing through the liquefied gas fuel tank or the fuel discharge line, wherein the controller performs a first process of closing the inert gas supply line and opening the fuel discharge line when it determines that the pressure detected by the pressure gauge is equal to or higher than a predetermined reference pressure when inert gas is supplied, after opening the inert gas supply line, and a second process of closing the fuel discharge line and opening the inert gas supply line when it determines that the pressure detected by the pressure gauge is equal to or lower than a predetermined reference pressure when mixed gas is discharged, which is lower than the reference pressure when inert gas is supplied, after closing the inert gas supply line and opening the fuel discharge line, and alternately repeats the first process and the second process until the concentration of the fuel gas detected by the analyzer becomes equal to or lower than the predetermined concentration.

[0069] According to this configuration, inerting and gas-freeing of the liquefied gas fuel tank can be performed with a simple configuration.

[0070] (Mode 7) The liquefied gas fuel tank facility according to Mode 4, further comprising an analyzer that detects the concentration of the fuel gas flowing through the liquefied gas fuel tank or the fuel discharge line, wherein the controller opens the fuel discharge line after opening the inert gas supply line or simultaneously with opening the inert gas supply line, and closes the fuel discharge line and the inert gas supply line when the concentration of the fuel gas detected by the analyzer falls below a predetermined concentration.

[0071] According to this configuration, inerting and gas-freeing of the liquefied gas fuel tank can be performed with a simple configuration.

[0072] (Mode 8) The liquefied gas fuel tank facility according to Mode 1, wherein the fuel gas is hydrogen gas, and the liquefied fuel gas is liquefied hydrogen.

[0073] This configuration allows the equipment for heating cryogenic liquefied hydrogen to be made compact.

[0074] (Mode 9) The liquefied gas fuel tank facility according to Mode 1, wherein the liquefied gas fuel tank facility is installed on a ship.

[0075] According to this configuration, the liquefied gas fuel tank can be inerted and gas-freed on board the ship, thereby shortening the berthing period.

[0076] (Mode 10) A method for inerting and gas-freeing a liquefied gas fuel tank, comprising: naturally circulating the fuel between a liquefied gas fuel tank that stores fuel including a fuel gas and a liquefied fuel gas; and a heat exchanger that is located below the liquefied gas fuel tank and heats the fuel; stopping the natural circulation of the fuel when the temperature of the liquefied gas fuel tank reaches or exceeds a reference temperature that is equal to or higher than a condensation temperature of an inert gas; supplying the inert gas to the liquefied gas fuel tank until the pressure inside the liquefied gas fuel tank reaches or exceeds a predetermined reference pressure when the inert gas is supplied; discharging a mixed gas containing the fuel and the inert gas from the liquefied gas fuel tank until the pressure inside the liquefied gas fuel tank reaches or exceeds a predetermined reference pressure when the mixed gas is discharged that is lower than the reference pressure when the inert gas is supplied; and repeatedly supplying the inert gas to the liquefied gas fuel tank and discharging the mixed gas from the liquefied gas fuel tank until a concentration of the fuel contained in the mixed gas reaches or exceeds a predetermined concentration.

[0077] According to this configuration, inerting and gas-freeing of the liquefied gas fuel tank can be performed with a simple configuration.

[0078] G Hydrogen gas LG Liquefied hydrogen 1 Liquefied gas fuel tank 2 First heat exchanger 3 Circulation line 4 Fuel discharge line 12 Controller 15 Pressure gauge 16 Thermometer 31 Low temperature side fuel line 32 High temperature side fuel line 33 Circulation line valve 42 Fuel discharge line valve 50 Liquefied gas fuel tank equipment

Claims

1. A liquefied gas fuel tank facility comprising: a liquefied gas fuel tank that stores fuel including fuel gas and liquefied fuel gas; a heat exchanger that is located below the liquefied gas fuel tank and heats the fuel; and a circulation line that connects the liquefied gas fuel tank and the heat exchanger and has a low-temperature side fuel line through which the fuel flows out of the liquefied gas fuel tank and into the heat exchanger, and a high-temperature side fuel line that connects the heat exchanger and the liquefied gas fuel tank and through which the fuel flows out of the heat exchanger and into the liquefied gas fuel tank.

2. A liquefied gas fuel tank facility as described in claim 1, wherein the heat exchanger is located below the bottom of the liquefied gas fuel tank.

3. A liquefied gas fuel tank facility as set forth in claim 1, further comprising: a thermometer that detects the temperature of the liquefied gas fuel tank; an inert gas supply device that supplies inert gas; an inert gas supply line that connects the inert gas supply device and the liquefied gas fuel tank and through which the inert gas supplied from the inert gas supply device flows into the liquefied gas fuel tank; a circulation line valve that opens and closes the circulation line; an inert gas supply line valve that opens and closes the inert gas supply line; and a controller that controls the circulation line valve and the inert gas supply line valve, wherein after opening the circulation line, the controller closes the circulation line, and after closing the circulation line, opens the inert gas supply line when it determines that the temperature detected by the thermometer is equal to or higher than a reference temperature that is equal to or higher than the condensation temperature of the inert gas.

4. The liquefied gas fuel tank facility according to claim 3, further comprising: a pressure gauge that detects the pressure inside the liquefied gas fuel tank; a fuel discharge line that is connected to the liquefied gas fuel tank and through which the fuel gas discharged from the liquefied gas fuel tank flows; and a fuel discharge line valve that opens and closes the fuel discharge line, wherein the controller controls the fuel discharge line valve to open the fuel discharge line if it determines that the pressure inside the liquefied gas fuel tank detected by the pressure gauge is equal to or higher than a predetermined upper reference pressure during the period from when the circulation line is opened to when the inert gas supply line is opened, and closes the fuel discharge line if it determines that the pressure inside the liquefied gas fuel tank detected by the pressure gauge is equal to or lower than a predetermined lower reference pressure that is lower than the upper reference pressure.

5. The liquefied gas fuel tank facility according to claim 4, further comprising a fuel gas consuming device connected to the fuel discharge line and consuming the fuel gas.

6. The liquefied gas fuel tank facility according to claim 4, further comprising an analyzer that detects the concentration of the fuel gas flowing through the liquefied gas fuel tank or the fuel discharge line, wherein the controller, after opening the inert gas supply line, performs a first process of closing the inert gas supply line and opening the fuel discharge line if it determines that the pressure detected by the pressure gauge is equal to or higher than a predetermined reference pressure when supplying inert gas, and performs a second process of closing the fuel discharge line and opening the inert gas supply line if it determines that the pressure detected by the pressure gauge is equal to or lower than a predetermined reference pressure when discharging mixed gas which is lower than the reference pressure when supplying inert gas, after closing the inert gas supply line and opening the fuel discharge line, and alternately repeats the first process and the second process until the concentration of the fuel gas detected by the analyzer becomes equal to or lower than the predetermined concentration.

7. A liquefied gas fuel tank facility as described in claim 4, further comprising an analyzer that detects the concentration of the fuel gas flowing through the liquefied gas fuel tank or the fuel discharge line, wherein the controller opens the fuel discharge line after opening the inert gas supply line or at the same time as opening the inert gas supply line, and closes the fuel discharge line and the inert gas supply line when the concentration of the fuel gas detected by the analyzer falls below a predetermined concentration.

8. The liquefied gas fuel tank facility according to claim 1, wherein the fuel gas is hydrogen gas, and the liquefied fuel gas is liquefied hydrogen.

9. A liquefied gas fuel tank installation according to claim 1, wherein the liquefied gas fuel tank installation is installed on a ship.

10. A method for inerting and gas-freeing a liquefied gas fuel tank, the method comprising: naturally circulating the fuel between a liquefied gas fuel tank that stores fuel including fuel gas and liquefied fuel gas; and a heat exchanger that is located below the liquefied gas fuel tank and heats the fuel; stopping the natural circulation of the fuel when the temperature of the liquefied gas fuel tank reaches a reference temperature that is equal to or higher than the condensation temperature of an inert gas; supplying the inert gas to the liquefied gas fuel tank until the pressure inside the liquefied gas fuel tank reaches a predetermined reference pressure when supplying the inert gas; discharging a mixed gas containing the fuel and the inert gas from the liquefied gas fuel tank until the pressure inside the liquefied gas fuel tank reaches a predetermined reference pressure when discharging the mixed gas that is lower than the reference pressure when supplying the inert gas; and repeatedly supplying the inert gas to the liquefied gas fuel tank and discharging the mixed gas from the liquefied gas fuel tank until the concentration of the fuel contained in the mixed gas reaches a predetermined concentration or lower.

Images