Liquefied gas introduction system

Abstract

To provide a liquefied gas introduction system and a liquefied gas introduction method, which can efficiently introduce liquefied gas into a liquefied gas tank.SOLUTION: A liquefied gas introduction system comprises: a liquid delivery pipe that receives liquefied gas from a supply source and delivers it downstream; a first introduction pipe that is connected to the liquid delivery pipe and introduces liquefied gas into a liquefied gas tank; a second introduction pipe that is connected to the liquid delivery pipe and has a discharge port disposed within the liquefied gas tank above the discharge port of the first introduction pipe to introduce liquefied gas into the liquefied gas tank; a first flow rate control valve that is interposed in at least one of the first introduction pipe and the second introduction pipe; a first sensor that detects the pressure inside the liquefied gas tank; and a controller. The controller controls the first flow rate control valve so that the higher the pressure inside the liquefied gas tank, the lower the flow rate in the first introduction pipe and the higher the flow rate in the second introduction pipe.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a liquefied gas introduction system. [Background technology]

[0002] When liquefied gas, such as liquefied hydrogen or liquefied natural gas, is introduced into a liquefied gas tank from a supply source such as a tank truck, boil-off gas is generated in the liquid transfer pipe and the liquefied gas tank, which can cause the pressure inside the liquefied gas tank to rise and exceed a predetermined range. Discharging the generated boil-off gas into the atmosphere to maintain the liquefied gas pressure within a predetermined range results in the waste of liquefied gas that could otherwise be used as fuel, which is uneconomical. Furthermore, additional equipment is required to safely discharge the flammable boil-off gas into the atmosphere.

[0003] Regarding such a liquefied gas introduction system, Patent Document 1 below discloses a configuration in which a bypass line is connected to an introduction line that introduces liquefied gas (LNG) from a tank truck into a tank, and a spray nozzle is connected to the tip of the bypass line. This spray nozzle is disposed at the top of the tank and is capable of spraying a portion of the LNG supplied from the tank truck. Patent Document 1 further discloses that by spraying LNG inside the tank, the temperature inside the tank is lowered and the internal pressure is made lower than the internal pressure of the tank truck, thereby allowing differential pressure pumping. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-147966 Summary of the Invention [Problem to be solved by the invention]

[0005] As described above, Patent Document 1 aims to lower the pressure inside the tank below the internal pressure of the tank truck, and does not describe specific control of the amount of spray from the spray nozzle. Therefore, the configuration of Patent Document 1 leaves room for improvement in terms of efficiently introducing liquefied gas into the liquefied gas tank.

[0006] The present disclosure has been made in consideration of the above-mentioned problems, and aims to provide a liquefied gas introduction system that can efficiently introduce liquefied gas into a liquefied gas tank. [Means for solving the problem]

[0007] A liquefied gas introduction system according to one embodiment of the present disclosure is a liquefied gas introduction system that introduces liquefied gas from a liquefied gas supply source into a liquefied gas tank for storing liquefied gas, and includes: a liquid delivery pipe that receives liquefied gas from the supply source and sends it downstream; a first introduction pipe connected to the liquid delivery pipe and introduces liquefied gas into the liquefied gas tank; a second introduction pipe connected to the liquid delivery pipe and having an outlet disposed within the liquefied gas tank above the outlet of the first introduction pipe and introducing liquefied gas into the liquefied gas tank; a first flow rate control valve interposed in at least one of the first introduction pipe and the second introduction pipe; a first sensor that detects the pressure within the liquefied gas tank; and a controller, wherein the controller controls the first flow rate control valve so that the flow rate of the first introduction pipe decreases and the flow rate of the second introduction pipe increases as the pressure within the liquefied gas tank increases.

[0008] A liquefied gas introduction system according to another aspect of the present disclosure is a liquefied gas introduction system that introduces liquefied gas from a liquefied gas supply source into a liquefied gas tank for storing liquefied gas, and includes a liquid transfer pipe that receives liquefied gas from the supply source and transfers it downstream, a first introduction pipe that is connected to the liquid transfer pipe and introduces liquefied gas into the liquefied gas tank, a second introduction pipe that is connected to the liquid transfer pipe and has a discharge port disposed in the liquefied gas tank above the discharge port of the first introduction pipe and introduces liquefied gas into the liquefied gas tank, and a coupling between at least the first introduction pipe and the second introduction pipe. the liquid supply piping includes a first flow rate control valve interposed in either one of the tanks, a second flow rate control valve interposed in the liquid supply piping, a first sensor that detects the pressure in the liquefied gas tank, a second sensor that detects the internal pressure or flow rate of the liquid supply piping, and a controller, wherein the controller controls the second flow rate control valve so that the flow rates of the liquid supply piping and the second inlet piping increase as the pressure in the liquefied gas tank increases, and controls the first flow rate control valve so that the flow rate of the first inlet piping decreases and the flow rate of the second inlet piping increases as the internal pressure of the liquid supply piping decreases or the flow rate of the liquid supply piping increases. [Effects of the Invention]

[0009] According to the present disclosure, liquefied gas can be efficiently introduced into a liquefied gas tank. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram showing a schematic configuration of a liquefied gas introduction system according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a timing chart illustrating the flow of introduction of liquefied gas in the liquefied gas introduction system of this embodiment. [Figure 3] FIG. 3 is a schematic diagram showing a schematic configuration of a liquefied gas introduction system according to a modified example of an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment will be described in detail with reference to the drawings. In the following, the same or corresponding elements will be designated by the same reference numerals throughout the drawings, and redundant description thereof will be omitted.

[0012] FIG. 1 is a schematic diagram showing a general configuration of a liquefied gas introduction system according to an embodiment of the present disclosure. The liquefied gas introduction system 1 in this embodiment is configured to introduce liquefied gas from a liquefied gas supply source 2, such as a tank truck, into a liquefied gas tank 3 for storing the liquefied gas. The liquefied gas tank 3 is, for example, a marine liquefied gas fuel tank mounted on a ship. Alternatively, the liquefied gas tank 3 may be a storage tank installed in a bunkering facility for temporarily storing liquefied gas before introducing it into the marine liquefied gas fuel tank. In this embodiment, the liquefied gas tank 3 is horizontally cylindrical. However, the liquefied gas tank 3 may also be vertically cylindrical. Alternatively, the tank 1 may be spherical or approximately rectangular.

[0013] Liquefied gases include, for example, liquefied hydrogen, liquefied natural gas, liquefied petroleum gas, liquefied ammonia, etc. In particular, liquefied hydrogen has a very low boiling point and a low density (kg / m) compared to liquefied natural gas, etc. 3 ) and latent heat of vaporization (kJ / kg), hydrogen generates a large amount of boil-off gas per volume of liquefied gas. Furthermore, because hydrogen has a low critical pressure, its latent heat of vaporization rapidly decreases even at a relatively low pressure of about 1 MPaG, which also contributes to the large amount of boil-off gas generated. Therefore, boil-off gas is likely to be generated during the process of introducing liquefied hydrogen into the liquefied gas tank 3. If a large amount of boil-off gas is generated, continuing to introduce liquefied hydrogen into the liquefied gas tank 3 without discharging the boil-off gas to the outside may increase the pressure inside the liquefied gas tank 3 and exceed a predetermined range, so this must be suppressed. However, boil-off gas may also be generated with liquefied gases other than liquefied hydrogen, such as liquefied natural gas, and similar issues arise. The present disclosure aims to suppress pressure increases outside the predetermined range inside the liquefied gas tank 3 caused by the vaporization of such various liquefied gases.

[0014] The liquefied gas introduction system 1 includes a piping path 14 for introducing liquefied gas from a supply source 2 into a liquefied gas tank 3. The piping path 14 includes a liquid delivery pipe 4, a first introduction pipe 5, and a second introduction pipe 6. The liquid delivery pipe 4 is a pipe for receiving liquefied gas from the supply source 2 and sending it downstream. The first introduction pipe 5 and the second introduction pipe 6 are each connected to the downstream end of the liquid delivery pipe 4 and introduce the liquefied gas into the liquefied gas tank 3. That is, the first introduction pipe 5 and the second introduction pipe 6 branch off and extend from the downstream end of the liquid delivery pipe 4. The inner diameter of the second introduction pipe 6 is preferably equal to or smaller than the inner diameter of the first introduction pipe 5.

[0015] The first inlet pipe 5 has a liquefied gas outlet 5a disposed downward within the liquefied gas tank 3. The second inlet pipe 6 has an outlet 6a disposed higher within the liquefied gas tank 3 than the outlet 5a of the first inlet pipe 5. Preferably, the outlet 6a is disposed near the top of the liquefied gas tank 3. The outlet 6a of the second inlet pipe 6 may include a spray nozzle for spraying liquefied gas into the liquefied gas tank 3, or may include a drip nozzle or hole for dropping droplets from the outlet 6a. The second inlet pipe 6 may also have multiple outlets 6a.

[0016] Furthermore, the liquefied gas introduction system 1 includes a first flow rate control valve 7, a first sensor 8, and a controller 9. In this embodiment, the first flow rate control valve 7 is installed in the first introduction pipe 5. The first flow rate control valve 7 adjusts the flow rate of the first introduction pipe 5. By adjusting the flow rate of the first introduction pipe 5, the flow rate of the second introduction pipe 6 is also adjusted. The first sensor 8 is a pressure sensor that detects the internal tank pressure P1, which is the pressure inside the liquefied gas tank 3. The controller 9 includes a processing circuit 10 that performs various types of signal processing.

[0017] The processing circuit 10 includes a computer such as a microcontroller, a personal computer, or a PLC (Programmable Logic Controller). More specifically, the processing circuit 10 includes a processor, a memory, and peripheral circuits. The processor includes, for example, a CPU or an MPU. The memory includes, for example, a ROM, a RAM, a register, a non-volatile storage, and the like. The peripheral circuits include an input / output interface, and the like. Furthermore, the controller 9 may include an input device for a user to input operations and an output device such as a monitor that outputs the control status.

[0018] It should be noted that 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 specification, a circuit, unit, means, or module 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 hardware is a processor, which is considered a type of circuit, the circuit, unit, or means is a combination of hardware and software, and the software is used to configure the hardware and / or processor.

[0019] The memory stores a control program. The processor reads the control program from the memory and generates a command value for controlling the first flow rate control valve 7, which is the object to be controlled, based on the control program. The controller 9 acquires the tank internal pressure P1 detected by the first sensor 8. The controller 9 controls the first flow rate control valve 7 so that the higher the tank internal pressure P1 detected by the first sensor 8, the lower the flow rate in the first inlet pipe 5 and the higher the flow rate in the second inlet pipe 12.

[0020] Of the first inlet pipe 5 and the second inlet pipe 6 branching off from the liquid delivery pipe 4, when the flow rate of the first inlet pipe 5 is reduced by the first flow control valve 7, the flow rate of the second inlet pipe 6 increases. This increases the amount of liquefied gas sprayed or dripped from above into the liquefied gas tank 3. This increases the surface area of ​​the liquefied gas in contact with the gas phase space in the liquefied gas tank 3, accelerating the cooling and condensation of the gas phase in the liquefied gas tank 3. During this process, the gas phase in the liquefied gas tank 3 is cooled before it falls from the discharge port 6a of the second inlet pipe 6 to the liquid surface of the liquefied gas accumulated in the liquefied gas tank 3, and the gas phase, including the generated boil-off gas of the liquefied gas, contracts and is partially liquefied.

[0021] Furthermore, when liquefied gas is introduced into the liquefied gas tank 3 and accumulates in the liquefied gas tank 3, different temperature layers may be formed in the liquid phase of the liquefied gas tank 3 between an area close to the liquid surface of the liquefied gas and an area far from the liquid surface. That is, a first temperature layer close to the saturation temperature at the pressure inside the liquefied gas tank 3 may be formed in an area close to the liquid surface of the liquefied gas, and a second temperature layer with a lower temperature may be formed in an area far from the liquid surface of the liquefied gas, i.e., near the bottom surface of the liquefied gas tank 3. When the liquid surface is at the saturation temperature, the cooling effect caused by the gas phase in the liquefied gas tank 3 coming into contact with the liquid surface is reduced, making it difficult for the gas phase in the liquefied gas tank 3 to contract or condense.

[0022] In response to this, the first temperature layer near the liquefied gas surface can be broken by dropping the liquefied gas from the discharge port 6a of the second inlet pipe 6. Breaking the first temperature layer creates a portion of the liquefied gas surface that is lower in temperature than the saturation temperature, which increases the cooling effect of the gas phase in contact with the liquid surface inside the liquefied gas tank 3. This makes it possible to prevent the pressure inside the liquefied gas tank 3 from rising and exceeding a predetermined range.

[0023] Here, when the flow rate of the first inlet pipe 5 is reduced by the first flow rate control valve 7, the flow rate of the liquefied gas in the liquid supply pipe 4 is reduced. For example, if the supply source 2 is a tank truck, there may be restrictions imposed by laws and regulations on the amount of time the tank truck can be parked in a parking space for connection to the liquid supply pipe 4. For this reason, it is desirable that the flow rate of the liquefied gas in the liquid supply pipe 4 be equal to or greater than a predetermined value regardless of the opening degree of the first flow rate control valve 7.

[0024] In this regard, in the present embodiment, the liquefied gas introduction system 1 further includes a second sensor 11 and a second flow rate adjustment valve 12. The second sensor 11 is configured as a pressure sensor that detects the internal pressure P2 of the liquid supply pipe 4. The second flow rate adjustment valve 12 is interposed in the liquid supply pipe 4 and adjusts the flow rate of the liquid supply pipe 4. The controller 9 acquires the pressure P2 of the liquid supply pipe 4 detected by the second sensor 11. The controller 9 controls the second flow rate adjustment valve 12 so as to maintain the internal pressure P2 of the liquid supply pipe 4 at a predetermined target value P2o. This makes it possible to maintain the flow rate of the liquefied gas in the liquid supply pipe 4 at or above a predetermined value regardless of the flow rate of the first introduction pipe 5.

[0025] Moreover, in this embodiment, the liquefied gas introduction system 1 is provided with a flow switching valve 13 that switches between flow and cut-off to the second introduction pipe 6. The flow switching valve 13 is disposed in the second introduction pipe 6. The controller 9 controls the flow switching valve 13 to allow the flow of liquefied gas to the second introduction pipe 6 when the tank internal pressure P1 is equal to or higher than a predetermined value P12. When the tank internal pressure P1 is lower than the predetermined value P12, the liquefied gas may be introduced into the liquefied gas tank 3 solely from the first introduction pipe 5.

[0026] Fig. 2 is a timing chart illustrating the flow of liquefied gas introduction in the liquefied gas introduction system of this embodiment. The timing chart in Fig. 2 includes graphs with the horizontal axis representing time t and the vertical axis representing, from top to bottom, the tank filling rate, the tank internal pressure P1 and the pipe internal pressure P2, the opening degree x2 of the second flow rate control valve 12, the opening degree x1 of the first flow rate control valve 7, and the on / off state of the flow switching valve 13. The on state of the flow switching valve 13 is a state in which the opening degree x3 is 100%, and the off state is a state in which the opening degree x3 is 0%.

[0027] Before the supply of liquefied gas, the opening degree x1 of the first flow rate control valve 7 and the opening degree x2 of the second flow rate control valve are 0%, i.e., in a shut-off state, and the flow switching valve 13 is in an off state, i.e., in a shut-off state. The tank filling rate of the liquefied gas tank 3 is at the minimum liquid level MIN. At time t=0, the supply of liquefied gas from the supply source 2 to the liquefied gas tank 3 begins. In the example of FIG. 2, the controller 9 increases the opening degree x1 of the first flow rate control valve 7 from 0% to 100% and maintains that opening degree. As a result, liquefied gas is introduced into the liquefied gas tank 3, and the tank filling rate gradually increases.

[0028] In parallel with the operation of opening the first flow rate control valve 7, the controller 9 sets a predetermined target value P2o for the internal pressure P2 of the liquid supply pipe 4, and controls the opening degree x2 of the second flow rate control valve 12 so as to maintain the target value P2o. The control of the second flow rate control valve 12 is performed by, for example, PI control.

[0029] After the introduction of liquefied hydrogen begins, boil-off gas is generated in the liquid delivery pipe 4, the first introduction pipe 5, and the liquefied gas tank 3 as the liquefied gas is introduced into the liquid delivery pipe 4, the first introduction pipe 5, and the liquefied gas tank 3. This, coupled with the decrease in the volume of the gas phase space in the liquefied gas tank 3, causes the tank internal pressure P1 to rise. At time t1, when the tank internal pressure P1 reaches or exceeds a predetermined value P12, the controller 9 switches the flow switching valve 13 from its OFF state to its ON state. As a result, liquefied gas is introduced into the liquefied gas tank 3 not only through the discharge port 5a of the first introduction pipe 5 but also through the discharge port 6a of the second introduction pipe 6. At this time, the opening degree x1 of the first flow control valve 7 remains at 100%.

[0030] If the tank internal pressure P1 further increases and becomes equal to or greater than the first pressure P1a at time t2, the controller 9 reduces the opening x1 of the first flow control valve 7 by one step so as to reduce the flow rate through the first inlet pipe 5. This increases the flow rate through the second inlet pipe 6, and suppresses the rate at which the tank internal pressure P1 increases.

[0031] As described above, the reduction in the aperture x1 of the first flow rate control valve 7 reduces the flow rate of the liquefied gas in the liquid supply pipe 4. Therefore, the controller 9 increases the aperture x2 of the second flow rate control valve 12 by one step so that the internal pressure P2 corresponding to the flow rate of the liquefied gas in the liquid supply pipe 4 is maintained at the target value P2o. This maintains the flow rate of the liquefied gas in the liquid supply pipe 4 at the state it was in before the aperture x1 of the first flow rate control valve 7 was reduced.

[0032] In the example of FIG. 2, the controller 9 controls the first flow rate adjustment valve 7 so as to gradually reduce the opening degree x1 of the first flow rate adjustment valve 7 as the tank internal pressure P1 increases. That is, when the tank internal pressure P1 reaches or exceeds a second pressure P1b higher than the first pressure P1a at time t3, the controller 9 further reduces the opening degree x1 of the first flow rate adjustment valve 7 by one step. Furthermore, when the tank internal pressure P1 reaches or exceeds a second pressure P1b higher than the first pressure P1a at time t4, the controller 9 further reduces the opening degree x1 of the first flow rate adjustment valve 7 by one step. If the tank pressure P1 becomes equal to or greater than the third pressure P1c, the opening degree x1 of the first flow control valve 7 is reduced by another step, and if, at time t5, the tank pressure P1 becomes equal to or greater than a fourth pressure P1d that is higher than the third pressure P1c, the opening degree x1 of the first flow control valve 7 is reduced by another step.

[0033] The higher the tank internal pressure P1, the smaller the aperture x1 of the first flow control valve 7, and thus the greater the amount of liquefied gas introduced into the liquefied gas tank 3 via the second inlet pipe 6. This improves the effect of suppressing the rise in the tank internal pressure P1 due to the liquefied gas. As shown in the graph of the tank internal pressure P1 in Figure 2, the smaller the aperture x1 of the first flow control valve 7, the smaller the slope of the rise in the tank internal pressure P1 with respect to time t.

[0034] As the opening degree x1 of the first flow control valve 7 gradually decreases, the flow rate of the liquefied gas in the liquid supply pipe 4 also gradually decreases, so the controller 9 gradually increases the opening degree x2 of the second flow control valve 12.

[0035] In the example of FIG. 2, the increase in the tank internal pressure P1 stops after time t5 and begins to decrease. The controller 9 controls the first flow rate control valve 7 to gradually increase the aperture x1 of the first flow rate control valve 7 as the tank internal pressure P1 decreases. However, if, at time t6, the tank internal pressure P1 becomes equal to or less than a fifth pressure P1e that is less than the fourth pressure P1d and greater than the third pressure P1c, the controller 9 increases the aperture x1 of the first flow rate control valve 7 by one step. If, at time t7, the tank internal pressure P1 becomes equal to or less than a sixth pressure P1f that is less than the third pressure P1c and greater than the second pressure P1b, the controller 9 increases the aperture x1 of the first flow rate control valve 7 by another step. Furthermore, if the tank internal pressure P1 becomes equal to or less than a seventh pressure P1g that is less than the second pressure P1b and greater than the first pressure P1a, the controller 9 increases the aperture x1 of the first flow rate control valve 7 by another step. 2, the tank internal pressure P1 does not become equal to or lower than the seventh pressure P1g after time t7. In this way, the change in the opening degree x1 of the first flow rate control valve 7 relative to the tank internal pressure P1 has hysteresis.

[0036] In this embodiment, the increase and decrease amounts of the opening x1 of the first flow rate control valve 7 are the same, but the increase and decrease amounts may be different. Furthermore, the increase amount of the opening x1 of the first flow rate control valve 7 may be different for each threshold value P1a, ..., P1d of the tank internal pressure P1. Similarly, the decrease amount of the opening x1 of the first flow rate control valve 7 may be different for each threshold value P1e, ..., P1g of the tank internal pressure P1.

[0037] Furthermore, the change in the aperture x1 of the first flow rate control valve 7 relative to the internal tank pressure P1 does not need to have hysteresis. That is, the controller 9 may increase the aperture x1 of the first flow rate control valve 7 by one step when the internal tank pressure P1 becomes less than the fourth pressure P1d, may increase the aperture x1 of the first flow rate control valve 7 by another step when the internal tank pressure P1 becomes less than the third pressure P1c, and may increase the aperture x1 of the first flow rate control valve 7 by another step when the internal tank pressure P1 becomes less than the second pressure P1b.

[0038] As the opening degree x1 of the first flow control valve 7 increases stepwise, the flow rate of the liquefied gas in the liquid supply pipe 4 also increases stepwise, so the controller 9 decreases the opening degree x2 of the second flow control valve 12 stepwise.

[0039] As described above, the opening degree x1 of the first flow rate control valve 7 is adjusted based on the internal tank pressure P1, and the opening degree x2 of the second flow rate control valve 12 is adjusted based on the internal pipe pressure P2 of the liquid supply pipe 4. This control continues until, at time t8, the tank filling rate of the liquefied gas tank 3 reaches a predetermined maximum liquid level MAX or the remaining amount in the supply source 2 becomes 0. After the tank filling rate of the liquefied gas tank 3 reaches the maximum liquid level MAX, a predetermined termination process or termination operation is executed.

[0040] According to this embodiment, the first flow rate control valve 7 is controlled so that the flow rate through the first inlet pipe 5 decreases as the tank internal pressure P1 increases. As a result, the flow rate of liquefied gas introduced from above into the liquefied gas tank 3 via the second inlet pipe 6 increases as the tank internal pressure P1 increases, thereby enhancing the effect of suppressing the tank internal pressure P1. In this way, by controlling the distribution ratio of liquefied gas between the first inlet pipe 5 and the second inlet pipe 6 based on the tank internal pressure P1, it is possible to efficiently introduce liquefied gas into the liquefied gas tank 3 with a simple configuration while suppressing an increase in the internal pressure of the liquefied gas tank 3. In particular, when the liquefied gas is liquefied hydrogen, which is prone to generating boil-off gas, it is possible to achieve suitable introduction of the liquefied gas into the liquefied gas tank 3.

[0041] Furthermore, since there is no need to discharge excess boil-off gas to the outside, it is possible to suppress increases in equipment costs and improve the utilization efficiency of the liquefied gas. Furthermore, since there is no need to manually distribute the liquefied gas between the first inlet pipe 5 and the second inlet pipe 6, it is also possible to reduce personnel costs, such as the need for an operator to constantly monitor the tank internal pressure P1 and to develop the skills required for manual operation.

[0042] Furthermore, according to this embodiment, the flow rate of the liquefied gas flowing through the liquid supply pipe 4 is maintained by adjusting the opening degree x2 of the second flow control valve 12 based on the internal pressure P2 of the liquid supply pipe 4. As a result, even if the flow rate of the first introduction pipe 5 is reduced in order to increase the flow rate of the second introduction pipe 6, it is possible to prevent the time required to introduce the liquefied gas into the liquefied gas tank 3 from becoming longer.

[0043] Furthermore, according to this embodiment, when the tank internal pressure P1 is less than a predetermined value P12, the flow switching valve 13 is turned off, and the flow of liquefied gas to the second inlet pipe 6 is blocked. Therefore, when the tank internal pressure P1 is less than the predetermined value P12, liquefied gas is introduced into the liquefied gas tank 3 from the first inlet pipe 5, whose opening degree x1 is 100%. This makes it possible to suppress an increase in pressure loss in each of the pipes 4, 5, and 6.

[0044] Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments, and various improvements, changes, and modifications are possible within the scope of the spirit of the present disclosure.

[0045] [Other embodiments] For example, in the above embodiment, an example has been given in which the opening degree x1 of the first flow rate control valve 7 is controlled in stages based on the internal tank pressure P1. However, instead of this, the opening degree x1 of the first flow rate control valve 7 may be controlled continuously based on the internal tank pressure P1.

[0046] In the above embodiment, the flow switching valve 13 provided in the second inlet pipe 6 is turned on when the tank internal pressure P1 reaches or exceeds the predetermined value P12 after the introduction of the liquefied gas has started. However, the flow switching valve 13 may be switched on after the introduction of the liquefied gas has started, regardless of the tank internal pressure P1. In the above embodiment, the predetermined value P12 of the tank internal pressure P1 at which the flow switching valve 13 is switched on is lower than the first pressure P1a, which is the minimum threshold value of the tank internal pressure P1 for controlling the first flow rate control valve 7 based on the tank internal pressure P1. However, the predetermined value P12 and the first pressure P1a may be the same value. The flow switching valve 13 may be configured to be manually operated. Alternatively, the flow switching valve 13 may be omitted.

[0047] Furthermore, in the above embodiment, an example has been shown in which the first flow rate adjustment valve 7 is installed in the first inlet pipe 5. Alternatively, the first flow rate adjustment valve 7 may be installed in the second inlet pipe 6. In this case, the inner diameter of the second inlet pipe 6 may be equal to or greater than the inner diameter of the first inlet pipe 5. Alternatively, the first flow rate adjustment valve 7 may be installed in both the first inlet pipe 5 and the second inlet pipe 6. In this case, the inner diameter of the first inlet pipe 5 and the inner diameter of the second inlet pipe 6 may be the same.

[0048] Alternatively, the controller 9 may control the second flow rate control valve 12 in the above embodiment based on the tank internal pressure P1, and control the first flow rate control valve 7 in the above embodiment based on the pipe internal pressure P2 of the liquid supply pipe 4. The controller 9 may be able to switch between a first mode in which the first flow rate control valve 7 is controlled based on the tank internal pressure P1 and the second flow rate control valve 12 is controlled based on the pipe internal pressure P2, and a second mode in which the first flow rate control valve 7 is controlled based on the pipe internal pressure P2 and the second flow rate control valve 12 is controlled based on the tank internal pressure P1.

[0049] In the second mode, for example, if the tank internal pressure P1 increases, the controller 9 controls the second flow rate control valve 12 to increase the aperture x2. As the aperture x2 of the second flow rate control valve 12 increases, the pipe internal pressure P2 decreases and the flow rate of the liquid supply pipe 4 increases. At this time, the controller 9 controls the first flow rate control valve 7 to decrease the aperture x1. As a result, the flow rate of the first inlet pipe 5 decreases and the flow rate of the second inlet pipe 6 increases. As the flow rate of the second inlet pipe 6 increases, the pressure loss in the second inlet pipe 6 and the first inlet pipe 5 increases, and the pipe internal pressure P2 of the liquid supply pipe 4 increases; that is, the flow rate of the liquid supply pipe 4 decreases. As a result, the pipe internal pressure P2 is maintained. On the other hand, if the tank internal pressure P1 decreases, the controller 9 controls the second flow rate control valve 12 to decrease the aperture x2. When the opening degree x2 of the second flow control valve 12 decreases, the internal pressure P2 increases and the flow rate of the liquid supply pipe 4 decreases. At this time, the controller 9 controls the first flow control valve 7 to increase the opening degree x1. As a result, the flow rate of the first inlet pipe 5 increases and the flow rate of the second inlet pipe 6 decreases. The decrease in the flow rate of the second inlet pipe 6 reduces the pressure loss in the second inlet pipe 6 and the first inlet pipe 5, and the internal pressure P2 of the liquid supply pipe 4 decreases, i.e., the flow rate of the liquid supply pipe 4 increases. This maintains the internal pressure P2.

[0050] Furthermore, in the above embodiment, an example has been given in which the second flow rate control valve 12 is controlled to maintain the internal pressure P2 of the liquid supply pipe 4 at a predetermined target value P2o in conjunction with the control of the first flow rate control valve 7 based on the internal tank pressure P1, but the control of the second flow rate control valve 12 does not have to be performed. For example, if there are no constraints such as a time limit on the supply source 2, the control of the second flow rate control valve 12 does not have to be performed. In this case, the second sensor 11 and the second flow rate control valve 12 may not be provided.

[0051] In addition, in the above embodiment, an example was given in which the second sensor 11 is a pressure sensor that detects the internal pressure P2 of the liquid supply pipe 4, but instead, the second sensor 11 may be a flow rate sensor that detects the flow rate of the liquid supply pipe 4.

[0052] Furthermore, the controller 9 may estimate the flow rate of the liquid supply pipe 4 and control the second flow control valve so as to maintain the estimated flow rate of the liquid supply pipe 4 at a predetermined target value. For example, the controller 9 may estimate the flow rate of the liquid supply pipe 4 from the total capacity coefficient CVt of the valves 7, 12, and 13 in the piping path 14 and the differential pressure ΔP between the internal pressure P2 of the liquid supply pipe 4 and the internal pressure P1 of the tank. For this purpose, the memory of the controller 9 stores data of flow characteristic functions that indicate the relationship between the capacity coefficient CVi and the opening degree xi for each of the first flow control valve 7, the second flow control valve 12, and the flow switching valve 13.

[0053] The controller 9 acquires the opening x1 of the first flow control valve 7, the opening x2 of the second flow control valve 12, and the opening x3 of the distribution switching valve 13. The controller 9 reads out data of the flow characteristic function for the first flow control valve 7, and acquires a first capacity coefficient CV1 corresponding to the acquired opening x1. Similarly, the controller 9 reads out data of the flow characteristic function for the second flow control valve 12, and acquires a second capacity coefficient CV2 corresponding to the acquired opening x2. Similarly, the controller 9 reads out data of the flow characteristic function for the distribution switching valve 13, and acquires a third capacity coefficient CV3 corresponding to the acquired opening x3.

[0054] In the above embodiment, the control to adjust the opening x2 of the second flow rate adjustment valve 12 is performed after time t1, when the flow switching valve 13 is turned on, and the flow switching valve 13 is in the on state after time t1. In other words, the opening x3 of the flow rate switching valve 13 is 100% after time t1. For this reason, the memory of the controller 9 may store the capacity coefficient CV3 when the opening x3 is 100%, instead of data of the flow rate specification function indicating the relationship between the opening x3 of the flow switching valve 13 and the capacity coefficient CV3.

[0055] The controller 9 calculates a total capacity coefficient CVt of the valves 7, 12, and 13 in the piping path 14 from the first capacity coefficient CV1, the second capacity coefficient CV2, and the third capacity coefficient CV3. The total capacity coefficient CVt is expressed by the following equation.

[0056]

number

[0057] Note that, in the above formula, CV1 may be replaced with CV1+A, CV2 with CV2+B, and CV3 with CV3+C, using an in-pipe resistance coefficient A excluding the first flow rate control valve 7 in the first inlet piping 5, an in-pipe resistance coefficient B excluding the second flow rate control valve 12 in the liquid delivery piping 4, and an in-pipe resistance coefficient C excluding the flow switching valve 13 in the second inlet piping 6. This can improve the accuracy of calculating the total capacity coefficient CVt.

[0058] The controller 9 acquires the pressure P2 inside the liquid supply pipe 4 and the pressure P1 inside the tank, and calculates the differential pressure ΔP = P2 - P1 between the pressure P2 inside the pipe and the pressure P1 inside the tank. The controller 9 estimates the flow rate of the liquid supply pipe 4 from the total capacity coefficient CVt and the differential pressure ΔP. The volumetric flow rate Q of the liquid supply pipe 4 is expressed by the following equation using the specific gravity G of the fluid and a coefficient α.

[0059]

number

[0060] The controller 9 uses the volumetric flow rate Q thus determined as the flow rate of the liquid supply pipe 4 and controls the second flow rate adjustment valve 12 to maintain the flow rate at a target value. This makes it possible to more accurately estimate the flow rate of the liquid supply pipe 4 from the openings x1, x2, and x3 of the valves 7, 12, and 13 included in the piping path 14. This therefore makes it possible to improve the control accuracy of the second flow rate adjustment valve 12.

[0061] Alternatively, the controller 9 may estimate the flow rate of the liquid supply pipe 4 from the liquid level in the liquefied gas tank 3. FIG. 3 is a schematic diagram showing a general configuration of a liquefied gas introduction system according to a modified example of an embodiment of the present disclosure. In the liquefied gas introduction system 1B shown in FIG. 3, the same components as those in the liquefied gas introduction system 1 shown in FIG. 1 are given the same reference numerals, and descriptions thereof will be omitted. In this modified example, the liquefied gas introduction system 1B is provided with a third sensor 15 that detects the liquid level L in the liquefied gas tank 3.

[0062] In this modification, the controller 9 acquires the liquid level L in the liquefied gas tank 3 detected by the third sensor 15 at predetermined intervals. The controller 9 calculates the change over time in the liquid level L from the liquid level acquired at the predetermined intervals. The controller 9 estimates the flow rate in the liquid supply pipe 4 from the change over time in the liquid level L. The controller 9 uses the flow rate thus determined as the flow rate in the liquid supply pipe 4 and controls the second flow control valve 12 to maintain the flow rate at a target value. In this case, it is not possible to estimate the instantaneous flow rate, as compared to when the flow rate in the liquid supply pipe 4 is estimated from the total capacity coefficient CVt and the differential pressure ΔP. Instead, this modification has the advantages of eliminating the need to install a second sensor 11 that measures the internal pressure P2 in the liquid supply pipe 4 and eliminating the need for complex calculations.

[0063] In this modification, the target value of the flow rate in the liquid supply pipe 4 may change depending on the liquid level L. For example, when the liquid level L is less than a predetermined reference value, the target value of the flow rate in the liquid supply pipe 4 may be set to a predetermined fixed value, and when the liquid level L is equal to or greater than the reference value, the target value of the flow rate in the liquid supply pipe 4 may be set to a value that gradually decreases from the fixed value as the liquid level L increases. In this case, a flow rate target value table indicating target values ​​of flow rates according to the liquid level L is stored in the memory. The controller 9 reads out the flow rate target value at the liquid level L detected by the third sensor 15 from the flow rate target value table and compares it with the calculated flow rate. If the flow rate is smaller than the flow rate target value, the controller 9 increases the opening degree x2 of the second flow rate control valve 12, and if the flow rate is greater than the flow rate target value, the controller 9 decreases the opening degree x2 of the second flow rate control valve 12.

[0064] In the above-described modification including the third sensor 15, instead of estimating the flow rate of the liquid supply pipe 4 from the change in the liquid level L over time, the controller 9 may control the second flow rate control valve 12 so that the liquid level L detected by the third sensor 15 becomes a target liquid level Lo corresponding to the elapsed time from the start of introduction of the liquefied gas into the liquefied gas tank 3. In this case, a target liquid level table indicating the target liquid level Lo corresponding to the elapsed time is stored in the memory. For example, the target liquid level Lo is set to monotonically increase with elapsed time. The controller 9 compares the liquid level L detected by the third sensor 15 with the target liquid level Lo corresponding to the elapsed time, and increases the aperture x2 of the second flow rate control valve 12 if the liquid level L is lower than the target liquid level Lo, or decreases the aperture x2 of the second flow rate control valve 12 if the liquid level L is higher than the target liquid level Lo. This allows the liquefied gas to be introduced into the liquefied gas tank 3 according to a predetermined schedule using a simple configuration without performing complex calculations.

[0065] Furthermore, in the above-described modified example provided with the third sensor 15, instead of estimating the flow rate of the liquid supply pipe 4 from the change over time of the liquid level L, the controller 9 may calculate a liquid level rate ΔL indicating the amount of liquid level rise per unit time from the liquid level L detected by the third sensor 15, and control the second flow control valve 12 so that the liquid level rate ΔL becomes a target liquid level rate ΔLo corresponding to the liquid level L. In this case, a target liquid level rate table indicating the target liquid level rate ΔLo corresponding to the liquid level L is stored in the memory. For example, the target liquid level rate ΔLo may be set to a predetermined fixed value when the liquid level L is below a predetermined reference value, and may be set to a value gradually decreasing from the fixed value as the liquid level L increases when the liquid level L is equal to or greater than the reference value. The controller 9 calculates the liquid level rate ΔL by time-differentiating the liquid level L detected by the third sensor 15. The controller 9 reads the target liquid level rate ΔLo at the liquid level L detected by the third sensor 15 from the target liquid level rate table and compares it with the calculated liquid level rate ΔL. If the liquid level rate ΔL is lower than the target liquid level rate ΔLo, the controller 9 increases the opening x2 of the second flow rate control valve 12, and if the liquid level rate ΔL is higher than the target liquid level rate ΔLo, the controller 9 decreases the opening x2 of the second flow rate control valve 12. This makes it possible to introduce liquefied gas into the liquefied gas tank 3 according to a predetermined schedule using a simple configuration without performing complex calculations.

[0066] Furthermore, in the above embodiment, an example has been given in which one controller 9 controls the first flow rate adjustment valve 7, the second flow rate adjustment valve 12, and the flow switching valve 13. Alternatively, two or more controllers may be configured as a controller for controlling the first flow rate adjustment valve 7, a controller for controlling the second flow rate adjustment valve 12, and a controller for controlling the flow switching valve 13.

[0067] Summary of this disclosure [Item 1] A liquefied gas introduction system according to one embodiment of the present disclosure is a liquefied gas introduction system that introduces liquefied gas from a liquefied gas supply source into a liquefied gas tank for storing liquefied gas, and includes: a liquid delivery pipe that receives liquefied gas from the supply source and sends it downstream; a first introduction pipe connected to the liquid delivery pipe and introduces liquefied gas into the liquefied gas tank; a second introduction pipe connected to the liquid delivery pipe and having an outlet disposed within the liquefied gas tank above the outlet of the first introduction pipe and introducing liquefied gas into the liquefied gas tank; a first flow rate control valve interposed in at least one of the first introduction pipe and the second introduction pipe; a first sensor that detects the pressure within the liquefied gas tank; and a controller, wherein the controller controls the first flow rate control valve so that the flow rate of the first introduction pipe decreases and the flow rate of the second introduction pipe increases as the pressure within the liquefied gas tank increases.

[0068] According to the above configuration, the first flow rate control valve is controlled so that the flow rate through the first inlet pipe decreases as the pressure inside the liquefied gas tank increases. As a result, the flow rate of liquefied gas introduced into the liquefied gas tank from above via the second inlet pipe increases as the pressure inside the liquefied gas tank increases, thereby enhancing the effect of suppressing the pressure inside the liquefied gas tank. In this way, by controlling the distribution ratio of liquefied gas between the first inlet pipe and the second inlet pipe based on the pressure inside the liquefied gas tank, it is possible to efficiently introduce liquefied gas into the liquefied gas tank while suppressing an increase in the internal pressure of the liquefied gas tank with a simple configuration.

[0069] [Item 2] In the liquefied gas introduction system of item 1, the first flow rate control valve is interposed in the first introduction pipe, and the liquefied gas introduction system includes a flow switching valve that switches between flow and blocking to the second introduction pipe, and the controller may control the flow switching valve to allow the liquefied gas to flow to the second introduction pipe when the pressure in the liquefied gas tank is equal to or higher than a predetermined value.

[0070] [Item 3] The liquefied gas introduction system of item 1 or 2 may further include a second sensor that detects the internal pressure or flow rate of the liquid supply pipe and a second flow rate adjustment valve that adjusts the flow rate of the liquid supply pipe, and the controller may control the second flow rate adjustment valve to maintain the internal pressure or flow rate of the liquid supply pipe at a predetermined target value. This maintains the flow rate of the liquefied gas flowing through the liquid supply pipe by adjusting the second flow rate adjustment valve based on the internal pressure or flow rate of the liquid supply pipe. This prevents an increase in the time required to introduce the liquefied gas into the liquefied gas tank, even if the pressure loss in each pipe increases due to the flow rate of the first introduction pipe being reduced in order to increase the flow rate of the second introduction pipe.

[0071] [Item 4] The liquefied gas introduction system of item 2 may include a second sensor that detects the pressure inside the liquid supply pipe and a second flow rate control valve that is interposed in the liquid supply pipe and adjusts the flow rate of the liquid supply pipe. The controller may acquire a first capacity coefficient of the first flow rate control valve, a second capacity coefficient of the second flow rate control valve, and a third capacity coefficient of the flow switching valve, calculate a total capacity coefficient of the valves in a piping path including the liquid supply pipe, the first introduction pipe, and the second introduction pipe from the first capacity coefficient, the second capacity coefficient, and the third capacity coefficient, calculate a differential pressure between the pressure inside the liquid supply pipe and the pressure in the liquefied gas tank, estimate the flow rate of the liquid supply pipe from the total capacity coefficient and the differential pressure, and control the second flow rate control valve to maintain the estimated flow rate of the liquid supply pipe at a predetermined target value. This allows the flow rate of the liquid supply pipe to be more accurately estimated from the capacity coefficient of each valve included in the piping path. This improves the control accuracy of the second flow rate control valve.

[0072] [Item 5] The liquefied gas introduction system of item 1 or 2 may further include a third sensor that detects the liquid level in the liquefied gas tank, and a second flow rate adjustment valve that is interposed in the liquid supply pipe and adjusts the flow rate of the liquid supply pipe, and the controller may acquire the liquid level, calculate a change in the liquid level over time, estimate the flow rate of the liquid supply pipe from the change in the liquid level over time, and control the second flow rate adjustment valve to maintain the estimated flow rate of the liquid supply pipe at a predetermined target value. This allows the flow rate of the liquid supply pipe to be estimated using a simple configuration without performing complex calculations.

[0073] [Item 6] The liquefied gas introduction system of item 1 or 2 may further include a third sensor that detects the liquid level in the liquefied gas tank, and a second flow rate adjustment valve that is interposed in the liquid feed pipe and adjusts the flow rate of the liquid in the liquid feed pipe, and the controller may control the second flow rate adjustment valve so that the liquid level becomes a target liquid level according to the elapsed time from the start of introduction of the liquefied gas into the liquefied gas tank. This allows the liquefied gas to be introduced into the liquefied gas tank according to a predetermined schedule using a simple configuration without performing complex calculations.

[0074] [Item 7] The liquefied gas introduction system of item 1 or 2 may further include a third sensor that detects the liquid level in the liquefied gas tank, and a second flow rate adjustment valve that is interposed in the liquid supply pipe and adjusts the flow rate of the liquid supply pipe, wherein the controller acquires the liquid level and calculates a liquid level rate that indicates the amount of liquid level rise per unit time, and controls the second flow rate adjustment valve so that the liquid level rate becomes a target liquid level rate corresponding to the liquid level. This allows liquefied gas to be introduced into the liquefied gas tank according to a predetermined schedule using a simple configuration without performing complex calculations.

[0075] [Item 8] In the liquefied gas introduction system according to any one of Items 1 to 7, the liquefied gas tank may be a marine liquefied gas fuel tank installed on a ship.

[0076] [Item 9] In the liquefied gas introduction system according to any one of Items 1 to 8, the liquefied gas may be liquefied hydrogen.

[0077] [Item 10] A liquefied gas introduction system according to another aspect of the present disclosure is a liquefied gas introduction system that introduces liquefied gas from a liquefied gas supply source into a liquefied gas tank for storing liquefied gas, and includes a liquid transfer pipe that receives liquefied gas from the supply source and transfers it downstream, a first introduction pipe that is connected to the liquid transfer pipe and introduces liquefied gas into the liquefied gas tank, a second introduction pipe that is connected to the liquid transfer pipe and has a discharge port disposed in the liquefied gas tank above the discharge port of the first introduction pipe and introduces liquefied gas into the liquefied gas tank, and a coupling between at least the first introduction pipe and the second introduction pipe. the liquid supply piping includes a first flow rate control valve interposed in either one of the tanks, a second flow rate control valve interposed in the liquid supply piping, a first sensor that detects the pressure in the liquefied gas tank, a second sensor that detects the internal pressure or flow rate of the liquid supply piping, and a controller, wherein the controller controls the second flow rate control valve so that the flow rates of the liquid supply piping and the second inlet piping increase as the pressure in the liquefied gas tank increases, and controls the first flow rate control valve so that the flow rate of the first inlet piping decreases and the flow rate of the second inlet piping increases as the internal pressure of the liquid supply piping decreases or the flow rate of the liquid supply piping increases. [Explanation of symbols]

[0078] 1,1B Liquefied gas introduction system 2 Source 3. Liquefied gas tanks 4 Liquid delivery piping 5. First introduction pipe 5a Discharge port of first inlet pipe 6 Second introduction pipe 6a Discharge port of second inlet pipe 7. First flow control valve 8 First Sensor 9 Controller 10 Processing circuit 11 Second sensor 12 Second flow control valve 13 Flow switching valve 15 Third Sensor

Claims

1. A liquefied gas introduction system that introduces liquefied gas from a liquefied gas supply source into a liquefied gas tank for storing liquefied gas, a liquid delivery pipe that receives the liquefied gas from the supply source and delivers it downstream; a first introduction pipe connected to the liquid delivery pipe and configured to introduce liquefied gas into the liquefied gas tank; a second introduction pipe connected to the liquid supply pipe, the second introduction pipe having a discharge port disposed in the liquefied gas tank above the discharge port of the first introduction pipe, and introducing the liquefied gas into the liquefied gas tank; a first flow rate control valve interposed in at least one of the first inlet pipe and the second inlet pipe; a first sensor for detecting a pressure in the liquefied gas tank; a controller; The controller controls the first flow rate control valve so that the flow rate of the first introduction pipe decreases and the flow rate of the second introduction pipe increases as the pressure in the liquefied gas tank increases.

2. the first flow rate control valve is interposed in the first introduction pipe, the liquefied gas introduction system includes a flow switching valve that switches between flow and cut-off to the second introduction pipe, 2. The liquefied gas introduction system according to claim 1, wherein the controller controls the flow switching valve to allow the liquefied gas to flow to the second introduction pipe when the pressure in the liquefied gas tank is equal to or higher than a predetermined value.

3. a second sensor for detecting an internal pressure or a flow rate of the liquid supply pipe; a second flow rate control valve interposed in the liquid supply pipe and controlling the flow rate of the liquid supply pipe; 3. The liquefied gas introducing system according to claim 1, wherein the controller controls the second flow rate adjustment valve so as to maintain the internal pressure or flow rate of the liquid supply pipe at a predetermined target value.

4. a second sensor for detecting a pressure inside the liquid supply pipe; a second flow rate control valve interposed in the liquid supply pipe and controlling the flow rate of the liquid supply pipe; The controller obtaining a first capacity coefficient of the first flow rate control valve, a second capacity coefficient of the second flow rate control valve, and a third capacity coefficient of the flow switching valve; calculating a total capacity coefficient of the valves in a piping path including the liquid delivery piping, the first inlet piping, and the second inlet piping from the first capacity coefficient, the second capacity coefficient, and the third capacity coefficient; Calculating a differential pressure between the pressure inside the liquid sending pipe and the pressure inside the liquefied gas tank; a flow rate of the liquid delivery pipe is estimated from the total capacity coefficient and the differential pressure; The liquefied gas introducing system according to claim 2 , wherein the second flow rate adjustment valve is controlled so as to maintain the estimated flow rate of the liquid supply pipe at a predetermined target value.

5. a third sensor for detecting a liquid level in the liquefied gas tank; a second flow rate control valve interposed in the liquid supply pipe and controlling the flow rate of the liquid supply pipe; The controller acquiring the liquid level, calculating a change in the liquid level over time, and estimating a flow rate of the liquid delivery pipe from the change in the liquid level over time; 3. The liquefied gas introducing system according to claim 1, wherein the second flow rate adjustment valve is controlled so as to maintain the estimated flow rate of the liquid supply pipe at a predetermined target value.

6. a third sensor for detecting a liquid level in the liquefied gas tank; a second flow rate control valve interposed in the liquid supply pipe and controlling the flow rate of the liquid supply pipe; The liquefied gas introduction system according to claim 1 or 2, wherein the controller controls the second flow control valve so that the liquid level becomes a target liquid level according to the elapsed time from the start of introduction of the liquefied gas into the liquefied gas tank.

7. a third sensor for detecting a liquid level in the liquefied gas tank; a second flow rate control valve interposed in the liquid supply pipe and controlling the flow rate of the liquid supply pipe; The controller The liquid level is acquired and a liquid level rate indicating the amount of liquid level rise per unit time is calculated; The liquefied gas introducing system according to claim 1 or 2, wherein the second flow rate adjustment valve is controlled so that the liquid level rate becomes a target liquid level rate corresponding to the liquid level.

8. 3. The liquefied gas introduction system according to claim 1, wherein the liquefied gas tank is a marine liquefied gas fuel tank mounted on a ship.

9. The liquefied gas introduction system according to claim 1 or 2, wherein the liquefied gas is liquefied hydrogen.

10. A liquefied gas introduction system that introduces liquefied gas from a liquefied gas supply source into a liquefied gas tank for storing liquefied gas, a liquid delivery pipe that receives the liquefied gas from the supply source and delivers it downstream; a first introduction pipe connected to the liquid delivery pipe and configured to introduce liquefied gas into the liquefied gas tank; a second introduction pipe connected to the liquid supply pipe, the second introduction pipe having a discharge port disposed in the liquefied gas tank above the discharge port of the first introduction pipe, and introducing the liquefied gas into the liquefied gas tank; a first flow rate control valve interposed in at least one of the first inlet pipe and the second inlet pipe; a second flow rate control valve interposed in the liquid delivery pipe; a first sensor for detecting a pressure in the liquefied gas tank; a second sensor for detecting an internal pressure or a flow rate of the liquid supply pipe; a controller; The controller controls the second flow rate control valve so that the flow rates of the liquid supply pipe and the second introduction pipe increase as the pressure in the liquefied gas tank increases, and controls the first flow rate control valve so that the flow rate of the first introduction pipe decreases and the flow rate of the second introduction pipe increases as the internal pressure of the liquid supply pipe decreases or the flow rate increases.

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