Hydrogen storage system

Abstract

The present invention addresses the problem of providing a hydrogen storage system in which the deterioration of a storage alloy can be suppressed.　The present invention relates to a hydrogen storage system provided with a hydrogen production part for producing hydrogen and a storage tank, wherein the storage tank is provided with: a storage alloy which stores the produced hydrogen; a housing in which the storage alloy is housed; a first opening which is provided in the housing and into which a supply gas containing the produced hydrogen is sent from the hydrogen production part side; and a second opening which is provided in the housing separately from the first opening and from which the supply gas is sent out to the outside.

Description

Hydrogen Storage System

[0001] The present disclosure relates to hydrogen storage systems.

[0002] Conventionally, a hydrogen storage system is known, as disclosed in Japanese Patent Application Laid-Open No. 2020-173972, in which hydrogen stored in a hydrogen storage alloy in a storage tank is sent from the storage tank to a hydrogen-utilizing device at a predetermined timing. In Japanese Patent Application Laid-Open No. 2020-173972, a hydrogen production device is provided upstream of the storage tank. A supply gas containing hydrogen produced by the hydrogen production device is sent into the storage tank through an opening provided in the storage tank. The hydrogen in the sent supply gas is stored in the hydrogen storage alloy by lowering the temperature of the hydrogen storage alloy.

[0003] Furthermore, in JP 2020-173972 A, a hydrogen-utilizing device is connected to the storage tank. The hydrogen stored in the hydrogen storage alloy is released from the hydrogen storage alloy by increasing the temperature of the hydrogen storage alloy. The hydrogen released from the hydrogen storage alloy is sent to the hydrogen-utilizing device via the same opening. Hereinafter, in this specification, the hydrogen storage alloy may also be simply referred to as the "storage alloy."

[0004] It is known that when hydrogen is stored in a hydrogen storage system, trace amounts of moisture contained in the gas supplied to the storage tank can cause the storage alloy to deteriorate. As a means for suppressing the deterioration of the storage alloy, Japanese Patent Application Laid-Open No. 2020-173972 discloses a hydrogen production device equipped with a dehumidifier. Specifically, the dew point temperature (in other words, the dew point) of the supply gas is lowered using a dehumidifier provided upstream of the storage tank. By reducing the moisture content of the supply gas, the deterioration of the storage alloy is suppressed.

[0005] Patent Document 1: JP 2020-173972 A

[0006] The present inventors have noted that when hydrogen is stored, the deterioration of the storage alloy progresses as the moisture concentration in the supply gas inside the storage tank increases. Based on this new finding, the present disclosure was developed based on the idea that the deterioration of the storage alloy can be suppressed by suppressing the increase in moisture concentration. In this regard, JP 2020-173972 A does not disclose the technical idea of ​​suppressing the deterioration of the storage alloy by suppressing the increase in moisture concentration, as disclosed in the present disclosure.

[0007] The present disclosure has been made in light of the above-mentioned problems, and provides a hydrogen storage system that can suppress the deterioration of the storage alloy.

[0008] The hydrogen storage system according to the first aspect comprises a hydrogen production unit that produces hydrogen, a storage alloy that stores the produced hydrogen, a housing that houses the storage alloy inside, and an absorption tank having a first opening provided in the housing and into which a supply gas containing the hydrogen produced from the hydrogen production unit side is supplied, and a second opening provided in the housing separately from the first opening and which sends the supply gas to the outside.

[0009] In a first embodiment, the storage tank is provided with a second opening for sending out the supply gas, separate from a first opening for sending in the supply gas. The supply gas sent in from the first opening at the inlet flows inside the housing of the storage tank and is sent out from the second opening at the outlet. That is, the first opening is an inlet for the supply gas containing hydrogen toward the storage alloy. The second opening is an outlet for the supply gas after flowing around the storage alloy.

[0010] Therefore, it is possible to send the supply gas to the outside of the housing from the second opening separately from the first opening. As a result, compared to, for example, a case where the storage tank is provided with only the first opening and no supply gas outlet, it is possible to reduce the retention of supply gas inside the housing during hydrogen storage. Therefore, the concentration of moisture contained in the supply gas inside the storage tank due to hydrogen storage is mitigated, thereby suppressing deterioration of the storage alloy.

[0011] In the hydrogen storage system of the second aspect, in the hydrogen storage system of the first aspect, the housing is cylindrical, the first opening is provided at one end in the axial direction of the cylindrical housing, and the second opening is provided at the other end in the axial direction.

[0012] In the second aspect, the first opening is provided at one axial end of the cylindrical housing, and the second opening is provided at the other axial end. That is, the inlet and the outlet are spaced apart at both ends of the cylindrical storage tank. Therefore, compared to a case where the first opening at the inlet and the second opening at the outlet are arranged side by side near one end of the housing, for example, the supply gas is less likely to stagnate inside the housing.

[0013] In the hydrogen storage system of the third aspect, in the hydrogen storage system of the first or second aspect, a dehumidifier is provided between the hydrogen production unit and the storage tank, and a return pipe is provided between the dehumidifier and the second opening to return the supply gas sent out from the second opening to the dehumidifier.

[0014] In a third aspect, a return pipe is provided between the dehumidifier and the second opening, for returning the supply gas discharged from the second opening to the dehumidifier, so that hydrogen in the supply gas discharged from the second opening can be reused for storage.

[0015] The hydrogen storage system according to the fourth aspect is a hydrogen storage system according to any one of the first to third aspects, and is equipped with an arithmetic and control device that calculates the moisture concentration in the supply gas inside the storage tank and sends the supply gas inside the storage tank to the outside in accordance with the calculated moisture concentration.

[0016] In the fourth aspect, when hydrogen is stored, an increase in the concentration of moisture contained in the supply gas inside the storage tank can be effectively suppressed, thereby suppressing deterioration of the storage alloy.

[0017] According to the present disclosure, it is possible to provide a hydrogen storage system that can suppress deterioration of the storage alloy.

[0018] Fig. 1 is a block diagram illustrating a hydrogen storage system according to an embodiment of the present disclosure; Fig. 2 is a block diagram illustrating a calculation and control device of the hydrogen storage system according to the present embodiment; Fig. 3 is a graph illustrating the relationship between the dew point temperature of the supply gas and the purity of hydrogen; Fig. 4 is a graph illustrating the relationship between the dew point temperature and the water vapor pressure; Fig. 5 is a flowchart illustrating a method for controlling the water concentration using the hydrogen storage system according to the present embodiment; Fig. 6 is a block diagram illustrating a hydrogen storage system according to a comparative example; Fig. 7 is a diagram illustrating another example of an occlusion tank;

[0019] Embodiments of the present disclosure will be described below. However, the present disclosure is not limited to the following embodiments. When embodiments are described with reference to drawings in the present disclosure, the configuration of the embodiment is not limited to the configuration shown in the drawings. Furthermore, the sizes of components in each drawing are conceptual, and the relative size relationships between components are not limited to these.

[0020] In the following description of the drawings, like parts are designated by like reference numerals. However, the drawings are schematic, and the relationship between thickness and planar dimensions, and the thickness ratio of each device and each component, differ from the actual ones. Therefore, specific thicknesses and dimensions should be determined by taking into consideration the following explanation. Furthermore, there are parts in which the dimensional relationships and ratios differ between the drawings. Furthermore, unless otherwise specified in the specification, the number of each component element of the present disclosure is not limited to one, and multiple elements may be present.

[0021] In the following embodiments, components (including element steps, etc.) are not essential unless otherwise specified. The same applies to numerical values ​​and their ranges, and do not limit the present disclosure. In the present disclosure, numerical ranges indicated using "to" include the numerical values ​​before and after "to" as the minimum and maximum values, respectively.

[0022] In the numerical ranges described in stages in this disclosure, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in the numerical ranges described in this disclosure, the upper or lower limit value of that numerical range may be replaced with a value shown in the examples.

[0023] In the present disclosure, when components are contained, each component may contain multiple types of corresponding substances. When multiple types of substances corresponding to each component are present in the composition, the content or amount of each component means the total content or amount of the multiple types of substances present in the composition, unless otherwise specified.

[0024] In the present disclosure, the particles corresponding to each component may contain multiple types of particles. When multiple types of particles corresponding to each component are present in the composition, the particle size of each component means the value for a mixture of the multiple types of particles present in the composition, unless otherwise specified.

[0025] In the present disclosure, the terms "layer" and "film" include cases where the layer or film is formed over the entire area when the area in which the layer or film is present is observed, as well as cases where the layer or film is formed over only a portion of the area.

[0026] <Hydrogen Storage System> First, a hydrogen storage system 10 according to this embodiment will be described with reference to Figures 1 to 4. As shown in Figure 1, the hydrogen storage system 10 according to this embodiment includes a water electrolysis device 12, a dehumidifier 14, an MH tank 16, hydrogen utilization equipment 30, and an arithmetic and control device 50.

[0027] The dehumidifier 14 is provided between the water electrolysis device 12 and the MH tank 16. The water electrolysis device 12 and the dehumidifier 14 are connected by a first pipe P1. The dehumidifier 14 and the MH tank 16 are connected by a second pipe P2. The MH tank 16 and the hydrogen-utilizing equipment 30 are connected by a third pipe P3.

[0028] The return pipe PR is provided between the dehumidifier 14 and the second opening 16A2. Specifically, the return pipe PR branches off from the third pipe P3 at a position between the MH tank 16 and the hydrogen-using device 30 and extends toward the first pipe P1. That is, the return pipe PR connects the second opening 16A2 at the outlet of the MH tank 16 to a position upstream of the dehumidifier 14. The return pipe PR returns the supply gas sent out from the second opening 16A2 to the dehumidifier 14.

[0029] A first valve 22 that opens and closes the second pipe P2 is provided in the second pipe P2 between the dehumidifier 14 and the MH tank 16. The first valve 22 controls the flow of fluid flowing inside the second pipe P2. A second valve 24 that opens and closes the third pipe P3 is provided in the third pipe P3 between the MH tank 16 and the hydrogen-using equipment 30. The second valve 24 controls the flow of fluid flowing inside the third pipe P3.

[0030] A pressure booster 18 is provided in the return pipe PR between the MH tank 16 and the dehumidifier 14. The pressure booster 18 can be configured, for example, by a blower or a pump. The pressure booster sends the gas out of the MH tank 16 and promotes the return of the gas to the dehumidifier 14. The returned gas may include any of hydrogen released by the storage alloy 16B, a supply gas containing hydrogen, and a mixed gas of hydrogen and the supply gas.

[0031] (Water Electrolysis Apparatus) The water electrolysis apparatus 12 corresponds to the hydrogen production unit of the present disclosure. The water electrolysis apparatus 12 produces hydrogen by electrolyzing water.

[0032] (MH Tank) The MH tank 16 corresponds to the storage tank of the present disclosure. In this embodiment, "MH" means a hydrogen storage alloy. The MH tank 16 functions as a hydrogen storage unit. The MH tank 16 has a housing 16A, a storage alloy 16B, a first opening 16A1, and a second opening 16A2. The MH tank 16 is provided with a thermal circuit (not shown). The thermal circuit heats the storage alloy 16B to increase its temperature, and cools the storage alloy 16B to decrease its temperature.

[0033] (Housing) In this embodiment, the housing 16A is cylindrical, but in the present disclosure, the shape of the housing (in other words, the tank shell) can be changed as appropriate. The storage alloy 16B is accommodated inside the housing 16A.

[0034] (Storage alloy) The storage alloy 16B stores the produced hydrogen. For example, the storage alloy 16B is lanthanum nickel (LaNi ５In the present disclosure, the type of the storage alloy 16B is not limited to this, and may be any type.

[0035] (Openings) The first opening 16A1 is provided at one axial end (left end in FIG. 1 ) of the cylindrical housing 16A. The second opening 16A2 is provided at the other axial end (right end in FIG. 1 ) of the cylindrical housing 16A. The second opening 16A2 is provided in the housing 16A separately from the first opening 16A1.

[0036] By connecting the second pipe P2 to the first opening 16A1, a supply gas containing hydrogen produced from the water electrolysis device 12 is sent to the first opening 16A1. By connecting the third pipe P3 to the second opening 16A2, a supply gas containing hydrogen released from the storage alloy 16B or sent from the water electrolysis device 12 is sent to the outside from the second opening 16A2. That is, the first opening 16A1 in this embodiment is a gas inlet. The second opening 16A2 in this embodiment is a gas outlet.

[0037] The number of first openings 16A1 functioning as inlets and the number of first openings 16A1 functioning as outlets can each be set to one or more. In addition, in the present embodiment, the first openings 16A1 and the second openings 16A2 are respectively provided at one end (the left end in FIG. 1 ) and the other end (the right end in FIG. 1 ) of the gas flow direction, and are spaced apart from each other. However, this disclosure is not limited to this. In the present embodiment, the first openings 16A1 and the second openings 16A2 may be arranged adjacent to each other, for example, on the side of one end of the gas flow direction.

[0038] (Hydrogen-utilizing equipment) The hydrogen-utilizing equipment 30 is located outside the MH tank 16. Hydrogen is delivered to the hydrogen-utilizing equipment 30 through the second opening 16A2. The hydrogen-utilizing equipment 30 is a device that utilizes the hydrogen delivered through the second opening 16A2. The hydrogen-utilizing equipment 30 of this embodiment is, for example, a power generation device. Note that, in the present disclosure, the type of hydrogen-utilizing equipment is not limited to this and can be set arbitrarily.

[0039] (Calculation and Control Device) The calculation and control device 50 is connected to the water electrolysis device 12, the dehumidifier 14, the MH tank 16, the booster device 18, the hydrogen-using equipment 30, the first valve 22, the second valve 24, and a thermal circuit (not shown).

[0040] (Concentration Control) The arithmetic and control device 50 calculates the moisture concentration in the supply gas inside the MH tank 16 (i.e., inside the housing 16A). In other words, the arithmetic and control device 50 predicts the moisture concentration inside the MH tank 16. A specific method for calculating the moisture concentration will be described later. Then, the arithmetic and control device 50 sends (i.e., purges) the supply gas inside the MH tank 16 to the outside in accordance with the calculated moisture concentration. The moisture concentration inside the MH tank 16 is controlled by sending the supply gas to the outside of the MH tank 16.

[0041] Specifically, when the calculated moisture concentration exceeds a preset reference concentration, the arithmetic and control device 50 sends the supply gas inside the MH tank 16 to the outside. Note that in the present disclosure, the condition for sending the supply gas to the outside is not limited to a comparison between the calculated moisture concentration and the reference concentration, and the condition may be set using, for example, an average or rate of change of multiple moisture concentrations calculated during a preset measurement time.

[0042] Next, the internal structure of the arithmetic and control device 50 will be described with reference to Fig. 2. As shown in Fig. 2, the arithmetic and control device 50 has a CPU (Central Processing Unit: processor) 51, a ROM (Read Only Memory) 52, a RAM (Random Access Memory) 53, a storage 54, a user interface 55, and a communication interface 56. Each component is connected to each other via a bus 57 so as to be able to communicate with each other.

[0043] The CPU 51 is a central processing unit that executes various programs and controls each part. That is, the CPU 51 reads programs from the ROM 52 or the storage 54 and executes the programs using the RAM 53 as a work area. The CPU 51 controls the above components and performs various arithmetic processing in accordance with the programs recorded in the ROM 52 or the storage 54. The arithmetic and control device 50 has at least one processor. In this embodiment, the ROM 52 or the storage 54 can store a concentration control program.

[0044] The ROM 52 stores various programs and various data. The RAM 53 temporarily stores programs or data as a working area. The storage 54 is configured with an HDD (Hard Disk Drive) or an SSD (Solid State Drive) and stores various programs including an operating system and various data. The programs may be provided in a form recorded on a recording medium such as a CD-ROM (Compact Disk Read Only Memory), a DVD-ROM (Digital Versatile Disk Read Only Memory), or a USB (Universal Serial Bus) memory. The programs may also be downloaded from an external device via a network.

[0045] The user interface 55 is an interface used when a user uses the arithmetic and control device 50. The user interface 55 may include, for example, at least one of a liquid crystal display equipped with a touch panel that allows the user to perform touch operations, a voice input receiving unit that receives voice input from the user, and a button that can be pressed by the user. The display unit of this embodiment is an example of the user interface 55. Note that the user interface 55 is not essential.

[0046] The communication interface 56 is an interface for the arithmetic and control device 50 to communicate with other devices, and uses standards such as Ethernet (registered trademark), FDDI, and Wi-Fi (registered trademark).

[0047] When executing the concentration control program of this embodiment, the arithmetic and control device 50 realizes various functions using the above hardware resources. The arithmetic and control device 50 has a calculation unit, a comparison unit, and a transmission unit as functional components realized by the arithmetic and control device 50. Each functional component is realized by the CPU 51 reading and executing the concentration control program stored in the ROM 52 or the storage 54.

[0048] (Reference Concentration) The reference concentration is determined taking into consideration the type of metal in the MH tank 16 and a preset allowable deterioration range. In this embodiment, the reference concentration is 300 ppm. However, in the present disclosure, the reference concentration is not limited to this and can be changed as appropriate.

[0049] Next, the knowledge regarding the relationship between the increase in water concentration and the deterioration of the storage alloy and the reference concentration in this embodiment will be described in detail with reference to Figures 3 and 4. First, it is known that hydrogen storage alloys deteriorate (in other words, corrode) depending on the cycle of absorption and desorption. Specific modes of deterioration include oxidation of the surface of the hydrogen storage alloy by water vapor and modes due to hydroxylation reactions.

[0050] Regarding the degradation behavior, for example, in the paper by GD Sandrock and PD Goodell, ５ It has been reported that in the case of hydrogen storage alloys of this type, degradation accelerates when the moisture concentration is 300 ppm or higher (GD Sandrock and P.D. Goodell, Journal of the Less Common Metals, Volume 73, Issue 1, September 1, 1980, Pages 161-168). In other words, a moisture concentration of 300 ppm is an indicator of degradation.

[0051] When the hydrogen supplied to the storage tank is mainly produced by electrolysis using a water electrolysis device, the supply gas containing the produced hydrogen contains moisture at an absolute humidity equivalent to the water electrolysis temperature. For this reason, a system is generally used in which moisture is removed from the supply gas using a dehumidifier to a dew point temperature of, for example, about −70° C. to −50° C., and then the hydrogen in the supply gas is absorbed into the storage alloy, thereby suppressing deterioration of the storage alloy.

[0052] On the other hand, inside a typical storage tank such as the one described above, basically only the hydrogen in the supply gas is stored. Therefore, when the storage alloy stores hydrogen, the trace amount of water vapor, which is the remaining component other than hydrogen in the supply gas, is concentrated, resulting in an increase in the moisture concentration in the supply gas.

[0053] Figure 3 is a graph showing the relationship between the dew point temperature of the supply gas and the purity of hydrogen, as disclosed in the above-mentioned paper by GD Sandrock and PD Goodell. ５ It is assumed that all impurities other than hydrogen in the hydrogen-containing supply gas are water vapor. The pressure of the supply gas is 0.9 MPa. In the graph of FIG. 3, a saturated region A and a degraded region B are illustrated by bidirectional arrows extending in the left-right direction.

[0054] Saturation region A is the range of dew point temperatures for hydrogen purity in which, when the supply gas is stored inside the storage tank from 0% to 100% and water vapor condenses as hydrogen is absorbed, the space inside the storage tank is filled with a saturated vapor pressure of 50° C. The space inside the storage tank is set to 50% of the total volume inside the housing excluding the storage alloy.

[0055] That is, the void filled with saturated vapor pressure at 50°C is assumed to be half the total volume of the part inside the housing excluding the storage alloy, as the dead volume of the storage tank. Furthermore, deterioration region B is the range of dew point temperatures relative to hydrogen purity where a moisture concentration of 300 ppm or more is formed, as an indicator of deterioration.

[0056] For example, in a supply gas containing hydrogen at a dew point temperature of −50° C. after passing through a dehumidifier, the ３ When 0.9 MPa of hydrogen is absorbed, the molar amount of absorbed hydrogen is 370 [mol / m ３ In addition, the storage alloy reaches ５ In this case, 1m ３ The molar amount of hydrogen absorbed by the hydrogen storage alloy per unit mass is 46,500 [mol / m ３ In this case, LaNi ５ When the maximum amount of hydrogen is absorbed in the hydrogen absorption alloy, the moisture concentration of the water vapor remaining in the supply gas is 7.41 [g / m ３ ] may be concentrated to about 7.41 [g / m ３ ] corresponds to a dew point temperature of approximately 44°C.

[0057] Furthermore, as described above, when the void (i.e., the dead volume of the storage tank) filled with the saturated vapor pressure at 50°C is set to half of the entire volume of the part inside the housing excluding the storage alloy, the moisture concentration is further increased to 7.41 [g / m ３ ], which is twice the ３ If the temperature at this time is assumed to be 50° C., water vapor of approximately 2000 Pa will accumulate inside the storage tank.

[0058] In other words, even if the dew point temperature of the supply gas is -50°C, the concentration of water vapor inside the storage tank generates a water vapor pressure of about 2000 Pa inside, resulting in a water concentration that far exceeds 300 ppm.

[0059] 4 shows the pressure that occurs when water vapor condenses, assuming that no condensation occurs. If the temperature inside the storage tank during storage is set to 50°C, water vapor with a dew point temperature of -33°C will condense at a pressure of approximately 12 kPa. Therefore, when water vapor with a dew point temperature below -33°C enters the storage tank, the internal water vapor pressure increases, raising concerns about condensation.

[0060] Considering this concentration, in the case of a conventional storage tank, in order to prevent deterioration of the storage alloy, it is necessary to achieve a dew point temperature of about -70°C to -60°C by removing moisture using, for example, a dehumidifier. This places a significant burden on the hydrogen storage system, i.e., the energy consumed for dehumidification.

[0061] Furthermore, when water vapor accumulates inside the storage tank, the water vapor fills the voids inside the storage alloy, creating a boundary film of water vapor in the storage alloy, resulting in a decrease in the storage rate. Based on the above findings, in this embodiment, deterioration of the storage alloy is suppressed by suppressing an increase in moisture concentration, and the reference concentration is set to 300 ppm, which is an index of deterioration.

[0062] <Method for Controlling Water Concentration> Next, a method for controlling water concentration using the hydrogen storage system 10 according to this embodiment will be described with reference to FIGS. 1 and 5. FIG.

[0063] In this embodiment, a case where the concentration control process is executed by the CPU of the arithmetic and control device 50 reading and executing a program stored in the ROM or storage will be described as an example. Note that in the present disclosure, a user may use the arithmetic and control device 50 to execute the series of concentration control processes exemplified in FIG. 5 .

[0064] In this embodiment, first, the supply gas is sent from the dehumidifier 14 to the MH tank 16. Specifically, for example, the supply gas is sent to the MH tank 16 in a state in which the first valve 22 in FIG.

[0065] 1 is controlled to be open, the arithmetic and control device 50 may simultaneously send the supply gas to the MH tank 16 via the first opening 16A1 and send hydrogen to the hydrogen-using device 30 via the second opening 16A2. Next, as shown in step S1 in FIG. 5, the calculation unit of the arithmetic and control device 50 calculates the moisture concentration in the supply gas.

[0066] The moisture concentration can be calculated, for example, by estimating the flow rate of the supply gas using the pressure difference before and after the first valve 22 located between the dehumidifier 14 and the MH tank 16, and integrating the estimated flow rate over time. Note that the hydrogen storage capacity can also be calculated using the pressure difference, similar to the moisture concentration.

[0067] The water concentration can also be calculated based on the estimated hydrogen absorption reaction amount, by estimating the hydrogen absorption reaction amount using the heat exchange amount measured during hydrogen absorption in the MH tank 16. The amount of supply gas sent into the MH tank 16 can also be calculated based on the absorption reaction amount, similar to the water concentration. The calculation of the water concentration is performed continuously over time while the control process is being performed. That is, multiple water concentrations are calculated while the control process is being performed.

[0068] Next, as shown in step S2 in Fig. 5, the comparison unit of the arithmetic and control device 50 compares the calculated moisture concentration with a reference concentration. If the calculated moisture concentration exceeds the reference concentration, the process proceeds to step S3 in Fig. 5. Then, in step S3, the delivery unit of the arithmetic and control device 50 delivers the supply gas inside the MH tank 16 to the outside.

[0069] Specifically, for example, the delivery unit of the arithmetic and control device 50 delivers the supply gas to the outside of the MH tank 16 using a passage formed between the first opening 16A1 and the second opening 16A2 at the inlet of the MH tank 16. The delivery unit also promotes the flow of the supply gas to the outside using the pressure booster 18. The supply gas is returned to the upstream stage of the dehumidifier 14 outside the MH tank 16 via the return pipe PR.

[0070] In the present disclosure, the method of promoting the flow of the supply gas when it is sent out is not limited to using the pressure booster 18. In the present disclosure, for example, hydrogen may be released to the outside of the MH tank 16 by raising the temperature of the storage alloy 16B using a thermal circuit (not shown) provided in the MH tank 16. The supply gas inside the MH tank 16 is sent out using the flow of released hydrogen.

[0071] When the supply gas is sent through the return pipe PR, the opening degrees of the first valve 22 and the second valve 24 do not need to be fully closed, and can be adjusted as appropriate. For example, a process of sending the supply gas from the dehumidifier 14 to the MH tank 16 and a process of sending the mixed gas of hydrogen and the supply gas to a stage upstream of the dehumidifier 14 through the return pipe PR may be executed in parallel. Also, for example, a process of sending the mixed gas of hydrogen and the supply gas to a stage upstream of the dehumidifier 14 through the return pipe PR and a process of sending the mixed gas of hydrogen and the supply gas to the hydrogen-utilizing device 30 may be executed in parallel.

[0072] The supply gas is sent out of the MH tank 16 via the return pipe PR in a pulsed manner, i.e., the amount of gas sent can be adjusted so as to pulse over time. After the supply gas inside the MH tank 16 is sent out, the process returns to step S1. Then, step S2 and subsequent steps are repeated.

[0073] On the other hand, if the calculated water concentration is equal to or less than the reference concentration in step S2, the process proceeds to step S4. As shown in step S4 in Fig. 5, if control is to be continued, the process returns to step S1. Then, the process from step S2 onwards is repeated.

[0074] If the control is not continued in step S4, the control process according to this embodiment ends. The above series of processes constitutes the water concentration control method according to this embodiment. In this embodiment, the control process continues until the calculated water concentration reaches or exceeds the reference concentration.

[0075] 6, the MH tank 16 of the hydrogen storage system 10Z according to the comparative example does not have a second opening. Specifically, the MH tank 16 of the comparative example has only one first opening 16A1 that serves as both a gas inlet and an outlet.

[0076] Furthermore, the branch pipe PB branches off from the second pipe P2 at a position between the first valve 22 and the MH tank 16 and extends toward the hydrogen-using equipment 30. That is, the branch pipe PB connects the second pipe P2 at a position between the first valve 22 and the MH tank 16 to the hydrogen-using equipment 30. In the comparative example, the second valve 24 is provided in the branch pipe PB and opens and closes the branch pipe PB. The second valve 24 controls the flow of fluid flowing inside the branch pipe PB.

[0077] The MH tank 16 of the hydrogen storage system 10Z according to the comparative example has only one first opening 16A1 that serves as both a gas inlet and an outlet, so that the supply gas is more likely to remain inside the housing during hydrogen storage than in the present embodiment. Therefore, when moisture contained in the supply gas inside the storage tank condenses as hydrogen is stored, the degree of deterioration of the storage alloy is greater than in the present embodiment.

[0078] (Effects) In the hydrogen storage system 10 according to this embodiment, the MH tank 16 is provided with a second opening 16A2 for sending out the supply gas, in addition to a first opening 16A1 for sending in the supply gas. The supply gas sent in from the first opening 16A1 at the inlet flows inside the housing 16A of the MH tank 16 and is sent out from the second opening 16A2 at the outlet. In other words, the first opening 16A1 is an inlet for the supply gas containing hydrogen that flows toward the storage alloy. The second opening 16A2 is an outlet for the supply gas after flowing around the storage alloy.

[0079] Therefore, it is possible to send the supply gas to the outside of the housing 16A from the second opening 16A2 separately from the first opening 16A1. As a result, the supply gas can be reduced from accumulating inside the housing 16A during hydrogen storage, compared to, for example, a case where the MH tank 16 is provided with only the first opening 16A1 without being provided with a supply gas outlet. This reduces the concentration of moisture contained in the supply gas inside the MH tank 16 as hydrogen is stored, thereby suppressing deterioration of the storage alloy.

[0080] In this embodiment, the first opening 16A1 is provided at one axial end of the cylindrical housing 16A. The second opening 16A2 is provided at the other axial end of the cylindrical housing 16A. That is, the inlet and outlet are spaced apart at opposite ends of the cylindrical MH tank 16. For this reason, the supply gas is less likely to stagnate inside the housing 16A than when, for example, the first opening 16A1 at the inlet and the second opening 16A2 at the outlet are arranged side by side and close to each other at one end of the housing 16A.

[0081] In this embodiment, a return pipe PR is provided between the dehumidifier 14 and the second opening 16A2, which returns the supply gas sent out from the second opening 16A2 to the dehumidifier 14. This allows the hydrogen in the supply gas sent out from the second opening 16A2 to be reused for storage.

[0082] The hydrogen storage system 10 according to this embodiment also includes a calculation and control device 50 that calculates the moisture concentration of the supply gas inside the MH tank 16 and sends the supply gas inside the MH tank 16 to the outside in accordance with the calculated moisture concentration. This effectively prevents an increase in the moisture concentration contained in the supply gas inside the MH tank 16 when hydrogen is stored. As a result, deterioration of the storage alloy 16B can be suppressed.

[0083] Furthermore, since the moisture concentration inside the MH tank 16 is controlled by sending the supply gas inside the MH tank 16 to the outside in accordance with the calculated moisture concentration, there is no need for a dehumidifier 14 that achieves a dew point temperature of, for example, about -70°C to -60°C. This reduces the load on the hydrogen storage system 10, i.e., the energy consumed for dehumidification. Furthermore, since water vapor is prevented from accumulating in the voids inside the storage alloy 16B, a water vapor boundary film is less likely to be formed on the storage alloy 16B, and as a result, a decrease in the storage rate can be suppressed.

[0084] (Other Examples of Storage Tank) The cylindrical MH tank 16 illustrated in Fig. 1 has a side length measured in the left-right direction in Fig. 1 that is longer than the diameter of the bottom measured in the up-down direction in Fig. 1. However, the shape of the storage tank of the present disclosure is not limited to this.

[0085] The cylindrical MH tank 17 illustrated in Figure 7 has a maximum diameter D measured along the radial direction of the MH tank 17 (the vertical direction in Figure 7) that is longer than a maximum length L measured along the axial direction of the MH tank 17 (the supply gas flow direction, which is parallel to the left-right direction in Figure 7). In other words, the MH tank 17 has a flat shape. In this specification, "a storage tank (i.e., the MH tank 17) is flat" means that the aspect ratio L / D is 1 or less.

[0086] The MH tank 17 illustrated in Figure 7 has a first opening 17A1 provided on one side of the bottom surface in the axial direction of the cylindrical MH tank 17 (left side in Figure 7), and a second opening 17A2 provided on the other side of the bottom surface in the axial direction (right side in Figure 7).

[0087] In the present disclosure, the shape of the cylindrical storage tank is not limited to a right cylinder with strictly rectangular side surfaces, such as the cylindrical MH tank 16 illustrated in FIG. 1 and the MH tank 17 illustrated in FIG. 7. Projections or depressions may be formed on the bottom surface and side surfaces. In the present disclosure, for example, the shape of the cylindrical storage tank may be not only cylindrical but also rectangular. Furthermore, the corners between the bottom surface and side surfaces of the cylindrical storage tank may be rounded or tapered.

[0088] 7, the MH tank 17 can reduce the time that moisture remains inside the MH tank 17 compared to MH tanks that have the same maximum diameter D and an aspect ratio L / D of more than 1. This can further suppress the deterioration of the storage alloy.

[0089] <Other Embodiments> The present disclosure has been described with reference to the above disclosed embodiments, but the descriptions and drawings forming part of this disclosure should not be understood to limit the present disclosure.

[0090] For example, the calculation and control device 50 of the hydrogen storage system may be configured to calculate the oxygen concentration in the supply gas inside the MH tank 16. Similar to the moisture concentration, the oxygen concentration can be calculated by estimating the flow rate of the supply gas using, for example, the pressure difference between the front and rear of a first valve located between the dehumidifier 14 and the MH tank 16, and integrating the estimated flow rate over time.

[0091] Furthermore, similarly to the water concentration, the hydrogen absorption reaction amount can be estimated using the heat exchange amount measured during hydrogen absorption in the MH tank 16, and the oxygen concentration can also be calculated based on the estimated absorption reaction amount. The arithmetic and control device 50 may be configured to send the supply gas inside the MH tank 16 to the outside in accordance with both the calculated water concentration and the calculated oxygen concentration. Because the supply gas inside the MH tank 16 is sent to the outside in accordance with both the water concentration and the oxygen concentration in the supply gas, deterioration of the storage alloy 16B due to oxygen can be suppressed in addition to deterioration of the storage alloy 16B due to water.

[0092] Additionally, in the present disclosure, instead of simply purging the supply gas, the purge timing may be determined by combining a hydrogen storage system with an energy management system (EMS). The combination of a hydrogen storage system with an EMS is effective in optimizing the energy of the entire system.

[0093] In addition, the present disclosure can be configured by partially combining the configurations illustrated in the attached drawings. As described above, the present disclosure includes various embodiments not described above, and the technical scope of the present disclosure is defined by the invention-specifying matters in the claims that are appropriate from the above description.

[0094] (Supplementary Note 1) A hydrogen storage system comprising: a hydrogen production unit that produces hydrogen; a storage alloy that stores hydrogen; a housing that houses the storage alloy inside; and an absorption tank having a first opening that is provided in the housing and into which a supply gas containing the hydrogen produced from the hydrogen production unit side is fed; and a second opening that is provided in the housing separately from the first opening and sends the supply gas to the outside.

[0095] (Supplementary Note 2) The hydrogen storage system according to Supplementary Note 1, wherein the housing is cylindrical, the first opening is provided at one end of the cylindrical housing in the axial direction, and the second opening is provided at the other end of the cylindrical housing in the axial direction.

[0096] (Supplementary Note 3) The hydrogen storage system according to Supplementary Note 1 or 2, wherein a dehumidifier is provided between the hydrogen production unit and the storage tank, and a return pipe is provided between the dehumidifier and the second opening to return the supply gas sent out from the second opening to the dehumidifier.

[0097] (Supplementary Note 4) A hydrogen storage system according to any one of Supplementary Notes 1 to 3, comprising an arithmetic and control device that calculates the moisture concentration in the supply gas inside the storage tank and sends the supply gas inside the storage tank to the outside in accordance with the calculated moisture concentration.

[0098] The disclosure of Japanese Patent Application No. 2023-208845, filed on December 11, 2023, is incorporated herein by reference in its entirety.

[0099] Furthermore, all publications, patent applications, and technical standards mentioned in this specification are incorporated by reference herein to the same extent as if each individual publication, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. A hydrogen storage system comprising: a hydrogen production unit that produces hydrogen; a storage alloy that stores the produced hydrogen; a housing inside which the storage alloy is housed; and an absorption tank having a first opening provided in the housing and into which a supply gas containing the hydrogen produced from the hydrogen production unit side is supplied; and a second opening provided in the housing separately from the first opening and which sends out the supply gas to the outside.

2. The hydrogen storage system according to claim 1, wherein the housing is cylindrical, the first opening is provided at one end in the axial direction of the cylindrical housing, and the second opening is provided at the other end in the axial direction.

3. A hydrogen storage system as described in claim 1 or 2, wherein a dehumidifier is provided between the hydrogen production unit and the storage tank, and a return pipe is provided between the dehumidifier and the second opening for returning the supply gas discharged from the second opening to the dehumidifier.

4. A hydrogen storage system as described in claim 1 or 2, comprising an arithmetic and control device that calculates the moisture concentration in the supply gas inside the storage tank and sends the supply gas inside the storage tank to the outside in accordance with the calculated moisture concentration.

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