Hydrogen storage system, control method, and pressure reducing valve control device

Abstract

To provide a hydrogen storage system capable of suppressing a required cooling capacity.SOLUTION: A hydrogen storage system for storing hydrogen gas in a hydrogen storage alloy, comprises: a decompression valve that decompresses hydrogen gas to be stored by a hydrogen storage alloy; and a decompression valve controller that repeats control to increase a pressure on a secondary side of the decompression valve when a flow rate of hydrogen gas stored by the hydrogen storage alloy falls below a threshold value.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a hydrogen storage system, a control method, and a pressure reducing valve control device.

Background Art

[0002] When hydrogen is occluded in a hydrogen storage alloy, reaction heat is generated, so it is necessary to cool the hydrogen storage alloy (see, for example, Patent Document 1). For example, when hydrogen is filled from a portable hydrogen candle into a hydrogen storage alloy, a large amount of reaction heat is generated.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, when the temperature of the hydrogen storage alloy rises, the amount of hydrogen that can be occluded decreases. Therefore, when a large amount of hydrogen is stored in a hydrogen storage alloy tank from a hydrogen candle or the like, a cooling system for the hydrogen storage alloy tank having a large cooling capacity is required to remove a large amount of reaction heat, which is a problem.

[0005] The present invention has been made in view of such circumstances, and provides a hydrogen storage system, a control method, and a pressure reducing valve control device capable of suppressing the required cooling capacity.

Means for Solving the Problems

[0006] The present invention has been made to solve the above-described problems, and one aspect of the present invention is a hydrogen storage system for storing hydrogen gas in a hydrogen storage alloy, the hydrogen storage system including a pressure reducing valve for reducing the pressure of the hydrogen gas to be stored in the hydrogen storage alloy, and a pressure reducing valve control device that repeatedly performs control to increase the secondary-side pressure of the pressure reducing valve when the flow rate of the hydrogen gas to be stored in the hydrogen storage alloy becomes equal to or less than a threshold value.

[0007] Another aspect of the present invention is the above-described hydrogen storage system, wherein the pressure reducing valve control device performs control to gradually decrease the secondary-side pressure until the flow rate becomes equal to or less than the threshold value after performing control to increase the secondary-side pressure of the pressure reducing valve.

[0008] Another aspect of the present invention is a hydrogen storage system for storing hydrogen gas in a hydrogen storage alloy, the hydrogen storage system including a pressure reducing valve for reducing the pressure of the hydrogen gas to be stored in the hydrogen storage alloy, and a pressure reducing valve control device that repeatedly performs control to increase the secondary-side pressure of the pressure reducing valve when the pressure difference between the secondary-side pressure of the pressure reducing valve and the internal pressure of the alloy tank pressure becomes equal to or less than a threshold value.

[0009] Another aspect of the present invention is the above-described hydrogen storage system, wherein the pressure reducing valve control device performs control to gradually decrease the secondary-side pressure until the pressure difference between the secondary-side pressure of the pressure reducing valve and the internal pressure of the alloy tank pressure becomes equal to or less than the threshold value after performing control to increase the secondary-side pressure of the pressure reducing valve.

[0010] Another aspect of the present invention is the above-described hydrogen storage system, which includes a first pump for circulating a heat medium for cooling the hydrogen storage alloy when the pressure of the supplied hydrogen gas is a first pressure, a first cooling unit for cooling the heat medium when the pressure of the supplied hydrogen gas is the first pressure, a second pump for circulating the heat medium for cooling the hydrogen storage alloy when the pressure of the supplied hydrogen gas is a second pressure higher than the first pressure, and a second cooling unit for cooling the heat medium when the pressure of the supplied hydrogen gas is the second pressure.

[0011] Another aspect of the present invention is the hydrogen storage system described above, in which the heat medium passes through the outer periphery of the storage alloy tank storing the hydrogen storage alloy and a pipeline penetrating the hydrogen storage alloy.

[0012] Another aspect of the present invention is a control method in a hydrogen storage system for storing hydrogen gas in a hydrogen storage alloy. When the flow rate of the hydrogen gas to be stored in the hydrogen storage alloy becomes equal to or less than a threshold value, control is repeated to increase the secondary side pressure of a pressure reducing valve for reducing the pressure of the hydrogen gas to be stored in the hydrogen storage alloy.

[0013] Another aspect of the present invention is a pressure reducing valve control device that repeats control to increase the secondary side pressure of a pressure reducing valve for reducing the pressure of the hydrogen gas to be stored in the hydrogen storage alloy when the flow rate of the hydrogen gas to be stored in the hydrogen storage alloy becomes equal to or less than a threshold value.

[0014] Another aspect of the present invention is a control method in a hydrogen storage system for storing hydrogen gas in a hydrogen storage alloy. When the pressure difference between the secondary side pressure of a pressure reducing valve provided between an alloy tank storing the hydrogen storage alloy and a hydrogen supply source and the internal pressure of the alloy tank pressure becomes equal to or less than a threshold value, control is repeated to increase the secondary side pressure of a pressure reducing valve for reducing the pressure of the hydrogen gas to be stored in the hydrogen storage alloy.

[0015] Another aspect of the present invention is a pressure reducing valve control device that repeats control to increase the secondary side pressure of a pressure reducing valve for reducing the pressure of the hydrogen gas to be stored in the hydrogen storage alloy when the pressure difference between the secondary side pressure of a pressure reducing valve provided between an alloy tank storing the hydrogen storage alloy and a hydrogen supply source and the internal pressure of the alloy tank pressure becomes equal to or less than a threshold value.

Advantages of the Invention

[0016] According to this invention, the cooling capacity required by the hydrogen storage system can be suppressed.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Embodiments for Carrying Out the Invention

[0018] <The First Embodiment> Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic block diagram showing the configuration of the hydrogen storage system 10 according to the first embodiment of the present invention. The hydrogen storage system 10 in the present embodiment stores hydrogen gas from the hydrogen supply source K1 by adsorbing it into a hydrogen storage alloy. The hydrogen storage system 10 includes a hydrogen supply unit including a hydrogen storage alloy tank T1, and a heating / cooling unit for the hydrogen storage alloy tank T1. (Hydrogen Supply Unit)

[0019] The hydrogen supply unit includes a hydrogen storage alloy tank T1, a flow meter F1, a pressure reducing valve R1, and a pressure reducing valve control device E1, and can supply hydrogen from a hydrogen source K1 to the hydrogen storage alloy tank T1 through the hydrogen flow path indicated by the thick line in FIG. 1. The hydrogen source K1 is a hydrogen candle, a water electrolysis device, etc., and supplies the hydrogen gas stored in the hydrogen storage system 10. The hydrogen gas stored in the hydrogen candle is, for example, 20 MPaG, while the hydrogen gas supplied from the water electrolysis device is, for example, about 1 MPaG, and these pressures are quite different. In this specification, the filling from a hydrogen candle or the like where the pressure of the supplied hydrogen gas exceeds the pressure of the hydrogen gas supplied from the water electrolysis device, specifically exceeds 1 MPaG, is called "rapid filling", and the filling from a water electrolysis device or the like where the pressure of the supplied hydrogen gas is 1 MPaG or less is called "normal filling".

[0020] In the hydrogen supply unit, the hydrogen supplied from the hydrogen source K1 sequentially passes through the pressure reducing valve R1 and the flow meter F1 and is supplied to the hydrogen storage alloy tank T1, where it is stored in the hydrogen storage alloy T31 of the hydrogen storage alloy tank T1 (FIG. 2). The flow meter F1 measures the flow rate of the hydrogen flowing into the hydrogen storage alloy tank T1. The pressure reducing valve R1 reduces the pressure of the hydrogen supplied to the hydrogen storage alloy tank T1. As the pressure reducing valve R1, various pressure reducing valves such as a direct-acting pressure reducing valve and a pilot-operated pressure reducing valve, as well as a regulating valve and a solenoid valve that can set the secondary-side pressure to a predetermined value, can be used. In the hydrogen supply unit according to this embodiment, a pressure reducing valve control device E1 is provided. Later, the configuration for adjusting the supply amount of the hydrogen gas supplied to the hydrogen storage alloy tank T1 by the pressure reducing valve control device E1 will be described in detail. (Heating / Cooling Unit)

[0021] The heating / cooling unit is composed of valves V1, V2, V3, V4, V5, V6, V7, pumps P1, P2, a heating section H1, a first cooling section C1, a second cooling section C2, and a hydrogen storage alloy tank T1, and the heat medium can circulate through the heat medium flow path indicated by the thin line in FIG. 1. Note that water or antifreeze may be used as this heat medium. The hydrogen storage alloy tank T1 stores a hydrogen storage alloy T31 that stores hydrogen (Fig. 2). The hydrogen storage alloy T31 in the hydrogen storage alloy tank T1 is heated by the heat medium circulated by the pump P1 or the pump P2 during hydrogen release and cooled during hydrogen filling. The pump P1 circulates the heat medium during normal filling or hydrogen release. The pump P2 is arranged in parallel with the pump P1 and circulates the heat medium during rapid filling. The pump P2 has a larger discharge flow rate per unit time, for example, 10 times that of the pump P1. The heating unit H1 is for heating the heat medium to heat the hydrogen storage alloy tank T1 when releasing hydrogen gas from the hydrogen storage alloy tank T1.

[0022] Hereinafter, the heating and cooling unit will be described in detail. Regarding the relative positions of the respective components, in the heating and cooling unit, focusing on the flow of the heat medium flowing out of and returning to the hydrogen storage alloy tank T1, the terms "upstream" and "downstream" will be used for the description. The flow path of the heat medium connected to the hydrogen storage alloy tank T1 branches into two and is respectively connected to the valve V1 and the valve V2. The valve V1 is installed on the upstream side of the pump P1 and controls the flow of the heat medium to the pump P1. The valve V2 is installed on the upstream side of the pump P2 and controls the flow of the heat medium to the pump P2. The pump P2 has a higher discharge capacity than the pump P1. Thus, by selectively turning on / off the valve V1 and the valve V2, the flow rate of the heat medium flowing through the hydrogen storage alloy tank T1 can be changed. Then, the heat medium discharged from the pump P1 and the heat medium discharged from the pump P2 merge once, become one flow, and then branch into two again, respectively connected to the valve V3 and the valve V4. The valve V4 is installed on the upstream side of the heating unit H1 and controls the flow of the heat medium to the heating unit H1. On the other hand, the valve V3 is installed so as to bypass the heating unit H1 and controls the flow of the heat medium bypassing the heating unit H1. Therefore, by selectively turning on / off the valve V3 and the valve V4, it is possible to change whether the heat medium flowing through the hydrogen storage alloy tank T1 is passed through the flow path heated by the heating unit H1 or bypassed without heating.

[0023] The heat medium discharged from the heating section H1 and the heat medium that has passed through the valve V3 rejoin, forming one flow. After that, the flow branches into three and is connected to the valves V5, V6, and V7 respectively. The valve V6 is installed upstream of the first cooling section C1 and controls the flow of the heat medium to the first cooling section C1. The valve V7 is installed upstream of the second cooling section C2, which has a cooling capacity larger than that of the first cooling section C1, and controls the flow of the heat medium to the second cooling section C2. The valve V5 is installed so as to bypass the first cooling section C1 and the second cooling section C2 and controls the flow of the heat medium that bypasses the first cooling section C1 and the second cooling section C2. Therefore, by selectively turning on / off the valves V5, V6, and V7, the flow path through which the heat medium flowing through the hydrogen storage alloy tank T1 is cooled by either the first cooling section C1 or the second cooling section C2 according to the required cooling capacity, or the flow path that bypasses the cooling and is not cooled, can be changed. The heat medium discharged from the first cooling section C1, the heat medium discharged from the second cooling section C2, and the heat medium that has passed through the valve V5 rejoin, forming one flow, and reach the hydrogen storage alloy tank T1 again to heat and cool the hydrogen storage alloy tank T1. In this embodiment, although the description has been made on the assumption that the heat medium exits the hydrogen storage alloy tank T1, passes through the pump P1 or P2, and then returns after passing through either the heating section H1, the first cooling section C1, or the second cooling section C2, it is not limited thereto, and it may follow the reverse path. In addition, in this embodiment, in order to separate the heating configuration and the cooling configuration, the heating configuration includes the heating section H1 and the bypass path, and the cooling configuration includes the first cooling section C1, the second cooling section C2, and in addition, the bypass path. However, it is not limited thereto, and it may be provided with a heating and cooling configuration in which the heating section H1, the first cooling section C1, and the second cooling section C2 are arranged in parallel without providing a bypass path.

[0024] Here, the hydrogen storage alloy tank T1 used in this embodiment and the cooling configuration during cooling of the hydrogen storage alloy tank T1 will be described. FIG. 2 is a schematic diagram showing a cross section of the hydrogen storage alloy tank T1 and the cooling configuration of the hydrogen storage alloy tank T1 in this embodiment. FIG. 2(a) is a longitudinal cross-sectional view of the hydrogen storage alloy tank T1, and FIG. 2(b) is a cross-sectional view in the X-X cross-sectional view of FIG. 2(a). The hydrogen storage alloy tank T1 is connected to a hydrogen supply path and a hydrogen release path (not shown), and a particulate or sandy hydrogen storage alloy layer T31 is stored inside. Also, an oil jacket T2 is covered on the outside of the hydrogen storage alloy tank T1. The hydrogen storage alloy layer T31 is configured to absorb hydrogen supplied from the hydrogen supply path in the hydrogen storage alloy layer T31 and release hydrogen from the hydrogen storage alloy layer T31 to the hydrogen release path. As shown in FIG. 2(a), the heat medium flows in from the pipeline P31, and from one end of the hydrogen storage alloy tank T1 to the other end, through a pipeline P33 formed by a heat medium pipe penetrating the hydrogen storage alloy layer T31 stored in the hydrogen storage alloy tank T1. That is, as shown in FIG. 2(a), the heat medium supplied from the pipeline P31 is configured to flow only from the space at one end of the hydrogen storage alloy tank T1 into the pipeline P33 provided in the hydrogen storage alloy layer T31. Then, the heat medium flows from the other end of the hydrogen storage alloy tank T1 through the region around the hydrogen storage alloy layer T31 shown in FIG. 2(b) and is discharged from the pipeline P32. Therefore, in FIG. 2(b), the direction of the heat medium flowing through the pipeline P33 and the direction of the heat medium flowing through the region around the hydrogen storage alloy layer T31 are opposite directions. In this way, since the heat medium can flow inside and outside the circumference of the hydrogen storage alloy tank T1, the area where the hydrogen storage alloy layer T31 contacts the heat medium becomes large, and the hydrogen storage alloy layer T31 can be cooled or heated efficiently. Note that the hydrogen storage alloy tank T1 may be composed of only one container that stores the hydrogen storage alloy layer T31, or may be composed of a plurality of containers each storing the hydrogen storage alloy layer T31. Also, for the heating unit H1, something that can heat the heat medium can be used, such as an electric heating wire, a heat pump, or further the exhaust heat of a fuel cell. In this embodiment, the exhaust heat of the fuel cell and a heat pump are used to heat the heat medium. The first cooling unit C1 cools the heat medium during normal filling, and a radiator, a fan, a chiller, etc. can be used. In this embodiment, a heat medium composed of water or antifreeze circulates inside the radiator and is cooled by dissipating heat. Furthermore, by configuring to blow air to the radiator with a fan, the cooling efficiency is enhanced.

[0025] The second cooling unit C2 has a larger cooling capacity than the first cooling unit C1 and cools the heat medium during rapid filling, and a chiller, a cold water tank, etc. can be used. Hereinafter, the configuration of the second cooling unit C2 having a large cooling capacity used in this embodiment will be described with reference to FIG. 3. The second cooling unit C2 includes a heat exchanger H21, a thermometer T21, a pump P21, a valve V21, a first cold water tank W21, a valve V22, and a second cold water tank W22. The second cooling unit C2 is configured such that the heat medium can circulate within the second cooling unit C2 through the second heat medium flow path shown in FIG. 2. Note that the first heat medium flow path is the heat medium flow path shown in FIG. 1. Specifically, the heat medium that has exited the heat exchanger H21 branches into a flow that passes through the first cold water tank W21 via the valve V21 and a flow that passes through the second cold water tank W22 via the valve V22, and then merges again and is configured to return to the heat exchanger H21 through the pump P21 and the thermometer T21 in sequence. In the following description, "upstream" and "downstream" refer to "upstream" and "downstream" in the flow of the heat medium that exits the heat exchanger H21, passes through the first cold water tank W21 or the second cold water tank W22, and returns to the heat exchanger H21. The heat exchanger H21 performs heat exchange between the heat medium that cools the occlusion alloy tank T1 and the heat medium circulated by the pump P21.

[0026] The flow path of the heat medium connected to the heat exchanger H21 branches into two, and each is connected to a valve V21 and a valve V22. The valve V21 is arranged on the upstream side of the first cold water tank W21. The valve V21 controls the flow of the heat medium circulated by the pump P21 and flowing into the first cold water tank W21. The first cold water tank W21 stores cold water for cooling the heat medium circulated by the pump P21. On the other hand, the valve V22 is arranged on the upstream side of the second cold water tank W22. The valve V22 controls the flow of the heat medium circulated by the pump P21 and flowing into the second cold water tank W22. The second cold water tank W22 is arranged in parallel with the first cold water tank W21 and stores cold water for cooling the heat medium circulated by the pump P21. The heat medium that has passed through the first cold water tank W21 and the second cold water tank W22 merges and is supplied to the pump P21. The pump P21 circulates the heat medium cooled by the first cold water tank W21 and the second cold water tank W22 to the heat exchanger H21 in order to cool the heat medium for cooling the hydrogen storage alloy tank T1 with the heat exchanger H21. The thermometer T21 is provided between the pump P21 and the heat exchanger H21 and is configured to be able to measure the temperature of the heat medium circulated by the pump P21 and flowing into the heat exchanger H21.

[0027] For example, initially, the valve V21 is opened and the valve V22 is closed so that the heat medium flows toward the first cold water tank W21. Then, when the cooling capacity of the first cold water tank W21 decreases and the temperature measured by the thermometer T21 reaches, for example, 40 °C or higher, the valve V22 is opened and the valve V21 is closed so that the heat medium flows toward the second cold water tank W22. Thereby, even if the temperature of the first cold water tank W21 rises, the cooling capacity can be maintained by using the second cold water tank W22, and thus a high cooling capacity can be continuously maintained.

[0028] Note that the second cooling unit C2 is configured to include two cold water tanks (the first cold water tank W21 and the second cold water tank W22), but the number of cold water tanks may be plural, and two or more may be provided. (Operation Modes of Hydrogen Storage System 10)

[0029] Figure 4 is a table for explaining the operation modes of the hydrogen storage system 10 in this embodiment. In Figure 4, for each of normal filling when filling hydrogen gas from a water electrolysis device or the like, rapid filling when filling hydrogen gas from a hydrogen candle or the like, and hydrogen release, the ON / OFF of pumps P1 and P2 of the heating / cooling unit and the opening / closing of valves V1, V2, V3, V4, V5, V6, and V7 are described.

[0030] During normal filling, pump P1 is set to "ON", pump P2 is set to "OFF", valve V1 is set to "open", valve V2 is set to "closed", valve V3 is set to "open", valve V4 is set to "closed", valve V5 is set to "closed", valve V6 is set to "open", and valve V7 is set to "closed". Thereby, the heat medium is circulated by pump P1 and cooled by the first cooling part C1. Therefore, the hydrogen storage alloy tank T1 is cooled by the heat medium.

[0031] Also, during rapid filling, pump P1 is set to "OFF", pump P2 is set to "ON", valve V1 is set to "closed", valve V2 is set to "open", valve V3 is set to "open", valve V4 is set to "closed", valve V5 is set to "closed", valve V6 is set to "closed", and valve V7 is set to "open". Thereby, the heat medium is circulated by pump P2 having a higher discharge performance than pump P1 and cooled by the second cooling part C2 having a higher cooling capacity than the first cooling part C1. Therefore, the hydrogen storage alloy tank T1 is cooled by the heat medium. For this reason, even during rapid filling when filling hydrogen gas from a hydrogen candle or the like, the rise of the hydrogen storage alloy tank T1 can be suppressed.

[0032] During hydrogen release, pump P1 is set to "ON", pump P2 is set to "OFF", valve V1 is set to "open", valve V2 is set to "closed", valve V3 is set to "closed", valve V4 is set to "open", valve V5 is set to "open", valve V6 is set to "closed", and valve V7 is set to "closed". Thereby, the heat medium is circulated by pump P1 and heated by the heating part H1. Therefore, the hydrogen storage alloy tank T1 is heated by the heat medium. (Regarding Control in Hydrogen Supply Unit) In the hydrogen supply unit according to this embodiment, a pressure reducing valve control device E1 is provided. The pressure reducing valve control device E1 controls the pressure reducing valve R1 using the measurement result of the flow meter F1. During rapid filling, the hydrogen gas is adiabatically expanded by reducing the pressure with the pressure reducing valve R1 so that the temperature of the hydrogen gas drops, and the hydrogen storage alloy in the hydrogen storage alloy tank T1 is cooled by the hydrogen gas to be filled. The pressure reducing valve control device E1 controls the pressure reducing valve R1 so that the temperature drop of the hydrogen gas becomes larger. Thereby, the cooling capacity required by the second cooling unit C2 can be suppressed.

[0033] Figure 5 is a flowchart for explaining the operation of the pressure reducing valve control device E1 according to this embodiment. First, the pressure reducing valve control device E1 controls the secondary side pressure (downstream pressure) of the pressure reducing valve R1 to a predetermined initial value Pi (step S51). That is, since the pressure reducing valve R1 can set the secondary side pressure to a predetermined pressure according to the opening degree, specifically, the pressure reducing valve R1 is set to a predetermined opening degree so that the secondary side pressure becomes the initial value Pi. Next, the pressure reducing valve control device E1 acquires the flow rate of the hydrogen gas measured by the flow meter F1, that is, the flow rate on the downstream side of the pressure reducing valve R1 (S52). Next, the pressure reducing valve control device E1 determines whether or not the flow rate acquired in step S52 is equal to or less than a predetermined threshold value Vt (step S53). When it is determined that the flow rate is not less than the threshold value Vt (step S53-No), the pressure reducing valve control device E1 performs control to gradually lower the secondary side pressure by adjusting the opening degree of the pressure reducing valve R1 (step S57). The speed (pressure / time) at which the secondary side pressure is lowered at this time may be predetermined, or may be set so that the higher the flow rate, the greater the lowering speed. After step S57, the process of the pressure reducing valve control device E1 returns to step S52. Also, in step S53, when it is determined that the flow rate is equal to or less than the threshold value Vt (step S53-Yes), the pressure reducing valve control device E1 performs control to increase the secondary side pressure by a predetermined value Pa by adjusting the opening degree of the pressure reducing valve R1 (step S54). Next, the pressure reducing valve control device E1 determines whether or not the secondary-side pressure of the pressure reducing valve R1 is equal to or higher than a predetermined threshold value Pt (step S55). Specifically, the secondary-side pressure of the pressure reducing valve R1 is calculated based on the opening degree of the pressure reducing valve R1, and it is determined whether or not it is equal to or higher than the predetermined threshold value Pt. When it is determined that the secondary-side pressure of the pressure reducing valve R1 is not equal to or higher than the threshold value Pt (step S55 - No), the process of the pressure reducing valve control device E1 returns to step S52. The predetermined threshold value Pt may be a value larger than the initial value Pi and may be the pressure in the hydrogen storage alloy tank T1 at the completion of filling. Also, in step S55, when it is determined that the secondary-side pressure of the pressure reducing valve R1 is equal to or higher than the threshold value Pt (step S55 - Yes), the pressure reducing valve control device E1 controls the secondary-side pressure to the threshold value Pt by adjusting the opening degree of the pressure reducing valve R1 (step S56), and returns to step S52.

[0034] FIG. 6 is a graph for explaining the control content by the pressure reducing valve control device E1 according to the present embodiment. In the graph of FIG. 6, the horizontal axis represents time, and the vertical axis represents the control value of the secondary-side pressure of the pressure reducing valve R1. First, in step S51 of FIG. 5, the pressure reducing valve control device E1 sets the opening degree of the pressure reducing valve R1 to a predetermined opening degree and controls the secondary-side pressure to the initial value Pi. This is the state at the left end of the graph in FIG. 6. If this initial value Pi is sufficiently small, hydrogen gas flows into the hydrogen storage alloy tank T1. At this time, since the hydrogen gas flowing into the hydrogen storage alloy tank T1 adiabatically expands to the pressure Pi by the pressure reducing valve R1, the temperature decreases.

[0035] While the flow rate of hydrogen gas into the hydrogen storage alloy tank T1 is equal to or less than Vt, the secondary-side pressure continues to decrease according to step S57. In the graph of FIG. 6, it is a line sloping downward to the right. At this time, since the hydrogen gas flowing into the hydrogen storage alloy tank T1 adiabatically expands to a pressure lower than the pressure Pi by the pressure reducing valve R1, the temperature further decreases compared to when the secondary-side pressure is Pi. However, if the secondary-side pressure of the pressure reducing valve R1 continues to decrease, the difference between the pressure in the hydrogen storage alloy tank T1 and the secondary-side pressure becomes smaller. Then, the flow rate of hydrogen gas flowing into the hydrogen storage alloy tank T1 decreases.

[0036] When the flow rate of the hydrogen gas flowing into the hydrogen storage alloy tank T1 becomes equal to or less than the threshold value Vt, in step S54, the pressure reducing valve control device E1 increases the secondary side pressure by Pa. In the graph of FIG. 6, it rises vertically by Pa. As a result, the difference between the pressure in the hydrogen storage alloy tank T1 and the secondary side pressure becomes sufficiently large, and the flow rate of the hydrogen gas flowing into the hydrogen storage alloy tank T1 becomes a value exceeding Vt. While the flow rate of the hydrogen gas into the hydrogen storage alloy tank T1 is equal to or less than Vt, the secondary side pressure continues to decrease according to step S57.

[0037] In this way, while the secondary side pressure does not exceed Pt, the pressure reducing valve control device E1 repeats decreasing the secondary side pressure step by step and increasing it by Pa. Thereby, the pressure difference when the hydrogen gas adiabatically expands is increased, that is, it is controlled so that the temperature drop width due to adiabatic expansion becomes large. As a result, the cooling capacity of the hydrogen storage alloy tank T1 by the hydrogen gas itself is increased, and the cooling capacity required for the second cooling unit C2 can be suppressed.

[0038] In this way, when repeating the control of decreasing the secondary side pressure step by step and the control of increasing it by Pa, when increasing it by Pa, it will exceed the threshold value Pt. In that case, in step S56, the pressure reducing valve control device E1 controls the secondary side pressure to the threshold value Pt. In this case, the rising width of the secondary side pressure becomes smaller than Pa. By setting the upper limit of the secondary side pressure to the threshold value Pt in this way, it is possible to avoid applying excessive pressure to the hydrogen storage alloy tank T1. (Modification example) In the above embodiment, based on the measurement result of the flow meter F1 that measures the flow rate of the hydrogen flowing into the hydrogen storage alloy tank T1, the pressure reducing valve control device E1 controls the opening degree of the pressure reducing valve to change the secondary side pressure, but it is not limited to this. For example, as shown in FIG. 7, a configuration may be provided with a pressure gauge M1 that measures the pressure (internal pressure) inside the hydrogen storage alloy tank T1 instead of the flow meter F1. Even with such a configuration, the same effects as those of the above embodiment can be obtained. In this configuration, as shown in FIG. 8, after the pressure reducing valve control device E1 controls the secondary-side pressure (downstream pressure) of the pressure reducing valve R1 to a predetermined initial value Pi (step S51), the pressure reducing valve control device E1 acquires the pressure in the hydrogen storage alloy tank T1 measured by the pressure gauge M1 (S58). Next, the pressure reducing valve control device E1 determines whether or not the difference between the pressure acquired in step S58 and the secondary-side pressure corresponding to the opening degree of the pressure reducing valve R1 is equal to or greater than a predetermined threshold value (step S59). When it is determined that the pressure difference is less than the threshold value (step S59 - No), the pressure reducing valve control device E1 performs control to gradually decrease the secondary-side pressure by adjusting the opening degree of the pressure reducing valve R1 (step S57). The rate of decreasing the secondary-side pressure at this time (pressure / time) may be a predetermined value, or may be such that the smaller the pressure difference, the greater the rate of decrease. After step S57, the process of the pressure reducing valve control device E1 returns to step S58. Also, in step S59, when it is determined that the pressure difference is less than the threshold value (step S59 - Yes), the pressure reducing valve control device E1 controls to increase the secondary-side pressure by a predetermined value Pa by adjusting the opening degree of the pressure reducing valve R1 (step S54). Steps S55 and S56 are the same as those in the above embodiment.

[0039] In this way, instead of the flow rate of the hydrogen gas flowing into the hydrogen storage alloy tank T1, based on the difference between the pressure in the hydrogen storage alloy tank T1 and the secondary-side pressure, the pressure reducing valve control device E1 adjusts the opening degree of the pressure reducing valve R1, so that the same cooling effect of the hydrogen storage alloy tank T1 as in the above embodiment can be obtained.

[0040] <Second Embodiment> In the first embodiment, the hydrogen storage alloy tank T1 was filled with hydrogen both during normal filling and rapid filling. In the hydrogen storage system 70 in the second embodiment, two hydrogen storage alloy tanks are provided. One is dedicated to rapid filling for filling high-pressure hydrogen gas such as a hydrogen cascade, and the other is dedicated to normal filling for filling hydrogen gas at a lower pressure than in the case of dedicated rapid filling, such as a water electrolysis device.

[0041] FIG. 9 is a schematic block diagram showing the configuration of the hydrogen storage system 70 in the second embodiment. Similar to the hydrogen storage system 10 in FIG. 1, the hydrogen storage system 70 includes valves V1, V2, V3, V4, V5, V6, V7, pumps P1, P2, a heating unit H1, a first cooling unit C1, a second cooling unit C2, a hydrogen storage alloy tank T1, a flow meter F1, a pressure reducing valve R1, and a pressure reducing valve control device E1.

[0042] In addition to these, the hydrogen storage system 70 includes a second hydrogen storage alloy tank T72 arranged in series with the hydrogen storage alloy tank T1. The low-pressure hydrogen supply source K72 is a water electrolysis device or the like, and supplies relatively low-pressure hydrogen gas to the second hydrogen storage alloy tank T72 of the hydrogen storage system 70. The high-pressure hydrogen supply source K71 is a hydrogen cascade or the like, and supplies hydrogen gas at a higher pressure than the low-pressure hydrogen supply source K72 to the hydrogen storage alloy tank T1 of the hydrogen storage system 70. Since the valves V1, V2, V3, V4, V5, V6, V7, pumps P1, P2, heating unit H1, first cooling unit C1, second cooling unit C2, hydrogen storage alloy tank T1, flow meter F1, pressure reducing valve R1, and pressure reducing valve control device E1 are the same as those in the first embodiment, the description thereof is omitted.

[0043] Thus, even if the hydrogen storage system 70 separately includes the hydrogen storage alloy tank T1 for the high-pressure hydrogen supply source K71 and the second hydrogen storage alloy tank T72 for the low-pressure hydrogen supply source K72, the same effects as those in the first embodiment can be obtained. Note that bypasses may be provided for each of the hydrogen storage alloy tank T1 and the second hydrogen storage alloy tank T72. In that case, valves are arranged in each of the bypasses, on the upstream side of the hydrogen storage alloy tank T1, and on the upstream side of the second hydrogen storage alloy tank T72 to control the inflow of the heat medium thereto. Thereby, hydrogen release can be performed using only one of the hydrogen storage alloy tank T1 and the second hydrogen storage alloy tank T72. Similar to the hydrogen storage alloy tank T1 shown in FIG. 2, the second hydrogen storage alloy tank T72 may be configured such that the heat medium flows inside and outside the second hydrogen storage alloy tank T72, or the heat medium may flow only inside.

[0044] Also, in step S57 of FIG. 5, the pressure reducing valve control device E1 controls to gradually decrease the secondary side pressure, but it is not necessary to change the secondary side pressure. That is, the pressure reducing valve control device E1 may repeat the control to increase the secondary side pressure of the pressure reducing valve R1 when the flow rate of the hydrogen gas occluded in the hydrogen storage alloy becomes equal to or less than the threshold value Vt. In that case, in the graph of FIG. 6, the downward-sloping line portion on the right shoulder becomes a horizontal line. Also, Pa in step S54 of FIG. 5 does not have to be a fixed value. For example, it may be changed according to the time during which the control to gradually decrease the secondary side pressure is continued in step S57. Specifically, Pa may be made smaller as the time is longer. Also, before actually performing the control in step S54, it may be determined whether or not the control result exceeds the threshold value Pt.

[0045] As described above, the embodiments of the present invention have been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and design changes and the like within the scope not departing from the gist of the present invention are also included.

Explanation of Reference Numerals

[0046] 10, 70... Hydrogen storage system C1... First cooling unit C2... Second cooling unit E1... Pressure reducing valve control device F1... Flow meter H1... Heating unit H21... Heat exchanger K1... Hydrogen supply source K71... High-pressure hydrogen supply source K72... Low-pressure hydrogen supply source P1, P2, P21... Pumps R1... Pressure reducing valve T1... Occlusion alloy tank T2... Oil jacket T21... Thermometer T72... Second occlusion alloy tank V1, V2, V3, V4, V5, V6, V7, V21, V22... Valves W21... First cold water tank W22... Second cold water tank

Claims

1. A hydrogen storage system for storing hydrogen gas in a hydrogen storage alloy, comprising: a pressure reducing valve for reducing the pressure of the hydrogen gas to be stored in the hydrogen storage alloy; a pressure reducing valve control device that repeatedly performs control to increase the secondary side pressure of the pressure reducing valve when the flow rate of the hydrogen gas to be stored in the hydrogen storage alloy becomes equal to or less than a threshold value. A hydrogen storage system comprising the above.

2. The hydrogen storage system according to claim 1, wherein the pressure reducing valve control device performs control to gradually decrease the secondary side pressure after performing control to increase the secondary side pressure of the pressure reducing valve until the flow rate becomes equal to or less than the threshold value.

3. A hydrogen storage system for storing hydrogen gas in a hydrogen storage alloy, comprising: a pressure reducing valve for reducing the pressure of the hydrogen gas to be stored in the hydrogen storage alloy; a pressure reducing valve control device that repeatedly performs control to increase the secondary side pressure of the pressure reducing valve when the pressure difference between the secondary side pressure of the pressure reducing valve and the internal pressure of the alloy tank pressure becomes equal to or less than a threshold value. A hydrogen storage system comprising the above.

4. The hydrogen storage system according to claim 3, wherein the pressure reducing valve control device performs control to gradually decrease the secondary side pressure after performing control to increase the secondary side pressure of the pressure reducing valve until the pressure difference between the secondary side pressure of the pressure reducing valve and the internal pressure of the alloy tank pressure becomes equal to or less than the threshold value.

5. A first pump for circulating a heat medium for cooling the hydrogen storage alloy when the pressure of the supplied hydrogen gas is a first pressure; a first cooling unit for cooling the heat medium when the pressure of the supplied hydrogen gas is the first pressure; a second pump for circulating the heat medium for cooling the hydrogen storage alloy when the pressure of the supplied hydrogen gas is a second pressure higher than the first pressure; a second cooling unit for cooling the heat medium when the pressure of the supplied hydrogen gas is the second pressure. The hydrogen storage system according to any one of claims 1 to 4, comprising the above.

6. The hydrogen storage system according to claim 5, wherein the heat medium passes through the outer periphery of the storage alloy tank storing the hydrogen storage alloy and a pipeline passing through the hydrogen storage alloy.

7. A control method in a hydrogen storage system for storing hydrogen gas in a hydrogen storage alloy, comprising: when the flow rate of the hydrogen gas to be stored in the hydrogen storage alloy becomes equal to or less than a threshold value, repeatedly performing control to increase the secondary side pressure of a pressure reducing valve for reducing the pressure of the hydrogen gas to be stored in the hydrogen storage alloy. A control method.

8. When the flow rate of the hydrogen gas to be occluded in the hydrogen storage alloy becomes equal to or less than the threshold value, a pressure reducing valve control device that repeatedly performs control to increase the secondary side pressure of a pressure reducing valve that reduces the pressure of the hydrogen gas to be occluded in the hydrogen storage alloy.

9. A control method in a hydrogen storage system for occluding hydrogen gas in a hydrogen storage alloy, when the pressure difference between the secondary side pressure of a pressure reducing valve provided between an alloy tank storing the hydrogen storage alloy and a hydrogen supply source and the internal pressure of the alloy tank becomes equal to or less than a threshold value, repeatedly performs control to increase the secondary side pressure of the pressure reducing valve that reduces the pressure of the hydrogen gas to be occluded in the hydrogen storage alloy, control method.

10. A pressure reducing valve control device that repeatedly performs control to increase the secondary side pressure of a pressure reducing valve that reduces the pressure of the hydrogen gas to be occluded in the hydrogen storage alloy when the pressure difference between the secondary side pressure of a pressure reducing valve provided between an alloy tank storing the hydrogen storage alloy and a hydrogen supply source and the internal pressure of the alloy tank becomes equal to or less than a threshold value.

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