JP7705635B2 - Hydrogen storage system, control method, and pressure reducing valve control device - Google Patents

Description

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

When hydrogen is absorbed into a hydrogen storage alloy, reaction heat is generated, so the hydrogen storage alloy must be cooled (see, for example, Patent Document 1). For example, when hydrogen is filled into a hydrogen storage alloy from a mobile hydrogen cartridge, a large amount of reaction heat is generated.

JP 2020-170691 A

However, as the temperature of a hydrogen storage alloy rises, the amount of hydrogen that can be absorbed decreases. Therefore, when storing a large amount of hydrogen from a hydrogen storage alloy tank, such as from a hydrogen cartridge, a cooling system with a large cooling capacity is required to remove the large amount of reaction heat.

The present invention was made in consideration of these circumstances, and provides a hydrogen storage system, a control method, and a pressure reducing valve control device that can reduce the required cooling capacity.

This invention has been made to solve the above-mentioned problems, and one aspect of the invention is a hydrogen storage system that causes a hydrogen storage alloy to absorb hydrogen gas, the hydrogen storage system comprising a pressure reducing valve that reduces the pressure of the hydrogen gas to be absorbed in the hydrogen storage alloy, and a pressure reducing valve control device that repeatedly controls to increase the secondary pressure of the pressure reducing valve when the flow rate of the hydrogen gas to be absorbed in the hydrogen storage alloy falls below a threshold value.

In another aspect of the present invention, the hydrogen storage system is such that, after increasing the secondary pressure of the pressure reducing valve, the pressure reducing valve control device controls the secondary pressure to be gradually decreased until the flow rate becomes equal to or less than the threshold value.

Another aspect of the present invention is a hydrogen storage system for storing hydrogen gas in a hydrogen storage alloy, the hydrogen storage system comprising a pressure reducing valve for reducing the pressure of the hydrogen gas stored in the hydrogen storage alloy, and a pressure reducing valve control device for repeatedly controlling the secondary pressure of the pressure reducing valve to increase when the pressure difference between the secondary pressure of the pressure reducing valve and the internal pressure of the alloy tank falls below a threshold value.

In another aspect of the present invention, the hydrogen storage system is such that, after increasing the secondary pressure of the pressure reducing valve, the pressure reducing valve control device controls the secondary pressure to be gradually decreased until the pressure difference between the secondary pressure of the pressure reducing valve and the internal pressure of the alloy tank becomes equal to or less than the threshold value.

Another aspect of the present invention is the hydrogen storage system described above, which includes a first pump that circulates 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 that cools the heat medium when the pressure of the supplied hydrogen gas is the first pressure, a second pump that circulates 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 that cools the heat medium when the pressure of the supplied hydrogen gas is the second pressure.

Another aspect of the present invention is the hydrogen storage system described above, in which the heat transfer medium passes through the outer periphery of the storage alloy tank that stores the hydrogen storage alloy and through a pipe that penetrates the hydrogen storage alloy.

Another aspect of the present invention is a control method for a hydrogen storage system in which hydrogen gas is absorbed in a hydrogen storage alloy, and when the flow rate of the hydrogen gas to be absorbed in the hydrogen storage alloy falls below a threshold value, the control method repeats control to increase the secondary pressure of a pressure reducing valve that reduces the pressure of the hydrogen gas to be absorbed in the hydrogen storage alloy.

Another aspect of the present invention is a pressure reducing valve control device that, when the flow rate of hydrogen gas to be absorbed in the hydrogen storage alloy falls below a threshold value, repeats control to increase the secondary pressure of a pressure reducing valve that reduces the pressure of the hydrogen gas to be absorbed in the hydrogen storage alloy.

Another aspect of the present invention is a control method for a hydrogen storage system in which hydrogen gas is absorbed in a hydrogen storage alloy, in which, when the pressure difference between the secondary pressure of a pressure reducing valve provided between an alloy tank containing 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, the control method repeats control to increase the secondary pressure of the pressure reducing valve that reduces the pressure of the hydrogen gas to be absorbed in the hydrogen storage alloy.

Another aspect of the present invention is a pressure reducing valve control device that, when the pressure difference between the secondary pressure of a pressure reducing valve provided between an alloy tank storing a hydrogen storage alloy and a hydrogen supply source and the internal pressure of the alloy tank, falls below a threshold value, repeatedly controls to increase the secondary pressure of the pressure reducing valve that reduces the pressure of the hydrogen gas to be stored in the hydrogen storage alloy.

This invention reduces the cooling capacity required by the hydrogen storage system.

1 is a schematic block diagram showing the configuration of a hydrogen storage system 10 according to a first embodiment. FIG. 2 is a schematic diagram showing a storage alloy tank T1 according to the first embodiment. 2 is a schematic block diagram showing the configuration of a second cooling section C2 according to the first embodiment. FIG. 4 is a table illustrating operation modes of the hydrogen storage system 10 according to the first embodiment. 4 is a flowchart illustrating the operation of the pressure reducing valve control device E1 according to the first embodiment. 4 is a graph illustrating the control performed by the pressure reducing valve control device E1 according to the first embodiment. FIG. 2 is a schematic block diagram showing the configuration of a hydrogen storage system 10 according to a modified example of the first embodiment. 5 is a flowchart illustrating an operation of the pressure reducing valve control device E1 according to a modified example of the first embodiment. FIG. 7 is a schematic block diagram showing the configuration of a hydrogen storage system 70 according to a second embodiment.

First Embodiment
Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a schematic block diagram showing the configuration of a hydrogen storage system 10 according to a first embodiment of the present invention. The hydrogen storage system 10 in this embodiment stores hydrogen gas from a hydrogen supply source K1 by having the hydrogen gas absorbed in a hydrogen storage alloy. The hydrogen storage system 10 includes a hydrogen supply unit including a storage alloy tank T1, and a heating and cooling unit for the storage alloy tank T1.
(Hydrogen supply unit)

The hydrogen supply unit includes an alloy storage tank T1, a flowmeter F1, a pressure reducing valve R1, and a pressure reducing valve control device E1, and is capable of supplying hydrogen from the hydrogen supply source K1 to the alloy storage tank T1 via the hydrogen flow path shown by the thick line in FIG. 1. The hydrogen supply source K1 is a hydrogen cardle, a water electrolysis device, or the like, and supplies hydrogen gas to be stored in the hydrogen storage system 10. The hydrogen gas stored in the hydrogen cardle is, for example, at 20 MPaG, whereas the hydrogen gas supplied from the water electrolysis device is, for example, at about 1 MPaG, and these pressures are significantly different. In this specification, filling from a hydrogen cardle or the like where the pressure of the hydrogen gas supplied exceeds the pressure of the hydrogen gas supplied from the water electrolysis device, specifically, 1 MPaG, is referred to as "rapid filling", and filling from a water electrolysis device or the like where the pressure of the hydrogen gas supplied is 1 MPaG or less is referred to as "normal filling".

In the hydrogen supply unit, hydrogen supplied from the hydrogen supply source K1 is supplied to the storage alloy tank T1 through the pressure reducing valve R1 and the flow meter F1 in sequence, and is stored in the hydrogen storage alloy T31 of the storage alloy tank T1 (FIG. 2). The flow meter F1 measures the flow rate of hydrogen flowing into the storage alloy tank T1. The pressure reducing valve R1 reduces the pressure of the hydrogen supplied to the storage alloy tank T1. As the pressure reducing valve R1, various pressure reducing valves such as direct acting pressure reducing valves and pilot operated pressure reducing valves, as well as control valves and solenoid valves that can set the secondary pressure to a predetermined value can be used. The hydrogen supply unit according to this embodiment is equipped with a pressure reducing valve control device E1. The configuration for adjusting the supply amount of hydrogen gas supplied to the storage alloy tank T1 by the pressure reducing valve control device E1 will be described in detail later.
(heating/cooling unit)

The heating and 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 storage alloy tank T1, and the heat medium can be circulated by a heat medium flow path shown by a thin line in Figure 1. Note that water or antifreeze liquid may be used as this heat medium.
The storage alloy tank T1 contains a hydrogen storage alloy T31 that absorbs hydrogen (FIG. 2). The hydrogen storage alloy T31 in the storage alloy tank T1 is heated by a heat medium circulated by the pump P1 or pump P2 when hydrogen is released, and is cooled when hydrogen is filled. The pump P1 circulates the heat medium when normal filling or when hydrogen is released. The pump P2 is arranged in parallel with the pump P1, and circulates the heat medium when rapid filling. The pump P2 has a discharge flow rate per hour that is greater than that of the pump P1, for example, 10 times that of the pump P1. The heating section H1 heats the heat medium to heat the storage alloy tank T1 when hydrogen gas is released from the storage alloy tank T1.

The heating and cooling unit will be described in detail below. The relative positions of each component will be described using the terms "upstream" and "downstream" with a focus on the flow of the heat medium leaving the storage alloy tank T1 and returning in the heating and cooling unit. The flow path of the heat medium connected to the storage alloy tank T1 branches into two, which are connected to valves V1 and V2, respectively. The valve V1 is installed upstream of the pump P1 and controls the flow of the heat medium to the pump P1. The valve V2 is installed upstream 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. This allows the flow rate of the heat medium flowing through the storage alloy tank T1 to be changed by selectively turning on and off the valves V1 and V2.
The heat medium discharged from pump P1 and the heat medium discharged from pump P2 join together once to form a single flow, and then branch into two again, which are connected to valves V3 and V4, respectively. Valve V4 is installed upstream of heating unit H1 and controls the flow of heat medium to heating unit H1. Meanwhile, valve V3 is installed so as to bypass heating unit H1 and controls the flow of heat medium bypassing heating unit H1. Therefore, by selectively turning on/off valves V3 and V4, it is possible to change the flow of heat medium flowing through storage alloy tank T1 between a flow path that is heated by heating unit H1 and a flow path that is bypassed and not heated.

The heat medium discharged from the heating section H1 and the heat medium that has passed through the valve V3 are merged again to form one flow, which then branches into three, which are connected to the valves V5, V6, and V7. 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 greater 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 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, it is possible to change the flow path of the heat medium flowing through the storage alloy tank T1 to one that is cooled by either the first cooling section C1 or the second cooling section C2, or to one that is bypassed and not cooled, depending on the required cooling capacity.
The heat transfer medium discharged from the first cooling section C1, the heat transfer medium discharged from the second cooling section C2, and the heat transfer medium that has passed through valve V5 merge again to become one flow and reach the storage alloy tank T1 again, heating and cooling the storage alloy tank T1.
In this embodiment, the heat medium is assumed to leave the storage alloy tank T1, pass through the pump P1 or P2, pass through the heating section H1, the first cooling section C1, or the second cooling section C2, and return, but this is not limited to the above, and the heat medium may follow the reversed 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 a bypass path, and the cooling configuration includes the first cooling section C1, the second cooling section C2, and a bypass path. However, this is not limited to the above, and the heating/cooling configuration may include the heating section H1, the first cooling section C1, and the second cooling section C2 arranged in parallel, without providing a bypass path.

Here, the storage alloy tank T1 used in this embodiment and the cooling configuration when cooling the storage alloy tank T1 will be described. Figure 2 is a schematic diagram showing a cross section of the storage alloy tank T1 and the cooling configuration of the storage alloy tank T1 in this embodiment. Figure 2(a) is a longitudinal cross section of the storage alloy tank T1, and Figure 2(b) is a cross section of the X-X cross section of Figure 2(a).
The storage alloy tank T1 is connected to a hydrogen supply path and a hydrogen release path (not shown), and stores a granular/sand-like hydrogen storage alloy layer T31 inside. An oil jacket T2 is also placed on the outside of the storage alloy tank T1. The hydrogen storage alloy layer T31 is configured to store 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 pipe P31 and flows through the pipe P33, which is a heat medium pipe that penetrates the hydrogen storage alloy layer T31 stored in the storage alloy tank T1, from one end of the storage alloy tank T1 to the other end. That is, as shown in FIG. 2(a), the heat medium supplied from the pipe P31 is configured to flow only from the space at one end of the storage alloy tank T1 to the pipe P33 provided in the hydrogen storage alloy layer T31. The heat medium flows from the other end of the storage alloy tank T1 through the area around the hydrogen storage alloy layer T31 shown in Fig. 2(b) and is discharged from the pipe P32. Therefore, in Fig. 2(b), the direction of the heat medium flowing through the pipe P33 and the direction of the heat medium flowing through the area around the hydrogen storage alloy layer T31 are opposite to each other. In this way, the heat medium can flow inside and around the periphery of the storage alloy tank T1, so that the area of contact between the hydrogen storage alloy layer T31 and the heat medium is increased, and the hydrogen storage alloy layer T31 can be cooled or heated efficiently. The storage alloy tank T1 may be composed of only one container that stores the hydrogen storage alloy layer T31, or may be composed of multiple containers each of which stores the hydrogen storage alloy layer T31.
The heating section H1 may be capable of heating the heat medium using an electric heating wire, a heat pump, or even exhaust heat from a fuel cell. In this embodiment, the heat medium is heated using exhaust heat from a fuel cell and a heat pump.
The first cooling section C1 cools the heat medium during normal filling, and may use a radiator, a fan, a chiller, etc. In this embodiment, the heat medium, which is made of water or antifreeze, circulates inside the radiator and dissipates heat, thereby cooling the heat medium. In addition, the cooling efficiency is improved by blowing air to the radiator using a fan.

The second cooling section C2 has a larger cooling capacity than the first cooling section C1 and cools the heat transfer medium when performing rapid filling, and a chiller, a cold water tank, etc. can be used. Below, the configuration of the second cooling section C2 used in this embodiment, which can ensure a large cooling capacity, will be explained using FIG. 3. The second cooling section 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 section C2 is capable of circulating the heat transfer medium within the second cooling section C2 by the second heat transfer medium flow path shown in FIG. 2. The first heat transfer medium flow path is the heat transfer medium flow path shown in FIG. 1. Specifically, the heat medium leaving the heat exchanger H21 is divided into a flow that flows through the first cold water tank W21 via the valve V21 and a flow that flows through the second cold water tank W22 via the valve V22, and then rejoins the two flows, and returns to the heat exchanger H21 via the pump P21 and the thermometer T21 in sequence. In the following description, "upstream" and "downstream" refer to the "upstream" and "downstream" of the flow of the heat medium that leaves 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 exchanges heat between the heat medium that cools the storage alloy tank T1 and the heat medium circulated by the pump P21.

The flow path of the heat medium connected to the heat exchanger H21 branches into two, which are connected to a valve V21 and a valve V22, respectively. The valve V21 is disposed upstream of the first cold water tank W21. The valve V21 is a heat medium circulated by the pump P21, and controls the flow of the heat medium 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 disposed upstream of the second cold water tank W22. The valve V22 is a heat medium circulated by the pump P21, and controls the flow of the heat medium flowing into the second cold water tank W22. The second cold water tank W22 is disposed 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 join together and is supplied to the pump P21. The pump P21 circulates the heat medium cooled in the first cold water tank W21 and the second cold water tank W22 to the heat exchanger H21 so that the heat medium for cooling the storage alloy tank T1 is cooled in 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.

For example, initially, valve V21 is opened and valve V22 is closed, allowing the heat transfer medium to flow into the first cold water tank W21. Then, when the cooling capacity of the first cold water tank W21 decreases and the temperature measured by thermometer T21 reaches, for example, 40°C or higher, valve V22 is opened and valve V21 is closed, allowing the heat transfer medium to flow into the second cold water tank W22. In this way, 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 maintained continuously.

Although the second cooling section C2 is configured to include two cold water tanks (the first cold water tank W21 and the second cold water tank W22), the number of cold water tanks may be more than one, and may be two or more.
(Operation Modes of Hydrogen Storage System 10)

Figure 4 is a table explaining the operating modes of the hydrogen storage system 10 in this embodiment. Figure 4 shows the ON/OFF of pumps P1 and P2 of the heating and cooling unit and the opening/closing of valves V1, V2, V3, V4, V5, V6, and V7 during normal filling when hydrogen gas is filled from a water electrolysis device or the like, during rapid filling when hydrogen gas is filled from a hydrogen card or the like, and during hydrogen release.

During normal filling, pump P1 is "ON", pump P2 is "OFF", valve V1 is "open", valve V2 is "closed", valve V3 is "open", valve V4 is "closed", valve V5 is "closed", valve V6 is "open", and valve V7 is "closed". As a result, the heat transfer medium is circulated by pump P1 and cooled by first cooling section C1. Therefore, storage alloy tank T1 is cooled by the heat transfer medium.

During rapid filling, pump P1 is turned "OFF", pump P2 is turned "ON", valve V1 is turned "closed", valve V2 is turned "open", valve V3 is turned "open", valve V4 is turned "closed", valve V5 is turned "closed", valve V6 is turned "closed", and valve V7 is turned "open". As a result, the heat transfer medium is circulated by pump P2, which has a higher discharge performance than pump P1, and is cooled by second cooling section C2, which has a higher cooling capacity than first cooling section C1. Therefore, storage alloy tank T1 is cooled by the heat transfer medium. For this reason, even during rapid filling, in which hydrogen gas is filled from a hydrogen cartridge or the like, the rise in the temperature of storage alloy tank T1 can be suppressed.

When releasing hydrogen, pump P1 is "ON", pump P2 is "OFF", valve V1 is "open", valve V2 is "closed", valve V3 is "closed", valve V4 is "open", valve V5 is "open", valve V6 is "closed", and valve V7 is "closed". As a result, the heat medium is circulated by pump P1 and heated by heating section H1. Therefore, storage alloy tank T1 is heated by the heat medium.
(Regarding control of hydrogen supply unit)
The hydrogen supply unit according to this embodiment is equipped with a pressure reducing valve control device E1. The pressure reducing valve control device E1 controls the pressure reducing valve R1 using the measurement results of the flow meter F1. During rapid filling, the hydrogen gas is adiabatically expanded by reducing the pressure using the pressure reducing valve R1, lowering the temperature of the hydrogen gas, and the hydrogen storage alloy in the storage alloy tank T1 is cooled by the hydrogen gas being filled. The pressure reducing valve control device E1 controls the pressure reducing valve R1 so that the temperature drop of the hydrogen gas is greater. This makes it possible to reduce the cooling capacity required by the second cooling section C2.

5 is a flow chart 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 pressure (downstream pressure) of the pressure reducing valve R1 to a predetermined initial value Pi (step S51). In other words, the pressure reducing valve R1 can set the secondary pressure to a predetermined pressure depending on the opening degree, so specifically, the pressure reducing valve R1 is set to a predetermined opening degree so that the secondary pressure is set to the initial value Pi. Next, the pressure reducing valve control device E1 obtains the flow rate of hydrogen gas measured by the flowmeter F1, i.e., the flow rate downstream of the pressure reducing valve R1 (S52).
Next, the pressure reducing valve control device E1 judges whether the flow rate acquired in step S52 is equal to or less than a predetermined threshold value Vt (step S53). When it is judged that the flow rate is not equal to or less than the threshold value Vt (step S53-No), the pressure reducing valve control device E1 performs control to gradually reduce the secondary pressure by adjusting the opening degree of the pressure reducing valve R1 (step S57). The speed (pressure/time) at which the secondary pressure is reduced at this time may be a predetermined one, or the speed at which the secondary pressure is reduced may be increased as the flow rate increases. After step S57, the process of the pressure reducing valve control device E1 returns to step S52. Also, when it is judged in step S53 that the flow rate is equal to or less than the threshold value Vt (step S53-Yes), the pressure reducing valve control device E1 controls to increase the secondary 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 judges whether the secondary side pressure of the pressure reducing valve R1 is equal to or greater 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 judges whether the secondary side pressure is equal to or greater than the predetermined threshold value Pt. When it is judged that the secondary side pressure of the pressure reducing valve R1 is not equal to or greater than the threshold value Pt (step S55-No), the processing of the pressure reducing valve control device E1 returns to step S52. The predetermined threshold value Pt may be a value greater than the initial value Pi, and may be the pressure in the storage alloy tank T1 at the time of completion of filling. Also, when it is judged in step S55 that the secondary side pressure of the pressure reducing valve R1 is equal to or greater than the threshold value Pt (step S55-Yes), the pressure reducing valve control device E1 adjusts the opening degree of the pressure reducing valve R1 to control the secondary side pressure to the threshold value Pt (step S56), and returns to step S52.

Figure 6 is a graph that explains the control contents by the pressure reducing valve control device E1 according to this embodiment. In the graph of Figure 6, the horizontal axis is time, and the vertical axis is the control value of the secondary pressure of the pressure reducing valve R1. First, in step S51 of Figure 5, the pressure reducing valve control device E1 sets the opening of the pressure reducing valve R1 to a predetermined opening, and controls the secondary pressure to an initial value Pi. This is the state at the left end of the graph in Figure 6. If this initial value Pi is sufficiently small, hydrogen gas flows into the storage alloy tank T1. At this time, the hydrogen gas flowing into the storage alloy tank T1 is adiabatically expanded to pressure Pi by the pressure reducing valve R1, so the temperature drops.

While the flow rate of hydrogen gas into the storage alloy tank T1 is below Vt, the secondary pressure continues to decrease in step S57. In the graph of FIG. 6, this is shown as a downward sloping line to the right. At this time, the hydrogen gas flowing into the storage alloy tank T1 is adiabatically expanded by the pressure reducing valve R1 to a pressure lower than pressure Pi, so the temperature drops further than when the secondary pressure is Pi. However, if the secondary pressure of the pressure reducing valve R1 continues to decrease, the difference between the pressure inside the storage alloy tank T1 and the secondary pressure becomes smaller. As a result, the flow rate of hydrogen gas flowing into the storage alloy tank T1 decreases.

When the flow rate of hydrogen gas flowing into the storage alloy tank T1 falls below the threshold value Vt, in step S54, the pressure reducing valve control device E1 increases the secondary pressure by Pa. In the graph of FIG. 6, the pressure increases vertically by Pa. This causes the difference between the pressure inside the storage alloy tank T1 and the secondary pressure to become large enough that the flow rate of hydrogen gas flowing into the storage alloy tank T1 exceeds Vt. As long as the flow rate of hydrogen gas into the storage alloy tank T1 is below Vt, the secondary pressure continues to decrease in step S57.

In this way, while the secondary pressure does not exceed Pt, the pressure reducing valve control device E1 repeatedly reduces the secondary pressure in stages and increases it by Pa. This controls the pressure difference when the hydrogen gas expands adiabatically, that is, controls the temperature drop due to adiabatic expansion to be larger. This increases the cooling capacity of the hydrogen gas itself for the storage alloy tank T1, and reduces the cooling capacity required for the second cooling section C2.

In this way, if the control to gradually lower the secondary pressure and the control to raise it by Pa are repeated, the threshold value Pt will be exceeded when Pa is raised by itself. In that case, in step S56, the pressure reducing valve control device E1 controls the secondary pressure to the threshold value Pt. In this case, the amount of increase in the secondary pressure is smaller than Pa. In this way, by setting the upper limit of the secondary pressure to the threshold value Pt, it is possible to prevent excessive pressure from being applied to the storage alloy tank T1.
(Modification)
In the above embodiment, the pressure reducing valve control device E1 controls the opening of the pressure reducing valve to change the secondary pressure based on the measurement result of the flow meter F1 that measures the flow rate of hydrogen flowing into the storage alloy tank T1, but this is not limited to this. For example, as shown in Figure 7, a pressure meter M1 that measures the pressure (internal pressure) inside the storage alloy tank T1 may be provided instead of the flow meter F1, and 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, 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), and then the pressure reducing valve control device E1 acquires the pressure inside the storage alloy tank T1 measured by the pressure gauge M1 (S58).
Next, the pressure reducing valve control device E1 judges whether the difference between the pressure acquired in step S58 and the secondary 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 judged that the pressure difference is not equal to or greater than the threshold value (step S59-No), the pressure reducing valve control device E1 performs control to gradually reduce the secondary pressure by adjusting the opening degree of the pressure reducing valve R1 (step S57). The speed (pressure/time) at which the secondary pressure is reduced at this time may be a predetermined speed, or the smaller the pressure difference, the greater the reduction speed. After step S57, the processing of the pressure reducing valve control device E1 returns to step S58.
Furthermore, when it is determined in step S59 that the pressure difference is less than the threshold value (step S59-Yes), the pressure reducing valve control device E1 controls the opening of the pressure reducing valve R1 to increase the secondary side pressure by a predetermined value Pa (step S54). Steps S55 and S56 are the same as those in the above embodiment.

In this way, instead of using the flow rate of hydrogen gas flowing into the storage alloy tank T1, the pressure reducing valve control device E1 adjusts the opening of the pressure reducing valve R1 based on the difference between the pressure inside the storage alloy tank T1 and the secondary pressure, thereby achieving the same cooling effect for the storage alloy tank T1 as in the above embodiment.

Second Embodiment
In the first embodiment, hydrogen was filled into the storage alloy tank T1 during both normal filling and rapid filling. In the hydrogen storage system 70 of the second embodiment, two storage alloy tanks are provided, one of which is dedicated to rapid filling, in which high-pressure hydrogen gas such as from a hydrogen cascade is filled, and the other is dedicated to normal filling, in which hydrogen gas such as from a water electrolysis device is filled at a lower pressure than that used for rapid filling.

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

In addition to these, the hydrogen storage system 70 includes a second storage alloy tank T72 arranged in series with the 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 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 high-pressure hydrogen gas compared to the low-pressure hydrogen supply source K72 to the storage alloy tank T1 of the hydrogen storage system 70. The valves V1, V2, V3, V4, V5, V6, V7, pumps P1, P2, heating unit H1, first cooling unit C1, second cooling unit C2, 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, so description thereof will be omitted.

In this way, even if the hydrogen storage system 70 is equipped with a separate storage alloy tank T1 for the high-pressure hydrogen supply source K71 and a second storage alloy tank T72 for the low-pressure hydrogen supply source K72, the same effects as in the first embodiment can be obtained.
Alternatively, a bypass may be provided for each of the storage alloy tank T1 and the second storage alloy tank T72. In this case, valves are provided on the upstream side of the storage alloy tank T1 and the upstream side of the second storage alloy tank T72 to control the flow of heat transfer medium thereto. This allows hydrogen to be released from only one of the storage alloy tank T1 and the second storage alloy tank T72.
Furthermore, similar to the storage alloy tank T1 shown in FIG. 2, the second storage alloy tank T72 may be configured so that the heat medium flows inside and around the second storage alloy tank T72, or the heat medium may flow only inside the tank.

In step S57 in Fig. 5, the pressure reducing valve control device E1 controls the secondary side pressure to be gradually lowered, but the secondary side pressure does not have to be changed. 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 hydrogen gas to be absorbed in the hydrogen storage alloy falls below the threshold value Vt. In that case, the line sloping downward to the right in the graph in Fig. 6 becomes a horizontal line.
5 does not have to be a fixed value. For example, it may be changed according to the time during which the control for gradually decreasing the secondary pressure in step S57 has been continued. Specifically, the longer the time, the smaller Pa may be. Furthermore, before actually performing the control in step S54, it may be determined whether the control result exceeds a threshold value Pt.

The above describes an embodiment of the present invention in detail with reference to the drawings, but the specific configuration is not limited to this embodiment, and design changes that do not deviate from the gist of the present invention are also included.

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

Claims (10)

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 absorbed in the hydrogen storage alloy;
and a pressure reducing valve control device that repeats control to increase the secondary pressure of the pressure reducing valve when the flow rate of hydrogen gas to be absorbed in the hydrogen storage alloy falls below a threshold value. The hydrogen storage system of claim 1, wherein the pressure reducing valve control device controls the secondary side pressure of the pressure reducing valve to be increased, and then controls the secondary side pressure to be gradually decreased until the flow rate becomes equal to or less than the threshold value. 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 absorbed in the hydrogen storage alloy;
a pressure reducing valve control device that, when a pressure difference between the secondary pressure of the pressure reducing valve and the internal pressure of the alloy tank becomes equal to or less than a threshold value, repeatedly controls to increase the secondary pressure of the pressure reducing valve. The hydrogen storage system of claim 3, wherein the pressure reducing valve control device controls the secondary side pressure of the pressure reducing valve to be increased, and then controls the secondary side pressure to be gradually decreased until the pressure difference between the secondary side pressure of the pressure reducing valve and the internal pressure of the alloy tank becomes equal to or less than the threshold value. a first pump for circulating a heat transfer medium for cooling the hydrogen storage alloy when the pressure of the supplied hydrogen gas is a first pressure;
a first cooling unit that cools the heat transfer medium when the pressure of the supplied hydrogen gas is the first pressure;
a second pump that circulates the heat transfer medium for cooling the hydrogen storage alloy when the pressure of the supplied hydrogen gas is a second pressure higher than the first pressure;
The hydrogen storage system according to claim 1 , further comprising: a second cooling unit that cools the heat transfer medium when a pressure of the supplied hydrogen gas is the second pressure. The hydrogen storage system according to claim 5, in which the heat transfer medium passes through the outer periphery of a storage alloy tank that stores the hydrogen storage alloy and through a pipe that penetrates the hydrogen storage alloy. A control method for a hydrogen storage system in which hydrogen gas is absorbed in a hydrogen storage alloy, comprising the steps of:
when the flow rate of the hydrogen gas to be absorbed in the hydrogen storage alloy becomes equal to or less than a threshold value, a control for increasing the secondary pressure of a pressure reducing valve for reducing the pressure of the hydrogen gas to be absorbed in the hydrogen storage alloy is repeated.
Control methods. A pressure reducing valve control device that, when the flow rate of hydrogen gas to be absorbed in a hydrogen storage alloy falls below a threshold value, repeatedly controls to increase the secondary pressure of a pressure reducing valve that reduces the pressure of the hydrogen gas to be absorbed in the hydrogen storage alloy. A control method for a hydrogen storage system in which hydrogen gas is absorbed in a hydrogen storage alloy, comprising the steps of:
when a pressure difference between a secondary pressure of a pressure reducing valve provided between an alloy tank storing the hydrogen storage alloy and a hydrogen supply source and an internal pressure of the alloy tank becomes equal to or less than a threshold value, a control for increasing the secondary pressure of the pressure reducing valve for reducing the pressure of the hydrogen gas to be absorbed in the hydrogen storage alloy is repeated.
Control methods. A pressure reducing valve control device that, when the pressure difference between the secondary pressure of a pressure reducing valve provided between an alloy tank storing a hydrogen storage alloy and a hydrogen supply source and the internal pressure of the alloy tank falls below a threshold value, repeatedly controls to increase the secondary pressure of the pressure reducing valve that reduces the pressure of the hydrogen gas to be absorbed in the hydrogen storage alloy.

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