Water electrolysis system, water electrolysis method, and computer program

Abstract

To provide a technology for producing hydrogen of a target dew point in a short time in a water electrolysis system.SOLUTION: The water electrolysis system comprises a water electrolysis device generating hydrogen by electrolyzing water, a flow path connected to the water electrolysis device for gas including the hydrogen generated by the water electrolysis device and water to flow therethrough, a storage connected to the flow path to store the gas supplied from the water electrolysis device, a cooler cooling the gas supplied to the storage, a temperature detector detecting a temperature in the storage, a pressure changer changing the pressure in the storage, and a controller estimating a target pressure using information indicating a relationship between the temperature and pressure in the storage for a dew point in the storage to become a target dew point and using the temperature detected by the temperature detector, to control the pressure changer so that the pressure in the storage becomes the target pressure.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a water electrolysis system, a water electrolysis method, and a computer program. [Background technology]

[0002] BACKGROUND ART Conventionally, water electrolysis systems that supply hydrogen generated by electrolysis of water have been known (for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-40637 [Patent Document 2] Japanese Patent Application Publication No. 2020-176309 Summary of the Invention [Problem to be solved by the invention]

[0004] However, even with the prior art such as that of Patent Document 1, there is still room for improvement in the technology for producing hydrogen having a target dew point in a short period of time in a water electrolysis system.

[0005] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a technique for producing hydrogen having a target dew point in a short period of time in a water electrolysis system. [Means for solving the problem]

[0006] The present invention has been made to solve at least part of the above-mentioned problems, and can be realized in the following aspects.

[0007] (1) According to one aspect of the present invention, there is provided a water electrolysis system comprising: a water electrolysis device that generates hydrogen by electrolysis of water; a flow path connected to the water electrolysis device and through which a gas containing water and hydrogen generated by the water electrolysis device flows; a storage unit connected to the flow path and accommodating the gas supplied from the water electrolysis device; a cooling unit that cools the gas supplied to the storage unit; a temperature detection unit that detects a temperature inside the storage unit; a pressure change unit that changes a pressure inside the storage unit; and a control unit that estimates a target pressure using information indicating a relationship between the temperature and pressure inside the storage unit so that a dew point inside the storage unit becomes a target dew point and the temperature detected by the temperature detection unit, and controls the pressure change unit to adjust the pressure inside the storage unit to the target pressure.

[0008] According to this configuration, the control unit estimates the target pressure for the dew point inside the storage unit, which stores a gas containing hydrogen and water, using information indicating the relationship between the temperature and pressure inside the storage unit so that the dew point inside the storage unit becomes the target dew point, and the temperature inside the storage unit detected by the temperature detection unit. The control unit controls the pressure change unit so that the pressure inside the storage unit becomes the target pressure. This makes it possible to produce hydrogen with the target dew point in a relatively short time.

[0009] (2) In the water electrolysis system of the above aspect, the control unit may use the information to estimate a standard pressure, which is the pressure inside the accommodating unit at which the dew point inside the accommodating unit becomes the target dew point when the temperature inside the accommodating unit becomes a preset standard temperature. If the temperature detected by the temperature detecting unit is higher than the standard temperature, the control unit may control the pressure changing unit so that the pressure inside the accommodating unit becomes the target pressure that is higher than the standard pressure and equal to or lower than a preset upper limit pressure. If the temperature detected by the temperature detecting unit is lower than the standard temperature, the control unit may control the pressure changing unit so that the pressure inside the accommodating unit becomes the target pressure that is lower than the standard pressure. According to this configuration, the control unit estimates the standard pressure, which is the pressure inside the accommodating unit at which the dew point inside the accommodating unit becomes the target dew point when the temperature inside the accommodating unit becomes the preset standard temperature, using the information indicating the relationship between the temperature and pressure inside the accommodating unit at which the dew point inside the accommodating unit becomes the target dew point. The control unit adjusts the pressure inside the accommodating unit relative to the standard pressure depending on whether the temperature detected by the temperature detecting unit is higher than the standard temperature. This allows hydrogen to be produced at the target dew point even when the temperature inside the storage unit is not at the standard temperature, thereby enabling hydrogen to be produced at the target dew point in an even shorter time.

[0010] (3) The water electrolysis system of the above aspect may further include a pressure detection unit that detects the pressure inside the storage unit; a supply flow path connected to the flow path and that supplies the gas inside the storage unit to a hydrogen consumer; and a flow control valve connected to the supply flow path and that adjusts the flow rate of the gas in the supply flow path. The control unit may estimate the dew point inside the storage unit using a map showing the correlation between the temperature, pressure, and dew point inside the storage unit, the temperature detected by the temperature detection unit, and the pressure detected by the pressure detection unit, and control the flow control valve using the estimated dew point inside the storage unit. According to this configuration, the control unit estimates the dew point inside the storage unit using the pressure detected by the pressure detection unit and the temperature detected by the temperature detection unit. The control unit supplies the gas inside the storage unit to a hydrogen consumer in accordance with the estimated dew point. This allows hydrogen having a target dew point with relatively high accuracy to be supplied to a hydrogen consumer.

[0011] (4) In the water electrolysis system of the above aspect, the pressure changing unit may include a compressor connected to the flow path and capable of pressurizing the gas supplied to the accommodating unit, and a back-pressure valve connected to the flow path and capable of maintaining the pressure inside the accommodating unit at the target pressure, and the control unit may control the compressor and the back-pressure valve. According to this configuration, the pressure changing unit that changes the pressure inside the accommodating unit includes the compressor that can pressurize the gas supplied to the accommodating unit, and the back-pressure valve that can maintain the pressure inside the accommodating unit at the target pressure. The control unit controls the compressor and the back-pressure valve in a coordinated manner to set the pressure inside the accommodating unit to the target pressure. This allows the pressure inside the accommodating unit to be set to the target pressure more quickly than in the case of using the back-pressure valve alone, thereby enabling hydrogen with a target dew point to be produced in an even shorter time.

[0012] (5) The water electrolysis system of the above aspect may further include a dew point detection unit that detects a dew point inside the accommodating unit. The control unit may use the information to estimate a standard pressure, which is the pressure inside the accommodating unit at which the dew point inside the accommodating unit will become the target dew point when the temperature inside the accommodating unit becomes a preset standard temperature. If the dew point detected by the dew point detection unit is lower than the target dew point, the control unit may control the pressure change unit so that the pressure inside the accommodating unit becomes an upper limit pressure that is preset as the target pressure. If the dew point detected by the dew point detection unit is the same as the target dew point, the control unit may control the pressure change unit so that the pressure inside the accommodating unit becomes the standard pressure as the target pressure. According to this configuration, the control unit controls the pressure change unit so that the pressure inside the accommodating unit becomes the upper limit pressure or the standard pressure depending on the dew point detected by the dew point detection unit. As a result, when the dew point inside the accommodating unit becomes the target dew point, the power consumption of the compressor can be reduced by setting the pressure inside the accommodating unit to a target pressure that is lower than the upper limit pressure. Therefore, hydrogen having a target dew point can be produced in a short time with little power consumption.

[0013] (6) According to another aspect of the present invention, there is provided a water electrolysis method using a water electrolysis system. The water electrolysis method includes: a water electrolysis step of generating hydrogen by electrolysis of water; a cooling step of cooling a gas containing hydrogen and water produced in the water electrolysis step, which is supplied to a storage unit; a temperature detection step of detecting a temperature inside the storage unit; and a pressure change step of estimating a target pressure using information indicating a relationship between the temperature and pressure inside the storage unit so that the dew point inside the storage unit becomes a target dew point and the temperature detected in the temperature detection step, and changing the pressure inside the storage unit so that the pressure inside the storage unit becomes the target pressure. According to this configuration, the pressure change step estimates the target pressure so that the dew point inside the storage unit becomes the target dew point using information indicating the relationship between the temperature and pressure inside the storage unit so that the dew point inside the storage unit becomes the target dew point and the temperature inside the storage unit detected by the temperature detection unit. The pressure change step changes the pressure inside the storage unit so that the pressure inside the storage unit becomes the target pressure. This enables hydrogen with the target dew point to be produced in a relatively short time.

[0014] (7) According to yet another aspect of the present invention, there is provided a computer program for causing a computer to execute hydrogen generation using a water electrolysis system. The computer program causes the computer to execute a water electrolysis function for generating hydrogen by electrolysis of water, a cooling function for cooling a gas containing hydrogen and water produced by the water electrolysis function that is supplied to a storage unit, a temperature detection function for detecting the temperature inside the storage unit, and a pressure change function for estimating a target pressure using information indicating a relationship between the temperature and pressure inside the storage unit so that the dew point inside the storage unit becomes a target dew point and the temperature detected by the temperature detection function, and for changing the pressure inside the storage unit so that the pressure inside the storage unit becomes the target pressure. According to this configuration, the pressure change function estimates the target pressure so that the dew point inside the storage unit becomes the target dew point using information indicating the relationship between the temperature and pressure inside the storage unit so that the dew point inside the storage unit becomes the target dew point and the temperature inside the storage unit detected by the temperature detection function. The pressure change function changes the pressure inside the storage unit so that the pressure inside the storage unit becomes the target pressure. This enables hydrogen with a target dew point to be produced in a relatively short time.

[0015] The present invention can be realized in various forms, such as a water electrolysis device that electrolyzes water, a hydrogen supply device provided in the water electrolysis device, a control method for these devices and water electrolysis systems, a computer program for causing these devices and water electrolysis systems to supply hydrogen, a server device for distributing the computer program, and a non-transitory storage medium on which the computer program is stored. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a schematic diagram illustrating a schematic configuration of a water electrolysis system according to a first embodiment. [Figure 2] 1 is a flowchart illustrating a water electrolysis method according to a first embodiment. [Figure 3] FIG. 1 is a first diagram illustrating a method for estimating a target pressure. [Figure 4]FIG. 10 is a second diagram illustrating a method for estimating a target pressure. [Figure 5] FIG. 4 is a schematic diagram illustrating a schematic configuration of a water electrolysis system according to a second embodiment. [Figure 6] FIG. 10 is a schematic diagram illustrating the general configuration of a water electrolysis system according to a third embodiment. [Figure 7] FIG. 10 is a diagram illustrating the effects of the water electrolysis system according to the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0017] First Embodiment FIG. 1 is a schematic diagram showing the overall configuration of a water electrolysis system 1 according to a first embodiment. The water electrolysis system 1 according to this embodiment supplies hydrogen generated by electrolysis of water to an external hydrogen consumer. The water electrolysis system 1 according to this embodiment adjusts the dew point (water content) of the hydrogen supplied to the hydrogen consumer to a preset target dew point. This allows the hydrogen consumer to more easily use the hydrogen supplied from the water electrolysis system 1. The water electrolysis system 1 according to this embodiment includes a water electrolysis apparatus 10, a compressor 21, a cooling unit 30, a separation tank 35, a temperature detection unit 41, a pressure detection unit 42, a backpressure valve 50, and a control unit 61.

[0018] The water electrolysis device 10 is a so-called PEM (Polymer Electrolyte Membrane) type water electrolysis device. The water electrolysis device 10 electrolyzes water supplied to the anode side to generate oxygen (O2) on the anode side and hydrogen (H2) on the cathode side.

[0019] The water electrolysis apparatus 10 is connected to a water supply flow path 11 for supplying water to the anode side, an oxygen flow path 12 through which oxygen generated on the anode side flows, and a hydrogen flow path 13 through which hydrogen generated on the cathode side flows. In the water electrolysis apparatus 10, of the water supplied to the anode side from a water supply destination (not shown) through the water supply flow path 11, most of the unreacted water that has not been electrolyzed flows through the oxygen flow path 12 together with oxygen generated at the anode. A regulator valve 12a for regulating the flow rate of a gas containing oxygen and water is connected to the oxygen flow path 12.

[0020] A portion of the water supplied to the anode side permeates a polymer membrane (not shown) separating the anode and cathode, and flows through the hydrogen flow channel 13 together with hydrogen produced at the cathode. That is, a gas containing hydrogen and water flows through the hydrogen flow channel 13. Here, the gas containing hydrogen and water flowing through the hydrogen flow channel 13 is referred to as a "mixed gas." A regulating valve 13a that regulates the flow rate of the mixed gas is connected to the hydrogen flow channel 13. In this specification, "hydrogen" in descriptions related to dew point refers to the above-mentioned mixed gas.

[0021] The compressor 21 is connected to the hydrogen flow path 13. In this embodiment, the compressor 21 is connected downstream of the regulator valve 13a in the flow of the mixed gas in the hydrogen flow path 13. The compressor 21 increases the pressure of the mixed gas flowing through the hydrogen flow path 13 to a predetermined pressure.

[0022] The cooling unit 30 is connected to the hydrogen flow path 13. In this embodiment, the cooling unit 30 is connected downstream of the compressor 21 in the flow of the mixed gas in the hydrogen flow path 13. The cooling unit 30 includes a heat exchanger 31 through which a refrigerant flows, and a chiller 32 that cools the refrigerant flowing through the heat exchanger 31 and circulates the refrigerant through the heat exchanger 31. The heat exchanger 31 is disposed so as to intersect with the hydrogen flow path 13, and uses the cold energy of the refrigerant to cool the mixed gas flowing through the hydrogen flow path 13. The chiller 32 cools the refrigerant that has exchanged heat with the mixed gas in the heat exchanger 31, and promotes the circulation of the refrigerant in the heat exchanger 31.

[0023] The separation tank 35 is connected to the hydrogen flow path 13. In this embodiment, the separation tank 35 is connected downstream of the cooling unit 30 in the flow of the mixed gas in the hydrogen flow path 13. The separation tank 35 stores the mixed gas cooled by the heat exchanger 31 and separates liquid water contained in the mixed gas from the mixed gas. As a result, the separated liquid water and the mixed gas from which the liquid water has been separated coexist in an interior 36 of the separation tank 35. The liquid water separated from the mixed gas in the separation tank 35 passes through a discharge valve 35a and is discharged to the outside of the water electrolysis system 1. The separation tank 35 corresponds to a "storage unit" in the claims.

[0024] The temperature detection unit 41 is provided in the separation tank 35. The temperature detection unit 41 is, for example, a thermocouple, and detects the temperature inside 36 of the separation tank 35, i.e., the temperature of the mixed gas after liquid water has been separated. The temperature detected by the temperature detection unit 41 is output to a control unit 61, which will be described later. The location at which the temperature detection unit 41 is provided is not limited to the separation tank 35, and may be any location where the temperature of the mixed gas after liquid water has been separated can be detected.

[0025] The pressure detection unit 42 is connected to the hydrogen flow path 13. In this embodiment, the pressure detection unit 42 is connected downstream of the separation tank 35 in the flow of the mixed gas in the hydrogen flow path 13. The pressure detection unit 42 detects the pressure in the interior 36 of the separation tank 35 via the hydrogen flow path 13. That is, the pressure detection unit 42 detects the pressure of the mixed gas after liquid water has been separated. The pressure in the interior 36 of the separation tank 35 detected by the pressure detection unit 42 is output to the control unit 61. The location at which the pressure detection unit 42 is provided is not limited to the hydrogen flow path 13 downstream of the separation tank 35, and may be any location where the pressure of the mixed gas after liquid water has been separated can be detected.

[0026] The back pressure valve 50 is connected to the hydrogen flow path 13. In this embodiment, the back pressure valve 50 is connected downstream of the pressure detection unit 42 in the flow of mixed gas in the hydrogen flow path 13. The back pressure valve 50 is electrically connected to the control unit 61, and changes the pressure in the interior 36 of the separation tank 35 in response to commands from the control unit 61. Details of how the back pressure valve 50 changes the pressure in the interior 36 of the separation tank 35 will be described later. The back pressure valve 50 corresponds to the "pressure changing unit" in the claims.

[0027] 1, a supply flow path 14 and an exhaust flow path 15 are connected to the hydrogen flow path 13. A flow rate adjustment valve 14a that adjusts the flow rate of gas flowing through the supply flow path 14 is connected to the supply flow path 14. A flow rate adjustment valve 15a that adjusts the flow rate of gas flowing through the exhaust flow path 15 is connected to the exhaust flow path 15. Each of the flow rate adjustment valves 14a, 15a is electrically connected to a control unit 61, and adjusts the flow rate of the mixed gas flowing through the supply flow path 14 or the exhaust flow path 15 in response to a command from the control unit 61.

[0028] The control unit 61 is a computer including a ROM, a RAM, and a CPU. The control unit 61 is electrically connected to the temperature detection unit 41, the pressure detection unit 42, the back pressure valve 50, the flow rate control valves 14a, 15a, etc. The control unit 61 controls each unit of the water electrolysis system 1 by loading a computer program stored in a read only memory (ROM) (not shown) into a random access memory (RAM) and executing the program.

[0029] In the water electrolysis system 1 of this embodiment, the controller 61 stores a map (hereinafter simply referred to as "map") indicating the correlation between the temperature, pressure, and dew point of the interior 36 of the separation tank 35, as well as information regarding a preset target dew point of hydrogen and a combination of a standard temperature Ts and a standard pressure Ps at which hydrogen reaches the target dew point. The map includes information indicating the relationship between the temperature and pressure of the interior 36 of the separation tank 35 at which the dew point of the interior 36 of the separation tank 35 reaches the target dew point.

[0030] The relationship between the standard temperature Ts and the standard pressure Ps for achieving a target dew point for hydrogen will now be described. In this embodiment, the output for cooling the mixed gas by the cooling unit 30 is preset. As a result, in the water electrolysis method of this embodiment, which will be described later, the temperature of the interior 36 of the separation tank 35 is constant when the water electrolysis system 1 is operating stably. In this embodiment, the temperature of the interior 36 of the separation tank 35 when the water electrolysis system 1 is operating stably is defined as the "standard temperature Ts." Therefore, the "standard pressure Ps," which is the pressure inside the separation tank 35 when the water electrolysis system 1 is operating stably, is determined from the relationship between the target dew point for hydrogen and the standard temperature Ts.

[0031] In the present embodiment, the controller 61 stores an equipment upper limit pressure Pm of the water electrolysis system 1. The equipment upper limit pressure Pm of the water electrolysis system 1 refers to the lowest of the upper limit pressures allowed to avoid damage to equipment included in the water electrolysis system 1 and provided on a path through which the mixed gas flows, such as the water electrolysis device 10, the hydrogen flow path 13, the compressor 21, the separation tank 35, and the back-pressure valve 50.

[0032] Next, details of the water electrolysis method of this embodiment using the water electrolysis system 1 will be described. In the water electrolysis method of this embodiment, the dew point of hydrogen produced in the water electrolysis apparatus 10 is adjusted, and hydrogen (product hydrogen) having a target dew point is supplied to a hydrogen utilization destination. The water electrolysis method of this embodiment is started, for example, when a user of the water electrolysis system 1 operates a start button on the water electrolysis system 1.

[0033] FIG. 2 is a flowchart illustrating the water electrolysis method of this embodiment. FIG. 2 is a flowchart illustrating a method for changing the pressure inside 36 of separation tank 35, part of the water electrolysis method of this embodiment. In the water electrolysis system 1 of this embodiment, as described above, the mixed gas contains unreacted water. Therefore, in order to supply the mixed gas output from the water electrolysis apparatus 10 to a hydrogen consumer as product hydrogen with an adjusted dew point, the product hydrogen needs to be adjusted to a predetermined target dew point. Note that the predetermined target dew point for product hydrogen may vary depending on the hydrogen utilization method at the hydrogen consumer. The water electrolysis method of this embodiment can produce product hydrogen at a target dew point that varies depending on the hydrogen utilization method at the hydrogen consumer.

[0034] In the water electrolysis method of this embodiment, after the start of water electrolysis in the water electrolysis apparatus 10, the operation of the cooling unit 30 is started (step S11). In step S11, the control unit 61 starts the operation of the cooling unit 30 to cool the mixed gas. In step S11, the control unit 61 sets the output of the chiller 32 so that the temperature of the mixed gas becomes the standard temperature Ts, and immediately after the operation of the cooling unit 30 is started, the temperature of the mixed gas gradually decreases.

[0035] Next, it is determined whether the temperature Tn of the interior 36 of the separation tank 35 is greater than the standard temperature Ts of the mixed gas (step S12). In step S12, the control unit 61 determines whether the temperature Tn of the interior 36 of the separation tank 35 is greater than the standard temperature Ts of the mixed gas. The temperature Tn of the interior 36 of the separation tank 35 is the temperature Tn of the mixed gas after being cooled by the cooling unit 30, and is detected by the temperature detection unit 41. The standard temperature Ts of the mixed gas is included in information stored in the memory unit 51 regarding the relationship between the standard temperature Ts and the standard pressure Ps. If the control unit 61 determines that the temperature Tn of the interior 36 of the separation tank 35 is greater than the standard temperature Ts of the mixed gas, the process proceeds to step S13. If the control unit 61 determines that the temperature Tn of the interior 36 of the separation tank 35 is equal to or lower than the standard temperature Ts of the mixed gas, the process proceeds to step S23.

[0036] If it is determined in step S12 that the temperature Tn of the interior 36 of the separation tank 35 is higher than the standard temperature Ts of the mixed gas, the control unit 61 estimates the target pressure Pc to be set in the back-pressure valve 50 (step S13). In step S13, the control unit 61 estimates the target pressure Pc using a map, the target dew point, and the temperature detected by the temperature detection unit 41. The target pressure Pc estimated in step S13 is higher than the standard pressure Ps.

[0037] Fig. 3 is a first diagram illustrating a method for estimating the target pressure. Fig. 4 is a second diagram illustrating a method for estimating the target pressure. Here, the method for estimating the target pressure Pc in step S13 will be described.

[0038] First, we will explain the map stored in the control unit 61. In this embodiment, when creating the map to be stored, the saturated water vapor amount at each of a plurality of temperatures is calculated using the following formula (1) (Tetens formula), and an approximation formula showing the relationship between the temperature and the water vapor amount is created.

number

[0039] Next, using equation (1), the water vapor pressure for each combination of multiple pressures and multiple temperatures is converted to water vapor pressure at atmospheric pressure. Finally, the converted water vapor pressure is substituted into the created approximation equation to calculate the dew point at atmospheric pressure. FIG. 4 is a map showing the correlation between the calculated dew point at atmospheric pressure, temperature, and pressure. In step S13, using a map such as that shown in FIG. 4 stored in the control unit 61, the pressure (the part shown by symbol F2 in the map shown in FIG. 4) at which the dew point is the same as the target dew point for the temperature detected by the temperature detection unit 41 (the part shown by symbol F1 in the map shown in FIG. 4) is found, and this pressure is set as the target pressure Pc. In this way, the control unit 61 estimates the target pressure Pc.

[0040] After estimating the target pressure Pc in step S13, the control unit 61 determines whether the target pressure Pc is greater than the equipment upper limit pressure Pm of the water electrolysis system 1 (step S14). In step S14, the control unit 61 determines whether the target pressure Pc estimated in step S13 is greater than the stored equipment upper limit pressure Pm. If the control unit 61 determines that the target pressure Pc is greater than the equipment upper limit pressure Pm, the process proceeds to step S15. If the control unit 61 determines that the target pressure Pc is equal to or less than the equipment upper limit pressure Pm, the process proceeds to step S16.

[0041] If it is determined in step S14 that the target pressure Pc is greater than the equipment upper limit pressure Pm, the control unit 61 sets the pressure of the back pressure valve 50 to the equipment upper limit pressure Pm (step S15). As a result, the pressure in the interior 36 of the separation tank 35 rises to the equipment upper limit pressure Pm, and water contained in the mixed gas is further liquefied in the interior 36 of the separation tank 35. In the process of step S15, the dew point of the mixed gas approaches the target dew point, but does not reach the target dew point.

[0042] If it is determined in step S14 that the target pressure Pc is equal to or lower than the equipment upper limit pressure Pm, the control unit 61 sets the pressure of the back pressure valve 50 to the target pressure Pc (step S16). As a result, the pressure in the interior 36 of the separation tank 35 rises to the target pressure Pc, so that the water contained in the mixed gas in the interior 36 of the separation tank 35 is further liquefied, and the dew point of the mixed gas becomes the target dew point. That is, in the process of step S16, the dew point of the mixed gas becomes the target dew point.

[0043] On the other hand, if it is determined in step S12 that the temperature Tn of the interior 36 of the separation tank 35 is equal to or lower than the standard temperature Ts of the mixed gas, it is determined whether the temperature Tn of the interior 36 of the separation tank 35 is lower than the standard temperature Ts of the mixed gas (step S23). If the control unit 61 determines that the temperature Tn of the interior 36 of the separation tank 35 is lower than the standard temperature Ts of the mixed gas, the process proceeds to step S24. If the control unit 61 determines that the temperature Tn of the interior 36 of the separation tank 35 is the same as the standard temperature Ts of the mixed gas, the process proceeds to step S25.

[0044] If it is determined in step S23 that the temperature Tn of the interior 36 of the separation tank 35 is lower than the standard temperature Ts of the mixed gas, the control unit 61 estimates the target pressure Pc to be set in the back-pressure valve 50 (step S24). In step S24, the control unit 61 estimates the target pressure Pc using a stored map, the target dew point, and the temperature detected by the temperature detection unit 41. The method for estimating the target pressure Pc in step S24 is the same as in step S13. Note that the target pressure Pc estimated in step S24 is a pressure lower than the standard pressure Ps. After step S24, the control unit 61 sets the pressure setting of the back-pressure valve 50 to the target pressure Pc (step S25). As a result, the dew point of the mixed gas becomes the target dew point.

[0045] If it is determined in step S23 that the temperature Tn of the interior 36 of the separation tank 35 is the same as the standard temperature Ts of the mixed gas, the pressure setting of the back pressure valve 50 is set to the standard pressure Ps (step S26). In step S26, since the temperature Tn of the interior 36 of the separation tank 35 is the same as the standard temperature Ts of the mixed gas, the control unit 61 sets the pressure of the back pressure valve 50 to a combination of the standard temperature Ts and the standard pressure Ps that will bring the dew point of the mixed gas to the target dew point. As a result, the dew point of the mixed gas becomes the target dew point.

[0046] In this way, the water electrolysis system 1 of the present embodiment uses a map showing the correlation between the temperature, pressure, and dew point of the interior 36 of the separation tank 35, the target dew point of the mixed gas, and a combination of the standard temperature Ts and standard pressure Ps at which the mixed gas reaches the target dew point, to change the pressure of the interior 36 of the separation tank 35 in accordance with the temperature Tn of the interior 36 of the separation tank 35. As a result, even when the temperature of the interior 36 of the separation tank 35 is not the standard temperature Ts, the dew point of the interior 36 of the separation tank 35 can be set to the target dew point, and hydrogen at the target dew point can be produced in a short period of time.

[0047] In the water electrolysis method using the water electrolysis system 1 of this embodiment, the controller 61 controls the flow rate control valve 14a of the supply flow path 14 and the flow rate control valve 15a of the exhaust flow path 15. The controller 61 estimates the dew point of the interior 36 of the separation tank 35 using the temperature and pressure of the interior 36 of the separation tank 35 in parallel with changing the pressure in the separation tank 35 as described with reference to FIG. 2 . When the controller 61 estimates that the dew point of the interior 36 of the separation tank 35 is not the target dew point, the controller 61 closes the flow rate control valve 14a of the supply flow path 14 and opens the flow rate control valve 15a of the exhaust flow path 15. This allows the mixed gas that does not have the target dew point to be discharged to the outside of the water electrolysis system 1 via the exhaust flow path 15. On the other hand, when the controller 61 estimates that the dew point of the interior 36 of the separation tank 35 is the target dew point, the controller 61 opens the flow rate control valve 14a of the supply flow path 14 and closes the flow rate control valve 15a of the exhaust flow path 15. This allows hydrogen having the target dew point to be supplied to the hydrogen destination via the supply flow path 14.

[0048] In the water electrolysis system 1 of the present embodiment described above, the control unit 61 estimates the target pressure Pc at which the dew point in the interior 36 of the separation tank 35 becomes the target dew point, using a map showing the correlation between the temperature, pressure, and dew point in the interior 36 of the separation tank 35 containing gas containing hydrogen and water, the target dew point, and the temperature in the interior 36 of the separation tank 35 detected by the temperature detection unit 41. The control unit 61 controls the back-pressure valve 50 so that the pressure in the interior 36 of the separation tank 35 becomes the target pressure Pc. This makes it possible to produce hydrogen having the target dew point in a relatively short time.

[0049] Furthermore, in the water electrolysis system 1 of this embodiment, the control unit 61 uses the map and the target dew point to estimate the standard pressure Ps, which is the pressure inside the separation tank 35 at which the dew point inside the separation tank 35 becomes the target dew point when the temperature inside the separation tank 35 becomes the preset standard temperature Ts. The control unit 61 adjusts the pressure inside the separation tank 35 with respect to the standard pressure Ps, depending on the magnitude relationship between the temperature detected by the temperature detection unit 41 and the standard temperature Ts. This makes it possible to produce hydrogen having a target dew point even when the temperature inside the separation tank 35 does not become the standard temperature Ts. Therefore, hydrogen having a target dew point can be produced even before the temperature inside the separation tank 35 becomes the standard temperature Ts, thereby enabling hydrogen having a target dew point to be produced in an even shorter time.

[0050] Furthermore, in the water electrolysis system 1 of this embodiment, the control unit 61 estimates the dew point in the interior 36 of the separation tank 35 using the temperature detected by the temperature detection unit 41 and the pressure detected by the pressure detection unit 42. The control unit 61 supplies the mixed gas in the interior 36 of the separation tank 35 to a hydrogen consumer in accordance with the estimated dew point. This makes it possible to supply hydrogen having a target dew point with relatively high accuracy to the hydrogen consumer.

[0051] Furthermore, according to the water electrolysis method of this embodiment, in steps S13 and S24, a target pressure Pc for bringing the dew point inside 36 of separation tank 35 to the target dew point is estimated using the map, a preset target dew point, and the temperature inside 36 of separation tank 35 detected by temperature detection unit 41. In steps S16 and S25, the pressure inside 36 of separation tank 35 is changed so that the pressure inside 36 of separation tank 35 reaches the target pressure Pc. This makes it possible to produce hydrogen at the target dew point in a relatively short time.

[0052] Furthermore, according to the computer program of this embodiment, the control unit 61 estimates the target pressure Pc at which the dew point in the interior 36 of the separation tank 35 will become the target dew point, using the map, a preset target dew point, and the temperature in the interior 36 of the separation tank 35 detected by the temperature detection unit 41. The control unit 61 changes the pressure in the interior 36 of the separation tank 35 so that the pressure in the interior 36 of the separation tank 35 becomes the target pressure. This makes it possible to produce hydrogen at the target dew point in a relatively short time.

[0053] Second Embodiment Fig. 5 is a schematic diagram illustrating the overall configuration of a water electrolysis system 2 according to a second embodiment. The water electrolysis system 2 according to the second embodiment differs from the water electrolysis system 1 according to the first embodiment (Fig. 1) in that a controller controls a compressor and a back-pressure valve.

[0054] The water electrolysis system 2 of this embodiment includes a water electrolysis apparatus 10, a compressor 22, a cooling unit 30, a separation tank 35, a temperature detection unit 41, a pressure detection unit 42, a back pressure valve 50, and a control unit 62. The water electrolysis system 2 of this embodiment adjusts the dew point of hydrogen produced by electrolysis of water to a preset target dew point. This makes it easier for hydrogen consumers to use hydrogen supplied from the water electrolysis system 2.

[0055] Compressor 22 is connected to hydrogen flow path 13. In this embodiment, compressor 21 is connected downstream of regulating valve 13a in the flow of mixed gas in hydrogen flow path 13. Compressor 22 is electrically connected to control unit 62, and in accordance with commands from control unit 62, increases the pressure of the mixed gas flowing through hydrogen flow path 13 to a predetermined pressure. Compressor 22 corresponds to the "pressure changing unit" in the claims.

[0056] The control unit 62 is a computer including a ROM, a RAM, and a CPU, and is electrically connected to the temperature detection unit 41, the pressure detection unit 42, the compressor 22, the back pressure valve 50, the flow rate adjustment valves 14a, 15a, etc. In addition to the functions of the control unit 61 in the first embodiment, the control unit 62 is capable of cooperatively controlling the compressor 22 and the back pressure valve 50. This allows the pressure inside the separation tank 35 to reach the target pressure Pc in a shorter time than in the first embodiment.

[0057] In the water electrolysis system 2 of the present embodiment described above, the controller 62 coordinates control of the compressor 22 and the back-pressure valve 50 so that the pressure in the interior 36 of the separation tank 35 becomes the target pressure Pc. This enables hydrogen having the target dew point to be produced in an even shorter time than when the pressure in the interior 36 of the separation tank 35 is controlled to become the target pressure Pc using only the back-pressure valve 50.

[0058] Third Embodiment 6 is a schematic diagram illustrating the overall configuration of a water electrolysis system 3 according to a third embodiment. The water electrolysis system 3 according to the third embodiment differs from the water electrolysis system 1 according to the second embodiment (FIG. 1) in that it includes a dew-point meter.

[0059] The water electrolysis system 3 of this embodiment includes a water electrolysis apparatus 10, a compressor 22, a cooling unit 30, a separation tank 35, a temperature detection unit 41, a pressure detection unit 42, a dew point detection unit 43, a back pressure valve 50, and a control unit 63. The water electrolysis system 3 of this embodiment adjusts the dew point of hydrogen generated by electrolysis of water to a preset target dew point. This makes it easier for hydrogen consumers to use hydrogen supplied from the water electrolysis system 3.

[0060] The dew point detection unit 43 is connected to the hydrogen flow path 13. In this embodiment, the dew point detection unit 43 is connected downstream of the separation tank 35 in the flow of the mixed gas in the hydrogen flow path 13. The dew point detection unit 43 detects the dew point of the interior 36 of the separation tank 35 via the hydrogen flow path 13. In other words, the dew point detection unit 43 detects the dew point of the mixed gas after liquid water has been separated. The dew point of the interior 36 of the separation tank 35 detected by the dew point detection unit 43 is output to the control unit 63.

[0061] The control unit 63 is a computer including a ROM, a RAM, and a CPU, and is electrically connected to the temperature detection unit 41, the pressure detection unit 42, the dew point detection unit 43, the compressor 22, the back pressure valve 50, the flow rate control valves 14a, 15a, etc. The control unit 63 has the functions of the control unit 62 of the second embodiment, and controls each unit of the water electrolysis system 3 using the map, a preset target dew point, information on combinations of standard temperature Ts and standard pressure Ps, and the dew point in the interior 36 of the separation tank 35 detected by the dew point detection unit 43.

[0062] In the water electrolysis method of this embodiment using the water electrolysis system 3, after starting operation of the cooling unit 30, the control unit 63 adjusts the dew point of the mixed gas while the set pressure of the back-pressure valve 50 is set to the equipment upper limit pressure Pm of the water electrolysis system 3. In the water electrolysis method of this embodiment, the dew point of the interior 36 of the separation tank 35 is constantly detected by the dew point detection unit 43. When the dew point of the interior 36 of the separation tank 35 detected by the dew point detection unit 43 reaches the target dew point, the control unit 63 sets the set pressure of the back-pressure valve 50 to the standard pressure Ps. In the water electrolysis method of this embodiment, when the dew point of the interior 36 of the separation tank 35 detected by the dew point detection unit 43 is the target dew point, the control unit 63 opens the flow control valve 14a of the supply flow path 14 and closes the flow control valve 15a of the exhaust flow path 15. As a result, hydrogen having the target dew point is supplied to a hydrogen consumer via the supply flow path 14. In this way, in the water electrolysis method of this embodiment using the water electrolysis system 3, the set pressure of the back-pressure valve 50 is changed in accordance with the dew point in the interior 36 of the separation tank 35 detected by the dew point detection unit 43. This makes it possible to produce hydrogen whose dew point has reached the target dew point in a short period of time.

[0063] FIG. 7 is a diagram illustrating the effects of the water electrolysis system 3 of this embodiment. The effects of the water electrolysis system 3 of this embodiment will now be described using a comparative example. FIG. 7 shows the time required to reach the target dew point ("target dew point attainment time") and the power consumed by the compressor ("power consumption") for each of three water electrolysis methods. Each of the three water electrolysis methods can be performed using the water electrolysis system 3 of this embodiment.

[0064] "Control A" in FIG. 7 shows the "target dew point achievement time" and "power consumption" in control in which the set pressure of the back-pressure valve is fixed to the standard pressure immediately after the start of operation of the cooling unit. "Control B" in FIG. 3 shows the "target dew point achievement time" and "power consumption" in control in which the set pressure of the back-pressure valve is fixed to the equipment upper limit pressure of the water electrolysis system immediately after the start of operation of the cooling unit. "Control C" in FIG. 3 shows the "target dew point achievement time" and "power consumption" in control in the water electrolysis method of this embodiment in which the set pressure of the back-pressure valve is the equipment upper limit pressure of the water electrolysis system from the start of operation of the cooling unit until the target dew point is reached, and then the set pressure of the back-pressure valve is set to the standard pressure after the target dew point is reached. The "target dew point achievement time" and "power consumption" in FIG. 7 are results obtained when the target dew point was set to minus 15°C.

[0065] As shown in Fig. 7, Control B has a shorter "target dew point achievement time" than Control A. On the other hand, Control B has a larger ratio of the pressure on the inlet side to the pressure on the outlet side of the compressor, resulting in a larger "power consumption" than Control A. In contrast to these results for Control A and Control B, Control C, which is the same control in the water electrolysis method of this embodiment, has a "target dew point achievement time" equivalent to Control B, but has a smaller "power consumption" than Control A.

[0066] In the water electrolysis system 3 of the present embodiment described above, the controller 63 controls the compressor 22 and the back pressure valve 50 in accordance with the dew point detected by the dew point detector 43 so that the pressure in the interior 36 of the separation tank 35 is equal to the facility upper limit pressure Pm or the standard pressure Ps. As a result, when the dew point in the interior 36 of the separation tank 35 is equal to the target dew point, the pressure in the interior 36 of the separation tank 35 is set to the standard pressure Ps, which is lower than the facility upper limit pressure Pm, thereby reducing the power consumption of the compressor 22. Therefore, hydrogen at the target dew point can be produced in a short time with little power consumption.

[0067] <Modification of this embodiment> The present invention is not limited to the above-described embodiment, and can be embodied in various forms without departing from the spirit of the invention. For example, the following modifications are also possible.

[0068] [Variation 1] In the above-described embodiment, the control unit stores a map, such as that shown in FIG. 4, that indicates the correlation between the temperature, pressure, and dew point inside the separation tank serving as the "storage unit." The information stored in the control unit does not have to be such a map. It is sufficient if information indicating the relationship between the temperature and pressure inside the separation tank so that the dew point inside the separation tank becomes the target dew point is stored.

[0069] [Variation 2] In the above-described embodiment, the separation tank that separates liquid water from the mixed gas is the "storage unit" that stores the mixed gas. However, the configuration that corresponds to the "storage unit" is not limited to this. Any member that forms a space in which the mixed gas exists may be used.

[0070] [Variation 3] In the first embodiment, in the water electrolysis method, the target pressure Pc estimated in step S13 is higher than the standard pressure Ps, and the target pressure Pc estimated in step S24 is lower than the standard pressure Ps. However, the target pressure Pc estimated in step S13 or step S24 is not limited to this. When the target pressure Pc estimated in step S13 is higher than the standard pressure Ps, the amount of water removed from the mixed gas can be increased. The same applies when the target pressure Pc estimated in step S24 is lower than the standard pressure Ps.

[0071] [Variation 4] In the first embodiment, the dew point in the interior 36 of the separation tank 35 is estimated using the temperature and pressure in the interior 36 of the separation tank 35. Instead of estimating the dew point, the water electrolysis system 1 of the first embodiment may be provided with the dew point detection unit 43 included in the water electrolysis system 3 of the third embodiment.

[0072] [Variation 5] In the third embodiment, the set pressure of the back-pressure valve 50 is changed in accordance with the dew point in the interior 36 of the separation tank 35 detected by the dew-point detection unit 43. In the water electrolysis system 3 of the third embodiment, the set pressure of the back-pressure valve 50 may be changed using the dew point estimated from the temperature and pressure in the interior 36 of the separation tank 35, as in the first embodiment.

[0073] This aspect has been described above based on embodiments and modifications. However, the above-described embodiments are intended to facilitate understanding of this aspect and are not intended to limit this aspect. This aspect may be modified or improved without departing from the spirit and scope of the claims, and equivalents thereof are included in this aspect. Furthermore, if a technical feature is not described as essential in this specification, it may be deleted as appropriate.

[0074] <Application example 1> A water electrolysis system, a water electrolysis device that generates hydrogen by electrolysis of water; a flow path connected to the water electrolysis device, through which a gas containing hydrogen and water produced by the water electrolysis device flows; a storage unit connected to the flow path and configured to store the gas supplied from the water electrolysis apparatus; a cooling unit that cools the gas supplied to the storage unit; a temperature detection unit that detects the temperature inside the storage unit; a pressure change unit that changes the pressure inside the storage unit; a control unit that estimates a target pressure using information indicating a relationship between the temperature and pressure inside the storage unit so that the dew point inside the storage unit becomes a target dew point and the temperature detected by the temperature detection unit, and controls the pressure change unit so that the pressure inside the storage unit becomes the target pressure. Water electrolysis system. <Application example 2> The water electrolysis system according to Application Example 1, The control unit Using the information, estimate a standard pressure, which is the pressure inside the storage unit at which the dew point inside the storage unit becomes the target dew point when the temperature inside the storage unit becomes a predetermined standard temperature; When the temperature detected by the temperature detection unit is higher than the standard temperature, the pressure change unit is controlled so that the pressure inside the storage unit becomes the target pressure that is higher than the standard pressure and equal to or lower than a preset upper limit pressure; When the temperature detected by the temperature detection unit is lower than the standard temperature, the pressure change unit is controlled so that the pressure inside the storage unit becomes the target pressure which is lower than the standard pressure. Water electrolysis system. <Application example 3> The water electrolysis system according to Application Example 1 or Application Example 2 further comprises: a pressure detection unit that detects the pressure inside the storage unit; a supply flow path connected to the flow path and configured to supply the gas inside the storage unit to a hydrogen utilization destination; a flow rate adjustment valve connected to the supply flow path and adjusting the flow rate of the gas in the supply flow path, The control unit estimating the dew point inside the storage unit using a map showing a correlation between the temperature, pressure, and dew point inside the storage unit, the temperature detected by the temperature detection unit, and the pressure detected by the pressure detection unit; controlling the flow rate adjustment valve using the estimated dew point inside the storage unit; Water electrolysis system. <Application Example 4> The water electrolysis system according to any one of Application Examples 1 to 3, The pressure changing unit is a compressor connected to the flow path and capable of compressing the gas to be supplied to the storage unit; a back pressure valve connected to the flow path and capable of maintaining the pressure inside the accommodation portion at the target pressure, The control unit controls the compressor and the back pressure valve. Water electrolysis system. <Application example 5> The water electrolysis system according to any one of Aspects 1 to 4 may further include: a dew point detector for detecting a dew point inside the container; The control unit Using the information, estimate a standard pressure, which is the pressure inside the storage unit at which the dew point inside the storage unit becomes the target dew point when the temperature inside the storage unit becomes a predetermined standard temperature; When the dew point detected by the dew point detection unit is lower than the target dew point, the pressure change unit is controlled so that the pressure inside the storage unit becomes an upper limit pressure that is preset as the target pressure; When the dew point detected by the dew point detection unit is the same as the target dew point, the pressure change unit is controlled so that the pressure inside the storage unit becomes the standard pressure as the target pressure. Water electrolysis system. <Application Example 6> A water electrolysis method using a water electrolysis system, a water electrolysis process for generating hydrogen by electrolysis of water; a storing step of storing the gas containing hydrogen and water produced in the water electrolysis step in a storing section; a cooling step of cooling the gas supplied to the storage section; a temperature detection step of detecting a temperature inside the storage unit; a pressure changing step of estimating a target pressure using information indicating a relationship between the temperature and pressure inside the storage unit so that the dew point inside the storage unit becomes a target dew point and the temperature detected in the temperature detecting step, and changing the pressure inside the storage unit so that the pressure inside the storage unit becomes the target pressure. Water electrolysis method. <Application Example 7> A computer program for causing a computer to execute hydrogen generation by a water electrolysis system, Water electrolysis function that generates hydrogen through the electrolysis of water, a cooling function that cools the gas containing hydrogen and water produced by the water electrolysis function and that is supplied to the storage unit; a temperature detection function for detecting the temperature inside the storage unit; a pressure change function that estimates a target pressure using information indicating a relationship between the temperature and pressure inside the storage unit so that the dew point inside the storage unit becomes a target dew point and the temperature detected by the temperature detection function, and changes the pressure inside the storage unit so that the pressure inside the storage unit becomes the target pressure; Computer program. [Explanation of symbols]

[0075] 1, 2, 3...Water electrolysis system 10...Water electrolysis device 13...Hydrogen flow path 14...Supply channel 14a...Flow control valve 21, 22...Compressor 30…Cooling section 35...Separation tank 36...Inside (of the containment unit) 41...Temperature detection unit 42...Pressure detection unit 43...Dew point detector 50...Back pressure valve 61, 62, 63...Control section Pc: Target pressure Ps...standard pressure Ts…Standard temperature

Claims

1. A water electrolysis system, a water electrolysis device that generates hydrogen by electrolysis of water; a flow path connected to the water electrolysis device, through which a gas containing hydrogen and water produced by the water electrolysis device flows; a storage unit connected to the flow path and configured to store the gas supplied from the water electrolysis apparatus; a cooling unit that cools the gas supplied to the storage unit; a temperature detection unit that detects the temperature inside the storage unit; a pressure change unit that changes the pressure inside the storage unit; a control unit that estimates a target pressure using information indicating a relationship between the temperature and pressure inside the storage unit so that the dew point inside the storage unit becomes a target dew point and the temperature detected by the temperature detection unit, and controls the pressure change unit so that the pressure inside the storage unit becomes the target pressure. Water electrolysis system.

2. The water electrolysis system according to claim 1, The control unit Using the information, estimate a standard pressure, which is the pressure inside the storage unit at which the dew point inside the storage unit becomes the target dew point when the temperature inside the storage unit becomes a predetermined standard temperature; When the temperature detected by the temperature detection unit is higher than the standard temperature, the pressure change unit is controlled so that the pressure inside the storage unit becomes the target pressure that is higher than the standard pressure and equal to or lower than a preset upper limit pressure; When the temperature detected by the temperature detection unit is lower than the standard temperature, the pressure change unit is controlled so that the pressure inside the storage unit becomes the target pressure which is lower than the standard pressure. Water electrolysis system.

3. The water electrolysis system according to claim 1 or 2 further comprises: a pressure detection unit that detects the pressure inside the storage unit; a supply flow path connected to the flow path and configured to supply the gas inside the storage unit to a hydrogen utilization destination; a flow rate adjustment valve connected to the supply flow path and adjusting the flow rate of the gas in the supply flow path, The control unit estimating the dew point inside the storage unit using a map showing a correlation between the temperature, pressure, and dew point inside the storage unit, the temperature detected by the temperature detection unit, and the pressure detected by the pressure detection unit; controlling the flow rate adjustment valve using the estimated dew point inside the storage unit; Water electrolysis system.

4. The water electrolysis system according to claim 1, The pressure changing unit a compressor connected to the flow path and capable of compressing the gas to be supplied to the storage unit; a back pressure valve connected to the flow path and capable of maintaining the pressure inside the accommodation portion at the target pressure, The control unit controls the compressor and the back pressure valve. Water electrolysis system.

5. The water electrolysis system according to claim 4 further comprises: a dew point detector for detecting a dew point inside the container; The control unit Using the information, estimate a standard pressure, which is the pressure inside the storage unit at which the dew point inside the storage unit becomes the target dew point when the temperature inside the storage unit becomes a predetermined standard temperature; When the dew point detected by the dew point detection unit is lower than the target dew point, the pressure change unit is controlled so that the pressure inside the storage unit becomes an upper limit pressure that is preset as the target pressure; When the dew point detected by the dew point detection unit is the same as the target dew point, the pressure change unit is controlled so that the pressure inside the storage unit becomes the standard pressure as the target pressure. Water electrolysis system.

6. A water electrolysis method using a water electrolysis system, a water electrolysis process for generating hydrogen by electrolysis of water; a cooling step of cooling the gas containing hydrogen and water produced in the water electrolysis step, which is supplied to the accommodation section; a temperature detection step of detecting a temperature inside the storage unit; a pressure changing step of estimating a target pressure using information indicating a relationship between the temperature and pressure inside the storage unit so that the dew point inside the storage unit becomes a target dew point and the temperature detected in the temperature detecting step, and changing the pressure inside the storage unit so that the pressure inside the storage unit becomes the target pressure. Water electrolysis method.

7. A computer program for causing a computer to execute hydrogen generation by a water electrolysis system, Water electrolysis function that generates hydrogen through the electrolysis of water, a cooling function that cools the gas containing hydrogen and water produced by the water electrolysis function and that is supplied to the storage unit; a temperature detection function for detecting the temperature inside the storage unit; a pressure change function that estimates a target pressure using information indicating a relationship between the temperature and pressure inside the storage unit so that the dew point inside the storage unit becomes a target dew point and the temperature detected by the temperature detection function, and changes the pressure inside the storage unit so that the pressure inside the storage unit becomes the target pressure; Computer program.

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