Water electrolysis system

Abstract

To provide a technique by which heated water can stably be supplied to a water electrolysis unit.SOLUTION: A water electrolysis system comprises: a water electrolysis unit; a water supply pipeline for supplying water to the water electrolysis unit; a mixture delivery pipeline for sending a mixture out of the water electrolysis unit; a first bypass pipeline for the water to branch off from a first position of the water supply pipeline and to merge at a second position; a second bypass pipeline for the mixture to branch off from a third position of the mixture delivery pipeline and to merge at a fourth position; a heat accumulator for exchanging heat between the water and the mixture circulating in the first and second bypass pipelines, respectively; a first route switching unit for switching a first route between the water supply pipeline and the first bypass pipeline; a second route switching unit for switching a second route between the mixture delivery pipeline and the second bypass pipeline; and a control unit for controlling the water electrolysis system. The control unit directs the second bypass pipeline as the second route in a heat accumulation mode, and the first bypass pipeline as the first route in a heat radiation mode.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a water electrolysis system. [Background technology]

[0002] Water electrolysis systems that generate hydrogen by electrolysis of water using an electrolyte membrane have been known for some time. Generally, the higher the temperature of the water electrolysis reaction, the more efficient it becomes, so it is preferable that the water used in the reaction is also at a high temperature. Patent Document 1 discloses a hydrogen and oxygen gas production device that supplies water stored in a solar thermal storage device and heated by sunlight to a water electrolysis cell. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 9-195076 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in bad weather such as cloudy or rainy weather, the amount of sunlight decreases, and therefore, in the device described in Patent Document 1, depending on the weather, the amount of sunlight reaching the solar thermal storage device decreases, making it impossible to supply heated water to the water electrolysis cell, which may result in a decrease in the reaction efficiency of the water electrolysis reaction. For this reason, there is room for improvement in maintaining a high reaction efficiency of the water electrolysis reaction.

[0005] The present invention has been made to solve at least part of the above-described problems, and an object of the present invention is to provide a water electrolysis system that can stably supply heated water to a water electrolysis unit. [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 unit that generates oxygen and hydrogen by electrolyzing water using an electrolyte membrane; a water supply pipe that forms a water supply flow path that supplies water to the water electrolysis unit; a mixture delivery pipe that forms a mixture delivery flow path that delivers a mixture of oxygen and water generated in the water electrolysis unit from the water electrolysis unit; a first bypass pipe that branches off from the water supply pipe at a first position and merges with the water supply pipe at a second position downstream of the first position; a second bypass pipe that branches off from the mixture delivery pipe at a third position and merges with the mixture delivery pipe at a fourth position downstream of the third position; and a water supply pipe that accommodates a portion of the first bypass pipe and a portion of the second bypass pipe and flows through the first bypass pipe. a heat accumulator accommodating a heat storage material capable of storing and releasing heat by heat exchange with water flowing through the heat accumulator and the mixture flowing through the second bypass pipe; a first path switching unit switching a first path, which is a path for water from the first position to the second position, between the water supply pipe and the first bypass pipe; a second path switching unit switching a second path, which is a path for the mixture from the third position to the fourth position, between the mixture delivery pipe and the second bypass pipe; and a control unit controlling the water electrolysis system, wherein the control unit uses the second path as the second bypass pipe when performing a heat storage mode in which heat is stored in the heat accumulator, and uses the first path as the first bypass pipe when performing a heat release mode in which heat is released from the heat accumulator.

[0008] A portion of the power supplied to the water electrolysis unit to perform water electrolysis (electrolysis) becomes Joule heat. The mixture of oxygen and water generated in the water electrolysis unit flows through the mixture delivery pipe in a state heated by this Joule heat. According to this configuration, when the heat storage mode is performed, the second path is the second bypass pipe. Therefore, the heated mixture flows through the second bypass pipe and can be stored in the heat storage material by heat exchange. Therefore, the Joule heat generated in the water electrolysis unit is stored in the heat storage material, thereby reducing the cooling load for cooling the water electrolysis unit. On the other hand, according to this configuration, when the heat release mode is performed, the first path is the first bypass pipe. Generally, the higher the temperature, the more efficient the water electrolysis reaction. In the heat release mode, the water supplied to the water electrolysis unit flows through the first bypass pipe, receives heat released from the heat storage material by heat exchange, and is then used in the electrolysis reaction by the water electrolysis unit, thereby improving the reaction efficiency of the electrolysis reaction. Therefore, this configuration can achieve both a reduction in the cooling load for cooling the water electrolysis unit and an improvement in the reaction efficiency of the electrolysis reaction in the water electrolysis unit. Furthermore, since the heat source for heating the water supplied to the water electrolysis unit is Joule heat constantly generated by the electrolysis reaction in the water electrolysis unit, heated water can be stably supplied to the water electrolysis unit. Therefore, the reaction efficiency of the water electrolysis reaction can be maintained high.

[0009] (2) In the water electrolysis system of the above aspect, the control unit may switch the second path from the second bypass pipe to the mixture delivery pipe when, during the heat storage mode, the temperature of the heat storage material becomes equal to or higher than a heat storage target temperature or when the temperature of the mixture circulating through the second bypass pipe becomes lower than a specified heat storage temperature. If the heat storage mode is continued even after the heat storage material reaches or exceeds the heat storage target temperature, the heat storage material is likely to deteriorate. Furthermore, if the Joule heat generated in the water electrolysis unit decreases and the temperature of the mixture of oxygen and water circulating through the second bypass piping falls below the specified heat storage temperature, the mixture is more likely to release heat from the heat storage material rather than store it in the heat storage material. Therefore, this configuration can reduce the possibility of the heat storage material deteriorating and the possibility of heat being released from the heat storage material even in the heat storage mode. Furthermore, if the pressure loss through the second bypass piping is greater than that through the mixture delivery piping in the second path, the amount of energy consumed to circulate water can be reduced by reducing such pressure loss.

[0010] (3) In the water electrolysis system of the above aspect, the control unit may switch the first path from the first bypass pipe to the water supply pipe when, during the heat release mode, the temperature of the heat storage material becomes lower than a specified heat release temperature or when the temperature of the water circulating through the first bypass pipe becomes equal to or higher than a target heat release temperature. When the temperature of the water flowing through the first bypass pipe becomes lower than the specified heat dissipation temperature, the heat storage material is more likely to absorb heat from the water flowing through the first bypass pipe. Furthermore, if the heat dissipation mode is continued even after the temperature of the water flowing through the first bypass pipe becomes equal to or higher than the heat dissipation target temperature, the heat storage material is more likely to absorb heat from the water flowing through the first bypass pipe, just as when the heat storage material becomes lower than the specified heat dissipation temperature. Therefore, this configuration can reduce the possibility that the heat storage material will absorb heat from the water flowing through the first bypass pipe in the heat dissipation mode. Furthermore, if the pressure loss through the first bypass pipe is greater than that through the water supply pipe in the first path, the amount of energy consumed to circulate the water can be reduced by reducing such pressure loss.

[0011] (4) In the water electrolysis system of the above aspect, the heat storage material may be a latent heat storage material or a chemical heat storage material. According to this configuration, by changing the state of the latent heat storage material or the chemical heat storage material, it is possible to store heat from the mixture of oxygen and water flowing through the second bypass pipe and release heat to the water flowing through the first bypass pipe.

[0012] (5) In the water electrolysis system of the above aspect, the heat storage material may be an adsorbent capable of releasing and storing heat by adsorbing and desorbing a substance. According to this configuration, by adsorption and desorption of substances by the adsorbent, it is possible to store heat from the mixture of oxygen and water flowing through the second bypass pipe and release heat to the water flowing through the first bypass pipe.

[0013] The present invention can be realized in various forms, such as a method for controlling a water electrolysis system, a computer program for controlling water electrolysis in a water electrolysis system, a server device for distributing the computer program, and a non-transitory storage medium storing the computer program. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is an explanatory diagram illustrating the configuration of a water electrolysis system according to a first embodiment. [Figure 2] FIG. 2 is an enlarged view of the inside of the heat accumulator. [Figure 3] FIG. 10 is an explanatory diagram showing a flow path in a heat storage mode. [Figure 4] FIG. 10 is an explanatory diagram showing a flow path in a heat dissipation mode. DETAILED DESCRIPTION OF THE INVENTION

[0015] First Embodiment 1 is an explanatory diagram illustrating the configuration of a water electrolysis system 1 according to one embodiment of the present invention. The water electrolysis system 1 is a system that produces oxygen and hydrogen by electrolysis of water. The water electrolysis system 1 includes a cell stack 10, a DC power supply 12, a converter 14, a hydrogen gas-liquid separator 20, a condenser 22, an oxygen gas-liquid separator 30, a condenser 32, a heat exchanger 34, a heat accumulator 40, and a controller 50. The water electrolysis system 1 also includes a first mixture delivery pipe P1, a second mixture delivery pipe P2, an oxygen delivery pipe P3, a water supply pipe P4, a first bypass pipe B1, and a second bypass pipe B2.

[0016] The cell stack 10 is composed of multiple water electrolysis cells stacked one on top of the other. Each water electrolysis cell is a water electrolysis unit that produces oxygen and hydrogen by electrolysis of water using an electrolyte membrane. The DC power supply 12 is the power source for the cell stack 10. The converter 14 converts the power supplied from the DC power supply 12 and supplies it to the cell stack 10.

[0017] The mixture of hydrogen and water produced in the cell stack 10 is sent to a first mixture delivery pipe P1, which forms a mixture delivery flow path that delivers the mixture from the cell stack 10. The first mixture delivery pipe P1 is provided with a hydrogen-gas-liquid separator 20 and a condenser 22. The hydrogen-gas-liquid separator 20 separates the mixture of hydrogen and water produced in the cell stack 10 into hydrogen and water. The condenser 22 is supplied with cooling water, and condenses water vapor contained in the mixture as the mixture passes through the condenser 22. The hydrogen separated through the hydrogen-gas-liquid separator 20 and the condenser 22 is sent to the outside of the water electrolysis system 1 through the first mixture delivery pipe P1.

[0018] The mixture of oxygen and water produced in the cell stack 10 is sent to a second mixture delivery pipe P2, which forms a mixture delivery flow path for delivering the mixture from the cell stack 10. The second mixture delivery pipe P2 connects the cell stack 10 and the oxygen-gas-liquid separator 30. The oxygen-gas-liquid separator 30 separates the mixture of oxygen and water produced in the cell stack 10 into oxygen and water. In addition to the oxygen-water mixture, pure water is appropriately supplied to the oxygen-gas-liquid separator 30 from a tank (not shown). The oxygen-gas-liquid separator 30 is also connected to an oxygen delivery pipe P3. A condenser 32 is provided in the oxygen delivery pipe P3. Similar to the condenser 22, cooling water is supplied to the condenser 32, and the condenser 32 condenses water vapor contained in the oxygen-water mixture as it passes through the interior thereof. The oxygen separated through the oxygen-gas-liquid separator 30 and the condenser 32 is sent to the outside of the water electrolysis system 1 through the oxygen delivery pipe P3.

[0019] The water supply pipe P4 is a pipe that forms a water supply flow path that supplies water to the cell stack 10. The water supply pipe P4 connects the oxygen-gas-liquid separator 30 and the cell stack 10. The water flowing through the water supply pipe P4 is water that has been separated in the oxygen-gas-liquid separator 30. The water supply pipe P4 is provided with a circulation pump PM and a heat exchanger 34. The circulation pump PM sends water from the oxygen-gas-liquid separator 30 to the cell stack 10. Water is circulated inside the heat exchanger 34, and when the water flowing through the water supply pipe P4 is at a relatively high temperature, the circulating water recovers heat.

[0020] The first bypass pipe B1 branches off from the water supply pipe P4 at a first position L1 and merges with the water supply pipe P4 at a second position L2 downstream of the first position L1. The first bypass pipe B1 is provided with a valve V1. The valve V1 is a shutoff valve that can block the flow of water from the first position L1 to the second position L2 via the first bypass pipe B1. Meanwhile, the water supply pipe P4 is provided with a valve V2 between the first position L1 and the second position L2. The valve V2 is a shutoff valve that can block the flow of water from the first position L1 to the second position L2 via the water supply pipe P4. In this embodiment, the valves V1 and V2 correspond to a first path switching unit that switches the first path, which is the water path from the first position L1 to the second position L2, between the water supply pipe P4 and the first bypass pipe B1.

[0021] The second bypass pipe B2 branches off from the second mixture delivery pipe P2 at a third position L3 and joins the second mixture delivery pipe P2 at a fourth position L4 downstream of the third position L3. The second bypass pipe B2 is provided with a valve V3. The valve V3 is a shutoff valve that can block the flow of the mixture from the third position L3 to the fourth position L4 via the second bypass pipe B2. Meanwhile, the second mixture delivery pipe P2 is provided with a valve V4 between the third position L3 and the fourth position L4. The valve V4 is a shutoff valve that can block the flow of the mixture from the third position L3 to the fourth position L4 via the second mixture delivery pipe P2. In this embodiment, the valves V3 and V4 correspond to a second path switching unit that switches the second path, which is a path for the oxygen and water mixture from the third position L3 to the fourth position L4, between the second mixture delivery pipe P2 and the second bypass pipe B2.

[0022] FIG. 2 is an enlarged view of the inside of the heat accumulator 40. The heat accumulator 40 accommodates a portion of the first bypass pipe B1 and the second bypass pipe B2, and accommodates a heat storage material 44 capable of storing and releasing heat through heat exchange with water flowing through the first bypass pipe B1 and a mixture flowing through the second bypass pipe B2. FIG. 2 shows a portion of the first bypass pipe B1 and the second bypass pipe B2 accommodated in the heat accumulator 40. In this embodiment, the heat accumulator 40 accommodates water, which is a fluid serving as the heat storage material 44, in a housing 42 made of a thermal insulating material. That is, when water flows through the first bypass pipe B1, or when a mixture of oxygen and water flows through the second bypass pipe B2, heat exchange occurs between the water or the mixture and the water serving as the heat storage material 44 accommodated in the heat accumulator 40.

[0023] Returning to the description of FIG. 1 , the controller 50 controls the water electrolysis system 1 based on information obtained from various sensors included in the water electrolysis system 1. Specific examples of control by the controller 50 include controlling the opening and closing of valves V1 to V4 and controlling the power supply from the DC power supply 12 to the cell stack 10. The controller 50 starts the supply of power from the DC power supply 12 to the cell stack 10, thereby starting the electrolysis reaction in the cell stack 10. At the start of the electrolysis reaction, the controller 50 closes valve V1 and opens valve V2, and also closes valve V3 and opens valve V4. Furthermore, while the electrolysis reaction is being carried out in the cell stack 10, the controller 50 executes either a heat storage mode in which heat is stored in the heat accumulator 40 or a heat release mode in which heat is released from the heat accumulator 40, based on information obtained from a temperature sensor (not shown) included in the water electrolysis system 1. Information obtained from the temperature sensors includes the temperatures in the second mixture delivery pipe P2 and the water supply pipe P4, the temperature in the heat accumulator 40, and the temperature in the cell stack 10.

[0024] FIG. 3 is an explanatory diagram showing the flow paths in the heat storage mode. When an electrolysis reaction is being carried out by the cell stack 10, the control unit 50 executes the heat storage mode if at least one of the temperature in the second mixture delivery pipe P2 and the temperature in the cell stack 10 is equal to or higher than a predetermined heat storage setting temperature for each temperature (i.e., the heat storage execution condition is satisfied). The heat storage setting temperature is a reference temperature at which the temperature in the second mixture delivery pipe P2 or the temperature in the cell stack 10 can be considered high enough to execute the heat storage mode. At this time, as shown in FIG. 3, the control unit 50 designates the first path (the water path from the first position L1 to the second position L2) as the water supply pipe P4 and the second path (the mixture path from the third position L3 to the fourth position L4) as the second bypass pipe B2. Specifically, the control unit 50 closes valve V1 and opens valve V2, and also opens valve V3 and closes valve V4.

[0025] In this state, water sent from the oxygen-gas-liquid separator 30 to the cell stack 10 passes through the entire water supply pipe P4 without passing through the first bypass pipe B1, as shown in Fig. 3, and reaches the cell stack 10. On the other hand, the mixture of oxygen and water sent from the cell stack 10 to the oxygen-gas-liquid separator 30 passes through the second mixture delivery pipe P2 to the third position L3, passes through the second bypass pipe B2 from the third position L3 to the fourth position L4, and then passes through the second mixture delivery pipe P2 again from the fourth position L4 to reach the oxygen-gas-liquid separator 30, as shown in Fig. 3. A portion of the power supplied to the cell stack 10 to perform the water electrolysis reaction becomes Joule heat, and the mixture of oxygen and water produced in the cell stack 10 is sent from the cell stack 10 to the oxygen-gas-liquid separator 30 in a heated state by this Joule heat. As described above, the heat storage mode is executed on the condition that at least one of the temperature inside the second mixture delivery pipe P2 and the temperature inside the cell stack 10 is equal to or higher than the heat storage set temperature that is preset for each temperature, and therefore the mixture of oxygen and water circulating inside the second bypass pipe B2 at this time is at a relatively high temperature. Therefore, heat is supplied to the heat storage material 44 from the mixture of oxygen and water circulating inside the second bypass pipe B2, and heat storage by the heat storage material 44 is executed.

[0026] Furthermore, during the heat storage mode, if the temperature of the heat storage material 44 becomes equal to or higher than the heat storage target temperature, or if the temperature of the oxygen-water mixture circulating through the second bypass pipe B2 becomes lower than the heat storage specified temperature, the control unit 50 switches the second path from the second bypass pipe B2 to the second mixture delivery pipe P2 and ends the heat storage mode. The heat storage target temperature is a target temperature for the heat storage material 44 and is a reference temperature at which it can be considered that heat has been sufficiently stored in the heat storage material 44. The heat storage specified temperature is a reference temperature at which the oxygen-water mixture circulating through the second bypass pipe B2 is more likely to release heat from the heat storage material 44 than to store heat in it. The temperature of the oxygen-water mixture circulating through the second bypass pipe B2 may be estimated from the temperature in the second mixture delivery pipe P2, or may be obtained from a temperature sensor provided to measure the temperature at the third position L3.

[0027] FIG. 4 is an explanatory diagram showing the flow paths in the heat release mode. When the electrolysis reaction is being performed in the cell stack 10, the controller 50 executes the heat release mode if the temperature of the water flowing through the water supply pipe P4 is below a predetermined lower-limit water temperature and the temperature in the heat accumulator 40 is equal to or higher than a predetermined heat release setting temperature (i.e., the heat release execution condition is satisfied). Note that if both the heat storage execution condition and the heat release execution condition are satisfied, the controller 50 executes only the heat release mode without executing the heat storage mode. The lower-limit water temperature is a reference temperature at which the water electrolysis system 1 is considered to be in a cold environment. The heat release setting temperature is a reference temperature at which the heat storage material 44 is considered to have stored heat to the extent that the heat release mode can be executed. In this case, as shown in FIG. 4, the controller 50 designates the first path as the first bypass pipe B1 and the second path (the path of the mixture from the third position L3 to the fourth position L4) as the second mixture delivery pipe P2. Specifically, the control unit 50 opens the valve V1 and closes the valve V2, and also closes the valve V3 and opens the valve V4.

[0028] In this state, as shown in FIG. 4 , the water sent from the oxygen-gas-liquid separator 30 to the cell stack 10 passes through the water supply pipe P4 up to the first position L1, passes through the first bypass pipe B1 from the first position L1 to the second position L2, and then passes through the water supply pipe P4 again from the second position L2 to reach the cell stack 10. On the other hand, as shown in FIG. 4 , the mixture of oxygen and water sent from the cell stack 10 to the oxygen-gas-liquid separator 30 passes through the entire second mixture delivery pipe P2 without passing through the second bypass pipe B2 and reaches the oxygen-gas-liquid separator 30. As described above, the heat release mode is executed on the condition that the temperature of the water circulating through the water supply pipe P4 is below the lower limit water temperature. Therefore, the water circulating through the first bypass pipe B1 is at a relatively low temperature. Therefore, the water circulating through the first bypass pipe B1 is heated by receiving heat released from the heat storage material 44.

[0029] Furthermore, during the heat release mode, if the temperature of the heat storage material 44 falls below the specified heat release temperature or if the temperature of the water flowing through the first bypass pipe B1 exceeds the target heat release temperature, the control unit 50 switches the first path from the first bypass pipe B1 to the water supply pipe P4 and ends the heat release mode. The specified heat release temperature is a reference temperature at which the heat storage material 44 is more likely to absorb heat from the water flowing through the first bypass pipe B1 than to release heat to the water. The target heat release temperature is a target temperature for the water supplied to the cell stack 10, and is a reference temperature at which it can be considered that the temperature rise is sufficient to increase the reaction efficiency of the electrolysis reaction in the cell stack 10. The temperature of the water flowing through the first bypass pipe B1 may be estimated from the temperature in the water supply pipe P4, or may be obtained from a temperature sensor that measures the temperature at the first position L1.

[0030] As described above, in the water electrolysis system 1 of the first embodiment, when the heat storage mode is performed, the second path is the second bypass pipe B2. Therefore, a mixture of heated oxygen and water flows through the second bypass pipe B2 and can store heat in the heat storage material 44 by heat exchange. Therefore, Joule heat generated in the cell stack 10 is stored in the heat storage material 44, thereby reducing the cooling load for cooling the cell stack 10. On the other hand, in the water electrolysis system 1 of the first embodiment, when the heat release mode is performed, the first path is the first bypass pipe B1. In general, the higher the temperature, the more efficient the water electrolysis reaction. In the heat release mode, water supplied to the cell stack 10 flows through the first bypass pipe B1 and receives heat released from the heat storage material 44 by heat exchange before being used in the electrolysis reaction in the cell stack 10, thereby improving the reaction efficiency of the electrolysis reaction. Therefore, the water electrolysis system 1 of the first embodiment can achieve both a reduction in the cooling load for cooling the cell stack 10 and an improvement in the reaction efficiency of the electrolysis reaction in the cell stack 10. Furthermore, the heat source for heating the water supplied to the cell stack 10 is Joule heat that is constantly generated by the electrolysis reaction in the cell stack 10, so heated water can be stably supplied to the cell stack 10. Therefore, the reaction efficiency of the water electrolysis reaction can be maintained high.

[0031] Furthermore, in the water electrolysis system 1 of the first embodiment, if the temperature of the heat storage material 44 becomes equal to or higher than the heat storage target temperature during the heat storage mode, or if the temperature of the mixture of oxygen and water circulating through the second bypass pipe B2 becomes lower than the specified heat storage temperature, the second path is switched from the second bypass pipe B2 to the second mixture delivery pipe P2. Continuing the heat storage mode after the temperature of the heat storage material 44 becomes equal to or higher than the heat storage target temperature increases the likelihood of deterioration of the heat storage material 44. Furthermore, if the Joule heat generated in the cell stack 10 decreases and the temperature of the mixture of oxygen and water circulating through the second bypass pipe B2 becomes lower than the specified heat storage temperature, such a mixture is more likely to radiate heat from the heat storage material 44 rather than store heat in the heat storage material 44. Therefore, the water electrolysis system 1 of the first embodiment can reduce the likelihood of deterioration of the heat storage material 44 and the likelihood of heat radiating from the heat storage material 44 even during the heat storage mode. Furthermore, in the second path, if the pressure loss is greater when the water passes through the second bypass pipe B2 than when the water passes through the second mixture delivery pipe P2, the amount of energy consumed to circulate the water can be reduced by reducing the pressure loss. The amount of energy here specifically refers to the amount of power consumed by the circulation pump PM.

[0032] Furthermore, in the water electrolysis system 1 of the first embodiment, when the temperature of the heat storage material 44 falls below the specified heat release temperature or when the temperature of the water circulating through the water supply pipe P4 exceeds the target heat release temperature during the heat release mode, the first path is switched from the first bypass pipe B1 to the water supply pipe P4. When the temperature falls below the specified heat release temperature, the heat storage material 44 is more likely to remove heat from the water circulating through the first bypass pipe B1. Furthermore, if the heat release mode is continued even after the temperature of the water circulating through the first bypass pipe B1 exceeds the target heat release temperature, the heat storage material 44 is more likely to remove heat from the water circulating through the first bypass pipe B1, as in the case where the heat storage material 44 falls below the specified heat release temperature. Therefore, the water electrolysis system 1 of the first embodiment can reduce the possibility that the heat storage material 44 removes heat from the water circulating through the first bypass pipe B1 during the heat release mode. Furthermore, in the first path, if the pressure loss is greater when passing through the first bypass pipe B1 than when passing through the water supply pipe P4, the amount of energy consumed by the water flow can be reduced by reducing such pressure loss. The amount of energy referred to here is the amount of power consumed by the circulation pump PM, as described above.

[0033] Second Embodiment The water electrolysis system of the second embodiment is the same as the water electrolysis system 1 of the first embodiment except that the heat storage material 44 accommodated in the housing 42 of the heat accumulator 40 is a latent heat storage material instead of water. Examples of latent heat storage materials include molten salts formed from a mixture of sodium nitrate, sodium nitrite, and potassium nitrate, paraffins (saturated hydrocarbon compounds), fatty acids (including fatty acid esters), and other organic compounds.

[0034] As in the first embodiment, the water electrolysis system of the second embodiment described above can simultaneously reduce the cooling load for cooling the cell stack 10 and improve the reaction efficiency of the electrolysis reaction in the cell stack 10. Furthermore, the water electrolysis system of the second embodiment can store heat from the mixture of oxygen and water circulating through the second bypass pipe B2 and release heat to the water circulating through the first bypass pipe B1, due to a change in the state of the latent heat storage material.

[0035] <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.

[0036] [Variation 1] In the above embodiment, the valves V1 and V2 correspond to the first path switching unit that switches the first path between the water supply pipe P4 and the first bypass pipe B1, but this is not limited to this. For example, instead of the valves V1 and V2, a three-way valve provided at the first position L1 may correspond to the first path switching unit. Similarly, instead of the valves V3 and V4, a three-way valve provided at the third position L3 may correspond to the second path switching unit.

[0037] [Variation 2] In the above embodiment, the second path is switched from the second bypass pipe to the second mixture delivery pipe P2 based on the heat storage target temperature or the heat storage specified temperature during the heat storage mode, but this is not limited to this. For example, the second path may be switched from the second bypass pipe B2 to the second mixture delivery pipe P2 after a certain time has elapsed since the heat storage mode was executed. Similarly, the first path may be switched from the first bypass pipe B1 to the water supply pipe P4 after a certain time has elapsed since the heat release mode was executed.

[0038] [Variation 3] In the above embodiment, the requirement for executing the heat release mode is that the temperature of the water circulating through the water supply pipe P4 is below a predetermined lower limit water temperature and the temperature in the heat accumulator 40 is equal to or higher than a predetermined heat release setting temperature. However, this is not limiting. For example, the requirement for executing the heat release mode may be that the temperature of at least one of the components of the water electrolysis system 1 is below a predetermined lower limit component temperature and the temperature in the heat accumulator 40 is equal to or higher than a predetermined heat release setting temperature. Furthermore, a requirement that the temperature of the water circulating through the water supply pipe P4 is below a predetermined lower limit water temperature may be added to this requirement.

[0039] [Variation 4] In the above embodiment, when both the heat storage execution condition and the heat release execution condition are satisfied, the heat storage mode is not executed and only the heat release mode is executed. However, this is not limited to this. For example, when both the heat storage execution condition and the heat release execution condition are satisfied, both the heat storage mode and the heat release mode may be executed. In this case, the control unit 50 sets the first path to the first bypass pipe B1 and the second path to the second bypass pipe B2. Specifically, the control unit 50 opens the valve V1 and the valve V2, and also opens the valve V3 and closes the valve V4.

[0040] [Variation 5] In the above embodiment, the heat storage material 44 is water or a latent heat storage material, but is not limited to this. For example, the heat storage material 44 may be a chemical heat storage material. Even in this form, heat can be stored from the mixture of oxygen and water flowing through the second bypass pipe B2 and released to the water flowing through the first bypass pipe B1 by changing the state of the chemical heat storage material. Examples of chemical heat storage materials include magnesium hydroxide, calcium hydroxide, calcium chloride, and calcium sulfate.

[0041] [Variation 6] Furthermore, the heat storage material 44 may be an adsorbent capable of storing and releasing heat by adsorbing and desorbing a substance. Even in this configuration, heat can be stored from the mixture of oxygen and water flowing through the second bypass pipe B2 and released to the water flowing through the first bypass pipe B1 by adsorbing and desorbing a substance using the adsorbent. An example of an adsorbent is activated carbon. In this configuration, heat exchange occurs between the mixture of oxygen and water flowing through the second bypass pipe B2 and the water flowing through the first bypass pipe B1 by passing through the adsorbent, which is the heat storage material 44.

[0042] 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. [Explanation of symbols]

[0043] 1...Water electrolysis system 10...Cell stack 12…DC power supply 14...Converter 20...Hydrogen gas-liquid separator 22...Condenser 30...Oxygen gas-liquid separator 32...Condenser 34...Heat exchanger 40... Heat storage device 42...Housing 44...Heat storage material 50...Control unit B1: First bypass piping B2: Second bypass piping L1…1st position L2…2nd position L3…3rd position L4…4th position P1...First mixture delivery pipe P2…Second mixture delivery pipe P3: Oxygen delivery piping P4…Water supply piping PM...Circulation pump V1~V4...Valves

Claims

1. A water electrolysis system, a water electrolysis unit which is a water electrolysis cell that generates oxygen and hydrogen by electrolysis of water using an electrolyte membrane; a water supply pipe forming a water supply flow path for supplying water to the water electrolysis unit; a mixture delivery pipe forming a mixture delivery flow path for delivering the mixture of oxygen and water produced in the water electrolysis unit from the water electrolysis unit; a first bypass pipe that branches off from the water supply pipe at a first position and merges with the water supply pipe at a second position downstream of the first position; a second bypass pipe branching from the mixture delivery pipe at a third position and joining the mixture delivery pipe at a fourth position downstream of the third position; a heat storage device that houses a heat storage material that is capable of storing and releasing heat by heat exchange with the water flowing through the first bypass pipe and the mixture flowing through the second bypass pipe; and a first path switching unit that switches a first path, which is a path of water from the first position to the second position, between the water supply pipe and the first bypass pipe; a second path switching unit that switches a second path, which is a path of the mixture from the third position to the fourth position, between the mixture delivery pipe and the second bypass pipe; a control unit that controls the water electrolysis system, The control unit When a heat storage mode in which heat is stored in the heat accumulator is executed, the second path is the second bypass pipe, the water electrolysis system, when a heat release mode in which heat is released to the heat accumulator is executed, the first path serves as the first bypass pipe.

2. The water electrolysis system according to claim 1, the control unit switches the second path from the second bypass pipe to the mixture delivery pipe when, during the heat storage mode, the temperature of the heat storage material becomes equal to or higher than a heat storage target temperature or when the temperature of the mixture circulating through the second bypass pipe becomes lower than a specified heat storage temperature.

3. The water electrolysis system according to claim 1 or 2, the control unit switches the first path from the first bypass pipe to the water supply pipe when, during the heat release mode, the temperature of the heat storage material becomes lower than a specified heat release temperature or when the temperature of the water circulating through the first bypass pipe becomes equal to or higher than a target heat release temperature.

4. The water electrolysis system according to any one of claims 1 to 3, The water electrolysis system, wherein the heat storage material is a latent heat storage material or a chemical heat storage material.

5. The water electrolysis system according to any one of claims 1 to 3, a water electrolysis system, wherein the heat storage material is an adsorbent material capable of storing and releasing heat by adsorption and desorption of a substance;

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