Reversible SOC System

Abstract

This invention provides a reversible SOC system that can shorten the time required for the vehicle to stabilize when switching between operating modes. [Solution] The reversible SOC system 10 includes a hydrogen supply unit 11 and a water supply unit 12 configured to supply a first fuel gas containing water vapor when hydrogen is generated in the electrochemical cell stack 30, and to supply a second fuel gas containing hydrogen and water vapor to the fuel electrode when power is generated in the electrochemical cell stack 30. The amount of water vapor contained in the first fuel gas is greater than the amount of water vapor that the electrochemical cell stack 30 can electrolyze, and the amount of water vapor contained in the second fuel gas is greater than or equal to the amount of water vapor contained in the first fuel gas supplied from the fuel gas supply unit to the fuel electrode.

Description

[Technical Field]

[0001] This disclosure relates to a reversible SOC system. [Background technology]

[0002] Conventionally, reversible SOC systems that can switch between a hydrogen production mode and an electricity generation mode are known. In the hydrogen production mode, the system is configured to produce hydrogen by electrolyzing water (steam) in an electrochemical cell stack. In the electricity generation mode, the system is configured to generate electricity by reacting hydrogen and oxygen in an electrochemical cell stack.

[0003] In an electrochemical cell stack, electricity is generated by the reaction of hydrogen and oxygen. Therefore, in the power generation mode, a gas containing hydrogen is supplied as fuel gas to the fuel electrode of each electrochemical cell in the electrochemical cell stack, and a gas containing oxygen is supplied to the air electrode of each electrochemical cell. On the other hand, in an electrochemical cell stack, hydrogen is produced by the electrolysis of water vapor (water). Therefore, in the hydrogen production mode, a gas containing water vapor is supplied as fuel gas to the fuel electrode of each electrochemical cell. Thus, the preferred components of the fuel gas (gas supplied to the fuel electrode) differ between the hydrogen production mode and the power generation mode in an electrochemical cell stack.

[0004] The reversible SOC systems disclosed in Patent Documents 1 and 2 are configured to supply more water vapor in the fuel gas during the hydrogen production mode compared to the fuel gas during the power generation mode, and to supply more hydrogen in the fuel gas during the power generation mode compared to the hydrogen production mode.

[0005] However, there is a certain distance in the path from the gas supply equipment to the electrochemical cell stack. Therefore, even if the fuel gas composition (ratio) is changed when switching operating modes, it takes a certain amount of time for the fuel gas with the changed composition to reach the electrochemical cell stack. In other words, after switching operating modes, "fuel gas with a composition unsuitable for the switched operating mode" is supplied for a certain period of time. As a result, the efficiency of hydrogen production or power generation decreases during this time. For example, in the configurations disclosed in the aforementioned patent documents, when switching from an operating mode for power generation to an operating mode for hydrogen production, there is a shortage of water vapor, which is the raw material for hydrogen, immediately after the switch, resulting in a "fuel depletion" state. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 6-163064 [Patent Document 2] Special Publication No. 2018-517233 [Overview of the Initiative]

[0007] This disclosure aims to solve the above-mentioned problems. Specifically, one of the objectives of this disclosure is to provide a reversible SOC system that can switch between an operating mode for hydrogen production and an operating mode for power generation, and that can shorten the time required for operation stabilization when switching operating modes.

[0008] To address the above issues, the reversible SOC system described herein is: An electrochemical cell comprising a fuel electrode and an air electrode, wherein when water vapor is supplied to the fuel electrode, hydrogen can be produced by electrolysis of the water vapor in the fuel electrode, and when hydrogen is supplied to the fuel electrode and an acidifying gas is supplied to the air electrode, electricity can be generated by reacting the hydrogen supplied to the fuel electrode with the acidifying gas supplied to the air electrode, A fuel gas supply unit is configured to supply a first fuel gas containing water vapor to the fuel electrode when generating hydrogen in the electrochemical cell stack, and to supply a second fuel gas containing hydrogen and water vapor to the fuel electrode when generating electricity in the electrochemical cell stack. Equipped with, The amount of water vapor contained in the first fuel gas supplied from the fuel gas supply unit to the fuel electrode per unit time is greater than the amount of water vapor that the electrochemical cell stack can electrolyze at the fuel electrode per unit time. The amount of water vapor contained in the second fuel gas supplied from the fuel gas supply unit to the fuel electrode per unit time is equal to or greater than the amount of water vapor contained in the first fuel gas supplied from the fuel gas supply unit to the fuel electrode per unit time.

[0009] According to this disclosure, the amount of water vapor contained in the fuel gas (second fuel gas) in the power generation operating mode is greater than or equal to the amount of water vapor contained in the fuel gas (first fuel gas) in the hydrogen production operating mode. Therefore, with this configuration, when switching from the power generation operating mode to the hydrogen production operating mode, at the time of the switch, the electrochemical cell stack is supplied with an amount of water vapor greater than the amount of water vapor that can be electrolyzed. Therefore, when switching from the power generation operating mode to the hydrogen production operating mode, hydrogen can be produced efficiently immediately after the switch. In other words, a reversible SOC system can be provided that can shorten the time required for operation stabilization when switching operating modes. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 shows the configuration of the main components of a reversible SOC system. [Figure 2] Figure 2 shows the operation of the reversible SOC system. [Modes for carrying out the invention]

[0011] Figure 1 is a diagram showing the configuration of the main parts of a reversible SOC system 10 according to an embodiment of the present invention. As shown in Figure 1, the reversible SOC system 10 comprises a hydrogen supply unit 11, a water supply unit 12, an air supply unit 13, a combustion hydrogen supply unit 14, a hot module 15, a power conditioner 16, a gas-liquid separator 17, a cooler 18, and a control unit 19 (control device). In the following description, "reversible SOC system 10" may be abbreviated as "r-SOC system 10," and "power conditioner 16" may be abbreviated as "powercon 16." Also, the hydrogen supply unit 11, the water supply unit 12, the first heater 32, the second heater 33, and the fourth heater 35, which will be described later, are examples of fuel gas supply units of the present invention.

[0012] The hydrogen supply unit 11 is connected to the electrochemical cell stack 30 of the hot module 15 (described later) via a hydrogen path 20 and a mixed gas path 22, and is configured to supply hydrogen from an external hydrogen source to the electrochemical cell stack 30. The water supply unit 12 is connected to the electrochemical cell stack 30 of the hot module 15 via a water path 21 and a mixed gas path 22, and is configured to sequentially supply water (pure water) from an external water source to the first heater 32 and the second heater 33, as well as to supply vaporized water vapor to the electrochemical cell stack 30. The air supply unit 13 is connected to the electrochemical cell stack 30 of the hot module 15 via an air path 23, and is configured to supply air to the electrochemical cell stack 30 of the hot module 15. Air is an example of an oxidizing gas in this invention. The combustion hydrogen supply unit 14 is connected to the fourth heater via a combustion hydrogen path 26, and is configured to supply hydrogen for combustion to the fourth heater. The configurations of the hydrogen supply unit 11, water supply unit 12, combustion hydrogen supply unit 14, and air supply unit 13 are not particularly limited, and various known air pumps or liquid pumps can be used.

[0013] The hot module 15 is constructed by covering the main components that become hot among the elements constituting the r-SOC system 10 with an insulating material, and is a device in which the main components are concentrated within an insulating member so that the high temperature state of the main components is maintained. The hot module 15 comprises an electrochemical cell stack 30, a cell stack heater 31, a first heater 32, a second heater 33, a third heater 34, a fourth heater 35, and an insulating member 36 that houses them.

[0014] The electrochemical cell stack 30 comprises multiple electrochemical cells. Each electrochemical cell comprises a fuel electrode, a solid electrolyte layer, and an air electrode, and is formed by stacking these. The electrochemical cell stack 30 is formed by stacking multiple electrochemical cells. A reversible solid oxide fuel cell-steam electrolysis cell is applied to each electrochemical cell. The reversible solid oxide fuel cell-steam electrolysis cell is configured to produce hydrogen by electrolyzing water (steam), and to generate electricity by reacting hydrogen with oxygen. The specific configuration of the reversible solid oxide fuel cell-steam electrolysis cell is not particularly limited, and conventionally known reversible solid oxide fuel cell-steam electrolysis cells can be applied.

[0015] The cell stack heater 31 heats the electrochemical cell stack 30 so that it is maintained at a predetermined operating temperature during the operation of the r-SOC system 10. Various known heaters, such as electric heaters, can be used for the cell stack heater 31.

[0016] In the following explanation, the gas supplied to (flowing into) the fuel electrode of each electrochemical cell in the electrochemical cell stack 30 may be referred to as fuel gas, and the gas discharged (leaving out) from the fuel electrode may be referred to as fuel electrode exhaust gas. In addition, the gas discharged (leaving out) from the air electrode of each electrochemical cell in the electrochemical cell stack 30 may be referred to as air electrode exhaust gas. As mentioned above, during the operation of the r-SOC system 10, the electrochemical cell stack 30 is heated by the cell stack heater 31, etc., so the fuel electrode exhaust gas and air electrode exhaust gas are high-temperature gases.

[0017] The first heater 32 is configured to be able to heat the hydrogen supplied by the hydrogen supply unit 11 and the water supplied by the water supply unit 12. Specifically, the first heater 32 is provided on the hydrogen path 20 and the water path 21, and heat exchange is carried out between the high-temperature fuel electrode exhaust gas discharged from the fuel electrode of the electrochemical cell stack 30 through the fuel electrode exhaust gas path 24 and the hydrogen supplied by the hydrogen supply unit 11 and the water supplied by the water supply unit 12. Also, the first heater 32 includes a first heat source 321. And the first heater 32 is configured to be able to heat the hydrogen supplied by the hydrogen supply unit 11 and the water supplied by the water supply unit 12 by the heat possessed by the fuel electrode exhaust gas and the heat generated by the first heat source 321. Also, the ends of the hydrogen path 20 and the water path 21 are connected to the end of the mixed gas path 22, and the hydrogen and water heated in the first heater 32 flow out from the first heater 32 through the mixed gas path 22.

[0018] The second heater 33 is configured to be able to generate a mixed gas of water vapor in which water is vaporized and hydrogen by heating the water and hydrogen heated in the first heater 32. Specifically, the second heater 33 is provided on the mixed gas path 22 and the combustion exhaust gas path 27 described later. And the second heater 33 is configured to carry out heat exchange between the combustion exhaust gas discharged from the fourth heater 35 and the water and hydrogen heated in the first heater 32. Also, the second heater 33 includes a second heat source 332. And the second heater 33 is configured to be able to heat the water and hydrogen heated in the first heater 32 by the heat possessed by the combustion exhaust gas and the heat generated by the heating source, vaporize the water, and generate a mixed gas of water vapor in which water is vaporized and hydrogen. This mixed gas is the fuel gas. And the mixed gas of hydrogen and water vapor (fuel gas) generated in the second heater 33 is supplied (flows in) to the fuel electrode of each electrochemical cell of the electrochemical cell stack 30.

[0019] The third heater 34 is configured to heat the hydrogen supplied by the combustion hydrogen supply unit 14. Specifically, the third heater 34 is provided on the fuel electrode exhaust gas path 24 and the combustion hydrogen path 26, and is configured to be able to perform heat exchange between the combustion hydrogen supplied by the combustion hydrogen supply unit 14 and the high-temperature fuel electrode exhaust gas.

[0020] The fourth heater 35 is configured to heat the mixture of hydrogen and steam (fuel gas) generated in the second heater 33 and the air supplied by the air supply unit 13. Specifically, the fourth heater 35 is provided on the mixture path 22 and the air path 23. Further, the fourth heater 35 is connected to the electrochemical cell stack 30 through the air electrode exhaust gas path 25 and communicates with the outside air through the combustion exhaust gas path 27. Furthermore, the fourth heater 35 is connected to the combustion hydrogen supply unit 14 through the combustion hydrogen path 26. And the fourth heater 35 is configured to be able to perform heat exchange between the air electrode exhaust gas supplied through the air electrode exhaust gas path 25 and the mixture of hydrogen and steam flowing through the mixture path 22 and the air flowing through the air path. Also, the fourth heater 35 is configured to be able to impart the combustion heat of the hydrogen supplied by the combustion hydrogen supply unit 14 to the mixture of hydrogen and steam flowing through the mixture path 22 and the air flowing through the air path 23. Thus, the fourth heater 35 is configured to be able to heat the mixture of hydrogen and steam (fuel gas) and the air by the combustion heat of the combustion hydrogen and the heat possessed by the air electrode exhaust gas.

[0021] The electrochemical cell stack 30, the cell stack heater 31, the first heater 32, the second heater 33, the third heater 34, and the fourth heater 35 are arranged inside the heat insulating member 36. Thereby, heat dissipation from each device to the outside of the hot module 15 is suppressed. For the heat insulating member 36, heat-resistant fibers such as ceramic wool, refractory ceramic fiber (RCF), bio-soluble fiber (AES), and / or heat-resistant containers formed of these heat-resistant fibers can be used. The heat-resistant fibers are arranged so as to fill the gaps between the electrochemical cell stack 30, the first heater 32, the second heater 33, the third heater 34, and the fourth heater 35.

[0022] The gas-liquid separator 17 is installed on the fuel electrode exhaust gas path 24. The gas-liquid separator 17 is configured to cool the fuel electrode exhaust gas, thereby condensing and liquefying the water vapor contained in the fuel electrode exhaust gas, and to separate the water generated by condensation from the hydrogen contained in the fuel electrode exhaust gas (gas-liquid separation). The configuration of the gas-liquid separator 17 is not particularly limited, and various known gas-liquid separators can be applied. The cooler 18 is installed on the air electrode exhaust gas path 25 and is configured to cool the air electrode exhaust gas. The configuration of the cooler 18 is not particularly limited, and various conventionally known coolers can be applied. Since the air electrode exhaust gas contains water vapor, a gas-liquid separator may be applied as the cooler.

[0023] The power conditioner 16 is configured to sweep the current generated in the electrochemical cell stack 30 when generating electricity in the electrochemical cell stack 30, adjust the swept power, and output it to the outside of the r-SOC system 10. Furthermore, when generating hydrogen in the electrochemical cell stack 30, the power conditioner 16 is configured to supply electrolytic current to each electrochemical cell in the electrochemical cell stack 30 using power supplied from outside the r-SOC system 10. The electrolytic current is the current used for the electrolysis of water (water vapor).

[0024] The control unit 19 is a device configured to control each part of the r-SOC system 10 (hydrogen supply unit 11, water supply unit 12, air supply unit 13, hot module 15, and power conditioner 16). The control unit 19 includes a computer comprising a CPU, ROM, RAM, and an I / F (interface). The computer's ROM pre-stores computer programs for controlling each of the aforementioned parts of the r-SOC system 10. The computer's CPU then reads and executes these computer programs from the ROM. This enables the operation of the r-SOC system 10, which will be described later.

[0025] Next, the operation of the r-SOC system 10 will be described. The r-SOC system 10 has two operating modes: a first mode (hydrogen production mode) and a second mode (fuel cell mode), and operation in either of these two modes can be selected. The first mode is the operating mode in which hydrogen is produced in the electrochemical cell stack 30. The second mode is the operating mode in which electricity is generated in the electrochemical cell stack 30. Note that the fuel gas supplied to the fuel electrode during operation in the first mode is sometimes referred to as the first fuel gas, and the fuel gas supplied to the fuel electrode during operation in the second mode is sometimes referred to as the second fuel gas to distinguish them.

[0026] First mode (hydrogen production mode) The first mode is an operating mode in which hydrogen is produced by electrolyzing water (steam) using power supplied from outside the r-SOC system 10. The control unit 19 controls the cell stack heater 31 so that the electrochemical cell stack 30 is maintained at a predetermined temperature, or controls the combustion hydrogen supply unit 14 in the fourth heater 35 to burn combustion hydrogen, thereby heating the fuel gas and air and heating the electrochemical cell stack 30 to a predetermined temperature. At the same time, the control unit 19 controls the power conditioner 16 to supply electrolytic current to each electrochemical cell of the electrochemical cell stack 30. In addition, the control unit 19 controls the water supply unit 12 to supply water (steam), which is the raw material for hydrogen, to the first heater 32, and controls the hydrogen supply unit 11 to supply hydrogen for reduction in the electrochemical cell stack 30 to the first heater 32.

[0027] The hydrogen supplied by the hydrogen supply unit 14 flows into the third heater 34 where it is heated, and then it is burned in the fourth heater 35.

[0028] Hydrogen supplied to the first heater 32 via the hydrogen path 20 by the hydrogen supply unit 11, and water supplied to the first heater 32 via the water path 21 by the water supply unit 12, are heated in the first heater 32. The heated hydrogen and water then flow into the second heater 33 via the mixed gas path 22. The hydrogen and water flowing into the second heater 33 are heated to form a mixture of hydrogen and water vapor (first fuel gas), which then flows into the fourth heater 35. The mixed gas (first fuel gas) flowing into the fourth heater 35 is heated in the fourth heater 35 and then flows into the fuel electrodes of each electrochemical cell in the electrochemical cell stack 30 (supplied to the fuel electrodes of each electrochemical cell).

[0029] The air supplied by the air supply unit 13 is heated in the fourth heater 35 and then flows into the air electrode of each electrochemical cell in the electrochemical cell stack 30 (it is supplied to the air electrode of each electrochemical cell).

[0030] As a result, the reaction shown in equation (1) below proceeds at the fuel electrode of each electrochemical cell in the electrochemical cell stack 30. H2O + 2e - →H2+O 2- ...Formula (1)

[0031] Furthermore, oxide ions (O) generated at the fuel electrode of each electrochemical cell in the electrochemical cell stack 30 2- ) moves to the air electrode through the electrolyte layer, and the reaction shown in equation (2) below proceeds at the air electrode. O 2- →(1 / 2)O2+2e - …Formula (2)

[0032] Thus, in the first mode, hydrogen is produced at the fuel electrode of each electrochemical cell in the electrochemical cell stack 30, and oxygen is produced at the air electrode.

[0033] The hydrogen generated at the fuel electrode of each electrochemical cell in the electrochemical cell stack 30 flows out (is discharged) from the fuel electrode of each electrochemical cell in the electrochemical cell stack 30 as fuel electrode exhaust gas, along with unreacted water vapor. As described above, the fuel electrode exhaust gas is a mixture of hydrogen and water vapor. The fuel electrode exhaust gas is passed sequentially through the third heater 34 and the first heater 32 to heat the combustion hydrogen, hydrogen, and water, and then flows into the gas-liquid separator 17. In the gas-liquid separator 17, the steam condenses into water, separating the hydrogen and water. The water produced in the gas-liquid separator 17 is supplied to the water supply source. The hydrogen separated from the water in the gas-liquid separator 17 is recovered.

[0034] The oxygen generated in the electrochemical cell stack 30 flows out (is discharged) from the electrochemical cell stack 30 as air electrode exhaust gas, along with the air supplied by the air supply unit 13. The air electrode exhaust gas flows into the fourth heater 35. The air electrode exhaust gas that flows into the fourth heater 35 is used to heat the mixture of hydrogen and water vapor (i.e., the first fuel gas) generated in the second heater 33, and the air supplied by the air supply unit 13. In addition, the oxygen contained in the air electrode exhaust gas that flows into the fourth heater 35 is used for the combustion of combustion hydrogen. The air electrode exhaust gas that has been used for the combustion of combustion hydrogen in the fourth heater 35 flows into the second heater 33, where it is used to heat hydrogen and water. The air electrode exhaust gas that flows out from the second heater 33 is then cooled in the cooler 18. Furthermore, the oxygen contained in the air electrode exhaust gas (oxygen remaining in the fourth heater 35 without being used for hydrogen combustion) is recovered, and the air electrode exhaust gas after the oxygen has been recovered is released into the atmosphere.

[0035] Thus, in the first mode, a mixture of hydrogen and water vapor is supplied as the first fuel gas to the fuel electrode of each electrochemical cell in the electrochemical cell stack 30. The water vapor contained in the first fuel gas is the raw material for hydrogen, and the hydrogen contained in the first fuel gas is a reducing agent that maintains a reducing atmosphere at the fuel electrode of each electrochemical cell in the electrochemical cell stack 30.

[0036] Second mode (fuel cell mode) The second mode is an operation mode in which power generation is performed by reacting hydrogen and oxygen in each of the electrochemical cells of the electrochemical cell stack 30. The control unit 19 controls the cell stack heater 31 so that the electrochemical cell stack 30 is maintained at a predetermined temperature, or controls the combustion hydrogen supply unit 14 with the fourth heater 35 to burn the combustion hydrogen, thereby heating the fuel gas and air to heat the electrochemical cell stack 30 to a predetermined temperature. At the same time, the control unit 19 controls the power conditioner 16 to sweep the power generated by the electrochemical cell stack 30. Further, the control unit 19 controls the water supply unit 12 to supply water to the first heater 32, and controls the hydrogen supply unit 11 to supply hydrogen that reacts with oxygen to the first heater 32. Furthermore, the control unit 19 controls the air supply unit 13 to supply a gas containing oxygen (air in this embodiment) to the fourth heater 35, and controls the combustion hydrogen supply unit 14 to supply combustion hydrogen to the fourth heater 35.

[0037] As a result, the reaction shown in the following formula (3) proceeds at the fuel electrode of each electrochemical cell of the electrochemical cell stack 30. H2+O 2- →H2O+2e - …Formula (3)

[0038] Also, the reaction shown in the following formula (4) proceeds at the air electrode of each electrochemical cell of the electrochemical cell stack 30. (1 / 2)O2+2e - →O 2- …Formula (4)

[0039] And, by the oxide ions (O 2- ) moving through the electrolyte layer, power generation is performed in each electrochemical cell of the electrochemical cell stack 30. Thus, in the second mode, power generation is performed in each electrochemical cell of the electrochemical cell stack 30. The generated power is swept by the power conditioner 16 and adjusted in the power conditioner 16, and is output to the outside of the r-SOC system 10.

[0040] Furthermore, as shown in equation (3), water (water vapor) is generated at the fuel electrode. The generated water (water vapor), along with unreacted hydrogen and water vapor, is discharged as fuel electrode exhaust gas from the fuel electrode of each electrochemical cell in the electrochemical cell stack 30. Therefore, the fuel electrode exhaust gas is a mixture of hydrogen and water vapor. Also, as shown in equation (4), oxygen is converted into oxygen ions and consumed at the air electrode. The remaining oxygen, along with the air that has passed through the air electrode, is discharged as air electrode exhaust gas from the air electrode of each electrochemical cell in the electrochemical cell stack 30. Therefore, the air electrode exhaust gas is the remaining gas (leany oxygen air) after some of the oxygen has been consumed at the air electrode.

[0041] The fuel electrode exhaust gas flowing out of the electrochemical cell stack 30 passes sequentially through the third heater 34 and the first heater 32, as in operation in the first mode, to heat the combustion hydrogen, hydrogen, and water, and then flows into the gas-liquid separator 17. In the gas-liquid separator 17, water vapor condenses into water, separating unreacted hydrogen from water. The water produced in the gas-liquid separator 17 is supplied to the water supply source. The unreacted hydrogen separated from the water in the gas-liquid separator 17 is recovered.

[0042] The air electrode exhaust gas flowing out of the electrochemical cell stack 30 flows into the fourth heater 35, where it is used to heat the mixture of hydrogen and water vapor generated in the second heater 33 (i.e., the second fuel gas) and the air supplied by the air supply unit 13. The oxygen contained in the air electrode exhaust gas flowing into the fourth heater 35 is used for the combustion of hydrogen for combustion. The air electrode exhaust gas used for the combustion of hydrogen for combustion in the fourth heater 35 flows into the second heater 33, where it is used to heat hydrogen and water. The air electrode exhaust gas flowing out of the second heater 33 is then cooled in the cooler 18. The oxygen contained in the air electrode exhaust gas (oxygen remaining in the fourth heater 35 that was not used for the combustion of hydrogen) is recovered, and the air electrode exhaust gas after the oxygen has been recovered is released into the atmosphere.

[0043] Thus, the r-SOC system 10 can selectively operate in a first mode and a second mode. The control unit 19 can switch between the first mode and the second mode of operation. Specifically, the control unit 19 can operate the r-SOC system 10 in the first mode by supplying electrolytic current to each electrochemical cell of the electrochemical cell stack 30 via the power conditioner 16, and can operate the r-SOC system 10 in the second mode by sweeping power from the electrochemical cell stack 30 via the power conditioner 16.

[0044] The control unit 19 controls the water supply unit 12 and the hydrogen supply unit 11 to adjust the amount and composition of fuel gas (first fuel gas and second fuel gas) supplied per unit time to the fuel electrode of each electrochemical cell in the electrochemical cell stack 30. Specifically, when the r-SOC system 10 is operated in first mode, the control unit 19 adjusts the amount of water supplied per unit time so that the amount of water vapor supplied per unit time to the electrochemical cell stack 30 (amount of water vapor contained in the first fuel gas) is greater than the amount of water vapor that can be electrolyzed per unit time by the electrochemical cell stack 30. With this configuration, it is possible to prevent or suppress a shortage of water (water vapor), which is the raw material for hydrogen, when producing hydrogen in the electrochemical cell stack 30. Furthermore, when the r-SOC system 10 is operated in the second mode, the control unit 19 controls the hydrogen supply unit 11 so that the amount of hydrogen supplied to the electrochemical cell stack 30 per unit time (the amount of hydrogen contained in the second fuel gas) is greater than the amount that can be reacted with oxygen in the electrochemical cell stack 30 per unit time.

[0045] As mentioned above, in the first mode, water vapor is electrolyzed in each electrochemical cell of the electrochemical cell stack 30. Also in the first mode, hydrogen is supplied to the fuel electrode as a reducing agent to suppress the deterioration (oxidation) of the fuel electrode of the electrochemical cell in the electrochemical cell stack 30. Therefore, from the viewpoint of operational efficiency, the first fuel gas is preferably a gas containing a large amount of water vapor, and the amount of hydrogen as a reducing agent is only necessary to suppress the deterioration of the fuel electrode. On the other hand, in the second mode, electricity is generated by the reaction of hydrogen and oxygen in each electrochemical cell of the electrochemical cell stack 30. Therefore, from the viewpoint of operational efficiency, the second fuel gas is preferably a gas containing a large amount of hydrogen, and the amount of water vapor is only necessary to maintain the temperature of the electrochemical cell. Theoretically, the second fuel gas does not need to contain water vapor. Thus, the preferred fuel gas components (specifically, the mixing ratio (molar ratio) of hydrogen and water vapor) differ between the first mode and the second mode from the viewpoint of efficiency.

[0046] Figure 2 is a schematic graph showing the ratio of water vapor in the fuel gas of the r-SOC system 10 according to this embodiment. In Figure 2, the solid line shows the ratio of water vapor in the fuel gas of the configuration of this embodiment (a configuration in which the fuel gas components are not changed between the first mode and the second mode), and the dashed line shows the water vapor concentration contained in the fuel electrode exhaust gas. In Figure 2, the period before time t1 and the period after time t2 are periods of operation in the second mode, and the period from time t1 to time t2 is a period of operation in the first mode. Time t1 is the time when the system switches from the second mode to the first mode, and time t2 is the time when the system switches from the first mode to the second mode.

[0047] As described above, the preferred components of the fuel gas differ between the first mode and the second mode. Therefore, in the conventional configuration, the proportion of water vapor in the first fuel gas is increased during operation in the first mode, and the proportion of water vapor in the second fuel gas is decreased (the proportion of hydrogen is increased) during operation in the second mode.

[0048] However, if the composition of the first fuel gas in the first mode and the second fuel gas in the second mode are different, as in the conventional configuration, "fuel depletion" may occur when switching between operating modes. "Fuel depletion" means that in the first mode, the amount of water vapor supplied to the electrochemical cell stack 30 per unit time is less than the amount of water vapor that can be decomposed in the electrochemical cell stack 30 per unit time. In the second mode, it means that the amount of hydrogen supplied to the electrochemical cell stack 30 per unit time is less than the amount of hydrogen that can be reacted with oxygen in the electrochemical cell stack 30 per unit time. It should be noted that the "amount of water vapor that can be decomposed in the electrochemical cell stack 30 per unit time" in the first mode can be said to be the "maximum amount of water vapor that can be decomposed when the electrochemical cell stack 30 is operating at its rated capacity." Similarly, the "amount of hydrogen that can be reacted with oxygen in the electrochemical cell stack 30 per unit time" in the second mode can be said to be the "maximum amount of hydrogen that can be reacted with oxygen when the electrochemical cell stack 30 is operating at its rated capacity."

[0049] Fuel depletion occurs because the hydrogen path 20, water path 21, and mixed gas path 22 that supply hydrogen and water from the hydrogen supply unit 11 and water supply unit 12 to the electrochemical cell stack 30 have a certain length. In other words, in a configuration where the fuel gas composition is changed between the first mode and the second mode, even if the hydrogen supply unit 11 and water supply unit 12 change the amount of hydrogen and water supplied per unit time, it takes a certain amount of time for the fuel gas with the changed composition to reach the fuel electrode of the electrochemical cell stack 30. When fuel depletion occurs, stable hydrogen production becomes impossible when switching from the second mode to the first mode, and stable power generation becomes impossible when switching from the first mode to the second mode.

[0050] Therefore, in order to prevent the above-mentioned problems from occurring, in this embodiment, when operating in the first mode, the control unit 19 controls the amount of water supplied from the water supply unit 12 per unit time so that the amount of water vapor contained in the first fuel gas (i.e., the amount of water vapor supplied to the electrochemical cell stack 30 per unit time) is greater than the amount of water vapor that the electrochemical cell stack 30 can electrolyze at the fuel electrode of each electrochemical cell per unit time. Furthermore, when operating in the second mode, the control unit 19 controls the amount of water supplied by the water supply unit 12 per unit time so that the amount of water vapor contained in the second fuel gas (i.e., the amount of water vapor supplied to the electrochemical cell stack 30 per unit time) is greater than or equal to the amount of water vapor contained in the first fuel gas. Preferably, as shown in Figure 2, the control unit 19 controls the water supply unit 12 so that the amount of water vapor contained in the first fuel gas and the amount of water vapor contained in the second fuel gas are the same.

[0051] With this configuration, the amount of water vapor supplied to the electrochemical cell stack 30 per unit time while operating in the second mode is "greater than or equal to the amount of water vapor supplied to the fuel electrode of each electrochemical cell in the electrochemical cell stack 30 per unit time when operating in the first mode." Therefore, when the operating mode of the r-SOC system 10 can be switched from the second mode to the first mode, at the moment the operating mode is switched, the electrochemical cell stack 30 is supplied with an amount of water vapor per unit time greater than or equal to the amount of water vapor that can be electrolyzed. Consequently, when switching from the second mode to the first mode, hydrogen can be produced efficiently immediately after the switch. In other words, it is possible to provide an r-SOC system 10 that can shorten the time required for operation stabilization when switching operating modes.

[0052] Furthermore, as mentioned above, it is preferable that the amount of water vapor contained in the fuel gas is the same in the first mode and the second mode. With such a configuration, fluctuations in the internal pressure (fuel gas pressure) at the fuel electrode are less likely to occur when switching operating modes. In other words, in a configuration where water supplied by the water supply unit 12 is vaporized in the second heater 33 and supplied to each electrochemical cell of the electrochemical cell stack 30, if the amount of water supplied fluctuates, the pressure of the fuel gas may fluctuate significantly. And when the pressure of the fuel gas fluctuates, it may put a strain on each electrochemical cell of the electrochemical cell stack 30. According to this embodiment, since fluctuations in the partial pressure of water vapor in the fuel gas can be prevented or suppressed, the strain on each electrochemical cell of the electrochemical cell stack 30 can be reduced.

[0053] Furthermore, in this embodiment, as shown in Figure 2, it is preferable that the ratio (molar ratio) of hydrogen to water vapor is the same in the fuel gas supplied to the fuel electrode when operating in the first mode (first fuel gas) and in the fuel gas supplied to the fuel electrode when operating in the second mode (second fuel gas). In other words, it is preferable that there is little change in the ratio (molar ratio) of hydrogen to water vapor between operation in the first mode and operation in the second mode.

[0054] With this configuration, even during operation in the first mode, the electrochemical cell stack 30 is supplied with an amount of hydrogen greater than the amount that can be reacted with oxygen in the electrochemical cell stack 30 when operating in the second mode. Therefore, when the operating mode switches from the first mode to the second mode, there is an amount of hydrogen in the fuel electrode of each electrochemical cell in the electrochemical cell stack 30 that will not cause fuel depletion. As a result, when the control unit 19 switches the operating mode of the r-SOC system 10 from the first mode to the second mode, fuel depletion is prevented or suppressed.

[0055] Furthermore, if the amount of water vapor contained in the first fuel gas is the same as the amount of water vapor contained in the second fuel gas, and the mixing ratio of water vapor to hydrogen in the first and second fuel gases is the same, then the time required for operation to stabilize can be shortened both when switching from the first mode to the second mode and when switching from the second mode to the first mode.

[0056] Furthermore, in this embodiment, in both the first and second modes, it is preferable that the ratio (molar ratio) of water vapor in the fuel gas is 50% or more, and more preferably 60% to 75%. Note that Figure 2 shows an example where the ratio of water vapor in the fuel gas (first fuel gas and second fuel gas) is 68%, but the ratio of water vapor is not limited to the example shown in Figure 2. Such a configuration allows for stable operation of the electrochemical cell stack 30. That is, the amount of water vapor (in moles) that the electrochemical cell stack 30 can electrolyze when operating in the first mode is greater than the amount of hydrogen (in moles) that the electrochemical cell stack 30 can react with oxygen when operating in the second mode. Therefore, in a configuration where the ratio of hydrogen to water vapor is the same in both the first and second modes, if the ratio of water vapor is greater than or equal to the ratio of hydrogen, the electrochemical cell stack 30 can be stabilized in both the first and second modes. In particular, when the ratio (molar ratio) of water vapor is between 60% and 75%, the effect of stabilizing the electrochemical cell stack 30 can be enhanced.

[0057] While embodiments of this disclosure have been described above, the technology relating to this disclosure is not limited to the embodiments described above. For example, although the embodiments described above describe a hydrogen production apparatus for producing hydrogen, this technology can be applied to apparatuses for producing gases other than hydrogen, such as carbon monoxide, or both hydrogen and carbon monoxide. Thus, the technology relating to this disclosure is modifiable as long as it does not depart from the spirit of the disclosure.

[0058] Furthermore, this disclosure may include the following aspects:

[0059] [1] An electrochemical cell stack comprising a fuel electrode and an air electrode, wherein when water vapor is supplied to the fuel electrode, hydrogen can be produced by electrolysis of the water vapor in the fuel electrode, and when hydrogen is supplied to the fuel electrode and an acidifying gas is supplied to the air electrode, power generation is possible by reacting the hydrogen supplied to the fuel electrode with the acidifying gas supplied to the air electrode, A fuel gas supply unit is configured to supply a first fuel gas containing water vapor to the fuel electrode when generating hydrogen in the electrochemical cell, and to supply a second fuel gas containing hydrogen and water vapor to the fuel electrode when generating electricity in the electrochemical cell. Equipped with, The amount of water vapor contained in the first fuel gas supplied from the fuel gas supply unit to the fuel electrode per unit time is greater than the amount of water vapor that the electrochemical cell stack can electrolyze at the fuel electrode per unit time. The amount of water vapor contained in the second fuel gas supplied from the fuel gas supply unit to the fuel electrode per unit time is equal to or greater than the amount of water vapor contained in the first fuel gas supplied from the fuel gas supply unit to the fuel electrode per unit time. Reversible SOC system.

[0060] [2] The reversible SOC system described in [1] above, The first fuel gas is a gas containing water vapor and hydrogen. The ratio of the amount of water vapor to the amount of hydrogen in the first fuel gas supplied from the fuel gas supply unit to the fuel electrode per unit time is the same as the ratio of the amount of water vapor to the amount of hydrogen in the second fuel gas supplied from the fuel gas supply unit to the fuel electrode per unit time. Reversible SOC system.

[0061] [3] The reversible SOC system described in [1] or [2] above, The ratio of water vapor in the first fuel gas and the second fuel gas is 50% or more. Reversible SOC system.

[0062] [4] A reversible SOC system according to any one of the above [1] to [3], The ratio of water vapor in the first fuel gas and the second fuel gas is 60% or more and 75% or less. Reversible SOC system. [Explanation of Symbols]

[0063] 10…Reversible SOC system (r-SOC system), 11…Hydrogen supply unit, 12…Water supply unit, 13…Air supply unit, 15…Hot module, 16…Power conditioner (powercon), 19…Control unit (control device), 30…Electrochemical cell stack

Claims

1. An electrochemical cell stack comprising a fuel electrode and an air electrode, wherein when water vapor is supplied to the fuel electrode, hydrogen can be produced by electrolysis of the water vapor in the fuel electrode, and when hydrogen is supplied to the fuel electrode and an acidifying gas is supplied to the air electrode, power generation is possible by reacting the hydrogen supplied to the fuel electrode with the acidifying gas supplied to the air electrode, A fuel gas supply unit is configured to supply a first fuel gas containing water vapor to the fuel electrode when generating hydrogen in the electrochemical cell stack, and to supply a second fuel gas containing hydrogen and water vapor to the fuel electrode when generating electricity in the electrochemical cell stack. Equipped with, The amount of water vapor contained in the first fuel gas supplied from the fuel gas supply unit to the fuel electrode per unit time is greater than the amount of water vapor that the electrochemical cell stack can electrolyze at the fuel electrode per unit time. The amount of water vapor contained in the second fuel gas supplied from the fuel gas supply unit to the fuel electrode per unit time is equal to or greater than the amount of water vapor contained in the first fuel gas supplied from the fuel gas supply unit to the fuel electrode per unit time. Reversible SOC system.

2. A reversible SOC system according to claim 1, The first fuel gas is a gas containing water vapor and hydrogen. The ratio of the amount of water vapor to the amount of hydrogen in the first fuel gas supplied from the fuel gas supply unit to the fuel electrode per unit time is the same as the ratio of the amount of water vapor to the amount of hydrogen in the second fuel gas supplied from the fuel gas supply unit to the fuel electrode per unit time. Reversible SOC system.

3. A reversible SOC system according to claim 1 or claim 2, The ratio of water vapor in the first fuel gas and the second fuel gas is 50% or more. Reversible SOC system.

4. A reversible SOC system according to claim 1 or claim 2, The ratio of water vapor in the first fuel gas and the second fuel gas is 60% or more and 75% or less. Reversible SOC system.

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