Reversible SOC System

Abstract

This provides a reversible SOC system that can shorten the time required for operation to stabilize when switching operating modes. [Solution] The reversible SOC system 10 is configured to be switchable between SOFC mode operation, in which the electrochemical cell stack 30 generates electricity, and SOEC mode operation, in which the electrochemical cell stack 30 generates hydrogen. During at least a portion of the transient temperature period, which is the period in which the temperature of the electrochemical cell stack 30 temporarily decreases when switching from SOFC mode operation to SOEC mode operation, a current greater than the rated current, which is the current when operating at rated speed in SOEC mode, is supplied to the electrochemical cell stack 30, and after the transient temperature period has elapsed, the rated current is supplied to the electrochemical cell stack 30.

Description

Technical Field

[0001] The present disclosure relates to a reversible SOC system.

Background Art

[0002] Conventionally, as disclosed in Patent Document 1 and Patent Document 2, a reversible SOC system that can be switched between an operation mode for producing hydrogen (SOEC mode) and an operation mode for generating power (SOFC mode) is known. During operation in the SOEC mode, while the electrochemical cell stack is heated to a predetermined temperature, hydrogen is produced by electrolyzing water (water vapor) in the electrochemical cell stack. During operation in the SOFC mode, while the electrochemical cell stack is heated to a predetermined temperature, power is generated by reacting hydrogen and oxygen in the electrochemical cell stack.

[0003] The reaction for generating hydrogen in the electrochemical cell stack is an endothermic reaction. On the other hand, the reaction for generating power in the electrochemical cell stack is an exothermic reaction. Therefore, when heating the electrochemical cell stack so that the temperature of the electrochemical cell stack becomes constant in the SOFC mode and the SOEC mode, the heating amount of the electrochemical cell stack in the SOEC mode must be made larger than the heating amount of the electrochemical cell stack in the SOFC mode. However, when the operation mode is switched from the SOFC mode to the SOEC mode, an endothermic reaction immediately occurs, while it takes a certain amount of time for the temperature of the electrochemical cell stack to rise due to the heating mechanism.

[0004] Therefore, when the operating mode is switched from SOFC mode to SOEC mode, the temperature of the electrochemical cell stack temporarily decreases. When the temperature of the electrochemical cell stack decreases, the internal resistance of the electrochemical cell stack increases, the voltage applied to the electrochemical cell stack increases, and as a result, the load on the electrochemical cell stack increases. Note that Patent Documents 1 and 2 do not disclose the configuration of operation when switching operating modes. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2024-90821 [Patent Document 2] Special Publication No. 2023-536351 [Overview of the Initiative]

[0006] 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 SOEC mode and SOFC mode, and that can prevent or suppress a temporary drop in the temperature of the electrochemical cell stack when switching the operating mode from SOFC mode to SOEC mode.

[0007] To address the above issues, the reversible SOC system described herein is: An electrochemical cell stack capable of reversibly performing both power generation as a solid oxide fuel cell and electrolysis as a solid oxide steam electrolysis cell, A power supply unit capable of supplying current to the electrochemical cell stack, A reversible SOC system comprising, configured to be switchable between operation in SOFC mode, in which the electrochemical cell stack generates electricity, and operation in SOEC mode, in which the electrochemical cell stack generates hydrogen, The power supply unit, during at least a portion of the transient temperature period, which is the period in which the temperature of the electrochemical cell stack temporarily drops below the steady temperature (the temperature when operating at rated capacity in SOEC mode) when switching from SOFC mode to SOEC mode, supplies a current to the electrochemical cell stack that is greater than the rated current (the current when operating at rated capacity in SOEC mode), and after the transient temperature period has elapsed, supplies the rated current to the electrochemical cell stack.

[0008] According to this disclosure, a current greater than the rated current is passed through the electrochemical cell stack during at least a portion of the transient temperature period, which is the period when the temperature of the electrochemical cell stack temporarily drops below the steady temperature. With this configuration, the Joule heat generated in the electrochemical cell stack is greater compared to when the rated current is passed through the electrochemical cell stack. Therefore, when switching the operating mode from SOFC mode to SOEC mode, the temperature drop of the electrochemical cell stack can be suppressed, and the transient temperature period can be shortened. In other words, the time required for operation stabilization when switching operating modes can be reduced. [Brief explanation of the drawing]

[0009] [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. [Figure 3A] Figure 3A is a flowchart showing the processes performed by the control unit of the reversible SOC system. [Figure 3B] Figure 3B is a flowchart showing the processes performed by the control unit of the reversible SOC system. [Figure 4] Figure 4 shows the operation of a conventional reversible SOC system. [Modes for carrying out the invention]

[0010] 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 includes a hydrogen supply unit 11, a water supply unit 12, an air supply unit 13, a hot module 14, a cell stack voltmeter 15, a cell stack ammeter 16, a cell stack thermometer 17, a gas-liquid separator 18, a power conditioner 19, and a control unit 20 (control device). In the following description, "reversible SOC system 10" may be abbreviated as "rSOC system 10," and the power conditioner 19 may be abbreviated as "power conditioner 19."

[0011] The hydrogen supply unit 11 is connected to the vaporizer 33 of the hot module 14 (described later) via a hydrogen path 21, and is configured to supply hydrogen to the vaporizer 33 from an external hydrogen supply source. The water supply unit 12 is connected to the vaporizer 33 of the hot module 14 via a water path 22, and is configured to supply water (pure water) from an external water supply source to the vaporizer 33. The air supply unit 13 is connected to the air electrode of each electrochemical cell 31 of the electrochemical cell stack 30 (described later) via an air path 24, and is configured to supply air to the air electrode of each electrochemical cell 31 of the electrochemical cell stack 30. The configurations of the hydrogen supply unit 11, the water supply unit 12, and the air supply unit 13 are not particularly limited, and conventionally known air pumps or liquid pumps can be used.

[0012] The hot module 14 is constructed by covering the main components of the rSOC system 10 that become hot with an insulating member 34, and is a device in which the main components are concentrated inside the insulating member 34 so that the high temperature state of the main components is maintained. The hot module 14 comprises an electrochemical cell stack 30, a vaporizer 33, and an insulating member 34 that houses them.

[0013] The electrochemical cell stack 30 is configured to reversibly perform both a power generation function as a solid oxide fuel cell and an electrolysis function as a solid oxide steam electrolysis cell. Specifically, the electrochemical cell stack 30 comprises a plurality of electrochemical cells 31. Each electrochemical cell 31 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 a plurality of electrochemical cells 31. A reversible solid oxide fuel cell-steam electrolysis cell is applied to each electrochemical cell 31. The reversible solid oxide fuel cell-steam electrolysis cell is configured to generate hydrogen by electrolyzing water (steam) and to generate electricity by reacting hydrogen with oxygen. The configuration of the electrochemical cell stack 30 and the configuration of each electrochemical cell 31 forming the electrochemical cell stack 30 are not particularly limited, and conventionally known configurations can be applied.

[0014] The cell stack heater 32 heats the electrochemical cell stack 30 to a predetermined temperature (specifically, the steady-state temperature T described later). S The cell stack heater 32 is configured to be able to heat the cell stack 30. The cell stack heater 32 is configured to be able to heat the electrochemical cell stack 30 by supplying a medium (fluid) heated by the heat source to the electrochemical cell stack 30. However, the configuration of the cell stack heater 32 is not particularly limited, and various conventionally known heaters can be applied.

[0015] The vaporizer 33 (heater) is configured to heat the hydrogen supplied by the hydrogen supply unit 11 and the water supplied by the water supply unit to vaporize the hydrogen and water and produce a mixture of water vapor. The vaporizer 33 is connected to the fuel electrode of each electrochemical cell 31 of the electrochemical cell stack 30 via the fuel gas path 23. The generated mixture of hydrogen and water vapor is then supplied (flows into) the fuel electrode of each electrochemical cell 31 of the electrochemical cell stack 30 via the fuel gas path 23.

[0016] The electrochemical cell stack 30, the cell stack heater 32, and the vaporizer 33 are arranged inside the insulating member 34. This suppresses heat dissipation from each device to the outside of the hot module 14. The insulating member 34 may be made of heat-resistant fibers such as ceramic wool, refractory ceramic fiber (RCF), biosoluble fiber (AES), and / or heat-resistant containers formed from these heat-resistant fibers. The heat-resistant fibers are arranged to fill the gaps between each member.

[0017] The gas-liquid separator 18 is configured to separate the fuel electrode exhaust gas into water and hydrogen (gas-liquid separation) by cooling the fuel electrode exhaust gas, which is the gas discharged from the fuel electrodes of each electrochemical cell 31 of the electrochemical cell stack 30, thereby condensing the water vapor contained in the fuel electrode exhaust gas. The gas-liquid separator 18 is connected to the fuel electrodes of each electrochemical cell 31 of the electrochemical cell stack 30 via the fuel electrode exhaust gas path 25, and is configured to receive the fuel electrode exhaust gas discharged from the fuel electrodes of each electrochemical cell 31 of the electrochemical cell stack 30. The configuration of the gas-liquid separator 18 is not particularly limited, and various known gas-liquid separators can be applied.

[0018] The cell stack voltmeter 15 is configured to continuously measure the voltage applied to the electrochemical cell stack 30 in real time and to output this measured voltage to the control unit 20. Hereinafter, the voltage applied to the electrochemical cell stack 30 may be referred to as "cell stack voltage V". The rSOC system 10 may also be equipped with a voltmeter capable of measuring the voltage applied to each electrochemical cell 31 (potential difference between the fuel electrode and the air electrode) instead of the cell stack voltmeter 15.

[0019] The cell stack ammeter 16 is configured to continuously measure the current flowing through the electrochemical cell stack 30 in real time and to output this measured current to the control unit 20.

[0020] The cell stack thermometer 17 is configured to continuously measure the temperature T of the electrochemical cell stack 30 in real time and to output the measured temperature T of the electrochemical cell stack 30 to the control unit 20. Hereinafter, "temperature T of the electrochemical cell stack 30" may be abbreviated as "cell stack temperature T".

[0021] The power conditioner 19 is an example of a power supply unit. When generating electricity in the electrochemical cell stack 30, the power conditioner 19 is configured to sweep power from the electrochemical cell stack 30, adjust the swept power, and output it to the outside of the rSOC system 10. Furthermore, when generating hydrogen in the electrochemical cell stack 30, the power conditioner 19 is configured to use power supplied from outside the rSOC system 10 to supply an electrolytic current I to each electrochemical cell 31 of the electrochemical cell stack 30. The electrolytic current I is the current used to electrolyze water (water vapor).

[0022] In this embodiment, the power conditioner 19 is equipped with two electrical circuits. One electrical circuit (hereinafter sometimes referred to as the "SOEC electrical circuit") is configured to adjust the power supplied from an external source and supply it to the electrochemical cell stack 30. The other electrical circuit (hereinafter sometimes referred to as the "SOFC electrical circuit") is configured to sweep the power generated in the electrochemical cell stack 30 and adjust the swept power to output it externally. The power conditioner 19 can selectively operate either the SOEC electrical circuit or the SOFC electrical circuit in response to control by the control unit 20.

[0023] The control unit 20 is configured to control each part of the rSOC system 10 (hydrogen supply unit 11, water supply unit 12, air supply unit 13, hot module 14, and power conditioner 19). The control unit 20 is also configured to continuously acquire in real time the measurement results of the cell stack voltage V from the cell stack voltmeter 15, the electrolysis current I from the cell stack ammeter 16, and the cell stack temperature T from the cell stack thermometer 17. The control unit 20 is a device equipped with a computer comprising a CPU, ROM, RAM, and an I / F (interface). The computer's ROM pre-stores computer programs for controlling each part of the rSOC system 10. The computer's CPU then reads and executes these computer programs from the ROM. This enables the operation of the rSOC system 10, which will be described later.

[0024] Next, the basic operation of the rSOC system 10 will be described. The rSOC system 10 has two operating modes: SOEC mode (hydrogen production mode) and SOFC mode (fuel cell mode). The rSOC system 10 can select to operate in one of the two operating modes.

[0025] SOEC mode (hydrogen production mode) The SOEC mode is an operating mode in which hydrogen is produced by electrolyzing water (water vapor) using power supplied from outside the rSOC system 10. The control unit 20 determines when the cell stack temperature T is a predetermined steady-state temperature T SThe control unit 20 controls the cell stack heater 32 to heat the electrochemical cell stack 30 so that it is maintained at a constant temperature. Simultaneously, the control unit 20 operates the SOEC electrical circuit of the power conditioner 19 to supply an electrolytic current I to each electrochemical cell 31 of the electrochemical cell stack 30. The control unit 20 also controls the water supply unit 12 to supply water, which is the raw material for hydrogen, to the vaporizer 33 of the hot module 14, and controls the hydrogen supply unit 11 to supply hydrogen for reduction in the electrochemical cell stack 30 to the vaporizer 33. Furthermore, the control unit 20 controls the air supply unit 13 to supply air to the air electrodes of each electrochemical cell 31 of the electrochemical cell stack 30.

[0026] The water supplied to the vaporizer 33 by the water supply unit 12 is heated and vaporized in the vaporizer 33. Then, a mixture of the generated water vapor and the water supplied by the hydrogen supply unit 11 is produced in the vaporizer 33. The generated mixture flows into the fuel electrodes of each electrochemical cell 31 of the electrochemical cell stack 30 through the fuel gas path 23 (it is supplied to the fuel electrodes of each electrochemical cell 31).

[0027] As a result, the reaction shown in equation (1) below proceeds at the fuel electrode of each electrochemical cell 31 in the electrochemical cell stack 30. H2O + 2e - →H2+O 2- …Formula (1)

[0028] Furthermore, oxide ions (O) generated at the fuel electrode of each electrochemical cell 31 of 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)

[0029] Thus, in SOEC mode, hydrogen is produced at the fuel electrode of each electrochemical cell 31 in the electrochemical cell stack 30, and oxygen is produced at the air electrode.

[0030] The above reaction in each of the electrochemical cells 31 of the electrochemical cell stack 30 is an endothermic reaction. A state where the Joule heat (heat generation amount) by the electrolysis current I and the endothermic amount by the above reaction become the same is sometimes referred to as a thermal neutral point. In the present embodiment, an electrolysis current I such that the state of each of the electrochemical cells 31 of the electrochemical cell stack 30 becomes the thermal neutral point is the "rated current I S ". Note that the rated current I s is not limited to this and may be set according to a desired amount of generated hydrogen. The internal resistance of each of the electrochemical cells 31 of the electrochemical cell stack 30 changes according to the temperature of each of the electrochemical cells 31.

[0031] The control unit 20 heats the electrochemical cell stack 30 to a predetermined steady temperature T S by the cell stack heater 32. This steady temperature T S is a temperature at which water vapor can be efficiently electrolyzed and can also be said to be the target temperature of the electrochemical cell stack 30 during operation in the SOEC mode. In addition, the control unit 20 passes (adjusts the magnitude of) an electrolysis current I so that the state of each of the electrochemical cells 31 of the electrochemical cell stack 30 becomes the thermal neutral point at the steady temperature T[[ID=一三]] S . In the present embodiment, the cell stack temperature T is the steady temperature T S , and the operation in a state where the state of each of the electrochemical cells 31 of the electrochemical cell stack 30 is the thermal neutral point (the state where the electrolysis current I is the rated current I S ) is the "rated operation" in the SOEC mode. Also, the cell stack voltage V during rated operation is the rated voltage V S . [[ID=二一]]

[0032] The hydrogen generated at the fuel electrode of each electrochemical cell 31 of the electrochemical cell stack 30 flows out (is discharged) from the fuel electrode of each electrochemical cell 31 of the electrochemical cell stack 30 as fuel electrode exhaust gas, along with unreacted water vapor. The fuel electrode exhaust gas is a mixture of hydrogen and water vapor. The fuel electrode exhaust gas is separated into hydrogen and water in the gas-liquid separator 18 when the water vapor condenses into water. The hydrogen separated from the water in the gas-liquid separator 18 is recovered. The water produced in the gas-liquid separator 18 may be discarded or supplied to a water source.

[0033] The oxygen generated in the electrochemical cell stack 30 flows out (is discharged) from the electrochemical cell stack 30 as air electrode exhaust gas, together with the air supplied by the air supply unit 13. The oxygen contained in the air electrode exhaust gas may be recovered or released into the atmosphere together with the air.

[0034] SOFC mode (fuel cell mode) SOFC mode is an operating mode in which power is generated by reacting hydrogen and oxygen in each electrochemical cell 31 of the electrochemical cell stack 30. The control unit 20 controls the cell stack heater 32 to heat the electrochemical cell stack 30 so that the cell stack temperature T is maintained at a predetermined temperature. In this embodiment, this predetermined temperature is the steady-state temperature T in SOEC mode. S The temperature is the same. In addition, the control unit 20 sweeps up the power generated in the electrochemical cell stack 30 by operating the SOFC electrical circuit of the power conditioner 19. The control unit 20 also supplies water to the vaporizer 33 by controlling the water supply unit 12 and supplies hydrogen to the vaporizer 33 by controlling the hydrogen supply unit 11. Furthermore, the control unit 20 supplies an oxygen-containing gas (air in this embodiment; however, this may be oxygen recovered during operation in SOEC mode) to the air electrode of each electrochemical cell 31 of the electrochemical cell stack 30 by controlling the air supply unit 13.

[0035] As a result, the reaction shown in equation (3) below proceeds at the fuel electrode of each electrochemical cell 31 in the electrochemical cell stack 30. H2 + O 2- →H2O+2e - ...Formula (3)

[0036] Furthermore, the reaction shown in equation (4) below proceeds at the air electrode of each electrochemical cell 31 in the electrochemical cell stack 30. (1 / 2)O2+2e - →O 2- ...Formula (4)

[0037] And oxide ions (O 2- As the electrolyte moves through the electrolyte layer, electricity is generated in each electrochemical cell 31 of the electrochemical cell stack 30. Thus, in SOFC mode, electricity is generated in each electrochemical cell 31 of the electrochemical cell stack 30. The generated electricity is swept and adjusted by the power conditioner 19 and output to the outside of the rSOC system 10 (an electrical load electrically connected to the rSOC system 10).

[0038] 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 31 in the electrochemical cell stack 30. The air that has passed through the air electrode is discharged as air electrode exhaust gas from the air electrode of each electrochemical cell 31 in the electrochemical cell stack 30.

[0039] The fuel electrode exhaust gas discharged from the fuel electrode of each electrochemical cell 31 of the electrochemical cell stack 30 is separated into unreacted hydrogen and water in the gas-liquid separator 18 by condensation of water vapor, similar to operation in SOEC mode. The unreacted hydrogen separated from the water in the gas-liquid separator 18 is then recovered. The water produced in the gas-liquid separator 18 may be discarded or supplied to a water source.

[0040] Thus, the rSOC system 10 can selectively operate in SOEC mode and SOFC mode. The control unit 20 can operate the rSOC system 10 in SOEC mode by operating the SOEC electrical circuit of the power conditioner 19 to supply electrolytic current I to each electrochemical cell 31 of the electrochemical cell stack 30. The control unit 20 can also operate the rSOC system 10 in SOFC mode by operating the SOFC electrical circuit of the power conditioner 19 to sweep power from the electrochemical cell stack 30. In both SOEC mode and SOFC mode operation, the control unit 20 ensures that the cell stack temperature T is at a steady-state temperature T. S The cell stack heater 32 is controlled to achieve this.

[0041] The control unit 20 then switches between SOEC mode and SOFC mode operation when predetermined switching conditions are met. These switching conditions are not particularly limited, but for example, the control unit 20 switches the operating mode when it receives a "signal instructing a switch in the operating mode" from outside the rSOC system 10, when it detects an "operation instructing a switch in the operating mode" to the rSOC system 10, or when a preset "time to switch the operating mode" arrives.

[0042] Incidentally, as mentioned above, the reaction that generates electricity in the electrochemical cell 31 is an exothermic reaction, and the reaction that produces hydrogen is an endothermic reaction. For this reason, when switching the operating mode from SOFC mode to SOEC mode in a conventional rSOC system, the following problem arises. Figure 4 is a chart showing the change in the state of the electrochemical cell stack over time when switching the operating mode of a conventional rSOC system from SOFC mode to SOEC mode. In Figure 4, time t1 is the time when operation in SOFC mode is stopped, and time t2 is the time when operation in SOEC mode is started. As shown in Figure 4, in the conventional rSOC system, at time t2, the electrolytic current I is set to the electrolytic current I of the electrochemical cell stack as the rated current I S Start playing it.

[0043] Furthermore, when switching the operating mode from SOFC mode to SOEC mode, the heating temperature of the medium by the cell stack heater is increased to compensate for the heat lost due to the endothermic reaction. Specifically, as shown in Figure 4, the heating temperature of the medium by the cell stack heater is increased from the point t1 when the SOFC mode operation is stopped. In Figure 4, the heating temperature of the medium is increased at T F This is the heating temperature of the medium suitable for SOFC mode, and T E This is the heating temperature of the medium suitable for SOEC mode (the same applies to Figure 2).

[0044] However, even if the heating temperature of the medium by the cell stack heater is increased, it takes some time for the medium to actually rise in temperature and for the heat from the heated medium to be transferred to the electrochemical cell stack. On the other hand, when an electrolytic current I is passed through each electrochemical cell of the electrochemical cell stack, the reactions shown in equations (1) and (2) above occur, and the temperature immediately begins to decrease. As a result, as shown in Figure 4, immediately after switching from SOFC mode to SOEC mode, the cell stack temperature T temporarily decreases, and the cell stack temperature T returns to the steady state T S It takes time to return to the normal state. In other words, immediately after switching from SOFC mode to SOEC mode, the cell stack temperature T returns to the steady state T. S A period occurs where the temperature is lower than the steady state. Note that at time t3, the cell stack temperature T is equal to the steady state T. S This is the point where the temperature returns to its previous state. This period (from time t2 to time t3) is an example of the non-steady-state temperature period of the present invention. As the cell stack temperature T decreases, the internal resistance of the electrochemical cells increases, causing the voltage applied to each electrochemical cell to rise. When this voltage increases, the load on each electrochemical cell increases.

[0045] Therefore, in this embodiment, the following configuration prevents or suppresses a temporary decrease in the cell stack temperature T when switching from SOFC mode to SOEC mode. In other words, it reduces the amount of decrease in the cell stack temperature T. This shortens the transient temperature period (the period from time t2 to time t3) when switching from SOFC mode to SOEC mode.

[0046] Figure 2 is a chart showing the change in the state of the electrochemical cell stack 30 over time when switching the operating mode of the rSOC system 10 according to this embodiment from SOFC mode to SOEC mode. In Figure 2, time t1 is the time when the conditions for switching the operating mode from SOFC mode to SOEC mode are met. When the conditions for switching the operating mode from SOFC mode to SOEC mode are met (time t1), the control unit 20 stops the operation of the SOFC electrical circuit of the power conditioner 19. At the same time, the control unit 20 changes the operating conditions of the cell stack heater 32 to conditions suitable for SOFC mode. Specifically, the control unit 20 increases the heating temperature of the medium by the cell stack heater 32.

[0047] Time t2 is the point at which operation in SOEC mode begins. At time t2, the control unit 20 starts the operation of the SOEC electrical circuit of the power conditioner 19, thereby supplying the rated current I to the electrochemical cell stack 30. S A larger electrolytic current I begins to flow. With this configuration, when switching operating modes, the rated current I S Compared to a configuration that flows an electrolytic current I equal to , this configuration allows for greater Joule heating in each electrochemical cell 31. As a result, a decrease in the cell stack temperature T can be prevented or suppressed, thus shortening the transient temperature period.

[0048] However, as the electrolytic current I increases, the cell stack voltage V increases, which increases the load on each electrochemical cell 31 of the electrochemical cell stack 30. Therefore, the control unit 20 sets the cell stack voltage V to the rated voltage V S Above, the protection voltage V PThe magnitude of the electrolytic current I (more specifically, the electrolytic current I and the rated current I) should be within the following range. S Adjust the magnitude of the difference between the two. Note that the protection voltage V P This is the upper limit of the allowable cell stack voltage V. Protection voltage V P The specific value is not limited and is set appropriately depending on the configuration of the electrochemical cell stack 30, etc.

[0049] The control unit 20 determines when the cell stack voltage V is the rated voltage V S Above, the protection voltage V P The cell stack voltage V is measured using the cell stack voltmeter 15, and the magnitude of the electrolytic current I is adjusted repeatedly until the cell stack voltage V falls within the following range. S Above, the protection voltage V P If the temperature falls within the following range, the control unit 20 acquires the measurement result of the cell stack temperature T from the cell stack thermometer 17, and the acquired cell stack temperature T is the steady-state temperature T S Determine whether the above is true. The cell stack temperature T is the steady-state temperature T. S If it is less than the specified value, the control unit 20 repeats the acquisition of the measurement result of the cell stack voltage V, the determination of the cell stack voltage V, and the adjustment of the electrolytic current I. The control unit 20 then repeats the above operation until the cell stack temperature T is equal to or above the steady-state temperature. During this time, the electrochemical cell stack 30 is supplied with the rated current I. S A larger electrolytic current I flows.

[0050] Furthermore, if the magnitude of the electrolytic current I is changed, it takes a certain amount of time for the cell stack temperature T to reach the temperature corresponding to the changed electrolytic current I. For this reason, the control unit 20 sets the cell stack voltage V to the rated voltage V S Above, the protection voltage V P It is preferable to adjust the magnitude of the electrolytic current I so that it falls within the following range, wait for a certain amount of time to elapse, and then determine the cell stack temperature T.

[0051] In Figure 2, at time t3, the cell stack temperature T is equal to the steady-state temperature T. SThis indicates the point in time when the cell stack temperature T reaches the steady-state temperature T. The control unit 20 indicates when the cell stack temperature T reaches the steady-state temperature T. S When it reaches (i.e., at time t3), the electrolytic current I is set to the rated current I S Set to this.

[0052] The operation is more specific as follows: The power conditioner 19, in accordance with the control of the control unit 20, starts to supply an electrolytic current I to the electrochemical cell stack 30 at time t2. At this time, the control unit 20 controls the electrolytic current I, Electrolysis current I = rated current I S +Initial increment current α Equation (5) Set to this value. This initial increment current α has a value greater than 0.

[0053] The control unit 20 sets the electrolytic current I as shown in equation (5) above, then obtains the measurement result of the cell stack voltage V from the cell stack voltmeter 15, and the obtained cell stack voltage V is set to the rated voltage V S Above, the protection voltage V P The control unit 20 determines whether the cell stack voltage V is within the following range. P If it is greater than, the electrolytic current I Electrolysis current I = rated current I S +Initial incremental current α-Sequential decrement current α1 Formula (6) The settings are configured as follows. Note that the successive decrementing current α1 is a current with a value greater than 0. Also, the absolute value of the successive decrementing current α1 is smaller than the absolute value of the initial incrementing current α. Meanwhile, the control unit 20 sets the cell stack voltage V to the rated voltage V S If it is less than, the electrolytic current I is Electrolysis current I = rated current I S +Initial increment current α + Sequential increment current α Equation (7) Set to the specified value. Note that the absolute value of the sequentially increasing current α2 is greater than 0 and less than the sequentially decreasing current α1. By setting the absolute value of the sequentially increasing current α2 in this way, a rapid increase in the cell stack voltage V due to a rapid increase in the electrolytic current I is prevented or suppressed.

[0054] Then, the control unit 20 determines that the cell stack voltage V is the rated voltage V S Above, the protection voltage V P The cell stack voltage V is acquired and the electrolytic current I is adjusted repeatedly until it falls within the following range. That is, the control unit 20 adjusts the electrolytic current I according to the magnitude of the cell stack voltage V at the time the measurement result of the cell stack voltage V is acquired. Electrolytic current I = Electrolytic current I at the time of cell stack voltage acquisition - successive decreasing current α Equation (8) or Electrolytic current I = Electrolytic current I at the time of cell stack voltage acquisition + successively increasing current α Equation 2 (9) Set to this.

[0055] The control unit 20 determines when the cell stack voltage V is the rated voltage V S Above, the protection voltage V P If the electrolytic current I falls within the following range, it is maintained at that value thereafter. Then, after a predetermined time has elapsed, the control unit 20 acquires the measurement result of the cell stack temperature T from the cell stack thermometer 17, and the acquired cell stack temperature T is set to a predetermined steady-state temperature T. S Determine whether the value is greater than or equal to the specified value.

[0056] The control unit 20 determines when the cell stack temperature T is at the steady state T S If it is less than the given value, the measurement of the cell stack voltage V, determination of the cell stack voltage V, adjustment of the electrolytic current I shown in equation (7) or equation (8), and waiting for a predetermined time are repeated. That is, the control unit 20 determines when the cell stack temperature T is less than the steady state temperature T S The above operation is repeated until the above is reached. Meanwhile, the control unit 20 checks when the cell stack temperature T reaches the steady state temperature T. S If the above is reached (i.e., at time t3), the electrolytic current I is set to the rated current I. S Set to this.

[0057] This operation makes it possible to shorten the transient temperature period (the period from time t2 to time t3 in Figure 2) that occurs when the operating mode is switched to SOEC mode. In addition, the control unit 20 controls the cell stack voltage V to the rated voltage V S Above, the protection voltage V P The electrolytic current I is adjusted to fall within the following range. This reduces the load on each electrochemical cell 31 of the electrochemical cell stack 30.

[0058] Furthermore, simultaneously with the start of operation in SOEC mode (or immediately after switching), the electrolytic current I is set to the rated current I. S If the configuration is made larger than the rated current I, the Joule heating can be increased before the internal resistance of each electrochemical cell 31 increases significantly due to the decrease in temperature. S Even when the value is increased, the rise in the cell stack voltage V can be prevented or suppressed. Therefore, the electrolysis current I can be increased while preventing or suppressing an increased load on the electrochemical cell 31, thereby greatly enhancing the effect of shortening the transient temperature period.

[0059] However, although the configuration shown involves increasing the electrolytic current I simultaneously with the start of operation in SOEC mode (or immediately after switching), the configuration is not limited to this. That is, the cell stack temperature T rises to the steady state temperature T due to the switch to the endothermic reaction. S While it is less than the rated current I, the electrolytic current I is set to the rated current I. S Any configuration that starts increasing the current I to a higher value is acceptable. Such a configuration can shorten the transient temperature period. For example, the point at which the electrolytic current I is increased can be any point before the cell stack temperature T stops decreasing (stops decreasing). Alternatively, even after the cell stack temperature T stops decreasing, any point before time t3 is acceptable. In other words, the rated current I can be increased at least for a portion of the transient temperature period. S Any configuration that allows a larger electrolytic current I to flow through the electrochemical cell stack 30 is acceptable.

[0060] Furthermore, although the above description shows a configuration in which the electrolytic current I is adjusted according to the cell stack voltage V, the system is not limited to this configuration. For example, the control unit 20 may adjust the electrolytic current I according to the voltage applied to each electrochemical cell 31. In this case, the control unit 20 calculates the average value of the voltage applied to each electrochemical cell 31 (the potential difference between the fuel electrode and the air electrode of each electrochemical cell 31) from the cell stack voltage V obtained from the cell stack voltage meter 15 (= (cell stack voltage V) / (number of electrochemical cells 31 included in the electrochemical cell stack 30)). The control unit 20 then adjusts the electrolytic current I according to whether this average value is less than or equal to the allowable voltage of each electrochemical cell 31. Alternatively, the rSOC system 10 may be equipped with a voltmeter capable of measuring the voltage applied to the electrochemical cells 31 instead of the cell stack voltage meter 15. In this case, the control unit 20 adjusts the electrolytic current I according to whether the voltage applied to the electrochemical cells 31 obtained from this voltmeter is greater than or less than the allowable voltage.

[0061] Also, steady temperature T S The temperature may not be a single point, but may have a certain range. In this case, the control unit 20 determines when the cell stack temperature T is the steady-state temperature T S If the electrolytic current I exceeds the lower limit, the rated current I S That's fine.

[0062] Next, we will describe the processes executed by the computer in the control unit 20. Figures 3A and 3B are flowcharts showing the processes executed by the computer in the control unit 20. Figure 3B is a flowchart showing in detail the process (routine) of step S105 in Figure 3A. The computer program for executing this series of processes is pre-stored in the ROM of the computer in the control unit 20. The CPU of the computer in the control unit 20 reads this computer program from the ROM and executes it repeatedly at predetermined short cycles. In the following description, the computer in the control unit 20 will be simply referred to as the computer.

[0063] In step S101, the computer determines whether the current operating mode is SOEC mode or SOFC mode. If the current operating mode is SOEC mode, the computer terminates the process. If the current operating mode is SOFC mode, the computer proceeds to step S102.

[0064] In step S102, the computer determines whether the conditions for switching the operating mode from SOFC mode to SOEC mode have been met. If the computer determines that the conditions have not been met, it terminates this series of processes. If the computer determines that the conditions have been met, it proceeds to step S103.

[0065] In step S103, the computer stops operation in SOFC mode. Specifically, the computer stops sweeping power from the electrochemical cell stack 30 by the power conditioner 19. At the same time, the computer switches the operating conditions of the cell stack heater 32 to conditions suitable for operation in SOEC mode. Specifically, the computer increases the heating temperature of the medium by the cell stack heater 32. Then, the computer proceeds to step S104.

[0066] In step S104, the computer switches the electrical circuit of the power conditioner 19 to be operated from the SOFC electrical circuit to the SOEC electrical circuit. Then the computer proceeds to step S105.

[0067] In step S105, the computer performs the process of supplying an electrolytic current I to the electrochemical cell stack 30. Specifically, in step S201, the computer starts the operation of the SOEC electrical circuit on the power conditioner 19. This starts the supply of an electrolytic current I from the power conditioner 19 to the electrochemical cell stack 30. At this time, the computer sets the electrolytic current I supplied from the power conditioner 19 to the electrochemical cell stack 30 to the value shown in equation (5). Then, the computer proceeds to step S202.

[0068] In step S202, the computer obtains the measurement result of the cell stack voltage V from the cell stack voltmeter 15. Then, the computer proceeds to step S203.

[0069] In step S203, the computer determines that the acquired cell stack voltage V is equal to the protection voltage V P The computer determines whether the following is true: the cell stack voltage V is the protection voltage V P If it is greater than, proceed to step S204. Meanwhile, the computer checks if the cell stack voltage V is greater than the protection voltage V P If the following conditions are met, proceed to step S205.

[0070] In step S204, the computer reduces the electrolytic current I. Specifically, the computer sets the electrolytic current I to the value shown in equation (8). Then, the computer returns to step S202.

[0071] In step S205, the computer determines that the cell stack voltage V is the rated voltage V S It determines whether the value is less than or equal to the rated voltage V. Then, the computer determines whether the cell stack voltage V is less than or equal to the rated voltage V. S If it is less than, proceed to step S206. Meanwhile, the computer checks if the cell stack voltage V is less than the rated voltage V S If the above conditions are met, proceed to step S207.

[0072] In step S206, the computer increases the electrolytic current I. Specifically, the computer sets the electrolytic current I to the value shown in equation (9). Then, the computer returns to step S202.

[0073] In step S207, the computer determines whether a predetermined time has elapsed since the cell stack voltage V was obtained in step S202. If the predetermined time has not elapsed, the computer temporarily suspends the process in this step. If the predetermined time has elapsed, the computer proceeds to step S208.

[0074] In step S208, the computer obtains the measurement result of the cell stack temperature T from the cell stack thermometer 17. Then, the computer proceeds to step S209.

[0075] In step S209, the computer determines that the cell stack temperature T is the steady state temperature T S Determine whether the above is true. The cell stack temperature T is the steady-state temperature T. S If it is less than, return to step S202. S If the above conditions are met, the computer proceeds to step S210.

[0076] In step S210, the electrolytic current I is set to the rated current I S This is set to the rated operating state. The computer then sets the electrolytic current I flowing through the electrochemical cell stack 30 to the rated current I. S Maintain it.

[0077] This process achieves the operation described above. While the above explanation shows a process of immediately increasing the electrolytic current I at the time of switching, the process is not limited to this.

[0078] Although embodiments of this disclosure have been described above, the technology relating to this disclosure should not be limited to the embodiments described above. The technology relating to this disclosure can be modified without departing from its spirit.

[0079] Furthermore, this disclosure may include the following aspects:

[0080] [1] An electrochemical cell stack capable of reversibly performing both power generation as a solid oxide fuel cell and electrolysis as a solid oxide steam electrolysis cell, A power supply unit capable of supplying current to the electrochemical cell stack, A reversible SOC system comprising, configured to be switchable between operation in SOFC mode, in which the electrochemical cell stack generates electricity, and operation in SOEC mode, in which the electrochemical cell stack generates hydrogen, The power supply unit, during at least a portion of the transient temperature period, which is the period in which the temperature of the electrochemical cell stack temporarily drops below the steady temperature (the temperature when operating at rated capacity in SOEC mode) when switching from SOFC mode to SOEC mode, supplies a current greater than the rated current (the current when operating at rated capacity in SOEC mode) to the electrochemical cell stack, and after the transient temperature period has elapsed, supplies the rated current to the electrochemical cell stack. Reversible SOC system.

[0081] [2] The reversible SOC system described in [1]1 above, The power supply unit starts supplying a current greater than the rated current to the electrochemical cell stack before the temperature of the electrochemical cell stack stops decreasing during the non-steady temperature period. Reversible SOC system.

[0082] [3] The reversible SOC system described in [1] or [2] above, The power supply unit, upon switching from SOFC mode operation to SOEC mode operation, simultaneously begins supplying a current greater than the rated current to the electrochemical cell stack. Reversible SOC system.

[0083] [4] A reversible SOC system according to any one of the above [1] to [3], During the non-steady temperature period, if the voltage applied to the electrochemical cell stack exceeds a threshold while a current greater than the rated current is flowing through the electrochemical cell stack, the power supply unit reduces the current flowing through the electrochemical cell stack. Reversible SOC system.

[0084] [5] A reversible SOC system according to any one of the above [1] to [4], The power supply unit increases the current flowing through the electrochemical cell stack if, during the non-steady temperature period, the voltage applied to the electrochemical cell stack is less than the voltage applied while the rated current is flowing. Reversible SOC system. [Explanation of Symbols]

[0085] 10…Reversible SOC system, 19…Power conditioner, 20…Control unit, 30…Electrochemical cell stack, 31…Electrochemical cell, 32…Cell stack heater

Claims

1. An electrochemical cell stack capable of reversibly performing both power generation as a solid oxide fuel cell and electrolysis as a solid oxide steam electrolysis cell, A power supply unit capable of supplying current to the electrochemical cell stack, A reversible SOC system comprising, configured to be switchable between operation in SOFC mode, in which the electrochemical cell stack generates electricity, and operation in SOEC mode, in which the electrochemical cell stack generates hydrogen, The power supply unit, during at least a portion of the non-steady-state temperature period, which is the period in which the temperature of the electrochemical cell stack temporarily drops below the steady-state temperature (the temperature when operating at rated capacity in SOEC mode) when switching from SOFC mode to SOEC mode, supplies a current greater than the rated current (the current when operating at rated capacity in SOEC mode) to the electrochemical cell stack, and after the non-steady-state temperature period has elapsed, supplies the rated current to the electrochemical cell stack. Reversible SOC system.

2. A reversible SOC system according to claim 1, The power supply unit starts supplying a current greater than the rated current to the electrochemical cell stack before the temperature of the electrochemical cell stack stops decreasing during the non-steady temperature period. Reversible SOC system.

3. A reversible SOC system according to claim 2, The power supply unit, upon switching from SOFC mode operation to SOEC mode operation, simultaneously begins supplying a current greater than the rated current to the electrochemical cell stack. Reversible SOC system.

4. A reversible SOC system according to any one of claims 1 to 3, During the non-steady temperature period, if the voltage applied to the electrochemical cell stack exceeds a threshold while a current greater than the rated current is flowing through the electrochemical cell stack, the power supply unit reduces the current flowing through the electrochemical cell stack. Reversible SOC system.

5. A reversible SOC system according to claim 4, The power supply unit increases the current flowing through the electrochemical cell stack if, during the non-steady temperature period, the voltage applied to the electrochemical cell stack is less than the voltage applied while the rated current is flowing. Reversible SOC system.

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