Solid-oxide cell system

Abstract

A solid-oxide cell system (1) includes a solid-oxide cell module (100) comprising at least one solid-oxide cell stack (10) and can be switched between an SOFC mode and an SOEC mode. The cell system (1) is controlled so that the solid-oxide cell stack (10) which is to be switched from one of the SOEC and SOFC modes to the other is continuously operated in said one mode and the temperature of the solid-oxide cell stack (10) is made closeer to a preset operation temperature for the other mode, by the heat reaction of the solid-oxide cell stack (10) operating in said one mode.

Description

Solid Oxide Cell System

[0001] The present disclosure relates to solid oxide cell systems.

[0002] A solid oxide fuel cell (SOFC) can output electricity and heat using hydrogen, hydrocarbon, or carbon monoxide as a raw material. It can also function as a solid oxide electrolysis cell (SOEC), which performs the reverse reaction of electrolysis, electrolyzing water vapor or carbon dioxide into hydrogen, carbon monoxide, or oxygen. A power storage and supply system using a reversible SOEC (solid oxide cell) capable of both power generation and electrolysis has been proposed (see, for example, Patent Document 1).

[0003] Patent No. 6881007

[0004] Typically, power storage and supply systems have a stack structure consisting of multiple stacked SOCs. In systems using conventional reversible SOCs, the operating temperatures differ for each operating mode, so switching between operating modes is accompanied by temperature changes. However, sudden temperature changes in the SOC can cause physical damage to the SOC due to heat, potentially reducing its durability.

[0005] The present disclosure discloses a technology for solving the above-mentioned problems, and aims to provide a solid oxide cell system that can suppress a decrease in durability of the SOC by controlling the temperature change of the SOC stack so that it does not change suddenly when switching operating modes.

[0006] The solid oxide cell system of the present disclosure comprises a solid oxide cell module having at least one solid oxide cell stack switchable between an SOFC mode in which a first gas is used to generate and output electric power, and an SOEC mode in which electric power is input and a second gas is electrolyzed, and a control device for controlling the operation of the solid oxide cell stack, wherein the control device is configured to operate the solid oxide cell stack, which switches from one of the SOEC mode and the SOFC mode to the other mode, continuously in the one mode, and to bring the temperature of the solid oxide cell stack close to a preset operating temperature for the other mode through a thermal reaction of the solid oxide cell stack due to operation in the one mode.

[0007] According to the solid oxide cell system of the present disclosure, it is possible to prevent a sudden change in the temperature of the SOC stack when switching between operation modes, and to suppress a decrease in the durability of the SOC stack.

[0008] 1 is a diagram showing the configuration of a solid oxide cell system according to embodiment 1. FIG. 2 is a diagram showing the configuration of an SOC stack according to embodiment 1. FIG. 3 is a diagram for explaining operation in SOFC mode in the solid oxide cell system according to embodiment 1. FIG. 4 is a diagram for explaining operation in SOEC mode in the solid oxide cell system according to embodiment 1. FIG. 5 is a diagram showing the relationship between the difference between the heat generation amount and the heat absorption amount of the SOC stack corresponding to the operation mode and the applied voltage. FIG. 6 is a diagram showing patterns of input / output control and temperature control of the SOC stack provided in the solid oxide cell system according to embodiment 1. FIG. 7 is a flowchart for explaining a control method when switching the operation mode of the SOC stack provided in the solid oxide cell system according to embodiment 1. FIG. 8 is a flowchart for explaining a control method when switching the operation mode of the SOC stack provided in the solid oxide cell system according to embodiment 1. FIG. 9 is a diagram showing patterns of input / output control and temperature control of the SOC stack provided in the solid oxide cell system according to embodiment 1. FIG. 10 is a flowchart for explaining a control method when switching the operation mode of the SOC stack provided in the solid oxide cell system according to embodiment 1. FIG. 2 is a diagram showing an example of the hardware configuration of a control device of the solid oxide cell system according to the first embodiment.

[0009] An embodiment of a solid oxide cell system according to the present disclosure will be described below with reference to the drawings. This disclosure focuses on a solid oxide cell system using a reversible SOC that has both SOFC and SOEC functions. Note that the same reference numerals in each drawing indicate the same or corresponding parts. Therefore, detailed descriptions of these parts may be omitted to avoid duplication. In the following, a solid oxide cell will be referred to as an SOC, a solid oxide cell stack will be referred to as an SOC stack, and a solid oxide cell module will be referred to as an SOC module. The operating mode in which the SOC stack operates as an SOFC will be referred to as the SOFC mode, and the operating mode in which it operates as an SOEC will be referred to as the SOEC mode.

[0010] First Embodiment A solid oxide cell system according to a first embodiment will be described below with reference to the drawings. <Configuration of the solid oxide cell system> Fig. 1 is a diagram showing the configuration of a solid oxide cell system according to a first embodiment, and Fig. 2 is a diagram showing the configuration of an SOC stack. In Fig. 1, the solid oxide cell system 1 includes a gas supply unit 21 that supplies the raw material gas required in the SOFC mode, and a gas supply unit 22 that supplies water vapor (H ２ The solid oxide cell system 1 includes a water vapor supply unit 22 that supplies a gas (water vapor) containing oxygen (O), a temperature adjustment device 20 that adjusts the temperature of the supplied gas and water vapor, an SOC module 100 to which gas adjusted to a preset temperature by the temperature adjustment device 20 is supplied, and a control device 200 that switches the operation modes of the temperature adjustment device 20 and the SOC module 100 and controls the opening and closing of valves V1-V6 provided in the gas piping. These constitute the main components 1A of the solid oxide cell system 1 shown by the dotted line area in Fig. 1. An external device 300 is connected to the SOC module 100. The external device 300 is a load to which power generated by the SOC module 100 in the SOFC mode is supplied, or a current source that supplies power to the SOC module 100 in the SOEC mode.

[0011] The SOC module 100 is an assembly of multiple SOC stacks 10_1-10_n (n is a natural number equal to or greater than 2) connected together. Each SOC stack 10 is provided with an SOC stack temperature regulator 18. The temperature regulator 18 is, for example, a heater or other heating device. Note that the SOC stacks are collectively referred to as the SOC stack 10.

[0012] <Configuration of SOC Stack> Here, the structure of the multiple SOC stacks 10 that make up the SOC module 100 will be described with reference to Fig. 2. The SOC module 100 is an assembly of multiple SOC stacks 10_1-10_n (n is a natural number of 2 or more) connected together. Each SOC stack 10 is configured by stacking multiple SOCs 11_1-11_m (m is a natural number of 2 or more).

[0013] Taking the kth (1<k≦m; k is a natural number) SOC11_k as an example, each SOC11 has a structure in which an electrolyte 13 is sandwiched between an air electrode 12 and an anode 14, and is connected to adjacent SOC11s by an interconnector 15. A diffusion prevention layer to suppress material degradation may be inserted between the air electrode 12 and the electrolyte 13. Note that SOCs are collectively referred to as SOC11.

[0014] The control device 200 includes a system control unit 201 and a temperature control unit 202. The system control unit 201 switches the operation mode of the SOC module 100 and controls the opening and closing of valves V1 to V6 provided in the gas piping. The temperature control unit 202 controls the temperature adjustment device 20 so that the supplied gas and steam reach a preset temperature, and also controls the SOC stack temperature regulator 18 so that each SOC stack 10 reaches a preset temperature.

[0015] As described above, the external device 300 is a load or a current source. The load to which the power generated by the SOC module 100 in the SOFC mode is supplied is, for example, a power converter or a motor connected via a power converter. The current source to which the SOC module 100 is supplied in the SOEC mode is, for example, a power converter or a current source such as a grid. The control device 200 controls the external device 300 to control the voltage of each SOC stack.

[0016] The gas supply unit 21 supplies hydrogen (H ２ ), etc., and in SOEC mode, hydrogen, carbon dioxide (CO ２ ) or the like. A gas cylinder may be provided externally and supplied to the gas supply unit 21. In addition, the gas supplied to the air electrode in the SOFC mode may be, for example, oxygen (O ２ ), air, etc. These are also used in the SOEC mode, and since the gas species are theoretically the same during supply (upstream) and after reaction (downstream), the gas may be circulated.

[0017] The temperature adjustment device 20 adjusts the temperature of the (upstream) gas and steam pipes supplied to the SOC module 100, and is, for example, a heater or a heating device provided around the pipes. In addition, the downstream gas generated from the SOC module 100 may be used as a heat source to heat the upstream gas.

[0018] Optional components of the solid oxide cell system 1 may include a reformer 30, a steam generator 31, a water storage unit 32, a condenser 33, a gas storage unit 34, and a storage gas adjustment unit 35. The reformer 30 is used when using city gas (gas mainly composed of methane) in the SOFC mode. Downstream gas generated from the SOC module 100 may be supplied as fuel to a burner, which is a heat source during reforming.

[0019] The water vapor generator 31 heats water supplied from the water storage unit 32 to generate water vapor, and supplies the water vapor to the SOC module 100 via the water vapor supply unit 22. Water vapor may be supplied directly from the outside without using the water vapor generator 31.

[0020] The water reservoir 32 stores water to be supplied to the steam generator 31. Steam in the downstream gas on the fuel electrode side discharged from the SOC module 100 may be recovered and reused as supply gas or fuel for the reformer 30.

[0021] The condenser 33 dehydrates the downstream gas on the fuel electrode side discharged from the SOC module 100. For example, in the SOFC mode, the condenser 33 separates the water vapor generated in the SOC module 100 from unreacted hydrogen and the like by dehydration, and in the SOEC mode, the condenser 33 separates the hydrogen and the like generated in the SOC module 100 from unreacted water vapor by dehydration.

[0022] The gas storage unit 34 recovers the downstream gas (hydrogen, etc.) on the fuel electrode side discharged from the SOC module 100 in the SOEC mode and stores it as the upstream gas on the fuel electrode side required in the SOFC mode. The gas discharged from the SOC module 100 may be directly supplied to the outside of the system.

[0023] The storage gas adjusting unit 35 adjusts the gas by appropriately processing it in order to store it in the gas storage unit 34. For example, the form of the gas is adjusted by compressing the gas using a compressor, separating a mixed gas of, for example, hydrogen and carbon monoxide (CO), which is the gas downstream on the fuel electrode side discharged from the SOC module 100 in the SOEC mode, using a separator, or synthesizing methane using hydrogen and carbon monoxide (CO) in a methanation reactor. The gas adjusted by the storage gas adjusting unit 35 is stored in the gas storage unit 34.

[0024] In Figure 1 and the following figures showing the configuration of a solid oxide cell system, each line indicates the following: Solid line: Pre-reaction gas flow path (upstream) Dash-dotted line: Post-reaction gas flow path (downstream) Dashed line: Flow path for gases used other than fuel cells and steam electrolysis reactions Black arrow: Gases supplied to or discharged from the fuel electrode (hydrogen, nitrogen, carbon monoxide, hydrocarbons, water vapor, carbon dioxide, etc.) Open arrow: Gases supplied to or discharged from the air electrode (oxygen, air, etc.)

[0025] <Operation in SOFC Mode> Next, the operation of the solid oxide cell system 1 in the SOFC mode will be described. Figure 3 shows the gas flow in the SOFC mode in Figure 1, indicated by the bold line. In the SOFC mode, gases described below are supplied to the anode 14 and the cathode 12, respectively, and the generated electric power is output.

[0026] (1) Gas Supply to SOC Module 100 (Upstream) A gas containing hydrogen as its main component is supplied to the fuel electrode 14 side. The gas containing hydrogen as its main component is supplied from the gas supply unit 21 to the SOC module 100 via the temperature adjustment device 20. A gas containing hydrogen as its main component may be supplied from the gas storage unit 34. A gas containing methane as its main component may be supplied to the fuel electrode 14 side. The gas containing methane as its main component may be supplied from the gas storage unit 34 to the SOC module 100 via the temperature adjustment device 20. Alternatively, the gas may be supplied from the outside via the reformer 30. Alternatively, the gas may be supplied from the gas storage unit 34 via the reformer 30. In the reformer 30, steam reforming is carried out using steam supplied from the water storage unit 32 through the following reaction, and the reformed gas is supplied to the fuel electrode 14 side. CH ４ +H ２ O → CO + 3H ２ As will be explained below, when the SOC module 100 is not operating in SOFC mode and is undergoing temperature adjustment or is at rest, a purge gas or reducing gas containing hydrogen and nitrogen as its main components is supplied from the gas supply unit 21 or the gas storage unit 34 to the fuel electrode 14 side of the SOC stack 10.

[0027] Oxygen or air is supplied to the air electrode 12 side from a gas supply unit 21. Oxygen or air is also supplied to the air electrode 12 side of the SOC stack 10 of the SOC module 100 that is not operating in SOFC mode and is undergoing temperature adjustment or is at rest. In gas supply to the SOC module 100, the gas supply source to the anode 14 side is determined by the opening and closing direction of valve V1. When the gas supplied to the anode 14 side is a gas mainly composed of methane, the opening and closing direction of valve V2 is controlled to supply the gas mainly composed of methane from a gas storage unit 34 to the reformer 30. The opening and closing direction of valve V3 is determined by whether or not gas is supplied from the reformer 30. These valves V1 to V3 are three-way valves, and their opening and closing directions are controlled by a system control unit 201.

[0028] (2) Gas Discharge from the SOC Module 100 (Downstream) When a gas containing hydrogen as a main component is supplied from the fuel electrode 14 side, water vapor and unreacted hydrogen, etc. are discharged, and when a gas containing methane as a main component is supplied, water vapor and carbon dioxide, etc. are discharged. The discharged gas may be discharged directly to the outside, or, as shown in FIG. 3 , the water vapor and other gases may be separated in a condenser 33, and then the hydrogen and carbon dioxide, etc. may be separated in a storage gas adjustment unit 35. The water vapor may be stored in a water reservoir 32. Unreacted oxygen or air is discharged from the air electrode 12 side. The discharged gas may be returned to the gas supply unit 21 to circulate through the system.

[0029] When gas is exhausted from the SOC module 100, water can be supplied from the water reservoir 32 when the reformer 30 is operating by opening and closing the valve V5. Also, part of the exhaust gas can be supplied as fuel for the heat supply burner of the reformer 30 by opening and closing the valve V4. The valve V4 is a three-way valve, and the valve V5 is an on-off valve, and the opening and closing directions and opening and closing operations are controlled by the system control unit 201.

[0030] The temperature adjustment device 20 may be provided with a heat exchange function so that the supply gas is heated by heat exchange with the exhaust gas. During operation, the temperatures of the temperature adjustment device 20, the SOC stack temperature regulator 18, and the reformer 30 are controlled to the respective set temperatures by a temperature control unit 202.

[0031] <Operation in SOEC Mode> Next, the operation of the solid oxide cell system 1 in the SOEC mode will be described. Figure 4 shows the gas flow in the SOEC mode in Figure 1, indicated by the bold line. In the SOEC mode, gases described below are supplied to the anode 14 and cathode 12, respectively, and an electrolysis reaction occurs due to the input power.

[0032] (1) Gas Supply to SOC Module 100 (Upstream) A gas containing water vapor as a main component is supplied to the anode 14 side from a water vapor supply unit 22. Water vapor may be introduced directly from the outside, or water supplied from a water reservoir 32 may be heated by a water vapor generator 31 to generate water vapor, as shown in FIG. 4 . Alternatively, hydrogen may be supplied from a gas storage unit 34 or a gas supply unit 21, mixed with water vapor by a temperature adjustment device 20, and supplied to the anode 14 side. Alternatively, a gas containing carbon dioxide as a main component may be supplied to the anode 14 side from the gas supply unit 21. At this time, a mixed gas of water vapor and carbon dioxide may be supplied to the anode 14 side. As will be described below, a purge gas or reducing gas containing hydrogen and nitrogen as main components is supplied from the gas supply unit 21 or a gas storage unit 34 to the anode 14 side of the SOC stack 10 of the SOC module 100 that is not operating in the SOEC mode and is undergoing temperature adjustment or is at rest.

[0033] Oxygen or air is supplied to the air electrode 12 side from a gas supply unit 21. Oxygen or air is also supplied to the air electrode 12 side of the SOC stack 10 of the SOC module 100 that is not operating in the SOEC mode and is undergoing temperature adjustment or is at rest. In supplying gas to the SOC module 100, the gas supply source to the fuel electrode 14 side is determined by the opening and closing direction of valve V1 and the opening and closing of valve V6. Valve V1 is a three-way valve, and valve V6 is an on-off valve, and the opening and closing direction and opening and closing operation are controlled by a system control unit 201.

[0034] (2) Gas Discharge (Downstream) from the SOC Module 100 When a gas primarily composed of water vapor is supplied, hydrogen and unreacted water vapor are discharged from the fuel electrode 14 side. When a gas primarily composed of carbon dioxide is supplied, carbon monoxide and unreacted carbon dioxide are discharged. The discharged gas may be discharged directly to the outside of the system. However, as shown in FIG. 4 , the water vapor and other gases may be separated in a condenser 33, and then the hydrogen and carbon monoxide may be separated in a storage gas adjustment unit 35. Alternatively, the mixed gas containing hydrogen and carbon monoxide may be introduced as is into the methanation reactor to produce methane. Gases such as hydrogen, carbon monoxide, and methane processed in the storage gas adjustment unit 35 are stored in a gas storage unit 34. Unreacted water vapor may be stored in a water reservoir 32 and then supplied to the fuel electrode 14 again. Generated oxygen or air with a high oxygen concentration is discharged from the air electrode 12 side. The discharged gas may be returned to the gas supply unit 21 to circulate through the system.

[0035] The temperature adjustment device 20 may be provided with a heat exchange function so that the supply gas is heated by heat exchange with the exhaust gas. Also, the steam generator 31 may be provided with a heat exchange function so that steam is generated by heat exchange with the exhaust gas. As in the SOFC mode, the temperature of the temperature adjustment device 20 during operation and the temperature of the SOC stack temperature regulator 18 are controlled to respective set temperatures by the temperature control unit 202.

[0036] <Relationship between Operation Mode and Amount of Heat Generated and Amount of Heat Absorbed by SOC Stack> Figure 5 is a diagram showing an example of the relationship between the SOC stack voltage and the difference between the amount of heat generated and the amount of heat absorbed in the SOC stack, relative to the input / output current density of the SOC stack at a certain temperature. In the diagram, the solid line indicates the SOC stack voltage, and the dashed dotted line indicates the difference between the amount of heat generated and the amount of heat absorbed in the SOC stack. Note that the voltage OCV (Open Circuit Voltage) in the diagram is the open circuit voltage.

[0037] The positive current density side is where the SOC stack generates power in SOFC mode, i.e., the current output side. The hydrogen combustion reaction (oxidation reaction) during power generation is an exothermic reaction, and the amount of heat generated increases as the output current density of the SOC stack increases. Therefore, if the SOC stack does not dissipate heat to the outside, the SOC stack temperature will rise.

[0038] The negative current density side is the input side where current is input to the SOC stack and electrolysis is performed in SOEC mode. Electrolysis is an endothermic reaction, but Joule heat (RI) is generated due to the electrical resistance of the SOC and peripheral components such as the interconnector. ２ ) also occurs. When the input current density to the SOC stack increases, the SOC stack voltage decreases to the thermal neutral voltage V ｔｈ The amount of heat absorbed exceeds the amount of heat generated until the temperature reaches 1000 K. Therefore, if there is no heat supply from outside the SOC stack, the temperature of the SOC stack will decrease. Hereinafter, the exothermic reaction and endothermic reaction in the SOC stack will be collectively referred to as thermal reaction.

[0039] The input current density to the SOC stack further increases, and the SOC stack voltage reaches the thermal neutral voltage V ｔｈ If the heat generated exceeds the heat absorbed, and there is no heat dissipation from the SOC stack to the outside, the SOC stack temperature will rise.

[0040] <Control Method When Switching Operation Mode from SOEC Mode to SOFC Mode> Next, a control method when switching operation mode from SOEC mode to SOFC mode in the solid oxide cell system 1 according to the first embodiment will be described with reference to Figures 6, 7A, and 7B. Figure 6 shows the magnitude of input / output of the SOC stack 10 and the time transition of the operating temperature of the SOC stack 10 when switching operation mode from SOEC mode to SOFC mode. The input / output current density of the SOC stack 10 is shown in arbitrary units from -3 to +3, with the positive direction representing the SOFC mode in which power is output to the outside, and the negative direction representing the SOEC mode in which electrolysis is performed by input from the outside. In addition, generally, the SOEC operating temperature T ＥＣ is the SOFC operating temperature T ＦＣ Since the temperature is set higher, the SOC stack 10 is ＥＣFrom the SOEC mode operating at the SOFC operating temperature T ＦＣ The temperature is lowered to operate in the SOFC mode.

[0041] In Fig. 6, first, the SOC stack 10 operates in the SOEC mode and is compatible with an input of "2 or more". At this time, the gas supply is as described with reference to Fig. 4. When the SOC stack 10 switches its operation mode from the SOEC mode to the SOFC mode, the system control unit 201 first checks whether the voltage of the SOC stack 10 is equal to the thermal neutral voltage V ｔｈ The input is controlled so that the thermal neutral voltage V ｔｈ The magnitude of the input corresponding to is "2". The stack voltage is the thermal neutral voltage V ｔｈ When the input is controlled so that the stack voltage is less than the thermal neutral voltage V ｔｈ Since the amount of heat generated exceeds the amount of heat absorbed until the temperature of the SOC stack 10 reaches the SOEC operating temperature T ＥＣ The stack voltage is maintained at the thermal neutral voltage V ｔｈ When the time t ＳＷ When the temperature of the SOC stack 10 reaches the SOFC operating temperature T ＦＣ When the voltage reaches 1 V, the system control unit 201 switches the SOC stack 10 to output control, and also switches the gas supply to the power generation gas supply described with reference to FIG. 3, causing the stack to operate in the SOFC mode.

[0042] As the temperature of the SOC stack 10 decreases, the resistance increases, and the amount of heat generated by electrical resistance increases for the same input. Therefore, the system control unit 201 adjusts the stack input amount in accordance with the temperature decrease. For example, as shown in FIG. 6, the thermal neutral voltage V ｔｈ By gradually and gently decreasing the input until the temperature reaches 0°C, the increase in the amount of heat generated is suppressed, the difference between the amount of heat generated and the amount of heat absorbed is maximized, and the temperature is controlled to decrease. After that, the input is set to "0".

[0043] As shown by the dashed line, at time t ＳＷ Time t before reaching ｒｅｓｔWhen the temperature of the SOC stack 10 reaches the SOFC operating temperature T ＦＣ and at time t ｒｅｓｔ and time t ＳＷ A temperature stabilization time for stabilizing the temperature may be provided between the above steps, and an input / output pause period for suspending input / output may be set.

[0044] <Cooling of SOC stack> Next, specific system control and temperature control procedures when switching the operation mode of the SOC stack 10 from the SOEC mode to the SOFC mode will be described with reference to Figures 7A and 7B. When switching the operation mode from the SOEC mode to the SOFC mode, first, the SOEC operating temperature T ＥＣ If heat is being supplied to the SOC stack 10 to maintain the temperature at the predetermined temperature, the temperature control unit 202 stops the heat supply. The heat supply may be, for example, a heater of the SOC stack temperature regulator 18 provided in the SOC stack 10, and may also include other heat supply sources if there are any (step S101).

[0045] Next, when the temperature of the SOC stack 10 reaches the SOFC operating temperature T ＦＣ The system control unit 201 controls the stack voltage to reach the thermal neutral voltage V ｔｈ The temperature is controlled within a range of less than 100°C (step S102). Next, it is determined whether to provide a temperature stabilization time for stabilizing the temperature when the operation mode is switched (step S103).

[0046] When the temperature settling time is set (Yes in step S103), the stack voltage is set to the thermal neutral voltage V ｔｈ When the temperature of the SOC stack 10 is controlled within a range of less than the SOFC operating temperature T ＦＣ This is because it is determined whether the SOFC operating temperature T ＦＣ It is to determine whether or not

[0047] SOFC operating temperature T ＦＣIf it is determined that the temperature does not reach the predetermined value (No in step S104), a means for cooling the temperature of the SOC stack 10 is added to reduce the temperature and accelerate the rate of reduction (step S105). In this state, the gas described with reference to Fig. 4 is supplied to the SOC stack 10, so that, for example, the temperature of the gas supplied by the temperature adjustment device 20 may be reduced, or the flow rate of the gas supplied may be increased to reduce the gas utilization rate of the SOC stack 10 and promote the endothermic reaction, or the temperature may be reduced by circulating the gas. These methods may be performed alone or in combination.

[0048] SOFC operating temperature T ＦＣ If it is determined that the temperature of the SOC stack 10 reaches the SOFC operating temperature T ＦＣ The stack voltage control continues until the voltage reaches the threshold (step S106).

[0049] The temperature of the SOC stack 10 is the SOFC operating temperature T ＦＣ When the temperature reaches the settling time (Yes in step S107), the input to the SOC stack 10 is set to 0, the gas supply is stopped, and the temperature settling time is set (step S108). ＳＷ When the temperature reaches the required value, the system control unit 201 and the temperature control unit 202 control the SOC stack 10 to operate in the SOFC mode by performing output control corresponding to the output request, gas supply and temperature control of the SOC stack 10 as described with reference to FIG. 3 (step S109).

[0050] If the temperature settling time is not set (No in step S103), the stack voltage is set to the thermal neutral voltage V ｔｈ When the temperature of the SOC stack 10 is controlled within a range of less than the SOFC operating temperature T ＦＣ (Step S110) Steps S110 to S113 are the same as steps S104 to S107 described above, and therefore the explanation will be omitted.

[0051] In step S113, the temperature of the SOC stack 10 is increased to the SOFC operating temperature T ＦＣ(Yes in step S113), the operation mode is switched. Then, the system control unit 201 and the temperature control unit 202 perform output control corresponding to the output request, gas supply described with reference to FIG. 3, and temperature control of the SOC stack 10, etc., so that the SOC stack 10 operates in the SOFC mode (step S114).

[0052] <Control Method When Switching Operation Mode from SOFC Mode to SOEC Mode> Next, specific system control and temperature control methods when switching the operation mode of the SOC stack 10 from the SOFC mode to the SOEC mode will be described with reference to Figures 8, 9A, and 9B. Figure 8 shows the magnitude of input / output of the SOC stack 10 and the time transition of the operating temperature of the SOC stack 10 when switching the operation mode from the SOFC mode to the SOEC mode. The input / output current density of the SOC stack 10 is shown in arbitrary units from -3 to +3, with the positive direction representing the SOFC mode in which power is generated and output to the outside, and the negative direction representing the SOEC mode in which electrolysis is performed by input from the outside. In addition, generally, the SOEC operating temperature T ＥＣ is the SOFC operating temperature T ＦＣ Since the temperature is set higher, the SOC stack 10 reaches the SOFC operating temperature T ＦＣ From the SOFC mode operating at the SOFC operating temperature T ＥＣ The temperature is raised to 100°C to operate the device in the SOEC mode.

[0053] In Fig. 8, first, the SOC stack 10 operates in the SOFC mode and corresponds to the output requirement of "2". At this time, the gas supply is as described with reference to Fig. 3. When the SOC stack 10 switches the operation mode from the SOFC mode to the SOEC mode, the system control unit 201 determines whether the temperature of the SOC stack 10 reaches the SOEC operating temperature T ＥＣ Adjust the output so that the temperature rises to .

[0054] The system control unit 201 adjusts the output of the SOC stack 10 in response to the temperature rise. Specifically, if the SOC stack 10 is operated in the SOFC mode so as not to reduce the output, the temperature of the SOC stack 10 rises. If the temperature rise is insufficient or the rate of rise is slow, the output is increased to "3" or heat is supplied to the SOC stack 10 to raise the temperature of the SOC stack 10. The insufficient temperature rise may be due to, for example, heat radiation loss to the outside of the SOC stack 10. Also, if the temperature of the SOC stack 10 does not reach the SOFC operating temperature T ＥＣ If it is predicted that the output will exceed this limit, the output will be reduced and controlled.

[0055] A preset time t ＳＷ By the time the temperature of the SOC stack 10 reaches the SOEC operating temperature T ＥＣ The system control unit 201 performs output control so that the output reaches the value t ＳＷ Time t before reaching ｒｅｓｔ When the temperature of the SOC stack 10 reaches the SOEC operating temperature T ＥＣ and at time t ｒｅｓｔ and time t ＳＷ A temperature stabilization time for stabilizing the temperature may be provided between the above steps, and an input / output pause period for suspending input / output may be set.

[0056] <Heating of SOC Stack> Next, specific system control and temperature control procedures when switching the operation mode of the SOC stack 10 from the SOFC mode to the SOEC mode will be described with reference to Figures 9A and 9B. When switching the operation mode from the SOFC mode to the SOEC mode, first, the temperature of the SOC stack 10 is heated to the SOEC operating temperature T ＥＣ The system control unit 201 controls the output of the SOC stack 10 so that the output voltage reaches 10 V (step S201).

[0057] Next, it is determined whether to provide a temperature stabilization time for stabilizing the temperature when switching the operation mode (step S202). If the temperature stabilization time is provided (Yes in step S202), the temperature of the SOC stack 10 is set to the SOEC operating temperature T ＥＣThis is done by determining whether the preset operation mode switching time t ＳＷ The SOEC operating temperature T ＥＣ It is to determine whether or not

[0058] SOEC operating temperature T ＥＣ If it is determined that the temperature does not reach the predetermined value (No in step S203), heat is supplied to the SOC stack 10 to increase the temperature and accelerate the rate of increase (step S204). Specifically, the output is increased or heat is supplied to the SOC stack 10 to increase the temperature of the SOC stack 10. The heat supply may be performed by heating using the SOC stack temperature regulator 18, or the like. Either the method of increasing the output or the method of supplying heat to the SOC stack 10 may be selected, or both may be combined.

[0059] The SOEC operating temperature T ＥＣ If it is determined that the output voltage Vcc reaches the predetermined value (Yes in step S203), the system control unit 201 continues to control the output of the SOC stack 10 (step S205).

[0060] The temperature of the SOC stack 10 is the SOEC operating temperature T ＥＣ When the temperature reaches the settling time (Yes in step S206), the output is set to 0, the gas supply is stopped, and the temperature settling time is set (step S207). ＳＷ When the input voltage reaches the threshold voltage, the system control unit 201 and the temperature control unit 202 perform input control corresponding to the input request, gas supply and temperature control of the SOC stack 10 as described with reference to FIG. 4, etc. so that the SOC stack 10 operates in the SOEC mode (step S208).

[0061] If the temperature stabilization time is not set (No in step S202), the temperature of the SOC stack 10 will not exceed the SOEC operating temperature T ＥＣ (Step S210) Steps S210 to S213 are the same as steps S203 to S206 described above, and therefore a description thereof will be omitted.

[0062] In step S213, the temperature of the SOC stack 10 is increased to the SOEC operating temperature T ＥＣ (Yes in step S213), the operation mode is switched. Then, the system control unit 201 and the temperature control unit 202 perform input control corresponding to the output request, gas supply and temperature control of the SOC stack 10 as described with reference to FIG. 4, etc., so that the SOC stack 10 operates in the SOEC mode (step S214).

[0063] 10 is a diagram showing an example of the hardware configuration of the control device 200 included in the solid oxide cell system according to embodiment 1. The control device 200 includes a processor 1000 and a storage device 2000. The processor 1000 includes, for example, a CPU (Central Processing Unit), an ASIC (Application Specific Integrated Circuit), a DSP (Digital Signal Processor), an FPGA (Field Programmable Gate Array), etc.

[0064] The main memory of the storage device 2000 is composed of a volatile memory device such as a random access memory, and the auxiliary memory device is a nonvolatile memory device such as a flash memory or a hard disk. The auxiliary memory device stores a predetermined program to be executed by the processor 1000, which reads and executes the program as appropriate to perform various arithmetic processing. At this time, the predetermined program is temporarily stored in the volatile memory device from the auxiliary memory device, and the processor 1000 reads the program from the volatile memory device. The processor 1000 may also output data such as arithmetic results to the volatile memory device of the storage device 2000, or may store the data in the auxiliary memory device via the volatile memory device.

[0065] In order to enable remote control, a transmitter and a receiver (neither of which are shown) may be provided as a communication module for communicating with the outside.

[0066] As described above, according to the first embodiment, the solid oxide cell system includes a solid oxide cell module having at least one solid oxide cell stack switchable between an SOFC mode, which generates electricity using a first gas and outputs electric power, and an SOEC mode, which receives electric power and electrolyzes a second gas, and a control device for controlling the operation of the solid oxide cell stack, wherein the control device operates the solid oxide cell stack continuously in one of the SOEC and SOFC modes when the solid oxide cell stack is switched from one mode to the other, and the control device operates the solid oxide cell stack in one mode, and the solid oxide cell stack's thermal reaction during operation in one mode brings the temperature of the solid oxide cell stack closer to a preset operating temperature for the other mode. This configuration enables the temperature of the SOC stack to change gradually rather than suddenly when switching between operating modes, thereby suppressing a decrease in the durability of the SOC stack. The first gas is, for example, a gas whose main component is hydrogen or a gas whose main component is methane supplied to the fuel electrode side, or oxygen or air supplied to the air electrode side, and the second gas is, for example, a gas whose main component is water vapor or a gas whose main component is carbon dioxide supplied to the fuel electrode side, or oxygen or air supplied to the air electrode side.

[0067] The control device continues to operate the SOC stack that is switching from the SOEC mode to the SOFC mode in the SOEC mode, sets the voltage of the solid oxide cell stack to be lower than the thermoneutral voltage at which the heat absorption and heat generation are balanced, and controls the temperature of the SOC stack to decrease. When a predetermined operating temperature in the SOFC mode is reached, the control device stops the input of power to the SOC stack and the supply of the second gas, and switches to the SOFC mode. The control device continues to operate the SOC stack that is switching from the SOFC mode to the SOEC mode in the SOFC mode, determines whether the predetermined operating temperature in the SOEC mode is reached through the SOFC mode operation, and if the predetermined operating temperature in the SOEC mode is not reached, controls the SOC stack to heat up to increase the temperature of the SOC stack. When the predetermined operating temperature in the SOEC mode is reached, the control device stops the output of power from the solid oxide cell stack and the supply of the first gas, and switches to the SOEC mode. This configuration enables precise temperature control during operation mode switching.

[0068] That is, the temperature change is controlled within the current operating mode in accordance with the endothermic reaction in the SOEC mode, the exothermic reaction in the SOFC mode, and the heat generation factors of the SOC stack, and taking into consideration the relationship between the input / output power (current density) of the SOC stack and the stack voltage, etc., so that the temperature change of the SOC stack can be made gradual rather than sudden. Furthermore, this effect can be obtained with a simple means that does not require a configuration for circulating a heat medium for temperature control.

[0069] The plurality of SOC stacks 10 included in the above-described SOC module 100 may be provided with pipes and valves (not shown) so as to be able to supply and discharge gases independently, and the control device may control the input and output of power so as to be able to control each operation mode independently, and may also be able to control the temperature independently. In addition to the effects of the first embodiment, the operating efficiency of the SOC module 100 can be expected to be improved by expanding the tolerance for the operation pattern and improving the ability to follow input and output requirements.

[0070] Furthermore, the plurality of SOC stacks 10 included in the above-described SOC module 100 may be configured to perform power input / output and temperature control by a control device so that the operation mode is uniformly controlled for each SOC module 100. In addition to the effects of the first embodiment, it becomes possible to control the SOC module 100 with a simple operation pattern.

[0071] Furthermore, although the above-described SOC module 100 is provided with a plurality of SOC stacks 10, the same effect can be achieved even if there is only one SOC stack 10.

[0072] Although exemplary embodiments are described in this disclosure, the various features, aspects, and functions described in the embodiments are not limited to the application of a particular embodiment, but may be applied to the embodiments alone or in various combinations. Therefore, countless variations not illustrated are anticipated within the scope of the technology disclosed in this specification. For example, this includes cases where at least one component is modified, added, or omitted.

[0073] 1: Solid oxide cell system, 10: SOC stack, 11: SOC, 12: Air electrode, 13: Electrolyte, 14: Anode, 15: Interconnector, 18: Temperature regulator for SOC stack, 20: Temperature regulator, 21: Gas supply unit, 22: Steam supply unit, 30: Reformer, 31: Steam generator, 32: Water storage unit, 33: Condenser, 34: Gas storage unit, 35: Storage gas adjustment unit, 100: SOC module, 200: Control device, 201: System control unit, 202: Temperature control unit, 1000: Processor, 2000: Storage device.

Claims

1. A solid oxide cell system comprising: a solid oxide cell module having at least one solid oxide cell stack switchable between an SOFC mode in which a first gas is used to generate electricity and output electric power, and an SOEC mode in which electric power is input and a second gas is electrolyzed; and a control device for controlling the operation of the solid oxide cell stack, wherein the control device causes the solid oxide cell stack, which is switched from one of the SOEC mode and the SOFC mode to be switched to the other mode, to continue operating in the one mode, and causes a thermal reaction of the solid oxide cell stack due to operation in the one mode to approach a preset operating temperature of the other mode.

2. The solid oxide cell system according to claim 1, wherein the control device controls the solid oxide cell stack, which switches from the SOEC mode as the one mode to the SOFC mode as the other mode, to continue to operate in the SOEC mode and controls the voltage of the solid oxide cell stack to be lower than a thermal neutral voltage at which the amount of heat absorbed by electrolysis and the amount of heat generated by the solid oxide cell stack are balanced, thereby lowering the temperature of the solid oxide cell stack.

3. The solid oxide cell system according to claim 2, wherein the control device stops the input of power to the solid oxide cell stack and the supply of the second gas when the temperature of the solid oxide cell stack reaches an operating temperature in the SOFC mode, thereby switching to the SOFC mode.

4. The solid oxide cell system according to claim 1, wherein the control device causes the solid oxide cell stack, which switches from the SOFC mode as the one mode to the SOEC mode as the other mode, to continue to operate in the SOFC mode, determines whether the operation in the SOFC mode reaches a preset operating temperature in the SOEC mode, and, if the preset operating temperature in the SOEC mode is not reached, controls the solid oxide cell stack to heat and raise the temperature of the solid oxide cell stack.

5. The solid oxide cell system according to claim 4, wherein the control device stops the output of power from the solid oxide cell stack and the supply of the first gas when the temperature of the solid oxide cell stack reaches a preset operating temperature in the SOEC mode, thereby switching to the SOEC mode.

6. A solid oxide cell system as claimed in any one of claims 1 to 3, comprising a temperature regulator for adjusting the temperature of the solid oxide cell stack and a temperature regulator for adjusting the temperatures of the first gas and the second gas, wherein the control device controls the temperature of the solid oxide cell stack by at least one of the following methods: stopping the heat supply by the temperature regulator to the solid oxide cell stack that switches from the SOEC mode to the SOFC mode, allowing it to continue operating in the SOEC mode, and increasing the flow rate of the second gas so that a preset operating temperature in the SOFC mode is reached within a preset time; and lowering the temperature of the second gas by the temperature regulator.

7. A solid oxide cell system as claimed in any one of claims 1, 4 and 5, comprising a temperature regulator for adjusting the temperature of the solid oxide cell stack and a temperature regulator for adjusting the temperatures of the first gas and the second gas, wherein the control device controls the temperature of the solid oxide cell stack by at least one of the following methods: causing the solid oxide cell stack which switches from the SOFC mode to the SOEC mode to continue to operate in the SOFC mode, and controlling the output power in the SOFC mode so that a preset operating temperature in the SOFC mode is reached within a preset time; and supplying heat to the solid oxide cell stack by the temperature regulator.

8. A solid oxide cell system according to any one of claims 1 to 3 and 6, wherein the control device, when the solid oxide cell stack to be switched from the SOEC mode to the SOFC mode reaches a preset operating temperature in the SOFC mode, stops the input of power to the solid oxide cell stack and the supply of the second gas, and switches to the SOFC mode after a preset temperature stabilization time has elapsed.

9. A solid oxide cell system as claimed in any one of claims 1, 4, 5 and 7, wherein the control device, when the solid oxide cell stack to be switched from the SOFC mode to the SOEC mode reaches a preset operating temperature in the SOEC mode, stops the output of power to the solid oxide cell stack and the supply of the first gas, and switches to the SOEC mode after a preset temperature stabilization time has elapsed.

10. A solid oxide cell system according to any one of claims 1 to 9, wherein the solid oxide cell module comprises a plurality of the solid oxide cell stacks, and the control device controls the input and output power and temperature for each of the solid oxide cell stacks.

11. A solid oxide cell system as described in any one of claims 1 to 9, wherein the solid oxide cell module comprises a plurality of the solid oxide cell stacks, and the control device uniformly controls the power and temperature input and output to the plurality of solid oxide cell stacks comprised by the solid oxide cell module.

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