Solid Oxide Cell System

Abstract

In a solid oxide fuel cell system (1) having a solid oxide fuel cell module (100) in which a plurality of solid oxide fuel cell stacks (10) are connected and capable of switching between an SOFC mode and an SOEC mode, the voltage of the plurality of solid oxide fuel cell stacks (10) during operation is acquired, and the voltage V of the acquired solid oxide fuel cell stack (10) s and a preset Value V ex The difference from is calculated, the degree of deterioration of the solid oxide fuel cell stack (10) is estimated based on the calculated difference value, and in the next operation mode, control is performed to preferentially operate the solid oxide fuel cell stack (10) with a smaller estimated degree of deterioration.

Description

Technical Field

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

Background Art

[0002] A solid oxide fuel cell (hereinafter referred to as SOFC) can output electric power and heat using hydrogen, hydrocarbons, or carbon monoxide as raw materials. Further, it can also operate as a solid oxide electrolysis cell (hereinafter referred to as SOEC) that electrolyzes water vapor or carbon dioxide into hydrogen, carbon monoxide, or oxygen in its reverse reaction. An electrolysis device using a reversible SOC (solid oxide cell) having such power generation and electrolysis functions has been proposed (see, for example, Patent Document 1).

[0003] The electrolysis device disclosed in Patent Document 1 produces hydrogen by operating in the electrolysis mode when the supplied power is equal to or higher than a threshold value, and generates electric power by operating in the power generation mode when the supplied power becomes less than the threshold value. As a result, the electrolysis device can be stably operated even when the power supply source has power fluctuations such as renewable energy. Further, when the electrolysis mode is stopped due to a power shortage, the SOC has to be heated up again, so it is more efficient to switch the operation mode and continue the operation as an electrolysis device.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In recent years, the development of reversible SOCs has advanced. In a solid oxide cell system equipped with a reversible SOC, the SOC has a stack structure in which a plurality of SOCs are stacked, and a large-capacity SOC module in which a plurality of such SOC stacks are connected has also been proposed. On the other hand, since the SOC is exposed to the reaction gas at a high temperature in both the power generation mode and the electrolysis mode, deterioration progresses. Therefore, in a large-capacity SOC module in which a plurality of SOC stacks are connected, deterioration variations occur such that the degree of deterioration differs for each SOC stack, and there is a risk that the SOC module cannot be stably operated. In the prior art, deterioration of the SOC or deterioration of the SOC stack has not been considered.

[0006] The present disclosure discloses a technique for solving the above problems. By detecting the deterioration of the SOC stack included in the SOC module and operating the SOC module based on the detected degree of deterioration, an object is to provide a solid oxide cell system capable of stable operation.

Means for Solving the Problems

[0007] The solid oxide cell system of the present disclosure has a solid oxide cell stack that can switch between an SOFC mode in which power is generated using a first gas and power is output, and an SOEC mode in which power is input and a second gas is electrolyzed, and a solid oxide cell module formed by connecting a plurality of the solid oxide cell stacks, and a control device that controls the operation of the plurality of the solid oxide cell stacks, wherein the control device has a stack voltage acquisition unit that acquires the voltages of the plurality of the solid oxide cell stacks operating in the SOFC mode or the SOEC mode, the voltage of the acquired solid oxide cell stack calculate the difference from a preset value, and the larger the calculated difference value, the the degree of deterioration of the solid oxide cell stack is estimated to be large and a degree-of-deterioration estimation unit. as the preset value, when the solid oxide cell stack is operating in the SOFC mode, use the theoretical voltage required for the power generation reaction by the first gas, and when the solid oxide cell stack is operating in the SOEC mode, use the theoretical voltage required for the electrolysis reaction by the second gas, or when the solid oxide cell stack is operating in the SOFC mode, use the theoretical voltage required for the power generation reaction by the first gas, the temperature of the solid oxide cell stack, and the theoretical operating voltage calculated using the gas pressure ratio before and after the power generation reaction by the first gas, and when the solid oxide cell stack is operating in the SOEC mode, use the theoretical voltage required for the electrolysis reaction by the second gas, the temperature of the solid oxide cell stack, and the theoretical operating voltage calculated using the gas pressure ratio before and after the electrolysis reaction by the second gas, In the next SOFC mode or the SOEC mode, perform control to preferentially operate the solid oxide cell stack with a smaller estimated degree of degradation. When there is a solid oxide cell stack whose input / output is stopped, store the degree of degradation in the previous operation mode of the solid oxide cell stack, and determine the priority of operation of the solid oxide cell stack using the stored degree of degradation.

Advantages of the Invention

[0008] According to the present disclosure, it is possible to provide a solid oxide cell system capable of stable operation.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

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Figure 6

Figure 7A

Figure 7B

Figure 7C

Figure 8A

Figure 8B

Figure 9

DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the solid oxide fuel cell system according to the present disclosure will be described with reference to the drawings. In the present disclosure, a solid oxide fuel cell system using a reversible SOC having both functions of SOFC and SOEC is targeted. In each figure, the same reference numerals denote the same or corresponding parts. Therefore, detailed description thereof may be omitted to avoid duplication. In addition, in the following, the solid oxide fuel cell is referred to as SOC, the solid oxide fuel cell stack is referred to as SOC stack, the solid oxide fuel cell module is referred to as SOC module, the operation mode in which the SOC stack operates as SOFC is referred to as SOFC mode, and the operation mode in which it operates as SOEC is referred to as SOEC mode.

[0011] <Configuration of Solid Oxide Fuel Cell System> FIG. 1 is a diagram showing the configuration of a solid oxide type cell system according to an embodiment, and FIG. 2 is a diagram showing the configuration of an SOC stack. In FIG. 1, the solid oxide type cell system 1 includes a gas supply unit 21 that supplies raw material gas required in the SOFC mode, a steam supply unit 22 that supplies steam (H2O) in the SOEC mode, a temperature adjustment device 20 that adjusts the temperature of the supplied gas and steam, an SOC module 100 to which the gas adjusted to a preset temperature by the temperature adjustment device 20 is supplied, and a control device 200 that controls the operation mode switching of the temperature adjustment device 20 and the SOC module 100 and the opening and closing of valves V1-V6 provided in the gas piping. These are the main components 1A of the solid oxide type cell system 1 shown in the dotted area of FIG. 1. An external device 300 is connected to the SOC module 100. The external device 300 is a load to which the electric power generated by the SOC module 100 in the SOFC mode is supplied or a current source that supplies electric power to the SOC module 100 in the SOEC mode.

[0012] The SOC module 100 is an aggregate in which a plurality of SOC stacks 10_1 - 10_n (n is a natural number of 2 or more) are connected. Each SOC stack 10 is provided with a temperature adjuster 18 for the SOC stack. The temperature adjuster 18 is, for example, a heater such as a heater. When collectively referring to the SOC stacks, they are referred to as SOC stack 10.

[0013] <Configuration of SOC Stack> Here, with reference to FIG. 2, the structure of the plurality of SOC stacks 10 that make up the SOC module 100 will be described. The SOC module 100 is an aggregate in which a plurality of SOC stacks 10_1 - 10_n (n is a natural number of 2 or more) are connected. Each SOC stack 10 is configured by stacking a plurality of SOCs 11_1 - 11_m (m is a natural number of 2 or more).

[0014] Taking the k-th (1 < k ≤ m; k is a natural number) SOC11_k as an example, SOC11 has a structure in which an air electrode 12 and a fuel electrode 14 sandwich an electrolyte 13, and is connected to an adjacent SOC11 by an interconnector 15. In some cases, a diffusion prevention layer for suppressing material deterioration is inserted between the air electrode 12 and the electrolyte 13. When SOCs are collectively referred to, they are called SOC11.

[0015] The control device 200 includes a system control unit 201 and a temperature control unit 202. The system control unit 201 performs operations such as switching the operation mode of the SOC module 100 and controlling the opening and closing of valves V1-V6 provided in the gas pipeline. Further, each SOC stack 10 of the SOC module 100 is controlled so that the output power required during the SOFC mode is achieved and electrolysis corresponding to the input power (input current) can be executed during the SOEC mode. The temperature control unit 202 controls the temperature adjustment device 20 so that the supplied gas and water vapor reach a preset temperature, and controls the temperature adjuster 18 for the SOC stack so that each SOC stack 10 reaches a preset temperature.

[0016] The external device 300 is a load or a current source as described above. Examples of the load to which the power generated by the SOC module 100 during the SOFC mode is supplied include, for example, a power converter or a motor connected via a power converter. Examples of the current source supplied to the SOC module 100 during the SOEC mode include current sources such as a power converter or a power grid. The control device 200 controls the external device 300 to control the voltage of each SOC stack.

[0017] The gas supply unit 21 supplies hydrogen (H2) or the like as the raw material gas on the fuel electrode side required during the SOFC mode, and supplies hydrogen, carbon dioxide (CO2), or the like during the SOEC mode. It may be in a form that has gas cylinders externally and supplies them to the gas supply unit 21. Also, the gas supplied to the air electrode during the SOFC mode is, for example, oxygen (O2), air, or the like. These are also used during the SOEC mode, and since the gas species are theoretically the same before (upstream) and after (downstream) the supply and reaction, the gas may be circulated and used.

[0018] The temperature adjustment device 20 adjusts the pipe temperature of the gas and steam supplied to the SOC module 100 (upstream), and is, for example, a heater, a heating device, or the like provided around the pipe. Also, the upstream gas may be heated using the downstream gas generated from the SOC module 100 as a heat source.

[0019] As an optional component of the solid oxide fuel cell system 1, a reformer 30, a steam generator 31, a water storage unit 32, a condenser 33, a gas storage unit 34, and a gas adjustment unit 35 for storage may be provided. The reformer 30 is used when using, for example, city gas (gas mainly composed of methane) during the SOFC mode. The downstream gas generated from the SOC module 100 may be supplied as fuel to the burner that is the heat source for reforming.

[0020] The steam generator 31 heats the water supplied from the water storage unit 32 to generate steam, and supplies it to the SOC module 100 via the steam supply unit 22. Instead of using the steam generator 31, steam may be directly supplied from the outside.

[0021] The water storage unit 32 stores the water supplied to the steam generator 31. The steam in the downstream gas on the fuel electrode side discharged from the SOC module 100 may be recovered and reused as the supply gas or the fuel for the reformer 30.

[0022] The condenser 33 dehydrates the fuel electrode side downstream gas discharged from the SOC module 100. For example, in the SOFC mode, water vapor and unreacted hydrogen generated in the SOC module 100 are separated by dehydration, and in the SOEC mode, hydrogen and the like generated in the SOC module 100 and unreacted water vapor are separated by dehydration.

[0023] The gas storage unit 34 recovers the fuel electrode side downstream gas (hydrogen, etc.) discharged from the SOC module 100 in the SOEC mode and stores it as the fuel electrode side upstream gas required in the SOFC mode. The gas discharged from the SOC module 100 may be directly supplied outside the system.

[0024] The storage gas conditioner 35 appropriately processes and adjusts the gas in order to store each gas in the gas storage unit 34. For example, the gas is compressed by a compressor, a mixed gas such as hydrogen and carbon monoxide (CO), which is the fuel electrode side downstream gas discharged from the SOC module 100 in the SOEC mode, is separated by a separator, or the form of the gas is adjusted by synthesizing methane with a methanation reactor using, for example, hydrogen and carbon monoxide (CO). The gas adjusted by the storage gas conditioner 35 is stored in the gas storage unit 34.

[0025] In addition, in FIG. 1 and the diagrams showing the configuration of the solid oxide type cell system hereinafter, each line shall indicate the following content. Solid line: Gas flow path before reaction (upstream) Dash-dotted line: Gas flow path after reaction (downstream) Dashed line: Gas flow path used other than for fuel cells and steam electrolysis reactions Black arrow: Gas (hydrogen, nitrogen, carbon monoxide, hydrocarbon, water vapor, carbon dioxide, etc.) supplied to or discharged from the fuel electrode White arrow: Gas (oxygen, air, etc.) supplied to or discharged from the air electrode

[0026] <Operation in SOFC mode> Next, the operation of the solid oxide cell system 1 in the SOFC mode will be described. FIG. 3 shows the gas flow in FIG. 1 in the SOFC mode by thick lines. In the SOFC mode, gases described below are supplied to the fuel electrode 14 and the air electrode 12 respectively, and the generated electric power is output.

[0027] (1) Gas supply to the SOC module 100 (upstream) A gas mainly composed of hydrogen is supplied to the fuel electrode 14 side. The gas mainly composed of hydrogen is supplied from the gas supply unit 21 to the SOC module 100 via the temperature adjustment device 20. A gas mainly composed of hydrogen may be supplied from the gas storage unit 34. A gas mainly composed of methane may be supplied to the fuel electrode 14 side. The gas mainly composed of methane is supplied from the gas storage unit 34 to the SOC module 100 via the temperature adjustment device 20. Alternatively, it may be supplied from the outside via the reformer 30. Also, it may be supplied from the gas storage unit 34 via the reformer 30. In the reformer 30, steam reforming is performed by the following reaction using the steam supplied from the water storage unit 32, and the reformed gas is supplied to the fuel electrode 14 side. CH4 + H2O → CO + 3H2 Note that, as will be described below, a purge gas or a reducing gas mainly composed of hydrogen and nitrogen 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 that is not operating in the SOFC mode of the SOC module 100 and is in the temperature adjustment or standby state.

[0028] Oxygen or air is supplied to the air electrode 12 side from the gas supply unit 21. Similarly, oxygen or air is supplied to the air electrode 12 side of the SOC stack 10 that is not operating in the SOFC mode of the SOC module 100 and is in the temperature adjustment or standby state. In the gas supply to the SOC module 100, the gas supply source to the fuel electrode 14 side is determined by the opening and closing direction of the valve V1. When the gas supplied to the fuel electrode 14 side is a gas mainly composed of methane, the gas mainly composed of methane is supplied from the gas storage unit 34 to the reformer 30 by the opening and closing direction operation of the valve V2. The opening and closing direction of the valve V3 is determined by whether to supply gas from the reformer 30. These valves V1 - V3 are three-way valves, and the opening and closing direction operations are controlled by the system control unit 201.

[0029] (2) Exhaust of gas from the SOC module 100 (downstream) From the fuel electrode 14 side, when a gas mainly composed of hydrogen is supplied, water vapor and unreacted hydrogen, etc. are exhausted. When a gas mainly composed of methane is supplied, water vapor and carbon dioxide, etc. are exhausted. The exhausted gas may be directly exhausted to the outside, but in FIG. 3, the water vapor and other gases may be separated by the condenser 33, and then hydrogen and carbon dioxide, etc. may be separated by the gas adjustment unit 35 for storage. The water vapor may be stored in the water storage unit 32. From the air electrode 12 side, unreacted oxygen or air is exhausted. The exhausted gas may be configured to return to the gas supply unit 21 to circulate the system.

[0030] In the exhaust of gas from the SOC module 100, when the reformer 30 operates by the opening and closing of the valve V5, water can be supplied from the water storage unit 32. Also, a part of the exhaust gas can be supplied as fuel for the heat supply burner of the reformer 30 according to the opening and closing direction of the valve V4. The valve V4 is a three-way valve, and the valve V5 is an on-off valve. The opening and closing direction and the opening and closing operations are controlled by the system control unit 201.

[0031] Note that the temperature adjustment device 20 can be configured to have a heat exchange function and heat the supply gas by heat exchange with the exhausted gas. Also, the temperature of the temperature adjustment device 20 during operation, the temperature of the temperature regulator 18 for the SOC stack, and the temperature of the reformer 30 are controlled to the set temperatures by the temperature control unit 202 respectively.

[0032] <Operation in SOEC mode> Next, the operation of the solid oxide cell system 1 in the SOEC mode will be described. FIG. 4 shows the gas flow in FIG. 1 in the SOEC mode with thick lines. In the SOEC mode, gases described below are supplied to the fuel electrode 14 and the air electrode 12 respectively, and an electrolysis reaction occurs due to the input power.

[0033] (1) Gas supply to the SOC module 100 (upstream) To the fuel electrode 14 side, a gas mainly composed of water vapor is supplied from the water vapor supply section 22. Although water vapor may be directly introduced from the outside, as shown in FIG. 4, the water supplied from the water storage section 32 may be heated by the water vapor generator 31 to generate water vapor. Also, hydrogen may be supplied from the gas storage section 34 or the gas supply section 21, mixed with water vapor by the temperature adjustment device 20, and then supplied to the fuel electrode 14 side. Also, a gas mainly composed of carbon dioxide may be supplied from the gas supply section 21 to the fuel electrode 14 side. At this time, a mixed gas of water vapor and carbon dioxide may be supplied to the fuel electrode 14 side. Note that, as will be described below, to the fuel electrode 14 side of the SOC stack 10 that is not operating in the SOEC mode of the SOC module 100 and is in the process of temperature adjustment or on standby, a purge gas or a reducing gas mainly composed of hydrogen and nitrogen is supplied from the gas supply section 21 or the gas storage section 34.

[0034] To the air electrode 12 side, oxygen or air is supplied from the gas supply section 21. Similarly, oxygen or air is supplied to the air electrode 12 side of the SOC stack 10 that is not operating in the SOEC mode of the SOC module 100 and is in the process of temperature adjustment or on standby. In the gas supply to the SOC module 100, the gas supply source to the fuel electrode 14 side is determined by the opening and closing directions of the valve V1 and the opening and closing of the valve V6. The valve V1 is a three-way valve, and the valve V6 is an on-off valve. The opening and closing directions and the opening and closing operations are controlled by the system control unit 201.

[0035] (2) Gas discharge from the SOC module 100 (downstream) From the fuel electrode 14 side, when a gas mainly composed of water vapor is supplied, hydrogen and unreacted water vapor are discharged, and when a gas mainly composed of carbon dioxide is supplied, carbon monoxide and unreacted carbon dioxide are discharged. The discharged gas may be directly discharged to the outside of the system. However, in FIG. 4, the water vapor and other gases are separated by the condenser 33, and then hydrogen and carbon monoxide are separated by the gas adjustment unit 35 for storage, or the mixed gas containing hydrogen and carbon monoxide may be directly introduced into the methanation reactor to generate methane. The gases such as hydrogen, carbon monoxide, and methane processed by the gas adjustment unit 35 for storage are stored in the gas storage unit 34. The unreacted water vapor may be stored in the water storage unit 32 and supplied to the fuel electrode 14 again. From the air electrode 12 side, the generated oxygen or air in a state with a high oxygen concentration is discharged. The discharged gas may be returned to the gas supply unit 21 to circulate the system.

[0036] Note that the temperature adjustment device 20 can be configured to have a heat exchange function and heat the supply gas by heat exchange with the discharged gas. Also, the water vapor generator 31 can be configured to have a heat exchange function and generate water vapor by heat exchange with the discharged gas. Also, similar to the SOFC mode, the temperature of the temperature adjustment device 20 and the temperature of the temperature adjuster 18 for the SOC stack during operation are controlled by the temperature control unit 202 to the set temperatures respectively.

[0037] <Configuration of the operating SOC stack selection unit 203> FIG. 5 is a diagram showing the configuration of the control device 200 according to the present embodiment. The control device 200 of the first embodiment of the present invention includes an operation SOC stack selection unit 203 in addition to the system control unit 201 and the temperature control unit 202 that control the above-described basic operations. In FIG. 5, the operation SOC stack selection unit 203 includes a stack voltage acquisition unit 231 that acquires the voltage of each SOC stack 10 included in the SOC module 100, and the stack voltage V of the acquired SOC stack 10 s and a preset value V exA degradation degree estimation unit 232 that calculates the difference from [a certain value] and estimates the degradation degree of each SOC stack 10 based on the calculated value, and an operation priority determination unit 233 that determines the priority of the SOC stack 10 to be operated next based on the estimated degradation degree are provided.

[0038] The stack voltage acquisition unit 231 acquires the voltage of each SOC stack 10 from, for example, a voltage sensor (not shown) provided in each SOC stack 10. Alternatively, the input / output power during the operation of each SOC stack 10 may be measured from the relationship between the input / output power and the stack voltage during the operation of each SOC stack 10 to acquire the voltage of each SOC stack 10.

[0039] The degradation degree estimation unit 232 calculates the difference between the acquired stack voltage V of the SOC stack 10 s and a preset value V ex and estimates that the greater the calculated difference value, the greater the degradation degree. The method for setting the value V ex will be described later.

[0040] The operation priority determination unit 233 compares the estimated degradation degrees of the respective SOC stacks 10 included in the SOC module 100, and determines to increase the priority of the SOC stack 10 with the smallest degradation degree as the SOC stack 10 to be operated next. The determined priority is transmitted to the system control unit 201.

[0041] <Operating Example 1 of the Solid Oxide Cell System 1> FIG. 6 is a flowchart showing the operation of the solid oxide cell system 1 according to the present embodiment. First, the SOC module 100 starts operation in the SOFC mode or the SOEC mode by the system control unit 201 (step S100). The stack voltage acquisition unit 231 acquires the stack voltage V of each operating SOC stack 10 s (step S101).

[0042] The degradation degree estimation unit 232 calculates the difference between the acquired stack voltage V s and a preset value V exCalculate the difference from it and estimate the degree of deterioration (step S102). The operation priority determination unit 233 compares the estimated degrees of deterioration of the respective SOC stacks 10 included in the SOC module 100, determines to increase the priority of the SOC stack 10 with the lower degree of deterioration as the SOC stack 10 to be operated next, and transmits the determined priority to the system control unit 201 (step S103). The system control unit 201 causes the SOC module 100 to stop operating (step S104).

[0043] The system control unit 201 operates the next operation starting from the SOC stack 10 with the highest priority among the SOC stacks 10 included in the SOC module 100 (step S105). If there is a SOC stack 10 that stops input / output (YES in step S106), store the degree of deterioration of the SOC stack 10 to be stopped (step S107). At the next operation, in step S101, the stack voltage V of the SOC stack 10 that was stopped s is not acquired, but since the previous degree of deterioration is stored, in step S103, the operation priority of the SOC stack 10 can be determined using the stored degree of deterioration. By repeating the operations from step S101 to step S107, the load on the SOC stack 10 with a large degree of deterioration is reduced, and the variation in deterioration between the SOC stacks 10 can be suppressed.

[0044] The system control unit 201 operates the SOC stacks 10 included in the SOC module 100 in response to the output power in the SOFC mode and the required input power in the SOEC mode. Usually, since the input / output of the SOC module 100 is designed with a margin with respect to the required input / output, in steps S106 and S107, for the SOC stack 10 that stops input / output, store the degree of deterioration, and at the next operation, consider the degree of deterioration stored in step S103 and determine the operation priority based on the degree of deterioration. By stopping or adjusting the input / output of the SOC stack 10 in this way, the load on the SOC stack 10 with a large degree of deterioration can be reduced.

[0045] The flow shown in FIG. 6 has been described by taking as an example the case where either the SOFC mode or the SOEC mode is repeated, but the operation mode may be switched.

[0046] <Value V ex Setting method> The value V used for comparison with the stack voltage V in step S102 s will be described by giving the following examples. ex The setting method of (1) The chemical reactions occurring at SOC11 are oxidation reactions in the SOFC mode and reduction reactions in the SOEC mode. The theoretical voltage V0 of these chemical reactions is called the theoretical electromotive force or theoretical decomposition voltage, etc., and its value is determined by the temperature. Therefore, the theoretical voltage V0 corresponding to the operating temperatures of the SOFC mode and the SOEC mode may be used as the value V ex for comparison.

[0047] (2) The chemical reactions occurring at SOC11 have a theoretical voltage V0 determined by its operating temperature, but the theoretical operating voltage of SOC11 changes depending on the pressures of the gases at the air electrode 12 and the fuel electrode 14 of SOC11. For example, when generating electricity using hydrogen in the SOFC mode or electrolyzing water vapor in the SOEC mode, if the theoretical voltage is V0 and the theoretical operating voltage is V r the relationship between the two is generally shown by the following formula (1) called the Nernst equation.

Equation

[0048] Here, the temperature T can be measured for each SOC stack 10, or obtained from the operating temperature preset for each SOC stack 10 in the temperature control unit 202. The temperature of the SOC stack 10 may be the average value of the temperatures of a plurality of SOC stacks 10. When the temperature varies depending on the position of the SOC stack 10 (when there is a temperature distribution within the SOC module 100), it is desirable to obtain the temperature near the SOC stack 10 whose stack voltage is to be measured. The pressure of each gas can be obtained, for example, using the supply amount (gas flow rate) of each gas controlled by the system control unit 201, etc. Specifically, the value of the mass flow controller that controls the gas flow rate may be used.

[0049] Therefore, based on Equation (1), the relationship between the theoretical voltage V0, the stack temperature T, the pressure P of each gas, and the theoretical operating voltage V r is tabulated and stored in the operating SOC stack selection unit 203 or the storage device within the control device 200, and the theoretical operating voltage V r may be used as the value V ex . Although Equation (1) was used to explain the power generation using hydrogen in the SOFC mode and the electrolysis of water vapor in the SOEC mode, in each mode, by using the supply gas, the generated gas, and the reaction formula, the pressure P term in Equation (1) can be obtained in the same manner.

[0050] (3) The stack voltage V s at the initial stage of operation of the solid oxide fuel cell system 1 may also be used as the value V ex . For example, when newly operating the solid oxide fuel cell system 1, the value V ex for each mode may be obtained from the average of the stack voltages during operation for a certain period of time in the SOEC mode and the SOFC mode respectively. In that case, the operation before step S100 is a period during which the value V ex is not set and is a period for setting the value V ex . (4) As the SOC stack deteriorates, the physical changes in the electrode structure and the resistance related to chemical reactions such as ion conduction in the electrode increase. As a result, in the case of the SOFC mode, the stack voltage V s decreases, and in the case of the SOEC mode, the stack voltage V s increases. Therefore, the above-described methods of setting the value V ex are merely examples, and the stack voltage V s of each SOC stack can show a significant difference, and a constant that can be used as a reference within a range that can determine the priority among the SOC stacks can be preset as the value V ex .

[0051] <Method for Determining Priority> In step S103, the degrees of deterioration estimated for each SOC stack 10 are compared to determine the priority of the SOC stack 10 to be operated next. An example of the method for determining the priority will be described below.

[0052] (1) Method of Assigning Priorities to All SOC Stacks In step S102, the degree of deterioration has been estimated for each SOC stack 10. The priority is increased in ascending order of the estimated degree of deterioration. That is, the n SOC stacks 10 included in the SOC module 100 are assigned high priorities in ascending order of the degree of deterioration.

[0053] (2) Method of Grouping SOC Stacks According to Predetermined Ranges of the Estimated Degrees of Deterioration and Determining Priorities Figures 7A, 7B, and 7C are diagrams for explaining a method of determining the priority of the SOC stack to be operated during the next operation based on the degree of deterioration. In each figure, the black circles (●) indicate the degrees of deterioration of the respective SOC stacks, and the overall distribution state of the degrees of deterioration can be understood.

[0054] (A) In FIG. 7A, a high priority is given to the SOC stack group A1 with a degradation degree smaller than a preset threshold α with respect to the degradation degree, and no priority is given to the individual SOC stacks within the SOC stack group A1, and they are operated in an arbitrary order. For the SOC stacks with a degradation degree equal to or higher than the threshold, a high priority is given in order from the one with the smallest degradation degree, following the priority of the SOC stack group A1.

[0055] (B) In FIG. 7B, the average value of the degradation degrees of all the SOC stacks is calculated, and a preset range with a difference from the average value is set, for example, a range from the average value +X% to the average value -Y%. The degradation degree of the average value +X% is set as the threshold β2, and the degradation degree of the average value -Y% is set as the threshold β1. The SOC stacks with a degradation degree equal to or higher than the threshold β2 are defined as the SOC stack group B2, and the SOC stacks with a degradation degree less than the threshold β1 are defined as the SOC stack group B1. Here, X may be equal to Y.

[0056] For the grouping shown in FIG. 7B, the priorities are determined as follows, for example. (B-1) For the SOC stacks other than those belonging to the SOC stack group B2, high priorities are given in ascending order of the degradation degree. (B-2) The highest priority is given to the SOC stack group B1, and no priority is given to the individual SOC stacks within the SOC stack group B1, and they are operated in an arbitrary order. For the SOC stacks with a degradation degree equal to or higher than the threshold β1, high priorities are given in ascending order of the degradation degree. (B-3) The SOC stacks with a degradation degree less than the average value are given high priorities but in an arbitrary order, and the SOC stacks with a degradation degree equal to or higher than the average value are given high priorities in ascending order of the degradation degree.

[0057] (C) In FIG. 7C, the degradation degrees of all SOC stacks are divided into three groups. They are the SOC stack group C1 with a low degradation degree, the SOC stack group C2 with an average degradation degree, and the SOC stack group C3 with a large degradation degree. Priorities are assigned with high priority in the order of the SOC stack group C1, the SOC stack group C2, and the SOC stack group C3, and for each group. For the SOC stacks within each SOC stack group, high priorities may be assigned in ascending order of the degradation degree, or the priorities of each SOC stack may be arbitrary. Although an example of dividing into three groups is shown, it is not limited to three, and it may be divided into any number.

[0058] Note that, as shown in the above example, priorities may be determined by mixing grouped and ungrouped ones. In that case, for the grouped ones, any value within the set degradation degree range is the representative degradation degree. Compare the degradation degrees of the ungrouped SOC stacks and stack groups, and give priority to the SOC stack or stack group with a lower degradation degree.

[0059] The priorities determined by the method shown in the above example are transmitted from the operation priority determination unit 233 to the system control unit. The system control unit 201 selects and operates the SOC stacks with high priorities in order to correspond to the power input / output during the next operation. Regarding the stack to be preferentially operated among the SOC stacks 10 in the next operation mode and its load, it may be calculated during the pause period between operation modes.

[0060] <Operation Example 2 of the Solid Oxide Cell System 1> It is generally known that for a solid oxide cell system equipped with a reversible SOC, the contribution to degradation is greater during operation in the SOEC mode than in the SOFC mode. That is, it is more likely to degrade during operation in the SOEC mode. Also, it has been confirmed that by alternately operating the SOFC mode and the SOEC mode, the degradation of the SOC stack is suppressed more than during continuous operation in one operation mode.

[0061] In the first operation example of the solid oxide type cell system 1 shown in FIG. 6, the operation mode was not considered. Hereinafter, an example of operating the SOC stack will be described with reference to FIG. 8 while considering both the operation mode and the degree of degradation of the SOC stack.

[0062] FIGS. 8A and 8B are flowcharts showing another operation of the solid oxide type cell system 1 according to the present embodiment. Steps S200 to S204 are the same as steps S100 to S104 in FIG. 6, and the description thereof will be omitted.

[0063] In step S205, the system control unit 201 determines whether the next operation mode is the SOEC mode or the SOFC mode. If it is the SOFC mode, in step S206, it determines whether the previous operation mode, that is, the operation mode at the time of determining the priority, is the SOEC mode or the SOFC mode.

[0064] If it is determined in step S205 that the next operation mode is the SOEC mode, the system control unit 201 operates the SOC stack 10 with the highest priority based on the priority determined in step S203 and transmitted from the operation priority determination unit 233, and operates in the SOEC mode so as to correspond to the input power (step S210). If it is determined in step S205 that the next operation mode is the SOFC mode, the process proceeds to step S206. In step S206, if the previous operation mode is the SOFC mode, the next operation mode is also the SOFC mode, and continuous operation is performed. Therefore, operation based on the degree of degradation of the SOC stack 10 is required, and the process proceeds to step S210. The next operation is started in the SOEC mode from the SOC stack 10 with the highest priority so as to be the input power required in step S210. In step S211, it is determined whether there is a SOC stack 10 that stops input and output. If there is a SOC stack 10 that stops input and output (YES in step S211), the process proceeds to step S212, and the degree of degradation of the SOC stack 10 to be stopped is stored. In step S211, if there is no SOC stack 10 that stops input / output (NO in step S211), the priority information of the SOC stack 10 determined in step S203 and transmitted from the operation priority determination unit 233 is reset (step S213).

[0065] In step S206, when the previous operation mode is the SOEC mode, since the next operation mode has switched to the SOFC mode, the process proceeds to step S207. In step S207, it is determined whether there is a SOC stack 10 that stops input / output. If there is a SOC stack 10 that stops input / output (YES in step S207), the process proceeds to step S208, the degradation degree of the SOC stack 10 to be stopped is stored, and then the process returns to step S200, and the operation is started in the SOFC mode using the SOC stack 10 that has not been stopped so as to obtain the required output power. In step S207, if there is no SOC stack 10 that stops input / output (NO in step S207), the priority information of the SOC stack 10 determined in step S203 and transmitted from the operation priority determination unit 233 is reset (step S209). Then, the process returns to step S200, and an arbitrary SOC stack 10 is used without considering the degradation degree of the SOC stack 10, and the operation is started in the SOFC mode so as to obtain the required output power.

[0066] As described above, when the next operation mode is the SOEC mode, and even when the next operation mode is the SOFC mode and the SOFC mode continues, the SOC stack 10 with a smaller degradation degree is preferentially operated, and the input / output of each SOC stack 10 is adjusted or stopped, so that the load on the SOC stack 10 with a larger degradation degree can be reduced. That is, for the SOC stack 10 with a large degradation degree and whose input / output is stopped, the degradation degree is stored and considered in the next operation priority determination. By repeating the operations after step S203, the load on the SOC stack 10 with a large degradation degree can be reduced, and the variation in degradation between the SOC stacks 10 can be suppressed. Also, when there is no SOC stack 10 that stops input / output, the priority information is reset, and based on the newly estimated degree of degradation, it is possible to grasp the variation in degradation among the SOC stacks 10 and suppress the variation in degradation among the SOC stacks 10 in order to determine the priority.

[0067] In FIGS. 8A and 8B, regardless of the operation mode, the example in FIG. 6 is to preferentially operate the SOC stack 10 with a smaller degree of degradation. Operating each SOC stack according to the priority and according to the input / output acts to adjust the degree of degradation of each individual SOC stack 10 and reduce the load. On the other hand, in order to operate each SOC stack 10 according to the priority and according to the input / output, in the system control unit 201, an operation plan for each SOC stack 10 is calculated. Therefore, when it is determined as alternate operation in step S206 as in the operation example 2 shown in FIGS. 8A and 8B, the calculation becomes unnecessary and the calculation load on the system control unit 201 is reduced.

[0068] As described above, it is more likely to deteriorate during operation in the SOEC mode, but the deterioration also varies depending on the gas species supplied to the SOC stack 10 and SOC11. That is because the theoretical operating voltage V r causing the chemical reaction is different. In the electrolysis in the SOEC mode, for the same input power, in the co-electrolysis of simultaneously decomposing both water vapor and carbon dioxide using water vapor and carbon dioxide, the stack voltage is equal to or higher than that of the electrolysis of water vapor, and it is known that the stack voltage of the electrolysis of carbon dioxide is even higher than that of the electrolysis of water vapor or co-electrolysis. Therefore, in the electrolysis in the SOEC mode, in the case of electrolysis using carbon dioxide, by applying the operation of the present embodiment, the effects of further suppressing degradation and suppressing variation in degradation can be achieved.

[0069] FIG. 9 is a diagram showing an example of the hardware configuration of a control device 200 included in a solid oxide cell system according to an embodiment. The control device 200 includes a processor 1000 and a storage device 2000. The processor 1000 is composed of, for example, a CPU (Central Processing Unit), an ASIC (Application Specific Integrated Circuit), a DSP (Digital Signal Processor), an FPGA (Field Programmable Gate Array), or the like.

[0070] The main storage device of the storage device 2000 is composed of a volatile storage device such as a random access memory, and includes a non-volatile storage device such as a flash memory or a hard disk as an auxiliary storage device. A predetermined program executed by the processor 1000 is stored in the auxiliary storage device. The processor 1000 appropriately reads and executes this program to perform various arithmetic processes. At this time, the predetermined program is temporarily stored from the auxiliary storage device to the volatile storage device, and the processor 1000 reads the program from the volatile storage device. Further, the processor 1000 may output data such as arithmetic results to the volatile storage device of the storage device 2000, or may store the data in the auxiliary storage device via the volatile storage device.

[0071] Note that, in order to enable remote control, a transmission device and a reception device (both not shown) may be provided as communication modules for communicating with the outside.

[0072] As described above, according to the present embodiment, the solid oxide cell system has an SOC stack that can switch between an SOFC mode in which power is generated using a first gas and power is output, and an SOEC mode in which power is input and a second gas is electrolyzed. The solid oxide cell system includes an SOC module formed by connecting a plurality of SOC stacks, and a control device that controls the operation of the plurality of SOC stacks. The control device has a stack voltage acquisition unit that acquires the voltages of the plurality of SOC stacks operating in the SOFC mode or the SOEC mode, and a degradation degree estimation unit that estimates the degradation degree of the SOC stack based on the acquired voltages of the solid oxide cell stacks. In the next operation mode, control is performed to preferentially operate the SOC stack with a smaller estimated degradation degree. With this configuration, since the SOC stack with a smaller degradation degree is preferentially operated, the variation in degradation between the SOC stacks can be suppressed, and stable operation of the solid oxide cell system becomes possible. Furthermore, the long life, maintenance, and simplification of the renewal of the solid oxide cell system can be achieved. The first gas is, for example, a gas mainly composed of hydrogen supplied to the fuel electrode side or a gas mainly composed of methane, or oxygen or air supplied to the air electrode side. The second gas is, for example, a gas mainly composed of steam supplied to the fuel electrode side or a gas mainly composed of carbon dioxide, or oxygen or air supplied to the air electrode side.

[0073] Also, when the control device operates the SOC stack in the SOEC mode next, control is performed to preferentially operate the SOC stack with a smaller estimated degradation degree. Since the degradation of the SOC stack progresses more in the SOEC mode than in the SOFC mode, by preferentially operating the SOC stack with a smaller degradation degree in the SOEC mode, the variation in degradation between the SOC stacks can be suppressed, and stable operation of the solid oxide cell system becomes possible.

[0074] In addition, since the deterioration of the SOC stack progresses more when operating continuously in the same mode than during alternating operation, when operating the SOC stack in the same mode continuously, by performing control to preferentially operate the SOC stack with a smaller estimated degree of deterioration, variations in deterioration between the SOC stacks can be suppressed, enabling stable operation of the solid oxide fuel cell system.

[0075] In addition, since the degree of deterioration is estimated based on the difference between the voltage of the SOC stack and a preset value, and the theoretical voltage required for the chemical reaction of the supply gas in each operating mode, or the theoretical operating voltage obtained from the temperature of the SOC stack and the pressure ratio of the gas before and after the chemical reaction, is used as the preset value, if it is stored in advance in the storage device within the control device, it becomes possible to easily perform calculations. Note that the degree of deterioration may be estimated without calculating the difference between the voltage of the SOC stack and a preset value. For example, consider the case where all the SOC stacks to be operated are operated under the same conditions. In this case, an estimation method may be applied that determines that in the case of the SOEC mode, the stack with a higher voltage has a higher degree of deterioration, and in the case of the SOFC mode, the SOC stack with a lower voltage has a higher degree of deterioration.

[0076] In addition, for the SOC stack having the degree of deterioration estimated by the degree-of-deterioration estimation unit, a plurality of SOC stacks within a preset range of the degree of deterioration are grouped and the operation is controlled with the same priority, so the amount of calculation for the priority is reduced.

[0077] 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 specific embodiment, but are applicable to the embodiments alone or in various combinations. Therefore, countless variations not illustrated are envisioned within the scope of the technology disclosed in this specification. For example, it is assumed to include cases where at least one component is modified, added, or omitted.

Explanation of Reference Numerals

[0078] 1: Solid oxide cell system, 10: SOC stack, 11: SOC, 12: Air electrode, 13: Electrolyte, 14: Fuel electrode, 15: Interconnector, 18: Temperature regulator for SOC stack, 20: Temperature control device, 21: Gas supply unit, 22: Steam supply unit, 30: Reformer, 31: Steam generator, 32: Water storage unit, 33: Condenser, 34: Gas storage unit, 35: Gas regulator for storage, 100: SOC module, 200: Control device, 201: System control unit, 202: Temperature control unit, 203: Operating SOC stack selection unit, 231: Stack voltage acquisition unit, 232: Degradation degree estimation unit, 233: Operating priority determination unit, 1000: Processor, 2000: Storage device.

Claims

1. A solid oxide cell module having a solid oxide cell stack capable of switching between an SOFC mode in which power is generated using a first gas and power is output, and an SOEC mode in which power is input and a second gas is electrolyzed, and a plurality of the solid oxide cell stacks are connected; A control device for controlling the operation of a plurality of the solid oxide cell stacks; and The control device is configured to: A stack voltage acquisition unit that acquires the voltages of a plurality of the solid oxide cell stacks operating in the SOFC mode or the SOEC mode; A degradation degree estimation unit that calculates the difference between the voltage of the acquired solid oxide cell stack and a preset value, and estimates that the higher the calculated difference value, the greater the degradation degree of the solid oxide cell stack; As the preset value, When the solid oxide cell stack is operating in the SOFC mode, the theoretical voltage required for the power generation reaction by the first gas is used, and when the solid oxide cell stack is operating in the SOEC mode, the theoretical voltage required for the electrolysis reaction by the second gas is used, or When the solid oxide cell stack is operating in the SOFC mode, the theoretical voltage required for the power generation reaction by the first gas, the temperature of the solid oxide cell stack, and the theoretical operating voltage calculated using the gas pressure ratio before and after the power generation reaction by the first gas are used, and when the solid oxide cell stack is operating in the SOEC mode, the theoretical voltage required for the electrolysis reaction by the second gas, the temperature of the solid oxide cell stack, and the theoretical operating voltage calculated using the gas pressure ratio before and after the electrolysis reaction by the second gas are used, In the next SOFC mode or SOEC mode, control is performed to preferentially operate the solid oxide cell stack with a smaller estimated degradation degree; When there is a solid oxide cell stack whose input / output is stopped, the degradation degree in the previous operation mode of the solid oxide cell stack is stored, and the operation priority of the solid oxide cell stack is determined using the stored degradation degree. A solid oxide cell system.

2. The control device is configured to: Next, when operating the solid oxide cell stack in the SOEC mode, control is performed to preferentially operate the solid oxide cell stack with a smaller estimated degree of degradation, according to the solid oxide cell system of claim 1.

3. The control device When continuously operating the solid oxide cell stack in the same mode, control is performed to preferentially operate the solid oxide cell stack with a smaller estimated degree of degradation, according to the solid oxide cell system of claim 1.

4. In the SOFC mode, power is output by a power generation reaction using hydrogen or a mixed gas of hydrogen and carbon monoxide as the first gas. In the SOEC mode, electrolysis is performed on at least one of steam and carbon dioxide as the second gas by input power, according to the solid oxide cell system of any one of claims 1 to 3.

5. The control device For the solid oxide cell stack having the degree of degradation estimated by the degree-of-degradation estimation unit, at least one stack group having a plurality of the solid oxide cell stacks within a preset range of the degree of degradation is provided. In the next SOFC mode or SOEC mode, for the stack group and the solid oxide cell stack not belonging to the stack group, the degrees of degradation of the stack group and the solid oxide cell stack not belonging to the stack group are compared, and control is performed to preferentially operate the solid oxide cell stack or the stack group with a smaller estimated degree of degradation, according to the solid oxide cell system of any one of claims 1 to 3.

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