Temperature control device for solid oxide electrolysis cell and temperature control method for solid oxide electrolysis cell

Abstract

To raise the temperature of a solid oxide electrolysis cell without generating NOx, and suppress increase of start-up energy of the solid oxide electrolysis cell.SOLUTION: A temperature adjustment device of a solid oxide electrolysis cell comprises: a hydrogen tank which stores hydrogen; an oxygen tank which stores oxygen; and a combustor which burns mixed gas in which the hydrogen supplied from the hydrogen tank is mixed with the oxygen supplied from the oxygen tank, and discharges combustion off gas to be supplied to the solid oxide electrolysis cell. The combustor includes at least one of a fuel side combustor which burns the hydrogen-rich mixed gas with a larger ratio of the hydrogen in comparison to a theoretical air fuel ratio and an oxygen side combustor which burns the oxygen-rich mixed gas with a larger ratio of the oxygen in comparison to the theoretical air fuel ratio.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to the technology of temperature regulation of solid oxide electrolysis cells. [Background technology]

[0002] SOFCs (Solid Oxide Fuel Cells) and SOECs (Solid Oxide Electrolyzer Cells) that operate at high temperatures of 600 to 700 degrees Celsius (°C) are known (see, for example, Patent Document 1). The SOFC system described in Patent Document 1 uses the combustion of a mixed gas of hydrogen and air in a combustor to raise the temperature of a fuel cell that generates electricity from hydrogen and oxygen to the operating temperature. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-207308 Summary of the Invention [Problem to be solved by the invention]

[0004] In the technology described in Patent Document 1, the combustion gas temperature is controlled to a temperature range that suppresses excessive temperature rise in the combustor and prevents a decrease in strength and durability due to localized high temperatures in the combustor. To control the temperature, a large amount of air must be supplied to the combustor. The SOFC system described in Patent Document 1 must be equipped with a treatment device for removing NOx to prevent N2 gas contained in the air supplied to the combustor from being released into the atmosphere as thermal NOx after combustion.

[0005] The present invention has been made to solve at least part of the above-mentioned problems, and an object of the present invention is to increase the temperature of a solid oxide electrolysis cell without generating NOx, and to suppress an increase in the startup energy of the solid oxide electrolysis cell. [Means for solving the problem]

[0006] The present invention has been made to solve at least part of the above-mentioned problems, and can be realized in the following forms. a combustor that burns a mixed gas obtained by mixing hydrogen supplied from the hydrogen tank and oxygen supplied from the oxygen tank, discharges combustion off-gas, and supplies the discharged combustion off-gas to the solid oxide electrolysis cell; a heat storage device that is supplied with the combustion off-gas and releases heat through an oxidation reaction, the heat storage device being capable of exchanging heat with the solid oxide electrolysis cell; and a combustion control unit that controls the combustion of the mixed gas by the combustor, wherein the combustor is configured to burn the mixed gas at a ratio of hydrogen to oxygen lower than the stoichiometric air-fuel ratio. and an oxygen-side combustor that combusts the oxygen-rich mixed gas having a higher proportion of oxygen than the stoichiometric air-fuel ratio, and wherein, when increasing the temperature of the solid oxide electrolysis cell, the combustion control unit combusts the mixed gas having a stoichiometric air-fuel ratio in the combustor if the temperature of the heat storage material is below a predetermined temperature and supplies the combustion off-gas to the heat storage device, and stops supplying the mixed gas to the combustor to stop combustion of the mixed gas if the temperature of the heat storage material is equal to or higher than the predetermined temperature.a combustor that burns a mixed gas obtained by mixing hydrogen supplied from the hydrogen tank and oxygen supplied from the oxygen tank, discharges combustion off-gas, and supplies the discharged combustion off-gas to the solid oxide electrolysis cell; a gas-liquid separator that separates moisture from the combustion off-gas that has passed through the solid oxide electrolysis cell; and a booster that boosts the pressure of the combustion off-gas from which moisture has been separated by the gas-liquid separator, wherein the combustor burns the hydrogen-rich mixed gas having a higher proportion of hydrogen than the stoichiometric air-fuel ratio, and a fuel-side combustor that supplies the combustion off-gas to a fuel side to which hydrogen is supplied, and an oxygen-side combustor that combusts the oxygen-rich mixed gas having a proportion of oxygen higher than that of a stoichiometric air-fuel ratio, wherein the booster stores the fuel-side combustion off-gas after pressurization in the hydrogen tank, and the temperature control device further comprises: a temperature sensor that acquires a temperature of the combustion off-gas supplied to the fuel side of the solid oxide electrolysis cell; and a cell temperature control unit that adjusts the temperature of the solid oxide electrolysis cell by controlling the flow rate of hydrogen and the flow rate of oxygen supplied to the fuel-side combustor using the temperature acquired by the temperature sensor.a combustor that burns a mixed gas obtained by mixing hydrogen supplied from the hydrogen tank and oxygen supplied from the oxygen tank, discharges combustion off-gas, and supplies the discharged combustion off-gas to the solid oxide electrolysis cell; a gas-liquid separator that separates moisture from the combustion off-gas that has passed through the solid oxide electrolysis cell; and a booster that boosts the pressure of the combustion off-gas from which moisture has been separated by the gas-liquid separator, wherein the combustor is configured to combust a hydrogen gas at a concentration higher than the stoichiometric air-fuel ratio. and an oxygen-side combustor that combusts the oxygen-rich mixed gas having a higher proportion of oxygen than the stoichiometric air-fuel ratio and supplies the combustion off-gas to the oxygen side to which oxygen is supplied in the solid oxide electrolysis cell, wherein the flow direction of the fuel-side combustion off-gas flowing from the fuel-side combustor into the fuel side of the solid oxide electrolysis cell is opposite to the flow direction of the oxygen-side combustion off-gas flowing from the oxygen-side combustor into the oxygen side of the solid oxide electrolysis cell.

[0007] (1) One aspect of the present invention provides a temperature control device for a solid oxide electrolysis cell, comprising: a hydrogen tank for storing hydrogen; an oxygen tank for storing oxygen; and a combustor that combusts a mixed gas obtained by mixing hydrogen supplied from the hydrogen tank and oxygen supplied from the oxygen tank, discharges combustion off-gas, and supplies the combustion off-gas to the solid oxide electrolysis cell, wherein the combustor has at least one of a fuel-side combustor that combusts the hydrogen-rich mixed gas having a higher proportion of hydrogen than the stoichiometric air-fuel ratio, and an oxygen-side combustor that combusts the oxygen-rich mixed gas having a higher proportion of oxygen than the stoichiometric air-fuel ratio.

[0008] According to this configuration, the combustion off-gas generated in the combustor is supplied to the solid oxide electrolysis cell, thereby increasing the temperature of the solid oxide electrolysis cell. Because the mixed gas combusted in the combustor does not contain air, the combustion off-gas generated after combustion does not contain thermal NOx, which is generated when nitrogen and oxygen contained in air react at high temperatures. Therefore, a system equipped with a solid oxide electrolysis cell does not need to include a device for removing thermal NOx. Furthermore, because a hydrogen-rich mixed gas is combusted in the fuel-side combustor, the adiabatic flame temperature during combustion of the mixed gas can be controlled by adjusting the flow rate of oxygen supplied to the fuel-side combustor. Similarly, because an oxygen-rich mixed gas is combusted in the oxygen-side combustor, the adiabatic flame temperature during combustion of the mixed gas can be controlled by adjusting the flow rate of hydrogen supplied to the oxygen-side combustor.

[0009] (2) The solid oxide electrolysis cell of the above aspect may further include a heat exchanger that exchanges heat between the combustion off-gas discharged from the solid oxide electrolysis cell and hydrogen supplied from the hydrogen tank or oxygen supplied from the oxygen tank. With this configuration, heat is transferred from the high-temperature combustion off-gas discharged from the solid oxide electrolysis cell to the hydrogen supplied from the hydrogen tank or the oxygen supplied from the oxygen tank through heat exchange in the heat exchanger. This allows the sensible heat of the combustion off-gas to be recovered and the temperature of the hydrogen or oxygen supplied to the solid oxide electrolysis cell to be increased. As a result, with this configuration, an increase in the startup energy of the solid oxide electrolysis cell can be suppressed.

[0010] (3) The solid oxide electrolysis cell of the above aspect may further include a heat storage device including a heat storage material that is supplied with the combustion off gas and releases heat through an oxidation reaction, the heat storage material being capable of heat exchange with the solid oxide electrolysis cell, and a combustion control device that controls the combustion of the mixed gas by the combustor, wherein, when increasing the temperature of the solid oxide electrolysis cell, the combustion control device may combust the mixed gas at a stoichiometric air-fuel ratio in the combustor when the temperature of the heat storage material is below a predetermined temperature and supply the combustion off gas to the heat storage device, and may stop the supply of the mixed gas to the combustor to stop the combustion of the mixed gas when the temperature of the heat storage material is equal to or higher than the predetermined temperature. According to this configuration, when the operation of a solid oxide electrolysis cell that has been operating at a high temperature is stopped, the heat accumulator can store excess heat from the solid oxide electrolysis cell. The heat stored in the heat accumulator can be used to heat the solid oxide electrolysis cell when the solid oxide electrolysis cell is operated again. Therefore, in this configuration, the heat storage and heat release of the heat accumulator are utilized, thereby suppressing an increase in the startup energy of the solid oxide electrolysis cell. Furthermore, the heat storage material that releases heat through an oxidation reaction increases in reaction rate of heat release as the temperature increases. Therefore, when the mixed gas combusted by the combustor is supplied to the heat storage material when the temperature of the solid oxide electrolysis cell is equal to or lower than a predetermined temperature during initial startup, the reaction rate of the heat storage material increases, and the temperature rise rate of the solid oxide electrolysis cell is accelerated. In other words, even without an external heat source for increasing the reaction rate of the heat storage material, the temperature rise rate of the solid oxide electrolysis cell can be accelerated by supplying the combustion off-gas to the heat accumulator.

[0011] (4) The solid oxide electrolysis cell of the above aspect may further include a gas-liquid separator that separates moisture from the combustion off-gas that has passed through the solid oxide electrolysis cell, and a booster that pressurizes the combustion off-gas from which moisture has been separated by the gas-liquid separator, wherein the combustor has a fuel-side combustor that supplies the combustion off-gas to a fuel side to which hydrogen is supplied in the solid oxide electrolysis cell, and the booster may store the fuel-side combustion off-gas after pressurization in the hydrogen tank. According to this configuration, the pre-combustion mixed gas of the combustion off-gas supplied to the fuel side of the solid oxide electrolysis cell is a hydrogen-rich gas. The combustion off-gas obtained by burning the hydrogen-rich mixed gas contains water vapor and unburned hydrogen, but does not contain oxygen. Therefore, the combustion off-gas from which the moisture has been removed by the gas-liquid separator contains only hydrogen. Therefore, by storing the combustion off-gas containing only hydrogen that has been pressurized by the booster in the hydrogen tank, the unburned hydrogen can be reused. As a result, an increase in the startup energy of the solid oxide electrolysis cell can be suppressed.

[0012] (5) The solid oxide electrolysis cell of the above aspect may further include a temperature sensor that acquires a temperature of the combustion off-gas supplied to a fuel side of the solid oxide electrolysis cell, and a cell temperature adjustment unit that adjusts the temperature of the solid oxide electrolysis cell by controlling the flow rate of hydrogen and the flow rate of oxygen supplied to the fuel-side combustor using the temperature acquired by the temperature sensor. According to this configuration, the cell temperature regulator adjusts the flow rates of hydrogen and oxygen supplied to the solid oxide electrolysis cell according to the temperature of the combustion offgas supplied to the solid oxide electrolysis cell to regulate the temperature of the solid oxide electrolysis cell. When the solid oxide electrolysis cell produces hydrogen from water vapor, the solid oxide electrolysis cell absorbs heat due to hydrogen production, releases heat to the outside, and generates ohmic heating (Joule heating) due to electrical resistance. A decrease in the temperature of the solid oxide electrolysis cell reduces the amount of hydrogen produced. In this configuration, the cell temperature regulator controls the supply rates of oxygen and hydrogen to maintain heat balance in the solid oxide electrolysis cell, thereby controlling the combustion of the mixed gas in the fuel-side combustor and regulating the temperature of the solid oxide electrolysis cell using the combustion heat. Compared to the amount of water vapor used as a feedstock for hydrogen production, the amount of water vapor generated after combustion of the mixed gas in the fuel-side combustor is extremely small. Therefore, in this configuration, the gas temperature of the feed steam supplied to the solid oxide electrolysis cell can be maintained constant without significantly changing the feedstock specifications (e.g., concentration and flow rate). As a result, even if fluctuations occur in the temperature of steam generated in an evaporator or the like that supplies feed steam to the solid oxide electrolysis cell, the temperature of the solid oxide electrolysis cell can be maintained constant by correcting the amount of heat in the fuel-side combustor.

[0013] (6) The solid oxide electrolysis cell of the above aspect may further include a gas-liquid separator that separates moisture from the combustion off-gas that has passed through the solid oxide electrolysis cell, and a booster that boosts the pressure of the combustion off-gas from which moisture has been separated by the gas-liquid separator, wherein the combustor has an oxygen-side combustor that supplies the combustion off-gas to an oxygen side to which oxygen is supplied in the solid oxide electrolysis cell, and the booster may store the compressed oxygen-side combustion off-gas in the oxygen tank. According to this configuration, the mixed gas before combustion of the combustion off gas supplied to the oxygen side of the solid oxide electrolysis cell is oxygen-rich gas. The combustion off gas obtained by combustion of the oxygen-rich mixed gas contains water vapor and unburned oxygen, but does not contain hydrogen. Therefore, the combustion off gas from which moisture has been removed by the gas-liquid separator contains only oxygen. Therefore, by storing the combustion off gas containing only oxygen, which has been pressurized by the booster, in the oxygen tank, the unburned oxygen can be reused. As a result, an increase in the startup energy of the solid oxide electrolysis cell can be suppressed.

[0014] (7) In the solid oxide electrolysis cell of the above aspect, the flow direction of the fuel-side combustion off gas flowing from the fuel-side combustor into the fuel side of the solid oxide electrolysis cell may be opposite to the flow direction of the oxygen-side combustion off gas flowing from the oxygen-side combustor into the oxygen side of the solid oxide electrolysis cell. According to this configuration, fuel off-gas is supplied to both the fuel side and the oxygen side of the solid oxide electrolysis cell. This increases the heat transfer area for heat exchange from the combustion off-gas to the solid oxide electrolysis cell. As a result, the time required for the temperature of the solid oxide electrolysis cell to rise to the operating temperature can be shortened, and an increase in the startup energy of the solid oxide electrolysis cell can be suppressed. Furthermore, because the combustion off-gas supplied to the fuel side and the oxygen side of the solid oxide electrolysis cell flow in opposite directions, differences in temperature distribution within the solid oxide electrolysis cell during temperature rise, which depend on the amount of heat transfer in the flow direction, can be reduced. Furthermore, the opposite flow directions of the two gases further shorten the temperature rise time of the solid oxide electrolysis cell and suppress the occurrence of differences in thermal expansion depending on the temperature distribution in the gas flow direction. As a result, damage to components and performance degradation can be suppressed when the solid oxide electrolysis cell is started up in a short time.

[0015] The present invention can be realized in various forms, for example, in the form of a solid oxide electrolysis cell, an SOEC, an SOFC, a temperature adjustment device for a solid oxide electrolysis cell, a temperature adjustment method for a solid oxide electrolysis cell, a temperature control method for a solid oxide electrolysis cell, a system including these devices, a computer program for executing these devices, a server device for distributing this computer program, a non-transitory storage medium storing the computer program, etc. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a schematic block diagram of an SOFC system according to one embodiment of the present invention. [Figure 2] FIG. 1 is a diagram showing the relationship between the oxygen excess rate and the adiabatic flame temperature. [Figure 3] FIG. 4 is an explanatory diagram of the flow direction of combustion off-gas flowing into the cell stack. [Figure 4] FIG. 4 is an explanatory diagram of the temperature of the cell stack that changes depending on the flow direction of the fuel off-gas. [Figure 5] FIG. 4 is an explanatory diagram of the temperature of the cell stack that changes depending on the flow direction of the fuel off-gas. [Figure 6] FIG. 1 is a schematic block diagram of an SOFC system according to a second embodiment. [Figure 7] 10 is a flowchart of a temperature adjustment control method according to a second embodiment. [Figure 8] FIG. 10 is a schematic block diagram of an SOEC system according to a third embodiment. [Figure 9] 10 is a flowchart of a control method for temperature adjustment according to a third embodiment. [Figure 10] FIG. 10 is a schematic block diagram of an SOEC system according to a fourth embodiment. [Figure 11] FIG. 1 is a schematic block diagram of an SOEC system when the temperature of the cell stack is equal to or higher than the operating temperature. [Figure 12] 10 is a flowchart of a temperature adjustment control method according to a fourth embodiment. [Figure 13]10 is a flowchart of a control method for adjusting the temperature of the cell stack 10 according to a modified example. DETAILED DESCRIPTION OF THE INVENTION

[0017] First Embodiment FIG. 1 is a schematic block diagram of an SOFC (Solid Oxide Fuel Cell) system 100 according to one embodiment of the present invention. In the SOFC system 100 (temperature control device) of this embodiment, a cell stack 10, which is made up of multiple stacked solid oxide electrolysis cells, generates electricity by chemically reacting supplied hydrogen and oxygen at an operating temperature of approximately 700 degrees Celsius (°C). In this embodiment, a fuel-side combustor 41 and an oxygen-side combustor 42 combust a mixed gas containing hydrogen and oxygen in the cell stack 10 that has not yet reached its operating temperature, and the combustion heat raises the temperature of the cell stack 10. Because the combustion in the fuel-side combustor 41 and the oxygen-side combustor 42 does not use air, nitrogen compounds (NOx) are not generated during the temperature rise process of the cell stack 10.

[0018] As shown in FIG. 1, the SOFC system 100 includes a cell stack 10, a hydrogen tank 31 for storing hydrogen, an oxygen tank 32 for storing oxygen, a fuel-side combustor 41 and an oxygen-side combustor 42 for burning the mixed gas, gas-liquid separators 51 and 52 for separating moisture from the gas, water tanks 71 and 72 for storing water, boosters 61 and 62 for pressurizing the gas, temperature sensors S1 to S4 for detecting the temperature of the gas, and a control unit 20 for controlling each part of the SOFC system 100.

[0019] In Fig. 1, the pipes that connect the various components and through which gas flows are indicated by solid lines. The state shown in Fig. 1 is the state before the cell stack 10 starts generating power. Specifically, Fig. 1 shows a state in which the temperature of the cell stack 10 has not yet risen to the operating temperature during power generation (approximately 700°C), and the cell stack 10 is being heated by combustion of the mixed gas in the fuel-side combustor 41 and the oxygen-side combustor 42. Note that hereinafter, the fuel-side combustor 41 and the oxygen-side combustor 42 will collectively be referred to simply as "combustors 41, 42."

[0020] For example, a fuel cell unit cell made of yttria-doped zirconia (YSZ), ytterbium- or scandium-doped zirconia, or a lanthanum gallate-based solid electrolyte can be used as the electrolysis cell constituting the cell stack 10. As shown in Fig. 1, the cell stack 10 has a fuel side (anode) 11 to which a gas containing hydrogen is supplied during power generation, and an oxygen side (cathode) 12 to which a gas containing oxygen is supplied.

[0021] The combustors 41, 42 are equipped with an ignition device that burns a mixed gas of hydrogen supplied from the hydrogen tank 31 and oxygen supplied from the oxygen tank 32. The mixed gas supplied to the fuel-side combustor 41 is controlled by the control unit 20 using a mass flow controller (not shown) to be hydrogen-rich, with a higher proportion of hydrogen than the stoichiometric air-fuel ratio. The fuel-side combustor 41 uses a diffusion combustion method that burns a mixed gas in which oxygen is injected into hydrogen. The combustion off-gas after combustion is supplied to the fuel side 11 of the cell stack 10. Because the mixed gas to be burned is hydrogen-rich, the combustion off-gas supplied to the fuel side 11, which is the fuel-side off-gas, contains hydrogen and water vapor but does not contain oxygen.

[0022] The mixed gas supplied to the oxygen-side combustor 42 is controlled to be oxygen-rich, that is, have a higher oxygen ratio than the theoretical air-fuel ratio. The oxygen-side combustor 42 uses a diffusion combustion method to combust a mixed gas in which hydrogen is injected into oxygen. The combustion off-gas after combustion is supplied to the oxygen side 12 of the cell stack 10. Because the mixed gas to be combusted is oxygen-rich, the combustion off-gas supplied to the oxygen side 12, that is, the oxygen-side off-gas, contains oxygen and water vapor but does not contain hydrogen.

[0023] The control unit 20 detects the temperature T of hydrogen detected by the temperature sensor S1. H2 and the temperature T of oxygen detected by the temperature sensor S2. O2and adjust the gas ratio of the mixed gas in the fuel-side combustor 41. Similarly, the control unit 20 adjusts the hydrogen temperature T detected by the temperature sensor S3. H2 and the temperature T of oxygen detected by the temperature sensor S4. O2 and adjust the gas ratio of the mixed gas in the oxygen-side combustor 42. The adjusted gas ratio of the mixed gas in the combustors 41 and 42 will be described in detail later.

[0024] The gas-liquid separator 51 separates water from the fuel-side off-gas discharged from the fuel side 11 of the cell stack 10 and stores the separated water in a water tank 71. The gas-liquid separator 51 also cools the fuel-side off-gas by dissipating heat into the atmosphere. The fuel-side off-gas from which the water has been separated by the gas-liquid separator 51 is composed of hydrogen. The fuel-side off-gas is pressurized by a booster 61 and stored in the hydrogen tank 31.

[0025] The gas-liquid separator 52 separates water from the oxygen-side off-gas discharged from the oxygen side 12 of the cell stack 10 and stores the separated water in a water tank 72. The gas-liquid separator 52 also cools the oxygen-side off-gas by releasing heat into the atmosphere. The oxygen-side off-gas from which the water has been separated by the gas-liquid separator 52 is composed of oxygen. The combustion off-gas is pressurized by a booster 62 and stored in the oxygen tank 32.

[0026] The control unit 20 calculates the gas temperature T H2 ,T O2 is used to control the combustion gas temperature (adiabatic flame temperature) of the mixed gas combusted in the combustors 41 and 42. The adiabatic flame temperature T is determined by the oxygen excess ratio K of the mixed gas to be combusted, as shown in the following formula (1).

number

[0027] Instead of the above formula (1), the control unit 20 uses the adiabatic flame temperature T and the temperature T of hydrogen in the mixed gas to be combusted. H2 and the temperature of oxygen, T O2Using these, the oxygen excess ratio K is calculated from the relationship shown in the following equation (2). The control unit 20 determines the amount of input hydrogen (hydrogen injection amount) Fa_H2 and the amount of input oxygen (oxygen injection amount) Fa_O2, which are determined by the amount of heat Q generated by the adiabatic flame temperature T and the oxygen excess ratio K. The control unit 20 controls the mass flow controllers to supply the determined amount of input hydrogen Fa_H2 and amount of input oxygen Fa_O2 to each combustor 41, 42. The amount of input hydrogen Fa_H2 and amount of input oxygen Fa_O2, which are determined by the amount of heat Q and the oxygen excess ratio K, are determined from a map measured in advance.

number

[0028] FIG. 2 is a relationship diagram between the oxygen excess ratio K and the adiabatic flame temperature T. In FIG. 2, a change curve C1 (solid line) of the oxygen excess ratio K in the oxygen-rich case, which changes with the adiabatic flame temperature T, is shown, corresponding to the values ​​on the left vertical axis. Also, in FIG. 2, a change curve C2 (dashed line) of the oxygen excess ratio K in the hydrogen-rich case, which changes with the adiabatic flame temperature T, is shown, corresponding to the values ​​on the right vertical axis. For example, when the temperature of the cell stack 10 is increased from 400°C (shown by the solid line in FIG. 2) to 830°C, the oxygen excess ratio K of the oxygen-rich mixed gas combusted in the oxygen-side combustor 42 should change from 40 to 17. Similarly, when the temperature of the cell stack 10 is increased to 830°C, the oxygen excess ratio K of the hydrogen-rich mixed gas combusted in the fuel-side combustor 41 should change from 0.05 to 0.11.

[0029] Fig. 3 is an explanatory diagram of the flow direction of combustion off-gas flowing into the cell stack 10. Fig. 3 shows a schematic perspective view of two stacked electrolysis cells (solid oxide electrolysis cells) 13 as part of the cell stack 10. Note that Fig. 3 defines an orthogonal coordinate system CS having an axis parallel to the stacking direction as the Z axis, and an X axis and a Y axis that are orthogonal to the Z axis.

[0030] 3, the electrolysis cell 13 has an electrolyte membrane 14 disposed between a fuel side (anode) 11 and an oxygen side (cathode) 12. In this embodiment, the flow direction of the fuel-side off-gas flowing from the fuel-side combustor 41 into the fuel side 11 of the electrolysis cell 13 is opposite to the flow direction of the oxygen-side off-gas flowing from the oxygen-side combustor 42 into the oxygen side 12 of the electrolysis cell 13. Hereinafter, the flow direction of the fuel-side off-gas flowing into the fuel side 11 will also be referred to as the "fuel-side flow direction," and the flow direction of the oxygen-side off-gas flowing into the oxygen side 12 will also be referred to as the "oxygen-side flow direction."

[0031] 4 and 5 are explanatory diagrams illustrating the temperature of the cell stack 10 that changes depending on the flow direction of the fuel off-gas. In FIG. 4, the solid line shows the temperature change C3 of the cell stack 10 in a counterflow manner in which the fuel side flow direction and the oxygen side flow direction are opposite to each other, as shown in FIG. 3. In addition, FIG. 4 shows the dashed line shows the temperature change C4 of the cell stack 10 in a parallel flow manner in which the fuel side flow direction and the oxygen side flow direction are the same. In addition, as a comparative example, FIG. 4 shows the dashed line shows the temperature change C5 when oxygen-side off-gas obtained by burning a mixed gas of hydrogen and air is supplied to the cell stack 10 only on the oxygen side 12. Note that in all of the temperature changes C3 to C5, the same flow rate of combustion off-gas with an adiabatic flame temperature T of 650°C is supplied to the cell stack 10.

[0032] 4, the temperature change C3 in the counterflow can raise the temperature of the cell stack 10 more than the temperature change C4 in the parallel flow. Also, as shown by the temperature changes C3 and C4 in the counterflow and parallel flow and the temperature change C5 in the comparative example, the temperature of the cell stack 10 can be raised more than in the comparative example in the counterflow and parallel flow.

[0033] Figure 5 shows the temperature distribution of the cell stack 10 in the flow direction of the combustion off gas (the Y-axis direction in Figure 3) two hours after the combustion off gas was supplied to heat the cell stack 10. Figure 5 shows the temperature according to the position normalized by the distance along the flow direction, with the distance from the inlet to the outlet of the fuel side 11 set to 1. Figure 5 shows the temperature change C6 (solid line) in the counterflow, the temperature change C7 (dashed line) in the parallel flow, and the temperature change C8 (dash-dotted line) in the comparative example.

[0034] As shown by temperature change C6 in Figure 5, the temperature difference between the inlet and outlet temperatures on the counterflow fuel side 11 is smaller than in the parallel flow and comparative examples. The outlet temperature of the parallel flow is slightly lower than the inlet temperature, as shown by temperature change C7. On the other hand, the outlet temperature of the comparative example is more than 100°C lower than the inlet temperature, as shown by temperature change C8.

[0035] As described above, the SOFC system 100 of this embodiment includes the hydrogen tank 31 that stores hydrogen, the oxygen tank 32 that stores oxygen, and the combustors 41 and 42 that combust the mixed gas. The combustors 41 and 42 combust a mixed gas of hydrogen supplied from the hydrogen tank 31 and oxygen supplied from the oxygen tank 32. Therefore, the combustion off-gas generated in the combustors 41 and 42 is supplied to the cell stack 10, thereby increasing the temperature of the cell stack 10. Because the mixed gas combusted in the combustors 41 and 42 does not contain air, the combustion off-gas generated after combustion does not contain thermal NOx, which is generated when nitrogen contained in air reacts with oxygen at high temperatures. Therefore, the SOFC system 100 does not require a device for removing thermal NOx. Furthermore, because the fuel-side combustor 41 combusts a hydrogen-rich mixed gas, the adiabatic flame temperature during combustion of the mixed gas can be controlled by adjusting the flow rate of oxygen supplied to the fuel-side combustor 41. Similarly, since an oxygen-rich mixed gas is burned in the oxygen-side combustor 42, the adiabatic flame temperature during combustion of the mixed gas can be controlled by adjusting the flow rate of hydrogen supplied to the oxygen-side combustor 42.

[0036] Furthermore, the gas-liquid separator 51 of this embodiment separates water from the fuel-side off-gas discharged from the fuel side 11 of the cell stack 10. The booster 61 pressurizes the fuel-side off-gas from which water has been separated by the gas-liquid separator 51 and stores it in the hydrogen tank 31. The pre-combustion mixed gas of the fuel-side off-gas supplied to the fuel side 11 of the cell stack 10 is a hydrogen-rich gas. The fuel-side off-gas obtained by burning the hydrogen-rich mixed gas contains water vapor and unburned hydrogen, but does not contain oxygen. Therefore, the fuel-side off-gas from which water has been removed by the gas-liquid separator 51 contains only hydrogen. Therefore, by storing the fuel-side off-gas containing only hydrogen that has been pressurized by the booster 61 in the hydrogen tank 31, the unburned hydrogen can be reused. As a result, an increase in the startup energy of the cell stack 10 can be suppressed.

[0037] Furthermore, the gas-liquid separator 52 of this embodiment separates water from the oxygen-side off-gas discharged from the oxygen side 12 of the cell stack 10. The pressure booster 62 boosts the pressure of the oxygen-side off-gas from which water has been separated by the gas-liquid separator 52 and stores it in the oxygen tank 32. The pre-combustion mixed gas of the oxygen-side off-gas supplied to the oxygen side 12 of the cell stack 10 is oxygen-rich. The oxygen-side off-gas obtained by burning the oxygen-rich mixed gas contains water vapor and unburned oxygen, but does not contain hydrogen. Therefore, the oxygen-side off-gas from which water has been removed by the gas-liquid separator 52 contains only oxygen. Therefore, by storing the oxygen-side off-gas containing only oxygen that has been boosted by the pressure booster 62 in the oxygen tank 32, the unburned oxygen can be reused. As a result, an increase in the startup energy of the cell stack 10 can be suppressed.

[0038] In addition, in this embodiment, as shown in FIG. 3 , the flow direction of the fuel-side offgas flowing from the fuel-side combustor 41 into the fuel side 11 of the electrolysis cell 13 is opposite to the flow direction of the oxygen-side offgas flowing from the oxygen-side combustor 42 into the oxygen side 12 of the electrolysis cell 13. That is, in this embodiment, fuel offgas is supplied to both the fuel side 11 and the oxygen side 12 of the cell stack 10. This increases the heat transfer area for heat exchange from the combustion offgas to the cell stack 10. As a result, the time required for the temperature of the cell stack 10 to rise to the operating temperature can be shortened, and an increase in the startup energy of the cell stack 10 can be suppressed. Furthermore, because the flow directions of the fuel-side offgas and the oxygen-side offgas are opposite to each other, as shown in FIG. 5 , the difference in temperature distribution within the cell stack 10 during temperature rise, which depends on the amount of heat transfer in the flow direction, can be reduced. Furthermore, the opposite flow directions of the two combustion offgases further shorten the temperature rise time of the cell stack 10 and suppress the occurrence of a difference in thermal expansion depending on the temperature distribution in the flow direction of the combustion offgas. As a result, damage to components and performance degradation when starting up the cell stack 10 in a short time can be suppressed.

[0039] In addition, in this embodiment, a diffusion combustion method is used in which oxygen is injected into hydrogen in the fuel-side combustor 41, and hydrogen is injected into oxygen in the oxygen-side combustor 42. Therefore, even if the temperature of the mixed gas before combustion is above the auto-ignition temperature, the occurrence of flashback, which is a problem in premixed combustion, can be suppressed. Therefore, the SOFC system 100 can combust the mixed gas with a simple configuration that does not require a device with a special flashback suppression function. Furthermore, in this embodiment, the oxygen partial pressure of the combustion off-gas is adjusted to the fuel side (low oxygen partial pressure due to water vapor and a large amount of hydrogen), so the impact on deterioration of the electrolysis cell 13 due to electrode oxidation is extremely small. Therefore, heat can be supplied to the cell stack 10 via the flow path on the fuel side 11.

[0040] Second Embodiment 6 is a schematic block diagram of an SOFC system 100a of the second embodiment. The SOFC system 100a of the second embodiment further includes a fuel-side heat exchanger (heat exchanger) 81, an oxygen-side heat exchanger (heat exchanger) 82, temperature sensors S5 and S6, and control valves CV1 to CV4 in addition to the components of the SOFC system 100 of the first embodiment. A control unit 20a of the second embodiment controls the gas temperatures T H2 ,T O2 , Ta, and Tc are used to control the control valves CV1 to CV4, thereby adjusting the flow rates of hydrogen and oxygen supplied to the combustors 41 and .

[0041] 6, the fuel-side heat exchanger 81 exchanges heat between the fuel-side off-gas discharged from the fuel side 11 of the cell stack 10 and hydrogen supplied from the hydrogen tank 31. Heat is transferred from the high-temperature fuel-side off-gas discharged from the fuel side 11 to the low-temperature hydrogen supplied to the fuel-side combustor 41, thereby heating the hydrogen. Similarly, the oxygen-side heat exchanger 82 exchanges heat between the oxygen-side off-gas discharged from the oxygen side 12 of the cell stack 10 and oxygen supplied from the oxygen tank 32. Heat is transferred from the high-temperature oxygen-side off-gas discharged from the oxygen side 12 to the low-temperature oxygen supplied to the oxygen-side combustor 42, thereby heating the oxygen.

[0042] The control unit 20a sets the adiabatic flame temperature T of the combustors 41 and 42. For example, the control unit 20a sets the adiabatic flame temperature T by receiving an operation by a user. The control unit 20a compares the set adiabatic flame temperature T with the temperature Ta of the fuel-side off-gas supplied to the fuel side 11 of the cell stack 10, detected by the temperature sensor S5, and controls the adjustment valves CV1 and CV2. By controlling the adjustment valve CV1, a flow rate F_cv1 of hydrogen heated by the fuel-side heat exchanger 81 and supplied to the fuel-side combustor 41 is set. By controlling the adjustment valve CV2, a flow rate F_cv2 of oxygen blown into the fuel-side combustor 41 is set. Note that in the second embodiment, the adiabatic flame temperature T set in the fuel-side combustor 41 and the adiabatic flame temperature T set in the oxygen-side combustor 42 are the same, but they may be different in other embodiments.

[0043] The control unit 20a combusts the mixed gas in the fuel-side combustor 41 when the temperature Ta of the fuel-side off-gas supplied to the fuel side 11 minus the adiabatic flame temperature T is smaller than a preset threshold value ε1. As in the first embodiment, the control unit 20a combusts the mixed gas in the fuel-side combustor 41 by subtracting the adiabatic flame temperature T from the adiabatic flame temperature T. H2 and the temperature of oxygen, T O2 The oxygen excess ratio K is calculated by using the above equation (2). The control unit 20a sets the flow rate F_cv1 of hydrogen and the flow rate F_cv2 of oxygen supplied to the fuel-side combustor 41 based on the calculated oxygen excess ratio K and the amount of heat Q generated by the adiabatic flame temperature T.

[0044] The control unit 20a compares the set adiabatic flame temperature T with the temperature Tc of the oxygen-side combustion off-gas supplied to the oxygen side 12 of the cell stack 10, detected by the temperature sensor S6, and controls the adjustment valves CV3 and CV4. By controlling the adjustment valve CV3, a flow rate F_cv3 of hydrogen heated by the oxygen-side heat exchanger 82 and supplied to the oxygen-side combustor 42 is set. By controlling the adjustment valve CV4, a flow rate F_cv4 of oxygen blown into the oxygen-side combustor 42 is set. The control unit 20a combusts the mixed gas in the oxygen-side combustor 42 when the temperature Tc of the oxygen-side off-gas supplied to the oxygen side 12 minus the adiabatic flame temperature T is smaller than a preset threshold value ε2. The control unit 20a compares the adiabatic flame temperature T with the temperature Tc of hydrogen in the mixed gas in the oxygen-side combustor 42. H2 and the temperature of oxygen, T O2 The control unit 20a determines the oxygen excess ratio K using the determined oxygen excess ratio K and the amount of heat Q generated by the adiabatic flame temperature T. The control unit 20a sets the flow rate F_cv3 of hydrogen and the flow rate F_cv4 of oxygen supplied to the oxygen-side combustor 42.

[0045] 7 is a flowchart of a control method for temperature regulation according to the second embodiment. In the temperature regulation flow shown in FIG. 7, first, the control unit 20a sets the adiabatic flame temperature T of the combustors 41 and 42 (step S1). The control unit 20a then calculates the temperature T of the hydrogen supplied to the fuel-side combustor 41, which is detected by the temperature sensors S1 and S2. H2 and the temperature of oxygen, T O2 and the temperature Ta of the fuel-side off-gas supplied to the fuel side 11 of the cell stack 10 (step S12).

[0046] The control unit 20a determines whether the difference obtained by subtracting the adiabatic flame temperature T from the temperature Ta of the fuel-side off-gas supplied to the fuel side 11 is smaller than a threshold value ε1 (step S13). If the difference is smaller than the threshold value ε1 (step S13: YES), the control unit 20a repeats the processing from step S12 onwards. If the difference is equal to or greater than the threshold value ε1 (step S13: NO), the control unit 20a calculates the difference between the adiabatic flame temperature T and the hydrogen temperature T H2 and the temperature of oxygen, T O2The control unit 20a calculates the oxygen excess ratio K using the calculated oxygen excess ratio K and the heat quantity Q calculated from the adiabatic flame temperature T (step S14). The control unit 20a calculates the hydrogen flow rate F_cv1 and the oxygen flow rate F_cv2 to be supplied to the fuel-side combustor 41 using the calculated oxygen excess ratio K and the heat quantity Q calculated from the adiabatic flame temperature T (step S15). The control unit 20a controls the adjustment valves CV1 and CV2 so that the hydrogen flow rate F_cv1 and the oxygen flow rate F_cv2 become the calculated values ​​(step S16). Thereafter, the control unit 20a determines whether or not to end the startup operation of the cell stack 10 (step S17). If the startup operation of the cell stack 10 is not to be ended (step S17: NO), the control unit 20a repeats the processing from step S12 onwards.

[0047] When the adiabatic flame temperature T is set in step S1, the control unit 20a calculates the temperature T of the hydrogen supplied to the oxygen-side combustor 42 detected by the temperature sensors S3 and S4. H2 and the temperature of oxygen, T O2 and the temperature Tc of the oxygen-side off-gas supplied to the oxygen side 12 of the cell stack 10 (step S22). The control unit 20a determines whether the difference obtained by subtracting the adiabatic flame temperature T from the temperature Tc of the oxygen side 12 is smaller than a threshold value ε2 (step S23). If the difference is smaller than the threshold value ε2 (step S23: YES), the control unit 20a repeats the processing from step S22 onwards. If the difference is equal to or greater than the threshold value ε1 (step S23: NO), the control unit 20a calculates the adiabatic flame temperature T and the hydrogen temperature T H2 and the temperature of oxygen, T O2The control unit 20a calculates the oxygen excess ratio K using the calculated oxygen excess ratio K and the heat quantity Q calculated from the adiabatic flame temperature T (step S25). The control unit 20a controls the adjustment valves CV3 and CV4 so that the hydrogen flow rate F_cv3 and the oxygen flow rate F_cv4 are the calculated values ​​(step S26). The control unit 20a then determines whether or not to terminate the operation of the cell stack 10 (step S27). If the startup operation of the cell stack 10 is not to be terminated (step S27: NO), the control unit 20a repeats the processing from step S22 onwards. If, in the processing of steps S17 and S27, the temperature of the cell stack 10 has risen to a temperature at which the cell stack 10 operates normally and the startup operation is to be stopped (steps S17 and S27: YES), the control unit 20a terminates the temperature adjustment flow. Thereafter, the cell stack 10 shifts to a steady state operation in which it generates electricity using hydrogen and oxygen.

[0048] As described above, the fuel-side heat exchanger 81 of the second embodiment exchanges heat between the fuel-side off-gas discharged from the fuel side 11 of the cell stack 10 and hydrogen supplied from the hydrogen tank 31. Similarly, the oxygen-side heat exchanger 82 exchanges heat between the oxygen-side off-gas discharged from the oxygen side 12 of the cell stack 10 and oxygen supplied from the oxygen tank 32. Therefore, through the heat exchange in the fuel-side heat exchanger 81, heat is transferred from the high-temperature fuel-side off-gas discharged from the cell stack 10 to the hydrogen supplied from the hydrogen tank 31. Similarly, through the heat exchange in the oxygen-side heat exchanger 82, heat is transferred from the high-temperature oxygen-side off-gas discharged from the cell stack 10 to the oxygen supplied from the oxygen tank 32. This makes it possible to recover sensible heat from the combustion off-gas and raise the temperature of the hydrogen or oxygen supplied to the cell stack 10. As a result, in the second embodiment, an increase in the startup energy of the cell stack 10 can be suppressed.

[0049] Third Embodiment FIG. 8 is a schematic block diagram of an SOEC system (temperature control device) 101 of the third embodiment. The SOEC system 101 of the third embodiment generates hydrogen in the cell stack 10 by electrolyzing high-temperature steam generated in the evaporator 19 in the cell stack 10. In the SOEC system 101, while the cell stack 10 is heated and generating hydrogen, high-temperature steam containing hydrogen supplied from the hydrogen tank 31 is supplied to the fuel-side combustor 41, and oxygen is injected into the fuel-side combustor 41 for combustion. The control unit 20b maintains a constant temperature of the cell stack 10 during hydrogen generation by adjusting the flow rate of oxygen supplied to the fuel-side combustor 41 and the flow rate of hydrogen injected, depending on the temperature of the high-temperature steam supplied to the cell stack 10. Note that in the third embodiment, configurations that differ from those of the SOFC system 100 of the first embodiment and the SOFC system 100a of the second embodiment will be described, and descriptions of the same configurations will be omitted.

[0050] As shown in Figure 8, the SOEC system 101 includes a cell stack 10, a hydrogen tank 31, an oxygen tank 32, a fuel-side combustor 41, a fuel-side heat exchanger 81, an oxygen-side heat exchanger 82, gas-liquid separators 51 and 52, pressure boosters 61 and 62, water tanks 71 and 72, an evaporator 19, temperature sensors S1, S2, and S5, control valves CV1b, CV2b, and CV5, and a control unit 20b (temperature control unit). The evaporator 19 generates high-temperature steam by heating liquid water supplied via the control valve CV5. The control valve CV5 adjusts the flow rate of water supplied to the evaporator 19. The control valve CV5 is adjusted according to the amount of hydrogen required to be produced by the cell stack 10.

[0051] The control unit 20b controls the gas temperature T H2 ,T O2, Ta to control the adjustment valves CV1b, CV2b, and adjust the flow rates of hydrogen and oxygen supplied to the fuel-side combustor 41. Specifically, first, the control unit 20b sets the adiabatic flame temperature T of the fuel-side combustor 41, as in the second embodiment. The control unit 20b compares the adiabatic flame temperature T with the temperature Ta of the fuel-side off-gas supplied to the fuel side 11 of the cell stack 10, which is detected by the temperature sensor S5, and controls the adjustment valves CV1, CV2. Controlling the adjustment valve CV1b sets the flow rate F_cv1 of hydrogen heated by the fuel-side heat exchanger 81 and supplied to the fuel-side combustor 41. Controlling the adjustment valve CV2b sets the flow rate F_cv2 of oxygen blown into the fuel-side combustor 41.

[0052] When the temperature Ta of the fuel-side off-gas supplied to the fuel side 11 minus the adiabatic flame temperature T is smaller than a preset threshold value ε3, the control unit 20b controls the flow rate of oxygen blown into the fuel-side combustor 41 to combust the mixed gas in the fuel-side combustor 41. When the temperature Ta of the cell stack 10 is sufficiently high, the mixed gas in the fuel-side combustor 41 burns without ignition. As in the first embodiment, the control unit 20b calculates the adiabatic flame temperature T and the hydrogen temperature T in the mixed gas in the fuel-side combustor 41. H2 and the temperature of oxygen, T O2 and into the above equation (2) to determine the oxygen excess ratio K. The control unit 20b sets the flow rate F_cv1 of hydrogen and the flow rate F_cv2 of oxygen supplied to the fuel-side combustor 41 based on the determined oxygen excess ratio K and the amount of heat Q generated by the adiabatic flame temperature T.

[0053] 9 is a flowchart of a control method for temperature regulation according to the third embodiment. In the temperature regulation flow shown in FIG. 9, first, the control unit 20b sets the adiabatic flame temperature T of the fuel-side combustor 41 (step S31). The control unit 20b calculates the temperature T of the hydrogen supplied to the fuel-side combustor 41, which is detected by the temperature sensors S1 and S2. H2 and the temperature of oxygen, T O2 and the temperature Ta of the fuel-side off-gas supplied to the fuel side 11 of the cell stack 10 (step S32).

[0054] The control unit 20b determines whether the difference obtained by subtracting the adiabatic flame temperature T from the temperature Ta of the fuel-side off-gas supplied to the fuel side 11 is smaller than a threshold value ε3 (step S33). If the difference is smaller than the threshold value ε3 (step S33: YES), the control unit 20b repeats the processing from step S32 onwards. If the difference is equal to or greater than the threshold value ε3 (step S33: NO), the control unit 20b calculates the difference between the adiabatic flame temperature T and the hydrogen temperature T H2 and the temperature of oxygen, T O2 The control unit 20b calculates the oxygen excess ratio K using the calculated oxygen excess ratio K and the heat quantity Q calculated from the adiabatic flame temperature T (step S35). The control unit 20b controls the adjustment valves CV1b and CV2b so that the hydrogen flow rate F_cv1 and oxygen flow rate F_cv2 to be supplied to the fuel-side combustor 41 are achieved (step S36). The mixed gas in the fuel-side combustor 41, whose gas ratio has been controlled, is combusted. Thereafter, the control unit 20b determines whether or not to terminate the operation of the cell stack 10 (step S37). If the startup operation of the cell stack 10 is not to be terminated (step S37: NO), the control unit 20b repeats the processing from step S32 onwards. If the operation of the cell stack 10 is to be ended (step S37: YES), the control unit 20b stops the supply of hydrogen and oxygen, ends the operation of the cell stack 10, and ends the temperature adjustment flow.

[0055] In the SOEC system 101 of the third embodiment, the control unit 20b controls the gas temperature T H2 ,T O2, Ta to control the control valves CV1b, CV2b, thereby adjusting the flow rates of hydrogen and oxygen supplied to the fuel-side combustor 41. When the cell stack 10 generates hydrogen from high-temperature steam, the cell stack 10 absorbs heat due to hydrogen generation, releases heat to the outside, and generates ohmic heating (Joule heating) due to electrical resistance. As the temperature of the cell stack 10 decreases, the amount of hydrogen generated decreases. In this embodiment, the control unit 20b controls the supply amounts of oxygen and hydrogen to maintain heat balance in the cell stack 10, thereby controlling the combustion of the mixed gas in the fuel-side combustor 41 and adjusting the temperature of the cell stack 10 using the combustion heat. Compared to the high-temperature steam used as a raw material for hydrogen generation, the amount of steam generated after combustion of the mixed gas in the fuel-side combustor 41 is extremely small. Therefore, in this embodiment, the gas temperature of the high-temperature steam supplied to the cell stack 10 can be maintained constant without significantly changing the raw material specifications (e.g., concentration and flow rate) in the evaporator 19. As a result, even if fluctuations occur in the steam temperature in the evaporator 19 that supplies high-temperature steam to the cell stack 10, the temperature of the cell stack 10 can be maintained constant by correcting the amount of heat in the fuel-side combustor 41.

[0056] <Fourth embodiment> 10 is a schematic block diagram of an SOEC system 101c of the fourth embodiment. The SOEC system 101c of the fourth embodiment is significantly different from the SOEC system 101 of the third embodiment in that it includes a heat accumulator 90. In the fourth embodiment, the heat accumulator 90 stores excess heat from the cell stack 10 when the operation of the cell stack 10 is stopped, and supplies the stored heat to the cell stack 10 when the operation of the cell stack 10 is restarted. In the fourth embodiment, only the configurations that are different from those of the SOEC system 101 of the third embodiment will be described, and descriptions of the same configurations will be omitted.

[0057] As shown in FIG. 10, an SOEC system 101c further includes a heat accumulator 90 and the fuel-side heat exchanger 81 of the first embodiment in addition to the components of the SOEC system 101 of the third embodiment. The heat accumulator 90 has a heat storage material capable of exchanging heat with the cell stack 10. The heat storage material is a metal oxide that stores heat through an oxidation reaction when combustion off-gas is supplied and is reduced during heat storage. In this embodiment, an Fe (iron)-based metal oxide is used that starts releasing heat through an oxidation reaction at approximately 150°C.

[0058] The SOEC system 101c also includes, instead of the control valves CV1b and CV2b, control valves CV1c, CV2c, CV3c, CV4c, and CV6, and three-way valves V6 and V7. The SOEC system 101c also includes, instead of the temperature sensors S1, S2, and S5, a temperature sensor S6 that detects the temperature Tsc of the cell stack 10, and a temperature sensor S7 that detects the temperature Ts of the heat storage material in the heat accumulator 90.

[0059] The control unit (combustion control unit) 20c controls the adjustment valves CV1c, CV2c, CV3c, CV4c, and CV6 and the three-way valves V6 and V7 to control the amount of hydrogen supplied from the hydrogen tank 31 to the combustors 41 and 42, the amount of oxygen supplied from the oxygen tank 32 to the combustors 41 and 42, and the amount of water vapor supplied from the evaporator 19 to the cell stack 10. In Fig. 10, when restarting the cell stack 10, the connected pipes are shown by solid lines and the unconnected pipes are shown by dashed lines through the control of the adjustment valves CV1c, CV2c, CV3c, CV4c, and CV6 and the three-way valves V6 and V7.

[0060] When increasing the temperature of the cell stack 10, if the temperature Ts of the heat storage material is below a predetermined temperature, the control unit 20c supplies a stoichiometric air-fuel ratio mixed gas to the oxygen-side combustor 42, burns it, and supplies the combustion off-gas to the heat accumulator 90. If the temperature Ts of the heat storage material is equal to or higher than a predetermined temperature, the control unit 20c stops the supply of the mixed gas to the oxygen-side combustor 42 and stops combustion of the mixed gas. Specifically, if the temperature Ts of the heat storage material detected by the temperature sensor S7 is below a predetermined target temperature Ts,t, the control unit 20c supplies hydrogen at a stoichiometric air-fuel ratio flow rate F_cv3 and oxygen at a flow rate F_cv4 from the evaporator 19 to the oxygen-side combustor 42, in addition to water vapor at a flow rate F_cv5. When the stoichiometric air-fuel ratio mixed gas in the oxygen-side combustor 42 is combusted, the oxygen-side combustion off-gas is supplied to the heat accumulator 90. In the heat accumulator 90, the water vapor heated by combustion reacts with the heat storage material, causing the heat storage material to start releasing heat and raising the temperature of the cell stack 10, which can exchange heat with the heat storage material. Note that because a mixed gas with a stoichiometric air-fuel ratio is being burned, the oxygen-side combustion off-gas does not contain hydrogen or oxygen. In this embodiment, the target temperature Ts,t is set to 200°C, at which the rate of the oxidation reaction of the heat storage material exceeds a certain level.

[0061] When the temperature Ts of the heat storage material is equal to or higher than the target temperature Ts,t, the control unit 20c stops the supply of hydrogen and oxygen to the oxygen-side combustor 42 and continues to supply water vapor at a flow rate F_cv5 from the evaporator 19. The control unit 20c closes the adjustment valves CV3c and CV4c to stop the supply of hydrogen and oxygen. The control unit 20c stops combustion in the oxygen-side combustor 42 and continues to supply water vapor at a flow rate F_cv5. In this case, the heat accumulator 90 performs an oxidation reaction at a constant rate, and the temperature Tsc of the cell stack 10 rises.

[0062] In addition to determining the temperature Ts of the heat storage material, the control unit 20c also determines the temperature Tsc of the cell stack 10 detected by the temperature sensor S6. When the temperature Tsc of the cell stack 10 is lower than the operating temperature Tsc,t of the cell stack 10, the control unit 20c supplies high-temperature steam generated by the evaporator 19 to the heat accumulator 90 via the oxygen-side combustor 42. On the other hand, when the temperature Tsc of the cell stack 10 is equal to or higher than the operating temperature Tsc,t, the control unit 20c changes the supply destination of the high-temperature steam supplied from the evaporator 19 to the cell stack 10 by switching the connection of the adjustment valves CV1c, CV2c, CV3c, CV4c, and CV6 and the connection of the three-way valves V6 and V7.

[0063] FIG. 11 is a schematic block diagram of an SOEC system 101c when the temperature Tsc of the cell stack 10 is equal to or higher than the operating temperature Tsc,t. As shown in FIG. 11, in a steady operating state in which the temperature Tsc of the cell stack 10 has changed to equal to or higher than the operating temperature Tsc,t, the control unit 20c opens the closed control valves CV3c and CV6. The control unit 20c also switches the three-way valve V6 to connect the evaporator 19 to the low-temperature side of the fuel-side heat exchanger 81. The control unit 20c also switches the three-way valve V7 to connect the booster 61 to the gas-liquid separator 51. As a result, the water vapor generated by the evaporator 19 is heated by the fuel-side heat exchanger 81, mixed with hydrogen supplied from the hydrogen tank 31, and supplied to the fuel side 11 of the cell stack 10, whereupon hydrogen is produced by the cell stack 10.

[0064] Fig. 12 is a flowchart of a control method for temperature adjustment according to the fourth embodiment. Fig. 12 shows a control flow for raising the temperature Tsc of the cell stack 10, which is at room temperature, to an operating temperature Tsc,t, and changing the cell stack 10 to a steady operating state. As shown in Fig. 12, first, the control unit 20c sets a target temperature Ts,t for the heat accumulator 90 and an operating temperature Tsc,t for the cell stack 10 (step S41). The control unit 20c sets the target temperature Ts,t and the operating temperature Tsc,t by accepting operations by the user, etc.

[0065] The control unit 20c sets the flow rate F_cv5 of water vapor generated by the evaporator 19, and the flow rate F_cv3 of hydrogen and the flow rate F_cv4 of oxygen that achieve the stoichiometric air-fuel ratio (step S42). The flow rate F_cv5 of water vapor, the flow rate F_cv3 of hydrogen, and the flow rate F_cv4 of oxygen may be set in advance during hydrogen production, or may be set by the user each time. The control unit 20c controls the connections of the adjustment valves CV1c, CV2c, CV3c, CV4c, and CV6 and the connections of the three-way valves V6 and V7 so as to supply the set flow rate F_cv5 of water vapor, the flow rate F_cv3 of hydrogen, and the flow rate F_cv4 of oxygen (step S43).

[0066] The control unit 20c starts combustion of the mixed gas in the oxygen-side combustor 42 (step S44). The mixed gas in the oxygen-side combustor 42 is ignited by the ignition device and combusted. The control unit 20c acquires the temperature Ts of the heat storage material detected by the temperature sensor S7 and the temperature Tsc of the cell stack 10 detected by the temperature sensor S6 (step S45). Thereafter, the control unit 20c continuously acquires the temperature Ts of the heat storage material and the temperature Tsc of the cell stack 10.

[0067] The control unit 20c determines whether the temperature Ts of the heat accumulator 90 is equal to or higher than the target temperature Ts,t (step S46). If the temperature Ts of the heat accumulator 90 is lower than the target temperature Ts,t (step S46: NO), the control unit 20c continues to wait until the temperature Ts changes to equal to or higher than the target temperature Ts,t. If the temperature Ts of the heat accumulator 90 is equal to or higher than the target temperature Ts,t (step S46: YES), the control unit 20c closes the adjustment valves CV3c and CV4c to stop the supply of hydrogen and oxygen to the fuel-side heat exchanger 81 and stop combustion in the fuel-side heat exchanger 81 (step S47).

[0068] The control unit 20c determines whether the temperature Tsc of the cell stack 10 is equal to or higher than the operating temperature Tsc,t (step S48). If the temperature Tsc of the cell stack 10 is lower than the operating temperature Tsc,t (step S48: NO), the control unit 20c continues to wait for the temperature Tsc to change to or higher than the operating temperature Tsc,t. If the temperature Tsc of the cell stack 10 is equal to or higher than the operating temperature Tsc,t (step S48: YES), the control unit 20c opens the adjustment valves CV3c and CV6 and switches the three-way valves V6 and V7 (step S49), ending the temperature adjustment flow. Thereafter, the cell stack 10 transitions to steady-state operation in which hydrogen is generated from the supplied water vapor.

[0069] As described above, in the SOEC system 101c of the fourth embodiment, the heat accumulator 90 has a heat storage material capable of heat exchange with the cell stack 10. The heat storage material is a metal oxide that is supplied with combustion off-gas, stores heat through an oxidation reaction, and is reduced during heat storage. When increasing the temperature Tsc of the cell stack 10, if the temperature Ts of the heat storage material is below the target temperature Ts,t, the control unit 20c supplies a mixed gas with a stoichiometric air-fuel ratio to the oxygen-side combustor 42, burns it, and supplies the combustion off-gas to the heat accumulator 90. If the temperature Ts of the heat storage material is equal to or higher than the target temperature Ts,t, the control unit 20c stops the supply of hydrogen and oxygen to the oxygen-side combustor 42 and stops the combustion of the mixed gas. Therefore, in the fourth embodiment, when the operation of the cell stack 10, which has been operating at a high temperature, is stopped, the heat accumulator 90 can store excess heat from the cell stack 10. The heat stored in the heat accumulator 90 can be used to heat the cell stack 10 when it is operated again. As a result, in the SOEC system 101c of the fourth embodiment, the heat storage and heat release of the heat accumulator 90 are utilized, thereby suppressing an increase in the startup energy of the cell stack 10. Furthermore, the heat storage material, which releases heat through an oxidation reaction, has an increased reaction rate of heat release as its temperature rises. Therefore, when the temperature of the cell stack 10 at the beginning of startup of the SOEC system 101c is below the operating temperature Tsc,t, if the mixed gas combusted by the oxygen-side combustor 42 is supplied to the heat storage material, the reaction rate of the heat storage material increases, and the temperature rise rate of the cell stack 10 is accelerated. In other words, even if the SOEC system 101c does not have an external heat source for increasing the reaction rate of the heat storage material, the temperature rise rate of the cell stack 10 can be accelerated by supplying the combustion off-gas to the heat accumulator 90.

[0070] <Modifications of the above embodiment> The present invention is not limited to the above-described embodiment, and can be implemented in various forms without departing from the spirit of the present invention, including, for example, the following modifications: In the above-described embodiment, part of the configuration realized by hardware may be replaced by software, and conversely, part of the configuration realized by software may be replaced by hardware.

[0071] <Variation 1> The SOFC systems 100, 100a of the first and second embodiments and the SOEC systems 101, 101c of the third and fourth embodiments are merely examples, and the configuration of the temperature control device for the solid oxide electrolysis cell can be modified. The temperature control device for the solid oxide electrolysis cell can be modified as long as it includes a hydrogen tank 31, an oxygen tank 32, and at least one of a fuel-side combustor 41 and an oxygen-side combustor 42. For example, the SOFC system 100 of the first embodiment may be an SOEC system, a reversible SOFC / SOEC system that functions as both an SOFC and an SOEC, or a temperature control system that does not include a cell stack 10. The cell stack 10, which is heated by combustion in the combustors 41, 42, may be a single electrolysis cell 14 that is not stacked as a solid oxide electrolysis cell. The SOFC system 100 may not include, for example, an oxygen-side combustor 42. Furthermore, the SOFC system 100 does not necessarily have to include the boosters 61 and 62 and the gas-liquid separators 51 and 52. When the SOFC system 100 includes both the fuel-side combustor 41 and the oxygen-side combustor 42, the fuel-side flow direction and the oxygen-side flow direction shown in Fig. 3 may be parallel flows rather than counter flows.

[0072] The SOFC system 100a of the second embodiment includes two combustors 41, 42 and two heat exchangers 81, 82, but may include, for example, the fuel-side combustor 41 and the fuel-side heat exchanger 81, and not the oxygen-side combustor 42 and the oxygen-side heat exchanger 82. Furthermore, the SOFC system 101 of the third embodiment combusts the mixed gas in the fuel-side combustor 41 so as to maintain the heat balance of the cell stack 10 after the cell stack 10 reaches its operating temperature, but temperature adjustment may not be required after the cell stack 10 reaches its operating temperature.

[0073] In the SOEC system 101c of the fourth embodiment, the oxygen-side offgas from the oxygen-side combustor 42 is supplied to the heat accumulator 90. However, the system may further include a fuel-side combustor 41 and a heat accumulator to which the combustion-side offgas is supplied. Alternatively, the fuel-side offgas from the fuel-side combustor 41 may be supplied to the same heat accumulator 90 to which the oxygen-side offgas is supplied. While the fuel-side combustor 41 is supplied with high-temperature steam generated by the evaporator 19, it may also be supplied with only hydrogen and oxygen at a stoichiometric air-fuel ratio without high-temperature steam. The heat storage material of the heat accumulator 90 can be modified. The heat storage material may be a metal oxide containing a different metal element instead of an Fe-based metal oxide, or may be another compound that begins to release heat through an oxidation reaction.

[0074] The threshold values ​​ε1 and ε2 used in the second embodiment and the threshold value ε3 used in the third embodiment may be the same value, or may be changed depending on the set temperature of the cell stack 10 to be controlled, etc. The adiabatic flame temperature T set in the second and third embodiments, and the target temperature Ts,t of the heat accumulator 90 and the operating temperature Tsc,t of the cell stack 10 set in the fourth embodiment may also be set appropriately.

[0075] <Variation 2> FIG. 13 is a flowchart of a control method for temperature adjustment of the cell stack 10 according to a modified example. In the temperature adjustment flow shown in FIG. 13, first, the control unit 20 supplies hydrogen from the hydrogen tank 31 to the combustors 41 and 42 (step S51). Similarly, the control unit 20 supplies oxygen from the oxygen tank 32 to the combustors 41 and 42 (step S52). The control unit 20 combusts the mixed gas of oxygen and hydrogen in the combustors 41 and 42 (step S53). In the fuel-side combustor 41, the flow rates of hydrogen and oxygen are controlled so that the mixed gas to be combusted becomes hydrogen-rich. In the oxygen-side combustor 42, the flow rates of hydrogen and oxygen are controlled so that the mixed gas to be combusted becomes oxygen-rich. The control unit 20 supplies the combustion offgas generated after combustion of the mixed gas in the combustors 41 and 42 to the cell stack 10 (step S54). The control unit 20 determines whether to terminate the startup operation of the cell stack 10 (step S55). If the control unit 20 does not want to end the startup operation of the cell stack 10 (step S55: NO), it repeats the processes from step S51 onwards. If the control unit 20 wants to end the startup operation of the cell stack 10 (step S55: YES), it stops the supply of hydrogen and oxygen to the combustor 41, stops combustion in the combustor 41, and ends the temperature adjustment flow. Thereafter, the cell stack 10 functions as an SOFC or SOEC.

[0076] This aspect has been described above based on embodiments and modifications. However, the above-described embodiments are intended to facilitate understanding of this aspect and are not intended to limit this aspect. This aspect may be modified or improved without departing from the spirit and scope of the claims, and equivalents thereof are included in this aspect. Furthermore, if a technical feature is not described as essential in this specification, it may be deleted as appropriate. [Explanation of symbols]

[0077] ε1~ε3...Threshold 10...Cell stack 11...Fuel side of cell stack (anode) 12...Oxygen side of cell stack (cathode) 13...Electrolytic cell (solid oxide electrolytic cell) 14...Electrolyte membrane 19...Evaporator 20, 20a, 20b, 20c, ...Control section 31...Hydrogen tank 32...Oxygen tank 41...Fuel side combustor 42...Oxygen side combustor 51,52...gas-liquid separator 61,62...Booster 71, 72...Water tank 81…Fuel side heat exchanger (heat exchanger) 82...Oxygen side heat exchanger (heat exchanger) 90... Heat storage device 100,100a...SOFC system (temperature control device) 101, 101c...SOEC system (temperature control device) C1, C2...Change curve C3~C8...Temperature change CS...Cartesian coordinate system CV1, CV1b, CV1c, CV2, CV2b, CV3, CV3c, CV4, CV5...control valve F_cv1, F_cv3...Hydrogen flow rate F_cv2, F_cv4...oxygen flow rate F_cv5...flow rate of water vapor Fa_H2: Amount of hydrogen input Fa_O2: Amount of oxygen input K: Oxygen excess rate S1 to S7: Temperature sensors T...Adiabatic flame temperature T H2 ...Hydrogen temperature T O2 …Oxygen temperature Ta: temperature of fuel-side off-gas Tc: Oxygen off-gas temperature Ts: Temperature of the heat storage tank Ts,t...Target temperature of the heat storage unit Tsc: Cell stack temperature Tsc,t: Cell stack operating temperature V6, V7...Three-way valve

Claims

1. 1. A temperature control device for a solid oxide electrolysis cell, comprising: a hydrogen tank for storing hydrogen; an oxygen tank for storing oxygen; a combustor that combusts a mixed gas obtained by mixing hydrogen supplied from the hydrogen tank and oxygen supplied from the oxygen tank, discharges combustion off-gas, and supplies the combustion off-gas to the solid oxide electrolysis cell; a heat storage unit having a heat storage material that is supplied with the combustion off gas and releases heat through an oxidation reaction, the heat storage material being capable of exchanging heat with the solid oxide electrolysis cell; a combustion control unit that controls combustion of the mixed gas by the combustor; Equipped with The combustor includes: a fuel-side combustor that combusts the hydrogen-rich mixed gas having a hydrogen ratio greater than that of the stoichiometric air-fuel ratio; an oxygen-side combustor that combusts the oxygen-rich mixed gas having a higher oxygen ratio than the stoichiometric air-fuel ratio; When increasing the temperature of the solid oxide electrolysis cell, the combustion control unit: When the temperature of the heat storage material is lower than a predetermined temperature, the mixed gas having a stoichiometric air-fuel ratio is combusted in the combustor, and the combustion off-gas is supplied to the heat storage device; a temperature adjustment device that stops the supply of the mixed gas to the combustor and stops combustion of the mixed gas when the temperature of the heat storage material is equal to or higher than the predetermined temperature;

2. A temperature control device for a solid oxide electrolysis cell, comprising: a hydrogen tank for storing hydrogen; an oxygen tank for storing oxygen; a combustor that combusts a mixed gas obtained by mixing hydrogen supplied from the hydrogen tank and oxygen supplied from the oxygen tank, discharges combustion off-gas, and supplies the combustion off-gas to the solid oxide electrolysis cell; a gas-liquid separator that separates moisture from the combustion off-gas that has passed through the solid oxide electrolysis cell; a booster that boosts the pressure of the combustion off-gas from which moisture has been separated by the gas-liquid separator; Equipped with The combustor includes: a fuel-side combustor that combusts the hydrogen-rich mixed gas having a hydrogen ratio greater than that of the stoichiometric air-fuel ratio and supplies the combustion off-gas to a fuel side of the solid oxide electrolysis cell to which hydrogen is supplied; an oxygen-side combustor that combusts the oxygen-rich mixed gas having a higher oxygen ratio than the stoichiometric air-fuel ratio; the booster stores the fuel-side combustion off-gas after being pressurized in the hydrogen tank; The temperature control device further comprises: a temperature sensor for acquiring the temperature of the combustion off-gas supplied to the fuel side of the solid oxide electrolysis cell; a cell temperature adjusting unit that adjusts the temperature of the solid oxide electrolysis cell by controlling the flow rate of hydrogen and the flow rate of oxygen supplied to the fuel-side combustor using the temperature acquired by the temperature sensor; and A temperature control device comprising:

3. A temperature control device for a solid oxide electrolysis cell, comprising: a hydrogen tank for storing hydrogen; an oxygen tank for storing oxygen; a combustor that combusts a mixed gas obtained by mixing hydrogen supplied from the hydrogen tank and oxygen supplied from the oxygen tank, discharges combustion off-gas, and supplies the combustion off-gas to the solid oxide electrolysis cell; a gas-liquid separator that separates moisture from the combustion off-gas that has passed through the solid oxide electrolysis cell; a booster that boosts the pressure of the combustion off-gas from which moisture has been separated by the gas-liquid separator; Equipped with The combustor includes: a fuel-side combustor that combusts the hydrogen-rich mixed gas having a hydrogen ratio greater than that of the stoichiometric air-fuel ratio; an oxygen-side combustor that combusts the oxygen-rich mixed gas having a ratio of oxygen greater than that of the stoichiometric air-fuel ratio and supplies the combustion off-gas to an oxygen side to which oxygen is supplied in the solid oxide electrolysis cell, a flow direction of the fuel-side combustion off gas flowing from the fuel-side combustor into the fuel side of the solid oxide electrolysis cell and a flow direction of the oxygen-side combustion off gas flowing from the oxygen-side combustor into the oxygen side of the solid oxide electrolysis cell are opposite to each other.

4. The temperature control device according to any one of claims 1 to 3, further comprising: a temperature adjustment device comprising a heat exchanger that exchanges heat between the combustion off-gas discharged from the solid oxide electrolysis cell and hydrogen supplied from the hydrogen tank or oxygen supplied from the oxygen tank.

5. 1. A method for regulating the temperature of a solid oxide electrolysis cell, comprising: supplying hydrogen from a hydrogen tank storing hydrogen to a combustor; supplying oxygen to the combustor from an oxygen tank storing oxygen; a step of burning a mixed gas of hydrogen and oxygen supplied to the combustor; supplying combustion off-gas from the combustor to the solid oxide electrolysis cell; a combustion control step of, when increasing the temperature of the solid oxide electrolysis cell, burning the mixed gas at a stoichiometric air-fuel ratio in the combustor and supplying the combustion off-gas to the heat storage material, the heat storage material being supplied with the combustion off-gas and releasing heat through an oxidation reaction, when the temperature of the heat storage material capable of heat exchange with the solid oxide electrolysis cell is lower than a predetermined temperature, and stopping the supply of the mixed gas to the combustor to stop combustion of the mixed gas when the temperature of the heat storage material is equal to or higher than the predetermined temperature; Run The combustor includes: a fuel-side combustor that burns the hydrogen-rich mixed gas having a hydrogen ratio greater than that of the stoichiometric air-fuel ratio; and an oxygen-side combustor that burns the oxygen-rich mixed gas having a higher oxygen ratio than the stoichiometric air-fuel ratio.

6. A method for regulating the temperature of a solid oxide electrolysis cell, comprising: supplying hydrogen from a hydrogen tank storing hydrogen to a combustor; supplying oxygen to the combustor from an oxygen tank storing oxygen; a step of burning a mixed gas of hydrogen and oxygen supplied to the combustor; supplying combustion off-gas from the combustor to the solid oxide electrolysis cell; a gas-liquid separation step of separating moisture from the combustion off-gas that has passed through the solid oxide electrolysis cell; a pressurization step of pressurizing the combustion off-gas from which moisture has been separated by the gas-liquid separation step; Run The combustor includes: a fuel-side combustor that combusts the hydrogen-rich mixed gas having a hydrogen ratio greater than that of the stoichiometric air-fuel ratio and supplies the combustion off-gas to a fuel side of the solid oxide electrolysis cell to which hydrogen is supplied; an oxygen-side combustor that combusts the oxygen-rich mixed gas having a higher oxygen ratio than the stoichiometric air-fuel ratio; the pressurization step includes storing the fuel-side combustion off-gas after pressurization in the hydrogen tank; The temperature control method further comprises: a temperature acquisition step of acquiring a temperature of the combustion off-gas supplied to a fuel side of the solid oxide electrolysis cell; a cell temperature adjusting step of adjusting the temperature of the solid oxide electrolysis cell by controlling the flow rate of hydrogen and the flow rate of oxygen supplied to the fuel-side combustor using the temperature acquired in the temperature acquiring step; A temperature control method that performs the following.

7. A method for regulating the temperature of a solid oxide electrolysis cell, comprising: supplying hydrogen from a hydrogen tank storing hydrogen to a combustor; supplying oxygen to the combustor from an oxygen tank storing oxygen; a step of burning a mixed gas of hydrogen and oxygen supplied to the combustor; supplying combustion off-gas from the combustor to the solid oxide electrolysis cell; a gas-liquid separation step of separating moisture from the combustion off-gas that has passed through the solid oxide electrolysis cell; a pressurization step of pressurizing the combustion off-gas from which moisture has been separated by the gas-liquid separation step; Run The combustor includes: a fuel-side combustor that combusts the hydrogen-rich mixed gas having a hydrogen ratio greater than that of the stoichiometric air-fuel ratio; an oxygen-side combustor that combusts the oxygen-rich mixed gas having a ratio of oxygen greater than that of the stoichiometric air-fuel ratio and supplies the combustion off-gas to an oxygen side to which oxygen is supplied in the solid oxide electrolysis cell, a flow direction of the fuel-side combustion off-gas flowing from the fuel-side combustor into the fuel side of the solid oxide electrolysis cell and a flow direction of the oxygen-side combustion off-gas flowing from the oxygen-side combustor into the oxygen side of the solid oxide electrolysis cell are opposite to each other.

Images