JP2023116093A - Temperature adjustment device of solid oxide electrolysis cell and temperature adjustment method of solid oxide electrolysis cell - Google Patents

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

The present invention relates to techniques for temperature control of solid oxide electrolysis cells.

SOFC (Solid Oxide Fuel Cell) and SOEC (Solid Oxide Electrolyser Cell) operating at high temperatures of 600 degrees Celsius (° C.) to 700° C. are known (for example, , see Patent Document 1). The SOFC system described in Patent Document 1 utilizes combustion of a gas mixture of hydrogen and air in a combustor to raise the temperature of a fuel cell that generates electricity from hydrogen and oxygen to operating temperature.

JP 2016-207308 A

In the technology described in Patent Document 1, the combustion gas temperature is controlled to a temperature within a range that suppresses excessive temperature rise of the combustor and prevents deterioration of strength and durability due to localized high temperature of the combustor. be done. To control that temperature, a large amount of air must be supplied to the combustor. The SOFC system of Patent Document 1 needs to be equipped with a NOx removal treatment device in order to prevent the _N2 gas contained in the air supplied to the combustor from being released into the atmosphere as thermal NOx after combustion. be.

The present invention has been made to solve at least a part of the above-described problems, and increases the starting energy of the solid oxide electrolytic cell by raising the temperature of the solid oxide electrolytic cell without generating NOx. The purpose is to suppress

The present invention has been made to solve at least part of the above problems, and can be implemented as the following modes.

(1) According to one aspect of the present invention, a temperature control device for a solid oxide electrolytic cell is provided. This temperature control device burns a mixed gas in which a hydrogen tank that stores hydrogen, an oxygen tank that stores oxygen, and hydrogen supplied from the hydrogen tank and oxygen supplied from the oxygen tank are mixed, a combustor that discharges combustion off-gas and supplies it to the solid oxide electrolysis cell, wherein the combustor is a fuel side that burns the hydrogen-rich mixed gas in which the proportion of hydrogen is larger than the stoichiometric air-fuel ratio It has at least one of a combustor and an oxygen-side combustor that burns the oxygen-rich mixed gas in which the proportion of oxygen is higher than the stoichiometric air-fuel ratio.

According to this configuration, the solid oxide electrolysis cell is heated by supplying the combustion off-gas burned in the combustor to the solid oxide electrolysis cell. Since the mixed gas that burns in the combustor does not contain air, the combustion off-gas after combustion does not contain thermal NOx generated by the reaction of nitrogen and oxygen contained in the air at high temperatures. . Therefore, a system with solid oxide electrolysis cells does not need to have a device for removing thermal NOx. In addition, since a hydrogen-rich mixed gas is burned 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, the oxygen-side combustor burns an oxygen-rich mixed gas, so by adjusting the flow rate of hydrogen supplied to the oxygen-side combustor, the adiabatic flame temperature during combustion of the mixed gas can be controlled. .

(2) In the solid oxide electrolysis cell of the above aspect, further, 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 A heat exchanger for heat exchange may be provided.
According to this configuration, due to heat exchange in the heat exchanger, heat is transferred from the high-temperature combustion off-gas discharged from the solid oxide electrolytic cell to hydrogen supplied from the hydrogen tank or oxygen supplied from the oxygen tank. do. As a result, the sensible heat of the combustion off-gas can be recovered to raise the temperature of the hydrogen or oxygen supplied to the solid oxide electrolysis cell. As a result, in this configuration, an increase in starting energy of the solid oxide electrolysis cell can be suppressed.

(3) In the solid oxide electrolysis cell of the aspect described above, 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. and a combustion control section for controlling combustion of the mixed gas by the combustor, wherein the combustion control section controls the heat storage when increasing the temperature of the solid oxide electrolysis cell. When the temperature of the material is lower than a preset predetermined temperature, the mixed gas having a stoichiometric air-fuel ratio is combusted by the combustor, the combustion off-gas is supplied to the heat accumulator, and the temperature of the heat storage material is equal to or higher than the predetermined temperature. , the supply of the mixed gas to the combustor may be stopped to stop the combustion of the mixed gas.
According to this configuration, when the operation of the solid oxide electrolysis cell that has been operating at a high temperature is stopped, the heat accumulator can store the surplus heat of the solid oxide electrolysis cell. The heat stored in the heat accumulator can be used to heat the solid oxide electrolysis cell when operating the solid oxide electrolysis cell again. Therefore, in this configuration, heat storage and heat dissipation of the heat accumulator are utilized, thereby suppressing an increase in starting energy of the solid oxide electrolytic cell. In addition, in the heat storage material that releases heat by an oxidation reaction, the heat release reaction speed increases as the temperature rises. Therefore, when the temperature of the solid oxide electrolytic cell at the initial stage of startup is below a predetermined temperature, when the mixed gas burned by the combustor is supplied to the heat storage material, the reaction rate of the heat storage material increases, and the solid oxide The temperature rise rate of the type electrolytic cell is accelerated. That is, even without an external heat source for increasing the reaction speed of the heat storage material, the combustion off-gas is supplied to the heat storage device, thereby accelerating the temperature rise rate of the solid oxide electrolysis cell.

(4) In the solid oxide electrolysis cell of the above aspect, a gas-liquid separator for separating moisture from the combustion off-gas that has passed through the solid oxide electrolysis cell; a booster for boosting the combustion off-gas, wherein the combustor has a fuel-side combustor for supplying the combustion off-gas to the fuel side to which hydrogen is supplied in the solid oxide electrolysis cell; The booster may store the combustion off-gas on the fuel side after boosting 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 resulting from combustion of the hydrogen-rich mixed gas contains water vapor and unburned hydrogen, and does not contain oxygen. Therefore, the combustion off-gas from which moisture has been removed by the gas-liquid separator contains only hydrogen. Therefore, by storing the combustion off-gas containing only hydrogen pressurized by the booster in the hydrogen tank, unburned hydrogen can be reused. As a result, an increase in starting energy of the solid oxide electrolytic cell can be suppressed.

(5) In the solid oxide electrolysis cell of the above aspect, a temperature sensor for acquiring the temperature of the combustion off-gas supplied to the fuel side of the solid oxide electrolysis cell, and the temperature acquired by the temperature sensor 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 good.
According to this configuration, the cell temperature adjustment unit adjusts the flow rates of hydrogen and oxygen supplied to the solid oxide electrolysis cell according to the temperature of the combustion off-gas supplied to the solid oxide electrolysis cell to Adjust the temperature of the oxide form electrolytic cell. When a solid oxide electrolysis cell generates hydrogen from water vapor, heat absorption due to hydrogen generation, heat radiation to the outside, and ohmic heating (Joule heating) due to electrical resistance occur in the solid oxide electrolysis cell. there is As the temperature of the solid oxide electrolytic cell decreases, the amount of hydrogen produced decreases. In this configuration, the cell temperature control section controls the combustion of the mixed gas in the fuel-side combustor by controlling the supply amounts of oxygen and hydrogen so as to maintain the heat balance in the solid oxide electrolysis cell. to adjust the temperature of the solid oxide electrolysis cell by the heat of combustion. The amount of water vapor produced after combustion of the gas mixture in the fuel side combustor is very small compared to the water vapor for feedstock for hydrogen production. Therefore, in this configuration, the gas temperature of the raw material steam supplied to the solid oxide electrolysis cell can be kept constant without greatly changing the raw material specifications (for example, concentration and flow rate). As a result, even if the temperature of the generated steam fluctuates in the evaporator or the like that supplies raw material steam to the solid oxide electrolysis cell, the temperature of the solid oxide electrolysis cell can be maintained by correcting the heat quantity in the fuel-side combustor. can be kept constant.

(6) The solid oxide electrolysis cell of the above aspect further includes a gas-liquid separator for separating moisture from the combustion off-gas that has passed through the solid oxide electrolysis cell, and moisture is separated by the gas-liquid separator. a booster for boosting the combustion off-gas, wherein the combustor has an oxygen-side combustor for supplying the combustion off-gas to the oxygen side to which oxygen is supplied in the solid oxide electrolysis cell; The booster may store the combustion off-gas on the oxygen side after boosting in the oxygen tank.
According to this configuration, the pre-combustion mixed gas of the combustion off-gas supplied to the oxygen side of the solid oxide electrolysis cell is an oxygen-rich gas. The combustion off-gas resulting from combustion of the oxygen-rich mixed gas contains water vapor and unburned oxygen, and 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 pressurized by the booster in the oxygen tank, the unburned oxygen can be reused. As a result, an increase in starting energy of the solid oxide electrolytic cell can be suppressed.

(7) In the solid oxide electrolysis cell of the aspect described above, the flow direction of the combustion off-gas on the fuel side flowing from the fuel side combustor into the fuel side of the solid oxide electrolysis cell, and the direction of flow from the oxygen side combustor. The flow direction of the combustion off-gas on the oxygen side flowing into the oxygen side of the solid oxide electrolysis cell may be opposite.
According to this configuration, the 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 start-up energy of the solid oxide electrolysis cell can be suppressed. In addition, since the flow directions of the combustion off-gas supplied to the fuel side and the oxygen side of the solid oxide electrolysis cell are opposite to each other, the solid oxide during temperature rise depends on the amount of heat transfer in the flow direction. It can reduce the difference in temperature distribution in the type electrolytic cell. In addition, since the two gas flow directions face each other, the heating time of the solid oxide electrolysis cell can be further shortened, and the generation of the thermal expansion difference depending on the temperature distribution in the gas flow direction can be suppressed. As a result, it is possible to suppress the breakage of the component parts and the deterioration of the performance when starting the solid oxide electrolysis cell in a short period of time.

The present invention can be implemented in various aspects, for example, solid oxide electrolysis cell, SOEC, SOFC, temperature control device for solid oxide electrolysis cell, temperature controller for solid oxide electrolysis cell An adjustment method, a temperature control method for a solid oxide electrolytic cell, a system comprising these devices, a computer program for executing these devices, a server device for distributing this computer program, and a non-temporary storage of the computer program It can be implemented in the form of a storage medium or the like.

1 is a schematic block diagram of an SOFC system as one embodiment of the present invention; FIG. FIG. 3 is a diagram showing the relationship between excess oxygen ratio and adiabatic flame temperature. FIG. 4 is an explanatory diagram of the flow direction of combustion off-gas flowing into a cell stack; FIG. 4 is an explanatory diagram of the cell stack temperature that changes according to the flow direction of the fuel off-gas; FIG. 4 is an explanatory diagram of the cell stack temperature that changes according to the flow direction of the fuel off-gas; FIG. 2 is a schematic block diagram of an SOFC system of a second embodiment; FIG. 8 is a flow chart of a temperature adjustment control method according to the second embodiment. FIG. 11 is a schematic block diagram of an SOEC system of a third embodiment; FIG. 9 is a flow chart of a control method for temperature adjustment according to the third embodiment; FIG. 11 is a schematic block diagram of an SOEC system of a fourth embodiment; FIG. 1 is a schematic block diagram of an SOEC system when the cell stack temperature is above the operating temperature; FIG. 10 is a flow chart of a control method for temperature adjustment according to the fourth embodiment; 5 is a flow chart of a control method for temperature adjustment of the cell stack 10 of the modification.

<First Embodiment>
FIG. 1 is a schematic block diagram of a SOFC (Solid Oxide Fuel Cell) system 100 as one embodiment of the present invention. In the SOFC system 100 (temperature control device) of the present embodiment, the cell stack 10 in which a plurality of solid oxide electrolytic cells are stacked is operated at an operating temperature of about 700 degrees Celsius (° C.) with supplied hydrogen. Electricity is generated by a chemical reaction with oxygen. In this embodiment, the fuel-side combustor 41 and the oxygen-side combustor 42 burn a mixed gas containing hydrogen and oxygen for the cell stack 10 that has not reached the operating temperature, and the combustion heat 10 is heated. Since air is not used in the combustion of the fuel-side combustor 41 and the oxygen-side combustor 42, nitrogen compounds (NOx) are not generated in the process of increasing the temperature of the cell stack 10. FIG.

As shown in FIG. 1, the SOFC system 100 includes a cell stack 10, a hydrogen tank 31 that stores hydrogen, an oxygen tank 32 that stores oxygen, a fuel side combustor 41 that burns a mixed gas, and an oxygen side combustion chamber. gas-liquid separators 51, 52 for separating moisture in the gas; water tanks 71, 72 for storing water; boosters 61, 62 for increasing the pressure of the gas; S1 to S4 and a control unit 20 for controlling each part of the SOFC system 100 are provided.

In FIG. 1 , piping that connects each part and through which gas flows is represented by a solid line. The state shown in FIG. 1 is the state before the cell stack 10 starts generating power. Specifically, FIG. 1 shows that the temperature of the cell stack 10 has not risen to the operation temperature (approximately 700° C.) during power generation, and the mixed gas in the fuel side combustor 41 and the oxygen side combustor 42 is combusted. shows that the cell stack 10 is heated by . Hereinafter, the fuel-side combustor 41 and the oxygen-side combustor 42 are collectively referred to simply as "the combustors 41 and 42."

As the electrolytic cell constituting the cell stack 10, for example, a fuel cell single cell made of yttria-doped zirconia (YSZ), yttrium- or scandium-doped zirconia, or a lanthanum gallate-based solid electrolyte can be used. As shown in FIG. 1, the cell stack 10 has a fuel side (anode) 11 supplied with a gas containing hydrogen and an oxygen side (cathode) 12 supplied with a gas containing oxygen during power generation. ing.

The combustors 41 and 42 are provided with ignition devices that burn 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 through a mass flow controller (not shown) so as to be hydrogen-rich, that is, the ratio of hydrogen is higher 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 blown into hydrogen. The combustion off-gas after combustion is supplied to the fuel side 11 of the cell stack 10 . Since the combusted gas mixture is hydrogen-rich, the fuel-side off-gas, which is the combustion off-gas supplied to the fuel side 11, contains hydrogen and water vapor, but no oxygen.

The mixed gas supplied to the oxygen-side combustor 42 is controlled to be oxygen-rich, that is, the ratio of oxygen is higher than the stoichiometric air-fuel ratio. The oxygen-side combustor 42 uses a diffusion combustion method that burns a mixed gas in which hydrogen is blown into oxygen. The combustion off-gas after combustion is supplied to the oxygen side 12 of the cell stack 10 . Since the combusted gas mixture is oxygen-rich, the combustion off-gas supplied to the oxygen side 12, the oxygen-side off-gas, contains oxygen and water vapor, but no hydrogen.

The control unit 20 adjusts the gas ratio of the mixed gas in the fuel-side combustor 41 using the temperature T _H2 of hydrogen detected by the temperature sensor S1 and the temperature T _O2 of oxygen detected by the temperature sensor S2. do. Similarly, the control unit 20 uses the temperature T _H2 of hydrogen detected by the temperature sensor S3 and the temperature T _O2 of oxygen detected by the temperature sensor S4 to determine the temperature of the mixed gas in the oxygen-side combustor 42. Adjust gas ratio. The details of the gas ratio of the mixed gas in the combustors 41 and 42 to be adjusted will be described later.

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 the water tank 71 . Further, the gas-liquid separator 51 cools the fuel-side off-gas by radiating heat to the atmosphere. The fuel-side off-gas from which water is separated by the gas-liquid separator 51 is composed of hydrogen. The fuel-side off-gas is pressurized by the booster 61 and stored in the hydrogen tank 31 .

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 the water tank 72 . Further, the gas-liquid separator 52 cools the oxygen-side off-gas by radiating heat to the atmosphere. The oxygen-side off-gas from which water has been separated by the gas-liquid separator 52 is composed of oxygen. The combustion off-gas is pressurized by the booster 62 and stored in the oxygen tank 32 .

The control unit 20 controls the combustion gas temperature (adiabatic flame temperature) of the mixed gas combusted in the combustors 41 and 42 using the gas temperatures T _H2 and T _O2 detected by the temperature sensors S1 to S4. The adiabatic flame temperature T is determined by the excess oxygen ratio K of the burning mixed gas, which is given by the following equation (1).

The control unit 20 uses the adiabatic flame temperature T, the temperature T _H2 of hydrogen in the mixed gas to be burned, and the temperature T _O2 of oxygen in the mixed gas to be burned, instead of the above equation (1), to obtain the following equation (2). The excess oxygen ratio K is determined from the relationship given. The control unit 20 determines an input hydrogen amount (hydrogen blowing amount) Fa_H2 and an input oxygen amount (oxygen blowing 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 supplies the determined input hydrogen amount Fa_H2 and input oxygen amount Fa_O2 to the combustors 41 and 42 by controlling the mass flow controllers. It should be noted that the input hydrogen amount Fa_H2 and the input oxygen amount Fa_O2, which are determined by the amount of heat Q and the excess oxygen rate K, are determined from maps that have been measured in advance.

FIG. 2 is a diagram showing the relationship between the excess oxygen ratio K and the adiabatic flame temperature T. As shown in FIG. FIG. 2 shows a change curve C1 (solid line) of the excess oxygen ratio K in the oxygen-rich case that changes according to the adiabatic flame temperature T so as to correspond to the numerical values on the left vertical axis. FIG. 2 also shows a change curve C2 (broken line) of the excess oxygen ratio K in the hydrogen-rich case that changes according to the adiabatic flame temperature T so as to correspond to the numerical values on the right vertical axis. For example, when the temperature of the cell stack 10 is raised from 400° C. to 830° C. indicated by the solid straight line in FIG. It can be changed up to 17. Similarly, when the temperature of the cell stack 10 is raised to 830° C., the excess oxygen ratio K of the hydrogen-rich mixed gas burned in the fuel-side combustor 41 should be changed from 0.05 to 0.11.

FIG. 3 is an explanatory diagram of the flow direction of the combustion off-gas flowing into the cell stack 10. As shown in FIG. 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 including an X-axis and a Y-axis that are orthogonal to the Z-axis, with an axis parallel to the stacking direction as the Z-axis.

As shown in FIG. 3, the electrolysis cell 13 has an electrolyte membrane 14 positioned 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 to the fuel-side 11 of the electrolysis cell 13 and the flow direction of the oxygen-side off-gas flowing from the oxygen-side combustor 42 to the oxygen-side 12 of the electrolysis cell 13 are determined. is opposite to the flow direction of Hereinafter, the flow direction of the fuel-side off-gas flowing into the fuel side 11 is also referred to as the "fuel-side flow direction", and the flow direction of the oxygen-side off-gas flowing into the oxygen side 12 is also referred to as the "oxygen-side flow direction". .

4 and 5 are explanatory diagrams of the temperature of the cell stack 10 that changes according to the flow direction of the fuel off-gas. In FIG. 4, as shown in FIG. 3, the solid line indicates the temperature change C3 of the cell stack 10 in the counter flow in which the fuel side flow direction and the oxygen side flow direction are opposed to each other. Further, in FIG. 4, the dashed line indicates the temperature change C4 of the cell stack 10 in the parallel flow in which the fuel side flow direction and the oxygen side flow direction are the same. Further, in FIG. 4, as a comparative example, the temperature change C5 in the case where the oxygen side off-gas in which the mixed gas of hydrogen and air is combusted only on the oxygen side 12 is supplied to the cell stack 10 is indicated by a dashed line. . In all the temperature changes C3 to C5, the combustion off-gas with the adiabatic flame temperature T of 650° C. is supplied to the cell stack 10 at the same flow rate.

As shown in FIG. 4, the counterflow temperature change C3 can raise the temperature of the cell stack 10 higher than the parallel flow temperature change C4. In addition, as shown by the temperature changes C3 and C4 of the countercurrent and parallel currents and the temperature change C5 of the comparative example, the temperature of the cell stack 10 can be increased more greatly in the countercurrent and parallel currents than in the comparative example.

FIG. 5 shows the temperature distribution of the cell stack 10 in the flow direction of the combustion off-gas (Y-axis direction in FIG. 3) two hours after the start of heating the cell stack 10 by supplying the combustion off-gas. FIG. 5 shows the temperature as a function of position normalized to the distance along the direction of flow, where the distance from the inlet to the outlet on the fuel side 11 is 1. FIG. 5 shows the temperature change C6 (solid line) in the counter flow, the temperature change C7 (broken line) in the parallel flow, and the temperature change C8 (chain line) of the comparative example.

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

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 burn mixed gas. The combustors 41 and 42 burn mixed gas of hydrogen supplied from the hydrogen tank 31 and oxygen supplied from the oxygen tank 32 . Therefore, the combustion off-gas burned in the combustors 41 and 42 is supplied to the cell stack 10, and the temperature of the cell stack 10 rises. Since the mixed gas that burns in the combustors 41 and 42 does not contain air, the combustion off-gas after combustion contains thermal NOx generated by the reaction of nitrogen and oxygen contained in the air at high temperatures. Not included. Therefore, the SOFC system 100 does not need to be equipped with a device for removing thermal NOx. In addition, since the fuel-side combustor 41 burns a hydrogen-rich mixed gas, the adiabatic flame temperature during combustion of the mixed gas can be controlled by adjusting the flow rate of the oxygen supplied to the fuel-side combustor 41. . Similarly, in the oxygen-side combustor 42, an oxygen-rich mixed gas is burned. Therefore, by adjusting the flow rate of hydrogen supplied to the oxygen-side combustor 42, the adiabatic flame temperature at the time of combustion of the mixed gas is increased. You can control it.

Further, 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 the water is 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 resulting from combustion of the hydrogen-rich mixed gas contains water vapor and unburned hydrogen, and 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, the fuel-side off-gas containing only hydrogen pressurized by the booster 61 is stored in the hydrogen tank 31, so that unburned hydrogen can be reused. As a result, an increase in activation energy of the cell stack 10 can be suppressed.

Further, the gas-liquid separator 52 of the present embodiment separates water from the oxygen side off-gas discharged from the oxygen side 12 of the cell stack 10 . The booster 62 pressurizes 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 an oxygen-rich gas. The oxygen-side off-gas resulting from combustion of 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 in the oxygen tank 32 the oxygen-side off-gas containing only oxygen pressurized by the booster 62, unburned oxygen can be reused. As a result, an increase in activation energy of the cell stack 10 can be suppressed.

Further, in this embodiment, as shown in FIG. The flow direction of the oxygen side off-gas flowing into the oxygen side 12 is opposite. That is, in this embodiment, fuel off-gas 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 off-gas 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 activation energy of the cell stack 10 can be suppressed. In addition, since the flow direction of the fuel-side off-gas is opposite to the flow direction of the oxygen-side off-gas, as shown in FIG. Distribution differences can be reduced. In addition, since the flow directions of the two combustion off-gases are opposed to each other, the temperature rise time of the cell stack 10 can be further shortened, and the occurrence of the thermal expansion difference depending on the temperature distribution in the flow direction of the combustion off-gases can be suppressed. As a result, it is possible to suppress the destruction of the components and the deterioration of performance when starting the cell stack 10 in a short period of time.

Further, a diffusion combustion method is used in which oxygen is blown into hydrogen in the fuel-side combustor 41 of the present embodiment, and hydrogen is blown into oxygen in the oxygen-side combustor 42 . Therefore, even if the temperature of the mixed gas before combustion is equal to or higher than the self-ignition temperature, it is possible to suppress the occurrence of flashback, which is a problem in premixed combustion. Therefore, the SOFC system 100 can burn mixed gas with a simple configuration that does not require a device having a special flashback suppression function. In addition, in this embodiment, since 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), the influence of deterioration due to electrode oxidation of the electrolytic cell 13 is extremely small. Therefore, heat can be supplied to the cell stack 10 through the flow path on the fuel side 11 .

<Second embodiment>
FIG. 6 is a schematic block diagram of the 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 and an oxygen-side heat exchanger (heat exchanger) 82, and a temperature It has sensors S5, S6 and control valves CV1-CV4. The control unit 20a of the second embodiment controls the control valves CV1 to CV4 using the gas temperatures T _H2 , T _O2 , Ta, and Tc detected by the temperature sensors S1 to S6, so that the combustors 41, 42 Adjust the flow rate of hydrogen and oxygen supplied to the

As shown in FIG. 6 , the fuel-side heat exchanger 81 exchanges heat between fuel-side off-gas discharged from the fuel side 11 of the cell stack 10 and hydrogen supplied from the hydrogen tank 31 . Hydrogen is heated by the transfer of heat from the hot fuel side off-gas discharged from the fuel side 11 to the cold hydrogen supplied to the fuel side combustor 41 . 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 the oxygen supplied from the oxygen tank 32 . Oxygen is heated by the transfer of heat from the hot oxygen side off-gas exiting the oxygen side 12 to the cooler oxygen supplied to the oxygen side combustor 42 .

The controller 20 a 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 or the like from the 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 operates the control valves CV1 and CV2. Control. By controlling the control valve CV1, the 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, the flow rate F_cv2 of oxygen blown into the fuel side combustor 41 is set. In the second embodiment, the adiabatic flame temperature T set for the fuel side combustor 41 and the adiabatic flame temperature T set for the oxygen side combustor 42 are the same, but they are different in other embodiments. may

When the temperature 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 preset threshold value ε1, the control unit 20a reduces the mixed gas in the fuel-side combustor 41. Burn. As in the first embodiment, the control unit 20a calculates the adiabatic flame temperature T, the hydrogen temperature T _H2 and the oxygen temperature T _O2 in the mixed gas in the fuel-side combustor 41 according to the above equation (2). The excess oxygen ratio K is obtained by using The controller 20a sets the flow rate F_cv1 of hydrogen and the flow rate F_cv2 of oxygen to be supplied to the fuel-side combustor 41 based on the obtained excess oxygen ratio K and the amount of heat Q generated by the adiabatic flame temperature T.

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 control valves CV3 and CV4. to control. By controlling the control valve CV3, the 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 control valve CV4, the flow rate F_cv4 of oxygen blown into the oxygen-side combustor 42 is set. When the temperature obtained by subtracting the adiabatic flame temperature T from the temperature Tc of the oxygen-side off-gas supplied to the oxygen-side 12 is smaller than a preset threshold value ε2, the control unit 20a reduces the mixed gas in the oxygen-side combustor 42. Burn. The control unit 20a uses the adiabatic flame temperature T, the hydrogen temperature T _H2 and the oxygen temperature T _O2 in the mixed gas in the oxygen-side combustor 42 to determine the excess oxygen ratio K. The controller 20a sets the flow rate F_cv3 of hydrogen and the flow rate F_cv4 of oxygen supplied to the oxygen side combustor 42 based on the calculated excess oxygen ratio K and the amount of heat Q generated by the adiabatic flame temperature T.

FIG. 7 is a flow chart of a temperature adjustment control method according to the second embodiment. In the temperature adjustment flow shown in FIG. 7, first, the controller 20a sets the adiabatic flame temperature T of the combustors 41 and 42 (step S1). The control unit 20a controls the temperature T _H2 of hydrogen and the temperature T _O2 of oxygen supplied to the fuel-side combustor 41 detected by the temperature sensors S1 and S2, and the fuel-side offgas supplied to the fuel side 11 of the cell stack 10. temperature Ta is acquired (step S12).

The control unit 20a determines whether the difference obtained by subtracting the adiabatic flame temperature T from the temperature Ta of the fuel-side offgas supplied to the fuel-side 11 is smaller than the threshold value ε1 (step S13). If the difference is smaller than the threshold value ε1 (step S13: YES), the control unit 20a repeats the processes after step S12. If the difference is equal to or greater than the threshold ε1 (step S13: NO), the control unit 20a uses the adiabatic flame temperature T, the hydrogen temperature T _H2 and the oxygen temperature T _O2 to obtain the excess oxygen rate K ( step S14). The control unit 20a uses the obtained excess oxygen ratio K and the amount of heat Q calculated from the adiabatic flame temperature T to calculate the flow rate F_cv1 of hydrogen and the flow rate F_cv2 of oxygen to be supplied to the fuel-side combustor 41 ( step S15). The control unit 20a controls the control valves CV1 and CV2 so as to achieve the calculated flow rate F_cv1 of hydrogen and F_cv2 of oxygen (step S16). After that, the control unit 20a determines whether or not to end the startup operation of the cell stack 10 (step S17). If the activation operation of the cell stack 10 is not finished (step S17: NO), the control unit 20a repeats the processes after step S12.

When the adiabatic flame temperature T is set in step S1, the control unit 20a controls the temperature T _H2 of hydrogen and the temperature T O2 of oxygen supplied to the oxygen side combustor 42 detected by the temperature sensors S3 and S4, and the temperature T _O2 of the cell The temperature Tc of the oxygen side off-gas supplied to the oxygen side 12 of the stack 10 is obtained (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 the threshold value ε2 (step S23). If the difference is smaller than the threshold value ε2 (step S23: YES), the control unit 20a repeats the processes after step S22. If the difference is equal to or greater than the threshold ε1 (step S23: NO), the control unit 20a uses the adiabatic flame temperature T, the hydrogen temperature T _H2 and the oxygen temperature T _O2 to obtain the excess oxygen rate K ( step S24). The control unit 20a uses the obtained excess oxygen ratio K and the amount of heat Q calculated from the adiabatic flame temperature T to calculate the hydrogen flow rate F_cv3 and the oxygen flow rate F_cv4 to be supplied to the oxygen side combustor 42 ( step S25). The control unit 20a controls the control valves CV3 and CV4 so as to achieve the calculated hydrogen flow rate F_cv3 and oxygen flow rate F_cv4 (step S26). After that, the control unit 20a determines whether or not to end the operation of the cell stack 10 (step S27). If the activation operation of the cell stack 10 is not finished (step S27: NO), the control unit 20a repeats the processes after step S22. In the processing of steps S17 and S27, when the temperature of the cell stack 10 rises to the temperature at which the steady operation is performed and the startup operation is stopped (steps S17, 27: YES), the control unit 20a performs the temperature adjustment flow exit. After that, the cell stack 10 shifts to steady operation of generating power using hydrogen and oxygen.

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 the hydrogen supplied from the hydrogen tank 31. conduct. 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 the oxygen supplied from the oxygen tank 32 . Therefore, due to 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, heat exchange in the oxygen side heat exchanger 82 transfers heat from the high temperature oxygen side off-gas discharged from the cell stack 10 to the oxygen supplied from the oxygen tank 32 . Thereby, the sensible heat of the combustion off-gas can be recovered and the temperature of the hydrogen or oxygen supplied to the cell stack 10 can be increased. As a result, in the second embodiment, an increase in activation energy of the cell stack 10 can be suppressed.

<Third Embodiment>
FIG. 8 is a schematic block diagram of the 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 the high-temperature steam generated in the evaporator 19 in the cell stack 10 . In the SOEC system 101, while the temperature of the cell stack 10 is rising and hydrogen is being generated, high-temperature steam containing hydrogen supplied from the hydrogen tank 31 is supplied to the fuel side combustor 41. Blow in oxygen and burn. The control unit 20b adjusts the flow rate of oxygen supplied to the fuel-side combustor 41 and the flow rate of hydrogen blown into the fuel-side combustor 41 according to the temperature of the high-temperature steam supplied to the cell stack 10, thereby controlling the flow rate of the cell stack 10 during hydrogen generation. maintain a constant temperature. In addition, in the third embodiment, the configuration and the like that are different from those of the SOFC system 100 of the first embodiment and the SOFC system 100a of the second embodiment will be described, and the description of the same configuration and the like will be omitted.

As shown in FIG. 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, and an oxygen side heat exchanger 82. , gas-liquid separators 51, 52, boosters 61, 62, water tanks 71, 72, evaporator 19, temperature sensors S1, S2, S5, control valves CV1b, CV2b, CV5, and control unit 20b (temperature control unit), and The evaporator 19 produces hot steam by heating liquid water supplied via a control valve CV5. A control valve CV5 regulates the flow rate of water supplied to the evaporator 19. FIG. The control valve CV5 is adjusted according to the amount of hydrogen required for the cell stack 10 to be produced.

The control unit 20b controls the control valves CV1b, CV2b using the gas temperatures T _H2 , T _O2 , Ta detected by the temperature sensors S1, S2, S5, thereby determining the amount of hydrogen supplied to the fuel-side combustor 41. and oxygen flow rate. Specifically, first, the controller 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 offgas supplied to the fuel side 11 of the cell stack 10 detected by the temperature sensor S5, and controls the control valves CV1 and CV2. By controlling the adjustment valve CV1b, the 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 CV2b, the flow rate F_cv2 of oxygen blown into the fuel side combustor 41 is set.

When the temperature 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 preset threshold value ε3, the control unit 20b controls the flow rate of oxygen blown into the fuel-side combustor 41. By controlling , the mixed gas in the fuel side combustor 41 is combusted. When the temperature Ta of the cell stack 10 is sufficiently high, the mixed gas inside the fuel-side combustor 41 burns without being ignited. As in the first embodiment, the control unit 20b converts the adiabatic flame temperature T, the hydrogen temperature T _H2 and the oxygen temperature T _O2 in the mixed gas in the fuel-side combustor 41 into the above equation (2). By substituting, the oxygen excess rate K is obtained. The controller 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 calculated excess oxygen ratio K and the amount of heat Q generated by the adiabatic flame temperature T.

FIG. 9 is a flow chart of a temperature adjustment control method according to the third embodiment. In the temperature adjustment flow shown in FIG. 9, first, the controller 20b sets the adiabatic flame temperature T of the fuel-side combustor 41 (step S31). The control unit 20b controls the temperature T _H2 of hydrogen supplied to the fuel-side combustor 41 and the temperature T _O2 of oxygen supplied to the fuel-side combustor 41 detected by the temperature sensors S1 and S2, and the fuel-side off-gas supplied to the fuel side 11 of the cell stack 10. temperature Ta is acquired (step S32).

The control unit 20b determines whether the difference obtained by subtracting the adiabatic flame temperature T from the temperature Ta of the fuel-side offgas supplied to the fuel-side 11 is smaller than the threshold value ε3 (step S33). If the difference is smaller than the threshold value ε3 (step S33: YES), the control unit 20b repeats the processes after step S32. If the difference is equal to or greater than the threshold ε3 (step S33: NO), the control unit 20b uses the adiabatic flame temperature T, the hydrogen temperature T _H2 and the oxygen temperature T _O2 to obtain the excess oxygen rate K ( step S34). The control unit 20b uses the calculated excess oxygen ratio K and the amount of heat Q calculated from the adiabatic flame temperature T to calculate the flow rate F_cv1 of hydrogen and the flow rate F_cv2 of oxygen to be supplied to the fuel-side combustor 41 ( step S35). The control unit 20b controls the control valves CV1b and CV2b so as to achieve the calculated hydrogen flow rate F_cv1 and oxygen flow rate F_cv2 (step S36). The mixed gas in the fuel-side combustor 41 whose gas ratio is controlled burns. After that, the control unit 20b determines whether or not to end the operation of the cell stack 10 (step S37). If the activation operation of the cell stack 10 is not finished (step S37: NO), the control unit 20b repeats the processes after step S32. When the operation of the cell stack 10 is finished (step S37: YES), the control unit 20b stops the supply of hydrogen and oxygen, finishes the operation of the cell stack 10, and finishes the temperature control flow.

In the SOEC system 101 of the third embodiment, the control unit 20b controls the control valves CV1b and CV2b using the gas temperatures T _H2 , T _O2 and Ta detected by the temperature sensors S1, S2 and S5. The flow rate of hydrogen and oxygen supplied to the fuel side combustor 41 is adjusted. When the cell stack 10 generates hydrogen from high-temperature steam, the cell stack 10 generates heat absorption due to hydrogen generation, heat radiation to the outside, and ohmic heating (Joule heat generation) due to electrical resistance. As the temperature of the cell stack 10 decreases, the amount of hydrogen produced decreases. In this embodiment, the control unit 20b controls the combustion of the mixed gas in the fuel-side combustor 41 by controlling the supply amounts of oxygen and hydrogen so as to maintain the heat balance in the cell stack 10. The temperature of the cell stack 10 is adjusted by combustion heat. The amount of steam produced after combustion of the mixed gas in the fuel-side combustor 41 is extremely small compared to the high-temperature steam used as the raw material for hydrogen production. Therefore, in this embodiment, the gas temperature of the high-temperature steam supplied to the cell stack 10 can be kept constant without greatly changing the raw material specifications (for example, concentration and flow rate) in the evaporator 19 . As a result, even if the steam temperature fluctuates in the evaporator 19 that supplies high-temperature steam to the cell stack 10 , the temperature of the cell stack 10 can be kept constant by correcting the amount of heat in the fuel-side combustor 41 .

<Fourth Embodiment>
FIG. 10 is a schematic block diagram of the SOEC system 101c of the fourth embodiment. The SOEC system 101c of the fourth embodiment differs greatly 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 surplus heat in the cell stack 10 whose operation has been stopped, and supplies the stored heat to the cell stack 10 when restarting. In the fourth embodiment, the configuration and the like that are different from those of the SOEC system 101 of the third embodiment will be described, and the description of the same configuration and the like will be omitted.

As shown in FIG. 10, the SOEC system 101c further includes a heat accumulator 90 and the fuel-side heat exchanger 81 of the first embodiment in addition to 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 is supplied with combustion off-gas, stores heat through an oxidation reaction, and is reduced during heat storage. In this embodiment, an Fe (iron)-based metal oxide is used, which starts releasing heat from an oxidation reaction at approximately 150°C.

Also, the SOEC system 101c includes control valves CV1c, CV2c, CV3c, CV4c, CV6 and three-way valves V6, V7 instead of the control valves CV1b, CV2b. The SOEC system 101c includes 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 of the heat storage device 90 instead of the temperature sensors S1, S2, and S5. ing.

The control unit (combustion control unit) 20c controls the amount of hydrogen supplied from the hydrogen tank 31 to the combustors 41 and 42 by controlling the adjustment valves CV1c, CV2c, CV3c, CV4c and CV6 and the three-way valves V6 and V7. Then, 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 are controlled. In FIG. 10, when the cell stack 10 is restarted, the pipes connected by the control of the control valves CV1c, CV2c, CV3c, CV4c, CV6 and the three-way valves V6, V7 are indicated by solid lines. Piping that is not connected is indicated by a dashed line.

When the temperature of the cell stack 10 is raised, the control unit 20c supplies a mixed gas having a stoichiometric air-fuel ratio to the oxygen side combustor 42 for combustion when the temperature Ts of the heat storage material is lower than a predetermined temperature. , and the combustion off-gas is supplied to the regenerator 90 . When the temperature Ts of the heat storage material is equal to or higher than a predetermined temperature, the control unit 20c stops supplying the mixed gas to the oxygen-side combustor 42 and stops burning the mixed gas. Specifically, when the temperature Ts of the heat storage material detected by the temperature sensor S7 is lower than the preset target temperature Ts,t, the control unit 20c, in addition to the water vapor at the flow rate F_cv5 from the evaporator 19, Hydrogen at a flow rate F_cv3 of the stoichiometric air-fuel ratio and oxygen at a flow rate F_cv4 are supplied to the oxygen side combustor 42 . When the mixed gas of the stoichiometric air-fuel ratio in the oxygen side combustor 42 burns, the oxygen side combustion off-gas is supplied to the regenerator 90 . In the heat accumulator 90, the water vapor whose temperature is raised by the combustion reacts with the heat storage material, whereby heat radiation from the heat storage material starts, and the temperature of the cell stack 10 capable of exchanging heat with the heat storage material rises. Note that the oxygen-side combustion off-gas does not contain hydrogen and oxygen because the mixed gas with the stoichiometric air-fuel ratio is combusted. In the present embodiment, the target temperature Ts,t is set at 200° C. at which the rate of oxidation reaction of the heat storage material reaches a certain level or higher.

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 supplying hydrogen and oxygen to the oxygen-side combustor 42, and continues to supply steam from the evaporator 19 at a flow rate F_cv5. . The control unit 20c closes the control 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 temperature Tsc of the cell stack 10 rises because the heat accumulator 90 performs an oxidation reaction at a constant rate.

In addition to determining the temperature Ts of the heat storage material, the control unit 20c 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 transfers the high-temperature steam generated by the evaporator 19 to the heat accumulator 90 via the oxygen-side combustor 42. supply. 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 switches between connecting the control valves CV1c, CV2c, CV3c, CV4c and CV6 and connecting the three-way valves V6 and V7. Thereby, the supply destination of the high-temperature steam supplied from the evaporator 19 to the cell stack 10 is changed.

FIG. 11 is a schematic block diagram of the 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 the steady operating state in which the temperature Tsc of the cell stack 10 has changed to the operating temperature Tsc,t or higher, the controller 20c opens the closed control valves CV3c and CV6. Further, the control unit 20c switches the three-way valve V6 so as to connect the evaporator 19 and the low temperature side of the fuel-side heat exchanger 81 to each other. The control unit 20c switches the three-way valve V7 so that the booster 61 and the gas-liquid separator 51 are connected. As a result, the steam 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. produces hydrogen.

FIG. 12 is a flow chart of a temperature adjustment control method according to the fourth embodiment. FIG. 12 shows a control flow for raising the temperature Tsc of the normal temperature cell stack 10 to the 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 the target temperature Ts,t of the heat accumulator 90 and the operating temperature Tsc,t of the cell stack 10 (step S41). The control unit 20c sets the target temperature Ts,t and the operating temperature Tsc,t by receiving an operation or the like by the user.

The control unit 20c sets the flow rate F_cv5 of water vapor generated by the evaporator 19, the flow rate F_cv3 of hydrogen and the flow rate F_cv4 of oxygen that provide the stoichiometric air-fuel ratio (step S42). The steam flow rate F_cv5, the hydrogen flow rate F_cv3, and the oxygen flow rate F_cv4 may be set in advance by hydrogen production, or may be set by the user each time. The control unit 20c connects the control valves CV1c, CV2c, CV3c, CV4c, and CV6, the three-way valve V6, V7 connection is controlled (step S43).

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 combusted by ignition by an ignition device. The controller 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). Note that the control unit 20c subsequently acquires the temperature Ts of the heat storage material and the temperature Tsc of the cell stack 10 continuously.

The control unit 20c determines whether or not the temperature Ts of the heat accumulator 90 is equal to or higher than the target temperature Ts,t (step S46). When the temperature Ts of the heat accumulator 90 is lower than the target temperature Ts,t (step S46: NO), the process waits until the temperature Ts changes to the target temperature Ts,t or higher. When 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 control valves CV3c and CV4c to supply hydrogen and oxygen to the fuel-side heat exchanger 81. is stopped, and combustion in the fuel-side heat exchanger 81 is stopped (step S47).

Control unit 20c determines whether or not temperature Tsc of cell stack 10 is equal to or higher than operating temperature Tsc,t (step S48). When the temperature Tsc of the cell stack 10 is lower than the operating temperature Tsc,t (step S48: NO), the process waits for the temperature Tsc to rise above the operating temperature Tsc,t. When 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 control valves CV3c and CV6, switches the three-way valves V6 and V7 (step S49), End the adjustment flow. After that, the cell stack 10 shifts to steady operation to generate hydrogen from the supplied steam.

As described above, in the SOEC system 101c of the fourth embodiment, the heat storage device 90 has a heat storage material capable of exchanging heat with the cell stack 10. FIG. 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 the temperature Tsc of the cell stack 10 is increased, the control unit 20c supplies a mixed gas having a stoichiometric air-fuel ratio to the oxygen side combustor 42 for combustion when the temperature Ts of the heat storage material is lower than the target temperature Ts,t. , and the combustion off-gas is supplied to the regenerator 90 . 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 supplying hydrogen and oxygen to the oxygen-side combustor 42 and stops burning the mixed gas. Therefore, in the fourth embodiment, the heat accumulator 90 can store the surplus heat of the cell stack 10 when the operation of the cell stack 10 that has been operating at a high temperature is stopped. The heat stored in the heat accumulator 90 can be used to heat the cell stack 10 when operating the cell stack 10 again. As a result, in the SOEC system 101c of the fourth embodiment, heat storage and heat dissipation of the heat accumulator 90 are utilized, thereby suppressing an increase in activation energy of the cell stack 10. FIG. In addition, in the heat storage material that releases heat by an oxidation reaction, the heat release reaction speed increases as the temperature rises. Therefore, when the temperature of the cell stack 10 at the beginning of the start-up of the SOEC system 101c is lower than the operating temperature Tsc,t, when the mixed gas burned by the oxygen-side combustor 42 is supplied to the heat storage material, the reaction speed of the heat storage material is increases, and the temperature rise rate of the cell stack 10 is accelerated. That is, even if the SOEC system 101c is not provided with an external heat source for increasing the reaction speed of the heat storage material, the combustion off-gas is supplied to the heat storage device 90, thereby accelerating the temperature rise rate of the cell stack 10. .

<Modification of above embodiment>
The present invention is not limited to the above-described embodiments, and can be implemented in various aspects without departing from the scope of the invention. For example, the following modifications are possible. Further, in the above embodiments, part of the configuration realized by hardware may be replaced with software, and conversely, part of the configuration realized by software may be replaced with hardware. may

<Modification 1>
The SOFC systems 100 and 100a of the first and second embodiments and the SOEC systems 101 and 101c of the third and fourth embodiments are examples, and are temperature control devices for solid oxide electrolytic cells. , etc. can be modified. The temperature control device for the solid oxide electrolysis cell can be modified within the scope of including the hydrogen tank 31, the oxygen tank 32, and at least one of the fuel-side combustor 41 and the oxygen-side combustor 42. . For example, the SOFC system 100 of the first embodiment may be an SOEC system, may be a reversible SOC (reversible SOFC/SOEC) that functions in both SOFC and SOEC, or may include the cell stack 10. It may also be a temperature control system that is not The cell stack 10 whose temperature is raised by combustion in the combustors 41 and 42 may be one electrolytic cell 14 in which the electrolytic cells 14 as solid oxide electrolytic cells are not stacked. SOFC system 100 may not include oxygen side combustor 42, for example. Also, the SOFC system 100 does not have to include the boosters 61 and 62 and the gas-liquid separators 51 and 52 . If the SOFC system 100 includes both a fuel-side combustor 41 and an oxygen-side combustor 42, the fuel-side and oxygen-side flow directions shown in FIG. 3 are co-flow rather than counter-flow. may

Although the SOFC system 100a of the second embodiment has two combustors 41, 42 and two heat exchangers 81, 82, for example, it has a fuel side combustor 41 and a fuel side heat exchanger 81, and oxygen The side combustor 42 and the oxygen side heat exchanger 82 may not be provided. Further, in the SOEC system 101 of the third embodiment, after the cell stack 10 reaches the operating temperature, the mixed gas is burned in the fuel-side combustor 41 so as to maintain the heat balance of the cell stack 10. No temperature adjustment is required after the operating temperature of the stack 10 is reached.

The SOEC system 101c of the fourth embodiment supplies the oxygen-side off-gas of the oxygen-side combustor 42 to the regenerator 90, and further includes the fuel-side combustor 41 and a regenerator to which the combustion-side off-gas is supplied. may Alternatively, the fuel-side off-gas of the fuel-side combustor 41 may be supplied to the same regenerator 90 to which the oxygen-side off-gas is supplied. Although the high-temperature steam generated by the evaporator 19 is supplied to the fuel-side combustor 41, only hydrogen and oxygen at the stoichiometric air-fuel ratio may be supplied without supplying the high-temperature steam. The heat storage material of the heat storage device 90 can be deformed. Instead of Fe-based metal oxides, the heat storage material may be metal oxides containing different metal elements, or other compounds that initiate heat dissipation through oxidation reactions.

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 according to the set temperature of the cell stack 10 to be controlled. It is possible. Regarding the adiabatic flame temperature T set in the second and third embodiments, and the target temperature Ts,t of the regenerator 90 and the operating temperature Tsc,t of the cell stack 10 set in the fourth embodiment, It may be set as appropriate.

<Modification 2>
FIG. 13 is a flow chart of a control method for temperature adjustment of the cell stack 10 of the modification. In the temperature control flow shown in FIG. 13, first, the controller 20 supplies hydrogen from the hydrogen tank 31 to the combustors 41 and 42 (step S51). Similarly, the controller 20 supplies oxygen from the oxygen tank 32 to the combustors 41 and 42 (step S52). The controller 20 burns 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 addition, 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 off-gas 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 or not to end the startup operation of the cell stack 10 (step S55). If the activation operation of the cell stack 10 is not finished (step S55: NO), the control unit 20 repeats the processes after step S51. When ending the activation operation of the cell stack 10 (step S55: YES), the control unit 20 stops the supply of hydrogen and oxygen to the combustor 41, stops combustion in the combustor 41, End the adjustment flow. The cell stack 10 then functions as an SOFC or SOEC.

The present aspect has been described above based on the embodiments and modifications, but the above-described embodiments are intended to facilitate understanding of the present aspect, and do not limit the present aspect. This aspect may be modified and modified without departing from the spirit and scope of the claims, and this aspect includes equivalents thereof. Also, if the technical features are not described as essential in this specification, they can be deleted as appropriate.

ε1 to ε3 Threshold 10 Cell stack 11 Fuel side (anode) of cell stack
12... Oxygen side of the cell stack (cathode)
13 ... electrolytic cell (solid oxide type electrolytic cell)
DESCRIPTION OF SYMBOLS 14... Electrolyte membrane 19... Evaporator 20, 20a, 20b, 20c,... Control part 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 accumulator 100, 100a... SOFC system (temperature control device)
101, 101c ... SOEC system (temperature control device)
C1, C2... Change curve C3 to C8... Temperature change CS... Cartesian coordinate system CV1, CV1b, CV1c, CV2, CV2b, CV3, CV3c, CV4, CV5... Control valves F_cv1, F_cv3... Flow rate of hydrogen F_cv2, F_cv4... Flow rate of oxygen Flow rate F_cv5... Flow rate of water vapor Fa_H2... Amount of hydrogen injected Fa_O2... Amount of oxygen injected K... Excess oxygen rate S1 to S7... Temperature sensor T... Adiabatic flame temperature T _H2 ... Hydrogen temperature T _O2 ... Oxygen temperature Ta... Fuel side off-gas Temperature Tc... Oxygen-side off-gas temperature Ts... Thermal storage device temperature Ts, t... Thermal storage target temperature Tsc... Cell stack temperature Tsc, t... Cell stack operating temperature V6, V7... Three-way valve

Claims (8)

A temperature control device for a solid oxide electrolytic cell,
a hydrogen tank for storing hydrogen;
an oxygen tank for storing oxygen;
a combustor that burns a mixed gas in which hydrogen supplied from the hydrogen tank and oxygen supplied from the oxygen tank is mixed, discharges combustion off-gas, and supplies it to the solid oxide electrolysis cell;
with
The combustor is
a fuel-side combustor that burns the hydrogen-rich mixed gas in which the ratio of hydrogen is higher than the stoichiometric air-fuel ratio;
and an oxygen-side combustor that burns the oxygen-rich mixed gas in which the ratio of oxygen is higher than the stoichiometric air-fuel ratio. The temperature control device of claim 1, further comprising:
A temperature control 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. The temperature control device according to claim 1 or claim 2, further comprising:
a heat accumulator 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;
with
When the combustion control unit increases the temperature of the solid oxide electrolytic cell,
when the temperature of the heat storage material is less than a predetermined temperature, burning the mixed gas with a stoichiometric air-fuel ratio in the combustor and supplying the combustion off-gas to the heat storage device;
A temperature control device that stops supplying the mixed gas to the combustor and stops burning the mixed gas when the temperature of the heat storage material is equal to or higher than the predetermined temperature. The temperature control device according to any one of claims 1 to 3, further comprising:
a gas-liquid separator for separating moisture from the combustion off-gas that has passed through the solid oxide electrolytic cell;
a booster for boosting the combustion off-gas from which moisture has been separated by the gas-liquid separator;
with
The combustor has a fuel-side combustor that supplies the combustion off-gas to the fuel side to which hydrogen is supplied in the solid oxide electrolysis cell,
The booster stores the combustion off-gas on the fuel side after boosting in the hydrogen tank. The temperature control device of claim 4, further comprising:
a temperature sensor for acquiring the temperature of the combustion off-gas supplied to the fuel side of the solid oxide electrolysis cell;
Cell temperature adjustment for 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 by the temperature sensor Department and
A temperature control device, comprising: A temperature control device according to any one of claims 1 to 5, further comprising:
a gas-liquid separator for separating moisture from the combustion off-gas that has passed through the solid oxide electrolytic cell;
a booster for boosting the combustion off-gas from which moisture has been separated by the gas-liquid separator;
with
The combustor has an oxygen side combustor that supplies the combustion off-gas to the oxygen side to which oxygen is supplied in the solid oxide electrolysis cell,
The booster stores the combustion off-gas on the oxygen side after pressurization in the oxygen tank. The temperature control device according to claim 6,
The flow direction of the combustion off-gas on the fuel side flowing from the fuel-side combustor into the fuel side of the solid oxide electrolysis cell, and the oxygen flowing from the oxygen-side combustor into the oxygen side of the solid oxide electrolysis cell. temperature control device opposite to the flow direction of said combustion off-gas on the side. A temperature control method for a solid oxide electrolytic cell, comprising:
supplying hydrogen from a hydrogen tank storing hydrogen to a combustor;
supplying oxygen from an oxygen tank storing oxygen to the combustor;
burning the mixed gas of hydrogen and oxygen supplied to the combustor;
a step of supplying combustion off-gas burned in the combustor to the solid oxide electrolysis cell;
with
The combustor is
a fuel-side combustor that burns the hydrogen-rich mixed gas in which the ratio of hydrogen is higher than the stoichiometric air-fuel ratio;
and an oxygen-side combustor for burning the oxygen-rich mixed gas in which the proportion of oxygen is higher than the stoichiometric air-fuel ratio.

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