Electrochemical system

Abstract

To provide an electrochemical system capable of shortening the time until load operation is ready for operation.SOLUTION: An electrochemical system comprises a stack in which a plurality of cells including a fuel electrode, an air electrode, and a solid oxide electrolyte that separates the fuel electrode and the air electrode are laminated; a control valve that controls the amount of gas supplied to the fuel electrode and the air electrode; and a heating device that heats the cells. The system further comprises a startup unit that controls the control valve and the heating device at startup when switching from no-load operation to load operation. The startup unit increases the output of the heating device and increases the amount of gas via the control valve.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an electrochemical system including a stack in which a plurality of solid oxide type cells including an electrolyte that separates a fuel electrode and an air electrode are stacked.

Background Art

[0002] An electrochemical system including a stack in which a plurality of solid oxide type cells are stacked has gas supplied to the stack heated to the operating temperature of the cells, converts the chemical energy of the gas into electrical energy to generate electricity, or electrolyzes the gas to synthesize fuel. In the prior art disclosed in Patent Document 1, during no-load operation waiting for power generation or electrolysis, the stack is maintained at a preset temperature by a heating device. When switching from no-load operation to load operation, gas is supplied to the stack and power generation or electrolysis occurs.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When switching from no-load operation to load operation, the amount of gas supplied to the stack increases, so the stack maintained at the operating temperature is cooled by the gas. In the prior art, when the temperature of the stack becomes lower than the preset temperature, the heating device heats the stack. However, since heating of the stack starts after detecting that the temperature of the stack has become lower, there is a problem that it takes time until the operation preparation for load operation is completed.

[0005] The present invention has been made to solve this problem, and an object thereof is to provide an electrochemical system capable of shortening the time until the operation preparation for load operation is completed.

Means for Solving the Problems

[0006] A first aspect for achieving this object is an electrochemical system including a stack in which a plurality of cells including a fuel electrode, an air electrode, and a solid oxide electrolyte separating the fuel electrode and the air electrode are stacked, a regulating valve for regulating the amount of gas supplied to the fuel electrode and the air electrode, and a heating device for heating the cells, the electrochemical system including a starting unit for controlling the regulating valve and the heating device at startup when switching from no-load operation to load operation, the starting unit increasing the output of the heating device and increasing the amount of gas by the regulating valve.

[0007] A second aspect is, in the first aspect, including a stopping unit for controlling the regulating valve and the heating device at shutdown when switching from load operation to no-load operation, the stopping unit decreasing the output of the heating device and decreasing the amount of gas by the regulating valve.

[0008] A third aspect is, in the first or second aspect, including a thermometer for detecting a temperature related to the temperature of the cell, the starting unit operating when the temperature detected by the thermometer is equal to or lower than a first temperature.

[0009] A fourth aspect is, in any one of the first to third aspects, including a thermometer for detecting a temperature related to the temperature of the cell, the stopping unit operating when the temperature detected by the thermometer is equal to or higher than a second temperature.

[0010] A fifth aspect is, in any one of the first to fourth aspects, the heating device including a heater for heating the gas.

[0011] A sixth aspect is, in the fifth aspect, including a thermometer for detecting a temperature related to the temperature of the cell and an adjusting unit for adjusting the output of the heater based on the temperature detected by the thermometer.

[0012] A seventh aspect is, in the fifth or sixth aspect, the adjusting unit making the output of the heater during load operation lower than the output of the heater at startup.

[0013] In the eighth aspect, in any one of the fifth to seventh aspects, the adjustment unit gradually reduces the output of the heater as the operating time elapses from startup.

[0014] In the ninth aspect, in any one of the fifth to eighth aspects, the thermometer includes a first thermometer that detects the temperature of the gas discharged from the stack, and the adjustment unit estimates the temperature detected by the first thermometer as the temperature of the cell during the load operation and adjusts the output of the heater.

[0015] In the tenth aspect, in any one of the first to ninth aspects, the cell is an electrolytic cell.

[0016] In the eleventh aspect, in any one of the first to ninth aspects, the cell serves as both a fuel cell and an electrolytic cell.

Advantages of the Invention

[0017] According to the present invention, when switching from no-load operation to load operation, the starting unit increases the output of the heating device and increases the amount of gas by the regulating valve, so that the heating device can heat the stack before the stack is cooled by the gas. Since the temperature change of the stack due to the gas supply can be reduced, the time until the load operation is ready can be shortened.

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0019] Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a block diagram of an electrochemical system 10 in one embodiment. The electrochemical system 10 includes a stack 11 in which cells 12 are stacked, a supply device 40 that supplies fuel gas and oxidant gas to the stack 11, and a heating device 50 that heats the stack 11 to an operating temperature of about 600° C. to 1000° C. The electrochemical system 10 is exemplified by a fuel cell that converts the chemical energy of fuel gas into electrical energy and outputs it, and an electrolyzer that electrolyzes a fuel gas containing water vapor, carbon dioxide, etc. to synthesize fuels such as hydrogen and hydrocarbons.

[0020] In the fuel cell, examples of the fuel gas include hydrogen, carbon monoxide, and hydrocarbons, and examples of the oxidant gas include oxygen and air. In the electrolyzer, examples of the fuel gas include a gas containing water vapor and a gas containing water vapor and carbon dioxide, and examples of the oxidant gas include oxygen and air. An electrolyzer using a fuel gas containing water vapor and carbon dioxide as a raw material corresponds to a co-electrolysis system that synthesizes a fuel containing hydrogen and carbon monoxide.

[0021] FIG. 2 is a cross-sectional view of the stack 11. FIG. 3 is a cross-sectional view of the stack 11 created using a cross-section orthogonal to the cross-section used to create FIG. 2. The stack 11 has a plurality of cells 12 stacked. For simplicity, FIGS. 2 and 3 show a stack 11 with two cells 12 stacked. The number of cells 12 is appropriately set according to the output of the stack 11.

[0022] FIG. 4 is a cross-sectional view of the cell 12. The cell 12 is in the form of a solid oxide and includes a fuel electrode 13, an electrolyte 14, and an air electrode 15 in that order. Although FIG. 4 shows a fuel electrode-supported type cell 12, it is not limited thereto. An air electrode-supported type, electrolyte-supported type, or metal-supported type cell 12 may also be used.

[0023] The fuel electrode 13 has a function of reacting oxide ions supplied from the electrolyte 14 with fuel gas to generate electrons in a fuel cell, and has a function of electrolyzing water vapor by energization to convert it into hydrogen and oxide ions in steam electrolysis. Examples of the material of the fuel electrode 13 include those containing a catalyst containing Ni and zirconia in which Y is solid-solved, and those containing a catalyst containing Ni and ceria in which Gd is solid-solved. Examples of the catalyst include Ni, Ni-based alloys, and cermets which are composites (sintered bodies) of NiO and an oxide (electrolyte). Ni is generated in the cermet by hydrogen reduction of NiO. Examples of the oxide (electrolyte) contained in the cermet include zirconia in which Y is solid-solved.

[0024] The electrolyte 14 is a plate-shaped member that exhibits oxide ion conductivity under the operating conditions of the cell 12. Examples of the electrolyte 14 include a solid solution of one or more selected from stabilized zirconia, ceria-based solid solutions, stabilized zirconia and ceria-based solid solutions, and alumina.

[0025] The air electrode 15 is a place where a gaseous oxidant (oxygen) reacts with electrons to become oxide ions in a fuel cell, and is a place where oxide ions release electrons to become oxygen in steam electrolysis. Examples of the material of the air electrode 15 include perovskite-type oxides such as La 1-X Sr X MnO 3-δ , La 1-X Sr X CoO 3-δ , La 1-X Sr X Co 1-Y Fe Y O 3-δ , Pr 1-X Sr X MnO 3-δ are exemplified.

[0026] Returning to FIG. 2 for explanation. The stack 11 includes end plates 16 and 17 disposed at both ends in the stacking direction of the cells 12, and an insulating plate 18 and a terminal plate 19 disposed in order inside the end plates 16 and 17. The terminal plate 19 includes a terminal (not shown) for connecting to an external electric circuit (not shown).

[0027] The terminal plate 19 is electrically connected to the separators 20, 21, and 22 arranged in sequence. The separators 20, 21, and 22 have a function of separating each other so that the fuel gas supplied to the fuel electrode 13 (see FIG. 4) of the cell 12 and the oxidant gas supplied to the air electrode 15 (see FIG. 4) of the cell 12 do not come into contact with each other. The material of the separators 20, 21, and 22 is exemplified by stainless steel. The separators 21 and 22 are provided with recesses 24 that form a fuel chamber 23 including the fuel electrode 13.

[0028] As shown in FIG. 3, the separators 21 and 22 are provided with a groove 25 connected to the fuel chamber 23 (see FIG. 2) and a recess 30 that forms an air chamber 29 including the air electrode 15 (see FIG. 4). The recess 30 is separated from the groove 25 and is not connected to the groove 25. The separators 20, 21 are provided with holes 32 penetrating in the thickness direction. The holes 32 are connected to the air chamber 29. A pipe 33 for supplying an oxidant gas to the stack 11 is arranged on the end plate 16. The end plate 16 is provided with a hole 34 penetrating in the thickness direction. The hole 34 is connected to the air chamber 29, and the pipe 33 is connected to the hole 34.

[0029] Returning to FIG. 2 for explanation. The separators 20, 21 are provided with a groove 31 connected to the air chamber 29 (see FIG. 3). The groove 31 is separated from the groove 25 (see FIG. 3) and is not connected to the fuel chamber 23. The separators 20, 21 are provided with holes 26 penetrating in the thickness direction. The holes 26 are connected to the fuel chamber 23. A pipe 27 for supplying fuel gas to the stack 11 is arranged on the end plate 16. The end plate 16 is provided with a hole 28 penetrating in the thickness direction. The hole 28 is connected to the fuel chamber 23, and the pipe 27 is connected to the hole 28.

[0030] The current collector 35 is a porous body through which fuel gas can diffuse, and is in contact with the fuel electrode 13 (see FIG. 4) of the cell 12 and the portion of the separators 21, 22 where the groove 25 is provided. The material of the current collector 35 is exemplified by a metal such as Ni.

[0031] The current collector 36 is a porous body through which the oxidant gas can diffuse, and is in contact with the air electrode 15 (see FIG. 4) of the cell 12 and the portion of the separators 20 and 21 where the groove 31 (see FIG. 3) is provided. Examples of the material of the current collector 36 include noble metals such as Au, Ag, and Pt.

[0032] The sealing material 37 is sandwiched between the separator 20 and the separator 21, and between the separator 21 and the separator 22, respectively. The sealing material 37 prevents leakage of the fuel gas and the oxidant gas from between the separators 20, 21, and 22. Examples of the material of the sealing material 37 include mica and vermiculite.

[0033] The stack 11 is provided with a hole 38 penetrating in the thickness direction. The hole 38 is located outside the recesses 24 and 30 provided in the separators 21 and 22. A pipe 39 for supplying a heat medium to the stack 11 is arranged at the position of the hole 38 in the end plates 16 and 17. The heat medium is a liquid or a gas used for heating or cooling the stack 11. Examples of the liquid heat medium include oil and molten salt, and examples of the gas heat medium include steam and flue gas.

[0034] Returning to FIG. 1 for explanation, the supply device 40 is a device for supplying an oxidant gas and a fuel gas to the stack 11. The supply device 40 includes a gas pipe 42 connected to an oxidant gas source 41, a first regulating valve 43 arranged in the gas pipe 42, a gas pipe 45 connected to a fuel gas source 44, and a second regulating valve 46 arranged in the gas pipe 45.

[0035] The gas pipe 42 is connected to one of the pipes 33 (see FIG. 3) of the stack 11 and leads to the air chamber 29. The first regulating valve 43 adjusts the flow rate of the oxidant gas supplied to the air chamber 29. The gas containing oxygen generated at the air electrode 15 (see FIG. 4) exits the stack 11 through the other pipe 33.

[0036] The gas pipe 45 is connected to one of the pipes 27 (see Figure 2) of the stack 11 and is connected to the fuel chamber 23. The second control valve 46 adjusts the flow rate of the fuel gas supplied to the fuel chamber 23. The gas containing the gas after the fuel gas reacts at the fuel electrode 13 (see Figure 4) exits the stack 11 through the other pipe 27.

[0037] The heating device 50 includes a heat medium pipe 52 connected to a heat medium source 51 that is a source of the heat medium, a third control valve 53 disposed in the heat medium pipe 52, and a third heater 56 disposed in the heat medium pipe 52 downstream of the third control valve 53. The heat medium pipe 52 is connected to the pipe 39 (see Figure 2) of the stack 11. The heat medium that has flowed through the hole 38 of the stack 11 and heated the stack 11 is returned to the heat medium pipe 52. Depending on the type of heat medium, the pipe 39 may also serve as the pipe 27, and the pipe 39 may also serve as the pipe 33.

[0038] The heat medium source 51 is selected according to the type of heat medium. For example, when the heat medium is steam, the heat medium source 51 may be a boiler. The third control valve 53 adjusts the flow rate of the heat medium supplied to the stack 11. The third heater 56 adjusts the temperature of the heat medium supplied to the stack 11. The third heater 56 can be used without limitation as long as it is a device that heats the heat medium. The third control valve 53 and the third heater 56 adjust the amount of heat of the heat medium supplied to the stack 11.

[0039] When the heat medium source 51 supplies a heat medium at a temperature higher than the operating temperature of the cell 12 to the heat medium pipe 52, a cooler may be disposed in the heat medium pipe 52 instead of the third heater 56, and the temperature of the heat medium supplied to the stack 11 may be adjusted by cooling the heat medium. The cooler can be used without limitation as long as it is a device that cools the heat medium. The cooler disposed in the heat medium pipe 52 instead of the third heater 56 is a part of the heating device 50 that heats the stack 11.

[0040] The heating device 50 includes a first heater 54 disposed in the gas pipe 42 downstream of the first regulating valve 43 and a second heater 55 disposed in the gas pipe 45 downstream of the second regulating valve 46. The first heater 54 heats the oxidant gas, and the second heater 55 heats the fuel gas. When the heated oxidant gas and fuel gas are supplied to the air chamber 29 and the fuel chamber 23, the cell 12 is heated. The first heater 54 and the second heater 55 are auxiliary heat sources of the heating device 50 that heats the stack 11.

[0041] The thermometer 60 detects the temperature related to the cell 12. The thermometer 60 includes a first thermometer 61 disposed in the gas pipe 42 downstream of the first heater 54, a second thermometer 62 disposed in the gas pipe 45 downstream of the second heater 55, and a third thermometer 63 disposed in the stack 11. The first thermometer 61 detects the temperature of the oxidant gas that has passed through the air chamber 29, and the second thermometer 62 detects the temperature of the fuel gas that has passed through the fuel chamber 23. The first thermometer 61 and the second thermometer 62 detect the temperature of the gas discharged from the stack 11 and indirectly detect the temperature of the stack 11.

[0042] Equipment 64 is connected to the fuel electrode 13 (see FIG. 4) and the air electrode 15 of the cell 12. The equipment 64 is a load through which current flows due to the potential difference between the fuel electrode 13 and the air electrode 15 in a fuel cell, and is a power source that applies a voltage between the fuel electrode 13 and the air electrode 15 in an electrolyzer.

[0043] FIG. 5 is a block diagram of the electrochemical system 10. The electrochemical system 10 includes a control device 65 that controls each part. The control device 65 includes a CPU, a ROM, a RAM, and a backup RAM (none of which are shown). The ROM is a non-volatile memory that stores the programs executed by the CPU. The CPU executes arithmetic processing based on the programs stored in the ROM. The RAM is a memory that temporarily stores the arithmetic results of the CPU, the data input from each sensor, etc. The backup RAM is a non-volatile memory that stores the data to be saved, etc.

[0044] The first thermometer 61 detects the temperature of the oxidant gas and inputs the result to the control device 65. The second thermometer 62 detects the temperature of the fuel gas and inputs the result to the control device 65. The third thermometer 63 detects the temperature of the stack 11 and inputs the result to the control device 65. Based on the detection results of the first thermometer 61, the second thermometer 62, and the third thermometer 63, the control device 65 operates at least one of the first heater 54, the second heater 55, and the third heater 56 to heat the stack 11 with the oxidant gas, the fuel gas, or the heat medium. Further, the control device 65 operates at least one of the first control valve 43, the second control valve 46, and the third control valve 53 to adjust the amount of heat of the oxidant gas, the fuel gas, or the heat medium.

[0045] The start switch 66 is a switch that switches the stack 11 from no-load operation to load operation. The stop switch 67 is a switch that switches the stack 11 from load operation to no-load operation. When the start switch 66 is turned on, the stop switch 67 is turned off, and when the stop switch 67 is turned on, the start switch 66 is turned off. The timer 68 is a device that measures the elapsed time since the start flag (described later) is turned on.

[0046] The operator of the electrochemical system 10 may turn on or off the start switch 66 or the stop switch 67. Further, a device for detecting whether or not the operation of the stack 11 (synthesis or power generation of fuel by electrolysis) is required may be provided, and the control device 65 to which the detection result of the device is input may turn on or off the start switch 66 or the stop switch 67.

[0047] The no-load operation of the stack 11 is to maintain the temperature of the stack 11 at a preset temperature, set the control valves 43 and 46 to preset opening degrees, and keep the device 64 in an inoperative state. The no-load operation is executed when waiting for the synthesis or power generation of fuel by electrolysis. The heating device 50 heats the stack 11 to a temperature suitable for no-load operation with the heat medium supplied from the heat medium pipe 52 to the stack 11.

[0048] The load operation of stack 11 is to heat stack 11 to the operating temperature of cell 12, set regulating valves 43, 46 to preset opening degrees, and put device 64 into an operating state. The load operation is executed when fuel synthesis or power generation by electrolysis is required. The activation of start switch 66 is a necessary condition but not a sufficient condition for the load operation. Heating device 50 heats stack 11 to a temperature suitable for the load operation by means of the heat medium supplied from heat medium pipe 52 to stack 11. Further, heating device 50 may heat stack 11 by means of the oxidant gas heated by first heater 54 or the fuel gas heated by second heater 55.

[0049] The temperature of stack 11 during no-load operation may be the same as the temperature of stack 11 during load operation, or may be lower than the temperature of stack 11 during load operation. It is preferable that the temperature of stack 11 during no-load operation is lower than the temperature of stack 11 during load operation because the energy required for heating stack 11 during no-load operation can be reduced. If the opening degrees of regulating valves 43, 46 during no-load operation are smaller than the opening degrees of regulating valves 43, 46 during load operation, the energy required for heating the fuel gas and oxidant gas during no-load operation can be reduced, which is preferable.

[0050] With reference to FIGS. 6 and 7, an example of the process executed by control device 65 will be described. FIG. 6 is a flowchart of flag management processing, and FIG. 7 is a flowchart of start pause processing. The flag management processing and the start pause processing are processes repeatedly executed by the CPU (not shown) of control device 65 while the power supply of electrochemical system 10 is turned on.

[0051] The flag management processing shown in FIG. 6 is processing related to the management of the start flag and the pause flag. The start flag is a variable into which a value representing on is entered when stack 11 switches from no-load operation to load operation (at startup), and a value representing off is entered at other times. The pause flag is a variable into which a value representing on is entered when stack 11 switches from load operation to no-load operation (at pause), and a value representing off is entered at other times.

[0052] Regarding the flag management process, after the control device 65 acquires the temperatures detected by the first thermometer 61, the second thermometer 62, and the third thermometer 63 (S1), it determines whether the startup flag is on (S2). When the startup flag is on (S2: Yes), the control device 65 ends the flag management process. When the startup flag is off (S2: No), it proceeds to the process of S3. In the process of S3, if the startup switch 66 is on (S3: Yes), it proceeds to the process of S4. If the startup switch 66 is off (S3: No), it proceeds to the process of S8.

[0053] In the process of S4, the control device 65 compares the temperature of the stack 11 detected by the third thermometer 63 with the set first temperature. The first temperature is the set value of the temperature of the stack 11 during no-load operation, and an example of a temperature lower than the operating temperature of the cell 12 set during load operation is given. The first temperature may be a preset temperature or a temperature set by the control device 65 through machine learning associated with the operation of the electrochemical system 10. The first temperature may also be equivalent to the operating temperature of the cell 12 set during load operation (for example, the operating temperature ±50°C).

[0054] When the temperature of the stack 11 is less than or equal to the first temperature (S4: Yes), the control device 65 turns on the startup flag (S5) and turns on the timer 68 (S6). On the other hand, when the temperature of the stack 11 is higher than the first temperature (S4: No), the control device 65 decreases the output of the third heater 56 (S7). Since the flag management process is repeatedly executed, when the startup switch 66 is on (S3: Yes), the output of the third heater 56 decreases until the temperature of the stack 11 becomes less than or equal to the first temperature (S7).

[0055] In the process of S3, if the activation switch 66 is off (S3: No), it is determined whether the pause flag is on (S8). When the pause flag is on (S8: Yes), the control device 65 ends the flag management process. When the pause flag is off (S8: No), the process proceeds to S9. In the process of S9, if the pause switch 67 is on (S9: Yes), the process proceeds to S10. If the pause switch 67 is off (S9: No), the flag management process ends.

[0056] In the process of S10, the control device 65 compares the temperature of the stack 11 detected by the third thermometer 63 with the set second temperature. The second temperature is the set value of the temperature of the stack 11 during the load operation, and examples include a temperature higher than the temperature of the stack 11 set during the no-load operation or a temperature equal to (for example, the first temperature ± 50 °C) or higher than the first temperature. The second temperature may be a preset temperature or a temperature set by the control device 65 through machine learning associated with the operation of the electrochemical system 10.

[0057] When the temperature of the stack 11 is equal to or higher than the second temperature (S10: Yes), the control device 65 turns on the pause flag (S11). On the other hand, when the temperature of the stack 11 is lower than the second temperature (S10: No), the control device 65 increases the output of the third heater 56 (S12). Since the flag management process is repeatedly executed, when the pause switch 67 is on (S9: Yes), the output of the third heater 56 increases (S12) until the temperature of the stack 11 becomes equal to or higher than the second temperature.

[0058] The startup / shutdown process shown in FIG. 7 is a process for switching from no-load operation to load operation (startup) or from load operation to no-load operation (shutdown). Regarding the startup / shutdown process, the control device 65 determines whether the startup flag is on (S13). When the startup flag is on (S13: Yes), the outputs of the first heater 54, the second heater 55, and the third heater 56 are increased (S14), and the opening degrees of the first regulating valve 43 and the second regulating valve 46 are increased (S15). The stack 11 heated by the third heater 56 has an increased amount of heat, and since the amounts of heat of the oxidant gas and the fuel gas supplied to the stack 11 also increase, the temperature of the stack 11 rises.

[0059] The heating device 50 heats the stack 11 including the cells 12 with the heated oxidant gas and fuel gas. Since it is possible to reduce the temperature drop of the stack 11 due to the supply of the oxidant gas and fuel gas for power generation or electrolysis, the time until the temperature of the stack 11 stabilizes at the set temperature can be shortened.

[0060] Since the stack 11 is heated using the oxidant gas and fuel gas heated by the first heater 54 and the second heater 55, finer temperature adjustment of the stack 11 is possible compared to the case where the temperature of the stack 11 is adjusted using only the third heater 56.

[0061] The processes of S14 and S15 when switching from no-load operation to load operation are executed when the temperature of the stack 11 is equal to or lower than the first temperature in the process of S4. Therefore, compared to the case of cooling the stack 11 maintained at a temperature higher than the operating temperature of the cell 12 to adjust the temperature of the cell 12, the operating temperature of the cell 12 can be reached in a short time. For temperature adjustment of the stack 11, since the amounts of the oxidant gas and fuel gas used before power generation or electrolysis can be reduced, the consumption of the oxidant gas and fuel gas that do not directly contribute to power generation or electrolysis can be reduced.

[0062] In the process of S16, the control device 65 compares the elapsed time measured by the timer 68 since the switch of the timer 68 was turned on in S6 with the set threshold value. When the elapsed time since the switch of the timer 68 was turned on, that is, since the start flag became on, is equal to or less than the threshold value (S16: No), the start pause process ends. Since the start pause process is repeatedly executed, when the start flag is on (S13: Yes), the outputs of the first heater 54 and the second heater 55 increase until the elapsed time measured by the timer 68 becomes longer than the threshold value (S14), and the opening degrees of the first control valve 43 and the second control valve 46 increase (S15). As a result, the temperature of the stack 11 heated by the oxidant gas and the fuel gas rises.

[0063] When the elapsed time measured by the timer 68 in the process of S16 is longer than the threshold value (S16: Yes), the control device 65 decreases the output of the first heater 54 and the output of the second heater 55 (S17), and compares the temperature of the oxidant gas and the temperature of the fuel gas with the threshold value (S18). When the temperature of the oxidant gas is lower than the threshold value and the temperature of the fuel gas is lower than the threshold value (S18: Yes), the start flag is turned off (S19), and the timer 68 is turned off (S20). As a result, the switching from the no-load operation to the load operation (start-up) ends, and thereafter, the operation shifts to the load operation.

[0064] The temperature of the stack 11 during the load operation is mainly maintained by the third heater 56 among the heating devices 50. The first heater 54 and the second heater 55 mainly stop operating. The control device 65 controls the opening degrees of the first control valve 43, the second control valve 46, and the third control valve 53, and the output of the third heater 56 so that the efficiency of power generation and electrolysis is increased.

[0065] The threshold value compared with the elapsed time in the process of S16 is a time sufficient to reach the temperature of the stack 11 suitable for the load operation and is the minimum time required for start-up. If the threshold value is too long or too short, the time required to reach the optimum temperature of the stack 11 set during the load operation becomes longer, so the threshold value is set to prevent this.

[0066] In the process of S18, when at least one of the temperature of the oxidant gas and the temperature of the fuel gas is equal to or higher than the threshold value (S18: No), the startup suspension process ends. Since the startup suspension process is repeatedly executed, when the elapsed time measured by the timer 68 is longer than the threshold value, the output of the first heater 54 and the second heater 55 decreases until the temperature of the oxidant gas is lower than the threshold value and the temperature of the fuel gas is lower than the threshold value (S17). As a result, the amount of heat of the oxidant gas and the fuel gas supplied to the stack 11 gradually decreases.

[0067] The threshold value for comparison with the gas temperature in the process of S18 includes the temperature of the stack 11 suitable for the load operation. During the no-load operation, by maintaining the stack 11 at a temperature equal to or lower than the temperature of the stack 11 suitable for the load operation and further reducing the flow rates of the oxidant gas and the fuel gas supplied to the stack 11, the energy for heating the stack 11 during the no-load operation can be reduced. At the time of startup, by supplying a large amount of oxidant gas or fuel gas at a temperature higher than or equal to the temperature of the stack 11 suitable for the load operation to the stack 11 and directly heating the fuel electrode 13 and the air electrode 15, the temperature of the stack 11 can be increased in a short time. Therefore, the time until the temperature of the stack 11 stabilizes at a temperature suitable for the load operation, that is, the time until the operation preparation for the load operation is completed, can be shortened.

[0068] Since the time of the load operation is much longer than the time of startup, by making the output of the first heater 54 and the second heater 55 during the load operation lower than the output of the first heater 54 and the second heater 55 at the time of startup, the energy consumed by the first heater 54 and the second heater 55 during the load operation can be reduced. As a result, it is possible to prevent the energy consumed by the first heater 54 and the second heater 55 from becoming excessive.

[0069] The outputs of the first heater 54 and the second heater 55 gradually decrease with the passage of the operating time since startup and shift to the load operation. Therefore, temperature changes in the oxidant gas and fuel gas heated by the first heater 54 and the second heater 55 can be reduced. Since temperature changes in the stack 11 heated by the oxidant gas and fuel gas can be reduced, it is advantageous for shortening the time until the temperature of the stack 11 stabilizes at a temperature suitable for the load operation.

[0070] During the load operation maintained at the operating temperature of the cell 12, since the temperature of the stack 11 is stable, the temperature of the oxidant gas detected by the first thermometer 61 may be estimated as the temperature of the cell 12. As a result, fine adjustment of the output of the first heater 54 can be performed based on the temperature of the oxidant gas detected by the first thermometer 61, so that the temperature of the stack 11 during the load operation can be stably maintained. Similarly, the temperature of the fuel gas detected by the second thermometer 62 may be estimated as the temperature of the cell 12. As a result, fine adjustment of the output of the second heater 55 can be performed based on the temperature of the fuel gas, so that the temperature of the stack 11 during the load operation can be stably maintained.

[0071] If the startup flag is off in the process of S13 (S13: No), the control device 65 determines whether the pause flag is on (S21). If the pause flag is off (S21: No), the startup pause process ends. If the pause flag is on (S21: Yes), the outputs of the first heater 54, the second heater 55, and the third heater 56 are decreased (S22), and the opening degrees of the first regulating valve 43 and the second regulating valve 46 are decreased (S23). Since the amount of heat supplied to the stack 11 by the heating device 50 decreases, the temperature of the stack 11 decreases.

[0072] In the process of S24, when the temperature of the stack 11 is equal to or higher than the threshold value (S24: No), the startup pause process ends. When the temperature of the stack 11 is lower than the threshold value (S24: Yes), the pause flag is turned off (S25), and the startup pause process ends. As a result, the switching (pause) from the load operation to the no-load operation is completed, and thereafter, the operation shifts to the no-load operation.

[0073] In the process of S24, when the temperature of the stack 11 is equal to or higher than the threshold value, the startup pause process is repeatedly executed until the temperature of the stack 11 becomes lower than the threshold value. Therefore, when the pause flag is on (S21: Yes), the outputs of the first heater 54, the second heater 55, and the third heater 56 decrease (S22), and the opening degrees of the control valves 43 and 46 decrease (S23) until the temperature of the stack 11 becomes lower than the threshold value. If the control valves 43 and 46 are closed all at once, the temperature of the stack 11 will rise rapidly. Therefore, in order to prevent this, the opening degrees of the control valves 43 and 46 are gradually decreased. When the temperature of the stack 11 is equal to or higher than the second temperature (S10: Yes), the stack 11 can be paused at any time and shifted from the load operation to the no-load operation.

[0074] The threshold value compared with the temperature of the stack 11 in the process of S24 includes the temperature of the stack 11 set during the no-load operation. During the no-load operation, by maintaining the stack 11 at a temperature lower than the temperature of the stack 11 suitable for the load operation, the energy for heating the stack 11 during the no-load operation can be reduced.

[0075] The temperature of the stack 11 during the no-load operation is maintained by the third heater 56 among the heating devices 50. The first heater 54 and the second heater 55 stop operating. The control device 65 can reduce the consumption of the oxidant gas and the fuel gas during the no-load operation by closing the first control valve 43 and the second control valve 46, or by slightly opening the second control valve 46 so that a small amount of fuel gas is supplied to the fuel electrode 13.

[0076] As described above, the present invention has been described based on the embodiments. However, it can be easily inferred that the present invention is not limited to the above embodiments at all, and various improvements and modifications are possible without departing from the spirit of the present invention. The structures and shapes of the separators 20, 21, and 22 of the stack 11 in the embodiments are merely examples and are not limited thereto.

[0077] In the embodiment, the heating device 50 for heating the stack 11 includes a heat medium source 51, a heat medium pipe 52, a third control valve 53, and a third heater 56, and the case where the stack 11 is heated by the heat medium supplied to the stack 11 has been described, but it is not necessarily limited thereto. It is of course possible to use a heating device 50 including a heating furnace for housing the stack 11. In this case, the stack 11 is heated by the heating furnace.

[0078] In the embodiment, the case where the stack 11 includes a terminal plate 19 connected to an external electric circuit has been described, but it is not necessarily limited thereto. By omitting the insulating plate 18 and the terminal plate 19 and connecting the separators 20, 21, 22 to the end plates 16, 17, the end plates 16, 17 may be connected to an external electric circuit.

[0079] In the embodiment, the case where, in the processes of S4 and S10, the temperature of the stack 11 detected by the third thermometer 63 is compared with the set temperature (the first temperature or the second temperature) has been described, but it is not necessarily limited thereto. Instead of the temperature of the stack 11, it is of course possible to make the temperature of the oxidant gas detected by the first thermometer 61 or the temperature of the fuel gas detected by the second thermometer 62 the object of comparison.

Explanation of Reference Numerals

[0080] 10 Electrochemical system 11 Stack 12 Cell 13 Fuel electrode 14 Electrolyte 15 Air electrode 43 First control valve (control valve) 46 Second control valve (control valve) 50 Heating device 54 First heater (heater) 55 Second heater (heater) 60 Thermometer 61 First thermometer

Claims

1. A stack in which a plurality of cells including a fuel electrode, an air electrode, and a solid oxide electrolyte that separates the fuel electrode and the air electrode are stacked, A control valve that adjusts the amount of gas supplied to the fuel electrode and the air electrode, An electrochemical system comprising a heating device that heats the cell, An activation unit that controls the control valve and the heating device during startup when switching from no-load operation to load operation, The activation unit increases the output of the heating device and increases the amount of gas by the control valve. An electrochemical system.

2. A shutdown unit that controls the control valve and the heating device during shutdown when switching from load operation to no-load operation, The shutdown unit reduces the output of the heating device and reduces the amount of gas by the control valve. The electrochemical system according to claim 1.

3. A thermometer that detects the temperature related to the temperature of the cell, The activation unit operates when the temperature detected by the thermometer is equal to or lower than a first temperature. The electrochemical system according to claim 1.

4. A thermometer that detects the temperature related to the temperature of the cell, The shutdown unit operates when the temperature detected by the thermometer is equal to or higher than a second temperature. The electrochemical system according to claim 2.

5. The heating device includes a heater that heats the gas. The electrochemical system according to any one of claims 1 to 4.

6. A thermometer that detects the temperature related to the temperature of the cell, An adjustment unit that adjusts the output of the heater based on the temperature detected by the thermometer. The electrochemical system according to claim 5.

7. The electrochemical system according to claim 6, wherein the adjusting unit makes the output of the heater during the load operation lower than the output of the heater at the time of startup. **Claim 8** The electrochemical system according to claim 6, wherein the adjusting unit gradually lowers the output of the heater as the operation time elapses from the startup. **Claim 9** The thermometer includes a first thermometer that detects the temperature of the gas discharged from the stack, The electrochemical system according to claim 6, wherein the adjusting unit estimates the temperature detected by the first thermometer as the temperature of the cell during the load operation and adjusts the output of the heater. **Claim 10** The electrochemical system according to any one of claims 1 to 4, wherein the cell is an electrolytic cell. **Claim 11** The electrochemical system according to any one of claims 1 to 4, wherein the cell serves as both a fuel cell and an electrolytic cell.

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