WO2020054048A1

WO2020054048A1 - Fuel cell system control method and fuel cell system

Info

Publication number: WO2020054048A1
Application number: PCT/JP2018/034142
Authority: WO
Inventors: 雅士佐藤
Original assignee: 日産自動車株式会社
Priority date: 2018-09-14
Filing date: 2018-09-14
Publication date: 2020-03-19

Abstract

This fuel cell system control method is a method for controlling a fuel cell system provided with a fuel cell, a combustor, a reformer, and a cathode gas supply means for supplying a cathode gas to the fuel cell. The reformer has a high-temperature chamber through which a gas from the combustor flows and a low-temperature chamber for reforming a supplied fuel into an anode gas and supplying the anode gas to the fuel cell, and is configured so as to be able to perform a thermal exchange between the high-temperature chamber and the low-temperature chamber. The control method has: a start-up determination step for determining whether start-up is a hot restart or not; a supply step for, when it is determined in the start-up determination step that the start-up is the hot restart, supplying the gas from the combustor to the high-temperature chamber in a state in which the supply of a fluid to the low-temperature chamber is stopped; and an estimation step for estimating the temperature of the low-temperature chamber in accordance with the temperature of the gas flowing through the high-temperature chamber.

Description

Fuel cell system control method and fuel cell system

The present invention relates to a control method for a fuel cell system and a fuel cell system.

2. Description of the Related Art There is known a fuel cell system in which a fuel is reformed in a reformer to generate anode gas, and the generated anode gas and cathode gas are reacted to generate power. In such a fuel cell system, when the temperature of the reformer has not reached the temperature at which the reformer can be reformed, for example, at the time of starting the system, the reforming of the fuel may not proceed sufficiently in the reformer. . In such a case, unreformed fuel may flow into the fuel cell stack, and carbon may be deposited on the anode side electrode.

For example, JP2009-51712A includes a temperature sensor inside a reformer in a fuel cell stack, and adjusts a flow rate of an anode gas in accordance with a temperature inside the reformer obtained by the temperature sensor when the system is started. A technique for controlling the supply of unreformed fuel by controlling the same is disclosed.

According to JP2009-51712A, it is necessary to provide a temperature sensor inside the reformer. However, it is not preferable to provide a temperature sensor inside the reformer in view of the reliability and robustness of the temperature sensor. Therefore, a method is known in which a gas such as air is introduced from the upstream of the reformer, and the temperature of the gas discharged from the reformer is obtained by a temperature sensor provided on the downstream side of the reformer. According to this method, the temperature inside the reformer is substantially equal to the temperature of the gas discharged from the downstream of the reformer. The temperature can be obtained.

However, at the time of restart immediately after the system is stopped (at the time of hot restart), since the fuel cell stack is at a high temperature, if gas such as air is supplied to the reformer, it flows into the fuel cell stack. As a result, the anode of the fuel cell stack may be oxidized and deteriorated. Therefore, there is a problem that the temperature inside the reformer must be estimated without providing a temperature sensor inside the reformer.

The present invention has been made to solve such a problem, and at the time of hot restart, it is necessary to estimate the temperature inside the reformer without providing a temperature sensor inside the reformer. Aim.

According to a control method of a fuel cell system of an aspect of the present invention, control of a fuel cell system including a fuel cell, a combustor, a reformer, and cathode gas supply means for supplying cathode gas to the fuel cell Is the way. The reformer has a high-temperature chamber through which gas from the combustor flows, and a low-temperature chamber that reforms supplied fuel to anode gas and supplies the anode gas to the fuel cell. It is configured to be able to exchange heat between. The control method includes: a start determination step for determining whether the start is a hot restart; and, when the start is determined to be a hot restart in the start determination step, the supply of the fluid to the low-temperature chamber is stopped. A supply step of supplying gas from the combustor to the high-temperature chamber in a state where the gas flows through the high-temperature chamber, and an estimation step of estimating an estimated temperature of the low-temperature chamber according to the temperature of the gas flowing through the high-temperature chamber.

FIG. 1 is a schematic configuration diagram of the fuel cell system according to the first embodiment. FIG. 2 is a flowchart showing the startup control of the fuel cell system. FIG. 3 is a schematic configuration diagram of the fuel cell system according to the second embodiment. FIG. 4 is a flowchart showing the startup control of the fuel cell system. FIG. 5 is a schematic configuration diagram of a fuel cell system according to a first modification. FIG. 6 is a schematic configuration diagram of a fuel cell system according to a second modification. FIG. 7 is a schematic configuration diagram of a fuel cell system according to a third modification. FIG. 8 is a schematic configuration diagram of a fuel cell system according to a fourth modification.

Hereinafter, a fuel cell system according to an embodiment of the present invention will be described with reference to the drawings.

(1st Embodiment)
FIG. 1 is a schematic configuration diagram of a fuel cell system 100 according to the first embodiment of the present invention.

The fuel cell stack 10 is configured by stacking a plurality of fuel cells or fuel cell unit cells, and each fuel cell that is a power generation source is, for example, a solid oxide fuel cell (SOFC: Solid Oxide Fuel Cell). . The fuel cell stack 10 performs power generation using the anode gas supplied through the anode flow path 20 and the cathode gas supplied through the cathode flow path 30. The fuel cell stack 10 is provided with a temperature sensor 11 for measuring the temperature of the stack surface.

The anode gas that has been reacted in the fuel cell stack 10 is discharged from the anode off-gas passage 41 as anode off-gas, and the reacted cathode gas is discharged from the cathode off-gas passage 42 as cathode off-gas. The anode off-gas and the cathode off-gas undergo an oxidation catalytic reaction (combustion) in the exhaust combustor 43. The high-temperature exhaust gas generated by the combustion is discharged to the outside via a cathode-side exhaust passage 44 and an anode-side exhaust passage 45 branched from the cathode-side exhaust passage 44. The high temperature exhaust gas after combustion in the exhaust combustor 43 passes through the cathode side exhaust path 44 and the anode side exhaust path 45. Therefore, as described later, the temperature of the adjacent components can be increased by heat exchange.

The anode flow path 20 is a system that supplies fuel (for example, hydrogen) as a reducing agent gas to the anode of the fuel cell stack 10. The anode flow path 20 is provided with a fuel tank 21, an evaporator 22, a superheater 23, and a reformer 24. The evaporator 22, the superheater 23, and the reformer 24 each include a low-temperature chamber and a high-temperature chamber, and heat exchange using high-temperature exhaust gas flowing through the high-temperature chamber so that the temperature of the low-temperature chamber increases. It is configured.

(4) The fuel tank 21 stores liquid fuel such as hydrous ethanol, and supplies the liquid fuel to the evaporator low-temperature chamber 22A of the evaporator 22. The evaporator low temperature chamber 22A evaporates the liquid fuel by heating to generate a fuel gas, and supplies the generated fuel gas to the superheater low temperature chamber 23A of the superheater 23. The superheater low-temperature chamber 23A further heats the fuel gas and supplies the fuel gas whose temperature has increased to the reformer low-temperature chamber 24A of the reformer 24. The reformer low temperature chamber 24A generates an anode gas by reforming the fuel gas, and supplies the anode gas to the anode electrode of the fuel cell stack 10.

Specifically, the evaporator 22 includes an adjacent evaporator low temperature chamber 22A and an evaporator high temperature chamber 22B. The low-temperature evaporator chamber 22A and the high-temperature evaporator chamber 22B are isolated from each other, and are not in communication with each other. The evaporator low temperature chamber 22A is a part of the anode flow path 20, and the evaporator high temperature chamber 22B is a part of the anode side exhaust passage 45. When the high-temperature exhaust gas from the exhaust combustor 43 passes through the high-temperature evaporator chamber 22B, the temperature of the low-temperature evaporator chamber 22A rises due to heat exchange, and the liquid fuel supplied to the low-temperature evaporator chamber 22A evaporates to produce fuel gas. Is generated.

(4) The superheater 23 includes a superheater low-temperature chamber 23A and a superheater high-temperature chamber 23B which are isolated and adjacent to each other. When high-temperature exhaust gas from the exhaust combustor 43 passes through the superheater high-temperature chamber 23B, the temperature of the superheater low-temperature chamber 23A increases due to heat exchange. Similarly, the reformer 24 includes a reformer low-temperature chamber 24A and a reformer high-temperature chamber 24B that can exchange heat. Further, a temperature sensor 25 for measuring the temperature of the gas discharged from the low-temperature reformer chamber 24A is provided in the anode flow path 20 downstream of the low-temperature reformer chamber 24A.

In the anode flow path 20, a valve 26 is provided between the fuel tank 21 and the evaporator low-temperature chamber 22A, and the supply of fuel to the anode flow path 20 is controlled by the valve 26. Further, the anode flow path 20 is provided with a fuel branch path 27 that branches from between the fuel tank 21 and the valve 26 and is connected to the exhaust combustor 43. The fuel branch passage 27 is provided with a valve 28. When the liquid fuel is supplied to the exhaust combustor 43 by opening the valve 28 at the time of startup or the like, the fuel cell system 100 can be warmed up by an oxidation catalytic reaction of the liquid fuel.

The cathode flow path 30 is a system for supplying a cathode gas (air in this embodiment) to the cathode of the fuel cell stack 10. A blower 31 and an air heat exchanger 32 are provided in the cathode channel 30.

The blower 31 takes in the cathode gas from outside the fuel cell system 100 and supplies the cathode gas to the air heat exchanger 32. The blower 31 is an example of a cathode gas supply unit.

The air heat exchanger 32 includes an air heat exchanger low temperature chamber 32A and an air heat exchanger high temperature chamber 32B which are separated and adjacent to each other, like the evaporator 22 and the like. The air heat exchanger low temperature chamber 32A is a part of the cathode channel 30, and the air heat exchanger high temperature chamber 32B is a part of the cathode side exhaust passage 44. When the high-temperature exhaust gas from the exhaust combustor 43 passes through the air heat exchanger high temperature chamber 32B, the temperature of the air heat exchanger low temperature chamber 32A is increased by heat exchange. Thus, the cathode gas heated by the air heat exchanger high temperature chamber 32B is supplied to the cathode of the fuel cell stack 10.

(4) In the cathode channel 30, the flow rate of the cathode gas supplied to the fuel cell stack 10 can be controlled by controlling the start / stop and the rotation speed of the blower 31. Further, the fuel cell system 100 includes a cathode branch passage 33 branched from the cathode passage 30 between the blower 31 and the air heat exchanger low-temperature chamber 32A and connected to the anode passage 20 upstream of the superheater 23. Is provided.

弁 A valve 34 is provided in the cathode branch passage 33. When the valve 34 is opened, the cathode gas flows to the reformer low temperature chamber 24A via the superheater low temperature chamber 23A. Thus, the temperature Tref_low inside the reformer low temperature chamber 24A can be obtained by measuring the temperature of the exhaust gas discharged from the reformer low temperature chamber 24A by the temperature sensor 25.

The connection between the cathode branch passage 33 and the anode passage 20 is not limited to the upstream of the superheater 23, but may be at any position as long as it is upstream of the reformer 24. If the cathode gas flows through the reformer low temperature chamber 24A, the temperature inside the reformer low temperature chamber 24A can be obtained. In the anode side exhaust passage 45, a temperature sensor 46 is provided downstream of the reformer high temperature chamber 24B. The temperature of the reformer high-temperature chamber 24B can be acquired by the temperature sensor 46.

The fuel cell system 100 includes the controller 90. The controller 90 controls the

valves

26, 28, 34 and the blower 31, and obtains temperatures by the

temperature sensors

11, 25, 46. The controller 90 controls the fuel cell system 100 by executing a stored program.

FIG. 2 is a flowchart showing start-up control of the fuel cell system 100. Before the start-up control, it is assumed that the

valves

26 and 28 in the anode system and the valve 34 in the cathode system are closed, and the blower 31 is stopped.

In step S1, the controller 90 accepts a start operation.

In step S2, the controller 90 determines whether or not the start operation in step S1 corresponds to a hot restart that is a restart immediately after the end operation. Specifically, the controller 90 estimates the stack temperature Tsta inside the fuel cell stack 10 from the surface temperature of the fuel cell stack 10 measured by the temperature sensor 11.

{Circle around (5)} When the stack temperature Tsta is equal to or higher than the hot restart determination temperature Th, the controller 90 determines that the hot restart has occurred. Here, the determination temperature Th is a lower limit temperature at which oxidation deterioration may occur at the anode electrode, and is, for example, about 400 degrees. When the stack temperature Tsta is lower than the determination temperature Th, the controller 90 determines that normal startup is performed instead of hot restart.

The determination of hot restart may be made by another method without using the stack temperature Tsta. For example, when the fuel cell system 100 receives a restart during the stop processing, it may be determined that the restart is a hot restart. In the case where the oxidant replacement of the anode electrode is performed in order to suppress the oxidative deterioration in the stop processing of the fuel cell system 100, it may be determined that the stop processing is being performed when the replacement is not completed. In addition, when restart is received within a predetermined elapsed time after the end of the fuel cell system 100, it may be determined that hot restart has been started.

If it is determined that the restart is a hot restart (S2: Yes), the controller 90 performs the process of step S9 in order to control the start of the hot restart. If it is determined that it is not a hot restart (S2: No), the controller 90 performs the process of step S3 to perform normal startup control. Note that the process in step S2 is an example of a startup determination step.

In step S3, the supply of the cathode gas to the anode of the fuel cell stack 10 is started. During normal startup, the temperature of the fuel cell stack 10 is low, so that even if the cathode gas flows into the anode, the anode gas is not oxidized and deteriorated.

When the controller 90 activates the blower 31 and opens the valve 34, the cathode gas taken in from the outside flows through the cathode branch passage 33 to the superheater low temperature chamber 23A and the reformer low temperature chamber 24A, It passes through the reformer low temperature chamber 24A. At the same time, the cathode gas is supplied to the fuel cell stack 10 via the cathode channel 30. Since the fuel cell stack 10 has not started power generation, the cathode gas is supplied to the exhaust combustor 43 via the cathode offgas flow path 42.

In step S4, the controller 90 acquires the temperature of the exhaust gas from the low-temperature reformer chamber 24A measured by the temperature sensor 25 as the temperature Tref_low inside the low-temperature reformer chamber 24A. The processing in step S4 is an example of a temperature acquisition step, and the temperature sensor 25 is an example of a second temperature sensor.

In step S5, the controller 90 determines whether or not the temperature Tref_low is equal to or higher than the reforming temperature Tref_th at which the reforming reaction proceeds in the reformer 24. If the temperature Tref_low is equal to or higher than the reforming temperature Tref_th (S5: Yes), the controller 90 determines that the reformer 24 is capable of reforming and can supply fuel, and starts the power generation. Step S7 is performed. When the temperature Tref_low is lower than the reforming temperature Tref_th (S5: No), the controller 90 determines that the reformer 24 is not sufficiently high, and performs the process of step S6.

If the temperature Tref_low is lower than the reforming temperature Tref_th (S5: No), the controller 90 opens the valve 28 and supplies the liquid fuel to the exhaust combustor 43 via the fuel branch 27 in step S6. . In the exhaust combustor 43, the liquid fuel undergoes an oxidation catalytic reaction to generate heat. Since the blower 31 is activated in step S3 and the supply of the cathode gas to the exhaust combustor 43 has been started, high-temperature exhaust is discharged from the exhaust combustor 43.

When the high-temperature exhaust gas from the exhaust combustor 43 is supplied to the high-temperature reformer chamber 24B via the anode-side exhaust path 45, heat exchange between the high-temperature reformer chamber 24B and the low-temperature reformer chamber 24A is performed. Thereby, the reformer low temperature chamber 24A is heated. Thus, the temperature Tref_low of the reformer low temperature chamber 24A can be increased. Similarly, the evaporator low temperature chamber 22A and the superheater low temperature chamber 23A are also heated by heat exchange with the exhaust gas. As described above, in step S6, the high-temperature exhaust gas discharged from the exhaust combustor 43 is used to warm up the low-temperature evaporator chamber 22A, the low-temperature superheater chamber 23A, and the low-temperature reformer chamber 24A. Will be.

When the temperature Tref_low is equal to or higher than the reforming temperature Tref_th (S5: Yes), in step S7, the controller 90 opens the valve 26 and transfers the liquid fuel stored in the fuel tank 21 to the anode flow path 20. Supply. The evaporator low temperature chamber 22A and the superheater low temperature chamber 23A have a high temperature similarly to the temperature Tref_low of the reformer low temperature chamber 24A. Therefore, the liquid fuel supplied from the fuel tank 21 evaporates in the evaporator low-temperature chamber 22A, is superheated in the superheater low-temperature chamber 23A, is reformed in the reformer low-temperature chamber 24A, and becomes fuel gas as anode gas. It is supplied to the anode of the battery stack 10. When the process proceeds to step S7 after the process of step S6, the valve 28 may be closed to terminate the supply of the liquid fuel to the exhaust combustor 43.

(4) In step S8, when the controller 90 instructs the fuel cell stack 10 to start power generation, the fuel cell stack 10 supplied with the anode gas and the cathode gas starts power generation. At this stage, the supply of the cathode gas to the anode may be stopped by closing the valve 34. Step S8 is an example of a power generation start step.

On the other hand, in step S9, activation control of hot restart is performed, and the controller 90 activates the blower 31 to supply the cathode gas to the cathode of the fuel cell stack 10. At this time, since the fuel cell 10 is not generating power, when the cathode gas is supplied to the high-temperature reformer chamber 24B via the cathode-side exhaust passage 44, the cathode gas is discharged from the cathode off-gas passage 42. . And the temperature sensor 46 provided downstream of the reformer high temperature chamber 24B acquires the temperature of the exhaust gas from the reformer high temperature chamber 24B as the temperature Tref_high inside the reformer high temperature chamber 24B. Step S9 is an example of a supply step.

In step S10, the controller 90 estimates an estimated temperature Tref_low ^* of the reformer low temperature chamber 24A using the temperature Tref_high. Step S10 is an example of an estimation step.

(4) At the time of hot restart, the fluid does not flow into the low-temperature reformer chamber 24A because the

valves

26 and 34 are closed. Therefore, heat exchange between the reformer low temperature chamber 24A and the reformer high temperature chamber 24B does not proceed, and the temperature of the reformer low temperature chamber 24A substantially matches the temperature of the exhaust gas flowing through the reformer high temperature chamber 24B.

Therefore, the controller 90 estimates the temperature Tref_high of the reformer high temperature chamber 24B acquired by the temperature sensor 46 as the estimated temperature Tref_low ^* of the reformer low temperature chamber 24A. The controller 90 calculates the estimated temperature Tref_low ^* with respect to the temperature of the reformer high-temperature chamber 24B in consideration of the temperature difference determined by the heat exchange ratio between the reformer low-temperature chamber 24A and the reformer high-temperature chamber 24B. It may be estimated.

In step S11, the controller 90 determines whether or not the estimated temperature Tref_low ^* is higher than the reforming temperature Tref_th. If the estimated temperature Tref_low ^* is higher than the reforming temperature Tref_th (S11: Yes), the controller 90 determines that reforming is possible, and performs the process of step S7. When the estimated temperature Tref_low ^* is equal to or lower than the reforming temperature Tref_th (S11: No), the controller 90 determines that the reforming is not properly performed and unreformed fuel may flow into the fuel cell stack 10. Then, the process of step S12 is performed.

In step S12, the controller 90 opens the valve 28 and supplies the liquid fuel to the exhaust combustor 43 via the fuel branch 27. In the exhaust combustor 43, the liquid fuel is burned by an oxidation catalytic reaction. In step S9, since the blower 31 has been activated and the supply of the cathode gas has been started, high-temperature exhaust is discharged from the exhaust combustor 43. When high-temperature exhaust gas from the exhaust combustor 43 is supplied to the reformer high-temperature chamber 24B via the anode-side exhaust passage 45, heat exchange between the reformer high-temperature chamber 24B and the reformer low-temperature chamber 24A is performed. Thereby, the reformer low temperature chamber 24A is heated. Thus, the temperature Tref_low of the reformer low temperature chamber 24A can be increased. Then, the controller 90 returns to the process of step S9.

If the estimated temperature Tref_low ^* is higher than the reforming temperature Tref_th (S11: Yes) and the process of step S7 is performed after step S12, in step S7, the controller 90 sets the valve 28 to ON. May be closed.

In this way, when it is determined that the normal startup is performed (S2: No), the controller 90 causes the cathode gas to flow into the reformer low-temperature chamber 24A and acquires the temperature Tref_low by the temperature sensor 25 (S4). On the other hand, if it is determined that the restart is a hot restart (S2: Yes), the controller 90 calculates the temperature Tref_high of the reformer high-temperature chamber 24B obtained by the temperature sensor 46 provided downstream of the reformer high-temperature chamber 24B. The estimated temperature Tref_low ^* of the reformer low temperature chamber 24A is estimated (S10). When the temperature Tref_low or the estimated temperature Tref_low ^* is higher than the reforming temperature Tref_th (S5: Yes, S11: Yes), power generation is started (S7). By doing so, it is possible to prevent the unreformed fuel from flowing into the fuel cell 10.

According to the first embodiment, the following effects can be obtained.

According to the control method of the fuel cell system 100 of the first embodiment, when the fuel is supplied to the reformer 24 when the temperature of the reformer low temperature chamber 24A is lower than the reforming temperature Tref_th, the unreformed fuel becomes unreformed. It may flow into the anode of the fuel cell stack 10 and carbon deposition (caulking) may occur. Therefore, when the temperature Tref_low of the reformer low-temperature chamber 24A is higher than the reforming temperature Tref_th, it is necessary to control the supply of the liquid fuel to the reformer 24. Therefore, it is necessary to obtain the temperature Tref_low of the reformer low temperature chamber 24A.

(4) If it is determined that the startup is not the hot restart but the normal startup (S2: No), even if the cathode gas flows into the fuel cell 10, there is no risk of oxidative deterioration. Then, the controller 90 supplies the cathode gas to the reformer low temperature chamber 24A (S3), and detects the temperature of the exhaust gas from the reformer low temperature chamber 24A by the temperature sensor 25 provided downstream of the reformer low temperature chamber 24A. Is measured, and the measured temperature is obtained as the temperature Tref_low inside the reformer low temperature chamber 24A. When the temperature Tref_low of the reformer low temperature chamber 24A is higher than the reforming temperature Tref_th (S5: Yes), the controller 90 determines that the reformer 24 is in a reformable state, and the valve 26 Is opened and fuel is supplied (S6). By doing so, it is possible to suppress the unreformed fuel from flowing into the anode of the fuel cell 10.

(4) When it is determined that the fuel cell system 100 is a hot restart (S2: Yes), the temperature of the fuel cell stack 10 is high. Therefore, in order to obtain the temperature Tref_low of the reformer low-temperature chamber 24A, the cathode gas is caused to flow through the reformer low-temperature chamber 24A and the temperature is measured by the temperature sensor 25. Will flow in. When the temperature of the fuel cell stack 10 is high, there is a possibility that the fuel cell stack 10 is oxidized and deteriorated. Therefore, it is not preferable that the cathode gas flows into the anode of the fuel cell 10 in such a high temperature state. Therefore, in the present embodiment, at the time of the hot restart (S2: Yes), the supply of the cathode gas to the low temperature chamber 24A of the reformer as in the normal start is stopped.

At the time of the hot restart, in step S9, the controller 90 activates the blower 31 to flow the cathode gas through the cathode flow path 30, the cathode off-gas flow path 42, and the anode-side exhaust path 45 to the reformer high temperature. Flow to room 24B. Then, in step S10, the estimated temperature Tref_low ^* of the reformer low temperature chamber 24A is estimated according to the state of the reformer high temperature chamber 24B. In this way, at the time of hot restart, the temperature inside the reformer 24 can be measured without providing a temperature sensor inside the reformer 24. If the estimated temperature Tref_low ^* is equal to or lower than the reforming temperature Tref_th (S11: No), the controller 90 may not perform reforming properly and unreformed fuel may flow into the fuel cell stack 10. Is determined, the warm-up is performed in step S12, and the temperature of the reformer low temperature chamber 24A is increased.

According to the control method of the fuel cell system 100 of the first embodiment, in step S11, if the estimated temperature Tref_low ^* is higher than the reforming temperature Tref_th (S11: Yes), the controller 90 Determines that reforming is possible, opens the valve 26, supplies the liquid fuel to the reformer 24, and supplies the anode gas reformed in the reformer 24 to the fuel cell stack 10 (S7). By doing so, it is possible to prevent the unreformed fuel from flowing from the reformer 24 into the fuel cell stack 10 and to cause carbon deposition (caulking). Then, since the blower 31 has already been activated (S9) and the supply of the cathode gas has been started, the power generation of the fuel cell 10 is started according to the instruction of the controller 90 (S8).

According to the control method of the fuel cell system 100 of the first embodiment, in step S2, when the stack temperature Tsta of the fuel cell stack 10 is equal to or higher than the determination temperature Th, the controller 90 controls the fuel cell system 100 to perform the cooling process. It is determined that the start at this timing is a hot restart. As the determination temperature Th, a temperature at which the anode of the fuel cell 10 may be oxidized and deteriorated is used.

By doing so, the supply of the fluid containing the cathode gas to the reformer low temperature chamber 24A is suppressed in the case of a hot restart, when the stack temperature Tsta is high and the anode electrode is likely to be oxidized and deteriorated. Therefore, the possibility that the anode electrode is oxidized and deteriorated can be reduced.

According to the control method of the fuel cell system 100 of the first embodiment, when it is determined that the restart is a hot restart (S2: Yes), the cathode gas is supplied to the fuel cell 10 (S9), and The cathode gas also flows into the high temperature chamber 24B. Therefore, the controller 90 acquires the temperature Tref_high of the reformer high temperature chamber 24B by the temperature sensor 46 provided downstream of the reformer high temperature chamber 24B. When the inflow of the fluid into the reformer low temperature chamber 24A is suppressed, the temperature of the reformer high temperature chamber 24B substantially matches the temperature of the reformer low temperature chamber 24A. Therefore, the controller 90 can estimate the temperature Tref_high of the reformer high temperature chamber 24B acquired by the temperature sensor 46 as the estimated temperature Tref_low ^* (S10).

According to the control method of the fuel cell system 100 of the first embodiment, when it is determined that the normal startup is performed instead of the hot restart (S2: No), the controller 90 sends the cathode gas to the reformer low-temperature chamber. 24A (S3). The controller 90 measures the temperature of the exhaust gas from the reformer low temperature chamber 24A by the temperature sensor 25 provided downstream of the reformer low temperature chamber 24A, and acquires the measured temperature as the temperature Tref_low of the reformer low temperature chamber 24A. (S4). As described above, since the temperature of the exhaust gas from the low temperature chamber 24A of the reformer can be directly measured by the temperature sensor 25, the temperature Tref_low inside the low temperature chamber 24A of the reformer can be accurately obtained.

Thereby, when the temperature Tref_low of the low temperature chamber 24A of the reformer is higher than the reforming temperature Tref_th (S5: Yes), the fuel can be supplied to generate the reformed gas (S7). Fuel can be prevented from flowing into the anode of the fuel cell 10. At the time of normal startup that is not a hot restart, the temperature is such that the anode of the fuel cell stack 10 is not oxidized and deteriorated, and the anode is not oxidized even if air flowing to the lower temperature side of the reformer flows into the anode. Therefore, the temperature of the exhaust gas from the low temperature chamber 24A of the reformer can be directly measured by the temperature sensor 25, so that the temperature Tref_low inside the low temperature chamber 24A of the reformer can be accurately obtained.

(2nd Embodiment)
In the first embodiment, an example has been described in which a gas is flowed into the reformer high-temperature chamber 24B at the time of hot restart, and the estimated temperature Tref_low ^* is estimated from the temperature Tref_high of the reformer high-temperature chamber 24B. In the second embodiment, an example will be described in which the estimated temperature Tref_low ^* is estimated according to the elapsed time after the fuel is supplied to the exhaust combustor 43 in order to perform warm-up at the time of hot restart.

FIG. 3 is a schematic configuration diagram of the fuel cell system 100 according to the second embodiment. According to this figure, as compared with the fuel cell system 100 of the first embodiment shown in FIG. 1, the temperature sensor 46 provided downstream of the reformer high temperature chamber 24B is omitted.

FIG. 4 is a flowchart of the startup control of the fuel cell system 100 of the present embodiment. According to this figure, steps S21 and S22 are provided instead of steps S9 and S10 as compared with the start control of the first embodiment shown in FIG. 2, and step S23 is added after step S11. If the temperature Tref_low is lower than the reforming temperature Tref_th in step S5 (S5: No), the controller 90 performs the warm-up process in step S21.

In the following, the configurations and controls denoted by the same reference numerals as those in the first embodiment are the same and will not be described.

において In step S21, warm-up is performed in the hot restart activation control. In step S21, first, the controller 90 activates the blower 31 to supply the cathode gas to the fuel cell stack 10. At this time, since the fuel cell 10 has not started power generation, the cathode gas is discharged from the cathode off-gas channel 42 and supplied to the reformer high temperature chamber 24B. When the process of step S21 is performed after step S3, since the blower 31 has already been activated, the activation process of the blower 31 in step S21 can be omitted.

Furthermore, the controller 90 opens the valve 28 and supplies the liquid fuel to the exhaust combustor 43 via the fuel branch channel 27. In the exhaust combustor 43, the liquid fuel and the cathode gas undergo an oxidation catalytic reaction to generate high-temperature combustion gas.

When the high-temperature exhaust gas discharged from the exhaust combustor 43 is supplied to the high-temperature reformer chamber 24B via the anode-side exhaust path 45, the high-temperature exhaust gas flows between the high-temperature reformer chamber 24B and the low-temperature reformer chamber 24A. The heat exchange heats the reformer low-temperature chamber 24A. Similarly, the evaporator low temperature chamber 22A and the superheater low temperature chamber 23A are also heated by heat exchange with the exhaust gas.

In step S22, the controller 90 determines the estimated temperature Tref_low of the reformer low temperature chamber 24A according to the elapsed time from step S21, that is, the elapsed time after supplying the high-temperature exhaust gas to the reformer high temperature chamber 24B. ^* Estimate. Step S22 is an example of an estimation step.

The controller 90 calculates the temperature increase ΔT after the start-up using parameters obtained in advance through experiments and simulations. For example, the controller 90 uses the previously stored calorific value Q of the exhaust combustor 43 per unit time and the reformer heat capacity Cp during warm-up of the reformer 24 to increase as follows: The temperature ΔT can be determined.

Rise temperature ΔT = calorific value Q × time t / reformer heat capacity Cp
The temperature of the reformer low-temperature chamber 24A is a predetermined drive temperature when the fuel cell system 100 is stopped, but thereafter decreases according to the elapsed time. Therefore, the controller 90 subtracts the decrease temperature according to the elapsed time after the stop of the fuel cell system 100 from the drive temperature, and adds the increase temperature ΔT to the stack temperature Tsta calculated in step S2, Estimate the estimated temperature Tref_low ^* .

As another method, the controller 90 may calculate the temperature increase ΔT with respect to the room temperature to estimate the estimated temperature Tref_low ^* . In this case, the estimated temperature Tref_low ^* may be lower than the actual temperature, but it can be determined in a later step S23 whether the reforming can be performed reliably.

In step S23, since the estimated temperature Tref_low ^* is higher than the reforming temperature Tref_th (S11: Yes), the controller 90 determines that reforming is possible in the reformer 24, closes the valve 28, and warms up. The machine control ends.

In the present embodiment, the example in which the valve 28 is opened and the warm-up of the exhaust combustor 43 is started in step S21 has been described, but the invention is not limited to this. In step S21, even if only the blower 31 is started and only the cathode gas is supplied to the exhaust combustor 43 without opening the valve 28, the controller 90 can estimate the estimated temperature Tref_low ^* . For example, based on the stack temperature Tsta of the fuel cell 10 obtained from the temperature obtained by the temperature sensor 11, an exchange heat amount Q exchanged with the reformer high-temperature chamber 24B via the exhaust gas per unit time is obtained. The rising temperature ΔT may be obtained using Q.

According to the second embodiment, the following effects can be obtained.

According to the control method of the fuel cell system 100 of the second embodiment, when liquid fuel is supplied to the exhaust combustor 43 and an exothermic reaction proceeds to generate high-temperature combustion gas, the high-temperature Exhaust gas flows into the reformer high-temperature chamber 24B (S21). Then, the controller 90 uses the calorific value Q per unit time of the reformer 24 stored in advance or the reformer heat capacity Cp during warm-up of the reformer 24 to calculate the elapsed time from step S21, That is, the temperature increase ΔT is determined according to the elapsed time from the start of warm-up when the liquid fuel is supplied via the exhaust combustor 43. The controller 90 can estimate the estimated temperature Tref_low ^* by adding the temperature increase ΔT to the estimated stack temperature Tsta (S22).

(First Modification)
In the first and second embodiments, an example in which the temperature of the surface of the fuel cell stack 10 obtained by the temperature sensor 11 is used as the temperature of the fuel cell stack 10 has been described, but the present invention is not limited to this.

As shown in FIG. 5, the temperature of the anode off gas obtained by the temperature sensor 12 provided in the anode off gas flow path 41, the temperature of the cathode off gas obtained by the temperature sensor 13 provided in the cathode off gas flow path 42, and The stack temperature Tsta may be obtained using any one of the temperatures obtained by the temperature sensor provided inside the fuel cell stack 10. With this configuration, the degree of freedom in the arrangement of the temperature sensor used for measuring the fuel cell stack 10 is improved.

(Second Modification)
In the first embodiment, the estimated temperature Tref_low ^* of the reformer low temperature chamber 24A was estimated using the temperature acquired by the temperature sensor 46 provided between the reformer high temperature chamber 24B and the superheater high temperature chamber 23B. However, it is not limited to this.

As shown in FIG. 6, the temperature was measured by a temperature sensor 47 provided downstream of the superheater high temperature chamber 23B and upstream of the evaporator high temperature chamber 22B, or a temperature sensor 48 provided downstream of the evaporator high temperature chamber 22B. Using the temperature, the estimated temperature Tref_low ^{* of the} reformer low-temperature chamber 24A may be estimated.

(4) When gas is not flowing through the anode channel 20, heat exchange is not active in the evaporator 22, the superheater 23, and the reformer 24. Therefore, the temperatures of the reformer high-temperature chamber 24B, the superheater high-temperature chamber 23B, and the evaporator high-temperature chamber 22B provided in the cathode-side exhaust passage 44 have a temperature distribution that gradually decreases.

By using this temperature distribution, the controller 90 estimates the temperature of the reformer high temperature chamber 24B using the temperature acquired by the

temperature sensor

47 or 48, and estimates the estimated temperature of the reformer low temperature chamber 24A. The temperature may be Tref_low ^* .

The

temperature sensors

47 and 48 used for estimating the estimated temperature Tref_low ^* are provided downstream of the reformer high-temperature chamber 24 </ b ^> B in the anode-side exhaust passage 45 and upstream of the junction with the cathode-side exhaust passage 44. Preferably. This is because the temperature of the anode-side exhaust passage 45 changes at the junction with the cathode-side exhaust passage 44.

According to such a second modification, the

temperature sensors

47 and 48 used for estimating the estimated temperature Tref_low ^* may be provided in the anode-side exhaust passage 45 downstream of the reformer high-temperature chamber 24B. In the anode-side exhaust passage 45, the lower the temperature, the lower the temperature. Therefore, by providing the temperature sensor downstream, the heat resistance requirement of the temperature sensor can be reduced and the measurement error due to the high temperature state can be reduced.

Note that, in the figure, a casing 49 that accommodates the fuel cell 10, the evaporator 22, the superheater 23, the reformer 24, and the air heat exchanger 32 in the fuel cell system 100 is shown by a dotted line. . The inside of the casing 49 becomes high temperature by the power generation of the fuel cell 10, but the outside of the casing 49 becomes relatively low temperature. By providing the temperature sensor 48 outside the housing 49, the degree of freedom in arranging the temperature sensor 48, the durability, and the like can be improved.

(Third Modification)
In the first and second embodiments, an example has been described in which the evaporator 22, the superheater 23, and the reformer 24 are separately configured, but the present invention is not limited to this.

As shown in FIG. 7, a unit 51 in which the evaporator 22, the superheater 23, and the reformer 24 are integrated may be provided. Specifically, it is configured such that a catalyst used for reforming is provided downstream of a heat-exchangeable point of the anode system in one unit. In such a case, the temperature of the unit high-temperature chamber 51B is measured using a temperature sensor 52 provided downstream of the unit high-temperature chamber 51B or a temperature sensor 53 provided inside the unit high-temperature chamber 51B, and the temperature is measured. The estimated temperature Tref_low ^* corresponding to the reformer low temperature chamber 24A may be used.

If the

temperature sensors

52 and 53 are provided on the downstream side of the portion corresponding to the reformer of the unit 51, and when the gas flows through the cathode exhaust path 44, the

temperature sensors

52 and 53 The temperature of the exhaust gas or the temperature downstream of the reformer 24 in the unit 51 can be obtained. Using the temperature thus obtained, a temperature corresponding to the reformer high temperature chamber 24B in the unit high temperature chamber 51B is estimated, and the estimated temperature is estimated to correspond to the reformer low temperature chamber 24A in the unit low temperature chamber 51A. It may be Tref_low ^* .

(Fourth modification)
In the fourth modification, as shown in FIG. 8, a unit 61 in which the evaporator 22 and the superheater 23 are integrated is provided, and the reformer 24 and the anode of the fuel cell 10 are integrated. An example will be described.

Similarly to the third modified example, the temperature sensor 62 provided downstream of the unit high-temperature chamber 61B and the temperature sensor 63 provided inside the unit high-temperature chamber 61B are used to form the reformer 24 integrated with the anode electrode. The temperature may be estimated.

Further, the temperature of the anode offgas obtained by the temperature sensor 12 provided in the anode offgas flow path 41, the temperature of the cathode offgas obtained by the temperature sensor 13 provided in the cathode offgas flow path 42, and the inside of the fuel cell stack 10 The temperature of the reformer 24 integrated with the anode can be estimated by using the temperature obtained by any of the temperature sensors provided in the above.

As described above, the embodiment of the present invention has been described. However, the above embodiment is only a part of an application example of the present invention, and the technical scope of the present invention is not limited to the specific configuration of the above embodiment. Absent. The above embodiments can be combined as appropriate.

Claims

A fuel cell that generates electricity by reacting anode gas and cathode gas;
A combustor configured to allow an anode offgas and a cathode offgas discharged from the fuel cell during power generation to undergo an oxidation catalytic reaction,
A high-temperature chamber through which gas from the combustor flows, and a low-temperature chamber that reforms supplied fuel to the anode gas and supplies the anode gas to the fuel cell; the high-temperature chamber and the low-temperature chamber; A reformer configured to allow heat exchange between
A cathode gas supply means for supplying the cathode gas to the fuel cell, a control method of a fuel cell system comprising:
When the fuel cell system is started, a start determination step of determining whether the start is a hot restart,
When the startup is determined to be the hot restart in the startup determination step, supply of gas from the combustor to the high-temperature chamber in a state in which supply of fluid to the low-temperature chamber is stopped. Steps and
An estimation step of estimating the estimated temperature of the low-temperature chamber according to the temperature of the gas flowing through the high-temperature chamber.
It is a control method of the fuel cell system of Claim 1, Comprising:
When the estimated temperature estimated in the estimation step is higher than a lower limit temperature at which the fuel can be reformed in the reformer, the fuel is supplied to the low temperature chamber and reformed in the low temperature chamber. A control method for a fuel cell system, further comprising a power generation start step of starting power generation of the fuel cell by supplying the anode gas to the fuel cell and supplying the cathode gas to the fuel cell.
It is a control method of the fuel cell system of Claim 1 or 2, Comprising:
Controlling the fuel cell system to determine that the startup is the hot restart when the temperature of the fuel cell at the time of startup exceeds the lower limit temperature at which the anode electrode is oxidized and degraded in the startup determination step; Method.
It is a control method of the fuel cell system as described in any one of Claims 1 to 3, Comprising:
The fuel cell system further includes a first temperature sensor downstream of the high temperature chamber,
A control method for a fuel cell system, wherein in the estimating step, the estimated temperature is estimated according to a temperature of the cathode gas discharged from the high temperature chamber acquired by the first temperature sensor.
It is a control method of the fuel cell system of Claim 4, Comprising:
The fuel cell system,
An evaporator that evaporates liquid fuel provided upstream of the reformer to generate a fuel gas, and at least one of a superheater that further heats the fuel gas,
The evaporator, and the superheater has a high-temperature part where exhaust gas from the combustor flows, and a low-temperature part that can exchange heat with the high-temperature part,
The control method of a fuel cell system, wherein the first temperature sensor is provided downstream of at least one of a high-temperature portion of the evaporator and a high-temperature portion of the superheater.
It is a control method of the fuel cell system as described in any one of Claims 1 to 3, Comprising:
In the supplying step, further, by supplying the fuel to the combustor to cause an oxidation catalytic reaction, the high-temperature gas is discharged from the combustor to the high-temperature chamber,
A control method for a fuel cell system, wherein in the estimating step, the estimated temperature is estimated based on an elapsed time after the supplying step.
It is a control method of the fuel cell system as described in any one of Claim 1 to 6, Comprising:
The fuel cell system further includes a second temperature sensor downstream of the low-temperature chamber,
A temperature obtaining step of supplying the cathode gas to the low-temperature chamber and obtaining the temperature of the low-temperature chamber by the second temperature sensor when the startup is determined not to be the hot restart in the startup determining step; A control method for a fuel cell system, further comprising:
A fuel cell that generates electricity by reacting anode gas and cathode gas;
A combustor configured to allow an anode offgas and a cathode offgas discharged from the fuel cell during power generation to undergo an oxidation catalytic reaction,
A high-temperature chamber through which gas from the combustor flows, and a low-temperature chamber that reforms supplied fuel to the anode gas and supplies the anode gas to the fuel cell; the high-temperature chamber and the low-temperature chamber; A reformer configured to allow heat exchange between
Cathode gas supply means for supplying the cathode gas to the fuel cell;
A valve provided in the preceding stage of the low-temperature chamber,
A blower provided before the high-temperature chamber,
A fuel cell system including the valve and a control unit configured to control the blower,
The control unit includes:
When the fuel cell system is started, it is determined whether the start is a hot restart,
When the activation is determined to be the hot restart, the blower is activated to supply gas to the high-temperature chamber while the valve is closed and the supply of fluid to the low-temperature chamber is stopped. And
A fuel cell system for estimating an estimated temperature of the low-temperature chamber according to a temperature of a gas flowing through the high-temperature chamber.