JP2010055910A - Solid oxide fuel cell system and method for operating it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control device and an operation method for reducing deterioration and breakage of a cell and damage of a module structure by a simple and assured configuration, in a solid oxide fuel cell system. <P>SOLUTION: The fuel cell system includes a solid oxide fuel cell, a fuel supply means for supplying fuel to an anode of the fuel cell, and an oxidizer supply means for supplying an oxidizer to a cathode of the fuel cell. The fuel cell system further includes a residual fuel estimating means for estimating a flow rate of the residual fuel in generating electricity in the fuel cell. This invention further includes: a system control device which, when the fuel cell system stops, supplies the fuel of the flow rate not exceeding the flow rate of the residual fuel estimated by the residual fuel estimating means to the fuel cell by the fuel supply means for system stop; and the operation method. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention appropriately controls the fuel supply flow rate and the oxidant supply flow rate when the solid oxide fuel cell system is stopped, and reduces fuel cell deterioration, cell breakage and module structure damage due to excessive temperature rise. The present invention relates to a battery system and a control method thereof.

  The fuel cell has an anode and a cathode on both sides of the electrolyte, and supplies fuel (anode gas) such as city gas and LNG and LPG to the anode side, and supplies an oxidant (cathode gas) such as air to the cathode side. And a power generation system that generates electricity by electrochemically reacting a fuel and an oxidant via an electrolyte. Solid oxide fuel cells, which are one field of fuel cells, have a high operating temperature of about 700 to 1000 ° C., high power generation efficiency, and easy use of exhaust heat, and are eagerly studied worldwide. ing.

Usually, a solid oxide fuel cell constitutes an assembly (module) in which several tens to several hundreds of fuel cells are integrated in order to obtain a desired electric output. Further, of the fuel supplied to the module, the remaining residual fuel used in the cell electrochemical reaction is burned on the cell outlet side. The reason for burning the remaining fuel is as follows.
(1) Remove excess fuel to prevent local shortage of fuel supply.
(2) Uniform temperature distribution near the cell outlet to prevent cell breakage and improve cell performance.
(3) The heat generated by the combustion of the remaining fuel is used for preheating the supplied gas.

  In an actual fuel cell system, assuming that the flow rate of supplied fuel at rated power generation is 100%, the proportion of fuel used for power generation by electrochemical reaction is about 70-80%, and the remaining 20-30% is the remaining It becomes fuel. Here, in the case of a shutdown or the like in which the fuel cell system stops power generation due to an emergency stop or the like, the surplus fuel combustion process becomes a problem.

That is, from the state where the fuel cell system is thermally balanced at the time of rated power generation, the electrochemical reaction stops, the current becomes zero, and the fuel consumption rate becomes 0%. Therefore, it excludes the unreacted fuel staying in injected in the module inert purge gas from the anode side, such as N _2. At this time, if the flow rate of the purge gas is made the same as the fuel flow rate at the rated power generation, the fuel consumption is 0, and the remaining fuel ratio which has been 20-30% so far on the cell outlet side increases rapidly to 100%. For this reason, the amount of fuel combustion at the cell outlet increases and the temperature rises excessively, which may lead to cell deterioration, cell breakage, and module structure damage.

  In order to reduce such thermal damage, there is an example in which cooling is performed by providing a cooling line for adding a cooling gas to the combustion chamber at the cell outlet as disclosed in Patent Document 1. In the above-mentioned known example, it is necessary to newly provide a cooling line, and a large amount of cooling gas is required, so that the point that the fuel cell system becomes complicated has not been solved.

JP 2006-261005 A

  The problem to be solved by the present invention is to properly control the fuel supply flow rate and the oxidant supply flow rate at the time of shutdown of the solid oxide fuel cell power generation system, etc. The object damage is to be reduced with a simple configuration and surely.

  The present invention relates to a fuel cell system having a fuel cell having an anode, a cathode and an electrolyte, a fuel supply means for supplying fuel to the anode of the fuel cell, and an oxidant supply means for supplying an oxidant to the cathode of the fuel cell. The fuel cell is provided with a residual fuel estimation means for estimating the residual fuel flow rate during power generation. When the fuel cell system is stopped, the fuel flow rate that does not exceed the residual fuel flow rate estimated by the residual fuel estimation means is supplied to the fuel cell by the fuel supply means. The main feature is the provision of a system controller that supplies and stops.

  The present invention also relates to a fuel cell system comprising a fuel cell, a fuel supply means for supplying fuel to the anode of the fuel cell, and an oxidant supply means for supplying an oxidant to the cathode of the fuel cell. A differential pressure measuring means for measuring the differential pressure of the fuel cell, a residual fuel estimating means for estimating the residual fuel flow rate during power generation of the fuel cell, and a residual fuel flow rate estimated by the residual fuel estimating means when the fuel cell system is stopped. A fuel flow rate is supplied to the fuel cell by the fuel supply means, and the oxidant supply flow rate on the cathode side is also reduced when the differential pressure becomes a threshold value or less by a signal from the differential pressure measurement means.

  Furthermore, the present invention relates to a fuel cell system comprising a fuel cell, a fuel supply means for supplying fuel to the anode of the fuel cell, and an oxidant supply means for supplying an oxidant to the cathode of the fuel cell. A residual fuel estimation means for estimating the residual fuel flow rate of the fuel cell system, and a residual oxidant supply flow rate is estimated by the residual fuel estimation means to estimate a ratio between the residual fuel flow rate and the residual oxidant flow rate during power generation of the fuel cell system. The fuel supply flow rate and the oxidant supply flow rate are controlled so that the ratio of the residual fuel flow rate and the residual oxidant flow rate estimated by the residual fuel estimation means is not larger than that during fuel cell system power generation when the fuel cell system is stopped. And

  According to the present invention, at the time of shutdown of the solid oxide fuel cell power generation system, the fuel supply flow rate and the oxidant supply flow rate are appropriately controlled, and cell deterioration, cell breakage and module structure damage due to excessive temperature can be easily and easily performed. It has the effect that it can reduce reliably.

  According to the most preferred embodiment of the present invention, there is provided residual fuel estimation means for estimating a residual fuel flow rate that is not used for power generation during power generation of the fuel cell, and the residual fuel estimated by the residual fuel estimation means when the fuel cell system is stopped. The fuel flow rate suppressed to an amount not exceeding the flow rate is supplied to the fuel cell by the fuel supply means and stopped. Thereby, it is possible to prevent the combustion temperature at the cell outlet from excessively rising even at the time of shutdown or the like, to reduce cell damage and to stop the fuel cell system safely.

  The present invention also provides a differential pressure measuring means for measuring the gas pressure differential pressure between the anode and the cathode of the fuel cell, and supplies the fuel cell with fuel that does not exceed the residual fuel flow rate when the fuel cell system is stopped. When the differential pressure becomes equal to or lower than the threshold value due to the signal from the means, the supply flow rate of the oxidant on the cathode side is also decreased. Thereby, even when the fuel supply flow rate at the time of shutdown or the like is changed, cell damage can be reduced while effectively preventing the backflow of the oxidant from the cathode side.

  The present invention also provides a residual fuel estimation means for estimating a ratio between a residual fuel flow rate and a residual oxidant flow rate during power generation in the fuel cell system, and the residual fuel flow rate and residual oxidation estimated by the residual fuel estimation means when the fuel cell system is stopped. The fuel supply flow rate and the oxidant supply flow rate are controlled so that the ratio of the agent flow rate does not become larger than that during power generation of the fuel cell system. As a result, the operating range of the fuel cell system can be expanded and the cell damage can be reduced while reducing the wasteful purge gas flow rate. Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

[First Embodiment]
1, 2, 3 and 4 show a solid oxide fuel cell system according to a first embodiment of the present invention. FIG. 2 shows a schematic diagram of the solid oxide fuel cell system of the first embodiment. Reference numeral 1 denotes a module container that accommodates the fuel cell module 30 and is formed of a metallic container including a heat insulating material. An oxidant composed of air or the like is supplied as the cathode gas 90 to the cathode side of the fuel cell 80. The cathode gas 90 is supplied to the fuel cell 80 through the cathode gas flow rate adjusting valve 90V, through the cathode gas header 91 and the cathode gas introduction pipe 92 for evenly distributing the gas to each cell.

  302S is a control signal for the cathode gas flow rate adjusting valve 90V output from the system control device 300. Usually, the module 30 which is an assembly of the fuel cells 80 is heated by a heating means H such as a burner or a heater, and when reaching a temperature capable of generating power, a predetermined amount of anode gas 100 and cathode gas 90 are converted into solid oxide fuel. The battery cell 80 is supplied to generate power. The anode gas 100 as a fuel is obtained by reforming at least a part of the gas, which is a mixture of city gas, hydrocarbon fuel such as LNG, LPG, and water vapor with the reformer 110 and then from below the module container 1. Supply to module 30. 100V is an anode gas flow rate adjusting valve, and 101a is a purge gas.

  Reference numeral 50 denotes a partition plate provided at the cell outlet in order to prevent mixing of the anode gas and the cathode gas. The partition plate 50 is made of a ceramic fiber having a flexible structure and air permeability in order to hold the fragile ceramic fuel cell 80. Reference numeral 51 denotes a dispersion plate for uniformly dispersing the anode gas 100 in the fuel chamber F. G is a power generation chamber that causes the module 30 to generate power by an electrochemical reaction. B is a combustion chamber provided in the upper part of the module container 1. Reference numeral 101 denotes a high-temperature exhaust gas after combustion in which fuel and an oxidant are mixed at the outlet of the module container 1.

  The system control device 300 activates the load control device 400 by the control signal 303S, starts the power generation by extracting the generated current I measured by the ammeter 401 from the module 30 by the control signal 304S. During power generation, the fuel cell 80 and the module 30 generate heat, so no heating means are required, and the fuel cell system is operated thermally independently at about 700 to 1000 ° C. 2A is a module temperature sensor, and 2AS is a module temperature detection signal. 3A is a combustion chamber temperature sensor, and 3AS is a combustion chamber temperature detection signal.

  FIG. 3 is a cross-sectional view taken along the line AA in FIG. FIG. 3 shows 36 solid oxide fuel cells 80 for convenience, but power generation is usually performed by integrating them in series or in parallel in the order of several tens to several hundreds. As shown in FIG. 4 as an enlarged vertical sectional view, the fuel cell 80 includes a cylindrical outer anode 80a, an inner cathode 80c, and a solid oxide electrolyte made of yttria-stabilized zirconia or the like sandwiched between them. 80e. 90co is the cathode gas after reaction, and 100ao is the anode gas after reaction.

Next, the operation of the first embodiment will be described below with reference to the flowchart of FIG. 1 and FIG.
(1) Step 801: Detection of the fuel supply flow rate Qin and the generated current I The fuel supply flow rate Qin is detected by the flow rate output signal 301So of the anode gas flow rate adjustment valve 100V. Further, the generated current I is detected by the output signal 401So of the ammeter 401.
(2) Step 802: the relationship between the fuel flow rate Qr that is consumed by the estimation generator current I and the electrochemical reaction of residual fuel flow Qout, for example when fuel is H ₂ represented by the following formula.

I (A) = Qr (mol / s) × F (C / mol) (1)
F (Faraday constant) = 96485 (C / mol)
Therefore, 301So and 401So are residual fuel flow estimation devices 310 that are residual fuel estimation means.
The remaining fuel flow rate Qout during rated operation is estimated by the following equation by calculating the signal 310
S is sent to the system controller 300 as S.

Qout = Qin−Qr (2)
(3) Step 803: Generation of Stop Signal of Fuel Cell Power Generation System As an example, the system stop signal 2AS generated by the temperature rise from the module temperature sensor 2A is input to the system controller 300.
(4) Step 804: Control the generated current to 0 The system control device 300 stops the load device 400 by the control signal 303S and sets the generated current to 0 by the system stop signal.
(5) Step 805: Control the purge gas flow rate The signal 301S is supplied to the anode gas flow rate adjustment valve 100V so that the fuel supply flow rate Qin, that is, the purge gas flow rate Qsdin, becomes an amount that the residual fuel flow rate estimated in Step 802 does not exceed Qout. Input and control (Qsdin ≦ Qout). Note that the purge gas 101a supplied when the system is stopped is preferably a gas capable of maintaining a reducing atmosphere (such as nitrogen gas containing 3% hydrogen).

  FIG. 5 is a time chart schematically showing the temperature, gas flow rate, and generated current at the time of shutdown. Case (a) As indicated by the two-dot chain line in the comparative example, if the purge gas flow rate Qsdin is larger than the estimated residual fuel Qout, the surplus fuel flow rate pushed into the combustion chamber B is large, and the combustion chamber heat generation immediately after shutdown is abrupt. Increase the thermal damage to the fuel cell system. On the other hand, as shown in case (b), when Qsdin is suppressed and Qsdin ≦ Qout, the exothermic peak is suppressed to a safe level.

  According to the present embodiment, by controlling the purge gas flow rate so as not to exceed the remaining fuel flow rate at the time of shutdown, the fuel flow rate at the cell outlet can be made substantially equal to or less than that during rated power generation. Therefore, since the fuel cell system can be stopped without increasing the combustion temperature at the cell outlet side, cell deterioration, cell breakage, and module structure damage can be reduced. Therefore, this fuel cell system does not require an additional cooling line and can be controlled in a simple manner.

  Further, during power generation, load response control corresponding to the load on the user side may be required on the fuel cell system side, and in that case, the fuel supply flow rate and the generated current change from moment to moment. Even in this case, when the stop signal is input to the fuel cell system, the remaining fuel flow rate is always estimated, so that the optimum purge gas flow rate can be controlled, so that the fuel cell system can be reliably stopped without overheating. In the present embodiment, the shutdown due to the excessive increase in the module temperature 2A is taken as an example. However, the stop factor of the power generation fuel cell system is not limited to this example.

  In order to grasp the residual fuel flow rate more directly, a data table in which the relationship between the measurement temperature of the combustion chamber temperature sensor 3A and the residual fuel flow rate is measured in advance is used as the residual fuel estimation means. The residual fuel flow rate can also be used for control.

[Second Embodiment]
FIG. 6 shows a second embodiment of the present invention. As described above, the gist of the present invention is to suppress the flow rate when surplus fuel that causes overheating at the time of shutdown is discharged to the fuel cell outlet. Therefore, once the surplus fuel is discharged, there is no problem even if the purge gas flow rate is increased in order to completely stop the fuel cell system.

  Based on this idea, in this embodiment, there is provided a control device that controls a necessary and sufficient supply time to flow while suppressing the purge gas flow rate Qsdin at the time of shutdown so as not to exceed Qout. This time may be determined in consideration of the volume of the module 30 or the reformer 110 and the flow rate of Qsdin. For example, in FIG. 6, the flow rate of Qsdin is once reduced and then returned to the flow rate during rated operation. By performing such system control, it is possible to separate overheating control immediately after shutdown and system stop control for completely purging the fuel from the module container 1, and to perform optimal control continuously for each.

[Third Embodiment]
It is also effective to control the purge gas flow rate by directly monitoring the combustion chamber temperature. As in the third embodiment shown in FIG. 7, after setting a threshold value for the combustion chamber temperature 3AS detected by the combustion chamber temperature sensor 3A and setting the purge gas flow rate to Qsdin ≦ Qout after the shutdown, the purge gas is reduced if the temperature falls below the threshold value. If the flow rate Qsdin is also controlled to return during rated operation, cell damage can be reduced more directly and reliably.

[Fourth Embodiment]
FIG. 8 is a schematic view showing a fourth embodiment of the present invention. A time chart at the time of shutdown in this embodiment is shown in FIG.

  In 4th Embodiment, the differential pressure measuring device 600 which measures the differential pressure before and behind the partition plate 50 of a cell exit is provided. The partition plate 50 is gas-permeable, and when the differential pressure is lost, the cathode gas flows back into the power generation chamber G, causing oxidative deterioration of the anode of the fuel cell. In order to prevent backflow (leakage) from the cathode to the anode when reducing the purge gas flow rate so that the remaining fuel supply flow rate does not exceed the remaining fuel supply flow rate during shutdown, differential pressure measurement provided in this embodiment By measuring the differential pressure at the anode outlet with the vessel 600 and reducing the cathode gas flow rate Qca at the same time when this differential pressure ΔP falls below a certain threshold value, leakage can be reduced and more reliable system shutdown can be achieved.

[Fifth Embodiment]
FIG. 10 shows a fifth embodiment. In the present embodiment, the ratio Qin / Qca between the remaining fuel flow rate Qin and the cathode gas flow rate Qca is focused on, and the ratio is controlled so as not to increase after shutdown. The combustion temperature at the cell outlet depends on Qin / Qca. In the embodiments so far, the combustion temperature is not raised by controlling only the purge gas flow rate Qsdin so as not to exceed Qin without changing Qca at the time of shutdown.

  In the present embodiment, focusing on the fact that the combustion temperature does not substantially increase if Qin / Qca is not increased, the purge flow rate of the anode gas is reduced and the cathode gas flow rate is also reduced. By performing such control, it is possible to provide a fuel cell system that can be stopped without consuming system energy when the system is stopped.

  In the above embodiments, the cylindrical fuel cell has been described. However, the present invention can be applied to a flat solid oxide fuel cell other than the cylindrical shape.

  According to the above-described embodiment of the present invention, a solid oxide fuel cell system capable of reducing cell deterioration, cell breakage, and module structure damage can be provided. Therefore, it can be used as a distributed power supply system that is friendly to the global environment.

It is a flowchart which shows the control of the 1st Embodiment of this invention. It is the schematic of the fuel cell system structure of the 1st Embodiment of this invention. FIG. 3 is a cross-sectional view of the module along the line AA in FIG. 2. It is an expansion longitudinal cross-sectional view of the single cell in the 1st Embodiment of this invention. It is a time chart of the fuel cell system of the 1st Embodiment of this invention. It is a time chart of the fuel cell system of the 2nd Embodiment of this invention. It is a time chart of the fuel cell system of the 3rd Embodiment of this invention. It is the schematic of the fuel cell system structure of the 4th Embodiment of this invention. It is a time chart of the fuel cell system of the 4th Embodiment of this invention. It is a time chart of the fuel cell system of the 5th Embodiment of this invention.

Explanation of symbols

  2A ... Module temperature sensor, 2AS ... Module temperature detection signal, 3A ... Combustion chamber temperature sensor, 3AS ... Combustion chamber temperature detection signal, 30 ... Module, 50 ... Partition plate, 80 ... Solid oxide fuel cell, 80a ... Anode 80c ... cathode, 80e ... solid electrolyte, 90 ... cathode gas, 90V ... cathode gas flow rate adjustment valve, 91 ... air header, 92 ... air introduction pipe, 100 ... anode gas, 100V ... anode gas flow rate adjustment valve, 101a ... purge gas , 101 ... exhaust gas, 110 ... reformer, 300 ... system controller, 301S ... control signal to fuel supply flow rate adjustment valve, 301So ... output signal from fuel supply flow rate adjustment valve, 302S ... to oxidant supply flow rate adjustment valve Control signal, 303S... Control signal to load control device, 304S... Control signal of module generated current, 31 ... residual fuel flow rate estimation device, 310S ... signal from residual fuel flow rate estimation device, 400 ... load control device, 401 ... ammeter, 401So ... detection signal of generated current, 600 ... differential pressure measuring instrument, 600S ... differential pressure measurement Output signal from the instrument.

Claims (16)

In a solid oxide fuel cell system having a fuel cell, a fuel supply means for supplying fuel to the anode of the fuel cell, and an oxidant supply means for supplying an oxidant to the cathode of the fuel cell,
The fuel cell has a residual fuel estimation means for estimating a residual fuel flow rate during power generation of the fuel cell, and when the fuel cell system is stopped, a fuel flow rate that does not exceed the residual fuel flow rate estimated by the residual fuel estimation means is A solid oxide fuel cell system comprising a control device for supplying a battery.   2. The solid oxide fuel cell system according to claim 1, wherein the residual fuel estimation unit includes a current detection unit that detects a power generation current and a fuel supply unit that detects a fuel supply flow rate. A solid oxide fuel cell system comprising a control device including residual fuel estimation means for estimating a residual fuel flow rate from a current and a fuel supply flow rate.   2. The solid oxide fuel cell system according to claim 1, wherein the residual fuel estimation means includes a temperature sensor provided on the fuel cell outlet side, and estimates the residual fuel flow rate from the fuel cell outlet side temperature. A solid oxide fuel cell system comprising a control device including an estimation means.   The solid oxide fuel cell system according to any one of claims 1 to 3, further comprising a control device that controls a supply time of a fuel flow rate that does not exceed a residual fuel flow rate when the system is stopped. Oxide fuel cell power generation system.   5. The solid oxide fuel cell system according to claim 4, wherein a control device for setting a supply time of the fuel flow rate not exceeding the residual fuel flow rate at the time of system stop from the fuel volume in the system or the temperature on the fuel cell outlet side. A solid oxide fuel cell power generation system comprising:   The solid oxide fuel cell system according to claim 1, further comprising a temperature sensor that monitors a fuel cell outlet side temperature when a system stop signal is input, and the fuel cell outlet side temperature falls to a predetermined threshold value. A solid oxide fuel cell power generation system comprising a control device for canceling a fuel flow rate value not exceeding a residual fuel flow rate supplied when the system is stopped.   2. The solid oxide fuel cell system according to claim 1, wherein the differential pressure measuring means for measuring the differential pressure between the anode and the cathode of the fuel cell, and the differential pressure measuring means for detecting that the differential pressure is below a threshold value. A solid oxide fuel cell power generation system comprising a control device for reducing the supply flow rate of the cathode side oxidant in accordance with a signal from.   The solid oxide fuel cell system according to claim 1, further comprising a residual fuel estimation means for estimating a residual oxidant supply flow rate, and estimating a ratio between the residual fuel flow rate and the residual oxidant flow rate during system power generation, A solid oxide comprising a control device for controlling the fuel supply flow rate and the oxidant supply flow rate so that the ratio of the residual fuel flow rate and the residual oxidant flow rate does not become larger than that during system power generation when the fuel cell system is stopped. Fuel cell power generation system. In a control method of a solid oxide fuel cell system, comprising: a fuel cell; a fuel supply means for supplying fuel to the anode of the fuel cell; and an oxidant supply means for supplying an oxidant to the cathode of the fuel cell.
A solid oxide fuel cell system characterized by estimating a residual fuel flow rate during power generation of the fuel cell and supplying the fuel cell with a fuel flow rate not exceeding the estimated residual fuel flow rate when the fuel cell system is stopped. Driving method.   10. The method for operating a solid oxide fuel cell system according to claim 9, wherein the residual fuel flow rate is estimated from the generated current and the fuel supply flow rate.   10. The method for operating a solid oxide fuel cell system according to claim 9, wherein the residual fuel flow rate is estimated from the fuel cell outlet side temperature.   The solid oxide fuel cell system control method according to any one of claims 9 to 11, wherein a time for supplying a fuel flow rate that does not exceed a residual fuel flow rate when the system is stopped is controlled. Operation method of oxide fuel cell power generation system.   13. The control method for a solid oxide fuel cell system according to claim 12, wherein the time for which the fuel supply flow rate when the system is stopped does not exceed the residual fuel flow rate is defined as the fuel volume in the system or the temperature on the fuel cell outlet side. A method for operating a solid oxide fuel cell power generation system, characterized in that the setting is made based on the above.   10. The control method for a solid oxide fuel cell system according to claim 9, wherein the temperature on the fuel cell outlet side is monitored by a temperature sensor when a system stop signal is input, and the residual when the temperature on the fuel cell outlet side falls to a predetermined threshold value. A method for operating a solid oxide fuel cell power generation system, wherein the flow restriction of the purge gas flow rate not exceeding the fuel flow rate is released.   10. The control method for a solid oxide fuel cell system according to claim 9, wherein a differential pressure between the anode and the cathode of the fuel cell is measured, and a fuel flow rate that does not exceed the estimated remaining fuel flow rate when the fuel cell system is stopped is defined as fuel supply means. The solid oxide fuel cell power generation system is characterized in that when the differential pressure becomes less than or equal to a threshold value by a signal from the differential pressure measuring means, the oxidant supply flow rate on the cathode side is also reduced. Method.   10. The control method for a solid oxide fuel cell system according to claim 9, wherein a residual fuel flow rate during power generation of the fuel cell is estimated, a residual oxidant supply flow rate is estimated, and a residual fuel flow rate and residual oxidation during system power generation are estimated. Calculate the ratio of oxidant flow rate, and control the fuel supply flow rate and oxidant supply flow rate so that the ratio of the estimated residual fuel flow rate and residual oxidant flow rate does not become larger than that during fuel cell system power generation when the fuel cell system is stopped A method for operating a solid oxide fuel cell power generation system.

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