CN1783562A - Fuel cell system and method of operation thereof - Google Patents

Abstract

A fuel cell system includes a fuel cell stack, piping and a circulation pump necessary for cooling water discharged from the fuel cell stack, feeding the cooling water to the fuel cell stack, and circulating the cooling water, a fuel humidifier humidifying fuel by heat exchange with the cooling water, an air humidifier humidifying air by heat exchange with the cooling water, and a control unit continuing circulation of the cooling water until a predetermined cooling stop condition is satisfied when the system is stopped. The fuel cell stack includes a stack of a membrane electrode assembly in which an anode is joined to one surface of an electrolyte membrane and a cathode is joined to the other surface of the electrolyte membrane, a fuel flow path plate provided with a fuel flow path for supplying fuel to the anode, an oxidant flow path plate provided with an oxidant flow path for supplying an oxidant to the cathode, and a cooling water flow path plate provided with a cooling water flow path through which cooling water flows.

Description

Fuel cell system and method of operation thereof

technical field

The present invention relates to a fuel cell system and an operating method thereof, and more particularly, to a fuel cell system and an operating method thereof for preventing deterioration of a fuel cell caused by a cycle of starting and stopping.

Background technique

Although we have entered the era when new technologies such as IT and biology are deployed on a global scale, the energy industry remains the largest backbone industry even in this situation. Recently, expectations for so-called new energy sources have gradually increased along with the infiltration of environmental awareness including the prevention of global warming. In addition to being environmentally friendly, renewable energy can also be produced in a decentralized manner close to power demanders, so it has advantages in terms of power transmission loss and safety of power supply. In addition, the development of new energy can also be expected to create a subsidiary effect of new peripheral industries. Enthusiasm for new energy was formalized by the oil crisis about 30 years ago. Now, new energy such as renewable energy such as solar power generation, recycling energy such as waste-to-energy, high-efficiency energy such as fuel cells, and net energy are emerging. Energy sources such as field energy are in the stage of being developed for practical use.

Among them, fuel cells are one of the most concerned energy sources in the industry. A fuel cell is a device that chemically reacts hydrogen produced by natural gas or methanol, etc., with water vapor and oxygen in the atmosphere to generate electricity and heat at the same time. The only by-product of power generation is water, even in low output areas. High efficiency, and power generation is not affected by the climate, very stable. In particular, solid polymer fuel cells are regarded as a next-generation standard power source for stationary, vehicle-mounted, and portable applications including residential use.

(1st subject)

In terms of putting fuel cells to practical use, improvement in durability during repeated start-stop operation has been a research topic, and stop methods for preventing deterioration of fuel cells have been proposed.

[Patent Document 1] JP-A-2002-093448

[Patent Document 2] JP-A-2005-071778

In a shutdown method similar to that in Patent Document 1, when the fuel cell system is stopped, the unit cells are made to generate electricity while the supply of oxygen-containing gas is stopped, and an oxygen consumption process that consumes oxygen on the cathode side is performed to realize the fuel cell system. Increased durability. However, in this method, while the fuel cell is out of storage, hydrogen diffuses from the anode through the electrolyte layer, or protons diffused through the electrolyte layer are reduced by a current (leakage current) flowing through a short-circuit through cooling water or the like, Hydrogen is generated in the cathode, and thus the generated hydrogen reacts with the remaining oxygen, thereby making it possible to generate hydrogen peroxide as shown in formula (1), or to cause a combustion reaction as shown in formula (2). Hydrogen peroxide has the effect of decomposing the electrolyte, and the combustion reaction will degrade the catalyst and electrolyte, causing deterioration of the fuel cell.

[chemical 1]

...(1)

[Chem 2]

...(2)

In addition, in the shutdown storage methods like those in Patent Documents 1 and 2, since the inert gas is injected into the cathode side during the shutdown of the fuel system, a mechanism for supplying the inert gas to the fuel cell is required, resulting in an increase in the size of the system. The problem.

(Session 2)

Stability at startup is also an important issue in a fuel cell that generates electricity by supplying a humidified reaction gas, such as a solid polymer fuel cell.

A solid polymer fuel cell unit cell (membrane electrode assembly) is integrally formed by bonding an anode (fuel electrode) to one surface of a solid polymer electrolyte membrane and a cathode (air electrode) to the other surface. A plurality of unit cells are sandwiched between a flat plate with grooved fuel flow paths on the surface facing the anode and a flat plate with grooved oxidant flow paths on the surface facing the cathode. , add end plates at both ends, and fasten with through bolts to form a fuel cell stack. In addition, the fuel (hydrogen or hydrogen-based reformed gas) is circulated in the fuel flow path, and the oxidant (usually air) is circulated in the oxidant flow path, and an electrochemical reaction is generated by sandwiching a solid polymer electrolyte membrane. DC power.

In such a solid polymer fuel cell, since the solid polymer electrolyte membrane functions properly in a saturated and wet state, the reactant gas (fuel and/or oxidant) is humidified with a humidifier or the like and then flowed through the plate. The flow path will keep the solid polymer electrolyte membrane in a saturated and wet state. In addition, although the operating temperature of the solid polymer fuel cell is about 80° C., the temperature rises during power generation because the electrochemical reaction is an exothermic reaction. In order to prevent this, generally, a cooling plate is installed in the fuel cell stack, and cooling water flows through the passage to keep the fuel cell stack at an operating temperature.

In a conventional fuel cell system that operates a solid polymer fuel cell, the flow of cooling water is stopped when the system is stopped (see Patent Document 3).

[Patent Document 3] JP-A-2004-296340

When the flow of cooling water is stopped when the system is stopped and the fuel cell stack is naturally cooled, the fuel cell stack is cooled sequentially from the outside, resulting in a temperature difference within the fuel cell stack. Since the water vapor in the fuel cell stack condenses first from places with low temperatures, the distribution of water in each unit cell changes during natural cooling. In this way, the distribution of the reactant gas to each unit cell becomes uneven at the next startup, the voltage of each unit cell becomes unstable during power generation, and some unit cells are degraded due to insufficient reactant gas. Or, it may not be able to start normally, and the protective function may be activated and then stopped. In addition, if the temperature (water temperature) of the fuel humidifier or air humidifier connected by piping is higher than the battery temperature, even if the supply of the reaction gas is stopped, the vapor will diffuse from the fuel humidifier or air humidifier to the battery, and the Condensation in the battery also changes the water distribution in the battery. Similarly, at the time of the next startup, the distribution of the reactant gas to each unit cell becomes uneven, which may cause deterioration of the unit cells or stop the system.

Contents of the invention

Embodiment 1 is made in view of the above-mentioned first problem, and its purpose is to prevent deterioration of the fuel cell due to the cycle of starting and stopping by improving the operation method of the fuel cell system without adding a new mechanism (device).

Embodiment 2 was completed in view of the second problem, and an object thereof is to provide a technique for stabilizing the output when starting the fuel cell system.

(Embodiment 1)

In order to achieve the above-mentioned first problem, one aspect of Embodiment 1 is to operate a fuel cell system including a reformer that reforms raw fuel into fuel containing hydrogen, and a fuel cell that generates electricity using the fuel. The method is characterized by comprising, when starting the fuel cell system, a carbon monoxide supply step of supplying the fuel cell with the fuel containing more carbon monoxide than during normal operation. Here, the raw fuel refers to hydrocarbon fuels containing hydrogen atoms, and specifically, LPG installed in general households, city gas, or alcohols such as methanol can be mentioned.

According to the above method, since fuel having a high concentration of carbon monoxide is supplied to the anode of the fuel cell, carbon monoxide is adsorbed on the catalyst (particularly, platinum) of the anode, thereby inhibiting the production of protons from the anode. Therefore, it is possible to suppress the generation of hydrogen on the cathode due to the leakage current and the direct reaction of hydrogen and oxygen or the generation of hydrogen peroxide when supplying the oxidizing agent to the cathode. In this way, deterioration of the fuel cell can be prevented.

The above aspect is characterized by including a step of starting power generation of the fuel cell at a temperature lower than a normal power generation temperature of the fuel cell. The usual power generation temperature of the fuel cell means, for example, if the fuel cell is a solid polymer fuel cell, it is 70 to 80°C, and the temperature lower than the usual power generation temperature is at least 10°C lower than 60°C, preferably Below 45°C.

According to the present embodiment, since the temperature of the fuel cell is low, the catalyst coverage of carbon monoxide during fuel supply increases and the catalyst activity decreases, thereby suppressing hydrogen generation on the cathode due to leakage current. In addition, since the diffusion rate of hydrogen and oxygen in the electrolyte is low when the temperature of the fuel cell is low, crossover is suppressed. In addition, since the temperature of the fuel cell is low, the reaction rate of hydrogen peroxide generation or fuel reaction also becomes low. In this way, the effect of the method can be further improved.

Another form of Embodiment 1 is a fuel cell system operating method, characterized in that, when stopping the fuel cell system, cooling the fuel cell to a temperature lower than the normal power generation temperature of the fuel cell is included. The fuel cell cooling step of setting the temperature, and the power generation stop step of stopping the power generation of the fuel cell, which are set in the latter stage of the fuel cell cooling step. Here, the normal power generation temperature in the case of solid polymer fuel cells means 70 to 80°C, and the temperature lower than the normal power generation temperature means at least 10°C lower, that is, 60°C or lower, preferably 45°C or lower.

According to the above aspect, when the fuel cell system is stopped, power generation of the fuel cell is stopped after the fuel cell is cooled, so that hydrogen and oxygen can be suppressed from diffusing and permeating in the electrolyte after the power generation is stopped. In this way, deterioration of the fuel cell can be prevented.

In the aspect described above, a method for operating a fuel cell system including a reformer for reforming raw fuel into fuel containing hydrogen and a fuel cell that generates electricity using the fuel is provided, and when the fuel cell system is stopped, the may include a carbon monoxide supply step of supplying the fuel containing more carbon monoxide to the fuel cell than in normal operation, and a battery cooling step of cooling the fuel cell to a temperature lower than a normal power generation temperature of the fuel cell step, a power generation stopping step of stopping power generation of the fuel cell, which is set in a subsequent stage of the battery cooling step.

According to this aspect, when the fuel cell system is stopped, since fuel with a high concentration of carbon monoxide is supplied to the anode of the fuel cell, carbon monoxide is adsorbed on the catalyst of the anode, and even if oxygen flows into the anode while the fuel cell system is stopped, the oxygen is It will be consumed in the process of oxidizing the carbon monoxide adsorbed on the catalyst. Therefore, an increase in the potential of the anode is suppressed, and deterioration of the catalyst, in particular, oxidation of ruthenium can be prevented. In addition, carbon monoxide is adsorbed on the anode catalyst, especially on platinum, which hinders the generation of protons from the anode, so that the generation of hydrogen on the cathode caused by leakage current and the direct reaction or overshoot of hydrogen and oxygen when oxygen flows into the cathode can be suppressed. Hydrogen oxide generation reaction. In this way, deterioration of the fuel cell can be prevented.

Another mode of the first embodiment is a fuel cell system operating method, characterized in that, when the fuel cell system is stopped, a power generation stop step of stopping power generation of the fuel cell is included, which is set in the A battery cooling step of cooling the fuel cell to a temperature lower than a normal power generation temperature of the fuel cell in the subsequent stage of the power generation stopping step. Here, in the case of solid polymer fuel cells, the normal power generation temperature refers to 70 to 80°C, and the temperature lower than the usual power generation temperature refers to a temperature lower by at least 10°C, that is, 60°C or less, preferably 45°C the following.

According to this aspect, when the fuel cell system is stopped, since the fuel cell is not naturally cooled after the power generation is stopped, but is forcibly cooled, it is possible to suppress the diffusion and permeation of hydrogen and oxygen in the electrolyte after the power generation is stopped. Case. In this way, deterioration of the fuel cell can be prevented.

In the above-mentioned form, it is a method of operating a fuel cell system including a reformer for reforming raw fuel into fuel containing hydrogen, and a fuel cell that generates electricity using the fuel. When the fuel cell system is stopped, the may include: a carbon monoxide supply step of supplying the fuel containing more carbon monoxide to the fuel cell than in normal operation; a power generation stop step of stopping power generation of the fuel cell; A subsequent cell cooling step of cooling the fuel cell to a temperature lower than the normal power generation temperature of the fuel cell.

According to this aspect, when the fuel cell system is stopped, since fuel with a high carbon monoxide concentration is supplied to the anode of the fuel cell, carbon monoxide is adsorbed on the catalyst of the anode, and even if oxygen flows into the anode while the fuel cell system is stopped, oxygen Consumed in the process of oxidizing carbon monoxide adsorbed on the catalyst. Therefore, an increase in the potential of the anode is suppressed, and deterioration of the catalyst, in particular, oxidation of ruthenium can be prevented. In addition, carbon monoxide is adsorbed on the anode catalyst, especially on platinum, which hinders the generation of protons from the anode, so that the generation of hydrogen on the cathode due to leakage current and the direct reaction of hydrogen and oxygen when oxygen flows into the cathode can be suppressed or hydrogen peroxide Generate a reaction. In this way, deterioration of the fuel cell can be prevented.

(Embodiment 2)

In order to achieve the object of the second problem, a mode of Embodiment 2 includes a fuel cell stack, a mechanism for circulating a heat medium, a fuel humidification mechanism, an oxidant humidification mechanism, and a control mechanism; wherein the fuel cell stack includes a stacked The laminated body is formed by combining the following components, that is, a membrane electrode assembly in which an anode is joined to one side of the electrolyte membrane and a cathode is joined to the other side of the electrolyte membrane, and a fuel flow for supplying fuel to the anode is provided. The fuel flow path plate of the channel, the oxidant flow path plate of the oxidant flow path for supplying the oxidant to the cathode, the heat medium flow path plate of the heat medium flow path through which the heat medium flows; the mechanism for circulating the heat medium , is a mechanism that cools the heat medium discharged from the fuel cell stack and puts it into the fuel cell stack to circulate the heat medium; the fuel humidification mechanism uses the heat exchange with the heat medium to humidify the fuel; The heat exchange of the medium humidifies the oxidant; the control mechanism, when the system stops, continues the circulation of the heat medium after the power generation of the fuel cell is stopped until the given cooling stop condition is established.

Furthermore, the fuel flow path plate, the oxidant flow path plate, and the heat medium flow path plate are not limited to being different members. For example, the following configurations are also included in the present invention, that is, by providing a fuel flow path on one side of the plate, The heat medium flow path is provided on the other surface, and the fuel flow path plate and the heat medium flow path plate are realized with one member.

According to the above configuration, by allowing the heat medium to flow through the fuel cell stack even after the power generation of the fuel cells is stopped, variations in the temperature distribution of the unit cells can be suppressed, thereby suppressing variations in the water distribution of the unit cells. As a result, the power generation amount of each unit cell at the time of the next start-up is equalized, and the output can be stabilized.

Another form of Embodiment 2 is characterized by including a fuel cell stack, a mechanism for circulating a heat medium, a fuel humidification mechanism, an oxidant humidification mechanism, and a control mechanism; wherein the fuel cell stack includes a stacked body that is a combination of components, that is, a membrane electrode assembly in which the anode is bonded to one side of the electrolyte membrane and the cathode is bonded to the other side of the electrolyte membrane, a fuel flow path plate is provided with a fuel flow path for supplying fuel to the anode, and a The oxidant flow path plate of the oxidant flow path for supplying oxidant to the cathode, and the heat medium flow path plate of the heat medium flow path through which the heat medium flows; After the heat medium is cooled, it is put into the fuel cell group to circulate the heat medium; the fuel humidification mechanism uses heat exchange with the heat medium to humidify the fuel; the oxidant humidification mechanism uses heat exchange with the heat medium to humidify the oxidant; The control means continues circulation of the heat medium when the system is stopped until a predetermined cooling stop condition is established, and continues power generation of the fuel cell, and stops power generation of the fuel cell when the predetermined cooling stop condition is satisfied.

According to the above configuration, since the degradation caused by the diffusion and permeation of hydrogen and oxygen in the electrolyte can be suppressed after the power generation is stopped, and the deviation of the water distribution of each unit cell can be suppressed, the power generation of each unit cell at the next startup Quantity equalization can achieve output stabilization.

In the above configuration, the control means may set the temperature of the heat medium discharged from the fuel cell stack to the temperature of the heat medium fed into the fuel cell stack for a period from the start of the system stop process until a predetermined cooling stop condition is established. The temperature difference of the temperature reaches a given range to adjust the circulation of the heat medium. In this way, the water distribution of each unit cell in the fuel cell stack can be further uniformed.

In the configuration described above, the control means may set, as the cooling stop condition, that the temperature of the heat medium discharged from the fuel cell stack is lower than a value determined by a function of the outside air temperature. In addition, the control means may set the fact that a predetermined time has elapsed since the system was stopped as the cooling stop condition. In this way, power consumption can be reduced by terminating the circulation of the heat medium within a moderate period of time.

Furthermore, an embodiment in which the above-mentioned elements are appropriately combined should also be included in the scope of the invention.

Description of drawings

FIG. 1 is a system configuration diagram schematically showing the configuration of a fuel cell system according to Embodiment 1. FIG.

FIG. 2 is a flowchart showing a method of operating the fuel cell system of Embodiment 1. FIG.

FIG. 3 is a flowchart showing a method of operating the fuel cell system of the second embodiment.

FIG. 4 is a flowchart showing a method of operating the fuel cell system of the third embodiment.

FIG. 5 is a diagram showing an overall configuration of a fuel cell system according to Embodiment 2. FIG.

Fig. 6 is a graph showing temperature changes during forced cooling.

Fig. 7 is a graph showing temperature changes during natural cooling (comparative example).

8 is a graph showing changes in cell current and voltage of each cell when the system is started after forced cooling.

9 is a graph showing changes in cell current and voltage of each cell when the system is started after natural cooling (comparative example).

Detailed ways

(Embodiment 1)

Next, a method of operating the fuel cell system of the present embodiment will be described using the drawings. First, FIG. 1 is a system configuration diagram schematically showing the configuration of a fuel cell system 1100 .

The fuel cell system 1100 includes: a reformer 1010 that reforms a raw fuel (hydrocarbon fuel) such as LPG or city gas to generate a reformed gas containing about 80% hydrogen (fuel); Fuel cell 1030 that generates electricity by reforming gas and oxygen (oxidant) in the air, and recovers and stores heat generated in the reformer 1010 or fuel cell 1030 as hot water (water above 40°C) The hot water storage device 1050 is a combined heat and power system that has both the power generation function and the hot water supply function.

Raw fuels such as LPG and city gas installed in households are usually smelly with sulfide as a safety measure against gas leakage. In step 1010, the sulfur compound in the raw fuel is firstly removed by using the desulfurizer 1012. The raw fuel desulfurized by the desulfurizer 1012 is then mixed with steam, subjected to steam reforming by the reformer 1014 , and introduced into the reformer 1016 . Thereafter, reformed gas of about 80% hydrogen, about 20% carbon dioxide, and less than 1% carbon monoxide is produced by the reformer 1016, and the reformed gas is supplied to the fuel cell 1030 operating at a low temperature (below 100°C) that is easily affected by carbon monoxide. In this fuel cell system 1100 of the gas, the reformed gas and oxygen are then mixed, and carbon monoxide is selectively oxidized by the CO remover 1018 . With the CO remover 1018, the carbon monoxide concentration in the reformed gas can be kept at 10 ppm or less.

The so-called reformer 1010 includes at least a reformer 1014 and a reformer 1016. In the case of using the gas installed in households as the raw fuel like this fuel cell system 1100, it also includes a desulfurizer 1012. When a low-temperature fuel cell 1030 such as a solid polymer fuel cell is used as the battery 1030 , a CO remover 1018 is further included.

Since steam reforming is an endothermic reaction, a burner 1020 is provided in the reformer 1014 . When the reformer 1010 is started, raw fuel is also supplied to the burner 1020 to raise the temperature of the reformer 1014 . The details will be described later, but in order to make the fuel cell system 1100 operate stably, by stopping the supply of the raw fuel to the burner 1020, the unreacted fuel discharged from the fuel cell 1030 is supplied to the burner 1020, and the Reformer 1014 supplies heat. Since the exhaust gas supplied with heat to the reformer 1014 by the burner 1020 still has a large amount of heat, the exhaust gas is heat-exchanged with the water in the hot water storage tank 1052 in the heat exchangers HEX01 and HEX02. Thereafter, the water exchanges heat with the exhaust gas from the cathode 1032 of the fuel cell 1030 (HEX03), then exchanges heat with the exhaust gas from the anode 1034 (HEX04), and returns to the hot water storage tank 1052. In the water piping 1054 passing through the heat exchangers HEX01, HEX02, HEX03, and HEX04, the temperature of the water (hot water) passing through the heat exchanger HEX04 can be used to raise or cool the cathode side humidification tank 1038. , and a branch pipe 1056 is provided. When the temperature of the cathode-side humidification tank 1038 is low, such as when the fuel cell system 1100 is started, water passes through the heat exchanger HEX04 and then passes through the branch pipe 1056 to supply heat to the cathode-side humidification tank 1038 through the heat exchanger HEX05. Return to storage hot water tank 1052 afterwards.

The cathode side humidification tank 1038 also functions as a cooling water tank, and the water in the cathode side humidification tank 1038 cools the fuel cell 1030 and returns to the cathode side humidification tank 1038 . As described above, when the temperature of the fuel cell 1030 is low such as when the fuel cell system 1100 is started, the fuel cell 1030 can be heated by supplying the cooling water heated by the heat exchanger HEX05 to the fuel cell 1030 . In addition, the cooling water passage 1040 through which the cooling water passes is connected to the heat exchanger HEX06 provided on the anode side humidification tank 1042, and the cooling water also serves to reduce the temperature of the cathode side humidification tank 1038 and the anode side humidification tank 1042 to the same temperature. Set to the effect of the same temperature.

The reformed gas from the reformer 1010 is supplied to the anode 1034 while being humidified (bubbling in the case of the fuel cell system 1100 of this fuel cell system 1100 ) in the anode-side humidification tank 1042 . Unreacted fuel that does not participate in power generation in the anode 1034 is discharged from the fuel cell 1030 and supplied to the burner 1020 . The fuel cell 1030 is usually operated to generate electricity in the range of 70 to 80°C. Since the exhaust gas discharged from the fuel cell 1030 has a heat value of about 80°C, it is processed in the heat exchanger HEX04 as described above. After the heat exchange, the temperature of the water supplied to the cathode side humidification tank 1038 and the anode side humidification tank 1042 is raised in the heat exchanger HEX07 and then supplied to the burner 1020 .

The water supplied to the cathode-side humidification tank 1038 and the anode-side humidification tank 1042 is preferably clean water with low electrical conductivity and little contamination of organic matter, so the water from upper water is treated with a water treatment device 1090 using a reverse osmosis membrane. Supply after water treatment with ion exchange resin. In addition, the water subjected to this water treatment is also used for steam reforming in the reformer 1014 . While upper water is also supplied to the hot water storage tank 1052 , upper water is supplied from the lower part of the hot water storage tank 1052 at this time. In addition, the water pipe 1054 also draws water at a lower temperature from the lower part of the hot water storage tank 1052, and returns the water that has exchanged heat with each heat exchanger to the upper part.

HEX10 is a total heat exchanger. Since the exhaust gas containing unreacted oxygen that does not participate in power generation in the cathode 1032 contains heat of about 80°C and produced water generated by the reaction, the air supplied to the cathode 1032 is supplied with heat and heat by the total heat exchanger HEX10. moisture. The air supplied to the cathode 1032 is then supplied to the cathode 1032 after being humidified (bubbling in the case of the present fuel cell system 1100 ) in the cathode-side humidification tank 1038, and heat and heat are supplied to the total heat exchanger HEX10. The moisture exhaust gas is then exhausted to the outside of the fuel cell system 1100 after exchanging heat with water in the heat exchanger HEX03 .

When starting such a fuel cell system 1100, conventionally, the temperature of the reformer 1010 is raised, and the temperature of the fuel cell 1030 is raised. When the carbon monoxide concentration of the reformed gas coming out of the CO remover 1018 is satisfied to be below 10 ppm, the fuel cell After the temperature of 1030 is 70° C. or higher, the supply of the reformed gas to the fuel cell 1030 is started, and then the supply of air is started. In addition, when stopping, the fuel cell system 1100 immediately stops the power generation of the fuel cell 1030 upon receiving the stop signal, and then stops the supply of air and reformed gas in that order.

In the conventional start-up method, when the temperature of the fuel cell 1030 is raised to 70°C, the gas diffusion rate in the electrolyte is high, the coverage rate of carbon monoxide adsorbed on the catalyst is low, and the activity of the catalyst is high, the anode 1034 is first supplied with heavy When the gas is adjusted, hydrogen diffuses from the anode to the cathode, and at the anode hydrogen becomes protons and moves to the cathode 1032 . Hydrogen is generated in the cathode 1032 when cooling water or the like passes therethrough to cause a leak current to flow. Next, when air is supplied to the cathode 1032, since direct combustion or generation of hydrogen peroxide occurs in the cathode 1032, there is a problem that the cathode 1032 or the solid polymer film 1033 is deteriorated. In addition, in the conventional shutdown method, as in the startup, there is a problem that direct combustion or generation of hydrogen peroxide is caused in the cathode 1032, or that air, especially oxygen, enters the anode from the outside or the cathode 1032 during shutdown. 1034, direct combustion or generation of hydrogen peroxide is also induced in the anode 1034. Therefore, an operation method for preventing the fuel cell 1030 from deteriorating when the fuel cell system 1100 is started or stopped will be described below as an example.

[Example 1]

FIG. 2 is a flowchart showing an operating method (starting method) of the present fuel cell system 1100 . As shown in FIG. 2 , when an operation start signal is input to the fuel cell system 1100 (S11), the temperature rise of the reformer 1010 and the fuel cell 1030 starts (S12R, S12F). When the temperature rise of the reformer 1010 ends (S13R), the reformer 1010 starts reforming (S14R). However, in the case of the past, the concentration of carbon monoxide contained in the reformed gas coming out of the reformer 1010 It is not supplied to the fuel cell 1030 until it is stabilized below 10 ppm. However, in the present embodiment, reforming (S14R) is started after the temperature rise of the reformer 1010 is completed (S13R), and conversion of the reformed gas to the fuel starts when the carbon monoxide concentration in the reformed gas is high (for example, 100 ppm). Supply of the battery 1030 (S15).

On the other hand, in the conventional case, when the supply of reformed gas to the fuel cell 1030 is started, the temperature of the fuel cell is raised so that the temperature of the fuel cell reaches 70° C. or higher. When the fuel cell 1030 is supplied (S15), the temperature of the fuel cell 1030 can be raised to about 40±10°C (S13F). 1010 temperature rise (S12R) at the same time.

After the supply of reformed gas to the fuel cell 1030 is started (S15), the supply of air to the fuel cell 1030 is started (S16), and the power generation of the fuel cell 1030 is started after checking the open circuit voltage (S17) (S18). That is, the fuel cell 1030 starts generating electricity at about 30 to 50°C.

By starting the fuel cell system 1100 in the flow described above, the following actions can be expected. (1) Since the supply of the reformed gas is started at a temperature lower than the normal power generation temperature, the diffusion rate of hydrogen and oxygen to the electrolyte (the electrolyte contained in the solid polymer membrane 33 or the cathode 1032 and the anode 1034) is low , so penetration is inhibited. (2) Before starting the power generation of the fuel cell 1030, since the reformed gas having a carbon monoxide concentration higher than the normal composition is supplied to the anode 1034, carbon monoxide is adsorbed on the catalyst (particularly platinum) of the anode 1034 and blocks the flow of gas in the anode 34. generation of protons. Therefore, the generation of hydrogen in the cathode 32 due to leakage current and the direct reaction of hydrogen and oxygen or the hydrogen peroxide generation reaction when air is supplied to the cathode 1032 can be suppressed. (3) When the power generation of the fuel cell 1030 is started, carbon monoxide is oxidized due to an increase in the potential of the anode 1034, so there is no need to remove the adsorbed carbon monoxide, and heat is generated due to the increase in overvoltage and the oxidation reaction of carbon monoxide , so it helps to increase the battery heating rate. (4) Although the voltage may become unstable due to the influence of carbon monoxide, in this case, if a small amount of air is added to the reformed gas when the fuel cell 1030 starts to generate electricity, the gas adsorbed on the anode 1034 Oxidation of carbon monoxide on the surface of the catalyst can improve the stability. (5) When increasing the carbon monoxide concentration contained in the reformed gas, you can choose to reduce the air supply to the CO remover 1018, lower the temperature of the CO remover 1018, raise the temperature of the reformer 1016, and reduce the temperature of the reformer. temperature of reformer 1014 or by reducing the ratio (S/C) of the amount of raw fuel supplied to reformer 1014 to the amount of water vapor (S/C), or because after the temperature rise of reformer 1010 is completed, it becomes Before steady state, carbon monoxide concentration is high, so it can also be utilized. In addition, in order to prevent the thermal balance of the reformer 1010 from being disrupted, the means for increasing the carbon monoxide concentration may be periodically changed. As another method, it is also possible to reduce the fuel supplied to the fuel cell and improve the fuel efficiency. As the fuel utilization rate increases, the temperature of the reformer 1014 decreases due to the reduction of unreacted fuel burned in the combustor 1020 of the reformer 1014 . In addition, even when the fuel composition is the same, since the CO concentration gradually increases along the flow direction of the fuel along with the consumption of hydrogen in the anode, the case of high fuel utilization rate is higher than the case of low fuel utilization rate. , the CO concentration on the downstream side of the fuel becomes high. (6) When the fuel cell system 1100 is started, since the reformer 1010 is not completely (stablely) started, the power generation of the fuel cell 1030 can be started from a state where the carbon monoxide concentration is high. Therefore, according to the starting method of this embodiment, The time taken for the startup of the fuel cell power generation system 1100 can be shortened. Furthermore, when the fuel cell temperature at the initial stage of starting is lower than 40° C., although the output of the fuel cell is lowered, it is not necessary to raise the temperature of the fuel cell because there is no hindrance to the starting.

[Example 2]

FIG. 3 is a flowchart showing an operation method (stop method) of the present fuel cell system 1100 . As shown in FIG. 3 , when an operation stop signal is input to the fuel cell system 1100 ( S21 ), the temperature of the fuel cell 1030 is cooled to about 40° C. ( S22 ). By cooling the fuel cell 1030, the gas diffusion rate in the electrolyte is low, the coverage of carbon monoxide adsorbed on the catalyst is high, and the activity of the catalyst is lowered. Even if the same amount of reformed gas and air is supplied, although the power generation amount of the fuel cell 1030 decreases, the fuel cell 1030 stops generating power after being sufficiently cooled (S23). Thereafter, after the power generation of the fuel cell 1030 is stopped, the supply to the fuel cell 1030 is stopped in the order of air (S24) and reformed gas (S25). At this time, after an operation stop signal is input to the fuel cell system 1100 , the reformed gas having a high carbon monoxide concentration (for example, 100 ppm or more) is supplied to the fuel cell 1030 . Furthermore, in order to reduce the amount of residual oxygen in the cathode, the power generation may be stopped after the air supply is stopped, and then the fuel supply may be stopped.

By stopping the fuel cell system 1100 using the flow shown above, the following actions can be expected. (1) Since the supply of the reformed gas is stopped at a temperature lower than that for normal power generation, the diffusion rate of hydrogen and oxygen in the electrolyte is low, and permeation is suppressed. (2) Before the power generation of the fuel cell 1030 is stopped, the concentration of carbon monoxide in the reformed gas is increased to adsorb the carbon monoxide on the catalyst. Therefore, even if the air flows into the anode 1034 while the fuel cell system 1100 is stopped, the oxygen in the air is It is consumed in oxidizing the carbon monoxide adsorbed on the catalyst, and the potential rise of the anode 1034 is suppressed, thereby preventing deterioration of the catalyst, especially oxidation of ruthenium. (3) Since the reformed gas having a carbon monoxide concentration higher than the normal composition is supplied to the anode 1034 before the power generation of the fuel cell 1030 is stopped, carbon monoxide is adsorbed on the catalyst (particularly, platinum) of the anode 1034 to block the flow from the anode 1034 Generate protons. Therefore, the generation of hydrogen in the cathode 1032 caused by leakage current and the direct reaction of hydrogen and oxygen or the hydrogen peroxide generation reaction when air (oxygen) flows into the cathode 1032 can be suppressed. (4) When starting the power generation of the fuel cell 1030, since the potential of the anode 1034 rises and carbon monoxide is oxidized, it is not necessary to remove the adsorbed carbon monoxide. In addition, due to the increase in overvoltage and the oxidation reaction of carbon monoxide Heats up, thus helping the battery to heat up. (5) When increasing the carbon monoxide concentration contained in the reformed gas, you can choose to reduce the air supply to the CO remover 1018, lower the temperature of the CO remover 1018, raise the temperature of the reformer 1016, and reduce the temperature of the reformer. 1014 temperature or at least one of the method of reducing the ratio (S/C) of the amount of raw fuel supplied to the reformer 1014 to the amount of water vapor (S/C). In addition, this means of increasing the concentration of carbon monoxide may also be to prevent heavy The heat balance of the whole device 1010 is shifted, so that it fluctuates periodically. As another method, it is also possible to reduce the fuel supplied to the fuel cell and improve the fuel efficiency.

[Example 3]

FIG. 4 is a flowchart showing an operation method (stop method) of the present fuel cell system 1100 . As shown in FIG. 4, when the operation stop signal is input to the fuel cell system 1100 (S31), the power generation of the fuel cell 1030 is stopped (S32), and thereafter, the supply of air to the fuel cell 1030 is stopped in the order of air (S33) and reformed gas. Supply of 1030 (S34). Thereafter, the temperature of the fuel cell 1030 is cooled to about 40°C (S35). By cooling the fuel cell 1030, the gas diffusion rate in the electrolyte is low, the coverage of carbon monoxide adsorbed on the catalyst is high, and the activity of the catalyst is lowered. Alternatively, after an operation stop signal is input to the fuel cell system 1100, reformed gas having a high carbon monoxide concentration (for example, 100 ppm or more) may be supplied to the fuel cell 1030, and power generation may be stopped after a certain period of time. In addition, in order to reduce the amount of residual oxygen in the cathode, the power generation may be stopped after the air supply is stopped, and then the fuel supply may be stopped.

By stopping the fuel cell system 1100 using the flow shown above, the following actions can be expected. (1) Since the fuel cell is forcibly cooled shortly after power generation is stopped, the diffusion rate of hydrogen and oxygen in the electrolyte is reduced compared to the case where the forced cooling is not performed, so that permeation after power generation is stopped is suppressed. (2) Before the power generation of the fuel cell 1030 is stopped, the concentration of carbon monoxide in the reformed gas is increased to adsorb the carbon monoxide on the catalyst. Therefore, even if the air flows into the anode 1034 while the fuel cell system 1100 is stopped, the oxygen in the air is It is consumed in oxidizing the carbon monoxide adsorbed on the catalyst, and the potential rise of the anode 1034 is suppressed, thereby preventing deterioration of the catalyst, especially oxidation of ruthenium. (3) Since the reformed gas having a carbon monoxide concentration higher than the normal composition is supplied to the anode 1034 before the power generation of the fuel cell 1030 is stopped, carbon monoxide is adsorbed on the catalyst (particularly, platinum) of the anode 1034 to block the flow from the anode 1034 Generate protons. Therefore, the generation of hydrogen in the cathode 1032 caused by leakage current and the direct reaction of hydrogen and oxygen or the hydrogen peroxide generation reaction when air (oxygen) flows into the cathode 1032 can be suppressed. (4) When starting the power generation of the fuel cell 1030, since the potential of the anode 1034 rises and carbon monoxide is oxidized, it is not necessary to remove the adsorbed carbon monoxide. In addition, due to the increase in overvoltage and the oxidation reaction of carbon monoxide Heats up, thus helping the battery to heat up. (5) When increasing the carbon monoxide concentration contained in the reformed gas, you can choose to reduce the air supply to the CO remover 1018, lower the temperature of the CO remover 1018, raise the temperature of the reformer 1016, and reduce the temperature of the reformer. The temperature at 1014 or the method of reducing the ratio (S/C) of the amount of raw fuel supplied to the reformer 1014 to the amount of water vapor is achieved by at least one of them. In addition, in order to prevent the breakdown of the thermal balance of the reformer 1010, the means for increasing the carbon monoxide concentration may be periodically changed. As another method, it is also possible to reduce the fuel supplied to the fuel cell and improve the fuel efficiency.

(Embodiment 2)

Embodiment 2 will be described below using the drawings. FIG. 5 shows the overall configuration of a fuel cell system 10 according to the second embodiment. The fuel cell system 10 includes a fuel cell stack 20, a fuel supply mechanism 30, a fuel humidifier 40, an air supply mechanism 50, an air humidifier 60, a heat medium heat exchanger 70, piping 80, a control valve 86, a circulation pump 90, and The control unit 100.

The fuel cell stack 20 includes a laminate formed by combining a membrane electrode assembly in which an anode is bonded to one surface of a polymer electrolyte membrane and a cathode is bonded to the other surface of the electrolyte membrane. A fuel channel plate with a fuel channel for supplying fuel to the anode, an oxidant channel plate with an oxidant channel for supplying oxidant to the cathode, and a heat medium channel plate with a heat medium channel through which the heat medium flows. The fuel cell stack 20 can employ a known configuration, and typical examples thereof include the configuration shown in FIG. 1 and FIG. 2 of JP-A-2004-185938, or the configuration shown in FIG. 1 of JP-A-2004-185934. In the fuel cell stack 20 of the present embodiment, the direction of flow of the fuel and air used for power generation and the heat medium used for cooling the anode and/or cathode is parallel flow in the direction of gravity. In the present embodiment, although water is used as the heat medium, other liquids or gases may be used as long as heat exchange is possible. Water used as a heat medium is hereinafter referred to as cooling water.

The fuel supply mechanism 30 is a mechanism for supplying hydrogen used as fuel. For example, the fuel supply mechanism 30 is mainly composed of a fuel tank for storing hydrocarbon gas such as natural gas or methane gas, a desulfurizer for removing sulfur components from the hydrocarbon gas supplied from the fuel tank, and reforming the desulfurized hydrocarbon gas to take out hydrogen. The structure of the reforming device.

The fuel humidifier 40 humidifies the fuel supplied from the fuel supply mechanism 30 . Specifically, the fuel humidifier 40 includes a fuel humidifying tank 42 and a fuel heat exchanger 44, uses water that has been added to the fuel humidifying tank 42 and has been heated by the fuel heat exchanger 44, and uses bubbling to humidify the fuel. The relative humidity of the fuel becomes 100% RH.

The air supply mechanism 50 is a mechanism for supplying air containing oxygen serving as an oxidizing agent. For example, the air supply mechanism 50 is composed of a blower for inputting outside air and a gas filter provided as necessary.

The air humidifier 60 humidifies the air supplied from the air supply mechanism 50 . Specifically, the air humidifier 60 includes an air humidification tank 62, and uses water added to the air humidification tank 62 to humidify the air by bubbling so that the relative humidity of the air becomes 100% RH.

The heat medium heat exchanger 70 lowers the temperature of the cooling water discharged from the fuel cell stack 20 by exchanging heat with outside air or the like. The temperature of the cooling water discharged from the fuel cell stack 20 can be effectively lowered by the heat exchanger 70 for heat medium.

The piping 80 has a configuration capable of circulating the cooling water so that the cooling water discharged after flowing through the heat medium flow path provided in the fuel cell stack 20 can be supplied to the heat medium flow path again. Specifically, the cooling water discharged from the fuel cell stack 20 is first guided to the heat medium heat exchanger 70, and branched at a given distribution ratio at a branch point 82 provided downstream of the heat medium heat exchanger 70. A branch line towards the fuel humidifier 40 , a branch line towards the air humidifier 60 . Part of the cooling water discharged from the fuel cell stack 20 flows through the fuel heat exchanger 44 included in the fuel humidifier 40 , and the rest of the cooling water discharged from the fuel cell stack 20 is directly supplied to the air humidifier 60 . The cooling water flowing through the fuel heat exchanger 44 and the cooling water flowing upstream of the air humidifier 60 through the branch line toward the air humidifier 60 join at a confluence point 84 . The merged cooling water flows through the air humidification tank 62 of the air humidifier 60 and then is discharged from the air humidifier 60 . The circulation pump 90 extracts the cooling water discharged from the air humidifier 60 and sends it to the fuel cell stack 20 as a predetermined amount of cooling water.

The control valve 86 is a valve provided between the branch point 82 and the confluence point 84 and whose opening and closing degree can be changed. By adjusting the opening degree of the control valve 86, the distribution ratio of the cooling water can be corrected. Furthermore, the installation of the control valve 86 is not indispensable, and it does not need to be installed when the distribution ratio of the cooling water does not need to be corrected according to the operating conditions.

In addition to controlling the power generation amount of the fuel cell stack 20 , the control unit 100 also adjusts the opening degree of the control valve 86 and the circulation pump 90 to control the amount of cooling water. In addition, the control unit 100 controls the fuel supply amount from the fuel supply mechanism 30 and the air supply amount from the air supply mechanism 50 as necessary.

(Operation when the system stops)

The operation of the fuel cell system 10 when the system is stopped will be described. In the following description, the temperature near the inlet of the cooling water provided in the fuel cell stack 20 is referred to as the cooling water inlet temperature (T1), and the temperature near the outlet of the cooling water provided in the fuel cell stack 20 is referred to as cooling water temperature (T1). Water outlet temperature (T2). In addition, the temperature of the fuel humidified by the fuel humidifier 40 is referred to as a humidified fuel temperature ( T3 ), and the temperature of the air humidified by the air humidifier 60 is referred to as a humidified air temperature ( T4 ). In addition, the dew point near the inlet of the fuel provided in the fuel cell stack 20 is referred to as a fuel dew point ( T5 ), and the dew point near the inlet of air provided in the fuel cell stack 20 is referred to as an air dew point ( T6 ). Furthermore, T1 , T2 , T3 , T4 , T5 , and T6 are measured by a temperature sensor (not shown) as necessary, and the measured values are sent to the control unit 100 .

When the system is stopped, the control unit 100 cuts off the load current and stops the power generation of the fuel cell while maintaining the circulation of the cooling water by the circulation pump 90 . Circulation of the cooling water is continued until a cooling water stop condition described later is satisfied. Then, the control unit 100 stops the supply of fuel from the fuel supply mechanism 30 and the supply of air from the air supply mechanism 50 . The stop of the fuel supply and the stop of the air supply may be performed first, or both may be stopped at the same time. The control unit 100 determines whether or not the cooling stop condition is satisfied after the power generation of the fuel cell is stopped. Examples of cooling stop conditions include a condition that any one of the battery temperature, cooling water outlet temperature ( T2 ), humidified fuel temperature ( T3 ), and humidified air temperature ( T5 ) reaches a set temperature. At this time, the set temperature is determined by, for example, a function of the outside air temperature such as (outside air temperature+5)°C. In addition, as the cooling stop condition, a condition that a certain period of time has elapsed since the power generation was stopped may be adopted. By stopping the circulation of the cooling water according to the establishment of such a cooling stop condition, it is possible to reduce power consumption while achieving uniform water distribution in each unit cell.

Moreover, the control unit 100 may also use the circulation pump 90 to adjust the amount of cooling water when the cooling water circulates after power generation is stopped, so that the difference between the cooling water outlet temperature (T2) and the cooling water inlet temperature (T1) reaches a predetermined temperature. , such as below 2°C. In this way, since the temperature distribution in the flow direction of the cooling water in the fuel cell stack 20 becomes smooth, it is possible to make it difficult to generate a difference in the water distribution in each unit cell.

Fig. 6 is a graph showing temperature changes when cooling water circulation is continued after power generation is stopped (hereinafter referred to as forced cooling). In addition, FIG. 7 is a graph showing temperature change (comparative example) when cooling water circulation is stopped simultaneously with power generation stop and natural cooling is performed (hereinafter referred to as natural cooling). The temperature was measured at four points in total, two locations on the surface of the battery, the surface of the fuel humidifier 40 , and the surface of the air humidifier 60 . As a result, during the forced cooling, it was confirmed that within one hour after the power generation was stopped, each temperature did not deviate and dropped rapidly to 40° C. or lower. On the other hand, in the case of natural cooling, each temperature remained at 40° C. or higher even after 4 hours or more had elapsed since the system was stopped, and no variation was observed in each temperature.

8 is a graph showing changes in cell current and voltage of each cell when the system is started after forced cooling. In addition, FIG. 9 is a graph showing changes in cell current and voltage of each cell when the system is started after natural cooling (comparative example). No variation was observed in the voltage of each unit cell after the system started after natural cooling. During the natural cooling, since the fuel cell stack 20 is cooled sequentially from the outside, a temperature difference occurs within the fuel cell stack 20 . Since the water vapor in the fuel cell stack 20 first condenses from a place with a low temperature, the water distribution in each unit cell changes during the natural cooling process. In this way, the distribution of the reactant gas to each unit cell becomes uneven at the next startup, and the voltage of each unit cell becomes unstable during power generation. In addition, when the temperature (water temperature) of the fuel humidifier 40 or the air humidifier 60 connected by the piping 80 is higher than the battery temperature, even if the reaction gas is stopped, the vapor will flow from the fuel humidifier 40 or the air humidifier 60 to the fuel cell. The stack 20 diffuses, and dew condenses in the fuel cell stack 20 , thereby also changing the water distribution in the fuel cell stack 20 .

On the other hand, in the voltage of each unit cell after the system startup after the forced cooling, the variation similar to that in the comparative example was not observed, and the output was stable. This is considered to be because, by continuing the circulation of the cooling water even after power generation is stopped, a temperature difference in the fuel cell stack 20 during cooling is suppressed, and as a result, the water distribution in the fuel cell stack 20 becomes uniform. In addition, since the temperature of the fuel humidifier 40 or the air humidifier 60 and the fuel cell stack 20 are changed to the same degree by continuing the circulation of the cooling water even after the power generation is stopped, the vapor flow from the fuel humidifier 40 or the air humidifier 60 is suppressed. In the case of diffusion to the fuel cell stack 20, this also becomes a factor for stabilizing the output.

This embodiment is not limited to the above-mentioned embodiments, and modifications such as various design changes can also be added based on the knowledge of those skilled in the art, and embodiments with such modifications added should also be included in the scope of this embodiment.

For example, in the above-mentioned embodiment, although cooling is started after power generation is stopped, it is also possible to start cooling first, stop power generation after the temperature of the fuel cell reaches a temperature lower than the normal power generation temperature, and stop according to a given cooling The condition is established to stop the cooling water circulation. In addition, it is also possible to stop power generation and stop the circulation of cooling water in accordance with the establishment of predetermined cooling conditions. At this time, when the output of the fuel cell at the start of the system shutdown process is large, the time for the shutdown process can be shortened by cooling while reducing the output.

In addition, in the above-mentioned embodiment, although the supply of fuel and air is also cut off after the power generation is stopped, in order to reduce the amount of residual oxygen in the cathode, it is also possible to stop the power generation after reducing the air supply and improving the air utilization rate, or After the air supply is stopped, the power generation is stopped, and after that, the fuel supply is stopped. As another method, in order to increase the CO concentration of the anode, it is also possible to reduce the fuel supplied to the fuel cell and stop the power generation after improving the fuel utilization rate, or stop the power generation after stopping the fuel supply, and then stop the air supply. In addition, the power generation may be stopped after the air utilization rate and the fuel utilization rate are increased, or the air supply and the fuel supply may be stopped, and then the power generation may be stopped.

By these methods, deterioration due to permeation of reactant gas after power generation is stopped can be suppressed, and the durability and output stability of the fuel cell can be further improved. In any case, in order to protect the unit cells, it is preferable to stop power generation when the voltage of at least one unit cell or the voltage of a unit cell block composed of a plurality of unit cells falls below a predetermined value.

According to the present invention described above, deterioration of the fuel cell can be prevented. In addition, the output stability at the start of the fuel cell system can be improved.

The present invention can be used in a fuel cell of the type that supplies reformed gas to the anode. In addition, the present invention can be used in a fuel cell that generates electricity by supplying a humidified reaction gas, such as a solid polymer fuel cell.

Claims (14)

1. A method of operating a fuel cell system, comprising a reformer for reforming a raw fuel into fuel containing hydrogen, and a fuel cell that generates electricity using the fuel, wherein: When starting the fuel cell system, a carbon monoxide supply step of supplying the fuel containing more carbon monoxide than in normal operation to the fuel cell is included. 2. The method for operating a fuel cell system according to claim 1, further comprising a step of starting power generation of the fuel cell at a temperature lower than a normal power generation temperature of the fuel cell. 3. A fuel cell system operating method, characterized in that, when the fuel cell system is stopped, comprising: a cell cooling step of cooling the fuel cell to a temperature lower than the usual power generation temperature of the fuel cell, A power generation stopping step of stopping power generation of the fuel cell, which is set at a later stage of the battery cooling step. 4. A method of operating a fuel cell system, comprising a reformer for reforming raw fuel into fuel containing hydrogen, and a fuel cell that generates electricity using the fuel, wherein: When shutting down the fuel cell system, including: a carbon monoxide supply step of supplying the fuel cell with the fuel containing more carbon monoxide than in normal operation, a cell cooling step of cooling the fuel cell to a temperature lower than the usual power generation temperature of the fuel cell, A power generation stopping step of stopping power generation of the fuel cell, which is set at a later stage of the battery cooling step. 5. A fuel cell system operating method, characterized in that, when the fuel cell system is stopped, comprising: a step of stopping power generation of the fuel cell, A battery cooling step of cooling the fuel cell to a temperature lower than a normal power generation temperature of the fuel cell, which is set at a later stage of the power generation stop step. 6. A method of operating a fuel cell system, comprising a reformer for reforming raw fuel into fuel containing hydrogen, and a fuel cell that generates electricity using the fuel, wherein: When shutting down the fuel cell system, including: a carbon monoxide supply step of supplying the fuel containing more carbon monoxide than during normal operation to the fuel cell, a step of stopping power generation of the fuel cell, A battery cooling step of cooling the fuel cell to a temperature lower than a normal power generation temperature of the fuel cell, which is set at a later stage of the power generation stop step. 7. A fuel cell system, comprising a fuel cell stack, a mechanism for circulating heat medium, a fuel humidification mechanism, an oxidant humidification mechanism, and a control mechanism, wherein: The fuel cell stack includes a laminate formed by combining a membrane electrode assembly in which an anode is bonded to one surface of an electrolyte membrane and a cathode is bonded to the other surface of the electrolyte membrane, A fuel channel plate provided with a fuel channel for supplying fuel to the anode, an oxidant channel plate provided with an oxidant channel for supplying an oxidant to the cathode, and a thermal plate provided with a heat medium channel through which a heat medium flows. Medium flow plate; The mechanism for circulating the heat medium is a mechanism that cools the heat medium discharged from the fuel cell stack and then injects it into the fuel cell stack to circulate the heat medium; The fuel humidification mechanism humidifies the fuel by exchanging heat with the heat medium; The oxidant humidifying mechanism utilizes heat exchange with the heat medium to humidify the oxidant; The control means, when the system is stopped, continues the circulation of the heat medium after power generation by the fuel cell is stopped until a predetermined cooling stop condition is satisfied. 8. A fuel cell system, comprising a fuel cell stack, a mechanism for circulating heat medium, a fuel humidification mechanism, an oxidant humidification mechanism, and a control mechanism, wherein: The fuel cell stack includes a laminate formed by combining a membrane electrode assembly in which an anode is bonded to one surface of an electrolyte membrane and a cathode is bonded to the other surface of the electrolyte membrane, A fuel channel plate provided with a fuel channel for supplying fuel to the anode, an oxidant channel plate provided with an oxidant channel for supplying an oxidant to the cathode, and a thermal plate provided with a heat medium channel through which a heat medium flows. Medium flow plate; The mechanism for circulating the heat medium is a mechanism that cools the heat medium discharged from the fuel cell stack and then injects it into the fuel cell stack to circulate the heat medium; The fuel humidification mechanism humidifies the fuel by exchanging heat with the heat medium; The oxidant humidifying mechanism utilizes heat exchange with the heat medium to humidify the oxidant; The control means continues the circulation of the heat medium when the system is stopped until a predetermined cooling stop condition is satisfied, and continues the power generation of the fuel cell, and stops the fuel cell when the predetermined cooling stop condition is satisfied. of power generation. 9. The fuel cell system according to claim 7, wherein the control means causes the fuel cell stack to The circulation amount of the heat medium is adjusted so that the temperature difference between the temperature of the discharged heat medium and the temperature of the heat medium fed into the fuel cell stack falls within a predetermined range. 10. The fuel cell system according to claim 8, wherein the control means causes the fuel cell stack to The circulation amount of the heat medium is adjusted so that the temperature difference between the temperature of the discharged heat medium and the temperature of the heat medium fed into the fuel cell stack falls within a predetermined range. 11. The fuel cell system according to claim 7, wherein the control means regards as the cooling condition that the temperature of the heat medium discharged from the fuel cell stack is lower than a value determined by a function of the outside air temperature. The stop condition is set. 12. The fuel cell system according to claim 8, wherein the control means regards as the cooling condition that the temperature of the heat medium discharged from the fuel cell stack is lower than a value determined by a function of the outside air temperature. The stop condition is set. 13. The fuel cell system according to claim 7, wherein the control means sets, as the cooling stop condition, a predetermined time elapsed from the start of the system stop process. 14. The fuel cell system according to claim 8, wherein the control means sets, as the cooling stop condition, a predetermined time elapsed from the start of the system stop process.

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