JP2012069383A - Fuel cell system and operational method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a fuel cell system capable of preventing deterioration in a polymer electrolyte membrane of a polymer electrolyte fuel cell operated under low humidification conditions with a simplified constitution; and an operational method of the fuel cell system.SOLUTION: A fuel cell system 101A includes: a polymer electrolyte fuel cell 1; a hydrogen generator 2; an oxidant gas supply device 3 supplying oxidant gas to a cathode 1b of the fuel cell 1; a burner 4 burning combustion fuel gas with combustion air to generate water-containing combustion exhaust gas and supplying heat required for a steam reforming reaction to the hydrogen generator 2 by the burning; and combustion exhaust gas supply mechanism 5 constituted such that the combustion exhaust gas generated by the burner 4 is supplied to the cathode 1b of the fuel cell 1 in a startup operation of the fuel cell system 101A.

Description

  The present invention relates to a fuel cell system and an operating method thereof, and more particularly to a mechanism for preventing deterioration of a polymer electrolyte membrane of a polymer electrolyte fuel cell operated under a low humidification condition.

  Currently, a polymer electrolyte fuel cell, a fuel gas supply device that supplies fuel gas containing moisture to the anode of the polymer electrolyte fuel cell, and an oxidant gas containing moisture to the cathode of the polymer electrolyte fuel cell Various studies have been made for the practical application of a fuel cell system including at least an oxidant gas supply device (for example, a power generation system for a moving body such as an electric vehicle and a practical cogeneration system for home use). ing.

  Among these examinations, technological development for ensuring sufficient energy conversion efficiency of the fuel cell system is one of the important considerations. For example, the dew point of the fuel gas is set to Tda and the dew point of the oxidant gas is set. When Tdc is set and the temperature of the polymer electrolyte fuel cell is Tcell, the fuel cell system is operated under operating conditions satisfying Tcell> Tda and Tcell> Tdc (hereinafter, these operating conditions are referred to as “low humidification conditions”). The fuel cell system which operates based on this, or the fuel cell system which operates based on this, is proposed as one of the fuel cell system which can fully ensure energy conversion efficiency, and its operation method.

  On the other hand, as a method of operating the fuel cell system, it is not necessary to operate the fuel cell system in a state where no electric energy or thermal energy is required. There is a need for a start-stop type operating method that starts the system and stops the operation of the fuel cell system when electrical energy or thermal energy is no longer needed.

  By the way, in the fuel cell system, when starting and stopping the polymer electrolyte fuel cell, the state of the polymer electrolyte fuel cell shifts from the closed circuit state to the open circuit state. Here, when the fuel cell system is operated under a low humidification condition, the polymer electrolyte membrane deteriorates when the state of the polymer electrolyte fuel cell shifts from the closed circuit state to the open circuit state with the start and stop of the fuel cell system. Progresses significantly. As a result, in such a fuel cell system, due to deterioration of the polymer electrolyte membrane, fluoride ions, which are decomposition products of the polymer electrolyte membrane, are discharged from the anode and cathode of the polymer electrolyte fuel cell. .

  Therefore, in order to solve this problem, when the power generation operation is stopped from a state where the fuel cell system is operating under low humidification conditions, the dew point of the fuel gas or oxidant gas is controlled to The polymer electrolyte membrane is made by matching the temperature of the molecular electrolyte fuel cell with the dew point of at least one of the fuel gas and the oxidant gas, and then disconnecting the electrical connection between the polymer electrolyte fuel cell and the load. There has been proposed a fuel cell system and a method for operating the same that control the moisture content in the inside, thereby avoiding a low humidified state when the power generation operation is stopped and preventing deterioration of the polymer electrolyte membrane (for example, Patent Documents) 1).

WO 2007/046483 A1

  However, in the above-described conventional technology, although an operation method at the time of stopping the fuel cell system has been proposed, it is insufficient at the time of startup. When starting the fuel cell system, it must be connected to an external circuit after supplying the fuel gas and the oxidant gas in order to prevent the stack from reversing. In this case, since the open circuit state is surely established before connection with the external circuit, it is difficult to prevent the open circuit state under low humidification conditions in which the polymer electrolyte membrane is likely to deteriorate.

  In particular, at the time of restart after an abnormal stop of the fuel cell system, it is difficult to rapidly reduce the temperature of the fuel cell operating under low humidification conditions. It is difficult to suppress deterioration of the polymer electrolyte membrane because it tends to be in an open circuit state below.

  The present invention has been made to solve the above-described conventional problems, and is a fuel capable of preventing deterioration of a polymer electrolyte membrane of a polymer electrolyte fuel cell operated under a low humidification condition with a simple configuration. It aims at providing a battery system and its operating method.

  As a result of intensive research to achieve the above object, the inventors of the present invention are generated when fuel gas for combustion is burned with a burner to supply heat necessary for the reforming reaction when the fuel cell is started. The present inventors have found that it is preferable to supply the combustion exhaust gas to the fuel cell cathode.

  Accordingly, a fuel cell system according to an aspect of the present invention is a polymer electrolyte fuel cell that generates power using a hydrogen-containing gas supplied to an anode and an oxidant gas containing oxygen supplied to a cathode. And a hydrogen generator for generating a hydrogen-containing gas by subjecting the raw material gas to a steam reforming reaction, and supplying the generated hydrogen-containing gas to the anode of the fuel cell; and supplying the oxidizing gas to the cathode of the fuel cell An oxidant gas supply device that burns combustion fuel gas with combustion air to produce combustion exhaust gas containing water, and supplies the hydrogen generator with heat necessary for the steam reforming reaction by the combustion And a combustion exhaust gas supply mechanism configured to supply the combustion exhaust gas generated by the burner to the cathode of the fuel cell at the start-up operation of the fuel cell system.

  According to this configuration, during the start-up operation of the fuel cell system, the combustion exhaust gas supply mechanism supplies the combustion exhaust gas containing water generated by the burner to the cathode of the fuel cell. The membrane is moistened and the water content of the polymer electrolyte membrane is relatively increased. For this reason, deterioration of the polymer electrolyte membrane of the polymer electrolyte fuel cell operated under low humidification conditions can be prevented with a simple configuration.

  The combustion exhaust gas supply mechanism is configured to selectively supply the oxidant gas from the oxidant gas supplier and the combustion exhaust gas generated by the burner to the cathode of the fuel cell, and the combustion exhaust gas The supply mechanism supplies the combustion exhaust gas generated by the burner to the cathode of the fuel cell during the start-up operation of the fuel cell system, and then supplies the oxidant gas from the oxidant gas supplier to the fuel cell. You may be comprised so that it may supply to a cathode.

  During the start-up operation of the fuel cell system, after the fuel gas supply device supplies the hydrogen-containing gas to the fuel cell anode, the combustion exhaust gas supply mechanism supplies the combustion exhaust gas generated by the burner to the fuel cell cathode. Then, the oxidant gas supply unit may be configured to supply the oxidant gas to the cathode of the fuel cell.

  According to this configuration, since the hydrogen-containing gas is supplied to the anode of the fuel cell before the oxidant gas is supplied to the cathode of the fuel cell, the oxidant gas is mixed into the anode through the polymer electrolyte membrane. As a result, an increase in potential of the anode can be prevented. As a result, deterioration of the anode catalyst can be suppressed.

  There may be further provided a radiator provided in the path of the combustion exhaust gas supplied from the burner to the cathode of the fuel cell by the combustion exhaust gas supply mechanism and releasing heat to the combustion exhaust gas.

  According to this configuration, the combustion exhaust gas whose temperature has been lowered by the radiator and increased in relative humidity is supplied to the cathode, so that the polymer electrolyte membrane can be more suitably moistened and its deterioration can be prevented.

Wherein provided from the burner by the combustion exhaust gas supply mechanism in the path of the flue gas supplied to the cathode of the fuel cell, a catalytic combustor which catalytic combustion of the flue gas so as to oxidize CO or NO _x in the combustion in the exhaust gas Further, it may be provided.

According to this configuration, since the combustion exhaust gas in which CO or NO _x contained therein is oxidized and removed by the catalytic combustor is supplied to the cathode of the fuel cell, poisoning of the cathode catalyst by CO or NO _x is prevented. can do.

  Also, a method for operating a fuel cell system according to another aspect of the present invention includes a polymer electrolyte that generates power using a hydrogen-containing gas supplied to an anode and an oxidant gas containing oxygen supplied to a cathode. -Type fuel cell, a hydrogen generator for generating a hydrogen-containing gas by subjecting a raw material gas to a steam reforming reaction, and supplying the generated hydrogen-containing gas to the anode of the fuel cell; and the oxidant gas for the fuel cell An oxidant gas supply device for supplying to the cathode of the combustion chamber, combustion fuel gas is combusted with combustion air to generate combustion exhaust gas containing water, and the hydrogen generator is required for the steam reforming reaction by the combustion And a combustion exhaust gas supply mechanism for supplying combustion exhaust gas generated by the burner to a cathode of the fuel cell. During the start-up operation of the pond system, with the combustion exhaust gas supply mechanism to supply the combustion exhaust gas generated by the burner to the cathode of the fuel cell.

  According to this configuration, as described above, it is possible to prevent deterioration of the polymer electrolyte membrane of the polymer electrolyte fuel cell operated under a low humidification condition with a simple configuration.

  According to the present invention, in the fuel cell system and the operation method thereof, it is possible to prevent deterioration of the polymer electrolyte membrane of the polymer electrolyte fuel cell operated under a low humidification condition with a simple configuration.

FIG. 1 is a block diagram schematically showing the configuration of the fuel cell system according to Embodiment 1 of the present invention. FIG. 2 is a flowchart showing the start-up operation of the fuel cell system of FIG. FIG. 3 is a block diagram schematically showing the configuration of the fuel cell system according to Embodiment 2 of the present invention. FIG. 4 is a flowchart showing the starting operation of the fuel cell system of FIG. FIG. 5 is a block diagram schematically showing the configuration of the fuel cell system according to Embodiment 3 of the present invention. FIG. 6 is a flowchart showing the starting operation of the fuel cell system of FIG. FIG. 7 is a block diagram schematically showing the configuration of the fuel cell system according to Embodiment 4 of the present invention. FIG. 8 is a block diagram schematically showing the configuration of the fuel cell system according to Embodiment 5 of the present invention. FIG. 9 is a flowchart showing the starting operation at the time of abnormal stop of the fuel cell system according to Embodiment 6 of the present invention.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. In the following description, the same or corresponding elements are denoted by the same reference symbols throughout the drawings, and redundant description thereof is omitted.

(Embodiment 1)
[Constitution]
FIG. 1 is a block diagram schematically showing the configuration of the fuel cell system according to Embodiment 1 of the present invention.

  As shown in FIG. 1, the fuel cell system 101A of the first embodiment includes a fuel cell 1, a hydrogen generator 2, an oxidant gas supply device 3, a burner 4, and a combustion exhaust gas supply mechanism 5. Prepare. The fuel cell 1 is operated under a low humidification condition.

<General elements>
The fuel cell 1 is a polymer electrolyte fuel cell. The polymer electrolyte fuel cell constituting the fuel cell 1 only needs to generate electricity using a hydrogen-containing gas as a fuel gas and an oxidant gas containing oxygen. Since such a polymer electrolyte fuel cell is well known, detailed description thereof will be omitted, and only matters relating to the present invention will be described. The fuel cell 1 is configured by stacking a plurality of cells each having an MEA (membrane-electrode assembly) including an anode 1a, a cathode 1b, and a polymer electrolyte membrane (not shown) sandwiched between them. In such a fuel cell 1, an internal fuel gas passage 11 for introducing a hydrogen-containing gas to the anode 1a and an internal oxidant gas passage 12 for introducing an oxidant gas to the cathode 1b are formed. A fuel gas discharge line 8 is connected to the downstream end of the internal fuel gas path 11, and an oxidant gas discharge line 9 is connected to the downstream end of the internal oxidant gas path 12. The fuel cell 1 generates power using a hydrogen-containing gas supplied from the outside to the anode 1a through the internal fuel gas path 11 and an oxidant gas containing oxygen supplied from the outside to the cathode 1b through the internal oxidant gas path 12. . Unconsumed hydrogen-containing gas (off-gas) that has not been used for power generation is discharged to the fuel gas discharge line 8 through the internal fuel gas path 11. Further, unconsumed oxidant gas that has not been used for power generation is discharged to the oxidant gas discharge line 9 through the internal oxidant gas path 12.

  A fuel gas supply line 6 is connected to the upstream end of the internal fuel gas path 11, and a hydrogen generator 2 is connected to the upstream end of the fuel gas supply line 6. The hydrogen generator 2 can be constituted by a known one. The hydrogen generator 2 generates a hydrogen-containing gas by subjecting a raw material gas supplied from the outside to a water-vapor reforming reaction with water supplied from the outside, and uses the generated hydrogen-containing gas as a fuel gas as described above. 1 to the anode 1a. As raw material gas, natural gas supplied from infrastructure, city gas mainly composed of natural gas, LPG (liquefied petroleum gas), etc., or hydrocarbon gas such as propane gas or butane gas filled in a cylinder Can be used.

  The hydrogen generator 2 is configured to be heated by the burner 4. The burner 4 can be constituted by a known one. The burner 4 burns combustion fuel gas with combustion air to generate combustion exhaust gas having a high dew point containing water and supplies heat necessary for the steam reforming reaction to the hydrogen generator 2 by this combustion. The combustion exhaust gas is discharged to the atmosphere through the combustion exhaust gas line 10. The combustion fuel gas only needs to generate combustion exhaust gas containing water by burning with combustion air. In general, a raw material gas and / or an off-gas is used as the combustion fuel gas. Of course, a dedicated fuel gas may be used as the combustion fuel gas.

  An oxidant gas supply line 7 is connected to the upstream end of the internal oxidant gas path 12 of the fuel cell 1. An oxidant gas supply device 3 is connected to the upstream end of the oxidant gas supply line 7. The oxidant gas supply device 3 is composed of, for example, a blower such as a sirocco fan, and air as an oxidant gas is supplied to the cathode 1b of the fuel cell 1 through the oxidant gas supply line 7 and the internal oxidant gas path 12 as described above. To supply.

<Combustion exhaust gas supply mechanism 5>
The combustion exhaust gas supply mechanism 5 is an element that characterizes the fuel cell system 101A of the first embodiment. The combustion exhaust gas supply mechanism 5 is configured to supply the combustion exhaust gas generated by the burner 4 to the cathode 1b of the fuel cell 1 during the startup operation of the fuel cell system 101A. In the first embodiment, the combustion exhaust gas supply mechanism 5 includes, for example, a combustion exhaust gas branch line 5a connecting the combustion exhaust gas line 10 and the oxidant gas supply line 7, and a first opening / closing provided in the combustion exhaust gas branch line 5a. A valve 5b; and a second on-off valve 5c provided in a portion upstream of a connection point between the combustion exhaust gas branch line 5a of the oxidant gas supply line 7 and the oxidant gas supply line 7. As will be described later, the first on-off valve 5b and the second on-off valve 5c are controlled by the controller 21, and the combustion exhaust gas generated by the burner 4 is removed from the fuel cell 1 during the start-up operation of the fuel cell system 101A. It operates to supply to the cathode 1b. In addition, the structure of the combustion exhaust gas supply mechanism 5 can be variously considered, and is not limited to this structure. Another configuration example of the combustion exhaust gas supply mechanism 5 will be described in the second embodiment.

<Controller 21>
The controller 21 controls the overall operation of the fuel cell system 101A. Necessary data is input to the controller 21 from a predetermined sensor and an input device, and the controller 21 processes these input data as appropriate to determine predetermined elements (hydrogen generator 2, oxidant gas supply device 3, Control signals are output to the burner 4 and the combustion exhaust gas supply mechanism 5 etc. to control them. The controller 21 only needs to have a control function. The controller 21 can be composed of, for example, a microcontroller, MPU, PLC (Programmable Logic Controller), logic circuit, or the like. Further, the controller 21 may be configured by a single controller that performs centralized control, or may be configured by a plurality of controllers that perform distributed control in cooperation with each other. For example, the controller 21 may be configured to control only the first on-off valve 5b and the second on-off valve 5c of the combustion exhaust gas supply mechanism 5, and to control other elements of the fuel cell system 101A. .

[Operation]
Next, an operation of the fuel cell system 101A configured as described above (an operation method of the fuel cell system 101A) will be described. The fuel cell system 101A includes a power generation operation for performing a power generation operation, a stop state in which elements other than the controller 21 are stopped (standby operation), a start operation for shifting the fuel cell system 101A from the stop state to a power generation operation, The fuel cell system 101A has four operation modes including a stop operation that shifts the fuel cell system 101A from the power generation operation to the stop state. Specifically, the activation operation refers to a period from when the controller 21 outputs an activation signal to immediately before the fuel cell 1 starts power generation.

  FIG. 2 is a flowchart showing the start-up operation of the fuel cell system of FIG. The following operations are performed under the control of the controller 21. In the stop state, both the first on-off valve 5b and the second on-off valve 5c are closed.

  As shown in FIG. 2, when the start-up operation is started, the hydrogen generator 2 is warmed up (step S1). Specifically, combustion air and combustion fuel gas are supplied to the burner 4 and the burner 4 is ignited. As a result, the combustion fuel gas is burned with the combustion air in the burner 4, and combustion exhaust gas with a high dew point is generated. This combustion exhaust gas is discharged to the atmosphere through the combustion exhaust gas line 10. Further, the hydrogen generator 2 is heated and warmed by the combustion in the burner 4. In accordance with this, the fuel cell 1 is also appropriately warmed up.

  When the warm-up of the hydrogen generator 2 is completed, combustion exhaust gas is supplied to the cathode 1b of the fuel cell 1 (step S2). Specifically, the first on-off valve 5b is opened while the second on-off valve 5c is closed. Then, the combustion exhaust gas generated by the burner 4 is supplied to the cathode 1b of the fuel cell 1 through the combustion exhaust gas line 10, the combustion exhaust gas branch line 5a, and the oxidant gas supply line 7. As a result, the polymer electrolyte membrane is moistened with water contained in the combustion exhaust gas having a high dew point, and the water content of the polymer electrolyte membrane is increased. Whether or not the hydrogen generator 2 has been warmed up is determined, for example, by monitoring the temperature of the hydrogen generator 2 or by measuring the elapsed time from the start of warm-up.

  Next, a hydrogen-containing gas is supplied to the anode 1a of the fuel cell 1 (step S3). Specifically, a raw material gas and water are supplied to the hydrogen generator 2, a hydrogen-containing gas is generated by a steam reforming reaction, and the generated hydrogen-containing gas passes through the fuel gas supply line 6 to form the fuel cell 1. To the anode 1a. The hydrogen-containing gas appropriately contains water that was not used for the steam reforming reaction.

  Next, an oxidant gas is supplied to the cathode 1b of the fuel cell 1 (step S4). Specifically, the second on-off valve 5c is opened and the oxidant gas supply device 3 is started, and air as the oxidant gas is mixed with the combustion exhaust gas in the middle through the oxidant gas supply line 7. To the cathode 1b of the fuel cell 1. Thereby, although the fuel cell 1 is in an open circuit state, the water content of the polymer electrolyte membrane is relatively increased by the water in the combustion exhaust gas having a high dew point, so that the deterioration of the polymer electrolyte membrane is suppressed. The

  Next, power generation is started (step S5). Specifically, the fuel cell 1 is connected to an external circuit (load), whereby the fuel cell 1 starts power generation. Thereby, the fuel cell system 101A shifts to the power generation operation, and the startup operation is completed. Thereafter, when a stop signal is output from the controller 21, the fuel cell system 101 </ b> A enters a stop state through a stop operation.

  Here, the supply period of the combustion exhaust gas to the cathode 1b is a period in which the polymer electrolyte membrane can be moistened to such an extent that deterioration of the polymer electrolyte membrane can be prevented while the fuel cell 1 is in an open circuit state. Good. Therefore, as long as the deterioration of the polymer electrolyte membrane can be prevented, the supply of combustion exhaust gas to the cathode 1b can be stopped at an arbitrary timing. For example, the supply of the combustion exhaust gas to the cathode 1b may be stopped before, simultaneously with, and after the supply of the oxidant gas to the cathode 1b. Further, in the power generation operation, the supply of the combustion exhaust gas to the cathode 1b may be continued.

  According to the fuel cell system and the operation method thereof according to the first embodiment as described above, the polymer electrolyte type operated under low humidification conditions with a simple configuration in which the combustion exhaust gas supply mechanism 5 is provided. Degradation of the polymer electrolyte membrane of the fuel cell 1 can be prevented.

(Embodiment 2)
FIG. 3 is a block diagram schematically showing the configuration of the fuel cell system according to Embodiment 2 of the present invention. FIG. 4 is a flowchart showing the starting operation of the fuel cell system of FIG.

  As shown in FIG. 3, the fuel cell system 101B of the second embodiment is different from the fuel cell system 101A of the first embodiment in the configuration of the combustion exhaust gas supply mechanism 5, and the others are the fuel cell system 101A of the first embodiment. Is the same.

  The combustion exhaust gas supply mechanism 5 in the fuel cell system 101B of Embodiment 2 includes a combustion exhaust gas branch line 5a and a three-way valve 5d. The three-way valve 5d is provided at the connection point between the combustion exhaust gas branch line 5a and the oxidant gas supply line 7, and is controlled by the controller 21 to combust with the upstream portion of the oxidant gas supply line 7 from the three-way valve 5d. The exhaust gas branch line 5a is selectively connected to a portion of the oxidant gas supply line 7 downstream from the three-way valve 5d. As a result, the oxidant gas from the oxidant gas supply device 3 and the combustion exhaust gas generated by the burner 4 are selectively supplied to the cathode 1 b of the fuel cell 1.

  As shown in FIG. 4, the operation (operating method) of the fuel cell system 101B configured as described above is the same as the operation of the fuel cell system 101A of the first embodiment except that step S4 is replaced with step S6. The operation is the same as that of the fuel cell system 101A of the first embodiment. In step S6, the oxidant gas is supplied to the cathode 1b of the fuel cell 1, and at the same time, the supply of combustion exhaust gas to the cathode 1b of the fuel cell 1 is stopped.

  According to the fuel cell system 101B of the second embodiment as described above, the same effects as those of the first embodiment can be obtained, and the configuration of the combustion exhaust gas supply mechanism 5 can be further simplified.

(Embodiment 3)
FIG. 5 is a block diagram schematically showing the configuration of the fuel cell system according to Embodiment 3 of the present invention. FIG. 6 is a flowchart showing the starting operation of the fuel cell system of FIG.

  As shown in FIG. 5, the fuel cell system 101C of the third embodiment is different from the fuel cell system 101A of the first embodiment in that the configuration for supplying the combustion fuel gas to the burner 4 is specifically specified. The other differences are the same as those of the fuel cell system 101A of the first embodiment.

  In the fuel cell system 101B of the third embodiment, the fuel gas discharge line 8 is connected to the combustion fuel gas inlet (not shown) of the burner 4. Further, a fuel gas bypass line 31 that connects the fuel gas supply line 6 and the fuel gas discharge line 8 is provided, and a three-way valve 32 is provided at a connection point between the fuel gas bypass line 31 and the fuel gas discharge line 8. Yes. Under the control of the controller 21, the three-way valve 32 selectively selects a portion upstream of the three-way valve 32 of the fuel gas supply line 6 as a portion downstream of the three-way valve 32 of the fuel gas supply line 6 and the fuel gas bypass line 31. Connect to. As a result, the hydrogen-containing gas generated by the hydrogen generator 2 is selectively supplied to the burner 4 and the anode 1 a of the fuel cell 1.

  Next, the operation (operation method) of the fuel cell system 101C configured as described above will be described.

  As shown in FIG. 6, when the start-up operation is started, the hydrogen generator 2 is warmed up (step S11). The method for warming up the hydrogen generator 2 is basically the same as in the first embodiment. However, in the third embodiment, the three-way valve 32 is controlled to connect the portion upstream of the three-way valve 32 of the fuel gas supply line 6 to the fuel gas bypass line 31, thereby generating the hydrogen generator 2. A hydrogen-containing gas is supplied to the burner 4 as a combustion fuel gas. The burner 4 warms up the hydrogen generator 2 by burning the hydrogen-containing gas.

  When the warm-up of the hydrogen generator 2 is completed, a hydrogen-containing gas is supplied to the anode 1a of the fuel cell 1 (step S12). Specifically, the three-way valve 32 is controlled to connect a portion of the fuel gas supply line 6 upstream of the three-way valve 32 to a portion of the fuel gas supply line 6 downstream of the three-way valve 32. As a result, the hydrogen-containing gas generated by the hydrogen generator 2 is supplied to the anode 1 a of the fuel cell 1. Further, the hydrogen-containing gas (off gas) that has not been consumed in the fuel cell 1 is supplied to the burner 4 through the fuel gas discharge line 8 as a combustion fuel gas, and is burned by the burner 4.

  Next, combustion exhaust gas is supplied to the cathode 1b of the fuel cell 1 (step S13), and then an oxidant gas is supplied to the cathode 1b of the fuel cell 1 (step S14), and then power generation is started (step S14). S15). Since specific operations in these steps are the same as those in the first embodiment, the description thereof is omitted.

  According to the fuel cell system 101C of the third embodiment, the same effect as that of the first embodiment can be obtained. Further, since the hydrogen-containing gas is supplied to the anode 1a before the oxidant gas is supplied to the cathode 1b of the fuel cell 1, the oxidant gas is mixed into the anode 1a through the polymer electrolyte membrane. An increase in potential of the anode 1a can be prevented, and deterioration of the catalyst of the anode 1a can be suppressed. Further, since the hydrogen-containing gas is supplied to the anode 1a and then air is supplied to the cathode 1b as the oxidant gas, even if air remains in the anode 1a, no polarity is reversed, and the anode 1a and It is possible to sufficiently ensure the durability of the catalyst layer of the cathode 1b.

  In addition, you may comprise so that raw material gas may be supplied to the burner 4 for the predetermined time after starting of the fuel cell system 101C.

(Embodiment 4)
FIG. 7 is a block diagram schematically showing the configuration of the fuel cell system according to Embodiment 4 of the present invention.

  As shown in FIG. 7, in the fuel cell system 101D of the fourth embodiment, a radiator 33 is provided in a portion of the combustion exhaust gas line 10 upstream of the connection point between the combustion exhaust gas line 10 and the combustion exhaust gas branch line 5a. This is different from the fuel cell system 101A of the first embodiment, and the other points are the same as those of the fuel cell system 101A of the first embodiment.

  The radiator 33 is configured to dissipate the combustion exhaust gas flowing through the combustion exhaust gas line 10. Specifically, for example, it can be constituted by a pipe line having fins on the surface thereof, through which the combustion exhaust gas flows, and a wind cooling fan that blows air to the surface of the pipe line to cool it. For example, you may comprise with the heat exchanger which makes a combustion exhaust gas heat-exchange with a cooling fluid, and cools it. In this case, hot water stored in a hot water supply system that recovers and uses the exhaust heat of the fuel cell 1 may be used as the cooling fluid.

  According to the fourth embodiment configured as described above, the same effect as that of the first embodiment is obtained, and the combustion exhaust gas in which the relative humidity is increased by lowering the temperature of the high-temperature combustion exhaust gas by the radiator 33 is the fuel cell. Since it is supplied to one cathode 1b, the polymer electrolyte membrane can be more suitably moistened.

(Embodiment 5)
FIG. 8 is a block diagram schematically showing the configuration of the fuel cell system according to Embodiment 5 of the present invention.

  As shown in FIG. 8, in the fuel cell system 101E of the fifth embodiment, a catalytic combustor 34 is provided in a portion of the combustion exhaust gas line 10 upstream of the connection point between the combustion exhaust gas line 10 and the combustion exhaust gas branch line 5a. This is different from the fuel cell system 101A of the first embodiment, and the other points are the same as those of the fuel cell system 101A of the first embodiment.

The catalytic combustor 34 is configured to catalytically burn the combustion exhaust gas flowing through the combustion exhaust gas line 10. Specifically, the catalytic combustor 34 is composed of, for example, a reaction vessel provided with a platinum catalyst supported on a honeycomb-like alumina carrier, and CO (carbon monoxide) and NO _x (nitrogen oxide) in the combustion exhaust gas. The combustion exhaust gas is catalytically burned to be oxidized. When supplying combustion exhaust gas to the cathode 1b of the fuel cell 1, it is necessary to reduce the ratio of oxygen in the combustion exhaust gas. This is because if the ratio of oxygen is high, the potential of the cathode 1b increases and the catalyst may be oxidized and deteriorated. However, in order to reduce the ratio of oxygen in the combustion exhaust gas, it is necessary to reduce the amount of combustion air supplied to the burner 4 as much as possible, and CO is easily produced as a by-product during combustion of the combustion fuel gas. Further, since the combustion temperature of the burner 4 is high, NO _x may be produced as a by-product. These CO and NO _x may poison the catalyst of the cathode 1b of the fuel cell 1. Therefore, by providing the catalytic combustor 34, CO and NO _x in the combustion exhaust gas is oxidized to a compound which does not poison the catalyst of the cathode 1b. Thereby, the catalyst poisonous substance in the combustion exhaust gas supplied to the cathode 1b can be removed. As a result, the same effect as in the first embodiment can be obtained, and the durability of the fuel cell 1 can be further improved. Note that the catalyst of the catalytic combustor 34 may oxidize either CO or NO _x .

(Embodiment 6)
The sixth embodiment of the present invention exemplifies the starting operation at the time of abnormal stop of the fuel cell systems 101A to 101E of the first to fifth embodiments.

  FIG. 9 is a flowchart showing the starting operation at the time of abnormal stop of the fuel cell system according to Embodiment 6 of the present invention.

  As shown in FIG. 9, in the sixth embodiment, after the fuel cell systems 101A to 101E stop abnormally, the hydrogen generator 2 is first started to restart (step S21).

  Next, a hydrogen-containing gas is supplied to the anode 1a of the fuel cell 1 (step S22).

  Next, combustion exhaust gas is supplied to the cathode 1b of the fuel cell 1 (step S23).

  Next, an oxidant gas is supplied to the cathode 1b of the fuel cell 1 (step S24).

  Next, power generation is started (step S25).

  In addition, since the specific operation | movement in step S22-24 is the same as the starting operation of fuel cell system 101A-101E of Embodiment 1 thru | or 5, the description is abbreviate | omitted.

For example, when methane gas is used as a raw material,
CH ₄ + 2O ₂ + 8N ₂ → CO ₂ + 2H ₂ O + 8N ₂
The reaction proceeds. When this reaction proceeds completely, 2 / (1 + 2 + 8) = 2/11 of the combustion gas becomes water. Here, since 1 atmospheric pressure = 1013 hPa, the water vapor pressure is 1013 × 2/11 = 184.18 hPa.

  And since the saturated water vapor pressure at the time of 58.3 degreeC is 184.18 hPa, the dew point of this combustion gas is 58 degreeC. Therefore, by burning the raw material containing methane gas as a main component as the combustion fuel in the burner 4, the temperature of the fuel cell 1 is 58 ° C. or higher and the oxidant gas dew point at the cathode 1b is 58 ° C. or lower. In the fuel cell systems 101A to 101E, when the fuel cell system 101A to 101E stops abnormally and then restarts, it is possible to prevent the open circuit state of the fuel cell 1 under the low humidification condition by this operation method. It is possible to ensure sufficient performance.

  In order to obtain such an effect, the fuel cell systems 101A to 101E of the first to fifth embodiments use, for example, natural gas (more preferably methane gas) as a raw material gas to generate hydrogen. What is necessary is just to comprise so that the said raw material gas may be supplied to the burner 4 as combustion fuel gas for a predetermined time from the starting of the device 2.

(Other embodiments)
In the first to sixth embodiments, the hydrogen generator 2 may be configured to include a reforming unit that generates a hydrogen-containing gas from the raw material gas by a steam reforming reaction, a shift unit, and / or a CO reduction unit. Here, the shift unit has a function of reducing the CO concentration of the hydrogen-containing gas generated in the reforming unit by a shift reaction. Further, the CO reduction unit has a function of reducing the CO concentration of the hydrogen-containing gas flowing out from the reforming unit or the shift unit by an oxidation reaction or a methanation reaction. With this configuration, a hydrogen-containing gas with a reduced CO concentration can be supplied to the anode 1a of the fuel cell 1 as a fuel gas.

  In Embodiments 1 to 6, the supply start timing of the hydrogen-containing gas to the anode 1a may be any timing from the completion of warming-up of the hydrogen generator 2 to the start of power generation. However, from the viewpoint of suppressing the deterioration of the catalyst of the anode 1a due to the oxidant gas being mixed into the anode 1a through the polymer electrolyte membrane, it is preferable before the supply of the oxidant gas to the cathode 1b is started.

  The second embodiment may be modified as in any of the third to sixth embodiments. In addition, Embodiments 1 to 6 may be combined as appropriate as long as they do not exclude each other.

  From the foregoing description, many modifications and other embodiments of the present invention are obvious to one skilled in the art. Accordingly, the foregoing description should be construed as illustrative only and is provided for the purpose of teaching those skilled in the art the best mode of carrying out the invention. The details of the structure and / or function may be substantially changed without departing from the spirit of the invention.

  INDUSTRIAL APPLICABILITY The fuel cell system and the operation method thereof according to the present invention are useful as a fuel cell system capable of preventing deterioration of a polymer electrolyte membrane due to an open circuit state under a low humidification condition when starting the fuel cell, and an operation method thereof. It is.

DESCRIPTION OF SYMBOLS 1 Fuel cell 1a Anode 1b Cathode 2 Hydrogen generator 3 Oxidant gas supply device 4 Burner 5 Combustion exhaust gas supply mechanism 5a Combustion exhaust gas branch line 5b 1st on-off valve 5c 2nd on-off valve 5d Three-way valve 6 Fuel gas supply line 7 Oxidant Gas supply line 8 Fuel gas discharge line 9 Oxidant gas discharge line 10 Combustion exhaust gas line 11 Internal fuel gas path 12 Internal oxidant gas path 21 Controller 31 Fuel gas bypass line 32 Three-way valve 33 Radiator 34 Catalytic combustor 101A Fuel cell System 101B Fuel cell system 101C Fuel cell system 101D Fuel cell system 101E Fuel cell system

Claims (10)

A polymer electrolyte fuel cell that generates electricity using a hydrogen-containing gas supplied to the anode and an oxidant gas containing oxygen supplied to the cathode;
A hydrogen generator for generating a hydrogen-containing gas by subjecting a raw material gas to a steam reforming reaction, and supplying the generated hydrogen-containing gas to the anode of the fuel cell;
An oxidant gas supply device for supplying the oxidant gas to the cathode of the fuel cell;
A burner for burning combustion fuel gas with combustion air to produce combustion exhaust gas containing water, and supplying the hydrogen generator with heat necessary for the steam reforming reaction by the combustion;
A fuel cell system comprising: a combustion exhaust gas supply mechanism configured to supply combustion exhaust gas generated by the burner to a cathode of the fuel cell during a startup operation of the fuel cell system. The combustion exhaust gas supply mechanism is configured to selectively supply the oxidant gas from the oxidant gas supplier and the combustion exhaust gas generated by the burner to the cathode of the fuel cell;
The combustion exhaust gas supply mechanism supplies the combustion exhaust gas generated by the burner to the cathode of the fuel cell during the start-up operation of the fuel cell system, and then supplies the oxidant gas from the oxidant gas supply device to the cathode. The fuel cell system according to claim 1, wherein the fuel cell system is configured to supply a cathode of the fuel cell.   During the start-up operation of the fuel cell system, after the fuel gas supply device supplies the hydrogen-containing gas to the anode of the fuel cell, the combustion exhaust gas supply mechanism converts the combustion exhaust gas generated by the burner into the cathode of the fuel cell. The fuel cell system of claim 1, wherein the oxidant gas supplier is configured to supply the oxidant gas to a cathode of the fuel cell.   2. The fuel cell system according to claim 1, further comprising a radiator that is provided in a path of combustion exhaust gas supplied from the burner to the cathode of the fuel cell by the combustion exhaust gas supply mechanism and releases heat to the combustion exhaust gas. Wherein it provided from the burner by the combustion exhaust gas supply mechanism in the path of the flue gas supplied to the cathode of the fuel cell, a catalytic combustor which catalytic combustion of the flue gas so as to oxidize CO or NO _x in the combustion in the exhaust gas The fuel cell system according to claim 1, further comprising: A polymer electrolyte fuel cell that generates electricity using a hydrogen-containing gas supplied to the anode and an oxidant gas containing oxygen supplied to the cathode;
A hydrogen generator for generating a hydrogen-containing gas by subjecting a raw material gas to a steam reforming reaction, and supplying the generated hydrogen-containing gas to the anode of the fuel cell;
An oxidant gas supply device for supplying the oxidant gas to the cathode of the fuel cell;
A burner for burning combustion fuel gas with combustion air to produce combustion exhaust gas containing water, and supplying the hydrogen generator with heat necessary for the steam reforming reaction by the combustion;
A combustion exhaust gas supply mechanism for supplying combustion exhaust gas generated by the burner to the cathode of the fuel cell, and a method for operating a fuel cell system,
A method for operating a fuel cell system, wherein the combustion exhaust gas generated by the burner is supplied to a cathode of the fuel cell by using the combustion exhaust gas supply mechanism during start-up operation of the fuel cell system. The combustion exhaust gas supply mechanism is configured to selectively supply the oxidant gas from the oxidant gas supplier and the combustion exhaust gas generated by the burner to the cathode of the fuel cell;
The combustion exhaust gas supply mechanism is used to supply the combustion exhaust gas generated by the burner to the cathode of the fuel cell during the start-up operation of the fuel cell system, and then the oxidant gas from the oxidant gas supplier The method for operating the fuel cell system according to claim 6, wherein the fuel cell system is supplied to a cathode of the fuel cell.   During the start-up operation of the fuel cell system, the fuel gas supply device is used to supply the hydrogen-containing gas to the fuel cell anode, and then the combustion exhaust gas generated by the burner is fueled using the combustion exhaust gas supply mechanism. The method for operating a fuel cell system according to claim 6, wherein the fuel cell system is supplied to the battery cathode, and then the oxidant gas is supplied to the cathode of the fuel cell using the oxidant gas supplier.   The fuel cell system according to claim 6, wherein heat is released to the combustion exhaust gas using a radiator provided in a path of the combustion exhaust gas supplied from the burner to the cathode of the fuel cell by the combustion exhaust gas supply mechanism. Driving method.   The combustion exhaust gas is catalyzed to oxidize carbon monoxide in the combustion exhaust gas by using a catalytic fuel device provided in a path of the combustion exhaust gas supplied from the burner to the cathode of the fuel cell by the combustion exhaust gas supply mechanism. The operation method of the fuel cell system according to claim 6, wherein the fuel cell system is burned.

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