JP2007042445A - Fuel cell system and power generation shutdown method of fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system capable of exhausting remaining water with a moisturized status of a solid polymer electrolyte membrane maintained at the time of stopping of the fuel cell system. <P>SOLUTION: The fuel cell system 1 controls power generation before stopping to make an amount of residual water per unit hour more than an amount at the time of normal power generation, subtracting an amount of drained water by a fuel cell 4 from an amount of water supplied to the fuel cell 4 and generated water, then the power generation before stopping is stopped after a predetermined time is passed, switching valves 8, 9, 13, 14 are switched to a bypass side, and the fuel cell 4 is purged by moisture gas lower in humidity than at the time of normal operation. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fuel cell system including a fuel cell that generates electric power by reacting a fuel gas and an oxidant gas by an electrochemical reaction, and in particular, when the fuel cell system is stopped, the wet state of the solid polymer electrolyte membrane is changed. The present invention relates to a fuel cell system that controls to discharge residual water while maintaining the power generation stop method.

  The fuel cell has a structure in which an electrolyte is sandwiched between a fuel electrode and an oxidant electrode, and generates power by supplying fuel gas to the fuel electrode and supplying oxidant gas to the oxidant electrode. When an automobile is used, a solid polymer electrolyte membrane generally having hydrogen ion conductivity is often used as an electrolyte. When hydrogen is supplied as the fuel gas and air is supplied as the oxidant gas to the fuel cell, electric power is generated by an electrochemical reaction between hydrogen and oxygen. At this time, since the fuel cell only discharges water as a by-product, there is an advantage that a substance that damages the global environment such as carbon dioxide as in an internal combustion engine is not released.

  However, if the generated water is not properly removed from the fuel cell, the water remains in the reaction gas flow path and the gas diffusion layer and inhibits diffusion of the reaction gas. In general, this phenomenon is called “flooding”, which is a factor that causes a decrease in power generation performance because it prevents the reaction gas from reaching the catalyst. As a countermeasure, a method of improving the removal performance of pure water by changing the operating conditions such as increasing the temperature of the reaction gas or increasing the flow rate of the reaction gas is often used.

  However, in such a method, much energy must be consumed for increasing the temperature of the reaction gas and increasing the flow rate, and the efficiency of the system is reduced. Further, if there is a portion where the temperature of the reaction gas decreases from the reaction gas inlet to the outlet in the fuel cell or the flow rate of the reaction gas decreases, water condenses as a result. Furthermore, when the outside air temperature is low, such as below freezing point, water saturation occurs in addition to the extremely low saturated water vapor pressure. As a result, removal of water by the reaction gas may become almost impossible.

Therefore, as a countermeasure, for example, in the fuel cell system disclosed in Japanese Patent Application Laid-Open No. 2004-111196 (Patent Document 1), when the operation is stopped, the dried fuel gas is supplied to the anode, and the dried oxidant gas is supplied to the cathode. While supplying, an output current smaller than the normal output current is taken out, and then the operation is stopped.
JP 2004-111196 A

  However, in the conventional fuel cell system described above, since the output current is small, there is a problem that it takes time until the inside of the fuel cell reaches a wet state.

  Moreover, since it is dry gas power generation, the water distribution inside the cell becomes non-uniform, and there is a problem that a place to dry out locally occurs.

  Further, since the operation is stopped as it is after power generation, there is a problem that the generated water staying in the gas flow path freezes in a sub-freezing environment to prevent restart.

  In order to solve the above-described problems, the present invention is characterized in that a fuel cell and an oxidant gas are supplied to a fuel cell having a structure in which a solid polymer electrolyte membrane is sandwiched between a fuel electrode and an oxidant electrode. In a fuel cell system that generates electricity, the amount of residual water per unit time obtained by subtracting the amount of water discharged by the fuel cell from the total amount of water supplied to the fuel cell and generated water is greater than during normal power generation. Power generation before stop is performed, and after a preset time has elapsed, power generation before stop is stopped, and the fuel cell is purged with a gas having a lower humidity than during normal operation.

  In the present invention, the power generation is stopped after the power generation before the stop is performed so that the amount of residual water per unit time is controlled to be larger than that during the normal power generation, and then the fuel cell is gas having a lower humidity than that during the normal operation. Therefore, it is possible to prevent only the water in the gas flow path from being discharged and remaining without keeping the solid polymer electrolyte membrane in a wet state. As a result, without causing flooding, even if the fuel cell system is in an environment below freezing point, it is possible to prevent the gas flow path from being blocked and to restart it.

  Embodiments of the present invention will be described below with reference to the drawings. In the description of the drawings, the same or similar parts are denoted by the same or similar reference numerals.

<First Embodiment>
DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, a first embodiment of the invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the fuel cell system according to this embodiment.

  As shown in FIG. 1, the fuel cell system 1 of this embodiment includes a fuel cell 4 having a fuel electrode 2 and an oxidant electrode 3, a control device 5 that controls the fuel cell system 1, and a fuel electrode 2. A fuel gas flow rate control device 6 that controls the flow rate of the supplied fuel gas, a fuel gas humidification device 7 that humidifies the fuel gas, and a fuel gas flow path is switched between the fuel gas humidification device 7 side and the bypass side. Fuel gas switching valves 8 and 9, a fuel gas outlet valve 10 installed at the reaction gas outlet of the fuel electrode 2, and an oxidant gas flow rate control device 11 that controls the flow rate of the oxidant gas supplied to the oxidant electrode 3. An oxidant gas humidifier 12 for humidifying the oxidant gas, oxidant gas switching valves 13 and 14 for switching the flow path of the oxidant gas to either the oxidant gas humidifier 12 side or the bypass side, and an oxidant At the reaction gas outlet of pole 3 And an oxidant gas outlet valve 15 which is location.

  Here, the fuel cell 4 is supplied with hydrogen gas, which is a fuel gas, at the fuel electrode 2, and is supplied with air gas, which is an oxidant gas, at the oxidant electrode 3, and generates power by the following electrochemical reaction.

Fuel ^{_{electrode: H 2 → 2H + + 2e}} - (1)
Oxidant electrode: 2H ⁺ + 2e ⁻ + (1/2) O ₂ → H ₂ O (2)
Although not shown, the control device 5 controls the fuel cell system 1 based on information from various sensors such as a pressure sensor and a temperature sensor to perform normal power generation and stop the fuel cell system 1. A stop process of the fuel cell 4 is performed. At this time, the humidity of the fuel gas is controlled by controlling the fuel gas switching valves 8 and 9, and the humidity of the oxidant gas is controlled by controlling the oxidant gas switching valves 13 and 14. The fuel gas outlet valve 10 and the oxidant gas outlet valve 15 are controlled to control the pressure of the fuel gas and the oxidant gas at the inlet of the fuel cell 4, and the fuel gas flow rate control device 6 and the oxidant gas flow rate control device are controlled. 11, the flow rates of the fuel gas and the oxidant gas are controlled.

  The fuel gas switching valves 8 and 9 and the oxidant gas switching valves 13 and 14 are three-way valves that switch the flow path between the humidifying device side and the bypass flow path side, and switch the flow paths based on the control of the control device 5. Yes.

  The fuel gas outlet valve 10 and the oxidant gas outlet valve 15 have their valves opened and closed and their opening degrees adjusted based on the control of the control device 5.

  In the fuel cell system 1 configured as described above, in the fuel gas supply system, the fuel gas flow control device 6 adjusts the flow rate of the high-pressure fuel gas supplied from the fuel tank. Then, during normal power generation, the fuel gas switching valves 8 and 9 are switched to the fuel gas humidifying device 7 side, and the fuel gas is sent to the fuel gas humidifying device 7 where it is humidified to the fuel electrode 2 of the fuel cell 4. Supplied. At this time, the pressure of the fuel gas at the inlet of the fuel cell 4 is adjusted by controlling the opening degree of the fuel gas outlet valve 10.

  On the other hand, in the oxidant gas supply system for supplying the oxidant gas, the oxidant gas flow rate control device 11 adjusts the flow rate of the oxidant gas introduced from the outside and pressurized. Then, during normal power generation, the oxidant gas switching valves 13 and 14 are switched to the oxidant gas humidifier 12 side, and the oxidant gas is sent to the oxidant gas humidifier 12, where it is humidified and is supplied to the fuel cell 4. It is supplied to the oxidant electrode 3. At this time, the pressure of the oxidant gas at the inlet of the fuel cell 4 is adjusted by controlling the opening degree of the oxidant gas outlet valve 15.

  Next, the fuel cell stop process by the fuel cell system 1 of the present embodiment will be described based on the flowchart of FIG. As shown in FIG. 2, when a command to stop the fuel cell system 1 is first input (S201), the control device 5 closes the fuel gas outlet valve 10 and the oxidant gas outlet valve 15 to close the inside of the fuel cell 4. The pressures of the fuel gas and oxidant gas are increased (S202). At the same time, the fuel gas flow rate control device 6 and the oxidant gas flow rate control device 11 are controlled to reduce the flow rates of the fuel gas and the oxidant gas supplied to the fuel cell 4 to the limit where the reaction gas deficiency can be avoided. In this way, power generation before stoppage is performed (S203). Thereby, the utilization factor of fuel gas and oxidant gas can be made larger than during normal power generation.

  Then, power generation before stop is performed until a preset time elapses (S204), and then power generation of the fuel cell 4 is stopped (S205). Thereafter, the fuel gas switching valves 8 and 9 and the oxidant gas switching valves 13 and 14 are switched to the bypass side (S206), and the flow path is switched to bypass the fuel gas humidifying device 7 and the oxidant gas humidifying device 12. Purging is performed by supplying dry fuel gas and oxidant gas to the battery 4 (S207).

  Then, after supplying dry gas until a preset time has elapsed (S208), the fuel cell system 1 is stopped (S209), and the fuel cell stop process by the fuel cell system 1 of the present embodiment is terminated.

  Here, the effect | action by the fuel cell system 1 of this embodiment is demonstrated based on FIG. FIG. 3 is a diagram showing a change in the amount of residual water remaining inside the fuel cell 4 in the fuel cell system 1 of the present embodiment. The amount of residual water shown here is the amount of residual water per unit time obtained by subtracting the amount of water discharged by the fuel cell 4 from the total amount of water supplied to the fuel cell 4 and produced water.

  As shown in FIG. 3, when the fuel cell system 1 is stopped, first, the power generation before stop shown in step S203 is performed, so that the residual water amount is before the fuel cell stop processing is performed, that is, compared with the normal power generation. It will increase. Then, by performing power generation before stopping for a preset time, more residual water remains in the fuel cell 4 than during normal power generation.

  Thereafter, when the power generation before the stop is stopped and the gas flow path is purged with the dry gas shown in step S207, the water remaining inside the fuel cell 4 is discharged, and the residual water amount decreases. At this time, if the purge condition is set optimally, only the water in the gas channel can be discharged to the outside while the solid polymer electrolyte membrane is kept wet. This optimal purge condition varies depending on the fuel cell specifications, but it can be optimized by using general methods to optimize parameters such as purge gas flow rate, purge time, purge gas temperature, and relative humidity. Can be set.

  As described above, in the fuel cell system 1 according to the present embodiment, the power generation is stopped after the power generation before stop is performed so that the residual water amount per unit time is controlled to be larger than that during normal power generation, and then the fuel cell 4 is stopped. Is purged with a gas having a humidity lower than that during normal operation, so that only the water in the gas flow path can be discharged to the outside without leaving the solid polymer electrolyte membrane in a wet state. As a result, without causing flooding, even if the fuel cell system 1 is in an environment below freezing point, it is possible to prevent the gas flow path from being blocked and to restart it.

  Further, in the fuel cell system 1 of the present embodiment, the pressure of the fuel gas or the oxidant gas at the inlet of the fuel cell 4 is controlled so as to be larger than that during normal power generation during power generation before stoppage. It is possible to control so that the amount of residual water per unit time during power generation is increased compared to that during normal power generation.

  Further, in the fuel cell system 1 of the present embodiment, the flow rate of the fuel gas or oxidant gas is set so that the utilization rate of the fuel gas or oxidant gas is greater than the utilization rate during normal power generation during power generation before stoppage. Since it controls, it can control so that the amount of residual water per unit time at the time of power generation before stop may be increased from that during normal power generation.

<Second Embodiment>
Hereinafter, a second embodiment of the present invention will be described with reference to the drawings. FIG. 4 is a block diagram showing the configuration of the fuel cell system according to this embodiment.

  As shown in FIG. 4, the fuel cell system 41 of the present embodiment includes a fuel electrode differential pressure gauge 42 that measures a differential pressure between the inlet and outlet of the fuel electrode 2, and an inlet and outlet of the oxidant electrode 3. The first embodiment differs from the first embodiment in that it further includes an oxidant electrode differential pressure gauge 43 that measures the differential pressure therebetween and a cooling system for cooling the fuel cell 4.

  Here, the cooling system includes a cooling liquid pump 44 for circulating the cooling liquid, a cooling liquid tank 45 for storing the cooling liquid, a cooling liquid flow path 46 provided in the fuel cell 4, and a radiator fan 47. And a radiator 48 that radiates the cooling water by cooling air.

  Next, the fuel cell stop process by the fuel cell system 41 of the present embodiment will be described based on the flowchart of FIG. As shown in FIG. 5, when a command to stop the fuel cell system 41 is input (S501), the control device 5 controls the fuel gas humidifier 7 and the oxidant gas humidifier 12 to enter the fuel cell 4 at the inlet. The relative humidity of the fuel gas and the oxidant gas is raised to be higher than that during normal power generation (S502). At the same time, the number of revolutions of the coolant pump 44 is increased to lower the temperature of the coolant flowing through the coolant flow path 46 inside the fuel cell 4 to lower the temperature of the fuel cell 4 (S503).

  In this state, the fuel gas flow rate control device 6 and the oxidant gas flow rate control device 11 are controlled so that the flow rates of the fuel gas and the oxidant gas supplied to the fuel cell 4 can be avoided by the reaction gas deficiency state. The power generation before stoppage is performed while reducing the power to the minimum (S504). Thereby, the utilization factor of fuel gas and oxidant gas can be made larger than during normal power generation.

  Here, during the power generation before the stop, it is monitored whether or not the differential pressure detected by the fuel electrode differential pressure gauge 42 or the oxidant electrode differential pressure gauge 43 exceeds a preset value (S505), and the differential pressure is set to a set value. If it does not exceed, power generation before stop is performed until a preset time elapses (S506), and then power generation of the fuel cell 4 is stopped (S507). In step S505, when the differential pressure detected by the fuel electrode differential pressure gauge 42 or the oxidant electrode differential pressure gauge 43 exceeds the set value, power generation is immediately stopped to prevent flooding (S507).

  When the power generation before the stop is thus stopped, the fuel gas switching valves 8 and 9 and the oxidant gas switching valves 13 and 14 are then switched to the bypass side (S508), and the fuel gas humidifier 7 and the oxidant gas humidifier 12 are bypassed. Thus, the flow path is switched and the fuel cell 4 is supplied with the dried fuel gas and oxidant gas to perform purging (S509).

  Then, after supplying dry gas until a preset time has elapsed (S510), the fuel cell system 1 is stopped (S511), and the fuel cell stop process by the fuel cell system 41 of the present embodiment is ended.

  Thus, in the fuel cell system 41 of the present embodiment, since the relative humidity of the fuel gas or the oxidant gas at the inlet of the fuel cell 4 is controlled to be greater than that during normal power generation during power generation before stoppage, It is possible to control so that the amount of residual water per unit time at the time of power generation before stoppage is increased compared to that at the time of normal power generation.

  Further, in the fuel cell system 41 of the present embodiment, since the internal temperature of the fuel cell 4 is controlled to be lower than that during normal power generation during power generation before stoppage, the residual per unit time during power generation before stoppage is maintained. The amount of water can be controlled so as to increase compared to that during normal power generation.

  Further, in the fuel cell system 41 of this embodiment, when the pressure of the fuel gas or oxidant gas at the inlet of the fuel cell 4 becomes higher than a predetermined pressure, the power generation of the fuel cell 4 is stopped and the normal operation is started. In addition, since the purge is performed with the low-humidity gas, the fuel cell system 41 can be stopped without causing the power generation stop due to flooding.

  Although the fuel cell system of the present invention has been described based on the illustrated embodiment, the present invention is not limited to this, and the configuration of each part is replaced with an arbitrary configuration having the same function. Can do.

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell system including a fuel cell that generates electric power by reacting a fuel gas and an oxidant gas by an electrochemical reaction, and particularly when the fuel cell system is stopped, the solid polymer electrolyte membrane remains in a wet state. It is extremely useful as a technique for enabling restarting even in a sub-freezing environment by controlling to discharge water.

1 is a block diagram showing a configuration of a fuel cell system according to a first embodiment of the present invention. It is a flowchart which shows the fuel cell stop process by the fuel cell system which concerns on the 1st Embodiment of this invention. It is a figure which shows the change of the residual water amount inside the fuel cell in the fuel cell system of this invention. It is a block diagram which shows the structure of the fuel cell system which concerns on the 2nd Embodiment of this invention. It is a flowchart which shows the fuel cell stop process by the fuel cell system which concerns on the 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 41 Fuel cell system 2 Fuel electrode 3 Oxidant electrode 4 Fuel cell 5 Control device 6 Fuel gas flow control device 7 Fuel gas humidification device 8, 9 Fuel gas switching valve 10 Fuel gas outlet valve 11 Oxidant gas flow control device 12 Oxidant gas humidifiers 13, 14 Oxidant gas switching valve 15 Oxidant gas outlet valve 42 Fuel electrode differential pressure gauge 43 Oxidant electrode differential pressure gauge 44 Coolant pump 45 Coolant tank 46 Coolant flow path 47 Radiator fan 48 Radiator

Claims (12)

In a fuel cell system for generating power by supplying a fuel gas and an oxidant gas to a fuel cell having a structure in which a solid polymer electrolyte membrane is sandwiched between a fuel electrode and an oxidant electrode,
Power generation before stop is performed so that the amount of residual water per unit time obtained by subtracting the amount of water discharged by the fuel cell from the total amount of water supplied to the fuel cell and produced water is greater than that during normal power generation. The fuel cell system is characterized in that after a preset time elapses, the power generation before the stop is stopped and the fuel cell is purged with a gas having a lower humidity than during normal operation.   2. The fuel cell system according to claim 1, wherein, during the power generation before the stop, the pressure of the fuel gas or the oxidant gas at the inlet of the fuel cell is controlled to be larger than that during normal power generation.   The flow rate of the fuel gas or oxidant gas is controlled so that the utilization rate of the fuel gas or oxidant gas is larger than the utilization rate during normal power generation during the power generation before the stop. Item 4. The fuel cell system according to Item 1.   2. The fuel cell system according to claim 1, wherein during the power generation before the stop, the relative humidity of the fuel gas or the oxidant gas at the inlet of the fuel cell is controlled to be larger than that during normal power generation. .   2. The fuel cell system according to claim 1, wherein during the power generation before the stop, the internal temperature of the fuel cell is controlled to be lower than that during normal power generation.   When the pressure of the fuel gas or oxidant gas at the inlet of the fuel cell becomes higher than a predetermined pressure, the power generation of the fuel cell is stopped and purged with a gas having a lower humidity than during normal operation. The fuel cell system according to any one of claims 1 to 5. A fuel cell system power generation stopping method for generating power by supplying fuel gas and oxidant gas to a fuel cell having a structure in which a solid polymer electrolyte membrane is sandwiched between a fuel electrode and an oxidant electrode,
Power generation before stop is performed so that the amount of residual water per unit time obtained by subtracting the amount of water discharged by the fuel cell from the total amount of water supplied to the fuel cell and produced water is greater than that during normal power generation. ,
A method for stopping power generation of a fuel cell system, wherein after the preset time has elapsed, the power generation before the stop is stopped and the fuel cell is purged with a gas having a lower humidity than during normal operation.   The power generation stop of the fuel cell system according to claim 7, wherein when performing the power generation before the stop, the pressure of the fuel gas or the oxidant gas at the inlet of the fuel cell is made larger than that during normal power generation. Method.   When performing power generation before stoppage, the flow rate of the fuel gas or oxidant gas is controlled so that the utilization rate of the fuel gas or oxidant gas is larger than the utilization rate during normal power generation. The method for stopping power generation of the fuel cell system according to claim 7.   8. The power generation of the fuel cell system according to claim 7, wherein when performing the power generation before the stop, the relative humidity of the fuel gas or the oxidant gas at the inlet of the fuel cell is made larger than that during normal power generation. How to stop.   The method for stopping power generation of a fuel cell system according to claim 7, wherein when performing power generation before stoppage, the internal temperature of the fuel cell is made lower than that during normal power generation.   When the pressure of the fuel gas or oxidant gas at the inlet of the fuel cell becomes higher than a predetermined pressure, the power generation of the fuel cell is stopped and purged with a gas having a lower humidity than during normal operation. The power generation stopping method for a fuel cell system according to any one of claims 7 to 11.

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