JP6122795B2 - FUEL CELL STACK DIAGNOSIS METHOD, FUEL CELL STACK OPERATION METHOD, FUEL CELL SYSTEM, AND FUEL CELL STACK - Google Patents

Description

  Embodiments described herein relate generally to a fuel cell stack diagnosis method, a fuel cell stack operation method, a fuel cell system, and a fuel cell stack.

  A conventional household fuel cell system supplies a fuel gas containing hydrogen and air to a combustion cell stack, generates electricity by an electrochemical reaction, collects reaction heat, and supplies hot water. This fuel cell stack is obtained by alternately stacking fuel cells (hereinafter also simply referred to as cells) and separators. This fuel cell is, for example, a solid polymer electrolyte fuel cell in which an anode and a cathode are arranged on both sides of a proton conductive electrolyte membrane.

  The electrolyte membrane has a property that allows protons and water to pass through but does not pass gas (specifically, fuel gas and air). Therefore, it also functions to seal the gas supplied to the anode and cathode. In other words, the electrolyte membrane prevents the efficiency of the fuel cell reaction from being reduced due to the direct reaction caused by the mixture of the gas of both electrodes.

JP 2009-301804 A JP 2010-287578 A

  However, when the fuel cell is operated for a long time, the electrolyte membrane deteriorates. Due to this deterioration, the gas seal function is lowered, and fuel gas and air may leak out (hereinafter referred to as cross leak). When fuel gas and air leak together, oxygen is consumed by the direct oxidation reaction of hydrogen, and the amount of oxygen used in the fuel cell reaction is reduced, so that the performance of the fuel cell is degraded. In addition, it is not preferable for safety that hydrogen and oxygen are mixed more than necessary.

  SUMMARY OF THE INVENTION Problems to be solved by the present invention include a fuel cell stack diagnosis method that facilitates diagnosis related to a fuel cell stack, a fuel cell stack operation method and fuel cell system that improve fuel cell safety, and fuel cell performance. It is to provide a fuel cell stack that can be operated safely while maintaining the above.

  According to this embodiment, the fuel cell stack diagnosis method supplies fuel gas and air to a fuel cell stack in which a plurality of fuel cells are stacked and stops supplying power to the outside of the fuel cell stack. , Measuring a first open circuit voltage of the fuel cell stack. Further, the diagnostic method includes a step of replacing the air supply pipe and the air exhaust pipe connected to the fuel cell stack. Further, this diagnosis method is performed in a state where the air supply pipe and the air exhaust pipe are replaced with each other, the fuel gas and air are supplied to the fuel cell stack, and the power supply to the outside of the fuel cell stack is stopped. Measuring a second open circuit voltage of the battery stack. Further, the diagnostic method includes a step of performing a diagnosis on the fuel cell stack based on a voltage difference between the first open circuit voltage and the second open circuit voltage.

FIG. 1 is a schematic block diagram showing the configuration of the fuel cell system SYS1 in the first embodiment. FIG. 2 is a diagram showing a connection mode of the air supply pipe AP1 and the air exhaust pipe AP2 when measuring the first open circuit voltage V1. FIG. 3 is a diagram showing a connection mode of the air supply pipe AP1 and the air exhaust pipe AP2 when measuring the second open circuit voltage V2. FIG. 4 is a diagram showing the direction of air flow in the separator 1 during normal operation. FIG. 5 is a diagram showing the flow direction of air in the separator 1 in a state where the air supply pipe AP1 and the air exhaust pipe AP2 are replaced. FIG. 6 shows the relationship between the normalized cross leak amount and the value ΔV / N obtained by dividing the voltage difference ΔV by the number of cells in six fuel cell stacks CSA provided with through holes in the vicinity of the air inlet of the electrolyte membrane. FIG. FIG. 7 is a schematic block diagram showing the configuration of the fuel cell system SYS2 in the second embodiment and the operation before switching the air output destination from the blower B. FIG. 8 is a schematic block diagram showing the operation of the fuel cell system SYS2 after switching the output destination of the air from the blower B in the second embodiment. FIG. 9 is a diagram showing a connection mode of the gas supply pipe GP1 and the gas exhaust pipe GP2 when measuring the first open circuit voltage V1. FIG. 10 is a diagram showing a connection mode of the gas supply pipe GP1 and the gas exhaust pipe GP2 when measuring the second open circuit voltage V2. FIG. 11 is a diagram illustrating the flow direction of the reformed gas in the separator 1 during normal operation. FIG. 12 is a diagram illustrating the flow direction of the reformed gas in the separator 1 in a state where the gas supply pipe GP1 and the gas exhaust pipe GP2 are replaced. FIG. 13 is a schematic block diagram showing the configuration of the fuel cell system SYS3 in the fourth embodiment and the operation before switching the output destination of the reformed gas from the reformer FPS. FIG. 14 is a schematic block diagram illustrating an operation after switching the output destination of the reformed gas from the reformer FPS in the fourth embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(First embodiment)
FIG. 1 is a schematic block diagram showing the configuration of the fuel cell system SYS1 in the first embodiment. As shown in FIG. 1, the fuel cell system SYS1 includes a blower B, a reformer FPS, an air manifold AM connected to the blower B through an air supply pipe AP1, and a reformation through a gas supply pipe GP1. And a fuel gas manifold GM connected to the vessel FPS.

  The fuel cell system SYS1 further includes a fuel cell stack CSA connected to the air manifold AM and the fuel gas manifold GM. Furthermore, the fuel cell system SYS1 is electrically connected to the heat exchanger HEX and the fuel cell stack CSA connected to the air manifold AM via the air exhaust pipe AP2 and to the fuel gas manifold GM via the gas exhaust pipe GP2. The AC / DC inverter INV is connected.

  The fuel cell system SYS1 further includes a control unit CON electrically connected to the blower B, the reformer FPS, and the fuel cell stack CSA.

The blower B supplies the air supplied from the outside of the blower B to the fuel cell stack CSA via the air supply pipe AP1 and the air manifold AM.
The reformer FPS generates a hydrogen-rich reformed gas from fuel gas (for example, natural gas or propane gas) supplied from the outside of the reformer FPS. The reformer FPS supplies the generated reformed gas to the fuel cell stack CSA via the gas supply pipe GP1 and the fuel gas manifold GM.

  The air manifold AM supplies the air supplied from the blower B to the fuel cell stack CSA. This air is warmed by circulating through the fuel cell stack CSA, and this warmed air is discharged to the air manifold AM. The air manifold AM supplies this warmed air to the heat exchanger HEX.

  The fuel gas manifold GM supplies the reformed gas supplied from the reformer FPS to the fuel cell stack CSA. The reformed gas is circulated through the fuel cell stack CSA and then discharged as exhaust gas to the fuel gas manifold GM. The fuel gas manifold GM supplies this exhaust gas to the heat exchanger HEX.

  The fuel cell stack CSA is formed by alternately stacking fuel cells and separators. The fuel cell stack CSA generates electric power by an electrochemical reaction using the supplied air and the reformed gas. The fuel cell stack CSA supplies DC power obtained by the electrochemical reaction to the AC / DC inverter INV.

  The cooling water that has flowed into the fuel cell stack CSA from the outside of the fuel cell stack CSA absorbs heat generated by the electrochemical reaction in the fuel cell stack CSA, becomes hot, and is discharged from the fuel cell stack CSA. Inflow.

  The secondary cooling water that has flowed into the heat exchanger HEX from the outside of the heat exchanger HEX is heated by the high-temperature cooling water that has flowed from the fuel cell stack CSA in the heat exchanger HEX, and becomes hot water from the heat exchanger HEX. It is discharged outside the heat exchanger HEX.

  The AC / DC inverter INV converts the DC power supplied from the fuel cell stack CSA into AC power, and outputs this AC power to the outside of the AC / DC inverter INV.

  The control unit CON controls the blower B, the reformer FPS, and the fuel cell stack CSA. Specifically, for example, the control unit CON controls the timing at which the blower B starts to move and the rotational speed. Further, the control unit CON controls the temperature of the reformer. For example, the controller CON raises the temperature of the reformer FPS at the time of startup, and thereafter maintains the temperature of the reformer FPS at a predetermined temperature. Further, for example, when the controller CON detects an abnormal temperature, the controller CON stops the reformer FPS.

  Further, for example, the control unit CON monitors the voltage of power generation by the fuel cell stack CSA, and stops the fuel cell stack CSA if there is an abnormality. In addition, for example, the control unit CON controls the fuel cell stack CSA so as to change the DC power output from the fuel cell stack CSA in accordance with household electric power demand.

  Next, a cross leak detection method according to this embodiment will be described with reference to FIGS. This cross leak detection method is used, for example, during periodic inspection.

  FIG. 2 is a diagram illustrating a connection mode of the air supply pipe AP1 and the air exhaust pipe AP2 in a normal state. As shown in FIG. 2, the fuel cell stack CSA includes a first end plate EF1, a second end plate EF2, and a fuel cell C sandwiched between the first end plate EF1 and the second end plate EF2. -1,..., C-N (N is a positive integer), N fuel cells C-i (i is an integer from 1 to N). The air manifold AM includes a first air port AI through which air passes and a second air port AO through which air passes. The air supply pipe AP1 is connected to the first air port AI, and the air exhaust pipe AP2 is connected to the second air port AO. Thereby, the air discharged from the blower B is supplied to the air manifold AM via the first air port AI, and the air discharged from the air manifold AM is supplied to the heat exchanger HEX via the second air port AO. Discharged.

  First, for example, when the normal air supply pipe AP1 and the air exhaust pipe AP2 are connected as shown in FIG. 2, the reformed gas and air are supplied to the fuel cell stack CSA and the electric power to the outside of the fuel cell stack CSA. With the supply stopped, the first open circuit voltage V1 of the fuel cell stack CSA is measured. Here, the open circuit voltage (OCV) is the anode and cathode of each fuel cell when the reformed gas and air are supplied without electrical resistance being connected to the fuel cell stack CSA. It is the sum of voltage values between.

Next, as shown in FIG. 3, the air supply pipe AP1 and the air exhaust pipe AP2 connected to the fuel cell stack CSA are replaced with each other.
FIG. 3 is a diagram illustrating a connection mode of the air supply pipe and the air exhaust pipe after replacement. As shown in FIG. 3, unlike FIG. 2, the air supply pipe AP1 is connected to the second air port AO, and the air exhaust pipe AP2 is connected to the first air port AI. Thereby, the air from the blower B is supplied to the air manifold AM via the second air port AO, and the air from the air manifold AM is discharged to the heat exchanger HEX via the first air port AI.

  Next, the second open circuit voltage V2 of the fuel cell stack CSA in a state where the fuel cell stack CSA is supplied and the reformed gas and air are supplied to the fuel cell stack CSA and the power supply to the outside of the fuel cell stack CSA is stopped. Measure.

  Next, a diagnosis relating to the fuel cell stack CSA is executed based on the voltage difference ΔV between the first open circuit voltage V1 and the second open circuit voltage V2. The object of this diagnosis is, for example, the deterioration state of the fuel cell stack CSA, safety, or whether the operation can be continued. In this embodiment, as an example of the deterioration state of the fuel cell stack CSA, the deterioration state of the electrolyte membrane included in the fuel cell C-i constituting the fuel cell stack CSA is set as a diagnosis target.

  When the electrolyte membrane is in a dry state, the deterioration of the electrolyte membrane is accelerated. In the fuel cell, water is generated by an electrochemical reaction. Since this water is generated by the catalyst applied to the cathode surface, it functions to humidify the electrolyte membrane. Therefore, the vicinity of the air inlet in the fuel cell is an area that is easy to dry because the humidification by the generated water is the least.

  Thus, since the vicinity of the air inlet in the fuel battery cell is an area that is easily dried, film deterioration is likely to proceed. The hydrogen concentration in the reformed gas supplied to the anode is approximately 70% or more, whereas the oxygen concentration in the air supplied to the cathode is 21%. Since oxygen and hydrogen react at a molar ratio of 1: 2 when generating water, the flow rate of air is greater than the flow rate of reformed gas. For this reason, the electrolyte membrane is more deteriorated by drying in the region near the air inlet in the fuel cell C-i than in the region near the reformed gas inlet in the fuel cell C-i.

  FIG. 4 is a diagram showing the direction of air flow in the separator 1 during normal operation. The separator 1 included in the fuel battery cell Ci includes gas grooves 2-1, 2-2, and 2-3 through which air passes. A catalyst is applied to both surfaces of the electrolyte membrane, and the reaction region 3 is a range where this catalyst is applied. When the deterioration of the electrolyte membrane progresses in the membrane degradation region 4 shown in FIG. 4, the OCV decreases due to hydrogen leaking from the membrane degradation region 4 to react with the cathode.

  FIG. 5 is a diagram showing the flow direction of air in the separator 1 in a state where the air supply pipe AP1 and the air exhaust pipe AP2 are replaced. When the air flow direction is reversed, the film deterioration region 4 is near the outlet of the air flow path as shown in FIG.

  At this time, the hydrogen leaking from the membrane degradation region 4 to the cathode is directly discharged out of the fuel cell stack CSA, so that the reduction in OCV is limited. Therefore, when there is a cross leak at the air inlet of the electrolyte membrane, a voltage difference ΔV between the first open circuit voltage V1 and the second open circuit voltage V2 occurs.

  Since the value of the voltage difference ΔV is determined by the number of cells included in the fuel cell stack, as an example, a value obtained by dividing the voltage difference ΔV by the number of cells is used for diagnosis.

  Generally, when the OCV is 0.95 V or more, it can be said that it is within a range where safe operation is possible. Conversely, if the OCV is less than 0.95V, there is a high possibility that a cross leak has started. This value corresponds to 0.03 to 0.05 V / cell in terms of the OCV difference when the air flow direction is reversed. When estimating a change in a single fuel cell from the voltage of the fuel cell stack CSA, the number of cells that are cross leaking also becomes a problem. In general, when the cause of cross leak is deterioration with time due to operation, cross leak proceeds in a plurality of cells. Since the degree of progress varies from cell to cell, it is unlikely that cross leakage will progress in all cells. Therefore, for example, in order to detect that a cross leak has occurred in 1/5 to 1/3 of all the cells, a preset set value is set to 0.01 (= 0.03 / 3). ) V.

  In the present embodiment, as an example, the voltage difference ΔV between the first open circuit voltage V1 and the second open circuit voltage V2 is calculated from the number of fuel cell cells C-i constituting the fuel cell stack CSA ( When the value ΔV / N divided by N (hereinafter also referred to as the number of cells) is a preset value (for example, 0.01 V) or more, it is determined that a cross leak has occurred in the electrolyte membrane.

  Subsequently, a method of operating the fuel cell stack in the present embodiment will be described. As the cross leak progresses, the OCV significantly decreases. In general, when the OCV is 0.9 V or less, the amount of cross leakage is large, which hinders safe operation of the fuel cell stack. Therefore, it is necessary to avoid driving in an unsafe state by applying the above diagnostic method. When the OCV is 0.9 V or less, the OCV difference corresponds to 0.08 to 0.1 V / cell. Considering the number of cells that are cross leaking, if the value obtained by dividing the voltage difference ΔV by the number of cells is 0.03 V or more, it is determined that a significant cross leak has occurred, and the fuel cell stack Stop driving.

  Thus, the value obtained by dividing the voltage difference between the first open circuit voltage V1 and the second open circuit voltage V2 by the number of fuel cells constituting the fuel cell stack CSA is a predetermined setting. When it is equal to or higher than the value (here, 0.03V as an example), the operation of the fuel cell system SYS1 including the fuel cell stack CSA is stopped.

  When the value ΔV / N obtained by dividing the voltage difference ΔV by the number of cells N is 0.01 V or more and less than 0.03 V, the operation is resumed with the air supply pipe AP1 and the air exhaust pipe AP2 being replaced. To do. At this time, since the film deterioration region corresponds to the outlet side of the air flow path, the progress of the film deterioration is suppressed. Furthermore, since the inlet side of the air flow path which is easy to dry is replaced with a region where the film is not deteriorated, the amount of cross leak can be suppressed and the operation of the fuel cell system SYS1 can be continued.

  Thus, in the operation method of the fuel cell stack according to the present embodiment, the second set value in which the value obtained by dividing the voltage difference ΔV by the number N of fuel cells is lower than the set value (for example, 0.03 V). When it is equal to or higher than (for example, 0.01 V) and lower than the set value (for example, 0.03 V), the operation of the fuel cell stack is continued with the air supply pipe AP1 and the air exhaust pipe AP2 replaced.

  FIG. 6 shows the relationship between the normalized cross leak amount and the value ΔV / N obtained by dividing the voltage difference ΔV by the number of cells in six fuel cell stacks CSA provided with through holes in the vicinity of the air inlet of the electrolyte membrane. FIG. The standardized cross leak amount is obtained by standardizing the amount of reformed gas flowing out from the cathode when the anode is held, with the maximum allowable cross leak amount being operable being set to 1. The permissible cross leak amount that can be operated here is the cross leak amount when it becomes 90% of the normal power generation amount.

  In stack 1 and stack 2 with a small amount of standardized cross leakage, a value ΔV / N (hereinafter also referred to as a voltage difference per cell) obtained by dividing the voltage difference ΔV by the number of cells N is less than 10 mV. It is determined that there is no hindrance.

  On the other hand, even if the normalized cross leak amount is about the same, in the stack 3 and the stack 4 where the film deterioration is further progressing, since the voltage difference per cell is 10 mV or more, it is determined that the cross leak occurs.

  When the stack 1 and the stack 3 are compared, even if the through-holes are about the same and the normalized cross leak amount when holding the anode is equal, film deterioration such as thinning that does not reach the through-holes proceeds. The first open circuit voltage V1 further decreases, and the voltage difference per cell increases. Here, hydrogen leaks somewhat from the electrolyte membrane during the electrochemical reaction together with the current during the electrochemical reaction, but the amount of leakage increases when the film is thinned. As the leakage amount increases, the first open circuit voltage V1 further decreases, and the voltage difference per cell increases.

  When the normalized cross leak amount at the time of holding pressure shown in FIG. 6 is measured, since no electrochemical reaction has occurred, the cross leak amount that leaks from the thinned electrolyte membrane during the electrochemical reaction is not included. Therefore, during actual operation that causes an electrochemical reaction, the stack 3 having a larger voltage difference per cell than the stack 1 has a larger actual cross leak amount.

  In the case of the stack 3 and the stack 4, the operation of the fuel cell stack CSA is continued with the air supply pipe AP1 and the air exhaust pipe AP2 replaced.

  In addition, since the voltage difference per cell is 30 mV or more for the stack 5 and the stack 6 in which the normalized cross leak amount is equal to or greater than the maximum allowable cross leak amount, it is difficult to safely operate the fuel cell stack CSA. Is determined. In such a case, the operation of the fuel cell stack CSA is stopped and the fuel cell stack CSA is replaced.

  The diagnosis of the fuel cell stack CSA in the first embodiment is assumed to be performed during regular maintenance, and the air supply pipe AP1 and the air exhaust pipe AP2 are replaced so that the pipes can be replaced manually. It is configured to be possible. Therefore, in order to facilitate replacement of the air supply pipe AP1 and the air exhaust pipe AP2, it is preferable that the pipe is made of a material that can be easily bent. As an example, the piping is a resin tube such as a Teflon (registered trademark) tube or a rubber tube.

  Furthermore, it is preferable that the air supply pipe AP1 and the air exhaust pipe AP2 have the same pipe diameter. This eliminates the need to adjust the diameter of the outlet of the air supply pipe AP1 to the diameter of the second air port AO when replacing each other, and the diameter of the inlet of the air exhaust pipe AP2 is the diameter of the first air port AI. Since it is not necessary to make adjustments to match the pipes, it is possible to facilitate the replacement work of the piping.

  As described above, in the first embodiment, the fuel cell stack CSA that can be continuously operated without doing anything after the periodic inspection supplies the hydrogen gas and air to the fuel cell stack CSA and supplies the fuel cell stack CSA to the outside. Measured with the first open circuit voltage V1 of the fuel cell stack CSA measured with the power supply stopped and the air supply pipe AP1 and the air exhaust pipe AP2 connected to the fuel cell stack CSA. The value ΔV / N obtained by dividing the voltage difference ΔV with respect to the second open circuit voltage V2 of the prepared fuel cell stack by the number N of fuel cells is less than a preset set value (for example, 10 mV) .

  According to this, since the cross leak amount is suppressed, the fuel cell stack CSA can be safely operated while maintaining the performance of the fuel cell.

  Further, the fuel cell stack diagnosis method according to the first embodiment supplies the reformed gas and air to the fuel cell stack CSA in which a plurality of fuel cells are stacked, and supplies power to the outside of the fuel cell stack CSA. The first open circuit voltage V1 of the fuel cell stack CSA, the step of replacing the air supply pipe AP1 and the air exhaust pipe AP2 connected to the fuel cell stack CSA, and the replacement Measuring the second open circuit voltage of the fuel cell stack CSA in a state where the reformed gas and air are supplied to the fuel cell stack CSA and the power supply to the outside of the fuel cell stack CSA is stopped. Performing a diagnosis on the fuel cell stack based on a voltage difference between the first open circuit voltage V1 and the second open circuit voltage V2. To.

  According to this, since the fuel cell stack can be diagnosed with such a simple operation, diagnosis relating to the fuel cell stack can be facilitated.

  The fuel cell stack operating method according to the first embodiment is the fuel cell stack in a state where the reformed gas and air are supplied to the fuel cell stack CSA and the power supply to the outside of the fuel cell stack CSA is stopped. A step of measuring the first open circuit voltage V1 of the stack, a step of replacing the air supply pipe and the air exhaust pipe connected to the fuel cell stack CSA, the state of the replacement, and the reformed gas and air as fuel A step of measuring the second open circuit voltage V2 of the fuel cell stack CSA in a state in which power is supplied to the battery stack CSA and the power supply to the outside of the fuel cell stack CSA is stopped; The value obtained by dividing the voltage difference ΔV between the two open circuit voltages V2 by the number of fuel cells constituting the fuel cell stack CSA is greater than or equal to a predetermined set value. If, and a step of stopping the operation of the fuel cell stack CSA including the fuel cell stack CSA, the.

  According to this, when the amount of cross leak becomes large, it is possible to stop the operation of the fuel cell stack CSA and prevent the hydrogen and oxygen from being mixed more than necessary, thereby improving the safety of the fuel cell. be able to.

(Second Embodiment)
Next, the second embodiment will be described. In the first embodiment, the air supply pipe and the air exhaust pipe are artificially replaced with each other, thereby reversing the air flow direction in the fuel cell. On the other hand, in the second embodiment, the fuel cell system switches the output destination of the air from the blower, thereby reversing the direction of air flow in the fuel cell.

  FIG. 7 is a schematic block diagram showing the configuration of the fuel cell system SYS2 in the second embodiment and the operation before switching the air output destination from the blower B. Elements common to those in FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted. The configuration of the fuel cell system SYS2 in the second embodiment is such that a switching unit SW1 is added to the configuration of the fuel cell system SYS1 in the first embodiment.

  The switching unit SW1 switches the direction in which the air supplied to the fuel battery cell Ci flows. The control unit CON controls the switching unit SW1 in addition to the function of the control unit CON of the first embodiment. The air manifold AM has a first air port AI and a second air port AO, as in the first embodiment.

  Next, the operation of the fuel cell system SYS2 in the present embodiment will be described with reference to FIGS. FIG. 8 is a schematic block diagram showing the operation of the fuel cell system SYS2 after switching the output destination of the air from the blower B in the second embodiment.

  As shown in FIG. 7, before switching the air output destination from the blower B, the switching unit SW1 discharges the air flowing from the blower B to a first air port AI (not shown) of the air manifold AM, The air flowing in from the second air port AO (not shown) of the manifold AM is discharged to the heat exchanger HEX.

  In this state, the control unit CON supplies the reformed gas and air to the fuel cell stack CSA and stops supplying power to the outside of the fuel cell stack CSA, and then the first open circuit voltage of the fuel cell stack CSA. V1 is measured.

  Next, the control unit CON controls the switching unit SW1 so that the direction of the air flowing through each of the fuel cells C-i is opposite. Under the control of the control unit CON, the switching unit SW1 discharges the air flowing from the blower B to a second air port AO (not shown) of the air manifold AM as shown in FIG. Air that flows in from a first air port AI (not shown) is discharged to the heat exchanger HEX.

  The control unit CON has the fuel cell stack in a state where the air flow direction is reversed, the reformed gas and air are supplied to the fuel cell stack CSA, and the power supply to the outside of the fuel cell stack CSA is stopped. A second open circuit voltage V2 of the CSA is measured.

  Then, the control unit CON obtains a value ΔV / a value obtained by dividing the voltage difference ΔV between the first open circuit voltage V1 and the second open circuit voltage V1 by the number N of fuel cells constituting the fuel cell stack CSA. When N is a preset value (for example, 0.03 V) or more, the operation of the fuel cell system SYS2 is stopped.

  As described above, according to the second embodiment, the control unit CON uses the voltage difference ΔV between the first open circuit voltage V1 and the second open circuit voltage V1 as a fuel cell constituting the fuel cell stack CSA. When the value ΔV / N divided by the number N is equal to or greater than a predetermined set value (for example, 0.03 V), the operation of the fuel cell stack CSA is stopped.

  As a result, when the amount of cross leak increases, the operation of the fuel cell stack CSA can be stopped to prevent more hydrogen and oxygen from being mixed than necessary, so that the safety of the fuel cell can be improved. it can.

(Third embodiment)
Subsequently, a third embodiment will be described. In the first embodiment, the air supply pipe and the air exhaust pipe connected to the fuel cell stack are replaced to determine the presence or absence of cross leak. On the other hand, in the third embodiment, the gas supply pipe and the gas exhaust pipe connected to the fuel cell stack are switched to determine the presence or absence of cross leak.

  Since the reformed gas flowing into the fuel cell stack CSA has a smaller flow rate than the air flowing into the fuel cell stack CSA, deterioration due to drying is less likely to proceed at the gas inlet of the fuel cell than at the air inlet of the fuel cell. . However, when the reformed gas supplied to the fuel cell stack CSA is humidified, the degree of progress of drying at the gas inlet of the fuel cell changes, and deterioration may progress at the gas inlet. Therefore, in the third embodiment, the open circuit voltage is measured before and after changing the direction in which the reformed gas flows in the fuel cell, and the cross leak is determined using the difference between the open circuit voltages. .

  The configuration of the fuel cell system SYS1 according to the third embodiment is the same as the configuration of the fuel cell system SYS1 according to the first embodiment shown in FIG.

  Next, a cross leak detection method according to this embodiment will be described with reference to FIGS. This cross leak detection method is used, for example, during periodic inspection.

  First, for example, when the normal air supply pipe AP1 and the air exhaust pipe AP2 are connected as shown in FIG. 9, the reformed gas and air are supplied to the fuel cell stack CSA and the electric power to the outside of the fuel cell stack CSA. With the supply stopped, the first open circuit voltage V1 of the fuel cell stack CSA is measured.

  FIG. 9 is a diagram illustrating a connection mode of the gas supply pipe and the gas exhaust pipe when the first open circuit voltage V1 is measured. Elements common to those in FIG. 2 are denoted by the same reference numerals, and detailed description thereof is omitted. The fuel gas manifold GM includes a first gas port FI through which the reformed gas passes and a second gas port FO through which the exhaust gas passes. The gas supply pipe GP1 is connected to the first gas port FI, and the gas exhaust pipe GP2 is connected to the second gas port FO. Thereby, the reformed gas from the reformer FPS is supplied to the fuel gas manifold GM via the first gas port FI, and the exhaust gas from the fuel gas manifold GM exchanges heat via the second gas port FO. Is discharged to the vessel HEX.

  Next, as shown in FIG. 10, the gas supply pipe GP1 and the gas exhaust pipe GP2 connected to the fuel cell stack CSA are replaced with each other. FIG. 10 is a diagram illustrating a connection mode of the gas supply pipe GP1 and the gas exhaust pipe GP2 after replacement. As shown in FIG. 10, unlike FIG. 9, the gas supply pipe GP1 is connected to the second gas port FO, and the gas exhaust pipe GP2 is connected to the first gas port FI. As a result, the reformed gas discharged from the reformer FPS is supplied to the fuel gas manifold GM via the second gas port FO, and the exhaust gas discharged from the fuel gas manifold GM passes through the first gas port FI. To the heat exchanger HEX.

  Next, the second open circuit voltage of the fuel cell stack CSA in the state where the replacement is performed, the reformed gas and air are supplied to the fuel cell stack CSA, and the power supply to the outside of the fuel cell stack CSA is stopped. V2 is measured.

  Next, a diagnosis relating to the fuel cell stack CSA is executed based on the voltage difference ΔV between the first open circuit voltage V1 and the second open circuit voltage V2. The object of this diagnosis is the deterioration state of the fuel cell stack CSA, safety, or whether or not the operation can be continued. In this embodiment, as an example of the deterioration state of the fuel cell stack CSA, the deterioration state of the electrolyte membrane included in the fuel cell C-i constituting the fuel cell stack CSA is set as a diagnosis target.

  Subsequently, the flow direction of the reformed gas in the separator 1 will be described with reference to FIGS. 11 and 12. FIG. 11 is a diagram illustrating the flow direction of the reformed gas in the separator 1 during normal operation. The separator 11 included in the fuel battery cell Ci includes gas grooves 12-1, 12-2, and 12-3 through which the reformed gas passes. The reaction region 13 is a range where this catalyst is applied. When the degradation of the electrolyte membrane proceeds in the membrane degradation region 14 shown in FIG. 11, the OCV is lowered by hydrogen leaking from the membrane degradation region 4 to the cathode and reacting with oxygen.

  FIG. 12 is a diagram illustrating the flow direction of the reformed gas in the separator 1 in a state where the gas supply pipe GP1 and the gas exhaust pipe GP2 are replaced. When the flow direction of the reformed gas is reversed, the film deterioration region 14 is near the outlet of the gas flow path as shown in FIG.

  At this time, since the hydrogen leaked from the membrane deterioration region 14 to the cathode is directly discharged out of the fuel cell stack CSA, the decrease in the OCV is limited. Therefore, when there is a cross leak at the gas inlet of the electrolyte membrane, a voltage difference ΔV between the first open circuit voltage V1 and the second open circuit voltage V2 occurs.

  Since the value of the voltage difference ΔV is determined by the number of cells included in the fuel cell stack, the value for each single cell is used for diagnosis as an example. That is, in this embodiment, as an example, a value obtained by dividing the voltage difference ΔV by the number of cells is used for diagnosis.

  As described above, in the present embodiment, as an example, the voltage difference ΔV between the first open circuit voltage V1 and the second open circuit voltage V2 is calculated from the number of fuel cell cells constituting the fuel cell stack CSA (hereinafter referred to as the fuel cell stack CSA). When the value ΔV / N divided by N is equal to or higher than a preset value (for example, 0.01 V), it is determined that a cross leak has occurred in the electrolyte membrane.

  Further, similarly to the first embodiment, in the fuel cell system according to the present embodiment, the voltage difference between the first open circuit voltage V1 and the second open circuit voltage V2 constitutes the fuel cell stack. If the value divided by the number of cells is equal to or greater than a predetermined set value, the operation of the fuel cell stack CSA is stopped.

  Similarly to the first embodiment, in the method for operating the fuel cell stack according to the present embodiment, a value obtained by dividing the voltage difference ΔV by the number N of fuel cells is the set value (for example, 0.03 V). When the lower second set value (for example, 0.01 V) or more and less than the set value (for example, 0.03 V), the fuel cell stack with the gas supply pipe GP1 and the gas exhaust pipe GP2 replaced. Continue CSA operation.

  The diagnosis of the fuel cell stack CSA in the third embodiment is assumed to be performed during regular maintenance, and the gas supply pipe GP1 and the gas exhaust pipe GP2 are replaced so that the pipes can be replaced manually. It is configured to be possible. Therefore, in order to facilitate replacement of the gas supply pipe GP1 and the gas exhaust pipe GP2, it is preferable that the pipe is made of a material that bends easily. As an example, the piping is a resin tube such as a Teflon (registered trademark) tube or a rubber tube.

  Furthermore, it is preferable that the gas supply pipe GP1 and the gas exhaust pipe GP2 have the same pipe diameter. This eliminates the need to adjust the diameter of the outlet of the gas supply pipe GP1 to the diameter of the second air port AO when replacing each other, and the diameter of the inlet of the gas exhaust pipe GP2 is the diameter of the first air port AI. Since it is not necessary to make adjustments to match the pipes, it is possible to facilitate the replacement work of the piping.

  As described above, in the third embodiment, the fuel cell stack CSA that can be continuously operated without doing anything after the periodic inspection supplies the hydrogen gas and air to the fuel cell stack CSA and supplies the fuel cell stack CSA to the outside. Fuel measured in a state where the first open circuit voltage V1 of the fuel cell stack CSA measured in a state where power supply is stopped and the gas supply pipe and the gas exhaust pipe connected to the fuel cell stack are replaced. A value ΔV / N obtained by dividing the voltage difference from the second open circuit voltage V2 of the battery stack CSA by the number N of fuel cells is less than a preset setting value (for example, 10 mV).

  According to this, since the cross leak amount is suppressed, the fuel cell stack CSA can be safely operated while maintaining the performance of the fuel cell.

  In the fuel cell stack diagnosis method according to the third embodiment, hydrogen gas and air are supplied to a fuel cell stack in which a plurality of fuel cells are stacked, and power supply to the outside of the fuel cell stack CSA is stopped. In this state, the step of measuring the first open circuit voltage V1 of the fuel cell stack CSA, the step of replacing the gas supply pipe GP1 and the gas exhaust pipe GP2 connected to the fuel cell stack CSA, and the state of the replacement And measuring the second open circuit voltage V2 of the fuel cell stack CSA in a state where hydrogen gas and air are supplied to the fuel cell stack CSA and power supply to the outside of the fuel cell stack CSA is stopped, Performing a diagnosis on the fuel cell stack CSA based on a voltage difference between the first open circuit voltage V1 and the second open circuit voltage V2. Having.

  According to this, since the fuel cell stack can be diagnosed with such a simple operation, diagnosis relating to the fuel cell stack can be facilitated.

  In addition, the fuel cell stack operating method according to the third embodiment is configured such that hydrogen gas and air are supplied to the fuel cell stack and power supply to the outside of the fuel cell stack CSA is stopped. Measuring the first open circuit voltage V1. Further, this operation method includes a step of replacing the gas supply pipe GP1 and the gas exhaust pipe GP2 connected to the fuel cell stack CSA with each other. Further, in this operation method, the gas supply pipe GP1 and the gas exhaust pipe GP2 are replaced with each other, hydrogen gas and air are supplied to the fuel cell stack CSA, and power supply to the outside of the fuel cell stack CSA is stopped. Measuring the second open circuit voltage V2 of the fuel cell stack CSA. Further, in this operation method, a value obtained by dividing the voltage difference between the first open circuit voltage V1 and the second open circuit voltage V2 by the number of fuel cells constituting the fuel cell stack CSA is determined in advance. If it is equal to or greater than the set value, the method includes a step of stopping the operation of the fuel cell stack including the fuel cell stack CSA.

  According to this, when the amount of cross leak becomes large, it is possible to stop the operation of the fuel cell stack CSA and prevent the hydrogen and oxygen from being mixed more than necessary, thereby improving the safety of the fuel cell. be able to.

(Fourth embodiment)
Subsequently, a fourth embodiment will be described. In the third embodiment, the gas supply pipe and the gas exhaust pipe are artificially replaced with each other to reverse the gas flow direction in the fuel cell. On the other hand, in the fourth embodiment, the fuel cell system switches the output destination of the reformed gas from the reformer FPS, thereby reversing the direction of air flow in the fuel cell.

  FIG. 13 is a schematic block diagram showing the configuration of the fuel cell system SYS3 in the fourth embodiment and the operation before switching the output destination of the reformed gas from the reformer FPS. Elements common to those in FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted. The configuration of the fuel cell system SYS3 in the fourth embodiment is such that a switching unit SW2 is added to the configuration of the fuel cell system SYS1 in the first embodiment.

  The switching unit SW2 switches the flow direction of the reformed gas supplied to the fuel battery cell Ci. The control unit CON controls the switching unit SW2 in addition to the function of the control unit CON of the first embodiment. The fuel gas manifold GM has a first gas port FI and a second gas port FO, as in the third embodiment.

  Subsequently, the operation of the fuel cell system SYS3 in the present embodiment will be described with reference to FIGS. FIG. 14 is a schematic block diagram illustrating an operation after switching the output destination of the reformed gas from the reformer FPS in the fourth embodiment.

  As shown in FIG. 13, before switching the output destination of the reformed gas from the reformer FPS, the switching unit SW2 converts the reformed gas that has flowed from the reformer FPS into a first (not shown) of the fuel gas manifold GM. The air that has flowed from the second gas port FO (not shown) of the fuel gas manifold GM is discharged to the heat exchanger HEX.

  In this state, the control unit CON supplies the reformed gas and air to the fuel cell stack CSA and stops supplying power to the outside of the fuel cell stack CSA, and then the first open circuit voltage of the fuel cell stack CSA. V1 is measured.

  Next, the control unit CON controls the switching unit SW2 so that the flow direction of the reformed gas flowing through each of the fuel cells C-i is opposite. Under the control of the control unit CON, the switching unit SW2 discharges the reformed gas flowing in from the reformer FPS to the second gas port FO (not shown) of the fuel gas manifold GM as shown in FIG. The exhaust gas flowing in from the first gas port FI (not shown) of the fuel gas manifold GM is discharged to the heat exchanger HEX.

  The control unit CON is in a state in which the flow direction of the fuel gas is reversed, the reformed gas and air are supplied to the fuel cell stack CSA, and the power supply to the outside of the fuel cell stack CSA is stopped. A second open circuit voltage V2 of the stack CSA is measured.

  Next, the control unit CON controls the switching unit SW1 so that the direction of the reformed gas flowing through each fuel cell C-i is opposite. Under the control of the control unit CON, the switching unit SW1 discharges the air flowing from the blower B to a second air port AO (not shown) of the air manifold AM as shown in FIG. Air that flows in from a first air port AI (not shown) is discharged to the heat exchanger HEX.

  The controller CON in the state where the flow direction of the reformed gas is reversed, the reformed gas and air are supplied to the fuel cell stack CSA, and the power supply to the outside of the fuel cell stack CSA is stopped. A second open circuit voltage V2 of the battery stack CSA is measured.

  Then, the control unit CON obtains a value ΔV / a value obtained by dividing the voltage difference ΔV between the first open circuit voltage V1 and the second open circuit voltage V1 by the number N of fuel cells constituting the fuel cell stack CSA. When N is a preset value (for example, 0.03 V) or more, the operation of the fuel cell system SYS3 is stopped.

  As described above, according to the fourth embodiment, the control unit CON uses the voltage difference ΔV between the first open circuit voltage V1 and the second open circuit voltage V1 as a fuel cell constituting the fuel cell stack CSA. When the value ΔV / N divided by the number N is equal to or greater than a predetermined set value (for example, 0.03 V), the operation of the fuel cell stack CSA is stopped.

  As a result, when the amount of cross leak increases, the operation of the fuel cell stack CSA can be stopped to prevent more hydrogen and oxygen from being mixed than necessary, so that the safety of the fuel cell can be improved. it can.

  In each embodiment, the deterioration state of the electrolyte membrane included in the fuel cells constituting the fuel cell stack is determined based on the voltage difference ΔV. However, the present invention is not limited to this. Based on the voltage difference ΔV, deterioration of the carbon material constituting the catalyst, separator, or electrode included in the fuel cell may be diagnosed.

  According to the embodiments described above, the fuel cell stack diagnosis method for facilitating diagnosis related to the fuel cell stack, the fuel cell stack operation method and fuel cell system for improving the safety of the fuel cell, and the performance of the fuel cell A fuel cell stack that can be operated safely while maintaining can be provided.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

SYS1, SYS2, SYS3 Fuel cell system B Blower FPS reformer AM Air manifold AP1 Air supply pipe AP2 Air exhaust pipe GP1 Gas supply pipe GP2 Exhaust pipe GM Fuel gas manifold CSA Fuel cell stack HEX Heat exchanger INV AC / DC inverter CON Control part EF1 1st end plate EF2 2nd end plate C-1, ..., CN Fuel cell 1,11 Separator 2-1, 2-2, 2-3, 12-1, 12-2, 12-3 Gas groove 3, 13 Reaction region 4, 14 Film degradation region AI 1st air port AO 2nd air port FI 1st gas port FO 2nd gas port SW1, SW2 switching part

Claims (11)

A first open circuit voltage of the fuel cell stack is measured in a state where fuel gas and air are supplied to a fuel cell stack in which a plurality of fuel cells are stacked and power supply to the outside of the fuel cell stack is stopped. And a process of
Replacing the air supply pipe and the air exhaust pipe connected to the fuel cell stack with each other;
The fuel cell stack in a state where the air supply pipe and the air exhaust pipe are replaced with each other, and in which fuel gas and air are supplied to the fuel cell stack and power supply to the outside of the fuel cell stack is stopped. Measuring a second open circuit voltage of:
Performing a diagnosis on the fuel cell stack based on a voltage difference between the first open circuit voltage and the second open circuit voltage;
A method for diagnosing a fuel cell stack comprising: In the step of executing the diagnosis relating to the fuel cell stack, when a value obtained by dividing the voltage difference by the number of fuel cells constituting the fuel cell stack is larger than a preset set value , The method for diagnosing a fuel cell stack according to claim 1, wherein it is determined that a cross leak has occurred in the electrolyte membrane . Measuring a first open circuit voltage of the fuel cell stack in a state where fuel gas and air are supplied to the fuel cell stack and power supply to the outside of the fuel cell stack is stopped;
Replacing the air supply pipe and the air exhaust pipe connected to the fuel cell stack with each other ;
The fuel cell stack in a state where the air supply pipe and the air exhaust pipe are replaced with each other , and in which fuel gas and air are supplied to the fuel cell stack and power supply to the outside of the fuel cell stack is stopped. Measuring a second open circuit voltage of:
A value obtained by dividing the voltage difference between the first open circuit voltage and the second open circuit voltage by the number of fuel cells constituting the fuel cell stack is larger than a predetermined set value. Stopping the operation of the fuel cell stack ;
A method for operating a fuel cell stack comprising: When the value obtained by dividing the voltage difference by the number of the fuel cells is larger than a second set value lower than the set value and less than the set value, the air supply pipe and the air exhaust pipe are replaced with each other . The operation method of the fuel cell stack according to claim 3, further comprising a step of continuing the operation of the fuel cell stack in a state. A fuel cell stack in which a plurality of fuel cells are stacked;
A switching unit for switching a flow direction of air supplied to the fuel battery cell;
A control unit for controlling the switching unit;
Equipped with a,
The control unit measures a first open circuit voltage of the fuel cell stack in a state where fuel gas and air are supplied to the fuel cell stack and power supply to the outside of the fuel cell stack is stopped.
The control unit controls the switching unit so that the direction of air flowing through each of the fuel cells is opposite ,
The control unit has the fuel cell stack in a state where the air flow direction is reversed, fuel gas and air are supplied to the fuel cell stack, and power supply to the outside of the fuel cell stack is stopped. Measuring the second open circuit voltage of
The control unit has a predetermined value obtained by dividing the voltage difference between the first open circuit voltage and the second open circuit voltage by the number of fuel cells constituting the fuel cell stack. A fuel cell system that stops the operation of the fuel cell stack when larger than a set value. A fuel cell stack in which a plurality of fuel cells are stacked,
A first open circuit voltage of the fuel cell stack measured with the fuel gas and air supplied to the fuel cell stack and the power supply to the outside of the fuel cell stack stopped, and connected to the fuel cell stack A value obtained by dividing a voltage difference between the second open circuit voltage of the fuel cell stack measured by replacing the air supply pipe and the air exhaust pipe with each other by the number of the fuel cells in advance. Fuel cell stack that is less than the set value. A first open circuit voltage of the fuel cell stack is measured in a state where fuel gas and air are supplied to a fuel cell stack in which a plurality of fuel cells are stacked and power supply to the outside of the fuel cell stack is stopped. And a process of
Replacing the gas supply pipe and the gas exhaust pipe connected to the fuel cell stack with each other ;
The fuel cell stack with the gas supply pipe and the gas exhaust pipe replaced with each other, with fuel gas and air supplied to the fuel cell stack, and power supply to the outside of the fuel cell stack stopped. Measuring a second open circuit voltage of:
Performing a diagnosis on the fuel cell stack based on a voltage difference between the first open circuit voltage and the second open circuit voltage;
A method for diagnosing a fuel cell stack comprising: In the step of executing the diagnosis relating to the fuel cell stack, when a value obtained by dividing the voltage difference by the number of fuel cells constituting the fuel cell stack is larger than a preset set value , The method for diagnosing a fuel cell stack according to claim 7, wherein it is determined that a cross leak has occurred in the electrolyte membrane . Measuring a first open circuit voltage of the fuel cell stack in a state where fuel gas and air are supplied to the fuel cell stack and power supply to the outside of the fuel cell stack is stopped;
Replacing the gas supply pipe and the gas exhaust pipe connected to the fuel cell stack with each other ;
The fuel cell stack with the gas supply pipe and the gas exhaust pipe replaced with each other, with fuel gas and air supplied to the fuel cell stack, and power supply to the outside of the fuel cell stack stopped. Measuring a second open circuit voltage of:
A value obtained by dividing the voltage difference between the first open circuit voltage and the second open circuit voltage by the number of fuel cells constituting the fuel cell stack is larger than a predetermined set value. Stopping the operation of the fuel cell stack;
A method for operating a fuel cell stack comprising: When the value obtained by dividing the voltage difference by the number of the fuel cells is larger than a second set value lower than the set value and less than the set value, the gas supply pipe and the gas exhaust pipe are replaced with each other. The operation method of the fuel cell stack according to claim 9, further comprising a step of continuing the operation of the fuel cell stack in a state. A fuel cell stack in which a plurality of fuel cells are stacked;
A switching unit for switching a flow direction of the fuel gas supplied to the fuel battery cell;
A control unit for controlling the switching unit;
With
The control unit measures a first open circuit voltage of the fuel cell stack in a state where fuel gas and air are supplied to the fuel cell stack and power supply to the outside of the fuel cell stack is stopped.
The control unit controls the switching unit so that the flow direction of the fuel gas flowing through each of the fuel cells is opposite;
The control unit has the fuel cell stack in a state in which the flow direction of the fuel gas is reversed, the fuel gas and air are supplied to the fuel cell stack, and power supply to the outside of the fuel cell stack is stopped. Measuring the second open circuit voltage of
The control unit has a predetermined value obtained by dividing the voltage difference between the first open circuit voltage and the second open circuit voltage by the number of fuel cells constituting the fuel cell stack. A fuel cell system that stops the operation of the fuel cell stack when larger than a set value .

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