JP2005079006A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve fuel economy performance of a fuel cell by reducing an amount of discharged hydrogen gas during purging. <P>SOLUTION: Unreacted hydrogen gas discharged from hydrogen pole outlet is circulated to hydrogen supply passage through a hydrogen circulation pipe 14. When hydrogen pole water clogs, or inpurity gas is stored in the hydrogen circulation passage, the hydrogen pole discharge gas is discharged to a tank 30 through a hydrogen discharge pipe 31 by opening a first opening/closing valve 35. A hydrogen separation membrane 60 for separating hydrogen from the discharge gas is provided in the tank 30. A pressure sensor 40 senses hydrogen pole outlet pressure P0, and a pressure sensor 41 senses internal pressure P1 in the tank 30. When an the opening/closing valve 35 is opened, a controller, not shown, drives a pump 34 as first flow rate control means so that hydrogen is returned to the hydrogen circulation passage from the tank 30 while keeping the difference pressure of the hydrogen pole outlet pressure P0 and the internal pressure P1 of the tank 30 constant. A water pump 52 provides water in use for humidification from the tank 30 to a humidifier 50 through a water pipe 51. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a fuel cell system, and more particularly to a fuel cell system in which a purge function is improved to improve fuel efficiency.

  In a fuel cell, a fuel gas such as hydrogen gas and an oxidizing gas containing oxygen are electrochemically reacted through an electrolyte, and electric energy is directly taken out between electrodes provided on both surfaces of the electrolyte. In particular, solid polymer fuel cells using solid polymer electrolytes are attracting attention as power sources for electric vehicles because of their low operating temperature and easy handling.

  Since a solid polymer membrane used in a polymer electrolyte fuel cell usually does not exhibit sufficient hydrogen ion conductivity unless it is in a humidified state, it humidifies hydrogen gas and / or oxidant gas supplied to the fuel cell. ing. However, depending on the operation state, the humidified water and the generated water may condense in the fuel cell stack and the reaction gas passage may be clogged.

  Also, in a fuel cell that uses air as the oxidant gas, nitrogen contained in the air permeates the solid polymer membrane and accumulates in the hydrogen circulation path, reducing the partial pressure of the hydrogen gas at the hydrogen electrode, thus reducing operating efficiency. descend. When water clogging or nitrogen gas accumulation occurs as described above, an operation generally called purging is performed to eliminate water clogging or nitrogen gas accumulation.

As an example of a purge operation in a conventional fuel cell, for example, a fuel cell system described in Patent Document 1 is known. In this fuel cell system, the hydrogen electrode exhaust gas is discharged out of the system by opening a purge valve provided in the hydrogen circulation passage in order to prevent the fluttering in the fuel cell.
Japanese Patent Laid-Open No. 2002-246045 (page 6, FIG. 1)

  However, in the above-described conventional fuel cell system, surplus hydrogen is released out of the system by opening the purge valve from the hydrogen circulation system, so that the amount of unreacted hydrogen released increases and system efficiency deteriorates. There was a point.

  In order to solve the above problems, the present invention provides a fuel cell system including a hydrogen circulation passage for circulating exhaust gas discharged from a hydrogen electrode outlet of a fuel cell to a hydrogen supply passage, through the hydrogen discharge pipe. A tank connected to the hydrogen circulation passage, a first on-off valve that opens and closes the hydrogen discharge pipe, a hydrogen return pipe that connects the tank and the hydrogen supply passage, and a flow rate of the hydrogen return pipe is adjusted. A first flow rate control means is provided.

  According to the present invention, in a fuel cell system including a hydrogen circulation channel that circulates exhaust gas discharged from the hydrogen electrode outlet of the fuel cell to a hydrogen supply channel, the fuel cell system is connected to the hydrogen circulation channel via a hydrogen discharge pipe. A first open / close valve that opens and closes the hydrogen discharge pipe, a hydrogen return pipe that connects the tank and the hydrogen supply flow path, and a first flow rate control means that adjusts the flow rate of the hydrogen return pipe. Therefore, by opening the first on-off valve, water clogging inside the fuel cell is eliminated or purging is performed to release nitrogen accumulated in the hydrogen circulation flow path out of the circulation flow path, and the discharged hydrogen is stored in the tank. Since it can be returned to the hydrogen flow path while being adjusted by the flow rate control means, hydrogen is not exhausted to the outside, so that the efficiency of the fuel cell system can be increased.

  In addition, since the pressure in the tank can be controlled by the flow control means and the first on-off valve, the water pressure and nitrogen release performance can be purged by lowering the pressure in the tank below the hydrogen circulation flow path, as in the case of atmospheric release. There is no deterioration in performance.

  Next, embodiments of the present invention will be described in detail with reference to the drawings. Each of the following embodiments, when applied to a fuel cell vehicle, can increase the efficiency of the fuel cell system and improve the fuel efficiency of the vehicle.

  FIG. 1 is a configuration diagram illustrating the configuration of a first embodiment of a fuel cell system according to the present invention. In FIG. 1, a fuel cell system includes a fuel cell (stack) 1 that generates power using hydrogen and air, an air supply device 2 such as a compressor, a humidifier 7 that humidifies air, and a high pressure that stores hydrogen at high pressure. Hydrogen tank 3, ejector 4 as a hydrogen circulation device, humidifier 50 that humidifies and supplies hydrogen sent from ejector 4 to fuel cell 1, and exhaust gas discharged from the hydrogen electrode outlet is returned to the hydrogen electrode inlet side. Hydrogen circulation pipe 14, tank 30 connected to hydrogen circulation pipe 14 through hydrogen discharge pipe 31, first on-off valve 35 for opening and closing hydrogen discharge pipe 31, and returning hydrogen from tank 30 to the hydrogen electrode inlet side A hydrogen return pipe 33 that is a path and a hydrogen pump 34 that pumps gas from the tank 30 to the hydrogen electrode inlet side through the hydrogen return pipe 33 are provided.

  A hydrogen separation membrane 60 is provided inside the tank 30. The hydrogen separation membrane 60 can separate hydrogen from the exhaust gas sent from the hydrogen discharge pipe 31 to the tank 30 and return the gas having an increased hydrogen concentration to the hydrogen electrode inlet side through the hydrogen return pipe 33.

  Moreover, the water piping 51 which connects the tank 30 and the humidifier 50, and the water pump 52 which sends the water of the tank 30 to the humidifier 50 through the water piping 51 are provided.

  Although not shown, a cell voltage detector for detecting the voltage of each cell of the fuel cell 1 or a cell group in which a certain number of cells are connected in series is provided, and the detection signal is transmitted to a controller (not shown), It is used for determining whether or not purging is necessary.

  Further, a pressure sensor 40 is provided at the hydrogen electrode outlet of the fuel cell 1, and a pressure sensor 41 is provided at the tank 30. The controller uses the detection values of the pressure sensors 40 and 41 to control the pump 34 that recirculates the hydrogen gas separated from the tank 30 by the hydrogen separation membrane 60 to the fuel cell 1 and also uses the first on-off valve. The opening / closing timing of 35 is controlled.

The operation of the fuel cell system of FIG. 1 is as follows.
The air from which dust is removed by an air filter (not shown) is compressed by the air supply device 2 and sent to the humidifier 7 via the air pipe 22. The air humidified by the humidifier 7 is supplied to the air electrode inlet of the fuel cell 1. An air pressure regulating valve 11 is provided at the air electrode outlet of the fuel cell 1, and the air electrode pressure of the fuel cell 1 is adjusted by the opening degree of the air pressure regulating valve 11 and the driving force of the air supply device 2. The air pressure regulating valve 11 discharges exhaust air to the outside of the system via the air discharge pipe 12.

  The hydrogen gas in the high-pressure hydrogen tank 3 is adjusted to the operating pressure via the on-off valve 6, the first pressure regulating valve 16 that regulates the pressure of the high-pressure hydrogen gas to a certain medium pressure, and the second pressure regulating valve 17. Supplied to the nozzle. The ejector 4 draws in the exhaust gas from the hydrogen circulation pipe 14 connected to the suction port using the new hydrogen gas supplied to the nozzle as the driving flow, and discharges the mixed gas of the new hydrogen gas and the exhaust gas from the diffuser. This mixed gas is humidified by the humidifier 50 and supplied to the hydrogen electrode of the fuel cell 1.

  Hydrogen that has not been used at the hydrogen electrode of the fuel cell 1 is discharged as exhaust gas from the hydrogen electrode outlet, and returns to the suction port of the ejector 4 through the hydrogen circulation pipe 14. Then, it is mixed with new hydrogen by the ejector 4 and supplied again to the hydrogen electrode of the fuel cell 1 through the humidifier 50.

  When water accumulates in the hydrogen flow path inside the fuel cell 1 or in the hydrogen flow path that supplies hydrogen to the fuel cell 1, the reaction is inhibited. Therefore, by temporarily increasing the flow rate of hydrogen passing through the fuel cell, Then, it is necessary to perform a purge (water purge) to remove water in the fuel cell.

  In this embodiment, the tank 30 is purged when a certain time has elapsed since the previous purge, or when the total voltage or a part of the cell voltage of the fuel cell 1 is lowered. At this time, the purge operation can be performed by opening the first on-off valve 35 and allowing hydrogen to flow out from the hydrogen discharge pipe 31 to the tank 30.

  Since the hydrogen separation membrane 60 is provided inside the tank 30, a gas with a high hydrogen concentration is separated from the hydrogen electrode exhaust gas discharged via the first on-off valve 35, and the humidifier 50 is connected via the pump 34. It is returned to the entrance side and reused.

  At this time, the pressure in the tank 30 is measured by the pressure sensor 41, and the pump 34 is operated so that the pressure is always lower than the pressure measured by the pressure sensor 40 provided in the hydrogen circulation passage. . This pressure difference is set experimentally so as to obtain a hydrogen flow rate necessary for the water purge of the fuel cell.

  Thus, the hydrogen discharged to the tank 30 can be supplied again to the fuel cell by the pump 34 and used for power generation. This eliminates wasteful exhausted hydrogen and improves system efficiency.

  In this embodiment, the water recovered in the tank 30 by the water purge is supplied to the humidifier 50. However, the present invention is not limited to this, and the recovered water may be supplied to the air humidifier 7.

  Next, the purge control operation in this embodiment will be described with reference to the flowchart of FIG. The flowchart in FIG. 4 is configured as a subroutine that is called and executed from the main routine of the controller every second, for example. It is assumed that the controller includes a purge timer Tp that measures an elapsed time since the previous purge, for example, as a software timer.

  First, at step (hereinafter, step is abbreviated as S) 10, the controller reads the purge timer Tp, and at S12, determines whether or not the value of the purge timer Tp exceeds a predetermined value T1. If it is determined in S12 that Tp exceeds T1, it is determined that a predetermined time has elapsed since the previous purge, and the process proceeds to S18 in order to perform the purge operation.

  If it is determined in S12 that Tp is equal to or less than T1, the process proceeds to S14, and the controller reads the cell voltage detected by the cell voltage detector. Next, in S16, the controller determines whether or not the cell voltage has decreased. If there is no drop in the cell voltage, return to the main routine without doing anything.

  If it is determined in S16 that the cell voltage falls below the specified value almost uniformly in the entire fuel cell 1, accumulation of nitrogen gas or the like is considered, and a purge is necessary. When water clogging occurs in the fuel cell 1, the cell voltage decreases unevenly, and the voltage of the cell in which water clogging has occurred or the cell group including the cell decreases, so that purging is performed. .

  If it is determined in S16 that the cell voltage is decreased, the process proceeds to S18, and the controller starts driving the pump 34. Next, in S20, the controller reads the pressure detection value from the pressure sensors 40 and 41. Next, in S22, the controller determines whether or not a value obtained by subtracting the internal pressure P1 of the tank 30 detected by the pressure sensor 41 from the pressure P0 detected by the pressure sensor 40 exceeds the predetermined pressure Pa. If the predetermined pressure is not exceeded, the process returns to S20.

  If P0-P1 exceeds Pa in S22, the process proceeds to S24, the first on-off valve 35 is opened, and the exhaust gas is introduced into the tank 30 through the hydrogen discharge pipe 31 from the hydrogen electrode outlet (or hydrogen circulation path).

  Next, in S26, the controller reads the pressure detection value from the pressure sensors 40 and 41. Next, in S28, the controller determines whether or not a value obtained by subtracting the internal pressure P1 of the tank 30 detected by the pressure sensor 41 from the pressure P0 detected by the pressure sensor 40 exceeds the predetermined pressure Pa. The predetermined value Pa of the pressure difference is experimentally obtained in advance so as to obtain a hydrogen flow rate necessary for water purge of the fuel cell, and is set as a constant in the controller.

  If it is determined in S28 that the predetermined pressure Pa is exceeded, the process proceeds to S30, and if it does not exceed the predetermined pressure Pa, the process proceeds to S32. In S30, the controller decreases the driving force of the pump 34 by a certain value and proceeds to S34. In S32, the controller increases the driving force of the pump 34 by a certain value and proceeds to S34.

  In S34, the controller determines whether or not a predetermined time has elapsed since the first on-off valve 35 was opened in S24. If the predetermined time has not elapsed, the process returns to S26. By the loop from S26 to S34, P0-P1 is maintained at the predetermined pressure difference Pa and purge is performed.

  If it is determined in S34 that the predetermined time has elapsed, the process proceeds to S36. The predetermined time is set as a constant in the controller by experimentally obtaining in advance the time required for water purge of the fuel cell.

  In S36, the pump 34 is stopped, and in S38, the first on-off valve 35 is closed, the purge timer Tp is reset in S40, the purge process is terminated, and the process returns to the main routine.

  As described above, according to the present embodiment, purge is performed by opening the first on-off valve 35, and the discharged hydrogen can be stored in the tank 30 and returned to the hydrogen flow path by the pump 34. Since hydrogen is not exhausted to the outside, the system can be made highly efficient.

  Further, since the pressure in the tank can be controlled by the pump 34 and the first on-off valve 35, the pressure in the tank 30 is made lower than the hydrogen circulation flow path, and then the first on-off valve 35 is opened, which is the same as when the atmosphere is released. Water removal performance can be obtained.

In addition, since the differential pressure between the hydrogen circulation passage and the tank internal pressure is always kept constant, even if the operating pressure is changed, a pressure difference necessary for purging can be secured and control can be performed in response to a sudden purge request.
Further, when the operating pressure is high, it is not necessary to raise the pump head unnecessarily by increasing the tank pressure accordingly, and the efficiency can be increased.

  In the present embodiment, the pump 34 is driven only at the time of purging so that the hydrogen gas does not flow back when the pump 34 is stopped like the diaphragm pump, but when using a pump that flows back when the operation is stopped, During the fuel cell operation, the pump operation may be continued, or an on-off valve may be provided in series with the pump.

  Further, since the hydrogen separation membrane 60 is provided in the hydrogen tank, the hydrogen concentration in the hydrogen circulation flow path can be increased by increasing the purity of the hydrogen discharged by the nitrogen purge and returning it to the hydrogen circulation flow path. In addition, the load on the hydrogen circulation device such as an ejector can be reduced and the hydrogen circulation rate can be increased.

  Further, when the fuel consumption rate is high at the hydrogen electrode of the fuel cell, condensed water is generated downstream of the fuel cell. Since this moisture is discharged into the tank at the time of purging, using this moisture for humidification eliminates the moisture thrown away into the exhaust together with the purge, thereby improving the water balance.

  Next, Example 2 will be described. FIG. 2 is a configuration diagram illustrating the configuration of a second embodiment of the fuel cell system according to the present invention.

  In FIG. 2, the fuel cell system includes a fuel cell (stack) 1 that generates power using hydrogen and air, an air supply device 2 such as a compressor, a humidifier 7 that humidifies air, and a high pressure that stores hydrogen at high pressure. The hydrogen tank 3, the ejector 4 as a hydrogen circulation device, the hydrogen circulation pipe 14 for returning the exhaust gas discharged from the hydrogen electrode outlet to the hydrogen electrode inlet side, and the hydrogen circulation pipe 14 are connected via the hydrogen discharge pipe 31. The tank 30, the first on-off valve 35 that opens and closes the hydrogen discharge pipe 31, the hydrogen return pipe 33 that is a path for returning hydrogen from the tank 30 to the hydrogen electrode inlet side, and the hydrogen electrode from the tank 30 via the hydrogen return pipe 33. And a hydrogen pump 34 for pumping gas to the inlet side.

  Although not shown, a cell voltage detector for detecting the voltage of each cell of the fuel cell 1 or a cell group in which a certain number of cells are connected in series is provided, and the detection signal is transmitted to a controller (not shown), It is used for determining whether or not purging is necessary.

Further, a pressure sensor 40 is provided at the hydrogen electrode outlet of the fuel cell 1, a pressure sensor 41 is provided at the tank 30, and a pressure sensor 42 is provided at the hydrogen electrode inlet of the fuel cell 1. The controller controls the second opening / closing valve 37 for recirculating hydrogen gas from the tank 30 to the fuel cell 1 using the detection values of the pressure sensors 40, 41, 42, and opens / closes the first opening / closing valve 35. Control timing.
Since the other components are the same as those in FIG. 1 of the first embodiment, the same reference numerals are given to the same components, and duplicate descriptions are omitted.

  In the second embodiment, when the pressure downstream of the fuel cell detected by the pressure sensor 40 is higher than the internal pressure of the tank 30, it is possible to perform the purge by opening the first on-off valve 35, and the pressure sensor 41 detects the pressure. When the internal pressure of the tank 30 is higher than the fuel cell inlet pressure detected by the pressure sensor 42, the second on-off valve 37 is opened to return the hydrogen in the tank 30 upstream of the fuel cell.

Next, the operation of the second embodiment will be described.
When purging is required, the second pressure regulating valve 17, the air supply device 2, and the air pressure regulating valve 11 are controlled to increase the operating pressure of the fuel cell 1, and the pressure downstream of the fuel cell is set to the tank. Purge is performed by raising the pressure from the internal pressure of 30, and thereafter, the operation pressure is lowered, and the second on-off valve 37 is controlled to lower the tank internal pressure.

  Next, the purge control operation in this embodiment will be described with reference to the flowchart of FIG. The flowchart of FIG. 5 is configured as a subroutine that is called and executed from the main routine of the controller every second, for example. It is assumed that the controller includes a purge timer Tp that measures an elapsed time since the previous purge, for example, as a software timer.

First, the processing from S10 to S16 is the same as that of the first embodiment shown in FIG.
If it is determined in S16 that the cell voltage has decreased, the process proceeds to S50, where the controller controls the second pressure regulating valve 17, the air supply device 2, and the air pressure regulating valve 11 to reduce the operating pressure of the fuel cell 1. Raise. Next, in S52, the controller reads the pressure detection value from the pressure sensors 40 and 41. Next, in S54, the controller determines whether or not the pressure P0 at the hydrogen electrode outlet detected by the pressure sensor 40 exceeds the internal pressure P1 of the tank 30 detected by the pressure sensor 41. If not, the process returns to S50.

  If it is determined in S54 that P0 exceeds P1, the process proceeds to S56, the first on-off valve 35 is opened, and the exhaust gas is introduced into the tank 30 through the hydrogen discharge pipe 31 from the hydrogen electrode outlet (or hydrogen circulation path). To do.

  Next, in S58, the controller determines whether or not a predetermined time has elapsed since the first on-off valve 35 was opened in S56. If the predetermined time has not elapsed, the process returns to S58. Purging is performed from the hydrogen circulation path to the tank 30 by the self-loop of S58.

  If the predetermined time has passed in the determination of S58, the process proceeds to S60. The predetermined time is set as a constant in the controller by experimentally obtaining in advance the time required for water purge of the fuel cell.

  In S60, the controller closes the first on-off valve 35, and in S62, the controller controls the second pressure regulating valve 17, the air supply device 2, and the air pressure regulating valve 11 to lower the operating pressure of the fuel cell 1. Next, in S <b> 64, the controller reads the pressure detection value from the pressure sensors 41 and 42. Next, in S66, the controller determines whether or not the internal pressure P1 of the tank 30 detected by the pressure sensor 41 exceeds the pressure P2 at the fuel cell hydrogen electrode inlet detected by the pressure sensor 42. If it is determined in S66 that P1 exceeds P2, the process proceeds to S68, the second on-off valve 37 is opened, and the process returns to S64.

  If P1 does not exceed P2 in the determination of S66, the process proceeds to S70 and the second on-off valve 37 is closed. Next, the purge timer Tp is reset to end the purge process, and the process returns to the main routine.

  As described above, in this embodiment, purging is performed using the change in operating pressure without using the hydrogen pump used in the first embodiment, and the purged hydrogen discharged into the tank is supplied to the hydrogen circulation passage. Can be returned.

  Next, Example 3 will be described. FIG. 3 is a configuration diagram illustrating the configuration of a third embodiment of the fuel cell system according to the present invention.

  In FIG. 3, the fuel cell system includes a fuel cell (stack) 1 that generates power using hydrogen and air, an air supply device 2 such as a compressor, a humidifier 7 that humidifies air, and a high pressure that stores hydrogen at high pressure. The hydrogen tank 3, the ejector 4 as a hydrogen circulation device, the hydrogen circulation pipe 14 for returning the exhaust gas discharged from the hydrogen electrode outlet to the hydrogen electrode inlet side, and the hydrogen circulation pipe 14 are connected via the hydrogen discharge pipe 31. The tank 30, the first on-off valve 35 that opens and closes the hydrogen discharge pipe 31, the hydrogen return pipe 33 that is a path for returning hydrogen from the tank 30 to the hydrogen electrode inlet side, and the hydrogen electrode from the tank 30 via the hydrogen return pipe 33. And a hydrogen pump 34 for pumping gas to the inlet side.

  Further, the tank 30 and the air discharge pipe 12 are connected by a third on-off valve 38 and an orifice 39 which are second flow rate control means, and the third on-off valve 38 is controlled after the first on-off valve 35 is opened so that the tank 30 is connected. The discharged gas can be discharged into the transfer pipe 12.

  Although not shown, a cell voltage detector for detecting the voltage of each cell of the fuel cell 1 or a cell group in which a certain number of cells are connected in series is provided, and the detection signal is transmitted to a controller (not shown), It is used for determining whether or not purging is necessary.

  Further, a pressure sensor 40 is provided at the hydrogen electrode outlet of the fuel cell 1, and a pressure sensor 41 is provided at the tank 30. The controller uses the detection values of the pressure sensors 40 and 41 to control the pump 34 for recirculating hydrogen gas from the tank 30 to the fuel cell 1 and to control the first on-off valve 35 and the third on-off valve 38. Controls opening and closing timing.

  Since the other components are the same as those in FIG. 1 of the first embodiment, the same reference numerals are given to the same components, and duplicate descriptions are omitted.

Next, the operation of the third embodiment will be described.
The tank 30 includes a pipe 70 communicating with the air discharge pipe 12, an on-off valve 38 and an orifice (throttle) 39 as second flow rate control means, and hydrogen, nitrogen, moisture released from the hydrogen circulation passage 14 to the tank 30. Flows out to the air discharge pipe 12 through the orifice 39.

  The orifice 39 is sized so as to be less than a flow rate that can dilute the hydrogen discharged from the tank 30 to a predetermined concentration or less that is safely set by the air electrode exhaust air of the fuel cell 1 flowing through the air discharge pipe 12. .

  Nitrogen permeates through the electrolyte membrane from the air electrode of the fuel cell to the hydrogen electrode of the fuel cell, so that nitrogen accumulates in the hydrogen circulation flow path, reducing the hydrogen concentration and reducing power generation efficiency. The hydrogen circulation flow rate obtained by the ejector 4 is also reduced, and the power generation efficiency of the fuel cell is further reduced.

  For this reason, it is necessary to discharge nitrogen out of the hydrogen circulation channel before the nitrogen concentration greatly reduces the power generation efficiency. For this reason, when the nitrogen concentration becomes so high as to affect the fuel cell performance, it is necessary to discharge nitrogen from the hydrogen circulation passage. If discharged directly into the exhaust air flow path, the exhaust air flow rate of the fuel cell becomes small at a low load, so that hydrogen has a concentration in the combustible range.

  In this embodiment, the hydrogen electrode exhaust gas containing hydrogen, nitrogen and moisture of the fuel cell 1 is once discharged from the hydrogen circulation flow path to the tank 30, and then the flow rate of the hydrogen released into the tank 30 is restricted by the orifice 39. By gradually flowing out to the air discharge pipe, it can be discarded at a concentration below the flammable range while being diluted with exhaust air.

  The above control is performed at predetermined time intervals or when the voltage is lowered by utilizing the fact that the accumulation of nitrogen is substantially proportional to the operation time of the fuel cell and that the cell voltage of the fuel cell generally decreases during the accumulation of nitrogen.

  Further, when it is detected by a cell voltage detector of a fuel cell (not shown) that a part of the cell voltage has decreased, that is, when water clogging occurs in the hydrogen electrode flow path of the fuel cell, the first on-off valve 35 Is opened, and water in the fuel cell channel is drained, and then the hydrogen-rich gas that has flowed into the tank 30 is re-flowed into the hydrogen circulation channel using the pump 34.

  As a result, the hydrogen-rich gas is discharged into the tank in a short time, so that the water in the fuel cell can be blown out. In this case, since the N2 concentration of the gas flowing into the tank 30 is still below the allowable concentration, the system returns to the hydrogen circulation flow path by the pump 34 so that hydrogen is not discharged out of the system. Energy efficiency can be improved.

  Further, when the tank internal pressure detected by the pressure sensor 41 installed in the tank is lower than a predetermined pressure, the air discharge pipe may be higher than the internal pressure of the tank 30 due to pipe pressure loss. The third on-off valve 38 is closed so as not to flow into the tank 30 from the discharge pipe 12. The predetermined pressure is assumed to be the pressure in the air exhaust pipe under the operating condition estimated in advance or clarified by experiment.

  Next, the purge control operation in this embodiment will be described with reference to the flowchart of FIG. The flowchart of FIG. 6 is configured as a subroutine that is called and executed from the main routine of the controller every second, for example. It is assumed that the controller includes a purge timer Tp that measures an elapsed time since the previous purge, for example, as a software timer.

  First, S10 to S16 are the same as those in the first embodiment shown in FIG. If it is determined in S16 that the cell voltage has decreased, the process proceeds to S80, and the controller opens the first on-off valve 35. Thereby, the exhaust hydrogen gas starts to flow out to the tank 30 from the hydrogen electrode or the hydrogen circulation path.

  Next, in S82, the controller determines whether or not there is a voltage drop in only some cells. If the voltage drop is only in some cells, the process proceeds to S100. If the voltage of all the cells is reduced, the hydrogen partial pressure has decreased due to accumulation of nitrogen or the like, so that a gas purge is required, and the process proceeds to S84.

  In S84, the controller opens the third on-off valve 38. Thereby, hydrogen containing nitrogen is discharged from the tank 30 to the air discharge pipe through the third on-off valve 38 and the orifice 39. Next, the controller reads the pressure detection value from the pressure sensor 41 in S86. Next, in S88, the controller determines whether or not the internal pressure P1 of the tank 30 detected by the pressure sensor 41 exceeds a predetermined pressure Pb. If it exceeds the predetermined pressure Pb, the process proceeds to S92. If it does not exceed the predetermined pressure Pb, the process proceeds to S90. The predetermined pressure Pb is preliminarily estimated or is the pressure in the air discharge pipe under the operating condition clarified through experiments, and is stored in the controller in advance.

  In S90, it is determined whether or not a predetermined time has elapsed since S84. If the predetermined time has not elapsed, the process returns to S86. If the predetermined time has elapsed, the process proceeds to S92, the controller closes the third on-off valve 38, and proceeds to S106.

  On the other hand, in S100, since the voltage of only a part of the cells is lowered, the drive of the pump 34 is started in order to perform the water purge for eliminating the water clogging. Next, in S102, it is determined whether or not a predetermined time has elapsed. If the predetermined time has not elapsed, a self-loop is performed in S102. If the predetermined time has elapsed in S102, the process proceeds to S104, the pump 34 is stopped, the first on-off valve 35 is closed in S106, the purge timer Tp is reset in S108, the purge operation is terminated, and the process returns to the main routine. .

  According to the present embodiment described above, the exhaust hydrogen gas is discharged from the hydrogen circulation path to the tank 30 in a short time, so that the water in the fuel cell can be efficiently discharged. In addition, it is determined whether the cell voltage drop is all cells or some cells, and it is controlled whether the gas in the tank is discharged out of the system or returned to the hydrogen circulation path. It is possible to improve the energy efficiency of the system.

1 is a system configuration diagram illustrating the configuration of a first embodiment of a fuel cell system according to the present invention. FIG. It is a system block diagram explaining the structure of Example 2 of the fuel cell system which concerns on this invention. It is a system block diagram explaining the structure of Example 3 of the fuel cell system which concerns on this invention. 3 is a flowchart for explaining the operation of the first embodiment. 10 is a flowchart for explaining the operation of the second embodiment. 10 is a flowchart for explaining the operation of the third embodiment.

Explanation of symbols

1: Fuel cell 2: Air supply device 3: High-pressure hydrogen tank 4: Ejector 7: Humidifier 11: Air pressure regulating valve 12: Air discharge pipe 14: Hydrogen circulation flow path 16: First pressure regulating valve 17: Second pressure regulating valve 22 : Air pipe 30: Tank 31: Hydrogen discharge pipe 33: Hydrogen return pipe 34: Pump 35: First on-off valve 37: Second on-off valve 38: Third on-off valve 39: Orifice 40: Pressure sensor 41: Pressure sensor 42: Pressure sensor 50: Humidifier 51: Water piping 52: Water pump 60: Hydrogen separation membrane 70: Waste hydrogen piping

Claims (9)

In a fuel cell system provided with a hydrogen circulation channel for circulating exhaust gas discharged from the hydrogen electrode outlet of the fuel cell to a hydrogen supply channel,
A tank connected to the hydrogen circulation passage through a hydrogen discharge pipe;
A first on-off valve for opening and closing the hydrogen discharge pipe;
A hydrogen return pipe connecting the tank and the hydrogen supply flow path;
First flow rate control means for adjusting the flow rate of the hydrogen return pipe;
A fuel cell system comprising: The first flow rate control means is a pump;
When returning the gas in the tank to the hydrogen supply passage, the pump sucks the gas in the tank so that the pressure in the tank is lower than the pressure in the hydrogen supply flow path. 2. The fuel cell system according to claim 1, wherein the fuel cell system is discharged into the fuel cell.   3. The fuel cell system according to claim 2, wherein the operation of the pump is controlled so that a differential pressure between a pressure in the hydrogen circulation passage and a pressure in the tank is constant.   Generates a predetermined differential pressure between the pressure of the hydrogen circulation flow path and the pressure in the tank by driving the pump every predetermined time or when the whole voltage or a part of the voltage of the fuel cell decreases. 3. The fuel cell system according to claim 2, wherein the first on-off valve is opened thereafter. The flow rate control means is a second on-off valve provided in the hydrogen return pipe;
When the operation pressure is high, the first on-off valve is opened to exhaust the exhaust gas from the hydrogen circulation passage to the tank,
2. The fuel cell system according to claim 1, wherein the second on-off valve is opened during operation at a low operating pressure, and gas is caused to flow from the tank into the hydrogen supply flow path by the internal pressure of the tank. A pipe connecting the tank and the air discharge pipe of the fuel cell;
Second flow rate control means for controlling the flow rate of the pipe,
The fuel cell according to any one of claims 1 to 5, wherein after the first on-off valve is opened, the second flow rate control means is controlled to discharge the gas in the tank to the air discharge pipe. system. If a drop in the cell voltage of some of the fuel cells is detected,
7. The fuel cell system according to claim 6, wherein after the first on-off valve is opened, the first flow rate control means is controlled to return the gas in the tank to the hydrogen supply channel. The tank includes a hydrogen separation membrane,
6. The gas component discharged into the tank from the hydrogen circulation channel is separated, and a gas having an increased hydrogen concentration is discharged to the hydrogen supply channel. The fuel cell system according to item.   A water pipe and a water pump connected to the tank are provided, and water supplied from the tank through the water pipe is used for humidifying at least one of hydrogen and air supplied to the fuel cell. The fuel cell system according to any one of claims 1 to 8.

Images