JP2006331966A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To restrain hydrogen gas from being exhausted in vain before being supplied to a fuel cell without using a check valve, in a fuel cell system utilizing hydrogen contained in anode offgas in circulation. <P>SOLUTION: A control computer detects a flow of anode offgas with the use of a flow meter 80, in which, if a flow is smaller than a reference value, exhaust of the anode offgas is carried out with a first exhaust valve 71 located at an upstream side of a circulation pump 40 in order to restrain fuel gas from flowing into a hydrogen circulation tube 33 from a branch point 38 to be wastefully exhausted. On the other hand, if a flow detected is larger than the reference value, it is judged that the fuel gas will not flow into the hydrogen circulation tube 33 from the branched part 38, and the anode offgas is exhausted with a second exhaust valve 72 located at a downstream side of the circulation pump 40. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fuel cell system that circulates and reuses hydrogen contained in an anode off gas.

  In recent years, fuel cells that generate electricity by an electrochemical reaction between hydrogen and oxygen have attracted attention as power sources mounted in electric vehicles. In a fuel cell system including such a fuel cell, the anode off gas discharged from the anode of the fuel cell is circulated and supplied to the fuel cell, so that the residual hydrogen contained in the anode off gas can be efficiently used. (See Patent Documents 1 to 4).

JP 2004-172025 A JP 2004-165094 A JP 200431234 A JP-A-6-223859

  For example, in the fuel cell system described in Patent Document 1, the hydrogen gas supplied from the hydrogen tank to the fuel cell does not flow into the circulation system that circulates the anode off-gas, so that the hydrogen supply system and the circulation system are connected to each other. A check valve is provided. Since the circulation system is provided with a discharge valve that periodically discharges the anode off gas to the outside, if hydrogen gas flows into the circulation system from the hydrogen supply system, hydrogen gas is supplied from the discharge valve to the fuel cell. This is because it may be discharged before.

  However, in a fuel cell system equipped with a check valve, when left in an environment of 0 ° C. or less, the check valve may freeze and hinder circulation of the anode off gas. Further, since the check valve normally does not require electric power for its operation and does not generate heat, once it is frozen, it is difficult to unfreeze the ice independently.

  In view of such circumstances, the problem to be solved by the present invention is to supply hydrogen gas to a fuel cell without using a check valve in a fuel cell system that circulates and uses hydrogen contained in the anode off-gas. This is to prevent wasteful discharge before being done.

In order to solve the above problems, the fuel cell system of the present invention is configured as follows. That is,
A fuel cell system comprising a fuel cell,
A hydrogen supply channel connected to the fuel cell and supplying hydrogen gas to the fuel cell;
A circulation flow path connected to the fuel cell and the hydrogen supply flow path for flowing an anode off-gas discharged from the fuel cell to the hydrogen supply flow path;
A circulation pump which is provided in the circulation flow path and pressurizes the anode off gas discharged from the fuel cell and flows it to the hydrogen supply flow path;
A first discharge valve provided between the fuel cell in the circulation flow path and the circulation pump, for discharging the anode off gas flowing in the circulation flow path to the outside;
A second discharge valve that is provided between the circulation pump in the circulation flow path and the hydrogen supply flow path, and discharges the anode off gas flowing in the circulation flow path to the outside;
Based on the state quantity of the anode off gas flowing in the circulation flow path, either the first exhaust valve or the second exhaust valve is selected, and the selected exhaust valve is opened and closed to bring the anode off gas to the outside. And a control unit for discharging.

  In the fuel cell system of the present invention, the first discharge valve provided on the upstream side (fuel cell side) of the circulation pump and the downstream side of the circulation pump (hydrogen supply) based on the state quantity of the anode off gas flowing in the circulation channel The anode off gas is discharged to the outside by properly using the second discharge valve provided on the flow path side). Therefore, if the state quantity of the anode off gas is such that the hydrogen gas does not flow from the hydrogen supply flow path into the circulation flow path, the anode off gas is discharged from the second discharge valve downstream of the circulation pump, If the state quantity is a state quantity that may cause hydrogen gas to flow from the hydrogen supply flow path to the circulation flow path, the hydrogen off gas is discharged by discharging the anode off-gas from the first discharge valve on the upstream side of the circulation pump. It is possible to suppress wasteful discharge before being supplied to the fuel cell. The state quantity of the anode off gas is a parameter that can be estimated that hydrogen gas may flow from the hydrogen supply flow path into the circulation flow path and be exhausted from the discharge valve. It refers to the flow rate and pressure.

In the fuel cell system configured as described above,
Furthermore, it comprises a flow rate detection means for detecting the flow rate of the anode off gas flowing in the circulation channel,
The control unit may select the discharge valve based on a flow rate detected by the flow rate detection unit as a state quantity of the anode off gas.
In this case, the control unit selects the first discharge valve when the flow rate detected by the flow rate detection unit is smaller than a predetermined reference value, and the flow rate is larger than the predetermined reference value. In this case, the second discharge valve can be selected.

  In the fuel cell system having such a configuration, since the flow rate of the anode off-gas is smaller than the reference value, when there is a possibility that hydrogen gas may flow from the hydrogen supply channel to the circulation channel, it is located upstream of the circulation pump. The anode off gas is discharged using the first discharge valve. Accordingly, the presence of the circulation pump suppresses the hydrogen gas from reaching the first discharge valve, so that it is possible to suppress the wasteful discharge of the hydrogen gas. Further, in such a configuration, when the flow rate of the anode off gas is higher than the reference value and the hydrogen gas can be prevented from flowing from the hydrogen supply channel to the circulation channel, the second gas is disposed downstream of the circulation pump. The anode off-gas can be discharged using two discharge valves. Accordingly, the amount of suction of the circulation pump increases as the circulation amount of the anode off gas increases, and the upstream side of the circulation pump becomes negative pressure, making it difficult to discharge the anode off gas from the first exhaust valve. In addition, the anode off gas can be discharged smoothly from the second discharge valve.

  The flow rate detection means estimates the flow rate of the anode off gas according to at least one of the pressure of the anode off gas, the temperature of the anode off gas, the driving amount of the circulation pump, and the power generation amount of the fuel cell. It is good also as what to do.

  With such a configuration, it is possible to select the discharge valve without directly detecting the flow rate of the anode off gas with a flow sensor or the like.

In the fuel cell system configured as described above,
Furthermore, it comprises a pressure detection means for detecting the pressure of the anode off gas flowing in the circulation channel,
The control unit may select the discharge valve based on a pressure detected by the pressure detection unit as a state quantity of the anode off gas.

In such a configuration,
The pressure detection means is provided between the circulation pump and the fuel cell in the circulation flow path,
The control unit has a predetermined reference value obtained by subtracting a pressure in a space in which the anode off-gas is discharged through the first discharge valve or the second discharge valve from the pressure detected by the pressure detection unit. The first discharge valve is selected when the pressure is larger than the second discharge valve, and the second discharge valve is selected when the differential pressure is smaller than the predetermined reference value.

  According to the fuel cell system having such a configuration, when the pressure of the anode off-gas on the upstream side of the circulation pump is reduced by the suction force of the circulation pump, the circulation is not performed on the first discharge valve located on the upstream side of the circulation pump. Since the anode off gas is discharged from the second discharge valve located on the downstream side of the pump, the anode off gas can be discharged smoothly. In such a case, since the circulation amount of the anode off gas is increased by the circulation pump, even if the anode off gas is discharged from the second discharge valve, the hydrogen gas flows from the hydrogen supply channel into the circulation channel. This prevents the hydrogen gas from being discharged wastefully. Further, in such a configuration, when the pressure on the upstream side of the circulation pump is large, the anode off gas can be smoothly discharged by opening and closing the first discharge valve located upstream of the circulation pump. In this case, even if hydrogen gas flows from the hydrogen supply flow path into the circulation flow path, the flow is hindered by the circulation pump, so that the wasteful discharge of hydrogen gas is suppressed. .

  The pressure in the space where the anode off gas is discharged through the first discharge valve or the second discharge valve may be atmospheric pressure. This is because the anode off gas is finally discharged into the atmosphere.

  With such a configuration, atmospheric pressure can be handled as a constant, so that it is not necessary to separately provide a sensor for detecting the pressure in the space, and the system can be simplified.

In the fuel cell system configured as described above,
The pressure detection means is provided between the circulation pump and the hydrogen supply channel in the circulation channel,
The control unit is configured such that a differential pressure obtained by subtracting a pressure of hydrogen gas upstream from a portion coupled with the circulation flow path in the hydrogen supply flow path from a pressure detected by the pressure detection unit is greater than a predetermined reference value. The first discharge valve is selected when the pressure is smaller, and the second discharge valve is selected when the differential pressure is larger than the reference value.

  According to the fuel cell system having such a configuration, if the pressure in the circulation channel is sufficiently larger than the pressure in the hydrogen supply channel, the hydrogen gas is prevented from flowing from the hydrogen supply channel into the circulation channel. Therefore, the anode off gas can be discharged using the second discharge valve located on the downstream side of the circulation pump. Furthermore, if the pressure in the circulation channel is lower than the pressure in the hydrogen supply channel, the anode off-gas is discharged using the first discharge valve located upstream of the circulation pump. Even if hydrogen gas flows into the circulation channel, the flow is hindered by the circulation pump, and it is possible to suppress the wasteful discharge of hydrogen gas.

Hereinafter, in order to further clarify the operations and effects of the present invention described above, embodiments of the present invention will be described based on examples in the following order.
A. First embodiment:
(A1) Configuration of fuel cell system:
(A2) Anode off gas discharge control:
B. Second embodiment:
(B1) Configuration of fuel cell system:
(B2) Anode off gas discharge control:
C. Third embodiment:
(C1) Configuration of fuel cell system:
(C2) Anode off gas discharge control:

A. First embodiment:
(A1) Configuration of fuel cell system:
FIG. 1 is an explanatory diagram showing the overall configuration of a fuel cell system 100a as a first embodiment. As shown in the figure, a fuel cell system 100a includes a fuel cell 10 that generates power by an electrochemical reaction between hydrogen and oxygen, a hydrogen tank 20 that stores high-pressure hydrogen gas, and an air compressor that supplies air to the fuel cell 10. 30, a circulation pump 40 for circulating the anode off gas discharged from the fuel cell 10, a control computer 60 for controlling the operation of the fuel cell system 100 a, and the like. The fuel cell system 100a is mounted on a vehicle and used as a power source for operating a load such as an axle driving motor 50.

  The fuel cell 10 is a solid polymer electrolyte type fuel cell, and has a stack structure in which a plurality of unit cells (not shown) are stacked. Each single cell has a configuration in which a hydrogen electrode (hereinafter referred to as an anode) and an oxygen electrode (hereinafter referred to as a cathode) are arranged with an electrolyte membrane interposed therebetween. By supplying a fuel gas containing hydrogen to the anode side of each single cell of the fuel cell 10 and supplying an oxidizing gas containing oxygen to the cathode side, an electrochemical reaction proceeds and an electromotive force is generated.

  An air supply pipe 31 and a cathode offgas discharge pipe 36 are connected to the cathode of the fuel cell 10. The air compressed by the air compressor 30 is supplied to the fuel cell 10 as an oxidizing gas through the air supply pipe 31. This air is exhausted to the outside through the cathode offgas exhaust pipe 36 after oxygen is consumed by an electrochemical reaction in the fuel cell 10. The gas discharged from the cathode in this way is called cathode off gas.

  A hydrogen supply pipe 32 and a hydrogen circulation pipe 33 are connected to the anode of the fuel cell 10. Hydrogen as fuel gas is supplied from the hydrogen tank 20 to the anode through the hydrogen supply pipe 32. The hydrogen supply pipe 32 is provided with a shut valve 34 and a pressure regulating valve 35. The shut valve 34 is a valve for shutting off the supply of fuel gas from the hydrogen tank 20. On the other hand, the pressure regulating valve 35 is a valve for reducing the pressure of the fuel gas supplied from the hydrogen tank 20 to a pressure suitable for power generation by the fuel cell 10.

  In the fuel cell 10, a part of the hydrogen in the fuel gas is consumed by the electrochemical reaction, and the hydrogen that cannot be consumed by the electrochemical reaction is discharged from the fuel cell 10 to the hydrogen circulation pipe 33 as the anode off gas. The hydrogen circulation pipe 33 is connected to the hydrogen supply pipe 32 via a branch portion 38 provided between the pressure regulating valve 35 and the fuel cell 10. In addition to hydrogen, the anode off gas flowing through the hydrogen circulation pipe 33 contains moisture, nitrogen, and the like that have permeated from the cathode side through the electrolyte membrane in the fuel cell 10.

  The anode off gas discharged to the hydrogen circulation pipe 33 is pressurized by a circulation pump 40 provided in the hydrogen circulation pipe 33. Then, the pressurized anode off gas is supplied again to the hydrogen supply pipe 32 through the branch portion 38. That is, the anode off gas discharged from the fuel cell 10 is circulated and supplied to the fuel cell 10. As described above, since the anode off gas contains hydrogen that could not be consumed by the electrochemical reaction by the fuel cell 10, the anode off gas is circulated and supplied to the fuel cell 10 to efficiently use hydrogen. can do.

  Adjustment of the circulation amount of the anode off gas by the circulation pump 40 is controlled by the control computer 60. Specifically, the control computer 60 increases the circulation amount of the anode off gas by increasing the drive amount of the circulation pump 40 so that more electric power is required for the load such as the motor 50. By doing so, a large amount of hydrogen is supplied to the fuel cell 10 and the amount of power generation increases.

  A first discharge valve 71 is provided on the upstream side (fuel cell 10 side) of the circulation pump 40 in the hydrogen circulation pipe 33, and a second discharge valve 72 is provided on the downstream side (hydrogen supply pipe 32 side). ing. The hydrogen circulation pipe 33 is connected to the anode offgas discharge pipe 75 through these discharge valves 71 and 72. In this embodiment, a flow meter 80 for detecting the flow rate of the anode off gas flowing in the hydrogen circulation pipe 33 is provided between the fuel cell 10 in the hydrogen circulation pipe 33 and the first discharge valve 71.

  Opening and closing of the first discharge valve 71 and the second discharge valve 72 is controlled by the control computer 60. In this embodiment, the control computer 60 selects which discharge valve to discharge the anode off gas according to the flow rate of the anode off gas detected by the flow meter 80. Then, by opening and closing the selected discharge valve at a predetermined timing, the anode off gas in the hydrogen circulation pipe 33 is discharged to the outside through the anode off gas discharge pipe 75. As described above, since the anode off gas contains moisture, nitrogen, and the like, the concentration thereof increases and the hydrogen partial pressure decreases when the circulation is repeated. Therefore, by periodically opening and discharging the first discharge valve 71 or the second discharge valve 72, these impurities can be discharged together with hydrogen to reduce the concentration thereof.

  The control computer 60 includes a CPU 61, a RAM 62, a ROM 63, and various input / output ports. The ROM 63 stores a program for performing opening / closing control of the first discharge valve 71 and the second discharge valve 72 and a program for performing operation control of the entire fuel cell system 100. The CPU 61 reads these programs from the ROM 63 and executes them using the RAM 62 as a work area. The control computer 60 is connected to a flow meter 80, a first discharge valve 71, a second discharge valve 72, a shut valve 34, a pressure regulating valve 35, an air compressor 30, a circulation pump 40, and the like via an input / output port. ing.

(A2) Anode off gas discharge control:
FIG. 2 is a flowchart of an anode offgas discharge control routine that is always executed by the control computer 60 during operation of the fuel cell system 100a. This anode off-gas discharge control routine is executed to discharge the anode off-gas circulating in the hydrogen circulation pipe 33 to the outside using the first discharge valve 71 or the second discharge valve 72.

  When this routine is executed, first, the control computer 60 detects the flow rate Q (l / s) of the anode off gas flowing through the hydrogen circulation pipe 33 using the flow meter 80 (step S100). Then, the flow rate Q is compared with a preset reference value α to determine whether or not the flow rate Q is less than the reference value α (step S110). The reference value α can be set, for example, by experimentally determining the flow rate of the anode off gas that can prevent the fuel gas from flowing into the hydrogen circulation pipe 33 from the branch portion 38.

  As a result of the determination in step S110, if the flow rate Q is less than the reference value α (step S110: Yes), the control computer 60 determines that the fuel gas may flow into the hydrogen circulation pipe 33 from the branch portion 38. Then, the first discharge valve 71 located upstream of the circulation pump 40 is selected as the discharge valve for discharging the anode off gas (step S120), and the second discharge valve 72 is closed (step S130). On the other hand, if the flow rate Q is equal to or greater than the reference value α (step S110: No), the control computer 60 determines that the fuel gas does not flow into the hydrogen circulation pipe 33 from the branch portion 38 and discharges the anode off-gas. The second discharge valve 72 located downstream of the circulation pump 40 is selected (step S140), and the first discharge valve is closed (step S150).

  Next, the control computer 60 opens the discharge valve selected in step S120 or step S140 for t1 seconds (step S160), and then closes the discharge valve for t2 seconds (step S170). As described above, the anode off gas contains impurities such as nitrogen and moisture. Therefore, in order to reduce impurities in the anode off gas, it is necessary to set the time t1 long. However, if the anode off-gas is discharged, hydrogen is discharged together with the impurities. Therefore, it is preferable to set the time t1 as short as possible from the viewpoint of safety while suppressing unnecessary discharge of hydrogen. Therefore, the times t1 and t2 can be set by obtaining the time that can satisfy both requirements by experiments. For example, the time t1 can be set in the range of several tens to several hundreds of milliseconds, and the time t2 can be set in the range of several seconds to several tens of seconds. These t1 and t2 may be fixed values, but the amount of impurities in the anode off-gas is estimated according to the outside air temperature, the amount of power generation, etc., and the duty ratio is adjusted according to the estimated amount of impurities. It may be a thing. Further, when the discharge valves 71 and 72 are provided with a variable throttle, the discharge amount of the anode off gas may be adjusted by adjusting the opening degree. The control computer 60 repeatedly executes the series of processes described above.

  In the fuel cell system 100a of the first embodiment configured as described above, when the power required for the load of the motor 50 or the like is small and the circulation amount of the anode off gas is small, such as immediately after the start of the fuel cell system 100a, the circulation pump The second discharge valve 72 on the downstream side of the 40 is closed, and the anode off gas is discharged from the first discharge valve 71 located on the upstream side of the circulation pump 40. Therefore, even if the fuel gas flows from the hydrogen supply pipe 32 into the hydrogen circulation pipe 33 because the circulation amount of the anode off gas is small, the flow is hindered by the circulation pump 40, and the fuel gas is wasted. Can be suppressed.

  Further, in this embodiment, when a large amount of electric power is required for the load such as the motor 50 and the circulation amount of the anode off gas is increased, the anode off gas is discharged from the second discharge valve 72 located on the downstream side of the circulation pump 40. Discharge. Accordingly, the amount of suction of the circulation pump 40 increases with the increase in the circulation amount of the anode off gas, so that the pressure on the upstream side of the circulation pump 40 decreases, and the pressure (atmospheric pressure) in the anode off gas discharge pipe 75 and the hydrogen circulation. Even when the pressure difference from the pressure in the pipe 33 is not sufficient and it is difficult to discharge the anode off gas from the first discharge valve 71, the anode off gas is discharged smoothly from the second discharge valve 72. It becomes possible. If the circulation amount of the anode off gas is large, the fuel gas is prevented from flowing from the hydrogen supply pipe 32 to the hydrogen circulation pipe 33. Therefore, even if the anode off gas is discharged from the second discharge valve 72, the second discharge valve It is suppressed that fuel gas is discharged from 72 wastefully.

  According to the first embodiment described above, the discharge valve for discharging the anode off gas according to the circulation amount of the anode off gas flowing in the hydrogen circulation pipe 33 is either the first discharge valve 71 or the second discharge valve 72. By switching to this, it is possible to suppress the wasteful discharge of the fuel gas without providing a check valve at the branch portion 38.

  In the present embodiment, the discharge valve for discharging the anode off-gas is switched according to the flow rate of the anode off-gas detected by the flow meter 80. However, the control computer 60 can be used in various ways without using the flow meter 80. It is also possible to estimate the circulation amount of the anode off-gas flowing through the hydrogen circulation pipe 33 from the state quantity and switch the discharge valve based on this estimated value.

  For example, if the circulation pump 40 is a positive displacement pump, the efficiency of this pump is γ, the container capacity is Vc (L), the rotational speed of the pump motor is R (rpm), and the rotational speed ratio of the rotor to the motor is K (= When the temperature and pressure of the anode off-gas sucked by the circulation pump 40 are T (° C.) and P (kPa), respectively, the anode off-gas flow rate Q ( NL / min) can be estimated. However, when the flow rate Q is estimated based on the formula (1), a temperature sensor for detecting the temperature of the anode off-gas and a pressure sensor for detecting the pressure are provided upstream of the circulation pump 40 in the hydrogen circulation pipe 33. And

Q = (γ * Vc * R * K * P * 273) / ((273 + T) * 101.3) (1)

  In the above equation (1), some of the variables may be fixed to predetermined values and the remaining variables may be actually measured. By doing so, the processing burden on the control computer 60 can be reduced.

  In addition to estimating the amount of circulation by the above equation (1), the current value output from the fuel cell 10, the number of revolutions of the circulation pump 40, or the voltage applied to the circulation pump 40 are detected, and from these values The circulation amount of the anode off gas may be estimated based on a predetermined map or function. In general, the higher the current value, the number of rotations, and the voltage, the greater the circulation amount of the anode off gas. It should be noted that the discharge valve may be switched by directly comparing current values, rotation speeds, and actual measured values of voltages with predetermined reference values corresponding to these values without estimating the circulation flow rate.

B. Second embodiment:
(B1) Configuration of fuel cell system:
FIG. 3 is an explanatory diagram showing the overall configuration of the fuel cell system 100b as the second embodiment. The fuel cell system 100b of the present embodiment has substantially the same configuration as the fuel cell system 100a of the first embodiment described above, but does not include the flow meter 80 and includes several pressure sensors. It is different. That is, the fuel cell system 100b according to the present embodiment is provided with a first pressure sensor 81 for detecting the pressure P1 of the anode off-gas at the upstream portion of the circulation pump 40 in the hydrogen circulation pipe 33, and further discharging the anode off-gas. A second pressure sensor 82 for detecting the pressure in the anode off-gas discharge pipe 75 is provided in the pipe 75, and a discharge valve 71 for discharging the anode off-gas according to the pressure detected by the pressure sensors 81 and 82, 72 is switched.

(B2) Anode off gas discharge control:
FIG. 4 is a flowchart of an anode off-gas discharge control routine in the second embodiment. When this routine is executed, first, the control computer 60 detects the pressure P1 of the anode offgas in the upstream portion of the circulation pump 40 using the first pressure sensor 81, and further uses the second pressure sensor 82. Then, the pressure P2 in the anode off gas discharge pipe 75 is detected (step S200). Then, a differential pressure ΔP (= P1−P2) between the detected pressure P1 and pressure P2 is obtained, and it is determined whether or not this differential pressure ΔP is larger than a reference value β (step S210). The reference value β can be set by experimentally obtaining a differential pressure at which the anode off gas in the hydrogen circulation pipe 33 can be smoothly discharged to the anode off gas discharge pipe 75 via the first discharge valve 71.

  If the result of determination in step S210 is that the differential pressure ΔP is larger than the reference value β (step S210: Yes), the control computer 60 can discharge the anode off gas from the first discharge valve 71 to the anode off gas discharge pipe 75. Therefore, the first discharge valve 71 is selected as a discharge valve for discharging the anode off-gas (step S220), and the second discharge valve 72 is closed (step S230). . On the other hand, if the differential pressure ΔP is equal to or less than the reference value β (step S210: No), the control computer 60 secures a differential pressure sufficient to discharge the anode off gas from the first discharge valve 71 to the anode off gas discharge pipe 75. Therefore, the second discharge valve 72 is selected as a discharge valve for discharging the anode off gas (step S240), and the first discharge valve 71 is closed (step S250).

  Next, the control computer 60 opens the discharge valve selected in step S220 or step S240 for t1 seconds (step S260), and then closes the discharge valve for t2 seconds (step S270). The control computer 60 repeatedly executes the series of processes described above.

  In the fuel cell system 100b of the second embodiment configured as described above, when the pressure P1 of the anode off-gas upstream of the circulation pump 40 decreases due to the suction force of the circulation pump 40, the fuel cell system 100b moves downstream of the circulation pump 40. The anode off gas is discharged from the second discharge valve 72 located. Therefore, the anode off gas can be discharged smoothly. In such a case, even if the anode off gas is discharged from the second discharge valve 72, the circulation amount of the anode off gas is increased by the circulation pump 40, so that the fuel gas flows from the hydrogen supply pipe 32 through the branch portion 38. This prevents the fuel gas from being discharged wastefully.

  Furthermore, in the fuel cell system 100b of this embodiment, when the pressure P1 of the anode off-gas upstream of the circulation pump 40 is sufficiently secured, the first discharge valve 71 located upstream of the circulation pump 40 is opened and closed. By doing so, the anode off-gas can be discharged smoothly. In this case, even if the fuel gas flows into the hydrogen circulation pipe 33 from the branch portion 38, the flow is hindered by the circulation pump 40, so that the fuel gas is discharged from the first discharge valve 71 wastefully. This will be suppressed.

  In the second embodiment, the second pressure sensor 82 is provided in the anode offgas discharge pipe 75. However, since the anode offgas discharge pipe 75 communicates with the atmosphere, the inside thereof is the same as the atmospheric pressure. It can be thought of as pressure. Therefore, the second pressure sensor 82 may be omitted, and only the anode off gas pressure P1 may be detected in step S200 of the anode off gas discharge control routine. In this case, the reference value β can be set to a value obtained by adding atmospheric pressure in advance, and the value can be compared with the pressure P1 in step S210.

  In the second embodiment, two pressure sensors, the first pressure sensor 81 and the second pressure sensor 82, are used. However, a differential pressure sensor that detects the differential pressure between the pressure P1 and the pressure P2 is used. Also good.

C. Third embodiment:
(C1) Configuration of fuel cell system:
FIG. 5 is an explanatory diagram showing the overall configuration of a fuel cell system 100c as a third embodiment. The fuel cell system 100c of the present embodiment has substantially the same configuration as the fuel cell system 100b of the second embodiment described above, but differs in the position where the pressure sensor is provided. That is, the fuel cell system 100c according to the present embodiment includes a third pressure sensor 83 that measures the pressure of the anode off-gas downstream of the circulation pump 40, and a branching portion that is downstream of the pressure regulating valve 35 of the hydrogen supply pipe 32. And a fourth pressure sensor 84 for measuring the pressure of the fuel gas upstream of 38, and the discharge valves 71 and 72 for discharging the anode off-gas are switched according to the pressure detected by these pressure sensors.

(C2) Anode off gas discharge control:
FIG. 6 is a flowchart of an anode offgas discharge control routine in the third embodiment. When this routine is executed, the control computer 60 first detects the pressure P3 of the anode off-gas downstream of the circulation pump 40 using the third pressure sensor 83, and further uses the fourth pressure sensor 84 to detect hydrogen. The pressure P4 of the fuel gas downstream of the pressure regulating valve 35 of the supply pipe 32 and upstream of the branch portion 38 is detected (step S300). Then, a differential pressure ΔPc (= P3−P4) between the detected pressure P3 and pressure P4 is obtained. It is determined whether or not this differential pressure ΔPc is smaller than a predetermined reference value βc (step S310). The reference value βc can be set, for example, by experimentally obtaining a differential pressure at which the pressure P3 does not become equal to or lower than the pressure P4 even when the second discharge valve 72 is opened for t1 seconds.

  If the result of determination in step S310 is that the differential pressure ΔPc is smaller than the reference value βc (step S310: Yes), the control computer 60 determines that fuel gas may flow into the hydrogen circulation pipe 33 from the branch portion 38. Then, the first discharge valve 71 is selected as a discharge valve for discharging the anode off gas (step S320), and the second discharge valve 72 is closed (step S330). On the other hand, if the differential pressure ΔPc is larger than the reference value βc (step S310: No), the control computer 60 determines that the fuel gas does not flow into the hydrogen circulation pipe 33 from the branch portion 38 and discharges the anode off gas. The second discharge valve 72 is selected as the discharge valve (step S340), and the first discharge valve 71 is closed (step S350).

  Next, the control computer 60 opens the discharge valve selected in step S320 or step S340 for t1 seconds (step S360), and then closes the discharge valve for t2 seconds (step S370). The control computer 60 repeatedly executes the series of processes described above.

  In the fuel cell system 100c of the third embodiment configured as described above, when the difference between the anode off-gas pressure P3 pressurized by the circulation pump 40 and the fuel gas pressure P4 in the hydrogen supply pipe 32 is small. The anode off gas is discharged from the first discharge valve 71. By doing so, even if the fuel gas flows into the hydrogen circulation pipe 33, the flow is hindered by the circulation pump 40, and the fuel gas can be prevented from being discharged wastefully.

  Further, in the fuel cell system 100c of the present embodiment, when the pressure P3 of the anode off gas pressurized by the circulation pump 40 is sufficiently higher than the pressure P4 of the fuel gas in the hydrogen supply pipe 32, the second exhaust valve 72 is used. The anode off gas is discharged from In such a case, since the suction force of the circulation pump 40 is large, the pressure on the upstream side of the circulation pump 40 becomes low, and it may be difficult to discharge the anode off gas from the first discharge valve 71. Therefore, by discharging the anode off gas using the second discharge valve 72, the anode off gas can be discharged smoothly. If the pressure P3 of the anode off gas is sufficiently higher than the pressure P4 of the fuel gas, hydrogen is prevented from flowing into the hydrogen circulation pipe 33 from the branch portion 38 of the hydrogen supply pipe 32. Even if the anode off gas is discharged by using the fuel gas, the fuel gas is not discharged wastefully.

  In the third embodiment, two pressure sensors, the third pressure sensor 83 and the fourth pressure sensor 84, are used. However, a differential pressure sensor that detects the differential pressure between the pressure P3 and the pressure P4 is used. Also good.

  In the third embodiment, the pressure of the fuel gas is detected by the fourth pressure sensor 84. Normally, this pressure can be considered as the pressure set in the pressure regulating valve 35. Therefore, the fourth pressure sensor 84 may be omitted, or only the anode offgas pressure P3 may be detected in step S300 of the anode offgas discharge control routine. In this case, ΔPc can be obtained by subtracting the pressure set in the pressure regulating valve 35 from the detected pressure P3.

  In the foregoing, various embodiments of the present invention have been described. According to each of the above-described embodiments, the fuel gas is exhausted before reaching the fuel cell 10 even if a check valve is not provided at a portion where the hydrogen circulation pipe 33 joins the hydrogen supply pipe 32. Can be suppressed. Needless to say, the present invention is not limited to such embodiments, and various configurations can be adopted without departing from the spirit of the present invention.

Explanatory drawing which shows the whole structure of the fuel cell system 100a as 1st Example. The flowchart of an anode off gas discharge control routine. Explanatory drawing which shows the whole structure of the fuel cell system 100b as 2nd Example. The flowchart of the anode offgas discharge | emission control routine in 2nd Example. Explanatory drawing which shows the whole structure of the fuel cell system 100c as a 3rd Example. The flowchart of the anode offgas discharge | emission control routine in 3rd Example.

Explanation of symbols

100a, 100b, 100c ... Fuel cell system 10 ... Fuel cell 20 ... Hydrogen tank 30 ... Air compressor 31 ... Air supply pipe 32 ... Hydrogen supply pipe 33 ... Hydrogen circulation pipe 34 ... Shut valve 35 ... Pressure regulating valve 36 ... Cathode off-gas discharge pipe 38 ... Branch 40 ... Circulation pump 50 ... Motor 60 ... Control computer 61 ... CPU
62 ... RAM
63 ... ROM
71 ... First discharge valve 72 ... Second discharge valve 75 ... Anode off-gas discharge piping 80 ... Flow meter 81 ... First pressure sensor 82 ... Second pressure sensor 83 ... Third pressure sensor 84 ... Fourth pressure sensor

Claims (8)

A fuel cell system comprising a fuel cell,
A hydrogen supply channel connected to the fuel cell and supplying hydrogen gas to the fuel cell;
A circulation flow path connected to the fuel cell and the hydrogen supply flow path for flowing an anode off-gas discharged from the fuel cell to the hydrogen supply flow path;
A circulation pump which is provided in the circulation flow path and pressurizes the anode off gas discharged from the fuel cell and flows it to the hydrogen supply flow path;
A first discharge valve provided between the fuel cell in the circulation flow path and the circulation pump, for discharging the anode off gas flowing in the circulation flow path to the outside;
A second discharge valve that is provided between the circulation pump in the circulation flow path and the hydrogen supply flow path, and discharges the anode off gas flowing in the circulation flow path to the outside;
Based on the state quantity of the anode off gas flowing in the circulation flow path, either the first exhaust valve or the second exhaust valve is selected, and the selected exhaust valve is opened and closed to bring the anode off gas to the outside. A fuel cell system comprising a control unit for discharging. The fuel cell system according to claim 1,
Furthermore, it comprises a flow rate detection means for detecting the flow rate of the anode off gas flowing in the circulation channel,
The said control part performs the selection of the said exhaust valve based on the flow volume detected by the said flow volume detection means as a state quantity of the said anode off gas. Fuel cell system. The fuel cell system according to claim 2, wherein
The control unit selects the first discharge valve when the flow rate detected by the flow rate detection unit is smaller than a predetermined reference value, and when the flow rate is larger than the predetermined reference value, Select a discharge valve of 2. Fuel cell system. The fuel cell system according to any one of claims 2 and 3,
The flow rate detection means estimates the flow rate of the anode offgas according to at least one of the pressure of the anode offgas, the temperature of the anode offgas, the driving amount of the circulation pump, and the power generation amount of the fuel cell. Battery system. The fuel cell system according to claim 1,
Furthermore, it comprises a pressure detection means for detecting the pressure of the anode off gas flowing in the circulation channel,
The said control part performs the selection of the said discharge valve based on the pressure detected by the said pressure detection means as a state quantity of the said anode off gas. Fuel cell system. The fuel cell system according to claim 5, wherein
The pressure detection means is provided between the circulation pump and the fuel cell in the circulation flow path,
The control unit has a predetermined reference value obtained by subtracting a pressure in a space in which the anode off-gas is discharged through the first discharge valve or the second discharge valve from the pressure detected by the pressure detection unit. The fuel cell system selects the first discharge valve when the pressure is larger than the first discharge valve, and selects the second discharge valve when the differential pressure is smaller than the predetermined reference value. The fuel cell system according to claim 6,
The pressure of the space where the anode off gas is discharged through the first discharge valve or the second discharge valve is an atmospheric pressure. The fuel cell system according to claim 5, wherein
The pressure detection means is provided between the circulation pump and the hydrogen supply channel in the circulation channel,
The control unit is configured such that a differential pressure obtained by subtracting a pressure of hydrogen gas upstream from a portion coupled with the circulation flow path in the hydrogen supply flow path from a pressure detected by the pressure detection unit is greater than a predetermined reference value. The first discharge valve is selected when the difference is smaller, and the second discharge valve is selected when the differential pressure is larger than the reference value.

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