JP2011171171A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system with improvement made on a hydrogen treatment method within the system in order to satisfy demand for restraint of hydrogen concentration of anode exhaust gas. <P>SOLUTION: In the case an actual power generation volume of a fuel cell stack 10 goes below a predicted power generation volume, a valve 28 is opened, and, as a result, anode exhaust gas in a hydrogen outlet piping 26 is guided into a hydrogen storage tank 30. After stoppage of a vehicle loading the fuel cell system is recognized (to be concrete, after an ECU 50 obtains various signals such as a vehicle stop signal like ignition OFF, a vehicle stop demand signal, or power generation finish signal of a fuel cell) the ECU 50 opens the valve 28. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a fuel cell system.

  Conventionally, as disclosed in, for example, Japanese Patent Application Laid-Open No. 2007-012335, a fuel cell system including a storage unit that stores (stores) an anode exhaust gas (anode offgas) of a fuel cell is known. Fuel cells generate electricity by supplying hydrogen and oxygen. At this time, when a part of the supplied hydrogen is discharged downstream of the anode, release of high-concentration hydrogen to the outside of the system (atmospheric release) becomes a problem.

  In this regard, the above-described conventional fuel cell system has a configuration in which an exhaust gas containing hydrogen (specifically, a purge gas) is stored in a storage chamber, and this hydrogen is diluted with a diluent gas such as air. Dilution suppresses high concentration hydrogen gas release from the system.

JP 2007-012335 A JP 2009-199760 A

  In order to suppress the hydrogen concentration of the anode exhaust gas, it is conceivable to perform power generation with a small amount of hydrogen supplied to the fuel cell. However, on the contrary, there are cases where it is desired to increase the hydrogen supply amount for various reasons. Specifically, for example, in a vehicle-mounted fuel cell system, directions for increasing the hydrogen flow rate are being studied from the viewpoint of improving the high-temperature performance of the fuel cell stack in order to reduce the size of the radiator. Concerning the increase in the hydrogen flow rate, there is a concern that the amount of unreacted hydrogen in the fuel cell and the amount of hydrogen in the exhaust gas will increase against the request to suppress the hydrogen concentration in the anode exhaust gas.

  The present invention has been made to solve the above-described problems, and provides a fuel cell system in which the hydrogen treatment system in the system is improved to satisfy the demand for suppressing the hydrogen concentration of the anode exhaust gas. Objective.

In order to achieve the above object, a first invention is a fuel cell system,
A fuel cell;
A hydrogen supply system connected to the anode of the fuel cell and supplying hydrogen to the anode;
An anode exhaust system in communication with the anode outlet of the fuel cell;
A hydrogen storage unit communicating with the anode exhaust system and capable of storing hydrogen therein;
A valve provided between the anode exhaust system and the hydrogen storage unit;
Control means for opening the valve when a predetermined condition is established in which hydrogen discharge exceeding an allowable amount to the anode exhaust system is recognized or may be recognized;
Resupply means for resupplying the hydrogen stored in the hydrogen storage unit to the fuel cell after stopping the power generation of the fuel cell;
It is characterized by providing.

According to a second invention, in the first invention,
The fuel cell system performs power generation of the fuel cell in a dead-end operation mode in which the fuel cell generates power without circulating the gas discharged to the anode exhaust system to the fuel cell. System that can
When the fuel cell is generating power in the dead end operation mode, the control means opens the valve when the amount of power generated by the fuel cell is smaller than the amount of hydrogen supplied to the anode of the fuel cell. It is characterized by doing.

According to a third invention, in the first or second invention,
The hydrogen storage unit is a reservoir capable of confining the gas of the anode exhaust system therein,
The re-supplying means is a means for opening the valve after the fuel cell stops generating power and after the pressure of the anode becomes lower than the pressure of the gas in the hydrogen storage due to the consumption of hydrogen inside the fuel cell. It is characterized by including.

4th invention is 1st or 2nd invention,
The hydrogen storage part is provided with a hydrogen storage alloy.

According to a fifth invention, in any one of the first to fourth inventions,
The control means includes valve opening control means for opening the valve when it is recognized that the actual power generation amount of the fuel cell is insufficient with respect to the hydrogen supply amount to the anode of the fuel cell. And

According to a sixth invention, in the fifth invention,
Obtaining means for obtaining a required output for the fuel cell system;
Calculating means for calculating a required output to be generated by the fuel cell based on the required output;
Power generation amount measuring means for measuring the power generation amount of the fuel cell;
With
The hydrogen supply system supplies hydrogen to the anode based on the required output calculated by the calculation means,
The valve opening control means includes
Means for calculating a hydrogen amount equivalent power generation amount that is a power generation amount according to the hydrogen supply amount to the anode of the fuel cell based on the hydrogen supply amount of the hydrogen supply system;
An opening determination means for determining whether or not to open the valve based on a comparison between the power generation amount equivalent to the hydrogen amount and the power generation amount measured by the power generation amount measuring means;
It is characterized by including.

  According to the first invention, when the amount of hydrogen in the anode exhaust gas exceeds the allowable amount, the anode exhaust gas can be introduced into the hydrogen storage unit. According to the first invention, after the fuel cell is stopped, the stored hydrogen can be returned to the inside of the fuel cell. Thereby, in order to suppress the trouble accompanying hydrogen shortage when the fuel cell system is stopped, hydrogen stored in the hydrogen storage unit can be effectively used from the viewpoint of suppressing hydrogen discharge to the outside of the system.

  According to the second aspect of the present invention, in a dead-end operation mode in which the anode off-gas having a high hydrogen concentration cannot be circulated to the fuel cell because it is a non-circulation system, hydrogen release to the outside of the system is suppressed and stored hydrogen is effectively utilized. Can do.

  According to the third aspect of the present invention, the hydrogen in the hydrogen reservoir is resupplied to the inside of the fuel cell by taking advantage of the fact that the anode pressure decreases with the consumption of hydrogen after the fuel cell is stopped. be able to.

  According to the fifth aspect, by using the power generation amount of the fuel cell as a determination index, the valve can be opened accurately in accordance with the time when hydrogen storage should be performed.

  According to the sixth aspect of the present invention, it is possible to more accurately identify and determine the timing at which hydrogen is to be stored in the hydrogen reservoir by the opening determination means, and to open and close the valve based on the determination.

It is a figure which shows the structure of the fuel cell system concerning embodiment of this invention. It is a flowchart of the routine which ECU performs during normal electric power generation of the fuel cell system concerning this embodiment.

Embodiment.
[Configuration of the embodiment]
FIG. 1 is a diagram showing a configuration of a fuel cell system according to an embodiment of the present invention. The fuel cell system according to the present embodiment can be suitably used for a moving body such as a vehicle. The fuel cell system according to this embodiment includes a fuel cell stack 10. The fuel cell stack 10 is a stacked body configured by stacking a large number of unit cells. In the present embodiment, description will be made assuming that the fuel cell stack 10 is a solid polymer membrane fuel cell (PEMFC).

  Each unit cell of the fuel cell stack 10 includes a proton-conducting solid polymer electrolyte membrane (hereinafter also simply referred to as “electrolyte membrane”). An electrode catalyst layer and a gas diffusion layer are laminated on both surfaces of the electrolyte membrane. Furthermore, a separator that also functions as a current collecting plate is provided thereon to partition individual unit cells. The unit cell, which is such a laminate, receives hydrogen supply to the anode electrode catalyst layer on one side and air supply to the cathode electrode catalyst layer on the other side, so that the electrochemical cell of hydrogen and oxygen is supplied. Power is generated by reaction. The anode inlets of a large number of unit cells are combined into one (or several) anode inlets of the fuel cell stack 10 by a manifold or the like provided therein. On the other hand, the outlets of the anodes of a large number of unit cells are combined into one (or several) anode outlets of the fuel cell stack 10 by a manifold or the like provided therein. In addition, since the structure of the fuel cell stack of such a system is already well-known, further description is abbreviate | omitted.

  FIG. 1 shows a configuration on the hydrogen side, that is, a system configuration around the anode, of the peripheral configuration of the fuel cell stack 10. The anode inlet of the fuel cell stack 10 communicates with a hydrogen inlet pipe 22 that bears a part of the hydrogen supply system. A fuel supply port 24 that is an end of the hydrogen inlet pipe 22 communicates with a hydrogen supply source (not shown) (specifically, for example, a hydrogen tank that stores high-pressure hydrogen). Although not shown, the gas supply path on the hydrogen inlet pipe 22 or between the hydrogen supply source and the anode inlet of the fuel cell stack 10 has various configurations for adjusting the amount of hydrogen supplied to the fuel cell stack 10 ( For example, a valve for controlling the hydrogen flow rate, and a shut valve if necessary) are also provided.

  A hydrogen outlet pipe 26 communicates with the anode outlet of the fuel cell stack 10. The hydrogen outlet pipe 26 includes a gas-liquid separator 32 and a hydrogen pump 34 on the way, and finally communicates with the hydrogen inlet pipe 22. As described above, the fuel cell system according to the present embodiment is a system that can re-supply (reflux) the gas discharged from the anode outlet of the fuel cell stack 10 to the anode outlet of the fuel cell stack 10 again. The gas-liquid separator 32 communicates with a discharge path 36 for discharging outside the vehicle. The gas in the hydrogen outlet pipe 26 is discharged out of the vehicle via the discharge path 36. The discharge path 36 may be connected to, for example, a diluter not shown.

  The hydrogen outlet pipe 26 communicates with the hydrogen reservoir 30 via the valve 28. By opening the valve 28, the hydrogen reservoir 30 communicates with the hydrogen outlet pipe 26. In the present embodiment, normally, the pressure inside the hydrogen reservoir 30 is assumed to be negative with respect to the pressure inside the hydrogen outlet pipe 26. When the valve 28 is opened, hydrogen can be stored by introducing the anode exhaust gas into the hydrogen reservoir 30 using the pressure difference.

  The fuel cell system according to the present embodiment includes an ECU (Electronic Control Unit) 50. The ECU 50 is connected to system devices such as the valve 28 and the hydrogen pump 34, and controls those devices. Although not shown, the fuel cell stack 10 is provided with a configuration for measuring the amount of power generation (specifically, for example, an ammeter, a cell voltage monitor, etc.). Connected. Moreover, ECU50 is comprised so that the input (request output) from a user can be acquired. More specifically, for example, the ECU 50 is connected to a required output acquisition device such as an accelerator pedal in a vehicle-mounted fuel cell system.

[Operation of the embodiment]
The operation of the fuel cell system according to the embodiment will be described below with reference to the control flowchart shown in FIG.

(Hydrogen storage control)
FIG. 2 is a flowchart of a routine executed by the ECU 50 during normal power generation of the fuel cell system according to the present embodiment. In the routine shown in FIG. 2, first, user input is acquired (step S100). In this step, the ECU 50 acquires the output value of the request output acquisition device described above in response to a user input.

  Next, based on the value acquired in step S100, the output currently requested by the user for the fuel cell system is calculated (step S102). In this step, a required output value in the fuel cell system is calculated based on the user input.

  Next, gas supply and voltage application are executed (step S104). In this step, the ECU 50 controls the opening of the valve in the hydrogen supply system so that hydrogen gas is supplied to the fuel cell stack 10 at a flow rate corresponding to the required output value calculated in step S102. Specifically, the opening degree control is performed so that the amount of hydrogen gas introduced at the stoichiometric ratio calculated according to the required output value flows into the fuel cell stack 10.

  Next, the output value is determined (step S106). In this step, it is determined whether or not the current output (actual power generation amount) of the fuel cell stack 10 is lower than the output (predicted power generation amount) that was to be realized by supplying hydrogen in step S104.

  If the actual power generation amount is not less than the predicted power generation amount in step S106, normal power generation is continued (step S108). That is, in this case, an output that is substantially balanced with the amount of hydrogen supplied to the fuel cell stack 10 is obtained, and it is considered that surplus hydrogen discharge does not have to be considered as a problem. Thereafter, the current routine ends.

  On the other hand, when the actual power generation amount is lower than the predicted power generation amount in step S106, the valve 28 is opened (step S110), and as a result, the anode exhaust gas in the hydrogen outlet pipe 26 is introduced into the hydrogen reservoir 30. (Step S112). That is, in this case, surplus hydrogen gas flows out to the hydrogen outlet pipe 26 as anode exhaust gas. As a result, the hydrogen concentration of the gas in the hydrogen outlet pipe 26 is high. Under such circumstances, hydrogen discharge to the outside of the vehicle through the discharge path 36 is regarded as a problem. Therefore, in this step, such a hydrogen release can be suppressed by the hydrogen reservoir 30 by opening the valve 28. Thereafter, the current routine ends.

(When the fuel cell system is stopped)
When the fuel cell system according to the present embodiment is stopped, the hydrogen stored in the hydrogen reservoir 30 is supplied to the anode of the fuel cell stack 10 according to the stoppage of power generation of the fuel cell stack 10. Specifically, after the stop of the vehicle equipped with the fuel cell system according to the present embodiment is recognized (specifically, a vehicle stop signal such as an ignition OFF, a vehicle stop request signal, a fuel cell power generation end signal, etc. Thereafter, the ECU 50 opens the valve 28. Thereby, the hydrogen gas in the hydrogen reservoir 30 can be released to the anode.

  It is known that after the fuel cell system is stopped, the hydrogen remaining in the anode of the fuel cell stack is consumed and an internal cell is formed. Since the internal cell reaction includes a carbon oxidation reaction, there is a problem that the durability of the fuel cell is lowered. In this regard, according to the fuel cell system according to the present embodiment, such harmful effects can be suppressed by supplying the stored hydrogen to the anode of the fuel cell stack 10 after the power generation is stopped.

  In addition, after the vehicle stops, the hydrogen in the fuel cell stack 10 is consumed, and the anode pressure is reduced to about 60 (kPa Abs). In this regard, the ECU 50 opens the valve 28 after a pressure drop is recognized to the extent that hydrogen can be released into the fuel cell stack 10 using the pressure difference between the hydrogen reservoir 30 and the fuel cell stack 10. Is preferred.

[Modification of Embodiment]
In the embodiment, surplus hydrogen downstream of the fuel cell stack 10 is stored using the hydrogen reservoir 30. However, the present invention is not limited to this. You may store hydrogen by making hydrogen adsorb | suck inside using the hydrogen storage part comprised using the hydrogen storage alloy. In this case, when releasing hydrogen after the vehicle is stopped, the hydrogen storage alloy can be heated using heater heating or heat of the cooling water line to release hydrogen as desired.

In the embodiment, a fuel cell system of the type in which the anode exhaust gas of the fuel cell stack 10 is circulated is assumed. However, the present invention is not limited to this.
A fuel cell system that generates power in an operation mode (also referred to as a “dead end operation mode”) in which power generation is performed without circulating the gas discharged to the anode exhaust system to the fuel cell stack 10 may be used. Further, the fuel cell system may be a type that can execute (switchable) both the operation of circulating the anode exhaust gas and the operation of not circulating (dead end mode). More specifically, the dead-end operation mode includes a power generation state in which the anode outlet side is closed (complete dead end), and a small flow rate (for example, power generation in the anode due to cross leaks) downstream of the anode outlet side. And generating electricity while discharging gas at a flow rate that allows only non-participating gas (impurity gas) to be discharged.
In these cases, when the fuel cell stack 10 is generating power in the dead end operation mode, the ECU 50 opens the valve 28 when the power generation amount of the fuel cell stack 10 is smaller than the hydrogen supply amount to the anode.

  In the embodiment, the ECU 50 opens the valve 28 when the power generation amount of the fuel cell stack 10 is lower than the predicted power generation amount. However, the present invention is not limited to this, and various modifications are possible. From the system specifications and theoretical values, the power generation amount (hydrogen amount equivalent power generation amount) corresponding to the hydrogen supply amount to the fuel cell stack 10 can be specified. Whether or not the actual amount of power generated by the fuel cell stack 10 is smaller than the amount of power generated corresponding to the amount of hydrogen is compared and determined based on the current power generation state or past operation history, etc. Can be the basis. Further, the valve 28 may be opened when the power generation amount is not only lower than the predicted power generation amount but also lower than a predetermined value. When hydrogen storage in the hydrogen reservoir 30 is required, even when a small amount of hydrogen is recognized in the anode exhaust system, or when a small amount of hydrogen is discharged, the valve 28 does not need to be opened immediately, but is so large that it cannot be ignored. It depends on the individual system. What is necessary is just to determine various situations where surplus hydrogen discharge to the anode exhaust system is regarded as a problem, and to open the valve 28 as necessary.

DESCRIPTION OF SYMBOLS 10 Fuel cell stack 22 Hydrogen inlet piping 24 Fuel supply port 26 Hydrogen outlet piping 28 Valve 30 Hydrogen reservoir 32 Gas-liquid separator 34 Hydrogen pump 36 Discharge passage

Claims (6)

A fuel cell;
A hydrogen supply system connected to the anode of the fuel cell and supplying hydrogen to the anode;
An anode exhaust system in communication with the anode outlet of the fuel cell;
A hydrogen storage unit communicating with the anode exhaust system and capable of storing hydrogen therein;
A valve provided between the anode exhaust system and the hydrogen storage unit;
Control means for opening the valve when a predetermined condition is established in which hydrogen discharge exceeding an allowable amount to the anode exhaust system is recognized or may be recognized;
Resupply means for resupplying the hydrogen stored in the hydrogen storage unit to the fuel cell after stopping the power generation of the fuel cell;
A fuel cell system comprising: The fuel cell system performs power generation of the fuel cell in a dead-end operation mode in which the fuel cell generates power without circulating the gas discharged to the anode exhaust system to the fuel cell. System that can
When the fuel cell is generating power in the dead end operation mode, the control means opens the valve when the amount of power generated by the fuel cell is smaller than the amount of hydrogen supplied to the anode of the fuel cell. The fuel cell system according to claim 1, wherein: The hydrogen storage unit is a reservoir capable of confining the gas of the anode exhaust system therein,
The re-supplying means is a means for opening the valve after the fuel cell stops generating power and after the pressure of the anode becomes lower than the pressure of the gas in the hydrogen storage due to the consumption of hydrogen inside the fuel cell. The fuel cell system according to claim 1, further comprising:   The fuel cell system according to claim 1 or 2, wherein the hydrogen storage unit includes a hydrogen storage alloy.   The control means includes valve opening control means for opening the valve when it is recognized that the actual power generation amount of the fuel cell is insufficient with respect to the hydrogen supply amount to the anode of the fuel cell. The fuel cell system according to any one of claims 1 to 4. Obtaining means for obtaining a required output for the fuel cell system;
Calculating means for calculating a required output to be generated by the fuel cell based on the required output;
Power generation amount measuring means for measuring the power generation amount of the fuel cell;
With
The hydrogen supply system supplies hydrogen to the anode based on the required output calculated by the calculation means,
The valve opening control means includes
Means for calculating a hydrogen amount equivalent power generation amount that is a power generation amount according to the hydrogen supply amount to the anode of the fuel cell based on the hydrogen supply amount of the hydrogen supply system;
An opening determination means for determining whether or not to open the valve based on a comparison between the power generation amount equivalent to the hydrogen amount and the power generation amount measured by the power generation amount measuring means;
The fuel cell system according to claim 5, comprising:

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