JP2005158556A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent hydrogen pressure of an anode from transiently rising at stoppage of a fuel cell system. <P>SOLUTION: A controller 30 controlling the fuel cell system as a whole is provided with an air pressure control part 20, a hydrogen pressure control part 21, a hydrogen supply source valve control part 22, a stoppage-time purge valve control part 23. At stoppage of the fuel cell system, the controller 30 increases air to be supplied to a combustor 8, and opens a purge valve 7. After opening of the purge valve 7, power taking-out from the fuel cell 1 is stopped, and later, a hydrogen tank main valve 3 is closed. After the hydrogen tank main valve 3 is closed, a compressor 9 is stopped. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a fuel cell system using a solid polymer electrolyte.

  In a fuel cell, a fuel gas such as hydrogen gas and an oxidant 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. That is, a fuel cell vehicle is equipped with a hydrogen storage device such as a high-pressure hydrogen tank, a liquid hydrogen tank, or a hydrogen storage alloy tank in the vehicle, and reacts by supplying hydrogen supplied therefrom and air containing oxygen to the fuel cell. This is the ultimate clean vehicle that drives the motor connected to the drive wheels with the electric energy extracted from the fuel cell, and the only exhaust material is water.

  As a hydrogen supply method in a fuel cell vehicle equipped with a high-pressure hydrogen tank, the difference between the maximum filling pressure (for example, 35 [MPa]) of the hydrogen tank and the supply pressure to the fuel cell is very large. Is often used. According to this method, the primary pressure reducing valve is provided in the middle of the piping from the hydrogen tank to the fuel cell, and the high-pressure hydrogen supplied from the hydrogen tank is reduced to a predetermined medium pressure. Further, a secondary pressure reducing valve (hereinafter referred to as a hydrogen supply valve) for reducing the pressure from a medium pressure to a desired hydrogen pressure (low pressure) that is an operating pressure of the fuel cell is provided downstream of the primary pressure reducing valve.

To compensate for the hydrogen consumed by the fuel cell, for example, if the hydrogen pressure at the anode (fuel electrode) of the fuel cell is controlled to a constant value by the hydrogen supply valve, hydrogen is consumed by the power generation and the pressure decreases That is, hydrogen is supplied from the hydrogen tank by the consumed amount (for example, Patent Document 1).
Japanese Patent Laid-Open No. 2002-37391 (page 4, FIG. 1)

  However, in the conventional hydrogen supply system, when the power generation of the fuel cell is stopped, if the power generation is stopped before the hydrogen supply is stopped, the hydrogen in the hydrogen system on the fuel cell side is consumed by the reaction from the hydrogen supply valve. Since the hydrogen pressure cannot be reduced, hydrogen pressure control may not be realized.

  In general, the hydrogen supply valve is designed to be sensitively controlled by the flow rate and pressure during normal operation, unlike the original valve of the hydrogen tank for the opening / closing function. For this reason, the hydrogen supply valve has a drawback that the sensitivity near the minute flow rate and the closed end is low, and the response speed until hydrogen can be completely shut off is low. In such a system using a hydrogen supply valve, if power generation is stopped before the hydrogen tank main valve is closed, the pressure reduction at the hydrogen supply valve becomes insufficient, the hydrogen pressure rises, and a high pressure is applied to the anode of the fuel cell. There is a problem that the hanging fuel cell may be deteriorated.

  On the other hand, if the power generation is stopped after the hydrogen supply is stopped first, the fuel cell generates power in a state of hydrogen deficiency, which may cause deterioration or failure of the fuel cell.

  In order to solve the above-described conventional problems, the present invention provides a hydrogen tank that stores hydrogen to be supplied to a fuel cell, and a hydrogen supply valve that adjusts the hydrogen pressure and hydrogen flow in the middle of the piping from the hydrogen tank to the fuel cell. A purge valve that discharges the anode off-gas from the fuel cell, and a purge valve control unit at the time of stop that controls to open the purge valve before the normal power supply from the fuel cell to the load device is stopped And the gist of the above.

  According to the present invention, since the purge valve is opened before the normal power supply from the fuel cell to the load device is stopped, the hydrogen flow rate is secured by discharging the hydrogen from the purge valve even after the hydrogen consumption by the normal power supply is stopped. Thus, there is an effect that the hydrogen pressure control by the hydrogen supply valve can be established and the increase of the hydrogen pressure can be prevented.

  According to the present invention, the purge valve is opened in advance before the normal power supply from the fuel cell to the load device is stopped, so that the hydrogen pressure can be reduced even if the normal power supply stop and the timing for closing the hydrogen supply valve are shifted. There is an effect that it is possible to prevent a sudden increase in the amount of water.

  Furthermore, according to the present invention, hydrogen can be supplied to the fuel cell until the normal power supply from the fuel cell to the load device is stopped, so that the fuel cell can be prevented from being deficient in hydrogen and the cause of deterioration of the fuel cell can be eliminated. There is an effect.

  Next, an embodiment of the present invention will be described with reference to the drawings. Each embodiment described below is a fuel cell system suitable for a fuel cell vehicle or an on-site cogeneration system.

  FIG. 1 is a system configuration diagram showing Embodiment 1 of a fuel cell system according to the present invention. In a fuel cell (main body) 1, an anode 1a and a cathode 1b are provided to face each other with a solid polymer electrolyte membrane 1c interposed therebetween.

  Further, pure water electrodes 1f and 1g are provided through an anode 1a and a cathode 1b inside the fuel cell 1 and porous separators 1d and 1e, respectively. As will be described later, pure water for humidification is supplied to the pure water electrodes 1f and 1g so that the anode hydrogen gas and the cathode air can be humidified through the porous separators 1d and 1e, respectively.

  The controller 30 that controls the entire fuel cell system includes an air pressure control unit 20 that controls the air pressure of the cathode 1b, a hydrogen pressure control unit 21 that controls the hydrogen pressure of the anode 1a, and hydrogen that controls a hydrogen tank main valve 3 described later. A supply source valve control unit 22 and a stop-time purge valve control unit 23 that controls the opening of a purge valve 7 (to be described later) before stopping the normal power supply from the fuel cell to the load device, which is a feature of the present invention, are provided. Yes.

  Here, the normal power supply to the load device is a power supply when the load device normally operates with the fuel cell as a power source. For example, when the fuel cell system is used in a fuel cell vehicle, Is the power supply when the fuel cell vehicle is in a running state and in a state where it can immediately run (idle operation state).

  Although not particularly limited, in this embodiment, the controller 30 is constituted by a microprocessor including a CPU, a program ROM, a working RAM, and an I / O interface.

  Hydrogen gas is supplied to the anode 1a of the fuel cell 1 and air is supplied to the cathode 1b, and the electrode reaction shown below proceeds to generate electric power.

(Chemical formula 1)
Anode (hydrogen electrode): H ₂ → 2H ⁺ + 2e ⁻ (1)
Cathode (oxygen electrode): 2H ⁺ + 2e ⁻ + (1/2) O ₂ → H ₂ O (2)
Hydrogen is supplied to the anode 1 a from the hydrogen tank 2 through the hydrogen tank main valve 3, the pressure reducing valve 301, and the hydrogen supply valve 4. The high-pressure hydrogen supplied from the hydrogen tank 2 is mechanically reduced to a predetermined pressure by the pressure reducing valve 301, further reduced to a desired hydrogen pressure by the hydrogen supply valve 4, and supplied to the anode 1a of the fuel cell. The ejector 5 is installed to recycle hydrogen (anode off gas) that has not been consumed by the anode 1a.

  The pressure sensor 6 a provided near the inlet of the anode 1 a detects the anode pressure and outputs a pressure signal to the hydrogen pressure control unit 21. The hydrogen pressure control unit 21 controls the hydrogen pressure of the anode 1a by driving the hydrogen supply valve 4 with reference to the pressure detected by the pressure sensor 6a. By controlling the hydrogen pressure of the anode 1a to be constant, the hydrogen consumed by the fuel cell 1 is automatically supplemented. A purge valve 7 is used to discharge hydrogen in the hydrogen circulation system in order to establish hydrogen pressure control when the fuel cell is stopped.

  The purge valve 7 is a gas flow path for discharging nitrogen accumulated in the hydrogen circulation system to recover the hydrogen partial pressure in the hydrogen circulation system and for restoring the cell voltage during normal operation of the fuel cell. It is also used for the purpose of purging water droplets clogged up (purging). The combustor 8 burns hydrogen discharged from the hydrogen circulation system by the purge valve 7.

  Air to the cathode 1b is supplied by the compressor 9. The air pressure of the cathode 1b is controlled by driving the air pressure regulating valve 10 by feeding back the pressure detected by the air pressure control unit 20 with the pressure sensor 6b.

  Pure water to the pure water electrodes 1 f and 1 g is supplied by a pure water tank 12 and a pure water pump 11. Air pressure, hydrogen pressure, and pure water pressure are set in consideration of power generation efficiency and water balance, and the pressures of the three parties are kept within a specified differential pressure so as not to cause mechanical distortion in the electrolyte membrane and separator. Managed.

  The power manager 13 extracts power from the fuel cell 1 and supplies power to, for example, a motor that drives a vehicle (not shown). The hydrogen supply source valve control unit 22 and the stop-time purge valve control unit 23 control the opening and closing of the hydrogen tank source valve 3 and the purge valve 7 based on the stop sequence of the fuel cell system, respectively.

  Next, based on the state transition diagram shown in FIG. 3, the stop sequence of the fuel cell system controlled by the controller 30 in the first embodiment will be described in detail.

  When the key SW for instructing the operation / stop of the fuel cell system is turned off (stop instruction) from the normal operation state (state A) of the fuel cell system, the controller 30 causes the hydrogen supply valve 4, the compressor 9 and the air pressure adjustment valve. 10 is controlled to shift the system to an idle operation state (state B) in which the pressures of the cathode 1b and the anode 1a are lower than the normal operation state.

  In the idling operation state (state B), when the pressures of the cathode 1b and the anode 1a become the set pressure during idling, the state transitions to the state C.

  In the state C, the controller 30 instructs the controller 30 to increase the rotational speed of the compressor 9 or increase the opening of the air pressure regulating valve 10, whereby the air flow rate is increased and the combustor 8 is prepared for ignition. After increasing the air flow rate, the state transitions to state D. In the state D, the purge valve 7 is opened, and the anode off gas (hydrogen) discharged from the purge valve 7 is mixed with air in the combustor 8 and burned.

  In this state D, since the purge valve 7 is opened, the hydrogen flow rate necessary for pressure control flows from the hydrogen supply valve 4 to the anode a of the fuel cell 1. For this reason, it is possible to avoid problems such as the pressure control by the hydrogen supply valve 4 becoming impossible due to the insufficient flow rate of the hydrogen supply valve 4 and the hydrogen pressure of the anode 1a downstream thereof abnormally rising.

  In the state E, the power extraction command to the power manager 13 is cut off, and the power extraction of the fuel cell 1 is stopped. In state F, the hydrogen tank main valve 3 is closed and the hydrogen supply is stopped. In state G, the compressor 9 is stopped and air supply is stopped, and in state H, the stop of the fuel cell power plant system is completed.

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

  A difference in configuration between the second embodiment and the first embodiment shown in FIG. 1 is that a dilution blower 15 is provided downstream of the purge valve 7 instead of the combustor 8, the pure water pump 11, and the fuel cell 1. The pure water recovery valves 14a, 14b, and 14c are added between them, the voltage sensor 16 that detects the voltage of the fuel cell 1, and the pure water recovery control unit 24 and the cathode oxygen consumption control unit 25 inside the controller 30. It has been added.

  The dilution blower 15 dilutes the hydrogen discharged from the purge valve 7 with air so that the hydrogen concentration is lower than the flammable concentration, and discharges the hydrogen outside the vehicle.

  The voltage sensor 16 detects a voltage for each cell of the fuel cell or a cell group including a certain number of cells or a total voltage of the fuel cell 1 and outputs the detected voltage to the controller 30.

  The controller 30 that controls the entire fuel cell system includes an air pressure control unit 20 that controls the air pressure of the cathode 1b, a hydrogen pressure control unit 21 that controls the hydrogen pressure of the anode 1a, and hydrogen that controls a hydrogen tank main valve 3 described later. The supply source valve control unit 22, the purge valve control unit 23 at the time of stop, which is a feature of the present invention, and controls to open a purge valve 7 described later before the supply of normal power from the fuel cell to the load device is stopped. A pure water recovery control unit 24 that performs control to recover pure water to the pure water tank 12 when the dead tech is stopped, and a cathode oxygen consumption control unit 25 that controls cathode oxygen consumption when stopped.

  The pure water recovery control unit 24 drives the pure water recovery valves 14a, 14b, and 14c to supply the pure water electrodes 1f and 1g of the fuel cell 1 and the pure water in the pure water system pipe to the pure water tank 12 by air pressure. to recover. If the operation of the fuel cell is stopped with pure water remaining in the pure water electrodes 1f and 1g, the electrochemical reaction of power generation stops and no reaction heat is generated, so that the pure water freezes and expands below freezing point. The fuel cell 1 may be deteriorated. For this reason, pure water is collected in the pure water tank 12. The pure water tank 12 has a structure that does not break even if the pure water freezes and expands inside, and can melt ice quickly when the fuel cell is started.

  The cathode oxygen consumption control unit 25 takes out electric power from the fuel cell 1 according to the fuel cell voltage detected by the voltage sensor 16 and the elapsed time when the fuel cell system is started and stopped, and consumes oxygen from the cathode 1b. Is to do.

  The operation during normal power generation in this embodiment is the same as that in Embodiment 1 except that the anode off-gas diluted with the dilution blower 15 is discharged at the time of purging.

  Next, based on the state transition diagram shown in FIG. 4, the stop sequence of the fuel cell system controlled by the controller 30 in the second embodiment will be described in detail.

  When the key SW for instructing the operation / stop of the fuel cell system is turned off (stop instruction) from the normal operation state (state A) of the fuel cell system, the controller 30 causes the hydrogen supply valve 4, the compressor 9 and the air pressure adjustment valve. 10 is controlled to shift the system to an idle operation state (state B) in which the pressures of the cathode 1b and the anode 1a are lower than the normal operation state.

  In the idling operation state (state B), when the pressures of the cathode 1b and the anode 1a become the set pressure during idling, the state transitions to the state C. In the state C, the dilution blower 15 for diluting the anode off gas (hydrogen) is activated. After the rotation of the dilution blower 15 rises, the state transitions to state D. In the state D, the purge valve 7 is opened, and the anode off gas (hydrogen) discharged from the purge valve 7 is diluted by the dilution blower 15 and then discharged outside the vehicle. In this state D, since the purge valve 7 is opened, the hydrogen flow rate necessary for pressure control flows from the hydrogen supply valve 4 to the anode a of the fuel cell 1. For this reason, it is possible to avoid problems such as the pressure control by the hydrogen supply valve 4 becoming impossible due to the insufficient flow rate of the hydrogen supply valve 4 and the hydrogen pressure of the anode 1a downstream thereof abnormally rising.

  After opening the purge valve 7 in the state D, the state transitions to the state E. In state E, the normal power supply from the fuel cell 1 to the load device is stopped by cutting off the power extraction command to the power manager 13.

  Next, the state transits to the state F, and in the state F, the pure water pump 11 is stopped. After the pure water pump 11 is stopped, the state G is changed. In the state G, the air pressure of the cathode 1b is set to a pressure necessary for pure water recovery. At this time, the hydrogen pressure of the anode 1a is also set to the same pressure as the cathode air pressure, and the pressure difference is controlled within a predetermined range on both sides of the electrolyte membrane 1c. When the cathode pressure becomes substantially pure water recovery pressure in the state G, the state transitions to the state H.

  In the state H, the pure water recovery valves 14a and 14b are opened to recover the pure water on the fuel cell 1 side from the pure water recovery valve 14a to the pure water tank 12 by air pressure. In the state H, the state transits to the state I after the time necessary for collecting pure water elapses. The time required for this pure water recovery is determined in advance by experiments or the like and stored in the controller 30 as a control parameter.

  Next, in the state I, the pure water recovery valve 14b is closed and the pure water recovery valve 14c is opened to recover the pure water on the pure water tank 11 side from the pure water recovery valve 14a. After the time necessary for this recovery has elapsed, the state transitions to state J. In the state J, the pure water recovery valve 14a is closed and the pure water recovery ends. In state J, after the pure water recovery valve 14a is closed, the state transitions to state K.

  Next, in the state K, the compressor 9 is stopped and the air pressure regulating valve 10 is fully closed. When the compressor 9 is stopped and the air pressure regulating valve 10 is fully closed, the state L is changed. In state L, the controller 30 issues a power extraction command to the power manager 13, power is extracted again from the fuel cell 1, and oxygen in the cathode 1b is consumed. The magnitude of the electric power extracted at this time may be equivalent to the electric power (or current) in the normal power generation state, but it is preferable that the electric power (or current) is smaller than this, and the cathode oxygen consumption is accurately controlled. be able to. By consuming oxygen at the cathode when the fuel cell system is stopped, poisoning of carbon used as a catalyst carrier on the electrolyte membrane surface can be suppressed.

  When the oxygen of the cathode 1b is completely consumed in the state L, the state transitions to the state M. As a transition condition at this time, when the time required for the cathode oxygen consumption in the state L elapses or the voltage of the fuel cell 1 detected by the voltage sensor 16 falls below a predetermined value, the oxygen at the cathode 1b Transition to the state M because it is determined that it has been completely consumed.

  Next, in the state M, the power extraction command for the cathode manager is stopped by stopping the power extraction command to the power manager 13. In this way, by continuing to supply the hydrogen to the anode 1a and stopping the air supply to the cathode 1b and taking out electric power from the fuel cell 1, the oxygen in the cathode 1b and the pipes before and after it is consumed, so that when the fuel cell is stopped, The fuel cell open-circuit voltage can be prevented from being raised. Thereby, deterioration of the fuel cell can be prevented. Next, in state N, the hydrogen tank main valve 3 is closed to stop the hydrogen supply.

  In the state N, when the hydrogen in the hydrogen system is discharged from the purge valve 7 and the anode hydrogen pressure detected by the pressure sensor 6a decreases to about atmospheric pressure, the state transitions to the state O. In the state O, the hydrogen dilution blower 15 is stopped, and in the state P, the stop of the fuel cell system is completed.

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. FIG. 3 is a state transition diagram during a stop operation in the fuel cell system according to the first embodiment. FIG. 6 is a state transition diagram during a stop operation in the fuel cell system of Example 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Fuel cell 2 ... Hydrogen tank 3 ... Hydrogen tank main valve 4 ... Hydrogen supply valve 5 ... Ejector 6a, 6b ... Pressure sensor 7 ... Purge valve 8 ... Combustor 9 ... Compressor 10 ... Air pressure regulating valve 11 ... Pure water pump 12 ... Pure water tank 13 ... Power manager 14a, 14b, 14c ... Pure water recovery valve 15 ... Dilution blower 16 ... Voltage sensor 20 ... Air pressure control part 21 ... Hydrogen pressure control part 22 ... Hydrogen supply source valve control part 23 ... When stopped Purge valve control unit 24 ... pure water recovery control unit 25 ... cathode oxygen consumption control unit 30 ... controller

Claims (7)

In a fuel cell system having a hydrogen tank for storing hydrogen to be supplied to the fuel cell, and a hydrogen supply valve for adjusting a hydrogen pressure and a hydrogen flow rate in the middle of piping from the hydrogen tank to the fuel cell,
A purge valve for discharging anode off-gas from the fuel cell;
A stop-time purge valve control means for controlling to open the purge valve before stopping normal power supply from the fuel cell to the load device;
A fuel cell system comprising: Hydrogen pressure control means for controlling the hydrogen pressure supplied to the fuel cell for a predetermined period after the supply of normal power from the fuel cell to the load device is stopped,
2. The stop purge valve control means opens the purge valve before stopping the normal power supply, and keeps the purge valve open until at least the start of hydrogen pressure control in the predetermined period. Fuel cell system.   The fuel cell system according to claim 2, wherein the pressure of hydrogen supplied to the fuel cell during the predetermined period is lower than the hydrogen pressure during normal power supply to the load device. A water tank for collecting water for humidifying the fuel cell electrolyte membrane;
Water recovery control means for recovering the humidifying water from the fuel cell to the water tank using the cathode air pressure;
4. The fuel cell system according to claim 2, wherein the hydrogen pressure control for the predetermined period by the hydrogen pressure control unit is performed at the time of water recovery by the water recovery control unit. Cathode oxygen consumption control for controlling the consumption of cathode oxygen by taking out power from the fuel cell while the supply of hydrogen gas to the fuel cell is stopped and the air supply is stopped after the normal power supply from the fuel cell to the load device is stopped With means,
4. The fuel cell system according to claim 2, wherein the hydrogen pressure control for the predetermined period by the hydrogen pressure control unit is performed during cathode oxygen consumption control by the cathode oxygen consumption control unit. 5. In addition to the hydrogen supply valve, a hydrogen tank main valve is provided,
The fuel cell system according to any one of claims 2 to 5, wherein the hydrogen tank main valve is closed after the hydrogen pressure control for the predetermined period is finished.   7. The apparatus according to claim 2, comprising at least one of a hydrogen dilution blower for diluting the anode off gas with air and a combustor for burning the anode off gas downstream of the purge valve. Fuel cell system.

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