JP2006049135A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system dispensing with a humidifier for the fuel cell system and enhancing the output density and gas mileage. <P>SOLUTION: Hydrogen gas, whose pressure is controlled with a hydrogen pressure control valve 5, is supplied to an anode 2a of an internal humidifying fuel cell 2 from a high-pressure hydrogen tank 4. Compressed air is supplied to a cathode 2b of the internal humidifying fuel cell 2 from a compressor 17. Pure water, stored in a pure water tank 31, is sent to the internal humidifying fuel cell 2 with a pure water pump 32. In the anode 2a and the cathode 2b, supplied hydrogen gas and air are humidified, and electrochemical reaction for power generation in the fuel cell is performed. Hydrogen gas and air that are unreacted in the internal humidifying fuel cell 2 contain water vapor humidified in the internal humidifying fuel cell and water vapor in water produced and are sent to the anode 3a and the cathode 3b of an external humidifying fuel cell 3. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fuel cell system including an internal humidification fuel cell and an external humidification fuel cell.

  In a fuel cell, a fuel gas such as hydrogen gas and an oxidizing gas containing oxygen are electrochemically reacted through an electrolyte, and electric energy is directly taken out between electrodes provided on both surfaces of the electrolyte. In particular, a polymer electrolyte fuel cell using a polymer electrolyte has attracted attention as a power source for electric vehicles because of its low operating temperature and easy handling. That is, a fuel cell vehicle has a hydrogen storage device and a fuel reformer mounted on the vehicle, and hydrogen supplied from the vehicle and oxygen-containing air are sent to the fuel cell to react with each other, and the electric energy extracted from the fuel cell is obtained. It drives the motor connected to the drive wheels, and it is the ultimate clean vehicle without the emission of air pollutants.

  By the way, the solid polymer electrolyte membrane used in the polymer electrolyte fuel cell does not exhibit good hydrogen ion conductivity unless it is kept in a wet state. In order to maintain the solid polymer membrane in a wet state, an external humidification method in which fuel gas or oxidant gas is humidified by a humidifier provided outside the fuel cell, or a pure water passage for humidification is provided inside the fuel cell. There is an internal humidification method in which fuel gas or oxidant gas is humidified through this pure water passage and a porous water permeable plate. The former humidification method is called an external humidification fuel cell, and the latter is called an internal humidification fuel cell.

  As an external humidification type fuel cell, a technique for humidifying a reaction gas by providing a spray chamber on a gas supply line and spraying heated water into the spray chamber is known (for example, Patent Document 1). . In addition, there is an external humidification type fuel cell using a water vapor exchange device using a porous water permeable membrane as a humidification device. This humidifies the reaction gas by water vapor exchange between the reaction gas supplied to the fuel cell via the water vapor permeable membrane or the hollow fiber membrane and the exhaust gas discharged from the fuel cell (for example, Patent Documents 2 and 3).

As an internal humidification type fuel cell, a technique for humidifying an electrode membrane assembly (MEA) directly from a water channel provided in a gas diffusion layer (for example, Patent Document 4) or a separator that separates a fuel gas channel from a cooling water channel. A technique is known in which water is oozed out from the cooling water channel side to the fuel gas channel side through a porous material to humidify the fuel gas (for example, Patent Document 5).
JP 2002-033111 (3rd page, FIG. 1) JP 2002-170584 A (page 3, FIG. 1) JP 2002-216814 A (page 4, FIG. 2) JP-A-8-306375 (page 5, FIG. 1) Japanese Patent Laid-Open No. 11-073979 (page 3, FIG. 1)

  However, in the conventional external humidification fuel cell, it is necessary to provide a humidification device separately from the fuel cell main body, which increases the volume of the fuel cell system and decreases the output density and the vehicle mountability. was there. Moreover, since the energy required to humidify the reaction gas by the humidifier is required, there is a problem in that the fuel efficiency performance of the fuel cell system as a whole is reduced.

  Further, in the above-described conventional internal humidification fuel cell, since the size of the cell that is a power generation unit constituting the fuel cell main body is increased as compared with the cell of the external humidification fuel cell, the volume of the fuel cell system is increased. There has been a problem that the power density and the vehicle mountability are reduced.

  In order to solve the above problems, the present invention includes a fuel gas supply means for supplying a fuel gas, an oxidant gas supply means for supplying an oxidant gas, the fuel gas supply means, and the oxidant gas supply means. An internal humidified fuel cell that generates power by receiving supply of fuel gas and oxidant gas, and an external humidified fuel that generates power by receiving supply of exhaust fuel gas and exhaust oxidant gas discharged from the internal humidified fuel cell, respectively A fuel cell system comprising a battery.

  According to the present invention, first, fuel gas and oxidant gas are supplied to an internal humidification type fuel cell that does not require a humidifier, and unreacted fuel gas discharged from the internal humidification type fuel cell, each containing water vapor, and Since unreacted oxidant gas can be supplied to the external humidification type fuel cell, the volume of the fuel cell system can be reduced without providing a humidifier in the fuel cell system, and the output density and the vehicle mountability can be improved. The fuel cell system can be provided.

  In addition, according to the present invention, since there is no energy consumption by the humidifier, there is an effect that fuel efficiency performance as a fuel cell system is improved.

  Next, embodiments of the present invention will be described in detail with reference to the drawings. In addition, although embodiment described below is not specifically limited, it is a fuel cell system excellent in the output density suitable for fuel cell vehicles, and vehicle mounting property.

  FIG. 1 is a system configuration diagram illustrating a configuration of an embodiment of a fuel cell system according to the present invention. In FIG. 1, a fuel cell system 1 includes an internal humidified fuel cell 2 that generates power upon receiving supply of fuel gas and oxidant gas, and exhaust fuel gas and exhaust oxidant gas discharged from the internal humidified fuel cell 2. And an external humidified fuel cell 3 that generates electric power upon supply.

  In the present embodiment, the internal humidification fuel cell 2 and the external humidification fuel cell 3 are solid polymer fuel cells. The electrochemical reaction at the anodes (fuel electrodes) 2a and 3a and the cathodes (oxidant electrodes) 2b and 3b of these fuel cells and the reaction as the whole fuel cell are expressed by the following equations (1) to (3).

[Chemical formula 1]
[Anode] H ₂ → 2H ⁺ + 2e ⁻ (1)
[Cathode] 1/2 O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O (2)
[Overall] H ₂ +1/2 O ₂ → H ₂ O (3)
Next, the fuel gas system will be described. The fuel cell system 1 includes, for example, a high-pressure hydrogen tank 4 and a hydrogen pressure adjustment valve 5 as fuel gas supply means. The high-pressure hydrogen in the high-pressure hydrogen tank 4 is pressurized by the hydrogen pressure adjustment valve 5 to a pressure suitable for operating conditions. It is lowered and supplied to the anode 2 a of the internal humidified fuel cell 2 through the fuel gas supply path 6. In the anode 2a, the supplied hydrogen gas is humidified with pure water supplied from a pure water pump 32 described later, and a part of the supplied hydrogen is used in an electrochemical reaction for power generation. The remaining hydrogen gas discharged from the anode 2a is supplied to the anode 3a of the external humidification type fuel cell 3 through the intermediate valve 7 and the inter-fuel cell fuel gas supply path 8 while containing water vapor.

  Unused fuel gas at the anode 3 a is circulated to the anode 3 a via the water recovery device 16, the fuel gas circulation path 14, and the fuel gas circulation pump 15. By providing the fuel gas circulation path 14 and the fuel gas circulation pump 15, unused fuel gas can be reused in the anode 3a, and the fuel efficiency of the fuel cell system can be improved.

  In the circulation path of the fuel gas from the anode 3a through the water recovery device 16, the fuel gas circulation path 14, and the fuel gas circulation pump 15 to the anode 3a, impurities such as nitrogen and argon in the air leaked from the cathode 3b. Gas or liquid water in which excessive moisture is liquefied may accumulate. These impurity gases lower the partial pressure of hydrogen to lower the power generation efficiency, increase the average molecular weight of the circulating gas, and make it difficult to circulate the fuel gas. Liquid water also hinders the circulation of fuel gas. For this reason, a fuel gas discharge passage 11 and a purge valve 12 for opening and closing the fuel gas discharge passage 11 are provided. When the impurity gas or liquid water accumulates, the purge valve 12 is opened for a short time in response to an instruction from the control device 43 to perform a purge for discharging the impurity gas or liquid water out of the system from the anode 3a. Thereby, the hydrogen partial pressure and the circulation performance in the fuel gas circulation path including the anode 3a can be recovered.

  It is obvious that an ejector that is a fluid pump may be used in place of the fuel gas circulation pump 15 as long as the operating conditions of the fuel cell are met.

  The water recovery unit 16 includes, for example, an air-cooled or liquid-cooled heat exchanger, and condenses and recovers water vapor from exhaust fuel gas containing water vapor discharged from the anode 3a. The water recovery unit 16 is provided with a water level sensor 41 that detects the level of recovered water stored therein. The detection signal of the water level sensor 41 is input to the control device 43 and used for opening / closing control of the opening / closing valve 36.

  In the unused fuel gas circulated to the anode 3a, the water vapor component is reduced by the water recovery unit 16, so that the average molecular weight of the circulated gas is lowered, and the fuel gas is easily circulated. The fuel consumption performance of the fuel cell system can be improved.

  Next, the oxidant gas system will be described. The fuel cell system 1 includes, for example, a compressor 17 that compresses and supplies air as oxidant gas supply means. The compressor 17 supplies the compressed air to the cathode 2 b of the internal humidification fuel cell 2 through the oxidant supply path 18. In the cathode 2b, the supplied air is humidified with pure water supplied from the pure water pump 32, and a part of oxygen in the air containing water vapor is used for an electrochemical reaction for power generation. The unused oxidant gas at the cathode 2b is pressure-adjusted by the air pressure regulating valve 21 and discharged from the air discharge path 20 to the outside of the system.

  Next, a pure water system will be described. The pure water system of the fuel cell system 1 includes a pure water tank 31, a pure water pump 32 that pumps pure water from the pure water tank 31 to the internal humidification fuel cell 2, a pure water supply path 33, and a pure water discharge path 34. And a water recovery device 16, a pure water recovery path 35, and an on-off valve 36.

  The pure water stored in the pure water tank 31 is pumped by the pure water pump 32 to the internal humidification fuel cell 2 through the pure water supply path 33 at a water pressure corresponding to the pressure of the anode 2a and the cathode 2b. The internal humidification fuel cell 2 humidifies hydrogen as a fuel gas and air as an oxidant gas with the supplied pure water. Pure water that has not been used for humidification returns to the pure water tank 31 via the pure water discharge passage 34. Further, the water recovery unit 16 sends pure water recovered from the exhaust fuel gas discharged from the anode 3 a of the external humidification type fuel cell 3 to the pure water tank 31 through the pure water recovery path 35 and the opening / closing valve 36. With this pure water recovery function, the pure water tank 31 does not need to be replenished with pure water, so that maintenance and maintenance work of the fuel cell system 1 can be omitted and the operating cost of the fuel cell system can be reduced.

  In the present embodiment, the installation position of the water recovery unit 16 is higher than the position above the pure water tank 31. As a result, the recovered water can flow into the pure water tank 31 from the water recovery device 16 by natural flow, and the pure water recovery pump and its energy consumption can be omitted.

  The voltage detector 42 is a voltage detector that detects a cell voltage for each cell of the external humidification fuel cell 3 or a voltage of a group of cells connected in series for each fixed number.

  The control device 43 is a control device that controls the entire fuel cell system 1 and controls purge based on the cell voltage or cell group voltage of the external humidification fuel cell 3 detected by the voltage detector 42.

  The control device 43 is connected to a water level sensor 41 that detects the level of pure water stored in the water recovery unit 16 and an open / close valve 36 that opens and closes the pure water recovery path 35. When the detection value of the water level sensor 41 reaches a predetermined value, the control device 43 temporarily opens the on-off valve 36 and recovers the pure water stored in the water recovery unit 16 to the pure water tank 31. Further, when the operation of the fuel cell system is stopped, the open / close valve 36 is temporarily opened to control the pure water stored in the water recovery unit 16 to be discharged to the pure water tank 31.

  In the present embodiment, the control device 43 is configured by a microprocessor including a CPU, a program ROM, a working RAM, and an input / output interface.

  FIG. 2A is a schematic cross-sectional view showing an example of an internal humidification fuel cell, and FIG. 2B is a schematic cross-sectional view showing an example of an external humidification fuel cell.

  As shown in FIG. 2 (a), the cell which is a unit of the internal humidification type fuel cell has an anode electrode catalyst layer 53 and a cathode electrode catalyst layer 54 on both surfaces of an electrolyte membrane 52 using a solid polymer electrolyte membrane. The formed membrane electrode assembly (MEA) 51, anode gas diffusion layers 55, cathode gas diffusion layers 56 disposed on both surfaces of the MEA 51, water permeable plates 57, 58, and separators 59, 60 are provided.

  The water permeable plates 57 and 58 are formed, for example, by embedding a porous material 62 having a humidifying function in a large number of through holes provided in a plate-like frame member 61 mainly having a mechanical strength. Pure water channels 73 and 74 are provided between the separator 59 and the water permeable plate 57, and between the separator 60 and the water permeable plate 58, respectively, and pure water is supplied thereto. Pure water permeates into the other surface through the porous material 62 from one surface in contact with the pure water flow paths 73 and 74 of the water transmission plates 57 and 58. A hydrogen channel 71 and an air channel 72 are provided on the other surfaces of the water permeable plates 57 and 58, respectively, so that pure water permeating from the pure water channel humidifies hydrogen and air, respectively.

  As shown in FIG. 2B, the cell which is a unit of the external humidification type fuel cell has an anode electrode catalyst layer 53 and a cathode electrode catalyst layer 54 on both surfaces of an electrolyte membrane 52 using a solid polymer electrolyte membrane. A formed membrane electrode assembly (MEA) 51, an anode gas diffusion layer 55, a cathode gas diffusion layer 56, and separators 59, 60 disposed on both surfaces of the MEA 51 are provided.

  A hydrogen channel 71 is provided between the separator 59 and the anode gas diffusion layer 55, and humidified hydrogen is supplied outside the fuel cell. Similarly, an air flow path 72 is provided between the separator 60 and the cathode gas diffusion layer 56, and air humidified outside the fuel cell is supplied.

  As apparent from comparison between FIGS. 2A and 2B, the internal humidification type fuel cell is stacked from the external humidification type fuel cell by the amount of the water permeable plates 57 and 58 and the pure water passages 73 and 74. The dimension in the stacking direction is large. If the power generation performance of the internal humidification fuel cell and that of the external humidification fuel cell are equivalent, the output density, which is the output power per unit volume, will be lower for the internal humidification fuel cell than for the external humidification fuel cell. .

  In the present invention, the external humidified fuel cell having a high output density is used as the main cell, the internal humidified fuel cell is used as the sub cell, the humidifier is removed, and the internal humidified fuel cell is added with water vapor by humidification and generated water By supplying unreacted fuel gas and oxidant gas to the external humidification type fuel cell, the power density of the fuel cell system is increased, the vehicle mountability is improved, and energy consumption by the humidifier is eliminated, resulting in fuel efficiency. Can be improved.

  Next, purge control by the control device 43 of the present embodiment will be described with reference to the control flowchart of FIG. In the present embodiment, the internal humidification type fuel cell 2 has no fuel gas circulation path, so there is no accumulation of impurity gas, and since the fuel gas and air are in humidity balance with the water permeable plate inside the fuel cell, There is no condensation of water. For this reason, the internal humidifying fuel cell 2 does not need to be purged, but the external humidifying fuel cell 3 needs to be purged.

  The control flowchart of FIG. 3 is called at regular intervals and executed by the control device 43 after starting the fuel cell system and shifting to the steady operation state.

  First, in step 10 (hereinafter, step is abbreviated as S), the state information of the external humidification fuel cell is read into the control device in order to determine whether or not purge is necessary. In the present embodiment, the state information of the external humidification fuel cell is a cell voltage read from the voltage detector 42 or a cell group voltage. In addition, the pressure difference between the inlet and outlet of the anode 3a of the external humidification fuel cell 2 and the elapsed time after the previous purge may be used as the state information of the external humidification fuel cell.

  Next, in S12, the control device determines whether purge is necessary (determines the purge start condition). In the present embodiment, when the cell voltage at the current output current value I of the external humidification fuel cell 2 is lower than the reference voltage stored in advance by a certain value or a certain rate, or the cell voltage or the voltage of the cell group varies. When the value exceeds a certain level, it is determined that purging is necessary. This is because the impurity gas accumulates in the fuel gas circulation path and the hydrogen partial pressure decreases, or the liquid water narrows the fuel gas passage inside the anode 3a, thereby determining the increase in dispersion of fuel gas distribution between cells. Will be.

  When the fuel cell state is a pressure difference between the inlet and the outlet of the anode 3a, the current pressure difference in the output current value I of the external humidification fuel cell 2 is a constant value or a constant value from a previously stored reference pressure difference. When the rate is increased, it is determined that purging is necessary. Further, when the external humidification type fuel cell is operated at a constant output, it can be determined that the purge is necessary if a certain time has elapsed after the previous purge.

  If it is determined in S12 that the purge is unnecessary, the process returns without executing anything. If it is determined in S12 that the purge is necessary, the process proceeds to S14, and the control device opens the purge valve 12. Next, after a predetermined time (for example, 0.2 [Sec]) has elapsed in S16 and the pressure of the anode 3a has settled, the process proceeds to S18, and the control device opens the bypass valve 10. As a result, supply of dried hydrogen gas from the hydrogen pressure adjustment valve 5 to the anode 3 a of the external humidification fuel cell 3 via the bypass passage 9 and the bypass valve 10 is started.

  Next, in S20, the control device moves to S22 after a predetermined time (for example, 0.2 [Sec]) has elapsed and the pressure of the anode 3a has settled, and then the anode 2a of the internal humidification fuel cell 2 and the external humidification fuel The intermediate valve 7 provided in the inter-fuel cell fuel gas supply path 8 that connects the anode 3a of the battery 3 is closed. Thereby, the supply of hydrogen gas from the internal humidification fuel cell 2 to the external humidification fuel cell 3 is stopped. Thereafter, all the gas supplied to the anode 3a of the external humidification type fuel cell becomes dry hydrogen gas from the hydrogen pressure regulating valve 5 via the bypass passage 9 and the bypass valve 10. Thereby, the impurity gas and liquid water inside the anode 3a can be effectively discharged out of the system via the hydrogen discharge path 11 and the purge valve 12.

  Next, in S24, the control device reads the state information of the external humidification fuel cell. This is the same type of status information as the status information in S10. Next, in S26, it is determined whether the purge end condition is satisfied based on the state information. The purge end condition corresponds to the purge start condition in S12. In the present embodiment, the current cell voltage at the output current value I of the external humidification fuel cell 2 recovers within a certain range from the previously stored reference voltage. Alternatively, when the cell voltage or cell group voltage variation is within a certain range, it is determined that the purge is completed.

  If the determination in S26 is No, that is, if the control device does not determine that the purge is complete, the process returns to S24. If the determination in S26 is Yes, that is, if the control device determines that the purge is complete, the process proceeds to S28, and the control device closes the purge valve 12. Next, in step S30, the n control device moves to step S32 after the pressure of the anode 3a has settled after a predetermined time (for example, 0.2 [Sec]), and the anode 2a of the internal humidification fuel cell 2 and the external humidification fuel The intermediate valve 7 provided in the inter-fuel cell fuel gas supply path 8 connecting the anode 3a of the battery 3 is opened.

  Next, after a predetermined time (for example, 0.2 [Sec]) has elapsed in S34 and the pressure of the anode 3a has settled, the process proceeds to S36, and the control device closes the bypass valve 10. Thus, after the purge is completed, the operation state is restored and the process returns.

  FIG. 4 is a diagram for explaining the temporal change of the water level in the pure water tank 31. The water level of the pure water tank decreases from the water level immediately before starting because pure water is supplied to the internal humidified fuel cell 2 as the fuel cell system starts. After lowering to some extent, pure water consumption for humidification in the internal humidification fuel cell 2 and pure water recovered by the water recovery unit from the exhaust fuel gas of the external humidification fuel cell and returned to the pure water tank Balance with recovery amount and maintain constant amount.

  After the fuel cell system is shut down, the pure water in the pure water flow path of the internal humidification fuel cell is collected in the pure water tank. At this time, the pure water stored in the water collector is collected in the pure water tank. If not, the water level of the pure water tank will only return to the water level before the start of operation.

  If the fuel cell system continues to be shut down for a long time in this state, the water retained on the water permeation plate of the internal humidification type fuel cell is dried, and the water permeation plate is dried when the operation is started next time. In order to make up for the water level, the water level will drop more than the previous water level drop, eventually resulting in a shortage of pure water. In order to avoid this, in the present embodiment, after the operation of the fuel cell system is stopped, the open / close valve 36 is controlled so that the pure water stored in the water recovery device is recovered in the pure water tank. Thereby, the water level of the pure water tank immediately after operation stop becomes a higher water level than before the operation start.

It is a system configuration figure explaining the composition of the embodiment of the fuel cell system concerning the present invention. (A) Schematic sectional view showing an example of an internal humidification fuel cell, (b) Schematic sectional view showing an example of an external humidification fuel cell. It is a flowchart explaining the purge control by the control apparatus of embodiment. It is a time chart explaining the time change of the water level of a pure water tank.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Fuel cell system 2 ... Internal humidification type fuel cell 3 ... External humidification type fuel cell 4 ... High-pressure hydrogen tank 5 ... Hydrogen pressure regulating valve 6 ... Fuel gas supply path 7 ... Intermediate valve 8 ... Fuel gas supply path 9 between fuel cells ... Bypass passage 10 ... Bypass valve 11 ... Fuel gas discharge passage 12 ... Purge valve 14 ... Fuel gas circulation passage 15 ... Fuel gas circulation pump 16 ... Water recovery device 17 ... Compressor 18 ... Oxidant gas supply passage 19 ... Inter-fuel cell oxidation Agent gas supply path 20 ... Oxidant gas discharge path 21 ... Air pressure adjustment valve 31 ... Pure water tank 32 ... Pure water pump 33 ... Pure water supply path 34 ... Pure water discharge path 35 ... Pure water recovery path 36 ... Open / close valve 41 ... Water level sensor 42 ... Voltage detector 43 ... Control device

Claims (5)

Fuel gas supply means for supplying fuel gas;
Oxidant gas supply means for supplying oxidant gas;
An internal humidification type fuel cell for generating electricity by receiving supply of fuel gas and oxidant gas from the fuel gas supply means and oxidant gas supply means, respectively;
An external humidified fuel cell that generates electric power by receiving supply of exhaust fuel gas and exhaust oxidant gas discharged from the internal humidified fuel cell;
A fuel cell system comprising:   2. The fuel cell system according to claim 1, further comprising a circulation path for circulating the exhaust fuel gas discharged from the fuel electrode outlet of the external humidification fuel cell to the fuel electrode inlet of the external humidification fuel cell. . A pure water tank for supplying water to the internal humidification fuel cell;
A water recovery device for recovering water from the exhaust fuel gas passing through the circulation path;
A pure water recovery path for supplying water recovered by the water recovery device to the pure water tank;
The fuel cell system according to claim 2, further comprising: An on-off valve for opening and closing the pure water recovery path;
The water collector is installed at a position higher than the upper part of the pure water tank,
The water in the water recovery device is moved to a pure water tank by opening the on-off valve when the water level of the water recovery device reaches a predetermined value or when the operation of the fuel cell system is stopped. The fuel cell system described.   2. The fuel cell system according to claim 1, further comprising a bypass path that bypasses the internal humidification fuel cell and supplies fuel gas directly from the fuel gas supply means to the external humidification fuel cell.

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