JP2004047154A - Reactive gas supplying method for fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To positively prevent condensation of humidifying water in a passage connecting a humidifier and a fuel cell by a simple process. <P>SOLUTION: Oxidizer gas supplied from an oxidizer gas supply source 14 is humidified via the humidifier 52, and then it is supplied to fuel cell stack 12 from piping 54b. In that case, a dew point of the oxidizer gas is detected by a humidity sensor 72, and an inner wall temperature of the piping 54b is detected via first to third temperature sensors 74a, 74b and 74c. When the dew point of the oxidizer gas is higher than the inner wall temperature, a solenoid valve 58 is opened, a bypass circuit 56 is opened, and a humidifying amount of the oxidizer gas is reduced. Consequently, the dew point of the oxidizer gas is lowered, and the dew point of the oxidizer gas is constantly maintained lower than the inner wall temperature. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention provides a fuel cell in which a humidifier for humidifying a reaction gas and a fuel cell are connected by a pipe and a bypass circuit for bypassing the humidifier is opened and closed to control humidification of the reaction gas supplied to the fuel cell. And a method for supplying a reaction gas.
[0002]
[Prior art]
For example, a polymer electrolyte fuel cell has an electrolyte (electrolyte membrane) -electrode assembly in which an anode electrode and a cathode electrode are respectively provided on both sides of an electrolyte membrane composed of a polymer ion exchange membrane (cation exchange membrane). Is sandwiched between separators. This type of fuel cell is usually used as a fuel cell stack by laminating a predetermined number of electrolyte-electrode assemblies and separators.
[0003]
In this fuel cell, a fuel gas supplied to the anode side electrode, for example, a gas mainly containing hydrogen (hereinafter, also referred to as a hydrogen-containing gas), has hydrogen ionized on the catalyst electrode and passes through the electrolyte to the cathode side. Move to the electrode side. The electrons generated during that time are taken out to an external circuit and used as DC electric energy. Since an oxidant gas, for example, a gas mainly containing oxygen or air (hereinafter also referred to as an oxygen-containing gas) is supplied to the cathode side electrode, hydrogen ions, electrons, And oxygen react to produce water.
[0004]
Usually, the fuel gas and the oxidizing gas supplied to the anode electrode and the cathode electrode are introduced into a reaction gas flow channel provided in the fuel cell stack as a fluid containing water vapor to humidify the electrolyte. Specifically, for example, a humidifier for humidifying the reaction gas and a fuel cell are connected by a pipe, and the humidifier is provided with a bypass circuit for bypassing the humidifier. A fuel cell humidification system for supplying a fuel cell is known (see JP-A-2001-216784).
[0005]
[Problems to be solved by the invention]
However, particularly when the fuel cell stack is operated at high output, a voltage drop phenomenon is likely to occur in the fuel cell at the end of the fuel cell stack, and a desired high output may not be achieved. That is, the moisture contained in the reaction gas supplied from the humidifier to the pipes forms dew before reaching the fuel cell stack, and condensed water tends to be concentrated and introduced into the fuel cell at the end of the fuel cell stack. Because. As a result, the fuel cell at the end of the fuel cell stack cannot generate power satisfactorily, and there is a problem that the power generation capability of the fuel cell stack cannot be sufficiently exhibited.
[0006]
The present invention solves this kind of problem, and in a simple process, reliably prevents humidification water from condensing in piping connecting a humidifier and a fuel cell, and effectively achieves a desired power generation capacity. It is an object of the present invention to provide a reaction gas supply method for a fuel cell that can be exerted.
[0007]
[Means for Solving the Problems]
In the method for supplying a reaction gas for a fuel cell according to claim 1 of the present invention, the inner wall temperature of a pipe connecting the humidifier for humidifying the reaction gas and the fuel cell and the dew point of the reaction gas in the pipe are detected, The inner wall temperature is compared with the dew point of the reaction gas. Then, the bypass circuit that bypasses the humidifier is opened and closed so that the inner wall temperature becomes higher than the dew point of the reaction gas.
[0008]
Specifically, when the dew point of the reaction gas is higher than the inner wall temperature, the humidification amount of the reaction gas is reduced by opening the bypass circuit. For this reason, the dew point of the reaction gas decreases and becomes lower than the inner wall temperature, and it is possible to prevent the moisture contained in the reaction gas from being condensed on the inner wall of the pipe. As a result, dew condensation water is not introduced into the fuel cell disposed particularly in the vicinity of the pipe, and it is possible to prevent a voltage drop phenomenon of the fuel cell and effectively exhibit a desired power generation capacity.
[0009]
In the method for supplying a reaction gas for a fuel cell according to the second aspect of the present invention, the outside gas temperature outside the pipe is detected, and when the outside air temperature is lower than the inner wall temperature, the bypass circuit is opened and closed to control the reaction gas. Is adjusted. Therefore, it is possible to effectively prevent the occurrence of dew condensation on the inner wall of the pipe due to a decrease in the outside air temperature.
[0010]
At this time, if the relationship between the outside air temperature and the inside wall temperature is mapped in advance, it is possible to always maintain the relationship that the inside wall temperature is higher than the dew point of the reaction gas even if the outside air temperature changes suddenly. It is.
[0011]
Furthermore, in the method for supplying a reaction gas for a fuel cell according to claim 3 of the present invention, the fuel cell is a polymer electrolyte fuel cell, and good power generation performance is maintained by preventing the generation of dew water. be able to.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a schematic configuration diagram of a fuel cell system 10 for carrying out a method for supplying a reaction gas for a fuel cell according to an embodiment of the present invention.
[0013]
The fuel cell system 10 includes a fuel cell stack 12, an oxidizing gas supply source 14 for supplying a reaction gas, for example, an oxidizing gas, and a humidifying unit for humidifying the oxidizing gas supplied from the oxidizing gas supply source 14. A control unit 18 is provided between the fuel cell stack 12 and the humidification mechanism 16 and adjusts the humidification state of the oxidizing gas supplied to the fuel cell stack 12.
[0014]
The fuel cell stack 12 includes a plurality of fuel cells 20 stacked in the direction of arrow A. As shown in FIG. 2, the fuel cell 20 includes an electrolyte membrane / electrode assembly 22 and first and second separators 24 and 26 formed of, for example, a metal plate and sandwiching the electrolyte membrane / electrode assembly 22. Is provided. A seal member 28 such as a gasket is interposed between the electrolyte membrane / electrode assembly 22 and the first and second separators 24 and 26 so as to cover the periphery of a communication hole described later and the outer periphery of an electrode surface (power generation surface). Is equipped.
[0015]
One end of the fuel cell 20 in the direction of arrow B (horizontal direction in FIG. 2) communicates with each other in the direction of arrow A, which is a stacking direction, to oxidize an oxidant gas, for example, an oxygen-containing gas. The agent gas supply communication hole 30a, the cooling medium discharge communication hole 32b for discharging the cooling medium, and the fuel gas discharge communication hole 34b for discharging the fuel gas, for example, the hydrogen-containing gas, are arranged in the direction of arrow C (vertical direction). Are arranged in a row.
[0016]
At the other end of the fuel cell 20 in the direction of arrow B, a fuel gas supply communication hole 34a for supplying fuel gas and a cooling medium supply communication hole for supplying a cooling medium are communicated with each other in the direction of arrow A. 32a and an oxidizing gas discharge communication hole 30b for discharging the oxidizing gas are arranged in the arrow C direction.
[0017]
The electrolyte membrane / electrode assembly 22 includes, for example, a solid polymer electrolyte membrane 36 in which a thin film of perfluorosulfonic acid is impregnated with water, an anode electrode 38 and a cathode electrode sandwiching the solid polymer electrolyte membrane 36. 40.
[0018]
The anode-side electrode 38 and the cathode-side electrode 40 are a gas diffusion layer made of carbon paper or the like, and an electrode catalyst in which porous carbon particles having a platinum alloy supported on the surface are uniformly coated on the surface of the gas diffusion layer. Layers. The electrode catalyst layers are joined to both surfaces of the solid polymer electrolyte membrane 36 so as to face each other with the solid polymer electrolyte membrane 36 interposed therebetween.
[0019]
An opening 45 is formed at the center of the seal member 28 so as to correspond to the anode 38 and the cathode 40. Instead of the seal member 28, a seal may be provided on the first and second separators 24 and 26 by baking or the like.
[0020]
On the surface 24a of the first separator 24 on the side of the electrolyte membrane / electrode assembly 22, for example, an oxidizing gas flow path 46 including a plurality of grooves extending in the direction of arrow B is provided. The passage 46 communicates with the oxidizing gas supply communication hole 30a and the oxidizing gas discharge communication hole 30b.
[0021]
A fuel gas flow path 48 communicating with the fuel gas supply passage 34a and the fuel gas discharge passage 34b is formed on the surface 26a of the second separator 26 on the side of the electrolyte membrane / electrode assembly 22. The fuel gas passage 48 has a plurality of grooves extending in the direction of arrow B. On the surface 26b of the second separator 26, a cooling medium flow path 50 communicating with the cooling medium supply communication hole 32a and the cooling medium discharge communication hole 32b is formed. The cooling medium flow path 50 has a plurality of grooves extending in the direction of arrow B.
[0022]
As shown in FIG. 1, the humidifying mechanism 16 includes a humidifier 52, and the humidifier 52 and the oxidizing gas supply source 14 are connected by a pipe 54a. The oxidizing gas supply communication hole 30a is connected by a pipe 54b. A bypass circuit 56 bypasses the humidifier 52 and communicates with the pipes 54a and 54b, and an electromagnetic valve 58 is disposed in the bypass circuit 56.
[0023]
As shown in FIG. 3, the humidifier 52 includes a hollow fiber membrane module 60, and a hollow fiber formed by bundling water-permeable hollow fiber membranes in a housing 62 constituting the hollow fiber membrane module 60. The membrane bundle 64 is accommodated. The hollow fiber membrane has a large number of fine capillaries having an opening diameter of several nanometers. In the capillaries, the vapor pressure is reduced to cause condensation of water, and the condensed water is sucked out by capillary action. It is configured so that water permeates the hollow fiber membrane.
[0024]
A plurality of oxidizing gas inlets 66a for introducing a low humidifying oxidizing gas into the housing 62 are formed at one edge of the housing 62 in the longitudinal direction (the direction of arrow D). A plurality of oxidizing gas outlets 66b for discharging the humidified oxidizing gas are formed at the other end in the longitudinal direction of the housing 62. In the housing 62, a potting portion 68a is provided near the oxidizing gas inlet 66a at a longitudinal end of the hollow fiber membrane bundle 64, and a potting portion 68b is provided near the oxidizing gas outlet 66b. Can be
[0025]
A humidification gas inlet 70a is formed outside the potting portion 68b, while a humidification gas outlet 70b is formed outside the potting portion 68a. The humidified gas inlet 70a is supplied with a humid gas, for example, an off-gas (a reaction gas discharged after the reaction). The humidified gas inlet 70a is connected to, for example, the oxidant gas discharge communication of the fuel cell stack 12. It communicates with the hole 30b.
[0026]
As shown in FIG. 1, the control unit 18 includes a humidity sensor 72 and first to third temperature sensors 74a, 74b, and 74c installed on the inner wall of the pipe 54b, and an outside air temperature detector disposed outside the pipe 54b. And a control unit 76 for receiving measurement results from the humidity sensor 72 and the first to fourth temperature sensors 74a to 74d and controlling opening and closing of the electromagnetic valve 58.
[0027]
In this embodiment, the humidifying mechanism 16 and the control unit 18 are provided between the oxidizing gas supply source 14 and the fuel cell stack 12, but the fuel gas supply source (not shown) is similarly provided. A humidifying mechanism and a control unit may be provided.
[0028]
The operation of the fuel cell system 10 configured as described above will be described below in relation to the reaction gas supply method according to the present embodiment.
[0029]
First, in the fuel cell 20, as shown in FIG. 2, a fuel gas such as a hydrogen-containing gas is supplied to the fuel gas supply communication hole 34a, and an oxidant gas such as an oxygen-containing gas is supplied to the oxidant gas supply communication hole 30a. Is supplied. Further, a cooling medium such as pure water, ethylene glycol, or oil is supplied to the cooling medium supply communication hole 32a.
[0030]
For this reason, the oxidizing gas is introduced into the oxidizing gas passage 46 of the first separator 24 from the oxidizing gas supply passage 30a, and moves along the cathode 40 constituting the electrolyte membrane / electrode assembly 22. . On the other hand, the fuel gas is introduced from the fuel gas supply passage 34a into the fuel gas flow channel 48 of the second separator 26, and moves along the anode 38 constituting the electrolyte membrane / electrode assembly 22.
[0031]
Therefore, in each of the electrolyte membrane / electrode assemblies 22, the oxidizing gas supplied to the cathode 40 and the fuel gas supplied to the anode 38 are consumed by the electrochemical reaction in the electrode catalyst layer, Power generation is performed.
[0032]
Next, the fuel gas supplied to the anode 38 and consumed is discharged in the direction of arrow A along the fuel gas discharge communication hole 34b. Similarly, the oxidant gas supplied to and consumed by the cathode electrode 40 is discharged in the direction of arrow A along the oxidant gas discharge communication hole 30b.
[0033]
The cooling medium supplied to the cooling medium supply communication hole 32a flows into the cooling medium flow path 50 of the second separator 26 and then flows in the direction of arrow B. This cooling medium is discharged from the cooling medium discharge passage 32b after cooling the electrolyte membrane / electrode assembly 22.
[0034]
As shown in FIG. 1, the oxidizing gas supplied from the oxidizing gas supply source 14 to the fuel cell stack 12 is humidified by a humidifier 52 disposed between the pipes 54a and 54b. Specifically, as shown in FIG. 3, the low humidification oxidizing gas flows into the housing 62 from the oxidizing gas inlet 66 a, and the outside of each hollow fiber membrane constituting the hollow fiber membrane bundle 64 is indicated by an arrow. It circulates in the D1 direction. On the other hand, the humidified oxidizing gas (hereinafter, also referred to as off-gas) discharged from the fuel cell stack 12 is supplied to the humidified gas inlet 70a, and flows from the potting portion 68b inside each hollow fiber membrane in the direction of arrow D2. I do.
[0035]
For this reason, the moisture separated from the off gas flowing inside the hollow fiber membrane passes through the hollow fiber membrane and moves outward, and humidifies the low humidification oxidant gas flowing outside the hollow fiber membrane. . The humidified oxidant gas is introduced from the oxidant gas outlet 66b into the pipe 54b, and supplied to the fuel cell stack 12.
[0036]
Next, the humidification control by the control unit 18 will be described below with reference to the flowchart shown in FIG.
[0037]
As shown in FIG. 1, a humidity sensor 72 and first to third temperature sensors 74a, 74b, and 74c are sequentially installed on the inner wall of the pipe 54b from the humidifier 52 toward the fuel cell stack 12. .
[0038]
Therefore, the humidity sensor 72 measures the humidity (dew point) of the oxidizing gas derived from the humidifier 52, and the measurement result is sent to the control unit 76. The first to third temperature sensors 74a, 74b, and 74c each detect the inner wall temperature of the pipe 54b and transmit the detection result to the control unit 76 (Step S1).
[0039]
In the control unit 76, the minimum value of the inner wall temperature detected from the first to third temperature sensors 74a, 74b and 74c is compared with the dew point of the oxidizing gas derived from the humidifier 52, and the inner wall temperature> gas dew point Is determined (step S2). If the inner wall temperature is higher than the gas dew point (YES in step S2), humidification of the oxidizing gas by the humidifier 52 is continued because no dew condensation occurs in the pipe 54b. Then, the humidified oxidant gas is supplied to the fuel cell stack 12.
[0040]
On the other hand, when it is determined that the inner wall temperature is lower than the gas dew point (low temperature) (NO in step S2), the process proceeds to step S3, and the opening / closing control of the electromagnetic valve 58 is performed. At this time, the opening of the electromagnetic valve 58 according to the difference between the inner wall temperature and the gas dew point is stored in the control unit 76 as a map, and the opening of the electromagnetic valve 58 is controlled according to this map.
[0041]
In this case, when the electromagnetic valve 58 is opened, a part of the low-humidification oxidizing gas supplied from the oxidizing gas supply source 14 is introduced into the pipe 54b through the bypass circuit 56. Therefore, the humidification amount of the oxidizing gas humidified by the humidifier 52 decreases, and the dew point of the entire oxidizing gas decreases. On the other hand, when the electromagnetic valve 58 is closed, the oxidizing gas is sufficiently humidified via the humidifier 52, so that the humidification amount increases, and the dew point of the oxidizing gas increases.
[0042]
Thus, the relationship of the inner wall temperature> the gas dew point is always maintained in the pipe 54b, and the effect of reliably preventing water from being mixed into the oxidizing gas supplied to the fuel cell stack 12 can be obtained. can get. Therefore, for example, during a high-power operation, the voltage drop phenomenon does not occur in the fuel cell 20 arranged particularly on the end side of the fuel cell stack 12, and the power generation capacity of the fuel cell stack 12 can be sufficiently increased. It is possible to demonstrate.
[0043]
Further, in the present embodiment, the outside air temperature (ambient temperature) is measured by the control unit 76 via the fourth temperature sensor 74d. The control unit 76 compares the outside air temperature with the inner wall temperature detected by the first to third temperature sensors 74a, 74b, and 74c, and controls the opening and closing of the electromagnetic valve 58 when the inner wall temperature> the outside air temperature. Be done.
[0044]
Specifically, for example, as shown in FIG. 5, the change in the humidification amount due to the temperature difference Δt between the inner wall temperature and the outside air temperature is stored in advance in a map, and when the outside air temperature decreases, the humidification amount Adjustments are made. At this time, different maps are created in advance according to various inner wall temperatures (for example, 50 ° C., 60 ° C., 70 ° C.,...). Thereby, even if the outside air temperature changes rapidly, the relationship of the inside wall temperature> the gas dew point can be always maintained by anticipating the change of the inside wall temperature, and the humidified water is condensed on the inside wall of the pipe 54b. Can be reliably prevented.
[0045]
In addition, in this embodiment, although the hollow fiber membrane module 60 was demonstrated as the humidifier 52, it is not limited to this, For example, the flat membrane type humidifier 80 shown in FIG. 6 may be used.
[0046]
The flat membrane humidifier 80 is configured by alternately disposing supply plates 82 and water permeable membranes 84. In the supply plate 82, a meandering reaction gas passage 86 is formed on one surface, and a meandering humidification water passage 88 is formed on the other surface. The supply plates 82 which face each other with the water permeable membrane 84 interposed therebetween are arranged such that the reaction gas passage 86 and the humidifying water passage 88 face each other on both sides of the water permeable membrane 84.
[0047]
At one lower end of the flat membrane humidifier 80, a humidification water inlet 90 for supplying humidification water (or off gas) to the humidification water channel 88 is provided, and at the other lower end of the flat membrane humidifier 80. Is provided with an oxidizing gas inlet 92 for introducing a reactive gas, for example, an oxidizing gas into the reactive gas passage 86. At one upper end of the flat membrane humidifier 80, a humidifying water outlet 94 for discharging humidifying water (or off-gas) to the outside, and an oxidizing agent for sending the humidified oxidizing gas to a fuel cell (not shown). A gas outlet 96 is provided.
[0048]
In the flat film type humidifier 80 configured as described above, when a low humidifying oxidizing gas is supplied to the oxidizing gas inlet 92, the oxidizing gas is introduced into the reaction gas passage 86, and the oxidizing gas is deflected while meandering. Move in the direction of gravity. On the other hand, the humidification water (or off-gas) supplied to the humidification water introduction port 90 is introduced into the humidification water channel 88 and moves in the antigravity direction while meandering.
[0049]
Therefore, the humidification water (or the water in the off-gas) supplied to the humidification water passage 88 passes through the water permeable membrane 84 and moves to the reaction gas passage 86. Accordingly, the oxidizing gas supplied to the reaction gas passage 86 is humidified, and the humidified oxidizing gas is supplied from the oxidizing gas outlet 96 to the fuel cell 20 (see FIGS. 1 and 2).
[0050]
Therefore, the flat membrane humidifier 80 can surely humidify the oxidizing gas (and / or the fuel gas), and can achieve the same function as the hollow fiber membrane module 60.
[0051]
【The invention's effect】
In the method for supplying a reaction gas for a fuel cell according to the present invention, the inner wall temperature of the pipe connecting the humidifier for humidifying the reaction gas and the fuel cell is controlled so as to be higher than the dew point of the reaction gas. The moisture contained in the gas does not condense on the inner wall of the pipe. As a result, dew condensation water is not introduced into the fuel cell disposed particularly in the vicinity of the pipe, and it is possible to prevent a voltage drop phenomenon of the fuel cell and effectively exhibit a desired power generation capacity.
[Brief description of the drawings]
FIG. 1 is a schematic configuration explanatory view of a fuel cell system for carrying out a method for supplying a reaction gas of a fuel cell according to an embodiment of the present invention.
FIG. 2 is an exploded perspective view of a fuel cell constituting the fuel cell system.
FIG. 3 is a partially sectional explanatory view of a humidifier constituting the fuel cell system.
FIG. 4 is a flowchart for explaining the reaction gas supply method.
FIG. 5 is a diagram showing an example of a map showing a relationship between a temperature difference between an inner wall temperature and an outside air temperature and a humidification amount.
FIG. 6 is a partially sectional explanatory view of a flat membrane humidifier.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Fuel cell system 12 ... Fuel cell stack 14 ... Oxidizing gas supply source 16 ... Humidifying mechanism 18 ... Control part 20 ... Fuel cell 22 ... Electrolyte membrane / electrode assembly 24, 26 ... Separator 30a ... Oxidizing gas supply communication hole 30b oxidant gas discharge communication hole 32a cooling medium supply communication hole 32b cooling medium discharge communication hole 34a fuel gas supply communication hole 34b fuel gas discharge communication hole 36 solid polymer electrolyte membrane 38 anode electrode 40 Cathode side electrode 46 Oxidant gas flow path 48 Fuel gas flow path 50 Cooling medium flow path 52 Humidifiers 54 a and 54 b Pipe 56 Bypass circuit 58 Electromagnetic valve 60 Hollow fiber membrane module 72 Humidity sensor 74 a 74d: temperature sensor 76: control unit 80: flat membrane humidification

Claims (3)

A humidifier for humidifying the reaction gas and a fuel cell are connected by a pipe, and a bypass circuit for bypassing the humidifier is opened and closed to supply a reaction gas for the fuel cell for controlling humidification of the reaction gas supplied to the fuel cell. The method,
Detecting the inner wall temperature of the pipe,
Detecting a dew point of the reaction gas in the pipe,
Comparing the detected inner wall temperature and the dew point of the reaction gas;
Controlling the opening and closing of the bypass circuit so that the detected inner wall temperature is higher than the dew point of the reaction gas;
A reaction gas supply method for a fuel cell, comprising: The method for supplying a reaction gas for a fuel cell according to claim 1, wherein a step of detecting an outside air temperature outside the pipe;
When the outside air temperature is lower than the inner wall temperature, the opening and closing control of the bypass circuit to adjust the humidification amount of the reaction gas,
A reaction gas supply method for a fuel cell, comprising: 3. The reaction gas supply method for a fuel cell according to claim 1, wherein the fuel cell is a polymer electrolyte fuel cell.

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