JP2914898B2 - Polymer electrolyte fuel cell system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a polymer film having hydrogen ion conductivity or an inorganic or organic material powder having hydrogen ion conductivity and a polymer material which imparts flexibility and denseness to the powder. The present invention relates to a polymer electrolyte fuel cell system using, as an electrolyte, a composite material added as a binder, or a composite material in which a polymer film is made of an inorganic or organic material powder or fiber as a reinforcing material.

[0002]

2. Description of the Related Art In recent years, fuel cells have attracted attention as high-efficiency energy conversion devices. Depending on the type of electrolyte used for the fuel cell, for example, an alkaline aqueous solution type, a phosphoric acid type, a low temperature operation fuel cell such as a solid polymer type, a molten carbonate type, a high temperature operation fuel cell such as a fixed oxide electrolyte type, and the like. Are roughly divided into

Among these fuel cells, a polymer electrolyte fuel cell using a polymer electrolyte membrane having hydrogen ion conductivity as an electrolyte has a compact structure without a pressurized container or the like and has a high output density. Since it can be operated by a simple and simple system, it has attracted attention as a mobile power supply for space use or a vehicle or a small stationary power supply for emergency use.

Examples of the polymer membrane include a polystyrene cation exchange membrane having a sulfonic acid group, a mixed membrane of fluorocarbon sulfonic acid and polyvinylidene fluoride, and a membrane obtained by grafting trifluoroethylene onto a fluorocarbon matrix. Recently, a perfluorocarbon sulfonic acid membrane (for example, Naphion: trade name, manufactured by DuPont) or the like has been used.

FIG. 8 is a schematic configuration diagram of a general polymer electrolyte fuel cell system. A polymer electrolyte fuel cell body 1 includes a pair of porous electrodes having functions as a gas diffusion layer and a catalyst layer. That is, a current collector (not shown) having the polymer electrolyte membrane 4 sandwiched between the fuel electrode 2 and the oxidant electrode 3 and having grooves serving as a fuel flow path and an oxidant flow path provided outside the both electrodes is arranged. The unit cell 5 is formed by stacking a plurality of such unit cells 5 in a horizontal state in a vertical state via a separator, a cooling plate 6 and the like.

A fuel gas supply system 10 for supplying fuel to the fuel electrode 2, an oxidant gas supply system 20 for supplying oxidant gas to the oxidant electrode 3, and cooling water in the cooling plate 6 by a pump The cooling water system 30 that circulates heat and removes heat generated during power generation, and other control systems constitute a polymer electrolyte fuel cell system.

That is, fuel supplied from a fuel source (not shown) is supplied to the fuel electrode 2 after being reformed into a fuel gas rich in hydrogen by the fuel processor 11, and oxidant gas is supplied to the oxidant electrode 3. An oxidant gas is supplied via the supply system 20. In the cooling water system 30, the cooling water 32 stored in the cooling water tank 31 is supplied to the cooling plate 6 by the pump 33, and the cooling water that has cooled the fuel cell main body 1 is supplied to the heat exchanger 3.
After returning to 4, the cooling water is returned to the tank 31. By the way, in the polymer electrolyte fuel cell, it is necessary to keep the polymer membrane as the electrolyte in a wet state, that is, to humidify it. Therefore, usually, humidifiers 12 and 21 are provided in the fuel gas supply system 10 and the oxidant gas supply system 20, and the polymer film is humidified by adding steam to the fuel gas and the oxidant gas. This method is known as external humidification.

On the other hand, a method for humidifying a polymer film without using an external device such as a humidifier is disclosed in
As described in Japanese Patent No. 68884, a direct water supply and humidification method in which water is directly supplied to a polymer membrane inside a fuel cell and humidified has been proposed.

FIG. 9 is a diagram showing the structure of a single cell of the direct water supply and humidification system. A fuel electrode 2 and an oxidizer electrode 3 sandwich the polymer electrolyte membrane 4 on both sides of the polymer electrolyte membrane 4. A fuel flow channel 7 made of a porous material is provided on the outer surface of the fuel electrode 2 (the surface opposite to the polymer electrolyte membrane 4), and is provided on the outer surface side of the fuel flow channel 7. A cooling water flow path 9 is provided via a humidified water permeable plate 8 made of a porous material. Thus, a part of the cooling water supplied to the cooling water flow path 9 penetrates the humidified water permeable plate 8 and the fuel flow path 7, and the polymer film 4 is humidified.

The direct water supply humidification method has advantages over the external humidification method in that the humidifier can be omitted, the system configuration can be simplified, and the humidification amount can be adjusted irrespective of the gas flow rate and operating temperature. There is. Further, Japanese Unexamined Patent Application Publication No.
As described in JP-A-309263, the supplied water evaporates into the supply gas, so that there is also an advantage that a cooling effect by the latent heat of evaporation can be obtained.

[0011]

In the direct water supply humidification method, since the cooling water evaporates into the supply gas as described above, the heat generated by the battery reaction is equal to the evaporation latent heat of water supplied as humidification water. The circulating water is cooled by the sensible heat. At that time, the amount of cooling by the latent heat of evaporation is controlled by the differential pressure between the cooling water and the fuel gas, and the amount of cooling by the sensible heat of the cooling water is controlled by the flow rate of the circulating cooling water. Therefore, it is necessary to control the pressure and the flow rate of the cooling water supplied to the fuel cell body independently.

However, in a cooling water system in which cooling water is simply circulated by a pump as shown in FIG. 8, it is impossible to independently control the pressure and flow rate of the cooling water. For example, when the rotation speed of the pump is increased, the flow rate of the cooling water can be increased, but at the same time, the pressure of the cooling water also increases.
For this reason, there is a problem that the pressure of the cooling water is increased in order to increase the cooling amount by the latent heat of evaporation, and at the same time, the flow rate of the cooling water is also increased, and the cooling amount by the sensible heat is also increased, so that the fuel cell body is excessively cooled. .

In view of the above, the present invention has a system suitable for a polymer electrolyte fuel cell using a direct water supply humidification method, that is, a cooling water system capable of independently controlling the pressure and flow rate of cooling water. An object is to obtain a polymer electrolyte fuel cell system.

[0014]

According to a first aspect of the present invention, a plurality of unit cells sandwiching a polymer electrolyte membrane between a fuel electrode and an oxidant electrode are stacked, and a cooling plate is inserted for each unit cell.
A part of the cooling water supplied to the cooling plate is supplied to the polymer electrolyte membrane through the porous humidified water permeable plate and the porous fuel electrode current collector plate, and the polymer electrolyte membrane is humidified. A solid polymer fuel cell system comprising: a fuel cell main body configured as described above; and a cooling water system configured to circulate cooling water by a pump through a cooling plate of the fuel cell main body to remove heat generated during power generation. A pressure adjusting means for controlling the cooling water pressure independently of the cooling water amount.

According to a second aspect of the present invention, there is provided a cooling water supply pipe for supplying cooling water to the fuel cell main body by providing a cooling water return pipe for supplying cooling water to the fuel cell main body by the pump, while providing a cooling water return pipe for sending cooling water flowing out of the fuel cell main body to a pump side. A bypass pipe that bypasses the fuel cell body and the pressure regulating valve is provided between the cooling water return pipe and the cooling water return pipe, and a flow control valve is provided in the bypass pipe.

According to a third aspect of the present invention, a cooling water tank for storing cooling water supplied to the cooling plate is provided in the cooling water system,
A conduit branched from an oxidizing gas supply pipe for supplying an oxidizing gas to the oxidizing electrode is connected to an upper portion of the cooling water tank via a pressure control valve, and one of the oxidizing gas supplied to the oxidizing electrode is The part is introduced into a cooling water tank, and cooling water is supplied to the fuel cell main body by the pressure of the oxidizing gas.

According to a fourth aspect of the present invention, a drain tank is connected to at least the oxidizer electrode of the fuel electrode and the oxidizer electrode, and the water condensed in the drain tank is humidified to the cooling plate via a pump and a cooling water supply pipe. The heat generated during power generation is caused by latent heat of vaporization when the cooling water supplied as water is circulated in the fuel gas or the oxidant gas together with the water produced by the battery reaction generated at the oxidant electrode. And evaporates in the oxidizing gas together with latent heat of vaporization in the fuel gas of the cooling water supplied as humidifying water to the cooling water supply pipe and water generated by the battery reaction generated at the oxidizing electrode. A flow meter or a pressure gauge for adjusting the flow rate and pressure of the cooling water is provided so that the amount of cooling by the latent heat of evaporation of the cooling water and the heat generated by the battery reaction are balanced.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 is a diagram showing a schematic configuration of a polymer electrolyte fuel cell system according to a first embodiment of the present invention.
The fuel cell body 1 is constructed by sandwiching a polymer electrolyte membrane 4 between a fuel electrode 2 and an oxidant electrode 3 and laminating a plurality of cooling electrodes 6 on the outside of the fuel electrode 2. I have.
Then, the fuel supplied from a fuel source (not shown) is reformed into a fuel gas rich in hydrogen in the fuel processor 11, the reformed fuel gas is supplied to the fuel electrode 2, and the oxidant electrode 3 The oxidizing gas is supplied via the oxidizing gas supply system 20.

On the other hand, a cooling water 32 stored in a cooling water tank 31 is supplied to the cooling plate 6 by a pump 33, and a part 32a of the supplied cooling water is supplied to the fuel electrode 2, and a polymer electrolyte membrane is provided. 4 is humidified and evaporates into fuel gas and oxidizing gas. Then, part of the battery reaction heat is removed by the latent heat of evaporation at that time. The remaining cooling water 32b is returned to the cooling water tank 31 via the heat exchanger 34 after removing the remaining battery reaction heat by sensible heat.

The above-mentioned structure is the same as the conventional one, but in the first embodiment of the present invention, the cooling water is introduced from the cooling plate 6 of the fuel cell body 1 to the heat exchanger 34 side. A back pressure valve 35 is provided in the return pipe. Therefore, the pressure of the upstream side of the back pressure valve 35, that is, the pressure of the cooling plate 6 is kept constant by the opening degree of the back pressure valve 35.

FIG. 2 shows that the cooling water flows through a cooling water system using only a conventional pump and a cooling water system provided with a back pressure valve according to the present invention. The relation of the plate inlet pressure is shown.

That is, in the conventional cooling water system, since the inside of the cooling water tank is open to the atmosphere, the pressure applied to the inlet of the cooling plate corresponds to the pressure loss of the cooling system. Therefore, when the rotation speed of the pump is increased and the flow rate of the cooling water is increased, the pressure loss increases, and the pressure at the inlet of the cooling plate increases as shown by the solid line A in the figure. On the other hand, in the case where the back pressure valve 35 is provided as described above,
Since the pressure of the cooling water is kept constant by the back pressure valve, the pressure of the cooling water can be kept substantially constant as shown by the solid line B in FIG. 2 irrespective of the change in the flow rate of the cooling water.

Thus, for example, by keeping the pressure of the cooling water constant, the differential pressure with the fuel gas is kept constant, and the amount of water supplied to the fuel electrode side as the humidifying water is kept constant.
The amount of circulating cooling water can be increased. Also,
By changing the opening of the back pressure valve 35 and increasing the pressure of the cooling water,
The amount of water supplied as humidification water can be increased without changing the amount of circulating cooling water.

FIG. 3 is a diagram showing a schematic configuration of a polymer electrolyte fuel cell system according to a second embodiment of the present invention.
A pressure control valve 36 is provided in the cooling water return pipe,
A bypass passage 37 is provided to bypass the fuel cell body 1 and the pressure control valve 36, and a flow control valve 38 is provided in the bypass passage 37.

The pressure of the cooling water can be adjusted by controlling the pressure adjusting valve 36.
By adjusting the flow rate of the cooling water flowing through the bypass passage 37 by the flow rate adjusting valve 38, the flow rate of the cooling water circulating through the fuel cell main body can be adjusted. This embodiment is effective when the flow rate of the circulating cooling water is a large flow rate at which the back pressure valve cannot be used, specifically, when the flow rate is 50 LM or more.

FIG. 4 is a view showing a third embodiment of the present invention. A second cooling water tank 40 is provided upstream of the cooling plate 6 in the cooling water system 30.
The cooling water in the cooling water tank 40 is supplied to the cooling plate 6,
Further, the cooling water is returned to the cooling water tank 31 via the flow control valve 41. The cooling water 32 in the cooling water tank 31 is supplied to the second cooling water tank 40 by the supply pump 4.
2, when the water level gauge 43 provided in the second cooling water tank 40 detects that the water level in the second cooling water tank 40 has become lower than the lower limit value. The supply pump 42 is operated to supply the cooling water to the second cooling water tank 40.

On the other hand, a conduit 44 is connected to the oxidizing gas supply system 20.
Is branched and led out, and the end of the conduit 44 is opened to the upper space of the second cooling water tank 40. And
The conduit 44 is provided with a pressure regulating valve 45. Therefore, a part of the oxidizing gas flowing through the oxidizing gas supply system is supplied to the upper part of the second cooling water tank 40, and the cooling is performed by the pressure of the oxidizing gas supplied to the second cooling water tank 40. Water is supplied to the cooling plate 6 of the fuel cell body.

The pressure of the oxidizing gas supplied to the second cooling water tank 40 is regulated by the pressure regulating valve 45. When the pressure is higher than the pressure of the fuel gas, the pressure is higher than the pressure of the fuel gas. Can be easily supplied to the cooling plate 6. When the pressure of the supplied oxidizing gas is equal to the pressure of the fuel gas, the second cooling water tank 40 is installed at a position higher than the fuel cell main body 1 so that the cooling water is supplied by the head difference. Can be
Also in this case, the pressure is adjusted by the pressure adjusting valve 45. On the other hand, the flow rate of the cooling water circulating through the fuel cell main body 1 is adjusted by a flow rate control valve 41 provided on the cooling water return pipe. Therefore, also in this embodiment, the pressure and flow rate of the cooling water can be controlled independently.

The system shown in FIG. 4 is effective when a large amount of latent heat can be expected and a small amount of circulating cooling water is required. That is, this is effective when the amount of cooling due to latent heat of evaporation accounts for 50% or more of the calorific value of the cell. As the flow rate of the circulating cooling water decreases, the number of times the replenishment pump operates is reduced, and the power for auxiliary equipment is reduced. ,
System efficiency is improved.

In the third embodiment, the latent heat of evaporation of a part of the cooling water is used for cooling the fuel cell body. However, the cooling water and the oxidizing gas which evaporate into the fuel gas are used. There is also a possibility that the heat generated during power generation can be cooled by the latent heat of evaporation of the cooling water evaporating at the time.

FIG. 5 shows a structure in which the fuel cell body 1 is cooled only by the latent heat of evaporation of the cooling water.
A drain tank 5 is provided for each of the fuel electrode 2 and the oxidizer electrode 3.
0, 51 are connected, and each drain tank 50, 51
The cooling water condensed in the cooling water tank 31 is
The cooling water in the cooling water tank 31 is returned to the pump 3
3 is supplied to the cooling plate 6 of the fuel cell main body 1. The cooling water return pipe connected to the cooling plate 6 itself is omitted.

Thus, part of the cooling water supplied to the cooling plate 6 by the pump 33 and flowing into the fuel passage evaporates into the fuel gas, and the remaining cooling water is used after the polymer electrolyte membrane 4 is humidified. Then, it evaporates in the oxidant gas together with the water produced by the battery reaction generated at the oxidant electrode. Therefore, all the battery reaction heat is removed by the latent heat of evaporation due to both types of evaporation. The water in the fuel gas and the water in the oxidant gas are condensed in the drain tanks 50 and 51 and
2 returns to the cooling water tank 31.

A cooling water supply pipe 53 for supplying cooling water to the cooling plate 6 by the pump 33 is provided with a flow meter 54 or a pressure gauge 55, and an output signal 56 from the flow meter 54 and a pressure gauge 55. Output signal 57 of the pump 3
3, and the output of the pump 33 is controlled so that the flow rate and pressure of the cooling water become predetermined values. This allows
The amount of cooling latent heat of cooling water evaporating in the oxidant gas together with the latent heat of evaporation of the cooling water evaporated in the fuel gas and the water produced by the battery reaction at the oxidant electrode balances the heat generated by the battery reaction. The amount of cooling water is adjusted.

FIG. 6 shows that the cell of the direct water supply humidification system has a pressure of 0.3 MPa, hydrogen having a utilization of 73%, and a pressure of 0.3 M.
Supply air with a utilization rate of 9 to 72% and a temperature of 70 to 1
It is a figure which shows the result of having examined the ratio (%) of the cooling amount by evaporation latent heat with respect to the cell heat generation amount at the time of electric power generation at 10 degrees and current density of 0.4 A / cm < ² >. As can be seen from FIG. 6, when the temperature is high and the air utilization rate is low, the ratio of the cooling amount due to the latent heat of vaporization to the cell heating value increases. There are conditions under which all heat can be removed by the latent heat of evaporation of cooling water. Therefore, the system shown in FIG. 5 is effective when all of the battery reaction heat can be removed by the latent heat of evaporation of the cooling water.

However, in the system shown in FIG. 5, by removing all of the battery reaction heat by the latent heat of evaporation of the cooling water, the required amount of cooling water can be reduced and the system efficiency can be improved.

FIG. 7 shows another modification of the system shown in FIG. 5. In this system, the cooling water tank 31 and the pump 52 are omitted from the system shown in FIG. The cooling water is supplied from the drain tank 51 to the cooling plate 6 by the pump 33 directly.

That is, when the moisture in the fuel gas is extremely small compared to the moisture in the oxidizing gas, the drain tank 51 is provided with the function of a cooling water tank as described above, and Only the drain can be returned to the cooling plate 6 side. Thus, in this case, the entire system can be simplified.

[0039]

The present invention is constructed as described above.
The flow rate and pressure of the cooling water can be controlled independently, and the differential pressure between the cooling water and the fuel gas and the flow rate of the circulating cooling water are controlled independently. The amount of cooling by the sensible heat of water can be appropriately controlled, and the fuel cell body can be reliably prevented from being excessively cooled.

[Brief description of the drawings]

FIG. 1 is a system diagram showing a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a relationship between a flow rate of cooling water and a cooling plate inlet pressure.

FIG. 3 is a system diagram showing a second embodiment of the present invention.

FIG. 4 is a system diagram showing a third embodiment of the present invention.

FIG. 5 is a system diagram showing a fourth embodiment of the present invention.

FIG. 6 is a diagram showing a ratio of a latent heat cooling amount to a heat generation amount.

FIG. 7 is a diagram showing another example of the system shown in FIG. 5;

FIG. 8 is a system diagram showing a conventional polymer electrolyte fuel cell system.

FIG. 9 is a sectional view showing the structure of a single cell of a direct water supply humidification system.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 solid polymer fuel cell main body 2 fuel electrode 3 oxidizer electrode 4 polymer electrolyte membrane 5 unit cell 6 cooling plate 8 humidified water permeable plate 10 fuel gas supply system 11 fuel processing device 20 oxidizer gas supply system 30 cooling water system 31 Cooling water tank 33 Pump 35 Back pressure valve 36 Pressure control valve 37 Bypass passage 38 Flow control valve 41 Flow control valve 50, 51 Drain tank

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-6-325780 (JP, A) JP-A-4-12462 (JP, A) JP-A-3-219565 (JP, A) JP-A-6-325 295734 (JP, A) Japanese Patent Laid-Open No. Hei 6-2311791 (JP, A) Japanese Glossary of Terms (II) Machine Edition, 1st Edition (November 1, 1978) Published by the Japan Standards Association, page 6 (58) Int.Cl. ⁶ , DB name) H01M 8/00-8/24

Claims (5)

(57) [Claims] 1. A unit cell comprising a fuel cell and an oxidant electrode sandwiching a polymer electrolyte membrane, a plurality of unit cells are stacked, and a cooling plate is inserted for each unit cell to form a porous humidified water permeable plate and a porous member. A fuel cell body configured to supply a part of the cooling water supplied to the cooling plate to the polymer electrolyte membrane through a solid-state fuel electrode current collector plate to humidify the polymer electrolyte membrane; A cooling water system that circulates cooling water by a pump through a cooling plate of the battery body and removes heat generated during power generation, wherein the cooling water pressure is applied to the cooling water system independently of the cooling water amount. A polymer electrolyte fuel cell system comprising a pressure adjusting means for controlling. 2. The polymer electrolyte type according to claim 1, wherein the pressure adjusting means is a back pressure valve provided in a cooling water return pipe for sending cooling water flowing out of the fuel cell body to a pump side. Fuel cell system. 3. A cooling water return pipe for sending cooling water flowing out of the fuel cell body to a pump, a pressure regulating valve provided, a cooling water supply pipe for supplying cooling water to the fuel cell body by the pump, and the cooling water supply pipe. 2. The polymer electrolyte fuel cell system according to claim 1, wherein a bypass pipe that bypasses the fuel cell body and the pressure control valve is provided between the return pipes, and a flow control valve is provided in the bypass pipe. 4. A unit cell comprising a fuel cell and an oxidizer electrode sandwiching a polymer electrolyte membrane, a plurality of unit cells are stacked, and a cooling plate is inserted for each unit cell to form a porous humidified water permeable plate and a porous plate. A fuel cell main body that supplies a part of the cooling water supplied to the cooling plate to the polymer electrolyte membrane through the solid fuel electrode current collector plate and humidifies the polymer electrolyte membrane; A cooling water system for removing heat generated during power generation by circulating cooling water by a pump through the cooling plate, wherein the cooling water supplied to the cooling plate is stored in the cooling water system. A cooling water tank is provided, a conduit branched from an oxidizing gas supply pipe for supplying an oxidizing gas to the oxidizing electrode is connected to an upper portion of the cooling water tank via a pressure control valve, and supplied to the oxidizing electrode. Part of the oxidizing gas introduced into the cooling water tank And, wherein the cooling water by the pressure of the oxidant gas to be supplied to the fuel cell body, the solid polymer fuel cell system. 5. A humidified water permeable plate made of a porous material and a porous plate, wherein a plurality of unit cells sandwiching a polymer electrolyte membrane between a fuel electrode and an oxidant electrode are stacked, and a cooling plate is inserted for each unit cell. A fuel cell main body that supplies a part of the cooling water supplied to the cooling plate to the polymer electrolyte membrane through the solid fuel electrode current collector plate and humidifies the polymer electrolyte membrane; In a polymer electrolyte fuel cell system comprising a cooling water system for circulating cooling water through a cooling plate by a pump to remove heat generated during power generation, a drain tank is connected to at least the oxidizer electrode of the fuel electrode and the oxidizer electrode Then, the water condensed in the drain tank is returned to the cooling plate as humidification water via a pump and a cooling water supply pipe, and the cooling water supplied as humidification water is generated in the fuel gas or at the oxidizer electrode. Water generated by the battery reaction In addition to evaporating in the oxidant gas and removing the heat generated during power generation by the latent heat of evaporation, the latent heat of evaporation in the fuel gas of the cooling water supplied as humidifying water to the cooling water supply pipe and A flow meter that adjusts the flow rate and pressure of the cooling water so that the amount of cooling by the latent heat of evaporation of the cooling water that evaporates in the oxidizing gas together with the water generated by the battery reaction generated at the oxidizing electrode balances the heat generated by the battery reaction. And a pressure gauge provided.
Solid polymer fuel cell system.