JPH06325780A - Fuel cell system - Google Patents

Abstract

PURPOSE:To let generating capacity be exhibited with the system kept wet at all times, and thereby keep system operations stable by providing each circulating line for the fuel gas system connected to a fuel cell main body, a humidifying and cooling water system and an air system respectively. CONSTITUTION:Hydrogen contained gas leaving a hydrogen electrode 13 as a stream 19, is taken out of a cell main body in a state of a mixed phase with water, and is introduced into a water separator and storage tank 51 so as to be separated into a gas phase and a liquid phase. Let a part of hydrogen contained gas 52 from which water has been separated, flow out of the system as a purge stream 53, it is sucked in by an ejector 55 as circulating hydrogen contained gas 54 thereafter, and subsequently it is mixed with hydrogen contained gas 16 which is newly charged from the outside of the system, so that it is then supplied to the hydrogen electrode 13 side as hydrogen contained gas. Next, water separated at the tank 51 is taken out as circulating water 56 by way of a pump 57 so as to be forwarded to a radiator 58. After water 56 has been cooled down to a specified temperature at the radiator 58, it is returned back as circulating water 59 to be supplied to the electrode 13, to a groove acting as a water channel which is formed in a porous carbon material provided for the hydrogen electrode side of a gas separator.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixed polymer electrolyte membrane fuel cell using a solid polymer electrolyte membrane, humidification of fuel hydrogen on the hydrogen electrode side and an air electrode necessary for wetting the electrolyte membrane. The present invention relates to a novel fuel cell system that facilitates dehumidification from the (or oxygen electrode) side, improvement of hydrogen utilization rate, reuse of water produced on the air electrode side, and adjustment of cell operating temperature.

[0002]

2. Description of the Related Art In a conventional fuel cell having a solid polymer electrolyte membrane, the solid polymer electrolyte membrane is used as a cation exchange membrane, and it is known that it exhibits maximum proton conductivity when it is saturated with water. There is. That is, as the electrolyte membrane, for example, a polystyrene cation exchange membrane having a sulfonic acid group, a membrane in which a fluorocarbon sulfonic acid and polyvinylidene fluoride are mixed, a perfluorocarbon sulfonic acid membrane, etc. are known. The electrolyte membrane has a proton exchange group in its molecular structure, and has good proton conductivity by moistening water until saturation (specific resistance at room temperature is approximately 20 Ω · cm or less).
And acts as an electrolyte membrane.

As a fuel cell using the electrolyte membrane,
An example of a conventionally proposed system is shown in FIG.
In the figure, a unit cell is formed by joining porous carbon electrodes (diffusion layers) with a porous carbon layer (reaction layer) carrying a platinum catalyst on both sides of the solid polymer electrolyte membrane 11. The fuel cell main body 12 is configured by alternately stacking a plurality of cells and cells and gas separators.

In order to keep the electrolyte membrane 11 of the fuel cell 12 in a wet state, it is necessary to supply the hydrogen-containing gas 14 containing water to the hydrogen electrode 13. Therefore, the humidifier 15
Is installed, the humidifying water 17 is supplied together with the hydrogen-containing gas 16 as a fuel, and the humidifying water 17 and the hydrogen-containing gas 16 are brought into contact with each other while being heated by an appropriate heating medium 18. Gas 14 is obtained.

The hydrogen-containing gas 14 flowing into the hydrogen electrode 13 reaches the outlet of the hydrogen electrode while distributing and supplying hydrogen and water to the cell, and is taken out as a stream 19 to the outside.

Next, the air (or oxygen-containing gas) 20 is pressurized through a blower 21 and then fed as a stream 22 to the air electrode 23 side to distribute oxygen to the cells.
At the same time as the supply, the produced water is entrained in the air and taken out as exhaust air 24.

At this time, the operating temperature of the fuel cell is determined by the temperature, the pressure, the supply amount of the hydrogen-containing gas 14 and the air 22 supplied, and the power generation efficiency of the cell, and the heat generation amount generated in the cell leaves the stream ( It is carried away to the outside by the hydrogen-containing gas) 19 and the exhaust air 24. If it is desired to lower the operating temperature to a predetermined value, the cooling medium 2
An operation of cooling the electrode portion of the battery body is performed by 5.

[0008]

The above-mentioned prior art system shown in FIG. 3 has the following drawbacks.

(1) A dedicated humidifier 15 is required to humidify the hydrogen-containing gas 16, and a heating medium (heating source) 18 for supplying a heat amount corresponding to the latent heat of vaporization of water is provided in the humidifier. is necessary. At this time, in order to supply a sufficient amount of humidifying water required for the fuel cell main body, a heating source higher than the operating temperature of the cell main body is indispensable, but a heat source other than the exhaust heat of the cell is used. If you do
This leads to a decrease in heat economy.

(2) Since the hydrogen-containing gas 16 unidirectionally flows from the inlet to the outlet in the fuel cell, it is difficult to obtain a large hydrogen utilization rate. If the hydrogen electrode 13 side outlet is closed and the containment operation is performed in order to increase the hydrogen utilization rate,
Accumulation of an inert gas occurs near the outlet, which results in a decrease in hydrogen partial pressure and therefore a decrease in the power generation capacity of the battery.

(3) Next, focusing on the air electrode 23 side,
Since the air introduces the outside air, the inlet air is generally in a dry state or a low temperature state. Therefore, when the air is introduced into the air electrode 23, a low-humidity atmosphere is created in the vicinity of the inlet of the air electrode, and the solid polymer electrolyte membrane cannot be maintained in a sufficiently wet state, resulting in a decrease in power generation capacity. . Further, since the outside air having a temperature lower than the operating temperature of the battery (generally 80 to 90 ° C.) is directly introduced into the air electrode, the vicinity of the inlet of the air electrode is operated at a low temperature, which also lowers the power generation capacity. Contribute.

The present invention has been made in order to solve the above-mentioned drawbacks of the prior art, and effectively utilizes the exhaust heat of the fuel cell to generate electricity by keeping the solid polymer electrolyte membrane in a wet state at all times. The present invention proposes a simple fuel cell system capable of exhibiting its capability, improving the utilization rate of fuel-hydrogen-containing gas, and maintaining a stable operating state.

[0013]

A fuel cell system according to the present invention for solving the above-mentioned problems is a fuel cell using a solid polymer electrolyte membrane, wherein a hydrogen-containing gas and water are provided on the hydrogen electrode side of a gas separator. And heating the hydrogen-containing gas and cooling the cell, and circulating the unused hydrogen-containing gas and water released from the hydrogen electrode to the hydrogen electrode of the battery body, respectively. To do.

That is, a circulation (recycling) line is provided for each of the fuel gas system, the humidifying / cooling water system and the air system connected to the fuel cell body. The outline of technical means is listed below. (1) The hydrogen-containing gas leaving the hydrogen electrode is recycled to the hydrogen electrode again by utilizing the pumping action of the ejector or the like after separating from the liquid phase water. (2) The liquid phase moisture that leaves the hydrogen electrode together with the hydrogen-containing gas is separated from the hydrogen-containing gas, cooled using a radiator or the like, and cooled to a predetermined temperature, and then recycled to the hydrogen-electrode side. Used for humidification and battery cooling. (3) Exhaust air that leaves the air electrode is separated into condensed water and wet exhaust air by using gas-liquid separation, and a part of the condensed water is used as humidifying and cooling water in the above process (2). Department is recycled to the cathode.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will now be described in detail with reference to the drawings.

FIG. 1 shows an outline of a solid polymer electrolyte membrane fuel cell system according to this embodiment, and FIG. 2 shows an example of a gas separator used in this system. The above-mentioned FIG.
The same members as those of the system shown in FIG.

As shown in FIG. 1, the solid polymer electrolyte membrane fuel cell main body 12 has conductivity and gas through a so-called reaction layer composed of a porous carbon layer carrying platinum on both sides of the solid polymer electrolyte membrane. A single cell formed by joining porous carbon electrodes having diffusivity is used as a basic unit, and a plurality of these cells are laminated in series in multiple stages with a device called a gas separator interposed therebetween. However, in FIG. 1, for simplicity, only the structure of the single cell is schematically shown, and the gas separator is not shown.

Next, an example of the structure of the gas separator which makes the fuel cell system according to the present invention effective will be described with reference to FIG. In the example shown in FIG. 2, the material contacting the air electrode side is the dense carbon material 30, and the material contacting the hydrogen electrode side is the porous carbon material 31 to form the gas separator 32.
Grooves are formed on the air electrode side of the carbon material 30 and on the hydrogen electrode side of the carbon material 31, respectively, and the concave portions are the air flow passage 33 and the hydrogen-containing gas flow passage 34, and the convex portions 35, 3
6 is brought into electrical contact with the air electrode and the hydrogen electrode of the cell, respectively.

Further, the groove 37 carved in the upper portion of the carbon material 31 is used as a flow path for water. That is, the gas separator 32 has a structure capable of supplying a hydrogen-containing gas, air (or oxygen-containing gas) and water, and the hydrogen-containing gas and air are not directly mixed, but the water is discharged from the cell. While being heated by heat, they are diffused and transported through the porous carbon material 31 and evaporated into the hydrogen-containing gas flowing through the flow path 34. That is, the hydrogen-containing gas can be humidified.

At the hydrogen electrode, most of hydrogen gas is consumed as fuel for power generation, and part of water is consumed for humidification.
Excess hydrogen and water are taken out of the fuel cell main body as they are from the outlet of the gas separator. By adopting the gas separator having the above-described structure and action in the fuel cell main body, the system of the present invention can effectively function.

Therefore, the configuration and operation of this embodiment will be described with reference to FIG. 1 again.

The hydrogen-containing gas leaving the hydrogen electrode as the stream 19 is taken out from the battery main body in a mixed phase with water and introduced into the steam / water separator / water storage tank 51, where the gas phase and the liquid phase are separated. A part of the hydrogen-containing gas 52 after separating the water is made to flow out of the system as a purge flow 53, then sucked as a circulating hydrogen-containing gas 54 by the ejector 55, and then newly introduced from the outside of the system. 16 is mixed and supplied as hydrogen-containing gas 14 containing water to the hydrogen electrode 13 side. Next, the water separated in the tank 51 is taken out as circulating water 56 via the pump 57 and fed into the radiator 58.

In the radiator 58, the circulating water 56 is cooled to a predetermined temperature and then the circulating water 5 supplied to the hydrogen electrode 13 is cooled.
As shown in FIG. 9, it is returned to the groove 37 as a water channel formed in the porous carbon material 31 provided on the hydrogen electrode side of the gas separator 32 shown in FIG. In the example of FIG. 1, the ejector is used for recycling the hydrogen-containing gas, but a rotating fluid device such as a blower may be used. Also, circulating water 55
In the example of FIG. 1, the radiator 58 with an air-cooling fan is used for the temperature adjustment of the air-cooling fan by the on-off operation of the air-cooling fan, but the present invention is not limited to this and, for example, cooling water You may make it flow and heat-exchange with this.

Next, the structure and operation of the air electrode will be described.
Exhaust air 24 leaving the air electrode 23 is generally discharged from the battery body 12 in a mixed phase with water.
It is fed into 1 and separated into gas and liquid. Exhaust air 62 after separating water
After discharging a part of it as stream 63 out of the system,
The remaining portion is mixed as a circulation stream 64 with the air (or oxygen-containing gas) 20 that is newly fed, and then supplied as a stream 22 to the air electrode 23 via the blower 21.

Further, the water phase separated by the steam separator 61 is taken out as condensed water 65 from the air electrode 23 and sent to a deaerator 66, where the gas dissolved in water is degassed. Then, a part of the degassed condensed water 68 is discharged to the outside of the system as drainage 69, and the remaining part is circulated water 70. Return to 51.

There are two reasons why the condensed water 65 is degassed from the air electrode. The first reason is that oxygen and nitrogen, which are components in the air, are dissolved in the condensed water 65. Therefore, when the condensed water 65 is mixed with the circulating water 55 introduced to the hydrogen electrode 13 side. This is because dissolved oxygen may be diffused from the liquid phase to the gas phase to form an explosive mixture of hydrogen and oxygen, and this is to be avoided. The second reason is that nitrogen or the like dissolved in the condensed water 65 is
When nitrogen and the like are inactive in the hydrogen electrode when entrained in the condensed water and moved to the hydrogen electrode 13, these gases are accumulated on the hydrogen electrode side, the hydrogen partial pressure is reduced, and the power generation capability is reduced. This is to avoid that.

If the condensed water from the air electrode is not recycled as described above, a shortage of circulating water occurs on the hydrogen electrode side, so that new water is replenished to the steam separator / water storage tank 12. The need arises. In order to avoid the need for this new makeup water, it is significant to reuse the condensed water generated on the air electrode side.

Next, the temperature of the exhaust air 62 after separating the water coming out from the gas-liquid separator 12 is the operating temperature of the battery body (80
~ 90 ° C) and its relative humidity is almost 100
%, And the oxygen concentration is relatively high at 10 to 15% or more.
Therefore, a part of the exhaust air is used as the circulation flow 64 and the air electrode 2
By recycling to 3, the sensible heat of the exhaust air and part of the latent heat of vaporization of water vapor are recovered, the wet state of the solid polymer electrolyte membrane 11 is maintained, and the power generation capacity is prevented from decreasing. There is.

(Test Example) Table 1 shows a test example based on the embodiment of the present invention shown in FIG.

[0030]

[Table 1]

In the example of Table 1, almost all of the unused hydrogen in the fuel cell body is recycled, and about 1% of the exhaust air from the cell body is recycled.
The power generation performance of the cell was measured by setting each supply amount so as to recycle / 3, and the power generation performance almost as intended was confirmed. Therefore, the management of water and heat proposed by the present invention The system proved to be effective.

[0032]

INDUSTRIAL APPLICABILITY The present invention is a fuel cell using a solid polymer electrolyte membrane, in which a hydrogen-containing gas and water are supplied to the hydrogen electrode side of a gas separator to cool the cell and simultaneously contain hydrogen in the gas passage. Essential for fuel cells of this type by humidifying the gas and recycling the hydrogen-containing gas and water leaving the hydrogen electrode to the cell body, more preferably by partially recycling the exhaust air on the air electrode side. The water and heat can be easily managed, and the following effects are achieved. (1) Since the water flow path and the hydrogen gas flow path are distinguished in the humidification process on the hydrogen electrode side, the hydrogen-containing gas flow path does not become a gas-liquid mixed phase, and a uniform hydrogen-containing gas distribution is achieved. It will be possible. (2) The water supplied to the separator simultaneously fulfills the two functions of cooling the cell and humidifying the cell, and the system is simplified in this respect. (3) By using the hydrogen-containing gas in a circulating manner, it is possible to prevent the hydrogen partial pressure from decreasing on the entire hydrogen electrode side and to improve the hydrogen utilization rate in the system. (4) Since the atmosphere is filled with water vapor on both electrode sides, the solid polymer electrolyte membrane is always kept in a wet state, so that the power generation capacity of the cell can be fully exhibited. (5) The waste heat and drainage of the battery main body are effectively used, so that a separate heat source and water supply from the outside are not required, so that the thermal economy is improved.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a solid polymer electrolyte membrane fuel cell system according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of an example of a gas separator used in the system of the present invention.

FIG. 3 is a diagram showing a configuration of a conventional solid polymer electrolyte membrane fuel cell.

[Explanation of symbols]

 11 Solid Polymer Electrolyte Membrane 12 Fuel Cell 13 Hydrogen Electrode 14 Hydrogen-Containing Gas Containing Hydrogen 15 Humidifier 16 Hydrogen-Containing Gas 17 Humidifying Water 18 Heat Carrier 19,22 Stream 20 Air 21 Blower 23 Air Electrode 24 Exhaust Air 31 Porous Carbon material 32 Gas separator 33 Air flow path 34 Hydrogen-containing gas flow path 35,36 Convex portion 37 Groove 51 Water-vapor separator / water tank 52 Hydrogen-containing gas 53 Purge flow 54 Circulating hydrogen-containing gas 55 Ejector 56,70 Circulating water 57 Pump 58 Radiator 59 Circulating water supplied to hydrogen electrode 61 Steam-water separator 62 Exhaust air 63 Stream 64 Circulating flow 65,68 Condensed water 66 Deaerator 67 Purge gas 69 Drainage

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kennosuke Kuroda Inventor, Kennosuke Kuroda 2-5-1, Marunouchi, Chiyoda-ku, Tokyo Within Sanryo Heavy Industries Co., Ltd. Mitsubishi Heavy Industries Ltd. Hiroshima Works

Claims (5)

[Claims] 1. In a fuel cell using a solid polymer electrolyte membrane, a hydrogen-containing gas and water are supplied to the hydrogen electrode side of a gas separator to heat the hydrogen-containing gas and cool the cell. At the same time, an unused hydrogen-containing gas released from the hydrogen electrode and water are circulated to the hydrogen electrode of the cell body, respectively. 2. The fuel cell system according to claim 1, wherein the gas separator is provided with a hydrogen-containing gas passage and a water passage separately on the hydrogen electrode side, and the passage wall is made of a porous material. The fuel cell system is characterized in that the water in the water channel diffuses and moves to humidify the hydrogen-containing gas. 3. The fuel cell according to claim 1, wherein a water cooling device is installed in the water circulation path to the hydrogen electrode to adjust the temperature of water supplied to the hydrogen electrode. system. 4. The fuel cell system according to claim 1, wherein a part of the exhaust air from the air electrode is circulated to the air electrode again. 5. The fuel cell system according to claim 1, wherein the condensed water discharged from the air electrode is combined with the water supplied to the hydrogen electrode side of the separator.