JPH06111841A - Solid high polymer electrolyte type fuel cell system - Google Patents

Abstract

PURPOSE:To miniaturize a cooling system with condensation heat lessened, by using vaporization heat of water for cooling reforming pas, and supplying steam, less in steam quantity, generated in the cooling process. CONSTITUTION:In order to heat a reformer 5 to 260 deg.C, gas 24, including hydrogen gas in fuel electrode 2 side exhaust, is mixed with air 26 from a pump 9 to be burnt in a burner 5B. Also methanol 25 is concurrently burnt as auxiliary fuel. Exhaust gas 27 after burning is used for preheating methanol 16 and water 17 in a heat exchanger 8. Reforming gas 19 at 260 deg.C makes humidifying water 21 steam by a vaporizer 10, is cooled to at 90 deg.C to concurrently become humidified reforming gas 20. On the one hand, water 23 from a water storage tank 7 is heated to at 90 deg.C by a heat exchanger 11 for cooling a fuel cell to be supplied to the fuel electrode 2. High-humidity air 29 from an oxidant electrode 3 side is steam-separated by an expander 14 and a condenser 15, and water 30 is recovered to be stored in the tank 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell system using a solid polymer electrolyte fuel cell.

[0002]

2. Description of the Related Art Conventionally, fuel cells have been developed as a large power generation system. Among various fuel cells, a fuel cell using a solid polymer electrolyte such as a perfluorocarbon sulfonic acid membrane can be operated at a relatively low temperature (room temperature to 100 ° C.).

Therefore, a power generator using a solid polymer electrolyte fuel cell is suitable for miniaturization, and is particularly suitable as a small power generator to be installed in an isolated system such as an electric vehicle or an artificial satellite.

In order to apply the power generation device using this solid polymer electrolyte fuel cell to an isolated system, there is a problem of minimizing energy loss related to the water supply system, as described below.

When this solid polymer electrolyte fuel cell is operated, water flows together with ions from the fuel electrode to the oxidizer electrode, so that the water content on the fuel electrode side gradually becomes insufficient and the efficiency decreases. On the other hand, the oxidant electrode side produces water by the electrode reaction in addition to the water flowing from the fuel electrode side, so that the water content becomes excessive.

Therefore, in order to continuously operate this fuel cell, it is necessary to balance the water balance, supply water to the fuel electrode side, and remove water from the oxidizer electrode side. As described above, a water replenishment mechanism for replenishing water to the fuel electrode is indispensable for this solid polymer electrolyte fuel cell.

In a conventional fuel cell system, as a method of supplying water to the fuel electrode, for example, 1 mol of methanol as a fuel is reformed with 1 mol of steam in a reformer, and 3 mol of hydrogen and 1 mol of carbon dioxide are reformed. There is known a method of increasing the amount of water added to methanol to humidify the reformed gas when the reformed gas composed of gas is generated, and replenishing the fuel electrode with water by the steam.

Since the reforming reaction of methanol and water in the reformer is an equimolar reaction, if water is added in excess of the required number of moles, excess water remains as steam. It is possible to replenish water to the fuel electrode side by supplying this steam together with the reformed hydrogen to the fuel electrode. However, this method has the following problems.

In the currently used reformer, in order to reform a fuel containing a hydrocarbon group such as methanol into hydrogen gas, the temperature of the reforming catalyst is kept at about 260 ° C. in view of the performance of the reforming catalyst. There is a need. However, application of the above method requires heat energy to vaporize the excess water and heat it up to 260 ° C.

However, if the operating temperature of the solid polymer electrolyte type fuel cell is 90 ° C., it is necessary to lower the temperature of the reformed gas from 260 ° C. to 90 ° C. and supply it to the fuel cell. That is, the thermal energy required to heat the steam in the reformed gas from 90 ° C. to 260 ° C. is unnecessary energy consumption, resulting in energy loss. Also from 260 ℃ to 90
Since supersaturated water in the reformed gas is condensed during the cooling process to ℃, the heat energy is consumed in vain.

In order to improve this, Japanese Patent Laid-Open No. 3-269
Japanese Patent No. 955 describes a method of adding steam to the reformed gas without adding extra water.

In this method, the water for replenishing the fuel electrode is steamed with the heat quantity of the exhaust gas burned in the reformer and the heat quantity of the reformed gas at 260 ° C., and the obtained steam is used to transform the reformed gas. It is a method of humidifying. According to this method, the above-mentioned problem, that is, the wasteful consumption of heat energy due to heating the temperature of the steam up to 260 ° C. is improved.

[0013]

However, the above method also has a problem. Since the calorific value of the exhaust gas burned in the reformer and the calorific value of the reformed gas are not so large as compared with the heat of vaporization of water, only part of the water required by the fuel electrode can be vaporized. Therefore, in order to vaporize the remaining water,
It needs to be heated with its own burner using the fuel methanol. However, it is not preferable in terms of increasing the consumption of methanol as fuel, complicating the system, and increasing the size.

Further, if all the water required by the fuel electrode is supplied as steam, it is necessary to supply a reformed gas of high-concentration steam having a temperature of 90 ° C. and a relative humidity of 100%. It is difficult to supply water vapor in a pipeline without condensing it.

Furthermore, inside the fuel cell at a temperature of 90 ° C., the high-concentration water vapor condenses into water, so that a large amount of condensation heat is generated. Due to this large amount of heat generation, it becomes necessary to upsize the cooling device of the fuel cell. That is, a large amount of heat consumption required for vaporization of water vapor and heat generation due to condensation are unnecessary energy consumption, and since the heat is discarded without being used, it is a large loss in terms of energy balance.

When a power generator using a solid polymer electrolyte fuel cell is used in an isolated system such as an electric vehicle, consumption of substances such as fuel is minimized and energy loss is wasted as waste heat. To a minimum,
The entire device must be miniaturized. as mentioned above,
This problem cannot be solved by the conventional method.

An object of the present invention is to solve the above problems, to develop an efficient water replenishment system with less energy loss, and to provide a small and highly efficient fuel cell system suitable for electric vehicles and the like.

[0018]

[Means for Solving the Problems] In order to achieve the above-mentioned object, as a result of research, in order to inject the reformed gas into the fuel cell, the amount of water added to the high-temperature reformed gas to be vaporized. Efficient water replenishment with low energy loss by limiting the amount required to cool to the required temperature for the necessary amount and supplying the remaining water required by the fuel electrode in the form of liquid water. They have found that the system can be configured and have completed the present invention.

That is, the present invention is a fuel cell having a fuel electrode, an oxidizer electrode, and a solid polymer electrolyte sandwiched between both electrodes, and a reformer that reforms fuel into hydrogen gas and supplies it to the fuel electrode. In a fuel cell system including a container, a device for mixing water with reformed gas, and a passage for supplying water formed on the fuel electrode surface are provided. It is a fuel cell system. In the fuel cell of the present invention, water is supplied to the fuel electrode in two forms: water vapor contained in the reformed gas and water supplied directly in the form of liquid water.

When the fuel cell of the present invention is operated at 90 ° C., for example, the reformed gas at 260 ° C. needs to be lowered to 90 ° C. when it is injected into the fuel electrode. Effective for this temperature decrease is the heat of vaporization of water. Since the heat of vaporization of water is large, it can be effectively reduced by adding a small amount of water. Therefore, water is added to the reformed gas, and the temperature of the reformed gas is lowered to 90 ° C. by the heat of vaporization. The amount of water added is limited to that required to bring it down to 90 ° C. In this way, the temperature 90
A reformed gas containing water vapor at 10 ° C. and a relative humidity of 10 to 20% is obtained. This corresponds to about 5% of the water supplied to the fuel electrode.

The remaining about 95% of the water required by the anode is supplied directly to the anode in the form of liquid water. Water can be supplied directly through a water passage made of a water-absorbing or water-permeable material such as a porous body formed on the surface of the fuel electrode.

Water supplied directly to the fuel electrode is 90 ° C. to the fuel electrode.
Need to be heated and supplied. To heat the water, the waste heat of the fuel cell including the heat of condensation of the steam in the reformed gas can be used by installing a heat exchanger. As the water supplied to the fuel electrode, water can be recovered from the gas containing water vapor discharged from the oxidizer electrode side, supplied again to the fuel electrode and circulated for use.

[0023]

In the fuel cell of the present invention, the heat of vaporization of water is effectively used to lower the temperature of the reformed gas to 90 ° C. The water vapor generated in this process is supplied to the fuel electrode of the fuel cell. Since the reformed gas containing steam obtained here has a low relative humidity, there is no fear of condensation in the pipeline. This water vapor condenses in the fuel cell to generate heat,
Since the amount of water vapor is small, the heat of condensation generated is small, and therefore the cooling device for the fuel cell can be downsized.

The waste heat of the fuel cell containing the heat of condensation is
By using a heat exchanger, it can be used to heat the liquid water supplied from the water passage formed on the surface of the fuel electrode to 90 ° C.

Further, in the present invention, the humidified reformed gas and liquid water are supplied to the fuel electrode, but this combination brings about another effect of the present invention described below.

If the dry reformed gas and the liquid water are supplied to the fuel electrode, the dry reformed gas injected into the fuel electrode has a moisture content in the porous body disposed in the fuel electrode. Are evaporated and the porous body is dried. Since the degree of drying is greater as it gets closer to the inlet, it causes a significant imbalance in the distribution of water in the porous body arranged at the fuel electrode,
As a result, the distribution of water inside the fuel cell becomes significantly uneven, and the power generation efficiency of the fuel cell is reduced.

On the other hand, since the reformed gas of the present invention is humidified, the evaporation of water in the porous body is alleviated, and as a result, the distribution of water in the fuel cell becomes uniform,
The power generation efficiency of the fuel cell is improved.

In the present invention, the calorific value of the waste gas after combustion discharged from the reformer is not for vaporizing the water to be supplied to the fuel electrode but for preheating the equimolar raw material to be injected into the reformer. It is preferable to use. The purpose is to reduce the heat load on the reformer as much as possible by preheating and to reduce the consumption of fuel methanol, which is an auxiliary fuel for heating the reformer. Further, it is preferable to use the waste heat of the fuel cell as the preliminary heating before the preliminary heating.

By the above preheating step, a high temperature raw material gas can be injected into the reformer, and it is possible to reduce the consumption of fuel containing a hydrocarbon group such as methanol in the reformer.

[0030]

EXAMPLES Examples of the present invention will be described below. (Example)

FIG. 1 is a system configuration diagram of a solid polymer electrolyte type fuel cell power generator according to the present invention. In the figure, a fuel cell 1 which is shown as a single cell for simplification shows a solid polymer electrolyte 36 sandwiched between a fuel electrode 2, an oxidizer electrode 3 and both electrodes, a surface of the fuel electrode 2 and water on the fuel electrode. A water passage (not shown) for supplying the heat is provided, and a heat exchanger 4 is further provided.

Methanol 16 from the fuel tank 6 and water 17 from the water storage tank 7 are sent to the reformer 5 by a predetermined amount, respectively, and the fuel 18 having a predetermined mixing ratio reacts in the reformer 5 to generate hydrogen. A reformed gas 19 containing as a main component is generated.

In order to heat the reformer 5 to 260 ° C., the gas 24 containing hydrogen exhausted from the fuel electrode side of the fuel cell is sent, mixed with the air 26 sent by the pump 9 and burned in the burner 5B. To be done. Further, methanol 25 in the fuel tank 6 is also sent as auxiliary fuel and is burned at the same time. The heat of the waste gas 27 after combustion is generated by the heat exchanger 8.
It is used to preheat the raw materials methanol 16 and water 17.

The reformed gas 19 at 260 ° C. is the water vaporizer 10
Sent to. Humidification water 21 is supplied to the vaporizer 10. The humidifying water 21 flows from the water storage tank 7 to the heat exchanger 12
And is preheated and then sent to the vaporizer 10. In the vaporizer 10, the reformed gas 19 at 260 ° C. vaporizes the humidifying water 21 and becomes the reformed gas 20 that is cooled to 90 ° C. and is humidified. The heat exchanger 12 is
Compressed by the compressor 13 to send to the oxidizer electrode 3,
This is for cooling the hot air 28 to 90 ° C. On the other hand, the water 23 sent from the water storage tank 7 is heated to 90 ° C. by the heat exchanger 11 for cooling the fuel cell and supplied to the fuel electrode 2.

The high-humidity air 29 discharged from the oxidizer electrode side in FIG. 1 is separated into steam and water by the expander 14 and the condenser 15, and water 30 is recovered. The recovered water is stored in the water storage tank 7. Although not shown, it is preferable to preheat the raw materials methanol 16 and water 17 supplied to the reformer 5 by the heat exchanger 11 of the fuel cell.

On the other hand, FIG. 2 shows a schematic view of the fuel cell 1 according to this embodiment. The fuel cell 1 is a solid polymer electrolyte membrane (trade name: Naf) made of perfluorocarbon sulfonic acid.
Ion; manufactured by Du Pont) 36, and a plurality of unit cells each having a fuel electrode 2 and an oxidant electrode 3 formed on both sides thereof are laminated. Further, each unit cell is separated by a separator made of a conductor and is electrically connected. A reformed gas passage 33 and an air passage 34 are formed along the fuel electrode 2 and the oxidizer electrode 3, respectively. The reformed gas and the air flow through the passages in the directions of arrows A and B, respectively.
A metal net for current collection is formed in each passage. On the surface of the fuel electrode 2, a water-absorbing or water-permeable substance (for example, a porous body) 31 that serves as a passage for moisture is formed. The water 23 of FIG. 1 flows through the water-absorbing or water-permeable substance 31 in the direction indicated by c in FIG. 2 to supply the water to the fuel electrode 2. FIG. 3 is a vertical sectional view of the fuel electrode 2. . As shown in FIG. 3, the water-absorbing or water-permeable substance 31 partially covers the fuel electrode 2. In the fuel electrode 2, water is supplied from the portion covered with the water absorbing or water permeable substance 31. Further, the electrode reaction with the reformed gas is carried out from the portion which is not covered with the water absorbing or water permeable substance.

On the other hand, a water-absorbing or water-permeable substance 37 is also formed on the surface of the air electrode 3 similarly to the fuel electrode 2. The water-absorbing or water-permeable substance formed in the air electrode 3 is used for absorbing the high-humidity gas 29 generated in the air electrode 3. The absorbed high-humidity gas 29 is transferred to the expander 14 shown in FIG.
Sent to.

[0038]

As described above, according to the present invention,
Since the reformed gas is humidified, heat loss due to vaporization and condensation of water can be minimized, and the reformer and the reformed gas supply line can be simplified and downsized. Further, by reducing the generation of condensation heat in the fuel cell, the fuel cell can be miniaturized, and by making the distribution of water in the fuel cell uniform, high efficiency of the fuel cell can be achieved. In the fuel cell system, reduce energy loss and material loss,
A compact and highly efficient power generation system was realized.

Therefore, the fuel cell of the present invention can be used not only as a general power generation device, but also for automobiles and other vehicles.
Especially suitable as a power generator for use in an isolated system,
The industrial benefits obtained by providing this device are great.

[Brief description of drawings]

FIG. 1 is an example of a configuration diagram of a fuel cell system of the present invention.

FIG. 2 is a partial cross-sectional view showing an embodiment of the fuel cell of the present invention.

FIG. 3 is a partial plan view showing an embodiment of the fuel cell of the present invention.

[Explanation of symbols]

1 ... Fuel cell 2 ... Fuel electrode 3 ... Oxidizer electrode 4, 8, 1
1, 12 ... Heat exchanger 5 ... Reformer 5B ... Burner 6 ... Fuel tank 7 ... Water tank 9 ... Pump 10 ... Vaporizer 13 ... Compressor 14 ... Expander 1
5 ... Condenser 16, 25 ... Methanol 17, 21, 23, 30 ... Water 18 ... Fuel mixture 19 ... Reformed gas 20 ... Humidified reformed gas 24 ... Gas exhausted from fuel electrode 26, 28 ... Air 27 ... Combustion waste gas 29 ... High humidity gas 31 ... Water-absorbing or water-permeable material formed on the fuel electrode 32 ... Solid polymer electrolyte 33 ... Reformed gas passage 34 ... Air passage 35 ... Separator 37 ... Water-absorbing or water-permeable material formed on the oxidizer electrode

Claims (1)

[Claims] 1. A fuel cell comprising a fuel electrode, an oxidizer electrode, and a solid polymer electrolyte sandwiched between both electrodes, and a reformer for reforming a fuel into hydrogen gas and supplying the hydrogen gas to the fuel electrode. In the fuel cell system, a solid polymer electrolyte fuel cell system comprising: a device for mixing water with the reformed gas; and a passage for supplying water formed on the surface of the fuel electrode.