JPS61185872A - Fuel cell device - Google Patents

Abstract

PURPOSE:To realize long life by controlling steam quantity to be added to fuel gas and oxidizing agent gas. CONSTITUTION:Steam SF, SA are added to fuel gas F and oxidizing agent gas A so as to keep the capacity of electrolyte in a fuel cell body 6 constant, however in recyclic operation, water quantity becomes excessive to give bad effect to the cell. Then in the fuel gas system, water content of recycle fuel gas is measured by a water content measuring unit 15F, and the measured value is transmitted to a fuel gas system steam quantity control unit 16F and water necessary is computed from the fuel gas flow rate, and opening of a fuel gas system steam quantity regulating valve 12F provided on a fuel gas system steam supplying unit 11F is regulated, and steam quantity SF to be added to fuel gas F is controlled. Simultaneously, measured value in an oxidizing agent system water content measuring unit 15A is transmitted to an oxidizing agent gas system steam quantity control unit 16A, and steam quantity SA to be added to oxidizing agent gas A is controlled to be optimum.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a fuel cell device, and more particularly to a fuel cell device including means for controlling the amount of humidifying water vapor that humidifies a fuel cell body.

[Technical Background of the Invention] Conventionally, a fuel cell is a device that directly converts chemical energy contained in fuel into electrical energy. In this fuel cell, a pair of porous electrodes are usually arranged with an electrolyte sandwiched between them, and a fuel gas such as hydrogen is brought into contact with the back surface of one electrode, and an oxidizing agent such as oxygen is brought into contact with the back surface of the other electrode.
The electrical energy generated by the electrochemical reaction that occurs at this time is extracted from between the pair of electrodes. In this case, the electrolyte may be a molten salt, an alkaline solution, an acidic solution, etc., but here, the principle will be explained using a typical fuel cell using phosphoric acid as an electrolyte.

FIG. 2 shows the basic structure of this type of fuel cell. In the diagram, electrolytes! No. 11 is a material in which a fibrous sheet or mineral powder is impregnated with phosphoric acid as an electrolyte. 2 and 3 are a pair of porous (carbonaceous) anode and cathode electrodes arranged with this electrolyte layer 1 in between.
A platinum catalyst is coated on the surface of the electrode in contact with the electrolyte layer 1. Further, 4 is a chamber through which a gas containing hydrogen flows, and 5 is a chamber through which an oxidizer gas such as oxygen (usually air) flows.

In such a fuel cell, hydrogen that has flowed into the gas flow chamber 4 diffuses through the space in the anode electrode 2 and reaches the catalyst. Here, hydrogen gas is dissociated into hydrogen ions and electrons by the action of a catalyst. The reaction formula is H2−+ 280+ 28
−(1). Then, the hydrogen ions enter the electrolyte layer 1 and migrate toward the cathode electrode 3 due to the action of electromotive force and concentration diffusion. On the other hand, electrons separated by dissociation of hydrogen gas flow into the anode electrode 2, and the electrode 2 is negatively charged. In addition, in the cathode electrode 3, hydrogen ions that have migrated from the anode electrode 2 side, oxygen that has been supplied to the gas distribution room 5 as an oxidizer and further diffused in the space of the cathode electrode 3, and an external power load from the anode electrode 2 The following reaction occurs on the surface of the catalyst: the electrons that pass through the catalytic converter, perform work, and return to the cathode electrode 3 of the battery.

4H" +4e +02-+2H20- (2) Thus, the reaction in which hydrogen is oxidized to water and the chemical energy at this time becomes electrical energy, which is used as a battery to provide electrical energy in an external power load. The entire reaction is completed. In this case, part of the electrical energy is dissipated in the electrolyte layer 1 by the internal resistance of the cell. This internal resistance of the cell is determined by the activation polarization resistance of the electrode reaction, in particular the cathode electrode reaction, It is the sum of the diffusion resistance of reactants such as hydrogen and oxygen, the inherent resistance of the electrolyte/constituent materials, and the contact resistance of the electrolyte layer-electrode-current collector plate.Therefore, in order to shorten the migration distance of hydrogen ions and reduce the resistance. First, the electrolyte layer is designed to be extremely thin.

[Problems with Background Art] By the way, it is already known that the concentration of phosphoric acid, which is an electrolyte, changes depending on the operating temperature and humidity conditions in the load 2 reaction gas, and as a result, the capacity of phosphoric acid changes. That is, phosphoric acid, which is an electrolyte, is a reaction product of water and phosphorus pentoxide as shown in the following reaction formula, and is also a highly hygroscopic desiccant. Therefore, in the reaction formula below, under high temperature and dry conditions, the reaction shifts to the left, and phosphoric acid dries and its capacity decreases; conversely, under low temperature and high humidity conditions, the reaction shifts to the right, and phosphoric acid absorbs moisture, its concentration decreases and its capacity increases.

3H20+1/2P40f O4-2H3PO4” (3
Although the reaction is simplified here to make the explanation easier to understand, there are many complex phosphoric acid condensates such as birophosphoric acid and metaphosphoric acid as intermediate products of the above reaction formula.

However, the transition of these reactions has the same tendency as explained above. Furthermore, water is produced as an electrochemical reaction product by loading, and in principle it is generated from the cathode side. Therefore, the humidity in the reaction gas changes depending on the magnitude of the load.

Therefore, in order to operate the fuel cell safely and with stable performance, it is required to keep the capacity of phosphoric acid, which is the electrolyte in the thin electrolyte layer, constant. In other words, when the capacity of phosphoric acid decreases during operation, voids occur in the thin electrolyte layer, making it porous, reducing the catalyst-electrolyte-reactant gas interface, which is the reaction point, and increasing contact resistance, which causes the battery to deteriorate. Performance decreases. In addition, even if the differential pressure between the fuel gas and the oxidant gas is small, mixing of the above two reaction gases (referred to as a crossover phenomenon) occurs, resulting in a decrease in power generation efficiency due to ineffective consumption of the above two reaction gases. This may cause trouble such as damage to the fuel cell body or explosion due to abnormal heat generation. on the other hand,
When the capacity of phosphoric acid increases during operation, phosphoric acid overflows out of the catalyst layer on the electrode, a so-called flooding phenomenon, which causes the catalyst on the electrode to be submerged in the phosphoric acid, and the reaction gas is directly The diffusion phenomenon is inhibited, resulting in an extreme drop in battery performance, and furthermore, the amount carried out as phosphoric acid mist in the gas increases. In other words, the amount of phosphoric acid, which is an electrolyte, decreases, eventually inducing a crossover phenomenon.

Therefore, in order to suppress the above-mentioned change in electrolyte capacity, it has been conventionally practiced to add an appropriate amount of water vapor to both the fuel and oxidizer gases.

However, when performing a so-called recycling operation in which part of the fuel gas and oxidant gas discharged from the fuel cell is circulated and used again as raw material gas, the amount of water contained in this recycled gas is This will be added to the amount of water vapor added to both gas systems.

On the other hand, in this recycle operation, the recycle rate (ratio of recycled gas amount/raw material gas inflow amount) may be varied in order to adjust the voltage generated by the fuel cell. Therefore, the amount of moisture brought in by the recycled gas is not constant, and the amount of water vapor supplied to the electrolyte may be excessive or insufficient, causing the volume of the electrolyte to change as described above, which has the negative effect of reducing battery performance and life. become.

[Object of the invention] The present invention has been made in consideration of the above circumstances,
The purpose is to provide a fuel cell device that can maintain high cell performance for a long period of time and extend its life.

[Summary of the Invention] In order to achieve the above object, the present invention arranges a pair of porous electrodes, an anode electrode and a cathode electrode with an electrolyte layer in between, and injects a fuel gas such as hydrogen onto the back surface of the anode electrode. In a fuel cell in which oxidizing gas such as oxygen is supplied to the back of each electrode and the electrical energy generated by the electrochemical reaction is extracted from between the pair of electrodes, the exhaust gas from the fuel cell is circulated and reused. During the above-mentioned recycling operation, which is used as a raw material gas, the amount of water vapor contained in this recycled gas is measured with a measuring device, and the optimum amount of water vapor is calculated based on this measurement value and the raw material gas flow rate of each group. By controlling the amount of water vapor added to the gas and oxidizing gas, changes in the capacity of the electrolyte are suppressed, thereby preventing deterioration and damage to the battery due to the aforementioned crossover phenomenon and Flanders ink phenomenon. do.

[Embodiments of the invention] An embodiment of the present invention shown in the drawings will be described below.

FIG. 1 shows in block form an example of the configuration of a fuel cell device according to the present invention. In the figure, on the gas inlet side of the fuel cell main body 6 configured as described above, there is a fuel gas supply section 7 that supplies a fuel gas F such as hydrogen, and an oxidant gas supply section that also supplies an oxidant gas A such as air. 8 are connected to each other. Furthermore, a fuel gas discharge section 9 and an oxidizing gas discharge section 10 are connected to each gas outlet side, respectively. Further, the fuel gas F is connected to the fuel gas supply section 7.
Fuel gas system steam supply section 11F that adds steam SF to
1 and a fuel gas system steam control valve 12 provided therein.
F, an oxidizing gas-based steam supply section 11A that is connected to the oxidizing gas supply section 8 and adds steam SA to the oxidizing gas A, and an oxidizing gas-based steam regulating valve 12A provided therein, respectively. We are prepared.

On the other hand, a cycle gas supply section 13F connected to the fuel gas discharge section 9 and returning a part of the exhaust gas to the fuel gas supply section 7, and a blower 14F provided therein, The moisture layer measuring device 15F in the recycled fuel gas that measures the moisture content and the opening degree of the fuel gas system steam control valve 12F are adjusted in response to the measurement signal, thereby controlling the amount of steam SF added to the fuel gas F. A recycle gas supply section 13A that is also connected to the fuel gas system water vapor amount controller 16F1 and the oxidizing gas discharge section 1o and returns a part of the exhaust gas to the oxidizing gas supply section 8, and a blower 14A provided therein. Then, a recycled oxidizing gas water content meter 15A measures the amount of water contained in this recycled gas, and in response to the measurement signal, the opening degree of the oxidizing gas system steam control valve 12A is adjusted, and the oxidizing gas is An oxidizing gas-based water vapor amount controller 16A that controls the amount of water vapor Sa added to the agent gas A is provided.

Next, the operation of this fuel cell device will be explained using FIG. 1.

First, a fuel gas F and an oxidizing gas A are supplied to the fuel cell main body 6 in which a pair of porous electrodes, an anode electrode and a cathode electrode are arranged with an electrolyte layer in between, through each gas supply section 7.8, In a fuel cell device that generates electrical energy by causing an electrochemical reaction within the cell, it is necessary to keep the capacity of the electrolyte in the fuel cell main body 6 constant as described above, so conventionally, fuel gas F and oxidation The agent gas A is supplied with water vapor Sp through the water vapor supply parts 11F and 11A, respectively.
, SA has been added.

On the other hand, the fuel gas F and oxidant gas A supplied to the fuel cell main body 6 are released through each system gas discharge section 9.10.
At this time, a part of both of the exhaust gases is passed through the recycled gas supply sections 13F and 13A, pressurized by the respective processors 14F and 14A, and then returned to the respective gas supply sections 7.8 to be used as raw materials again. Cycle used as gas
During operation, the water m contained in both of these recycled gases becomes excessive, which adversely affects the battery as described above.

Therefore, the moisture content during both recycling was measured using the recycled fuel gas moisture measuring device 15F for the fuel gas system, and the recycled oxidizing gas moisture measuring device @15A for the oxidizing gas system.
Measure each. This measured value is first sent to the fuel gas water vapor amount controller 16F in the fuel gas system, and this controller 16F collects the water vapor necessary to keep the electrolyte capacity in the fuel cell main body 6 constant. It is calculated from the fuel gas flow rate supplied to the fuel cell main body 6 at that time, and the value is compared with the moisture content in the recycled gas, and the excess amount is calculated from the fuel gas system water vapor ma provided in the fuel gas system steam supply section 11F. By adjusting the opening degree of the moderation valve 12F, the amount SF of water vapor added to the fuel gas F can be adjusted to an optimal value. On the other hand, for the oxidizing gas system, the measured value from the oxidizing gas moisture measuring device 15A is sent to the oxidizing gas system water vapor pre-controller 16A, and this controller 16A sends the measured value of the oxidizing gas system moisture measuring device 15A to the oxidizing gas system water vapor pre-controller 16A. By adjusting the opening degree of the oxidizing gas system steam amount control valve 12A provided in the steam supply section 11A, the steam ISA added to the oxidizing gas A can be adjusted to an optimal value.

In addition, with this configuration, the amount of water vapor supplied to the electrolyte can be optimized even when operating in a region where the recycle rate (recycle gas flow rate/raw material gas) is low (in other words, the amount of water in the recycle gas is low). can be maintained.

As described above, by using the fuel cell device having the configuration of this embodiment, the amount of water vapor for keeping the capacity of the electrolyte in the fuel cell main body 6 constant can always be kept at an optimum value, and as a result, as described above, the amount of water vapor can be maintained at an optimum value. It is now possible to reliably prevent the deterioration of battery performance and lifespan due to crossover phenomena caused by insufficient or excessive amounts, and in turn, it is possible to maintain stable battery performance over a long period of time and extend its lifespan. .

[Effects of the Invention] As explained above, according to the present invention, during the above-mentioned recycling operation in which the exhaust gas from the fuel cell is circulated and used again as raw material gas, the amount of water vapor contained in this recycled gas is measured using a measuring device. The optimum amount of water vapor is calculated based on this measured value and the raw material gas flow rate of each prefecture, and the amount of water vapor added to the fuel gas and oxidizer gas is controlled, so high battery performance can be maintained for a long time. An extremely reliable fuel cell device that can be maintained for a long period of time and has a long service life can be provided.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIG. 2 is a conceptual diagram showing the principle structure of a fuel cell. DESCRIPTION OF SYMBOLS 1... Electrolyte layer, 2... Anode electrode, 3... Cathode electrode, 6... Fuel cell main body, 11F... Fuel gas system steam supply part, 11A... Oxidizing gas system steam supply Part, 12F...Fuel gas system steam control valve, 12A
... Oxidizing gas system water vapor control valve, 15F... Moisture measuring device in recycled fuel gas, 15F... Moisture measuring device in recycled oxidizing gas, 16F... Fuel gas system water vapor amount controller, 16A. ... Oxidizing gas system water vapor amount controller. Applicant's agent Patent attorney Takehiko Suzue Figure 1 Figure 2

Claims (1)

[Claims] A pair of porous electrodes, an anode electrode and a cathode electrode, are arranged with an electrolyte layer in between, and a fuel gas is supplied to the back surface of the anode electrode, and an oxidant gas is supplied to the back surface of the cathode electrode. In a fuel cell that extracts generated electrical energy from between the pair of porous electrodes, a recycling system is configured to circulate the exhaust gas from the fuel cell and use it again as raw material gas, and water vapor is added to the fuel gas and oxidizing gas. a measuring device for measuring the amount of water vapor contained in the recycled gas of the recycling system; and a measuring device for measuring the amount of water vapor contained in the recycled gas of the recycling system, and calculating an optimum amount of water vapor based on the measured value from the measuring device and the raw material gas flow rate of each system to 1. A fuel cell device comprising means for controlling the amount of water vapor added to gas and oxidizing gas.