JP2002298880A - Fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell system having satisfactory startability. SOLUTION: This fuel system comprises a fuel cell stack 1 for supplying an anode gas containing hydrogen and a cathode gas containing oxygen to respective electrodes to generate power, a humidifier 2 for humidifying at least one of the anode gas and cathode gas supplied to the fuel cell stack 1, and a pure water passage 13a for supplying pure water to the humidifier 2. The pure water in the pure water passage is heated by forming a high-temperature fluid passage, for carrying the fluid discharged from the fuel cell stack 1 in contact with the pure water passage, whereby the temperature of the pure water at starting can be raised quickly.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a fuel cell system.

[0002]

2. Description of the Related Art In a fuel cell, a fuel such as hydrogen is supplied to an anode, and an oxidant such as oxygen is supplied to a cathode. Solid polymer electrolyte fuel cells, which use a polymer ion exchange membrane as the electrolyte, convert electricity into electrical energy.They have features such as high output density, simple structure, and relatively low operating temperature. The technology is being developed as a promising structure of a fuel cell.

A unit cell battery, which is a basic configuration of a solid polymer electrolyte fuel cell, will be described with reference to FIG. 8. An anode 29 and a cathode 30 are sandwiched between a solid polymer membrane 28.
Is installed. A fuel gas supply groove 31 for supplying fuel to the anode 29 is formed between the anode 29 and the gas impermeable anode separator 33, and an oxidant gas supply groove 32 for similarly supplying an oxidant to the cathode 32 is It is formed between 30 and a gas impermeable cathode separator 34. A water impermeable water separator 35 is provided outside the anode separator 33, and a cooling water supply groove 36 is formed facing the water separator 35 and through which cooling water for adjusting the cell temperature passes. Thus, one unit cell 37 is configured.

Next, an electrochemical reaction occurring in the cell will be described. When hydrogen as a fuel and oxygen as an oxidant are supplied to each electrode, the following electrochemical reaction occurs to generate an electromotive force.

Anode reaction: H ₂ → 2H ⁺ + 2e ⁻ Cathode reaction: 2H ⁺ + (１ ／) O ₂ + 2e ⁻ → 2H ₂ O That is, at the anode 29, hydrogen is converted into hydrogen ions (hereinafter, referred to as protons) and electrons. To dissociate. Protons pass through the solid polymer membrane, and electrons move to the cathode 30 through an external circuit (not shown).

At the cathode 30, the supplied oxygen, protons, and electrons react to generate water, and at this time, the electrons passing through the external circuit become electric current and can supply electric power. The generated water and the hydrogen and oxygen not used in the reaction are discharged from each electrode as exhaust gas.

[0007] Since the electromotive force per unit cell is as low as 1 V or less, a normal fuel cell stacks several hundred cells and generates power as a fuel cell stack connected in series.

[0008] Perfluorocarbon sulfonic acid is known as a solid polymer membrane. In this membrane, when the amount of water contained in the membrane becomes small, protons become difficult to permeate, and the fuel and the oxidizing agent are mixed. , Power generation becomes impossible. For this reason, it is necessary that the solid polymer membrane be kept in a saturated water-containing state.

In addition, during the above-mentioned electrochemical reaction, when protons pass through the solid polymer membrane, water in the fuel also moves to the cathode side, so that the polymer membrane on the anode side tends to dry. Even when the amount of water in the supplied fuel and oxidant is small, the solid polymer membrane tends to dry. Therefore, the fuel and the oxidizing agent are supplied to the fuel in a humidified state so that the solid polymer film maintains a predetermined amount of water.

As a prior art using such a fuel cell, a fuel cell system disclosed in Japanese Patent Application Laid-Open No. H11-162490 is known, in which at least one of a fuel supply pipe and an oxidant supply pipe is provided with steam or atomized water. The fuel and the oxidizing agent are humidified in advance by supplying the water, and the humidifying agent is supplied to the fuel cell.

[0011]

However, in such a fuel cell system, in order to prevent the accumulation of impurities contained in water in the fuel cell stack or in the humidifier, the system is further charged by water charging. In general, pure water is used to humidify the fuel and oxidizer to prevent electric leakage to the fuel cell.However, when the operating environment temperature of the fuel cell stack falls below the freezing point, pure water freezes and the fuel There is a problem that the battery system does not start, or it takes time to start because of thawing.

It is an object of the present invention to provide a fuel cell system which solves the above problems.

[0013]

According to a first aspect of the present invention, a fuel cell stack for generating electricity by supplying an anode gas containing hydrogen and a cathode gas containing oxygen to respective poles, and supplying the fuel cell stack to the fuel cell stack A fuel cell system comprising: a humidifier that humidifies at least one of an anode gas and a cathode gas; and a pure water flow path that supplies pure water to the humidifier. The high-temperature fluid flow path through which the fluid discharged from the stack flows is formed in contact with the pure water flow path to heat the stack.

[0014] In a second aspect based on the first aspect, the flow direction of the pure water flowing through the pure water flow path and the flow direction of the fluid for heating the pure water are opposite to each other.

In a third aspect based on the first or second aspect, cooling water for adjusting the temperature of the fuel cell stack flows through the high-temperature fluid flow path.

In a fourth aspect based on the first or second aspect, the exhaust gas discharged from the fuel cell stack flows through the high-temperature fluid flow path.

In a fifth aspect based on the first or second aspect, the exhaust gas discharged from the fuel cell stack is burned,
A reformer for generating reformed gas from fuel is provided, and combustion exhaust gas discharged from the reformer flows through the high-temperature fluid flow path.

According to a sixth aspect of the present invention, in any one of the first to fifth aspects of the present invention, there is provided a discharge channel for branching off the high-temperature fluid channel and discharging a high-temperature fluid unnecessary for heating the pure water to the outside,
A temperature detecting means provided near the pure water inlet of the humidifier for detecting the temperature of the pure water, and a flow rate provided at a branch of the high temperature fluid flow path to control the flow rate of the high temperature fluid to the discharge flow path A control unit for controlling the flow rate control valve based on a detection result of the temperature detecting means and a requirement for a humidifier.

According to a seventh aspect of the present invention, in any one of the first to sixth aspects, the pure water flow path and the high-temperature fluid flow path have a double pipe structure, and pure water flows through the inner pipe and the inner pipe and the outer pipe. A flow path configuration in which a high-temperature fluid flows between the pipe and the pipe.

In an eighth aspect based on any one of the first to sixth aspects, a plurality of high-temperature fluid flow paths are provided so as to surround the outer periphery of the pure water flow path.

[0021]

According to the first aspect of the present invention, at least one of the anode gas and the cathode gas is humidified by forming a high-temperature fluid flow path through which the fluid discharged from the fuel cell stack for generating power flows in contact with the pure water flow path. Pure water is heated, so even if the outside air temperature is below the freezing point, it is possible to suppress the freezing of the pure water in the humidifier or to quickly thaw it, resulting in a stable supply of pure water to the humidifier. The reaction and start-up of the fuel cell stack can be improved without being affected by the outside air temperature.

In the second aspect, since the flow direction of the pure water flowing through the pure water flow path is opposite to the flow direction of the fluid for heating the pure water, the heat of the high-temperature fluid is efficiently transmitted to the pure water. be able to.

In the third aspect, the reaction heat of the fuel cell stack is used for heating pure water through the cooling water by flowing cooling water for adjusting the temperature of the fuel cell stack through the high-temperature fluid flow path. Thus, the efficiency of the fuel cell system can be improved.

In the fourth invention, the exhaust gas discharged from the fuel cell stack is caused to flow through the high-temperature fluid flow path,
By using the hottest exhaust gas in the fuel cell system, pure water can be quickly thawed at the time of startup or the like, and as a result, the startup time of the fuel cell system can be greatly reduced.

According to a fifth aspect of the present invention, there is provided a reformer which burns the exhaust gas discharged from the fuel cell stack and generates a reformed gas from the fuel, and transfers the combustion exhaust gas discharged from the reformer to the high-temperature fluid flow path. In this way, the unburned components in the exhaust gas can be burned, and the pure gas can be heated by the combustion gas, so that the efficiency of the fuel cell system can be improved.

In the sixth aspect of the present invention, a discharge channel for branching off from the high-temperature fluid flow path and discharging a high-temperature fluid unnecessary for heating the pure water to the outside, and a vicinity of the pure water inlet of the humidifier are provided. ,
Temperature detection means for detecting the temperature of pure water; a flow control valve installed at a branch of the high-temperature fluid flow path to control the flow rate of the high-temperature fluid to the discharge flow path; and a detection result of the temperature detection means and humidification. A control unit that controls the flow control valve based on the requirements for the humidifier, without being affected by the operating conditions and the outside air temperature of the fuel cell system, it is possible to maximize the performance of the humidifier, As a result, the efficiency of the fuel cell system can be improved.

In the seventh invention, a pure water flow path and a high-temperature fluid flow path have a double pipe structure, and a flow path structure in which pure water flows in the inner pipe and high-temperature fluid flows between the inner pipe and the outer pipe. By doing so, the heat of the high-temperature fluid can be efficiently transmitted to the pure water, and the efficiency of the fuel cell system can be improved.

According to the eighth aspect of the present invention, a plurality of high-temperature fluid flow paths are provided so as to surround the outer periphery of the pure water flow path, so that the flow path structure between the pure water flow path and the high-temperature fluid flow path can be easily manufactured. To help reduce the cost of the fuel cell system.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of a fuel cell system according to the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a diagram for explaining the configuration of the first embodiment of the present invention. This fuel cell system stores a fuel cell stack 1 that generates power from fuel and air, a humidifier 2 that humidifies the fuel and air supplied to the fuel cell stack 1, and stores water for cooling the fuel cell stack 1. Water tank 1
1 and a pure water tank 1 for storing pure water supplied to the humidifier 2
4 and a flow path communicating between the constituent elements.

The humidifier 2 is connected to an air supply passage 3 for supplying air and a fuel supply passage 4 for supplying fuel, and a pure water tank 14 for humidifying the fuel and air.
Is connected to a pure water flow path 12a. Pure water discharged from the humidifier 2 returns to the pure water tank 14 through the discharged pure water channel 12b, so that the pure water circulates.

The fuel and air humidified independently in the humidifier 2 are supplied to the anode and the cathode of the fuel cell stack 1 through the humidified air flow path 5 and the humidified fuel flow path 6. After power generation, the fuel and air supplied to the fuel cell stack 1 are exhausted as exhaust gas from the air exhaust passage 7 and the fuel gas exhaust passage 8 to the outside.

A cooling water passage 9a for supplying cooling water from a water tank 11 for cooling the fuel cell stack 1 heated in accordance with the above-mentioned reaction communicates with the fuel cell stack 1,
Exhaust cooling water passage (high-temperature fluid passage) through which cooling water after cooling passes
9b is a flow passage for cooling water flowing in a direction opposite to the flow direction of the pure water flow path 12a and the exhaust pure water flow path 12b.
a, it is formed so as to be in contact with the pure water flow passage 12 b and the pure water tank 14. The exhaust cooling water channel 9b is a pure water channel 12a,
The configuration is such that the heat of the exhaust cooling water is transferred to the pure water by contact with the exhaust pure water flow path 12b to increase the temperature of the pure water, and it is needless to say that the contact length is preferably longer. Therefore, in the present embodiment, the exhaust cooling water flow path 9b is connected to the pure water flow path 12a from as close as possible to the pure water inlet of the humidifier 2.
Is configured to be in contact with The cooling water is supplied to the exhaust cooling water passage 9b.
From the water tank 11 and circulates. Note that a circulation pump 10 is provided in the cooling water passage 9a.

Next, an example of the configuration of the exhaust cooling water channel 9b shown in FIG. 2, and the pure water channel 12a and the exhaust pure water channel 12b that are in contact therewith will be described. In this case, the inside of one pipe 16 is partitioned into two spaces by a heat transfer partition 15, and each of the two spaces is used as an exhaust cooling water passage 9b, a pure water passage 12a, and an exhaust pure water passage 12b.

With the above configuration, the flow directions of the cooling water and the pure water are opposite to each other as described above.
5, the heat of the cooling water is easily transmitted to the pure water, and the contact area between the cooling water and the pure water in the heat transfer partition 15 is large, so that the heat of the cooling water can be efficiently transmitted to the pure water. Can be. Therefore, even when the outside air temperature is below the freezing point, the freezing of the pure water in the humidifier 2, especially near the pure water inlet, can be suppressed or the thawing can be quickly performed. Therefore, the reaction and the startability of the fuel cell stack 1 can be improved without being affected by the outside air temperature.

Next, a second embodiment shown in FIG. 3 will be described. This uses exhaust air discharged from the fuel cell stack 1 instead of the cooling water of the first embodiment as a heat source for supplying heat to pure water.

The configuration of FIG. 3 will be described. Here, a configuration is shown in which pure water is heated by exhaust air discharged from the anode.
a, 12b. On the other hand, the cooling water passage 9 is configured to directly return the cooling water that has cooled the fuel cell stack 1 to the water tank 11. Note that the flow direction of the exhaust air and the flow direction of the pure water are opposite to each other, as in the first embodiment.

With such a configuration, the temperature can be quickly raised even when the temperature of the system is low, such as at the time of startup, and the exhaust air from the fuel cell stack 1, which has the highest temperature in the fuel cell system, can be obtained. Since the pure water is heated by this, the time required for defrosting the pure water at the time of starting from below the freezing point of the outside temperature can be shortened, and the starting time of the fuel cell system can be shortened.

In the third embodiment shown in FIG. 4, a reforming type fuel cell system which generates a reformed gas and generates electric power using the reformed gas is used as the fuel cell system, and the present invention is applied to this.

Comparing the configuration with the second embodiment shown in FIG. 3, this embodiment is characterized in that the reformer 18 is provided downstream of the fuel cell stack 1 and the combustion exhaust gas discharged from the reformer 18 is pure. The difference is that the water is heated. More specifically, the reformer 18 includes a catalytic reaction section 18a and a combustion burner section 18b, and the exhaust gas discharged from the fuel cell stack 1 is sent to the combustion burner 18b through the passages 7 and 8 and burns. The fuel supplied from the pre-reformation fuel supply passage 17 to the catalytic reaction section 18a by the combustion heat of the combustion exhaust gas causes a reforming reaction by the catalyst of the reforming reaction section 18a, and the fuel supply flow as a hydrogen-rich reformed gas. The fuel is introduced into the passage 4 and is used for power generation in the fuel cell 1 through the humidifier 2.

On the other hand, the combustion exhaust gas, which has heated the fuel before reforming in the catalytic reaction section 18a, is discharged to the outside from the combustion exhaust gas passage 19, and the combustion exhaust gas passage 19 is connected to the pure water passage 12a.
And the exhausted pure water flow path 12b, and the flow directions thereof are opposite to each other, and the pure water is heated by transferring the heat of the combustion exhaust gas to the pure water. .

Therefore, in the third embodiment, in addition to the effect of the second embodiment, the exhaust gas discharged from the fuel cell stack 1 is burned, and the reforming reaction is promoted by using the energy of the unburned components in the exhaust gas. In addition, since the pure water is heated, the efficiency of the reforming fuel cell system can be improved.

FIG. 5 shows a fourth embodiment. This embodiment is different from the second embodiment in the configuration of the fuel cell stack 1.
The downstream air discharge channel 7a is configured to branch into a heating channel 7b for heating the pure water by the exhaust air and a discharge channel 7c for discharging the exhaust air to the outside as it is,
At this branch position, a three-way valve (flow control valve) 22 is installed, and by adjusting the three-way valve 22, the respective flow rates of the exhaust air flowing through the heating flow path 7b and the discharge flow path 7c are controlled. It was done. Although the present embodiment has been described using exhaust air, cooling water or combustion exhaust gas may be used as shown in the first and third embodiments.

The pure water flow path 12 upstream of the pure water inlet of the humidifier 2
a is provided with a temperature sensor 21 for detecting the temperature of the pure water flowing through the pure water flow path 12a, and the detection result of the temperature sensor 21 is sent to the control unit 23, which is determined from the temperature and the power generation request value of the fuel cell stack. The control unit 23 estimates the opening of the three-way valve 2 based on the required humidification condition of the humidifier 22, and controls the opening of the three-way valve 22 so as to reach the estimated opening.

Therefore, the flow rate of the exhaust air for heating the pure water can be adjusted based on the temperature of the pure water flowing into the humidifier 2 and the target humidification of the humidifier 2. Can be controlled to an optimum temperature, the performance of the humidifier 2 can be maximized without being affected by the operating conditions of the fuel cell system and the outside air temperature, and as a result, the efficiency of the fuel cell system can be improved. Can be improved.

FIG. 6 shows the exhaust cooling water passage 9b shown in FIG.
Another example of the flow path configuration of the pure water flow path 12a and the drained pure water flow path 12b in contact therewith is shown. As described in the first to fourth embodiments, the fluid as the heat source for heating the pure water is not limited to the exhaust cooling water, and therefore, the fluid flowing through the exhaust cooling water passage 9b is not limited to the exhaust cooling water. Absent.

In the configuration shown in FIG. 6, the exhaust cooling water passage 9b, the pure water passage 12a and the exhaust pure water passage 12b are formed in a double pipe structure. Of pure water or waste water, and the outer pipe 2
5 is configured such that high-temperature exhaust cooling water as a fluid for heating the pure water flows.

Therefore, the pure water and the exhausted pure water can be heated from the entire circumference of the inner pipe 24, and the heat of the exhausted cooling water can be efficiently transmitted to the pure water and the exhausted pure water. Further, after the fuel cell system is stopped, the heat radiation of the pure water and the exhaust pure water is suppressed by the exhaust cooling water having a large heat capacity,
The temperature drop of pure water and exhaust water can be delayed, the temperature of pure water can be maintained at a higher temperature than the outside temperature for a long time, and the temperature of pure water at the time of restarting the fuel cell system can be restarted. Easy to do. As shown in FIG. 6, a heat insulating material 26 is provided around the outer tube 25 in order to suppress heat radiation of pure water and waste water.
Is also effective.

By adopting the double pipe structure as the flow path configuration, the flow path configuration can be simplified, the strength of the flow path is further improved, and the flow path can be used as a structural member. Therefore, there is a possibility that the configuration of the structural member is simplified and the number of parts is reduced.

FIG. 7 shows another example of the flow path configuration, which is configured so that the outer circumference of the inner pipe 24 through which pure water and exhausted pure water flows is surrounded by a plurality of pipes 27 through which exhaust cooling water flows. . Further, as shown in FIG. 7, a heat insulating material 26 may be provided on the outer periphery of the plurality of pipes 27.

Therefore, it is possible to manufacture by joining a plurality of pipes 27 around one inner pipe 24, and it is possible to simplify the method of manufacturing the flow path as compared with the double pipe structure, Cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a fuel cell system illustrating a first embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating a flow path configuration of a waste cooling water flow path and a pure water flow path.

FIG. 3 is a schematic diagram of a fuel cell system illustrating a second embodiment.

FIG. 4 is a schematic diagram of a fuel cell system illustrating a third embodiment.

FIG. 5 is a schematic diagram illustrating a fuel cell system according to a fourth embodiment.

FIG. 6 is a cross-sectional view illustrating another example of the flow path configuration of the exhaust cooling water flow path and the pure water flow path.

FIG. 7 is a cross-sectional view illustrating another example of the flow path configuration of the exhaust cooling water flow path and the pure water flow path.

FIG. 8 is a schematic diagram illustrating an internal configuration of a fuel cell stack.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 fuel cell stack 2 humidifier 3 air supply flow path 4 fuel supply flow path 5 humidified air flow path 6 humidified fuel flow path 7 air discharge flow path 8 fuel gas discharge flow path 9 a cooling water flow path 9 b drain cooling water flow path 11 water tank 12a Pure water flow path 12b Drained pure water flow path 14 Pure water tank

Claims (8)

[Claims] 1. A fuel cell stack for generating electricity by supplying an anode gas containing hydrogen and a cathode gas containing oxygen to respective poles, and humidifying at least one of the anode gas and the cathode gas supplied to the fuel cell stack. A humidifier, and a pure water flow path for supplying pure water to the humidifier, wherein the high-temperature fluid through which the fluid discharged from the fuel cell stack flows through the pure water flowing through the pure water flow path A fuel cell system characterized in that the flow path is heated by forming the flow path in contact with the pure water flow path. 2. The fuel cell system according to claim 1, wherein the flow direction of the pure water flowing through the pure water flow path and the flow direction of the fluid for heating the pure water are opposite to each other. 3. The fuel cell system according to claim 1, wherein cooling water for adjusting the temperature of the fuel cell stack flows through the high-temperature fluid flow path. 4. The system according to claim 1, wherein the exhaust gas discharged from the fuel cell stack flows through the high-temperature fluid flow path.
Or the fuel cell system according to 2. 5. A reformer that burns exhaust gas discharged from the fuel cell stack and generates reformed gas from fuel is provided, and the combustion exhaust gas discharged from the reformer flows through the high-temperature fluid flow path. The fuel cell system according to claim 1 or 2, wherein: 6. A discharge passage branched from the high-temperature fluid flow passage and discharging a high-temperature fluid unnecessary for heating the pure water to the outside, and provided near a pure water inlet of the humidifier. Temperature detection means for detecting a temperature, a flow control valve installed at a branch of the high-temperature fluid flow path to control the flow rate of the high-temperature fluid to the discharge flow path, and a detection result of the temperature detection means and a humidifier. The fuel cell system according to claim 1, further comprising a control unit that controls the flow control valve based on a required condition. 7. A structure wherein the pure water flow path and the high temperature fluid flow path have a double pipe structure, in which pure water flows in an inner pipe and high temperature fluid flows between an inner pipe and an outer pipe. The fuel cell system according to any one of claims 1 to 6, wherein 8. The fuel cell system according to claim 1, wherein a plurality of high-temperature fluid channels are provided so as to surround an outer periphery of the pure water channel.