JP2004119299A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system with an excellent start-up property capable of stably supplying heat at a start-up and treating exhaust gas. <P>SOLUTION: The fuel cell system is provided with a fuel cell element equipped with an anode and a cathode at either side of an electrolyte, an air flow channel supplying air to the cathode side of the fuel cell element, a fuel flow channel supplying fuel to the anode side of the fuel cell element, and a temperature-raising gas flow channel supplying gas for raising temperature of the fuel cell element. By setting an electric air heater in the air flow channel and a partial oxidation catalyst in a flow channel communicating with the fuel flow channel, unburned gas contained in the exhaust gas at raising of temperature can be decreased. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a fuel cell system for electrochemically reacting fuel and air.
[0002]
[Prior art]
A fuel cell is a power generation element that has an anode and a cathode on both sides of an electrolyte, and supplies fuel to the anode and an oxidant to the cathode to electrochemically react the fuel and the oxidant to convert it to electric energy. . Further, by forming a fuel cell module in which a plurality of elements are electrically connected, the scale of the power generation output can be increased.
The types of fuel cells can be classified according to the type of electrolyte (see, for example, Non-Patent Document 1). Particularly, the solid oxide fuel cell has a high operating temperature exceeding 700 ° C. In some cases, it is necessary to supply a large amount of heat and raise the temperature to a temperature at which power generation can be started. Further, when the temperature of the solid oxide fuel cell is raised, it is necessary to keep the air side in an oxidizing atmosphere and the fuel side in a reducing atmosphere in order to avoid deterioration of the electrode material.
[0003]
In the prior art, this heat is supplied by a combustor provided on the air side and the fuel side, and the combustor on the air side maintains an oxidizing atmosphere having an air ratio of 1 or more, and the combustion on the fuel side. The vessel raises the temperature by maintaining a reducing atmosphere having an air ratio of 1 or less (for example, see Patent Document 1).
[0004]
A conventional technique will be described with reference to FIG.
The fuel cell element 1 shows a longitudinal section of a cylindrical fuel cell element. A cathode electrode is provided inside the element and an anode electrode is provided outside the element with an electrolyte interposed therebetween. An oxidant such as air is provided on the cathode electrode. When a fuel such as hydrogen or carbon monoxide flows through the anode electrode, a power generation reaction occurs.
When the temperature of the fuel cell element 1 is raised to a temperature at which power can be generated, air is supplied to the cathode side, which is inside the fuel cell element 1, through the air flow path 2, the air distributor 3, and the air introduction pipe 4. The air that has flowed out from the tip of the air introduction pipe 4 turns upward because the lower part of the fuel cell element is sealed, passes through the vicinity of the cathode of the fuel cell element 1, and contributes to the power generation reaction. It is exhausted as exhaust air from the upper opening. On the other hand, the fuel gas is supplied to the anode side outside the fuel cell element 1 through the fuel flow path 5, the fuel chamber 6, and the fuel distribution plate 7, and contributes to the power generation reaction in the power generation chamber 8; Is discharged as exhaust fuel. When the operating temperature of the fuel cell element 1 is high, the temperature of the exhaust air and the exhaust fuel is high, and the temperature of the mixed gas is higher than the temperature at which self-combustion occurs, the unburned fuel and the exhaust air in the exhaust fuel are burned in the combustion chamber 12. And is discharged as exhaust gas.
On the other hand, in the prior art shown in FIG. 7, the first combustor 51 has an air ratio of 1 or more as a means for raising the temperature of the fuel cell element to an operating temperature (for example, 700 ° C. or more in a solid oxide fuel cell). The combustion is performed to supply heat to the cathode side and maintain an oxidizing atmosphere on the cathode side. The second combustor 52 burns at an air ratio of 1 or less to supply heat to the anode side and maintain a reducing atmosphere on the anode side.
[0005]
[Non-patent document 1]
Hiroaki Tagawa, "Solid Oxide Fuel Cell and Global Environment", published by Agune Shofusha, June 20, 1998 (pp. 48-49)
[Patent Document 1]
JP 2001-155754 A (page 6, FIG. 1)
[0006]
[Problems to be solved by the invention]
However, in the conventional technique described in Patent Document 1, since the heat source for raising the temperature is a combustor, the flame of the combustor extinguishes during the temperature rising process at the time of starting the system, and the temperature rise does not occur. There has been a problem that the temperature may become complete and the temperature may not reach the power generation possible temperature.
Further, in the prior art described in Patent Document 1, since there is no device for treating exhaust gas, there is a problem that unburned gas contained in the gas generated by the fuel device on the fuel side is directly discharged out of the system. Was. In particular, when hydrocarbons or the like are used as fuel to be supplied to the combustor, there is a problem that not only hydrogen but also carbon monoxide is emitted.
[0007]
The present invention has been made in view of the above-described problems of the related art, and has an object to provide a fuel cell system with excellent start-up performance, in which heat supply is performed stably at the time of start-up and exhaust gas can be processed. And
[0008]
[Means for Solving the Problems]
In order to solve the problems of the conventional system as described above,
In the first invention, a fuel cell element having an anode and a cathode on both sides of an electrolyte;
An air flow path for supplying air to the cathode side of the fuel cell element,
A fuel flow path for supplying fuel to the anode side of the fuel cell element,
A fuel cell system having a fuel gas flow path and a temperature-raising gas flow path for supplying a gas for raising the temperature of a fuel cell element,
Installing an electric air heater in the air flow path,
Provided is a fuel cell system in which a partial oxidation catalyst is provided in a flow path communicating with the fuel flow path.
According to the present invention, by raising the temperature of the fuel cell element using the electric air heater, the oxidizing atmosphere on the cathode side can be maintained, and the amount of heat supplied can be easily adjusted. It is possible to do. Further, by providing the partial oxidation catalyst, the reducing atmosphere on the anode side can be maintained, the temperature distribution of the fuel cell element can be reduced, and damage to the element due to thermal stress can be prevented.
The partial oxidation catalyst referred to here is for causing an oxidation reaction with an air amount smaller than the theoretical air amount for completely burning the fuel. When the fuel and air come into contact with the activated catalyst, heat is generated by combustion. Further, since the fuel is oxidized with an air amount smaller than the theoretical air amount, a part of the fuel is discharged without being oxidized.
The catalyst varies depending on the type of fuel. For example, in the case of a hydrocarbon fuel, a nickel catalyst or the like can be used.
Since the gas to be heated on the anode side is a flammable gas, it is difficult to directly contact and heat with an electric heater. growing. On the other hand, the partial oxidation catalyst has an exothermic partial oxidation reaction, can supply a high-temperature gas and generate a reducing gas at the same time, and can be a compact system.
[0009]
According to a second aspect of the present invention, there is provided a fuel cell system in which the temperature of the partial oxidation catalyst is raised using the air heated by the electric air heater.
According to the present invention, at the start of the temperature increase, the partial oxidation catalyst becomes active, and heat can be supplied to a temperature at which the partial oxidation reaction proceeds using the air heated by the electric air heater.
[0010]
In a third aspect, the present invention provides a fuel cell system in which the temperature of the partial oxidation catalyst is raised by an electric heater.
According to the present invention, by supplying heat to the partial oxidation catalyst using the heater at the start of the temperature rise, the partial oxidation catalyst becomes active, and the partial oxidation reaction can proceed.
[0011]
According to a fourth aspect of the present invention, there is provided a fuel cell system for recirculating exhaust gas including exhaust air and exhaust fuel discharged from a fuel cell element to an air passage.
ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to recirculate the heat which the exhaust gas discharged from a fuel cell element has during a temperature rise, to reduce the amount of heat required for the temperature rise, or to increase the temperature rise rate. .
[0012]
According to a fifth aspect of the present invention, there is provided a fuel cell system for recirculating exhaust fuel discharged from a fuel cell element to the fuel passage.
According to the present invention, it is possible to recirculate the heat of the exhaust fuel discharged from the fuel cell element during the temperature increase, to reduce the amount of heat required for the temperature increase, or to increase the temperature increase rate. Become. Also, by recirculating the exhaust fuel, it is possible to reduce the amount of unburned fuel released outside the system.
[0013]
According to a sixth aspect of the present invention, there is provided a fuel cell system in which a combustion catalyst for burning exhaust gas including exhaust air and exhaust fuel discharged from a fuel cell element is provided in an exhaust gas passage.
Here, the exhaust gas flow path indicates the entire flow path in which the exhaust air and the exhaust fuel discharged from the fuel cell element are mixed, and includes not only a pipe through which the mixed exhaust gas flows but also a space. In.
According to the present invention, it is possible to perform processing so that the exhaust fuel discharged from the fuel cell element during the temperature rise is not released to the outside of the system.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is an example of a fuel cell system according to the first invention of the present invention.
The fuel cell element 1 shows a longitudinal section of a cylindrical fuel cell element. A cathode electrode is provided inside the element and an anode electrode is provided outside the element with an electrolyte interposed therebetween. An oxidant such as air is provided on the cathode electrode. When a fuel such as hydrogen or carbon monoxide flows through the anode electrode, a power generation reaction occurs.
[0015]
When the temperature of the fuel cell element 1 is raised to a temperature at which power can be generated, air is supplied to the cathode side, which is inside the fuel cell element 1, through the air flow path 2, the air distributor 3, and the air introduction pipe 4. The air that has flowed out from the tip of the air introduction pipe 4 turns upward because the lower part of the fuel cell element is sealed, passes through the vicinity of the cathode of the fuel cell element 1, and contributes to the power generation reaction. It is exhausted as exhaust air from the upper opening. On the other hand, the fuel gas is supplied to the anode side outside the fuel cell element 1 through the fuel flow path 5, the fuel chamber 6, and the fuel distribution plate 7, and contributes to the power generation reaction in the power generation chamber 8; Is discharged as exhaust fuel. The fuel supplied for power generation includes, for example, city gas. In this case, a reformer that generates hydrogen and carbon monoxide from the city gas is installed in the fuel flow path 5. Sometimes.
When the operating temperature of the fuel cell element 1 is high, the temperature of the exhaust air and the exhaust fuel is high, and the temperature of the mixed gas is higher than the temperature at which self-combustion occurs, the unburned fuel and the exhaust air in the exhaust fuel are burned in the combustion chamber 12. And is discharged as exhaust gas.
[0016]
On the other hand, an electric air heater 61 is installed in the air flow path 2 as a means for raising the temperature of the fuel cell element to an operating temperature (for example, 700 ° C. or higher in a solid oxide fuel cell), and heat to the cathode side is provided. And an oxidizing atmosphere on the cathode side is maintained. Further, fuel and air are sent to the partial oxidation catalyst 62 to cause a partial oxidation reaction, and the resulting high-temperature reducing gas is supplied to the anode side through the fuel flow path 5 to maintain heat and maintain a reducing atmosphere on the anode side. ing. When a city gas containing hydrocarbons as a main component is supplied as a fuel gas to the partial oxidation catalyst 62, the generated gas is a gas containing hydrogen, carbon monoxide, nitrogen, water vapor, and carbon dioxide. The exothermic reaction produces a high-temperature gas of several hundred degrees Celsius. In order to maintain the fuel side in the reducing atmosphere, it is possible to control the fuel by changing the ratio of fuel and air supplied to the partial oxidation catalyst 62. When a hydrocarbon is used as a fuel, a catalyst containing nickel as a main component can be used.
[0017]
Since the gas to be heated on the anode side is a flammable gas, it is difficult to directly contact and heat with an electric heater, and when heating indirectly with an electric heater, The device becomes larger. On the other hand, the partial oxidation catalyst has an exothermic partial oxidation reaction, can supply a high-temperature gas and generate a reducing gas at the same time, and can be a compact system.
According to the present invention, since the temperature is raised using the electric air heater 61 and the partial oxidation catalyst 62, the temperature can be raised more stably than when a combustor such as a burner is used, and the controllability is also improved. A good fuel cell system can be provided.
[0018]
FIG. 2 is an example of a fuel cell system according to the second invention of the present invention.
The partial oxidation catalyst 62 needs to be heated to a temperature at which a partial oxidation reaction occurs. Therefore, by raising the temperature of the air heated by the electric air heater 61 as a heat source of the partial oxidation catalyst 62, the partial oxidation reaction can proceed. In addition, since the partial oxidation reaction is an exothermic reaction, when the reaction starts to proceed, external heat supply is not required. As an example of a method of supplying heat to the partial oxidation catalyst 62, the partial oxidation catalyst 62 is provided in a container having good heat conductivity, and the structure in which the heated air gives heat to the container of the catalyst is adopted. Is achieved. In this case, in order to effectively use the heat remaining in the air after supplying the heat to the partial oxidation catalyst 62, the heat may be recirculated to the air flow path 2.
The start-up of the partial oxidation catalyst 62 can be enhanced by using the air heated by the electric air heater 61 as the air to be supplied to the partial oxidation catalyst 62.
[0019]
FIG. 3 is an example of a fuel cell system according to the third invention of the present invention.
In order to raise the temperature of the partial oxidation catalyst 62, an electric catalyst activation heater 63 is provided, and it is possible to improve the controllability of raising the temperature of the partial oxidation catalyst 62 by using the electric heater.
[0020]
FIG. 4 is an example of a fuel cell system according to a fourth invention of the present invention.
In the fuel cell system of FIG. 4, the exhaust gas discharged from the module container 11 is returned to the air flow path 2. According to this system, in the heating process, the heat of the exhaust gas can be recirculated, and the energy required for heating can be reduced. In addition, when comparing the system having no configuration for recirculating exhaust gas with the condition that the amount of heat supplied to the module container 11 by the electric air heater 61 and the partial oxidation catalyst 62 is constant, it is possible to improve the rate of temperature rise. It is possible, and the start-up of the fuel cell system can be accelerated.
[0021]
FIG. 5 is an example of a fuel cell system according to a fifth aspect of the present invention.
In the fuel cell system of FIG. 5, a partition 64 and a power generation chamber partition 9 are provided between the power generation chamber 8 and the combustion chamber 12, and exhaust fuel is recirculated to the fuel flow path 5 from between the two partition walls. I have. According to this system, in the heating process, the heat of the exhaust fuel is recirculated, and the energy required for heating can be reduced. In the heating process, when the mixed gas of the exhaust fuel and the exhaust air present in the combustion chamber 12 has not reached the self-combustion temperature, the unburned fuel contained in the exhaust fuel is discharged out of the system of the system. Will be. When city gas is used as an example of the fuel gas in FIG. 5, the gas generated by the partial oxidation catalyst 62 contains hydrogen and carbon monoxide, and these gases are discharged. According to the present invention, since the exhaust fuel is recirculated, it is also possible to reduce hydrogen and carbon monoxide released outside the system of the system.
[0022]
FIG. 6 is an example of a fuel cell system according to a sixth aspect of the present invention.
The fuel cell system of FIG. 6 has a configuration in which a combustion catalyst 65 is provided in an exhaust gas passage. In the heating process, unburned fuel in exhaust gas discharged from the fuel cell module can be processed.
Here, the exhaust gas flow path indicates the entire flow path in which the exhaust air and the exhaust fuel discharged from the fuel cell element are mixed, and includes not only a pipe through which the mixed exhaust gas flows but also a space. In. That is, the example of FIG. 6 shows an example in which the combustion catalyst is installed in the middle of a flow path such as a pipe. However, it is the combustion chamber 12 where the exhaust fuel and the exhaust air are actually mixed. A combustion catalyst may be installed in the combustion chamber. By providing the combustion catalyst in the exhaust gas flow path including the combustion chamber, it is possible to suppress the discharge of unburned fuel from the fuel cell system during temperature rise. It becomes.
[0023]
【The invention's effect】
As described above, according to the fuel cell system of the present invention, it is possible to improve the controllability of the temperature rise during the temperature rise process at the time of starting the fuel cell system, and to improve the system of the unburned fuel. It is possible to reduce discharge to the outside of the system.
[Brief description of the drawings]
FIG. 1 is an example of a fuel cell system according to a first invention of the present invention. FIG. 2 is an example of a fuel cell system according to a second invention of the present invention. FIG. 3 is a fuel according to a third invention of the present invention. FIG. 4 shows an example of a fuel cell system according to a fourth invention of the present invention. FIG. 5 shows an example of a fuel cell system according to a fifth invention of the present invention. FIG. 7 shows an example of a fuel cell system according to the present invention.
1: fuel cell element 2: air flow path 3: air distributor 4: air introduction pipe 5: fuel flow path 6: fuel chamber 7: fuel distribution plate 8: power generation chamber 9: power generation chamber partition 10: heat insulating material 11: module Vessel 12: combustion chamber 51: first combustor 52: second combustor 61: electric air heater 62: partial oxidation catalyst 63: electric catalyst activation heater 64: partition 65: combustion catalyst

Claims (6)

A fuel cell element having an anode and a cathode on both sides of the electrolyte,
An air flow path for supplying air to the cathode side of the fuel cell element,
A fuel flow path for supplying fuel to the anode side of the fuel cell element,
A fuel cell system having a fuel gas flow path and a temperature-raising gas flow path for supplying a gas for raising the temperature of a fuel cell element,
Installing an electric air heater in the air flow path,
A fuel cell system, wherein a partial oxidation catalyst is provided in a flow path communicating with the fuel flow path. 2. The fuel cell system according to claim 1, wherein the temperature of the partial oxidation catalyst is raised using air heated by the electric air heater. 3. 2. The fuel cell system according to claim 1, wherein the temperature of the partial oxidation catalyst is increased by an electric heater. 4. The fuel cell system according to claim 1, wherein exhaust gas including exhaust air and exhaust fuel discharged from the fuel cell element is recirculated to the air flow path. The fuel cell system according to any one of claims 1 to 3, wherein exhaust fuel discharged from the fuel cell element is recirculated to the fuel flow path. The combustion catalyst for burning exhaust gas composed of exhaust air and exhaust fuel discharged from the fuel cell element is provided in an exhaust gas flow path, according to any one of claims 1 to 5, characterized in that: Fuel cell system.

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