JP2005203194A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system in which deterioration of a reformer is suppressed and emission of combustion is improved by controlling optimally the combustion amount for reforming reaction. <P>SOLUTION: The fuel cell system comprises the reformer 12 which is supplied with hydrocarbon system fuel and generates a reformed gas containing hydrogen by reforming reaction, a fuel cell 14 which is supplied with the reformed gas at an anode and also supplied with an oxidation gas containing oxygen at a cathode and generates electric power, an anode off-gas passage 16 in which the anode off-gas exhausted from the anode is supplied as a combustion fuel for generating reforming reaction, and a three-way valve 18 which controls the supply of the anode off-gas. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a fuel cell system, and is particularly suitable for application to a fuel cell system including a reforming unit that generates hydrogen from a hydrocarbon-based fuel using a reforming reaction.

  When using a fuel cell as a power generator, it is necessary to supply hydrogen to the anode of the fuel cell. In order to generate hydrogen to be supplied to the anode, a method is known in which hydrogen is extracted from a hydrocarbon-based fuel such as gasoline, methanol or natural gas by a reforming reaction.

As the reforming reaction, there are various reactions such as a steam reforming reaction and a partial oxidation reaction. As an example, the reforming reaction of isooctane (C ₈ H ₁₈ ), which is a gasoline component, is shown below.

C ₈ H ₁₈ + 8H ₂ O → 8CO + 17H ₂ (1)
C ₈ H ₁₈ + 4O ₂ → 8CO + 9H ₂ (2)

  The reaction represented by the above formula (1) is a steam reforming reaction, and the reaction represented by the above formula (2) is a partial oxidation reaction. The steam reforming reaction is an endothermic reaction, and the partial oxidation reaction is an exothermic reaction. Usually, these reforming reactions are performed in a reactor called a reformer. Any one of these reforming reactions can be employed, but both can occur simultaneously in one reformer. As represented by the formulas (1) and (2), the steam reforming reaction is promoted by supplying water, and the partial oxidation reaction is promoted by supplying oxygen.

  Since the steam reforming reaction is an endothermic reaction, it is necessary to supply heat from the outside in order to cause the reaction. For this reason, a method is known in which fuel (isooctane) and air are supplied to a combustion burner of a reformer, and heat of the combustion burner is applied to generate a steam reforming reaction.

  In a system using such a reforming reaction, Japanese Patent Application Laid-Open No. 2003-217603 discloses a technique for supplying an anode off-gas of a fuel cell to a combustion burner of a reformer when power demand is high. .

JP 2003-217603 A JP 2002-289245 A JP-A-7-220744

  However, when the anode off gas is supplied to the combustion burner of the reformer, there is a problem that combustion in the combustion burner becomes excessive and the reformer is excessively heated.

  A catalyst for promoting the reforming reaction is provided inside the reformer. If the reformer is heated excessively, the catalyst deteriorates due to sintering or the like, and the desired reforming performance cannot be obtained. If the reformed gas supplied to the anode cannot be sufficiently obtained due to the deterioration of the reforming performance, it becomes difficult for the fuel cell to exhibit the desired performance. Furthermore, it is difficult to obtain a desired reforming performance even when the reformer is melted by excessive combustion.

  In particular, the anode off gas is in a high temperature state, and contains hydrogen in the reformed gas that has not reacted at the anode, and therefore, when a large amount of anode off gas is supplied to the combustion burner, excessive combustion is more likely to occur. Become.

  The present invention has been made to solve the above-described problems, and an object thereof is to optimally control the combustion for the reforming reaction and suppress the deterioration of the reforming performance.

  In order to achieve the above object, a first invention is characterized by receiving a hydrocarbon-based fuel and generating a reformed gas containing hydrogen by a reforming reaction, and supplying the reformed gas to an anode. A fuel cell that generates power by receiving supply of an oxidizing gas containing oxygen to the cathode, and an anode that supplies anode off-gas discharged from the anode as combustion fuel for causing the reforming reaction An off gas supply means and an anode off gas control means for controlling the supply of the anode off gas are provided.

  According to a second aspect, in the first aspect, the anode off-gas control means includes a control valve that is provided in a path of the anode off-gas and controls a flow rate of the anode off-gas.

  In a third aspect based on the first aspect, the anode off-gas control means supplies a hydrogen separation membrane for separating hydrogen contained in the anode off-gas, and supplies the anode off-gas to one side of the hydrogen separation membrane. Means, means for supplying a purge gas to the other side of the hydrogen separation membrane, and means for controlling the flow rate of the purge gas.

  In a fourth aspect based on the third aspect, the purge gas is an exhaust gas generated by combustion of the combustion fuel, a cathode off-gas discharged from the cathode, or a cooling off-gas discharged after cooling the fuel cell. It is characterized by that.

  In order to achieve the above object, a fifth aspect of the invention provides a reforming unit that receives supply of hydrocarbon fuel and generates reformed gas containing hydrogen by a reforming reaction, and supplies the reformed gas to the anode. A fuel cell that generates power by receiving supply of an oxidizing gas containing oxygen to the cathode, and an anode that supplies anode off-gas discharged from the anode as combustion fuel for causing the reforming reaction Supply off gas supply means, cooling gas supply means for supplying cooling gas to the fuel cell, and cooling off gas discharged after cooling the fuel cell as combustion air for causing the reforming reaction And a cooling off-gas supply means.

  According to a sixth aspect, in the fifth aspect, the apparatus further comprises a cooling off gas supply amount control means for controlling the supply amount of the cooling off gas.

  A seventh invention is characterized in that, in the fifth or sixth invention, anode offgas control means for controlling supply of the anode offgas is further provided.

  According to the first invention, since the supply of the anode off gas can be controlled, it is possible to optimally control the amount of combustion for causing the reforming reaction. As a result, the optimum reforming reaction is always performed. Can be done. Further, by controlling the supply amount of the anode off gas, it is possible to suppress the reforming section from being heated excessively, and it is possible to suppress the deterioration of the reforming performance. Therefore, it is possible to improve the reliability of the fuel cell system.

  According to the second aspect of the invention, the supply amount of the anode off gas can be reliably controlled by providing the control valve for controlling the flow rate of the anode off gas in the anode off gas path.

  According to the third aspect of the invention, the anode off gas is supplied to one side of the hydrogen separation membrane and the flow rate of the purge gas supplied to the other side of the hydrogen separation membrane is controlled, so that the hydrogen contained in the anode off gas is reduced. The amount separated by the hydrogen separation membrane can be varied. Therefore, the amount of hydrogen in the anode off gas can be controlled, and the amount of combustion for causing the reforming reaction can be optimally controlled. Further, by controlling the amount of hydrogen in the anode off-gas, it is possible to prevent the reforming section from being heated excessively, and it is possible to suppress degradation of reforming performance. Therefore, it is possible to improve the reliability of the fuel cell system.

  According to the fourth aspect of the present invention, the exhaust gas from combustion of the combustion fuel, the cathode off-gas of the fuel cell, or the cooling off-gas of the fuel cell is used as the purge gas. The amount can be controlled.

  According to the fifth aspect, since the cooling off gas can be used as combustion air, facilities such as a pump and piping for sending the combustion air become unnecessary. Accordingly, it is possible to minimize the loss of auxiliary equipment in the system, and it is possible to increase the efficiency of the entire fuel cell system.

  According to the sixth aspect of the invention, since the supply amount of the cooling off gas can be controlled, the air-fuel ratio can be optimally maintained during the combustion for the reforming reaction, and the combustion state can be optimally controlled. It becomes possible. Therefore, it is possible to always perform an optimal reforming reaction, and it is possible to improve the emission of combustion exhaust gas.

  According to the seventh aspect of the invention, the supply of the anode off gas can be controlled, so that the amount of combustion for causing the reforming reaction can be optimally controlled, and as a result, the optimum reforming reaction is always performed. It becomes possible. Thereby, it can suppress that a reforming part is heated too much, and it becomes possible to suppress degradation of reforming performance.

  Several embodiments of the present invention will be described below with reference to the drawings. In addition, the same code | symbol is attached | subjected to the element which is common in each figure, and the overlapping description is abbreviate | omitted. The present invention is not limited to the following embodiments.

Embodiment 1 FIG.
FIG. 1 is a schematic diagram showing a configuration of a fuel cell system 10 according to a first embodiment of the present invention. The fuel cell system 10 mainly includes an externally heatable reformer 12 that generates hydrogen-rich fuel gas (reformed gas) using hydrocarbon fuel, water, and air as raw materials, and a reformed gas. And a fuel cell 14 that generates electric power using air as an oxidizing gas.

  The fuel cell 14 may be of any type that generates water (water vapor) when generating power, and specifically includes a solid polymer type (PEM), a solid electrolyte type (SOFC), and a phosphoric acid type (PAFC). ), A hydrogen separation membrane type fuel cell. For example, taking a solid polymer type as an example, the fuel cell 14 is configured by laminating a plurality of cells including an electrolyte membrane, an anode, a cathode, and a separator. A fuel gas (reformed gas) and oxidizing gas flow path is formed between the anode and the cathode. The electrolyte membrane is a proton-conductive ion exchange membrane formed of a solid polymer material such as a fluorine-based resin. Both the anode and the cathode are made of carbon cloth woven from carbon fibers. The separator is formed of a gas-impermeable conductive member such as dense carbon which is compressed by gas and impermeable to gas.

In view of its function, the reformer 12 performs a reforming side that causes a reforming reaction represented by the above formulas (1) and (2) and a steam reforming reaction represented by the formula (1). It can be divided into a combustion side that supplies heat for the purpose. Gasoline containing isooctane (C ₈ H ₁₈ ) as a component is supplied to the reforming side. Further, steam and air (oxygen) are supplied to the reforming side. And the reforming reaction represented by the above formulas (1) and (2) is performed from these gasoline, water vapor, and air supplied to the reforming side. As the fuel sent to the reforming side, various hydrocarbon fuels such as other hydrocarbon fuels such as natural gas and oxygen-containing fuels such as alcohol can be used. In addition, ether, aldehyde, etc. can also be used as fuel.

  In order to promote the reforming reaction, a reforming catalyst is provided on the reforming side. When gasoline or natural gas is used as a raw material, for example, a nickel catalyst or rhodium noble metal can be used as a reforming catalyst. When methanol is used as a raw material, a CuO—ZnO catalyst, a Cu—ZnO catalyst, etc. Is known to be effective.

The hydrogen-rich reformed gas generated by the reforming reaction is supplied to the anode of the fuel cell 14 through the reformed gas channel 15. On the other hand, air (cathode gas) as an oxidizing gas is supplied to the cathode of the fuel cell 14. When the reformed gas is sent to the anode of the fuel cell 14, hydrogen ions are generated from hydrogen in the reformed gas (H ₂ → 2H ⁺ + 2e ⁻ ), and when the oxidizing gas is sent to the cathode, the oxidation gas is oxidized. Oxygen ions are generated from oxygen in the gas, and electric power is generated in the fuel cell 14. At the same time, water is generated from the hydrogen ions and oxygen ions at the cathode ((1/2) O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O). Most of the water is generated as water vapor by absorbing heat generated in the fuel cell 14.

  The anode of the fuel cell 14 is connected to the combustion side of the reformer 12 by the anode off-gas flow path 16. Among the reformed gases sent to the fuel cell 14, anode off-gas containing hydrogen that has not reacted at the anode. Is supplied to the combustion side of the reformer 12. Further, combustion air is supplied to the combustion side. A catalyst such as platinum (Pt) is provided on the combustion side, and an exothermic reaction is performed by combustible gas such as hydrogen, methane, and carbon monoxide remaining in the anode off-gas and oxygen in the combustion air. . Thereby, heat for performing the steam reforming reaction is generated on the combustion side.

  Note that the combustion side of the reformer 12 may include a combustor provided separately from the reformer 12. In this case, the anode off-gas and combustion air are burned in the combustor, and heat for performing the steam reforming reaction is supplied by the high-temperature combustion gas discharged from the combustor.

  In this way, by supplying heat from the combustion side of the reformer 12, gasoline, water vapor, and air (oxygen) sent to the reforming side react, and are expressed by the above formulas (1) and (2). The steam reforming reaction and the partial oxidation reaction occur together, and the reforming catalyst promotes the reactions, and a hydrogen-rich reformed gas is generated. In the fuel cell system 10 of the present embodiment, the combustible gas containing unreacted hydrogen remaining in the anode off-gas can be burned and used to supply heat to the reforming side, so that the efficiency of the entire system can be improved. it can.

  As shown in FIG. 1, a three-way valve 18 is provided in the anode off gas passage 16. The three-way valve 18 has a function of distributing the anode off gas supplied to the reformer 12 and exhausting an appropriate amount. Therefore, the amount of anode off gas supplied to the combustion side of the reformer 12 can be adjusted by varying the amount of anode off gas distributed by the three-way valve 18. Thereby, since the amount of combustible gas containing hydrogen supplied to the combustion side can be adjusted, the combustion state on the combustion side can be optimally controlled. Moreover, since the reaction on the reforming side depends on the combustion state on the combustion side, the reaction on the reforming side can always be kept in an optimal state by controlling the combustion state.

  Adjustment of the anode off-gas amount is preferably performed based on the temperature of the reformer 12, the amount of reformed gas generated on the reforming side, the amount of electric power generated in the fuel cell 14, and the like. Thereby, the combustion state on the combustion side can be controlled to an optimum state.

  It is desirable that the hydrogen in the anode off-gas exhausted from the three-way valve 18 is discharged outside after being combusted by a combustor or the like. In order to suppress the exhaust of the anode off gas, a control valve for controlling the anode off gas flow rate without changing the opening diameter by changing the opening diameter may be provided instead of the three-way valve 18.

  If the supply of anode off gas to the combustion side becomes excessive, combustion on the combustion side becomes excessive and the reformer 12 may be heated excessively. In the present embodiment, the amount of anode off-gas supplied to the reformer 12 by the three-way valve 18 can be adjusted, so that the reformer 12 is reliably prevented from being heated excessively due to excessive supply of anode off-gas. Is possible.

  In addition, when it is necessary to generate more reformed gas at the time of start-up or transient operation, the three-way valve 18 is controlled to increase the amount of anode off-gas sent to the combustion side. Thereby, the combustion amount on the combustion side can be increased, the steam reforming reaction on the reforming side can be promoted, and the hydrogen-rich reformed gas can be generated to the maximum extent. When a larger amount of reformed gas is generated, it is preferable to supply a part of the fuel supplied to the reforming side to the combustion side and further increase the heat generation amount on the combustion side.

  As described above, according to the first embodiment, since the three-way valve 18 is provided in the anode off gas flow path 16, the amount of anode off gas sent to the combustion side of the reformer 12 is adjusted to optimize the combustion amount on the combustion side. Can be controlled. Thereby, it becomes possible to always keep the heating amount on the combustion side and the reaction on the reforming side optimal. Further, by controlling the supply amount of the anode off gas to the combustion side, it is possible to suppress the reformer 12 from being heated excessively, and to suppress deterioration of the reforming performance. Therefore, it is possible to improve the reliability of the fuel cell system.

Embodiment 2. FIG.
Next, a second embodiment of the present invention will be described. The second embodiment controls the supply amount of the anode off gas to the reformer 12 as in the first embodiment, but the control method is different from the first embodiment. The basic configuration of the fuel cell system is the same as that of the first embodiment.

  FIG. 2 is a schematic diagram illustrating a configuration of the fuel cell system 10 according to the second embodiment. As shown in FIG. 2, in Embodiment 2, a hydrogen separation membrane 20 is provided in the anode offgas flow channel 16, and the anode offgas is supplied to one side of the hydrogen separation membrane 20. The hydrogen separation membrane 20 has a property of selectively allowing only hydrogen to permeate.

  FIG. 3 is a schematic diagram showing the configuration and function of the hydrogen separation membrane 20. 3A is a perspective view of the hydrogen separation membrane 20, and FIG. 3B is a cross-sectional view of the hydrogen separation membrane 20. As shown in FIGS. 3A and 3B, the hydrogen separation membrane 20 is configured by stacking palladium (Pd) films on both sides of a vanadium (V) film.

As shown in FIG. 3A, when the anode off-gas is caused to flow to one side of the hydrogen separation membrane 20, hydrogen (H ₂ ) in the anode off-gas is dissociated and permeates the hydrogen separation membrane 20, and the hydrogen separation membrane 20 Reach the other side. On the other hand, other components (H ₂ O, CO, CO _2, etc.) in the anode off gas do not permeate the hydrogen separation membrane 20. Therefore, by flowing the anode off gas to one side of the hydrogen separation membrane 20, hydrogen in the anode off gas can be selectively separated.

  Here, the amount of hydrogen that permeates the hydrogen separation membrane 20 depends on the partial pressure of hydrogen on both sides of the hydrogen separation membrane 20, and the greater the difference in partial pressure, the greater the amount of hydrogen that permeates the hydrogen separation membrane 20. Become. For this reason, in order to allow more hydrogen to permeate the hydrogen separation membrane 20, it is desirable to sequentially remove the hydrogen that has permeated the hydrogen separation membrane 20 and reached the opposite side, and to reduce the partial pressure of the permeated hydrogen.

  For this reason, as shown in FIG. 3B, the anode off gas is allowed to flow on one side of the hydrogen separation membrane 20, and the purge gas for purging the permeated hydrogen is allowed to flow on the other side. Thereby, the difference in the hydrogen partial pressure on both sides of the hydrogen separation membrane 20 is increased, and more hydrogen can be transmitted through the hydrogen separation membrane 20.

  Further, when the flow rate of the purge gas is decreased, the amount of hydrogen to be purged is reduced, so that the difference in partial pressure of hydrogen on both sides of the hydrogen separation membrane 20 is reduced, and the amount of hydrogen permeating the hydrogen separation membrane 20 can be reduced. it can. Therefore, the amount of hydrogen selectively separated from the anode off-gas can be varied by adjusting the amount of purge gas.

  In the present embodiment, the combustion side exhaust gas discharged from the combustion side of the reformer 12 is used as the purge gas. For this reason, as shown in FIG. 2, a combustion side exhaust gas passage 22 for sending the combustion side exhaust gas to the hydrogen separation membrane 20 is provided. The anode off gas is allowed to flow from the anode off gas flow path 16 to one side of the hydrogen separation membrane 20, and the combustion side exhaust gas is allowed to flow from the combustion side exhaust gas flow path 22 to the other side of the hydrogen separation membrane 20. .

  A three-way valve 24 is provided in the combustion side exhaust gas passage 22. The three-way valve 24 distributes the combustion side exhaust gas and exhausts an appropriate amount. Therefore, the amount of hydrogen separated from the anode off-gas can be optimally controlled by changing the flow rate of the combustion side exhaust gas flowing through the hydrogen separation membrane 20 by the three-way valve 24. Thereby, the amount of hydrogen sent from the anode off-gas flow path 16 to the combustion side of the reformer 12 can be varied.

  Therefore, the amount of hydrogen supplied to the combustion side of the reformer 12 can be adjusted, and the combustion state on the combustion side can be optimally controlled. Thereby, it becomes possible to always keep the heating amount on the combustion side and the reaction on the reforming side optimal. Then, by optimally controlling the amount of hydrogen supplied to the combustion side, it is possible to reliably suppress the reformer 12 from being heated excessively due to excessive supply of hydrogen.

  Further, when it is necessary to generate more reformed gas, the amount of hydrogen permeating the hydrogen separation membrane 20 can be reduced by controlling the three-way valve 24 to reduce the amount of combustion side exhaust gas sent to the hydrogen separation membrane 20. Can be reduced, and more hydrogen can be supplied to the combustion side of the reformer 12. Therefore, the steam reforming reaction can be promoted, and hydrogen-rich reformed gas can be generated to the maximum extent.

  The amount of hydrogen in the anode off-gas is preferably adjusted based on the temperature of the reformer 12, the amount of reformed gas generated on the reforming side, the amount of electric power generated in the fuel cell 14, and the like. Thereby, the combustion state on the combustion side can be controlled to an optimum state.

  In addition, as the purge gas supplied to the hydrogen separation membrane 20, a gas other than the combustion side exhaust gas can be used. For example, various gases that flow in the system, such as a cathode off gas and a cooling off gas of the fuel cell 14, can be used as the purge gas. Further, a part of the steam supplied to the reforming side may be branched and used as a purge gas.

Preferably, a gas containing oxygen (O ₂ ) is used as the purge gas. When a purge gas containing oxygen is used, hydrogen that has passed through the hydrogen separation membrane 20 reacts with oxygen in the purge gas to generate water, so that the hydrogen concentration on the side where the purge gas is flowing can always be kept low. Become. As a result, hydrogen can easily pass through the hydrogen separation membrane 20, and the area of the hydrogen separation membrane 20 can be minimized.

  When a purge gas containing oxygen is used, it is possible to determine the amount of hydrogen that passes through the hydrogen separation membrane 20 and is bonded to oxygen by detecting the amount of oxygen in the purge gas. Therefore, for example, when the combustion side exhaust gas is purge gas as described above, the oxygen amount remaining in the combustion side exhaust gas is detected by the oxygen sensor, and the amount of hydrogen separated from the anode off gas by controlling this oxygen amount It is possible to control the amount of hydrogen supplied to the combustion side.

  As described above, according to the second embodiment, the amount of hydrogen in the anode off-gas sent to the combustion side of the reformer 12 is optimally controlled by adjusting the amount of purge gas sent to the hydrogen separation membrane 20. Can do. Therefore, the combustion amount on the combustion side of the reformer 12 can be optimally controlled, and the heating amount on the combustion side and the reaction on the reforming side can always be kept optimal. In addition, by optimally controlling the amount of hydrogen in the anode off-gas, it is possible to suppress the reformer 12 from being heated excessively, and to suppress deterioration of the reforming performance. Therefore, it is possible to improve the reliability of the fuel cell system.

Embodiment 3 FIG.
Next, a third embodiment of the present invention will be described. FIG. 4 is a schematic diagram illustrating a configuration of the fuel cell system 10 according to the third embodiment. The basic configuration of the fuel cell system 10 of the third embodiment is the same as that of the first embodiment, and an anode offgas passage 16 is provided to supply the anode offgas to the combustion side of the reformer 12.

  In the fuel cell 14, heat is generated by a reaction when generating electric power. The fuel cell system 10 of the present embodiment includes a cooling air pump 25, and the cooling gas is sent from the cooling air pump 25 to the fuel cell 14 so that the fuel cell 14 is cooled by air cooling.

  The combustion side of the fuel cell 14 and the reformer 12 is connected by a cooling off gas passage 26. The cooling gas (cooling off gas) after cooling the fuel cell 14 is supplied to the combustion side of the reformer 12 through the cooling off gas passage 26. Then, on the combustion side of the reformer 12, the oxygen in the cooling off gas and the combustible gas containing unreacted hydrogen remaining in the anode off gas are reacted to generate heat for causing the steam reforming reaction. I am doing so.

  This eliminates the need to send new combustion air to the combustion side of the reformer 12, and eliminates the need for equipment such as a pump and piping for sending the combustion air. Therefore, the pump for sending the cooling gas and the pump for sending the combustion air can be made common, and the auxiliary machine loss in the system can be minimized. Further, the exhaust heat of the fuel cell 14 can be effectively used on the combustion side of the reformer 12, and combustion on the combustion side can be promoted. Therefore, the efficiency of the entire fuel cell system can be increased.

  As described above, according to the third embodiment, by using the cooling off gas as combustion air on the combustion side, the cooling off gas can be used effectively, and the loss in the system can be minimized. Therefore, the efficiency of the fuel cell system can be further improved.

Embodiment 4 FIG.
Next, a fourth embodiment of the present invention will be described. FIG. 5 is a schematic diagram showing the configuration of the fuel cell system 10 according to the fourth embodiment of the present invention. In the fourth embodiment, a three-way valve 28 is provided in the cooling off-gas channel 26 in the system of the third embodiment.

  By providing the three-way valve 28 in the cooling off-gas flow path 26, the cooling off-gas can be exhausted and distributed by the three-way valve 28, and the amount of cooling off-gas sent to the combustion side of the reformer 12 can be controlled. Thereby, on the combustion side of the reformer 12, the air-fuel ratio at the time of combustion can be varied, and the combustion state on the combustion side can be maintained in an optimum state. Therefore, it can suppress that the reformer 12 is heated too much. Further, by maintaining the air-fuel ratio on the combustion side in an optimal state, the emission of the combustion side exhaust gas can be improved. Thereby, discharge of hydrocarbons, nitrogen oxides and the like can be suppressed.

  The adjustment of the cooling off-gas amount is preferably performed based on the temperature of the reformer 12, the air-fuel ratio on the reforming side, the amount of reformed gas generated on the reforming side, the amount of electric power generated on the fuel cell 14, and the like. It is. Thereby, the combustion state on the combustion side can be controlled to an optimum state.

  As described above, according to the fourth embodiment, since the amount of the cooling off gas sent to the combustion side can be varied by the three-way valve 28, the air-fuel ratio on the combustion side of the reformer 12 can be kept optimal. The combustion state of the reformer 12 can be optimally controlled. Therefore, it is possible to always keep the heating amount on the combustion side and the reaction on the reforming side optimal. Further, it is possible to improve the emission of the combustion side exhaust gas by optimally controlling the air-fuel ratio on the combustion side.

  In the third and fourth embodiments, in order to control the amount of anode off-gas sent to the combustion side of the reformer 12, the three-way valve 18 or the hydrogen separation membrane is provided in the anode off-gas flow path 16 as in the first and second embodiments. 20 may be provided.

It is a schematic diagram which shows the structure of the fuel cell system concerning Embodiment 1 of this invention. It is a schematic diagram which shows the structure of the fuel cell system concerning Embodiment 2 of this invention. It is a schematic diagram which shows the structure and function of a hydrogen separation membrane. It is a schematic diagram which shows the structure of the fuel cell system concerning Embodiment 3 of this invention. It is a schematic diagram which shows the structure of the fuel cell system concerning Embodiment 4 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Fuel cell system 12 Reformer 14 Fuel cell 16 Anode off gas flow path 18, 24, 28 Three-way valve 20 Hydrogen separation membrane 22 Combustion side exhaust gas flow path 25 Cooling air pump 26 Cooling off gas flow path

Claims (7)

A reforming section that receives supply of hydrocarbon fuel and generates reformed gas containing hydrogen by a reforming reaction;
A fuel cell that receives the supply of the reformed gas at the anode and receives an oxidizing gas containing oxygen at the cathode to generate electric power;
Anode off gas supply means for supplying anode off gas discharged from the anode as combustion fuel for causing the reforming reaction;
Anode offgas control means for controlling the supply of the anode offgas;
A fuel cell system comprising:   2. The fuel cell system according to claim 1, wherein the anode off-gas control means includes a control valve that is provided in a path of the anode off-gas and controls a flow rate of the anode off-gas. The anode off gas control means includes:
A hydrogen separation membrane for separating hydrogen contained in the anode offgas;
Means for supplying the anode off gas to one side of the hydrogen separation membrane;
Means for supplying a purge gas to the other side of the hydrogen separation membrane;
Means for controlling the flow rate of the purge gas;
The fuel cell system according to claim 1, comprising:   4. The fuel cell according to claim 3, wherein the purge gas is an exhaust gas resulting from combustion of the combustion fuel, a cathode off-gas exhausted from the cathode, or a cooling off-gas exhausted by cooling the fuel cell. system. A reforming section that receives supply of hydrocarbon fuel and generates reformed gas containing hydrogen by a reforming reaction;
A fuel cell that receives the supply of the reformed gas at the anode and receives an oxidizing gas containing oxygen at the cathode to generate electric power;
Anode off gas supply means for supplying anode off gas discharged from the anode as combustion fuel for causing the reforming reaction;
A cooling gas supply means for supplying a cooling gas to the fuel cell;
A cooling off-gas supply means for supplying cooling off-gas discharged after cooling the fuel cell as combustion air for causing the reforming reaction;
A fuel cell system comprising:   6. The fuel cell system according to claim 5, further comprising cooling off gas supply amount control means for controlling the supply amount of the cooling off gas.   7. The fuel cell system according to claim 5, further comprising anode off gas control means for controlling supply of the anode off gas.

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