JP2004355965A - Exhaust gas treatment technology for fuel cells - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology of suppressing local temperature rise in a catalyst layer. <P>SOLUTION: This fuel cell comprises an anode offgas exhaust piping for exhausting anode offgas to the outside and a catalyst layer 220 which carries in the carrier an oxidation catalyst for oxidizing the fuel remaining in the anode offgas. The catalyst layer 220 has a gas diffusion structure for promoting diffusion of the fuel in the catalyst layer 220. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a technique for oxidizing fuel in exhaust gas of a fuel cell, and more particularly to a technique for oxidizing fuel using a catalyst layer.
[0002]
[Prior art]
Since the fuel that has not undergone the fuel cell reaction remains in the exhaust gas (anode off-gas) on the anode side of the fuel cell, a process for oxidizing the fuel in the anode off-gas has been performed. As a fuel oxidation treatment technique, for example, the present applicant has disclosed a technique of oxidizing fuel with an oxidation catalyst (see, for example, Patent Documents 1 and 2). According to this technique, the fuel in the anode off-gas can be oxidized even if the fuel has a low concentration.
[0003]
[Patent Document 1]
JP 2001-313059 PR
[Patent Document 2]
JP 2002-289237 A
[Patent Document 3]
Japanese Patent Application Laid-Open No. 11-233129
[0004]
[Problems to be solved by the invention]
However, when the mixing of the anode off-gas and the oxidizing gas is insufficient, a region where the fuel concentration is high and a region where the fuel concentration is low occur in the catalyst layer. In the region where the fuel concentration is high, the reaction amount of the oxidation reaction increases, and the heat of reaction accumulates locally. When the temperature of the catalyst layer rises due to the accumulated reaction heat, the activity of the reaction increases and the amount of reaction further increases, so that the temperature of the catalyst layer may become excessively high.
[0005]
The present invention has been made to solve the above-described conventional problems, and has as its object to provide a technique for suppressing a local temperature rise in a catalyst layer.
[0006]
[Means for Solving the Problems and Their Functions and Effects]
In order to achieve at least a part of the above object, a first fuel cell system of the present invention generates electric power by a reaction between a fuel gas and an oxidizing gas, and uses a spent fuel gas and an anode off gas which is an oxidizing gas. A fuel cell for discharging the cathode offgas, an anode offgas discharge pipe connected to the fuel cell for discharging the anode offgas to the outside, and a fuel cell connected to the anode offgas discharge pipe for oxidizing fuel remaining in the anode offgas. A catalyst layer having an oxidation catalyst supported on a carrier, wherein the catalyst layer has a gas diffusion structure that promotes diffusion of the fuel in the catalyst layer.
[0007]
In this fuel cell, when a large amount of reaction heat due to the oxidation reaction is generated in a region where the fuel concentration in the catalyst layer is high, a temperature rise and a pressure rise occur locally. The gas diffusion structure in the catalyst layer diffuses the gas having a high fuel concentration and the heat of reaction to a region having a lower fuel concentration in response to the pressure increase. Therefore, the temperature in the catalyst layer can be made uniform.
[0008]
The gas diffusion structure may be a structure provided on the support and having a flow path in a direction different from a main flow direction of the gas in the catalyst layer.
[0009]
According to this configuration, since the gas is rapidly diffused through the flow path in a direction different from the main flow direction, the fuel concentration and the temperature in the catalyst layer can be made uniform even when the fuel concentration is largely uneven.
[0010]
The carrier may have a plurality of main flow paths formed in a main flow direction of the gas in the catalyst layer, and the gas diffusion structure may have a communication hole communicating between the adjacent main flow paths. Good.
[0011]
By providing communication holes between the main flow paths of the carrier, gas can be more easily diffused.
[0012]
The carrier may be a metal honeycomb having a communication hole in a core member.
[0013]
In this configuration, the mechanical strength of the carrier is high, so that the carrier can be hardly broken even when subjected to an impact or the like.
[0014]
The gas diffusion structure may be a random flow path provided in the carrier.
[0015]
By providing a random flow path in the carrier, the gas can be more easily diffused.
[0016]
The carrier having the random flow path may be a porous body.
[0017]
According to this configuration, the surface area per volume can be increased. Therefore, the entire catalyst layer can be made smaller.
[0018]
The porous body may be formed of a foamed metal.
[0019]
With this configuration also, the mechanical strength of the carrier can be increased, so that the carrier can be hardly broken even when subjected to an impact or the like.
[0020]
The catalyst layer has two regions, a first region on the upstream side and a second region on the downstream side, and the first and second regions are separated from each other and supplied with a gas having the same fuel concentration. Assuming that, the first region has a configuration in which the amount of oxidation reaction per volume is smaller than the second region, and at least one of the first region and the second region is A fuel cell system having a gas diffusion structure.
[0021]
According to this configuration, even when a gas having a high fuel concentration and a large unevenness in the fuel concentration flows in, the fuel concentration can be reduced without causing an excessive temperature rise in the first region. Temperature rise can be suppressed. In addition, since a fuel having a low concentration can be easily oxidized, the entire catalyst layer can be downsized.
[0022]
In addition, the first region may have at least one of a heat capacity per volume larger than the second region and a surface area per volume smaller than the second region. Good.
[0023]
When the heat capacity per volume is large, the temperature rise is suppressed and the activity of the oxidation reaction is suppressed, so that the amount of the oxidation reaction can be reduced. Further, when the surface area per volume is small, the contact area with the catalyst becomes small, and the amount of oxidation reaction as a catalytic reaction can be reduced.
[0024]
Further, the first region may have better heat conduction in the carrier than the second region.
[0025]
According to this configuration, a large amount of reaction heat generated in the high fuel concentration region can be dispersed to the low fuel concentration region by heat conduction. Thereby, even if the fuel concentration is high and there is a bias, it is possible to suppress excessive temperature rise of the catalyst layer.
[0026]
Note that the length of the first region may be shorter than that of the second region.
[0027]
With this configuration, the entire catalyst layer can be made smaller.
[0028]
Further, the above-described fuel cell system may include a cathode off-gas discharge pipe that guides the cathode off-gas discharged from the fuel cell to a flow path on the upstream side of the catalyst layer of the anode off-gas discharge pipe.
[0029]
Since the oxidizing gas is supplied from the cathode chamber, the power load for supplying the oxidizing gas is reduced, and the system efficiency can be improved.
[0030]
The present invention can be realized in various forms, and includes, for example, a catalyst layer having a gas diffusion structure, a method for manufacturing the catalyst layer, a fuel cell system including the catalyst layer, and the fuel cell system. The present invention can be realized in the form of a vehicle, a moving body, a power generation system, or the like.
[0031]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, embodiments of the present invention will be described in the following order based on examples.
A. Example 1
B. Example 2:
C. Example 3
D. Example 4:
E. FIG. Example 5:
F. Modification:
[0032]
A. Example 1
FIG. 1 is a schematic configuration diagram of an electric vehicle as one embodiment of the present invention. The wheel drive mechanism of the electric vehicle (hereinafter simply referred to as “vehicle”) includes a motor 20 and a speed reducer 40. The motor 20 is connected to the speed reducer 40 via the rotating shaft 13. The speed reducer 40 is connected to wheels via an output shaft 15, a differential gear 16, and an axle 17. Thus, the rotation of the motor 20 is transmitted to the wheel 18, and the rotation of the wheel 18 is transmitted to the motor 20.
[0033]
The motor 20 includes a rotor 22 and a stator 24. The rotor 22 is provided with a plurality of permanent magnets. The stator 24 has a plurality of coils, and an alternating current having an appropriate phase is applied to each coil to generate a rotating magnetic field in the rotor 22. The interaction between the rotating magnetic field and the magnetic field of the permanent magnet provided on the rotor 22 causes the rotor 22 to rotate. When an external force is applied to the rotor 22, a current is generated in a coil provided on the stator 24 by the magnetic field of the permanent magnet, and the motor 20 acts as a generator.
[0034]
The vehicle of this embodiment includes a battery 50 and a fuel cell system 60 as a DC power supply. The bidirectional converter 51 connected to the battery 50 controls charging and discharging of the battery 50 by adjusting the voltage on the battery side. The bidirectional converter 51, the fuel cell system 60, and the inverter 80 are connected to each other, and exchange DC current with each other.
[0035]
The inverter 80 converts a DC current supplied from the bidirectional converter 51 or the fuel cell system 60 into an AC current by turning on / off a transistor.
When the alternating current supplied from the inverter 80 is transmitted to the motor 20, a rotating magnetic field is induced and the motor 20 rotates. When the vehicle decelerates, electric power from the motor 20 is supplied to the battery 50 via the inverter 80 and the bidirectional converter 51, and energy is regenerated.
[0036]
The control unit 70 controls each part of the vehicle according to a command from the driver given from the shift lever 72, the accelerator pedal 74, and the brake pedal 76.
The control unit 70 controls the rotation speed of the motor 20 by controlling the on / off time of the transistor provided in the inverter 80 and the like.
[0037]
Control of the vehicle by the control unit 70 is realized by executing a computer program recorded in a memory incorporated in the control unit 70. This program is provided by various media such as a ROM and a hard disk in the control unit.
[0038]
FIG. 2 is an explanatory diagram showing the configuration of the fuel cell system 60. The fuel cell system 60 includes a fuel cell 100 and an anode off-gas processing device 200. The fuel cell 100 includes a cathode chamber 102, an anode chamber 104, a cathode 106, an anode 108, and an electrolyte 110. The fuel gas introduced into the anode chamber 104 causes a fuel cell reaction with the oxidizing gas introduced into the cathode chamber 102. The fuel cell reaction takes place via cathode 106, anode 108, and electrolyte 110. With the fuel cell reaction, power is delivered from the cathode 106 and the anode 108 to an external load.
[0039]
The oxidizing gas supply pump 126 supplies an oxidizing gas to the cathode chamber 102 from an external oxidizing gas supply source. The oxidizing gas (cathode off-gas) used in the fuel cell reaction is discharged outside through a cathode off-gas discharge pipe 160.
[0040]
Fuel gas is introduced into the anode chamber 104 from an external fuel gas supply source through a fuel gas supply valve 120 and a fuel gas supply pipe 142. A part of the fuel gas reacts in the anode chamber 104. The fuel gas circulation pump 124 recirculates gas containing unreacted fuel to the anode chamber 104 from the fuel gas circulation pipe 144 through the fuel gas supply pipe. Thus, by refluxing the gas containing the unreacted fuel, most of the fuel can be used for the fuel cell reaction.
[0041]
The fuel gas circulation pipe 144 has a branch between the fuel cell 100 and the fuel gas circulation pump 124. The branched pipe 146 is connected to the anode offgas discharge valve 122. The anode off-gas discharge valve 122 is an on-off valve for discharging fuel exhaust gas (anode off-gas) to the outside as necessary.
[0042]
The anode off-gas discharged from the anode off-gas discharge valve 122 is introduced into the premixing section 202 inside the anode off-gas processing device 200 via the anode off-gas discharge pipe 140. An oxidizing gas is supplied to the premixing unit 202 from an external oxidizing gas supply source by an oxidizing gas supply pump 128. The premixing unit 202 mixes the supplied anode off-gas and the oxidizing gas, and supplies the mixed gas (mixed gas) to the catalyst layer 220.
[0043]
The catalyst layer 220 supports an oxidation catalyst for oxidizing fuel. By the action of the oxidation catalyst, the fuel in the mixed gas flowing into the catalyst layer 220 reacts with the oxidizing gas in the mixed gas while passing through the catalyst layer 220 and is oxidized. The mixed gas obtained by oxidizing the fuel is discharged to the outside of the fuel cell system 60 as an exhaust gas. The oxidation catalyst carried on the catalyst layer 220 is appropriately selected according to the type of fuel, operating conditions of the fuel cell system, and the like. For example, when the fuel is hydrogen, platinum is used.
[0044]
FIG. 3A is a schematic diagram of a vertical cross section of the catalyst layer 220, and FIG. 3B is a schematic diagram of a horizontal cross section of the catalyst layer 220. The catalyst layer 220 includes a flat plate member 232 and a wavy member 234. The flat plate member 232 and the corrugated member 234 form the honeycomb carrier 230. As shown in FIG. 3A, the honeycomb carrier 230 has a large number of main flow paths from left to right. The mixed gas flowing into the catalyst layer 220 from the left side flows along the main flow direction toward the right side as a whole, and flows out as exhaust gas from the right side.
A large number of ventilation holes (communication holes) are formed in the flat plate member 232 and the corrugated member 234, respectively. Since these members 232 and 234 have air permeability, a channel in a direction different from the main flow direction exists in the honeycomb carrier 230, and the mixed gas is diffused through the channel.
[0045]
Incidentally, it is desirable that the mixed gas introduced into the catalyst layer 220 be sufficiently homogenized in the premixing section 202. However, the premixing unit 202 cannot be made large to prevent flashback. Since gas diffusion tends to be insufficient in a small premixing section, mixing of the anode off-gas and the oxidizing gas tends to be insufficient.
[0046]
When the mixing of the anode off-gas and the oxidizing gas is insufficient, a portion where the fuel concentration is high and a portion where the fuel concentration is low occur in the mixed gas. When the heterogeneous mixed gas flows into the catalyst layer 220, the reaction amount of the oxidation reaction increases in a region where the fuel concentration is high (hereinafter, also referred to as a “high concentration region”). Therefore, in the high concentration region, the temperature rises locally due to the heat of reaction, and at the same time, the pressure rises due to the temperature rise.
[0047]
FIG. 3C shows a change in the average temperature in the mainstream direction of the catalyst layer 220 when a mixed gas having a non-uniform fuel concentration flows. The graph of the comparative example in this figure shows an example in which the flat plate member 232 and the corrugated member 234 are not provided with the ventilation holes. In the comparative example, the fuel concentration is increased only in some of the main flow passages, so that the temperature is significantly increased in the upstream portion of the catalyst layer 220. On the other hand, in the downstream part of the catalyst layer 220, the fuel concentration becomes low throughout the catalyst layer, and the activity of the oxidation reaction decreases, so that the temperature hardly increases. On the other hand, in the present embodiment, the temperature distribution in the catalyst layer 220 is more uniform than in the comparative example, and the activity of the oxidation reaction is well maintained throughout the catalyst layer 220.
[0048]
By the way, in order to increase the surface area per volume of the catalyst carrier, the flow path wall is often thinned. Since the thin channel wall has high thermal resistance, heat conduction inside the carrier is not good. Therefore, in the comparative example in which the gas does not diffuse in the catalyst layer 220, a large amount of reaction heat accumulates in the high concentration region. Since the temperature rise due to the accumulation of reaction heat further enhances the activity of the oxidation reaction, the oxidation reaction may proceed excessively in the region where the fuel concentration is high. In this case, the temperature of the catalyst layer 220 locally becomes excessively high, and the catalyst deteriorates. On the other hand, in this embodiment, the local increase in pressure promotes the diffusion of high-concentration fuel and reaction heat. Therefore, an excessive oxidation reaction does not occur, and an excessive temperature rise of the catalyst layer 220 is suppressed.
[0049]
In addition, in the case of the comparative example, in a region where the fuel concentration is low (hereinafter, also referred to as a “low concentration region”), the amount of heat of the oxidation reaction is small and thus the amount of heat generated is small. Further, since heat is hardly supplied from other portions such as the high concentration region, the temperature of the low concentration region does not rise sufficiently. In a low concentration region where the temperature of the catalyst layer 220 does not rise, the activity of the oxidation reaction is low. Thus, in the comparative example, since there is a region where the activity of the oxidation reaction is low, the length of the catalyst layer 220 needs to be increased in the mainstream direction in order to sufficiently oxidize the fuel and reduce the concentration to a predetermined concentration. Required.
[0050]
In this embodiment, since the high-temperature and high-concentration gas diffuses through the flow path in a direction different from the main flow direction, the concentration and temperature of the fuel are uniform over the entire catalyst layer 220. As described above, even if the fuel concentration in the mixed gas is uneven, the oxidation reaction is favorably activated in the entire catalyst layer 220. Therefore, even if the fuel concentration in the mixed gas is uneven, the oxidation reaction proceeds sufficiently, and the length of the catalyst layer in the mainstream direction can be reduced.
[0051]
Further, in the comparative example having no communication between the main flow paths, the main flow path is closed in a region where the pressure is locally increased, so that the pressure loss of the catalyst layer 220 increases. On the other hand, in the present embodiment, the pressure is released through the flow path in a direction different from the main flow direction, so that the flow path is not closed. Therefore, the pressure loss of the catalyst layer 220 does not increase, and the exhaust resistance can be reduced. The reduction of the exhaust resistance reduces the power burden on the oxidizing gas supply pump 128 and the like, and improves the system efficiency.
[0052]
The honeycomb carrier 230 of the present embodiment may be any as long as the flow path wall of the honeycomb has air permeability. For example, a metal honeycomb using punched metal as a core member, a gas-permeable ceramic honeycomb, or the like can be used.
[0053]
In the present embodiment, both the flat plate member 232 and the wavy member 234 have been described as having air permeability. However, only one of the flat plate member 232 and the wavy member 234 may have air permeability. Further, the flat plate member 232 may be a curved surface instead of being flat.
[0054]
B. Example 2:
FIG. 4 is a schematic diagram of the catalyst layer 240 according to the second embodiment of the present invention. In this embodiment, a carrier made of a porous body 250 is used instead of the honeycomb carrier 230 of the first embodiment. The porous body 250 only needs to have a large number of communicating pores, and for example, foamed metal can be used.
[0055]
As in the first embodiment, the mixed gas flowing into the catalyst layer 240 from the left side in FIG. 4A flows along the main flow direction toward the right side as a whole, and flows out as the exhaust gas from the right side. The porous body 250 has a large number of pores communicating with each other.
Since the large number of holes form a random flow path, a flow path different from the main flow direction exists in the porous body 250, and the mixed gas is diffused through this flow path.
[0056]
With the catalyst layer 240 of the second embodiment, substantially the same effects as those of the first embodiment can be obtained. Further, since the porous body 250 has a high gas diffusion effect, the porous body 250 is more preferable than the honeycomb carrier 230 of the first embodiment in making the gas uniform. On the other hand, the honeycomb carrier 230 of the first embodiment is preferable to the porous body 250 of the second embodiment in that the manufacture is easy and the size of the catalyst layer can be made relatively large.
[0057]
C. Example 3
FIG. 5A shows a cross section of the catalyst layer 260 of the third embodiment. The catalyst layer 260 includes two supports 270 and 280 made of the same material on the upstream side and the downstream side. The flow path wall 272 of the carrier 270 on the upstream side is thicker than the flow path wall 282 of the carrier 280 on the downstream side. The flow path wall 272 of the carrier 270 on the upstream side does not have a communication hole, and the flow path wall 282 of the carrier 280 on the downstream side has a communication hole. Therefore, the carrier 270 has a larger heat capacity per volume (hereinafter simply referred to as “heat capacity”) and a smaller surface area per volume (hereinafter simply referred to as “specific surface area”) than the carrier 280.
[0058]
Since the flow path wall 272 is thicker than the flow path wall 282, the cross-sectional area of the flow path wall 272 is larger than the cross-sectional area of the thin flow path wall 282. In addition, since the channel walls 272 and 282 of the same material have the same thermal conductivity, the channel wall 272 having a large cross-sectional area has a larger cross-section than the channel wall 282 having a small cross-sectional area. And heat conduction in a direction perpendicular to the direction. Thus, the heat conduction in the carrier through the flow path wall is better in the carrier 270 than in the carrier 280. Therefore, as described below, this catalyst layer 260 can prevent an excessive rise in temperature when a gas having a high fuel concentration is temporarily supplied.
[0059]
A gas having a high fuel concentration may be temporarily discharged to the anode off-gas discharge pipe 140 (FIG. 2) of the fuel cell 100. For example, when the fuel cell 100 is started, low-purity gas in the anode chamber 104 is scavenged, and when the fuel cell 100 is stopped, the residual pressure of the fuel gas in the anode chamber 104 is removed. Released from Further, the circulating fuel gas is released as an anode off-gas under certain conditions. When the fuel gas or the anode off-gas is released, a mixed gas having a high fuel concentration temporarily flows into the catalyst layer 260.
[0060]
FIGS. 5B and 5C show how the average temperature and the fuel concentration change along the mainstream direction of the catalyst layer 260 when such a mixed gas having a high fuel concentration flows. . The graph of the comparative example in this figure shows an example in which a single metal honeycomb having no communication hole is used for the catalyst layer as the carrier. The heat capacity of the carrier used in the comparative example is smaller than that of the carrier 270 on the upstream side in this embodiment, and is larger than that of the carrier 280 on the downstream side in this embodiment. Further, the specific surface area of the carrier of the comparative example is larger than that of the carrier 270 on the upstream side in the present example, and smaller than that of the carrier 280 on the downstream side. For this reason, if fuel gas of the same concentration flows in, the oxidation reaction amount in the comparative example is larger than that in the upstream side of this embodiment, and smaller than that in the downstream side.
[0061]
In the comparative example, a large amount of reaction heat is generated because the oxidation reaction amount is large in the upstream portion where the fuel concentration is high. Since the heat capacity of the catalyst layer is not sufficient for this large amount of heat generation, the temperature of the catalyst layer rises rapidly in the upstream part. Then, as the temperature rises, the activity of the oxidation reaction increases, and the fuel concentration rapidly decreases. Further, in the downstream portion of the catalyst layer, the calorific value decreases because the fuel concentration decreases and the amount of oxidation reaction decreases. Since the heat capacity of the catalyst layer is larger than the calorific value, the temperature of the catalyst layer does not rise sufficiently. Then, since the temperature does not rise sufficiently, the activity of the oxidation reaction decreases, and the oxidation treatment of the fuel cannot be completely performed with a short catalyst layer.
[0062]
On the other hand, in the present embodiment, the upstream honeycomb carrier 270 has a larger heat capacity and a smaller specific surface area than the carrier of the comparative example. Therefore, even if a mixed gas having a high fuel concentration flows, the reaction amount and temperature rise in the carrier 270 can be suppressed to a low level. Therefore, as shown in the graph, the temperature of the carrier 270 rises slowly and the fuel concentration does not decrease much.
[0063]
Further, the honeycomb carrier 280 at the downstream portion of this embodiment has a smaller heat capacity and a larger specific surface area than the carrier of the comparative example. Since the heat capacity of the carrier 280 is small, even when the fuel concentration is low and the calorific value is small, the temperature easily rises and the activity of the oxidation reaction increases. Therefore, even in the downstream portion where the gas with a low fuel concentration flows, the temperature of the carrier 280 increases, and the fuel concentration after passing through the catalyst layer 260 is sufficiently reduced.
[0064]
As described above, in the catalyst layer 260 of the present embodiment, by appropriately selecting the heat capacity / specific surface area of the carrier 270 and the length in the main flow direction, the high-concentration fuel can be heated to the extent that excessive temperature does not occur on the downstream side. Can be reduced. The heat capacity and the specific surface area of the carrier 270 in the upstream portion are preferably selected so that the desired fuel concentration can be reduced to the desired fuel concentration in the upstream portion shorter than the downstream portion, from the viewpoint of miniaturization of the catalyst.
[0065]
Meanwhile, when the fuel concentration of the mixed gas is not uniform and a high concentration region occurs in the catalyst layer 260, the temperature of the catalyst layer of the comparative example may be locally excessively increased. On the other hand, in the carrier 270 on the upstream side in the present embodiment, the heat of reaction inside the carrier is better than that in the comparative example, and the heat of reaction is dispersed throughout the carrier. Therefore, the carrier 270 does not have a gas diffusion structure, but suppresses local excessive temperature rise. Further, in the carrier 280 on the downstream side, a communication hole is provided in the flow path wall 282 to form a flow path different from the main flow direction. As described above, since the carrier 280 has the gas diffusion structure, local excessive temperature rise can be suppressed even when the fuel concentration is not uniform.
[0066]
Note that other configurations and effects of the present embodiment are almost the same as those of the first embodiment, and a description thereof will not be repeated.
[0067]
In the present embodiment, the metal honeycomb 270 having a thick flow path wall 272 without a communication hole is used on the upstream side. However, the upstream carrier has a larger heat capacity or a smaller specific surface area than the downstream carrier. Or any of them. For example, instead of the honeycomb carrier 270 of the present embodiment, a ceramic honeycomb having a thick channel wall or a metal honeycomb having a large pitch can be used.
[0068]
In the present embodiment, the metal honeycomb 280 having the communication hole and the thin channel wall 282 is used on the downstream side. However, for example, instead of the carrier 280 of the present embodiment, a ceramic honeycomb having a thin channel wall or a metal having a small pitch Honeycombs and the like can also be used.
[0069]
Further, in this embodiment, only the carrier 280 on the downstream side of the catalyst layer 260 has the gas diffusion structure. However, in order to make the fuel concentration uniform, the carrier on the upstream side or the carrier on the downstream side is used. At least one has only to have a gas diffusion structure.
[0070]
D. Example 4:
FIG. 6 is a schematic cross-sectional view of the catalyst layer 290 according to the fourth embodiment. The difference from the third embodiment shown in FIG. 5 is that a porous body 300 is used instead of the honeycomb carrier 280 on the downstream side. In this embodiment, by using the porous body 300, the heat capacity is smaller and the specific surface area is larger than that of the carrier 270 on the upstream side. The porous body 300 may have any of a large number of communicating pores, and for example, a foamed metal can be used.
[0071]
As in the third embodiment, in the carrier 270 in the upstream portion into which the mixed gas having a high fuel concentration flows, the fuel concentration can be reduced to a desired concentration without causing excessive temperature rise. The temperature of the porous body 300 also increases in the downstream part where the gas with a low fuel concentration flows, and the fuel concentration after passing through the catalyst layer 290 is sufficiently reduced. Further, when a gas having a non-uniform fuel concentration flows into the catalyst layer 290, the gas is diffused through the pores communicating with each other in the porous body 300 at the downstream portion, and local excessive temperature rise is suppressed.
[0072]
As described above, the same effect as that of the third embodiment can be obtained by the catalyst layer 290 of the fourth embodiment. Further, since the porous body 300 has a high gas diffusion effect, the porous body 300 is more preferable than the honeycomb carrier 280 of the third embodiment in making the gas uniform. On the other hand, the honeycomb carrier 280 of the third embodiment is more preferable than the porous body 300 of the fourth embodiment in that the manufacture is easy and the size of the catalyst layer can be made relatively free.
[0073]
In the third embodiment and the fourth embodiment, the carriers having different cross-sectional shapes are used on the upstream side and the downstream side of the catalyst layer. Various configurations other than the above can be adopted. In general, if it is assumed that the upstream and downstream regions are cut and separated into two, and gases having the same fuel concentration flow into each of them, the oxidation reaction amount on the upstream side is smaller than that on the downstream side. What is necessary is just a structure.
For example, by setting the amount of the catalyst supported on the upstream carrier to be smaller than the amount of the catalyst supported on the downstream carrier, substantially the same effect as in the above embodiment can be obtained.
[0074]
E. FIG. Example 5:
FIG. 7 is an explanatory diagram illustrating the configuration of the fuel cell system 60 according to the fifth embodiment. The difference from the first embodiment shown in FIG. 2 is that the cathode off-gas is introduced into the premixing unit 202 instead of the oxidizing gas supplied from the outside.
[0075]
The cathode chamber 102 is pressurized by an oxidizing gas supplied from outside by an oxidizing gas supply pump 126. The cathode offgas discharged from the pressurized cathode chamber 102 is led to the premixing section 202 upstream of the catalyst layer 220 through the cathode offgas discharge pipe 162. Therefore, the oxidizing gas supply pump 127 used in the first embodiment becomes unnecessary. By eliminating the power burden on the oxidizing gas supply pump 127 in this manner, the system efficiency of the fuel cell system 60 is improved.
[0076]
The present invention is not limited to the above-described examples and embodiments, but can be implemented in various modes without departing from the gist of the invention, and for example, the following modifications are possible.
[0077]
F. Modification:
In the above embodiment, an example of an electric vehicle using the fuel cell system 60 has been described. However, the present invention relates to a hybrid vehicle (hybrid vehicle) using two motors, a motor and an internal combustion engine, as motors for driving wheels. Can also be applied. The present invention is also applicable to mobile objects other than automobiles, such as ships and trains. Further, the present invention is also applicable to a small fuel cell power generation system such as a portable power generation device and a home power generation device. That is, the present invention is generally applicable to a power supply system including a fuel cell and an anode offgas processing device.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an electric vehicle as one embodiment of the present invention.
FIG. 2 is an explanatory diagram showing a configuration of a fuel cell system 60 according to the first embodiment.
FIG. 3 is an explanatory diagram showing a configuration and an effect of a catalyst layer 220 in the first embodiment.
FIG. 4 is a schematic view of a catalyst layer 240 according to a second embodiment.
FIG. 5 is an explanatory diagram showing a configuration and effects of a catalyst layer 260 in a third embodiment.
FIG. 6 is a schematic view of a catalyst layer 290 according to a fourth embodiment.
FIG. 7 is an explanatory diagram showing a configuration of a fuel cell system 60 according to a fifth embodiment.
[Explanation of symbols]
13 ... Rotary axis
15 Output shaft
16 ... Differential gear
17 ... axle
18 ... wheels
20 ... motor
22 ... rotor
24 ... stator
40 ... reducer
50 ... Battery
51 ... Bidirectional converter
60 ... Fuel cell system
70 ... Control unit
72 ... Shift lever
74 ... accelerator pedal
76… Brake pedal
80 ... Inverter
100 ... fuel cell
102 ... Cathode chamber
104… Anode chamber
106 ... Cathode
108… Anode
110 ... electrolyte
120 ... Fuel gas supply valve
122 ... Anode off-gas discharge valve
124 ... Fuel gas circulation pump
126 ... Oxidizing gas supply pump
128 oxidizing gas supply pump
140… Anode off-gas discharge pipe
142 ... Fuel gas supply pipe
144: fuel gas circulation pipe
146 ... Branch piping
150: Oxidizing gas supply pipe
152: Oxidizing gas supply pipe
160 ... Cathode offgas discharge pipe
162 ... Cathode offgas discharge pipe
200 ... Anode off-gas treatment device
202 ... Premixing part
220 ... catalyst layer
230 ... honeycomb carrier
232 flat plate member
234: corrugated member
240 ... catalyst layer
250 ... porous body
260 ... catalyst layer
270 ... Honeycomb carrier
272: Channel wall
280: honeycomb carrier
282: Channel wall
290: catalyst layer
300: porous body

Claims (12)

A fuel cell system,
A fuel cell that generates electric power by a reaction between the fuel gas and the oxidizing gas and discharges the used fuel gas and the oxidizing gas, ie, the anode off gas and the cathode off gas,
An anode offgas discharge pipe connected to the fuel cell and discharging the anode offgas to the outside,
A catalyst layer which is connected to the anode offgas discharge pipe and has a carrier carrying an oxidation catalyst for oxidizing fuel remaining in the anode offgas,
The fuel cell system, wherein the catalyst layer has a gas diffusion structure that promotes diffusion of the fuel in the catalyst layer. The fuel cell system according to claim 1, wherein
The fuel cell system, wherein the gas diffusion structure is a structure provided on the support and having a flow path in a direction different from a main flow direction of the gas in the catalyst layer. The fuel cell system according to claim 1 or 2,
The carrier has a plurality of main flow paths formed in a main flow direction of the gas in the catalyst layer,
The fuel cell system, wherein the gas diffusion structure has a communication hole communicating between the adjacent main flow paths. The fuel cell system according to claim 3, wherein
The fuel cell system, wherein the carrier is a metal honeycomb having a communication hole in a core member. The fuel cell system according to claim 1 or 2,
The fuel cell system, wherein the gas diffusion structure is a random flow path provided in the carrier. The fuel cell system according to claim 5, wherein
The fuel cell system, wherein the carrier having the random flow path is a porous body. The fuel cell system according to claim 6, wherein
The fuel cell system, wherein the porous body is formed of a foam metal. The fuel cell system according to claim 1, wherein:
The catalyst layer has two regions, a first region on the upstream side and a second region on the downstream side,
Assuming that the first and second regions are separated from each other and supply gases having the same fuel concentration, the first region has a smaller amount of oxidation reaction per volume than the second region. Has a configuration,
A fuel cell system, wherein at least one of the first region and the second region has the gas diffusion structure. The fuel cell system according to claim 8, wherein
Whether the first region has a larger heat capacity per volume than the second region,
The fuel cell system according to claim 1, wherein the first region has at least one of a surface area per volume smaller than that of the second region. The fuel cell system according to claim 8, wherein:
The fuel cell system, wherein the first region has better heat conduction in the carrier than the second region. The fuel cell system according to claim 8, wherein:
A fuel cell system, wherein the length of the first region is shorter than the second region. The fuel cell system according to claim 1, further comprising:
A fuel cell system, comprising: a cathode offgas discharge pipe that guides a cathode offgas discharged from the fuel cell to a flow path of the anode offgas discharge pipe upstream of the catalyst layer.

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