JP2000327308A - Carbon monoxide reduction device and fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To selectively reduce carbon monoxide from a gas mainly containing hydrogen with a small catalyst volume. SOLUTION: In a carbon monoxide reduction apparatus 100 for reducing carbon monoxide from a gas containing hydrogen as a main component, a porosity is inclined so that a gas inlet side is large and a gas outlet side is small. Carbon oxide reduction device 100
And a fuel cell stack 40 that uses the reformed gas in which carbon monoxide is reduced from a gas reformed from hydrocarbon-based fuel using the carbon monoxide reduction device 100 to generate power. Fuel cell system.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carbon monoxide reducing apparatus and a fuel cell system for reducing carbon monoxide from a gas containing hydrogen as a main component.

[0002]

2. Description of the Related Art In recent years, a method of reforming a hydrocarbon fuel into a reformed gas containing hydrogen as a main component with a catalyst and using the reformed gas as a hydrogen fuel has been actively studied. Fuel cells are being actively developed as a promising method utilizing the reformed gas. The fuel cell is a battery that generates power by a reverse reaction of electrolysis using hydrogen and oxygen, and has attracted attention as a clean power generation device that has no emissions other than water.

[0003] In order to reduce air pollution as much as possible, measures against exhaust gas from automobiles have become important, and as one of the measures, electric vehicles have been used. Not in. A fuel cell loaded with a hydrogen cylinder has also been trial manufactured, but it has to load a high-pressure cylinder of hydrogen, and there is a problem that the traveling distance is not sufficient.

[0004] Vehicles using fuel cells fueled with hydrocarbon fuels are seen as the most promising clean vehicles. Methanol is considered to be most suitable as a hydrocarbon fuel. The fuel cell has less emissions other than carbon dioxide, and the amount of carbon dioxide emitted,
Taking into account the carbon dioxide emitted when producing electricity at power plants, it is about the same as electric vehicles, and is also a measure against global warming.

[0005] In the fuel cell, methanol, which is a hydrocarbon fuel, is evaporated and reformed into a reformed gas containing hydrogen as a main component by a catalyst (for example, a Cu-Zn catalyst). The reformed gas contains 0.3 to 1% of carbon monoxide, and when sent to a fuel cell as it is, poisons the electrode catalyst of the fuel cell and significantly lowers the power generation performance of the fuel cell.

In order to avoid poisoning of the electrode catalyst of the fuel cell, the concentration of carbon monoxide needs to be 100 ppm or less. Therefore, a carbon monoxide reduction device is used which oxidizes the carbon monoxide with a catalyst (for example, a Pt catalyst or the like) and converts the carbon dioxide into non-poisoning carbon dioxide to reduce the carbon dioxide. In particular, for use in vehicles such as automobiles, it is necessary to make the carbon monoxide reduction device as small and light as possible and to send a large amount of gas to the fuel cell.

As a prior art, Japanese Patent Application Laid-Open No. 8-100184
In the publication, a first reaction section and a second reaction section are provided, and when the temperature of the second reaction section is low, a hydrogen-rich fuel gas is passed through both the first reaction section and the second reaction section, There is disclosed a carbon monoxide reduction device that allows the fuel gas to pass only through the second reaction section when the temperature of the second reaction section is high.

[0008]

However, in the prior art, since the catalyst concentration and the porosity are constant in the traveling direction of the gas in both the first reaction section and the second reaction section, the inlet of each reaction section having a large oxygen concentration is required. There is a problem that it is inevitable that the temperature of the catalyst section rapidly rises, and it becomes difficult to control the temperature of the catalyst layer.

A platinum (Pt) catalyst is generally used as a catalyst for reducing carbon monoxide. The reaction for reducing carbon monoxide is the following oxidation reaction.

[0010] _{CO + 1 / 2O 2 → CO} 2 - 2
57.2 KJ In the case of the catalyst, the reaction takes place at a catalyst temperature of 70 ° C. or higher, and the reaction rate increases as the temperature increases. However, above 200 ° C., the oxidation reaction of hydrogen becomes active,
Hydrogen as fuel for the fuel cell is consumed.

The above reaction is accelerated as the oxygen concentration increases. The reaction is a large exothermic reaction. At the inlet of each reaction section, the reaction is accelerated due to the high oxygen concentration, and the temperature rises excessively due to the exothermic reaction, and as a result, there is a problem that hydrogen is oxidized. On the other hand, it is conceivable to reduce the amount of catalyst as a whole in order to suppress the rapid oxidation reaction at the inlet, but in this case, the reactants (carbon monoxide and oxygen) become thinner toward the outlet of the catalyst layer. There is a problem that it is difficult for the catalytic reaction to occur, and as a result, it is difficult to sufficiently reduce the concentration of carbon monoxide.

The optimum space velocity (also referred to as the SV value) of the first reaction section and the second reaction section is obtained by dividing the flow rate of the gas to be treated by the apparent catalyst volume. Means about 500 h each.
⁻¹ , 1000 h ^{−1, which} is too small. In order to avoid a rise in temperature at the inlet of the reaction section, the SV value cannot be increased. If the SV value is small, the volume of the catalyst must be increased when a large amount of gas is processed, and the apparatus becomes large.

The present invention has solved the above-mentioned problems.
Provided are a small and lightweight carbon monoxide reduction device and a fuel cell system which can efficiently reduce carbon monoxide from a gas containing hydrogen as a main component efficiently with a small catalyst volume.

[0014]

Means for Solving the Problems In order to solve the above technical problems, the technical means adopted in claim 1 of the present invention (hereinafter referred to as first technical means) is mainly composed of hydrogen. In the carbon monoxide reduction device for reducing carbon monoxide from a gas to be used, the porosity is inclined so that the gas inlet side is large and the gas outlet side is small.

The effects of the first technical means are as follows.

That is, by increasing the porosity on the gas inlet side where the oxygen concentration is high and decreasing the porosity on the gas outlet side where the oxygen concentration is low, the calorific value of all the catalyst layers becomes uniform. Since the temperature of the catalyst layer becomes uniform, carbon monoxide can be efficiently and selectively reduced from a gas containing hydrogen as a main component, and a small and lightweight carbon monoxide reduction device can be obtained. In addition, there is an effect that the temperature control of the catalyst layer is facilitated.

In order to solve the above technical problem, the technical means (hereinafter referred to as second technical means) taken in claim 2 of the present invention is a means for inclining the porosity, 2. The apparatus for reducing carbon monoxide according to claim 1, wherein the volume ratio of the catalyst support, which is a ratio of the volume of the catalyst support to the total volume, is changed.

The effects of the second technical means are as follows.

That is, since the volume of the catalyst support can be easily calculated at the design stage, the design of the carbon monoxide reduction device can be facilitated.

In order to solve the above technical problem, the technical means (hereinafter referred to as third technical means) taken in claim 3 of the present invention is a means for inclining the porosity. The carbon monoxide reducing device according to claim 1, wherein the packing density of the catalyst particles is changed.

The effects of the third technical means are as follows.

That is, since the porosity can be changed only by changing the packing density of the catalyst particles, there is an effect that a catalyst cell having the same structure can be used and an inexpensive apparatus for reducing carbon monoxide can be obtained.

The technical means (hereinafter referred to as fourth technical means) employed in claim 4 of the present invention for solving the above technical problem is described in any one of claims 1 to 3. A fuel cell system comprising: a fuel cell stack that generates electricity using a reformed gas in which carbon monoxide is reduced from a gas reformed from a hydrocarbon-based fuel using a carbon monoxide reduction device. It is.

The effects of the fourth technical means are as follows.

That is, the carbon monoxide reduction device is an SV
Even if the value is large, it is possible to efficiently reduce carbon monoxide, and since the temperature of the catalyst layer of the carbon monoxide reduction device is uniform, a large amount of reformed gas can be sent in a small volume, so that the fuel cell system Has the effect of being small, lightweight and easy to control.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below.

FIG. 1 is a cross-sectional view perpendicular to the gas flow direction of the catalyst layer cell 101 of the carbon monoxide reduction device used in the embodiment. In order to control the temperature of the catalyst, a finned pipe 3 with a fin 4 through which a heat refrigerant circulates is provided inside. The heat refrigerant enters from the heat refrigerant inlet 1, flows through the finned pipe 3, and is discharged from the heat refrigerant outlet 2. The fin 4 is a catalyst-carrying support having a function of carrying a catalyst on its surface. Γ-alumina as a catalyst carrier is supported on the surface of the fin 4, and platinum is supported on the γ-alumina as a catalyst.

The apparatus for reducing carbon monoxide in this embodiment is constructed by stacking a plurality of the catalyst layer cells.

FIG. 2 is a schematic configuration diagram of a reformer according to an embodiment of the present invention. The present reformer uses a combustion unit 21 for burning methanol and water, which is a hydrocarbon fuel, by burning methanol, an evaporation unit 22 for evaporating and gasifying methanol and water by the heat of the combustion unit 21, and a catalyst. Reforming unit 2 that produces reformed gas containing hydrogen as a main component from methanol and water
3 and a carbon monoxide reducing unit 100 that is the carbon monoxide reducing device. As the hydrocarbon fuel, not only methanol but also many hydrocarbon fuels such as gasoline and natural gas can be used.

The combustion section 21 includes a flow control valve V3,
It is connected to the methanol tank 2 via a pump P2. The evaporator 22 includes a flow control valve V1, a pump P
1 and a flow control valve V
2. It is connected to the methanol tank 2 via the pump P2. The gas inlet of the reforming section 23 is connected to the air compressor 3 via a flow control valve V4. The gas inlet of the carbon monoxide reducing unit 100 is connected to the air compressor 3 via a flow control valve V5.

The carbon monoxide reducing section 100 is configured by stacking catalyst layer cells 101 to 106. In this drawing, six catalyst layer cells are stacked, but the number of catalyst layer cells may be changed as necessary. The catalyst layer cell 101
The area between to 106 is sealed with an O-ring so that gas does not leak.

The heat refrigerant inlets and the heat refrigerant outlets of the catalyst layer cells 101 to 106 are connected in parallel by a heat refrigerant line 5, and a flow control valve is provided at the heat refrigerant outlet. The heat refrigerant pipe 5 is provided with a pump 6 for circulating the heat refrigerant, a reservoir tank 7 for storing the heat refrigerant, and a radiator 8 for cooling the heat refrigerant.

3 to 8 show catalyst layer cells 101 to 101, respectively.
FIG. 10 is an explanatory cross-sectional view in which a portion of fins 4 a to 4 f of 106 is enlarged. The number of cells of these catalyst layer cells 101 to 106 is 60, 120, 200, 250, 400,
600 cells / in ² . The number of cells is an index indicating the roughness of the fin, and is represented by the number of triangles formed by the fin peaks per square inch. The larger the number of cells, the finer the fins and the lower the porosity.

The porosity is a volume through which gas can flow through the entire internal volume of the catalyst layer cell. In the case of the present embodiment, it can be calculated by a ratio obtained by dividing the cross-sectional area through which the gas in the catalyst layer cell can flow by the total cross-sectional area inside the catalyst layer cell. Since the thickness of the fins 4a to 4f is 0.1 mm, the total cross-sectional area of the fin can be calculated from the design drawing, and the porosity can be easily calculated from this. In this embodiment, since the porosity can be calculated at the design stage, the design of the carbon monoxide reduction device can be facilitated.

The porosity of the catalyst layer cells 101 to 106 is 73.3%, 70.1%, 66.4%, and 6%, respectively.
2.0%, 56.8% and 50.2%. The internal volumes of the catalyst layer cells 101 to 106 and the amount of the supported catalyst are the same.
The internal volume is 750 mL, and the platinum catalyst carrying amount is 0.5 g / L.

FIG. 9 shows a solid polymer electrolyte type fuel cell system incorporating the reforming apparatus according to the embodiment of the present invention, which is mounted on a vehicle such as an automobile.

The fuel cell system comprises a water tank 1 for storing water as a reforming material, a methanol tank 2 for storing methanol as a hydrocarbon-based fuel as a reforming material, and a reforming device 30 as the reforming device. , A fuel cell stack 40, a combustion burner 60, and a turbo assist compressor 80.

The reformer 30 is provided with an air compressor 3
2 except that a turbo assist compressor 80 is used. The same reference numerals are used for the same parts and the description is omitted.

The reformed gas discharged from the carbon monoxide reducing section 100 switches the three-way switching valve 10 to switch the combustion burner 6
0 or to the fuel cell stack 40.

The fuel cell stack 40 generates power by an electrochemical reaction using hydrogen in the reformed gas and oxygen in the air sent from the turbo assist compressor 80.

In the combustion burner 60, the reformed gas sent by switching the three-way switching valve 10 or the unused hydrogen discharged from the fuel cell stack 40 through the unused hydrogen gas line 9a is used as a fuel. Unused air discharged from the battery stack 40 via the air line 9b is burned as a combustion aid.

The turbo assist compressor 80 comprises a turbine 81, a motor 82 and a compressor 83. The turbine 81 is connected to the combustion burner 60 via an exhaust gas line 9c.
It rotates with the energy of the exhaust gas. The compressor 8
3 is rotated by the power of the turbine 81 and the motor 82, compresses the air, reforms the fuel cell 23 via the flow control valve V4, and reduces the carbon monoxide reducing unit 100 and the fuel cell through the flow control valve V5. Supply to the stack 40.

In the embodiment, the same methanol tank 2 is used for the methanol as the raw material of the reformed gas containing hydrogen as a main component and the methanol of the fuel in the combustion section 21 of the reformer 30 to be sent to the fuel cell stack 40. . The above-mentioned methanol of the raw material of the reformed gas and the methanol of the fuel of the combustion section 21 may be in different tanks.

The methanol supplied from the methanol tank 2 to the combustion section 21 is burned using the air supplied by the blower 70 as an auxiliary agent. The methanol and water supplied from the methanol tank 2 and the water tank 1 to the evaporating section 22 are evaporated by the heat of combustion of the combustion section 21 to become gas and sent to the reforming section 23.

The methanol and water vapor sent from the evaporator 22 to the reformer 23 is mixed with air sent from the compressor 83 via the flow control valve V4.
A reformed gas containing hydrogen as a main component is formed by a catalyst (for example, a Cu—Zn catalyst or the like).

The reformed gas contains carbon monoxide in an amount of 0.3 to 1%.
The reformed gas that has been contained and exited from the reforming section 23 is sent to the carbon monoxide reducing section 100. The carbon monoxide reducing unit 100
Is mixed with air sent from the compressor 83 via the flow control valve V5, and selectively oxidizes carbon monoxide with a catalyst (for example, a Pt catalyst). The fuel is sent to the fuel cell stack 40 at a concentration of 100 ppm or less.

Immediately after startup, the temperature of the reformer 30 has not risen sufficiently and the carbon monoxide concentration has not dropped below 100 ppm even after passing through the carbon monoxide reducing section 100. The valve 10 is switched to be sent to the combustion burner 60.

The fuel cell stack 40 generates power using hydrogen in the reformed gas and air sent from the compressor 83. In the fuel cell stack 40, hydrogen is 100%
It is not used and is about 80% utilization.
The gas containing unused hydrogen is sent to the combustion burner 60 via the unused hydrogen gas line 9a. Since excess air is sent to the fuel cell stack 40, unused air remains, and the unused air is sent to the combustion burner 60 via the air line 9b and becomes a combustion aid.

In the combustion burner 60, the reformed gas sent from the carbon monoxide reduction unit 100 by switching the three-way switching valve 10 or the unreacted gas sent from the fuel cell stack 40 via the unused hydrogen gas pipe 9a. The used hydrogen is burned, and the exhaust gas is sent to the turbine 81 of the turbo-assisted compressor 80 via the exhaust gas line 9c to rotate the turbine 81.

The compressor 83 is rotated by the turbine 81 and the motor 82 and compresses the air. The compressor 83 reforms the air through the flow control valve V4, the carbon monoxide reduction unit 100 through the flow control valve V5, and the fuel cell. It is supplied to the stack 40.

The carbon monoxide reducing unit 100 was evaluated by measuring the carbon monoxide concentration of each of the gas at the outlet of the reforming unit 22 and a part of the gas at the outlet of the carbon monoxide reducing unit 100 using a carbon monoxide concentration meter. I went. In addition, the catalyst layer cells 101 to 1
The measurement was carried out by measuring the temperature of the central portions M1 to M6 of the sample No. 06 using a thermocouple. The flow rate of the reformed gas when measured is 60000 NL
/ H, the SV value was 13000 h ⁻¹ .

The carbon monoxide concentration at the outlet of the reforming section 22 was 1.0%.
pm. Central part M of catalyst layer cells 101 to 106
The temperatures of 1 to 6 are 185 ° C, 185 ° C, and 175 ° C, respectively.
At 170 ° C., 170 ° C., 140 ° C., and 120 ° C., all of the catalyst layer cells fall within the optimum temperature of the catalyst. SV value about 130
Even with a large value of 00h- ¹ , carbon monoxide is efficiently reduced.

As a result of this embodiment, carbon monoxide can be selectively reduced from a reformed gas containing hydrogen as a main component efficiently with a large SV value, that is, with a small catalyst volume.
The reformed gas containing less carbon monoxide required for power generation of the fuel cell can be supplied to the fuel cell by a lightweight carbon monoxide reduction device. Further, since the temperature of the catalyst layer is uniform and stable, control is easy.

The volume of the entire fuel cell system including the reformer incorporating the carbon monoxide reduction device can be reduced in size and weight, and the control becomes easier.

In the present embodiment, the platinum catalyst is supported on the fins. However, the catalyst cells may be filled with catalyst particles on the catalyst supporting particles made of ceramic particles such as aluminum oxide and magnesium oxide. . In this case, as a method of changing the porosity, changing the particle size of the catalyst particles,
There is a method of changing the particle size distribution. For this reason, since the catalyst cells having the same structure can be used, the cost of the carbon monoxide reduction device can be reduced. In the case of a honeycomb or the like, the porosity can be changed by changing the cell density of the honeycomb.

[0056]

As described above, according to the present invention, in a carbon monoxide reducing apparatus for reducing carbon monoxide from a gas containing hydrogen as a main component, the porosity is inclined so that the gas inlet side is large and the gas outlet side is small. Carbon monoxide reduction device characterized by the following, and fuel for generating electricity using a reformed gas obtained by reducing carbon monoxide from a gas reformed from a hydrocarbon-based fuel using the carbon monoxide reduction device Since the fuel cell system is provided with a cell stack, it is possible to efficiently reduce carbon monoxide from a hydrogen-based reformed gas efficiently with a large SV value, that is, with a small catalyst volume. Therefore, the carbon monoxide reduction device and the fuel cell system can be reduced in size and weight, and can be easily controlled.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a catalyst layer cell 101 of a carbon monoxide reduction device used in an example, which is perpendicular to a gas flow direction.

FIG. 2 is a schematic configuration diagram of a reformer according to an embodiment of the present invention.

FIG. 3 is an explanatory sectional view in which a fin portion of the catalyst layer cell 101 is enlarged.

FIG. 4 is an explanatory sectional view in which a fin portion of the catalyst layer cell 102 is enlarged.

FIG. 5 is an explanatory sectional view in which a fin portion of the catalyst layer cell 103 is enlarged.

FIG. 6 is an explanatory sectional view showing an enlarged fin portion of the catalyst layer cell 104;

FIG. 7 is an explanatory sectional view showing an enlarged fin portion of the catalyst layer cell 105;

FIG. 8 is an explanatory sectional view in which a fin portion of the catalyst layer cell 106 is enlarged.

FIG. 9 is a solid polymer electrolyte fuel cell system for mounting on a vehicle, such as an automobile, incorporating the reforming apparatus of the embodiment of the present invention.

[Explanation of symbols]

4, 4a to 4f fin (catalyst supporting member) 23 reforming unit 30 reforming device 40 fuel cell stack 100 carbon monoxide reducing unit (carbon monoxide reducing device) 101, 102, 103, 104, 105, 106 ... catalyst layer cell

Claims (4)

[Claims] 1. A carbon monoxide reducing apparatus for reducing carbon monoxide from a gas containing hydrogen as a main component, wherein a porosity is inclined so that a gas inlet side is large and a gas outlet side is small. Carbon oxide reduction device. 2. As means for inclining the porosity,
2. The apparatus for reducing carbon monoxide according to claim 1, wherein the volume ratio of the catalyst support, which is a ratio of the volume of the catalyst support to the total volume, is changed. 3. The apparatus for reducing carbon monoxide as claimed in claim 1, wherein the means for inclining the porosity changes the packing density of the catalyst particles. 4. Use of the carbon monoxide reduction device according to claim 1 to generate power using a reformed gas obtained by reducing carbon monoxide from a gas reformed from a hydrocarbon fuel. A fuel cell system comprising a fuel cell stack.