JP2002308604A - Fuel reformer - Google Patents

Abstract

(57) [Problem] To provide a technology for improving the efficiency of reforming a fuel in a fuel reformer utilizing a partial oxidation reaction and a steam reforming reaction. SOLUTION: The reformer 10 has a high density part 12 and a low density part 14. The high-density part 12 has a larger specific surface area of the catalyst than the low-density part 14. In addition, both are provided with a catalyst for promoting a steam reforming reaction and a partial oxidation reaction. Hydrocarbon-based fuel, water vapor, and air are supplied to the reformer 10 via a raw fuel gas supply path. Due to the large specific surface area of the catalyst, the partial oxidation reaction actively proceeds in the high-density portion 12. Further, since the specific surface area of the catalyst is smaller, the activity of the steam reforming reaction in the low-density portion 14 is excessively increased, and the temperature is decreased. Is prevented from decreasing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel reformer for reforming a hydrocarbon fuel to generate hydrogen.

[0002]

2. Description of the Related Art As a fuel reformer for reforming a hydrocarbon fuel to generate hydrogen, a partial oxidation reaction and a steam reforming reaction using a hydrocarbon fuel are advanced in a reformer.
2. Description of the Related Art A fuel reformer that uses a heat generated by a partial oxidation reaction to advance a steam reforming reaction is known (for example, Japanese Unexamined Patent Application Publication No.
000-247603).

[0003] In such a fuel reformer, it is possible to improve the efficiency of the fuel reformer to reform the fuel by improving the efficiency of the partial oxidation reaction and the steam reforming reaction that proceed on the catalyst. it can. Here, as one of the methods of improving the activity of each of the above reactions, a method of increasing the specific surface area of the catalyst can be considered. The partial oxidation reaction is activated by increasing the specific surface area of the catalyst in this manner, and exhibits a high activity even at a lower temperature.

[0004]

However, with respect to the steam reforming reaction, there is a problem that when the specific surface area of the catalyst is increased, the reaction is not always activated in the entire fuel reforming apparatus. That is, since the steam reforming reaction is an endothermic reaction, if the contact area between the catalyst and the reactant increases and the steam reforming reaction partially proceeds actively, a decrease in ambient temperature is caused. There is a possibility that the activity of the steam reforming reaction may be rather lowered due to an excessive temperature drop.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and a technique for improving the efficiency of reforming a fuel in a fuel reformer utilizing a partial oxidation reaction and a steam reforming reaction. The purpose is to provide.

[0006]

Means for Solving the Problems and Actions and Effects Therefor To achieve the above object, a fuel reformer of the present invention is a fuel reformer for reforming a hydrocarbon-based fuel to generate hydrogen. A reforming unit that includes a catalyst that promotes an oxidation reaction and a steam reforming reaction using the hydrocarbon-based fuel, and that proceeds the steam reforming reaction by using heat generated in the oxidation reaction; A supply section for supplying the hydrocarbon-based fuel and oxygen to the reforming section, and the reforming section includes a high-density section in which the specific surface area of the catalyst is formed to be larger, and a downstream side of the high-density section. And a low-density portion provided with a smaller specific surface area of the catalyst.

[0007] In such a fuel reforming apparatus, since the specific surface area of the catalyst is formed larger in the high-density portion, the activity of the oxidation reaction becomes higher. In the low-density portion, since the specific surface area of the catalyst is formed to be smaller, the steam reforming reaction is prevented from progressing too much, and the catalyst temperature is lowered due to the progress of the endothermic steam reforming reaction. Is prevented. Therefore, the efficiency of generating hydrogen can be further improved in the entire fuel reforming apparatus.

Further, the activity of the oxidation reaction is increased in the high-density portion, so that the activity of the oxidation reaction in the high-density portion can be increased more quickly when the fuel reformer is started. In this manner, the warm-up time of the fuel reformer can be reduced by activating the oxidation reaction, which is an exothermic reaction, more quickly.

In the fuel reformer of the present invention, the hydrocarbon-based fuel may be a hydrocarbon containing no oxygen. Oxygen-free hydrocarbons are generally
The temperature suitable for the steam reforming reaction is high, and the reaction temperature of the steam reforming reaction is easily limited by the reaction temperature. Therefore, the effect of the configuration of the present invention that prevents an undesired temperature drop by providing a low-density portion in which the specific surface area of the catalyst is made smaller can be more remarkably obtained.

[0010] In the fuel reformer of the present invention, the reforming section includes a monolithic carrier supporting the catalyst, and the high-density section has a smaller number of cells per unit cross-sectional area than the low-density section. Many monolith carriers may be provided.

At this time, it is also preferable that the high-density part has a number of cells per unit cross-sectional area that is twice or more that of the low-density part.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described based on examples in the following order. A. Overall configuration of device: Configuration of Reformer 10: Conversion results: Effect: E. Second embodiment F. Modified example

A. Overall Configuration of Apparatus: FIG. 1 is an explanatory view schematically showing the configuration of a fuel cell system 20 as an embodiment. The fuel cell system 20 includes a raw fuel tank 22 for storing natural gas, a water tank 24 for storing water, a desulfurizer 26 for removing sulfur from natural gas, an evaporator 32 provided with a heating unit 28, a reforming reaction. Reformer 10 that generates hydrogen-rich gas by the process, carbon monoxide (CO) in the hydrogen-rich gas
CO reduction unit 36 for reducing concentration, fuel cell 40 for obtaining electromotive force by electrochemical reaction, fuel cell 40 for compressing air
The main components are a blower 38 to be supplied to the controller and a control unit 50 constituted by a computer. Hereinafter, each component will be described in order.

The natural gas stored in the raw fuel tank 22 is supplied to the desulfurizer 26 via the raw fuel flow channel 60.
The raw fuel passage 60 is provided with a valve 23. The valve 23 is driven by a signal output from the control unit 50 and controls the amount of natural gas supplied to the desulfurizer 26.

The desulfurizer 26 removes sulfur such as mercaptan added to the supplied natural gas as an odorant. Since the sulfur content lowers the activity of the catalyst provided in the reformer 10 and hinders the reforming reaction, in the fuel cell system 20, the desulfurizer 2
6 is provided to remove this sulfur content. Desulfurizer 2
The desulfurized gas from which the sulfur content has been removed in step 6
Is supplied to the evaporator 32 via the

A pump 72 is provided in a water supply path 62 for feeding water from the water tank 24 to the evaporator 32. The pump 72 is driven by a signal output from the control unit 50, and adjusts the amount of water supplied to the evaporator 32. The water supply path 62 joins the raw fuel supply path 63, and the desulfurization gas and water are mixed by a predetermined amount and supplied to the evaporator 32.

The evaporator 32 is a device for evaporating water supplied from the water tank 24, and receives the desulfurization gas and water as described above, and discharges the heated gas mixture of steam and desulfurization gas. . The mixed gas of the steam and the desulfurized gas discharged from the evaporator is supplied to the reformer 10 via the raw fuel gas supply path 64.

The evaporator 32 is provided with a heating section 28 as a heat source for vaporizing water. The heating unit 28 includes a combustion catalyst, and generates heat required for vaporizing water by a combustion reaction. As the fuel used for this combustion reaction, natural gas stored in the raw fuel tank 22 and anode exhaust gas discharged from the anode side of the fuel cell 40 are used.

A blower 37 is connected to the raw fuel gas supply path 64 via an air supply path 39. The blower 37 supplies oxygen required for a partial oxidation reaction that proceeds in the reformer 10. The air taken in by the blower 37 is mixed with the mixed gas in the raw fuel gas supply path 64,
It is supplied to the reformer 10.

The reformer 10 performs a reforming reaction using the supplied gas mixture. In the reformer 10, a steam reforming reaction is advanced by utilizing heat generated by the partial oxidation reaction, and a hydrogen-rich gas is generated. Since the main component of natural gas is methane, a reaction formula representing a steam reforming reaction of methane is shown below.

CH ₄ + 2H ₂ O → 4H ₂ + CO ₂ (1)

The reformer 10 is provided with a reforming catalyst for promoting such a steam reforming reaction and a partial oxidation reaction.
In this example, a rhodium catalyst was used as the reforming catalyst. The detailed configuration of the reformer 10 will be described later. The hydrogen-rich gas generated by the reformer 10 is supplied to the reformed gas passage 6
5 to the CO reduction unit 36.

The CO reduction unit 36 is a device for reducing the concentration of carbon monoxide in the hydrogen-rich gas supplied from the reformer 10. When the reforming reaction is actually performed in the reformer 10, the steam reforming reaction does not proceed ideally as shown in the above equation (1), but the hydrogen-rich gas generated in the reformer 10 Contains a predetermined amount of carbon monoxide. In addition, when carbon monoxide is contained in the gas supplied to the fuel cell 40, the carbon monoxide is adsorbed on the platinum catalyst provided in the fuel cell 40, which causes a decrease in cell performance. Therefore, a CO reduction unit 36 is provided, and the fuel cell 4
The aim is to reduce the concentration of carbon monoxide in the hydrogen-rich gas supplied to zero. The CO reduction unit 36 reduces the concentration of carbon monoxide in the hydrogen-rich gas by oxidizing the carbon monoxide in preference to hydrogen abundantly contained in the hydrogen-rich gas. Examples of the carbon monoxide selective oxidation catalyst included in the CO reduction unit 36 include a platinum catalyst, a ruthenium catalyst, a palladium catalyst, a gold catalyst, and an alloy catalyst using these as the first element. The CO reduction unit 36 is filled with a carrier that supports such a carbon monoxide selective oxidation catalyst.

The fuel cell system 20 is provided with a blower 33 for compressing and taking in air from the outside in order to supply oxygen required for the selective oxidation reaction of carbon monoxide which proceeds in the CO reduction section 36. The blower 33 has an air supply path 34.
The compressed air is supplied to the CO reducing unit 36 through the reformed gas flow path 65 through the air passage.
The amount of air supplied from the blower 33 is adjusted by the control unit 50.

The hydrogen-rich gas whose carbon monoxide concentration has been reduced as described above in the CO reduction unit 36 is supplied to the fuel gas supply path 6.
The fuel gas is guided to the fuel cell 40 by 6 and is supplied to the cell reaction on the anode side as a fuel gas. The anode exhaust gas after being subjected to the cell reaction in the fuel cell 40 is supplied to the fuel discharge passage 6
It is discharged to 7. This anode exhaust gas is used as fuel for combustion in the heating unit 28 as described above. On the other hand, the oxidizing gas related to the cell reaction on the cathode side of the fuel cell 40 is supplied from the blower 38 to the oxidizing gas supply path 6.
8 is supplied as compressed air. The remaining cathode exhaust gas used for the battery reaction is discharged to the outside via the oxidizing exhaust gas passage 69.

The fuel cell 40 is a solid polymer electrolyte type fuel cell and has a stack structure in which a plurality of unit cells as constituent units are stacked. By supplying a fuel gas containing hydrogen to the anode side and supplying an oxidizing gas containing oxygen to the cathode side of each single cell, an electrochemical reaction proceeds and an electromotive force is generated. The power generated by the fuel cell 40 is
The power is supplied to a predetermined load connected to the fuel cell 40.

The control unit 50 is configured as a logic circuit centered on a microcomputer, and has a CPU, ROM,
An AM or an input / output port for inputting / outputting various signals is provided. The control unit 50 inputs detection signals from various sensors included in the fuel cell system 20 and outputs drive signals to the above-described blowers, valves, pumps, and the like to control the operation state of the entire fuel cell system 20. .

The fuel cell system 20 shown in FIG.
In the above, the desulfurization gas and water supplied to the reforming reaction were supplied together to the evaporator 32, but after the water was vaporized by the evaporator 32 to form steam, the desulfurization gas and the good. Alternatively, the temperature of the air supplied from the blower 37 to the reformer 10 may be increased in advance before the air is supplied to the reformer 10. The configuration in which these gases are heated and mixed for the reforming reaction can be variously modified.

B. Configuration of Reformer 10: FIG.
It is explanatory drawing which represents the structure of 0 typically. Reformer 10
Is provided with a honeycomb monolithic carrier having a rhodium catalyst supported on the surface. In this example, a monolithic carrier made of ceramic was used. When a rhodium catalyst is supported on a monolithic carrier, first, a slurry prepared by adding a predetermined binder to powdered zirconium oxide (zirconia) is applied on a ceramic honeycomb, and then fired once. The ceramic honeycomb coated with zirconium oxide is immersed in a solution containing a rhodium salt to impregnate and support rhodium on zirconium oxide, and then fired and reduced.

As shown in FIG. 2, the reformer 10 includes a high-density section 12 and a low-density section 14 disposed downstream thereof.
And Both the high-density portion 12 and the low-density portion 14 are formed of a monolithic carrier supporting the above-mentioned rhodium catalyst. The monolith carrier included in the high-density part 12 is
The number of cells provided per unit flow path cross-sectional area is larger than that of the monolithic carrier provided in the low-density portion 14, whereby the high-density portion 12 has a higher catalyst ratio than the low-density portion 14. The surface area is large. In the reformer 10 according to the present embodiment, the high-density section 12 and the low-density section 14 have substantially the same channel cross-sectional area and channel length.
The gas composed of the desulfurization gas, steam, and air supplied from the raw fuel gas supply passage 64 is supplied to the high-density portion 12 and the low-density portion 14.
Pass through the inside of the monolithic carrier provided in each order.
At this time, it is subjected to a partial oxidation reaction and a steam reforming reaction that proceed on the catalyst to become a hydrogen-rich gas, and is discharged to the reformed gas passage 65.

C. FIG. 3 shows the result of verifying the efficiency of reforming the fuel in the reformer 10 based on experiments. As described above, the reformer 10 includes the high-density section 12 and the low-density section 14. Here, a reformer including three types of catalysts having different configurations of the monolithic carrier is prepared. Its performance was investigated. The monolithic carrier constituting the catalyst 1 has 900 cells per unit square inch in the cross section of the high-density section 12 and 300 cells per unit square inch in the low-density section 14. In the monolithic carrier constituting the catalyst 2, the number of cells per unit square inch in the high density part 12 is 1200, and the number of cells per unit square inch in the low density part 14 is 200. In the monolithic carrier constituting the catalyst 3, the number of cells per unit square inch in the high-density section 12 is 900, and the number of cells per unit square inch in the low-density section 14 is 200.
Further, here, as a comparative example, there is no distinction between the high-density portion 12 and the low-density portion 14, and the reforming includes the catalyst 4 having the monolith carrier having the number of cells per unit square inch of 400 as a whole. A vessel was prepared.

In order to compare the performances of these four reformers, each reformer was provided with a model gas of the raw fuel gas.
A gas obtained by mixing methane, steam and air was supplied to cause a reforming reaction. The conditions of the gas supplied to the reformer are shown below. S (mol number of water) / C (mol number of carbon atom) = 2.0 O (mol number of oxygen atom constituting oxygen molecule) / C (mol number of carbon atom) = 1.0 Space velocity for methane SV = 2000h ^-1

When supplying the above gas to the reformer, the temperature of the gas to be supplied is gradually increased from 300 ° C. in steps of 25 ° C., and the temperature in each reformer and the gas discharged from each reformer are increased. Of methane was measured. When the temperature of the supplied gas is low and the partial oxidation reaction and the steam reforming reaction do not proceed in the reformer, the temperature in the reformer becomes substantially equal to the temperature of the supplied gas. Further, the amount of methane in the discharged gas is substantially equal to the amount of methane in the supplied gas.
When the temperature of the supplied gas is gradually increased and the partial oxidation reaction is started in the reformer, the temperature in the reformer rapidly rises due to heat generated by the partial oxidation reaction. This also starts a steam reforming reaction, and the amount of methane in the discharged gas starts to decrease. In FIG. 3, for each reformer, the temperature of the supply gas when the reaction is started as described above is shown as the reaction start temperature.

After the reaction is started in the reformer as described above, if the temperature of the feed gas is further increased, the activity of the reaction progressing in the reformer gradually increases, and eventually reaches a steady state. Therefore, a condition that the temperature of the supplied gas was 400 ° C. was selected as a condition in which each of the reformers was in a steady state, and the conversion at this time was examined for each catalyst. The conversion is the ratio of the amount of methane consumed in the steam reforming reaction and the partial oxidation reaction to the total amount of methane supplied. The amount of methane consumed in the reaction is estimated based on the difference between the amount of methane in the supplied gas and the amount of methane in the discharged gas. It is considered that the higher the conversion, the better the catalytic performance. FIG. 3 shows the conversion ratio when the temperature of the supply gas was 400 ° C. for each reformer.

As shown in FIG. 3, the reformer provided with the catalysts 1 to 3 showed a higher conversion rate than the reformer of the comparative example.
Moreover, the reformer provided with the catalysts 1 to 3 started the reaction at a lower temperature than the reformer of the comparative example.

D. Effect: Since the reformer 10 included in the fuel cell system 20 according to the present embodiment configured as described above includes the reformer 10 having the high-density section 12 and the low-density section 14, natural gas can be highly efficiently used. Can be modified. That is, since the specific surface area of the catalyst is large in the high-density portion 12, which activates the partial oxidation reaction, it is presumed that the heat required to advance the steam reforming reaction can be efficiently generated. . Further, since the specific surface area of the catalyst is suppressed in the low-density portion 14, the steam reforming reaction is not activated to an undesired extent and the internal temperature of the reformer is not lowered. Therefore, by suppressing the specific surface area of the catalyst in this way, the efficiency of the reforming reaction in the entire reformer can be further increased.

Further, since the reformer 10 included in the fuel cell system 20 of the present embodiment can start the reaction at a lower temperature, the reformer 10 can be brought into a steady state more quickly. Therefore, the fuel cell system 20
Warm-up time can be reduced.

The performance of the reformer represented by the above-mentioned conversion rate, reaction start temperature and the like is affected by the space velocity in the reformer, the composition of the supplied gas, and the like. Therefore, in consideration of these conditions, the number of cells in the monolithic carrier may be set so that the effect of improving the conversion or lowering the reaction start temperature can be sufficiently obtained. In order to sufficiently obtain the above-described effect, the value of the ratio of the number of cells per unit square inch in the high-density portion 12 and the low-density portion 14 is preferably 2 or more, and more preferably 3 or more. More preferred.

Here, among the catalysts of the embodiment shown in FIG. 3, the low-density portion 14 has the same number of cells as the catalyst 1 in which the number of cells per unit square inch of the cross section of the low-density portion 14 is 300.
The catalysts 2 and 3, which have 200 cells, exhibit higher conversion. Therefore, in order to ensure a sufficiently high conversion in the reformer 10, not only the number of cells in the low-density section 14 but also the specific surface area of the catalyst in the low-density section 14 are reduced. It is desirable to make itself small enough.

As shown in FIG. 3, the catalyst 2 having 1200 cells per unit square inch in the cross section of the high-density section 12 is the same as the catalyst 1 having 900 cells in the high-density section 12. The reaction start temperature is lower than that of No. 3. Therefore, in order to sufficiently reduce the warm-up time of the reformer 10, it is necessary to not only increase the number of cells in the high-density section 12 than in the low-density section 14, but also to increase the specific surface area of the catalyst in the high-density section 12. It is desirable to make itself large enough.

As an effect of this embodiment, since the conversion rate in the reformer can be improved, the reformer can be further downsized. In addition, the fact that the warm-up time can be reduced means that the fuel cell system 2 including the reformer 10
This is particularly advantageous when starting and stopping are repeated, as in the case where 0 is mounted on an electric vehicle and used as a power supply for driving the electric vehicle.

Although the monolithic carrier provided in the reformer 10 is made of ceramic in the above embodiment, it may be made of other materials such as aluminum.

E. Second Embodiment FIG. 4 is an explanatory diagram schematically showing a configuration of a reformer 110 according to a second embodiment. This reformer 110 is used instead of the reformer 10 in the fuel cell system 20 of the first embodiment. In the reformer 110, the first high-density portion 112 and the first
, A low-density portion 114, a second high-density portion 116, and a second low-density portion 118. First high density portion 11
Like the high-density section 12 of the first embodiment, the second and second high-density sections 116 are formed of a monolithic carrier having a catalyst on the surface and having a larger number of cells per square inch. On the other hand, the first low-density section 114 and the second low-density section 118 are formed of a monolithic carrier having a catalyst on the surface and having a smaller number of cells per square inch.

An air supply path 139 for supplying air into the reformer 10 is connected to the mixing space 115 between the first low-density section 114 and the second high-density section 116. I have. In the second embodiment, the air supplied to the partial oxidation reaction that proceeds in the reformer is not supplied at once from the inlet of the reformer, but is supplied to the raw fuel gas supply passage 64 and the air supply passage 13.
9 and is supplied in two parts. The air supplied through the air supply path 139 is mixed in the gas that has passed through the first high-density section 112 and the first low-density section 114 while undergoing the partial oxidation reaction and the reforming reaction. Are mixed. After that, the mixed air is subjected to the partial oxidation reaction while the second high-density portion 11
6, and further pass through the second low density portion 118.

According to the reformer 110 of the present embodiment, the air used for the partial oxidation reaction is divided and supplied into the reformer, whereby the partial oxidation reaction for supplying the heat required for the steam reforming reaction is activated. Can be dispersed. Therefore, the heat required for the steam reforming reaction can be efficiently transmitted further downstream, and the efficiency of the reforming reaction that proceeds in the entire reformer can be improved. Also, when air is supplied on the downstream side, the specific surface area of the catalyst is increased near the region where the air flows, and the specific surface area of the catalyst is reduced on the downstream side. Therefore, similarly to the first embodiment, the effect of increasing the efficiency of the reforming reaction in the entire reformer can be obtained. Further, an effect of shortening the warm-up time at the time of starting can be obtained.

In addition, as shown in FIG. 4, the configuration in which the air is divided and supplied may be such that the supplied oxygen is divided into two parts, or may be divided into more than two parts. In such a case, the same effect can be obtained by increasing the specific surface area of the catalyst in the vicinity of each of the air inflow portions and decreasing the specific surface area of the catalyst downstream thereof.

In the reformer 110, the flow path lengths of the first high-density section 112 and the second high-density section 116 are the same as those of the first low-density section 114 and the second low-density section 118. It was formed shorter than the length. In the reformer 10 of the first embodiment, the high-density section 12
And the low-density portion 14 have substantially the same flow path length. As described above, the ratio of the size (the flow path length) of the high-density portion and the low-density portion disposed downstream thereof is various values. can do. However, the efficiency of generating hydrogen from natural gas is higher in the steam reforming reaction than in the partial oxidation reaction. Therefore, in order to further increase the activity of the steam reforming reaction and improve the efficiency of hydrogen generation, it is preferable to make the flow path length of the low density portion longer.

As described above, in the reformer 110, the first
Between the low density portion 114 and the second high density portion 116
A mixing space 115 is provided for mixing air supplied later with the gas flowing from the upstream side (see FIG. 4). A space in which gases discharged from each cell included in the high-density portion are once mixed may be provided between each high-density portion and the low-density portion located downstream of the high-density portion (see FIG. 2).

F. Modifications: The present invention is not limited to the above-described examples and embodiments, and can be carried out in various modes without departing from the gist thereof. For example, the following modifications are also possible. is there.

F-1. Modification 1 In the first and second embodiments, the specific surface area of the catalyst was changed by changing the number of cells per unit square inch of the cross section in the monolithic carrier provided in the reformer. By other methods, the same effect can be obtained by changing the surface area that substantially contributes as a catalyst (hereinafter, referred to as “effective surface area”). For example, even if the number of cells per unit cross-sectional area of the monolithic carrier is almost the same, the effective surface area can be changed by changing the shape of the cell cross section. That is, when the cross-sectional shape of each cell constituting the monolithic carrier is hexagonal, it is known that the effective surface area substantially exhibiting catalytic activity increases as compared with a monolithic carrier composed of cells having a rectangular cross-sectional shape. Therefore, the upstream cell shape is a shape having a larger effective surface area, such as a hexagonal cross section, and the cell shape on the downstream side is a square cross section,
The shape may be such that the effective surface area is smaller.

F-2. Modification 2: The catalyst provided in the reformer may have a shape other than being supported on a monolithic carrier. For example, the catalyst may be supported on a pellet-shaped carrier. In such a case, the upstream side corresponding to the high-density portion may be filled with catalyst-carrying pellets having a smaller particle diameter, and the downstream side may be filled with catalyst-carrying pellets having a larger particle diameter. In this case, it is possible to obtain a reformer having a larger specific surface area of the catalyst on the upstream side and a smaller specific surface area of the catalyst on the downstream side.

F-3. Modification 3: In the embodiment described above,
Although a rhodium catalyst is used as a catalyst included in the reformer, another kind of noble metal-based catalyst such as a platinum-iridium alloy catalyst may be used. In the embodiment, rhodium is supported on zirconium oxide. However, a metal oxide other than zirconium oxide (for example, aluminum oxide) can be used. Various catalysts supporting a noble metal on a metal oxide can promote the steam reforming reaction and the partial oxidation reaction, as in the examples.

F-4. Modification 4: In the above embodiment, the partial oxidation reaction and the steam reforming reaction are promoted by a single catalyst, but a plurality of catalysts may be used. For example,
A configuration is possible in which an oxidation catalyst having a higher activity for promoting the partial oxidation reaction is supported on at least a part of the high-density portion.

F-5. Modification 5: As in the above embodiment,
In a reformer that uses a heat generated by a partial oxidation reaction to advance a steam reforming reaction, additional heating means such as a heater may be provided in the reformer to supplement the heat required in the steam reforming reaction. good. The present invention can be applied to any reformer that advances both the partial oxidation reaction and the steam reforming reaction.

F-6. Modification 6: In the above embodiment, natural gas is used as the raw fuel used for generating hydrogen in the reformer, but a different hydrocarbon-based fuel may be used. In addition to natural gas, any fuel that can generate hydrogen by reforming, such as hydrocarbons such as gasoline, alcohols such as methanol, and aldehydes, is applicable. In addition, if the hydrocarbon-based fuel to be used is a hydrocarbon not containing oxygen, such as natural gas or gasoline, the effect of the present invention can be particularly remarkably obtained. Since the oxygen-free hydrocarbon has a high temperature for the reforming reaction, usually, the speed of the reforming reaction is
Limited by temperature. Therefore, the effect of suppressing the catalyst density particularly in the subsequent stage and preventing the steam reforming reaction from partially proceeding excessively and lowering the temperature can be remarkably obtained.

F-7. Modification 7: The fuel cell system 20 of the above embodiment stores natural gas and water to be used for the reforming reaction in a tank. Therefore, the fuel cell system 20 can be mounted on a moving body such as a vehicle, and the fuel cell 40 can be used as a power supply for driving the moving body. On the other hand, a fuel cell system including a fuel reforming apparatus to which the present invention is applied can be used as a stationary type. When used for stationary fuel cell systems,
Instead of storing natural gas in the raw fuel tank 22, a supply line for supplying natural gas as commercial gas and a fuel cell system can be connected. Further, instead of storing water in the water tank 24, a water supply line and a fuel cell system can be connected. Of course, the fuel reformer of the present invention may be used for supplying hydrogen to a hydrogen consuming device other than the fuel cell.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a schematic configuration of a fuel cell system 20 as an embodiment.

FIG. 2 is an explanatory diagram schematically showing a configuration of a reformer 10.

FIG. 3 is a diagram showing the results of comparison of conversion rates using various monolith carriers.

FIG. 4 is an explanatory diagram illustrating a configuration of a reformer 110 as a modification.

[Explanation of symbols]

 10, 110 reformer 12 high density part 14 low density part 20 fuel cell system 22 raw fuel tank 23 valve 24 water tank 26 desulfurizer 28 heating part 32 evaporator 33 blower 34 ... air supply path 36 ... CO reduction unit 37, 38 ... blower 39, 139 ... air supply path 40 ... fuel cell 50 ... control unit 60 ... raw fuel flow path 62 ... water supply path 63 ... raw fuel supply path 64 ... raw fuel Gas supply path 65 Reformed gas flow path 66 Fuel gas supply path 67 Fuel discharge path 68 Oxidation gas supply path 69 Oxidation exhaust gas path 72 Pump 1 112 First high density section 114 1st low density Part 116: second high density part 118: second low density part 115: mixed space

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4G040 EA03 EA06 EA07 EB03 EB12 EB13 EB23 EB31 EB42 EB43 EC03 EC07 4G140 EA03 EA06 EA07 EB03 EB12 EB13 EB23 EB31 EB42 EB43 EC03 EC07 5H027 AA02 BA06

Claims (4)

[Claims] 1. A fuel reformer for reforming a hydrocarbon-based fuel to generate hydrogen, comprising: a catalyst for promoting an oxidation reaction using the hydrocarbon-based fuel and a steam reforming reaction; A reforming unit that performs the steam reforming reaction using heat generated by the reaction; and a supply unit that supplies the hydrocarbon-based fuel and oxygen to the reforming unit. A fuel, comprising: a high-density part in which the specific surface area of the catalyst is formed larger; and a low-density part provided downstream of the high-density part and formed in a smaller specific surface area of the catalyst. Reformer. 2. The fuel reformer according to claim 1, wherein the hydrocarbon-based fuel is a hydrocarbon containing no oxygen. 3. The fuel reforming apparatus according to claim 1, wherein the reforming section includes a monolithic carrier that supports the catalyst, and the high-density section is smaller than the low-density section. A fuel reformer including a monolith carrier having a large number of cells per unit cross-sectional area. 4. The fuel reformer according to claim 3, wherein the number of cells per unit sectional area of the high-density section is twice or more as large as that of the low-density section.