JP2003331898A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system enabling a stable operation having high cell efficiency over a long time by restraining the production of ammonium causing poisoning of a cell body. <P>SOLUTION: This fuel cell system is provided with: a fuel processing system 1 for reforming a hydrocarbon-based fuel containing nitrogen into a hydrogen- rich fuel gas by a steam reform reaction; and a cell body 2 for adding and reacting oxygen to/with the fuel gas reformed into the hydrogen-rich one to extract power generated at that time. A reformer 6 of the processing system 1 is filled with reform catalyst 22 in the form of two layers. In this case, a reform catalyst layer 22a (22c) having low activity for ammonia production is enclosed as the first layer on the side of a supply port 23 of the fuel gas with a temperature in the operation set at 250-600°C or lower, and a reform catalyst layer 22b having high ammonia decomposition performance is enclosed as the second layer on the side of an exit of the fuel gas with a temperature in operation set above 550-750°C. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention reforms a hydrocarbon-based fuel containing nitrogen gas into a hydrogen-rich fuel gas by a steam reforming reaction and reacts the reformed hydrogen gas with oxygen gas to generate electricity. The present invention relates to a fuel cell system.

[0002]

2. Description of the Related Art Recent fuel cells, such as polymer electrolyte fuel cells, have a compact shape, a high power output density, and a simplified system for easy operation. Is expected to be a promising future power supply system for homes and homes.

This fuel cell has a structure including a fuel processing system for reforming a raw fuel such as city gas into a hydrogen-rich fuel gas, and a cell body for reacting oxygen gas with the reformed fuel to generate electricity. Has become.

The cell body is provided with a fuel electrode and an oxidant electrode through a solid polymer membrane, and hydrogen-rich fuel gas reformed from raw fuel is supplied to the fuel electrode and air is supplied to the oxidant electrode. Further, of the fuel gas, only protons (H ⁺ ) are passed through the solid polymer membrane to the oxidizer electrode, and the electromotive force generated when the chemical reaction is performed is taken out. It is supposed to be supplied.

[0005]

By the way, as the hydrocarbon fuel gas used as a raw fuel, nitrogen gas is used.
Some include about%. For example, when city gas is used as a raw fuel, the city gas 6B and 6C contains about 10 to 20
Contains% nitrogen.

As described above, when a relatively large amount of nitrogen is present in the hydrogen-rich gas, ammonia is produced in the reforming catalyst layer. This ammonia poisons the catalyst attached to the fuel electrode of the cell body and is a factor that significantly reduces cell performance.

For this reason, an ammonia removing device is provided on the inlet side of the fuel electrode to remove the produced ammonia. However, it could not be removed sufficiently, and as a result of long-term use, the activity of the catalyst was remarkably reduced, and some new improvement was required.

The present invention has been made under such circumstances, and suppresses the production of ammonia, which causes poisoning of the battery main body, and enables stable operation with high battery efficiency for a long time. An object is to provide a fuel cell system.

[0009]

In order to achieve the above-mentioned object, a fuel cell system according to the present invention, as set forth in claim 1, hydrogenates a hydrocarbon fuel containing nitrogen by a steam reforming reaction. A fuel cell provided with a fuel processing system for reforming into a rich fuel gas, and a cell body for electrochemically reacting the fuel gas reformed into a hydrogen-rich gas with oxygen in the air and taking out electric power generated at that time In the system, the reformer of the fuel processing system is filled with the reforming catalyst layer in two layers, and the first side is the fuel gas supply port side where the temperature during operation is 250 ° C. to 600 ° C. or less. It is filled with a reforming catalyst with low activity of ammonia generation, and the temperature during operation is 550 ° C.
The outlet side of the fuel gas having a temperature of ˜750 ° C. or higher is used as the second layer, and the reforming catalyst layer having high ammonia decomposition performance is filled.

Further, the fuel cell system according to the present invention is
In order to achieve the above-mentioned object, as described in claim 2, the reforming catalyst having a low activity of producing ammonia is a nickel-based reforming catalyst.

Further, the fuel cell system according to the present invention is
In order to achieve the above-mentioned object, as described in claim 3, the reforming catalyst having a low activity of producing ammonia is a rhodium-based reforming catalyst.

Further, the fuel cell system according to the present invention is
In order to achieve the above object, as described in claim 4, the reforming catalyst having high ammonia decomposing performance is a ruthenium-based reforming catalyst.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a fuel cell system according to the present invention will be described below with reference to the drawings and the reference numerals attached to the drawings.

FIG. 1 is a system diagram showing an overall outline of a fuel cell system according to the present invention.

The fuel cell system according to the present invention is
A polymer electrolyte fuel cell is used as an example of the fuel cell body.

The fuel cell system 21 according to this embodiment
Are roughly divided into Fuel Processing Systems (FPS; Furl Proc)
essing System 1 and battery body (CSA;
Cell Stack Assembly 2).

The fuel processing system 1 includes a fuel section 3, a desulfurizer 4, a reformer 6, a combustion section 5a integrally incorporated in the reformer 6 and a steam generating section 5b in order along the flow of the raw fuel F. ,
A CO shift reactor 7, a CO selective oxidizer 8, a steam separator 9, a reforming water tank 10, a reforming water pump 11, an exhaust heat heat exchanger 12, an exhaust heat supply water pump 13 and the like are provided.

As the raw fuel F supplied from the fuel section 3 to the desulfurizer 4, a hydrocarbon fuel such as city gas, propane, or gasified kerosene is appropriately selected and used.

On the other hand, the battery main body 2 includes an anode 14, a cathode 15, a water cooling unit 16, a battery cooling water pump 17, and the like.

The components common to the fuel processing system 1 and the cell body 2 include an air blower 18 and a condensing heat exchanger 19.
Etc. are provided.

The power generation principle of the polymer electrolyte fuel cell having such a structure will be briefly described.

When, for example, propane is selected from the raw fuel F such as propane or city gas, the reforming of propane to hydrogen gas is performed in the fuel processing system 1.

First, when the raw fuel F for selecting propane passes through the desulfurizer 4, the sulfur content is removed from the water vapor separator 9 contained in the container, for example, by activated carbon or zeolite adsorption. It is supplied to the reformer 6 by merging with the steam.

This steam separator 9 is used in the reforming water tank 1
Water supplied from 0 through the reforming water pump 11 and the water supply system 11a is heated in the steam generation unit 5b to be converted into gaseous steam, which is supplied to the reformer 6 where it is merged with the raw fuel F. It is like this. The steam separator 9 is
Drain water separated from gaseous water vapor is used as a water recovery system 11b.
It is collected in the reforming water tank 10 via the.

On the other hand, in the reformer 6, the reforming catalyst causes a steam reforming reaction of the supplied raw fuel (propane) F and steam to produce CO, CO _{2 and the} like in addition to hydrogen gas. . At that time, the steam reforming becomes an endothermic reaction. For this reason, the reformer 6 incorporates the steam generation section 5b and the combustion section 5a that secures a heat source in one container.

By the way, in the polymer electrolyte fuel cell, when the reforming CO concentration of the fuel gas supplied to the anode 14 is high, a membrane electrode assembly composed of an electrolyte membrane and a catalyst layer forming a part of the cell body 2 is joined. Body (MEA; Membrane
Electrode Assembly (hereinafter referred to as MEA) (not shown) is poisoned, its activity is reduced, and battery performance is significantly deteriorated. Therefore, CO
Needs to be previously oxidized to CO ₂ .

In the present embodiment, in consideration of such a point, the CO shift reactor 7 and the CO selective oxidizer 8 are provided on the downstream side of the reformer 6, and the air blower 18 is provided in the CO selective oxidizer 8. Of the reformed gas produced in the reformer 6 by supplying air from the CO 2 to the CO shift reactor 7 and CO.
While flowing through the selective oxidizer 8, the oxidation is promoted together with the catalyst.

Although not shown, the catalytic reaction temperatures of the reformer 6 and the CO selective oxidizer 8 are different from each other and are different from each other.
Since the temperature difference between the upstream side and the downstream side of the reformed gas is large, from several hundred degrees to several hundred degrees of the CO selective oxidizer 8, a water heat exchanger for lowering the downstream temperature is actually required. C
A water heat exchanger may be provided between the O shift reactor 7 and the CO selective oxidizer 8.

Further, for example, when propane of the raw fuel F is reformed, steam reforming by omitting the oxidation reaction of CO to CO ₂ and passing through the whole is according to the following equation (1).

[0030]

[Chemical 1]

The reformed gas passing through the CO selective oxidizer 8 is mainly composed of components such as hydrogen, carbon dioxide and steam. When these gases are supplied to the anode 14 of the battery main body 2, hydrogen gas passes through the catalyst layer (not shown) of the membrane electrode assembly MEA, the protons H ⁺ flow through the electrolyte membrane (not shown), and the air blower. It combines with oxygen and electrons in the air flowing from 18 to the cathode 15 to generate water.

Therefore, the anode 14 becomes a minus (-) pole and the cathode 15 becomes a plus (+) pole, and DC electric power is generated with a potential. When an electric load is present between these potentials, it can function as a power source.

On the other hand, the gas remaining from the outlet of the anode 14 that does not contribute to power generation is used as a combustion gas for heating the combustion section 5a and the steam generation section 5b via the unburned gas system 20.

Further, the water vapor emitted from the outlet of the cathode 15 and the water vapor in the combustion exhaust gas merge with the combustion gas in the water vapor generating section 5b and are recovered in the reforming water tank 10 via the condensation heat exchanger 19 to be supplied to the fuel cell. Water independence in the system 21 is aimed at.

The reaction temperature of the catalyst in the membrane electrode assembly MEA of the battery body 2 is usually suitable to be 100 degrees Celsius or less. Therefore, the battery cooling pump 17 cools the battery body 2 so that the temperature falls below that temperature. Circulate water to exhaust heat exchanger 12
The heat is dissipated and the temperature of the cooling water on the inlet side of the battery body 2 is controlled by an electric control unit (not shown) so as to be constant.

The medium or hot water such as antifreeze solution which is heated by exchanging heat as high temperature water from the water cooling unit 16 of the battery body 2 in the exhaust heat heat exchanger 12 is driven by the exhaust heat supply water pump 13, for example. It is supplied to water heaters and used as hot water for hot water and baths.

FIG. 2 is a conceptual diagram showing an embodiment of the reformer 6 applied to the fuel cell system according to the present invention.

The reformer 6 according to the present embodiment mixes the raw fuel F from the fuel section 3 shown in FIG. 1 with the steam from the steam separator 9 in the reforming catalyst 22 filled in the reactor. , The nickel-based reforming catalyst 2 on the side of the mixed fuel gas supply port 23.
2a, and the ruthenium-based reforming catalyst 22b is further filled on the downstream side of the nickel-based reforming catalyst 22a.

In the reformer 6 having such a configuration, the raw fuel F is mixed with steam, and the mixed fuel gas is guided to the supply port 23 and the nickel-based reforming catalyst 22.
Each of a and the ruthenium-based reforming catalyst 22b is reformed into hydrogen-rich fuel gas.

At this time, the temperature of the nickel-based reforming catalyst 22a is about 250 ° C to 600 ° C, and the temperature of the ruthenium-based reforming catalyst 22b is about 550 ° C to 750 ° C.

Due to such a high temperature, in the nickel-based reforming catalyst 22a, at the same time as the steam reforming reaction, the nitrogen contained in the raw fuel F reacts with the hydrogen produced by the reforming,
It produces ammonia.

In the ruthenium-based reforming catalyst 22b,
Ammonia generated by the nickel-based reforming catalyst 22a is decomposed.

In this embodiment, the nickel-based reforming catalyst 22a is provided on the mixed fuel gas supply port 23 side of the reformer 6.
The ruthenium-based reforming catalysts 22b were respectively filled on the downstream side, but not limited to this example, the rhodium-based reforming catalysts 22c instead of the nickel-based reforming catalysts are provided on the mixed fuel gas supply port 23 side. May be filled. Also in the case of the rhodium-based reforming catalyst 22c, the temperature range is about 250 ° C. to 600 ° C., and the nitrogen contained in the mixed fuel gas described above reacts with the hydrogen produced by the reforming to produce ammonia.
The amount thereof is about the same as that of the nickel-based reforming catalyst 22a. And the produced ammonia is the same as above.
It is decomposed by the ruthenium-based reforming catalyst 22b.

FIG. 3 shows a nickel-based reforming catalyst 22a and a ruthenium-based catalyst 2 packed in the reformer 6 according to this embodiment.
It is a graph which shows the ammonia formation characteristic of 2b and the rhodium type | system | group reforming catalyst 22c.

FIG. 3 shows that the inlet temperature is 25 when the fuel gas containing nitrogen and hydrogen is filled with each single catalyst.
When the maximum concentration is 1 with the horizontal axis representing the temperature obtained from the sampling ports installed at equal intervals in the fuel gas flow direction in a reaction tube simulating a catalyst layer so that the outlet temperature is 0 ° C and the outlet temperature is 750 ° C. The relative ammonia concentration of is shown on the vertical axis.

From this graph, at a temperature of 600 ° C. or lower, the nickel-based reforming catalyst 22a and the rhodium-based reforming catalyst 22
It was found that the amount of ammonia produced in c was small and the amount of ammonia produced in the ruthenium-based reforming catalyst 22b was the largest.

However, at temperatures above 550 ° C., the nickel-based reforming catalyst 22a and the rhodium-based reforming catalyst 22
In c, no decrease in ammonia was observed, but in the ruthenium-based reforming catalyst 22b, a decrease due to decomposition of ammonia was observed.

From such an event, in the reforming catalyst 22 of the reformer 6 for reforming the hydrocarbon fuel containing nitrogen into the hydrogen-rich fuel gas by the steam reforming reaction, the reforming catalyst 22
Is composed of two layers, and the nickel-based reforming catalyst 22a having low ammonia production activity and low cost is selected for the first layer of the reforming catalyst 22 having a temperature of 550 ° C. to 600 ° C. It is effective to combine the second layer having a temperature of 600 ° C. or higher with the ruthenium-based reforming catalyst 22b having a high activity of decomposing ammonia.

The ammonia production concentration in each temperature range of the reforming catalyst 22 at that time is shown in the graph of FIG. As for the relative ammonia concentration in this graph, the maximum concentration is 1 as in the case shown in FIG.

From FIG. 3, the ammonia concentration is the temperature 600.
It was found that the highest data was obtained at around 0 ° C., then decreased, and became lower at the outlet side of the reformer 6 than when the nickel-based reforming catalyst 22a alone and the ruthenium-based reforming catalyst 22b alone were used. .

Needless to say, both reforming catalysts 22a and 22b maintain sufficient steam reforming reaction characteristics.

[0052]

As described above, according to the fuel cell system of the present invention, when the hydrocarbon-based fuel containing nitrogen gas is reformed into the hydrogen-rich fuel gas by the steam reforming reaction, the temperature is In the range of 550 ° C to 600 ° C or less, the first
Since, for example, a nickel-based reforming catalyst or a rhodium-based reforming catalyst is arranged in the second layer, it is possible to suppress the production amount of ammonia, and in the region where the temperature is 550 ° C to 600 ° C or higher, the second layer is formed. Since, for example, a ruthenium-based reforming catalyst is arranged, the produced ammonia can be decomposed, the production of ammonia that poisons the fuel cell as a whole is suppressed, and a high cell efficiency and stable operation can be achieved for a long time. Can be realized.

[Brief description of drawings]

FIG. 1 is a system diagram showing an overall outline of a fuel cell system according to the present invention.

FIG. 2 is a conceptual diagram showing an embodiment of a reformer applied to the fuel cell system according to the present invention.

FIG. 3 is a graph showing ammonia generation characteristics when the reforming catalyst is a single layer.

FIG. 4 is a graph showing ammonia generation characteristics when the reforming catalyst has two layers.

[Explanation of symbols]

1 Fuel processing system 2 Battery body 3 Fuel Department 4 desulfurizer 5a Combustion section 5b Steam generator 6 reformer 7 CO shift reactor 8 CO selective oxidizer 9 Water vapor separator 10 Reforming water tank 11 Reforming water pump 11a Water supply system 11b Water recovery system 12 Exhaust heat heat exchanger 13 Waste heat supply water pump 14 Anode 15 cathode 16 Water cooling unit 17 Battery cooling water pump 18 air blower 19 Condensation heat exchanger 20 unburned gas system 21 Fuel cell system 22 Reforming catalyst 22a Nickel-based reforming catalyst 22b Ruthenium-based reforming catalyst 22c Rhodium-based reforming catalyst 23 Supply port

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Claims (4)

[Claims] 1. A fuel processing system for reforming a nitrogen-containing hydrocarbon fuel into a hydrogen-rich fuel gas by a steam reforming reaction, and an electrochemical reaction between the hydrogen-rich reformed fuel gas and oxygen in the air. In a fuel cell system including a cell body for reacting and extracting electric power generated at that time, the reformer of the fuel processing system is filled with two layers of reforming catalyst layers, and the temperature during operation is The reforming catalyst having a low activity of generating ammonia is filled with the supply port side of the fuel gas of 250 ° C to 600 ° C or less as the first layer, and the temperature during operation is 550 ° C.
A fuel cell system characterized in that a reforming catalyst layer having high ammonia decomposing performance is filled with a second layer on the outlet side of the fuel gas at 750 ° C or higher. 2. The fuel cell system according to claim 1, wherein the reforming catalyst having a low activity of producing ammonia is a nickel-based reforming catalyst. 3. The fuel cell system according to claim 1, wherein the reforming catalyst having a low activity of producing ammonia is a rhodium-based reforming catalyst. 4. A reforming catalyst having a high ammonia decomposing performance,
A ruthenium-based reforming catalyst, characterized in that
The fuel cell system described.