JP2002110207A - Fuel cell system and operation method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase freedom in miniaturizing a fuel cell system and reduce the work for replacement of cylinders and the cost by reducing the space for installing an inert gas storage means such as the cylinder. SOLUTION: This fuel cell system is provided with a nitrogen separating and producing device. When the fuel cell system is started and stopped, the inside of the fuel cell system is purged using nitrogen separated and produced from air by the nitrogen separating and producing device. When the system is started, fuel is combusted using oxygen-enriched air in which nitrogen is separated by the nitrogen separating and producing device and oxygen concentration is increased following the purge to heat a desired part of the fuel cell system by the combustion heat. When the desired part of the fuel cell system is heated by the combustion heat, heat exchange is done between combustion gas combusting fuel using oxygen-enriched air and the produced nitrogen to heat the produced nitrogen so that the heated and produced nitrogen flows into a desired part in the 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 fuel cell system for performing power generation or cogeneration by electrochemically reacting a fuel and an oxidant, and to an operation method thereof.

[0002]

2. Description of the Related Art There are various types of fuel cells currently in practical use depending on the electrolyte used. The basic principle is that a fuel such as hydrogen or hydrocarbon and an oxidizing agent such as air are electrochemically used. It reacts to obtain electrical energy. Therefore, the fuel cell system has a fuel supply unit, an oxidant supply unit, and a fuel cell as basic components.

[0003] When starting and stopping a fuel cell system, an inert gas typified by nitrogen gas is introduced into the system for warming-up and purging of combustible gas, etc., and in some cases, circulation is widely performed. Have been done. In this case, the fuel cell system has an inert gas supply means. Conventionally, a storage device such as a cylinder or a tank is generally used as the inert gas supply means.

[0004] On the other hand, miniaturization of fuel cell systems has been promoted in recent years, and it is thought that the needs thereof will increase more and more in the future. In a fuel cell system, when an inert gas is provided in a storage means such as a cylinder, an installation space is required for the storage means, and there is a problem that it becomes an obstacle to downsizing. In addition, there is a problem in that it takes time and effort to replace the cylinder and replenish the tank, and thus the running cost is also increased.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and reduces the space for installing an inert gas storage means such as a cylinder.
Increased flexibility in miniaturizing fuel cell systems,
Moreover, it aims at reducing the work and cost for cylinder replacement etc.

[0006]

SUMMARY OF THE INVENTION The present invention provides a fuel cell system having a fuel cell, a fuel supply means for supplying fuel to the fuel cell, an oxidant supply means for supplying an oxidant to the fuel cell, and an inert gas supply means. , The inert gas supply means is a nitrogen separation generator.

The present invention also relates to a method of operating a fuel cell system provided with a nitrogen separation generator for separating nitrogen from air, wherein the nitrogen generated by the nitrogen separation generator is separated from the air when the system is started. A method for operating a fuel cell system, characterized in that the inside of the fuel cell system is purged by using the method.

Following the purging, the fuel is burned using oxygen-enriched air in which nitrogen has been separated and the oxygen concentration has been increased by a nitrogen separation generator, and the desired heat of the fuel cell system is heated by the combustion heat. Is preferred.

Further, when a desired portion of the fuel cell system is heated by the combustion heat, heat is exchanged between a combustion gas obtained by burning fuel using oxygen-enriched air and generated nitrogen. Preferably, the generated nitrogen is heated, and the heated generated nitrogen flows to a desired portion in the fuel cell system.

[0010] The present invention also relates to a method of operating a fuel cell system provided with a nitrogen separation generator for separating nitrogen from air, wherein when the system is shut down, the generated nitrogen separated from the air by the nitrogen separation generator. A method for operating a fuel cell system, characterized in that the inside of the fuel cell system is purged by using the method.

[0011]

FIG. 1 is a block diagram showing a schematic configuration example of a solid polymer electrolyte fuel cell system using a hydrocarbon as a fuel. Hereinafter, the present invention will be described with reference to FIG. 1, but the present invention is not limited to the embodiment shown in FIG. The fuel cell system can take various forms depending on the type of fuel cell and the fuel used.

The fuel cell system according to the present invention comprises a fuel cell 1
Having. The fuel cell is not particularly limited according to the present invention, and may be any type of fuel cell, such as a phosphoric acid type, a molten carbonate type, and a high temperature solid electrolyte type, in addition to the polymer solid electrolyte type. The fuel cell may be a single cell, but in practice, a cell stack or a module in which the single cells are stacked or assembled is preferable for higher voltage and higher output.

The fuel supply means is for supplying a fuel such as hydrogen which undergoes an electrochemical reaction in the fuel cell, and is not particularly limited according to the present invention. Can be used. There is no particular limitation on the fuel to be used, and hydrogen, alcohol such as methanol, or hydrocarbon such as natural gas, LP gas, gasoline, naphtha or kerosene can be used.

In FIG. 1, the fuel supply means comprises a raw fuel storage means 11, a pipe 12, a reformer 13, and a pipe 14. Here, a hydrocarbon such as naphtha, kerosene or the like is used as a raw fuel and the storage means 11 is provided. However, when the raw fuel is supplied from outside the system through a line, the storage means may be omitted. Raw fuel is supplied from storage means to pipe 12
Is supplied to the reforming reaction chamber 13a of the reformer 13 via

The pipe 12 may be provided with a boosting means such as a pump, a compressor, a blower and the like, if necessary.

The reformer 13 is for obtaining hydrogen from raw fuel by a reforming reaction such as a steam reforming reaction or a partial oxidation reaction. This is preferably used when the electrochemical reaction does not sufficiently proceed even when the raw fuel is directly supplied to the fuel cell. For example, if the raw fuel is hydrogen, a reformer is typically not required. Although not shown, steam and oxygen (such as air) required for reforming are appropriately supplied to the reforming reaction chamber.

Although the reforming method is not particularly limited, reforming suitable for a fuel cell system using naphtha or kerosene as a raw fuel is described in, for example, JP-A-4-265156 and JP-A-Hei.
-281845. In these techniques, as a reforming catalyst, ceria or ceria containing 0.2 to 20 wt% of one or more metals selected from an alkali metal and an alkaline earth metal as a metal oxide is used as a main component. A catalyst in which a platinum group metal is supported on a rare earth oxide to be used is used, or ceria or a rare earth oxide containing ceria as a main component is 5 to 40 wt.
% Of ruthenium supported on a carrier containing 60 to 95% by weight of alumina and 60 to 95% by weight of alumina, wherein the atomic ratio of cerium to ruthenium (Ce / Ru) is more than 10 to 200 is used. . According to the steam reforming reaction using these catalysts, carbon deposition is small even at a low pressure and a low steam / carbon ratio, and the catalyst is kept highly active for a long time.

The reformed gas whose hydrogen concentration has been increased by the reformer is introduced into the anode chamber 1a of the fuel cell 1 through the pipe 14.

Although not shown, a CO converter (shift converter) for reducing the CO concentration may be provided between the reformer 13 and the fuel cell 1. CO may poison the catalyst in the fuel cell, and in this case, a CO converter is preferably used to avoid this. The effect of increasing the hydrogen concentration can be expected at the same time as the reduction of the CO concentration.

The anode exhaust gas discharged from the anode chamber 1a can be directly discharged to the atmosphere.
Unreacted fuel is contained in the anode exhaust gas, and C
Since toxic substances such as O may be contained, it is preferable to use and treat in a fuel cell system.

In the embodiment shown in FIG. 1, the anode exhaust gas is supplied to the combustion chamber 13b of the reformer 13 via the pipe 15. Here, combustible components such as hydrogen, CO, and residual hydrocarbons in the anode exhaust gas are burned by a combustion oxidant supplied from a pipe 25, and combustion heat generated at that time is used for a reforming reaction, which is an endothermic reaction. You.

The combustion gas discharged from the combustion chamber 13b is discharged to the atmosphere via a pipe 18 after water is separated by a condensing / water separator 17 via a pipe 16. The piping 18 may be provided with a processing device such as a flare stack, if necessary.

If there is a substance in the raw fuel that may harm the components of the fuel cell system, it is preferable to provide a device for removing the substance. For example, since sulfur content can be a catalyst poisoning substance, for example, when a fuel cell or a reformer is provided with a catalyst and a hydrocarbon containing sulfur content is used as a raw fuel, for example, upstream of the reformer 13 (in FIG. It is preferable to provide a desulfurizer at line 12). On the other hand, the oxidant supply means is for supplying an oxidant (usually air) such as oxygen which undergoes an electrochemical reaction in the fuel cell,
There is no particular limitation on the present invention, and any device applicable to a fuel cell system can be used in the present invention.

In the embodiment of FIG. 1, the air pressurized by the air blower 21 is branched and supplied to the cathode chamber 1b of the fuel cell and the combustion chamber 13b of the reformer. In this embodiment, a nitrogen separation generator 31 is provided before branching. Cathode exhaust gas discharged from the cathode chamber may be discharged to the outside of the system as it is, and may be appropriately used in the system, for example, recycled or recovered by a heat exchanger.

The air supplied to the combustion chamber 13b is supplied to the pipe 15
It is used for combustion of the anode exhaust gas supplied from.

The recovered water that has been condensed and separated by the condensing / water / water separator and recovered is bubbled by a recovered water deaerator 42. This is performed to drive off carbon dioxide gas in the recovered water and reduce the acidity of the water. The water that has exited the degassing device is supplied to the fuel cell 1 as cooling water for cooling the fuel cell via a pump 45 after impurities are removed by, for example, an ion exchange resin in a water treatment device 44. This water may be used for other purposes such as steam reforming.

The above is the schematic flow of the system shown in FIG. 1 during normal operation. When the fuel cell system is started and stopped, the following operation is performed.

At the time of startup, first, the air blower 21 is operated, and the inside of the system is purged with nitrogen generated by the nitrogen separation generator 31. In FIG. 1, the generated nitrogen is
2 and 34, and is supplied to the reforming reaction chamber 13a.
4, anode chamber 1a, pipe 15, combustion chamber 13a, pipe 1
6. Purge the condensing / water separator 17 and the piping 18. This line is a line through which or there is a possibility that combustibles can pass. The line to be purged is determined according to the necessity in design. For example, if there is a line to be purged other than this line, the generated nitrogen may be supplied by appropriately branching or the like.

After purging, combustion is started in the combustion chamber of the reformer, and the temperature of the reformer is raised. At this time, in this embodiment, the pipe 1
Since no combustible substance is contained in the gas from the fuel cell 5, fuel is supplied from the raw fuel storage means to the combustion chamber 13b by a bypass line (not shown), and an oxidant (here, the nitrogen concentration is reduced and the oxygen concentration is increased) from the pipe 25. Supplied air) to ignite the burners in the combustion chamber. The combustion method in the combustion chamber is not limited by the present invention, and may be appropriately designed such as a burner type, a combustion catalyst type, or a combination thereof.

It is preferable to use the thermal energy of the combustion gas discharged from the pipe 16 as a heat source for heating another fluid from the viewpoint of thermal efficiency. Here, the generated nitrogen is heated by the heat exchanger 35, but by providing a heat exchanger in a desired line, heating of another fluid can be performed.

When the fuel cell system is stopped, the supply of the raw fuel is first stopped, then the generated nitrogen is introduced into the system, and the combustibles are purged. In the embodiment of FIG. 1, the generated nitrogen is supplied and purged in the same manner as at the time of startup. At the time of shutdown, it is not necessary to warm up the inside of the system. Therefore, if it can be determined that there is no need to purge the combustion chamber 13b and thereafter, it is only necessary to purge up to the fuel cell anode exhaust gas line (pipe 15).

Even during normal operation, the generated nitrogen gas can be effectively used. The degassing of recovered water is usually performed with air, but nitrogen with a lower carbon dioxide concentration than normal air can be produced by a nitrogen separation membrane. In comparison, the concentration of carbon dioxide in water can be further reduced, which is preferable. FIG.
In the embodiment, the generated nitrogen is supplied to the deaerator 42 from the pipe 36.

Further, in the nitrogen separation / generation apparatus, as a result of separation of nitrogen, a gas enriched with oxygen is produced as a by-product. Supplying this oxygen-enriched gas to the cathode compartment of the fuel cell
It is preferable from the viewpoint that the power generation efficiency of the battery can be improved. Furthermore, supplying this oxygen-enriched gas to the reformer combustion chamber at the time of startup and using it as combustion air,
The combustion temperature can be raised, and the temperature of the reformer can be raised in a short time,
Further, the system can be warmed up, which is preferable.

Here, the combustion is performed in the reformer combustion chamber. However, other than this, any other device that can perform combustion, such as a combustor or a device having a combustor or a combustion chamber, may be used.
Any equipment may be used for combustion. As with the combustion chamber of the reformer, there is no particular limitation on the combustion method in these devices according to the present invention. Regardless of which type of equipment is used for combustion, the desired portion is heated by performing combustion at a relatively high temperature using an oxygen-enriched gas at the time of start-up, and furthermore, the nitrogen gas generated by exchanging heat with the combustion gas It is preferable from the viewpoint of the temperature increase rate to heat the fluid by heating the fluid to a desired portion.

A nitrogen storage container may be provided in the generated nitrogen line (the pipe 32 in FIG. 1) downstream of the nitrogen separation generator to store the generated nitrogen. This can be used as a buffer tank, from which nitrogen can be supplied, especially at startup, until the desired nitrogen comes out of the nitrogen separation generator. From this point of view, it is preferable to provide the nitrogen storage container. However, this is not necessarily preferable from the viewpoint of further downsizing because a pressurized compressor is provided in some cases, similarly to the provision of the nitrogen cylinder.

For operation control, instrumentation control-related devices can be appropriately provided around the nitrogen separation generator. FIG. 1 shows an oximeter 33 as an example, which monitors whether the oxygen concentration is below a desired level and discharges the generated nitrogen by-passing until the desired nitrogen purity is obtained. And so on.

As the nitrogen separation generator that can be used in the present invention, any apparatus can be used as long as it can separate nitrogen, such as a membrane, a PSA apparatus, and a cryogenic separation apparatus. Devices comprising a membrane are preferred. This is because it has features such as its configuration and easy operation, and is suitable for miniaturization. There is no particular limitation on the nitrogen separation membrane according to the present invention, and the material, shape and the like can be appropriately determined. For example, a nitrogen separation generator having a configuration in which a hollow fiber nitrogen separation membrane made of a resin such as a polyimide resin is bundled and modularized can be preferably used. As a commercially available product, a UBE nitrogen gas generator manufactured by Ube Industries, Ltd. can be mentioned as a suitable example.

The purity and amount of the generated nitrogen gas generated by the nitrogen separation generator can be determined as appropriate during the design or operation of the system. The main points to keep in mind are that other components contained in this gas, especially oxygen, do not form an explosive mixture in the system, and that the equipment (particularly the catalyst) in the system is not damaged. Is to do so.

From such a viewpoint, the residual oxygen concentration in the generated nitrogen gas is preferably as low as possible, preferably 5% by volume or less, more preferably 1% by volume or less, further preferably 0.5% by volume or less, and most preferably. 0.1 volume% or less. The purity of nitrogen may be set so as to obtain such an oxygen concentration.

The pressure of the air supplied to the nitrogen separation generator is set to 10 atm in terms of gauge pressure from the viewpoint of avoiding a large-scale system, and when using a nitrogen separation membrane, from the viewpoint of the pressure resistance of the membrane. (1 MPa) or less is preferable. Further, in particular, in a fuel cell system for a mobile object, etc., it is often desired to simplify and reduce the weight of the system, and from this viewpoint, a pressure of 3 atm (0.3 MPa) or less is preferable. The lower limit of the pressure is preferably a pressure exceeding the atmospheric pressure from the viewpoint of avoiding a negative pressure in the fuel cell system. In practice, this pressure is appropriately determined from the pressure balance of the system, including the differential pressure required for nitrogen separation.

Regarding the operating temperature of the nitrogen separation generator,
There is no particular limitation according to the present invention, and it may be appropriately determined mainly depending on the type of separation. It is preferable to use a nitrogen separation membrane also from the viewpoint that it can be operated at room temperature.

In addition to the nitrogen separation generator, for example, an inert gas storage means such as a minimum necessary nitrogen cylinder or a tank may be provided in case of emergency.

In the present invention, it has been described above that the generated nitrogen gas or the oxygen-enriched gas is appropriately branched and used for various applications and devices. It can be mixed with air.

[0044]

According to the present invention, by using a nitrogen separation generator in a fuel cell system, even if there is no inert gas storage means such as a cylinder, an inert gas used when the system is started or stopped is supplied. Thus, the space for the storage means can be reduced, the degree of freedom in reducing the size of the fuel cell system can be increased, and the work and cost for cylinder replacement and the like can be reduced. Furthermore, by using not only the nitrogen generated from the nitrogen separation generator but also the oxygen-enriched air produced as a by-product, the temperature of a desired portion can be raised more quickly when the system is started.

[Brief description of the drawings]

FIG. 1 is a block diagram schematically showing an embodiment of a fuel cell system according to the present invention. In the figure, broken lines and dashed lines indicate lines through which generated nitrogen and oxygen-enriched air can flow, respectively.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fuel cell 1a Anode chamber 1b Cathode chamber 11 Raw fuel storage means 13 Reformer 13a Reforming reaction chamber 13b Combustion chamber 17 Condensing / water separator 18 Piping 21 Air blower 31 Nitrogen separation generator 33 Oxygen meter 35 Heat exchanger 42 Collected water deaerator 44 Water treatment device 45 Cooling water pump

Continued on the front page F term (reference) 5H026 AA06 5H027 AA04 AA05 AA06 BA01 BA05 BA09 BA13 BA16 BA17 BA19 BC06 BC07 BC19 BC20 CC06 KK01 KK11 KK31 MM01 MM03 MM13

Claims (5)

[Claims] 1. A fuel cell system comprising: a fuel cell; a fuel supply means for supplying fuel to the fuel cell; an oxidant supply means for supplying an oxidant to the fuel cell; and an inert gas supply means. Is a nitrogen separation generator. 2. A method for operating a fuel cell system comprising a nitrogen separation generator for separating nitrogen from air, wherein when the system is started, generated nitrogen separated from air by the nitrogen separation generator is used. A method for operating a fuel cell system, wherein the inside of the fuel cell system is purged. 3. Following the purging, the fuel is burned using oxygen-enriched air in which nitrogen has been separated and the oxygen concentration has been increased by a nitrogen separation generator, and the heat of combustion burns the desired portion of the fuel cell system. The method for operating a fuel cell system according to claim 2, wherein the fuel cell system is heated. 4. When heating a desired portion of the fuel cell system by the combustion heat, heat exchange is performed between combustion gas obtained by burning fuel using oxygen-enriched air and generated nitrogen. The method for operating a fuel cell system according to claim 3, wherein the generated nitrogen is heated, and the heated generated nitrogen is caused to flow to a desired portion in the fuel cell system. 5. A method for operating a fuel cell system comprising a nitrogen separation generator for separating nitrogen from air, wherein when the system is stopped, the generated nitrogen separated from air by the nitrogen separation generator is used. A method for operating a fuel cell system, wherein the inside of the fuel cell system is purged.