JPH09115541A - Fuel cell system and operation method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve over all energy efficiency by improving hydrogen utilization rate in a system without reducing the power generation efficiency of a fuel cell. SOLUTION: A fuel cell system is provided with a reformer 20 which receives methane, carbon dioxide, and water to produce a fuel gas containing hydrogen and carbon dioxide as main components and a fuel cell 30 which receives the fuel gas produced by the reformer 20 and generates electricity. An exhaust gas contained in a fuel gas system exhausted from the fuel cell 30 is supplied to the reformer 20 as a carbon dioxide. Hydrogen which has not been used for power generation is intermingled in the exhaust gas in the fuel gas system, but the hydrogen passes through the reformer 20 and is supplied to the fuel cell 30 as it is. As a result, a hydrogen utilization rate can be improved in the 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 and a method of operating the same, and more specifically, a reformer for producing a fuel gas containing hydrogen and carbon dioxide as a main component from a hydrocarbon, and the produced fuel gas. TECHNICAL FIELD The present invention relates to a fuel cell system including a fuel cell that generates electric power using hydrogen in the fuel, and an operating method thereof.

[0002]

2. Description of the Related Art Conventionally, as a fuel cell system of this type, a reformer for producing a fuel gas containing hydrogen as a main component from natural gas, and a fuel gas produced by the reformer are supplied. A fuel cell system including a fuel cell for generating power has been proposed (for example, JP-A-5-114414).
No.).

The reformer of this system uses so-called steam reforming reaction represented by the following formula (1) using natural gas and water (steam) as raw materials, and carbon monoxide and water by-produced by this steam reforming reaction. By the so-called shift reaction represented by the following formula (2) with (water vapor), the fuel gas containing hydrogen and carbon dioxide as main components is generated by the following formula (3) as a whole. Since these reactions are endothermic reactions as a whole, the reformer is provided with a burner for heating the reaction part in order to supply heat (energy) necessary for this reaction.

[0004]

(Equation 1)

The fuel gas thus generated is supplied to the fuel cell. However, in order to improve the power generation efficiency of the fuel cell, that is, in the electrode portion arranged near the fuel gas outlet of the fuel cell, other fuel gas is used. In the same manner as the part, the electrochemical reaction shown in the following formulas (4) and (5) is performed to generate power,
A fuel gas is supplied which has an excess hydrogen amount of about 20 to 30% with respect to the hydrogen amount required by the fuel cell. Therefore, the exhaust gas of the fuel gas system discharged from the fuel cell contains unused hydrogen gas. In the above system, the exhaust gas of the fuel gas system is sent to the burner that heats the reaction part of the reformer, and unused hydrogen in the exhaust gas is burned as fuel.

[0006]

(Equation 2)

[0007]

However, if the unused hydrogen in the exhaust gas is used as the fuel for heating the reaction part of the reformer, the energy efficiency as a whole is lowered. there were. The unused hydrogen in the exhaust gas is generated by the endothermic reaction from natural gas, and therefore, due to the endothermic effect compared to the case where natural gas is used as it is as a fuel for heating the reaction part of the reformer. The energy generated by combustion is reduced by the amount of energy.

To solve these problems, it is sufficient if the amount of fuel gas supplied to the fuel cell can be set to the amount required for power generation.
In this case, a sufficient amount of hydrogen necessary for the electrochemical reaction is not supplied to the electrode portion arranged near the fuel gas outlet of the fuel cell, which lowers the power generation efficiency of the fuel cell.

An object of the fuel cell system and its operating method of the present invention is to improve the hydrogen utilization rate in the system and improve the energy efficiency as a whole without lowering the power generation efficiency of the fuel cell.

[0010]

Means for Solving the Problem and Its Action / Effect The fuel cell system of the present invention comprises a first reaction part for producing an intermediate gas containing hydrogen and carbon monoxide as main components from hydrocarbon and carbon dioxide. A hydrocarbon reformer having a second reaction part for producing a fuel gas containing hydrogen and carbon dioxide as main components from the produced intermediate gas and water, and the fuel gas produced by the hydrocarbon reformer And a fuel cell for generating electricity using hydrogen in the fuel gas as a fuel, wherein at least a part of the exhaust gas of the fuel gas system discharged from the fuel cell is the hydrocarbon. It is a gist to provide an exhaust gas supply means for supplying the first reaction section of the reformer as a part of a raw material for generating the intermediate gas.

In this fuel cell system, the first reaction section of the hydrocarbon reformer produces an intermediate gas containing hydrogen and carbon monoxide as main components from the supplied hydrocarbon and carbon dioxide, and The second reaction section of the reformer produces a fuel gas containing hydrogen and carbon dioxide as main components from the produced intermediate gas and water. The fuel cell is supplied with the fuel gas generated by the hydrocarbon reformer, and uses the hydrogen in the fuel gas as fuel to generate electricity. Then, the exhaust gas supply means supplies at least a part of the exhaust gas of the fuel gas system discharged from the fuel cell to the first reaction section of the hydrocarbon reformer as a part of the raw material for generating the intermediate gas.

Here, the exhaust gas of the fuel gas system contains carbon dioxide which is the main component of the fuel gas and hydrogen which has not been used in the fuel cell. Therefore, by supplying a part of the exhaust gas of the fuel gas system to the first reaction section of the hydrocarbon reformer, carbon dioxide in the exhaust gas can be reused as a raw material. Moreover, since hydrogen not used in the fuel cell passes through the hydrocarbon reforming section as it is and is supplied to the fuel cell together with the fuel gas, the hydrogen consumed by the fuel cell relative to the amount of hydrogen produced by the hydrocarbon reformer. The utilization rate of hydrogen, which is the ratio of the amounts, can be increased, and the operating efficiency can be improved.

In the fuel cell system of the present invention,
A hydrogen separation means for separating hydrogen from the exhaust gas of the fuel gas system discharged from the fuel cell; and a hydrogen supply means for supplying the separated hydrogen as fuel to the fuel cell,
The exhaust gas supply means uses at least a part of the residual gas from which hydrogen has been separated by the hydrogen separation means, as a part of a raw material that produces the intermediate gas in the first reaction section of the hydrocarbon reformer. It is also possible to adopt a mode that is a supply means.

In this aspect, the hydrogen separating means separates hydrogen from the exhaust gas of the fuel gas system discharged from the fuel cell,
The hydrogen supply means supplies the separated hydrogen to the fuel cell as a fuel. Then, the exhaust gas supply means supplies at least a part of the residual gas from which the hydrogen has been separated by the hydrogen separation means, as a part of the raw material for producing the intermediate gas to the first reaction section of the hydrocarbon reformer.

According to this aspect, since hydrogen in the fuel gas system is separated and supplied to the fuel cell as fuel, the utilization rate of hydrogen in the fuel cell system can be increased and the operating efficiency can be improved. it can. Of course, since at least a part of the residual gas from which hydrogen has been separated is supplied to the first reaction section of the hydrocarbon reformer, carbon dioxide in the exhaust gas can be reused.

In the fuel cell system, hydrogen separating means for separating hydrogen from the residual exhaust gas not supplied to the first reaction section of the hydrocarbon reformer by the exhaust gas supply means, and the separated hydrogen separating means. A hydrogen supply means for supplying hydrogen to the fuel cell as a fuel may be used.

In this aspect, the hydrogen separation means separates hydrogen from the residual exhaust gas that has not been supplied to the first reaction section of the hydrocarbon reformer by the exhaust gas supply means, and the hydrogen supply means separates this. Hydrogen is supplied to the fuel cell as fuel. According to this aspect, the hydrogen in the residual exhaust gas that has not been supplied to the first reaction section of the hydrocarbon reformer by the exhaust gas supply means is separated and supplied to the fuel cell as fuel, so that the hydrogen in the fuel cell system is used. It is possible to increase the utilization rate of the fuel cell and improve the operation efficiency.

The fuel cell system is provided with a carbon dioxide separating means for separating carbon dioxide from the exhaust gas of the fuel gas system discharged from the fuel cell, and the exhaust gas supplying means is the carbon dioxide separating means. A mode in which at least a part of carbon is supplied to the first reaction section of the hydrocarbon reformer as a part of a raw material for generating the intermediate gas may be adopted.

In this aspect, the carbon dioxide separating means separates carbon dioxide from the exhaust gas of the fuel gas system discharged from the fuel cell, and the exhaust gas supplying means at least part of the carbon dioxide separated by the carbon dioxide separating means. Is supplied to the first reaction section of the hydrocarbon reformer as a part of the raw material for generating the intermediate gas. According to this aspect, carbon dioxide in the exhaust gas can be reused.

In the fuel cell system including the carbon dioxide separating means, the residual gas supply means for supplying the residual gas obtained by separating the carbon dioxide by the carbon dioxide separating means to the fuel cell as a fuel may be adopted. it can. With this, hydrogen contained in the exhaust gas is supplied to the fuel cell as a fuel, so that the utilization rate of hydrogen in the fuel cell system can be increased and the operation efficiency can be further improved.

In the fuel cell system according to each of these aspects, the hydrocarbon reformer is provided with a selective oxidation reaction section that selectively oxidizes carbon monoxide in the fuel gas into carbon dioxide. You can also In this way, the system can be configured with a fuel cell of a type having an extremely low allowable concentration of carbon monoxide in the fuel gas.

In the fuel cell system, the hydrocarbon may be methane or a gas containing a plurality of compounds having different carbon numbers.

The operating method of the fuel cell system of the present invention is as follows:
A first reaction section for producing an intermediate gas containing hydrogen and carbon monoxide as main components from hydrocarbon and carbon dioxide, and a fuel gas containing hydrogen and carbon dioxide as main components from the produced intermediate gas and water A fuel comprising a hydrocarbon reformer having a second reaction part for producing hydrogen and a fuel cell for receiving the supply of the fuel gas produced by the hydrocarbon reformer and generating electricity using hydrogen in the fuel gas as fuel. A method of operating a battery system,
At least a part of the exhaust gas of the fuel gas system discharged from the fuel cell is supplied to the first reaction section of the hydrocarbon reformer as a part of a raw material for generating the intermediate gas. .

According to this operating method, the exhaust gas of the fuel gas system contains carbon dioxide, which is the main component of the fuel gas, and hydrogen that has not been used in the fuel cell. By supplying to the first reaction section of the hydrocarbon reformer, carbon dioxide in the exhaust gas can be reused as a raw material. Moreover, since hydrogen that has not been used in the fuel cell passes through the hydrocarbon reforming section as it is and is supplied to the fuel cell together with the fuel gas, it is possible to increase the utilization rate of hydrogen in the fuel cell system and improve the operating efficiency. You can get better.

[0025]

Next, embodiments of the present invention will be described based on examples. FIG. 1 is a block diagram illustrating a schematic configuration of a fuel cell system 10 that is a preferred embodiment of the present invention. As shown, the fuel cell system 1
0 is a methane tank 12 that stores methane, a water tank 14 that stores water, and a reformer that reforms methane supplied from the methane tank 12 to generate a fuel gas containing hydrogen and carbon dioxide as main components. Oxidizing gas (for example, air) containing oxygen and the fuel gas produced in the reformer 20
And a reformer 20 for generating power by receiving the supply of
And an electronic control unit 40 that controls the operation of the fuel cell 30.

The reformer 20 receives the supply of methane from the methane tank 12 and the exhaust gas of the fuel gas system discharged from the fuel cell 30, and produces carbon monoxide and hydrogen according to the reaction equation shown in the following equation (6). The reforming reaction part 22 for generating a reformed gas containing as a main component, carbon monoxide in the reformed gas, and water supplied from the water tank 14 are converted into carbon dioxide and hydrogen by the reaction formula shown in Formula (7). And the shift reaction part 24 which uses the reformed gas as the fuel gas, and the minute amount of carbon monoxide which cannot be completely reacted in the shift reaction part 24 and remains in the fuel gas is selected by oxygen in the air supplied by the blower 27. Which is selectively oxidized to reduce carbon monoxide concentration in the fuel gas as carbon dioxide, and a fuel which is provided in a connecting pipe between the shift reaction section 24 and the selective oxidation section 28 and which is generated by the shift reaction section 24 Monoxide in gas And a carbon monoxide sensor 26 for detecting the oxygen concentration. The overall reaction including the reaction of the reforming reaction section 22 and the reaction of the shift reaction section 24 is as shown in formula (8).

[0027]

(Equation 3)

The reforming reaction section 22 is filled with a catalyst (for example, a Ni-based catalyst) that promotes the reaction of the above formula (6).
Further, since the reaction of the formula (6) is an endothermic reaction, the reforming reaction section 22 is supplied in order to supply the heat amount necessary for this reaction.
Includes a combustor 23 that combusts methane supplied from the methane tank 12 and a part of the exhaust gas of the fuel gas system discharged from the fuel cell 30. In addition, the reforming reaction section 22
Although not shown, includes a temperature sensor that detects the temperature inside the reaction unit. The reforming reaction section 22 is connected to the electronic control unit 40 by a signal line, and the electronic control unit 40 operates to keep the operating temperature of the reforming reaction section 22 at a predetermined temperature (750 ° C. in the case of the embodiment). The temperature control and the supply amount control of the methane and the exhaust gas of the fuel gas system to the reforming reaction section 22 are performed. The operation temperature control of the reforming reaction section 22 is performed by controlling the supply amount of methane to the combustion section 23 based on the temperature inside the reaction section detected by the temperature sensor.

The shift reaction section 24 is filled with a catalyst (for example, a Cu--ZnO type catalyst) that promotes the reaction of the above formula (7). Although not shown, the shift reaction unit 24 includes a temperature sensor that detects the temperature inside the reaction unit and a temperature adjustment mechanism (for example, a heat exchanger) that adjusts the temperature inside the reaction unit. The shift reaction unit 24 is connected to the electronic control unit 40 by a signal line, and the electronic control unit 40 controls the operating temperature of the shift reaction unit 24 to a predetermined temperature (250 ° C. in the embodiment) and The amount of water supplied to the shift reaction unit 24 is controlled. In the operating temperature control performed in the shift reaction section 24 of the embodiment, the reforming gas supplied to the shift reaction section 24 is maintained at a temperature of about 750 ° C. by keeping the reforming reaction section 22 at 750 ° C. And that equation (7) is an exothermic reaction,
The flow rate of cooling water circulated through the heat exchanger is adjusted to control the inside of the reaction section.

The selective oxidizer 28 is filled with a catalyst (for example, Ru-based catalyst) that preferentially performs the oxidation reaction of a small amount of carbon monoxide in the hydrogen-rich gas over the oxidation reaction of hydrogen. Although not shown, the selective oxidation unit 28 includes a temperature sensor that detects the temperature inside the reaction unit and a temperature adjustment mechanism (for example, a heat exchanger) that adjusts the temperature inside the reaction unit. The selective oxidation unit 28 is connected to the electronic control unit 40 by a signal line, and by the electronic control unit 40,
An operating temperature control for maintaining the operating temperature of the selective oxidation section 28 at a predetermined temperature (90 ° C. in the case of the embodiment) and an introduction amount of air from the blower 27 to the selective oxidation section 28 are performed. The operating temperature control performed in the selective oxidation section 28 of the embodiment is such that the shift reaction section 24 is kept at 250 ° C., and therefore the cooling is circulated to the heat exchanger in the same manner as the operating temperature control in the shift reaction section 24. The control is to cool the inside of the reaction part by adjusting the flow rate of water. In addition, the introduction amount of air is controlled by detecting the carbon monoxide concentration in the fuel gas generated by the shift reaction unit 24 by the carbon monoxide sensor 26, and the oxygen amount according to the detected carbon monoxide concentration, that is, the fuel gas. The amount of air that is sufficient to oxidize all of the carbon monoxide in the carbon dioxide into carbon dioxide is calculated, and based on this calculation result, a valve for an air inlet (not shown) provided in the selective oxidation unit 28. This is done by adjusting the opening degree of.

The fuel cell 30 is a polymer electrolyte fuel cell, and has the structure shown in FIG. 2 as its single cell structure. As shown in the figure, the cell contains an electrolyte membrane 31, which is a proton conductive membrane formed of a solid polymer material such as a fluororesin, and a catalyst of platinum or an alloy of platinum and another metal. Anode 3 serving as a gas diffusion electrode having a sandwich structure in which an electrolyte membrane 31 is sandwiched by a surface formed of carbon cloth and containing a catalyst.
2 and a cathode 33, and a separator 34 that forms a flow path of a fuel gas and an oxidizing gas with the anode 32 and the cathode 33 while sandwiching the sandwich structure from both sides.
35, and a collector plate 36 disposed outside the separators 34, 35 and serving as a collector electrode for the anode 32 and the cathode 33,
And 37. In FIG. 2, the configuration of a single cell of the fuel cell 30 is shown for the sake of description, but in reality, a plurality of separators 34, an anode 32, an electrolyte membrane 31, a cathode 33, and a separator 35 are laminated in this order, and the lamination is performed. The fuel cell 30 is configured by disposing the current collector plates 36 and 37 at the ends. Although not shown, the fuel cell 30 includes a temperature sensor that detects the internal temperature and a temperature adjustment mechanism, and the operating temperature is controlled by the electronic control unit 40.

The inlet of the fuel gas system of the fuel cell 30 is connected to the reformer 20 by a fuel gas supply pipe 29, and the fuel gas generated in the reformer 20 is supplied through the fuel gas supply pipe 29. To be done. The outlet of the fuel gas system exhaust gas of the fuel cell 30 is connected to the supply port of the reforming reaction section 22 of the reformer 20 by an exhaust gas supply pipe 38, and the fuel gas system exhaust gas is connected to the reforming reaction section 22. Is supplied to. Further, a branch pipe 38B is branched to the exhaust gas supply pipe 38, and the residual exhaust gas supplied to the reforming reaction part 22 is supplied to the combustion part 23 of the reforming reaction part 22 and burned. .

The electronic control unit 40 is configured as a logic circuit centering on a microcomputer, and more specifically, a CPU 42 that executes a predetermined calculation and the like according to a preset control program, and various calculation processes are executed by the CPU 42. ROM 44 in which control programs and control data necessary for the above are stored in advance, RAM 46 in which various data necessary for executing various arithmetic processing in the CPU 42 are temporarily read and written, and detection signals from various sensors of each unit. And an input / output port 48 for outputting a drive signal to each section according to the calculation result in the CPU 42.

Next, the operation of the fuel cell system 10 thus constructed will be described. If the fuel cell 30 can use all the hydrogen in the supplied fuel gas for power generation, the fuel cell 30 calculates the amount of hydrogen consumed by the fuel cell 30, and calculates the calculated hydrogen amount. It is sufficient to supply the fuel gas that becomes In this case, the reforming reaction unit 22 is supplied with the amounts of methane and carbon dioxide that generate the calculated amount of hydrogen. However, the fuel cell 30
In order to make each of the cells composing the fuel cell evenly and efficiently generate power in any part of each cell, a fuel gas having a hydrogen amount that is about 20 to 30% more than the hydrogen amount consumed in the fuel cell 30 is used. It is necessary to supply the fuel cell 30. Therefore, the exhaust gas of the fuel gas system discharged from the fuel cell 30 contains hydrogen not used in the fuel cell 30.

In the fuel cell system 10, the amount of methane supplied to the reforming reaction section 22 is 1 [mol / min] and the amount of carbon dioxide and hydrogen contained in the exhaust gas of the fuel gas system discharged from the fuel cell 30. It is assumed that the amounts are 2 [mol / min] and 2α [mol / min], respectively, in a steady operation state. With respect to 1 [mol / min] methane supplied to the reforming reaction section 22, the equivalent amount of carbon dioxide in the reaction of the above formula (6) is 1
Since it is [mol / min], half of the exhaust gas of the fuel gas system discharged from the fuel cell 30 is supplied to the reforming reaction section 22. Therefore, the reforming reaction section 22 has 1
As [mol / min] carbon dioxide is supplied, α [mol / min] hydrogen is supplied. Reforming reaction section 2
The hydrogen of α [mol / min] supplied to 2 is supplied to the reforming reaction section 22.
And 1 [mol / min] of methane and 1 [mol / min] of carbon dioxide react with 2 [mol / min] of carbon monoxide and 2 [mol / min] by the reaction of the above formula (6). Therefore, 2 [mol / min] of carbon monoxide and (2 + α) [mol / min] of hydrogen are supplied to the shift reaction part 24. The other half of the exhaust gas of the fuel gas system discharged from the fuel cell 30 is the combustion part 23 of the reforming reaction part 22.
The hydrogen contained in the exhaust gas is burned in the combustion section 23.

In addition to 2 [mol / min] of carbon monoxide and (2 + α) [mol / min] of hydrogen, the shift reaction section 24 has 2
[Mol / min] water is supplied. Carbon monoxide and water supplied to the shift reaction unit 24 are converted into 2 by the reaction of the above formula (7).
It becomes [mol / min] carbon dioxide and 2 [mol / min] hydrogen, and (2 + α) [mol / min] hydrogen passes through the shift reaction section 24 as it is. Therefore, the selective oxidation unit 28
2 (mol / min) of carbon dioxide and (4 + α) [mol / min] of hydrogen are introduced into. The carbon monoxide concentration in the fuel gas introduced into the selective oxidation unit 28 is
It is extremely small compared to hydrogen concentration and carbon dioxide concentration,
The amounts of carbon dioxide and hydrogen supplied to the fuel cell 30 may be considered to be the same as those introduced into the selective oxidation section 28. Actually, the amount of carbon dioxide increases by the amount of carbon monoxide oxidized in the selective oxidation unit 28, and the selective oxidation unit 2
When the amount of oxygen introduced into 8 is excessive, hydrogen corresponding to the excessive amount is oxidized, so that the amount of hydrogen is reduced by this amount.

In the fuel cell 30, (4-α) [mol / in the fuel gas supplied in each cell constituting the fuel cell 30]
Min] hydrogen is consumed by the electrochemical reaction of the above formulas (4) and (5) to generate electricity, and 2 [mol / min] carbon dioxide and 2
The hydrogen of α [mol / min] is discharged.

Here, the hydrogen amount α [mol / min] supplied to the reforming reaction section 22 is a ratio of the hydrogen amount consumed in the fuel cell 30 to the hydrogen amount in the fuel gas supplied to the fuel cell 30. It is expressed by the following equation (9) using a certain hydrogen consumption rate S. For example, when the hydrogen consumption rate S is 80%, the hydrogen amount α is 0.444 [mol / min]. Therefore,
Fuel cell 3 for the amount of hydrogen produced by the reformer 20
The hydrogen utilization rate R, which is the ratio of the amount of hydrogen consumed by 0, is
It is expressed by the following equation (10). For example, when the hydrogen consumption rate S is 80%, the hydrogen utilization rate R becomes 88.9%, and the hydrogen utilization rate R of the type in which the entire amount of the fuel gas system exhaust gas discharged from the fuel cell 30 is introduced into the combustion section 23. 8
Hydrogen can be used more efficiently than 0%.

Α = 4 (100−S) / (100 + S) (9) R = {1− (α / 4)} × 100 (10)

The fuel cell system 1 of the embodiment described above
According to 0, a part of the exhaust gas of the fuel gas system discharged from the fuel cell 30 can be reused. Moreover, since hydrogen contained in the exhaust gas of the fuel gas system is supplied to the fuel cell 30 again, the hydrogen utilization rate R in the system can be increased, and the energy efficiency as a whole can be further increased.

In the fuel cell system 10 of the embodiment, the fuel cell 30 is constructed as a polymer electrolyte fuel cell.
The fuel cell is not limited to the solid polymer type, and may be any type of fuel cell as long as it is a fuel cell using hydrogen as a fuel, such as a phosphoric acid type fuel cell. In this case, in the fuel cell system 10 of the embodiment, the reformer 20 is configured to include the selective oxidation unit 28. However, the fuel cell 30 is a fuel cell of a type having a high allowable concentration of carbon monoxide (for example, a phosphoric acid type). In a fuel cell or the like), it is not necessary to make the carbon monoxide concentration extremely small, and thus the reformer 20 may not have the selective oxidation unit 28. The reformer that does not include the selective oxidation unit 28 does not need to detect the carbon monoxide concentration in the fuel gas, and thus does not need to include the carbon monoxide sensor 26.

Further, in the fuel cell system 10 of the embodiment, methane is supplied as a raw material of the reformed gas generated in the reforming reaction section 22, but paraffin hydrocarbon such as ethane or propane is supplied as a raw material. Alternatively, it may be configured such that an olefinic hydrocarbon such as ethylene or propylene, an acetylene hydrocarbon, or an aromatic hydrocarbon is used as a raw material. Further, a single hydrocarbon may be supplied to the reforming reaction section 22 as a raw material, or a mixed gas of plural kinds of hydrocarbons may be supplied to the reforming reaction section 22. For example, natural gas containing methane as a main component may be supplied as it is. As described above, when a hydrocarbon other than methane is supplied to the reforming reaction section 22 or a mixed gas of a plurality of kinds of hydrocarbons including methane is supplied to the reforming reaction section 22, the above formulas (6) to (8) are used. ) Instead of the following formula (1
From 1) to (13), the amount of carbon dioxide equivalent to the amount of hydrocarbons supplied to the reforming reaction section 22 is calculated,
The fuel gas-type exhaust gas discharged from the fuel cell 30 is supplied so as to achieve this amount.

[0043]

(Equation 4)

Next, a fuel cell system 10B which is a second embodiment of the present invention will be described. FIG. 3 is a block diagram illustrating the outline of the configuration of the fuel cell system 10B of the second embodiment. As shown in the figure, the fuel cell system 10B of the second embodiment has the same configuration as the fuel cell system 10 of the first embodiment except that it includes a hydrogen separator 50 that separates hydrogen from the exhaust gas of the fuel gas system. Are doing Therefore, of the constitutions of the fuel cell system 10B of the second embodiment, the same constitutions as those of the fuel cell system 10 of the first embodiment are designated by the same reference numerals, and the description thereof will be omitted.

The hydrogen separator 50 included in the fuel cell system 10B of the second embodiment is connected to the fuel cell 30 through the exhaust gas supply pipe 38, and receives the fuel gas system exhaust gas from the fuel cell 30. Further, the hydrogen separator 50 is connected to the fuel gas supply pipe 29 for supplying the fuel gas from the reformer 20 to the fuel cell 30 by the hydrogen supply pipe 52, and hydrogen separated from the exhaust gas of the fuel gas system is The fuel gas is injected into the fuel gas in the fuel gas supply pipe 29. The hydrogen separator 50 is connected to the reforming reaction section 22 of the reformer 20 by a residual gas supply pipe 54, and the residual gas obtained by separating hydrogen from the exhaust gas of the fuel gas system via the residual gas supply pipe 54. (Residual gas) is supplied to the reforming reaction section 22. The residual gas supply pipe 54 is provided with a branch pipe 54B, and an excess gas of the residual gas, which is equal to or more than the amount required by the reforming reaction section 22, is discharged to the outside air by the branch pipe 54B.

FIG. 4 is an explanatory view illustrating the outline of the configuration of the hydrogen separator 50. The hydrogen separator 50 is an exhaust gas chamber 50 into which the exhaust gas of the fuel gas system is introduced from the exhaust gas supply pipe 38.
a, a hydrogen chamber 50b for separating hydrogen from the exhaust gas of the fuel gas system, and a hydrogen permeable membrane 50c forming partition walls of the exhaust gas chamber 50a and the hydrogen chamber 50b. Hydrogen permeable membrane 5
0c is formed of a palladium alloy into a film having a thickness of 50 to 80 μm. The state of hydrogen separation by the hydrogen permeable membrane 50c will be described below with reference to FIG.

Hydrogen molecules in the exhaust gas introduced into the exhaust gas chamber 50a are dissociated into two hydrogen atoms on the surface of the hydrogen permeable film 50c, releasing electrons to the hydrogen permeable film 50c and stored as protons (hydrogen ions). To be done. It is well known that hydrogen absorption by such a palladium alloy is well known.
The protons stored in the hydrogen permeable membrane 50c are stored in the exhaust gas chamber 5
Due to the concentration difference (partial pressure difference) between the hydrogen concentration (hydrogen partial pressure) of 0a and the hydrogen concentration (hydrogen partial pressure) of the hydrogen chamber 50b, the hydrogen permeable film 50c moves from the higher hydrogen concentration to the lower hydrogen concentration. Now, if hydrogen in the hydrogen chamber 50b is supplied to the fuel cell 30 through the hydrogen supply pipe 52 to reduce the hydrogen concentration in the hydrogen chamber 50b, protons pass through the hydrogen permeable membrane 50c from the exhaust gas chamber 50a side to the hydrogen chamber 50b side. Moving. The protons that have moved inside the hydrogen permeable membrane 50c are stored in the hydrogen chamber 50 of the hydrogen permeable membrane 50c.
On the b-side surface, electrons emitted on the opposite side are obtained and appear as hydrogen atoms on the surface of the hydrogen permeable membrane 50c, and two hydrogen atoms become hydrogen molecules using the palladium alloy (hydrogen permeable membrane 50c) as a catalyst, and the hydrogen permeable membrane 50c. Get away from.

From this principle of hydrogen separation, in order to improve the efficiency of hydrogen separation by the hydrogen separator 50, the contact area between the hydrogen permeable membrane 50c and the exhaust gas should be increased so that the exhaust gas chamber 5
It is easily understood that the pressure of 0a should be set higher than that of the hydrogen chamber 50b. For example, the hydrogen permeable membrane 50c may be formed of a palladium alloy into a tube shape having a diameter of about 1 mm, and the exhaust gas may be pressure-fed to this tube.
In such a case, the inside of the tube becomes the exhaust gas chamber 50a, and the outside of the tube becomes the hydrogen chamber 50b.

Next, the operation of the fuel cell system 10B of the second embodiment thus constructed will be described. In addition,
Since the operation is basically the same as the operation of the fuel cell system 10 of the first embodiment, detailed description of the same operation points will be omitted.

Now, the fuel cell system 10 of the second embodiment.
B indicates that the amount of methane supplied to the reforming reaction section 22 is 1 [mol / min] and the amount of carbon dioxide and hydrogen contained in the exhaust gas of the fuel gas system discharged from the fuel cell 30 are 2 [mol / min], respectively. And β [mol / min] in a steady operation state. In the reforming reaction section 22, one from the methane tank 12
[Mole / min] methane and 1 [mol / min] carbon dioxide are supplied from the hydrogen separator 50 through the residual gas supply pipe 54. The residual gas supplied from the hydrogen separator 50 does not contain hydrogen because hydrogen has been separated by the hydrogen separator 50, and is a gas containing only carbon dioxide. Actually, it is difficult to completely separate the total amount of hydrogen in the exhaust gas by the hydrogen separator 50, and thus some hydrogen may be mixed in the residual gas.

In the reformer 20, the reaction of the above equation (6) is carried out in the reforming reaction section 22 and the reaction of the above equation (7) is carried out in the shift reaction section 24, so that 2 [mol / min] of carbon dioxide is obtained. And 4 [mol / min] of hydrogen is produced. In the fuel gas supply pipe 29,
Since β [mol / min] of hydrogen in the exhaust gas of the fuel gas system separated by the hydrogen separator 50 is injected, 2 [mol / min] carbon dioxide and (4 + β) [mol] are injected into the fuel cell 30. /
Min] hydrogen will be supplied. In the fuel cell 30, 4 [mol / min] hydrogen in the fuel gas is used for power generation and consumed, and 2 [mol / min] carbon dioxide and β [mol / min] hydrogen are discharged. As described above, 2 [mol / min] carbon dioxide and β [mol / min] hydrogen discharged from the fuel cell 30 are separated by the hydrogen separator 50 to be β [mol / min] hydrogen. Is press-fitted into the fuel gas supply pipe 29 by the hydrogen supply pipe 52, 1 [mol / min] of 2 [mol / min] carbon dioxide is supplied to the reforming reaction part 22, and the remaining 1 [mol / min] Carbon dioxide of the branch pipe 54B
Is discharged to the outside air.

The amount of hydrogen β discharged from the fuel cell 30 by the above operation is represented by the following equation (14) using the hydrogen consumption rate S of the fuel cell 30, and for example, the hydrogen consumption rate S is 8
When it is 0%, it becomes 1 [mol / min]. Further, the hydrogen utilization rate R of the fuel cell system 10B is 100% because the total amount of hydrogen produced by the reformer 20 is consumed by the fuel cell 30.

Β = 400 / S-4 (14)

Since it is difficult to completely separate the total amount of hydrogen in the exhaust gas by the hydrogen separator 50 as described above, some hydrogen may be mixed in the residual gas. In this case, , A small amount of hydrogen is supplied to the reforming reaction section 22 together with carbon dioxide, and a small amount of hydrogen is discharged to the outside air through the branch pipe 54B together with carbon dioxide.
Does not reach 100%. In this case, it is preferable that the branch pipe 54B is connected to the combustion section 23 of the reforming reaction section 22, and a certain amount of hydrogen is burned and then discharged to the outside air.

According to the fuel cell system 10B of the second embodiment described above, the hydrogen in the exhaust gas of the fuel gas system discharged from the fuel cell 30 is separated and supplied again to the fuel cell 30 as a fuel. The utilization rate of hydrogen in the battery system 10 can be improved, and the energy efficiency as a whole can be further enhanced. Moreover, the residual gas (remaining gas) after hydrogen is separated can be reused as the raw material for generating the reformed gas in the reforming reaction section 22 of the reformer 20.

In the second embodiment, the entire amount of the fuel gas-type exhaust gas discharged from the fuel cell 30 is introduced into the hydrogen separator 50 to separate the hydrogen in the exhaust gas, which is shown in the fuel cell system 10C of FIG. As described above, half of the exhaust gas may be directly supplied to the reforming reaction section 22, and the other half may be introduced into the hydrogen separator 55. The hydrogen separator 55 is the second
Hydrogen separator 5 included in the fuel cell system 10B of the embodiment
It has the same configuration as 0.

In this fuel cell system 10C, half of the exhaust gas of the fuel gas system discharged from the fuel cell 30 is directly supplied to the reforming reaction section 22, so that 1 [mol / min].
(Β / 2) [mol / min] hydrogen is supplied along with the supply of carbon dioxide. The hydrogen supplied to the reforming reaction section 22 is directly used for the reforming reaction section 22 and the shift reaction section 2
4 and the selective oxidation unit 28, the reformer 20 supplies 2 [mol / min] carbon dioxide and (4 + β / 2) [mol / min] hydrogen as fuel gas. . On the other hand, the hydrogen separator 55 separates half of the introduced exhaust gas of the fuel gas system into (β / 2) [mol / min] hydrogen and 1 [mol / min] carbon dioxide. The separated hydrogen is pressed into the fuel gas supply pipe 29 by the hydrogen supply pipe 58,
The carbon dioxide is discharged to the outside air through the exhaust pipe 59. Therefore, 2 [mol / min] carbon dioxide and (4 + β) [mol / min] hydrogen are supplied to the fuel cell 30.

According to the fuel cell system 10C, which is a modified example of the second embodiment described above, only half of the exhaust gas of the fuel gas system needs to be separated by the hydrogen separator 55, so the hydrogen separator 50 for separating the entire amount. It can be made smaller than. Of course, the hydrogen utilization rate R in the fuel cell system 10C can be improved and the energy efficiency can be further increased.

Next, a fuel cell system 10D which is a third embodiment of the present invention will be described. FIG. 7 is a block diagram illustrating the outline of the configuration of the fuel cell system 10D of the third embodiment. As shown in the figure, the fuel cell system 10D of the third embodiment includes a carbon dioxide separator 60 that separates carbon dioxide from a fuel gas exhaust gas, instead of the hydrogen separator 50 that separates hydrogen from a fuel gas exhaust gas. The fuel cell system 10B has the same configuration as that of the fuel cell system 10B of the second embodiment except that it is provided. Therefore, of the constitutions of the fuel cell system 10D of the third embodiment, the same constitutions as those of the fuel cell system 10B of the second embodiment are designated by the same reference numerals, and the description thereof will be omitted.

The carbon dioxide separator 60 included in the fuel cell system 10D of the third embodiment is connected to the fuel cell 30 through the exhaust gas supply pipe 38 and receives the supply of the fuel gas system exhaust gas from the fuel cell 30. Further, the carbon dioxide separator 60 is connected to the reforming reaction section 22 of the reformer 20 by the carbon dioxide supply pipe 66, and supplies the carbon dioxide separated from the exhaust gas of the fuel gas system to the reforming reaction section 22. To do. A branch pipe 67 is provided in the carbon dioxide supply pipe 66, and excess carbon dioxide of the separated carbon dioxide in excess of the amount required by the reforming reaction section 22 is released to the outside air through the branch pipe 67. The carbon dioxide separator 60 is connected to the fuel gas supply pipe 29 that supplies the fuel gas from the reformer 20 to the fuel cell 30 through the residual gas supply pipe 68, and separates carbon dioxide from the exhaust gas of the fuel gas system. The remaining residual gas (residual gas) is press-fitted into the fuel gas in the fuel gas supply pipe 29.

FIG. 8 is an explanatory view illustrating the outline of the configuration of the carbon dioxide separator 60. The carbon dioxide separator 60 is
Zeolite that preferentially adsorbs carbon dioxide (synthetic zeolite: trade name "Molecular Sieves" manufactured by Union Carbide Corp. in the United States) is filled with two adsorbents 62A and 62B as carbon dioxide adsorbents, and these two adsorbents 62A and 62B. Adsorption part 6
Inflow valves 63A and 63B provided in the pipes of 2A and 62B and the exhaust gas supply pipe 38, carbon dioxide discharge valves 64A and 64B provided in the pipes of the adsorption units 62A and 62B and the carbon dioxide supply pipe 66, and adsorption The residual gas discharge valves 65A and 65B provided in the pipes of the parts 62A and 62B and the residual gas supply pipe 68 are provided.

As can be seen from the relationship between the adsorption / retention amount of carbon dioxide and temperature in FIG. 9 and the relationship between the adsorption / retention amount of carbon dioxide and pressure in FIG. The amount of adsorbed and retained carbon dioxide increases, and the amount of adsorbed and retained carbon dioxide decreases when the temperature is raised and the pressure is lowered. Therefore, for example, the inflow valve 63A and the residual gas exhaust valve 65A of the adsorption unit 62A are opened, and the carbon dioxide exhaust valve 64A is closed, and at the same time, the adsorption unit 62A.
If the pressure of A is increased and the temperature is lowered, carbon dioxide in the exhaust gas of the fuel gas system is adsorbed by the carbon dioxide adsorbent (zeolite) filled in the adsorption part 62A, and carbon dioxide is discharged from the residual gas discharge valve 65A. Residual gas not containing hydrogen, that is, hydrogen is discharged in the fuel cell system 10. After the carbon dioxide in the exhaust gas is adsorbed by the carbon dioxide adsorbent in this way, the inflow valve 63A and the residual gas exhaust valve 65A of the adsorption part 62A are closed, the carbon dioxide exhaust valve 64A is opened, and the pressure of the adsorption part 62A is adjusted. When the temperature is lowered and the temperature is raised, the carbon dioxide adsorbed on the carbon dioxide adsorbent is released from the carbon dioxide adsorbent and the carbon dioxide exhaust valve 64
Emitted from A.

In the carbon dioxide separator 60 of the embodiment, the inflow valve and the residual gas exhaust valve of one of the two adsorbing parts 62A and 62B are opened, and the carbon dioxide exhaust valve is closed and the pressure of the adsorbing part is closed. At the same time as adsorbing carbon dioxide in the exhaust gas with the carbon dioxide adsorbent filled at a high temperature and a low temperature, the inlet valve and residual gas exhaust valve of the other adsorption part are closed and the carbon dioxide exhaust valve is opened. The pressure is lowered and the temperature is raised to release the carbon dioxide adsorbed by the filled carbon dioxide adsorbent and supply it to the reforming reaction section 22. Then, when a predetermined time has passed,
The operation of each valve and the adjustment of the pressure and temperature of each adsorption part are performed so as to switch between the adsorption part that desorbs carbon dioxide and the adsorption part that adsorbs carbon dioxide. Thus, in the carbon dioxide separator 60, the two adsorption parts 62A,
Since 62B is alternately used for adsorption and desorption of carbon dioxide, carbon dioxide in the exhaust gas of the fuel gas system can be continuously separated.

The operation of the fuel cell system 10D of the third embodiment thus constructed is the operation of the fuel cell system 10B of the second embodiment except that the carbon dioxide separator 60 is operated in place of the hydrogen separator 50. Is the same as. The operation of the carbon dioxide separator 60 is different from that of the hydrogen separator 50 of the second embodiment which separates hydrogen from the exhaust gas of the fuel gas system in that carbon dioxide is separated from the exhaust gas of the fuel gas system, Since the main components of the exhaust gas are carbon dioxide and hydrogen, the separation of one of them has the same result as the separation of the other. Therefore, the fuel cell system 10D of the third embodiment
The ratio of the main components of the gas in each part in the steady operation state is the same as the ratio of the main components of the gas in each part in the steady operation state of the fuel cell system 10B of the second embodiment. Therefore, also in 10D of the third embodiment, as in the fuel cell system 10B of the second embodiment, the hydrogen amount β in the exhaust gas of the fuel gas system discharged from the fuel cell 30 is expressed by the above formula (14). And, for example, the hydrogen consumption rate S of the fuel cell 30 is 80
When it is%, it becomes 1 [mol / min], and the hydrogen utilization rate R of the fuel cell system 10D becomes 100%.

The adsorption part 62 of the carbon dioxide separator 60
It is difficult to completely adsorb carbon dioxide at A and 62B and to press only hydrogen into the fuel gas supply pipe 29 through the residual gas supply pipe. It is necessary to remove carbon dioxide from the adsorption portion that adsorbs carbon dioxide. Since hydrogen in the adsorption unit is supplied to the reforming reaction unit 22 together with carbon dioxide when switching to the operation, some carbon dioxide is actually injected together with hydrogen into the fuel gas supply pipe 29 by the residual gas supply pipe 68, Since some hydrogen is supplied to the reforming reaction section 22 together with carbon dioxide, the hydrogen utilization rate R in the fuel cell system 10D is slightly below 100%. In addition,
In this case, it is preferable that the branch pipe 67 is connected to the combustion section 23 of the reforming reaction section 22, and the mixed hydrogen is burned and then discharged to the outside air.

According to the fuel cell system 10D of the third embodiment described above, the carbon dioxide in the exhaust gas of the fuel gas system discharged from the fuel cell 30 is separated and is fed to the reforming reaction section 22 of the reformer 20. It can be reused as a raw material for producing the reformed gas. Moreover, since the residual gas (remaining gas) after separating the carbon dioxide is supplied again to the fuel cell 30 as fuel, the utilization rate of hydrogen generated by the reformer 20 by the fuel cell 30 can be improved, The energy efficiency as a whole can be further improved.

Although the embodiments of the present invention have been described above, the present invention is not limited to these embodiments. For example, the fuel cell system 1 according to the second embodiment.
0B and its modified fuel cell system 10C, and the fuel cell system 10D of the third embodiment, the reforming reaction section 22 of the reformer 20 is supplied with paraffinic hydrocarbon such as ethane or propane as a raw material. Within a range not departing from the gist of the present invention, such as a constitution using olefin hydrocarbons such as ethylene and propylene or acetylene hydrocarbons or aromatic hydrocarbons as a raw material, a constitution for supplying a mixed gas of plural kinds of hydrocarbons, etc. Of course, it can be implemented in various forms.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a schematic configuration of a fuel cell system 10 that is a preferred embodiment of the present invention.

FIG. 2 is an explanatory diagram illustrating the outline of the configuration of each cell that constitutes the fuel cell 30.

FIG. 3 is a block diagram illustrating a schematic configuration of a fuel cell system 10B according to a second embodiment.

FIG. 4 is an explanatory view illustrating the outline of the configuration of a hydrogen separator 50.

FIG. 5 is an explanatory diagram illustrating a state of hydrogen separation.

FIG. 6 is a fuel cell system 1 which is a modification of the second embodiment.
It is a block diagram which illustrates the outline of a structure of 0C.

FIG. 7 is a block diagram illustrating a schematic configuration of a fuel cell system 10D according to a third embodiment.

FIG. 8 is an explanatory diagram illustrating the schematic configuration of a carbon dioxide separator 60.

FIG. 9 is a graph exemplifying the relationship between the adsorption holding amount of carbon dioxide of zeolite filled in the adsorption units 62A and 62B and the temperature.

FIG. 10 is a graph exemplifying the relationship between the adsorption holding amount of carbon dioxide of the zeolite filled in the adsorption portions 62A and 62B and the pressure.

[Explanation of symbols]

 10 ... Fuel cell system 10B ... Fuel cell system 10C ... Fuel cell system 10D ... Fuel cell system 12 ... Methane tank 14 ... Water tank 20 ... Reformer 22 ... Reforming reaction part 23 ... Combustion part 24 ... Shift reaction part 26 ... Carbon monoxide sensor 27 ... Blower 28 ... Selective oxidation part 29 ... Fuel gas supply pipe 30 ... Fuel cell 31 ... Electrolyte membrane 32 ... Anode 33 ... Cathode 34, 35 ... Separator 36, 37 ... Current collector plate 38 ... Exhaust gas supply pipe 38B ... Branch pipe 40 ... Electronic control unit 42 ... CPU 44 ... ROM 46 ... RAM 48 ... Input / output port 50 ... Hydrogen separator 50a ... Exhaust gas chamber 50b ... Hydrogen chamber 50c ... Hydrogen permeable membrane 52 ... Hydrogen supply pipe 54 ... Residual gas supply Pipe 54B ... Branch pipe 55 ... Hydrogen separator 58 ... Hydrogen supply pipe 59 ... Exhaust pipe 60 ... Carbon dioxide separator 62 , 62B ... adsorption unit 63A, 63B ... inlet valve 64A, 64B ... carbon dioxide exhaust valve 65A, 65B ... residual gas exhaust valve 66 ... carbon dioxide supply tube 67 ... branch pipes 68 ... residual gas supply pipe

Claims (9)

[Claims] 1. A first reaction part for producing an intermediate gas containing hydrogen and carbon monoxide as main components from a hydrocarbon and carbon dioxide, and mainly producing hydrogen and carbon dioxide from the produced intermediate gas and water. A hydrocarbon reformer having a second reaction part for producing a fuel gas as a component, and a fuel for receiving the fuel gas produced by the hydrocarbon reformer and generating electricity using hydrogen in the fuel gas as a fuel A fuel cell system comprising: a battery, wherein at least a part of a fuel gas-type exhaust gas discharged from the fuel cell is generated in the first reaction section of the hydrocarbon reformer. A fuel cell system comprising an exhaust gas supply means for supplying as a part of a raw material. 2. The fuel cell system according to claim 1, wherein hydrogen separating means separates hydrogen from exhaust gas of a fuel gas system discharged from the fuel cell, and the separated hydrogen is supplied to the fuel cell as fuel. The exhaust gas supply means supplies at least a part of the residual gas in which hydrogen has been separated by the hydrogen separation means to the first reaction section of the hydrocarbon reformer. A fuel cell system that is a means of supplying an intermediate gas as a part of a raw material for producing. 3. The fuel cell system according to claim 1, wherein the exhaust gas supply means separates hydrogen from residual exhaust gas not supplied to the first reaction section of the hydrocarbon reformer. A fuel cell system comprising means and hydrogen supply means for supplying the separated hydrogen as fuel to the fuel cell. 4. The fuel cell system according to claim 1, further comprising a carbon dioxide separation unit that separates carbon dioxide from the exhaust gas of the fuel gas system discharged from the fuel cell, wherein the exhaust gas supply unit includes the carbon dioxide. A fuel cell system which is a means for supplying at least a part of carbon dioxide separated by a carbon separating means to the first reaction section of the hydrocarbon reformer as a part of a raw material for producing the intermediate gas. 5. The fuel cell system according to claim 4, further comprising residual gas supply means for supplying the residual gas, from which carbon dioxide has been separated by the carbon dioxide separation means, as fuel to the fuel cell. 6. The fuel cell system according to claim 1, wherein the hydrocarbon reformer includes a selective oxidation reaction unit that selectively oxidizes carbon monoxide in the fuel gas into carbon dioxide. . 7. The hydrocarbon is methane.
7. The fuel cell system according to any one of 6 to 6. 8. The fuel cell system according to claim 1, wherein the hydrocarbon is a gas containing a plurality of compounds having different carbon numbers. 9. A first reaction part for producing an intermediate gas containing hydrogen and carbon monoxide as main components from hydrocarbon and carbon dioxide, and hydrogen and carbon dioxide mainly from the produced intermediate gas and water. A hydrocarbon reformer having a second reaction part for producing a fuel gas as a component, and a fuel for receiving the fuel gas produced by the hydrocarbon reformer and generating electricity using hydrogen in the fuel gas as a fuel A method of operating a fuel cell system including a battery, wherein at least a part of the exhaust gas of a fuel gas system discharged from the fuel cell is supplied to the first reaction section of the hydrocarbon reformer with the intermediate gas. A method of operating a fuel cell system, which is supplied as a part of the raw material produced.