WO2008099575A1 - Fuel cell power generation system and operation method thereof - Google Patents

Fuel cell power generation system and operation method thereof Download PDF

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Publication number
WO2008099575A1
WO2008099575A1 PCT/JP2008/000029 JP2008000029W WO2008099575A1 WO 2008099575 A1 WO2008099575 A1 WO 2008099575A1 JP 2008000029 W JP2008000029 W JP 2008000029W WO 2008099575 A1 WO2008099575 A1 WO 2008099575A1
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power generation
stacks
fuel cell
sub
fuel
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PCT/JP2008/000029
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French (fr)
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Masaharu Hatano
Keiko Kushibiki
Tatsuya Yaguchi
Itaru Shibata
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Nissan Motor Co., Ltd.
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    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL INTO ELECTRICAL ENERGY
    • H01M8/00Fuel cells; Manufacture thereof
    • H01M8/24Grouping of fuel cells, e.g. stacking of fuel cells
    • H01M8/249Grouping of fuel cells, e.g. stacking of fuel cells comprising two or more groupings of fuel cells, e.g. modular assemblies
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL INTO ELECTRICAL ENERGY
    • H01M8/00Fuel cells; Manufacture thereof
    • H01M8/04Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04007Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids related to heat exchange
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL INTO ELECTRICAL ENERGY
    • H01M8/00Fuel cells; Manufacture thereof
    • H01M8/04Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04007Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids related to heat exchange
    • H01M8/04014Heat exchange using gaseous fluids; Heat exchange by combustion of reactants
    • H01M8/04022Heating by combustion
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL INTO ELECTRICAL ENERGY
    • H01M8/00Fuel cells; Manufacture thereof
    • H01M8/04Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04007Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids related to heat exchange
    • H01M8/04029Heat exchange using liquids
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL INTO ELECTRICAL ENERGY
    • H01M8/00Fuel cells; Manufacture thereof
    • H01M8/04Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04007Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids related to heat exchange
    • H01M8/04037Electrical heating
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL INTO ELECTRICAL ENERGY
    • H01M8/00Fuel cells; Manufacture thereof
    • H01M8/04Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04007Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids related to heat exchange
    • H01M8/04052Storage of heat in the fuel cell system
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL INTO ELECTRICAL ENERGY
    • H01M8/00Fuel cells; Manufacture thereof
    • H01M8/24Grouping of fuel cells, e.g. stacking of fuel cells
    • H01M8/241Grouping of fuel cells, e.g. stacking of fuel cells with solid or matrix-supported electrolytes
    • H01M8/2425High-temperature cells with solid electrolytes
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL INTO ELECTRICAL ENERGY
    • H01M8/00Fuel cells; Manufacture thereof
    • H01M8/24Grouping of fuel cells, e.g. stacking of fuel cells
    • H01M8/2465Details of groupings of fuel cells
    • H01M8/247Arrangements for tightening a stack, for accommodation of a stack in a tank or for assembling different tanks
    • H01M8/2475Enclosures, casings or containers of fuel cell stacks
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL INTO ELECTRICAL ENERGY
    • H01M8/00Fuel cells; Manufacture thereof
    • H01M8/10Fuel cells with solid electrolytes
    • H01M8/12Fuel cells with solid electrolytes operating at high temperature, e.g. with stabilised ZrO2 electrolyte
    • H01M2008/1293Fuel cells with solid oxide electrolytes

Abstract

A fuel cell power generation system includes a plurality of sub-stacks. Each of the sub-stacks is composed by stacking a plurality of power generation cells on one another. Each of the power generation cells includes: a fuel electrode; an air electrode; and an electrolyte membrane having ion conductivity and being sandwiched between the fuel electrode and the air electrode. The fuel cell power generation system further includes: a plurality of preheaters which preheat the respective sub-stacks; and heat insulators which shield radiant heat. The preheaters are individually provided for the respective sub-stacks. The heat insulators are provided among the respective sub-stacks.

Description

Description

FUEL CELL POWER GENERATION SYSTEM AND OPERATION METHOD THEREOF

Technical Field

[0001] The present invention relates to a power generation system using a fuel cell and to an operation method of the system. Specifically, the present invention relates to a fuel cell power generation system excellent in activation characteristics and capable of power generation in which a dynamic range is wide, and relates to an operation method of the system. Background Art

[0002] A fuel cell power generation system is studied to be utilized as a stationary distributed power supply and a power supply for a mobile unit such as an automobile. As a fuel cell applied to such a power generation system, various ones are studied. In particular, a solid oxide fuel cell using, as an electrolyte membrane, an inorganic material that is an oxygen ion conductor or a proton conductor has a variety for fuel and has high power generation efficiency, and accordingly, is expected to be put into practical use.

[0003] In the above-described solid oxide fuel cell, it is necessary to perform a fuel cell reaction at a high temperature in order to sufficiently enhance ion conductivity of the material composing the electrolyte membrane. For example, an operation temperature of the solid oxide fuel cell reaches approximately 700 to 1000 degrees Celsius (refer to Japanese Patent Unexamined Publication No. 2003-263996). Moreover, in recent years, development of a solid oxide fuel cell capable of operating at a lower temperature has also been progressed, and for example, one capable of operating at 400 degrees Celsius has also been proposed (refer to Lecture Proceedings (A20) of 11th Fuel Cell Symposium).

[0004] In any of the cases, the above-described fuel cell cannot operate at the room temperature. Therefore, in the case of applying the fuel cell to the power generation system and activating the fuel cell from a stopped state to a power generation state, the fuel cell must be preheated and heated up to the operation temperature by some means. In this case, a time required for the preheating and the heating and an energy loss caused thereby become factors to decrease the efficiency of the power generation system. Therefore, it is necessary to make some contrivance on the power generation system in order to minimize the time and the energy loss.

[0005] In this connection, heretofore, a fuel cell power generation system has been proposed, in which a plurality of power generation cells as power generation elements are stacked on one another to compose stacks, and a small stack easy to be activated and a large stack serving as a main power generator are combined with each other (EP1507302A2). This fuel cell power generation system supplies high-temperature reformed gas, which is discharged from a fuel reformer, only to the small stack and heats up the small stack to an operatable temperature thereof at the time of the activation, and thereafter, preheats the large stack by using heat emitted by the small stack. In such a way, this fuel cell power generation system makes it possible to reduce the energy for the activation and to shorten the activation time. Disclosure of Invention

[0006] The conventional fuel cell power generation system can deal with the case where an output as small as Wl or less is required at the time of the activation when a maximum output value per unit time of the small stack is defined as Wl, and a maximum output value per unit time of the large stack is defined as W2. However, when the maximum output that is W1+W2 is required at the time of the activation, it becomes difficult to sufficiently ensure a quantity of heat for assisting the heating of the large stack since the heating is assisted by the waste heat of the small stack. Therefore, it is difficult to rapidly heat the large stack, and it takes time to activate the power generation system with a large output. Moreover, it is difficult to deal with a quick output variation from a small output to the large output. As a result, there has been a problem that a power generation operation mode is limited to a narrow range.

[0007] The present invention has been made in consideration for the conventional circumstances described above. It is an object of the present invention to provide a fuel cell power generation system capable of performing efficient power generation with a small energy loss, rapidly dealing also with the activation with the large output and the output variation, and realizing a variety of power generation operation modes.

[0008] The first aspect of the present invention provides a fuel cell power generation system comprising: a plurality of sub-stacks, each of which is composed by stacking a plurality of power generation cells on one another, each of the power generation cells comprising: a fuel electrode; an air electrode; and an electrolyte membrane having ion conductivity and being sandwiched between the fuel electrode and the air electrode; a plurality of preheaters which preheat the respective sub-stacks, the preheaters being individually provided for the respective sub-stacks; and heat insulators which shield radiant heat, the heat insulators being provided among the respective sub-stacks.

[0009] The second aspect of the present invention provides a fuel cell power generation system comprising: a plurality of sub-stacks, each of which is composed by stacking a plurality of power generation cells on one another, each of the power generation cells comprising: a fuel electrode; an air electrode; and an electrolyte membrane having ion conductivity and being sandwiched between the fuel electrode and the air electrode; a plurality of preheating means for preheating the respective sub-stacks, the preheating means being individually provided for the respective sub-stacks; and heat insulating means for shielding radiant heat, the heat insulating means being provided among the respective sub-stacks. Brief Description of the Drawings

[0010] [fig. I]FIG. 1 is an explanatory view showing an embodiment of a fuel cell power generation system of the present invention.

[fig.2]FIG. 2 is an explanatory view showing another embodiment of the fuel cell power generation system of the present invention.

[fig.3]FIG. 3 is an explanatory view showing still another embodiment of the fuel cell power generation system of the present invention.

[fig.4]FIG. 4 is an explanatory view showing yet another embodiment of the fuel cell power generation system of the present invention.

[fig.5]FIG. 5 is a perspective view showing an example of a sub-stack usable for the fuel cell power generation system of the present invention. Best Mode for Carrying Out the Invention

[0011] A fuel cell power generation system of the present invention is a fuel cell power generation system including a plurality of sub-stacks. Each of the sub-stacks is composed by stacking a plurality of power generation cells on one another. Moreover, each of the power generation cells is composed by sandwiching an electrolyte membrane having ion conductivity between a fuel electrode and an air electrode, and in particular, it is preferable that the power generation cell be that of a solid oxide fuel cell.

[0012] Then, in the fuel cell power generation system, preheaters which preheat the respective sub-stacks are individually provided. Specifically, each of the preheaters is at least one of a combustion burner, an electric heater, a fuel reforming reactor, and a heat exchanger having a heat source in an outside of the system. Moreover, the fuel cell power generation system provides heat insulators, which shield radiant heat, among the respective sub-stacks. Specifically, the heat insulators are made of either one of a ceramic material and a metal material or made of a combination of both thereof.

[0013] When n pieces of sub-stacks are assumed, and maximum outputs of the respective sub-stacks are defined as Wl, W2..., Wn having a relationship in Mathematical expression 1, the fuel cell power generation system can set a variety of output values within a range from Wl as the minimum to W1+W2+..., +Wn as the maximum in matching with a power generation output required at the time of activation. [Math.l]

Wl < W2 <..., < Wn

If a using environment, using situation and power pattern of the power generation system become obvious in advance, then the optimum power generation system can be constructed by defining a value of the above-described n and the respective values of Wl, W2..., Wn at a designing stage.

[0014] Then, in the fuel cell power generation system, the heat insulators provided among the respective sub-stacks inhibit the respective sub-stacks from thermally interfering with one another, thereby contributing to realization of a precise control. Moreover, the preheaters provided for the respective sub-stacks, and more desirably, preheaters with capabilities and modes, which are suitable for the individual sub-stacks, also suppress an energy loss, thereby contributing to the precise control.

[0015] With regard to one using the power generation cells of the solid oxide fuel cell as the power generation cells containing the electrolyte having the ion conductivity, a variety for fuel for use is mentioned as an advantage thereof in comparison with the case of using power generation cells of a polymer electrolyte fuel cell containing a proton- conductive electrolyte.

[0016] In the power generation cells of the polymer electrolyte fuel cell, since the electrolyte is one having a proton conductor, a fuel cell reaction is not progressed even if hydrocarbon fuel is directly supplied to the power generation cells. Moreover, in the power generation cells of the polymer electrolyte fuel cell, an operation temperature thereof is as low as approximately 100 degrees Celsius, the hydrocarbon fuel cannot be reformed to generate hydrogen in an inside of the polymer electrolyte fuel cell, and accordingly, fuel to be supplied thereto is limited to pure hydrogen. In this case, an electrode reaction in the fuel electrode is represented by Chemical formula 1. [Chem.l]

H2 → 2H+ + 2e'

[0017] Therefore, in the power generation cells of the polymer electrolyte fuel cell, a high- pressure tank that stores hydrogen or a fuel reformer in an outside of the polymer electrolyte fuel cell becomes essential. However, the high-pressure tank for the hydrogen becomes an extremely large one. Moreover, in the case where the operation temperature is approximately 100 degrees Celsius, the electrodes are poisoned by carbon monoxide. Accordingly, even if the hydrogen is generated by the fuel reformer in the outside of the polymer electrolyte fuel cell, it is necessary to decrease a concentration of the carbon monoxide in the generated gas to the minimum. In such a way, the fuel reformer becomes large.

[0018] As opposed to this, in the case of using the power generation cells of the solid oxide fuel cell like the fuel cell power generation system of the present invention, the large high-pressure tank and the large reformer are unnecessary. The hydrocarbon fuel transportable in a state of liquid, for example, fuel such as gasoline, light oil, kerosene and liquefied propane can be used. Moreover, in the case of using an oxygen ion conductor as the electrolyte, the hydrocarbon fuel can be directly supplied to the fuel cell. In this case, an electrode reaction in the fuel electrode is represented by Chemical formula 2. [Chem.2]

CnHm + (2n+m/2)O2" → nCO2 + m/2H2O + (4n+m)e~

[0019] Moreover, in the case of using the power generation cells of the solid oxide fuel cell like the fuel cell power generation system of the present invention, a reforming reaction in an inside of the solid oxide fuel cell can also be put to use. This reforming reaction is represented by Chemical formula 3. [Chem.3]

CnHm + (q+x+2y)H2O → pH2 + qH2O + xCO + yCO2

[0020] With regard to H2 generated here, an electrode reaction thereof is progressed in a reaction represented by Chemical formula 4. Moreover, with regard to CO, an electrode reaction thereof is progressed in a reaction represented by Chemical formula 5. [Chem.4]

H2 + O2" → H2O + 2e~

[Chem.5]

CO + O2' → CO2 + 2e'

[0021] Hence, in the fuel cell power generation system of the present invention, the fuel cell reaction can be performed in both of the direct supply of the hydrocarbon fuel and the reforming reaction. Moreover, in the case of using the proton conductor as the electrolyte, with regard to hydrogen generated by reformation in an inside of the fuel cell, an electrode reaction thereof is progressed in a reaction represented by Chemical formula 6. Furthermore, CO is converted into hydrogen by a shift reaction represented by Chemical formula 7 in the inside of the fuel cell, and thereafter, an electrode reaction thereof is progressed in a reaction similar to the above. [Chem.6]

H2 → 2H+ + 2e"

[Chem.7]

CO + H2O → CO2 + H2

[0022] Here, in the case of using the power generation cells of the solid oxide fuel cell like the fuel cell power generation system of the present invention, as described above, the solid oxide fuel cell has adaptability to the variety of fuels. However, in the case of generating power by using the hydrocarbon fuel, carbon precipitation onto the electrode sometimes causes a problem. A reaction of this carbon precipitation is progressed in a reaction represented by Chemical formula 8. [Chem.8]

CnHm → nC + m/2H2 2CO → C + CO2

[0023] Carbon is generated mainly on a surface of the fuel electrode of the fuel cell, and is in a state of solid. Therefore, when an amount of the generated carbon is large, there is an apprehension that the carbon may block up active reaction sites present on the surface of the fuel electrode and inhibit the electrode reaction, resulting in a decrease of power generation efficiency of the entire system. By some methods, it is possible to remove the carbon thus precipitated. Examples of carbon removal reactions are represented in Chemical formula 9. [Chem.9]

C + H2O → CO + H2 C + CO2 → 2CO

C + 1/2O2 → CO C + O2 → CO2

[0024] Among the above-described reactions, the removal reaction using H2O or CO2 can be progressed at a temperature of 700 degrees Celsius or more. Moreover, the removal reaction using O2 is a reaction that is sufficiently possible at the room temperature or more from a thermodynamic viewpoint.

[0025] Here, a material for use in the fuel electrodes of many solid oxide fuel cells is nickel cermet that is a mixture of nickel and an oxide. The nickel in this nickel cermet tends to become nickel oxide under the presence of oxidation gas. If oxidation-reduction of the nickel and the nickel oxide is progressed, then the material is expanded and contracted owing to a difference in volume per mol between the nickel and the nickel oxide, and in the worst case, there is an apprehension that a structure of the material may be broken, causing a decrease of durability. Therefore, it is necessary that the fuel cell be prevented as much as possible from being exposed to such an oxidation atmosphere.

[0026] Each of H2O, CO2 and O2, which are required for the above-described carbon removal reactions, acts as an oxidizing agent to the nickel metal. However, in particular, O2 has high oxidizing power, and accordingly, it is more desirable to use H2 O or CO2, of which oxidizing power is comparatively lower, for the carbon removal reaction.

[0027] As described above, the efficiency decrease owing to the carbon precipitation can be avoided by restoring the fuel electrode by means of the carbon removal reaction. However, in order to process such restoration, it is necessary to temporarily stop the power generation.

[0028] In this connection, an operation method of the fuel cell power generation system according to the present invention is characterized in that, in the event of operating the above-mentioned fuel cell power generation system, while a part of the plurality of sub-stacks is being operated for the power generation, the other sub-stacks are operated for the electrode restoration.

[0029] The fuel cell power generation system of the present invention is a system formed of the plurality of sub-stacks. Therefore, a part of the sub-stacks is operated for the power generation, and at the same time, the other sub-stacks are operated for the electrode restoration, whereby the electrode restoration is performed without completely stopping the power generation. In such a way, a long-term stability of the fuel cell power generation system can be ensured. At this time, there is a possibility that temperatures of the respective processes for the power generation and the electrode restoration may differ from each other; however, if the fuel cell power generation system is used, then such an event that the respective sub-stacks thermally interfere with one another can be prevented by the heat insulators.

[0030] Moreover, the carbon removal reaction using H2O or CO2 is an endothermic reaction, where it is necessary to supply heat to the sub-stacks. In this case, if the fuel cell power generation system is used, then waste heat from the adjacent sub-stacks can be supplied to the sub-stacks subjected to the carbon removal reaction, and the preheaters for the sub-stacks can be effectively put to use.

[0031] Moreover, the operation method of the fuel cell power generation system according to the present invention is characterized in that, in the event of operating the fuel cell power generation system having the above-mentioned configuration, the fuel is se- quentially supplied in series to the respective sub-stacks, and at the same time, air is supplied in parallel to the respective sub-stacks.

[0032] In the fuel cell power generation system, when the fuel gas is supplied in series to the respective sub-stacks, necessarily, a reaction rate of the fuel gas becomes low on an upstream side, and the reaction rate becomes high on a downstream side. Accordingly, a composition of reaction gas (fuel gas) completely differs between the upstream side and the downstream side. When an m-th sub-stack among the plurality of sub-stacks is considered in the case where the respective sub-stacks are steadily operated, a heat balance thereof is represented as in Mathematical expression 2. [Math.2]

WIm + WRm = WOm

WIm is a quantity of heat per unit time, which is supplied to the sub-stack, WRm is a quantity of heat per unit time, which is generated following an electrochemical reaction, and WOm is a quantity of heat per unit time, which is lost by heat radiation and gas exhaustion from the sub-stack.

[0033] When the sum of the quantities of supplied and generated heat of the sub-stack exceeds the quantity of lost heat thereof (WIm + WRm > WOm), there is an apprehension that the temperature of the sub-stack may continue to rise, causing thermal runaway. Meanwhile, when the sum of the quantities of supplied and generated heat of the sub-stack does not reach the quantity of lost heat thereof (WIm + WRm < WOm), there is an apprehension that the temperature of the sub-stack may continue to drop down, causing the stop of the power generation itself. Hence, it is necessary to attain the heat balance in the sub-stack.

[0034] In a system that generates the power by a single stack unlike the system of the present invention, the heat balance is established individually on the upstream side and downstream side of the supply of the fuel gas. However, since it is impossible to separately control the respective temperatures on the upstream side and the downstream side, the temperature in the steady state largely differs between the upstream side and the downstream side. Moreover, paying attention to selection of the material of the fuel electrodes in the fuel cell, in usual, there is an assumed temperature condition, activity of the fuel electrodes runs short at the assumed temperature condition or less, and deterioration thereof owing to heat is accelerated at the assumed temperature condition or more. Therefore, when the temperature is distributed with large variations in the one sub-stack as mentioned above, a portion in which performance cannot be fully exerted sometimes occurs in the fuel electrodes. Also in the case of supplying the fuel gas in series to the respective sub-stacks like the operation method of the fuel cell power generation system according to the present invention, since the composition of the gas differs among the respective sub-stacks as mentioned above, the quantity of supplied heat WIm and the quantity of generated heat WRm differ among the respective sub-stacks.

[0035] In the operation method of the fuel cell power generation system according to the present invention, while the fuel is sequentially supplied in series to the respective sub- stacks, the air is supplied in parallel to the respective sub-stacks. Moreover, the flow rates of the fuel and the air to the respective sub-stacks are individually controlled. In such a way, it is made possible to individually control the quantities of lost heat WOm in the respective sub-stacks, and at the same time, it is made possible to equally control the temperatures of the respective sub-stacks. Furthermore, the temperatures of the respective sub-stacks are controlled to an operation temperature assumed at the time of designing the electrodes, thus making it possible to enhance the power generation efficiency of the system to the maximum.

[0036] Moreover, in the operation method of the fuel cell power generation system according to the present invention, in the case where the fuel gas is supplied in series to the respective sub-stacks, an oxygen partial pressure in equilibrium with the reaction gas on the downstream side is necessarily increased. At this time, if the nickel in the nickel cermet for use in the fuel electrodes of the solid oxide fuel cell is undesirably oxidized as mentioned above, then there is a possibility that the activity of the electrodes may be decreased, and that a microstructure of the electrodes may be broken down owing to expansion thereof. However, if such an event is assumed in advance, then an effective countermeasure against such a high equilibrium oxygen partial pressure can be taken for the sub-stack on the downstream side. For example, a component of the oxide in the nickel cermet is increased in advance in the sub-stack on the downstream side, thus making it possible to suppress the volume expansion owing to the oxidation.

[0037] As a more preferable embodiment, the fuel cell power generation system of the present invention can include plural types of sub-stacks different in composition of the electrodes composing the power generation cells. For example, different materials are applied as the electrode material of the respective power generation cells between the sub-stacks on the upstream side and the sub-stacks on the downstream side, thus making it possible to construct the optimum system.

[0038] When the electrode materials are different as described above, it is necessary to also change the operation conditions (temperature condition and the like). However, in accordance with the present invention, the heat insulators are provided among the respective sub-stacks, and accordingly, the sub-stacks do not thermally interfere with one another. Therefore, the optimum operation conditions can be set. [0039] A description will be made below of some embodiments of the fuel cell power generation system of the present invention and the operation method thereof based on the drawings.

[0040] A fuel cell power generation system shown in FIG. 1 includes four sub-stacks S 1 to S4 in a housing H. Each of the sub-stacks S 1 to S4 is composed in such a manner that an electrolyte membrane having ion conductivity is sandwiched between a fuel electrode and an air electrode to compose a power generation cell of a solid oxide fuel cell, and a plurality of the power generation cells are stacked on one another. Then, for the respective sub-stacks Sl to S4, preheaters Bl to B4 which preheat the same are provided, respectively. Moreover, heat insulators A, which shield radiant heat, are provided among the respective sub-stacks Sl to S4. In such a way, the individual sub- stacks S 1 to S4 are surrounded together with the respective preheaters B 1 to B4 by the heat insulators A disposed so as to partition an inside of the housing H. Note that FIG. 5 shows an example of a sub-stack usable for the fuel cell power generation system of the present invention. A sub-stack 70 of FIG. 5 is composed in such a manner that an electrolyte membrane 71 is sandwiched between a fuel electrode 72 and an air electrode 73 to compose a power generation cell 74, and a plurality of the power generation cells 74 are stacked on one another while interposing separators 75 therebetween.

[0041] Here, as each of the preheaters Bl to B4, there is used at least one of a combustion burner that burns fuel, an electric heater including an external power supply, a fuel reforming reactor for reforming the fuel to generate hydrogen, and a heat exchanger having a heat source in an outside of the system. Moreover, as the heat insulators A, heat shield plates are used, which are made of either one of a ceramic material and a metal material or made of a combination of both thereof.

[0042] Moreover, the fuel cell power generation system includes, in an outside of the housing H, external supply pipes 11 and 21 for supplying the fuel (fuel gas) and air to the system, and external discharge pipes 12 and 22 for discharging these fuel and air therefrom. Furthermore, the fuel cell power generation system includes, in the inside of the housing H, internal supply pipes 13 and 23 coupled to the external supply pipes 11 and 21.

[0043] Branching pipes 14 and 24, which supply the fuel and the air to the respective sub- stacks Sl to S4, respectively, are coupled to the internal supply pipes 13 and 23. Valves V are individually provided for these branching pipes 14 and 24.

[0044] Moreover, on the first sub-stack Sl, for the fuel and the air, there are provided branching/coupling pipes 15 and 25, respectively, which form supply routes to the second sub-stack S2 and discharge routes to the external discharge pipes 12 and 22. On the second sub-stack S2, for the fuel and the air, there are provided branching/coupling pipes 16 and 26, respectively, which form supply routes to the third sub-stack S3 and discharge routes to the external discharge pipes 12 and 22. On the third sub-stack S2, for the fuel and the air, there are provided branching/coupling pipes 17 and 27, respectively, which form supply routes to the fourth sub-stack S4 and discharge routes to the external discharge pipes 12 and 22. On the fourth sub-stack S4, for the fuel and the air, there are provided coupling pipes 18 and 28, respectively, which form discharge routes to the external discharge pipes 12 and 22. Furthermore, valves V are individually provided on branch points of the branching/coupling pipes 15 to 17 and 25 to 27.

[0045] In such a way, the fuel cell power generation system has a configuration, in which the fuel and the air are supplied in parallel to the respective sub-stacks S 1 to S4 by the internal supply pipes 13 and 23 and the respective branching pipes 14 and 24, and the fuel and the air are supplied in series thereto by the respective branching/coupling pipes 15 to 17 and 25 to 27 and the coupling pipes 18 and 28.

[0046] In accordance with the fuel cell power generation system having the above-described configuration, the heat insulators A provided among the respective sub-stacks Sl to S4 inhibit the respective sub-stacks Sl to S4 from thermally interfering with one another, thereby contributing to the realization of the precise control. Moreover, the energy loss is suppressed by the preheaters B provided for the respective sub-stacks Sl to S4, whereby the precise control is realized, and in addition, it is made possible to construct the optimum power generation system.

[0047] Moreover, in the fuel cell power generation system of the present invention, while the fuel is sequentially supplied in series to the respective sub-stacks Sl to S4, the air is supplied in parallel to the respective sub-stacks Sl to S4, and the flow rates of the fuel and the air are individually controlled. In such a way, it is made possible to individually control quantities of lost heat in the respective sub-stacks Sl to S4, and at the same time, it is made possible to equally control temperatures of the respective sub- stacks S 1 to S4, thus making it possible to enhance the power generation efficiency of the system to the maximum.

[0048] A fuel cell power generation system shown in FIG. 2 has a similar configuration to that shown in FIG. 1, and on the fuel discharge routes of the respective sub-stacks Sl to S4, return pipes 19 which form return routes to the respective sub-stacks Sl to S4 are provided.

[0049] The fuel cell power generation system can obtain similar function and effect to those of the previous embodiment, and in addition, resupplies the fuel (discharged gas), which is from the respective sub-stacks Sl to S4, to the respective sub-stacks Sl to S4, thus making it possible to recycle the fuel gas.

[0050] In a fuel cell power generation system shown in FIG. 3, the respective sub-stacks Sl to S4 include the preheaters Bl to B4, respectively, and the respective sub-stacks Sl to S4 are surrounded by the heat insulators A. With regard to the fuel, the system includes: a supply pipe 41 from a supply side (FUEL IN); and a discharge pipe 45 that reaches a discharge side (FUEL OUT). Moreover, the system further includes: branching pipes 42 which individually reach the first and second sub-stacks Sl and S2 from the supply pipe 41; coupling pipes 43 which reach the discharge pipe 45 from the respective sub-stacks Sl to S4; return pipes 44 which individually reach the third and fourth sub-stacks S3 and S4 from the discharge pipe 45; and valves V at appropriate spots.

[0051] Moreover, with regard to the air, the system includes: a supply pipe 51 from a supply side (AIR IN); branching pipes 52 which reach the respective sub-stacks Sl to S4 from the supply pipe 51; and valves V. Moreover, on the respective sub-stacks Sl to S4, there are provided branching/coupling pipes 53 which reach the next sub-stacks S2 to S4 and the atmosphere (or AIR OUT), and valves V.

[0052] The fuel cell power generation system is applied to the operation method according to the present invention, that is, a method in which, while a part of the plurality of sub- stacks Sl to S4 is being operated for the power generation, other sub-stacks are operated for the electrode restoration.

[0053] Specifically, in the fuel cell power generation system, the fuel is supplied to the first and second sub-stacks Sl and S2, and the power is generated there, and a part of the fuel before being discharged is supplied to the third and fourth sub-stacks S3 and S4, and the fuel electrodes thereof are restored. At this time, large amounts of H2O and CO 2 are contained in the discharge gas of the fuel, and accordingly, carbon precipitated on the fuel electrodes can be thereby removed.

[0054] Hence, in the fuel cell power generation system and the operation method of FIG. 3, first, similar function and effect to those of FIGS. 1 and 2 can be obtained. In addition, the electrodes (fuel electrodes) are restored in the third and fourth sub-stacks S3 and S4 without completely stopping the power generation, and the long-term stability of the system can be ensured.

[0055] In the system of FIG. 1, both of the fuel and the air are supplied in series and in parallel to the respective sub-stacks Sl to S4. However, a fuel cell power generation system shown in FIG. 4 has the minimum necessary configuration as a system applicable to the operation method according to the present invention, that is, an operation method in which the fuel is sequentially supplied in series to the respective sub-stacks Sl to S4, and at the same time, the air is supplied in parallel to the respective sub-stacks S 1 to S4.

[0056] Specifically, in the fuel cell power generation system of FIG. 4, the respective sub- stacks Sl to S4 include the preheaters Bl to B4, respectively, and the respective sub- stacks S 1 to S4 are surrounded by the heat insulators A. Moreover, with regard to the fuel, the system includes fuel coupling pipes 51 and valves V at spots between a supply side (FUEL IN) and the sub-stack Sl, between the sub-stacks Sl and S2, between the sub-stacks S2 and S3, between the sub-stacks S3 and S4, and between the sub-stack S4 and a discharge side (FUEL OUT).

[0057] Moreover, with regard to the air, the system includes: a supply pipe 61 from a supply side (AIR IN); branching pipes 62 which individually reach the respective sub-stacks Sl to S4 from the supply pipe 61; and valves V. Furthermore, on the respective sub- stacks S 1 to S4, there are provided discharge pipes 63 which reach the atmosphere or a discharge side (AIR OUT), and valves V.

[0058] The fuel cell power generation system of FIG. 4 can obtain similar function and effect to those of the previous embodiments with a simple configuration.

[0059] Note that a detailed configuration of the fuel cell power generation system of the present invention is not limited only to the above-described respective embodiments, and the details of the configuration can be appropriately changed within the scope without departing from the spirit of the present invention.

[0060] The entire content of a Japanese Patent Application No. P2007-030709 with a filing date of February 9, 2007 is herein incorporated by reference.

Although the invention has been described above by reference to certain embodiments of the invention, the invention is not limited to the embodiments described above and modifications may become apparent to these skilled in the art, in light of the teachings herein. The scope of the invention is defined with reference to the following claims. Industrial Applicability

[0061] In accordance with the fuel cell power generation system of the present invention, when the output required at the time of the activation is small, a small number of the stacks is activated by being preheated by the individual preheaters thereof, and the other stacks are preheated by the waste heat of the activated stacks, whereby the energy required for the activation is made as small as possible, and the power can be generated efficiently. Meanwhile, when the output required at the time of the activation is approximate to the maximum output of the system, all of the sub-stacks are activated by being preheated by the individual preheaters thereof, whereby large output power can also be generated quickly. Moreover, the number of sub-stacks is set appropriately, thus making it possible to deal with various operation modes of the power generation.

[0062] Furthermore, the respective sub-stacks are efficiently heat-insulated from one another by providing the heat insulators thereamong. In such a way, when it is desired that a small number of the sub-stacks be heated, heat is inhibited from being dissipated, and the heat for the preheating is efficiently supplied only to the sub-stacks. Therefore, the energy loss can be suppressed to the minimum, and the power generation can be made far more efficient.

Claims

Claims
[1] A fuel cell power generation system, comprising: a plurality of sub-stacks, each of which is composed by stacking a plurality of power generation cells on one another, each of the power generation cells comprising: a fuel electrode; an air electrode; and an electrolyte membrane having ion conductivity and being sandwiched between the fuel electrode and the air electrode; a plurality of preheaters which preheat the respective sub-stacks, the preheaters being individually provided for the respective sub-stacks; and heat insulators which shield radiant heat, the heat insulators being provided among the respective sub-stacks.
[2] The fuel cell power generation system according to claim 1, wherein the power generation cells are power generation cells of a solid oxide fuel cell.
[3] The fuel cell power generation system according to claim 1, wherein each of the preheaters is at least one of a combustion burner, an electric heater, a fuel reforming reactor, and a heat exchanger having a heat source in an outside of the system.
[4] The fuel cell power generation system according to claim 1, wherein the heat insulators are heat shield plates made of either one of a ceramic material and a metal material or made of a combination of both thereof.
[5] The fuel cell power generation system according to claim 1, wherein plural types of sub-stacks different in composition of the electrodes composing the power generation cells are provided.
[6] An operation method of a fuel cell power generation system, comprising: providing a fuel cell power generation system according to claim 1 ; operating, for power generation, a part of the sub-stacks among the plurality of sub-stacks; and operating the other sub-stacks for electrode restoration while the part of sub- stacks is being operated for the power generation.
[7] An operation method of a fuel cell power generation system, comprising: providing a fuel cell power generation system according to claim 1 ; and sequentially supplying fuel in series to the respective sub-stacks, and supplying air in parallel to the respective sub-stacks.
[8] A fuel cell power generation system, comprising: a plurality of sub-stacks, each of which is composed by stacking a plurality of power generation cells on one another, each of the power generation cells comprising: a fuel electrode; an air electrode; and an electrolyte membrane having ion conductivity and being sandwiched between the fuel electrode and the air electrode; a plurality of preheating means for preheating the respective sub-stacks, the preheating means being individually provided for the respective sub-stacks; and heat insulating means for shielding radiant heat, the heat insulating means being provided among the respective sub-stacks.
PCT/JP2008/000029 2007-02-09 2008-01-16 Fuel cell power generation system and operation method thereof WO2008099575A1 (en)

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