JP3094099B2 - Dual temperature controlled solid oxide fuel cell - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a novel solid oxide fuel cell and a power generation method using the same.

[0002]

2. Description of the Related Art In general, in a solid oxide fuel cell using a fuel such as methane or natural gas as a fuel and nickel as a fuel electrode, carbon is deposited due to decomposition of the hydrocarbon, thereby damaging the nickel electrode. It is known. Therefore, conventionally, a method has been known in which a hydrocarbon is heated and reacted with water or a combustion gas containing carbon dioxide and water vapor as main components, reformed into hydrogen and carbon monoxide, and then used as a fuel for a solid oxide fuel cell (JP-A-Hei. No. 9-129256) has been proposed. However, in a fuel cell equipped with this type of reformer, the reforming reaction section is an endothermic area as a whole, and the other power generating section is a heat generating area, so that the transfer of heat generated in this power generating section can be efficiently performed. It is necessary to develop internal reforming technology. Further, in the reforming type fuel cell, there is a problem that the reforming reaction does not contribute to the power generation and the thermal efficiency and the power generation efficiency are lowered as a whole. Therefore, in order to improve the overall heat efficiency, the exhaust heat from the fuel cell and the heat obtained by burning the unburned fuel are supplied to the reformer, and the heat is used to operate the steam turbine. The combined method is adopted. However, these methods require peripheral equipment such as a fuel reformer, a shift converter, and a water tank, and in order to achieve a high overall conversion efficiency of the fuel, the size of the equipment is unavoidable. However, a small and highly efficient fuel cell cannot be manufactured.

[0003] On the other hand, in a solid oxide fuel cell using methane as a fuel, a method has been found which is capable of sustaining power generation by using iron or the like as an anode material even if a carbon deposition reaction occurs. ing. In this case, the partial oxidation reaction of methane occurs preferentially, and this partial oxidation reaction is as shown in the following equation. CH ₄ + 0.5O ₂ = CO + 2H ₂ The Gibbs energy change accompanying the occurrence of this reaction is 100
At 0 ° C., it is −273.18 kJ / mol, and the absolute value is larger than the enthalpy change of −21.7 kJ / mol. This means that in order for the oxidation reaction to proceed, it is necessary to supply heat from the outside, and this fuel cell alone cannot be operated while maintaining a thermally independent state. I have.

[0004] Therefore, in order to oxidize methane without supplying heat from the outside, it is necessary to carry out a complete oxidation reaction of methane. At this time, the iron electrode is also oxidized at the same time and the activation of the electrode deteriorates. However, there is a problem that power generation cannot be continued. A conventional solid oxide fuel cell is operated at a constant temperature. At that time, a solid oxide fuel cell and a solid oxide fuel cell capable of efficiently generating power using a complete oxidation reaction of a hydrocarbon fuel such as methane. There is still no satisfactory operation method for operating the fuel cell smoothly.

Recently, a mobile body such as an automobile equipped with a solid polymer electrolyte fuel cell using methanol or gasoline as a fuel has been proposed. In this fuel cell, fuel is reformed into hydrogen and carbon monoxide. In addition, the fuel cell generates electricity after being further converted to hydrogen, and the mobile body is driven using the energy. Therefore, in this method, it is necessary to mount a reformer, a shift converter, and the like, and the peripheral devices of the fuel cell are increased in size and weight, so that the acceleration efficiency and the energy efficiency are reduced. Energy loss increases in the process of obtaining hydrogen, and furthermore, in order to prevent chemical decomposition of the polymer electrolyte, it is essential to maintain a state in which water is present at 80 ° C. The development of a fuel cell which has problems such as extremely complicatedness, and is small and lightweight, and which can drive an automobile with high fuel efficiency has not been realized.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above situation in the prior art. That is, an object of the present invention is to provide a small-sized solid oxide fuel cell capable of continuing power generation with high efficiency using hydrocarbons as fuel and effectively utilizing heat of chemical reaction, and a smooth operation using the same. It is to provide a method. Another object of the present invention is to provide an automobile equipped with the above-mentioned small solid oxide fuel cell.

[0007]

Means for Solving the Problems The inventors of the present invention have made intensive studies to solve the above-mentioned problems, and as a result, by operating two types of solid oxide fuel cells having different functions in combination, it has become possible to obtain hydrocarbons. The present inventors have found that a solid oxide fuel cell capable of generating power by efficiently utilizing the heat of oxidation reaction of a system fuel can be obtained, and have completed the present invention. That is, two temperature controlled articulated solid oxide fuel cell of the present invention, the hydrocarbon-based fuel
-Temperature solid oxide fuel cell that performs partial oxidation reaction and power generation, and monoxide that flows out of the reaction system of the fuel cell
Reaction gas containing hydrogen and hydrogen as main components as fuel
A high-temperature operating solid oxide fuel cell that generates electricity by performing an oxidation reaction is provided in connection with the fuel cell.

Further, according to the power generation method of the present invention, a partial oxidation reaction and power generation of a hydrocarbon-based fuel are performed by a solid oxide fuel cell operating at a low temperature using the above-mentioned dual temperature control connected solid oxide fuel cell. After the reaction, a reaction product gas containing oxygen monoxide and hydrogen flowing out of the reaction system as main components is used as a fuel to perform an oxidation reaction by a solid oxide fuel cell operating at high temperature to generate power. At this time, it is preferable to use heat generated in the solid oxide fuel cell operating at high temperature for the partial oxidation reaction and power generation in the solid oxide fuel cell operating at low temperature. Further, the present invention is characterized in that the above-mentioned dual temperature control connected solid oxide fuel cell is mounted as a power source cell of an automobile.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. The present inventors have conducted intensive studies on a fuel electrode (anode) for combustion of hydrocarbon fuels. When iron / yttrium-stabilized zirconia (Fe / YSZ) was used for the fuel electrode, partial oxidation to carbon monoxide and hydrogen was performed. Although it has a durability of about 200 hours even if carbon deposition occurs, the performance of the complete oxidation reaction is higher than when nickel / yttrium stabilized zirconia (Ni / YSZ) is used for the fuel electrode. Was inferior.

Next, when the combustion of methane is carried out as a two-stage electrochemical reaction as shown in the following formulas (1) and (2), the former stage is an endothermic process and the latter stage is an exothermic process. As shown in FIG. 1, almost the same efficiency as the direct use of methane can be achieved. _{CH 4 + 0.5O 2 = CO +} 2H 2 (1) CO + 2H 2 + 1.5O 2 = CO 2 + 2H 2 O (2)

Therefore, in the present invention, the above formula (1)
The electrochemical reaction involving endotherm represented by the formula and the electrochemical reaction involving heat generation represented by the above formula (2) are divided into two regions.
Allowing a fuel cell reaction to take place in each area of the stage;
Further, a solid oxide fuel cell which is small and can be used as a portable type and a stationary type is obtained by effectively transferring a substance and utilizing heat between these regions.

The solid oxide fuel cell of the present invention comprises at least two types of solid oxide fuel cells having different operating temperatures and electrode materials, that is, a low-temperature operating solid oxide fuel cell (hereinafter simply referred to as a "power generation unit"). I ") and a solid oxide fuel cell operating at a high temperature (hereinafter simply referred to as" power generation section II ").
A step of performing a partial oxidation reaction and power generation of the hydrocarbon fuel in the power generation unit I, and introducing a product gas containing oxygen monoxide and hydrogen obtained by the partial oxidation reaction into the other power generation unit II to perform oxidation and By going through the process of generating electricity,
As a whole, it is possible to achieve a power generation efficiency corresponding to the complete oxidation reaction of hydrocarbon-based fuel, and it is possible to achieve two temperatures and two stages (Tw
o-Temperature-Two-stage) can also be called a solid oxide fuel cell (TTT-SOFC). This T
FIG. 2 is a conceptual diagram showing the flow of energy in the TT-SOFC.

In the dual temperature controlled solid oxide fuel cell of the present invention, in order to efficiently supply heat, the operating temperature of the power generation unit I for performing partial oxidation reaction of hydrocarbon fuel and power generation is set as follows. The operation temperature of the power generation unit II for oxidizing carbon monoxide and hydrogen obtained in the partial oxidation reaction step is lower than the operating temperature, and in the power generation unit II, carbon monoxide and hydrogen are oxidized. The solid oxide fuel cell is designed so that the reaction heat generated at this time and the Joule heat accompanying the power generation are supplied to the power generation unit I that performs a partial oxidation reaction of the hydrocarbon fuel.

FIG. 3 shows an example of the structure of the dual temperature controlled solid oxide fuel cell of the present invention and its heat and mass transfer. In FIG. 3, in one stack, a lower-stage power generation unit I for performing partial oxidation reaction and power generation of a hydrocarbon-based fuel is provided in a lower stage, and the carbon monoxide obtained in the power generation unit I and It is provided with a high-temperature operating power generation unit II for oxidizing hydrogen.

The hydrocarbon fuel used in the present invention includes:
Any hydrocarbon that generates carbon monoxide and hydrogen by partial oxidation can be used.Specifically, it is possible to use methane, ethane, propane, butane, ethylene, propylene, etc. alone or a mixture thereof. Methane or natural gas containing methane as a main component is more preferable. Further, these fuels can be used as gas or liquid, but it is preferable to use liquid as a fuel source for automobiles. On the other hand, air is preferable as oxygen used for the oxidation reaction of these fuels, but other oxygen-containing substances can also be used.

The low-temperature power generation unit I used in the present invention produces carbon monoxide and hydrogen by introducing a hydrocarbon fuel such as methane and air and thereby performing a partial oxidation reaction of the fuel accompanying the power generation. A fuel cell reaction occurs. When the fuel is methane, the reaction is controlled so that the reaction proceeds at a rate of 0.5 mole of oxygen to 1 mole of methane to generate carbon monoxide and hydrogen as shown in the following equation. CH ₄ + 0.5O ₂ → CO + 2H _{2 When} other hydrocarbons are used as the fuel, the control is performed so that the reaction proceeds as in the following formula, as in the case of methane. C _n H _{2n + 2} +0.5 nO ₂ → nCO + (n + 1) H
_{2 In} this power generation unit I, the conversion rate of fuel to electric power is HH
It is about 20 to 25% on a V basis.

The operating temperature of the power generation section I depends on the type of fuel to be used, the structure of the battery, and the like, but is a temperature suitable for the progress of the partial oxidation reaction of the fuel and the power generation, and is generally 800 to 950. C., but at 880
To 920 ° C, more preferably about 900 ° C.
As the solid oxide electrolyte of the power generation unit I, among known solid oxides conventionally used, those having relatively high ionic conductivity at an operating temperature of about 900 ° C. can be used. And a solid metal oxide such as yttria-stabilized zirconia (YSZ), rare earth-doped ceria, and lanthanum gallate-based electrolyte.

In the present invention, when YSZ is used as the solid oxide electrolyte, it is preferable to use a lanthanum manganite perovskite oxide as the air electrode and iron / YSZ as the fuel electrode. On the other hand, when a rare earth-added ceria or lanthanum gallate-based electrolyte is used, it is preferable to use a lanthanum cobaltite-based perovskite oxide as the air electrode and iron / YSZ as the fuel electrode. This iron / YSZ has the property of being resistant to carbon dioxide and water, while being able to withstand the precipitation of carbon. In addition, any other material suitable for partial oxidation of fuel and power generation can be used as the other material of the power generation unit I, and a lanthanum chromite perovskite oxide or the like is preferable as the interconnect material.

Next, in the power generation section II operating at high temperature, the power generation section I
The carbon monoxide and hydrogen obtained in step (1) are oxidized to generate carbon dioxide gas and water, respectively, and generate heat, generate power, and generate Joule heat accordingly. The heat generated in the power generation unit II is used by being transferred to the power generation unit I. In this power generation unit II, the conversion rate of fuel to electric power is about 55 to 60% based on HHV. The operating temperature of the power generation unit II depends on the structure of the battery used, but the oxidation reaction of carbon monoxide and hydrogen easily proceeds,
A temperature suitable for improving the power generation efficiency, which is usually 950 to 1
The reaction is performed in the range of 050 ° C, preferably 980 to 1020 ° C, and more preferably about 1000 ° C.

As the solid oxide electrolyte of the power generation unit II, 100% of known solid oxides conventionally used are used.
Although a material having high ionic conductivity at about 0 ° C. can be used, specifically, yttria-stabilized zirconia or the like is preferable. As a material of the power generation unit II, a lanthanum manganite-based perovskite oxide is used as an air electrode,
It is preferable to use nickel / YSZ as the fuel electrode. As other materials of the power generation unit II, any material suitable for oxidizing carbon monoxide and hydrogen fuel and generating power can be used, and a lanthanum manganite perovskite oxide or the like is preferable as the interconnect material.

FIGS. 4 and 5 are schematic views showing an example of the configuration of the main part of the solid oxide fuel cell. FIG. 4 shows the layer configuration of the power generation unit, the reaction raw materials flowing therebetween, and the direction in which the generated current flows. FIG. 5 shows the flow of the material and the reaction material used for the power generation unit and the connection unit.

In the present invention, as described above, the two solid oxide fuel cells having different operating temperatures, that is, the power generating unit I operating at low temperature and the power generating unit II operating at high temperature are connected. . As the material used in the present invention, it is important to use a different material for the fuel electrode. For example, Fe / YSZ is used for the low-temperature operation power generation unit I, and the high-temperature operation power generation unit II is used.
Use Ni / YSZ for the fuel electrode. The connection between the power generation unit I and the power generation unit II in the present invention can be adopted as long as the heat generated in the power generation unit II is connected so as to be effectively used as a heat source of the power generation unit I. ,
For example, the following method is available.

I) Method of Directly Connecting Power Generation Sites Using the same solid oxide electrolyte (for example, YSZ) cylindrical type, the fuel introduction side is a low temperature operation power generation site I, and behind it is a high temperature operation power generation. The site II is arranged, and one example is shown in FIG. As the oxygen used as the oxidizing agent in the reaction of the fuel cell, air is caused to flow inside the cylindrical electrolyte from the power generating part II operating at high temperature to the power generating part I operating at low temperature. The heat generated in the power generation site II is sent to the power generation site I by heat conduction in a solid material such as an electrolyte and transport by air. A plurality of such cylindrical types are collected into a unit, and power is separately collected in the low-temperature power generation site I and the high-temperature power generation site II.

Ii) A method in which the low-temperature power generation section and the high-temperature power generation section are separately stacked and connected by a gas manifold. The first low-temperature power generation stack oxidizes to CO + H ₂ to generate power, and the generated gas is obtained. Are collected and introduced again into the second-stage high-temperature power generation stack. Then, the heat of the high-temperature power generation stack is transferred to the low-temperature power generation stack by heat conduction between the stacks. The discharged air from the high-temperature power generation stack is supplied to the low-temperature power generation stack as necessary to supply heat, and FIG. 7 shows an embodiment thereof.

In the power generation method of the present invention, first, the raw material hydrocarbon-based fuel and air are heated by exchanging heat with the exhaust gas of the solid oxide fuel cell in advance.
Before starting the fuel cell, the fuel and the air are heated by using a high-temperature gas obtained by previously burning a part of the fuel. Next, the heated fuel is introduced into the low-temperature power generation section, and the heated air is introduced into the high-temperature power generation section. In the low-temperature power generation unit, a partially oxidized reaction between the partially used air and the fuel discharged from the high-temperature power generation unit occurs to generate power, and a fuel-generating gas mainly composed of carbon monoxide and hydrogen is released. Then
The fuel-producing gas discharged from the low-temperature power generation unit is introduced into the high-temperature power generation unit as fuel, and power is generated by an oxidation reaction of carbon monoxide and hydrogen. FIG. 8 shows the relationship between the fuel cell and the flow of the raw material.

In the present invention, when the low-temperature power generation section (power generation section I) and the high-temperature power generation section (power generation section II) are combined, the following reaction proceeds as a whole in the case of methane fuel. CH ₄ + 2O ₂ = CO ₂ + H ₂ O The above reaction corresponds to the direct oxidation reaction of methane. The power generation efficiency (theoretical value) of this reaction is 99.9% at 800 ° C., and reaches 99.7% at 1000 ° C.
It is possible to generate power with much higher efficiency than a conventional solid oxide fuel cell.

The dual temperature controlled solid oxide fuel cell of the present invention does not require external heat supply, and therefore does not require an external heating device, a fuel reforming device, a shift device, and the like. , Portable and stationary solid oxide fuel cells. Further, in the present invention, the heat released by the oxidation reaction between carbon monoxide and hydrogen in the solid oxide fuel cell operating at a high temperature generates the heat of the hydrocarbon fuel supplied into the solid oxide fuel cell operating at a low temperature. By promoting the partial oxidation reaction, a fuel cell operation method with high thermal efficiency can be achieved without external heating.

Therefore, in the present invention, by mounting the secondary battery and the dual-temperature controlled solid oxide fuel cell of the present invention on an automobile, the driving energy thereof is supplied by the fuel cell, and at the time of departure. The high output can be handled by both the fuel cell and the secondary battery, and the kinetic energy of the vehicle when the vehicle is stopped can be operated by recovering the kinetic energy to the secondary battery using a regenerative brake or the like. Further, since there is no peripheral device for fuel treatment, there is an advantage that it is small and lightweight, and it is useful for automobiles loaded with liquid fuel such as buses, trucks, taxis and other commercial passenger cars.

[0029]

According to the present invention, it is possible to operate a solid oxide fuel cell using a hydrocarbon-based fuel with higher operation efficiency than the conventional type. Further, the solid oxide fuel cell of the present invention does not require an external heating device or a fuel reforming device provided in the conventional type, so that the structure of peripheral devices of the solid oxide fuel cell can be simplified. In addition, a small and lightweight product can be economically manufactured. Further, according to the present invention, a compact and lightweight but high efficiency is obtained, and a portable and stationary solid oxide fuel cell can be obtained. It is also possible to configure a cogeneration system.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between reaction temperature and efficiency when a fuel electrochemical reaction is performed in two stages.

FIG. 2 is a conceptual diagram showing a flow of energy in the solid oxide fuel cell of the present invention.

FIG. 3 is a schematic diagram showing an example of heat transfer and mass transfer in the solid oxide fuel cell of the present invention.

FIG. 4 is a schematic diagram showing an example of a layer configuration of a main part of a solid oxide fuel cell.

FIG. 5 is a schematic diagram illustrating an example of a flow of a material and a reaction material used for a power generation unit and a connection unit, which are main parts of a solid oxide fuel cell.

FIG. 6 is a schematic view showing a structure of an example of a solid oxide fuel cell according to the present invention.

FIG. 7 is a schematic view showing the structure of another example of the solid oxide fuel cell according to the present invention.

FIG. 8 is a conceptual diagram showing the relationship between the solid oxide fuel cell of the present invention and the flow of raw materials.

Continued on the front page (72) Inventor Natsuko Sakai 1-1-1, Higashi, Tsukuba, Ibaraki Pref., National Institute of Industrial Science and Technology (72) Inventor Hideyuki Negishi 1-1-1, Higashi, Tsukuba, Ibaraki Pref. In the laboratory (56) References JP-A-63-91968 (JP, A) JP-A-8-17453 (JP, A) JP-A-8-31423 (JP, A) JP-A-4-286867 (JP, A) US Patent 5712055 (US, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 8/00-8/24 B60L 11/18

Claims (5)

(57) [Claims] 1. A partial oxidation reaction and generation of a hydrocarbon fuel.
Solid oxide fuel cell and the fuel cell of the low-temperature operation performing photoelectric
With oxygen monoxide and hydrogen flowing out of the reaction system
Generated by the oxidation reaction using the reaction product gas
A dual temperature controlled solid oxide fuel cell comprising a high temperature operating solid oxide fuel cell connected to the fuel cell. 2. After performing a partial oxidation reaction of hydrocarbon fuel and power generation by a solid oxide fuel cell operating at low temperature,
A dual temperature control connection type wherein electricity is generated by performing an oxidation reaction with a solid oxide fuel cell operating at a high temperature using a reaction product gas mainly containing oxygen monoxide and hydrogen flowing out of the reaction system as a fuel. A power generation method using a solid oxide fuel cell. 3. The method according to claim 2, wherein the hydrocarbon-based fuel is methane or natural gas containing methane as a main component. 4. The method according to claim 2, wherein heat generated in the solid oxide fuel cell operated at a high temperature is used for a partial oxidation reaction and power generation in the solid oxide fuel cell operated at a low temperature. A power generation method using a dual temperature controlled solid oxide fuel cell. 5. An automobile equipped with the dual temperature controlled solid oxide fuel cell according to claim 1 as a power source battery.