JP4849201B2 - Solid oxide fuel cell - Google Patents

Description

  The present invention relates to an exhaust gas exhaust structure of a solid oxide fuel cell.

  The solid oxide fuel cell has been developed as a third generation fuel cell for power generation, and three types are currently known: a cylindrical type, a monolith type, and a flat plate type. Each of these solid oxide fuel cells has a laminated structure in which a solid electrolyte layer made of an oxide ion conductor is sandwiched between an air electrode layer (cathode) and a fuel electrode layer (anode) from both sides. A plurality of power generation cells and separators are alternately stacked to form a tack, and the fuel cell stack is housed in a housing to be modularized.

In a solid oxide fuel cell, an oxidant gas (oxygen) is supplied to the air electrode layer side as a reaction gas, and a fuel gas (H ₂ , CO, CH _4, etc.) is supplied to the fuel electrode layer side. The air electrode layer and the fuel electrode layer are both porous layers so that the reaction gas can reach the interface with the solid electrolyte layer.

In the power generation cell, oxygen supplied to the air electrode layer passes through the pores in the air electrode layer and reaches the vicinity of the interface with the solid electrolyte layer. It is ionized to (O ²⁻ ). The oxide ions diffuse and move in the solid electrolyte layer toward the fuel electrode layer. Oxide ions that have reached the vicinity of the interface with the fuel electrode layer react with the fuel gas at this portion to generate reaction products (H ₂ O, CO _2, etc.), and discharge electrons to the fuel electrode layer.
Electrons generated by such an electrode reaction can be taken out as an electromotive force at an external load of another route.

The electrode reaction when hydrogen is used as the fuel is as follows.
Air electrode: 1/2 O ₂ + 2e ⁻ → O ²⁻
Fuel electrode: H ₂ + O ²⁻ → H ₂ O + 2e ⁻
Overall: H ₂ +1/2 O ₂ → H ₂ O

  By the way, in the solid oxide fuel cell, the electrochemical reaction of the power generation cell is performed in a high-temperature oxidizing atmosphere at about 650 to 1000 ° C. It is necessary to preheat oxygen (air), fuel gas, steam for reforming, and the like supplied to a required temperature in advance.

  Conventionally, many attempts have been made to improve the energy efficiency of a fuel cell by using high-temperature exhaust gas discharged from the fuel cell during power generation as heat energy for preheating the reaction gas.

FIG. 3 shows the configuration of a conventional solid oxide fuel cell. Reference numeral 1 denotes a fuel cell stack formed by laminating a large number of power generation cells. The fuel cell stack 1 is modularized by being housed in a housing 30 in which a heat insulating material 31 is interposed.
During operation, the fuel cell stack 1 is supplied with a reaction gas such as fuel gas, air, and water vapor preheated to an appropriate temperature to cause a power generation reaction in the power generation cell, and the high-temperature exhaust gas generated at that time It is discharged into the internal space of the housing 30.

In addition, a heat exchanging unit 20 surrounded by a heat insulating material 31 is disposed at the lower part of the housing 30, and exhaust gas discharged into the housing 30 is guided into the heat exchanging unit 20. It has become. The fuel gas and air supplied from the outside are once preheated to a required temperature by exchanging heat with the high-temperature exhaust gas in the heat exchanging section, and the externally supplied water becomes high-temperature steam by heat exchange. These reaction gases are each guided into the fuel cell stack 1 through piping.
On the other hand, the exhaust gas that has undergone heat exchange becomes low temperature and is discharged out of the module through the exhaust pipe 20a of the heat exchanging unit 20, and is recovered by an externally installed exhaust heat recovery device.

  Thus, the energy efficiency of the fuel cell system can be improved by using the exhaust gas discharged from the fuel cell stack 1 as preheating energy such as reaction gas.

Patent Documents 1 and 2 are disclosed as fuel cell systems that improve thermal energy efficiency by utilizing exhaust gas.
JP 2003-151609 A JP 2003-132922 A

By the way, in the case of a solid oxide fuel cell, even at a low temperature operation type with an operating temperature of around 700 ° C., an extremely high temperature exhaust gas of 450 to 600 ° C. is discharged from the battery stack 1 during power generation. However, since the exhaust gas after the heat exchange described above falls from a high temperature of 450 to 600 ° C. to 150 to 250 ° C., the use of exhaust heat in the exhaust heat recovery device is also limited (for example, hot water supply in stores and homes) Energy) and exhaust heat utilization efficiency were not satisfactory.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a solid oxide fuel cell that can obtain high-temperature exhaust gas together with low-temperature exhaust gas after thermal recycling.

That is, according to the first aspect of the present invention, a fuel cell stack formed by stacking a large number of power generation cells is housed in a heat insulating housing, and a reaction gas is supplied into the fuel cell stack during operation to generate a power generation reaction. together causes, in the solid oxide fuel cell sealless structure for exhausting the exhaust gas generated in the power generation reaction in the adiabatic housing, on top of the heat insulating housing, a portion of the exhaust gas from the fuel cell stack An exhaust pipe that exhausts directly to the outside is provided, and is a space that is partitioned from the inside of the heat insulating housing by a bottom plate at the lower part of the heat insulating housing and surrounded by a heat insulating material, and is supplied from the outside using the exhaust gas as a heat source A heat exchanging part having heat exchangers for preheating water, fuel gas and air is disposed, and the bottom plate is provided with an inside of the heat insulating housing. It is characterized in that the part of exhaust gases to the exhaust port is provided to divert to the heat exchanger, and provided with an exhaust pipe for discharging the exhaust gas after heat exchange is discharged from the heat exchanger such to the heat exchanger unit Yes.

In the configuration according to claim 1, high-temperature exhaust gas can be obtained from the exhaust gas exhaust mechanism without being affected by the heat exchange action during heat recycling. For example, this high-temperature exhaust gas is generated by steam in a factory or the like. It can be used as thermal energy.
In addition , by providing the heat exchange part outside the housing, heat exchange for heat recycling can be performed in the heat exchange part without affecting the temperature in the module. At the same time, high temperature exhaust gas is obtained from another exhaust gas exhaust mechanism.

  As described above, according to the present invention, a part of the exhaust gas from the fuel cell stack is used for heat recycling, and the remaining exhaust gas is directly exhausted outside the module. At the same time, high-temperature exhaust gas can be obtained at the same time, whereby the thermal energy of the exhaust gas can be used effectively and the efficiency of the power generation system can be further enhanced.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows a configuration of a solid oxide fuel cell to which the present invention is applied, and FIG. 2 shows a gas flow during operation of the fuel cell stack. In addition, in order to simplify description, the same code | symbol was used about the member common in the past in the following description.

  As shown in FIGS. 1 and 2, the fuel cell stack 1 includes a power generation cell 5 in which a fuel electrode layer 3 and an air electrode layer 4 are disposed on both surfaces of a solid electrolyte layer 2, and a fuel disposed on the outside of the fuel electrode layer 3. A single cell 10 composed of an electrode current collector 6, an air electrode current collector 7 arranged outside the air electrode layer 4, and a separator 8 arranged outside each current collector 6, 7 is vertically arranged. Many are stacked.

Here, the solid electrolyte layer 2 is composed of stabilized zirconia (YSZ) or the like to which yttria is added, and the fuel electrode layer 3 is composed of a metal such as Ni or Co or a cermet such as Ni—YSZ or Co—YSZ, and air. The electrode layer 4 is made of LaMnO ₃ , LaCoO ₃ or the like, the fuel electrode current collector 6 is made of a sponge-like porous sintered metal plate such as a Ni-based alloy, and the air electrode current collector 7 is made of an Ag-based alloy or the like. The separator 8 is made of stainless steel or the like.

  The separator 8 has a function of electrically connecting the power generation cells 5 and supplying a reaction gas to the power generation cells 5. The fuel of the separator 8 is introduced by introducing fuel gas from the outer peripheral surface of the separator 8. The fuel gas passage 11 discharged from the substantially central portion 11a of the surface facing the electrode current collector 6 and the surface of the surface of the separator 8 facing the air electrode current collector 7 by introducing oxidant gas from the outer peripheral surface of the separator 8 An oxidant gas passage 12 that discharges from approximately the center 12a is provided.

  A solid oxide fuel cell (fuel cell module) is configured by storing the fuel cell stack 1 having the above configuration in a cylindrical housing 30 in which a heat insulating material 31 is interposed and modularizing the fuel cell stack 1.

  In addition, this solid oxide fuel cell has a sealless structure in which a gas leakage prevention seal is not provided on the outer peripheral portion of the power generation cell 5, and during operation, as shown in FIG. The fuel electrode layer 3 and the air electrode layer 4 are diffused in the outer peripheral direction of the power generation cell 5 while the fuel gas and the oxidant gas (air) supplied from the substantially central portion of the separator 8 through the gas passage 12 toward the power generation cell 5 are diffused. The power generation reaction is caused to spread over the entire surface of the gas generator, and a surplus gas (exhaust gas) that has not been consumed in the power generation reaction is freely discharged from the outer peripheral portion of the power generation cell 5 into the housing 30. .

  The upper portion of the housing 30 is for exhausting exhaust gas of high temperature (450 to 600 ° C. in the case of a solid oxide fuel cell having an operating temperature of around 700 ° C.) discharged into the internal space directly outside the module. An exhaust pipe 30a is provided. This high-temperature exhaust gas is heat-recovered by an external heat-recovery device, and is used, for example, as heat energy for generating steam used in a factory.

A heat exchanging unit 20 that is partitioned from the inside of the housing 30 by the bottom plate 25 and that uses high-temperature exhaust gas as a heat source is disposed at the lower part of the housing 30 .
The heat exchange unit 20 includes heat exchangers (not shown) for individually preheating externally supplied water, fuel gas, air, and the like in a space surrounded by the heat insulating material 32. Fuel gas, air, etc. exchange heat with the high temperature exhaust gas in the housing 30 introduced through the exhaust port 21 formed in the bottom plate 25 in each heat exchanger to become high temperature steam, preheated fuel gas, preheated air, It is guided into the fuel cell stack 1 through piping.
On the other hand, the exhaust gas from each heat exchanger that has completed heat exchange becomes low temperature (150 to 250 ° C.) and is discharged out of the module through the exhaust pipe 20a of the heat exchanging unit 20, and is heated by an external heat recovery device. Collected. The recovered heat can be used as heat energy for hot water supply, for example, in stores and homes.

  In this way, when a part of the exhaust gas from the fuel cell stack 1 is guided to the heat exchanging unit 20 for heat recycling, the remaining exhaust gas is exhausted directly outside the module without exchanging heat. In the equipment, together with the low temperature exhaust gas after heat recycling, high temperature exhaust gas can be obtained at the same time without being affected by this heat recycling. The efficiency of the system can be further increased.

The figure which shows the structure of the solid oxide fuel cell to which this invention was applied. The figure which shows the flow of the gas at the time of operation | movement of a fuel cell stack. The figure which shows the structure of the conventional solid oxide fuel cell.

Explanation of symbols

1 Fuel cell stack 5 Power generation cell 20 Heat exchange section
25 Bottom plate 30 Housing 20a, 30a exhaust pipe

Claims (1)

A fuel cell stack formed by stacking a large number of power generation cells is housed in a heat insulating housing, and during operation, a reaction gas is supplied into the fuel cell stack to cause a power generation reaction, and an exhaust gas generated by the power generation reaction is generated. In a solid oxide fuel cell having a sealless structure that exhausts into the heat insulating housing ,
Wherein the top of the heat insulating housing is provided with an exhaust pipe for exhausting a part of the exhaust gas from the fuel cell stack directly to the outside,
Heat that is separated from the inside of the heat insulating housing by a bottom plate at the lower part of the heat insulating housing and is surrounded by a heat insulating material, and preheats water, fuel gas, and air supplied from the outside using the exhaust gas as a heat source. A heat exchanging part provided with exchangers is provided, an exhaust port for guiding a part of the exhaust gas in the heat insulating housing to the heat exchanging part is provided on the bottom plate, and the heat exchanging part is provided with the heat exchanging part. A solid oxide fuel cell, characterized in that an exhaust pipe for discharging exhaust gas after heat exchange discharged from the vessels is provided .

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