JP2006318938A - Solid electrolyte fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid electrolyte fuel cell system to improve efficiency. <P>SOLUTION: A part of exhaust fuel exhausted from an SOFC 11 is cooled by an exhaust fuel cooler 24, and then mixed with fuel charged from outside of the system by an exhaust fuel fan 25. The fuel mixed with the exhaust fuel is raisen in temperature by a fuel heater 26, and charged into the SOFC 11. In this way, the exhaust fuel is recycled, electric power generating efficiency is improved by reusing unreacted hydrogen in the exhaust fuel, and fuel quantity for the SOFC 11 is increased, suppressing a fuel temperature rise in an outlet of the SOFC 11, and improving durability and reliability of the SOFC 11, piping, and the like. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a solid oxide fuel cell system, and more particularly to a system for recirculating a part of fuel exhaust gas discharged from a fuel cell main body.

FIG. 8 shows the configuration of a cogeneration system using a solid oxide fuel cell (SOFC). The SOFC 1 uses, for example, natural gas desulfurized by the desulfurization apparatus 2 as a fuel and generates electricity by a reaction at a high temperature of about 1000 ° C. using air as an oxidant. By introducing the high-temperature exhaust gas discharged from the SOFC 1 into the exhaust heat recovery boiler 3, hot water or steam is produced here and used for various applications. The air used for the reaction in the SOFC 1 is preheated by the exhaust heat recovery boiler 3 and then supplied to the SOFC 1.
Such a cogeneration system makes it possible to use heat together with power generation.

However, sufficient heat recovery could not be performed only by passing the high-temperature exhaust gas from the SOFC 1 through the exhaust heat recovery boiler 3 once. The efficiency of the system was not satisfactory. In particular, even if an exhaust gas from SOFC1 is introduced into a high-pressure evaporator to produce, for example, 10 kgf / cm ² , steam for an absorption refrigerator of about 175 ° C., heat recovery is not satisfactory, and a cogeneration system The efficiency of was low.
The present invention has been made to solve such problems, and an object thereof is to provide a solid oxide fuel cell system capable of improving efficiency.

A solid oxide fuel cell system according to a first aspect of the present invention is a system for recirculating a part of exhaust fuel discharged from a solid oxide fuel cell to the fuel cell, wherein a part of the exhaust fuel discharged from the fuel cell is recycled. A cooler for cooling, an exhaust fuel fan for mixing the exhaust fuel cooled by the cooler with the supply fuel, and a fuel heater for raising the temperature of the supply fuel mixed with the exhaust fuel are provided.
A solid oxide fuel cell system according to a second aspect of the present invention is a system for recirculating part of exhaust fuel discharged from a solid oxide fuel cell to the fuel cell, wherein the exhaust fuel and exhaust air discharged from the fuel cell are A combustor that mixes and burns, a heat exchanger that recovers the heat of the exhaust gas from the combustor, and a part of the exhausted fuel that is discharged from the fuel cell using the exhaust gas discharged from the heat exchanger as a drive gas And an ejector for recirculation to the battery.
A solid oxide fuel cell system according to a third aspect of the invention is a system that recirculates a part of the exhausted fuel discharged from the solid oxide fuel cell to the fuel cell, and the exhausted fuel discharged from the fuel cell and the exhausted fuel. A combustor that mixes and combusts air, an evaporator that produces steam using heat of exhaust gas from the combustor, and exhaust fuel that is discharged from the fuel cell using steam produced by the evaporator as drive gas And an ejector for recirculating a part of the fuel cell to the fuel cell.

According to the first aspect of the invention, since the exhaust fuel is mixed with the supplied fuel by the exhaust fuel fan after part of the exhaust fuel discharged from the fuel cell is cooled by the cooler, the exhaust fuel is recirculated. This makes it possible to reuse unreacted hydrogen in the exhausted fuel, thereby improving power generation efficiency. Further, an increase in the fuel amount of the SOFC suppresses an increase in the fuel temperature at the outlet of the SOFC, thereby improving durability and reliability of the SOFC and piping.
According to the second invention, the ejector recirculates part of the exhausted fuel discharged from the fuel cell to the fuel cell using the exhaust gas discharged from the heat exchanger as the drive gas. The power generation efficiency can be improved by reusing the fuel, and the fuel temperature at the outlet of the SOFC 11 is suppressed from increasing due to the increase in the fuel amount of the SOFC 11, thereby improving the durability and reliability of the SOFC 11 and piping.
According to the third aspect of the invention, the ejector recirculates part of the exhausted fuel discharged from the fuel cell to the fuel cell using the water vapor produced by the evaporator as the drive gas. It is possible to improve the power generation efficiency by reusing hydrogen, and the increase in the fuel amount of the SOFC 11 suppresses the fuel temperature at the outlet of the SOFC 11 from increasing, thereby improving the durability and reliability of the SOFC 11 and piping. .

Embodiments of the present invention will be described below with reference to the accompanying drawings.
Embodiment 1 FIG.
FIG. 1 shows the configuration of a solid oxide fuel cell system according to Embodiment 1 of the present invention. A combustor 12 is connected to exhaust ports of exhaust fuel and exhaust air of a SOFC (solid oxide fuel cell) 11, and a second air preheater 13, an evaporator 14, and a first air preheater are disposed downstream of the combustor 12. The devices 15 are sequentially connected. A compressor 16 is disposed downstream of the first air preheater 15, and an outlet of the compressor 16 is connected to a fuel inlet of the SOFC 11 via an ejector 17. An exhaust fuel line of the SOFC 11 is connected to the ejector 17.
An air fan 18 for supplying air is connected to the first air preheater 15, and the air line exiting the first air preheater 15 is in the SOFC 11 for recovering heat loss from the SOFC 11 and the entire system. Alternatively, an intake air heat exchanger 19 provided outside (shown in FIG. 1 is disposed inside the SOFC, but may be provided outside the SOFC; the same shall apply hereinafter) and the SOFC 11 via the second air preheater 13. Connected to the air inlet.
The evaporator 14 forms the first heat recovery device of the present invention.

  Next, the operation of the first embodiment will be described. Fuel and air are supplied to the SOFC 11, and the reaction proceeds at a high temperature of about 1000 ° C. to generate power. High-temperature exhaust fuel and exhaust air discharged from the SOFC 11 are sent to the combustor 12, where unreacted hydrogen is completely combusted. The high-temperature exhaust gas discharged from the combustor 12 is cooled by heat exchange in the second air preheater 13, the evaporator 14, and the first air preheater 15, respectively. And is supplied to the ejector 17 at a predetermined pressure as a drive gas together with fuel supplied from the outside. As a result, part of the exhausted fuel discharged from the SOFC 11 is sucked into the ejector 17 and is supplied to the SOFC 11 together with the exhaust gas that has passed through the first air preheater 15 and the fuel that has been input from the outside.

On the other hand, the air sent from the outside by the air fan 18 is preheated by the first air preheater 15, then preheated again by the intake air heat exchanger 19 in the SOFC 11, and further preheated by the second air preheater 13. After that, it is thrown into the SOFC 11.
Further, water or hot water is supplied to the evaporator 14, where it is heated by the high-temperature exhaust gas discharged from the second air preheater 13 to produce water vapor. This water vapor is used for various purposes in a steam engine or the like.

Thus, since the exhaust fuel and exhaust air discharged from the SOFC 11 are burned by the combustor 12, unreacted hydrogen is not discharged outside the system, and the safety of the system is ensured. Further, since the high-temperature exhaust gas discharged from the combustor 12 is configured to exchange heat with the second air preheater 13, the evaporator 14, and the first air preheater 15, respectively, the heat recovery of the exhaust gas is sufficiently performed. This can be done and the efficiency of the system is improved. Furthermore, since the supply air is preheated by the intake air heat exchanger 19 in the SOFC 11, heat loss is reduced.
Further, since a part of the exhausted fuel is recirculated by the ejector 17 using the exhaust gas, the unreacted hydrogen in the exhausted fuel can be reused to improve the power generation efficiency and the fuel amount of the SOFC 11 is increased. As a result, the fuel temperature at the outlet of the SOFC 11 is suppressed from increasing, and the durability and reliability of the SOFC 11 and piping and the like are improved.

Embodiment 2. FIG.
The configuration of the solid oxide fuel cell system according to Embodiment 2 is shown in FIG. This system is obtained by interposing another evaporator 20 serving as a second heat recovery unit between the SOFC 11 and the combustor 12 in the system of the first embodiment shown in FIG.
Steam can be produced using the heat of the high-temperature exhaust fuel discharged from the SOFC 11 by the evaporator 20, and at the same time heat exchange is performed in the evaporator 20, so that the exhaust fuel introduced into the combustor 12 The temperature is reduced and the combustion temperature in the combustor 12 is reduced. As a result, a general-purpose material such as SUS can be used for the combustor 12, the second air preheater 13, and the second air preheater 15, and the cost can be reduced.

The evaporator 20 can be interposed not in the exhaust fuel line from the SOFC 11 but in the exhaust air line. Moreover, you may use a warm water heater and an air preheater instead of the evaporator 20 as a 2nd heat recovery device.
In FIG. 2, the two evaporators 14 and 20 are connected in series. However, the present invention is not limited to this, and the evaporators 14 and 20 can be used independently.

Embodiment 3 FIG.
The configuration of the solid oxide fuel cell system according to Embodiment 3 is shown in FIG. In this system, the low temperature exhaust gas downstream of the first air preheater 15 is introduced into the combustor 12 in the system of the first embodiment shown in FIG. It is what. Thereby, general purpose materials, such as SUS, can be used for the combustor 12, the 2nd air preheater 13, and the 2nd air preheater 15, and it becomes possible to aim at cost reduction.
When the amount of exhaust gas on the downstream side of the first air preheater 15 is insufficient, an ejector 21 is disposed between the outlet side of the compressor 16 and the combustor 12 as shown in FIG. 21 is preferably connected to the downstream side of the first air preheater 15. With the exhaust gas compressed by the compressor 16, the exhaust gas on the downstream side of the first air preheater 15 is sucked into the ejector 21 and introduced into the combustor 12.
In the system according to the second embodiment, the exhaust gas on the downstream side of the first air preheater 15 may be introduced into the combustor 12.

Embodiment 4 FIG.
The configuration of the solid oxide fuel cell system according to Embodiment 4 is shown in FIG. This system is provided with an air / fuel heat exchanger 22 for exchanging heat between fuel and air introduced into the SOFC 11 in the system of the third embodiment shown in FIG. By doing so, the temperature difference between the fuel and air introduced into the SOFC 11 is reduced, and the durability of the material such as ceramic used in the SOFC 11 is improved.
The air / fuel heat exchanger 22 can also be incorporated into the system of the first or second embodiment.

Embodiment 5. FIG.
The configuration of the solid oxide fuel cell system according to Embodiment 5 is shown in FIG. In this system of the fourth embodiment shown in FIG. 4, a fuel preheater 23 is disposed upstream of the ejector 17, and exhaust fuel recirculated by the ejector 17 is introduced into the fuel preheater 23. It is what I did. As a result, fuel input from the outside of the system is preheated by the heat of the recirculated exhaust fuel, and burns when it reaches the self-ignition temperature. For this reason, fuel combustion in the ejector 17 can be prevented, and the safety of system operation is ensured.
This fuel preheater 23 can be applied not only to the system of the fourth embodiment but also to each system of the first to third embodiments.
In the first to fifth embodiments, a hot water heater may be used as the first heat recovery device instead of the evaporator 14.

Embodiment 6 FIG.
FIG. 6 shows the main configuration of a solid oxide fuel cell system according to Embodiment 6. In this system, a part of the exhaust fuel discharged from the SOFC 11 is cooled by the exhaust fuel cooler 24, and this exhaust fuel is mixed with the fuel input from the outside of the system by the exhaust fuel fan 25, and the exhaust fuel is further mixed. The heated fuel is heated by the fuel heater 26 and is then introduced into the SOFC 11. By adopting such a configuration, the exhaust fuel can be recirculated using the exhaust fuel fan 25 instead of the ejector 17 shown in the first to fifth embodiments. However, the exhaust fuel needs to be cooled by the exhaust fuel cooler 24 to a temperature at which the exhaust fuel fan 25 can be used. Further, the fuel heater 26 is used for heating to the SOFC 11.

Embodiment 7 FIG.
FIG. 7 shows the main configuration of a solid oxide fuel cell system according to Embodiment 7. In this system, the water vapor produced by the evaporator 14 as the first heat recovery device is introduced into the ejector 17 as a drive gas, and a part of the exhausted fuel discharged from the SOFC 11 is sucked into the ejector 17 by the pressure of the water vapor. And recirculated. Fuel is supplied from the outside on the downstream side or upstream side of the ejector 17 and supplied to the SOFC 11 together with the exhaust fuel.

1 is a block diagram showing a configuration of a solid oxide fuel cell system according to Embodiment 1 of the present invention. FIG. 6 is a block diagram showing a configuration of a solid oxide fuel cell system according to Embodiment 2. FIG. 6 is a block diagram showing a configuration of a solid oxide fuel cell system according to Embodiment 3. FIG. 6 is a block diagram showing a configuration of a solid oxide fuel cell system according to Embodiment 4. FIG. FIG. 6 is a block diagram showing a configuration of a solid oxide fuel cell system according to Embodiment 5. FIG. 10 is a block diagram showing a main configuration of a solid oxide fuel cell system according to Embodiment 6. FIG. 10 is a block diagram showing a main configuration of a solid oxide fuel cell system according to Embodiment 7. It is a block diagram which shows the structure of the cogeneration system using a solid oxide fuel cell.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 SOFC, 12 Combustor, 13 2nd air preheater, 14,20 Evaporator, 15 1st air preheater, 16 Compressor, 17, 21 Ejector, 18 Air fan, 19 Intake air heat exchanger, 22 Air / Fuel heat exchanger, 23 Fuel preheater, 24 Waste fuel cooler, 25 Waste fuel fan, 26 Fuel heater.

Claims (3)

In a system for recirculating a part of the exhausted fuel discharged from the solid oxide fuel cell to the fuel cell,
A cooler for cooling part of the exhausted fuel discharged from the fuel cell;
An exhaust fuel fan for mixing the exhaust fuel cooled by the cooler with the supply fuel;
A solid oxide fuel cell system, comprising: a fuel heater that raises the temperature of the supplied fuel mixed with the exhaust fuel. In a system for recirculating a part of the exhausted fuel discharged from the solid oxide fuel cell to the fuel cell,
A combustor for mixing and burning exhaust fuel and exhaust air discharged from a fuel cell;
A heat exchanger for recovering heat of exhaust gas from the combustor;
A solid oxide fuel cell system comprising: an ejector for recirculating a part of the exhausted fuel discharged from the fuel cell to the fuel cell using the exhaust gas discharged from the heat exchanger as drive gas. In a system for recirculating a part of the exhausted fuel discharged from the solid oxide fuel cell to the fuel cell,
A combustor for mixing and burning exhaust fuel and exhaust air discharged from a fuel cell;
An evaporator that produces water vapor using the heat of exhaust gas from the combustor;
A solid oxide fuel cell system comprising: an ejector for recirculating a part of the exhausted fuel discharged from the fuel cell to the fuel cell using water vapor produced by the evaporator as a drive gas.

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