JP3913008B2 - Solid oxide fuel cell system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
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.
[0002]
[Prior art]
FIG. 6 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.
[0003]
[Problems to be solved by the invention]
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 at 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.
[0004]
[Means for Solving the Problems]
According to a first aspect of the present invention, a solid oxide fuel cell system includes a combustor that mixes and burns exhaust fuel and exhaust air discharged from a fuel cell, and steam that uses heat of exhaust gas from the combustor. Or it connects between the 1st heat recovery device which manufactures warm water, the 1st air preheater which preheats the supply air to a fuel cell with the exhaust gas discharged | emitted from the heat recovery device, and a combustor and a heat recovery device A second air preheater that is further preheated with exhaust gas from the combustor and preheated by the first air preheater to supply the fuel cell to the fuel cell, and the first air disposed inside the fuel cell A supply air heat exchanger is provided that heats the supply air preheated by the preheater in the fuel cell and introduces it into the second air preheater .
[0005]
A solid oxide fuel cell system according to a second aspect is the system according to the first aspect, wherein the exhaust gas discharged from the first air preheater is used as a drive gas and a part of the exhausted fuel discharged from the fuel cell is used as the fuel cell. An ejector for recirculation is further provided.
A solid oxide fuel cell system according to a third aspect is the system according to the first or second aspect , wherein the heat of exhaust fuel or exhaust air connected between the fuel cell and the combustor and exhausted from the fuel cell is used. And a second heat recovery device for producing steam or warm water.
[0006]
The solid oxide fuel cell system according to claim 4 is the system according to any one of claims 1 to 3 , wherein the exhaust gas discharged from the first air preheater to lower the temperature in the combustor is combustor. Is to be introduced.
The solid oxide fuel cell system according to claim 5 is the system according to any one of claims 1 to 4 , wherein fuel is supplied to the fuel cell, and air is supplied to the fuel cell from the second air preheater. And a fuel / air heat exchanger for exchanging heat between the two.
The solid oxide fuel cell system according to claim 6 is the system of claim 2 , wherein the supplied fuel is introduced into the exhaust gas discharged from the first air preheater, and the heat of the exhaust fuel recirculated by the ejector is used. And a fuel preheater for preheating the supplied fuel.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
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.
In addition, 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 . It is connected to the air inlet of SOFC11 through the intake air heat exchanger 1 9及 beauty second air preheater 13 provided.
The evaporator 14 forms the first heat recovery device of the present invention, and the intake air heat exchanger 19 forms the supply air heat exchanger of the present invention .
[0009]
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. The 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.
[0010]
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.
[0011]
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. In addition, 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 increases. 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.
[0012]
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.
[0013]
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.
[0014]
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.
[0015]
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.
[0016]
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.
[0019]
【The invention's effect】
As described above, according to the present invention, the high-temperature exhaust fuel discharged from the SOFC is completely combusted in the combustor, and the exhaust gas discharged from the combustor is converted into the first heat recovery device and the first and second exhaustors. Each of the air preheaters recovers heat, and the supply air preheated by the first air preheater is heated by the supply air heat exchanger in the fuel cell and then introduced into the second air preheater. Efficiency can be improved.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a solid oxide fuel cell system according to Embodiment 1 of the present invention.
FIG. 2 is a block diagram showing a configuration of a solid oxide fuel cell system according to a second embodiment.
FIG. 3 is a block diagram showing a configuration of a solid oxide fuel cell system according to a third embodiment.
4 is a block diagram showing a configuration of a solid oxide fuel cell system according to Embodiment 4. FIG.
5 is a block diagram showing a configuration of a solid oxide fuel cell system according to Embodiment 5. FIG.
FIG. 6 is a block diagram showing a configuration of a 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 .

Claims (6)

In a system that recovers heat from exhaust gas discharged from a solid oxide fuel cell,
A combustor for mixing and burning exhaust fuel and exhaust air discharged from a fuel cell;
A first heat recovery device for producing steam or hot water using heat of exhaust gas from the combustor;
A first air preheater that preheats the supply air to the fuel cell with the exhaust gas discharged from the heat recovery device;
Second air preheating connected between the combustor and the heat recovery unit and preheated by the exhaust gas from the combustor and preheated by the first air preheater and supplied to the fuel cell and the vessel,
A supply air heat exchanger disposed inside the fuel cell and heated in the fuel cell after the supply air preheated by the first air preheater is introduced into the second air preheater. A solid oxide fuel cell system characterized by the above. The first system of claim 1 in which a portion of the exhaust fuel discharged from the fuel cell the discharged exhaust as a drive gas from the air preheater further comprising an ejector for recirculating the fuel cell. Claim 1 or further comprising a second heat recovery unit to produce steam or hot water using the heat of the exhaust fuel or waste air discharged from the connected and the fuel cell between the fuel cell and the combustor 2. The system according to 2 . The system according to any one of claims 1 to 3 , wherein exhaust gas discharged from the first air preheater is introduced into the combustor in order to lower a temperature in the combustor. Claim 1, further comprising a fuel / air heat exchanger for heat exchange between the fuel and the second air preheater to be supplied to the fuel cell and the air supplied to the fuel cell The system described in. 3. The fuel preheater according to claim 2 , further comprising: a fuel preheater that preheats the supplied fuel using heat of the exhausted fuel that is recirculated by the ejector when the supplied fuel is input to the exhaust gas discharged from the first air preheater. The described system.

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