fuel cell system

Abstract

To provide a fuel cell system that achieves a high carbon dioxide recovery rate.SOLUTION: A fuel cell system 100 comprises a fuel cell 1 and a carbon dioxide recovery unit 2. The fuel cell comprises: a stack 11 including an air electrode 13 and a fuel electrode 14; a mixer 17; a reformer 12; a combustor 18; a reformed gas supply path L2; an air electrode exhaust gas path L3; a fuel electrode exhaust gas path L4; and a hydrogen collection path L8 for sending hydrogen-rich gas sent from the carbon dioxide recovery unit to the combustor. The fuel electrode exhaust gas path is branched into a fuel electrode exhaust gas recycling path L6 for sending fuel electrode exhaust gas to the mixer and a carbon dioxide recovery path L7 for sending fuel electrode exhaust gas to the carbon dioxide recovery unit. The carbon dioxide recovery unit comprises: a compressor 22 for compressing the fuel electrode exhaust gas; a storage tank 23 for storing the fuel electrode exhaust gas; and a carbon dioxide separation unit 24 for separating the fuel electrode exhaust gas to carbon dioxide and the hydrogen-rich gas.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to fuel cell systems. [Background technology]

[0002] Solid oxide fuel cells (SOFCs) are known for use by small- to medium-sized power consumers such as convenience stores, apartment complexes, and buildings, as well as for private power generation and cogeneration in large facilities such as factories and data centers. Compared to other types of fuel cells, SOFCs have features such as a higher operating temperature, high power generation efficiency, and compatibility with a variety of fuels. SOFCs generate power in a stack in which an electrolyte is placed between an anode and an cathode. Carbon dioxide is contained in the anode exhaust gas discharged from the anode. A fuel cell system has been disclosed that separates and recovers the carbon dioxide contained in this anode exhaust gas using a carbon dioxide separation device (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 3000118 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in conventional fuel cell systems, the fuel electrode exhaust gas is directly supplied to the carbon dioxide separation device, which has the problem of low carbon dioxide recovery rate.

[0005] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a fuel cell system with a high carbon dioxide recovery rate. [Means for solving the problem]

[0006] The fuel cell system disclosed herein is a fuel cell system having a fuel cell and a carbon dioxide recovery unit that recovers carbon dioxide from anode exhaust gas discharged from the fuel cell, wherein the fuel cell comprises a stack having an air electrode and an anode arranged opposite each other with an electrolyte between them, a mixer that mixes raw fuel with steam and anode exhaust gas discharged from the anode, a reformer that reforms the raw fuel mixed with steam and anode exhaust gas in the mixer to produce reformed gas, a combustor that maintains a reforming catalyst provided inside the reformer at a high temperature, a reformed gas supply path that sends the reformed gas to the anode, an air electrode exhaust gas path that sends air electrode exhaust gas discharged from the air electrode to the combustor, an anode exhaust gas path through which the anode exhaust gas flows, and a hydrogen recovery path that sends hydrogen-rich gas sent from the carbon dioxide recovery unit to the combustor, and the anode exhaust gas path is branched into an anode exhaust gas recycling path that sends the anode exhaust gas to the mixer and a carbon dioxide recovery path that sends the anode exhaust gas to the carbon dioxide recovery unit. The carbon dioxide capture unit includes a compressor that compresses the anode exhaust gas flowing through the carbon dioxide capture path, a storage tank that stores the anode exhaust gas pressurized by the compressor, and a carbon dioxide separation unit that separates the anode exhaust gas discharged from the storage tank into carbon dioxide and hydrogen-rich gas. The fuel cell further includes an air heat exchanger that exchanges heat between the combustion exhaust gas discharged from the combustor and the air sent to the air electrode, and a second carbon dioxide separation unit that separates the combustion exhaust gas discharged from the air heat exchanger into carbon dioxide and gases other than carbon dioxide. are. [Effects of the Invention]

[0007] In the fuel cell system of the present disclosure, the carbon dioxide capture unit includes a compressor that pressurizes the anode exhaust gas flowing through the carbon dioxide capture path, a storage tank that stores the anode exhaust gas pressurized by the compressor, and a carbon dioxide separation unit that separates the anode exhaust gas discharged from the storage tank into carbon dioxide and hydrogen-rich gas. The fuel cell further comprises an air heat exchanger for exchanging heat between the combustion exhaust gas discharged from the combustor and the air sent to the air electrode, and a second carbon dioxide separation unit for separating the combustion exhaust gas discharged from the air heat exchanger into carbon dioxide and gases other than carbon dioxide. This allows for an improved carbon dioxide recovery rate. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a configuration diagram of a fuel cell system according to a first embodiment. [Figure 2] FIG. 10 is a configuration diagram of a fuel cell system according to a second embodiment. [Figure 3] FIG. 10 is a configuration diagram of a fuel cell system according to a third embodiment. [Figure 4] FIG. 10 is a configuration diagram of a fuel cell system according to a fourth embodiment. [Figure 5] FIG. 10 is a configuration diagram of a fuel cell system according to a fifth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, a fuel cell system according to an embodiment of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same reference numerals indicate the same or corresponding parts.

[0010] Embodiment 1 Fig. 1 is a configuration diagram of a fuel cell system according to embodiment 1. As shown in Fig. 1, a fuel cell system 100 according to this embodiment is made up of a fuel cell 1 and a carbon dioxide capture unit 2. In this embodiment, the fuel cell 1 will be described as an SOFC.

[0011] First, the configuration of the fuel cell 1 will be described. The fuel cell 1 has a stack 11 and a reformer 12. The stack 11 is composed of an air electrode 13, an anode 14, and an electrolyte 15 disposed between the air electrode 13 and the anode 14. Air is supplied to the air electrode 13 from an air supply source 3 via an air heat exchanger 16 and an air supply path L1. Reformed gas is supplied to the anode 14 from a raw fuel supply source 4 via a mixer 17, the reformer 12, and a reformed gas supply path L2. In the fuel cell system 100 of this embodiment, city gas containing methane as a main component is used as the raw fuel. In addition to city gas, liquefied petroleum gas (LP gas) such as propane or butane, biogas, etc. can also be used as the raw fuel.

[0012] The temperature of the stack 11 is maintained at 600 to 1000°C by an insulating box (not shown). At the air electrode 13 of the stack 11, a reduction reaction shown in the following reaction formula (1) takes place. At the air electrode 13, oxygen in the air supplied through the air supply path L1 receives electrons from the load connected to the stack 11 and is converted into oxygen ions. The air electrode exhaust gas after the reaction is discharged to the air electrode exhaust gas path L3. 1 / 2O2+ 2e - → O 2- ······(1) Oxygen ions produced by the reduction reaction move to the fuel electrode 14 via the electrolyte 15. The air electrode exhaust gas flowing through the air electrode exhaust gas path L3 has a composition in which oxygen is reduced compared to the air flowing through the air supply path L1.

[0013] The raw fuel supplied from the raw fuel supply source 4 is mixed with steam and anode exhaust gas in a mixer 17 and sent to the reformer 12. In order for a reforming reaction to occur in the reforming catalyst installed inside the reformer 12, the reforming catalyst needs to be heated to 500 to 700°C. To heat the reforming catalyst, a combustor 18 is provided adjacent to the reformer 12. The reforming catalyst in the reformer 12 is heated to 500 to 700°C using the combustion heat from the combustor 18. In the reformer 12, the reforming reactions of the following reaction formulas (2) and (3) proceed due to the reforming catalyst, and the raw fuel is converted into a reformed gas containing a certain amount of hydrogen. CH4+ H2O → CO + 3H2···(2) CO + H2O → CO2+ H2···(3) The reformed gas contains hydrogen, water vapor, carbon monoxide, carbon dioxide, and unreacted methane, and is supplied to the fuel electrode 14 via a reformed gas supply path L2.

[0014] At the anode 14 of the stack 11, an oxidation reaction shown in the following reaction formula (4) proceeds. That is, at the anode 14, oxygen ions that have migrated from the cathode 13 via the electrolyte 15 react with hydrogen supplied to the anode 14 to convert into water and electrons. Anode exhaust gas is discharged from the anode 14 to anode exhaust gas path L4. O2- + H2 → H2O + 2e - (4) The methane and water vapor supplied to the anode 14 of the stack 11 are converted into hydrogen, carbon monoxide, and carbon dioxide inside the stack 11 through a chemical reaction known as the internal reforming reaction. The internal reforming reaction is the same as the reforming reactions of the above reaction formulas (2) and (3).

[0015] The anode exhaust gas flowing through the anode exhaust gas path L4 contains carbon dioxide, hydrogen, water vapor, and carbon monoxide. The temperature of the anode exhaust gas varies depending on the type of stack 11, the operating conditions, etc., but is generally between 500 and 700°C. This reaction generates a current to a load connected between the air electrode 13 and the anode 14 of the stack 11.

[0016] The air electrode exhaust gas flowing through the air electrode exhaust gas path L3 is supplied to the combustor 18. The anode exhaust gas path L4 is provided with a water vapor generator 19 and a condenser 20. The water vapor generator 19 converts water supplied from the water supply source 5 into water vapor by utilizing the heat of the anode exhaust gas. The water vapor converted by the water vapor generator 19 is sent to the mixer 17 via the water vapor supply path L5. The condenser 20 converts the water vapor contained in the anode exhaust gas into liquid water, and the water is sent to the water supply source 5.

[0017] Anode exhaust gas path L4 branches into two paths downstream of condenser 20. One path is anode exhaust gas recycle path L6, which is connected to mixer 17 via recycle blower 21. The other path is carbon dioxide recovery path L7, which is connected to carbon dioxide recovery unit 2.

[0018] City gas as raw fuel is supplied from raw fuel supply source 4, steam is supplied from steam supply path L5, and anode exhaust gas is supplied from anode exhaust gas recycling path L6 to mixer 17. Mixer 17 mixes the city gas, steam, and anode exhaust gas.

[0019] The combustor 18 receives the air electrode exhaust gas from the air electrode exhaust gas passage L3, and also receives hydrogen from the carbon dioxide recovery unit 2 (described later) via the hydrogen recovery passage L8. The combustor 18 combusts the oxygen contained in the air electrode exhaust gas with the hydrogen supplied from the hydrogen recovery passage L8, and maintains the temperature of the reforming catalyst installed inside the reformer 12 at 500 to 700°C. The combustion exhaust gas combusted in the combustor 18 is sent to the air heat exchanger 16. The temperature of the combustion exhaust gas discharged from the combustor 18 is several hundred degrees. The air heat exchanger 16 uses the heat of the combustion exhaust gas to raise the temperature of the air supplied from the air supply source 3 to 400 to 600°C.

[0020] Next, the configuration of the carbon dioxide recovery unit 2 will be described. The carbon dioxide capture unit 2 has a compressor 22, a storage tank 23, and a carbon dioxide separation unit 24. The carbon dioxide capture path L7 is connected to the carbon dioxide separation unit 24 via the compressor 22 and the storage tank 23. The carbon dioxide capture path L7, which passes through the carbon dioxide separation unit 24, is connected to, for example, a carbon dioxide storage tank (not shown). The carbon dioxide captured by the carbon dioxide capture unit 2 is stored in the carbon dioxide storage tank.

[0021] The carbon dioxide separation unit 24 is equipped with a carbon dioxide separation membrane. This carbon dioxide separation membrane has the property of allowing carbon dioxide to pass through but preventing other gases such as hydrogen from passing through. Examples of the carbon dioxide separation membrane that can be used include polymer membranes such as polyimide and polycarbonate, facilitated transport membranes such as polyamidoamine dendrimers, and inorganic membranes such as zeolite and amorphous silica. The anode exhaust gas flowing through the carbon dioxide capture path L7 contains carbon dioxide, hydrogen, and carbon monoxide. The carbon dioxide separation unit 24 separates the anode exhaust gas into carbon dioxide and other gases.

[0022] The gas separated from carbon dioxide in the carbon dioxide separation unit 24 is a gas that is rich in hydrogen. Hereinafter, this gas will be referred to as hydrogen-rich gas. The hydrogen-rich gas separated from carbon dioxide in the carbon dioxide separation unit 24 is sent to the combustor 18 provided in the fuel cell 1 via the hydrogen recovery path L8.

[0023] The permeation characteristics of gases passing through carbon dioxide separation membranes can be explained, for example, by the plug flow model. Plug flow is a flow in which the velocity is constant and the velocity distribution is flat across the cross section of the tube through which the gas permeates. According to this plug flow model, the carbon dioxide recovery rate in a carbon dioxide separation membrane depends on the partial pressure difference between the inlet and outlet sides, and the recovery rate increases as the partial pressure difference between the inlet and outlet sides increases.

[0024] In the fuel cell system of this embodiment, the anode exhaust gas flowing through carbon dioxide capture path L7 is pressurized by compressor 22, and the pressurized anode exhaust gas is temporarily stored in storage tank 23. By sending the carbon dioxide stored in storage tank 23 to carbon dioxide separation unit 24 at a constant high pressure, it is possible to increase the partial pressure difference between the inlet and outlet sides of the carbon dioxide separation membrane. As a result, it is possible to improve the carbon dioxide capture rate.

[0025] In this embodiment, the permeation characteristics of the carbon dioxide separation membrane have been explained using a plug flow model. However, even when using another model, such as a laminar flow model, the carbon dioxide recovery rate depends on the partial pressure difference between the inlet and outlet sides, and the recovery rate increases as the partial pressure difference between the inlet and outlet sides increases.

[0026] Embodiment 2 2 is a configuration diagram of a fuel cell system according to embodiment 2. A fuel cell system 100 according to this embodiment is the same as the fuel cell system described in embodiment 1, except that a second carbon dioxide separation unit is provided downstream of the air heat exchanger.

[0027] As shown in FIG. 2, in the fuel cell system 100 according to this embodiment, a second carbon dioxide separation unit 25 is connected downstream of the air heat exchanger 16. The combustion exhaust gas discharged from the air heat exchanger 16 is supplied to the second carbon dioxide separation unit 25. The second carbon dioxide separation unit 25 separates the combustion exhaust gas into carbon dioxide and other gases. The carbon dioxide separated in the second carbon dioxide separation unit 25 is sent to the carbon dioxide recovery line L7 downstream of the carbon dioxide separation unit 24 via the second carbon dioxide recovery line L9. The gases other than carbon dioxide separated in the second carbon dioxide separation unit 25 are discharged to the outside of the fuel cell 1.

[0028] Carbon dioxide remains in the hydrogen-rich gas sent from the carbon dioxide recovery unit 2 to the combustor 18 via the hydrogen recovery path L8. The carbon dioxide contained in the hydrogen-rich gas is not consumed in the combustor 18 and remains in the fuel exhaust gas. In the fuel cell system of the first embodiment, the combustion exhaust gas containing carbon dioxide passes through an air heat exchanger and is discharged to the outside of the fuel cell. In the fuel cell system of the present embodiment, the carbon dioxide contained in the combustion exhaust gas is separated in the second carbon dioxide separation unit 25, so that the carbon dioxide discharged to the outside of the fuel cell 1 can be reduced as much as possible.

[0029] In the fuel cell system 100 of the present embodiment, the second carbon dioxide recovery pathway L9 is connected to the carbon dioxide recovery pathway L7 downstream of the carbon dioxide separation unit 24, but may also be connected to the carbon dioxide recovery pathway L7 upstream of the compressor 22. The connection destination of the second carbon dioxide recovery pathway L9 can be selected appropriately depending on the amount and concentration of carbon dioxide separated in the second carbon dioxide separation unit 25.

[0030] Embodiment 3 3 is a configuration diagram of a fuel cell system according to embodiment 3. A fuel cell system 100 according to this embodiment is the same as the fuel cell system described in embodiment 1, except that three flow rate adjustment valves are provided in the carbon dioxide recovery path.

[0031] As shown in Figure 3, in the fuel cell system 100 of this embodiment, a first flow control valve V1 is provided upstream of the compressor 22 in the carbon dioxide recovery path L7, a second flow control valve V2 is provided between the storage tank 23 and the carbon dioxide separation section 24, and a third flow control valve V3 is provided downstream of the carbon dioxide separation section 24.

[0032] In the fuel cell system 100 according to this embodiment, the ratio of the anode exhaust gas flowing through the anode exhaust gas recycle path L6 to the carbon dioxide capture path L7 can be adjusted by adjusting the flow rate of the anode exhaust gas flowing through the carbon dioxide capture path L7 with the first flow control valve V1. For example, if the air electrode exhaust gas and the anode exhaust gas decrease due to fluctuations in the load connected between the air electrode 13 and the anode 14 of the stack 11, the combustion amount in the combustor 18 may decrease. In this case, by adjusting the aperture of the first flow control valve V1 to increase the amount of the anode exhaust gas flowing through the carbon dioxide capture path L7, the amount of hydrogen-rich gas flowing through the hydrogen capture path L8 can be increased, thereby suppressing the decrease in the combustion amount in the combustor 18. As a result, the fuel cell system 100 according to this embodiment can generate electricity stably without being affected by fluctuations in the load.

[0033] Furthermore, in the fuel cell system 100 according to this embodiment, the partial pressure difference between the inlet and outlet sides of the carbon dioxide separation unit 24 can be adjusted by adjusting the apertures of the second flow control valve V2 and the third flow control valve V3. The greater the partial pressure difference between the inlet and outlet sides of a carbon dioxide separation membrane, the higher the carbon dioxide recovery rate. However, from the standpoint of the durability of the carbon dioxide separation membrane and because an increase in compressor power reduces system efficiency, it is desirable to avoid making the pressure difference too large. In the fuel cell system 100 according to this embodiment, the partial pressure difference can be kept within a certain range by adjusting the apertures of the second flow control valve V2 and the third flow control valve V3.

[0034] Embodiment 4 4 is a configuration diagram of a fuel cell system according to embodiment 4. A fuel cell system 100 according to this embodiment is the same as the fuel cell system described in embodiment 3, except that it is provided with a temperature regulator that adjusts the temperature of the carbon dioxide separation section, a temperature sensor that measures the temperature of the carbon dioxide separation section, and a pressure sensor that measures the gas pressure in the carbon dioxide recovery path.

[0035] 4, the fuel cell system 100 according to this embodiment is provided with a temperature regulator 26 that regulates the temperature of the carbon dioxide separation section 24 in the fuel cell system described in the third embodiment. Also provided are a temperature sensor 31a that measures the temperature T1 on the inlet side of the carbon dioxide separation section 24 and a temperature sensor 31b that measures the temperature T2 on the outlet side. Furthermore, a pressure sensor 32a is provided on the carbon dioxide capture path L7 between the second flow control valve V2 and the carbon dioxide separation section 24, and a pressure sensor 32b is provided between the carbon dioxide separation section 24 and the third flow control valve V3.

[0036] The permeability characteristics of gases that pass through carbon dioxide separation membranes also depend on temperature. Gas separation in polymer membranes and the like involves the process of dissolution, diffusion, and desorption before passing through the separation membrane. In this case, the temperature dependence of the gas permeability characteristics generally follows the Arrhenius equation. The Arrhenius equation is an equation that predicts the rate of a chemical reaction at a certain temperature, and the reaction rate constant k is expressed as k = Aexp(-Ea / RT). Here, A is a constant independent of temperature, Ea is the activation energy, R is the gas constant, and T is the absolute temperature. Therefore, the higher the temperature, the faster the reaction rate. In other words, the higher the temperature, the higher the carbon dioxide recovery rate of a carbon dioxide separation membrane.

[0037] In the fuel cell system 100 of this embodiment, a temperature regulator 26 is provided to adjust the temperature of the carbon dioxide separation section 24, and the temperature of the carbon dioxide separation membrane can be increased, thereby improving the carbon dioxide recovery rate.

[0038] However, it is desirable to set an upper limit on the temperature from the viewpoint of the heat resistance and durability of the material of the carbon dioxide separation membrane. Furthermore, the temperature of the carbon dioxide separation membrane also changes due to changes in the flow rate and temperature of the anode exhaust gas flowing through the carbon dioxide capture path L7. Even in such cases, it is desirable to keep the temperature of the carbon dioxide separation membrane within a certain range in order to achieve a predetermined carbon dioxide capture rate in the carbon dioxide capture unit 2.

[0039] In the fuel cell system of this embodiment, pressure sensors 32a, 32b are used to monitor the pressure difference between the upstream and downstream sides of carbon dioxide separation section 24, and second flow control valve V2 and third flow control valve V3 are adjusted to adjust the flow rate of anode exhaust gas, and temperature regulator 26 is adjusted based on inlet temperature T1 and outlet temperature T2 detected by temperature sensors 31a and 31b, respectively, to keep the temperature of the carbon dioxide separation membrane within a certain range. As a result, in fuel cell system 100 of this embodiment, the carbon dioxide recovery rate can be stably improved.

[0040] In the fuel cell system of this embodiment, the temperature of the entire carbon dioxide separation unit 24 is adjusted by temperature regulator 26, but the temperature may also be adjusted separately along the path of the gas flowing through carbon dioxide separation unit 24. For example, the anode exhaust gas may be heated or cooled while passing through the carbon dioxide separation membrane of carbon dioxide separation unit 24, increasing the difference between the temperature T1 on the inlet side and the temperature T2 on the outlet side. This will result in a decrease in either the carbon dioxide recovery rate on the inlet side or the carbon dioxide recovery rate on the outlet side of carbon dioxide separation unit 24.

[0041] In such a case, it is desirable that the temperature regulator 26 independently regulates the temperature on the inlet side and outlet side of the carbon dioxide separation unit 24. By independently regulating the temperature on the inlet side and outlet side of the carbon dioxide separation unit 24, it is possible to prevent a decrease in the carbon dioxide recovery rate.

[0042] Embodiment 5 5 is a configuration diagram of a fuel cell system according to embodiment 5. A fuel cell system 100 according to this embodiment is the fuel cell system described in embodiment 4, provided with a carbon dioxide concentration meter that measures the carbon dioxide concentration in the carbon dioxide recovery path.

[0043] As shown in FIG. 5, in the fuel cell system 100 according to this embodiment, in the fuel cell system described in the fourth embodiment, a carbon dioxide concentration meter 33 is provided downstream of the third flow control valve V3 in the carbon dioxide recovery path L7.

[0044] In the fuel cell system 100 of this embodiment, the carbon dioxide concentration meter 33 measures the concentration of carbon dioxide sent from the carbon dioxide capture unit 2 to the outside, and the second flow control valve V2 and the third flow control valve V3 are adjusted so that the carbon dioxide concentration becomes a predetermined value. In addition, the temperature regulator 26 adjusts the temperature of the carbon dioxide separation unit 24 so that the carbon dioxide capture rate also falls within a predetermined range.

[0045] A fuel cell system configured in this manner can output carbon dioxide at a predetermined concentration.

[0046] Various aspects of the present disclosure are summarized below as appendices. (Appendix 1) A fuel cell system having a fuel cell and a carbon dioxide recovery unit that recovers carbon dioxide from a fuel electrode exhaust gas discharged from the fuel cell, the fuel cell comprises a stack having an air electrode and an anode arranged opposite to each other with an electrolyte therebetween, a mixer that mixes steam and the anode exhaust gas discharged from the anode with a raw fuel, a reformer that generates a reformed gas by reforming the raw fuel mixed with the steam and the anode exhaust gas in the mixer, a combustor that maintains a reforming catalyst provided inside the reformer at a high temperature, a reformed gas supply path that sends the reformed gas to the anode, a cathode exhaust gas path that sends the air electrode exhaust gas discharged from the air electrode to the combustor, a fuel electrode exhaust gas path through which the anode exhaust gas flows, and a hydrogen recovery path that sends hydrogen-rich gas sent from the carbon dioxide recovery unit to the combustor, the anode exhaust gas path is branched into an anode exhaust gas recycling path that sends the anode exhaust gas to the mixer and a carbon dioxide recovery path that sends the anode exhaust gas to the carbon dioxide recovery unit, a storage tank for storing the anode exhaust gas pressurized by the compressor; and a carbon dioxide separation unit for separating the anode exhaust gas discharged from the storage tank into carbon dioxide and the hydrogen-rich gas. (Appendix 2) The fuel cell system described in Appendix 1 is characterized in that the fuel cell further comprises an air heat exchanger that performs heat exchange between the combustion exhaust gas discharged from the combustor and the air sent to the air electrode, and a second carbon dioxide separation unit that separates the combustion exhaust gas discharged from the air heat exchanger into carbon dioxide and gases other than carbon dioxide. (Appendix 3) The fuel cell system described in Appendix 1 or 2, characterized in that the carbon dioxide capture unit has a first flow control valve upstream of the compressor in the carbon dioxide capture path, a second flow control valve between the storage tank and the carbon dioxide separation unit, and a third flow control valve downstream of the carbon dioxide separation unit. (Appendix 4) 4. The fuel cell system according to claim 3, wherein the carbon dioxide capture unit further includes a temperature regulator that adjusts the temperature of the carbon dioxide separation unit. (Appendix 5) 5. The fuel cell system according to claim 4, wherein the carbon dioxide recovery unit is provided with a carbon dioxide concentration meter downstream of the third flow rate adjustment valve. (Appendix 6) 6. The fuel cell system according to claim 4, wherein the temperature regulator independently regulates the temperature on the inlet side and the temperature on the outlet side of the carbon dioxide separation section.

[0047] While the present disclosure describes various exemplary embodiments and examples, the various features, aspects, and functions described in one or more embodiments are not limited to application to a particular embodiment, but may be applied to the embodiments alone or in various combinations. Therefore, countless variations not exemplified are conceivable within the scope of the technology disclosed in this specification, including, for example, cases where at least one component is modified, added, or omitted, and cases where at least one component is extracted and combined with components of another embodiment. [Explanation of symbols]

[0048] 1 fuel cell, 2 carbon dioxide capture section, 3 air supply source, 4 raw fuel supply source, 5 water supply source, 11 stack, 12 reformer, 13 air electrode, 14 fuel electrode, 15 electrolyte, 16 air heat exchanger, 17 mixer, 18 combustor, 19 steam generator, 20 condenser, 21 recycle blower, 22 compressor, 23 storage tank, 24 carbon dioxide separation section, 25 second carbon dioxide separation section, 26 temperature controller, 31a, 31b temperature sensors, 32a, 32b pressure sensors, 33 carbon dioxide concentration meter, 100 fuel cell system, L1 air supply path, L2 reformed gas supply path, L3 air electrode exhaust gas path, L4 fuel electrode exhaust gas path, L5 water vapor supply path, L6 fuel electrode exhaust gas recycling path, L7 carbon dioxide capture path, L8 hydrogen recovery path, L9 second carbon dioxide capture path, V1 First flow control valve, V2 second flow control valve, V3 third flow control valve.

Claims

1. A fuel cell system having a fuel cell and a carbon dioxide recovery unit that recovers carbon dioxide from anode exhaust gas discharged from the fuel cell, the fuel cell comprises a stack having an air electrode and an anode arranged opposite to each other with an electrolyte therebetween, a mixer that mixes steam and the anode exhaust gas discharged from the anode with a raw fuel, a reformer that generates a reformed gas by reforming the raw fuel mixed with the steam and the anode exhaust gas in the mixer, a combustor that maintains a reforming catalyst provided inside the reformer at a high temperature, a reformed gas supply path that sends the reformed gas to the anode, a cathode exhaust gas path that sends the air electrode exhaust gas discharged from the air electrode to the combustor, a fuel electrode exhaust gas path through which the anode exhaust gas flows, and a hydrogen recovery path that sends hydrogen-rich gas sent from the carbon dioxide recovery unit to the combustor, the anode exhaust gas path is branched into an anode exhaust gas recycling path that sends the anode exhaust gas to the mixer and a carbon dioxide recovery path that sends the anode exhaust gas to the carbon dioxide recovery unit, the carbon dioxide capture unit includes a compressor that compresses the anode exhaust gas flowing through the carbon dioxide capture path, a storage tank that stores the anode exhaust gas pressurized by the compressor, and a carbon dioxide separation unit that separates the anode exhaust gas discharged from the storage tank into carbon dioxide and the hydrogen-rich gas, a second carbon dioxide separation unit that separates the combustion exhaust gas discharged from the air heat exchanger into carbon dioxide and gases other than carbon dioxide; and a fuel cell system characterized in that the fuel cell further comprises an air heat exchanger that performs heat exchange between the combustion exhaust gas discharged from the combustor and the air sent to the air electrode.

2. A fuel cell system having a fuel cell and a carbon dioxide recovery unit that recovers carbon dioxide from anode exhaust gas discharged from the fuel cell, the fuel cell comprises a stack having an air electrode and an anode arranged opposite to each other with an electrolyte therebetween, a mixer that mixes steam and the anode exhaust gas discharged from the anode with a raw fuel, a reformer that generates a reformed gas by reforming the raw fuel mixed with the steam and the anode exhaust gas in the mixer, a combustor that maintains a reforming catalyst provided inside the reformer at a high temperature, a reformed gas supply path that sends the reformed gas to the anode, a cathode exhaust gas path that sends the air electrode exhaust gas discharged from the air electrode to the combustor, a fuel electrode exhaust gas path through which the anode exhaust gas flows, and a hydrogen recovery path that sends hydrogen-rich gas sent from the carbon dioxide recovery unit to the combustor, the anode exhaust gas path is branched into an anode exhaust gas recycling path that sends the anode exhaust gas to the mixer and a carbon dioxide recovery path that sends the anode exhaust gas to the carbon dioxide recovery unit, the carbon dioxide capture unit includes a compressor that compresses the anode exhaust gas flowing through the carbon dioxide capture path, a storage tank that stores the anode exhaust gas pressurized by the compressor, and a carbon dioxide separation unit that separates the anode exhaust gas discharged from the storage tank into carbon dioxide and the hydrogen-rich gas, a first flow control valve provided upstream of the compressor in the carbon dioxide capture path, a second flow control valve provided between the storage tank and the carbon dioxide separation unit, and a third flow control valve provided downstream of the carbon dioxide separation unit.

3. 3. The fuel cell system according to claim 2, wherein the carbon dioxide capture unit further comprises a temperature regulator that regulates the temperature of the carbon dioxide separation unit.

4. 4. The fuel cell system according to claim 3, wherein the carbon dioxide recovery unit is provided with a carbon dioxide concentration meter downstream of the third flow rate adjustment valve.

5. 5. The fuel cell system according to claim 3, wherein the temperature regulator independently regulates the temperature on the inlet side and the temperature on the outlet side of the carbon dioxide separation section.

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