fuel cell system

Abstract

To provide a fuel cell system in which a recycling rate is improved by concentrating carbon dioxide contained in fuel electrode exhaust gas.SOLUTION: A fuel cell system 100 comprises a fuel cell 1 and a carbon dioxide recovery part 2. The fuel cell has a stack 11 having an air electrode 13 and a fuel electrode 15, a mixer 17, a reformer 12, a combustor 18, a fuel supply path L2, an air electrode exhaust gas path L3, and a fuel electrode exhaust gas path L4. The carbon dioxide recovery part has: a first carbon dioxide separation part 23 and a second carbon dioxide separation part 25; a first hydrogen recovery path L8 which feeds hydrogen-rich gas separated in the first carbon dioxide separation part to the fuel supply path; and a second hydrogen recovery path L9 which feeds hydrogen-rich gas separated in the second carbon dioxide separation part to the combustor. The fuel electrode exhaust gas path branches into a fuel electrode exhaust gas recycling path L6 connected to the mixer and a carbon dioxide recovery path L7 connected to the first carbon dioxide separation part.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 as fuel cells for small- to medium-sized electricity consumers such as convenience stores and apartment complexes. Although SOFCs have a higher operating temperature than other types of fuel cells, they are characterized by high power generation efficiency, compatibility with a variety of feedstocks, and the ability to utilize high-temperature waste heat. SOFCs generate electricity in a stack in which an electrolyte is placed between an anode and an cathode. Anode exhaust gas discharged from the anode contains hydrogen. A fuel cell system has been disclosed in which the hydrogen contained in this anode exhaust gas is reintroduced into the stack (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2023-72684 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in conventional fuel cell systems, the anode exhaust gas is directly reintroduced into the stack, so the carbon dioxide contained in the anode exhaust gas is not concentrated, resulting in a low recycling rate.

[0005] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a fuel cell system that concentrates carbon dioxide contained in a fuel electrode exhaust gas to improve the recycling rate. [Means for solving the problem]

[0006] The fuel cell system of the present disclosure includes a fuel cell and a carbon dioxide capture unit that captures carbon dioxide from anode exhaust gas discharged from the fuel cell. The fuel cell includes a stack having an air electrode and an anode arranged opposite each other with an electrolyte therebetween, a mixer that mixes steam and anode exhaust gas discharged from the anode with a feedstock, a reformer that produces fuel by reforming the feedstock mixed with steam and anode exhaust gas in the mixer, a combustor that maintains a reforming catalyst provided inside the reformer at a high temperature, a fuel supply path that sends fuel to the anode, an air electrode exhaust gas path that sends air electrode exhaust gas discharged from the air electrode to the combustor, and an anode exhaust gas path through which the anode exhaust gas flows. The fuel cell system includes a first carbon dioxide separation section that separates the anode exhaust gas into carbon dioxide and hydrogen-rich gas, a second carbon dioxide separation section that is provided downstream of the first carbon dioxide separation section, a first hydrogen recovery path that sends the hydrogen-rich gas separated in the first carbon dioxide separation section to a fuel supply path, and a second hydrogen recovery path that sends the hydrogen-rich gas separated in the second carbon dioxide separation section to a combustor, and further the anode exhaust gas path is branched into an anode exhaust gas recycling path connected to a mixer and a carbon dioxide recovery path connected to the first carbon dioxide separation section. [Effects of the Invention]

[0007] The fuel cell system of the present disclosure includes a first hydrogen recovery path that sends the hydrogen-rich gas separated in the first carbon dioxide separation unit to a fuel supply path, and a second hydrogen recovery path that sends the hydrogen-rich gas separated in the second carbon dioxide separation unit to a combustor.Furthermore, the anode exhaust gas path is branched into an anode exhaust gas recycling path connected to a mixer and a carbon dioxide recovery path connected to the first carbon dioxide separation unit, so that the carbon dioxide contained in the anode exhaust gas can be concentrated to improve the recycling 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 characteristic diagram showing the recovery rate of carbon dioxide in the fuel cell system according to the third embodiment. [Figure 5] FIG. 10 is a configuration diagram of a fuel cell system according to a fourth embodiment. [Figure 6] 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. Fuel is supplied to the anode 14 from a raw material supply source 4 via a mixer 17, the reformer 12, and a fuel 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 material. In addition to city gas, liquefied petroleum gas (LP gas) such as propane or butane, biogas, etc. can also be used as the raw material.

[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) proceeds, and air electrode exhaust gas is discharged from the air electrode 13 to an air electrode exhaust gas path L3. The electrons involved in reaction formula (1) are supplied from an external circuit connected between the air electrode 13 and the fuel electrode 14. 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 contains oxygen and nitrogen.

[0013] The raw material supplied from the raw material 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 must be heated to 500 to 700°C. To heat the reforming catalyst, a combustor 18 is provided adjacent to the reformer 12. The heat of combustion in the combustor 18 heats the reforming catalyst in the reformer 12 to 500 to 700°C. In the reformer 12, the reforming reactions of the following reaction formulas (2) and (3) proceed due to the reforming catalyst, converting the raw material into a fuel whose main component is hydrogen. CH4+ H2O → CO + 3H2...(2) CO + H2O → CO2+ H2···(3) The fuel contains hydrogen, water vapor, carbon monoxide, carbon dioxide, and unreacted methane, and is supplied to the fuel electrode 14 via a fuel supply path L2.

[0014] At the anode 14 of the stack 11, an oxidation reaction shown in the following reaction formula (4) proceeds, and the anode exhaust gas is discharged from the anode 14 to the anode exhaust gas path L4. The oxygen ions involved in reaction formula (4) have migrated from the cathode 13 via the electrolyte 15. O 2- + 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 is approximately 600°C. This reaction generates a current in an external circuit 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 a combustor 18. A water vapor generator 19 and a condenser 20 are provided in the anode exhaust gas path L4. 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 liquid water is sent to the water supply source 5. Note that the condenser 20 is not necessarily provided.

[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] Mixer 17 is supplied with raw city gas from raw material supply source 4, steam from steam supply path L5, and anode exhaust gas from anode exhaust gas recycling path L6. Mixer 17 mixes the city gas, steam, and anode exhaust gas.

[0019] Next, the configuration of the carbon dioxide recovery unit 2 will be described. The carbon dioxide capture unit 2 has a first compressor 22, a first carbon dioxide separation unit 23, a second compressor 24, and a second carbon dioxide separation unit 25. The carbon dioxide capture path L7 is connected to the first carbon dioxide separation unit 23 via the first compressor 22. The carbon dioxide capture path L7, which passes through the first carbon dioxide separation unit 23, is further connected to the second carbon dioxide separation unit 25 via the second compressor 24. The carbon dioxide capture path L7, which passes through the second carbon dioxide separation unit 25, is connected to, for example, a carbon dioxide storage tank (not shown). The carbon dioxide captured in the carbon dioxide capture unit 2 is stored in the carbon dioxide storage tank.

[0020] The first carbon dioxide separation unit 23 and the second carbon dioxide separation unit 25 are equipped with carbon dioxide separation membranes. These carbon dioxide separation membranes allow carbon dioxide to pass through while blocking other substances such as hydrogen. Examples of carbon dioxide separation membranes 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 first carbon dioxide separation unit 23 and the second carbon dioxide separation unit 25 separate the anode exhaust gas into carbon dioxide and other gases. The carbon dioxide separation efficiency of the carbon dioxide separation membrane increases with the partial pressure difference between the upstream and downstream sides of the carbon dioxide separation membrane. Therefore, a first compressor 22 is provided upstream of the first carbon dioxide separation unit 23, and a second compressor 24 is provided upstream of the second carbon dioxide separation unit 25.

[0021] The gas separated from carbon dioxide in the first carbon dioxide separation unit 23 and the second carbon dioxide separation unit 25 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 first carbon dioxide separation unit 23 is sent to the fuel supply line L2 via the first hydrogen recovery line L8. The hydrogen-rich gas separated from carbon dioxide in the second carbon dioxide separation unit 25 is sent to the combustor 18 via the second hydrogen recovery line L9.

[0022] The combustor 18 is supplied with air electrode exhaust gas from the air electrode exhaust gas passage L3 and hydrogen-rich gas from the second hydrogen recovery passage L9. The combustor 18 combusts the oxygen contained in the air electrode exhaust gas with the hydrogen contained in the hydrogen-rich gas, 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 approximately 500°C. 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 500°C.

[0023] In the fuel cell system 100 configured as described above, the hydrogen-rich gas recovered in the carbon dioxide recovery unit 2 is supplied to the fuel supply path L2 and also to the combustor 18. This improves the power generation efficiency of the entire system. Furthermore, in the fuel cell system 100 of this embodiment, the anode exhaust gas is reintroduced into the reformer 12, thereby improving the recycling rate of the entire system. The recycling rate here refers to the proportion of the anode exhaust gas that is supplied to the reformer 12. Specifically, the recycling rate refers to the proportion of the anode exhaust gas that flows through the anode exhaust gas recycling path L6 to the total amount of anode exhaust gas that flows through the anode exhaust gas path L4. By recycling the anode exhaust gas, the carbon dioxide produced in the reformer 12 and the carbon dioxide produced by the internal reforming reaction in the stack 11 are reintroduced into the reformer 12. The higher the recycling rate, the greater the flow rate of the anode exhaust gas containing carbon dioxide that is supplied to the reformer, enhancing the carbon dioxide concentration effect.

[0024] Furthermore, in the fuel cell system 100 of this embodiment, the hydrogen-rich gas separated in the first carbon dioxide separation section 23, which has a high hydrogen concentration, is supplied to the fuel supply path L2, so that the power generation efficiency of the stack 11 is improved.

[0025] 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 path branching off from the first hydrogen recovery path is provided.

[0026] 2, the fuel cell system 100 according to this embodiment is provided with a third hydrogen recovery path L10 branching off from the first hydrogen recovery path L8 through which the hydrogen-rich gas separated in the first carbon dioxide separation unit 23 flows. The third hydrogen recovery path L10 is connected to the combustor 18.

[0027] In the fuel cell system 100 configured in this manner, if there is insufficient combustion heat in the combustor 18 to maintain the temperature of the reforming catalyst in the reformer 12 at 500 to 700°C, the amount of hydrogen sent to the combustor 18 can be increased.

[0028] 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 configured by adding a decompression pump to the carbon dioxide capture unit in the fuel cell system described in embodiment 1.

[0029] As shown in Figure 3, in the fuel cell system 100 of this embodiment, a first pressure reduction pump 26 is provided between the first carbon dioxide separation section 23 and the second compressor 24 of the carbon dioxide recovery section 2, and a second pressure reduction pump 27 is provided downstream of the second carbon dioxide separation section 25.

[0030] In the fuel cell system 100 configured in this manner, it is possible to increase the pressure difference between the upstream and downstream sides of each of the first carbon dioxide separation section 23 and the second carbon dioxide separation section 25. As a result, it is possible to improve the carbon dioxide recovery rate in each of the first carbon dioxide separation section 23 and the second carbon dioxide separation section 25.

[0031] Fig. 4 is a characteristic diagram showing the carbon dioxide recovery rate in the fuel cell system 100 of this embodiment. The horizontal axis represents the pressure difference between the upstream and downstream sides of the carbon dioxide separation membrane, and the vertical axis represents the carbon dioxide recovery rate. Fig. 4 shows the results of a simulation performed using a mixed gas of carbon dioxide and hydrogen. In Fig. 4, the solid line represents the recovery rate when a compressor is installed upstream of the carbon dioxide separation membrane and a pressure reducing pump is installed downstream, and the dashed line represents the recovery rate when a compressor is installed only upstream of the carbon dioxide separation membrane.

[0032] 4, in the fuel cell system 100 according to this embodiment, a compressor is installed upstream of the first carbon dioxide separation unit 23 and a pressure reducing pump is installed downstream of the first carbon dioxide separation unit 23 and the second carbon dioxide separation unit 25, respectively, so that the difference in carbon dioxide partial pressure between the upstream and downstream sides of the carbon dioxide separation membrane increases. As a result, the carbon dioxide recovery rate in the carbon dioxide recovery unit 2 improves.

[0033] Embodiment 4 5 is a configuration diagram of a fuel cell system according to embodiment 4. A fuel cell system 100 according to this embodiment uses an ejector instead of the mixer in the fuel cell system described in embodiment 1. An ejector is a device that uses the force of a high-pressure fluid to suck in a low-pressure fluid.

[0034] As shown in Fig. 5, the fuel cell system 100 according to this embodiment includes an ejector 30 instead of the mixer in the fuel cell system described in the first embodiment, and the first hydrogen recovery path L8 is connected to the ejector 30 instead of the fuel supply path L2. The recycle blower is also removed from the anode exhaust gas path L4. Furthermore, the water vapor supply path L5 is connected midway through the first hydrogen recovery path L8. Therefore, the hydrogen-rich gas introduced from the first hydrogen recovery path L8 to the ejector 30 contains water vapor.

[0035] The ejector 30 uses the hydrogen-rich gas sent from the first hydrogen recovery path L8 as a high-pressure fluid to drive the ejector 30, and sucks in the low-pressure fluid raw material and anode exhaust gas to mix the hydrogen-rich gas containing water vapor with the raw material and anode exhaust gas.

[0036] In the fuel cell system 100 configured in this manner, the anode exhaust gas can be introduced into the reformer without using a driving device such as a recycle blower, etc. This improves the efficiency of the entire fuel cell system 100.

[0037] Embodiment 5. 6 is a configuration diagram of a fuel cell system according to embodiment 5. A fuel cell system 100 according to this embodiment is configured by adding a third compressor and a third carbon dioxide separation unit to the carbon dioxide capture unit in the fuel cell system described in embodiment 1.

[0038] 6, the fuel cell system 100 according to this embodiment is provided with a third compressor 28 and a third carbon dioxide separation section 29 downstream of the second carbon dioxide separation section 25 of the carbon dioxide recovery section 2. The hydrogen-rich gas from which carbon dioxide has been separated in the third carbon dioxide separation section 29 is sent to the combustor 18 via a second hydrogen recovery path L9.

[0039] In the fuel cell system 100 configured in this manner, the recovery rate of carbon dioxide in the carbon dioxide recovery section 2 can be improved.

[0040] 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 material, a reformer that reforms the raw material mixed with the steam and the anode exhaust gas in the mixer to produce fuel, a combustor that maintains a reforming catalyst provided inside the reformer at a high temperature, a fuel supply path that sends the fuel to the anode, a cathode exhaust gas path that sends the air electrode exhaust gas discharged from the air electrode to the combustor, and an anode exhaust gas path through which the anode exhaust gas flows, the carbon dioxide recovery unit includes a first carbon dioxide separation unit that separates the anode exhaust gas into carbon dioxide and a hydrogen-rich gas, a second carbon dioxide separation unit that is provided downstream of the first carbon dioxide separation unit, a first hydrogen recovery path that sends the hydrogen-rich gas separated in the first carbon dioxide separation unit to the fuel supply path, and a second hydrogen recovery path that sends the hydrogen-rich gas separated in the second carbon dioxide separation unit to the combustor, a fuel cell system characterized in that the anode exhaust gas path is branched into an anode exhaust gas recycling path connected to the mixer and a carbon dioxide recovery path connected to the first carbon dioxide separation unit; (Appendix 2) 2. The fuel cell system according to claim 1, further comprising a third hydrogen recovery path branched from the first hydrogen recovery path for sending the hydrogen-rich gas to the combustor. (Appendix 3) 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 interposed therebetween; an ejector that uses hydrogen-rich gas sent from the carbon dioxide capture unit as a high-pressure fluid to suck in a feedstock and the anode exhaust gas and mixes the hydrogen-rich gas, steam, and the anode exhaust gas with the feedstock; a reformer that reforms the feedstock, which is a mixture of the hydrogen-rich gas, the steam, and the anode exhaust gas in the ejector, to produce fuel; a combustor that maintains a reforming catalyst provided inside the reformer at a high temperature; a fuel supply path that sends the fuel to the anode; an air electrode exhaust gas path that sends air electrode exhaust gas discharged from the air electrode to the combustor; and an anode exhaust gas path through which the anode exhaust gas flows, the carbon dioxide recovery unit includes a first carbon dioxide separation unit that separates the anode exhaust gas into carbon dioxide and a hydrogen-rich gas, a second carbon dioxide separation unit that is provided downstream of the first carbon dioxide separation unit, a first hydrogen recovery path that sends the hydrogen-rich gas separated in the first carbon dioxide separation unit to the ejector, and a second hydrogen recovery path that sends the hydrogen-rich gas separated in the second carbon dioxide separation unit to the combustor, a fuel cell system, wherein the anode exhaust gas path is branched into an anode exhaust gas recycling path connected to the ejector and a carbon dioxide recovery path connected to the first carbon dioxide separation unit; (Appendix 4) The fuel cell system described in any one of appendices 1 to 3, characterized in that the carbon dioxide recovery unit has a first compressor on the upstream side and a first pressure reduction pump on the downstream side of the first carbon dioxide separation unit, and a second compressor on the upstream side and a second pressure reduction pump on the downstream side of the second carbon dioxide separation unit. (Appendix 5) 5. The fuel cell system according to any one of claims 1 to 4, wherein the carbon dioxide capture unit further comprises a third carbon dioxide separation unit downstream of the second carbon dioxide separation unit.

[0041] 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]

[0042] 1 fuel cell, 2 carbon dioxide recovery section, 3 air supply source, 4 raw material 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 first compressor, 23 first carbon dioxide separation section, 24 second compressor, 25 second carbon dioxide separation section, 26 first pressure reduction pump, 27 second pressure reduction pump, 28 third compressor, 29 third carbon dioxide separation section, 30 ejector, 100 fuel cell system, L1 air supply path, L2 fuel 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 recovery path, L8 first hydrogen recovery path, L9 second hydrogen recovery path, L10 Third hydrogen recovery route.

Claims

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 material, a reformer that reforms the raw material mixed with the steam and the anode exhaust gas in the mixer to produce fuel, a combustor that maintains a reforming catalyst provided inside the reformer at a high temperature, a fuel supply path that sends the fuel to the anode, a cathode exhaust gas path that sends the air electrode exhaust gas discharged from the air electrode to the combustor, and an anode exhaust gas path through which the anode exhaust gas flows, the carbon dioxide recovery unit includes a first carbon dioxide separation unit that separates the anode exhaust gas into carbon dioxide and a hydrogen-rich gas, a second carbon dioxide separation unit that is provided downstream of the first carbon dioxide separation unit, a first hydrogen recovery path that sends the hydrogen-rich gas separated in the first carbon dioxide separation unit to the fuel supply path, and a second hydrogen recovery path that sends the hydrogen-rich gas separated in the second carbon dioxide separation unit to the combustor, a fuel cell system characterized in that the anode exhaust gas path is branched into an anode exhaust gas recycle path connected to the mixer and a carbon dioxide recovery path connected to the first carbon dioxide separation unit.

2. 2. The fuel cell system according to claim 1, further comprising a third hydrogen recovery path branched from the first hydrogen recovery path for sending the hydrogen-rich gas to the combustor.

3. 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 interposed therebetween; an ejector that uses hydrogen-rich gas sent from the carbon dioxide capture unit as a high-pressure fluid to suck in a feedstock and the anode exhaust gas and mixes the hydrogen-rich gas, steam, and the anode exhaust gas with the feedstock; a reformer that reforms the feedstock, which is a mixture of the hydrogen-rich gas, the steam, and the anode exhaust gas in the ejector, to produce fuel; a combustor that maintains a reforming catalyst provided inside the reformer at a high temperature; a fuel supply path that sends the fuel to the anode; an air electrode exhaust gas path that sends air electrode exhaust gas discharged from the air electrode to the combustor; and an anode exhaust gas path through which the anode exhaust gas flows, the carbon dioxide recovery unit includes a first carbon dioxide separation unit that separates the anode exhaust gas into carbon dioxide and a hydrogen-rich gas, a second carbon dioxide separation unit that is provided downstream of the first carbon dioxide separation unit, a first hydrogen recovery path that sends the hydrogen-rich gas separated in the first carbon dioxide separation unit to the ejector, and a second hydrogen recovery path that sends the hydrogen-rich gas separated in the second carbon dioxide separation unit to the combustor, a fuel cell system, characterized in that the anode exhaust gas path is branched into an anode exhaust gas recycling path connected to the ejector and a carbon dioxide recovery path connected to the first carbon dioxide separation unit;

4. 4. A fuel cell system as described in any one of claims 1 to 3, characterized in that the carbon dioxide recovery unit is provided with a first compressor on the upstream side and a first pressure reduction pump on the downstream side of the first carbon dioxide separation unit, and a second compressor on the upstream side and a second pressure reduction pump on the downstream side of the second carbon dioxide separation unit.

5. 4. The fuel cell system according to claim 1, wherein the carbon dioxide capture section further comprises a third carbon dioxide separation section downstream of the second carbon dioxide separation section.

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