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 a fuel cell system.

Background Art

[0002] Solid oxide fuel cells (SOFCs) are known for small-scale power consumers such as convenience stores, apartment buildings, and buildings, and for on-site power generation and cogeneration in large facilities such as factories and data centers. SOFCs have a higher operating temperature than other types of fuel cells and have characteristics such as high power generation efficiency and compatibility with various fuels. Power generation in an SOFC is performed by a stack in which an electrolyte is disposed between a fuel electrode and an air electrode. The fuel electrode exhaust gas discharged from the fuel electrode contains carbon dioxide. A fuel cell system has been disclosed in which carbon dioxide contained in this fuel electrode exhaust gas is separated and recovered by a carbon dioxide separation device (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

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

[0005] The present disclosure has been made to solve the above-described problems, and an object thereof is to provide a fuel cell system having a high carbon dioxide recovery rate.

Means for Solving the Problems

[0006] The fuel cell system of the present disclosure is a fuel cell system having a fuel cell and a carbon dioxide recovery unit that recovers carbon dioxide from the fuel electrode exhaust gas discharged from the fuel cell. The fuel cell includes a stack having an air electrode and a fuel electrode disposed opposite each other with an electrolyte interposed therebetween, a mixer that mixes steam and the fuel electrode exhaust gas discharged from the fuel electrode into the raw fuel, a reformer that reforms the raw fuel in which steam and the fuel electrode exhaust gas are mixed by the mixer to generate a reformed gas, a combustor that holds a reforming catalyst provided inside the reformer at a high temperature, a reformed gas supply path that sends the reformed gas to the fuel electrode, an air electrode 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 fuel electrode exhaust gas flows, and a hydrogen recovery path that sends the 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 recycle path that sends the fuel electrode exhaust gas to the mixer and a carbon dioxide recovery path that sends the fuel electrode exhaust gas to the carbon dioxide recovery unit. The carbon dioxide recovery unit includes a compressor that pressurizes the fuel electrode exhaust gas flowing through the carbon dioxide recovery path, a storage tank that stores the fuel electrode exhaust gas pressurized by the compressor, and a carbon dioxide separation unit that separates the fuel electrode exhaust gas discharged from the storage tank into carbon dioxide and hydrogen-rich gas.

Advantages of the Invention

[0007] Since the fuel cell system of the present disclosure includes a compressor that pressurizes the fuel electrode exhaust gas flowing through the carbon dioxide recovery path, a storage tank that stores the fuel electrode exhaust gas pressurized by the compressor, and a carbon dioxide separation unit that separates the fuel electrode exhaust gas discharged from the storage tank into carbon dioxide and hydrogen-rich gas, the recovery rate of carbon dioxide can be improved.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying out the Invention

[0009] Hereinafter, a fuel cell system according to an embodiment for carrying out the present disclosure will be described in detail with reference to the drawings. In each figure, 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, the fuel cell system 100 according to the present embodiment is composed of a fuel cell 1 and a carbon dioxide recovery unit 2. In the present embodiment, the fuel cell 1 will be described as a 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 and a fuel electrode 14, and an electrolyte 15 installed between the air electrode 13 and the fuel electrode 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. Reformate gas is supplied to the fuel electrode 14 from a raw fuel supply source 4 via a mixer 17, a reformer 12, and a reformate gas supply path L2. In the fuel cell system 100 of the present embodiment, city gas mainly composed of methane is used as the raw fuel. In addition to city gas, liquefied petroleum gas (LP gas) such as propane and butane, and biogas can be used as the raw fuel.

[0012] The temperature of the stack 11 is maintained at 600 to 1000 °C by a heat insulation box (not shown). In the air electrode 13 of the stack 11, the reduction reaction shown in the following reaction formula (1) proceeds. In the air electrode 13, oxygen in the air supplied from the air supply path L1 receives electrons from the load connected to the stack 11 and changes 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) The oxygen ions generated 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 with less oxygen than 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 fuel electrode exhaust gas in the mixer 17 and sent to the reformer 12. In order for the reforming reaction to be carried out by the reforming catalyst installed inside the reformer 12, it is necessary to raise the temperature of the reforming catalyst to 500 to 700 °C. In order to raise the temperature of the reforming catalyst, a combustor 18 is provided in the reformer 12. The combustion heat of the combustor 18 raises the temperature of 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 by 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, steam, carbon monoxide, carbon dioxide and unreacted methane. The reformed gas is supplied to the fuel electrode 14 via the reformed gas supply path L2.

[0014] In the fuel electrode 14 of the stack 11, the oxidation reaction shown in the following reaction formula (4) proceeds. That is, in the fuel electrode 14, the oxygen ions that have moved from the air electrode 13 via the electrolyte 15 react with the hydrogen supplied to the fuel electrode 14 and change into water and electrons. The fuel electrode exhaust gas is discharged from the fuel electrode 14 to the fuel electrode exhaust gas path L4. O2- + H2 → H2O + 2e - (4) Note that the methane and steam supplied to the fuel electrode 14 of the stack 11 are converted into hydrogen, carbon monoxide, and carbon dioxide inside the stack 11 by a chemical reaction called an internal reforming reaction. The internal reforming reaction is the same as the reforming reactions in the above reaction formulas (2) and (3).

[0015] The fuel electrode exhaust gas flowing through the fuel electrode exhaust gas path L4 contains carbon dioxide, hydrogen, steam, and carbon monoxide. The temperature of the fuel electrode exhaust gas varies depending on the type of the stack 11, operating conditions, etc., but is 500 to 700°C. By such a reaction, an electric current can be extracted from a load connected between the air electrode 13 and the fuel electrode 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 fuel electrode exhaust gas path L4 is provided with a steam generator 19 and a condenser 20. The steam generator 19 converts the water supplied from the water supply source 5 into steam using the heat of the fuel electrode exhaust gas. The steam converted by the steam generator 19 is sent to the mixer 17 via the steam supply path L5. The condenser 20 converts the steam contained in the fuel electrode exhaust gas into liquid water, and the water is sent to the water supply source 5.

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

[0018] The mixer 17 is supplied with the town gas as the raw fuel from the raw fuel supply source 4, steam from the steam supply path L5, and fuel electrode exhaust gas from the fuel electrode exhaust gas recycle path L6. The mixer 17 mixes the town gas, steam, and fuel electrode exhaust gas.

[0019] To the combustor 18, air electrode exhaust gas is sent from the air electrode exhaust gas path L3, and hydrogen is sent via the hydrogen recovery path L8 from the carbon dioxide recovery unit 2 described later. The combustor 18 burns oxygen contained in the air electrode exhaust gas and hydrogen supplied from the hydrogen recovery path L8 to maintain the temperature of the reforming catalyst installed inside the reformer 12 at 500 to 700 °C. The combustion exhaust gas burned 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 recovery unit 2 includes a compressor 22, a storage tank 23, and a carbon dioxide separation unit 24. The carbon dioxide recovery path L7 is connected to the carbon dioxide separation unit 24 via the compressor 22 and the storage tank 23. The carbon dioxide recovery path L7 passing through the carbon dioxide separation unit 24 is connected to, for example, a carbon dioxide storage tank (not shown). The carbon dioxide recovered by the carbon dioxide recovery unit 2 is stored in the carbon dioxide storage tank.

[0021] The carbon dioxide separation unit 24 is provided with a carbon dioxide separation membrane. This carbon dioxide separation membrane has the property of allowing carbon dioxide to permeate and making it difficult for hydrogen and the like other than carbon dioxide to permeate. As the carbon dioxide separation membrane, for example, polymer membranes such as polyimide and polycarbonate, facilitated transport membranes such as polyamidoamine dendrimer, and inorganic membranes such as zeolite and silica amorphous can be used. The fuel electrode exhaust gas flowing through the carbon dioxide recovery path L7 contains carbon dioxide, hydrogen, and carbon monoxide. The carbon dioxide separation unit 24 separates the fuel electrode 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 rich in hydrogen. Hereinafter, this gas is referred to as a 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 the gas permeating through the carbon dioxide separation membrane can be explained by, for example, a plug flow model. Plug flow refers to a flow in which the velocity is constant and the velocity distribution is flat across the cross-section of the pipe through which the gas permeates. According to this plug flow model, the recovery rate of carbon dioxide in the carbon dioxide separation membrane depends on the partial pressure difference between the inlet side and the outlet side, and the recovery rate increases as the partial pressure difference between the inlet side and the outlet side increases.

[0024] In the fuel cell system of the present embodiment, the fuel electrode exhaust gas flowing through the carbon dioxide recovery path L7 is pressurized by the compressor 22, and the pressurized fuel electrode exhaust gas is temporarily stored in the storage tank 23. By sending the carbon dioxide stored in the storage tank 23 to the carbon dioxide separation unit 24 at a certain high pressure, the partial pressure difference between the inlet side and the outlet side of the carbon dioxide separation membrane can be increased. As a result, the recovery rate of carbon dioxide can be improved.

[0025] In the present embodiment, the permeation characteristics of the carbon dioxide separation membrane are explained by a plug flow model. However, even if it is another model, for example, a laminar flow model, the recovery rate of carbon dioxide depends on the partial pressure difference between the inlet side and the outlet side, and the recovery rate increases as the partial pressure difference between the inlet side and the outlet side increases.

[0026] Embodiment 2. FIG. 2 is a configuration diagram of a fuel cell system according to Embodiment 2. The fuel cell system 100 according to the present embodiment is the fuel cell system described in Embodiment 1, in which 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 the present 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 by the second carbon dioxide separation unit 25 is sent to the carbon dioxide recovery path L7 downstream of the carbon dioxide separation unit 24 via the second carbon dioxide recovery path L9. The gases other than carbon dioxide separated by 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 Embodiment 1, the combustion exhaust gas containing carbon dioxide is discharged to the outside of the fuel cell via the air heat exchanger. In the fuel cell system of the present embodiment, since the carbon dioxide contained in the combustion exhaust gas is separated by the second carbon dioxide separation unit 25, the amount of 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, although the second carbon dioxide recovery path L9 is connected to the carbon dioxide recovery path L7 downstream of the carbon dioxide separation unit 24, it may be connected to the carbon dioxide recovery path L7 upstream of the compressor 22. The connection destination of the second carbon dioxide recovery path L9 can be appropriately selected according to the amount and concentration of carbon dioxide separated by the second carbon dioxide separation unit 25.

[0030] Embodiment 3. FIG. 3 is a configuration diagram of a fuel cell system according to Embodiment 3. The fuel cell system 100 according to the present embodiment is the fuel cell system described in Embodiment 1, in which three flow rate adjustment valves are provided in the carbon dioxide recovery path.

[0031] As shown in FIG. 3, in the fuel cell system 100 according to the present embodiment, a first flow rate adjustment valve V1 is provided upstream of the compressor 22 in the carbon dioxide recovery path L7, a second flow rate adjustment valve V2 is provided between the storage tank 23 and the carbon dioxide separation unit 24, and a third flow rate adjustment valve V3 is provided downstream of the carbon dioxide separation unit 24, respectively.

[0032] In the fuel cell system 100 according to the present embodiment, by adjusting the flow rate of the fuel electrode exhaust gas flowing through the carbon dioxide recovery path L7 with the first flow rate adjustment valve V1, the ratio of the fuel electrode exhaust gas flowing through the fuel electrode exhaust gas recycle path L6 and the carbon dioxide recovery path L7 can be adjusted. For example, when the air electrode exhaust gas and the fuel electrode exhaust gas decrease due to a change in the load connected between the air electrode 13 and the fuel electrode 14 of the stack 11, the combustion amount of the combustor 18 may decrease. In that case, by adjusting the opening degree of the first flow rate adjustment valve V1 to increase the amount of the fuel electrode exhaust gas flowing through the carbon dioxide recovery path L7, the amount of the hydrogen-rich gas flowing through the hydrogen recovery path L8 can be increased to suppress the decrease in the combustion amount of the combustor 18. As a result, in the fuel cell system 100 according to the present embodiment, stable power generation can be performed without being affected by load fluctuations.

[0033] Further, in the fuel cell system 100 according to the present embodiment, by adjusting the opening degrees of the second flow rate adjustment valve V2 and the third flow rate adjustment valve V3, the partial pressure difference between the inlet side and the outlet side of the carbon dioxide separation unit 24 can be adjusted. The carbon dioxide separation membrane has a higher carbon dioxide recovery rate as the partial pressure difference between the inlet side and the outlet side is larger. However, from the viewpoints of the durability of the carbon dioxide separation membrane and the like, and since the power of the compressor increases and the system efficiency decreases, it is desirable to avoid making the pressure difference extremely large. In the fuel cell system 100 according to the present embodiment, by adjusting the opening degrees of the second flow rate adjustment valve V2 and the third flow rate adjustment valve V3, the partial pressure difference can be kept within a certain range.

[0034] Embodiment 4. FIG. 4 is a configuration diagram of a fuel cell system according to Embodiment 4. The fuel cell system 100 according to the present embodiment is the fuel cell system described in Embodiment 3, provided with a temperature regulator for adjusting the temperature of the carbon dioxide separation unit, a temperature sensor for measuring the temperature of the carbon dioxide separation unit, and a pressure sensor for measuring the gas pressure in the carbon dioxide recovery path.

[0035] As shown in FIG. 4, the fuel cell system 100 according to the present embodiment is the fuel cell system described in Embodiment 3, provided with a temperature regulator 26 for adjusting the temperature of the carbon dioxide separation unit 24. Further, a temperature sensor 31a for measuring the temperature T1 on the inlet side of the carbon dioxide separation unit 24 and a temperature sensor 31b for measuring the temperature T2 on the outlet side are provided. Furthermore, a pressure sensor 32a is provided between the second flow rate adjustment valve V2 in the carbon dioxide recovery path L7 and the carbon dioxide separation unit 24, and a pressure sensor 32b is provided between the carbon dioxide separation unit 24 and the third flow rate adjustment valve V3.

[0036] The permeation characteristics of the gas permeating through the carbon dioxide separation membrane also depend on temperature. The separation of gas in a polymer membrane etc. permeates through the separation membrane via the processes of dissolution, diffusion, and desorption. In this case, the temperature dependence of the gas permeation characteristics generally follows the Arrhenius equation. The Arrhenius equation is an equation for predicting 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. That is, the recovery rate of carbon dioxide in the carbon dioxide separation membrane increases as the temperature increases.

[0037] In the fuel cell system 100 of the present embodiment, a temperature regulator 26 for adjusting the temperature of the carbon dioxide separation unit 24 is provided, and the temperature of the carbon dioxide separation membrane can be increased, so the recovery rate of carbon dioxide can be improved.

[0038] However, from the viewpoints of the heat resistance and durability of the material of the carbon dioxide separation membrane, it is desirable to set an upper limit for the temperature. Also, the temperature of the carbon dioxide separation membrane changes due to changes in the flow rate and temperature of the fuel electrode exhaust gas flowing through the carbon dioxide recovery path L7. Even in such a case, in order to make the recovery rate of carbon dioxide in the carbon dioxide recovery unit 2 a predetermined recovery rate, it is desirable to keep the temperature of the carbon dioxide separation membrane within a certain range.

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

[0040] Note that in the fuel cell system of the present embodiment, the temperature regulator 26 adjusts the overall temperature of the carbon dioxide separation unit 24, but the temperature may be adjusted separately along the path of the gas flowing through the carbon dioxide separation unit 24. For example, the fuel electrode exhaust gas may be heated or cooled while passing through the carbon dioxide separation membrane of the carbon dioxide separation unit 24, and the difference between the inlet-side temperature T1 and the outlet-side temperature T2 may increase. Then, either the carbon dioxide recovery rate at the inlet side or the outlet side of the carbon dioxide separation unit 24 will decrease.

[0041] In such a case, it is desirable for the temperature regulator 26 to perform temperature adjustment independently at the inlet side and the outlet side of the carbon dioxide separation unit 24. By performing temperature adjustment independently at the inlet side and the outlet side of the carbon dioxide separation unit 24, a decrease in the carbon dioxide recovery rate can be prevented.

[0042] Embodiment 5. FIG. 5 is a configuration diagram of a fuel cell system according to Embodiment 5. The fuel cell system 100 according to the present embodiment is the fuel cell system described in Embodiment 4, and is provided with a carbon dioxide concentration meter for measuring the carbon dioxide concentration in the carbon dioxide recovery path.

[0043] As shown in FIG. 5, in the fuel cell system 100 according to the present embodiment, in the fuel cell system described in Embodiment 4, a carbon dioxide concentration meter 33 is provided downstream of the third flow rate adjustment valve V3 in the carbon dioxide recovery path L7.

[0044] In the fuel cell system 100 of the present embodiment, the carbon dioxide concentration meter 33 measures the concentration of carbon dioxide sent from the carbon dioxide recovery unit 2 to the outside, and adjusts the second flow rate adjustment valve V2 and the third flow rate adjustment valve V3 so as to obtain a predetermined carbon dioxide concentration. Further, the temperature of the carbon dioxide separation unit 24 is adjusted by the temperature controller 26 so that the carbon dioxide recovery rate is also within a predetermined range.

[0045] The fuel cell system configured as described above can send out carbon dioxide at a predetermined concentration.

[0046] Hereinafter, various aspects of the present disclosure will be collectively described as appendices. (Appendix 1) A fuel cell system having a fuel cell and a carbon dioxide recovery unit that recovers carbon dioxide from the fuel electrode exhaust gas discharged from the fuel cell, The fuel cell includes a stack having an air electrode and a fuel electrode disposed opposite each other with an electrolyte therebetween, a mixer that mixes steam and the fuel electrode exhaust gas discharged from the fuel electrode into the raw fuel, a reformer that reforms the raw fuel in which the steam and the fuel electrode exhaust gas are mixed by the mixer to generate a reformed gas, a combustor that holds a reforming catalyst provided inside the reformer at a high temperature, a reformed gas supply path that sends the reformed gas to the fuel electrode, an air electrode 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 fuel electrode exhaust gas flows, and a hydrogen recovery path that sends the 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 recycle path that sends the fuel electrode exhaust gas to the mixer and a carbon dioxide recovery path that sends the fuel electrode exhaust gas to the carbon dioxide recovery unit. The carbon dioxide recovery unit includes a compressor that pressurizes the fuel electrode exhaust gas flowing through the carbon dioxide recovery path, a storage tank that stores the fuel electrode exhaust gas pressurized by the compressor, and a carbon dioxide separation unit that separates carbon dioxide and the hydrogen-rich gas from the fuel electrode exhaust gas discharged from the storage tank. A fuel cell system characterized by this. (Appendix 2) The fuel cell further includes 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 carbon dioxide and gases other than carbon dioxide from the combustion exhaust gas discharged from the air heat exchanger. The fuel cell system according to Appendix 1, characterized by this. (Appendix 3) In the carbon dioxide recovery unit, a first flow rate adjustment valve is provided upstream of the compressor in the carbon dioxide recovery path, a second flow rate adjustment valve is provided between the storage tank and the carbon dioxide separation unit, and a third flow rate adjustment valve is provided downstream of the carbon dioxide separation unit. The fuel cell system according to Appendix 1 or 2, characterized by this. (Appendix 4) The fuel cell system according to Supplementary Note 3, wherein the carbon dioxide recovery unit further includes a temperature regulator that regulates the temperature of the carbon dioxide separation unit. (Supplementary Note 5) The fuel cell system according to Supplementary Note 4, wherein a carbon dioxide concentration meter is provided downstream of the third flow rate adjustment valve in the carbon dioxide recovery unit. (Supplementary Note 6) The fuel cell system according to Supplementary Note 4 or 5, wherein the temperature regulator independently regulates the temperature on the inlet side and the outlet side of the carbon dioxide separation unit.

[0047] Although various exemplary embodiments and examples are described in the present disclosure, the various features, aspects, and functions described in one or more embodiments are not limited to the application of a specific embodiment, but are applicable to the embodiments alone or in various combinations. Therefore, countless variations not illustrated are envisioned within the scope of the technology disclosed in this specification. For example, it includes the case where at least one component is modified, added, or omitted, and further, the case where at least one component is extracted and combined with the components of other embodiments.

Description of Reference Numerals

[0048] 1 Fuel cell, 2 Carbon dioxide recovery section, 3 Air supply source, 4 Primary 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 Recycling blower, 22 Compressor, 23 Storage tank, 24 Carbon dioxide separation section, 25 Second carbon dioxide separation section, 26 Temperature regulator, 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 Steam supply path, L6 Fuel electrode exhaust gas recycling path, L7 Carbon dioxide recovery path, L8 Hydrogen recovery path, L9 Second carbon dioxide recovery path, V1 First flow rate adjustment valve, V2 Second flow rate adjustment valve, V3 Third flow rate adjustment valve.

Claims

1. A fuel cell system comprising a fuel cell and a carbon dioxide recovery unit that recovers carbon dioxide from the fuel electrode exhaust gas discharged from the fuel cell, wherein the fuel cell includes a stack having an air electrode and a fuel electrode disposed opposite each other with an electrolyte interposed therebetween, a mixer that mixes steam and the fuel electrode exhaust gas discharged from the fuel electrode with the raw fuel, a reformer that reforms the raw fuel in which the steam and the fuel electrode exhaust gas are mixed by the mixer to generate a reformed gas, a combustor that holds a reforming catalyst provided inside the reformer at a high temperature, a reformed gas supply path that sends the reformed gas to the fuel electrode, an air electrode 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 fuel electrode exhaust gas flows, and a hydrogen recovery path that sends the 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 recycle path that sends the fuel electrode exhaust gas to the mixer and a carbon dioxide recovery path that sends the fuel electrode exhaust gas to the carbon dioxide recovery unit, the carbon dioxide recovery unit includes a compressor that pressurizes the fuel electrode exhaust gas flowing through the carbon dioxide recovery path, a storage tank that stores the fuel electrode exhaust gas pressurized by the compressor, and a carbon dioxide separation unit that separates carbon dioxide and the hydrogen-rich gas from the fuel electrode exhaust gas discharged from the storage tank. The fuel cell system is characterized by this.

2. The fuel cell further includes 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 carbon dioxide and gases other than carbon dioxide from the combustion exhaust gas discharged from the air heat exchanger. The fuel cell system according to claim 1 is characterized by this.

3. The carbon dioxide recovery unit is characterized in that a first flow rate adjustment valve is provided upstream of the compressor in the carbon dioxide recovery path, a second flow rate adjustment valve is provided between the storage tank and the carbon dioxide separation unit, and a third flow rate adjustment valve is provided downstream of the carbon dioxide separation unit. The fuel cell system according to claim 1 or 2 is characterized by this.

4. The carbon dioxide recovery unit further includes a temperature regulator that regulates the temperature of the carbon dioxide separation unit. The fuel cell system according to claim 3 is characterized by this.

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

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.

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