Fuel cell system

Abstract

To provide a fuel cell system that is easily controlled, and can stably separate and recover hydrogen contained in fuel electrode exhaust gas.SOLUTION: A fuel cell system 100 has a fuel cell 1 and a carbon dioxide recovery unit 2. The fuel cell comprises a stack 11 having 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, a hydrogen separation unit 24 separating hydrogen from a hydrogen-rich gas fed from the carbon hydrogen recovery unit, and a first hydrogen recovery path L8 feeding hydrogen separated by the hydrogen separation unit to the combustor. The carbon dioxide recovery unit includes a carbon dioxide separation unit 23, and a second hydrogen recovery path L9 feeding the hydrogen-rich gas separated by the carbon dioxide separation unit to the hydrogen separation unit. The hydrogen separation unit includes a noble metal thin film, an organic thin film, and a hydrogen separation film including at least one of an organic porous membrane and an inorganic porous membrane.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, as well as for on-site power generation and cogeneration in large facilities such as factories and data centers. SOFCs operate at a higher temperature than other types of fuel cells and have characteristics such as high power generation efficiency and compatibility with various fuels. In an SOFC, power generation 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 hydrogen. A fuel cell system has been disclosed in which the hydrogen contained in the fuel electrode exhaust gas is once occluded and separated by a hydrogen storage alloy, and then the hydrogen occluded in the hydrogen storage alloy is released and supplied to a combustor (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 hydrogen is separated and recovered using a hydrogen storage alloy, there is a problem that heating is required during hydrogen occlusion and release, making control difficult. Furthermore, the hydrogen storage alloy has a large deterioration due to hydrogen occlusion and release, resulting in a problem that the hydrogen separation and recovery performance deteriorates.

[0005] The present disclosure has been made to solve the above-described problems, and an object thereof is to provide a fuel cell system that is easy to control and can stably separate and recover hydrogen contained in the fuel electrode exhaust gas.

Means for Solving the Problems

[0006] The fuel cell system of the present disclosure is a fuel cell system including 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 to 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 steam and the fuel electrode exhaust gas are mixed by the mixer to generate a reformed gas containing hydrogen, 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, a hydrogen separation unit that separates hydrogen from the hydrogen-rich gas sent from the carbon dioxide recovery unit, and a first hydrogen recovery path that sends the hydrogen separated by the hydrogen separation 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 carbon dioxide separation unit that separates the fuel electrode exhaust gas into carbon dioxide and a hydrogen-rich gas, and a second hydrogen recovery path that sends the hydrogen-rich gas separated by the carbon dioxide separation unit to the hydrogen separation unit. The hydrogen separation unit includes a hydrogen separation membrane including at least one of a noble metal thin film, an organic thin film, an organic porous membrane, and an inorganic porous membrane.

Advantages of the Invention

[0007] Since the hydrogen separation unit of the fuel cell system of the present disclosure includes a hydrogen separation membrane including at least one of a noble metal thin film, an organic thin film, an organic porous membrane, and an inorganic porous membrane, it is easy to control and can stably separate and recover hydrogen contained in the fuel electrode exhaust gas.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

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. Reformed gas is supplied to the fuel electrode 14 from a raw fuel supply source 4 via a mixer 17, a reformer 12, and a reformed 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, biogas, etc. 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 / 2O 2 + 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 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. CH 4 + H 2 O → CO + 3H 2 ···(2) CO + H 2 O → CO 2 + H 2 ····(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, at the fuel electrode 14, oxygen ions that have migrated from the air electrode 13 via the electrolyte 15 react with the hydrogen supplied to the fuel electrode 14 to change into water and electrons. Fuel electrode exhaust gas is discharged from the fuel electrode 14 to the fuel electrode exhaust gas path L4. O 2- + H 2 → H 2 O + 2e - (4) Note that the methane and water vapor 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, water vapor, 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 taken out to 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. A steam generator 19 and a condenser 20 are provided in the fuel electrode exhaust gas path L4. 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 water vapor 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 the fuel electrode exhaust gas from the fuel electrode exhaust gas recycle path L6. The mixer 17 mixes the town gas, steam, and the fuel electrode exhaust gas.

[0019] The combustor 18 is supplied with the air electrode exhaust gas from the air electrode exhaust gas path L3 and hydrogen from the hydrogen separation unit 24 described later via the first hydrogen recovery path L8. The combustor 18 burns the oxygen contained in the air electrode exhaust gas and the hydrogen supplied from the first 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 and a carbon dioxide separation unit 23. The carbon dioxide recovery path L7 is connected to the carbon dioxide separation unit 23 via the compressor 22. The carbon dioxide recovery path L7 passing through the carbon dioxide separation unit 23 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 23 is provided with a carbon dioxide separation membrane. This carbon dioxide separation membrane has the property of allowing carbon dioxide to permeate while 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 23 separates the fuel electrode exhaust gas into carbon dioxide and other gases. The separation characteristics of carbon dioxide in the carbon dioxide separation membrane become more efficient as the partial pressure difference between the upstream side and the downstream side of the carbon dioxide separation membrane increases. Therefore, a compressor 22 is provided on the upstream side of the carbon dioxide separation unit 23.

[0022] The gas separated from carbon dioxide in the carbon dioxide separation unit 23 is a gas rich in hydrogen. Hereinafter, this gas is referred to as hydrogen-rich gas. The hydrogen-rich gas separated from carbon dioxide in the carbon dioxide separation unit 23 is sent to the hydrogen separation unit 24 provided in the fuel cell 1 via the second hydrogen recovery path L9.

[0023] The hydrogen separation unit 24 is provided with a hydrogen separation membrane. This hydrogen separation membrane has the property of allowing hydrogen to permeate while not allowing carbon monoxide and the like other than hydrogen to permeate. As the hydrogen separation membrane, for example, noble metal thin films such as palladium and niobium, organic thin films such as polyimide, organic porous membranes such as polyamide and polyimide, and inorganic porous membranes such as carbon and zeolite can be used. The hydrogen-rich gas flowing through the first hydrogen recovery path L8 contains hydrogen, carbon monoxide, and a small amount of carbon dioxide. The hydrogen separation unit 24 separates the hydrogen-rich gas into hydrogen and other gases. The hydrogen separated in the hydrogen separation unit 24 is sent to the combustor 18 via the first hydrogen recovery path L8. The gas separated from hydrogen in the hydrogen separation unit 24 is sent to the carbon dioxide recovery path L7 on the downstream side of the carbon dioxide separation unit 23 via the recovery path L10.

[0024] In the fuel cell system 100 configured as described above, since the hydrogen-rich gas recovered by the carbon dioxide recovery unit 2 is separated into hydrogen and other gases by the hydrogen separation unit 24, the concentration of hydrogen supplied to the combustor 18 can be increased. Further, since the hydrogen separation unit 24 separates hydrogen from other gases, the gas flowing through the first hydrogen recovery path L8 does not contain carbon dioxide. Therefore, the carbon dioxide recovery rate of the entire system can be made almost 100%. That is, the combustion exhaust gas burned in the combustor 18 is discharged to the outside via the air heat exchanger 16, and the concentration of carbon dioxide in the exhaust gas can be made extremely low.

[0025] Also, in the fuel cell system 100 of the present embodiment, since the fuel electrode exhaust gas is re-introduced into the reformer 12, the recycling rate of the entire system is improved. Here, the recycling rate is the ratio of the gas supplied to the reformer 12 among the fuel electrode exhaust gas. Specifically, the recycling rate is the ratio of the fuel electrode exhaust gas flowing through the fuel electrode exhaust gas recycling path L6 to the total amount of the fuel electrode exhaust gas flowing through the fuel electrode exhaust gas path L4. The fuel electrode exhaust gas is recycled, and the carbon dioxide generated by the reformer 12 and the carbon dioxide generated by the internal reforming reaction of the stack 11 are re-introduced into the reformer 12. The higher the recycling rate, the greater the flow rate of the fuel electrode exhaust gas containing carbon dioxide supplied to the reformer, and the higher the carbon dioxide concentration effect. As a result, in the carbon dioxide recovery unit 2, the power of the compressor 22 required for separating carbon dioxide from other gases can be reduced.

[0026] Furthermore, in the fuel cell system 100 of the present embodiment, the hydrogen separation membrane of the hydrogen separation unit 24 is made of a material other than a hydrogen storage alloy, such as a noble metal thin film, an organic thin film, an organic porous membrane, or an inorganic porous membrane. The hydrogen separation membrane made of these materials does not require heating to separate hydrogen and has little deterioration when separating hydrogen from other gases. Therefore, in the fuel cell system 100 of the present embodiment, compared with the case where a hydrogen storage alloy is used in the hydrogen separation unit, control is easier and hydrogen contained in the fuel electrode exhaust gas can be stably separated and recovered.

[0027] 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 provided with a path branched from the first hydrogen recovery path in the fuel cell system described in Embodiment 1, and a path for sending the raw fuel supplied from the raw fuel supply source to the combustor.

[0028] As shown in FIG. 2, the fuel cell system 100 according to the present embodiment is provided with a third hydrogen recovery path L11 branched from the first hydrogen recovery path L8 through which the hydrogen separated by the hydrogen separation unit 24 flows. This third hydrogen recovery path L11 is connected to the reformed gas supply path L2.

[0029] Also, as shown in FIG. 2, the fuel cell system 100 according to the present embodiment is provided with a raw fuel supply path L12 for sending the raw fuel supplied from the raw fuel supply source 4 to the combustor 18. Further, as shown in FIG. 2, flow rate adjustment valves V1, V2, V3, and V4 are provided in the carbon dioxide recovery path L7, the first hydrogen recovery path L8, the third hydrogen recovery path L11, and the raw fuel supply path L12, respectively.

[0030] In the fuel cell system 100, the amount of the fuel electrode exhaust gas varies due to fluctuations in the load connected between the air electrode 13 and the fuel electrode 14 of the stack 11. For example, when the amount of the fuel electrode exhaust gas decreases, the amount of hydrogen separated by the hydrogen separation unit 24 decreases, and the amount of hydrogen supplied to the reformed gas supply path L2 via the third hydrogen recovery path L11 also decreases. Then, the internal reforming reaction in the stack 11 is reduced and the temperature of the stack 11 decreases.

[0031] In the fuel cell system 100 of the present embodiment, the flow rate adjustment valve V2 provided in the first hydrogen recovery path L8 reduces the hydrogen sent to the combustor 18, and the flow rate adjustment valve V3 provided in the third hydrogen recovery path L11 can increase the hydrogen sent to the fuel electrode 14. As a result, a temperature drop of the stack 11 can be prevented. However, since the hydrogen flowing through the first hydrogen recovery path L8 decreases and sufficient hydrogen is not supplied to the combustor 18, the combustion amount of the combustor 18 decreases and the amount of heat supplied to the reformer 12 decreases, so the reforming reaction in the reformer 12 may not proceed sufficiently. In the fuel cell system 100 of the present embodiment, since the raw fuel can be sent from the raw fuel supply source 4 to the combustor 18 by opening the flow rate adjustment valve V4 provided in the raw fuel supply path L12, a decrease in the combustion amount of the combustor 18 can be prevented. As a result, in the fuel cell system 100 of the present embodiment, stable power generation can be performed regardless of fluctuations in the load connected to the stack.

[0032] Note that even when the amount of fuel electrode exhaust gas increases due to load fluctuations, stable power generation can be performed by adjusting the flow rate of the gas flowing through each path with the flow rate adjustment valves installed in each path. As described above, in the fuel cell system 100 of the present embodiment, the third hydrogen recovery path L11 that supplies the hydrogen separated and recovered from the fuel electrode exhaust gas to the stack and the raw fuel supply path L12 that sends the raw fuel from the raw fuel supply source to the combustor are provided. Further, flow rate adjustment valves V1, V2, V3, and V4 are provided in the carbon dioxide recovery path L7, the first hydrogen recovery path L8, the third hydrogen recovery path L11, and the raw fuel supply path L12, respectively. Therefore, the fuel cell system of the present embodiment can perform stable power generation regardless of fluctuations in the load connected to the stack.

[0033] 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 obtained by adding a hydrogen storage tank between the hydrogen separation unit and the first hydrogen recovery path in the fuel cell system described in Embodiment 2.

[0034] As shown in FIG. 3, in the fuel cell system 100 according to the present embodiment, a hydrogen storage tank 25 is added between the hydrogen separation unit 24 and the first hydrogen recovery path L8. The third hydrogen recovery path L11 is connected between the hydrogen storage tank 25 and the reformed gas supply path L2. The hydrogen separated by the hydrogen separation unit 24 is temporarily stored in the hydrogen storage tank 25. The hydrogen stored in the hydrogen storage tank 25 is sent to the combustor 18 via the first hydrogen recovery path L8 and sent to the fuel electrode 14 via the third hydrogen recovery path L11.

[0035] Generally, a nickel-based material is used for the fuel electrode 14 of the stack 11 of the fuel cell 1. However, when the fuel electrode is exposed to an oxidizing atmosphere at a high temperature, the fuel electrode is oxidized, causing problems such as deterioration of the stack and a decrease in output.

[0036] In the fuel cell system, during normal operation, a gas in a reducing atmosphere containing hydrogen is sent from the reformer 12 to the fuel electrode 14. However, when the gas in the reducing atmosphere is not sent from the reformer 12 to the fuel electrode 14 during startup, shutdown, or emergency shutdown of the fuel cell system, the fuel electrode 14 may be in an oxidizing atmosphere.

[0037] In the fuel cell system 100 of the present embodiment, even when the gas in the reducing atmosphere is not sent from the reformer 12 to the fuel electrode 14 during startup, shutdown, or emergency shutdown, the hydrogen stored in the hydrogen storage tank 25 can be sent to the fuel electrode 14 via the third hydrogen recovery path L11. Therefore, even during startup, shutdown, or emergency shutdown of the fuel cell system, the fuel electrode can be maintained in a reducing atmosphere. As a result, deterioration of the stack can be prevented.

[0038] 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, in which a flow rate adjustment valve is provided in the steam supply path and a flow rate adjustment valve is provided between the raw fuel supply source and the mixer.

[0039] As shown in Fig. 4, in the fuel cell system 100 according to this embodiment, in the fuel cell system described in Embodiment 3, a flow rate adjustment valve V5 is provided in the water vapor supply path L5. Further, a flow rate adjustment valve V6 is provided between the raw fuel supply source 4 and the mixer 17. Furthermore, in the fuel cell system 100 according to this embodiment, although not shown in the figure, a temperature sensor for measuring the temperature T1 of the stack 11, a temperature sensor for measuring the temperature T2 of the reformer 12, a voltage sensor for measuring the output voltage V of the stack 11, and a pressure sensor for measuring the gas pressure P of the hydrogen storage tank 25 are provided.

[0040] In the fuel cell system 100 configured as described above, when the output power of the stack 11, that is, the output voltage V, varies with the load fluctuation, the opening and closing amounts of the flow rate adjustment valves V5 and V6 are adjusted to adjust the amounts of the raw fuel and water vapor sent to the mixer 17. At the same time, the opening and closing amounts of the flow rate adjustment valves V2 and V3 are adjusted to adjust the amounts of hydrogen sent from the hydrogen storage tank 25 to the fuel electrode 14 and the combustor 18 so that the temperature T1 of the stack 11 and the temperature T2 of the reformer 12 are maintained within a preset temperature range. At this time, the amount of hydrogen sent from the hydrogen storage tank 25 to the combustor 18 is adjusted by the flow rate adjustment valve V2 so that the gas pressure P of the hydrogen storage tank 25 always remains equal to or higher than a preset threshold value. When the amount of hydrogen sent from the hydrogen storage tank 25 to the combustor 18 is insufficient, the amount of the raw fuel sent from the raw fuel supply source 4 to the combustor 18 is increased by the flow rate adjustment valve V4 in the raw fuel supply path L12. The threshold value of the gas pressure P of the hydrogen storage tank 25 is the gas pressure required to secure a certain amount of hydrogen in the hydrogen storage tank 25 to keep the fuel electrode in a reducing atmosphere when the fuel cell is stopped.

[0041] In the fuel cell system 100 configured as described above, since the gas pressure P of the hydrogen storage tank 25 can always be maintained at or above the threshold value, a certain amount of hydrogen necessary to keep the fuel electrode in a reducing atmosphere can be secured in the hydrogen storage tank 25 when the fuel cell is stopped. Therefore, even when the fuel cell system is stopped, the fuel electrode can be surely maintained in a reducing atmosphere. As a result, in the fuel cell system of the present embodiment, the reliability of the system is improved.

[0042] Although various exemplary embodiments and examples are described in the present disclosure, the various features, aspects, and functions described in one or more of the 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 cases where at least one component is deformed, added, or omitted, and further, cases where at least one component is extracted and combined with components of other embodiments.

Description of Reference Numerals

[0043] 1 Fuel cell, 2 Carbon dioxide recovery unit, 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 Combuster, 19 Steam generator, 20 Condenser, 21 Recycling blower, 22 Compressor, 23 Carbon dioxide separation unit, 24 Hydrogen separation unit, 25 Hydrogen storage tank, 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 First hydrogen recovery path, L9 Second hydrogen recovery path, L10 Recovery path, L11 Third hydrogen recovery path, L12 Primary fuel supply path, V1, V2, V3, V4, V5, V6 Flow rate adjustment valves.

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, 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 with the fuel electrode exhaust gas discharged from the fuel electrode in the raw fuel, a reformer that reforms the raw fuel in which the steam and the fuel electrode exhaust gas are mixed to generate a reformed gas containing hydrogen, 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, a hydrogen separation unit that separates hydrogen from the hydrogen-rich gas sent from the carbon dioxide recovery unit, and a first hydrogen recovery path that sends the hydrogen separated by the hydrogen separation 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 carbon dioxide separation unit that separates carbon dioxide and the hydrogen-rich gas from the fuel electrode exhaust gas, and a second hydrogen recovery path that sends the hydrogen-rich gas separated by the carbon dioxide separation unit to the hydrogen separation unit, and the hydrogen separation unit is characterized by including a hydrogen separation membrane including at least one of a noble metal thin film, an organic thin film, an organic porous membrane, and an inorganic porous membrane. A fuel cell system.

2. The fuel cell according to claim 1, further comprising a third hydrogen recovery path that sends the hydrogen separated by the hydrogen separation unit to the reformed gas supply path, and a raw fuel supply path that sends the raw fuel to the combustor.

3. The fuel cell according to claim 2, further comprising a hydrogen storage tank between the hydrogen separation unit and the first hydrogen recovery path, and the third hydrogen recovery path is connected to the hydrogen storage tank.

4. Flow control valves are respectively provided in the first hydrogen recovery path, the third hydrogen recovery path, and the raw fuel supply path, and by adjusting the opening and closing amount of the flow control valve, the temperature of the stack and the temperature of the reformer are maintained within a preset temperature range, and the gas pressure of the hydrogen storage tank is maintained at a preset threshold value or more. The fuel cell system according to claim 3, characterized in that.

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