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 fuel cell systems. [Background technology]

[0002] Solid oxide fuel cells (SOFCs) are known for use by small- to medium-sized power consumers such as convenience stores, apartment complexes, and buildings, as well as for private power generation and cogeneration in large facilities such as factories and data centers. Compared to other types of fuel cells, SOFCs have features such as a higher operating temperature, high power generation efficiency, and compatibility with a variety of fuels. SOFCs generate power in a stack with an electrolyte disposed 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 first absorbed and separated by a hydrogen storage alloy, and then the hydrogen absorbed by the alloy is released and supplied to a combustor (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-108620 Summary of the Invention [Problem to be solved by the invention]

[0004] However, conventional fuel cell systems use hydrogen storage alloys to separate and recover hydrogen, which requires heating during hydrogen storage and release, making it difficult to control.Furthermore, hydrogen storage alloys are subject to significant degradation due to hydrogen storage and release, resulting in a decrease in hydrogen separation and recovery performance.

[0005] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a fuel cell system that is easy to control and can stably separate and recover hydrogen contained in anode exhaust gas. [Means for solving the problem]

[0006] The fuel cell system of the present disclosure has a fuel cell and a carbon dioxide recovery unit that recovers carbon dioxide from anode exhaust gas discharged from the fuel cell, and the fuel cell includes a stack having an air electrode and anode that are arranged opposite each other with an electrolyte therebetween, a mixer that mixes raw fuel with steam and anode exhaust gas discharged from the anode, a reformer that reforms the raw fuel mixed with steam and anode exhaust gas in the mixer to produce a reformed gas containing hydrogen, and a combustion catalyst that maintains a high temperature inside the reformer. The system includes a reactor, a reformed gas supply path that sends the reformed gas to the anode, an air electrode exhaust gas path that sends the air electrode exhaust gas discharged from the air electrode to the combustor, an anode exhaust gas path through which the anode exhaust gas flows, a hydrogen separation unit that separates hydrogen from the hydrogen-rich gas sent from the carbon dioxide capture unit, and a first hydrogen recovery path that sends the hydrogen separated in the hydrogen separation unit to the combustor. The anode exhaust gas path is branched into an anode exhaust gas recycle path that sends the anode exhaust gas to the mixer and a carbon dioxide recovery path that sends the anode exhaust gas to the carbon dioxide capture unit. The carbon dioxide capture unit includes a carbon dioxide separation unit that separates the anode exhaust gas into carbon dioxide and hydrogen-rich gas, and a second hydrogen recovery path that sends the hydrogen-rich gas separated in the carbon dioxide separation unit to the hydrogen separation unit. The hydrogen separation unit includes a hydrogen separation membrane that includes at least one of a precious metal thin film, an organic thin film, an organic porous membrane, and an inorganic porous membrane. [Effects of the Invention]

[0007] The fuel cell system disclosed herein has a hydrogen separation section equipped with a hydrogen separation membrane that includes at least one of a precious metal thin film, an organic thin film, an organic porous membrane, and an inorganic porous membrane, and therefore is easy to control and can stably separate and recover hydrogen contained in the anode exhaust gas. [Brief explanation of the drawings]

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

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

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

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

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

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

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

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

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

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

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

[0019] The combustor 18 receives the air electrode exhaust gas from the air electrode exhaust gas passage L3, and also receives hydrogen from the hydrogen separation unit 24 (described later) via the first hydrogen recovery passage L8. The combustor 18 combusts the oxygen contained in the air electrode exhaust gas with the hydrogen supplied from the first hydrogen recovery passage L8, and maintains the temperature of the reforming catalyst installed inside the reformer 12 at 500 to 700°C. The combustion exhaust gas combusted in the combustor 18 is sent to the air heat exchanger 16. The temperature of the combustion exhaust gas discharged from the combustor 18 is several hundred degrees. The air heat exchanger 16 uses the heat of the combustion exhaust gas to raise the temperature of the air supplied from the air supply source 3 to 400 to 600°C.

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

[0021] The carbon dioxide separation unit 23 is equipped with a carbon dioxide separation membrane. This carbon dioxide separation membrane has the property of allowing carbon dioxide to pass through while being difficult to pass other gases 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 carbon dioxide separation unit 23 separates the anode exhaust gas into carbon dioxide and other gases. The carbon dioxide separation efficiency of the carbon dioxide separation membrane increases as the partial pressure difference between the upstream and downstream sides of the carbon dioxide separation membrane increases. For this reason, a compressor 22 is provided upstream of the carbon dioxide separation unit 23.

[0022] The gas separated from carbon dioxide in the carbon dioxide separation unit 23 is a gas that is rich in hydrogen. Hereinafter, this gas will be referred to as hydrogen-rich gas. The hydrogen-rich gas separated from carbon dioxide in the carbon dioxide separation unit 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 includes a hydrogen separation membrane. This hydrogen separation membrane allows hydrogen to pass through while blocking other substances, such as carbon monoxide. Examples of hydrogen separation membranes include thin films of precious metals such as palladium and niobium, thin organic films such as polyimide, organic porous films such as polyamide and polyimide, and inorganic porous films such as carbon and zeolite. The hydrogen-rich gas flowing through the first hydrogen recovery path L8 contains hydrogen, carbon monoxide, and a trace amount of carbon dioxide. The hydrogen separation unit 24 separates the hydrogen-rich gas into hydrogen and other gases. The hydrogen separated by the hydrogen separation unit 24 is sent to the combustor 18 via the first hydrogen recovery path L8. The gas separated from the hydrogen by the hydrogen separation unit 24 is sent to the carbon dioxide recovery path L7 downstream of the carbon dioxide separation unit 23 via the recovery path L10.

[0024] In the fuel cell system 100 configured as described above, the hydrogen-rich gas recovered in the carbon dioxide recovery unit 2 is separated into hydrogen and other gases in the hydrogen separation unit 24, so the concentration of hydrogen supplied to the combustor 18 can be increased. Furthermore, because the hydrogen is separated into hydrogen and other gases in the hydrogen separation unit 24, 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 nearly 100%. In other words, the combustion exhaust gas combusted in the combustor 18 is discharged to the outside via the air heat exchanger 16, but the concentration of carbon dioxide in the exhaust gas can be made as low as possible.

[0025] 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. Here, the recycling rate 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. The anode exhaust gas is recycled, and 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, and the greater the carbon dioxide concentration effect. As a result, the power required for the compressor 22 to separate carbon dioxide from other gases in the carbon dioxide capture unit 2 can be reduced.

[0026] Furthermore, in the fuel cell system 100 of this 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 precious metal thin film, an organic thin film, an organic porous membrane, or an inorganic porous membrane. Hydrogen separation membranes made of these materials do not require heating to separate hydrogen, and are less susceptible to deterioration when separating hydrogen from other gases. Therefore, in the fuel cell system 100 of this embodiment, control is easier and hydrogen contained in the anode exhaust gas can be stably separated and recovered compared to when a hydrogen storage alloy is used in the hydrogen separation unit.

[0027] 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 from the first hydrogen recovery path is provided, and a path for sending raw fuel supplied from a raw fuel supply source to a combustor is also provided.

[0028] 2, the fuel cell system 100 according to this embodiment is provided with a third hydrogen recovery path L11 branching off from the first hydrogen recovery path L8 through which hydrogen separated in the hydrogen separation unit 24 flows. The third hydrogen recovery path L11 is connected to the reformed gas supply path L2.

[0029] 2, the fuel cell system 100 according to this embodiment is provided with a raw fuel supply path L12 that sends raw fuel supplied from the raw fuel supply source 4 to the combustor 18. Furthermore, as shown in FIG. 2, 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 are provided with flow rate adjustment valves V1, V2, V3 and V4, respectively.

[0030] In the fuel cell system 100, the amount of anode exhaust gas varies due to fluctuations in the load connected between the air electrode 13 and the anode 14 of the stack 11. For example, if the amount of anode exhaust gas decreases, the amount of hydrogen separated in 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. This reduces the internal reforming reaction in the stack 11, causing the temperature of the stack 11 to drop.

[0031] In the fuel cell system 100 of this embodiment, the flow rate control valve V2 provided in the first hydrogen recovery path L8 can reduce the amount of hydrogen sent to the combustor 18, and the flow rate control valve V3 provided in the third hydrogen recovery path L11 can increase the amount of hydrogen sent to the anode 14. As a result, a decrease in the temperature of the stack 11 can be prevented. However, if the amount of hydrogen flowing through the first hydrogen recovery path L8 decreases and not enough hydrogen is supplied to the combustor 18, the amount of combustion in the combustor 18 decreases, and the amount of heat provided to the reformer 12 decreases, which may prevent the reforming reaction in the reformer 12 from proceeding sufficiently. In the fuel cell system 100 of this embodiment, raw fuel can be sent from the raw fuel supply source 4 to the combustor 18 by opening the flow rate control valve V4 provided in the raw fuel supply path L12, so a decrease in the amount of combustion in the combustor 18 can be prevented. As a result, the fuel cell system 100 of this embodiment can generate stable power regardless of fluctuations in the load connected to the stack.

[0032] Even if the amount of anode exhaust gas increases due to load fluctuations, stable power generation can be achieved by adjusting the flow rate of gas flowing through each path using a flow rate control valve installed in each path. Thus, fuel cell system 100 of this embodiment includes a third hydrogen recovery path L11 that supplies hydrogen separated and recovered from anode exhaust gas to the stack, and a raw fuel supply path L12 that sends raw fuel from a raw fuel supply source to the combustor. Furthermore, flow rate control valves V1, V2, V3, and V4 are provided in carbon dioxide recovery path L7, first hydrogen recovery path L8, third hydrogen recovery path L11, and raw fuel supply path L12, respectively. Therefore, the fuel cell system of this embodiment can generate stable power generation regardless of fluctuations in the load connected to the stack.

[0033] Embodiment 3 3 is a configuration diagram of a fuel cell system according to embodiment 3. A fuel cell system 100 according to this embodiment is the same as the fuel cell system described in embodiment 2, except that a hydrogen storage tank is added between the hydrogen separation section and the first hydrogen recovery path.

[0034] 3, in the fuel cell system 100 according to this embodiment, a hydrogen storage tank 25 is added between the hydrogen separation unit 24 and the first hydrogen recovery path L8. A third hydrogen recovery path L11 is connected between the hydrogen storage tank 25 and the reformed gas supply path L2. The hydrogen separated in 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 to the anode 14 via the third hydrogen recovery path L11.

[0035] Nickel-based materials are generally used for the fuel electrode 14 of the stack 11 of the fuel cell 1, but when the fuel electrode is exposed to an oxidizing atmosphere at high temperatures, the fuel electrode becomes oxidized, causing deterioration of the stack and problems such as reduced output.

[0036] During normal operation of a fuel cell system, a reducing atmosphere gas containing hydrogen is sent from the reformer 12 to the fuel electrode 14. However, if the reducing atmosphere gas is not sent from the reformer 12 to the fuel electrode 14 when the fuel cell system is started up, stopped, or in an emergency, the fuel electrode 14 may become an oxidizing atmosphere.

[0037] In the fuel cell system 100 of this embodiment, even if the gas in a reducing atmosphere is no longer 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, the fuel electrode can be maintained in a reducing atmosphere even during startup, shutdown, or emergency shutdown of the fuel cell system. As a result, deterioration of the stack can be prevented.

[0038] Embodiment 4 4 is a configuration diagram of a fuel cell system according to embodiment 4. A fuel cell system 100 according to this embodiment is the same as the fuel cell system described in embodiment 3, except that a flow control valve is provided in the water vapor supply path and between the raw fuel supply source and the mixer.

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

[0040] In the fuel cell system 100 configured as described above, when the output power of the stack 11, i.e., the output voltage V, fluctuates in accordance with a change in the load, the amounts of raw fuel and steam sent to the mixer 17 are adjusted by adjusting the opening and closing amounts of the flow control valves V5 and V6. At the same time, the amounts of hydrogen sent from the hydrogen storage tank 25 to the anode 14 and the combustor 18 are adjusted by adjusting the opening and closing amounts of the flow control valves V2 and V3 so that the temperature T1 of the stack 11 and the temperature T2 of the reformer 12 are maintained within preset temperature ranges. At this time, the amount of hydrogen sent from the hydrogen storage tank 25 to the combustor 18 is adjusted by the flow control valve V2 so that the gas pressure P of the hydrogen storage tank 25 is always maintained above a preset threshold. If the amount of hydrogen sent from the hydrogen storage tank 25 to the combustor 18 is insufficient, the amount of raw fuel sent from the raw fuel supply source 4 to the combustor 18 is increased by the flow control valve V4 on 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 ensure in the hydrogen storage tank 25 a certain amount of hydrogen necessary to maintain a reducing atmosphere at the fuel electrode when the fuel cell is stopped.

[0041] In the fuel cell system 100 configured in this manner, the gas pressure P in the hydrogen storage tank 25 can be constantly maintained above a threshold value, so that a constant amount of hydrogen necessary to maintain a reducing atmosphere at the anode can be secured in the hydrogen storage tank 25 when the fuel cell is stopped. Therefore, the anode can be reliably maintained in a reducing atmosphere even when the fuel cell system is stopped. As a result, the reliability of the fuel cell system of this embodiment is improved.

[0042] 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]

[0043] 1 fuel cell, 2 carbon dioxide recovery section, 3 air supply source, 4 raw fuel supply source, 5 water supply source, 11 stack, 12 reformer, 13 air electrode, 14 fuel electrode, 15 electrolyte, 16 air heat exchanger, 17 mixer, 18 combustor, 19 steam generator, 20 condenser, 21 recycle blower, 22 compressor, 23 carbon dioxide separation section, 24 hydrogen separation section, 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 Raw fuel supply path, V1, V2, V3, V4, V5, V6 flow rate adjustment valve.

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 interposed therebetween; a mixer that mixes steam and the anode exhaust gas discharged from the anode with a raw fuel; a reformer that reforms the raw fuel mixed with the steam and the anode exhaust gas in the mixer to produce a reformed gas containing hydrogen; a combustor that maintains a reforming catalyst provided inside the reformer at a high temperature; a reformed gas supply path that sends the reformed gas to the anode; an air electrode exhaust gas path that sends the air electrode exhaust gas discharged from the air electrode to the combustor; an anode exhaust gas path through which the anode 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 in the hydrogen separation unit to the combustor, the anode exhaust gas path is branched into an anode exhaust gas recycling path that sends the anode exhaust gas to the mixer and a carbon dioxide recovery path that sends the anode exhaust gas to the carbon dioxide recovery unit, a second hydrogen recovery path for sending the hydrogen-rich gas separated in the carbon dioxide separation section to the hydrogen separation section; and a hydrogen separation membrane comprising at least one of a precious metal thin film, an organic thin film, an organic porous membrane, and an inorganic porous membrane.

2. 2. The fuel cell system according to claim 1, wherein the fuel cell further comprises a third hydrogen recovery path that sends hydrogen separated in 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. 3. The fuel cell system according to claim 2, wherein the fuel cell further comprises 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. 4. The fuel cell system according to claim 3, wherein the first hydrogen recovery path, the third hydrogen recovery path and the raw fuel supply path are each provided with a flow control valve, and the opening and closing amounts of the flow control valves are adjusted to maintain the temperature of the stack and the temperature of the reformer within a predetermined temperature range, and to maintain the gas pressure of the hydrogen storage tank above a predetermined threshold.

5. A fuel cell system as described in Claim 4, characterized in that it is equipped with a pressure sensor that measures the gas pressure in the hydrogen storage tank, and adjusts the opening and closing amount of the flow control valve to maintain the gas pressure measured by the pressure sensor above a predetermined threshold value.

6. A fuel cell system described in any one of claims 3 to 5, characterized in that when the fuel cell is started, stopped or emergency stopped, hydrogen is supplied from the hydrogen storage tank to the fuel electrode, thereby maintaining the fuel electrode in a reducing atmosphere.

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