JP6126154B2 - Fuel cell system - Google Patents

Description

  The present invention relates to a fuel cell system.

  In high temperature operation fuel cell systems such as solid oxide fuel cells and molten carbonate fuel cells that normally operate at temperatures of 600 ° C. or higher, they are discharged from the anode of the high temperature operation fuel cells in order to increase efficiency. Reusing the anode exhaust gas is being studied. For example, several techniques for improving the fuel utilization rate of the entire system by removing carbon dioxide or water vapor from the anode exhaust gas and reusing the gas have been proposed.

For example, by removing water vapor from the anode off-gas of a solid oxide fuel cell to regenerate the anode off-gas and reusing the regenerated off-gas as fuel for the solid oxide fuel cell, the solid oxide fuel cell itself A power generation method using a solid oxide fuel cell that improves fuel utilization has been proposed (see, for example, Patent Document 1).
In addition, the exhaust fuel gas discharged from the fuel cell is recirculated to the fuel cell via a fuel recirculation line, thereby being reused as the fuel gas of the fuel cell, and the recirculation line In addition, there has been proposed a fuel cell system including a gas regulator that simultaneously removes water vapor and carbon dioxide from the exhausted fuel gas being recycled (see, for example, Patent Document 2).
In addition, the fuel cell stack supplied with the fuel intake flow is operated to generate electricity and a fuel exhaust flow having a temperature exceeding 200 ° C., and the temperature of the fuel exhaust flow is lowered to 200 ° C. or less, There has been proposed a method of operating a fuel cell system in which the first fuel exhaust split is divided into the first fuel exhaust split and the first fuel exhaust split is recycled to the fuel intake flow (for example, a patent) Reference 3).

  In addition, a circulation type fuel cell system has been proposed in which carbon dioxide or water vapor in the anode exhaust gas is removed using a separation membrane. For example, air is supplied to the permeation side of the separation membrane to remove carbon dioxide or water vapor in the anode exhaust gas, or carbon dioxide or water vapor in the anode exhaust gas is reduced by reducing the pressure on the permeation side of the separation membrane by a vacuum pump. A circulation type fuel cell system that employs a method for removing the fuel cell has been proposed (see, for example, Patent Document 4).

JP 2006-31989 JP 2006-139984 A Japanese Patent No. 5542332 US Patent Application Publication No. 2013/0108936

When a separation membrane for removing carbon dioxide or water vapor in the anode exhaust gas is provided in the fuel cell system described in Patent Documents 1 to 3, as in the circulation type fuel cell system described in Patent Document 4, carbon dioxide or water vapor is used. In order to separate efficiently, it is necessary to supply air to the permeation side of the separation membrane or to reduce the pressure on the permeation side of the separation membrane.
Here, in order to supply air to the permeation side of the separation membrane or to depressurize the permeation side of the separation membrane, a route for supplying air and an air blower or a decompression pump are separately required. There is a problem that the manufacturing cost increases, and the power generation efficiency of the entire system decreases due to an increase in power consumption by the air blower or the decompression pump. Furthermore, there is a problem that the system becomes complicated and the reliability of the system is lowered.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a fuel cell system that is excellent in power generation efficiency of the entire system and improved in reliability by simplifying the system.

The above problem is solved by, for example, the following means.
<1> A reformer having a reforming unit that generates a reformed gas by steam reforming a raw material gas and a combustion unit that heats the reforming unit by a combustion reaction, and the reformer supplied from the reforming unit A first fuel cell that generates power using a gas, a separation membrane that separates at least one of water vapor and carbon dioxide from an off-gas containing the unreacted reformed gas discharged from the first fuel cell; A second fuel cell disposed downstream of the separation membrane and generating power using the off-gas from which at least one of water vapor and carbon dioxide has been separated; and disposed on the permeate side of the separation membrane, the first fuel cell and the An oxygen supply path through which a gas containing unreacted oxygen discharged from at least one of the second fuel cells circulates, or an exhaust path through which the exhaust gas discharged from the combustion section is arranged on the permeation side of the separation membrane; , A fuel cell system comprising:

  The fuel cell system according to the present embodiment is a multistage fuel cell system including a first fuel cell and a second fuel cell. For this reason, the multi-stage fuel cell system as in the present embodiment has an improved fuel utilization rate as compared with the circulation fuel cell system, and can achieve high power generation efficiency.

  Furthermore, in the fuel cell system according to the present embodiment, the separation membrane separates at least one of water vapor and carbon dioxide from off-gas containing unreacted reformed gas discharged from the first fuel cell, and the second fuel cell is Power generation is performed using off-gas from which at least one of water vapor and carbon dioxide is separated. Therefore, in the second fuel cell, the theoretical voltage caused by the oxygen partial pressure difference between the electrodes is improved, and the concentration overvoltage caused by water vapor or carbon dioxide in the offgas is reduced. Therefore, the fuel cell system according to the present embodiment can obtain higher power generation efficiency than an ordinary multistage fuel cell system.

  Further, at least one of water vapor and carbon dioxide separated by the separation membrane is supplied to either an oxygen supply path disposed on the permeation side of the separation membrane or an exhaust path disposed on the permeation side of the separation membrane. The gas containing unreacted oxygen discharged from at least one of the first fuel cell and the second fuel cell flows in the oxygen supply path, and the exhaust gas discharged from the combustion section flows in the exhaust path, so that it is separated. At least one of the water vapor and carbon dioxide flows in the oxygen supply path or the exhaust path together with the gas or exhaust gas containing unreacted oxygen. Therefore, by providing an oxygen supply path or an exhaust path on the permeation side of the separation membrane, there is no need to separately provide a route for supplying oxygen to the permeation side of the separation membrane and an air blower or a vacuum pump, thereby reducing manufacturing costs. The power generation efficiency of the entire system can be increased. Furthermore, the reliability of the system is improved by simplifying the system.

  <2> A reformer having a reforming unit that generates a reformed gas by steam reforming the raw material gas and a combustion unit that heats the reforming unit by a combustion reaction, and the reformer supplied from the reforming unit A fuel cell that generates power using a gas, a separation membrane that separates at least one of water vapor and carbon dioxide from an off-gas containing the unreacted reformed gas discharged from the fuel cell, and downstream of the separation membrane An off-gas circulation path that supplies the fuel cell with the off-gas from which at least one of water vapor and carbon dioxide has been separated, and unreacted oxygen that is disposed on the permeate side of the separation membrane and discharged from the fuel cell. A fuel cell system comprising: an oxygen supply path through which a gas containing gas circulates; or an exhaust path through which exhaust gas discharged from the combustion section flows and is disposed on the permeation side of the separation membrane.

  The fuel cell system according to the present embodiment is a circulating fuel cell system that supplies the off-gas from which water vapor has been separated to the fuel cell. Even in such a system, the fuel utilization rate is improved and the power generation efficiency is high. Can be obtained.

  Further, in the fuel cell system according to the present embodiment, the separation membrane separates at least one of water vapor and carbon dioxide from the off gas containing the unreacted reformed gas discharged from the fuel cell, and passes through the off gas circulation path through the water vapor and the carbon dioxide. Off-gas from which at least one of carbon has been separated is supplied to the fuel cell. Therefore, in the fuel cell, the theoretical voltage due to the oxygen partial pressure difference between the electrodes is improved, and the concentration overvoltage due to water vapor or carbon dioxide in the offgas is reduced. Therefore, the fuel cell system according to this embodiment can obtain higher power generation efficiency than a normal circulation fuel cell system.

  Further, at least one of water vapor and carbon dioxide separated by the separation membrane is supplied to either an oxygen supply path disposed on the permeation side of the separation membrane or an exhaust path disposed on the permeation side of the separation membrane. Since the gas containing unreacted oxygen discharged from the fuel cell flows in the oxygen supply path and the exhaust gas discharged from the combustion section flows in the exhaust path, at least one of the separated water vapor and carbon dioxide is Along with a gas or exhaust gas containing unreacted oxygen, it flows in the oxygen supply path or the exhaust path. Therefore, by providing an oxygen supply path or an exhaust path on the permeation side of the separation membrane, there is no need to separately provide a route for supplying oxygen to the permeation side of the separation membrane and an air blower or a vacuum pump, thereby reducing manufacturing costs. The power generation efficiency of the entire system can be increased. Furthermore, the reliability of the system is improved by simplifying the system.

  <3> The oxygen supply path is disposed on the permeation side of the separation membrane, and the oxygen supply path includes at least one of water vapor and carbon dioxide separated by the separation membrane, and a gas containing unreacted oxygen. The fuel cell system according to <1> or <2>, which is supplied to the combustion unit.

  The fuel cell system according to the present embodiment uses a gas containing unreacted oxygen discharged from a fuel cell (may be a first fuel cell or a second fuel cell) for a combustion reaction in a combustion section. Yes. Therefore, there is no need to separately supply oxygen to the combustion section. Furthermore, an oxygen supply path for circulating a gas containing unreacted oxygen is provided on the permeation side of the separation membrane so that at least one of water vapor and carbon dioxide permeates the permeation side of the separation membrane. Therefore, it is not necessary to separately provide a path for supplying oxygen to the permeation side of the separation membrane and an air blower or a decompression pump, and the system is simplified.

  <4> The fuel cell system according to <3>, wherein water vapor is separated from the exhaust gas discharged from the combustion unit, and the separated water vapor is supplied to the reforming unit.

  In the fuel cell system according to the present embodiment, at least one of water vapor and carbon dioxide and a gas containing unreacted oxygen are supplied to the combustion unit from the oxygen supply path. Then, the steam is separated from the exhaust gas discharged from the combustion section after the combustion reaction, and the separated steam is used for steam reforming of the raw material gas in the reforming section. Therefore, the steam in the exhaust gas is effectively used, and the system is simplified as compared with the case where a steam supply means for steam reforming of the raw material is separately provided.

  <5> The exhaust path is disposed on the permeate side of the separation membrane, and water vapor is generated from a mixed gas of exhaust gas flowing through the exhaust path and at least one of water vapor and carbon dioxide separated by the separation membrane. The fuel cell system according to <1> or <2>, in which the separated water vapor is supplied to the reforming unit.

  In the fuel cell system according to this embodiment, an exhaust path for circulating exhaust gas is provided on the permeation side of the separation membrane, and at least one of water vapor and carbon dioxide is permeated to the permeation side of the separation membrane. Therefore, it is not necessary to separately provide a path for supplying oxygen to the permeation side of the separation membrane and an air blower or a decompression pump, and the system is simplified.

  Furthermore, the water vapor is separated from the mixed gas of the exhaust gas and at least one of water vapor and carbon dioxide separated by the separation membrane, and the separated water vapor is used for the steam reforming of the raw material gas in the reforming section. Therefore, the steam in the exhaust gas is effectively used, and the system is simplified as compared with the case where a steam supply means for steam reforming of the raw material is separately provided.

  <6> As the separation membrane, a water vapor separation membrane that separates water vapor from off gas containing unreacted reformed gas, and a carbon dioxide separation membrane that separates carbon dioxide from off gas containing unreacted reformed gas, respectively The fuel cell system according to any one of <1> to <5>.

  The fuel cell system according to this embodiment includes a water vapor separation membrane and a carbon dioxide separation membrane as the separation membrane. Therefore, the separation conditions of water vapor or carbon dioxide in each separation membrane can be adjusted, and water vapor and carbon dioxide can be separated efficiently.

  <7> A water vapor removing unit disposed upstream or downstream of the separation membrane and removing water vapor from the off gas, and a carbon dioxide removing unit disposed upstream or downstream of the separation membrane and removing carbon dioxide from the off gas. The fuel cell system according to any one of <1> to <6>, further comprising at least one of the following.

  In the fuel cell system according to this embodiment, at least one of the water vapor removing unit and the carbon dioxide removing unit is disposed upstream or downstream of the separation membrane, and the water vapor concentration in the off-gas supplied to the fuel cell (second fuel cell) And the carbon dioxide concentration is further reduced. Therefore, the fuel cell system according to the present embodiment can obtain higher power generation efficiency.

  <8> A water vapor removing unit that is disposed upstream or downstream of the separation membrane and removes water vapor from the off-gas, and supplies the water vapor removed by the water vapor removing unit to the reforming unit <1> to < The fuel cell system according to any one of 7>.

  In the fuel cell system according to the present embodiment, the water vapor removing unit is arranged upstream or downstream of the separation membrane, and the water vapor concentration in the off-gas supplied to the fuel cell (second fuel cell) is further reduced. Therefore, the fuel cell system according to the present embodiment can obtain higher power generation efficiency. Furthermore, the water vapor removed by the water vapor removing unit is used for the steam reforming of the raw material gas, and the water vapor in the off-gas is effectively utilized.

  <9> A heat exchanger that further performs heat exchange between the off-gas flowing upstream of the separation membrane and the off-gas separated from water vapor flowing downstream of the separation membrane <1> to <1. The fuel cell system according to any one of 8>.

  In the fuel cell system according to the present embodiment, heat exchange is performed between the off gas flowing upstream of the separation membrane and the off gas flowing downstream of the separation membrane. Therefore, the off gas supplied to the separation membrane is cooled to a temperature suitable for the separation of water vapor and carbon dioxide, and the off gas after the water vapor separation is heated to a temperature suitable for power generation in the fuel cell (second fuel cell). The Therefore, the power generation efficiency and thermal efficiency of the entire system are further improved.

  According to the present invention, it is possible to provide a fuel cell system that is excellent in power generation efficiency and improved in reliability by simplifying the system.

1 is a schematic configuration diagram showing a fuel cell system according to a first embodiment. It is a schematic block diagram which shows the fuel cell system which concerns on 2nd Embodiment. It is a schematic block diagram which shows the fuel cell system which concerns on 3rd Embodiment. It is a schematic block diagram which shows the fuel cell system which concerns on 4th Embodiment. It is a schematic block diagram which shows the fuel cell system which concerns on 5th Embodiment. It is a schematic block diagram which shows the fuel cell system which concerns on 6th Embodiment. It is a schematic block diagram which shows the fuel cell system which concerns on 7th Embodiment. It is a schematic block diagram which shows the fuel cell system which concerns on 8th Embodiment. It is a schematic block diagram which shows the fuel cell system which concerns on 9th Embodiment. It is a schematic block diagram which shows the fuel cell system which concerns on 10th Embodiment. It is a schematic block diagram which shows the circulation type fuel cell system which concerns on 11th Embodiment. It is a schematic block diagram which shows the circulation type fuel cell system which concerns on 12th Embodiment.

  In this specification, a numerical range expressed using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value.

[First Embodiment]
Hereinafter, an embodiment of a fuel cell system of the present invention will be described with reference to FIG. FIG. 1 is a schematic configuration diagram showing a fuel cell system according to the first embodiment. The fuel cell system 10 according to the first embodiment includes a reformer 14 having a reforming unit 19 that generates a reformed gas by steam reforming a raw material gas and a combustion unit 18 that heats the reforming unit 19 by a combustion reaction. Water vapor and carbon dioxide from the first fuel cell 11 that generates power using the reformed gas supplied from the reforming unit 19 and off-gas containing unreacted reformed gas discharged from the first fuel cell 11 Are disposed on the permeation side 16B of the separation membrane 16, and the second fuel cell 12 that is disposed downstream of the separation membrane 16 and that generates power using off-gas from which water vapor and carbon dioxide have been separated. And an oxygen supply path 44 through which a gas containing unreacted oxygen discharged from the second fuel cell 12 circulates.

  The fuel cell system 10 according to the present embodiment is a multistage fuel cell system including a first fuel cell 11 and a second fuel cell 12. In a circulation type fuel cell system, in order to suppress an increase in the carbon dioxide concentration in the circulation system, it is necessary to partially discharge off-gas discharged from the anode to the outside of the circulation system. Since the quality gas is also partially discharged outside the circulation system, there is a limit to increasing the fuel utilization rate. On the other hand, in the multistage fuel cell system, all the reformed gas contained in the off-gas discharged from the anode of the preceding fuel cell is supplied to the anode of the subsequent fuel cell. Therefore, the multi-stage fuel cell system has an improved fuel utilization rate as compared with the circulation type fuel cell system, and can obtain high power generation efficiency.

  Furthermore, in the fuel cell system 10 according to the present embodiment, the separation membrane 16 separates the water vapor and carbon dioxide from the off-gas containing the unreacted reformed gas discharged from the first fuel cell 11, and the second fuel cell 12 Performs power generation using off-gas from which water vapor and carbon dioxide are separated. Therefore, in the second fuel cell 12, the theoretical voltage due to the oxygen partial pressure difference between the electrodes is improved, and the concentration overvoltage due to water vapor and carbon dioxide in the offgas is reduced. Therefore, the fuel cell system 10 can obtain higher power generation efficiency than a normal multistage fuel cell system.

  Further, the water vapor and carbon dioxide separated by the separation membrane 16 are supplied to the oxygen supply path 44 disposed on the permeation side of the separation membrane 16. Since the cathode off-gas that is a gas containing unreacted oxygen discharged from the second fuel cell 12 circulates in the oxygen supply path 44, the separated water vapor and carbon dioxide together with the cathode off-gas pass through the oxygen supply path 44. Circulate. Therefore, by providing the oxygen supply path 44 on the permeation side 16B of the separation membrane 16, it is not necessary to separately provide a path for supplying oxygen to the permeation side 16B of the separation membrane 16, and an air blower or a decompression pump. This can reduce the power generation efficiency of the entire system. Furthermore, the reliability of the system is improved by simplifying the system.

  Further, since the water vapor and carbon dioxide that have permeated through the separation membrane 16 circulate in the oxygen supply path 44 together with the cathode off-gas, the water vapor partial pressure and the carbon dioxide partial pressure on the permeate side 16B of the separation membrane 16 become low, and the water vapor and carbon dioxide. Separation is promoted. Therefore, in the fuel cell system 10, the separation of water vapor and carbon dioxide is promoted with simplification of the system. As a result, the water vapor concentration and the carbon dioxide concentration in the off-gas supplied to the second fuel cell 12 can be further reduced, and the power generation efficiency of the fuel cell system 10 can be further increased.

  Next, the fuel cell system 10 according to the present embodiment is superior in power generation efficiency to a case where a path for supplying air as a gas containing oxygen to the cathode of the fuel cell is provided on the permeation side 16B of the separation membrane 16, and The fact that the durability of the separation membrane is suitably maintained will be described.

  By providing a passage for supplying air to the cathode of the fuel cell on the permeate side of the separation membrane, an air blower for supplying oxygen to the cathode of the fuel cell is used to increase the efficiency of separation of water vapor and carbon dioxide by the separation membrane. There is no need to separately provide a path for supplying oxygen to the permeation side of the separation membrane and an air blower or a vacuum pump. However, in such a configuration, carbon dioxide and water vapor are contained in the gas supplied to the cathode of the fuel cell, and the oxygen partial pressure on the cathode side is lowered, and as a result, the electromotive force of the fuel cell is lowered. End up.

  Further, when carbon dioxide and water vapor are separated from off-gas discharged from the anode of the fuel cell by the separation membrane, hydrogen and carbon monoxide contained in the off-gas can be separated in minute amounts. Since hydrogen and carbon monoxide are highly reactive with oxygen, hydrogen and carbon monoxide separated on the permeation side of the separation membrane react with oxygen flowing through the permeation side, so that the local separation membrane Temperature rise is likely to occur, and the durability of the separation membrane may be reduced. Therefore, in order to suitably maintain the durability of the separation membrane, it is preferable to supply a gas having a lower oxygen ratio to the permeation side of the separation membrane.

  In the fuel cell system 10 according to the present embodiment, since the cathode offgas having a smaller oxygen ratio than air is supplied to the permeation side 16B of the separation membrane 16, the reaction between oxygen and hydrogen or carbon monoxide is unlikely to occur. The temperature rise of the separation membrane 16 is suppressed, and the durability of the separation membrane 16 can be suitably maintained.

  Further, the cathode offgas discharged from the second fuel cell 12 of the fuel cell system 10 is substantially free of carbon dioxide and water vapor. Therefore, the fuel cell system 10 supplies more exhaust gas (gas containing carbon dioxide and water vapor) to the permeation side 16B of the separation membrane 16 than the fuel cell system 60 according to a sixth embodiment to be described later on the supply side in the separation membrane 16. The water vapor partial pressure difference and the carbon dioxide partial pressure difference between 16A and the permeate side 16B are large, and the separation of water vapor and carbon dioxide is promoted. Therefore, the fuel cell system 10 is more excellent in power generation efficiency.

  Hereinafter, each configuration of the fuel cell system 10 according to the present embodiment will be described.

(Raw gas supply route)
The fuel cell system 10 according to the present embodiment includes a source gas supply path 24 that supplies a source gas to the reformer 14, and the source gas supply path 24 is provided with a blower 25 for circulating the source gas. ing.

  The raw material gas that circulates in the raw material gas supply path 24 is not particularly limited as long as it is a gas capable of steam reforming, and includes hydrocarbon fuel. Examples of the hydrocarbon fuel include natural gas, LP gas (liquefied petroleum gas), coal reformed gas, lower hydrocarbon gas, and the like. Examples of the lower hydrocarbon gas include lower hydrocarbons having 4 or less carbon atoms such as methane, ethane, ethylene, propane, butane, and methane is particularly preferable. The hydrocarbon fuel may be a mixture of the above-described lower hydrocarbon gas, and the above-described lower hydrocarbon gas may be a gas such as natural gas, city gas, or LP gas.

  The source gas supply path 24 is connected to a later-described steam supply path 37, and steam flowing through the steam supply path 37 is supplied to the source gas supply path 24. Then, the steam supplied from the steam supply path 37 is supplied to the reformer 14 together with the raw material gas. Note that the raw material gas supply path 24 is configured to be directly connected to the reformer 14 through the steam supply path 37 without being connected to the steam supply path 37 from the viewpoint of preventing condensation of the steam in the path. Also good.

(Reformer)
The fuel cell system 10 according to the present embodiment includes a reformer 14 that generates reformed gas by steam reforming a raw material gas. The reformer 14 includes, for example, a combustion unit 18 provided with a burner or a combustion catalyst, and a reforming unit 19 including a reforming catalyst.

  The reforming unit 19 is connected to the source gas supply path 24 on the upstream side, and is connected to the reformed gas supply path 42 on the downstream side. Therefore, a raw material gas such as methane is supplied to the reforming unit 19 through the raw material gas supply path 24, and after the raw material gas is steam reformed in the reforming unit 19, the generated reformed gas is supplied to the reformed gas supply path 42. To be supplied to the first fuel cell 11.

  The combustion unit 18 is connected to the oxygen supply path 44 and the off-gas path 46 on the upstream side, and is connected to the exhaust path 48 on the downstream side. The combustion unit 18 burns a mixed gas of a gas containing unreacted oxygen discharged from the cathode side of the second fuel cell 12 and supplied through the oxygen supply path 44 and an off-gas supplied through the off-gas path 46. The reforming catalyst in the reforming unit 19 is heated. The exhaust gas from the combustion unit 18 circulates in the exhaust path 48.

  Since the steam reforming that occurs in the reforming unit 19 involves a large endotherm, it is necessary to supply heat from the outside for the progress of the reaction. For this reason, the reforming unit 19 is heated by the combustion heat generated in the combustion unit 18. It is preferable to do.

When methane, which is an example of the raw material gas, is steam reformed, carbon monoxide and hydrogen are generated in the reforming unit 19 by the reaction of the following formula (a).
CH ₄ + H ₂ O → CO + 3H ₂ ... (A)

  The reforming catalyst installed in the reforming unit 19 is not particularly limited as long as it becomes a catalyst for the steam reforming reaction, but Ni, Rh, Ru, Ir, Pd, Pt, Re, Co, Fe And a steam reforming catalyst containing at least one of Mo and Mo as a catalyst metal.

  The number S of steam molecules per unit time supplied to the reforming unit 19 of the reformer 14 and the number of carbon atoms C of the raw material gas per unit time supplied to the reforming unit 19 of the reformer 14 The steam carbon ratio S / C, which is the ratio, is preferably 1.5 to 3.5, more preferably 2.0 to 3.0, and further preferably 2.0 to 2.5. preferable. When the steam carbon ratio S / C is in this range, the raw material gas is efficiently steam reformed, and a reformed gas containing hydrogen and carbon monoxide is generated. Furthermore, carbon deposition in the fuel cell system 10 can be suppressed, and the reliability of the fuel cell system 10 can be improved.

  In addition, the combustion unit 18 preferably heats the reforming unit 19 to 600 ° C. to 800 ° C., more preferably 600 ° C. to 700 ° C., from the viewpoint of efficiently performing steam reforming.

  The exhaust gas flowing in the exhaust path 48 exchanges heat with the reformed water flowing in the reformed water supply path 33 in the heat exchanger 31 having the role of a vaporizer. Thereby, the exhaust gas flowing in the exhaust passage 48 is cooled and then supplied to the water tank 32 (condenser), and the reformed water flowing in the reforming water supply passage 33 is vaporized and then passed through the water vapor supply passage 37. It is supplied to the source gas supply path 24.

  The water tank 32 is a container for storing water obtained by condensing water vapor contained in the exhaust gas flowing through the exhaust passage 48. In the water tank 32, exhaust gas other than water vapor is discharged to the outside, and when a predetermined amount or more of water is stored, drainage is performed by overflow, for example.

  The water tank 32 is connected to the reforming water supply path 33, and the reforming water supply path 33 is provided with a reforming water pump 34. The water stored in the water tank 32 is supplied to the heat exchanger 31 through the reforming water supply path 33 as reforming water by the reforming water pump 34.

  The structure for separating the water vapor from the exhaust gas flowing in the exhaust path 48 is not limited to the water tank 32. For example, the separation film may separate the water vapor and the gas other than the water vapor. Gas for steam reforming may be separated by adsorbing gas other than steam.

  Further, in place of the heat exchanger 31 that performs heat exchange between the exhaust gas flowing in the exhaust path 48 and the reformed water flowing in the reformed water supply path 33, the reforming unit 19, the first fuel cell. 11. A vaporizer that vaporizes the reformed water using heat released from at least one of the second fuel cells 12 may be provided.

  The oxygen supply path 44 is a path through which a gas containing oxygen such as air flows. The oxygen supply path 44 is provided with the heat exchanger 22, and the oxygen supply path 44 upstream of the first fuel cell 11 is connected to the oxygen supply path 44. Then, heat exchange is performed with the oxygen supply path 44 on the downstream side of the second fuel cell 12. As a result, the cathode off-gas flowing in the oxygen supply path 44 on the downstream side of the second fuel cell 12 is cooled to a preferable temperature when the water vapor and carbon dioxide are separated by the separation membrane 16, and the upstream side of the first fuel cell 11. The oxygen-containing gas flowing in the oxygen supply path 44 is heated to a temperature suitable for the operating temperature of the first fuel cell 11 and then supplied to the cathode of the first fuel cell 11.

(First fuel cell)
The fuel cell system 10 according to this embodiment includes a first fuel cell 11 that generates power using the reformed gas supplied from the reformer 14 through the reformed gas supply path 42. The first fuel cell 11 may be, for example, a fuel cell including an air electrode (cathode), an electrolyte, and a fuel electrode (anode), or a fuel cell stack in which a plurality of fuel cells are stacked. The first fuel cell is a high-temperature fuel cell that operates at about 600 ° C. to 800 ° C., for example, a solid oxide fuel cell that operates at about 700 ° C. to 800 ° C., and that operates at about 600 ° C. to 700 ° C. And a molten carbonate fuel cell.

When the first fuel cell 11 is a solid oxide fuel cell, a gas containing oxygen is supplied to the cathode (not shown) of the first fuel cell 11 through the oxygen supply path 44. When a gas containing oxygen is supplied to the cathode, a reaction shown in the following formula (b) occurs, and oxygen ions move inside a solid oxide electrolyte (not shown).
O ₂ + 4e ⁻ → 2O ²⁻ (b)

When the first fuel cell 11 is a solid oxide fuel cell, a reformed gas containing hydrogen is supplied to the anode (not shown) of the first fuel cell 11 through the reformed gas supply path 42. When hydrogen receives electrons from the oxygen ions moving inside the solid oxide electrolyte at the interface between the anode and the solid oxide electrolyte, a reaction represented by the following formula (c) occurs.
H ₂ + O ²⁻ → H ₂ O + 2e ⁻ (c)

When the first fuel cell 11 is a molten carbonate fuel cell, a gas containing oxygen and carbon dioxide is supplied to the cathode (not shown) of the first fuel cell 11 through the oxygen supply path 44. When a gas containing oxygen and carbon dioxide is supplied to the cathode, a reaction represented by the following formula (d) occurs, and at this time, carbonate ions move inside the electrolyte (not shown).
O ₂ + 2CO ₂ + 4e ⁻ → 2CO ₃ ²⁻ (d)

When the first fuel cell 11 is a molten carbonate fuel cell, a reformed gas containing hydrogen is supplied to the anode (not shown) of the first fuel cell 11 through the reformed gas supply path 42. When hydrogen receives electrons from the carbonate ions moving inside the electrolyte at the interface between the anode and the electrolyte, a reaction represented by the following formula (e) occurs.
H ₂ + CO ₃ ²⁻ → H ₂ O + CO ₂ + 2e ⁻ (e)

  As shown in the above formulas (c) and (e), the electrochemical reaction of the reformed gas in the first fuel cell 11 mainly generates water vapor in the solid oxide fuel cell, and the molten carbonate In the fuel cell, water vapor and carbon dioxide are mainly produced. Further, the electrons generated at the anode move to the cathode through an external circuit. In this way, the electrons move from the anode to the cathode, whereby electric power is generated in the first fuel cell 11. Even in a solid oxide fuel cell, carbon dioxide is generated by using a portion of carbon monoxide for power generation.

  The gas containing unreacted oxygen discharged from the cathode is supplied to the cathode (not shown) of the second fuel cell 12 through the downstream oxygen supply path 44.

  On the other hand, the off gas containing the unreacted reformed gas discharged from the anode is supplied to the supply side 16 </ b> A of the separation membrane 16 through the off gas path 52. Here, the off gas containing the unreacted reformed gas is a mixed gas containing hydrogen, carbon monoxide, carbon dioxide, water vapor, and the like.

  The heat exchanger 21 is installed in the off gas path 52 and the off gas path 54, and the off gas flowing through the off gas path 52 and the water vapor and carbon dioxide flowing through the off gas path 54 are separated by the heat exchanger 21. Heat exchange with off-gas is performed. Thereby, the off-gas flowing through the off-gas passage 52 is cooled to a preferable temperature when the water vapor and carbon dioxide are separated by the separation membrane 16, and the off-gas from which the water vapor and carbon dioxide flowing through the off-gas passage 54 are separated is The second fuel cell 12 is heated to a temperature suitable for the operating temperature. Therefore, the power generation efficiency and thermal efficiency of the entire system are further improved.

(Separation membrane)
The fuel cell system 10 according to the present embodiment includes a separation membrane 16 that separates water vapor and carbon dioxide from off-gas containing unreacted reformed gas discharged from the first fuel cell 11. Off-gas flowing in the off-gas path 52 is supplied to the supply side 16A of the separation membrane 16, and water vapor and carbon dioxide in the off-gas pass through the separation membrane 16 in the direction of arrow A from the supply side 16A to the permeation side 16B. The off gas after separating the water vapor and carbon dioxide flows through the off gas path 54 from the supply side 16 </ b> A and is supplied to the second fuel cell 12. On the other hand, the separated water vapor and carbon dioxide are mixed with the cathode off-gas (gas containing unreacted oxygen) discharged from the second fuel cell 12 flowing through the permeation side 16B, and the oxygen supply path 44 passes through the permeation side 16B. It is distributed and supplied to the combustion section 18 of the reformer 14. Therefore, the cathode off-gas discharged from the second fuel cell 12 is used for the combustion reaction in the combustion unit 18, and there is no need to separately supply oxygen to the combustion unit 18.

  Further, an oxygen supply path 44 for circulating the cathode off gas is provided on the permeation side of the separation membrane 16 so that water vapor and carbon dioxide are permeated to the permeation side of the separation membrane 16. Therefore, it is not necessary to separately provide a path for supplying oxygen to the permeation side of the separation membrane 16 and an air blower or a decompression pump, and the system is simplified.

  Furthermore, since the water vapor and carbon dioxide that have permeated through the separation membrane 16 circulate in the oxygen supply path 44 together with the cathode off gas, the water vapor partial pressure and the carbon dioxide partial pressure on the permeation side 16B of the separation membrane 16 become lower, and the supply side 16A and The water vapor partial pressure difference and the carbon dioxide partial pressure difference from the permeation side 16B can be increased. Therefore, more water vapor and carbon dioxide can be moved to the permeation side 16B, and separation of water vapor and carbon dioxide is promoted.

  Therefore, in the fuel cell system 10, the separation of water vapor and carbon dioxide is promoted with simplification of the system. As a result, the water vapor concentration and the carbon dioxide concentration in the off-gas supplied to the second fuel cell 12 can be further reduced, and the power generation efficiency of the fuel cell system 10 can be further increased.

  The separation membrane is not particularly limited as long as it is a membrane that transmits water vapor and carbon dioxide, and examples thereof include an organic polymer membrane, an inorganic material membrane, an organic polymer-inorganic material composite membrane, and a liquid membrane. The separation membrane is more preferably a glassy polymer membrane, a rubbery polymer membrane, an ion exchange resin membrane, an alumina membrane, a silica membrane, a carbon membrane, a zeolite membrane, a ceramic membrane, an amine aqueous solution membrane or an ionic liquid membrane. preferable.

  Examples of the separation membrane include organic polymer membranes such as glassy polymer membranes, rubbery polymer membranes, and ion exchange resin membranes. Materials for the organic polymer film include polyolefin resins such as polyethylene, polypropylene, polybutene, and polymethylpentene, fluorine resins such as polytetrafluoroethylene, polyvinyl fluoride, and polyvinylidene fluoride, polystyrene, cellulose acetate, polyurethane, and polyacrylonitrile. And various organic materials such as polysulfone, polyethersulfone, polyphenylene sulfide, polyimide, polyamide, polyetherimide, polypyrrole, polyphenylene oxide, polyaniline, polyvinyl alcohol, polyacrylic acid, and polyethylene glycol. The organic polymer film may be a film composed of one kind of organic material or a film composed of two or more kinds of organic materials.

  In addition, as the separation membrane, for example, water-absorbing organic polymer such as polyvinyl alcohol, polyacrylic acid, polyvinyl alcohol-polyacrylate copolymer, polyethylene glycol, etc., carbon dioxide and water-soluble It may be an organic polymer film containing a carbon dioxide carrier exhibiting properties.

  As the carbon dioxide carrier, inorganic materials and organic materials are used. For example, inorganic materials include alkali metal salts (preferably alkali metal carbonates), ammonia, ammonium salts, and the like. Examples include amines, amine salts, and polyamines. The carbon dioxide carrier may be contained in an inorganic material film, an organic polymer-inorganic material composite film, a liquid film, or the like.

  Examples of the separation membrane include inorganic material membranes such as an alumina membrane, a silica membrane, a carbon membrane, a zeolite membrane, and a ceramic membrane. Among these, a zeolite membrane is preferable. Examples of the zeolite include A type, Y type, T type, ZSM-5 type, ZSM-35 type, and mordenite type. The inorganic material film may be a film composed of one kind of inorganic material or a film composed of two or more kinds of inorganic materials.

  The separation membrane may be an organic polymer-inorganic material composite membrane. The organic polymer-inorganic material composite film is not particularly limited as long as it is a film composed of an organic material and an inorganic material. For example, at least one organic material selected from the above-described organic materials and the above-described inorganic material A composite film composed of at least one inorganic material selected from the above is preferable.

  Examples of the separation membrane include liquid membranes such as an aqueous amine solution and an ionic liquid. These liquid films may be obtained by impregnating the above-described organic polymer film, inorganic material film, or organic polymer-inorganic material composite film with an aqueous amine solution or an ionic liquid.

  When an amine aqueous solution membrane is used as the separation membrane, carbon dioxide in the off-gas is chemically adsorbed on the amine aqueous solution membrane and then heated to separate the carbon dioxide. Moving. Examples of the aqueous amine solution include amino alcohols such as monoethanolamine.

  When an ionic liquid membrane is used as the separation membrane, carbon dioxide in the off-gas is adsorbed on the ionic liquid membrane, and the adsorbed carbon dioxide is separated from the ionic liquid membrane, so that carbon dioxide is formed on the permeate side of the ionic liquid membrane. Moving. Here, the ionic liquid is a salt having a relatively low melting point of 150 ° C. or lower. For example, a cation such as imidazolium ion or pyridinium ion, trifluoromethanesulfonate ion, tetrafluoroborate ion, hexafluoro And anions such as phosphate ions.

  The thickness of the separation membrane is not particularly limited, but from the viewpoint of mechanical strength, it is usually preferably in the range of 10 μm to 3000 μm, more preferably in the range of 10 μm to 500 μm, and still more preferably in the range of 15 μm to 150 μm. is there.

  The separation membrane may be supported by a porous support. Examples of the material for the support include paper, cellulose, polyester, polyolefin, polyamide, polyimide, polysulfone, polycarbonate, metal, glass, and ceramic.

As a separation membrane for separating carbon dioxide and water vapor, for example, a membrane described in “Zi Tong et al.,“ Water vapor and CO ₂ transport through amine-containing facilitated transport membranes ”, Reactive & Functional Polymers (2014) is used. May be.

  The off gas after separating the water vapor and carbon dioxide flows through the off gas path 54 from the supply side 16 </ b> A and is supplied to the second fuel cell 12. At this time, as described above, the heat exchanger 21 installed in the off-gas path 52 and the off-gas path 54 causes the off-gas after steam separation flowing through the off-gas path 54 to be suitable for the operating temperature of the second fuel cell 12. Heated to temperature.

(Second fuel cell)
The fuel cell system 10 according to this embodiment includes a second fuel cell 12 that is disposed downstream of the separation membrane 16 and that generates power using off-gas from which water vapor and carbon dioxide have been separated. The second fuel cell 12 may be, for example, a fuel cell including an air electrode (cathode), an electrolyte, and a fuel electrode (anode), or a fuel cell stack in which a plurality of fuel cells are stacked. Note that the second fuel cell 12 has the same configuration as that of the first fuel cell 11 described above, and thus description regarding common matters is omitted.

  In the fuel cell system 10, the second fuel cell 12 generates power using off-gas from which water vapor and carbon dioxide are separated. Therefore, in the second fuel cell 12, the theoretical voltage due to the oxygen partial pressure difference between the electrodes is improved and the concentration overvoltage due to water vapor and carbon dioxide in the off-gas is reduced, and particularly exhibits high performance at high current density. can do. Therefore, the fuel cell system 10 can obtain higher power generation efficiency than a multi-stage fuel cell system that generates power using off-gas from which water vapor is not separated in the subsequent fuel cell.

  The cathode off-gas discharged from the cathode of the second fuel cell 12 is supplied to the combustion unit 18 of the reformer 14 together with the water vapor and carbon dioxide separated by the separation membrane 16 through the downstream oxygen supply path 44. On the other hand, the off gas discharged from the anode of the second fuel cell 12 is supplied to the combustion unit 18 of the reformer 14 through the off gas path 46.

  In this embodiment, since the oxygen supply path 44 is in series, oxygen is supplied to the second fuel cell 12 after supplying oxygen to the first fuel cell 11, but the oxygen supply path 44 is parallel. May be. That is, the oxygen supply path 44 through which oxygen flows may be branched to supply oxygen to the cathodes of the first fuel cell 11 and the second fuel cell 12, respectively. At this time, it is sufficient that at least one of the cathode offgas discharged from the cathode of the first fuel cell 11 and the cathode offgas discharged from the cathode of the second fuel cell 12 is supplied to the permeation side 16B of the separation membrane 16. .

  In the present embodiment, the fuel cell system including two fuel cells (the first fuel cell 11 and the second fuel cell 12) has been described. However, the present invention is not limited thereto, and the fuel includes three or more fuel cells. A battery system may be sufficient, for example, the structure provided with a 3rd fuel cell downstream of the 2nd fuel cell 12 may be sufficient. At this time, the cathode off-gas discharged from the cathode of the third fuel cell is supplied to the combustion section of the reformer together with the water vapor and carbon dioxide separated by the separation membrane through the downstream oxygen supply path. The off gas (anode off gas) discharged from the anode may be supplied to the combustion section of the reformer through the off gas path.

[Second Embodiment]
The fuel cell system 20 according to the second embodiment as shown in FIG. 2 is the first embodiment except that the separation membrane 16 uses a water vapor separation membrane that separates water vapor instead of the separation membrane that separates water vapor and carbon dioxide. This is the same as the fuel cell system 10 according to the embodiment. In addition, in 2nd Embodiment-12th Embodiment, the description is abbreviate | omitted about the structure which is common in the fuel cell system 10 which concerns on the above-mentioned 1st Embodiment.

  In the fuel cell system 20 as well, the second fuel cell 12 performs power generation using off-gas from which water vapor has been separated. Therefore, in the second fuel cell 12, the theoretical voltage resulting from the oxygen partial pressure difference between the electrodes is improved. The concentration overvoltage caused by water vapor in the off-gas is reduced. Therefore, the fuel cell system 20 can obtain higher power generation efficiency than a normal multistage fuel cell system.

  Although it will not specifically limit if it is a film | membrane which permeate | transmits water vapor | steam as a water vapor | steam separation membrane, For example, an organic polymer film | membrane, an inorganic material film | membrane, an organic polymer-inorganic material composite film | membrane, a liquid film etc. are mentioned. The separation membrane is more preferably a glassy polymer membrane, a rubbery polymer membrane, an ion exchange resin membrane, an alumina membrane, a silica membrane, a carbon membrane, a zeolite membrane, a ceramic membrane, an amine aqueous solution membrane or an ionic liquid membrane. preferable. The material for the water vapor separation membrane is the same as the material for the separation membrane described above.

  The fuel cell system 20 is preferably further provided with a carbon dioxide removal unit that is disposed downstream of the first fuel cell 11 and upstream of the second fuel cell 12 and removes carbon dioxide from off-gas. Thus, as in the first embodiment, the second fuel cell 12 performs power generation using off-gas from which water vapor and carbon dioxide have been separated, so that power generation efficiency can be further increased.

  The carbon dioxide removing unit is for removing carbon dioxide from off-gas. For example, a filter that adsorbs and absorbs carbon dioxide, a carbon dioxide absorbent that absorbs carbon dioxide, and a carbon dioxide removing material that removes carbon dioxide. In addition, the carbon dioxide may be removed from the off-gas by an electrochemical reaction.

  Examples of the filter that absorbs and absorbs carbon dioxide, the carbon dioxide absorbent, and the carbon dioxide removing material include a chemical adsorbent, a physical adsorbent, and a porous ceramic filter. More specifically, there may be mentioned activated carbon, zeolite, dibarium titanate, lithium silicate, alumina, silica, zirconia, titania and other metal oxides, lithiated zirconia, lithium silicate, etc., and these materials may be combined or mixed You may use it. Further, a material having finer pores may be coated on the porous ceramic filter. Specific examples of the coating include a method of coating the surface of the pores of the porous ceramic filter with mesoporous silica or zeolite modified with an amino group-based silane coupling agent. Thereby, high selectivity of carbon dioxide can be realized, and carbon dioxide can be suitably removed. As the porous ceramic filter, a commercially available one may be used. For example, a sub-nano ceramic membrane filter manufactured by Nippon Choshi Co., Ltd. can be used.

The carbon dioxide removal unit may remove carbon dioxide from off-gas by an electrochemical reaction. For example, the carbon dioxide removal unit includes an anode, an electrolyte, and a cathode, and a power source may be connected to the anode and the cathode. As the power source, the first fuel cell 11 or the second fuel cell 12 may be used. At this time, when an off gas containing carbon dioxide is supplied to the anode and a voltage is applied to the anode and the cathode, the following reactions occur at the anode and the cathode, respectively. As a result, carbon dioxide is removed from the cathode.
Anode: 2H ₂ O → 2H ₂ + O ₂ O ₂ + 2CO ₂ + 4e ⁻ → 2CO ₃ ²⁻
Cathode: 2CO ₃ ²⁻ → O ₂ + 2CO ₂ + 4e ⁻

  In the case where the carbon dioxide removal unit removes carbon dioxide from off-gas by an electrochemical reaction, the above-described anode reaction requires water (water vapor), so carbon dioxide removal is performed upstream of the separation membrane 16. It is preferable to arrange the parts. As a result, water necessary for performing the electrochemical reaction can be sufficiently supplied, and carbon dioxide can be suitably removed.

  The location of the carbon dioxide removal unit is not particularly limited as long as it is disposed downstream of the first fuel cell 11 and upstream of the second fuel cell 12.

  For example, the carbon dioxide removal unit is disposed upstream of the supply side 16A of the separation membrane 16 and downstream of the heat exchanger 21, or downstream of the supply side 16A of the separation membrane 16 and upstream of the heat exchanger 21. Since the off gas that has passed through the heat exchanger 21 has a relatively low temperature (for example, about 200 ° C.) due to heat exchange, the carbon dioxide removal unit is configured to be able to remove carbon dioxide in a low temperature range. Is preferred.

  Further, for example, the carbon dioxide removal unit may be disposed downstream of the first fuel cell 11 and upstream of the heat exchanger 21, or downstream of the heat exchanger 21 and upstream of the second fuel cell 12. At this time, the off gas before passing through the heat exchanger 21 in the off gas path 52 or the off gas after passing through the heat exchanger 21 in the off gas path 54 is relatively high temperature (for example, 750 ° C.) The carbon dioxide removal unit is preferably configured to remove carbon dioxide in a high temperature region.

  In the fuel cell system 10 according to the first embodiment, the carbon dioxide removal unit described above may be further provided downstream of the first fuel cell 11 and upstream of the second fuel cell 12.

[Third Embodiment]
The fuel cell system 30 according to the third embodiment as shown in FIG. 3 is the same as the separation membrane 16 except that a carbon dioxide separation membrane that separates carbon dioxide is used instead of the separation membrane that separates water vapor and carbon dioxide. This is the same as the fuel cell system 10 according to one embodiment.

  Also in the fuel cell system 30, the second fuel cell 12 performs power generation using off-gas from which carbon dioxide has been separated. Therefore, in the second fuel cell 12, the theoretical voltage due to the oxygen partial pressure difference between the electrodes is improved. At the same time, concentration overvoltage caused by carbon dioxide in the off-gas is reduced. Therefore, the fuel cell system 30 can obtain higher power generation efficiency than a normal multistage fuel cell system.

  The carbon dioxide separation membrane is not particularly limited as long as it is a membrane that transmits carbon dioxide, and examples thereof include an organic polymer membrane, an inorganic material membrane, an organic polymer-inorganic material composite membrane, and a liquid membrane. The carbon dioxide separation membrane is a glassy polymer membrane, rubbery polymer membrane, ion exchange resin membrane, alumina membrane, silica membrane, carbon membrane, zeolite membrane, ceramic membrane, amine aqueous solution membrane or ionic liquid membrane. Is more preferable. The material of the carbon dioxide separation membrane is the same as the material of the separation membrane described above.

  The fuel cell system 30 is preferably further provided with a water vapor removing unit that is disposed downstream of the first fuel cell 11 and upstream of the second fuel cell 12 and removes water vapor from the off-gas. Thus, as in the first embodiment, the second fuel cell 12 performs power generation using off-gas from which water vapor and carbon dioxide have been separated, so that power generation efficiency can be further increased.

  The water vapor removing unit is for removing water vapor from off-gas, and may be a separation membrane for separating water vapor, an adsorbent for adsorbing water vapor, a condenser for condensing water vapor, or the like.

  When the water vapor removing unit is a condenser, it is preferable to change the arrangement location according to the heating temperature of the separation membrane 16 when carbon dioxide is separated from off-gas. For example, when the separation membrane 16 is heated to a high temperature to separate carbon dioxide, it is preferable to dispose the water vapor removal portion downstream of the supply side 16A of the separation membrane 16. At this time, if the water vapor removing unit is arranged upstream of the supply side 16A of the separation membrane 16, for example, it is necessary to reheat the off-gas cooled to condense the water vapor again in order to separate the carbon dioxide. It is disadvantageous.

  For example, when separating the carbon dioxide by heating the separation membrane 16 to 40 ° C. or higher, it is preferable to dispose a water vapor removing unit as a condenser downstream of the supply side 16A of the separation membrane 16.

  On the other hand, in the case where carbon dioxide is separated at around room temperature without heating the separation membrane 16 to a high temperature, it is preferable to dispose a water vapor removing unit as a condenser upstream of the supply side 16A of the separation membrane 16. At this time, by disposing the water vapor removing unit upstream of the supply side 16A of the separation membrane 16, the separation membrane 16 can suppress the generation of liquid water that inhibits the separation of carbon dioxide.

  For example, when the separation membrane 16 separates carbon dioxide at a room temperature of less than 40 ° C., it is preferable to dispose a water vapor removal unit that is a condenser upstream of the supply side 16A of the separation membrane 16.

  In the fuel cell system 10 according to the first embodiment, the above-described water vapor removal unit may be further provided downstream of the first fuel cell 11 and upstream of the second fuel cell 12.

[Fourth Embodiment]
The fuel cell system 40 according to the fourth embodiment as shown in FIG. 4 mainly uses a carbon dioxide separation membrane for separating carbon dioxide instead of the separation membrane for separating water vapor and carbon dioxide as the separation membrane 16. The fuel cell system 10 according to the first embodiment is different from the fuel cell system 10 according to the first embodiment in that a water tank 35 (condenser) is further provided downstream of the supply side 16A of the separation membrane 16 and upstream of the heat exchanger 21.

  In the fuel cell system 40, carbon dioxide is separated by the separation membrane 16, and water vapor is separated by the water tank 35 which is a condenser. Therefore, since the second fuel cell 12 generates power using off-gas from which water vapor and carbon dioxide are separated, in the second fuel cell 12, the theoretical voltage due to the oxygen partial pressure difference between the electrodes is improved and the off-gas is increased. Concentration overvoltage due to water vapor and carbon dioxide therein is reduced. Therefore, the fuel cell system 40 can obtain higher power generation efficiency than a normal multistage fuel cell system.

  A heat exchanger 41 is installed in the off gas path 54 and the oxygen supply path 44 on the upstream side of the water tank 35, and the off gas from which carbon dioxide flowing through the off gas path 54 is separated by the heat exchanger 41, Heat exchange is performed with a gas containing oxygen flowing through the oxygen supply path 44. As a result, the off-gas flowing through the off-gas path 54 is cooled and then supplied to the water tank 35 to condense the water vapor, so that the heat of the off-gas can be used effectively.

  The water tank 35 is a container for storing water obtained by condensing water vapor contained in the offgas flowing in the offgas passage 54. The water stored in the water tank 35 is supplied to the water tank 32 through the water supply path 36 and used for steam reforming of the raw material gas.

[Fifth Embodiment]
The fuel cell system 50 according to the fifth embodiment as shown in FIG. 5 separates the water vapor and the carbon dioxide separation membrane 16 ′ that separates carbon dioxide and the water vapor instead of the separation membrane that separates the water vapor and carbon dioxide as the separation membrane 16. The fuel cell system 10 is the same as the fuel cell system 10 according to the first embodiment except that each of the water vapor separation membranes 16 ″ is used.

  The fuel cell system 50 includes a carbon dioxide separation membrane 16 ′ and a water vapor separation membrane 16 ″ as separation membranes. Accordingly, the off gas flowing through the off gas path 52 is supplied to the supply side 16A ′ of the carbon dioxide separation membrane 16 ′, and the carbon dioxide in the off gas is oxidized in the direction of arrow A ′ from the supply side 16A ′ to the permeation side 16B ′. Passes through the carbon separation membrane 16 ''. Further, the off-gas flowing through the off-gas passage 52 is supplied to the supply side 16A '' of the water vapor separation membrane 16 '', and the water vapor in the off-gas flows from the supply side 16A '' to the permeation side 16B '' by the arrow A ''. It passes through the water vapor separation membrane 16 '' in the direction.

  At this time, since the separation conditions in the carbon dioxide separation membrane 16 ′ and the separation conditions in the water vapor separation membrane 16 ″ can be adjusted, the water vapor and carbon dioxide can be separated more efficiently than the fuel cell system 10.

  The carbon dioxide separation membrane 16 ′ and the water vapor separation membrane 16 ″ need not be strictly distinguished, and the carbon dioxide separation membrane 16 ′ may be a separation membrane that transmits water vapor together with carbon dioxide. '' May be a separation membrane that separates carbon dioxide together with water vapor. The order of providing the carbon dioxide separation membrane 16 ′ and the water vapor separation membrane 16 ″ is not particularly limited, and the order may be determined according to the heating temperature of the carbon dioxide separation membrane 16 ′ and the water vapor separation membrane 16 ″. For example, a separation membrane having a high heating temperature may be disposed upstream. A heat exchanger may be provided between the carbon dioxide separation membrane 16 ′ and the water vapor separation membrane 16 ″.

  The carbon dioxide separation membrane described in the third embodiment may be used as the carbon dioxide separation membrane 16 ′, and the water vapor separation membrane described in the second embodiment may be used as the water vapor separation membrane 16 ″.

[Sixth Embodiment]
Hereinafter, a sixth embodiment of the fuel cell system of the present invention will be described with reference to FIG. FIG. 6 is a schematic configuration diagram showing a fuel cell system according to the sixth embodiment. A fuel cell system 60 according to the sixth embodiment includes a reformer 14 having a reforming unit 19 that generates reformed gas by steam reforming a raw material gas and a combustion unit 18 that heats the reforming unit 19 by a combustion reaction. Water vapor and carbon dioxide from the first fuel cell 11 that generates power using the reformed gas supplied from the reforming unit 19 and off-gas containing unreacted reformed gas discharged from the first fuel cell 11 Are disposed on the permeation side 16B of the separation membrane 16, and the second fuel cell 12 that is disposed downstream of the separation membrane 16 and that generates power using off-gas from which water vapor and carbon dioxide have been separated. And an exhaust path 48 through which the exhaust gas discharged from the combustion unit 18 circulates. This system is different from the fuel cell system 10 mainly in that the oxygen supply path 44 is not disposed on the permeation side 16B of the separation membrane 16 and the exhaust path 48 is disposed on the permeation side 16B of the separation membrane 16.

  In the fuel cell system 60, the water vapor and carbon dioxide separated by the separation membrane 16 are supplied to an exhaust path 48 disposed on the permeate side of the separation membrane 16. Since the exhaust gas discharged from the combustion unit 18 flows through the exhaust path 48, the separated water vapor and carbon dioxide flow through the exhaust path 48 together with the exhaust gas. Therefore, by providing the exhaust passage 48 on the permeation side 16B of the separation membrane 16, there is no need to separately provide a route for supplying oxygen to the permeation side of the separation membrane and an air blower or a decompression pump, thereby reducing manufacturing costs. The power generation efficiency of the entire system can be increased. Furthermore, the reliability of the system is improved by simplifying the system.

  Further, since the water vapor and carbon dioxide that have permeated through the separation membrane 16 circulate in the exhaust path 48 together with the exhaust gas, the water vapor partial pressure and the carbon dioxide partial pressure on the permeate side 16B of the separation membrane 16 become low, and the water vapor and carbon dioxide are separated. Is promoted. Therefore, in the fuel cell system 60, separation of water vapor and carbon dioxide is promoted along with simplification of the system. As a result, the water vapor concentration and the carbon dioxide concentration in the off-gas supplied to the second fuel cell 12 can be further reduced, and the power generation efficiency of the fuel cell system 60 can be further increased.

  Furthermore, the fuel cell system 60 according to the present embodiment is provided with a path for supplying air as a gas containing oxygen to the cathode of the fuel cell on the permeate side of the separation membrane, similarly to the fuel cell system 10 according to the first embodiment. The power generation efficiency is better than the case.

  Further, in the fuel cell system 60 according to the present embodiment, since the exhaust gas discharged from the combustion unit 18 having an oxygen ratio smaller than that of air is supplied to the permeation side 16B of the separation membrane 16, oxygen and the separation membrane 16 are supplied. The reaction with permeating hydrogen or carbon monoxide hardly occurs, the local temperature rise of the separation membrane 16 is suppressed, and the durability of the separation membrane 16 can be suitably maintained.

  In the fuel cell system 60, unlike the first embodiment, the heat exchanger 22 is installed in the exhaust path 48 and the oxygen supply path 44, and the heat exchanger 22 causes the exhaust gas flowing in the exhaust path 48 and oxygen Heat exchange is performed with a gas containing oxygen flowing through the supply path 44. Thereby, the exhaust gas flowing in the exhaust passage 48 is cooled and then supplied to the water tank 32 (condenser), and the reformed water flowing in the reforming water supply passage 33 is vaporized and then passed through the water vapor supply passage 37. It is supplied to the source gas supply path 24.

  After heat exchange is performed in the heat exchanger 22, a gas containing oxygen is supplied to the cathode of the first fuel cell 11 through the oxygen supply path 44, and then power generation is performed. The gas containing unreacted oxygen discharged from the cathode is supplied to the cathode of the second fuel cell 12 through the oxygen supply path 44 on the downstream side to generate electric power.

  The gas containing unreacted oxygen discharged from the cathode of the second fuel cell 12 is supplied to the combustion unit 18 of the reformer 14 through the downstream oxygen supply path 44. On the other hand, the off gas discharged from the anode of the second fuel cell 12 is supplied to the combustion unit 18 of the reformer 14 through the off gas path 46.

  Exhaust gas generated by burning the mixed gas of the gas containing unreacted oxygen supplied through the oxygen supply path 44 and the off-gas supplied through the off-gas path 46 in the combustion unit 18 is discharged to the exhaust path 48. .

  The exhaust gas flowing through the exhaust path 48 exchanges heat with the reforming water in the heat exchanger 31 that vaporizes the reforming water flowing through the reforming water supply path 33. As a result, the exhaust gas flowing in the exhaust path 48 on the downstream side of the heat exchanger 31 is cooled to a preferable temperature when separating the water vapor and carbon dioxide by the separation membrane 16, and the reformed gas flowing in the reforming water supply path 33. The quality water is vaporized and then supplied to the raw material gas supply path 24 through the water vapor supply path 37.

  The fuel cell system 60 according to this embodiment includes a separation membrane 16 that separates water vapor and carbon dioxide from off-gas containing unreacted reformed gas discharged from the first fuel cell 11. Therefore, the separated water vapor and carbon dioxide are mixed with the exhaust gas discharged from the combustion section 18 flowing through the permeate side 16B, and circulate in the exhaust path 48 from the permeate side 16B. The heat exchanger 22 performs heat exchange between the exhaust gas flowing through the exhaust path 48 and the gas containing oxygen flowing through the oxygen supply path 44.

[Seventh Embodiment]
A fuel cell system 70 according to the seventh embodiment as shown in FIG. 7 is the sixth embodiment except that a water vapor separation membrane for separating water vapor is used as the separation membrane 16 instead of the separation membrane for separating water vapor and carbon dioxide. This is the same as the fuel cell system 60 according to the embodiment.

  The water vapor separation membrane used in the fuel cell system 70 is the same as the water vapor separation membrane used in the fuel cell system 20 according to the second embodiment.

  It is preferable that the fuel cell system 70 further includes a carbon dioxide removal unit that is disposed downstream of the first fuel cell 11 and upstream of the second fuel cell 12 and removes carbon dioxide from off-gas. Thus, as in the second embodiment, the second fuel cell 12 performs power generation using off-gas from which water vapor and carbon dioxide have been separated, so that the power generation efficiency can be further increased. The configuration of the carbon dioxide removal unit, the installation location, and the like are the same as in the second embodiment.

[Eighth Embodiment]
The fuel cell system 80 according to the eighth embodiment as shown in FIG. 8 is the same except that a carbon dioxide separation membrane for separating carbon dioxide is used as the separation membrane 16 instead of the separation membrane for separating water vapor and carbon dioxide. This is the same as the fuel cell system 60 according to the sixth embodiment.

  The carbon dioxide separation membrane used in the fuel cell system 80 is the same as the water vapor separation membrane used in the fuel cell system 30 according to the third embodiment.

  It is preferable that the fuel cell system 80 further includes a water vapor removing unit that is disposed downstream of the first fuel cell 11 and upstream of the second fuel cell 12 and removes water vapor from the off-gas. Thus, as in the third embodiment, the second fuel cell 12 performs power generation using off-gas from which water vapor and carbon dioxide have been separated, so that the power generation efficiency can be further increased. The configuration of the water vapor removal unit, the installation location, and the like are the same as in the third embodiment.

[Ninth Embodiment]
The fuel cell system 90 according to the ninth embodiment as shown in FIG. 9 mainly uses a carbon dioxide separation membrane for separating carbon dioxide instead of the separation membrane for separating water vapor and carbon dioxide as the separation membrane 16. In addition, it is different from the fuel cell system 60 according to the sixth embodiment in that a water tank 35 (condenser) is further provided downstream of the supply side 16A of the separation membrane 16 and upstream of the heat exchanger 21.

[Tenth embodiment]
The fuel cell system 100 according to the tenth embodiment as shown in FIG. 10 separates the water vapor and the carbon dioxide as a separation membrane 16 and separates the carbon dioxide separation membrane 16 ′ and the water vapor. The fuel cell system 60 is the same as the fuel cell system 60 according to the sixth embodiment except that each of the water vapor separation membranes 16 ″ is used.

  The carbon dioxide separation membrane 16 ′ and the water vapor separation membrane 16 ″ used in the fuel cell system 100 are the carbon dioxide separation membrane 16 ′ and the water vapor separation membrane 16 ″ used in the fuel cell system 50 according to the fifth embodiment. It is the same.

[Eleventh embodiment]
Although the first to tenth embodiments described above are multistage fuel cell systems, the present invention is not limited to this, and may be a circulation type fuel cell system. Hereinafter, a circulating fuel cell system 200 according to an embodiment of the present invention will be described with reference to FIG. FIG. 11 is a schematic configuration diagram showing a circulating fuel cell system according to an eleventh embodiment.

  As shown in FIG. 11, the fuel cell system 200 according to the eleventh embodiment is a circulation type fuel cell system including off-gas circulation paths 56 and 57 that supply off-gas from which water vapor and carbon dioxide are separated to the fuel cell 61 again. It is. In addition, the description is abbreviate | omitted about the structure which is common in the fuel cell system 10 which concerns on 1st Embodiment. Further, since the fuel cell 61 has the same configuration as that of the first fuel cell 11 described above, the description thereof is omitted.

  In the fuel cell system 200, the separation membrane 16 separates water vapor and carbon dioxide from off gas containing unreacted reformed gas discharged from the fuel cell 61, and uses the off gas from which water vapor and carbon dioxide are separated to use the fuel cell. Power is generated at 61. Therefore, in the fuel cell 61, the theoretical voltage caused by the oxygen partial pressure difference between the electrodes is improved, and the concentration overvoltage caused by water vapor and carbon dioxide in the off gas is reduced. Therefore, the fuel cell system 200 can obtain higher power generation efficiency than a circulating fuel cell system that reuses off-gas without separating water vapor and carbon dioxide.

  A recycle blower 28 for circulating the reformed gas is disposed in the off gas circulation path 57. The arrangement of the recycle blower is not particularly limited, and may be upstream of the separation membrane 16 or downstream of the separation membrane 16. However, in the case of being provided upstream of the separation membrane 16, the heat exchanger 21 is preferably disposed between the separation membrane 16 and, when provided downstream of the separation membrane 16, it is preferably disposed between the separation membrane 16 and the heat exchanger 21.

  Further, the water vapor and carbon dioxide separated by the separation membrane 16 are supplied to the oxygen supply path 44 disposed on the permeation side 16B of the separation membrane 16. Since the gas containing unreacted oxygen discharged from the fuel cell 61 flows in the oxygen supply path 44, the separated water vapor and carbon dioxide flow in the oxygen supply path 44 together with the gas containing unreacted oxygen. To do. Therefore, by providing the oxygen supply path 44 on the permeation side 16B of the separation membrane 16, it is not necessary to separately provide a path for supplying oxygen to the permeation side 16B of the separation membrane 16, and an air blower or a decompression pump. This can reduce the power generation efficiency of the entire system. Furthermore, the reliability of the system is improved by simplifying the system.

[Twelfth embodiment]
Hereinafter, a twelfth embodiment of the fuel cell system of the present invention will be described with reference to FIG. FIG. 12 is a schematic configuration diagram showing a circulating fuel cell system according to a twelfth embodiment. The fuel cell system 300 according to the twelfth embodiment is the eleventh embodiment in that water vapor and carbon dioxide separated by the separation membrane 16 are mainly supplied to an exhaust path 48 disposed on the permeate side of the separation membrane 16. This is different from the fuel cell system 200 according to the embodiment.

  In the fuel cell system 300, the water vapor and carbon dioxide separated by the separation membrane 16 are supplied to an exhaust path 48 disposed on the permeation side 16 </ b> B of the separation membrane 16. Since the exhaust gas discharged from the combustion unit 18 circulates in the exhaust path 48, the separated water vapor and carbon dioxide circulate in the exhaust path 48 together with the exhaust gas. Therefore, by providing the exhaust passage 48 on the permeation side 16B of the separation membrane 16, it is not necessary to separately provide a route for supplying oxygen to the permeation side 16B of the separation membrane 16, and an air blower or a decompression pump, thereby reducing manufacturing costs In addition, the power generation efficiency of the entire system can be increased. Furthermore, the reliability of the system is improved by simplifying the system.

  The present invention is not limited to the first to twelfth embodiments described above, and is implemented by a person skilled in the art in combination with the above embodiments within the technical idea of the present invention. For example, for the fuel cell system 200 according to the eleventh embodiment and the fuel cell system 300 according to the twelfth embodiment, the configurations of the fuel cell systems according to the second to tenth embodiments may be appropriately combined. Further, the installation location and combination of heat exchangers are not limited to these embodiments.

[Contrast of gas composition]
In the following, when water vapor and carbon dioxide are completely separated by the separation membrane 16, the gas composition of the cathode off-gas discharged from the second fuel cell 12 and the exhaust gas discharged from the combustion unit 18 and air are compared. did. The simulation was performed on the premise of the fuel cell system 10 according to the aforementioned first embodiment as the gas composition of the cathode off-gas, and the fuel cell system 60 according to the aforementioned sixth embodiment as the gas composition of the exhaust gas. As simulation conditions, the oxygen utilization rate in the first fuel cell 11 and the second fuel cell 12 is 50%, the fuel utilization rate in the first fuel cell 11 is 60%, and the fuel in the second fuel cell 12 is used. The utilization rate was 75%. The results are shown in Table 1.

  As shown in Table 1, the oxygen concentration in the cathode offgas and exhaust gas is about half that of air. Therefore, in the fuel cell system 10 and the fuel cell system 60, due to the reaction between hydrogen or carbon monoxide that permeates the separation membrane 16 in a minute amount and oxygen that flows through the permeation side of the separation membrane 16, which causes a decrease in durability. It is estimated that the local temperature rise of the separation membrane 16 hardly occurs, and the durability of the separation membrane 16 can be suitably maintained.

10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300 ... fuel cell system, 11 ... first fuel cell, 12 ... second fuel cell, 14 ... reformer, 16 ... Separation membrane, 16 '... carbon dioxide separation membrane, 16 "... steam separation membrane, 16A, 16'A, 16" A ... supply side, 16B, 16B', 16B "... permeation side, 18 ... combustion section, DESCRIPTION OF SYMBOLS 19 ... Reforming part, 21, 22, 31, 41 ... Heat exchanger, 24 ... Raw material gas supply path, 25 ... Blower, 28 ... Recycle blower, 32, 35 ... Water tank, 33 ... Reformed water supply path, 34 ... reformed water pump, 36 ... water supply path, 37 ... steam supply path, 42 ... reformed gas supply path, 44 ... oxygen supply path, 46, 52, 54 ... off gas path, 48 ... exhaust path, 56, 57 ... off gas Circulation path, 61 ... Fuel cell

Claims (9)

A reformer having a reforming unit for steam reforming a raw material gas to generate a reformed gas and a combustion unit for heating the reforming unit by a combustion reaction;
A first fuel cell that generates electric power using the reformed gas supplied from the reformer;
A separation membrane that separates at least one of water vapor and carbon dioxide from the off-gas containing the unreacted reformed gas discharged from the first fuel cell through the permeate side ;
A second fuel cell that is disposed downstream of the supply side of the separation membrane and that generates power using the off-gas from which at least one of water vapor and carbon dioxide has been separated;
Oxygen that is disposed upstream and downstream of the permeation side of the separation membrane and on the permeation side of the separation membrane and through which a gas containing unreacted oxygen discharged from at least one of the first fuel cell and the second fuel cell flows. A fuel cell system comprising: a supply path or an exhaust path that is disposed on the permeate side of the separation membrane and through which exhaust gas discharged from the combustion section flows. A reformer having a reforming unit for steam reforming a raw material gas to generate a reformed gas and a combustion unit for heating the reforming unit by a combustion reaction;
A fuel cell that generates power using the reformed gas supplied from the reforming unit;
A separation membrane that separates the off-gas containing the unreacted reformed gas discharged from the fuel cell by transmitting at least one of water vapor and carbon dioxide to the permeate side ;
An off-gas circulation path that is arranged downstream of the supply side of the separation membrane and supplies the off-gas from which at least one of water vapor and carbon dioxide has been separated to the fuel cell;
Located on the permeation side upstream of the separation membrane and on the permeation side of the separation membrane, on the oxygen supply path through which the gas containing unreacted oxygen discharged from the fuel cell flows, or on the permeation side of the separation membrane And an exhaust path through which the exhaust gas discharged from the combustion section flows. The oxygen supply path is disposed upstream and downstream of the permeation side of the separation membrane and on the permeation side of the separation membrane,
3. The fuel cell system according to claim 1, wherein the oxygen supply path supplies gas containing at least one of water vapor and carbon dioxide separated by the separation membrane and unreacted oxygen to the combustion unit.   The fuel cell system according to claim 3, wherein water vapor is separated from the exhaust gas discharged from the combustion section, and the separated water vapor is supplied to the reforming section. The exhaust path is disposed on the permeate side of the separation membrane;
The water vapor is separated from a mixed gas of exhaust gas flowing through the exhaust path and at least one of water vapor and carbon dioxide separated by the separation membrane, and the separated water vapor is supplied to the reforming unit. Item 3. The fuel cell system according to Item 2. As the separation membrane, a water vapor separation membrane that separates the off-gas containing unreacted reformed gas by permeating water vapor to the permeate side , and allows carbon dioxide to permeate to the permeate side from off-gas containing the unreacted reformed gas. the fuel cell system according to any one of claims 1 to 5 comprising respectively a carbon dioxide separation membrane for separating Te. Dioxide wherein disposed upstream or downstream of the supply side of the separation membrane, the water vapor removing section for removing water vapor from the off-gas, and that is disposed upstream or downstream of the supply side of the separation membrane, to remove carbon dioxide from the off-gas The fuel cell system according to any one of claims 1 to 6, further comprising at least one of carbon removal units. The water vapor removal part which is arrange | positioned in the upstream or downstream of the supply side of the said separation membrane, and removes water vapor | steam from the said off gas is further provided, The water vapor | steam removed by the said water vapor removal part is supplied to the said modification | reformation part. Item 8. The fuel cell system according to any one of Items 7. The off-gas and the separation membrane according to claim steam flowing in the downstream of the supply-side further comprises said off-gas are separated, the heat exchanger for performing heat exchange between the flowing upstream of the supply side of the separation membrane The fuel cell system according to any one of claims 1 to 8.