JP6734455B1 - Fuel cell unit and fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the carbon dioxide concentration of a fuel electrode off-gas with a simple structure. A fuel cell system (10A) includes a fuel electrode channel (27A) located downstream of a fuel electrode (22A) in a fuel channel (26A), and an air channel (28A) adjacent to the fuel electrode channel (27A) with a cylindrical substrate (30) in between. A hydrogen permeable portion 30 having a hydrogen ion permeable membrane 36 that is provided between the air electrode channel 29A and the fuel electrode channel 27A and allows hydrogen ions to permeate from the fuel electrode channel 27A to the air electrode channel 29A. A carbon dioxide recovery unit 16 for recovering the discharged off-gas. [Selection diagram]

Description

The present invention relates to a fuel cell unit and a fuel cell system, and more particularly to a fuel cell unit and a fuel cell system that generate electricity using a carbon compound fuel.

When a carbon compound fuel is used in the fuel cell system, carbon dioxide is contained in the fuel electrode off-gas discharged from the fuel electrode of the fuel cell stack. Although this carbon dioxide is being collected, components other than carbon dioxide are mixed in the fuel electrode off-gas. Therefore, for example, Patent Document 1 discloses a technique of recovering carbon dioxide by burning the fuel electrode off-gas with oxygen and further removing steam by condensation.

Patent 5581240

By burning the fuel electrode off-gas with oxygen as in Patent Document 1, hydrogen and hydrocarbon compounds in the fuel electrode off-gas can be reduced. In this case, it is required to reduce hydrogen from the fuel electrode off-gas with a simpler configuration.

Variables The present invention has been made in consideration of the above facts, and an object thereof is to increase the carbon dioxide concentration of the fuel electrode off-gas with a simple configuration.

The fuel cell unit according to claim 1 is a cylindrical solid oxide fuel cell unit that uses a carbon compound as a fuel to generate electric power, and has a tubular shape, in which a fuel electrode, an electrolyte membrane, and an air electrode are stacked. A cylindrical substrate having battery cells, a fuel flow path located inside or outside the cylindrical substrate and through which a fuel gas containing a carbon compound flows, and either inside or outside the cylindrical substrate. An air flow path located on the other side, through which an oxidant gas containing oxygen flows, and is laminated on the cylindrical substrate downstream of the fuel electrode, and carbon dioxide is positioned downstream of the fuel electrode of the fuel flow path. And a hydrogen removing unit configured to reduce hydrogen in the fuel electrode passage by ion movement between the fuel electrode passage for sending gas to the recovery unit and the air electrode passage communicating with the air passage.

In the fuel cell unit according to the first aspect, the fuel flow path is formed inside or outside the cylinder of the cylindrical substrate, and the air flow path is formed on the other side. A hydrogen removing portion is laminated on the cylindrical substrate downstream of the fuel electrode, and hydrogen in the fuel electrode passage is reduced by ion movement between the fuel electrode passage and the air electrode passage. The ion transfer may be hydrogen ion transfer from the fuel electrode channel to the air electrode channel, or oxygen ion transfer from the air electrode channel to the fuel electrode channel. When oxygen ions move, hydrogen is reduced due to an oxidation reaction with hydrogen in the fuel electrode passage.

In this way, by stacking and forming the hydrogen removing portion on the cylindrical substrate, it is possible to increase the carbon dioxide concentration of the fuel electrode off-gas with a simple structure.

In the fuel cell unit according to a second aspect, the hydrogen removing unit has a hydrogen ion permeable membrane that allows hydrogen ions to permeate from the fuel electrode channel side to the air electrode channel side.

According to the fuel cell unit of the second aspect, hydrogen can be reduced from the fuel electrode off-gas by transmitting hydrogen ions from the fuel electrode flow channel side to the air electrode flow channel side.

In the fuel cell unit according to claim 3, a hydrogen ion oxidation catalyst is laminated on the hydrogen ion permeable membrane on the side of the air electrode channel.

In the fuel cell unit according to the third aspect, the hydrogen ion oxidation catalyst promotes the generation of water vapor by the combination of oxygen flowing in the air electrode passage and hydrogen ions moved to the air electrode passage. Therefore, the hydrogen partial pressure of the air electrode channel can be kept low, and hydrogen ion permeation from the fuel electrode channel to the air electrode channel can be promoted.

In the fuel cell unit according to a fourth aspect, the hydrogen removing section has an oxygen ion permeable membrane that allows oxygen ions to permeate from the air electrode passage side to the fuel electrode passage side.

According to the fuel cell unit of claim 4, oxygen ions permeate from the air electrode flow passage side to the fuel electrode flow passage side to oxidize hydrogen in the fuel electrode off-gas to generate water vapor, thereby reducing hydrogen. You can It is also possible to oxidize and reduce hydrocarbon compounds other than hydrogen.

In the fuel cell unit according to a fifth aspect, an oxidation catalyst is laminated on the oxygen ion permeable membrane on the fuel electrode channel side.

According to the fuel cell unit of the fifth aspect, the generation of water vapor is promoted by the combination of hydrogen flowing in the fuel electrode channel and oxygen ions moved from the air electrode channel side to the fuel electrode channel side. Therefore, by lowering the hydrogen partial pressure in the fuel electrode channel, carbon dioxide and hydrogen are produced by the shift reaction between carbon monoxide and water vapor. As a result, carbon monoxide in the fuel electrode off gas can also be reduced.

In the fuel cell unit according to a sixth aspect, the gas flowing through the fuel electrode passage and the gas flowing through the air electrode passage are in parallel flow.

According to the fuel cell unit of the sixth aspect, since the oxidant gas having a high oxygen concentration is supplied to the air flow passage portion corresponding to the upstream side of the fuel flow passage, the power generation efficiency of the fuel cell stack is maintained. be able to.

Fuel cell system according to claim 7, the fuel cell unit according to any one of claims 1 to 6, wherein the carbon dioxide recovery unit for recovering the fuel electrode off-gas discharged from the fuel electrode flow path And are equipped with.

According to the fuel cell system of the invention of claim 7, carbon dioxide can be recovered by the carbon dioxide recovery part.

A fuel cell system according to an eighth aspect includes a current supply unit that causes a current to flow between the hydrogen removing unit between the fuel electrode passage side and the air electrode passage side.

According to the fuel cell system of the eighth aspect, it is possible to promote the permeation of ions between the fuel electrode passage and the air electrode passage by passing an electric current through the hydrogen removing portion.

A fuel cell system according to a ninth aspect of the present invention includes a condenser provided downstream of the hydrogen removal section of the fuel electrode channel and upstream of the carbon dioxide recovery section.

According to the fuel cell system of the ninth aspect, it is possible to obtain a high-concentration carbon dioxide gas by removing water contained in the gas flowing through the fuel electrode passage with the condenser.

According to the fuel cell unit and the fuel cell system of the present invention, the carbon dioxide concentration of the fuel electrode off gas can be increased with a simple configuration.

It is a schematic diagram of a fuel cell system concerning a 1st embodiment. It is a schematic perspective view of the fuel cell stack of 1st Embodiment. It is a partial cross section figure of the fuel cell stack of 1st Embodiment. It is a schematic diagram of a fuel cell system concerning a modification of a 1st embodiment. It is a schematic perspective view of the fuel cell stack of 2nd Embodiment. It is a partial cross section figure of the fuel cell stack of 2nd Embodiment. It is a partially exploded perspective view of a fuel cell stack according to a third embodiment. It is a partially expanded schematic diagram of the fuel cell stack of 3rd Embodiment. It is a partially exploded perspective view of the fuel cell stack concerning 4th Embodiment. It is a partially expanded schematic diagram of the fuel cell stack of 4th Embodiment.

[First Embodiment]
Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a schematic explanatory diagram of a fuel cell system 10A according to an embodiment of the present invention. The fuel cell system 10A includes a fuel cell stack 12A, a condenser 14, a carbon dioxide recovery unit 16, and a current controller 18 as main components.

A fuel cell stack 12A as a fuel cell unit of the present invention is a fuel cell having an electrolyte layer 20A, a fuel electrode (anode) 22A and an air electrode (cathode) 24A that are respectively laminated on the front and back surfaces of the electrolyte layer 20A. It has a plurality of cells. A fuel channel 26A is formed on the fuel electrode 22A side of the fuel cell stack 12A, and an air channel 28A is formed on the air electrode 24A side.

A fuel gas supply pipe P1 is connected to the fuel flow path 26A of the fuel cell stack 12A. A steam supply pipe P2 is joined to the fuel gas supply pipe P1, and the fuel gas containing steam is supplied from the fuel gas supply pipe P1 to the fuel flow path 26A.

The fuel gas contains a carbon compound. In the present embodiment, an example in which methane is used as the fuel gas will be described, but there is no particular limitation as long as it is a gas that can generate hydrogen by reforming, and a hydrocarbon fuel can be used. Examples of hydrocarbon fuels include natural gas, LP gas (liquefied petroleum gas), biogas, coal reformed gas, and lower hydrocarbon gas. Examples of the lower hydrocarbon gas include lower hydrocarbons having 4 or less carbon atoms such as methane, ethane, ethylene, propane and butane, and methane used in the present embodiment is preferable. The hydrocarbon fuel may be a mixture of the above-mentioned lower hydrocarbon gas, and the above-mentioned lower hydrocarbon gas may be a gas such as natural gas, city gas or LP gas. If the fuel gas contains impurities, a desulfurizer or the like is required, but it is omitted in the figure.

An air supply pipe P3 is connected to the air flow path 28A of the fuel cell stack 12A to supply air.

At the fuel electrode 22A, the fuel gas is steam-reformed to generate hydrogen and carbon monoxide, as shown in the following formula (1). Further, as shown in the following equation (2), carbon dioxide and hydrogen are produced by the shift reaction between the produced carbon monoxide and water vapor.

CH ₄ +H ₂ O→3H ₂ +CO (1)
CO+H ₂ O→CO ₂ +H ₂ (2)

Then, in the fuel electrode 22A, hydrogen is separated into hydrogen ions and electrons as shown in the following formula (3).

(Fuel electrode reaction)
_{^{H 2 → 2H + + 2e -}} ... (3)

Hydrogen ions move to the air electrode 24A through the electrolyte layer 20A. The electrons move to the air electrode 24A through an external circuit (not shown). As a result, power is generated in the fuel cell stack 12A. During power generation, the fuel cell stack 12A generates heat.

On the other hand, in the air electrode 24A, as shown in the following formula (4), hydrogen ions that have moved from the fuel electrode 22A through the electrolyte layer 20A and electrons that have moved from the fuel electrode 22A through the external circuit are oxygen in the air. Reacts with water vapor to produce steam.

(Air electrode reaction)
2H ⁺ +2e ⁻ +1/2O ₂ →H ₂ O (4)

An air electrode offgas passage P4 is connected to the downstream end of the air passage 28A. The air electrode off-gas passage P4 is connected to the condenser 14, and the off gas discharged from the air electrode 24A is discharged to the outside from the exhaust pipe P7 after water is removed by the condenser 14.

A fuel electrode offgas passage P5 is connected to the downstream end of the fuel passage 26A. After the water is removed by the condenser 14, the fuel electrode off-gas is supplied to the carbon dioxide recovery unit 16 via the recovery path P6. The carbon dioxide recovery unit 16 may be a tank that stores gas under compression, or may be a portion that supplies carbon dioxide to a demand line. Further, it may have a PSA, a carbon dioxide separation membrane or the like to further increase the carbon dioxide concentration.

A densitometer 15 is provided on the recovery path P6. The densitometer 15 measures the carbon dioxide concentration of the fuel electrode off-gas on the downstream side of the condenser 14. The densitometer 15 is electrically connected to the current controller 18, and information on the carbon dioxide concentration measured by the densitometer 15 is sent to the current controller 18.

A current controller 18 is provided in the fuel cell system 10A. The current controller 18 supplies a direct current to the hydrogen permeation section 34, which will be described later, based on the carbon dioxide concentration information measured by the densitometer 15. The current controller 18 uses the electric power generated by the fuel cell stack 12A to flow the above DC current.

[Fuel cell stack]
Next, the fuel cell stack 12A used in the fuel cell system 10A will be described. It should be noted that the fuel cell stack 12A in the present embodiment does not simply refer to a portion where fuel cells are stacked, but includes a fuel flow path, an air flow path, and a hydrogen permeation part, as described later.

The fuel cell stack 12A of the present embodiment is a hydrogen ion conductive type solid oxide fuel cell (PCFC: Proton Ceramic Solid Oxide Fuel Cell), and as shown in FIG. 2, is a horizontal striped cylindrical type. ..

The fuel cell stack 12A includes a cylindrical substrate 30, a fuel cell 32, and a hydrogen permeable portion 34.

The cylindrical substrate 30 has a cylindrical shape, and as shown in FIG. 3, a fuel battery cell 32 in which a fuel electrode 22A, an electrolyte layer 20A, and an air electrode 24A are annularly laminated in this order on the outer surface is formed. .. The cylindrical substrate 30 can be formed of, for example, a ceramic porous material. The fuel cells 32 are arranged in a plurality (in the present embodiment, five cells are shown) arranged at intervals in the cylinder axis direction of the cylindrical substrate 30. The fuel cells 32 adjacent to each other are electrically connected in series by the interconnector 33, and are connected to the current controller 18 via the electric wiring E1.

The inside of the cylinder of the cylindrical base body 30 serves as the fuel flow path 26A, and the outside of the cylinder of the cylindrical base body 30 serves as the air flow path 28A. The air flow passage 28A is surrounded by an outer peripheral wall 39, and a cylindrical air flow passage 28A is formed between the outer peripheral wall 39 and the cylindrical base body 30.

A hydrogen permeable portion 34 is formed at one end of the cylindrical substrate 30. The hydrogen permeable portion 34 is formed by annularly stacking an ionization catalyst layer 35, a hydrogen permeable membrane 36, and a proton oxidation catalyst layer 37 in this order on the outer surface of the cylindrical substrate 30. As the ionization catalyst layer 35, nickel, ruthenium, or the like can be used. As the proton oxidation catalyst layer 37, LSCF (a compound consisting of La, Sr, Co, Fe and oxygen) or the like can be used. As the hydrogen permeable film 36, doped barium zirconium oxide (BaZrO ₃ ), a mixture of doped BaZrO ₃ and an electron conductive oxide, a palladium alloy, or the like can be used. Yttrium (Y) is the element to be doped into BaZrO ₃ . A combination of one or more rare earth elements such as ytterbium (Yb) and cerium (Ce) is desirable. The dope ratio is preferably 5% to 30%. BaZr _0.8 Yb _0.2 O _3-δ doped with 20% Yb and BaZr _0.8 Y _0.2 O _3-δ doped with 20% Y are particularly promising because they have high hydrogen ion conductivity. The rare earth-doped LaCrO ₃ is desirable as the electronically conductive oxide to be mixed with the doped BaZrO ₃ . In particular, La _0.8 Sr _0.2 CrO ₃ doped with 20% strontium has high electron conductivity and is promising. The mixing ratio of the electronically conductive oxide is preferably 0% to 40%. Some or all of Ba in BaZrO ₃ may be replaced with strontium (Sr), calcium (Ca), lanthanum (La), or a combination thereof. The hydrogen permeable portion 34 is connected to the current controller 18 via the electric wiring E2.

As shown in FIG. 2, in the fuel passage 26A, the fuel gas supply pipe P1 is connected to the end portion side opposite to the end portion where the hydrogen permeation portion 34 is formed, and the fuel passage 26A Fuel gas and water vapor are supplied to. The air supply pipe P3 is connected to the air passage 28A on the same end side as the fuel gas supply pipe P1, and air is supplied to the air passage 28A in parallel flow with the fuel gas. In the figure, reference numeral A is given to the gas flowing in the fuel flow path 26A and its downstream side, and reference numeral C is given to the gas flowing in the air flow path 28A and its downstream side.

The fuel electrode off-gas passage P5 is connected to the end portion side of the fuel passage 26A where the hydrogen permeation portion 34 is formed. The air electrode off-gas passage P4 is connected to the air passage 28A on the same end side as the fuel electrode off-gas passage P5.

In the fuel cell stack 12A of this embodiment, the downstream side of the fuel electrode 22A of the fuel flow path 26A is referred to as the fuel electrode flow path 27A, and the downstream side of the air flow path 28A of the air electrode 24A is the air flow path. It is referred to as road 29A. The fuel electrode channel 27A and the air electrode channel 29A are partitioned by the cylindrical base body 30 and are provided in the fuel cell stack 12A.

The current controller 18 is capable of controlling the magnitude of the current flowing through the electric wiring E1, and the power generation amount in the fuel cell stack 12A is based on the input from the control unit (not shown). Is controlled by. Further, the current controller 18 uses the electric power generated by the fuel cell stack 12A to pass a current between the ionization catalyst layer 35 and the proton oxidation catalyst layer 37 via the electric wiring E2. The current supplied from the current controller 18 is based on the carbon dioxide concentration information from the densitometer 15. That is, when the carbon dioxide concentration measured by the densitometer 15 is lower than the predetermined concentration, the supply current is increased to promote the hydrogen permeation in the hydrogen permeation unit 34.

Next, the operation of the fuel cell system 10A will be described.

Fuel gas containing water vapor is supplied from the fuel gas supply pipe P1 to the fuel flow passage 26A, and air is supplied from the air supply pipe P3 to the air flow passage 28A. In the fuel flow path 26A, the fuel gas is steam reformed to generate hydrogen and carbon monoxide. Further, carbon dioxide and hydrogen are produced by the shift reaction between the produced carbon monoxide and water. Then, in each of the fuel cells 32, the above-described power generation reaction occurs and power generation is performed.

In the fuel flow path 26A, the fuel gas flows from the upstream side to the downstream side while gradually reducing the fuel component by the reforming and power generation reaction. Then, mainly carbon dioxide, water vapor, carbon monoxide, and hydrogen flow into the fuel electrode channel 27A at the downstream end. In the fuel electrode channel 27A, ionization of hydrogen is promoted in the ionization catalyst layer 35, and the ionized hydrogen (hydrogen ions) permeates the hydrogen permeable membrane 36 and moves to the proton oxidation catalyst layer 37 side. Oxidation of the migrated hydrogen ions by oxygen in the air electrode channel 29A is promoted by the proton oxidation catalyst layer 37 to become water vapor in the air electrode channel.

In the fuel electrode channel 27A, the hydrogen content decreases as hydrogen moves to the air electrode channel 29A, so that the shift reaction between carbon monoxide and water proceeds, and carbon dioxide and hydrogen are generated. Then, the generated hydrogen moves from the fuel electrode channel 27A side to the air electrode channel 29A side as described above.

The fuel electrode off-gas is delivered from the fuel electrode flow passage 27A to the fuel electrode off-gas passage P5. As described above, since hydrogen is moving from the fuel electrode channel 27A side to the air electrode channel 29A side, the fuel electrode off-gas mainly contains carbon dioxide and water vapor. After the water is removed by the condenser 14, the fuel electrode off-gas is supplied to the carbon dioxide recovery unit 16 through the recovery path P6, and the carbon dioxide is recovered.

The air electrode off-gas is sent from the air electrode flow path 29A to the air electrode off-gas passage P4. The air electrode off-gas is discharged to the outside after water is removed by the condenser 14.

According to the fuel cell system 10A of the present embodiment, since hydrogen moves in the hydrogen permeation section 34 from the fuel electrode channel 27A side to the air electrode channel 29A side, hydrogen and water vapor remaining in the fuel electrode off-gas are reduced, The carbon dioxide concentration can be increased. Since the movement of the hydrogen is performed using the hydrogen permeable membrane, it is not necessary to supply oxygen to the fuel passage 26A.

Further, in the hydrogen permeable portion 34, since the proton oxidation catalyst layer 37 is laminated on the side of the hydrogen permeable membrane 36 on the side of the air electrode channel 29A, the oxygen flowing through the air electrode channel 29A moves to the air electrode channel 29A. The generation of water vapor is promoted by the bonding with hydrogen ions. Therefore, the hydrogen partial pressure of the air electrode channel 29A can be maintained low, and hydrogen ion permeation from the fuel electrode channel 27A to the air electrode channel 29A can be promoted.

Further, in the fuel cell system 10A of the present embodiment, the hydrogen permeation part 34 is provided inside the fuel cell stack 12A. By thus providing the fuel cell stack 12A in the fuel cell stack 12A, the hydrogen permeable portion 34 can have a simple structure.

Further, in the present embodiment, the hydrogen permeable portion 34 is laminated on the end portion of the cylindrical substrate 30 that divides the fuel flow passage 26A and the air flow passage 28A. Therefore, the hydrogen permeable portion 34 can be easily formed. Further, by providing the hydrogen permeable portion 34 on the integrally formed cylindrical substrate 30, the temperature change due to start-up and stop and long-term operation are associated with the case where a separate member is prepared and the hydrogen permeable portion is provided. The sealability and durability can be improved.

Further, in the present embodiment, the current controller 18 causes a current to flow between the fuel electrode passage 27A side and the air electrode passage 29A side of the hydrogen permeation section 34. As a result, the permeation of hydrogen ions from the fuel electrode channel 27A to the air electrode channel 29A can be promoted. In the present embodiment, the carbon dioxide concentration is measured by the densitometer 15, but the hydrogen concentration may be measured by the densitometer 15, or the concentrations of both carbon dioxide and hydrogen may be measured respectively to obtain the current controller. It may also be sent to 18 and used as information for controlling the supply current.

Further, since the electric current generated from the fuel cell stack 12A is used for the current supply from the current controller 18, the direct current can be used as it is, and when the alternating current from the outside is converted to the direct current and used. Is more efficient than The current supply to the hydrogen permeation section 34 by the current controller 18 is not always necessary.

Further, in this embodiment, since the condenser 14 removes water vapor from the fuel electrode off-gas, the carbon dioxide concentration of the gas recovered by the carbon dioxide recovery unit 16 can be increased. Although the condenser 14 is used in the present embodiment, carbon dioxide may be separated by other means, for example, a carbon dioxide separation membrane, or carbon dioxide may be separated by a PSA device.

Further, in the present embodiment, the gas flowing through the fuel electrode passage 27A and the gas flowing through the air electrode passage 29A are in parallel flow. Therefore, air having a high oxygen concentration is supplied to the air flow path 28A corresponding to the upstream side of the fuel flow path 26A, and the power generation efficiency of the fuel cell stack 12A can be maintained. In addition, the amount of air sent from the air supply pipe P3 can be reduced in order to maintain the same level of power generation efficiency.

The air may be supplied to the air passage 28A from the side corresponding to the downstream side of the fuel passage 26A, and the air flow and the fuel gas flow may be counter flows. In this case, the temperature distribution in the cylinder axis direction of the fuel cell stack 12A can be made smaller than in the case of parallel flow.

Further, in the present embodiment, since the fuel cell stack 12A is the hydrogen ion conductive type solid oxide fuel cell, water vapor is generated on the air electrode 24A side in the power generation reaction. Therefore, the water vapor content of the gas flowing through the fuel electrode passage 27A can be reduced, and the amount of water removed by the condenser 14 can be further reduced.

The fuel cell stack 12A may be an oxygen ion transfer type solid oxide fuel cell (SOFC). In this case, as shown in FIG. 4, the reformer 13 is provided, the fuel gas is steam-reformed on the upstream side of the fuel passage 26A, and the reformed gas pipe P1-1 is changed to the fuel passage 26A. Supply quality gas. The following reactions occur at the fuel electrode 22A and the air electrode 24A.

At the air electrode 24A, oxygen in the air reacts with electrons to generate oxygen ions, as shown in the following formula (5). The generated oxygen ions reach the fuel electrode 22A of the fuel cell stack 12A through the electrolyte layer 20A.

(Air electrode reaction)
1/2O ₂ +2e ⁻ →O ^{2 −} (5)

On the other hand, in the fuel electrode 22A of the fuel cell stack 12A, oxygen ions that have passed through the electrolyte layer 20A react with hydrogen and carbon monoxide in the fuel gas as shown in the following formulas (6) and (7). , Water vapor and carbon dioxide and electrons are generated. Electrons generated at the fuel electrode 22A move from the fuel electrode 22A to an air electrode 24A through an external circuit, thereby generating power.

(Fuel electrode reaction)
^{_{H 2 + O 2- → H 2}} O + 2e - ... (6)
CO+O ^{2 −} →CO ₂ +2e ⁻ (7)

In this solid oxide fuel cell, since water vapor is generated at the fuel electrode 22A, the amount of water vapor contained in the fuel electrode off-gas is larger than that in the hydrogen ion conductive solid oxide fuel cell.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. In this embodiment, the same parts as those in the first embodiment are designated by the same reference numerals, and detailed description thereof will be omitted.

The fuel cell system 10B of the present embodiment has an oxygen permeable portion 64 instead of the hydrogen permeable portion 34 of the first embodiment. Further, in the present embodiment, the concentrations of carbon dioxide and oxygen are measured by the densitometer 15 and output to the current controller 18. Other configurations are similar to those of the first embodiment.

As shown in FIG. 5, an oxygen permeable portion 64 is formed at one end of the cylindrical substrate 30. As shown in FIG. 6, the oxygen permeable portion 64 is formed by annularly stacking an oxygen permeable film 66 on the outer surface of the cylindrical substrate 30 and annularly stacking an oxidation catalyst 68 on the inner surface of the cylindrical substrate 30. There is.

As the oxygen permeable film 66, mixed conductive ceramics including LSCF (compound composed of La, Sr, Co, Fe and oxygen), BSCF (compound composed of Ba, Sr, Co, Fe and oxygen) and the like, and yttria stabilization It can be formed of oxygen ion conductive ceramics such as zirconia (YSZ). As the oxidation catalyst 68, nickel (Ni), ruthenium (Ru), or the like can be used.

The oxygen permeation portion 64 is connected to the current controller 18 via the electric wiring E2. The current controller 18 uses the electric power generated by the fuel cell stack 12B to pass a current between the oxygen permeable film 66 and the oxidation catalyst 68 via the electric wiring E2. The current supplied from the current controller 18 is based on the carbon dioxide concentration information and the oxygen concentration information from the densitometer 15. That is, feedback control is performed so that the carbon dioxide concentration measured by the densitometer 15 increases and the oxygen concentration decreases.

Although the carbon dioxide concentration and the oxygen concentration are measured by the densitometer 15 in the present embodiment, feedback control may be performed by measuring only the carbon dioxide concentration, or oxygen other than carbon dioxide, hydrogen, carbon monoxide, Feedback control may be performed by measuring any one or more of methane.

Next, the operation of the fuel cell system 10B will be described.

Fuel gas containing water vapor is supplied from the fuel gas supply pipe P1 to the fuel flow passage 26A, and air is supplied from the air supply pipe P3 to the air flow passage 28A. In the fuel flow path 26A, the fuel gas is steam reformed to generate hydrogen and carbon monoxide. Further, carbon dioxide and hydrogen are produced by the shift reaction between the produced carbon monoxide and water vapor. Then, in each of the fuel cells 32, the above-described power generation reaction occurs and power generation is performed.

In the fuel flow path 26A, the fuel gas flows from the upstream side to the downstream side while gradually reducing the fuel component by the reforming and power generation reaction. Then, mainly carbon dioxide, water vapor, carbon monoxide, and hydrogen flow into the fuel electrode channel 27A at the downstream end. In the air flow passage 28A, the air flows to the air electrode flow passage 29A on the downstream side while gradually reducing the oxygen component due to the power generation reaction. In the air electrode channel 29A, oxygen is ionized and permeates the oxygen permeable film 66 toward the fuel electrode channel 27A. Then, the oxidation catalyst 68 promotes the binding of carbon monoxide, hydrogen, and methane in the fuel electrode channel 27A, and carbon dioxide and water vapor are generated.

In the fuel electrode channel 27A, the concentrations of hydrogen, carbon monoxide, and methane thus decrease, and the concentrations of carbon dioxide and water vapor increase. After water is removed by the condenser 14, the carbon dioxide concentration and oxygen concentration of the fuel electrode off-gas are measured by the densitometer 15 and are supplied to the carbon dioxide recovery unit 16 to recover carbon dioxide.

The air electrode off-gas is sent from the air electrode flow path 29A to the air electrode off-gas passage P4. The air electrode off-gas is discharged to the outside after water is removed by the condenser 14.

According to the fuel cell system 10B of the present embodiment, oxygen from the air electrode channel 29A moves to the fuel electrode channel 27A side in the oxygen permeation section 64, and carbon monoxide, hydrogen, and methane in the fuel electrode off-gas Oxidized to carbon dioxide and water vapor. As a result, a high concentration of carbon dioxide can be recovered from the fuel electrode off gas.

Further, in the fuel cell system 10B of the present embodiment, the oxygen permeable portion 64 is provided in the fuel cell stack 12B, so that the oxygen permeable portion 64 can have a simple configuration.

Also in the present embodiment, the oxygen permeation portion 64 is laminated on the end portion of the cylindrical substrate 30 that divides the fuel flow passage 26A and the air flow passage 28A. Therefore, the oxygen permeable portion 64 can be easily formed.

[Third Embodiment]
Next, a third embodiment of the present invention will be described. In this embodiment, the same parts as those in the first embodiment are designated by the same reference numerals, and detailed description thereof will be omitted.

The fuel cell system 10C of the present embodiment differs from the first embodiment only in the fuel cell stack to be used, and other configurations are the same as in the first embodiment. The fuel cell stack 12B of the present embodiment is a hydrogen ion conductive type solid oxide fuel cell (PCFC), and as shown in FIG. 7, is a vertical striped cylindrical type.

The fuel cell stack 12C includes a cylindrical substrate 40, a fuel cell 42, and a hydrogen permeable portion 44. The cylindrical substrate 40 has a bottomed cylindrical shape, and a plurality of (six in the present embodiment) are arranged in parallel. A tubular air tube 41 is inserted into each cylindrical base 40. The insertion tip of the air tube 41 is arranged at a position separated from the bottom portion 40A of the cylindrical substrate 40.

As shown in FIG. 8, an electrolyte layer 20B and a fuel electrode 22B are annularly laminated in this order on the outer side surface of each cylindrical substrate 40. Further, the cylindrical substrate 40 itself in the portion where the electrolyte layer 20B and the fuel electrode 22B are laminated constitutes the air electrode 24B, and the fuel cell 22 is formed by the fuel electrode 22B, the electrolyte layer 20B and the air electrode 24B. .. The fuel cell 42 is formed along the cylinder axis direction from the end of the cylindrical base 40 on the bottom 40A side. The fuel cells 32 adjacent to each other are electrically connected in series with each other by the unillustrated connectors, and are connected to the current controller 18 via the electric wiring E1.

The inside of the cylinder of the cylindrical base 40 (outside the cylinder of the air pipe 41) becomes the air flow path 28B, and the outside of the cylinder of the cylindrical base 40 becomes the fuel flow path 26B. The fuel flow passage 26B is surrounded by an outer peripheral wall 39, and the fuel flow passage 26B is formed between the outer peripheral wall 39 and the outer periphery of the cylindrical base 40.

A hydrogen permeable portion 44 is formed at the open end (the end opposite to the bottom 40A) of the cylindrical substrate 40. The hydrogen permeable portion 44 is formed by annularly laminating the ionization catalyst layer 35, the hydrogen permeable membrane 36, and the proton oxidation catalyst layer 37 in this order on the outer surface of the cylindrical substrate 40. The hydrogen permeable portion 44 is connected to the current controller 18 via the electric wiring E2.

As shown in FIGS. 7 and 8, in the fuel flow path 26B, the fuel gas supply pipe P1 is connected to the end portion side opposite to the end portion where the hydrogen permeation portion 44 is formed, and the fuel flow Fuel gas and water vapor are supplied to the passage 26A. The air supply pipe P3 is connected to the air pipe 41, and air is supplied from the bottom portion 40A side of the cylindrical substrate 40 to the air flow path 28B in parallel with the fuel gas.

A fuel electrode off-gas passage P5 is connected to the end of the fuel flow passage 26B where the hydrogen permeation portion 44 is formed. The air electrode off-gas passage P4 is connected to the air passage 28A on the same end side as the fuel electrode off-gas passage P5.

In the fuel cell stack 12C of this embodiment, the downstream side of the fuel electrode 22B of the fuel flow path 26B is referred to as the fuel electrode flow path 27B, and the downstream side of the air flow path 28B of the air electrode 24B is the air pole flow. It is called path 29B. The fuel electrode channel 27B and the air electrode channel 29B are partitioned by the cylindrical base 40 and are provided in the fuel cell stack 12C.

Next, the operation of the fuel cell system 10C will be described.

Fuel gas containing water vapor is supplied from the fuel gas supply pipe P1 to the fuel flow passage 26B, and air is supplied from the air supply pipe P3 to the air flow passage 28B via the air pipe 41. In the fuel flow path 26B, the fuel gas is steam reformed to generate hydrogen and carbon monoxide. Further, carbon dioxide and hydrogen are produced by the shift reaction between the produced carbon monoxide and water vapor. Then, in each fuel battery cell 42, the above-described power generation reaction occurs, and power generation is performed.

In the fuel flow path 26B, the fuel gas flows from the upstream to the downstream while gradually reducing the fuel component by the reforming and power generation reaction. Then, mainly carbon dioxide, water vapor, carbon monoxide, and hydrogen flow into the fuel electrode channel 27B at the downstream end. In the fuel electrode channel 27B, ionization of hydrogen is promoted in the ionization catalyst layer 35, and the ionized hydrogen (hydrogen ions) permeates the hydrogen permeable membrane 36 and moves to the proton oxidation catalyst layer 37 side. The moved hydrogen ions are oxidized by oxygen in the air electrode channel 29B by the proton oxidation catalyst layer 37 to become steam.

In the fuel electrode channel 27B, the hydrogen content rate decreases as hydrogen moves to the air electrode channel 29B side, so the shift reaction between carbon monoxide and water vapor proceeds, and carbon dioxide and hydrogen are generated. Then, the generated hydrogen moves from the fuel electrode channel 27B side to the air electrode channel 29B side as described above.

From the fuel electrode flow passage 27B, the fuel electrode off gas is sent to the fuel electrode off gas passage P5. After the water is removed by the condenser 14, the fuel electrode off-gas is supplied to the carbon dioxide recovery unit 16 through the recovery path P6, and the carbon dioxide is recovered.

The air electrode off-gas is sent from the air electrode flow path 29B to the air electrode off-gas passage P4. The air electrode off-gas is discharged to the outside after water is removed by the condenser 14.

Also in the fuel cell system 10C of the present embodiment, hydrogen moves in the hydrogen permeation section 44 from the fuel electrode channel 27B side to the air electrode channel 29B side, so that the hydrogen remaining in the fuel electrode off-gas is reduced and the carbon dioxide concentration is reduced. Can be higher. Since the movement of hydrogen is performed using the hydrogen permeable membrane, it is not necessary to supply oxygen to the fuel flow passage 26B.

Further, also in the fuel cell system 10C of the present embodiment, the hydrogen permeable portion 44 is provided inside the fuel cell stack 12B, so that the hydrogen permeable portion 44 can have a simple structure.

Also in this embodiment, since the hydrogen permeable portion 44 is laminated on the end portion of the cylindrical substrate 40 that divides the fuel flow passage 26B and the air flow passage 28B, the hydrogen permeable portion 44 can be easily formed. ..

In the present embodiment as well, the current controller 18 causes a current to flow between the fuel electrode passage 27B side and the air electrode passage 29B side of the hydrogen permeation section 44, so that the fuel electrode passage 27B is connected to the air electrode passage 27B. Permeation of hydrogen ions into 29B can be promoted. The current supply to the hydrogen permeation part 44 by the current controller 18 is not always necessary.

Also in this embodiment, since the gas flowing through the fuel electrode passage 27B and the gas flowing through the air electrode passage 29B are in parallel flow, the oxygen concentration in the air passage 28B portion corresponding to the upstream side of the fuel passage 26B is reduced. The air having a high temperature is supplied, and the power generation efficiency of the fuel cell stack 12C can be maintained.

The air may be supplied to the air passage 28B from the side corresponding to the downstream side of the fuel passage 26B, and the air flow and the fuel gas flow may be counter flows.

Further, in the present embodiment, since the fuel cell stack 12B is a hydrogen ion conductive type solid oxide fuel cell, water vapor is generated on the air electrode 24B side in the power generation reaction. Therefore, the water vapor content of the gas flowing through the fuel electrode passage 27B can be reduced, and the amount of water removed by the condenser 14 can be reduced.

The fuel cell stack 12C may be an oxygen ion transfer type solid oxide fuel cell (SOFC).

[Fourth Embodiment]
Next, a third embodiment of the present invention will be described. In this embodiment, the same parts as those in the first and second embodiments are designated by the same reference numerals, and detailed description thereof will be omitted.

The fuel cell system 10D of the present embodiment has an oxygen permeable portion 74 instead of the hydrogen permeable portion 44 of the third embodiment. Further, in the present embodiment, the concentrations of carbon dioxide and oxygen are measured by the densitometer 15 and output to the current controller 18. Other configurations are similar to those of the third embodiment.

As shown in FIG. 9, an oxygen permeable portion 74 is formed at one end of the cylindrical substrate 40. As shown in FIG. 10, the oxygen permeable portion 74 is formed by the oxygen permeable film 66 being annularly laminated on the inner surface of the cylindrical substrate 40 and the oxidation catalyst 68 being annularly laminated on the outer surface of the cylindrical substrate 40. There is.

The oxygen permeation part 74 is connected to the current controller 18 via the electric wiring E2. The current controller 18 uses the electric power generated by the fuel cell stack 12D to pass a current between the oxygen permeable film 66 and the oxidation catalyst 68 via the electric wiring E2. The current supplied from the current controller 18 is feedback-controlled as in the second embodiment.

Next, the operation of the fuel cell system 10D will be described.

Fuel gas containing water vapor is supplied from the fuel gas supply pipe P1 to the fuel flow passage 26B, and air is supplied from the air supply pipe P3 to the air flow passage 28B. In the fuel flow path 26B, the fuel gas is steam reformed to generate hydrogen and carbon monoxide. Further, carbon dioxide and hydrogen are produced by the shift reaction between the produced carbon monoxide and water vapor. Then, in each of the fuel cells 32, the above-described power generation reaction occurs and power generation is performed.

In the fuel flow path 26B, the fuel gas flows from the upstream to the downstream while gradually reducing the fuel component by the reforming and power generation reaction. Then, mainly carbon dioxide, water vapor, carbon monoxide, and hydrogen flow into the fuel electrode channel 27B at the downstream end. In the air flow path 28B, the air flows to the air electrode flow path 29B on the downstream side while gradually reducing the oxygen component due to the power generation reaction. In the air electrode channel 29B, oxygen is ionized and permeates the oxygen permeable membrane 66 to the fuel electrode channel 2BA side. Then, the oxidation catalyst 68 promotes the binding of carbon monoxide, hydrogen, and methane in the fuel electrode channel 27B, and carbon dioxide and water vapor are generated.

In the fuel electrode channel 27B, the concentrations of hydrogen, carbon monoxide, and methane thus decrease, and the concentrations of carbon dioxide and water vapor increase. After water is removed by the condenser 14, the carbon dioxide concentration and oxygen concentration of the fuel electrode off-gas are measured by the densitometer 15 and are supplied to the carbon dioxide recovery unit 16 to recover carbon dioxide.

The air electrode off-gas is sent from the air electrode flow path 29B to the air electrode off-gas passage P4. The air electrode off-gas is discharged to the outside after water is removed by the condenser 14.

According to the fuel cell system 10D of the present embodiment, oxygen from the air electrode flow passage 29B moves to the fuel electrode flow passage 27B side in the oxygen permeation portion 74, and carbon monoxide, hydrogen, and methane in the fuel electrode off-gas, Oxidized to carbon dioxide and water vapor. As a result, a high concentration of carbon dioxide can be recovered from the fuel electrode off gas.

Further, also in the fuel cell system 10D of the present embodiment, the oxygen permeable portion 74 is provided in the fuel cell stack 12D, so that the oxygen permeable portion 74 can have a simple structure.

Also in this embodiment, the oxygen permeation portion 74 is laminated on the end portion of the cylindrical substrate 40 that divides the fuel flow passage 26B and the air flow passage 28B. Therefore, the oxygen permeable portion 74 can be easily formed.

10A, 10B, 10C, 10D Fuel cell system 12A, 12B, 12C, 12D Fuel cell stack (fuel cell unit)
14 Condenser 16 Carbon dioxide recovery unit 18 Current controller (current supply unit)
22A, 22B Fuel electrode 24A, 24B Air electrode 27A, 27B Fuel electrode channel 28A, 28B Air channel 29A, 29B Air electrode channel 30, 40 Cylindrical base 32, 42 Fuel cell 34, 44 Hydrogen permeation part 35 Ionization catalyst Layer 36 Hydrogen permeable membrane 37 Proton oxidation catalyst layer (hydrogen ionization catalyst)
64, 74 Oxygen permeable portion 66 Oxygen permeable membrane 68 Oxidation catalyst

Claims (9)

A cylindrical solid oxide fuel cell unit for generating electricity using a carbon compound as a fuel,
A cylindrical base having a fuel cell in which a fuel electrode, an electrolyte membrane, and an air electrode are laminated in a tubular shape;
A fuel flow path in which the fuel gas containing a carbon compound is located in either one of the inside and the outside of the cylindrical base,
An air flow path in which the oxidant gas containing oxygen is located, which is located in the other of the inside and the outside of the cylinder of the cylindrical substrate,
Communicating with the air flow passage and the fuel flow passage, which is laminated on the cylindrical substrate downstream of the fuel electrode, is located on the downstream side of the fuel flow passage in the fuel flow passage, and delivers gas to the carbon dioxide recovery unit. A hydrogen removing section for reducing hydrogen in the fuel electrode channel by ion movement between the air electrode channel and
A fuel cell unit equipped with. The fuel cell unit according to claim 1, wherein the hydrogen removing unit has a hydrogen ion permeable membrane that allows hydrogen ions to permeate from the fuel electrode channel side to the air electrode channel side. The fuel cell unit according to claim 2, wherein a hydrogen ion oxidation catalyst is laminated on the hydrogen ion permeable membrane on the air electrode channel side. The fuel cell unit according to claim 1, wherein the hydrogen removing unit has an oxygen ion permeable membrane that allows oxygen ions to permeate from the air electrode channel side to the fuel electrode channel side. The fuel cell unit according to claim 4, wherein an oxidation catalyst is laminated on the oxygen ion permeable membrane on the fuel electrode channel side. The fuel cell unit according to claim 1, wherein the gas flowing through the fuel electrode channel and the gas flowing through the air electrode channel are parallel flows. A fuel cell unit according to any one of claims 1 to 6,
It said carbon dioxide recovery unit for recovering the fuel electrode off-gas discharged from the fuel electrode flow path,
A fuel cell system equipped with. The fuel cell system according to claim 7, further comprising: a current supply unit that causes a current to flow between the fuel electrode channel side and the air electrode channel side of the hydrogen removing unit. 9. The fuel cell system according to claim 7, further comprising a condenser provided downstream of the hydrogen removal unit of the fuel electrode channel and upstream of the carbon dioxide recovery unit.