JP6470633B2 - Fuel cell system - Google Patents

Description

  The present invention relates to a fuel cell system.

In a fuel cell system, as a configuration for improving energy utilization efficiency, a single fuel cell stack is used, and a recycle type in which unreacted fuel gas discharged from the fuel cell stack is circulated and reused, A multi-stage system is known in which a plurality of battery stacks are provided, and unreacted fuel gas discharged from the preceding fuel cell stack is reused in the subsequent fuel cell stack. In any configuration, if the water vapor and carbon dioxide (CO ₂ ) contained in the unreacted fuel gas can be removed, the concentration of hydrogen and carbon monoxide contributing to the reaction increases, so that the fuel gas to be reused is supplied. The fuel cell stack performance is expected to improve.

In relation to the above, Patent Documents 1 and 2 disclose that carbon dioxide is absorbed from spent fuel discharged from the fuel cell stack in a solid oxide fuel cell (SOFC) fuel processing process. A technique of absorbing with a material and reusing it as fuel gas is disclosed. Patent Document 1 describes lithiated zirconia (Li ₂ ZrO ₃ or Li ₄ ZrO ₄ ) as an example of a carbon dioxide absorbent.

  Thus, when carbon dioxide absorbent is used to remove carbon dioxide from spent fuel, the amount of carbon dioxide absorbed is limited, so carbon dioxide is released from the carbon dioxide absorbent that has absorbed carbon dioxide. Therefore, a process for regenerating the carbon dioxide absorbing material is required. In Patent Document 1, the carbon dioxide absorbent is regenerated using cathode offgas discharged from the cathode of the fuel cell stack. In Patent Document 2, the carbon dioxide absorbent is regenerated using dry air.

JP 2002-313402 A Special table 2009-503789

  However, the cathode off-gas and dry air contain a relatively large amount of oxygen. When these gases are used to regenerate the carbon dioxide absorbent (the release of carbon dioxide from the carbon dioxide absorbent), the conditions are particularly high. Then, hydrogen and carbon monoxide remaining in the container that absorbs carbon dioxide may burn. This combustion may cause a sudden temperature change or pressure change in the container, leading to performance deterioration of the carbon dioxide absorbent or damage to the container.

  The present invention has been made in consideration of the above facts, and obtains a fuel cell system that can effectively use anode off-gas from the fuel electrode of the fuel cell while suppressing a rapid temperature change and pressure change in the carbon dioxide absorption part. Is the purpose.

  According to a first aspect of the present invention, there is provided a fuel cell system that generates electric power using fuel gas supplied to a fuel electrode and air supplied to an air electrode, and discharges anode off-gas from the fuel electrode and cathode off-gas from the air electrode. Supplying the anode off-gas to a fuel cell from which carbon dioxide is discharged, a plurality of carbon dioxide absorbers containing carbon dioxide absorbents, and a part of the carbon dioxide absorbers among the plurality of carbon dioxide absorbers The carbon dioxide in the anode offgas is absorbed by the carbon dioxide absorber to generate a regenerated fuel gas, and the oxygen concentration is lower than that of the cathode offgas to the other carbon dioxide absorber and used for system operation And a control unit for releasing carbon dioxide from the carbon dioxide absorbent by supplying the gas as a sweep gas.

In the fuel cell system according to the first aspect of the present invention, the anode offgas discharged from the fuel cell is supplied to some of the carbon dioxide absorbers of the plurality of carbon dioxide absorbers, and the carbon dioxide in the anode offgas is supplied. Is absorbed by a carbon dioxide absorbent to generate regenerated fuel gas. As a result, the concentration of carbon dioxide in the anode off-gas is reduced and the concentration of hydrogen and carbon monoxide contributing to the reaction is increased, so that it can be effectively reused as a regenerated fuel gas for power generation. In the present invention, the fuel cell may be singular or plural.

  On the other hand, to the other carbon dioxide absorbers among the plurality of carbon dioxide absorbers, a sweep gas having a lower oxygen concentration than the cathode offgas discharged from the air electrode and used for system operation is supplied. Carbon dioxide is released from the absorbent material to regenerate the carbon dioxide absorbent material.

  Here, the sweep gas refers to a gas for releasing carbon dioxide from a carbon dioxide absorbent that has absorbed carbon dioxide. Since the sweep gas in the present invention has a relatively low or zero oxygen content, combustion of residual hydrogen and carbon monoxide in the carbon dioxide absorber is suppressed. Thereby, it is possible to suppress a sudden change in temperature or pressure due to the combustion of hydrogen or carbon monoxide remaining in the carbon dioxide absorption part.

In the fuel cell system according to the first aspect of the present invention, the sweep gas is any one of the anode off gas, water vapor, and hydrocarbon fuel.

  These are used for the operation of the fuel cell system, and can be effectively used as the oxygen concentration is lower than the cathode off gas.

According to a second aspect of the present invention, there is provided a fuel cell system in which the fuel cell is configured to supply a first fuel cell for sending an anode off gas to the carbon dioxide absorber, the regenerated fuel gas being supplied to a fuel electrode, and the regenerated fuel gas. And a second fuel cell that generates electricity.

In the fuel cell system according to the second aspect of the present invention, the anode off-gas discharged from the fuel cell is supplied to the anode of the second fuel cell as a regenerated fuel gas after the carbon dioxide is absorbed by the carbon dioxide absorber. Thus, a multi-stage fuel cell system to be used is realized.

In the fuel cell system according to a third aspect of the invention, the control unit supplies the regenerated fuel gas from the carbon dioxide absorption unit to the fuel electrode.

In the fuel cell system according to the third aspect of the present invention, the anode off-gas discharged from the fuel cell is used by being supplied to the fuel electrode as a regenerated fuel gas after carbon dioxide is absorbed by the carbon dioxide absorber. A circulation type fuel cell system is realized.

The fuel cell system according to a fourth aspect of the present invention further includes a water vapor removing unit that removes water vapor from the anode off gas before being supplied to the carbon dioxide absorbing unit used for generating the regenerated fuel gas. .

According to the fuel cell system of the present invention as set forth in claim 4, since the partial pressure of carbon dioxide of the anode off-gas supplied to the carbon dioxide absorber is increased by removing water vapor, the carbon dioxide produced by the carbon dioxide absorbent The amount of absorption can be increased.

The fuel cell system according to a fifth aspect of the present invention further includes a water vapor removing unit that removes water vapor from the anode off gas after carbon dioxide is absorbed by the carbon dioxide absorbing unit.

According to the fuel cell system of the fifth aspect of the present invention, the anode off-gas before being supplied to the carbon dioxide absorption part contains water vapor at a relatively high concentration, so that absorption by the carbon dioxide absorbent is performed. The effect that the amount increases can be obtained.

A fuel cell system according to a sixth aspect of the present invention further includes a reformer that reforms a hydrocarbon fuel to generate the fuel gas containing hydrogen and supplies the fuel gas to the fuel cell. Yes.

According to the fuel cell system of the sixth aspect of the invention, the fuel cell system can be operated by generating the fuel gas containing hydrogen by the reformer by supplying the hydrocarbon fuel and the water vapor.

According to a seventh aspect of the present invention, in the fuel cell system according to the seventh aspect , when the sweep gas is steam, the steam discharged from the carbon dioxide absorption section is supplied to the reformer, and the hydrocarbon fuel is steamed. Reform.

According to the fuel cell system of the seventh aspect of the present invention, the steam used for regenerating the carbon dioxide absorbent can be used for steam reforming of hydrocarbon fuel.

When the sweep gas is a hydrocarbon fuel, the hydrocarbon fuel discharged from the carbon dioxide absorption part is supplied to the reformer, and the hydrocarbon cell system according to the invention of claim 8 Reform fuel.

According to the fuel cell system of the eighth aspect of the invention, the fuel gas can be obtained by reforming the hydrocarbon fuel used for the regeneration of the carbon dioxide absorbent.

  According to the fuel cell system of the present invention, it is possible to effectively use the anode off-gas from the fuel electrode of the fuel cell while suppressing a rapid temperature change and pressure change in the carbon dioxide absorption part.

1 is a schematic configuration diagram of a fuel cell system according to a first embodiment. It is a graph which shows the relationship between the temperature of a carbon dioxide absorber, and carbon dioxide absorption and discharge | release. It is a schematic block diagram of the fuel cell system which concerns on 2nd Embodiment. It is a schematic block diagram of the fuel cell system of 3rd Embodiment. It is a schematic block diagram which shows the other structure of the fuel cell system of 3rd Embodiment. It is a schematic block diagram of the fuel cell system of 4th Embodiment. It is a schematic block diagram of the fuel cell system which concerns on the modification of 4th Embodiment. It is a schematic block diagram of the fuel cell system of 5th Embodiment. It is a schematic block diagram of the fuel cell system which concerns on the modification of 5th Embodiment. It is a schematic block diagram of the fuel cell system of 6th Embodiment. It is a schematic block diagram of the fuel cell system which concerns on the modification of 6th Embodiment. It is a schematic block diagram of the fuel cell system of 7th Embodiment. It is a schematic block diagram of the fuel cell system which concerns on the modification of 7th Embodiment.

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

[First Embodiment]
FIG. 1 shows a fuel cell system 10A according to the first embodiment of the present invention. The fuel cell system 10A includes a steam reformer 12, a fuel cell stack 14, a first carbon dioxide absorber 22, a second carbon dioxide absorber 24, a combustor 18, and a controller 70 as main components. .

  One end of a source gas pipe 28 is connected to the steam reformer 12, and the other end of the source gas pipe 28 is connected to a gas source (not shown). A raw material gas (hydrocarbon fuel) from which sulfur compounds are adsorbed and removed by a desulfurizer is supplied to the raw material gas pipe 28 from a gas source. The raw material gas supplied from the gas source to the raw material gas pipe 28 is heated by a heat exchanger (not shown) and then supplied to the steam reformer 12.

  One end of a water supply pipe 26 is connected to the steam reformer 12, and water (steam) is supplied through the water supply pipe 26. The steam reformer 12 is heated and steam reformed from the source gas supplied via the source gas pipe 28 using water (steam) supplied via the water supply pipe 26, and contains hydrogen 600 A fuel gas G1 having a temperature of about 0 ° C. is generated. The steam reformer 12 is connected to an anode (fuel electrode) 14 </ b> A of the fuel cell stack 14. The fuel gas G1 generated by the steam reformer 12 is supplied to the anode (fuel electrode) 14A of the fuel cell stack 14 via the fuel gas pipe 32.

  The fuel cell stack 14 is a solid oxide fuel cell stack, and has a plurality of stacked fuel cells. The fuel cell stack 14 is an example of a fuel cell according to the present invention. In this embodiment, the operating temperature is about 700 ° C. Each fuel cell has an electrolyte layer, and an anode (fuel electrode) 14A and a cathode (air electrode) 14B laminated on the front and back surfaces of the electrolyte layer. In FIG. 1, individual anodes and cathodes of a plurality of fuel cells are collectively shown as “anode 14A” and “cathode 14B”, respectively.

Oxidizing gas (air) is supplied to the cathode 14B of the fuel cell stack 14 via an oxidizing gas pipe 30 for supplying oxidizing gas (air). In the cathode 14B, as shown in the following formula (1), oxygen and electrons in the oxidizing gas react to generate oxygen ions. The generated oxygen ions reach the anode 14A of the fuel cell stack 14 through the electrolyte layer.

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

The cathode 14B is connected to a cathode offgas pipe 31 that guides the cathode offgas G2 discharged from the cathode 14B. The oxygen concentration of the cathode off gas G2 is 10% to 15%.

  On the other hand, in the anode 14A of the fuel cell stack 14, as shown in the following formulas (2) and (3), oxygen ions that have passed through the electrolyte layer react with hydrogen and carbon monoxide in the fuel gas, and water ( Steam) and carbon dioxide and electrons are generated. Electrons generated at the anode 14A move from the anode 14A through the external circuit to the cathode 14B, thereby generating electric power in each fuel cell. Each fuel cell generates heat during power generation.

(Fuel electrode reaction)
H ₂ + O ²⁻ → H ₂ O + 2e ⁻ (2)
CO + O ²⁻ → CO ₂ + 2e ⁻ (3)

  One end of an anode offgas pipe 34 is connected to the anode 14A of the fuel cell stack 14, and the anode offgas G3 is discharged from the anode 14A to the anode offgas pipe 34. The anode off gas G3 contains unreacted hydrogen, unreacted carbon monoxide, carbon dioxide, and water. The anode off gas G3 contains almost no oxygen, and the oxygen concentration is zero or less than 1%.

The fuel cell of the present invention is not limited to a solid oxide fuel cell (SOFC), and may be, for example, a molten carbonate fuel cell (MCFC).

  A branch portion 48 is provided in the middle of the anode off gas pipe 34, and is branched into two at the branch portion 48. One side is connected to the first carbon dioxide absorber 22 and the second carbon dioxide absorber 24 via an absorption switching valve 40. The other side is connected to the first carbon dioxide absorption part 22 and the second carbon dioxide absorption part 24 via the release switching valve 46, respectively. Hereinafter, the pipe branched to the absorption switching valve 40 side is referred to as an anode off absorption gas pipe 37, and the pipe branched to the discharge switching valve 46 side is referred to as an anode off discharge gas pipe 38. In the branch portion 48, the anode off gas G3 is distributed to the anode off absorption gas pipe 37 and the anode off discharge gas pipe 38 at a constant rate, for example, a ratio of 4: 6.

The reference sign of the anode off absorption gas pipe 37 from the absorption switching valve 40 to the first carbon dioxide absorption section 22 is indicated by “37-1”, and the anode off absorption from the absorption switching valve 40 to the carbon dioxide absorption section 24 is indicated. The code | symbol of the gas pipe 37 is shown by "37-2". Further, the sign of the anode off-releasing gas pipe 38 from the discharge switching valve 46 to the first carbon dioxide absorption unit 22 is indicated by “38-1”, and the anode off-releasing gas from the discharge switching valve 46 to the carbon dioxide absorption unit 24 is indicated. The code | symbol of the gas pipe 38 is shown by "38-2".

  The absorption switching valve 40 is supplied from the anode off absorption gas pipe 37 by communicating the anode off absorption gas pipe 37 with either the first carbon dioxide absorption section 22 or the second carbon dioxide absorption section 24. The anode off gas G3 is alternatively supplied to the first carbon dioxide absorber 22 or the second carbon dioxide absorber 24. The supplied anode off gas G3 is about 650 ° C. Switching of the piping by the absorption switching valve 40 is controlled by the control unit 70.

  The discharge switching valve 46 communicates the anode off-releasing gas pipe 38 with one of the first carbon dioxide absorbing part 22 and the second carbon dioxide absorbing part 24 (which is not communicated with the anode off absorbing gas pipe 37). As a result, the anode off gas G3 supplied from the anode off discharge gas pipe 38 is alternatively supplied to the first carbon dioxide absorber 22 or the second carbon dioxide absorber 24. The supplied anode off gas G3 is heated to 750 ° C. to 950 ° C. by a heat exchanger (not shown). For the heating in the heat exchanger, combustion exhaust gas G5 from the combustor 18 described later can be used. The switching of the piping by the discharge switching valve 46 is controlled by the control unit 70.

The first carbon dioxide absorption part 22 and the second carbon dioxide absorption part 24 have a carbon dioxide absorbent 23 housed therein, and the carbon dioxide absorbent 23 absorbs carbon dioxide with respect to the gas introduced therein. Release takes place. As the carbon dioxide absorbent, for example, can be used _{Li 2 ZrO 3, LiFeO 2,} Li 4 material mainly composed of any of lithium-based composite oxides such as SiO ₄ and Ba ₂ TiO _4. For example, the reaction of Li ₄ SiO ₄ is represented by the following formula (4).

Li ₄ SiO ₄ + CO ₂ → Li ₂ SiO ₃ + Li ₂ CO ₃ (4)

Li ₄ SiO ₄ reversibly changes the direction of reaction depending on the temperature and the partial pressure of carbon dioxide. Here, FIG. 2 shows the relationship between temperature and carbon dioxide mass when a gas having a partial pressure of carbon dioxide of about 15% is supplied to Li ₄ SiO ₄ used as the carbon dioxide absorbent 23. Yes. Even if the partial pressure of carbon dioxide of the supplied gas is about 15%, Li ₄ SiO ₄ has the characteristic that when the temperature reaches 690 ° C. or higher, the mass of carbon dioxide decreases and the absorbed carbon dioxide is released. Have.

The anode off gas G3 supplied from the anode off absorption gas pipe 37 to the first carbon dioxide absorption unit 22 and the second carbon dioxide absorption unit 24 has a temperature of about 650 ° C. and a relatively high concentration of carbon dioxide (about 15%). ). Since the carbon dioxide absorbent 23 has the above characteristics, the first carbon dioxide absorber 22 and the second carbon dioxide absorber 24 supplied with the anode off gas G3 from the anode off absorbent gas pipe 37 are The carbon absorbent 23 becomes an environmental condition for absorbing carbon dioxide, and the carbon dioxide contained in the anode offgas G3 is absorbed by the carbon dioxide absorbent 23. Hereinafter, the anode offgas G3 in which carbon dioxide has been absorbed by the first carbon dioxide absorber 22 and the second carbon dioxide absorber 24 is referred to as “CO ₂ removal offgas G4”.

On the other hand, the anode off-gas G3 supplied from the anode off-releasing gas pipe 38 to the first carbon dioxide absorbing section 22 and the second carbon dioxide absorbing section 24 is the same as the anode off absorbing gas pipe 37 in terms of carbon dioxide concentration. However, the temperature is as high as about 700 ° C to 900 ° C. Since the carbon dioxide absorbent 23 has the above-described characteristics, the first carbon dioxide absorber 22 and the second carbon dioxide absorber 24 to which the anode off gas G3 is supplied from the anode off discharge gas pipe 38 are The carbon absorbing material 23 releases the carbon dioxide, and the first carbon dioxide absorbing portion 22 and the second carbon dioxide absorbing portion 24 release carbon dioxide from the carbon dioxide absorbing material 23. As described above, the anode off-gas G3 supplied to the first carbon dioxide absorber 22 or the second carbon dioxide absorber 24 at a high temperature of 700 ° C. to 900 ° C. is a sweep gas that releases carbon dioxide from the carbon dioxide absorber. Function. Hereinafter, the anode offgas G3 containing carbon dioxide released from the first carbon dioxide absorber 22 and the second carbon dioxide absorber 24 is referred to as “CO ₂ -containing offgas G7”.

  One end of a recovery gas supply pipe 35 is connected to the gas discharge side of the first carbon dioxide absorption part 22 and the second carbon dioxide absorption part 24, and a recovery switching valve 42 is provided in the recovery gas supply pipe 35. ing. In addition, one end of a carbon dioxide discharge pipe 36 is further connected to the gas discharge side of the first carbon dioxide absorption section 22 and the second carbon dioxide absorption section 24, and the carbon dioxide discharge pipe 36 has a carbon dioxide discharge. A switching valve 44 is provided.

Hereinafter, the symbol of the recovery gas supply pipe 35 from the first carbon dioxide absorption part 22 to the recovery switching valve 42 is indicated by “35-1”, and the recovery gas supply pipe from the second carbon dioxide absorption part 24 to the recovery switching valve 42 is indicated. The code | symbol of 35 is shown by "35-2". Moreover, the code | symbol of the carbon dioxide discharge pipe 36 from the 1st carbon dioxide absorption part 22 to the carbon dioxide discharge switching valve 44 is shown by "36-1," and the 2nd carbon dioxide absorption part 24 to the carbon dioxide discharge switching valve 44 is shown. The code | symbol of the carbon dioxide discharge pipe 36 is shown by "36-2".

  The recovery switching valve 42 is one of the first carbon dioxide absorber 22 and the second carbon dioxide absorber 24 (the first carbon dioxide absorber 22 and the second carbon dioxide absorber communicated with the anode off-absorption gas pipe 37). Unit 24) is in communication with the recovered gas supply pipe 35. The carbon dioxide discharge switching valve 44 causes the other of the first carbon dioxide absorption part 22 and the second carbon dioxide absorption part 24 (one not communicating with the recovered gas supply pipe 35) to communicate with the carbon dioxide discharge pipe 36. Switching of the piping by the recovery switching valve 42 and the carbon dioxide discharge switching valve 44 is controlled by the control unit 70.

The other end of the recovered gas supply pipe 35 is connected to the steam reformer 12. The steam reformer 12 is supplied with the CO ₂ removal off-gas G4 from the recovered gas supply pipe 35. The CO ₂ removal off gas G4 is sent to the anode 14A via the steam reformer 12.

The other end of the carbon dioxide discharge pipe 36 is connected to the combustor 18. The other end of the cathode offgas pipe 31 is also connected to the combustor 18. The combustor 18 mixes the CO ₂ -containing offgas G7 supplied from one of the first carbon dioxide absorber 22 and the second carbon dioxide absorber 24 with the cathode offgas G2 from the cathode offgas pipe 31 and burns it. . The high-temperature combustion exhaust gas G5 obtained in the combustor 18 is directly and indirectly supplied to other parts in the fuel cell system 10A such as heating of the catalyst in the steam reformer 12.

The absorption switching valve 40, the recovery switching valve 42, the carbon dioxide discharge switching valve 44, the release switching valve 46, and the control unit 70 are examples of the control unit in the present invention.

  Next, the operation of the fuel cell system 10A according to the first embodiment will be described. First, the operation mode M1 in which the carbon dioxide absorption of the anode off gas G3 is performed by the first carbon dioxide absorption section 22 and the carbon dioxide is released from the carbon dioxide absorbent 23 by the second carbon dioxide absorption section 24 will be described.

  In the fuel cell system 10 </ b> A, a raw material gas and water (steam) are supplied to the steam reformer 12. The steam reformer 12 is heated and steam reforms the raw material gas using steam to generate a fuel gas G1 containing hydrogen and having a temperature of about 600 ° C. The fuel gas G1 is supplied from the steam reformer 12 to the anode 14A of the fuel cell stack 14 via the fuel gas pipe 32. On the other hand, an oxidizing gas (air) is supplied to the cathode 14B of the fuel cell stack 14. As a result, the fuel cell stack 14 generates power by the above-described reaction. Along with this power generation, an anode off-gas G3 containing unreacted hydrogen, unreacted carbon monoxide, carbon dioxide and water is discharged from the anode 14A of the fuel cell stack 14.

  On the other hand, the control unit 70 controls the absorption switching valve 40, the recovery switching valve 42, the release switching valve 46, and the carbon dioxide discharge switching valve 44 so as to be in the following open / closed state. The absorption switching valve 40 is opened on the anode off absorption gas pipe 37-1 side and closed on the anode off absorption gas pipe 37-2 side. The recovery switching valve 42 is opened on the recovery gas supply pipe 35-1 side and closed on the recovery gas supply pipe 35-2 side. The carbon dioxide discharge switching valve 44 is opened on the carbon dioxide discharge pipe 36-2 side and closed on the carbon dioxide discharge pipe 36-1 side. The discharge switching valve 46 is closed on the anode-off discharge gas pipe 38-1 side and opened on the anode-off discharge gas pipe 38-2 side.

The anode off gas G3 having a temperature of about 650 ° C. discharged from the anode 14A is branched into two at the branch portion 48. The anode off gas G <b> 3 distributed to the anode off absorption gas pipe 37 side is supplied to the first carbon dioxide absorption unit 22. In the first carbon dioxide absorber 22, carbon dioxide contained in the anode offgas G <b> 3 is absorbed by the carbon dioxide absorbent 23. The CO ₂ removal off-gas G4 from which carbon dioxide has been removed is discharged from the first carbon dioxide absorption unit 22, supplied to the steam reformer 12 through the recovered gas supply pipe 35, and regenerated for power generation in the fuel cell stack 14. Used.

On the other hand, the anode off-gas G3 distributed to the anode off-releasing gas pipe 38 side is heated to 700 ° C. to 900 ° C. by the heat exchanger and supplied to the second carbon dioxide absorber 24. In the second carbon dioxide absorber 24, the carbon dioxide absorbed by the carbon dioxide absorber 23 is released. The CO ₂ -containing offgas G ₇ containing the released carbon dioxide is supplied to the combustor 18 through the carbon dioxide discharge pipe 36. In the combustor 18, the supplied CO ₂ removal off gas G 7 is mixed with the cathode off gas G 2 from the cathode off gas pipe 31 and burned. The high-temperature combustion exhaust gas G5 obtained by the combustor 18 is supplied to and used for each part in the fuel cell system 10A, such as heating of the catalyst in the steam reformer 12.

  The operation mode M1 includes the absorption capacity of carbon dioxide in the carbon dioxide absorbent 23 accommodated in the first carbon dioxide absorber 22, and the release of carbon dioxide from the carbon dioxide absorbent 23 in the second carbon dioxide absorber 24. It is continued for a predetermined time T1, which is determined according to the speed or the like. After the elapse of the predetermined time T1, the operation mode M2 is executed. In the operation mode M <b> 2, the carbon dioxide absorption of the anode off gas G <b> 3 is performed by the second carbon dioxide absorption unit 24, and the carbon dioxide is released from the carbon dioxide absorbent 23 by the first carbon dioxide absorption unit 22.

  The control unit 70 controls the open / close states of the absorption switching valve 40, the recovery switching valve 42, the release switching valve 46, and the carbon dioxide discharge switching valve 44 as follows. The absorption switching valve 40 is closed on the anode off absorption gas pipe 37-1 side and opened on the anode off absorption gas pipe 37-2 side. The recovery switching valve 42 is closed on the recovery gas supply pipe 35-1 side and opened on the recovery gas supply pipe 35-2 side. The carbon dioxide discharge switching valve 44 is closed on the carbon dioxide discharge pipe 36-2 side and opened on the carbon dioxide discharge pipe 36-1 side. The discharge switching valve 46 is opened on the anode off discharge gas pipe 38-1 side and closed on the anode off discharge gas pipe 38-2 side.

The anode off gas G3 having a temperature of about 650 ° C. branched into two at the branching portion 48 and distributed to the anode off absorbing gas pipe 37 side is supplied to the second carbon dioxide absorbing portion 24. In the second carbon dioxide absorber 24, the carbon dioxide contained in the anode off gas G <b> 3 is absorbed by the carbon dioxide absorber 23. The CO ₂ removal off-gas G4 from which carbon dioxide has been removed is discharged from the second carbon dioxide absorption unit 24, supplied to the steam reformer 12 through the recovery gas supply pipe 35, and regenerated for power generation in the fuel cell stack 14. Used.

On the other hand, the anode off gas G3 distributed to the anode off discharge gas pipe 38 side is heated to 700 ° C. to 900 ° C. by the heat exchanger, and is supplied to the first carbon dioxide absorber 22. In the first carbon dioxide absorber 22, the carbon dioxide absorbed by the carbon dioxide absorbent 23 is released. The CO ₂ -containing offgas G ₇ containing the released carbon dioxide is supplied to the combustor 18 through the carbon dioxide discharge pipe 36. In the combustor 18, the supplied CO ₂ removal off gas G 7 is mixed with the cathode off gas G 2 from the cathode off gas pipe 31 and burned. The high-temperature combustion exhaust gas G5 obtained by the combustor 18 is supplied to and used for each part in the fuel cell system 10A, such as heating of the catalyst in the steam reformer 12.

  Also in the operation mode M2, the carbon dioxide absorption capacity of the carbon dioxide absorbent 23 accommodated in the second carbon dioxide absorbent 24 and the carbon dioxide absorbent 23 of the carbon dioxide absorbent 23 accommodated in the first carbon dioxide absorbent 22 are used. This is continued for a predetermined time T2 determined according to the carbon release rate or the like. The time T2 may be set to be the same as the time T1, or may be set to a different time. After the elapse of the predetermined time T2, the control unit 70 switches to the operation mode M1. By alternately repeating the operation mode M1 and the operation mode M2, the first carbon dioxide absorption unit 22 and the second carbon dioxide absorption unit 24 alternately absorb and release carbon dioxide, and the fuel cell stack 14 continues. It can generate electricity.

  In the fuel cell system 10A of the present embodiment, the anode off-gas G3 having a zero or slightly contained oxygen content is used as a gas for releasing carbon dioxide from the carbon dioxide absorbent 23 at a high temperature. . Therefore, it is possible to suppress a sudden change in temperature or pressure in the container due to the combustion of hydrogen and carbon monoxide remaining in the first carbon dioxide absorber 22 and the second carbon dioxide absorber 24. Thereby, the damage to the carbon dioxide absorber 23 and the container is suppressed, and the useful life of these can be extended.

Moreover, in this embodiment, since the unreacted hydrogen and carbon monoxide contained in the anode off gas G3 discharged from the fuel cell stack 14 are reused, the fuel utilization efficiency can be improved. Further, since the CO ₂ removal off gas G4 after the concentration of carbon dioxide is reduced in the carbon dioxide absorption units 22 and 24 is used for reuse, the anode off gas G3 that does not remove CO ₂ is reused. In comparison, the power generation efficiency in the fuel cell stack 14 can be increased.

The fuel cell system 10A is an example of a fuel cell system according to claims 4 and 7. Further, in the present embodiment, the reformer 12 that performs steam reforming has been described as an example, but other reformers that perform partial oxidation reforming, shift reaction reforming, carbon dioxide reforming, and the like are also available. The vessel may produce hydrogen and carbon monoxide.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. In addition, the same code | symbol is attached | subjected to the part same as 1st Embodiment, and description is abbreviate | omitted.

  FIG. 3 shows a fuel cell system 10B according to the second embodiment. The fuel cell system 10B is mainly different from the fuel cell system 10A described in the first embodiment in that a second fuel cell stack 50 is provided. In the present embodiment, the same fuel cell stack as the fuel cell stack 14 of the first embodiment is referred to as a first fuel cell stack 15.

  The branch portion 48 is not provided on the downstream side of the anode 14 </ b> A of the first fuel cell stack 15, and the anode off-gas pipe 34 is connected to the first carbon dioxide absorber 22 and the second carbon dioxide absorber 24 via the absorption switching valve 40. Is connected to each. In addition, the code | symbol of the anode off gas pipe 34 from the absorption switching valve 40 to the 1st carbon dioxide absorption part 22 is shown by "34-1", and the code | symbol of the anode off gas pipe 34 from the absorption switching valve 40 to the carbon dioxide absorption part 24 is shown. This is indicated by “34-2”. The anode off gas G3 supplied to the first carbon dioxide absorber 22 or the second carbon dioxide absorber 24 is about 650 ° C.

The other end of the recovered gas supply pipe 35 is connected to an anode 50A of a second fuel cell stack 50 described later. The anode 50A is supplied with the CO ₂ removal off gas G4 from the recovered gas supply pipe 35.

Similar to the first fuel cell stack 15, the second fuel cell stack 50 includes an anode 50A and a cathode 50B. The other end of the recovered gas supply pipe 35 is connected to the anode 50A, and the CO ₂ removal off-gas G4 discharged from the first carbon dioxide absorber 22 and the second carbon dioxide absorber 24 is supplied to the anode 50A. The cathode 50B is connected to the cathode offgas pipe 31, and the cathode offgas G2 discharged from the cathode 14B is supplied to the cathode 50B.

  Electric power is generated on the anode 50A and the cathode 50B of the second fuel cell stack 50 by the same operation principle as that of the first fuel cell stack 15, respectively. In the present embodiment, the second fuel cell stack 50 is a solid oxide fuel cell stack. Alternatively, a molten carbonate fuel cell stack may be provided.

  One end of a second anode off-gas pipe 58 is connected to the outlet side of the anode 50 </ b> A of the second fuel cell stack 50. The second anode off-gas G6 discharged from the anode 50A is connected to the first carbon dioxide absorber 22 and the second carbon dioxide absorber 24 via the release switching valve 46. The second anode off gas G6 is heated to 750 ° C. to 900 ° C. by a heat exchanger (not shown) on the upstream side of the discharge switching valve 46.

One end of a combustion supply gas pipe 39 is connected to the cathode 50B of the second fuel cell stack 50, the other end of the combustion supply gas pipe 39 is connected to the combustor 18, and the cathode offgas G2 is sent to the combustor 18. Supplied. The CO ₂ -containing offgas G7 discharged from the first carbon dioxide absorber 22 and the second carbon dioxide absorber 24 and supplied to the combustor 18 is mixed with the cathode offgas G2 exhausted from the cathode 50B, and the combustor 18 is mixed. Burned in.

  Next, the operation of the fuel cell system 10B according to the second embodiment will be described.

  Also in the second embodiment, the operation mode M1-2 and the operation mode M2-2 are alternately performed. In the operation mode M1-2, the carbon dioxide absorption of the anode off gas G3 is performed by the first carbon dioxide absorption unit 22, and the carbon dioxide is released from the carbon dioxide absorbent 23 by the second carbon dioxide absorption unit 24. In the operation mode M2-2, the carbon dioxide absorption of the anode off gas G3 is performed by the second carbon dioxide absorber 24, and the carbon dioxide is released from the carbon dioxide absorber 23 by the first carbon dioxide absorber 22.

In the operation mode M1-2, the anode off gas G3 is supplied to the first carbon dioxide absorber 22. The CO ₂ removal off-gas G4 whose carbon dioxide concentration has been reduced by the first carbon dioxide absorber 22 is supplied to the anode 50A of the second fuel cell stack 50 via the recovery gas supply pipe 35. The cathode off gas G2 discharged from the cathode 50B of the first fuel cell stack 15 is supplied to the cathode 50B. In the second fuel cell stack 50, power generation is performed using the CO ₂ removal off gas G4 as fuel.

  The second anode off-gas G6 discharged from the anode 50A of the second fuel cell stack 50 is heated and then supplied to the second carbon dioxide absorber 24 via the release switching valve 46. In the second carbon dioxide absorber 24, regeneration of the carbon dioxide absorbent 23 (discharge of carbon dioxide) is performed by supplying the heated second anode off gas G6.

On the other hand, in the operation mode M2-2, the anode off gas G3 is supplied to the second carbon dioxide absorber 24. The CO ₂ removal offgas G4 whose carbon dioxide concentration has been reduced by the second carbon dioxide absorber 24 is supplied to the anode 50A of the second fuel cell stack 50 via the recovery gas supply pipe 35. The cathode off gas G2 discharged from the cathode 50B of the first fuel cell stack 15 is supplied to the cathode 50B. In the second fuel cell stack 50, power generation is performed using the CO ₂ removal off gas G4 as fuel.

The second anode off-gas G6 discharged from the anode 50A of the second fuel cell stack 50 is heated and then supplied to the first carbon dioxide absorber 22 through the release switching valve 46. In the 1st carbon dioxide absorption part 22, reproduction | regeneration of the carbon dioxide absorber 23 (release of a carbon dioxide) is performed by supply of the heated 2nd anode off gas G6.

In the fuel cell system 10B according to the second embodiment, since the second fuel cell stack 50 that generates power using unreacted hydrogen and carbon monoxide contained in the CO ₂ removal off-gas G4 as fuel gas is provided, fuel utilization efficiency Can be improved. Further, the fuel cell system 10B can achieve the same effects as those of the other first embodiments.

The fuel cell system 10B is an example of a fuel cell system according to claims 3 and 7.

[Third Embodiment]
Next, a third embodiment of the present invention will be described. In addition, the same code | symbol is attached | subjected to the part same as 1st, 2nd embodiment, and description is abbreviate | omitted.

  FIG. 4 shows a fuel cell system 10C according to the third embodiment. The fuel cell system 10C is different from the fuel cell system 10B described in the second embodiment in that a water vapor removal unit 52 is provided between the anode 14A of the first fuel cell stack 15 and the absorption switching valve 40. It is different.

  The water vapor removing unit 52 includes a water vapor separation membrane, and removes water vapor from the anode off gas G3 discharged from the anode 14A. As the water vapor separation membrane, a polymer-based, polymer-inorganic molecular hybrid membrane, or zeolite-based membrane can be used. In the water vapor removing unit 52, the anode off gas G3 is cooled to a temperature at which water vapor separation by the water vapor separation membrane is possible. The water vapor may be removed by reducing the temperature and condensing without using a water vapor separation membrane.

The anode off-gas G3 whose water vapor concentration has been reduced through the water vapor removal unit 52 is heated to about 650 ° C. by a heat exchanger (not shown), passes through the absorption switching valve 40, and absorbs the first carbon dioxide absorption unit 22 or the second carbon dioxide absorption. Sent to the unit 24. The CO ₂ removal offgas G4 whose carbon dioxide concentration has been reduced by the first carbon dioxide absorber 22 or the second carbon dioxide absorber 24 is supplied to the anode 50A of the second fuel cell stack 50 through the recovery gas supply pipe 35. Used for power generation in the second fuel cell stack 50.

  According to the third embodiment, the regenerated fuel gas in which the water vapor contained in the anode off-gas G3 is reduced and the concentration of the fuel gas (hydrogen or carbon monoxide) contributing to the reaction is increased is supplied to the second fuel cell stack 50. Supplied. Therefore, the second fuel cell stack 50 can efficiently generate power.

  In addition, since the carbon dioxide concentration of the anode offgas G3 supplied to the first carbon dioxide absorber 22 or the second carbon dioxide absorber 24 can be increased, the first carbon dioxide absorber 22 and the second carbon dioxide absorber 24 The amount of carbon dioxide absorbed can be increased. Further, the fuel cell system 10C can achieve the same effects as those of the other second embodiment.

In the above description, the water vapor removal unit 52 is provided between the anode 14A of the first fuel cell stack 15 and the absorption switching valve 40. However, as shown in FIG. 5, the water vapor removal unit 52 is replaced with the first carbon dioxide absorption unit. 22. The fuel cell system 10D may be provided between the second carbon dioxide absorber 24 and the second fuel cell stack 50. As described above, when the water vapor removal by the water vapor removal unit 52 is performed on the CO ₂ removal off-gas G4 in which the carbon dioxide concentration is reduced, the cooling target gas to be cooled for the water vapor removal and the reheating after the cooling. Carbon dioxide is reduced from the gas to be heated, and the amount of gas to be heated is small. Therefore, the amount of heat required for heating can be reduced, and the thermal efficiency can be improved.

The fuel cell system 10C is an example of a fuel cell system according to the invention described in claim 5, and the fuel cell system 10D is an example of the fuel cell system according to the invention described in claim 6.

[Fourth Embodiment]
Next, a fourth embodiment of the present invention will be described. In addition, the same code | symbol is attached | subjected to the part same as 1st-3rd embodiment, and description is abbreviate | omitted.

FIG. 6 shows a fuel cell system 10E according to the fourth embodiment. The fuel cell system 10E is a gas that releases carbon dioxide from the carbon dioxide absorbent 23 of the first carbon dioxide absorber 22 and the second carbon dioxide absorber 24 as compared with the fuel cell system 10A described in the first embodiment. Is mainly a hydrocarbon fuel gas.

The steam reformer 12 is not connected to the raw material gas pipe 28 but is connected to a post-purge fuel gas supply pipe 60 described later. A carbon dioxide-containing fuel gas G8 described later is supplied from the purged fuel gas supply pipe 60 to the steam reformer 12.

In the branch part 48 provided in the middle of the anode off-gas pipe 34, one side branched into two is connected to the first carbon dioxide absorption part 22 and the second carbon dioxide absorption part 24 via the absorption switching valve 40, respectively. Has been. The other side is connected to the combustor 18 as a combustion gas supply pipe 62.

A material gas pipe 28 is connected to the discharge switching valve 46. From the source gas pipe 28, a high-temperature hydrocarbon fuel gas G <b> 9 of 700 ° C. to 900 ° C. is supplied to the first carbon dioxide absorber 22 and the second carbon dioxide absorber 24. The oxygen concentration of the hydrocarbon fuel gas G9 is lower than the oxygen concentration of the cathode offgas G2, and is zero or less than 1%. Hereinafter, the code | symbol of the raw material gas pipe 28 from the discharge switching valve 46 to the 1st carbon dioxide absorption part 22 is shown by "28-1," and the raw material gas pipe 28 from the discharge switching valve 46 to the 2nd carbon dioxide absorption part 24 is shown. The code is indicated by “28-2”. The release switching valve 46 communicates the source gas pipe 28 with one of the first carbon dioxide absorption part 22 and the second carbon dioxide absorption part 24 (one that is not in communication with the anode offgas pipe 34), so that the source gas is supplied. The hydrocarbon fuel gas G9 supplied from the pipe 28 is alternatively supplied to the first carbon dioxide absorber 22 or the second carbon dioxide absorber 24.

The first carbon dioxide absorber 22 and the second carbon dioxide absorber 24 to which the hydrocarbon fuel gas G9 is supplied are in an environmental condition in which the carbon dioxide absorber 23 releases carbon dioxide, and the first carbon dioxide absorber 22, In the carbon dioxide absorber 24, carbon dioxide is released from the carbon dioxide absorber 23. Hereinafter, the hydrocarbon fuel gas G9 containing carbon dioxide released from the first carbon dioxide absorber 22 and the second carbon dioxide absorber 24 is referred to as “carbon dioxide-containing fuel gas G8”.

  One end of a purged fuel gas supply pipe 60 is connected to the gas discharge side of the first carbon dioxide absorption part 22 and the second carbon dioxide absorption part 24, and carbon dioxide discharge is connected to the purged fuel gas supply pipe 60. A switching valve 44 is provided. Hereinafter, the symbol of the purged fuel gas supply pipe 60 from the first carbon dioxide absorption unit 22 to the carbon dioxide discharge switching valve 44 is indicated by “60-1”, and the carbon dioxide discharge switching valve 44 from the second carbon dioxide absorption unit 24 is indicated. The symbol of the purged fuel gas supply pipe 60 up to is indicated by “60-2”.

  The other end of the purged fuel gas supply pipe 60 is connected to the steam reformer 12. The steam reformer 12 is supplied with the carbon dioxide-containing fuel gas G8 from the purged fuel gas supply pipe 60.

  In the steam reformer 12, the supplied carbon dioxide-containing fuel gas G8 is steam-reformed using water (steam) supplied through the water supply pipe 26, and the temperature of about 600 ° C. containing hydrogen is increased. Fuel gas G1 is generated. The steam reformer 12 is connected to the anode 14 </ b> A of the fuel cell stack 14, and supplies the fuel gas G <b> 1 to the anode 14 </ b> A of the fuel cell stack 14 via the fuel gas pipe 32.

  Next, the operation of the fuel cell system 10A according to the fourth embodiment will be described. Also in this embodiment, the operation mode M1-4 and the operation mode M2-4 are performed alternately. In the operation mode M1-4, the carbon dioxide absorption of the anode offgas G3 is performed by the first carbon dioxide absorption section 22, and the carbon dioxide is released from the carbon dioxide absorbent 23 by the second carbon dioxide absorption section 24. In the operation mode M2-2, the carbon dioxide absorption of the anode off gas G3 is performed by the second carbon dioxide absorber 24, and the carbon dioxide is released from the carbon dioxide absorber 23 by the first carbon dioxide absorber 22.

The anode off gas G3 at about 650 ° C. distributed to the anode off absorption gas pipe 37 side at the branching section 48 is supplied to the first carbon dioxide absorption section 22. In the first carbon dioxide absorber 22, carbon dioxide contained in the anode offgas G <b> 3 is absorbed by the carbon dioxide absorbent 23. The CO ₂ removal off-gas G4 from which carbon dioxide has been removed is discharged from the first carbon dioxide absorption unit 22, supplied to the steam reformer 12 through the recovered gas supply pipe 35, and regenerated for power generation in the fuel cell stack 14. Used. On the other hand, the anode off gas G3 distributed to the combustion gas supply pipe 62 side is supplied to the combustor 18, and mixed with the cathode off gas G2 and burned. The high-temperature combustion exhaust gas G5 obtained by the combustor 18 is supplied to and used for each part in the fuel cell system 10E such as heating of the catalyst in the steam reformer 12.

  The hydrocarbon fuel gas G9 heated to 700 ° C. to 900 ° C. is supplied to the second carbon dioxide absorber 24. In the second carbon dioxide absorber 24, the carbon dioxide absorbed by the carbon dioxide absorber 23 is released. The carbon dioxide-containing fuel gas G8 containing the released carbon dioxide is supplied to the steam reformer 12 via the purged fuel gas supply pipe 60. In the steam reformer 12, the carbon dioxide-containing fuel gas G8 is steam reformed using water (steam) to generate a fuel gas G1 containing hydrogen and having a temperature of about 600 ° C.

  Said operation mode M1-4 is the carbon dioxide absorption capacity in the carbon dioxide absorber 23 accommodated in the 1st carbon dioxide absorber 22, and the carbon dioxide of the carbon dioxide absorber 23 in the 2nd carbon dioxide absorber 24. For a predetermined time T1-4 determined according to the release rate of After the elapse of the predetermined time T1-4, the operation mode M2-4 is executed. In the operation mode M2-4, the carbon dioxide absorption of the anode off gas G3 is performed by the second carbon dioxide absorption unit 24, and the carbon dioxide is released from the carbon dioxide absorbent 23 by the first carbon dioxide absorption unit 22.

The anode off gas G3 at about 650 ° C. distributed to the anode off absorption gas pipe 37 side at the branching section 48 is supplied to the second carbon dioxide absorption section 24. In the first carbon dioxide absorber 22, carbon dioxide contained in the anode offgas G <b> 3 is absorbed by the carbon dioxide absorbent 23. The CO ₂ removal off-gas G4 from which carbon dioxide has been removed is discharged from the second carbon dioxide absorption unit 24, supplied to the steam reformer 12 through the recovery gas supply pipe 35, and regenerated for power generation in the fuel cell stack 14. Used.

  On the other hand, the hydrocarbon fuel gas G9 heated to 700 ° C. to 900 ° C. by the heat exchanger is supplied to the first carbon dioxide absorber 22. In the first carbon dioxide absorber 22, the carbon dioxide absorbed by the carbon dioxide absorbent 23 is released. The carbon dioxide-containing fuel gas G8 containing the released carbon dioxide is supplied to the steam reformer 12 via the purged fuel gas supply pipe 60. In the steam reformer 12, the carbon dioxide-containing fuel gas G8 is steam reformed using water (steam) to generate a fuel gas G1 containing hydrogen and having a temperature of about 600 ° C.

  Also in the above operation mode M2-4, the carbon dioxide absorption capacity in the carbon dioxide absorbent 23 accommodated in the second carbon dioxide absorber 24, and the carbon dioxide absorbent 23 accommodated in the first carbon dioxide absorber 22. This is continued for a predetermined time T2-4 determined according to the release rate of carbon dioxide. After the elapse of the predetermined time T2-4, the controller 70 switches to the operation mode M1-4. By alternately repeating the operation mode M1-4 and the operation mode M2-4, the first carbon dioxide absorption unit 22 and the second carbon dioxide absorption unit 24 alternately absorb and release carbon dioxide, and the fuel cell stack 14 Continuous power generation at can be performed.

  In the fuel cell system 10E of the present embodiment, a gas (sweep gas) for releasing carbon dioxide from the carbon dioxide absorbent 23 by setting the hydrocarbon fuel gas G9 having an oxygen content of zero or less than 1% to a high temperature. Used as Therefore, it is possible to suppress a sudden change in temperature or pressure in the container due to the combustion of hydrogen and carbon monoxide remaining in the first carbon dioxide absorber 22 and the second carbon dioxide absorber 24. Thereby, the damage to the carbon dioxide absorber 23 and the container is suppressed, and the useful life of these can be extended.

Moreover, in this embodiment, since the unreacted hydrogen and carbon monoxide contained in the anode off gas G3 discharged from the fuel cell stack 14 are reused, the fuel utilization efficiency can be improved. Further, since the CO ₂ removal off gas G4 after the concentration of carbon dioxide is reduced in the carbon dioxide absorption units 22 and 24 is used for reuse, the anode off gas G3 that does not remove CO ₂ is reused. In comparison, the power generation efficiency in the fuel cell stack 14 can be increased.

  In this embodiment, the steam reformer 12 is used as the reformer. However, as shown in FIG. 7, a fuel cell system 10F using a carbon dioxide reformer 12A may be used as the reformer. . In this case, since water for reforming is unnecessary, the water supply pipe 26 is not connected to the carbon dioxide reformer 12A.

The fuel cell systems 10E and 10F are examples of the fuel cell system according to claims 4 and 9.

[Fifth Embodiment]
Next, a fifth embodiment of the present invention will be described. In addition, the same code | symbol is attached | subjected to the part same as 1st-5th embodiment, and description is abbreviate | omitted.

FIG. 8 shows a fuel cell system 10G according to the fifth embodiment. The fuel cell system 10G is mainly different from the fuel cell system 10F described in the fourth embodiment in that a second fuel cell stack 50 is provided.

In the present embodiment, the first fuel cell stack 15 and the second fuel cell stack 50 are provided as in the second embodiment. The other end of the recovered gas supply pipe 35 is connected to the anode 50A of the second fuel cell stack 50, and the CO ₂ removal off-gas G4 discharged from the first carbon dioxide absorber 22 and the second carbon dioxide absorber 24 is Supplied to the anode 50A. The cathode 50B is connected to the cathode offgas pipe 31, and the cathode offgas G2 discharged from the cathode 14B is supplied to the cathode 50B.

  One end of a second anode off-gas pipe 58 is connected to the outlet side of the anode 50A. The other end of the second anode offgas pipe 58 is connected to the combustor 18. The second anode off gas G6 discharged from the anode 50A is supplied to the combustor 18.

  Next, the operation of the fuel cell system 10G according to the fifth embodiment will be described.

  Also in this embodiment, the operation mode M1-5 and the operation mode M2-5 are performed alternately. In the operation mode M1-5, the carbon dioxide absorption of the anode off gas G3 is performed by the first carbon dioxide absorption unit 22, and the carbon dioxide is released from the carbon dioxide absorbent 23 by the second carbon dioxide absorption unit 24. In the operation mode M2-5, the carbon dioxide absorption of the anode off gas G3 is performed by the second carbon dioxide absorption section 24, and the carbon dioxide is released from the carbon dioxide absorbent 23 by the first carbon dioxide absorption section 22.

In the present embodiment, the CO ₂ removal off-gas G4 from which carbon dioxide has been removed by the first carbon dioxide absorption unit 22 and the second carbon dioxide absorption unit 24 passes through the recovery gas supply pipe 35 and is supplied to the second fuel cell stack 50. Supplied to the anode 50A and used for power generation. The second anode off gas G6 discharged from the anode 50A is supplied to the combustor 18, mixed with the cathode off gas G2 discharged from the cathode 50B, and burned. Other operations are the same as those in the fourth embodiment.

In the fuel cell system 10G according to the fifth embodiment, since the second fuel cell stack 50 that generates power using unreacted hydrogen and carbon monoxide contained in the CO ₂ removal off-gas G4 as fuel gas is provided, the fuel utilization efficiency Can be improved. Further, the fuel cell system 10G can achieve the same effects as those of the other fourth embodiment.

  In this embodiment, the steam reformer 12 is used as the reformer. However, as shown in FIG. 9, a fuel cell system 10H using a carbon dioxide reformer 12A may be used as the reformer. . In this case, since water for reforming is unnecessary, the water supply pipe 26 is not connected to the carbon dioxide reformer 12A.

The fuel cell systems 10G and 10H are examples of the fuel cell system according to the third and ninth aspects of the invention.

[Sixth Embodiment]
Next, a sixth embodiment of the present invention will be described. In addition, the same code | symbol is attached | subjected to the part same as 1st-5th embodiment, and description is abbreviate | omitted.

FIG. 10 shows a fuel cell system 10I according to the sixth embodiment. The fuel cell system 10I is a gas that releases carbon dioxide from the carbon dioxide absorbent 23 of the first carbon dioxide absorber 22 and the second carbon dioxide absorber 24 compared to the fuel cell system 10A described in the first embodiment. The main difference is that the (sweep gas) is water vapor.

The steam reformer 12 is not connected to the water supply pipe 26 but is connected to a post-purging steam supply pipe 64 described later. Carbon dioxide-containing steam G12, which will be described later, is supplied to the steam reformer 12 from the purged steam supply pipe 64.

In the branch part 48 provided in the middle of the anode off-gas pipe 34, one side branched into two is connected to the first carbon dioxide absorption part 22 and the second carbon dioxide absorption part 24 via the absorption switching valve 40, respectively. Has been. The other side is connected to the combustor 18 as a combustion gas supply pipe 62.

A water supply pipe 26 is connected to the discharge switching valve 46. From the water supply pipe 26, high-temperature steam G 13 having a temperature of 700 ° C. to 900 ° C. is supplied to the first carbon dioxide absorber 22 and the second carbon dioxide absorber 24. The oxygen concentration of the water vapor G13 is lower than the cathode off gas G2 and is 1% or less. Hereinafter, the code | symbol of the water supply pipe 26 from the discharge switching valve 46 to the 1st carbon dioxide absorption part 22 is shown by "26-1", The code is indicated by “26-2”. The discharge switching valve 46 supplies the water by connecting the water supply pipe 26 to one of the first carbon dioxide absorption part 22 and the second carbon dioxide absorption part 24 (one not connected to the anode offgas pipe 34). The water vapor G13 supplied from the pipe 26 is alternatively supplied to the first carbon dioxide absorber 22 or the second carbon dioxide absorber 24.

The first carbon dioxide absorber 22 and the second carbon dioxide absorber 24 supplied with the water vapor G13 are in an environmental condition in which the carbon dioxide absorber 23 releases carbon dioxide, and the first carbon dioxide absorber 22, the second carbon dioxide In the absorber 24, carbon dioxide is released from the carbon dioxide absorbent 23. The water vapor G13 here functions as a sweep gas. Hereinafter, the water vapor G13 containing carbon dioxide released from the first carbon dioxide absorption unit 22 and the second carbon dioxide absorption unit 24 is referred to as “carbon dioxide-containing water vapor G12”.

  One end of a post-purging steam supply pipe 64 is connected to the gas discharge side of the first carbon dioxide absorption section 22 and the second carbon dioxide absorption section 24, and a carbon dioxide discharge switching valve is connected to the post-purging steam supply pipe 64. 44 is provided. Hereinafter, the symbol of the post-purging water vapor supply pipe 64 from the first carbon dioxide absorption unit 22 to the carbon dioxide discharge switching valve 44 is indicated by “64-1”, and from the second carbon dioxide absorption unit 24 to the carbon dioxide discharge switching valve 44. The purged steam supply pipe 64 is indicated by “64-2”.

  The other end of the purged steam supply pipe 64 is connected to the steam reformer 12. The steam reformer 12 is supplied with the carbon dioxide-containing steam G12 from the steam supply pipe 64 after purging.

  In the steam reformer 12, the raw material gas (hydrocarbon fuel) supplied from the raw material gas pipe 28 is steam reformed using the carbon dioxide-containing steam G12, and the fuel gas G1 containing hydrogen and having a temperature of about 600 ° C. Is generated. The steam reformer 12 is connected to the anode 14 </ b> A of the fuel cell stack 14, and supplies the fuel gas G <b> 1 to the anode 14 </ b> A of the fuel cell stack 14 via the fuel gas pipe 32.

  Next, the operation of the fuel cell system 10A according to the sixth embodiment will be described. Also in the present embodiment, the operation mode M1-6 and the operation mode M2-6 are performed alternately. In the operation mode M1-6, the carbon dioxide absorption of the anode off gas G3 is performed by the first carbon dioxide absorption section 22, and the carbon dioxide is released from the carbon dioxide absorbent 23 by the second carbon dioxide absorption section 24. In the operation mode M2-6, the carbon dioxide absorption of the anode off gas G3 is performed by the second carbon dioxide absorption section 24, and the carbon dioxide is released from the carbon dioxide absorbent 23 by the first carbon dioxide absorption section 22.

The anode off gas G3 distributed to the anode off absorption gas pipe 37 side at the branching section 48 is cooled to about 650 ° C. by the heat exchanger and supplied to the first carbon dioxide absorption section 22. In the first carbon dioxide absorber 22, carbon dioxide contained in the anode offgas G <b> 3 is absorbed by the carbon dioxide absorbent 23. The CO ₂ removal off-gas G4 from which carbon dioxide has been removed is discharged from the first carbon dioxide absorption unit 22, supplied to the steam reformer 12 through the recovered gas supply pipe 35, and regenerated for power generation in the fuel cell stack 14. Used. On the other hand, the anode off gas G3 distributed to the combustion gas supply pipe 62 side is supplied to the combustor 18, and mixed with the cathode off gas G2 and burned. The high-temperature combustion exhaust gas G5 obtained by the combustor 18 is supplied to and used for each part in the fuel cell system 10I such as heating of the catalyst in the steam reformer 12.

  The steam G13 heated to 700 ° C. to 900 ° C. is supplied to the second carbon dioxide absorber 24. In the second carbon dioxide absorber 24, the carbon dioxide absorbed by the carbon dioxide absorber 23 is released. The carbon dioxide-containing steam G12 containing the released carbon dioxide is supplied to the steam reformer 12 through the steam supply pipe 64 after purging. In the steam reformer 12, the raw material gas is steam reformed using this steam to generate a fuel gas G 1 containing hydrogen and having a temperature of about 600 ° C.

  Said operation mode M1-6 is the carbon dioxide absorption capacity in the carbon dioxide absorber 23 accommodated in the 1st carbon dioxide absorber 22, and the carbon dioxide of the carbon dioxide absorber 23 in the 2nd carbon dioxide absorber 24. This is continued for a predetermined time T1-6 determined according to the release rate and the like. After the elapse of the predetermined time T1-6, the operation mode M2-6 is executed. In the operation mode M2-6, the carbon dioxide absorption of the anode off gas G3 is performed by the second carbon dioxide absorption section 24, and the carbon dioxide is released from the carbon dioxide absorbent 23 by the first carbon dioxide absorption section 22.

The anode off gas G3 at about 650 ° C. distributed to the anode off absorption gas pipe 37 side at the branching section 48 is supplied to the second carbon dioxide absorption section 24. In the first carbon dioxide absorber 22, carbon dioxide contained in the anode offgas G <b> 3 is absorbed by the carbon dioxide absorbent 23. The CO ₂ removal off-gas G4 from which carbon dioxide has been removed is discharged from the second carbon dioxide absorption unit 24, supplied to the steam reformer 12 through the recovery gas supply pipe 35, and regenerated for power generation in the fuel cell stack 14. Used.

  On the other hand, the water vapor G13 heated to 700 ° C. to 900 ° C. by the heat exchanger is supplied to the first carbon dioxide absorber 22. In the first carbon dioxide absorber 22, the carbon dioxide absorbed by the carbon dioxide absorbent 23 is released. The carbon dioxide-containing steam G13 containing the released carbon dioxide is supplied to the steam reformer 12 via the steam supply pipe 64 after purging. In the steam reformer 12, the raw material gas is steam reformed using the steam to generate a fuel gas G1 containing hydrogen and having a temperature of about 600 ° C.

  Also in the above operation mode M2-6, the carbon dioxide absorption capacity in the carbon dioxide absorbent 23 accommodated in the second carbon dioxide absorber 24, and the carbon dioxide absorbent 23 accommodated in the first carbon dioxide absorber 22. This is continued for a predetermined time T2-6 determined according to the release rate of carbon dioxide. After the elapse of the predetermined time T2-6, the controller 70 switches to the operation mode M1-6. By alternately repeating the operation mode M1-6 and the operation mode M2-6, the first carbon dioxide absorption unit 22 and the second carbon dioxide absorption unit 24 alternately absorb and release carbon dioxide, and the fuel cell stack 14 Continuous power generation at can be performed.

  In the fuel cell system 10 </ b> E of the present embodiment, the water vapor G <b> 13 whose oxygen content is zero or slightly contained is used as a gas for releasing carbon dioxide from the carbon dioxide absorbent 23 at a high temperature. Therefore, it is possible to suppress a sudden change in temperature or pressure in the container due to the combustion of hydrogen and carbon monoxide remaining in the first carbon dioxide absorber 22 and the second carbon dioxide absorber 24. Thereby, the damage to the carbon dioxide absorber 23 and the container is suppressed, and the useful life of these can be extended.

Moreover, in this embodiment, since the unreacted hydrogen and carbon monoxide contained in the anode off gas G3 discharged from the fuel cell stack 14 are reused, the fuel utilization efficiency can be improved. Further, since the CO ₂ removal off gas G4 after the concentration of carbon dioxide is reduced in the carbon dioxide absorption units 22 and 24 is used for reuse, the anode off gas G3 that does not remove CO ₂ is reused. In comparison, the power generation efficiency in the fuel cell stack 14 can be increased.

  In this embodiment, the steam reformer 12 is used as the reformer. However, as shown in FIG. 11, a fuel cell system 10J using a carbon dioxide reformer 12A may be used as the reformer. . In this case, water for reforming is not necessary. Therefore, a water vapor removal unit 52 is provided between the carbon dioxide discharge switching valve 44 and the carbon dioxide reformer 12A to remove water vapor from the carbon dioxide-containing water vapor G12. The steam removal carbon dioxide gas G14 containing a large amount of carbon dioxide from which the steam has been removed is supplied from the steam removal unit 52 to the carbon dioxide reformer 12A, and the reforming of the raw material gas is performed using the steam removal carbon dioxide gas G14. Done.

The fuel cell systems 10I and 10J are examples of the fuel cell system according to the inventions of claims 4 and 8.

[Seventh Embodiment]
Next, a seventh embodiment of the present invention will be described. In addition, the same code | symbol is attached | subjected to the part same as 1st-6th embodiment, and description is abbreviate | omitted.

FIG. 12 shows a fuel cell system 10K according to the seventh embodiment. The fuel cell system 10K is mainly different from the fuel cell system 10G described in the sixth embodiment in that a second fuel cell stack 50 is provided.

In the present embodiment, the first fuel cell stack 15 and the second fuel cell stack 50 are provided as in the second embodiment. The other end of the recovered gas supply pipe 35 is connected to the anode 50A of the second fuel cell stack 50, and the CO ₂ removal off-gas G4 discharged from the first carbon dioxide absorber 22 and the second carbon dioxide absorber 24 is Supplied to the anode 50A. The cathode 50B is connected to the cathode offgas pipe 31, and the cathode offgas G2 discharged from the cathode 14B is supplied to the cathode 50B.

  One end of a second anode off-gas pipe 58 is connected to the outlet side of the anode 50A. The other end of the second anode offgas pipe 58 is connected to the combustor 18. The second anode off gas G6 discharged from the anode 50A is supplied to the combustor 18.

  Next, the operation of the fuel cell system 10K according to the seventh embodiment will be described.

  Also in this embodiment, the operation mode M1-7 and the operation mode M2-7 are performed alternately. In the operation mode M1-7, the carbon dioxide absorption of the anode off gas G3 is performed by the first carbon dioxide absorption section 22, and the carbon dioxide is released from the carbon dioxide absorbent 23 by the second carbon dioxide absorption section 24. In the operation mode M2-7, the carbon dioxide absorption of the anode off gas G3 is performed by the second carbon dioxide absorption unit 24, and the carbon dioxide is released from the carbon dioxide absorbent 23 by the first carbon dioxide absorption unit 22.

In the present embodiment, the CO ₂ removal off-gas G4 from which carbon dioxide has been removed by the first carbon dioxide absorption unit 22 and the second carbon dioxide absorption unit 24 passes through the recovery gas supply pipe 35 and is supplied to the second fuel cell stack 50. Supplied to the anode 50A and used for power generation. The second anode off gas G6 discharged from the anode 50A is supplied to the combustor 18, mixed with the cathode off gas G2 discharged from the cathode 50B, and burned. Other operations are the same as in the sixth embodiment.

In the fuel cell system 10K according to the seventh embodiment, since the second fuel cell stack 50 that generates power using unreacted hydrogen and carbon monoxide contained in the CO ₂ removal off gas G4 as fuel gas is provided, the fuel utilization efficiency Can be improved. Further, the fuel cell system 10K can also achieve the same effects as those of the other seventh embodiment.

  In this embodiment, the steam reformer 12 is used as the reformer. However, as shown in FIG. 13, a fuel cell system 10L using a carbon dioxide reformer 12A may be used as the reformer. . In this case, since water for reforming is not required, a water vapor removing unit 52 is provided between the carbon dioxide discharge switching valve 44 and the carbon dioxide reformer 12A, as in the sixth embodiment, to provide carbon dioxide. Water vapor is removed from the contained water vapor G12. The steam removal carbon dioxide gas G14 containing a large amount of carbon dioxide from which the steam has been removed is supplied from the steam removal unit 52 to the carbon dioxide reformer 12A, and the reforming of the raw material gas is performed using the steam removal carbon dioxide gas G14. Done. The water vapor here can be condensed and used for cooling in the apparatus.

The fuel cell systems 10K and 10L are examples of the fuel cell system according to the third and eighth aspects of the invention.

10A-10L Fuel cell system 12 Steam reformer (reformer), 12A Carbon dioxide reformer (reformer)
14A, 50A Anode (fuel electrode)
14 fuel cell stack 15 first fuel cell stack, 50 second fuel cell stack 18 combustor, 22 first carbon dioxide absorber 23 first carbon dioxide absorber, 24 second carbon dioxide absorber 44 carbon dioxide emission switching valve, 46 discharge switching valve, 52 water vapor removal unit 70 control unit, G1 fuel gas, G3 anode off gas, G5 combustion exhaust gas G9 hydrocarbon fuel gas, G13 water vapor

Claims (8)

A fuel cell that generates power from fuel gas supplied to the fuel electrode and air supplied to the air electrode, wherein anode off-gas is discharged from the fuel electrode and cathode off-gas is discharged from the air electrode;
A plurality of carbon dioxide absorbers containing carbon dioxide absorbers;
The anode offgas is supplied to a part of the carbon dioxide absorbers of the plurality of carbon dioxide absorbers, and the carbon dioxide in the anode offgas is absorbed by the carbon dioxide absorber to generate regenerated fuel gas. The other carbon dioxide absorbers are supplied with any one of the anode offgas, water vapor, and hydrocarbon fuel as a sweep gas having a lower oxygen concentration than the cathode offgas and used for system operation. A controller that releases carbon dioxide from the carbon absorbent;
A fuel cell system comprising: The fuel cell includes a first fuel cell for delivering anode off to the carbon dioxide absorption unit, and a second fuel cell that generates electricity by regeneration fuel gas the regeneration fuel gas is supplied to the fuel electrode, according Item 4. The fuel cell system according to Item 1 . The fuel cell system according to claim 1 , wherein the control unit supplies the regenerated fuel gas from the carbon dioxide absorption unit to the fuel electrode. The steam removal part which removes steam from the anode off gas before being supplied to the carbon dioxide absorption part used for generation of the regenerated fuel gas is further provided in any 1 paragraph of Claims 1-3. The fuel cell system described. The fuel cell system according to any one of claims 1 to 3 , further comprising a water vapor removing unit that removes water vapor from the anode off-gas after carbon dioxide is absorbed by the carbon dioxide absorbing unit. And generates the fuel gas containing hydrogen to hydrocarbon fuel reforming, reformer to supply the fuel gas to the fuel cell, further comprising a any one of claims 1 to 5 The fuel cell system described in 1. 7. The fuel cell system according to claim 6 , wherein when the sweep gas is steam, the steam discharged from the carbon dioxide absorption unit is supplied to the reformer to steam reform the hydrocarbon fuel. . The fuel according to claim 6 , wherein, when the sweep gas is a hydrocarbon fuel, the hydrocarbon fuel discharged from a carbon dioxide absorption unit is supplied to the reformer to reform the hydrocarbon fuel. Battery system.

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