JP6847900B2 - Carbon dioxide capture fuel cell power generation system - Google Patents

Description

The present invention relates to a carbon dioxide recovery type fuel cell power generation system, and more particularly to a carbon dioxide recovery type fuel cell power generation system that generates power using a carbon compound fuel and recovers carbon dioxide generated by the power generation.

When a carbon compound fuel is used in a fuel cell power generation 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 recovered, components other than carbon dioxide are mixed in the fuel electrode off-gas. Therefore, for example, Patent Document 1 discloses a technique of burning fuel electrode off-gas with oxygen and further removing water vapor by condensation to recover carbon dioxide.

Japanese Unexamined Patent Publication No. 2012-164423

While recovering carbon dioxide, fuel cell power generation systems are required to improve power generation efficiency. Therefore, in order to reuse the unreacted fuel gas component contained in the fuel electrode off gas, the fuel electrode off gas is used again as the fuel gas for power generation of another fuel cell stack. Patent Document 1 also provides a second SOFC and uses off-gas fuel electrode to generate electricity. However, since the fuel electrode off gas supplied to the second SOFC is after the oxygen combustion process, the fuel component used for power generation is less than that before oxygen combustion, and the power generation efficiency is lowered. ..

The present invention has been made in consideration of the above facts, and provides a carbon dioxide recovery type fuel cell power generation system capable of recovering a high concentration of carbon dioxide from a fuel electrode off-gas while improving power generation efficiency. With the goal.

The carbon dioxide recovery type fuel cell power generation system according to the invention according to claim 1 includes a fuel gas containing a carbon compound and supplied to the first fuel electrode, an oxidizing agent gas containing oxygen and supplied to the first air electrode, and the like. The first fuel cell is generated by, and the first fuel electrode off gas is sent from the first fuel electrode, and carbon dioxide is supplied to the second fuel electrode without being removed after being discharged from the first fuel cell. A second fuel cell that generates power using the first fuel electrode off gas and the oxidizing agent gas supplied to the second air electrode, and sends the second fuel electrode off gas from the second fuel electrode to the fuel electrode off gas flow path. The air electrode off gas flow path that sends out the air electrode off gas from at least one of the first air electrode and the second air electrode and the air electrode off gas flow path are connected to supply the air electrode off gas, and the air is supplied. The oxygen separation section that separates oxygen from the pole off gas is connected to the fuel pole off gas flow path, and the second fuel pole off gas is supplied from the second fuel pole through the fuel pole off gas flow path and the oxygen separation. A combustion unit in which oxygen separated by the unit is supplied and the second fuel electrode off gas is burned and reacted by the oxygen, and a carbon dioxide separation unit that separates carbon dioxide from the combustion off gas sent from the combustion unit are provided. ing.

The carbon dioxide recovery type fuel cell power generation system according to claim 1 includes a first fuel cell and a second fuel cell. In the first fuel cell, power generation is performed by the fuel gas supplied to the first fuel electrode and the oxidant gas supplied to the second air electrode. In the second fuel cell, power generation is performed by the first fuel pole off gas supplied from the first fuel pole to the second fuel pole and the oxidant gas supplied to the second air pole.

From at least one of the first air electrode and the second air electrode, the air electrode off gas is sent out to the air electrode off gas flow path, and the air electrode off gas is supplied to the oxygen separation section via the air electrode off gas flow path. In the oxygen separation section, oxygen is separated from the air electrode off gas, and the separated oxygen is supplied to the combustion section. Further, the second fuel electrode off gas is sent from the second fuel electrode to the fuel electrode off gas flow path, and the second fuel electrode off gas is supplied to the combustion unit via the fuel electrode off gas flow path. In the combustion section, a combustion reaction occurs between the combustible component in the second fuel electrode off gas and oxygen, and the combustion off gas is sent out from the combustion section. The combustion off gas is sent to the carbon dioxide separation unit, and carbon dioxide is separated from the combustion off gas.

In the carbon dioxide recovery type fuel cell power generation system according to claim 1, since the second fuel pole off gas after being sent from the second fuel cell is burned in the combustion section, it is used for power generation in the second fuel cell. The amount of unreacted fuel gas supplied to the second fuel cell is larger than that in the case of burning the previous first fuel pole off gas. Therefore, the power generation efficiency of the second fuel cell can be improved. Further, in the combustion unit, carbon dioxide and water vapor are generated by a combustion reaction between oxygen and a combustible component contained in the second fuel electrode off-gas. Therefore, it is possible to recover a high concentration of carbon dioxide by reducing the combustible gas from the second fuel electrode off gas. Further, the second fuel electrode off gas contains a smaller amount of unreacted fuel gas than the first fuel electrode off gas, and has a high carbon dioxide content. Therefore, the amount of unreacted fuel gas burned in the combustion unit can be reduced, and the amount of oxygen required to burn the unreacted fuel gas can be reduced.

In the carbon dioxide recovery type fuel cell power generation system according to claim 3, the first fuel cell and the second fuel cell are hydrogen ion conduction type solid oxide fuel cells (PCFC: Proton Ceramic Solid Oxide Fuel Cell).

In the hydrogen ion conduction type solid oxide fuel cell, water vapor is generated by the power generation reaction on the air electrode side. Therefore, since the amount of water vapor contained in the first fuel electrode off gas is reduced, the decrease in the concentration of the fuel gas supplied to the second fuel electrode is small, and the power generation efficiency in the second fuel cell can be improved. Further, since the amount of water vapor contained in the second fuel electrode off gas is also reduced, the amount of water vapor removed from the second fuel electrode off gas can be reduced.

In the carbon dioxide recovery type fuel cell power generation system according to claim 4, the first fuel cell and the second fuel cell are oxygen ion conduction type solid oxide fuel cells (SOFC: Solid Oxide Fuel Cell), and the first fuel cell and the second fuel cell are the above-mentioned first fuel cell. It has a fuel regeneration unit that separates water vapor from the first fuel electrode off gas delivered from one fuel electrode to generate a regenerated fuel gas, and the regenerated fuel gas is supplied to the second fuel electrode.

In the oxygen ion conduction type solid oxide fuel cell, since water vapor is generated by the power generation reaction on the fuel electrode side, the amount of water vapor contained in the first fuel electrode off gas increases. Therefore, the fuel regeneration unit removes water vapor from the first fuel electrode off gas to generate the regenerated fuel gas, and supplies the regenerated fuel gas to the second fuel electrode. As a result, the power generation efficiency of the second fuel cell can be improved.

The carbon capture and storage fuel cell power generation system according to claim 5 includes a circulation flow path for supplying a part of the second fuel electrode off gas to the first fuel electrode from the upstream side of the combustion unit.

According to the carbon dioxide recovery type fuel cell power generation system according to claim 5 , a part of the second fuel electrode off gas is supplied to the first fuel electrode via the circulation flow path, so that the second fuel electrode off gas is contained. Unreacted fuel gas and steam can be used for power generation and steam reforming of fuel gas, respectively.

In the carbon dioxide recovery type fuel cell power generation system according to claim 6, the oxygen separation section has an oxygen permeable membrane that selectively permeates oxygen, and the combustion section has a combustion space arranged on the permeation side of the oxygen permeable membrane. Has been done.

According to the carbon capture and storage fuel cell power generation system according to claim 6 , the combustion unit can be arranged adjacent to the oxygen permeation membrane of the oxygen separation unit, and the combustion unit and the oxygen separation unit can be compactly configured.

The carbon dioxide recovery type fuel cell power generation system according to claim 1 generates power by a fuel gas containing a carbon compound and supplied to the first fuel electrode and an oxidizing agent gas containing oxygen and supplied to the first air electrode. The first fuel cell in which the first fuel pole off gas is sent from the first fuel pole, and the first fuel cell in which carbon dioxide is supplied to the second fuel pole without removing carbon dioxide after being discharged from the first fuel cell. A second fuel cell that generates electricity using the fuel electrode off gas and the oxidant gas supplied to the second air electrode, and sends the second fuel electrode off gas from the second fuel electrode to the fuel electrode off gas flow path, and the above. The branched air is connected to an air electrode off gas flow path that sends out air electrode off gas from at least one of the first air electrode and the second air electrode, and a branched air electrode off gas flow path branched from the air electrode off gas flow path. The air electrode off gas is supplied from the pole off gas flow path, and the oxygen separation unit that separates oxygen from the air electrode off gas is connected to the fuel electrode off gas flow path to supply the second fuel electrode off gas and the oxygen. A combustion unit in which oxygen separated by the separation unit is supplied and the second fuel electrode off gas is burned and reacted by the oxygen, a carbon dioxide separation unit that separates carbon dioxide from the combustion off gas sent from the combustion unit, and the above. The amount of the air electrode off gas branched from the air electrode off gas flow path to the branched air electrode off gas flow path so that the combustible gas concentration and the oxygen concentration in the carbon dioxide rich gas separated by the carbon dioxide separation unit are equal to or less than the threshold value. It is equipped with a control unit that controls a flow control valve that adjusts the amount of carbon dioxide.

According to the carbon capture and storage fuel cell power generation system according to claim 2 , the amount of air electrode off gas sent to the oxygen separation unit can be easily adjusted.

The carbon dioxide recovery type fuel cell power generation system according to claim 6 comprises an electric turbo chiller that is driven by power generated by power generation in at least one of the first fuel cell and the second fuel cell to generate cold heat. The carbon dioxide separation unit cools the combustion off-gas with the cold heat generated by the electric turbo chiller to condense the water vapor in the combustion off-gas.

According to the carbon dioxide recovery type fuel cell power generation system according to claim 6 , the electric turbo chiller efficiently cools the combustion off-gas to condense water vapor using the electric power generated in the system, and carbon dioxide is produced. Can be separated.

According to the carbon dioxide recovery type fuel cell power generation system according to the present invention, it is possible to recover high-concentration carbon dioxide from the fuel electrode off-gas while improving the power generation efficiency.

It is the schematic of the fuel cell power generation system which concerns on 1st Embodiment. It is a block diagram of the control system of the fuel cell power generation system which concerns on 1st Embodiment. It is a flowchart of the flow rate adjustment process of 1st Embodiment. It is a flowchart of the cooling water temperature adjustment process of 1st Embodiment. It is the schematic of the fuel cell power generation system which concerns on 2nd Embodiment. It is the schematic of the fuel cell power generation system which concerns on 3rd Embodiment. It is the schematic of the fuel cell power generation system which concerns on 4th Embodiment. It is the schematic of the fuel cell power generation system which concerns on 5th Embodiment. It is the schematic of the fuel cell power generation system which concerns on 6th Embodiment. It is the schematic of the fuel cell power generation system which concerns on 7th Embodiment. It is the schematic of the fuel cell power generation system which concerns on 8th Embodiment. It is the schematic of the fuel cell power generation system which concerns on 9th Embodiment. It is the schematic of the fuel cell power generation system which concerns on the modification of 1st Embodiment.

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

[First Embodiment]
FIG. 1 shows the fuel cell power generation system 10A according to the first embodiment as an example of the carbon capture and storage fuel cell power generation system of the present invention. The fuel cell power generation system 10A has the first fuel cell stack 12, the second fuel cell stack 14, the combustor 20 with an oxygen permeable film, the condenser 26, the carbon dioxide recovery tank 28, and the first heat exchange as the main configurations. It includes a vessel 30, a second heat exchanger 32, an exhaust heat input type absorption refrigerating machine 36, and a water tank 27. Further, as shown in FIG. 2, a control unit 40 for controlling the fuel cell power generation system 10A is provided.

The first fuel cell stack 12 is a hydrogen ion conduction type solid oxide fuel cell (PCFC), and is a first layer of the electrolyte layer 12C and the front and back surfaces of the electrolyte layer 12C, respectively. It has one fuel electrode (fuel electrode) 12A and a first air electrode (air electrode) 12B.

The basic configuration of the second fuel cell stack 14 is the same as that of the first fuel cell stack 12, and the second fuel pole 14A corresponding to the first fuel pole 12A and the first air pole 12B corresponding to the first air pole 12A are the same. It has two air electrodes 14B and an electrolyte layer 14C corresponding to the electrolyte layer 12C.

One end of the fuel gas pipe P1 is connected to the first fuel pole 12A of the first fuel cell stack 12, and the other end of the fuel gas pipe P1 is connected to a gas source (not shown). From the gas source, fuel gas is sent to the first fuel pole 12A by the fuel supply blower B1. In the present embodiment, methane is used as the fuel gas, but the gas is not particularly limited as long as it can generate hydrogen by reforming, and a hydrocarbon fuel can be used. Examples of the hydrocarbon fuel include natural gas, LP gas (liquefied petroleum gas), biogas, coal reforming 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 raw material gas contains impurities, a desulfurizer or the like is required, but it is omitted in the figure.

A water vapor pipe P2 is joined and connected to the fuel gas pipe P1, and water vapor is appropriately sent from a water vapor source (not shown) at the time of starting or stopping. Methane and water vapor are merged at the fuel gas pipe P1 and supplied to the first fuel electrode 12A. In the present embodiment, as will be described later, a part of the second fuel electrode off gas is returned to the first fuel electrode 12A and the water vapor is reused. Therefore, the water vapor from the steam pipe P2 is the fuel cell power generation system 10A. It is supplementarily supplied when necessary in the start and stop processes of.

At the first fuel electrode 12A, as shown in the following equation (1), the fuel gas is steam reformed to generate hydrogen and carbon monoxide. Further, as shown in the following equation (2), carbon dioxide and hydrogen are produced by a shift reaction between the produced carbon monoxide and water.

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

Then, in the first fuel electrode 12A, hydrogen is separated into hydrogen ions and electrons as shown in the following equation (3).

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

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

Oxidizing agent gas (air) is supplied from the oxidizing agent gas pipe P5 to the first air electrode 12B of the first fuel cell stack 12. Air is introduced into the oxidant gas pipe P5 by the oxidant gas blower B2. The oxidant gas pipe P5 is provided with a second heat exchanger 32, and the air flowing through the oxidant gas pipe P5 is heated by heat exchange with the air electrode off gas flowing through the air electrode off gas pipe P6 described later. The heated air is supplied to the first air pole 12B.

In the first air pole 12B, as shown in the following equation (4), hydrogen ions that have moved from the first fuel pole 12A through the electrolyte layer 12C and electrons that have moved from the first fuel pole 12A through the external circuit , Water vapor is generated by reacting with oxygen in the oxidant gas.

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

Further, an air electrode off gas pipe P6 is connected to the first air electrode 12B. The air electrode off gas is discharged from the first air electrode 12B to the air electrode off gas pipe P6. The oxidant gas pipe P5 and the air pole off gas pipe P6 are similarly connected to the second air pole 14B, and the first air pole 12B and the second air pole 14B are connected in parallel.

One end of the first fuel pole off-gas pipe P7 is connected to the first fuel pole 12A of the first fuel cell stack 12, and the other end of the first fuel pole off-gas pipe P7 is the second of the second fuel cell stack 14. 2 It is connected to the fuel pole 14A. The first fuel pole off gas is sent from the first fuel pole 12A to the first fuel pole off gas pipe P7. The fuel electrode off-gas contains unreformed fuel gas components, unreacted hydrogen, unreacted carbon monoxide, carbon dioxide, water vapor and the like.

One end of the second fuel pole off gas pipe P7-2 is connected to the second fuel pole 14A of the second fuel cell stack 14, and the second fuel pole off gas is sent out from the second fuel pole 14A. The other end of the second fuel pole off gas pipe P7-2 is connected to the combustor 20 with an oxygen permeable membrane. A circulating gas pipe P3 is branched from the second fuel pole off gas pipe P7-2, and the circulating gas pipe P3 is connected to a fuel gas pipe P1 connected to the first fuel pole 12A. A circulating gas blower B3 is provided in the circulating gas pipe P3.

In the second fuel cell stack 14, the same power generation reaction as in the first fuel cell stack 12 is performed, and the air electrode off gas is sent from the second air electrode 14B to the air electrode off gas pipe P6. The air pole off-gas pipe P6 connected to the second air pole 14B is branched on the upstream side of the confluence with the air pole off-gas pipe P6 connected to the first air pole 12B, and the branched air pole off-gas pipe P6 -2 is formed. The branch air electrode off gas pipe P6-2 is provided with a flow rate adjusting valve 42 whose flow rate can be adjusted. The flow rate adjusting valve 42 is connected to the control unit 40. The flow rate adjusting valve 42 is controlled by the control unit 40, and the flow rate of the air electrode off gas branching to the branch air electrode off gas pipe P6-2 is adjusted. The downstream end of the branched air electrode off gas pipe P6-2 is connected to the combustor 20 with an oxygen permeable membrane.

The combustor 20 with an oxygen permeable film has a multi-cylindrical shape, and has a combustion unit 22 forming an outer peripheral cylinder of the multi-cylinder and an oxygen separation unit 24 arranged radially inside the combustion unit 22. .. A combustion space 22A is formed in the combustion unit 22.

The oxygen separation unit 24 is arranged inside the combustion unit 22 in the radial direction, and an air flow path 24A is formed adjacent to the combustion space 22A. The air flow path 24A and the combustion space 22A are separated by an oxygen permeable membrane 23. For the oxygen permeable film 23, for example, a mixed conductive ceramics of electrons and oxygen ions such as LSCF, or an oxygen ion conductive ceramics dense film such as YSZ can be used. The other end of the second fuel electrode off-gas pipe P7-2 is connected to the inlet of the combustion space 22A, and the downstream end of the branched air electrode off-gas pipe P6-2 is connected to the inlet of the air flow path 24A. An oxidation catalyst is arranged inside the combustion space 22A. As the oxidation catalyst, for example, nickel, ruthenium, or the like can be used.

The second air electrode off gas is supplied to the air flow path 24A, and oxygen contained in the second air electrode off gas passes through the oxygen permeable membrane 23 and moves to the combustion space 22A. The second air electrode off gas that does not move to the combustion space 22A is exhausted to the outside from the exhaust pipe P12 connected to the outlet side of the air flow path 24A.

The second fuel electrode off gas is supplied to the combustion space 22A and mixed with oxygen that has moved from the oxygen separation unit 24 through the oxygen permeation membrane 23. As a result, a combustion reaction occurs between the combustible gas components (unmodified methane, unreacted hydrogen, unreacted carbon monoxide, etc.) in the second fuel electrode off-gas and oxygen via the oxidation catalyst, and carbon dioxide is produced. And water vapor is generated. A combustion off gas pipe P8 is connected to the outlet side of the combustion space 22A, and the combustion off gas is sent out from the combustion space 22A.

The other end of the combustion off-gas pipe P8 is connected to the condenser 26 via the first heat exchanger 30. In the first heat exchanger 30, the fuel gas is heated by heat exchange between the fuel gas and the combustion off gas. A cooling water circulation flow path 26A is piped to the condenser 26, and cooling water from the exhaust heat input type absorption chiller 36, which will be described later, is circulated and supplied by driving the pump 26P to cool the combustion off gas. As a result, the water vapor in the combustion off gas is condensed. The condensed water is sent to the water tank 27 via the water pipe P9. One end of the pipe P11 is connected to the water tank 27, and the other end of the pipe P11 is branched into two and connected to the cooling tower 38 and the cooling water circulation flow path 26A.

The combustion off gas from which water vapor has been separated and removed is sent to the carbon dioxide gas pipe P10. The combustion off-gas from which water (liquid phase) has been removed by the condenser 26 is a gas having a high carbon dioxide concentration, and the combustion off-gas is referred to as carbon dioxide-rich gas. The carbon dioxide gas pipe P10 is provided with a composition detection unit 44. The composition detection unit 44 detects the composition of the carbon dioxide-rich gas delivered from the condenser 26. Specifically, the concentrations of combustible gases such as methane, carbon monoxide, and hydrogen, and the concentrations of carbon dioxide and oxygen are detected. The composition detection unit 44 is connected to the control unit 40, and the composition information of the detected carbon dioxide rich gas is transmitted to the control unit 40.

The carbon dioxide gas pipe P10 is branched on the downstream side of the composition detection unit 44, and one of the branched carbon dioxide gas pipes P10-1 is connected to the carbon dioxide recovery tank 28. The other carbon dioxide gas pipe P10-2 of the branch is connected to the carbon dioxide supply line 29. The carbon dioxide gas pipe P10-1 and the carbon dioxide gas pipe P10-2 are provided with opening / closing valves V1 and V2, respectively. A carbon dioxide blower B4 is provided on the upstream side of the carbon dioxide gas pipe P10 on the upstream side of the above-mentioned branch.

A second heat exchanger 32 is provided on the downstream side of the confluence portion where the air pole off gas pipes P6 from the first air pole 12B and the second air pole 14B are merged. In the second heat exchanger 32, heat exchange is performed between the air electrode off gas flowing through the air electrode off gas pipe P6 and the oxidant gas flowing through the oxidant gas pipe P5, the oxidant gas is heated, and the air electrode off gas is generated. It is cooled. The air electrode off gas is supplied to the exhaust heat input type absorption chiller 36 via the second heat exchanger 32.

The exhaust heat input type absorption chiller 36 is a heat pump that generates cold heat using exhaust heat, and as an example, a steam / exhaust heat input type absorption chiller can be used. In the vapor / exhaust heat input type absorption chiller, water is separated from the absorption liquid and regenerated by heating the absorption liquid that has absorbed water vapor (for example, lithium bromide aqueous solution or ammonia aqueous solution) by the heat of the air electrode off gas. To do. Water vapor is condensed in the air electrode off gas cooled by heating the absorption liquid, and the condensed water is supplied to the water tank 27 by the water pipe P36-2. The air electrode off gas after the water vapor is condensed and removed is sent to the exhaust pipe P36-1 and exhausted to the outside of the exhaust heat input type absorption chiller 36.

The absorption liquid regenerated by heating promotes the evaporation of water by absorbing water vapor and contributes to the generation of cold heat. The exhaust heat input type absorption chiller 36 is connected to the cooling tower 38 via a heat dissipation circuit 37. A pump 37P is installed in the heat radiating circuit 37, and cooling water is supplied to the heat radiating circuit 37 by the pump 37P. The absorbed heat generated when the absorption liquid absorbs water vapor in the exhaust heat input type absorption chiller 36 is released from the cooling tower 38 to the atmosphere through the cooling water flowing through the heat dissipation circuit 37.

The cold heat generated by the exhaust heat input type absorption chiller 36 is sent to the condenser 26 via the cooling water flowing through the cooling water circulation flow path 26A, the combustion off gas is cooled by the condenser 26, and the combustion off gas is further contained. Water vapor is condensed and removed.

The water tank 27 is connected to a cooling water circulation flow path 26A, a heat dissipation circuit 37, and a heat medium flow path (not shown) through which water flows as a heat medium of the exhaust heat input type absorption chiller 36. In the cooling water circulation flow path 26A, the heat dissipation circuit 37, and the heat medium flow path, when water is insufficient, water is appropriately replenished from the water tank 27.

The control unit 40 controls the entire fuel cell power generation system 10A, and includes a CPU, a ROM, a RAM, a memory, and the like. The memory stores data and procedures necessary for the flow rate adjustment process, the cooling water temperature adjustment process, and the process during normal operation, which will be described later. As shown in FIG. 2, the control unit 40 is connected to a flow rate adjusting valve 42, a composition detecting unit 44, an exhaust heat input type absorption chiller 36, an opening / closing valve V1, and an opening / closing valve V2. The flow rate adjusting valve 42, the composition detection unit 44, the exhaust heat input type absorption chiller 36, the opening / closing valve V1, and the opening / closing valve V2 are controlled by the control unit 40. Note that FIG. 2 shows a part of the connection relationship of the control unit 40 in the fuel cell power generation system 10A, and although not shown in FIG. 2, the control unit 40 is also connected to other devices.

In the fuel cell power generation system 10A, the pump, blower, and other auxiliary equipment are driven by the electric power generated by the fuel cell power generation system 10A. In order to efficiently use the electric power generated by the fuel cell power generation system 10A without converting it into alternating current as it is in direct current, it is preferable that the auxiliary machine is driven by direct current.

Next, the operation of the fuel cell power generation system 10A of the present embodiment will be described.

In the fuel cell power generation system 10A, methane is sent from the gas source to the fuel gas pipe P1 by the fuel supply blower B1, heated by passing through the first heat exchanger 30, and supplied to the first fuel electrode 12A. From the steam pipe P2, steam for steam reforming is supplied to the first fuel pole 12A via the fuel gas pipe P1. The water vapor is supplied at the time of start-up and at the time of shortage, and at the time of rated operation, the water vapor in the second fuel electrode off gas returned from the circulation gas pipe P3 is used as reformed water, as will be described later.

At the first fuel pole 12A of the first fuel cell stack 12, the fuel gas is steam reformed to produce hydrogen and carbon monoxide. In addition, carbon dioxide and hydrogen are produced by a shift reaction between the produced carbon monoxide and water.

Air is supplied to the first air electrode 12B of the first fuel cell stack 12 via the oxidant gas pipe P5. In the first fuel cell stack 12, hydrogen ions move in the first fuel pole 12A and the first air pole 12B, and the above-mentioned reaction occurs to generate electricity. The first fuel pole off gas is sent from the first fuel pole 12A of the first fuel cell stack 12 to the first fuel pole off gas pipe P7. Further, the air electrode off gas is sent from the first air electrode 12B to the air electrode off gas pipe P6.

The first fuel pole off gas delivered from the first fuel pole 12A is guided to the first fuel pole off gas pipe P7 and supplied to the second fuel pole 14A of the second fuel cell stack 14. Air is supplied to the second air electrode 14B of the second fuel cell stack 14 via the oxidant gas pipe P5. The second fuel cell stack 14 also generates electricity in the same manner as the first fuel cell stack 12. The second fuel pole off gas is sent from the second fuel pole 14A of the second fuel cell stack 14 to the second fuel pole off gas pipe P7-2. Further, the air electrode off gas is sent from the second air electrode 14B to the air electrode off gas pipe P6. A part of the air electrode off gas sent out from the second air electrode 14B is branched to the branched air electrode off gas pipe P6-2, and the other part is merged with the air electrode off gas sent out from the first air electrode 12B.

The air electrode off gas is supplied to the exhaust heat input type absorption chiller 36 via the second heat exchanger 32. In the second heat exchanger 32, heat exchange is performed between the air electrode off gas and the oxidant gas, and the oxidant gas is heated by the air electrode off gas. In the exhaust heat input type absorption chiller 36, as described above, cold heat is generated by utilizing the heat of the air electrode off gas.

A part of the second fuel pole off gas branches to the circulating gas pipe P3 and is returned to the first fuel pole 12A. The other second fuel pole off gas is supplied to the combustion section 22 of the combustor 20 with an oxygen permeable membrane and flows through the combustion space 22A.

The air electrode off gas branched to the branched air electrode off gas pipe P6-2 is supplied to the oxygen separation section 24 of the combustor 20 with an oxygen permeable membrane. The air electrode off gas supplied to the oxygen separation unit 24 flows through the air flow path 24A. In the air flow path 24A, oxygen contained in the air electrode off gas passes through the oxygen permeable membrane 23 and moves to the combustion space 22A side. In the combustion space 22A, a combustion reaction occurs between combustible gas (methane, hydrogen, carbon monoxide, etc.) in the second fuel electrode off gas and oxygen, and carbon dioxide and water vapor are generated. The combustion off gas containing carbon dioxide and water vapor is sent from the combustion space 22A to the combustion off gas pipe P8. The combustion off gas delivered to the combustion off gas pipe P8 is supplied to the condenser 26 via the first heat exchanger 30.

The combustion off-gas supplied to the condenser 26 is cooled by the cooling water from the exhaust heat input type absorption chiller 36 that is circulated and supplied via the cooling water circulation flow path 26A, and the water vapor in the combustion off-gas is condensed. The condensed water is sent to the water tank 27 via the water pipe P9. Water is stored in the water tank 27, and the stored water is appropriately replenished with cooling water in the heat radiation circuit 37 of the cooling tower 38 and the cooling water circulation flow path 26A of the exhaust heat input type absorption chiller 36.

The combustion off-gas from which water vapor has been removed by the condenser 26 becomes a carbon dioxide-rich gas having a high carbon dioxide concentration, is sent to the carbon dioxide gas pipe P10 by the carbon dioxide blower B4, and is sent to the composition detection unit 44. The composition detection unit 44 detects the composition of the carbon dioxide rich gas, and the detected information is transmitted to the control unit 40.

Based on the composition information transmitted from the composition detection unit 44, the control unit 40 controls the flow rate adjusting valve 42 to adjust the amount of air electrode off gas branched to the branch air electrode off gas pipe P6-2, and exhaust heat input. The mold absorption chiller 36 controls the temperature of the cooling water sent to the cooling water circulation flow path 26A. Specifically, the control unit 40 executes the following flow rate adjustment process and cooling water temperature adjustment process.

As shown in FIG. 3, in the flow rate adjustment process, in step S10, it is determined whether or not the concentration of the combustible gas is within the threshold value G1 in the composition information of the carbon dioxide rich gas detected by the composition detection unit 44. Here, the threshold value G1 is a sufficiently low concentration in carbon dioxide rich gas and can be set to about 0.1 to 5 vol%, and more preferably in the range of 0.1 to 1 vol%. When the concentration of the combustible gas is higher than the threshold value G1, the flow rate adjusting valve 42 is controlled in step S12 to increase the flow rate of the air electrode off gas branching to the branch air electrode off gas pipe P6-2. As a result, the amount of oxygen that permeates the oxygen permeable membrane 23 and moves to the combustion space 22A increases, and the combustion reaction in the combustion space 22A can reduce the combustible gas contained in the carbon dioxide rich gas.

When the concentration of the combustible gas is equal to or less than the threshold value G1 in step S10, it is determined in step S14 whether or not the oxygen concentration is within the threshold value O1 in the composition information of the carbon dioxide rich gas detected by the composition detection unit 44. Here, the threshold value O1 is a sufficiently low concentration in carbon dioxide rich gas and can be set to about 0.1 to 5 vol%, and more preferably in the range of 0.1 to 1 vol%. When the oxygen concentration is higher than the threshold value O1, the flow rate adjusting valve 42 is controlled in step S16 to reduce the flow rate of the air electrode off gas branching to the branched air electrode off gas pipe P6-2. As a result, the amount of oxygen that permeates the oxygen permeable membrane 23 and moves to the combustion space 22A can be reduced, and the oxygen that remains without being subjected to the combustion reaction in the combustion space 22A can be reduced.

After steps S12, S14, and S16, the process returns to step S10 and the above-described processing is repeated. This flow rate adjustment process starts when the operation of the fuel cell power generation system 10A starts, continues during the operation, and ends when the operation is stopped.

Further, as shown in FIG. 4, in the condensation amount adjusting process, in step S20, it is determined whether or not the concentration of water vapor is within the threshold value M in the composition information of the carbon dioxide rich gas detected by the composition detection unit 44. Here, the threshold value M is a sufficiently low concentration in carbon dioxide-rich gas and can be set to about 0.1 to 5 vol%, and more preferably in the range of 0.1 to 1 vol%. When the concentration of water vapor is higher than the threshold value M, condensation strengthening is performed in step S22. Specifically, the exhaust heat input type absorption chiller 36 is controlled to lower the temperature of the cooling water sent to the cooling water circulation flow path 26A, or increase the circulation flow rate of the cooling water. As a result, the amount of water separated from the combustion off gas by the condensation in the condenser 26 is increased, and the proportion of water vapor contained in the carbon dioxide rich gas can be reduced.

After steps S20 and S22, the process returns to step S20 and the above-mentioned process is repeated. This condensation amount adjustment process is started when the operation of the fuel cell power generation system 10A is started, is continued during the operation, and is ended when the operation is stopped.

The carbon dioxide-rich gas delivered to the carbon dioxide gas pipe P10 is sent to the carbon dioxide recovery tank 28 or the carbon dioxide supply line as required. When it is sent to the carbon dioxide capture tank 28, the on-off valve V1 is opened and the on-off valve V2 is closed. When sent to the carbon dioxide line, the on-off valve V1 is closed and the on-off valve V2 is opened.

In the fuel cell power generation system 10A of the present embodiment, the second fuel cell off gas sent from the second fuel cell 14A of the second fuel cell stack 14 is burned in the combustion unit 22, so that the second fuel cell stack 14 The amount of unreacted fuel gas used for power generation in the second fuel cell stack 14 is larger than that in the case of burning the first fuel pole off gas before being used for power generation in. Therefore, the power generation efficiency of the second fuel cell stack 14 can be improved.

Further, in the combustion unit 22, carbon dioxide and water vapor are generated by a combustion reaction between the combustible gas contained in the second fuel electrode off gas and oxygen. Therefore, it is possible to recover a high concentration of carbon dioxide by reducing the combustible gas from the second fuel electrode off gas. Further, only oxygen in the air electrode off gas is supplied to the combustion unit 22, and the amount of unreacted fuel gas contained in the second fuel electrode off gas is smaller than that in the first fuel electrode off gas, and carbon dioxide is used. Content is high. Therefore, the amount of unreacted fuel gas burned in the combustion unit 22 and the amount of oxygen required to burn the unreacted fuel gas can be reduced.

Further, since the fuel cell power generation system 10A of the present embodiment has the branched air electrode off gas pipe P6-2 branched from the air electrode off gas pipe P6, the composition of the carbon dioxide rich gas detected by the composition detection unit 44 Based on the information, the flow rate of the air electrode off gas branched to the branched air electrode off gas pipe P6-2 can be easily adjusted. Thereby, the amount of oxygen flowing into the combustion space 22A of the combustion unit 22 can be adjusted so that the amounts of the combustible gas and oxygen contained in the combustion off gas are lower than the predetermined threshold value.

Further, in the fuel cell power generation system 10A of the present embodiment, the amount of water to be condensed by the condenser 26 is adjusted based on the composition information of the carbon dioxide rich gas detected by the composition detection unit 44, thereby producing the carbon dioxide rich gas. The carbon dioxide concentration can be increased.

Further, in the fuel cell power generation system 10A of the present embodiment, since the hydrogen ion conduction type solid oxide fuel cell is used for the fuel cell stack, water vapor is not generated at the first fuel pole 12A. Therefore, since the amount of water vapor contained in the first fuel electrode off gas is reduced, the power generation efficiency of the second fuel cell can be improved. Further, since the amount of water vapor contained in the second fuel electrode off gas is also reduced, the amount of water vapor removed from the second fuel electrode off gas can be reduced.

Further, the fuel cell power generation system 10A of the present embodiment includes a circulation gas pipe P3 that supplies a part of the second fuel pole off gas to the first fuel pole 12A from the upstream side of the combustion unit 22. Therefore, a part of the unreacted fuel gas and steam in the second fuel electrode off gas can be reused for power generation and steam reforming of the fuel gas, respectively.

Further, in the fuel cell power generation system 10A of the present embodiment, the combustion unit 22 and the oxygen separation unit 24 are integrally formed by arranging the combustion unit 22 adjacent to the oxygen permeation membrane 23 of the oxygen separation unit 24, so that a compact oxygen permeation unit is formed. A combustor with a membrane 20 can be configured.

Further, in the fuel cell power generation system 10A of the present embodiment, since the heat of the air electrode off gas is used for cold heat generation in the exhaust heat input type absorption chiller 36, the first fuel cell cell stack 12 and the second fuel cell cell stack The exhaust heat from 14 can be effectively used. Further, since the air electrode off gas contains a large amount of water vapor, the heat of condensation can be effectively used by condensing the water vapor at the time of heat exchange in the exhaust heat input type absorption chiller 36.

In the present embodiment, carbon dioxide is separated from the combustion off-gas by condensing and removing the water vapor in the combustion off-gas with the condenser 26, but carbon dioxide is separated by other means, for example, a carbon dioxide separation membrane. Alternatively, carbon dioxide may be separated by a PSA device.

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

As shown in FIG. 5, the fuel cell power generation system 10B of the present embodiment includes a high-temperature oxygen production apparatus 50 and a combustor 52 in place of the combustor 20 with an oxygen permeable membrane of the first embodiment. The configurations other than the high temperature oxygen production apparatus 50 and the combustor 52 are the same as those in the first embodiment.

The downstream end of the branch air electrode off gas pipe P6-2 is connected to the inlet side of the high temperature oxygen production apparatus 50. The high temperature oxygen production device 50 is a device that separates oxygen from the air electrode off gas, and as an example, a PSA device that adsorbs and desorbs at a high temperature can be used. One end of the oxygen supply pipe PO is connected to the oxygen outlet side of the high temperature oxygen production apparatus 50. An exhaust pipe P13 is connected to the air electrode off gas outlet side after the oxygen of the high temperature oxygen production apparatus 50 is separated. The other end of the oxygen supply pipe PO is connected to the inlet side of the combustor 52. The exhaust pipe P13 is open to the outside of the fuel cell power generation system 10B.

The other end of the oxygen supply pipe PO described above and the downstream end of the second fuel pole off gas pipe P7-2 are connected to the inlet side of the combustor 52. Inside the combustor 52, the combustible gas components (unmodified methane, unreacted hydrogen, unreacted carbon monoxide, etc.) in the second fuel electrode off-gas and the oxygen supplied from the oxygen supply pipe PO A combustion reaction occurs, producing carbon dioxide and water vapor. A combustion off gas pipe P8 is connected to the outlet side of the combustor 52, and the combustion off gas is sent out from the combustor 52.

Next, the operation of the fuel cell power generation system 10B of the present embodiment will be described.

Also in this embodiment, power is generated by the first fuel cell stack 12 and the second fuel cell stack 14 as in the fuel cell power generation system 10A of the first embodiment. The second air electrode off gas sent out from the second air electrode 14B and branched to the branched air electrode off gas pipe P6-2 is supplied to the high temperature oxygen production apparatus 50. In the high temperature oxygen production apparatus 50, oxygen is separated from the second air electrode off gas, and the separated oxygen is supplied to the combustor 52 via the oxygen supply pipe PO. The air electrode off gas after the oxygen is separated is discharged to the outside from the exhaust pipe P13.

In the combustor 52, a combustion reaction occurs between the combustible gas components (unmodified methane, unreacted hydrogen, unreacted carbon monoxide, etc.) in the second fuel electrode off-gas and oxygen, and carbon dioxide and water vapor are generated. Will be generated. The combustion off gas is sent to the combustion off gas pipe P8, water is separated by the condenser 26 in the same manner as in the first embodiment, the separated water is recovered in the water tank 27, and the carbon dioxide rich gas is the carbon dioxide recovery tank. It is recovered to 28 or supplied to the carbon dioxide line.

Also in the present embodiment, in the combustor 52, carbon dioxide and water vapor are generated by the combustion reaction between the combustible gas contained in the second fuel electrode off gas and oxygen. Therefore, it is possible to recover a high concentration of carbon dioxide by reducing the combustible gas from the second fuel electrode off gas.

[Third Embodiment]
Next, a third embodiment of the present invention will be described. In the present 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 power generation system 10C of the present embodiment mainly includes the reformer 54, does not include the circulating gas pipe P3, and the piping flow path related to these configurations is the first embodiment. Is different. Other configurations are the same as those in the first embodiment.

As shown in FIG. 6, the fuel cell power generation system 10C includes a reformer 54. One end of the fuel gas pipe P1-1 is connected to the inlet side of the reformer 54. Further, one end of the water supply pipe P2-2 is connected to the inlet side of the reformer 54. The other end of the water supply pipe P2-2 is connected to the water tank 27. The water supply pipe P2-2 is provided with an ion exchange resin 56 and a pump 27B. By driving the pump 27B, the water stored in the water tank 27 is supplied to the reformer 54 via the ion exchange resin 56.

One end of the reforming gas pipe P1-2 is connected to the outlet side of the reformer 54. The other end of the reformed gas pipe P1-2 is connected to the first fuel pole 12A of the first fuel cell stack 12.

Next, the operation of the fuel cell power generation system 10C of the present embodiment will be described.

In the reformer 54, a mixed gas of fuel gas and steam is heated by heat exchange with combustion off gas, and hydrogen and carbon monoxide are produced by the steam reforming reaction. In addition, carbon dioxide and hydrogen are generated by a shift reaction between the generated carbon monoxide and water vapor. A reformed gas containing unreacted fuel gas (methane), hydrogen, carbon monoxide, and carbon dioxide is supplied to the first fuel electrode 12A through the reformed gas pipe P1-2. In the first fuel cell stack 12 and the second fuel cell stack 14, power generation is performed in the same manner as in the first embodiment.

From the second fuel pole 14A, the second fuel pole off gas is sent to the second fuel pole off gas pipe P7-2. The second fuel electrode off gas is supplied to the combustion section 22 of the combustor 20 with an oxygen permeable membrane without being branched. From the second air electrode 14B, the air electrode off gas is sent to the air electrode off gas pipe P6, and a part of the air electrode off gas is branched to the branched air electrode off gas pipe P6-2 as in the first embodiment. It merges with the air electrode off gas delivered from the first air electrode 12B.

In the combustor 20 with an oxygen permeable membrane and the condenser 26, the treatment is performed in the same manner as in the first embodiment, and the carbon dioxide rich gas is recovered in the carbon dioxide recovery tank 28 or supplied to the carbon dioxide line.

Also in this embodiment, in the combustor 20 with an oxygen permeable membrane, carbon dioxide and water vapor are generated by the combustion reaction between the combustible gas contained in the second fuel electrode off gas and oxygen. Therefore, it is possible to recover a high concentration of carbon dioxide by reducing the combustible gas from the second fuel electrode off gas.

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

The fuel cell power generation system 10D of the present embodiment includes the high temperature oxygen production apparatus 50 of the second embodiment and the combustor 52 in place of the combustor 20 with the oxygen permeable membrane of the third embodiment. The configurations other than the high temperature oxygen production apparatus 50 and the combustor 52 are the same as those in the third embodiment.

The downstream end of the branched air electrode off gas pipe P6-2 is connected to the inlet side of the high temperature oxygen production apparatus 50, and one end of the oxygen supply pipe PO is connected to the oxygen outlet side of the high temperature oxygen production apparatus 50. An exhaust pipe P13 is connected to the air electrode off gas outlet side after the oxygen of the high temperature oxygen production apparatus 50 is separated. The other end of the oxygen supply pipe PO is connected to the inlet side of the combustor 52. The exhaust pipe P13 is open to the outside of the fuel cell power generation system 10D.

The other end of the oxygen supply pipe PO described above and the downstream end of the second fuel pole off gas pipe P7-2 are connected to the inlet side of the combustor 52. Inside the combustor 52, the combustible gas components (unmodified methane, unreacted hydrogen, unreacted carbon monoxide, etc.) in the second fuel electrode off-gas and the oxygen supplied from the oxygen supply pipe PO A combustion reaction occurs, producing carbon dioxide and water vapor. A combustion off gas pipe P8 is connected to the outlet side of the combustor 52, and the combustion off gas is sent out from the combustor 52.

Next, the operation of the fuel cell power generation system 10D of the present embodiment will be described.

Also in the present embodiment, similarly to the fuel cell power generation system 10C of the third embodiment, the fuel gas is steam reformed by the reformer 54 to generate the reformed gas, and the first fuel cell stack 12 and the second Power is generated in the fuel cell stack 14. The second air electrode off gas sent out from the second air electrode 14B and branched to the branched air electrode off gas pipe P6-2 is supplied to the high temperature oxygen production apparatus 50. In the high temperature oxygen production apparatus 50, oxygen is separated from the second air electrode off gas, and the separated oxygen is supplied to the combustor 52 via the oxygen supply pipe PO. The air electrode off gas after the oxygen is separated is discharged to the outside from the exhaust pipe P13.

In the combustor 52, a combustion reaction occurs between the combustible gas components (unmodified methane, unreacted hydrogen, unreacted carbon monoxide, etc.) in the second fuel electrode off-gas and oxygen, and carbon dioxide and water vapor are generated. Will be generated. The combustion off gas is sent to the combustion off gas pipe P8, water is separated by the condenser 26 in the same manner as in the first embodiment, the separated water is recovered in the water tank 27, and the carbon dioxide rich gas is the carbon dioxide recovery tank. It is recovered to 28 or supplied to the carbon dioxide line.

Also in the present embodiment, in the combustor 52, carbon dioxide and water vapor are generated by the combustion reaction between the combustible gas contained in the second fuel electrode off gas and oxygen. Therefore, it is possible to recover a high concentration of carbon dioxide by reducing the combustible gas from the second fuel electrode off gas.

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

The fuel cell power generation system 10E of the present embodiment is different from the first embodiment in that a third heat exchanger 34 and a condenser 35 are provided in the path of the first fuel electrode off-gas pipe P7.

The first fuel pole off-gas pipe P7 extends from the first fuel pole 12A and is connected to the condenser 35 via the third heat exchanger 34. The first anode-off gas pipe P7 from the first fuel pole 12A to the condenser 35 is indicated by reference numeral P7A. The first fuel pole off gas pipe P7A extends from the gas side outlet of the condenser 35 and is connected to the second fuel pole 14A via the third heat exchanger 34. The first anode-off gas pipe P7 from the condenser 35 to the second fuel pole 14A is indicated by reference numeral P7B. One end of the water pipe P9-2 is connected to the liquid side outlet of the condenser 35. The other end of the water pipe P9-2 is connected to the water tank 27. A cooling water circulation flow path 35A is piped to the condenser 35, and the cooling water from the exhaust heat input type absorption chiller 36 is circulated and supplied by driving the pump 35P. As a result, the first fuel electrode off gas is cooled, and the water vapor in the first fuel electrode off gas is condensed. The condensed water is sent to the water tank 27 via the water pipe P9-2.

Next, the operation of the fuel cell power generation system 10E of the present embodiment will be described.

Also in this embodiment, power is generated by the first fuel cell stack 12 as in the fuel cell power generation system 10A of the first embodiment. The first fuel pole off gas sent from the first fuel pole 12A to the first fuel pole off gas pipe P7-1 is cooled by heat exchange with the regenerated fuel gas described later in the third heat exchanger 34 and supplied to the condenser 35. Will be done. In the condenser 35, the cooling water circulating in the cooling water circulation flow path 35A further cools the first fuel electrode off gas, and the water vapor in the first fuel electrode off gas is condensed. Here, the temperature of the cooling water circulating in the cooling water circulation flow path 35A is such that the amount of water vapor remaining in the regenerated fuel gas improves the power generation efficiency in the second fuel cell stack 14 and the water vapor in the first fuel electrode off gas. Is set to condense. The condensed water is sent to the water tank 27 via the water pipe P9-2.

The first fuel electrode off gas from which the condensed water is separated is sent to the first fuel electrode off gas pipe P7B as a regenerated fuel gas, and heat with the first fuel electrode off gas before the water is separated by the third heat exchanger 34. It is heated by exchange and supplied to the second fuel pole 14A. In the second fuel cell stack 14, power generation is performed in the same manner as in the fuel cell power generation system 10A of the first embodiment.

In the present embodiment, since the regenerated fuel gas generated by separating a part of water vapor from the first fuel electrode off gas is supplied to the second fuel electrode 14A, the power generation efficiency in the second fuel cell stack 14 is improved. Can be done.

Further, also in the present embodiment, carbon dioxide and water vapor are generated in the combustion unit 22 of the combustor 20 with an oxygen permeable membrane by the combustion reaction between the combustible gas contained in the second fuel electrode off gas and oxygen. Therefore, it is possible to recover a high concentration of carbon dioxide by reducing the combustible gas from the second fuel electrode off gas.

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

As shown in FIG. 9, in the fuel cell power generation system 10F of the present embodiment, the first fuel cell stack 62 and the second fuel cell stack 64 are the hydrogen ion conduction type solid oxide fuel cell of the first embodiment. Instead, an oxygen ion conduction type solid oxide fuel cell (SOFC) is used. Therefore, at the first fuel pole 62A (fuel pole) and the first air pole 62B (air pole), the reaction occurs as follows. The same applies to the second fuel pole 64A and the second air pole 64B.

In the first air electrode 62B, as shown in the following equation (5), oxygen and electrons in the oxidant gas react with each other to generate oxygen ions. The generated oxygen ions pass through the electrolyte layer 62C and reach the first fuel pole 62A of the first fuel cell stack 62.

(Air electrode reaction)
1 / 2O ₂ + 2e ⁻ → O ^2- … (5)

On the other hand, in the first fuel pole 62A of the first fuel cell stack 62, as shown in the following equations (6) and (7), oxygen ions passing through the electrolyte layer 62C are hydrogen and monoxide in the fuel gas. It reacts with carbon to produce water vapor, carbon dioxide and electrons. The electrons generated in the first fuel pole 62A move from the first fuel pole 62A to the first air pole 62B through an external circuit to generate electricity.

(Fuel electrode reaction)
H ₂ + O ^2- → H ₂ O + 2e ⁻ … (6)
CO + O ^2- → CO ₂ + 2e ⁻ … (7)

In the solid oxide fuel cell, since water vapor is generated at the first fuel pole 62A and the second fuel pole 64A, the first fuel pole off-gas and the first fuel pole off-gas are compared with those of the hydrogen ion conduction type solid oxide fuel cell. 2 Fuel pole Off gas contains a large amount of water vapor. On the other hand, water vapor is not generated in the first air pole 62B and the second air pole 64B. The air electrode off gas supplied to the exhaust heat input type absorption chiller 36 is exhausted from the exhaust pipe P36-1 after heat exchange.

In the fuel cell power generation system 10F of the present embodiment, other configurations are the same as those of the fifth embodiment, and the third heat exchanger 34 and the condenser 35 are provided in the path of the first fuel pole off gas pipe P7. ing. Here, since the amount of water vapor contained in the first fuel electrode off gas and the second fuel electrode off gas is larger than that of the fuel cell power generation system 10E, the amount of water vapor removed by condensation in the condenser 35 is increased. The temperature of the cooling water circulating in the cooling water circulation flow path 35A is set. The condensed water is sent to the water tank 27 via the water pipe P9-2.

In the present embodiment, since the regenerated fuel gas generated by separating a part of water vapor from the first fuel electrode off gas is supplied to the second fuel electrode 14A, the power generation efficiency in the second fuel cell stack 14 is improved. Can be done.

Further, also in the present embodiment, carbon dioxide and water vapor are generated in the combustion unit 22 of the combustor 20 with an oxygen permeable membrane by the combustion reaction between the combustible gas contained in the second fuel electrode off gas and oxygen. Therefore, it is possible to recover a high concentration of carbon dioxide by reducing the combustible gas from the second fuel electrode off gas.

[7th Embodiment]
Next, a seventh embodiment of the present invention will be described. In the present embodiment, the same parts as those in the first to sixth embodiments are designated by the same reference numerals, and detailed description thereof will be omitted.

As shown in FIG. 10, in the fuel cell power generation system 10G of the present embodiment, instead of the combustor 20 with an oxygen permeable membrane of the sixth embodiment, the high temperature oxygen production apparatus 50 and combustion similar to those of the second embodiment. It is equipped with a vessel 52. The configuration other than the high temperature oxygen production apparatus 50, the combustor 52, and the piping related thereto is the same as that of the sixth embodiment.

Also in the present embodiment, since the regenerated fuel gas generated by separating a part of water vapor from the first fuel electrode off gas is supplied to the second fuel electrode 14A, the power generation efficiency in the second fuel cell stack 14 is improved. be able to.

Further, also in the present embodiment, in the combustor 52, carbon dioxide and water vapor are generated by the combustion reaction between the combustible gas contained in the second fuel electrode off gas and oxygen. Therefore, it is possible to recover a high concentration of carbon dioxide by reducing the combustible gas from the second fuel electrode off gas.

[8th Embodiment]
Next, an eighth embodiment of the present invention will be described. In the present embodiment, the same parts as those in the first to seventh embodiments are designated by the same reference numerals, and detailed description thereof will be omitted.

As shown in FIG. 11, the fuel cell power generation system 10H of the present embodiment is provided with the reformer 54, is not provided with the circulating gas pipe P3, and is similar to the third embodiment. The piping flow path related to the configuration is different from that of the sixth embodiment. Other configurations are the same as those in the sixth embodiment.

Also in the present embodiment, since the regenerated fuel gas generated by separating a part of water vapor from the first fuel electrode off gas is supplied to the second fuel electrode 14A, the power generation efficiency in the second fuel cell stack 14 is improved. be able to.

Further, also in the present embodiment, carbon dioxide and water vapor are generated in the combustion unit 22 by the combustion reaction between the combustible gas contained in the second fuel electrode off gas and oxygen. Therefore, it is possible to recover a high concentration of carbon dioxide by reducing the combustible gas from the second fuel electrode off gas.

[9th Embodiment]
Next, a ninth embodiment of the present invention will be described. In the present embodiment, the same parts as those in the first to eighth embodiments are designated by the same reference numerals, and detailed description thereof will be omitted.

As shown in FIG. 11, in the fuel cell power generation system 10I of the present embodiment, the high temperature oxygen production apparatus 50 and the combustor 52 of the seventh embodiment are replaced with the combustor 20 with the oxygen permeable membrane of the eighth embodiment. It has. The configurations other than the high temperature oxygen production apparatus 50 and the combustor 52 are the same as those in the eighth embodiment.

Also in the present embodiment, since the regenerated fuel gas generated by separating a part of water vapor from the first fuel electrode off gas is supplied to the second fuel electrode 14A, the power generation efficiency in the second fuel cell stack 14 is improved. be able to.

Further, also in the present embodiment, in the combustor 52, carbon dioxide and water vapor are generated by the combustion reaction between the combustible gas contained in the second fuel electrode off gas and oxygen. Therefore, it is possible to recover a high concentration of carbon dioxide by reducing the combustible gas from the second fuel electrode off gas.

As the fuel cell of the present invention, other fuel cells such as molten carbonate fuel cell (MCFC), phosphoric acid fuel cell (PAFC), and polymer electrolyte fuel cell (PEFC) can also be used.

Further, the carbon dioxide supply line 29 may be connected to a carbon dioxide liquefaction device or a carbon separation device to produce liquid carbon dioxide, powdered carbon, or the like.

In the above-mentioned first to ninth embodiments, cold heat is generated by using the exhaust heat input type absorption chiller 36, but other exhaust heat is used instead of the exhaust heat input type absorption chiller 36. Cold heat may be generated using a heat pump, for example, an adsorption chiller.

Further, instead of the exhaust heat input type absorption chiller 36, the fuel cell power generation system 10J may use an electric turbo chiller 60 that generates cold heat by using electric power without utilizing exhaust heat. FIG. 13 shows, as an example, a configuration in which the exhaust heat input type absorption chiller 36 is replaced with an electric turbo chiller 60 in the fuel cell power generation system 10A of the first embodiment. The second to ninth embodiments can be replaced in the same manner. In the fuel cell power generation system 10J, the cathode off gas flow path P6 is exhausted to the outside of the system after heat exchange in the second heat exchanger 32. The electric turbo chiller 60 can be driven by the electric power generated by the fuel cell power generation system 10J. Since the electric turbo chiller 60 generally has high cooling efficiency, the fuel cell power generation system 10J can be operated with high efficiency even if the generated electric power is used. Also in this case, it is preferable to drive the electric turbo chiller 60 with a direct current in order to efficiently use the generated electric power without converting it into alternating current.

10A-10J Fuel cell power generation system (carbon dioxide recovery type fuel cell power generation system)
12, 62 1st fuel cell cell stack (1st fuel cell)
12A, 62A 1st fuel pole 12B, 62B 1st air pole 14,64 2nd fuel cell cell stack (2nd fuel cell)
14A, 64A 2nd fuel pole 14B, 64B 2nd air pole 20 Combustor with oxygen permeable membrane 22 Combustor, 22A Combustion space 23 Oxygen permeable membrane, 24 Oxygen separator 26 Condenser (carbon dioxide separator)
35 Condenser (fuel regeneration section)
50 High temperature oxygen production equipment (oxygen separator)
52 Combustor (combustor), 54 Reformer, 60 Electric turbo chiller P3 Circulation gas pipe (circulation flow path)
P6 Air electrode off gas pipe (air electrode off gas flow path)
P6-2 Branch air electrode off gas pipe (branch air electrode off gas flow path)
P7-2 Second fuel pole off gas pipe (fuel pole off gas flow path)

Claims (6)

A fuel gas containing a carbon compound and supplied to the first fuel electrode and an oxidant gas containing oxygen and supplied to the first air electrode generate power, and the first fuel electrode off gas is sent from the first fuel electrode. 1st fuel cell and
Power is generated by using the first fuel pole off gas supplied to the second fuel pole without removing carbon dioxide after being discharged from the first fuel cell and the oxidant gas supplied to the second air pole. A second fuel cell in which the second fuel electrode off gas is sent from the second fuel electrode to the fuel electrode off gas flow path, and
An air electrode off gas flow path that sends out air electrode off gas from at least one of the first air electrode and the second air electrode, and an air electrode off gas flow path.
An oxygen separator which is connected to a branched air electrode off gas flow path branched from the air electrode off gas flow path, the air electrode off gas is supplied from the branched air electrode off gas flow path, and oxygen is separated from the air electrode off gas flow path.
A combustion unit that is connected to the fuel electrode off gas flow path to supply the second fuel electrode off gas and oxygen separated by the oxygen separation unit to cause a combustion reaction of the second fuel electrode off gas with the oxygen. ,
A carbon dioxide separation unit that separates carbon dioxide-rich gas from the combustion off gas sent from the combustion unit,
Of the air electrode off gas branched from the air electrode off gas flow path to the branched air electrode off gas flow path so that the combustible gas concentration and the oxygen concentration in the carbon dioxide rich gas separated by the carbon dioxide separation unit are equal to or less than the threshold value. A control unit that controls the flow rate adjustment valve that adjusts the amount,
Carbon dioxide capture type fuel cell power generation system equipped with. The carbon dioxide recovery type fuel cell power generation system according to claim 1 , wherein the first fuel cell and the second fuel cell are hydrogen ion conduction type solid oxide fuel cells. The first fuel cell and the second fuel cell are oxygen ion conduction type solid oxide fuel cells, and separate water from the first fuel electrode off gas sent from the first fuel electrode to generate a regenerated fuel gas. The carbon dioxide recovery type fuel cell power generation system according to claim 1 , further comprising a fuel regeneration unit to generate, and supplying the regenerated fuel gas to the second fuel electrode. The carbon dioxide according to any one of claims 1 to 3 , further comprising a circulation flow path for supplying a part of the second fuel electrode off gas from the upstream side of the combustion unit to the first fuel electrode. Recovery type fuel cell power generation system. Any one of claims 1 to 4 , wherein the oxygen separation section has an oxygen permeable membrane that selectively permeates oxygen, and the combustion section has a combustion space arranged on the permeation side of the oxygen permeable membrane. The carbon dioxide recovery type fuel cell power generation system described in the section. An electric turbo chiller that is driven by electric power obtained by power generation in at least one of the first fuel cell and the second fuel cell to generate cold heat is provided.
The carbon dioxide separation unit according to any one of claims 1 to 5 , wherein the combustion off gas is cooled by the cold heat generated by the electric turbo chiller to condense the water vapor in the combustion off gas. Carbon dioxide recovery type fuel cell power generation system.

Images