JP2008204784A - Fuel cell power generation system, and fuel cell power generation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make recycle of fuel electrode exhaust gas unnecessary in a fuel cell power generation system having a solid oxide fuel cell or a molten carbonate fuel cell and make water self-sustainable. <P>SOLUTION: Mixture gas of fuel such as natural gas and steam or reformed gas produced by reforming the mixture gas is supplied to a fuel electrode 54 of the solid oxide fuel cell 57, and a steam separator 4 to which fuel electrode exhaust gas 61 exhausted from the fuel electrode 54 is supplied, selectively separating steam in the fuel electrode exhaust gas 61, and mixing the steam with fuel is installed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fuel cell power generation system and a fuel cell power generation method in which fuel and an oxidant are supplied to generate power in a fuel cell, and in particular, reforming fuel at a reformer and / or a fuel electrode of a fuel cell. The present invention relates to a fuel cell power generation system and a fuel cell power generation method for generating reformed gas and generating power in a fuel cell.

  2. Description of the Related Art A fuel cell power generation system that generates power by being supplied with fuel and an oxidant is configured by combining a fuel cell that generates power and various auxiliary devices that assist the operation of the fuel cell. Examples of the fuel supplied to the fuel cell power generation system include hydrogen, natural gas, and other hydrocarbons. Examples of the oxidant include air and oxygen.

  Hereinafter, a conventional fuel cell power generation system will be described by taking a fuel cell power generation system using a solid oxide fuel cell as a fuel cell as an example. A fuel cell power generation system using a solid oxide fuel cell is described in Non-Patent Document 1, for example.

The conventional fuel cell power generation system shown in FIG. 3 is supplied with natural gas 1 as a fuel and uses air 18 as an oxidant. The natural gas 1 generally contains methane (CH ₄ ) as a main component and contains propane (C ₃ H ₈ ) and butane (C ₄ H ₁₀ ) in addition to methane.

  In the fuel cell power generation system shown in FIG. 3, water vapor is mixed as a main component with a desulfurizer 2 that adsorbs and removes sulfur in the natural gas 1 and a desulfurized natural gas 29 obtained from the desulfurizer 2. The reformer 3 for performing a steam reforming reaction on the mixed gas 28 of steam and desulfurized natural gas, the solid oxide fuel cell 57, and the air supplied to the solid oxide fuel cell 57 are preheated. An air preheater 80, an air preheater burner 81 provided in the air preheater 80, and a power regulator 86 provided between the fuel cell DC output 88 of the solid oxide fuel cell 57 and the load 87. I have. The output terminal of the output adjustment device 86 is a power transmission terminal AC output 89. Further, the fuel cell power generation system includes an air blower 13 for supplying air 18 to an air preheater 80, a recycle blower 14 for recycling a reformer recycle fuel electrode exhaust gas 60, which will be described later, a flow control valve 37, 59, 62 and various pipes. The solid oxide fuel cell 57 includes a fuel electrode 54 to which the hydrogen-rich reformed gas 27 obtained from the reformer 3 is supplied, and a solid oxide fuel cell air 58 preheated by an air preheater 80. A supplied oxidant electrode 56 and a solid oxide electrolyte 55 sandwiched between the fuel electrode 54 and the oxidant electrode 56 are provided. The flow control valve 37 is for controlling the supply amount of the natural gas 1 to the desulfurizer 2. The flow control valve 62 is provided in the piping of the air 18 between the air blower 13 and the air preheater 80.

With the operation of the solid oxide fuel cell 57, the fuel electrode exhaust gas 61 is exhausted from the fuel electrode 54, and the oxidant electrode exhaust gas 63 is exhausted from the oxidant electrode 56. The fuel electrode exhaust gas 61 contains water vapor (H ₂ O) and carbon dioxide (CO ₂ ) as main components, and also contains hydrogen (H ₂ ), methane (CH ₄ ), and carbon monoxide (CO). A part of the fuel electrode exhaust gas 61 becomes a reformer recycle fuel electrode exhaust gas 60 through the recycle blower 14 and the flow rate control valve 59, and the reformer recycle fuel electrode exhaust gas 60 and the desulfurized natural gas 29. Are mixed to become a mixed gas 28 of water vapor and desulfurized natural gas. The remainder of the fuel electrode exhaust gas 61 is supplied to the air preheater burner 81 as an air preheater burner fuel electrode exhaust gas 64 that serves as fuel for the air preheater burner 81. The oxidant electrode exhaust gas 63 is also supplied to the air preheater burner 81, and the air preheater burner exhaust gas 84 is discharged from the air preheater burner 81.

  Hereinafter, the operation of this conventional fuel cell power generation system will be described with reference to FIG.

  The fuel natural gas 1 is supplied to a desulfurizer 2. The supply amount of the natural gas 1 is controlled based on a preset relationship between the battery current at the fuel cell DC output 88 and the opening of the flow control valve 37 (that is, the supply amount of the natural gas 1). By controlling the opening degree of the valve 37, a value corresponding to the battery current of the fuel cell DC output 88 is set.

  The desulfurizer 2 is added as an odorant to the natural gas 1 which causes deterioration of the reforming catalyst of the reformer 3 and also causes deterioration of the electrode catalyst at the fuel electrode 54 of the solid oxide fuel cell 57. Sulfur content such as mercaptans is removed by adsorption. The desulfurized natural gas 29 desulfurized in the desulfurizer 2 is mixed with the reformer recycling fuel electrode exhaust gas 60 containing water vapor generated by the cell reaction in the solid oxide fuel cell 57, and then the water vapor and the desulfurized natural gas are mixed. The mixed gas 28 is supplied to the reformer 3. The supply amount of the reformer recycle fuel electrode exhaust gas 60 includes the opening degree of the flow control valve 37 (ie, the supply amount of natural gas 1) and the opening degree of the flow control valve 59 (ie, the reformer recycle fuel electrode exhaust gas). 60), by controlling the opening degree of the flow rate control valve 59, a predetermined steam carbon ratio (in accordance with the supply amount of the natural gas 1) ( steam-to-carbon ratio).

  In the reformer 3, a steam reforming reaction of hydrocarbons contained in the natural gas 1 is performed by the action of a reforming catalyst such as a nickel-based catalyst or a ruthenium-based catalyst filled therein, and a hydrogen-rich reformed gas 27 is created. The steam reforming reaction of methane, which is the main component of natural gas 1, is expressed by equation (1).

(Methane steam reforming reaction)
CH ₄ + H ₂ O → CO + 3H ₂ (1)
The hydrocarbon steam reforming reaction such as the methane steam reforming reaction shown in the equation (1) is an endothermic reaction. Therefore, in order to generate hydrogen efficiently, the necessary reaction heat is supplied to the reformer 3. However, the temperature of the reformer 3 must be maintained at 700 to 750 ° C. For this reason, a solid oxide fuel cell 57 (described later) that generates power at 800 to 1000 ° C. is installed in the vicinity of the reformer 3, and exhaust heat from the solid oxide fuel cell 57 is converted to hydrocarbon steam reforming. It is supplied to the reformer 3 as reaction heat necessary for the quality reaction.

  The hydrogen-rich reformed gas 27 produced by the reformer 3 is supplied to the fuel electrode 54 of the solid oxide fuel cell 57. The hydrogen-rich reformed gas 27 contains unreacted methane, water vapor, and carbon dioxide in addition to carbon monoxide and hydrogen. On the other hand, air is supplied as an oxidant to the oxidant electrode 56 of the solid oxide fuel cell 57. That is, the temperature of the air 18 taken in using the air blower 13 is raised by an air preheater 80 to be described later, and supplied to the oxidant electrode 56 as solid oxide fuel cell air 58. The supply amount of the solid oxide fuel cell air 58 includes the opening degree of the flow control valve 37 (ie, the supply amount of natural gas 1) and the opening degree of the flow control valve 62 (ie, the solid oxide fuel cell air 58). By controlling the opening degree of the flow rate control valve 62 based on a preset relationship with respect to the supply amount), a value corresponding to the supply amount of the natural gas 1 is set.

  Next, details of the operation of the solid oxide fuel cell 57 will be described. In FIG. 3, the solid oxide fuel cell 57 is depicted as a single cell comprising a fuel electrode 54, a solid oxide electrolyte 55, and an oxidant electrode 56, but the generated voltage of the single cell is as low as 1V or less. In order to extract predetermined electric power, a cell stack is actually constructed by combining a plurality of single cells, and the solid oxide fuel cell 57 is composed of this cell stack.

In the oxidant electrode 56 of the solid oxide fuel cell 57, oxygen in the solid oxide fuel cell air 58 is converted into electrons by the oxidant electrode reaction shown in the equation (2) by the action of the metal oxide electrode catalyst. Reacts with oxide ions (O ²⁻ ).

(Oxidant electrode reaction)
^{_{1 / 2O 2 + 2e - →}} O 2- (2)
The oxide ions generated at the oxidizer electrode 56 move inside the solid oxide electrolyte 55 made of yttria-stabilized zirconia (YSZ) or the like and reach the fuel electrode 54. In the fuel electrode 54, oxide ions that have moved from the oxidizer electrode 56 to the fuel electrode 54 inside the solid oxide electrolyte 55 by the action of a metal-based electrode catalyst such as nickel-YSZ cermet, ruthenium-YSZ cermet, By the fuel electrode reaction shown in the equations (3) and (4), it reacts with hydrogen and carbon monoxide in the hydrogen-rich reformed gas 27 supplied to the fuel electrode 54 to generate water vapor or carbon dioxide and electrons.

(Fuel electrode reaction)
H ₂ + O ²⁻ → H ₂ O + 2e ⁻ (3)
_{^{CO + O 2- → CO 2 +}} 2e - (4)
Electrons generated at the fuel electrode 54 travel through an external circuit and reach the oxidant electrode 56. The electrons that have reached the oxidant electrode 56 react with oxygen by the oxidant electrode reaction shown in the above formula (2). In the process in which the electrons move through the external circuit, electric energy can be taken out from the solid oxide fuel cell 57 as the fuel cell DC output 88.

  Summarizing formulas (2) and (3), and formulas (2) and (4), the cell reaction of the solid oxide fuel cell 57 generates water vapor from hydrogen and oxygen shown in formula (5). It can be expressed as a reverse reaction of water electrolysis and a reaction in which carbon dioxide is generated from carbon monoxide and oxygen shown in the formula (6).

(Battery reaction)
H ₂ + 1 / 2O ₂ → H ₂ O (5)
CO + 1 / 2O ₂ → CO ₂ (6)
The fuel cell direct current output 88 obtained by the power generation of the solid oxide fuel cell 57 is subjected to voltage conversion and direct current to alternating current conversion in accordance with the load 87 in the output adjusting device 86, and then to the power transmission end alternating current. The output 89 is supplied to the load 87. In the example of FIG. 3, the output adjustment device 86 performs conversion from direct current to alternating current. However, the output adjustment device 86 performs only voltage conversion and supplies the power transmission end DC output to the load 87. Good.

  The power generation temperature of the solid oxide fuel cell 57 is generally 800 to 1000 ° C., and the solid oxide fuel cell 57 is maintained at the power generation temperature by heat generated by the cell reaction. Therefore, the exhaust heat of the solid oxide fuel cell 57 can be used as the reaction heat of the hydrocarbon steam reforming reaction in the reformer 3. In fact, in the conventional solid oxide fuel cell power generation system, the amount of heat generated by the cell reaction in the solid oxide fuel cell 57 is large and exceeds the level necessary for maintaining the power generation temperature. In order to maintain the temperature of the fuel cell 57 at the power generation temperature, a large amount of air 58 for the solid oxide fuel cell 57 is supplied to the oxidant electrode 56 of the solid oxide fuel cell 57 and the solid oxide fuel cell 57 is supplied. The cooling is done. With respect to the air 58 for the solid oxide fuel cell, the oxygen utilization rate at the oxidizer electrode 56 is about 20%.

  As described above, a part of the fuel electrode exhaust gas 61 containing water vapor generated by the cell reaction at the fuel electrode 54 supplies steam necessary for the steam reforming reaction of hydrocarbons in the reformer 3, It is recycled as the fuel electrode exhaust gas 60 for reformer recycling and mixed with the desulfurized natural gas 29. At that time, in a small solid oxide fuel cell having a power generation output of 10 kW or less, the supply amount of the fuel electrode exhaust gas 60 for reformer recycling is small, and therefore, from the fuel electrode 54 as shown in FIG. A recycle blower 14 is provided in the recycle path to the reformer 3, and the reformer recycle fuel electrode exhaust gas 60 is recycled using the recycle blower 14 and mixed with the desulfurized natural gas 29.

  The air preheater burner fuel electrode exhaust gas 64 and the oxidant electrode exhaust gas 63 are supplied to the air preheater burner 81, and the unreacted fuel, unreacted hydrogen, and unreacted fuel in the air preheater burner fuel electrode exhaust gas 64 are supplied. The reactive carbon monoxide is combusted with unreacted oxygen in the oxidant electrode exhaust gas 63. Heat generated by the combustion is exchanged to raise the temperature of the air 18. The combustion reaction of hydrogen and carbon monoxide in the air preheater burner 81 is shown in equations (7) and (8).

(Hydrogen combustion reaction)
H ₂ + 1 / 2O ₂ → H ₂ O (7)
(Combustion reaction of carbon monoxide)
CO + 1/2 O ₂ → CO ₂ (8)
The air 18 heated by the air preheater 80 is supplied to the solid oxide fuel cell 57 as solid oxide fuel cell air 58 and used for power generation of the solid oxide fuel cell 57. The air preheater burner 81 discharges the air preheater burner exhaust gas 84 generated by burning the fuel electrode exhaust gas 64 for the air preheater burner and the oxidant electrode exhaust gas 63.

  Next, problems of the conventional fuel cell power generation system shown in FIG. 3 will be described.

In the conventional fuel cell power generation system shown in FIG. 3, as described above, in the case of the solid oxide fuel cell 57 with an output of 10 kW or less and a small supply amount of the reformer recycle fuel electrode exhaust gas 60. As shown in FIG. 3, the recycle blower 14 is provided, and the recycle blower 14 is used to recycle the reformer recycle fuel electrode exhaust gas 60 and mix it with the desulfurized natural gas 29. The steam necessary for steam reforming of the natural gas 1 is supplied. In this case, the reformer recycle fuel electrode exhaust gas 60 is at a high temperature of 500 ° C. or higher. Therefore, the recycle of the reformer recycle fuel electrode exhaust gas 60 is expensive, has a short life, and is reliable. It is necessary to provide a low-temperature recycle blower 14 for high-temperature gas, which reduces the reliability of the fuel cell power generation system and raises the system cost and the maintenance cost. Further, it is necessary to accurately control the recycle amount, that is, the supply amount, of the reformer recycle fuel electrode exhaust gas 60 by adjusting the opening of the flow control valve 59 according to the supply amount of the natural gas 1 of the fuel. There is a problem that the control of the fuel cell power generation system becomes complicated.
The Institute of Electrical Engineers, Fuel Cell Power Generation Next Generation System Technology Research Special Edition: “Fuel Cell Technology”, Ohm, pp. 203-208 (2002)

  The object of the present invention is that there is no need to recycle the anode discharge gas of the fuel cell, and water self-sustainment is possible, thereby eliminating the need to install a recycle blower and control the amount of anode electrode exhaust gas recycled. An object of the present invention is to provide an inexpensive and highly reliable fuel cell power generation system and fuel cell power generation method.

  The fuel cell power generation system of the present invention is a fuel cell power generation system in which fuel and an oxidant are supplied to generate power in the fuel cell, and is generated by reforming a mixed gas of fuel and water vapor or a mixed gas A fuel cell having a fuel electrode to which reformed gas is supplied and an electrolyte that permeates anions, and fuel electrode exhaust gas discharged from the fuel electrode are supplied to selectively separate water vapor in the fuel electrode exhaust gas. And a water vapor separation means for mixing with the fuel.

  Alternatively, the fuel cell power generation system of the present invention is a fuel cell power generation system in which fuel and an oxidant are supplied to generate power in the fuel cell, and is generated by reforming a mixed gas of fuel and water vapor or a mixed gas. A fuel cell comprising a fuel electrode supplied with a reformed gas and an electrolyte that permeates anions, a fuel electrode exhaust gas discharged from the oxidizer electrode and / or a fuel electrode exhaust gas discharged from the fuel electrode and / or Burner for burning with an oxidant, and steam separation means for supplying burner combustion exhaust gas discharged from the burner and selectively separating water vapor in the burner combustion exhaust gas and mixing it with fuel.

  In each of the fuel cell power generation systems described above, it is possible to use a water vapor separation means that uses a hydrocarbon gas as a fuel and has a porous thin film having pores of a size that allows water vapor to permeate selectively.

  Alternatively, the fuel cell power generation system of the present invention includes a reformer that reacts hydrocarbon gas and water vapor to generate carbon monoxide and hydrogen, and an oxidant electrode that reacts oxygen and electrons to generate oxide ions. The solid oxide electrolyte that passes the oxide ions and the reformed gas from the reformer are supplied to react hydrogen and oxide ions to produce water and electrons, and carbon monoxide and oxide ions And a fuel electrode that generates carbon dioxide and electrons by reacting with each other, and a water vapor separator that separates water vapor from a gas discharged from the fuel electrode, separated by the water vapor separator Water vapor is supplied to the reformer, and the water vapor separator has a porous thin film having pores having a size that allows water vapor to permeate selectively.

  The fuel cell power generation method of the present invention is a fuel cell power generation method in which fuel and an oxidant are supplied to generate power in the fuel cell, and the fuel and water vapor are provided at the fuel electrode of the fuel cell including an electrolyte that transmits anions. A gas generation process in which a mixed gas or a reformed gas generated by reforming the mixed gas is supplied to generate power, and water vapor is selectively separated from the fuel electrode exhaust gas discharged from the fuel electrode. And a water vapor separation step to be mixed.

  Alternatively, the fuel cell power generation method of the present invention is a fuel cell power generation method in which fuel and an oxidant are supplied to generate power in the fuel cell, and the fuel electrode of the fuel cell including an electrolyte that allows permeation of anions to the fuel electrode. A power generation process for generating power by supplying a mixed gas of water vapor or a reformed gas generated by reforming the mixed gas, and a fuel discharged from the oxidizer electrode by the fuel electrode exhaust gas discharged from the fuel electrode A combustion step of burning with the polar exhaust gas and / or oxidant, and a water vapor separation step of selectively separating the water vapor in the exhaust gas from the combustion step and mixing with the fuel.

  Alternatively, the fuel cell power generation method of the present invention comprises a reforming step for reacting a hydrocarbon gas with water vapor to generate carbon monoxide and hydrogen, and an electrolyte that allows the oxide ions to permeate. In a fuel cell to which a gas is supplied, oxygen and electrons are reacted to generate oxide ions, hydrogen and oxide ions in the reformed gas are reacted to generate water and electrons, and the reformed gas Carbon monoxide and oxide ions react to produce carbon dioxide and electrons, and a porous thin film consisting of pores of a size that allows water vapor to permeate selectively. A water vapor separation step of separating water vapor from the discharged gas, and a step of supplying the water vapor separated in the water vapor separation step to the reforming step.

  According to the present invention, it is unnecessary to recycle the fuel electrode exhaust gas to the reformer or the fuel electrode, which is a fuel reforming means, and it is expensive, has a short life, and has low reliability for recycling the fuel electrode exhaust gas. Since it is not necessary to provide a gas recycle blower, an inexpensive and highly reliable fuel cell power generation system can be realized. Further, according to the present invention, water self-sustainability is possible, that is, after power generation starts, power generation can be continued without external water supply, and fuel electrode exhaust gas is recycled to the reformer or the fuel electrode. Since there is no need to control the recycle amount, that is, the supply amount, the control of the fuel cell power generation system can be simplified.

  Next, a preferred embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 shows a configuration of a fuel cell power generation system according to a first embodiment of the present invention. In FIG. 1, the same reference numerals are given to the same components as those in FIG. 3, and duplicate descriptions are omitted.

  The fuel cell power generation system shown in FIG. 1 is different from the fuel cell power generation system shown in FIG. 3 in that a steam separator 4 is provided instead of recycling a part of the fuel electrode exhaust gas 61 using a recycle blower. The exhaust gas 61 is supplied to the water vapor separator 4, the water vapor in the fuel electrode exhaust gas 61 is selectively separated by the water vapor separator 4, and the desulfurized natural gas 29 that is also supplied to the water vapor separator 4 A mixed gas 28 of steam and desulfurized natural gas is produced by mixing. The water vapor separator 4 includes a water vapor separation membrane, an ion exchange resin that selectively permeates water vapor, and the like. The fuel electrode exhaust gas 61 from which the water vapor has been separated in the water vapor separator 4 is supplied to the air preheater burner 81 as the water vapor separator exhaust gas 5. The air preheater burner 81 is supplied with air preheater burner air 83 from the air blower 13 via the flow control valve 85. Therefore, the fuel cell power generation system shown in FIG. 1 is a fuel cell that generates power by supplying a desulfurizer 2, a reformer 3 as fuel reforming means, and fuel and an oxidant as main components. A solid oxide fuel cell 57, an air preheater 80, an air preheater burner 81, a water vapor separator 4 which is a water vapor separating means, an output adjusting device 88, flow control valves 37, 62, 85, an air blower 13 and piping. I have.

  Next, the operation of this fuel cell power generation system will be described.

  The fuel electrode exhaust gas 61 discharged from the fuel electrode 54 of the solid oxide fuel cell 57 contains a large amount of water vapor generated by the cell reaction in the solid oxide fuel cell 57. By separating the water vapor in the fuel electrode exhaust gas 61 and supplying it to the desulfurized natural gas 29 in the reactor 4, the water vapor necessary for the steam reforming reaction of the natural gas 1 in the reformer 3 as the fuel reforming means is obtained. I can cover enough. The fuel electrode exhaust gas 61 from which the water vapor has been separated in the water vapor separator 4 is supplied to the air preheater burner 81 as the water vapor separator exhaust gas 5, and the oxidant electrode exhaust gas 63 supplied to the air preheater burner 81 and It is made to burn with air preheater burner air 83 which is / or an oxidizing agent. When the steam separator exhaust gas 5 is combusted with the air preheater burner air 83 in the air preheater burner 81, the flow rate control valve 85 is used to change the air preheater burner air 83 to the air preheater burner 81. Control the supply amount.

  Note that hydrogen contained in the fuel electrode exhaust gas 61 together with the water vapor may be mixed with the water vapor through the water vapor separator 4 into the desulfurized natural gas 29. Even if such hydrogen is mixed, the present embodiment is implemented. The operation of the fuel cell power generation system of the embodiment is not affected. In the fuel cell power generation system of this embodiment, steam is supplied from the outside using a small steam generator only at the time of startup. Once the solid oxide fuel cell 57 starts power generation, water vapor is generated by the cell reaction, so that it is not necessary to supply water vapor from the outside.

  Although not shown in FIG. 1, in order to promote the separation of water vapor in the fuel electrode exhaust gas 61 in the water vapor separator 4, the fuel electrode exhaust gas 61 is pressurized using pressurizing means such as a compressor. You may supply to the water vapor separator 4 later.

  FIG. 2 shows a fuel cell power generation system according to a second embodiment of the present invention. In FIG. 2, the same reference numerals are given to the same components as those in FIG. 3, and duplicate descriptions are omitted.

  The fuel cell power generation system shown in FIG. 2 is different from the fuel cell power generation system shown in FIG. 3 in that a steam separator 4 is provided in place of recycling a part of the fuel electrode exhaust gas 61 using a recycle blower. Steam separation is performed on the air preheater burner combustion exhaust gas 84 generated by burning the exhaust gas 61, the oxidant electrode exhaust gas 63 and / or the air preheater burner air 83 which is an oxidant in the air preheater burner 81. The water vapor in the air preheater burner combustion exhaust gas 84 is selectively separated by the water vapor separator 4, and the separated water vapor is mixed with the desulfurized natural gas 29 supplied to the water vapor separator 4. A mixed gas 28 of steam and desulfurized natural gas is generated. As in the case of the first embodiment, the water vapor separator 4 includes a water vapor separation membrane, an ion exchange resin that selectively permeates water vapor, and the air preheater burner air 83 is supplied from the air blower 13. It is supplied to the air preheater burner 81 via the flow rate control valve 85. The air preheater burner combustion exhaust gas 84 from which the water vapor has been separated in the water vapor separator 4 is discharged from the water vapor separator 4 as the water vapor separator exhaust gas 5. Therefore, the fuel cell power generation system shown in FIG. 2 includes a desulfurizer 2, a reformer 3 that is a fuel reforming unit, and a fuel cell that generates power by supplying fuel and an oxidant as main components. An oxide fuel cell 57, an air preheater 80, an air preheater burner 81, a water vapor separator 4 as a water vapor separation means, an output adjusting device 88, flow rate control valves 37, 62, 85, an air blower 13 and piping are provided. ing.

  Next, the operation of this fuel cell power generation system will be described.

  The air preheater burner combustion exhaust gas 84 contains a large amount of water vapor generated by the cell reaction in the solid oxide fuel cell 57 and the combustion reaction in the air preheater 80. By separating the steam in the air preheater burner combustion exhaust gas 84 and supplying it to the desulfurized natural gas 29, the steam necessary for the steam reforming reaction of the natural gas 1 in the reformer 3 as fuel reforming means is obtained. I can cover enough. When the air preheater burner combustion exhaust gas 84 is combusted with the air preheater burner air 83 in the air preheater burner 81, the air preheater burner air to the air preheater burner 81 is used by using the flow control valve 85. The supply amount of 83 is controlled.

  Although not shown in FIG. 2, in order to promote the separation of water vapor in the air preheater burner combustion exhaust gas 84 in the water vapor separator 4, an air preheater is used using a pressurizing means such as a compressor. The pressure of the combustion exhaust gas 84 may be increased and then supplied to the steam separator 4.

  Next, the mixing of water vapor and desulfurized natural gas 29 separated in the water vapor separator 4 which is the water vapor separation means in the present invention will be described.

  The mixing ratio of water vapor and desulfurized natural gas 29 is generally represented by a steam carbon ratio. As is well known to those skilled in the art, the steam carbon ratio is a molar ratio between water vapor molecules and carbon atoms contained in a natural gas composed of hydrocarbons such as methane, ethane, propane, and butane. Here, when the steam carbon ratio is low, there is a risk that carbon is deposited in the reformer or the like. In addition, the preferred steam carbon ratio depends on the catalyst used, and when using a ruthenium-based catalyst in which carbon is difficult to precipitate, the steam carbon ratio is reduced compared to the case of using a nickel-based catalyst in which carbon is likely to precipitate. be able to. However, it will be described below that hydrogen cannot be efficiently generated by reforming unless the steam carbon ratio is larger than the theoretical amount of 2.

  Assuming that the hydrocarbon gas is methane, let us consider the hydrogen generation process by the following steam reforming reaction of methane and carbon monoxide shift reaction.

(Methane steam reforming reaction)
CH ₄ + H ₂ O → CO + 3H ₂
(Carbon monoxide shift reaction)
CO + H ₂ O → CO ₂ + H ₂
Thus, when supplying the theoretical amount of water vapor necessary for generating hydrogen from methane, 1 mol of methane (carbon atoms) and 2 mol of water (ie, water vapor) are required. It can be seen that it must be 2 or more. In the first and second embodiments, it is necessary to mix the water vapor and the desulfurized natural gas 29 so that the steam carbon ratio is 2 or more. Furthermore, considering that the steam carbon ratio depends on the composition of natural gas, the concentration distribution of water vapor, and the like, in each of the above embodiments, the steam carbon ratio is preferably 2.5 to 3.5. Such a mixing ratio can be adjusted by increasing or decreasing the area of the water vapor separation membrane in the water vapor separator 4.

Next, the water vapor separator 4 which is the water vapor separation means in the present invention will be described. In the fuel cell power generation systems of the first and second embodiments described above, the water vapor separator 4 having a water vapor separation membrane can be preferably used. As the water vapor separation membrane, the fuel electrode exhaust gas 61 or the air preheater combustion exhaust gas is used. Since the temperature of 84 is a relatively high temperature of 200 ° C. or higher, it is preferably made of a ceramic material that can withstand these temperatures. In particular, alumina (Al ₂ O ₃ ), silica (SiO ₂ ), or zirconia (ZrO ₂ ) is suitable as a material for the water vapor separation membrane because of its high corrosion resistance and chemical stability. It is also possible to use these ceramics in combination. The water vapor separation membrane can be obtained by making the ceramics into a porous thin film having fine pores. Although the water vapor separation mechanism of the water vapor separation membrane is not particularly limited, it is considered that the surface diffusion in the pores or the capillary condensation mechanism is dominant because the water vapor is condensable. Therefore, in order to make this separation mechanism work effectively, the average pore diameter of the water vapor separation membrane is preferably 10 nm or less, more preferably 5 nm or less. As a method for obtaining such a water vapor separation membrane, a method of applying a ceramic sol of the type described above to the surface of the porous support is simple and preferable for obtaining a good porous thin film. In addition, a good water vapor separation membrane can also be obtained by using a method such as CVD, PVD, or sputtering.

  In such a water vapor separator 4, the flow path through which the fuel electrode exhaust gas 61 or the air preheater combustion exhaust gas 84 flows and the flow path through which the desulfurized natural gas 29 flows are disposed across the water vapor separation membrane, The water vapor contained in the fuel electrode exhaust gas 61 or the air preheater combustion exhaust gas 84 moves to the flow path side of the desulfurized natural gas 29 in the water vapor separation membrane, and as a result, the desulfurized natural gas 29 contains water vapor.

  In the present invention, a water vapor permeable ion exchange resin can be used in the water vapor separator 4 which is a water vapor separation means. As such an ion exchange resin, for example, a resin such as a polyester polyether nonporous resin can be used.

  In the fuel cell power generation systems of the first and second embodiments shown in FIGS. 1 and 2, respectively, the reformer 3 reforms the natural gas 1 as the fuel, and the solid oxide fuel cell 57 is obtained. Hydrogen and carbon monoxide necessary for the cell reaction of the present are generated, and the hydrogen-rich reformed gas 27 is supplied to the fuel electrode 54 of the solid oxide fuel cell 57 to generate power in the solid oxide fuel cell 57. However, the reforming of the natural gas 1 as the fuel is performed directly at the fuel electrode 54 of the solid oxide fuel cell 57 without using the reformer 3, and is necessary for the cell reaction of the solid oxide fuel cell 57. Hydrogen and carbon monoxide may be generated and the solid oxide fuel cell 57 may generate power. In that case, the mixed gas 28 of water vapor and desulfurized natural gas is directly supplied to the fuel electrode 54 of the solid oxide fuel cell 57. Further, in the fuel cell power generation system of these embodiments, the solid oxide fuel cell 57 is used as the fuel cell, but a molten carbonate fuel cell may be used instead of the solid oxide fuel cell 57.

  The present invention is not limited to the above-described embodiment, and various modifications are of course added without departing from the spirit of the present invention.

It is a figure which shows the structure of the fuel cell power generation system of the 1st Embodiment of this invention. It is a figure which shows the structure of the fuel cell power generation system of the 2nd Embodiment of this invention. It is a figure which shows the structure of the conventional fuel cell power generation system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Natural gas 2 Desulfurizer 3 Reformer 4 Steam separator 5 Steam separator exhaust gas 13 Air blower 14 Recycle blower 18 Air 27 Hydrogen rich reformed gas 28 Mixed gas of steam and desulfurized natural gas 29 Desulfurized natural gas 37, 59, 62, 85 Flow control valve 54 Fuel electrode 55 Solid oxide electrolyte 56 Oxidant electrode 57 Solid oxide fuel cell 58 Air for solid oxide fuel cell 60 Fuel electrode exhaust gas for reformer recycling 61 Fuel electrode discharge Gas 63 Oxidant electrode exhaust gas 64 Fuel electrode exhaust gas for air preheater burner 80 Air preheater 81 Air preheater burner 83 Air preheater burner air 84 Air preheater burner combustion exhaust gas 86 Output regulator 87 Load 88 Fuel cell DC output 89 Transmission end AC output

Claims (7)

A fuel cell power generation system in which fuel and an oxidant are supplied to generate power in a fuel cell,
A fuel cell comprising a fuel electrode supplied with a mixed gas of the fuel and water vapor, or a reformed gas generated by reforming the mixed gas, and an electrolyte that transmits anions;
A water vapor separation means for supplying a fuel electrode exhaust gas discharged from the fuel electrode, selectively separating water vapor in the fuel electrode exhaust gas and mixing it with the fuel;
A fuel cell power generation system. A fuel cell power generation system in which fuel and an oxidant are supplied to generate power in a fuel cell,
A fuel cell comprising a fuel electrode supplied with a mixed gas of the fuel and water vapor, or a reformed gas generated by reforming the mixed gas, and an electrolyte that transmits anions;
A burner that combusts fuel electrode exhaust gas discharged from the fuel electrode with fuel electrode exhaust gas discharged from the oxidant electrode and / or the oxidant;
A steam separation means for supplying burner combustion exhaust gas discharged from the burner, selectively separating water vapor in the burner combustion exhaust gas and mixing it with the fuel;
A fuel cell power generation system.   3. The fuel cell power generation system according to claim 1, wherein the fuel is made of a hydrocarbon gas, and the water vapor separation means has a porous thin film made of pores having a size to selectively permeate water vapor. , Fuel cell power generation system. A reformer that reacts hydrocarbon gas with water vapor to produce carbon monoxide and hydrogen;
An oxidant electrode that generates oxide ions by reacting oxygen and electrons, a solid oxide electrolyte that passes the oxide ions, and a reformed gas from the reformer are supplied to supply the hydrogen and the oxide. A fuel cell comprising: a fuel electrode that reacts with ions to produce water and electrons, and reacts the carbon monoxide and the oxide ions to produce carbon dioxide and electrons;
A water vapor separator that separates water vapor from the gas discharged from the fuel electrode;
And the water vapor separated by the water vapor separator is supplied to the reformer, and the water vapor separator has a porous thin film having pores of a size that selectively allows water vapor to permeate. Power generation system. A fuel cell power generation method in which fuel and an oxidant are supplied to generate power in a fuel cell,
A power generation step of generating power by supplying a fuel gas of the fuel cell having an electrolyte that transmits anions to the fuel electrode and a reformed gas generated by reforming the mixed gas or the mixed gas; ,
A water vapor separation step of selectively separating water vapor from the fuel electrode exhaust gas discharged from the fuel electrode and mixing it with the fuel;
A fuel cell power generation method. A fuel cell power generation method in which fuel and an oxidant are supplied to generate power in a fuel cell,
A power generation step of generating power by supplying a fuel gas of the fuel cell having an electrolyte that transmits anions to the fuel electrode and a reformed gas generated by reforming the mixed gas or the mixed gas; ,
A combustion step of burning the fuel electrode exhaust gas discharged from the fuel electrode with the fuel electrode exhaust gas discharged from the oxidant electrode and / or the oxidant;
A water vapor separation step of selectively separating water vapor in the exhaust gas from the combustion step and mixing it with the fuel;
A fuel cell power generation method. A reforming process in which hydrocarbon gas and water vapor are reacted to generate carbon monoxide and hydrogen;
In a fuel cell having an electrolyte that allows oxide ions to pass therethrough and supplied with reformed gas from the reformer, oxygen and electrons are reacted to generate oxide ions, and hydrogen in the reformed gas and Reacting the oxide ions to produce water and electrons, and reacting the carbon monoxide and the oxide ions in the reformed gas to produce carbon dioxide and electrons;
A water vapor separation step for separating water vapor from the gas discharged from the fuel electrode, using a porous thin film having pores of a size that allows water vapor to selectively permeate;
Supplying the steam separated in the steam separation step to the reforming step;
A fuel cell power generation method.

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