JP2016100137A - Fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell system which can acquire high power generation efficiency.SOLUTION: In a fuel cell system, a plurality of fuel cells is disposed along a supply direction of fuel, the fuel cells including an electrolyte, a fuel electrode, and air electrode. At least the electrolyte of the fuel cell located at the most upstream side includes a proton conductive electrolyte.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a fuel cell system.

  In recent years, attention has been focused on fuel cell power generation systems as new energy sources. There are various types of fuel cells provided in the fuel cell power generation system. Among them, a solid oxide fuel cell (SOFC) using a solid oxide as an electrolyte has the highest power generation efficiency. It is known to be a fuel cell and promising.

As the SOFC, a fuel cell stack including a plurality of unit cells each including an oxygen ion conductive electrolyte, a fuel electrode, and an air electrode is used. In a power generation method using SOFC, for example, hydrogen (H ₂ ) generated by supplying steam to methane (CH ₄ ) and steam serving as fuel to a reformer outside the SOFC and performing steam reforming is used as an air electrode. The oxygen in the air introduced into the gas dissociates at the interface with the electrolyte (O ²⁻ ) and generates an electrochemical reaction at the interface between the electrolyte and the fuel electrode. Water is generated by this electrochemical reaction, and electricity is generated by the electrons emitted at that time. In the power generation method using SOFC, the chemical energy of the fuel is directly converted into electric energy, so that energy conversion loss is small and highly efficient power generation is possible.

In addition, the SOFC includes not only a fuel cell system using an oxygen ion conductive electrolyte in which oxide ions (O ²⁻ ) move from the air electrode side to the fuel electrode side as a (solid oxide) electrolyte, but also a fuel. A fuel cell system using a proton conductive electrolyte in which protons (H ⁺ ) move from the electrode side to the air electrode side as a (solid oxide) electrolyte is known. More specifically, it has a plurality of fuel cells, and the former fuel cell uses an oxygen ion conductive electrolyte as the (solid oxide) electrolyte, and the latter fuel cell uses proton conductive as the (solid oxide) electrolyte. A fuel cell system (fuel cell power generation system) using an electrolyte is known (see, for example, Patent Documents 1 and 2).

JP-A-4-87262 JP 2011-181489 A

  The fuel cell systems described in Patent Documents 1 and 2 include a plurality of fuel cells, and water vapor is generated on the fuel electrode side of the preceding fuel cell. Then, after steam reforming the fuel using the steam generated from the fuel electrode side, the reformed fuel is supplied to the subsequent fuel cell to generate power, thereby improving the power generation efficiency. However, in these fuel cell systems, since the water vapor generated on the fuel electrode side of the preceding fuel cell is supplied to the subsequent fuel cell, the concentration of the fuel supplied to the subsequent fuel cell decreases. As a result, the voltage of the fuel cell in the subsequent stage is lowered, and there is a problem that high power generation efficiency cannot be obtained for the entire fuel cell system.

  The present invention has been made in view of the above problems, and is to provide a fuel cell system capable of obtaining high power generation efficiency.

The above problem is solved by the following means.
<1> A fuel cell system in which a plurality of fuel cells each including an electrolyte, a fuel electrode, and an air electrode are installed along a fuel supply direction, and the electrolyte of at least the most upstream fuel cell includes a proton conductive electrolyte.

  In the above configuration, the electrolyte included in the most upstream fuel cell includes a proton conductive electrolyte. In the fuel cell, protons derived from hydrogen contained in the fuel gas supplied to the fuel electrode side move to the air electrode side through the electrolyte and react with oxygen to generate electricity. The water vapor generated with this power generation is generated on the air electrode side, and the fuel is not diluted with water vapor. Therefore, compared with the case where the fuel cell which does not contain a proton conductive electrolyte is provided in the most upstream, power generation efficiency can be improved more.

  <2> The fuel cell system according to <1>, wherein the electrolyte of at least one fuel cell other than the fuel cell at the most upstream includes a proton conductive electrolyte.

  Thereby, the cell voltage in the fuel cell in which the electrolyte includes a proton conductive electrolyte can be further increased.

  <3> The fuel cell includes a first fuel cell and a second fuel cell, and the first fuel cell includes an electrolyte including a proton conductive electrolyte, a fuel electrode, and an air electrode, The fuel cell 2 includes an electrolyte, a fuel electrode, and an air electrode, and is disposed downstream of the first fuel cell. An exhaust gas discharged from the fuel electrode side of the first fuel cell is The fuel cell system according to <1> or <2>, which is supplied to the fuel electrode side of the second fuel cell.

  In the above configuration, the electrolyte included in the first fuel cell includes a proton conductive electrolyte. In the first fuel cell, protons derived from hydrogen contained in the fuel gas supplied to the fuel electrode side move to the air electrode side through the electrolyte and react with oxygen to generate power. The water vapor generated with this power generation is generated on the air electrode side, and the fuel is not diluted with water vapor. Therefore, compared with the case where the 1st fuel cell stack which does not contain a proton conductive electrolyte is used, electric power generation efficiency can be improved more.

  <4> The fuel cell system according to <3>, wherein the total fuel utilization ratio of the first fuel cell and the second fuel cell is 80% to 95%.

  When the total fuel utilization is 80% to 95%, high power generation efficiency can be obtained in the fuel cell system.

  <5> The fuel cell system according to <3> or <4>, wherein the electrolyte of the second fuel cell includes a proton conductive electrolyte.

  When the electrolyte of the second fuel cell includes the proton conductive electrolyte, the cell voltage in the second fuel cell can be further increased.

<6> The ratio r ₁ of the amount of fuel used in the second fuel cell (the amount by which the fuel is electrochemically oxidized) to the amount of fuel used in the first fuel cell is 0.35 ≦ r ₁ The fuel cell system according to any one of <3> to <5>, which satisfies ≦ 1.0.

When the ratio r ₁ is 0.35 or more, the value of the cell voltage in the second fuel cell is maintained to some extent, and oxidation of the electrode (fuel electrode) of the second fuel cell is suppressed. Therefore, long-term durability of the fuel cell can be ensured. Furthermore, in the fuel cell system described above, high power generation efficiency can be obtained.

When the ratio r ₁ is 1.0 or less, the fuel utilization rate in the second fuel cell is suppressed from becoming too high. Thereby, while maintaining the long-term stability of a fuel cell, high power generation efficiency can be obtained.

  <7> Located upstream of the first fuel cell, reforms the hydrocarbon fuel to generate a reformed gas, and supplies the generated reformed gas to the fuel electrode side of the first fuel cell. The fuel according to any one of <3> to <6>, further comprising: a first reformer; and a first fuel supply unit that supplies a hydrocarbon fuel to the first reformer. Battery system.

  According to the above configuration, a reformed gas containing hydrogen is generated by reforming the hydrocarbon fuel in the first reformer, and the reformed gas is supplied to the first fuel cell stack to generate power. Done.

<8> An exhaust gas including water vapor, which includes an electrolyte including a proton conductive electrolyte, a fuel electrode, and an air electrode, is disposed upstream of the first reformer, and is discharged from the fuel electrode side. The fuel cell further includes a third fuel cell that supplies the first reformer, and a ratio r ₂ of a fuel usage amount in the third fuel cell to a fuel usage amount in the first fuel cell is 0. The fuel cell system according to <7>, wherein 0.1 ≦ r ₂ <4.0 is satisfied.

When the ratio r ₂ is 0.1 or more, high power generation efficiency can be obtained in the fuel cell system.

When the ratio r ₂ is less than 4.0, an increase in the fuel utilization rate in the third fuel cell stack is suppressed, and the amount of fuel consumed before being supplied to the first fuel cell stack is suppressed. can do. As a result, an increase in the fuel utilization rate of the third fuel cell stack and a decrease in the closed circuit voltage (OCVAi) at the inlet of the first fuel cell stack can be suppressed at the same time, and the fuel cell has superior long-term durability of the fuel cell stack. A system can be provided.

  <9> Located upstream of the third fuel cell, reforms the hydrocarbon fuel to generate a reformed gas, and supplies the generated reformed gas to the fuel electrode side of the third fuel cell. The fuel cell system according to <8>, further comprising a second reformer and a second fuel supply unit that supplies hydrocarbon fuel to the second reformer.

  According to the above configuration, the reformed gas containing hydrogen is generated by reforming the hydrocarbon fuel in the second reformer, and the reformed gas is supplied to the third fuel cell to generate power. It is.

  <10> The number S of water vapor molecules per unit time supplied to the second reformer and the number C of carbon atoms of the hydrocarbon fuel per unit time supplied to the second reformer. The fuel cell system according to <9>, wherein a steam carbon ratio S / C that is a ratio is 1.6 to 3.5.

  When S / C is within the above numerical range, the hydrocarbon fuel is efficiently reformed, and a reformed gas containing hydrogen is generated.

<11> the ratio _{r 2} satisfies 0.5 ≦ _{r 2} ≦ 3.0, <8> The fuel cell system according to any one of ~ <10>.

By the ratio r ₂ is 0.5 or more, it is possible to provide a higher fuel cell system of the power generation efficiency. In addition, since the ratio r ₂ is 3.0 or less, a decrease in the closed circuit voltage (OCVAi) at the inlet of the first fuel cell stack can be further suppressed, and a fuel cell system that is superior in long-term durability of the fuel cell stack Can be provided.

<12> the ratio _{r 2} satisfies _{2.0 ≦ r 2 ≦ 3.0, <} 8> ~ fuel cell system according to any one of <11>.

By the ratio r ₂ is 2.0 or more, it is possible to provide a higher fuel cell system of the power generation efficiency.

<13> The ratio r ₂ satisfies 1.0 ≦ r ₂ ≦ 3.0, and the flow rate of the hydrocarbon fuel supplied to the first reformer and the second reformer are supplied. The fuel cell system according to <9> or <10>, wherein a ratio r _{3 to} a flow rate of the hydrocarbon fuel to be satisfied satisfies r ₃ ≧ 4.

  According to this configuration, it is possible to provide a fuel cell system in which carbon deposition is suitably suppressed, the fuel cell stack has excellent long-term durability, and high power generation efficiency.

  <14> The wall portion has gas permeability, a gas containing oxygen or hydrogen fuel flows, and at least a part of the wall portion on the outer periphery has a plurality of the fuel cells along the gas flow direction. A hollow substrate that is arranged in parallel and that is supplied to the fuel electrode side or the air electrode side of the fuel cell through which the gas passes through the wall; and a fuel electrode between the adjacent fuel cells that has electronic conductivity. A fuel cell system according to <1> or <2>, comprising a conductive member that connects the air electrode.

  <15> The fuel cell system according to <14>, wherein the hollow base body supplies a gas containing flowing hydrogen fuel to the fuel electrode side of the fuel cell through the wall portion.

  According to these configurations, the gas containing oxygen or hydrogen fuel flowing through the hollow substrate is supplied to the air electrode through the wall when the gas contains oxygen, and when the gas contains hydrogen fuel, the fuel electrode is supplied. To be used for power generation. In particular, when the gas contains hydrogen fuel, protons derived from the hydrogen fuel move to the air electrode side through the electrolyte, react with oxygen, and water vapor is generated on the air electrode side. Therefore, for the gas containing hydrogen fuel flowing through the hollow substrate, the fuel is not diluted with water vapor, and the power generation efficiency can be further improved as compared with the case of using the fuel cell stack not containing the proton conductive electrolyte. it can.

<16> The proton conductive electrolyte is any one of <1> to <15>, which is at least one selected from a compound represented by the following formula (I) and a compound represented by the formula (II): The fuel cell system described in 1.
M _1-δ (Ce _1-xy Zr _x R _y ) O ₃ ... (I)
_{(La 2-z Ca z)} Ce 2 O 7 ···· (II)
(In the formula (I), M represents Ba or Sr, R represents Y, Gd, In or Yb, δ represents −0.1 to 0.1, x represents 0 to 1, and y represents 0 to 0. .5, and 1-xy ≧ 0 is satisfied.In formula (II), z represents 0 to 1.)

  These compounds can be suitably used as a proton conductive electrolyte.

  According to the present invention, it is possible to provide a fuel cell system capable of obtaining high power generation efficiency.

FIG. 1 is a schematic configuration diagram showing a fuel cell system according to an embodiment of the present invention, (a) is a diagram showing an overall configuration of the fuel cell system, and (b) is a fuel cell stack in a fuel cell system. It is a figure which shows having been laminated | stacked. 1 is a schematic exploded perspective view showing a fuel cell stack included in a fuel cell system according to an embodiment of the present invention. In the present embodiment, it is a graph showing the power generation efficiency of the fuel cell system when changing the r _1. In the present embodiment, it is a graph showing a fuel utilization rate of the first fuel cell stack and the second fuel cell stack when changing the r _1. FIG. 4 is a schematic configuration diagram showing a fuel cell system according to another embodiment of the present invention, (a) is a diagram showing an overall configuration of the fuel cell system, and (b) is a fuel cell stack in the fuel cell system. It is a figure which shows that is laminated | stacked. It is a schematic block diagram which shows the fuel cell system which concerns on other embodiment of this invention, (a) is the sectional drawing, (b) is the top view. It is a schematic block diagram which shows the fuel cell system which concerns on other embodiment of this invention, (a) is the perspective view, (b) is the sectional drawing. In Comparative Example is a graph showing the power generation efficiency of the fuel cell system when changing the r _1.

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

In the fuel cell system according to the present invention, a plurality of fuel cells each including an electrolyte, a fuel electrode, and an air electrode are installed along a fuel supply direction, and the electrolyte of at least the most upstream fuel cell includes a proton conductive electrolyte. Including.
In the above configuration, the electrolyte included in the most upstream fuel cell includes a proton conductive electrolyte. In the fuel cell, protons derived from hydrogen contained in the fuel gas supplied to the fuel electrode side move to the air electrode side through the electrolyte and react with oxygen to generate electricity. The water vapor generated with this power generation is generated on the air electrode side, and the fuel is not diluted with water vapor. Therefore, compared with the case where the fuel cell which does not contain a proton conductive electrolyte is provided in the most upstream, power generation efficiency can be improved more.

  Further, in the fuel cell system according to the present invention, it is only necessary that the electrolyte of the fuel cell at the most upstream contains a proton conductive electrolyte, and the electrolyte of the fuel cell installed downstream from the fuel cell is proton conductive. It may or may not contain an electrolyte. When the electrolyte of the fuel cell installed downstream includes a proton conductive electrolyte, it is preferable that the electrolyte of at least one fuel cell other than the most upstream fuel cell includes a proton conductive electrolyte, and all the fuel cell electrolytes More preferably includes a proton conductive electrolyte.

  In the fuel cell system of the present invention, it is sufficient that at least two fuel cells are installed along the fuel supply direction (in a row), and two fuel cells (fuel cell stacks) described below are used. ) Or a fuel cell system 200 including three fuel cells (fuel cell stack) is merely one embodiment of the present invention, and the present invention is not limited to these embodiments.

  Next, an exemplary embodiment of the present invention will be described with reference to FIG. FIG. 1 is a schematic configuration diagram illustrating a fuel cell system according to the present embodiment, (a) is a diagram illustrating an overall configuration of the fuel cell system, and (b) is a fuel cell ( It is a figure which shows that the fuel cell stack is laminated | stacked.

[Fuel cell system 100]
A fuel cell system 100 according to an embodiment of the present invention includes a first fuel cell stack 5 and a second fuel cell stack 7 as fuel cells, and the first fuel cell stack 5 includes a proton conductive electrolyte. The second fuel cell stack 7 includes an electrolyte, a fuel electrode, and an air electrode, and is disposed downstream of the first fuel cell stack 5. The exhaust gas discharged from the fuel electrode side of one fuel cell stack 5 is directly directed to the fuel electrode side of the second fuel cell stack 7 (that is, the first fuel cell stack 5 and the second fuel cell stack 7 (Without going through a reformer). Further, the fuel cell system 100 is disposed upstream of the first fuel cell stack 5, reforms the hydrocarbon fuel to generate a reformed gas, and uses the generated reformed gas as the first fuel cell stack 5. The first reformer 3 that supplies fuel to the fuel electrode side and first fuel supply means that supplies hydrocarbon fuel to the first reformer 13 are provided.

When reforming hydrocarbon fuel with a reformer (first reformer, second reformer), reforming methods include steam reforming, CO ₂ reforming (dry reforming), and the like. Among them, steam reforming is preferable. In the following fuel cell system 100, a case where steam reforming, which is a preferred reforming method, is described, but the present invention is not limited to this.

  As shown in FIG. 1B, the fuel cell system 100 is a two-stage fuel cell system in which a first fuel cell stack 5 and a second fuel cell stack 7 are stacked and electrically connected in series. . By electrically connecting in series, the structure of the fuel cell system 100 is simplified, and the cost of the system can be reduced.

  In the fuel cell system 100, the electrolyte included in the first fuel cell stack 5 includes a proton conductive electrolyte. In the first fuel cell stack 5, protons derived from hydrogen contained in the fuel gas (reformed gas) supplied to the fuel electrode side move to the air electrode side through the electrolyte and react with oxygen to generate power. To do. The water vapor generated with this power generation is generated on the air electrode side, and the fuel is not diluted with water vapor. Therefore, compared with the case where the fuel is an oxygen ion conductive electrolyte and does not include a proton conductive electrolyte, the power generation efficiency can be further increased.

  Further, in the fuel cell system 100, since fuel dilution does not occur, a decrease in the cell voltage of the downstream fuel cell stack, that is, the second fuel cell stack 7 is suppressed, and the fuel cell stack is excellent in long-term stability.

  Exhaust gas (unreacted gas containing hydrogen) discharged from the fuel electrode side of the first fuel cell stack 5 is supplied to the fuel electrode side of the second fuel cell stack 7 via the exhaust gas supply pipe 6. . Electric power is generated in the second fuel cell stack 7 by reacting the supplied gas, and additional hydrocarbon fuel is supplied between the first fuel cell stack and the second fuel cell stack. I have not done it. Therefore, an increase in carbon activity is suppressed in the fuel cell system 100 (for example, inside the exhaust gas supply pipe 6 or inside the second fuel cell stack 7), and carbon deposition is suppressed.

  The hydrocarbon fuel used in the fuel cell system 100 according to the present embodiment is a gas that is steam reformed in the first reformer 3. Examples of the hydrocarbon fuel include natural gas, LPG (liquefied petroleum gas), coal reformed gas, and lower hydrocarbon gas. Examples of the lower hydrocarbon gas include lower hydrocarbons having 4 or less carbon atoms such as methane, ethane, ethylene, propane, and butane, and methane is preferable. The hydrocarbon fuel may be a mixture of the above-described lower hydrocarbon gas, or a gas such as natural gas, city gas, or LP gas containing the above-described lower hydrocarbon gas.

  The hydrocarbon fuel is supplied from the first fuel supply source (not shown) to the first reformer 3 through the hydrocarbon fuel supply pipe 2. Further, the reforming water used for the steam reforming of the hydrocarbon fuel is supplied from the reforming water supply source (not shown) to the first reformer 3 through the reforming water supply pipe 1. The first fuel supply means includes a hydrocarbon fuel supply pipe 2 and a first fuel supply source, and the hydrocarbon fuel supply pipe 2 constitutes a part of the first fuel supply means.

  The first reformer 3 is for generating a reformed gas containing hydrogen by steam reforming the supplied hydrocarbon fuel. The first reformer 3 is disposed upstream of the first fuel cell stack 5 and is connected to the reformed water supply pipe 1 and the hydrocarbon fuel supply pipe 2.

  The steam reforming that occurs in the reforming part involves a large endotherm, so that it is necessary to supply heat from the outside for the progress of the reaction, and therefore, the reforming part can be heated by the combustion heat generated in the combustion part. preferable. Or you may heat using the heat discharge | released from each fuel cell stack.

  When methane, which is an example of a hydrocarbon fuel, is steam reformed, carbon monoxide and hydrogen are generated in the first reformer 3 by the reaction of the following formula (a), and the following formula (b ) To generate carbon dioxide and hydrogen.

CH ₄ + H ₂ O → CO + 3H ₂ ... (A)
CO + H ₂ O → CO ₂ + H ₂ ... (B)

  It is a ratio between the number S of water vapor molecules per unit time supplied to the first reformer 3 and the number C of carbon atoms of hydrocarbon fuel per unit time supplied to the first reformer 3. The steam carbon ratio S / C is preferably 1.6 to 3.5, more preferably 2.0 to 3.5, and still more preferably 2.5 to 3.0. When the steam carbon ratio S / C is within this range, the hydrocarbon fuel is efficiently steam reformed, and a reformed gas containing hydrogen is generated. Furthermore, carbon deposition in the fuel cell system 100 can be suppressed.

  The reformed gas generated by the first reformer 3 is supplied to the first fuel cell via the reformed gas supply pipe 4 that communicates the first reformer 3 and the first fuel cell stack 5. It is supplied to the fuel electrode side of the stack 5.

  The first fuel cell stack 5 includes an electrolyte, a fuel electrode, and an air electrode, and is connected to the reformed gas supply pipe 4 and the exhaust gas supply pipe 6 on the fuel electrode side. Further, in the fuel cell system 100, the electrolyte of the first fuel cell stack 5 includes a proton conductive electrolyte. The first fuel cell stack 5 electrically supplies hydrogen ions derived from hydrogen contained in the reformed gas supplied from the reformed gas supply pipe 4 to the fuel electrode side and oxygen supplied to the air electrode side. Power is generated by chemical reaction. Water vapor generated by reacting hydrogen ions is discharged from the air electrode side, and unreacted reformed gas is discharged to the exhaust gas supply pipe 6 as exhaust gas. The specific configuration of the fuel cell stack, electrolyte, fuel electrode, and air electrode will be described later.

  The exhaust gas is discharged from the fuel electrode side of the first fuel cell stack 5 and supplied to the fuel electrode side of the second fuel cell stack 7 through the exhaust gas supply pipe 6.

  The second fuel cell stack 7 includes an electrolyte, a fuel electrode, and an air electrode, is disposed downstream of the first fuel cell stack 5, and is connected to the exhaust gas supply pipe 6 on the fuel electrode side. Yes. The electrolyte of the second fuel cell stack 7 according to the present embodiment may not include a proton conductive electrolyte, but preferably includes a proton conductive electrolyte.

  In the case where the electrolyte of the second fuel cell stack 7 does not contain a proton conductive electrolyte, the second fuel cell stack 7 contains hydrogen contained in the exhaust gas supplied from the exhaust gas supply pipe 6 to the fuel electrode side. Then, electricity is generated by electrochemically reacting oxygen ions derived from oxygen supplied to the air electrode side. Then, water vapor and unreacted gas generated by the reaction are discharged from the fuel electrode side.

  On the other hand, when the electrolyte of the second fuel cell stack 7 includes a proton conductive electrolyte, the second fuel cell stack 7 is included in the exhaust gas supplied from the exhaust gas supply pipe 6 to the fuel electrode side. Electricity is generated by electrochemically reacting hydrogen ions derived from hydrogen and oxygen supplied to the air electrode side. The water vapor generated by the reaction is discharged from the air electrode side, and the unreacted gas is discharged from the fuel electrode side. According to such a configuration, since the exhaust gas discharged from the fuel electrode side of the second fuel cell stack 7 does not contain water vapor, the unreacted gas is not diluted and the second fuel cell stack It is possible to flexibly expand the system configuration, for example, by disposing a fuel cell stack further in the subsequent stage.

The ratio r ₁ of the amount of fuel used in the second fuel cell stack 7 to the amount of fuel used in the first fuel cell stack 5 (the amount by which the fuel is electrochemically oxidized) is 0.35 ≦ r ₁ ≦ It is preferable that 1.0 is satisfied.

When the ratio r ₁ is 0.35 or more, the value of the cell voltage in the second fuel cell stack 7 is maintained to some extent, and the oxidation of the electrode (fuel electrode) of the second fuel cell stack 7 is suppressed. . Therefore, long-term durability of the fuel cell stack can be ensured. Furthermore, in the fuel cell system 100 described above, high power generation efficiency can be obtained.

When the ratio r ₁ is 1.0 or less, it is possible to suppress the fuel utilization rate in the second fuel cell stack 7 from becoming too high. Thereby, the long-term stability of the fuel cell stack can be maintained.

In order for the ratio r ₁ of the fuel usage in the second fuel cell stack 7 to the fuel usage in the first fuel cell stack 5 to satisfy 0.35 ≦ r ₁ ≦ 1.0, simply When the current density per battery (cell) electrode area is equal between the first fuel cell stack 5 and the second fuel cell stack 7, the second fuel cell stack 7 has an effective electrode area relative to the effective electrode area of the first fuel cell stack 5. Since the ratio of the effective electrode area or the ratio of the number of stacked cells of the second fuel cell stack 7 to the number of stacked cells of the first fuel cell stack 5 corresponds to r ₁ , this value is 0.35 or more and 1 Adjust to less than 0.0.
Here, the ratio of the effective electrode area of the second fuel cell stack 7 to the effective electrode area of the first fuel cell stack 5 is the area ratio when the cell areas of the stacked cells of each fuel cell stack are summed. Means. The ratio of the number of stacked cells in the second fuel cell stack 7 to the number of stacked cells in the first fuel cell stack 5 is based on the assumption that the cell areas of each fuel cell stack are equal.

  Hereinafter, the structure of the first fuel cell stack 5 will be described with reference to FIG. FIG. 2 is a schematic exploded perspective view showing the first fuel cell stack 5 provided in the fuel cell system 100 according to the present embodiment. The first fuel cell stack 5 includes a plurality of single cells 208 having an electrolyte 202, a fuel electrode 204, and an air electrode 206. In FIG. 2, the first fuel cell stack 5 includes two unit cells, but is not limited to this configuration. That is, the fuel cell stack used in the present invention may include a plurality (n; n is an integer satisfying n ≧ 2).

  The first fuel cell stack 5 has a stack body having a plurality of unit cells 208 and the fuel electrode 204 and the reformed gas supply pipe 4 (not shown) of each unit cell 208 in the first fuel cell stack 5. Are connected, and the fuel electrode 204 of each unit cell 208 and the exhaust gas supply pipe 6 (not shown) are connected. Further, in the first fuel cell stack 5, the air electrode of each unit cell 208 and an oxidant gas supply pipe (not shown) for supplying oxidant gas are connected, and the exhaust gas on the air electrode side is connected. Is provided with a discharge port (not shown).

  As shown in FIG. 2, the unit cell 208 of the first fuel cell stack 5 includes a layered electrolyte 202, a layered fuel electrode 204 joined to one surface of the layered electrolyte 202, and a layered electrolyte 202. It is comprised with the laminated body of the layered air electrode 206 joined to one surface. The plurality of single cells 208 are stacked via an interconnector (conductive member) 210. That is, each of the plurality of single cells 208 has a structure sandwiched between a pair of interconnectors 210. In addition, although not shown in figure, each cell 208 and the interconnector 210 are in the state which clamped the gas seal body in the outer periphery part.

  The electrolyte 202 may be an electrolyte containing a proton conductive electrolyte. The proton conductive electrolyte is not particularly limited as long as it is an electrolyte having proton conductivity. For example, an electrolyte having a perovskite structure, a pyrochlore structure, or the like is preferable. The proton conductive electrolyte is preferably at least one of a compound represented by the following formula (I) (perovskite structure) and a compound represented by formula (II) (pyrochlore structure).

M _1-δ (Ce _1-xy Zr _x R _y ) O ₃ ... (I)
_{(La 2-z C z)} Ce 2 O 7 ···· (II)
(In the formula (I), M represents Ba or Sr, R represents Y, Gd, In or Yb, δ represents −0.1 to 0.1, x represents 0 to 1, and y represents 0 to 0. .5 and satisfies 1-xy ≧ 0. In formula (II), C represents Co or Ca, z represents 0 to 1, and C is preferably Ca.)

  The proton conductive electrolyte is more preferably at least one of the compounds represented by the following formulas (III) to (VI). In consideration of stability, the proton conductive electrolyte is represented by formulas (V) and (VI). More preferably, it is any of the represented compounds.

Ba _1-δ (Ce _1-xy Zr _x Y _y ) O ₃ (BCZY) (III)
Ba _1-δ (Zr _x Ce _1-xy Y _y ) O ₃ (BZCY) (IV)
Ba _1-δ (Zr _x In _y ) O ₃ (BZI) (V)
_{La 2-z Ca z Ce 2} O 7 (LCCO) ··· (VI)
(In the formulas (III) to (VI), δ represents −0.1 to 0.1, x represents 0 to 1, y represents 0 to 0.5, and z represents 0 to 1, and 1−xy ≧ (However, in formula (III), 1-2x−y ≧ 0 is satisfied, and in formula (IV), 2x + y−1 <0 is satisfied.)

Further, as the BCZY, for _example, preferably _{Ba 0.98 Ce 0.6 Zr 0.2 Y 0.2} O 3 _{over d,} As the BZCY, for _example, BaZr _{0.6 Ce} 0.4 _{Y 0.} preferably ₂ O _3-d, as the above BZI, for _example, preferably _BaZr 0.7 _{in 0.3} O _{3 over d,} as the LCCO, for _{example, La 1.95 Ca 0.05 Ce 2 O} 7 _{over d} is preferable (d≈0).

  The electrolyte 202 may be an electrolyte made of a proton conductive electrolyte, or may be an electrolyte containing an oxygen ion conductive electrolyte. When the electrolyte 202 contains an oxygen ion conductive electrolyte, the content of the oxygen ion conductive electrolyte is preferably 10% by mass or less.

The oxygen ion conductive electrolyte is composed of, for example, a dense body of oxide ion conductive solid oxide. Examples of the solid oxide include stabilized zirconia and partially stabilized zirconia. Specific examples of the stabilized zirconia include yttria stabilized zirconia (YSZ), scandia stabilized zirconia (ScSZ), and the like. Specific examples of the partially stabilized zirconia include yttria partially stabilized zirconia (YSZ), scandia partially stabilized zirconia (ScSZ), and the like. In addition, as the solid oxide, for example, ceria-based oxide doped with Sm, Gd, etc .; La _0.8 Sr ₀ in which LaGaO ₃ is used as a base and a part of La and Ga are respectively replaced by Sr and Mg. _.2 Perovskite oxides such as Ga _0.8 Mg _0.2 O _(3-δ) ;

  The fuel electrode 204 is an anode. In the fuel electrode 204, the supplied hydrogen reacts to emit electrons. The fuel electrode 204 is preferably, for example, porous, has high ion conductivity, and does not easily cause a solid-solid reaction with the electrolyte 202 or the like at a high temperature. The fuel electrode 204 may be made of, for example, a material such as NiO, BCZY-NiO, BZCY-NiO, BZI-NiO, LCCO-NiO, and BCZY-NiO, BZCY-NiO, BZI-NiO, LCCO-NiO. About, it is preferable that 50 mass%-70 mass% NiO is included with respect to the whole material. The fuel electrode 204 may be made of a mixed material obtained by mixing two or more of the above materials.

  The air electrode 206 is a cathode. In the air electrode 206, when oxygen in the oxidant gas reacts with protons that have moved from the fuel electrode side, electrons are taken in to form water (water vapor). The air electrode 206 is preferably, for example, porous, has high electron conductivity, and does not easily cause a solid-solid reaction with the electrolyte 202 or the like at a high temperature. The air electrode 206 includes, for example, BSCF (compound composed of Ba, Sr, Co, Fe and oxygen), BSCFT (compound composed of Ba, Sr, Co, Fe, Ti and oxygen), PBC (Pr, Br, Co and oxygen). Compound), BZYP (compound consisting of Ba, Zr, Y, Fe, Pr and oxygen), LSCF (compound consisting of La, Sr, Co, Fe and oxygen), BSCF-BCZY, BSCFT-BZCY, PBC-BZYP Or LSCF-LCCO. About BSCF-BCZY, BSCFT-BZCY, PBC-BZYP, and LSCF-LCCO, it is preferable that 50 mass%-70 mass% BSCF, BSCFT, PBC, and LSCF are included respectively with respect to the whole material. The air electrode 206 may be composed of a mixed material obtained by mixing two or more of the above materials.

Further, as the BSCF, for example, Ba _0.5 Sr _0.5 Co _0.8 Fe _0.2 O _3-d is preferable, and as the BSCFT, for example, Ba _0.5 Sr _0.5 (Co _{0 .8} Fe _0.2 ) _0.9 Ti _0.1 O _3-d is preferable, and as the PBC, for example, PrBrCo ₂ O _{5 + d} is preferable, and as the BZYP, for example, BaZr _0.7 Y _0.2 FePr _0.1 O _3-d is preferable, and as the LSCF, for example, LaSr ₃ Co _1.5 Fe _1.5 O _10-d is preferable (d≈0).

  The interconnector 210 is composed of an electron conductive member in order to exchange electrons with the fuel electrode 204 or the air electrode 206. The interconnector 210 supplies the reformed gas flow path forming groove 210A for supplying the reformed gas to the surface facing the fuel electrode 204 and the oxidant gas to the surface facing the air electrode 206. An oxidant gas flow path forming groove 210B is formed. The reformed gas flow path forming groove 210A and the oxidant gas flow path forming groove 210B are formed, for example, along directions intersecting each other. The reformed gas channel forming groove 210 </ b> A functions as a reformed gas channel for supplying the reformed gas to the fuel electrode 204 when the interconnector 210 is disposed in close contact with the fuel electrode 204. On the other hand, the oxidant gas flow path forming groove 210 </ b> B functions as an oxidant gas flow path for supplying an oxidant gas to the air electrode 206 when the interconnector 210 is disposed in close contact with the air electrode 206.

The constituent material of the interconnector 210 is not particularly limited. The interconnector 210 generally uses an alloy. For example, SUS310S and ZMG232 (made by Hitachi Metals, Ltd.) are mentioned. The constituent material of the interconnector 210 may be an oxide having electronic conductivity, specifically, a dense body of LaCrO ₃ oxide.

  Next, an electrochemical reaction that occurs in the unit cell 208 will be described. First, a reformed gas containing hydrogen is supplied to the fuel electrode 204 of the unit cell 208, and a reaction represented by the following formula (c) occurs with respect to the hydrogen. To move.

H ₂ → 2H ⁺ + 2e ⁻ (c)

  The air electrode 206 is supplied with an oxidant gas containing oxygen. The supplied oxygen reacts with hydrogen ions moving inside the electrolyte 202 at the interface between the air electrode 206 and the electrolyte 202. The reaction formula is as shown in the following formula (d).

4H ⁺ + O ₂ + 4e ⁻ → 2H ₂ O (d)

  Water vapor is generated by the electrochemical reaction of hydrogen ions in the unit cell as shown in the above formula (d), and power is generated.

  Hydrogen that has not been used in the first fuel cell stack 5 is discharged from the fuel electrode side of the first fuel cell stack 5, and the fuel electrode of the second fuel cell stack 7 is passed through the exhaust gas supply pipe 6. It is supplied directly to the side and used for power generation. As described above, since no additional hydrocarbon fuel is supplied between the first fuel cell stack 5 and the second fuel cell stack 7, the carbon activity in the fuel cell system 100 is increased. Is suppressed, and carbon deposition is suitably suppressed.

  Note that the second fuel cell stack 7 may be a stack containing a proton conductive electrolyte in the electrolyte as in the first fuel cell stack 5, and in this case, the configuration of the second fuel cell stack 7 is This is the same as the first fuel cell stack 5. On the other hand, the second fuel cell stack 7 may be a stack including an electrolyte made of the above-described oxygen ion conductive electrolyte without including a proton conductive electrolyte in the electrolyte.

When the second fuel cell stack 7 includes an electrolyte made of an oxygen ion conductive electrolyte, the fuel electrode is made of, for example, Ni, yttria stabilized zirconia (YSZ) -nickel metal porous cermet, scandia stabilized zirconia (ScSZ). ) -Nickel metal porous cermet or the like. The air electrode can be composed of, for example, a PrCoO ₃ oxide, a LaFeO ₃ oxide, a LaCoO ₃ oxide, a LaMnO ₃ oxide, or the like. Specific examples of the LaMnO ₃ -based oxide include La _0.8 Sr _0.2 MnO ₃ (LSM) and La _0.6 Ca _0.4 MnO ₃ (LCM). The fuel electrode and the air electrode may be composed of a mixed material obtained by mixing two or more of the above materials.

  Next, a fuel cell system of a form different from the fuel cell system 100 shown in FIG. 1 will be described below with reference to FIGS. 6 and 7 are schematic configuration diagrams showing a fuel cell system according to another embodiment of the present invention. In addition, about the structure of the same name as each structure of the 1st fuel cell stack 5 mentioned above, the description in the 1st fuel cell stack 5 shall be used, and the detailed description is abbreviate | omitted.

  The fuel cell system 300 shown in FIG. 6 includes a hollow base body (support base body) 301 in which a wall portion has gas permeability and a gas containing hydrogen fuel circulates. A plurality of fuel cells 308 including a fuel electrode 304, an electrolyte 302 containing a proton conductive electrolyte (or made of a proton conductive electrolyte), and an air electrode 306 are arranged in parallel along the gas flow direction. As for the fuel cell 308, as viewed from the wall side, a fuel electrode 304, an electrolyte 302, and an air electrode 306 are stacked in this order. In the present embodiment, a unit cell including the electrolyte 302 and the air electrode 306 in this order is a fuel cell.

  The hollow substrate 301 is connected to a reformed gas supply pipe (not shown) on the upstream side, and connected to an exhaust gas supply pipe on the downstream side, and the reformed gas supplied from the reformed gas supply pipe ( Gas containing hydrogen fuel) flows through the reformed gas passage 311 inside the hollow substrate. The wall portion of the hollow substrate 301 has gas permeability, and a plurality of fuel cells 308 are arranged along the gas flow direction on the outer periphery of the wall portion. Therefore, the reformed gas is supplied to the fuel electrode 304 side of the fuel cell 308 through the wall having gas permeability, and the reaction represented by the above formula (c) occurs with respect to hydrogen contained in the reformed gas, At that time, hydrogen ions move inside the electrolyte 302.

  In addition, a gas containing oxygen (oxidant gas) is supplied to the air electrode 306 side of the fuel cell 308, and the supplied oxygen and hydrogen ions moving inside the electrolyte 302 form the air electrode 306 and the electrolyte 302. It reacts at the interface (the above formula (d)). As a result, water vapor is generated by the electrochemical reaction of hydrogen ions in the fuel cell 308 to generate power.

  A fuel electrode and an air electrode between adjacent fuel cells are connected via an interconnector 310 having electronic conductivity. The interconnector 310 is composed of an electron conductive member in order to exchange electrons with the fuel electrode 304 or the air electrode 306. As a result, the plurality of fuel cells 308 are electrically connected in series. It is generated on the air electrode 306 side by changing the shape of the interconnector 310 so that the fuel electrodes 304 of the plurality of fuel cells 308 are connected to each other and a mesh electrode or the like is connected so as to cover the air electrode 306. It is also possible to electrically connect a plurality of fuel cells 308 in parallel without hindering the discharge of water vapor. In FIG. 6B, the interconnector 310 is omitted.

  Since an electrochemical reaction of hydrogen ions occurs at the interface between the air electrode 306 and the electrolyte 302, water vapor is generated on the air electrode 306 side during power generation. Here, when the electrolyte does not include a proton conductive electrolyte, water vapor is generated on the fuel electrode side during power generation, and the generated water vapor is supplied to the reformed gas flow path 311 through the wall portion of the hollow substrate 301. As a result, the fuel may be diluted. However, when the electrolyte includes a proton conductive electrolyte as in this embodiment, since water vapor is generated on the air electrode side during power generation, the generated water vapor flows through the wall portion of the hollow base body 301. Supply to the path 311 is suppressed, fuel dilution does not occur, and power generation efficiency can be further increased.

  The hollow substrate 301 is preferably formed of a porous material having gas permeability, and for example, a ceramic material, a metal material, or the like can be suitably used. The shape of the hollow substrate 301 is not particularly limited as long as the fuel cell 308 can be installed on the outer periphery of the wall of the hollow substrate 301. For example, the hollow substrate 301 may have a rectangular shape, a cylindrical shape, or the like.

  In the fuel cell system 300, not only a plurality of fuel cells 308 are juxtaposed along the gas flow direction only on the upper part of the wall of the hollow substrate 301, but as shown in FIG. A plurality of fuel cells 308 may be juxtaposed along the gas flow direction at the lower portion of the wall portion 301. That is, even if a plurality of (n ′: n ′ is an integer of 2 or more) fuel cells 308 are juxtaposed along the gas flow direction on the wall portion of the hollow substrate 301, a fuel cell group 312 is formed in a row. Alternatively, two or more rows may be formed. In FIG. 6A, a shielding member (not shown) for preventing leakage of fuel gas is provided on the peripheral surface of the hollow base 301 excluding the portion where the fuel cell 308 is disposed.

  Next, a fuel cell system 400 shown in FIG. 7 includes a hollow base body 401 having a gas permeable wall portion and a gas containing hydrogen fuel flowing therethrough, and the gas flow on the outer periphery of the wall portion. A plurality of fuel cells 408 are arranged in parallel along the direction, and a plurality of fuel cells 408 including a fuel electrode 404, an electrolyte 402 including a proton conductive electrolyte (or made of a proton conductive electrolyte), and an air electrode 406 in this order. As for the fuel cell 408, as viewed from the wall side, a fuel electrode 404, an electrolyte 402, and an air electrode 406 are stacked in this order. The fuel electrode and the air electrode between adjacent fuel cells are connected via an interconnector 410 having electronic conductivity, and a protective film 412 for protecting the interconnector 410 is provided on the interconnector 410. It has been. A plurality of fuel cells 408 are electrically connected in series by the interconnector 410.

  In the fuel cell system 300 shown in FIG. 6, a plurality of rectangular fuel cells 308 are provided on a part of the outer periphery of the wall portion of the hollow base 301. In the fuel cell system 400 shown in FIG. The difference is that a plurality of annular fuel cells 408 are provided on the outer periphery of the wall portion.

  Similarly to the fuel cell system 300, even when the fuel cell system 400 is used, an electrochemical reaction of hydrogen ions occurs at the interface between the air electrode 406 and the electrolyte 402. Is generated. Therefore, the generated water vapor is suppressed from being supplied to the reformed gas flow path 411 via the wall portion of the hollow base body 401, fuel is not diluted, and the power generation efficiency can be further increased.

  In the fuel cell system 300 shown in FIG. 6 and the fuel cell system 400 shown in FIG. 7, the gas flowing through the hollow substrate is not limited to a gas containing hydrogen fuel, but a gas containing oxygen (oxidant gas). There may be. At this time, as for the fuel cell, it is only necessary that the air electrode, the electrolyte, and the fuel electrode are laminated in this order on the outer periphery of the wall portion of the hollow base body as viewed from the wall portion side. With this configuration, hydrogen ions derived from hydrogen supplied from the fuel electrode side and moving inside the electrolyte react with oxygen supplied to the air electrode side through the wall of the hollow substrate to generate power. Is done.

  Next, it will be described below that the fuel cell system 100 having a two-stage stack has excellent long-term stability and high power generation efficiency. First, the performance and conditions of the fuel cell stack (single stage stack) used in the fuel cell system 100 are set as follows.

[Fuel cell stack performance and conditions]
Assuming that the fuel utilization rate of a fuel cell stack (single stage stack) is 75%, the system efficiency in the fuel cell stack is 55% LHV (low heating value), and the loss due to efficiency conversion from the stack to the system is assumed to be 10% To do. From this assumption, the stack efficiency is calculated to be 61.1%. When the current density is 0.2 A / cm ² , this performance is obtained if the internal resistance (ASR) of the fuel cell stack is 0.3517 ohm (Ω) · cm ² when the fuel utilization rate is low.
It is assumed that the steam carbon ratio S / C is 3.0 for the hydrocarbon fuel and steam supplied to the reformer provided upstream of the fuel cell stack. Further, the oxygen partial pressure P _O2 (in) at the fuel electrode side inlet of the fuel cell stack is 3.77 × 10 ⁻²¹ (atm), and the oxygen partial pressure P _O2 (out) at the fuel electrode side outlet of the fuel cell stack is 8 915 × 10 ⁻¹⁹ (atm), the reaction temperature inside the stack is 750 ° C., and the supplied hydrocarbon fuel is methane.
At this time, the oxygen potential at the fuel electrode side inlet of the stack is calculated as -0.99 V in terms of the potential with respect to air, and the oxygen potential is determined as -0.877 V at the fuel electrode side outlet of the stack.

[Two-stage fuel cell system]
Using the single-stage stack having the system efficiency of 55% LHV as described above, the fuel cell stack (the first fuel cell stack 5 and the second fuel cell stack 7) having a two-stage structure as shown in FIG. 1 is provided. The fuel cell system 100 is prepared. The overall fuel usage rate of the fuel cell system 100 (Uf (total), unit%), the fuel usage rate of the first fuel cell stack 5 (Uf (A), unit%), and the second fuel cell stack 7 The relationship with the fuel utilization rate (Uf (B), unit%) will be described below.

  First, the overall fuel utilization rate (Uf (total)) was used in the first fuel cell stack 5 and the second fuel cell stack 7 with respect to the amount of fuel supplied to the first fuel cell stack 5. Calculated as a percentage of the total amount of fuel. Therefore, the supply amount to the first fuel cell stack 5 is S, the fuel use amount in the first fuel cell stack 5 is Con (A), and the fuel use amount in the second fuel cell stack 7 is Con (B ), The following relational expression (1) is established.

Uf (total) / 100 = (Con (A) + Con (B)) / S (1)

By using the ratio r ₁ of the fuel consumption in the second fuel cell stack 7 to the fuel consumption at the first fuel cell stack 5, the fuel used in the first fuel cell stack and the second fuel cell stack The following equation (2) for the quantity is obtained:

Con (B) = r ₁ Con (A) (2)

  The following equation (3) is obtained from the relationship between the fuel utilization rate and the fuel usage amount in the first fuel cell stack 5, and the relationship between the fuel utilization rate and the fuel usage amount in the second fuel cell stack 7 is obtained. Thus, the following formula (4) is obtained.

Uf (A) / 100 = Con (A) / S (3)
Uf (B) / 100 = Con (B) / S (1-Uf (A) / 100) (4)

  From the above formulas (1) to (4), the following formulas (5) and (6) are established for Uf (A) and Uf (B).

Uf (A) = Uf (total) / (1 + r ₁ ) (5)
Uf (B) = r ₁ Uf (total) / (1 + r ₁ −Uf (total) / 100) (6)

FIG. 4 is a graph showing the fuel utilization rates of the first fuel cell stack 5 and the second fuel cell stack 7 when r ₁ is changed. This graph is obtained by setting Uf (total) = 85 (%) in the above formulas (5) and (6). As shown in the figure, when r ₁ is decreased, the fuel utilization rate (Uf (A)) of the first fuel cell stack 5 is increased and the fuel utilization rate (Uf (B)) of the second fuel cell stack 7 is increased. ) Becomes smaller. On the other hand, when r ₁ is increased, the fuel utilization rate (Uf (A)) of the first fuel cell stack 5 is decreased and the fuel utilization rate (Uf (B)) of the second fuel cell stack 7 is increased. .

If Uf (A) and Uf (B) greatly exceed 75%, the long-term durability is reduced. Therefore, Uf (A) and Uf (B) are preferably 80% or less, and more preferably 75% or less. Therefore, the range of _{r 1,} preferably Uf (A) and Uf (B) is 0.063 ≦ _{r 1} ≦ 2.4 which satisfies 80% or less, Uf (A) and Uf (B) is It is more preferable that 0.134 ≦ r ₁ ≦ 1.125 satisfying 75% or less. Furthermore, to maintain over a long stability of the first fuel cell stack 5 and the second fuel cell stack 7, the range of r _1, preferably from 0.2 ≦ r ₁ ≦ 1.0, More preferably, 0.35 ≦ r ₁ ≦ 1.0.

FIG. 3 is a graph showing the power generation efficiency of the fuel cell system 100 when r ₁ is changed in the present embodiment in which the electrolyte includes a proton conductive electrolyte. That is, this graph shows a change in the power generation efficiency of the fuel cell system 100 having a two-stage configuration including the first fuel cell stack 5 and the second fuel cell stack 7 when r ₁ is changed. It is assumed that Uf (total) = 85% and when operating at a current density of 0.2 A / cm ² , the first fuel cell is assumed to have an internal resistance (ASR) of the stack of 0.3517 Ω · cm ^2. It is assumed that the electrolyte of each of the stack 5 and the second fuel cell stack 7 includes a proton conductive electrolyte.
Here, the power generation efficiency of the fuel cell system refers to the ratio of the actual power generation amount to the theoretical power generation amount obtained from the fuel supplied to the fuel cell system (%: low calorific value standard).

FIG. 3 shows that the power generation efficiency reaches the maximum value (about 69.5%) when r ₁ is in the vicinity of 0.4 to 0.7. Therefore, the range of _{r 1,} preferably from 0.35 ≦ _{r 1} ≦ 0.7, it is preferable that 0.4 ≦ _{r 1} ≦ 0.6.

Next, the power generation efficiency of the fuel cell system of the comparative example will be described with reference to FIG. FIG. 8 is a graph showing the power generation efficiency of the fuel cell system when r ₁ is changed in the comparative example. In the fuel cell system of the comparative example, the first fuel cell stack and the second fuel cell stack use an electrolyte made of an oxygen ion conductive electrolyte without including a proton conductive electrolyte, and the other configurations are fuels. This is the same as the battery system 100. Note that Uf (total) = 85%.

From FIG. 8, the power generation efficiency is the maximum value (about 62%) when r ₁ is around 0.4 to 0.5, and the value of the power generation efficiency is 7% or more smaller than the result of FIG. I understand. Therefore, since the fuel cell system 100 of the present embodiment includes a proton conductive electrolyte as an electrolyte, it is possible to obtain higher power generation efficiency than a fuel cell system of a comparative example that does not include a proton conductive electrolyte. Further, even when the fuel cell system 100 of the present embodiment uses a stack having the same internal resistance as the fuel cell system of the comparative example that does not include the proton conductive electrolyte, the electrolyte contains the proton conductor, Does not occur on the fuel electrode side, and in the multistage fuel cell system 100, the power generation efficiency can be significantly increased.

  The overall fuel utilization rate (Uf (total), unit%) of the first fuel cell stack 5 and the second fuel cell stack 7 is preferably 80% to 95%. Thereby, high power generation efficiency can be obtained.

  Here, when Uf (A) and Uf (B) match, the following equation (7) is established from equations (5) and (6).

r ₁ = (100−Uf (total)) ^1/2 / 10... (7)

As r ₁ , when Uf (A) and Uf (B) match (in the vicinity of r ₁ = 0.4 as shown in FIG. 4), or Uf (A) and Uf (B) are close It is preferable to take a value, and assuming that Uf (total) is 80% to 95%, it is preferable that 0.25 ≦ r ₁ ≦ 0.6, and 0.35 ≦ r ₁ ≦ 0.6. More preferably. As the distance from the range in which Uf (A) and Uf (B) coincide with each other, either Uf (A) or Uf (B) becomes a higher value as shown in FIG. For this reason, it is desirable that Uf (A) and Uf (B) have the same value or close values.

Considering the graph shown in FIGS. 3 and 4 and the range of r ₁ when Uf (A) and Uf (B) are equal or close to each other, as r ₁ , 0.35 ≦ r ₁ ≦ 1 0.0 is preferable, and 0.35 ≦ r ₁ ≦ 0.6 is more preferable. As described above, the ratio r ₁ of the fuel usage is the ratio of the effective electrode area of the second fuel cell stack 7 to the effective electrode area of the first fuel cell stack 5 or the cells of the first fuel cell stack 5. Since this corresponds to the ratio of the number of stacked cells of the second fuel cell stack 7 to the number of stacked layers, it is necessary to satisfy 0.35 ≦ r ₁ ≦ 1.0, preferably 0.35 ≦ r ₁ ≦ 0.6. The effective electrode area or the number of stacked cells in the first fuel cell stack 5 and the second fuel cell stack 7 may be set. The effective electrode area or the number of stacked cells in the fuel cell stacks 5 and 7 can be set to a desired range in the design stage of the fuel cell system 100 or the like. Thereby, the fuel cell system 100 having excellent long-term stability and high power generation efficiency can be obtained.

[Fuel cell system 200]
Next, a fuel cell system 200 according to another embodiment of the present invention will be described with reference to FIG. FIG. 5 is a schematic configuration diagram showing a fuel cell system according to another embodiment, (a) is a diagram showing an overall configuration of the fuel cell system, and (b) is a fuel cell in the fuel cell system. It is a figure which shows that a stack is laminated | stacked.
In addition, about the structure of the same name as each structure of the fuel cell system 100 mentioned above, the description in the fuel cell system 100 shall be used, and the detailed description is abbreviate | omitted.

Similar to the fuel cell system 100, the fuel cell system 200 according to another embodiment of the present invention includes a first fuel cell stack 15, a second fuel cell stack 17, and a first reformer 13. ing. Further, the fuel cell system 200 includes an electrolyte including a proton conductive electrolyte, a fuel electrode, and an air electrode, and is disposed upstream of the first reformer 13 and is discharged from the fuel electrode side. Is supplied to the first reformer 13, and the ratio r of the fuel usage amount in the third fuel cell stack 25 to the fuel usage amount in the first fuel cell stack 15 is r. ₂ satisfies 0.1 ≦ r ₂ <4.0.

The fuel cell system 200 is a three-stage fuel cell system in which a first fuel cell stack 15, a second fuel cell stack 17, and a third fuel cell stack 25 are stacked as shown in FIG. is there. The ratio r ₂ of the fuel usage amount in the third fuel cell stack 25 to the fuel usage amount in the first fuel cell stack 15 satisfies 0.1 ≦ r ₂ <4.0. Furthermore, in this embodiment, a configuration in which a proton conductive electrolyte is included in all the electrolytes of the first fuel cell stack 15, the second fuel cell stack 17, and the third fuel cell stack 25 will be described.

When the ratio r ₂ is 0.1 or more, high power generation efficiency can be obtained in the fuel cell system 200.

When the ratio r ₂ is less than 4.0, an increase in the fuel utilization rate in the third fuel cell stack 25 is suppressed, and the amount of fuel consumed before being supplied to the first fuel cell stack 15. Can be suppressed. As a result, an increase in the fuel utilization rate of the third fuel cell stack 25 and a decrease in the closed circuit voltage (OCVAi) at the inlet of the first fuel cell stack can be suppressed at the same time.

  In the fuel cell system 200, since the electrolyte of the third fuel cell stack 25 includes a proton conductive electrolyte, hydrogen ions move from the fuel electrode side to the air electrode side and react with oxygen to generate power. Therefore, the water vapor generated inside the third fuel cell stack 25 is discharged from the air electrode side, and the amount of water vapor contained in the exhaust gas discharged from the fuel electrode side is reduced. Therefore, dilution of the fuel concentration by water vapor does not occur, and a decrease in the cell voltage of the first fuel cell stack 15 and the second fuel cell stack 17 in the subsequent stage can be suppressed, and the long-term stability of the fuel cell stack can be improved. Can be secured. Furthermore, higher power generation efficiency can be obtained for the entire fuel cell system.

  The third fuel cell stack 25 includes an electrolyte, a fuel electrode, and an air electrode, and is disposed upstream of the first reformer 13, and the reformed gas supply pipe 24 and the exhaust gas are disposed on the fuel electrode side. A supply pipe 11 is connected. The third fuel cell stack 25 electrically connects hydrogen ions derived from hydrogen contained in the reformed gas supplied from the reformed gas supply pipe 24 to the fuel electrode side and oxygen supplied to the air electrode side. Power is generated by chemical reaction. And the water (water vapor | steam) produced | generated by the electrochemical reaction (reaction shown to Formula (d)) at the time of electric power generation is discharged | emitted from the air electrode side. On the other hand, steam (steam not used in steam reforming in a second reformer described later) and unreacted contained in the reformed gas supplied to the fuel electrode side of the third fuel cell stack 25 The hydrogen is discharged from the fuel electrode side as exhaust gas, and is supplied to the first reformer 13 through the exhaust gas supply pipe 11. The structure of the third fuel cell stack 25 is the same as that of the first fuel cell stack 5 described above, and a detailed description thereof will be omitted.

  The fuel cell system 200 is disposed upstream of the third fuel cell stack 25, steam reforms the hydrocarbon fuel to generate a reformed gas, and the generated reformed gas is supplied to the third fuel cell stack 25. A second reformer 23 to be supplied, and a second fuel supply means for supplying hydrocarbon fuel to the second reformer 23 are further provided.

  The second reformer 23 is for generating a reformed gas containing hydrogen by steam reforming the supplied hydrocarbon fuel. The second reformer 23 is disposed upstream of the third fuel cell stack 25 and is connected to the reformed water supply pipe 21 and the hydrocarbon fuel supply pipe 22.

  The hydrocarbon fuel is supplied from the second fuel supply source (not shown) to the second reformer 23 via the hydrocarbon fuel supply pipe 22. Further, the reforming water used for the steam reforming of the hydrocarbon fuel is supplied from the reforming water supply source (not shown) to the second reformer 23 via the reforming water supply pipe 21. The second fuel supply means includes a hydrocarbon fuel supply pipe 22 and a second fuel supply source, and the hydrocarbon fuel supply pipe 22 constitutes a part of the second fuel supply means.

  Here, the hydrocarbon fuel supplied to the second reformer 23 and the hydrocarbon fuel supplied to the first reformer 13 are preferably the same. At this time, the first reformer 13 and the second reformer 23 have a common hydrocarbon fuel supply source, that is, the first fuel supply source and the second fuel supply source are the same. It is preferable from the viewpoint of reducing the equipment cost. Here, the hydrocarbon fuel supplied to the second reformer 23 is preferably methane.

  The second reformer 23 has the same configuration as the first reformer 3 described above. A reformed gas containing hydrogen is generated by steam reforming the hydrocarbon fuel in the second reformer 23. The reformed gas is supplied to the fuel electrode side of the third fuel cell stack 25 via the reformed gas supply pipe 24.

  As shown in FIG. 5A, the fuel cell system 200 includes a first fuel cell stack 15 and a fuel electrode side of the first fuel cell stack 15 that is disposed downstream of the first fuel cell stack 15. The exhaust gas discharged from the fuel cell is disposed upstream of the second fuel cell stack 17 and the first fuel cell stack 15 that are directly supplied to the fuel electrode side, and reforms and reforms the hydrocarbon fuel. A first reformer 13 that generates gas and supplies the generated reformed gas to the fuel electrode side of the first fuel cell stack 15, and is disposed upstream of the first reformer 13 and fuel A third fuel cell stack 25 that supplies exhaust gas discharged from the pole side to the first reformer 13 and an upstream side of the third fuel cell stack 25 are provided to reform hydrocarbon fuel. The reformed gas is generated, and the generated reformed gas is supplied to the third fuel cell system. Tsu and a second reformer 23 is supplied to the fuel electrode side of the click 25, the electrolyte of at least a third fuel cell stack 25 includes a proton conductive electrolyte.

The fuel cell system 200 may have a configuration in which the second reformer 23 and the third fuel cell stack 25 are added to the fuel cell system 100 described above. As a result, the exhaust gas of the third fuel cell stack 25 is reformed by the first reformer 13 provided in the uppermost stream of the fuel cell system 100, so that the ratio r ₁ of the fuel usage is appropriately set. Therefore, the driving conditions of the fuel cell system 100 set to be highly efficient and maintained are reliably maintained, and the fuel cell system 100 can be expanded (addition of functions and configurations) flexibly and easily. The third fuel cell stack 25 may be a stack that includes a proton conductive electrolyte in the electrolyte, and the first fuel cell stack 15 and the second fuel cell stack 17 include a proton conductive electrolyte in the electrolyte. A stack may be sufficient and the stack which does not contain a proton conductive electrolyte in electrolyte may be sufficient.

  This is a ratio between the number S of water vapor molecules per unit time supplied to the second reformer 23 and the number C of carbon atoms of the hydrocarbon fuel per unit time supplied to the second reformer 23. The steam carbon ratio S / C is preferably 1.6 to 3.5, more preferably 2.0 to 3.0, and even more preferably 2.5 to 3.0. When the steam carbon ratio S / C is within this range, the steam reforming of the hydrocarbon fuel can be performed efficiently, and the carbon deposition in the fuel cell system 200 can be suppressed.

  In the present invention, the first fuel cell stack and the second fuel cell stack may be a stack containing a proton conductive electrolyte in the electrolyte similarly to the third fuel cell stack. The configuration of the fuel cell stack is the same as that of the third fuel cell stack. On the other hand, either one of the first fuel cell stack and the second fuel cell stack, or both stacks do not include a proton conductive electrolyte in the electrolyte, and include an electrolyte made of the above-described oxygen ion conductive electrolyte. It may be a stack.

  In the fuel cell system 200, the reformer need not be attached to the outside of the first fuel cell stack 15 or the second fuel cell stack 17, and steam reforming (internal reforming) is performed inside each fuel cell stack. ). Since the reaction temperature inside the fuel cell stack is as high as 700 ° C. to 1000 ° C., steam reforming can be performed in the fuel cell stack by the catalytic action of nickel constituting the fuel electrode.

[3-stage fuel cell system]
Using a single-stage stack having a system efficiency of 55% LHV as described above, a fuel cell stack having a three-stage configuration as shown in FIG. 5 (first fuel cell stack 15, second fuel cell stack 17 and third A fuel cell system including a fuel cell stack 25) is prepared. The overall fuel utilization rate of the fuel cell system 200 (Uf (total), unit%), the fuel utilization rate of the first fuel cell stack 15 (Uf (A), unit%), and the second fuel cell stack 17 The relationship between the fuel usage rate (Uf (B), unit%) and the fuel usage rate (Uf (C), unit%) of the third fuel cell stack 25 will be described below.

  Note that the overall fuel usage rate (Uf (total), unit%) of the fuel cell system 200 is the total fuel usage rate of the first fuel cell stack 15 and the second fuel cell stack 17 as described above. (The third fuel cell stack 25 is not included). Therefore, also in the fuel cell system shown in FIG. 5, Uf (A) and Uf (B) satisfy the above formulas (5) and (6).

Next, for the fuel cell system 200 having a three-stage configuration, the ratio r ₂ of the fuel usage amount in the third fuel cell stack 25 to the fuel usage amount in the first fuel cell stack 15, and the first reformer The ratio (mass flow rate ratio) r ₃ (flow rate) of the flow rate (flow rate 1) of the hydrocarbon fuel supplied to 13 and the flow rate (flow rate 2) of the hydrocarbon fuel additionally supplied to the second reformer 23 2 / closed circuit voltage (OCVAi) at the inlet of the first fuel cell stack, carbon activity (ActCAi) at the inlet of the first fuel cell stack, and fuel utilization rate of the third fuel cell stack when the flow rate 1) is changed The long-term durability is evaluated by obtaining a numerical value as an index of long-term stability. In addition, the power generation efficiency of the fuel cell system 200 is also obtained.

As shown in FIG. 3, when the overall fuel utilization rate satisfies 85%, the ratio r ₁ of the fuel usage in the second fuel cell stack to the fuel usage in the first fuel cell stack is 0. In the case of 4 to 0.7, the power generation efficiency of the two-stage fuel cell stack is maximized. Accordingly, the overall fuel utilization rate Uf (total) is fixed to 85% and r ₁ is fixed to 0.5, and a numerical value serving as the above-mentioned long-term stability index is obtained. At this time, from the above formulas (5) and (6), Uf (A) is 56.67% and Uf (B) is 65.38%. Note that methane is assumed as the hydrocarbon fuel.

  In the two-stage fuel cell system 100 as shown in FIG. 1, the open circuit voltage at the first fuel cell stack inlet is 0.99V. Further, in the three-stage fuel cell system 200 as shown in FIG. 5, if the open circuit voltage at the first fuel cell stack inlet is 0.99 V or more, the cell voltage of the second fuel cell stack 17 is Since it becomes more than the cell voltage of the 2nd fuel cell stack 7 in a 2 step | paragraph structure and the oxidation of an electrode (fuel electrode) is suppressed in the 2nd fuel cell stack 17, it is preferable from the point of long-term stability. Therefore, the open circuit voltage (OCVAi) at the inlet of the first fuel cell stack is based on 0.99 V or more.

  When the carbon activity (ActCAi) at the inlet of the first fuel cell stack is 1.0 or more, the risk of carbon deposition and damage to the stack becomes extremely high. Therefore, considering the safety factor, the carbon activity at the inlet of the first fuel cell stack is based on 0.2 or less.

Here, in order to lower the carbon activity at the inlet of the first fuel cell stack, it is necessary to increase r ₃ to some extent and increase the amount of steam supplied to the first reformer 13. However, if too large _{r 3,} a first fuel cell stack inlet of OCVAi decreases.

Then, a large r _2, a first fuel cell stack inlet of OCVAi fuel consumption amount consumed by the third fuel cell stack 25 is increased is reduced. Therefore, when r ₂ and r ₃ are increased, the OCVAi at the inlet of the first fuel cell stack is lowered and is easily below the reference value. Therefore, there is a suitable range for r ₂ and r ₃ .

  If Uf (C) greatly exceeds 75%, which is the premise of the single-stage stack performance, it causes a decrease in long-term durability. Therefore, Uf (C) is based on 80% or less.

  In the results of long-term durability evaluation shown below, when OCVAi, ActCAi, and Uf (C) all meet the standards, the stability is A (good stability), and when one does not meet the standards, it is stable. Property B (stability failure).

  Further, the power generation efficiency of the fuel cell system 200 is obtained and the power generation efficiency is evaluated. The case where the power generation efficiency is 68% or less is evaluated as C, the case where it is over 68% and 74% or less is evaluated as B, and the case where it is over 74% is evaluated as A. And if it is more than evaluation B, it will be judged that high electric power generation efficiency is acquired.

First, for comparison with the fuel cell system 200 according to the present embodiment, a long-term durability and power generation efficiency of a fuel cell system in which the electrolyte of each fuel cell stack is an oxygen ion conductive electrolyte and does not include a proton conductive electrolyte. To evaluate. The fuel cell system to be compared is the same as the fuel cell system 200 with respect to the configuration other than the electrolyte. For the fuel cell system to be compared, the ratio r ₂ of the fuel usage amount in the third fuel cell stack to the fuel usage amount in the first fuel cell stack is set to 0.5 to 0.7, and the first reforming is performed. The ratio r ₃ (flow rate 2 / flow rate 1) of the flow rate of hydrocarbon fuel supplied to the reactor (flow rate 1) and the flow rate of hydrocarbon fuel supplied to the second reformer (flow rate 2) is 1 or Table 1 shows the long-term durability index and power generation efficiency results when 0.8. The hydrocarbon fuel supplied to the first reformer and the second reformer is methane, and the second reformer is based on the flow rate of methane supplied to the first reformer. The value of r ₃ is adjusted by changing the flow rate of methane supplied to the vessel.

  As shown in Table 1, in the fuel cell system to be compared, since all the long-term durability indicators satisfy the standards, the safety is good, but the power generation efficiency is about 65%, and the power generation efficiency is It was insufficient.

Next, the long-term stability and power generation efficiency of the fuel cell system 200 according to this embodiment were evaluated. First, the ratio r ₂ of the amount of fuel used in the third fuel cell stack 25 to the amount of fuel used in the first fuel cell stack 15 is fixed to 0.1 and supplied to the first reformer 13. and the flow rate of the hydrocarbon fuel, Table 2 the results of the indicator and the power generation efficiency of the long-term durability of changing the ratio r ₃ between the flow rate of the hydrocarbon fuel supplied to the second reformer 23 to 1-4 Shown in The hydrocarbon fuel supplied to the first reformer 13 and the second reformer 23 is methane regardless of whether r ₂ is 0.1 to 5.0, and the first reformer The value of r ₃ is adjusted by changing the flow rate of methane supplied to the second reformer 23 with reference to the flow rate of methane supplied to the reactor 13.

As shown in Table 2, when _{r 3} is 1.0, ActCAi has become greater than 0.2. Therefore, it is determined that r ₃ is when the 1.0 and a stability defect, is determined that the stability is good otherwise. Further, since the power generation efficiency is 68% or more, regardless of the value of r _3, it was determined to be high power generation efficiency was obtained.

Next, Table 3 shows long-term durability indices and power generation efficiency results when r ₂ is fixed to 0.5 and r ₃ is changed to 1 to 10.

As shown in Table 3, when _{r 3} is 1.0, ActCAi has become greater than 0.2. Therefore, it is determined that r ₃ is when the 1.0 and a stability defect, is determined that the stability is good otherwise. Further, since the power generation efficiency is 70% or more, regardless of the value of r _3, it was determined to be high power generation efficiency was obtained.

Next, Table 4 shows long-term durability indicators and power generation efficiency results when r ₂ is fixed at 1.0 and r ₃ is changed to 1 to 10.

As shown in Table 4, when _{r 3} is 1.0, ActCAi has become greater than 0.2. Therefore, it is determined that r ₃ is when the 1.0 and a stability defect, is determined that the stability is good otherwise. Further, since the power generation efficiency is 72% or more, regardless of the value of r _3, it was determined to be high power generation efficiency was obtained.

Next, Table 5 shows the long-term durability index and the result of the power generation efficiency when r ₂ is fixed to 2.0 and r ₃ is changed to 1 to 10.

As shown in Table 5, when _{r 3} is 1.0, ActCAi has become greater than 0.2. Therefore, it is determined that r ₃ is when the 1.0 and a stability defect, is determined that the stability is good otherwise. Moreover, since the power generation efficiency was 74% or more, it was judged that a very high power generation efficiency was obtained regardless of the value of r ₃ .

Next, Table 6 shows long-term durability indicators and results of power generation efficiency when r ₂ is fixed to 3.0 and r ₃ is changed to ₃ to 1000.

As shown in Table 6, when _{r 3} is 3.0, Uf (C) is 80% greater. Therefore, it is determined that when r ₃ is 3.0 and a stability defect, is determined that the stability is good otherwise. Further, since the power generation efficiency is 75% or more, regardless of the value of r _3, determines that a very high power generation efficiency was obtained.

Next, Table 7 shows long-term durability indicators and results of power generation efficiency when r ₂ is fixed to 4.0 and r ₃ is changed to 4 to 20.

As shown in Table 7, when r ₃ is 4.0, Uf (C) exceeds 80%, and when r ₃ is 4, 10, or 20, OCVAi is less than 0.989V. Therefore, when r indicating the result was 4.0, it was determined that the stability was poor.

Next, Table 8 shows the long-term durability index and the results of power generation efficiency when r ₂ is fixed to 5.0 and r ₃ is changed to 5 to 100.

As shown in Table 8, when _{r 3} is 5.0, when Uf (C) is 80% ultra next, _{r 3} is 5,100, OCVAi has become less than 0.99 V. Therefore, when r ₁ indicating the result was 5.0, it was determined that the stability was poor.

  As described above, as shown in Tables 1 to 8, since the fuel cell system 200 of the present embodiment includes the proton conductive electrolyte as the electrolyte in each fuel cell stack, the comparison does not include the proton conductive electrolyte. It is possible to obtain higher power generation efficiency than the example fuel cell system. Further, even when the fuel cell system 200 of the present embodiment uses a stack having the same internal resistance as that of the fuel cell system of the comparative example not including the proton conductive electrolyte, the electrolyte includes the proton conductor. Thus, water vapor is not generated on the fuel electrode side, and in this way, in the multistage fuel cell system 200, the power generation efficiency can be significantly increased.

As shown in Tables 2 to 8, in order to ensure the long-term stability of the fuel cell system 200, the amount of fuel used in the third fuel cell stack 25 relative to the amount of fuel used in the first fuel cell stack 15 is shown. It is preferable that the ratio r ₂ satisfies 0.1 ≦ r ₂ <4.0. Here, in order to satisfy this numerical range, the ratio of the effective electrode area of the third fuel cell stack 25 to the effective electrode area of the first fuel cell stack 15 or the cell stack of the first fuel cell stack 15 Since the ratio of the number of stacked cells of the third fuel cell stack 25 to the number corresponds to r ₂ , this value may be adjusted to 0.1 or more and less than 4.0.
Here, the ratio of the effective electrode area of the third fuel cell stack 25 to the effective electrode area of the first fuel cell stack 15 is the area ratio when the cell areas of the stacked cells of each fuel cell stack are summed. Means. In addition, regarding the ratio of the cell stack number of the third fuel cell stack 25 to the cell stack number of the first fuel cell stack 15, it is assumed that the cell areas of each fuel cell stack are equal.

The r ₂ may satisfy 0.1 ≦ r ₂ <4.0, but preferably satisfies 0.5 ≦ r ₂ ≦ 3.0, and satisfies 2.0 ≦ r ₂ ≦ 3.0. It is more preferable. Thereby, it is possible to obtain a power generation efficiency equal to or higher than that of the state-of-the-art large-scale concentrated thermal power generation, and it is possible to provide a distributed fuel cell system with higher power generation efficiency.

The ratio r ₂ satisfies 1.0 ≦ r ₂ ≦ 3.0, and the flow rate of the hydrocarbon fuel supplied to the first reformer 13 and the carbonization supplied to the second reformer 23. The ratio r ₃ to the hydrogen fuel flow rate preferably satisfies r ₃ ≧ 4. According to this configuration, it is possible to provide a fuel cell system in which carbon deposition is suppressed, the fuel cell stack has excellent long-term stability, and power generation efficiency is high.

100, 200, 300, 400 Fuel cell system 1, 21 Reformed water supply pipe 2, 12, 22 Hydrocarbon fuel supply pipe 3, 13 First reformer 4, 14, 24 Reformed gas supply pipe 5, 15 First fuel cell stack 6, 11, 16 Exhaust gas supply pipe 7, 17 Second fuel cell stack 23 Second reformer 25 Third fuel cell stack 202, 302, 402 Electrolyte 204, 304, 404 Fuel Electrode 206, 306, 406 Air electrode 208 Single cell 308, 408 Fuel cell 210, 310, 410 Interconnector 210A Reformed gas flow path forming groove 210B Oxidant gas flow path forming groove 301, 401 Hollow substrate 311, 411 Reformed gas Flow path 312 Fuel cell group 412 Protective film

Claims (16)

A plurality of fuel cells including an electrolyte, a fuel electrode, and an air electrode are installed along the fuel supply direction,
The fuel cell system, wherein the electrolyte of at least the most upstream fuel cell includes a proton conductive electrolyte.   The fuel cell system according to claim 1, wherein the electrolyte of at least one fuel cell other than the fuel cell located upstream is a proton conductive electrolyte. The fuel cell includes a first fuel cell and a second fuel cell,
The first fuel cell includes an electrolyte including a proton conductive electrolyte, a fuel electrode, and an air electrode.
The second fuel cell includes an electrolyte, a fuel electrode, and an air electrode, is disposed downstream of the first fuel cell, and is discharged from the fuel electrode side of the first fuel cell. The fuel cell system according to claim 1 or 2, wherein is supplied to a fuel electrode side of the second fuel cell.   The fuel cell system according to claim 3, wherein the total fuel utilization of the first fuel cell and the second fuel cell is 80% to 95%.   The fuel cell system according to claim 3 or 4, wherein the electrolyte of the second fuel cell includes a proton conductive electrolyte. The ratio r ₁ of the fuel usage amount in the second fuel cell to the fuel usage amount in the _first fuel cell satisfies 0.35 ≦ r ₁ ≦ 1.0. The fuel cell system according to any one of claims. The first fuel cell is disposed upstream of the first fuel cell, reforms the hydrocarbon fuel to generate a reformed gas, and supplies the generated reformed gas to the fuel electrode side of the first fuel cell. A reformer,
First fuel supply means for supplying hydrocarbon fuel to the first reformer;
The fuel cell system according to any one of claims 3 to 6, further comprising: An exhaust gas including water vapor, which includes an electrolyte including a proton conductive electrolyte, a fuel electrode, and an air electrode, is disposed upstream of the first reformer, and is discharged from the fuel electrode side. A third fuel cell that supplies the first reformer;
8. The fuel cell according to claim 7, wherein a ratio r ₂ of a fuel usage amount in the third fuel cell to a fuel usage amount in the first fuel cell satisfies 0.1 ≦ r ₂ <4.0. system. The second fuel cell is disposed upstream of the third fuel cell, reforms the hydrocarbon fuel to generate a reformed gas, and supplies the generated reformed gas to the fuel electrode side of the third fuel cell. A reformer,
Second fuel supply means for supplying hydrocarbon fuel to the second reformer;
The fuel cell system according to claim 8, further comprising:   The ratio between the number S of water vapor molecules per unit time supplied to the second reformer and the number of carbon atoms C of hydrocarbon fuel per unit time supplied to the second reformer. The fuel cell system according to claim 9, wherein the steam carbon ratio S / C is 1.6 to 3.5. 11. The fuel cell system according to claim 8, wherein the ratio r ₂ satisfies 0.5 ≦ r ₂ ≦ 3.0. The fuel cell system according to claim 8, wherein the ratio r ₂ satisfies 2.0 ≦ r ₂ ≦ 3.0. The ratio r ₂ satisfies 1.0 ≦ r ₂ ≦ 3.0, and the flow rate of the hydrocarbon fuel supplied to the first reformer and the carbonization supplied to the second reformer. 11. The fuel cell system according to claim 9, wherein a ratio r _{3 to} a flow rate of hydrogen fuel satisfies r ₃ ≧ 4. The wall portion has gas permeability, a gas containing oxygen or hydrogen fuel flows, and a plurality of the fuel cells are arranged in parallel along the gas flow direction at least at a part on the outer periphery of the wall portion. A hollow substrate through which the gas passes through the wall and is supplied to the fuel electrode side or the air electrode side of the fuel cell;
The fuel cell system according to claim 1, further comprising: a conductive member having electronic conductivity and connecting a fuel electrode and an air electrode between the adjacent fuel cells.   The fuel cell system according to claim 14, wherein the hollow base body supplies a gas containing flowing hydrogen fuel to the fuel electrode side of the fuel cell through the wall portion. 16. The proton conductive electrolyte according to claim 1, wherein the proton conductive electrolyte is at least one selected from a compound represented by the following formula (I) and a compound represented by the formula (II). Fuel cell system.
M _1-δ (Ce _1-xy Zr _x R _y ) O ₃ ... (I)
_{(La 2-z Ca z)} Ce 2 O 7 ···· (II)
(In the formula (I), M represents Ba or Sr, R represents Y, Gd, In or Yb, δ represents −0.1 to 0.1, x represents 0 to 1, and y represents 0 to 0. .5, and 1-xy ≧ 0 is satisfied.In formula (II), z represents 0 to 1.)