JP2015179622A - Evaluation method for solid oxide fuel cell cell, and solid oxide fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cell evaluation method based on a carbon deposition mechanism in an anode support body for a solid oxide fuel cell, and a technology for suppressing an expansion failure of the anode support body caused by carbon deposition.SOLUTION: According to an embodiment, an evaluation method for an anode support body for a solid oxide fuel cell includes an evaluation of a solid oxide fuel cell by comparing a depth D from an outermost surface of the anode support body facing a gas passage with a predetermined reference depth D, where carbon concentration from the outermost surface to the depth D is equal to or larger than reference concentration C. A control unit controls at least one of a start condition, power generation operation condition, and stop condition so that the depth D, which is an index of carbon concentration at a surface of the anode support body, is not equal to or larger than the reference depth D.

Description

  The present invention relates to a solid oxide fuel cell evaluation method and a solid oxide fuel cell system.

  Solid oxide fuel cells (SOFC) generally have higher power conversion efficiency than solid polymer fuel cells (PEFC). Further, not only hydrogen but also reformed gas obtained by reforming raw fuel such as hydrocarbon, alcohol and dimethyl ether (DME) can be used as the fuel. Furthermore, carbon monoxide, unreformed methane, etc. produced as a by-product during reforming of the raw fuel can also be used as a fuel for power generation. Generally, in one thermal closed system, heat for reforming is supplied by using the amount of heat generated in SOFC or heat obtained by burning surplus gas not used for power generation in the upper part of the cell. The ability to balance heat contributes to the high efficiency of SOFC.

  The operating temperature of SOFC has often been 700 ° C or higher in the past, but it is possible to operate at lower temperatures by using low-temperature (below 700 ° C) electrolyte materials and air electrode materials that have been developed recently. It is becoming. Thereby, the practicality of SOFC can be improved, for example, an inexpensive material with low heat resistance can be adopted. However, on the other hand, if the operating temperature of the cell decreases, the temperature of the reformer that is thermally balanced with the cell also decreases. As a result, fuel gas having a high methane ratio is supplied to the cell due to thermal equilibrium in the reforming reaction. In addition, when using raw fuel containing hydrocarbons having 2 or more carbon atoms (C2 or more hydrocarbons) such as natural gas or LPG with adjusted calorie, C2 or more hydrocarbons are converted to C1 species (carbon number 1) in the reformer. There is a growing concern about the occurrence of slippage of so-called C2 or higher hydrocarbons that are supplied to the cell without being converted into hydrocarbons.

  The problem of the supply of gas with high methane concentration or the occurrence of slippage of C2 or higher hydrocarbons is that the reformer is sufficient at startup and shutdown even for SOFCs operating at normal operating temperatures (700 ° C or higher). It may be caused by some trouble in the system, such as when the heater is not heated, or the reforming water pump stops or the flow rate decreases even during power generation, or the reformer temperature decreases due to the loss of thermal balance between the cell stack and the reformer There is.

  By the way, in an anode (fuel electrode) -supported SOFC, a cermet containing nickel (Ni) having high conductivity is preferably used as an anode support. When the reformed gas supplied from the reformer contains high-concentration methane and C2 or higher hydrocarbons, most of the methane and C2 or higher hydrocarbons are combined with coexisting steam by the catalytic action of Ni contained in the anode support. As the reforming reaction proceeds, the hydrogen-rich gas is used as a fuel for power generation. However, some methane and C2 or higher hydrocarbons may precipitate as carbon on the anode support.

In particular, carbon deposition on the anode support tends to occur under conditions of low S / C (steam / carbon ratio) where the water vapor partial pressure is low and the hydrocarbon partial pressure is high. Examples of the carbon deposition reaction include a direct thermal decomposition reaction of methane (the following formula (1)), a steam reforming reaction (the following formula (2)), or an aqueous transfer reaction (a water gas shift reaction) (the following formula (3)). The disproportionation reaction of CO produced by the above (formula (4) below) is known.

  The carbon deposited on the anode support causes the anode support to expand. As a result, there is a risk of damaging the electrode and electrolyte layer provided on the surface of the anode support. Also, the expansion of the anode support due to carbon deposition and the resulting cracking of the electrolyte layer are irreversible phenomena. For this reason, a case in which the occurrence of cracks in the electrolyte layer due to the expansion of the anode support has become seriously unusable as a cell (see Non-Patent Documents 1 and 2).

J.H.Koh, Y.S.Yoo, J.W.Park, H.C.Lim, Solid State Ionics, 149 (2002) 157 -166 C. M. Finnery, N.J. Coe, R.H.Cunninghum, R.M.Ormerod, Catal.Today, 46 (1998) 137 -145

  As a means of preventing the problems caused by carbon deposition as described above, the mechanism and threshold are grasped for individual phenomena such as carbon deposition, anode support expansion, and associated electrolyte layer breakage (crack generation). Therefore, there is a need for a SOFC cell or system evaluation method based on these.

  Furthermore, when the above evaluation method has been established, it is required to put it into a control method based on the evaluation method, that is, a technology that can minimize troubles caused by carbon deposition in the system start / stop process and operation control conditions. Yes.

  However, the cell evaluation method based on the carbon deposition mechanism in the anode support for the solid oxide fuel cell and the carbon deposition suppression technology based on the cell deposition method have not been presented so far, so far. There was room for consideration.

  The present invention has been made in view of such circumstances, and its purpose is to provide a cell evaluation method based on a carbon deposition mechanism in an anode support for a solid oxide fuel cell, and an expansion failure of the anode support due to carbon deposition. It is in the provision of technology to suppress.

  One embodiment of the present invention is a method for evaluating a solid oxide fuel cell. The evaluation method includes an anode support formed of a porous material containing nickel metal and having a gas flow path through which fuel gas flows, and a fuel electrode layer and a solid oxide electrolyte formed on the anode support. A solid oxide fuel cell comprising: a laminate in which a layer and an air electrode layer are laminated, based on a carbon concentration in the vicinity of the surface of the anode support facing the gas flow path, The solid oxide fuel cell is evaluated.

  In the evaluation method of the above aspect, the depth from the outermost surface of the anode support facing the gas flow path, where the carbon concentration is equal to or higher than a predetermined reference concentration, is acquired, and the depth is set to a predetermined reference depth. The solid oxide fuel cells may be evaluated by comparison. Further, when the depth is equal to or greater than a predetermined reference depth, it may be determined that processing for recovering the performance of the solid oxide fuel cell is necessary. The reference depth may be in the range of 1 to 200 μm. The reference concentration of the carbon concentration may be in a range of 100 ppm to 10% by weight with respect to the anode support. The anode support may include nickel cermet. At the time of producing the anode support, the Ni oxide content relative to the total mass of the anode support may be 40% by mass or more.

  Another aspect of the present invention is a solid oxide fuel cell system. The solid oxide fuel cell system includes a reformer that generates a hydrogen-rich fuel gas by a reforming reaction, and an anode support that is formed of a porous material containing nickel metal and has a gas path through which the fuel gas flows. And a stack formed on the support, the fuel electrode layer, the solid oxide electrolyte layer, and the air electrode layer being stacked, and the fuel gas and air supplied from the reformer The solid oxide fuel cell that generates electric power by reaction and the power generation so that the depth from the outermost surface where the carbon concentration of the surface of the anode support is not less than a predetermined reference concentration does not exceed the predetermined reference depth. And a controller that controls at least one of a start condition until start, a power generation operation condition during power generation, and a stop condition after power generation is stopped.

  In the solid oxide fuel cell system according to the aspect described above, the control unit, as the start condition, has a water vapor mole ratio (S / C value) with respect to the number of moles of carbon of the hydrocarbon fuel supplied to the fuel cell. May be set higher than in normal operation. In addition, when it is determined that the carbon accumulation amount on the anode support has increased at any point during the power generation operation, the control unit determines the water vapor mole ratio (S / C) relative to the number of carbon moles of the hydrocarbon fuel. The value may be increased for a predetermined time to control the removal of accumulated carbon. Further, the control unit continues the supply of the fuel gas to the fuel cell even after the power generation is stopped as the stop condition, and the water vapor mole ratio (S / (C value) may be set higher than in normal operation.

  A combination of the above-described elements as appropriate can also be included in the scope of the invention for which patent protection is sought by this patent application.

  According to the solid oxide fuel cell evaluation method of the present invention, the fuel cell can be appropriately evaluated based on the carbon deposition mechanism of the anode support for the solid oxide fuel cell. Moreover, according to the solid oxide fuel cell system of the present invention, expansion failure of the anode support due to carbon deposition is effectively suppressed.

It is a perspective view which shows schematic structure of the principal part of the fuel cell system which concerns on embodiment. It is the schematic which shows typically the structure of the principal part of the fuel cell system which concerns on embodiment. 2 is a horizontal sectional view schematically showing the structure of a fuel cell stack. FIG. It is a schematic diagram which expands and shows a part of anode support. It is the graph which showed the carbon element density | concentration with respect to the depth (distance) from the surface of an anode support body by the mass%. It is a graph in which the deepest depth (distance) from the surface of the anode support that is equal to or higher than a predetermined carbon concentration (mass%) is defined as “carbon deposition thickness” and arranged with respect to exposure time. It is a graph which shows the change of the expansion coefficient with respect to carbon deposition thickness. It is a graph which shows the relationship between the expansion coefficient of a sample, and the number of cracks visually observed. It is a flowchart which shows a certain aspect of the evaluation method of a solid oxide fuel cell. It is a graph which shows the change of the relative value of an output voltage on the basis of the output voltage before a test start about each fuel cell of the reference example 1, the comparative example 1, and Examples 1 and 2 with which the durability test was implemented. It is a graph which shows the change of the relative value of an output voltage on the basis of the output voltage before a test start about each fuel cell of the reference example 2, the comparative example 2, and Example 3 in which the durability test was implemented.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all the drawings, the same reference numerals are given to the same components, and the description will be omitted as appropriate.

  FIG. 1 is a perspective view showing a schematic structure of a main part of a fuel cell system according to an embodiment. FIG. 2 is a schematic diagram schematically showing the structure of the main part of the fuel cell system according to the embodiment. FIG. 1 shows a state where the inside of the module case 2 is seen through. Since FIG. 2 is a schematic diagram, the arrangement, the number of installations, and the like of each part do not necessarily match those in FIG. The fuel cell system 100 includes a hot module 1. The hot module 1 includes a module case 2, a fuel cell stack 10 accommodated in the module case 2, a water vaporizer 50, and a reformer 6.

  The module case 2 is composed of, for example, a substantially rectangular parallelepiped outer frame formed of a heat-resistant metal and a heat insulating material lined on the inner surface of the outer frame. The module case 2 is provided with a supply pipe 3, a supply pipe 4 and a supply pipe 52. The supply pipe 3 is a pipe that supplies raw fuel into the case from the outside of the case. The supply pipe 4 is a pipe for supplying cathode air (oxygen-containing gas) from the outside of the case into the case. The supply pipe 52 is a pipe for supplying reforming water used for the steam reforming reaction from the outside of the case into the case. The module case 2 is provided with an exhaust port 5. As raw fuel, city gas, LPG, methanol, dimethyl ether (DME), kerosene and the like are used. The fuel supply pipe 3, the water supply pipe 52, and the cathode air supply pipe 4 correspond to the fuel, water, and cathode air supply amounts, respectively, so that they can be adjusted. A supply amount control means (pump and / or control valve) (not shown) is provided, and these are appropriately controlled by a control signal from the control unit 200 provided in the fuel cell system 100.

  The water vaporizer 50 and the reformer 6 are arranged in the upper part of the module case 2 and above the fuel cell stack 10. A supply pipe 52 is connected to the water vaporizer 50, and a supply pipe 3 is connected to the reformer 6. The water vaporizer 50 vaporizes the reforming water supplied from the supply pipe 52. Vaporized reforming water (steam) is supplied to the reformer 6. The reformer 6 includes a case formed of a heat-resistant metal and a reforming catalyst that is accommodated in the case and used for reforming raw fuel. The reformer 6 reforms the raw fuel supplied from the supply pipe 3 into a hydrogen-rich fuel gas (reformed gas) by a steam reforming reaction using the steam supplied from the water vaporizer 50.

  One end of a reformed gas supply pipe 7 is connected to the reformed gas outlet 6 a of the reformer 6. The other end of the reformed gas supply pipe 7 is connected to the manifold 8. The manifold 8 is a fuel supply path that is supplied to an anode catalyst layer 23 described later. The manifold 8 is disposed below the fuel cell stack 10 and distributes the reformed gas supplied from the reformer 6 to the plurality of fuel cells 20 included in the fuel cell stack 10. The fuel cell stack 10 is disposed in the lower part of the module case 2, below the reformer 6 and the water vaporizer 50, and fixed on the manifold 8.

  The manifold 8 includes a box-shaped main body having an opening and an upper lid that closes the opening of the box-shaped main body. The upper lid is fixed to the box-shaped main body by, for example, an inorganic glass composition. The upper lid functions as a holding member for the fuel cell stack 10. The upper lid is provided with a plurality of holes for fixing the anode support 21 of each fuel cell 20, and the lower end portion of each anode support 21 is inserted into each opening, and a fixing material such as an adhesive is provided. It is fixed by. Examples of the adhesive used as the fixing material include silica-alumina based inorganic adhesives. In this case, the anode support 21 is fixed to the upper lid by solidifying the inorganic adhesive by firing in a state where the lower end portion of each anode support 21 is held in each opening of the upper lid via the inorganic adhesive. can do. Further, an adhesive layer for fixing the anode support 21 and the upper lid is covered with a sealing material. Thereby, the junction part of the anode support body 21 and an upper cover is sealed gas tight (airtight).

  The fuel cell stack 10 is an assembly of a plurality of fuel cells 20 (cells). When, for example, a cylindrical flat plate type fuel cell is used as the fuel cell 20, a plurality of (e.g., five are shown for simplicity) vertically long fuel cells 20 are arranged in a row in the horizontal direction. A current collecting member 30 is interposed between the side surfaces of the adjacent fuel cells 20. A plurality of fuel cells 20 in a row are arranged on a plane, so that a large number of fuel cells 20 are arranged in a matrix (see FIG. 3). The outermost current collecting member 30 in each row is electrically connected to the conductive member 40.

  Each of the fuel cells 20 is provided with a plurality of gas flow paths 22 extending from the lower end to the upper end of the fuel cell 20. Each gas channel 22 communicates with the manifold 8 at its lower end. The upper end portion of the gas flow path 22 is opened to a space sandwiched between the reformer 6 and the water vaporizer 50 and the fuel cell stack 10. The space constitutes a combustion portion for fuel gas discharged from the upper end portion of the gas flow path 22. Most of the fuel gas flowing from the manifold 8 into the gas flow path 22 is supplied to the fuel cell 20. Excess fuel gas that is not supplied to the fuel cell 20 is supplied from the upper end of the gas flow path 22 to the combustion unit.

  Next, the structure of the fuel cell stack 10 will be described in more detail. FIG. 3 is a horizontal sectional view schematically showing the structure of the fuel cell stack. As shown in FIG. 3, in the present embodiment, a cylindrical flat plate fuel cell 20 is illustrated. The fuel cell 20 is an anode-supported solid oxide fuel cell, and includes an anode support 21, a gas flow path 22, an anode catalyst layer 23 (fuel electrode layer), and an electrolyte layer 24 (solid oxide electrolyte layer). A cathode catalyst layer 25 (air electrode layer), and an interconnector 26.

  The anode support 21 is a porous body containing at least one of Ni metal and Ni oxide. The anode support 21 is a plate-like piece having a flat oval horizontal cross-sectional shape and extending in the vertical direction (vertical direction) (see FIG. 2). The anode support 21 has a lower surface located on the manifold 8 side, an upper surface located on the reformer 6 side, two flat side surfaces (flat side surfaces) facing each other, and two semi-cylindrical surface shapes facing each other. And side surfaces (two curved side surfaces arranged in a direction orthogonal to the direction in which the two flat side surfaces are arranged).

  The anode support 21 has a plurality of gas flow paths 22 at the center thereof. The gas flow path 22 is provided along the longitudinal direction of the anode support 21. One end (lower end) of the gas passage 22 is located on the lower surface of the anode support 21, and the other end (upper end) of the gas passage 22 is located on the upper surface of the anode support 21. In the present embodiment, four gas flow paths 22 are provided in each anode support 21. The anode support 21 is fixed to the manifold 8, and one end of the gas flow path 22 is communicated with the manifold 8. The reformed gas generated in the reformer 6 is distributed to the gas flow path 22 of each fuel cell 20 by the manifold 8 and flows from one end of the gas flow path 22 to the other end side.

  The interconnector 26 is provided on one flat side surface of the anode support 21 (on the left flat side surface in the fuel cell stack 10-1 in the first row in FIG. 3). The interconnector 26 is a conductive member for collecting current from the anode of each fuel cell 20. The interconnector 26 can be made of, for example, a conductive ceramic.

  The anode catalyst layer 23 is provided on the surface of the anode support 21. In the present embodiment, the anode catalyst layer 23 is laminated at least on the other flat side surface of the anode support 21 (on the right flat side surface in the fuel cell stack 10-1 in the first row in FIG. 3).

  The electrolyte layer 24 is provided on the surface of the anode catalyst layer 23 opposite to the anode support 21. In the present embodiment, the electrolyte layer 24 covers the entire surface of the anode catalyst layer 23. The cathode catalyst layer 25 is provided on the surface of the electrolyte layer 24 opposite to the anode catalyst layer 23. In the present embodiment, the cathode catalyst layer 25 is laminated on the main surface of the electrolyte layer 24. Therefore, the anode support 21 is disposed on the side opposite to the interconnector 26. That is, in the fuel cell 20, the anode catalyst layer 23, the electrolyte layer 24, and the cathode catalyst layer 25 are laminated in this order on one surface of the anode support 21 having the gas flow path 22, and the other surface of the anode support 21. And an interconnector 26 is formed. The constituent materials of the anode support 21, the anode catalyst layer 23, the electrolyte layer 24, and the cathode catalyst layer 25 will be described in detail later.

  The plurality of fuel cells 20 are arranged in a row so that one cathode catalyst layer 25 and the other interconnector 26 in two adjacent fuel cells 20 face each other, and are joined to each other via a current collecting member 30. The That is, as shown in FIG. 3, the interconnector 26 located on the left side of each fuel cell 20 is joined to the cathode catalyst layer 25 located on the right side of the adjacent fuel cell 20 via the current collecting member 30. As a result, a plurality of fuel cells 20 arranged in a row are connected in series to form the fuel cell stack 10. In the present embodiment, the fuel cell stack 10 includes a first row of fuel cell stacks 10-1 and a second row of fuel cell stacks 10-2. The current collecting member 30 can be composed of a member having a predetermined shape formed from a metal or alloy having elasticity, or a member obtained by performing a predetermined surface treatment on a felt made of metal fiber or alloy fiber.

  In the hot module 1 having the above-described configuration, raw fuel for hydrogen production is supplied from the supply pipe 3 to the reformer 6, and reforming water is supplied from the supply pipe 52 to the water vaporizer 50. The reformer 6 reforms the raw fuel by a steam reforming reaction to generate a hydrogen-rich reformed gas used for power generation of the fuel cell 20. The generated reformed gas is supplied to the manifold 8 via the reformed gas supply pipe 7. The reformed gas supplied to the manifold 8 is distributed to each fuel cell 20 and rises in the gas flow path 22 of each fuel cell 20. In this process, hydrogen in the reformed gas permeates through the anode support 21 and reaches the anode catalyst layer 23. On the other hand, cathode air is introduced into the module case 2 from the supply pipe 4. The cathode air introduced into the module case 2 is supplied to each fuel cell 20, and oxygen in the cathode air reaches the cathode catalyst layer 25.

In the cathode catalyst layer 25 located on the outer peripheral side of each fuel cell 20, an electrode reaction represented by the following formula (5) occurs. O ²⁻ produced in the cathode catalyst layer 25 permeates the electrolyte layer 24 and reaches the anode catalyst layer 23. Further, an electrode reaction represented by the following formula (6) occurs in the anode catalyst layer 23 located on the center side of the fuel cell 20. Thereby, power generation is performed in the fuel cell 20.
1 / 2O ₂ + 2e ⁻ → O ²⁻ (5)
O ²⁻ + H ₂ → H ₂ O + 2e ⁻ (6)

  Of the reformed gas flowing through the gas flow path 22, surplus reformed gas that has not been used for the electrode reaction is released into the module case 2 from the upper end of the anode support 21. This reformed gas is burned in the combustion section located between the reformer 6 and the water vaporizer 50 and the fuel cell stack 10. Predetermined ignition means (not shown) is provided in the module case 2, and when the reformed gas starts to be released to the combustion section, the ignition means is activated and combustion of the reformed gas is started. Of the cathode air introduced into the module case 2, surplus air that has not been used for the electrode reaction is used for combustion of the reformed gas. The inside of the module case 2 becomes a high temperature of about 600 ° C. to 1000 ° C., for example, due to heat generated by the power generation of each fuel cell 20 and heat generated by combustion of the surplus reformed gas. The water vaporizer 50 and the reformer 6 perform the vaporization and reforming reaction of the reforming water using the heat generated from the fuel cell 20 and the heat generated by the combustion of the reformed gas. The exhaust gas generated by the combustion of the reformed gas in the module case 2 is discharged out of the module case 2 through the exhaust port 5.

  Next, the composition of each part constituting the fuel cell 20 will be described in detail. FIG. 4 is an enlarged schematic view showing a part of the anode support. The anode support 21 is required to have gas permeability in order to permeate fuel from the gas flow path 22 to the anode catalyst layer 23. Further, the anode support 21 is required to have conductivity in order to transmit electrons generated in the anode catalyst layer 23 to the interconnector 26.

  Therefore, the anode support 21 according to the present embodiment has a base 210 that is porous. By making the base 210 porous, the reformed gas can be transmitted from the gas flow path 22 to the anode catalyst layer 23. Further, the base 210 includes at least one of Ni metal and Ni oxide. Ni contained in the base 210 takes the state of Ni oxide during the manufacture of the anode support 21 and the fuel cell 20, and becomes substantially Ni metal after a predetermined reduction process. Further, before driving the fuel cell system 100, a mixed state of oxidized Ni / Ni metal in which a part of the particle surface is oxidized is taken, and reducing reformed gas is circulated while the fuel cell system 100 is driven. In the meantime, most of the metal is reduced and can be substantially in the state of Ni metal. In FIG. 4, Ni metal and Ni oxide are not distinguished from each other and are illustrated as a nickel portion 212. Since the base 210 has the nickel portion 212, conductivity can be imparted to the anode support 21.

The base 210 includes at least one of Ni metal and Ni oxide (that is, the nickel portion 212), and at least one oxide 214 selected from the group consisting of Y ₂ O ₃ , a zirconia-based composite oxide, and a ceria-based composite oxide. It is preferable that the composite is That is, the base 210 is preferably a nickel cermet composed of Ni metal and / or Ni oxide and a porous conductive ceramic. Examples of the zirconia-based composite oxide include YSZ, ScSZ (Scandia Stabilized Zirconia) and the like. Examples of the ceria-based composite oxide include SDC (Samaria-Doped Ceria), YDC (Yttria-Doped Ceria), LDC (La ₂ O ₃ -doped Ceria), GDC (Gadolinia-doped Ceria), and the like.

  The anode support 21 preferably has an open porosity of 20% or more, more preferably 25% to 50%. The anode support 21 preferably has a conductivity of 100 S / cm or higher, more preferably 200 S / cm or higher. In order to satisfy these requirements, when the anode support 21 is manufactured, the base 210 is preferably 40% by mass or more, more preferably 40% by mass or more, in terms of Ni oxide, with respect to the total mass of the anode support 21. It contains 80 mass%, more preferably 40 mass% to 75 mass% Ni atoms. By setting the content of Ni atoms in the base 210 to 40 mass% or more in terms of Ni oxide, desired conductivity can be more reliably imparted to the anode support 21. Moreover, a desired open porosity can be more reliably imparted to the anode support 21 by setting the content of Ni atoms in the base 210 to 80% by mass or less in terms of Ni oxide. As for the dimension of the anode support 21, the height (length from the upper end to the lower end) is, for example, 7 cm to 20 cm.

  As a manufacturing method of the base 210, a composite composition containing nickel oxide and oxide 214 is processed into a support shape by means of extrusion molding or the like, and subjected to appropriate firing treatment to obtain predetermined dimensions and porosity. A preferred example is a method of forming a cermet having the same. The cermet is subjected to a reduction treatment before it is used as a fuel cell after all cell constituent layers are finally formed. This reduction treatment is usually performed by heating the fuel cell 20 or the fuel cell stack 10 to a predetermined temperature in a reducing gas stream such as hydrogen gas or hydrogen gas diluted with nitrogen. By this reduction treatment, almost all of the nickel oxide contained in the base portion 210 is reduced to Ni metal.

  Conventionally, the operating temperature of SOFC is often a high temperature of 700 ° C. or higher. On the other hand, in recent years, improvements in electrolyte materials and air electrode materials have progressed, and SOFCs capable of operating at a low temperature of about 600 ° C. or lower are being used. However, when the operating temperature of the fuel cell 20 decreases, the temperature of the reformer 6 also decreases in the hot module 1 that performs the reforming reaction in the reformer 6 using the heat generated by the fuel cell 20. In this case, a reformed gas having a high methane ratio may be generated due to thermal equilibrium.

  Further, when a raw fuel containing C2 or higher hydrocarbons is used, the reformer 6 may cause the C2 or higher hydrocarbons to be supplied to the fuel cell 20 without being converted into C1 chemical species (C2 or higher hydrocarbon slips). Occurrence). Further, the fuel cell system 100 may be stopped due to various reasons such as a user instruction, a purpose of improving the energy saving effect, and a trouble of the device. In the system stop process and the subsequent restart process, the reformer 6 may not be sufficiently heated even with a conventional SOFC operating at a high temperature. Also in this case, the above-described methane concentration increase or a situation where the reformed gas mixed with C2 or more hydrocarbons is supplied to the fuel cell 20 may occur.

  In particular, in the system stop process, after the power generation of the fuel cell 20 is stopped, the fuel cell 20 may be gradually cooled while the reformed gas is continuously supplied to the fuel cell 20. The reformed gas is supplied for the purpose of preventing air from flowing into the anode support 21 and the anode catalyst layer 23 and re-oxidation of the anode support 21. In this case, the reformed gas is supplied to the fuel cell 20 for several hours even after the power generation of the fuel cell 20 is stopped. On the other hand, as the temperature of the fuel cell 20 decreases, the temperature of the reformer 6 also decreases. For this reason, there is a high possibility that high-concentration methane or unreformed C2 or higher hydrocarbon compound is supplied from the reformer 6 to the fuel cell 20.

  When high-concentration methane or C2 or higher hydrocarbon compounds are supplied to the fuel cell 20, the fuel cell system having the conventional anode support may cause various forms of carbon deposition in various places. Such carbon deposition is likely to occur, for example, in the manifold, the upstream portion of the anode support in the fuel gas flow direction, in the pores of the anode support, or in places where the potential changes due to the external current collecting structure in the hot module. .

  For example, carbon deposition includes a large amount of hydrocarbons containing C2 or more and low S / C reformed gas is supplied to the fuel cell, or high concentration of methane is included and low S / C reformed gas is supplied. Occurs when it is done. When carbon is deposited in the pores of the anode support 21 or on the Ni particles, this causes dimensional expansion of the anode support. When the anode support is expanded, there is a possibility that stress deformation and cracks may occur. In addition, stress deformation occurs in the sealing material covering the joint between the anode support and the manifold, which may lead to cracking or peeling. In particular, when the raw fuel contains a hydrocarbon compound having 2 or more carbon atoms in an amount of 5 mol% or more based on the total molar amount of the raw fuel, the above-described carbon deposition tends to occur.

  The anode catalyst layer 23 is a composite composed of at least one of Ni metal and Ni oxide and at least one composite oxide selected from the group consisting of zirconia composite oxide, ceria composite oxide, and LSGM. Preferably there is. Specifically, the anode catalyst layer 23 is made of Ni / YSZ, Ni / ScSZ, Ni / SDC, Ni / YDC, Ni / LDC, Ni / GDC, Ni / LSGM (La—Sr—Ga—Mg composite oxide). Preferably, at least one cermet selected from the group consisting of: The layer thickness of the anode catalyst layer 23 is, for example, 0.1 μm to 50 μm.

  The electrolyte layer 24 functions as an electrolyte that bridges electron conduction and ion conduction between the electrodes, and also functions as a gas barrier layer for preventing leakage of fuel gas and air. The electrolyte layer 24 preferably includes at least one composite oxide selected from the group consisting of a zirconia composite oxide, a ceria composite oxide, and LSGM. Specifically, a solid electrolyte selected from the group consisting of YSZ, ScSZ, SDC, YDC, LDC, GDC, and LSGM is preferably used for the electrolyte layer 24. The layer thickness of the electrolyte layer 24 is, for example, 0.2 μm to 200 μm.

The cathode catalyst layer 25 can be formed using a conductive ceramic composed of a so-called ABO ₃ type perovskite oxide. The cathode catalyst layer 25 is required to have gas permeability. Therefore, the open porosity of the cathode catalyst layer 25 is preferably 20% or more, and more preferably 30% to 50%. Therefore, the cathode catalyst layer 25 preferably contains a composite oxide such as LSM (La Sr Mn), LSC (La Sr Co), or LSCF (La Sr Co Fe). The layer thickness of the cathode catalyst layer 25 is, for example, 2 μm to 200 μm. However, this does not apply when the cathode catalyst layer 25 has a function of electrically connecting to the current collector 30 or when the cathode catalyst layer 25 itself has a function of collecting current. Depending on the materials of the anode catalyst layer 23, the electrolyte layer 24 and / or the cathode catalyst layer 25 described above, the operation of the fuel cell 20 at a temperature of about 600 ° C. or lower can be realized.

  The anode catalyst layer 23, the electrolyte layer 24, and the cathode catalyst layer 25 are laminated on the anode support 21 in this order. Further, the interconnector 26 is sintered to the anode support 21. Thereby, the fuel cell 20 is formed. In the process of forming the anode support 21 described above, by sintering the composite composition to be the anode support 21 and simultaneously sintering the anode catalyst layer 23 and the electrolyte layer 24 to the composite composition, residual stress can be reduced. A structure including the anode support 21, the anode catalyst layer 23, and the electrolyte layer 24 can be formed in a small amount.

(Evaluation method of solid oxide fuel cell)
With respect to the nickel cermet used for the anode support 21, the present inventors have found that the carbon accumulation behavior on the anode support 21 under the condition where the low S / C hydrocarbon-containing gas is exposed, the structure change of the support and the accompanying change. As a result of earnestly examining the macroscopic dimensional expansion behavior of the support itself, regarding the mechanism of carbon deposition, the state / physical property change of the anode support 21 when carbon deposition occurs, the critical conditions for dimensional expansion, and the recovery conditions The following findings were obtained.

(1) Low S / C, specifically, a mixed gas of hydrocarbons and steam with S / C <1 in which hydrocarbon reforming of hydrocarbons occurs without complete steam reforming in thermodynamic equilibrium with nickel cermet When exposed to a containing anode support at elevated temperatures, carbon deposits on the nickel particles in the anode support.

(2) Carbon deposition proceeds sequentially from the surface of the anode support on the side in contact with the fuel gas, and gradually diffuses into the inside through the pores of the nickel cermet, so that the carbon deposition site gradually expands inside. To do.

(3) When carbon deposition proceeds, at least the surface exposed to the mixed gas expands two-dimensionally, and if there are a plurality of exposed surfaces depending on the shape of the anode support, the entire anode support expands three-dimensionally. Then, dimensional expansion is observed by a displacement meter (Dilatometer). At this time, dimensional expansion starts when the thickness of the carbon deposition site (depth from the surface layer) exceeds a certain value.

The analysis results related to the findings (2) and (3) are described below.
NiO (Sumitomo Metal Mining, NiO-FP) and YSZ (Tosoh, TZ8YS) were wet-mixed at a volume ratio of 40:60, dried, and then fired at 600 ° C. for 1 hour. Cross-linked polymethyl methacrylate (Sekisui Chemical Co., Ltd.) was mixed with the obtained powder at a weight ratio of 30%, and after dry grinding, a pellet-like sample was molded with an isostatic press of 100 MPa. NiO / YSZ pellets were prepared by firing the green compact pellets at 1300 ° C. for 4 hours in the air. An approximately 2 × 2 × 10 mm rectangular parallelepiped sample was cut out from this pellet and subjected to a reduction treatment in hydrogen at 800 ° C. for 5 hours to prepare a Ni / YSZ sample for a hydrocarbon exposure test. The porosity of NiO / YSZ before the reduction was about 17%, and the porosity of the Ni / YSZ sample after the reduction treatment was about 35%.

In order to evaluate the deformation of the Ni / YSZ sample due to carbon deposition, a hydrocarbon exposure test was performed in a Diatomometer manufactured by Netzsch. The gas was supplied at a rate of 100 cc / min. The change in length of the long side of the rectangular parallelepiped was measured as the change in shape of the sample. The Ni / YSZ sample was heated at 5 ° C./min in a dry 5% H ₂ / N ₂ atmosphere and maintained at 800 ° C. After confirming that the sample length was stable, the supply of 1% propane / N2 gas was started, and at a predetermined hydrocarbon exposure time (10 minutes, 20 minutes, 30 minutes, 60 minutes, 90 minutes, 120 minutes) The samples were exposed to 1% propane / N2 gas so that The amount of water vapor in the hydrocarbon fuel was controlled by bubbling temperature-controlled water. When the change in the shape of the sample was large, the fuel was purged with dry N ₂ without waiting for the end of the deformation behavior, and then the temperature was lowered and the sample was taken out.

  The sample taken out was cut at a cross-section including the sample surface that was most susceptible to gas exposure when the Dilatometer was installed. With respect to the obtained cut surface, each element concentration (count number) of Ni, Zr, and C was measured for each distance from the surface layer by SEM-EDX, and the intensity ratio of each element and the elemental composition of the original sample were determined. Each element concentration was calculated by multiplication. FIG. 5 is a graph showing the carbon element concentration with respect to the depth (distance) from the surface of the anode support in mass%.

FIG. 6 is a graph in which the deepest depth (distance) from the surface of the anode support that is a predetermined carbon concentration (1% by mass in this case) or more is defined as “carbon deposition thickness” and is arranged with respect to the exposure time. is there. As shown in FIG. 6, the carbon deposition thickness was found to be nearly zero until the exposure time was 10 minutes and then increased. In addition, the coefficient of expansion relative to the sample major axis also increases in correlation with the carbon deposition thickness. FIG. 7 is a graph showing changes in expansion coefficient with respect to carbon deposition thickness. As shown in FIG. 7, it was clarified that the expansion starts when the carbon deposition thickness is constant (hereinafter referred to as D_allow) or more (in this case, about 60 μm). D_allow was investigated for anode supports formed with various compositions. The results are shown in Table 1.

The sample cut from the Ni / YSZ sample described above is set in a heating furnace with a quartz window, and the gas atmosphere is changed from N ₂ to diluted propane gas (S / C = 0.1) while heating to 400 ° C. with an infrared lamp. Switched. A dimensional expansion coefficient was measured by image processing with a CCD camera, and the number of cracks on the electrolyte surface was visually measured. FIG. 8 is a graph showing the relationship between the expansion rate of the sample and the number of cracks visually observed. As shown in FIG. 8, cracks were not observed up to an expansion rate of 0.2%, but cracks occurred in any of the four samples between 0.2 and 0.4%.
(4) Since dimensional expansion due to such hydrocarbon exposure occurs selectively in the support Ni cermet site and not in adjacent layers such as electrolyte, stress in the support / electrolyte (extension stress with respect to the electrolyte) When this stress exceeds a certain critical point, the electrolyte layer is broken (cracked).

(5) When the support on which carbon deposition has once occurred is exposed to a gas of S / C> 1 in which steam reforming and removal of the precipitated carbon are predominantly thermodynamically, a part of the deposited carbon may be depending on conditions. Removed. However, when dimensional expansion of the support occurs due to carbon deposition, the dimensions are not completely restored until before exposure.

  From the above findings (1), (2), and (3), it was found that if the carbon deposition state in the depth direction from the surface of the anode support was observed by some method, the dimensional expansion of the support was in advance or very small. But the degree can be quantified. In addition, from the above knowledge (3), there is a “allowable value D_allow that does not lead to dimensional expansion even when carbon is deposited”, and the potential destruction risk is predicted according to the amount of deposited carbon even if dimensional change does not occur. It became possible to do. That is, the depth profile of the amount of carbon deposition from the anode support surface is a good evaluation index regarding the degree of progress of destruction due to carbon deposition or the potential risk until the destruction due to carbon deposition in the fuel cell system. I found it.

  From the above findings (1) and (4), it is possible to predict how much carbon deposition has progressed from the operating conditions or operating history of the fuel cell. For example, it is possible to make a self-diagnosis in light of the above-mentioned evaluation index to determine whether the progress of destruction related to carbon deposition or an increase in the risk of destruction has occurred due to a decrease in the temperature of the reformer, a decrease in the output of the reforming water pump, or the like.

  Furthermore, from the above knowledge (5), in the region where carbon is deposited but not yet destroyed, a recovery method is found to remove the deposited carbon and reduce the risk of destruction once increased.

  By combining these fuel cell evaluation methods, self-diagnosis methods, and return methods, the risk of destruction due to carbon deposition on the fuel cell stack can be correctly grasped, and the return operation can be performed appropriately to avoid destruction, and in turn fuel cells. It has been found that the reliability and long-term durability of the system can be increased.

  A method for evaluating the solid oxide fuel cell according to the present embodiment devised based on the above knowledge will be described. In the evaluation method, the performance of the solid oxide fuel cell is evaluated based on the carbon concentration near the surface of the anode support facing the gas flow path.

  FIG. 9 is a flowchart showing an aspect of a method for evaluating a solid oxide fuel cell. As shown in FIG. 9, first, as the information on the carbon concentration near the surface of the anode support facing the gas flow path, the outermost surface of the anode support facing the gas flow path where the carbon concentration is equal to or higher than the reference concentration C. Depth D (corresponding to the aforementioned deepest depth or carbon deposition thickness) is acquired (S10). The “depth from the outermost surface of the anode support” is determined by the distance from the outermost surface in the normal direction of the outermost surface of the anode support. The reference concentration C is usually determined in the range of 100 ppm to 10% by weight ratio of carbon to the anode support.

  Depth direction analysis methods such as secondary ion mass spectrometry (SIMS), X-ray photoelectron spectroscopy (XPS / ESCA), Auger electron spectroscopy (AES), etc. And elemental analysis of the sample cross section by SEM / EDX. These analyzes are usually performed on sample pieces taken from the anode support.

By comparing the depth D obtained with a predetermined reference depth D _0, a solid oxide fuel cell is evaluated. Specifically, when the acquired distance D is less than the reference depth D ₀ , the process proceeds to yes of S20, and it is determined that there is no possibility of cell destruction due to carbon deposition (S30). On the other hand, if the obtained distance D is the reference depth D ₀ or more, the process proceeds to no in S20, it is determined that there is a possibility of cell destruction by carbon deposition (S40). Note that the reference depth D ₀ is usually determined in the range of 1 to 200 μm, and if the acquired distance D is equal to or greater than the reference depth D _0, it is necessary to perform some processing for restoring the cell performance. It can be judged that there is.

Note that D ₀ is determined based on the allowable value D_allow that does not lead to dimensional expansion even when carbon is deposited as described above, and the same value as D_allow may be used. It may be used with some safety factor N by comparing with the actual test results for the fuel cell system.
D ₀ = D_allow × N
The safety factor N in this case is usually in the range of 0.2 to 5, preferably 0.5 to 3. If N does not fall within the above range and is a value significantly deviating from 1, the result of the physical property test of the support does not reflect the actual fuel cell system, and from the viewpoint of the validity of the test conditions. It is not preferable. In such a case, it is preferable to acquire physical property information again using hydrocarbon species close to the actual system, temperature, and S / C range so that N is within the above range.

(Control method of solid oxide fuel cell system)
A control method of the solid oxide fuel cell system implemented in relation to the above-described fuel cell evaluation method will be described below.

Controller 200 is indicative of the carbon concentration in the surface of the anode support, as the depth D does not become higher than the reference depth D _0, start condition, the power generation operation conditions, at least one control of the stop condition To do. The start condition refers to an operation condition set at start-up until the temperature of the fuel cell reaches a predetermined temperature (for example, 600 ° C.) after the start of start of the fuel cell system and power generation is started. The power generation operation condition is an operation condition set at the time of the power generation operation until the power generation is stopped and the amount of fuel to be supplied is started to be reduced after the startup. The stop condition refers to an operation condition that is set when the fuel cell system stops completely after power generation stops.

(Startup condition control)
In the starting condition control, the water vapor molar ratio (S / C value) with respect to the number of moles of hydrocarbons contained in the fuel gas supplied to the fuel cell before the start of power generation is determined during normal operation (eg, 2.2 to 2.5 ) Is set higher.

(Power generation operating condition control)
When it is determined that the amount of carbon accumulated on the anode support has increased from the reference value at any time during the power generation operation, the water vapor molar ratio (S / C value) to the number of moles of hydrocarbon fuel is calculated. Accumulated carbon removal control is performed for a predetermined time period higher than that during normal operation (eg, 2.2 to 2.5).

  Examples of the case where the carbon accumulation amount on the anode support is judged to have increased from the reference value include a decrease in the steam supply amount for fuel gas reforming, an increase in the hydrocarbon feed rate, or a steam reforming reaction. A case where the degree of temperature drop of the vessel exceeds a predetermined reference value can be mentioned.

(Stop condition control)
In the stop condition control, the fuel gas is continuously supplied to the fuel cells, and the water vapor molar ratio (S / C value) to the number of moles of hydrocarbon fuel supplied to the fuel cells is normally operated. Set higher than time (for example, 2.2 to 2.5).

  As described above, according to the present embodiment, cell evaluation based on the carbon deposition mechanism can be appropriately performed on the anode support for a solid oxide fuel cell. Further, by making use of the knowledge about the carbon deposition mechanism, even when the raw fuel contains C2 or more and 5 mol% or more of hydrocarbons, the expansion failure of the anode support due to the carbon deposition can be effectively suppressed. .

  The present invention is not limited to the above-described embodiments, and various modifications such as design changes can be added based on the knowledge of those skilled in the art. Embodiments to which such modifications are added Can also be included in the scope of the present invention.

  Examples of the present invention will be described below. However, these examples are merely examples for suitably explaining the present invention, and do not limit the present invention.

(Reference Example 1)
Anode support made of 50% Ni / YSZ, anode catalyst layer made of Ni / YSZ, electrolyte layer made of YSZ, LSCF (La _0.6 Sr _0.4 Co _0.2 Fe _0.8 A cylindrical flat plate type fuel cell having a laminate in which a cathode catalyst layer formed of O _3−δ was used was used as a fuel gas, 70% H ₂ /20% H ₂ O / 15% CO ₂ / A steam reformed gas containing a base gas having a composition of 10% CO / 5% CH ₄ was supplied to the anode catalyst layer, and air was supplied as an oxidant gas to the cathode catalyst layer at a cell temperature of 670 ° C. during normal operation. The fuel gas utilization rate was 75% and the oxidant gas utilization rate was 40% .At the time of shutdown, steam reformed gas was introduced until the cell temperature became less than 350 ° C. When stopped The S / C ratio was set to 2.2, and a 200 cycle endurance test was conducted with a start time of 3 h, normal operation time of 8 h, stop time of about 6 h, and an interval of about 7 h as one cycle. After the cell was stopped, a part of the cell was extracted, and the carbon deposition thickness was measured.Specifically, the cylindrical flat plate cell was cut out perpendicular to the height direction, and the carbon concentration in the depth direction from the fuel gas flow path was measured. The distribution was measured by EDX, and the measured carbon deposition thickness (standard concentration 1% by SEM / EDX) was 4 μm.

(Comparative Example 1)
In order to intentionally create a state in which the anode support is damaged due to carbon deposition, propane (concentration: 1) is used in the state in which the reforming water pump is forcibly stopped at the same time as power generation is stopped. %) Was fed to the fuel cell over 30 minutes. Specifically, propane as a raw material gas was directly introduced into the fuel cell by bypassing the reformer and then returning to the fuel gas supply line on the downstream side of the reformer outlet. A 200 cycle endurance test was performed on the cell of Comparative Example 1 under the same conditions as Reference Example 1 except that only propane was supplied to the cell at the time of stopping. The carbon deposition thickness (reference concentration 1%) measured after stopping the first cycle was 38 μm.

Example 1
Similarly to Comparative Example 1, after stopping only by supplying propane to the fuel cell at the time of stoppage, the recovery operation was performed with an S / C ratio of 3.5 over 30 minutes in the steam reforming process at the second start-up time. Carried out. The other conditions were the same as those in Reference Example 1, and a 200-cycle durability test was performed on the cell of Example 1. The carbon deposition thickness (reference concentration 1%) measured after the stop of the first cycle was 36 μm, but the carbon deposition thickness (reference concentration 1%) after the second cycle stop was reduced to 7 μm. .

(Example 2)
As in Comparative Example 1, only propane was supplied to the fuel cell when stopped. In Example 2, the recovery operation was performed with an S / C ratio of 3 over 30 minutes at the start-up after the second cycle. The other conditions were the same as those in Reference Example 1, and a 200-cycle durability test was performed on the cell of Example 1. The carbon deposition thickness (reference concentration 1%) measured after stopping the first cycle was 47 μm.

  FIG. 10 shows the relative value of the output voltage for each fuel cell of Reference Example 1, Comparative Example 1, and Examples 1 and 2 in which the durability test was performed as described above, based on the output voltage before the start of the test. It is a graph which shows a change. When it was defined as the life until the voltage drop rate from the output voltage before the start of the test exceeded 10%, in Comparative Example 1, the life was about 10 cycles. In Comparative Example 1, the amount of deposited carbon accumulates with the start and stop, cracks occur in the electrolyte layer when the stress limit is exceeded, and the voltage drops significantly due to reoxidation of the anode support accompanying fuel gas leakage, It was confirmed that power generation would eventually become impossible.

  On the other hand, in Example 1 in which the S / C ratio was set larger than that in Comparative Example 1 when stopped, and in Example 2 in which the S / C ratio was set larger than that in Comparative Example 1 at start-up, Comparative Example 1 Such a remarkable voltage drop was not recognized, and it was confirmed that the life exceeded 200 cycles as in Reference Example 1 in which propane was not supplied at the time of stoppage.

(Reference Example 2)
A 10-cycle endurance test was performed under the same conditions as in Reference Example 1 except that the S / C ratio was set to 2.5 during startup, during power generation, and during shutdown. The carbon deposition thickness (reference concentration 1%) measured after stopping the first cycle was 3 μm.

(Comparative Example 2)
In Comparative Example 2, during normal operation, only propane (concentration: 1%) was supplied to the fuel cell for 30 minutes. The other conditions were the same as in Reference Example 2, and a 10-cycle durability test was performed on the cell of Comparative Example 2. The carbon deposition thickness (reference concentration 1%) measured after stopping the first cycle was 78 μm.

(Example 3)
Similarly to Comparative Example 2, during the normal operation, after supplying only propane to the fuel cell, the recovery operation was carried out with an S / C ratio of 5 over 30 minutes. The other conditions were the same as in Reference Example 2, and a 10-cycle durability test was performed on the cell of Example 1. The carbon deposition thickness (reference concentration 1%) measured after stopping the first cycle was 16.5 μm.

  FIG. 11 shows the change in the relative value of the output voltage for each fuel cell of Reference Example 2, Comparative Example 2, and Example 3 where the durability test was performed as described above, with reference to the output voltage before the start of the test. It is a graph to show.

  In Comparative Example 2, in the second cycle, the output voltage decreased by about 23% from the value before the start of the test, and the lifetime was one cycle. On the other hand, in Example 3, it was confirmed that the lifetime was 10 cycles or more, as in Reference Example 2 in which only propane was not supplied during normal operation.

6 reformer, 20 fuel cell, 21 anode support, 23 anode catalyst layer, 24 electrolyte layer, 25 cathode catalyst layer, 100 fuel cell system, 210 base, 212 nickel part, 214 oxide

Claims (11)

An anode support formed of a porous material containing nickel metal and having a gas flow path through which fuel gas flows, and a fuel electrode layer, a solid oxide electrolyte layer, and an air electrode layer formed on the anode support A method for evaluating a solid oxide fuel cell comprising:
A method for evaluating a solid oxide fuel cell, wherein the solid oxide fuel cell is evaluated based on a carbon concentration in the vicinity of the surface of the anode support facing the gas flow path.   Obtaining the depth from the outermost surface of the anode support facing the gas flow path where the carbon concentration is equal to or higher than a predetermined reference concentration, and comparing the depth with a predetermined reference depth, the solid oxidation 2. The method for evaluating a solid oxide fuel cell according to claim 1, wherein the physical fuel cell is evaluated.   3. The solid oxide according to claim 2, wherein when the depth is equal to or greater than a predetermined reference depth, it is determined that a process for recovering the performance of the solid oxide fuel cell is necessary. Of evaluating fuel cell.   The method for evaluating a solid oxide fuel cell according to claim 3, wherein the reference depth is in the range of 1 to 200 μm.   5. The method for evaluating a solid oxide fuel cell according to claim 1, wherein the reference concentration of the carbon concentration is in a range of 100 ppm to 10% by weight with respect to the anode support.   The method for evaluating a solid oxide fuel cell according to any one of claims 1 to 5, wherein the anode support includes nickel cermet.   The method for evaluating a solid oxide fuel cell according to claim 6, wherein the Ni oxide content is 40% by mass or more based on the total mass of the anode support when the anode support is manufactured. A reformer that generates hydrogen-rich fuel gas through a reforming reaction;
An anode support formed of a porous material containing nickel metal and having a gas path through which the fuel gas flows, and a fuel electrode layer, a solid oxide electrolyte layer, and an air electrode layer formed on the support are laminated. A solid oxide fuel cell that generates electric power by reacting fuel gas supplied from the reformer and air,
In order to prevent the depth from the outermost surface where the carbon concentration of the surface of the anode support becomes equal to or higher than a predetermined reference concentration from exceeding the predetermined reference depth, the start conditions until the start of power generation, the power generation operation conditions during power generation, A control unit that controls at least one of the stop conditions after the stop;
A solid oxide fuel cell system comprising:   The said control part sets the water vapor | steam molar ratio (S / C value) with respect to the carbon mole number of the supply hydrocarbon fuel of the fuel gas supplied to the said fuel cell as a said starting condition higher than the time of normal operation. 2. A solid oxide fuel cell system according to 1.   When it is determined that the amount of carbon stored in the anode support has increased at any point during the power generation operation, the control unit determines the water vapor mole ratio (S / C value) relative to the number of moles of hydrocarbon fuel. The solid oxide fuel cell system according to claim 8 or 9, wherein the control for removing the accumulated carbon is performed by raising the value for a predetermined time.   The control unit continues the supply of the fuel gas to the fuel cell after the power generation is stopped as the stop condition, and the water vapor molar ratio (S / C value to the number of carbon moles of the supplied hydrocarbon fuel at that time ) Is set higher than that during normal operation. 10. The solid oxide fuel cell system according to claim 8, wherein:

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