JP2012142191A - Solid oxide fuel battery operating state monitoring method and solid oxide fuel battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for monitoring the operating state of a solid oxide fuel battery based on a simple technique.SOLUTION: Following means are included: first cell monitoring voltage measurement means 300A which measures a first cell monitoring voltage (E) of fuel battery cells adjacent to or in proximity to each other on a fuel outlet side of a cell tube 202A; first oxygen partial pressure calculation means 301A which calculates oxygen partial pressure in fuel from a measured first cell monitoring voltage by using the relationship between a first cell monitoring voltage and oxygen partial pressure at a prescribed temperature calculated in advance; and first determination means 302A which compares the oxygen partial pressure and a prescribed threshold value to determine whether there is a possibility of the fuel battery cell being damaged.

Description

  The present invention relates to a method for monitoring the operating state of a solid oxide fuel cell and a solid oxide fuel cell.

  A solid oxide fuel cell (SOFC) is a fuel cell that generates electric power by an electrochemical reaction between a fuel gas reformed by reacting a hydrocarbon or oxygen-containing hydrocarbon with water vapor and oxygen. During this power generation, water is generated.

  A cylindrical solid oxide fuel cell is known as one embodiment of the solid oxide fuel cell. In this cylindrical solid oxide fuel cell, a power generation element is formed by laminating a fuel electrode, a solid oxide electrolyte, and an air electrode on the outer peripheral surface of a cylindrical base tube. A plurality of power generating elements are connected in series by an interconnector.

  Therefore, when fuel gas is supplied into the base tube and oxygen is supplied to the air electrode, the oxygen supplied to the air electrode is ionized and permeates the electrolyte membrane and reaches the fuel electrode. A potential difference is generated between the fuel electrode and the air electrode due to an electrochemical reaction between oxygen and fuel gas that has reached the fuel electrode, and electricity is generated by taking out the generated potential difference to the outside.

As a voltage monitoring method for operation of a conventional solid oxide fuel cell system, a method of monitoring the entire voltage of the entire submodule or cartridge (for example, about 100 cells) is known (Patent Documents 1 and 2).
There is also a proposal to determine the deterioration of a specific part by measuring the voltage at a part where the gas flow rate is slow (Patent Document 3).

JP-A-11-195423 JP 2007-87686 A JP 2010-27580 A

By the way, if the oxygen partial pressure in the fuel becomes high and the metal Ni constituting the fuel electrode is oxidized, the cell may be damaged. Therefore, it is necessary to monitor the oxygen partial pressure in the fuel.
On the other hand, if the oxygen partial pressure in the air is reduced and the constituent material of the air electrode (for example, LaSrCaMnO ₃ ) is reduced and decomposed, the cell may be damaged. Therefore, it is necessary to monitor the oxygen partial pressure in the air.
On the other hand, the above-mentioned abnormality determination such as cell damage cannot be made by measuring only the voltage of the entire cell stack.

  In view of the above problems, an object of the present invention is to provide a method for monitoring the operating state of a solid oxide fuel cell and a solid oxide fuel cell by a simple method.

  A first invention of the present invention for solving the above-mentioned problem is that a base tube having a cylindrical shape, a fuel electrode, an electrolyte, and an air electrode are laminated, and along the outer surface axial direction of the base tube. In the method of monitoring the operating state of a solid oxide fuel cell having a cell tube comprising a plurality of arranged fuel cells and an interconnector for connecting adjacent fuel cells in series, the fuel outlet side of the cell tube Measuring a first cell monitoring voltage between the fuel cells adjacent to or adjacent to each other, a step of obtaining an oxygen partial pressure in the fuel from the first cell monitoring voltage, and the obtained oxygen partial pressure And a method of monitoring the operating state of the solid oxide fuel cell, comprising the step of comparing with a predetermined threshold value.

  According to a second invention, in the method for monitoring the operating state of the solid oxide fuel cell according to the first invention, the relationship between the first cell monitoring voltage and the oxygen partial pressure at a predetermined temperature obtained in advance is used. The method for monitoring the operating state of a solid oxide fuel cell, comprising the step of determining the partial pressure of oxygen in the fuel.

  According to a third aspect of the present invention, in the method for monitoring an operating state of the solid oxide fuel cell according to the first aspect, the first cell monitoring voltage is measured and the temperature of the outer surface of the fuel cell is measured. And a step of calculating an equilibrium electromotive force from the first cell monitoring voltage and obtaining an oxygen partial pressure in the fuel. .

  According to a fourth aspect of the present invention, a cylindrical base tube, a fuel electrode, an electrolyte, and an air electrode are laminated, and a plurality of fuel cells arranged along the outer surface axial direction of the base tube are adjacent to each other. In the method of monitoring the operating state of a solid oxide fuel cell having a cell tube comprising an interconnector for connecting the fuel cells in series, a second of the interconnector on the fuel outlet side of the cell tube and the electrolyte Measuring the cell monitoring voltage of the fuel cell, determining the partial pressure of oxygen in the fuel from the second cell monitoring voltage, and comparing the determined partial pressure of oxygen with a predetermined threshold value. The feature is a method for monitoring the operating state of a solid oxide fuel cell.

  According to a fifth aspect of the present invention, in the method for monitoring the operating state of the solid oxide fuel cell according to the fourth aspect, the relationship between the second cell monitoring voltage and the oxygen partial pressure at a predetermined temperature obtained in advance is used. The method for monitoring the operating state of a solid oxide fuel cell, comprising the step of determining the partial pressure of oxygen in the fuel.

  According to a sixth aspect of the present invention, in the method for monitoring the operating state of the solid oxide fuel cell according to the fifth aspect, the second cell monitoring voltage is measured and the temperature of the outer surface of the fuel cell is measured. And a step of calculating an equilibrium electromotive force from the second cell monitoring voltage and obtaining an oxygen partial pressure in the fuel. .

  In a seventh aspect of the present invention, a cylindrical base tube, a fuel electrode, an electrolyte, and an air electrode are laminated, and a plurality of fuel cells arranged along the outer surface axial direction of the base tube are adjacent to each other. In the method for monitoring the operating state of a solid oxide fuel cell having a cell tube having an interconnector for connecting the fuel cells in series, the fuel cells adjacent to or adjacent to each other on the air outlet side of the cell tube A step of measuring a third cell monitoring voltage; a step of obtaining an oxygen partial pressure in the air from the third cell monitoring voltage; and a step of comparing the obtained oxygen partial pressure with a predetermined threshold value. This is a method for monitoring the operating state of a solid oxide fuel cell.

  According to an eighth aspect of the present invention, in the method for monitoring the operating state of the solid oxide fuel cell according to the seventh aspect, the relationship between the third cell monitoring voltage and the oxygen partial pressure at a predetermined temperature obtained in advance is used. The method for monitoring the operating state of a solid oxide fuel cell, comprising the step of determining the partial pressure of oxygen in the fuel.

  A ninth invention is the method for monitoring the operating state of the solid oxide fuel cell according to the eighth invention, wherein the third cell monitoring voltage is measured and the temperature of the outer surface of the fuel cell is measured. And a step of calculating an equilibrium electromotive force from the third cell monitoring voltage and obtaining a partial pressure of oxygen in the air. .

  In a tenth aspect of the invention, a cylindrical base tube, a fuel electrode, an electrolyte, and an air electrode are stacked, and a plurality of fuel cells arranged along the outer surface axial direction of the base tube are adjacent to each other. In a solid oxide fuel cell having a cell tube comprising an interconnector for connecting the fuel cells in series, a first cell monitoring voltage between the fuel cells adjacent to or adjacent to each other on the fuel outlet side of the cell tube Using the cell monitoring voltage measuring means for measuring the relationship between the first cell monitoring voltage and the oxygen partial pressure at a predetermined temperature obtained in advance, the oxygen partial pressure in the fuel from the measured first cell monitoring voltage A solid oxide comprising: an oxygen partial pressure calculating means for determining the fuel cell; and a determination means for comparing the oxygen partial pressure with a predetermined threshold to determine whether or not the fuel cell is likely to be damaged Fuel cell Located in.

  In an eleventh aspect of the present invention, a cylindrical base tube, a fuel electrode, an electrolyte, and an air electrode are stacked, and a plurality of fuel cells arranged along the outer surface axial direction of the base tube are adjacent to each other. In a solid oxide fuel cell having a cell tube provided with an interconnector for connecting the fuel cells in series, a second cell monitoring voltage between the interconnector and the electrolyte on the fuel outlet side of the cell tube is measured The oxygen partial pressure in the fuel is obtained from the measured second cell monitoring voltage using the cell monitoring voltage measuring means for measuring and the relationship between the second cell monitoring voltage and the oxygen partial pressure at a predetermined temperature obtained in advance. Solid oxide fuel characterized by comprising: oxygen partial pressure calculating means; and determining means for comparing the oxygen partial pressure with a predetermined threshold to determine whether or not the fuel cell is likely to be damaged battery A.

  In a twelfth aspect of the present invention, a cylindrical base tube, a fuel electrode, an electrolyte, and an air electrode are stacked, and a plurality of fuel cells arranged along the outer surface axial direction of the base tube are adjacent to each other. In a solid oxide fuel cell having a cell tube comprising an interconnector for connecting the fuel cells in series, a third cell monitoring voltage between the fuel cells adjacent to or adjacent to each other on the air outlet side of the cell tube Using the cell monitoring voltage measuring means for measuring the relationship between the third cell monitoring voltage and the oxygen partial pressure at a predetermined temperature determined in advance, the oxygen partial pressure in the fuel is determined from the measured third cell monitoring voltage. A solid oxide comprising: an oxygen partial pressure calculating means for determining the fuel cell; and a determination means for comparing the oxygen partial pressure with a predetermined threshold to determine whether or not the fuel cell is likely to be damaged Fuel cell Located in.

  According to the present invention, since the oxygen concentration in the fuel can be monitored by monitoring the voltage of the fuel outlet cell, cell damage due to a change in the operating state can be avoided.

FIG. 1-1 is a schematic view of one cell tube. FIG. 1-2 is a schematic view of a cell tube of a solid oxide fuel cell having first monitoring means. FIG. 1-3 is a schematic view of a cell tube of a solid oxide fuel cell having a second monitoring means. 1-4 is a schematic view of a cell tube of a solid oxide fuel cell having a third monitoring means. FIG. 2-1 is a diagram for measuring a cell voltage between cells on the fuel outlet side. FIG. 2B is a circuit corresponding to FIG. FIG. 3 is a schematic diagram showing the electric resistance of the cell. FIG. 4 is a relationship diagram between current density and voltage. FIG. 5 is a relationship diagram between the oxygen partial pressure and the equilibrium electromotive force. FIG. 6 is a relationship diagram between the cell monitoring voltage and the oxygen concentration. FIG. 7 is a diagram showing the measurement result of the oxygen partial pressure from the fuel inlet side (cell No. 1) to the outlet side (cell No. 48) of the cell stack. FIG. 8-1 is a diagram for measuring the cell voltage between the interconnector on the fuel outlet side and the solid electrolyte. FIG. 8B is a circuit corresponding to FIG. FIG. 9 is a relationship diagram between the oxygen partial pressure and the equilibrium electromotive force. FIG. 10A is a diagram of measuring a cell voltage between cells on the air outlet side. FIG. 10B is a circuit corresponding to FIG. FIG. 11 is a schematic configuration diagram illustrating a fuel cell according to the present embodiment. FIG. 12 is a schematic configuration diagram showing a fuel cell module.

  Hereinafter, the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments. In addition, constituent elements in the following embodiments include those that can be easily assumed by those skilled in the art or those that are substantially the same.

  A fuel cell operation monitoring method according to an embodiment of the present invention will be described with reference to the drawings. FIG. 11 is a schematic configuration diagram illustrating a fuel cell according to the present embodiment. FIG. 12 is a schematic configuration diagram showing a fuel cell module.

  As shown in FIG. 12, the fuel cell module 200 of the present embodiment includes a casing 201, a plurality of cell tubes (or “cell stacks”) 202 formed in a substantially cylindrical shape, and both ends of the cell tubes 202. The upper and lower tube plates (first partition members) 203a and 203b to be supported and upper and lower heat insulators 204a and 204b disposed between the upper and lower tube plates 203a and 203b are configured.

  A power generation chamber 205 is formed in a space between the upper and lower heat insulators 204a and 204b. A fuel supply chamber 206 is formed between the casing 201 and the upper tube plate 203a. A fuel discharge chamber 207 is formed between the casing 201 and the lower tube plate 203b. An air supply chamber 208 is formed between the lower tube sheet 203b and the lower heat insulator 204b. An air discharge chamber 209 is formed between the upper tube sheet 203a and the upper heat insulator 204a.

  The upper tube plate 203a is a plate-like member disposed on one side (upper side) of the casing 201 in the longitudinal direction (vertical direction in FIG. 12), and the lower tube plate 203b is the other side (lower side) of the casing 201 in the longitudinal direction. ) Is a plate-shaped member. The cell tube 202 is a substantially cylindrical tube formed of porous ceramics, and is provided with a plurality of fuel cells 210 that generate power at the center in the longitudinal direction (vertical direction in FIG. 12). The cell tube 202 is supported by the upper and lower tube plates 203a and 203b so that one open end opens into the fuel supply chamber 206 and the other open end opens into the fuel discharge chamber 207. Further, the cell tube 202 is arranged so that the fuel battery cell (power generation element) 210 is located only in the power generation chamber 205.

  The upper heat insulator 204a is a member that is disposed on one side (upper side) of the casing 201 in the longitudinal direction and is formed into a blanket shape or a board shape using a heat insulating material. The lower heat insulating material 204b is a member that is disposed on the other side (lower side) of the casing 201 in the longitudinal direction and formed in a blanket shape or a board shape using a heat insulating material. The heat insulators 204a and 204b are formed with holes 211a and 211b through which the cell tube 202 is inserted. The diameters of the holes 211a and 211b are larger than the diameter of the cell tube 202.

  The inner peripheral surfaces of the holes 211a and 211b may be formed in a substantially cylindrical shape, or may be formed with a spiral or linear concave portion (groove) or convex portion (a ridge-like projection), There is no particular limitation. With such a configuration, the heat of the lower heat insulator 204b is easily transferred to the air flowing into the power generation chamber 205 through the space between the cell tube 202 and the holes 211a and 211b, and the temperature of the power generation chamber 205 is reduced. It can be easily maintained at a high temperature.

  Here, the outline | summary of operation | movement of the fuel cell module 200 which consists of the said structure is demonstrated using FIG.

  Air flows into the air supply chamber 208 of the fuel cell module 200. The air is supplied into the power generation chamber 205 through a gap between the hole 211 b of the lower heat insulating material 204 b and the cell tube 202. On the other hand, fuel gas flows into the fuel supply chamber 206. The fuel gas is supplied into the power generation chamber 205 through the inside of the base tube of the cell tube 202. Air and fuel gas are used for power generation in the fuel battery cell 210. Thereafter, air flows into the air discharge chamber 209, and fuel flows into the fuel discharge chamber 207, and is discharged to the outside of the fuel cell module 200, respectively.

  At this time, the air and the fuel gas flow in opposite directions on the inner surface or outer surface of the cell tube 202. As a result, the fuel gas and air that have been used for power generation and have reached a high temperature are each subjected to heat exchange with the air and fuel gas before being used for power generation. That is, heat exchange is performed between the fuel gas and the air in the region where the fuel cell 210 is not formed at both axial ends of the cell tube 202.

  As described above, in the fuel cell module 200, the fuel gas and air that have been used for the reaction and have become high temperature are cooled by heat exchange, and then supplied to the fuel discharge chamber 207 and the air discharge chamber 209. This can prevent the upper tube plate 203a and the lower tube plate 203b having metal members from being exposed to a high temperature atmosphere. As a result, in the fuel cell module 200, the operating temperature of the fuel cell 210 can be increased, for example, from 800 ° C. to 950 ° C.

  Next, the cell tube (fuel cell) 202 used in the fuel cell module 200 of the fuel cell system described above will be described in detail.

  As shown in FIG. 11, the cell tube (fuel cell) 202 according to the embodiment generates power by laminating a fuel electrode 103, a solid electrolyte 104, and an air electrode 105 on the outer surface of a cylindrical tube 101 facing outward. An element, that is, a fuel battery cell (cell) 210 is formed, a plurality of fuel battery cells 210 are arranged in the axial direction of the base tube 101, and a plurality of cells 210 are connected in series by an interconnector 106. . In FIG. 11, reference numeral 107 indicates a central axis.

The cell tube 202 of an Example is demonstrated concretely. The base tube 101 is a ceramic cylinder and contains an iron group metal (for example, Ni), an iron group metal oxide (for example, NiO) having an internal reforming ability, an alloy or an alloy oxide thereof. For example, a mixture of Ni and CSZ (calcia stabilized zirconia-CaO stabilized ZrO ₂ ). A fuel passage is formed by the inner peripheral surface of the base tube 101. In this case, since the base tube 101 needs to pass the fuel gas F flowing through the fuel passage 102 to the fuel electrode 103, it is necessary to make the base tube 101 porous. It is necessary to mix.

The fuel electrode 103 is, for example, a mixture of Ni and YSZ (yttrium stabilized zirconia-Y ₂ O ₃ stabilized ZrO ₂ ), and has conductivity and is a porous material. A solid electrolyte 104 is laminated on the surface of the fuel electrode 103 opposite to the base tube 101, and is formed so as to exist between the fuel electrode 103 and the other fuel electrode 103 adjacent in the axial direction of the base tube 101. The solid electrolyte 104 is, for example, YSZ (yttrium stabilized zirconia-Y ₂ O ₃ stabilized ZrO ₂ ), and is made nonporous to avoid contact between the fuel gas F and air. The air electrode 105 is made of, for example, at least one kind of porous conductive ceramics such as a LaMnO ₃ material, a LaFeO ₃ material, and a LaCoO ₃ material.

In order to configure the cell tube 202, in the fuel cells 210 adjacent in the axial direction of the base tube 101, the fuel electrode 103 of one fuel cell 210 and the air electrode 105 of the other fuel cell 210 are They are connected by an interconnector 106. A part of the fuel electrode 103 is covered with a solid electrolyte 104 and a part thereof is covered with an interconnector 106. The interconnector 106 is made of, for example, a perovskite oxide such as SrTiO ₃ , a LaCrO ₃ based material, and the like, and is made nonporous to prevent gas leakage. Thus, since the interconnector 106 is not a metal material, it does not deteriorate due to oxidation or the like at high temperatures. Accordingly, the operating temperature of the fuel battery cell 210 can be increased, for example, 800 ° C. to 950 ° C.

  Further, the cell tube 202 of this embodiment is obtained by laminating and sintering the fuel electrode 103, the solid electrolyte 104, the interconnector 106, and the air electrode 105 on the outer surface of the base tube 101.

The cell tube (fuel cell) 202 described above performs a battery reaction by the following operation. That is, as shown in FIG. 11, the fuel gas F serving as the fuel for the cell reaction flows inside the base tube 101, passes through the pores of the base tube 101, and reaches the fuel electrode 103. This fuel gas F is steam reformed by the active metal contained in the fuel electrode 103. Hydrogen produced by steam reforming passes through the pores of the fuel electrode 103 and reaches the solid electrolyte 104. On the other hand, air (O ₂ ) flows outside the base tube 101 (air electrode 105). The oxygen in the air ionizes while passing through the pores of the air electrode 105 or reaches the solid electrolyte 104. The ionized oxygen passes through the solid electrolyte 104 and reaches the fuel electrode 103. The oxygen ions that have passed through the solid electrolyte 104 react with the fuel gas F. The potential difference generated by such a cell reaction is extracted from the fuel electrode 103 and the air electrode 105 to be generated.

Next, a method for monitoring the operating state of the solid oxide fuel cell will be described.
FIG. 1-1 is a schematic view of one cell tube. 1-1, fuel is introduced into the tube from the upper side, and the lower side is the fuel outlet. Moreover, air is introduced into the outside of the cell from the lower side in FIG. 1-1, and the upper side is the air outlet.

FIG. 1-2 is a schematic view of a cell tube of a solid oxide fuel cell having first monitoring means. As shown in FIG. 1-2, the cell tube 202A of the solid oxide fuel cell having the first monitoring means 300A is the first of the fuel cells adjacent to or adjacent to the fuel outlet side of the cell tube 202A. The first cell monitoring voltage measuring means 300A for measuring the cell monitoring voltage (E ₁ ) of the first cell monitoring voltage and the relationship between the first cell monitoring voltage and the oxygen partial pressure at a predetermined temperature obtained in advance are measured. A first oxygen partial pressure calculating means 301A for obtaining an oxygen partial pressure in fuel from one cell monitoring voltage, and comparing the oxygen partial pressure with a predetermined threshold value to determine whether or not the fuel cell may be damaged. It has the 1st determination means 302A which determines.

In this embodiment, when monitoring the operating state of the solid oxide fuel cell, first, adjacent or adjacent cells (No. n-1, No. n) on the fuel outlet side of the cell tube (cell stack) 202A. the first cell monitoring voltage E ₁ of) measured by the first cell monitoring voltage measuring means 300A. Then, using the relationship between the first cell monitoring voltage and the oxygen partial pressure obtained at a predetermined temperature obtained in advance, a first oxygen partial pressure is calculated from the measured first cell monitoring voltage. Obtained from means 301A.
Next, the oxygen partial pressure is compared with a predetermined threshold value, and the first determination unit 302A determines whether or not the fuel cell is likely to be damaged.

Although FIG. 1 shows a case where n cells are provided, a case where n = 34 will be described in the present embodiment.
FIG. 2-1 is a diagram for measuring cell voltages of the fuel outlet side cell (No. 33) and the cell (No. 34).
2A, the first terminal 111A is provided on the air electrode 105 of the cell (No. 33), and the second terminal 111B is provided on the air electrode 105 of the cell (No. 34). Then, the cell monitoring voltage E ₁ between the adjacent cells is measured.
The cell specifications and power generation conditions at this time are shown in Table 1 below.

In this embodiment, the operation is performed at a current density of 0.28 A / cm ² .
As for the temperature, the temperature of the cell surface is measured by temperature measuring means 112 such as a thermocouple.
Here, the cells adjacent to the fuel outlet side cell are the cells (No. 33) and the cell (No. 34), and the adjacent cells are the cell (No. 32) and the cell (No. The relationship between the cells in which at least one cell (No. 33) is skipped as in the relationship with (34).

FIG. 2B is a circuit corresponding to FIG.
Here, the cell monitoring voltage (E ₁ ) is obtained from the equation (1) shown in the following “Equation 1”.

ここで、
Ｅ₁：セル監視電圧
Ｅｒｅｖ：平衡起電力
Ｒｃ（ｎ）：空気極抵抗
Ｒｉ：インターコネクタ抵抗
Ｒａ：燃料極抵抗
Ｒｃ（ｎ＋１）：空気極抵抗
ηａ：燃料極及び空気極の活性化分極
ηｃ：燃料極及び空気極の濃度分極
ｎ＝３４である。

here,
E ₁ : cell monitoring voltage Erev: equilibrium electromotive force Rc (n): air electrode resistance Ri: interconnector resistance Ra: fuel electrode resistance Rc (n + 1): air electrode resistance ηa: activation polarization ηc of fuel electrode and air electrode: The concentration polarization of the fuel electrode and the air electrode is n = 34.

  Since the equilibrium electromotive force (Erev) depends on the oxygen concentration of the fuel and the air, if the equilibrium electromotive force (Erev) is obtained from the equation (1), the equation (2) shown in the following “Expression 2” An oxygen partial pressure is required. The oxygen partial pressure in the air is obtained by calculation from the oxygen inlet concentration.

FIG. 3 is a schematic diagram showing the electric resistance of the cell. FIG. 3 schematically shows the cell of FIG. 2-1.
Here, in FIG. 3, assuming that the electrical resistances of the blocks (1) to (8) are R1 to R8, respectively, the electrical resistances are approximated by the equations (11) to (24) shown in the following “Equation 3”. Indicated by.

Further, the electrode overvoltage (activation polarization) is obtained by the equation (3) shown in the following “Equation 4”.
The relationship between the electrode overvoltage η and the current density i is approximately expressed by the Butler-Volmer equation.

  The concentration polarization is obtained by the following equations (4) and (5) shown in “Equation 5”.

  Table 2 shows the calculation results of electrical resistance.

The calculation result of the activation polarization is shown in the following “Equation 6”.
Here, in Equation 6, Expression (3-1) indicates “air electrode activation polarization”, and Expression (3-2) indicates “fuel electrode activation polarization”.

また、空気極及び燃料極の濃度分極の計算結果を下記「表３」に示す。

The calculation results of the concentration polarization of the air electrode and the fuel electrode are shown in “Table 3” below.

From the above results, the oxygen concentration is obtained by calculation from the cell monitoring voltage (E ₁ ) as shown in the following “Equation 7”.

As shown in Equation 7, the oxygen partial pressure on the fuel electrode side is calculated as 2.7 × 10 ^{−16 from} Equation (2) of Equation 2 from the equilibrium electromotive force.

FIG. 4 is a relationship diagram between current density and voltage. As shown in FIG. 4, the first cell monitoring voltage (E ₁ ) at a current density of 0.28 A / cm ² was 0.572V.
When this is analyzed, the oxygen partial pressure on the fuel electrode side obtained from the equilibrium electromotive force of 0.866 V is 2.7 × 10 ⁻¹⁶ atm.

FIG. 5 shows the relationship between the logarithm of oxygen partial pressure in fuel at 900 ° C. and the equilibrium electromotive force.
Ni contained in the fuel electrode 103 is oxidized to NiO at 900 ° C. at an oxygen partial pressure higher than 10 ⁻¹² atm, and is stable at Ni at an oxygen partial pressure lower than that. Here, at 900 ° C., the equilibrium electromotive force when the oxygen partial pressure is 10 ⁻¹² atm corresponds to 0.66V.
When the equilibrium electromotive force is higher than 0.66 V, the oxygen partial pressure in the fuel is lower than 10 ⁻¹² atm and stable with Ni, but when the equilibrium electromotive force is lower than 0.66 V, the oxygen partial pressure in the fuel is Becomes higher than 10 ⁻¹² atm and becomes NiO.
As a method for obtaining the oxygen partial pressure in the fuel from the cell monitoring voltage (E _1), if seeking relationship beforehand cell monitoring voltage (E ₁₎ and the partial pressure of oxygen in the fuel, the cell monitoring voltage (E ₁₎ Monitoring can be easily performed without calculating the equilibrium electromotive force.

In order to obtain the relationship (900 ° C.) between the cell monitoring voltage (E ₁ ) and the oxygen partial pressure in the fuel in advance, Erev (equilibrium electromotive force) of the cell monitoring voltage (E ₁ ) of equation (1) shown in “Equation 1” As an equilibrium electromotive force indicating the equilibrium state of Ni and NiO, 0.66V is used, and electrical resistance such as air electrode resistance, activation polarization, and concentration polarization may be subtracted.
Rc (n): air electrode resistance, Ri: interconnector resistance, Ra: fuel electrode resistance, Rc (n + 1): air electrode resistance was 0.055Ω in total from R1 to R8 in “Table 2” below.
ηa: The activation polarization of the fuel electrode and the air electrode was 0.015 V from (1) and (2) of “Equation 6” below.
ηc: The concentration polarization of the fuel electrode and the air electrode was 0.0056 V from the following “Table 3”, and the concentration polarization of 0.0012 V from the air electrode was used.
When the cell monitoring voltage (E1) is below 0.37 V as a threshold value, monitoring is performed to determine that the oxygen concentration in the fuel is higher than the oxygen concentration of Ni oxidation.

FIG. 6 shows the relationship between the cell monitoring voltage and the oxygen concentration.
As shown in FIG. 6, the cell monitoring voltage (E ₁ ) is measured, and it can be determined that the oxygen concentration is not high until it becomes close to the oxygen concentration threshold value.

That is, in the actual operation of the fuel cell, in order to make a simple determination, by measuring the cell monitoring voltage (E ₁ ) adjacent to or adjacent to the fuel gas outlet side, it is possible to determine whether or not the oxygen concentration of the fuel electrode has increased. Judgment can be made.

If it is determined that the oxygen partial pressure has increased, for example, the operating load is reduced to reduce the oxygen partial pressure.
Even if this measure is taken, if the oxygen partial pressure is high, a detailed analysis is performed. Also, measures such as removing the circuit of the cell stack portion (a part of the cartridge or module) where the oxygen concentration has increased are taken.

  Although more than 100 cell tubes are loaded in the cartridge, it is desirable to monitor all of these cell tubes. However, it is desirable to monitor cell voltages by selecting a plurality of cell tubes and measuring cell monitoring voltages. May be performed.

FIG. 7 shows the measurement result of the oxygen partial pressure from the fuel inlet side (cell No. 1) to the outlet side (cell No. 48) of the cell stack.
From the result of FIG. 7, it was confirmed that the oxygen partial pressure on the fuel outlet side was higher than that on the fuel inlet side.
However, since the oxygen partial pressure is the threshold value of 10 ⁻¹² atm or less in all the elements, it can be confirmed that it is in the Ni stable region.

  By the way, when an unexpected event such as current concentration, fuel leak, or excessive current occurs during operation of the fuel cell, the oxygen partial pressure in the fuel at the fuel outlet cell increases, and the fuel electrode caused by the increase in oxygen concentration is removed. Oxidation of the constituent material (for example, Ni) is promoted. As this oxidation progresses, there is a possibility of cell breakage or damage, and this can be grasped in advance by measuring and monitoring the cell monitoring voltage as in the present invention.

That is, as shown below, the partial pressure of oxygen in the fuel can be obtained to avoid cell damage.
Step 1: The cell monitoring voltage (E ₁ ) is monitored by measuring the cell voltage adjacent or adjacent to the fuel outlet side where the oxygen concentration in the fuel is high.
Step 2: Since the temperature is required for the oxygen concentration calculation, the temperature is measured on the outer surface of the cell to be monitored by a temperature measuring means such as a thermocouple.
Step 3: The cell monitoring voltage (E ₁ ) is analyzed to calculate the equilibrium electromotive force, and the oxygen partial pressure in the fuel is obtained.
Step 4: It is determined whether Ni is not oxidized from the obtained oxygen partial pressure in the fuel.

As described above, the oxygen partial pressure can be obtained by analysis from the cell monitoring voltage (E ₁ ). Under such conditions, the relationship between the cell monitoring voltage and the oxygen partial pressure is obtained in advance. Can be determined that the oxygen partial pressure has increased. When it is determined that the oxygen partial pressure has increased, for example, the operating load is reduced to reduce the oxygen partial pressure. Even if this measure is taken, if the oxygen partial pressure is high, a detailed analysis is performed. Also, measures such as removing the circuit of the cell stack portion (a part of the cartridge or module) where the oxygen concentration has increased are taken.

  According to this embodiment, the oxygen concentration in the fuel can be monitored by measuring the first cell monitoring voltage between adjacent or adjacent cells on the fuel outlet side of the fuel electrode of one cell tube. Therefore, cell damage due to changes in the operating state (for example, unexpected things such as current concentration, fuel leakage, excessive current, etc.) can be avoided.

A fuel cell operation monitoring method according to an embodiment of the present invention will be described with reference to the drawings.
FIG. 8-1 is a diagram for measuring the cell voltage between the interconnector on the fuel outlet side and the solid electrolyte. FIG. 8-2 is a circuit corresponding to FIG.
FIG. 1-3 is a schematic view of a cell tube of a solid oxide fuel cell having a second monitoring means. As shown in FIG. 1-3, the cell tube 202B of the solid oxide fuel cell having the second monitoring means 300B is a second cell monitoring of the interconnector and the electrolyte on the fuel outlet side of the cell tube 202B. The second cell monitoring voltage measuring means 300B for measuring the voltage (E ₂ ) and the measured second cell using the relationship between the second cell monitoring voltage and the oxygen partial pressure at a predetermined temperature obtained in advance. A second oxygen partial pressure calculating means 301 for obtaining the oxygen partial pressure in the fuel from the monitoring voltage is compared with the predetermined partial threshold value to determine whether or not the fuel cell is likely to be damaged. Second determination means 302B.

As shown in FIG. 8A, in this embodiment, the monitoring voltage E between the interconnector 106 and the solid electrolyte 104 sandwiched between the cells (No. 33) and (No. 34) on the fuel outlet side. ₂ is measured by the second cell monitoring voltage measuring means 300B.
Specifically, as shown in FIG. 8A, the third terminal 111C is provided in the interconnector 106 of the cell (No. 33), and the fourth terminal 111D is provided in the solid electrolyte 104 of the cell (No. 34). And the second cell monitoring voltage E ₂ between them is measured by the second cell monitoring voltage measuring means 300B. Then, using the relationship between the second cell monitoring voltage and the oxygen partial pressure obtained at a predetermined temperature obtained in advance, the oxygen partial pressure in the fuel is calculated from the measured second cell monitoring voltage by the second oxygen partial pressure. Obtained from means 301B.
Next, the oxygen partial pressure is compared with a predetermined threshold value, and the second determination unit 302B determines whether or not the fuel cell is likely to be damaged.
The cell specifications and power generation conditions at this time are the same as in Table 1 of Example 1.

In the present embodiment, unlike the first embodiment, the cell monitoring voltage is not obtained, and the second cell monitoring voltage E ₂ is calculated from the balanced electromotive force as shown in the equation (7) shown in the following “Equation 8”. The connector resistance (Ri) and the fuel electrode resistance (Ra) are subtracted.
Unlike the first embodiment, since there are few items to be subtracted from the balanced electromotive force, the measurement accuracy is simple and improved in the analysis.

Specifically, assuming that the second cell monitoring voltage E ₂ is 0.846 V, the fuel electrode (under the electrolyte) R7 (= 0.006Ω) and the fuel electrode connection part (R8 = 0.002Ω) in Table 2 0.883V is calculated by subtracting the sum of the current value (4.68A) and the sum of the values.
Then, when the oxygen polarization is calculated from the equation (2) shown in Equation 2, it becomes 1.4 × 10 ⁻¹⁶ atm.

FIG. 9 shows the relationship between the logarithm of oxygen partial pressure in fuel at 900 ° C. and the equilibrium electromotive force.
Ni is oxidized to NiO at an oxygen partial pressure higher than 10 ⁻¹² atm at 900 ° C., and Ni is stable at an oxygen partial pressure lower than that. The equilibrium electromotive force when the oxygen partial pressure is 10 ⁻¹² atm at 900 ° C. corresponds to 0.66V.
When the equilibrium electromotive force is higher than 0.66 V, the oxygen partial pressure in the fuel is lower than 10 ⁻¹² atm and stable with Ni, but when the equilibrium electromotive force is lower than 0.66 V, the oxygen partial pressure in the fuel is Is higher than 10 ⁻¹² atm and becomes NiO. Therefore, when the equilibrium electromotive force falls below this threshold with 0.66 V as a threshold, monitoring is performed to determine that the oxygen concentration in the fuel is high.

In Example 2, the third terminal 111C is attached to the interconnector 106 of the “fuel outlet cell (cell (No. 33))” having a high oxygen partial pressure in the fuel, and the fourth terminal 111D is attached to the solid electrolyte 104. .
Specifically, in order to monitor the monitoring voltage between the interconnector 106 and the solid electrolyte 104, a platinum paste is applied to the surface of the interconnector 106 and the surface of the solid electrolyte 104, and a platinum wire for voltage monitoring is attached to the surface of the interconnector 106 and the surface of the interconnector 106. Contact the surface of the solid electrolyte 104.
Next, the “oxygen concentration in the fuel” is obtained by calculation from the second cell monitoring voltage E _{2 at} the third terminal 111C and the fourth terminal 111D.
The “oxygen concentration” is obtained by calculation from the measured monitoring voltage E ₂ and is compared with the oxygen concentration at which Ni is oxidized in the cell temperature environment.

  According to the present embodiment, the oxygen concentration in the fuel is monitored by monitoring the monitoring voltage between the interconnector and electrolyte sandwiched between adjacent or adjacent cells on the fuel outlet side of the fuel electrode of one cell tube. Therefore, it is possible to avoid cell damage due to changes in operating conditions (for example, unexpected current concentration, fuel leak, excessive current, etc.).

A fuel cell operation monitoring method according to an embodiment of the present invention will be described with reference to the drawings.
In the first embodiment, the oxygen concentration in the fuel on the fuel electrode side is obtained, but in this embodiment, the oxygen concentration in the air on the air electrode side is obtained.
For example, in the case of LaMnO ₃ which is a constituent material of the air electrode, the oxygen partial pressure becomes low, and the cell may be damaged by reductive decomposition. Therefore, the oxygen partial pressure in the air is obtained in the same manner as in Example 1. To monitor.
Here, the oxygen partial pressure in the air becomes lower as oxygen is consumed on the air outlet side than on the air inlet side.

Therefore, in this embodiment, the third cell monitoring voltage E ₃ between adjacent or adjacent cells on the air outlet side of the air electrode of one air cell tube is measured, and the third cell monitoring voltage E ₃ obtained in advance is measured. Whether or not there is a decrease in the oxygen concentration in the air is determined from the relationship between the oxygen concentration and the oxygen concentration.

1-4 is a schematic view of a cell tube 202C of a solid oxide fuel cell having a third monitoring means. As shown in FIG. 1-3, the cell tube 202C of the solid oxide fuel cell having the third monitoring means 300C is the third of the fuel cells adjacent to or adjacent to the air outlet side of the cell tube 202C. Using the third cell monitoring voltage measuring means 300C for measuring the cell monitoring voltage (E ₃ ) and the relationship between the third cell monitoring voltage and the oxygen partial pressure at a predetermined temperature obtained in advance, the measured third The third partial pressure calculation means 301C for determining the partial pressure of oxygen in the fuel from the cell monitoring voltage is compared with the predetermined partial threshold value to determine whether or not the fuel cell is likely to be damaged. And third determination means 301C for determination.

FIG. 10A is a diagram of measuring cell voltages of the cell (No. 1) and the cell (No. 2) on the air outlet side.
As shown in FIG. 10A, the fifth terminal 111E is provided on the air electrode 105 of the cell (No. 1), and the sixth terminal 111F is provided on the air electrode 105 of the cell (No. 2). Then, to measure the third cell monitoring voltage E ₃ between cells of the adjacent by the third cell monitoring voltage measuring unit 300C. Then, using the relationship between the first cell monitoring voltage and the oxygen partial pressure obtained at a predetermined temperature obtained in advance, the oxygen partial pressure in the fuel is calculated from the measured third cell monitoring voltage by the third oxygen partial pressure. Obtained from means 301C.
Next, the oxygen partial pressure is compared with a predetermined threshold value, and the third determination unit 302C determines whether or not the fuel cell is likely to be damaged.
Here, the cell adjacent to the air outlet side cell refers to the cell (No. 1) and the cell (No. 2), and the adjacent cell refers to the cell (No 1) and the cell (No 3). Like each other, it means a relationship between cells in which at least one cell (No. 2) is skipped.

FIG. 10B is a circuit corresponding to FIG.
Here, the third cell monitoring voltage (E ₃ ) is obtained from the equation (1) shown in the “Equation 1”.
Since the equilibrium electromotive force (Erev) depends on the oxygen concentration of the fuel and the air, if the equilibrium electromotive force (Erev) is obtained from the equation (1), the equation (2) shown in the “Equation 2” can be used. An oxygen partial pressure is required. The oxygen partial pressure in the fuel is calculated from the fuel inlet concentration.

In the present embodiment, first, the third cell monitoring voltage E ₃ is measured in the vicinity of the air outlet.
Next, the second cell monitoring voltage E ₃ is analyzed in the same manner as in Example 1, the equilibrium electromotive force is calculated, and the oxygen partial pressure in the air is obtained.
When the obtained oxygen partial pressure in the air approaches an arbitrary value (for example, a management oxygen concentration due to deterioration of the air electrode (LaMnO ₃ system or the like) is approached), control is performed to issue an operation alarm.

According to this embodiment, since the oxygen concentration in the air can be monitored by monitoring the voltage of the air outlet cell, unexpected changes such as changes in operating conditions (eg current concentration, fuel leak, excessive current) ) Can be avoided.
Further, when monitoring the operating state of the solid oxide fuel cell, the monitoring method of the first embodiment and the monitoring method of the third embodiment may be performed together.
Thereby, the oxygen concentration on the fuel side and the air side can be monitored, and the change in the operating state can be properly monitored.

DESCRIPTION OF SYMBOLS 101 Base tube 103 Fuel electrode 104 Solid electrolyte 105 Air electrode 106 Interconnector 200 Fuel cell module 202, 202A-202C Cell tube (fuel cell)
210 Fuel cell (power generation element)

Claims (12)

A cylindrical base tube, a fuel electrode, an electrolyte, and an air electrode are stacked, and a plurality of fuel cells arranged along the outer surface axial direction of the base tube, and the adjacent fuel cells are connected in series. In a method for monitoring the operating state of a solid oxide fuel cell having a cell tube with an interconnector connected to
Measuring the first cell monitoring voltage between the fuel cells adjacent to or adjacent to the fuel outlet of the cell tube;
Obtaining a partial pressure of oxygen in the fuel from the first cell monitoring voltage;
A method for monitoring the operating state of a solid oxide fuel cell, comprising: comparing the determined oxygen partial pressure with a predetermined threshold value. In the monitoring method of the operating state of the solid oxide fuel cell according to claim 1,
An operation state of the solid oxide fuel cell, comprising a step of obtaining an oxygen partial pressure in the fuel using a relationship between the first cell monitoring voltage and the oxygen partial pressure at a predetermined temperature obtained in advance. Monitoring method. In the monitoring method of the operating state of the solid oxide fuel cell according to claim 1,
Measuring the first cell monitoring voltage and measuring the temperature of the outer surface of the fuel cell; and
And a step of calculating an equilibrium electromotive force from the first cell monitoring voltage and obtaining an oxygen partial pressure in the fuel. A cylindrical base tube, a fuel electrode, an electrolyte, and an air electrode are stacked, and a plurality of fuel cells arranged along the outer surface axial direction of the base tube, and the adjacent fuel cells are connected in series. In a method for monitoring the operating state of a solid oxide fuel cell having a cell tube with an interconnector connected to
Measuring a second cell monitoring voltage between the interconnector on the fuel outlet side of the cell tube and the electrolyte;
Obtaining an oxygen partial pressure in the fuel from the second cell monitoring voltage;
A method for monitoring the operating state of a solid oxide fuel cell, comprising: comparing the determined oxygen partial pressure with a predetermined threshold value. In the monitoring method of the operating state of the solid oxide fuel cell according to claim 4,
An operating state of the solid oxide fuel cell comprising a step of obtaining an oxygen partial pressure in the fuel by using a relationship between a second cell monitoring voltage and an oxygen partial pressure at a predetermined temperature obtained in advance. Monitoring method. In the monitoring method of the operating state of the solid oxide fuel cell according to claim 5,
Measuring the second cell monitoring voltage and measuring the temperature of the outer surface of the fuel cell;
And a step of calculating an equilibrium electromotive force from the second cell monitoring voltage and obtaining an oxygen partial pressure in the fuel. A cylindrical base tube, a fuel electrode, an electrolyte, and an air electrode are stacked, and a plurality of fuel cells arranged along the outer surface axial direction of the base tube, and the adjacent fuel cells are connected in series. In a method for monitoring the operating state of a solid oxide fuel cell having a cell tube with an interconnector connected to
Measuring a third cell monitoring voltage between the fuel cells adjacent to or adjacent to the air outlet side of the cell tube;
Obtaining a partial pressure of oxygen in the air from the third cell monitoring voltage;
A method for monitoring the operating state of a solid oxide fuel cell, comprising: comparing the determined oxygen partial pressure with a predetermined threshold value. In the monitoring method of the operating state of the solid oxide fuel cell according to claim 7,
An operating state of the solid oxide fuel cell comprising a step of obtaining an oxygen partial pressure in the fuel using a relationship between a third cell monitoring voltage and an oxygen partial pressure at a predetermined temperature obtained in advance. Monitoring method. In the monitoring method of the operating state of the solid oxide fuel cell according to claim 8,
Measuring the third cell monitoring voltage and measuring the temperature of the outer surface of the fuel cell;
And a step of calculating an equilibrium electromotive force from the third cell monitoring voltage and obtaining an oxygen partial pressure in the air. A cylindrical base tube, a fuel electrode, an electrolyte, and an air electrode are stacked, and a plurality of fuel cells arranged along the outer surface axial direction of the base tube, and the adjacent fuel cells are connected in series. A solid oxide fuel cell having a cell tube with an interconnector connected to
Cell monitoring voltage measuring means for measuring a first cell monitoring voltage between the fuel cells adjacent to or adjacent to each other on the fuel outlet side of the cell tube;
An oxygen partial pressure calculating means for obtaining an oxygen partial pressure in the fuel from the measured first cell monitoring voltage using a relationship between the first cell monitoring voltage and the oxygen partial pressure at a predetermined temperature obtained in advance;
A solid oxide fuel cell comprising: determination means for comparing the partial pressure of oxygen with a predetermined threshold value to determine whether or not the fuel cell is likely to be damaged. A cylindrical base tube, a fuel electrode, an electrolyte, and an air electrode are stacked, and a plurality of fuel cells arranged along the outer surface axial direction of the base tube, and the adjacent fuel cells are connected in series. A solid oxide fuel cell having a cell tube with an interconnector connected to
Cell monitoring voltage measuring means for measuring a second cell monitoring voltage between the interconnector on the fuel outlet side of the cell tube and the electrolyte;
An oxygen partial pressure calculating means for obtaining an oxygen partial pressure in the fuel from the measured second cell monitoring voltage using a relationship between the second cell monitoring voltage and the oxygen partial pressure at a predetermined temperature obtained in advance;
A solid oxide fuel cell comprising: determination means for comparing the partial pressure of oxygen with a predetermined threshold value to determine whether or not the fuel cell is likely to be damaged. A cylindrical base tube, a fuel electrode, an electrolyte, and an air electrode are stacked, and a plurality of fuel cells arranged along the outer surface axial direction of the base tube, and the adjacent fuel cells are connected in series. A solid oxide fuel cell having a cell tube with an interconnector connected to
Cell monitoring voltage measuring means for measuring a third cell monitoring voltage between the fuel cells adjacent to or adjacent to the air outlet side of the cell tube;
An oxygen partial pressure calculating means for determining an oxygen partial pressure in the fuel from the measured third cell monitoring voltage using a relationship between the third cell monitoring voltage and the oxygen partial pressure at a predetermined temperature determined in advance;
A solid oxide fuel cell comprising: determination means for comparing the partial pressure of oxygen with a predetermined threshold value to determine whether or not the fuel cell is likely to be damaged.

Images