JP2010238527A - Method for operating solid oxide fuel battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for operating a solid oxide fuel cell capable of preventing oxidation of a fuel electrode layer without separately supplying nitrogen gas or hydrogen gas to a power generation cell. <P>SOLUTION: The solid oxide fuel battery includes: a fuel battery cell stack 10 formed by stacking a power generation cell 16 through a separator 2; a reformer 45 producing reformed gas from introduced fuel gas and steam; a fuel gas supply line 40 between which the reformer is interposed; a steam supply line 60 between which a steam generator 41 is interposed; and heating means 6a to 6d capable of heating the reformed gas within the reformer. In the method for operating the solid oxide fuel cell, heating of the reformed gas within the reformer is controlled by the heating means so that, when the temperature X of the power generating cell is 300°C or higher and the maximum temperature Y of the reformed gas within the reformer is 550°C or lower, the difference obtained by subtracting the maximum temperature Y of the reformed gas from the temperature X of the power generating cell becomes within 100°C. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for operating a solid oxide fuel cell including a power generation cell in which a fuel electrode layer and an air electrode layer are disposed on both sides of a solid electrolyte layer.

  In recent years, fuel cells that directly convert chemical energy of fuel into electrical energy have attracted attention as highly efficient and clean power generators. This fuel cell has a fuel cell stack in which a power generation cell in which an air electrode layer (cathode) and a fuel electrode layer (anode) are arranged on both sides of a solid electrolyte layer made of an oxide ion conductor is stacked via a separator. Have.

At the time of power generation, a reformer reforms an oxidizing gas (oxygen) on the air electrode layer side and a fuel gas (city gas containing CH ₄ etc.) on the fuel electrode layer side as a reaction gas. Gas (H ₂ , CO, CO ₂ , H ₂ O, etc.) is supplied. These air electrode layer and fuel electrode layer are both porous layers so that the reaction gas can reach the interface with the solid electrolyte layer.

Thereby, in the power generation cell, oxygen supplied to the air electrode layer side passes through pores in the air electrode layer and reaches the vicinity of the interface with the solid electrolyte layer, and receives electrons from the air electrode layer in this portion. It is ionized to oxide ions (O ²⁻ ). The oxide ions diffuse and move in the solid electrolyte layer toward the fuel electrode layer. The oxide ions that have reached the vicinity of the interface with the fuel electrode layer react with the reformed gas at this portion to generate a reaction product (H ₂ O, CO _2, etc.) and discharge electrons to the fuel electrode layer. Electrons generated by the electrode reaction can be taken out as an electromotive force at an external load on another route.

  By the way, this fuel cell has a high temperature atmosphere around the fuel cell stack during power generation, so that the reformer can sufficiently reform the fuel gas by absorbing the surrounding heat, At start-up, reforming, which is an endothermic reaction, cannot be performed by the reformer, so that unreformed fuel gas is supplied to the fuel electrode layer. Thus, even if unreformed fuel gas is supplied to the fuel electrode layer, not only does it contribute to power generation, but also a reducing gas such as hydrogen gas is not supplied, so the fuel electrode layer is oxygen in the air in the external atmosphere. As a result, there is a problem that the fuel electrode layer expands and contracts and peels off from the solid electrolyte layer.

  Therefore, at the time of start-up, instead of the fuel gas, nitrogen gas or hydrogen gas is supplied to the power generation cells of each fuel cell stack, the fuel electrode layer is kept at least in a non-oxidizing atmosphere, preferably a reducing atmosphere, and hydrogen gas In general, a fuel cell is provided with a storage of nitrogen gas or hydrogen gas in the apparatus in order to cause an electrode reaction by the reaction between oxygen and the oxygen (see Patent Document 1). The entire device has become larger than necessary.

Japanese Patent Laid-Open No. 05-054901

  To provide a method for operating a solid oxide fuel cell that can prevent oxidation of the fuel electrode layer due to the supply of unreformed fuel gas without supplying nitrogen gas or hydrogen gas from these storages to the power generation cell. Is an issue.

In other words, the solid oxide fuel cell operating method according to the first aspect of the present invention includes a fuel electrode layer disposed on one surface of the solid electrolyte layer and an oxidant electrode layer disposed on the other surface. A fuel cell stack in which the generated power cells are stacked via a separator, and a reformer that generates reformed gas by absorbing the heat released from the fuel cell stack during power generation when the fuel gas is introduced together with water vapor And a reformer, a fuel gas supply line for supplying the reformed gas to the fuel cell stack, and water are introduced to absorb heat released from the fuel cell stack during power generation. A water vapor generator that generates water vapor, and a water vapor supply line that is provided with the water vapor generator and supplies the water vapor to the upstream side of the reformer in the fuel gas supply line. And a heating means capable of heating the reformed gas in the reformer, wherein the temperature X of the power generation cell is 300 ° C. or higher, and the reformer When the maximum temperature Y of the reformed gas is 550 ° C. or less, the heating means controls the temperature so that the difference obtained by subtracting the maximum temperature Y of the reformed gas from the temperature X of the power generation cell is within 100 ° C. The reformed gas in the reformer is controlled by heating, and the city gas containing 89.6 vol% methane, 5.6 vol% ethane, 3.4 vol% propane, and 1.4 vol% butane is used as the fuel gas. The hydrogen amount corresponding to the equilibrium composition when water is supplied so that the water vapor (S) / carbon (C) molar ratio is 12.0 or more with respect to carbon in the city gas is 0141 NL / min or more. Power generation above It is characterized by supplying the fuel gas and the water to be introduced to the area 100 cm ² per Le.
Here, NL / min means a flow rate per minute in a standard state of 0 ° C. and 1 atm.

According to a second aspect of the present invention, there is provided a solid oxide fuel cell operating method in which a fuel electrode layer is disposed on one surface of a solid electrolyte layer and an oxidant electrode layer is disposed on the other surface. A fuel cell stack in which the generated power cells are stacked via a separator, and a reformer that generates reformed gas by absorbing the heat released from the fuel cell stack during power generation when the fuel gas is introduced together with water vapor And a reformer, a fuel gas supply line for supplying the reformed gas to the fuel cell stack, and water are introduced to absorb heat released from the fuel cell stack during power generation. A water vapor generator that generates water vapor and a water vapor supply line through which the water vapor generator is interposed to supply the water vapor to the upstream side of the reformer in the fuel gas supply line In the method of operating a solid oxide fuel cell having heating means capable of heating the reformed gas in the reformer, the temperature X of the power generation cell is 300 ° C. or higher, and the temperature in the reformer is When the maximum temperature Y of the reformed gas exceeds 550 ° C., city gas containing 89.6 vol% methane, 5.6 vol% ethane, 3.4 vol% propane, and 1.4 vol% butane as the above fuel gas Is equivalent to the equilibrium composition when water is supplied in such a manner that the molar ratio of water vapor (S) / carbon (C) is 12.0 or more with respect to carbon in the city gas, 0.0141 NL / min or more. The fuel gas and the water are supplied so that the amount of hydrogen to be introduced is introduced per 100 cm ² area of the power generation cell.

  The invention described in claim 3 is the operation method of the solid oxide fuel cell according to claim 1 or 2, wherein the fuel gas supply line is provided with an activation device downstream of the reformer. The reformer is interposed, and the start-up reformer is installed at a position facing the start-up heating means that operates at the start-up, which is the heating means.

  The invention described in claim 4 is the operation method of the solid oxide fuel cell according to any one of claims 1 to 3, wherein the fuel cell stack includes the reformer, the steam generator, and the It is installed in the inner can body together with the starter reformer, and a heat insulating material is disposed on the outer periphery of the inner can body, and a plurality of the fuel cell stacks are arranged in a plane in the inner can body. A plurality of fuel cell stack groups constituted by a plurality of fuel cell stacks arranged in the vertical direction by being arranged in a plurality in the vertical direction. It is arranged at a position sandwiched between battery stack groups.

  According to the operation method of the solid oxide fuel cell of the first aspect of the invention, the temperature X of the power generation cell is 300 ° C. or higher and the maximum temperature Y of the reformed gas in the reformer is 550 ° C. or lower. In this case, the reformer gas in the reformer is controlled by heating so that the difference obtained by subtracting the maximum reformed gas temperature Y from the temperature X of the power generation cell is within 100 ° C. It is possible to prevent the reforming reaction rate from decreasing due to the low temperature, and to prevent the fuel electrode layer in the power generation cell having a temperature of 300 ° C. or higher from being oxidized by oxygen or the like in the external atmosphere.

In addition to this, a city gas containing 89.6 vol% methane, 5.6 vol% ethane, 3.4 vol% propane, and 1.4 vol% butane as fuel gas is 0.0141 NL / min or more, and carbon in the city gas. The amount of hydrogen corresponding to the equilibrium composition when water is supplied so that the molar ratio of water vapor (S) / carbon (C) is 12.0 or more is introduced per 100 cm ² area of the power generation cell. By supplying the fuel gas and the water as described above, the shortage of hydrogen generation due to the shortage of the fuel gas or water is prevented, and the fuel electrode layer in the power generation cell having a temperature of 300 ° C. or higher is in the external atmosphere. It can be prevented from being oxidized by oxygen.
Therefore, oxidation of the fuel electrode layer due to the supply of unreformed fuel gas can be prevented without supplying nitrogen gas or hydrogen gas.

On the other hand, according to the operation method of the solid oxide fuel cell according to claim 2, the temperature X of the power generation cell is 300 ° C. or more and the maximum temperature Y of the reformed gas in the reformer exceeds 550 ° C. In the case of temperature, since reforming can be sufficiently performed by the reformer, the molar ratio of city gas to 0.0141 NL / min or more and water to steam (S) / carbon (C) is 12.0 or more. When the fuel gas and the water are supplied so that the amount of hydrogen corresponding to the equilibrium composition is supplied per 100 cm ² area of the power generation cell, Prevents the shortage of hydrogen production due to oxygen and prevents the fuel electrode layer in the power generation cell at 300 ° C or higher from being oxidized by oxygen in the external atmosphere without separately supplying nitrogen gas or hydrogen gas so That.

  In particular, according to the operation method of the solid oxide fuel cell according to claim 3, the start-up reformer is separately provided on the downstream side of the reformer, and this start-up reformer faces the start-up heating means. By installing in the position, even when the maximum temperature Y of the reformed gas in the reformer at the start-up when the temperature of the entire apparatus is low, heating can be easily performed.

Furthermore, according to the method of operating a solid oxide fuel cell according to claim 4, the fuel cell stack is installed in the inner can body together with the start-up reformer and the like, and a heat insulating material is arranged on the outer periphery of the inner can body. Therefore, even during startup, the temperature inside the internal can is efficiently raised by the heating means for startup and the heat released by the electrode reaction in the power generation cell, and the oxygen gas and reformed gas are also heated. It is possible to shorten the time until the start of power generation.
In addition, the fuel cell stack group includes a plurality of fuel cell stacks arranged in the vertical direction, and the reformer is disposed at a position sandwiched between the fuel cell stack groups. Since the reformer is efficiently heated by heat radiation, the time from startup to the start of power generation is shortened, and the operating time of the heating means for startup is shortened. It can be prevented from being used. In addition, since the reforming reaction in the reformer is an endothermic reaction, the temperature distribution in the inner can is obtained by installing the reformer at a position sandwiched between the fuel cell stacks where the temperature is highest in the inner can. It is possible to reduce the difference between the solid electrolyte layers and prevent the solid electrolyte layer from being damaged due to thermal distortion caused by the temperature difference.

1 is a plan view of a flat plate type solid oxide fuel cell according to the present invention. It is the II-II arrow directional view in FIG. It is the III-III arrow directional view in FIG. It is explanatory drawing of the fuel gas supply line in the flat plate type solid oxide fuel cell which concerns on this invention. 2 is a partial explanatory diagram of a fuel cell stack 10. FIG. 3 is a plan view of a separator 2. FIG. It is explanatory drawing of the air heater 51 for starting. It is a graph which shows the relationship between the exit temperature of the reformer for starting, and the flow volume of each gas.

  Hereinafter, in describing the operation method of a flat plate type solid oxide fuel cell according to the present invention, an embodiment of the solid oxide fuel cell will be described with reference to FIGS.

In the fuel cell according to this embodiment, as shown in FIG. 5, the fuel electrode layer 12 is disposed on one surface of the solid electrolyte layer 11 and the air electrode layer (oxidant electrode layer) 13 is disposed on the other surface. The fuel cell stack 10 is configured to have a substantially rectangular columnar shape as viewed from the outside, in which a plurality of the power generation cells 16 arranged are stacked via the separator 2.
A fuel electrode current collector 14 is disposed between the fuel electrode layer 12 and the separator 2 of the power generation cell 16, and an air electrode current collector 15 is disposed between the air electrode layer 13 and the separator 2. Is arranged.

Here, the solid electrolyte layer 11 is formed in a disk shape with a stabilized zirconia (YSZ) or lanthanum gallate material (LaGaO ₃ ) to which yttria is added, and the fuel electrode layer 12 is made of a metal such as Ni or Ni—YSZ. The air electrode layer 13 is formed in a circular shape with LaMnO ₃ , LaCoO ₃ or the like. The fuel electrode current collector 14 is formed in a circular shape with a sponge-like porous sintered metal plate such as Ni, and the air electrode current collector 15 is formed in a circular shape with a sponge-like porous sintered metal plate such as Ag. Has been.

  Further, as shown in FIG. 6, the separator 2 is made of a substantially square plate made of stainless steel having a thickness of several millimeters, and is a center where the power generation cell 16 and the current collectors 14, 15 described above are stacked. The separator main body 21 and a pair of separator arms 24 and 25 that extend in the surface direction from the separator main body 21 and support opposing edges of the separator main body 21 at two locations.

  The separator body 21 has a function of electrically connecting the power generation cells 16 via the current collectors 14 and 15 and supplying a reaction gas to the power generation cells 16. Is introduced from the edge of the separator 2 and ejected from the discharge port 2x at the center of the surface of the separator 2 facing the anode current collector 14, and the oxidant gas (air) is fed to the edge of the separator 2. And an oxidant gas passage 23 ejected from the discharge port 2y in the center of the surface of the separator 2 that faces the air electrode current collector 15 of the separator 2.

Each separator arm 24, 25 has a structure in which it is flexible in the laminating direction as an elongated band extending to the opposite corner with a slight gap along the outer periphery of the separator body 21. In addition, a pair of gas holes 28x and 28y penetrating in the plate thickness direction are provided in the end portions 26 and 27 of the separator arms 24 and 25, respectively.
One gas hole 28x communicates with the fuel gas passage 22 of the separator 2, and the other gas hole 28y communicates with the oxidant gas passage 23 of the separator 2. The gas passages 28x, 28y are connected to the gas passages 22, 23, respectively. The fuel gas and the oxidant gas are supplied to the surfaces of the electrodes 12 and 13 of the power generation cells 16 through the through holes.

  Then, by interposing the power generation cell 16 and the current collectors 14 and 15 between the main bodies 21 of the separators 2 and interposing the insulating manifold rings 29 between the gas holes 28x and 28y of the separators 2 respectively, A fuel cell stack 10 having a substantially rectangular columnar shape in appearance is formed, which includes a fuel gas manifold 48 formed by the gas holes 28x and the manifold ring 29 and an air manifold 54 formed by the gas holes 28y and the manifold ring 29.

  The fuel cell stack 10 thus configured has a plurality of rows in the vertical and horizontal directions (in the present embodiment, in the central portion in the inner can body 3 constituted by the rectangular cylindrical side plate 3a, the top plate, and the bottom plate. 2 rows) A plurality of columns (two columns in this embodiment) are arranged side by side, and the fuel cell stacks 10 are arranged in parallel with the side plate 3a surface with a gap between them, and the gantry 33 It is arranged in a state where it is placed on. As a result, a large number (four in the present embodiment) are arranged in a plane, and a plurality (four in the present embodiment) are also arranged in the vertical height direction. The fuel cell stack groups 1a to 1d constituted by a plurality of fuel cell stacks 10 arranged in the vertical height direction are arranged.

A reformer 45 having a cross-shaped cross section is disposed in the gap between the stack groups 1a to 1d, and the reformer 45 is located between the uppermost fuel cell stacks 10 between the lowermost fuel cell stacks 10. The fuel cell stack 10 has a height that extends to between the fuel cell stacks 10.
On the other hand, two fuel heat exchangers 44a and 44b made of a rectangular parallelepiped casing are disposed along one opposing side plate 3a of the inner can body 3, and these fuel heat exchangers 44a and 44b are respectively The two stack groups 1a and 1b or 1c and 1d are arranged so as to face each other. The fuel heat exchangers 44a and 44b are connected to a fuel pipe 39 having a fuel gas inlet on the outside of the internal can body 3, and discharged from the fuel heat exchangers 44a and 44b. Each side is connected to a reformer 45.
The reformer 45 has a fuel pipe 49 connected to the ceiling surface at each end of the blades 45a and 45b extending from the center of the cross section toward the fuel heat exchangers 44a and 44b. The other ends of these fuel pipes 49 are connected to the upper portions of the fuel heat exchangers 44a and 44b, respectively.

Moreover, the outer periphery of the inner can body 3 is covered with a heat insulating material 31, and the four side plates 3 a are respectively activated for starting to dissipate heat toward the can body in the center portion in the width direction and the center portion in the vertical direction. Infrared burners (heating means) 6 a to 6 d are installed with the back side embedded in the heat insulating material 31.
These four infrared burners 6a to 6d are each made of an SUS inner box 61 formed in an elongated box shape and a porous ceramic plate attached to the front opening thereof, as shown in FIG. A combustion plate 66 and a supply pipe 67 for supplying combustion gas for burners connected to a gas inlet 63 formed on the back surface of the inner box 61 are configured. The inner box 61 has a SUS outer box 62 of the same shape that is slightly larger on the back surface thereof, and the inner box 61 and the outer box 62 are overlapped with flanges 61m and 62m provided at the respective peripheral edges. As a result, the air channel 69 is formed between the two.

In addition, an air pipe 64 having an air introduction port outside the internal can body 3 is connected to the introduction port of the air flow channel 69 at one longitudinal end of the outer box 62, and the other end of the air flow channel 69 is It is connected to the introduction side of air heat exchangers 52a and 52b, which will be described later, via an air pipe 65.
Thus, when the mixed gas is supplied from the supply pipe 67, the inner box 61 functions as a mixed gas chamber for combustion filled with the mixed gas, and air is supplied from the air pipe 64 to the air flow path 69 at the time of activation. Since the air in the air flow path 69 is heated by being supplied, each of the infrared burners 6a to 6d and the outer box 62 constitute activation air heaters 51a to 51d, respectively. Each outer box 62 also functions as a cooling mechanism for the infrared burners 6a to 6d.

Between the combustion plates 66 of the infrared burners 6a and 6c and the fuel heat exchangers 44a and 44b, start-up steam generators 43a and 43b each having a rectangular parallelepiped enclosure are disposed. The start-up steam generators 43a and 43b overlap with the combustion plate 66 in a side view, particularly in the vertical direction of the steam generators 43a and 43b in this embodiment, so as to efficiently absorb the radiant heat from the combustion plate 66. The combustion plate 66 is disposed at the center.
The start-up steam generators 43a and 43b are connected to the fuel pipe 39 through a steam pipe (not shown) on the discharge side, respectively, and a steam buffer tank 42 on the introduction side and a steam generator 41 on the upstream side, respectively. Are connected.

  On the other hand, two air heat exchangers 52a and 52b made of a rectangular parallelepiped casing are disposed along the other opposing side plate 3a of the inner can body 3, and these air heat exchangers 52a and 52b are respectively Two fuel cell stack groups 1b and 1c, or 1d and 1a are arranged so as to face each other. The other ends of the air pipes 56 connected to the upper portions of these air heat exchangers 52a and 52b are air buffer tanks 53a for supplying an oxidant gas to the fuel cell stack groups 1a and 1b or 1c and 1d, respectively. , 53b. Accordingly, air heat exchangers 52a and 52b are connected to the introduction side of the air buffer tanks 53a and 53b, respectively, and further, an air pipe 59 having an air inlet is connected to the outside of the internal can body 3. .

  Further, between the air heat exchangers 52a and 52b and the combustion plates 66 of the infrared burners 6b and 6d, start-up reformers 46a and 46b each having a rectangular parallelepiped enclosure are disposed, The start-up reformers 46a and 46b each overlap with the combustion plate 66 in a side view so as to efficiently absorb the radiant heat from the combustion plate 66, particularly in this embodiment, the start-up reformers 46a and 46b. The combustion plate 66 is disposed so as to be positioned at the center in the vertical direction. The lower ends of the start reformers 46a and 46b are connected to the other ends of fuel pipes (not shown) connected to the discharge ports at the lower portions of the reformers 45, respectively. A fuel buffer tank for supplying fuel gas to the fuel cell stack groups 1b and 1c or 1d and 1a, respectively, is connected to the other ends of the fuel pipes (not shown) connected to the upper discharge ports of the reformers 46a and 46b. 47a and 47b, respectively.

As a result, the fuel pipe 39 having the fuel gas inlet, the fuel heat exchangers 44a and 44b, the reformer 45, the start-up reformers 46a and 46b, and the fuel buffer tanks 47a and 47b are moved from the upstream side to the downstream side. A fuel gas supply line 40 is configured by fuel pipes such as a pipe 49 that supplies the reformed gas obtained by reforming the fuel gas to each fuel cell stack 10 in order. Further, the steam generator 41, the steam buffer tank 42, and the startup steam generators 43a and 43b are connected in order from the upstream side to the downstream side, and the steam is supplied by the steam pipe for supplying the steam to the fuel gas supply line 40. Line 60 is configured.
On the other hand, the air pipe 64 having an air inlet, the activation air heaters 51a to 51d, the air heat exchangers 52a and 52b, and the air buffer tanks 53a and 53b are connected in order from the upstream side to the downstream side, The start-up air supply line 50 is constituted by air pipes such as pipes 65 and 56 that supply air to each fuel cell stack 10. In addition, an air supply line 55 during operation is configured by the air pipe 59 having an air inlet and the air pipe connecting the air buffer tanks 53 a and 53 b and the fuel cell stack 10.

Next, a method for operating the solid oxide fuel cell according to the present invention will be described.
When starting the fuel cell, first, the burner fuel gas is supplied to the supply pipe 67 to ignite the infrared burners 6a to 6d. In parallel with this, fuel gas is supplied from the inlet of the fuel pipe 39 to the fuel gas supply line 40, pure water is supplied to the water vapor supply line 60, and external air is supplied from the inlet of the air pipe 64 to the startup air supply line 50. Supply and actuate the steam generator 41.

Then, the heat from the combustion plate 66 of the infrared burners 6a to 6d gradually raises the temperature of the combustion battery stack 10, and the temperature in the inner can 3 also rises. At the same time, the water vapor supplied through the water vapor supply line 60 by the operation of the water vapor generator 41 is divided into two while being heated in the water vapor buffer tank 42 and supplied to the activation water vapor generators 43a and 43b. Next, the starting steam generators 43a and 43b are sufficiently heated by the infrared burners 6a and 6c, supplied to the fuel gas supply line 40, and mixed with the fuel gas on the discharge side of the fuel pipe 39.
On the other hand, the fuel gas supplied to the fuel gas supply line 40 is divided into two on the introduction side of the fuel pipe 39, and then supplied to the fuel heat exchangers 44a and 44b while being mixed with the water vapor supplied from the water vapor supply line 60, respectively. Then, it is indirectly heated by the temperature atmosphere in the inner can body 3 and then introduced into the reformer 45 through the fuel pipe 49 from the blade portions 45a and 45b.

  Thus, the fuel gas is directly reformed by radiant heat by the infrared burners 6b and 6d through two fuel pipes (not shown) in a state where the fuel gas is partially reformed in the reformer 45, respectively. , 46b, and then sufficiently reformed by the start-up reformers 46a, 46b to become reformed gas, which is then supplied to the fuel buffer tanks 47a, 47b. Then, the reformed gas is distributed and supplied from the fuel buffer tanks 47a and 47b to the fuel gas manifolds 48 of the fuel cell stack groups 1b and 1c or 1d and 1a. Then, the fuel gas manifold 48 reaches the discharge port 2x through the fuel gas passage 22 of the separator 2, the fuel electrode current collector 14 is diffused and moved from the discharge port 2x, and the fuel electrode layer 12 is moved to the solid electrolyte layer 11 side. Move towards.

At this time, if the temperature of the power generation cell 16 becomes 300 ° C. or higher at the time of startup, the fuel electrode layer 12 may be oxidized by oxygen in the air in the external atmosphere.
Therefore, when the temperature X of the power generation cell 16 is 300 ° C. or higher and the outlet temperature Y of the starter reformers 46a and 46b is 550 ° C. or lower, the outlet temperature Y is subtracted from the temperature X of the power generation cell 16. The reforming gas in the starter reformers 46a and 46b is heated and controlled by the infrared burners 6b and 6d so that the difference is within 100 ° C., and methane 89.6 vol%, ethane 5.6 vol%, propane as fuel gas The city gas containing 3.4 vol% and butane 1.4 vol% is 0.0141 NL / min or more, and the molar ratio of water vapor (S) / carbon (C) to carbon in the city gas is 12.0. The fuel gas and water are supplied so that the amount of hydrogen corresponding to the case where each is supplied as described above is introduced per 100 cm ² of area of the power generation cell 16.

Here, the area 100 cm ² of the power generation cell 16 means that the solid electrolyte layer 11 and the fuel electrode layer 12 and the air electrode layer 13 arranged on both sides thereof all contribute to the power generation reaction. It means an overlapping area of 100 cm ² where the fuel electrode layer 12 and the air electrode layer 13 arranged on both surfaces are all overlapped.

Thereafter, even when the outlet temperature Y of the starter reformers 46a and 46b exceeds 550 ° C., the above-mentioned city gas is 0.0141 NL / min or more, and water is water vapor (S) / carbon (C) molar ratio. There supplying fuel gas and water as the amount of hydrogen equivalent to a case of supplying each to be 12.0 or higher is introduced to the area 100 cm ² per power generation cell 16.

  This is because the outlet temperature of the starting reformers 46a and 46b is the highest temperature of the reformed gas in the reformer 45 and the starting reformers 46a and 46b, and the highest temperature of the reformed gas is 550 ° C. or higher. Then, as shown in FIG. 8, hydrogen is kept constant at the maximum flow rate. For this reason, it is sufficient to adjust only the supply amounts of fuel gas and water.

  On the contrary, the test Nos. 6, when the outlet temperature of the reformer is constant at 250 ° C., the temperature difference obtained by subtracting the outlet temperature of the reformer from the temperature of the power generation cell at the time of startup is not within 100 ° C. It has been oxidized.

In addition, the flow rate with respect to the outlet temperature of the starter reformers 46a and 46b shown in FIG. 8 is measured using the solid oxide fuel cell of the above-described embodiment. Moreover, the test of Table 1 uses the fuel cell of the same structure which the solid electrolyte layer 11, the fuel electrode layer 12, and the air electrode layer 13 consist of a single cell with a diameter of 120 mm. Supply city gas and pure water containing 89.6 vol%, ethane 5.6 vol%, propane 3.4 vol%, butane 1.4 vol% so that only the city gas flow rate, pure water flow rate, and S / C change. It was done. The temperature of the power generation cell is measured by a thermocouple fixed to the separator, and the state of the fuel electrode layer 12 in Table 1 is x when the fuel electrode layer 12 is oxidized and is partially oxidized. When it is, Δ is shown, and when it is not oxidized, it is shown as ○, and the city gas flow rate and the pure water flow rate are shown in terms of single cell 100 cm ² .

As shown in Table 1, test no. 1-3, when the city gas flow rate is less than 0.0141 NL / min, the fuel electrode layer 12 has been oxidized. 7 to 8, even when water is supplied so that the molar ratio of water vapor (S) / carbon (C) is less than 12.0, the fuel electrode layer 12 is partially or wholly oxidized. I know that.
Thus, 0.0141 NL / min or more of city gas containing 89.6 vol% of methane, 5.6 vol% of ethane, 3.4 vol% of propane, and 1.4 vol% of butane, and water is steam (S) / carbon ( By supplying the fuel gas and water so that the hydrogen amount corresponding to the equilibrium composition when each is supplied so that the molar ratio of C) is 12.0 or more is introduced per 100 cm ^{2 of the} power generation cell, The shortage of hydrogen generation due to the shortage of fuel gas or water is prevented, and the oxidation of the fuel electrode layer 12 due to oxygen or the like in the external atmosphere is prevented.

  Here, 0.0141 NL / min or more of city gas containing 89.6 vol% of methane, 5.6 vol% of ethane, 3.4 vol% of propane, and 1.4 vol% of butane and water as water vapor (S) / carbon (C) As for the amount of hydrogen corresponding to the equilibrium composition when the molar ratio of each is supplied so as to be 12.0 or more, the sum of the Gibbs free energy of each substance generated by each reaction of the reforming reaction is minimized. The equilibrium constant is determined and calculated.

For example, in the case of city gas having the above composition, a shift reaction of the formula (6) occurs simultaneously with the steam reforming reactions of the following formulas (1) to (5).
CH ₄ + H ₂ O 3H ₂ + CO (1)
C ₂ H ₆ + 2H ₂ O⇔5H ₂ + 2CO (2)
C ₃ H ₈ + 3H ₂ O⇔7H ₂ + 3CO (3)
_{n-C 4 H 10 + 4H} 2 O⇔9H 2 + 4CO ·· (4)
i-C ₄ H ₁₀ + 4H ₂ O 9H ₂ + 4CO (5)
CO + H ₂ O⇔CO ₂ + H ₂ (6)

The equilibrium constant K (1) of the steam reforming reaction of methane in the formula (1) is as follows when R is a gas constant, T is an absolute temperature, and ΔG (1) is a change in free energy of the steam reforming reaction: 7) It is as a formula.
K (1) = exp (−ΔG (1) / RT) (7)
Also,
ΔG (1) = 3 × ΔG _f ^T (H ₂ ) + 1 × ΔG _f ^T (CO) − (1 × ΔG _f ^T (CH ₄ ) + 1 × ΔG _f ^T (H ₂ O)) (8)
ΔG _f ^T = ΔH _f ^T −T × S ^T (9)

ΔG _f ^T is Gibbs free energy specific to each substance at temperature T, 1 atm, ΔH _f ^T is enthalpy specific to each substance at temperature T, 1 atm, ΔH _f ⁰ is temperature 25 ° C., 1 atm. It means the enthalpy specific to each substance, that is, the standard production enthalpy. Further, [Delta] S ^T is the temperature T, the substance-specific entropy at 1 atm, [Delta] S ⁰ is a temperature 25 ° C., meaning each substance-specific entropy at 1 atm.

Therefore, the equilibrium constant is obtained by substituting the equations (8) to (11) into the equation (7). Similarly, the equilibrium constants K (2) to (6) of the reforming reaction expressed by the equations (2) to (6) can be calculated in the same manner. Specifically, the equilibrium constant and the equilibrium composition can be calculated by general-purpose equilibrium calculation software such as FastStage and MALT.
As a result, the amount of H ₂ produced can be calculated, so that even if the fuel gas component changes, the city contains 89.6 vol% methane, 5.6 vol% ethane, 3.4 vol% propane, and 1.4 vol% butane. Whether or not it corresponds to the amount of hydrogen corresponding to the equilibrium composition when the gas is supplied at 0.0141 NL / min or higher and the water vapor (S) / carbon (C) molar ratio is 12.0 or higher. It can be calculated.

On the other hand, after the air supplied to the startup air supply line 50 is supplied from the air pipe 64 to the startup air heaters 51a to 51d and directly heated while cooling the infrared burners 6a to 6d. The two are combined and heated indirectly by the two air heat exchangers 52a and 52b, and then supplied to the air buffer tanks 53a and 53b.
Then, this air is distributed and supplied from the air buffer tanks 53a and 53b to the air manifolds 54 of the fuel cell stack groups 1a and 1b or 1c and 1d. Then, the air manifold 54 reaches the discharge port 2y through the oxidant gas passage 23 of the separator 2 and diffuses and moves the air electrode current collector 15 from the discharge port 2y. Further, oxygen in the air is converted into electrons in the air electrode layer 13. Receiving oxide ions. The oxide ions diffuse and move in the solid electrolyte layer 11 toward the fuel electrode layer 12, whereby the oxide ions that have reached the vicinity of the interface with the fuel electrode layer 12 react with the reformed gas in this portion. As a result, a reaction product such as water vapor is generated, and electrons are emitted to the fuel electrode layer 12.

Such an electrode reaction progresses slowly because the temperature of the fuel cell stack 10 is low in addition to the low air temperature and reformed gas temperature at the time of startup, but the temperature in the internal can 3 increases. To get faster.
Therefore, at the time of power generation when the temperature in the internal can body 3 becomes high, the air supply is switched from the startup air supply line 50 to the operating air supply line 55, that is, from the air pipe 64 to the air pipe 59, and to the infrared ray. The operation of the burners 6a to 6d is stopped.
Then, the air is divided into two in the air pipe 59 and supplied to the two air buffer tanks 53a and 53b. Next, as in the start-up, the air buffer tanks 53a, 53b are distributed and supplied to the air manifolds 54 of the fuel cell stack groups 1a and 1b, or 1c and 1d, and the reformer 45 It reacts in the vicinity of the interface between the reformed reformed gas and the fuel electrode layer 12 of the solid electrolyte layer 11.
At that time, even if the fuel gas is not sufficiently heated in the start-up steam generators 43a, 43b and the start-up reformers 46a, 46b by stopping the operation of the infrared burners 6a-6d, the reformer 45 and the steam buffer tank Since it is sufficiently heated at 42, it becomes a reformed gas and reacts with oxide ions as described above.

  According to the operation method of the solid oxide fuel cell of this embodiment, the temperature X of the power generation cell 16 is 300 ° C. or higher, and the maximum temperature Y of the reformed gas in the starter reformers 46a and 46b is 550 ° C. or lower. In this case, the reformer in the reformer is heated and controlled by the heating means so that the difference obtained by subtracting the maximum temperature Y of the reformed gas from the temperature X of the power generation cell 16 is within 100 ° C. The reduction of the reforming reaction rate due to the low temperatures of 45, 46a, and 46b can be prevented, and oxidation due to oxygen or the like in the external atmosphere of the fuel electrode layer 12 in the power generation cell 16 at 300 ° C. or higher can be prevented.

In addition to this, when the temperature X of the power generation cell 16 is 300 ° C. or higher, 89.6 vol% of methane as the fuel gas, regardless of the maximum temperature Y of the reformed gas in the starter reformers 46a and 46b, 0.0141 NL / min or more of city gas containing 5.6 vol% of ethane, 3.4 vol% of propane, and 1.4 vol% of butane, and water is water vapor (S) / carbon (C) with respect to carbon in the city gas. By supplying the fuel gas and the water so that the amount of hydrogen corresponding to the equilibrium composition when the molar ratio of each is supplied to 12.0 or more is introduced per 100 cm ^{2 of the} power generation cell, The shortage of hydrogen generation due to the shortage of fuel gas and water is prevented, and the fuel electrode layer 12 in the power generation cell 16 at 300 ° C. or higher is oxidized by oxygen or the like in the external atmosphere. It is possible to prevent that.
Therefore, oxidation of the fuel electrode layer 12 due to the supply of unreformed fuel gas can be prevented without supplying nitrogen gas or hydrogen gas.

  Furthermore, according to the operation method of the solid oxide fuel cell of the present embodiment, the starter reformers 46a and 46b are interposed in the fuel gas supply line 40, and the starter steam generator 43a and the steam supply line 60 are provided. 43b and these are installed at positions facing the infrared burners 6a to 6d, so that the start-up reformers 46a and 46b and the start-up steam are generated using the burners 6a to 6d even when the temperature of the entire apparatus is low. The vessels 43a and 43b can be heated. For this reason, heating of fuel gas etc. at the time of starting can be performed rapidly.

  Furthermore, since the start-up reformers 46a and 46b are installed on the downstream side of the reformer 45, the infrared rays for the start-up reformers 46a and 46b are instantaneously adjusted in accordance with the temperature change in the internal can body 3. The heating temperature can be adjusted by the burners 6b and 6d. Similarly, the heating temperature by the infrared burners 6a and 6c for the activation steam generators 43a and 43b can be instantaneously adjusted. The fuel cell can be started using the minimum energy without heating the reformed gas supplied to the battery more than necessary.

  The present invention can be used as a method for operating a solid oxide fuel cell including a power generation cell in which a fuel electrode layer and an air electrode layer are disposed on both surfaces of a solid electrolyte layer.

DESCRIPTION OF SYMBOLS 1a-1d Fuel cell stack group 10 Fuel cell stack 11 Solid electrolyte layer 12 Fuel electrode layer 13 Air electrode layer (oxidant electrode layer)
16 Power generation cell 41 Steam generator 43a, 43b Startup steam generator 45 Reformer 46a, 46b Startup reformer 40 Fuel gas supply line 48 Fuel gas manifold 60 Steam supply line

Claims (4)

A fuel cell stack in which a fuel electrode layer is disposed on one surface of a solid electrolyte layer, and a power generation cell in which an oxidant electrode layer is disposed on the other surface is stacked via a separator;
A reformer that generates reformed gas by introducing fuel gas together with water vapor and absorbing heat released from the fuel cell stack during power generation; and
A fuel gas supply line through which the reformer is interposed to supply the reformed gas to the fuel cell stack;
A water vapor generator that generates water vapor by absorbing heat released from the fuel cell stack when power is introduced; and
A steam supply line through which the steam generator is interposed to supply the steam to the upstream side of the reformer in the fuel gas supply line;
In a method for operating a solid oxide fuel cell having heating means capable of heating the reformed gas in the reformer,
When the temperature X of the power generation cell is 300 ° C. or higher and the maximum temperature Y of the reformed gas in the reformer is 550 ° C. or lower,
The heating gas is used to control the reformed gas in the reformer so that the difference obtained by subtracting the reformed gas maximum temperature Y from the temperature X of the power generation cell is within 100 ° C., and the fuel gas As a city gas containing methane 89.6 vol%, ethane 5.6 vol%, propane 3.4 vol%, butane 1.4 vol%, 0.0141 NL / min or more, and water with water vapor ( The fuel is so introduced that an amount of hydrogen corresponding to the equilibrium composition when the molar ratio of S) / carbon (C) is supplied to 12.0 or more is introduced per 100 cm ² area of the power generation cell. A method for operating a solid oxide fuel cell, characterized by supplying gas and water. A fuel cell stack in which a fuel electrode layer is disposed on one surface of a solid electrolyte layer, and a power generation cell in which an oxidant electrode layer is disposed on the other surface is stacked via a separator;
A reformer that generates reformed gas by introducing fuel gas together with water vapor and absorbing heat released from the fuel cell stack during power generation; and
A fuel gas supply line through which the reformer is interposed to supply the reformed gas to the fuel cell stack;
A water vapor generator that generates water vapor by absorbing heat released from the fuel cell stack when power is introduced; and
A steam supply line through which the steam generator is interposed to supply the steam to the upstream side of the reformer in the fuel gas supply line;
In a method for operating a solid oxide fuel cell having heating means capable of heating the reformed gas in the reformer,
When the temperature X of the power generation cell is 300 ° C. or higher and the maximum temperature Y of the reformed gas in the reformer exceeds 550 ° C.,
A city gas containing 89.6 vol% methane, 5.6 vol% ethane, 3.4 vol% propane, and 1.4 vol% butane as the fuel gas is 0.0141 NL / min or more, and water relative to the carbon in the city gas. Is introduced with respect to an area of 100 cm ^{2 of the} power generation cell, when hydrogen is supplied so that the molar ratio of water vapor (S) / carbon (C) is 12.0 or more. A method for operating a solid oxide fuel cell, wherein the fuel gas and the water are supplied to the fuel cell.   The fuel gas supply line is provided with a start-up reformer downstream of the reformer, and the start-up reformer serves as a start-up heating means that operates at start-up, which is the heating means. The solid oxide fuel cell operating method according to claim 1, wherein the solid oxide fuel cell operating method is installed at a position facing it. The fuel cell stack is installed in an inner can body together with the reformer, the steam generator and the starter reformer, and a heat insulating material is disposed on the outer periphery of the inner can body,
A plurality of the fuel cell stacks are arranged in a plane in the inner can body, and a plurality of fuel cell stacks are arranged in the vertical direction, thereby being constituted by a plurality of fuel cell stacks arranged in the vertical direction. Multiple fuel cell stack groups
4. The method for operating a solid oxide fuel cell according to claim 1, wherein the reformer is disposed at a position sandwiched between the fuel cell stack groups.

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