JP6521233B2 - Solid oxide fuel cell system - Google Patents

Description

  The present invention relates to a solid oxide fuel cell system, and more particularly to a solid oxide fuel cell system that generates electric power by reacting hydrogen obtained by steam reforming a raw fuel gas and an oxidant gas.

  Japanese Patent No. 4906242 (Patent Document 1) describes a method of stopping operation of a fuel cell. In this fuel cell operation stop method, after stopping the power generation by the fuel cell, the supply amount of the raw fuel gas (hydrocarbon gas) is reduced while the air supply into the fuel cell is continuously performed A mixed gas of the raw fuel gas and the steam is supplied into the fuel cell through the reformer. The supply of the mixed gas after the power generation is stopped is stopped when the temperature of the reforming catalyst falls to the range of the oxidation generation temperature of the catalyst ± 150 ° C. Thereafter, air or raw fuel gas is flowed through the reformer as a purge gas to the fuel cell and purged.

  In the invention described in the patent 4906242, it is a technical object that air is reversely flowed through the fuel cell to the reformer after power generation is stopped, and the high temperature reforming catalyst in the reformer is oxidized in the atmosphere. In the present invention, the backflow of air is prevented by continuing the supply of the mixed gas of the raw fuel gas and the water vapor through the reformer even after the power generation is stopped. Further, the supply of the mixed gas is stopped until there is no possibility that the catalyst of the reformer is oxidized in the atmosphere, that is, when the temperature of the catalyst is reduced to a temperature within ± 150 ° C.

  Japanese Patent No. 5316830 (Patent Document 2) describes a solid oxide fuel cell. In this solid oxide fuel cell, the consumption of fuel that does not contribute to power generation is avoided by stopping the supply of the raw fuel gas as well as stopping the power generation. Further, in the present invention, temperature drop control for supplying air to the air electrode side of the fuel cell stack is executed in a state where the pressure on the fuel electrode side of the fuel cell stack is high immediately after the power generation is stopped. As a result, the backflow of air is suppressed until the temperature of the fuel electrode of the fuel cell stack is substantially reduced to a temperature at which atmospheric oxidation does not occur, and the atmospheric oxidation of the fuel electrode is prevented.

Patent No. 4906242 Patent No. 5316830 gazette

  However, as in the inventions described in Patent Documents 1 and 2, even if atmospheric oxidation occurring in a relatively high temperature region is prevented, electrochemical oxidation occurs by a mechanism different from atmospheric oxidation, which adversely affects the fuel cell. A new technical problem has been found by the present inventor that In particular, in the fuel electrode of the fuel cell stack, which has been a problem in the invention described in Japanese Patent No. 5316830, a microstructural change occurs due to an electrochemical oxidation reaction, and solid oxide fuel has been used by many years of use. The present inventor has found a new problem that the battery system may be damaged if it is repeatedly started and stopped repeatedly.

  Therefore, the present invention is a solid oxide fuel cell which is less likely to cause a microstructural change in the fuel electrode even after repeated start-up and shut-down of the fuel cell system over many years, and can ensure a sufficiently long service life. The purpose is to provide a system.

In order to solve the problems described above, the present invention is a solid oxide fuel cell system that generates electricity by reacting hydrogen obtained by steam reforming a raw fuel gas and an oxidant gas in turn, the fuel electrode layer, a solid body electrolyte layer mainly composed of nickel, and the oxidant gas electrode layer is provided tubular fuel cells, by steam reforming to produce hydrogen from the raw fuel gas, produced A reforming unit that supplies hydrogen from the lower end to the fuel electrode side of the fuel cell, a fuel supply device that supplies the raw fuel gas to the reforming unit, a water supply device that supplies water for steam reforming; An evaporator configured to generate steam from water supplied from the water supplier and supply the water vapor to the reformer, an oxidant gas supplier that supplies oxidant gas to the oxidant gas electrode of the fuel cell, and a fuel cell Cell module containing fuel and fuel supply A controller for controlling the removal of power from the fuel cell module while controlling the storage, the water supply device, and the oxidant gas supply device, and the controller controls the removal of the power from the fuel cell module, The cell protection circuit performs cell protection control for protecting the fuel cells, and the cell protection circuit supplies a smaller amount of raw fuel gas and water than during power generation operation even after stopping power extraction from the fuel cell module. Are programmed to perform cell protection control to supply gas to the fuel electrode side of the fuel cell via the reforming unit by continuing the operation of the fuel supply device and the water supply device as described above, The controller continues the operation of the oxidant gas supply device even after the removal of power and stops the temperature in the fuel cell module, and at least Of without the supply of oxidant gas to the fuel electrode side of the fuel cell after the extraction stop, the temperature of the fuel cell performs cell protection control until drops in a temperature band 200 ° C. to 100 ° C., the cells During the cell protection control, the protection circuit continues the operation of the fuel supply device for a predetermined time after stopping the operation of the water supply device, purges the water vapor remaining on the fuel electrode side of the fuel cell, and then While stopping the operation of the fuel supply device, the operation of the oxidant gas supply device is continued for a predetermined time, and the raw fuel gas that has flowed out from the fuel electrode side of the fuel cell to the oxidant gas electrode side is made to the outside of the fuel cell module It is characterized in that the fuel cell is protected by purging and thereby suppressing the occurrence of the local cell phenomenon.

  In the conventional fuel cell system, the atmosphere oxidation of the fuel electrode after stopping power generation has been considered as a problem. In particular, in the case of shutdown where power generation is stopped (power extraction is stopped) and the supply of raw fuel gas is also stopped, if the oxidant gas flows back from the oxidant gas electrode side to the fuel electrode side at high temperature, The fuel electrode may be oxidized and the fuel cell may be damaged. The problem of the atmosphere oxidation of the fuel electrode of such a fuel cell has already been solved by the present inventor as described in Japanese Patent No. 5316830 (Patent Document 2).

  However, the present inventor has found a new technical problem that when the shutdown stop is performed, the fuel electrode can be oxidized by a mechanism completely different from atmospheric oxidation. That is, after the fuel cell system is shut down and stopped, the oxidant gas on the oxidant gas electrode side of the fuel cell gradually starts to flow back to the fuel electrode side. Since the backflow of this oxidant gas is extremely little by little, the oxidant gas which backflows to the fuel electrode side is very small in the temperature zone where the atmospheric oxidation can occur after shutdown is stopped, and the atmosphere of the fuel electrode is substantially It is not oxidized. However, the inventors of the present invention have found that the fuel electrode is oxidized electrochemically in a state where the temperature is lowered to a zone where oxidation of the atmosphere in the fuel electrode does not matter after time passes.

  That is, in a relatively low temperature zone where oxidation in the atmosphere is not a problem, the oxidant gas electrode layer and the LSGM electrolyte layer still maintain the catalytic activity, while the catalytic activity of the nickel-based fuel electrode layer Is lowered. In such a state, the oxidant gas electrode layer and the electrolyte layer can permeate oxygen ions, whereas the fuel electrode layer can not react the permeated oxygen ions with hydrogen ions. The inventors of the present invention have found that such oxygen ions which can permeate to the fuel electrode layer and can not react with hydrogen ions electrochemically oxidize the fuel electrode layer. Although this electrochemical oxidation is a very small amount and does not immediately reduce the performance of the fuel cell, the solid oxide fuel cell system is used for a long time, and the start and stop are repeated many times. Fuel cells may be damaged.

  Furthermore, as long as oxygen ions which do not react in such a fuel electrode layer are uniformly generated in each part of the fuel cell, even if the fuel cell system is repeatedly turned on and off many times, there is almost no problem. . However, in the fuel cell after shutdown of the fuel cell system, when the oxidant gas starts to flow backward from the oxidant gas electrode side to the fuel electrode side, the hydrogen concentration is different in the fuel electrode of one fuel cell. It has been found by the present inventors that this concentration gradient promotes the electrochemical oxidation of the fuel electrode. That is, if there is a concentration gradient of hydrogen on the fuel electrode side, the oxygen partial pressure difference between the fuel electrode side and the oxidant gas electrode side will be different in each part of the fuel cell. Here, in the portion where the oxygen partial pressure difference of the fuel cell is large, a large electromotive force is generated between the fuel electrode and the oxidant gas electrode, while the electromotive force is small in the portion where the oxygen partial pressure difference is small. As described above, the inventors of the present invention have found that when there is a large portion and a small portion of the electromotive force in one fuel cell, a "local cell phenomenon" in which current flows in one fuel cell occurs. It was found. When this "local cell phenomenon" occurs, the effect of electrochemical oxidation in the fuel electrode layer is concentrated on a part of one fuel cell, and the fuel cell is made by repeating start and stop many times. It can lead to damage.

  In order to avoid such a "local cell phenomenon", the inventor of the present invention, as in the invention described in Japanese Patent No. 4906242 (Patent Document 1), supplies the raw fuel gas even after the fuel cell system stops power generation. An attempt was made to continue (The invention described in Patent Document 1 aims to prevent the atmospheric oxidation of the reforming catalyst in the reformer, and aims to avoid the electrochemical oxidation of the fuel electrode. The technical idea of the present invention is completely different. As described above, although the negative effect of electrochemical oxidation is reduced by continuing the supply of the raw fuel gas even after the power generation of the fuel cell system is stopped, the fuel is not sufficient, and the fuel is not repeated if the start and stop are repeated many times. It has been confirmed by the present inventors that microstructural change has occurred in the electrode layer.

  That is, in the invention described in Japanese Patent No. 4906242 (Patent Document 1), when the temperature of the reforming catalyst is lowered to about 350 ° C., the supply of the mixed gas of the raw fuel gas and the water vapor is stopped, and then the air is Purge is performed by However, although it is possible to avoid the atmospheric oxidation of the reforming catalyst and the fuel electrode layer when such a stopping step is performed, it is possible that the "local cell phenomenon" in the fuel cell is rather promoted. Have been found by This is a temperature zone at about 350 ° C. where the gas supplied to the fuel electrode side is switched from the mixed gas to the purge gas is a temperature zone where electrochemical oxidation is likely to occur, and when the gas supplied in this zone is switched, A concentration gradient is generated on the fuel electrode side, and a "local cell phenomenon" occurs.

  In order to solve these problems, in the present invention, the fuel cell protection control continues to supply a smaller amount of raw fuel gas and water than during power generation operation after stopping power extraction from the fuel cell module. Is carried out until the temperature of 200 ° C. to 100 ° C. falls. According to the present invention configured as described above, since the cell protection control is continued until the temperature drops to a temperature range of 200 ° C. to 100 ° C. after stopping the extraction of power, in a temperature range where electrochemical oxidation tends to occur. The generation of the concentration gradient on the fuel electrode side is suppressed, and the deterioration of the fuel cell due to the occurrence of the "local cell phenomenon" can be effectively suppressed.

  In the present invention, preferably, the controller further comprises a purge control circuit that supplies the raw fuel gas to the fuel cell and purges the residual gas on the fuel electrode side after completion of the cell protection control, and the controller controls the fuel The cell protection control is ended until the temperature of the battery cell falls to the temperature zone of 200 ° C. to 130 ° C., and then the residual gas on the fuel electrode side is purged.

  Since the solid electrolyte layer made by LSGM retains catalytic activity to a temperature zone significantly lower than the nickel-based fuel electrode layer, cell protection control to continue the supply of raw fuel gas and water It is preferable to carry out to a low temperature zone. However, when cell protection control is performed up to about 100 ° C., another problem occurs in that the supplied water vapor condenses at the fuel electrode of the fuel cell, which causes oxidation of the fuel electrode. In particular, in a solid oxide fuel cell system not equipped with a device for supplying oxidant gas (air) to the fuel electrode side of a fuel cell, water vapor remaining on the fuel electrode side is purged with a large amount of oxidant gas. Condensation problems are likely to occur. According to the present invention configured as described above, since the cell protection control is terminated in the temperature range of 200 ° C. to 130 ° C. of the fuel cell, the occurrence of condensation can be suppressed and a small amount The source fuel gas can be used to purge the gas remaining on the fuel electrode side. As a result, even in a solid oxide fuel cell system that does not have a system for supplying oxidant gas (air) to the fuel electrode side, it is possible to avoid wasting a large amount of fuel by the raw fuel gas purge. it can.

  In the present invention, preferably, the controller ends the cell protection control until the temperature of the fuel cell falls to the temperature range of 150 ° C. to 130 ° C., and then purges the residual gas on the fuel electrode side.

  According to the present invention configured as described above, the cell protection control is completed in the temperature range of 150 ° C. to 130 ° C., thereby achieving both suppression of electrochemical oxidation and suppression of water vapor condensation at the highest level. be able to.

In the present invention, preferably, the cell protection circuit makes the supply amount of raw fuel gas and the supply amount of water constant at all times during the cell protection control.
According to the present invention configured as described above, the supply amount of the raw fuel gas and the supply amount of water are always made constant during the cell protection control, so that the fuel electrode side of the fuel cell is under the cell protection control. Can be maintained extremely uniformly, and the occurrence of electrochemical oxidation due to the concentration gradient can be reliably suppressed.

  In the present invention, preferably, further, a heater for heating the evaporation unit is provided, and the controller activates the heater to promote the generation of water vapor when the temperature of the fuel cell decreases to 350 ° C. or lower. .

  According to the present invention configured as described above, since the heater is activated when the temperature of the fuel cell falls to 350 ° C. or less, even in the state where the temperature of the fuel cell module is decreasing, It is possible to reliably generate a certain amount of water vapor. As a result, the occurrence of the concentration gradient on the fuel electrode side of the fuel cell can be minimized, and the occurrence of electrochemical oxidation can be more reliably suppressed.

  According to the solid oxide fuel cell system of the present invention, the fuel electrode is unlikely to undergo microstructural changes even after repeated start-up and shut-down of the fuel cell system over many years, and a sufficiently long service life is ensured. Can.

FIG. 1 is an overall configuration view showing a fuel cell system according to an embodiment of the present invention. FIG. 1 is a front cross-sectional view showing a fuel cell module of a fuel cell system according to an embodiment of the present invention. FIG. 3 is a cross-sectional view taken along the line III-III in FIG. 1A is a partial cross-sectional view and FIG. 1B is a cross-sectional view showing a fuel cell of a fuel cell system according to an embodiment of the present invention. FIG. 1 is a perspective view of a fuel cell stack of a fuel cell system according to an embodiment of the present invention. FIG. 1 is a block diagram illustrating a fuel cell system according to an embodiment of the present invention. It is a time chart which shows an example of each amount of supply of a fuel etc. in a starting process of a fuel cell system by one embodiment of the present invention, and temperature of each part. 7 is a flowchart showing a processing procedure when shutdown stop is performed in the fuel cell system according to one embodiment of the present invention. 7 is a flowchart showing a processing procedure when shutdown stop is performed in the fuel cell system according to one embodiment of the present invention. It is a time chart which represented typically an example of stop behavior in a fuel cell system by one embodiment of the present invention by time series. FIG. 7 is a diagram for describing control in a case where the stopping step is performed, a temperature in the fuel cell module, and a state of the tip of the fuel cell in chronological order in the fuel cell system according to one embodiment of the present invention. FIG. 10 is a front cross-sectional view showing a fuel cell module of a fuel cell system according to a modified embodiment of the present invention. FIG. 7 is a diagram for describing the temperature and pressure in the fuel cell module and the state of the tip of the fuel cell in time series in the case where shutdown stop is performed in the conventional solid oxide fuel cell system. It is explanatory drawing which shows typically the relationship between the activation temperature of the fuel electrode which comprises a fuel cell, an electrolyte, and an air electrode, and a stop process. It is a graph which shows the electromotive force which a single fuel battery cell generate | occur | produces in the state which supplied hydrogen gas to the fuel electrode side, and supplied air to the air electrode side. It is a figure which shows the behavior of the fuel cell in case the temperature in a fuel cell module passes an electrochemical oxidation generation | occurrence | production temperature zone. It is a figure which shows typically the local cell phenomenon in a fuel cell.

A solid oxide fuel cell (SOFC) system according to an embodiment of the present invention will now be described with reference to the accompanying drawings.
FIG. 1 is an overall configuration diagram showing a solid oxide fuel cell (SOFC) system according to an embodiment of the present invention. As shown in FIG. 1, a solid oxide fuel cell (SOFC) system 1 according to an embodiment of the present invention includes a fuel cell module 2 and an accessory unit 4.

  The fuel cell module 2 includes a housing 6, and a metal case 8 is incorporated in the housing 6 via a heat insulating material 7. In a power generation chamber 10 which is a lower portion of the case 8 which is a sealed space, a fuel cell assembly 12 is arranged to perform a power generation reaction with fuel (hydrogen) and an oxidant gas (air). The fuel cell assembly 12 includes ten fuel cell stacks 14 (see FIG. 5), and the fuel cell stack 14 includes 16 fuel cells 16 (see FIG. 4). . As described above, the fuel cell assembly 12 includes 160 fuel cells 16, and all the fuel cells 16 are connected in series.

A combustion chamber 18 which is a combustion unit is formed above the above-described power generation chamber 10 of the case 8 of the fuel cell module 2, and in this combustion chamber 18, the remaining fuel (off gas) remaining without being used for the power generation reaction. And the remaining oxidant (air) are combusted to produce exhaust gas. Furthermore, the case 8 is covered with the heat insulating material 7 to suppress the heat inside the fuel cell module 2 from being released to the outside air.
Further, a reformer 20 for reforming the raw fuel gas is disposed above the combustion chamber 18, and the heat of combustion of the residual gas heats the reformer 20 to a temperature at which the reforming reaction is possible. doing. Further, above the reformer 20, an air heat exchanger 22, which is a heat exchanger for heating the power generation air by the combustion gas of the residual gas and preheating the power generation air, is disposed.

  Next, the auxiliary unit 4 stores the water obtained by condensing the water contained in the exhaust from the fuel cell module 2 and uses the filter as pure water to obtain pure water, and the water supplied from the water storage tank The water flow rate adjustment unit 28 (a motor driven by a motor such as a "water pump"), which is a water supply device for adjusting the flow rate of water. The auxiliary unit 4 also includes a gas shut-off valve 32 for blocking the raw fuel gas supplied from a fuel supply source 30 such as city gas, a desulfurizer 36 for removing sulfur from the raw fuel gas, and a raw fuel gas A fuel flow control unit 38 (motor-driven "fuel pump" or the like) that adjusts the flow rate of the fuel and a valve 39 that shuts off the source fuel gas flowing out of the fuel flow control unit 38 when power is lost. Furthermore, the auxiliary unit 4 includes a solenoid valve 42 for blocking air that is an oxidant gas supplied from the air supply source 40, a reforming air flow rate adjustment unit 44 for adjusting the flow rate of air, and an air flow rate adjustment for power generation. A unit 45 ("air blower" driven by a motor, etc.), a first heater 46 for heating reforming air supplied to the reformer 20, and a generator for heating power generation air supplied to the power generation chamber 2 heater 48 is provided. The first heater 46 and the second heater 48 are provided to efficiently perform the temperature rise at the time of activation, but may be omitted.

Next, the fuel cell module 2 is connected to a combustion catalyst 49 having a combustion catalyst incorporated therein for purifying exhaust gas, and the exhaust gas purified by the combustion catalyst 49 is supplied to the hot water producing apparatus 50. It has become so. Further, the combustion catalyst 49 incorporates a catalytic heater 49a that heats the catalyst to the activation temperature. Tap water is supplied from the water supply source 24 to the hot water producing apparatus 50, and the tap water becomes hot water by the heat of the exhaust gas, and is supplied to a hot water storage tank of an external water heater (not shown).
Further, a control box 52 for controlling the supply amount of fuel gas and the like is attached to the fuel cell module 2.
Further, the fuel cell module 2 is connected to an inverter 54 which is a power extraction unit (power conversion unit) for supplying the power generated by the fuel cell module to the outside.

Next, the internal structure of a fuel cell module of a solid oxide fuel cell (SOFC) system according to an embodiment of the present invention will be described with reference to FIGS. 2 and 3. FIG. 2 is a side sectional view showing a fuel cell module of a solid oxide fuel cell (SOFC) according to an embodiment of the present invention, and FIG. 3 is a sectional view taken along the line III-III of FIG. .
As shown in FIGS. 2 and 3, in the case 8 in the housing 6 of the fuel cell module 2, as described above, the fuel cell assembly 12, the reformer 20, and the heat exchanger for air are sequentially arranged from the lower side. 22 are arranged.

The reformer 20 is provided with a reformer introduction pipe 62 for introducing pure water, a raw fuel gas to be reformed, and reforming air on the end side surface on the upstream end side.
The reformer introduction pipe 62 is a circular pipe extending from the side wall surface at one end of the reformer 20, is bent by 90 °, extends substantially in the vertical direction, and penetrates the upper end face of the case 8. The reformer introduction pipe 62 functions as a water introduction pipe for introducing water to the reformer 20. In addition, a T-shaped pipe 62a is connected to the upper end of the reformer introduction pipe 62, and raw fuel gas and pure water are added to both ends of the pipe extending in a substantially horizontal direction of the T-shaped pipe 62a. Piping for supplying is connected respectively. The water supply pipe 63a extends obliquely upward from one side end of the T-shaped tube 62a. The fuel gas supply piping 63b extends in the horizontal direction from the other side end of the T-shaped tube 62a, is bent in a U-shape, and extends substantially horizontally in the same direction as the water supply piping 63a.

  On the other hand, an evaporation unit 20a, a mixing unit 20b, and a reforming unit 20c are formed in the reformer 20 in this order from the upstream side, and the reforming unit 20c is filled with a reforming catalyst. The evaporation unit 20 a is configured to heat and evaporate the pure water introduced through the reformer introduction pipe 62. Moreover, the heater 81 (FIG. 2) for assisting the heating of the evaporation part 20a is provided in the evaporation part 20a. The heater 81 is configured to be energized when water vapor is generated in a state where the temperature in the fuel cell module 2 is lowered, such as after power generation is stopped, so that the supplied pure water can be evaporated.

  Furthermore, the water vapor generated in the evaporation unit 20a is mixed with the raw fuel gas in the mixing unit 20b, and flows into the reforming unit 20c. The steam and raw fuel gas introduced into the reforming unit 20c are reformed by the reforming catalyst charged in the reforming unit 20c. In the present embodiment, as the reforming catalyst, one provided with ruthenium on the surface of alumina spheres is used. Further, as the reforming catalyst, a noble metal-based reforming catalyst such as one obtained by adding rhodium to the surface of alumina spheres can be used. The noble metal-based reforming catalyst generally has an oxidation temperature of about 700 ° C. or higher and is very high temperature, and air may enter the reformer 20 after the solid oxide fuel cell system 1 is stopped. The reforming catalyst is not oxidized in the atmosphere.

  A fuel gas supply pipe 64 is connected to the downstream end of the reformer 20, and the fuel gas supply pipe 64 extends downward, and further, in a manifold 66 formed under the fuel cell assembly 12. Extends horizontally. A plurality of fuel supply holes 64 b are formed on the lower surface of the horizontal portion 64 a of the fuel gas supply pipe 64, and the reformed fuel gas is supplied into the manifold 66 from the fuel supply holes 64 b. Further, a pressure fluctuation suppressing flow path resistance portion 64c having a narrowed flow path is provided in the middle of the vertical portion of the fuel gas supply pipe 64, and the flow resistance of the fuel gas supply flow path is adjusted. The adjustment of the flow path resistance will be described later.

  A lower support plate 68 having a through hole for supporting the fuel cell stack 14 described above is attached above the manifold 66, and the fuel gas in the manifold 66 is supplied into the fuel cell 16. Be done.

On the other hand, an air heat exchanger 22 is provided above the reformer 20.
Further, as shown in FIG. 2, an igniter 83 for starting the combustion of the fuel gas and the air is provided in the combustion chamber 18.

Next, the fuel cell 16 will be described with reference to FIG. FIG. 4A is a partial cross-sectional view showing a fuel cell of a solid oxide fuel cell (SOFC) system according to an embodiment of the present invention. FIG. 4 (b) is a partial cross-sectional view of a fuel cell.
As shown in FIG. 4A, the fuel cell 16 includes a fuel cell 84 and an inner electrode terminal 86 which is a cap connected to both ends of the fuel cell 84.
The fuel cell 84 is a tubular structure extending in the vertical direction, and has a cylindrical inner electrode layer 90 forming a fuel gas channel 88 therein, a cylindrical outer electrode layer 92, an inner electrode layer 90, and an outer side. And a solid electrolyte layer 94 between the electrode layer 92 and the electrode layer 92. The inner electrode layer 90 is a fuel electrode through which fuel gas (hydrogen) passes, and is a (-) electrode, while the outer electrode layer 92 is an air electrode in contact with air, and is a (+) electrode. There is.

  Since the inner electrode terminal 86 attached to the lower end side which is the first end of the fuel cell 84 and the upper end side which is the second end has the same structure, here, the inner side attached to the upper end The electrode terminal 86 will be specifically described. An upper portion 90 a of the inner electrode layer 90 includes a solid electrolyte layer 94, an outer peripheral surface 90 b exposed to the outer electrode layer 92, and an upper end surface 90 c. The inner electrode terminal 86 is connected to the outer peripheral surface 90 b of the inner electrode layer 90 via the conductive seal material 96, and is in direct contact with the upper end surface 90 c of the inner electrode layer 90 to connect with the inner electrode layer 90. It is electrically connected. At a central portion of the inner electrode terminal 86, a fuel gas channel thin tube 98 communicating with the fuel gas channel 88 of the inner electrode layer 90 is formed.

  The fuel gas channel thin tube 98 is an elongated throttle portion provided so as to extend in the axial direction of the fuel cell 84 from the center of the inner electrode terminal 86. For this reason, a predetermined pressure loss occurs in the flow of fuel gas flowing from the manifold 66 (FIG. 2) through the fuel gas flow passage narrow tube 98 of the lower inner electrode terminal 86 into the fuel gas flow passage 88. . Therefore, the fuel gas flow passage thin tube 98 of the lower side inner electrode terminal 86 acts as an inflow side flow passage resistance portion, and the flow passage resistance thereof is set to a predetermined value. In addition, a predetermined pressure loss also occurs in the flow of the fuel gas flowing out of the fuel gas flow passage 88 through the fuel gas flow passage narrow tube 98 of the upper inner electrode terminal 86 to the combustion chamber 18 (FIG. 2). Therefore, the fuel gas flow passage thin tube 98 of the upper side inner electrode terminal 86 acts as an outflow side flow passage resistance portion, and the flow passage resistance thereof is set to a predetermined value.

  The inner electrode layer 90 is, for example, a mixture of Ni and zirconia doped with at least one selected from rare earth elements such as Ca, Y, and Sc, Ni, and ceria doped with at least one selected from rare earth elements. It is formed of at least one of a mixture, and a mixture of Ni and a lanthanum gallate doped with at least one selected from Sr, Mg, Co, Fe, and Cu.

  The solid electrolyte layer 94 is, for example, zirconia doped with at least one selected from rare earth elements such as Y and Sc, ceria doped with at least one selected from rare earth elements, and lanthanum gallate doped with at least one selected from Sr and Mg. , Formed of at least one of.

  The outer electrode layer 92 is, for example, lanthanum manganite doped with at least one selected from Sr, Ca, lanthanum ferrite doped with at least one selected from Sr, Co, Ni, Cu, Sr, Fe, Ni, Cu It is formed of at least one of lanthanum cobaltite, silver, etc. doped with at least one selected from

Next, the structure of the fuel cell 84 will be described in detail with reference to FIG. 4 (b).
As shown in FIG. 4 (b), the inner electrode layer 90 is composed of a first fuel electrode 90d and a second fuel electrode 90e constituting the fuel electrode layer, and further, the fuel electrode protective layer 90f is used as the first fuel electrode. It is included between 90d and the second fuel electrode 90e. The outer electrode layer 92 is composed of an air electrode 92a which is an oxidant gas electrode layer and a current collecting layer 92b.

In the present embodiment, the first fuel electrode 90 d is made of Ni / YSZ, and is formed by firing a mixture of Ni and YSZ, which is zirconia doped with Y, into a cylindrical shape. The fuel electrode protective layer 90f is a thin film formed of a mixture of strontium zirconate and nickel (Ni / SrZrO ₃ ) and thinner than the first fuel electrode 90d and the second fuel electrode 90e. The second fuel electrode 90e is Ni / GDC, and is formed by depositing a mixture of Ni and GDC, which is ceria doped with Gd, on the outside of the fuel electrode protective layer 90f. As described above, in the present embodiment, the fuel electrode layer mainly contains nickel.

  Further, in the present embodiment, the solid electrolyte layer 94 is formed by laminating LSGM, which is lanthanum gallate doped with Sr and Mg, on the outside of the second fuel electrode 90 e. The fired body was configured by firing the formed body thus formed.

  In the present embodiment, the air electrode 92a is formed by depositing LSCF, which is lanthanum cobaltite doped with Sr and Fe, on the outside of the sintered body. The current collection layer 92b is configured by forming an Ag layer outside the air electrode 92a.

Next, the fuel cell stack 14 will be described with reference to FIG. FIG. 5 is a perspective view showing a fuel cell stack of a solid oxide fuel cell (SOFC) system according to an embodiment of the present invention.
As shown in FIG. 5, the fuel cell stack 14 includes 16 fuel cells 16, and the fuel cells 16 are arranged in two rows of eight each. Each fuel cell 16 is supported by a rectangular lower support plate 68 (FIG. 2) on the lower end side of the ceramic rectangular shape, and on the upper end side, two substantially square upper supports each having four fuel cells 16 at both ends. It is supported by a plate 100. The lower support plate 68 and the upper support plate 100 are each formed with a through hole through which the inner electrode terminal 86 can pass.

  Furthermore, a current collector 102 and an external terminal 104 are attached to the fuel cell 16. The current collector 102 includes a fuel electrode connecting portion 102 a electrically connected to the inner electrode terminal 86 attached to the inner electrode layer 90 which is a fuel electrode, and an outer peripheral surface of an outer electrode layer 92 which is an air electrode. It is integrally formed so as to connect with the air electrode connection portion 102b to be electrically connected. Further, a silver thin film is formed on the entire outer surface of the outer electrode layer 92 (air electrode) of each fuel cell 16 as an electrode on the air electrode side. The current collector 102 is electrically connected to the entire air electrode by bringing the air electrode connection portion 102 b into contact with the surface of the thin film.

  Furthermore, two external terminals 104 are respectively connected to the air electrode 86 of the fuel cell 16 located at the end of the fuel cell stack 14 (the far side in the left end in FIG. 5). These external terminals 104 are connected to the inner electrode terminals 86 of the fuel cells 16 at the end of the adjacent fuel cell stack 14, and all 160 fuel cells 16 are connected in series as described above. It is supposed to be.

Next, sensors attached to the solid oxide fuel cell (SOFC) system according to the present embodiment will be described with reference to FIG. FIG. 6 is a block diagram illustrating a solid oxide fuel cell (SOFC) system according to one embodiment of the present invention.
As shown in FIG. 6, the solid oxide fuel cell system 1 includes a control unit 110 which is a controller, and the control unit 110 performs operations such as "ON" and "OFF" for the user to operate. An operation device 112 equipped with a button, a display device 114 for displaying various data such as a power generation output value (wattage), and a notification device 116 that issues a warning in the event of an abnormal state are connected. There is. The notification device 116 may be connected to a management center at a remote location to notify the management center of an abnormal state. In addition, the control unit 110 incorporates a microprocessor, a memory, and a program (not shown) for operating them, thereby aiding the accessory unit 4 based on the input signal from each sensor. The inverter 54 and the like are controlled.

Next, signals from various sensors described below are input to the control unit 110.
First, the combustible gas detection sensor 120 is for detecting a gas leak, and is attached to the fuel cell module 2 and the accessory unit 4.
The CO detection sensor 122 detects whether CO in the exhaust gas, which is originally discharged to the outside through the exhaust gas passage 80 and the like, leaks to an external housing (not shown) covering the fuel cell module 2 and the auxiliary unit 4. It is to do.
The hot water storage state detection sensor 124 is for detecting the temperature and the amount of hot water in a water heater (not shown).

The power state detection sensor 126 is for detecting the current and voltage of the inverter 54 and the distribution board (not shown).
The power generation air flow rate detection sensor 128 is for detecting the flow rate of power generation air supplied to the power generation chamber 10.
The reforming air flow rate sensor 130 is for detecting the flow rate of the reforming air supplied to the reformer 20.
The fuel flow rate sensor 132 is for detecting the flow rate of the fuel gas supplied to the reformer 20.

The water flow rate sensor 134 is for detecting the flow rate of pure water supplied to the reformer 20.
The water level sensor 136 is for detecting the water level of the pure water tank 26.
The pressure sensor 138 is for detecting the pressure upstream of the reformer 20.
The exhaust temperature sensor 140 is for detecting the temperature of the exhaust gas flowing into the hot water producing device 50.

As shown in FIG. 3, the power generation chamber temperature sensor 142 is provided on the front and back sides in the vicinity of the fuel cell assembly 12 and detects the temperature in the vicinity of the fuel cell stack 14 to detect the fuel cell stack It is for estimating the temperature of 14 (ie, the fuel cell 84 itself).
The combustion chamber temperature sensor 144 is for detecting the temperature of the combustion chamber 18.
The exhaust gas chamber temperature sensor 146 is for detecting the temperature of the exhaust gas of the exhaust gas chamber 78.
The reformer temperature sensor 148 is for detecting the temperature of the reformer 20, and calculates the temperature of the reformer 20 from the inlet temperature and the outlet temperature of the reformer 20.
The outside air temperature sensor 150 is for detecting the temperature of outside air when the solid oxide fuel cell (SOFC) system is placed outdoors. Further, a sensor may be provided to measure the humidity and the like of the outside air.

  Signals from these sensors are sent to the control unit 110, and the control unit 110 controls the water flow adjustment unit 28, the fuel flow adjustment unit 38, the ignition air flow adjustment unit 44, oxidation based on the data of these signals. A control signal is sent to the power generation air flow rate adjustment unit 45, which is an agent gas supply device, to control each flow rate in these units.

  As shown in FIGS. 2 and 3, the air heat exchanger 22 has a plurality of combustion gas pipes 70 and a power generation air passage 72. Further, as shown in FIG. 2, an exhaust gas collecting chamber 78 is provided at one end of the plurality of combustion gas pipes 70, and the exhaust gas collecting chamber 78 is communicated with the respective combustion gas pipes 70. ing. Further, an exhaust gas discharge pipe 82 is connected to the exhaust gas concentration chamber 78. Furthermore, the other end of each combustion gas pipe 70 is open, and the open end communicates with the combustion chamber 18 in the case 8 through the communication opening 8 a formed in the upper surface of the case 8. It is done.

  The combustion gas piping 70 is a plurality of metal circular pipes directed in the horizontal direction, and the respective circular pipes are arranged in parallel. On the other hand, the power generation air flow path 72 is configured by the space outside the respective combustion gas pipes 70. In addition, a power generation air introduction pipe 74 is connected to an end of the power generation air flow path 72 on the exhaust gas discharge pipe 82 side, and the air outside the fuel cell module 2 is connected to the power generation air introduction pipe 74. Through the air flow path 72 for power generation. The power generation air introduction pipe 74 protrudes horizontally from the air heat exchanger 22 in parallel with the exhaust gas discharge pipe 82. Furthermore, a pair of communication flow paths 76 (FIG. 3) are connected to both side surfaces of the other end of the power generation air flow path 72, and the power generation air flow path 72 and each communication flow path 76 are respectively , And an outlet port 76a.

  As shown in FIG. 3, power generation air supply paths 77 are respectively provided on both side surfaces of the case 8. The communication channels 76 provided on both sides of the air heat exchanger 22 are respectively communicated with the upper portions of the power generation air supply paths 77 provided on both sides of the case 8. Further, at the lower part of each of the power generation air supply paths 77, a large number of outlets 77a are provided side by side in the horizontal direction. The power generation air supplied through each power generation air supply passage 77 is injected toward the lower side of the fuel cell stack 14 in the fuel cell module 2 from the multiple outlets 77 a.

Further, a straightening vane 21 which is a partition wall is attached to a ceiling surface inside the case 8, and the straightening vane 21 is provided with an opening 21 a.
The straightening vane 21 is a plate disposed horizontally between the ceiling surface of the case 8 and the reformer 20. The straightening vane 21 is configured to adjust the flow of gas flowing upward from the combustion chamber 18 and to guide it to the inlet (the communication opening 8 a in FIG. 2) of the air heat exchanger 22. The power generation air and combustion gas directed upward from the combustion chamber 18 flow through the opening 21 a provided at the center of the straightening vane 21 into the upper side of the straightening vane 21, and the top face of the straightening vane 21 and the ceiling face of the case 8 The exhaust passage 21 b between them flows in the left direction in FIG. 2 and is led to the inlet of the air heat exchanger 22. Further, the opening 21a is provided above the reforming unit 20c of the reformer 20, and the gas that has risen through the opening 21a is the exhaust on the left side in FIG. 2 opposite to the evaporation unit 20a. It flows into the passage 21b. For this reason, the space above the evaporation unit 20a (right side in FIG. 2) has a slower flow of exhaust than the space above the reforming unit 20c, and acts as a gas retention space 21c in which the flow of exhaust stagnates.

  Further, a vertical wall 21d is provided along the entire circumference at the edge of the opening 21a of the straightening vane 21, and the exhaust air of the upper side of the straightening vane 21 from the space below the straightening vane 21 by this vertical wall 21d. The flow path flowing into the passage 21 b is narrowed. Furthermore, a falling wall 8b (FIG. 2) is provided over the entire circumference at the edge of the communication opening 8a that communicates the exhaust passage 21b with the air heat exchanger 22, and the exhaust passage 21b is formed by the falling wall 8b. The flow path from the air flow to the air heat exchanger 22 is narrowed. By providing the vertical wall 21 d and the lower wall 8 b, the flow passage resistance in the exhaust passage from the combustion chamber 18 through the air heat exchanger 22 to the outside of the fuel cell module 2 is adjusted. The adjustment of the flow path resistance will be described later.

Next, flows of fuel, air for power generation, and exhaust gas during power generation operation of the solid oxide fuel cell system 1 will be described.
First, the raw fuel gas is introduced into the evaporation section 20a of the reformer 20 through the fuel gas supply pipe 63b, the T-shaped pipe 62a, and the reformer introduction pipe 62, and the pure water is supplied into the water supply pipe. 63a, introduced into the evaporation section 20a through the T-shaped tube 62a and the reformer introduction pipe 62. Therefore, the supplied raw fuel gas and water are merged in the T-shaped pipe 62 a and introduced into the evaporation section 20 a through the reformer introduction pipe 62. During the power generation operation, since the evaporating unit 20a is heated to a high temperature, the pure water introduced into the evaporating unit 20a is evaporated relatively quickly to become water vapor. The evaporated steam and raw fuel gas are mixed in the mixing unit 20 b and flow into the reforming unit 20 c of the reformer 20. The raw fuel gas introduced into the reforming unit 20c together with the steam is steam-reformed here to be reformed into a hydrogen-rich fuel gas. The fuel reformed in the reforming unit 20c descends downward through the fuel gas supply pipe 64 and flows into the manifold 66 which is a dispersion chamber.

  The manifold 66 is a relatively large volume rectangular parallelepiped space disposed under the fuel cell stack 14, and each of the fuel cells constituting the fuel cell stack 14 has a large number of holes provided on the upper surface thereof. It communicates with the inside of 16. The fuel introduced into the manifold 66 flows out from the upper end of the fuel cell 16 through the fuel electrode side of the fuel cell 16, that is, the inside of the fuel cell 16 through a number of holes provided on the top surface thereof. Further, when hydrogen gas as a fuel passes through the inside of the fuel cell 16, it reacts with oxygen in the air passing outside the fuel cell 16 as an air electrode (oxidant gas electrode) to generate charge. . The remaining fuel not used for power generation flows out from the upper end of each fuel cell 16 and is burned in a combustion chamber 18 provided above the fuel cell stack 14.

  On the other hand, the power generation air, which is an oxidant gas, is fed into the fuel cell module 2 via the power generation air introduction pipe 74 by the power generation air flow rate adjustment unit 45 which is an oxidant gas supply device. The air fed into the fuel cell module 2 is introduced into the power generation air flow path 72 of the air heat exchanger 22 through the power generation air introduction pipe 74 and is preheated. Preheated air flows out to each communication channel 76 through each outlet port 76a (FIG. 3). The power generation air that has flowed into each of the communication channels 76 flows downward through the power generation air supply passages 77 provided on both sides of the fuel cell module 2, and the fuel cell stacks 14 from the multiple outlets 77a. Toward the power generation chamber 10.

  The air injected into the power generation chamber 10 contacts the outer surface of each fuel cell 16 which is the air electrode side (oxidant gas electrode side) of the fuel cell stack 14, and a part of oxygen in the air generates power. Used for Further, the air injected to the lower part of the power generation chamber 10 via the blowout port 77a rises in the power generation chamber 10 while being used for power generation. The air rising in the power generation chamber 10 burns the fuel flowing out from the upper end of each fuel cell 16. The heat of combustion heats the evaporation portion 20a, the mixing portion 20b and the reforming portion 20c of the reformer 20 disposed above the fuel cell stack 14. The fuel is burned, and the generated combustion gas heats the upper reformer 20 and then flows to the upper side of the straightening vane 21 through the opening 21 a above the reformer 20. The combustion gas which has flowed into the upper side of the straightening vane 21 is led to the communication opening 8a which is the inlet of the air heat exchanger 22 through the exhaust passage 21b constituted by the straightening vane 21. The combustion gas that has flowed into the air heat exchanger 22 from the communication opening 8a flows into the end of each open combustion gas pipe 70, and flows through the power generation air flow path 72 outside each combustion gas pipe 70. And exchange heat with each other to be concentrated in the exhaust gas concentration chamber 78. Exhaust gas collected in the exhaust gas collecting chamber 78 is discharged to the outside of the fuel cell module 2 via the exhaust gas discharge pipe 82. As a result, evaporation of water in the evaporation unit 20a and steam reforming reaction which is an endothermic reaction in the reforming unit 20c are promoted, and power generation air in the air heat exchanger 22 is preheated. Further, the exhaust gas discharged from the fuel cell module 2 flows into the combustion catalyst 49, where harmful components such as carbon monoxide are removed, and sent to the hot water producing apparatus 50.

Next, control in the startup process of the solid oxide fuel cell system 1 will be described with reference to FIG.
FIG. 7 is a time chart showing an example of each supply amount of fuel and the like in the start-up step and the temperature of each part. The scale on the vertical axis in FIG. 7 indicates the temperature, and the supply amounts of fuel and the like schematically indicate the increase and decrease thereof.

In the start-up steps shown in FIGS. 7 and 8, the temperature of the fuel cell stack 14 in the normal temperature state is raised to a temperature at which power can be generated.
First, at time t0 in FIG. 7, the supply of power generation air, ignition air, and water is started (prepurge step). Specifically, the control unit 110, which is a controller, sends a signal to the power generation air flow rate adjustment unit 45, which is an oxidant gas supply device for power generation, to operate it.
As described above, the power generation air is introduced into the fuel cell module 2 through the power generation air introduction pipe 74, and flows into the power generation chamber 10 through the air heat exchanger 22 and the power generation air supply passage 77. . Further, the control unit 110 sends a signal to the ignition air flow rate adjustment unit 44, which is an oxidant gas supply device for ignition, to operate it. Ignition air introduced into the fuel cell module 2 flows into the interior of each fuel cell 16 through the reformer 20 and the manifold 66 and flows out from the upper end thereof. Also, the control unit 110 sends a signal to the water flow rate adjustment unit 28 to operate it. The pure water pressure-fed from the water flow rate adjustment unit 28 reaches the T-shaped pipe 62a through the water supply pipe 63a. The water supply piping 63a from the water flow rate adjustment unit 28 to the T-shaped pipe 62a is filled with water for at least a predetermined time (water filling period: t0 to t1) from time t0, and a small amount of water is added. It arrange | positions in the evaporation part 20a. At time t0, the fuel is not supplied yet, so that the reforming reaction does not occur in the reformer 20. In the present embodiment, the supply amount of generation air started at time t0 in FIG. 7 is about 50 L / min, the supply amount of ignition air is about 4.8 L / min, and the supply amount of water is It is 2.5 cc / min.

Next, at time t1 which is a predetermined time after time t0 in FIG. 7, the supply of fuel is started, and an ignition process to the supplied fuel is started. Specifically, the control unit 110 sends a signal to the fuel flow control unit 38, which is a fuel supply device, to operate it. In the present embodiment, the fuel supply amount started at time t1 is about 4.0 L / min.
The fuel introduced into the fuel cell module 2 flows into the interior of each fuel cell 16 through the reformer 20 and the manifold 66 and flows out from the upper end thereof. At time t1, the reforming reaction does not occur in the reformer 20 because the temperature of the reformer is still low.

In the ignition step, the control unit 110 sends a signal to the ignition device 83 (FIG. 2) which is an ignition means, and ignites the fuel flowing out from the upper end of each fuel cell 16. The igniter 83 repeatedly generates sparks in the vicinity of the upper end of the fuel cell stack 14 and ignites the fuel flowing out of the upper end of each fuel cell 16.
In addition, since the water supply pipe 63a is filled with water at time t1 and a small amount of water is disposed in the evaporation unit 20a, the control unit 110 reduces the water supply amount to 2.06 cc / min. . Thereby, a small amount of water starts to be supplied to the reformer 20 during the ignition process.

At time t2 in FIG. 7, the process proceeds from the ignition process to the combustion process. In the combustion process, the temperature of the reformer 20 is raised by the off-gas combustion heat.
When the ignition process is completed, the control unit 110 stops the supply of ignition air at time t2 (supply amount 0.0 L / min). Therefore, although the air for ignition flows through the reformer 20 before ignition, it does not flow through the reformer 20 after ignition, and the reforming reaction in the reformer 20 (POX) It is not intended to be supplied for the reaction). Therefore, as another embodiment, the ignition air may be supplied to the fuel cell 16 through another pipe without passing through the reformer 20.

  Further, at time t2, the control unit 110 reduces the fuel supply amount to 3.14 L / min and increases the power generation air supply amount to about 70 L / min. The amount of water supplied is maintained at 2.06 cc / min, and is maintained at a minimum value at least immediately after ignition during the start-up step and during the combustion step.

  In the combustion process, the supplied fuel flows out as an off gas from the upper end of each fuel cell 16 and is burned here. The heat of combustion heats the reformer 20 disposed above the fuel cell stack 14. Here, the evaporation chamber heat insulating material 23 is disposed above the reformer 20 (on the top of the case 8), whereby the temperature of the reformer 20 rapidly increases from normal temperature immediately after the start of fuel combustion. To rise. Since the outside air is introduced into the air heat exchanger 22 disposed on the evaporation chamber heat insulator 23, the air heat exchanger 22 has a low temperature, particularly immediately after the start of combustion, and serves as a cooling source. Cheap. In the present embodiment, since the evaporation chamber heat insulator 23 is disposed between the upper surface of the case 8 and the bottom surface of the air heat exchanger 22, the reformer 20 disposed in the upper portion in the case 8 The transfer of heat to the air heat exchanger 22 is suppressed, and heat is likely to stagnate in the vicinity of the reformer 20 in the case 8. In addition, the space above the flow straightening plate 21 above the evaporation portion 20a is configured as a gas retention space 21c (FIG. 2) in which the flow of combustion gas is delayed, so the vicinity of the evaporation portion 20a is double-insulated And the temperature rises more rapidly.

  As described above, the temperature of the evaporating unit 20a is rapidly increased, so that the water vapor can be generated in a short time after the start of the off gas combustion. In addition, since a small amount of reforming water is supplied to the evaporation unit 20a little by little (minimum amount in the start-up process), the heat is small compared to the case where a large amount of water is stored in the evaporation unit 20a. The water can be heated to the boiling point, and the supply of steam can be started immediately. Furthermore, since water flows in immediately after the start of the operation of the water flow rate adjustment unit 28, it is possible to avoid an excessive temperature rise of the evaporation unit 20a and a delayed supply of water vapor due to a delayed supply of water.

In this manner, the temperature of the reformer 20 rises during the combustion process, and at time t3, the combustion process is transferred to the first steam reforming reaction process (SR1 process). In the SR1 process, a steam reforming reaction occurs with the fuel and steam that flowed into the reforming unit 20c through the evaporation unit 20a. The steam reforming reaction is an endothermic reaction represented by the following formula (1).
C _m H _n + x H ₂ O → aCO ₂ + bCO + cH ₂ (1)

Further, when the first steam reforming reaction step (SR1 step) is started at time t3, the consumption amount of water increases, so the control unit 110 maintains the supply amounts of fuel and air for power generation. Increase the water supply only to 3.82 cc / min.
In the time chart shown in FIG. 7, the reformer temperature at time t3 is about 250.degree.

  Next, when the temperature detected by the reformer temperature sensor 148 reaches approximately 450 ° C., at time t4 in FIG. 7, the first steam reforming reaction step (SR1 step) to the second steam reforming reaction step (SR2) are performed. Process). At time t4, the power generation air supply is reduced to 59 L / min, and the water supply is further increased to 5.0 cc / min. Also, the fuel supply amount is maintained at the previous value. As a result, in the SR2 process, the molar ratio S / C of water vapor to carbon is increased as compared to the SR1 process.

  Furthermore, when the temperature detected by the power generation chamber temperature sensor 142 reaches about 550 ° C. at time t5 in FIG. 7, the second steam reforming reaction step (SR2 step) to the third steam reforming reaction step (SR3 step) Transition to Accordingly, the fuel supply amount is reduced to 2.02 L / min, the power generation air supply amount is further reduced to 47 L / min, and the water supply amount is reduced to 4.75 cc / min. As a result, in the SR3 step, the molar ratio S / C of water vapor to carbon is further increased than in the SR2 step, and the value is set to a value suitable for the steam reforming reaction.

  Furthermore, after the SR3 process is performed for a predetermined time, when the temperature detected by the power generation chamber temperature sensor 142 reaches approximately 600 ° C., the process shifts to the power generation process. In the power generation process, power is taken from the fuel cell stack 14 to the inverter 54 (FIG. 6) to start power generation. Further, in the power generation process, the fuel supply amount, the power generation air supply amount, and the water supply amount are changed according to the output power required for the fuel cell module 2.

  Next, shutdown stop processing in the conventional solid oxide fuel cell system will be described with reference to FIGS. 12 to 15b.

  First, when a shutdown stop is performed, the supply of raw fuel gas, the supply of water, and the supply of air for power generation are stopped in a short time. In addition, the extraction of power from the fuel cell module is also stopped (output current = 0). After shutdown stop, the fuel cell module is left naturally in this state. For this reason, the fuel existing on the fuel electrode side inside each fuel cell is jetted to the air electrode side based on the pressure difference with the external air electrode side. Further, the air (and the fuel ejected from the fuel electrode side) existing on the air electrode side of each fuel battery cell is based on the pressure difference between the pressure on the air electrode side (pressure in the power generation chamber) and the atmospheric pressure. Exhausted to the outside of the fuel cell module. Therefore, after the shutdown stop, the pressure on the anode side and the anode side of each fuel cell naturally decreases.

  However, the pressure drop on the fuel electrode side after fuel supply and power generation are stopped is reduced by the pressure drop on the air electrode side by providing the narrowed portion which is a large capillary tube of the flow path resistance portion at the upper end portion of each fuel cell It is configured to be more gradual and allow fuel to remain for an extended period of time after shutdown. As described above, also in the conventional solid oxide fuel cell system, the pressure on the fuel electrode side is maintained below the oxidation suppression temperature while maintaining the pressure higher than the pressure on the air electrode side after being left naturally after the shutdown stop. The risk is reduced that the fuel electrode is oxidized to the atmosphere.

  In the present specification, the oxidation suppression temperature means a temperature at which the risk of the fuel electrode being oxidized in the atmosphere is sufficiently reduced. The risk of the fuel electrode being oxidized decreases gradually with decreasing temperature and eventually becomes zero. For this reason, even if it is the oxidation suppression temperature of a temperature zone a little higher than the oxidation lower limit temperature which is the lowest temperature which oxidation of a fuel electrode may generate | occur | produce, the risk of fuel electrode oxidation can fully be reduced. In a general fuel cell, such an oxidation suppression temperature is considered to be about 350 ° C. to 400 ° C., and the oxidation lower limit temperature is about 250 ° C. to 300 ° C.

  FIG. 12 is a diagram for explaining the operation after shutdown shutdown of the conventional solid oxide fuel cell system. The upper part of FIG. 12 shows a graph schematically representing pressure changes on the fuel electrode side and the air electrode side, the middle part shows the control operation and the temperature inside the fuel cell module in time series, and the lower part shows the fuel at each time point The state of the upper end of the battery cell is shown.

  First, before the shutdown stop in the middle stage of FIG. 12, a normal power generation operation is performed. In this state, the temperature in the fuel cell module is about 600 to 700.degree. Further, as shown in the lower part (1) of FIG. 12, the fuel gas remaining without being used for power generation is ejected from the upper end of the fuel cell, and the ejected fuel gas is burned at the upper end. Next, when the supply of the raw fuel gas, the water for reforming, and the air for power generation is stopped due to the shutdown stop, the flow rate of the fuel gas to be jetted decreases, as shown in the lower part (2) of FIG. The flame at the end of the fuel cell disappears.

  As shown in the lower part (3) of FIG. 12, since the pressure inside the fuel cell (fuel electrode side) is higher than the outside (air electrode side) even after the flame is extinguished after shutdown is stopped, the fuel is The ejection of the fuel gas from the battery cells is continued. Further, as shown in the upper part of FIG. 12, immediately after the shutdown is stopped, the pressure on the fuel electrode side is higher than the pressure on the air electrode side, and each pressure decreases while maintaining this relationship. The pressure difference between the fuel electrode side and the air electrode side decreases with the ejection of the fuel gas after the shutdown is stopped. The amount of fuel gas ejected from the fuel cell decreases as the pressure difference between the fuel electrode side and the air electrode side decreases (lower stage (4) and (5) in FIG. 12).

  About 5 to 6 hours after shutdown stop, when the temperature in the fuel cell module falls to the oxidation suppression temperature, both the fuel electrode side and the air electrode side of each fuel cell decrease to almost atmospheric pressure, and air The air on the pole side begins to diffuse to the fuel electrode side (lower stage (6) and (7) in FIG. 12). Further, in the vicinity of the oxidation suppression temperature, the temperature of the fuel electrode is low, and the oxidation generated when air contacts the fuel electrode is slight, and the adverse effect caused by the oxidation can be substantially ignored. Furthermore, as shown in the lower part (8) of FIG. 12, after the temperature of the fuel electrode falls below the oxidation lower limit temperature, even if the fuel electrode side of each fuel cell is filled with air, the fuel electrode is oxidized in the atmosphere. There is nothing to do. As described above, in the conventional solid oxide fuel cell system, the mechanical configuration prevents air entering the fuel electrode above the oxidation suppression temperature from contacting and oxidizing the fuel electrode from the atmosphere.

  However, the inventors of the present invention have found that even if atmosphere oxidation of the fuel electrode is prevented, the fuel electrode is electrochemically oxidized by a mechanism different from atmosphere oxidation.

Next, with reference to FIG. 13, the electrochemical oxidation phenomenon of the fuel electrode will be described.
FIG. 13 is an explanatory view schematically showing the relationship between the activation temperature of the fuel electrode, the electrolyte and the air electrode constituting the fuel cell 16 and the stop control.
In the present embodiment, the first fuel electrode 90d is formed of Ni / YSZ, the second fuel electrode 90e is formed of Ni / GDC, the solid electrolyte layer 94 is formed of LSGM, and the air electrode 92a is formed of LSCF. ing. Further, a fuel electrode protective layer 90f made of Ni / SrZrO ₃ is formed between the first fuel electrode 90d and the second fuel electrode 90e.

  In the stopping step, the risk that the nickel contained in the first fuel electrode 90d and the second fuel electrode 90e is oxidized in the atmosphere becomes high. The risk of the atmospheric oxidation decreases with the temperature decrease, and decreases sufficiently when the temperature in the fuel cell module 2 decreases to the oxidation suppression temperature Te (about 350 ° C.) of nickel, and the risk decreases when the temperature falls to the atmospheric oxidation safety temperature Ts. It disappears. In the present embodiment, control is performed with the ambient oxidation safety temperature Ts set to about 300.degree.

  In the present embodiment, the activation state of the catalyst of the first fuel electrode 90d and the second fuel electrode 90e starts to decrease from about 450 ° C., and the fuel activation lower limit temperature Ta which is the lower limit temperature of the activation state is about 290 ° C. It is. The fuel electrode receives oxygen ions from the solid electrolyte layer 94 and reacts the received oxygen ions with fuel (hydrogen) to generate water and emit electrons, but this catalytic action decreases with a decrease in temperature. When the temperature of the fuel electrode falls to the lower limit temperature of activity Ta, its ability is lost, and even if it receives oxygen ions, it can not be reacted with the fuel to cause a power generation reaction.

On the other hand, the active state in which the solid electrolyte layer 94 can transmit oxygen ions from the air electrode to the fuel electrode starts to decrease from about 350 ° C., and the activity lower limit temperature Tb is about 150 ° C. The activation lower limit temperature Tb of the electrolyte is lower than the activation lower limit temperature Ta of the fuel electrode. The solid electrolyte layer 94 can transmit oxygen ions received from the air electrode to the fuel electrode until the operating temperature of the fuel cell module 2 is lowered to the lower limit temperature Tb. However, when the temperature is lower than the lower limit temperature Tb, the solid electrolyte layer 94 can not transmit oxygen ions to the fuel electrode even if it receives oxygen ions from the air electrode.
Further, the air electrode is in an active state capable of converting oxygen in the air to oxygen ions at the active lower limit temperature Tb or more of the solid electrolyte layer 94.

  Generally, in order to enable power generation at lower temperatures, it is preferable that the activation temperature of the fuel electrode, the solid electrolyte layer, and the air electrode of the fuel cell be low. The lowering of the activation temperature is achieved not only by selecting the material itself but by tuning the particle size, layer thickness, manufacturing process parameters and the like of the selected material. As described above, when the temperature of each activation temperature is lowered, the activation lower limit temperatures of the fuel electrode, the solid electrolyte layer, and the air electrode can be set lower than the oxidation suppression temperature Te of nickel. The lower limit temperature of activation of the solid electrolyte layer and the air electrode is lower than the lower limit temperature of activation of the fuel electrode.

  FIG. 13 shows the relationship between the fuel activation lower limit temperature Ta and the electrolyte activation lower limit temperature Tb. As described above, the activated state of the fuel electrode starts to decrease from about 450 ° C. and becomes inactivated at the lower limit temperature of activation Ta (about 290 ° C.). On the other hand, the active state of the solid electrolyte layer starts to decrease from about 350 ° C., and becomes inactive at the lower limit temperature of activity Tb (about 150 ° C.). Therefore, from the power generation operation temperature to the lower limit activity temperature Tb of the solid electrolyte layer, the solid electrolyte layer 94 is in a state capable of transmitting oxygen ions to the fuel electrode, but the active state of the fuel electrode starts to decrease from about 450 ° C. There is. Therefore, in the temperature zone Tc (electrochemical oxidation generation temperature zone) from about 450 ° C. to the lower limit activity temperature Tb of the solid electrolyte layer, the solid electrolyte layer 94 permeates oxygen ions, but permeates oxygen ions at the fuel electrode The ability to react with fuel (hydrogen) is reduced.

FIG. 14 is a graph showing an electromotive force generated by a single fuel cell 16 in a state where hydrogen gas is supplied to the fuel electrode side and air is supplied to the air electrode side.
In the graph of FIG. 14, the horizontal axis indicates the temperature of the fuel cell 16 and the vertical axis indicates the generated electromotive force. In addition, the broken line in FIG. 14 indicates the electromotive force obtained by theoretical calculation assuming that the fuel electrode layer, the solid electrolyte layer, and the air electrode layer are all in the active state, and the solid line indicates the experimentally measured value. Power is shown. As apparent from this graph, in the temperature range of about 450 ° C. or more, the theoretically calculated electromotive force and the experimentally obtained electromotive force are relatively well matched. On the other hand, it can be seen that as the temperature decreases, the emf obtained by the experiment is lower than the emf calculated theoretically. This is considered to be because the activity of the fuel electrode layer having the highest activation temperature among the fuel electrode layer, the solid electrolyte layer, and the air electrode layer is lowered, and the ability to generate a power generation reaction is lowered.

Next, with reference to FIGS. 15a and 15b, the behavior of the fuel cell in the case where the temperature in the fuel cell module passes through the electrochemical oxidation occurrence temperature zone will be described.
As described above, in the temperature zone Tc, the solid electrolyte layer 94 and the air electrode 92a are in the active state, and oxygen ions can pass through the air electrode 92a and the solid electrolyte layer 94 to the fuel electrode, but the first fuel electrode 90d The second fuel electrode 90e has a reduced catalytic activity. Therefore, the fuel electrode has a reduced ability to generate a power generation reaction that causes the supplied oxygen ions to react with the fuel (hydrogen).

The fuel electrode contains nickel, and nickel easily reacts with oxygen in the air to become nickel oxide in a high temperature atmosphere above the oxidation suppression temperature Te (about 350 ° C.), but a temperature zone lower than the oxidation suppression temperature Te In this case, nickel is in a state of being difficult to react with oxygen in the air.
However, even if the temperature zone is lower than the oxidation suppression temperature Te, when the oxygen ions having passed through the solid electrolyte layer 94 are supplied to the fuel electrode, the nickel in the fuel electrode is oxidized by the electrochemical oxidation reaction. Can be linked to nickel oxide. When this reaction occurs, electrons are emitted. Therefore, when the above-mentioned electrochemical oxidation reaction occurs, charges are generated by a mechanism different from that of the normal power generation reaction.
It is considered that when the fuel electrode activation state is not reduced, only a normal power generation reaction in which oxygen ions are linked to the fuel occurs, and an abnormal reaction in which oxygen ions are linked to nickel does not substantially occur.

  On the other hand, in the stopping step, since the extraction of the electric power from the fuel cell module 2 is stopped, it is considered that substantially no current flows even if a charge is generated by the electrochemical oxidation reaction. However, the inventor of the present invention has been aware that even if the extraction of power is stopped and the anode and cathode are electrically disconnected (open circuit), a weak current can flow locally. I found it.

  That is, the electrochemical oxidation reaction occurs based on the difference in oxygen partial pressure between the fuel electrode side and the air electrode side. Therefore, when a large amount of hydrogen remains on the fuel electrode side, the oxygen partial pressure on the fuel electrode side is low, and the difference in oxygen partial pressure from the air electrode side is large. Oxygen ions can easily flow. However, in the case where the oxygen partial pressure difference is uniform in each part of one fuel battery cell 16, the fuel electrode into which the oxygen ions flow in through the solid electrolyte layer 94 has the same potential in each part, so Almost no current flows.

  However, as described with reference to FIG. 12, when time after shutdown is stopped, air begins to diffuse little by little from the air electrode side to the fuel electrode side, so the concentration of hydrogen remaining near the upper end of the fuel cell 16 is descend. As a result, as shown in FIG. 15b, in one fuel battery cell 16, the difference in oxygen partial pressure between the fuel electrode side and the air electrode side is small near the upper end, and the oxygen partial pressure is low near the lower end. The difference is large.

  As described above, a large amount of electric charge is generated in the vicinity of the lower end portion of the fuel cell 16 due to the occurrence of a large amount of electrochemical oxidation reaction, and the electric charge generated is relatively reduced in the vicinity of the upper end portion. As a result, a potential difference is generated in the fuel electrode of one fuel cell 16 and local charge transfer (weak current) occurs. When a weak current flows due to such a local cell phenomenon, the electrochemical oxidation reaction of nickel proceeds significantly. In particular, a large amount of oxygen ions flow into the fuel electrode through the solid electrolyte layer 94 near the lower end of each fuel cell 16 where the difference in oxygen partial pressure between the fuel electrode side and the air electrode side is large. An oxidation reaction occurs.

Nickel oxide produced by the electrochemical oxidation reaction is reduced by the fuel (hydrogen) supplied to the fuel electrode side during power generation operation. Thus, when the nickel contained in the fuel electrode causes electrochemical oxidation / reduction reaction due to shutdown and start and subsequent operation, the fuel electrode changes in its microstructure and volume.
Furthermore, in addition to the frequent repetition of fuel cell module shutdown / startup, the electrochemical oxidation reaction of nickel takes a relatively long time in the shutdown and startup processes, particularly in the shutdown process requiring a long time.

Thus, when the change in the microstructure and volume of the fuel electrode occurs, tensile stress is applied to the solid electrolyte layer. And each fuel cell in which the flow of oxygen ions by the local cell phenomenon is concentrated when the stop and start are repeated many times due to long-term use and the accumulated amount of nickel undergoing electrochemical oxidation / reduction reaction increases In the vicinity of the lower end of 16, the microcracks finally occur in the solid electrolyte layer.
Thus, in the temperature zone Tc, the present inventor is in a state where nickel, which is a specific substance contained in the fuel electrode, is subjected to electrochemical oxidation, electrochemically oxidizes, and reduces during the subsequent operation. It has been discovered that when it is subjected to changes in the microstructure and volume of the fuel electrode, tensile stress is applied to the solid electrolyte layer, and finally the microcracks in the solid electrolyte layer cause damage to the fuel cell.

Next, the shutdown process in the solid oxide fuel cell system 1 according to the embodiment of the present invention will be described. This stopping step is configured for the purpose of sufficiently suppressing the deterioration of the fuel cell due to the above-mentioned atmospheric oxidation and electrochemical oxidation.
FIGS. 8a and 8b are flowcharts showing a processing procedure when a normal shutdown process is performed in the solid oxide fuel cell system 1 according to the embodiment of the present invention. FIG. 9 is a time chart schematically showing an example of stop behavior when shutdown stop is executed in time series. FIG. 10 is a diagram for explaining the control when the stopping step is performed, the temperature in the fuel cell module, and the state of the front end of the fuel cell in time series.

The control unit 110, which is a controller, executes the processing of the flowcharts shown in FIGS. 8a and 8b by the built-in microprocessor, the memory, and the program for operating these. Further, a microprocessor, a memory and the like operated by the built-in program function as a cell protection circuit 110a (FIG. 6) for executing cell protection control and a purge control circuit 110b (FIG. 6).
First, in step S1 of FIG. 8a, it is determined whether the solid oxide fuel cell system 1 is in a power generation operation. If the power generation operation is being performed, the process proceeds to step S2. If the power generation operation is not being performed, one process of the flowcharts shown in FIGS. 8a and 8b is ended.
Next, in step S2, it is determined whether the stop process to be executed is a normal stop. In the case of an abnormal stop, one process of the flowcharts shown in FIGS. 8a and 8b is ended. In the case of the normal stop, the processing after step S3 of FIG. 8a is executed. In the present embodiment, “normally stopping” refers to stopping based on the stopping operation of the solid oxide fuel cell system 1 by the user, or periodic stopping set in advance by a program incorporated in the control unit 110. Corresponds to this.

  In step S3, the extraction of power from the fuel cell module 2 is stopped. Further, in the example of the time chart shown in FIG. 9, at time t301, the user operates the stop switch (upper stage (1) in FIG. 10), and the output of power from the fuel cell module 2 is zero.

  Next, in step S4, restart of the solid oxide fuel cell system 1 is prohibited. That is, when the solid oxide fuel cell system 1 is started again before the process is terminated after the termination step is started in step S3, the temperature condition inside the fuel cell module 2 becomes inappropriate, and the fuel cell Since there is a possibility that the cell 16 may be degraded, the restart is prohibited.

  Furthermore, in step S5, the fuel supply amount and the water supply amount for reforming are set to the minimum supply amount that can be supplied by the fuel flow control unit 38 and the water flow control unit 28. That is, during the stop process, the cell protection circuit 110a incorporated in the control unit 110 executes cell protection control for supplying a smaller amount of raw fuel gas and water than during power generation operation. The raw fuel gas and water supplies are always maintained at a constant value during cell protection control. Moreover, S / C which is ratio of the supply amount of the water vapor | steam and fuel supplied at this time is about 3, and is comparable as S / C in electric power generation driving | operation. Note that S / C can be further increased during the stopping step. On the other hand, air for power generation (however, power generation is completely stopped) is supplied by the maximum supply amount of air flow control unit for power generation 45 as cooling control after the stop operation at time t301 in FIG. . Thus, the air in the fuel cell module 2 (air electrode side of the fuel cell stack 14), the combustion gas of the remaining fuel, and the fuel that has flowed out from the fuel electrode side of the fuel cell stack 14 during the stop process (FIG. The upper stage (2) is discharged from the fuel cell module 2. In addition, the combustion of the fuel gas flowing out of the upper end of each fuel cell 16 gradually disappears as the raw fuel gas supply amount is minimized.

  Since the minimum amount of fuel supply is continued even after the stop operation at time t301 in FIG. 9, the air does not enter the fuel electrode side even if the power generation air is supplied. Thereby, in the high temperature state in the stopping step, the backflow of air to the fuel electrode side of each fuel cell 16 is suppressed, and the atmosphere oxidation of the fuel electrode layer of each fuel cell 16 is prevented. Further, even after the stopping operation at time t301, the reforming unit 20c is still at a high temperature, and thus the supplied raw fuel gas and steam generate a steam reforming reaction to generate hydrogen gas. The reforming reaction after such a stop operation gradually ceases to occur as the temperature of the reforming unit 20c decreases, so that the unreformed raw fuel gas and the steam are supplied to the fuel electrode side of each fuel cell 16. (Bottom of FIG. 10).

  Next, in step S6 of FIG. 8a, it is determined whether the temperature of the fuel cell stack 14 in the fuel cell module 2 has decreased to 300.degree. If the temperature has dropped to 300 ° C. or less, the process proceeds to step S7. If the temperature has not dropped, the control state up to step S5 is maintained. Here, when the temperature of the fuel cell stack 14 is in the temperature range of about 450 ° C. to about 150 ° C., the fuel electrode layer may be subjected to electrochemical oxidation (FIG. 13). However, in the present embodiment, since a constant amount of fuel supply continues even after the stop operation at time t301 in FIG. 9, the atmosphere on the fuel electrode side of each fuel cell 16 becomes constant, and the concentration gradient of fuel Is suppressed. By suppressing the concentration gradient in each part on the fuel electrode side, the occurrence of the local cell phenomenon in each fuel cell 16 is suppressed. As a result, electrochemical oxidation of the fuel electrode layer of each fuel cell 16 is prevented (the lower part of FIG. 10). Further, since the supply of steam is also continued along with the supply of fuel, carbon deposition on the fuel electrode layer of the fuel cell 16 and the reforming catalyst in the reforming unit 20c is also prevented.

  In the present embodiment, the temperature detected by a thermocouple, which is a temperature sensor disposed in the vicinity of the fuel cell stack 14, is referred to as the temperature of the fuel cell stack 14. By referring to the temperature of the fuel cell stack 14, atmospheric oxidation and electrochemical oxidation of the fuel electrode layer of each fuel cell 16 can be reliably suppressed. On the other hand, since the temperature of the reforming unit 20c largely changes due to the steam reforming reaction which is an endothermic reaction generated inside, it is difficult to grasp the temperature of the fuel electrode layer, and the atmosphere oxidation and electrochemical oxidation of the fuel electrode layer Not suitable for suppression.

  In step S7, energization to the heater 81 (FIG. 2) provided in the evaporation unit 20a is started (time t302 in FIG. 9). That is, in the state where the temperature of the fuel cell stack 14 is lowered to 300 ° C., the temperature of the evaporation section 20a is also lowered, and the supplied water is difficult to evaporate. For this reason, the evaporation unit 20a is heated by the heater 81 so that the water vapor is surely generated. Preferably, in the state where the temperature of the fuel cell 16 is lowered to 350 ° C. or less, the heater 81 is operated to promote the generation of water vapor.

  Next, in step S8 of FIG. 8a, it is determined whether the temperature of the fuel cell stack 14 has dropped to 150.degree. If the temperature drops to 150 ° C. or less, the process proceeds to step S9 (FIG. 8B) to end the cell protection control, and when not decreased, the control state up to step S7 is maintained. In the example shown in FIG. 9, the temperature of the fuel cell stack 14 has dropped to 150 ° C. at time t303. In the present embodiment, the cell protection control is ended when the temperature of the fuel cell stack 14 decreases to 150 ° C. However, the temperature at which the cell protection control is ended depends on the structure of the fuel cell stack 14 or the like. Accordingly, a temperature zone between about 200 ° C. and about 100 ° C. can be set.

  In step S9, the energization of the heater 81 is stopped, and the supply of water to the evaporation unit 20a by the water flow rate adjustment unit 28 is stopped. On the other hand, the supply of the raw fuel gas by the fuel flow control unit 38 and the supply of the air by the power generation air flow control unit 45 are continued with the previous supply amount (time t 303 in FIG. 9; )). As described above, the purge control circuit 110 b built in the control unit 110 stops the supply of water to stop the generation of water vapor, and continues the supply of the raw fuel gas, whereby the fuel of each fuel cell 16 is obtained. Purge the water vapor remaining on the pole side. As a result, the water vapor remaining on the fuel electrode side of each fuel cell 16 is solidified to prevent the fuel electrode layer from being adversely affected. In addition, when the temperature of the fuel cell 16 is in a temperature zone between about 200 ° C. and about 130 ° C., cell protection control is ended and purge is performed to prevent electrochemical oxidation and condensation. It can be compatible. Furthermore, when the temperature of the fuel cell 16 is in the temperature zone between about 150 ° C. and about 130 ° C., by terminating the cell protection control, electrochemical oxidation can be prevented more reliably. Further, in the state where the temperature of the fuel cell stack 14 is lowered to 150 ° C., even if only the raw fuel gas is supplied to each fuel cell 16, carbon deposition does not occur.

Next, in step S10, it is determined whether 20 minutes have elapsed after the water supply is stopped. If 20 minutes have elapsed, the process proceeds to step S11. If not, the control state up to step S9 is maintained.
Next, in step S11, the supply of the raw fuel gas by the fuel flow control unit 38 is stopped. As a result, the raw fuel gas remaining on the fuel electrode side of each of the fuel cells 16 is discharged little by little to the air electrode side, and finally all the raw fuel gas is replaced with air (the upper row in FIG. 10). (4) to (6)). On the other hand, the supply of air by the power generation air flow rate adjustment unit 45 is continued with the previous supply amount (time t304 in FIG. 9). Thus, by stopping the supply of the raw fuel gas and continuing the supply of air, the raw fuel gas that has flowed out from the fuel electrode side of each fuel cell 16 to the air electrode side is supplied to the air electrode side. The fuel cell module 2 is purged with the air.

Next, in step S12, it is determined whether 10 minutes have elapsed after the supply of the raw fuel gas is stopped. If 10 minutes have elapsed, the process proceeds to step S13, and if not, the control state up to step S11 is maintained.
Furthermore, in step S13, it is determined whether the temperature of the fuel cell stack 14 has dropped to 90.degree. If the temperature of the fuel cell stack 14 has decreased to 90 ° C., the process proceeds to step S14. If the temperature has not elapsed, the control state up to step S13 is maintained.

Next, in step S14, the supply of air by the power generation air flow rate adjustment unit 45 is stopped, and the supply of the raw fuel gas, water, and power generation air are all stopped (time t305 in FIG. 9). As described above, when the temperature of the fuel cell stack 14 is lowered to 90 ° C. or less, the risk of the atmosphere oxidation of the fuel electrode layer and the electrochemical oxidation occurring is completely eliminated, and the solid oxide fuel cell Restarting the system 1 will not adversely affect each fuel cell 16.
Furthermore, in step S15, restart of the solid oxide fuel cell system 1 prohibited in step S4 of FIG. 8a is permitted, and one process of the flowchart shown in FIGS. 8a and 8b is ended. This completes the stopping process.

  According to the solid oxide fuel cell system 1 of the embodiment of the present invention, after stopping extraction of power from the fuel cell module 2 (time t301 in FIG. 9), the amount of raw fuel gas and water smaller than during power generation operation The cell protection control to continue the supply is performed until the temperature of the fuel cell decreases to 150 ° C. (time t303 in FIG. 9, step S8 in FIG. 8a). According to the solid oxide fuel cell system 1 of the present embodiment configured as described above, the generation of the concentration gradient on the fuel electrode side is suppressed in the temperature zone in which electrochemical oxidation is likely to occur. It is possible to effectively suppress the deterioration of the fuel cell 16 due to the generation.

  Further, according to the solid oxide fuel cell system 1 of the present embodiment, the cell protection control (time t301 to t303 in FIG. 9) is completed at the temperature of the fuel cell 16 at 150 ° C. While being able to control, it is possible to purge the gas remaining on the fuel electrode side with a small amount of raw fuel gas. As a result, even in the solid oxide fuel cell system 1 not provided with the oxidant gas (air) supply device to the fuel electrode side, it is possible to avoid wasting a large amount of fuel by the raw fuel gas purge. It is possible to achieve both the suppression of electrochemical oxidation and the suppression of water vapor condensation at the highest level.

  Furthermore, according to the solid oxide fuel cell system 1 of the present embodiment, the supply amount of the raw fuel gas and the supply amount of water are always made constant during the cell protection control (time t301 to t303 in FIG. 9). During step S5 to step S8 in FIG. 8a, cell protection control is performed, the atmosphere on the fuel electrode side of the fuel cell 16 can be maintained extremely uniformly, and generation of electrochemical oxidation due to concentration gradient is assured. It can be suppressed.

  Further, according to the solid oxide fuel cell system 1 of the present embodiment, the heater is activated when the temperature of the fuel cell 16 drops to 300 ° C. (time t 302 in FIG. 9, step S 6 in FIG. 8 a Even when the temperature of the fuel cell module 2 is decreasing, it is possible to reliably generate a certain amount of water vapor in the evaporation section 20a. As a result, the occurrence of the concentration gradient on the fuel electrode side of the fuel cell 16 can be minimized, and the occurrence of electrochemical oxidation can be suppressed more reliably.

  Although the preferred embodiments of the present invention have been described above, various modifications can be added to the above-described embodiments. In particular, in the embodiment described above, the reformer 20 is disposed inside the fuel cell module 2, and the evaporator that generates steam for steam reforming is provided inside the reformer 20, The present invention can be applied to a solid oxide fuel cell system provided with fuel cell modules of different configurations.

FIG. 11 is a front cross-sectional view of a fuel cell module provided in a solid oxide fuel cell system according to a modification of the present invention.
As shown in FIG. 11, the fuel cell module 200 according to this modification distributes fuel gas to a module case 208, a plurality of fuel cells 216 housed in the module case 208, and the fuel cells 216. It has a manifold 266, a reformer 220 which is a reformer disposed above the fuel cell 216, and an air heat exchanger 222 which is a heat exchanger disposed above the module case 208. Further, the fuel cell module 200 includes a combustion catalyst 249 disposed above the air heat exchanger 222, an evaporator 224 which is an evaporation unit disposed above the combustion catalyst 249, and a combustion catalyst 249. And a heater 250 disposed between the evaporator 224 and heating the same. Moreover, the heat insulating material 207 is arrange | positioned so that the above structure may be surrounded, and heat dissipation in module case 208 is suppressed. Furthermore, a thermal insulator is disposed between the module case 208 and the air heat exchanger 222 and between the combustion catalyst 249 and the air heat exchanger 222 to suppress the transfer of heat therebetween.

  In this modification, the fuel left unused for power generation is burned at the upper end of each fuel cell 216 to heat the reformer 220 disposed above. Further, the high temperature exhaust gas discharged from the module case 208 flows into the air heat exchanger 222 disposed outside the module case 208, and heats the supplied power generation air. The exhaust gas that has heated the power generation air flows into the combustion catalyst 249 to heat the combustion catalyst. Furthermore, the exhaust gas which has heated the combustion catalyst flows into the evaporator 224 and heats the supplied water to generate steam.

  The generated steam is mixed with the raw fuel gas and flows into the reformer 220. The raw fuel gas is steam-reformed in the reformer 220 and flows into the manifold 266. The fuel gas flowing into the manifold 266 flows into the fuel electrode inside each fuel cell 216, and flows upward in each fuel cell 216. On the other hand, the power generation air heated by the air heat exchanger 222 flows downward through an air passage (not shown) provided on the outside of the module case 208 and provided at the lower side wall surface of the module case 208. It is injected from a plurality of outlets. The power generation air injected from the outlet flows into the air electrode side (outside of each fuel cell 216) in the module case 208, and a power generation reaction occurs with the fuel in each fuel cell 216. The fuel left unused for power generation is burned at the top end of each fuel cell 216.

  Further, the heater 250 is energized in the startup process of the solid oxide fuel cell system, and heats the evaporator 224 and the combustion catalyst 249 in the low temperature state at the initial startup. As a result, since the temperatures of the evaporator 224 and the combustion catalyst 249 can be raised from the initial stage of startup, water vapor can be generated early in the evaporator 224, and the exhaust gas can be purified early by the combustion catalyst. Becomes possible. Furthermore, the heater 250 is also energized in the shutdown step of the solid oxide fuel cell system, and after the power generation is stopped, heats the evaporator 224 and the combustion catalyst 249 whose temperature has dropped. Thus, even after time elapses from the power generation stop, the steam can be generated in the evaporator 224 and the exhaust can be purified by the combustion catalyst 249. In addition, when the temperatures of the evaporator 224 and the combustion catalyst 249 rise sufficiently during the start-up process or power generation operation, the energization of the heater 250 is stopped, and the evaporator 224 and the combustion catalyst 249 It is heated. The start-up of the solid oxide fuel cell system according to the present modification is the same as that of the embodiment of the present invention described above except for the points described above.

On the other hand, the process after stopping power generation in this modification is the same as the embodiment of the present invention described above, and the heater 250 is energized in step S7 of FIG. 8a to reliably evaporate the water in the evaporator 224. I am trying to
Further, in the embodiment described above, although one fuel cell having one set of fuel electrode and air electrode was used as the fuel battery cell 16, as a modification, one fuel cell and one fuel cell are used. The present invention is applied to a fuel cell system using an arbitrary fuel cell such as a cylindrical horizontal stripe type fuel cell in which a plurality of air electrodes are formed and a single cell formed by each pair of electrodes is connected in series. can do.

DESCRIPTION OF SYMBOLS 1 solid oxide fuel cell system 2 fuel cell module 4 accessory unit 7 heat insulating material 8 case 8 a communication opening 8 b lower wall 10 power generating chamber 12 fuel cell assembly 14 fuel cell stack 16 fuel cell 18 combustion chamber (combustion chamber (combustion chamber) Department)
20 reformer 20a evaporation section (evaporation chamber)
20b mixing section (pressure fluctuation absorption means)
20c reforming unit 21 baffle plate (partition wall)
21a opening 21b exhaust passage 21c gas residence space 21d vertical wall 22 heat exchanger for air (heat exchanger)
23 Heat insulation for evaporation chamber (internal heat insulation)
24 Water supply source 26 Pure water tank 28 Water flow rate adjustment unit (water supply device)
30 Fuel supply source 38 Fuel flow adjustment unit (fuel supply device)
39 valve 40 air supply source 44 air flow rate adjusting unit for ignition 45 air flow rate adjusting unit for power generation (oxidizer gas supply device)
46 1st heater 48 2nd heater 49 combustion catalyst 49a catalytic heater 50 hot water production system (heat exchanger for exhaust heat recovery)
52 control box 54 inverter 62 reformer introduction pipe (water introduction pipe, preheating part, condensation part)
62a T-tube (condensed area)
63a water supply piping 63b fuel gas supply piping 64 fuel gas supply piping 64c flow resistance for pressure fluctuation control portion 66 manifold (dispersion chamber)
76 Air introduction pipe 76a Air outlet 81 Heating heater 82 Exhaust gas exhaust pipe 83 Ignition device 84 Fuel cell 85 Exhaust valve 86 Inner electrode terminal (cap)
90d 1st fuel electrode (fuel electrode layer)
90e 2nd fuel electrode (fuel electrode layer)
92a air electrode (oxidant gas electrode layer)
94 Solid Electrolyte Layer 98 Fuel gas flow channel capillary (throttle portion)
110 control unit (controller)
110a Cell protection circuit 110b Purge control circuit 112 Operation device 114 Display device 116 Alarm device 126 Power state detection sensor 132 Fuel flow rate sensor (fuel supply amount detection sensor)
138 Pressure sensor (reformer pressure sensor)
142 Generation chamber temperature sensor (temperature detection means)
148 Reformer temperature sensor 150 Outside air temperature sensor 200 Fuel cell module 207 according to a modification of the present invention Heat insulator 208 Module case 216 Fuel cell 220 Reformer (reforming section)
222 Heat exchanger for air (heat exchanger)
224 Evaporator (Evaporation Unit)
249 combustion catalyst 250 heating heater 266 manifold

Claims (5)

A solid oxide fuel cell system that generates electricity by reacting hydrogen obtained by steam reforming a raw fuel gas and an oxidant gas,
In order from the inner side, and nickel as a main component fuel electrode layer, solid-solid electrolyte layer, the oxidant gas electrode layer is provided tubular fuel cells,
A reforming unit that generates hydrogen from a raw fuel gas by steam reforming and supplies the generated hydrogen from the lower end to the fuel electrode side of the fuel cell;
A fuel supply device for supplying raw fuel gas to the reforming section;
A water supply device for supplying water for steam reforming;
An evaporation unit that generates steam from the water supplied from the water supply device and supplies the steam to the reforming unit;
An oxidant gas supply device for supplying oxidant gas to the oxidant gas electrode side of the fuel cell;
A fuel cell module containing the fuel cell;
A controller that controls the fuel supply device, the water supply device, and the oxidant gas supply device, and controls extraction of power from the fuel cell module;
The controller has a cell protection circuit that performs cell protection control to protect the fuel cell after stopping extraction of power from the fuel cell module.
The cell protection circuit continues the operation of the fuel supply device and the water supply device so that a smaller amount of raw fuel gas and water are supplied even after power generation from the fuel cell module is stopped. Are programmed to execute the cell protection control for supplying gas to the fuel electrode side of the fuel cell via the reforming unit.
The controller continues the operation of the oxidant gas supply device even after stopping the extraction of electric power to lower the temperature in the fuel cell module, and at least to the fuel electrode side of the fuel cell after stopping the extraction of electric power. of without the supply of oxidant gas, running the cell protection control until the temperature of the fuel cell drops to a temperature range of 200 ° C. to 100 ° C.,
The cell protection circuit continues the operation of the fuel supply device for a predetermined time even after stopping the operation of the water supply device during the cell protection control, and the water vapor remaining on the fuel electrode side of the fuel cell And the operation of the oxidant gas supply device is continued for a predetermined period of time, and the source that has flowed out from the fuel electrode side of the fuel cell to the oxidant gas electrode side A solid oxide fuel cell system characterized in that a fuel gas is purged to the outside of the fuel cell module, thereby suppressing the occurrence of a local cell phenomenon to protect the fuel cell.   The controller further includes a purge control circuit that supplies the raw fuel gas to the fuel cell and purges the residual gas on the fuel electrode side after the end of the cell protection control, the controller including the fuel cell 2. The solid oxide fuel cell system according to claim 1, wherein the cell protection control is terminated until the temperature of the fuel cell falls to a temperature zone of 200.degree. C. to 130.degree.   3. The solid oxide according to claim 2, wherein the controller ends the cell protection control until the temperature of the fuel cell falls to a temperature zone of 150 ° C. to 130 ° C., and then purges the residual gas on the fuel electrode side. Fuel cell system.   The solid oxide fuel cell system according to any one of claims 1 to 3, wherein the cell protection circuit keeps the supply amount of raw fuel gas and the supply amount of water constant at all times during the execution of the cell protection control.   Furthermore, it has a heater for heating the evaporation section, and the controller operates the heater to promote the generation of water vapor when the temperature of the fuel cell falls to 350 ° C. or lower. Solid oxide fuel cell system as described.

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