JP2014186923A - Solid oxide type fuel battery system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid oxide type fuel battery system which is arranged so that the fuel electrode oxidation and the air electrode reduction of a fuel battery cell can be avoided by shutdown stop.SOLUTION: A solid oxide type fuel battery system 1 comprises: a fuel battery module 2; a fuel-supply device 38; a water-supply device 28; an air-supply device 45; a reformer 20; a temperature detection sensor for detecting a temperature of a fuel battery cell stack; a shutdown-stop circuit; and a before-stop processing circuit. The shutdown-stop circuit executes a shutdown stop for stopping fuel supply and power generation when being put in the condition of an oxidation-suppressing temperature or higher. The before-stop processing circuit executes a before-stop process for lowering the temperature of the fuel battery cell stack. The before-stop processing circuit executes different before-stop processes according to the temperature of the fuel battery cell stack before the shutdown stop.

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 generated by steam reforming of fuel with an oxidant gas.

  A solid oxide fuel cell (hereinafter also referred to as “SOFC”) uses an oxide ion conductive solid electrolyte as an electrolyte, attaches electrodes on both sides thereof, and supplies fuel gas on one side, The fuel cell operates at a relatively high temperature by supplying an oxidant (air, oxygen, etc.) to the other side.

  Japanese Unexamined Patent Publication No. 2012-3850 (Patent Document 1) describes a solid oxide fuel cell. In this fuel cell, when stopping a fuel cell operating at a high temperature, supplying a small amount of fuel and water for fuel reforming while supplying air to the air electrode side of the fuel cell stack, Due to the cooling effect of the air, the temperature in the fuel cell module is lowered. That is, in this fuel cell, first, in the stopping step, the fuel cell stack is formed by sending a large amount of cooling air while continuing to supply fuel even after the extraction of power from the fuel cell module is stopped. Cool down. Next, supply of fuel is stopped when the temperature of the cell stack drops below the oxidation temperature of the fuel cell. After that, only the cooling air is supplied until the temperature drops sufficiently, and the fuel cell is safely stopped. I am letting.

Further, in the stop process, the so-called shutdown stop is performed in which the extraction of electric power and the supply of fuel, water for fuel reforming, and power generation air (air sent to the air electrode side) are completely stopped in a short time. Fuel cells are also known.
Japanese Unexamined Patent Publication No. 2010-27579 (Patent Document 2) describes a fuel cell system. In this fuel cell system, at the time of an emergency stop, a delivery pump that supplies fuel to the reformer, a reforming water pump that supplies water for steam reforming, and an air blower that sends air to the air electrode side of the cell stack Stop. After that, when the delivery pump and the reforming water pump are operated again by the emergency stop operation control, the fuel gas adsorbed in the adsorber is in a state where the supply of the fuel gas from the fuel supply source is shut off. Is sent to the reformer, and steam reforming is performed by the water supplied from the reforming water pump. Thereby, even after the supply of the fuel gas is interrupted, the reformed fuel is supplied to the fuel electrode of the cell stack for a predetermined period, and the oxidation of the fuel electrode due to the backflow of air is prevented.

  Furthermore, JP 2012-138186 A (Patent Document 3) describes a high-temperature operating fuel cell system. In this high temperature operation type fuel cell system, at the time of emergency stop, the raw fuel pump that supplies fuel gas is stopped, while the reforming water pump that supplies water to the reformer is operated. When the reforming water pump is operated, the supplied water expands in volume by being evaporated in the reformer. For this reason, even when the supply of the source fuel gas from the fuel supply source is shut off, the fuel gas remaining in the fuel gas supply line downstream of the reformer is expanded by the pressure of the volume-expanded water vapor. Is pushed out to the fuel cell (cell stack) side. Thereby, the oxidation of the fuel electrode due to the backflow of air is prevented.

JP 2012-3850 A JP 2010-27579 A JP 2012-138186 A

  In the fuel cell described in Japanese Patent Application Laid-Open No. 2012-3850 (Patent Document 1), fuel is supplied until the fuel cell stack is lowered to a predetermined temperature even during the stop process, so that fuel that does not contribute to power generation is wasted. There is a problem of being. In addition, when the supply of fuel is stopped before the temperature of the cell stack sufficiently decreases and cooling air is supplied, the cooling air supplied to the air electrode side of the fuel battery cell flows backward to the fuel electrode side, The backflowed air oxidizes the fuel electrode of the fuel cell and damages the cell. For this reason, it is necessary to continue supplying the fuel until the temperature of the fuel cell falls below the oxidation temperature, and to prevent the backflow of the cooling air supplied to the air electrode side of the fuel cell. The time until the temperature of the fuel cell stack that has been operating falls below the oxidation temperature in the stop process depends on the heat insulation performance of the fuel cell module, etc. It is necessary to continue supplying fuel that does not contribute to power generation over time.

  On the other hand, in the shutdown stop, the supply of fuel and water for fuel reforming is completely stopped in a short time, so that waste of fuel can be suppressed. Further, in the shutdown stop, the fuel cell stack is stopped in a high temperature state, so that the fuel supply is stopped, so that the supply of cooling air to be sent to the air electrode side of the fuel cell stack is stopped together with the fuel supply stop, Backflow of air to the fuel electrode side and oxidation of the fuel electrode are avoided.

  However, when the shutdown is stopped, the present inventor oxidizes the fuel electrode of the fuel cell and deteriorates the cell even if the air sent to the air electrode side of the fuel cell stack is stopped when the fuel supply is stopped. And found a new technical problem that leads to cell damage.

  On the other hand, in the fuel cell system described in Japanese Patent Application Laid-Open No. 2010-27579 (Patent Document 2), even after the supply from the fuel supply source is cut off, the delivery pump is operated to be adsorbed by the adsorber for a certain period. The spent fuel gas can be sent to the cell stack to prevent oxidation of the fuel electrode. However, in this fuel cell system, it is necessary to provide a special adsorber in order to store the fuel in advance. Further, in this fuel cell system, the fuel gas adsorbed by the delivery pump is sent out even after the supply from the fuel supply source is cut off. Extruded from the pole side to the air electrode side. However, since the air supplied to the air electrode side is stopped, there is a problem that the fuel pushed out to the air electrode side may partially reduce the air electrode and damage the air electrode.

  Furthermore, in the high temperature operation type fuel cell system described in Japanese Patent Application Laid-Open No. 2012-138186 (Patent Document 3), the reforming water pump is operated immediately after the raw fuel pump is stopped, Residual fuel is pushed out to the cell stack side by volume expansion of the evaporated water. Therefore, also in this high temperature operation type fuel cell system, the fuel pushed out to the air electrode side may partially reduce the air electrode and damage the air electrode, as in the fuel cell system described in Patent Document 2. There is a problem.

  Therefore, the present invention sufficiently suppresses the oxidation of the fuel electrode of the fuel cell while performing the shutdown stop, and can also avoid the reduction of the oxidant gas electrode (air electrode). The purpose is to provide a system.

  In order to solve the above-described problems, the present invention provides a solid oxide fuel cell system that generates power by reacting hydrogen generated by steam reforming a fuel and an oxidant gas, and comprising a fuel cell stack. A fuel cell module, a fuel supply device for supplying fuel to the fuel cell module, a water supply device for supplying water for steam reforming to the fuel cell module, and an oxidant gas electrode side of the fuel cell stack An oxidant gas supply device that supplies oxidant gas and a fuel cell module that is disposed in the fuel cell module and reforms the fuel supplied from the fuel supply device with water vapor using the water supplied from the water supply device. A reformer that supplies the fuel to the fuel electrode side of the fuel cell stack, a temperature detection sensor that detects the temperature of the fuel cell stack, a fuel supply device, a water supply device, and an oxidizer gas And a controller programmed to control the extraction of power from the fuel cell module, the controller comprising a shutdown stop circuit and a stop pre-processing circuit, the shutdown stop circuit being a fuel In a state where the battery cell stack is at or above the oxidation suppression temperature, a shutdown stop is performed to stop fuel supply and power generation, and the pre-stop processing circuit is configured to execute a pre-stop process that reduces the temperature of the fuel cell stack. The pre-stop processing circuit is characterized by executing pre-stop processing that varies depending on the temperature of the fuel cell stack before the shutdown stop.

  In the present invention configured as described above, fuel and water are respectively supplied to the reformer disposed in the fuel cell module by the fuel supply device and the water supply device, and the reformer converts the fuel into steam reforming. To do. The reformed fuel is supplied to the fuel electrode side of the fuel cell stack. On the other hand, the oxidant gas is supplied to the oxidant gas electrode side of the fuel cell stack by the oxidant gas supply device. The temperature detection sensor detects the temperature of the fuel cell stack. The controller is programmed to control power extraction from the fuel supply device, water supply device, oxidant gas supply device, and fuel cell module. The controller includes a shutdown stop circuit and a stop pre-processing circuit. The shutdown stop circuit executes shutdown stop for stopping fuel supply and power generation when the fuel cell stack is at the oxidation suppression temperature or higher. The pre-stop processing circuit is configured to perform pre-stop processing that lowers the temperature of the fuel cell stack, and the pre-stop processing circuit performs different pre-stop processing depending on the temperature of the fuel cell stack before shutdown. To run.

  In a conventional solid oxide fuel cell system, when shutting down, supply of fuel, supply of water for fuel reforming, extraction of electric power from the fuel cell module, and supply of oxidant gas are all performed. Stop at the same time. In the conventional technology, the supply of the oxidant gas is stopped simultaneously with the stop of the fuel and power extraction, the fuel cell stack temperature is immediately higher than the oxidation temperature immediately after the power extraction stop, and the fuel is stopped. This is because when only the oxidant gas is supplied, the oxidant gas flows backward to the fuel electrode side of the fuel cell unit, and the fuel electrode may be damaged.

  However, the present inventors have found a new problem that the oxidant gas may oxidize the fuel electrode even when the supply of the oxidant gas is stopped simultaneously. This problem is caused by the occurrence of a temperature difference between the fuel electrode side and the oxidant gas electrode side of each fuel cell unit after stopping power extraction. First, on the oxidant gas electrode side of each fuel cell unit, since the supply of the oxidant gas for power generation is stopped, the cooling effect by the oxidant gas is lost and the temperature tends to rise. On the other hand, since the extraction of electric power is stopped on the fuel electrode side of each fuel cell unit, no heat is generated. The fuel remaining in the reformer and the like flows into the fuel electrode side of each fuel cell unit even after the fuel supply by the fuel supply means is stopped. The fuel flowing into the fuel electrode side is generated by a steam reforming reaction that is an endothermic reaction in the reformer, and is generally lower than the temperature on the oxidant gas electrode side of the fuel cell unit. . As described above, the oxidant gas electrode side of each fuel cell unit tends to increase in temperature after stopping the fuel supply and power extraction, whereas the fuel electrode side loses power generation heat or has a low temperature. The temperature tends to decrease due to the inflow of the remaining fuel. In the portion where the temperature has decreased, the surrounding gas contracts and the pressure decreases, and in the portion where the temperature has increased, the surrounding gas expands and the pressure increases. Due to these phenomena, the pressure on the oxidant gas electrode side of each fuel cell unit becomes high and the pressure on the fuel electrode side becomes low, and this pressure difference causes the oxidant gas to flow from the oxidant gas electrode side to the fuel electrode side. It may flow backward.

  The present inventor has solved this new technical problem by executing a pre-stop process for reducing the temperature of the fuel cell stack immediately before the shutdown stop. When the solid oxide fuel cell system is in a high-output power generation operation, the inside of the fuel cell module is generally at a high temperature. The present inventor has found that when the shutdown stop is executed in such a state, a reverse flow of the oxidant gas from the oxidant gas electrode side to the fuel electrode side is likely to occur due to the above phenomenon. In the present invention, since the temperature of the fuel cell side of the fuel cell stack approaches the temperature of the oxidant gas electrode side by executing the pre-stop process, the fuel gas staying on the fuel electrode side contracts due to the temperature drop. Thus, the phenomenon that the oxidant gas is drawn from the oxidant gas electrode side to the fuel electrode side can be prevented, and the oxidation of the fuel electrode can be suppressed.

  Furthermore, when the solid oxide fuel cell system is operating at a high output, particularly during the period when the pressure on the fuel electrode side is high after shutdown, a large amount of fuel is transferred from the fuel electrode side to the oxidant gas electrode side. Spill to As a result, there is a possibility that the fuel flowing out to the oxidant gas electrode side contacts the oxidant gas electrode and the oxidant gas electrode is partially reduced and damaged. In the present invention, the pre-stop process is performed before the shutdown stop, so that the amount of fuel flowing out to the oxidant gas electrode side after the shutdown stop can be suppressed, and the reduction of the oxidant gas electrode can be suppressed. it can. In addition, since the pre-stop processing circuit executes pre-stop processing different depending on the temperature of the fuel cell stack before shutting down, the shutdown stop is executed at an appropriate temperature, and the fuel electrode side and the oxidizer after the shutdown is stopped. The risk of the oxidation of the fuel electrode or the reduction of the oxidant gas electrode can be suppressed from the collapse of the temperature balance on the gas electrode side.

  In the present invention, it is preferable that the pre-stop processing circuit lowers the amount of fuel supplied by the fuel supply device and the amount of electric power taken out from the fuel cell module during the pre-stop processing than during the power generation operation.

  According to the present invention configured as described above, the fuel supply amount and the amount of electric power taken out are reduced during the pre-stop process, so that the temperature of the fuel cell stack can be reduced and the shutdown is stopped. Thus, the amount of fuel remaining on the fuel electrode side of the fuel cell stack can be reduced, and the reduction of the oxidant gas electrode can be more reliably suppressed.

  In the present invention, preferably, the pre-stop processing circuit increases the amount of oxidant gas supplied by the oxidant gas supply device during the pre-stop processing more than the amount corresponding to the electric power extracted from the fuel cell module. Reduce the temperature of the fuel cell stack.

  According to the present invention configured as described above, since the supply amount of the oxidant gas is increased during the pre-stop process, the temperature of the fuel cell stack can be lowered and the fuel supply is continued. By increasing the supply amount of the oxidant gas during the pretreatment, the temperature of the fuel cell stack can be effectively lowered while avoiding the risk of oxidant gas backflow.

In the present invention, the pre-stop processing circuit preferably increases the amount of temperature decrease due to the pre-stop processing when the temperature of the fuel cell stack is high than when the temperature is low.
According to the present invention configured as described above, when the temperature is high, the amount of temperature decrease due to the stop pretreatment increases, so that the shutdown stop can be performed in a state where the temperature is lowered to an appropriate temperature. And the risk of oxidant gas electrode reduction can be suppressed.

In the present invention, preferably, the pre-stop processing circuit does not execute the pre-stop processing when the temperature detected by the temperature detection sensor is lower than a predetermined shutdown temperature.
If the temperature of the fuel cell stack at shutdown shutdown is too high, as described above, the risk of fuel electrode oxidation and the risk of oxidant gas electrode reduction increases, but also when the temperature at shutdown shutdown is too low. The risk of anode oxidation increases. This is because when the temperature at the time of shutdown stop is too low, the amount of fuel remaining on the fuel electrode side decreases, and the temperature balance between the fuel electrode side and the oxidant gas electrode side of the fuel cell stack is lost. This is because the pressure on the fuel electrode side cannot be kept high until the temperature of the fuel electrode falls below the oxidation suppression temperature. According to the present invention configured as described above, the pre-stop process is not executed when the temperature is lower than the shutdown temperature, so that the risk of fuel electrode oxidation due to the shutdown stop being performed at an excessively low temperature is suppressed. Can do.

  In the present invention, preferably, the stop pre-processing circuit performs pre-stop processing when the temperature detected by the temperature detection sensor is higher than the shutdown temperature, and the pre-stop processing is continued until the detected temperature decreases to the shutdown temperature. Thereafter, shutdown stop is executed.

  According to the present invention configured as described above, since the pre-stop process is continued until the shutdown temperature is lowered to the shutdown temperature, the shutdown stop can be executed at an appropriate temperature, and an excessively high temperature at the shutdown stop or an excessive By avoiding the low temperature, the risk of fuel electrode oxidation and the risk of oxidant gas electrode reduction can be reliably suppressed.

  In the present invention, preferably, the controller controls the fuel supply device so that the temperature of the fuel cell stack is within a predetermined power generation temperature range during the power generation operation for extracting power from the fuel cell module. It is executed when the temperature detected by the temperature detection sensor is higher than the upper limit temperature of the power generation temperature range.

  According to the present invention configured as described above, during the power generation operation, the temperature of the fuel cell stack is controlled with the power generation temperature range as a target, so that the shutdown stop can be executed at an appropriate temperature. Further, when the temperature of the fuel cell stack is higher than the upper limit temperature of the power generation temperature range, the pre-stop process is executed, so that the shutdown stop can be executed in a state where the temperature is lowered to an appropriate temperature.

  In the present invention, preferably, the controller performs exhaust control for exhausting the gas remaining on the oxidant gas electrode side in the fuel cell module by operating the oxidant gas supply device after shutdown is stopped. When a control circuit is included and the detected temperature is higher than the upper limit temperature of the power generation temperature range, after the stop pre-processing circuit executes the pre-stop processing, exhaust control is executed and the detected temperature is within the power generation temperature range In such a case, the exhaust control is executed without executing the pre-stop process, and the pre-stop process and the exhaust control are not executed when the detected temperature is lower than the lower limit temperature of the power generation temperature range.

  According to the present invention configured as described above, when the temperature is higher than the upper limit temperature of the power generation temperature range, and within the power generation temperature range, the exhaust control is executed after the shutdown stop. The fuel remaining in the fuel cell module can be discharged out of the fuel cell module, and reduction of the oxidant gas electrode can be reliably prevented. Further, since exhaust control is not executed when the temperature is lower than the lower limit temperature of the power generation temperature range, the risk of fuel electrode oxidation due to excessive decrease in the temperature of the fuel cell stack can be suppressed.

  According to the solid oxide fuel cell system of the present invention, the shutdown of the fuel electrode of the fuel cell is sufficiently suppressed while the shutdown is stopped, and the reduction of the oxidant gas electrode (air electrode) is also avoided. Can do.

1 is an overall configuration diagram showing a solid oxide fuel cell system according to an embodiment of the present invention. 1 is a front sectional view showing a fuel cell module of a solid oxide fuel cell system according to an embodiment of the present invention. FIG. 3 is a cross-sectional view taken along line III-III in FIG. 2. It is a fragmentary sectional view showing a fuel cell unit of a solid oxide fuel cell system by one embodiment of the present invention. 1 is a perspective view showing a fuel cell stack of a solid oxide fuel cell system according to an embodiment of the present invention. 1 is a block diagram illustrating a solid oxide fuel cell system according to an embodiment of the present invention. 1 is a perspective view of a reformer of a solid oxide fuel cell system according to an embodiment of the present invention. 1 is a perspective view showing an interior of a reformer by removing a top plate of the reformer of a solid oxide fuel cell system according to an embodiment of the present invention. 1 is a cross-sectional plan view showing a fuel flow inside a reformer of a solid oxide fuel cell system according to an embodiment of the present invention. 1 is a perspective view showing a metal case and an air heat exchanger housed in a housing of a solid oxide fuel cell system according to an embodiment of the present invention. It is sectional drawing which shows the positional relationship of the heat insulating material for heat exchangers of the solid oxide fuel cell system by one Embodiment of this invention, and an evaporation part. It is a time chart which shows an example of each supply_amount | feed_rate of fuel etc. in the starting process of the solid oxide fuel cell system by one Embodiment of this invention, and the temperature of each part. 5 is a flowchart of stop determination for selecting a stop mode in a solid oxide fuel cell system according to an embodiment of the present invention. 4 is a time chart schematically showing an example of stop behavior when stop mode 1 is executed in a solid oxide fuel cell system according to an embodiment of the present invention. In the solid oxide fuel cell system according to the embodiment of the present invention, the control when the stop mode 1 is executed, the temperature and pressure in the fuel cell module, and the state of the tip of the fuel cell unit in time series. It is a figure for demonstrating. 4 is a time chart schematically showing an example of stop behavior when stop mode 2 is executed in a solid oxide fuel cell system according to an embodiment of the present invention. In the solid oxide fuel cell system according to the embodiment of the present invention, the control when the stop mode 2 is executed, the temperature and pressure in the fuel cell module, and the state of the tip of the fuel cell unit in time series. It is a figure for demonstrating. 4 is a time chart schematically showing an example of stop behavior when stop mode 3 is executed in a solid oxide fuel cell system according to an embodiment of the present invention. 6 is an enlarged time chart showing immediately after shutdown stop in stop mode 3 of a solid oxide fuel cell system according to an embodiment of the present invention. In the solid oxide fuel cell system according to the embodiment of the present invention, the control when the stop mode 3 is executed, the temperature and pressure in the fuel cell module, and the state of the tip of the fuel cell unit in time series. It is a figure for demonstrating. It is a flowchart of the water supply in a stop pretreatment. 10 is a time chart showing a modified example of stop mode 3. 4 is a time chart schematically showing an example of stop behavior when stop mode 4 is executed in a solid oxide fuel cell system according to an embodiment of the present invention. In the solid oxide fuel cell system according to the embodiment of the present invention, the control when the stop mode 4 is executed, the temperature and pressure in the fuel cell module, and the state of the tip of the fuel cell unit in time series. It is a figure for demonstrating. 4 is a flowchart for controlling execution of stop pretreatment and exhaust control in a solid oxide fuel cell system according to an embodiment of the present invention. It is a figure which shows the correction coefficient of the air supply amount for electric power generation in exhaust control in the solid oxide fuel cell system by one Embodiment of this invention. 5 is an execution condition table of stop pretreatment and exhaust control in each stop mode and temperature band in the solid oxide fuel cell system according to the embodiment of the present invention. 7 is a flowchart of stop determination for selecting a stop mode in a modification of the solid oxide fuel cell system according to the embodiment of the present invention. It is the time chart which represented an example of the stop behavior of the conventional solid oxide fuel cell system typically in time series.

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

  The fuel cell module 2 includes a housing 6, and a metal case 8 is built in the housing 6 via a heat insulating material 7. A fuel cell assembly 12 that performs a power generation reaction with fuel and oxidant gas (air) is disposed in a power generation chamber 10 that is a lower portion of the case 8 that is a sealed space. The fuel cell assembly 12 includes ten fuel cell stacks 14 (see FIG. 5), and the fuel cell stack 14 includes 16 fuel cell unit 16 (see FIG. 4). Yes. Thus, the fuel cell assembly 12 has 160 fuel cell units 16, and all of these fuel cell units 16 are connected in series.

A combustion chamber 18 that is a combustion section is formed above the above-described power generation chamber 10 of the case 8 of the fuel cell module 2. In this combustion chamber 18, the remaining fuel and the remaining oxidant that have not been used for the power generation reaction. (Air) is combusted to generate exhaust gas. Further, the case 8 is covered with a heat insulating material 7 to suppress the heat inside the fuel cell module 2 from being diffused to the outside air.
Further, a reformer 20 for reforming the fuel is disposed above the combustion chamber 18, and the reformer 20 is heated to a temperature at which a reforming reaction can be performed by the combustion heat of the residual gas. Yes. Further, an air heat exchanger 22, which is a heat exchanger for heating the power generation air with the remaining combustion gas and preheating the power generation air, is disposed above the reformer 20.

  Next, the auxiliary unit 4 stores pure water tank 26 that stores water condensed from moisture contained in the exhaust from the fuel cell module 2 and makes it pure water with a filter, and water supplied from the water storage tank. Is provided with a water flow rate adjusting unit 28 (such as a “water pump” driven by a motor). In addition, the auxiliary unit 4 adjusts the flow rate of the fuel gas, the gas shutoff valve 32 for shutting off the fuel supplied from the fuel supply source 30 such as city gas, the desulfurizer 36 for removing sulfur from the fuel gas, A fuel flow adjustment unit 38 (such as a “fuel pump” driven by a motor) and a valve 39 that shuts off fuel gas flowing out from the fuel flow adjustment unit 38 when power is lost. Further, the auxiliary unit 4 includes an electromagnetic valve 42 that shuts off air that is an oxidant gas supplied from an air supply source 40, a reforming air flow rate adjusting unit 44 that adjusts the flow rate of air, and a power generation air flow rate adjustment. A unit 45 (such as an “air blower” driven by a motor), a first heater 46 for heating the reforming air supplied to the reformer 20, and a first heater for heating the power generating air supplied to the power generation chamber 2 heaters 48. The first heater 46 and the second heater 48 are provided in order to efficiently raise the temperature at startup, but may be omitted.

Next, a hot water production apparatus 50 to which exhaust gas is supplied is connected to the fuel cell module 2. The hot water production apparatus 50 is supplied with tap water from the water supply source 24, and the tap water is heated by the heat of the exhaust gas and supplied to a hot water storage tank of an external hot water heater (not shown).
The fuel cell module 2 is provided with a control box 52 for controlling the amount of fuel gas supplied and the like.
Furthermore, the fuel cell module 2 is connected to an inverter 54 that 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 the fuel cell module of the solid oxide fuel cell system (SOFC) according to the embodiment of the present invention will be described with reference to FIGS. 2 is a side sectional view showing a fuel cell module of a solid oxide fuel cell system (SOFC) according to an embodiment of the present invention, and FIG. 3 is a sectional view taken along line III-III in FIG. is there.
As shown in FIGS. 2 and 3, the case 8 in the housing 6 of the fuel cell module 2 has a fuel cell assembly 12, a reformer 20, and an air heat exchanger in order from the bottom as described above. 22 is arranged.

The reformer 20 is provided with a reformer introduction pipe 62 for introducing pure water, 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 ° and extends in a substantially vertical direction, and penetrates the upper end surface of the case 8. The reformer introduction pipe 62 functions as a water introduction pipe for introducing water into the reformer 20. Further, a T-shaped tube 62a is connected to the upper end of the reformer introduction tube 62, and fuel gas and pure water are supplied to both ends of the T-shaped tube 62a extending in a substantially horizontal direction. Pipes for connecting are connected to each other. The water supply pipe 63a extends obliquely upward from one side end of the T-shaped pipe 62a. The fuel gas supply pipe 63b extends in the horizontal direction from the other side end of the T-shaped pipe 62a, then bends in a U shape, and extends substantially horizontally in the same direction as the water supply pipe 63a.

  On the other hand, an evaporation unit 20a, a mixing unit 20b, and a reforming unit 20c are formed in the reformer 20 sequentially from the upstream side, and the reforming unit 20c is filled with a reforming catalyst. The fuel gas and air mixed with the steam (pure water) introduced into the reformer 20 are reformed by the reforming catalyst filled in the reformer 20. As the reforming catalyst, a catalyst obtained by imparting nickel to the alumina sphere surface or a catalyst obtained by imparting ruthenium to the alumina sphere surface is appropriately used.

  A fuel gas supply pipe 64 is connected to the downstream end side of the reformer 20, and the fuel gas supply pipe 64 extends downward and further in an manifold 66 formed below the fuel cell assembly 12. It extends horizontally. A plurality of fuel supply holes 64 b are formed in 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, in the middle of the vertical portion of the fuel gas supply pipe 64, a pressure fluctuation suppressing flow path resistance portion 64c having a narrow flow path is provided, and the flow path resistance of the fuel gas supply flow path is adjusted. The adjustment of the channel 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 flows into the fuel cell unit 16. Supplied.

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

Next, the fuel cell unit 16 will be described with reference to FIG. FIG. 4 is a partial cross-sectional view showing a fuel cell unit of a solid oxide fuel cell system (SOFC) according to an embodiment of the present invention.
As shown in FIG. 4, the fuel cell unit 16 includes a fuel cell 84 and inner electrode terminals 86 that are caps respectively connected to both ends of the fuel cell 84.
The fuel cell 84 is a tubular structure extending in the vertical direction, and includes a cylindrical inner electrode layer 90 that forms a fuel gas flow path 88 therein, a cylindrical outer electrode layer 92, an inner electrode layer 90, and an outer side. An electrolyte layer 94 is provided between the electrode layer 92 and the electrode layer 92. The inner electrode layer 90 is a fuel electrode through which fuel gas passes and becomes a (−) electrode, while the outer electrode layer 92 is an air electrode in contact with air and becomes a (+) electrode.

  Since the inner electrode terminal 86 attached to the upper end side and the lower end side of the fuel cell 84 has the same structure, the inner electrode terminal 86 attached to the upper end side will be specifically described here. The upper portion 90 a of the inner electrode layer 90 includes an outer peripheral surface 90 b and an upper end surface 90 c exposed to the electrolyte layer 94 and the outer electrode layer 92. The inner electrode terminal 86 is connected to the outer peripheral surface 90b of the inner electrode layer 90 through a conductive sealing material 96, and is further in direct contact with the upper end surface 90c of the inner electrode layer 90, thereby Electrically connected. At the center of the inner electrode terminal 86, a fuel gas channel capillary 98 that communicates with the fuel gas channel 88 of the inner electrode layer 90 is formed.

  The fuel gas passage narrow tube 98 is an elongated thin tube 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 the fuel gas flowing from the manifold 66 (FIG. 2) into the fuel gas passage 88 through the fuel gas passage narrow tube 98 of the lower inner electrode terminal 86. . Accordingly, the fuel gas flow passage narrow tube 98 of the lower inner electrode terminal 86 acts as an inflow side flow passage resistance portion, and the flow passage resistance is set to a predetermined value. Further, a predetermined pressure loss also occurs in the flow of the fuel gas flowing out from the fuel gas flow path 88 to the combustion chamber 18 (FIG. 2) through the fuel gas flow path narrow tube 98 of the upper inner electrode terminal 86. Therefore, the fuel gas flow passage narrow tube 98 of the upper inner electrode terminal 86 acts as an outflow side flow passage resistance portion, and the flow passage resistance is set to a predetermined value.

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

  The electrolyte layer 94 includes, 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, lanthanum gallate doped with at least one selected from Sr and Mg, Formed from at least one of the following.

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

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 system (SOFC) according to an embodiment of the present invention.
As shown in FIG. 5, the fuel cell stack 14 includes 16 fuel cell units 16, and these fuel cell units 16 are arranged in two rows of 8 each. Each fuel cell unit 16 is supported at its lower end by a rectangular lower support plate 68 (FIG. 2) made of ceramic. It is supported by the upper support plate 100. The lower support plate 68 and the upper support plate 100 are formed with through holes 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 unit 16. The current collector 102 includes a fuel electrode connection portion 102a that is electrically connected to an inner electrode terminal 86 attached to the inner electrode layer 90 that is a fuel electrode, and an outer peripheral surface of the outer electrode layer 92 that is an air electrode. It is integrally formed so as to connect the air electrode connecting portion 102b that is electrically connected. In addition, a silver thin film is formed on the entire outer surface of the outer electrode layer 92 (air electrode) of each fuel cell unit 16 as an electrode on the air electrode side. When the air electrode connecting portion 102b contacts the surface of the thin film, the current collector 102 is electrically connected to the entire air electrode.

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

Next, sensors and the like attached to the solid oxide fuel cell system (SOFC) according to the present embodiment will be described with reference to FIG. FIG. 6 is a block diagram illustrating a solid oxide fuel cell system (SOFC) according to an embodiment of the present invention.
As shown in FIG. 6, the solid oxide fuel cell system 1 includes a control unit 110. The control unit 110 includes operation buttons such as “ON” and “OFF” for operation by the user. The operation device 112, a display device 114 for displaying various data such as a power generation output value (wattage), and a notification device 116 for issuing a warning (warning) in an abnormal state are connected. In addition, the control unit 110 incorporates a microprocessor, a memory, and a program (not shown) for operating these components, and thereby, based on input signals from the respective sensors, the auxiliary unit 4, The inverter 54 and the like are controlled. The notification device 116 may be connected to a remote management center and notify the management center of an abnormal state.

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 auxiliary unit 4.
The CO detection sensor 122 detects whether or not CO in the exhaust gas originally discharged to the outside through the exhaust gas passage 80 or the like leaks to an external housing (not shown) that covers the fuel cell module 2 and the auxiliary unit 4. Is to do.
The hot water storage state detection sensor 124 is for detecting the temperature and amount of hot water in a water heater (not shown).

The power state detection sensor 126 is for detecting the output current and voltage of the fuel cell module 2.
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 sensor 130 is for detecting the flow rate of the reforming air supplied to the reformer 20.
The fuel flow 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 on the upstream side outside the reformer 20.
The exhaust temperature sensor 140 is for detecting the temperature of the exhaust gas flowing into the hot water production apparatus 50.

As shown in FIG. 3, the power generation chamber temperature sensor 142 is provided on the front side and the back side in the vicinity of the fuel cell assembly 12, and detects the temperature in the vicinity of the fuel cell stack 14 to thereby detect the fuel cell stack. 14 (ie, the fuel cell 84 itself) is estimated.
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 in 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 the outside air when the solid oxide fuel cell system (SOFC) is disposed outdoors. Further, a sensor for measuring the humidity or the like of the outside air may be provided.

  Signals from these sensors are sent to the control unit 110, and the control unit 110, based on data based on these signals, the water flow rate adjustment unit 28, the fuel flow rate adjustment unit 38, the reforming air flow rate adjustment unit 44, A control signal is sent to the power generation air flow rate adjusting unit 45 to control each flow rate in these units.

Next, the detailed configuration of the reformer 20 will be described with reference to FIGS.
FIG. 7 is a perspective view of the reformer 20, and FIG. 8 is a perspective view showing the inside of the reformer 20 with the top plate removed. FIG. 9 is a plan sectional view showing the flow of fuel inside the reformer 20.

  As shown in FIG. 7, the reformer 20 is a rectangular parallelepiped metal box, and is filled with a reforming catalyst for reforming fuel. A reformer introduction pipe 62 for introducing water, fuel, and reforming air is connected to the upstream side of the reformer 20. Further, a fuel gas supply pipe 64 for discharging the internally reformed fuel is connected to the downstream side of the reformer 20.

  As shown in FIG. 8, inside the reformer 20, an evaporation unit 20a that is an evaporation chamber is provided on the upstream side, and a mixing unit 20b is provided on the downstream side adjacent to the evaporation unit 20a. ing. Further, a reforming section 20c is provided on the downstream side adjacent to the mixing section 20b. Inside the evaporation part 20a, a plurality of partition plates are arranged to form a meandering and meandering passage. The water introduced into the reformer 20 is evaporated in the evaporation unit 20a in a state where the temperature is increased, and becomes water vapor. Furthermore, the mixing part 20b is comprised from the chamber which has a predetermined | prescribed volume, and the path | route which meanders meanderingly by the several partition plate being arrange | positioned also in the inside is formed. The fuel gas and the reforming air introduced into the reformer 20 are mixed with the water vapor generated in the evaporation unit 20a while passing through the winding path of the mixing unit 20b.

On the other hand, a meandering passage is formed in the reforming section 20c by arranging a plurality of partition plates, and the passage is filled with a catalyst. When a mixture of fuel gas, water vapor and reforming air is introduced through the evaporation unit 20a and the mixing unit 20b, a partial oxidation reforming reaction and a steam reforming reaction occur in the reforming unit 20c. Furthermore, when a mixture of fuel gas and steam is introduced, only the steam reforming reaction occurs in the reforming unit 20c.
In this embodiment, the evaporation unit, the mixing unit, and the reforming unit are integrally configured to form one reformer. However, as a modification, a reformer including only the reforming unit is used. It is also possible to provide a mixing section and an evaporation chamber adjacent to the upstream side.

As shown in FIGS. 8 and 9, the fuel gas, water, and reforming air introduced into the evaporator 20a of the reformer 20 meander in the transverse direction of the reformer 20, and are introduced during this period. The evaporated water evaporates to become water vapor. An evaporation / mixing unit partition 20d is provided between the evaporation unit 20a and the mixing unit 20b, and a partition opening 20e is provided in the evaporation / mixing unit partition 20d. This partition opening 20e is a rectangular opening provided in an upper half of the half of one side of the evaporation / mixing section partition 20d.
Further, a mixing / reforming section partition wall 20f is provided between the mixing section 20b and the reforming section 20c, and a narrow flow path is formed by providing a large number of communication holes 20g in the mixing / reforming section partition wall 20f. Has been. The fuel gas or the like mixed in the mixing unit 20b flows into the reforming unit 20c through these communication holes 20g.

  The fuel or the like that has flowed into the reforming unit 20c flows in the longitudinal direction in the center of the reforming unit 20c, and then splits into two to be folded back, and the two passages are folded back again toward the downstream end of the reforming unit 20c. Therefore, they are merged and flow into the fuel gas supply pipe 64. The fuel is reformed by the catalyst filled in the passage while passing through the meandering passage. In the evaporation unit 20a, bumping may occur in which a certain amount of water rapidly evaporates in a short time, and the internal pressure may increase. However, since the mixing unit 20b has a chamber with a predetermined volume and the mixing / reforming unit partition wall 20f has a narrow flow path, the reforming unit 20c has a sudden pressure fluctuation in the evaporation unit 20a. The influence of is difficult to reach. Therefore, the chamber of the mixing unit 20b and the narrow channel of the mixing / reforming unit partition 20f function as pressure fluctuation absorbing means.

  Next, referring to FIGS. 10 and 11 again, and referring again to FIGS. 2 and 3, the structure of the air heat exchanger 22 which is a heat exchanger for the power generation oxidant gas will be described in detail. FIG. 10 is a perspective view showing the metal case 8 and the air heat exchanger 22 housed in the housing 6. FIG. 11 is a cross-sectional view showing the positional relationship between the evaporation chamber heat insulating material and the evaporation section.

  As shown in FIG. 10, the air heat exchanger 22 is a heat exchanger disposed above the case 8 in the fuel cell module 2. Further, as shown in FIGS. 2 and 3, a combustion chamber 18 is formed inside the case 8, and a plurality of fuel cell units 16, a reformer 20 and the like are accommodated therein. 22 is located above these. The air heat exchanger 22 collects and uses the heat of the combustion gas that is combusted in the combustion chamber 18 and discharged as exhaust gas so as to preheat the power generation air introduced into the fuel cell module 2. It is configured. Further, as shown in FIG. 10, an evaporation chamber heat insulating material 23, which is an internal heat insulating material, is disposed between the upper surface of the case 8 and the bottom surface of the air heat exchanger 22 so as to be sandwiched between them. Has been. That is, the evaporation chamber heat insulating material 23 is disposed between the reformer 20 and the air heat exchanger 22. Furthermore, the outside of the air heat exchanger 22 and the case 8 shown in FIG. 10 is covered with a heat insulating material 7 as an outer heat insulating material (FIG. 2).

  As shown in FIGS. 2 and 3, the air heat exchanger 22 includes a plurality of combustion gas pipes 70 and a power generation air flow path 72. 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 each combustion gas pipe 70. ing. Further, an exhaust gas discharge pipe 82 is connected to the exhaust gas collecting chamber 78. Further, the other end of each combustion gas pipe 70 is open, and this open end communicates with the combustion chamber 18 in the case 8 via a communication opening 8 a formed on the upper surface of the case 8. Has been.

  The combustion gas pipe 70 is a plurality of metal circular pipes oriented in the horizontal direction, and the circular pipes are arranged in parallel. On the other hand, the power generation air flow path 72 is constituted by a space outside each combustion gas pipe 70. A power generation air introduction pipe 74 (FIG. 10) is connected to the end of the power generation air flow path 72 on the exhaust gas discharge pipe 82 side so that the air outside the fuel cell module 2 is used for power generation. The air is introduced into the power generation air flow path 72 through the air introduction pipe 74. As shown in FIG. 10, the power generation air introduction pipe 74 protrudes in the horizontal direction from the air heat exchanger 22 in parallel with the exhaust gas discharge pipe 82. Further, a pair of communication flow paths 76 (FIGS. 3 and 10) 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 connected. Are communicated with each other via an exit port 76a.

  As shown in FIG. 3, a power generation air supply passage 77 is provided on each side surface of the case 8. Each communication channel 76 provided on both side surfaces of the air heat exchanger 22 communicates with an upper portion of a power generation air supply channel 77 provided on both side surfaces of the case 8. In addition, a large number of air outlets 77 a are arranged in the horizontal direction at the lower portion of each power generation air supply passage 77. The power generation air supplied through each power generation air supply path 77 is injected toward the lower side surface of the fuel cell stack 14 in the fuel cell module 2 from a large number of air outlets 77a.

A rectifying plate 21 that is a partition wall is attached to the ceiling surface inside the case 8, and the rectifying plate 21 has an opening 21 a.
The rectifying plate 21 is a plate member disposed horizontally between the ceiling surface of the case 8 and the reformer 20. The rectifying plate 21 is configured to adjust the flow of the gas flowing upward from the combustion chamber 18 and to guide it to the inlet of the air heat exchanger 22 (communication opening 8a in FIG. 2). The power generation air and the combustion gas traveling upward from the combustion chamber 18 flow into the upper side of the rectifying plate 21 through the opening 21 a provided in the center of the rectifying plate 21, and the upper surface of the rectifying plate 21 and the ceiling surface of the case 8. 2 flows to the left in FIG. 2 and is led to the inlet of the heat exchanger 22 for air. Further, as shown in FIG. 11, the opening 21a is provided above the reforming unit 20c of the reformer 20, and the gas rising through the opening 21a is on the side opposite to the evaporation unit 20a. , Flows to the left exhaust passage 21b in FIGS. For this reason, the space above the evaporation unit 20a (the right side in FIGS. 2 and 11) acts as a gas retention space 21c in which the flow of exhaust gas is slower than the space above the reforming unit 20c and the flow of exhaust gas is stagnant.

  Further, a vertical wall 21d is provided at the edge of the opening 21a of the rectifying plate 21 over the entire circumference, and the vertical wall 21d allows the exhaust above the rectifying plate 21 from the space below the rectifying plate 21. The flow path flowing into the passage 21b is narrowed. Further, a falling wall 8b (FIG. 2) is provided over the entire circumference at the edge of the communication opening 8a that allows the exhaust passage 21b and the air heat exchanger 22 to communicate with each other. The flow path flowing into the air heat exchanger 22 is narrowed. By providing the vertical wall 21d and the falling wall 8b, the flow resistance in the exhaust passage from the combustion chamber 18 to the outside of the fuel cell module 2 through the air heat exchanger 22 is adjusted. The adjustment of the channel resistance will be described later.

  The heat insulating material 23 for the evaporation chamber is a heat insulating material attached to the bottom surface of the air heat exchanger 22 so as to substantially cover the whole. Therefore, the heat insulating material 23 for evaporation chamber is arrange | positioned over the whole evaporation part 20a. The evaporating chamber heat insulating material 23 is formed so that the high-temperature gas in the exhaust passage 21 b and the gas retention space 21 c formed between the upper surface of the rectifying plate 21 and the ceiling surface of the case 8 flows on the bottom surface of the air heat exchanger 22. It arrange | positions so that it may suppress direct heating. For this reason, during the operation of the fuel cell module 2, the heat directly transferred to the bottom surface of the air heat exchanger 22 from the exhaust gas remaining in the exhaust passage above the evaporation unit 20a is reduced, and the surroundings of the evaporation unit 20a are reduced. The temperature tends to rise. In addition, after the fuel cell module 2 is stopped, the evaporation chamber heat insulating material 23 is disposed, so that heat dissipation from the reformer 20 is suppressed, that is, the heat around the evaporation unit 20a is used for air. The heat exchanger 22 is less likely to be deprived, and the temperature drop of the evaporation unit 20a is moderated.

  In addition, the heat insulating material 23 for the evaporation chamber includes a heat insulating material 7 that is an outer heat insulating material covering the case 8 of the fuel cell module 2 and the entire air heat exchanger 22 in order to suppress the dissipation of heat to the outside air. Apart from this, it is a heat insulating material arranged inside the heat insulating material 7. The heat insulating material 7 is configured to have higher heat insulating properties than the heat insulating material 23 for the evaporation chamber. That is, the thermal resistance between the inner surface and the outer surface of the heat insulating material 7 is larger than the thermal resistance between the upper surface and the lower surface of the evaporation chamber heat insulating material 23. That is, when the heat insulating material 7 and the evaporation chamber heat insulating material 23 are made of the same material, the heat insulating material 7 is made thicker than the evaporation chamber heat insulating material 23.

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

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

  On the other hand, the power generation air that is the oxidant gas is sent into the fuel cell module 2 through the power generation air introduction pipe 74 by the power generation air flow rate adjustment unit 45 that is a power generation oxidant gas supply device. The air sent into the fuel cell module 2 is introduced into the power generation air passage 72 of the air heat exchanger 22 via the power generation air introduction pipe 74 and preheated. The preheated air flows out to each communication channel 76 via each outlet port 76a (FIG. 3). The power generation air flowing into each communication channel 76 flows downward through the power generation air supply passages 77 provided on both side surfaces of the fuel cell module 2, and the fuel cell stack 14 from a number of outlets 77a. Toward the power generation chamber 10.

  The air injected into the power generation chamber 10 comes into contact with the outer surface of each fuel cell unit 16 on the air electrode side (oxidant gas electrode side) of the fuel cell stack 14, and a part of oxygen in the air is in contact with it. Used for power generation. Moreover, the air injected to the lower part of the power generation chamber 10 through the blower outlet 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 unit 16. The combustion heat generated by this combustion heats the evaporation section 20a, the mixing section 20b, and the reforming section 20c of the reformer 20 disposed above the fuel cell stack 14. The combustion gas generated by burning the fuel heats the upper reformer 20 and then flows into the upper side of the rectifying plate 21 through the opening 21 a above the reformer 20. The combustion gas that has flowed into the upper side of the rectifying plate 21 is guided to the communication opening 8 a that is the inlet of the air heat exchanger 22 through the exhaust passage 21 b formed by the rectifying plate 21. The combustion gas that has flowed into the air heat exchanger 22 from the communication opening 8 a flows into the open end of each combustion gas pipe 70 and flows through the power generation air flow path 72 outside each combustion gas pipe 70. Are exchanged with each other and collected in an exhaust gas collecting chamber 78. The exhaust gas collected in the exhaust gas collection chamber 78 is discharged to the outside of the fuel cell module 2 through the exhaust gas discharge pipe 82. As a result, the evaporation of water in the evaporation unit 20a and the steam reforming reaction, which is an endothermic reaction in the reforming unit 20c, are promoted, and the power generation air in the air heat exchanger 22 is preheated.

Next, control in the starting process of the solid oxide fuel cell system 1 will be described with reference to FIG.
FIG. 12 is a time chart showing an example of each supply amount of fuel and the like and the temperature of each part in the startup process. In addition, the scale of the vertical axis | shaft of FIG. 12 has shown temperature, and each supply amount of fuel etc. has shown those increase / decrease roughly.

In the starting process shown in FIG. 12, the temperature of the fuel cell stack 14 at room temperature is raised to a temperature at which power generation is possible.
First, at time t0 in FIG. 12, the supply of power generation air and reforming air is started. Specifically, the control unit 110 that is a controller sends a signal to the power generation air flow rate adjustment unit 45 that is a power generation oxidant gas supply device 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 path 77. . In addition, the control unit 110 sends a signal to the reforming air flow rate adjustment unit 44 which is a reforming oxidant gas supply device to operate it. The reforming air introduced into the fuel cell module 2 flows into the interior of each fuel cell unit 16 through the reformer 20 and the manifold 66, and flows out from the upper end thereof. Note that at time t0, no reforming reaction occurs in the reformer 20 because fuel has not yet been supplied. In this embodiment, the supply amount of power generation air started at time t0 in FIG. 12 is about 100 L / min, and the supply amount of reforming air is about 10.0 L / min.

  Next, fuel supply is started at time t1 after a predetermined time from time t0 in FIG. Specifically, the control unit 110 sends a signal to the fuel flow rate adjustment 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 5.0 L / min. The fuel introduced into the fuel cell module 2 flows into the interior of each fuel cell unit 16 through the reformer 20 and the manifold 66, and flows out from the upper end thereof. At time t1, the reformer reaction is not generated in the reformer 20 because the temperature of the reformer is still low.

  Next, at time t2 when a predetermined time has elapsed from time t1 in FIG. 12, an ignition process for the supplied fuel is started. Specifically, in the ignition process, the control unit 110 sends a signal to an ignition device 83 (FIG. 2) that is an ignition means, and ignites the fuel flowing out from the upper end of each fuel cell unit 16. The ignition device 83 repeatedly generates a spark in the vicinity of the upper end of the fuel cell stack 14 and ignites the fuel flowing out from the upper end of each fuel cell unit 16.

When ignition is completed at time t3 in FIG. 12, supply of reforming water is started. Specifically, the control unit 110 sends a signal to the water flow rate adjustment unit 28 (FIG. 6), which is a water supply device, to activate it. In the present embodiment, the supply amount of water started at time t3 is 2.0 cc / min. At time t3, the fuel supply amount is maintained at about 5.0 L / min. Further, the supply amounts of the power generation air and the reforming air are also maintained at the previous values. At this time t3, the ratio O ₂ / C of oxygen O ₂ in the reforming air and carbon C in the fuel becomes about 0.32.

  After being ignited at time t3 in FIG. 12, the supplied fuel flows out as off-gas from the upper end of each fuel cell unit 16, and is burned here. This combustion heat heats the reformer 20 disposed above the fuel cell stack 14. Here, an evaporating chamber heat insulator 23 is disposed above the reformer 20 (above the case 8), so that immediately after the start of fuel combustion, the temperature of the reformer 20 suddenly increases from room temperature. To rise. Since the outside air is introduced into the air heat exchanger 22 disposed on the heat insulating material 23 for the evaporation chamber, 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, the evaporation chamber heat insulating material 23 is disposed between the upper surface of the case 8 and the bottom surface of the air heat exchanger 22, so that the reformer 20 disposed in the upper portion of the case 8 The movement of heat to the air heat exchanger 22 is suppressed, and heat is easily trapped in the vicinity of the reformer 20 in the case 8. In addition, the space above the rectifying plate 21 above the evaporation unit 20a is configured as a gas retention space 21c (FIG. 2) in which the flow of combustion gas is slow, so that the vicinity of the evaporation unit 20a is double insulated. And the temperature rises more rapidly.

  As described above, the temperature of the evaporation unit 20a rapidly increases, so that water vapor can be generated in a short time after the start of off-gas combustion. In addition, since the reforming water is supplied to the evaporation unit 20a little by little, it is possible to heat the water to the boiling point with a slight amount of heat compared to the case where a large amount of water is stored in the evaporation unit 20a. The supply of water vapor 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 increase in temperature of the evaporation unit 20a and a delay in supply of water vapor due to a delay in supply of water.

  When a certain amount of time elapses after the start of off-gas combustion, the temperature of the air heat exchanger 22 also rises due to the exhaust gas flowing from the combustion chamber 18 into the air heat exchanger 22. The evaporation chamber heat insulating material 23 that insulates between the reformer 20 and the air heat exchanger 22 is a heat insulating material provided inside the heat insulating material 7. Therefore, the heat insulating material 23 for the evaporation chamber does not suppress the dissipation of heat from the fuel cell module 2, but immediately increases the temperature of the reformer 20, particularly the evaporation section 20a immediately after the start of off-gas combustion. Let

In this way, at time t4 when the temperature of the reformer 20 rises, the fuel and the reforming air that have flowed into the reforming unit 20b through the evaporation unit 20a undergo the partial oxidation reforming reaction represented by the equation (1). Get up.
_{C m H n + xO 2 →} aCO 2 + bCO + cH 2 (1)
Since this partial oxidation reforming reaction is an exothermic reaction, when the partial oxidation reforming reaction occurs in the reforming part 20b, the ambient temperature rapidly rises locally.

On the other hand, in the present embodiment, the supply of the reforming water is started from time t3 immediately after the ignition is confirmed, and the temperature of the evaporation unit 20a is rapidly increased. At time t4, water vapor has already been generated in the evaporator 20a and supplied to the reformer 20b. That is, after the off-gas is ignited, the supply of water is started a predetermined time before the temperature of the reforming unit 20b reaches the temperature at which the partial oxidation reforming reaction occurs, and reaches the temperature at which the partial oxidation reforming reaction occurs. At that time, a predetermined amount of water is stored in the evaporation unit 20a, and water vapor is generated. For this reason, when the temperature rapidly rises due to the occurrence of the partial oxidation reforming reaction, a steam reforming reaction occurs in which the reforming steam supplied to the reforming unit 20b reacts with the fuel. This steam reforming reaction is an endothermic reaction shown in Formula (2), and occurs at a higher temperature than the partial oxidation reforming reaction.
C _m H _n + xH ₂ O → aCO ₂ + bCO + cH ₂ (2)

As described above, when the time t4 in FIG. 12 is reached, the partial oxidation reforming reaction occurs in the reforming unit 20b, and the steam reforming is caused by the temperature rise caused by the partial oxidation reforming reaction. Reaction will also occur at the same time. Therefore, the reforming reaction that occurs in the reforming unit 20b after time t4 is an autothermal reforming reaction (ATR) shown in Formula (3) in which the partial oxidation reforming reaction and the steam reforming reaction are mixed. That is, the ATR1 process is started at time t4.
_{C m H n + xO 2 +} yH 2 O → aCO 2 + bCO + cH 2 (3)

  Thus, in the solid oxide fuel cell system 1 according to the embodiment of the present invention, water is supplied during the entire start-up process, and the partial oxidation reforming reaction (POX) does not occur alone. In the time chart shown in FIG. 12, the reformer temperature at time t4 is about 200.degree. The reformer temperature is lower than the temperature at which the partial oxidation reforming reaction occurs, but the temperature detected by the reformer temperature sensor 148 (FIG. 6) is the average temperature of the reforming unit 20b. Actually, even at time t4, the reforming unit 20b partially reaches the temperature at which the partial oxidation reforming reaction occurs, and the steam reforming reaction is performed by the reaction heat of the generated partial oxidation reforming reaction. Is also triggered. As described above, in this embodiment, after the ignition, the supply of water is started before the reforming unit 20b reaches the temperature at which the partial oxidation reforming occurs, and the partial oxidation reforming reaction is performed independently. Will not occur.

Next, when the temperature detected by the reformer temperature sensor 148 reaches about 500 ° C. or higher, the process shifts from the ATR1 process to the ATR2 process at time t5 in FIG. At time t5, the water supply amount is changed from 2.0 cc / min to 3.0 cc / min. Further, the fuel supply amount, the reforming air supply amount, and the power generation air supply amount are maintained at the previous values. As a result, the steam / carbon ratio S / C in the ATR2 step is increased to 0.64, while the reforming air / carbon ratio O ₂ / C is maintained at 0.32. Thus, by maintaining the ratio of reforming air and carbon O ₂ / C constant, the ratio S / C of steam and carbon is increased, so that the amount of carbon that can be partially oxidized and reformed is not reduced. In addition, the amount of carbon that can be steam reformed is increased. This makes it possible to increase the amount of carbon subjected to steam reforming as the temperature of the reforming unit 20b increases while reliably avoiding the risk of carbon deposition in the reforming unit 20b.

Further, in the present embodiment at time t6 in FIG. 12, when the temperature detected by the power generation chamber temperature sensor 142 reaches about 400 ° C. or more, the ATR2 process is shifted to the ATR3 process. Accordingly, the fuel supply amount is changed from 5.0 L / min to 4.0 L / min, and the reforming air supply amount is changed from 9.0 L / min to 6.5 L / min. Also, the previous values are maintained for the water supply amount and the power generation air supply amount. This increases the steam / carbon ratio S / C in the ATR3 step to 0.80, while the reforming air to carbon ratio O ₂ / C is reduced to 0.29.

  Furthermore, when the temperature detected by the power generation chamber temperature sensor 142 reaches about 550 ° C. or higher at time t7 in FIG. 12, the process proceeds to the SR1 process. Along with this, the fuel supply amount is changed from 4.0 L / min to 3.0 L / min, and the water supply amount is changed from 3.0 cc / min to 7.0 cc / min. Further, the supply of the reforming air is stopped, and the power supply air supply amount is maintained at the previous value. Thus, in the SR1 process, steam reforming occurs exclusively in the reforming unit 20b, and the steam / carbon ratio S / C is 2 which is appropriate for steam reforming the entire amount of supplied fuel. .49. At time t7 in FIG. 12, since the temperature of both the reformer 20 and the fuel cell stack 14 is sufficiently increased, the steam reforming is performed even if the partial oxidation reforming reaction has not occurred in the reforming unit 20b. The reaction can be generated stably.

  Next, at time t8 in FIG. 12, when the temperature detected by the power generation chamber temperature sensor 142 reaches about 600 ° C. or more, the process proceeds to the SR2 process. Accordingly, the fuel supply amount is changed from 3.0 L / min to 2.5 L / min, and the water supply amount is changed from 7.0 cc / min to 6.0 cc / min. In addition, the previous value of the power supply air supply amount is maintained. Thereby, in the SR2 step, the ratio S / C of water vapor to carbon is set to 2.56.

  Further, after executing the SR2 process for a predetermined time, the process proceeds to the power generation process. In the power generation process, power is extracted from the fuel cell stack 14 to the inverter 54 (FIG. 6), and power generation is started. In the power generation process, the reforming unit 20b reforms the fuel exclusively by steam reforming. Further, during the power generation operation, the fuel supply amount, the power generation air supply amount, and the water supply amount are changed in accordance with the output power required for the fuel cell module 2. Further, during the power generation operation, the control unit 110 sets the fuel supply amount, the power generation air supply amount, and the water supply amount so that they are within an appropriate temperature range in which the temperature of the fuel cell stack 14 is within a predetermined power generation temperature range. Is controlling.

Next, stop of the solid oxide fuel cell system 1 according to the embodiment of the present invention will be described with reference to FIGS.
First, with reference to FIG. 29, the behavior at the time of shutdown stop in the conventional solid oxide fuel cell system will be described. FIG. 29 is a time chart schematically showing an example of a stop behavior of a conventional solid oxide fuel cell system in time series.

  First, at time t501 in FIG. 29, the shutdown stop operation of the fuel cell that has been operating for power generation is performed. As a result, without waiting for the temperature in the fuel cell module to drop, the fuel supply amount, the water supply amount for reforming, and the air supply amount for power generation are reduced to zero and removed from the fuel cell module in a short time. The generated current (generated current) is also made zero. That is, the supply of fuel, water, and power generation air to the fuel cell module is stopped in a short time, and the extraction of electric power from the fuel cell module is stopped. Further, even when the supply of fuel and electricity to the solid oxide fuel cell system is lost due to a disaster or the like, the stop behavior becomes the same state as in FIG. In addition, the graph of each supply amount in FIG. 29, an electric current, and a voltage shows only a change tendency, and does not represent a specific value.

  As power extraction is stopped at time t501, the voltage value generated in the fuel cell stack rises (however, the current is zero). Further, at time t501, the air supply amount for power generation is set to zero, so that air is not forcibly sent into the fuel cell module. After time t501, the fuel cell stack is kept for a long time. Naturally cooled.

  If the air continues to be supplied into the fuel cell module after time t501, the pressure in the fuel cell module rises due to the air that has been sent. On the other hand, since the fuel supply has already been stopped, the pressure inside the fuel cell unit begins to drop. For this reason, it is considered that the air sent into the power generation chamber of the fuel cell module flows backward from the upper end to the fuel electrode inside the fuel cell unit. At time t501, since the fuel cell stack is in a high temperature state, when the air flows backward to the fuel electrode side, the fuel electrode is oxidized and the fuel cell unit is damaged. In order to avoid this, in the conventional fuel cell, as shown in FIG. 29, immediately after the fuel supply is stopped by the shutdown stop, even if the power supply is not lost, the power generation air is also quickly supplied. It was stopped.

  Furthermore, after about 6 to 7 hours have passed after the shutdown stop, after the temperature in the fuel cell module has dropped below the oxidation lower limit temperature of the fuel electrode, air is again supplied into the fuel cell module. (Not shown). Such air supply is performed for the purpose of discharging the staying fuel gas. However, in the state where the temperature of the fuel cell stack is lower than the oxidation lower limit temperature of the fuel electrode, the fuel is temporarily supplied. Even if air flows back to the pole, the fuel pole is not oxidized.

  However, the present inventor has found that there is a risk that air flows backward to the fuel electrode side and the fuel electrode is oxidized even if the shutdown stop in such a conventional fuel cell is performed.

  The backflow of air from the air electrode side to the fuel electrode side is generated based on the pressure difference between the inside (fuel electrode side) and the outside (air electrode side) of the fuel cell unit. In a state before shutdown stop to which fuel gas and power generation air are supplied, the reformed fuel is pumped to the fuel electrode side of the fuel cell unit. On the other hand, power generation air is also sent to the air electrode side of the fuel cell unit. In this state, the pressure on the fuel electrode side of the fuel cell unit is higher than the pressure on the air electrode side, and fuel is ejected from the fuel electrode side of the fuel cell unit to the air electrode side.

  Next, when the supply of fuel gas and power generation air is stopped due to the shutdown stop, the fuel is ejected from the fuel electrode side where the pressure is high to the air electrode side where the pressure is low. In addition, since the pressure on the air electrode side in the fuel cell module is also higher than the outside air pressure (atmospheric pressure), the air on the air electrode side in the fuel cell module (and from the fuel electrode side) after shutdown is stopped. The ejected fuel gas is discharged to the outside of the fuel cell module through the exhaust passage. For this reason, after the shutdown is stopped, the pressure decreases on the fuel electrode side and the air electrode side of the fuel cell unit, and finally converges to atmospheric pressure. Therefore, the behavior in which the pressure decreases on the fuel electrode side and the air electrode side is the flow resistance between the fuel electrode side and the air electrode side of the fuel cell unit, and between the air electrode side and the outside air in the fuel cell module. It will be affected by channel resistance. When the pressures on the fuel electrode side and the air electrode side are equal, the air on the air electrode side enters the fuel electrode side due to diffusion.

  However, in reality, since the inside of the fuel cell module is in a high temperature state, the behavior of pressure after shutdown is also affected by temperature changes on the fuel electrode side and the air electrode side. For example, when the temperature on the fuel electrode side of the fuel cell unit is drastically lower than that on the air electrode side, the volume of fuel gas in the fuel cell unit shrinks, so the pressure on the fuel electrode side decreases and air Backflow occurs. Thus, the pressure on the fuel electrode side and air electrode side after shutdown is affected by the flow resistance of each part in the fuel cell module, the temperature distribution in the fuel cell module, the amount of accumulated heat, etc. It changes complicatedly.

  The gas components present on the fuel electrode side and the air electrode side of the fuel cell unit can be estimated based on the output voltage of the cell stack when no current is taken out (output current = 0). As shown by the thick broken line in FIG. 29, immediately after the shutdown stop at time t501, the output voltage of the cell stack rises rapidly (A part in FIG. 29). This is because immediately after the shutdown is stopped, a lot of hydrogen is present on the fuel electrode side, air is present on the air electrode side, and the current extracted from the cell stack is set to zero. Next, the output voltage of the cell stack rapidly decreases (part B in FIG. 29). This is because the hydrogen that was present on the fuel electrode side of each fuel cell unit flows out after the shutdown is stopped and the fuel electrode side. It is estimated that this is because the concentration of hydrogen decreases and the concentration of air on the air electrode side decreases due to the outflowing hydrogen.

  Next, the output voltage of the cell stack decreases with time, and at the time when the temperature in the fuel cell module decreases below the oxidation lower limit temperature (C portion in FIG. 29), the output voltage greatly decreases. In this state, it is presumed that almost no hydrogen remains on the fuel electrode side of each fuel cell unit, and in the conventional fuel cell, the fuel electrode is exposed to the risk of oxidation. Actually, in the conventional fuel cell, in many cases, a phenomenon occurs in which the pressure on the fuel electrode side becomes lower than the pressure on the air electrode side before the temperature in the fuel cell module falls below the lower oxidation limit temperature. However, it is considered that the fuel cell unit has an adverse effect.

  Further, depending on the structure of the fuel cell module and the operating conditions before the shutdown stop, a phenomenon occurs in which the temperature inside the fuel cell module rises after the shutdown stop despite the fuel supply being stopped ( Not shown). In other words, the temperature in the fuel cell module may rise more than the time of power generation operation for about an hour after the shutdown is stopped. Such a temperature rise is caused by a steam reforming reaction, which is an endothermic reaction occurring in the reformer during the power generation operation, due to the stop of the fuel supply. It is considered that the fuel remaining in the manifold that distributes the fuel continuously burns in the combustion chamber even after the fuel supply is stopped.

  Thus, while the temperature in the vicinity of the reformer in the fuel cell module rises, the extraction of current from the fuel cell stack is stopped, so that no heat is generated in the fuel cell stack. As a result, the temperature above the fuel cell stack rises and the pressure rises, while the pressure inside each fuel cell unit drops due to the temperature drop. Due to such a temperature gradient in the fuel cell module, the pressure on the fuel electrode side of each fuel cell unit may be lower than the pressure on the air electrode side. In such a case, there is a high possibility that the air on the air electrode side outside the fuel cell unit will flow backward to the internal fuel electrode side and the fuel cell unit will be damaged.

  In the solid oxide fuel cell system 1 according to the embodiment of the present invention, the flow path resistance of each part in the fuel cell module is set to an appropriate value, and the shutdown stop circuit 110a built in the controller 110 which is a controller. By controlling the pressure holding control circuit 110b, the stop pre-processing circuit 110c, the exhaust control circuit 110d, and the exhaust control stop circuit 110e (hereinafter, FIG. 6), the risk of oxidation of the fuel electrode is greatly suppressed. Specifically, the control unit 110 includes a built-in microprocessor, memory, program (not shown), and the like. The control unit 110 constitutes each circuit described above and executes the control described below. .

Next, stop of the solid oxide fuel cell system 1 according to the embodiment of the present invention will be described with reference to FIGS.
FIG. 13 is a flowchart of stop determination for selecting a stop mode in the solid oxide fuel cell system 1 according to the embodiment of the present invention. The flowchart in FIG. 13 is a flowchart for determining which stop mode to select based on a predetermined condition, and is repeatedly executed at predetermined time intervals during operation of the solid oxide fuel cell system 1. Is done.

  First, in step S1 of FIG. 13, it is determined whether or not the supply of fuel gas from the fuel supply source 30 (FIG. 1) and the supply of electric power from the commercial power source are stopped. When the supply of both fuel gas and electric power is stopped, the process proceeds to step S2, and in step S2, stop mode 1 which is an emergency stop mode is selected, and one process of the flowchart of FIG. 13 is performed. finish. As the case where the stop mode 1 is selected, it is assumed that the supply of fuel gas and electric power is stopped due to a natural disaster or the like, and it is considered that the frequency of such stop is extremely low.

  On the other hand, when at least one of the fuel gas and the electric power is supplied, the process proceeds to step S3. In step S3, it is determined whether the supply of the fuel gas is stopped and the electric power is supplied. To be judged. If the supply of fuel gas is stopped and power is supplied, the process proceeds to step S4, and otherwise, the process proceeds to step S5. In step S4, stop mode 2 which is one of the normal stop modes is selected, and one process of the flowchart of FIG. 13 is completed. As the case where the stop mode 2 is selected, it is assumed that the supply of the fuel gas is temporarily stopped due to the construction of the fuel gas supply path or the like, and it is considered that such a stop is performed less frequently. .

  Further, in step S5, it is determined whether or not the stop switch has been operated by the user. If the stop switch is operated by the user, the process proceeds to step S6, and if not, the process proceeds to step S7. In step S6, the stop mode 3 that is one of the switch stop modes in the normal stop mode is selected, and one process of the flowchart of FIG. 13 is completed. When the stop mode 3 is selected, since the user of the solid oxide fuel cell system 1 is absent for a long period of time, the operation of the solid oxide fuel cell system 1 is intentionally performed for a relatively long period of time. It is assumed that the frequency of stopping is not so high.

  On the other hand, in step S7, it is determined whether or not it is a periodic stop periodically executed at a scheduled time. If it is a regular stop, the process proceeds to step S8. If it is not a regular stop, the one-time process in the flowchart of FIG. 13 is terminated. In step S8, the stop mode 4 which is one program stop mode among the normal stop modes is selected, and one process of the flowchart of FIG. 13 is completed. As a case where the stop mode 4 is selected, correspondence to the microcomputer meter provided in the fuel supply source 30 is assumed. That is, generally, the fuel supply source 30 is provided with a microcomputer meter (not shown), and the microcomputer meter is in a state where the supply of fuel gas is completely stopped for about one month. When it does not exist for about one hour or more, it is determined that a gas leak has occurred, and the fuel gas supply is shut off. For this reason, in general, the solid oxide fuel cell system 1 needs to be stopped for about one hour or more once a month. Therefore, it is assumed that the stop by the stop mode 4 is performed at a frequency of about once or more per month, and is the most frequently performed stop.

  Note that when the supply of electric power is stopped and the supply of fuel gas is continued, no stop mode is selected according to the flowchart of FIG. In such a case, the solid oxide fuel cell system 1 according to the present embodiment can continue the power generation by operating the auxiliary unit 4 with the electric power generated by the fuel cell stack 14. Note that the present invention can be configured such that the stop mode 4 is selected in order to safely stop the solid oxide fuel cell system 1 even when only the supply of power is stopped.

Next, the stop process in each stop mode will be described with reference to FIGS.
FIG. 14 is a time chart schematically showing an example of stop behavior when the stop mode 1 (step S2 in FIG. 13) is executed in the solid oxide fuel cell system 1 according to the embodiment of the present invention. It is. FIG. 15 is a diagram for explaining the control, the temperature and pressure in the fuel cell module, and the state of the tip of the fuel cell unit in time series when the stop mode 1 is executed.

  First, at time t101 in FIG. 14, when shutdown is stopped, fuel is supplied by the fuel flow rate adjustment unit 38, water is supplied by the water flow rate adjustment unit 28, and power generation air is supplied by the power generation air flow rate adjustment unit 45. Stops for a short time. Further, the extraction of electric power from the fuel cell module 2 by the inverter 54 is also stopped (output current = 0). Since the stop mode 1 is executed when both the fuel gas supply and the power supply are stopped, in the stop mode 1, the fuel cell module 2 is naturally left in this state after the shutdown stop. For this reason, the fuel existing on the fuel electrode side in each fuel cell unit 16 passes through the fuel gas flow channel 98 (FIG. 4) based on the pressure difference from the external air electrode side. Erupted to the side. Moreover, the air (and the fuel ejected from the fuel electrode side) that existed on the air electrode side of each fuel cell unit 16 is the pressure on the air electrode side (pressure in the power generation chamber 10 (FIG. 1)) and atmospheric pressure. Is discharged to the outside of the fuel cell module 2 through the exhaust passage 21b, the air heat exchanger 22 and the like. Accordingly, after the shutdown is stopped, the pressure on the fuel electrode side and the air electrode side of each fuel cell unit 16 naturally decreases.

  However, a fuel gas flow passage narrow tube 98 which is an outflow side flow passage resistance portion is provided at the upper end portion of each fuel cell unit 16, and the vertical wall 21d and the falling wall 8b (FIG. 2) are provided in the exhaust passage 21b. ) Is provided. The flow resistance of the fuel gas flow narrow tube 98 is set so that the pressure drop on the fuel electrode side after the fuel supply and power generation is stopped is more gradual than the pressure drop on the air electrode side. The solid oxide fuel cell system 1 of the present embodiment appropriately tunes the flow resistance in each part of the fuel and exhaust passages, so that the fuel cell unit 16 can be placed on the fuel electrode side even after shutdown. The fuel is configured to remain for a long time. For example, if the flow path resistance of the exhaust path from the power generation chamber 10 to the outside air is too small with respect to the flow path resistance in the fuel gas flow narrow tube 98, the pressure on the air electrode side rapidly decreases after the shutdown is stopped. The pressure difference between the fuel electrode side and the air electrode side increases, and on the contrary, the outflow of fuel from the fuel electrode side is promoted. Conversely, when the flow path resistance of the exhaust path is too large relative to the flow resistance of the fuel gas flow narrow tube 98, the pressure drop on the air electrode side is moderate compared to the pressure drop on the fuel electrode side. Thus, since the pressures on the fuel electrode side and the air electrode side approach, the risk of air backflow to the fuel electrode side increases.

  Thus, in the present embodiment, the fuel // exhaust gas that leads the fuel and / or exhaust gas from the fuel flow rate adjustment unit 38 to the outside of the fuel cell module 2 through the reformer 20 and the fuel electrode of each fuel cell unit 16. The exhaust gas passage is tuned as described above. For this reason, even when left undisturbed after shutdown, the pressure on the fuel electrode side decreases while maintaining a pressure higher than the pressure on the air electrode side, and the temperature of the fuel electrode decreases to the oxidation suppression temperature. In this case, the pressure is maintained at a pressure higher than the atmospheric pressure, and the risk that the fuel electrode is oxidized can be sufficiently suppressed. As shown in FIG. 14, in the solid oxide fuel cell system 1 of the present embodiment, after the shutdown stop is performed at time t101, the output voltage of the fuel cell stack 14 shown by the thick broken line once greatly increases. However, the drop is less than that of the conventional solid oxide fuel cell system (FIG. 29), and a relatively high voltage continues for a long time. In the example shown in FIG. 14, a relatively high voltage is maintained until time t <b> 102 when the temperature on the fuel electrode side and the air electrode side decreases to a predetermined oxidation suppression temperature after shutdown. This indicates that the fuel remains on the fuel electrode side of each fuel cell unit 16 until time t102 when the temperature drops to the oxidation suppression temperature.

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

  That is, in the solid oxide fuel cell system 1 according to the present embodiment, the fuel / exhaust gas passage is disposed in the air electrode in the fuel cell module 2 until the temperature of the fuel electrode decreases to the oxidation suppression temperature after the shutdown is stopped. The pressure on the fuel electrode side is maintained higher than the atmospheric pressure, and the pressure on the fuel electrode side is maintained higher than the pressure on the air electrode side. Therefore, the fuel / exhaust gas passage functions as a mechanical pressure holding means for extending the time until the pressure on the fuel electrode side approaches the pressure on the air electrode side.

  FIG. 15 is a diagram for explaining the operation in the stop mode 1, in which the upper stage shows a graph schematically showing the pressure change on the fuel electrode side and the air electrode side, and the middle stage shows the control operation by the control unit 110 and the fuel cell module. The temperature in 2 is shown in time series, and the lower part shows the state of the upper end portion of the fuel cell unit 16 at each time point.

  First, the power generation operation is performed before the shutdown stop in the middle stage of FIG. In the example shown in FIGS. 14 and 15, the temperature in the fuel cell module 2 during the power generation operation is about 700 ° C. Further, as shown in the lower part (1) of FIG. 15, the fuel gas remaining without being used for power generation is ejected from the fuel gas channel narrow tube 98 at the upper end of the fuel cell unit 16. The gas is combusted at the upper end of the fuel gas passage narrow tube 98. Next, when the supply of fuel gas, reforming water, and power generation air is stopped due to the shutdown stop, the flow rate of the ejected fuel gas decreases, and as shown in the lower part (2) of FIG. The flame at the tip of the gas flow path narrow tube 98 disappears. Since the fuel gas channel narrow tube 98 is formed in an elongated shape, when the flame is drawn into the fuel gas channel narrow tube 98 due to a decrease in the fuel gas flow rate, the flame disappears quickly. By quickly extinguishing the flame, consumption of the fuel gas remaining inside the fuel cell unit 16 and the like is suppressed, and the time during which the remaining fuel can be maintained on the fuel electrode side is extended.

  As shown in the lower part (3) of FIG. 15, the pressure inside the fuel cell unit 16 (fuel electrode side) is higher than the outside (air electrode side) even after the flame is extinguished after the shutdown is stopped. The ejection of the fuel gas from the fuel gas flow path narrow tube 98 is continued. Further, as shown in the upper part of FIG. 15, 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 stop.

  The amount of fuel gas ejected from the fuel gas channel narrow tube 98 decreases as the pressure difference between the fuel electrode side and the air electrode side decreases (lower stage (4) (5) in FIG. 15). On the other hand, when the shutdown is stopped, the reformed fuel gas, the unreformed fuel gas, the water vapor, and the water remain in the reformer 20, and after the shutdown is stopped, the reformed fuel gas remains unreformed due to residual heat. The fuel gas is reformed by steam. Further, the remaining water is also vaporized by residual heat and becomes steam because the evaporator 20a is integrally provided in the reformer 20. In the reformer 20, volume expansion occurs as the fuel gas is reformed and water is evaporated, so that the fuel gas remaining in the reformer 20, the fuel gas supply pipe 64, and the manifold 66 (FIG. 2). Are sequentially pushed into each fuel cell unit 16 (fuel electrode side). For this reason, the pressure drop on the fuel electrode side due to the ejection of the fuel gas from the fuel gas passage narrow tube 98 is suppressed.

  Furthermore, since the reforming part 20c in the reformer 20 is filled with a catalyst, the flow path resistance is relatively large. For this reason, when the remaining water is evaporated in the evaporation section 20a, the water vapor flows into the reforming section 20c, while flowing backward to the reformer introduction pipe 62 (FIG. 2). The reformer introduction pipe 62 is configured to extend substantially horizontally from the side surface of the evaporation section 20a, then bend, and extend substantially vertically upward. Accordingly, the back-flowed steam rises in the reformer introduction pipe 62 in the vertical direction and reaches the T-shaped pipe 62 a connected to the upper end of the reformer introduction pipe 62. Here, the reformer introduction pipe 62 extending from the evaporation section 20 a is disposed inside the heat insulating material 7 covering the case 8, and therefore has a high temperature. Moreover, since the upper end part of the reformer introduction pipe 62 and the T-shaped pipe 62a are located outside the heat insulating material 7, the temperature is low. For this reason, the water vapor that has risen in the reformer introduction pipe 62 hits the upper end portion of the reformer introduction pipe 62 having a low temperature and the inner wall surface of the T-shaped pipe 62a, and is condensed to form water.

  The water generated by the condensation falls from the upper ends of the T-shaped tube 62a and the reformer introduction pipe 62 to the inner wall surface below the reformer introduction pipe 62, where it is heated again and the temperature rises and evaporates. It flows into the part 20a again. Since the reformer introduction pipe 62 is configured to be bent, water drops that have fallen after condensation have not directly flown into the evaporation section 20a and fall onto the inner wall surface below the reformer introduction pipe 62. Therefore, the portion disposed inside the heat insulating material 7 of the reformer introduction pipe 62 functions as a preheating unit for preheating supplied water or condensed water, and the reformer having a temperature lower than that of the preheating unit. The upper end portion of the introduction tube 62 and the T-shaped tube 62a function as a dew condensation portion.

  Further, the steam that has risen in the reformer introduction pipe 62 may flow backward from the T-shaped pipe 62a to the water supply pipe 63a. However, since the water supply pipe 63a is disposed so as to be inclined upward from the T-shaped pipe 62a, the condensed water is supplied to the water supply even when water vapor is condensed in the water supply pipe 63a. It flows from the pipe 63 a toward the T-shaped pipe 62 a and falls into the reformer introduction pipe 62. Further, as shown in FIG. 2, the lower portion of the reformer introduction pipe 62 is disposed in the vicinity of the inside of the heat insulating material 7 so as to intersect the exhaust gas discharge pipe 82. For this reason, heat exchange is performed between the reformer introduction pipe 62 and the exhaust gas discharge pipe 82 which are preheating parts, and it is also heated by the heat of the exhaust.

  In this way, a part of the water vapor evaporated in the evaporator 20a flows back to the reformer introduction pipe 62, which generates condensed water and is evaporated again in the evaporator 20a. For this reason, even after the supply of water is stopped when the shutdown is stopped, the remaining water is gradually evaporated in the evaporation unit 20a, and the evaporation of water occurs for a relatively long time after the shutdown is stopped. To do. Further, the reformer introduction pipe 62 extends from the side surface of the evaporation section 20a, is bent, extends substantially vertically upward, and penetrates the heat insulating material 7. Therefore, the portion where the reformer introduction pipe 62 penetrates the heat insulating material 7 is out of the region vertically above the reformer 20, and the heat of the reformer 20 is insulated by the reformer introduction pipe 62. It is difficult for the material 7 to escape to the outside through the through portion of the material 7, and the heat insulating property is not significantly impaired by the reformer introduction pipe 62.

  On the other hand, the evaporation of water generated in the reformer 20 may occur abruptly depending on the temperature distribution in the evaporator 20a. In such a case, since the pressure in the evaporation part 20a rises rapidly, a high pressure may propagate downstream, and the fuel gas in the fuel cell unit 16 may be suddenly ejected to the air electrode side. However, since the fuel gas supply pipe 64 is provided with the pressure fluctuation suppressing flow path resistance portion 64c (FIG. 2), the fuel cell supply pipe 64 has an internal pressure in the fuel cell unit 16 based on a rapid pressure rise in the reformer 20. Rapid ejection of the fuel gas is suppressed. Further, since the fuel gas channel narrow tube 98 (FIG. 4) is also provided at the lower end of each fuel cell unit 16, the inside of each fuel cell unit 16 is caused by the channel resistance of the fuel gas channel narrow tube 98. The rapid increase in pressure is suppressed. Therefore, the fuel gas flow passage narrow tube 98 and the pressure fluctuation suppressing flow passage resistance portion 64c at the lower end of each fuel cell unit 16 function as mechanical pressure holding means for maintaining the pressure on the fuel electrode side high.

  In this way, the pressure drop on the fuel electrode side of each fuel cell unit 16 is suppressed for a long time after shutdown by the mechanical pressure holding means. When about 5 to 6 hours have passed after the shutdown, and when the temperature in the fuel cell module 2 decreases to the oxidation suppression temperature, both the fuel electrode side and the air electrode side of each fuel cell unit 16 decrease to almost atmospheric pressure. Then, the air on the air electrode side begins to diffuse toward the fuel electrode side (lower stage (6) and (7) in FIG. 15). However, the portion where the outer electrode layer 92 at the upper end portion of the fuel gas passage narrow tube 98 and the fuel cell 84 is not formed (A portion in the lower stage (6) in FIG. 15) is oxidized even if air enters. No, this part functions as a buffer part. In particular, since the fuel gas passage narrow tube 98 is configured to be elongated, the buffer portion becomes long, and even when air enters from the upper end of the fuel cell unit 16, the fuel electrode is hardly oxidized. In the vicinity of the oxidation suppression temperature, the temperature of the fuel electrode is low, little oxidation occurs even when the fuel electrode is in contact with air, and the frequency of execution of the stop mode 1 is extremely low. The adverse effects caused by can be substantially ignored. Further, as shown in the lower part (8) of FIG. 15, after the temperature of the fuel electrode falls below the oxidation lower limit temperature, the fuel electrode is oxidized even if the fuel electrode side of each fuel cell unit 16 is filled with air. It will never be done.

Next, stop mode 2 will be described with reference to FIGS. 16 and 17.
FIG. 16 is a time chart schematically showing an example of stop behavior when the stop mode 2 (step S4 in FIG. 13) is executed in the solid oxide fuel cell system 1 according to the embodiment of the present invention. It is. FIG. 17 is a diagram for explaining the control, the temperature and pressure in the fuel cell module, and the state of the tip of the fuel cell unit in time series when the stop mode 2 is executed.

  First, stop mode 2 is a stop mode that is executed when only the supply of fuel gas is stopped. When shutdown stop is performed at time t201 in FIG. 16, the supply of fuel by the fuel flow rate adjustment unit 38 and the supply of water by the water flow rate adjustment unit 28 are stopped in a short time. Further, the extraction of electric power from the fuel cell module 2 by the inverter 54 is also stopped (output current = 0). When the stop mode 2 is executed, the shutdown stop circuit 110a built in the control unit 110 executes the exhaust control immediately after the shutdown stop at time t201, and the power generation air flow rate adjustment unit 45 is moved to a predetermined exhaust time. Operate over heat time. In the present embodiment, the predetermined exhaust heat time is about 2 minutes at the maximum, and the water flow rate adjustment unit 28 is stopped during this period. Further, after the power generation air flow rate adjustment unit 45 is stopped at time t202 in FIG. The exhaust control end time will be described later.

  In the stop by the stop mode 2, air is sent to the air electrode side of the fuel cell unit 16 by exhaust control after the shutdown stop. Thereby, in the A part of FIG. 16, the temperature by the side of the air electrode has fallen more rapidly than the case of the stop mode 1 (FIG. 14). As described above, after the fuel supply is completely stopped, there is a risk that the fuel electrode is oxidized and damaged until the temperature of the fuel cell stack 14 is lowered to the oxidation suppression temperature. It was stopped. However, the present inventors have found that immediately after the fuel supply is stopped, the power generation air can be safely supplied to the air electrode side.

  That is, immediately after the shutdown is stopped, a sufficient amount of fuel gas remains on the fuel electrode side of each fuel cell unit 16, and this is in a state of being ejected from the upper end of each fuel cell unit 16. By sending air to the side, air does not flow backward to the fuel electrode side. That is, in this state, the pressure on the air electrode side rises by sending air by exhaust control, but the pressure on the fuel electrode side is still higher than the pressure on the air electrode side. The fuel gas channel narrow tube 98 provided at the upper end of each fuel cell unit 16 is a throttle channel having a narrow channel cross-sectional area, which allows the fuel gas flowing out from each fuel cell unit 16 to flow. The flow rate increases. Accordingly, the fuel gas flow path narrow tube 98 provided at the upper end functions as an accelerating unit that increases the flow rate of the fuel gas. Further, after the supply of air is stopped at time t202, it is left as it is in the same manner as in stop mode 1, and the state where the pressure on the fuel electrode side is higher than the pressure on the air electrode side is maintained for a predetermined period by the mechanical pressure holding means. Is done. However, in the stop mode 2, since the high-temperature air and combustion gas staying in the fuel cell module 2 are discharged by the exhaust control, the natural leaving is started from a temperature lower than that in the stop mode 1. For this reason, the risk of air backflow occurring before the temperature of the fuel electrode decreases to the oxidation suppression temperature is reduced. Thus, after the shutdown is stopped, the pressure drop on the fuel electrode side becomes more gradual than the pressure drop on the air electrode side. Further, since the temperature in the fuel cell module 2 is made uniform by the exhaust control, the risk that the fuel gas inside the fuel cell unit 16 contracts rapidly and air is drawn into the fuel electrode side is reduced.

  Furthermore, after the shutdown is stopped, air is sent to the air electrode side by the exhaust control, so that the flame at the upper end of the fuel gas passage narrow tube 98 disappears more quickly, and the consumption of the remaining fuel is suppressed. Further, immediately after the shutdown is stopped, a lot of fuel gas ejected from the fuel cell unit 16 flows out to the air electrode side of the fuel cell unit 16 without being burned. In the stop mode 2, after the shutdown is stopped, air is sent to the air electrode side, and the ejected fuel gas is discharged together with the air, so that the fuel gas flowing out from the fuel electrode touches the air electrode and the air electrode partially The risk of being reduced is avoided.

  FIG. 17 is a diagram for explaining the operation in the stop mode 2. In the upper stage, a graph schematically showing the pressure change on the fuel electrode side and the air electrode side is shown, and in the middle stage, the control operation by the control unit 110 and the fuel cell module are shown. The temperature in 2 is shown in time series, and the lower part shows the state of the upper end portion of the fuel cell unit 16 at each time point.

  First, the power generation operation is performed before the shutdown stop in the middle stage of FIG. 17, and the exhaust control is executed after the shutdown stop. After the exhaust control for about 2 minutes, the power generation air flow rate adjustment unit 45 is stopped, and thereafter, it is left as it is as in the stop mode 1. However, in the stop mode 2, the temperature in the fuel cell module 2 and the pressure on the fuel electrode side and the air electrode side at the time when the natural standing is started (time t202 in FIG. 16) are lower than in the stop mode 1. Has been. For this reason, before the temperature of a fuel electrode falls to oxidation suppression temperature, the risk that air infiltrates into the fuel electrode side is further reduced.

Next, the stop mode 3 will be described with reference to FIGS.
FIG. 18 is a time chart schematically showing an example of stop behavior when the stop mode 3 (step S6 in FIG. 13) is executed in the solid oxide fuel cell system 1 according to the embodiment of the present invention. It is. FIG. 19 is an enlarged time chart immediately after the shutdown is stopped. FIG. 20 is a diagram for explaining the control, the temperature and pressure in the fuel cell module, and the state of the tip of the fuel cell unit in time series when the stop mode 3 is executed. FIG. 22 is a time chart showing a modification of the stop mode 3.

  First, stop mode 3 is a stop mode that is executed when a stop switch is operated by a user. As shown in FIGS. 18 and 19, the temperature drop control is executed in the stop mode 3, and this temperature drop control is performed by the pre-stop process before the power extraction from the fuel cell stack 14 is completely stopped. The exhaust control is performed after the power extraction is stopped. The exhaust control is the same as the exhaust control in the stop mode 2, and the pre-stop process is executed before the power extraction is stopped.

  In the example of the time chart shown in FIG. 19, at time t301, the stop switch is operated by the user, and pre-stop processing is started. In the pre-stop process, first, the output of the power generated by the fuel cell module 2 to the inverter 54 is stopped. As a result, as indicated by a thin one-dot chain line in FIG. 19, the current and power taken out from the fuel cell module 2 rapidly decrease. In the pre-stop process, the current output from the fuel cell module 2 to the inverter 54 is stopped, but a certain weak current (1A) for operating the auxiliary unit 4 of the solid oxide fuel cell system 1 is stopped. Degree) is continued. For this reason, a weak current is taken out from the fuel cell module 2 during the pre-stop process even after the generated current significantly decreases at time t301. Further, as indicated by a broken line in FIG. 19, the output voltage of the fuel cell module 2 increases with a decrease in the extracted current. In this way, during the pre-stop process, by limiting the amount of power to be extracted and continuing power generation with a predetermined power while extracting a weak current, a part of the supplied fuel is used for power generation. Thus, a significant increase in surplus fuel that remains unused is avoided, and the temperature in the fuel cell module 2 is lowered.

  Further, in the pre-stop process, after time t301, the fuel supply amount indicated by the dotted line in FIG. 19 and the supply amount of reforming water indicated by the thin solid line are linearly reduced. On the other hand, the air supply amount for power generation indicated by the thick one-dot chain line is set to the maximum value. Therefore, during the pre-stop process, more air is supplied than the amount corresponding to the electric power extracted from the fuel cell module 2. In this way, by increasing the air supply amount, heat is taken from the reformer 20 and the temperature rise in the fuel cell module 2 is suppressed. Subsequently, in the example shown in FIG. 19, at time t302 about 20 seconds after time t301, the fuel supply amount and the water supply amount are reduced to the supply amount corresponding to the weak current extracted from the fuel cell module 2. And then the reduced supply is maintained. As described above, by reducing the fuel supply amount and the water supply amount as the pre-stop process, the air flow in the fuel cell module 2 caused by the rapid stop of the large flow rate of fuel when the fuel supply completely stops. It prevents turbulence and a large amount of fuel remaining in the reformer 20 and the manifold 66 after the fuel supply is completely stopped. Note that, after time t301, by decreasing the fuel supply amount and increasing the air supply amount, the temperature on the air electrode side in the fuel cell module 2 indicated by a thick solid line in FIG. 19 is lowered. However, a large amount of heat is still accumulated in the heat insulating material 7 and the like surrounding the fuel cell module 2. In addition, during the pre-stop process, the current output to the inverter 54 is stopped, but the fuel and water are continuously supplied. Air does not flow backward to the fuel electrode inside the unit 16. Therefore, the supply of air can be continued safely.

  In the example shown in FIG. 19, the fuel supply amount and the water supply amount for reforming are set to zero at time t303 approximately two minutes after the time t301 when the pre-stop processing is started, and the current taken out from the fuel cell module 2 It is also zeroed and shutdown is stopped. The end time of the pre-stop process will be described later. In the example shown in FIG. 19, at time t303, the water supply amount is slightly increased immediately before the current taken out from the fuel cell module 2 is made zero. This increase in the amount of water supply is to adjust the amount of water so that an appropriate amount of water remains in the evaporator 20a at the time of shutdown stop. The control of the water supply amount will be described later.

  In the example shown in FIG. 19, the supply of power generation air (however, the power generation is completely stopped) is continued by the exhaust control even after the shutdown stop at time t303. As a result, the air in the fuel cell module 2 (air electrode side of the fuel cell stack 14), the remaining fuel combustion gas, and the fuel that has flowed out from the fuel electrode side of the fuel cell stack 14 after shutdown is discharged. In the present embodiment, after the fuel supply is completely stopped at time t303, the supply of power generation air is continued until time t304. Further, the air supply amount for power generation is reduced from the maximum air supply amount during the pre-stop process to a predetermined supply amount.

  As shown in FIG. 18, after the supply of power generation air is stopped at time t <b> 304, it is left as it is in the stop mode 1. However, in stop mode 3, pre-stop processing is executed before shutdown stop, and exhaust control is executed after shutdown stop, so the temperature drop in part A in FIG. Natural standing is started from a low pressure state.

  FIG. 20 is a diagram for explaining the operation in the stop mode 3. In the upper part, a graph schematically showing the pressure change on the fuel electrode side and the air electrode side is shown, and in the middle part, the control operation by the control unit 110 and the fuel cell module are shown. The temperature in 2 is shown in time series, and the lower part shows the state of the upper end portion of the fuel cell unit 16 at each time point.

  First, the power generation operation is performed before the stop switch operation in the middle stage of FIG. 20, and the pre-stop process is executed after the stop switch operation. In the pre-stop process, the amount of fuel gas supplied is reduced. Therefore, as shown in the lower part (1) of FIG. 20, the flame at the upper end of each fuel cell unit 16 that was large during the power generation operation is It becomes small as shown in. Thus, since the supply amount of fuel gas and the power generation amount are reduced, the temperature in the fuel cell module 2 is lowered than during the power generation operation. After the pre-stop process, shutdown stop is performed. After shutting down, the power generation air flow rate adjusting unit 45 supplies power generation air for 2 minutes by exhaust control. After the exhaust control, the power generation air flow rate adjustment unit 45 is stopped, and thereafter, it is left as it is as in the stop mode 1.

  As described above, since the pressure on the fuel electrode side of each fuel cell unit 16 is higher than the pressure on the air electrode side at the time of shutdown stop, the fuel gas on the fuel electrode side after the fuel supply is stopped. Is ejected from the upper end of each fuel cell unit 16. The flame in which the fuel gas is burned disappears when the shutdown is stopped. After the shutdown is stopped, the fuel gas ejected from the upper end of each fuel cell unit 16 is the largest immediately after the shutdown is stopped, and then gradually decreases. A large amount of fuel gas ejected immediately after the shutdown is stopped is discharged out of the fuel cell module 2 by the power generation air supplied in the exhaust control. Even after the exhaust control is completed, the fuel gas is ejected from the upper end of each fuel cell unit 16, but the amount of the fuel gas is relatively small.

  For this reason, hydrogen, which is the fuel gas ejected after the exhaust control is completed, stays in the upper part of the fuel cell module 2 (above the fuel cell stack 14), but the ejected fuel gas remains in each fuel cell. The unit 16 does not substantially contact the air electrode. Therefore, the fuel gas is reduced by contacting the hot air electrode, and the air electrode is not deteriorated. Further, in the pre-stop process before the shutdown stop, water is supplied so that an appropriate amount of water in a predetermined range is stored in the evaporation unit 20a. For this reason, during the exhaust control after the shutdown is stopped, the water is evaporated in the evaporation section 20a, whereby the pressure on the fuel electrode side of each fuel cell unit 16 is increased, and an appropriate amount of fuel gas is supplied to each fuel cell. It is ejected from the upper end of the unit 16. The fuel gas ejected during the exhaust control is quickly discharged from the fuel cell module 2. Since an appropriate amount of fuel gas is ejected during exhaust control, an excessive amount of fuel gas is ejected from each fuel cell unit 16 after exhaust control, and the air electrode is not deteriorated.

  Here, in the stop mode 3, the temperature in the fuel cell module 2 and the pressure on the fuel electrode side and the air electrode side at the time when the natural leaving is started after the exhaust control is finished (time t304 in FIG. 18) It is lower than the cases of 1 and 2. Further, in the stop mode 3, the supply amount of fuel gas, the supply amount of water, etc. before shutdown stop are fixed to predetermined values by the pre-stop process. As a result, variations in pressure, temperature distribution, and the like at the point of time when natural leaving starts depending on the operating state during the power generation operation are reduced, and natural standing is always started from an appropriate state. For this reason, before the temperature of a fuel electrode falls to oxidation suppression temperature, the risk that air will penetrate into the fuel electrode side becomes extremely low.

Next, with reference to FIG. 21, the supply of water in the stop pretreatment will be described.
FIG. 21 is a flowchart of water supply in the stop pretreatment, and is repeatedly executed at predetermined time intervals by the shutdown stop circuit 110a during operation of the solid oxide fuel cell system 1. First, in step S11 of FIG. 21, it is determined whether or not pre-stop processing is started. When the pre-stop process is started, the process proceeds to step S12. When the pre-stop process is not started, one process of the flowchart of FIG. 21 is ended.

  Next, in step S12, as a supply water securing step, a water heater radiator (not shown) built in the hot water production apparatus 50 (FIG. 1) is operated for 2 minutes. This water heater radiator is configured to warm water by exchanging heat with the high-temperature exhaust gas from the fuel cell module 2 and recover the exhaust heat in the exhaust gas. On the other hand, the exhaust gas contains water vapor, and this water vapor exchanges heat with the water heater radiator and becomes water when it is cooled, resulting in condensation. By operating the water heater radiator, the amount of cooling of the exhaust gas increases and the amount of condensed water increases. The increased dew condensation water is collected and stored in the pure water tank 26 (FIG. 1). The water collected in the pure water tank 26 is used as water for steam reforming after undergoing filter processing (not shown) and the like. The water produced | generated by the process of this step S12 is utilized for the pressure supply control performed in the supply of the water during a stop pre-processing, and the stop mode 4 mentioned later. Note that the amount of water used during pre-stop treatment and pressure holding control is small, but high-temperature exhaust gas containing a large amount of water vapor is rapidly cooled by a water heater radiator (not shown). A sufficient amount of water can be secured in 2 minutes during the stop pretreatment.

  Next, in step S13, the power generation amount time series data W0 for 10 minutes immediately before time t301 in FIG. Furthermore, in step S14, an average value W1 for 10 minutes of the time-series data W0 of the read power generation amount is calculated. Next, in step S15, a difference W2 between the maximum rated power generation amount of the solid oxide fuel cell system 1 and the average value W1 is calculated. Furthermore, in step S16, the insufficient water amount Q1 is calculated based on the difference W2. Finally, in step S17, the calculated deficient water amount Q1 is supplied immediately before the end of the pre-stop process (FIG. 19, immediately before time t303), and one process of the flowchart of FIG. 21 is ended.

  By supplying the insufficient water amount Q1, the evaporation unit 20a stores the same amount of reforming water as when the shutdown stop is performed after the operation of the maximum rated power generation amount is continued. The water is evaporated during the exhaust control after the shutdown stop (time t303 to t304 in FIG. 19), whereby the pressure on the fuel electrode side of each fuel cell unit 16 is increased, and an appropriate amount of fuel gas is supplied to each water. It is ejected from the upper end of the fuel cell unit 16.

Next, a modified example of the stop mode 3 will be described with reference to FIG.
In the modification shown in FIG. 22, the method of supplying power generation air in the second temperature drop step is different from that in FIG. 19. As shown in FIG. 22, in this modification, after a shutdown stop is performed at time t303, a predetermined amount of power generation air is supplied until time t304. At time t304, the supply amount of power generation air is decreased stepwise, and the reduced supply amount is continued until time t305.

  In this modification, by supplying a large amount of power generation air in a state where the pressure on the fuel electrode side is high immediately after the shutdown is stopped, high-temperature air on the air electrode side is quickly discharged. On the other hand, when a certain amount of time has passed since the shutdown stopped and the pressure on the fuel electrode side has decreased, the amount of power generation air supplied is reduced to discharge the hot air while avoiding the risk of backflow. To do.

Next, the stop mode 4 will be described with reference to FIGS. 23 and 24.
FIG. 23 is a time chart schematically showing an example of stop behavior when the stop mode 4 (step S8 in FIG. 13) is executed in the solid oxide fuel cell system 1 according to the embodiment of the present invention. It is. FIG. 24 is a diagram for explaining the control, the temperature and pressure in the fuel cell module, and the state of the tip of the fuel cell unit in the time series when the stop mode 4 is executed.

  First, as described above, the stop mode 4 is a stop that is periodically executed at a rate of about once a month in order to support a microcomputer meter (not shown), and is executed in the stop mode. It is the one with the highest frequency. Accordingly, when the stop mode 4 is executed, any slight adverse effect such as oxidation of the fuel electrode on the fuel cell unit 16 has a great influence on the durability of the fuel cell stack 14, so that the fuel electrode It is necessary to prevent oxidation. The stop in the stop mode 4 is periodically executed based on a program built in the shutdown stop circuit 110a.

  First, at time t401 in FIG. 23, when a predetermined time before the shutdown stop time scheduled by the program of the shutdown stop circuit 110a, the shutdown stop circuit 110a starts pre-stop processing. Also in the stop mode 4, as in the stop mode 3, pre-stop processing and exhaust control are executed. That is, in the stop pretreatment, first, the output of the power generated by the fuel cell module 2 to the inverter 54 is stopped, and a weak current (1 A) for operating the auxiliary unit 4 of the solid oxide fuel cell system 1 is stopped. Only) is taken out. Further, during the pre-stop process, the pre-stop water supply flow shown in FIG. 21 is also executed as described above.

  Further, in the stop pretreatment, after time t401, the fuel supply amount indicated by a thick dotted line in FIG. 23 and the supply amount of reforming water indicated by a thin solid line are reduced. On the other hand, the air supply amount for power generation indicated by the thick one-dot chain line is increased to the maximum value.

  Next, at time t402, the shutdown stop circuit 110a executes shutdown stop. When the shutdown stop is performed, the fuel supply by the fuel flow rate adjustment unit 38 and the water supply by the water flow rate adjustment unit 28 are stopped in a short time. Further, the extraction of electric power from the fuel cell module 2 by the inverter 54 is also stopped (output current = 0).

  The shutdown stop circuit 110a executes exhaust control after the shutdown stop at time t402, and operates the power generation air flow rate adjustment unit 45 for a predetermined period. Further, after the power generation air flow rate adjustment unit 45 is stopped at time t403 in FIG.

  Further, in the stop mode 4, the shutdown stop circuit 110a is operated at the pressure holding control circuit 110b (FIG. 6) at time t404 when the temperature in the fuel cell module 2 has decreased to a predetermined temperature after about 5 hours have elapsed after the shutdown. Is activated. In the present embodiment, when the temperature in the fuel cell module 2 is lowered to a predetermined temperature of about 400 ° C., the pressure on the fuel electrode side of the fuel cell unit 16 is also reduced, and the pressure on the air electrode side Is approaching. The pressure holding control circuit 110b sends a signal to the water flow rate adjusting unit 28 to operate it. By operating the water flow rate adjustment unit 28, water is supplied to the evaporation unit 20 a of the reformer 20. Since the inside of the fuel cell module 2 is still at a temperature of about 400 ° C. even at time t404 when about 5 hours have passed after the shutdown is stopped, the water supplied to the evaporation unit 20a is evaporated there. In this embodiment, water is intermittently supplied, and the water supply amount is set to about 1 mL per minute, and this water supply amount is smaller than the minimum water supply amount during power generation operation. It is.

  As water evaporates and expands in the evaporation section 20a, the fuel gas passages extending from the reformer 20 to the fuel cell units 16 through the fuel gas supply pipe 64 and the manifold 66 (FIG. 2) are provided. Pressure is increased. Thereby, the fall of the pressure on the fuel electrode side of each fuel cell unit 16 is suppressed, and the backflow of air to the fuel electrode side is more reliably prevented. In addition, since the flow paths of the evaporation unit 20a, the mixing unit 20b, and the reforming unit 20c in the reformer 20 are all meandering, when rapid evaporation of water occurs in the evaporation unit 20a However, the effect of the pressure rise is less likely to propagate downstream. As a result, the pressure on the inner side (fuel electrode side) of each fuel cell unit 16 suddenly increases due to the rapid evaporation, and the fuel gas staying inside is prevented from being ejected in a large amount in a short time. be able to.

  Further, there are a pressure fluctuation suppressing flow path resistance portion 64 c (FIG. 2) provided in the middle of the fuel gas supply pipe 64, and an inflow side flow path resistance portion provided at the lower end of each fuel cell unit 16. The fuel gas channel narrow tube 98 also functions to suppress a rapid increase in the pressure on the fuel electrode side and to retain the fuel gas on the fuel electrode side for a long time.

  The pressure holding control circuit 110b stops the water flow rate adjustment unit 28 at time t405 in FIG. 23 when the temperature in the fuel cell module 2 has decreased to the oxidation lower limit temperature, and thereafter the fuel cell module 2 is allowed to stand naturally.

  Further, the shutdown stop circuit 110a sends a signal to the reforming air flow rate adjustment unit 44 and the power generation air flow rate adjustment unit 45 at time t406 when the temperature in the fuel cell module 2 further decreases to operate them. As a result, the reformer 20, the fuel gas supply pipe 64, the fuel gas passages such as the manifold 66, and the fuel electrode inside each fuel cell unit 16 are purged with air. In addition, the air electrode side in the power generation chamber 10, the exhaust passage 21b, and the exhaust gas passages such as the air heat exchanger 22 are also purged with air. By purging the fuel gas passage and the fuel electrode, water vapor remaining inside these is condensed, and oxidation of the fuel gas passage and the fuel electrode due to the condensed water is prevented. Further, by purging the exhaust gas passage, condensation of the water vapor discharged from the fuel electrode in the exhaust gas passage is prevented. Further, by purging the air electrode side in the power generation chamber 10, reduction by the fuel gas discharged from the fuel electrode side is prevented.

  FIG. 24 is a diagram for explaining the operation in the stop mode 4. The upper stage shows a graph schematically showing the pressure change on the fuel electrode side and the air electrode side, and the middle stage shows the control operation by the control unit 110 and the fuel cell module. The temperature in 2 is shown in time series, and the lower part shows the state of the upper end portion of the fuel cell unit 16 at each time point.

  First, the power generation operation is performed before the shutdown stop in the middle stage of FIG. 24, and the pre-stop process is executed 10 minutes before the shutdown stop time scheduled by the program. After the shutdown is stopped, power generation air is supplied as exhaust control, and the power generation air flow rate adjustment unit 45 is stopped. After the power generation air flow rate adjusting unit 45 is stopped, it is left as it is in the stop mode 3.

  In addition, in the stop mode 4, when the pressure on the fuel electrode side of each fuel cell unit 16 approaches the pressure on the air electrode side due to natural standing, the pressure holding control circuit 110b is activated, and each fuel cell unit The pressure on the fuel electrode side of 16 is increased. By the pressure holding control, first, the reformed fuel gas staying in the manifold 66 and the fuel gas supply pipe 64 (FIG. 2) is gradually fed into the fuel electrode of each fuel cell unit 16, and then the reforming is performed. The unreformed fuel gas remaining in the vessel 20 is gradually fed into the fuel electrode. Furthermore, after all the unreformed fuel gas has been sent, the water vapor evaporated in the evaporating section 20a is sent little by little to the fuel electrode of each fuel cell unit 16. At the time when the pressure holding control circuit 110b is activated, the temperature of the fuel electrode of each fuel cell unit 16 has been lowered to near the oxidation suppression temperature, and therefore, a backflow of air to the fuel electrode side has occurred. However, the effect is slight. However, since the program stop for executing the stop mode 4 is the stop mode that is executed most frequently, the risk of oxidation of the fuel electrode is further reduced, and the influence of the oxidation on each fuel cell unit 16 is limited. Has been reduced to.

  Further, as shown in the upper left side of FIG. 24, in the stop modes 1 to 3, the pressure on the fuel electrode side of each fuel cell unit 16 decreases after the shutdown is stopped, and the temperature of the fuel electrode is near the oxidation suppression temperature. When the pressure decreases to the air pressure, the pressure is close to the air electrode side pressure. On the other hand, in the stop mode 4, as shown in the upper right side of FIG. 24, the pressure holding control by the pressure holding control circuit 110b is executed in a region where the pressure on the fuel electrode side and the pressure on the air electrode side are close to each other. Further, it is possible to more reliably prevent the pressure on the fuel electrode side from lowering than that on the air electrode side.

  Further, as shown in the lower part of FIG. 24, during the natural standing after the end of the second temperature lowering step (“natural leaving 1” in the middle part of FIG. 24), it stays in the fuel electrode of each fuel cell unit 16. The fuel gas gradually flows out, and at the end, the air on the air electrode side may begin to diffuse toward the fuel electrode side (lower part (1) in FIG. 24). However, since the pressure holding control is started thereafter, the fuel gas staying in the fuel gas passage on the downstream side of the reformer 20 is again returned to each fuel cell unit by the pressure of the water vapor generated in the evaporator 20a. 16, the fuel gas concentration in the fuel electrode rises again (lower stage (2) in FIG. 24). After that, since the water vapor is generated in the evaporation unit 20a by the pressure holding control, the outflow of the fuel gas from the fuel electrode of each fuel cell unit 16 is compensated by the fuel gas staying in the fuel gas passage. Therefore, the backflow of air to the fuel electrode is prevented. Further, at the end of the pressure holding control, as shown in the lower part (3) of FIG. 24, even when almost all of the staying fuel gas has flowed out, the fuel electrode of each fuel cell unit 16 has no pressure. Since the water vapor generated by the holding control is filled, the backflow of air to the fuel electrode is reliably prevented.

  Furthermore, after the pressure holding control is completed, the pressure is left to stand naturally (“Natural Standing 2” in the middle of FIG. 24), and then reforming air and power generation air (reforming and power generation are not performed) are supplied and purge is performed. Executed. As a result, the fuel gas and water vapor remaining on the fuel electrode side of each fuel cell unit 16 are discharged, and the fuel gas remaining on the air electrode side in the power generation chamber 10 is also discharged from the fuel cell module 2. The Thereby, in the stop mode 4 executed most frequently, oxidation of the fuel electrode of each fuel cell unit 16 is reliably avoided.

Next, with reference to FIGS. 25 to 27, stop pre-processing and exhaust control executed in stop modes 2 to 4 will be described (only exhaust control is executed in stop mode 2).
FIG. 25 is a flowchart for controlling execution of pre-stop processing and exhaust control. This flowchart is executed at predetermined time intervals during operation of the solid oxide fuel cell system. FIG. 26 is a diagram illustrating a correction coefficient for the power generation air supply amount in the exhaust control. FIG. 27 is an execution condition table for pre-stop processing and exhaust control in each stop mode and temperature band.

  In the solid oxide fuel cell system 1 of the present embodiment, the stop pre-processing and the exhaust control execution mode are performed based on the temperature of the fuel cell stack 14 detected by the power generation chamber temperature sensor 142 that is a temperature detection sensor. Be changed. In the present embodiment, the exhaust control being executed is stopped based on the voltage detected by the power state detection sensor 126 that is a voltage detection sensor.

  First, during the power generation operation of the solid oxide fuel cell system 1, the control unit 110 controls the fuel cell module 2 to generate the required power, and the temperature of the fuel cell stack 14 is a predetermined power generation. The temperature is within an appropriate temperature range. In the present embodiment, the appropriate temperature range of the fuel cell stack 14 is 620 ° C. to 680 ° C., and the temperature of the fuel cell stack 14 is controlled with this temperature band as a target.

  The flowchart of FIG. 25 is executed during the power generation operation, and in step S21, it is determined whether there is an operation stop instruction to the control unit 110. When the stop mode 2 is executed, the stop of the fuel gas supply corresponds to the operation stop instruction. When the stop mode 3 is executed, an operation of a stop switch (not shown) corresponds to an operation stop instruction. Further, when the stop mode 4 is executed, the arrival of a predetermined program stop execution time corresponds to the operation stop instruction. When the stop mode 4 is executed by stopping the supply of power to the solid oxide fuel cell system 1, the stop of power supply corresponds to the operation stop instruction. In this case, the control unit 110, the power generation air flow rate adjustment unit 45, and the like are operated by the electric power generated by the fuel cell module 2 itself after the supply of electric power is stopped.

When there is no operation stop instruction, the one-time process of the flowchart of FIG. 25 ends, and when there is an operation stop instruction, the process proceeds to step S22.
In step S22, it is determined whether or not the temperature of the fuel cell stack 14 detected by the power generation chamber temperature sensor 142 is within an appropriate temperature range. If it is within the proper temperature range, the process proceeds to step S28, and if it is outside the proper temperature range, the process proceeds to step S23.

  In step S23, it is determined whether or not the temperature of the fuel cell stack 14 is higher than an appropriate temperature range. If the temperature is higher than the appropriate temperature range, the process proceeds to step S25. If the temperature is lower than the appropriate temperature range, the process proceeds to step S24.

  In step S24, the shutdown stop circuit 110a (FIG. 6) built in the control unit 110 executes a shutdown stop that stops the fuel supply, water supply, power generation air supply, and power extraction in a short time. After the shutdown is stopped, the fuel cell module 2 is left as it is. That is, when the temperature of the fuel cell stack 14 is lower than the lower limit temperature of the appropriate temperature range, the stop pre-processing circuit 110c (FIG. 6) is used regardless of which of the stop modes 2 to 4 is selected. The stop pretreatment and the exhaust control by the exhaust control circuit 110d (FIG. 6) are not executed (see “low temperature range” in FIG. 27). When the stop mode 4 is selected, the pressure holding control by the pressure holding control circuit 110b is executed after the process of the flowchart of FIG. 25 is completed (t404 to t405 in FIG. 23).

  As described above, when the temperature is lower than the lower limit temperature of the appropriate temperature range, it is not necessary to lower the temperature of the fuel cell stack 14 by the stop pretreatment, and the fuel electrode can be sufficiently obtained even when left as it is. The risk of oxidation can be avoided. Further, when the temperature is lower than the lower limit temperature of the appropriate temperature range, the amount of power generated immediately before the shutdown stop is small, so the amount of fuel supplied immediately before the shutdown stop is small, and the fuel electrode side of the fuel cell stack 14 and the reformer 20 Relatively little fuel remains inside. For this reason, after the shutdown is stopped, the amount of fuel flowing out from the fuel electrode side of the fuel cell stack 14 to the air electrode side is relatively small, and even if the exhaust control is not performed after the shutdown stop, It is not partially reduced. Further, when air is supplied into the fuel cell module 2 by exhaust control in a state where there is little fuel remaining in the fuel electrode side or the reformer 20, the air flows backward from the air electrode side to the fuel electrode side, The risk of oxidation of the fuel electrode increases. In the present embodiment, this risk is avoided by not performing the exhaust control.

On the other hand, if it is determined in step S22 of FIG. 25 that the temperature of the fuel cell stack 14 is within the appropriate temperature range, the process proceeds to step S28, and in step S28, the shutdown is stopped by the shutdown stop circuit 110a. The This shutdown stop is the same as step S24.
Next, in step S29, exhaust control by the exhaust control circuit 110d is executed. That is, when the temperature of the fuel cell stack 14 is within an appropriate temperature range, even if the stop mode 3 or 4 is selected, the pre-stop processing by the pre-stop processing circuit 110c is not executed, and the exhaust control is performed. Only the exhaust control by the circuit 110d is executed (see “appropriate temperature range” in FIG. 27). As described above, when the temperature is within the appropriate temperature range, it is not necessary to lower the temperature of the fuel cell stack 14 by the stop pretreatment, and the risk of the fuel electrode oxidation can be sufficiently avoided only by the exhaust control for a predetermined period. .

  Further, the longest execution period of the exhaust control is determined by multiplying the correction coefficient based on the temperature of the fuel cell stack 14 at the time when the exhaust control is started. As shown in FIG. 26, the correction coefficient is set so that the exhaust control execution time becomes longer when the temperature of the fuel cell stack 14 at the start of exhaust control is high than when the temperature is low. That is, exhaust control is executed according to the temperature detected by the power generation chamber temperature sensor 142. In the present embodiment, the reference exhaust control execution period is 2 minutes, and the supply amount of air is 15 L / min. Further, when the temperature of the fuel cell stack 14 is 660 to 680 ° C., 3 minutes obtained by multiplying the reference exhaust control execution period by 1.5 is set as the exhaust control execution period, and is 640 to 659 ° C. In this case, 2 minutes 30 seconds multiplied by 1.25 is set as the exhaust control execution period, and when it is 620 to 639 ° C., 2 minutes is set as the exhaust control execution period. As described above, when the detected temperature of the power generation chamber temperature sensor 142 is low, exhaust in the exhaust control is suppressed as compared to when it is high, and when the detected temperature is low, it is supplied during the exhaust control than when it is high. The total amount of air is reduced. As a modification, the supply amount of air in the exhaust control is corrected by a correction coefficient, and the supply amount of air can be increased when the detected temperature is high than when the detection temperature is low. Further, both the exhaust control execution period and the air supply amount can be corrected by the correction coefficient.

  Further, when the exhaust control is started in step S29, the exhaust control stop circuit 110e (FIG. 6) built in the control unit 110 starts monitoring the output voltage of the fuel cell module 2 during the exhaust control execution period. That is, the exhaust control stop circuit 110e monitors a decrease in the output voltage of the fuel cell module 2 detected by the power state detection sensor 126. In addition, since the extraction of electric power from the fuel cell module 2 is stopped after the shutdown stop when the exhaust control is started, the voltage detected by the power state detection sensor 126 is the output voltage when the output current is zero. It is.

  Next, in step S30, it is determined whether the exhaust control execution period has elapsed after the start of exhaust control, or whether the output voltage monitored by the exhaust control stop circuit 110e satisfies a predetermined stop condition. To be judged. If neither condition is satisfied, the exhaust control is continued. Thus, when the stop condition is satisfied during the exhaust control execution period, the exhaust control is executed until that point, and when the stop condition is not satisfied during the exhaust control execution period, the exhaust control execution period elapses. Exhaust control is executed until. After the exhaust control is finished, the fuel cell module 2 is left undisturbed. When the stop mode 4 is selected, the pressure holding control by the pressure holding control circuit 110b is executed after the process of the flowchart of FIG. 25 is completed (t404 to t405 in FIG. 23).

  In the present embodiment, 160 fuel cell units 16 connected in series are accommodated in the fuel cell module. When sufficient fuel gas (hydrogen) and air (oxygen) are supplied to the fuel electrode side and the air electrode side of each fuel cell unit 16 respectively, The output voltage is about 160V. When a back flow of air from the air electrode side to the fuel electrode side occurs after the shutdown is stopped, the partial pressure of hydrogen gas on the fuel electrode side decreases, so the output voltage of the fuel cell module 2 rapidly decreases. The exhaust control stop circuit 110e monitors the decrease in the output voltage (OCV) of the fuel cell module 2 when the electric power is not extracted, and immediately performs exhaust control by the exhaust control circuit 110d when the output voltage decreases. Discontinue. Thereby, the supply of air into the fuel cell module 2 is stopped, and the backflow of air is suppressed by reducing the pressure on the air electrode side.

  In the present embodiment, the exhaust control stop circuit 110e determines that the stop condition is satisfied when the detection voltage (OCV) of the power state detection sensor 126 decreases by 40V with respect to the reference voltage 160V and becomes 120V or less. Control is aborted. The reference voltage is a predetermined voltage set in advance based on the configuration of the fuel cell module. Further, as a modification, the exhaust control may be stopped when the detected voltage decreases by a predetermined percentage from the reference voltage. For example, the present invention can be configured such that the exhaust control is stopped at 120 V when the voltage is reduced by 25% with respect to the reference voltage 160 V. Alternatively, instead of the reference voltage, the exhaust control is stopped when a predetermined amount (for example, 40 V) is decreased from the detection voltage at the time of shutdown stop or when a predetermined ratio (for example, 25%) is decreased from the detection voltage at the time of shutdown stop. The present invention can also be configured as follows. Further, the exhaust control may be stopped when the detected voltage decreases by a predetermined amount or more per unit time. For example, the present invention can be configured such that the exhaust control is stopped when the detected voltage decreases at a rate of 5 V / sec or more.

  On the other hand, if it is determined in step S23 of FIG. 25 that the temperature of the fuel cell stack 14 is higher than the upper limit temperature of the appropriate temperature range that is the shutdown temperature, the process proceeds to step S25. In step S25, it is determined whether or not the selected stop mode is stop mode 2. If it is the stop mode 2, the process proceeds to step S28, and if it is the stop mode 3 or 4, the process proceeds to step S26. In step S26, pre-stop processing is executed by the pre-stop processing circuit 110c. As described above, when the stop mode 3 or 4 is selected and the temperature of the fuel cell stack 14 is higher than the upper limit temperature (shutdown temperature) of the appropriate temperature range, the shutdown stop ( Step S28) is executed, and then exhaust control (steps S29 and S30) is executed (see “high temperature range” in FIG. 27). On the other hand, when the temperature of the fuel cell stack 14 is lower than the shutdown temperature, the pre-stop process is not executed (steps S22 → S28 and steps S23 → S24). In the examples of FIGS. 18, 19 and 23 in the stop modes 3 and 4 described above, the temperatures at the time of the operation stop instruction are all higher than the appropriate temperature range (620 to 680 ° C.). Processing and exhaust control are performed.

  Further, in the stop mode 2, since the fuel gas supply is stopped, the pre-stop process cannot be performed, and the exhaust control (steps S29 and S30) is performed without performing the pre-stop process. . After the exhaust control is finished, the fuel cell module 2 is left undisturbed. When the stop mode 4 is selected, the pressure holding control by the pressure holding control circuit 110b is executed after the process of the flowchart of FIG. 25 is completed (t404 to t405 in FIG. 23).

  In the pre-stop process, the amount of fuel supplied to the fuel cell module 2, the amount of water supplied, and the amount of electric power taken out from the fuel cell module 2 are lower than those during power generation operation. On the other hand, the air supply amount is made larger than the amount corresponding to the electric power extracted from the fuel cell module 2 and increased to the maximum value of the supply capability of the power generation air flow rate adjustment unit 45. By this stop pretreatment, the temperature of the fuel cell stack 14 is lowered.

  Next, in step S27, it is determined whether or not the temperature of the fuel cell stack 14 has dropped below the upper limit temperature of the appropriate temperature range. When the temperature does not fall below the upper limit temperature of the appropriate temperature range, the pre-stop process is continued, and when the temperature falls below the upper limit temperature (shutdown temperature), the process proceeds to step S28, where shutdown stop is executed. As described above, the pre-stop process is continued until the temperature of the fuel cell stack 14 is lowered to the shutdown temperature. Therefore, in the present embodiment, different pre-stop processing is executed according to the temperature of the fuel cell stack 14 at the time of the operation stop instruction, and when the temperature of the fuel cell stack 14 is low, it is higher than when it is high. The amount of temperature decrease in the stop pretreatment is reduced. After completion of the pre-stop process, the shutdown stop is executed, and the exhaust control in subsequent steps S29 and S30 is as described above. Note that since a small amount of fuel is supplied during the pre-stop process, there is no possibility of air flowing back to the fuel electrode side even when the pre-stop process is executed for a long time. By executing the pre-stop process, the temperature of the fuel cell stack 14 is lowered to an appropriate temperature range, and an appropriate amount of fuel remains on the fuel electrode side of the fuel cell stack 14 when the shutdown is stopped. The risk of electrode oxidation and air electrode reduction can be avoided.

  In the solid oxide fuel cell system 1 according to the embodiment of the present invention, the problem of air flowing backward from the air electrode side to the fuel electrode side is solved just before execution of shutdown stop (time t303 in FIG. 18, time t402 in FIG. 23). This is solved by executing pre-stop processing (time t303 to t304 in FIG. 18, time t402 to t403 in FIG. 23) for lowering the temperature of the fuel cell stack. When the solid oxide fuel cell system 1 is performing a high-output power generation operation, the inside of the fuel cell module 2 is at a high temperature. The present inventor has found that when a shutdown stop is executed in such a state, a backflow of air to the fuel electrode side is likely to occur. According to the present embodiment, since the temperature of the fuel electrode side and the air electrode side of the fuel cell stack approaches each other by executing the pre-stop process, the fuel gas staying on the fuel electrode side contracts due to the temperature drop. Thus, it is possible to prevent the phenomenon that air is drawn into the fuel electrode side and to suppress the oxidation of the fuel electrode.

  Further, when the solid oxide fuel cell system 1 is in a high-output power generation operation, particularly during the period when the pressure on the fuel electrode side is high after shutdown, a large amount of fuel flows from the fuel electrode side to the air electrode side. leak. As a result, the fuel that has flowed out to the air electrode may come into contact with the air electrode and the air electrode may be partially reduced and damaged. In the present embodiment, the pre-stop process is executed before the shutdown stop, so that the amount of fuel flowing out to the air electrode side after the shutdown stop can be suppressed, and the reduction of the air electrode can be suppressed. Further, in the present embodiment, different pre-stop processing is executed depending on the temperature of the fuel cell stack 14 (steps S26, S27, and FIG. 27 in FIG. 25), so that the shutdown is stopped (step S28 in FIG. 25). Is executed at an appropriate temperature, and the risk of the oxidation of the fuel electrode or the reduction of the air electrode can be suppressed from the collapse of the temperature balance between the fuel electrode side and the air electrode side after shutdown.

  Further, according to the solid oxide fuel cell system 1 of the present embodiment, the fuel supply amount and the power extraction amount are reduced during the pre-stop process (time t301 to t303 in FIG. 19). The temperature of the cell stack 14 can be lowered, and the amount of fuel remaining on the fuel electrode side of the fuel cell stack 14 after the shutdown is stopped (time t303 in FIG. 19) can be reduced. Can be reduced.

  Furthermore, according to the solid oxide fuel cell system 1 of the present embodiment, the air supply amount is increased during the stop pretreatment (time t301 to t303 in FIG. 19), so the temperature of the fuel cell stack 14 is decreased. In addition, the temperature of the fuel cell stack 14 can be effectively reduced while avoiding the risk of air backflow by increasing the air supply amount to the maximum value during the stop pre-treatment in which the fuel supply is continued. Can be reduced.

  Further, according to the solid oxide fuel cell system 1 of the present embodiment, when the temperature is high, the amount of temperature decrease due to the stop pretreatment increases (steps S26 and S27 in FIG. 25), so that the shutdown stop is properly performed. The temperature can be lowered to 680 ° C., and the risk of fuel electrode oxidation and the risk of air electrode reduction can be suppressed.

  Furthermore, according to the solid oxide fuel cell system 1 of the present embodiment, when the temperature is lower than the shutdown temperature (680 ° C.), the pre-stop process is not executed (steps S22 → S28 in FIG. 25). The risk of fuel electrode oxidation due to shutdown stop at low temperature can be suppressed.

  Further, according to the solid oxide fuel cell system 1 of the present embodiment, the pre-stop process (time t301 to t303 in FIG. 19) is continued until the shutdown temperature is lowered (steps S26 and S27 in FIG. 25). The shutdown stop can be executed at an appropriate temperature, and the risk of fuel electrode oxidation and the risk of air electrode reduction can be reliably suppressed by avoiding an excessively high temperature or an excessively low temperature at the time of shutdown stop. .

  Furthermore, according to the solid oxide fuel cell system 1 of the present embodiment, during the power generation operation, the temperature of the fuel cell stack 14 is controlled to target the power generation temperature range (“appropriate temperature range” in FIG. 27). Therefore, shutdown stop can be executed at an appropriate temperature. In addition, when the temperature of the fuel cell stack 14 is higher than the upper limit temperature of the power generation temperature range, the pre-stop process is executed (“high temperature range” in FIG. 27), so that the fuel cell stack 14 is lowered to an appropriate temperature. A shutdown stop can be performed.

  Further, according to the solid oxide fuel cell system 1 of the present embodiment, when the temperature is higher than the upper limit temperature of the power generation temperature range (“high temperature range” in FIG. 27), the power generation temperature range (“appropriate temperature range” in FIG. 27). )), The exhaust control (time t303 to t304 in FIG. 19) is executed after the shutdown is stopped, so that the fuel remaining on the fuel electrode side after the shutdown is stopped is discharged out of the fuel cell module 2. And reduction of the air electrode can be reliably prevented. Further, when the temperature is lower than the lower limit temperature of the power generation temperature range (“low temperature range” in FIG. 27), the exhaust control is not executed, so that the risk of fuel electrode oxidation due to excessive decrease in the temperature of the fuel cell stack 14 is suppressed. can do.

  In the above-described embodiment, when the stop mode 4 is selected, the pressure holding control by the pressure holding control circuit 110b is executed, but the mechanical pressure holding means by the configuration of the fuel / exhaust gas passage allows When the risk of fuel electrode oxidation is sufficiently reduced, the pressure holding control can be omitted.

  Further, in the above-described embodiment of the present invention, when the stop switch is operated by the user (step S5 in FIG. 13), the stop mode 3 is executed. As a modification, FIG. As described above, the stop mode 2 may be executed. FIG. 28 is a flowchart of stop determination for selecting a stop mode in a solid oxide fuel cell system according to a modification of the present invention. That is, in this modification, when the fuel gas is stopped and only electricity is supplied (step S3 → S4 in FIG. 28), and when the stop switch is operated by the user (step S5 → FIG. 28). In S4), stop mode 2 is executed. According to this modification, when the stop switch is operated, the shutdown stop is executed without executing the pre-stop process. Therefore, after the user operates the stop switch, the control related to the shutdown stop is promptly performed. Can be terminated.

DESCRIPTION OF SYMBOLS 1 Solid oxide fuel cell system 2 Fuel cell module 4 Auxiliary machine unit 7 Heat insulation material (heat storage material)
8 Case 8a Communication opening 8b Falling wall 10 Power generation chamber 12 Fuel cell assembly 14 Fuel cell stack 16 Fuel cell unit (solid oxide fuel cell)
18 Combustion chamber (combustion section)
20 Reformer 20a Evaporating section (evaporating chamber)
20b Mixing part (pressure fluctuation absorbing means)
20c reforming part 20d evaporation / mixing part partition 20e partition opening 20f mixing / reforming part partition (pressure fluctuation absorbing means)
20g communication hole (narrow channel)
21 Rectifier plate (partition wall)
21a Opening 21b Exhaust passage 21c Gas residence space 21d Vertical wall 22 Air heat exchanger (heat exchanger)
23 Heat insulating material for evaporation chamber (internal heat insulating material)
24 Water supply source 26 Pure water tank 28 Water flow rate adjustment unit (water supply device)
30 Fuel supply source 38 Fuel flow rate adjustment unit (fuel supply device)
39 Valve 40 Air supply source 44 Air flow rate adjustment unit for reforming (oxidizing gas supply device for reforming)
45 Air flow adjustment unit for power generation (oxidizer gas supply device for power generation)
46 1st heater 48 2nd heater 50 Hot water production apparatus (heat exchanger for exhaust heat recovery)
52 Control box 54 Inverter 62 Reformer introduction pipe (water introduction pipe, preheating part, condensation part)
62a T-shaped tube (condensation part)
63a Water supply pipe 63b Fuel gas supply pipe 64 Fuel gas supply pipe 64c Pressure fluctuation suppressing flow path resistance 66 Manifold (dispersion chamber)
76 Air introduction pipe 76a Air outlet 82 Exhaust gas discharge pipe 83 Ignition device 84 Fuel cell 85 Exhaust valve 86 Inner electrode terminal (cap)
98 Fuel gas channel narrow tube (inflow side channel resistance, outflow side channel resistance, throttle channel, acceleration unit)
110 Controller (Controller)
110a Shutdown stop circuit 110b Pressure holding control circuit 110c Pre-stop processing circuit 110d Exhaust control circuit 110e Exhaust control stop circuit 112 Operating device 114 Display device 116 Alarm device 126 Power state detection sensor (voltage detection sensor)
132 Fuel flow sensor (fuel supply detection sensor)
138 Pressure sensor (reformer pressure sensor)
142 Power generation chamber temperature sensor (temperature detection sensor)
148 Reformer Temperature Sensor 150 Outside Temperature Sensor

Claims (8)

A solid oxide fuel cell system that generates power by reacting hydrogen generated by steam reforming of fuel and an oxidant gas,
A fuel cell module having a fuel cell stack; and
A fuel supply device for supplying fuel to the fuel cell module;
A water supply device for supplying water for steam reforming to the fuel cell module;
An oxidant gas supply device for supplying an oxidant gas to the oxidant gas electrode side of the fuel cell stack;
The fuel cell module is disposed in the fuel cell module, and the fuel supplied from the fuel supply device is steam-reformed using water supplied from the water supply device, and the reformed fuel is converted into the fuel cell stack. A reformer to be supplied to the fuel electrode side;
A temperature detection sensor for detecting the temperature of the fuel cell stack;
A controller programmed to control power extraction from the fuel supply device, the water supply device, the oxidant gas supply device, and the fuel cell module;
The controller includes a shutdown stop circuit and a stop pre-processing circuit,
The shutdown stop circuit executes a shutdown stop to stop fuel supply and power generation when the fuel cell stack is at an oxidation suppression temperature or higher,
The pre-stop processing circuit is configured to perform pre-stop processing for reducing the temperature of the fuel cell stack,
The solid-state fuel cell system, wherein the pre-stop processing circuit performs pre-stop processing different depending on the temperature of the fuel cell stack before the shutdown stop.   2. The solid oxidation according to claim 1, wherein the pre-stop processing circuit reduces the amount of fuel supplied by the fuel supply device and the amount of electric power taken out from the fuel cell module during the pre-stop processing more than during power generation operation. Physical fuel cell system.   The pre-stop processing circuit increases the amount of oxidant gas supplied by the oxidant gas supply device during the pre-stop processing to be greater than the amount corresponding to the electric power extracted from the fuel cell module. The solid oxide fuel cell system according to claim 2, wherein the temperature of the battery cell stack is lowered.   4. The solid oxide fuel cell system according to claim 3, wherein the pre-stop processing circuit increases the amount of temperature decrease due to the pre-stop processing when the temperature of the fuel cell stack is high than when the temperature is low.   The solid oxide fuel cell system according to claim 4, wherein the pre-stop processing circuit does not execute the pre-stop processing when the temperature detected by the temperature detection sensor is lower than a predetermined shutdown temperature.   The pre-stop processing circuit executes the pre-stop processing when the temperature detected by the temperature detection sensor is higher than the shutdown temperature, and the pre-stop processing is continued until the detected temperature decreases to the shutdown temperature. The solid oxide fuel cell system according to claim 5, wherein the shutdown stop is performed thereafter.   The controller controls the fuel supply device so that the temperature of the fuel cell stack is within a predetermined power generation temperature range during a power generation operation for extracting power from the fuel cell module. The solid oxide fuel cell system according to claim 6, which is executed when a temperature detected by a temperature detection sensor is higher than an upper limit temperature of the power generation temperature range.   The controller includes an exhaust control circuit that performs exhaust control for discharging the gas remaining on the oxidant gas electrode side in the fuel cell module by operating the oxidant gas supply device after the shutdown is stopped. And the detected temperature is higher than the upper limit temperature of the power generation temperature range, the exhaust pre-processing is performed after the stop pre-processing circuit executes the pre-stop processing, and the detected temperature is When the temperature is within the temperature range, the exhaust control is executed without executing the stop pretreatment, and when the detected temperature is lower than the lower limit temperature of the power generation temperature range, the stop pretreatment and the exhaust are performed. The solid oxide fuel cell system according to claim 7, wherein the control is not executed.

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