JP2012094478A - Solid oxide fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid oxide fuel cell having high comprehensive energy efficiency and preventing an excessive temperature rise.SOLUTION: A solid oxide fuel cell (1) comprises a fuel cell module (2), fuel supply means (38), means (45) for supplying an oxidant gas for power generation, a heat storage material (7), and controlling means (110) for controlling the fuel supply means based on power demand so that the fuel utilization efficiency is high when generated power is high, and low when the generated power is low, and for varying actual output power after varying the amount of fuel supply. The controlling means comprises heat storage estimating means (110b) for estimating the amount of surplus heat based on the fuel supply and the power output with a delay, and reduces the amount of fuel supply so that the fuel utilization efficiency is high with respect to the same amount of generated power when the heat storage estimating means estimates that the heat storage material stores available heat.

Description

  The present invention relates to a solid oxide fuel cell, and more particularly to a solid oxide fuel cell that generates variable generated power according to demand power.

  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.

  In this SOFC, water vapor or carbon dioxide is generated by the reaction between oxygen ions that have passed through the oxide ion conductive solid electrolyte and fuel, and electric energy and thermal energy are generated. Electric energy is taken out of the SOFC and used for various electrical applications. On the other hand, thermal energy is used to raise the temperature of fuel, reformer, water, oxidant and the like.

  Japanese Unexamined Patent Application Publication No. 2010-92836 (Patent Document 1) describes a fuel cell device. This fuel cell device is a solid oxide fuel cell of a type that changes generated power according to demand power, and in a low load region where the generated power is low, a fuel utilization rate is higher than in a high load region where the generated power is large. It is disclosed that the operation is performed with reduced pressure. That is, in Patent Document 1, when the generated power is low, the ratio of the supplied fuel used for power generation is reduced, but on the other hand, it is not used for power generation but used for heating the fuel cell module. The fuel cell module is configured so that a large proportion of fuel is used to heat the fuel cell module without causing a significant decrease in the fuel generated, so that the fuel cell module is thermally self-supported and maintained at a temperature capable of generating electricity. Is.

  Specifically, in the region where the generated power is low, the heat generated in the fuel cell unit decreases with the power generation, so the temperature inside the fuel cell module tends to decrease, so the region where the generated power is low However, if a constant fuel utilization rate is maintained, the temperature inside the fuel cell module will decrease, making it difficult to maintain the temperature at which power can be generated. This makes it possible to increase the amount of fuel used to enable thermal independence.

  In the fuel cell device described in Japanese Patent Application Laid-Open No. 2010-92936, in order to solve this problem, the fuel utilization rate is lowered in a low load region where the generated power is low, and an excessive temperature drop of the fuel cell module is prevented. In this configuration, a constant high temperature state is stably maintained.

  On the other hand, Japanese Unexamined Patent Application Publication No. 2009-104886 (Patent Document 2) describes an operation method when the load of a fuel cell system is increased. In this operation method, when the power generation amount of the fuel cell system is increased, first, the air supply amount to the fuel cell is increased, and then the supply amount is increased in the order of the water supply amount and the fuel supply amount. The electric power taken out from the fuel cell is increased. In the operation method of this fuel cell system, the supply amount is increased in this order to prevent the occurrence of air depletion, carbon deposition, and fuel depletion.

  Furthermore, in general, a solid oxide fuel cell has a high operating temperature, and it is necessary to maintain the fuel cell at a high operating temperature during power generation. Therefore, in order to increase the overall energy efficiency of the fuel cell system, it is important to reduce the heat dissipated from the fuel cell to the outside air and reduce the fuel required to maintain the temperature. Become. For this reason, it is preferable to store a fuel battery cell etc. in a housing | casing with high heat insulation.

  On the other hand, Japanese Unexamined Patent Application Publication No. 2010-205670 (Patent Document 3) describes a fuel cell system and a fuel cell operation method. In this fuel cell system, an integrated value of the electric load of the fuel cell is acquired, and the fuel utilization rate is controlled based on the acquired integrated value. In the control of the fuel utilization rate, the temperature of the fuel cell is estimated based on the integral value of the electric load of the fuel cell, and the fuel utilization rate is controlled based on the estimation result. For this reason, the thermal independent operation of the fuel cell is enabled without using a temperature sensor. In addition, when the integrated value of the electric load is equal to or greater than a predetermined value, the control unit corrects the fuel utilization rate to a value equal to or greater than a reference value that allows the fuel cell to perform thermal self-sustained operation. In this case, since the temperature of the fuel cell has risen, the fuel cell has residual heat, and the thermal self-sustained operation is maintained even if the fuel utilization rate is corrected to a value equal to or higher than the reference value that allows the heat self-sustaining operation. . This improves the system efficiency of the fuel cell system.

JP 2010-92936 JP 2009-104886 A JP 2010-205670 A

  However, as described above, reducing the fuel utilization rate means increasing the amount of fuel that does not contribute to power generation even if thermal independence is achieved. There is a problem in that the overall energy efficiency of the fuel cell is reduced. Thus, the longer the operation in a state where the fuel utilization rate is lowered, the lower the overall energy efficiency. Therefore, solid oxidation generally considered to be higher in energy efficiency than a polymer membrane fuel cell (PEFC). This leads to the loss of the superiority of the physical fuel cell (SOFC).

  In particular, assuming that a solid oxide fuel cell is used for home use, the fuel cell must be used with a small amount of generated power for a predetermined time of the day, such as late at night when a householder is sleeping. This will significantly reduce the overall energy efficiency of the solid oxide fuel cell. Therefore, even in such a low power generation state, the fuel efficiency is high and the efficiency is high. An excellent technology capable of realizing operation has been desired for a solid oxide fuel cell.

  On the other hand, if the heat insulation of the housing for storing the fuel cells is increased, the remaining fuel that is supplied to the fuel cells and not used for power generation heats the inside of the housing. The problem of rising too much occurs. If the temperature in the casing rises excessively, the fuel cell in the casing, the reformer, etc. may be damaged. In addition, the excessively increased temperature is not easy to reduce to an appropriate temperature because the heat insulating property of the casing is high and the heat capacity is extremely large.

  If the fuel cell system is operated with a constant generated power, the fuel supply amount is constant so that the thermal balance is maintained under the high heat insulation conditions even when the heat insulation of the housing is high. If the amount is set, an excessive temperature rise can be avoided. However, in a fuel cell that generates variable generated power according to demand power, it is necessary to change the fuel supply amount in accordance with the generated power. In the fuel cell system for changing the generated power, as in the invention described in Japanese Patent Application Laid-Open No. 2009-104886, when the generated power is increased, the fuel supply amount is increased first, and then the fuel supply is delayed. It is necessary to increase the power extracted from the battery cell. For this reason, in the fuel cell system in which the generated power is changed, the residual fuel that does not contribute to the power generation increases when the generated power is increased or decreased, which causes an excessive temperature rise. Further, if the delay until the electric power is taken out from the fuel cell is reduced in order to reduce the residual fuel when the generated power is increased or decreased, the fuel cell is exposed to the risk of fuel depletion.

On the other hand, Japanese Patent Application Laid-Open No. 2010-205670 discloses that the fuel utilization rate is increased by using the residual heat accumulated in the fuel cell system. When excessive temperature rise occurs in the fuel cell system, a lot of residual heat is accumulated, so it is conceivable to suppress the temperature increase by increasing the fuel utilization rate and consuming the residual heat. . However, in the invention described in Japanese Patent Application Laid-Open No. 2010-205670, the accumulation of the residual heat is obtained from the integrated value of the electric load. Therefore, after the fuel supply amount is increased, the power to be taken out is delayed and increased. It is impossible to grasp the increase of the remaining fuel generated at all. Therefore, it is difficult to apply the invention described in Japanese Patent Application Laid-Open No. 2010-205670 to the suppression of excessive temperature rise caused by power delay.
Specifically, in the invention described in Japanese Patent Application Laid-Open No. 2010-205670, the generated heat (Joule heat) generated when generating power in the fuel cell is estimated based on the amount of power generation, and thereby the residual heat is estimated. . On the other hand, the heat generated by the delay in power generation of the fuel cell device is combustion heat generated by burning the remaining fuel that is not used for power generation, and is disclosed in Japanese Patent Application Laid-Open No. 2010-205670. It is not possible to estimate the amount of heat stored during the start-up process using the technology that is being used.

An object of the present invention is to provide a solid oxide fuel cell that is extremely useful in practice and can improve the overall energy efficiency while maintaining stable thermal independence.
Another object of the present invention is to provide a solid oxide fuel cell capable of preventing an excessive temperature rise while improving the overall energy efficiency.

  In order to solve the above-described problems, the present invention provides a solid oxide fuel cell that generates variable generated power according to demand power, a fuel cell module that generates power using supplied fuel, and the fuel cell. Fuel supply means for supplying fuel to the module, oxidant gas supply means for power generation for supplying oxidant gas for power generation to the fuel cell module, a heat storage material for storing heat generated in the fuel cell module, and demand power Based on the demand power detection means to be detected and the demand power detected by this demand power detection means, the fuel supply rate is high when the generated power is large, and the fuel supply rate is low when the generated power is small. In addition to controlling the means, the fuel supply amount is changed according to the change in the demand power, and then the control is performed to change the power actually output from the fuel cell module with a delay. And the control means comprises a fuel storage amount estimation means for estimating the surplus heat amount based on the fuel supply by the fuel supply means and the power output delayed with respect to the fuel supply, and this heat storage amount estimation means Therefore, when it is estimated that the amount of heat that can be used in the heat storage material is accumulated, the fuel utilization rate becomes higher for the same generated power than in the case where the amount of available heat is not accumulated. It is characterized by reducing the fuel supply amount.

  In the present invention configured as described above, the fuel supply unit and the power generation oxidant gas supply unit respectively supply the fuel and the power generation oxidant gas to the fuel cell module. The fuel cell module generates power with the supplied fuel and power generation oxidant gas, and the generated heat is accumulated in the heat storage material. Based on the demand power detected by the demand power detection means, the control means controls the fuel supply means so that the fuel utilization rate is high when the generated power is large and the fuel utilization rate is low when the generated power is small. Further, the control means changes the amount of fuel supplied in accordance with the change in demand power, and then changes the power actually output from the fuel cell module with a delay. The heat storage amount estimation means estimates the surplus heat amount based on the fuel supply by the fuel supply means and the electric power output with a delay with respect to the fuel supply. When it is estimated that the amount of heat available for the heat storage material is accumulated by the heat storage amount estimation means, the control means uses the fuel utilization rate for the same generated power as compared with the case where the amount of available heat is not accumulated. Decrease the fuel supply so that the

  In general, in a solid oxide fuel cell, when the generated power is small, the generated heat decreases, so the temperature of the fuel cell module tends to decrease. For this reason, at the time of small power generation, the fuel utilization rate is lowered, fuel that has not been used for power generation is burned, and the fuel cell module is heated to prevent an excessive temperature drop. In particular, in a solid oxide fuel cell of a type in which a reformer is disposed in a fuel cell module, an endothermic reaction occurs in the reformer, so that the temperature is more likely to decrease. According to the present invention configured as described above, when it is estimated by the heat storage amount estimation means that the amount of heat available to the heat storage material is accumulated, the fuel supply amount is reduced so that the fuel utilization rate is increased. Let Thereby, it is possible to improve the overall energy efficiency of the solid oxide fuel cell while maintaining the thermal independence of the solid oxide fuel cell and avoiding an excessive temperature drop.

  Further, according to the present invention configured as described above, since the surplus heat amount is estimated based on the fuel supply by the fuel supply means and the power output delayed with respect to the fuel supply, the control means, After the fuel supply amount is changed, the accumulated heat amount can be accurately estimated by changing the output power with a delay. For this reason, the amount of heat accumulated in the heat storage material can be fully utilized while reliably avoiding the risk of a rapid temperature drop of the fuel cell module. Furthermore, in the type of fuel cell in which the output power is changed with a delay after changing the fuel supply amount, frequent fluctuations in the output power generate a lot of surplus fuel, and the temperature in the fuel cell module rises excessively. However, according to the present invention configured as described above, it is possible to accurately grasp the heat storage by the surplus fuel generated in this way. In general, an excessive temperature rise due to surplus fuel is suppressed by introducing a cooling medium into the fuel cell module, but according to the present invention, the amount of heat due to surplus fuel can be accurately grasped, This can be effectively utilized to suppress an excessive increase in temperature. Thereby, the cooling medium input in order to reduce temperature can be decreased, and the total energy efficiency of a solid oxide fuel cell can be improved.

In the present invention, preferably, the control means increases the fuel utilization rate significantly as the heat storage amount estimated by the heat storage amount estimation means increases.
According to the present invention configured as described above, a large amount of heat storage is used when the estimated amount of heat storage is large, and less heat storage is used when the amount of heat storage is small, so heat storage is used more effectively. And the risk of temperature drop can be reliably avoided.

In the present invention, it is preferable that the control unit significantly increases the fuel utilization rate with respect to the change of the estimated heat storage amount in the region where the estimated heat storage amount estimated by the heat storage amount estimation unit is large than in the region where the estimated heat storage amount is small. To change.
According to the present invention configured as described above, when the estimated heat storage amount is large, a large amount of heat storage is used to avoid excessive temperature rise, and when the estimated heat storage amount is small, the heat storage is little by little. Can be used to prevent overcooling.

In the present invention, preferably, the heat storage amount estimation means estimates the heat storage amount by integrating the addition / subtraction values reflecting the surplus heat amount due to the output of electric power delayed with respect to the fuel supply.
According to the present invention configured as described above, since the heat storage amount is estimated by integrating the addition / subtraction values reflecting the surplus heat amount, it is possible to accurately estimate the heat storage amount by accumulating the generated surplus heat amount. it can.

In the present invention, preferably, the addition / subtraction value is based on the temperature in the fuel cell module, the amount of surplus heat calculated from the relationship between the fuel supply amount and the generated power, the increase / decrease amount of the generated power, or the number of increases / decreases in the generated power per time. Can be decided.
According to the present invention configured as described above, the temperature in the fuel cell module, the amount of surplus heat calculated from the relationship between the fuel supply amount and the generated power, the increase / decrease amount of the generated power, or the increase / decrease number of the generated power per time Since the addition / subtraction value is determined based on this, the heat storage generated by delaying the generated power can be accurately estimated.

In the present invention, it is preferable that the control unit is configured to perform predetermined intermediate power generation so that the heat stored in the large power generation can be used in the small power generation when the heat storage available in the heat storage material is not stored. The fuel supply means is controlled so that a larger amount of heat is accumulated in the heat storage material in a region larger than electric power.
According to the present invention configured as described above, since a larger amount of heat is accumulated in the heat storage material in a region larger than the middle power generation power, it is positive in a region larger than the middle power generation power that can increase the fuel utilization rate. High efficiency of fuel utilization that effectively uses the amount of heat stored by consuming heat at low power generation, where the temperature of the fuel cell module is relatively low and heat independence is difficult Can be performed reliably.

In the present invention, preferably, the control means controls the fuel supply means so that a larger amount of heat is accumulated in the heat storage material in a region where the generated power is larger than the median value of the generated power range.
According to the present invention configured as described above, a larger amount of heat is accumulated in the heat storage material in a region where the generated power is larger than the median value of the generated power range. For this reason, in the vicinity of the median value of the frequently used power generation range, the amount of surplus heat accumulated is suppressed, and a large amount of heat is accumulated in the heat storage material at the peak of power demand. As a result, when a solid oxide fuel cell is used in a house, excessive fuel consumption to store a large amount of heat is suppressed in the time zone where the most frequent power demand is at moderate power demand such as daytime. On the other hand, since it can be configured so that a large amount of heat is accumulated during the nighttime hours when power demand peaks, the amount of heat stored in the nighttime hours can be consumed immediately at midnight in the following time zone Therefore, it is possible to realize high-efficiency operation that effectively uses the heat that is reliably stored in the late-night time when the generated power is greatly reduced while the amount of heat is not stored unnecessarily for a long time.

In the present invention, preferably, the control unit increases the fuel utilization rate when the heat storage amount estimated by the heat storage amount estimation unit is equal to or greater than a predetermined change execution heat storage amount.
According to the present invention configured as described above, since the heat storage amount of the heat storage material is estimated by the heat storage amount estimation means, it is possible to change the fuel utilization rate safely, and the estimated heat storage amount is a predetermined change. Since change is performed when it is more than the amount of execution heat storage, excessive cooling can be prevented more reliably.

In the present invention, preferably, the control means determines a predetermined change execution period based on the heat storage amount estimated by the heat storage amount estimation means at the start of the high-efficiency control with an increased fuel utilization rate. Execute high-efficiency control.
According to the present invention configured as described above, since the change is executed within the change execution period determined based on the heat storage amount estimated by the heat storage amount estimation means, high efficiency using heat storage with simpler control. Control can be realized.

In the present invention, preferably, there is further provided a change period extending means for suppressing a decrease in the heat storage amount of the heat storage material and extending a period for executing the high efficiency control during execution of the high efficiency control with an increased fuel utilization rate. .
According to the present invention configured as described above, since the change period extending means for extending the period for executing the high-efficiency control is provided, the accumulated heat amount can be effectively used according to the situation.

In the present invention, preferably, the change period extending means decreases the change amount for increasing the fuel utilization rate as the period of executing the high efficiency control becomes longer as the heat storage amount of the heat storage material decreases.
According to the present invention configured as described above, the amount of change in high-efficiency control is reduced with a decrease in the amount of heat storage, so that an excessive temperature drop of the fuel cell module and performance deterioration are not caused. The period for increasing the fuel utilization rate can be extended.

In the present invention, preferably, the change period extending means decreases the change amount that increases the fuel utilization rate as the generated power is smaller.
According to the present invention configured as described above, since the amount of change in high-efficiency control is reduced as the generated power is small, the amount of change is small at the time of small generated power when the amount of heat storage is increased. It is possible to extend the period during which the fuel utilization rate is increased while reliably avoiding excessive module temperature drop and performance degradation.

In the present invention, preferably, the change period extension means controls the power generation oxidant gas supply means so as to decrease the power generation oxidant gas supplied to the fuel cell module during execution of the high efficiency control.
According to the present invention configured as described above, the oxidant gas for power generation supplied to the fuel cell module is reduced during execution of the change, so that the amount of heat accumulated in the heat storage material is taken away by the oxidant gas. The heat storage can be effectively used for a longer time.

In the present invention, it is preferable that there is further provided an overcooling prevention means for preventing overcooling of the fuel cell module when the heat storage amount of the heat storage material is small.
According to the present invention configured as described above, since the excessive cooling preventing means is provided, it is possible to reliably prevent excessive cooling by increasing the fuel utilization rate in a state where the heat storage amount is reduced.

In the present invention, preferably, the overcooling prevention means improves the followability of the fuel supply amount by the fuel supply means more than the followability during normal operation during execution of high efficiency control with an increased fuel utilization rate.
According to the present invention configured as described above, the followability of the fuel supply amount during the period when the high-efficiency control is being performed is improved, so that the fuel utilization rate after the change is reduced as the heat storage amount decreases. As you go, you can quickly increase the fuel supply. Thereby, it is possible to prevent overcooling of the fuel cell module due to a delay in response to increase the fuel supply amount.

According to the solid oxide fuel cell of the present invention, it is possible to improve the overall energy efficiency while stably operating while maintaining thermal independence.
Moreover, according to the solid oxide fuel cell of the present invention, it is possible to prevent an excessive temperature rise while enhancing the overall energy efficiency.

1 is an overall configuration diagram showing a fuel cell device according to an embodiment of the present invention. It is front sectional drawing which shows the fuel cell module of the fuel cell apparatus by one Embodiment of this 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 fuel cell device by one embodiment of the present invention. It is a perspective view which shows the fuel cell stack of the fuel cell apparatus by one Embodiment of this invention. 1 is a block diagram showing a fuel cell device according to an embodiment of the present invention. It is a time chart which shows the operation | movement at the time of starting of the fuel cell apparatus by one Embodiment of this invention. It is a time chart which shows the operation | movement at the time of the stop of the fuel cell apparatus by one Embodiment of this invention. It is a graph which shows the relationship between the output electric current and fuel supply amount in the solid oxide fuel cell of 1st Embodiment of this invention. It is a graph which shows the relationship between the output electric current in the solid oxide fuel cell of 1st Embodiment of this invention, and the calorie | heat amount which generate | occur | produces with the supplied fuel. It is a control flowchart of the fuel supply amount in the solid oxide fuel cell of 1st Embodiment of this invention. It is a heat storage amount estimation table used in order to estimate the heat amount stored in the heat insulating material in the solid oxide fuel cell according to the first embodiment of the present invention. 13 is a graph of the heat storage amount estimation table of FIG. It is a graph which shows the value of the 1st correction coefficient with respect to the output current in the solid oxide fuel cell of 1st Embodiment of this invention. It is a graph which shows the value of the 2nd correction coefficient with respect to the output current in the solid oxide fuel cell of 1st Embodiment of this invention. It is a flowchart for changing the correction amount when the fuel cell module is deteriorated. It is a figure which shows typically the transition of the daily demand electric power in a general house, and the transition of the calorie | heat amount accumulate | stored in a heat insulating material. It is a graph which shows the electric current correction coefficient in the modification of 1st Embodiment of this invention. It is the graph which showed typically the relation of the change of demand electric power, the amount of fuel supply, and the current actually taken out from a fuel cell module. It is the graph which showed an example of the relationship of the electric current actually taken out from the air supply amount for power generation, the water supply amount, the fuel supply amount, and the fuel cell module. It is a flowchart which shows the procedure which determines the air supply amount for electric power generation, the water supply amount, and the fuel supply amount based on detection temperature Td. It is a graph which shows the temperature of the appropriate fuel cell stack with respect to a generated electric current. It is a graph which shows the fuel usage rate determined according to an integrated value. It is a graph which shows the range of the value of the fuel utilization factor which can be determined with respect to each generated electric current. It is a graph which shows the air utilization factor determined according to an integrated value. It is a graph which shows the range of the value of the air utilization factor which can be determined with respect to each generated electric current. It is a graph for determining water supply with respect to the determined air utilization rate. It is a graph which shows the electric power generation voltage of the fuel cell module appropriate with respect to electric power generation current. In 2nd Embodiment of this invention, it is a flowchart which shows the procedure which restrict | limits the range of the electric power which a fuel cell module produces | generates. It is a map which shows the electric current limitation with respect to a generated electric current and detected temperature. It is a time chart which shows an example of the effect | action in 2nd Embodiment of this invention. It is a graph which shows an example of the relationship between the temperature in a fuel cell module, and the maximum electric power which can be generated. It is a flowchart which shows the procedure which calculates a 1st addition / subtraction value based on the detection temperature of a some temperature sensor. It is a flowchart which shows the calculation procedure of the addition / subtraction value by the modification of 2nd Embodiment of this invention. It is a flowchart which shows the calculation procedure of the addition / subtraction value by the modification of 2nd Embodiment of this invention.

Next, a solid oxide fuel cell (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 (SOFC) according to an embodiment of the present invention. As shown in FIG. 1, a solid oxide fuel cell (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 sealed space 8 is formed inside the housing 6 via a heat insulating material 7. A fuel cell assembly 12 that performs a power generation reaction with fuel gas and an oxidant (air) is disposed in a power generation chamber 10 that is a lower portion of the sealed space 8. 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 is formed above the above-described power generation chamber 10 in the sealed space 8 of the fuel cell module 2. In this combustion chamber 18, the remaining fuel gas that has not been used for the power generation reaction and the remaining oxidant (air) ) And combusted to generate exhaust gas.
Further, a reformer 20 for reforming the fuel gas 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. ing. Further, an air heat exchanger 22 is disposed above the reformer 20 to heat the air by receiving heat from the reformer 20 and suppress a temperature drop of the reformer 20.

  Next, the auxiliary unit 4 stores a pure water tank 26 that stores water from a water supply source 24 such as tap water and uses the filter to obtain pure water, and a water flow rate that adjusts the flow rate of the water supplied from the water storage tank. An adjustment unit 28 (such as a “water pump” driven by a motor) is provided. The auxiliary unit 4 also includes a gas shut-off valve 32 that shuts off the fuel gas supplied from a fuel supply source 30 such as city gas, a desulfurizer 36 for removing sulfur from the fuel gas, and a flow rate of the fuel gas. A fuel flow rate adjusting unit 38 (such as a “fuel pump” driven by a motor) is provided. Further, the auxiliary unit 4 includes an electromagnetic valve 42 that shuts off air that is an oxidant supplied from the 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 adjusting 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 second for heating the power generating air supplied to the power generation chamber And a heater 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 a solid oxide fuel cell (SOFC) fuel cell module according to an embodiment of the present invention will be described with reference to FIGS. FIG. 2 is a side sectional view showing a solid oxide fuel cell (SOFC) fuel cell module according to an embodiment of the present invention, and FIG. 3 is a sectional view taken along line III-III in FIG. .
As shown in FIGS. 2 and 3, in the sealed space 8 in the housing 6 of the fuel cell module 2, as described above, the fuel cell assembly 12, the reformer 20, and the air heat exchange are sequentially performed from below. A vessel 22 is arranged.

  The reformer 20 is provided with a pure water introduction pipe 60 for introducing pure water and a reformed gas introduction pipe 62 for introducing reformed fuel gas and reforming air to the upstream end side thereof. In the reformer 20, an evaporator 20a and a reformer 20b are formed in this order from the upstream side, and the evaporator 20a and the reformer 20b are 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.

  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.

  Next, an air heat exchanger 22 is provided above the reformer 20. The air heat exchanger 22 includes an air aggregation chamber 70 on the upstream side and two air distribution chambers 72 on the downstream side. The air aggregation chamber 70 and the air distribution chamber 72 include six air flow path tubes 74. Connected by. Here, as shown in FIG. 3, three air flow path pipes 74 form a set (74a, 74b, 74c, 74d, 74e, 74f), and the air in the air collecting chamber 70 is in each set. It flows into each air distribution chamber 72 from the air flow path pipe 74.

The air flowing through the six air flow path pipes 74 of the air heat exchanger 22 is preheated by exhaust gas that burns and rises in the combustion chamber 18.
An air introduction pipe 76 is connected to each of the air distribution chambers 72, the air introduction pipe 76 extends downward, and the lower end side communicates with the lower space of the power generation chamber 10, and the air that has been preheated in the power generation chamber 10. Is introduced.

Next, an exhaust gas chamber 78 is formed below the manifold 66. Further, as shown in FIG. 3, an exhaust gas passage 80 extending in the vertical direction is formed inside the front surface 6 a and the rear surface 6 b which are surfaces along the longitudinal direction of the housing 6, and the upper end of the exhaust gas chamber passage 80 is formed. The side communicates with the space in which the air heat exchanger 22 is disposed, and the lower end side communicates with the exhaust gas chamber 78. Further, an exhaust gas discharge pipe 82 is connected to substantially the center of the lower surface of the exhaust gas chamber 78, and the downstream end of the exhaust gas discharge pipe 82 is connected to the above-described hot water producing apparatus 50 shown in FIG.
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 sectional view showing a fuel cell unit of a solid oxide fuel cell (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 respectively connected to the vertical 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 16 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. A fuel gas passage 98 communicating with the fuel gas passage 88 of the inner electrode layer 90 is formed at the center of the inner electrode terminal 86.

  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 (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 the lower end side and the upper end side of these fuel cell units 16 are a ceramic lower support plate 68 and an upper side, respectively. It is supported by the support plate 100. The lower support plate 68 and the upper support plate 100 are formed with through holes 68a and 100a 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 entire outer peripheral surface of the outer electrode layer 92 that is an air electrode. And an air electrode connecting portion 102b electrically connected to each other. The air electrode connecting portion 102b is formed of a vertical portion 102c extending in the vertical direction on the surface of the outer electrode layer 92 and a plurality of horizontal portions 102d extending in a horizontal direction along the surface of the outer electrode layer 92 from the vertical portion 102c. Has been. The fuel electrode connection portion 102a is linearly directed obliquely upward or obliquely downward from the vertical portion 102c of the air electrode connection portion 102b toward the inner electrode terminal 86 positioned in the vertical direction of the fuel cell unit 16. It extends.

  Further, the inner electrode terminals 86 at the upper end and the lower end of the two fuel cell units 16 located at the ends of the fuel cell stack 14 (the far left side and the near side in FIG. 5) are external terminals, respectively. 104 is connected. These external terminals 104 are connected to the external terminals 104 (not shown) of the fuel cell unit 16 at the end of the adjacent fuel cell stack 14, and as described above, the 160 fuel cell units 16 Everything is connected in series.

Next, sensors and the like attached to the solid oxide fuel cell (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 (SOFC) according to an embodiment of the present invention.
As shown in FIG. 6, the solid oxide fuel cell 1 includes a control unit 110, and the control unit 110 includes operation buttons such as “ON” and “OFF” for operation by the user. An 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. 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 current and voltage of the inverter 54 and the distribution board (not shown).
The power generation air flow rate detection sensor 128 is for detecting the flow rate of power generation air supplied to the power generation chamber 10.
The reforming air flow 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 (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 operation at the time of start-up by the solid oxide fuel cell (SOFC) according to the present embodiment will be described with reference to FIG. FIG. 7 is a time chart showing the operation at the start-up of the solid oxide fuel cell (SOFC) according to the embodiment of the present invention.
Initially, in order to warm the fuel cell module 2, the operation is started in a no-load state, that is, in a state where a circuit including the fuel cell module 2 is opened. At this time, since no current flows through the circuit, the fuel cell module 2 does not generate power.

First, reforming air is supplied from the reforming air flow rate adjustment unit 44 to the reformer 20 of the fuel cell module 2 via the first heater 46. At the same time, the power generation air is supplied from the power generation air flow rate adjustment unit 45 to the air heat exchanger 22 of the fuel cell module 2 via the second heater 48, and this power generation air is supplied to the power generation chamber 10 and the combustion chamber. Reach chamber 18.
Immediately after this, the fuel gas is also supplied from the fuel flow rate adjustment unit 38, and the fuel gas mixed with the reforming air passes through the reformer 20, the fuel cell stack 14, and the fuel cell unit 16, and It reaches the combustion chamber 18.

  Next, the ignition device 83 is ignited to burn the fuel gas and air (reforming air and power generation air) in the combustion chamber 18. Exhaust gas is generated by the combustion of the fuel gas and air, and the power generation chamber 10 is warmed by the exhaust gas, and when the exhaust gas rises in the sealed space 8 of the fuel cell module 2, The fuel gas containing the reforming air is warmed, and the power generation air in the air heat exchanger 22 is also warmed.

  At this time, the fuel gas mixed with the reforming air is supplied to the reformer 20 by the fuel flow rate adjusting unit 38 and the reforming air flow rate adjusting unit 44. The partial oxidation reforming reaction POX shown in FIG. Since the partial oxidation reforming reaction POX is an exothermic reaction, the startability is good. Further, the heated fuel gas is supplied to the lower side of the fuel cell stack 14 through the fuel gas supply pipe 64, whereby the fuel cell stack 14 is heated from below, and the combustion chamber 18 also has the fuel gas and air. The fuel cell stack 14 is also heated from above, and as a result, the fuel cell stack 14 can be heated substantially uniformly in the vertical direction. Even if the partial oxidation reforming reaction POX proceeds, the combustion reaction between the fuel gas and air continues in the combustion chamber 18.

_{C m H n + xO 2 →} aCO 2 + bCO + cH 2 (1)

  When the reformer temperature sensor 148 detects that the reformer 20 has reached a predetermined temperature (for example, 600 ° C.) after the partial oxidation reforming reaction POX is started, the water flow rate adjustment unit 28 and the fuel flow rate adjustment unit 38 are detected. In addition, the reforming air flow rate adjusting unit 44 supplies a gas in which fuel gas, reforming air, and water vapor are mixed in advance to the reformer 20. At this time, in the reformer 20, an autothermal reforming reaction ATR in which the partial oxidation reforming reaction POX described above and a steam reforming reaction SR described later are used proceeds. Since the autothermal reforming reaction ATR is thermally balanced internally, the reaction proceeds in the reformer 20 in a thermally independent state. That is, when oxygen (air) is large, heat generation by the partial oxidation reforming reaction POX is dominant, and when there is much steam, an endothermic reaction by the steam reforming reaction SR is dominant. At this stage, the initial stage of startup has already passed, and the temperature inside the power generation chamber 10 has been raised to a certain temperature. Therefore, even if the endothermic reaction is dominant, no significant temperature drop is caused. Further, the combustion reaction continues in the combustion chamber 18 even while the autothermal reforming reaction ATR is in progress.

  When the reformer temperature sensor 146 detects that the reformer 20 has reached a predetermined temperature (for example, 700 ° C.) after the start of the autothermal reforming reaction ATR shown in Formula (2), the reforming air flow rate The supply of reforming air by the adjustment unit 44 is stopped, and the supply of water vapor by the water flow rate adjustment unit 28 is increased. As a result, the reformer 20 is supplied with a gas that does not contain air and contains only fuel gas and water vapor, and the steam reforming reaction SR of formula (3) proceeds in the reformer 20.

_{C m H n + xO 2 +} yH 2 O → aCO 2 + bCO + cH 2 (2)
C _m H _n + xH ₂ O → aCO ₂ + bCO + cH ₂ (3)

  Since the steam reforming reaction SR is an endothermic reaction, the reaction proceeds while maintaining a heat balance with the combustion heat from the combustion chamber 18. At this stage, since the fuel cell module 2 is in the final stage of start-up, the power generation chamber 10 is heated to a sufficiently high temperature. Therefore, even if the endothermic reaction proceeds, the power generation chamber 10 is greatly reduced in temperature. There is nothing. Even if the steam reforming reaction SR proceeds, the combustion reaction continues in the combustion chamber 18.

  In this way, after the fuel cell module 2 is ignited by the ignition device 83, the partial oxidation reforming reaction POX, the autothermal reforming reaction ATR, and the steam reforming reaction SR proceed in sequence, so that the inside of the power generation chamber 10 The temperature gradually increases. Next, when the temperature in the power generation chamber 10 and the fuel cell 84 reaches a predetermined power generation temperature lower than the rated temperature at which the fuel cell module 2 is stably operated, the circuit including the fuel cell module 2 is closed, and the fuel cell Power generation by the module 2 is started, so that a current flows in the circuit. Due to the power generation of the fuel cell module 2, the fuel cell 84 itself also generates heat, and the temperature of the fuel cell 84 also rises. As a result, the rated temperature at which the fuel cell module 2 is operated becomes, for example, 600 ° C. to 800 ° C.

  Thereafter, in order to maintain the rated temperature, more fuel gas and air than the amount of fuel gas and air consumed in the fuel cell 84 are supplied, and combustion in the combustion chamber 18 is continued. During power generation, power generation proceeds in a steam reforming reaction SR with high reforming efficiency.

Next, the operation when the operation of the solid oxide fuel cell (SOFC) according to the present embodiment is stopped will be described with reference to FIG. FIG. 8 is a time chart showing the operation when the solid oxide fuel cell (SOFC) is stopped according to this embodiment.
As shown in FIG. 8, when the operation of the fuel cell module 2 is stopped, first, the fuel flow rate adjustment unit 38 and the water flow rate adjustment unit 28 are operated to supply fuel gas and water vapor to the reformer 20. Reduce the amount.

  Further, when the operation of the fuel cell module 2 is stopped, the amount of fuel gas and water vapor supplied to the reformer 20 is reduced, and at the same time, the fuel cell module for generating air by the reforming air flow rate adjusting unit 44 The supply amount into 2 is increased, the fuel cell assembly 12 and the reformer 20 are cooled by air, and these temperatures are lowered. Thereafter, when the temperature of the reformer 20 decreases to a predetermined temperature, for example, 400 ° C., the supply of fuel gas and steam to the reformer 20 is stopped, and the steam reforming reaction SR of the reformer 20 is ended. . This supply of power generation air continues until the temperature of the reformer 20 decreases to a predetermined temperature, for example, 200 ° C., and when this temperature is reached, the power generation air from the power generation air flow rate adjustment unit 45 is supplied. Stop supplying.

  As described above, in the present embodiment, when the operation of the fuel cell module 2 is stopped, the steam reforming reaction SR by the reformer 20 and the cooling by the power generation air are used in combination. The operation of the fuel cell module can be stopped.

Next, control of the solid oxide fuel cell 1 according to the first embodiment of the present invention will be described with reference to FIGS. 9 to 17.
FIG. 9 is a graph showing the relationship between the output current and the fuel supply amount in the solid oxide fuel cell 1 of the present embodiment. FIG. 10 is a graph showing the relationship between the output current in the solid oxide fuel cell 1 and the amount of heat generated by the supplied fuel.

  First, as shown by the solid line in FIG. 9, the solid oxide fuel cell 1 of the present embodiment is configured such that the output can be varied within 700 W (output current 7 A), which is the rated output power, according to the demand power. Has been. The fuel supply amount (L / min) required to output the required power is set as a basic fuel supply table indicated by a solid line in FIG. The control unit 110 serving as the control means determines the fuel supply amount based on the basic fuel supply table in accordance with the demand power detected by the power state detection sensor 126 serving as the demand power detection means, and supplies the fuel based on this. It is configured to control the fuel flow rate adjusting unit 38 as a means.

  The amount of fuel required for power generation is proportional to the output power (output current), but as shown by the solid line in FIG. 9, the fuel supply amount set in the basic fuel supply table is not proportional to the output current. This is because if the fuel supply amount is reduced in proportion to the output power, the fuel cell unit 16 in the fuel cell module 2 cannot be maintained at a temperature at which power can be generated. For this reason, in the present embodiment, the basic fuel supply table is set to a fuel utilization rate of about 70% when the generated power is near the output current 7A, and is set to about 50% when the generated power is about 2A. Is set. In this way, the fuel utilization rate in the small power generation region is reduced, the fuel not used for power generation is burned and used to heat the reformer 20, etc., thereby suppressing the temperature drop of the fuel cell unit 16 In addition, the inside of the fuel cell module 2 is maintained at a temperature capable of generating power.

  However, since the fuel that does not contribute to power generation is increased by reducing the fuel utilization rate, the energy efficiency of the solid oxide fuel cell 1 in the small power generation region is reduced. In the solid oxide fuel cell 1 of the present embodiment, the fuel table changing means 110a (FIG. 6) built in the control unit 110 sets the fuel supply amount set in the basic fuel supply table according to a predetermined condition. By changing / correcting, the fuel supply amount is decreased as shown in the broken line in FIG. 9, and the fuel utilization rate in the small power generation region is increased. Thereby, the energy efficiency of the solid oxide fuel cell 1 is improved.

  FIG. 10 is a graph schematically showing the relationship between the output current and the amount of heat of the supplied fuel when the fuel is supplied based on the basic fuel supply table in the solid oxide fuel cell 1 of the present embodiment. is there. As shown by the one-dot chain line in FIG. 10, the amount of heat necessary to make the fuel cell module 2 thermally independent and operate stably increases monotonically with an increase in output current. A graph indicated by a solid line in FIG. 10 indicates the amount of heat when fuel is supplied according to the basic fuel supply table. In the present embodiment, in a region lower than the output current 5A corresponding to the medium generated power, the required amount of heat indicated by the alternate long and short dash line and the amount of heat supplied based on the basic fuel supply table indicated by the solid line substantially coincide.

  Further, in a region higher than the output current 5A, the amount of heat indicated by the solid line supplied in accordance with the basic fuel supply table exceeds the amount of heat indicated by the one-dot chain line necessary for heat self-sustainment. The surplus heat amount between the solid line and the broken line is accumulated in the heat insulating material 7 that is a heat storage material provided in the fuel cell module 2. Further, the output current from the solid oxide fuel cell 1 is correlated with the temperature of the fuel cell unit 16 in the fuel cell module 2 when this current is constantly output, and the output current is increased. In order to do so, it is necessary to increase the temperature of the fuel cell unit 16, and therefore the temperature of the fuel cell unit 16 is high when the output current is large. In the present embodiment, the output current 5A corresponds to about 633 ° C. which is the heat storage temperature Th. Therefore, in the solid oxide fuel cell 1 of the present embodiment, a larger amount of heat is accumulated in the heat insulating material 7 when the output current is 5 A and the heat storage temperature Th is about 633 ° C. or higher.

  This heat storage temperature Th is set to a temperature corresponding to 500 W (output current 5 A) that is larger than 350 W, which is the median value of 0 W to 700 W that is the generated power range. In the region where the output current is 5 A or less, the amount of heat supplied based on the basic fuel supply table is substantially the same as the minimum amount of heat necessary for heat self-sustainment (the amount of heat of the basic fuel supply table is slightly larger). Is set. For this reason, as shown by an example of the broken line in FIG. 10, when the fuel supply amount by the basic fuel supply table is corrected and the fuel supply amount is reduced, the amount of heat necessary for thermal independence is insufficient.

  In the present embodiment, as will be described later, in a region where the generated power is small, the fuel supply rate set in the basic fuel supply table is corrected so as to be temporarily reduced to improve the fuel utilization rate. On the other hand, the amount of heat that is deficient by reducing the fuel supply amount of the basic fuel supply table uses the amount of heat accumulated in the heat insulating material 7 while the fuel cell module 2 is operated in a region higher than the heat storage temperature Th. And replenished. In this embodiment, since the heat capacity of the heat insulating material 7 is very large, the heat insulating material is operated when the fuel cell module 2 is operated in a region where the generated power is small after being operated for a predetermined time with large generated power. The amount of heat stored in 7 can be used for 2 hours or more, and the fuel utilization rate is improved by performing correction to reduce the fuel supply amount during this period.

  In the present embodiment, the basic fuel supply table is set so that more heat is accumulated in the heat insulating material 7 when the output current is 5A and the heat storage temperature Th is about 633 ° C. or higher. Even in the region where the current is 5 A or more, the basic fuel supply table can be set to be substantially the same as the minimum amount of heat necessary for heat self-sustainment (the amount of heat of the basic fuel supply table is slightly larger). That is, in the region where the generated power is large, the operating temperature of the fuel cell module 2 is higher than when the generated power is small, so even if the fuel supply amount is set to the minimum heat amount necessary for heat self-sustaining, The amount of heat available at the time of small power generation can be stored in the heat insulating material 7. As in this embodiment, by actively setting a large amount of fuel supply at the time of large power generation, the amount of heat necessary for the heat insulating material 7 can be reliably accumulated in a short period of time during the night when power demand peaks. be able to.

Next, specific control of the solid oxide fuel cell 1 according to the first embodiment of the present invention will be described with reference to FIGS. 11 to 17.
FIG. 11 is a control flowchart of the fuel supply amount in the present embodiment. FIG. 12 is a heat storage amount estimation table used for estimating the amount of heat accumulated in the heat insulating material 7. FIG. 13 is a graph of the heat storage amount estimation table. FIG. 14 is a graph showing the value of the first correction coefficient with respect to the output current. FIG. 15 is a graph showing the value of the second correction coefficient with respect to the output current.

  The flowchart shown in FIG. 11 is executed at predetermined time intervals in the control unit 110 during the power generation operation of the solid oxide fuel cell 1. First, in step S1 of FIG. 11, an integration process is performed based on the heat storage amount estimation table shown in FIG. As will be described later, the integrated value Ni calculated in step S1 is a value serving as an index of the available heat storage amount accumulated in the heat insulating material 7 and the like, and takes a value between 0 and 1.

  Next, in step S2, it is determined whether or not the integrated value Ni calculated in step S1 is zero. If the integrated value Ni is 0, the process proceeds to step S3, and if it is not 0, the process proceeds to step S4.

  When the integrated value Ni is 0, it is presumed that the heat quantity is not accumulated in the heat insulating material 7 or the like so that it can be used. Therefore, in step S3, the control unit 110 sets the fuel supply amount to the basic fuel. Determined based on supply table. The controller 110 sends a signal to the fuel flow rate adjustment unit 38 to supply the determined fuel supply amount to the fuel cell module 2. Therefore, in this case, even if the generated power is small, correction for increasing the fuel utilization rate is not executed. After step S3, one process of the flowchart shown in FIG. 11 is terminated.

  On the other hand, in step S4, the usage rate change amount with respect to the fuel supply amount determined by the basic fuel supply table is determined based on the integrated value Ni. That is, when the integrated value Ni is 1, the fuel supply amount is reduced most greatly, the fuel utilization rate is improved, and the reduction amount of the fuel supply amount is reduced as the integrated value Ni is smaller.

  Next, in step S5, the first correction coefficient is determined based on the graph shown in FIG. As shown in FIG. 14, the first correction coefficient is 1 in a region where the output current is small, and becomes 0 when the output current exceeds 4.5A. That is, in the region where the generated power is small, correction is made to reduce the amount of fuel supply using the amount of heat accumulated in the heat insulating material 7 to improve the fuel utilization rate, while in the region where the generated power is large, the correction is performed. Not executed. This is because in the region where the generated power is large, operation with a sufficiently high fuel utilization rate is possible even with the basic fuel supply table, and since the temperature in the fuel cell module 2 is high at the time of large generated power, the heat insulating material 7 This is because it is difficult to use heat storage.

Next, in step S6, the second correction coefficient is determined based on the graph shown in FIG. As shown in FIG. 15, the second correction coefficient is 0.5 in the region where the output current is 1 A or less, increases linearly in the region where the output current is 1 to 1.5 A, and the output current is 1. It becomes 1 in the area of 5A or more. That is, in the region where the generated power is 150 W or less, which is the utilization rate restrained power generation amount, the absolute value of the fuel supply amount based on the basic fuel supply table is small. This is because the battery cell unit 16 may be damaged. Further, by keeping the correction amount of the basic fuel supply table small, the amount of heat accumulated in the heat insulating material 7 can be used little by little, and heat storage can be used for a long time. Therefore, the second correction coefficient functions as a change period extending means for reducing the correction amount of the basic fuel supply table as the generated power is smaller, and extending the period for changing and correcting the basic fuel supply table. This change period extending means uses the amount of heat accumulated in the heat insulating material 7 after the correction of the basic fuel supply table is started, so that the amount of stored heat gradually decreases as the period of executing the correction becomes longer. When the amount of stored heat decreases, the correction amount of the fuel utilization rate decreases, so that the period in which the stored heat can be used is further extended.
As a modification, the correction amount using the second correction coefficient may not be corrected.

  Next, in step S7, the usage rate change amount determined in step S4 is multiplied by the first correction coefficient determined in step S5 and the second correction coefficient determined in step S6 to obtain a final usage rate. Determine the amount of change. Further, the correction amount of the water supply amount is determined corresponding to the determined fuel supply amount, and the power generation air supply amount is reduced by 10% with respect to the normal air supply amount. In addition, the control gain of the fuel supply amount is increased by 10% with respect to the control gain during normal operation, and the followability when changing the fuel supply amount is improved.

  In this way, by increasing the control gain of the fuel supply amount when executing the correction of the basic fuel supply table and setting the fuel supply amount followability high, the estimated heat storage amount decreases. When the corrected fuel utilization rate is reduced (the fuel supply amount is increased), the fuel supply amount can be quickly increased. As a result, excessive cooling of the fuel cell module 2 due to a delay in response to increase the fuel supply amount is prevented. Therefore, the control for increasing the control gain in step S7 acts as an excessive cooling preventing means. In addition, by reducing the amount of secondary air for power generation by 10%, cooling into the fuel cell module 2 such as a cell or a reformer can be suppressed, so it is possible to effectively use the heat storage while suppressing a decrease in the heat storage amount. It becomes. Therefore, the control for reducing the amount of the next air by 10% also acts as an excessive cooling preventing means.

  In step S8, the control unit 110 sends a signal to the fuel flow rate adjustment unit 38, the water flow rate adjustment unit 28, and the power generation air flow rate adjustment unit 45, and supplies the amount of fuel, water, and power generation air determined in step S7. The fuel cell module 2 is supplied. After step S8, one process of the flowchart shown in FIG. 11 is terminated. Further, when the integrated value Ni decreases to 0 by executing the correction of the basic fuel supply table, the process shifts from step S2 to step S3 again. Thereby, the correction of the basic fuel supply table is completed, and the control of the fuel supply amount based on the basic fuel supply table is executed again.

Next, with reference to FIG.12 and FIG.13, estimation of the heat storage amount accumulate | stored in the heat insulating material 7 grade | etc., Is demonstrated.
The estimation of the heat storage amount is executed by the heat storage amount estimation means 110b (FIG. 6) built in the control unit 110. When step S1 of the flowchart shown in FIG. 11 is executed, the heat storage amount estimation unit 110b reads the temperature of the power generation chamber from the power generation chamber temperature sensor 142 which is a temperature detection unit. Next, the heat storage amount estimation means 110b refers to the heat storage amount estimation table shown in FIG. 12 based on the detected temperature Td of the power generation chamber temperature sensor 142, and determines an addition / subtraction value. For example, when the detected temperature Td is 645 ° C., the added value is determined to be 1 / 50,000, and this value is added to the integrated value Ni. Such integration is performed at predetermined time intervals after the solid oxide fuel cell 1 is started. In the present embodiment, since the flowchart shown in FIG. 11 is executed every 0.5 sec, the integration is executed once every 0.5 sec. For this reason, for example, when the detected temperature Td is constant at 645 ° C., the value of 1/50000 is integrated once every 0.5 sec, and the integrated value Ni increases.

  Such an integrated value Ni reflects the temperature history in the fuel cell module 2 and the power generation chamber 10, and is a value that serves as an index indicating the degree of heat storage accumulated in the heat insulating material 7 and the like. This integrated value Ni is limited to a range of 0 to 1. When the integrated value Ni reaches 1, the value is held at 1 until the next subtraction is performed, and the integrated value Ni is decreased to 0. If so, the value is held at 0 until the next addition. In the present specification, it is assumed that a value serving as an index indicating the degree of the heat storage amount is an estimated value of the heat storage amount, like the integrated value Ni in the present embodiment. Therefore, in this embodiment, the heat storage amount is estimated based on the temperature of the fuel cell module 2.

  The utilization rate change amount for the basic fuel supply table calculated in step S4 of the flowchart shown in FIG. 11 is determined by multiplying the integrated value Ni by a predetermined correction amount. Therefore, the correction amount increases as the integrated value Ni, which is an estimated value of the heat storage amount, increases. When the integrated value Ni is 1, the utilization rate change amount becomes maximum, and when the integrated value Ni is 0, no correction is performed (utilization rate). Change amount = 0). That is, when the integrated value Ni is 0, it is determined that the estimated value of the heat storage amount is less than the change execution heat storage amount for executing the correction of the basic fuel supply table, and the fuel utilization rate correction is not executed.

  As shown in FIGS. 12 and 13, in this embodiment, the integration is performed when the detected temperature Td is higher than 635 ° C., which is the changed reference temperature Tcr, and is subtracted when the detected temperature Td is lower. . That is, when the detected temperature Td is higher than the changed reference temperature Tcr, the amount of heat that can be used for improving the fuel utilization rate is accumulated in the heat insulating material 7 or the like, and when it is lower than the changed reference temperature Tcr, the heat insulating material 7 is used. The integrated value Ni is calculated assuming that the heat accumulated in etc. is taken away. In other words, the integrated value Ni corresponds to the time integration of the temperature deviation of the detected temperature Td with respect to the change reference temperature Tcr, and the heat storage amount is estimated based on the integrated value Ni.

  In the present embodiment, the change reference temperature Tcr that serves as a reference for estimating the amount of heat storage is set slightly higher than the heat storage temperature Th at which heat accumulation increases (FIG. 10). For this reason, the estimated value of the heat storage amount is estimated to be less than the actual value. Thereby, based on the heat storage amount estimated larger than actual, the correction which raises a fuel utilization factor is implemented excessively and it avoids causing the excessive temperature fall of the fuel cell module 2. FIG.

  Therefore, when the detected power Td is higher than the changed reference temperature Tcr and the generated power is reduced, the basic fuel supply table is corrected. On the other hand, when the detected power Td is lower than the changed reference temperature Tcr and the generated power is reduced, the correction amount for the basic fuel supply table is decreased (by reducing the integrated value Ni), or the correction is performed. Is not executed (when the integrated value Ni is 0).

  Specifically, as shown in FIGS. 12 and 13, when the detected temperature Td is lower than 580 ° C., 20/50000 is subtracted from the integrated value Ni. When the detected temperature Td is not less than 580 ° C. and less than 620 ° C., 10/50000 × (620−Td) / (620−580) is subtracted from the integrated value Ni. When the detected temperature Td is 620 ° C. or higher and lower than 630 ° C., 1 / 50,000 is subtracted from the integrated value Ni. Thus, as the detected temperature Td is lower than the detected temperature Td, the integrated value Ni is rapidly decreased, and the correction amount of the fuel utilization rate is also rapidly decreased accordingly.

  On the other hand, when the detected temperature Td is 650 ° C. or higher, 1/50000 × (Td−650) is added to the integrated value Ni. When the detected temperature Td is 640 ° C. or higher and lower than 650 ° C., 1 / 50,000 is added to the integrated value Ni. Thus, as the detected temperature Td is higher than the detected temperature Td, the integrated value Ni increases rapidly, and accordingly, the correction amount of the fuel utilization rate also increases rapidly.

Furthermore, when the detected temperature Td is between 630 and 640 ° C., the processing differs depending on whether the detected temperature Td is increasing or decreasing.
That is, when the detected temperature Td is 630 ° C. or higher and lower than 632 ° C., the added value is set to 0 (no addition / subtraction) when the detected temperature Td tends to increase, and 1 / 50,000 when the detected temperature Td tends to decrease. Is subtracted. As described above, when the detected temperature Td is lower than the change reference temperature Tcr and the difference between them is 5 ° C. or less which is a minute deviation temperature, when the detected temperature Td tends to decrease, the detected temperature Td tends to increase The integrated value Ni is decreased more rapidly than. Here, the heat insulating material 7 or the like has a very large heat capacity, and once the detected temperature Td starts to decrease, it is expected that the temperature will continue to decrease for a while. Accordingly, in such a situation, the fuel cell module 2 undergoes a significant temperature drop by quickly reducing the integrated value Ni and suppressing the correction that increases the fuel utilization rate (decreases the fuel supply amount). There is a need to avoid risk.

  On the other hand, when the detected temperature Td is not less than 638 ° C. and less than 640 ° C., 1/50000 is added when the detected temperature Td tends to increase, and the added value is 0 (not added or subtracted) when the detected temperature Td tends to decrease ). As described above, the heat insulating material 7 and the like have a very large heat capacity, and once the detected temperature Td starts to rise, it is expected that the temperature will continue to rise for a while. Therefore, in such a situation, by quickly increasing the integrated value Ni, the fuel usage rate is increased (decreasing the fuel supply amount) and the correction is promoted, and the heat usage is actively used to improve the fuel usage rate. Let

As described above, the addition / subtraction value with respect to the integrated value Ni takes different values depending on the change state of the detected temperature Td. Therefore, the relationship between the temperature deviation between the detected temperature Td and the changed reference temperature Tcr and the integrated value Ni reflecting the heat storage amount is changed according to the change state of the detected temperature Td.
When the detected temperature Td is 632 ° C. or higher and lower than 638 ° C., the detected temperature Td is in the vicinity of 635 ° C., which is the change reference temperature Tcr, and is considered to be stable, regardless of the tendency of the detected temperature Td. The current state is maintained by setting the addition value to 0 (no addition / subtraction is performed).

  Next, a process when the fuel cell module 2 is deteriorated will be described with reference to FIG. FIG. 16 is a flowchart for changing the correction amount when the fuel cell module 2 deteriorates.

  When the fuel cell unit 16 deteriorates as a result of being used for many years, the power that can be taken out with respect to the same fuel supply amount decreases. Along with this, the temperature of the fuel cell unit 16 when the same electric power is generated also rises. In the solid oxide fuel cell 1 of the present embodiment, the deterioration of the fuel cell module 2 is determined based on the temperature of the fuel cell module 2 (fuel cell unit 16) at a predetermined generated power. It should be noted that the deterioration of the fuel cell module can also be determined by the power or voltage that can be taken out with respect to a predetermined fuel supply amount.

  The flowchart shown in FIG. 16 is executed by the control unit 110 every predetermined period, for example, every several months to several years. First, in step S21 of FIG. 16, it is determined whether or not the fuel cell unit 16 has deteriorated. If it is determined that the fuel cell unit 16 has not deteriorated, the one-time process of the flowchart shown in FIG. 16 is terminated. If it is determined that the fuel cell unit 16 has deteriorated, the process proceeds to step S22.

  In step S22, the change reference temperature Tcr is changed to a value higher by 5 ° C., the third correction coefficient is set to 0.8, and one process of the flowchart shown in FIG. 16 is terminated. This is because when the fuel cell unit 16 is deteriorated, the operating temperature of the fuel cell module 2 is shifted to the higher temperature as a whole, and therefore the temperature used as the reference for correcting the fuel utilization rate is changed accordingly. . Further, the third correction coefficient is a coefficient to be multiplied by the usage rate change amount determined in step S4 of FIG. The third correction coefficient is set to 1 before the fuel cell unit 16 deteriorates. If it is determined that the fuel cell unit 16 has deteriorated, the third correction coefficient is changed to 0.8, and the usage rate change amount is reduced by 20%. Thereby, promotion of deterioration of the fuel cell unit 16 by largely correcting the fuel utilization rate in a state where the fuel cell unit 16 is deteriorated is prevented. When it is once determined that the fuel cell module 2 has deteriorated and the progress of further deterioration thereafter is determined, the temperature threshold for determining deterioration is updated. This makes it possible to determine the degree of progress of deterioration a plurality of times. Further, the value of the change reference temperature Tcr is changed every time it is determined that it has deteriorated.

Next, the operation of the solid oxide fuel cell 1 according to the first embodiment of the present invention will be described with reference to FIG. FIG. 17A is a diagram conceptually illustrating the operation of the solid oxide fuel cell 1 according to the present embodiment, and FIG. 17B is a diagram showing changes in daily power demand and heat insulation in a general house. It is a figure which shows typically transition of the calorie | heat amount accumulate | stored. The upper graph in FIG. 17 (a) conceptually shows the operation when the amount of heat available in the heat insulating material 7 is not accumulated, and the middle and lower graphs show the case where the accumulated heat amount is small and Each case is shown. As shown in the upper part of FIG. 17A, when the generated power is large and the operation with a large amount of fuel supply is performed for a short time, the heat insulating material 7 does not accumulate available heat, so the generated power decreases. The operation is determined based on the basic fuel supply table, and the fuel utilization rate is not increased. On the other hand, as shown in the middle stage of FIG. 17A, when the operation with large generated power is performed for a certain period of time, the operation after the decrease in generated power is accumulated in the heat insulating material 7 when the generated power is large. Since this is performed using the amount of heat, while the amount of heat available in the heat insulating material 7 remains, high-efficiency circular rolling in which the fuel supply amount is smaller than that of the basic fuel supply table is performed. This saves fuel corresponding to the hatched portion of the middle graph. Furthermore, as shown in the lower part of FIG. 17 (a), when the operation with large generated power is performed for a long time, a large amount of heat is accumulated in the heat insulating material 7, so that it is accumulated over a longer time. High-efficiency operation using the amount of heat generated is executed, and more fuel is saved.
Next, in FIG. 17B, the demand power used in the house is indicated by a solid line, the power generated by the solid oxide fuel cell 1 is indicated by a broken line, and the integrated value Ni serving as an index of the heat storage amount is indicated by a one-dot chain line. ing.

  First, at times t0 to t1 when the family is sleeping, the demand power used in the house is small, and the demand power increases when the family wakes up at time t1. Along with this, the generated power of the solid oxide fuel cell 1 also increases, and the power exceeding the rated power of the fuel cell is supplied from the grid power among the demand power. Moreover, since the state where the electric power used is low for about 6 to 8 hours while the family is sleeping, the heat storage amount (integrated value Ni) estimated by the heat storage amount estimation means 110b is 0 or 0 at the time of wakeup t1. The value is very small.

  When the generated power increases at time t1 and the fuel cell module 2 is operated at a temperature higher than the heat storage temperature Th, the amount of heat storage gradually increases, and increases to about 1 at the maximum integrated value at time t2. Thereafter, when the householder goes out at time t3, the power demand decreases rapidly. As described above, when the generated power decreases in a state where the heat storage amount is equal to or greater than the change execution heat storage amount, the basic fuel supply table is corrected by the fuel table changing unit 110a, and the fuel utilization rate in the small power generation is increased. When the operation with an increased fuel utilization rate is performed, the amount of heat accumulated in the heat insulating material 7 is used, so the integrated value Ni also decreases. In the present embodiment, it is possible to perform an operation with an increased fuel utilization rate for about 1 to 3 hours.

Next, when the householder comes home at time t4, the demand power increases again. The integrated value Ni increases after an increase in demand power at time t4 (time t4 to t5), and reaches the maximum value again. Next, at time t6, the householder goes to bed and the power demand decreases, and then the operation with an increased fuel utilization rate is performed (after time t6).
When the demand power in the house changes in this way, an operation that increases the fuel utilization rate using the amount of heat accumulated in the heat insulating material 7 is performed twice a day. The operation period in which the fuel utilization rate is increased reaches 20 to 50% of the period in which the generated power is low, and greatly improves the overall energy efficiency of the solid oxide fuel cell 1.

  In the conventional solid oxide fuel cell, when the generated power is small, the generated heat is reduced, so that the temperature of the fuel cell module is likely to decrease. For this reason, when the amount of power generated is small, the fuel utilization rate is lowered, and the fuel cell module is heated with fuel that has not been used for power generation to prevent an excessive temperature drop. In particular, in a solid oxide fuel cell of a type in which a reformer is disposed in a fuel cell module, an endothermic reaction occurs in the reformer, and thus a temperature drop is likely to occur.

  According to the solid oxide fuel cell 1 of the embodiment of the present invention, when the generated power is small, it is estimated by the heat storage amount estimation means 110b that the heat amount usable in the heat insulating material 7 is accumulated. The basic fuel supply table is corrected so as to temporarily increase the fuel utilization rate (FIG. 11, step S7). As a result, the overall energy efficiency of the solid oxide fuel cell 1 can be improved while maintaining the thermal independence of the solid oxide fuel cell 1 and avoiding an excessive temperature drop.

  According to the solid oxide fuel cell 1 of the present embodiment, it is set so that a larger amount of heat is accumulated in the heat insulating material 7 in a region higher than the predetermined heat storage temperature Th (FIG. 10). By actively accumulating heat in a region higher than the heat storage temperature Th that can increase the fuel utilization rate, and consuming this heat at the time of small power generation where the temperature of the fuel cell module 2 is relatively low and heat storage is easy to use. The amount of heat stored can be used effectively.

  According to the solid oxide fuel cell 1 of the present embodiment, the detected temperature Td detected by the power generation chamber temperature sensor 142 substantially reflects the amount of heat accumulated in the heat insulating material 7, and therefore changes from the detected temperature Td. The basic fuel supply table can be easily corrected only from the relationship of the reference temperature Tcr.

  According to the solid oxide fuel cell 1 of the present embodiment, the change reference temperature Tcr is set higher than the heat storage temperature Th (FIG. 10), so the heat storage temperature Th at which the amount of heat stored in the heat insulating material 7 increases. Therefore, the stored heat is used at a temperature higher than the change reference temperature Tcr, and the stored heat is used in a state where the amount of stored heat is small, thereby avoiding the risk of causing an excessive temperature drop.

  According to the solid oxide fuel cell 1 of the present embodiment, the heat storage amount estimation means 110b estimates the heat storage amount based on the history of the detected temperature Td (FIG. 11, step S4, FIG. 13), so the current detected temperature The heat storage amount can be estimated more accurately than the case where the heat storage amount is estimated only from Td, and the heat storage can be utilized more effectively.

  According to the solid oxide fuel cell 1 of the present embodiment, the heat storage amount accumulated in the heat insulating material 7 is estimated by integrating the temperature deviation with time (FIG. 11, Step S4, FIG. 13). ), When the time of operation at a temperature higher than the heat storage temperature Th is long, the estimated heat storage amount is large, and when it is short, the estimated heat storage amount is small, and the heat storage amount can be estimated more accurately. it can. Thereby, risks, such as an excessive temperature fall by utilizing heat storage, can be avoided reliably.

  According to the solid oxide fuel cell 1 of the present embodiment, the correction amount for increasing the fuel utilization rate is increased as the heat storage amount is increased (FIG. 11, step S4, FIG. 13). It is possible to execute a correction that significantly improves the fuel utilization rate while reliably avoiding the above.

  According to the solid oxide fuel cell 1 of the present embodiment, the correction amount is rapidly increased as the detection temperature Td is higher, while the correction amount is rapidly decreased as the detection temperature Td is lower (FIG. 13). When the temperature Td is high, the fuel utilization rate can be significantly corrected, and when the detected temperature Td is low, the correction amount can be rapidly reduced, so that an excessive temperature drop can be reliably prevented. .

  According to the solid oxide fuel cell 1 of the present embodiment, the relationship between the estimated value of the heat storage amount and the correction amount is changed according to the detected temperature Td or the state of the generated power (FIG. 13, 630 to 640). C, FIG. 14, FIG. 15 and FIG. 18), prevention of excessive temperature drop and effective utilization of heat storage can be achieved at the same time.

  According to the solid oxide fuel cell 1 of the present embodiment, the fuel table changing means 110a reduces the correction amount when the generated power is small (FIG. 15), so that the amount of heat storage used is reduced and the heat storage is reduced. The period that can be used can be extended.

  According to the solid oxide fuel cell 1 of the present embodiment, when the difference between the detected temperature Td and the change reference temperature Tcr is equal to or less than a predetermined minute deviation temperature and the detected temperature Td tends to decrease, the estimated value of the heat storage amount Is rapidly decreased (FIG. 13, 630 to 632 ° C.), the estimated value of the heat storage amount is rapidly decreased in a phase where the detected temperature Td tends to decrease, and an excessive temperature decrease can be reliably prevented. .

  According to the solid oxide fuel cell 1 of the present embodiment, the correction amount for increasing the fuel utilization rate is changed according to the state of the fuel cell module 2 (FIGS. 14, 15, and 16). Correction of the fuel utilization rate that does not conform to the state of 2 can be prevented.

  According to the solid oxide fuel cell 1 of the present embodiment, when the fuel cell module 2 deteriorates, the change reference temperature Tcr is changed to a high value (FIG. 16), so the fuel whose operating temperature has increased due to deterioration. The fuel utilization rate can be corrected without imposing an excessive burden on the battery module 2.

  According to the solid oxide fuel cell 1 of the present embodiment, when the fuel cell module 2 is deteriorated, the correction amount is reduced (FIG. 16, step S22), so that the deterioration caused by correcting the fuel utilization rate is reduced. Promotion can be suppressed.

  Further, in the above-described first embodiment of the present invention, the addition / subtraction value added to or subtracted from the integrated value Ni is calculated based only on the detected temperature Td as in the heat storage amount estimation table shown in FIG. However, as a modification, the addition / subtraction value can be determined in consideration of the output current. For example, the integrated value Ni can be calculated by integrating the value obtained by multiplying the addition / subtraction value determined based on the heat storage amount estimation table of FIG. 12 by the current correction coefficient shown in FIG. As shown in FIG. 18, the current correction coefficient is set to 1/7 when the output current is 3A or less, is set to 1/12 when the output current is 3A or more, and is linear from 1/7 to 1/12 between 3 and 4A. Has declined.

  By multiplying the current correction coefficient set in this way, the integrated value Ni rapidly increases and decreases in a region where the generated power is small, and the increase and decrease of the integrated value Ni becomes gentle in a region where the generated power is equal to or higher. For this reason, the integrated value Ni is rapidly reduced by the correction of the basic fuel supply table at the time of small power generation that consumes a large amount of heat accumulated in the heat insulating material 7. As a result, it is possible to more reliably prevent the risk of causing a significant temperature drop by overestimating the heat storage amount.

  In the above-described embodiment, the addition / subtraction value to be added to or subtracted from the integrated value Ni is determined only by the detected temperature Td as shown in FIG. 13, but the addition / subtraction value depends on the output current. The invention can also be configured. For example, when the output current is 3 A (output power 300 W) or less, the change reference temperature Tcr may be changed higher by about 2 ° C., and the entire graph of FIG. 13 may be shifted to the left by about 2 ° C. With this configuration, when the generated power is small, the change reference temperature Tcr is changed to a high value, and the estimated value of the heat storage amount is calculated to a small value. As a result, the correction amount for increasing the fuel utilization rate is reduced, so that the fuel utilization rate is significantly improved in the region where the generated power is small and the absolute amount of the fuel supply amount is small, and the fuel supply amount is reduced excessively. Can be suppressed.

Next, a solid oxide fuel cell according to a second embodiment of the present invention will be described with reference to FIGS.
The solid oxide fuel cell of the present embodiment is different from the first embodiment described above in the control by the control unit 110. Accordingly, here, only the portions of the second embodiment of the present invention that are different from the first embodiment will be described, and descriptions of similar configurations, operations, and effects will be omitted.

  In the first embodiment described above, the fuel supply amount is determined based on the basic fuel supply table according to the demand power, and the determined fuel supply amount is decreased based on the heat amount accumulated in the heat insulating material 7. The fuel usage rate was temporarily increased. On the other hand, in the solid oxide fuel cell according to the second embodiment, the process of determining the fuel supply amount by the basic fuel supply table and changing the fuel supply amount based on the estimated heat storage amount is not executed, and the fuel supply amount is It is directly calculated based on the detected temperature Td and the like. However, in the present embodiment, the fuel supply amount that is directly determined based on the detected temperature Td and the like is the amount of heat accumulated in the heat insulating material 7 and the like, and in a state where the heat storage amount is large, Since the fuel utilization rate is improved by using heat storage, it can be said that the technical idea similar to that of the first embodiment is realized.

  Furthermore, in the first embodiment described above, the change in the fuel supply amount for increasing the fuel utilization rate based on the estimated heat storage amount is changed to the first correction coefficient (step S5 in FIG. 11, FIG. 14). Therefore, it was performed exclusively when the generated power was small (first correction coefficient = 0 at an output current of 4.5 A or more). On the other hand, in the present embodiment, a coefficient corresponding to the first correction coefficient in the first embodiment is not used. Therefore, in this embodiment, high-efficiency control using the amount of heat accumulated in the heat insulating material 7 and the like is executed not only in a region where the generated power is small but also in a region where the generated power is large. For this reason, according to the solid oxide fuel cell of the present embodiment, in addition to the effect of improving the fuel utilization rate by using heat storage, the heat insulation is performed when the temperature in the fuel cell module 2 is excessively increased. By consuming the amount of heat accumulated in the material 7 or the like, an effect of suppressing the temperature rise can be obtained. In the first embodiment described above, the same effect can be obtained by omitting the first correction coefficient (not multiplying the change amount by the first correction coefficient).

  FIG. 19 is a graph schematically showing the relationship between the change in demand power, the fuel supply amount, and the current actually taken from the fuel cell module 2. FIG. 20 is a graph showing an example of the relationship between the power generation air supply amount, the water supply amount, the fuel supply amount, and the current actually taken from the fuel cell module 2.

  As shown in FIG. 19, the fuel cell module 2 is controlled so as to be able to generate electric power according to the demand electric power shown in the uppermost stage of FIG. Based on the demand power, the control unit 110 sets a fuel supply current value If, which is a target current to be generated by the fuel cell module 2, as shown in the second graph of FIG. Although the fuel supply current value If is set so as to substantially follow the change in demand power, the response speed of the fuel cell module 2 is extremely slow with respect to the change in demand power. It is set so as to follow the demand power gently without following the change. In addition, when the demand power exceeds the maximum rated power of the solid oxide fuel cell, the fuel supply current value If follows the current value corresponding to the maximum rated power and is set to a current value higher than that. There is no.

  As shown in the third graph of FIG. 19, the control unit 110 controls the fuel flow rate adjustment unit 38, which is a fuel supply unit, so as to generate a fuel supply amount at a flow rate that can generate power corresponding to the fuel supply current value If. Fr is supplied to the fuel cell module 2. If the fuel utilization rate, which is the ratio of the fuel actually used for power generation with respect to the fuel supply amount, is constant, the fuel supply current value If and the fuel supply amount Fr are proportional. The graph of FIG. 19 is drawn on the assumption that the fuel supply current value If and the fuel supply amount Fr are proportional, but as will be described later, the fuel utilization rate is actually not constant in this embodiment as well.

  Further, as shown in the lowermost graph in FIG. 19, the control unit 110 outputs a signal that instructs the inverter 54 about the extractable current Iinv that is a current value that can be extracted from the fuel cell module 2. The inverter 54 extracts current (electric power) from the fuel cell module 2 within the range of the extractable current Iinv according to the demand power that changes suddenly every moment. The portion where the demand power exceeds the extractable current Iinv is supplied from the grid power. Here, as shown in FIG. 19, when the current tends to increase, the extractable current Iinv instructed by the control unit 110 to the inverter 54 changes so as to be delayed by a predetermined time with respect to the change in the fuel supply amount Fr. Is set. For example, at time t10 in FIG. 19, after the fuel supply current value If and the fuel supply amount Fr start to increase, an increase in the extractable current Iinv is started with a delay. Also at time t12, after the fuel supply current value If and the fuel supply amount Fr increase, the increase of the extractable current Iinv is started with a delay. As described above, after the fuel supply amount Fr is increased, the timing at which the electric power actually extracted from the fuel cell module 2 is increased is delayed so that the fuel supplied to the fuel cell module 2 passes through the reformer 20 and the like. A time delay until the fuel cell stack 14 is reached and a time delay until the actual power generation reaction becomes possible after the fuel reaches the battery cell stack 14 are dealt with. This reliably prevents the fuel battery cell unit 16 from being depleted of fuel and damaging the fuel battery cell unit 16.

  FIG. 20 shows in more detail the relationship between the power supply air supply amount, the water supply amount, and the fuel supply amount and the extractable current Iinv. Note that the graphs of the power supply air supply amount, the water supply amount, and the fuel supply amount shown in FIG. 20 are all converted into current values corresponding to the respective supply amounts. That is, if the supplied power generation air, water, and fuel are all set to supply amounts that are used for power generation, the graphs of the respective supply amounts overlap the graph of the extractable current Iinv. It has been converted. Therefore, the amount of deviation of each supply amount graph with respect to the extractable current Iinv corresponds to the surplus of each supply amount. The remaining fuel that is not used for power generation is burned in the combustion chamber 18 that is a combustion section above the fuel cell stack 14 and is used for heating in the fuel cell module 2.

  As shown in FIG. 20, the power supply air supply amount, the water supply amount, and the fuel supply amount always exceed the extractable current Iinv, and the current exceeding the current that can be generated by each supply amount is greater than the fuel cell module 2. The fuel cell unit 16 is prevented from being damaged by fuel exhaustion, air exhaustion, and the like. Further, the water supply amount is set to a supply amount capable of steam reforming all of the supplied fuel with respect to the fuel supply amount supplied exceeding the extractable current Iinv. That is, the amount of water supplied is the ratio of the amount of water vapor necessary for steam reforming and the amount of carbon contained in the fuel, so that all of the supplied fuel is steam reformed. It is set in consideration. This prevents carbon deposition in the reformer. Further, in the region A and region C of FIG. 20 in which the extractable current Iinv tends to increase with the increase in demand power, a margin such as the fuel supply amount is larger than the region B in which the extractable current Iinv is flat. Is set large (low fuel utilization). Further, when the generated power is increased, the fuel supply amount supplied to the fuel cell module 2 is increased by the power extraction delay means 110c (FIG. 6) built in the control unit 110, and then the fuel cell is delayed. The generated power output from the module 2 is increased. That is, after the fuel supply amount is changed according to the change in demand power, the power actually output from the fuel cell module 2 is changed with a delay. Furthermore, when the extractable current Iinv is suddenly reduced according to the reduction in demand power (the initial period of the region C and the region D), each supply amount decreases with a predetermined time delay from the decrease of the extractable current Iinv. Is done. Therefore, a very large amount of residual fuel is generated during a predetermined time after the extractable current Iinv suddenly decreases. Such a rapid decrease in the extractable current Iinv is performed in order to prevent a reverse current flow when the demand power rapidly decreases. Thus, when the generated power is increased and when the generated power is decreased, more residual fuel is generated than when the generated power is constant, and this residual fuel is used for heating the fuel cell module 2. Will be. For this reason, the fuel cell module 2 is strongly heated not only when the fuel cell module 2 is operated for a long time with high generated power but also when the generated power is frequently increased or decreased, and a large amount of heat is accumulated in the heat insulating material 7. Is done.

  In the solid oxide fuel cell of this embodiment, after operating for a long time with high generated power, not only the heat storage is used when the generated power decreases, but also the amount of heat that is being accumulated due to the increase or decrease of the generated power, etc. Are used sequentially depending on the situation.

Next, a procedure for determining the power generation air supply amount, the water supply amount, and the fuel supply amount based on the detected temperature Td will be described with reference to FIGS.
FIG. 21 is a flowchart showing a procedure for determining the power supply air supply amount, the water supply amount, and the fuel supply amount based on the detected temperature Td. FIG. 22 is a graph showing an appropriate temperature of the fuel cell stack 14 with respect to the generated current. FIG. 23 is a graph showing the fuel utilization rate determined according to the integrated value. FIG. 24 is a graph showing a range of values of fuel utilization rates that can be determined for each generated current. FIG. 25 is a graph showing the air utilization rate determined according to the integrated value. FIG. 26 is a graph showing a range of air utilization values that can be determined for each generated current. FIG. 27 is a graph for determining the water supply amount with respect to the determined air utilization rate. FIG. 28 is a graph showing an appropriate generated voltage of the fuel cell module 2 with respect to the generated current.

  As indicated by a one-dot chain line in FIG. 22, in this embodiment, an appropriate temperature Ts (I) of the fuel cell stack 14 is defined for the current to be generated by the fuel cell module 2. The control unit 110 controls the fuel supply amount and the like so that the temperature of the fuel cell stack 14 approaches the appropriate temperature Ts (I). That is, the control unit 110 roughly indicates that when the temperature of the fuel cell stack 14 is higher than the generated current (when the temperature of the fuel cell stack 14 is above the one-dot chain line in FIG. 22). The fuel utilization rate is increased, the amount of heat accumulated in the heat insulating material 7 and the like is actively consumed, and the temperature in the fuel cell module 2 is lowered. On the other hand, when the temperature of the fuel cell stack 14 is lower than the generated current, the fuel utilization rate is reduced so that the temperature in the fuel cell module 2 does not decrease. Specifically, the fuel utilization rate is not determined based on the simple detected temperature Td, but is calculated by adding the addition / subtraction values determined based on the detected temperature Td and the like to reflect the heat storage. The fuel utilization rate and the like are determined based on this amount. An estimated value of the heat storage amount by integrating the addition and subtraction values is calculated by the heat storage amount estimation means 110b built in the control unit.

  The flowchart shown in FIG. 21 determines the power generation air supply amount, the water supply amount, and the fuel supply amount based on the detected temperature Td and the like detected by the power generation chamber temperature sensor 142 that is a temperature detection means. It is executed at the time interval.

First, in step S31 of FIG. 21, the first addition / subtraction value M1 is calculated based on the detected temperature Td and FIG. First, when the detected temperature Td is within a predetermined temperature range (between two solid lines in FIG. 22) with respect to the appropriate temperature Ts (I) of the fuel cell stack 14, the first addition / subtraction value M1. Is set to zero.
That is, the detected temperature Td is
Ts (I) −Te ≦ Td ≦ Ts (I) + Te
Is within the range, the first addition / subtraction value M1 = 0. Here, Te is the first addition / subtraction value threshold temperature. In the present embodiment, the first addition / subtraction value threshold temperature Te is 3 ° C.

Further, the detected temperature Td is lower than the appropriate temperature Ts (I),
Td <Ts (I) −Te (4)
Is within the range (below the lower solid line in FIG. 22), the first addition / subtraction value M1 is
M1 = Ki × (Td− (Ts (I) −Te)) (5)
Calculated by At this time, the first addition / subtraction value M1 is a negative value (subtraction value). Ki is a predetermined proportionality constant.

Further, the detected temperature Td is higher than the appropriate temperature Ts (I),
Td> Ts (I) + Te (6)
Is within the range (above the upper solid line in FIG. 22), the first addition / subtraction value M1 is
M1 = Ki × (Td− (Ts (I) + Te)) (7)
Calculated by At this time, the first addition / subtraction value M1 is a positive value (addition value). As described above, the first addition / subtraction value M1 is determined based on the generated current in addition to the detected temperature Td, and the heat storage amount is estimated by integrating the value. That is, the appropriate temperature Ts (I) is set to be different depending on the generated current (electric power), and the value of (Ts (I) + Te) determined based on the appropriate temperature Ts (I) and (Ts Based on the value of (I) −Te), the first addition / subtraction value M1 is determined as a positive or negative value.

  If the detected temperature Td exceeds (Ts (I) + Te), the first addition / subtraction value M1 becomes a positive value, and the fuel supply amount is changed to increase the fuel utilization rate as will be described later. In the document, the temperature (Ts (I) + Te) for each generated power is referred to as the fuel utilization rate change temperature. Moreover, after the fuel utilization rate change temperature (Ts (I) + Te) is exceeded, after shifting to the high efficiency control in which the fuel utilization rate is increased, the target temperature range in which the amount of heat accumulated from the high efficiency control is not consumed. As will be described later, the timing for returning to control is when the integrated value N1id such as the first addition / subtraction value M1 has decreased to zero. For this reason, even after the detected temperature Td falls below the fuel utilization rate changing temperature (Ts (I) + Te), the integrated value N1id is maintained at a value larger than 0 for a while, and high efficiency control is performed. Therefore, the target temperature range control return temperature for returning from the high efficiency control to the target temperature range control is lower than the fuel utilization rate changing temperature.

  Next, in step S32 of FIG. 21, a second addition / subtraction value M2 is calculated based on the latest detected temperature Td and the detected temperature Tdb detected one minute ago. First, when the absolute value of the difference between the latest detected temperature Td and the detected temperature Tdb one minute ago is less than a predetermined second addition / subtraction value threshold temperature, the second addition / subtraction value M2 is set to zero. In the present embodiment, the second addition / subtraction value threshold temperature is 1 ° C.

When the change temperature difference that is the difference between the latest detected temperature Td and the detected temperature Tdb one minute ago is equal to or higher than a predetermined second addition / subtraction value threshold temperature, the second addition / subtraction value M2 is:
M2 = Kd × (Td−Tdb) (8)
Calculated by The second addition / subtraction value M2 becomes a positive value (addition value) when the detected temperature Td tends to increase, and becomes a negative value (subtraction value) when the detected temperature Td tends to decrease. Kd is a predetermined proportional constant. Therefore, when the detected temperature Td is increasing, the second addition / subtraction value M2, which is the quick response estimated value, is greatly increased in the region where the change temperature difference (Td−Tdb) is large compared to the region where the change temperature difference is small. Is done. On the other hand, when the detected temperature is low, the second addition / subtraction value M2 is greatly reduced in the region where the absolute value of the change temperature difference (Td−Tdb) is large than in the region where the absolute value of the change temperature difference is small. Is done.

  In the present embodiment, the proportionality constant Kd is a constant value, but as a modification, different proportionality constants Kd can be used depending on whether the change temperature difference is positive or negative. For example, the proportionality constant Kd can be set large when the change temperature difference is negative. As a result, when the detected temperature is lowered, the estimated quick response value is changed more rapidly with respect to the change temperature difference than when the detected temperature is increased. Alternatively, as a modification, the proportionality constant Kd can be set larger in the region where the absolute value of the change temperature difference is large than in the small region. As a result, in the region where the absolute value of the change temperature difference is large, the estimated quick response value is changed more rapidly than the region where the absolute value of the change temperature difference is small. Further, the change of the proportional constant Kd based on the sign of the change temperature difference can be combined with the change of the proportional constant Kd based on the magnitude of the absolute value of the change temperature difference.

  Next, in step S33 of FIG. 21, the first addition / subtraction value M1 calculated in step S31 and the second addition / subtraction value M2 calculated in step S32 are integrated into the first integration value N1id. In the first integrated value N1id, the available heat storage amount accumulated in the heat insulating material 7 and the like is reflected by the first addition / subtraction value M1, and the latest change in the detected temperature Td is reflected by the second addition / subtraction value M2. . That is, the first integrated value N1id can be used as an estimated value of the available heat storage amount accumulated in the heat insulating material 7 or the like. Further, the integration is performed every time the flowchart of FIG. 21 is executed continuously after the operation of the solid oxide fuel cell is started, and the first addition value N1id and the first addition / subtraction value M1 are added to the previously calculated first integration value N1id. The 2 addition / subtraction value M2 is added or subtracted and updated to a new first integrated value N1id. The first integrated value N1id is limited to take a value between 0 and 4, and when the first integrated value N1id reaches 4, the value is held at 4 until the next subtraction is performed. When the first integrated value N1id decreases to 0, the value is held at 0 until the next addition is performed.

  In step S33, in addition to the first integrated value N1id, the value of the second integrated value N2id is also calculated. As will be described later, the second integrated value N2id is calculated in the same manner as the first integrated value N1id until the fuel cell module 2 is deteriorated, and takes the same value as the first integrated value N1id.

As described above, in the present embodiment, the integrated value is calculated by integrating the sum of the first addition / subtraction value M1 and the second addition / subtraction value M2 to the first integration value N1id. That is,
N1id = N1id + M1 + M2 (9)
Thus, the first integrated value N1id is calculated. Here, as a modification, the integrated value may be calculated by integrating the product of the first addition / subtraction value M1 and the second addition / subtraction value M2. That is, in this modification, the first integrated value N1id is
N1id = N1id + Km × M1 × M2 (10)
Is calculated by Here, Km is a variable coefficient that is changed according to a predetermined condition. In this modified example, when the absolute value of the difference between the latest detected temperature Td and the detected temperature Tdb one minute ago is less than a predetermined second addition / subtraction value threshold temperature, the second addition / subtraction value M2 is 1. Is done.

Further, in step S34 of FIG. 21, the fuel utilization rate is determined using the graphs of FIGS. 23 and 24 based on the calculated first integrated value N1id.
FIG. 23 is a graph showing a set value of the fuel utilization rate Uf with respect to the calculated first integrated value N1id. As shown in FIG. 23, when the first integrated value N1id is 0, the fuel usage rate Uf is set to the minimum fuel usage rate Ufmin, which is the minimum value. Further, as the first integrated value N1id increases, the fuel utilization rate Uf also increases, and becomes the maximum fuel utilization rate Ufmax that is the maximum value at the first integrated value N1id = 1. During this time, the fuel utilization rate Uf has a small slope in the region where the first integrated value N1id is small, and the slope increases as the first integrated value N1id approaches 1. That is, in the region where the estimated heat storage amount is large, the fuel utilization rate Uf is significantly changed with respect to the change in the estimated heat storage amount, compared to the region where the estimated heat storage amount is small. In other words, the fuel supply amount is decreased so that the fuel utilization rate Uf is significantly increased as the estimated heat storage amount is larger. Further, when the first integrated value N1id is larger than 1, the fuel usage rate Uf is fixed to the maximum fuel usage rate Ufmax. Specific values of the minimum fuel utilization rate Ufmin and the maximum fuel utilization rate Ufmax are determined by the graph shown in FIG. 24 based on the generated current. Thus, when it is estimated that the amount of heat that can be used is accumulated in the heat insulating material 7 and the like, the fuel utilization rate is higher for the same generated power than in the case where the amount of available heat is not accumulated. The fuel supply is reduced to be higher.

  FIG. 24 is a graph showing the range of values that the fuel utilization rate Uf can take for each generated current, and shows the maximum value and the minimum value of the fuel utilization rate Uf for each generated current. As shown in FIG. 24, the minimum fuel utilization rate Ufmin for each generated current is set to increase as the generated current increases. That is, the fuel utilization rate is set high when the generated power is large, and the fuel utilization rate is set low when the generated power is small. This straight line of the minimum fuel utilization rate Ufmin corresponds to the basic fuel supply table in FIG. 9 of the first embodiment, and when it is set to the fuel utilization rate on this straight line, it accumulates in the heat insulating material 7 and the like. The fuel cell module 2 can be thermally independent without using the amount of heat generated.

  On the other hand, the maximum fuel utilization rate Ufmax is set so as to change in a polygonal line with respect to each generated current. Here, the range of values that the fuel utilization rate Uf can take for each generated current (the difference between the maximum fuel utilization rate Ufmax and the minimum fuel utilization rate Ufmin) is the narrowest at the maximum generated current, and as the generated current decreases. Become wider. This is because, in the vicinity of the maximum generated current, the minimum fuel utilization rate Ufmin that can be thermally independent is high, and there is little room for increasing the fuel utilization rate Uf (reducing the fuel supply amount) even when using heat storage. Furthermore, since the minimum fuel utilization rate Ufmin that can be thermally self-sustained decreases as the generated current decreases, there is room for reducing the amount of fuel supplied by using heat storage, and when there is a large amount of heat storage, fuel use The rate Uf can be significantly increased. For this reason, in the region where the generated power is small, the fuel utilization rate is changed in a wider range than in the region where the generated power is large.

  Further, in a region where the generated current is very small and is less than or equal to the predetermined utilization rate suppressed power generation amount IU, the range of possible values of the fuel utilization rate Uf is set to be narrower as the generated power is reduced. This is because in the region where the generated current is small, the minimum fuel utilization rate Ufmin that can be thermally independent is low, and there is much room for improvement. However, in the region where the generated current is small, the temperature in the fuel cell module 2 is low. Therefore, if the fuel utilization rate Uf is significantly improved in this state and the amount of heat accumulated in the heat insulating material 7 or the like is consumed rapidly, There is a risk of causing an excessive temperature drop in the battery module 2. For this reason, in the area | region below the utilization factor suppression electric power generation amount IU in which an electric power generation current is very small, the change amount which raises the fuel utilization factor Uf is significantly suppressed, so that generated electric power becomes small. That is, the amount of change to decrease the fuel supply amount decreases as the power generation amount of the fuel cell module 2 decreases. This avoids the risk of a sudden temperature drop and makes it possible to use the accumulated heat for a long time.

  In the present embodiment, the fuel supply amount is reduced so that the fuel utilization rate Uf becomes higher than the minimum fuel utilization rate Ufmin by the fuel supply amount changing means 110a built in the control unit 110. Although this fuel supply amount changing means 110a does not change the basic fuel supply table, it operates to change the fuel supply rate as a base to increase the fuel utilization rate, so that the fuel table change in the first embodiment is performed. It is the structure corresponding to a means.

  In step S34 of FIG. 21, specific values of the minimum fuel utilization rate Ufmin and the maximum fuel utilization rate Ufmax are determined based on the generated current using the graph of FIG. Next, the determined minimum fuel utilization rate Ufmin and maximum fuel utilization rate Ufmax are applied to the graph of FIG. 23, and the fuel utilization rate Uf is determined based on the first integrated value N1id calculated in step S33.

Next, in step S35 of FIG. 21, the air utilization rate is determined using the graphs of FIGS. 25 and 26 based on the second integrated value N2id.
FIG. 25 is a graph showing a set value of the air utilization rate Ua with respect to the calculated second integrated value N2id. As shown in FIG. 25, when the second integrated value N2id is 0 to 1, the air utilization rate Ua is set to the maximum air utilization rate Uamax that is the maximum value. Further, as the second integrated value N2id increases beyond 1, the air utilization rate Ua decreases, and becomes the minimum air utilization rate Uamin that is the minimum value at the second integrated value N2id = 4. Thus, since the increased amount of air due to the reduction in the air utilization rate Ua acts as a cooling fluid, the setting of the air utilization rate Ua shown in FIG. 25 acts as a forced cooling means. Specific values of the minimum air utilization rate Uamin and the maximum air utilization rate Uamax are determined by the graph shown in FIG. 26 based on the generated current.

  FIG. 26 is a graph showing the range of values that the air utilization rate Ua can take for each generated current, and shows the maximum value and the minimum value of the fuel utilization rate Ua for each generated current. As shown in FIG. 26, the maximum air utilization rate Uamax for each generated current is set to be slightly increased as the generated current increases. On the other hand, the minimum air utilization rate Uamin decreases as the generated current increases. Reducing the air utilization rate Ua below the maximum air utilization rate Uamax (increasing the air supply amount) introduces more air into the fuel cell module 2 than is necessary for power generation. The temperature in the fuel cell module 2 is lowered. Therefore, when the temperature in the fuel cell module 2 rises excessively and the temperature needs to be lowered, the air utilization rate Ua is lowered. In this embodiment, when the minimum air utilization rate Uamin is decreased (the air supply amount is increased) as the generation current is increased, the air supply amount corresponding to the minimum air utilization rate Uamin is generated for power generation at a predetermined generation current. The maximum air supply amount of the air flow rate adjustment unit 45 will be exceeded. For this reason, in the region where the minimum air utilization rate Uamin is equal to or greater than the predetermined generated current indicated by the broken line in FIG. 26, the air utilization rate Ua set by the graph of FIG. 25 may not be realized. In this case, the actually supplied air supply amount is fixed to the maximum air supply amount of the power generation air flow rate adjustment unit 45 regardless of the set air utilization rate Ua. Along with this, the minimum air utilization rate Ua actually realized increases above a predetermined generated current. Further, when a power generation air flow rate adjustment unit having a large maximum air supply amount is used, the minimum air utilization rate Uamin in the portion indicated by the broken line in FIG. 26 can also be realized. The air utilization rate Ua defined by reaching the maximum air supply amount of the power generation air flow rate adjustment unit 45 is referred to as a limit minimum air utilization rate ULamin.

  In step S35 of FIG. 21, the specific values of the minimum air utilization rate Uamin and the maximum air utilization rate Uamax are determined based on the generated current using the graph of FIG. Next, the determined minimum air utilization rate Uamin and maximum air utilization rate Uamax are applied to the graph of FIG. 25, and the air utilization rate Ua is determined based on the second integrated value N2id calculated in step S33.

Next, in step S36 of FIG. 21, based on the air utilization rate Ua determined in step S35, S / C which is the ratio of the water vapor amount and the carbon amount is determined using FIG.
FIG. 27 is a graph in which the horizontal axis represents the air utilization rate Ua and the vertical axis represents the ratio S / C between the supplied water and the carbon contained in the fuel.

  First, in the region of the generation current (between Uamax and ULamin in FIG. 27) where the air utilization rate Ua set in step S35 is not defined by the maximum air supply amount of the power generation air flow rate adjustment unit 45, the amount of water vapor and carbon The value of the quantity ratio S / C is fixed at 2.5. The ratio of the amount of water vapor to the amount of carbon S / C = 1 means that the total amount of carbon contained in the supplied fuel is chemically steam-reformed by the supplied water (steam). means. Therefore, the ratio S / C = 2.5 of the amount of steam and the amount of carbon is 2.5 times the amount of steam (water) that is 2.5 times the minimum amount of steam that is chemically necessary for steam reforming the fuel. Means the state. Actually, carbon precipitation occurs in the reformer 20 at the amount of steam at which S / C = 1, so that the amount of steam at which S / C = 2.5 is for steam reforming the fuel. Appropriate amount.

  Next, in the region of the power generation current in which the air utilization rate Ua set in step S35 is limited by the maximum air supply amount of the power generation air flow rate adjustment unit 45, the water vapor amount and the carbon amount using the graph of FIG. The ratio S / C is determined. In FIG. 27, the horizontal axis represents the air utilization rate Ua, the air utilization rate Ua is larger, and the closer to the maximum air utilization rate Uamax, the smaller the air supply amount. On the other hand, when the air utilization rate Ua is lowered and approaches the minimum air utilization rate Uamin (broken line in FIG. 26), the air supply amount reaches the limit, and the air utilization rate Ua becomes the limit minimum air utilization rate ULamin. As shown in FIG. 27, when the air utilization rate Ua is larger than the limit minimum air utilization rate ULamin (the air supply amount is small), the ratio S / C = 2.5 of the water vapor amount and the carbon amount is set. . Further, when the air utilization rate Ua determined in step S35 is smaller than the limit minimum air utilization rate ULamin (the air supply amount is large) (between Uamin and ULamin in FIG. 27), the air utilization rate Ua decreases. The ratio S / C between the water vapor amount and the carbon amount is increased, and S / C = 3.5 is set at the minimum air utilization rate Uamin. That is, when the air utilization rate Ua determined in step S35 cannot be realized by the limit minimum air utilization rate ULamin (when the air utilization rate Ua is determined within the hatched range in FIG. 26), the water vapor amount and carbon Increase the quantity ratio S / C and increase the water supply. Thereby, the temperature of the reformed fuel gas flowing out from the reformer 20 is lowered, and the temperature in the fuel cell module 2 tends to be lowered. In this way, when the water supply amount is increased after the air supply rate Ua is decreased and the air supply amount is increased, the increased amount of water (water vapor) acts as a cooling fluid. The water supply setting shown acts as a forced cooling means.

  In step S37, specific fuel supply is performed based on the fuel utilization rate Uf, air utilization rate Ua, the ratio S / C of water vapor amount and carbon amount determined in steps S34, S35, and S36, and the generated current. Determine the volume, air supply, and water supply. That is, the actual fuel supply amount is calculated by dividing the fuel supply amount when the total amount is used for power generation by the determined fuel utilization rate Uf, and the total amount is used for power generation. The actual air supply amount is calculated by dividing the air supply amount by the determined air utilization rate Ua. Further, the water supply amount is calculated based on the calculated fuel supply amount and the ratio S / C of the water vapor amount and the carbon amount determined in step S36.

  Next, in step S38, the control unit 110 sends a signal to the fuel flow rate adjustment unit 38, the power generation air flow rate adjustment unit 45, and the water flow rate adjustment unit 28 serving as water supply means, and the amount of fuel calculated in step S37. , Air and water are supplied, and one process of the flowchart of FIG. 21 is completed.

  Next, a time interval for executing the flowchart of FIG. 21 will be described. In the present embodiment, when the output current is large, the flowchart of FIG. 21 is executed every 0.5 seconds. As the output current decreases, it is doubled for 1 second, 4 times for 2 seconds, and 8 times. It is executed every 4 seconds. Thus, when the first and second addition / subtraction values are constant values, the change in the first or second integrated value per time becomes gentler as the output current is smaller. That is, the heat storage amount estimation unit 110b changes the estimated value of the heat storage amount rapidly with respect to time as the output current (generated power) increases. Thereby, the estimation of the heat storage amount by the integrated value well reflects the actual heat storage amount.

  Next, a procedure for determining the fuel supply amount, the air supply amount, and the water supply amount when the fuel cell module 2 is deteriorated will be described with reference to FIG. FIG. 28 is a diagram showing a generated voltage with respect to a generated current by the fuel cell module 2. In general, since an internal resistance exists in the fuel cell stack 14, the voltage decreases as the current output from the fuel cell module 2 increases as shown in FIG. The alternate long and short dash line shown in FIG. 28 indicates the relationship between the generated current and the generated voltage when the fuel cell module 2 is not deteriorated. On the other hand, when the fuel cell module 2 deteriorates, the internal resistance of the fuel cell stack 14 increases, so that the generated voltage for the same generated current decreases.

  In the solid oxide fuel cell according to the present embodiment, when the generated voltage drops by 10% or more with respect to the initial generated voltage and the generated voltage enters a region below the solid line in FIG. The fuel supply amount, air supply amount, and water supply amount are determined by the processing.

  That is, when the generated voltage is in the region below the solid line in FIG. 28, the integration of the first integrated value N1id is stopped and only the integration of the second integrated value N2id is continued in step S33 of FIG. . Accordingly, the value of the first integrated value N1id used when referring to the graph of FIG. 23 for determining the fuel utilization rate Uf is fixed to a constant value. As a result, the fuel utilization rate Uf is fixed until the generated voltage deviates from the region below the solid line in FIG. Thus, after the fuel cell module 2 has deteriorated, changes to increase the fuel utilization rate Uf are less than before the fuel cell module 2 deteriorates. On the other hand, the value of the second integrated value N2id used when referring to the graph of FIG. 26 for determining the air utilization rate Ua is increased or decreased as before, and the increase or decrease in the air utilization rate Ua is continued. Thus, the fuel utilization rate Uf is changed based on the deterioration of the fuel cell module 2 in addition to the first and second integrated values and the demand power corresponding to the estimated heat storage amount.

Next, the operation of the solid oxide fuel cell realized by the flowchart of FIG. 21 will be described.
First, when the value of the first integrated value N1id calculated in step S33 is 0, the fuel utilization rate Uf determined in step S34 is the minimum fuel utilization rate Ufmin (maximum fuel supply amount) in the generated current. Set to As a result, even when the value of the first integrated value N1id is 0 and the amount of heat accumulated in the heat insulating material 7 or the like is small, sufficient fuel is supplied so that the fuel cell module 2 can be thermally independent. When the value of the second integrated value N2id calculated in step S33 is 0 as in the case of the first integrated value N1id, the air utilization rate Ua determined in step S35 is the maximum air in the generated current. The utilization rate Uafmax (air supply amount minimum) is set. For this reason, the effect | action which cools the fuel cell stack 14 with the air for electric power generation introduced into the fuel cell module 2 is minimized, and the temperature of the fuel cell stack 14 can be made to rise.

  Next, when the detected temperature Td is higher than the appropriate temperature Ts (I) and the fuel cell module 2 is operated in a state of Td> Ts (I) + Te, the value of the first addition / subtraction value M1 becomes a positive value, The value of 1 integrated value N1id becomes larger than 0. Accordingly, in FIG. 23, a fuel utilization rate Uf higher than the minimum fuel utilization rate Ufmin is set, the fuel supply amount is decreased, and the amount of remaining fuel that is not used for power generation is decreased. The fuel utilization rate Uf is significantly increased by the fuel supply amount changing unit 110a as the value of the first integrated value N1id corresponding to the estimated heat storage amount increases. By increasing the fuel utilization rate Uf, the fuel supply amount is made smaller than the supply amount capable of self-sustaining heat, and high-efficiency control using the heat amount accumulated in the heat insulating material 7 or the like is executed. Since the amount of residual fuel is reduced and the amount of heat accumulated in the heat insulating material 7 or the like is used, the fuel supply amount changing means 110a suppresses the temperature rise in the fuel cell module 2 while continuing power generation. When the operation is continued in the state of Td> Ts (I) + Te, the integration of the positive first addition / subtraction value M1 is repeated, and the value of the first integration value N1id also increases. When the first integrated value N1id reaches 1, the fuel usage rate Uf is set to the maximum fuel usage rate Uafmax (fuel supply amount minimum). Thus, the fuel supplied to the fuel cell module 2 is determined based on the past history of the detected temperature Td reflecting the amount of heat accumulated in the heat insulating material 7 and the like.

  Even when the first integrated value N1id further increases and exceeds 1, as shown in FIG. 23, the fuel utilization rate Uf is maintained at the maximum fuel utilization rate Uafmax (minimum fuel supply amount). On the other hand, since the value of the second integrated value N2id that takes the same value as the first integrated value N1id (when the fuel cell module 2 is not deteriorated) also exceeds 1, the air utilization rate Ua decreases based on FIG. (Air supply amount increased). Thereby, the inside of the fuel cell module 2 tends to be cooled due to an increase in supplied air.

  On the other hand, when the detected temperature Td is lower than the appropriate temperature Ts (I) and the fuel cell module 2 is operated in a state where Td <Ts (I) −Te, the value of the first addition / subtraction value M1 is a negative value. Thus, the value of the first integrated value N1id is decreased. Thus, the fuel utilization rate Uf is maintained (first integrated value N1id> 1) or decreased (first integrated value N1id ≦ 1). Further, the air utilization rate Ua is increased (second integrated value N2id> 1) or maintained (second integrated value N2id ≦ 1). Thereby, the temperature in the fuel cell module 2 can be increased.

  The above is the operation of the solid oxide fuel cell focusing only on the first addition / subtraction value M1 calculated based on the history of the detected temperature Td. The first integrated value N1id and the second integrated value N2id are It is also affected by the addition / subtraction value M2. The fuel cell module 2, particularly the fuel cell stack 14, has a very large heat capacity, and the change in the detected temperature Td is extremely slow. For this reason, once the detected temperature Td starts to increase, it is difficult to suppress the temperature increase in a short time, and when the detected temperature Td starts to decrease, this is returned to the upward trend. Takes a long time. For this reason, when the detected temperature Td tends to increase or decrease, it is necessary to react quickly to correct the first and second integrated values.

  That is, when the latest detected temperature Td is higher than the detected temperature Tdb one minute ago by the second addition / subtraction value threshold temperature, the second addition / subtraction value M2 becomes a positive value, and the first and second integrated values increase. Is done. Thereby, it can reflect in the 1st, 2nd integrated value that the detected temperature Td entered into the upward tendency. Similarly, when the latest detected temperature Td is lower than the detected temperature Tdb one minute ago by the second addition / subtraction value threshold temperature, the second addition / subtraction value M2 is a negative value, and the first and second integrated values are Will be reduced. In other words, the second addition / subtraction value M2, which is a rapid response estimated value, is calculated based on the change temperature difference that is the difference between the latest detected temperature Td detected by the power generation chamber temperature sensor 142 and the past detected temperature Tdb. Therefore, when the detected temperature Td is drastically reduced, the amount of change that increases the fuel utilization rate Uf is greatly suppressed, and the generated power is reduced by the utilization rate-suppressed power generation amount, compared with the case where the detected temperature Td is gradually decreasing. Since the maximum fuel utilization rate Ufmax is also set low in the region below IU, the amount of change is more greatly suppressed. Thereby, it can reflect in the 1st, 2nd integrated value that detected temperature Td entered into the fall tendency. Thus, in the present embodiment, the difference based on the integrated value of the first addition / subtraction value M1 determined based on the detected temperature Td and the difference between the newly detected detected temperature Td and the detected temperature Tdb detected in the past. The amount of heat storage is estimated based on the value. That is, in the present embodiment, the integrated value of the first addition / subtraction value M1, which is a basic estimated value calculated based on the history of the detected temperature Td, and the detected temperature Td in a period shorter than the history of calculating the basic estimated value. Based on the second addition / subtraction value M2, which is a quick response estimated value calculated based on the rate of change, the heat storage amount estimation unit 110b estimates the heat storage amount. Thus, in this embodiment, the heat storage amount is estimated based on the sum of the basic estimated value and the quick response estimated value.

  Note that the temperature change of the fuel cell module 2 is extremely slow compared to 1 minute, which is the interval at which the detected temperatures Td and Tdb are detected, so the second addition / subtraction value M2 is often zero. For this reason, the first and second integrated values are mainly governed by the first addition / subtraction value M1, and when the detected temperature Td increases or decreases, the second addition / subtraction value M2 becomes the first and second integration values. Acts to correct the value of. Thus, in addition to the detected temperature history, the most recent change in the detected temperature Td is added to the estimated value of the heat storage amount by the second addition / subtraction value M2. For this reason, when the most recent change in detected temperature Td is large (change greater than or equal to the second addition / subtraction value threshold temperature), since the second addition / subtraction value M2 has a value, the estimated value of the heat storage amount is corrected, and the fuel utilization rate Uf is significantly changed.

Next, the limitation on the variable range of the generated power will be described with reference to FIGS.
As described above, in the solid oxide fuel cell according to the present embodiment, the amount of heat accumulated in the heat insulating material 7 and the like is used to increase the fuel utilization rate, and the fuel is obtained by actively utilizing the heat storage. The temperature in the battery module 2 is controlled to an appropriate temperature. On the other hand, as described with reference to FIGS. 19 and 20, when the power generated by the fuel cell module 2 is frequently increased or decreased according to the demand power, the temperature in the fuel cell module 2 may excessively increase. . Such an excessive temperature rise can be suppressed by increasing the fuel utilization rate and positively using the amount of heat accumulated in the heat insulating material 7 or the like. However, as described with reference to FIG. 24, in the region where the power to be generated is large, the set minimum fuel utilization rate Ufmin is a large value, so there is little room for increasing the fuel utilization rate and using the heat storage. . Therefore, when the generated power is large, it is difficult to effectively reduce the excessively increased temperature in the fuel cell module 2 even if the fuel utilization rate is increased and heat storage is used. For this reason, in this embodiment, when the excessive temperature rise in the fuel cell module 2 occurs, the variable range in which the generated power follows the demand power is limited to be low. As a result, the fuel cell module 2 is operated with a small amount of generated power, so that room for using heat storage is increased, and the temperature in the fuel cell module 2 can be effectively reduced. Moreover, the temperature rise by the frequent increase / decrease in generated electric power is suppressed by narrowing the variable range which makes generated electric power track demand electric power.

  The temperature rise in the fuel cell module 2 due to frequent increase / decrease in demand power described with reference to FIGS. 19 and 20 also occurs in the solid oxide fuel cell according to the first embodiment of the present invention described above. Therefore, the limitation of the variable range of the generated power described below with reference to FIGS. 29 to 32 can also be implemented in combination with the above-described first embodiment of the present invention.

  FIG. 29 is a flowchart showing a procedure for limiting the range of power generated by the fuel cell module in the present embodiment. FIG. 30 is a map showing current limitations on the generated current and the detected temperature Td. FIG. 31 is a time chart showing an example of the operation in the present embodiment. FIG. 32 is a graph showing an example of the relationship between the temperature in the fuel cell module and the maximum power that can be generated.

  First, as shown by the solid line in FIG. 30, in the solid oxide fuel cell of this embodiment, an appropriate temperature in the fuel cell module 2 is set for each generated current. This appropriate temperature corresponds to the alternate long and short dash line in FIG. In addition, as shown in FIG. 30, a current maintaining region is set in a region where the temperature is higher than the appropriate temperature. The minimum temperature of the current maintaining region is set to be different depending on the power generated by the fuel cell module 2, and the minimum temperature of the current maintaining region is set higher as the generated power is larger. Further, the minimum temperature of the current maintenance region for each generated power is set such that the difference from the appropriate temperature of the fuel cell module 2 increases as the generated power decreases. When the operating state of the fuel cell module 2 enters this current maintenance region, an increase in output current from the fuel cell module 2 is prohibited. Furthermore, a current reduction region is set in a region where the temperature is higher than the current maintaining region. When the operating state enters this current reduction region, the output current from the fuel cell module 2 is forcibly reduced. An air cooling region is set in a region where the temperature is higher than the current lowering region. When the operating state enters this air cooling region, the supply amount of power generation air is set to the maximum flow rate that can be supplied by the power generation air flow rate adjustment unit 45. An operation stop region is set in a region where the temperature is higher than the air cooling region. When the operation state enters this operation stop region, the power generation by the fuel cell module 2 is stopped to prevent a failure of the solid oxide fuel cell.

  Further, when the detected temperature Td rises rapidly, the temperature that defines the current maintaining region is lowered as shown by a one-dot chain line in FIG. In this case, the temperature defining the current reduction region is lowered as shown by a two-dot chain line in FIG. As a result, when the detected temperature Td rises rapidly, current limitation is performed at an early stage to reliably suppress an excessive temperature rise.

Next, a procedure for limiting the current generated by the fuel cell module will be described with reference to FIG.
First, in step S41 of FIG. 29, the detected temperature Td is read. Next, in step S42, the detected temperature Td read in step S41 is compared with the detected temperature Td before a predetermined time. If the difference between the detected temperature Td read in step S41 and the detected temperature Td before a predetermined time is equal to or lower than a predetermined threshold temperature, the process proceeds to step S43.

  In step S43, a basic characteristic indicated by a solid line in FIG. 30 is selected as a map for determining the temperature region. On the other hand, if the difference between the latest detected temperature Td and the detected temperature Td before the predetermined time is larger than the predetermined threshold temperature, the process proceeds to step S44. In step S44, as a map for determining the temperature region, FIG. The rapid temperature rise characteristics indicated by the alternate long and short dashed lines are selected.

  Next, in step S45, it is determined whether or not the detected temperature Td is within the operation stop region. In the present embodiment, when the detected temperature Td is 780 ° C. or higher, it is determined that it is in the operation stop region. If it is determined that the detected temperature Td is within the operation stop region, the process proceeds to step S46. In step S46, power generation by the fuel cell module 2 is stopped and the solid oxide fuel cell system is urgently stopped.

  On the other hand, if it is determined in step S45 that the detected temperature Td is not within the operation stop region, the process proceeds to step S47. In step S47, it is determined whether or not the detected temperature Td is within the air cooling region. In the present embodiment, when the detected temperature Td is 750 ° C. or higher, it is determined that it is in the air cooling region. If it is determined that the detected temperature Td is within the air cooling region, the process proceeds to step S48.

  In step S <b> 48, the generated current is fixed to 1 A, which is the minimum current, and this current is not output to the inverter 54 but is consumed by the auxiliary unit 4. The air supply amount is set to the maximum flow rate that can be supplied by the power generation air flow rate adjustment unit 45. Further, the supply amount of water is also increased, the ratio of the water vapor amount to the carbon amount S / C = 4 is set, and one process of the flowchart of FIG. 29 is completed.

  On the other hand, if it is determined in step S47 that the detected temperature Td is not within the air cooling region, the process proceeds to step S49. In step S49, it is determined whether or not the detected temperature Td and the generated current are within the current decrease region. If they are within the current decrease region, the process proceeds to step S50.

  In step S50, the current generated by the fuel cell module 2 is forcibly reduced to 4A or less. That is, the upper limit value of the electric power generated by the fuel cell module 2 is reduced to a temperature rise suppression power (400 W) higher than a half of 700 W which is the maximum rated power. Thereafter, when the demand power decreases, the upper limit value of the generated power (current) is decreased following the demand power, and even if the demand power increases, the generated current is maintained without increasing. Thereby, the one-time process of the flowchart of FIG. 29 is completed. Such limitation of the generated current is continued until the detected temperature Td and the generated current are out of the current decrease region.

  On the other hand, if it is determined in step S49 that the detected temperature Td and the generated current are not within the current decrease region, the process proceeds to step S51. In step S51, it is determined whether or not the detected temperature Td and the generated current are within the current maintenance region. If they are within the current maintenance region, the process proceeds to step S52.

  In step S52, an increase in the generated current is prohibited, and thereafter, even if the demand power increases, the generated current is maintained without increasing. In addition, when the demand power decreases, the upper limit value of the generated current (electric power) is decreased following the decrease in the demand power, and even if the demand power increases, the upper limit value of the generated current (electric power) is increased. Maintained without. Such limitation of the generated current is continued until the detected temperature Td and the generated current are out of the current maintaining region and the excessive temperature rise of the fuel cell module 2 is resolved. Thereby, the one-time process of the flowchart of FIG. 29 is completed.

  In the present embodiment, for each generated current, when the detected temperature Td exceeds the minimum temperature of the current maintenance region, the regulation of the generated power is started. Therefore, in this specification, the minimum of the current maintenance region for each generated current The temperature is referred to as a generated power regulation temperature (FIG. 30). In this embodiment, the generated power regulation temperature is set to be higher than the fuel utilization rate change temperature (Ts (I) + Te) (FIG. 22) at which the change to increase the fuel utilization rate is started.

  On the other hand, when it is determined in step S51 that the detected temperature Td and the generated current are not within the current maintaining region, the process proceeds to step S53. In step S53, the generated current is not limited, and control using heat storage is performed.

Next, an example of generated current limitation will be described with reference to FIG.
The time chart shown in FIG. 31 is a diagram schematically showing changes in detected temperature Td, target current, generated current, fuel supply amount, fuel utilization rate, and air supply amount in order from the top. Here, the target current is a current obtained from demand power and generated voltage.

First, at time t20 in FIG. 31, the generated current is about 6A, and the detected temperature Td is in a state slightly lower than the appropriate temperature in the generated current about 6A (corresponding to t20 in FIG. 30).
Next, at times t20 to t21, since the demand power repeatedly fluctuates greatly in a short time, the target current also greatly increases and decreases, and the generated current also increases and decreases to follow this. On the other hand, as described with reference to FIG. 20, the fuel supply amount is maintained for a predetermined time after the generation current is reduced and is increased prior to the increase in the generation current. And excess fuel is generated. Since this surplus fuel is used for heating in the fuel cell module 2, the detected temperature Td tends to increase from time t20 to t21.

  Further, at time t21, the detected temperature Td reaches the temperature of the current maintaining region at the generated current of about 6A (corresponding to t21 in FIG. 30 and steps S51 to S52 in FIG. 29). Thereby, step S52 of FIG. 29 is executed, and thereafter, the increase in generated current is prohibited and the generated current is maintained. For this reason, from time t21 to t22, the target current increases to about 7A, but the generated current is maintained at about 6A. By prohibiting the increase in the generated current, the upper limit value of the variable range of the generated power is reduced and the variable range is narrowed, so that the amount of residual fuel accompanying a change in the generated power is reduced. In this way, step S52 in FIG. 29, which reduces the amount of residual fuel while continuing power generation, acts as a temperature rise suppression means. Further, step S51 for determining whether or not to execute step S52 acting as a temperature rise suppression means acts as an excessive temperature rise estimation means for estimating the occurrence of an excessive temperature rise in the fuel cell module 2.

  Further, at times t21 to t22, since the detected temperature Td rises, the first addition / subtraction value M1 becomes a positive large value, and the value of the first integrated value N1id also increases significantly. As a result, the fuel supply amount is decreased so as to increase the fuel utilization rate Uf (FIG. 23). This increase in the fuel utilization rate Uf also acts as a temperature rise suppression means because it acts to reduce the amount of residual fuel and lower the temperature in the fuel cell module 2. At times t21 to t22, the fuel utilization rate Uf is increased and the amount of heat accumulated in the heat insulating material 7 and the like is actively consumed. However, since the heat capacity of the fuel cell module 2 is very large, the detected temperature Td continues to rise.

  Next, at time t22, the increased fuel utilization rate Uf reaches the maximum fuel utilization rate Ufmax (= 75%), which is the maximum fuel utilization rate at the generated current of about 6A (N1id = 1 in FIG. 23, FIG. 24). Since the fuel utilization rate Uf is increased to the maximum fuel utilization rate Ufmax at time t22, the fuel utilization rate Uf is maintained at the maximum fuel utilization rate Ufmax from time t22 to t23. On the other hand, since the detected temperature Td continues to rise from time t22 to t23, the value of the second integrated value N2id (the same value as the first integrated value N1id) also increases. Along with this, the air utilization rate Ua is reduced (N2id> 1 in FIG. 25), that is, the air supply amount is increased.

  Furthermore, at time t23, the detected temperature Td reaches the temperature of the current drop region at the generated current of about 6A (corresponding to steps S49 → S50 in FIG. 29). Accordingly, step S50 in FIG. 29 is executed, and the generated current is rapidly reduced from about 6A to 4A (t23 → t23 ′ in FIG. 30), and the upper limit value of the variable range of the generated power is further reduced. Is further narrowed. For this reason, the fuel utilization rate Uf is slightly reduced from the maximum fuel utilization rate Ufmax at the generated current of about 6A to the maximum fuel utilization rate Ufmax at the generated current 4A (FIGS. 24 and 31). At time t23, the fuel utilization rate Uf is reduced, but since the generated current is reduced to 4A, the absolute amount of fuel supply and the absolute amount of residual fuel are reduced. Since the fuel utilization rate Uf is maintained at the maximum fuel utilization rate Ufmax while the generated current is reduced, the consumption of the accumulated heat amount is further promoted. In this way, step S50 in FIG. 29, which reduces the amount of residual fuel while continuing power generation by reducing the generated current, also acts as temperature rise suppression means. However, the detected temperature Td still rises from time t23 to t24.

  Next, at time t24, the detected temperature Td reaches the temperature of the air cooling region (corresponding to steps S47 → S48 in FIG. 29, t24 in FIG. 30). Thus, step S48 of FIG. 29 is executed, and the air supply amount is increased to the maximum air supply amount of the power generation air flow rate adjustment unit 45. Further, the generated current gradually decreases from 4A to 1A. Thereafter, the generated current that has been reduced to 1 A, which is the temperature increase suppressing power generation amount, is kept constant until the detected temperature Td decreases to a temperature lower than the current maintaining region. Further, the generated current reduced to 1 A is not output to the inverter 54, and the entire amount is consumed by the auxiliary unit 4. As the generated current decreases, the fuel utilization rate Uf decreases from the maximum fuel utilization rate Ufmax at the generated current 4A to the maximum fuel utilization rate Ufmax (= 50%) at the generated current 1A (FIG. 24).

  As described above, after the temperature increase suppression for reducing the amount of residual fuel is executed in step S50 of FIG. 29, which is the temperature increase suppression means, the air supplied when the temperature increase needs to be further suppressed. Is increased. Since the increased amount of air increased beyond the supply amount necessary for power generation acts as a cooling fluid flowing into the fuel cell module 2, step S48 in FIG. 29 functions as a forced cooling means.

  On the other hand, if the detected temperature Td decreases without reaching the temperature in the air cooling region by executing step S50, which is a temperature rise suppression means for reducing the amount of residual fuel, the process proceeds to step S48, which is a forced cooling means. No cooling is performed. Therefore, whether or not the temperature rise suppression by the forced cooling means is executed is determined based on the temperature change in the fuel cell module 2 after the temperature rise suppression by the temperature rise suppression means is executed.

  After time t24, the detected temperature Td continues to increase, but starts decreasing at time t25 (t24 → t25 in FIG. 30). Thereafter, the detected temperature Td decreases, and at time t26, the detected temperature Td decreases to the upper limit temperature of the current decrease region (t25 → t26 in FIG. 30). Thereby, the reduction of the air supply amount is started.

  Next, at time t27, the temperature decreases to the upper limit temperature of the current maintaining region (t26 → t27 in FIG. 30). The detected temperature Td continues to further decrease, and at time t28, the detected temperature Td decreases to the lower limit temperature of the current maintaining region (t27 → t28 in FIG. 30).

  When the detected temperature Td goes out of the current maintaining region at time t28, the generated current starts to increase to follow the target current. Along with this, the fuel supply amount also increases. Further, the fuel utilization rate Uf increases while taking the maximum fuel utilization rate Ufmax corresponding to each generated current.

  In the above-described embodiment, the temperature rise is suppressed by lowering the upper limit value of the variable range of the generated power in accordance with the temperature in the fuel cell module 2. Temperature rise can also be suppressed by reducing the frequency. That is, when the temperature in the fuel cell module 2 rises, the rise in temperature can be suppressed by reducing the followability of increasing the generated power following the increase in demand power. When the followability to the increase in demand power is reduced, the generated power increases more slowly when the demand power increases. For this reason, when the demand power is frequently increased or decreased, the increase / decrease width of the generated power to follow this is reduced as a result, the frequency of increase / decrease is reduced, and the amount of residual fuel generated is also reduced. . Such a decrease in followability with respect to an increase in demand power continues until the excessive temperature rise in the fuel cell module 2 is resolved.

  Alternatively, it is possible to limit the frequency per hour for increasing the generated power following the increase in demand power. In this case, a limit is imposed on the number of times per predetermined time at which the generated power turns to an increasing trend, and if the number of times per predetermined time increases, the generated power will not follow the increase in demand power. To control.

  In the above-described embodiment, when the detected temperature Td reaches the temperature in the current reduction region, the upper limit value of the generated current is reduced to 4 A. However, as a modified example, the upper limit value of the generated power to be reduced is variable. You can also For example, the upper limit value of the generated power to be reduced can be set lower as the temperature in the fuel cell module 2 is higher.

Next, the relationship between the temperature in the fuel cell module 2 and the maximum power that can be generated will be described with reference to FIG.
As described above, there is a correlation between the generated power (current) of the fuel cell module 2 and the appropriate temperature in the fuel cell module 2, and in order to obtain large generated power, the temperature in the fuel cell module 2 is increased. There is a need to. However, in the temperature range in which the fuel cell module 2 is higher than the appropriate temperature for the generated power and exceeds about 700 ° C., the potential generated by each fuel cell unit 16 decreases due to the characteristics of the fuel cell stack 14. For this reason, when a large current is drawn from the fuel cell stack 14 in order to obtain a large amount of power, the temperature of the fuel cell stack 14 further rises and the generated potential decreases. Therefore, even if the current is increased, the output power The phenomenon that does not increase occurs. Thus, as shown in FIG. 32, in the region where the temperature in the fuel cell module 2 is high, the maximum power that can be generated decreases as the temperature rises. In such a temperature range, if the maximum rated power is to be extracted from the fuel cell module 2, the current is increased to increase the extracted power, and this current rise further increases the temperature of the fuel cell module 2 and is extracted. The power will be reduced. If such a state continues, in order to obtain a predetermined rated power, a thermal runaway in which the temperature of the fuel cell module 2 rapidly rises is caused.

  In the present embodiment, in a region where the temperature in the fuel cell module 2 is higher than the appropriate temperature, thermal runaway can be prevented by maintaining or reducing the generated current even when demand power is increased. Yes.

Next, with reference to FIG. 33, the measurement of the detected temperature Td in the present embodiment will be described.
FIG. 33 is a flowchart showing a procedure for calculating the first addition / subtraction value M1 based on the detected temperatures Td of the plurality of temperature sensors.

  As shown in FIG. 3, in the present embodiment, two power generation chamber temperature sensors 142 are provided in the power generation chamber 10. Here, in this embodiment, in the fuel cell module 2, 20 fuel cell units 16 are arranged in the width direction (FIG. 2), and 8 fuel cell units 16 are arranged in the depth direction. (FIG. 3). Accordingly, all 160 fuel cell units 16 are arranged in a rectangular shape in plan view. In the present embodiment, one of the two power generation chamber temperature sensors 142 is disposed adjacent to the vertex of the rectangle, and the other is disposed adjacent to the midpoint of the long side of the rectangle. As described above, in this embodiment, the two power generation chamber temperature sensors 142 are arranged at different positions so that different temperatures in the fuel cell module 2 are detected.

  Therefore, the detected temperature Td of the power generation chamber temperature sensor 142 disposed adjacent to the vertex of the rectangle mainly reflects the temperature of the fuel cell unit 16 disposed near the vertex of the rectangle, and the length of the rectangle is long. The detected temperature Td of the power generation chamber temperature sensor 142 disposed adjacent to the middle point of the side mainly reflects the temperature of the fuel cell unit 16 disposed near the middle point (intermediate part) of the long side of the rectangle. ing. Since the fuel cell unit 16 arranged near the top of the rectangle is easily deprived of heat by the surrounding heat insulating material 7 or the like, the temperature is the lowest, and the fuel cell unit arranged near the midpoint of the long side of the rectangle 16 is higher in temperature than the fuel cell unit 16 disposed near the apex. In the present embodiment, the temperature difference between these fuel battery cell units 16 may reach several tens of degrees. The fuel cell unit 16 arranged near the intersection of the rectangular diagonal lines is considered to have the highest temperature, and a power generation chamber temperature sensor may be arranged to measure this temperature.

  First, in step S61 of FIG. 33, the detected temperatures Td are read from the two power generation chamber temperature sensors 142, respectively. Next, in step S62, an average value of the two detected temperatures Td read is calculated, and it is determined whether or not the averaged temperature is higher than the appropriate temperature Ts (I) (FIG. 22). When the averaged temperature is higher than the appropriate temperature Ts (I), the process proceeds to step S63, and when lower than the appropriate temperature Ts (I), the process proceeds to step S64.

  In step S63, the first addition / subtraction value M1 is calculated based on the higher detection temperature Td of the two detection temperatures Td (the first addition / subtraction value M1 becomes a positive value or 0). One process of the flowchart is terminated. That is, the estimated increase amount of the heat storage amount is determined based on the higher detection temperature Td of the two detection temperatures Td. On the other hand, in step S64, the first addition / subtraction value M1 is calculated based on the lower detection temperature Td of the two detection temperatures Td (the first addition / subtraction value M1 becomes a negative value or 0). The one-time processing of the flowchart of 33 is finished. That is, the estimated reduction amount of the heat storage amount is determined based on the lower detection temperature Td of the two detection temperatures Td. Thus, when the temperature is higher than the appropriate temperature Ts (I), the detected temperature Td on the high temperature side is adopted, and when it is lower, the detected temperature Td on the low temperature side is adopted. Thereby, when an excessive temperature rise becomes a problem, the heat storage amount is estimated based on the temperature of the fuel cell unit 16 having a high temperature. Further, when the temperature drop becomes a problem, the amount of stored heat is estimated based on the temperature of the fuel cell unit 16 having a low temperature (usually, the fuel cell unit located at the top of the rectangle). Even if the temperature of the cell unit 16 is different, the heat storage amount can be estimated on the safe side.

  In the embodiment described above, the high temperature side or the low temperature side of the detected temperature Td is selected, and the integrated value is calculated based on this. However, as a modification, the integrated value is obtained for each detected temperature Td. Also good. That is, an addition / subtraction value is determined based on each of a plurality of detected temperatures, and the stored heat amount is estimated by adding the determined addition / subtraction values for each detected temperature and calculating a plurality of integration values, and a plurality of integration values When all are increasing, select a large numerical value among the plurality of integrated values, and when some of the multiple integrated values are decreasing, select a small numerical value among the plurality of integrated values, You may use this as an estimated value of heat storage amount.

In the embodiment described above, the high temperature side of the detected temperature is employed in step S63 and the low temperature side of the detected temperature is employed in step S64. However, as a modification, based on a weighted average of two detected temperatures. Thus, the first addition / subtraction value M1 can be calculated to estimate the heat storage amount. For example, in step S63, the first addition / subtraction value M1 is calculated based on a value obtained by adding a value obtained by multiplying the high temperature side of the detected temperature by 0.7 and a value obtained by multiplying the low temperature side by 0.3. In S64, the first addition / subtraction value M1 can be calculated based on a value obtained by adding a value obtained by multiplying the high temperature side of the detected temperature by 0.3 and a value obtained by multiplying the low temperature side by 0.7. Thus, in step S63 in which the detected temperature Td is high and the estimated value of the heat storage amount is increased (the first addition / subtraction value M1 is positive or 0), the highest temperature among the plurality of detected temperatures Td is the factor with the highest weight. Is used for estimating the amount of stored heat, and the estimated value of the stored amount of heat is reduced (the first addition / subtraction value M1 is negative or 0). In step S64, the lowest temperature is used as the factor with the largest weight for estimating the amount of stored heat. The
Alternatively, the first addition / subtraction value M1 can always be calculated from a value obtained by simply averaging the detected temperatures Td without weighting the detected temperatures Td.

  Further, the first addition / subtraction value M1 is determined so as to suppress the increase in the fuel utilization rate Uf when the temperature of the fuel cell unit located at the vertex of the rectangle falls below a predetermined use suppression cell unit temperature. You can also

  Next, with reference to FIG. 34, calculation of addition / subtraction values according to a modification of the present embodiment will be described. Note that the addition / subtraction value calculation according to the present modification may be used in combination with the processing shown in FIG. 33, or may be applied independently. When this modification is applied alone, the number of power generation chamber temperature sensors 142 may be one.

  FIG. 34 is a flowchart showing a procedure for calculating the first addition / subtraction value M1 based on the temperature detected by the reformer temperature sensor 148 as another temperature detection means in addition to the power generation chamber temperature sensor 142 as the temperature detection means. It is.

  First, in step S71 of FIG. 34, the detected temperature is read from the reformer temperature sensor 148. In the present embodiment, the reformer 20 is provided with reformer temperature sensors 148 at two locations on the inlet side and the outlet side, and the temperature near the inlet of the reformer 20 and the temperature near the outlet inlet. Is to be measured. Normally, the temperature of the reformer 20 is low at the inlet side where many steam reforming reactions, which are endothermic reactions, occur, and the temperature at the outlet side is high.

  Next, in step S72, each detected temperature of the reformer 20 is compared with a predetermined use suppression reformer temperature. First, of the two detected temperatures of the reformer 20, the lower detected temperature is lower than the low-temperature side use suppression reformer temperature Tr0, and the higher detection temperature is the high-temperature side use suppression reformer temperature Tr1. If it is lower, the process proceeds to step S73. On the other hand, of the two detected temperatures of the reformer 20, the higher detected temperature is higher than the high-temperature side use suppression reformer temperature Tr1, and the lower detection temperature is the low-temperature side use suppression reformer temperature Tr0. If higher, the process proceeds to step S75. If none of these applies, the process proceeds to step S74.

  In step S73, since the temperature of the reformer 20 is lower than each use suppression reformer temperature, the first addition / subtraction value M1 is corrected so that the fuel utilization rate Uf decreases (the fuel supply amount increases). . That is, a value obtained by subtracting 10% of the absolute value of the first addition / subtraction value M1 calculated based on the temperature Td detected by the power generation chamber temperature sensor 142 from the first addition / subtraction value M1 is used for integration as the first addition / subtraction value M1. To do. As a result, the first integrated value N1id, which is an estimated value of the heat storage amount, decreases (inhibition is increased), so the fuel utilization rate Uf tends to decrease (increase in fuel utilization rate is suppressed), and the reformer The temperature of 20 is raised.

  On the other hand, in step S75, since the temperature of the reformer 20 is higher than each use suppression reformer temperature, the first addition / subtraction value M1 is set so that the fuel utilization rate Uf increases (the fuel supply amount decreases). to correct. That is, a value obtained by adding 10% of the absolute value of the first addition / subtraction value M1 calculated based on the temperature Td detected by the power generation chamber temperature sensor 142 to the first addition / subtraction value M1 is used for integration as the first addition / subtraction value M1. To do. As a result, the first integrated value N1id, which is an estimated value of the heat storage amount, increases (decrease is suppressed), so the fuel utilization rate Uf tends to increase, and the temperature of the reformer 20 decreases. Thereby, damage to the reformer 20 due to the temperature of the reformer 20 rising excessively is prevented.

  In step S74, since the temperature of the reformer 20 is within the appropriate temperature range, the correction of the first addition / subtraction value M1 is not executed, and the one-time process of the flowchart of FIG. 34 is terminated. (Since there is a correlation between the two detected temperatures of the reformer 20, the lower detected temperature is lower than the low-temperature use suppression reformer temperature, and the higher detected temperature is the high-temperature use suppression reformer. (Higher temperatures usually do not occur.)

  In the present modification, the fuel utilization rate is corrected by averaging the detected temperatures by the two reformer temperature sensors 148 and comparing the averaged detected temperature with one or two use suppression reformer temperatures. May be. Further, when the change rate is high according to the change rate per time of the temperature detected by the reformer temperature sensor 148, the amount for correcting the fuel utilization rate may be increased.

  Next, with reference to FIG. 35, calculation of addition / subtraction values according to a modification of the present embodiment will be described. The addition / subtraction value calculation according to the present modification may be used in combination with the processing shown in FIGS. 33 and 34, or may be applied alone. When this modification is applied alone, the number of power generation chamber temperature sensors 142 may be one.

  FIG. 35 is a flowchart showing a procedure for calculating the first addition / subtraction value M1 based on the temperature detected by the exhaust temperature sensor 140 as another temperature detection means in addition to the power generation chamber temperature sensor 142 as the temperature detection means. .

  First, in step S81 of FIG. 35, the detected temperature is read from the exhaust temperature sensor 140. In the present embodiment, the exhaust temperature sensor 140 is arranged to measure the temperature of the exhaust gas that is combusted in the combustion chamber 18 and flows out through the exhaust gas discharge pipe 82.

  Next, in step S82, the detected exhaust gas temperature is compared with a predetermined use-suppressed exhaust temperature. First, when the detected temperature of the exhaust gas is lower than the predetermined low temperature side use suppression exhaust temperature Tem0, the process proceeds to step S83. On the other hand, when the detected temperature of the exhaust gas is higher than the predetermined high-temperature side use suppression exhaust temperature Tem1, the process proceeds to step S85. When the detected temperature of the exhaust gas is lower than the high temperature side use suppression exhaust temperature Tem1 and higher than the low temperature side use suppression exhaust temperature Tem0, the process proceeds to step S84.

  In step S83, since the temperature of the exhaust gas is lower than the appropriate temperature, the first addition / subtraction value M1 is corrected so that the fuel utilization rate Uf decreases (the fuel supply amount increases). That is, a value obtained by subtracting 10% of the absolute value of the first addition / subtraction value M1 calculated based on the temperature Td detected by the power generation chamber temperature sensor 142 from the first addition / subtraction value M1 is used for integration as the first addition / subtraction value M1. To do. As a result, the first integrated value N1id, which is an estimated value of the heat storage amount, decreases (increase is suppressed), so that the fuel utilization rate Uf tends to decrease (increase in the fuel utilization rate Uf is suppressed), and the exhaust gas The temperature of the is raised.

  On the other hand, in step S85, since the temperature of the exhaust gas is higher than the appropriate temperature, the first addition / subtraction value M1 is corrected so that the fuel utilization rate Uf increases (the fuel supply amount decreases). That is, a value obtained by adding 10% of the absolute value of the first addition / subtraction value M1 calculated based on the temperature Td detected by the power generation chamber temperature sensor 142 to the first addition / subtraction value M1 is used for integration as the first addition / subtraction value M1. To do. As a result, the first integrated value N1id, which is an estimated value of the heat storage amount, increases (decrease is suppressed), the fuel utilization rate Uf tends to increase, and the temperature of the exhaust gas decreases. Thereby, the temperature in the fuel cell module 2 is optimized.

  In step S84, since the temperature of the exhaust gas is within the appropriate temperature range, the correction of the first addition / subtraction value M1 is not executed, and the one-time process of the flowchart of FIG. 35 is terminated.

  In this modification, when the change rate is high according to the change rate per hour of the temperature detected by the exhaust temperature sensor 140, the range for correcting the fuel utilization rate may be increased.

  As mentioned above, although preferable embodiment of this invention was described, a various change can be added to embodiment mentioned above. In particular, in the above-described embodiment, the heat capacity of the heat insulating material (heat storage material) is constant, but as a modification, the fuel cell module can be configured so that the heat capacity can be changed. In this case, the additional heat capacity member having a large heat capacity is arranged so as to be thermally connected to and disconnected from the fuel cell module. When the heat capacity is to be increased, the additional heat capacity member is thermally connected to the fuel cell module, and when the heat capacity is to be decreased, the additional heat capacity member is thermally disconnected. For example, when starting up the solid oxide fuel cell, the heat capacity is reduced by separating the additional heat capacity member, and the temperature of the fuel cell module is increased quickly. On the other hand, when the solid oxide fuel cell is expected to be operated for a long time with large generated power, the additional heat capacity member is connected so that the fuel cell module can accumulate a larger amount of surplus heat.

Moreover, as a preferred embodiment, the present invention can be configured as follows.
1. A solid oxide fuel cell that generates variable generated power according to demand power, a fuel cell module that generates power using the supplied fuel, a fuel supply unit that supplies fuel to the fuel cell module, and a fuel cell Power generation oxidant gas supply means for supplying power generation oxidant gas to the module, heat storage material for accumulating heat generated in the fuel cell module, demand power detection means for detecting demand power, and this demand power detection means Based on the demand power detected by the above, the fuel supply rate is determined by referring to the basic fuel supply table set so that the fuel utilization rate is high when the generated power is large and the fuel utilization rate is low when the generated power is small. Control means for controlling the fuel supply means so that the determined fuel supply amount is supplied and when the generated power is large when the generated power is small Fuel table changing means for changing the basic fuel supply table so as to temporarily increase the fuel utilization rate during the period in which the accumulated available heat amount is accumulated in the heat storage material, and reducing the fuel supply amount; It is characterized by having.

  In the present invention configured as described above, the fuel supply unit and the power generation oxidant gas supply unit respectively supply the fuel and the power generation oxidant gas to the fuel cell module. The fuel cell module generates power with the supplied fuel and power generation oxidant gas, and heat generated in the fuel cell module is accumulated in a heat storage material. Based on the demand power detected by the demand power detection means, the control means is a basic fuel supply table set so that the fuel utilization rate is high when the generated power is large and the fuel utilization rate is low when the generated power is small. To determine the fuel supply amount and control the fuel supply means. The fuel table changing means is configured so that when the generated power is small, the basic fuel is used so that the fuel utilization rate temporarily increases during the period in which the available heat amount accumulated when the generated power is large is accumulated in the heat storage material. Change the supply table to reduce the fuel supply.

  In general, in a solid oxide fuel cell, when the generated power is small, the generated heat decreases, so the temperature of the fuel cell module tends to decrease. For this reason, at the time of small power generation, the fuel utilization rate is lowered, fuel that has not been used for power generation is burned, and the fuel cell module is heated to prevent an excessive temperature drop. In particular, in a solid oxide fuel cell of a type in which a reformer is disposed in a fuel cell module, an endothermic reaction occurs in the reformer, so that the temperature is more likely to decrease. According to the present invention configured as described above, the amount of heat stored in the heat storage material when the generated power is large is used positively when the generated power is small, thereby suppressing the temperature drop. Because it is possible to control the fuel utilization rate only for a temporary period that can be performed, the solid oxide fuel cell is maintained while maintaining the thermal independence of the solid oxide fuel cell and avoiding excessive temperature drop. It is now possible to improve the overall energy efficiency.

  2. In the present invention configured as described above, preferably, the fuel table changing means temporarily changes the basic fuel supply table for reducing the fuel supply amount when the generated power is small, and then ends the change. The control means controls the fuel supply means based on the original basic fuel supply table.

  According to the present invention configured as described above, the fuel table changing means temporarily changes the basic fuel supply table and then ends the change, and thereafter the fuel supply means based on the basic fuel supply table. Since the amount of heat accumulated in the heat storage material is excessively reduced, the risk of causing a significant temperature drop can be reliably avoided.

  3. In the present invention configured as described in 2 above, the basic fuel supply table is preferably configured in a region larger than a predetermined medium power generation power so that the amount of heat accumulated during the large power generation power can be used during the small power generation power. The amount of heat is set so as to be accumulated in the heat storage material.

  According to the present invention configured as described in 3 above, since the basic fuel supply table is set so that a larger amount of heat is accumulated in the heat storage material in a region larger than the middle power generation power, the fuel utilization rate The amount of heat stored by actively accumulating heat in a region that is larger than the medium generated power, which can be increased, and consuming this heat at the time of small generated power where the temperature of the fuel cell module is relatively low and heat independence is difficult It is possible to reliably perform highly efficient operation with a high fuel utilization rate that effectively utilizes the.

  4). In the present invention configured as described above, preferably, the basic fuel supply table is set so that a larger amount of heat is accumulated in the heat storage material in a region where the generated power is larger than the median value of the generated power range. Has been.

  According to the present invention configured as described above, a larger amount of heat is accumulated in the heat storage material in a region where the generated power is larger than the median value of the generated power range. For this reason, in the vicinity of the median value of the frequently used power generation range, the amount of surplus heat accumulated is suppressed, and a large amount of heat is accumulated in the heat storage material at the peak of power demand. As a result, when a solid oxide fuel cell is used in a house, excessive fuel consumption to store a large amount of heat is suppressed in the time zone where the most frequent power demand is at moderate power demand such as daytime. On the other hand, since it can be configured so that a large amount of heat is accumulated during the nighttime hours when power demand peaks, the amount of heat stored in the nighttime hours can be consumed immediately at midnight in the following time zone Therefore, it is possible to realize high-efficiency operation that effectively uses the heat that is reliably stored in the late-night time when the generated power is greatly reduced while the amount of heat is not stored unnecessarily for a long time.

  5). In the present invention configured as described in 3 above, preferably, it further includes a heat storage amount estimation means for estimating a heat storage amount of the heat storage material, and the fuel table changing means has a heat storage amount estimated by the heat storage amount estimation means. The basic fuel supply table is changed when it is equal to or greater than a predetermined change execution heat storage amount, and the basic fuel supply table is not changed when the estimated heat storage amount is less than the change execution heat storage amount.

  According to the present invention configured as described in 5 above, since the heat storage amount of the heat storage material is estimated by the heat storage amount estimation means, it is possible to safely change the fuel utilization rate, and the estimated heat storage amount is predetermined. Since the change is executed when it is equal to or greater than the change execution heat storage amount, excessive cooling can be prevented more reliably.

  6). In the present invention configured as described above, preferably, the fuel table changing means increases the change amount of the basic fuel supply table that decreases the fuel supply amount as the heat storage amount estimated by the heat storage amount estimating means increases. To do.

  According to the present invention configured as described in 6 above, as the estimated heat storage amount is larger, the fuel utilization rate can be greatly improved, so that the overall energy efficiency can be greatly improved more safely. it can.

  7). In the present invention configured as described above, preferably, the fuel table changing means changes the period for executing the change of the basic fuel supply table based on the heat storage amount estimated by the heat storage amount estimation means, and the basic At least one change of the change amount of the fuel supply table is selected and executed.

  According to the present invention configured as described above, since the period or amount of change of the basic fuel supply table is changed, the overall energy efficiency can be reliably improved.

8). In the present invention configured as described in 5 above, preferably, the heat storage amount estimation means estimates the heat storage amount of the heat storage material based on the temperature of the fuel cell module.
According to the present invention configured as described above, since the heat storage amount is estimated based on the temperature of the fuel cell module having a strong relationship with the stored heat amount, it is relatively accurate without providing a special sensor. The amount of stored heat can be estimated, and performance deterioration of the fuel cell module and excessive temperature drop can be reliably avoided.

9. In the present invention configured as described in 5 above, preferably, the heat storage amount estimation means estimates the heat storage amount of the heat storage material based on the past operation history of the fuel cell module.
According to the present invention configured as described in 9 above, the amount of stored heat is estimated based on the operation history before the generated power is reduced and the change of the basic fuel supply table is started. Compared to control based only on temperature, more accurate control based on the remaining heat storage amount is possible, and the heat storage amount can be estimated safely, simply, and accurately.

  10. In the present invention configured as described above, preferably, the heat storage amount estimation means estimates the heat storage amount of the heat storage material based on the past generated power of the fuel cell module and the time operated with the generated power. .

  According to the present invention configured as described above, since the heat storage amount is estimated based on the generated power of the fuel cell module and its time, the heat storage amount is accurately estimated without providing a special sensor. be able to.

  11. In the present invention configured as described above, preferably, the fuel table changing means determines a predetermined change execution period based on the heat storage amount estimated by the heat storage amount estimating means at the start of changing the basic fuel supply table. The change is executed within the change execution period.

  According to the present invention configured as described above, since the change is executed within the change execution period determined based on the heat storage amount estimated by the heat storage amount estimation means, the heat storage is utilized with simpler control. A change of the basic fuel supply table can be realized.

  12 In the present invention configured as described in 3 above, preferably, during the execution of the change of the basic fuel supply table by the fuel table changing means, it is possible to suppress a decrease in the heat storage amount of the heat storage material and to change the basic fuel supply table. There is a change period extension means for extending the period of execution.

  According to the present invention configured as described above, since the change period extending means for extending the period for executing the change of the basic fuel supply table is provided, the accumulated heat amount is effectively used according to the situation. can do.

  13. In the present invention configured as in the above 12, preferably, the change period extending means increases the basic fuel supply as the period during which the change of the basic fuel supply table is executed becomes longer as the heat storage amount of the heat storage material decreases. Reduce the amount of table changes.

  According to the present invention configured as described above, since the amount of change with respect to the basic fuel supply table is reduced as the amount of heat stored is reduced, the temperature of the fuel cell module is excessively lowered and the performance is deteriorated. The period for increasing the fuel utilization rate can be extended.

14 In the present invention configured as described above, preferably, the change period extension means decreases the change amount of the basic fuel supply table as the generated power is smaller.
According to the present invention configured as described above, since the amount of change to the basic fuel supply table is reduced as the generated power is smaller, the amount of change is reduced at the time of small generated power that uses more heat storage. In addition, it is possible to extend the period during which the fuel utilization rate is increased while reliably avoiding excessive temperature drop and performance deterioration of the fuel cell module.

  15. In the present invention configured as described above, preferably, the change period extending means generates power so as to reduce the oxidant gas for power generation supplied to the fuel cell module during execution of the change of the basic fuel supply table. The oxidant gas supply means is controlled.

  According to the present invention configured as described in 15 above, since the oxidant gas for power generation supplied to the fuel cell module is reduced during execution of the change, the amount of heat accumulated in the heat storage material is taken away by the oxidant gas. The heat storage can be effectively utilized for a longer time.

16. In the present invention configured as described in 3 above, preferably, it further includes an overcooling preventing means for preventing overcooling of the fuel cell module when the heat storage amount of the heat storage material is small.
According to the present invention configured as described in 16 above, since the excessive cooling prevention means is provided, it is possible to reliably prevent excessive cooling by increasing the fuel utilization rate in a state where the heat storage amount is reduced. it can.

  17. In the present invention configured as described in 16 above, preferably, the overcooling preventing means has a followability of the fuel supply amount by the fuel supply means during a period in which the fuel supply amount change is being executed by the fuel table changing means. Improves the followability during normal operation.

  According to the present invention configured as described in 17 above, the followability of the fuel supply amount during the period in which the fuel supply amount is changed is improved, so that the use of the fuel after the change as the heat storage amount decreases As the rate decreases, the amount of fuel supply can be quickly increased. Thereby, it is possible to prevent overcooling of the fuel cell module due to a delay in response to increase the fuel supply amount.

DESCRIPTION OF SYMBOLS 1 Solid oxide fuel cell 2 Fuel cell module 4 Auxiliary machine unit 7 Heat insulation material (heat storage material)
8 Sealed space 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 22 Heat exchanger for air 24 Water supply source 26 Pure water tank 28 Water flow rate adjustment unit (water supply means)
30 Fuel supply source 38 Fuel flow rate adjustment unit (fuel supply means)
40 Air supply source 44 Reforming air flow rate adjustment unit 45 Power generation air flow rate adjustment unit (power generation oxidizing gas supply means)
46 1st heater 48 2nd heater 50 Hot water production apparatus 52 Control box 54 Inverter 83 Ignition apparatus 84 Fuel cell 110 Control part (control means)
110a Fuel table changing means (fuel supply amount changing means)
110b Heat storage amount estimation means 110c Power extraction delay means 112 Operation device 114 Display device 116 Alarm device 126 Power state detection sensor (demand power detection means)
132 Fuel flow sensor (fuel supply detection sensor)
138 Pressure sensor (reformer pressure sensor)
140 Exhaust temperature sensor (temperature detection means)
142 Power generation chamber temperature sensor (temperature detection means)
148 Reformer temperature sensor (temperature detection means)
150 Outside temperature sensor

Claims (15)

A solid oxide fuel cell that generates variable generation power according to demand power,
A fuel cell module for generating electricity from the supplied fuel;
Fuel supply means for supplying fuel to the fuel cell module;
Power generation oxidant gas supply means for supplying power generation oxidant gas to the fuel cell module;
A heat storage material for accumulating heat generated in the fuel cell module;
Demand power detection means for detecting demand power;
Based on the demand power detected by the demand power detection means, the fuel supply means is controlled so that the fuel utilization rate is high when the generated power is large and the fuel utilization rate is low when the generated power is small. Control means for changing the power to be actually output from the fuel cell module after changing the fuel supply amount in accordance with the change in power, and
The control means includes
A heat storage amount estimating means for estimating a surplus heat amount based on a fuel supply by the fuel supply means and an electric power output delayed with respect to the fuel supply, and a heat amount available to the heat storage material by the heat storage amount estimation means; Is estimated to be accumulated, the fuel supply amount is reduced so that the fuel utilization rate is higher for the same generated power than when the available heat amount is not accumulated. Solid oxide fuel cell.   2. The solid oxide fuel cell according to claim 1, wherein the control means increases the fuel utilization rate significantly as the heat storage amount estimated by the heat storage amount estimation means increases.   The said control means changes a fuel usage rate largely with respect to the change of an estimated heat storage amount in the area | region where the estimated heat storage amount estimated by the said heat storage amount estimation means is large rather than the area | region where an estimated heat storage amount is small. 3. The solid oxide fuel cell according to 2.   3. The solid oxide fuel cell according to claim 2, wherein the heat storage amount estimation means estimates the heat storage amount by integrating addition / subtraction values reflecting surplus heat amounts due to output of electric power delayed with respect to fuel supply. .   The addition / subtraction value is determined based on a temperature in the fuel cell module, a surplus heat amount calculated from a relationship between a fuel supply amount and generated power, an increase / decrease amount of generated power, or a frequency of increase / decrease of generated power per hour. 5. The solid oxide fuel cell according to 4.   The control means has a region larger than a predetermined medium power generation power so that the heat amount stored at the time of the large power generation power can be used at the time of the small power generation power when the heat storage material does not store the heat amount available. 3. The solid oxide fuel cell according to claim 2, wherein the fuel supply means is controlled so that a larger amount of heat is accumulated in the heat storage material.   The solid oxide mold according to claim 6, wherein the control means controls the fuel supply means so that a larger amount of heat is accumulated in the heat storage material in a region where the generated power is larger than a median value of the generated power range. Fuel cell.   7. The solid oxide fuel cell according to claim 6, wherein the control means increases the fuel utilization rate when the heat storage amount estimated by the heat storage amount estimation means is equal to or greater than a predetermined change execution heat storage amount.   The control means determines a predetermined change execution period based on the heat storage amount estimated by the heat storage amount estimation means at the start of high efficiency control with an increased fuel utilization rate, and performs high efficiency control within the change execution period. The solid oxide fuel cell according to claim 2 to be executed.   The change period extending means for suppressing a decrease in a heat storage amount of the heat storage material and extending a period for executing the high efficiency control during execution of the high efficiency control with an increased fuel utilization rate. Solid oxide fuel cell.   The solid oxide according to claim 10, wherein the change period extension means decreases the change amount that increases the fuel utilization rate as the period of executing the high efficiency control becomes longer as the heat storage amount of the heat storage material decreases. Type fuel cell.   11. The solid oxide fuel cell according to claim 10, wherein the change period extending means decreases the change amount that increases the fuel utilization rate as the generated power is smaller.   11. The power generation oxidant gas supply unit controls the power generation oxidant gas supply unit so as to decrease a power generation oxidant gas supplied to the fuel cell module during execution of the high efficiency control. Solid oxide fuel cell.   3. The solid oxide fuel cell according to claim 2, further comprising an overcooling prevention means for preventing overcooling of the fuel cell module when the heat storage amount of the heat storage material is small.   15. The solid according to claim 14, wherein the overcooling prevention means improves the followability of the fuel supply amount by the fuel supply means more than the followability during normal operation during execution of high efficiency control with an increased fuel utilization rate. Oxide fuel cell.

Images