JP5783369B2 - Solid oxide fuel cell - Google Patents

Description

  The present invention relates to a solid oxide fuel cell, and more particularly to a solid oxide fuel cell that outputs variable generated power to an inverter 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.

  Japanese Patent Laying-Open No. 2004-265671 (Patent Document 1) describes a fuel cell operation control method and apparatus. In this fuel cell, the battery voltage is detected, and when the battery voltage decreases, the current command value obtained by converting the power command value for the fuel cell into a current is decreased. The current limiter uses a current command value when the battery voltage is reduced as a limit value, and reduces the limit value in accordance with a decrease in the battery voltage. Specifically, when the battery voltage reaches a voltage drop alarm level that is a first threshold, the battery current starts to drop, and when the battery voltage reaches a voltage drop protection level that is a second threshold, the battery current is zero. Thus, the current command value is limited.

JP 2004-265671 A

  However, in the fuel cell described in Japanese Patent Application Laid-Open No. 2004-265671, since the voltage drop of the fuel cell is simply detected to limit the current value, the fuel cell is sufficiently protected from deterioration and damage. There is a problem that can not be. The inventor of the present invention has a deep relationship with the temperature of the fuel cell stack (the temperature in the fuel cell module), and the temperature of the fuel cell stack is inverted by a predetermined power drop. It has been found that when the temperature Tc is exceeded, sufficient electric power cannot be extracted from the fuel cell stack, and operating the fuel cell in this state may lead to damage to the fuel cell stack.

  In general, in a fuel cell capable of outputting variable power, it is known that the temperature in the fuel cell module is low when the output power is low, and the temperature in the fuel cell module increases as the output power increases. Furthermore, as long as the electric power is extracted in the temperature range in which the fuel cell stack can be used, it has been considered that more electric power can be extracted as the temperature rises. FIG. 10 is a graph schematically showing the relationship between the temperature in the fuel cell module found by the present inventors and the generated power that can be output. As shown in FIG. 10, the output power changes as shown in this figure even when the output current is constant. Specifically, until the fuel cell module reaches the power drop reversal temperature Tc, the generated power that can be output from the fuel cell module increases as the temperature rises, as conventionally considered.

  However, when the temperature in the fuel cell module reaches a predetermined power drop inversion temperature Tc, the generated power that can be output from the fuel cell module starts to decrease conversely as the temperature increases. This is because the fuel cells constituting the fuel cell module are not made of a simple ceramic material and contain various metal materials, so that the resistance of the ceramic decreases as the temperature rises, but the metal does the opposite. As the resistance value increases and this sum is improving the cells of the fuel cell, it is considered that not only the power that can be extracted is reduced, but also the situation is reversed. Therefore, in the case where a fuel cell module composed of high-performance fuel cells in recent years is in such a temperature range that exceeds Tc, if the power to be extracted is increased, the target power can be extracted from the fuel cell module. The drawn current increases, thereby further increasing the temperature in the fuel cell module. When the temperature in the fuel cell module further rises, a situation like a negative spiral occurs in which the electric power that can be taken out further decreases as the resistance value increases. Therefore, if more power is taken out from the fuel cell module in which the power generation capacity is reduced or the temperature rises excessively, the output current increases and the temperature in the fuel cell module increases more and more. Once the control of the fuel cell module falls into such a spiral state, a rapid current increase and a temperature increase occur, and the fuel cell stack is damaged in a short time. This is a problem.

  Therefore, it is absolutely necessary to avoid operating the fuel cell module in a temperature range exceeding the power drop inversion temperature Tc. However, the fuel cell stack and the fuel cell module incorporating the fuel cell stack have an extremely large heat capacity, and the temperature change is slow. For this reason, once the temperature in the fuel cell module starts to rise, it is not easy to stop the temperature rise even if it is close to the power drop inversion temperature Tc. In addition, since the temperature change is very slow in the fuel cell module composed of various materials with large heat capacity, the detection time constant of the temperature detection sensor is increased and slowed down in order to adapt to this slow temperature change environment. There must be. Therefore, it becomes difficult to quickly grasp the temperature rising and falling trends in the fuel cell module.

  The present invention has been made to solve such problems, and provides a solid oxide fuel cell that can reliably prevent the fuel cell module from falling into a spiral state in which the temperature rises and the current increases. The purpose is to do.

In order to solve the above-described problem, the present invention provides a solid oxide fuel cell that outputs variable generated power to an inverter according to demand power, and includes a plurality of oxide ion conductive electrolyte layers. It is composed of fuel cell units, and at temperatures below a specified power drop reversal temperature, the power that can be output increases as the temperature rises, and when it exceeds the power drop reversal temperature, the power that can be output decreases as the temperature rises. a fuel cell stack has a fuel cell module with a built-in fuel cell stack, a fuel supply means, the interior of the reforming catalyst, the supplied fuel, steam reforming the fuel containing hydrogen gas a reformer for supplying to the fuel cell stack, and the electrical generation oxidant gas supply means for supplying oxidant gas for power generation in the fuel cell stack, the generated power according to the power demand The fuel supply means and the control means for controlling the oxidant gas supply means for power generation, and the control means has a normal output in a temperature band where the temperature of the fuel cell stack is lower than the power drop inversion temperature. While performing power control, when it is estimated that the temperature range is equal to or higher than the power drop inversion temperature, the temperature range output limiting means is provided for limiting the output current from the fuel cell module and fixing it to a predetermined output current. It is characterized by that.

  In the present invention configured as described above, the control means controls the fuel supply means and the power generation oxidant gas supply means, and the fuel cell in which the fuel and the power generation oxidant gas are built in the fuel cell module. The power is supplied to the cell stack, and output power corresponding to the demand power is generated in a temperature band lower than the power drop inversion temperature. On the other hand, even if a temporary excessive temperature rise occurs and the power drop inversion temperature is exceeded, the temperature range output limiting means provided in the control means reduces the output current from the fuel cell module. Limit and fix to a predetermined output current.

  According to the present invention configured as described above, the fuel cell module can be reliably prevented from falling into a spiral state in which the temperature rises and the current increases. That is, when it is estimated that the temperature of the fuel cell stack is equal to or higher than the power drop inversion temperature, if the output current from the fuel cell module is increased, the fuel cell module falls into a spiral state of temperature increase and current increase. End up. However, according to the present invention, in such a case, by fixing the output current to a small amount of output current, not only the increase of the output current is restricted, but also the power generation is possible even with a small amount without making the output current zero. By continuing, it prevents the increase in residual fuel caused by prohibiting power generation, suppresses further temperature rise in the fuel cell module accompanying the increase in residual fuel, and quickly lowers the temperature to reduce the power drop inversion temperature It can be reduced to: In addition, by fixing the output current to a constant current, it is possible to prevent an increase or decrease in the output current, so that it is possible to reduce the surplus fuel that supplies fuel ahead of the output current provided for protecting the fuel cell. From this point as well, the temperature can be quickly lowered to a temperature lowering inversion temperature or lower in the fuel cell module.

  In the present invention, preferably, the temperature range output limiting means suppresses the power output to the inverter when the temperature of the fuel cell stack reaches a predetermined output suppression temperature set lower than the power drop inversion temperature.

  According to the present invention configured as described above, when the output suppression temperature set lower than the power drop inversion temperature is reached, the output power is suppressed, so that it is difficult to grasp the temperature change in the fuel cell module, Even when the detection of the temperature rise is delayed, it is possible to prevent the power drop inversion temperature from being exceeded with certainty because a safety margin for the temperature detection delay can be provided.

  In the present invention, preferably, the control means increases the supply amount of the oxidant gas for power generation when the temperature of the fuel cell stack rises above a predetermined forced cooling temperature set lower than the power drop inversion temperature. And cooling the fuel cell stack.

  According to the present invention configured as described above, since the cooling with the oxidant gas for power generation is used together with the output limitation, the temperature in the fuel cell module can be effectively reduced, and the power can be more reliably supplied. It is possible to prevent the drop inversion temperature from being exceeded.

  In the present invention, it is preferable that the control unit further suppresses the power output to the inverter when the output current necessary for outputting the predetermined power to the inverter becomes equal to or greater than a predetermined current determined according to the power. Current range output limiting means.

  According to the present invention configured as described above, by adding power suppression by the current range output limiting unit in addition to the temperature range output limiting unit, the burden on the fuel cell stack can be more reliably reduced. it can.

  In the present invention, preferably, the temperature range output limiting means limits the power output to the inverter based on the change in the output voltage of the fuel cell module with respect to the change in the current output from the fuel cell module to the inverter.

  According to the present invention configured as described above, since the power is limited based on the change in the output voltage with respect to the change in the output current, the spiral of the temperature increase and the current increase is based on the temperature of the fuel cell stack. Rather than detecting the state, it can be surely prevented from falling into a spiral state.

  In the present invention, it is preferable that the temperature range output limiting unit is configured such that when the current output from the fuel cell module to the inverter is substantially constant, the output voltage of the fuel cell module decreases by a predetermined power drop inversion temperature determination voltage or more. In addition, the power output to the inverter is limited.

  According to the present invention configured as described above, since the spiral state of the temperature increase and the current increase is detected based on the decrease of the output voltage when the output current is substantially constant, the spiral state can be determined more accurately. Can do.

  According to the present invention, it is possible to reliably prevent the fuel cell module from entering the spiral state of temperature rise and current increase.

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 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 a graph which shows the relationship between the temperature in a fuel cell module, and generated electric power. It is a flowchart of control by the temperature range output restriction means built in the control part. It is a graph which shows the restriction | limiting by the current range output restriction | limiting means incorporated in the control part. 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.

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 and 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, residual fuel and residual oxidant (air) that have not been used for the power generation reaction. Burns and produces exhaust gas.
Further, a reformer 20 for reforming the fuel is disposed above the combustion chamber 18, and the reformer 20 is heated to a temperature at which a reforming reaction can be performed by the combustion heat of the residual gas. Yes. Further, an air heat exchanger 22 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. In addition, the auxiliary unit 4 adjusts the flow rate of the fuel gas, the gas shutoff valve 32 for shutting off the fuel supplied from the fuel supply source 30 such as city gas, the desulfurizer 36 for removing sulfur from the fuel gas, A fuel flow rate adjustment 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 is, for example, zirconia doped with at least one selected from rare earth elements such as Y and Sc, ceria doped with at least one selected from rare earth elements, 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 embodiment of the present invention will be described with reference to FIGS. 9 to 12.
FIG. 9 is a graph schematically showing the relationship between the change in power demand, the amount of fuel supplied, and the current actually taken from the fuel cell module. FIG. 10 is a graph showing the relationship between the temperature in the fuel cell module and the generated power. FIG. 11 is a flowchart of the control by the temperature range output limiting means built in the control unit. FIG. 12 is a graph showing the restriction by the current range output restriction means built in the control unit.

  As shown in FIG. 9, the fuel cell module 2 is controlled so as to be able to generate power corresponding to the demand power shown in the uppermost stage of FIG. The control unit 110 serving as a control unit sets a fuel supply current value If, which is a target current to be generated by the fuel cell module 2, based on the demand power 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. 9, 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 electric 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. In the graph of FIG. 9, the fuel supply current value If and the fuel supply amount Fr are drawn as being proportional to each other, but actually, the fuel utilization rate is changed according to the operating state.

  Further, as shown in the lowermost graph in FIG. 9, 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. 9, 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. 9, after the fuel supply current value If and the fuel supply amount Fr start to increase, the increase of 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. 10 is a graph schematically showing the relationship between the temperature of the fuel cell stack 14 and the power that can be output to the inverter 54 in the embodiment of the present invention. As shown in FIG. 10, until the temperature of the fuel cell stack 14 reaches 750 ° C., which is the power drop inversion temperature Tc, the power that can be output from the fuel cell module 2 increases as the temperature rises. In the fuel cell module 2 in the present embodiment, when the temperature of the fuel cell stack 14 reaches a predetermined power drop inversion temperature Tc, the power that can be output from the fuel cell module 2 starts to decrease conversely as the temperature increases. Has characteristics. The characteristics shown in FIG. 10 are measured as output power in a state where the current output from the fuel cell module 2 is constant. In the present specification, the temperature of the fuel cell stack 14 means an arbitrary temperature that reflects the temperature of the fuel cell stack 14, and an arbitrary temperature detection arranged in the fuel cell module 2. The temperature detected by the means can be used as the temperature of the fuel cell stack 14.

  Since the fuel cell module 2 has the characteristics as shown in FIG. 10, when the power taken out to the inverter 54 is increased when the fuel cell stack 14 is in a temperature band equal to or higher than the power drop inversion temperature Tc, the fuel cell module 2 The drawn current increases, and thereby the temperature of the fuel cell stack 14 rises. As the temperature of the fuel cell stack 14 increases, the power that can be output further decreases. If further power is taken out from the fuel cell module 2 having a reduced power generation capability, the output current increases and the temperature of the fuel cell stack 14 increases further. Once the control of the fuel cell module 2 falls into such a spiral state, a rapid current increase and a temperature increase occur, and the fuel cell stack 14 may be damaged in a short time.

  The temperature range output limiting means 110a (FIG. 6) built in the control unit 110 is arranged inside the fuel cell module 2 to prevent the control of the fuel cell module 2 from falling into the spiral state as described above. It operates so that it may be maintained at 550 to 650 ° C., which is the use band temperature indicated by diagonal lines. Specifically, the temperature range output restriction means 110a executes the control flow shown in FIG. Note that the control flow shown in FIG. 11 is repeatedly executed at predetermined time intervals during operation of the solid oxide fuel cell 1.

  First, in step S1 of FIG. 11, the temperature range output restriction means 110a determines the value of the temperature range output preliminary restriction flag F2. The temperature range output preliminary restriction flag F2 is a flag indicating whether or not the output power preliminary restriction is performed by the temperature range output restriction means 110a, and when the output power preliminary restriction is performed. F2 = 1, and F2 = 0 if not performed. In step S1, when the temperature range output preliminary restriction flag F2 = 1, the process proceeds to step S8, and when F2 = 0, the process proceeds to step S2.

  Next, in step S2, the temperature range output restriction unit 110a determines the value of the temperature range output restriction flag F1. The temperature range output limit flag F1 is a flag that indicates whether or not the output power limit is performed by the temperature range output limit unit 110a. When the output power limit is performed, F1 = 1. If not, F1 = 0 is set. In step S2, if the temperature range output restriction flag F1 = 1, the process proceeds to step S13, and if F1 = 0, the process proceeds to step S3.

  In step S3, it is determined whether or not the temperature of the fuel cell stack 14 detected by the power generation chamber temperature sensor 142 (FIG. 6), which is a temperature detection means, is equal to or higher than 650 ° C., which is the second output suppression temperature. The If it is equal to or higher than the second output suppression temperature, the process proceeds to step S11. If it is not equal to or higher than the second output suppression temperature, the process proceeds to step S4.

  In step S4, it is determined whether or not the current drawn from the fuel cell module 2 to the inverter 54 is substantially constant. In the present embodiment, the temperature range output limiting means 110a determines that the current is substantially constant when the fluctuation of the current taken out to the inverter 54 in the last three minutes is ± 100 mA or less. In this way, the state in which the current taken out to the inverter 54 is substantially constant is, for example, a state in which the demand power fluctuates at a value larger than the rated power of the solid oxide fuel cell 1 and the fuel cell module 2 This occurs when the engine is operated so as to output the rated power, or when the fuel cell module 2 is operated so as to output the electric power when the demand power is constant for a predetermined time or longer. When it is determined that the current is substantially constant, the process proceeds to step S5, and when it is not constant, one process of the flowchart of FIG. 11 is terminated.

  Next, in step S5, it is determined whether or not a voltage drop equal to or higher than a predetermined power drop inversion temperature determination voltage has occurred during the period in which the output current determined in step S4 is constant. In the present embodiment, the temperature range output limiting means 110a determines that a voltage drop equal to or higher than the power drop inversion temperature determination voltage has occurred when the voltage drops by 3 V or more in 3 minutes when the current is substantially constant. If it is determined that a voltage drop equal to or higher than the power drop inversion temperature determination voltage has occurred, the process proceeds to step S6. If no voltage drop has occurred, the one-time process in the flowchart of FIG. 11 is terminated. That is, in a situation where the temperature of the fuel cell stack 14 is lower than the second output suppression temperature and no voltage drop equal to or higher than the power drop inversion temperature determination voltage has occurred, the fuel cell stack 14 reaches the power drop inversion temperature. Therefore, the process of the flowchart of FIG. 11 is terminated without limiting the power.

  On the other hand, in step S6, since a voltage drop equal to or higher than the power drop inversion temperature determination voltage has occurred, the current that can be taken out from the fuel cell module 2 to the inverter 54 is 50. % Reduced. That is, as described with reference to FIG. 9, the current value Iinv that can be taken out is instructed to the inverter 54 as a current value that can be taken out by the inverter 54 in accordance with the amount of fuel supplied to the fuel cell module 2. Current value. The temperature range output limiting means 110a reduces this extractable current value Iinv by 50%, and reduces the current extracted from the fuel cell module 2 to the inverter 54.

  Note that when the extractable current value Iinv reduced by 50% is less than 1A, the extractable current value Iinv is set to 1A. Further, the fuel supply amount (fuel supply current value If) supplied to the fuel cell module 2 is also reduced to a value corresponding to the extractable current value Iinv. When the current taken out from the fuel cell module 2 is reduced to 1 A or less, it may remain unused for power generation, and the amount of fuel burned in the combustion chamber 18 may increase, causing the temperature of the fuel cell stack 14 to rise. is there. For this reason, it is advantageous to continue the current output of about 1 A in order to reduce the temperature of the fuel cell stack 14.

  As described above, when a voltage drop occurs despite the output current being substantially constant (step S4 → S5 → S6 path), a part of the fuel cell stack 14 has a power drop inversion temperature Tc. May have been reached. Therefore, in this case, the current taken out from the fuel cell module 2 to the inverter 54 is greatly reduced, and the fuel cell module 2 is reliably prevented from falling into a spiral state in which the current increases and the temperature rises.

  Next, in step S7, the value of the temperature range output preliminary limit flag F2 is changed to 1, and the integration of the output preliminary limit timer is started, and the process of the flowchart of FIG. 11 is ended.

  After the value of the temperature range output preliminary restriction flag F2 is changed to 1, when the flowchart of FIG. 11 is executed, the process proceeds from step S1 to step S8. In step S8, it is determined whether or not 15 minutes have elapsed since the start of integration of the output preliminary limit timer in step S7. If 15 minutes have passed, the process proceeds to step S9. If not, the process of the flowchart of FIG. That is, for 15 minutes after the start of the accumulation of the output preliminary limit timer, the state where the extractable current value Iinv set in step S6 is reduced by 50% is continued.

  In the present embodiment, the temperature of the fuel cell stack 14 is not judged for 15 minutes after the start of the output preliminary limit timer, and the state where the extractable current value Iinv is reduced by 50% is maintained. As another example, the present invention can be configured such that the processing of steps S13 to S18 in FIG. 11 is performed during the accumulation of the output preliminary limit timer (after step S8).

  When 15 minutes have elapsed since the start of the output preliminary limit timer integration, step S9 is executed. In step S9, the restriction on the extractable current value Iinv set in step S6 is released. Next, in step S10, the value of the temperature range output preliminary restriction flag F2 is returned to zero. In a series of processes using these temperature range output preliminary restriction flags F2, the detected temperature of the fuel cell stack 14 has not reached 650 ° C., which is the second output suppression temperature (step S3). Since the output voltage is in a state where the current is almost constant (steps S4 and S5), the output is limited preliminary (step S6), and the state is maintained for 15 minutes (step S8). It is. That is, the temperature of the fuel battery cell stack 14 detected by the power generation chamber temperature sensor 142 is not a direct measurement of the temperature of the fuel battery cell stack 14, and the actual temperature change of the fuel battery cell stack 14 is not affected. The value changes with a delay. For this reason, even when the temperature of the fuel cell stack 14 (the temperature detected by the power generation chamber temperature sensor 142) has not reached the second output suppression temperature, a drop in output voltage occurs. Since it is suspected that a part of the fuel cell stack 14 has reached the power drop inversion temperature Tc, preliminary output restriction is performed. After the preliminary output restriction is executed for a predetermined time, the output restriction is once released, and it is determined again in step S3 and after whether or not the output restriction is necessary.

  On the other hand, if it is determined in step S3 that the temperature of the fuel cell stack 14 is equal to or higher than the second output suppression temperature, the process proceeds to step S11, and the generated power is limited in step S11. In step S11, as a current that can be extracted from the fuel cell module 2 to the inverter 54, the extractable current value Iinv instructed to the inverter 54 is reduced by 30%. Thus, when the representative temperature detected by the power generation chamber temperature sensor 142 is equal to or higher than the second output suppression temperature, a part of the fuel cell stack 14 may reach the power drop inversion temperature Tc. Therefore, by limiting the generated power, further increase in the temperature of the fuel cell stack 14 is suppressed. When the extractable current value Iinv reduced by 30% is less than 1A, the extractable current value Iinv is set to 1A. Further, the fuel supply amount (fuel supply current value If) supplied to the fuel cell module 2 is also reduced to a value corresponding to the extractable current value Iinv.

  Further, in step S12, the value of the temperature range output restriction flag F1 is changed to 1, and one process of the flowchart of FIG. 11 is terminated. That is, the temperature range output restriction unit 110a determines that the risk that the fuel cell module 2 falls into a spiral state of current increase and temperature rise is increased, and sets the temperature range output restriction flag F1 to 1. Thereby, when the flowchart of FIG. 11 is executed thereafter, the temperature range output restriction control in step S13 and subsequent steps is executed until the temperature of the fuel cell stack 14 is sufficiently lowered. The temperature range output restriction flag F1 is a flag indicating that the temperature range output is being restricted.

On the other hand, when the temperature range output restriction flag F1 is changed to 1, steps S13 and after are executed following steps S1 and S2.
In step S13, it is determined whether or not the temperature of the fuel cell stack 14 is equal to or higher than 750 ° C., which is the power drop inversion temperature Tc. If the temperature of the fuel cell stack 14 is equal to or higher than the power drop inversion temperature Tc, the process proceeds to step S14. If not, the process proceeds to step S15.

  In step S14, the extractable current value Iinv is fixed at 1A, which is a predetermined temperature decrease current. Further, the fuel supply amount (fuel supply current value If) supplied to the fuel cell module 2 is also reduced to a value corresponding to the extractable current value Iinv. Furthermore, the power generation air supplied into the fuel cell module 2 is increased by 40% by the power generation air flow rate adjustment unit 45 which is a power generation oxidant gas supply means. Thereby, the fuel cell stack 14 in the fuel cell module 2 is cooled by the flow of air for power generation, and one process of the flowchart of FIG. 11 is completed. That is, when the temperature of the fuel cell stack 14 is equal to or higher than the power drop reversal temperature Tc, the extractable current value Iinv is fixed to a low current value at which the temperature of the fuel cell stack 14 can be reduced most efficiently. Thus, the fuel cell module 2 is prevented from falling into a spiral state of current increase and temperature increase.

  As will be described later, in the solid oxide fuel cell 1 of the present embodiment, when the temperature in the fuel cell module 2 is high and a large amount of heat is accumulated in the heat insulating material 7 or the like, the control unit 110 Execute operation with increased fuel utilization (reduced fuel supply). When an operation with an increased fuel utilization rate is performed, the heat accumulated in the heat insulating material 7 and the like is consumed to make the fuel cell module 2 self-supporting, so the temperature in the fuel cell module 2 decreases. Further, the temperature in the fuel cell module 2 is more likely to be lowered in a state where a small amount of current of about 1 A is taken out than in a state where no current is taken out from the fuel cell stack 14. This is because in the state where no current is taken out, all of the supplied fuel is burned in the combustion chamber 18 and used for heating, whereas a small amount of current is taken out with a small amount of fuel supply. However, the fuel burned in the combustion chamber 18 is reduced, and the temperature is likely to be lowered. For this reason, in the present embodiment, a constant current of 1 A is taken out as the temperature decrease current, and the temperature in the fuel cell module 2 is decreased.

  Furthermore, the temperature in the fuel cell module 2 can be effectively lowered by making the current taken out from the fuel cell module 2 constant. As described with reference to FIG. 9, when the extractable current value Iinv is increased, the fuel supply amount is increased in advance, and the extractable current value Iinv is increased after a predetermined time delay. For this reason, after the fuel supply amount is increased, the fuel supplied until the current is actually taken out becomes surplus fuel, which is burned in the combustion chamber 18 and the temperature in the fuel cell module 2 is raised. The Therefore, by setting the current to be taken out constant, surplus fuel is reduced, and the temperature in the fuel cell module 2 can be lowered. In addition, when the power demand is significantly reduced, the current that needs to be taken out from the fuel cell module 2 may be less than 1A. In such a case, the solid oxide fuel cell 1 can be configured so that power is consumed inside the solid oxide fuel cell 1 as power for operating the auxiliary unit 4 and the like. . Thereby, the electric current taken out from the fuel cell module 2 can be completely fixed to the temperature decrease current.

  On the other hand, in step S15, it is determined whether or not the temperature of the fuel cell stack 14 is equal to or higher than 740 ° C., which is a forced cooling temperature. If the temperature of the fuel cell stack 14 is equal to or higher than the forced cooling temperature and lower than the power drop inversion temperature Tc, the process proceeds to step S16. If not, the process proceeds to step S17.

  In step S16, the extractable current value Iinv instructed to the inverter 54 is reduced by 70%. When the extractable current value Iinv decreased by 70% is less than 1A, the extractable current value Iinv is set to 1A. Further, the fuel supply amount (fuel supply current value If) supplied to the fuel cell module 2 is also reduced to a value corresponding to the extractable current value Iinv. Further, in step S16, the power generation air supplied into the fuel cell module 2 is increased by 30% by the power generation air flow rate adjustment unit 45, which is a power generation oxidant gas supply means. Thereby, the fuel cell stack 14 in the fuel cell module 2 is cooled by the flow of air for power generation, and one process of the flowchart of FIG. 11 is completed.

  On the other hand, in step S17, it is determined whether or not the temperature of the fuel cell stack 14 is equal to or higher than 720 ° C., which is an output suppression temperature. If it is equal to or higher than the output suppression temperature, the process proceeds to step S18. If it is not equal to or higher than the output suppression temperature, the process proceeds to step S19. In the present embodiment, the output suppression temperature is set to be 30 ° C. lower than the power drop inversion temperature Tc.

  In step S18, as the current that can be extracted from the fuel cell module 2 to the inverter 54, the extractable current value Iinv instructed to the inverter 54 is reduced by 50%, and one process of the flowchart of FIG. Note that when the extractable current value Iinv reduced by 50% is less than 1A, the extractable current value Iinv is set to 1A. Further, the fuel supply amount (fuel supply current value If) supplied to the fuel cell module 2 is also reduced to a value corresponding to the extractable current value Iinv.

  On the other hand, in step S19, it is determined whether or not the temperature of the fuel cell stack 14 is 640 ° C. or less, which is the normal use temperature. If the temperature of the fuel cell stack 14 is equal to or lower than the normal use temperature, the process proceeds to step S20. If the temperature exceeds the normal use temperature, one time in the flowchart of FIG. 11 while maintaining the previous extractable current value Iinv. Terminate the process.

  In step S20, the restriction on the extractable current value Iinv is released, the temperature range output restriction flag F1 is set to 0, and the one-time process in the flowchart of FIG. 11 is ended. That is, when the temperature of the fuel cell stack 14 is lowered to the normal operating temperature or less, it is determined that there is no risk of a current increase and a temperature increase spiral state, and the temperature range output restriction flag F1 returns to 0. Then, the temperature range output restriction control is terminated. It should be noted that the temperature range output restriction flag F1 is changed to 1, the second output suppression temperature for starting the temperature range output restriction control is set to 650 ° C. (step S3), and the normal use temperature for ending the temperature range output restriction control is The reason why the temperature is set to 640 ° C. is to prevent a hunting phenomenon in which the start and release of the temperature range output restriction control are repeated. On the other hand, when the temperature of the fuel cell stack 14 exceeds the normal use temperature, the temperature range output restriction flag F1 is maintained at 1, and the temperature range output restriction control is continued.

  Next, with reference to FIG. 12, the limitation of power output by the current range output limiting means 110b (FIG. 6) built in the control unit 110 will be described. The limitation of the output by the current region output limiting means 110b is to limit the output without increasing the current any more when the current necessary for outputting the predetermined power exceeds the predetermined current. Such an output limiting function is also provided in a conventional solid oxide fuel cell. The solid oxide fuel cell 1 of the present embodiment has both the output limiting function by the temperature range output limiting means 110a and the output limiting function by the current range output limiting means 110b, which are necessary. The output is limited accordingly.

  Curves P1 and P2 in FIG. 12 represent the relationship between the output voltage and output current of the fuel cell module 2. Curves Q1 and Q2 are curves showing the relationship between voltage and current necessary for outputting predetermined power from the fuel cell module 2. Curve Q1 shows the relationship between the voltage and current necessary for outputting 700 W, which is the rated power of the solid oxide fuel cell 1, and curve Q2 shows the relationship between the voltage and current necessary for outputting 590 W. Show.

  When the solid oxide fuel cell 1 is initially used, the output voltage and output current of the fuel cell module 2 substantially follow the curve P1. Therefore, when 590 W is output, the voltage value and current value at the intersection R2 between the curve P1 and the curve Q2 are obtained. Here, when the output power is increased to 700 W, the output current increases and the output voltage decreases. As a result, 700 W of power is output based on the voltage value and current value at the intersection R1 between the curve P1 and the curve Q1.

  Here, when the power generation capability of the fuel cell module 2 is reduced for some reason, such as when the fuel cell stack 14 is deteriorated, the output voltage and output current of the fuel cell module 2 follow, for example, the curve P2. . Thus, when the power generation capability of the fuel cell module 2 is reduced, the voltage value and current value when outputting 590 W are the intersection R4 of the curve P2 and the curve Q2. Thus, when the power generation capability of the fuel cell module 2 is reduced, the current required to output the same power increases and the voltage at that time decreases. In this state, in order to obtain 700 W of power from the fuel cell module 2, a current at the intersection R3 where the curve P2 and the curve Q1 intersect is required.

  However, if the output current increases as at the intersection R3, the deterioration of the fuel cell stack 14 may proceed rapidly, or the fuel cell stack 14 may be damaged. Therefore, the current range output limiting means 110b limits the output current by the current limit line L1, and limits the power output by the current value and voltage value on the right side of the current limit line L1. Note that the current limit line can be shifted to the left in FIG. 12 depending on the degree of progress of the deterioration of the fuel cell stack 14.

Next, with reference to FIGS. 13 to 19, a procedure for determining the power generation air supply amount, the water supply amount, and the fuel supply amount based on the required power generation amount and the temperature Td detected by the power generation chamber temperature sensor 142 will be described. To do.
FIG. 13 is a flowchart showing 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. FIG. 14 is a graph showing the proper temperature of the fuel cell stack 14 with respect to the generated current. FIG. 15 is a graph showing the fuel utilization rate determined according to the integrated value. FIG. 16 is a graph showing a range of fuel utilization rate values that can be determined for each generated current. FIG. 17 is a graph showing the air utilization rate determined according to the integrated value. FIG. 18 is a graph showing a range of air utilization rate values that can be determined for each generated current. FIG. 19 is a graph for determining the water supply amount with respect to the determined air utilization rate.

  As indicated by a one-dot chain line in FIG. 14, in this embodiment, the temperature Ts ( I) is defined. 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). In other words, 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. 14). 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. The estimated value of the heat storage amount by integrating the addition / subtraction values is calculated by the heat storage amount estimation means 110c (FIG. 6) built in the control unit.

  The flowchart shown in FIG. 13 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 serving as the temperature detection means. It is executed at the time interval.

First, in step S31 of FIG. 13, 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 the two solid lines in FIG. 14) 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. 14), the first addition / subtraction value M1 is
M1 = Ki × (Td− (Ts (I) −Te)) (5)
Is 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. 14), the first addition / subtraction value M1 is
M1 = Ki × (Td− (Ts (I) + Te)) (7)
Is 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. 13, the 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)
Is 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. 13, 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. 13 is executed continuously after the operation of the solid oxide fuel cell is started. 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.

Furthermore, in step S34 of FIG. 13, the fuel utilization rate is determined using the graphs of FIGS. 15 and 16 based on the calculated first integrated value N1id.
FIG. 15 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. 15, when the first integrated value N1id is 0, the fuel utilization rate Uf is set to the minimum fuel utilization 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. 16 based on the generated current (fuel supply current value If in FIG. 9). 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. 16 is a graph showing a 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. 16, the minimum fuel utilization rate Ufmin for each generated current is set so as 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. When the fuel usage rate on the straight line of the minimum fuel usage rate Ufmin is set, the fuel cell module 2 can be thermally independent without using the amount of heat accumulated in the heat insulating material 7 or the like.

  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 step S34 of FIG. 13, 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. 15, 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. 13, the air utilization rate is determined using the graphs of FIGS. 17 and 18 based on the second integrated value N2id.
FIG. 17 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. 17, 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. 17 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. 18 based on the generated current.

  FIG. 18 is a graph showing a 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. 18, the maximum air utilization rate Uamax for each generated current is set to be slightly increased with an increase in the generated current. 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, the air utilization rate Ua set by the graph of FIG. 17 may not be realized in a region where the minimum air utilization rate Uamin is equal to or greater than a predetermined generated current indicated by a broken line in FIG. 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 of the portion indicated by the broken line in FIG. 18 can 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. 13, based on the generated current, specific values of the minimum air utilization rate Uamin and the maximum air utilization rate Uamax are determined 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. 17, 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. 13, 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. 19 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 amount of supplied water vapor and the amount of carbon contained in the fuel.

  First, in the region of the power generation current (between Uamax and ULamin in FIG. 19) 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 generated 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. 19, 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. 18), 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. 19, 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. . Furthermore, 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. 19), 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. 18), 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. As described above, when the water supply amount is increased after decreasing the air utilization rate Ua and increasing the air supply amount, 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. 13 is completed.

  Next, the time interval for executing the flowchart of FIG. 13 will be described. In the present embodiment, when the output current is large, the flowchart of FIG. 13 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 means 110c 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, the operation of the solid oxide fuel cell realized by the flowchart of FIG. 13 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. 15, a fuel utilization rate Uf higher than the minimum fuel utilization rate Ufmin is set, the fuel supply amount is reduced, and the amount of residual fuel that remains without being used for power generation is reduced. The fuel utilization rate Uf is significantly increased 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 temperature rise in the fuel cell module 2 is suppressed while power generation is continued. 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, the fuel utilization rate Uf is maintained at the maximum fuel utilization rate Uafmax (minimum fuel supply amount) as shown in FIG. 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. The heat storage amount is estimated by the heat storage amount estimation means 110c based on the second addition / subtraction value M2, which is a speed response estimation value calculated based on the change rate. 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.

  According to the solid oxide fuel cell 1 of the embodiment of the present invention, the fuel cell module 2 can be reliably prevented from falling into a spiral state in which the temperature rises and the current increases. That is, when the temperature of the fuel cell stack 14 is equal to or higher than the power drop inversion temperature, or when the output voltage of the fuel cell stack 14 decreases as the temperature of the fuel cell stack 14 increases, the output from the fuel cell module 2 If an attempt is made to increase the current, the fuel cell module 2 falls into a spiral state in which the temperature rises and the current increases (FIG. 10). Therefore, in such a case, the heat accumulated in the fuel cell module 2 is consumed while the remaining fuel that is not used for power generation is reduced by fixing the output current to a small amount of temperature-decreasing current. And can effectively reduce the temperature. Further, by fixing the output current to a constant temperature drop current, it is possible to reduce the surplus fuel that is generated as the output current increases or decreases (FIG. 9), and to ensure that the temperature in the fuel cell module 2 is increased. Can be reduced.

  Furthermore, according to the solid oxide fuel cell 1 of the present embodiment, when the output suppression temperature and the second output suppression temperature set lower than the power drop inversion temperature Tc are reached, the output power is suppressed ( 11, steps S3 → S11 and steps S17 → S18), it is difficult to detect the temperature change of the fuel cell stack 14, and even if it is difficult to detect the temperature rise, the power drop inversion temperature Tc is reliably prevented from exceeding. can do.

  Further, according to the solid oxide fuel cell 1 of the present embodiment, when the temperature of the fuel cell stack 14 rises to a predetermined forced cooling temperature or higher, the power generation air supplied by the power generation air flow rate adjustment unit 45 is reduced. The supply amount is increased (FIG. 11, steps S15 → S16). As described above, in the present embodiment, the cooling of the power generation air is used together with the output restriction, so that the temperature of the fuel cell stack 14 can be effectively reduced, and the power drop inversion temperature is more reliably performed. Exceeding Tc can be prevented.

  Furthermore, according to the solid oxide fuel cell 1 of the present embodiment, since the power is suppressed by the current range output limiting means 110b in addition to the temperature range output limiting means 110a (FIG. 12), more reliable fuel The burden on the battery cell stack 14 can be reduced.

  Further, according to the solid oxide fuel cell 1 of the present embodiment, the temperature rise and the current increase are based on the decrease in the output voltage when the output current is substantially constant (FIG. 11, steps S4 → S5 → S6). Since the spiral state is detected, the spiral state can be determined more accurately.

  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 spiral state of the temperature increase and the current increase is detected based on the decrease in the output voltage when the output current is substantially constant. However, the current output from the fuel cell module to the inverter Based on the change in the output voltage of the fuel cell module with respect to this change, the power output to the inverter can also be limited.

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 Temperature range output limiting means 110b Current range output limiting means 110c Heat storage amount estimation means 112 Operating 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 142 Power generation chamber temperature sensor (temperature detection means)
148 Reformer temperature sensor (temperature detection means)
150 Outside temperature sensor

Claims (6)

A solid oxide fuel cell that outputs variable generated power to an inverter according to demand power,
Consists of a plurality of fuel cell units having an oxide ion conductive electrolyte layer. At temperatures below a predetermined power drop inversion temperature, the power that can be output increases with the temperature rise and exceeds the power drop inversion temperature. And a fuel cell stack with the characteristic that the power that can be output decreases with increasing temperature ,
A fuel cell module incorporating this fuel cell stack ,
And fuel supply means,
A reformer for steam-reforming the supplied fuel into a fuel containing hydrogen gas by an internal reforming catalyst and supplying the fuel to the fuel cell stack;
Power generation oxidant gas supply means for supplying power generation oxidant gas to the fuel cell stack;
Control means for controlling the fuel supply means and the oxidant gas supply means for power generation so that electric power according to demand power can be generated,
In the case where the control means performs normal output power control in a temperature band where the temperature of the fuel cell stack is lower than the power drop inversion temperature, while it is estimated that the temperature is higher than the power drop inversion temperature. A solid oxide fuel cell comprising temperature range output limiting means for limiting an output current from the fuel cell module and fixing the output current to a predetermined output current.   2. The temperature range output limiting means suppresses power output to the inverter when the temperature of the fuel cell stack reaches a predetermined output suppression temperature set lower than the power drop inversion temperature. Solid oxide fuel cell.   When the temperature of the fuel cell stack rises above a predetermined forced cooling temperature set lower than the power drop inversion temperature, the control means increases the supply amount of oxidant gas for power generation, and The solid oxide fuel cell according to claim 2, wherein the battery cell stack is cooled.   The control means further provides a current range output restriction that suppresses the power output to the inverter when the output current required to output the predetermined power to the inverter is equal to or greater than a predetermined current determined according to the power. The solid oxide fuel cell according to claim 3, further comprising means.   The temperature range output limiting means limits the power output to the inverter based on a change in output voltage of the fuel cell module with respect to a change in current output from the fuel cell module to the inverter. Solid oxide fuel cell.   When the output voltage of the fuel cell module decreases by a predetermined power drop inversion temperature determination voltage or more when the current output from the fuel cell module to the inverter is substantially constant, The solid oxide fuel cell according to claim 4, wherein power output to the inverter is limited.

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