JP5804261B2 - 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 changes generated power according to demand power.

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

  Japanese Unexamined Patent Application Publication No. 2008-234869 (Patent Document 1) describes a fuel cell system, and this fuel cell system can perform water self-sustained operation without replenishing water from the outside. As described above, in a fuel cell that performs water self-sustained operation, exhaust gas from the fuel cell is guided to a condenser to condense moisture in the exhaust gas and store the condensed moisture in a recovered water tank. The water stored in the recovered water tank is supplied to a reformer for reforming the fuel gas and used as water for steam reforming the fuel gas.

  In the fuel cell system described in Japanese Patent Application Laid-Open No. 2008-234869, the water level of a recovered water tank that temporarily accumulates condensed water is detected by a water level sensor, and when the detected water level is lower than a preset set water level, the cathode of the fuel cell The amount of reaction air supplied per unit time is reduced to increase the air utilization rate. On the contrary, when the water level of the recovered water tank is higher than the set water level, the amount of reaction air supplied to the cathode of the fuel cell is increased to reduce the air utilization rate of the fuel cell.

  As described above, in the invention described in Japanese Patent Application Laid-Open No. 2008-234869, when the water level of the recovered water tank is low, by increasing the air utilization rate, the amount of supplied air is reduced and the capacity of the condenser is increased. The amount of recovered water is increased by fully exerting it.

JP 2008-234869 A

  However, in actual solid oxide fuel cell operation, the concentration of carbon monoxide in exhaust gas is suppressed, the temperature in the fuel cell module is maintained, excessive temperature rise in the module is suppressed, and the fuel utilization rate is improved. There are various constraints such as improvement of energy efficiency due to heat and securing of hot water supply temperature generated by exhaust heat. Therefore, as in the invention described in Japanese Patent Application Laid-Open No. 2008-234869, if the air utilization rate is increased (the air amount is decreased) in order to increase the amount of recovered water, the temperature in the fuel cell module depends on the operating state. There is a problem that will rise excessively. As described above, the operating conditions of the solid oxide fuel cell are related to each other, and simply trying to increase the amount of recovered water may lead to deterioration of exhaust performance, or in the fuel cell module. Thermal balance is lost, and in the worst case, the fuel cell stack may be damaged.

  Accordingly, an object of the present invention is to provide a solid oxide fuel cell capable of promoting the recovery of condensed water and maintaining water independence while properly maintaining various operating conditions.

In order to solve the above-described problems, the present invention is a solid oxide fuel cell that recovers moisture in exhaust gas, steam-reforms fuel using the recovered water, and generates electric power. A fuel cell module having a battery cell stack, a condenser for condensing moisture in the exhaust of the fuel cell module, a condensed water tank for storing condensed water condensed by the condenser, and a stored in the condensed water tank Storage amount detecting means for detecting the amount of condensed water generated, a reformer for generating hydrogen by steam reforming the fuel and supplying the fuel cell stack, and a fuel supply for supplying fuel to the reformer Means, water supply means for supplying condensed water stored in the condensed water tank to the reformer, oxidant gas supply means for power generation for supplying oxidant gas for power generation to the fuel cell stack, and fuel supply Means, water supply means, and power generation And controls the oxidant gas supply means, the fuel cell module comprises a control means for generating the required generated power, the control means comprises a condensed water fast generation means for executing a condensed water fast generation control, the condensed The water high-speed generating means reduces the generated power to increase the condensed water condensed by the condenser when the stored water amount detecting means detects that the condensed water in the condensed water tank is below a predetermined amount. The control means increases the supply amount of the oxidant gas for power generation when the temperature of the fuel cell stack is equal to or higher than the predetermined temperature even during the execution of the condensed water high-speed generation control. It is characterized by cooling the temperature to an appropriate temperature and then reducing the ratio of oxidant gas / fuel supplied to the fuel cell module .

In the present invention configured as described above, the control means controls the fuel supply means and the water supply means to supply fuel and water to the reformer. In the reformer, the fuel is steam reformed to generate hydrogen, and this hydrogen is supplied to the fuel cell stack built in the fuel cell module. Further, the oxidant gas for power generation is supplied to the fuel cell stack by the oxidant gas supply means for power generation. The condenser condenses moisture in the exhaust gas from the fuel cell module, and the condensed water condensed is stored in a condensed water tank. The condensed water high-speed generating means provided in the control means is configured to increase the condensed water condensed by the condenser when the stored water amount detecting means detects that the condensed water in the condensed water tank is below a predetermined amount. Reduce generated power.
Further, in the present invention configured as described above, when the temperature of the fuel cell stack is high, the supply amount of the oxidant gas for power generation is increased, thereby cooling the fuel cell stack. However, when the supply amount of the oxidant gas for power generation is increased in this way, there is a problem that the exhaust temperature from the fuel cell module decreases and the amount of condensed water condensed in the condenser decreases. According to the present invention, the generation of condensed water can be facilitated simply by reducing the generated power by the condensed water high-speed generating means.

  In general, when the power generated by the fuel cell module is large, the operating temperature of the fuel cell stack becomes high. In such a state, in order to increase the amount of condensed water condensed in the condenser in order to make the solid oxide fuel cell self-supporting, the amount of oxidant gas supplied relative to the amount of fuel supplied to the fuel cell module is increased. There is a need to reduce, ie reduce the oxidant gas / fuel ratio and increase the proportion of water vapor contained in the exhaust from the fuel cell module. However, if the oxidant gas / fuel ratio is decreased while the temperature of the fuel cell stack is high, the temperature of the fuel cell stack may increase excessively and the fuel cell stack may be damaged. For this reason, it is difficult to generate condensed water at high speed when the temperature of the fuel cell stack is high. According to the present invention, when the condensed water in the condensed water tank is insufficient, the condensed water high-speed generating means reduces the generated power to increase the condensed water, so that the temperature of the fuel cell stack is reduced, This creates room for reducing the oxidant gas / fuel ratio supplied to the fuel cell module. That is, even if the fuel cell stack and the exhaust gas temperature are raised by reducing the ratio of oxidant gas / fuel, damage to the fuel cell stack can be reliably avoided and condensed water can be discharged at high speed. Can be generated.

  In the present invention, it is preferable that the control unit controls the fuel supply unit so that the fuel utilization rate is always within a permissible range of the fuel utilization rate set in advance according to the generated power. The allowable range is set to be wider when the generated power is small than when the generated power is large.

  In the present invention configured as described above, it is possible to perform operation with a high fuel utilization rate when the generated power is large. However, if the fuel utilization rate is reduced in this state, the temperature of the fuel cell stack becomes excessive. Will rise. For this reason, it is difficult to promote the generation of condensed water when the generated power is large. On the other hand, since the operating temperature is low when the generated power is low, there is room for reducing the fuel utilization rate, and the allowable range of the fuel utilization rate can be widened. Thereby, the production | generation of condensed water can be accelerated | stimulated by reducing generated electric power.

  In the present invention, preferably, the control means controls the fuel supply means so that the fuel utilization rate is always within a permissible range of the fuel utilization rate set in advance according to the generated power, and the condensed water high-speed generation means. The oxidant gas supply means for power generation and the fuel supply means are arranged so that the ratio of the fuel to the oxidant gas for power generation increases within the allowable range of the oxidant gas utilization rate for power generation and the allowable range of the fuel utilization rate. Control.

  According to the present invention thus configured, the fuel utilization rate and the power generation oxidant gas utilization rate are changed within a preset allowable range, and the ratio of the fuel to the power generation oxidant gas is increased. While maintaining the thermal balance of the solid oxide fuel cell, the exhaust temperature can be increased and the generation of condensed water can be promoted.

In the present invention, preferably, the condensed water fast generation means reduces the generated power, the control unit Accordingly reduces the fuel supply amount, thereby, after the temperature of the fuel cell stack is lowered, oxidation power The power generation oxidant gas supply means and the fuel supply means are controlled so that the ratio of the fuel to the agent gas increases.

  According to the present invention configured as described above, since the condensed water high-speed generating means reduces the generated power, first, the fuel supply amount is reduced, and the temperature of the fuel cell stack is lowered. The proportion of fuel is increased. For this reason, prevention of excessive temperature rise of the fuel cell stack and promotion of condensed water generation can be realized at the same time.

In the present invention, preferably, the condensed water high-speed generating means increases the power generation oxidant gas utilization rate within a predetermined maximum power generation oxidant gas utilization rate.
According to the present invention configured as described above, the power generation oxidant gas utilization rate is increased to decrease the power generation oxidant gas, thereby increasing the exhaust gas temperature, promoting the generation of condensed water, and generating power. By increasing the oxidant gas utilization rate within the range of the maximum power generation oxidant gas utilization rate, the concentration of carbon monoxide in the exhaust from the fuel cell module can be suppressed.

  In the present invention, it is preferable that the control means generates the condensed water at a high speed from the state where the condensed water in the condensed water tank is larger when the temperature of the fuel cell stack is high than when the temperature of the fuel cell stack is low. Execute means.

According to the present invention configured as described above, when the temperature of the fuel cell stack is high, the condensate high-speed generation control is started from a state where there is a lot of condensed water, so that the fuel cell stack temperature is lowered. Therefore, even when an increase in actual condensed water is delayed, it is possible to prevent the water supplied to the reformer from being depleted.
In the present invention, preferably, the condensed water high-speed generating means lowers the generated power more significantly when the condensed water in the condensed water tank is small than when the condensed water is large.

  According to the present invention configured as described above, since the limit of generated power is changed according to the amount of condensed water, water depletion is surely prevented while minimizing the influence of the generated power limit. be able to.

  According to the solid oxide fuel cell of the present invention, it is possible to promote the recovery of condensed water and maintain water independence while properly maintaining various operating conditions.

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 schematic which shows the water flow volume adjustment unit of the solid oxide fuel cell by one Embodiment of this invention. It is a flowchart of the condensed water high-speed production | generation control in one Embodiment of this invention. In one Embodiment of this invention, it is a time chart which shows the change of each parameter in case condensed water high speed production | generation control is performed. 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, the water flow rate adjusting unit 28 according to this embodiment described above will be described in detail with reference to FIG. FIG. 9 is a schematic diagram illustrating a water flow rate adjustment unit of a solid oxide fuel cell (SOFC) according to an embodiment of the present invention.

  As shown in FIG. 9, the water flow rate adjustment unit 28 that is a water supply means that generates pure water and supplies it to the reformer 20 is sequentially condensed from the upstream side in the hot water production apparatus 50 (FIG. 1). A heat exchanger 160, a first water storage tank 26 a for temporarily storing water droplets condensed on the surface of the heat exchanger 160, and a pump 154 for supplying water in the first water storage tank 26 a An RO membrane (reverse osmosis membrane) 156 for purifying the supplied water to produce pure water, and a second water storage tank which is a condensed water tank for temporarily storing the produced pure water (Pure water tank) 26b and a pulse pump 158 that intermittently supplies this pure water to the reformer 20 of the fuel cell module 2 by pulse control.

  The heat exchanger 160 is configured to exchange heat between the tap water for generating hot water in the hot water production apparatus 50 and the exhaust from the fuel cell module 2. Thereby, the tap water introduced into the hot water production apparatus 50 is preheated by the heat of the exhaust of the fuel cell module 2. The tap water introduced into the hot water production apparatus 50 and flowing inside the heat exchanger 160 is for use as hot water in a facility or the like, and is used for steam reforming in the reformer 20. Absent. On the other hand, the exhaust from the fuel cell module 2 is cooled by contacting the surface of the heat exchanger 160. At this time, the moisture contained in the exhaust is condensed by cooling on the surface of the heat exchanger 160 and becomes water droplets. The water condensed on the surface of the heat exchanger 160 flows into the first water storage tank 26a and is temporarily stored. This water is sent to the second water storage tank 26b, and steam reforming in the reformer 20 is performed. Used for quality.

  In the present embodiment, the heat exchanger 160 provided in the hot water production apparatus 50 is used as a condenser for recovering moisture from the exhaust of the fuel cell module 2, but other heat exchangers or the like Any configuration that can condense the moisture therein can be used as a condenser.

In addition, a heater 162 is provided for preventing the water and pure water stored in the first water storage tank 26a, the second water storage tank 26b, and the like from freezing.
Further, the first water storage tank 26a includes water level sensors 136a and 136b for detecting the predetermined upper limit water level and the lower limit water level, respectively, and the water level sensors 136a and 136b detect the respective water levels. Can be detected (for example, the full water amount of the first water storage tank 26a, etc.).

  Similarly, the second water storage tank 26b also includes water level sensors 136c and 136d that respectively detect the predetermined upper limit water level and lower limit water level, and these water level sensors 136c and 136d detect the respective water levels, thereby The water storage amount corresponding to the water level (for example, the lower limit water storage amount of the second water storage tank 26b, etc.) can be detected. Further, the second water storage tank 26b is provided with a water level sensor 136e as a water storage amount detection means between the upper limit water level and the lower limit water level, and detects a decrease in the water storage amount in the second water storage tank 26b. ing. As will be described later, in the present embodiment, when the water level in the second water storage tank 26b is lower than the water level of the water level sensor 136e, the control unit 110 executes condensate high-speed generation control, and the second water storage tank Increase the water in 26b.

Next, with reference to FIG. 10 and FIG. 11, the high-speed condensed water generation control in the solid oxide fuel cell 1 according to the embodiment of the present invention will be described.
FIG. 10 shows a flowchart of the condensed water high-speed generation control. FIG. 11 is a time chart showing the change of each parameter when the condensed water high-speed generation control is executed.

  The control unit 110 serving as a control unit includes a condensed water high-speed generation unit 110a, and the condensed water high-speed generation unit 110a is configured to repeatedly execute the flowchart illustrated in FIG. 10 at predetermined time intervals.

  First, in step S1 of FIG. 10, it is determined whether or not there is an abnormality in the amount of water in the second water storage tank 26b. That is, based on the detection signal of the water level sensor 136d, it is determined whether or not the water level in the second water storage tank 26b is lower than the lower limit water level. When the water level in the second water storage tank 26b is lower than the lower limit water level, the process proceeds to step S2, and when it is equal to or higher than the lower limit water level, the process proceeds to step S3.

  In step S2, the operation of the solid oxide fuel cell 1 is stopped, and notification is made that water for steam reforming is insufficient. That is, when the water level in the second water storage tank 26b is lower than the lower limit water level, even if the condensate high-speed generation control is executed and the generation of water is promoted, the generation of water is not in time, and the steam level is changed. There is a risk of depleting quality water. For this reason, when the water level in the 2nd water storage tank 26b has fallen from the minimum water level, the driving | operation of the solid oxide fuel cell 1 is stopped and the damage to the fuel cell module 2 is prevented.

  On the other hand, when there is no abnormality in the amount of water in the second water storage tank 26b, the process proceeds to step S3, and in step S3, it is determined whether or not the amount of water is insufficient. That is, it is determined whether or not the water level in the second water storage tank 26b is lower than the predetermined condensate high-speed generation control start water level based on the detection signal of the water level sensor 136e, which is the water storage amount detection means. If it is not lower than the condensed water high-speed generation control start water level, the process proceeds to step S4. If it is lower than the condensed water high-speed generation control start water level, the process proceeds to step S7. When the water level in the second water storage tank 26b is lower than the condensed water high-speed generation control start water level, the condensed water high-speed generation control in step S7 and below is started and is equal to or higher than the condensed water high-speed generation control start water level. In this case, the amount of water stored in the second water storage tank 26b is not insufficient, and the condensed water high-speed generation control is not executed.

  In step S4, it is determined whether or not the amount of water in the second water storage tank 26b is sufficient. That is, based on the detection signal of the water level sensor 136c, it is determined whether or not the water level in the second water storage tank 26b is equal to or higher than the upper limit water level. When the water level in the 2nd water storage tank 26b is more than an upper limit water level, it progresses to step S5, and when it is less than an upper limit water level, it progresses to step S8.

  In step S5, the upper limit of the generated power is released. As will be described later, the upper limit value of the generated power of the fuel cell module 2 is limited to be lower than the maximum rated power during the execution of the condensed water high-speed generation control executed in step S7 and subsequent steps. In step S5, since it is determined in step S4 that the amount of water in the second water storage tank 26b is sufficient, such restriction on the upper limit of the generated power is released. If the generated power is not limited, that state is maintained.

  Next, in step S6, the value of the condensed water high speed generation control flag F is set to 0, and one process of the flowchart of FIG. The condensed water high-speed generation control flag F is a flag indicating that the condensed water high-speed generation control is being executed, and the value is set to 1 while the condensed water high-speed generation control is being executed. In step S6, since it is determined in step S4 that the amount of water in the second water storage tank 26b is sufficient, the condensed water high speed generation control flag F is set to 0, and the condensed water high speed generation control is ended. In addition, when the value of the condensed water high speed production | generation control flag F is 0, the value is maintained.

  On the other hand, if it is determined in step S4 that the amount of water in the second water storage tank 26b is not sufficient, the process proceeds to step S8. In step S8, whether or not the value of the condensed water high-speed generation control flag F is 1 is determined. Is judged. When the value of the condensed water high-speed generation control flag F is not 1, the one-time process of the flowchart of FIG. That is, when the condensed water high speed generation control flag F = 0 and the condensed water high speed generation control is not being performed, the condensed water high speed generation control is started even if the water level in the second water storage tank 26b is less than the upper limit water level. Not. That is, when the process of steps S3 → S4 → S8 is performed, the water level in the second water storage tank 26b is equal to or higher than the condensed water high-speed generation control start water level and lower than the upper limit water level, but the flag F = 0. In this case, the condensed water high-speed generation control is not performed, and when the flag F = 1, the condensed water high-speed generation control is continued.

  On the other hand, if it is determined in step S3 that the amount of water in the second water storage tank 26b is insufficient, the process proceeds to step S7. In step S7, the value of the condensed water high-speed generation control flag F is set to 1, and condensation is performed. Water high-speed generation control is started.

  When the condensed water high-speed generation control flag F is set to 1 in step S7, the process proceeds from step S8 to S9. In step S9, it is determined whether or not the inside of the fuel cell module 2 is being cooled due to excessive temperature rise. Is done. As will be described later, in a predetermined state where the temperature in the fuel cell module 2 is higher than the appropriate temperature, the control unit 110 increases the supply amount of power generation air by decreasing the power generation air utilization rate. Thus, the inside of the fuel cell module 2 is cooled. In step S9, it is determined whether or not such cooling is performed. If the inside of the fuel cell module 2 is being cooled due to excessive temperature rise, the process proceeds to step S13, and if not, the process proceeds to step S10.

  In step S10, the upper limit of the current generated by the fuel cell module 2 is limited to 6A, thereby limiting the generated power. The reason why the generation of condensed water in the heat exchanger 160 is promoted by limiting the power generated by the fuel cell module 2 will be described later.

  Next, in step S11, it is determined whether or not the state where the amount of water in the second water storage tank 26b is insufficient continues. That is, whether a predetermined time has elapsed since the state of the condensed water high speed generation control flag F = 0 where the condensed water high speed generation control is not performed is changed to the state of f = 1 where the condensed water high speed generation control is performed. It is determined whether or not. If the water shortage continues for a predetermined time or longer, the process proceeds to step S12. If not, the one-time process in the flowchart of FIG. 10 is terminated.

  In step S12, the upper limit of the current generated by the fuel cell module 2 is limited to 4A, thereby limiting the generated power. In other words, after the condensate high-speed generation control is started, the condensate high-speed generation control is carried out without increasing the power purchased from the system power supply as much as possible by keeping the generated current limit at 6A until a predetermined time elapses. To do. On the other hand, after the start of the condensed water high-speed generation control, if the water shortage state is not resolved even after a predetermined time has passed, the power generation current limit is further strengthened so that the water shortage state is quickly resolved. The fuel cell module 2 is operated.

  On the other hand, if it is determined in step S9 that the fuel cell module 2 is being cooled due to excessive temperature rise, the process proceeds to step S13. In step S13, the amount of water in the second water storage tank 26b is insufficient. It is determined whether the current state is continuous. In step S13, if it is determined that the water shortage is not continuous, the process proceeds to step S14. In step S14, the upper limit of the generated current by the fuel cell module 2 is limited to 4A, thereby limiting the generated power. Is done.

  In step S14, even if the amount of water is not insufficient, the fuel cell module 2 is being cooled due to excessive temperature rise, so that the limit of the generated current is strengthened more than in step S10. As will be described later, in the state where the amount of air supply for power generation is increased in order to cool the fuel cell module 2, the heat exchanger 160 is unlikely to generate condensed water. Promote water production more.

  On the other hand, if it is determined in step S13 that the water shortage continues, the process proceeds to step S15, and in step S15, the upper limit of the current generated by the fuel cell module 2 is limited to 3A, thereby generating the generated power. Is also limited. That is, in step S13, when it is determined that the water shortage continues, the inside of the fuel cell module 2 is being cooled, and the state of water shortage has not been resolved for a predetermined time or longer. The most restrictive is to promote the formation of condensed water.

Next, with reference to FIG. 11, the operation of the condensed water high-speed generation control will be described.
FIG. 11 is a time chart showing an example of the operating state of the solid oxide fuel cell 1 according to the present embodiment. In order from the top, the temperature of the fuel cell stack 14, the power supply air supply amount, the fuel supply amount, and the power generation The ratio of the supply air amount to the fuel supply amount, the generated current by the fuel cell module 2, the difference between the surface temperature of the heat exchanger 160 and the exhaust temperature flowing into the heat exchanger 160 are shown.

  First, at times t10 to t11 in FIG. 11, the generated current is set to the maximum rated current of the fuel cell module 2 (FIG. 11, fifth stage time chart). Corresponding to this generated current, as indicated by broken lines in FIG. 11, the appropriate temperature of the fuel cell stack 14 in the fuel cell module 2 (FIG. 11, the uppermost time chart), the appropriate power supply air supply The amount (FIG. 11, the second stage time chart) and the reference fuel supply amount (FIG. 11, the third stage time chart) are set.

  From time t10 to t11, since the temperature of the fuel cell stack 14 is higher than the appropriate temperature, the control unit 110 reduces the temperature in the fuel cell module 2 from an appropriate power generation air supply amount. A large amount of air is supplied to the fuel cell module 2 to cool the fuel cell stack 14 (corresponding to “cooling due to excessive temperature rise” in FIG. 10, step S9). Further, the control unit 110 makes the fuel supply amount supplied to the fuel cell module 2 smaller than the reference fuel supply amount. Thereby, the heat accumulated in the fuel cell module 2 is consumed to maintain the temperature of the fuel cell stack 14, so that the temperature in the fuel cell module 2 can be lowered. The specific setting of the fuel supply amount and the power generation air supply amount will be described later.

  As described above, from time t10 to t11, the temperature of the fuel cell stack 14 is higher than the appropriate temperature, and the power supply air supply amount is increased and the fuel supply amount is decreased in order to lower the temperature. When the fuel cell module 2 is operated in this manner, the ratio A / F of the power generation air to the fuel to be supplied increases (FIG. 11, fourth stage time chart). Moreover, since the exhaust gas temperature from the fuel cell module 2 is lowered by reducing the fuel supply amount and increasing the power generation air supply amount, the exhaust temperature flowing into the heat exchanger 160 and the surface of the heat exchanger 160 are reduced. The temperature difference from the temperature becomes smaller (FIG. 11, the bottom time chart). In the state where the ratio of power generation air and fuel is large and the temperature difference between the exhaust and the heat exchanger 160 is small, the moisture in the exhaust is hardly condensed on the surface of the heat exchanger 160, and the amount of water generated by the condensation is reduced. . For this reason, the ratio A / F of the power generation air to the fuel exceeds the upper limit value (dashed line in the time chart of FIG. 11, 4th stage) at which a required amount of condensed water is generated and water can be self-supporting. Further, the temperature difference between the exhaust gas and the heat exchanger 160 is also lower than a lower limit value (FIG. 11, a broken line in the time chart at the lowest stage) at which a required amount of condensed water is generated and water self-sustained.

  As a result of the fuel cell module 2 being operated in a state where the required amount of condensed water cannot be generated from time t10 to t11, the amount of water in the second water storage tank 26b is insufficient at time t11 (FIG. 10, step). Corresponds to “water shortage” in S3). Thereby, the condensed water high speed production | generation means 110a incorporated in the control part 110 reduces the upper limit of a generated electric current to 4 A at the time t11 (FIG. 10, step S14). Although the amount of fuel supply is reduced with the decrease in the generated current, the fuel cell stack 14 has a very large heat capacity, so that the fuel cell stack 14 continues to be higher than the appropriate temperature. For this reason, the power generation air supply amount is maintained in a state larger than the appropriate power generation air supply amount.

  Thus, at time t11, the fuel supply amount is reduced by reducing the upper limit of the generated current, while the power generation air supply amount continues to be increased. / F increases (FIG. 11, fourth stage time chart), the ratio of moisture contained in the exhaust gas decreases, and the temperature difference between the exhaust gas and the heat exchanger 160 also decreases. Therefore, immediately after the generated current is reduced by the condensed water high-speed generating means 110a, the fuel cell module 2 is in a state where it is difficult to generate condensed water.

  Next, at time t12, when a predetermined time has elapsed after the start of the condensed water high-speed generation control (corresponding to “continuous water shortage” in FIG. 10, step S13), the condensed water high-speed generation means 110a sets the upper limit of the generated current. Further, it is lowered to 3A (FIG. 10, step S15). In the present embodiment, the upper limit of the generated current is further reduced when the water amount shortage continues for about 30 minutes after the start of the condensed water high-speed generation control. Immediately after the power generation current is reduced at time t12, the fuel supply amount is reduced, while the power generation air supply amount continues to be increased, so the ratio A / F of power generation air to fuel further increases. However, the temperature difference between the exhaust gas and the heat exchanger 160 is further reduced (FIG. 11, the lowest time chart).

  When a further time elapses after reducing the generated current, the temperature of the fuel cell stack 14 decreases. When the temperature of the fuel cell stack 14 is lowered, the control unit 110 decreases the power supply air supply amount and increases the fuel supply amount to the reference fuel supply amount. Along with this, the ratio A / F of power generation air to fuel decreases, so that the ratio of moisture in the exhaust begins to increase, and the temperature difference between the exhaust and the heat exchanger 160 also begins to increase. Thereby, at time t13, the ratio A / F of the power generation air to the fuel is below the upper limit value at which water self-sustainability is possible, and the temperature difference between the exhaust and the heat exchanger 160 also exceeds the lower limit value at which water self-sustainability is possible. By operating the fuel cell module 2 in this state, the amount of water in the second water storage tank 26b increases.

  Next, at time t14, the water in the second water storage tank 26b reaches a predetermined upper limit water level (corresponding to “water amount satisfaction” in FIG. 10, step S4), and the condensed water high-speed generating means 110a End generation control. Condensed water high-speed generation control 110a cancels the upper limit of the generated current (corresponding to “cancel upper limit of power generation” in FIG. 10, step S5), and the generated current is increased again.

  Thus, the condensed water high speed generation means 110a first reduces the temperature of the fuel cell stack 14 by limiting the upper limit value of the generated current. That is, in a state where the temperature is high, it is necessary to lower the temperature in order to avoid damage to the fuel cell stack 14, and the air supply amount must be maintained in a large state. As described above, in a state where the temperature is high, it is necessary to maintain a large air supply amount (low air utilization rate) and a small fuel supply amount (high fuel utilization rate), and operating conditions in which condensed water is easily generated. There is little room to achieve. After the temperature has dropped, it is possible to operate with a reduced air supply amount (higher air utilization rate) and a higher fuel supply amount (lower fuel utilization rate). As a result, after the temperature is lowered, the power generation air flow rate adjustment unit 44 and the fuel flow rate adjustment unit 38 are controlled so that the ratio of the fuel supply amount to the power generation air supply amount increases, and the heat exchanger 160 It promotes the generation of condensed water and generates condensed water at high speed. The condensate high-speed generation unit 110a indirectly limits the upper limit value of the generated current by reducing the fuel supply amount, and after the temperature is lowered by this, the generation air supply amount is decreased. Therefore, an operation condition in which condensed water is easily generated is created, and the amount of water in the second water storage tank 26b is increased.

  Next, with reference to FIGS. 12 to 18, 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. 12 is a flowchart showing a procedure for determining the power supply air supply amount, the water supply amount, and the fuel supply amount based on the detected temperature Td. FIG. 13 is a graph showing an appropriate temperature of the fuel cell stack 14 with respect to the generated current. FIG. 14 is a graph showing the fuel utilization rate determined according to the integrated value. FIG. 15 is a graph showing a range of values of the fuel utilization rate that can be determined for each generated current. FIG. 16 is a graph showing the air utilization rate determined according to the integrated value. FIG. 17 is a graph showing a range of values of air utilization rates that can be determined for each generated current. FIG. 18 is a graph for determining the water supply amount with respect to the determined air utilization rate.

  As shown by a one-dot chain line in FIG. 13, in this embodiment, an appropriate temperature Ts (I) of the fuel cell stack 14 is defined for the current to be generated by the fuel cell module 2 (FIG. 11). , Broken line in the top time chart). The control unit 110 controls the fuel supply amount and the like so that the temperature of the fuel cell stack 14 approaches the appropriate temperature Ts (I). That is, the control unit 110 roughly indicates that when the temperature of the fuel cell stack 14 is higher than the generated current (when the temperature of the fuel cell stack 14 is above the one-dot chain line in FIG. 13). 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 110b (FIG. 6) built in the control unit.

  The flowchart shown in FIG. 12 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. 12, 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. 13) 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)
1 (below the lower solid line in FIG. 13), 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)
1 (above the upper solid line in FIG. 13), 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. 12, 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. 12, 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. 12 is executed continuously after the start of operation of the solid oxide fuel cell, and the first addition value N1id and the first addition / subtraction value M1 are added to the previously calculated first integration value N1id. The 2 addition / subtraction value M2 is added or subtracted and updated to a new first integrated value N1id. The first integrated value N1id is limited to take a value between 0 and 4, and when the first integrated value N1id reaches 4, the value is held at 4 until the next subtraction is performed. When the first integrated value N1id decreases to 0, the value is held at 0 until the next addition is performed.

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

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

Further, in step S34 of FIG. 12, the fuel utilization rate is determined using the graphs of FIGS. 14 and 15 based on the calculated first integrated value N1id.
FIG. 14 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. 14, 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 these minimum fuel utilization rate Ufmin and maximum fuel utilization rate Ufmax are determined by the graph shown in FIG. 15 based on the generated current (the time chart in the fifth stage in FIG. 11). 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. That is, in the vicinity of time t10 to t13 in FIG. 11, since the temperature in the fuel cell module 2 is high and the amount of heat that can be used is accumulated, the amount of fuel supply decreases so as to increase the fuel utilization rate. Has been.

  FIG. 15 is a graph showing the range of values that the fuel utilization rate Uf can take for each generated current, and shows the maximum and minimum values of the fuel utilization rate Uf for each generated current. As shown in FIG. 15, 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 is set on the straight line of the minimum fuel usage rate Ufmin, the fuel cell module 2 can thermally stand by itself 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 this way, the control unit 110 controls the fuel flow rate adjustment unit 38 so that the fuel usage rate Uf is always within the allowable range of the fuel usage rate Uf set in advance according to the generated current (generated power). As shown in FIG. 15, the allowable range of the fuel utilization rate Uf is set to be wider when the generated current (generated power) is small than when the generated current is large. The condensed water high speed generation means 110a reduces the generated current by limiting the upper limit value of the generated current (FIG. 11, time t11), and operates the fuel cell module 2 in a wide range of allowable range of the fuel utilization rate Uf. In this region, the controller 110 increases the ratio of the fuel to the power generation air within the allowable range of the air usage rate and the allowable range of the fuel usage rate by performing an operation with the fuel usage rate Uf lowered. (FIG. 11, time t13 on the fourth stage time chart), condensed water is generated at high speed.

  In step S34 of FIG. 12, 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. 14, 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. 12, the air utilization rate is determined using the graphs of FIGS. 16 and 17 based on the second integrated value N2id.
FIG. 16 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. 16, when the second integrated value N2id is 0 to 1, the air utilization rate Ua is set to the maximum air utilization rate Uamax, which is the maximum power generation oxidant gas utilization rate. 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. 16 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. 17 based on the generated current.

  FIG. 17 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. 17, the maximum air utilization rate Uamax for each generated current is set to be slightly increased as the generated current increases. On the other hand, the minimum air utilization rate Uamin decreases as the generated current increases. Reducing the air utilization rate Ua below the maximum air utilization rate Uamax (increasing the air supply amount) introduces more air into the fuel cell module 2 than is necessary for power generation. The temperature in the fuel cell module 2 is lowered. Therefore, when the temperature in the fuel cell module 2 rises excessively and the temperature needs to be lowered, the air utilization rate Ua is lowered. In this embodiment, when the minimum air utilization rate Uamin is decreased (the air supply amount is increased) as the generation current is increased, the air supply amount corresponding to the minimum air utilization rate Uamin is generated for power generation at a predetermined generation current. The maximum air supply amount of the air flow rate adjustment unit 45 will be exceeded. For this reason, the air utilization rate Ua set by the graph of FIG. 16 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 in the portion indicated by the broken line in FIG. 17 can also be realized. The air utilization rate Ua defined by reaching the maximum air supply amount of the power generation air flow rate adjustment unit 45 is referred to as a limit minimum air utilization rate ULamin.

  In step S35 of FIG. 12, specific values of the minimum air utilization rate Uamin and the maximum air utilization rate Uamax are determined based on the generated current using the graph of FIG. Next, the determined minimum air utilization rate Uamin and maximum air utilization rate Uamax are applied to the graph of FIG. 16, 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. 12, based on the air utilization rate Ua determined in step S35, S / C that is the ratio of the water vapor amount to the carbon amount is determined using FIG.
FIG. 18 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 generated current (between Uamax and ULamin in FIG. 18) 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. 18, 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. 17), 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. 18, 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. 18), 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. 17), 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 air supply rate is increased by decreasing the air utilization rate Ua and then increasing the water 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. 12 is completed.

  Next, the time interval for executing the flowchart of FIG. 12 will be described. In the present embodiment, when the output current is large, the flowchart of FIG. 12 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. 12 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. 14, a fuel utilization rate Uf higher than the minimum fuel utilization rate Ufmin is set, the fuel supply amount is decreased, and the amount of remaining fuel that is not used for power generation is decreased. The fuel utilization rate Uf is significantly increased 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.

  By executing such control, in the time chart shown in FIG. 11, the minimum fuel utilization rate Ufmin (FIG. 11, the third stage) when the temperature of the fuel cell stack 14 is high (near times t10 to t13). (Corresponding to the broken line in the time chart of FIG. 4), the fuel utilization rate Uf is increased (the fuel supply amount is reduced).

Even when the first integrated value N1id further increases and exceeds 1, as shown in FIG. 14, the fuel utilization rate Uf is maintained at the maximum fuel utilization rate Uafmax (minimum fuel supply amount). On the other hand, since the value of the second integrated value N2id that takes the same value as the first integrated value N1id (when the fuel cell module 2 is not deteriorated) also exceeds 1, the air utilization rate Ua decreases based on FIG. (Air supply amount increased). Thereby, the inside of the fuel cell module 2 tends to be cooled due to an increase in supplied air.
By executing such control, in the time chart shown in FIG. 11, the maximum air utilization rate Uamax (FIG. 11, the second stage) when the temperature of the fuel cell stack 14 is high (near times t10 to t13). Operation corresponding to a lower air utilization rate Ua (increasing the air supply amount) than the time chart of FIG. 13 until the fuel cell stack 14 reaches an appropriate temperature (corresponding to the one-dot chain line in FIG. 13). To be cooled.

  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, when the condensed water in the second water storage tank 26b is insufficient (FIG. 10, step S3), the condensed water high-speed generating means 110a is condensed. Since the generated power is reduced to increase the water (FIG. 10, steps S10, S12, S14, S15), the temperature of the fuel cell stack 14 is lowered, and thereby the ratio of the air supply amount for fuel generation / the fuel supply amount There is room to raise In this manner, condensed water can be generated at high speed while reliably avoiding damage to the fuel cell stack 14 and the like.

  Moreover, according to the solid oxide fuel cell 1 of the present embodiment, when the temperature of the fuel cell stack 14 is high, the amount of power generation air supplied is increased (FIG. 11, times t10 to t13), thereby The fuel cell stack 14 is cooled. However, in the state where the supply air amount for power generation is increased in this way, the ratio of the supply air amount for power generation / fuel supply amount increases and the amount of condensed water condensed in the heat exchanger 160 decreases. is there. According to the solid oxide fuel cell 1 of the present embodiment, the generation of condensed water can be facilitated simply by reducing the generated power by the condensed water high-speed generating means 110a.

  Further, according to the solid oxide fuel cell 1 of the present embodiment, it is possible to perform operation with a high fuel utilization rate when the generated power is large (FIG. 15), but the fuel utilization rate is reduced in this state. If it does, the temperature of the fuel cell stack 14 will rise excessively. For this reason, it is difficult to promote the generation of condensed water when the generated power is large. On the other hand, since the operating temperature is low when the generated power is low (FIG. 13), there is room for lowering the fuel utilization rate, and the allowable range of the fuel utilization rate can be widened (FIG. 15). Thereby, the production | generation of condensed water can be accelerated | stimulated by reducing generated electric power.

  Furthermore, according to the solid oxide fuel cell 1 of the present embodiment, the fuel utilization rate and the power generation air utilization rate are changed within a preset allowable range (FIGS. 15 and 17), and the fuel to the power generation air is changed. Since the ratio is increased, the exhaust temperature can be increased while maintaining the thermal balance of the solid oxide fuel cell 1, and the generation of condensed water can be promoted.

  Further, according to the solid oxide fuel cell 1 of the present embodiment, the condensed water high-speed generating means 110a reduces the generated power (FIG. 10, steps S10, S12, S14, S15), so the fuel supply amount first decreases. (FIG. 11, third stage time chart time t11) After the temperature of the fuel cell stack 14 drops, the ratio of fuel to the power generation air is increased (FIG. 11, fourth stage time chart time t13). ). For this reason, prevention of excessive temperature rise of the fuel cell stack 14 and promotion of condensed water generation can be realized simultaneously.

  Further, according to the solid oxide fuel cell 1 of the present embodiment, the power generation air utilization rate is increased to decrease the power generation air, thereby increasing the exhaust temperature, promoting the generation of condensed water, and generating power. By increasing the operating air utilization rate within the range of the oxidant gas utilization rate for maximum power generation (FIG. 17), the carbon monoxide concentration in the exhaust from the fuel cell module 2 can be suppressed, and the emission performance Can be improved.

  As mentioned above, although preferable embodiment of this invention was described, a various change can be added to embodiment mentioned above. In the embodiment described above, when the water level sensor 136e is attached to a predetermined water level in the second water storage tank 26b and falls below this water level (FIG. 10, step S3), the condensed water high-speed generation control has been started. Other configurations can also be employed.

  For example, a plurality of water level sensors can be provided at different water levels in the water storage tank, or a water meter that can detect the amount of water in the water storage tank can be provided. In the modified example configured as described above, when the temperature of the fuel cell stack 14 is high, the condensed water speed increases from the state where the condensed water in the water storage tank is larger than when the temperature of the fuel cell stack 14 is low. The present invention can also be configured such that generation control is initiated.

  According to the modified example configured as described above, when the temperature of the fuel cell stack 14 is high, the condensed water high-speed generation control is started from a state where there is a lot of condensed water. Even when a long time is required for the reduction and the actual increase of condensed water is delayed, it is possible to prevent the water supplied to the reformer 20 from being depleted.

  In the above-described embodiment of the present invention, when the state where the water level in the water storage tank is low continues for a predetermined time (FIG. 10, steps S11 and S13), the generated power is reduced more significantly. As a modification, the generated power can be reduced according to the amount of water stored in the water storage tank. For example, when the condensed water in the water storage tank is small, the condensed water high-speed generating means can be configured to reduce the generated power more significantly than when the condensed water is large.

  According to the modified example configured as described above, since the limit of the generated power is changed according to the amount of the condensed water, the depletion of water is surely prevented while suppressing the influence of the generated power limit to the minimum. be able to.

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 26b second water storage tank (condensed 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 Condensate high-speed generation means 110b Heat storage amount estimation means 112 Operation device 114 Display device 116 Alarm device 126 Power state detection sensor (buy power detection means)
132 Fuel flow sensor (fuel supply detection sensor)
136e Water level sensor (water storage amount detection means)
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 154 Pump 156 RO membrane (reverse osmosis membrane)
158 Pulse pump 160 Heat exchanger (condenser)
162 Heater

Claims (7)

A solid oxide fuel cell that collects moisture in exhaust gas and steam-reforms fuel using the collected water to generate electric power,
A fuel cell module having a fuel cell stack; and
A condenser for condensing moisture in the exhaust of the fuel cell module;
A condensed water tank for storing condensed water condensed in this condenser;
A storage amount detecting means for detecting the amount of condensed water stored in the condensed water tank;
A reformer for steam-reforming the fuel to produce hydrogen and supplying the fuel cell stack;
Fuel supply means for supplying fuel to the reformer;
Water supply means for supplying condensed water stored in the condensed water tank to the reformer;
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, the water supply means, and the oxidant gas supply means for power generation to generate required generated power by the fuel cell module,
The control means includes condensed water high-speed generation means for executing condensed water high-speed generation control. The condensed water high-speed generation means is configured such that the condensed water in the condensed water tank is equal to or less than a predetermined amount by the stored water amount detection means. Is detected, the generated power is reduced to increase the condensed water condensed by the condenser ,
Even when the condensate high-speed generation control is being executed, the control means increases the power generation oxidant gas supply amount when the temperature of the fuel cell stack is equal to or higher than a predetermined temperature, and A solid oxide fuel cell, wherein the temperature of the battery cell stack is cooled to an appropriate temperature, and then the ratio of oxidant gas / fuel supplied to the fuel cell module is decreased . The control means controls the fuel supply means so that the fuel utilization rate is always within the allowable range of the fuel utilization rate set in advance according to the generated power, and the allowable range of the fuel utilization rate is: when generated power is small, the solid oxide fuel cell according to claim 1, wherein is set to be wider than the generated power is large. The control means controls the fuel supply means so that the fuel usage rate is always within a permissible range of the fuel usage rate set in advance according to the generated power, and the condensed water high-speed generation means The oxidant gas supply means for power generation and the fuel supply means are arranged so that the ratio of the fuel to the oxidant gas for power generation increases within the allowable range of the oxidant gas utilization rate and the allowable range of the fuel utilization rate. The solid oxide fuel cell according to claim 2 to be controlled. The condensed water fast generation means reduces the electric power generated, the said control means with this, to reduce the fuel supply amount, thereby, after the temperature of the fuel cell stack is decreased, the fuel for the oxidizing gas for power generation 4. The solid oxide fuel cell according to claim 3 , wherein the power generating oxidant gas supply means and the fuel supply means are controlled so that the ratio of the fuel cell is increased. 5. The solid oxide fuel cell according to claim 4, wherein the condensed water high-speed generating means increases the power generation oxidant gas utilization rate within a predetermined maximum power generation oxidant gas utilization rate. When the temperature of the fuel cell stack is high, the control means starts the condensed water high-speed generation means from a state in which the condensed water in the condensed water tank is larger than when the temperature of the fuel cell stack is low. The solid oxide fuel cell according to claim 5 to be executed. 7. The solid oxide fuel cell according to claim 6, wherein the condensed water high-speed generating means lowers the generated power more significantly when the condensed water in the condensed water tank is small than when the condensed water is large.

Images