JP5783370B2 - 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 power generation capacity in accordance with demand power and commands an inverter to take out a current.

  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. 2011-76934 (Patent Document 1) describes a solid oxide fuel cell. This solid oxide fuel cell has a load following function that changes the fuel supply amount according to the required power determined from the demand power, and after supplying fuel to the fuel cell so that the required power can be generated The electric power that can be drawn from the fuel cell module is instructed to the inverter. The inverter is configured to draw power from the fuel cell module within the range of the inverter permitted power value indicated by the solid oxide fuel cell. That is, since the fuel cell module generally has poor responsiveness, even if the fuel supply amount is increased in accordance with the increase in demand power, the power corresponding to the changed fuel supply amount cannot be immediately drawn out. For this reason, after increasing the fuel supply amount, the power allowed to be pulled out to the inverter is increased after a predetermined time, and the inverter actually powers from the fuel cell module within the range of power permitted to be pulled out. Pull out.

JP 2011-76934 A

  However, there is a problem that even if a current (electric power) permitting the drawing is instructed to the inverter, the current is not actually drawn to the inverter up to the upper limit permitted to be drawn due to the characteristics of the inverter. Thus, as a cause of the difference between the current permitted to be drawn and the current actually drawn, the fuel cell module may be damaged if the current actually drawn by the inverter exceeds the permitted current. Therefore, it can be mentioned that the characteristics of the inverter are designed in advance on the safe side. Even with inverters of the same specification, due to individual differences, there is a variation in the current that is actually drawn with respect to the current that is allowed to be drawn, and in order to absorb this individual difference, It is necessary to design few. As described above, it is difficult to avoid a design that gives a margin to the current that the inverter actually draws, particularly when a fuel cell system is configured by combining a general-purpose inverter with a fuel cell module.

  On the other hand, in the state where the current actually drawn out is smaller than the current permitted to be drawn out to the inverter, the fuel cell module side has the ability to generate the current allowed to draw out, but the amount of that capacity Since power generation is not performed, there is a problem that part of the fuel supplied to the fuel cell module is wasted and energy efficiency is lowered. Furthermore, in the type of fuel cell in which the remaining fuel that is supplied to the fuel cell module and is not used for power generation is used for heating in the fuel cell module, the heating becomes excessive, and the fuel cell module is excessively heated. There is a problem that it causes a significant temperature rise.

  Accordingly, an object of the present invention is to provide a solid oxide fuel cell capable of improving energy efficiency while avoiding excessive current drawing from the fuel cell module to the inverter.

In order to solve the above-described problems, the present invention is a solid oxide fuel cell that changes power generation capacity in accordance with demand power and commands an inverter to take out a current, and includes a fuel cell stack. Fuel cell module, reformer for reforming fuel supplied to fuel cell stack, fuel supply means for supplying fuel to the reformer, and water supply for supplying reforming water to the reformer Means, oxidant gas supply means for supplying power to the fuel cell stack, and fuel supply means, water supply so that the power generation capacity of the fuel cell module can be changed according to demand power And a control means for controlling the oxidant gas supply means for power generation, and the control means converts the current that can be taken out from the fuel cell module into an inverter according to the state of the fuel cell module. Extractable current instruction means for sequentially instructing, extractable current instructed to the inverter, current monitoring means for monitoring the actual generated current actually taken out by the inverter within the range of extractable current, and monitoring results of this current monitoring means And an inverter characteristic correction unit that corrects a fuel supply amount or a current that can be taken out based on the fuel supply amount, and the inverter characteristic correction unit includes a fuel in a state where the current that can be taken out and the actual generated current are constant due to the characteristics of the inverter is characterized that you lack of actual generated current to power generation capacity of the battery module to correct the fuel supply amount or obtainable current to decrease.

  In the present invention configured as described above, the control unit controls the fuel supply unit, the water supply unit, and the power generation oxidant gas supply unit, and the fuel and the power generation oxidant gas are built in the fuel cell module. The fuel cell stack is supplied, and the power generation capacity of the fuel cell module is changed according to the demand power. The extractable current indicating means provided in the control means sequentially instructs the inverter on the extractable current that can be extracted from the fuel cell module according to the state of the fuel cell module. The current monitoring means provided in the control means monitors the extractable current commanded to the inverter and the actual generated current actually extracted by the inverter within the range of the extractable current. Further, the inverter characteristic correcting means provided in the control means supplies the fuel so that the shortage of the actual power generation current with respect to the power generation capability of the fuel cell module due to the characteristics of the inverter is reduced based on the monitoring result of the current monitoring means. Correct the quantity or current that can be taken out.

  According to the present invention configured as described above, the current monitoring means monitors the current that can be taken out and the actual power generation current, and the inverter characteristic correction means performs the actual power generation with respect to the power generation capacity caused by the characteristics of the inverter based on the monitoring result. Reduce current shortage. As a result, even when the inverter has a characteristic of taking out less current than the instructed current that can be taken out, a current close to the power generation capacity is actually taken out from the fuel cell module, and extra power is generated in the fuel cell module. It is possible to suppress the waste of fuel due to the capability. In addition, surplus fuel generated by providing the fuel cell module with an extra power generation capability heats the inside of the fuel cell module, and an excessive increase in the temperature inside the fuel cell module can be suppressed.

  In the present invention, it is preferable that the inverter characteristic correcting unit corrects the fuel supply amount or the extractable current based on the history of past extractable current and actual generated current data acquired by the current monitoring unit.

  According to the present invention configured as described above, the correction is performed based on the history of the data of the past extractable current and the actual generated current, and therefore the risk that the actual generated current exceeds the extractable current due to excessive correction. Can be avoided, and energy efficiency can be improved more safely.

  In the present invention, preferably, the inverter characteristic correcting means corrects the fuel supply amount or the extractable current based on the data of the extractable current and the actual generated current when the actual generated current is increased or constant.

  According to the present invention configured as described above, the correction is executed based on the data of the extractable current and the actual generated current when the actual generated current is increased or constant. As a result, data at the time of a decrease in the actual power generation current that tends to cause a difference between the current that can be taken out and the actual power generation current is excluded, so that the inverter characteristics can be corrected more accurately.

  In the present invention, preferably, the control means further includes a high-speed follow-up means for executing a high-speed follow-up mode operation in which the fuel supply amount is rapidly increased so that the power generation capacity of the fuel cell module rapidly follows the increase in demand power. The inverter characteristic correction unit does not execute correction during the high-speed tracking mode operation, or suppresses the correction amount of the fuel supply amount or the current that can be taken out.

  According to the present invention configured as described above, the correction at the time of the high-speed tracking mode operation that rapidly increases the power generation capability of the fuel cell module is prohibited or suppressed. However, it is possible to reliably avoid the risk of occurrence of problems such as fuel depletion, which exceeds the current that can be taken out.

  In the present invention, it is preferable that the inverter characteristic correcting unit also executes correction for reducing the supply amount of the oxidant gas and water for power generation as well as correction for reducing the fuel supply amount.

  According to the present invention configured as described above, the supply amount of oxidant gas and water for power generation is corrected together with the supply amount of fuel, so the emission performance such as the concentration of carbon monoxide in the exhaust gas, the temperature of the fuel cell module The energy efficiency can be improved while avoiding adverse effects on the reforming reaction and the like in the reformer.

  According to the solid oxide fuel cell of the present invention, it is possible to improve energy efficiency while avoiding excessive current drawing from the fuel cell module to the inverter.

1 is an overall configuration diagram showing a fuel cell device according to an embodiment of the present invention. It is front sectional drawing which shows the fuel cell module of the fuel cell apparatus by one Embodiment of this invention. FIG. 3 is a cross-sectional view taken along line III-III in FIG. 2. It is a fragmentary sectional view showing a fuel cell unit of a fuel cell device by one embodiment of the present invention. It is a perspective view which shows the fuel cell stack of the fuel cell apparatus by one Embodiment of this invention. 1 is a block diagram showing a fuel cell device according to an embodiment of the present invention. It is a time chart which shows the operation | movement at the time of starting of the fuel cell apparatus by one Embodiment of this invention. It is a time chart which shows the operation | movement at the time of the stop of the fuel cell apparatus by one Embodiment of this invention. It is the graph which showed typically the change of the demand electric power, the amount of fuel supply, and the actual electric power generation current actually taken out from a fuel cell module. It is a flowchart which shows the control by the current monitoring means and inverter characteristic correction means which are built in the control part. It is a flowchart of fuel, air for power generation, and water supply amount control by a control part. It is the time chart which showed in detail the relationship of the amount of power generation in the fuel, air for power generation, and water supply in 1st delay control. It is the time chart which showed in detail the relationship of the amount of power generation in the fuel, the air for power generation, and water supply in 2nd delay control. 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 range of the value of the air utilization factor which can be determined with respect to each generated electric current.

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

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

A combustion chamber 18 is formed above the above-described power generation chamber 10 in the sealed space 8 of the fuel cell module 2. In this combustion chamber 18, residual fuel and residual oxidant (air) that have not been used for the power generation reaction. Burns and produces exhaust gas.
Further, a reformer 20 for reforming the fuel is disposed above the combustion chamber 18, and the reformer 20 is heated to a temperature at which a reforming reaction can be performed by the combustion heat of the residual gas. Yes. Further, an air heat exchanger 22 is disposed above the reformer 20 to heat the air by receiving heat from the reformer 20 and suppress a temperature drop of the reformer 20.

  Next, the auxiliary unit 4 stores a pure water tank 26 that stores water from a water supply source 24 such as tap water and uses the filter to obtain pure water, and a water flow rate that adjusts the flow rate of the water supplied from the water storage tank. An adjustment unit 28 (such as a “water pump” driven by a motor) is provided. In addition, the auxiliary unit 4 adjusts the flow rate of the fuel gas, the gas shutoff valve 32 for shutting off the fuel supplied from the fuel supply source 30 such as city gas, the desulfurizer 36 for removing sulfur from the fuel gas, A fuel flow rate adjustment unit 38 (such as a “fuel pump” driven by a motor) is provided. Further, the auxiliary unit 4 includes an electromagnetic valve 42 that shuts off air that is an oxidant supplied from the air supply source 40, a reforming air flow rate adjusting unit 44 that adjusts the flow rate of air, and a power generation air flow rate adjusting unit. 45 (such as an “air blower” driven by a motor), a first heater 46 for heating the reforming air supplied to the reformer 20, and a second for heating the power generating air supplied to the power generation chamber And a heater 48. The first heater 46 and the second heater 48 are provided in order to efficiently raise the temperature at startup, but may be omitted.

Next, a hot water production apparatus 50 to which exhaust gas is supplied is connected to the fuel cell module 2. The hot water production apparatus 50 is supplied with tap water from the water supply source 24, and the tap water is heated by the heat of the exhaust gas and supplied to a hot water storage tank of an external hot water heater (not shown).
The fuel cell module 2 is provided with a control box 52 for controlling the amount of fuel gas supplied and the like.
Furthermore, the fuel cell module 2 is connected to an inverter 54 that is a power extraction unit (power conversion unit) for supplying the power generated by the fuel cell module to the outside.

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

  The reformer 20 is provided with a pure water introduction pipe 60 for introducing pure water and a reformed gas introduction pipe 62 for introducing reformed fuel gas and reforming air to the upstream end side thereof. In the reformer 20, an evaporator 20a and a reformer 20b are formed in this order from the upstream side, and the evaporator 20a and the reformer 20b are filled with a reforming catalyst. The fuel gas and air mixed with the steam (pure water) introduced into the reformer 20 are reformed by the reforming catalyst filled in the reformer 20. As the reforming catalyst, a catalyst obtained by imparting nickel to the alumina sphere surface or a catalyst obtained by imparting ruthenium to the alumina sphere surface is appropriately used.

  A fuel gas supply pipe 64 is connected to the downstream end side of the reformer 20, and the fuel gas supply pipe 64 extends downward and further in an manifold 66 formed below the fuel cell assembly 12. It extends horizontally. A plurality of fuel supply holes 64 b are formed in the lower surface of the horizontal portion 64 a of the fuel gas supply pipe 64, and the reformed fuel gas is supplied into the manifold 66 from the fuel supply holes 64 b.

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

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

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

Next, an exhaust gas chamber 78 is formed below the manifold 66. Further, as shown in FIG. 3, an exhaust gas passage 80 extending in the vertical direction is formed inside the front surface 6 a and the rear surface 6 b which are surfaces along the longitudinal direction of the housing 6, and the upper end of the exhaust gas chamber passage 80 is formed. The side communicates with the space in which the air heat exchanger 22 is disposed, and the lower end side communicates with the exhaust gas chamber 78. Further, an exhaust gas discharge pipe 82 is connected to substantially the center of the lower surface of the exhaust gas chamber 78, and the downstream end of the exhaust gas discharge pipe 82 is connected to the above-described hot water producing apparatus 50 shown in FIG.
As shown in FIG. 2, an ignition device 83 for starting combustion of fuel gas and air is provided in the combustion chamber 18.

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

  Since the inner electrode terminal 86 attached to the upper end side and the lower end side of the fuel cell 16 has the same structure, the inner electrode terminal 86 attached to the upper end side will be specifically described here. The upper portion 90 a of the inner electrode layer 90 includes an outer peripheral surface 90 b and an upper end surface 90 c exposed to the electrolyte layer 94 and the outer electrode layer 92. The inner electrode terminal 86 is connected to the outer peripheral surface 90b of the inner electrode layer 90 through a conductive sealing material 96, and is further in direct contact with the upper end surface 90c of the inner electrode layer 90, thereby Electrically connected. A fuel gas passage 98 communicating with the fuel gas passage 88 of the inner electrode layer 90 is formed at the center of the inner electrode terminal 86.

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

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

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

Next, the fuel cell stack 14 will be described with reference to FIG. FIG. 5 is a perspective view showing a fuel cell stack of a solid oxide fuel cell (SOFC) according to an embodiment of the present invention.
As shown in FIG. 5, the fuel cell stack 14 includes 16 fuel cell units 16, and the lower end side and the upper end side of these fuel cell units 16 are a ceramic lower support plate 68 and an upper side, respectively. It is supported by the support plate 100. The lower support plate 68 and the upper support plate 100 are formed with through holes 68a and 100a through which the inner electrode terminal 86 can pass.

  Furthermore, a current collector 102 and an external terminal 104 are attached to the fuel cell unit 16. The current collector 102 includes a fuel electrode connection portion 102a that is electrically connected to an inner electrode terminal 86 attached to the inner electrode layer 90 that is a fuel electrode, and an entire outer peripheral surface of the outer electrode layer 92 that is an air electrode. And an air electrode connecting portion 102b electrically connected to each other. The air electrode connecting portion 102b is formed of a vertical portion 102c extending in the vertical direction on the surface of the outer electrode layer 92 and a plurality of horizontal portions 102d extending in a horizontal direction along the surface of the outer electrode layer 92 from the vertical portion 102c. Has been. The fuel electrode connection portion 102a is linearly directed obliquely upward or obliquely downward from the vertical portion 102c of the air electrode connection portion 102b toward the inner electrode terminal 86 positioned in the vertical direction of the fuel cell unit 16. It extends.

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

Next, sensors and the like attached to the solid oxide fuel cell (SOFC) according to the present embodiment will be described with reference to FIG. FIG. 6 is a block diagram illustrating a solid oxide fuel cell (SOFC) according to an embodiment of the present invention.
As shown in FIG. 6, the solid oxide fuel cell 1 includes a control unit 110, and the control unit 110 includes operation buttons such as “ON” and “OFF” for operation by the user. An operation device 112, a display device 114 for displaying various data such as a power generation output value (wattage), and a notification device 116 for issuing a warning (warning) in an abnormal state are connected. The notification device 116 may be connected to a remote management center and notify the management center of an abnormal state.

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

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

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

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

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

Next, the operation at the time of start-up by the solid oxide fuel cell (SOFC) according to the present embodiment will be described with reference to FIG. FIG. 7 is a time chart showing the operation at the start-up of the solid oxide fuel cell (SOFC) according to the embodiment of the present invention.
Initially, in order to warm the fuel cell module 2, the operation is started in a no-load state, that is, in a state where a circuit including the fuel cell module 2 is opened. At this time, since no current flows through the circuit, the fuel cell module 2 does not generate power.

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

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

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

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

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

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

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

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

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

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

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

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

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

Next, control of the solid oxide fuel cell 1 according to the embodiment of the present invention will be described with reference to FIGS. 9 to 14.
FIG. 9 is a graph schematically showing the relationship between the change in power demand, the amount of fuel supplied, and the current actually taken from the fuel cell module.

  As shown in FIG. 9, the fuel cell module 2 is controlled so as to be able to generate power corresponding to the demand power shown in the uppermost stage of FIG. The control unit 110 serving as a control unit sets a fuel supply current value If, which is a target current to be generated by the fuel cell module 2, based on the demand power as shown in the second graph of FIG. Although the fuel supply current value If is set so as to substantially follow the change in demand power, the response speed of the fuel cell module 2 is extremely slow with respect to the change in demand power. It is set so as to follow the demand power gently without following the change. In addition, when the demand power exceeds the rated generated power of the solid oxide fuel cell, the fuel supply current value If follows the current value corresponding to the rated generated power and is set to a current value higher than that. There is no.

  As shown in the third graph of FIG. 9, the control unit 110 controls the fuel flow rate adjustment unit 38 that is a fuel supply means, and sets the fuel supply amount Fr at a flow rate that can generate the fuel supply current value If to the fuel cell. Supply to module 2. If the fuel utilization rate, which is the ratio of the fuel actually used for power generation with respect to the fuel supply amount, is constant, the fuel supply current value If and the fuel supply amount Fr are proportional. In the graph of FIG. 9, the fuel supply current value If and the fuel supply amount Fr are drawn as being proportional to each other, but actually, the fuel utilization rate is changed according to the operating state.

  Further, as indicated by a solid line in the lowermost graph of FIG. 9, the extractable current indicating means 110 a (FIG. 6) built in the control unit 110 is an extractable current value that can be extracted from the fuel cell module 2. A signal indicating the current Iinv to the inverter 54 is output. The inverter 54 extracts the current from the fuel cell module 2 within the range of the extractable current Iinv in accordance with the demand power that changes abruptly from moment to moment, as indicated by the one-dot chain line in the lowermost graph of FIG. Thus, the current actually taken out from the fuel cell module 2 becomes the actual power generation current Ia. The portion where the demand power exceeds the extractable current Iinv is supplied from the grid power, and this is the purchased power.

  Here, as shown in FIG. 9, the extractable current Iinv instructed by the extractable current indicating means 110a to the inverter 54 changes with a predetermined time delay with respect to the change in the fuel supply amount Fr when the current tends to increase. Set to do. For example, at time t10 in FIG. 9, after the fuel supply current value If and the fuel supply amount Fr start to increase, the increase of the extractable current Iinv is started with a delay. Also at time t12, after the fuel supply current value If and the fuel supply amount Fr increase, the increase of the extractable current Iinv is started with a delay. As described above, after the fuel supply amount Fr is increased, the timing at which the current actually taken out from the fuel cell module 2 is increased is delayed so that the fuel supplied to the fuel cell module 2 passes through the reformer 20 and the like. A time delay until the fuel cell stack 14 is reached and a time delay until the actual power generation reaction becomes possible after the fuel reaches the battery cell stack 14 are dealt with. This reliably prevents the fuel battery cell unit 16 from being depleted of fuel and damaging the fuel battery cell unit 16. FIG. 9 shows macroscopically and schematically the timing of the increase in the fuel supply amount Fr and the increase in the extractable current Iinv, and details will be described later.

  In addition, as shown in the lowermost graph of FIG. 9, the actual power generation current Ia (dashed line) that is actually extracted to the inverter 54 is extracted even when the current corresponding to the demand power exceeds the extractable current Iinv. Slightly less than the possible current Iinv (solid line). The difference between the extractable current Iinv and the actual generated current Ia is large when the extractable current Iinv tends to increase (t10 to t11, t12 to t14 in FIG. 9), and the extractable current Iinv is a constant value. Will be smaller. This is for surely preventing the actual power generation current Ia from temporarily exceeding the extractable current Iinv due to overshoot or the like in a transient state in which the extractable current Iinv is increased.

  Furthermore, even when the extractable current Iinv is substantially constant, there is a difference between the extractable current Iinv and the actual power generation current Ia. This difference is because the current extraction characteristic of the inverter 54 is designed to be safe in order to prevent the actual power generation current Ia from exceeding the extractable current Iinv and damaging the fuel cell module 2. . The current monitoring unit 110b (FIG. 6) built in the control unit 110 monitors the actual generated current Ia actually extracted by the inverter 54 with respect to the extractable current Iinv. Further, the inverter characteristic correction unit 110c (FIG. 6) built in the control unit 110 is based on the difference between the extractable current Iinv and the actual power generation current Ia due to the characteristic of the inverter 54 based on the monitoring result by the current monitoring unit 110b ( The fuel supply amount is corrected so that the difference between the power generation capacity of the fuel cell module 2 and the actual power generation current Ia) decreases.

  FIG. 10 is a flowchart showing control by the current monitoring unit 110b and the inverter characteristic correcting unit 110c. The flowchart shown in FIG. 10 is repeatedly executed at predetermined time intervals while the solid oxide fuel cell 1 is in operation.

  First, in step S1 of FIG. 10, the current monitoring unit 110b calculates a moving average current Av that is the difference between the current Iinv that can be taken out and the actual power generation current Ia in the last one minute. Note that the data of the extractable current Iinv and the actual generated current Ia when the actual generated current Ia tends to decrease is excluded from the calculation of the moving average current Av. That is, when the demand power is lower than the generated power (reverse power flow) as the demand power decreases, the inverter decreases the actual power generation current Ia until the reverse power flow disappears. Therefore, when the actual power generation current Ia decreases, the difference between the extractable current Iinv and the actual power generation current Ia increases transiently. If this transient difference is included in the moving average current Av, It becomes impossible to correct the characteristics accurately. As described above, the correction by the inverter characteristic correcting unit 110c is performed based on the data history of the past extractable current Iinv and the actual generated current Ia, and based on the data when the extractable current Iinv is increased or constant. Done.

  Next, in step S2, it is determined whether or not the high-speed tracking mode operation is being performed. If the high-speed tracking mode operation is being performed, the process proceeds to step S3. If the high-speed tracking mode operation is not being performed, the process proceeds to step S4. The high-speed tracking mode operation is an operation mode executed by the high-speed tracking means 110d (FIG. 6) built in the control unit 110. The high-speed follow-up means 110d has a power generation capability (removable current Iinv) of the fuel cell module 2 when the demand power is significantly higher than the power corresponding to the extractable current Iinv and the purchased power supplied from the system power is large. Is made to follow the demand power rapidly. The high-speed tracking mode operation will be described later with reference to FIGS. 11 to 15.

  In step S3, the correction by the inverter characteristic correcting unit 110c is not executed, and one process of the flowchart shown in FIG. 10 is terminated. This is because during the high-speed tracking mode operation, the extractable current Iinv increases abruptly. Therefore, when the correction by the inverter characteristic correcting means 110c is executed in this state, the actual generated current Ia is transiently converted into the extractable current Iinv. This is because there is a risk of exceeding. Alternatively, as a modification, the present invention can be configured to suppress the correction amount by the inverter characteristic correction unit 110c during the high-speed tracking mode operation.

  On the other hand, in step S4, the fuel supply amount, the power generation air supply amount, and the water supply amount are corrected based on the moving average current Av calculated in step S1. Specifically, a current obtained by multiplying the moving average current Av by a predetermined coefficient of 0.8 is subtracted from the fuel supply current value If (FIG. 9), and fuel is generated based on the reduced fuel supply current value If. A supply amount, a power generation air supply amount, and a water supply amount are calculated. Thus, the correction for reducing the fuel supply amount and the correction for reducing the power supply air supply amount and the water supply amount are also executed. As a result, as the difference (moving average) between the extractable current Iinv and the actual power generation current Ia is larger, the fuel supply amount, the power generation air supply amount, and the water supply amount are corrected to decrease significantly. On the other hand, the value based on the moving average current Av is not changed for the extractable current Iinv. For this reason, the fuel supply amount, the power generation air supply amount, and the water supply amount are reduced with respect to the same extractable current Iinv, and the actual power generation capability of the fuel cell module 2 is reduced. Thereby, the difference between the power generation capability of the fuel cell module 2 and the actual power generation current Ia lower than the extractable current Iinv is reduced.

Next, control of the fuel, power generation air, water supply amount, and extractable current by the control unit 110 and the high-speed tracking means 110d built in the control unit 110 will be described with reference to FIGS.
FIG. 11 is a flowchart of fuel, power generation air, and water supply amount control by the control unit. FIG. 12 is a time chart showing an example of the first delay control by the control unit, and FIG. 13 is a time chart showing an example of the second delay control which is the high-speed tracking mode operation by the high-speed tracking means 110d. FIG. 14 is a graph showing a range of values of the fuel utilization rate that can be determined for each generated current. FIG. 15 is a graph showing a range of values of air utilization rates that can be determined for each generated current.

  In the present embodiment, the control unit 110 includes first delay control means (not shown) that executes first delay control, and high-speed tracking means 110d that executes second delay control. The first delay control is control executed in step S22 of the flowchart shown in FIG. Also, the second delay control is a control mode that is executed in step S6 or less or step S14 or less in the flowchart shown in FIG. 11, and is a control mode in which the followability to the demand power is improved as compared with the first delay control.

  First, the first delay control executed by the first delay control means (not shown) will be described with reference to FIG. The time chart shown in FIG. 12 shows demand power in the upper stage, purchased power in the middle stage, fuel, air for power generation, water supply amount, and extractable current Iinv in the lower stage.

  First, at time t21 in FIG. 12, the demand power starts to increase, but the extractable current Iinv does not immediately follow this increase, so the power taken out from the fuel cell module 2 does not change and the demand power increases. Since all the portion is covered by grid power, the purchased power increases with the demand power. Next, at time t22, in order to increase the power generated by the fuel cell module 2, the first delay control means (not shown) built in the control unit 110 sends a signal to the water flow rate adjustment unit 28 which is water supply means. To increase the water supply. At this point in time, since the extractable current Iinv has not been increased, the purchased power increases with the demand power.

  Next, at time t23, which is 5 seconds after time t22, the first delay control means (not shown) sends a signal to the power generation air flow rate adjustment unit 45, which is power generation oxidant gas supply means, and supplies the air supply amount. Increase. Even at this time, since the extractable current Iinv is not increased, the increase in demand power is all covered by the purchased power. Further, at time t24, five seconds after time t23, the first delay control means (not shown) sends a signal to the fuel flow rate adjustment unit 38, which is fuel supply means, to increase the fuel supply amount. Even at this time, since the extractable current Iinv is not increased, the increase in demand power is all covered by the purchased power.

  Next, at time t25, 10 seconds after time t24, the extractable current instruction means 110a sends a signal to the inverter 54 to increase the extractable current Iinv by 20 mA. With the increase in the extractable current Iinv, the actual power generation current Ia that is actually extracted from the fuel cell module 2 also increases, so part of the increase in demand power is covered by the solid oxide fuel cell 1 and the purchased power decreases. To do. Thus, in order to increase the extractable current Iinv at time t25, the supply amounts of water, power generation air, and fuel are increased in advance, and then the extractable current Iinv is increased with a predetermined time delay. Thereby, after the increased fuel is reformed in the reformer 2 and reaches the fuel cell stack 14, the extractable current Iinv is increased, and the actual power generation current Ia actually extracted from the fuel cell module 2 is also increased. Will be increased. In addition, each increase amount of water, power generation air, and fuel at times t22, t23, and t24 is set to an amount corresponding to an increase in the generated current 20 mA.

  Furthermore, at time t25, the water supply amount is increased by one more stage in order to further increase the extractable current Iinv. Similarly, the supply amounts of power generation air and fuel are increased at times t26 and t27, respectively, and the extractable current Iinv is further increased by 20 mA at time t28. This reduces power purchases. As described above, the extractable current Iinv is increased by 5 steps of 20 mA once every 20 seconds, so that the extractable current Iinv catches up with the increase in demand power at time t29, and the purchased power is obtained at time t21. Decrease to level. As described above, in the first delay control, after increasing the water supply amount, the power generation air supply amount, and the fuel supply amount, the current that can be extracted up to the power corresponding to the increased fuel supply amount is delayed by a predetermined time. By increasing Iinv (generated power) and repeating this control, the extractable current Iinv is brought close to the actual generated current Ia corresponding to the demand power. In the solid oxide fuel cell 1 of the present embodiment, the power generated by the fuel cell module 2 is always 20 W less than the demand power even when the demand power is small in order to prevent reverse power flow to the grid power and the like. Since the power is set, the purchased power never becomes 0.

Next, switching between the first delay control and the second delay control will be described with reference to FIGS. 11 to 15.
First, in step S <b> 1 of FIG. 11, the control unit 110 reads the purchased power amount QW from the power state detection sensor 126 that is a purchased power detection unit. Next, in step S2, it is determined how much W the current generated power of the fuel cell module 2 is less than the rated generated power. If this difference is less than 200W, the process proceeds to step S22, and if it is 200W or more, the process proceeds to step S3. In this embodiment, since the rated generated power is 700 W, when the generated power of the fuel cell module 2 is 500 W or more, the process proceeds to step S22. In step S22, the first delay control described with reference to FIG. 12 is executed, and one process of the flow of FIG. 11 is terminated. This is because there is little room for increase in the generated power when the current generated power by the fuel cell module 2 is close to the rated generated power, and there is little need to improve the followability by the second delay control.

  Next, in step S3, the control unit 110 determines whether or not the output voltage of the fuel cell module 2 is equal to or lower than 100 V, which is the second delay control prohibiting voltage. When it is 100V or less, the process proceeds to step S22, and when it is higher than 100V, the process proceeds to step S4. That is, in the state where the output voltage of the fuel cell module 2 drops to 100 V or less, if the followability is improved by the second delay control, the fuel cell stack 14 may be deteriorated. In such a case, the first delay control is selected that hardly places a burden on the fuel cell stack 14.

  Further, in step S4, control unit 110 determines whether or not purchased power amount QW is 200 W or less. If it is 200 W or less, the process proceeds to step S22, and if it is greater than 200 W, the process proceeds to step S5. In step S22, the first delay control is executed, and one process of the flow of FIG. 11 is terminated. This is because, in a state where the purchased power amount QW is 200 W or less, there is little room for an increase in generated power, and there is little need to improve follow-up by the second delay control.

  Next, in step S5, the control unit 110 determines whether or not the purchased power amount QW is 400 W or more. When it is 400 W or more, the process proceeds to step S14, and when it is less than 400 W (in the case of 200 to 400 W), the process proceeds to step S6. The double speed second delay control is executed after step S6, and the triple speed second delay control is executed after step S14. Here, in the double speed second delay control, the increase amount of the fuel supply amount or the like for two stages in the first delay control is increased in one stage, and in the triple speed second delay control, 3 in the first delay control. The amount of increase in fuel supply amount for each stage is increased in one stage. As described above, in the second delay control, when the amount of purchased power, which is the difference between the current power generated by the fuel cell module 2 and the demand power, is large, the amount of increase in one step is increased compared with the case where the purchased power amount is small. High control is selected. However, two types of second delay control executed by the high-speed tracking means 110d are set in advance, ie, double speed second delay control and triple speed second delay control, and one of these is selected. Therefore, also in the second delay control, the amount of increase in one stage is limited to the amount of increase in three stages in the first delay control.

  In step S14, the supply amounts of water, power generation air, and fuel by the triple speed second delay control are calculated by the high speed follower 110d. In the first delay control described with reference to FIG. 12, the extractable current Iinv is increased by 20 mA per stage, and the supply amounts of water, power generation air, and fuel are also set to supply amounts corresponding to the increased extractable current Iinv. It was changed in advance. On the other hand, as shown in FIG. 13, in the triple speed second delay control, water, power generation air, and fuel corresponding to the increase in the extractable current Iinv of 60 mA corresponding to the three stages in the first delay control are once. The amount is increased. In step S14, the supply amounts of water, power generation air, and fuel corresponding to the extractable current Iinv increased by three stages are calculated.

  Next, in step S15, it is determined whether or not a sudden decrease in the purchased power amount QW has occurred. If the purchased power amount QW is rapidly decreasing, the process proceeds to step S22, and if not, the process proceeds to step S16. The amount of power purchased QW decreases sharply as the demand power decreases rapidly. Accordingly, if the purchased power amount QW is drastically reduced before actually starting the triple speed second delay control, it is expected that the purchased power amount QW will further decrease. The triple speed second delay control for sudden increase is stopped, and the first delay control is executed.

  In step S16, it is determined whether or not each supply amount of power generation air and fuel calculated in step S14 is within a range of allowable utilization rates. First, for fuel, the range of fuel utilization rates allowed for each generated current is preset as shown in FIG. The fuel utilization rate is a value obtained by dividing the fuel supply amount necessary for outputting the generated current by the fuel supply amount actually supplied. The higher the fuel utilization rate, the higher the efficiency of power generation. However, when the fuel utilization rate is too high, fuel withering occurs, and the fuel cell module 2 cannot be thermally independent, and the temperature of the fuel cell stack 14 decreases. Conversely, when the fuel utilization rate is low, the power generation efficiency decreases, and when it is too low, the amount of fuel burned in the combustion chamber 18 without being used for power generation increases. The temperature rises excessively. For this reason, an allowable range is set in advance for the fuel utilization rate.

  Therefore, in step S16, whether the fuel supply amount increased at time t34 is within the allowable range of the fuel utilization rate defined as shown in FIG. 14 with respect to the current Iinv that can be taken out at time t34 in FIG. It is determined whether or not. Further, it is determined whether or not the fuel supply amount increased at time t34 is within the allowable range of the fuel utilization rate with respect to the extractable current Iinv after being increased by three stages at time t38.

  Similarly, for power generation air, the range of the air utilization rate allowed for each power generation current is set in advance as shown in FIG. The air utilization rate is a value obtained by dividing the power generation air supply amount necessary for outputting the extractable current Iinv by the power supply air supply amount actually supplied. If this air utilization rate is too high, air dying may occur and the fuel cell stack 14 may be damaged. Conversely, when the air utilization rate is low, more air than necessary passes through the fuel cell module 2, so that the heat of the fuel cell stack 14 is taken away by the air, and the fuel is used to supplement this heat. As power is consumed, power generation efficiency decreases. For this reason, an allowable range is set in advance for the air utilization rate.

  Therefore, in step S16, the power generation air supply amount increased at time t33 with respect to the extractable current Iinv at time t33 in FIG. 13 is within the allowable range of the air utilization rate as shown in FIG. It is determined whether or not there is. Further, it is determined whether or not the power supply air supply increased at time t33 is within the allowable range of the air utilization rate with respect to the extractable current Iinv after being increased by three stages at time t38.

  When the fuel usage rate and the air usage rate are within the permissible ranges, the process proceeds to step S18, and when not within the permissible range, the process proceeds to step S17. In step S17, the fuel supply amount and power generation air calculated in step S14 are corrected. That is, when the fuel usage rate determined in step S16 is higher than the allowable fuel usage rate, the fuel is corrected to increase so that the fuel usage rate falls within the allowable range. Conversely, when the fuel usage rate determined in step S16 is lower than the allowable fuel usage rate, the fuel is corrected to decrease so that the fuel usage rate falls within the allowable range. Similarly, each air utilization rate determined in step S16 is also corrected to be within the allowable range.

  Next, in step S18, the S / C (ratio of water vapor amount to carbon amount) calculated from the water supply amount calculated in step S14 and the fuel supply amount calculated in step S14 or corrected in step S17. ) Is within an allowable range. Here, the ratio S / C = 1 of the amount of water vapor and the amount of carbon is a state in which the total amount of carbon contained in the supplied fuel is chemically steam-reformed by the supplied water (steam). Means. In the present embodiment, the allowable range of S / C is set to 2.5 to 3.5. 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. In practice, carbon deposition occurs in the reformer 20 at the amount of steam at which S / C = 1, so that the amount of steam at about S / C = 2.5 steam reforms the fuel. For the right amount.

  In step S18, it is determined whether the S / C before and after the fuel supply amount is increased is within an allowable range. That is, after the water supply amount is increased at time t32 in FIG. 13, the S / C until the fuel supply amount is increased at time t34, and the time when both the water supply amount and the fuel supply amount are increased. It is determined whether or not the S / C between t34 and t35 is within the range of 2.5 to 3.5. If both S / Cs are within the allowable range, the process proceeds to step S20, and if not, the process proceeds to step S19.

  In step S19, the water supply amount is corrected so that each S / C falls within the allowable range. That is, when S / C is smaller than 2.5, the water supply amount is corrected to increase, and when S / C is larger than 3.5, the water supply amount is corrected to decrease.

  In step S20, the amount of water, power generation air, and fuel calculated in step S14 or corrected in step S17 or S19 are sequentially supplied. That is, after the power demand increases at time t31 in FIG. 13, the water supply amount is increased at time t32. Next, at time t33, which is five seconds after time t32, the high-speed tracking unit 110d increases the air supply amount. Furthermore, at time t34, which is five seconds after time t33, the high-speed tracking unit 110d increases the fuel supply amount. In this manner, in the triple speed second delay control, the amount of increase of about three times in the first delay control is increased by one time, so the supply amount of water, power generation air, and fuel is more drastically than in the first delay control. Is increased.

  Next, in step S21 of FIG. 11, the extractable current Iinv is increased three times step by step. That is, at time t35, which is 10 seconds after time t34, the extractable current instruction means 110a sends a signal to the inverter 54 to increase the extractable current Iinv by 20 mA. Further, at time t36 0.5 seconds after time t35, the extractable current Iinv is further increased by 20 mA, and at time t37 0.5 seconds later, the extractable current Iinv is further increased by 20 mA. Thereby, the extractable current Iinv is increased by 60 mA for three stages in the first delay control in 21 seconds after the water supply amount is increased at time t32. As described above, the one-step increase amount of the extractable current Iinv (generated power) in the triple speed second delay control is the same as the one-step increase amount in the first delay control. However, in the triple speed second delay control, the amount of supply of water, power generation air, and fuel is increased at a time by three increments of the extractable current Iinv.

  Thus, by the triple speed second delay control executed in step S14 and subsequent steps in FIG. 11, the extractable current Iinv follows the demand power at about three times the speed, thereby reducing the purchased power amount QW. The Further, in the triple speed second delay control, the increase amount of about three times in the first delay control is increased by one time, and the supply amount is increased more rapidly than in the first delay control, whereas the extractable current is increased. The increase in Iinv (generated power) does not increase the extractable current Iinv for three stages at a time, but increases at three times with an interval of 0.5 seconds. As described above, the increase in the extractable current Iinv is performed more slowly than the increase in the fuel supply amount or the like.

  Next, at time t37 in FIG. 13, the power purchase amount QW exceeds 200 W and is less than 400 W, and therefore double speed second delay control of step S6 and subsequent steps in FIG. 11 is executed. In the double speed second delay control executed in steps S6 to S13, the one time increase in water, power generation air, and fuel calculated in step S6 is doubled from the increase in the first delay control. Except for this, it is the same as the above-mentioned triple speed second delay control.

  That is, in step S12, the amount of water, power generation air, and fuel calculated in step S6 or corrected in step S8 or S11 are sequentially supplied. That is, the water supply amount is increased at time t37 in FIG. Next, at time t38, which is 5 seconds after time t37, the high-speed tracking unit 110d increases the air supply amount. Further, at time t39, which is 5 seconds after time t38, the high-speed tracking unit 110d increases the fuel supply amount.

  Next, in step S13, the extractable current Iinv is increased twice by one step. That is, at time t40, which is 10 seconds after time t39, the extractable current instruction means 110a increases the extractable current Iinv by 20 mA. Further, at time t41 0.5 seconds after time t40, the extractable current Iinv is further increased by 20 mA. As a result, the extractable current Iinv is increased by 40 mA for two stages in the first delay control in 20.5 seconds after the water supply amount is increased at time t37. Thus, by the double speed second delay control executed in step S6 and subsequent steps of FIG. 11, the extractable current Iinv follows the demand power at about twice the speed, thereby reducing the purchased power amount QW. The

  According to the solid oxide fuel cell 1 of the embodiment of the present invention, the current monitoring unit 110b monitors the extractable current Iinv and the actual generated current Ia (FIG. 10, step S1), and the inverter characteristic correcting unit 110c Based on the monitoring result, the shortage of the actual power generation current with respect to the power generation capacity due to the characteristics of the inverter 54 is reduced (step S4 in FIG. 10). As a result, even when the inverter 54 has a characteristic of taking out less current than the instructed current Iinv, a current close to the power generation capacity is actually taken out from the fuel cell module 2, and the fuel cell module 2 It is possible to suppress the waste of fuel due to the provision of extra power generation capacity. In addition, surplus fuel generated by providing the fuel cell module 2 with an extra power generation capability heats the inside of the fuel cell module 2, and an excessive increase in temperature inside the fuel cell module 2 can be suppressed.

  Further, according to the solid oxide fuel cell 1 of the present embodiment, correction is performed based on the data history of the past extractable current Iinv and the actual power generation current Ia (FIG. 10, step S1) (FIG. 10, Since step S4), the risk that the actual generated current Ia exceeds the extractable current Iinv due to excessive correction can be avoided, and the energy efficiency can be improved more safely.

  Furthermore, according to the solid oxide fuel cell 1 of the present embodiment, correction is performed based on the data of the extractable current Iinv and the actual generated current Ia when the actual generated current Ia is increased or constant (FIG. 10, step S1). Is executed (FIG. 10, step S4). As a result, the data at the time of decrease in the actual power generation current Ia in which the detachable current Iinv and the actual power generation current Ia are likely to deviate is excluded, so that the inverter characteristics can be corrected more accurately.

  Further, according to the solid oxide fuel cell 1 of the present embodiment, the correction during the high-speed follow-up mode operation (FIG. 13) that rapidly increases the power generation capacity of the fuel cell module 2 is prohibited, so that the transient change Among them, the actual power generation current Ia exceeds the extractable current Iinv, and it is possible to reliably avoid the risk of occurrence of problems such as fuel depletion.

  Furthermore, according to the solid oxide fuel cell 1 of the present embodiment, the supply amount of power generation air and water are corrected together with the supply amount of fuel (FIG. 10, step S4), so the concentration of carbon monoxide in the exhaust gas The energy efficiency can be improved while avoiding adverse effects on the emission performance such as the above, the temperature in the fuel cell module 2, the reforming reaction in the reformer 20, and the like.

  As mentioned above, although preferable embodiment of this invention was described, a various change can be added to embodiment mentioned above. In particular, in the above-described embodiment, by reducing the fuel supply amount with respect to the extractable current Iinv, the power generation capacity of the fuel cell module is lowered, and the difference between the power generation capacity and the actual power generation current actually taken out is reduced. However, as a modification, the actual generation current actually extracted is increased by increasing the extractable current Iinv with respect to the fuel supply amount (making the extractable current Iinv larger than the actually extractable current). The present invention can also be configured to reduce the difference between the power generation capacity and the actual power generation current.

  In the above-described embodiment, the fuel supply amount is corrected based on the data when the actual power generation current is increased or constant except for the data when the actual power generation current is decreasing. As another example, the present invention can be configured to correct the fuel supply amount or the extractable current Iinv using the data when the actual power generation current is decreasing. Alternatively, the moving average current is calculated for each of the cases where the actual generated current is decreasing, the actual generated current is constant, and the actual generated current is increasing, and correction is performed based on these moving average currents. Thus, the present invention can also be configured. Further, the difference between the extractable current Iinv and the actual generated current is stored in accordance with the change tendency of the actual generated current, and the difference between the extractable current Iinv and the actual generated current is reduced based on the stored difference. The present invention can also be configured to learn the correction amount.

DESCRIPTION OF SYMBOLS 1 Solid oxide fuel cell 2 Fuel cell module 4 Auxiliary machine unit 7 Heat insulation material (heat storage material)
8 Sealed space 10 Power generation chamber 12 Fuel cell assembly 14 Fuel cell stack 16 Fuel cell unit (solid oxide fuel cell)
18 Combustion chamber (combustion section)
20 Reformer 22 Heat exchanger for air 24 Water supply source 26 Pure water tank 28 Water flow rate adjustment unit (water supply means)
30 Fuel supply source 38 Fuel flow rate adjustment unit (fuel supply means)
40 Air supply source 44 Reforming air flow rate adjustment unit 45 Power generation air flow rate adjustment unit (power generation oxidizing gas supply means)
46 1st heater 48 2nd heater 50 Hot water production apparatus 52 Control box 54 Inverter 83 Ignition apparatus 84 Fuel cell 110 Control part (control means)
110a Extractable current instruction means 110b Current monitoring means 110c Inverter characteristic correction means 110d High-speed tracking 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)
138 Pressure sensor (reformer pressure sensor)
140 Exhaust temperature sensor 142 Power generation chamber temperature sensor (temperature detection means)
148 Reformer temperature sensor (temperature detection means)
150 Outside temperature sensor

Claims (5)

A solid oxide fuel cell that changes power generation capacity according to demand power and commands an inverter to take out a current,
A fuel cell module having a fuel cell stack; and
A reformer for reforming the fuel supplied to the fuel cell stack;
Fuel supply means for supplying fuel to the reformer;
Water supply means for supplying water for reforming 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 so that the power generation capacity of the fuel cell module is changed according to demand power,
The control means includes a takeable current indicating means for sequentially instructing the inverter an extractable current that can be taken out from the fuel cell module according to a state of the fuel cell module, an extractable current instructed to the inverter, and Current monitoring means for monitoring the actual power generation current actually taken out by the inverter within the range of extractable current, and inverter characteristic correction means for correcting the fuel supply amount or the extractable current based on the monitoring result of the current monitoring means; comprises, the inverter characteristic correcting means, due to the characteristics of the inverter, the obtainable current and the actual generated current constant state, so that the lack of actual generated current to the power generation capability of the fuel cell module is reduced solid oxide fuel cell characterized that you correct the fuel supply amount or obtainable current to.   2. The solid oxide according to claim 1, wherein the inverter characteristic correcting unit corrects the fuel supply amount or the extractable current based on a history of data of past extractable current and actual power generation current acquired by the current monitoring unit. Type fuel cell.   3. The solid oxide fuel according to claim 2, wherein the inverter characteristic correcting means corrects the fuel supply amount or the extractable current based on data of the extractable current and the actual generated current when the actual generated current is increased or constant. battery.   The control means further includes high-speed follow-up means for executing a high-speed follow-up mode operation in which the fuel supply amount is rapidly increased so that the power generation capacity of the fuel cell module rapidly follows the increase in demand power, and the inverter 4. The solid oxide fuel cell according to claim 3, wherein the characteristic correction means does not execute correction during the high-speed tracking mode operation, or suppresses the correction amount of the fuel supply amount or the extractable current.   4. The solid oxide fuel cell according to claim 3, wherein the inverter characteristic correcting means executes correction for reducing the supply amount of the oxidant gas and water for power generation as well as correction for reducing the fuel supply amount.

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