JP2014194855A - Solid oxide fuel battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid oxide fuel battery arranged so as to be able to suppress the occurrence of damage to a fuel battery cell unit by the shrinkage of a fuel electrode owing to oxidation.SOLUTION: A solid oxide fuel battery generates electric power by causing a reaction of hydrogen and an oxidant gas in a fuel battery cell unit (16). The fuel battery cell unit (16) includes: a fuel electrode (90); an oxidant gas electrode (92); and a solid electrolyte (94) provided between the fuel electrode (90) and the oxidant gas electrode (92). The fuel electrode (90) is formed of a nickel-containing composite material. The solid oxide fuel battery holds the fuel electrode (90) under a non-oxygen atmosphere until the temperature of the fuel electrode (90) lowers to 350°C after the stop of power generation, thereby preventing the shrinkage of the fuel electrode owing to oxidation thereof.

Description

  The present invention relates to a solid oxide fuel cell, and more particularly to a solid oxide fuel cell in which a fuel electrode of a fuel cell is made of a composite material containing nickel.

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

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

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

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

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

  It has been known that when air is brought into contact with the fuel electrode side of the high-temperature fuel cell stack in the fuel cell stop process, the fuel electrode oxidizes and expands, resulting in damage to the fuel cell unit.

  In the fuel cell described in Japanese Patent Application Laid-Open No. 2012-3850 (Patent Document 1), as described above, the fuel cell is supplied even during the stop process until the fuel cell stack is lowered to a predetermined temperature. The backflow of the cooling air supplied to the air electrode side of the cell to the fuel electrode side is prevented, and as a result, oxidation of the fuel electrode of the fuel cell is prevented.

  Also in the fuel cell system described in Japanese Patent Application Laid-Open No. 2010-27579 (Patent Document 2), even after the supply from the fuel supply source is cut off, the delivery pump is operated to be adsorbed by the adsorber for a certain period. The spent fuel gas is sent to the cell stack to prevent oxidation of the fuel electrode.

  Furthermore, also in the high-temperature operation type fuel cell system described in Japanese Patent Application Laid-Open No. 2012-138186 (Patent Document 3), the water vapor evaporated and expanded in the reformer by operating the reforming water pump immediately after stopping the raw fuel pump. Thus, the fuel electrode is prevented from being oxidized by pushing the residual fuel to the cell stack side. And according to Unexamined-Japanese-Patent No. 2012-138186 (patent document 3), the temperature at which a fuel electrode is oxidized is normally about 400 degreeC or more.

  However, when the present inventor introduced air to the fuel electrode side of the fuel cell stack at a temperature lower than 400 ° C. in the fuel cell stop process, the temperature is low so that oxidative expansion of the fuel electrode should not occur. In spite of this, we found an event that some fuel cells were damaged. Therefore, as a result of repeating various experiments and studies to elucidate the cause of such an event, the present inventor, as will be described below, is a low temperature region that has not been previously considered to oxidize the fuel electrode. We have discovered the surprising phenomenon that in a specific temperature range, the fuel electrode contracts rather than expands due to oxidation.

With reference to FIG. 27, it will be described that the nickel-containing composite material constituting the fuel electrode shrinks due to oxidation in a predetermined temperature range.
In the graph of FIG. 27, the horizontal axis indicates temperature (° C.), and the vertical axis indicates linear expansion coefficient (%). A thick line I in the graph indicates a linear expansion coefficient when the reductant of the fuel electrode material of the fuel battery cell is gradually heated in an air atmosphere. The fuel electrode is made of a nickel-containing composite material made of a mixture of nickel and zirconia doped with yttrium (NiYSZ). A broken line II in the graph indicates a linear expansion coefficient when the temperature of the NiYSZ oxidant is similarly raised. The thin line III in the graph indicates the linear expansion coefficient when the temperature of the nickel reductant is similarly raised. Both the fuel electrode material and nickel were heated from room temperature (25 ° C.) to 700 ° C. at a rate of 0.5 ° C./min. The linear expansion coefficient of the anode material and nickel was measured using a thermomechanical analysis (TMA) apparatus based on the volume at room temperature.

The fuel electrode material used for the measurement is a reductant of a nickel-containing composite material made of a mixture of nickel and zirconia doped with yttrium (NiYSZ). The mixing ratio of Ni and YSZ oxide is 50:50.
Since the fuel electrode material is supplied with hydrogen during operation of the fuel cell, it is a reductant immediately after the fuel cell is stopped.

  First, paying attention to the broken line II in the graph, the length of the oxidant of the composite material monotonously increases at a substantially constant rate as the temperature increases. Since the oxidant of the composite material has already been oxidized, this increase in volume is considered to be due to thermal expansion without the influence of oxidation.

  Next, paying attention to the thick line I in the graph, the increase in volume of the reductant composite material in the region from room temperature to around 350 ° C. and in the region higher than about 480 ° C. is that the thick line I is almost parallel to the broken line II. Therefore, it is thought that it is due to thermal expansion. On the other hand, the length of the reductant composite material decreases slightly from around 350 ° C. to around 400 ° C., then becomes minimal at around 380 ° C., and then suddenly increases from around 400 ° C. to around 480 ° C. It has increased. As described above, it has been conventionally considered that the reductant composite material only expands due to oxidation, but in fact, it has been found that the reductant composite material contracts in a temperature range from about 350 ° C. to about 400 ° C.

  Furthermore, paying attention to the thin line III in the graph, it can be seen that the volume of nickel alone also decreases from 350 ° C. to 480 ° C. as the temperature increases. From this, the peculiar volume change of the reductant composite material from about 350 ° C. to about 480 ° C. shown in the thick line I is not the already oxidized YSZ oxide among the components of the reductant composite material, but nickel It is thought to be caused by

  Next, with reference to FIG. 28, it will be described in more detail that the nickel-containing composite material constituting the fuel electrode contracts due to oxidation in a predetermined temperature range. The material of the fuel electrode used for the measurement shown in FIG. 28 is the same component as the material used for the measurement shown in FIG.

  The horizontal axis of the graph of FIG. 28 shows the elapsed time (minutes) from the start of temperature rise, and the vertical axis shows the linear expansion coefficient (%). The broken line I in the graph shows the fuel electrode material when the material of the fuel electrode of the reductant is rapidly heated to 500 ° C. at a temperature increase rate of 6 ° C./min in the air atmosphere and the temperature is maintained at 500 ° C. The time change of the length of is shown. As shown by the broken line I, the fuel electrode material rapidly expands until it reaches 500 ° C. about 100 minutes after the start of heating, and its length increases by about 0.7%. Subsequently, after about 100 minutes, the length of the fuel electrode material gradually increases with time in an air atmosphere at 500 ° C. In this case, the anode material is substantially oxidized at 500 ° C. Therefore, it can be seen that the fuel electrode material expands as conventionally considered when oxidized at 500 ° C.

  Next, a solid line II in the graph shows a case where the material of the fuel electrode of the reductant is rapidly heated to 400 ° C. at a temperature increase rate of 6 ° C./min in the air atmosphere, and the temperature of 400 ° C. is maintained. The time change of the length of an anode material is shown. In this case, the anode material is substantially oxidized at 400 ° C. As shown by the solid line II, the fuel electrode material undergoes rapid thermal expansion until reaching 400 ° C. about 60 minutes after the start of heating, and its length increases by about 0.4%.

  However, from about 60 minutes to about 100 minutes later, the length of the fuel electrode material rapidly decreases to a level of about 0.23% in an air atmosphere at 400 ° C. Therefore, it is considered that the fuel electrode material was greatly contracted by oxidation at 400 ° C.

  Subsequently, after about 100 minutes, the length of the material of the fuel electrode gradually increases with time in an air atmosphere at 400 ° C. This is considered to correspond to the conventionally known expansion due to oxidation.

  Thus, it can be seen from the solid line II that when the material of the fuel electrode is oxidized at 400 ° C., it does not simply expand, but rapidly contracts at least temporarily.

  Next, an alternate long and short dash line III in the graph shows that the material of the fuel electrode of the reductant is rapidly heated to 300 ° C. at a temperature increase rate of 6 ° C./min in an air atmosphere, and the temperature of 300 ° C. is maintained. The time change of the material length of the fuel electrode is shown. As indicated by the alternate long and short dash line III, the material of the fuel electrode rapidly expands until it reaches 300 ° C. about 50 minutes after the start of heating, and its length increases by about 0.33%. However, after about 50 minutes, the length of the material of the fuel electrode gradually decreases in an air atmosphere at 300 ° C. In this case, the anode material is substantially oxidized at 300 ° C. Therefore, it can be seen that the material of the fuel electrode gradually contracts, though slightly, when oxidized at 300 ° C.

  As described above, the material of the fuel electrode simply expands when oxidized at 500 ° C., but when oxidized at 400 ° C., the material of the fuel electrode expands gradually after being contracted, and is oxidized at 300 ° C. It can be seen that in some cases, it gradually contracts. Therefore, it can be seen that the material of the anode is not only expanded by oxidation, but also contracted in a specific temperature range.

  Here, referring again to FIG. 27, as shown by the thick line II, the degree of oxidative shrinkage of the fuel electrode material from around 350 ° C. to around 400 ° C. is slightly smaller than the degree of oxidative expansion at higher temperatures. is there. As a result, the stress applied to the fuel cell unit due to the oxidation contraction is also smaller than the stress due to the oxidative expansion at a higher temperature. As long as the fuel cell unit has a strength capable of withstanding the stress caused by the oxidation shrinkage, the fuel cell unit is not damaged even if the stress caused by the oxidation shrinkage is applied. Until now, it is considered that the temperature at which the fuel electrode is oxidized is usually about 400 ° C. or higher, and has not occurred so frequently that damage to the fuel cell unit due to oxidation contraction at 400 ° C. or lower becomes a problem. The reason is considered.

  However, in recent years, in order to lower the operating temperature of the solid oxide fuel cell, for example, it is required to reduce the thickness of the power generator including the fuel electrode and the air electrode of the fuel cell unit. If the power generator of the fuel cell unit is made thinner, the strength of the fuel cell unit is reduced and damage is likely to occur. For this reason, if the fuel ionization cell unit becomes thinner in the future, there will be a problem that damage due to oxidation shrinkage occurs in a low temperature range where it has not been conventionally thought that the fuel ionization cell unit is oxidized. is expected.

  Therefore, the present inventor, in the shutdown process of the solid oxide fuel cell, the fuel electrode does not undergo oxidative expansion, but oxidatively shrinks even in a low temperature range where it has not been conventionally thought that the fuel electrode oxidizes. A new technical problem has been found that this leads to damage of the fuel cell unit.

  Accordingly, an object of the present invention is to provide a solid oxide fuel cell capable of suppressing the occurrence of damage to the fuel cell unit due to oxidation contraction of the fuel electrode.

  In order to solve the above-described problems, a solid oxide fuel cell according to the present invention is a solid oxide fuel cell that generates power by reacting hydrogen with an oxidant gas in a fuel cell unit, The battery cell unit includes a fuel electrode to which the hydrogen is supplied, an oxidant gas electrode to which the oxidant gas is supplied, and a solid electrolyte provided between the fuel electrode and the oxidant gas electrode. The fuel electrode is made of a composite material containing nickel, and the solid oxide fuel cell is placed in a non-oxygen atmosphere until the temperature of the fuel electrode decreases to 350 ° C. after power generation is stopped. By maintaining, the shrinkage due to oxidation of the fuel electrode is prevented.

  In the present invention configured as described above, in the solid oxide fuel cell stop process, in the low temperature range up to 350 ° C., which was not conventionally thought to oxidize the fuel electrode, from the composite material containing nickel The constructed fuel electrode is maintained in a non-oxygen atmosphere. As a result, shrinkage due to oxidation of the fuel electrode in such a low temperature region is suppressed. Therefore, the present invention can suppress the occurrence of damage to the fuel cell unit due to the oxidative expansion and contraction of the fuel electrode rather than the oxidative expansion of the fuel electrode.

  In the present invention, it is preferable that the fuel cell unit has a fuel gas channel through which the fuel gas containing hydrogen flows, and the fuel cell unit has the fuel electrode in order from the fuel gas channel side. The solid electrolyte and the oxidant gas electrode are stacked, and the solid oxide fuel cell has a fuel electrode temperature of 350 ° C. or higher and 400 ° C. or lower after power generation is stopped. By maintaining the entire surface on the fuel gas flow path side of the fuel electrode constituting the power generation stack portion in a non-oxygen atmosphere, the portion of the fuel electrode due to partial oxidation of the fuel electrode constituting the power generation stack portion Prevent general shrinkage.

  In the low temperature range of 350 ° C. or higher and 400 ° C. or lower, the fuel electrode contracts due to oxidation. Since the contraction rate due to oxidation of the fuel electrode is smaller than the expansion rate due to oxidation of the fuel electrode in a higher temperature region, the stress due to oxidation contraction of the fuel electrode is generally higher than the stress due to oxidation expansion of the fuel electrode in a higher temperature region. Is also small. However, when only a part of the fuel electrode is oxidized in such a low temperature region, only that part contracts, and stress concentrates on the boundary between the oxidized part and the non-oxidized part. As a result, the fuel cell unit is more likely to be damaged near the boundary between the oxidized portion and the non-oxidized portion. In particular, in the fuel cell unit, when stress is concentrated on a part of the power generation stack portion in which the fuel electrode, the solid electrolyte, and the oxidant gas electrode are stacked, the oxidant gas electrode tends to peel off.

  Therefore, in the present invention, when the temperature of the fuel electrode is 350 ° C. or more and 400 ° C. or less, the entire surface on the fuel gas flow path side of the fuel electrode constituting the power generation stack is maintained in a non-oxygen atmosphere, thereby generating the power generation stack It is preferable to prevent partial contraction of the fuel electrode due to partial oxidation of the fuel electrode constituting the fuel cell. As a result, the occurrence of damage to the fuel cell unit due to the peeling of the oxidant gas electrode in the power generation unit is suppressed.

  In the present invention, it is preferable that the fuel gas flow path has an outflow side open end that communicates with the outside of the fuel cell unit, and the fuel cell unit flows along the fuel gas flow path. A buffer portion is provided between the side opening end and the power generation laminate portion, and the buffer portion has an outflow side flow path resistance portion.

  By appropriately setting the flow path resistance of the outflow side flow path resistance section such as a narrow tube, the pressure in the fuel gas flow path in the fuel cell unit for a while after power generation is stopped It can be kept higher than the external pressure. While the pressure in the fuel gas flow path is maintained, the risk that the oxidant gas outside the fuel cell unit will flow backward from the outflow side opening end into the fuel gas flow path and the fuel electrode is oxidized is reduced. .

  However, the risk of the anode being oxidized is sufficiently reduced, but there is a concern that the pressure in the fuel gas flow path cannot be maintained if an unexpected disturbance occurs, such as a change in pressure outside the design range. is there. In particular, in a low temperature region where the oxidative shrinkage of the fuel electrode occurs, the pressure in the fuel gas flow path is also low, so that there is a high possibility that an oxidant gas backflow will occur.

  Therefore, it is preferable to provide a buffer portion having an outflow side flow path resistance portion between the outflow side opening end and the power generation stacking portion. By appropriately setting the outflow side flow path resistance part and the buffer part, pressure fluctuation can be allowed and attenuated. As a result, even when the oxidant gas flows backward from the outflow side opening end, if the oxidant gas stays up to the buffer part, the fuel electrode of the power generation stacking part is avoided from being oxidized. Therefore, by providing the buffer part and the outflow side flow path resistance part, the fuel electrode of the power generation stacking part is suppressed from being partially oxidized.

  In the present invention, preferably, the solid oxide fuel cell supplies air to the fuel gas flow path after the temperature of the fuel electrode is lowered to a predetermined temperature of 300 ° C. or less after power generation is stopped. To discharge the residual gas in the fuel gas flow path.

  According to the present invention configured as above, after the fuel electrode is lowered to a predetermined temperature of 300 ° C. or less where the risk of oxidative shrinkage is low, if the residual gas in the fuel gas flow path is discharged, Only a part of the fuel electrode of the power generation stack can be prevented from being oxidized. Moreover, if air is supplied as the oxidant gas, the fuel gas flow path can be purged at once with simple equipment.

  The solid oxide fuel cell includes a fuel cell module including the fuel cell unit, a fuel supply device that supplies fuel to the fuel cell module, and water for steam reforming to the fuel cell module. A water supply device, an oxidant gas supply device that supplies an oxidant gas to an oxidant gas electrode of the fuel cell unit, and a fuel that is disposed in the fuel cell module and is supplied from the fuel supply device. A reformer for generating hydrogen by steam reforming using water supplied from a water supply device, the reformer from the fuel supply device, and the fuel gas flow path of the fuel cell unit. A fuel / exhaust gas passage for guiding fuel / exhaust gas to the outside of the fuel cell module; the fuel supply device; the water supply device; the oxidant gas supply device; and the fuel cell module. And a controller for controlling the extraction of electric power from the fuel module. The controller includes a shutdown stop circuit for stopping fuel supply and power generation, and the fuel / exhaust gas passage is supplied with fuel and generated by the shutdown stop circuit. Until the temperature of the fuel electrode drops to 400 ° C., the pressure in the fuel gas channel of the fuel cell unit is set to be higher than the pressure outside the fuel cell unit in the fuel cell module. The shutdown circuit is configured to function as a mechanical pressure maintaining unit that maintains high, and the shutdown stop circuit is generated by a temperature decrease of the fuel electrode until the temperature of the fuel electrode decreases to 400 ° C. and then reaches 350 ° C. Execute pressure holding control to increase the pressure in the fuel gas flow path so as to suppress the pressure drop in the fuel gas flow path A pressure holding control circuit that.

  According to the present invention configured as described above, the fuel electrode can be provided after the shutdown stop by appropriately distributing the balance of the flow resistance and the like of each part of the fuel / exhaust gas passage functioning as the mechanical pressure holding means. It has succeeded in maintaining the pressure in the fuel gas flow path of the fuel cell unit higher than the pressure outside the fuel cell unit until the temperature drops to 400 ° C. As a result, the backflow of the oxidant gas from the outflow side opening end into the fuel gas flow path can be prevented. This mechanical pressure holding means can sufficiently reduce the risk of oxidation of the anode, but in the event of an unexpected disturbance such as a change in pressure outside the design value, depending on this mechanical means alone, There is concern that the pressure on the fuel electrode side cannot be maintained. In particular, in a low temperature range of 350 ° C. to 400 ° C. at which the fuel electrode undergoes oxidative shrinkage, the pressure in the fuel gas flow path is also low, and the risk of oxidant gas backflow increases.

  Therefore, the shutdown stop circuit executes pressure holding control for increasing the pressure in the fuel gas flow path until the temperature of the fuel electrode decreases to 400 ° C. and then reaches 350 degrees. Since the pressure holding control is executed after the temperature of the fuel electrode is lowered to 400 ° C., the pressure inside and outside the fuel cell unit is greatly reduced, and the pressure on the fuel electrode side only needs to be compensated slightly. By performing the pressure holding control in the temperature region where the temperature of the fuel electrode is 350 ° C. to 400 ° C., it is possible to prevent the fuel electrode of the power generation stacked portion from being partially oxidized in this temperature region.

  In the present invention, preferably, the pressure holding control circuit is configured such that when the temperature of the fuel electrode is within a temperature range of 20 ° C. before and after 380 ° C., the pressure in the fuel gas flow path is The pressure holding control for increasing the pressure in the fuel gas flow path is executed so that the pressure is maintained at a pressure equal to or higher than the external pressure.

  As shown in FIG. 27, the composite material containing nickel shows the largest shrinkage at 380 ° C. Therefore, in the temperature range of about 20 ° C. around 380 ° C., it is possible to prevent the fuel cell unit from being damaged by preventing the fuel electrode of the power generation stacking portion from being oxidized even by one minute. .

  In the present invention, preferably, the fuel / exhaust gas passage is disposed in the fuel / exhaust gas passage until the temperature of the fuel electrode decreases to 400 ° C. after water supply, fuel supply, and power generation are stopped by the shutdown stop circuit. The pressure holding control circuit is configured to function as a mechanical pressure holding means for maintaining the pressure in the fuel gas flow path of the battery unit higher than the pressure outside the fuel cell unit in the fuel cell module. Then, after the temperature of the fuel electrode is lowered to 400 ° C., the water supply device is operated to evaporate water in the reformer to generate water vapor. By suppressing the pressure drop in the fuel gas channel, the flow of the oxidant gas into the fuel gas channel is suppressed, and the controller When the water supply by the holding control circuit is finished and the temperature of the fuel electrode is lowered to a predetermined temperature of 300 ° C. or less, the fuel remaining in the fuel gas flow path of the fuel cell unit is discharged. In order to do so, air is supplied to the fuel gas flow path.

  In the present invention configured as described above, after the shutdown is stopped, the supply of water is stopped until the temperature of the fuel electrode is lowered to 400 ° C., so even after the temperature of the fuel electrode is lowered to 400 ° C. The reformer temperature is maintained at a relatively high temperature. For this reason, even after the pressure holding by the mechanical pressure holding means is completed, water can be evaporated in the reformer to suppress the pressure drop on the fuel electrode side, and the oxidation of the fuel electrode can be prevented. .

  Preferably, in the present invention, the shutdown stop circuit executes a stop in a program stop mode in which fuel supply and power generation are stopped at a scheduled time, and the program stop mode is immediately before the fuel supply and power generation is stopped. A first temperature drop step for reducing the temperature outside the fuel cell unit in the fuel cell module, and the temperature outside the fuel cell unit in the fuel cell module immediately after stopping the fuel supply and power generation. A second temperature lowering step for lowering the temperature, and after the temperature of the fuel electrode is lowered to 400 ° C., by operating the water supply device, water is evaporated in the reformer to generate water vapor, By suppressing the pressure drop in the fuel gas channel of the fuel cell unit by the pressure of water vapor, When the supply of water by the pressure holding control circuit is finished and the temperature of the fuel electrode has dropped to a predetermined temperature of 300 ° C. or less, the step of suppressing the inflow of the agent gas Supplying air to the fuel gas flow path in order to discharge the fuel remaining in the fuel gas flow path.

  In the present invention configured as described above, the mechanical pressure is maintained by performing the temperature drop control by the first temperature drop process immediately before the stop of the fuel supply and power generation and the second temperature drop process immediately after the stop. The temperature and pressure inside and outside the fuel cell unit at the time of start can be lowered, further reducing the risk of oxidant gas backflow until the temperature of the anode decreases to 400 ° C. be able to.

  According to the solid oxide fuel cell of the present invention, in the stopping process of the solid oxide fuel cell, the fuel electrode is oxidatively expanded even in a low temperature region, which has not been conventionally considered to oxidize the fuel electrode. Instead, it is possible to solve the new technical problem of oxidative shrinkage, which leads to damage of the fuel cell unit. That is, according to the solid oxide fuel cell of the present invention, it is possible to suppress the occurrence of damage to the fuel cell unit due to the oxidation contraction of the fuel electrode.

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. 1 is a perspective view of a reformer of a fuel cell device according to an embodiment of the present invention. FIG. 3 is a perspective view showing the inside of the reformer with the top plate of the reformer of the fuel cell device according to an embodiment of the present invention removed. It is a top sectional view showing a flow of fuel inside a reformer of a fuel cell device by one embodiment of the present invention. It is a perspective view which shows the metal case and the air heat exchanger which were accommodated in the housing of the fuel cell apparatus by one Embodiment of this invention. It is sectional drawing which shows the positional relationship of the heat insulating material for heat exchangers of the fuel cell apparatus by one Embodiment of this invention, and an evaporation part. It is a time chart which shows an example of each supply_amount | feed_rate of fuel etc. in the starting process of the fuel cell apparatus by one Embodiment of this invention, and the temperature of each part. 5 is a flowchart of stop determination for selecting a stop mode in the fuel cell device according to the embodiment of the present invention. 4 is a time chart schematically showing an example of stop behavior when stop mode 1 is executed in the fuel cell device according to the embodiment of the present invention. In the fuel cell device according to the embodiment of the present invention, the control when the stop mode 1 is executed, the temperature and pressure in the fuel cell module, and the state of the tip of the fuel cell unit are described in time series. FIG. 6 is a time chart schematically showing an example of stop behavior when stop mode 2 is executed in the fuel cell device according to the embodiment of the present invention. In the fuel cell device according to the embodiment of the present invention, the control when the stop mode 2 is executed, the temperature and pressure in the fuel cell module, and the state of the tip of the fuel cell unit are described in time series. FIG. 4 is a time chart schematically showing an example of a stop behavior when a stop mode 3 is executed in a fuel cell device according to an embodiment of the present invention. 6 is an enlarged time chart showing immediately after shutdown stop in the stop mode 3 of the fuel cell device according to the embodiment of the present invention. In the fuel cell device according to the embodiment of the present invention, the control when the stop mode 3 is executed, the temperature and pressure in the fuel cell module, and the state of the tip of the fuel cell unit are described in time series. FIG. It is a flowchart of the water supply in a stop pretreatment. 10 is a time chart showing a modified example of stop mode 3. 6 is a time chart schematically showing an example of a stop behavior when stop mode 4 is executed in the fuel cell device according to the embodiment of the present invention. In the fuel cell device according to the embodiment of the present invention, the control when the stop mode 4 is executed, the temperature and pressure in the fuel cell module, and the state of the tip of the fuel cell unit are described in time series. FIG. 9 is a flowchart of stop determination for selecting a stop mode in a modification of the fuel cell device according to the embodiment of the present invention. It is the time chart which represented an example of the stop behavior of the conventional solid oxide fuel cell typically in time series. It is a graph explaining that the nickel containing composite material which comprises a fuel electrode shrinks by oxidation in a predetermined temperature range. It is a graph explaining in more detail that the nickel containing composite material which comprises a fuel electrode shrink | contracts by the oxidation in a predetermined temperature range.

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

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

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

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

Next, the internal structure of 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, the case 8 in the housing 6 of the fuel cell module 2 has a fuel cell assembly 12, a reformer 20, and an air heat exchanger in order from the bottom as described above. 22 is arranged.

The reformer 20 is provided with a reformer introduction pipe 62 for introducing pure water, fuel gas to be reformed, and reforming air on the end side surface on the upstream end side.
The reformer introduction pipe 62 is a circular pipe extending from the side wall surface at one end of the reformer 20, is bent by 90 ° and extends in a substantially vertical direction, and penetrates the upper end surface of the case 8. The reformer introduction pipe 62 functions as a water introduction pipe for introducing water into the reformer 20. Further, a T-shaped tube 62a is connected to the upper end of the reformer introduction tube 62, and fuel gas and pure water are supplied to both ends of the T-shaped tube 62a extending in a substantially horizontal direction. Pipes for connecting are connected to each other. The water supply pipe 63a extends obliquely upward from one side end of the T-shaped pipe 62a. The fuel gas supply pipe 63b extends in the horizontal direction from the other side end of the T-shaped pipe 62a, then bends in a U shape, and extends substantially horizontally in the same direction as the water supply pipe 63a.

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

  A fuel gas supply pipe 64 is connected to the downstream end side of the reformer 20, and the fuel gas supply pipe 64 extends downward and further in an manifold 66 formed below the fuel cell assembly 12. It extends horizontally. A plurality of fuel supply holes 64 b are formed in the lower surface of the horizontal portion 64 a of the fuel gas supply pipe 64, and the reformed fuel gas is supplied into the manifold 66 from the fuel supply holes 64 b. Further, in the middle of the vertical portion of the fuel gas supply pipe 64, a pressure fluctuation suppressing flow path resistance portion 64c having a narrow flow path is provided, and the flow path resistance of the fuel gas supply flow path is adjusted. The adjustment of the channel resistance will be described later.

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

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

Next, the fuel cell unit 16 will be described with reference to FIG. FIG. 4 is a partial 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 that are caps respectively connected to both ends of the fuel cell 84.
The fuel cell 84 is a tubular structure extending in the vertical direction, and includes a cylindrical inner electrode layer 90 that forms a fuel gas flow path 88 therein, a cylindrical outer electrode layer 92, an inner electrode layer 90, and an outer side. An electrolyte layer 94 is provided between the electrode layer 92 and the electrode layer 92. The inner electrode layer 90 is a fuel electrode through which fuel gas passes and becomes a (−) electrode, while the outer electrode layer 92 is an air electrode (oxidant gas electrode) in contact with air and a (+) electrode. It has become.

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

  The fuel gas passage narrow tube 98 is an elongated thin tube provided so as to extend in the axial direction of the fuel cell 84 from the center of the inner electrode terminal 86. For this reason, a predetermined pressure loss occurs in the flow of the fuel gas flowing from the manifold 66 (FIG. 2) into the fuel gas passage 88 through the fuel gas passage narrow tube 98 of the lower inner electrode terminal 86. . Accordingly, the fuel gas flow passage narrow tube 98 of the lower inner electrode terminal 86 acts as an inflow side flow passage resistance portion, and the flow passage resistance is set to a predetermined value. Further, a predetermined pressure loss also occurs in the flow of the fuel gas flowing out from the fuel gas flow path 88 to the combustion chamber 18 (FIG. 2) through the fuel gas flow path narrow tube 98 of the upper inner electrode terminal 86. Therefore, the fuel gas flow passage narrow tube 98 of the upper inner electrode terminal 86 acts as an outflow side flow passage resistance portion, and the flow passage resistance is set to a predetermined value. The upper fuel gas channel narrow tube 98 communicates with the outside of the fuel cell unit 16 at the outflow side opening end 98a.

  Further, in the fuel cell 84, a portion where the fuel electrode 90, the reaction preventing layer 95, the solid electrolyte 94, and the air electrode (oxidant gas electrode) 92 are stacked in this order from the fuel gas flow path side constitutes the power generation stacking portion 16c. ing. A buffer portion 16b is provided along the fuel gas flow path 88 between the power generation stacking portion 16c and the outflow side opening end 98a.

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

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

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

Next, the fuel cell stack 14 will be described with reference to FIG. FIG. 5 is a perspective view showing a fuel cell stack of a solid oxide fuel cell (SOFC) according to an embodiment of the present invention.
As shown in FIG. 5, the fuel cell stack 14 includes 16 fuel cell units 16, and these fuel cell units 16 are arranged in two rows of 8 each. Each fuel cell unit 16 is supported at its lower end by a rectangular lower support plate 68 (FIG. 2) made of ceramic. It is supported by the upper support plate 100. The lower support plate 68 and the upper support plate 100 are formed with through holes through which the inner electrode terminal 86 can pass.

  Furthermore, a current collector 102 and an external terminal 104 are attached to the fuel cell unit 16. The current collector 102 includes a fuel electrode connection portion 102a that is electrically connected to an inner electrode terminal 86 attached to the inner electrode layer 90 that is a fuel electrode, and an outer peripheral surface of the outer electrode layer 92 that is an air electrode. It is integrally formed so as to connect the air electrode connecting portion 102b that is electrically connected. In addition, a silver thin film is formed on the entire outer surface of the outer electrode layer 92 (air electrode) of each fuel cell unit 16 as an electrode on the air electrode side. When the air electrode connecting portion 102b contacts the surface of the thin film, the current collector 102 is electrically connected to the entire air electrode.

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

Next, sensors and the like attached to the solid oxide fuel cell (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.
In addition, the control unit 110 incorporates a microprocessor, a memory, and a program (not shown) for operating these components, and thereby, based on input signals from the respective sensors, the auxiliary unit 4, The inverter 54 and the like are controlled. The notification device 116 may be connected to a remote management center and notify the management center of an abnormal state.

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

The power state detection sensor 126 is for detecting the 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 detailed configuration of the reformer 20 will be described with reference to FIGS.
FIG. 7 is a perspective view of the reformer 20, and FIG. 8 is a perspective view showing the inside of the reformer 20 with the top plate removed. FIG. 9 is a plan sectional view showing the flow of fuel inside the reformer 20.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

  The air injected into the power generation chamber 10 comes into contact with the outer surface of each fuel cell unit 16 on the air electrode side (oxidant gas electrode side) of the fuel cell stack 14, and a part of oxygen in the air is in contact with it. Used for power generation. Moreover, the air injected to the lower part of the power generation chamber 10 through the blower outlet 77a rises in the power generation chamber 10 while being used for power generation. The air rising in the power generation chamber 10 burns the fuel flowing out from the upper end of each fuel cell unit 16. The combustion heat generated by this combustion heats the evaporation section 20a, the mixing section 20b, and the reforming section 20c of the reformer 20 disposed above the fuel cell stack 14. The combustion gas generated by burning the fuel heats the upper reformer 20 and then flows into the upper side of the rectifying plate 21 through the opening 21 a above the reformer 20. The combustion gas that has flowed into the upper side of the rectifying plate 21 is guided to the communication opening 8 a that is the inlet of the air heat exchanger 22 through the exhaust passage 21 b formed by the rectifying plate 21. The combustion gas that has flowed into the air heat exchanger 22 from the communication opening 8 a flows into the open end of each combustion gas pipe 70 and flows through the power generation air flow path 72 outside each combustion gas pipe 70. Are exchanged with each other and collected in an exhaust gas collecting chamber 78. The exhaust gas collected in the exhaust gas collection chamber 78 is discharged to the outside of the fuel cell module 2 through the exhaust gas discharge pipe 82. As a result, the evaporation of water in the evaporation unit 20a and the steam reforming reaction, which is an endothermic reaction in the reforming unit 20c, are promoted, and the power generation air in the air heat exchanger 22 is preheated.

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

In the starting process shown in FIG. 12, the temperature of the fuel cell stack 14 at room temperature is raised to a temperature at which power generation is possible.
First, at time t0 in FIG. 12, the supply of power generation air and reforming air is started. Specifically, the control unit 110 that is a controller sends a signal to the power generation air flow rate adjustment unit 45 that is a power generation oxidant gas supply device to operate it. As described above, the power generation air is introduced into the fuel cell module 2 through the power generation air introduction pipe 74 and flows into the power generation chamber 10 through the air heat exchanger 22 and the power generation air supply path 77. . In addition, the control unit 110 sends a signal to the reforming air flow rate adjustment unit 44 which is a reforming oxidant gas supply device to operate it. The reforming air introduced into the fuel cell module 2 flows into the interior of each fuel cell unit 16 through the reformer 20 and the manifold 66, and flows out from the upper end thereof. Note that at time t0, no reforming reaction occurs in the reformer 20 because fuel has not yet been supplied. In this embodiment, the supply amount of power generation air started at time t0 in FIG. 12 is about 100 L / min, and the supply amount of reforming air is about 10.0 L / min.

  Next, fuel supply is started at time t1 after a predetermined time from time t0 in FIG. Specifically, the control unit 110 sends a signal to the fuel flow rate adjustment unit 38 which is a fuel supply device to operate it. In the present embodiment, the fuel supply amount started at time t1 is about 5.0 L / min. The fuel introduced into the fuel cell module 2 flows into the interior of each fuel cell unit 16 through the reformer 20 and the manifold 66, and flows out from the upper end thereof. At time t1, the reformer reaction is not generated in the reformer 20 because the temperature of the reformer is still low.

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

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

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

  As described above, the temperature of the evaporation unit 20a rapidly increases, so that water vapor can be generated in a short time after the start of off-gas combustion. In addition, since the reforming water is supplied to the evaporation unit 20a little by little, it is possible to heat the water to the boiling point with a slight amount of heat compared to the case where a large amount of water is stored in the evaporation unit 20a. The supply of water vapor can be started immediately. Furthermore, since water flows in immediately after the start of the operation of the water flow rate adjustment unit 28, it is possible to avoid an excessive increase in temperature of the evaporation unit 20a and a delay in supply of water vapor due to a delay in supply of water.

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

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

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

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

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

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

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

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

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

  Further, after executing the SR2 process for a predetermined time, the process proceeds to the power generation process. In the power generation process, power is extracted from the fuel cell stack 14 to the inverter 54 (FIG. 6), and power generation is started. In the power generation process, the reforming unit 20b reforms the fuel exclusively by steam reforming. Further, in the power generation process, the fuel supply amount, the power generation air supply amount, and the water supply amount are changed corresponding to the output power required for the fuel cell module 2.

Next, stop of the solid oxide fuel cell 1 according to the embodiment of the present invention will be described with reference to FIGS.
First, with reference to FIG. 26, the behavior at the time of shutdown stop in the conventional solid oxide fuel cell will be described. FIG. 26 is a time chart schematically showing an example of stop behavior of a conventional solid oxide fuel cell in time series.

  First, at time t501 in FIG. 26, the shutdown stop operation of the fuel cell that is in the power generation operation is performed. As a result, without waiting for the temperature in the fuel cell module to drop, the fuel supply amount, the water supply amount for reforming, and the air supply amount for power generation are reduced to zero and removed from the fuel cell module in a short time. The generated current (generated current) is also made zero. That is, the supply of fuel, water, and power generation air to the fuel cell module is stopped in a short time, and the extraction of electric power from the fuel cell module is stopped. In addition, even when the supply of fuel and electricity to the solid oxide fuel cell is lost due to a disaster or the like, the stop behavior is the same as in FIG. In addition, the graph of each supply amount in FIG. 26, an electric current, and a voltage shows only a change tendency, and does not represent a specific value.

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

  If the air continues to be supplied into the fuel cell module after time t501, the pressure in the fuel cell module rises due to the air that has been sent. On the other hand, since the fuel supply has already been stopped, the pressure inside the fuel cell unit begins to drop. For this reason, it is considered that the air sent into the power generation chamber of the fuel cell module flows backward from the upper end to the fuel electrode inside the fuel cell unit. At time t501, since the fuel cell stack is in a high temperature state, when the air flows backward to the fuel electrode side, the fuel electrode is oxidized and the fuel cell unit is damaged. In order to avoid this, in the conventional fuel cell, as shown in FIG. 26, immediately after the fuel supply is stopped by the shutdown stop, the power generation air is also promptly supplied even if the power source is not lost. It was stopped.

  Furthermore, after about 6 to 7 hours have passed after the shutdown, the temperature in the fuel cell module has dropped below the lower oxidation limit temperature (about 250 ° C. to 300 ° C.) of the fuel electrode, and then air is again introduced into the fuel cell module. Supply is also performed (not shown). Such air supply is performed for the purpose of discharging the staying fuel gas. However, in the state where the temperature of the fuel cell stack is lower than the oxidation lower limit temperature of the fuel electrode, the fuel is temporarily supplied. Even if air flows back to the pole, the fuel pole is not oxidized.

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

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

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

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

  The gas components present on the fuel electrode side and the air electrode side of the fuel cell unit can be estimated based on the output voltage of the cell stack when no current is taken out (output current = 0). As shown by the thick broken line in FIG. 26, immediately after the shutdown stop at time t501, the output voltage of the cell stack rapidly increases (A part in FIG. 26). This is because immediately after the shutdown is stopped, a lot of hydrogen is present on the fuel electrode side, air is present on the air electrode side, and the current extracted from the cell stack is set to zero. Next, the output voltage of the cell stack rapidly decreases (part B in FIG. 26). This is because the hydrogen that was present on the fuel electrode side of each fuel cell unit flows out after the shutdown is stopped and the fuel electrode side. It is estimated that this is because the concentration of hydrogen decreases and the concentration of air on the air electrode side decreases due to the outflowing hydrogen.

  Next, the output voltage of the cell stack decreases with time, and when the temperature in the fuel cell module decreases below the lower oxidation limit temperature (about 250 ° C. to 300 ° C.) (C portion in FIG. 26), the output voltage is It has greatly decreased. In this state, it is presumed that almost no hydrogen remains on the fuel electrode side of each fuel cell unit, and in the conventional fuel cell, the fuel electrode is exposed to the risk of oxidation. Actually, in the conventional fuel cell, in many cases, a phenomenon occurs in which the pressure on the fuel electrode side becomes lower than the pressure on the air electrode side before the temperature in the fuel cell module falls below the lower oxidation limit temperature. However, it is considered that the fuel cell unit has an adverse effect.

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

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

  In the solid oxide fuel cell 1 according to the embodiment of the present invention, the flow resistance of each part in the fuel cell module is set to an appropriate value, and the shutdown stop circuit 110a built in the control unit 110 (FIG. 6). By controlling this, the risk of oxidation of the fuel electrode is greatly suppressed.

Next, stop of the solid oxide fuel cell 1 according to the embodiment of the present invention will be described with reference to FIGS. 13 to 25.
FIG. 13 is a flowchart of stop determination for selecting a stop mode in the solid oxide fuel cell 1 according to the embodiment of the present invention. The flowchart of FIG. 13 is a flowchart for determining which stop mode to select based on a predetermined condition, and is repeatedly executed at predetermined time intervals during operation of the solid oxide fuel cell 1. The

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

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

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

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

  Note that when the supply of electric power is stopped and the supply of fuel gas is continued, no stop mode is selected according to the flowchart of FIG. In such a case, the solid oxide fuel cell 1 according to the present embodiment can continue power generation by operating the auxiliary unit 4 with the electric power generated by the fuel cell stack 14. Note that the present invention can also be configured so that power generation is stopped when the supply of power continues for a predetermined long time.

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

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

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

  Thus, in the present embodiment, the fuel // exhaust gas that leads the fuel and / or exhaust gas from the fuel flow rate adjustment unit 38 to the outside of the fuel cell module 2 through the reformer 20 and the fuel electrode of each fuel cell unit 16. The exhaust gas passage is tuned as described above. For this reason, even when left undisturbed after shutdown, the pressure on the fuel electrode side decreases while maintaining a pressure higher than the pressure on the air electrode side, and the temperature of the fuel electrode decreases to 350 ° C. to 400 ° C. Even at this point, the pressure higher than the atmospheric pressure is maintained, and the risk that the fuel electrode is oxidized can be sufficiently suppressed. As shown in FIG. 14, in the solid oxide fuel cell 1 of the present embodiment, after the shutdown stop is performed at time t101, the output voltage of the fuel cell stack 14 shown by the thick broken line once increases greatly, The drop is less than that of the conventional solid oxide fuel cell (FIG. 26), and a relatively high voltage continues for a long time. In the example shown in FIG. 14, a relatively high voltage is maintained until time t102 when the temperature on the fuel electrode side and the air electrode side decreases to 400 ° C. after shutdown. This indicates that fuel remains on the fuel electrode side of each fuel cell unit 16 until time t102 when the temperature drops to 400 ° C.

  Note that when the fuel electrode is oxidized in a temperature range of 400 ° C. to 350 ° C. (particularly, a range of 20 ° C. before and after 380 ° C.), the fuel electrode contracts. Conventionally, this temperature range is a temperature at which the risk of oxidation of the fuel electrode is sufficiently reduced, but here, by preventing oxidation of the fuel electrode in this temperature range, it is due to oxidation contraction of the fuel electrode. Prevents damage to the fuel cell unit. In particular, when the temperature of the fuel electrode is 350 ° C. or more and 400 ° C. or less, the fuel constituting the power generation stack is maintained by maintaining the entire surface on the fuel gas flow path side of the fuel electrode constituting the power generation stack in a non-oxygen atmosphere. Prevent partial contraction of the fuel electrode due to partial oxidation of the electrode.

  In other words, in the solid oxide fuel cell 1 of the present embodiment, the fuel / exhaust gas passage is air in the fuel cell module 2 until the temperature of the fuel electrode decreases to 350 ° C. to 400 ° C. after shutdown stop. The pressure on the electrode side is maintained higher than the atmospheric pressure, and the pressure on the fuel electrode side is maintained higher than the pressure on the air electrode side. Therefore, the fuel / exhaust gas passage functions as a mechanical pressure holding means for extending the time until the pressure on the fuel electrode side approaches the pressure on the air electrode side.

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

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

  As shown in the lower part (3) of FIG. 15, the pressure inside the fuel cell unit 16 (fuel electrode side) is higher than the outside (air electrode side) even after the flame is extinguished after the shutdown is stopped. The ejection of the fuel gas from the fuel gas flow path narrow tube 98 is continued. Further, as shown in the upper part of FIG. 15, immediately after the shutdown is stopped, the pressure on the fuel electrode side is higher than the pressure on the air electrode side, and each pressure decreases while maintaining this relationship. The pressure difference between the fuel electrode side and the air electrode side decreases with the ejection of the fuel gas after the shutdown stop.

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

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

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

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

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

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

  In this way, the pressure drop on the fuel electrode side of each fuel cell unit 16 is suppressed for a long time after shutdown by the mechanical pressure holding means. About 5 to 6 hours have passed after the shutdown, and when the temperature in the fuel cell module 2 decreases to 400 ° C., both the fuel electrode side and the air electrode side of each fuel cell unit 16 decrease to almost atmospheric pressure. Then, the air on the air electrode side begins to diffuse toward the fuel electrode side (lower stage (6) (7) in FIG. 15). However, the portion where the outer electrode layer 92 at the upper end portion of the fuel gas passage narrow tube 98 and the fuel cell 84 is not formed (A portion in the lower stage (6) in FIG. 15) is oxidized even if air enters. No, this part functions as a buffer part. In particular, since the fuel gas passage narrow tube 98 is configured to be elongated, the buffer portion becomes long, and even when air enters from the upper end of the fuel cell unit 16, the fuel electrode is hardly oxidized. Also, in the vicinity of 400 ° C., the temperature of the fuel electrode is low, and even when the fuel electrode is in contact with air, the oxidation that occurs is slight, and the frequency at which the stop mode 1 is executed is extremely low. The adverse effects that occur can be virtually ignored. Further, as shown in the lower part (8) of FIG. 15, after the temperature of the fuel electrode falls below the oxidation lower limit temperature (about 250 ° C. to 300 ° C.), air flows to the fuel electrode side of each fuel cell unit 16. The fuel electrode is not oxidized even if it is full.

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

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

  In the stop by the stop mode 2, after the shutdown is stopped, air is sent to the air electrode side of the fuel cell unit 16 by temperature drop control. Thereby, in the A part of FIG. 16, the temperature by the side of the air electrode has fallen more rapidly than the case of the stop mode 1 (FIG. 14). As described above, after the fuel supply is completely stopped, there is a risk of oxidizing and damaging the fuel electrode until the temperature of the fuel cell stack 14 is lowered to 400 ° C. Therefore, the air supply must be stopped. It had been. However, the present inventors have found that power generation air can be safely supplied to the air electrode side for a predetermined time even immediately after the fuel supply is stopped.

  That is, immediately after the shutdown is stopped, a sufficient amount of fuel gas remains on the fuel electrode side of each fuel cell unit 16, and this is in a state of being ejected from the upper end of each fuel cell unit 16. By sending air to the side, air does not flow backward to the fuel electrode side. That is, in this state, the pressure on the air electrode side rises by sending air by temperature drop control, but the pressure on the fuel electrode side is still higher than the pressure on the air electrode side. The fuel gas channel narrow tube 98 provided at the upper end of each fuel cell unit 16 is a throttle channel having a narrow channel cross-sectional area, which allows the fuel gas flowing out from each fuel cell unit 16 to flow. The flow rate increases. Accordingly, the fuel gas flow path narrow tube 98 provided at the upper end functions as an accelerating unit that increases the flow rate of the fuel gas. Further, after the supply of air is stopped at time t202, it is left as it is in the same manner as in stop mode 1, and the state where the pressure on the fuel electrode side is higher than the pressure on the air electrode side is maintained for a predetermined period by the mechanical pressure holding means. Is done. However, in the stop mode 2, since the high-temperature air and combustion gas staying in the fuel cell module 2 are discharged by the temperature drop control, the natural leaving is started from a temperature lower than that in the stop mode 1. For this reason, the risk of air backflow occurring before the temperature of the fuel electrode decreases to 350 ° C. is reduced. Thus, after the shutdown is stopped, the pressure drop on the fuel electrode side becomes more gradual than the pressure drop on the air electrode side. Moreover, since the temperature in the fuel cell module 2 is made uniform by the temperature drop control, the risk that the fuel gas inside the fuel cell unit 16 contracts rapidly and air is drawn into the fuel electrode side is reduced.

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

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

  First, the power generation operation is performed before the shutdown stop in the middle stage of FIG. 17, and the temperature drop control is executed after the shutdown stop. After the temperature drop control for about 2 minutes, the power generation air flow rate adjustment unit 45 is stopped, and then left as it is in the stop mode 1 in the same manner. However, in the stop mode 2, the temperature in the fuel cell module 2 and the pressure on the fuel electrode side and the air electrode side at the time when the natural standing is started (time t202 in FIG. 16) are lower than in the stop mode 1. Has been. For this reason, before the temperature of the fuel electrode falls to 350 ° C., the risk of air entering the fuel electrode side is further reduced.

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

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

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

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

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

  In the example shown in FIG. 19, after the shutdown stop at time t303, the supply of power generation air (however, the power generation is completely stopped) is continued as the second temperature drop process of the temperature drop control. As a result, the air in the fuel cell module 2 (air electrode side of the fuel cell stack 14), the remaining fuel combustion gas, and the fuel flowing out from the fuel electrode side of the fuel cell stack 14 after shutdown is discharged. The second temperature drop process functions as an exhaust process. In the present embodiment, after the fuel supply is completely stopped at time t303, a large amount of power generation air is continuously supplied for a predetermined period until time t304. In addition, the air supply amount for power generation is increased to the maximum air supply amount during the stop pretreatment, and then maintained at the maximum value.

  As shown in FIG. 18, after the supply of power generation air is stopped at time t <b> 304, it is left as it is in the stop mode 1. However, in the stop mode 3, the first temperature drop process is executed before the shutdown stop, and the second temperature drop process is executed after the shutdown stop. Natural standing is started from a state of larger than 2, lower temperature and lower pressure.

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

  First, the power generation operation is performed before the stop switch operation in the middle stage of FIG. 20, and after the stop switch operation, the pre-stop process step that is the first temperature drop step is executed. In the pre-stop treatment process, the amount of fuel gas supplied is reduced, so that the flame at the upper end of each fuel cell unit 16 that was large during the power generation operation, as shown in the lower part (1) of FIG. ) Becomes smaller. Thus, since the supply amount of fuel gas and the power generation amount are reduced, the temperature in the fuel cell module 2 is lowered than during the power generation operation. A shutdown stop is performed after the stop pre-treatment process for about 2 minutes. After the shutdown is stopped, power generation air is supplied for 2 minutes by the power generation air flow rate adjustment unit 45 as the second temperature drop step. After the second temperature lowering step, the power generation air flow rate adjustment unit 45 is stopped, and then left naturally as in the stop mode 1.

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

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

  Here, in the stop mode 3, the temperature in the fuel cell module 2 and the pressure on the fuel electrode side and the air electrode side at the time when the natural standing is started after the exhaust process is finished (time t304 in FIG. 18) It is lower than the cases of 1 and 2. In stop mode 3, the supply amount of fuel gas, the amount of water supply, etc. before shutdown stop is fixed at predetermined values by the pre-stop processing step. As a result, variations in pressure, temperature distribution, and the like at the point of time when natural leaving starts depending on the operating state during the power generation operation are reduced, and natural standing is always started from an appropriate state. For this reason, before the temperature of a fuel electrode falls to 350 degreeC, the risk that air will penetrate | invade into a fuel electrode side will become very low.

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

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

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

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

Next, a modified example of the stop mode 3 will be described with reference to FIG.
In the modification shown in FIG. 22, the method of supplying power generation air in the second temperature drop step is different from that in FIG. 19. As shown in FIG. 22, in this modification, after the shutdown stop is performed at time t303, the power generation air is supplied in the maximum amount until time t304. At time t304, the supply amount of power generation air is decreased stepwise, and the reduced supply amount is continued until time t305. Preferably, it is set to about 2 to 5 minutes between time t303 and time t304, and is set to about 2 to 20 minutes between time t304 and t305.

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

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

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

First, at time t401 in FIG. 23, when a predetermined time before the shutdown stop time scheduled by the program of the shutdown stop circuit 110a comes, the shutdown stop circuit 110a executes temperature drop control. In the stop mode 4, as in the stop mode 3, the temperature drop control is executed by the first temperature drop process and the second temperature drop process.
That is, in the stop pretreatment that is the first temperature drop step, first, the output of the power generated by the fuel cell module 2 to the inverter 54 is stopped, and the auxiliary unit 4 of the solid oxide fuel cell 1 is operated. Therefore, only the extraction of the weak current (about 1 A) is continued. Further, during the pre-stop process, the pre-stop water supply flow shown in FIG. 21 is also executed as described above.

  Further, in the stop pretreatment, after time t401, the fuel supply amount indicated by a thick dotted line in FIG. 23 and the supply amount of reforming water indicated by a thin solid line are reduced. On the other hand, the air supply amount for power generation indicated by the thick dashed line is increased. In the stop mode 4, the first temperature drop process is continued for 10 minutes longer than the stop mode 3 after the time t401.

  At time t402 when 10 minutes have elapsed after time t401, the shutdown stop circuit 110a executes shutdown stop. When the shutdown stop is performed, the fuel supply by the fuel flow rate adjustment unit 38 and the water supply by the water flow rate adjustment unit 28 are stopped in a short time. Further, the extraction of electric power from the fuel cell module 2 by the inverter 54 is also stopped (output current = 0).

  The shutdown stop circuit 110a executes the second temperature drop step of the temperature drop control after the shutdown stop at time t402, and operates the power generation air flow rate adjustment unit 45 at the maximum output for about 2 minutes. Further, after the power generation air flow rate adjustment unit 45 is stopped at time t403 in FIG.

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

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

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

  The pressure holding control circuit 110b stops the water flow rate adjustment unit 28 at time t405 in FIG. 23 when the temperature in the fuel cell module 2 has decreased to the oxidation lower limit temperature (for example, 350 ° C.). Left unattended.

  Further, the shutdown stop circuit 110a sends a signal to the reforming air flow rate adjustment unit 44 and the power generation air flow rate adjustment unit 45 at time t406 when the temperature in the fuel cell module 2 drops to a temperature of 300 ° C. or lower. Is activated. As a result, the reformer 20, the fuel gas supply pipe 64, the fuel gas passages such as the manifold 66, and the fuel electrode inside each fuel cell unit 16 are purged with air. In addition, the air electrode side in the power generation chamber 10, the exhaust passage 21b, and the exhaust gas passages such as the air heat exchanger 22 are also purged with air. By purging the fuel gas passage and the fuel electrode, water vapor remaining inside these is condensed, and oxidation of the fuel gas passage and the fuel electrode due to the condensed water is prevented. Further, by purging the exhaust gas passage, condensation of the water vapor discharged from the fuel electrode in the exhaust gas passage is prevented. Further, by purging the air electrode side in the power generation chamber 10, reduction by the fuel gas discharged from the fuel electrode side is prevented.

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

  First, the power generation operation is performed before the shutdown stop in the middle stage of FIG. 24, and the first temperature drop step in the temperature drop control is executed 10 minutes before the shutdown stop time scheduled by the program. In the stop mode 4, the first temperature drop process is performed for about 10 minutes, so the temperature in the fuel cell module 2 and the pressure on the fuel electrode side and the air electrode side at the time of shutdown stop are higher than those in the stop mode 3. Has also been lowered. After the shutdown is stopped, power generation air is supplied for about 2 minutes as the second temperature decrease process of the temperature decrease control, and the power generation air flow rate adjustment unit 45 is stopped. After the power generation air flow rate adjusting unit 45 is stopped, it is left as it is in the stop mode 3. Here, in the stop mode 4, the temperature in the fuel cell module 2 and the pressure on the fuel electrode side and the air electrode side at the time when the natural standing is started (time t 403 in FIG. 23) are higher than in the stop mode 3. It is further lowered. For this reason, before the temperature of the fuel electrode falls to 350 ° C., the risk of air entering the fuel electrode side is further reduced.

  In addition, in the stop mode 4, when the pressure on the fuel electrode side of each fuel cell unit 16 approaches the pressure on the air electrode side due to natural standing, the pressure holding control circuit 110b is activated, and each fuel cell unit The pressure on the fuel electrode side of 16 is increased. By the pressure holding control, first, the reformed fuel gas staying in the manifold 66 and the fuel gas supply pipe 64 (FIG. 2) is gradually fed into the fuel electrode of each fuel cell unit 16, and then the reforming is performed. The unreformed fuel gas remaining in the vessel 20 is gradually fed into the fuel electrode. Furthermore, after all the unreformed fuel gas has been sent, the water vapor evaporated in the evaporating section 20a is sent little by little to the fuel electrode of each fuel cell unit 16. At the time when the pressure holding control circuit 110b is activated, the temperature of the fuel electrode of each fuel cell unit 16 has dropped to around 400 ° C., so even if a backflow of air to the fuel electrode side occurs. The effect is slight. However, since the program stop for executing the stop mode 4 is the stop mode that is executed most frequently, the risk of oxidation of the fuel electrode is further reduced, and the influence of the oxidation on each fuel cell unit 16 is limited. Has been reduced to.

  Further, as shown in the upper left side of FIG. 24, in the stop modes 1 to 3, the pressure on the fuel electrode side of each fuel cell unit 16 decreases after the shutdown is stopped, and the temperature of the fuel electrode reaches about 400 ° C. When the pressure decreases, the pressure approaches the pressure on the air electrode side. On the other hand, in the stop mode 4, as shown in the upper right side of FIG. 24, the pressure holding control by the pressure holding control circuit 110b is executed in a region where the pressure on the fuel electrode side and the pressure on the air electrode side are close to each other. Further, it is possible to more reliably prevent the pressure on the fuel electrode side from lowering than that on the air electrode side.

  Further, as shown in the lower part of FIG. 24, during the natural standing after the end of the second temperature lowering step (“natural leaving 1” in the middle part of FIG. 24), it stays in the fuel electrode of each fuel cell unit 16. The fuel gas gradually flows out, and at the end, the air on the air electrode side may begin to diffuse toward the fuel electrode side (lower part (1) in FIG. 24). However, after that, when the temperature of the fuel electrode decreases to 400 ° C., pressure holding control is started, so that the fuel electrode stays in the fuel gas passage on the downstream side of the reformer 20 due to the pressure of the water vapor generated in the evaporator 20a. The fuel gas thus moved is moved again into each fuel cell unit 16, and the fuel gas concentration in the fuel electrode rises again (lower stage (2) in FIG. 24). After that, since the water vapor is generated in the evaporation unit 20a by the pressure holding control, the outflow of the fuel gas from the fuel electrode of each fuel cell unit 16 is compensated by the fuel gas staying in the fuel gas passage. Therefore, the backflow of air to the fuel electrode is prevented. Further, at the end of the pressure holding control, as shown in the lower part (3) of FIG. 24, even when almost all of the staying fuel gas has flowed out, the fuel electrode of each fuel cell unit 16 has no pressure. Since the water vapor generated by the holding control is filled, the backflow of air to the fuel electrode is reliably prevented.

  Further, after completion of the pressure holding control when the temperature of the fuel electrode becomes 350 ° C. or less, the fuel electrode is left to stand naturally (“Natural Standing 2” in the middle of FIG. 24), and then reforming air and power generation air (reforming and power generation). Is not performed), and the purge is executed when the temperature of the fuel electrode decreases to 150 ° C. As a result, the fuel gas and water vapor remaining on the fuel electrode side of each fuel cell unit 16 are discharged, and the fuel gas remaining on the air electrode side in the power generation chamber 10 is also discharged from the fuel cell module 2. The Thereby, in the stop mode 4 executed most frequently, oxidation of the fuel electrode of each fuel cell unit 16 is reliably avoided.

  According to the solid oxide fuel cell 1 of the embodiment of the present invention, it is possible to prevent the backflow of air from the air electrode side to the fuel electrode side by providing the mechanical pressure holding means and the pressure holding control. it can. In the present embodiment, the fuel passage is configured so as to reach the outer air electrode side from the fuel flow rate adjustment unit 38 through the reformer 20 and the fuel electrode of each fuel cell unit 16. The exhaust gas passage is configured to reach from the air electrode side in the fuel cell module 2 to the outside air outside the fuel cell module 2. As mechanical pressure maintaining means, by appropriately distributing the balance of flow resistance and the like of each part of the fuel / exhaust gas passage, shutdown stop (time t101 in FIG. 14, time t201 in FIG. 16, time t303 in FIG. 18, After time t402 in FIG. 23), until the temperature drops to 350 ° C. (time t102 in FIG. 14, time t204 in FIG. 16, time t305 in FIG. 18, time t404 in FIG. 23), the pressure on the air electrode side is changed from the atmospheric pressure. And the pressure on the fuel electrode side has been successfully maintained higher than that on the air electrode side (the upper part of FIG. 15, the upper part of FIG. 17, the upper part of FIG. 20, the upper part of FIG. 24).

  The risk of oxidation of the fuel electrode is sufficiently reduced by the mechanical pressure holding means, but by this mechanical means alone, the temperature on the fuel electrode side is reduced to a temperature at which no oxidation of the fuel electrode occurs (oxidation lower limit temperature). It is difficult to maintain the pressure. Therefore, the shutdown stop circuit 110a executes pressure holding control for increasing the pressure on the fuel electrode side after the temperature of the fuel electrode is lowered to 400 ° C. (time t404 to t405 in FIG. 23). Since the pressure holding control is executed after the temperature of the fuel electrode is lowered to 400 ° C., the pressure is greatly reduced on both the fuel electrode side and the air electrode side, and the pressure on the fuel electrode side only needs to be compensated slightly. . Further, since the pressure holding control is executed in a state where the risk of oxidation is sufficiently reduced, the oxidation of the fuel electrode can be reliably prevented without performing precise control.

  Further, according to the solid oxide fuel cell 1 of the present embodiment, after the fuel supply and power generation are stopped by the mechanical pressure holding means, the pressure on the fuel electrode side is higher than the pressure on the air electrode side. Even when the temperature of the fuel electrode decreases to 350 ° C. while maintaining the pressure, the pressure is maintained higher than the atmospheric pressure. For this reason, the backflow of the air on the air electrode side can be prevented by the mechanical pressure holding means until the temperature falls to 350 ° C.

  Furthermore, according to the solid oxide fuel cell 1 of the present embodiment, by appropriately setting the channel resistance of the fuel gas channel capillary 98 (FIG. 4) at the upper end of the fuel cell unit 16, the fuel electrode side and It is possible to balance the flow resistance on the air electrode side and the flow resistance on the air electrode side and outside air, making the pressure drop on the fuel electrode side more gradual than that on the air electrode side, and preventing backflow of air. be able to.

  Moreover, in the reformer 20, even after the shutdown is stopped, the pressure may rapidly increase due to evaporation of residual water or the like. According to the solid oxide fuel cell 1 of the present embodiment, since the inflow side flow path resistance portion (fuel gas flow path narrow tube 98 (FIG. 4)) is also provided on the inflow side of the fuel electrode, the reformer It is possible to prevent the fuel remaining on the fuel electrode side from suddenly flowing out to the air electrode side due to a rapid pressure increase in the inside 20 or the like. As a result, the pressure drop on the fuel electrode side can be moderated and the backflow of air can be prevented.

  Furthermore, in general, the temperature decrease of the fuel electrode becomes gentler as the temperature becomes lower. For this reason, it takes a long time to reach 350 ° C. and further to the oxidation lower limit temperature after the temperature is lowered to 400 ° C. at which the risk of oxidation of the fuel electrode is reduced. Therefore, assuming an unexpected disturbance such as a change in atmospheric pressure that deviates from the design value over a long period of time during which the temperature drops, under any circumstances, until the lower limit of oxidation temperature is reached by the mechanical pressure holding means Maintaining pressure is difficult to design. According to the solid oxide fuel cell 1 of the present embodiment, the pressure is held by the mechanical pressure holding means up to 350 ° C. which is higher than the lower limit oxidation temperature. Can be reduced.

  Further, in the solid oxide fuel cell 1 of the present embodiment, the oxidation of the fuel electrode is actively prevented in the temperature range of 350 ° C. or higher and 400 ° C. or lower (preferably 360 ° C. or higher and 400 ° C. or lower). This prevents the fuel cell unit from being damaged due to the oxidation contraction of the fuel electrode in this temperature region. In particular, when the temperature of the fuel electrode is 350 ° C. or more and 400 ° C. or less, the fuel constituting the power generation stack is maintained by maintaining the entire surface on the fuel gas flow path side of the fuel electrode constituting the power generation stack in a non-oxygen atmosphere. Prevent partial contraction of the fuel electrode due to partial oxidation of the electrode.

  Furthermore, according to the solid oxide fuel cell 1 of the present embodiment, the water flow rate adjustment unit 28 is kept until the temperature of the fuel electrode is lowered to 400 ° C. and the pressure holding control is started (time t404 in FIG. 14). Since the operation is stopped, it is possible to eliminate a factor that breaks the pressure balance between the fuel electrode side and the air electrode side during the pressure holding by the mechanical pressure holding means. Thereby, the temperature and the pressure can be reliably reduced according to the mechanical design until the temperature is lowered to 400 ° C.

  Immediately after the shutdown is stopped, the pressure on the fuel electrode side is sufficiently higher than the pressure on the air electrode side, and even if the power generation air flow rate adjustment unit 45 is operated to increase the pressure on the air electrode side, the air flows backward. Never do. According to the solid oxide fuel cell 1 of the present embodiment, the power generation air flow rate is adjusted over a predetermined exhaust heat time (time t303 to t304 in FIG. 18, time t402 to t403 in FIG. 23) without risk of backflow. By operating the unit 45, the high-temperature air immediately after the shutdown stop can be discharged. As a result, pressure holding by the mechanical pressure holding means can be started from a lower temperature state, and oxidation of the fuel electrode can be reliably prevented up to 400 ° C.

  Further, according to the solid oxide fuel cell 1 of the present embodiment, immediately before stopping the fuel supply and the power generation, the generated power is decreased and the air supply amount is increased (time t301 to t303 in FIG. 18, FIG. 23). Therefore, the temperatures on the fuel electrode side and the air electrode side can be lowered without any risk of air backflow. As a result, the pressure holding by the mechanical pressure holding means can be started from a lower temperature state, and the initial state for starting the pressure holding can be adjusted to a predetermined state, thereby preventing the fuel electrode from being oxidized more reliably. can do.

  Furthermore, according to the solid oxide fuel cell 1 of the present embodiment, after the shutdown is stopped, the supply of water is stopped until the temperature of the fuel electrode decreases to 400 ° C. (time t404 in FIG. 23). Even after the temperature of the fuel electrode has decreased to 400 ° C., the temperature of the reformer 20 is maintained at a relatively high temperature. For this reason, even after the pressure holding by the mechanical pressure holding means is completed, water can be evaporated in the reformer 20 to suppress the pressure drop on the fuel electrode side, and the fuel electrode is reliably prevented from being oxidized. be able to.

  Further, according to the solid oxide fuel cell 1 of the present embodiment, in the pressure holding control (time t404 to t405 in FIG. 23), a smaller amount of water is supplied than during the power generation operation, so The amount of fuel can be reduced, and the residual fuel on the fuel electrode side can be prevented from excessively flowing out to the air electrode side, and the fuel electrode side can be maintained in the fuel atmosphere for a long time.

  Furthermore, according to the solid oxide fuel cell 1 of the present embodiment, since water is intermittently supplied, the amount of water supplied per hour can be greatly reduced. Further, by supplying water intermittently, a sudden pressure increase due to evaporated water vapor is likely to occur. However, since the pressure fluctuation suppressing flow path resistance portion 64c (FIG. 2) is provided, the pressure increase The influence hardly affects the fuel electrode, and excessive fuel outflow from the fuel electrode side can be prevented.

  In addition, according to the solid oxide fuel cell 1 of the present embodiment, after the fuel electrode is lowered to a temperature lower than the oxidation lower limit temperature (for example, 300 ° C.), the fuel remaining on the fuel electrode side is discharged (see FIG. 23, from time t406 to t407), it is possible to discharge residual fuel without any risk of oxidation and to prevent excess fuel from remaining in the fuel cell module 2 at the next start-up. Can do.

  In the above-described embodiment of the present invention, when the stop switch is operated by the user (step S5 in FIG. 13), the stop mode 3 is executed. As described above, the stop mode 2 may be executed. FIG. 25 is a flowchart of stop determination for selecting a stop mode in a fuel cell device according to a modification of the present invention. That is, in this modification, when the fuel gas is stopped and only electricity is supplied (step S3 → S4 in FIG. 25), and when the stop switch is operated by the user (step S5 → FIG. 25). In S4), stop mode 2 is executed. According to this modified example, when the stop switch is operated, the shutdown stop is executed without executing the stop pre-processing (first temperature drop step). Therefore, after the stop switch operation by the user, Control related to shutdown stop can be promptly terminated.

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

Claims (8)

A solid oxide fuel cell that generates electricity by reacting hydrogen and oxidant gas in a fuel cell unit,
The fuel cell unit is
A fuel electrode to which the hydrogen is supplied;
An oxidant gas electrode to which the oxidant gas is supplied;
A solid electrolyte provided between the fuel electrode and the oxidant gas electrode;
The fuel electrode is composed of a composite material containing nickel,
The solid oxide fuel cell prevents contraction due to oxidation of the fuel electrode by maintaining the fuel electrode in a non-oxygen atmosphere until the temperature of the fuel electrode decreases to 350 ° C. after power generation is stopped. A solid oxide fuel cell. The fuel cell unit has a fuel gas flow path through which the fuel gas containing hydrogen flows.
The fuel cell unit has a power generation stacking unit in which the fuel electrode, the solid electrolyte, and the oxidant gas electrode are stacked in order from the fuel gas flow path side.
When the temperature of the fuel electrode is 350 ° C. or more and 400 ° C. or less after the power generation is stopped, the solid oxide fuel cell is configured so that the entire surface on the fuel gas flow path side of the fuel electrode constituting the power generation stack portion 2. The solid oxide fuel according to claim 1, wherein partial contraction of the fuel electrode due to partial oxidation of the fuel electrode constituting the power generation stack is prevented by maintaining an oxygen atmosphere. battery. The fuel gas channel has an outflow side open end communicating with the outside of the fuel cell unit,
The fuel cell unit has a buffer portion between the outflow side opening end and the power generation stacking portion along the fuel gas flow path,
3. The solid oxide fuel cell according to claim 2, wherein the buffer section has an outflow side flow path resistance section. After the power generation is stopped, the solid oxide fuel cell is configured to supply air to the fuel gas passage after the temperature of the fuel electrode has decreased to a predetermined temperature of 300 ° C. or less. The solid oxide fuel cell according to claim 3, wherein the residual gas is discharged. The solid oxide fuel cell is
A fuel cell module comprising the fuel cell unit;
A fuel supply device for supplying fuel to the fuel cell module;
A water supply device for supplying water for steam reforming to the fuel cell module;
An oxidant gas supply device for supplying an oxidant gas to the oxidant gas electrode of the fuel cell unit;
A reformer that is disposed in the fuel cell module and steam-reforms the fuel supplied from the fuel supply device using the water supplied from the water supply device;
A fuel / exhaust gas passage for guiding fuel / exhaust gas from the fuel supply device to the outside of the fuel cell module through the reformer, the fuel gas flow path of the fuel cell unit;
The fuel supply device, the water supply device, the oxidant gas supply device, and a controller that controls the extraction of electric power from the fuel cell module,
The controller includes a shutdown stop circuit for stopping fuel supply and power generation,
The fuel / exhaust gas passage is a pressure in the fuel gas passage of the fuel cell unit until the temperature of the fuel electrode decreases to 400 ° C. after the fuel supply and power generation are stopped by the shutdown stop circuit. Is configured to function as a mechanical pressure holding means for maintaining the pressure higher than the pressure outside the fuel cell unit in the fuel cell module,
The shutdown stop circuit is configured to suppress the pressure drop in the fuel gas flow path caused by the temperature decrease of the fuel electrode until the temperature of the fuel electrode decreases to 400 ° C. and then reaches 350 ° C. 5. The solid oxide fuel cell according to claim 4, further comprising a pressure holding control circuit that executes pressure holding control for increasing the pressure in the fuel gas flow path. The pressure holding control circuit is configured such that when the temperature of the fuel electrode is within a temperature range of 20 ° C. before and after 380 ° C., the pressure in the fuel gas flow path becomes equal to or higher than the pressure outside the fuel cell unit. 6. The solid oxide fuel cell according to claim 5, wherein pressure holding control for increasing the pressure in the fuel gas flow path is executed so as to be maintained. The fuel / exhaust gas passage is connected to the fuel gas flow path of the fuel cell unit until the temperature of the fuel electrode drops to 400 ° C. after water supply, fuel supply, and power generation are stopped by the shutdown stop circuit. Is configured to function as a mechanical pressure holding means for maintaining the internal pressure higher than the pressure outside the fuel cell unit in the fuel cell module,
The pressure holding control circuit generates water vapor by evaporating water in the reformer by operating the water supply device after the temperature of the fuel electrode is lowered to 400 ° C. By suppressing the pressure drop in the fuel gas flow path of the fuel cell unit, the inflow of oxidant gas into the fuel gas flow path is suppressed,
The controller remains in the fuel gas flow path of the fuel cell unit when the supply of water by the pressure holding control circuit is finished and the temperature of the fuel electrode is lowered to a predetermined temperature of 300 ° C. or lower. 6. The solid oxide fuel cell according to claim 5, wherein air is supplied to the fuel gas flow path in order to discharge the fuel being discharged. The shutdown stop circuit executes a stop in a program stop mode for stopping fuel supply and power generation at a scheduled time,
The program stop mode is
A first temperature drop step for reducing the temperature outside the fuel cell unit in the fuel cell module immediately before stopping fuel supply and power generation;
A second temperature drop step for reducing the temperature outside the fuel cell unit in the fuel cell module immediately after stopping fuel supply and power generation;
After the temperature of the fuel electrode is lowered to 400 ° C., the water supply device is operated to evaporate water in the reformer to generate water vapor, and the pressure of the fuel cell unit by the pressure of the water vapor Suppressing the flow of oxidant gas into the fuel gas channel by suppressing the pressure drop in the fuel gas channel;
The fuel remaining in the fuel gas flow path of the fuel cell unit when the supply of water by the pressure holding control circuit is finished and the temperature of the fuel electrode is lowered to a predetermined temperature of 300 ° C. or lower. Supplying air to the fuel gas flow path in order to discharge
6. The solid oxide fuel cell according to claim 5, wherein:

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