JP5801583B2 - Solid oxide fuel cell system - Google Patents

Description

  The present invention relates to a solid oxide fuel cell system including a fuel cell that generates power by oxidation and reduction of a fuel gas and an oxidant.

  A fuel cell in a solid oxide fuel cell system includes a solid electrolyte that conducts oxygen ions, a fuel electrode that oxidizes fuel gas is provided on one side of the solid electrolytic chamber, and oxygen in the air is reduced on the other side. An air electrode is provided. As a material for the solid electrolyte, zirconia doped with yttria is generally used, and hydrogen, carbon monoxide, carbonization in fuel gas (for example, natural gas, city gas, etc.) at a high temperature of 600 to 1000 ° C. Hydrogen and oxygen in an oxidant gas (for example, air) undergo an electrochemical reaction to generate power. The solid oxide fuel cell system has been developed as a promising power generation technology because it can generate power with particularly high power generation efficiency as compared with other fuel cell systems and gas engines.

  Since such a solid oxide fuel cell system operates under a high temperature condition of 600 ° C. or higher, an oxide material that is thermodynamically stable in an oxidizing atmosphere is used on the air electrode side of the fuel cell, and A mixture of metal and oxide materials that are stable in a reducing atmosphere is used on the fuel electrode side, and the air electrode side is oxidized during high-temperature conditions (300 to 400 ° C or higher) during power generation and startup / stop. Atmospheric gas flows, and reducing atmosphere gas needs to flow on the fuel electrode side.

As the material of the air electrode, lanthanum manganite oxide, lanthanum cobaltite oxide, lanthanum ferrite oxide, etc. are used, and these materials are exposed to a reducing atmosphere at a high temperature of 500 ° C. or higher. If it is reduced, it is rapidly reduced and expands, cracks and peeling occur, and the performance deteriorates. As a material for the fuel electrode, a cermet made of nickel and zirconium oxide or the like (referred to as “nickel cermet”) is used. The nickel cermet depends on the particle size of nickel, but 350 When exposed to an oxidizing atmosphere at ˜400 ° C. or higher, nickel reacts as follows to oxidize nickel to nickel oxide (N _i O).

2N _i (s) + O ₂ (g) → 2N _i O (s)
If the oxygen partial pressure is at a level that oxidizes, the oxidation reaction proceeds at a higher temperature and proceeds from the surface of the nickel particles. In a solid oxide fuel cell (fuel cell), the reformed fuel gas is fed during power generation, and the fuel electrode side is maintained in a high temperature / reducing atmosphere, so that the oxidized portion of nickel particles is reduced and metallic nickel is reduced. It becomes. For this reason, the nickel cermet microstructure and dimensions change due to repeated oxidation and reduction of the nickel cermet used in the fuel electrode of the fuel cell and the structural support, resulting in cracking of the fuel cell. It is known to cause performance degradation. For this reason, development of fuel cells that are resistant to repeated oxidation and reduction on the fuel electrode side has been carried out.

  In general, medium- and large-sized solid oxide fuel cell systems are configured in such a way that, under any circumstances, reducing gas flows to the fuel electrode side and air flows to the air electrode side at high temperatures. A high-pressure cylinder rack is provided, and a reducing gas (such as a nitrogen-hydrogen mixed gas) is supplied from the high-pressure cylinder rack to the fuel electrode side. However, in a small solid oxide fuel cell system (especially a fuel cell system used for a home cogeneration system), reducing gas is supplied to the fuel electrode side and air to the air electrode side at high temperatures in any situation. It is difficult to increase the initial cost and the maintenance cost, and it is not easy from the viewpoint of legal regulations such as installation space and storage of high-pressure gas.

  For this reason, it is known to add an aqueous methanol solution or the like in order to supply the reducing gas to the fuel electrode side of the fuel cell in the fuel cell system (see, for example, Patent Document 1). It is also known that dimethyl ether is added when the fuel cell system is stopped (in addition to this, it is desirable to add water) (see, for example, Patent Document 2). In these fuel cell systems, reducing gas is generated by steam reforming of methanol (or dimethyl ether), and the generated reducing gas is supplied to the oxygen electrode side of the fuel cell, thus suppressing oxidation of the fuel electrode. be able to.

JP 2005-535072 A JP 2006-310128 A

  In a solid oxide fuel cell system used for a household cogeneration system using city gas, the hydrogen-rich gas produced by steam reforming the city gas at the start-up and shutdown of the fuel cell system is solid oxide. It is supplied to the fuel electrode side of the fuel cell (fuel cell), and a reducing atmosphere is maintained with this hydrogen-rich gas. At start-up, the amount of city gas supplied is increased, so that the temperature of the solid oxide fuel cell and the like is increased by combustion of the hydrogen-rich gas. In addition, when the vehicle is stopped, the supply amount of the city gas is reduced, so that a heat balance is maintained such that the temperature of the solid oxide fuel cell (fuel cell) itself is lowered while flowing the reducing gas. It is like that.

  However, when a failure of the city gas supply system as raw fuel gas or a failure of the water supply system for steam reforming occurs (that is, abnormally stopped), the natural gas is steam reformed and the hydrogen rich gas is solid-oxidized. The fuel cell cannot be supplied to the fuel electrode side of the physical fuel cell (fuel cell), and as a result, the fuel cell may be damaged or the performance may be deteriorated in the abnormal stop state.

  In a home cogeneration system, the durability required for household equipment is secured with a high probability, and reducing gas is supplied to the fuel electrode side even under abnormal stop conditions under the necessary initial and maintenance costs of the system. For example, adding a methanol aqueous solution (Patent Document 1) is effective as a means for flowing a reducing gas to the fuel electrode side of the fuel cell, but it is useful for a household cogeneration system. However, there is a problem in the method for controlling the amount of methanol aqueous solution added to cope with the maximum number of abnormal stops (for example, 10 times or more) assumed in the maintenance interval (2 to 3 years). To meet this challenge, the necessary protection needs to be achieved while minimizing the amount of methanol added. Such a problem has the same problem when dimethyl ether is added (Patent Document 2).

  An object of the present invention is to provide a solid oxide fuel cell system capable of remarkably suppressing breakage of a fuel electrode of a fuel cell and performance deterioration with a minimum addition amount while making use of basic resistance against an emergency stop. Is to provide.

A solid oxide fuel cell system according to claim 1 of the present invention includes a reformer for steam reforming a raw fuel gas, and a reformed fuel gas and an oxidizing material reformed by the reformer. A cell stack including a plurality of fuel cells for generating power by oxidation and reduction of the fuel, a fuel pump for supplying raw fuel gas to the reformer, and reforming water to the reformer A water pump for supplying the reformer with a mixed liquid pump for supplying a mixed liquid of methanol and water, and a control means for controlling the fuel pump, the water pump and the mixed liquid pump. A solid oxide fuel cell system,
The control means is configured to set an abnormal stop operation mode for setting an abnormal stop operation mode for abnormal stop while suppressing oxidation of the fuel electrode of the fuel cell, and an abnormal stop determination means for determining that the high-temperature abnormal stop state is present. And the abnormal stop determination means is configured such that the supply amount of raw fuel gas from the fuel pump and / or the supply amount of reforming water from the water pump is abnormally reduced and the temperature of the cell stack is When the temperature of the fuel cell is higher than the oxidation temperature at which oxidation of the fuel electrode occurs, it is determined as a high temperature abnormal stop state, and the abnormal stop operation mode setting means is abnormally stopped when the abnormal stop determination means is determined as a high temperature abnormal stop state. An operation mode is set, and in the abnormal stop operation mode, the control means operates the mixed liquid pump to supply the mixed liquid to the reformer. That.

In the solid oxide fuel cell system according to claim 2 of the present invention, when the temperature of the cell stack is lowered to a stop temperature lower than the oxidation temperature in the abnormal stop operation mode, the control means The stop operation mode is canceled to stop the operation of the mixed liquid pump.

  In the solid oxide fuel cell system according to claim 3 of the present invention, in the abnormal stop operation mode, the control means controls the operation of the mixed liquid pump based on the temperature of the cell stack. The supply amount of the mixed liquid supplied to the reformer is adjusted.

In the solid oxide fuel cell system according to claim 4 of the present invention, in the abnormal stop operation mode, the control means controls the fuel electrode of the fuel cell while suppressing the supply flow rate of the mixed liquid. In order to maintain the reduced state, the liquid mixture supplied to the reformer by controlling the operation of the liquid mixture pump so that the cell voltage per cell in the cell stack becomes greater than 0.75 to 0.85 V It is characterized by adjusting the supply amount.

  Furthermore, in the solid oxide fuel cell system according to claim 5 of the present invention, the mixed solution contains ethanol in addition to the methanol and water.

According to the solid oxide fuel cell system of the first aspect of the present invention, power is generated by reforming the raw fuel gas with steam, and oxidizing and reducing the reformed fuel gas and the oxidizing material. A cell stack having a plurality of fuel cells, a fuel pump for supplying raw fuel gas to the reformer, a water pump for supplying reforming water to the reformer, and a reformer A mixed liquid pump for supplying a mixed liquid of methanol and water, and when the temperature of the cell stack is equal to or higher than the oxidation temperature , the supply amount of raw fuel gas from the fuel pump (and / or reforming from the water pump) When the water supply amount) drops abnormally, the abnormal stop determination means determines that the high-temperature abnormal stop state is established, and the abnormal stop operation mode setting means sets the abnormal stop operation mode when the high-temperature abnormal stop determination means determines that the abnormal stop state exists. To do. In the abnormal stop operation mode, the mixed liquid pump is operated, and the mixed liquid is supplied to the reformer by the mixed liquid pump. Therefore, the reducing gas is generated by steam reforming of the mixed liquid (methanol) in the reformer. Is generated, and the generated reducing gas is fed to the fuel electrode side of the cell stack. Therefore, even if the supply amount of raw fuel gas (and / or the supply amount of reforming water) is abnormally low and steam reforming cannot be performed, the mixture liquid supplied from the mixture liquid pump Reducing gas can be generated by steam reforming, and oxidation of the fuel electrode in the cell stack can be suppressed by this reducing gas.

The fuel electrode of the cell stack (for example, formed from nickel cermet) has a high oxidation rate at a temperature higher than the oxidation temperature at which the oxidation takes place , and supply of a mixed liquid to suppress oxidation at such a high temperature. However, when the temperature is lower than the oxidation temperature , the oxidation of the fuel electrode of the cell stack hardly causes a problem. In such a case, the mixed solution is not supplied. When nickel cermet is used as the fuel electrode, the oxidation temperature is set to about 450 ° C., and the abnormal stop operation mode is performed when the abnormal stop determination means determines that the high temperature abnormal stop state occurs at a temperature of 450 ° C. or higher. . As described above, by supplying the mixed liquid only when the fuel electrode is easily oxidized, it is possible to suppress the amount of the mixed liquid used and to suppress the oxidation of the fuel electrode over a long period of time.

Further, according to the solid oxide fuel cell system according to claim 2 of the present invention, the temperature of the cell stack during operation of the abnormal stop operating mode is lowered to stop temperature, the operation of the abnormal stop operating mode is finished To do. The stop temperature, which is the reference when terminating the operation in the abnormal stop operation mode, is a temperature at which the fuel electrode of the fuel cell does not oxidize or hardly occurs. When nickel cermet is used as the fuel electrode, this stop temperature Is set to about 300-450 ° C.

  According to the solid oxide fuel cell system of claim 3 of the present invention, the supply of the mixed liquid supplied to the reformer based on the temperature of the cell stack during the operation in the abnormal stop operation mode. By adjusting the supply amount of the mixed solution in this way, it is possible to suppress the oxidation of the fuel electrode of the fuel cell over a long period of time by supplying the minimum necessary mixed solution. It is desirable to adjust the supply amount of the mixed liquid based on this temperature, so that the supply amount increases as the temperature of the cell stack increases. In this way, more reducing gas (modified) can be obtained in an oxidative environment. Gas reformed in the mass device) is supplied to the fuel electrode side of the cell stack (fuel cell), and the oxidation of the fuel electrode of the cell stack can be suppressed while minimizing the supply amount of the mixed solution.

In the solid oxide fuel cell system according to claim 4 of the present invention, the cell voltage per cell in the cell stack is from 0.75 to 0.85 V during the operation in the abnormal stop operation mode. Since the supply amount of the mixed solution supplied to the reformer is adjusted so as to increase, the fuel electrode of the fuel cell can be kept in a reduced state while suppressing the supply flow rate of the mixed solution. It is possible to suppress the oxidation of the fuel electrode of the fuel cell over a long period by supplying the minimum liquid mixture.

  In general, in a solid oxide fuel cell system, when the fuel gas and water for reforming the fuel gas by steam reforming are shut off, the voltage per cell of the cell stack (cell stack voltage / series) The number of connected fuel cells is about 0.6 to 0.8 V (when the temperature of the cell stack is about 600 ° C.). For this reason, the supply voltage is controlled by controlling the supply flow rate of the mixed solution (mixed solution of methanol and water) so that the output voltage of the cell stack is larger than 0.75 to 0.85 V per cell. The oxidation rate of the fuel electrode (for example, nickel cermet) of the fuel cell can be managed low while minimizing the flow rate, and the reliability in the abnormal stop operation mode can be greatly improved with the minimum addition amount.

For example, the reduction of nickel cermet (nickel particles) proceeds rapidly at a relatively low temperature (for example, a temperature environment of 300 ° C. or lower), but the oxidation depends on temperature and time and is higher in temperature (for example, 400) than the reduction. Because of these characteristics, the nickel cermet does not oxidize completely (flowing reducing gas sufficiently), and the oxidation rate of nickel can be suppressed. This is to control the supply amount of the liquid mixture. By doing this, the consumption of the liquid mixture (mixed liquid of meth-anol and water) is suppressed and the number of times of reliability that can cope with “abnormal stop” is increased. Can do.

Furthermore, according to the solid oxide fuel cell system according to claim 5 of the present invention, since ethanol is added to the mixed solution of methanol and water, an azeotropic point can be formed and water is extremely reduced. The reducing gas can be reliably supplied to the fuel electrode side of the cell stack.

  In general, since “emergency stop” is not a regular operation, it may not be operated for several months to a year or more. In such a case, a flow path for supplying a mixture of methanol and water to the reformer In such a case, methanol in the liquid mixture may evaporate and become almost water only, but adding ethanol to this liquid mixture makes it extremely water only. Disappears.

1 is a simplified diagram showing an embodiment of a solid oxide fuel cell system according to the present invention. The block diagram which shows the control system of the solid oxide fuel cell system of FIG. The flowchart which shows the flow of the operation control by the control system of FIG. The figure which shows the relationship between the voltage per cell when a liquid mixture is added, and the temperature of a cell stack.

  Hereinafter, an embodiment of a solid oxide fuel cell system according to the present invention will be described with reference to the accompanying drawings. In FIG. 1, the illustrated solid oxide fuel cell system 2 is modified by a reformer 4 for reforming raw fuel gas (for example, natural gas, city gas) as a fuel, and a reformer 4. And a cell stack 6 that generates power by oxidizing and reducing the reformed fuel gas and the oxidizing material air. The cell stack 6 is configured by arranging a plurality of solid oxide fuel cells (not shown) for generating power by an electrochemical reaction. Each fuel cell of the cell stack 6 includes a solid electrolyte that conducts oxygen ions, a fuel electrode provided on one side of the solid electrolyte, and an air electrode provided on the other side of the solid electrolyte, As the electrolyte, for example, zirconia doped with yttria is used.

  The fuel electrode side of the cell stack 6 (a plurality of fuel cells) is connected to the reformer 4 via the reformed fuel gas feed line 8. The reformer 4 is connected to the fuel gas / steam feed line 10. The vaporizer 12 is connected via a fuel gas supply line 14 to a raw fuel gas supply source (not shown) such as a buried pipe or a storage tank. The fuel gas supply line 14 is provided with a fuel pump 16, a desulfurizer 18 and an on-off valve 20. The desulfurizer 18 removes sulfur components contained in the raw fuel gas, and the fuel pump 16 pressurizes the raw fuel gas supplied through the fuel gas supply line 20. The on-off valve 20 opens and closes the fuel gas supply line 14 to supply the raw fuel gas when the fuel gas supply line 14 is open, and stops the supply of the raw fuel gas when the fuel gas supply line 14 is closed. The fuel gas supply line 14 is provided with first flow rate detection means 22 (fuel gas flow rate sensor). The first flow rate detection means 22 measures the flow rate of the raw fuel gas flowing through the fuel gas supply line 14, and 1, the number of times of the fuel pump 16 is controlled while monitoring the detected flow rate value of the flow rate detection means 22, whereby the supply amount of the raw fuel gas supplied through the fuel gas supply line 20 is controlled. Moreover, the abnormality of a fuel gas supply system is detected using a measured value.

  The air electrode side of the cell stack 6 is connected to an air preheater 26 for preheating air via an air supply line 24, and this air preheater 26 is connected to an air blower 30 via an air supply line 28. By controlling the rotational speed of the air blower 30, the amount of air supplied to the air electrode side of the cell stack 6 (a plurality of fuel cells) through the air supply line 28 is controlled. The air supply line 28 is provided with second flow rate detection means 32 (air flow rate sensor), and the second flow rate sensor 32 measures the flow rate of air supplied through the air supply line 28. The air supply line 28 and the air blower 30 constitute an air supply means 33 for supplying air to the air electrode side of the cell stack 6.

  Combustion chambers 34 are provided on the discharge side of the fuel electrode side and the air electrode side of the cell stack 6 (plural fuel cells), and the reaction fuel gas (including residual fuel gas) and air discharged from the fuel electrode side. Air (including oxygen) discharged from the pole side is supplied to the combustion chamber 34 and combusted, and the reformer 4, the cell stack 6, and the vaporizer 12 are heated using this combustion heat. The combustion chamber 34 is connected to an air preheater 26 via an exhaust gas line 36, and an exhaust gas discharge line 38 is connected to the air preheater 26.

  In the solid oxide fuel cell 2, a water supply line 40 for supplying water (reforming water) for reforming raw fuel gas is connected to the vaporizer 12, and a water pump is connected to the water supply line 40. 42 is disposed. The water supply line 40 is connected to a water tank 44 that stores water used for reforming, and water in the water tank 44 is supplied to the vaporization mixer 12 through the water supply line 40 by the water pump 42. By controlling the rotation speed, the supply amount of water used for reforming is controlled.

  In this embodiment, the water tank 44, the water supply line 40, and the water pump 42 constitute water supply means 46 for supplying water to the vaporizer 12 (in other words, the reformer 4), and the water supply means 46. The third flow rate detection means 48 (water detection sensor) is disposed in the water supply line 40, and the third flow rate detection means 48 measures the flow rate of the reforming water supplied through the water supply line 40. The value is used to detect abnormalities in the water supply system. Note that the water for reforming the raw fuel gas is not supplied from the water tank 44 but, for example, condensed water obtained by condensing and recovering water vapor contained in the exhaust gas from the combustion chamber 34 is used. May be.

  In this embodiment, a battery housing 50 whose interior is covered with a heat insulating material is provided. The battery housing 50 defines a high-temperature space 52 that is maintained at a high temperature during operation, and the reformer is provided in the high-temperature space 52. 4, the cell stack 6, the vaporizer 12 and the air preheater 26 are accommodated.

  The operation of the solid oxide fuel cell system 2 is performed as follows. Raw fuel gas from a raw fuel gas supply source (not shown) is supplied to the vaporizer 12 through the fuel gas supply line 14. Further, the water from the water tank 44 is supplied to the vaporizer 12 through the water supply line 40. In the vaporizer 12, the supplied raw fuel gas and water are heated, and the water is vaporized to become water vapor. The heated raw fuel gas and water vapor are supplied to the reformer 4 through the fuel gas / water vapor supply line 10. Be sent.

  The reformer 4 is filled with a reforming catalyst for promoting steam reforming, and the raw fuel gas fed to the reformer 4 is steam reformed by steam, thus reforming. The reformed fuel gas is supplied to the fuel electrode side 12 of the cell stack 6 (a plurality of fuel cells) via the reformed fuel gas supply line 8. Further, air from the air blower 30 is supplied to the air preheater 26 through the air supply line 28, heat is exchanged with the exhaust gas in the air preheater 26 and heated, and then air is supplied. It is fed to the air electrode side of the cell stack 6 via the line 24.

  In the cell stack 6, the reformed fuel gas reformed on the fuel electrode side is oxidized, oxygen in the air is reduced on the air electrode side, and by an electrochemical reaction due to oxidation on the fuel electrode side and reduction on the air electrode side. Power generation is performed. The reaction fuel gas from the fuel electrode side of the cell stack 6 and the air from the air electrode side are discharged into the combustion chamber 34, and excess fuel gas is burned using oxygen in the air, and this combustion heat is used. The reformer 4 is maintained at the reforming temperature, and the vaporizer 12 is maintained at the vaporization temperature.

  Exhaust gas from the combustion chamber 34 is supplied to the air preheater 26 through the exhaust gas line 36 and is used for heat exchange with air from the air blower 30 in the air preheater 26, and then exhaust gas is discharged. It is discharged to the atmosphere through line 38.

  This solid oxide fuel cell system 2 is further configured as follows in order to prevent oxidation of the fuel electrode of the cell stack 6 (plural fuel cells) during an abnormal stop. In this embodiment, a mixed liquid supply means 54 for supplying a mixed liquid of methanol and water is provided in association with the vaporizer 12 (in other words, the reformer 4). The mixed liquid supply means 54 includes a mixed liquid tank 56 that stores the mixed liquid, and a mixed liquid supply line 58 that supplies the mixed liquid in the mixed liquid tank 56 to the vaporizer 12. A liquid mixture pump 60 is disposed in the middle. With this configuration, when the mixed liquid pump 60 operates, the mixed liquid in the mixed liquid tank 56 is supplied to the vaporization mixer 12 through the mixed liquid supply line 58, and the reformer passes through the vaporized mixer 12. 4 is sent. Further, temperature detection means 62 for detecting the temperature of the cell stack 6 is provided in association with the cell stack 6.

In this embodiment, the mixed solution is fed to the reformer 4 via the vaporizer 12, but instead of such a configuration, the mixed solution is directly passed through the mixed solution supply line 58. You may make it send to the reformer 4. FIG.
The operation of the solid oxide fuel cell system 2 is controlled by the control system shown in FIG. 2 when an abnormal state occurs in the fuel gas supply system and / or the water supply system, resulting in an abnormal stop. The solid oxide fuel cell system 2 further includes control means 72 for controlling the system, and the control means 72 is constituted by, for example, a microprocessor. The illustrated control means 72 includes an operation control means 74, an abnormal stop determination means 76, an abnormal stop operation mode setting means 78, and a memory means 80. The operation control unit 74 controls the operation of the fuel pump 16, the water pump 42, the air blower 30, the mixed liquid pump 60, and the like, and the abnormal stop determination unit 76 determines an abnormal stop state when a condition described later is satisfied, The abnormal stop operation mode setting unit 78 sets the abnormal stop operation mode when the abnormal stop determination unit 76 determines that it is in an abnormal stop state. The memory unit 80 stores in advance an oxidation temperature that is a reference temperature for determining an abnormally stopped state and a stop temperature that is a reference temperature for ending the operation in the abnormally stopped operation mode.

  The oxidation temperature that is a criterion for determining the abnormally stopped state is, for example, when nickel cermet is used as the fuel electrode of the cell stack 6 (fuel cell), this oxidation temperature is set to about 450 ° C., and the temperature of the cell stack 6 ( That is, when the temperature detection temperature of the temperature detection unit 62 is 450 ° C. or higher, the abnormal stop determination unit determines that the abnormal stop state is set as described later. The stop temperature that is the reference temperature for the end of the operation in the abnormal stop operation mode is a temperature at which the fuel electrode of the fuel cell does not oxidize or hardly occurs. When, for example, nickel cermet is used as the fuel electrode, this stop temperature is When the temperature of the cell stack 6 is set to about 300 to 450 ° C. and the temperature of the cell stack 6 decreases to the stop temperature during the operation in the abnormal stop operation mode, the operation in the abnormal stop operation mode is finished.

  Detection signals from the temperature detection means 62 and the first to third flow rate detection means 22, 32, 48 are sent to the control means 72, and the detection temperature of these detection means 22 and the first to third flow rate detection means 32, 48 are sent. , 62, the solid oxide fuel cell system 2 is controlled as shown in FIG.

  With reference to FIG. 3 together with FIG. 1 and FIG. 2, the control operation when an abnormal stop state occurs during the normal operation of the solid oxide fuel cell system 2 will be described. For example, the supply amount of the fuel gas supplied through the fuel gas supply line 14 due to a failure of the fuel pump 16 (detected flow rate of the first flow rate detection means 22) decreases abnormally (and / or, for example, the water pump 42 fails) Then, when the amount of reforming water supplied through the water supply line 48 (the detected flow rate of the third flow rate detecting means 48) is abnormally reduced), the control means 72 determines that an abnormal stop state has occurred, and step The process advances from step S1 to step S3 via step S2. On the other hand, when the operation of the system is stopped during the normal operation, the process proceeds from step S2 to step S4 through step S4, and the solid oxide fuel cell system 2 does not use the mixed liquid from the mixed liquid supply means 54. Stop operation as usual.

  When the abnormal stop state of the solid oxide fuel cell system 2 occurs and the process proceeds to step S3, the temperature of the cell stack 6 is detected. That is, the temperature detection unit 62 detects the temperature of the cell stack 6, and a detection signal from the temperature detection unit 62 is sent to the control unit 72. If the temperature detected by the temperature detection means 62 is equal to or higher than the oxidation temperature (for example, 450 ° C.), the process proceeds from step S6 to step S7, and the abnormal stop determination means 76 determines that the temperature is abnormally stopped. On the other hand, when the temperature detected by the temperature detecting means 62 is lower than the oxidation temperature, the control means 72 is in the form of a solid oxide because the fuel electrode of the cell stack 6 (a plurality of fuel cells) is not oxidized or hardly generated. The fuel cell system 2 is abnormally stopped (step S8). That is, the control means 72 stops the operation of the fuel pump 16, the water pump 42, and the air blower 30 without operating the mixed liquid pump 60.

  If it is determined in step S7 that the high temperature abnormal stop state has occurred, the abnormal stop operation mode setting unit 78 determines that the temperature of the cell stack 6 is high and oxidation of the combustion electrode proceeds. Based on this determination, an abnormal stop operation mode is set (step S9). Thus, the operation in the abnormal stop operation mode is performed, and the mixed solution supply means 54 operates to supply the mixed solution (mixed solution of methanol and water) (step S10). That is, the operation control means 74 operates the mixed liquid pump 60, and the mixed liquid in the mixed liquid tank 56 is supplied to the vaporization mixer 12 through the mixed liquid supply line 58. In this vaporization mixer 12, the methane in the mixed liquid is supplied. As the water is heated, water in the mixed solution is vaporized to become water vapor. Then, the heated methanol and steam are supplied to the reformer 4, in which the methanol is steam reformed to generate a reducing gas containing hydrogen, and the steam reformed reformed Gas (reducing gas) is fed to the fuel electrode side of the cell stack 6 (plural fuel cells) through the reformed fuel gas feed line 8.

  As described above, when the supply amount of the fuel gas is abnormally decreased (and / or the supply amount of the reforming water is abnormally decreased), the reformer 4 does not generate the reformed fuel gas, and the cell stack. There is a possibility that oxidation of the fuel electrode 6 will proceed, but the oxygen electrode side is reduced by supplying the mixed solution and feeding the steam reformed gas of methanol to the fuel electrode side of the cell stack 6 in this way. As a result, the progress of oxidation of the fuel electrode of the cell stack 6 can be suppressed.

  The operation of the mixed liquid pump 60 is performed until the temperature of the cell stack 6 (detected temperature of the temperature detecting means 62) is lowered to a stop temperature (a temperature set within a range of 300 to 450 ° C.). If it decreases to step S11, the process proceeds from step S11 to step S12, and the solid oxide fuel cell system 2 is abnormally stopped, assuming that oxidation of the fuel electrode of the cell stack 6 does not occur or hardly occurs. That is, the control means 72 stops the operation of the fuel pump 16, the water pump 42, the air blower 30, and the mixed liquid pump 60, and thus abnormally stops after the operation in the abnormal stop operation mode.

  In this embodiment, the fuel pump 16 and the water pump 42 are operated during the operation in the abnormal stop operation mode. However, during this operation, the liquid mixture supply means 54 supplies the liquid mixture. The pump 42 may be deactivated.

  Supply of the mixed liquid (mixed liquid of methanol and water) from the mixed liquid supply means 54 during the operation in the abnormal stop operation mode is performed by controlling the rotation speed of the mixed liquid pump 60 based on the temperature of the cell stack 6. It is desirable to adjust the amount. That is, it is preferable to increase the supply amount of the mixed liquid as the temperature of the cell stack 6 increases, and to decrease the supply amount of the mixed liquid as the temperature approaches the stop temperature. By adjusting the supply amount in this way, It is possible to effectively suppress the progress of oxidation of the fuel electrode of the cell stack 6 while suppressing the amount used. In this case, for example, a control map (not shown) indicating the relationship between the temperature of the cell stack 6 and the rotation speed of the mixed liquid pump 60 is registered in the memory means 80 of the control means 72, and mixing is performed based on this control map. The operation of the liquid pump 60 may be controlled.

  Further, during operation in the abnormal stop operation mode, instead of controlling the operation of the liquid mixture pump 60 based on the temperature of the cell stack 6, the operation of the liquid mixture 60 is controlled based on the output voltage of the cell stack 6. It can also be done. That is, the supply amount of the mixed liquid may be controlled by controlling the rotational speed of the mixed liquid pump so that the cell voltage per cell in the cell stack 6 is larger than 0.75 to 0.85 V. By controlling the cell voltage in this way, the fuel electrode side of the cell stack 6 is kept in a reduced state by the reformed gas by the mixed solution and the progress of oxidation is suppressed, and the cell stack 6 is used by using the minimum necessary mixed solution. It is possible to effectively suppress the progress of oxidation of the fuel electrode. In this case, for example, the cell stack 6 is provided with voltage detection means (not shown) for detecting the output voltage, and the control means 72 is provided with one fuel cell per cell (per cell) based on the detection voltage of this voltage detection output stage. And the unit output voltage calculation means for calculating the output voltage of the mixed liquid pump 60 may be controlled based on the output voltage per cell by the unit output voltage calculation means.

  In addition, although a mixture of methanol and water is used as the mixture supplied from the mixture supply means 54, a mixture of ethanol in addition to methanol and water may be used. By adding ethanol, an azeotropic point is formed, and there is no fear that only water will be formed, and the reducing gas can be reliably supplied to the fuel electrode side of the cell stack 6.

  In addition, when the air blower 30 continues to stop, if a mixed liquid is supplied, there is a possibility that the air electrode side of the cell stack 6 becomes a reducing atmosphere, and in that case, the air electrode is reduced and damaged. When supplying the mixed liquid, it is desirable to operate the air blower 30. Further, the operation of the air blower 30 has an advantage that the temperature of the cell stack 6 is rapidly reduced as compared with the case where the air blower 30 is not operated, and the degree of oxidation on the fuel electrode side is reduced.

  As mentioned above, although one embodiment of the solid oxide fuel cell system according to the present invention has been described, the present invention is not limited to this embodiment, and various modifications or corrections can be made without departing from the scope of the present invention. Is possible.

  For example, in the above-described embodiment, the vaporizer 12 and the reformer 4 are configured separately, but the present invention is not limited to such a configuration, and the vaporizer 12 and the vaporizer 4 are integrally configured. You may make it do.

  Further, for example, in the above-described embodiment, the vaporizer 12 is used as a mixer, and water used for reforming is vaporized in the vaporizer 12 to generate water vapor, and the generated water vapor and raw fuel gas are mixed. However, instead of such a configuration, a dedicated vaporizer for vaporizing water used for reforming is provided, and this water is vaporized in the vaporizer to generate water vapor, and the generated water vapor and raw fuel gas May be fed to a mixer, and in this mixer, water vapor and raw fuel gas may be mixed.

  In order to confirm the effect of the present invention, the following experiment was conducted. In this experiment, a solid oxide fuel cell system having the configuration shown in FIG. 1 was used, and its rated output was 700 W. Using solid city gas (13A gas) as the raw fuel gas, the solid oxide fuel cell system is operated for power generation at a rated output of 700 W, and the supply of the raw fuel gas is stopped at time “0” during the power generation operation. The abnormal stop state is generated and the operation of the abnormal stop operation mode is performed. The temperature of the cell stack during the operation of the abnormal stop operation mode, the transition of the average cell voltage (output voltage per cell), and the mixed liquid (methanol and The change state of the added amount of the mixed solution with water was examined, and the result was as shown in FIG.

  In this experiment, city gas was supplied to the vaporization mixer under the condition of water vapor / carbon molar ratio = 2.5 to generate 700 W (power transmission end) of the rated output. At time “0”, the operation is switched to the supply cutoff operation of the raw fuel gas (city gas). Even after the raw fuel gas was shut off, the air was continuously supplied at 50 NL / min. When the voltage of the fuel cell (voltage per cell) dropped below 0.85V, the supply of the liquid mixture was started, and when the voltage exceeded 0.85V, the supply of the liquid mixture was stopped. Regarding the supply of the mixed liquid, the maximum flow rate was set to 0.4 cc / min. The mixing ratio of methanol and water in the mixed solution was 33% methanol and 66% water by weight. When the temperature of the cell stack dropped to 450 ° C., the mixed solution was not supplied, and the temperature dropped as it was. After the supply of the raw fuel gas was shut off and the abnormal stop was repeated five times as described above, the performance degradation of the cell stack was examined, but there was no performance degradation. In addition, when this abnormal stop was performed, the usage-amount of the liquid mixture was as little as 20 cc per stop.

From FIG. 4, the following became clear. That is, if the voltage / temperature characteristics can be grasped, the cell stack is not controlled by incorporating the relationship between the temperature shown in FIG. It was found that the amount of the mixed solution added could be adjusted in relation to the temperature of

Claims (5)

A reformer for steam reforming the raw fuel gas, and a plurality of fuel cells for generating power by oxidation and reduction of the reformed fuel gas and the oxidizing material reformed by the reformer A cell stack, a fuel pump for supplying raw fuel gas to the reformer, a water pump for supplying reformed water to the reformer, and a mixture of methanol and water in the reformer A solid oxide fuel cell system comprising: a mixed liquid pump for supplying; and a control means for controlling the fuel pump, the water pump, and the mixed liquid pump,
The control means is configured to set an abnormal stop operation mode for setting an abnormal stop operation mode for abnormal stop while suppressing oxidation of the fuel electrode of the fuel cell, and an abnormal stop determination means for determining that the high-temperature abnormal stop state is present. And the abnormal stop determination means is configured such that the supply amount of raw fuel gas from the fuel pump and / or the supply amount of reforming water from the water pump is abnormally reduced and the temperature of the cell stack is When the temperature of the fuel cell is higher than the oxidation temperature at which oxidation of the fuel electrode occurs, it is determined as a high temperature abnormal stop state, and the abnormal stop operation mode setting means is abnormally stopped when the abnormal stop determination means is determined as a high temperature abnormal stop state An operation mode is set, and in the abnormal stop operation mode, the control means operates the mixed liquid pump to supply the mixed liquid to the reformer. Solid oxide fuel cell system that. When the temperature of the cell stack is lowered to a stop temperature lower than the oxidation temperature in the abnormal stop operation mode, the control unit cancels the abnormal stop operation mode and stops the operation of the liquid mixture pump. The solid oxide fuel cell system according to claim 1. In the abnormal stop operation mode, the control means controls the operation of the liquid mixture pump based on the temperature of the cell stack to adjust the supply amount of the liquid mixture supplied to the reformer. The solid oxide fuel cell system according to claim 1 or 2. In the abnormal stop operation mode, the control means maintains a cell voltage per cell in the cell stack of 0 in order to keep the fuel electrode of the fuel cell in a reduced state while suppressing the supply flow rate of the mixed solution. 3. The solid according to claim 1, wherein the supply amount of the liquid mixture supplied to the reformer is adjusted by controlling the operation of the liquid mixture pump so as to be greater than .75 to 0.85 V. Oxide fuel cell system. The solid oxide fuel cell system according to any one of claims 1 to 4, wherein the mixed solution contains ethanol in addition to the methanol and water.

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