JP5336818B2 - Solid oxide fuel cell system - Google Patents

Description

  The present invention relates to a reformed fuel gas obtained by reforming a raw fuel gas and a solid oxide fuel cell system that generates power by oxidizing and reducing an oxidant.

  Conventionally, there is known a solid oxide fuel cell in which a fuel cell using a solid electrolyte as a membrane for conducting oxide ions is housed in a housing container. In this solid oxide fuel cell, zirconia doped with yttria is generally used as a solid electrolyte, and a fuel electrode for oxidizing fuel gas is provided on one side of the solid electrolyte, and the other On the side, an oxygen electrode for reducing oxygen in the air (oxidant) is provided (see, for example, Patent Document 1). The operating temperature of a solid oxide fuel cell (fuel cell) is relatively high at about 700 to 1000 ° C. Under such high temperatures, hydrogen, carbon monoxide, hydrocarbons in fuel gas and oxygen in air Electricity is generated by causing an electrochemical reaction.

  Such a solid oxide fuel cell has been developed as a promising power generation technology because it can generate power with higher power generation efficiency than other fuel cell systems and gas engines. In particular, since high power generation efficiency can be obtained even in a low power generation output region of 1 kW or less, development is being promoted aiming at practical use as a home cogeneration system.

  On the one hand, the durability for 10 years is required for home equipment for home use. A solid oxide fuel cell (fuel cell) has a high power generation temperature of 700 ° C or higher, and an electrode material with high performance as a fuel cell is used. Ferrite stainless steel is used as a stack material due to cost constraints. As a result, deterioration due to the reaction between the electrode material and the electrolyte material, deterioration due to the progress and poisoning of the electrode material, and the progress of oxidation deterioration of the stainless steel occur. When the generated voltage decreases due to the increase in internal resistance, and the deterioration becomes large, the lifetime is reached.

JP 2008-159362 A

  Since this solid oxide fuel cell (fuel cell stack) is operated at a temperature as high as about 750 ° C., it is surrounded by a casing and a heat insulating material. Then, piping materials and bolts may be burned out. For this reason, it is difficult to replace the solid oxide fuel cell (fuel cell stack) at the installation site (for example, a detached house) in terms of both technical and cost. For example, it is desired to realize a fuel cell system that does not require replacement of a solid oxide fuel cell over 10 years.

  Moreover, in such a household cogeneration system using a solid oxide fuel cell, the solid oxide fuel cell is operated and controlled so as to generate electric power following a household electrical load. For operation, it is necessary to satisfy desired durability, and it is also important to make it difficult to cause variations in the life of the solid oxide fuel cell. Therefore, it is necessary to consider not only countermeasures for deterioration of materials such as electrode materials that cause deterioration of the solid oxide fuel cell, but also countermeasures for extending the life of the fuel cell system as a whole and for suppressing variations in the life.

  In a fuel cell system using such a solid oxide fuel cell, generally, the operating temperature of the solid oxide fuel cell (fuel cell) is set to an upper limit temperature (for example, 700 to 800 ° C.), Even if the deterioration progresses, the upper limit temperature is controlled so as not to exceed the upper limit temperature. The control increases the flow rate of air supplied by the blower or the supply amount of the raw fuel gas supplied by the fuel supply control valve. It is performed by decreasing (and thereby reducing the power generation output).

When the power generation output of the solid oxide fuel cell is kept constant, if the power generation voltage decreases by 10% due to the deterioration, the heat generation (joule heat generation) of the solid oxide fuel cell increases by about 25 to 30%. In order to suppress the deterioration, for example, the air flow rate by the blower means is increased in order to perform cooling for this increase in heat generation.

  However, when the air flow rate is increased for cooling, not only the high temperature portion (for example, the central portion) of the solid oxide fuel cell (fuel cell stack) but also the low temperature portion (for example, both end portions) is cooled, As a result, the temperature distribution of the solid oxide fuel cell is expanded, and as a result, the problem that the power generation performance becomes lower than the deterioration level of the original solid oxide fuel cell is likely to occur. Further, when the air flow rate is increased for cooling, problems such as an increase in power consumption of the blower means (for example, a blower blower) and an increase in operating noise of the blower means arise. For this reason, at the deterioration stage when the power generation voltage is reduced by about 10%, the effect of energy saving and economic efficiency of the installation site is lost due to the decrease in the power generation efficiency of the fuel cell, rather than the blower means (the blower blower). It becomes an operational limit that the cooling due to the increase in flow rate) cannot be properly performed.

  An object of the present invention is to provide a solid oxide fuel cell system that can be stably operated over a long period of time.

The solid oxide fuel cell system according to claim 1 of the present invention includes a reformer for reforming a raw fuel gas, a reformed fuel gas reformed by the reformer, and an oxidizing material. A solid oxide fuel cell that generates power by oxidation and reduction; a blowing means for supplying an oxidant to the solid oxide fuel cell; and a supply amount of raw fuel gas supplied to the reformer. A solid oxide fuel cell system comprising: a fuel supply control valve for controlling; and a control means for controlling the blower means and the fuel supply control valve,
The apparatus further comprises operating temperature detecting means for detecting an operating temperature of the solid oxide fuel cell, and the control means includes limit temperature setting means for setting a limit temperature of operation of the solid oxide fuel cell; A time counting means for measuring a cumulative operating time from the start of operation of the solid oxide fuel cell ,
An upper limit temperature is set as an upper limit of the operating temperature of the solid oxide fuel cell, the operation is performed in the first operation mode until the limit temperature by the limit temperature setting means reaches the upper limit temperature, and the limit temperature is set to the upper limit temperature. After reaching the temperature, it is operated in the second operation mode,
In the first operation mode, the limit temperature setting means sets the limit temperature to be higher as the cumulative operation time by the time counting means becomes longer, and the control means detects the operating temperature detection means. The blowing means and / or the fuel supply valve are controlled so that the temperature does not exceed the limit temperature. In the second operation mode, the control means detects the operating temperature detecting means so that the detected temperature is the upper limit temperature. The air blowing means and / or the fuel supply valve are controlled so as not to exceed .

Note that the temperature measured by the operating temperature detection means may be any temperature that is linked to the temperature of the solid oxide fuel cell itself, and there is a difference of several tens of degrees Celsius or more from the temperature of the solid oxide fuel cell itself. Also good.

In the solid oxide fuel cell system according to claim 2 of the present invention, the operation period in the first operation mode is 0.3 to 0.6 times the design life time of the solid oxide fuel cell. It is characterized by that.

  In the solid oxide fuel cell system according to claim 3 of the present invention, the initial limit temperature of the solid oxide fuel cell is 30 to 100 ° C. lower than the upper limit temperature.

  Furthermore, in the solid oxide fuel cell system according to claim 4 of the present invention, the upper limit temperature and the initial limit temperature of the solid oxide fuel cell are the upper limit temperature and the initial limit temperature, respectively. It is characterized in that the voltage difference of the solid oxide fuel cell is set to 5 to 20% when power is generated with a direct current value at a rated output in an initial state.

  According to the solid oxide fuel cell system of the first aspect of the present invention, the limit temperature for operation of the solid oxide fuel cell is increased as the cumulative operating time of the solid oxide fuel cell is increased. One of the characteristics is to set. Degradation of the solid oxide fuel cell appears as an increase in operating temperature. In general, when the generated voltage at the same generated current as the initial operating conditions decreases, the heat generation of the solid oxide fuel cell (fuel cell stack) increases, and when the cooling conditions such as the air flow rate are constant, the operating temperature is reduced. To rise. When the temperature rises in this way, the internal resistance of the solid oxide fuel cell becomes smaller, thereby increasing the power generation voltage. As a result, the solid oxide fuel cell generates more heat than before the temperature rise. It will decrease and settle down to a higher operating temperature than before the deterioration. That is, in this solid oxide fuel cell, the deterioration appears as an increase in operating temperature. When this temperature increase is within a predetermined range, that is, within a range not exceeding the upper limit temperature, the solid oxide fuel cell is deteriorated. As it progresses, it is not necessary to increase the cooling in order to suppress the increase in operating temperature. This characteristic is used, and the degree of deterioration due to the accumulated operating time is allowed to increase in operating temperature, and the limit temperature of the operating temperature is increased along with the accumulated power generation time.

In this solid oxide fuel cell system, an upper limit temperature is set as the upper limit of the operating temperature of the solid oxide fuel cell, and the system is operated in the first operation mode until the limit temperature by the limit temperature setting means reaches the upper limit temperature. After the limit temperature reaches the upper limit temperature, the operation is performed in the second operation mode. By switching the operation mode at the upper limit temperature as described above, the solid oxide fuel cell system can be stably operated over a long period of time. Can be made. In the first operation mode, the limit temperature setting means sets the limit temperature to be higher as the cumulative operation time becomes longer, and the control means sets the blowing means (and / or the fuel supply so as not to exceed the limit temperature). Therefore, the solid oxide fuel cell can be operated while allowing the operating temperature to rise, thereby suppressing the progress of the deterioration. In the second operation mode, the upper limit temperature is set, and the control unit controls the blower unit (and / or the fuel supply valve) so as not to exceed the upper limit temperature. It can be operated while suppressing rapid progress.

  In addition, stainless steel is used as a stack material for solid oxide fuel cells, and the degree of oxidative deterioration of stainless steel, that is, the oxidation progress rate (in other words, the deterioration rate) is strongly dependent on temperature. The temperature history of the solid oxide fuel cell (fuel cell stack) is directly related to the deterioration rate. If this deterioration rate is large due to the condition of the power load at the installation site or the manufacturing variation of the solid oxide fuel cell system, the operating temperature will rise quickly. Therefore, in solid oxide fuel cells with a high deterioration rate, the operating temperature also rises quickly, and this tends to cause further deterioration. As described above, control is performed so as not to exceed the limit temperature set by the cumulative operation time. By doing so, it is possible to manage the variation in the life of the solid oxide fuel cell.

In the solid oxide fuel cell system according to claim 2 of the present invention, the operation period in the first operation mode is 0.3 to 0.6 times the design life time of the solid oxide fuel cell. By setting in this way, the lifetime of the solid oxide fuel cell system can be extended.

  In the solid oxide fuel cell system according to claim 3 of the present invention, the initial limit temperature of the solid oxide fuel cell is set to 30 to 100 ° C. lower than the upper limit temperature. In addition, the lifetime of the solid oxide fuel cell can be extended while taking into consideration the efficient generated power.

  Furthermore, in the solid oxide fuel cell system according to claim 4 of the present invention, the upper limit temperature and the initial limit temperature of the solid oxide fuel cell are in the initial state with the upper limit temperature and the initial limit temperature. The voltage difference of the solid oxide fuel cell when it is generated at the DC current value when obtaining the rated output is set to 5 to 20%, and the voltage change due to these temperatures (that is, the power is generated at a constant current) In this range, the life of the solid oxide fuel cell can be extended while taking into account efficient generated power.

  Hereinafter, an embodiment of a solid oxide fuel cell system according to the present invention will be described with reference to the accompanying drawings. 1 is a cross-sectional view schematically illustrating a solid oxide fuel cell system according to an embodiment, and FIG. 2 is a block diagram illustrating a control system of the solid oxide fuel cell system of FIG. FIG. 4 is a diagram showing the relationship between the generated current and the generated voltage when the operating temperature of the solid oxide fuel cell changes, and FIG. 4 shows the control by the control system of the solid oxide fuel cell system of FIG. FIG. 5 is a flowchart showing a flow of operation in the first operation mode in the flowchart of FIG. 4, and FIG. 6 is a flowchart showing a flow of operation in the second operation mode in the flowchart of FIG. .

  In FIG. 1, the illustrated solid oxide fuel cell system 2 includes a reformer 4 for reforming raw fuel gas (for example, natural gas, city gas) as raw fuel, and a reformer 4. A solid oxide fuel cell 6 that generates electric power by oxidizing and reducing the reformed reformed fuel gas and air as an oxidant; and a blowing means 8 for supplying air to the solid oxide fuel cell 6 It is equipped with.

  The solid oxide fuel cell 6 includes a fuel cell main body 12 and a fuel cell stack 14 in which a plurality of solid oxide fuel cells for generating electric power by electrochemical reaction are arranged. The fuel cell main body 12 includes a shielding wall 16. A high temperature space 18 is defined inside the shielding wall 16, and the fuel cell stack 14 is disposed in the high temperature space 18. The solid oxide fuel cell includes a solid electrolyte 20 that conducts oxygen ions, a fuel electrode (not shown) provided on one side of the solid electrolyte 20, and an oxygen electrode provided on the other side of the solid electrolyte 20. (Not shown) and, for example, zirconia doped with yttria is used as the solid electrolyte 20. Further, an operating temperature detecting means 22 for detecting the operating temperature of the solid oxide fuel cell 6 (specifically, the fuel cell stack 14), and the solid oxide fuel cell 6 (specifically, the fuel cell). A power measuring means 24 (see FIG. 2) for measuring the power generation output of the stack 14) is provided.

  The introduction side of the fuel electrode side 26 of the fuel cell stack 14 is connected to the reformer 4 via a reformed fuel gas supply line 28, and the reformer 4 is connected to the raw material via a raw fuel gas supply line 30. It is connected to a raw fuel gas supply source 32 (for example, a buried pipe or a storage tank) for supplying fuel gas. The raw fuel gas supply line 30 is provided with a fuel supply control valve 34 for controlling the supply amount of the raw fuel gas. The fuel supply control valve 34 is configured to supply the raw fuel gas to the reformer 4. Control the amount of feed.

  The introduction side of the oxygen electrode side 36 of the fuel cell stack 14 is connected to an air preheater 40 for preheating air via an air supply line 38, and the air preheater 40 is connected to an air supply line 42. It is connected to the air blowing means 8 via. The feeding means 8 is composed of, for example, a feeding blower, and the amount of air supplied through the air supply line 38 is controlled by controlling the rotational speed of the feeding blower.

  A combustion chamber 44 is provided on each discharge side of the fuel electrode stack 26 and the oxygen electrode side 36 of the fuel cell stack 14, and the reaction fuel gas (including residual fuel gas) discharged from the fuel electrode side 26 and the oxygen electrode side 36. The air (including oxygen) discharged from the air is supplied to the combustion chamber 44 and burned. The combustion chamber 44 is connected to an air preheater 40 through an exhaust gas supply line 46, and an exhaust gas discharge line 48 is connected to the air preheater 40.

  Further, in the solid oxide fuel cell system 2, a water supply line 50 for supplying reforming water to the reformer 4 is connected, and the water supply line 50 is connected to a water supply source 52 (for example, a water tank). )It is connected to the. A water supply control valve 54 is disposed in the water supply line 50, and the water supply control valve 54 controls the amount of reforming water supplied to the reformer 4 through the water supply line 50. Such reformed water may be obtained by condensing and recovering water vapor contained in the exhaust gas discharged from the combustion chamber 44, and using the recovered condensed water. May be supplied.

  The operation of the solid oxide fuel cell system 2 is controlled by a control unit 56 including, for example, a microprocessor. Referring mainly to FIG. 2, the illustrated control means 56 includes an operation control means 58, an operation mode switching means 60, a limit temperature reading means 62, a limit temperature setting means 64, a limit temperature determination means 66, and an upper limit temperature determination means 68. Contains. The operation control means 58 controls the solid oxide fuel cell 6, the air blowing means 8, the fuel supply control valve 34 and the like as will be described later, and the limit temperature reading means 62 reads the limit temperature as will be described later. The setting unit 64 sets the limit temperature read by the limit temperature reading unit 62 as a limit temperature for controlling the solid oxide fuel cell 6. Further, the operation mode switching means 60 is set when the limit temperature set by the limit temperature setting means 64 reaches the upper limit temperature (the upper limit operating temperature set to suppress the progress of deterioration of the solid oxide fuel cell). The operation is switched from the operation in the first operation mode to the operation in the second operation mode. Further, the limit temperature determination means 66 compares the detected temperature of the operating temperature detection means 22 with the limit temperature set by the limit temperature setting means 64 during operation in the first operation mode, and the detected temperature exceeds the limit temperature. The upper limit temperature determining means 68 determines whether the detected temperature exceeds the upper limit temperature by comparing the detected temperature of the operating temperature detecting means 22 with the upper limit temperature during the operation in the second operation mode. .

  The control means 56 further includes a time measuring means 70, an integrated time measuring means 72 and a storage means 74. The time measuring means 70 measures the time, and the time counting means 72 counts the cumulative operating time in which the solid oxide fuel cell system 2 (specifically, the solid oxide fuel cell 6) has been operated. The storage means 74 stores switching time data, a limit temperature map, limit temperature data, upper limit temperature data, and the like. The switching time data is a switching time when switching from the operation in the first operation mode to the operation in the second operation mode, and the limit temperature set by the limit temperature setting means 64 when the switching time is reached is the upper limit. It reaches the temperature. In the limit temperature map, the relationship between the accumulated time (that is, cumulative operating time) and the limit temperature is registered as a map, and when the cumulative operating period (cumulative operating time) reaches a predetermined time, the limit temperature reading means 62 The limit temperature corresponding to the predetermined time is read from the limit temperature map, the limit temperature setting means 64 sets the read limit temperature as a new limit temperature, and the set limit temperature is stored in the storage means 74 as limit temperature data. Is done. The upper limit temperature data is data related to the upper limit temperature used in the operation in the second operation mode, and a temperature of 700 to 850 ° C., for example, 800 ° C. is set as the upper limit temperature.

  The relationship between the integrated time set in the limit temperature map and the limit temperature is set so that the limit temperature increases as the cumulative operation time from the start of operation of the solid oxide fuel cell 6 becomes longer. By setting, the operating temperature of the solid oxide fuel cell is allowed to rise as the cumulative operation time becomes longer, and thereby, the solid oxide fuel cell 6 is increased without increasing the blowing amount of the feeding means 8. It becomes possible to suppress the progress of deterioration of the (fuel cell stack 14).

  In this solid oxide fuel cell system 2, it is desirable that the limit temperature at the initial operation of the solid oxide fuel cell 6 is set to a temperature 30 to 100 ° C., for example, 50 ° C. lower than the upper limit temperature, for example 700 ° C. The temperature range between the limit temperature and the upper limit temperature in the initial stage of operation is the allowable range for the temperature rise accompanying the deterioration of the solid oxide fuel cell 6. If this allowable range is small, that is, if the difference between the limit temperature and the upper limit temperature in the initial stage of operation is small, the time until the limit temperature reaches the upper limit temperature with the deterioration of the solid oxide fuel cell 6 is shortened. If the life of the fuel cell is shortened and this allowable range is large, that is, if the difference between the limit temperature and the upper limit temperature in the initial stage of operation is large, the power generation efficiency in the initial stage of operation of the solid oxide fuel cell is lowered. The power generation efficiency of the entire system is reduced.

  Further, in relation to the temperature difference between the limit temperature and the upper limit temperature in the initial stage of operation, the generated voltage (so-called stack voltage) of the solid oxide fuel cell 6 (specifically, the fuel cell stack 14) is reduced. It is desirable to set the temperature limit at the beginning of operation so that the voltage difference is 5 to 20%. The stack power generation characteristics (relationship between generated current and generated voltage) of the fuel cell stack 14 of the solid oxide fuel cell 6 are temperature dependent. For example, the fuel cell stack 14 is installed in an electric furnace, By controlling the temperature, the stack power generation characteristics can be obtained. FIG. 3 shows the stack power generation characteristics of the fuel cell stack 14, and a solid line A represents a generated current and a generated voltage when the fuel cell stack 14 is operated at the initial operating temperature limit temperature and at the rated output. The solid line B shows the relationship between the generated current and the generated voltage when the fuel cell stack 14 is operated at the upper limit temperature and the rated output in the initial state. In FIG. In order to generate the fuel cell DC current value at the output (current value b in FIG. 3), the stack voltage difference, that is, the power generation voltage difference at the current value b in FIG. A limit temperature and an upper limit temperature are set, and by setting in this way, it is possible to extend the life of the solid oxide fuel cell 6 while suppressing a decrease in power generation efficiency.

  Note that at the initial operation start time of the solid oxide fuel cell, the operating temperature during rated power generation should be the same as the initial limit temperature (for example, 750 ° C.) or within a range of about 5 to 10 ° C. desirable. The temperature limit at the time of initial rated power generation is determined by the balance between heat generation and heat dissipation in the solid oxide fuel cell system 2 and the influence of outside air temperature. When generating the same power output, the solid oxide fuel When the number of fuel cell stacks in the fuel cell stack 14 of the battery 6 is increased, the operating temperature at the initial rated power generation decreases, and when the number of stacks is decreased, the operating temperature at the initial rated power generation increases. Therefore, at the initial stage of power generation, the number of fuel cells stacked in the fuel cell stack 14 is set so that the operating temperature during rated power generation is the same as the initial limit temperature or about 5 to 10 ° C. Will be set.

  The operation of the solid oxide fuel cell system 2 is performed as follows. The raw fuel gas from the raw fuel gas supply source 32 is supplied to the reformer 4 through the raw fuel gas supply line 30, and the water from the water supply source 52 is supplied to the reformer 4 through the water supply line 50. The In the reformer 4, part of the raw fuel gas and water are reformed and reformed, and the reformed fuel gas reformed in this way passes through the reformed fuel gas supply line 28 and is a fuel cell stack. 14 to the fuel electrode side 26. Further, the air from the blower 8 is supplied to the air preheater 40 through the air supply line 42, heat is exchanged with the exhaust gas in the air preheater 40 and heated, and then the air supply line 38. To the oxygen electrode side 36 of the fuel cell stack 14.

  The fuel electrode side 26 of the fuel cell stack 14 oxidizes the reformed reformed fuel gas, and its oxygen electrode side 36 reduces oxygen in the air, oxidation on the fuel electrode side 26 and reduction on the oxygen electrode side 36. Electricity is generated by an electrochemical reaction. The power generation output of the solid oxide fuel cell 6 is adjusted by adjusting the opening of the fuel supply control valve 34 by the operation control means 58. That is, the generated current of the solid oxide fuel cell 6 and the supply flow rate of the raw fuel gas are linked, and when the generated current is reduced, the fuel supply control valve 34 also reduces the supply flow rate of the raw fuel gas. Controlled.

  The reaction fuel gas from the fuel electrode side 26 and the air from the oxygen electrode side 36 are fed to the combustion chamber 44, and excess fuel gas is burned using oxygen in the air. Exhaust gas from the combustion chamber 44 is supplied to the air preheater 40 through the exhaust gas supply line 46, and is used for heat exchange with the air from the blower 8 in the air preheater 40 and passes through the exhaust gas discharge line 48. It is discharged outside.

  Next, the operation control of the solid oxide fuel cell system 2 described above will be described with reference to FIGS. When the solid oxide fuel cell 2 is operated (step S1), the integrated operation time (cumulative operation time) measured by the integrated time measuring means 72 has reached the switching time, in other words, the limit temperature has reached the upper limit temperature. Is determined (step S2).

  If the accumulated operation time of the fuel cell system 2 has not reached this switching time, the process proceeds from step S2 to step S3, and the solid oxide fuel cell system 2 is operated in the first operation mode as described later (step S3). ), The operation in the first operation mode is continued until this operation ends (step S4). Then, during the operation in the first operation mode, when the accumulated operation time reaches the switching time (in other words, the limit temperature reaches the upper limit temperature), the process proceeds from step S2 to step S5.

  In addition, when the accumulated operation time reaches the switching time and moves to step S2 to step S5, the operation mode switching means 60 switches from the operation in the first operation mode to the operation in the second operation mode, and the solid oxide fuel cell system In No. 2, the operation in the second operation mode is performed as described later, and the operation in the second operation mode is continuously performed until the operation is completed (step S6).

  In the operation in the first operation mode, the operation is controlled using the limit temperature set by the limit temperature setting means 64. Referring to FIG. 5 together with FIGS. 1 and 2, in the operation in the first operation mode, the operating temperature of the solid oxide fuel cell 6 (fuel cell stack 14) is detected by the operating temperature detecting means 22 (step) In step S3-1, a determination is made between the detected temperature and the limit temperature set by the limit temperature setting means 64 (step S3-2).

  When the limit temperature determination unit 66 determines that the temperature detected by the operation temperature detection unit 22 exceeds the limit temperature, the process proceeds from step S3-3 to step S3-4, and the operation control unit 58 performs the blower unit 8 (air blower). Increase the rotation speed of the blower. As a result, the amount of air blown to the solid oxide fuel cell 6 is increased, thereby enhancing the cooling effect of the air and reducing the limit temperature of the solid oxide fuel cell 6 (fuel cell stack 14). Exceeding temperature rise is suppressed.

  Further, when the limit temperature determination unit 66 determines that the temperature detected by the operating temperature detection unit 22 is equal to or lower than the limit temperature, the process proceeds from step S3-3 to step S3-5, and the amount of air blown by the blower unit 8 is normal. It is determined whether the air flow rate is normal, and when the air flow rate is normal, the rotational speed of the air blowing means 8 is maintained (the air flow rate is maintained) (step S3-6), and is not a normal air flow rate. Then, when it is larger than the normal air blowing amount, the rotational speed of the air blowing means 8 is lowered and the air blowing amount is reduced (step S3-7).

  Thereafter, when the process proceeds to step S3-8, it is determined whether or not the accumulated operation time by the accumulated time measuring means 72 has reached the next rank (step S3-8), and step S4 is performed until this accumulated operation time (cumulative operation time) is ranked up. Proceed to On the other hand, when the accumulated operation time is ranked up, the process proceeds from step S3-8 to step S3-9, and the limit temperature reading means 62 is limited to the accumulated operation time ranked up from the limit temperature map stored in the storage means 72. The temperature is read, and the limit temperature setting means 64 sets the read limit temperature as a new limit temperature (step S3-10), and the above-described operation control of the solid oxide fuel cell 6 is performed using this new limit temperature. Is called.

  In this embodiment, when the temperature detected by the operating temperature detecting means 22 exceeds the above limit temperature, the rotational speed of the air blowing means 8 (air blowing blower) is increased to increase the amount of air flow to increase the solid oxide fuel cell 6. Although the temperature rise of the (fuel cell stack 14) is suppressed, instead of such control, or in addition to such control, the fuel supply control valve 34 is controlled to be supplied to the reformer 4. The supply amount of the fuel gas is reduced to suppress the generated current of the solid oxide fuel cell 6, and the increase in the temperature of the solid oxide fuel cell 6 (fuel cell stack 14) is suppressed by the decrease in the generated current. Also good.

  In the operation in the second operation mode, the operation is controlled using the upper limit temperature registered in the storage unit 74. Referring to FIG. 6 together with FIG. 1 and FIG. 2, in the operation in the second operation mode, the operating temperature of the solid oxide fuel cell 6 (fuel cell stack 14) is detected by the operating temperature detecting means 22 (step) S5-1), the detected temperature and the upper limit temperature stored in the storage means 74 are determined (step S5-2).

  When the upper limit temperature determination unit 68 determines that the temperature detected by the operating temperature detection unit 22 exceeds the upper limit temperature, the process proceeds from step S5-3 to step S5-4. The rotational speed of the blower is increased, whereby the air cooling action is enhanced in the same manner as described above, and the temperature rise exceeding the upper limit temperature of the solid oxide fuel cell 6 (fuel cell stack 14) is suppressed.

  On the other hand, when the upper limit temperature determination means 68 determines that the temperature detected by the operating temperature detection means 22 is equal to or lower than the above limit temperature, the process proceeds from step S5-3 to step S5-5. It is determined whether the air flow rate is normal, and if it is a normal air flow rate, the rotation speed of the air blowing means 8 is maintained (the air flow rate is maintained) (step S5-6), and it is not a normal air flow rate. Then, when it is larger than the normal air flow rate, the rotational speed of the air blowing means 8 is decreased, the air flow rate is reduced (step S5-7), and then the process proceeds to step S6 (see FIG. 4).

  In this embodiment, when the temperature detected by the operating temperature detecting means 22 exceeds the upper limit temperature, the rotational speed of the air blowing means 8 (air blowing blower) is increased to increase the air flow rate, thereby increasing the solid oxide fuel cell 6. Although the temperature rise exceeding the upper limit temperature of the (fuel cell stack 14) is suppressed, the fuel supply control valve 34 is controlled to the reformer 4 in place of or in addition to such control. The supply amount of the supplied raw fuel gas is reduced to suppress the generated current of the solid oxide fuel cell 6, and the upper limit temperature of the solid oxide fuel cell 6 (fuel cell stack 14) is reduced by reducing the generated current. You may make it suppress the temperature rise which exceeds.

  Although one embodiment of the solid oxide fuel cell system according to the present invention has been described above, the present invention is not limited to such an embodiment, and various changes or modifications can be made without departing from the scope of the present invention. It is.

  For example, in the above-described embodiment, the limit temperature map is registered in the storage unit 74, and when the cumulative operating time of the solid oxide fuel cell reaches a predetermined switching time, the upper limit temperature corresponding to the switching time is read and set. However, it can replace with such a structure and can be comprised as follows. For example, a limiting temperature calculation unit is used in place of the limiting temperature reading unit 62, and a calculation formula for the limiting temperature set in the storage unit 74, for example, a proportional calculation formula in which the limiting temperature rises proportionally as the cumulative operating time increases. The limit temperature stored and calculated by the limit temperature calculation means may be set by the limit temperature setting means 64.

[Examples and Comparative Examples]
First, as a comparative example, an operation experiment was performed using a solid oxide fuel cell system having the configuration shown in FIG. The rated power output of the solid oxide fuel cell was 700 W, and it was operated to maintain the rated power output even after the solid oxide fuel cell deteriorated. In the solid oxide fuel cell used in this comparative example, the number of fuel cells in the fuel cell stack was 50. The air flow rate was adjusted from the beginning of operation to control the temperature of the solid oxide fuel cell (near the fuel cell stack) at about 800 ° C.

  Changes in the operating temperature of the solid oxide fuel cell (fuel cell stack), its DC power generation efficiency, and air supply flow rate with respect to the operating time when operating at the rated power output from the beginning of operation. Measured. FIG. 7A shows the transition of the operating temperature in the comparative example, and FIG. 7B shows the DC power generation efficiency and the air supply flow rate in the comparative example.

  Next, as Example 1, an operation experiment was performed using a solid oxide fuel cell system having the same form as that of the comparative example. The rated power output of the solid oxide fuel cell was 700 W, and it was operated to maintain the rated power output even after the solid oxide fuel cell deteriorated. The number of fuel cells in the fuel cell stack was 50 in the comparative example, but in this Example 1, the number of fuel cells was increased to 70. In Example 1, power generation was started from the reduced operating temperature (around 750 ° C. decreased by about 50 ° C.) by increasing the number of fuel cells to 70 with the same rated power generation output and the same air supply flow rate as the comparative example. .

  Changes in the operating temperature of the solid oxide fuel cell (fuel cell stack), its DC power generation efficiency, and air supply flow rate with respect to the operating time when operating at the rated power output from the beginning of operation. Measured. FIG. 8A shows the transition of the operating temperature in the first embodiment, and FIG. 8B shows the DC power generation efficiency and the air supply flow rate in the first embodiment.

  As can be understood from FIGS. 7 and 8, in the comparative example, the power generation efficiency greatly decreases soon after the operation, and the air supply flow rate by the blowing means reaches the upper limit (120 NL / min) when about 6500 hours have elapsed. The operation of the rated power output can no longer be maintained. On the other hand, in Example 1, the decrease in power generation efficiency was small until the operating temperature of the solid oxide fuel cell reached about 800 ° C., and there was no increase in the air supply flow rate by the blowing means, and about 13500 hours passed. At the time, the air supply flow rate by the air blowing means reaches the upper limit (120 NL / min), and the operation of the rated power output of the cumulative operating time is about twice as long as the number of fuel cells is increased by 40% compared to the comparative example. Was possible.

  Next, as Example 2, an operation experiment was performed using a solid oxide fuel cell system having the same form as that of the comparative example. The rated power output of the solid oxide fuel cell was 700 W, and it was operated to maintain the rated power output even after the solid oxide fuel cell deteriorated. As in Example 1, the number of fuel cells in the fuel cell stack was 70. In the second embodiment, compared with the comparative example and the first embodiment, the specification has a voltage drop rate of 1.5 times (in other words, a deterioration rate of 1.5 times) at the same operating temperature and the same generated current. A solid product fuel cell containing a fuel cell stack was used. This operation experiment of Example 2 was performed in order to grasp the influence of the variation in the manufacture of the solid oxide fuel cell. Like Example 1, the same rated power output and the same air as in the comparative example were used. Electric power generation was started from the reduced operating temperature (around 750 ° C., which was reduced by about 50 ° C.) by increasing the number of fuel cells to 70 at the feed flow rate.

  Changes in the operating temperature of the solid oxide fuel cell (fuel cell stack), its DC power generation efficiency, and air supply flow rate with respect to the operating time when operating at the rated power output from the beginning of operation. Measured. FIG. 9A shows the transition of the operating temperature in Example 2, and FIG. 9B shows the DC power generation efficiency and the air supply flow rate in Example 2. In Example 2, as in Example 1, the decrease in power generation efficiency is small until the operating temperature of the solid oxide fuel cell reaches about 800 ° C., and there is no increase in the air supply flow rate by the blowing means. Although the voltage drop rate (deterioration rate) is 1.5 times that of the comparative example, the air supply flow rate by the blowing means reaches the upper limit (120 NL / min) when about 9000 hours have passed. Compared to the above, it was possible to operate at the rated power output with a cumulative operating time of about 1.5 times.

  Next, as Example 3, an operation experiment was performed using a solid oxide fuel cell system having the same form as that of the comparative example. The rated power output of the solid oxide fuel cell was 700 W, and it was operated to maintain the rated power output even after the solid oxide fuel cell deteriorated. The number of fuel cells in the fuel cell stack was 70 as in Example 2. In this third embodiment, the same fuel cell stack as in the second embodiment (that is, one having the same operating temperature and the same generated current as that of the first comparative example and the first embodiment, and 1.5 times the voltage drop rate). Was used. In the operation experiment of Example 3, the operation was performed with the limit temperature calculated by the equation (1) set until the operating temperature of the solid oxide fuel cell (fuel cell stack) reached 800 ° C.

Control temperature = (0.00000051694xY2) + (0.0010318xY) +742.05 (1)
Y: Cumulative operating time (cumulative power generation time)
In the third embodiment, a limit temperature calculated by the calculation formula (1) is set from the initial stage of operation, and the air blowing flow rate by the blowing means is controlled so as not to exceed the limit temperature, so that the solid oxide fuel cell (fuel) The rise in temperature of the battery stack was suppressed.

  Changes in the operating temperature of the solid oxide fuel cell (fuel cell stack), its DC power generation efficiency, and air supply flow rate with respect to the operating time when operating at the rated power output from the beginning of operation. Measured. FIG. 10A shows the transition of the operating temperature in the third embodiment, and FIG. 10B shows the DC power generation efficiency and the air supply flow rate in the third embodiment. In Example 3, the air supply flow rate by the blowing means increases little by little until the operating temperature of the solid oxide fuel cell reaches about 800 ° C., but the decrease in power generation efficiency is small, and about 10750 hours have passed. At that time, the air supply flow rate by the blowing means reached the upper limit (120 NL / min), and the cumulative operating time of the rated power output could be extended by about 20% compared to Example 2.

BRIEF DESCRIPTION OF THE DRAWINGS Sectional drawing which shows the solid oxide fuel cell system of one Embodiment simply. The block diagram which shows the control system of the solid oxide fuel cell system of FIG. The figure which shows the relationship between the generated electric current and the generated voltage when the operating temperature in a solid oxide fuel cell changes. The flowchart which shows the control by the control system of the solid oxide fuel cell system of FIG. 5 is a flowchart specifically showing a flow of operation in the first operation mode in the flowchart of FIG. 4. 5 is a flowchart specifically illustrating a flow of operation in a second operation mode in the flowchart of FIG. 4. FIG. 7A is a diagram showing the transition of the operating temperature in the comparative example, and FIG. 7B is a diagram showing the DC power generation efficiency and the air supply flow rate in the comparative example. FIG. 8A is a diagram showing the transition of the operating temperature in the first embodiment, and FIG. 8B is a diagram showing the DC power generation efficiency and the air supply flow rate in the first embodiment. FIG. 9A is a diagram showing the transition of the operating temperature in the second embodiment, and FIG. 9B is a diagram showing the DC power generation efficiency and the air supply flow rate in the second embodiment. FIG. 10A is a diagram illustrating the transition of the operating temperature in the third embodiment, and FIG. 10B is a diagram illustrating the DC power generation efficiency and the air supply flow rate in the third embodiment.

Explanation of symbols

2 Solid Oxide Fuel Cell System 4 Reformer 6 Solid Oxide Fuel Cell 8 Blower Unit 14 Fuel Cell Stack 22 Operating Temperature Detection Unit 56 Control Unit 58 Operation Control Unit 60 Operation Mode Switching Unit 64 Limit Temperature Setting Unit 66 Limit Temperature determining means 68 Upper limit temperature determining means 72 Accumulated time measuring means

Claims (4)

A reformer for reforming the raw fuel gas, a solid oxide fuel cell that generates power by oxidation and reduction of the reformed fuel gas and the oxidant reformed by the reformer, and an oxidant Blower means for feeding to the solid oxide fuel cell, a fuel supply control valve for controlling the supply amount of raw fuel gas supplied to the reformer, the blower means and the fuel supply control A solid oxide fuel cell system comprising control means for controlling the valve,
The apparatus further comprises operating temperature detecting means for detecting an operating temperature of the solid oxide fuel cell, and the control means includes limit temperature setting means for setting a limit temperature of operation of the solid oxide fuel cell; A time counting means for measuring a cumulative operating time from the start of operation of the solid oxide fuel cell ,
An upper limit temperature is set as an upper limit of the operating temperature of the solid oxide fuel cell, the operation is performed in the first operation mode until the limit temperature by the limit temperature setting means reaches the upper limit temperature, and the limit temperature is set to the upper limit temperature. After reaching the temperature, it is operated in the second operation mode,
In the first operation mode, the limit temperature setting means sets the limit temperature to be higher as the cumulative operation time by the time counting means becomes longer, and the control means detects the operating temperature detection means. The blowing means and / or the fuel supply valve are controlled so that the temperature does not exceed the limit temperature. In the second operation mode, the control means detects the operating temperature detecting means so that the detected temperature is the upper limit temperature. The solid oxide fuel cell system is characterized in that the blower means and / or the fuel supply valve are controlled so as not to exceed the range . 2. The solid oxide fuel cell system according to claim 1, wherein an operation period in the first operation mode is 0.3 to 0.6 times a design life time of the solid oxide fuel cell. . 3. The solid oxide fuel cell system according to claim 1, wherein the initial limit temperature of the solid oxide fuel cell is lower by 30 to 100 ° C. than the upper limit temperature. 4. The upper limit temperature and the initial limit temperature of the solid oxide fuel cell are the solid oxide form when power is generated with a direct current value at a rated output in an initial state with the upper limit temperature and the initial limit temperature. The solid oxide fuel cell system according to claim 1 or 2, wherein the voltage difference of the fuel cell is set to 5 to 20%.

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