JP6654463B2 - Solid oxide fuel cell system - Google Patents

Description

  The present invention provides a solid oxide fuel cell system including a fuel cell stack for generating electric power using fuel gas as fuel, and storing the exhaust heat of the combustion exhaust gas from the fuel cell stack as hot water in a hot water storage device. About.

  There has been proposed a cogeneration system in which the surplus power of the power generated by the power generating means is stored as hot water (see, for example, Patent Document 1). In this cogeneration system, the power generation means includes an engine and a generator operated by the engine, and is provided with a hot water storage tank for storing exhaust heat as hot water. Exhaust gas from the engine is configured to flow through the hot water storage tank, and heat exchange is performed between the exhaust gas and hot water stored in the hot water storage tank in the hot water storage tank. The water is warmed. Further, an electric heater is provided in the hot water storage tank, and surplus power generated by the generator is supplied to the electric heater, and the electric heater heats the hot water in the hot water storage tank.

  Further, a solid oxide fuel cell system in which a solid oxide fuel cell stack is used as power generation means and a hot water storage device is combined with the fuel cell stack has been proposed (for example, see Patent Document 2). In this solid oxide fuel cell system, the combustion exhaust gas from the fuel cell stack is discharged through the combustion exhaust gas discharge passage, and the exhaust heat of the combustion exhaust gas is transferred to the hot water in association with the combustion exhaust gas discharge passage. A hot water storage device for storing heat is provided. The hot water storage device includes a hot water storage tank for storing hot water, a circulation flow path for circulating the hot water in the hot water storage tank, a circulation pump provided in the circulation flow path, and a heat supply provided in the circulation flow path. Heat exchange is performed between the combustion exhaust gas flowing through the combustion exhaust gas discharge passage and the hot water stored in the circulation passage in the heat exchanger, and the exhaust heat is recovered by the heat exchange. Heat is stored in the hot water storage tank in the form of warm water.

JP 2000-320401 A JP 2012-202579 Public Relations

  In such a solid oxide fuel cell system, it is desirable that the hot water storage tank be compact and small in capacity from the viewpoint of installation, but the amount of heat recovered from the fuel cell system, the temperature of hot water stored, The tank capacity is set to an appropriate value in consideration of the amount of heat demand, manufacturing cost, and the like. In this hot water storage tank, if the tank capacity is constant, the higher the temperature of the hot water stored, the more desirable in terms of heat storage.

  However, the higher the temperature of the hot water stored in the hot water storage tank, the higher the outlet temperature (outflow side temperature) of the heat exchanger for recovering heat, so that the inside of the heat exchanger, piping members and joint members around it, etc. Sufficient durability and heat resistance are required. In consideration of this, for example, it is desirable to store hot water of about 65 ° C. in the hot water storage tank. However, with hot water of such a temperature, the amount of heat stored in the hot water storage tank may be insufficient.

  An object of the present invention is to reduce the temperature of hot water in and around a heat exchanger, and to store hot water at a higher temperature in a hot water tank, thereby increasing the amount of heat stored in the hot water tank. And a solid oxide fuel cell system.

The solid oxide fuel cell system according to claim 1 of the present invention includes a fuel gas supply unit for supplying a fuel gas, a reformer for reforming the fuel gas, and the reformer. A fuel cell stack for generating electric power by oxidizing and reducing the reformed reformed fuel gas and oxidant; a combustion exhaust gas discharge passage for discharging combustion exhaust gas from the fuel cell stack; A hot water storage device for recovering heat of gas as hot water, the hot water storage device includes a hot water storage tank for storing hot water, a circulation flow path for circulating hot water in the hot water storage tank, and the circulation A solid pump comprising: a circulation pump disposed in the flow passage; and a heat exchanger disposed in the circulation flow passage for exchanging heat between combustion exhaust gas and hot water flowing through the circulation flow passage. A physical fuel cell system,
On the downstream side of the circulation path of the hot water storage device relative to the location of the heat exchanger, a heater that is operated by surplus power generated by the fuel cell stack is disposed, and the heating path in the circulation path is Downstream from the location of the heater, a temperature detector for detecting the temperature of the hot water flowing through the circulation channel is provided, and a controller for controlling the operation of the heater and the circulation pump. Is provided,
The control unit controls the operation of the heating heater by a supply flow rate of the fuel gas or a heater power corresponding to a power generation output of the fuel cell stack. The operation of the circulation pump is controlled.

Further, in the solid oxide fuel cell system according to claim 2 of the present invention, the first heat storage operation mode in which the hot water is stored without operating the heater and the first heat storage operation mode in which the heater is operated. Heat storage operation switching means for switching to a second heat storage operation mode in which hot water is stored at a high temperature is provided, and in addition to the heat storage operation switching means, for determining a heat storage state in the hot water storage tank of the hot water storage device. The heat storage determination means is provided, and when the heat storage determination means determines that the heat storage is insufficient, the heat storage operation switching means switches from the first heat storage operation mode to the second heat storage operation mode.

Further, in the solid oxide fuel cell system according to claim 3 of the present invention, when the heat storage determining means determines that the heat storage is excessive in the operating state of the second heat storage operation mode, the heat storage operation switching means performs the second heat storage operation. It is characterized by switching from the two heat storage operation modes to the first heat storage operation mode.

According to the solid oxide fuel cell system of the first aspect of the present invention, a hot water storage device for recovering heat of the combustion exhaust gas from the fuel cell stack as hot water is provided, and the circulation flow path of the hot water storage device is provided. The heater is disposed downstream of the heat exchanger in the first embodiment, and the temperature detector is further disposed downstream of the heater. The controller detects the temperature detected by the temperature detector as a target temperature (for example, 75 ° C.). The temperature of the hot water stored in the hot water storage tank reaches the target temperature because the operation of the circulation pump is controlled so that the temperature of the hot water storage tank becomes approximately the same as before and after. it can. Further, since the power generation output of the fuel cell stack and the calorific value of the combustion exhaust gas flowing through the heat exchanger are substantially proportional, the heater power corresponding to the fuel gas supply flow rate or the power generation output of the fuel cell stack is heated. By supplying the hot water to the heater and operating it, the hot water can be heated to approximately the first target temperature by heat exchange in the heat exchanger.

Further, according to the solid oxide fuel cell system of the second aspect of the present invention, the first heat storage operation mode for storing hot water without operating the heater and the second heat storage operation for storing hot water by operating the heater. The operation mode can be switched between the operation mode and the operation mode. In the operation state of the second heat storage operation mode, the temperature of the hot water is raised to the second target temperature (for example, about 75 ° C.) by the heater, and is stored in the hot water storage tank. The amount of heat can be increased. Further, when the heat storage determining means determines that the heat storage is insufficient, the operation state is switched from the first heat storage operation mode to the second heat storage operation mode. Therefore, the amount of heat that can be stored in the hot water storage tank is increased, and the occurrence of the insufficient heat storage is suppressed. it can.

Further, according to the solid oxide fuel cell system of the third aspect of the present invention, when the heat storage determining means determines that the heat storage is excessive, the operation state is switched from the second heat storage operation mode to the first heat storage operation mode. In addition, the amount of heat stored in the hot water storage tank is reduced, and the occurrence of excessive heat storage is reduced, so that unnecessary heat storage can be suppressed.

1 is an overall view schematically showing a first embodiment of a solid oxide fuel cell system according to the present invention. FIG. 2 is a block diagram showing a control system in the solid oxide fuel cell system of FIG. The figure which shows the change of the total efficiency of the whole system in the case where a heater is used and the case where it is not used. FIG. 4 is a block diagram showing a control system of a second embodiment of the solid oxide fuel cell system according to the present invention. FIG. 6 is a block diagram showing a control system of a third embodiment of the solid oxide fuel cell system according to the present invention. FIG. 9 is an overall view schematically showing a fourth embodiment of the solid oxide fuel cell system according to the present invention. FIG. 7 is a block diagram showing a control system in the solid oxide fuel cell system of FIG. 8 is a flowchart showing the flow of control by the control system of FIG.

  Hereinafter, various embodiments of a solid oxide fuel cell system according to the present invention will be described with reference to the accompanying drawings.

[First Embodiment]
First, a first embodiment of a solid oxide fuel cell system will be described with reference to FIGS. In FIG. 1, the illustrated solid oxide fuel cell system 2 consumes fuel gas (for example, city gas, LP gas, etc.) to generate power, and is a reformer for reforming the fuel gas. And a solid oxide fuel cell stack 6 that generates power by oxidizing and reducing fuel gas reformed by the reformer 4 and air as an oxidizing agent.

  The fuel cell stack 6 is formed by stacking a plurality of solid oxide fuel cells for generating power by a fuel cell reaction via a current collecting member. A solid electrolyte that conducts, a fuel electrode provided on one side of the solid electrolyte, and an air electrode (oxygen electrode) provided on the other side of the solid electrolyte, for example, zirconia doped with yttria is used as the solid electrolyte. Can be

  The fuel electrode introduction side of the fuel cell stack 6 is connected to the reformer 4 via a reformed fuel gas supply channel 8, and the reformer 4 is connected via a gas / steam supply channel 10. Connected to the vaporizer 12. The vaporizer 12 is connected to a fuel gas supply source 16 (for example, a buried pipe, a storage tank, or the like) for supplying a fuel gas through a fuel gas supply passage 14, and the fuel gas supply source 16 and the fuel gas supply flow The passage 14 constitutes fuel gas supply means for supplying fuel gas. Further, the vaporizer 12 is connected to a reforming water tank 20 via a water supply passage 18, and the water supply passage 18 and the reforming water tank 20 serve as a water supply unit for supplying the reforming water. Constitute.

  The reformer 4 contains a reforming catalyst, and for example, a catalyst in which ruthenium is supported on alumina is used as the reforming catalyst. The fuel gas supplied through the fuel gas supply passage 14 by the reforming catalyst is subjected to steam reforming. Quality. In this embodiment, the reformer 4 and the vaporizer 12 are formed separately, but they may be formed integrally. Further, in this embodiment, the fuel gas from the fuel gas supply means is supplied to the vaporizer 12, but may be directly supplied to the reformer 4 instead of the vaporizer 12. Good.

  In the fuel gas supply passage 14, a desulfurizer 22, a buffer tank 24, a booster pump 26, a gas flow sensor 28, a gas pressure sensor 30, and a shutoff valve 31 are provided. The desulfurizer 22 removes a sulfur component (sulfur component in the odorant) contained in the fuel gas, and in the buffer tank 24, the fluctuation of the pressure of the fuel gas flowing through the fuel gas supply passage 14 is reduced, and The control of the flow rate is stabilized. The booster pump 26 boosts the pressure of the fuel gas flowing through the fuel gas supply flow path 14 and supplies the fuel gas from the fuel gas supply source 16 to the carburetor 12. The gas flow rate sensor 28 measures the flow rate of the fuel gas supplied through the fuel gas supply flow path 14, and the gas pressure sensor 30 measures the pressure of the fuel gas flowing through the fuel gas supply flow path 14, and shuts off. When the valve 31 is closed, the fuel gas supply passage 14 is shut off to stop the supply of the fuel gas. Further, a water pump 32 is provided in the water supply channel 18, and the water (recovered water) in the reforming water tank 20 is supplied to the vaporizer 12 through the water supply channel 18 by the operation of the water pump 32. You.

  The introduction side of the air electrode of the fuel cell stack 6 is connected to a blowing means 36 via an air supply passage 34, and an air flow sensor 38 is provided in the air supply passage 34. The blowing means 36 is composed of, for example, a blowing blower. By the action of the blowing means 36, air (oxidizing material) is supplied to the air electrode side of the fuel cell stack 6 through the air supply passage 34, and the air flow sensor 38 The flow rate of the air flowing through the air supply channel 34 is measured. The air supply passage 34 and the blowing means 36 constitute an air supply means for supplying air for power generation.

  A combustion area 40 is provided on the fuel cell stack 6 on the discharge side of the fuel electrode and the air electrode, and reacts with the reactive fuel gas (including excess fuel gas) discharged from the fuel electrode side of the fuel cell stack 6. Air (containing oxygen) discharged from the air electrode side is burned in the combustion zone 40, and the vaporizer 12 and the reformer 4 are heated by using the combustion heat of the fuel gas. The combustion exhaust gas is discharged to the atmosphere through the exhaust gas discharge channel 42. The combustion exhaust gas may be used to heat the air supplied to the air electrode side of the fuel cell stack 6 through the air supply passage 34.

  In this embodiment, the hot water storage device 44 is provided so that the heat of the combustion exhaust gas is stored as hot water, and the condensed water recovery means is configured to recover the moisture contained in the combustion exhaust gas and use it as reforming water. 46 are provided. More specifically, a heat exchanger 48 for recovering exhaust heat is provided in the exhaust gas discharge channel 40, and a hot water storage device 44 and condensed water recovery means 46 are provided in association with the heat exchanger 48.

  The illustrated hot water storage device 44 includes a hot water storage tank 50 for storing hot water, and a circulation for circulating hot water stored in the hot water storage tank 50 (water when the temperature is low, but becomes hot water when the temperature is high) through the heat exchanger 48. And a circulation pump 54 that circulates the hot water stored in the hot water storage tank 50 through the circulation flow path 52. The configuration related to the hot water storage device 4 will be described later.

  The illustrated condensed water recovery means 46 includes a condensed water recovery flow channel 56 extending from the heat exchanger 48 to the reformed water tank 20, and a water purifier 58 is disposed in the condensed water recovery flow channel 56. . With such a configuration, the combustion exhaust gas is cooled by the heat exchange by the heat exchanger 48, whereby water contained in the combustion exhaust gas is condensed and collected, and the collected condensed water is subjected to water purification. After being purified into pure water by the vessel 58, it is stored in the reformed water tank 20.

  Next, the hot water storage device 44 and a configuration related thereto will be described. The circulation pump 54 of the hot water storage device 44 is disposed on the upstream side portion 60 of the circulation flow path 52, and one end side of the upstream side portion 60 is a bottom portion of the hot water storage tank 50. And the other end is connected to the inflow side of the heat exchanger 48. One end of the downstream portion 62 of the circulation flow path 50 is connected to the outflow side of the heat exchanger 48, and the other end is connected to the upper part of the hot water storage tank 50.

  A heater 64 for heating hot water (hot water heated by the heat exchanger 48) to be supplied to the hot water storage tank 50 is further provided on the downstream side portion 62 of the circulation flow path 52. As will be described later, the heater 64 generates a surplus power of the power output from the fuel cell stack 6 (excess power after the power generated by removing the power consumed by the power load from the power output). It is operated using.

  A first temperature sensor 66 (constituting first temperature detecting means) and a second temperature sensor 68 (constituting second temperature detecting means) are further provided on the downstream side portion 62 of the circulation flow path 52. I have. The first temperature sensor 66 is provided between a portion of the downstream side portion 62 connected to the heat exchanger 48 and a portion where the heater 64 is provided, and the stored hot water flowing out of the heat exchanger 48 ( The temperature of the hot water heated by the heat exchanger 48 is detected. The second temperature sensor 68 is disposed between the portion of the downstream side portion 62 where the heater 64 is provided and the portion connected to the hot water storage tank 50, and the hot water stored in the heater 64 after being heated by the heater 64. The temperature of water (in other words, hot water stored in hot water storage tank 50) is detected.

  In the hot water storage device 50, a water inflow channel 70 is further connected to the bottom of the hot water storage tank 50, and the water inflow channel 70 is connected to a water supply source 72 such as a water pipe. The hot water storage tank 50 is supplied through the water inflow passage 70. A hot water flow path 74 is connected to an upper portion of the hot water storage tank 50, and hot water (hot water) stored in the hot water storage tank 50 is discharged through the hot water flow path 74.

  The solid oxide fuel cell system 2 is controlled by a control system shown in FIG. 2, the solid oxide fuel cell system 2 includes a controller 78 for controlling the operation of the entire system, and detection signals from the first and second temperature sensors 66 and 68 are sent to the controller 78. .

  The illustrated controller 78 includes a first temperature comparison unit 80, a second temperature comparison unit 82, a control unit 84, and a memory unit 86. The control unit 84 includes a heater control unit 88 and a pump control unit 90. In the memory means 86, a first target temperature (for example, set to about 65 ° C.) as a target temperature of the hot water (hot water) on the outflow side of the heat exchanger 48 and the hot water stored in the hot water storage tank 50 ( A second target temperature (for example, set to about 75 ° C.) as a target temperature of hot water is registered. The first temperature comparing means 80 compares the first target temperature registered in the memory means 86 with the detected temperature of the first temperature sensor 66, and the pump control means 90 performs the operation based on the comparison result of the first temperature comparing means 80. The operation of the circulation pump 54 is controlled as described later. Further, the second temperature comparing means 82 compares the second target temperature registered in the memory means 86 with the detected temperature of the second temperature sensor 68, and the heater control means 88 calculates the comparison result of the second temperature comparing means 82. In accordance with this control of the heater 64, the control means 84 controls the booster pump 26, the water pump 32, and the air blower 36 to control the operation of the fuel cell To control the power generation output.

  Next, the power generation operation of the solid oxide fuel cell system 2 will be described. At the time of the power generation operation, the fuel gas from the fuel gas supply source 16 flows through the fuel gas supply flow path 14 by the action of the boosting pump 26, and is supplied to the vaporizer 12 after being desulfurized by the desulfurizer 22. Further, the water (pure water) from the reforming water tank 20 is supplied to the vaporizer 12 through the water supply channel 18 by the operation of the water pump 32, and is vaporized by the vaporizer 12 to become steam, and the generated steam The fuel gas is supplied to the reformer 4 through the gas / steam supply passage 10.

  In the reformer 4, the fuel gas is steam-reformed by steam supplied through the gas / steam supply passage 10, and the steam-reformed fuel gas is passed through the reformed fuel gas supply passage 8. The fuel is fed to the fuel electrode side of the fuel cell stack 6. In addition, the air from the blowing means 36 is supplied to the air electrode side of the fuel cell stack 6 through the air supply channel 32.

  In the fuel cell stack 6, power is generated by oxidizing and reducing reformed fuel gas flowing on the fuel electrode side and air (oxygen in the air) flowing on the air electrode side, and the DC power obtained by the power generation is converted into an inverter. After being converted into AC power by a (not shown), it is sent to a power load (not shown).

  Reacted fuel gas (including surplus fuel gas) is discharged from the fuel electrode side of the fuel cell stack 6 to the combustion region 40, and air (containing oxygen) enters the combustion region 40 from the air electrode side. Is discharged, and the reaction fuel gas is burned in the combustion zone 40, and the combustion exhaust gas from the combustion zone 40 is discharged to the atmosphere through an exhaust gas discharge passage 42.

  When the combustion exhaust gas flows through the heat exchanger 48, heat exchange is performed between the combustion exhaust gas and the stored hot water flowing through the circulation flow path 52 of the hot water storage device 44. Further, moisture contained in the combustion exhaust gas is condensed by heat exchange in the heat exchanger 46, and the condensed water passes through the condensed water recovery flow path 56 and is purified by the water purifier 58 before being stored in the reformed water tank 20. .

  During this power generation operation, the pump control means 90 controls the operation of the circulation pump 54, and the hot water stored at the bottom of the hot water storage tank 50 flows to the heat exchanger 48 through the upstream side 60 of the circulation flow path 50, and this heat exchange is performed. Heated by heat exchange with the combustion exhaust gas flowing through the combustion exhaust gas discharge passage 42 while flowing through the heat exchanger 48. Then, the heated hot water (hot water) flows through the downstream side portion 62 of the circulation flow path 50, is heated by the heater 64, is fed to the upper portion of the hot water storage tank 50, and from the upper side to the lower side. Accumulate in layers.

  When the stored hot water is circulated through the circulation flow path 52, the pump control unit 90 determines that the temperature of the stored hot water (hot water) flowing out of the heat exchanger 48 reaches the first target temperature (for example, 65 ° C.). The operation of the circulation pump 54 is controlled as described above. That is, the first temperature comparison unit 80 compares the detected temperature of the first temperature sensor 66 with the first target temperature, and the pump control unit 90 determines that the rotation speed of the circulation pump 54 is lower when the detected temperature is lower than the first target temperature. (Thus, the flow rate of the stored water decreases, the time flowing through the heat exchanger 48 increases, and the temperature of the stored water increases). When the detected temperature is higher than the first target temperature, the rotation of the circulation pump 54 is reduced. The number is increased (this increases the flow rate of the hot water, shortens the flow time through the heat exchanger 48 and lowers the temperature of the hot water), and thus the downstream side of the circulation flow path 50 from the heat exchanger 48 The temperature of the hot water flowing through 62 is maintained at the first target temperature (for example, 65 ° C.).

  During the circulation of the hot water, the heater control unit 88 controls the operation of the heater 64 so that the temperature of the hot water (hot water) stored in the hot water tank 50 becomes the second target temperature (for example, 75 ° C.). I do. That is, the second temperature comparing unit 82 compares the detected temperature of the second temperature sensor 68 with the second target temperature, and the heater control unit 88 supplies the detected temperature to the heater 44 when the detected temperature is lower than the second target temperature. The heater power (that is, the heater current) is increased (the amount of heat generated by the heater 64 is increased and the temperature of the hot water is increased). When the detected temperature is higher than the second target temperature, the heater power is supplied to the heater 44. The heater power (heater current) is reduced (this reduces the amount of heat generated by the heater 64 and lowers the temperature of the hot water), and is thus sent to the hot water storage tank 50 through the downstream side portion 62 of the circulation flow path 50. The temperature of the supplied hot water is maintained at the second target temperature (for example, 75 ° C.).

  When the heater power to the heater 64 is increased, the power generation output of the fuel cell stack 6 is controlled to be increased (that is, the supply amount of the fuel gas is increased). It is desirable to control so as to reduce the power generation output of the battery cell stack 6 (that is, to reduce the supply amount of the fuel gas).

  The solid oxide fuel cell system 2 uses the surplus power generated from the power output from the fuel cell stack 6 as the drive power supplied to the heater 64, and thus has the following features. Referring also to FIG. 3, the power transmission end of the fuel cell stack 6 of a solid oxide fuel cell system having, for example, a rating of 700 W and not having the heater 64 described above (ie, a conventional solid oxide fuel cell system). The AC efficiency changes as indicated by the dashed line A when the AC power output of the fuel cell stack 6 (the output after converting the DC power output into AC power by the inverter) changes, and the AC power output is, for example, 700 W. Sometimes it is about 48%, but when the AC power generation output drops to, for example, 200W, it drops to about 26%. The overall efficiency at this time (the overall efficiency including the heat storage in the hot water storage tank 50) changes as shown by the two-dot chain line B. For example, when the AC power generation output is 700 W, for example, it is about 86%. When the AC generated power drops to, for example, 200 W, the power drops to about 68%, and as the AC power output decreases, the transmitting end AC efficiency and the overall efficiency also decrease. Then, in an operation range where the power generation output of the fuel cell stack 6 (in other words, the AC power generation output) is somewhat low (for example, an operation range in which the power generation output is lower than 500 W, for example), the overall efficiency of the solid oxide fuel cell system is low. If, for example, the power falls below 200 W, the overall efficiency also drops significantly.

  For this reason, in an operation range where the power generation output of the fuel cell stack 6 is somewhat low (for example, in a range of 500 W or less), the fuel cell stack 6 operates in the conventional manner (by following the power load without providing the heater 64). By operating as in the above-described embodiment, the overall efficiency of the solid oxide fuel cell system 2 can be increased. That is, in the operating range where the power generation output of the fuel cell stack 6 is somewhat low, the power generated by increasing the power by, for example, about 100 to 200 W with respect to the power generation output (for example, 300 W) that follows the power load is generated. By increasing the output, the power generation efficiency output from the fuel cell stack 6 is increased. The surplus power generated by the operation is consumed by the heater 64 by the surplus power generated by the operation (excess power generated by removing the power consumption consumed by the power load from the power output), so that the surplus power is generated by heating. By storing the heat in the hot water storage tank 50 with hot water at a high temperature, the power consumption to the heater is subtracted from the power output from the fuel cell stack 6, and the effective power generation efficiency supplied to the power transmission end is: As shown by the broken line C in FIG. 3 according to the fluctuation of the AC power generation output, the AC power efficiency becomes lower than the power transmission end AC efficiency of the fuel cell system not provided with the heater 64 (the efficiency indicated by the dashed line A). The overall efficiency of the physical fuel cell system 2 changes as shown by a solid line D in FIG. It is higher than the stem overall efficiency (efficiency indicated by the two-dot chain line B).

  Therefore, in a range where the output power of the fuel cell stack 6 is somewhat low (for example, in a range of 400 to 500 W or less), the power generation output power is increased by 100 to 200 W, and the power generation surplus generated by increasing the output power is generated. By consuming the electric power by the heater 64 and storing the heat as the heat in the hot water storage tank 50 with the hot water, the overall efficiency of the solid oxide fuel cell system 2 can be increased. Since the hot water is stored at the second target temperature, the occurrence of heat storage shortage can be suppressed.

  In the above-described embodiment, the power generation output power is increased by 100 to 200 W in a range where the power generation output power of the fuel cell stack 6 is low to some extent. In the range of 400 W or less, the power generation operation may be performed such that the generated output power becomes 400 W, and the surplus power generated in the power generation operation may be consumed by the heater 64 and stored in the hot water storage tank 50 as hot water.

[Second embodiment]
Next, a second embodiment of the solid oxide fuel cell system according to the present invention will be described with reference to FIG. In the second embodiment, the control system is modified. In the following embodiments, substantially the same components as those in the above-described first embodiment are denoted by the same reference numerals, and description thereof will be omitted.

  In FIG. 4 showing a control system of the solid oxide fuel cell system, in the second embodiment, a temperature sensor 66A (corresponding to the first temperature sensor 66 in the first embodiment) is provided with a circulating flow of a hot water storage device. It is disposed on the downstream side of the road and detects the temperature of hot water stored and flowing out of the heat exchanger. On the other hand, the temperature sensor (corresponding to the second temperature sensor 68 in the first embodiment) for detecting the temperature of the hot water (hot water) fed to the hot water storage tank is omitted, and the temperature of the hot water is directly detected. Instead of controlling the operation of the heater 64, the flow rate of the stored hot water is detected, and the flow rate of the stored hot water, the first target temperature (for example, 65 ° C.) and the second target temperature (for example, 75 ° C.) The heater power (heater current) supplied to the heater 64 is calculated based on the temperature difference between the heater and the heater.

  More specifically, a hot water flow sensor 92 (constituting a hot water flow detecting means) is provided in the circulation flow path (for example, on the upstream side), and the hot water flow sensor 92 is configured to store hot water flowing in the circulation flow path. The flow rate of the water is detected, and this detection signal is sent to the controller 78A. Further, the controller 78A includes, in addition to the first temperature comparing means 80, a stored hot water flow rate calculating means 94, a heating amount calculating means 96, and a heater power calculating means 98.

  The hot water flow rate calculating means 94 calculates the flow rate of the hot water based on the detection signal from the hot water flow sensor 92, and the heating amount calculating means 96 converts the hot water flowing through the circulation channel from the first target temperature to the second temperature. The amount of heat required to raise the temperature to the target temperature is calculated, and the heater power calculation unit 98 calculates the heater power required to obtain the amount of heat calculated by the heating amount calculation unit 96. Other configurations of the solid oxide fuel cell system according to the second embodiment are substantially the same as those of the above-described first embodiment.

  In the second embodiment, the pump control means 90 sets the temperature of the hot water (hot water) flowing out of the heat exchanger to the first target temperature (for example, as in the first embodiment). (65 ° C.). That is, the first temperature comparing means 80 compares the detected temperature of the temperature sensor 66A with the first target temperature, and the pump control means 90 reduces the rotation speed of the circulation pump 54 when the detected temperature is lower than the first target temperature. When the detected temperature is higher than the first target temperature, the rotation speed of the circulation pump 54 is increased. In this way, the temperature of the hot water flowing from the heat exchanger to the downstream side of the circulation flow path becomes the first target temperature (for example, , 65 ° C).

  Also, during the circulation of the hot water, the heater control means 88A controls the operation of the heater 64 so that the temperature of the hot water (hot water) stored in the hot water tank becomes the second target temperature (for example, 75 ° C.). . That is, the hot water calculating means 94 calculates the flow rate of the hot water flowing through the circulation flow path based on the detection signal of the hot water flow sensor 92, and the heating amount calculating means 96 calculates the second flow rate of the hot water flowing through the circulation flow path. In this embodiment, the amount of heat required to increase the temperature by 10 ° C. from the first target temperature is calculated. The heater power calculating means 98 calculates the heater power (heater current) required to increase the calculated amount of heat. ), And the heater control means 84A supplies the calculated heater power to the heater 64. Therefore, the stored hot water (hot water) flowing on the downstream side of the circulation flow path is heated by the heater 64 controlled by the heater power, whereby the temperature of the stored hot water supplied to the hot water storage tank is set to the second target. The temperature (for example, 75 ° C.) is maintained, and the same operation and effect as in the first embodiment can be achieved.

  Also in this embodiment, when the heater power to the heater 64 increases, the power generation output of the fuel cell stack is controlled to increase, and when the heater power decreases, the power generation output of the fuel cell stack decreases. It is desirable to control so as to reduce the value.

  In this embodiment, the stored hot water flow rate sensor 92 is provided in the circulation flow path, and the flow rate of the stored hot water is detected based on the detection signal. However, the present invention is not limited to such a configuration. The flow rate of the stored hot water may be calculated based on the rotation speed of the provided circulation pump.

[Third embodiment]
Next, a third embodiment of the solid oxide fuel cell system according to the present invention will be described with reference to FIG. Also in the third embodiment, the control system is modified.

  In FIG. 5 showing the control system of the solid oxide fuel cell system, in the third embodiment, a temperature sensor 68B (corresponding to the second temperature sensor 68 in the first embodiment) is provided with a circulating flow of a hot water storage device. It is arranged on the downstream side of the road and detects the temperature of hot water (hot water) flowing into the hot water storage tank after being heated by the heater 64. The heater power corresponding to the supply flow rate of the fuel gas supplied from the fuel gas supply means is supplied to the heater 64, and the heater power is supplied to the fuel gas supply flow path to detect the supply flow rate of the fuel gas. The provided gas flow sensor 28 (constituting fuel gas flow detecting means) is used. Then, the pump control means 90B controls the operation of the circulation pump 54 so that the temperature detected by the temperature sensor 68B becomes the target temperature (corresponding to the second target temperature in the first embodiment).

  In this regard, the controller 78B includes, in addition to the second temperature comparing means 82, a fuel gas flow rate calculating means 102 and a heater power calculating means 98B, and the first temperature sensor 86 and the first temperature sensor 86 in the first embodiment described above. The first temperature comparing means 86 is omitted. The fuel gas flow rate calculation means 102 calculates the supply flow rate of the fuel gas flowing through the fuel gas supply flow path based on the detection signal from the gas flow rate sensor 28, and the heater power calculation means 98B responds to the fuel gas supply flow rate. The calculated heater power is calculated.

  In the solid oxide fuel cell system, the calorific value of the combustion exhaust gas discharged from the fuel cell stack and flowing through the combustion exhaust gas discharge passage (that is, the heat exchanger The calorific value of the flowing combustion exhaust gas also fluctuates, and the power generation output and the calorific value of the combustion exhaust gas are substantially proportional to each other. Thus, the heater power is calculated based on the fuel gas supply flow rate. For example, the relationship between the supply flow rate of the fuel gas and the heater power is represented in the form of a map, and the heater power can be calculated using this map (not shown). In this case, this map is registered in the memory means 86B. You. Other configurations of the solid oxide fuel cell system according to the third embodiment are substantially the same as those of the above-described first embodiment.

  In the third embodiment, in the heat exchanger, heat exchange is performed between the combustion exhaust gas flowing through the combustion exhaust gas discharge passage and the hot water flowing through the circulation passage, and the heat is heated by the heat exchange. Hot water flows on the downstream side of the circulation channel. At this time, if the power generation output of the fuel cell stack is large (or small), the calorific value of the combustion exhaust gas flowing through the combustion exhaust gas discharge passage also becomes large (or small), and the calorific value of this combustion exhaust gas is large (or small). (Small), the heater power supplied to the heater 64 also becomes large (or small), and accordingly, the flow rate of the stored hot water flowing through the circulation flow path also becomes large (or small). For this reason, the stored hot water is heated to a temperature close to the first target temperature (for example, 65 ° C.) by heat exchange in the heat exchanger.

  The heated hot water (hot water) is further heated by the heater 64. That is, the heater control means 88B heats the hot water with heater power corresponding to the detected flow rate of the gas flow rate sensor 28, and the pump control means 90B sets the detected temperature of the temperature sensor 68B to the target temperature (for example, 75 ° C.). The operation of the circulation pump 54 is controlled so that the hot water (hot water) flowing on the downstream side of the circulation flow path (in other words, the hot water flowing in the hot water storage tank) is set to a target temperature (for example, , 75 ° C.), so that substantially the same functions and effects as in the first embodiment can be achieved.

  In the third embodiment, the heater power to be supplied to the heater 64 is calculated based on the detection signal (ie, the supply flow rate of the fuel gas) of the gas flow sensor 28 disposed in the fuel gas supply flow path. However, instead of the gas flow sensor 28, the supply flow rate of the fuel gas may be calculated based on the rotation speed of the booster pump 26, and the heater power may be calculated based on the calculated supply flow rate of the fuel gas. Alternatively, the heater power may be calculated based on the detected power of a power generation output sensor (not shown) (constituting a power generation output detection unit) provided on the power generation output side of the fuel cell stack.

[Fourth embodiment]
Next, a fourth embodiment of the solid oxide fuel cell system will be described with reference to FIGS. In the fourth embodiment, the solid oxide fuel cell system performs the first heat storage operation mode in which hot water is stored without operating the heater according to the heat storage state of the hot water storage tank, and performs hot water storage by operating the heater. The operation is switched to the second heat storage operation mode and the operation is performed.

  6 and 7, in the fourth embodiment, in order to detect the heat storage state of the hot water storage tank 50, for example, the ratio of heat storage to full heat storage, the heat storage temperature detection means 112 and the inflow water temperature sensor 114 (inflow water) (Constituting a temperature detecting means). The heat storage temperature detecting means 112 includes five heat storage temperature sensors disposed in the hot water storage tank 50 (or on the outer surface thereof) at substantially equal intervals in the vertical direction, that is, first, second, third, and third heat storage sensors. Fourth and fifth heat storage temperature sensors 116, 118, 120, 122, 124, for example, the first heat storage temperature sensor 116 is at the upper end of the hot water storage tank 50, and the fifth heat storage temperature sensor 124 is at the bottom of the hot water storage tank 50. The third heat storage temperature sensor 120 is provided between the first and fifth heat storage temperature sensors 116 and 124, and the second heat storage temperature sensor 118 is provided between the first and third heat storage temperature sensors 116 and 120. The fourth heat storage temperature sensor 122 is disposed between the third and fifth heat storage temperature sensors 120 and 124, and the first to fifth heat storage temperature sensors 116 to 124 detect the temperature of the hot water in the hot water storage tank 50. To knowledge. Further, the inflow water temperature sensor 114 is disposed in the water inflow channel 70 and detects the temperature of water flowing into the hot water storage tank 50 through the water inflow channel 70.

  In this connection, in addition to the first temperature comparing means 86, the second temperature comparing means 88, the control means 84 and the memory means 86C, the controller 78C includes a heat storage ratio calculating means 126, a maximum heat storage ratio extracting means 128, It includes a determination unit 130 and a heat storage operation switching unit 132. The heat storage ratio calculation means 126 calculates the heat storage ratio (the ratio of the current heat storage to the full heat storage) of the hot water storage tank 50 based on the temperatures detected by the heat storage temperature detecting means 112 and the inflow water temperature sensor 114 as follows.

  For example, if the detection temperatures of the first to fifth heat storage temperature sensors 116 to 124 are T1 to T5 and the detection temperature of the inflow water temperature sensor 114 is T0, the detection temperature T1 of the first heat storage temperature sensor and the inflow water temperature sensor 114 Is the temperature up to the full heat storage (TX = T1−T0). The temperature difference TZ between the average temperature TA [TA = (T1 + T2 + T3 + T4 + T5) / 5] of the detected temperatures T1 to T5 of the first to fifth heat storage temperature sensors 116 to 124 and the detected temperature T0 of the inflow water temperature sensor 114 is the current value. If the ratio TH (TH = TZ / TX) of the current heat storage temperature TZ to the temperature TX up to full heat storage is calculated, the calculated value becomes the current heat storage ratio of the hot water storage tank 50. The calculated heat storage ratio TH thus calculated is stored in the memory means 86C.

  The maximum heat storage ratio extraction means 128 extracts the maximum heat storage ratio from the calculated heat storage ratio TH stored in the memory means 86C, and the heat storage determination means 130 reads the extracted maximum heat storage ratio and the first heat storage ratio registered in the memory means 86C. A reference heat storage ratio (for example, 50%) is compared, and if the maximum heat storage ratio is equal to or less than the first reference heat storage ratio, it is determined that the heat storage is insufficient, and the extracted maximum heat storage ratio and the second heat storage ratio registered in the memory unit 86C are stored. The reference heat storage ratio (a value larger than the first reference heat storage ratio, for example, 85%) is compared, and if the maximum heat storage ratio is equal to or higher than the second reference heat storage ratio, it is determined that the heat storage is excessive.

  In the solid oxide fuel cell system 2C, the first heat storage operation mode in which the heater 64 is not operated (in the first heat storage operation mode, the temperature of the hot water stored in the hot water storage tank 50 is a first target temperature, for example, 65 ° C. And a second heat storage operation mode in which the heater 64 is operated (in this second heat storage operation mode, the temperature of the hot water stored in the hot water storage tank 50 becomes the second target temperature, for example, 75 ° C.). The heat storage operation switching means 132 switches from the first heat storage operation mode to the second heat storage operation mode when the heat storage determination means 130 determines that the heat storage is insufficient, as described later. Is switched from the second heat storage operation mode to the first heat storage operation mode. Other configurations of the solid oxide fuel cell system 2C of the fourth embodiment are substantially the same as those of the above-described first embodiment.

  The operation of the solid oxide fuel cell system 2C is performed, for example, as follows. Referring mainly to FIGS. 7 and 8, during the operation of fuel cell system 2 </ b> C, when a first predetermined time (for example, an appropriate time of 10 to 120 minutes, for example, can be set to 60 minutes) elapses The process proceeds from step S1 to step S2, where the heat storage state of the hot water storage tank 50, for example, the heat storage ratio TH is calculated. That is, the heat storage ratio calculating means 126 calculates the heat storage ratio TH as described above based on the detection signals of the heat storage temperature detecting means 112 and the inflow water temperature sensor 114, and the calculated heat storage ratio TH is stored in the memory means 86C. (Step S3).

  The calculation of the heat storage state (heat storage ratio TH) of the hot water storage tank 50 is performed until the second predetermined time (for example, an appropriate time of 6 to 24 hours, for example, can be set to 24 hours) elapses. It is performed every time elapse. Then, when the second predetermined time has elapsed, the process proceeds to step S5 via step S4, and the maximum heat storage ratio extracting means 128 calculates the calculated heat storage ratio during the second predetermined time (calculated heat storage ratio for each first predetermined time). The maximum heat storage ratio is extracted.

  When the maximum heat storage ratio is extracted in this way, the heat storage determination unit 130 compares the extracted maximum heat storage ratio with the first and second reference heat storage ratios registered in the memory unit 86C, and compares the extracted maximum heat storage ratio with the hot storage tank 50. The heat storage state is determined (step S6).

  In this heat storage determination, if the extracted maximum heat storage ratio is equal to or less than the first reference heat storage ratio (for example, 50%), the process proceeds from step S7 to step S8, and the heat storage determination unit 130 determines that the heat storage is insufficient. If the operation has been performed in the first heat storage operation mode, the process proceeds from step S9 to step S10, and the heat storage operation switching unit 132 switches from the first heat storage operation mode to the second heat storage operation mode. In the operation operation in the second heat storage operation mode, the heater 64 is operated, the temperature of the hot water in the hot water storage tank 50 becomes the second target temperature (for example, 75 ° C.), and the heat storage amount in the hot water storage tank 50 increases. Therefore, the shortage of heat storage is eliminated.

  In the above-described heat storage determination, if the extracted maximum heat storage ratio is equal to or more than the second reference heat storage ratio (for example, 85%), the process proceeds from step S7 to step S12 via step S11, and the heat storage determination unit 130 determines that the heat storage is excessive. I do. If the operation has been performed in the second heat storage operation mode, the process proceeds from step S13 to step S14, and the heat storage operation switching unit 132 switches from the second heat storage operation mode to the first heat storage operation mode. In the operation operation in the first heat storage operation mode, the heater 64 is not operated, the temperature of the hot water stored in the hot water storage tank 50 reaches the first target temperature (for example, 65 ° C.), and the amount of heat stored in the hot water storage tank 50 is reduced. Due to the decrease, the excess heat storage is eliminated.

  When the maximum heat storage ratio is in the range between the first reference heat storage ratio and the second reference heat storage ratio, the heat storage state in the hot water storage tank 50 is in a state where there is no excess or shortage. In this case, the operation mode is not switched. Returning to step S1, operation is continued in the same operation mode.

  In the above-described fourth embodiment, as the heat storage temperature detecting means 112 for detecting the temperature distribution state of the hot water stored in the hot water storage tank 50, the first to fifth heat storage temperature sensors 116 to 124 are used. Although the configuration is not limited to such a configuration, the thermal storage temperature detecting means may be configured by one to four or six or more thermal storage temperature sensors. Further, although the heat storage temperature detecting means 112 and the detection signal of the inflow water temperature sensor 114 are used to detect the heat storage state (for example, heat storage ratio) of the hot water storage tank 50, the inflow water temperature sensor 114 is omitted and the heat storage The heat storage state of hot water storage tank 50 may be detected using only the detection signal of temperature detection means 112. In the case of a single heat storage temperature sensor, it is desirable to dispose this heat storage temperature sensor slightly below the center of the hot water storage tank 50 in the vertical direction. The time during which the temperature is equal to or higher than a predetermined temperature (for example, can be set to about 40 ° C.) is accumulated, and based on the operation accumulation time, insufficient heat storage (when the operation accumulation time is equal to or less than a first predetermined time); The determination of excessive heat storage (when the calculated cumulative time is equal to or longer than a second predetermined time longer than the first predetermined time) can be performed.

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

  The technique relating to the switching of the operation mode between the first heat storage operation mode and the second heat storage operation mode in the fourth embodiment can be similarly applied to the above-described second and third embodiments.

2, 2C solid oxide fuel cell system 4 Reformer 6 Fuel cell cell stack 44 Hot water storage device 50 Hot water storage tank 52 Circulating flow path 64 Heater 66, 66A, 68, 68B Temperature sensor (temperature detecting means)
78, 78A, 78B, 78C Controller 80, 82 Temperature comparison means 84, 84A Control means 98B Heater power calculation means 112 Heat storage temperature detection means 126 Heat storage ratio calculation means 130 Heat storage determination means 132 Heat storage operation switching means

Claims (3)

Fuel gas supply means for supplying fuel gas, a reformer for reforming the fuel gas, and power generation by oxidizing and reducing the reformed fuel gas and the oxidizing material reformed by the reformer. A fuel cell stack to be performed, a combustion exhaust gas discharge flow path for discharging combustion exhaust gas from the fuel cell stack, and a hot water storage device for recovering heat of the combustion exhaust gas as hot water, The hot water storage device has a hot water storage tank for storing hot water, a circulation flow path for circulating hot water in the hot water storage tank, a circulation pump disposed in the circulation flow path, and a circulation pump disposed in the circulation flow path. A heat exchanger that performs heat exchange between the combustion exhaust gas and the stored hot water flowing through the circulation flow path, and a solid oxide fuel cell system comprising:
On the downstream side of the circulation path of the hot water storage device relative to the location of the heat exchanger, a heater that is operated by surplus power generated by the fuel cell stack is disposed, and the heating path in the circulation path is Downstream from the location of the heater, a temperature detector for detecting the temperature of the hot water flowing through the circulation channel is provided, and a controller for controlling the operation of the heater and the circulation pump. Is provided,
The control means controls the operation of the heater by a heater power corresponding to a supply flow rate of the fuel gas or a power generation output of the fuel cell stack, and the detection temperature of the temperature detection means becomes a target hot water storage temperature. A solid oxide fuel cell system, wherein the operation of the circulation pump is controlled. Heat storage operation switching means for switching between a first heat storage operation mode for storing hot water without operating the heater and a second heat storage operation mode for operating the heater to store hot water at a higher temperature than the first heat storage operation mode; A heat storage determining means for determining a heat storage state of the hot water storage device in the hot water storage tank, wherein the heat storage determining means determines that the heat storage is insufficient. 2. The solid oxide fuel cell system according to claim 1 , wherein the heat storage operation switching means switches from the first heat storage operation mode to the second heat storage operation mode. Wherein the heat storage judging means determines that excessive heat accumulation in the operating state of the second thermal storage operation mode, the heat storage operation changeover means, claims, characterized in that switching from the second thermal storage operation mode to the first thermal storage operation mode 3. The solid oxide fuel cell system according to 2.

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