JP5588709B2 - Solid oxide fuel cell system and cogeneration system equipped with the same - Google Patents

Description

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

  Conventionally, a solid oxide fuel cell system in which a fuel cell stack using a solid electrolyte as a membrane for conducting oxygen ions is housed in a fuel cell housing is known. In this solid oxide fuel cell system, 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 on the other side. An oxygen electrode for reducing oxygen (oxidant) in the air is provided. In the fuel cell stack, electric power is generated by electrochemical reaction of hydrogen, carbon monoxide, hydrocarbons and oxygen as an oxidant in the reformed fuel gas obtained by reforming the fuel gas at a high temperature of 700 to 1000 ° C. Done. In recent years, such a solid oxide fuel cell system has attracted attention as a promising power generation technology, and is also used in, for example, a cogeneration system.

  In this solid oxide fuel cell system, since it is necessary to keep the operating temperature in the fuel cell stack high, surplus fuel gas that was not used for power generation (electrochemical reaction) in this fuel cell stack ( Reformed fuel gas) is combusted in the combustion chamber. In addition, a vaporizer and a reformer are disposed in the vicinity of the combustion chamber, and water (reforming water) is vaporized in the vaporizer using the combustion heat of excess fuel gas in the combustion chamber. At the same time, a reforming reaction using steam is performed in the reformer (see, for example, Patent Document 1). Further, at the time of starting the solid oxide fuel cell system, the fuel cell stack is heated by using a combustion reaction of fuel gas or an autothermal reforming reaction until the temperature rises to a temperature at which power generation is possible (for example, Patent Documents). 2).

  During the steady power generation operation of such a solid oxide fuel cell system, surplus fuel gas that has not been used for power generation in the fuel cell stack is burned in the combustion chamber, and the combustion heat is converted into heat of vaporization in the vaporizer. And used for reforming heat in the reformer. The combustion exhaust gas from the combustion chamber is discharged out of the fuel cell housing, and at the time of this discharge, heat exchange is performed between the combustion exhaust gas and air as an oxidizing material. The air heated by this heat exchange is fed to the air electrode side of the fuel cell stack.

  In this solid oxide fuel cell system, the power generation efficiency of the fuel cell stack increases as the fuel utilization rate (that is, the ratio of how much generated current is extracted with respect to the consumption rate of the valence electrons of the fuel gas) increases. Become. In general, when this fuel utilization rate is high, the amount of surplus fuel gas that is not used for power generation is reduced, so that the combustion heat obtained by combustion in the combustion chamber is reduced. Therefore, if this fuel utilization rate becomes too high, the amount of heat for keeping the temperature inside the fuel cell housing constant will be insufficient, leading to a decrease in the operating temperature of the fuel cell stack, and the power generation performance will be reduced. Occurs. For this reason, it is difficult to increase the fuel utilization rate beyond a certain value, although it depends on the rated power generation capacity.

JP 2006-19084 A JP 2008-243597 A

  The above-described conventional solid oxide fuel cell system has the following problems. As described above, since the vaporization reaction and the reforming reaction, which are endothermic reactions, are performed in the vaporizer and the reformer, respectively, the surplus fuel gas that is not used for power generation is necessary for the thermal self-sustaining operation of the fuel cell stack. It is necessary to heat the vaporizer and the reformer using this combustion heat. However, increasing the amount of surplus fuel gas during steady power generation operation leads to a decrease in fuel utilization rate, that is, a decrease in power generation efficiency in the fuel cell stack.

  In order to reduce the surplus amount of fuel gas and increase the power generation efficiency, a vaporizer that performs a vaporization reaction that is an endothermic reaction is disposed outside the fuel cell housing and is discharged from the combustion chamber to the outside of the fuel cell housing. A method of vaporizing using the heat of combustion exhaust gas is conceivable. However, in the low-load operation state at the partial load, the fuel gas supply amount is reduced compared to the high-load operation state at the rated load. The heat exchange temperature in the vessel decreases. In this state, if a large amount of water (reforming water) is supplied from the low load operation state to the high load operation state, the amount of combustion exhaust gas to be supplied to the vaporizer can be increased in time. However, there is a risk that vaporization failure occurs instantaneously. If vaporization failure occurs in this way, the supply amount of water vapor to the reformer becomes lower than the supply amount of carbon in the carbon hydrogen contained in the fuel gas, which may cause damage to the fuel cell stack. There is.

  SUMMARY OF THE INVENTION An object of the present invention is to burn a combustible component contained in combustion exhaust gas so as to suppress the occurrence of poor vaporization in the second vaporizer, and a cogeneration system including the solid oxide fuel cell system. Is to provide.

In the solid oxide fuel cell system according to claim 1 of the present invention, a reformer for reforming reaction with hydrocarbon fuel gas and steam, and reforming reformed by the reformer Fuel cell stack comprising a plurality of fuel cells for generating power by oxidizing and reducing fuel gas and oxidizing material, and combustion for burning surplus fuel gas that does not contribute to power generation in the fuel cell stack A chamber, a fuel cell housing covered with a heat insulating material to accommodate the reformer, the fuel cell stack, and the combustion chamber; and exhausting combustion exhaust gas from the combustion chamber to the outside of the fuel cell housing A solid oxide fuel cell system comprising:
A first vaporizer and a second vaporizer are provided for vaporizing water to be supplied to the reformer, and the first vaporizer is formed by combustion of excess fuel gas in the combustion chamber. The second carburetor is disposed outside the fuel cell housing so as to be heated by the combustion exhaust gas flowing through the combustion exhaust gas discharge line .
A combustion catalyst for combusting combustible components contained in the combustion exhaust gas is disposed in the second carburetor located outside the fuel cell housing or the combustion exhaust gas exhaust line on the upstream side thereof ,
Further, in relation to the second vaporizer, a fuel utilization rate control temperature detecting means for detecting the temperature of water vapor generated in the second vaporizer, and a fuel utilization rate in the fuel cell stack. Control means for controlling is provided, and when the temperature detected by the fuel utilization rate control temperature detection means is lower than the set temperature for fuel utilization rate control, the control means is configured to use the fuel utilization rate in the fuel cell stack. It is characterized by lowering .

  Further, in the solid oxide fuel cell system according to claim 2 of the present invention, the temperature control means for heating control for detecting the temperature of the water vapor generated by the second vaporizer, and the second vaporizer Auxiliary heating means for auxiliary heating of the water vapor generated by the above, when the detection temperature of the heating control temperature detection means is lower than the set temperature for heating control, the auxiliary heating means is activated, The water vapor generated by the second vaporizer is heated by the auxiliary heating means.

  Moreover, in the solid oxide fuel cell system according to claim 3 of the present invention, the auxiliary heating means is disposed in the second vaporizer, and the water vapor generated by the second vaporizer and the second vaporizer. The combustion catalyst disposed in the vaporizer is heated.

  In the solid oxide fuel cell system according to claim 4 of the present invention, the auxiliary oxide fuel cell system further includes a water vapor supply line for supplying water vapor generated by the second vaporizer to the reformer, and the auxiliary The heating means is disposed at a predetermined portion of the combustion exhaust gas discharge line upstream of the second carburetor located outside the fuel cell housing, and the steam flowing through the steam supply line and the combustion exhaust gas discharge line The combustion catalyst disposed at a predetermined site is heated.

In the cogeneration system according to claim 5 of the present invention, a reformer for reforming reaction with hydrocarbon fuel gas and steam, and a reformed fuel gas reformed by the reformer And a fuel cell stack comprising a plurality of fuel cells for generating power by oxidizing and reducing the oxidizing material, and a combustion chamber for burning surplus fuel gas that does not contribute to power generation in the fuel cell stack A fuel cell housing covered with a heat insulating material to accommodate the reformer, the fuel cell stack and the combustion chamber, and combustion for discharging combustion exhaust gas from the combustion chamber to the outside of the fuel cell housing An exhaust gas exhaust line; and exhaust heat recovery means for recovering exhaust heat of the combustion exhaust gas discharged from the combustion exhaust gas exhaust line as hot water, wherein the exhaust heat recovery means A heat exchanger for exhaust heat recovery for exchanging heat between exhaust heat and water of the exhaust gas discharged from the exhaust gas exhaust line, and hot water after heat exchange in the heat exchanger for exhaust heat recovery is stored. A cogeneration system having a hot water storage tank, and a circulation line for circulating water between the heat exchanger for exhaust heat recovery and the hot water storage tank,
A first vaporizer and a second vaporizer are provided for vaporizing water to be supplied to the reformer, and the first vaporizer is formed by combustion of excess fuel gas in the combustion chamber. accommodated in the fuel cell housing to be heated, the second vaporizer is arranged outside the fuel cell housing to be heated by the combustion exhaust gas flowing through the combustion gas discharge line,
A combustion catalyst for combusting combustible components contained in the combustion exhaust gas is disposed in the second carburetor located outside the fuel cell housing or the combustion exhaust gas exhaust line on the upstream side thereof ,
Further, in relation to the second vaporizer, a fuel utilization rate control temperature detecting means for detecting the temperature of water vapor generated in the second vaporizer, and a fuel utilization rate in the fuel cell stack. Control means for controlling is provided, and when the temperature detected by the fuel utilization rate control temperature detection means is lower than the set temperature for fuel utilization rate control, the control means is configured to use the fuel utilization rate in the fuel cell stack. It is characterized by lowering .

In the cogeneration system according to claim 6 of the present invention, the heat exchanger for exhaust heat recovery is disposed in the combustion exhaust gas discharge line on the downstream side of the second vaporizer. And

According to the solid oxide fuel cell system of claim 1 and the cogeneration system of claim 5 of the present invention, the second carburetor located outside the fuel cell housing or the combustion exhaust gas exhaust line upstream thereof Since a combustion catalyst is disposed in the flammable gas, combustible components contained in the combustion exhaust gas are burned by the action of the combustion catalyst. The heat exchange temperature in the second vaporizer can be increased by the combustion heat of the combustion exhaust gas and the amount of retained heat. Therefore, for example, even when a large amount of water (reforming water) is supplied to the second vaporizer when the low load operation state at the partial load is switched to the high load operation state at the rated load, This supplied water can be reliably vaporized, and the occurrence of poor vaporization in the second vaporizer can be suppressed. Further, when the temperature detected by the fuel utilization rate control temperature detecting means is lower than the fuel utilization rate control set temperature, the control means reduces the fuel utilization rate in the fuel cell stack. By reducing the fuel utilization rate in this way, the amount of surplus fuel gas that is not used for power generation in the fuel cell stack increases, the amount of heat retained in the combustion exhaust gas increases, and the heat exchange temperature in the second vaporizer increases. Since it raises, generation | occurrence | production of the vaporization defect in a 2nd vaporizer can be suppressed more effectively.

  Further, according to the solid oxide fuel cell system according to claim 2 of the present invention, the auxiliary heating means for supplementarily heating the water vapor generated by the second vaporizer is provided. When the temperature of the water vapor generated by the two vaporizer is lower than the set temperature for heating control, the water vapor is heated by the heat from the auxiliary heater. Thereby, the vaporization failure of water can be suppressed and water vapor of desired temperature can be supplied to a reformer.

  In the solid oxide fuel cell system according to claim 3 of the present invention, since the auxiliary heating means is disposed in the second vaporizer, the water vapor generated by the second vaporizer and the second The combustion catalyst disposed in the vaporizer is heated by auxiliary heating means. By heating the water vapor in this way, water vaporization defects can be suppressed. Further, by heating the combustion catalyst, the activity of the combustion catalyst can be kept constant, and the activity of the combustion catalyst can be quickly expressed even at the time of cold start of the solid oxide fuel cell system.

  In the solid oxide fuel cell system according to claim 4 of the present invention, the auxiliary heating means is provided at a predetermined portion of the combustion exhaust gas exhaust line upstream of the second carburetor located outside the fuel cell housing. Since it is disposed, the steam flowing through the steam supply line and the combustion catalyst disposed at the predetermined portion are heated by the auxiliary heating means. By heating the water vapor in this way, water vaporization defects can be suppressed. Further, by heating the combustion catalyst, the activity of the combustion catalyst can be kept constant, and the activity of the combustion catalyst can be quickly expressed even at the time of cold start of the solid oxide fuel cell system.

In the cogeneration system according to claim 6 of the present invention, the exhaust heat recovery heat exchanger is disposed in the combustion exhaust gas discharge line on the downstream side of the second carburetor. The combustion exhaust gas is absorbed by the exhaust heat recovery heat exchanger on the downstream side of the vaporizer. As a result, the temperature of the combustion exhaust gas flowing through the second vaporizer increases, and the exhaust heat of the combustion exhaust gas can be used for vaporizing water (reforming water) in the second vaporizer, and the second vaporizer Then, the exhaust heat of the combustion exhaust gas after being used for heat exchange can be effectively recovered as hot water by the heat exchanger for exhaust heat recovery.

1 is a block diagram schematically showing a configuration of a solid oxide fuel cell system according to a first embodiment of the present invention. It is a flowchart which shows the flow of control of the solid oxide fuel cell system of FIG. It is a block diagram which shows simply the structure of the solid oxide fuel cell system by the 2nd Embodiment of this invention. It is a flowchart which shows the flow of control of the solid oxide fuel cell system of FIG. It is a block diagram which shows simply the structure of the solid oxide fuel cell system by the 3rd Embodiment of this invention. It is a flowchart which shows the flow of control of the solid oxide fuel cell system of FIG. It is a block diagram which shows simply the structure of the solid oxide fuel cell system by the 4th Embodiment of this invention. It is a flowchart which shows the flow of control of the solid oxide fuel cell system of FIG.

Hereinafter, various embodiments of a solid oxide fuel cell system according to the present invention and a cogeneration system including the same will be described with reference to the accompanying drawings.
[First Embodiment]
First, with reference to FIG.1 and FIG.2, the solid oxide fuel cell system by 1st Embodiment is demonstrated. FIG. 1 is a block diagram schematically showing a configuration of a solid oxide fuel cell system according to a first embodiment of the present invention, and FIG. 2 is a control flow of the solid oxide fuel cell system of FIG. It is a flowchart which shows.

  Referring to FIG. 1, the illustrated solid oxide fuel cell system 2 includes a reformer 4, a fuel cell stack 6, an air preheater 8, a first vaporizer 10, and a second vaporizer 12. Hereinafter, the configuration of the solid oxide fuel cell system 2 will be described in detail.

  In the reformer 4, for example, a catalyst in which ruthenium is supported on alumina is used as a reforming catalyst. By this reforming catalyst, for example, a hydrocarbon-based fuel gas (hereinafter referred to as “fuel”) containing methane such as natural gas as a main component. Gas)) is steam reformed. The reformer 4 is connected to the first vaporizer 10 via a gas / steam feed line 14.

  The fuel cell stack 6 is configured by stacking a plurality of solid oxide fuel cells (not shown) for generating power by an electrochemical reaction via current collecting members. The fuel cell stack 6 includes a solid electrolyte (not shown) that conducts oxygen ions, a fuel electrode (not shown) provided on one side of the solid electrolyte, and an oxygen electrode provided on the other side of the solid electrolyte. (Not shown), and, for example, zirconia doped with yttria is used as the solid electrolyte.

  The fuel electrode introduction side of the fuel cell stack 6 is connected to the reformer 4 via a reformed fuel gas supply line 16. The oxygen electrode introduction side of the fuel cell stack 6 is connected to an air preheater 8 for preheating air (oxidant) via an air supply line 18. The air preheater 8 is connected to the blower blower 22 via the air supply line 20. By controlling the rotational speed of the blower blower 22, the amount of air supplied through the air supply line 20 is controlled.

  A combustion chamber 24 is provided at each discharge side of the fuel electrode and the oxygen electrode of the fuel cell stack 6, and excess fuel gas discharged from the fuel electrode side of the fuel cell stack 6 (that is, in the fuel cell stack 6). The fuel gas that has not been used for power generation) and the air (including oxygen) discharged from the oxygen electrode are supplied to the combustion chamber 24 and burned. The combustion chamber 24 is connected to the air preheater 8 via a first combustion exhaust gas discharge line 26, and the air preheater 8 is further connected to the second carburetor 12 via a second combustion exhaust gas discharge line 28. . In the air preheater 8, heat exchange is performed between the air supplied through the air supply line 20 and the combustion exhaust gas supplied through the first combustion exhaust gas discharge line 26, and the air heated by this heat exchange is performed. Is fed to the oxygen electrode side of the fuel cell stack 6 through the air feed line 18.

  The first vaporizer 10 is connected to a fuel gas supply source 32 for supplying fuel gas via a fuel gas supply line 30. The fuel gas supply line 30 is provided with a desulfurizer 34, a fuel gas supply pump 35, and a fuel flow rate sensor 36. The fuel gas supply line 30 is further provided with two open / close valves 40 and 42. The two on-off valves 40 and 42 are configured to be openable and closable, and the fuel gas supply line 30 is opened / closed to stop supplying / stopping the fuel gas. The desulfurizer 34 removes sulfur components contained in the fuel gas. The fuel gas supply pump 35 boosts the fuel gas flowing through the fuel gas supply line 30 and supplies the fuel gas from the fuel gas supply source 32 to the fuel gas supply line so that the flow rate of the fuel flow sensor 36 becomes a set value. 30 is supplied to the first vaporizer 10. The first vaporizer 10 is connected to the second vaporizer 12 via a water vapor feed line 44, and water vapor (described later) generated by the second vaporizer 12 is fed through the water vapor feed line 44. Be paid.

  The above-described reformer 4, fuel cell stack 6, air preheater 8, and first vaporizer 10 are each accommodated in a fuel cell housing 46. The inner wall surface of the fuel cell housing 46 is covered with a heat insulating material to define a high temperature chamber 48, and the reformer 4, the fuel cell stack 6, the air preheater 8 and the first vaporizer 10 are in a high temperature state in the high temperature chamber 48. To be kept. The first carburetor 10 and the reformer 4 are disposed in the vicinity of the combustion chamber 24. By disposing the first carburetor 10 and the reformer 4 in this way, the first carburetor 10 and the reformer are generated by the combustion heat of the fuel gas in the combustion chamber 24. The vessel 4 is heated. Thereby, in the first vaporizer 10, the steam supplied from the second vaporizer 12 is further heated by the combustion heat of the fuel gas in the combustion chamber 24, thereby generating reforming steam.

  The second vaporizer 12 is connected to a reforming water supply source 52 (for example, a water pipe or a water tank) via a water supply line 50, and water (reforming water) is supplied to the water supply line 50. A water supply pump 54 is provided for this purpose. Water from the reforming water supply source 52 is supplied to the second vaporizer 12 through the water supply line 50. An exhaust gas flow path (not shown) through which the combustion exhaust gas in the second vaporizer 12 flows is filled with a combustion catalyst 56, which is a noble metal combustion catalyst such as platinum or palladium, or manganese, for example. And a base metal combustion catalyst such as iron. In particular, platinum and palladium are highly active against various gas components, and can be used even in a low temperature range of 300 ° C. or lower. In addition, a temperature detection sensor 58 (constituting temperature detection means for controlling fuel utilization) is disposed in the vicinity of a water vapor channel (not shown) through which water vapor (including water) flows in the second vaporizer 12. Has been. This temperature detection sensor 58 detects the temperature of the water vapor generated in the second vaporizer 12 and flowing through the water vapor channel. Note that the temperature detection sensor 58 is supported by a metal casing (not shown) where the temperature of the water vapor can be lowered most, for example, a water flow path, in order to reliably detect the temperature drop of the water vapor. It is preferable to arrange in a place. Further, the exhaust gas passage and the water vapor passage in the second vaporizer 12 are configured to be able to transfer heat to each other via the combustion catalyst 58.

  The second carburetor 12 is disposed outside the fuel cell housing 46. By disposing the second carburetor 12 in this manner, the water flowing in the second combustion exhaust gas discharge line 28 is used for vaporization of water in the second carburetor 12. The heat of the exhaust gas is used, and the heat in the fuel cell housing 46 is not used. When the combustion exhaust gas from the second combustion exhaust gas discharge line 28 flows through the exhaust gas passage in the second carburetor 12, the combustible component contained in the combustion exhaust gas is caused by the action of the combustion catalyst 56 filled in the exhaust gas passage. Burned. The amount of heat retained in the combustion exhaust gas and the combustion heat are transmitted to the steam flow path in the second vaporizer 12 via the combustion catalyst 56, and supplied from the reforming water supply source 52 through the water supply line 50 by this transmitted heat. The water is vaporized to generate water vapor.

  In the solid oxide fuel cell system 2 of the present embodiment, a controller 60 (which constitutes a control means) for controlling the fuel utilization rate in the fuel cell stack 6 is provided. The fuel utilization rate is the ratio of the amount of fuel gas consumed for power generation in the fuel cell stack 6 to the amount of fuel gas supplied to the fuel cell stack 6. The controller 60 controls the fuel utilization rate by controlling the output of the fuel gas supply pump 35 based on the temperature detected by the temperature detection sensor 58 and controlling the amount of fuel gas supplied to the fuel cell stack 6. To do. In the present embodiment, when the temperature detected by the temperature detection sensor 58 becomes equal to or higher than the first set temperature (for example, 120 ° C.), the controller 60 increases the fuel utilization rate to set the second set value (for example, 77%). When the detected temperature of the temperature detection sensor 58 becomes equal to or lower than a second set temperature (for example, 110 ° C.) (which constitutes the set temperature for fuel utilization rate control), the controller 60 reduces the fuel utilization rate to a first set value (for example, 65 %). When the fuel utilization rate is reduced in this way, the ratio of the fuel gas consumed for power generation in the fuel cell stack 6 is reduced, so that the amount of surplus fuel gas is increased. Thereby, while being able to raise the heat exchange temperature in the 1st vaporizer | carburetor 10, the retained heat amount of the combustion exhaust gas discharged | emitted from the combustion chamber 24 increases, and the heat exchange temperature in the 2nd vaporizer | carburetor 12 is raised. Can do.

  Referring also to FIG. 2, the power generation operation of the solid oxide fuel cell system 2 of the present embodiment is performed as follows. When the solid oxide fuel cell system 2 is started (step S1), the blower blower 22 is activated, and the air from the blower blower 22 passes through the air supply line 20, the air preheater 8, and the air supply line 18, and the fuel cell stack. 6 is supplied to the oxygen electrode side 6 (step S2). The air discharged from the oxygen electrode side of the fuel cell stack 6 is sent to the combustion chamber 24. Further, the two on-off valves 40 and 42 are held in the open state, the fuel gas supply pump 35 is operated, and the fuel gas from the fuel gas supply source 32 is desulfurized by the desulfurizer 34 and then the fuel gas. It is supplied to the first vaporizer 10 through the supply line 30. The fuel gas supplied to the first vaporizer 10 is supplied to the fuel electrode side of the fuel cell stack 6 through the gas / steam supply line 14, the reformer 4, and the reformed fuel gas supply line 16 (step). S3). The fuel gas discharged from the fuel electrode side of the fuel cell stack 6 is sent to the combustion chamber 24.

  In such a state where air and fuel gas are supplied, an ignition device (not shown) disposed in the combustion chamber 24 is ignited to be discharged from the air electrode side of the fuel cell stack 6. The fuel gas discharged from the fuel electrode side of the fuel cell stack 6 is combusted using air as combustion air (step S4). The fuel cell stack 6, the reformer 4 and the first vaporizer 10 are heated by the combustion heat of the fuel gas in the combustion chamber 24.

  The flue gas discharged from the combustion chamber 24 is fed to the second carburetor 12 through the first flue gas discharge line 26, the air preheater 8 and the second flue gas exhaust line 28. When fed in this way, combustible components contained in the combustion exhaust gas are burned by the action of the combustion catalyst 56 filled in the exhaust gas flow path in the second vaporizer 12. When the temperature in the second vaporizer 12 rises due to the amount of heat of combustion exhaust gas and the combustion heat, water from the reforming water supply source 52 is supplied to the second vaporizer 12 through the water supply line 50 (step S5). . In the second vaporizer 12, water is vaporized by the retained heat amount of the combustion exhaust gas and the combustion heat to generate water vapor, and the generated water vapor is supplied to the first vaporizer 10 through the water vapor supply line 44. .

  In the first vaporizer 10, the fuel gas is heated by the combustion heat of the fuel gas in the combustion chamber 24, and the steam supplied from the second vaporizer 12 is further heated to generate reforming steam. Is done. The heated fuel gas and the generated steam are fed to the reformer 4 through the gas / steam feed line 14.

  In the reformer 4, the steam reforming reaction is performed between the fuel gas and the steam by the combustion heat of the fuel gas in the combustion chamber 24. The reformed fuel gas (reformed fuel gas) is fed to the fuel electrode side of the fuel cell stack 6 through the reformed fuel gas feed line 16. In the air preheater 8, heat exchange is performed between the air from the blower blower 22 and the combustion exhaust gas discharged from the combustion chamber 24 and flowing through the first combustion exhaust gas discharge line 26. The air heated by heat exchange is supplied to the oxygen electrode side of the fuel cell stack 6 through the air supply line 18. The fuel gas discharged from the fuel electrode side of the fuel cell stack 6 is combusted using the air discharged from the oxygen electrode side of the fuel cell stack 6 as combustion air.

  When the temperature of the fuel cell stack 6 reaches the operating temperature in this way, the process proceeds from step S6 to step S7, and the steady power generation operation of the solid oxide fuel cell system 2 is performed. In this steady power generation operation, the flow rate of the fuel gas from the fuel gas supply source 32 is controlled by controlling the output of the fuel gas supply pump 35 so that the flow rate of the fuel flow sensor 36 becomes a set value. Then, the fuel is supplied to the first vaporizer 10 through the fuel gas supply line 30. Further, the water from the reforming water supply source 52 is supplied to the second vaporizer 12 through the water supply line 50, and the water is vaporized in the second vaporizer 12 as described above to become steam. The steam from the second vaporizer 12 is fed to the first vaporizer 10 through the steam feed line 44 and further heated. The fuel gas and water vapor from the first vaporizer 10 are fed to the reformer 4 through the gas / steam feed line 14, and the fuel gas (reformed fuel gas) reformed by the reformer 4 is supplied. The fuel is fed to the fuel electrode side of the fuel cell stack 6 through the reformed fuel gas feed line 16. Further, the air from the blower blower 22 is supplied to the air preheater 8 through the air supply line 20, and heat exchange is performed between the air preheater 8 and the combustion exhaust gas flowing through the first combustion exhaust gas discharge line 26. The air heated by heat exchange is supplied to the oxygen electrode side of the fuel cell stack 6 through the air supply line 18.

  The reformed fuel gas is oxidized on the fuel electrode side of the fuel cell stack 6, oxygen in the air is reduced on the oxygen electrode side, and by an electrochemical reaction due to oxidation on the fuel electrode side and reduction on the oxygen electrode side Power generation is performed. Excess fuel gas and air discharged from the fuel electrode side and the oxygen electrode side of the fuel cell stack 6 are supplied to the combustion chamber 24, and the excess fuel gas is combusted using oxygen in the air. The first vaporizer 10 and the reformer 4 are heated by the combustion heat of the fuel gas in the combustion chamber 24. Combustion exhaust gas generated by the combustion reaction in the combustion chamber 24 is supplied to the air preheater 8 through the first combustion exhaust gas discharge line 26, and heat exchange with air supplied from the blower blower 22 in the air preheater 8 is performed. Used for Thereafter, the combustion exhaust gas is supplied to the second vaporizer 12 through the second combustion exhaust gas discharge line 28, and is used for vaporizing water in the second vaporizer 12 and then discharged to the atmosphere.

  In the initial stage of the steady power generation operation, the temperature of the water vapor generated by the second vaporizer 12 is not sufficiently increased, that is, the temperature detected by the temperature detection sensor 58 is equal to or lower than the first set temperature (for example, 120 ° C.). Sometimes, the controller 60 controls the fuel utilization rate in the fuel cell stack 6 to a first set value (for example, 65%) by reducing the fuel utilization rate (step S8). Thereby, the solid oxide fuel cell system 2 is operated in the first operation state in which the fuel utilization rate is reduced (step S9). As described above, when the fuel utilization rate is reduced, the amount of surplus fuel gas is increased, the amount of heat retained in the combustion exhaust gas is increased, and the heat exchange temperature in the second carburetor 12 is increased. 12 can increase the temperature of the water vapor generated.

  When the temperature detected by the temperature detection sensor 58 is equal to or higher than the first set temperature, the process proceeds from step S10 to step S11, and the controller 60 increases the fuel utilization rate in the fuel cell stack 6 to increase the second set value (for example, 77%). Thereby, the solid oxide fuel cell system 2 is operated in the second operation state in which the fuel utilization rate is increased (step S12). By increasing the fuel utilization rate in this way, the ratio of the fuel gas consumed for power generation in the fuel cell stack 6 increases, and the power generation efficiency in the fuel cell stack 6 is increased.

  Further, in the low load operation state at the partial load, the amount of fuel gas supplied is lower than in the high load operation state at the rated load, so that the retained heat amount is reduced by reducing the amount of combustion exhaust gas, and the second The heat exchange temperature in the vaporizer 12 decreases. In such a case, when the temperature detected by the temperature detection sensor 58 becomes equal to or lower than the second set temperature (eg, 110 ° C.), the process returns from step S13 to step S8, and the controller 60 uses the fuel utilization rate in the fuel cell stack 6 Is controlled to the first set value, and the solid oxide fuel cell system 2 is operated in the first operating state (step S9). As a result, the amount of surplus fuel gas increases, the amount of heat retained in the combustion exhaust gas increases, and the heat exchange temperature in the second vaporizer 12 rises, so that the occurrence of poor vaporization in the second vaporizer 12 is suppressed. Can do.

  As described above, in the solid oxide fuel cell system 2 of the present embodiment, since the combustion catalyst 56 is disposed in the second carburetor 12, it is contained in the combustion exhaust gas by the action of the combustion catalyst 56. By burning the combustible component, the heat exchange temperature in the second vaporizer 12 can be increased. Therefore, for example, when a low load operation state at a partial load is switched to a high load operation state at a rated load, a large amount of water is supplied from the reforming water supply source 52 to the second vaporizer 12. However, the supplied water can be reliably vaporized, and the occurrence of poor vaporization in the second vaporizer 12 can be suppressed.

In the present embodiment, the combustion catalyst 56 is disposed in the second carburetor 12, but the second combustion exhaust gas discharge line on the upstream side of the second carburetor 12 is located outside the fuel cell housing 46. The combustion catalyst 56 may be arranged on the 28.
[Second Embodiment]
Next, a solid oxide fuel cell system according to a second embodiment will be described with reference to FIGS. 3 and 4. FIG. 3 is a block diagram schematically showing the configuration of the solid oxide fuel cell system according to the second embodiment of the present invention, and FIG. 4 is a control flow of the solid oxide fuel cell system of FIG. It is a flowchart which shows. In each of the embodiments described below, the same reference numerals are given to substantially the same components as those in the first embodiment, and the description thereof is omitted.

  Referring to FIG. 3, in the solid oxide fuel cell system 2 </ b> A of the present embodiment, a predetermined portion of the second combustion exhaust gas discharge line 28 located outside the fuel cell housing 46 and upstream of the second carburetor 12 and An auxiliary heater 62 (constituting auxiliary heating means) is disposed in the steam supply line 44. A combustion catalyst 56 is disposed at the predetermined portion of the second combustion exhaust gas discharge line 28. The auxiliary heater 62 is composed of, for example, an electric heater or the like, and heats the steam flowing through the steam supply line 44 and the combustion catalyst 56 disposed at the predetermined portion of the second combustion exhaust gas discharge line 28, respectively. A part of the electric power generated by the fuel cell stack 6 is supplied to the auxiliary heater 62, and the auxiliary heater 62 is operated by this electric power. Further, a first temperature detection sensor 64 is disposed in the vicinity of a water vapor flow path (not shown) in the second vaporizer 12, and the first temperature detection sensor 64 is generated by the second vaporizer 12. The temperature of water vapor flowing through the water vapor channel is detected. A second temperature detection sensor 66 (which constitutes temperature detection means for heating control) is disposed in the auxiliary heater 62 in the vicinity of the water vapor supply line 44, and the second temperature detection sensor 66 is provided with the water vapor supply line. The temperature of water vapor flowing through 44 is detected.

  The controller 60A controls the fuel utilization rate based on the temperature detected by the first temperature detection sensor 64, and controls the operation of the auxiliary heater 62 based on the temperature detected by the second temperature detection sensor 66. When the temperature detected by the first temperature detection sensor 64 becomes equal to or higher than the first set temperature (for example, 120 ° C.), the controller 60A increases the fuel utilization rate and sets the second set value (for example, 77%). When the temperature detected by the second temperature detection sensor 66 becomes equal to or lower than a second set temperature (for example, 130 ° C.) (which constitutes the set temperature for heating control), the controller 60A starts the operation of the auxiliary heater 62, and When the detected temperature of the two-temperature detecting means 66 becomes equal to or higher than a third set temperature (for example, 150 ° C.), the controller 60A stops the operation of the auxiliary heater 62.

  Referring also to FIG. 4, the power generation operation of the solid oxide fuel cell system 2A of the present embodiment is performed as follows. In the steady power generation operation of the solid oxide fuel cell system 2A, first, steps S21 to S25 are performed as in the first embodiment. In step S26, for example, when the heat exchange temperature in the second vaporizer 12 is lowered in the low load operation state at the time of partial load and the detected temperature of the second temperature detection sensor 66 becomes equal to or lower than the second set temperature, the steps from step S26 to step S26 are performed. In S27, the controller 60A starts the operation of the auxiliary heater 62. When the auxiliary heater 62 is actuated, the water vapor flowing through the water vapor supply line 44 is heated by the heat from the auxiliary heater 62, thereby suppressing water vaporization failure. In addition, the combustion catalyst 56 disposed at the predetermined portion of the second combustion exhaust gas discharge line 28 is heated by the heat from the auxiliary heater 62, whereby the activity of the combustion catalyst 56 can be kept constant, Even when the solid oxide fuel cell system 2A is cold-started, the activity of the combustion catalyst 56 can be rapidly expressed.

When the temperature of the water vapor flowing through the water vapor supply line 44 rises and the temperature detected by the second temperature detection sensor 66 becomes equal to or higher than the third set temperature, the process proceeds from step S28 to step S29, and the controller 60A activates the auxiliary heater 62. Stop. Thereafter, the process returns to step S25, and the above-described steps S25 to S29 are repeated.
[Third Embodiment]
Next, a solid oxide fuel cell system according to a third embodiment will be described with reference to FIGS. FIG. 5 is a block diagram schematically showing a configuration of a solid oxide fuel cell system according to a third embodiment of the present invention, and FIG. 6 is a control flow of the solid oxide fuel cell system of FIG. It is a flowchart which shows.

  Referring to FIG. 5, in the solid oxide fuel cell system 2B of the present embodiment, the auxiliary heater 62B is built in the second vaporizer 12B, and combustion in the second vaporizer 12B is performed by the heat from the auxiliary heater 62B. The catalyst 56 is configured to be heated. Further, a timer (not shown) for measuring the operation time of the auxiliary heater 62B is provided in association with the controller 60B. The controller 60B controls the fuel utilization rate based on the detection temperature of the first temperature detection sensor 64B and the measurement time of the timer, and based on the detection temperature of the second temperature detection sensor 66B (which constitutes the temperature detection means for heating control). Then, the operation of the auxiliary heater 62B is controlled. When the detected temperature of the first temperature detection sensor 64B becomes equal to or higher than the first set temperature (for example, 120 ° C.), the controller 60B increases the fuel utilization rate and sets the second set value (for example, 77%) to perform the second operation. It becomes a state. In this second operating state, when the temperature detected by the second temperature detection sensor 66B becomes equal to or lower than the second set temperature (for example, 130 ° C.) (which constitutes the set temperature for heating control), the controller 60B operates the auxiliary heater 62B. The time measurement by the timer is started. When the detected temperature of the second temperature detection sensor 66B becomes equal to or higher than a third set temperature (for example, 150 ° C.), the controller 60B stops the operation of the auxiliary heater 62B. Alternatively, when the time measured by the timer exceeds a predetermined set time (for example, 5 minutes), the controller 60B decreases the fuel utilization rate and sets the first set value (for example, 65%) to perform the first operation. In this first operating state, when the temperature detected by the second temperature detection sensor 66B becomes equal to or higher than the third set temperature, the controller 60B stops the operation of the auxiliary heater 62B.

  The power generation operation of the solid oxide fuel cell system 2B of the present embodiment will be described with reference to FIG. In the steady power generation operation of the solid oxide fuel cell system 2B, first, Steps S41 to S45 are performed as in the first embodiment. In step S46, for example, when the heat exchange temperature in the second vaporizer 12B decreases in the low load operation state at the time of partial load, and the detected temperature of the second temperature detection sensor 66B becomes equal to or lower than the second set temperature, the process proceeds from step S46 to step S46. Proceeding to S47, the operation of the auxiliary heater 62B is started, and the operation time of the auxiliary heater 62B is measured by a timer (step S48). When the auxiliary heater 62B is activated, the water vapor flowing in the second vaporizer 12B is heated by the heat from the auxiliary heater 62B, and the combustion catalyst 56 in the second vaporizer 12B is heated. By heating the combustion catalyst 56 in this manner, the activity of the combustion catalyst 56 can be kept constant, and the activity of the combustion catalyst 56 can be quickly expressed even when the solid oxide fuel cell system 2B is cold-started. be able to.

  When the temperature of the water vapor flowing through the water vapor supply line 44 rises and the temperature detected by the second temperature detection sensor 66B becomes equal to or higher than the third set temperature within the set time of the timer, the process proceeds from step S49 to step S50, and the auxiliary The operation of the heater 62B is stopped and the timer is reset (step S51). Thereafter, the process returns to step S45.

  In step S49, even if the set time has elapsed, the temperature of the water vapor flowing through the water vapor supply line 44 does not rise to the third set temperature, that is, the detected temperature of the second temperature detection sensor 66B is equal to or lower than the third set temperature and When the measured time of the timer exceeds the set time, the process proceeds from step S49 to step S53 through step S52. The controller 60B reduces the fuel utilization rate in the fuel cell stack 6 to control the first set value, and the solid oxide fuel cell system 2B is operated in the first operation state (step S54). Thereby, the amount of surplus fuel gas increases, the amount of heat retained in the combustion exhaust gas increases, the heat exchange temperature in the second vaporizer 12B is increased, and the temperature of the steam flowing through the steam supply line 44 is increased. Can do.

  When the temperature of the water vapor flowing through the water vapor supply line 44 rises and the temperature detected by the second temperature detection sensor 66B becomes equal to or higher than the third set temperature, the process proceeds from step S55 to step S56, and the operation of the auxiliary heater 62B is stopped. At the same time, the timer is reset (step S57). Thereafter, the process returns to step S44.

When the combustion catalyst 56 is arranged in the second combustion exhaust gas discharge line 28 on the upstream side of the second carburetor 12B, the upstream side of the second carburetor 12B located outside the fuel cell housing 46. You may make it arrange | position the auxiliary heater 62B in the 2nd combustion exhaust gas discharge line 28 and the water vapor | steam supply line 44 in the side.
[Fourth Embodiment]
Next, with reference to FIG.7 and FIG.8, the solid oxide fuel cell system of 4th Embodiment is demonstrated. FIG. 7 is a block diagram schematically showing a configuration of a solid oxide fuel cell system according to the fourth embodiment of the present invention, and FIG. 8 is a control flow of the solid oxide fuel cell system of FIG. It is a flowchart which shows.

  Referring to FIG. 7, the solid oxide fuel cell system 2C of the present embodiment is applied to a cogeneration system, and is provided with exhaust heat recovery means 68 for recovering exhaust heat of combustion exhaust gas. The exhaust heat recovery means 68 includes an exhaust heat recovery heat exchanger 70 for exchanging heat between exhaust heat of the combustion exhaust gas flowing through the second combustion exhaust gas discharge line 28 and water, and an exhaust heat recovery heat exchanger 70. A hot water storage tank 72 for storing hot water after heat exchange, and a circulation line 74 for circulating water between the heat exchanger for exhaust heat recovery 70 and the hot water storage tank 72 are provided. The circulation line 74 is provided with a circulation pump 76 for feeding water. When the circulation pump 76 is activated, the water in the hot water storage tank 72 flows through the circulation line 74, and the water flowing through the circulation line 74 and the combustion exhaust gas flowing through the second combustion exhaust gas discharge line 28 in the heat exchanger 70 for exhaust heat recovery. Heat exchange takes place between them. The hot water heated by the heat exchange flows into the hot water storage tank 72 through the circulation line 74, and thus the exhaust heat of the combustion exhaust gas is stored in the hot water storage tank 72 as hot water.

  In addition, it is preferable to arrange | position the heat exchanger 70 for waste heat collection | recovery downstream from the arrangement | positioning site | part of the 2nd vaporizer | carburetor 12B in the 2nd combustion exhaust gas discharge line 28. FIG. By arranging in this way, the combustion exhaust gas is absorbed by the exhaust heat recovery heat exchanger 70 on the downstream side of the second vaporizer 12B, so the temperature of the combustion exhaust gas flowing through the second vaporizer 12B becomes higher. The exhaust heat of the combustion exhaust gas can be used for the vaporization of water (reforming water) in the second vaporizer 12B, and the exhaust heat of the combustion exhaust gas after being used for heat exchange in the second vaporizer 12B. Can be effectively recovered as warm water by the heat exchanger 70 for exhaust heat recovery.

  The controller 60C controls the fuel utilization rate based on the detected temperatures of the first and second temperature detection sensors 64B and 66B, and controls the operation of the auxiliary heater 62B based on the detected temperature of the second temperature detection sensor 66B. When the detected temperature of the first temperature detection sensor 64B becomes equal to or higher than the first set temperature (for example, 120 ° C.), the controller 60C increases the fuel utilization rate and sets the second set value (for example, 77%). The detection temperature of the second temperature detection sensor 66B (which constitutes the temperature detection means for heating control and the temperature detection means for fuel utilization rate control) is the second set temperature (for example, 130 ° C.) (the set temperature for heating control and the fuel use). The controller 60C starts the operation of the auxiliary heater 62B at the same time, lowers the fuel utilization rate and sets it to the first set value (for example, 65%). When the temperature detected by the two-temperature detection sensor 66B becomes equal to or higher than a third set temperature (for example, 150 ° C.), the controller 60C stops the operation of the auxiliary heater 62B and simultaneously increases the fuel utilization rate and sets it to the second set value. To do.

  Referring also to FIG. 8, the power generation operation of the solid oxide fuel cell system 2C of the present embodiment is performed as follows. In the steady power generation operation of the solid oxide fuel cell system 2C, first, Steps S61 to S65 are performed as in the first embodiment. In step S66, for example, when the heat exchange temperature in the second vaporizer 12B is lowered in the low load operation state at the time of partial load, and the detected temperature of the second temperature detection sensor 66B becomes equal to or lower than the second set temperature, the steps from step S66 to step S66 are performed. Proceeding to S67, the operation of the auxiliary heater 62B is started, and at the same time, the fuel utilization rate is lowered and set to the first set value, and the solid oxide fuel cell system 2C is operated in the first operation state. (Step S68). By operating the auxiliary heater 62B, the water vapor flowing in the second vaporizer 12B is heated by the heat from the auxiliary heater 62B, and the combustion catalyst 56 in the second vaporizer 12B is heated. Further, as the fuel utilization rate decreases, the amount of surplus fuel gas increases, the amount of heat retained in the combustion exhaust gas increases, the heat exchange temperature in the second vaporizer 12B increases, and the steam supply line 44 increases. The temperature of the water vapor flowing through is increased.

  When the temperature of the water vapor flowing through the water vapor supply line 44 rises and the temperature detected by the second temperature detection sensor 66B becomes equal to or higher than the third set temperature, the process proceeds from step S69 to step S70, and the operation of the auxiliary heater 62B is stopped. At the same time, the fuel utilization rate is increased and set to the second set value, and the solid oxide fuel cell system 2C is operated in the second operation state (step S65).

  When the combustion catalyst 56 is arranged in the second combustion exhaust gas discharge line 28 on the upstream side of the second carburetor 12B, the upstream side of the second carburetor 12B located outside the fuel cell housing 46. You may make it arrange | position the auxiliary heater 62B in the 2nd combustion exhaust gas discharge line 28 and the water vapor | steam supply line 44 in the side.

  The various embodiments of the solid oxide fuel cell system and the cogeneration system including the solid oxide fuel cell system according to the present invention have been described above, but the present invention is not limited to such embodiments and departs from the scope of the present invention. Various modifications or corrections can be made without any problem.

  For example, two water supply lines (including a reforming water supply source, a water supply pump, etc.) are provided, and water from one water supply line is supplied to the first vaporizer 10 and the other water is supplied. You may make it supply the water from a supply line to the 2nd vaporizer | carburetor 12 (12B). In such a case, the second vaporizer 12 (12B) is connected to the reformer 4 through the steam supply line 44, and the steam from the second vaporizer 12 (12B) is reformed through the steam supply line 44. You may comprise so that it may send to the device 4.

  Further, for example, in each of the above embodiments, the fuel gas supply line 30 is connected to the first vaporizer 10, but instead of such a configuration, the fuel gas supply line 30 is connected to the reformer 4, The fuel gas from the fuel gas supply source 32 may be directly supplied to the reformer 4.

2, 2A, 2B, 2C Solid oxide fuel cell system 4 Reformer 6 Fuel cell stack 10 First vaporizer 12, 12B Second vaporizer 24 Combustion chamber 34 Desulfurizer 35 Fuel gas supply pump 36 Fuel flow rate Sensor 46 Fuel cell housing 56 Combustion catalyst 58 Temperature detection sensor 60, 60A, 60B, 60C Controller 62, 62A Auxiliary heater 64, 64B First temperature detection sensor 66, 66B Second temperature detection sensor 68 Waste heat recovery means 70 Waste heat Heat exchanger for recovery 72 Hot water storage tank 74 Circulation line

Claims (6)

A reformer for reforming reaction with hydrocarbon-based fuel gas and steam, and a plurality of units for generating power by oxidation and reduction of the reformed fuel gas and the oxidizing material reformed by the reformer. A fuel cell stack including fuel cells, a combustion chamber for burning surplus fuel gas that does not contribute to power generation in the fuel cell stack, the reformer, the fuel cell stack, and the combustion chamber. A solid oxide fuel cell system comprising: a fuel cell housing covered with a heat insulating material for housing; and a combustion exhaust gas discharge line for discharging combustion exhaust gas from the combustion chamber to the outside of the fuel cell housing. There,
A first vaporizer and a second vaporizer are provided for vaporizing water to be supplied to the reformer, and the first vaporizer is formed by combustion of excess fuel gas in the combustion chamber. The second carburetor is disposed outside the fuel cell housing so as to be heated by the combustion exhaust gas flowing through the combustion exhaust gas discharge line .
A combustion catalyst for combusting combustible components contained in the combustion exhaust gas is disposed in the second carburetor located outside the fuel cell housing or the combustion exhaust gas exhaust line on the upstream side thereof ,
Further, in relation to the second vaporizer, a fuel utilization rate control temperature detecting means for detecting the temperature of water vapor generated in the second vaporizer, and a fuel utilization rate in the fuel cell stack. Control means for controlling is provided, and when the temperature detected by the fuel utilization rate control temperature detection means is lower than the set temperature for fuel utilization rate control, the control means is configured to use the fuel utilization rate in the fuel cell stack. solid oxide fuel cell system characterized by lowering. A heating control temperature detecting means for detecting the temperature of the water vapor generated by the second vaporizer; and an auxiliary heating means for auxiliary heating of the water vapor generated by the second vaporizer. When the temperature detected by the temperature control means for heating control is lower than the set temperature for heating control, the auxiliary heating means is activated, and the water vapor generated by the second vaporizer is heated by the auxiliary heating means. The solid oxide fuel cell system according to claim 1. The auxiliary heating means is disposed in the second vaporizer, and heats the water vapor generated by the second vaporizer and the combustion catalyst disposed in the second vaporizer. 3. The solid oxide fuel cell system according to 2. A water vapor supply line for supplying water vapor generated by the second vaporizer to the reformer; and the auxiliary heating means is located upstream of the second vaporizer located outside the fuel cell housing. The steam disposed in the predetermined part of the combustion exhaust gas discharge line in the combustion chamber, and the steam flowing through the steam supply line and the combustion catalyst disposed in the predetermined part of the combustion exhaust gas discharge line are heated. 3. The solid oxide fuel cell system according to 2. A reformer for reforming reaction with hydrocarbon-based fuel gas and steam, and a plurality of units for generating power by oxidation and reduction of the reformed fuel gas and the oxidizing material reformed by the reformer. A fuel cell stack including fuel cells, a combustion chamber for burning surplus fuel gas that does not contribute to power generation in the fuel cell stack, the reformer, the fuel cell stack, and the combustion chamber. A fuel cell housing covered with a heat insulating material for housing, a combustion exhaust gas discharge line for discharging the combustion exhaust gas from the combustion chamber to the outside of the fuel cell housing, and a combustion exhaust gas discharged from the combustion exhaust gas discharge line Exhaust heat recovery means for recovering the exhaust heat of the exhaust gas as hot water, wherein the exhaust heat recovery means comprises the exhaust heat and water of the combustion exhaust gas discharged from the combustion exhaust gas discharge line. An exhaust heat recovery heat exchanger for exchange, a hot water storage tank for storing hot water after heat exchange in the exhaust heat recovery heat exchanger, and between the exhaust heat recovery heat exchanger and the hot water storage tank A cogeneration system having a circulation line for circulating water at
A first vaporizer and a second vaporizer are provided for vaporizing water to be supplied to the reformer, and the first vaporizer is formed by combustion of excess fuel gas in the combustion chamber. The second carburetor is disposed outside the fuel cell housing so as to be heated by the combustion exhaust gas flowing through the combustion exhaust gas discharge line .
A combustion catalyst for combusting combustible components contained in the combustion exhaust gas is disposed in the second carburetor located outside the fuel cell housing or the combustion exhaust gas exhaust line on the upstream side thereof ,
Further, in relation to the second vaporizer, a fuel utilization rate control temperature detecting means for detecting the temperature of water vapor generated in the second vaporizer, and a fuel utilization rate in the fuel cell stack. Control means for controlling is provided, and when the temperature detected by the fuel utilization rate control temperature detection means is lower than the set temperature for fuel utilization rate control, the control means is configured to use the fuel utilization rate in the fuel cell stack. Cogeneration system characterized by lowering The cogeneration system according to claim 5 , wherein the heat exchanger for exhaust heat recovery is disposed in the combustion exhaust gas discharge line on the downstream side of the second vaporizer.

Images