JP6721363B2 - Fuel cell system and operating method thereof - Google Patents

Description

The present invention relates to a fuel cell system including a fuel cell stack that generates electric power using fuel gas as a fuel, and an operating method thereof.

Generally, a fuel cell system uses fuel gas supply means for supplying a fuel gas, water supply means for supplying reforming water, and water supplied from the water supply means to steam the fuel gas. A reformer for reforming, a fuel cell stack for generating electricity by oxidizing and reducing the reformed fuel gas and oxidant steam-reformed by the reformer, a fuel gas supply means and a water supply means. And a control means for controlling. In such a fuel cell system (for example, a small-sized home-use fuel cell system), operation control of power load follow-up is performed, and the power generation output of the fuel cell stack changes depending on the magnitude of the power load. Then, in the case of the partial load operation, the power generation output of the fuel cell stack is controlled to be a power value obtained by subtracting the guaranteed power purchase power from the power load, and the power generation output is controlled from the fuel gas supply means. It is performed by controlling the supply flow rate of the fuel gas and the supply flow rate of the reforming water from the water supply means.

When controlling the power generation output of the fuel cell stack according to the power load, the fuel gas supply means is configured to supply the fuel gas to a slightly larger amount with a certain margin in preparation for the increase in the power generation output due to the increase in the power load. Is controlled, in other words, the fuel utilization rate of the system is controlled to be a little smaller than the limit fuel utilization rate without increasing the fuel utilization rate of the system to near the limit, and the fuel gas supply flow rate is controlled in this way. This prevents the occurrence of fuel gas shortage due to a rapid increase in generated power and prevents damage to the fuel cell stack.

However, in such an operation, the fuel gas is supplied to the slightly larger amount even in the rated load operation in which the generated power does not increase. The bad condition continues.

In order to improve the power generation efficiency of this fuel cell system, for example, there has been proposed one in which a reaction fuel gas (including unreacted fuel gas) discharged from a fuel cell stack is reused. (For example, refer to Patent Document 1). For example, carbon dioxide contained in the reaction fuel gas discharged from the fuel cell stack is absorbed and removed using an absorbent, and the reaction fuel gas from which carbon dioxide has been removed is recycled and mixed with new fuel gas for power generation. It is used as fuel gas and is reused in this way to increase the power generation efficiency of the system.

JP, 2002-313402, A

However, the above-described fuel cell system requires an absorbent that absorbs carbon dioxide, and it is necessary to provide a recycling flow path for recycling the reaction fuel gas that has absorbed and removed carbon dioxide. There are problems such as complexity.

An object of the present invention is to provide a fuel cell system and a method of operating the same, which can increase the power generation efficiency of the system with a relatively simple structure.

The fuel cell system according to claim 1 of the present invention comprises a fuel gas supply means for supplying a fuel gas, a water supply means for supplying reforming water, and a water supply means for supplying water. A reformer for steam-reforming the fuel gas supplied from the fuel gas supply means, and power generation by oxidizing and reducing the reformed fuel gas and the oxidant steam-reformed by the reformer. A fuel cell stack for performing combustion, a combustion zone for burning the reaction fuel gas discharged from the fuel cell stack, and a control means for controlling the fuel gas supply means and the water supply means. A fuel cell system,
The control means sets a first fuel utilization rate setting means for setting a partial load fuel utilization rate in the partial load operation based on the relationship between the power generation current of the fuel cell stack and the fuel utilization rate, and in the rated load operation. It includes a second fuel utilization rate setting means for setting a rated load fuel utilization rate, and a rated power generation determination means for determining the rated power generation based on the generated current of the fuel cell stack.
When the fuel cell stack is in the rated power generation state, the second fuel utilization rate setting means increases from the variation value of the partial load fuel utilization rate in the partial load operation based on the rated power generation determination by the rated power generation determination means. The rated load fuel utilization rate is set to the above value, and the control means controls the fuel gas supply means so that the rated load fuel utilization rate becomes a value increased from the fluctuation value of the partial load fuel utilization rate. It is characterized by

Further, in the fuel cell system according to claim 2 of the present invention, the control means further sets an S/C setting for setting the S/C of the reformed fuel gas fed to the fuel cell stack. The fuel cell unit, wherein the S/C setting unit sets S/C based on a S/C-stack temperature characteristic indicating a relationship between S/C and a stack temperature of the fuel cell stack. When the stack is in the rated power generation state, the control means controls the water supply means such that the water supply means has a value smaller than the S/C value in the S/C-stack temperature characteristic.

Furthermore, the operating method of the fuel cell system according to claim 3 of the present invention is the fuel gas supply means for supplying the fuel gas, the water supply means for supplying the reforming water, and the water supply means. A reformer for steam reforming the fuel gas supplied from the fuel gas supply means using the supplied water, and an oxidation of the reformed fuel gas steam-reformed by the reformer and the oxidizer. And a fuel cell cell stack for generating power by reduction, and a combustion zone for burning a reaction fuel gas discharged from the fuel cell stack, and a method for operating a fuel cell system,
When the fuel cell stack is operated under partial load, the fuel gas supply means is controlled so that the partial load fuel utilization rate is set based on the relationship between the power generation current of the fuel cell stack and the fuel utilization rate, Further, when the fuel cell stack is operated at a rated load, the fuel gas supply means is controlled such that the rated load fuel utilization rate is a value increased from the fluctuation value of the partial load fuel utilization rate.

According to the fuel cell system of claim 1 and the method of operating the fuel cell system of claim 3, when the fuel cell stack is in the partial load power generation state, the generated current and fuel of the fuel cell stack The fuel gas supply means is controlled so that the partial load fuel utilization rate is set based on the relationship with the utilization rate, and when the fuel cell stack is in the rated power generation state, it rises from the fluctuation value of the partial load fuel utilization rate. Since the fuel gas supply means is controlled so that the rated load fuel utilization rate becomes the above value, the power generation efficiency of the system in this rated load operation can be improved.

In the rated power generation state of the fuel cell stack, the rated power generation is not substantially exceeded, and therefore it is not necessary to supply the fuel gas a little to the eyes, and in the partial load power generation state. It is possible to make the fuel utilization rate (that is, the rated load fuel utilization rate) in the rated power generation state larger than the fuel utilization rate (that is, the partial load fuel utilization rate). From this point of view, in the rated power generation state, the rated load fuel utilization rate is increased from the fluctuation value of the partial load fuel utilization rate to increase the fuel utilization rate to perform the power generation operation. This fuel utilization rate is the proportion of the fuel gas that contributes to power generation in the fuel gas supplied to the fuel cell stack, and when this fuel utilization rate increases, the fuel gas consumed in the power generation reaction increases The fuel gas used as the fuel cell stack is reduced, and the power generation efficiency of the fuel cell stack is increased.

Since the fuel utilization rate is increased in this way in the rated power generation state, it is possible to improve the power generation efficiency of the fuel cell stack, and the effect of improving the power generation efficiency is that the rated power generation state continues for a long time. growing.

Further, according to the fuel cell system of the second aspect of the present invention, when the fuel cell stack is in the rated power generation state, the water is adjusted so as to have a value smaller than the S/C value in the S/C-stack temperature characteristic. Since the supply means is controlled, the water component (water vapor) sent to the fuel cell stack is reduced, and the decrease in the stack temperature of the fuel cell stack due to the increased fuel utilization rate is suppressed, and the desired stack temperature is achieved. Can be maintained.

S/C is a molar ratio (steam/carbon ratio) between water vapor added during the reaction and carbon contained in the fuel gas (hydrocarbon-based gas), and when the S/C becomes small, the S/C is added. The amount of generated steam decreases and the stack temperature of the fuel cell stack rises.

1 is a simplified diagram illustrating an embodiment of a fuel cell system according to the present invention. FIG. 2 is a block diagram showing a control system of the fuel cell system of FIG. 1. 3 is a flowchart showing the flow of control by the control system of FIG. The figure which shows the relationship of the electric power generation electric current in the fuel cell system of FIG. 1, a limit fuel utilization rate, and a control fuel utilization rate. The figure for demonstrating the change of the electric power generation current when it becomes a rated electric power generation state and a fuel utilization rate is raised. FIG. 4 is a diagram for explaining a rated power generation state when the fuel cell stack is deteriorated. The figure which shows the relationship between the fuel utilization rate of a fuel cell stack, and stack temperature. The figure which shows the relationship between stack temperature and S/C of the fuel gas sent to a fuel cell stack. The figure which shows the relationship of the electric power generation electric current in a conventional fuel cell system, and a limit fuel utilization rate and a control fuel utilization rate.

An embodiment of a fuel cell system and an operating method thereof according to the present invention will be described below with reference to the accompanying drawings.

In FIG. 1, the illustrated fuel cell system 2 consumes a hydrocarbon-based fuel gas, for example, natural gas (city gas) as fuel gas to generate electric power, and reforms the fuel gas for reforming. a vessel 4, the fuel cell stack 6 which generates power by oxidation and reduction of air as a fuel gas (reformed fuel gas) and oxidizing agent that has been modified by the reformer 4, the fuel air cell stack 6 And a blower means 8 for feeding to the.

The fuel battery cell stack 6 is made of, for example, a solid oxide type, and a plurality of fuel battery cells for generating power by a fuel cell reaction are stacked via a current collecting member. Is provided, a fuel electrode provided on one side of the solid electrolyte, and an oxygen electrode provided on the other side of the solid electrolyte. For example, yttria-doped zirconia is used as the solid electrolyte.

The fuel electrode stack side of the fuel cell stack 6 is connected to a reformer 4 via a reformed fuel gas feed line 10, and this reformer 4 is vaporized via a gas/steam feed line 12. The vaporizer 14 is connected to a fuel gas supply source 18 (for example, a buried pipe or a storage tank) for supplying a fuel gas through a fuel gas supply line 16 and is connected to a water tank. It is connected to a water supply source 22 (for example, a water tank or the like) via a supply line 20. The reformer 4 includes, for example, alumina-supported ruthenium as a reforming catalyst, and the reforming catalyst steam-reforms the fuel gas. Further, the vaporizer 14 vaporizes the water supplied through the water supply line 20 to generate water vapor. In addition, the reformer 4 and the vaporizer 14 may be integrally formed.

The fuel gas supply line 16 is provided with a desulfurizer 24, a fuel gas pump 26, a fuel gas flow rate detection sensor 28, and a shutoff valve 30. The desulfurizer 24 removes the sulfur component contained in the fuel gas, the fuel gas pump 26 sends the fuel gas from the fuel gas supply source 18 to the vaporizer 14 through the fuel gas supply line 16, and the fuel gas flow rate detection sensor 28 The flow rate of the fuel gas fed through the fuel gas supply line 16 is detected, and the shutoff valve 30 opens and closes the fuel gas supply line 16 to supply and stop the fuel gas. In this embodiment, the supply flow rate of the fuel gas supplied through the fuel gas supply line 16 is controlled by controlling the rotation speed of the fuel gas pump 26, and when the rotation speed increases (or decreases), the fuel gas The supply flow rate increases (or decreases), and the fuel gas supply source 18, the fuel gas pump 26, and the fuel gas supply line 16 constitute fuel gas supply means.

Further, a water pump 34 and a water flow rate detection sensor 35 (water flow rate detection means) are arranged in the water supply line 20, and the water pump 34 supplies the water from the water supply source 22 to the carburetor 14. The water flow rate detection sensor 35 detects the flow rate of the reforming water supplied through the water supply line 20. In this embodiment, by controlling the rotation speed of the water pump 34, the supply flow rate of the reforming water supplied through the water supply line 20 is controlled, and when the rotation speed increases (or decreases), the reforming water increases. The supply flow rate of the water increases (or decreases), and the water supply source 22, the water pump 34, and the water supply line 20 constitute water supply means.

An oxygen electrode introduction side of the fuel cell stack 6 is connected to an air preheater 38 for preheating air ( oxidizer ) via an air supply line 36. The air preheater 38 is connected to the air supply line. It is connected to the blowing means 8 via 40. The blower unit 8 is composed of, for example, a blower blower, and by controlling the rotation speed of the blower blower, the feed amount of the air supplied through the air supply line 40 is controlled, and the rotation speed of the blower blower increases ( (Or decreases), the supply flow rate of the air supplied through the air supply line 40 increases (or decreases), and the air supply means 8 (air blower) and the air supply line 40 are the air supply means ( oxidant supply means ). Make up.

Combustion zones 44 are provided on the respective discharge sides of the fuel electrode and the oxygen electrode of the fuel cell stack 6, and the reaction fuel gas (including excess fuel gas) discharged from one end of the fuel cell stack 6 The air (containing oxygen) discharged from the oxygen electrode side is fed to the combustion zone 44 and burned. The combustion region 44 is connected to the air preheater 38 via an exhaust gas supply line 46, and the exhaust gas flowing through the air preheater 38 is discharged to the atmosphere via an exhaust gas discharge line 48. In the air preheater 38, heat is exchanged between the air flowing through the air supply line 40 and the exhaust gas flowing through the exhaust gas supply line 46, and the air heated by this heat exchange is the air supply line 36. Through the fuel cell stack 6.

In this embodiment, a stack temperature detection sensor 50 is arranged in association with the fuel cell stack 6, the stack temperature detection sensor 50 is arranged in the vicinity of the fuel cell stack 6, and Detects temperature. Further, a power generation current detection sensor 52 (see FIG. 2) is arranged at a power output portion (not shown) of the fuel cell stack 6, and the power generation current detection sensor 52 is a power generation current from the fuel cell stack 6. To detect.

In this embodiment, the reformer 4, the fuel cell stack 6, the vaporizer 14, and the air preheater 38 are also housed in a battery housing housing 54, and the inner wall surface of the battery housing housing 54 is covered with a heat insulating material. Thus, the high temperature chamber 56 is formed, and the reformer 4, the fuel cell stack 6, the vaporizer 14, and the air preheater 38 are kept in a high temperature state in the high temperature chamber 56.

The fuel cell system 2 operates as follows, for example, to generate power. Fuel gas (eg, city gas) from a fuel gas source 18 is supplied to the vaporizer 14 through the fuel gas supply line 16, and water from a water source 22 is supplied to the vaporizer 14 through a water supply line 20. To be done. In the vaporizer 14, the water is heated to become steam, and the heated fuel gas and the generated steam are mixed and sent to the reformer 4 via the gas/steam supply line 12.

In the reformer 4, the steam reforming reaction is performed with the fuel gas and steam, and the steam-reformed fuel gas (reformed fuel gas) passes through the reformed fuel gas feed line 10 to form the fuel cell stack 6. It is delivered to the fuel electrode side. Further, the air from the blower means 8 is supplied to the air preheater 38 through the air supply line 40, and heat is exchanged with the exhaust gas flowing from the combustion region 44 through the exhaust gas supply line 46 in the air preheater 38. After being heated by heating, the air is fed to the oxygen electrode side of the fuel cell stack 6 through the air feeding line 36.

The fuel electrode side of the fuel cell stack 6 oxidizes the reformed fuel gas, and the oxygen electrode side reduces oxygen in the air, and an electrochemical reaction occurs due to oxidation on the fuel electrode side and reduction on the oxygen electrode side. Power is generated. The reaction fuel gas and air discharged from one end side of the fuel cell stack 6 are sent to the combustion zone 44 and burned, and the combustion heat of this reaction fuel gas is used to heat the reformer 4 and the vaporizer 14. To be done. Exhaust gas from the combustion zone 44 is fed to the air preheater 38 through the exhaust gas feed line 46, is used for heat exchange with the air supplied from the blower means 8 in the air preheater 38, and then is exhausted. It is discharged to the atmosphere through the discharge line 48.

The fuel cell system 2 further includes a controller 60 for controlling the operation of the fuel gas pump 28, the water pump 34, and the blowing means 8. To further explain with reference to FIG. 2, in this embodiment, the controller 60 includes a first fuel utilization rate setting means 62, a second fuel utilization rate setting means 64, a rated power generation determining means 66, an S/C setting means 68, The operation control means 70 and the memory means 72 are provided. The first fuel utilization rate setting means 62 sets the fuel utilization rate during partial load operation (partial load fuel utilization rate) as described later, and the second fuel utilization rate setting means 64 sets the fuel utilization rate during rated load operation. The (rated load fuel utilization rate) is set as described later, the rated power generation determining means 66 determines the rated power generation based on the detection signal from the generated current detection sensor 52 as described later, and the S/C setting means 68 is set. , S/C is set as described later. Further, the operation control means 70 controls the operation of the fuel pump 26, the water pump 34, etc. as described later. The memory means 72 serves as a base for setting the fuel utilization rate characteristic map, the fuel utilization rate at the rated load, and the S/C, which is a base for setting the fuel utilization rate during the partial load operation. The S/C-stack temperature characteristic map and the like are registered.

From the fuel gas flow rate detection sensor 28 (fuel gas flow rate detection means), the water flow rate detection sensor 35 (water flow rate detection means), the stack temperature detection sensor 50 (stack temperature detection means) and the generated current detection sensor 52 (generated current detection means) Is sent to the controller 60, and based on these detection signals, the controller 60 controls the operation of the fuel gas pump 26, the water pump 34, and the blowing means 8 as follows.

Mainly referring to FIGS. 2 and 3, when the fuel cell system 2 is operated for power generation, the fuel cell stack 6 generates power as described above. In this power generation operation, first, a partial load operation is performed (step S1), and thereafter, when the electric power load increases, the rated load operation is performed.

In this partial load operation, the power generation current detection sensor 52 detects the power generation current from the fuel cell stack 6 (step S2), and the first fuel utilization rate setting means 62 causes the detection signal of the power generation current detection sensor 52 to be detected. Based on the above, the fuel utilization rate in the partial load operation is set (step S3). A generated current-fuel utilization rate characteristic map as shown in FIG. 4 is registered in the memory means 72, and in this generated current-fuel utilization rate characteristic map, the fuel utilization rate increases as the generated current increases. Therefore, the first fuel utilization rate setting means 62 sets the partial load fuel utilization rate using this generated current-fuel utilization rate characteristic map. ..

Therefore, in this partial load operation, the fuel utilization rate is changed and set as shown by the solid line in FIG. 4 in relation to the generated current of the fuel cell stack 6, and the operation control means 70 is set in this way. The fuel gas pump 26 and the water pump 34 are controlled to achieve the partial load fuel utilization rate and the power generation operation is performed (at this time, the blower unit 8 is also controlled so that the required air amount is fed). In this partial load operation, when the operation of stopping the power generation is performed, the process proceeds from step S4 to step S5 to step S6, and the power generation operation ends.

In such a partial load operation, when the power generation output of the fuel cell stack 6 rises and the detection signal from the power generation current detection sensor 52 reaches the rated power generation current, that is, in the rated power generation state, the process proceeds from step S4 to step S7. The rated power generation determining unit 66 determines that the rated power generation is in the rated power generation state, and the rated power generation operation is performed based on the determination result (step S8).

When the rated power generation operation is performed in this way, the generated current detection sensor 52 detects the generated current of the fuel cell stack 6 (step S9), and if the rated power generation state of the fuel cell stack 6 is maintained, the second The fuel utilization rate setting means 64 sets the rated load fuel utilization rate registered in the memory means 72 (step S10). The rated load fuel utilization rate is set to a value lower than the limit fuel utilization rate by, for example, about 5%, and the operation control means 70 controls the fuel gas pump 26 and the water pump 34 so as to attain the rated load fuel utilization rate. A power generation operation is performed (at this time, the air blowing unit 8 is also controlled so that the required air amount is sent).

The setting of the fuel utilization rate in the conventional fuel cell system is performed using the generated current-fuel utilization rate characteristic map shown in FIG. 9, and the value is 10 to 20% lower than the limit fuel utilization rate even in the rated power generation state ( For example, the power generation operation is performed at a fuel utilization rate of about 75%. On the other hand, the setting of the fuel utilization rate in this embodiment is performed as shown in FIG. 4, and when the fuel cell stack 6 is in the rated power generation state, the rated load fuel utilization rate larger than the conventional fuel utilization rate is used. (For example, the fuel utilization rate: about 80%) is set, and the value is continuously increased as indicated by "●-●" in FIG. 4 so as to reach the rated load fuel utilization rate. After reaching the rated fuel utilization rate, the rated fuel utilization rate, that is, a value that is, for example, about 5% larger than the conventional fuel utilization rate in the rated power generation state is maintained.

When the fuel utilization rate is increased in this way, the proportion of the fuel gas supplied from the fuel gas supply unit that contributes to power generation in the fuel cell stack 6 increases, and as a result, the power generation efficiency of the fuel cell system can be increased. it can.

If the fuel utilization rate is increased in this way during the partial load operation of the fuel cell stack 6, it may not be possible to cope with an increase in the power generation output of the fuel cell stack 6, and a fuel gas shortage may occur. However, in the rated power generation state, the power generation output does not substantially increase, and it is not necessary to consider such increase in the power generation output. Therefore, the inconvenience caused by increasing the fuel utilization rate does not occur, and only the merit of improving the power generation efficiency by increasing the fuel utilization rate can be obtained.

After the rated load fuel utilization rate is set in this way, the S/C setting means 68 changes the S/C of the reformed fuel gas fed to the fuel cell stack 6 (step S11). In the power generation operation of the fuel cell stack 6, the relationship between the fuel utilization rate and the temperature of the fuel cell stack 6 (stack temperature) changes as shown in the fuel utilization rate-stack temperature characteristic of FIG. Becomes larger (or smaller), the proportion of fuel gas that contributes to power generation in the fuel cell stack 6 increases (or decreases), and the stack temperature decreases (or increases). Further, the relationship between the S/C and the stack temperature changes as shown in the S/C-stack temperature characteristic of FIG. 8, and when the S/C increases (or decreases), it is included in the reformed fuel gas. Moisture (steam) increases (or decreases) and the stack temperature decreases (or increases).

Since the temperature of the fuel cell stack 6, the fuel utilization rate, and the S/C have the relationships shown in FIGS. 7 and 8, it is understood from FIG. 7 that the fuel utilization rate is increased in the rated load operation as described above. As described above, the temperature of the fuel cell stack 6 lowers, and when the stack temperature lowers in this way, the power generation voltage of the fuel cell stack 6 generally lowers. In order to maintain the output of the fuel cell stack 6, the power generation current increases as shown by "●-●" in FIG. 5, and the supplied fuel gas amount increases. As a result, the above-described increase in power generation efficiency is offset, and the desired effect cannot be obtained.

Therefore, when the fuel cell stack 6 is in the rated load operation (that is, in the rated power generation state), the S/C setting means 68 sets S/C based on the S/C-stack temperature characteristic shown in FIG. The value is set to be a value (for example, 1.5 to 2.4) smaller than the C value (for example, 2.4 to 3.0). When the fuel utilization rate is increased in the rated load operation as described above, the fuel gas that does not contribute to the power generation decreases and the stack temperature tends to decrease. However, the S/C value is reduced to form the reformed fuel gas. By reducing the water content, it is possible to suppress the tendency of the stack temperature to decrease, and thus to suppress the decrease of the power generation voltage and the increase of the power generation current of the fuel cell stack 6.

As described above, in the rated load operation, the fuel utilization rate is set to be higher than that in the partial load operation, and the S/C value is accordingly set to be smaller. The power generation operation of the battery system 2 is performed. Even in this rated load operation, the generated current of the fuel cell stack 6 is continuously detected by the generated current detection sensor 52 (step S9), and when the detected current falls below the rated generated current value, the process returns to step S1. Thus, the partial load operation of the fuel cell system 2 is performed. In this rated load operation, if the operation of stopping the power generation is performed, the process proceeds from step S12 to step S13 to step S14, and the power generation operation ends.

The fuel cell system 2 is operated for power generation as described above, but if this power generation operation is performed for a long period of time, the deterioration of the fuel cell stack 6 progresses. As shown in FIG. 6, in the initial installation of the fuel cell system 2 (initial state of use), there is no deterioration of the fuel cell stack 6, and as shown by the thick solid line in FIG. Although it is in a power generation state, when it is operated for a long period of time, the current value in the rated power generation state increases and the current value gradually increases. As shown by the thin solid line in FIG. 6, a current value larger than the initial current value. Therefore, the rated power generation state is established, and the rated equivalent current value in such a rated power generation state is also described as the rated power generation current in this specification.

Although the embodiment of the fuel cell system and the operating method thereof according to the present invention has been described above, the present invention is not limited to such an embodiment, and various changes and modifications are made without departing from the scope of the present invention. Is possible.

For example, in the above-described embodiment, a water tank or the like is used as the water supply source 22, but instead of such a configuration, water contained in the exhaust gas discharged through the exhaust gas discharge line 48 is condensed to generate water. The water recovered in the recovery tank can be used as the reforming water.

Further, for example, it can be used in combination with a hot water storage device provided with a hot water storage tank that stores the heat of exhaust gas as hot water. For example, a heat exchanger is provided in the exhaust gas discharge line 48, and heat is exchanged between the exhaust gas flowing through the exhaust gas discharge line 48 and the water from the hot water storage tank in this heat exchanger, and the heat exchange adds heat. The heated hot water may be stored in the hot water storage tank.

2 Fuel Cell System 4 Reformer 6 Fuel Cell Cell Stack 8 Blower Means 14 Vaporizer 18 Fuel Gas Supply Source 22 Water Supply Source 26 Fuel Gas Pump 28 Fuel Gas Flow Rate Detection Sensor 34 Water Pump 35 Water Flow Rate Detection Sensor 44 Combustion Area 50 Stack Temperature detection sensor 52 Generation current detection sensor 60 Controller 62 First fuel utilization rate setting means 64 Second fuel utilization rate setting means 66 Rated power generation determination means 68 S/C setting means 70 Operation control means

Claims (3)

A fuel gas supply unit for supplying a fuel gas, a water supply unit for supplying reforming water, and a fuel gas supplied by the fuel gas supply unit using water supplied by the water supply unit. A reformer for steam reforming, a fuel cell stack for generating electricity by oxidizing and reducing the reformed fuel gas and oxidant steam-reformed by the reformer, and discharge from the fuel cell stack A fuel cell system comprising: a combustion zone for burning the reaction fuel gas, and a control means for controlling the fuel gas supply means and the water supply means,
The control means includes a first fuel utilization rate setting means for setting a partial load fuel utilization rate in the partial load operation based on the relationship between the power generation current of the fuel cell stack and the fuel utilization rate, and in the rated load operation. It includes a second fuel utilization rate setting means for setting a rated load fuel utilization rate, and a rated power generation determination means for determining the rated power generation based on the generated current of the fuel cell stack.
When the fuel cell stack is in the rated power generation state, the second fuel utilization rate setting means increases from the fluctuation value of the partial load fuel utilization rate in the partial load operation based on the rated power generation determination by the rated power generation determination means. And the control means controls the fuel gas supply means so that the rated load fuel utilization rate becomes a value increased from the fluctuation value of the partial load fuel utilization rate. A fuel cell system characterized by the above. The control means further includes S/C setting means for setting the S/C of the reformed fuel gas fed to the fuel cell stack, and the S/C setting means When the S/C is set based on the S/C-stack temperature characteristic showing the relationship with the stack temperature of the fuel cell stack, and the fuel cell stack is in the rated power generation state, the control means causes the S/C to The fuel cell system according to claim 1, wherein the water supply means is controlled so as to have a value smaller than the S/C value in the rated power generation state in the C-stack temperature characteristic. A fuel gas supply unit for supplying a fuel gas, a water supply unit for supplying reforming water, and a fuel gas supplied by the fuel gas supply unit using water supplied by the water supply unit. A reformer for steam reforming, a fuel cell stack for generating electricity by oxidizing and reducing the reformed fuel gas and oxidant steam-reformed by the reformer, and discharge from the fuel cell stack And a combustion zone for burning the reaction fuel gas, and a method for operating a fuel cell system comprising:
When the fuel cell stack is operated under partial load, the fuel gas supply means is controlled so that the partial load fuel utilization rate is set based on the relationship between the power generation current of the fuel cell stack and the fuel utilization rate, Further, when the fuel cell stack is operated at the rated load, the fuel gas supply means is controlled so that the rated load fuel utilization rate is a value increased from the variation value of the partial load fuel utilization rate. How to operate the battery system.

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