JP5473823B2 - Fuel cell system - Google Patents

Description

  The present invention relates to a fuel cell system.

  Conventionally, as shown in Patent Document 1 below, a reformer that generates a reformed gas containing hydrogen by reforming raw fuel with a reforming catalyst, and electric power and heat using the reformed gas. There is known a fuel cell system having a fuel cell to be generated and a hot water storage tank for storing hot water heated by heat generated by the fuel cell.

  In the fuel cell system described in Patent Document 1 below, a process gas burner for heating the water in the hot water storage tank and a reformer burner for maintaining the temperature of the reforming catalyst are connected to the fuel cell by piping. Each pipe is provided with an on-off valve. After starting the fuel cell operation, the anode off-gas (hereinafter referred to as “off-gas”) that has not reacted in the fuel cell is introduced into the process gas burner until the temperature of the fuel cell is stabilized, and the temperature of the fuel cell is stabilized. After that, the flow of the off gas is switched by opening / closing the on / off valve, and the off gas is introduced into the reformer burner.

JP 2001-291525 A

  However, in the above fuel cell system, although it is disclosed that the operation of the fuel cell system is started by switching the flow of off-gas, the amount of power generated by the fuel cell according to the demand power during the operation of the fuel cell system is disclosed. No measures for temperature balance in the case of changing the temperature were disclosed. For this reason, for example, when the power generation amount of the fuel cell is sharply reduced in accordance with a decrease in demand power, the amount of off-gas introduced into the reformer burner increases, and the temperature balance in the reformer may be lost. As described above, when the amount of power generation is changed in accordance with the demand power, it is difficult to maintain the temperature balance of the reformer, and it is difficult to realize stable operation.

  Accordingly, an object of the present invention is to provide a fuel cell system that can suppress the temperature balance of the reformer from being lost even when, for example, the amount of power generation changes.

To achieve the above object, a fuel cell system according to the present invention comprises a reformer that contains a reforming catalyst and generates a reformed gas containing hydrogen by reforming raw fuel with the reforming catalyst. A temperature detecting means for detecting the temperature of the reforming catalyst, a fuel cell stack for generating electric power and heat using the reformed gas, a power generation amount detecting means for detecting the power generation amount of the fuel cell stack, and a fuel cell stack. The first burner combustor that heats the reforming catalyst using the supplied reformed gas off gas, the off gas circulation line that circulates the off gas to the first burner combustor, and the heat generated by the fuel cell stack. A hot water storage unit for storing hot water, a second burner combustor for heating the hot water stored in the hot water storage unit, an offgas introduction line for introducing offgas to the second burner combustor, and a first burner combustor for offgas Control for controlling the opening of the off-gas distribution valve so that the temperature of the reforming catalyst detected by the temperature detection means and the off-gas distribution valve distributed to the second burner combustor falls within a predetermined temperature range. And the control means has a temperature of the reforming catalyst within a predetermined temperature range when a fluctuation amount per unit time of the power generation amount detected by the power generation amount detection means is a predetermined value or more. It is characterized by controlling the opening degree of an off-gas distribution valve .

According to the fuel cell system of the present invention, the opening of the offgas distribution valve is controlled by the control means so that the temperature of the reforming catalyst is within a predetermined temperature range, and the offgas introduced into the first burner combustor. The amount is controlled. The surplus off gas is introduced into the second burner combustor through the off gas introduction line and consumed for heating the hot water stored in the hot water storage unit. Thus, for example, even when the power generation amount changes, the amount of off-gas introduced into the first burner combustor is adjusted, so that it is possible to suppress the temperature balance of the reformer from being lost. Further, when the amount of power generation is fluctuating, that is, when the amount of raw fuel input to the reformer changes and the temperature of the reforming catalyst is likely to fluctuate, the temperature of the reforming catalyst falls within a predetermined temperature range. As described above, the opening degree of the off-gas distribution valve is controlled. Therefore, it is not necessary to constantly monitor the temperature of the reforming catalyst, and the temperature balance of the reformer can be easily and reliably controlled. Moreover, the opening degree of the off-gas distribution valve is controlled so that the temperature of the reforming catalyst falls within a predetermined temperature range when the fluctuation amount of the power generation amount per unit time is equal to or greater than a predetermined value. Therefore, it is not necessary to control the opening of the offgas distribution valve in response to a slight change in the amount of power generation or an instantaneous increase or decrease in the amount of power generation, simplifying the control of the offgas distribution valve and extending the life of the offgas distribution valve Can be achieved.

  Further, it is preferable that a hot water outlet line of the hot water storage unit passes through the second burner combustor, and the second burner combustor heats hot water passing through the hot water outlet line by using at least one of raw fuel and off gas as fuel.

  According to this invention, the off gas introduced into the second burner combustor by the off gas introduction line is also used for heating the hot water passing through the tapping line. Therefore, by suppressing the excessive temperature change of the reformer and maintaining a suitable temperature balance, it is possible to stably supply a desired amount of the reformed gas, and to stabilize the operation while removing excess off-gas. It can be used effectively.

  According to the present invention, for example, even when the power generation amount changes, it is possible to suppress the temperature balance of the reformer from being lost.

It is a block diagram which shows roughly the reference form of the fuel cell system which concerns on this invention. 2 is a flowchart showing a control procedure in the fuel cell system shown in FIG. 1. It is a flowchart which shows the control procedure in one Embodiment of a fuel cell system.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

( Reference form)
As shown in FIG. 1, a fuel cell system 1 is installed for home use, for example, and supplies electric power and hot water to a home. A fuel cell unit 2, a hot water storage unit 3, an operation control device (control means) 20).

  The fuel cell unit 2 generates electric power and heat by using raw fuel. The fuel cell unit 2 includes a reformer 6, a solid polymer cell stack (fuel cell stack) 7, and a power conditioner (hereinafter referred to as “PCS”) 40.

  The reformer 6 accommodates a reforming catalyst 6a inside. Further, the reformer 6 is provided with a burner combustor (first burner combustor) 8 for heating the reforming catalyst 6a to a temperature necessary for the reforming reaction. In the reformer 6, the raw fuel and water undergo a steam reforming reaction in the reforming catalyst 6a heated by the burner combustor 8, and a reformed gas containing hydrogen is generated. The burner combustor 8 burns raw fuel when the fuel cell system 1 is started up, and burns off-gas derived from the anode side of the cell stack 7 during normal operation of the fuel cell system 1. Further, the reformer 6 is provided with a thermometer (temperature detecting means) 10 for detecting the temperature of the reforming catalyst 6a. The thermometer 10 detects the temperature of the reforming catalyst 6 a and outputs the detected temperature to the operation control device 20. As the thermometer 10, for example, a thermocouple is used, but the thermometer is not limited to this. As the raw fuel used in the reformer 6, hydrocarbon gas fuels such as natural gas, LPG (liquefied petroleum gas) and city gas, and hydrocarbon liquid fuels such as kerosene can be used. The reformer 6 is provided with a vaporizer for vaporizing water.

  The cell stack 7 is formed by laminating a plurality of cells called PEFC (Polymer Electrolyte Fuel Cell). Each cell is configured by disposing an electrolyte, which is a polymer film, between a fuel electrode and an air electrode. In the cell stack 7, the reformed gas generated by the reformer 6 is introduced to the fuel electrode side, and air is introduced to the air electrode side. Thus, the cell stack 7 generates electric power and heat using the reformed gas and air (oxygen). The electric power generated in the cell stack 7 is supplied via the PCS 40 to a domestic load EI that is an electric appliance in the home.

  The hot water storage unit 3 includes a hot water storage tank 11 and a backup boiler (second burner combustor) 12. The hot water storage tank 11 is a container having a substantially cylindrical shape, and stores hot water heated by heat generated in the cell stack 7. The hot water storage tank 11 is connected to the heat recovery line L2 at the upper part, and is configured such that the hot water transferred from the cell stack 7 can flow through the heat recovery line L2. The hot water tank 11 is connected to the heat recovery line L1 at the lower part, and the hot water stored in the lower part of the hot water tank 11 flows out to the heat exchange part of the cell stack 7 by the pump 14 provided in the heat recovery line L1. It is configured to be able to send water. The hot water tank 11 is provided with a thermometer (not shown) for detecting the temperature of the hot water stored in the hot water tank 11.

  Further, the unreacted off gas out of the reformed gas introduced to the fuel electrode side of the cell stack 7 passes through the off gas circulation line L5 and the three-way valve 17 provided in the off gas circulation line L5 to the burner combustor 8. It is introduced and reused for heating the reforming catalyst 6a. The three-way valve 17 is provided at a branch point where the off-gas introduction line L6 connected to the backup boiler 12 of the hot water storage unit 3 branches from the off-gas circulation line L5, and is controlled by the operation control device 20 from the cell stack 7. It has a function of distributing the discharged off gas to the off gas circulation line L5 and the off gas introduction line L6. That is, a part of the off gas is introduced into the burner combustor 8 through the off gas circulation line L5, and a part of the off gas is introduced into the backup boiler 12 through the off gas introduction line L6.

  Furthermore, the above-described heat recovery lines L1 and L2 connected to the hot water storage tank 11 of the hot water storage unit 3 are connected to the cell stack 7. The heat recovery lines L <b> 1 and L <b> 2 are connected to water flow paths arranged between the cells of the cell stack 7. With such a configuration, the heat generated in the cell stack 7 is transmitted to the water flowing in the heat recovery lines L <b> 1 and L <b> 2, and the hot water warmed by the heat transfer is stored in the hot water storage tank 11.

  The fuel cell unit 2 is provided with a surplus power heater 9. The surplus power heater 9 is provided in the heat recovery line L2, and when a surplus that is not used at home is generated in the power generated by the cell stack 7, hot water in the heat recovery line L2 is generated using the surplus. Is for heating.

  The PCS 40 is connected to the cell stack 7 and supplies power generated in the cell stack 7 to the home load EI. The PCS 40 detects demand power of the home load EI. In the PCS 40, a power generation amount detector (power generation amount detection means) 30 for detecting the power generation amount in the cell stack 7 is provided. The demand power of the household load EI detected by the PCS 40 and the power generation amount of the cell stack 7 detected by the power generation amount detector 30 are transmitted to the operation control device 20, and the operation control device 20 The fuel cell system 1 is controlled so that the generated power does not flow backward to the system power supply CE. On the other hand, the grid power supply CE is connected to the domestic load EI, and when the generated power of the fuel cell unit 2 is less than the demand power of the domestic load EI, auxiliary power is supplied from the grid power supply CE to the domestic load EI. Supplied.

  The three-way valve 15 of the hot water storage unit 3 allows the hot water transferred in the cell stack 7 to flow into the hot water storage tank 11 or repeatedly introduces the hot water into the heat exchange section of the cell stack 7 without flowing into the hot water storage tank 11. can do.

  Furthermore, the hot water tank 11 is connected to the water supply line L3 on the lower side, and clean water is supplied to the lower side of the hot water tank 11 through the water supply line L3. The hot water tank 11 is connected to the hot water line L4 on the upper side, and hot water can be discharged from the upper side of the hot water tank 11 through the hot water line L4. A flow meter (not shown) is provided in each of the water supply line L3 and the hot water line L4.

  The backup boiler 12 is provided in the hot water line L4, and heats hot water passing through the hot water line L4 using raw fuel such as kerosene or offgas introduced through the offgas introduction line L6 as fuel. The backup boiler 12 has a burner 13 for combusting raw fuel or off-gas. When the temperature of hot water discharged through the hot water line L4 does not reach a desired temperature by the burner 13, the hot water is discharged. Heat. As the fuel burned in the burner 13, off-gas is used when off-gas is introduced through the off-gas introduction line L6, and raw fuel is used when off-gas is not introduced. Further, when the amount of hydrogen contained in the off gas is insufficient, the off gas and the raw fuel may be burned simultaneously. The burner 13 may be composed of a kerosene burner and an off-gas burner, or may be a burner capable of co-firing kerosene and off-gas.

  Further, the backup boiler 12 also has a function of heating hot water in the heat recovery line L2. That is, the hot water line L4 and the heat recovery line L2 pass through the backup boiler 12. Even if it is not necessary to heat the hot water discharged from the hot water line L4, the hot water in the heat recovery line L2 is burned by the burner 13 when the off gas is introduced through the off gas introduction line L6. Is heated.

  The operation control device 20 controls the entire system of the fuel cell system 1. The operation control device 20 controls the operation of the reformer 6 and the cell stack 7. More specifically, the operation control device 20 controls the power generation amount in the cell stack 7. Further, the operation control device 20 stores in advance an appropriate temperature range (predetermined temperature range) of the reforming catalyst 6a. Furthermore, the operation control device 20 acquires the temperature of the reforming catalyst 6a output from the thermometer 10 of the reformer 6, and executes predetermined processing based on the acquired temperature of the reforming catalyst 6a. The opening degree of the three-way valve 17 is controlled. The operation control device 20 controls (adjusts) the flow rate of the off gas flowing in the off gas circulation line L5 and the off gas introduction line L6 by controlling the opening degree of the three-way valve 17.

  The operation control device 20 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), an input / output interface, and the like. When the fuel cell unit 2 or the hot water storage unit 3 is provided with a CPU, ROM, RAM, etc., it may operate using the hardware resources.

  Next, the operation in the fuel cell system 1 will be described. FIG. 2 is a flowchart showing a control procedure in the fuel cell system 1. Each process shown in FIG. 2 is repeatedly executed by the operation control device 20 during normal operation of the fuel cell system 1.

  First, a change in demand power of the household load EI is detected (S1). Next, it is determined whether or not the demand power of the household load EI detected by the PCS 40 is increasing (S2). When the demand power is increasing, the amount of raw fuel supplied to the reformer 6 is increased (S3). In this case, the endothermic reaction in the reformer 6 is promoted, and the temperature of the reforming catalyst 6a tends to decrease.

  On the other hand, if the demand power has not increased, it is determined whether the demand power of the household load EI detected by the PCS 40 has decreased (S4). When the demand power is decreasing, the amount of raw fuel supplied to the reformer 6 is decreased (S5). In this case, the endothermic reaction in the reformer 6 is suppressed, and the temperature of the reforming catalyst 6a tends to increase.

  On the other hand, when the demand power of the household load EI detected by the PCS 40 is not decreasing, that is, not changing, the supply amount of raw fuel to the reformer 6 is maintained (S6).

  Next, the temperature T of the reforming catalyst 6a output from the thermometer 10 is acquired (S7), and the acquired temperature T of the reforming catalyst 6a is stored in the operation controller 20 in an appropriate temperature range (Tmin). It is determined whether it is higher than the upper limit value Tmax of ≦ T ≦ Tmax) (S8).

  When the temperature T of the reforming catalyst 6a is equal to or lower than the upper limit value Tmax of the appropriate temperature range stored in advance in the operation control device 20, the temperature T of the reforming catalyst 6a is stored in the operation control device 20 in advance. It is determined whether it is lower than the lower limit value Tmin of the range (Tmin ≦ T ≦ Tmax) (S9).

  When the temperature T of the reforming catalyst 6a is equal to or higher than the lower limit value Tmin of the proper temperature range stored in advance in the operation control device 20, that is, the temperature T of the reforming catalyst 6a is within the proper temperature range (Tmin ≦ T ≦ In the case of Tmax), the opening degree of the three-way valve 17 is maintained (S10). Then, the process shown in FIG. 2 ends.

  On the other hand, when the temperature T of the reforming catalyst 6a is lower than the lower limit value Tmin of an appropriate temperature range (Tmin ≦ T ≦ Tmax), the opening degree of the three-way valve 17 is adjusted, and the off gas distribution amount to the burner combustor 8 is reduced. Increased (S11). For example, when the power generation instruction amount in the cell stack 7 is suddenly increased by the operation control device 20, the amount of raw fuel input to the reformer 6 increases (S3), so the temperature in the reformer 6 tends to decrease. And such an event can occur. Here, the opening degree of the three-way valve 17 is controlled by the operation control device 20, and the amount of off-gas introduced through the off-gas circulation line L5 is increased (S11). By such control, the heating amount of hot water in the backup boiler 12 is reduced, the flow rate of the off gas flowing in the off gas circulation line L5 is increased, and the temperature drop of the reforming catalyst 6a is suppressed. Then, the process shown in FIG. 2 ends.

  On the other hand, when the temperature T of the reforming catalyst 6a is higher than the upper limit value Tmax of the appropriate temperature range (Tmin ≦ T ≦ Tmax), the opening degree of the three-way valve 17 is adjusted, and the off-gas distribution amount to the backup boiler 12 increases. (S12). For example, when the power generation instruction amount in the cell stack 7 is suddenly lowered by the operation control device 20, the amount of raw fuel input to the reformer 6 decreases (S4), so the temperature of the reformer 6 tends to increase. And such an event can occur. Here, the opening degree of the three-way valve 17 is controlled by the operation control device 20, and the amount of off-gas introduced through the off-gas introduction line L6 is increased (S12). By such control, the heating amount of hot water in the backup boiler 12 is increased, the flow rate of the off gas flowing in the off gas circulation line L5 is decreased, and the temperature rise of the reforming catalyst 6a is suppressed. Then, the process shown in FIG. 2 ends.

  Through the above series of processes, the off-gas flow rate control in the fuel cell system 1 is executed, and the temperature of the reforming catalyst 6a falls within an appropriate temperature range.

According to the fuel cell system 1 of this reference embodiment, with the power generation amount of change in the cell stack 7, even if the off-gas the amount derived from the cell stack 7 is changed, the temperature range the temperature is in a predetermined reforming catalyst 6a The opening degree of the three-way valve 17 is controlled by the operation control device 20 so that the amount of off-gas introduced into the burner combustor 8 is controlled. Then, surplus off-gas is introduced into the backup boiler 12 by the off-gas introduction line L6 and consumed for heating the hot water passing through the heat recovery line L2. Thus, for example, even when the power generation amount changes so as to follow the change in power demand, the amount of off-gas introduced into the burner combustor 8 is adjusted, so that the temperature balance of the reformer 8 is lost. (Excessive temperature change of the reformer 6 and the like) can be suppressed, and stable operation can be realized.

  It should be noted that the temperature of the reforming catalyst 6a may change due to other factors even when the power generation amount is maintained substantially constant, not only when the power generation amount changes. However, according to the fuel cell system 1, the temperature balance of the reformer 6 can be prevented from being lost regardless of the temperature change factor of the reforming catalyst 6a, and stable operation can be realized. Become.

  Moreover, since the off gas introduced into the backup boiler 12 by the off gas introduction line L6 is also used for heating hot water passing through the tapping line L4, an excessive temperature change of the reformer 6 is suppressed and the temperature balance is suitably maintained. Thus, a desired amount of the reformed gas can be stably supplied, and surplus off-gas can be effectively used while stabilizing the operation. And energy saving is achieved by the effective use of surplus off-gas.

( One embodiment)
Subsequently, an embodiment of the present invention will be described. The fuel cell system of one embodiment also has the same configuration as that of the fuel cell system 1 of the reference embodiment shown in FIG. In one embodiment, the processing executed by the operation control device 20 is different from the reference embodiment. FIG. 3 is a flowchart showing a control procedure in the fuel cell system. Each process shown in FIG. 3 is repeatedly executed by the operation control device 20 during normal operation of the fuel cell system. In the following description, the same processes as those in the reference embodiment are denoted by the same reference numerals, and redundant description is omitted.

After the same processing of steps S1 to S6 as in the reference mode, the power generation amount detector 30 acquires the fluctuation amount ΔW per unit time of the power generation amount of the cell stack 7 (S13), and the fluctuation amount ΔW is a predetermined fluctuation. It is determined whether or not the amount is Wref or more (S14).

  When the fluctuation amount ΔW per unit time of the power generation amount of the cell stack 7 is less than the predetermined fluctuation amount Wref, it is determined that the temperature of the reforming catalyst 6a is also slight, and the opening degree of the three-way valve 17 is maintained. (S10). Then, the process shown in FIG. 3 ends.

On the other hand, when the fluctuation amount ΔW per unit time of the power generation amount of the cell stack 7 is equal to or larger than the predetermined fluctuation amount Wref, the temperature of the reforming catalyst 6a fluctuates due to increase / decrease of the raw fuel input amount to the reformer 6. The temperature T of the reforming catalyst 6a output from the thermometer 10 is acquired (S7), and the processing after step S8, which is the same as that of the reference embodiment (according to the temperature of the reforming catalyst 6a). Shift to processing).

Also in the process of the present embodiment, similarly to the reference embodiment, the off-gas flow rate control in the fuel cell system 1 is executed, and the temperature of the reforming catalyst 6a is maintained within an appropriate temperature range.

  According to the fuel cell system of the present embodiment, surplus off gas is introduced into the backup boiler 12 by the off gas introduction line L6 in accordance with the temperature change of the reforming catalyst 6a when the power generation amount of the cell stack 7 is fluctuating. And consumed for heating the hot water passing through the heat recovery line L2. Therefore, it is not always necessary to monitor the temperature of the reformer 6 in order to control the opening degree of the three-way valve 17, and the temperature balance of the reformer 6 can be controlled easily and reliably.

  In addition, by determining whether or not there is a fluctuation in the power generation amount based on whether or not it is greater than or equal to a predetermined fluctuation amount per unit time, a three-way valve can be used according to a slight change in the power generation amount or an instantaneous increase or decrease in the power generation amount. Therefore, the control of the three-way valve 17 can be simplified and the life of the three-way valve 17 can be extended.

  In addition, when it is determined that the temperature of the reforming catalyst 6a is not within the predetermined temperature range, the introduction of the off-gas introduced into the backup boiler 12 so that the temperature of the reforming catalyst 6a is within the proper temperature range. Since the amount is controlled, the temperature balance of the reformer 6 can be easily and reliably controlled even when the power generation amount in the cell stack 7 is rapidly reduced.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment. In the above embodiment, the case where the flow rate of the off gas is controlled by controlling the three-way valve 17 has been described, but the off gas distribution valve may be any valve that can adjust the flow rate. Further, a throttle may be provided in the off-gas circulation line L5, and an electromagnetic valve may be provided in the off-gas introduction line L6, and the flow rate of the off-gas circulation line L5 may be controlled by opening / closing control of the electromagnetic valve. Further, an off-gas flow meter may be provided in the off-gas circulation line L5 and the off-gas introduction line L6, and more precise flow control may be performed by referring to the indicated value of the flow meter.

  Further, the backup boiler 12 to which the off-gas introduction line L6 is connected may be provided in any one of the tapping line L4 and the heat recovery line L2.

  Moreover, although the case where the surplus power heater 9 was provided was demonstrated in the said embodiment, when demand power falls rapidly according to this invention, generated electric power is reduced rapidly and the surplus off gas generated at that time is backed up boiler By introducing it to 12, the surplus power heater 9 can be omitted.

  Further, for example, the reformer 6 is not limited to one using a steam reforming reaction, and may use another reforming reaction. The cell stack 7 is not limited to the solid polymer type, and may be an alkaline electrolyte type, a phosphoric acid type, a molten carbonate type, a solid oxide type, or the like. The power generation amount detector 30 is not limited to being provided in the PCS 40, and may be provided in the subsequent stage of the fuel cell stack.

  DESCRIPTION OF SYMBOLS 1 ... Fuel cell system, 3 ... Hot water storage unit, 6 ... Reformer, 6a ... Reforming catalyst, 7 ... Cell stack (fuel cell stack), 8 ... Burner combustor (first burner combustor), 10 ... Thermometer (Temperature detection means), 12 ... backup boiler (second burner combustor), 17 ... three-way valve (off-gas distribution valve), 20 ... operation control device (control means), 30 ... power generation amount detector (power generation amount detection means) , L4 ... tapping line, L5 ... off-gas circulation line, L6 ... off-gas introduction line.

Claims (2)

A reformer containing a reforming catalyst and generating a reformed gas containing hydrogen by reforming raw fuel with the reforming catalyst;
Temperature detecting means for detecting the temperature of the reforming catalyst;
A fuel cell stack for generating electric power and heat using the reformed gas;
A power generation amount detecting means for detecting a power generation amount of the fuel cell stack;
A first burner combustor for heating the reforming catalyst using an off-gas of the reformed gas supplied to the fuel cell stack;
An off-gas circulation line for circulating the off-gas to the first burner combustor;
A hot water storage unit for storing hot water heated by heat generated in the fuel cell stack;
A second burner combustor for heating the hot water stored in the hot water storage unit;
An off-gas introduction line for introducing the off-gas into the second burner combustor;
An off-gas distribution valve for distributing the off-gas to the first burner combustor and the second burner combustor;
Control means for controlling the opening of the off-gas distribution valve so that the temperature of the reforming catalyst detected by the temperature detection means falls within a predetermined temperature range ,
The control means has a temperature of the reforming catalyst within a predetermined temperature range when a fluctuation amount per unit time of the power generation amount detected by the power generation amount detection means is a predetermined value or more. Thus, the opening degree of the off-gas distribution valve is controlled . The hot water storage line of the hot water storage unit passes through the second burner combustor,
2. The fuel cell system according to claim 1, wherein the second burner combustor heats hot water passing through the hot water line using at least one of the raw fuel and the off gas as fuel.

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