JP2010080192A - Operation shutdown method for fuel battery, and fuel battery system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique which shortens the shutdown time of a fuel battery system and makes it less likely to oxidize a catalyst in a reformer, at an operation shutdown, and to provide a fuel electrode for fuel battery cell. <P>SOLUTION: An amount of supply of a hydrocarbon gas supplied via a hydrocarbon line 12 is reduced, while an oxidizer gas is continuously supplied to a power generating stack 10 via an oxidant line 14 at the time of the operation shutdown and air only is supplied to a heating burner 30, and a mixed gas, where the molar ratio of steam content/carbon content of a hydrocarbon gas and steam is 2-4 is supplied to the power generating stack 10 through the reformer 40. When the temperature of the reformer 40, obtained from a reformer temperature sensor 42, lowers to 200-550°C, supplying of the hydrocarbon gas is stopped. Furthermore, while supplying steam continuously, supplying of water is stopped, at a stage where the temperature of a vaporizer 50, obtained from a vaporizer temperature sensor 52, reaches 100°C, after a fixed quantity of water is supplied to and stored in the vaporizer 50. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a fuel cell operation stop method and a fuel cell system, and more particularly to a fuel cell system using a solid oxide fuel cell stack operating at a high temperature and a method for stopping the fuel cell system.

Since the solid oxide fuel cell system is operated at a high temperature, it is necessary to purge the combustible gas when the system is stopped and to cool the power generation stack constituting the solid oxide fuel cell. Therefore, conventionally, water vapor is used to purge the combustible gas, and the system is stopped by cooling the power generation stack from the inside. (For example, refer to Patent Documents 1 and 2).
JP 2005-340075 A JP 2005-044684 A

  However, in the above method, the solid fuel cell system only cools the power generation stack from the inside even though the power generation stack is housed in a heat insulating container in order to increase the startup time. It was not structured to cool. Therefore, since the power generation stack cannot be cooled in a short time when the system is stopped, there is a problem that it takes time to stop the system.

Further, if the fuel cell interior is filled with air when the system is stopped, the catalyst in the reformer and the fuel electrode of the fuel cell are easily oxidized after the system is stopped.
The present invention has been made in view of these problems, and provides a technique for shortening the stop time of the fuel cell system and making it difficult to oxidize the catalyst in the reformer and the fuel electrode of the fuel cell when the operation is stopped. For the purpose.

  In order to solve such a problem, the fuel cell shutdown method of the present invention receives an external supply of air and fuel gas, and receives a heat insulating container (20: In this section, in order to facilitate understanding of the invention, Where necessary, the reference numerals used in the column “Best Mode for Carrying Out the Invention” are attached, but this reference is not meant to limit the scope of claims. ) To obtain a mixed gas of water vapor and hydrocarbon gas by the vaporizer (50), and the hydrogen-containing gas obtained by passing the mixed gas through the reformer (40), and the oxidant gas is flowed. In the method of stopping the operation of the fuel cell that supplies power to the power generation stack (10) and generates power, when the operation is stopped, only the air is supplied to the heating means (30), and the amount of hydrocarbon gas supplied is reduced. A mixed gas having a water vapor / carbon molar ratio of 2 to 4 between the generated hydrocarbon gas and water vapor is obtained, and the hydrogen-containing gas obtained by passing the mixed gas through the reformer (40) is converted into an oxidant. When the gas is continuously supplied to the power generation stack (10) and the temperature of the reformer (40) is lowered to 200 ° C. to 550 ° C., the supply of hydrocarbon gas is stopped, The supply of water is continued, and when the temperature of the vaporizer (50) reaches 100 ° C, a certain amount of water is supplied to the vaporizer (50) and stored, and then the water supply is stopped. It is characterized by.

  According to such a fuel cell shutdown method, the oxidant gas and hydrogen are continuously supplied to the power generation stack (10) until the temperature of the reformer (40) drops to 200 ° C. to 550 ° C. at the time of shutdown. The contained gas is supplied.

  That is, until the temperature of the reformer (40) drops to 200 ° C. to 550 ° C., an oxidant gas is supplied to the cathode and a mixed gas of hydrocarbon gas and water vapor is supplied to the anode via the reformer (40). The And if the temperature of a reformer (40) falls to 200 to 550 degreeC, supply of hydrocarbon gas will be stopped.

  Since the spontaneous ignition temperature of hydrogen generated by reforming is 550 ° C., the supply of hydrocarbon gas is stopped when the reformer (40) temperature is lowered to 550 ° C. Then, spontaneous combustion of hydrogen generated by reforming stops, and heat generation in the fuel cell is eliminated, so that the fuel cell is cooled.

  The water vapor amount / carbon amount of the mixed gas of hydrocarbon gas and water vapor is 2 to 4 in terms of a molar ratio (hereinafter, the water vapor amount / carbon amount is referred to as S / C). When the S / C is less than 2, carbonization of the reforming catalyst of the power generation stack (10) anode and the reformer (40) is likely to occur, and when the S / C is greater than 4, the amount of water supply increases. As a result, only the vaporizer (50) is rapidly cooled, so that no steam is generated, resulting in no steam reforming reaction. Therefore, S / C is suitably 2-4.

  Furthermore, when the operation is stopped, only air is supplied to the heating means (30) which receives the supply of air and fuel and heats it. That is, since the fuel supply is lost, heating is not performed, and the outside of the fuel cell is cooled by the supplied air, so that the cooling time can be shortened.

  In addition, when the temperature of the vaporizer (50) reaches 100 ° C. while the supply of water vapor is continued, a certain amount of water is supplied to the vaporizer (50) and stored, and then the supply of water is stopped. If it does in this way, since a downstream side will be filled with water vapor | steam from the vaporizer | carburetor (50), the oxidation of an anode or a reforming catalyst can be suppressed.

  Here, when the supply of the hydrocarbon gas is stopped at the temperature of the reformer (40) higher than 550 ° C. and only water vapor is supplied, the anode and the reforming catalyst are easily oxidized. On the other hand, when the supply of hydrocarbon gas is stopped at a temperature lower than 200 ° C. and only steam is supplied, the steam is condensed in the reformer (40), and the downstream side of the vaporizer (50) cannot be filled with the steam. It will be. Therefore, the temperature of the reformer (40) is appropriately 200 ° C to 550 ° C.

Here, “a certain amount of water” means an amount that does not cause condensation due to supersaturation of water in the anode.
By the way, since the steam reforming is performed in the reformer (40) by reducing the supply amount of the hydrocarbon gas when the fuel cell is stopped, the endothermic reaction proceeds and the gas cooling in the reformer (40) is performed. Is moderately promoted. However, if the amount of reduction of the hydrocarbon gas is too large, the amount of hydrocarbon gas to be supplied is reduced, so that there is a high possibility that the oxidant gas on the cathode side will circulate to the anode side and cause oxidation of the anode.

  Therefore, as in the present invention, when the supply amount of hydrocarbon gas when the fuel cell is stopped is reduced to 0.1 to 0.7 times the maximum input amount during power generation, the gas in the reformer (40) is reduced. As a result, the oxidant gas on the cathode side can be prevented from entering the anode side and the oxidation of the anode can be suppressed.

  In addition, since the mixed gas of water vapor and hydrocarbon gas obtained by the vaporizer is supplied to the reformer (40) while reducing the amount, the reforming reaction proceeds and hydrogen is generated, so the anode is reduced. It is suitable because it is exposed to the atmosphere.

  By the way, there is a case where it is desired to stop the fuel cell rapidly such as in an emergency. At that time, as in the present invention, the supply of the hydrocarbon gas is stopped, and the vaporizer (50) is continuously supplied with the steam to the power generation stack 10 in which the oxidant gas is continuously supplied. When the temperature reaches 100 ° C., a certain amount of water is supplied to the vaporizer (50) and stored, and then the water supply is stopped.

  In this way, power generation can be stopped rapidly by stopping the supply of hydrocarbon gas, and a certain amount of water is supplied into the vaporizer (50) at a temperature of the vaporizer (50) of 100 ° C. Since the supply of water to the vaporizer (50) is stopped in this state, the downstream side of the vaporizer (50) is filled with water vapor. Therefore, oxidation of the reforming catalyst of the reformer (40) and the power generation stack (10) anode can be suppressed.

  In addition, as in the present invention, when a certain amount of water is supplied to the vaporizer (50) and stored after the fuel cell operation is stopped until the next start-up, the following operation is performed after the operation is stopped. Since the downstream side of the vaporizer (50) is filled with water vapor until the start of activation, oxidation of the reforming catalyst of the reformer (40) and the anode of the power generation stack (10) can be suppressed.

  By the way, it is considered that the reforming catalyst in the reformer (40) and the anode in the power generation stack (10) are exposed to a steam atmosphere as the simplest oxidation suppressing method. If it stays in the anode line, there will be a large loss in restarting the system.

  Therefore, as in the present invention, it is provided with switching means (94) for sending the oxidant gas supplied to the cathode side of the power generation stack (10) to the anode side, and the vaporizer ( When the temperature of 50) reaches 100 ° C., the switching means (94) may be switched to purge the water vapor by sending the oxidant gas supplied to the cathode side to the anode side.

  If it does in this way, the purge of water vapor | steam can be performed by flowing the oxidizing gas supplied to the cathode to an anode by switching a switching means (94). This purge with the oxidant gas can prevent the anode side from becoming supersaturated with water vapor, that is, the water vapor supplied to the anode side can be prevented from condensing and retaining. Therefore, there is no stagnation of water at the anode at the time of restarting, so that the gas supply to the anode becomes smooth.

  At this time, an oxidant gas is introduced into the anode. Since the oxidant gas is at a temperature lower than the oxidation temperature of the reforming catalyst and the anode of the reformer (40), the oxidation of the reforming catalyst and the anode is performed. Can be suppressed.

  Furthermore, it is not necessary to separately prepare a steam purge blower (pump), and the system configuration is simplified. In addition, when the next start-up is performed after the operation of the fuel cell is temporarily stopped, since a certain amount of water is stored in the vaporizer (50), the anode line is turned on at the stack temperature rising stage at the start-up. When the water stored in the vaporizer (50) is vaporized, the oxidant gas is purged.

  By the way, as the power generation stack (10) used in the fuel cell system (1), the solid oxide fuel cell stack as in the present invention has a relatively high operating temperature of 700 ° C. to 1000 ° C. The effect of shortening the cooling time is easily obtained.

  The fuel cell system (1) of the present invention includes a power generation stack (10), a hydrocarbon line (12), an oxidant line (14), a discharge line (16), a reformer (40) in a heat insulating container (20). ), A reformer temperature detecting means (42), a vaporizer (50), a vaporizer temperature detecting means (52), a heating means (30), and a control means (60).

  The power generation stack (10) is configured to generate electricity by receiving supply of hydrocarbon gas and oxidant gas, and the hydrocarbon line (12) supplies hydrocarbon gas to the power generation stack (10) to generate oxidant line. (14) supplies an oxidant gas to the power generation stack (10), and discharges from the power generation stack (10) a gas that does not contribute to power generation and a used gas.

  The reformer (40) reforms the hydrocarbon gas into a hydrogen-containing gas by steam reforming, and the reformer temperature detection means (42) detects the temperature of the reformer (40) and vaporizes it. The vaporizer (50) vaporizes water to supply steam to the reformer (40), and the vaporizer temperature detection means (52) detects the temperature of the vaporizer (50). The heating means (30) receives the supply of air and fuel gas from the outside and heats the inside of the heat insulating container (20).

Furthermore, the control means (60) supplies only air to the heating means (30) when the operation is stopped, and reduces the supply amount of hydrocarbon gas supplied via the hydrocarbon line (12).
And the mixed gas whose molar ratio of the water vapor amount / carbon amount of the reduced hydrocarbon gas and water vapor is 2 to 4 is obtained, and the hydrogen-containing gas obtained by passing the mixed gas through the reformer (40) is obtained. The oxidant gas is continuously supplied to the power generation stack (10).

  And when the temperature of the reformer (40) is acquired from the reformer temperature detecting means (42) and the temperature of the acquired reformer (40) is lowered to 200 ° C. to 550 ° C., the hydrocarbon gas While the supply is stopped and the water vapor is continuously supplied, the temperature of the vaporizer (50) is acquired from the vaporizer temperature detecting means (52), and the temperature of the acquired vaporizer (50) is 100 ° C. At the reached stage, a certain amount of water is supplied to the vaporizer (50) and stored, and then the water supply is stopped.

  In such a fuel cell system (1), when the operation is stopped, the oxidizing gas and the hydrogen-containing gas are continuously supplied to the power generation stack (10) until the temperature of the reformer (40) is lowered to 200 ° C to 550 ° C. Is supplied.

  That is, until the temperature of the reformer (40) drops to 200 ° C. to 550 ° C., the oxidizing gas is supplied to the cathode of the power generation stack (10) and the hydrogen-containing gas is supplied to the anode via the reformer (40). The And if the temperature of a reformer (40) falls to 200 to 550 degreeC, supply of hydrocarbon gas will be stopped.

  Since the spontaneous ignition temperature of hydrogen generated by reforming is 550 ° C., the supply of hydrocarbon gas is stopped when the reformer (40) temperature is lowered to 550 ° C. Then, the spontaneous ignition of hydrogen generated by the reforming stops and heat generation in the fuel cell is eliminated, so that the fuel cell is cooled.

  Moreover, S / C of the mixed gas of hydrocarbon gas and water vapor of hydrocarbon gas and water vapor is 2-4. When the S / C is less than 2, carbonization of the anode and the reforming catalyst is likely to occur. When the S / C is greater than 4, the amount of water supplied increases, and only the vaporizer (50) rapidly Since it is cooled, no steam is generated, resulting in no steam reforming reaction. Therefore, S / C is suitably 2-4.

  Furthermore, when the operation is stopped, only air is supplied to the heating means (30) which receives the supply of air and fuel and heats it. That is, since the fuel supply is lost, heating is not performed, and the outside of the fuel cell is cooled by the supplied air, so that the cooling time of the fuel cell system (1) can be shortened.

  In addition, when the temperature of the vaporizer (50) reaches 100 ° C. while the supply of water vapor is continued, a certain amount of water is supplied to the vaporizer (50) and stored, and then the supply of water is stopped. If it does in this way, since a downstream side will be filled with water vapor | steam from the vaporizer | carburetor (50), the oxidation of an anode or a reforming catalyst can be suppressed.

  Here, when the supply of the hydrocarbon gas is stopped at the temperature of the reformer (40) higher than 550 ° C. and only water vapor is supplied, the anode and the reforming catalyst are easily oxidized. On the other hand, when the supply of the hydrocarbon gas is stopped at a temperature lower than 200 ° C. and only the steam is supplied, the steam is condensed in the reformer (40), and the downstream side of the vaporizer (50) is filled with the steam. It will disappear. Therefore, the temperature of the reformer (40) is appropriately 200 ° C to 550 ° C.

  Further, as in the present invention, when the control means (60) reduces the supply amount of hydrocarbon gas when stopped to 0.1 to 0.7 times the maximum input amount during power generation, the reformer (40) As a result, the cooling of the gas is moderately promoted, and the oxidant gas on the cathode side is prevented from entering the anode side, thereby suppressing the oxidation of the anode.

  Further, as in the present invention, the control means (60) stops the supply of the hydrocarbon gas, the oxidant gas is continuously supplied to the power generation stack (10), and continuously to the vaporizer (50). When a temperature of the vaporizer (50) obtained from the vaporizer temperature detection means (52) reaches 100 ° C., a certain amount of water is supplied to the vaporizer (50), Stop supplying.

  Then, power generation can be stopped rapidly by stopping the supply of hydrocarbon gas, and a certain amount of water is supplied into the vaporizer (50) at a temperature of the vaporizer (50) of 100 ° C. The water supply to the vaporizer (50) is stopped.

Therefore, the downstream side of the vaporizer (50) is filled with water vapor. Accordingly, oxidation of the fuel cell reforming catalyst and the anode can be suppressed.
In addition, as in the present invention, when a certain amount of water is supplied to the vaporizer (50) and stored after the fuel cell operation is stopped until the next start-up, the following operation is performed after the operation is stopped. Since the downstream side of the vaporizer (50) is filled with water vapor until the start of startup, oxidation of the reforming catalyst and the anode can be suppressed.

  Further, as in the present invention, there is provided switching means (94) for sending the oxidant gas supplied to the cathode side of the power generation stack (10) to the anode side, and the control means (60) operates the fuel cell. When the temperature of the vaporizer (50) reaches 100 ° C. at the time of stopping, the switching means (94) is switched to purge the water vapor by sending the oxidant gas supplied to the cathode side to the anode side. .

If it does in this way, the purge of water vapor | steam can be performed by flowing the oxidizing gas supplied to the cathode to an anode by switching a switching means (94). This purge with the oxidant gas can prevent the anode side from becoming supersaturated with water vapor, that is, the water vapor supplied to the anode side can be prevented from condensing and retaining. Accordingly, there is no stagnation of water at the anode at the time of restarting, so that the gas can be supplied smoothly.
By the way, as the power generation stack (10) used in the fuel cell system (1), the solid oxide fuel cell stack as in the present invention has a relatively high operating temperature of 700 ° C. to 1000 ° C. The effect of shortening the cooling time is easily obtained.

[First Embodiment]
Embodiments to which the present invention is applied will be described below with reference to the drawings. The embodiment of the present invention is not limited to the following embodiment, and can take various forms as long as they belong to the technical scope of the present invention.

(Configuration of solid oxide fuel cell system 1)
FIG. 1 is a block diagram showing a schematic configuration of a solid oxide fuel cell system 1 to which the present invention is applied.

  As shown in FIG. 1, the solid oxide fuel cell system 1 includes a power generation stack 10, a hydrocarbon line 12, an oxidant line 14, a discharge line 16, a reformer 40, a reformer temperature, in a heat insulating container 20. A sensor 42, a vaporizer 50, a vaporizer temperature sensor 52, and a heating burner 30 are provided, and a controller 60 is provided outside the heat insulating container 20.

The power generation stack 10 is a stack of solid oxide fuel cells. In the fuel cell, an electrolyte layer is formed between an anode (fuel electrode) and a cathode (air electrode).
The anode is formed of cermet of Ni or Ni and ceramic, and the cathode is formed of perovskite oxide, various noble metals and cermet of noble metal and ceramic. The electrolyte layer is made of a solid oxide such as YSZ, ScSZ, SDC, GDC, or perovskite oxide.

  A hydrogen-containing gas obtained by reforming the hydrocarbon gas supplied from the hydrocarbon line 12 by the reformer 40 is supplied to the anode, and air supplied from the oxidant line 14 is supplied to the cathode. The Moreover, it heats with the heating burner 30 at 700 to 1000 degreeC, and generates electric power. When the power generation stack 10 reaches a temperature at which power generation is possible, the heating burner 30 is extinguished, but since the power generation stack 10 is in the heat insulating container 20, the heat self-sustains within a range of 700 ° C to 1000 ° C.

The hydrocarbon line 12 is a line for supplying hydrocarbon gas to the power generation stack 10, and is provided with a desulfurizer 80, a fuel pump 74, and a solenoid valve 92.
The desulfurizer 80 desulfurizes hydrocarbon gas such as city gas and propane gas supplied from the outside using existing infrastructure, and the fuel pump 74 vaporizes the hydrocarbon gas desulfurized by the desulfurizer 80. 50.

  The solenoid valve 92 is a switching valve for switching the supply or shut-off of the hydrocarbon gas from the outside to the hydrocarbon line 12, and two solenoid valves 92 are arranged in the hydrocarbon line 12 from the viewpoint of fail-safe. ing.

In addition, the controller 60 controls the operation / inactivation of the fuel pump 74 and the amount of hydrocarbon gas to be supplied.
The oxidant line 14 is a line that supplies air, which is an oxidant gas, to the power generation stack 10, and an air pump 70 is installed in the vicinity of the air intake. The air pump 70 supplies air taken from the air intake to the power generation stack 10. The controller 60 controls the operation / non-operation of the air pump 70 and the amount of air to be supplied.

The discharge line 16 is a line for discharging gas that does not contribute to power generation and used gas from the power generation stack 10.
The reformer 40 is a device that generates hydrogen necessary for power generation in the power generation stack 10, and reforms a hydrocarbon gas into a hydrogen-containing gas by steam reforming.

  Hydrocarbon gas reforming methods include partial oxidation reforming and steam reforming. There is a difference between partial oxidation reforming and exothermic reaction, and steam reforming is an endothermic reaction, and steam reforming is easy for temperature control of the power generation stack 10, and therefore steam reforming is performed in this embodiment. Further, steam reforming is generally applied because power generation efficiency is increased by using steam reforming rather than partial oxidation reforming.

The reformer 40 is provided with a reformer temperature sensor 42 that detects the temperature of the reformer and outputs it to the controller 60.
The vaporizer 50 vaporizes water to supply the reformer 40 with steam for steam reforming. A front stage of the vaporizer 50 is provided with a water supply pump 72 for supplying pure water for generating water vapor, and the vaporizer 50 vaporizes the pure water supplied by the water supply pump 72, It is mixed with the hydrocarbon gas supplied from the hydrocarbon line 12 and supplied to the reformer 40.

The controller 60 controls the operation / non-operation of the water supply pump 72 and the amount of pure water to be supplied.
Further, a vaporizer temperature sensor 52 that detects the temperature of the vaporizer and outputs the vaporizer temperature to the controller 60 is attached to the vaporizer 50.

  The heating burner 30 is supplied with air and fuel gas from the outside, and heats the power generation stack 10 to 700 ° C. to 1000 ° C., and is housed in the heat insulating container 20 together with the power generation stack 10 and the like.

  The heating burner 30 is fed with air by an air blower 76 and fuel gas through a proportional valve 90 in which an air-fuel ratio is set in accordance with the amount of air supplied by the air blower 76, and is ignited by an ignition source (not shown). 20 The inside is heated.

  In addition, two electromagnetic valves 92 for switching the supply or shutoff of the fuel gas from the outside are arranged on the line for supplying the fuel gas to the proportional valve. The two electromagnetic valves 92 are arranged from the viewpoint of fail-safe, like the electromagnetic valves 92 arranged in the hydrocarbon line 12.

  Further, since the vaporizer 50 and the reformer 40 need to be heated, the vaporizer 50 and the reformer 40 are brought together with the power generation stack 10 by the heating burner 30 by being stored in the same heat insulating container 20 as the power generation stack 10. Heated. Further, it is not necessary to separately prepare a steam purge blower (pump), and the system configuration is simplified.

  The controller 60 controls the solid oxide fuel cell system 1 during operation and when operation is stopped, and includes a CPU, a ROM, a RAM, and an I / O (not shown). The controller 60 is connected to an output of a sensor (not shown) necessary for driving the pumps 70, 72, 74 and 76.

  The controller 60 has built-in control software programmed in advance for how to control the auxiliary equipment in each sequence of start-up, power generation, steady stop, and emergency stop. Based on this control software, solid oxidation is performed. The physical fuel cell system 1 operates.

(Steady stop sequence)
Next, a steady stop sequence by the controller 60 when the solid oxide fuel cell system 1 in the operating state is stopped will be described with reference to FIG.

  The operation of the steady stop sequence is performed based on control software built in the controller 60. When a signal for starting a stationary stop sequence is input from the outside to the controller 60, the stationary stop sequence is started.

  When the steady stop is started, as shown in FIG. 2, in order to cool the stack quickly, first, the air blower 76 supplies fresh air to the insulated container via the heating burner 30 and cools it. To do. The amount of cooling air supplied by the air blower 76 is preferably the maximum amount of air that can be supplied by the air blower 76.

Further, in order to perform cooling from the inside of the stack, the oxidant gas is continuously supplied to the cathode of the stack.
In addition, the hydrogen-containing gas that has been supplied to the anode during power generation reacts with oxygen in the air in the fuel cell to generate Joule heat. Therefore, the amount of hydrocarbon gas supplied from the fuel pump 74 is reduced in order to reduce the supply amount of the hydrogen-containing gas. In this case, considering the practical operating range of the fuel pump 74, the hydrocarbon gas supply amount is set to 0.1 to 0.7 times the maximum supply amount during power generation.

  Thus, since the steam reforming is performed in the reformer 40 by reducing the hydrocarbon gas supply amount, the endothermic reaction proceeds, and the cooling of the gas in the reformer 40 is appropriately promoted. In the case of a supply amount larger than 0.7 times the hydrocarbon gas, since the spontaneous ignition temperature of hydrogen generated by reforming is about 550 ° C., and the amount of heat of the hydrogen-containing gas supplied is large, the fuel of the power generation stack 10 Battery cells are less likely to cool.

On the other hand, when the supply amount is less than 0.1 times the hydrocarbon gas, there is a high possibility that the oxidant gas on the cathode side will circulate to the anode side and cause oxidation of the anode.
Further, in order to suppress carbonization of the reforming catalyst, the supply amount of water vapor needs to be the same as or larger than the amount of carbon contained in the hydrocarbon gas, and is a numerical value expressed as a ratio. C (water vapor amount / carbon amount: molar ratio) is set to 2 to 4. The value of S / C is preferably 2.5-3.

  In this way, burner air, oxidant gas, hydrocarbon gas, and water vapor are supplied until the temperature of the reformer falls to a range of 200 ° C to 550 ° C. Since the spontaneous ignition temperature of hydrogen generated by reforming is 550 ° C., if the supply of hydrocarbon gas is stopped when the reformer temperature reaches the range of 200 ° C. to 550 ° C., the hydrogen generated by reforming Since spontaneous ignition stops, the gas temperature discharged from the power generation stack 10 decreases.

  On the other hand, when the reformer temperature is higher than 550 ° C. and the supply of hydrocarbon gas is stopped and only steam is supplied to the anode line, oxidation of the reforming catalyst and the anode by steam is likely to occur. When the supply of hydrocarbon gas is stopped at a temperature lower than 200 ° C. and only the steam is supplied to the anode line, the steam may be condensed inside the reformer 40.

Therefore, the supply of hydrocarbon gas is stopped when the reformer temperature reaches the range of 200 ° C to 550 ° C.
Then, after the supply of hydrocarbon gas is stopped, only water vapor is supplied to the anode, and cooling air is supplied to the outside of the power generation stack 10 by the air blower 76 and oxidant gas is supplied to the cathode. .

  Thereby, the purge of the combustible gas in the anode line and the cooling of the power generation stack 10 can be accelerated. Further, it is possible to suppress the oxidizing gas supplied to the cathode side from flowing into the anode side and oxidizing the anode.

  When the temperature of the vaporizer 50 is lowered to 100 ° C., the supply of water to the vaporizer 50 is stopped while the supply of the oxidant gas to the cathode is continued, and the supply of water vapor to the anode is stopped. To do. Thereby, the condensation by the supersaturation of the water vapor in the anode can be prevented.

  Further, when the supply of water is stopped, in order to prevent the anode from being exposed to the oxidizing atmosphere, the supply of water is stopped after supplying a certain amount of water to the vaporizer 50. . The “constant amount” in this case means an amount that does not cause condensation due to supersaturation of water in the anode.

  Then, after the temperature of the power generation stack is sufficiently cooled, the supply of the air supplied to cool the outside of the stack and the oxidant gas to the cathode side is stopped, and the steady stop sequence ends.

(Emergency stop sequence)
Next, the steady stop sequence by the controller 60 when the solid oxide fuel cell system 1 in the operating state is brought to an emergency stop will be described with reference to FIG. The emergency stop sequence is also performed based on control software built in the controller 60.

  When an emergency stop sequence start signal is externally input to the controller 60, the emergency stop sequence is started. In the emergency stop sequence, in order to cool the power generation stack 10, first, fresh air is supplied into the insulated container via the heating burner 30 and cooled by the air blower 76. The amount of cooling air supplied by the air blower 76 is preferably the maximum amount of air that can be supplied by the air blower 76.

  In order to perform cooling also from the inside of the power generation stack 10, an oxidant gas is supplied to the cathode of the power generation stack 10. Further, the hydrogen-containing gas supplied to the anode during power generation needs to be purged at an early stage because of the combustible gas. Therefore, when an emergency stop start signal is output, the supply of hydrocarbon gas by the fuel pump 74 is stopped.

  However, in this case, since the reforming catalyst is likely to be at the oxidation temperature, water is supplied to the vaporizer 50 and water vapor is supplied to the anode from the cathode side while purging the hydrogen-containing gas in the anode. This prevents the oxidant gas from flowing in and suppresses oxidation of the anode and oxidation of the reforming catalyst.

In this way, the oxidant gas and water vapor are supplied to the power generation stack 10 until the temperature of the vaporizer 50 drops to 100 ° C.
When the vaporizer temperature is lowered to 100 ° C., the water supply to the vaporizer 50 is stopped while the supply of the oxidant gas to the cathode is continued, and the supply of water vapor to the anode is stopped. Further, condensation due to supersaturation of water vapor in the anode can be prevented.

  However, in order to prevent the anode from being exposed to the oxidizing atmosphere, the supply of water is stopped after supplying the vaporizer 50 so that a certain amount of water is stored. The fixed amount in this case is an amount that does not cause condensation due to supersaturation of water in the anode.

  Then, after the temperature of the power generation stack 10 is sufficiently cooled, the supply of the oxidant gas to the cathode and the air supplied to cool the outside of the power generation stack 10 is stopped, and an emergency steady stop sequence Ends.

(Operation from shutdown to startup)
Next, the operation from when the solid oxide fuel cell system 1 is stopped to when it is started next time will be described.

  The solid oxide fuel cell system 1 can be stopped in three ways: steady stop and emergency stop, as well as blackouts. In either case, the reforming catalyst carbonization, oxidation, and anode oxidation are suppressed. There is a need to.

  In order to suppress the oxidation of the anode, it is most desirable to always be in a reducing atmosphere, but in order to achieve the reducing atmosphere, it is necessary to keep hydrogen on the anode side. However, since hydrogen is a flammable gas, it is not desirable in consideration of safety.

In addition, as a second best plan, it may be possible to use an inert gas, but there is a problem that the incidental facilities become large. In view of this, it is conceivable to expose the reforming catalyst and the anode to a steam atmosphere during the period from the steady stop, emergency stop, and power failure until the next system startup. Therefore, by supplying a predetermined amount of water to the vaporizer 50 and storing it at the end of the steady stop sequence, from the end of the emergency stop sequence and from the time of power failure to the start of the next operation start sequence, the reforming catalyst is stored. And the anode can be prevented from being exposed to an oxidizing atmosphere.
[Second Embodiment]
Next, a second embodiment will be described with reference to FIGS. FIG. 4 is a block diagram showing a schematic configuration of the solid oxide fuel cell system 2, and FIG. 5 is a sequence diagram when the solid oxide fuel cell system 2 is stopped steadily. FIG. 6 is a sequence diagram when the solid oxide fuel cell system 2 is brought to an emergency stop.

  Although it is considered that the reforming catalyst in the reformer 40 and the anode in the power generation stack 10 are exposed to a steam atmosphere as the simplest oxidation suppressing method, when the steam condenses and the condensed water stays in the anode line. When restarting the system, it will be a big loss and must be prevented.

  Therefore, as shown in FIG. 4, with respect to the solid oxide fuel cell system 1 shown in FIG. 1, the flow path of the cathode oxidant gas to the anode line on the upstream side of the vaporizer 50 and the flow path switching valve 94. And a check valve 96 is provided. The check valve 96 is a valve for preventing the anode gas from flowing into the cathode when the flow path switching valve 94 fails.

  The operation of the stop sequence in this case is shown in FIGS. FIG. 5 is a diagram showing a change from FIG. 2, that is, a sequence diagram when the solid oxide fuel cell system 2 is steadily stopped. FIG. 6 is a diagram showing a change from FIG. 3, that is, a sequence diagram when the solid oxide fuel cell system 2 is brought to an emergency stop.

  The sequence shown in FIGS. 5 and 6 is different from the sequence shown in FIGS. 2 and 3 when the temperature of the vaporizer 50 is lowered to 100 ° C., the oxidant gas supplied to the cathode is changed to the flow path switching valve. After the supply of a minimum flow rate Qmin (> 0) that allows the air pump 70 to flow to the anode by switching 94, the flow path switching valve 94 is switched again to supply the anode. Stop introducing oxidant gas to the line.

Further, the water supply to the vaporizer 50 is stopped only after a certain amount of water is stored in the vaporizer 50 (the period indicated by A in FIGS. 5 and 6).
In this stop sequence, an oxidant gas is introduced into the anode, but since the temperature is lower than the oxidation temperature of the reforming catalyst and the anode of the reformer 40, the oxidation of the reforming catalyst and the anode can be suppressed.

  Furthermore, it is not necessary to separately prepare a steam purge blower (pump), and the system configuration is simplified. In addition, when the next start-up is performed, since a certain amount of water is stored in the vaporizer 50, the water stored in the vaporizer 50 is vaporized in the anode line at the stack temperature rising stage at the start-up. By doing so, the oxidant gas is purged.

[Other Embodiments]
In the above embodiment, a stack of solid oxide fuel cells (solid oxide fuel cell stack) is used as the power generation stack 10, but a stack of solid polymer fuel cells ( Solid polymer fuel cell stack).

  A blower may be used instead of the air pump 70.

1 is a block diagram showing a schematic configuration of a solid oxide fuel cell system 1. FIG. It is a steady stop sequence diagram by the controller 60 when the solid oxide fuel cell system 1 is stopped steadily. It is a steady stop sequence diagram by the controller 60 when the solid oxide fuel cell system 1 is brought to an emergency stop. 1 is a block diagram showing a schematic configuration of a solid oxide fuel cell system 2. FIG. It is a stationary stop sequence diagram by the controller 60 when the solid oxide fuel cell system 2 is stopped steadily. It is a steady stop sequence diagram by the controller 60 when the solid oxide fuel cell system 2 is brought to an emergency stop.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1, 2 ... Solid oxide fuel cell system, 10 ... Power generation stack, 12 ... Hydrocarbon line, 14 ... Oxidant line, 16 ... Discharge line, 20 ... Thermal insulation container, 30 ... Heating burner, 40 ... Reformer, 42 ... reformer temperature sensor, 50 ... vaporizer, 52 ... vaporizer temperature sensor, 60 ... controller, 70 ... air pump, 72 ... water supply pump, 74 ... fuel pump, 76 ... air blower, 80 ... desulfurizer 90 ... Proportional valve, 92 ... Solenoid valve, 94 ... Flow path switching valve, 96 ... Check valve.

Claims (12)

It is heated by heating means that receives the supply of air and fuel gas from the outside and heats the inside of the heat insulating container,
A fuel that generates a mixed gas of water vapor and hydrocarbon gas by a vaporizer and supplies the hydrogen-containing gas obtained by passing the mixed gas through a reformer to a power generation stack in which an oxidant gas is flowed to generate power. In the battery shutdown method,
When the operation is stopped
Supplying only air to the heating means;
Reducing the supply of hydrocarbon gas,
Obtaining a mixed gas having a water vapor / carbon molar ratio of 2 to 4 between the reduced hydrocarbon gas and the water vapor,
Supplying the hydrogen-containing gas obtained by passing the mixed gas through the reformer to the power generation stack in which an oxidant gas is continuously flowed;
When the temperature of the reformer falls to 200 ° C. to 550 ° C., the supply of the hydrocarbon gas is stopped,
Furthermore, the water supply is continuously performed, and when the temperature of the vaporizer reaches 100 ° C., a certain amount of water is supplied to the vaporizer and stored, and then the water supply is stopped. A fuel cell shutdown method. In the fuel cell shutdown method according to claim 1,
A method of stopping a fuel cell, comprising reducing the amount of hydrocarbon gas supplied when the fuel cell is stopped to 0.1 to 0.7 times the maximum amount of fuel gas input during power generation. It is heated by heating means that receives the supply of air and fuel gas from the outside and heats the inside of the heat insulating container,
A fuel that generates a mixed gas of water vapor and hydrocarbon gas by a vaporizer and supplies the hydrogen-containing gas obtained by passing the mixed gas through a reformer to a power generation stack in which an oxidant gas is flowed to generate power. In the battery shutdown method,
When the operation is stopped
Supplying only air to the heating means;
In the power generation stack where the supply of the hydrocarbon gas is stopped and the oxidant gas is continuously flowed,
The supply of water is stopped after supplying a certain amount of water to the vaporizer and storing it when the temperature of the vaporizer reaches 100 ° C. while continuously supplying water vapor. To stop the operation of the fuel cell. In the fuel cell operation stop method according to any one of claims 1 to 3,
A fuel cell operation stop method comprising: supplying a predetermined amount of water to the vaporizer and storing after the fuel cell operation stop until the next start-up. In the fuel cell operation stop method according to any one of claims 1 to 4,
Comprising switching means for sending the oxidant gas supplied to the cathode side of the power generation stack to the anode side,
When the temperature of the vaporizer reaches 100 ° C. when the operation of the fuel cell is stopped, the steam is purged by sending the oxidant gas supplied to the cathode side to the anode side by switching the switching means. A method for stopping the operation of a fuel cell. The fuel cell system according to any one of claims 1 to 5,
The fuel cell operation stop method, wherein the power generation stack is a solid oxide fuel cell stack. In an insulated container,
A power generation stack that generates electricity by receiving supply of hydrocarbon gas and oxidant gas;
A hydrocarbon line for supplying hydrocarbon gas to the power generation stack;
An oxidant line for supplying oxidant gas to the power generation stack;
An exhaust line for discharging gas that does not contribute to power generation and used gas from the power generation stack;
A reformer for reforming the hydrocarbon gas into a hydrogen-containing gas by steam reforming;
Reformer temperature detecting means for detecting the temperature of the reformer;
A vaporizer for vaporizing water to supply steam to the reformer;
Vaporizer temperature detection means for detecting the temperature of the vaporizer;
Heating means for heating the inside of the heat insulation container by receiving supply of air and fuel gas from the outside;
With
Furthermore, when the operation is stopped, only air is supplied to the heating means,
Reducing the supply amount of the hydrocarbon gas to be supplied through the hydrocarbon line, obtaining a mixed gas having a water vapor amount / carbon amount molar ratio of 2 to 4 between the reduced hydrocarbon gas and water vapor; Supplying the hydrogen-containing gas obtained by passing the mixed gas through the reformer to the power generation stack in which an oxidant gas is continuously flowed;
Obtaining the temperature of the reformer from the reformer temperature detecting means, and when the obtained temperature of the reformer is lowered to 200 ° C. to 550 ° C., the supply of the hydrocarbon gas is stopped,
Furthermore, while continuously supplying water vapor, the temperature of the vaporizer is acquired from the vaporizer temperature detecting means, and when the acquired temperature of the vaporizer reaches 100 ° C., a certain amount is supplied to the vaporizer. A fuel cell system comprising control means for stopping the supply of water after the water is supplied and stored. The fuel cell system according to claim 7, wherein
The control means includes
A fuel cell system, wherein the supply amount of hydrocarbon gas at the time of stopping the operation is reduced to 0.1 to 0.7 times the maximum input amount at the time of power generation. In an insulated container,
A power generation stack that generates electricity by receiving supply of hydrocarbon gas and oxidant gas;
A hydrocarbon line for supplying hydrocarbon gas to the power generation stack;
An oxidant line for supplying oxidant gas to the power generation stack;
An exhaust line for discharging gas that does not contribute to power generation and used gas from the power generation stack;
A reformer for reforming the hydrocarbon gas into a hydrogen-containing gas by steam reforming;
Reformer temperature detecting means for detecting the temperature of the reformer;
A vaporizer for vaporizing water to supply steam to the reformer;
Vaporizer temperature detection means for detecting the temperature of the vaporizer;
Heating means for heating the inside of the heat insulation container by receiving supply of air and fuel gas from the outside;
With
The control means includes
The supply of the hydrocarbon gas is stopped, the oxidant gas is continuously supplied to the power generation stack, the water is continuously supplied to the vaporizer, and the vaporization obtained from the vaporizer temperature detection means When the temperature of the vessel reaches 100 ° C., the supply of water is stopped after supplying a certain amount of water to the vaporizer. The fuel cell system according to any one of claims 7 to 9,
The control means includes
A fuel cell system characterized in that a certain amount of water is supplied to the vaporizer and stored after the operation is stopped until the next start-up. The fuel cell system according to any one of claims 7 to 10,
Comprising switching means for sending the oxidant gas supplied to the cathode side of the power generation stack to the anode side,
The control means includes
When the temperature of the vaporizer obtained from the vaporizer temperature detection means reaches 100 ° C. when the operation is stopped, the oxidant gas supplied to the cathode side is sent to the anode side by switching the switching means, thereby steaming Purging the fuel cell system The fuel cell system according to any one of claims 7 to 11,
The fuel cell system, wherein the power generation stack is a solid oxide fuel cell stack.

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