Control method for fuel cell system, and fuel cell system

Abstract

A method for controlling a fuel cell system including a reformer that reforms raw fuel to generate anode gas, a fuel cell that consumes the anode gas to generate power, and a recycle line that supplies a portion of anode off-gas discharged from the fuel cell to the reformer, wherein when the flow rate of first water vapor supplied to the reformer is insufficient, the flow rate of second water vapor taken into the recycle line is increased by changing the operating state of the fuel cell in a direction in which the flow rate of second water vapor contained in the anode off-gas increases.

Description

Control method for fuel cell systems, fuel cell systems

[0001] This invention relates to a control method for a fuel cell system and to a fuel cell system.

[0002] JPH9-180748A discloses a method for recovering a portion of the anode off-gas emitted from the fuel cell stack and utilizing the water vapor contained in the recovered anode off-gas for fuel reforming.

[0003] However, because JPH09-180748A is configured to control the amount of anode off-gas recovered according to the type of raw fuel, it becomes difficult to secure a sufficient amount of steam when the amount of steam required to reform the raw fuel increases sharply due to an increase in the power generation demand from the fuel cell system.

[0004] Therefore, the present invention aims to provide a control method for a fuel cell system and a fuel cell system that can secure the amount of water vapor required for reforming the raw fuel even when the amount of water vapor required for reforming the raw fuel increases rapidly.

[0005] According to one aspect of the present invention, there is a control method for a fuel cell system including a reformer that reforms raw fuel to produce anode gas, a fuel cell that generates electricity by consuming the anode gas, and a recycling line that supplies a portion of the anode off gas discharged from the fuel cell to the reformer. In this control method, when the flow rate of the first steam supplied to the reformer is insufficient, the operating state of the fuel cell is changed in a direction that increases the flow rate of the second steam contained in the anode off gas, thereby increasing the flow rate of the second steam taken into the recycling line.

[0006] Figure 1 is a schematic diagram showing the basic configuration of the fuel cell system of this embodiment. Figure 2 is a diagram illustrating the electrochemical reaction that occurs in an oxide ion conducting fuel cell. Figure 3 is a diagram showing the relationship between the IV characteristics of the fuel cell, the change in the fuel cell output, and the change in the fuel cell's extraction current. Figure 4 is a control time chart of the fuel cell system of this embodiment. Figure 5 is a schematic diagram of a modified fuel cell. Figure 6 is a diagram illustrating the electrochemical reaction that occurs in a proton exchange membrane fuel cell and the permeation of water into the electrolyte layer.

[0007] Embodiments of the present invention will be described below with reference to the drawings.

[0008] [Basic Configuration of a Fuel Cell System]

[0009] The fuel cell system of this embodiment includes a fuel supply line 2 that supplies fuel (anode gas) to the fuel cell stack 1, a steam supply line 3 that supplies steam to the fuel supply line 2, an air supply line 4 that supplies air (cathode gas) to the fuel cell stack 1, an exhaust gas line 5 that exhausts the gas discharged from the fuel cell stack 1, a recycling line 6 that recirculates a portion of the anode off gas discharged from the fuel cell stack 1 back to the fuel supply line 2, a power supply line 7 that extracts power from the fuel cell stack 1, and a control unit 8 that controls the entire system.

[0010] The fuel supply line 2 includes a fuel tank 21, a pump 22, a desulfurizer 23, a heat exchanger 24, and a reformer 25.

[0011] The fuel tank 21 contains raw fuels (for example, methane (CH4)) that will be used as raw materials for the anode gas of the fuel cell stack 1. ４ )) to store.

[0012] Pump 22 pumps the raw fuel stored in fuel tank 21 to desulfurizer 23.

[0013] The desulfurizer 23 removes sulfur components from the raw fuel and supplies it to the heat exchanger 24.

[0014] The heat exchanger 24 heats the raw fuel (and steam supplied from the steam supply line 3) by exchanging heat with the combustion gas discharged from the combustor 51 (described later) and supplies it to the reformer 25.

[0015] The reformer 25 reacts the raw fuel with steam to produce reformed fuel (anode gas), which is then supplied to the fuel cell stack 1 (anode).

[0016] The steam supply line 3 includes a water tank 31, a valve 32, a pump 33, and a vaporizer 34. The steam supply line 3 merges with the fuel supply line 2 at a position between the heat exchanger 24 and the reformer 25 of the fuel supply line 2.

[0017] The water tank 31 stores water that will be used as raw material for the steam used in the reformer 25.

[0018] Valve 32 is opened when steam is needed in the reformer 25.

[0019] The pump 33 pressurizes the water stored in the water tank 31 and sends it to the vaporizer 34.

[0020] The vaporizer 34 vaporizes water to generate steam (first steam) and supplies it to the heat exchanger 24 of the fuel supply line 2.

[0021] The air supply line 4 includes a blower 41 and a heat exchanger 42.

[0022] The blower 41 takes in air from the outside and supplies it to the heat exchanger 42.

[0023] The heat exchanger 42 heats the air (cathode gas) by exchanging heat with the combustion gas discharged from the combustor 51 (described later) and supplies it to the fuel cell stack 1 (cathode).

[0024] The fuel cell stack 1 has a stack structure obtained by stacking a large number of oxide ion conducting type battery cells (Figure 2), or a stack structure obtained by stacking a large number of proton exchange membrane type battery cells (Figure 6).

[0025] The fuel cell stack 1 introduces anode gas from the anode inlet of the fuel cell stack 1 and cathode gas from the cathode inlet of the fuel cell stack 1.

[0026] The fuel cell stack 1 generates electricity through an electrochemical reaction between the anode gas (reformed fuel) supplied to the anode and the cathode gas (oxygen) supplied to the cathode, and outputs the generated electricity to the power supply line 7.

[0027] The fuel cell stack 1 discharges the anode off-gas used in the electrochemical reaction from the anode outlet of the fuel cell stack 1, and discharges the cathode off-gas used in the electrochemical reaction from the cathode outlet of the fuel cell stack 1.

[0028] In this embodiment, the reformer 25 may be omitted, and a catalyst capable of reforming the raw fuel may be placed inside the fuel cell stack 1 to make the fuel cell stack 1 an internally reforming type fuel cell stack 1, thereby enabling a configuration in which the reforming reaction of the raw fuel and the electrochemical reaction (power generation) using the reformed fuel are carried out simultaneously.

[0029] A combustor 51 is located in the exhaust gas line 5. Upstream of the combustor 51, the exhaust gas line 5 communicates with the anode outlet and cathode outlet of the fuel cell stack 1, while downstream of the combustor 51, it communicates with the heat exchangers 24 and 42 and is open to the outside.

[0030] The combustor 51 burns a mixed gas obtained by mixing the anode-off gas and cathode-off gas discharged from the fuel cell stack 1, and supplies the resulting combustion gas to the heat exchangers 24 and 42.

[0031] The combustor 51 is formed integrally with the reformer 25 and the fuel cell stack 1, and heats the reformer 25 and the fuel cell stack 1 with the heat generated by the combustion of the mixed gas. The combustor 51 has an ignition device (not shown) for igniting the mixed gas and a catalyst (not shown) for catalytic combustion of the mixed gas.

[0032] The recycling line 6 is equipped with a valve 61, a booster 62, and a steam sensor 63. The recycling line 6 branches off from the anode off-gas line of the exhaust gas line 5 and merges with the fuel supply line 2 at a position between the heat exchanger 24 and the reformer 25 of the fuel supply line 2.

[0033] The valve 61 adjusts the flow rate of anode off gas supplied to the combustor 51 and the flow rate of anode off gas supplied to the recycling line 6 by adjusting its opening degree, but it is normally kept constant.

[0034] The booster 62 is, for example, an ejector or a pump, which boosts the anode off gas introduced into the recycling line 6 and pumps it toward the fuel supply line 2.

[0035] The water vapor sensor 63 detects the water vapor flow rate (the flow rate of the second water vapor taken into the recycling line 6) by detecting the flow rate of the anode off gas flowing through the recycling line 6 and the concentration of water vapor in the anode off gas.

[0036] The power supply line 7 includes a DC / DC converter 71, a power buffer device 72, and an inverter 73.

[0037] The DC / DC converter 71 boosts the output voltage generated by the fuel cell stack 1 and outputs it to the power buffer device 72.

[0038] The power buffer device 72 is equipped with a battery that stores the power output from the DC / DC converter 71. Furthermore, when the inverter 73 is driven, the power buffer device 72 outputs a DC voltage to the inverter 73 under control from the control unit 8.

[0039] The inverter 73 has a switching element driven by a PWM signal, and converts the DC voltage of the power buffer device 72, which receives the PWM signal transmitted from the control unit 8, into a three-phase AC voltage and outputs it to the load (for example, a drive motor).

[0040] The control unit 8 controls the following: pump 22, valve 32, pump 33, blower 41, combustor 51, valve 61, booster 62, DC / DC converter 71, power buffer device 72, and inverter 73.

[0041] The control unit 8 includes a program for executing the control method of the fuel cell system of this embodiment, and executes control based on the program.

[0042] When the fuel cell stack 1 is started, the control unit 8 starts the pump 22 to supply raw fuel to the fuel supply line 2 (fuel cell stack 1 (anode), exhaust gas line 5), starts the blower 41 to supply air to the fuel supply line 2 (fuel cell stack 1 (cathode), exhaust gas line 5), and starts the ignition device (not shown) of the combustor 51 to burn the mixed gas of raw fuel and air that flows into the combustor 51, thereby heating the reformer 25 and the fuel cell stack 1 with the heat generated.

[0043] The control unit 8 opens the valve 32 and starts the pump 33 to supply water (steam) to the reformer 25.

[0044] The combustion gas generated in the combustor 51 is supplied to the heat exchanger 24 and the heat exchanger 42, where the raw fuel is heated in the heat exchanger 24 and the air is heated in the heat exchanger 42.

[0045] The raw fuel heated in the heat exchanger 24 heats the reformer 25 and the fuel cell stack 1 (anode), and the air heated in the heat exchanger 42 heats the fuel cell stack 1 (cathode).

[0046] The control unit 8 extinguishes the ignition device when the temperature of the combustor 51 reaches a temperature at which catalytic combustion is possible.

[0047] When the temperature of the reformer 25 reaches a temperature at which the raw fuel can be converted into reformed fuel (anode gas) and the temperature of the fuel cell stack 1 reaches a temperature at which power generation can be started, the control unit 8 controls the DC / DC converter 71 to extract a predetermined amount of current and start power generation.

[0048] The control unit 8 opens the valve 61 and activates the pressurizer 62, thereby returning a portion of the anode-off gas to the reformer 25 and using the water vapor contained in the anode-off gas to reform the raw fuel.

[0049] [Electrochemical Reactions and IV Characteristics of Oxygen Ion Conducting Fuel Cells] Figure 2 is a diagram illustrating the electrochemical reactions that occur in an oxygen ion conducting fuel cell. Figure 3 is a diagram showing the relationship between the IV characteristics of the fuel cell, the change in the fuel cell's output, and the change in the fuel cell's output current.

[0050] As shown in Figure 2, the oxygen ion conducting fuel cell has a laminated structure consisting of an anode electrode layer 101, a solid electrolyte layer 102, and a cathode electrode layer 103, with the solid electrolyte layer 102 being oxygen ion conductive.

[0051] As shown in Figure 2, the anode electrode layer 101 contains anode gas (H ２ ) is supplied, and cathode gas (O) is supplied to the cathode electrode layer 103. ２ ) will be supplied.

[0052] In the cathode electrode layer 103, oxygen molecules ((1 / 2)O ２ ), by taking in electrons (2e － ), become oxygen ions (O ２－ ), and the oxygen ions (O ２－ ), pass through the solid electrolyte layer 102 and reach the anode electrode layer 101.

[0053] The hydrogen molecules (H ２ ) supplied to the anode electrode layer 101 combine with oxygen ions (O ２－ ) to produce generated water (water vapor) (H ２ O) and release electrons (2e － ).

[0054] Therefore, the load (DC / DC converter 71) connected to the anode electrode layer 101 and the cathode electrode layer 103 of the fuel cell can take in current in a mode of supplying electrons (2e － ) from the anode electrode layer 101 to the cathode electrode layer 103.

[0055] As shown in FIG. 3, the IV characteristics of the fuel cell are such that the voltage is maximum (open-circuit voltage) when the current value is zero, and the voltage decreases as the current value increases. Usually, the control unit 8 sets the output current value (I １ ) of the fuel cell so that the current (I １ ) × voltage (V １ ) is maximum.

[0056] When the control unit 8 increases the power generation power of the fuel cell stack 1 due to a load request or the like, the control unit 8 increases the output of the pump 22 to increase the flow rate of the raw fuel or reformed fuel in the anode off-gas supplied to the combustor 51. As a result, by increasing the combustion amount of the raw fuel or reformed fuel in the combustor 51, the temperature of the fuel cell stack 1 is increased, and as shown in FIG. 2, the IV characteristics of the fuel cell stack 1 are improved. At that time, the control unit 8 increases the amount of water vapor supplied from the water vapor supply line 3 to the reformer 25 by increasing the output of the pump 33.

[0057] By the way, in the reformer 25, for example, [CH ４ + H ２ O → CO + 3H ２A reforming reaction such as -206.1 [kJ / mol] is carried out. However, it may take a predetermined amount of time for the water vapor flow rate to converge to the desired flow rate after increasing the output of the pump 33. Therefore, when the above reforming reaction is carried out during this predetermined time, if the molar ratio of water vapor to carbon (methane) (S / C) falls below 2, carbon deposition (coking) will occur in the reformer 25 or the fuel cell stack 1, leading to a decrease in the performance of the fuel cell system.

[0058] JPH9-180748A is designed to prevent carbon deposition in reformers and other equipment by placing shut-off valves and control valves in the anode off-gas recycling line, and by changing the recycled gas flow rate according to the flow rate of the raw fuel, thereby compensating for any shortage of steam for reforming.

[0059] However, in the above configuration, an ejector is required as a control valve, but flow rate adjustment is difficult with high-temperature gas, making it difficult to satisfy the amount of steam required for reforming. In addition, the anode off-gas component that should be used for waste heat also increases with the increase in the amount of steam recycled, making it difficult to control the aforementioned molar ratio (S / C).

[0060] On the other hand, in this embodiment, the amount of water (water vapor) can be increased, for example, by increasing the amount of electrochemical reaction. Specifically, with respect to the IV characteristics shown in Figure 2, the control unit 8 sets the current value to, for example, I during the predetermined time (the time when water vapor is insufficient in the reformer 25). １ From I, where the current value is greater ２ By sliding it in this direction, the steam flow rate can be temporarily increased, compensating for any shortage of steam in the reformer 25.

[0061] [Time Chart] Figure 4 is a time chart of the control of the fuel cell system in this embodiment.

[0062] Before time t1, the flow rate (FF) of the raw fuel (output of pump 22) reaches a predetermined flow rate (FF) １ The first flow rate is set to (1st flow rate). Also, the steam flow rate (FV) (output of pump 33) is set when the raw fuel flow rate (FF) is equal to the flow rate (FF) １ The flow rate (FV1) at which the molar ratio (S / C) is a predetermined value (2 or more) is when the flow rate is such that the molar ratio (S / C) is a predetermined value (2 or more).１ It shall be set to (second flow rate). Also, the flow rate (FV2) of steam flowing through the recycling line 6 shall be the flow rate (FV2) １ ) It is assumed that it is set to ).

[0063] At time t1, the control unit 8 determines the flow rate (FF) of the raw fuel (output of pump 22) １ ) from flow rate (FF ２ Switch to (third flow rate). As a result, the flow rate (FF) of the raw fuel will be (FF) at time t1. １ ) from flow rate (FF ２ ) will immediately switch to this.

[0064] At time t1, the control unit 8 controls the flow rate of water vapor (FV1) (output of pump 33) １ ) from flow rate (FV1 ２ Switch to (Fourth flow rate). Here, the flow rate (FV1 ２ ) (Fourth flow rate) is when the flow rate (FF) of the raw fuel is equal to the flow rate (FF) ２ This is the flow rate at which the molar ratio (S / C) is a predetermined value (2 or more) when the ) is such that the flow rate is such that the molar ratio (S / C) is a predetermined value (2 or more). As a result, the flow rate (FV1) of the water vapor generated in the water vapor supply line 3 is the flow rate (FV1) at time t1. １ ) begins to increase, but at time t2, a predetermined time has elapsed from time t1, the flow rate (FV1 ２ )

[0065] At time t1, the control unit 8 determines the flow rate of water vapor (FV2) detected by the water vapor sensor 63. １ ) and the flow rate of steam supplied from steam supply line 3 (FV1 １ The sum of (estimated by the output of pump 33) and (FV1) is the flow rate of steam supplied with a delay in the steam supply line 3. ２If the amount is less than 2, the control unit 8 determines that the flow rate of steam (first steam) to be supplied to the reformer 25 is insufficient. If it is determined that the amount of steam is insufficient (S / C becomes less than 2), the control unit 8 executes a control to increase the intake current of the DC / DC converter 71 (extraction current of the fuel cell stack 1) as described below (a control to increase the flow rate of steam (second steam) in the anode off-gas). On the other hand, if it is determined that the amount of steam is not insufficient, the control to increase the extraction current as described below is not executed.

[0066] If the control unit 8 determines that the steam flow rate in the reformer 25 is insufficient, at time t1, the control unit 8 will set the intake current of the DC / DC converter 71 to current (I １ ) from current (I ２ ) is switched to this. As a result, the flow rate (FV2) of steam circulating in the recycling line 6 is changed to the flow rate (FV2 １ ) from flow rate (FV2 ２ ) switches immediately. Here, the current (I ２ ) is the flow rate of water vapor in the water vapor supply line 3 at time t1 (FV1 １ ) and the input current (I ２ After setting the flow rate of water vapor taken into the recycling line 6 (FV2 ２ The sum of ) and the water vapor flow rate (FV1) that converges in the water vapor supply line 3 after time t2 is ２ ) matches or the flow rate (FV1 ２ Set to be greater than (FV1). As a result, at time t1, the flow rate of steam (FV1 + FV2) flowing through the reformer 25 is set to the flow rate (FV1 １ ) from flow rate (FV1 ２ The system immediately switches to a flow rate of ), or greater than that.

[0067] At time t2, the flow rate (FV1) of the steam supply line 3 is equal to the flow rate (FV1) ２ At this time, the flow rate of steam (FV1 + FV2) circulating in the reformer 25 is equal to the flow rate (2FV1 ２ - FV1 １ ) (>FV1 ２ It has reached ).

[0068] At time t2, the control unit 8 sets the input current of the DC / DC converter 71 to current (I ２ ) from current (I １ This returns the flow rate (FV2) of steam circulating through the recycling line 6 to the current flow rate (FV2). ２ ) from flow rate (FV2 １ ) immediately returns to ). As a result, the flow rate of steam (FV1 + FV2) circulating in the reformer 25 becomes the flow rate (2FV1 ２ - FV1 １ ) from flow rate (FV1 ２ ) will immediately switch to this.

[0069] Through the above control, the flow rate (FV) of water vapor in the water vapor supply line 3 generated during a predetermined time from time t1 to time t2 is controlled. １ The shortfall in ) is compensated by the flow rate (FV) of steam supplied from the recycling line 6. ２ This can be compensated for by the above, and the flow rate of steam flowing through the recycling line 6 can be rapidly increased without controlling the valve 61 and the booster 62 located in the recycling line 6.

[0070] [Modified Example] Figure 5 is a schematic diagram of a modified fuel cell. As shown in Figure 5, the fuel cell stack 1 includes a first fuel cell stack 11 and a second fuel cell stack 12.

[0071] The anode inlet of the first fuel cell stack 11 is in communication with the reformer 25 (Figure 1), and the cathode inlet of the first fuel cell stack 11 is in communication with the blower 41 (Figure 1).

[0072] The anode outlet of the first fuel cell stack 11 is connected to the anode inlet of the second fuel cell stack 12, and the cathode outlet of the first fuel cell stack 11 is connected to the cathode inlet of the second fuel cell stack 12.

[0073] The anode outlet and cathode outlet of the second fuel cell stack 12 are in communication with the combustor 51.

[0074] The outputs of the first fuel cell stack 11 and the second fuel cell stack 12 are connected in series, for example.

[0075] As described above, in the anode electrode layer 101, water (water vapor) is produced by an electrochemical reaction (H ２ 0) is generated. Meanwhile, in the reformer 25, carbon monoxide (CO) is generated by the above reforming reaction and supplied to the fuel cell stack 1. As a result, a water-gas shift reaction [CO + H] occurs within the fuel cell stack 1. ２ O⇔CO ２ +H ２ A pressure of +41.2 [kJ / mol] is generated, and the generated water is consumed. Therefore, even if the current drawn from the fuel cell stack 1 is increased, there are cases where the increase in the flow rate (partial pressure) of the generated water (water vapor) is insufficient.

[0076] Therefore, as in the modified example, the fuel cell stack 1 is separated into two (or more) such as a first fuel cell stack 11 and a second fuel cell stack 12, and when increasing the total current drawn from the fuel cell stack 1, the current drawn from the second fuel cell stack 12 (Is ２ It is preferable to increase only ).

[0077] In this case, the generated water (steam) produced in the first fuel cell stack 11 is supplied to the second fuel cell stack 12 and then consumed by the water-gas shift reaction. On the other hand, the generated water (steam) produced in the second fuel cell stack 12 has already had carbon monoxide (CO) used in the water-gas shift reaction, so the reduction due to this reaction is zero or minimal. Therefore, the flow rate (partial pressure) of the generated water (steam) at the anode outlet of the second fuel cell stack 12 can be efficiently increased, and the flow rate of steam in the recycling line 6 can be efficiently increased.

[0078] Furthermore, the total current drawn from the fuel cell stack 1 (I １ The current (Is) of the first fuel cell stack 11 is kept constant, and the current (Is) of the first fuel cell stack 11 is kept constant. １ ) reduces the extraction current (Is ２ The same effect as above can be obtained by increasing the current (I) of the fuel cell stack 1. １ Since this value remains constant, the control burden on the DC / DC converter 71 can be reduced.

[0079] [Proton Exchange Membrane Fuel Cell] Figure 6 is a diagram illustrating the electrochemical reaction that occurs in a proton exchange membrane fuel cell and the permeation of water in the electrolyte layer 105. The fuel cell system of this embodiment can also be applied to a proton exchange membrane fuel cell.

[0080] As shown in Figure 6, the proton exchange membrane fuel cell has a laminated structure consisting of an anode electrode layer 104, an electrolyte layer 105, and a cathode electrode layer 106, with the electrolyte layer 105 being proton conductive.

[0081] As shown in Figure 6, the anode electrode layer 104 contains anode gas (H ２ O is supplied to the cathode electrode layer 106, and cathode gas (O ２ ) will be supplied.

[0082] Hydrogen molecules (H) supplied to the anode electrode layer 101 ２ ) is an electron (2e － ) releases hydrogen ions (2H ＋ ) becomes hydrogen ions (2H ＋ The ) permeates through the electrolyte layer 105 and reaches the cathode electrode layer 106.

[0083] Oxygen molecules ((1 / 2)O) in the cathode electrode layer 103 ２ ) is an electron (2e － By taking in oxygen ions (O ２－ ) becomes hydrogen ions (2H ＋ ) and oxygen ions (O ２－ ) combines with the generated water (water vapor) (H ２ 0) is generated.

[0084] Therefore, the load (DC / DC converter 71) connected to the anode electrode layer 104 and cathode electrode layer 106 of the fuel cell transmits electrons (2e) from the anode electrode layer 104 to the cathode electrode layer 106. － It is possible to take in current in a manner that supplies (a power source).

[0085] As shown in Figure 6, in a proton exchange membrane fuel cell, the water generated by the electrochemical reaction is not generated in the anode electrode layer 104. However, the partial pressure of water vapor is high at the cathode of the fuel cell, while it is low at the anode. Therefore, due to this partial pressure difference, the water generated (water vapor) produced in the cathode electrode layer 106 permeates through the electrolyte layer 105 and is introduced into the anode electrode layer 104, resulting in water vapor being included in the anode off-gas.

[0086] The flow rate of generated water (steam) supplied to the anode side increases as the difference obtained by subtracting the partial pressure of generated water (steam) on the anode side of the fuel cell from the partial pressure of generated water (steam) on the cathode side of the fuel cell becomes larger.

[0087] To increase this difference, the current drawn from the fuel cell stack 1 can be increased in the same manner as described above, and / or the flow rate of the cathode gas (output of the blower 41) can be decreased.

[0088] As described above, increasing the current drawn from the fuel cell stack 1 can increase the amount of generated water (water vapor) produced, and therefore the amount of generated water that permeates to the anode can be increased accordingly.

[0089] Furthermore, by reducing the cathode gas flow rate (output of blower 41), the proportion of generated water (water vapor) increases, and therefore the partial pressure of the generated water (water vapor) rises.

[0090] Therefore, when the fuel cell stack 1 is a proton exchange membrane type fuel cell, the flow rate of steam supplied to the recycling line 6 can be increased by increasing the extraction current of the fuel cell stack 1 and / or decreasing the flow rate of the cathode gas (output of the blower 41) during a predetermined time between time t1 and time t2 in Figure 4, thereby quickly and efficiently compensating for any shortage of steam in the reformer 25.

[0091] [Effects of this embodiment] The control method for the fuel cell system of this embodiment is a control method for a fuel cell system that includes a reformer 25 that reforms raw fuel to produce anode gas, a fuel cell (fuel cell stack 1) that consumes the anode gas to generate electricity, and a recycling line 6 that supplies a portion of the anode off gas discharged from the fuel cell (fuel cell stack 1) to the reformer 25. When the flow rate (FV1) of the first steam supplied to the reformer 25 is insufficient, the operating state of the fuel cell (fuel cell stack 1) is changed in a direction that increases the flow rate of the second steam contained in the anode off gas, thereby increasing the flow rate (FV2) of the second steam taken into the recycling line 6.

[0092] By the above method, the flow rate (FV) of the first steam in the reformer 25 is determined. １ The deficit in ) is compensated by the flow rate (FV) of the second steam supplied from the recycling line 6. ２ This can be compensated for by the flow rate (FV) of the second steam flowing through the recycling line 6 without controlling the valve 61 and the booster 62 located in the recycling line 6. ２ By rapidly increasing the amount of steam, carbon deposition (coking) in the reformer 25 can be reduced. Therefore, this is a control method for a fuel cell system that can secure the amount of steam required for reforming the raw fuel even when the amount of steam required increases rapidly.

[0093] Furthermore, the control method for the fuel cell system of this embodiment includes a fuel cell (fuel cell stack 1) capable of generating electricity while reforming raw fuel, and a recycling line 6 that supplies a portion of the anode off-gas discharged from the fuel cell (fuel cell stack 1) to the anode inlet of the fuel cell (fuel cell stack 1), wherein the flow rate (FV) of the first steam supplied to the anode inlet of the fuel cell (fuel cell stack 1) is controlled. １ If the amount of second water vapor (FV) is insufficient, the operating state of the fuel cell (fuel cell stack 1) is changed in a direction that increases the flow rate of second water vapor contained in the anode off gas, thereby increasing the flow rate of second water vapor (FV) taken into the recycling line 6. ２ ) increases.

[0094] By the above method, the shortage of the flow rate of the first steam (FV １ ) in the internally reformed fuel cell (fuel cell stack 1) can be compensated by the flow rate of the second steam (FV ２ ) supplied from the recycle line 6, and the flow rate of the second steam (FV ２ ) flowing through the recycle line 6 can be rapidly increased without controlling the valve 61 and the booster 62 arranged in the recycle line 6, thereby reducing carbon deposition (coking) in the fuel cell stack 1. Therefore, even when the amount of steam required for reforming the raw fuel rapidly increases, it becomes a control method of a fuel cell system capable of securing the amount of steam.

[0095] In the present embodiment, it includes a fuel supply line 2 for supplying raw fuel to the reformer 25 and a steam supply line 3 for supplying the first steam to the reformer 25. The raw fuel is supplied from the fuel supply line 2 to the reformer 25 at a predetermined first flow rate (FF １ ), and the first steam is supplied from the steam supply line 3 to the reformer 25 at a second flow rate (FV1 １ ) such that the flow rate ratio with respect to the flow rate of the raw fuel is a predetermined flow rate ratio (a value of S / C = 2 or more). The flow rate of the raw fuel (FF) is increased from the first flow rate (FF １ ) to a third flow rate (FF ２ ), and the flow rate of the first steam (FV1) is increased from the second flow rate (FV1 １ ) to a fourth flow rate (FV1 ２ ), and the fourth flow rate (FV1 ２ ) is set such that the flow rate ratio with respect to the third flow rate (FF ２ ) is a predetermined flow rate ratio (a value of S / C = 2 or more). When it takes a predetermined time for the flow rate of the first steam (FV1) to increase from the second flow rate (FV1 １ ) to the fourth flow rate (FV1 ２ ), simultaneously with the start of the increase in the flow rate of the raw fuel (FF), the operating state of the fuel cell (fuel cell stack 1) is changed in the direction in which the flow rate of the second steam increases, and the second flow rate (FV1 １ ) at the start of the increase in the flow rate of the raw fuel (FF) and the flow rate of the second steam (FV2 ２The sum of ) and is the fourth flow rate (FV1 ２ The operating state of the fuel cell (fuel cell stack 1) is changed in a direction that increases the amount of second steam so that the result is greater than or equal to ).

[0096] By the above method, the deficiency in the flow rate (FV1) of the first steam transiently generated in the reformer 25 can be easily compensated for.

[0097] In this embodiment, the fuel supply line 2 supplies raw fuel to the fuel cell (fuel cell stack 1), and the steam supply line 3 supplies first steam to the fuel cell (fuel cell stack 1), wherein the raw fuel is supplied from the fuel supply line 2 to the fuel cell (fuel cell stack 1) at a predetermined first flow rate (FF １ ) is supplied, and the first steam is supplied from the steam supply line 3 to the fuel cell (fuel cell stack 1) at a second flow rate (FV1) such that the flow rate ratio to the flow rate of the raw fuel is a predetermined flow rate ratio (a value such that S / C = 2 or more). １ ) is supplied, and the flow rate of the raw fuel and the first flow rate (FF １ ) to the third flow rate (FF ２ ) is increased to and the flow rate of the first steam (FV1) is increased to the second flow rate (FV1) １ ) to the fourth flow rate (FV1 ２ ) is increased to the fourth flow rate (FV1 ２ ) to the third flow rate (FF ２ The flow rate ratio to ) is set to a predetermined flow rate ratio (a value such that S / C = 2 or more), and the flow rate of the first steam (FV1) is set to the second flow rate (FV1) １ ) to the fourth flow rate (FV1 ２ If it takes a predetermined amount of time for the flow rate of the raw fuel (FF) to increase to ), the operating state of the fuel cell (fuel cell stack 1) is changed in the direction of increasing the flow rate of the second steam at the same time as the start of the increase in the flow rate of the raw fuel (FF), and the second flow rate (FV1) at the start of the increase in the flow rate of the raw fuel (FF) is changed. １ ) and the flow rate (FV2) of the second steam taken into the recycling line 6 after the change in the operating state of the fuel cell (fuel cell stack 1) ２ The sum of ) and is the fourth flow rate (FV1 ２ The operating state of the fuel cell (fuel cell stack 1) is changed in a direction that increases the amount of second steam so that the result is greater than or equal to ).

[0098] The above method makes it possible to easily compensate for the deficiency in the flow rate (FV1) of the first steam transiently generated in the internal reforming type fuel cell stack 1.

[0099] In this embodiment, the predetermined flow rate ratio (S / C) is set to 2 or more.

[0100] By supplying steam in a stoichiometric ratio or higher using the method described above, carbon deposition (coking) during the reforming of raw fuel can be reduced.

[0101] In this embodiment, the operating state of the fuel cell (fuel cell stack 1) is returned to its original state after a predetermined time has elapsed since the start of increasing the flow rate (FF) of the raw fuel.

[0102] By the above method, reformed fuel (anode gas) can be stably supplied to the fuel cell stack 1, thereby stabilizing power generation.

[0103] In this embodiment, when the fuel cell (fuel cell stack 1) is capable of generating second steam by generating generated water on the anode side of the fuel cell (fuel cell stack 1) during power generation, the operating state of the fuel cell (fuel cell stack 1) is changed in a direction that increases the flow rate of the second steam by increasing the current drawn from the fuel cell (fuel cell stack 1), and the current drawn from the fuel cell (fuel cell stack 1) (the intake current of the DC / DC converter 71) is used to charge the battery (power buffer device 72).

[0104] By using the above method, carbon deposition (coking) in the reformer 25 or the internally reformed fuel cell (fuel cell stack 1) can be reduced by generating more water. In addition, since the extracted current is used to charge the battery (power buffer device 72), electricity costs can be saved.

[0105] In this embodiment, the fuel cell (fuel cell stack 1) includes a first fuel cell (first fuel cell stack 11) and a second fuel cell (second fuel cell stack 12), the anode outlet of the first fuel cell (first fuel cell stack 11) is in communication with the anode inlet of the second fuel cell (second fuel cell stack 12), the anode outlet of the second fuel cell (second fuel cell stack 12) is in communication with the recycling line 6, and when the first fuel cell (first fuel cell stack 11) and the second fuel cell (second fuel cell stack 12) generate electricity simultaneously to produce second steam, the extraction current (Is) of the second fuel cell (second fuel cell stack 12) is increased when the extraction current of the fuel cell (fuel cell stack 1) is increased. ２ Make it bigger.

[0106] The above method allows for an efficient increase in the flow rate of generated water (second steam) that can be produced throughout the entire fuel cell stack 1.

[0107] In this embodiment, the fuel cell (fuel cell stack 1) includes a first fuel cell (first fuel cell stack 11) and a second fuel cell (second fuel cell stack 12), the anode outlet of the first fuel cell (first fuel cell stack 11) is in communication with the anode inlet of the second fuel cell (second fuel cell stack 12), the anode outlet of the second fuel cell (second fuel cell stack 12) is in communication with the recycling line 6, and when the first fuel cell (first fuel cell stack 11) and the second fuel cell (second fuel cell stack 12) generate electricity simultaneously to produce second steam, the current taken out of the first fuel cell (first fuel cell stack 11) is (Is １ ) and the current (Is) taken from the second fuel cell (second fuel cell stack 12) ２ With the sum of the values ​​constant, the current (Is) taken out of the first fuel cell (first fuel cell stack 11) １ ) reduces and the output current (Is ２ By increasing the amount of the second steam, the operating state of the fuel cell (fuel cell stack 1) is changed in a direction that increases the flow rate of the second steam.

[0108] The above method efficiently increases the flow rate of generated water (second steam) that can be produced throughout the entire fuel cell stack 1. Furthermore, since there is no change in the current drawn from the entire fuel cell stack 1, the control burden on the load (DC / DC converter 71) connected to the fuel cell stack 1 can be reduced.

[0109] In this embodiment, when a fuel cell (fuel cell stack 1) generates generated water on the cathode side of the fuel cell (fuel cell stack 1) during power generation and the generated water permeates to the anode side of the fuel cell (fuel cell stack 1) to generate a second steam, the operating state of the fuel cell (fuel cell stack 1) is changed in a direction that increases the flow rate of the second steam by increasing the water vapor partial pressure at the cathode of the fuel cell (fuel cell stack 1) that is due to the generated water and increasing the amount of generated water permeating to the anode side.

[0110] By the above method, in a proton exchange membrane type fuel cell (fuel cell stack 1), the flow rate of the second water vapor in the anode off-gas can be controlled by allowing the generated water produced on the cathode side to permeate to the anode side.

[0111] In this embodiment, the water vapor partial pressure is increased by increasing the extraction current of the fuel cell (fuel cell stack 1).

[0112] The above method allows for a simple increase in the water vapor partial pressure in the anode off-gas of a proton exchange membrane type fuel cell (fuel cell stack 1).

[0113] In this embodiment, the water vapor partial pressure is increased by reducing the flow rate of air supplied to the cathode of the fuel cell (fuel cell stack 1) (output of the blower 41).

[0114] The above method allows for a simple increase in the water vapor partial pressure in the anode off-gas of a proton exchange membrane type fuel cell (fuel cell stack 1).

[0115] The fuel cell system of this embodiment includes a reformer 25 that reforms raw fuel to produce anode gas, a fuel cell (fuel cell stack 1) that consumes the anode gas to generate electricity, and a recycling line 6 that supplies a portion of the anode off gas discharged from the fuel cell (fuel cell stack 1) to the reformer 25. In the case where the flow rate of the first steam supplied to the reformer 25 is insufficient, the operating state of the fuel cell (fuel cell stack 1) is changed in a direction that increases the flow rate of the second steam contained in the anode off gas, thereby increasing the flow rate of the second steam taken into the recycling line 6.

[0116] With the above configuration, the flow rate (FV) of the first steam in the reformer 25 １ The deficit in ) is compensated by the flow rate (FV) of the second steam supplied from the recycling line 6. ２ This can be compensated for by the flow rate (FV) of the second steam flowing through the recycling line 6 without controlling the valve 61 and the booster 62 located in the recycling line 6. ２ By rapidly increasing the amount of steam, carbon deposition (coking) in the reformer 25 can be reduced. Therefore, even when the amount of steam required for reforming the raw fuel increases sharply, the fuel cell system can secure the amount of steam.

[0117] Furthermore, the fuel cell system of this embodiment includes a fuel cell (fuel cell stack 1) capable of generating electricity while reforming the raw fuel, and a recycling line 6 that supplies a portion of the anode off-gas discharged from the fuel cell (fuel cell stack 1) to the anode inlet of the fuel cell (fuel cell stack 1). When the flow rate of the first steam supplied to the anode inlet of the fuel cell (fuel cell stack 1) is insufficient, the operating state of the fuel cell (fuel cell stack 1) is changed in a direction that increases the flow rate of the second steam contained in the anode off-gas, thereby increasing the flow rate of the second steam taken into the recycling line 6.

[0118] With the above configuration, the flow rate (FV) of the first steam in the internally reformed fuel cell (fuel cell stack 1) １ The deficit in ) is compensated by the flow rate (FV) of the second steam supplied from the recycling line 6. ２This can be compensated for by the flow rate (FV) of the second steam flowing through the recycling line 6 without controlling the valve 61 and the booster 62 located in the recycling line 6. ２ By rapidly increasing the amount of water vapor, carbon deposition (coking) in the fuel cell stack 1 can be reduced. Therefore, even when the amount of water vapor required for reforming the raw fuel increases sharply, the fuel cell system can secure that amount of water vapor.

[0119] Although embodiments of the present invention have been described above, these embodiments only represent a part of the application examples of the present invention, and are not intended to limit the technical scope of the present invention to the specific configurations of the above embodiments.

Claims

1. A control method for a fuel cell system comprising: a reformer that reforms raw fuel to produce anode gas; a fuel cell that consumes the anode gas to generate electricity; and a recycling line that supplies a portion of the anode off gas discharged from the fuel cell to the reformer, wherein when the flow rate of first steam supplied to the reformer is insufficient, the operating state of the fuel cell is changed in a direction that increases the flow rate of second steam contained in the anode off gas, thereby increasing the flow rate of the second steam taken into the recycling line.

2. A control method for a fuel cell system, comprising a fuel cell capable of generating electricity while reforming raw fuel, and a recycling line that supplies a portion of the anode off gas discharged from the fuel cell to the anode inlet of the fuel cell, wherein when the flow rate of first steam supplied to the anode inlet of the fuel cell is insufficient, the operating state of the fuel cell is changed in a direction that increases the flow rate of second steam contained in the anode off gas, thereby increasing the flow rate of the second steam taken into the recycling line.

3. The system includes a fuel supply line for supplying the raw fuel to the reformer, and a steam supply line for supplying the first steam to the reformer, wherein the raw fuel is supplied to the reformer from the fuel supply line at a predetermined first flow rate, the first steam is supplied to the reformer from the steam supply line at a second flow rate such that the flow rate ratio to the flow rate of the raw fuel is a predetermined flow rate ratio, the flow rate of the raw fuel is increased from the first flow rate to a third flow rate, and the flow rate of the first steam is increased from the second flow rate to a fourth flow rate, and the flow rate ratio of the fourth flow rate to the third flow rate is set to the predetermined flow rate ratio, and a predetermined time is required for the flow rate of the first steam to increase from the second flow rate to the fourth flow rate, A method for controlling a fuel cell system according to claim 1, wherein the operating state of the fuel cell is changed in a direction that increases the flow rate of the second steam at the same time as the flow rate of the raw fuel starts to increase, and the operating state of the fuel cell is changed in a direction that increases the amount of the second steam so that the sum of the second flow rate at the start of the increase in the flow rate of the raw fuel and the flow rate of the second steam taken into the recycling line after the change in the operating state of the fuel cell is equal to or greater than the fourth flow rate.

4. The fuel supply line includes a fuel supply line for supplying the raw fuel to the fuel cell, and a steam supply line for supplying the first steam to the fuel cell, wherein the raw fuel is supplied to the fuel cell from the fuel supply line at a predetermined first flow rate, the first steam is supplied to the fuel cell from the steam supply line at a second flow rate such that the flow rate ratio to the flow rate of the raw fuel is a predetermined flow rate ratio, the flow rate of the raw fuel is increased from the first flow rate to a third flow rate, and the flow rate of the first steam is increased from the second flow rate to a fourth flow rate, and the flow rate ratio of the fourth flow rate to the third flow rate is set to the predetermined flow rate ratio, and a predetermined time is required for the flow rate of the first steam to increase from the second flow rate to the fourth flow rate, A control method for a fuel cell system according to claim 2, wherein the operating state of the fuel cell is changed in a direction that increases the flow rate of the second steam at the same time as the flow rate of the raw fuel starts to increase, and the operating state of the fuel cell is changed in a direction that increases the amount of the second steam so that the sum of the second flow rate at the start of the increase in the flow rate of the raw fuel and the flow rate of the second steam taken into the recycling line after the change in the operating state of the fuel cell is equal to or greater than the fourth flow rate.

5. A control method for a fuel cell system according to claim 3 or claim 4, wherein the predetermined flow rate ratio is set to 2 or more.

6. A control method for a fuel cell system according to claim 3 or 4, wherein the operating state of the fuel cell is returned to its original state after a predetermined time has elapsed since the start of increasing the flow rate of the raw fuel.

7. A control method for a fuel cell system according to claim 1 or 2, wherein the fuel cell is capable of generating the second steam by generating generated water on the anode side of the fuel cell during power generation, the operating state of the fuel cell is changed in a direction that increases the flow rate of the second steam by increasing the current drawn from the fuel cell, and the current drawn from the fuel cell is used to charge a battery.

8. A control method for a fuel cell system according to claim 7, wherein the fuel cell includes a first fuel cell and a second fuel cell, the anode outlet of the first fuel cell is in communication with the anode inlet of the second fuel cell, the anode outlet of the second fuel cell is in communication with the recycling line, and the second steam is generated by the simultaneous power generation of the first and second fuel cells, the method for controlling a fuel cell system wherein the current drawn from the second fuel cell is increased when the current drawn from the first fuel cell is increased.

9. A control method for a fuel cell system according to claim 7, wherein the fuel cell includes a first fuel cell and a second fuel cell, the anode outlet of the first fuel cell is in communication with the anode inlet of the second fuel cell, the anode outlet of the second fuel cell is in communication with the recycling line, and the second steam is generated by the simultaneous power generation of the first fuel cell and the second fuel cell, wherein the operating state of the fuel cell is changed in a direction that increases the flow rate of the second steam by decreasing the extraction current of the first fuel cell and increasing the extraction current of the second fuel cell while the sum of the extraction currents of the first fuel cell and the second fuel cell remains constant.

10. A control method for a fuel cell system according to claim 1 or 2, in which the fuel cell generates generated water on the cathode side of the fuel cell during power generation and the generated water permeates to the anode side of the fuel cell to generate the second water vapor, wherein the operating state of the fuel cell is changed in a direction that increases the flow rate of the second water vapor by increasing the water vapor partial pressure at the cathode of the fuel cell, which is due to the generated water, and increasing the amount of the generated water permeating to the anode side.

11. A control method for a fuel cell system according to claim 10, wherein the water vapor partial pressure is increased by increasing the current drawn from the fuel cell.

12. A control method for a fuel cell system according to claim 10, wherein the water vapor partial pressure is increased by reducing the flow rate of air supplied to the cathode of the fuel cell.

13. A fuel cell system comprising: a reformer that reforms raw fuel to produce anode gas; a fuel cell that consumes the anode gas to generate electricity; and a recycling line that supplies a portion of the anode off gas discharged from the fuel cell to the reformer, wherein, when the flow rate of first steam supplied to the reformer is insufficient, the operating state of the fuel cell is changed in a direction that increases the flow rate of second steam contained in the anode off gas, thereby increasing the flow rate of the second steam taken into the recycling line.

14. A fuel cell system comprising a fuel cell capable of generating electricity while reforming raw fuel, and a recycling line that supplies a portion of the anode off gas discharged from the fuel cell to the anode inlet of the fuel cell, wherein, when the flow rate of first steam supplied to the anode inlet of the fuel cell is insufficient, the operating state of the fuel cell is changed in a direction that increases the flow rate of second steam contained in the anode off gas, thereby increasing the flow rate of the second steam taken into the recycling line.

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