JP2009123472A - Operation method of fuel cell and fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable to surely correspond to fluctuation of heating values and superbly exhaust excess moisture inside a fuel cell outside the fuel cell as vapor. <P>SOLUTION: A control device 20 includes a moisture volume calculating part 80 calculating a moisture volume mixed in the air and supplied to a fuel cell stack 12, a product water calculating part 82 calculating a volume of product water from an output current of the fuel cell stack 12, a dew-point calculating part 84 calculating a dew point of outlet gas capable of exhausting all of the moisture and the product water supplied into the fuel cell stack 12 as vapor from the fuel cell stack 12, a heating volume calculating part 86 calculating a heating volume by power generation of the fuel cell stack 12, and a coolant flow setting part 88 setting a coolant flow capable of maintaining a temperature of the outlet gas at the dew point based on the heating volume calculated by the heating volume calculating part 86. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method of operating a fuel cell in which power is generated by an electrochemical reaction of an oxidant gas supplied to a cathode side electrode and a fuel gas supplied to an anode side electrode, and a cooling medium for temperature adjustment is supplied. The present invention relates to a fuel cell system including the fuel cell and a control device.

  A fuel cell supplies a fuel gas (mainly hydrogen-containing gas) and an oxidant gas (mainly oxygen-containing gas) to the anode-side electrode and the cathode-side electrode and causes them to react electrochemically. It is a system that obtains electrical energy.

  For example, a polymer electrolyte fuel cell includes a power generation cell in which an electrolyte membrane / electrode structure provided with an anode side electrode and a cathode side electrode is sandwiched between separators on both sides of an electrolyte membrane made of a polymer ion exchange membrane. ing. This type of power generation cell is normally used as a fuel cell stack mounted on a vehicle such as an automobile, for example, by alternately stacking a predetermined number of electrolyte membrane / electrode structures and separators.

  In this type of fuel cell, it is necessary to maintain the electrolyte membrane in a wet state in order to exhibit a desired power generation function. Therefore, usually, the oxidant gas (and / or fuel gas) is humidified in advance and then supplied to the fuel cell.

  On the other hand, in the fuel cell, water is generated at the cathode side electrode by a power generation reaction. For this reason, if excessive generated water is present in the fuel cell, there is a possibility that the gaps of the gas diffusion layer constituting the reaction gas passage and the electrode are blocked by the condensed water. Therefore, it is desired to control the water content in the fuel cell well.

  Therefore, for example, in the fuel cell system disclosed in Patent Document 1, the amount of electric current generated by the fuel cell stack, the supply amount of the oxidizing gas supplied to the fuel cell stack, and the fuel cell stack from the fuel cell stack A moisture change amount estimating means for estimating the amount of change of moisture in the fuel cell stack based on the discharge amount of the oxidizing gas is provided.

  This moisture change amount estimation means calculates the amount of water produced in the electrochemical reaction based on the amount of electricity generated by the fuel cell stack and the amount of oxygen in the oxidizing gas consumed in the electrochemical reaction. Yes. When the amount of generated water is Wp, the amount of consumed oxygen is Oe, the amount of oxidizing gas supplied to the fuel cell stack is As, and the amount of oxidizing gas discharged from the fuel cell stack is Gs, the fuel cell stack The amount of water change Wc is calculated based on the formula of Wc = As−Gs + Wp−Oe.

JP 2005-222854 A

  By the way, in the fuel cell system described above, heat is generated by the power generation of the fuel cell, and the amount of generated heat is likely to vary with the load. For this reason, there is a problem that the amount of water in the fuel cell stack fluctuates due to a change in the load, and the amount of water change Wc cannot be calculated accurately.

  The present invention solves this type of problem, can reliably cope with load fluctuations, and can effectively discharge excess water in the fuel cell to the outside of the fuel cell as water vapor. An object of the present invention is to provide a fuel cell operating method and a fuel cell system.

  The present invention relates to a method of operating a fuel cell in which power is generated by an electrochemical reaction between an oxidant gas supplied to a cathode side electrode and a fuel gas supplied to an anode side electrode, and a cooling medium for temperature adjustment is supplied. It is.

  This operating method includes a step of calculating the amount of water supplied to the fuel cell mixed with at least an oxidant gas, a step of calculating the amount of generated water from the output current of the fuel cell, Based on the step of calculating the dew point of the outlet gas that can be discharged from the fuel cell as all the supplied water and the generated water as water vapor, the step of calculating the amount of heat generated by power generation of the fuel cell, and the amount of generated heat And a step of setting the temperature of the outlet gas to a cooling medium flow rate capable of maintaining the dew point.

  The present invention also provides a fuel cell that generates power by an electrochemical reaction between an oxidant gas supplied to the cathode side electrode and a fuel gas supplied to the anode side electrode, and is supplied with a cooling medium for temperature adjustment, and a control. The present invention relates to a fuel cell system including the apparatus.

  The control device includes a water amount calculation unit that calculates the amount of water supplied to the fuel cell mixed with at least an oxidant gas, and a generated water calculation unit that calculates the amount of generated water from the output current of the fuel cell. A dew point calculator that calculates the dew point of the outlet gas that can be discharged from the fuel cell as all water and the generated water supplied into the fuel cell, and a calorific value generated by the power generation of the fuel cell And a cooling medium flow rate setting unit that sets the temperature of the outlet gas to a cooling medium flow rate that can be maintained at the dew point based on the heating value calculated by the heating value calculation unit. .

  In the present invention, at least the water supplied to the fuel cell mixed with the oxidant gas and the generated water generated in the fuel cell are all discharged to the outside of the fuel cell as water vapor. In particular, the coolant flow rate is set based on the load that varies with the power generation of the fuel cell. For this reason, regardless of the power generation state of the fuel cell, it is possible to maintain the desired drainage, prevent flooding as much as possible, and continuously perform good power generation.

  FIG. 1 is a schematic configuration diagram of a fuel cell system 10 for implementing a fuel cell operating method according to an embodiment of the present invention.

  The fuel cell system 10 includes a fuel cell stack 12, an oxidant gas supply device 14 for supplying an oxidant gas to the fuel cell stack 12, a fuel gas supply device 16 for supplying a fuel gas to the fuel cell stack 12, A cooling medium supply device 18 for supplying a cooling medium to the fuel cell stack 12 and a control device 20 are provided.

  The fuel cell stack 12 is configured by stacking a plurality of fuel cells 22. Each fuel cell 22 includes an electrolyte membrane / electrode structure 30 in which a solid polymer electrolyte membrane 24 is sandwiched between an anode side electrode 26 and a cathode side electrode 28, and the electrolyte membrane / electrode structure 30 is paired with a pair of separators 32, 34.

  The separator 32 is formed with a fuel gas flow path 36 for supplying fuel gas to the anode side electrode 26, and the separator 34 is formed with an oxidant gas flow path 38 for supplying oxidant gas to the cathode side electrode 28. Is done. A cooling medium flow path 40 for temperature adjustment is formed between the separators 32 and 34.

  An oxidant gas inlet communication hole 42a for supplying an oxidant gas (hereinafter also simply referred to as air) such as air (oxygen-containing gas) to one end of the fuel cell stack 12, and for discharging the air An oxidant gas outlet communication hole 42b is formed. The other end of the fuel cell stack 12 has a fuel gas inlet communication hole 44a for supplying a fuel gas such as a hydrogen-containing gas (hereinafter also simply referred to as hydrogen gas), and a fuel gas for discharging the fuel gas. An outlet communication hole 44b is formed.

  The fuel cell stack 12 is further formed with a cooling medium inlet communication hole 46a for supplying a cooling medium such as pure water or ethylene glycol, and a cooling medium outlet communication hole 46b for discharging the cooling medium.

  The oxidant gas inlet communication hole 42a and the oxidant gas outlet communication hole 42b communicate with the oxidant gas flow path 38 of each fuel cell 22, and the fuel gas inlet communication hole 44a and the fuel gas outlet communication hole 44b communicate with the fuels. It communicates with the fuel gas flow path 36 of the battery 22. The cooling medium inlet communication hole 46 a and the cooling medium outlet communication hole 46 b communicate with the cooling medium flow path 40 of each fuel cell 22.

  The oxidant gas supply device 14 includes an air compressor 50 that compresses and supplies air from the atmosphere, and the air compressor 50 is disposed in the air supply passage 52. The air supply passage 52 communicates with the oxidant gas inlet communication hole 42 a of the fuel cell stack 12. The oxidant gas supply device 14 includes an air discharge passage 54 communicating with the oxidant gas outlet communication hole 42b. The air discharge passage 54 is provided with a gas-liquid separator 56 for separating the exhaust gas into discharged air and moisture.

  The fuel gas supply device 16 includes a hydrogen tank 58 that stores high-pressure hydrogen (hydrogen-containing gas). The hydrogen tank 58 communicates with the fuel gas inlet communication hole 44 a of the fuel cell stack 12 through the hydrogen supply passage 60. . An ejector 62 is provided in the hydrogen supply passage 60.

  The ejector 62 supplies the hydrogen gas supplied from the hydrogen tank 58 to the fuel cell stack 12 through the hydrogen supply passage 60, and exhaust gas containing unused hydrogen gas that has not been used in the fuel cell stack 12. Then, the gas is sucked from the hydrogen circulation passage 64 communicating with the fuel gas outlet communication hole 44b and supplied to the fuel cell stack 12 again.

  The cooling medium supply device 18 includes a refrigerant pump 66, and this pump 66 is connected to the cooling medium inlet communication hole 46 a of the fuel cell stack 12 through the cooling medium supply passage 68. A cooling medium discharge passage 70 is connected to the cooling medium outlet communication hole 46 b of the fuel cell stack 12. The cooling medium supply passage 68 and the cooling medium discharge passage 70 are connected to a cooling medium storage tank (not shown) and circulate the cooling medium.

  The fuel cell stack 12 is connected to a voltage / current monitor 72 that monitors the voltage and current during power generation. In the air supply passage 52, a flow meter 74 for detecting the inlet flow rate of the air supplied to the fuel cell stack 12 and a hygrometer 76 for obtaining the amount of moisture contained in the air are disposed.

  The cooling medium supply passage 68 is provided with a first thermometer 78a for detecting the inlet temperature of the cooling medium supplied to the fuel cell stack 12, and the cooling medium discharge passage 70 is provided with the fuel cell stack 12 from the fuel cell stack 12. A second thermometer 78b for detecting the outlet temperature of the discharged cooling medium is provided. The second thermometer 78 b substantially detects the outlet temperature of the air discharged from the fuel cell stack 12, and may be provided in the air discharge passage 54.

  The control device 20 includes a water amount calculation unit 80 that calculates the amount of water supplied to the fuel cell stack 12 mixed with the air supplied to the air supply passage 52, and water generated from the output current of the fuel cell stack 12. And a dew point of an outlet gas (exhaust air) that can discharge all of the water and the generated water supplied into the fuel cell stack 12 as water vapor from the fuel cell stack 12. A dew point calculator 84 for calculating the amount of heat generated by power generation of the fuel cell stack 12, and a calorific value calculated by the calorific value calculator 86 based on the calorific value calculated by the calorific value calculator 86. A cooling medium flow rate setting unit 88 for setting the cooling medium flow rate to maintain the temperature at the dew point.

  The operation of the fuel cell system 10 configured as described above will be described below.

  In the oxidant gas supply device 14, the air compressor 50 is driven. The compressed air supplied from the air compressor 50 is supplied to the oxidant gas inlet communication hole 42 a of the fuel cell stack 12 through the air supply passage 52. On the other hand, in the fuel gas supply device 16, the hydrogen gas supplied from the hydrogen tank 58 is supplied to the fuel gas inlet communication hole 44 a of the fuel cell stack 12 through the hydrogen supply passage 60 via the ejector 62.

  In each fuel cell 22 constituting the fuel cell stack 12, after the air supplied to the oxidant gas inlet communication hole 42 a is introduced into the oxidant gas flow path 38 and moves along the electrode surface of the cathode side electrode 28. The oxidant gas outlet communication hole 42b is discharged.

  On the other hand, the hydrogen gas supplied to the fuel gas inlet communication hole 44a is introduced into the fuel gas flow path 36 and moves along the electrode surface of the anode side electrode 26 of each fuel cell 22, and then the fuel gas outlet communication hole 44b. To be discharged. Therefore, in each fuel cell 22, oxygen in the air supplied to the cathode side electrode 28 and hydrogen supplied to the anode side electrode 26 react to generate power.

  A hydrogen circulation passage 64 communicates with the fuel gas outlet communication hole 44 b of the fuel cell stack 12. For this reason, the exhaust gas (exhaust fuel gas containing unused hydrogen) discharged to the hydrogen circulation passage 64 is returned to the hydrogen supply passage 60 under the suction action of the ejector 62 and then again as fuel gas. It is supplied to the battery stack 12.

  In the cooling medium supply device 18, the cooling medium supplied to the cooling medium supply passage 68 under the action of the pump 66 is introduced into the cooling medium flow path 40 from the cooling medium inlet communication hole 46 a of the fuel cell stack 12. The cooling medium is discharged to the cooling medium discharge passage 70 from the cooling medium outlet communication hole 46b after each fuel cell 22 is cooled.

  Next, an operation method according to an embodiment of the present invention will be described below along the flowchart shown in FIG.

First, in the control device 20, an inlet flow rate Vin (unhumidified gas) of air supplied to the fuel cell stack 12 via the oxidant gas supply device 14 is detected by the flow meter 74. Further, the humidity (dew point) of the air supplied to the fuel cell stack 12 is detected by the hygrometer 76, and the water vapor pressure P (H ₂ O) in the air is calculated. The water content calculator 80 calculates the water content (mass) Vin (H ₂ O) of the inlet gas (supply air) from the following equation (step S1). However, Pin is an inlet gas pressure (absolute pressure) of air.
Vin (H ₂ O) = Vin × P (H ₂ O) / {Pin−P (H ₂ O)}

Next, the current value I obtained by the power generation of the fuel cell stack 12 is detected via the voltage / current monitor 72. Based on the current value I, the generated water calculation unit 82 calculates the generated water amount Vgen in the fuel cell stack 12 from the following equation (step S2). However, n is the number of cells and F is a Faraday constant.
Vgen = n × I / 2 / F

Thereby, the water content Vfc (H ₂ O) discharged from the inside of the fuel cell stack 12 as water vapor is obtained from the following equation (step S3).
Vfc (H ₂ O) = Vin (H ₂ O) + Vgen

On the other hand, based on the current value I, the amount of oxygen Vcons consumed by the electrochemical reaction in the fuel cell stack 12 is calculated. For this reason, the dry air amount (mass) Vout (G) in the exhaust gas discharged from the fuel cell stack 12 to the air discharge passage 54 is calculated from the following equation.
Vout (G) = Vin−Vcons

In the dew point calculation unit 84, the absolute humidity H of the outlet gas of the fuel cell stack 12 is calculated from the following equation.
H = Vfc (H ₂ O) / Vout (G)

  Based on the calculated absolute humidity H, the dew point Td (out) of the outlet gas of the fuel cell stack 12 is obtained from the humidity chart shown in FIG. 3 (step S4).

The calorific value calculation unit 86 calculates the calorific value Q generated by the power generation of the fuel cell stack 12 (step S5). Specifically, this calorific value Q is based on the following formula based on the lower calorific value (true calorific value) E, the cell voltage vcell during power generation of the fuel cell stack 12, the number of cells n, and the current value I during power generation. Is calculated from
Q = (E-vcell) × n × I

On the other hand, in the cooling medium supply device 18, based on the cooling medium inlet temperature Tw (in) and the dew point Td (out) detected by the first thermometer 78a, the required temperature difference ΔT of the cooling medium is expressed by the following equation. Is calculated from
ΔT = Td (out) −Tw (in)

Accordingly, the coolant flow rate setting unit 88 calculates the coolant flow rate (mass) w from the following equation (step S6). Here, c is the specific heat of the cooling medium.
w = Q / (c × ΔT)

  Therefore, in the cooling medium supply device 18, the rotational speed of the pump 66 is controlled so that the cooling medium has a flow rate w. Specifically, when the rotational speed of the pump 66 is increased, the flow rate w of the cooling medium is increased and the outlet temperature is decreased. On the other hand, when the rotational speed of the pump 66 is decreased, the flow rate w of the cooling medium is decreased. The outlet temperature rises. At this time, the relationship between the flow rate w of the cooling medium and the rotational speed of the pump 66 is stored in advance as a map.

  The above process is repeated as necessary until the operation of the fuel cell system 10 is stopped (YES in step S7).

  In this case, in this embodiment, the moisture mixed in the air and supplied to the fuel cell stack 12 and the generation generated in the fuel cell stack 12 by the power generation of the fuel cell stack 12 are all as water vapor. It can be discharged from the fuel cell stack 12.

  Moreover, the flow rate w of the cooling medium is set based on the calorific value Q that varies with the load of the fuel cell stack 12. For this reason, regardless of the power generation state of the fuel cell stack 12, it is possible to maintain the desired drainage and to prevent flooding as much as possible. Thereby, the fuel cell system 10 can obtain an effect that a high-performance power generation state can be favorably secured over a long period of time.

  In the present embodiment, the case where the moisture and generated water mixed in the air (oxidant gas) and supplied to the fuel cell stack 12 are all discharged as water vapor to the outside of the fuel cell stack 12 has been described. It is not limited to this. For example, excess water can be discharged to the outside of the fuel cell stack 12 including the water supplied to the fuel cell stack 12 mixed with hydrogen gas (fuel gas).

It is a schematic block diagram of the fuel cell system for enforcing the operating method of the fuel cell concerning the embodiment of the present invention. It is a flowchart explaining the said driving | running method. It is a humidity chart.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Fuel cell system 12 ... Fuel cell stack 14 ... Oxidant gas supply device 16 ... Fuel gas supply device 18 ... Cooling medium supply device 20 ... Control device 22 ... Fuel cell 24 ... Solid polymer electrolyte membrane 26 ... Anode side electrode 28 ... cathode side electrode 36 ... fuel gas flow path 38 ... oxidant gas flow path 40 ... cooling medium flow path 80 ... moisture amount calculation section 82 ... generated water calculation section 84 ... dew point calculation section 86 ... calorific value calculation section 88 ... cooling medium Flow rate setting section

Claims (2)

A method for operating a fuel cell in which an electric power is generated by an electrochemical reaction of an oxidant gas supplied to a cathode side electrode and a fuel gas supplied to an anode side electrode, and a cooling medium for temperature adjustment is supplied.
Calculating the amount of moisture supplied to the fuel cell mixed with at least the oxidant gas; and
Calculating the amount of generated water from the output current of the fuel cell;
Calculating the dew point of the outlet gas that can be discharged from the fuel cell as all the water and the produced water supplied into the fuel cell as water vapor;
Calculating the amount of heat generated by power generation of the fuel cell;
Setting the temperature of the outlet gas to a coolant flow rate capable of maintaining the dew point based on the heat generation amount;
A method for operating a fuel cell, comprising: A fuel cell comprising: a fuel cell that generates electricity by an electrochemical reaction between an oxidant gas supplied to the cathode side electrode and a fuel gas supplied to the anode side electrode, and is supplied with a cooling medium for temperature adjustment; and a control device A system,
The control device includes a moisture amount calculation unit that calculates the amount of moisture supplied to the fuel cell mixed with at least the oxidant gas;
A generated water calculation unit for calculating the amount of generated water from the output current of the fuel cell;
A dew point calculator that calculates the dew point of the outlet gas that can be discharged from the fuel cell as all the water and the generated water supplied into the fuel cell as water vapor;
A calorific value calculation unit for calculating a calorific value due to power generation of the fuel cell;
A cooling medium flow rate setting unit that sets the temperature of the outlet gas to a cooling medium flow rate that can be maintained at the dew point, based on the heating value calculated by the heating value calculation unit;
A fuel cell system comprising:

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