JP5109284B2 - Fuel cell system - Google Patents

Description

  The present invention relates to a power generation system using a fuel cell.

  A fuel cell is an electrochemical device that directly converts fuel energy into electrical energy through an electrochemical reaction. Fuel cells are roughly classified into phosphoric acid fuel cells, molten carbonate fuel cells, solid oxide fuel cells, polymer electrolyte fuel cells (hereinafter abbreviated as PEFC), and alkaline fuel cells, depending on the charge carrier used. Is done.

  Among these various fuel cells, PEFC can be operated at a high current density power generation or at a relatively low temperature, and therefore is expected to be applied to various uses including a mobile power source.

  At the time of PEFC power generation, water is generated by the chemical reaction. However, when the generated water condenses and stays in the gas flow path in the fuel cell stack (flooding), the diffusion of the reaction gas is hindered, so that the battery performance is deteriorated. If this state continues for a long time, the fuel cell stack may be damaged.

  In such a case, as a method of eliminating the clogging of the gas flow path, in Patent Document 1, an operation for continuously increasing / decreasing the anode hydrogen pump drive amount is performed, and when it is not resolved, control for operating the on-off valve is performed. It was.

JP 2005-637112 A

  However, when the voltage changes due to water clogging, the voltage of the unit cell may be inverted to zero volts or less, and if the inversion occurs, the damage to the battery component increases. Therefore, an immediate recovery operation is required, and a countermeasure that is faster than a change in pump operation is desired.

  An object of the present invention is to propose a fuel cell system having a control method and a configuration for quickly recovering from changes in battery characteristics caused by flooding.

  A fuel cell stack that is supplied with fuel and an oxidant to generate electric power, and a control valve that controls a pressure for supplying fuel to the fuel cell stack, and the gas flow path is blocked by condensed water inside the stack In addition, the fuel cell system increases and decreases the pressure controlled by the control valve over time.

  The present invention proposes a fuel cell system having a control method and configuration for quickly recovering from changes in battery characteristics caused by flooding.

  Embodiments of the present invention are as follows.

  A fuel cell stack, a fuel cell temperature sensor that measures the temperature inside the fuel cell, a voltage sensor that measures the power generation voltage of the fuel cell, a current sensor that measures the current flowing from the fuel cell, and the heat generated in the fuel cell A radiator for radiating heat, a fan attached to the radiator for controlling the amount of heat radiation, a cooling water pump for boosting the cooling fluid, a bypass unit for controlling the amount of cooling fluid flowing into the radiator, and water generated by power generation A cathode line provided with a humidifier to be added to air, a pressure control valve that controls the hydrogen supply pressure to the fuel cell stack, and hydrogen that boosts the hydrogen discharged from the fuel cell stack and circulates it to the fuel cell stack inlet It has a pump, a humidity controller that adjusts the water content of the circulating hydrogen, and a controller that controls the operation of auxiliary equipment in the system. Voltage information measured by the voltage sensor, When the controller determines that the gas flow path is blocked by condensed water from the current information measured by the sensor, the secondary pressure controlled by the pressure control valve is increased or decreased over time. Thus, the fuel cell system performs control for removing condensed water at a gas flow rate.

  In addition, the fuel cell system uses a control that increases or decreases the discharge amount of the hydrogen pump in synchronization with the secondary pressure controlled by the pressure control valve.

  The cathode line has an air supply unit, a humidity controller, a humidifier, a fuel cell stack, a heat exchanger, a bypass valve and a bypass line connected to it, and supplies the humidifier by opening and closing the bypass valve. And a battery system for simultaneously controlling the amount of fluid supplied to the heat exchanger.

  By opening and closing the bypass valve when the control unit determines from the voltage information measured by the voltage sensor and the current information measured by the current sensor that the gas flow path is blocked by condensed water inside the battery. This is a fuel cell system that simultaneously controls the fluid supplied to the humidifier and the amount of fluid supplied to the heat exchanger.

  A fuel cell system including a pressure sensor for measuring the pressure of an anode gas and a cathode gas supplied to a fuel cell stack.

  Based on the voltage information measured by the voltage sensor, the current information measured by the current sensor, and the pressure information detected by the pressure sensor, the pole in which the gas flow path is blocked by condensed water inside the battery is the anode or cathode. The fuel cell system controls the operation of the pressure control valve, the hydrogen pump, and the bypass valve according to the determination result.

  From the voltage information measured by the voltage sensor, the current information measured by the current sensor, the pressure information detected by the pressure sensor, and the temperature information measured by the temperature sensor, the gas flow path is blocked by condensed water. If the control unit determines that there is a fuel cell stack, the operation amount of the cooling water pump and the bypass unit is changed to change the operation amount to be higher than the fuel cell stack temperature so far.

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

Example 1
FIG. 1 shows a system configuration diagram of the first embodiment. A polytetrafluoroethylene (PTFE) is formed on the front and back surfaces of an electrode electrolyte membrane in which a perfluorocarbon sulfonic acid electrolyte membrane and an electrode mainly composed of a catalyst having platinum particles supported on a carbon support are integrated. A cathode diffusion layer and an anode diffusion layer, which are carbon papers in which water repellency is controlled by being dispersed on the surface, are arranged, and metal separators are arranged on both sides to form the basic configuration of the power generation cell. The fuel cell stack 1 was fabricated by combining 120 power generation cells and 60 cooling cells for circulating the cooling water and lowering the battery temperature.

  A hydrogen pump 51 for increasing the pressure of hydrogen discharged from the fuel cell stack 1 to supply the fuel cell stack 1 again, a pressure control valve 52 for controlling the hydrogen pressure supplied to the fuel cell stack 1, and a fuel cell Anode line 2 provided with a humidity controller 53 for adjusting the amount of moisture contained in the stack discharge hydrogen, a cathode line 4 provided with a humidifier 5 made of a water permeable membrane for collecting and humidifying the generated water, and cooling A cooling water pump 10 for supplying water, a radiator 7 with a fan 8 attached thereto, a cooling water bypass line 11 and a cooling line having a bypass valve 9 for controlling the flow rate thereof were connected to the fuel cell stack 1. A current sensor 14, a voltage sensor 12, and a temperature sensor 13 for measuring the temperature at the center of the fuel cell stack are attached to the output line 16 for taking out the output from the fuel cell stack 1, and each sensor information is connected to the control unit 15. The control unit 15 controls the pressure control valve operating state based on information from each sensor. Further, when the control unit determines, the operation state of the hydrogen pump is also controlled in synchronization with the change in the secondary pressure. FIG. 3 shows a change in the secondary pressure by controlling the pressure control valve 52, and FIG. 4 shows a change in the discharge pressure of the hydrogen pump.

  In the first embodiment, a control unit 15 capable of detecting and determining that flooding has occurred in the fuel cell stack 1 by the voltage sensor 12 is incorporated. The contents to be judged include, for example, a state in which the average voltage of the stack has rapidly decreased from the voltage that should be shown in a short time as a result of checking the current-voltage correspondence table in the memory of the control unit, or the stack voltage Is divided into a plurality of parts, for example, when a stack composed of 100 cells is divided into 5 parts by 20 cells, the measurement voltage of a part is shorter than the others. When the state is decreasing or fluctuating over time, the control unit performs the following operation.

When the control unit 15 determines that flooding has occurred, it instructs the secondary pressure of the anode to the pressure control valve 52 to change it over time, thereby facilitating the discharge of water remaining in the gas flow path in the fuel cell stack, and promptly. Recover fuel cell stack voltage. Here, the meaning of changing the secondary pressure with time is to accelerate the gas flow by making the pressure fluctuate rapidly in a short time, and to make it easy to discharge water staying in the stack.

  Furthermore, when water clogging is not eliminated by the change in the secondary pressure by the pressure control valve, flooding is eliminated by increasing or decreasing the discharge amount of the hydrogen pump according to the judgment of the control unit. At this time, in order to enhance the synergistic effect, control for synchronizing the maximum value of the secondary pressure change and the maximum value of the discharge amount of the hydrogen pump is applied. According to this method, since the amount of hydrogen discharged without being used for power generation by hydrogen purge is zero, the influence on power generation efficiency reduction is small. Further, since the condensed water removal is attempted by the pressure control valve operation as a first-stage countermeasure for eliminating the flooding, the power consumption of the auxiliary equipment can be suppressed to a slight extent. Further, as can be understood by comparing FIG. 3 and FIG. 4, the secondary pressure change can change state more quickly than the pump. Therefore, when flooding occurs in the fuel cell stack 1 and the fuel cell stack 1 is assumed to be damaged, a quick recovery operation is required, but this can be realized quickly by controlling the secondary pressure. It becomes possible.

(Example 2)
The system configuration of the second embodiment is shown in FIG. The heat exchanger 61 to which the exhaust gas from the humidifier is connected, the humidity controller 53, and the bypass valve 62 for branching the exhaust gas from the fuel cell stack 1 are provided, and the fuel cell stack is operated by the operation of the bypass valve. The cathode line 4 capable of changing the amount of gas supplied from the exhaust gas 1 to the humidity controller 53 and the subsequent heat exchanger 61, and the pressure of the anode gas and cathode gas supplied to the fuel cell stack 1 A fuel cell system having an anode pressure sensor 71 and a cathode pressure sensor 72 to be measured and having the same configuration as that of the first embodiment was manufactured as the second embodiment. FIG. 5 shows changes in the amount of exhaust gas from the fuel cell stack supplied to the humidifier 5 and the heat exchanger 61 before and after the bypass valve 62 is operated.

  The gas humidification mechanism of Example 2 will be described in detail. Since the cathode gas uses air in the atmosphere, if the cathode gas is supplied to the stack as it is, the inside of the battery is dried, and the battery performance is lowered due to an increase in internal resistance. Therefore, it is generally necessary to add water vapor to the gas supplied to the fuel cell. In this embodiment, the humidifier 5 is provided, and a necessary amount of water vapor is added to the supplied cathode gas. The humidifier 5 is composed of a material that allows moisture to permeate and a gas flow path that guides two kinds of gases through the material. Since the moisture permeation material blocks the gas itself, when a gas containing a lot of water vapor is supplied to one side and a dry gas is supplied to the humidifier on the other side, moisture moves through the permeation material, so that the dry gas contains water vapor. And the gas components themselves are discharged without being mixed with each other. In a fuel cell, the product of the electrochemical reaction is water, so the cathode exhaust gas from the cell contains moisture. Therefore, by adding the moisture of the exhaust gas to the cathode gas supplied to the stack, it is not necessary to newly supply moisture necessary for humidification from the outside, and a simple system configuration is realized.

  In the second embodiment, the heat of the cathode gas discharged from the humidifier 5 is effectively transferred to the cathode gas supplied from the air supplier 81 by using the heat exchanger 61. The cathode gas whose temperature has been raised by exhaust heat by the heat exchanger 61 can also contain more moisture because the saturated water vapor pressure also increases. Therefore, the cathode gas that has passed through the heat exchanger 61 is more effectively deprived of moisture from the humidity controller 53 by the humidity controller 53 than when the heat exchanger is not provided, that is, the amount of moisture in the anode line is further reduced. It will be possible.

  However, even in a configuration where the humidified state is good in the normal power generation state, for example, if the battery temperature becomes lower than the set value, condensed water tends to be generated inside the stack, and voltage fluctuation due to flooding occurs. It becomes easy.

  In this case, by operating the bypass valve 62 provided immediately before the cathode line of the humidifier 5, part of the cathode gas discharged from the fuel cell stack 1 is discharged outside the system through the bypass line. The cathode gas contains power generation water, and the flow rate of the gas flowing to the humidifier 5 and the heat exchanger 61 connected in series to the humidifier 5 and the amount of moisture contained in the gas are controlled by the operation of the bypass valve 62. Can do. Since the humidifier 5 adds the moisture contained in the fuel cell stack exhaust gas to the fuel cell stack supply gas, the amount of moisture supplied to the fuel cell stack 1 can be reduced by the operation of the bypass valve 62. Further, by operating the bypass valve 62, energy lost in the humidifier 5 of the stack exhaust gas is reduced, and more energy is supplied to the heat exchanger 61. As a result, the temperature of the gas supplied from the air supply device 81 can be further increased, and saturated water vapor is increased, so that the dehumidifying effect of the anode line 2 in the humidity controller 53 is increased. Therefore, the amount of water in both the cathode and the anode can be reduced by the operation of the bypass valve 62, and flooding can be suppressed. This effect can also be obtained with only the valve operating power, and the effect of the reduction in efficiency on the whole is minor, and not only the flooding caused by the anode line 2 but also the clogging of the cathode line 4 is supported. It became possible.

  Further, the control unit 15 determines the measured values of the anode pressure sensor 71 and the cathode pressure sensor 72 attached to the fuel cell stack gas supply unit, so that it is possible to detect a change in gas pressure caused by condensation of moisture in the gas flow path. Even in the initial flooding situation, it was possible to deal with it promptly. Further, by independently measuring the pressure conditions of the anode line 2 and the cathode line 4, it is possible to cope with each line alone.

(Example 3)
Based on the determination of the control unit 15, the operation amount of the bypass valve 9 that controls the flow rate of the cooling water bypass line 11, the cooling water pump 10, and the fan 8 provided in the radiator 7 is changed as necessary, A fuel cell system having a cooling line capable of increasing / decreasing the fuel cell stack temperature and a control method and having the other configurations equivalent to those of the second embodiment was manufactured as a third embodiment.

  In the system of the third embodiment, when the control unit 15 determines that flooding has occurred, a control method for increasing the fuel cell stack temperature by changing at least one operation amount of the bypass valve 9, the cooling water pump 10, and the fan 8. Has been applied. FIG. 6 shows a change in the temperature of the fuel cell stack by the control of the cooling line. At time to in FIG. 6, the control unit determines the occurrence of flooding from the measured values of various sensors, and simultaneously raises the fuel cell stack temperature from st2 to st1 by controlling the cooling auxiliary device operation amount. Here, the control of the cooling auxiliary unit operation amount is provided in the radiator 7 or a method of suppressing the heat amount taken from the stack by decreasing the operation amount of the cooling water pump 10 and reducing the amount of water supplied to the stack. The amount of cooling water that flows to the radiator 7 by changing the operating amount of the bypass valve 9 is further reduced by reducing the amount of heat released by reducing the operating amount of the fan 8 and increasing the stack temperature by increasing the cooling water temperature. However, it is conceivable to select one of the methods for raising the stack temperature by relatively increasing the amount of cooling water that directly returns to the stack through the bypass line, or to combine a plurality of methods. .

  By increasing the fuel cell stack temperature, the saturated water vapor pressure in the fuel cell stack also increases, and the amount of water present as water vapor increases. As a result, the influence of flooding caused by clogging of the gas flow path due to condensed water is mitigated. It is also effective for preventing flooding.

It is a figure which shows the electric power generation system structure of Example 1 in connection with this invention. It is a figure which shows the electric power generation system structure of Example 2 and Example 3 in connection with this invention. It is a figure which shows the time change of the secondary pressure by the pressure control valve concerning this invention. It is a figure which shows the time change of the discharge amount of the hydrogen pump in connection with this invention. It is a figure which shows the change of the fuel cell stack exhaust gas flow volume which flows into the humidifier and heat exchanger by the bypass valve concerning this invention. It is a figure which shows the temperature change of a fuel cell stack by control of the cooling system auxiliary machine in connection with this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Fuel cell stack, 2 ... Anode line, 4 ... Cathode line, 5 ... Humidifier, 6 ... Cooling line, 7 ... Radiator, 8 ... Fan, 9,62 ... Bypass valve, 10 ... Cooling water pump, 11 ... Cooling Water bypass line, 12 ... Voltage sensor, 13 ... Temperature sensor, 14 ... Current sensor, 15 ... Control unit, 16 ... Output line, 51 ... Hydrogen pump, 52 ... Pressure control valve, 53 ... Humidifier, 61 ... Heat exchange 71 ... Anode pressure sensor 72 ... Cathode pressure sensor 80 ... Purge valve 81 ... Air supply device

Claims (4)

A fuel cell stack that is supplied with anode gas and cathode gas to generate electricity;
An anode line having a control valve for controlling a pressure for supplying fuel to the fuel cell stack;
The cathode gas is supplied to the fuel cell stack through a first region of a humidifier having two regions partitioned by a water permeable material, and the cathode exhaust gas discharged from the fuel cell stack is passed outside the system through the second region. A cathode line that discharges to
A cathode bypass line for discharging the cathode exhaust gas to the outside without passing through the second region of the humidifier, a cathode bypass valve provided in the cathode bypass line,
The fuel cell to determine the blockage by condensed water of the stack, when said anode gas passage within the stack is determined to have been closed by condensation water coagulation is time and is repeatedly increasing or decreasing the pressure controlled by said control valve, If it is determined that the cathode gas channel within the stack are closed by condensation water coagulation includes a control unit for controlling opening said cathode bypass valve,
A pump for boosting the anode gas discharged from the fuel cell stack to the anode line and circulatingly supplying the anode gas to the fuel cell stack,
A fuel cell system that increases or decreases the amount of fuel supplied from the pump in synchronization with an increase or decrease in pressure controlled by the control valve . The fuel cell system of claim 1, wherein determining that it has been closed by condensation water coagulation is the anode gas passage in the stack inside based on the current flowing through the power generation voltage of the fuel cell stack the fuel cell stack. The control unit includes an anode gas channel and a cathode gas channel inside the fuel cell stack from voltage information of the fuel cell stack, current information of the fuel cell stack, and pressure information of the fuel cell stack. the fuel cell system of claim 1, wherein the determining whether it is closed by either the condensable water. A cooling line having a cooling water pump that circulates and supplies cooling water to the fuel cell stack; a radiator that is provided in the cooling line; and that the cooling water flows in, and is discharged from the fuel cell stack without passing through the radiator. the cooling water and the cooling water bypass line back to the fuel cell stack, and a cooling water bypass valve provided in the coolant bypass line has,
When the control unit determines from the temperature information of the fuel cell stack that the gas flow path is blocked by condensed water, the cooling water bypass valve provided in the cooling water pump and the cooling water bypass line 2. The fuel cell system according to claim 1, wherein control is performed to raise the temperature of the fuel cell stack so far by changing at least one of the operation amounts of the fuel cell system.

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