JP2009164050A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system capable of restraining performance deterioration of a humidifier as compared with a prior art. <P>SOLUTION: The fuel cell system is provided with a fuel cell 20 generating power by electrochemical reaction between fuel gas and oxidation gas, an oxidation gas supply pipe 32 supplying oxidation gas to the fuel cell, an oxidation offgas exhaust pipe 35 exhausting oxidation offgas exhausted from the fuel cell, a humidifier 33 fitted at the oxidation gas supply pipe and the oxidation offgas exhaust pipe and humidifying the oxidation gas by giving moisture contained in the oxidation offgas to the oxidation gas, and an adjusting system 50 changing a gas flow volume or pressure passing through the humidifier to reduce a load of the humidifier in case an oxidation gas flow volume introduced into the humidifier is to be or more than a predetermined humidifier deterioration threshold. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fuel cell system including a fuel cell, and more particularly to a humidifier for adjusting the water content of a gas supplied to the fuel cell.

  A fuel cell generates electric power by an electrochemical reaction between a fuel gas typified by hydrogen gas and an oxidizing gas typified by air, and simultaneously generates moisture. A polymer electrolyte fuel cell, which is a type of fuel cell, has a structure in which a solid polymer electrolyte membrane is sandwiched between a hydrogen electrode (also referred to as an anode) and an oxygen electrode (also referred to as a cathode). In this type of fuel cell, the electrolyte membrane is responsible for the conduction of protons in the reaction between the fuel gas and the oxygen gas. Therefore, in order to maintain the power generation performance, it is necessary to control the moisture in the electrolyte membrane to an appropriate state. Therefore, the fuel cell system is provided with a humidifier for humidifying the gas supplied to the fuel cell.

  Inside the humidifier is a hollow fiber membrane module (exchange resin) for exchanging moisture between the used gas exhausted from the fuel cell and the dry gas (humidified gas) supplied to the fuel cell. Is provided. The hollow fiber membrane module is a bundle of many hollow fiber membranes. Normally, the gas exhausted from the fuel cell is in a wet state including moisture generated during power generation, so this gas (humidified gas) is circulated inside (or outside) the hollow fiber membrane module. By allowing the humidified gas to flow outside (or inside) the module, the moisture contained in the humidified gas is absorbed by the hollow fiber membrane, and this moisture is given to the humidified gas.

  However, when such a hollow fiber membrane module deteriorates, the humidifying performance of the humidifier decreases, and the humidified gas cannot be sufficiently humidified. Therefore, a countermeasure that can suppress the deterioration of the hollow fiber membrane bundle is desired.

Patent Document 1 discloses a fuel cell system in which a bypass passage that bypasses a humidifier is provided on each of a gas supply side and a discharge side to a cathode, and when the fuel cell is stopped, the fuel cell system is switched to the bypass passage to remove moisture in the system It is disclosed. However, in this system, since the load is always applied to the humidifier during the operation of the system, it is not possible to suppress a decrease in the performance of the humidifier.
JP 2005-251576 A

  Then, an object of this invention is to provide the fuel cell system which can suppress the performance fall of a humidifier compared with the past.

In order to achieve the above object, a fuel cell system according to one aspect of the present invention includes a fuel cell that generates power by an electrochemical reaction between a fuel gas and an oxidizing gas, and an oxidizing gas supply path that supplies the oxidizing gas to the fuel cell And an oxidizing off-gas exhaust path for discharging the oxidizing off-gas discharged from the fuel cell, an oxidizing gas supply path, and an oxidizing off-gas exhaust path, and providing the oxidizing gas with moisture contained in the oxidizing off-gas And a gas passing through the humidifier so as to reduce the load on the humidifier when the flow rate of the oxidizing gas introduced into the humidifier exceeds a predetermined humidifier deterioration threshold. And an adjustment system for changing the flow rate or pressure of the gas.
Here, the humidifier deterioration threshold is a lower limit value of the gas flow rate that may cause deterioration of the humidifier.

  According to one aspect of the present invention, when the flow rate of the oxidizing gas introduced into the humidifier increases, the load of the humidifier is reduced by changing the flow rate or pressure of the gas. Can be suppressed.

The adjustment system may bypass the humidifier with the oxidizing gas and the oxidizing off gas when the flow rate of the oxidizing gas introduced into the humidifier becomes equal to or higher than the predetermined humidifier deterioration threshold.
Thus, the load on the humidifier can be reduced by bypassing the humidifier to the oxidizing gas and the oxidizing off gas.

  In this case, the adjustment system includes a flow sensor that measures the flow rate of the oxidizing gas introduced into the humidifier, or a pressure sensor that measures the pressure of the oxidizing gas, and the oxidizing gas supply pipe. A first bypass passage that bypasses the humidifier, a first valve that adjusts the flow rate of the oxidizing gas that flows through the first bypass passage, and the humidifier that is provided in the oxidizing off-gas discharge pipe is bypassed. A second bypass passage, a second valve for adjusting a flow rate of the oxidizing off-gas flowing through the second bypass passage, and the first and second valves based on a measurement value by the flow sensor or the pressure sensor. A control unit that controls the oxidant gas so that the oxidizing gas bypasses the humidifier and is supplied to the fuel cell when the measured value is equal to or greater than the predetermined humidifier deterioration threshold. To the first Together to the valve operation, may be operated with the second valve so that the oxidizing off gas is discharged bypassing said humidifier.

  Further, the fuel cell system includes an impedance measurement unit that measures the impedance of the fuel cell, and the adjustment system is configured such that when the impedance value measured by the impedance measurement unit is equal to or greater than a predetermined impedance threshold value, It is desirable to let the oxidizing gas and oxidizing off gas pass through the humidifier without bypassing it.

  When the value of the impedance of the fuel cell increases, it is considered that the moisture content of the cells in the fuel cell is decreased. In this case, the oxidizing gas and the oxidizing off gas are used regardless of the flow rate of the oxidizing gas. The bypass is stopped and these gases are introduced into the humidifier. As a result, the humidified oxidizing gas is supplied again to the fuel cell, so that an increase in the impedance of the fuel cell is suppressed, and as a result, the power generation performance of the fuel cell can be maintained.

Alternatively, the adjustment system reduces a differential pressure between the oxidizing gas and the oxidizing off gas in the humidifier when the flow rate of the oxidizing gas introduced into the humidifier becomes equal to or higher than the predetermined humidifier deterioration threshold. You may do it.
Thus, by reducing the differential pressure between the oxidizing gas and the oxidizing off gas in the humidifier, the volume flow rate of the gas passing through the humidifier can be reduced while ensuring the stoichiometric ratio.

  In this case, the adjustment system includes a flow rate sensor that measures the flow rate of the oxidizing gas introduced into the humidifier, or a pressure sensor that measures the pressure of the oxidizing gas, and the pressure of the oxidizing off-gas flowing out of the humidifier. A third valve to be adjusted; and a control unit that controls the third valve based on a measured value by the flow rate sensor or the pressure sensor, wherein the measured value is the predetermined humidifier deterioration. The third valve may be controlled so as to increase the pressure of the oxidizing off gas flowing out of the humidifier when the threshold value is exceeded.

  According to the present invention, in the fuel cell system, since the flow rate or pressure of the gas passing through the humidifier is changed so as to reduce the load on the humidifier, it is possible to suppress deterioration of the humidifier.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The same constituent elements are denoted by the same reference numerals, and the description thereof is omitted.
FIG. 1 is a system diagram showing a configuration of a fuel cell system 1 according to a first embodiment of the present invention. The fuel cell system 1 is used as an in-vehicle power generation system for fuel cell vehicles, a power generation system for any moving body such as a ship, an aircraft, a train, or a walking robot, and also as a power generation facility for buildings (housing, buildings, etc.). It can be applied to stationary power generation systems. In this embodiment, it is for automobiles.

  The fuel cell system 1 includes a fuel cell 20, an oxidizing gas piping system 30 that supplies air as oxidizing gas to the fuel cell 20, and a fuel gas piping system 40 that supplies hydrogen gas as fuel gas to the fuel cell 20. Prepare.

  The fuel cell 20 is, for example, a solid polymer electrolyte type, and has a stacked structure in which a plurality of cells 21 including an electrolyte and electrode layers (anode and cathode) disposed on both sides thereof are stacked. The fuel cell 20 generates electric power by an electrochemical reaction between the oxidizing gas and the fuel gas.

  The oxidizing gas piping system 30 includes an air compressor 31 that takes in and compresses outside air, an oxidizing gas supply pipe 32 that supplies the compressed outside air as an oxidizing gas to the fuel cell 20 via the humidifier 33, and discharges from the fuel cell 20. An oxidized off-gas exhaust pipe 35 for discharging the used oxidizing gas (oxidized off-gas) through the humidifier 33 is included. An air cleaner for cleaning the outside air may be further provided upstream of the air compressor 31. Alternatively, a diluter or a muffler may be further provided in the oxidizing off gas discharge pipe 35.

The humidifier 33 humidifies the oxidizing gas using a high-humidity oxidizing off gas containing moisture generated during the electrochemical reaction in the fuel cell 20.
FIG. 2 is a view showing the internal structure of the humidifier 33. The casing 300 of the humidifier 33 is provided with an inlet 301 and an outlet 302 for oxidizing gas, and an inlet 303 and an outlet 304 for oxidizing off gas. Further, inside the humidifier 33, a hollow fiber membrane bundle (hollow fiber membrane module) 305 in which a plurality of hollow fiber membranes that preferably allow only water vapor to permeate is bundled is disposed. Further, the inside of the humidifier 33 is partitioned by a partition member 306 into an oxidizing gas channel (dry side channel) 307 and an oxidizing off gas channel (wet side channel) 308. In the humidifier 33, an oxidizing off gas is circulated inside the hollow fiber membrane module 305 and an oxidizing gas is circulated outside the hollow fiber membrane module 305. Then, the moisture of the oxidizing off gas is absorbed by the hollow fiber membrane, and the moisture is given to the oxidizing gas.

  Referring again to FIG. 1, the fuel gas piping system 40 includes a fuel gas supply path 41 that supplies the fuel gas to the fuel cell 20, and a fuel that discharges the used fuel gas (fuel offgas) discharged from the fuel gas. Off-gas discharge passage 42. The fuel gas piping system 40 may further be provided with a high-pressure gas tank for storing fuel gas, a circulation pump for reusing fuel off-gas, and the like.

  Furthermore, the fuel cell system 1 includes a control unit 51, a flow sensor 52, a three-way valve 53, an oxidizing gas bypass passage 54, and a three-way valve as an adjustment system 50 that changes the flow rate of gas passing through the humidifier 33. 55, an oxidizing off-gas bypass 56, and an impedance measuring unit 57.

  The flow sensor 52 measures the volume flow rate of the oxidizing gas introduced into the humidifier 33 and outputs the measurement result to the control unit 51.

  The oxidizing gas bypass channel 54 guides the oxidizing gas to the fuel cell 20 so as to bypass the humidifier 33. The oxidizing off gas bypass 56 guides the oxidizing off gas to the exhaust system so as to bypass the humidifier 33.

  The three-way valve 53 is provided at a branch point between the oxidizing gas supply pipe 32 and the oxidizing gas bypass passage 54. Further, the three-way valve 55 is provided at a branch point of the oxidation off gas discharge pipe 35 with the oxidation off gas bypass path 56. These three-way valves 53 and 55 are, for example, electromagnetic valves that operate under the control of the control unit 51, and determine whether to introduce oxidizing gas and oxidizing off gas into the humidifier 33 or to bypass the humidifier 33. Switch. In a normal operation state, the three-way valves 53 and 55 are open in a direction to introduce the oxidizing gas and the oxidizing off gas into the humidifier 33.

  The impedance measuring unit 57 measures the impedance of the fuel cell 20 and outputs the measured value to the control unit 51.

  When the flow rate of the oxidizing gas measured by the flow sensor becomes equal to or higher than a predetermined value (for example, 1000 NL / min), the control unit 51 controls the three-way valve so that the oxidizing gas and the oxidizing off gas bypass the humidifier 33. Switch between 53 and 55. Thereby, it is possible to avoid a large flow rate of gas flowing through the humidifier 33. In the present application, this predetermined value is referred to as a “humidifier deterioration threshold”. Here, NL (normal liter) represents the volume (liter) of gas at 1 atm 0 ° C. In addition, when the flow rate of the oxidizing gas becomes smaller than the humidifier deterioration threshold, the control unit 51 switches the three-way valves 53 and 55 again and introduces the oxidizing gas and the oxidizing off gas into the humidifier 33.

  Further, the control unit 51 determines that the measured value of the impedance of the fuel cell 20 is a predetermined impedance threshold value (for example, about 1.5 times the normal value) even while the oxidizing gas and the oxidizing off gas bypass the humidifier 33. The three-way valves 53 and 55 are switched so that the oxidizing gas and the oxidizing off gas are introduced into the humidifier 33.

  Here, it is generally known that in a fuel cell, the impedance of the fuel cell 20 increases when the water content of each cell 21 decreases. Therefore, when the impedance of the fuel cell 20 is increased, the bypass of the oxidizing gas and the oxidizing off gas is stopped, and these gases are introduced into the humidifier 33. As a result, the humidified oxidizing gas is again introduced into the fuel cell 20, so that an increase in impedance is suppressed. As a result, the power generation performance of the fuel cell 20 can be maintained.

  In the above embodiment, the electromagnetic three-way valves 53 and 55 are used. However, the flow path of the oxidizing gas and the oxidizing off gas may be switched using other types of valves (for example, motor-operated valves). good. Moreover, you may switch a flow path by combining two or more valves instead of a three-way valve.

  Further, in the present embodiment, switching is performed between bypassing all of the oxidizing gas and the oxidizing off gas or introducing all of them into the humidifier. It may be introduced into the humidifier 33. In this case, the flow rate of the oxidizing gas to be bypassed and the flow rate of the oxidizing gas introduced into the humidifier 33, or the ratio of these flow rates may be determined based on the measured value by the flow rate sensor 52, for example, You may determine based on the measured value by the measurement part 57. FIG. Alternatively, an upper limit of the flow rate of the oxidizing gas introduced into the humidifier 33 may be set in advance, and an amount exceeding the upper limit may be bypassed.

Next, a fuel cell system according to a second embodiment of the present invention will be described with reference to FIG.
The fuel cell system 2 shown in FIG. 3 includes an adjustment system 60 instead of the adjustment system 50 shown in FIG. Other configurations are the same as those shown in FIG.

The adjustment system 60 includes a control unit 61, a flow rate sensor 62, and a pressure adjustment valve 63.
The flow sensor 62 measures the volume flow rate of the oxidizing gas flowing into the humidifier 33 and outputs the measurement result to the control unit 61.
The pressure adjustment valve 63 adjusts the pressure of the oxidizing off gas flowing out from the humidifier 33.

  When the flow rate of the oxidizing gas measured by the flow sensor 62 becomes equal to or higher than the humidifier deterioration threshold (for example, 1000 NL / min), the control unit 61 adjusts the pressure adjustment valve 63 and flows out of the humidifier 33. By increasing the pressure of the off gas, the differential pressure between the dry side channel 307 and the wet side channel 308 in the humidifier 33 is reduced. Thus, the volume flow rate of the oxidizing gas can be reduced while ensuring the air stoichiometric ratio (oxygen surplus rate). Here, the air stoichiometric ratio is a value indicating how much oxygen is supplied relative to oxygen necessary to react with hydrogen without excess or deficiency.

  According to the present embodiment, it is possible to reduce the load on the humidifier 33 and suppress the performance degradation while maintaining a simple piping structure. In addition, since the humidified oxidizing gas is always supplied to the fuel cell 20, it is possible to suppress a decrease in power generation performance due to the water content of the cell 21.

  In the first and second embodiments of the present invention described above, the flow rate of the oxidizing gas introduced into the humidifier 33 is measured by the flow rate sensors 52 and 62 provided in the oxidizing gas flow path. A pressure sensor is provided in the oxidizing gas supply pipe 32 instead of the sensor or together with the flow rate sensor, and based on the measured value of the pressure sensor, it is determined whether or not the humidifier 33 is bypassed by the oxidizing gas. The back pressure of the device 33 may be determined. In this case, the control units 51 and 61 may calculate the flow rate of the oxidizing gas introduced into the humidifier 33 based on the measurement value of the pressure sensor, and compare the calculated value with the humidifier deterioration threshold value. Alternatively, a pressure threshold value corresponding to the oxidation humidifier deterioration threshold value (gas flow rate threshold value) may be obtained in advance, and the measured value of the pressure sensor may be directly compared with the pressure threshold value.

1 is a diagram showing a configuration of a fuel cell system according to a first embodiment of the present invention. It is a figure which shows the internal structure of the humidifier shown in FIG. It is a figure which shows the structure of the fuel cell system which concerns on the 2nd Embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1, 2 ... Fuel cell system, 20 ... Fuel cell, 32 ... Oxidation gas supply pipe, 33 ... Humidifier, 35 ... Oxidation off gas discharge pipe, 50, 60 ... Adjustment system, 51, 61 ... Control part, 52, 62 ... Flow sensor, 53, 55 ... three-way valve, 54 ... oxidizing gas bypass, 56 ... oxidizing off gas bypass, 57 ... impedance measuring unit, 63 ... pressure regulating valve

Claims (6)

A fuel cell that generates electricity by an electrochemical reaction between a fuel gas and an oxidizing gas;
An oxidizing gas supply path for supplying an oxidizing gas to the fuel cell;
An oxidation off-gas discharge path for discharging the oxidation off-gas discharged from the fuel cell;
A humidifier that is provided in the oxidizing gas supply path and the oxidizing off gas discharge path, and humidifies the oxidizing gas by supplying moisture contained in the oxidizing off gas to the oxidizing gas;
When the flow rate of the oxidizing gas introduced into the humidifier exceeds a predetermined humidifier deterioration threshold, the flow rate or pressure of the gas passing through the humidifier is changed so as to reduce the load on the humidifier. An adjustment system;
A fuel cell system comprising:   2. The adjustment system according to claim 1, wherein when the flow rate of the oxidizing gas introduced into the humidifier becomes equal to or higher than the predetermined humidifier deterioration threshold, the humidifying device is bypassed by the oxidizing gas and the oxidizing off gas. Fuel cell system. The adjustment system includes:
A flow sensor for measuring the flow rate of the oxidizing gas introduced into the humidifier, or a pressure sensor for measuring the pressure of the oxidizing gas;
A first bypass passage provided in the oxidizing gas supply pipe and bypassing the humidifier;
A first valve for adjusting a flow rate of the oxidizing gas flowing through the first bypass path;
A second bypass path provided in the oxidizing off-gas discharge pipe to bypass the humidifier;
A second valve for adjusting the flow rate of the oxidizing gas flowing through the second bypass path;
A control unit for controlling the first and second valves based on a measured value by the flow sensor or the pressure sensor;
With
The control unit operates the first valve so that oxidizing gas is supplied to the fuel cell by bypassing the humidifier when the measured value is equal to or greater than the predetermined humidifier deterioration threshold. In addition, the fuel cell system according to claim 2, wherein the second valve is operated so that the oxidizing off gas is discharged by bypassing the humidifier. An impedance measuring unit for measuring the impedance of the fuel cell;
The adjustment system, when the impedance value measured by the impedance measurement unit is equal to or greater than a predetermined impedance threshold, allows the oxidizing gas and the oxidizing off gas to pass therethrough without bypassing the humidifier. The fuel cell system described.   The adjustment system reduces a differential pressure between the oxidizing gas and the oxidizing off gas in the humidifier when a flow rate of the oxidizing gas introduced into the humidifier is equal to or higher than the predetermined humidifier deterioration threshold. The fuel cell system according to claim 1. The adjustment system includes:
A flow sensor for measuring the flow rate of the oxidizing gas introduced into the humidifier, or a pressure sensor for measuring the pressure of the oxidizing gas;
A third valve for adjusting the pressure of the oxidizing off gas flowing out of the humidifier;
A control unit for controlling the third valve based on a measured value by the flow sensor or the pressure sensor;
With
The said control part controls the said 3rd valve so that the pressure of the oxidation off gas which flows out out of the said humidifier may be made high, when the said measured value becomes more than the said predetermined humidifier deterioration threshold value. Or 5. The fuel cell system according to 5.

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