JP2008234991A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform optimum moisture removal in accordance with an operation mode when circulating fuel off-gas. <P>SOLUTION: This fuel cell system is to remove moisture of fuel off-gas exhausted from a fuel cell 20. A pipe 54 to connect a shut-off valve 52 and a gas-liquid separator 53 is provided and a bypass route 56 is connected to both ends of the pipe 54 in a circulation passage 51, a three way valve 55 is provided in the pipe 54, a heat exchanger 57 is provided in the bypass route 56, the three way valve 55 selects the pipe 54 in a normal operation mode to feed the fuel off-gas to the gas-liquid separator 53 from the fuel cell 20 as it is, the three way valve 55 selects the bypass route 56 in a scavenging operation mode to cool the fuel off-gas exhausted from the fuel cell 20 by cooling water from a cooling system in the heat exchanger 57 and to feed cooled fuel off-gas to the gas-liquid separator 53, and humidity removing ability in the scavenging operation mode is thereby heightened. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fuel cell system, and in particular, to an exhaust gas treatment technology for fuel off gas.

Conventionally, when fuel off-gas exhausted from the anode side of a fuel cell is pressurized by a pressurizing means such as a pump, merged with new fuel gas, and supplied again to the fuel cell, the fuel cell in the circulation path of the fuel off-gas A heat exchanger is provided at the fuel off-gas outlet of the fuel, and heat exchange with the coolant (cooling water) of the cooling system of the fuel cell is performed with this heat exchanger to lower the temperature of the fuel off-gas, and to remove moisture contained in the fuel off-gas. There has been proposed a fuel cell system in which water contained in fuel off-gas is collected and removed by a gas-liquid separator after condensation (see Patent Document 1). According to this fuel cell system, when the fuel off-gas is circulated, the temperature of the fuel off-gas is lowered by heat exchange with the refrigerant of the cooling system, so that the charging efficiency is increased due to the decrease in temperature with respect to the pressurizing means. Since the fuel off-gas is supplied, the pressurizing means can circulate the required fuel with less power than when pressurizing at a high temperature.
In addition, Japanese Patent Application Laid-Open No. 2002-313383 (Patent Document 2) and Japanese Patent Application Laid-Open No. 11-111315 (Patent Document 3) also disclose inventions related to removal of moisture in exhaust gas.

JP 2005-235462 A JP 2002-313383 A JP-A-11-111315

  In the normal power generation mode of the fuel cell system, saturated water vapor circulates in the circulation path of the fuel off-gas (exhaust gas). For the humidity control on the electrolyte membrane and anode side of the fuel cell, the gas is separated by a gas-liquid separator. It is sufficient to remove the components, and removing any more liquid components will result in excessive drying. On the other hand, in the scavenging operation mode, it is not sufficient to dry the saturated water vapor only by removing the liquid component with the gas-liquid separator, and it is necessary to further reduce the humidity in the circulation path of the fuel off gas.

  However, in the fuel cell system described in Patent Document 1 and the like, condensation of water vapor always starts when the coolant pump operates. However, when the coolant pump is driven to cool the fuel cell, and the circulation path of the fuel off gas No consideration is given to the timing of dehumidification.

  Accordingly, an object of the present invention is to perform optimum water removal according to the operation mode when circulating the fuel off gas.

  In order to solve the above problems, a fuel cell system according to the present invention is a fuel cell system that removes moisture from a fuel off-gas exhausted from a fuel cell, and when the fuel cell is in a scavenging operation mode, The fuel cell is configured to be able to enhance the humidity removal capability as compared with a case where the fuel cell is in an operation mode other than the scavenging operation mode.

  That is, when the moisture of the fuel off-gas exhausted from the fuel cell is removed by, for example, a gas-liquid separator, when the fuel cell is in an operation mode other than the scavenging operation mode, Therefore, simply removing the water contained in the fuel off-gas with a gas-liquid separator is sufficient for humidity control on the electrolyte membrane and anode side of the fuel cell. However, when the fuel cell is in the scavenging operation mode, simply removing the water contained in the fuel off-gas with the gas-liquid separator is difficult to dry the saturated water vapor, and is not sufficient to lower the humidity.

  Therefore, the ability to remove the moisture contained in the fuel off-gas is switched according to the operation mode, and in the scavenging operation mode, the humidity removal ability in the circulation path of the fuel off-gas is higher than in other operation modes. Thus, it is possible to remove water optimally.

  When the fuel cell is in the scavenging operation mode, it is desirable to provide the following elements in the fuel off-gas circulation path in order to increase the humidity removal capability as compared to when the fuel cell is in an operation mode other than the scavenging operation mode.

  Preferably, a pipe for circulating the fuel off gas exhausted from the fuel cell, a bypass path having both ends connected to the pipe, a cooling device provided in the bypass path, and the pipe and the bypass path And a path switch provided at the upstream connection portion of the two connection portions.

  According to such a configuration, when the path switching device is switched to the piping side, the fuel off-gas exhausted from the fuel cell can be circulated through the piping, and when the path switching device is switched to the bypass path side, The fuel off-gas exhausted from the battery can be introduced into the bypass path, the fuel off-gas can be cooled by the cooling device provided in the bypass path, the water contained in the fuel off-gas can be removed, and the humidity removal capability can be enhanced.

  Preferably, the path switching unit is switched so that the fuel off-gas flows through the bypass path when the fuel cell is in the scavenging operation mode.

  According to such a configuration, when the fuel cell is in an operation mode other than the scavenging operation mode, the path switching device is switched to the pipe side, and the fuel off-gas exhausted from the fuel cell is circulated through the pipe, so that the fuel cell Is switched to the bypass path side by the path switching device, the fuel off-gas exhausted from the fuel cell is introduced into the bypass path, the fuel off-gas is cooled by the cooling device provided in the bypass path, By removing the moisture contained in the off gas, the humidity removal capability in the scavenging operation mode can be enhanced.

  Preferably, the cooling device is a heat exchanger through which the coolant of the fuel cell circulates, and the coolant is forcibly circulated when the cooling device is driven.

  According to such a configuration, since the coolant is forcedly circulated when the cooling device is driven, when the fuel cell is in the scavenging operation mode, the fuel offgas and the coolant are forced to exchange heat, thereby circulating the fuel offgas. The humidity removal capability in the path can be increased.

Preferably the cooling device is a rapid cooler.
According to such a configuration, when the fuel cell is in the scavenging operation mode, the fuel off-gas exhausted from the fuel cell is rapidly cooled by the rapid cooler, so that the humidity removal capability in the circulation path of the fuel off-gas is quickly increased. Can be increased.

  When driving the path switch and the cooling device, for example, a control unit configured by a microcomputer determines whether the fuel cell is in a scavenging operation mode or other operation modes, and this determination The control unit controls the driving of the path switching device and the cooling device according to the result, so that the path switching device and the cooling device can be automatically controlled according to the operation mode.

  ADVANTAGE OF THE INVENTION According to this invention, when circulating a fuel off gas, the water | moisture-content removal capacity in the circulation path | route of a fuel off gas can be made into the optimal state according to an operation mode.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
First, prior to the embodiment, a schematic configuration of a fuel cell system mounted on a fuel cell electric vehicle will be described with reference to FIG.

  The fuel cell system 10 mainly includes a fuel gas supply device 40, an oxidizing gas supply device 73, a fuel cell 20, and a control unit 80. The fuel gas is, for example, hydrogen gas, and the oxidizing gas is, for example, air. The control unit 80 is configured using, for example, a microcomputer, and obtains the required power generation amount of the fuel cell 20 from the accelerator opening detected by the accelerator sensor 84, and supplies the fuel gas so that a desired power generation amount can be obtained. The apparatus 40 and the oxidizing gas supply device 73 are controlled to adjust the flow rate of the fuel gas and the oxidizing gas supplied to the fuel cell 20. The PCU 82 is a power control device including an inverter and a DC / DC converter. The PCU 82 converts the DC power generated by the fuel cell 20 into AC power and supplies it to the motor 83 for running the vehicle, and also supplies surplus power to the secondary battery 81. To store electricity. The secondary battery 81 plays a role as a regenerative energy storage source at the time of brake regeneration and an energy backup at the time of load fluctuation accompanying acceleration or deceleration of the vehicle.

(First embodiment)
FIG. 1 shows a system configuration centering on a piping system of a fuel cell system in a first embodiment of the present invention. As shown in FIG. 1, the fuel cell system 10 includes a fuel gas supply device 40 for supplying a fuel gas (hydrogen gas) to the fuel cell 20 and an oxidation for supplying an oxidizing gas (air) to the fuel cell 20. A gas supply device 73 and a cooling 30 for cooling the fuel cell 20 are provided.

The fuel cell 20 is a membrane / electrode assembly in which an anode electrode 22 and a cathode electrode 23 are formed by screen printing or the like on both surfaces of a polymer electrolyte membrane 21 made of a proton conductive ion exchange membrane or the like formed of a fluorine-based resin or the like. 24. Both surfaces of the membrane / electrode assembly 24 are sandwiched by separators (not shown) having flow paths of fuel gas, oxidizing gas, and cooling water, and grooves are respectively formed between the separator and the anode electrode 22 and the cathode electrode 23. An anode gas channel 25 and a cathode gas channel 26 are formed. The anode electrode 22 undergoes an oxidation reaction of the following formula (1), and the cathode electrode 23 undergoes a reduction reaction of the following formula (2). In the secondary battery 20 as a whole, an electromotive reaction of the following formula (3) occurs.
H ₂ → 2H ⁺ + 2e ⁻ (1)
(1/2) O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O (2)
H ₂ + (1/2) O ₂ → H ₂ O (3)
For convenience of explanation, the figure schematically shows the structure of a unit cell composed of a membrane / electrode assembly 24, an anode gas channel 25, and a cathode gas channel 26. A plurality of unit cells connected in series.

  The cooling device 30 of the fuel cell system 10 includes a cooling path 31 for circulating the cooling water, a temperature sensor 32 for detecting the temperature of the cooling water drained from the fuel cell 20, and a radiator (heat) that radiates the heat of the cooling water to the outside. 33), a valve 34 for adjusting the amount of cooling water flowing into the radiator 33, a cooling water pump 35 for pressurizing and circulating the cooling water, and a temperature sensor 36 for detecting the temperature of the cooling water supplied to the fuel cell 20. Etc. are provided.

  The fuel gas supply device 40 of the fuel cell system 10 includes a fuel gas source 42, a fuel gas passage 41 for supplying fuel gas to the anode gas channel 25, and a fuel gas passage for supplying fuel off-gas exhausted from the anode gas channel 25. A circulation flow path (circulation path) 51 for circulation to 41 is provided, and a fuel gas circulation system is constituted by these gas flow paths.

  In the fuel gas passage 41, a shutoff valve 43 for controlling supply / stop of the fuel gas from the fuel gas source 42, a pressure sensor 44 for detecting the pressure of the fuel gas, a regulator 45 for adjusting the pressure of the fuel gas, a fuel cell A shut-off valve 46 for opening and closing the fuel gas supply port (inlet) is installed. The fuel gas source 42 includes, for example, a high pressure hydrogen tank, a hydrogen storage alloy, a reformer, and the like.

  The circulation channel 51 is formed with a shut-off valve 52 for discharging the fuel off-gas from the fuel cell 20, a gas-liquid separator 53 for recovering water from the fuel off-gas, and a channel connecting the shut-off valve 52 and the gas-liquid separator 53. In addition, a pipe 54 through which the fuel off-gas exhausted from the fuel cell 20 circulates, a three-way valve 55 provided in the middle of the pipe 54, a bypass path 56 connected to both ends of the pipe 54, and provided in the middle of the bypass path 56 The heat exchanger 57, the drain valve 58 for collecting the water collected by the gas-liquid separator 53 in a tank (not shown), the circulation pump (pressurizing means) 59 driven by the motor, and the fuel gas in the fuel gas passage 41 A backflow prevention valve 60 or the like for preventing backflow to the circulation flow path 51 side is installed.

  The three-way valve 55 is provided at a connection portion on the upstream side of the connection portion between the pipe 54 and the bypass route 56 in the circulation passage 51, and is configured as a route switching device that switches the route according to a control signal from the control unit 80. When the fuel cell 20 is in an operation mode other than the scavenging operation mode, for example, in the normal power generation operation mode, the pipe 54 is selected as a route, and when the fuel cell 20 is in the scavenging operation mode, the bypass is selected. Path 56 is selected. A rotary valve can be used instead of the three-way valve 55.

  Cooling water (coolant) from the cooling device 30 is introduced into the heat exchanger 57 as a cooling device via a pipe 37. The heat exchanger 57 performs heat exchange between the fuel off-gas introduced into the bypass passage 56 and the cooling water (coolant) from the cooling device 30, and the fuel off-gas whose temperature has decreased due to the heat exchange is removed from the gas-liquid separator. To 53. In the normal power generation operation mode, the gas-liquid separator 53 introduces a fuel off-gas that is not heat-exchanged by the heat exchanger 57 from the pipe 54, collects the moisture, and in the scavenging operation mode, The fuel off-gas whose temperature is lowered by the heat exchange in the exchanger 57 is introduced, the water is collected, and the fuel off-gas from which the water has been collected is supplied to the circulation pump 59.

  Based on the control of the control unit 80, the circulation pump 59 compresses the fuel off-gas that has been subjected to pressure loss to a suitable gas pressure when passing through the anode gas channel 25, and returns the fuel off-gas to the fuel gas passage 41. . The fuel off-gas is combined with the fuel gas supplied from the fuel gas source 42 in the fuel gas passage 41, and then supplied to the fuel cell 20 for reuse.

  Further, an exhaust passage 61 for exhausting the fuel off-gas exhausted from the fuel gas circulation system to the outside of the vehicle via a diluter (for example, a hydrogen concentration reducing device) 62 is branched and connected to the circulation passage 51. ing. An exhaust valve (exhaust means) 63 is installed in the exhaust flow path 61, and is configured to perform exhaust control of the fuel off gas. By opening and closing the exhaust valve 63, it is possible to repeatedly circulate in the fuel cell 20, discharge the fuel off-gas having increased impurity concentration to the outside, and introduce new fuel gas to prevent the cell voltage from decreasing. . It is also possible to remove the water accumulated in the gas flow path by causing a pulsation in the internal pressure of the circulation flow path 51.

  On the other hand, the oxidizing gas supply device 73 of the fuel cell system 10 includes an oxidizing gas passage 71 for supplying oxidizing gas to the cathode gas channel 26 and a cathode for exhausting cathode off-gas exhausted from the cathode gas channel 26. An off gas passage 72 is piped. The oxidizing gas flow path 71 includes an air filter 74 that removes dust and the like contained in air taken from the atmosphere, an air compressor 75 that is driven by a motor, and the like.

  In addition, in the humidifier 76 disposed downstream of the oxidizing gas supply device 73, the cathode off gas that has become highly wet by the generated water generated by the cell reaction of the fuel cell 20, and the low wet humidity oxidizing gas that has been taken in from the atmosphere. Moisture exchange takes place between the two. The back pressure of the cathode gas channel 26 is adjusted to a substantially constant pressure by a pressure regulating valve 77 installed in the cathode off gas flow path 72. The cathode off gas flowing through the cathode off gas flow path 72 is exhausted to the outside of the vehicle via a gas-liquid separator 78 and a muffler 79 according to the design, and part of the cathode off gas flows into the diluter 62 and stays in the diluter 62. The fuel off gas is mixed and diluted and exhausted outside the vehicle.

  The control unit 80 is configured using, for example, a microcomputer, and monitors the state of the fuel cell 20 to determine whether or not the fuel cell 20 is in the scavenging operation mode, and the three-way valve 55 is determined according to the determination result. Controls the switching of the path to. Further, the control unit 80 receives sensor signals from the temperature sensor T and the pressure sensor P installed in each flow path, and drives each motor according to the state of battery operation, for example, the electric power load, and the circulation pump 59 and the air. The number of rotations of the compressor 74 is adjusted, and various valve opening / closing controls or valve opening adjustments are performed.

(Description of operation)
Next, the operation of this embodiment will be described with reference to the flowchart of FIG.
First, the control unit 80 determines whether or not it is a scavenging process as a process to be periodically performed (S1). That is, the control unit 80 monitors the operating state of the fuel cell 20, determines whether or not the fuel cell 20 is in the scavenging operation mode, and the fuel cell 20 operates in an operation mode other than the scavenging operation mode, for example, normal power generation operation. In the mode, the bypass path 56 is closed to the three-way valve 55, and a control signal for selecting the pipe 54 as the path is output (S2). When the pipe 54 is selected as a route, as a normal power generation mode, the fuel off-gas discharged from the shutoff valve 52 is supplied to the gas-liquid separator 53 via the three-way valve 55 and the pipe 54, and the moisture is removed. Collected. In this normal invention mode, the fuel off-gas is not particularly cooled, so that the water droplets as excess water are discharged through the gas-liquid separator 58, but the vaporized water is not removed. Circulates through the circulation channel 51. For this reason, the electrolyte membrane in the anode gas channel 25 of the fuel cell 20 is not excessively dried.

  On the other hand, when the fuel cell 20 is in the scavenging operation mode, the control unit 80 outputs a control signal for selecting the bypass path 56 to the three-way valve 55 instead of the pipe 54 (S3). At this time, the control unit 80 performs control for driving the cooling water pump 35 (S4). At this time, the fuel off-gas discharged from the shutoff valve 52 is introduced from the three-way valve 55 into the heat exchanger 57 via the bypass path 56. Then, the cooling water is circulated to the heat exchanger 57 by driving the cooling water pump 35, and as a result of taking heat away from the fuel off-gas flowing through the bypass path 56, moisture is condensed and discharged through the gas-liquid separator 58. Will be.

  According to the first embodiment, since more water is recovered from the fuel off-gas whose temperature has decreased due to heat exchange compared to the normal operation mode, the humidity removal capability in the circulation channel 51 is normally increased in the scavenging operation mode. It can be higher than in the power generation mode.

(Second embodiment)
Next, a second embodiment of the present invention will be described with reference to FIG.
In this embodiment, a quick cooler 64 is provided instead of the heat exchanger 57, and the quick cooler 64 is driven using a power source (not shown). Is the same as

Next, the operation of the second embodiment will be described with reference to the flowchart of FIG.
First, the control unit 80 determines whether or not it is a scavenging process as a process to be performed periodically (S11). That is, the control unit 80 monitors the operating state of the fuel cell 20, determines whether or not the fuel cell 20 is in the scavenging operation mode, and the fuel cell 20 operates in an operation mode other than the scavenging operation mode, for example, normal power generation operation. In the mode, the bypass path 56 is closed to the three-way valve 55, and a control signal for selecting the pipe 54 as the path is output (S12). When the pipe 54 is selected as a route, as a normal power generation mode, the fuel off-gas discharged from the shutoff valve 52 is supplied to the gas-liquid separator 53 via the three-way valve 55 and the pipe 54, and the moisture is removed. Collected.

  On the other hand, when the fuel cell 20 is in the scavenging operation mode, the control unit 80 outputs a control signal for selecting the bypass path 56 to the three-way valve 55 instead of the pipe 54 (S13). At this time, the control unit 80 performs control for driving the rapid cooler 64 (S14). At this time, the fuel off-gas discharged from the shutoff valve 52 is introduced from the three-way valve 55 through the bypass path 56 to the rapid cooler 64 and rapidly cooled by the rapid cooler 64. The fuel off-gas whose temperature has been lowered by the rapid cooling by the rapid cooler 64 is sent to the gas-liquid separator 53, and its moisture is recovered.

  According to the second embodiment, the rapid cooler 64 is used instead of the heat exchanger of the first embodiment. Since the rapid cooler 64 has a higher cooling capacity than the heat exchanger, the humidity removal capacity in the circulation passage 51 is much higher in the scavenging operation mode than in the normal power generation mode. be able to.

(Modification)
The present invention is not limited to the above-described embodiments, and can be variously modified and applied, for example, by combining the configurations of the first embodiment and the second embodiment.

  For example, in the first embodiment, the heat exchanger 57 is provided in the bypass path 56, but the bypass path 56 is removed, the heat exchanger 57 is inserted into the three-way valve 55, and the open / close valve in the pipe 37. In the normal power generation mode, the on-off valve in the pipe 37 is closed, and the fuel off-gas discharged from the shut-off valve 52 is directly supplied to the gas-liquid separator 53. In the scavenging operation mode, the on-off valve in the pipe 37 is provided. The cooling water is introduced into the heat exchanger 57, the fuel off-gas discharged from the shut-off valve 52 is cooled by the heat exchanger 57, and the cooled fuel off-gas is supplied to the gas-liquid separator 53. You can also

  In the second embodiment, the quick cooler 64 is provided in the bypass path 56. However, the bypass path 56 is removed and the quick cooler 64 is inserted into the three-way valve 54. The operation of the cooler 64 is stopped, and the fuel off-gas discharged from the shut-off valve 52 is supplied to the gas-liquid separator 53 as it is. On the other hand, in the scavenging operation mode, the quick cooler 64 is driven and discharged from the shut-off valve 52. It is also possible to adopt a configuration in which the fuel offgas is cooled by the rapid cooler 64 and the cooled fuel offgas is supplied to the gas-liquid separator 53.

It is a block diagram centering on the piping system of the fuel cell system in 1st Example of this embodiment. It is a flowchart for demonstrating the effect | action of the fuel cell system in 1st Example. It is a principal lineblock diagram of the fuel cell system of this embodiment. It is a block diagram centering on the piping system of the fuel cell system in 2nd Example of this embodiment. It is a flowchart for demonstrating the effect | action of 2nd Example.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Fuel cell system, 20 Fuel cell, 31 Cooling furnace, 35 Cooling water pump, 41 Fuel gas flow path, 51 Circulation flow path, 53 Gas-liquid separator, 54 Piping, 56 Bypass path, 57 Heat exchanger, 59 Circulation pump 64 Quick cooler 55 Three-way valve 80 Control unit

Claims (5)

A fuel cell system for removing moisture from fuel off-gas exhausted from a fuel cell,
A fuel cell system characterized in that when the fuel cell is in a scavenging operation mode, the humidity removal capability can be increased more than when the fuel cell is in an operation mode other than the scavenging operation mode. The fuel cell system according to claim 1, wherein
Piping for distributing fuel off-gas exhausted from the fuel cell;
A bypass path having both ends connected to the pipe;
A cooling device provided in the bypass path;
A fuel cell system, comprising: a path switching unit provided at an upstream connection part of the two connection parts between the pipe and the bypass path. The fuel cell system according to claim 2, wherein
The fuel cell system according to claim 1, wherein the path switcher is switched so that the fuel off-gas flows through the bypass path when the fuel cell is in a scavenging operation mode. The fuel cell system according to claim 2, wherein
The cooling device is a heat exchanger in which a coolant of the fuel cell circulates, and the coolant is forcibly circulated when the cooling device is driven. The fuel cell system according to claim 2, wherein
The fuel cell system, wherein the cooling device is a rapid cooler.

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