JP2006252919A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system with little energy loss capable of detecting abnormality thereof with high accuracy. <P>SOLUTION: The fuel cell system is composed of a fuel cell stack 2; an off-gas exhaust pipe 5 connected to the fuel cell stack 2; a hydrogen detection means 9 having a hygroscopic exothermal body 14 arranged on the off-gas exhaust tube 5; a ventilation gas exhaust tube 6 connected to the fuel cell stack 2; a ventilation gas supplying piping 7 branched from the ventilation gas exhaust tube 6, passing through the hygroscopic exothermal body 14 of the hydrogen detection means 9, and connected to the off-gas exhaust pipe 5; and a flow passage control device (a valve 8) arranged on the ventilation gas supplying piping 7 at upstream side of the hydrogen detection means 9. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fuel cell system capable of monitoring an abnormality during power generation.

  A fuel cell is a device that generates power by reacting hydrogen gas and oxygen gas using hydrogen gas as fuel, has high power generation efficiency, and is low in pollution. For this reason, research and development of a vehicle equipped with a fuel cell as a power source for a motor that operates in place of an internal combustion engine is underway. As a fuel cell for vehicle mounting, since high output and miniaturization are required, the application of a polymer electrolyte fuel cell has been particularly studied.

  A polymer electrolyte fuel cell is composed of a fuel cell stack in which a plurality of unit cells (single cells) serving as basic units for power generation are stacked. A single cell is formed by arranging a fuel electrode and an oxidant electrode on both sides of a solid polymer electrolyte membrane to constitute a membrane electrode assembly (MEA), and arranging separators on both sides of each electrode.

  In the polymer electrolyte fuel cell, hydrogen gas and air containing oxygen gas are respectively introduced from the gas flow path formed in the separator, and the chemical reaction shown in Chemical Formula 1 and Chemical Formula 2 proceeds in the fuel electrode and the oxidant electrode. I am letting.

H ₂ → 2H ⁺ + 2e ⁻ (fuel electrode side) (Chemical formula 1)
1 / 2O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O + Q (heat of reaction) (oxidant electrode side) (Chemical formula 2)
As a whole battery, a chemical reaction shown in Chemical Formula 3 proceeds, an electromotive force is generated, and electrical work is performed on an external load.
H ₂ + 1 / 2O ₂ → H ₂ O + Q (heat of reaction) (Chemical formula 3)
A solid polymer electrolyte membrane is formed of a polymer material into which a large number of proton exchange groups (for example, sulfonic acid groups) are introduced. The solid polymer electrolyte membrane is in a wet state and conducts protons using proton exchange groups. I am letting. If a portion of the solid polymer electrolyte membrane becomes insufficient in water content, the solid polymer electrolyte membrane is damaged, hydrogen gas passes through the damaged portion, and hydrogen gas is contained in the offgas in the offgas exhaust pipe discharged from the fuel cell stack. Will be mixed. For this reason, hydrogen detection means is installed in the off-gas exhaust pipe to detect the hydrogen gas mixed in the off-gas and monitor the abnormality of the fuel cell system.

  However, the off gas contains moisture such as generated water and humidified water, and the hydrogen detection means is exposed to the gas containing moisture. For this reason, condensation is likely to occur in the hydrogen detection means, the detection accuracy of the hydrogen detection means is lowered, and the hydrogen detection means is damaged or deteriorated.

Therefore, a technology of a fuel cell system in which a heater for heating off gas is installed adjacent to the upstream side of the hydrogen detection means is disclosed (see Patent Document 1). According to this fuel cell system, by heating off-gas with a heater, the occurrence of dew condensation in the hydrogen detection means is prevented, and the detection accuracy of the hydrogen detection means is lowered, and further, damage and deterioration of the hydrogen detection means are suppressed. .
JP 2004-69436 A

  However, in the conventional fuel cell system, since a heater for heating off-gas is installed, not only a heater installation space is required, but also electric energy is indispensable.

  In addition, in the conventional fuel cell system, it is necessary to always heat the fuel cell system even during operation. Therefore, when the electric energy during the stoppage of the fuel cell system cannot be used, it is possible to prevent the hydrogen detection means from causing condensation. I couldn't.

  Furthermore, energy is consumed to heat off-gas, which is disadvantageous from the viewpoint of energy efficiency of the entire fuel cell system.

  The present invention has been made to solve the above-described problems. That is, the fuel cell system of the present invention is installed in a fuel cell stack, an offgas exhaust pipe connected to the fuel cell stack, and an offgas exhaust pipe. Hydrogen detection means having a moisture absorption heating element, a ventilation gas exhaust pipe connected to the fuel electric stack, and a branching connection from the ventilation gas exhaust pipe, passing through the moisture absorption heating element of the hydrogen detection means, and off-gas exhaust The gist is to include a ventilation gas supply pipe connected to the pipe, and a flow path control device installed in the ventilation gas supply pipe upstream of the hydrogen detection means.

  According to the present invention, it is possible to detect a fuel cell system abnormality with high accuracy by suppressing deterioration, breakage, and deterioration of detection accuracy due to the occurrence of dew condensation in the hydrogen detection means, and further, a fuel cell with less energy loss. A system can be provided.

  Hereinafter, a fuel cell system according to an embodiment of the present invention will be described with reference to the accompanying drawings.

First Embodiment FIG. 1 shows the configuration of a fuel cell system according to an embodiment of the present invention. The fuel cell system 1 includes a fuel cell stack 2 in which a plurality of single cells each having a solid polymer electrolyte membrane sandwiched between an anode and a cathode are stacked. Connected to the fuel cell stack 2 are a hydrogen gas supply pipe 3 and an air supply pipe 4 for supplying hydrogen gas a serving as fuel and air b containing oxygen gas, respectively. An off-gas exhaust pipe 5 to be discharged is connected. A ventilation gas pipe 6 for discharging a ventilation gas d for ventilating a fuel cell case (not shown) that houses the fuel cell stack 2 is connected, and the ventilation gas pipe 6 is connected to an off-gas exhaust pipe 5.

  A ventilation gas supply pipe 7 is branched and connected to the ventilation gas pipe 6. The ventilation gas supply pipe 7 is provided with a valve 8 which is a flow path control device, and is connected to the off-gas exhaust pipe 5. The off-gas exhaust pipe 5 is provided with hydrogen detection means 9, for example, a catalytic catalyst type hydrogen detector can be cited as the hydrogen detection means 9.

  A cross-sectional structure of the hydrogen detection means 9 is shown in FIG. The hydrogen detection means 9 is provided with a catalytic catalytic hydrogen detection unit 11 at the upper part of the frame body 10, and has a detection port 12 at the lower part of the frame body 10. . A hygroscopic heating element 14 is disposed between the hydrogen detection unit 11 and the detection port 12 in the frame 10. A ventilation gas introduction pipe 15 and a ventilation gas discharge pipe 16 are connected to both ends in the longitudinal direction of the frame body 10 so that the ventilation gas d from the ventilation gas introduction pipe 15 flows through the hygroscopic heating element 14. . Further, the ventilation gas introduction pipe 15 and the exhaust gas discharge pipe 16 are respectively connected to the ventilation gas supply pipe 7.

  As the hygroscopic heating element 14, it is preferable to use a hygroscopic exothermic fiber that can be regenerated by applying heat. This moisture-absorbing heat-generating fiber generates heat by absorbing moisture, and conversely has a property of releasing moisture and returning to its original state in a dry environment. In addition to the heat of condensation of water vapor released when natural fibers such as wool and cotton absorb moisture (heat in the direction opposite to the heat of evaporation), the heat generated during moisture absorption is caused by heat of hydration due to moisture absorption by the hydrophilic device. It is considered that the total calorific value reaches several times the heat of aggregation. This hydrophilic group is provided in the fiber material itself, and is formed by chemically treating the surface of the fiber. The hygroscopic exothermic fibers are those sold by each textile company. For example, Breath Thermo (trade name) jointly developed by Mizuno Co., Ltd. and Toyobo Co., Ltd., Moiscare (trade name) manufactured by Toyobo Co., Ltd., Eco Worm (trade name) manufactured by Fuji Boseki Co., Ltd., Luneth (trade name) manufactured by Mitsubishi Rayon Co., Ltd., and Worm Sensor (trade name) manufactured by Toray Industries, Inc. can be used.

  Further, as shown in FIG. 1, a temperature sensor 17 for detecting heat generation of the hygroscopic heating element 14 is connected to the hydrogen detection means 9, and the valve 8 is opened and closed by the output of the temperature sensor 17. An electronic control unit 18 for transmitting the control signal is connected. A humidity sensor 19 is provided in the offgas exhaust pipe 5. In addition, the temperature sensor 17 should just be a place which can measure the temperature change of the moisture absorption heat generating body 14, and the position of the temperature sensor 17 is not limited. Similarly, the humidity sensor 19 may be any place where the humidity of the gas to be detected can be measured, and the position of the humidity sensor is not limited.

  In the fuel cell system 1, the offgas c flowing in the offgas exhaust pipe 5 flows from the detection port 12 of the hydrogen detection means 9, and the waterdrops are removed by the waterdrop removal film 13. When the humidity of the offgas c flowing from the detection port 12 is high, moisture in the offgas c is absorbed by the hygroscopic heating element 14 to reach the hydrogen detection unit 11, thereby preventing condensation at the hydrogen detection unit 11. Can do. Further, the moisture-absorbing heating element 14 generates heat during moisture absorption. By using this heat generation for heating the hydrogen detection means 9, it is difficult for condensation to occur in the hydrogen detection unit 11.

  In the fuel cell system 1, the moisture absorption state of the moisture absorption heating element 14 is always based on the relationship between the temperature change of the moisture absorption heating element 14 measured from the temperature sensor 17 and the humidity in the offgas c measured from the hygrometer 19. Is being monitored. Then, the temperature of the hygroscopic heating element 14 measured from the temperature sensor 17 decreases, the humidity in the offgas c measured from the hygrometer 19 increases, and the hygroscopic heating element 14 reaches a saturated state by the electronic control unit 18. If it is determined, the control signal is transmitted from the electronic control unit 18 to the valve 8 to open the valve 8. When the valve 8 is opened, the ventilation gas d is introduced into the hydrogen detection means 9 from the ventilation gas supply pipe 7 via the ventilation gas introduction pipe 15. The ventilation gas d introduced into the hydrogen detection means 9 dries the moisture-absorbing heating element 14, and at the same time, drys the gas around the hydrogen detection unit 11 and replaces it with a high-temperature gas, thereby condensing in the hydrogen detection unit 11. Is prevented.

  After introducing the ventilation gas d into the hydrogen detection means 9 and drying the hygroscopic heating element 14 for a certain period of time, a control signal is transmitted from the electronic control unit 18 to the valve 8 and the valve 8 is closed to introduce the ventilation gas d. Stop. It should be noted that the moisture-absorbing heating element 14 may be dried at regular intervals, thereby omitting the sensors. Further, by detecting a change in the weight of the hygroscopic heating element 14, it is possible to optimally determine the timing for drying the hygroscopic heating element 14 and the drying time.

  The fuel cell system of the present invention is not limited to the configuration of the fuel cell system 1 shown in FIG. 1, and the ventilation gas d flowing through the ventilation gas pipe 6 is supplied from, for example, the air supply pipe 4 supplied to the cathode side. A line may be provided which is branched and supplied into the fuel cell case, or a line for supplying ventilation gas d such as air to the fuel cell case.

  According to the present embodiment, moisture in the gas to be detected (off gas c or ventilation gas d) is adsorbed by the hygroscopic heating element 14 in the hydrogen detection means 9, and hydrogen is detected by the heat generation of the hygroscopic heating element 14. The means 9 is heated to reduce the humidity in the gas to be detected due to the moisture absorption effect. For this reason, generation | occurrence | production of the dew condensation in the hydrogen detection part 11 of the hydrogen detection means 9 can be prevented, and the fall of detection accuracy of the hydrogen detection means 9 accompanying a generation | occurrence | production of dew condensation, damage, and deterioration can be suppressed. As a result, the hydrogen gas concentration in the off-gas c or the ventilation gas d can be detected to diagnose the leaked portion of the hydrogen gas a, and abnormalities during power generation can be monitored with high accuracy.

  In addition, according to the present embodiment, it is possible to selectively switch between the off-gas c and the ventilation gas d, which are the gases to be detected, which are installed in the hydrogen detection means 9 by installing the valve 8 which is a flow path control device. . For this reason, it is possible to detect single gas, either off-gas c or ventilation gas d.

  Furthermore, according to the present embodiment, the state of the hygroscopic heating element 14 is monitored by the output of the temperature sensor 17 connected to the hydrogen detection means 9, and when the hygroscopic heating element 14 is in a non-hygroscopic state, the high temperature, low Since the humidity ventilation gas can be supplied to the hydrogen detection means 9, it is possible to reliably prevent the occurrence of dew condensation in the hydrogen detection means 9 even if the limit amount of the moisture absorption heating element 14 is reached and moisture absorption becomes impossible. it can. Further, the hygroscopic heating element 14 can be repeatedly used by introducing a high-temperature, low-humidity ventilation gas d into the hydrogen detection means 9 and drying the hygroscopic heating element 14 after moisture absorption.

  Further, even when a high-humidity gas to be detected flows through the hydrogen detection means 9 when the system is stopped, the amount of moisture absorbed by the moisture-absorbing heating element 14 varies depending on the relative humidity, and thus automatically absorbs and generates heat. Even in a state where electric energy cannot be used such as when the fuel cell system is stopped, there is an effect of preventing the occurrence of dew condensation in the hydrogen detecting means 9.

Second Embodiment A fuel cell system according to a second embodiment of the present invention is to reduce the humidity of the offgas c in the offgas exhaust pipe before stopping the fuel cell system. Since the basic configuration of the fuel cell system according to the present embodiment is the same as that of the fuel cell system 1 shown in the first embodiment, the same portions are denoted by the same reference numerals and the description thereof is omitted.

  FIG. 3 shows the configuration of the fuel cell system 20 according to the second embodiment of the present invention. In the fuel cell system 20, a valve 21 as a first flow path control device is installed in the ventilation gas pipe 6 before the ventilation gas supply pipe 7 branches from the ventilation gas pipe 6. Further, a valve that is a second flow path control device is provided in the off-gas exhaust pipe 5 between the junction of the ventilation gas pipe 6 and the off-gas exhaust pipe 5 and the junction of the ventilation gas supply pipe 7 and the off-gas exhaust pipe 5. 22 is installed. Further, the two valves 21 and 22 are connected to the electronic control unit 18.

  In the fuel cell system 20, before stopping the fuel cell system 20, a control signal is transmitted from the electronic control device 18 so that the valve 8 is opened and the valves 21 and 22 are closed. Then, off-gas c discharged from the fuel cell stack 2 is introduced from the upstream of the off-gas exhaust pipe 5 into the hydrogen detection means 9 via the ventilation gas supply pipe 7 and forcibly passes through the hygroscopic heating element 14. . When the off gas c passes through the hygroscopic heating element 14, the moisture in the off gas c is absorbed, so that the humidity of the off gas c flowing in the off gas exhaust pipe 5 is lowered. Thereafter, a control signal is transmitted from the electronic control unit 18 so that the valve 8 is closed. Then, the high-humidity off gas c discharged from the fuel cell stack 2 can be prevented from flowing into the hydrogen detection means 9.

  Therefore, according to the present embodiment, when the fuel cell system 20 is stopped, the off-gas c in the vicinity of the hydrogen detection means 9 can be kept in a low humidity state, and the occurrence of condensation in the hydrogen detection means 9 is prevented. be able to.

  The drying method of the hygroscopic heating element 14 is the same as that of the first embodiment. By omitting the temperature sensor 17 and the humidity sensor 19 and detecting a change in the weight of the hygroscopic heating element 14, the drying process is performed. The timing and drying time can also be determined optimally.

Other Embodiments As an improved example of the first embodiment, the valve 8 which is a normal flow path control device is opened, and a ventilation gas having a relatively low hydrogen concentration is allowed to flow into the hydrogen detection means 9. And when detecting the offgas in the offgas exhaust pipe 5, the valve 8 which is a flow path control device is closed. In this case, the pipe diameter of the ventilation gas pipe 6 may be smaller than the pipe diameter of the ventilation gas supply pipe 7. In addition, when a three-way valve is installed in the branch path with the bypass path instead of the valve 8 as the flow path control device, it is not necessary to define the size of the pipe diameter.

  According to the present embodiment, the life of the hydrogen detection means 9 can be extended by allowing the ventilation gas d having a relatively low hydrogen concentration to flow into the hydrogen detection means 9. This improved example can also be applied to the second embodiment.

It is a figure which shows the structure of the fuel cell system which concerns on 1st Embodiment in this invention. It is sectional drawing which shows the internal structure of the hydrogen detection means shown in FIG. It is a figure which shows the structure of the fuel cell system which concerns on 2nd Embodiment in this invention.

Explanation of symbols

1 ... Fuel cell system,
2 ... Fuel cell stack,
3 ... Hydrogen gas supply piping,
4 ... Air supply piping,
5 ... Off-gas exhaust pipe,
6… Ventilation gas piping,
7… Ventilation gas supply piping,
8 ... Valve (flow path control device),
9 ... Hydrogen detection means,
17 ... temperature sensor,
18 ... Electronic control unit,
19 ... Hygrometer,
a… hydrogen gas,
b… Air,
c ... off gas,
d… Ventilation gas,

Claims (5)

A fuel cell stack;
An off-gas exhaust pipe connected to the fuel cell stack;
Hydrogen detection means having a hygroscopic heating element installed in the off-gas exhaust pipe;
A ventilation gas exhaust pipe connected to the fuel electric stack;
A ventilation gas supply pipe branched from the ventilation gas exhaust pipe and connected to the off-gas exhaust pipe through the hygroscopic heating element of the hydrogen detection means;
A flow path control device installed in the ventilation gas supply pipe upstream of the hydrogen detection means;
A fuel cell system comprising: Furthermore, a first flow path control device installed in the ventilation gas exhaust pipe on the downstream side of the fuel cell stack,
A second flow path control device installed in the off-gas exhaust pipe upstream of the hydrogen detection means;
The fuel cell system according to claim 1, further comprising:   The hydrogen detection means is arranged between a frame, a hydrogen detection unit installed at the upper part of the frame, a detection port arranged at the lower part of the frame, and between the hydrogen detection unit and the detection port. A moisture absorption heating element that can be regenerated by applying heat, and a ventilation gas introduction pipe that supplies a ventilation gas connected to the ventilation gas supply pipe to the inside of the frame. The fuel cell system described. Further, a temperature sensor connected to the hydrogen detection means and detecting heat generation of the hygroscopic heating element,
An electronic control unit for transmitting a signal for controlling the opening and closing of the flow path control unit based on information from the temperature sensor;
The fuel cell system according to any one of claims 1 to 3, further comprising:   The fuel cell system according to any one of claims 1 to 4, further comprising a humidity sensor that measures the humidity of the offgas installed in the offgas exhaust pipe.

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