JP2002015761A - Heat insulation device for fuel cell stack - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat insulation device for a fuel cell stack in which heat insulation control is safely done and, when the thermostat is in abnormal state by adhering to the conducting state to the heater, the emergency of the restoration work is reduced at its discovery and further, its adherence state can be easily and safely discovered. SOLUTION: At least one electric heater 54 and at least two thermostats 55 are connected in series at the prescribed position at the periphery 51 of the fuel cell stack between the outside power source 53. A detection circuit 58 for detecting the abnormality of the thermostat is led from the connection point 57 provided at the position interposed by the adjoining two thermostats. And the terminal 59 at the terminal end of the detecting circuit is grounded. Further, for example, a differential voltage detector 100 which is connected in series with a light emitting diode that is illuminated by micro current and a current limiting resister is provided in the detecting circuit 58.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat retaining device for a fuel cell stack, and more particularly to a heat retaining device provided with an electric heater and a thermostat for a phosphoric acid type fuel cell.

[0002]

2. Description of the Related Art A raw fuel gas mainly containing a hydrocarbon such as city gas or LPG is reformed into a hydrogen-rich fuel gas by steam, and the reformed fuel gas and oxidant gas (for example, air) A fuel cell power generator is known which continuously supplies the fuel electrode and the oxidizer electrode with each other to electrochemically convert the energy of the fuel into electric energy. Such a fuel cell power generator generally has a structure as shown in FIG. System is adopted.

FIG. 6 shows an example of a schematic system diagram of a conventional fuel cell power generator.
Is a cell having a fuel electrode 21 and an oxidant electrode 22
The fuel cell stack is formed by laminating cooling plates through which cooling water flows each time eight fuel cells are stacked, and a fuel gas and an oxidizing gas are supplied to the fuel electrode 21 and the oxidizing electrode 22, respectively, to generate power. . In FIG. 4, the fuel gas is supplied from the reformer 4 through the CO converter 5 to reduce the CO concentration.

[0004] Since the fuel cell generates heat with power generation, cooling is required during power generation, and its cooling water 40 is supplied to the steam separator 7.
Is supplied to the fuel cell body 20 via the pump 50 and the heat exchanger 30. The temperature of the cooling water is usually about 160 ° C. during the operation of the fuel cell, flows in the state of pressurized water, and is separated into gas and liquid by the steam separator 7. The water that has flowed out of the steam separator 7 cools the fuel cell body 20 after the temperature of the cooling water is controlled by the heat exchanger 30, and is returned to the steam separator 7.

[0005] The vapor separated by the steam separator 7 is
The raw fuel (gas) is introduced into the ejector 3 through the steam pipe 9, and is sucked from the raw fuel supply line 8 by the ejector suction force of the steam flow, and a mixture of the raw fuel and the steam is introduced into the reformer 4. The raw fuel is reformed into a hydrogen-rich gas by a reforming reaction in a reformer.

[0006] The raw fuel supply line 8 is provided with a raw fuel supply source 15.
A fuel and gas shutoff valve 10, a raw fuel control valve 1, and a desulfurizer 2 are provided between the fuel and the ejector 3, and the fuel (gas) supply amount is adjusted by the raw fuel control valve 1 according to the load of the fuel cell. .
Raw fuel such as city gas contains a sulfur component as a deodorant, and therefore a desulfurizer 2 is provided to remove the sulfur component.

[0007] A part of the raw fuel is supplied to the auxiliary combustion gas supply line 14.
Is also supplied to the reformer 4. Auxiliary gas supply line 14
The fuel supply line 8 branches from the raw fuel cutoff valve 10 and the raw fuel control valve 1 in the raw fuel supply line 8 and includes an auxiliary gas shutoff valve 13. Since the reaction of the reformer 4 is an endothermic reaction, heat needs to be supplied. This heat is mainly provided by off-gas combustion of fuel gas not consumed in the power generation reaction in the fuel cell. At the time of startup, auxiliary fuel is required, and the auxiliary combustion gas is used as the auxiliary fuel.

When the fuel cell is started, the cooling water is heated in the heat exchanger 30 by a heater or a boiler (not shown), the temperature is gradually increased, and after reaching a predetermined temperature, the operation is shifted to a steady operation.

Incidentally, the above-described fuel cell power generator usually includes a heat retaining device for the fuel cell stack in order to prevent phosphoric acid freezing particularly in the case of a phosphoric acid type fuel cell.

In a phosphoric acid type fuel cell, phosphoric acid as an electrolyte freezes during the period when the operation of the fuel cell is stopped, for example, during construction or maintenance of the power generator or peripheral equipment, or during transportation of the power generator. In order to prevent accidents such as breakage of the porous matrix holding phosphoric acid due to volume expansion, various measures for preventing freezing of phosphoric acid are employed as follows. 1) An electric heater is provided on the upper and lower fastening members and the manifold of the fuel cell stack, and a current is supplied from an external power supply to prevent the temperature of the fuel cell stack from lowering. 2) The cooling water of the fuel cell is heated and circulated to prevent the temperature of the cell stack from lowering. For heating and circulation of the cooling water, a boiler, a pump, etc. of a power generation device are used. 3) When the fuel cell is stopped, the phosphoric acid is humidified so that it does not freeze even when the temperature drops to the ambient temperature. 4) Warm air is blown around the fuel cell stack to heat it from the surroundings.

[0011] Of the above methods, the heat retention method using an electric heater of 1) is relatively frequently adopted because of its simple structure and handling. In this case, the electric heater is turned on / off by a thermocouple or a thermostat so that the fuel cell stack is kept at an appropriate temperature. A heat insulating device that performs control using a thermostat is suitable as a heat insulating device for a fuel cell stack because it is small and inexpensive.

[0012]

However, in the heat retention device using the electric heater and the thermostat,
There are the following problems. An abnormal state may occur in which the thermostat is stuck in a state where the power supply to the heater is maintained, and if the fuel cell power generation device is stopped without knowing the abnormal state, the fuel cell stack temperature becomes a predetermined heat retaining temperature set value. Even if the temperature exceeds the limit, the electric heater remains turned on, and there is a danger of causing a heating accident or a burning accident of surrounding structures.

In order to prevent this accident, it is sufficient to confirm that the electric heater does not operate during the operation of the fuel cell in which the temperature of the fuel cell stack is high, and that the thermostat is not stuck. However, when the fuel cell stack is found to be stuck, the power supply to the electric heater of the fuel cell stack must be stopped when stopping the fuel cell power generator. As a result, the fuel cell stack is in a state without heat retention, and therefore, it is necessary to immediately start a recovery operation and complete the operation. Also, in order to check the operation of the electric heater during the operation of the power generator, it is necessary to measure the current of the electric heater, but if an ammeter is installed, it can be easily and safely checked. Become. A portable ammeter can be checked at a low cost, but it involves danger because the generator must be close to the live part of the electric heater power supply circuit during operation.

SUMMARY OF THE INVENTION The present invention has been made to solve these problems, and an object of the present invention is to provide a thermostat in which the temperature is safely adjusted and the thermostat is fixed in a state of maintaining the power supply to the heater. It is an object of the present invention to provide a fuel cell stack heat insulating device that can reduce the urgency of recovering the device when it is found even if it is in an abnormal state, and that can easily and safely detect the stuck state.

[0015]

In order to solve the above-mentioned problems, according to the present invention, there is provided a heat retaining apparatus provided for keeping a temperature of a fuel cell stack during a stop period of a fuel cell and provided with an electric heater and a thermostat. , At least one electric heater and at least two thermostats are connected in series between external power supplies, and a thermostat abnormality is detected from a connection point provided at a position sandwiched between two adjacent thermostats. (The invention of claim 1).

According to an embodiment of the first aspect of the present invention,
It is preferable to configure as in the invention of claim 2 or 3. That is, in the thermal insulation device according to the first aspect, the detection circuit is grounded, and a differential voltage detector is provided between the connection point and the ground point (the invention of the second aspect). . Further, in the thermal insulation device according to the second aspect, the differential voltage detector is configured by connecting a light emitting diode lit by a small current and a current limiting resistor in series (the invention of the third aspect).

With the above arrangement, the electric heater is not energized unless two thermostats are closed at the same time. Therefore, even if one of the thermostats is fixed, if the two are not fixed at the same time, the energization of the electric heater and the heat retention control are performed safely. If there are more than two thermostats, the safety is further improved.

If one of the thermostats is fixed, the voltage of the heater power supply is supplied to a connection point sandwiched between the thermostats, and a voltage difference from the ground potential is generated.
This difference voltage can be easily and safely confirmed even during operation of the power generator by measuring a difference voltage between a detection circuit terminal provided on an electric board or the like and a ground potential. Furthermore, if the difference voltage detector is formed by connecting a light emitting diode that emits light with a small current and a current limiting resistor in series, the lighting of the light emitting diode makes it easier for the naked eye. Thermostat abnormality can be determined.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a system diagram of a heat retaining device for a fuel cell stack according to an embodiment of the present invention. In FIG.
Two electric heaters 54 connected to a power supply 53 are provided at predetermined positions in the periphery 51 of the fuel cell stack, and are configured to keep the temperature of the fuel cell stack. In addition, the above 2
Two thermostats 55 are provided corresponding to the two electric heaters 54, respectively.
The detection circuit 58 is drawn out from the intermediate circuit 56 sandwiched between 5 to a safe position, for example, the electric board 52. The detection circuit 58 is insulated up to the terminal 59 from the ground potential. A terminal block or a connector is installed on the terminal 59 of the terminal. By detecting the difference voltage between the terminal 59 and the ground potential,
An abnormal fixation of the thermostat 55 can be detected.

FIG. 2 shows an embodiment according to the second aspect of the present invention. 2, the same members as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted. 2 differs from FIG. 1 in that the detection circuit 58 is connected to a ground potential 110 via a differential voltage detector 100. In the above, the current flowing through the differential voltage detector 100 needs to be suppressed to a very small current that does not lead to a ground fault.

FIG. 3 shows an embodiment according to the third aspect of the present invention. 3, the same members as those in FIG. 2 are denoted by the same reference numerals, and description thereof will be omitted. In FIG. 3, the differential voltage detector 1
00 is a light emitting diode 120 and a current limiting resistor 130 connected in series, and is arranged in the detection circuit 58.
Thus, the fixation abnormality of the thermostat 55 can be easily determined by the naked eye by turning on the light emitting diode.

FIGS. 4 and 5 show another embodiment of the present invention which is different from FIG. The difference between FIGS. 4 and 5 and FIG. 1 is the number of heaters, and FIG. 4 or FIG.
The heater 54 is placed at the upper side of the drawing with the connection point 57 as a boundary.
An example in which one or one is provided on the lower side is shown.

If both thermostats on both sides of the connection point 57 are sound, the connection point 57 and the terminal 59
The circuit voltage of the external power supply 53 is not applied and no voltage is applied. However, if one of the thermostats is fixed, the voltage of one pole of the external power supply is applied. Can be detected. Therefore, according to the embodiment of FIG. 4 or FIG. 5, it is possible to detect a thermostat abnormality.

However, the thermostat that caused the abnormality is
If it is connected to the ground potential side of the external power supply 53, it may not be detected, so the type of the external power supply needs to be confirmed. Normally, since one phase of the three-phase power supply is used, both poles of the heater power supply are different from the ground potential,
Detection is possible.

[0026]

As described above, according to the present invention, at least one of the heat retaining devices provided for retaining the temperature of the fuel cell stack during the stop period of the fuel cell and including the electric heater and the thermostat is provided. A heater and at least two thermostats are connected in series between an external power supply, and a detection circuit for detecting a thermostat abnormality is derived from a connection point provided at a position sandwiched between two adjacent thermostats. In addition, the detection circuit is grounded, and furthermore, a difference voltage detector in which a light emitting diode lit by a small current and a current limiting resistor are connected in series is provided in the detection circuit. In addition, even if the thermostat is in an abnormal state where it is stuck in a state where the power to the heater is maintained, this is discovered. Reduce the urgency of the device recovery if further thermostat abnormality can be easily and safely determined.

[Brief description of the drawings]

FIG. 1 is a system diagram of a heat retaining device for a fuel cell stack according to an embodiment of the present invention.

FIG. 2 is a system diagram of a heat retaining device for a fuel cell stack according to an example of the embodiment of FIG. 1;

FIG. 3 is a system diagram of a heat retaining device for a fuel cell stack according to an example of the embodiment of FIG. 2;

FIG. 4 is a system diagram of a heat retaining device according to an embodiment different from FIG. 1 of the present invention.

FIG. 5 is a system diagram of a heat retaining device of an embodiment different from FIG. 4 of the present invention.

FIG. 6 is a schematic system diagram of a conventional fuel cell power generator.

[Explanation of symbols]

51: Peripheral part of fuel cell stack, 52: Electric board, 53:
External power supply, 54: electric heater, 55: thermostat,
57: connection point, 58: detection circuit, 59: terminal, 100:
Difference voltage detector, 110: ground point, 120: light emitting diode, 130: current limiting resistance.

Claims (3)

[Claims] 1. A warming device provided for keeping a fuel cell stack warm during a fuel cell shutdown period and comprising an electric heater and a thermostat, comprising: at least one electric heater and at least two thermostats; A fuel cell stack, wherein a detection circuit for detecting a thermostat abnormality is derived from a connection point connected in series between external power supplies and provided at a position sandwiched between two adjacent thermostats. Insulation device. 2. The fuel cell stack according to claim 1, wherein the detection circuit is grounded, and a difference voltage detector is provided between the connection point and the ground point. Insulation device. 3. The fuel cell stack according to claim 2, wherein the differential voltage detector is configured by connecting a light emitting diode lit by a small current and a current limiting resistor in series. Insulation device.