JP2003187832A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system which enables keeping temperature of water to be substantially constant, in a water tank of the fuel cell system by preheating water being supplied to the water tank, using exhaust heat generated in the fuel cell system. <P>SOLUTION: Electric power is generated, by supplying an anode of a fuel cell 5 reformed gas being mainly constituted of hydrogen, which is made from raw fuel gas (domestic fuel gas, etc.), using a fuel reforming device A comprising, desulfurization equipment 1, reforming equipment 2, a carbon monoxide transformer 3 and carbon monoxide eliminating equipment, and by supplying a cathode of the fuel cell 5 humidified air made by bubbling air in a water tank 6. A first preheating circuit 9, through which ion exchange water from a demineralized water device 7 flows to the water tank 6 via a cell-exhausting air heat exchanger 8, is disposed. The ion exchange water is preheated to an appropriate temperature, by exchanging heat between air from the cathode flowing into the cell exhausting air heat exchanger 8 before the bubbling and the ion exchange water of the normal temperature. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell system, and is particularly characterized by means for supplying water to a water tank.

[0002]

2. Description of the Related Art A fuel cell system for generating electric power with a fuel cell is a fuel reformer for reforming a raw fuel gas (city gas, etc.), which is a hydrocarbon fuel, into a fuel gas mainly containing hydrogen as shown in FIG. Device A (desulfurizer 1, reformer 2, CO shifter 3,
A CO remover 4) is provided, fuel gas is supplied from the fuel reformer A to the anode (fuel electrode) of the fuel cell 5, reaction air is supplied from the reaction air supply device B to the cathode (air electrode), and an electrolyte is provided. It is a system that generates electricity by an electrochemical reaction via. Further, the fuel cell system is the fuel cell 5
It is provided with a water tank 6 that stores water that also serves as cooling water for cooling and water for humidifying reaction air, and a water supply device C for supplying water to this water tank 6.

Since the electrochemical reaction in the fuel cell 5 is an exothermic reaction, the temperature of the fuel cell rises during operation. The fuel cell 5 has an appropriate operating temperature (for example, about 80 ° C. for the polymer electrolyte fuel cell), and cooling water is supplied from the water tank 6 to the cooling section of the fuel cell 5 in order to prevent temperature rise. The fuel cell 5 is supplied to cool the fuel cell 5.

Further, in the polymer electrolyte fuel cell 5, the reaction air supplied to the cathode must be humidified in order to keep the polymer electrolyte membrane wet. Therefore, the reaction air is bubbled in the water tank 6 and appropriately humidified before being supplied to the fuel cell 5.

[0005]

In the above fuel cell system, the cooling water supplied from the water tank 6 to the cooling portion of the fuel cell 5 is collected in the water tank 6 and is circulated for use. Since it is also used for humidifying the reaction air, the amount of water in the water tank 6 gradually decreases. In order to make up for this decrease, ion-exchanged water (pure water) is supplied from the water supply device C.
Is being supplied to the water tank 6.

However, since the conventional water tank 6 is supplied with ion-exchanged water at room temperature, as shown in FIG. 6, the water temperature of the water tank 6 immediately after the water supply is from 78 ° C to 80 ° C to 74 ° C.
It drops to 76 ° C. Therefore, the temperature of the cooling water and the temperature of the reaction air decrease by 2 ° C to 4 ° C. Along with this, there is a problem that the battery temperature becomes unstable and the average cell voltage also decreases.

In view of this, the present invention utilizes the exhaust heat generated in the fuel cell system to preheat the water supplied to the water tank, thereby preventing a decrease in the water tank water temperature during water supply. It is intended to provide a battery system.

[0008]

As means for achieving the above object, the present invention provides a reformer for reforming a raw fuel into a reformed gas containing hydrogen as a main component, as in claim 1. A CO shifter for converting carbon monoxide in the reformed gas generated in the quality chamber into carbon dioxide, a CO remover for selectively oxidizing carbon monoxide to a predetermined concentration or less, and a reformed gas and reaction air are supplied. In a fuel cell system that includes a fuel cell that generates electricity and a water tank that stores both cooling water for the fuel cell and water for humidifying reaction air, control the water temperature of the water tank during operation to control the exhaust heat in the system. The gist of the present invention is a fuel cell system characterized by being carried out by a department. Further, as in claim 2, the exhaust heat portion is a heat exchanger for exhaust air of a fuel cell, and as in claim 3, the exhaust heat portion is on the downstream side of the reformer exhaust gas heat exchanger. Is a supply water preheat exchanger, the exhaust heat unit is a heat exchanger for recovering exhaust heat from a fuel cell system, and the water tank of the water tank is a heat exchanger. The water supplied to the water tank is used for the water temperature control, and the water recovered from the system is used together for the water temperature control of the water tank as in claim 6, and the water tank as in claim 7. For the water temperature control of the
It is characterized by.

In the present invention, heat exchange with the supply water at room temperature is performed in the exhaust heat section in the fuel cell system, so that the water supply to the water tank can be preheated to an appropriate temperature.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Next, an embodiment of a fuel cell system according to the present invention will be described with reference to the accompanying drawings.
Here, the same members as those in the conventional example are designated by the same reference numerals.
FIG. 1 shows a first embodiment of the present invention, and the operating conditions (ratings) of the fuel cell system are as follows. Raw fuel gas amount (for city gas 13A): 4.5 L / m
in S / C (steam / carbon ratio) of reformer: 4 System rated output: 1 kW (AC)

The fuel gas (reforming gas) supplied to the anode of the fuel cell 5 has a temperature of about 38 L / min and a temperature of about 80 ° C., and the amount of reaction air supplied to the cathode is about 80 L / m.
and is bubbled in the water tank 6 having a water temperature of about 80 ° C. before the supply to be properly humidified.

The capacity of the water tank 6 is about 4 L, and the cooling water circulates at 2 to 3 L / min. Since part of the water in the water tank 6 is used for humidifying the reaction air, the water level in the water tank 6 gradually decreases. The water supply interval to the water tank 6 is once or twice every several minutes and is set to several tens cc / min.
However, it may change depending on operating conditions.

In this case, there is provided a first preheating circuit 9 through which the ion-exchanged water from the pure water device 7 passes through the battery exhaust air heat exchanger 8 to the water tank 6. The cell exhaust air heat exchanger 8 is installed on the downstream side of the cathode of the fuel cell 5, and the exhaust air that has not reacted in the fuel cell 5 passes therethrough. This exhaust air has almost the same temperature as the operating temperature of the fuel cell 5 is about 80 ° C., and the exhaust air and the ion-exchanged water at room temperature from the pure water device 7 have heat exchange with the battery exhaust air. Heat is exchanged in vessel 8. As a result, the ion-exchanged water is 78 ° C to 80 ° C.
After being preheated, the water flows into the water tank 6.

The cooling water returned from the cooling section of the fuel cell 5 to the water tank 6 is heated by heat exchange in the cooling section and is heated to 80%.
Although the temperature is higher than 0 ° C, the temperature is lowered to about 80 ° C by the auxiliary heat exchanger H installed on the downstream side of the cooling unit and flows into the water tank 6. Therefore, when water is supplied to the water tank 6, the ion-exchanged water preheated by the battery exhaust air heat exchanger 8 and the return cooling water from the cooling unit of the fuel cell 5 flow into the water tank 6. Fuel cell 5 when water is not supplied
Only the return cooling water from the cooling unit of the above flows into the water tank 6.

As a result, the water temperature in the water tank 6 is kept substantially uniform (78 ° C to 80 ° C), the temperatures of the battery cooling water and the humidified reaction air are stabilized, and the battery performance (average cell voltage) is higher than that of the conventional one. Then there is no noticeable drop and it stabilizes. FIG. 4 is a graph in which the battery temperature, the average cell voltage, and the tank water temperature are measured. Measurement graph in the conventional example (Fig. 6)
It can be seen that the battery temperature, the average cell voltage, and the tank water temperature are remarkably stable in comparison with the above. The first preheating circuit 9
It is preferable to provide the flow rate controller 10 in the above to control the flow rate of the ion-exchanged water.

FIG. 2 shows a second embodiment of the present invention, in which the operating condition (rating) of the fuel cell system is the same as that of the first embodiment. In this case, the ion-exchanged water from the pure water device 7 passes through the second preheating circuit 13 that leads to the water tank 6 through the feedwater preheating heat exchanger 12 provided on the downstream side of the reformer exhaust gas heat exchanger 11. The configuration is provided.

The heat exchanger 11 for the reformer exhaust gas is installed above the reformer 2, and the combustion exhaust gas from the burner 2a disposed below the reformer 2 passes through the heat exchanger 11. This combustion exhaust gas has a high temperature of about 400 ° C. In the reformer 2, the raw fuel gas desulfurized by the desulfurizer 1 is steam-reformed to generate a reformed gas mainly containing hydrogen, but the catalyst has a high temperature (650 ° C.
Since it reacts at 700 ° C.), the raw fuel gas or the unreacted reformed gas discharged from the anode of the fuel cell 5 is supplied to the burner 2a and burned.

When the fuel cell 5 is started, a part of the raw fuel gas is sent to the burner 2a of the reformer 2 and burned, and during operation, unreacted gas is discharged from the anode of the fuel cell 5 instead of the raw fuel gas. The reformed gas of is sent and burned. Air required for combustion is supplied by the fan 2b. Water required for steam reforming is supplied from the water tank 6.

Since the temperature of the combustion exhaust gas passing through the reformer exhaust gas heat exchanger 11 is high (about 400 ° C.) as described above, it is usually supplied from a hot water storage tank (not shown) provided in the fuel cell system. Heat is exchanged through this water, and it is returned to the hot water storage tank as hot water.

As a result, most of the combustion exhaust gas is recovered in heat, and the combustion exhaust gas whose temperature has dropped to 80 ° C. to 90 ° C. passes through the heat exchanger 12 for preheating feed water. In this heat exchanger 12 for preheating water, heat is exchanged with the ion-exchanged water at room temperature from the pure water device 7, and the ion-exchanged water has a temperature of about 80 ° C.
Is preheated and flows into the water tank 6.

Also in the second embodiment, as in the first embodiment, the water temperature in the water tank 6 is kept substantially uniform (78 ° C. to 80 ° C.), and the temperatures of the battery cooling water and the humidified reaction air are stable. Therefore, the battery performance (average cell voltage) becomes stable.
In addition to the heat exchanger 12 for preheating feed water, the CO shifter 3
Alternatively, it is possible to use a heat exchanger provided in association with the CO remover 4 to preheat the ion-exchanged water.

FIG. 3 shows a third embodiment of the present invention, in which the operating condition (rating) of the fuel cell system is the same as that of the first embodiment. In this case, the ion-exchanged water from the pure water device 7 is the heat exchanger 14 for recovering exhaust heat from the fuel cell system.
A third preheating circuit 15 that leads to the water tank 6 is provided.

Unreacted air discharged from the cathode of the fuel cell 5 and combustion exhaust gas discharged from the burner 2a of the reformer 2 flow into the heat exchanger 14 for recovering exhaust heat. The temperature of the unreacted air is about 80 ° C., and the temperature of the combustion exhaust gas is about 80 ° C. to 90 ° C. after the heat is recovered for the hot water storage tank on the way as described above. Heat exchange is performed with the ion-exchanged water from the water device 7.

Due to the heat exchange in the heat exchanger 14 for recovering exhaust heat, the ion-exchanged water is preheated to 78 to 80 ° C. and flows into the water tank 6, and the temperature of the inflowing gas is lowered to 50 ° C. or lower. Exhausted outside the system.

Also in the third embodiment, the water temperature in the water tank 6 is substantially uniform (78 ° C. to 80 ° C.) as in the first and second embodiments.
C.) and the temperatures of the battery cooling water and the humidified reaction air are stable, so that the battery performance (average cell voltage) is stable. It should be noted that it is also possible to implement any of the first to third preheating circuits in combination.

[0026]

As described above, according to the present invention, when water is supplied to the water tank in the fuel cell system, the waste heat generated in the system is effectively used to preheat the water to an appropriate temperature, and then the water is allowed to flow into the water tank. Since the configuration is adopted, the water temperature of the water tank can be kept substantially constant. This allows
The fluctuation range of the water temperature in the water tank becomes small, the temperatures of the battery cooling water and the humidified reaction air become almost constant, and the battery performance becomes stable and the system has a long service life.

[Brief description of drawings]

FIG. 1 is a system flow chart showing a first embodiment of a fuel cell system according to the present invention.

FIG. 2 is a system flow chart showing a second embodiment of the fuel cell system according to the present invention.

FIG. 3 is a system flow chart showing a third embodiment of the fuel cell system according to the present invention.

FIG. 4 is a graph showing measured values of battery temperature, average cell voltage, and water tank water temperature in the first embodiment.

FIG. 5 is a system flow chart showing a conventional fuel cell system.

FIG. 6 is a graph showing measured values of battery temperature, average cell voltage, and water tank water temperature in a conventional example.

[Explanation of symbols]

1 ... Desulfurizer 2 ... reformer 2a ... Burner 3 ... CO transformer 4 ... CO remover 5 ... Fuel cell 6 ... water tank 7 ... Pure water device 8 ... Battery exhaust air heat exchanger 9 ... 1st preheating circuit 10 ... Flow controller 11 ... Reformer exhaust gas heat exchanger 12 ... Heat exchanger for preheating water supply 13 ... Second preheating circuit 14 ... Heat exchanger for exhaust heat recovery 15 ... Third preheating circuit

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Ryuji Yukawa             2-5-3 Keihan Hondori, Moriguchi City, Osaka Prefecture             Within Yo Denki Co., Ltd. (72) Inventor Katsuyuki Makihara             2-5-3 Keihan Hondori, Moriguchi City, Osaka Prefecture             Within Yo Denki Co., Ltd. (72) Inventor Yukinori Akiyama             2-5-3 Keihan Hondori, Moriguchi City, Osaka Prefecture             Within Yo Denki Co., Ltd. F term (reference) 4G040 EA03 EA06 EB01 EB03 EB31                       EB32 EB43 EB44                 5H027 AA06 BA01 BA16 BA17 CC06                       KK28 MM16

Claims (7)

[Claims] 1. A reformer for reforming raw fuel into reformed gas containing hydrogen as a main component, and a CO shifter for converting carbon monoxide in the reformed gas produced by the reformer into carbon dioxide. A CO remover that selectively oxidizes carbon monoxide to a predetermined concentration or less, a fuel cell that supplies reformed gas and reaction air to generate power, and a cooling water for the fuel cell and water for humidifying the reaction air were housed together. In a fuel cell system including a water tank, a water temperature control of the water tank during operation is performed by an exhaust heat section in the system. 2. The fuel cell system according to claim 1, wherein the exhaust heat section is a heat exchanger for exhaust air of a fuel cell. 3. The fuel cell system according to claim 1, wherein the exhaust heat section is a feed water preheating heat exchanger provided downstream of the reformer exhaust gas heat exchanger. 4. The fuel cell system according to claim 1, wherein the exhaust heat section is a heat exchanger for recovering exhaust heat from the fuel cell system. 5. The fuel cell system according to claim 1, wherein water supplied to the water tank is used for controlling the water temperature of the water tank. 6. The fuel cell system according to claim 1, wherein water recovered from the system is also used for controlling the water temperature of the water tank. 7. The fuel cell system according to claim 1, further comprising a flow rate controller for supply water for controlling the water temperature of the water tank.