JP2002313403A - Method of discharging generated water in fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a power generating efficiency from being lowered by generated water and reduce the consumption of fuel gas. SOLUTION: In this method of discharging water generated when a fuel cell 2 generates a power from the inside of a fuel gas flow passage 3 in a fuel cell system 1, the generated water is led and stored in a storage part 13 provided under the fuel gas flow passage 3, the level of water in the storage part 13 is detected, and when the water level exceeds a preset upper limit, the generated water in the storage part 13 is discharged from the underside of the storage part 13.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for discharging generated water from a fuel cell system.

[0002]

2. Description of the Related Art A fuel cell comprises a flat plate-shaped single cell formed by sandwiching an electrode structure comprising an anode electrode and a cathode electrode on both sides of a solid polymer electrolyte membrane with a pair of separators. And a plurality of such layers are stacked in the thickness direction.

In each single cell, a fuel gas (for example,
An oxidant gas (for example, hydrogen) is provided on one surface of the cathode-side separator, which is disposed to face the cathode electrode.
(Air containing oxygen). Further, between adjacent separators of adjacent single cells, a flow path of a cooling medium (for example, water) is provided.

When hydrogen as a fuel gas is supplied to the electrode reaction surface of the anode electrode, the hydrogen is ionized here and moves to the cathode electrode through the solid polymer electrolyte membrane. The electrons generated during this time are taken out to an external circuit and used as DC electric energy. Since air, which is an oxidizing gas, is supplied to the cathode electrode, hydrogen ions, electrons, and oxygen in the air react to generate water.

[0005] Such generated water is mainly generated in the oxidizing gas flow path in the fuel cell, but is also generated in the fuel gas flow path. If the generated water stays in the oxidizing gas flow path and the fuel gas flow path, power generation in the staying portion is hindered, and the power generation efficiency may be reduced. Therefore, the generated water may be generated periodically or as necessary. Water is discharged from the gas passage in the fuel cell.

Heretofore, such a discharge operation of generated water has been performed based on a voltage value output from voltage measuring means arranged for each single cell of the fuel cell, and the voltage value has dropped below a predetermined threshold value. The oxidizing gas flow through the oxidizing gas flow path,
In the fuel gas flow path, the generated water is discharged (purged) by supplying the fuel gas at a large flow rate. That is, when the voltage value generated by the single cell decreases, it can be determined that the generated water remains in a part of the gas flow path and the power generation in that region is hindered. Purging of the generated water based on the

[0007]

However, when purging generated water based on the voltage value of a single cell, when purging generated water, the power generation efficiency of the fuel cell is already reduced. That is not desirable. on the other hand,
It is conceivable that the purging is performed periodically, for example, by a timer without using the voltage value of the single cell, but in this case, unnecessary purging work may be performed in a state where water is not generated. is there. Further, in purging the fuel gas flow path using the fuel gas, it is necessary to take care not to wastefully discharge the fuel gas.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is possible to prevent a decrease in power generation efficiency due to generated water and to prevent wasteful discharge of fuel gas in a fuel cell system. It is intended to provide an emission method.

[0009]

In order to achieve the above object, the present invention proposes the following means. Claim 1
The invention according to the present invention is a method of discharging water generated at the time of power generation of a fuel cell from a reaction gas flow path, while guiding and storing the generated water in a storage section provided below the reaction gas flow path, A water discharge method for a fuel cell system that detects a water level in a storage section and discharges water generated in the storage section from below when the water level exceeds a preset upper limit water level is proposed.

According to the method for discharging generated water according to the present invention,
During power generation of the fuel cell, water generated in the fuel cell flows into a storage section provided below the reaction gas flow path, is temporarily stored therein, and the water level is monitored there. Until the storage section overflows, the generated water continues to flow into the storage section without staying in the reaction gas flow path, thereby preventing inconvenience such as the reaction gas flow path being partially blocked by the generated water.

Further, when the water level in the storage section exceeds a preset upper limit water level, the generated water in the storage section is discharged, so that the generated water does not overflow from the storage section and the reaction gas flow path is formed by the generated water. It will not be blocked. Furthermore, since the generated water in the storage section is discharged from the lower part, the reaction gas in contact with the liquid level of the generated water is discharged to the outside by the generated water itself stored in the storage section even if the liquid level of the generated water drops during discharge. Leakage will be prevented.

According to a second aspect of the present invention, in the method for discharging the generated water according to the first aspect, when the water level of the storage section falls below a preset lower limit water level, the discharge of the generated water of the storage section is stopped. A method for discharging generated water in a fuel cell system is proposed. According to the generated water discharge method according to the present invention, the generated water is discharged from the storage unit, and the discharge of the generated water is stopped when the generated water falls below the lower limit water level, so that the generated water remains in the lower part of the storage unit. The leakage of the reaction gas to the outside is prevented.

[0013]

Embodiments of the present invention will be described below with reference to the accompanying drawings. As shown in FIG. 1, the fuel cell system 1 to which the generated water discharge method according to the present embodiment is applied includes a fuel cell 2, a fuel gas flow path 3 for supplying a fuel gas into the fuel cell 2, An oxidizing gas flow path 4 for supplying the oxidizing gas.

The fuel gas flow path 3 is mainly provided with a fuel gas source 5 (high-pressure tank) for supplying a pressurized fuel gas.
A shut-off valve 6 for switching supply / stop of the fuel gas from the fuel gas source 5 to the fuel gas flow path 3; and an ejector 7 for circulating the fuel gas by forming the fuel gas flow path 3 into a loop. And a humidifier 8 for humidifying the fuel gas flowing through the inlet-side flow path 3b with the fuel gas flowing through the outlet-side flow path 3a of the fuel cell 2. The oxidizing gas flow path 4 is mainly provided with a supercharger 9, a humidifier 10, and a back pressure valve 11 for taking in and supplying an oxidizing gas.

A drain device 12 is provided in the fuel gas passage 3 disposed in the fuel cell 2. This drain device 12, as shown in FIG.
It is provided near the outlet of the internal fuel gas flow path 3. In FIG. 2, reference symbol A indicates the direction of flow of the fuel gas.

As shown in FIG. 3, the drain device 12 has a tank-shaped storage section 13 and a storage section 13.
A discharge port 14 provided at the lower part of the tank, a valve 15 for opening and closing the discharge port 14, a water level sensor 16 for measuring a water level of water stored in the storage section 13, and a pressure of fuel gas in the storage section 13 It has a first pressure sensor 17 for detecting and a second pressure sensor 18 for detecting the pressure on the discharge port side.

The valve 15 has a structure that is opened and closed by a plunger 20 driven by a solenoid 19, as shown in FIG. 3, and is normally closed by a spring 21. The outputs of the water level sensor 16 and the pressure sensors 17 and 18 are connected to a control device 22, and the output from the control device 22
The solenoid 19 is driven.

The fuel cell system 1 configured as described above
The operation of is described below. To generate power in the fuel cell system 1, first, for example, by turning on an ignition switch, the shut-off valve 6 is turned on.
Then, the back pressure valve 11 is opened, and the supercharger 9 is started. As a result, the fuel gas 5 supplied from the fuel gas source 5 is supplied to the fuel gas flow path 3, and the oxidizing gas taken in by the supercharger 9 is supplied to the oxidizing gas flow path 4. Humidifiers 8 and 10 are provided in the fuel gas flow path 3 and the oxidizing gas flow path 4, respectively. Power is supplied and power generation is started.

When power generation is started, the fuel cell system 1
Then, the generated water discharge process is started according to the flow shown in FIG. In the generated water discharge process, first, it is determined whether or not the ignition is ON, that is, whether or not the power is being generated (step S1).

When the power generation state is determined and the power generation state is continued, the fuel gas and the oxidizing gas flow through the fuel gas passage 3 and the oxidizing gas passage 4 arranged in the fuel cell 2. As it is consumed, water is generated in these flow paths 3 and 4. In particular, water generated by power generation mainly accumulates in the oxidizing gas channel 4, and the generated water accumulated in the oxidizing gas channel 4 flows into the fuel gas channel 3 through the electrolyte membrane. In addition, both reaction gas passages 3 and 4
The water that accumulates inside includes the water from the humidifier. The water collected in the fuel gas flow path 3 as described above is supplied to the fuel cell 2
Flows into the storage section 13 disposed below the fuel gas flow path 3 on the outlet side of the fuel cell. Since the outlet 14 of the storage unit 13 is closed by the valve 15, the generated water flowing in the storage unit 13 is stored without being discharged, and the water level gradually rises.

At this time, the water level in the storage section 13 is continuously or periodically detected by the operation of the water level sensor 16. Further, the fuel gas pressure P1 and the outlet pressure P2 in the storage section 13 are detected continuously or periodically by the pressure sensors 17 and 18, respectively (step S2). Next, the pressure values P1 and P2 measured by the pressure sensors 17 and 18 are compared (step S3), and when the pressure P1 of the fuel gas in the storage unit 13 is lower than the pressure P2 on the discharge port 14 side, When the valve 15 is opened, there is a possibility that outside air may enter through the discharge port 14, so that the valve 15 is maintained in a closed state.

On the other hand, when the pressure value P1 of the pressure sensor 17 is higher than the pressure value P2 of the pressure sensor 18, the water level in the storage section 13 detected by the water level sensor 16 is a predetermined threshold value (upper limit water level) L It is determined whether it is _H or more (step S4). Level L of the water in the reservoir 13, if it is determined to be lower than a predetermined threshold L _H again, pressure detection and the water level sensor 1 by the pressure sensors 17 and 18
6 the water level detection performed by (step S2), and when the water level L is equal to or greater than a predetermined threshold value L _H determines the valve opening time T1 (step S5).

The valve opening time T1 is determined, for example, based on an opening time table (not shown) stored in relation to the pressure difference ΔP (= P1-P2) between the pressure sensors 17 and 18. When the pressure difference ΔP is large, the water stored in the storage section 13 can be sufficiently discharged even if the valve opening time T1 is short, and when the pressure difference ΔP is small,
This is because if the valve open time T1 is not long, the generated water is not sufficiently discharged.

The valve opening time T1 is determined by the storage unit 13
It is preferred that the water level is set to a time which is a lower limit level L _L. By opening the valve 15, the water in the storage unit 13 is not completely discharged from the outlet 14,
By leaving a minimum amount of water in 3, the fuel gas disposed above the water surface of the storage unit 13 can be prevented from leaking from the outlet 14, and wasteful consumption of fuel gas can be reduced. It is.

Thereafter, the valve 15 is opened (the valve is energized) (step S6), and after a lapse of the valve opening time T1 determined in step S6 (step S7).
Then, a signal is sent from the control device 22 to the solenoid 19 (energization is stopped), the plunger 20 is moved by the elastic restoring force of the spring 21, and the valve 15 is closed (step S8). Thereafter, the process returns to step S1 to determine whether or not the ignition is ON. If it is determined that power is being generated, steps S2 to S8 described above are repeated.

On the other hand, if it is determined in step S1 that the ignition is turned off, that is, the power generation is stopped, the pressures P1, P2 around the valve 15 of the storage unit 13 are determined.
P2 is detected (step S9), compared (step S10), and provided that the pressure value P1 is larger than the pressure value P2, the valve opening time T2 is set based on the pressure difference ΔP (step S11). , The valve 15 is opened (step S12). After the valve opening time T2 has elapsed (step S13), the valve 15
Is closed (step S14), and the generated water discharge process ends.

[0027] In this case, the valve opening time T2 is the time the water level of the reservoir 13 is the lower limit level L _L, or, it is preferable to set to a time when the water level reaches to the discharge port 14. It is possible to prevent wasteful discharge of fuel gas, and to eliminate or minimize water that freezes near the valve 15 when the fuel cell system 1 is left in a low temperature state, for example. Because it can be.

That is, according to the method for removing residual water in the fuel cell system 1 according to the present embodiment, during the power generation by the fuel cell 2, water generated inside the fuel cell 2 is supplied to the lower part of the fuel gas flow path 3. Is stored in the storage section 13 provided in the fuel cell 2 and temporarily stored therein, so that water is prevented from staying in the fuel gas flow path 3 inside the fuel cell 2. Further, to detect the water level L of the reservoir 13, since the discharge of produced water when the water level L exceeds the upper limit level L _H, generated water staying in the fuel cell 2 within the fuel gas passage 3 This can be reliably prevented.

As a result, when compared with the conventional method of detecting that the power generation voltage of the fuel cell 2 has started to decrease and discharging the generated water, it is possible to discharge the generated water without lowering the generated voltage. Therefore, power generation efficiency can be improved.

Further, the generated water is stored in the storage unit 13,
By employing the drain device 12 that discharges from below the storage unit 13, the fuel gas present above the water surface is discharged from the discharge port 14 by the generated water itself existing in the storage unit 13 during discharge of the generated water. Therefore, wasteful consumption of fuel gas during power generation can be prevented. In addition, since the discharge of the generated water is terminated in a state where the minimum generated water is left in the storage section 13 by the valve opening times T1 and T2, the release of the fuel gas can be reliably prevented.

Further, by adjusting the valve opening time T2, the generated water remaining in the vicinity of the valve 15 can be minimized while preventing the release of the fuel gas from the storage section 13. However, the amount of water to be frozen can be reduced, and the function of the valve 15 can be maintained at the time of starting.

In the above-described embodiment, the case where the drain device 12 is provided only in the fuel gas flow path 3 has been described from the viewpoint of preventing the power generation efficiency of the fuel cell 2 from lowering and reducing the consumption of fuel gas. It is not limited to
As shown in FIG. 5, a humidifier 8 provided in the fuel gas flow path 3 is provided with a drain device 23 similar to that of the above embodiment, and a sequence equivalent to that shown in FIG. 4 is executed. Is also good. According to this, it is possible to prevent the generated water from closing the fuel gas flow path 3 inside the humidifier 8 also in the humidifier 8, so that the function of the humidifier 8 is maintained and the consumption of the fuel gas is improved. There is an effect that reduction can be achieved.

Although there is no fuel gas consumption reduction effect,
As shown in FIG. 5, a humidifier 10 provided in the oxidant gas flow path 4 may be provided with a drain device equivalent to that of the above embodiment. In this case, the humidifier on the oxidant flow path 4 side 10 can be prevented from being deteriorated.

[0034] In the above embodiment, the valve opening time determined from the pressure difference across the valve 15, although the water level L of the reservoir 13 is open the valve 15 for a time enough to the lower limit level L _L, to Alternatively, the by the water level sensor 16, the water level L of the reservoir 13 also detects whether or not below the lower limit level L _L, may be to close the valve 15 on the basis of the detection result.

[0035]

As is clear from the above description, the present invention has the following effects. (1) According to the method for discharging generated water of the fuel cell system according to the first aspect of the present invention, the water generated in the reaction gas flow path is guided to the storage section disposed below the reaction gas flow path, and the water level of the storage section is adjusted. Since the generated water is discharged when the detected water level exceeds the upper limit, the generated water can be reliably prevented from staying in the reaction gas flow path.

Therefore, in the fuel cell disposed on the reaction gas flow path, water generated in the fuel cell flow path is discharged before the voltage of the fuel cell drops, so that the power generation efficiency during power generation is reduced. This has the effect that it can be prevented. Further, in other devices such as a humidifier disposed on the reaction gas flow path, it is possible to prevent the reaction gas flow path in the device from being blocked or reduced by the generated water, thereby preventing malfunction. This has the effect.

Further, by providing a storage section and storing the generated water so as to form a water surface between the reaction gas flow path and the discharge port, especially when the reaction gas is a fuel gas, the fuel gas is Leakage from the outlet can be blocked by the product water itself. Therefore, there is an effect that the release of the fuel gas during the discharge of the generated water can be prevented, and the consumption of the fuel gas can be reduced.

(2) According to the method for discharging generated water of the fuel cell system according to the second aspect of the present invention, at the time of discharging the generated water, the surface of the generated water is always kept between the reaction gas flow path and the discharge port. Since it can be maintained, there is an effect that the reaction gas, especially the fuel gas, can be reliably prevented from leaking from the outlet.

[Brief description of the drawings]

FIG. 1 is a block diagram schematically showing a fuel cell system to which a generated water discharge method according to an embodiment of the present invention is applied.

FIG. 2 is a schematic diagram showing an arrangement of a drain device of a fuel gas flow path to which the generated water discharge method according to one embodiment of the present invention is applied.

FIG. 3 is a detailed view of the drain device of FIG. 2;

FIG. 4 is a flowchart illustrating a generated water discharge process according to an embodiment of the present invention.

FIG. 5 is a block diagram schematically showing a fuel cell system to which a generated water discharge method according to another embodiment of the present invention is applied.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fuel cell system 2 Fuel cell 3 Fuel gas flow path 13 Storage part

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tomoki Kobayashi 1-4-1 Chuo, Wako-shi, Saitama Pref. Inside Honda R & D Co., Ltd. (72) Inventor Yasushi Kanai 1-4-1 Chuo, Wako-shi, Saitama F-term in Honda R & D Co., Ltd. (reference) 5H026 AA06 5H027 AA06 KK00

Claims (2)

[Claims] 1. A method for discharging water generated at the time of power generation of a fuel cell from a reaction gas flow path, wherein the generated water is guided and stored in a storage section provided below the reaction gas flow path. A method for discharging generated water of a fuel cell system, comprising detecting a water level of a storage section, and discharging the generated water of the storage section from below when the water level exceeds a preset upper limit water level. 2. The method according to claim 1, wherein when the water level in the storage section falls below a predetermined lower limit water level, the discharge of the generated water in the storage section is stopped.