JP2003331889A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system capable of surely starting in a short time even after being left unattended over a long time. <P>SOLUTION: A hydrogen substitution valve 8 using a closing valve is a fuel gas discharge means or replacing a hydrogen line with hydrogen, and has an opening area set larger than that of a purge valve 7. When starting, the substitution valve 8 is opened for replacing the gases in a fuel electrode and in a fuel pipe with hydrogen to supply hydrogen to the system from a variable throttle valve 3 at a nearly constant flow rate, and thereby hydrogen substitution (fuel gas substitution) for replacing the inside of a hydrogen line comprising a hydrogen pipe 4, the inside of the fuel electrode and a hydrogen return pipe 6 with newly supplied hydrogen is carried out. <P>COPYRIGHT: (C)2004,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 more particularly to a fuel cell system capable of shortening start-up time.

[0002]

2. Description of the Related Art For example, as a method for starting a fuel cell system, there is one described in Japanese Patent No. 2735396. In this conventional example, fuel and air are supplied at startup,
The output voltage of the fuel cell is monitored, and when the output voltage value exceeds the voltage allowable lower limit value, the electric power load is taken out.

[0003]

However, even if the output voltage of the fuel cell is increased, a problem may occur when the power load is taken out. For example, consider a case where the fuel cell system is left without operating for a long time. When left unattended, the fuel gas in the fuel electrode and fuel pipes of the fuel cell gradually diffuses out of the system, and gradually reacts with oxygen in the air in the fuel cell and is lost. The inside is filled with air or nitrogen.

Here, in order to start the fuel cell system, fuel gas and air are supplied to the fuel electrode and the air electrode, respectively. Even if the air in the fuel electrode or the fuel passage is not sufficiently replaced with the fuel gas, the fuel gas is immediately replaced. Then, the output voltage of the fuel cell rises. However, if you immediately remove the load here,
Since the concentration of the fuel gas in the fuel passage or the fuel electrode is insufficient, there is a problem that a sudden voltage drop occurs and the load cannot be taken out stably.

The present invention has been made in order to solve the above-mentioned problems of the prior art, and an object thereof is a fuel cell system which can be started reliably and in a short time even after being left for a long time. Is to provide.

[0006]

In order to achieve the above object, the present invention provides a fuel cell system with a fuel gas discharge means for discharging exhaust fuel gas discharged from a fuel cell body to the outside, and When the fuel gas is supplied from the fuel gas supply means to the fuel electrode at the time of start-up, the exhausted fuel gas is discharged from the fuel gas discharge means, thereby replacing the fuel gas supply passage and the inside of the fuel electrode with the fuel gas. To do.

[0007]

According to the present invention, at the time of starting the fuel cell system, the fuel gas passage and the fuel electrode of the fuel cell are surely replaced by the fuel gas, and even after being left for a long time, the fuel gas passage is surely done in a short time. The effect is that it can be activated.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will now be described in detail with reference to the drawings. [First Embodiment] FIG. 1 is a configuration diagram illustrating a configuration of a first embodiment of a fuel cell system according to the present invention. In the figure, the fuel cell stack 1, which is the fuel cell body, is
A fuel cell structure having a solid polymer electrolyte membrane sandwiched between an oxidizer electrode and a fuel electrode is sandwiched between separators, and a plurality of these are stacked. Hydrogen is used as the fuel gas supplied to the fuel electrode, and air is used as the oxidant supplied to the oxidant electrode.

Hydrogen gas in the hydrogen tank 2 (fuel gas supply means) is supplied to the fuel cell stack 1 via the variable throttle valve 3. The variable throttle valve 3 is controlled by the controller 15 so that the hydrogen supply pressure to the fuel cell stack 1 becomes appropriate during normal operation.

In this embodiment, a pressure regulator 12 is provided between the hydrogen tank 2 and the variable throttle valve 3 to supply the constant pressure hydrogen gas to the variable throttle valve 3 regardless of the residual pressure of the hydrogen tank 2. It is controlled to supply.

An ejector 5 is provided in the hydrogen pipe 4 (fuel gas supply passage) between the variable throttle valve 3 and the fuel cell stack 1. Excess hydrogen, which is exhausted fuel gas discharged from the fuel cell stack 1, is returned to the intake port of the ejector 5 through a hydrogen return pipe 6 which is a fuel circulation pipe, and during normal operation, the ejector 5 circulates hydrogen. As a result, the reaction efficiency of the fuel cell stack 1 is increased.

The purge valve 7 using an on-off valve is a purging means for temporarily purging the hydrogen line during normal operation, for example, when the hydrogen passage in the fuel cell stack is blocked by water.

The hydrogen replacement valve 8 using an on-off valve is a fuel gas discharge means for replacing the hydrogen line with hydrogen at the time of startup, and has a larger opening area than the purge valve 7. The compressor 9 compresses air and supplies the compressed air to the inlet of the oxidant electrode of the fuel cell stack 1, and the air pressure of the oxidant electrode is adjusted by an air pressure adjusting valve 11 provided at the outlet of the oxidant electrode. The supply of air to the fuel cell stack 1 and the control of the air pressure are performed by the controller 15 controlling the compressor 9 and the air pressure adjusting valve 11.

Next, an outline of the starting procedure of the fuel cell system having the above configuration will be described with reference to the flowchart of FIG. First, step (hereinafter, step is abbreviated as S)
When the starting operation is started at 11, an instruction to start replacement of the gas in the fuel electrode and the fuel pipe is issued. Next, in S12, the hydrogen substitution valve 8 is opened, and subsequently in S13, a substantially constant flow rate (for example, 1
Hydrogen is supplied to the system at a rate of about 00 L / min), and hydrogen replacement (fuel gas replacement) is performed to replace the inside of the hydrogen line consisting of the hydrogen pipe 4, the inside of the fuel electrode and the hydrogen return pipe 6 with newly supplied hydrogen.

In the present embodiment, in order to supply hydrogen at a constant flow rate, the opening of the variable throttle valve 3 at the time of hydrogen replacement is made constant. When the upstream / downstream pressure ratio of the variable throttle valve 3 is 1.9 or more, the variable throttle valve 3 is in the choked state. Therefore, if the set pressure of the pressure regulator 12 is made sufficiently high, the flow rate becomes constant if the opening is constant, without being influenced by the downstream pressure of the variable throttle valve 3.

In S14, a predetermined time (for example, about 10 seconds)
After the passage of time, it is determined that the hydrogen line has been sufficiently replaced, the hydrogen replacement is completed, that is, the variable throttle valve 3 is closed, and the supply of hydrogen is stopped. As the predetermined time, the minimum required time for sufficient replacement can be experimentally obtained in advance with the above-mentioned replacement flow rate, and a certain degree of margin is added to this minimum required time to replace only that time. Of.

The hydrogen substitution valve 8 is closed in S15, and S16
Then, air and hydrogen are supplied based on normal operation, and power load extraction is started.

In the present embodiment, apart from the purge valve 7, a hydrogen replacement valve 8 having an opening area larger than that of the purge valve 7 is provided.
Was set up. The reason why the hydrogen replacement valve 8 is provided separately from the conventional purge valve 7 is that the purge valve 7 should have a minimum required opening area so as not to deteriorate the fuel consumption rate. This is because the pressure loss becomes large when trying to flow a large flow rate.

Of course, one on-off valve may be used as the purge valve 7 and hydrogen replacement valve. In this case, if the valve opening area is increased, the purge flow rate for purging during normal operation unnecessarily increases and fuel consumption increases.

On the contrary, if the valve opening area is reduced and the hydrogen replacement flow rate is increased at startup,
The pressure loss of the valve increases the pressure applied to the fuel cell stack, which may damage the fuel cell stack.Therefore, the hydrogen replacement flow rate must be reduced, and the required replacement time becomes longer and the startup time becomes longer. Will be extended.

However, the cost can be reduced by using only one valve, and one valve or two valves should be selected depending on the balance of fuel consumption rate, starting time and cost.

Although the system in which hydrogen is circulated by the ejector has been described above, the present invention can be applied to a system in which hydrogen is circulated by using a hydrogen circulation pump with external power and a system in which hydrogen is not circulated. Needless to say.

As described above, according to this embodiment,
At the time of start-up, the fuel gas supply passage and the inside of the fuel electrode are reliably and sufficiently replaced with hydrogen.
This has the effect of enabling reliable startup in a short time.

In particular, by making the supply flow rate of the fuel gas substantially constant, it is possible to determine that the replacement has been sufficiently performed after a lapse of a predetermined time, so that the above effect can be obtained by simple control.

Further, by making the opening of the variable throttle valve constant, the supply flow rate of the fuel gas becomes substantially constant, so that the control structure becomes simpler.

[Second Embodiment] FIG. 3 is a configuration diagram for explaining the configuration of a second embodiment of the fuel cell system according to the present invention. The difference between the present embodiment and the first embodiment is that a pressure sensor 13 that detects the ejector inlet pressure is provided between the variable throttle valve 3 and the ejector 5, and that the hydrogen pressure supplied to the fuel cell stack 1 is Pressure sensor 14 for detecting
Is provided. Since other configurations are the same as those in FIG. 1, the same components are designated by the same reference numerals and redundant description will be omitted.

In this embodiment, the controller 15 controls the opening degree of the variable throttle valve 3 so that the ejector inlet pressure detected by the pressure sensor 13 is constant (for example, about 0.5 bar) during hydrogen replacement at the time of startup. I adjusted it.

Since the flow path of the ejector 5 is narrowed by the nozzle on the inlet side, a pressure loss occurs when hydrogen is flown.
Therefore, if the ejector inlet pressure at the time of hydrogen replacement is set high and the ejector 5 chokes at the time of replacement, the supply hydrogen flow rate at the time of hydrogen replacement can be made constant by making the upstream pressure of the ejector 5 constant. .

Next, the hydrogen substitution procedure in this embodiment will be described with reference to the flow chart of FIG. First, when a replacement start instruction is issued in S21, the hydrogen replacement valve 8 is opened in S22, and the opening degree of the variable throttle valve 3 is adjusted so that the inlet pressure of the ejector 5 detected by the pressure sensor 13 reaches a predetermined value in S23. Supply hydrogen while adjusting. When the hydrogen supply, that is, the actual replacement time reaches the predetermined time, the variable throttle valve 3
To close the hydrogen supply, and in S25, the hydrogen replacement valve 8
To close the series of permutation actions.

Depending on the size of the nozzle of the ejector 5, the hydrogen replacement flow rate, etc., the ejector 5 may not be in the choked state during hydrogen replacement.

The size of the ejector should be determined by the amount of hydrogen desired to be circulated by the ejector during normal operation, which is determined by the characteristics of the fuel cell stack.

Further, if the hydrogen replacement flow rate is too large, the amount of hydrogen discharged becomes large, the combustor (not shown) for burning the discharged hydrogen becomes large, and the fuel consumption deteriorates, so it cannot be extremely increased.

For example, when an ejector having a large nozzle area is used and the hydrogen replacement flow rate is set to be small, the ejector cannot be maintained in a choked state during replacement.

In such a case, as shown in FIG. 5, the ejector inlet pressure at which the required hydrogen flow rate becomes a predetermined constant value is stored in the controller 15 in advance according to the inlet pressure of the fuel cell stack 1, If the variable throttle valve 3 is adjusted so as to attain that pressure, the same effect can be obtained.

As described above, according to this embodiment, as in the first embodiment, the necessary and sufficient hydrogen substitution is surely performed at the time of startup, so that reliable startup is possible even after being left for a long time. Has become possible.

Particularly, by using the existing ejector and utilizing the characteristic that the ejector chokes, the variable throttle valve opening is adjusted simply and surely so that the fuel gas pressure upstream of the ejector becomes a predetermined value. The supply flow rate of the fuel gas can be made substantially constant.

Further, since the fuel gas pressure on the upstream side of the ejector is determined according to the fuel gas pressure on the downstream side of the ejector, even if the fuel gas pressure on the downstream side of the ejector fluctuates, the supply flow rate of the fuel gas can be kept substantially constant. You can

[Third Embodiment] The configuration of this embodiment is the same as that of the second embodiment shown in FIG. FIG. 6 shows the transition of the fuel cell stack inlet pressure during hydrogen replacement. The solid line in FIG. 6 is the case where the hydrogen line of the fuel cell system is completely filled with air before starting and the replacement takes the longest time.

When the hydrogen supply is started, the fuel cell stack inlet pressure rises once, and the pressure decreases as the replacement progresses. When the hydrogen line is completely filled with hydrogen, the pressure becomes constant (P0) (for example, 3 kPa). Become.

This is because air has a large molecular weight with respect to hydrogen, and when it is replaced at a constant flow rate, the pressure when passing through the hydrogen replacement valve is large with respect to hydrogen. That is, when the replacement flow rate is constant, it is possible to determine how much air remains in the hydrogen line at the ejector downstream pressure.

In this embodiment, the fuel cell stack inlet pressure is used as the ejector downstream pressure.

The broken line in the figure is an example of the case where hydrogen remains in the hydrogen line of the fuel cell system before starting. It can be seen that in the case of the solid line in which the hydrogen line is filled with air, the replacement needs to be performed for t1 hours, whereas in the case of the broken line in which hydrogen remains, t2 (t2 <t1) is sufficient.

In the present embodiment, by utilizing this characteristic, the replacement is completed when the inlet pressure of the fuel cell stack becomes lower than the predetermined value (P0) during the hydrogen replacement. That is,
Since the pressure sensor 13 for detecting the ejector inlet pressure also serves as a means for detecting the fuel gas concentration, the fact that the inlet pressure of the fuel cell stack falls below the predetermined value (P0) indicates that the hydrogen concentration in the fuel gas passage is within the fuel electrode. It is considered that the value has been exceeded (above the minimum concentration required for power generation).

Next, hydrogen replacement at the time of startup in this embodiment will be described with reference to the flowchart of FIG.

First, when an instruction to start replacement is issued in S31, S
At 32, the hydrogen replacement valve 8 is opened, and at S33, the pressure sensor 1
Hydrogen is supplied while adjusting the opening of the variable throttle valve 3 so that the ejector inlet pressure detected by 3 becomes a predetermined value. S3
In step 4, it is determined whether the inlet pressure of the fuel cell stack 1 detected by the pressure sensor 14 is less than or equal to a predetermined value. If it is greater than or equal to the predetermined value, hydrogen supply is continued as it is.
In step S36, the variable throttle valve 3 is closed to terminate the hydrogen supply, and in step S36, the hydrogen replacement valve 8 is closed to complete the series of replacement work.

By doing so, it becomes possible to set the necessary minimum replacement time in accordance with the remaining amount (concentration) of hydrogen in the hydrogen line of the fuel cell system, and to minimize the amount of hydrogen lost by replacement, It has become possible to start up reliably while shortening the startup time.

Further, the amount of hydrogen remaining (concentration) in the hydrogen line can be determined by the gas pressure value upstream of the hydrogen substitution valve 8 which is the fuel gas discharge means, and it is also necessary to use a sensor dedicated to hydrogen concentration. There is no.

Further, by keeping the supply flow rate of the fuel gas substantially constant, the pressure upstream of the fuel gas discharge means may become less than or equal to a predetermined value as the fuel gas in the fuel electrode or in the fuel gas passage increases. It will be easier to judge. When the present invention is not applied, the supply flow rate of the fuel gas is not substantially constant, and even if the pressure upstream of the fuel gas discharge means becomes equal to or lower than a predetermined value, the fuel gas in the fuel electrode or the fuel gas passage is increased. It is difficult to determine whether the change is due to the fluctuation of the fuel gas supply flow rate, and the control becomes uncertain.

Although the pressure sensor 14 for detecting the inlet pressure of the fuel cell stack is used in this embodiment, it goes without saying that the pressure sensor may be located downstream of the ejector, for example, downstream of the fuel cell stack. .

Originally, it is ideal to use the hydrogen substitution valve inlet pressure, but if the pressure loss of the fuel cell stack is sufficiently small, the fuel cell stack inlet pressure can be substituted as described above.

Although the replacement flow rate is made constant by making the ejector inlet pressure constant, the variable throttle valve opening may be made constant to make the replacement flow rate constant.

[Fourth Embodiment] The configuration of this embodiment is the same as that of the second embodiment shown in FIG. In the third embodiment described above, when the hydrogen line is filled with air, the fuel cell stack inlet pressure at the time of replacement is, for example, 4 at maximum.
When the hydrogen replacement flow rate is increased to 0 kPa and the hydrogen replacement valve is set, the pressure becomes about 3 kPa in a state after sufficient replacement. An expensive pressure sensor is required to withstand such a maximum pressure of 40 kPa and accurately detect a low pressure.

When the accuracy of the pressure sensor is low, it is predicted that the replacement is not completed even though it has not been sufficiently replaced, or the replacement will not end because the pressure does not drop to P0 on the sensor indication value. It

Therefore, in the present embodiment, the judgment pressure is set as shown in FIG.
P1 (for example, 6 kPa), which is slightly higher than P0, was set, and instead, hydrogen supply was continued for a predetermined time (for example, about 3 seconds) even after the fuel cell stack inlet pressure became P1 or less.

FIG. 8 is a flow chart for explaining the hydrogen replacement operation of this embodiment. The difference from the third embodiment of FIG. 7 is that in S45, after the stack inlet pressure becomes equal to or lower than a predetermined value (P1), hydrogen is further supplied for a predetermined time and replacement is continued.

By doing so, necessary and sufficient replacement can be reliably performed while using an inexpensive and low-precision pressure sensor.
It became possible to start up stably.

The replacement flow rate is made constant by making the ejector inlet pressure constant, but the variable throttle valve opening may be made constant to make the replacement flow rate constant.

[Brief description of drawings]

FIG. 1 is a configuration diagram illustrating a configuration of a first embodiment of a fuel cell system according to the present invention.

FIG. 2 is a flowchart illustrating the operation of the first embodiment.

FIG. 3 is a configuration diagram illustrating a configuration of a second embodiment of a fuel cell system according to the present invention.

FIG. 4 is a flowchart illustrating the operation of the second embodiment.

FIG. 5 is a diagram showing an ejector inlet pressure at which a hydrogen flow rate with respect to a fuel cell stack inlet pressure has a predetermined value.

FIG. 6 is a diagram showing a time change of a fuel cell stack inlet pressure at the time of hydrogen replacement in the third embodiment.

FIG. 7 is a flowchart illustrating an operation of the third embodiment.

FIG. 8 is a flowchart illustrating an operation of the fourth embodiment.

[Explanation of symbols]

1 ... Fuel cell stack 2 ... Hydrogen tank 3 ... Variable throttle valve 4 ... Hydrogen piping 5 ... Ejector 6 ... Hydrogen return piping 7 ... Purge valve 8 ... Hydrogen replacement valve 9 ... Compressor 10 ... Air piping 11 ... Air pressure control valve 12 ... Pressure regulator 13 ... Pressure sensor 14 ... Pressure sensor 15 ... Controller

Claims (11)

[Claims] 1. A fuel cell main body in which a fuel electrode and an oxidizer electrode are opposed to each other with an electrolyte membrane sandwiched between them, and a fuel gas supply means for supplying a fuel gas to the fuel cell main body through a fuel gas supply passage. In the fuel cell system, a fuel gas discharge means for discharging exhaust fuel gas discharged from the fuel cell body to the outside is provided, and when the fuel cell system is started, the fuel gas is supplied from the fuel gas supply means to the fuel electrode at a substantially constant flow rate. A fuel cell system in which exhaust gas is supplied from the fuel gas exhausting means while gas is being supplied to replace the inside of the fuel gas supply passage and the inside of the fuel electrode with the fuel gas. 2. A purge means for temporarily discharging at least a part of the exhausted fuel gas discharged from the fuel cell main body to the outside during the operation of the fuel cell, wherein the fuel gas discharge means is provided by the purge means. The fuel cell system according to claim 1, wherein the fuel cell system also has a large opening area. 3. The fuel according to claim 1, wherein a variable throttle valve is provided in the fuel gas supply passage, and the opening of the variable throttle valve is made constant when the fuel gas is replaced. Battery system. 4. A variable throttle valve for controlling the flow rate of the fuel gas supply passage, an ejector arranged between the variable throttle valve and the fuel cell main body, and exhaust fuel gas discharged from the fuel cell main body. A fuel circulation pipe for returning to the intake port of the ejector; and a pressure detection means for detecting the fuel gas pressure upstream of the ejector, so that the fuel gas pressure upstream of the ejector becomes a predetermined value when the fuel gas is replaced. The fuel cell system according to claim 1 or 2, wherein the opening of the variable throttle valve is adjusted. 5. A pressure detecting means for detecting a fuel gas pressure downstream of the ejector is provided, and a predetermined value of the fuel gas pressure upstream of the ejector is determined according to the fuel gas pressure downstream of the ejector when the fuel gas is replaced. The fuel cell system according to claim 4, wherein the fuel cell system is a fuel cell system. 6. The fuel cell system according to claim 1, wherein the replacement of the fuel gas is terminated after a predetermined time has elapsed. 7. A fuel gas concentration detecting means for detecting a fuel gas concentration in a fuel electrode of a fuel cell main body or in a fuel gas passage, the fuel gas concentration detecting means detecting the fuel gas concentration based on the fuel gas concentration detected by the fuel gas concentration detecting means. The fuel cell system according to any one of claims 1 to 5, wherein the fuel gas replacement is completed. 8. The fuel gas discharge means is provided with a pressure detecting means for detecting a fuel gas pressure upstream, and the fuel gas replacement is terminated based on the pressure detected by the pressure detecting means. The fuel cell system according to any one of claims 1 to 5. 9. The fuel cell system according to claim 8, wherein the fuel gas replacement is terminated after a lapse of a predetermined time from the time when the pressure detecting means detects a predetermined pressure drop. 10. A fuel cell main body in which a fuel electrode and an oxidizer electrode are opposed to each other with an electrolyte membrane sandwiched between them, and a fuel gas supply means for supplying fuel gas to the fuel cell main body through a fuel gas supply passage. A fuel cell system comprising: a fuel gas discharge means for discharging exhaust fuel gas discharged from the fuel cell body to the outside; and a pressure detection means for detecting a fuel gas pressure upstream of the fuel gas discharge means. When the fuel cell is started, the fuel gas is supplied from the fuel gas supply means to the fuel electrode, and the exhaust fuel gas is discharged from the fuel gas discharge means, so that the fuel gas is supplied to the fuel gas supply passage and the inside of the fuel electrode of the fuel cell body. A fuel cell system, wherein fuel gas replacement for gas replacement is performed, and the fuel gas replacement is terminated based on the pressure detected by the pressure detection means. 11. The fuel cell system according to claim 10, wherein the fuel gas replacement is terminated after a lapse of a predetermined time from the time when the pressure detected by the pressure detecting means decreases to a predetermined value.