JP4106961B2 - Fuel cell system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fuel cell system, and more particularly to a fuel cell system capable of shortening a startup time.
[0002]
[Prior art]
For example, there is a method described in Japanese Patent No. 2735396 as a method for starting a fuel cell system.
In this conventional example, at the time of start-up, fuel and air are supplied, the output voltage of the fuel cell is monitored, and the power load is taken out when the output voltage value exceeds the allowable voltage lower limit value.
[0003]
[Problems to be solved by the invention]
However, even when the output voltage of the fuel cell is increased, there may be a problem if 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 pipe of the fuel cell gradually diffuses out of the system or gradually reacts with oxygen in the air inside the fuel cell and is lost. The inside is filled with air or nitrogen.
[0004]
Here, when fuel gas and air are supplied to the fuel electrode and the air electrode, respectively, to start the fuel cell system, the fuel cell is immediately replaced even if the air in the fuel electrode or fuel passage is not sufficiently replaced by the fuel gas. The output voltage rises. However, if the load is taken out immediately here, the concentration of the fuel gas in the fuel passage or the fuel electrode is insufficient, so that a sudden voltage drop occurs and the load cannot be taken out stably.
[0005]
The present invention has been made to solve the above-described problems of the prior art, and an object of the present invention is to provide a fuel cell system that can be reliably and quickly started even after being left for a long time. That is.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a fuel cell main body in which a fuel electrode and an oxidant electrode are provided with an electrolyte membrane interposed therebetween, and a fuel gas for supplying fuel gas to the fuel cell main body via a fuel gas supply passage A fuel cell body during operation of the fuel cell by opening and closing a supply means, a fuel circulation pipe for circulating the exhaust fuel gas discharged from the fuel cell body to the fuel gas supply passage, and the fuel circulation pipe and outside air in the fuel cell system and a purge valve for discharging temporarily outside air the exhaust fuel gas discharged from, has an opening area at the opening area larger than the discharge operation when the discharge operation of the purge valve , provided with a fuel gas exhaust valve for discharging exhaust fuel gas discharged from the fuel cell main body at startup of the fuel cell to the outside air by opening and closing between the fuel circulation pipe and the outside air, when starting the fuel cell system, While supplying fuel gas to the fuel electrode in serial fuel gas supply means or al a constant flow rate, by discharging the exhaust fuel gas from the fuel gas exhaust valve, with the fuel gas supply passage and the fuel electrode inside the fuel gas The gist is to perform replacement of the replacement fuel gas.
[0007]
【The invention's effect】
According to the present invention, when the fuel cell system is started, the fuel gas passage and the fuel electrode of the fuel cell are surely replaced with the fuel gas, so that the fuel cell system can be started in a short time even after being left for a long time. is there.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described in detail with reference to the drawings.
[First Embodiment]
FIG. 1 is a configuration diagram illustrating the configuration of a first embodiment of a fuel cell system according to the present invention. In the figure, a fuel cell stack 1 as a fuel cell main body is a structure in which a fuel cell structure in which a solid polymer electrolyte membrane is sandwiched between an oxidant electrode and a fuel electrode is sandwiched between separators, and a plurality of them are stacked. is there. Hydrogen is used as the fuel gas supplied to the fuel electrode, and air is used as the oxidant supplied to the oxidant electrode.
[0009]
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 is appropriate during normal operation.
[0010]
In this embodiment, a pressure regulator 12 is provided between the hydrogen tank 2 and the variable throttle valve 3 so that hydrogen gas at a constant pressure is supplied to the variable throttle valve 3 regardless of the residual pressure in the hydrogen tank 2. Is controlling.
[0011]
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. The surplus hydrogen that is the exhaust fuel gas discharged from the fuel cell stack 1 is returned to the suction port of the ejector 5 through the hydrogen return pipe 6 that is a fuel circulation pipe, and hydrogen is circulated by the ejector 5 during normal operation. As a result, the reaction efficiency of the fuel cell stack 1 is increased.
[0012]
The purge valve 7 using an on-off valve is a purge means for temporarily purging the hydrogen line during normal operation, for example, when the hydrogen passage in the fuel cell stack is blocked with water.
[0013]
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 activation, and is set to have 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 the air pressure adjusting valve 11 provided at the outlet of the oxidant electrode. Supply of air to the fuel cell stack 1 and control of air pressure are performed by the controller 15 controlling the compressor 9 and the air pressure adjusting valve 11.
[0014]
Next, an outline of the startup procedure of the fuel cell system having the above configuration will be described based on the flowchart of FIG.
First, when starting operation is started in step (hereinafter abbreviated as S) 11, an instruction to start replacement of the fuel electrode and the gas in the fuel pipe is given. Next, in S12, the hydrogen replacement valve 8 is opened, and in S13, hydrogen is supplied to the system at a substantially constant flow rate (for example, about 100 L / min), and the hydrogen line comprising the hydrogen pipe 4, the fuel electrode inside, and the hydrogen return pipe 6 is supplied. Hydrogen replacement (fuel gas replacement) is performed to replace the inside with newly supplied hydrogen.
[0015]
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. If the upstream / downstream pressure ratio of the variable throttle valve 3 is 1.9 or more, the variable throttle valve 3 is choked. Therefore, if the set pressure of the pressure regulator 12 is sufficiently high, the flow rate becomes constant if the opening degree is constant without being influenced by the downstream pressure of the variable throttle valve 3.
[0016]
In S14, it is determined that the hydrogen line has been sufficiently replaced when a predetermined time (for example, about 10 seconds) has elapsed, and the hydrogen replacement is completed, that is, the variable throttle valve 3 is closed, and the supply of hydrogen is stopped. The predetermined time is experimentally obtained in advance as a necessary minimum time at which sufficient replacement can be performed with the above-described replacement flow rate, and a certain degree of margin is added to the minimum required time, and replacement is performed only for that time. It is.
[0017]
In S15, the hydrogen replacement valve 8 is closed, and in S16, air and hydrogen are supplied based on the normal operation, and power load extraction is started.
[0018]
In the present embodiment, a hydrogen replacement valve 8 having an opening area larger than that of the purge valve 7 is provided separately from the purge valve 7. The reason why the hydrogen replacement valve 8 is provided separately from the conventional purge valve 7 is that the purge valve 7 wants to 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.
[0019]
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 when purging during normal operation is unnecessarily increased, and fuel consumption increases.
[0020]
On the other hand, if the valve opening area is reduced and the hydrogen replacement flow rate is increased during startup, the pressure applied to the fuel cell stack may increase due to valve pressure loss, which may damage the fuel cell stack. Therefore, the hydrogen replacement flow rate has to be reduced, the required replacement time is lengthened, and the startup time is extended.
[0021]
However, the cost can be reduced by using one valve, and one or two valves should be selected according to the balance of fuel consumption rate, start-up time, and cost.
[0022]
Although the system for circulating hydrogen with the ejector has been described above, it goes without saying that the present invention can be applied to a system for circulating hydrogen using a hydrogen circulation pump by external power and a system for not circulating hydrogen.
[0023]
As described above, according to the present embodiment, necessary and sufficient hydrogen replacement is reliably performed in the fuel gas supply passage and the fuel electrode at the time of startup. There is an effect that it becomes possible.
[0024]
In particular, by making the supply flow rate of the fuel gas substantially constant, it can be determined that the fuel gas has been sufficiently replaced when a predetermined time has elapsed, and thus the above-described effect can be obtained by simple control.
[0025]
Further, by making the opening of the variable throttle valve constant, the fuel gas supply flow rate becomes substantially constant, so that the control configuration becomes simpler.
[0026]
[Second Embodiment]
FIG. 3 is a configuration diagram illustrating the configuration of the 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 for detecting the ejector inlet pressure is provided between the variable throttle valve 3 and the ejector 5, and the hydrogen pressure supplied to the fuel cell stack 1 is changed. This is to provide a pressure sensor 14 for detection. Since other configurations are the same as those in FIG. 1, the same components are denoted by the same reference numerals and redundant description is omitted.
[0027]
In the present embodiment, the controller 15 adjusts the opening 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 made it.
[0028]
Since the flow path of the ejector 5 is restricted by the nozzle on the inlet side, pressure loss occurs when hydrogen is passed. Therefore, by setting the ejector inlet pressure at the time of hydrogen replacement to a value that 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. .
[0029]
Next, the hydrogen replacement procedure in this embodiment will be described with reference to the flowchart of FIG. First, when an instruction to start replacement is issued in S21, the hydrogen replacement valve 8 is opened in S22, and the opening of the variable throttle valve 3 is adjusted so that the inlet pressure of the ejector 5 detected by the pressure sensor 13 becomes a predetermined value in S23. Supply hydrogen while adjusting. When the hydrogen supply, that is, the actual replacement time reaches a predetermined time, the variable throttle valve 3 is closed at S24 to end the hydrogen supply, and the hydrogen replacement valve 8 is closed at S25 to end the series of replacement actions.
[0030]
Depending on the size of the nozzle of the ejector 5, the hydrogen replacement flow rate, etc., the ejector 5 may not be in a choked state during hydrogen replacement.
[0031]
The size of the ejector should be determined by the amount of hydrogen that is desired to be circulated by the ejector during normal operation, which is determined by the characteristics of the fuel cell stack.
[0032]
Further, if the hydrogen replacement flow rate is too large, the amount of hydrogen discharged increases, and a combustor (not shown) for burning the discharged hydrogen becomes larger or the fuel consumption deteriorates, so it cannot be increased extremely.
[0033]
For example, when an ejector having a large nozzle area is used and the hydrogen replacement flow rate is set to a small value, the ejector cannot be maintained in a choked state during replacement.
[0034]
In such a case, as shown in FIG. 5, in accordance with the inlet pressure of the fuel cell stack 1, the ejector inlet pressure at which the required hydrogen flow rate becomes a predetermined constant value is stored in the controller 15 in advance. If the variable throttle valve 3 is adjusted so that the same effect can be obtained, the same effect can be obtained.
[0035]
As described above, according to the present embodiment, as in the first embodiment, necessary and sufficient hydrogen replacement is surely performed at the time of start-up, and therefore, reliable start-up is possible even after standing for a long time. It became.
[0036]
In particular, by using an existing ejector and adjusting the variable throttle valve opening so that the fuel gas pressure upstream of the ejector becomes a predetermined value by utilizing the choke characteristic of the ejector, the fuel gas can be easily and reliably supplied. The supply flow rate can be made substantially constant.
[0037]
Further, since the fuel gas pressure upstream of the ejector is determined according to the fuel gas pressure downstream of the ejector, the fuel gas supply flow rate can be made substantially constant easily and reliably even if the fuel gas pressure downstream of the ejector fluctuates.
[0038]
[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 startup, and the replacement takes the longest time.
[0039]
When the hydrogen supply is started, the fuel cell stack inlet pressure once increases, and the pressure decreases as the replacement proceeds. When the hydrogen line is completely filled with hydrogen, the pressure becomes constant (P0) (for example, 3 kPa).
[0040]
This is because air has a higher molecular weight than hydrogen, and when it is replaced at a constant flow rate, the pressure when passing through the hydrogen replacement valve is higher than that of 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.
[0041]
In this embodiment, the fuel cell stack inlet pressure is used as the ejector downstream pressure.
[0042]
Moreover, the broken line in the figure is an example when hydrogen remains in the hydrogen line of the fuel cell system before startup. In the case of the solid line where the hydrogen line is filled with air, it is necessary to perform the replacement for t1 time, whereas in the case of the broken line where hydrogen remains, t2 (t2 <t1) is sufficient.
[0043]
In this embodiment, this characteristic is utilized, and the replacement is terminated when the inlet pressure of the fuel cell stack falls below a predetermined value (P0) during the hydrogen replacement.
That is, the pressure sensor 13 that detects the ejector inlet pressure also serves as a means for detecting the fuel gas concentration, and the hydrogen concentration in the fuel electrode and the fuel gas passage indicates that the inlet pressure of the fuel cell stack has fallen below a predetermined value (P0). Is considered to have exceeded the prescribed value (above the minimum concentration required for power generation).
[0044]
Next, hydrogen replacement at start-up in the present embodiment will be described based on the flowchart of FIG.
[0045]
First, when an instruction to start replacement is issued in S31, the hydrogen replacement valve 8 is opened in S32, and hydrogen is adjusted while adjusting the opening of the variable throttle valve 3 so that the ejector inlet pressure detected by the pressure sensor 13 becomes a predetermined value in S33. Supply. In S34, it is determined whether the inlet pressure of the fuel cell stack 1 detected by the pressure sensor 14 is equal to or lower than a predetermined value. When the pressure is higher than the predetermined value, the hydrogen supply is continued as it is. The hydrogen supply is finished by closing, the hydrogen replacement valve 8 is closed in S36, and the series of replacement work is completed.
[0046]
By doing so, it becomes possible to make the necessary minimum replacement time according to the remaining amount (concentration) of hydrogen in the hydrogen line of the fuel cell system, minimizing the amount of hydrogen lost by replacement, and reducing the startup time. It was possible to start reliably while shortening.
[0047]
In addition, the hydrogen remaining amount (concentration) in the hydrogen line can be determined from the gas pressure value upstream of the hydrogen replacement valve 8 serving as the fuel gas discharge means, and there is no need to use a sensor dedicated to hydrogen concentration.
[0048]
Further, by making the fuel gas supply flow rate substantially constant, it is easy to determine that the pressure upstream of the fuel gas discharge means has become a predetermined value or less as the fuel gas in the fuel electrode or the fuel gas passage increases. Become. When the present invention is not applied, even if the supply flow rate of the fuel gas becomes substantially constant and the pressure upstream of the fuel gas discharge means becomes a predetermined value or less, the increase in the fuel gas in the fuel electrode or in the fuel gas passage may occur. Therefore, it is difficult to determine whether the fuel gas supply flow rate fluctuates, and control becomes uncertain.
[0049]
In this embodiment, the pressure sensor 14 that detects the fuel cell stack inlet pressure is used. However, it goes without saying that the pressure sensor may be located downstream of the ejector, for example, downstream of the fuel cell stack.
[0050]
Originally, the hydrogen replacement valve inlet pressure is ideally used, 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.
[0051]
Although the replacement flow rate is made constant by making the ejector inlet pressure constant, the replacement flow rate may be made constant by making the variable throttle valve opening constant.
[0052]
[Fourth Embodiment]
The configuration of this embodiment is the same as that of the second embodiment shown in FIG.
In the third embodiment, when the hydrogen line is filled with air, the fuel cell stack inlet pressure at the time of replacement is, for example, sufficient when the hydrogen replacement flow rate and the hydrogen replacement valve are set to a maximum of 40 kPa. In the state after the replacement, the pressure is about 3 kPa. In order to withstand such a maximum pressure of 40 kPa and accurately detect a low pressure, an expensive pressure sensor is required.
[0053]
If the accuracy of the pressure sensor is low, it is predicted that the replacement will be completed even though the pressure sensor is not sufficiently replaced, or that the pressure will not drop to P0 on the sensor indication value and the replacement will not be completed.
[0054]
Therefore, in the present embodiment, the determination pressure is set to P1 (for example, 6 kPa) that is slightly higher than P0 in FIG. 6, and instead, after the fuel cell stack inlet pressure becomes P1 or less, a predetermined time (for example, about 3 seconds). ) The hydrogen supply was continued.
[0055]
FIG. 8 is a flowchart for explaining the hydrogen replacement operation of the present 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 the predetermined value (P1), hydrogen is continuously supplied for a predetermined time and the replacement is continued.
[0056]
By doing so, it was possible to reliably perform necessary and sufficient replacement while using a low-cost and low-accuracy pressure sensor, and to start up stably.
[0057]
Although the replacement flow rate is made constant by making the ejector inlet pressure constant, the replacement flow rate may be made constant by making the variable throttle valve opening constant.
[Brief description of the 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 for explaining 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 for explaining the operation of the second embodiment.
FIG. 5 is a diagram showing an ejector inlet pressure at which a hydrogen flow rate becomes a predetermined value with respect to a fuel cell stack inlet pressure.
FIG. 6 is a graph showing a change with time in the fuel cell stack inlet pressure during hydrogen replacement in the third embodiment.
FIG. 7 is a flowchart for explaining the operation of the third embodiment.
FIG. 8 is a flowchart for explaining the operation of the fourth embodiment.
[Explanation of symbols]
DESCRIPTION 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 substitution valve 9 ... Compressor 10 ... Air piping 11 ... Air pressure adjustment valve 12 ... Pressure Regulator 13 ... Pressure sensor 14 ... Pressure sensor 15 ... Controller

Claims (8)

A fuel cell main body in which a fuel electrode and an oxidant electrode are provided with an electrolyte membrane interposed therebetween, fuel gas supply means for supplying fuel gas to the fuel cell main body via a fuel gas supply passage, and exhausted from the fuel cell main body A fuel circulation pipe that circulates the exhaust fuel gas to the fuel gas supply passage, and a gap between the fuel circulation pipe and the outside air are opened and closed to temporarily remove the exhaust fuel gas discharged from the fuel cell body during fuel cell operation. In a fuel cell system comprising a purge valve that discharges to outside air,
Exhaust fuel discharged from the fuel cell main body when the fuel cell is started up by opening and closing between the fuel circulation pipe and outside air having an opening area larger than the opening area during the purge valve discharge operation. It has a fuel gas discharge valve that discharges gas to the outside air.
When the fuel cell system is started up, the fuel gas is supplied from the fuel gas supply means to the fuel electrode at a constant flow rate, and the exhaust gas is discharged from the fuel gas discharge valve, whereby the fuel gas supply passage and the fuel electrode are discharged. A fuel cell system for performing fuel gas replacement for replacing the inside with fuel gas. A variable throttle valve is provided in the fuel gas supply passage,
2. The fuel cell system according to claim 1, wherein the opening of the variable throttle valve is made constant at the time of the fuel gas replacement. A variable throttle valve for controlling the flow rate of the fuel gas supply passage;
An ejector disposed between the variable throttle valve and the fuel cell body;
A fuel circulation pipe for returning exhaust fuel gas discharged from the fuel cell main body to the intake port of the ejector;
Pressure detecting means for detecting fuel gas pressure upstream of the ejector,
The fuel cell system according to claim 1, wherein the variable throttle valve opening is adjusted so that the fuel gas pressure upstream of the ejector becomes a predetermined value when the fuel gas is replaced. Pressure detecting means for detecting fuel gas pressure downstream of the ejector;
4. The fuel cell system according to claim 3, wherein a predetermined value of the fuel gas pressure upstream of the ejector is determined according to the fuel gas pressure downstream of the ejector during the replacement of the fuel gas.   The fuel cell system according to any one of claims 1 to 4, wherein the fuel gas replacement is terminated when a predetermined time elapses. A fuel gas concentration detecting means for detecting the fuel gas concentration in the fuel electrode of the fuel cell body or in the fuel gas passage;
The fuel cell system according to any one of claims 1 to 4, wherein the fuel gas replacement is terminated based on the fuel gas concentration detected by the fuel gas concentration detecting means. Pressure detecting means for detecting a fuel gas pressure upstream of the fuel gas discharge valve;
The fuel cell system according to any one of claims 1 to 4, wherein the fuel gas replacement is terminated based on a pressure detected by the pressure detecting means. Pressure detecting means for detecting a fuel gas pressure upstream of the fuel gas discharge valve;
The fuel cell system according to any one of claims 1 to 4, characterized in that said pressure detecting means after a predetermined time has elapsed from when detecting a predetermined pressure drop, to terminate the fuel gas replacement.

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