JP2006127831A - Fuel cell system and control method of fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system capable of efficiently utilizing energy consumed during scavenging treatment and enhancing starting performance of a fuel cell by enhancing exhausting performance of residual water in addition to condensed water, and to provide the control method of the fuel cell system. <P>SOLUTION: Scavenging gas is passed to at least one of a fuel gas supply passage supplying fuel gas to the fuel cell and an oxidant gas supply passage supplying oxidant gas to conduct scavenging. When necessity of scavenging is judged, scavenging gas is supplied at low pressure and then the scavenging gas is supplied at higher pressure than the low pressure. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fuel cell system that performs a scavenging process for discharging residual water from a fuel cell, and a control method for the fuel cell system.

  In recent years, a fuel cell vehicle provided with a fuel cell as a vehicle drive source has been proposed. As this type of fuel cell, a fuel cell having a structure in which a predetermined number of unit cells each having a solid polymer electrolyte membrane interposed between an anode and a cathode is laminated is known. Then, hydrogen (fuel gas) is introduced into the anode and air (oxidant gas) is introduced into the cathode, thereby generating electric power through an electrochemical reaction between hydrogen and oxygen.

  Since the fuel cell generates water during power generation, the fuel cell contains water when power generation is stopped. If the fuel cell is stopped with water remaining in the fuel cell, for example, when starting a fuel cell vehicle in a low temperature environment, the residual water freezes and the reaction gas flow path is blocked, resulting in a long start time. End up. From the viewpoint of preventing such a situation, there has been proposed a technique for performing a purge process for discharging residual water when the fuel cell is stopped.

For example, Patent Document 1 proposes a technique for discharging the residual water in the gas flow path to the outside by purging the gas flow path of the reaction gas when the fuel cell is stopped. According to this technique, residual water in the gas flow path is discharged to the outside by circulating the dried purified gas by providing a gas supply line dedicated to purging.
JP 2000-512068 A

However, in the conventional technology, when the scavenging process is performed, the process of simply discharging the residual water to the outside of the fuel cell by simply increasing the gas flow rate in the gas flow path is performed. It cannot be said that the energy to be used is used efficiently, and further efficiency is desired.
Conventionally, although the residual water in the reaction gas channel can be removed as condensed water, the water remaining in the electrolyte membrane or the water on the surface of the reaction gas channel (these waters are referred to as “residual moisture”). ")" As a water vapor may be insufficient, and in this respect, improvement in discharge performance is required.

  Therefore, the present invention can efficiently use the energy consumed during the scavenging process, and can improve the startability of the fuel cell by improving the discharge performance of not only condensed water but also residual moisture. It is an object to provide a system and a control method for a fuel cell system. Here, as described above, the residual moisture refers to the moisture remaining inside the electrolyte membrane or the moisture on the surface of the reaction gas channel. The same applies to the following description.

  The invention according to claim 1 is a fuel cell (for example, fuel cell 1 in the embodiment) that generates power by supplying a fuel gas and an oxidant gas, and a fuel gas supply channel that supplies the fuel gas. (For example, the hydrogen supply channel 3 in the embodiment), the oxidant gas supply channel for supplying the oxidant gas (for example, the air supply channel 6 in the embodiment), the fuel gas channel, and the A scavenging means (for example, the air compressor 5 in the embodiment) that scavenges at least one of the oxidant gas flow paths by a scavenging gas supply, and a scavenging determination means (for example, an implementation) that determines whether scavenging by the scavenging means is necessary. Low pressure scavenging process for supplying scavenging gas supplied by the scavenging means at a low pressure when the scavenging determination means determines that scavenging is necessary And scavenging gas supply control means (for example, ECU 12, anode pressure adjusting valve 17, cathode pressure adjusting valve 18 in the embodiment) for performing high pressure scavenging processing for supplying scavenging gas at a pressure higher than the low pressure. To do.

  According to the present invention, when the scavenging determination means determines that scavenging is necessary, the scavenging gas supplied to the fuel cell is supplied at a large flow rate by performing a low pressure scavenging process by the scavenging gas supply control means. By scavenging. That is, when the low-pressure scavenging process is performed when the scavenging gas supplied by the scavenging means is a substantially constant amount, the volume of the scavenging gas increases according to Boyle's law (PV = constant). In other words, scavenging with a scavenging gas can be performed with a large volume flow rate by performing the low-pressure scavenging process. Therefore, residual water (condensed water) remaining as droplets in the fuel cell can be discharged by performing the low-pressure scavenging process.

  Then, after performing the low-pressure scavenging process, scavenging with a scavenging gas can be performed with a small volume flow rate by performing the high-pressure scavenging process. Therefore, residual moisture can be taken into the scavenging gas as water vapor (saturated), and the residual moisture can be discharged by discharging the scavenging gas. The startability of the battery can be improved.

  The invention according to claim 2 is a fuel cell in which scavenging gas is circulated through at least one of a fuel gas supply channel for supplying fuel gas to the fuel cell and an oxidant gas supply channel for supplying oxidant gas. The system control method is characterized in that when it is determined that scavenging is necessary, scavenging gas is supplied at a low pressure, and thereafter scavenging gas is supplied at a pressure higher than the low pressure.

  According to the present invention, when it is determined that scavenging is necessary, scavenging with a scavenging gas can be performed with a large volume flow rate by performing a low-pressure scavenging process. Therefore, residual water (condensed water) remaining as droplets in the fuel cell can be discharged by performing the low-pressure scavenging process. Then, after performing the low-pressure scavenging process, scavenging with a scavenging gas can be performed with a small volume flow rate by performing the high-pressure scavenging process. Therefore, residual moisture can be taken into the scavenging gas as water vapor (saturated), and the residual moisture can be discharged by discharging the scavenging gas. The startability of the battery can be improved.

  According to the first and second aspects of the invention, the energy consumed during the scavenging process can be efficiently used, and the discharge performance of not only the condensed water but also the residual moisture can be improved to start the fuel cell. Can increase the sex.

A fuel cell system according to an embodiment of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram showing a fuel cell system according to an embodiment of the present invention.
The fuel cell 1 is configured by stacking a plurality of cells formed by sandwiching a solid polymer electrolyte membrane 1a made of, for example, a solid polymer ion exchange membrane between an anode 1b and a cathode 1c from both sides. FIG. 1 shows only a single cell for simplification.

  Hydrogen is supplied as fuel to the anode 1b of the fuel cell 1 configured as described above, and air containing oxygen as an oxidant is supplied to the cathode 1c. As a result, hydrogen ions generated by the catalytic reaction at the anode 1b move to the cathode 1c through the electrolyte membrane 1a, and generate an electric power by causing an electrochemical reaction with oxygen at the cathode 1c. At this time, water is generated. The At this time, part of the generated water generated on the cathode 1c side is back-diffused to the anode 1b side through the electrolyte membrane 1a, so that the generated water is also present on the anode 1b side.

Hydrogen supplied from the hydrogen cylinder 2 is supplied to the anode 1 b of the fuel cell 1 through the hydrogen supply channel 3 via the shutoff valve 4.
On the other hand, air is pumped to the air supply channel 6 by the air compressor 5 and supplied to the cathode 1 c of the fuel cell 1.

  Further, the hydrogen supply flow path 3 and the air supply flow path 6 are connected via a merging flow path 9. The merging flow path 9 is provided with a scavenging valve 10. By controlling the opening and closing of the scavenging valve 10, it is possible to allow or prevent the merging of reaction gases (hydrogen, air) flowing through the flow paths 3 and 6, respectively. it can. In the present embodiment, the scavenging valve 10 is used for control when air is allowed to flow into the hydrogen supply channel 3 as a scavenging gas.

  Unreacted hydrogen that has not been consumed by the electrochemical reaction of the fuel cell 1 is discharged from the anode 1b to the circulation flow path 13 together with residual water such as produced water on the anode 1b side, and is supplied to the hydrogen supply flow via the ejector 14. Merge onto Road 3. That is, the hydrogen discharged from the fuel cell 1 merges with fresh hydrogen supplied from the hydrogen cylinder 2 and is supplied again to the anode 1 b of the fuel cell 1.

  The hydrogen discharge flow path 7 branched from the circulation flow path 13 is provided with an anode pressure adjustment valve 17, and the used hydrogen off-gas is discharged from the hydrogen discharge flow path 7 by opening the anode pressure adjustment valve 17. . Further, the pressure of the gas (hydrogen or scavenging gas described later) supplied to the anode 1 b of the fuel cell 1 through the hydrogen supply flow path 3 is adjusted by adjusting the opening of the anode pressure adjusting valve 17. The hydrogen off gas discharged from the hydrogen discharge channel 7 is diluted to a predetermined concentration or less by a dilution box (not shown), but the details are omitted.

  On the other hand, a cathode pressure adjusting valve 18 is provided in the air discharge channel 8. By opening the cathode pressure regulating valve 18, the reacted air-off gas is discharged from the air discharge channel 8. Further, the air pressure (cathode pressure) supplied to the cathode 1 c of the fuel cell 1 can be adjusted by adjusting the opening of the cathode pressure adjusting valve 18. The hydrogen supply channel 3 and the air supply channel 6 are provided with pressure sensors 19 and 20 for measuring the anode pressure and the cathode pressure, respectively. The fuel cell 1 is provided with a voltage sensor 21 for measuring the generated voltage.

The fuel cell system is provided with a control unit (ECU) 12 that controls various devices.
An ignition switch 15 is connected to the control unit 12, and ignition ON / OFF (IG-ON, IG-OFF) signals are input from these.
In addition, pressure sensors 19 and 20 and a voltage sensor 21 are connected to the control unit 12, and an anode pressure, a cathode pressure, and a power generation voltage are input from these.

  Then, the control unit 12 outputs signals for driving the air compressor 5, the shutoff valve 4, the scavenging valve 10, the anode pressure adjustment valve 17, and the cathode pressure adjustment valve 18 based on these input detection values and signals. .

The operation of the fuel cell system configured as described above will be described with reference to FIG. FIG. 2 is a flowchart showing the processing contents of the scavenging control of the fuel cell system shown in FIG.
First, in step S10, when the ignition switch 15 is switched from ON to OFF and an operation stop signal is input (IG-OFF), the shutoff valve 4 of the hydrogen supply flow path 3 is closed in step S12. The supply of hydrogen to the anode 1b of the fuel cell 1 is stopped (power generation is stopped). Then, when the voltage value detected by the voltage sensor 21 becomes a predetermined value or less, the process proceeds to step S14.

  In step S14, the scavenging valve 10 is opened. Thereby, the gas flow of the confluence | merging flow path 9 is enabled. In this state, the air compressor 5 is driven to supply air to the air supply flow path 6, whereby air can be supplied also to the hydrogen supply flow path 3 through the merging flow path 9. Therefore, not only the cathode 1c side but also the scavenging treatment on the anode 1b side can be performed together. Therefore, the scavenging process can be performed without consuming hydrogen.

  At this time, an air low pressure supply process is performed at step S16. This air low pressure supply process is performed by increasing the opening degree of the anode pressure regulating valve 17 and the cathode pressure regulating valve 18 (for example, a fully opened state or a substantially fully opened state). Thereby, the air pressure supplied to the anode 1b and the cathode 1c can be reduced.

  When the low-pressure scavenging process is performed in this manner, the volume of air that is the scavenging gas increases according to Boyle's law (PV = constant). In other words, by performing the low-pressure scavenging process, it is possible to perform scavenging with air at a large volume flow rate. By performing the low-pressure scavenging process and increasing the differential pressure between the residual water accumulation site in the anode 1b and the cathode 1c of the fuel cell 1 and the hydrogen discharge channel 7 and the air discharge channel 8, the fuel cell 1 The discharge of residual water (condensed water) remaining as droplets can be promoted. Here, the low pressure is, for example, a pressure lower than the pressure supplied to the cathode 1 c during normal power generation of the fuel cell 1.

  In step S18, it is determined whether or not the low pressure scavenging process is completed. If the determination result is YES, the process proceeds to step S20, and if the determination result is NO, the process of step S18 is repeated. In the present embodiment, the completion of the scavenging process is determined by measuring whether a preset scavenging time has elapsed using a timer. In place of the timer, the pressure sensors 19 and 20 may be used to detect a change in pressure, or pressure sensors are provided on the inlet side and the outlet side of the anode 1b and the cathode 1c, respectively. You may carry out by detecting a differential pressure.

  In step S20, an air high pressure supply process is performed. This air high pressure supply process is performed by reducing the opening degree of the anode pressure adjusting valve 17 and the cathode pressure adjusting valve 18 (for example, in a half-open state). Thereby, the air pressure supplied to the anode 1b and the cathode 1c can be increased. Thereby, scavenging by air can be performed with a small volume flow rate. Therefore, the residual moisture can be discharged by taking the residual moisture as water vapor into the air (saturating) and discharging the air. Thus, by performing low-pressure scavenging (in other words, small-flow scavenging), it is possible to increase the efficiency of taking in (saturating) residual moisture as water vapor.

  This point will be described more specifically. Since the water accumulated in the electrolyte membrane 1a and the like of the fuel cell 1 is accumulated in the pores such as the diffusion layer, the surface tension is large, and it is difficult to drain by physical force (suction force due to differential pressure). It is. In discharging such residual moisture, it is necessary to convert the moisture into water vapor and remove it in order to reduce the surface tension. Therefore, in order to remove the water accumulated in the electrolyte membrane 1a and the like in the fuel cell 1, the air is supplied into the fuel cell 1 by increasing the pressure of the air supplied to the fuel cell 1 and decreasing the volume flow rate. The residence time can be increased. Thereby, since the air supplied to the fuel cell 1 can sufficiently contain the accumulated moisture (in other words, it can be removed as water vapor), the removal of residual moisture can be promoted.

  In step S22, it is determined whether high-pressure scavenging has been completed. If the determination result is YES, the process proceeds to step S24, and if the determination result is NO, the process returns to step S22. This determination method may be performed by a timer or by detecting the differential pressure as described above. In step S24, the scavenging valve 10 is closed and the compressor 5 is stopped to stop the supply of air. And the process of this flowchart is complete | finished.

  Next, a second embodiment of the present invention will be described. Hereinafter, the same reference numerals are given to the same configurations and processing contents as those of the above-described embodiment, and the description thereof will be omitted as appropriate. FIG. 3 is a block diagram showing a fuel cell system according to the second embodiment of the present invention. As shown in the figure, the fuel cell system in the present embodiment includes a scavenging gas supply device 23 separately from the air compressor 5. Here, the scavenging gas may be air or an inert gas such as nitrogen. A scavenging gas supply passage 24 is connected to the scavenging gas supply device 23. The scavenging gas supply flow path is connected to the hydrogen supply flow path 3 and the air supply flow path 6 via the merge flow paths 25 and 27, respectively. The merging passages 25 and 27 are provided with scavenging valves 26 and 28, respectively.

  FIG. 4 is a flowchart showing the processing contents of the scavenging control of the fuel cell system shown in FIG. As shown in the figure, after the power generation stop process is performed in step S12, a scavenging gas low pressure supply process is performed in step S32. In step S32, the scavenging valves 26 and 28 are opened to allow the gas flow in the merging passages 25 and 27, respectively. In this state, the scavenging gas is circulated from the scavenging gas supply device 23 to the hydrogen supply channel 3 and the air supply channel 6 through the scavenging gas supply channel 24 and the merging channels 25 and 27, and the anode of the fuel cell 1. 1b, scavenging gas is supplied to the cathode 1c. The opening of the anode pressure adjustment valve 17 and the cathode pressure adjustment valve 18 is increased, and the low pressure scavenging process of step S32 is performed. In step S18 described above, it is determined whether or not the low-pressure scavenging process has been completed.

  If the decision result in the step S18 is YES, the opening degree of the anode pressure adjusting valve 17 or the cathode pressure adjusting valve 18 is reduced, and a scavenging gas high pressure supply process is performed in a step S34. In step S22 described above, it is determined whether or not the high-pressure scavenging process has been completed. If the decision result in the step S22 is YES, the scavenging valves 26 and 28 are closed in a step S36, a process of stopping the supply of the scavenging gas is performed, and the process of this flowchart is ended.

Differences between the scavenging process in the first and second embodiments of the present invention described above and the scavenging process in the comparative example corresponding to the prior art will be described with reference to FIGS.
First, in the comparative example, as shown in FIG. 6, the scavenging gas pressure is maintained at a substantially constant high pressure from the start to the end of the scavenging process. In such control, although residual water in the fuel cell 1 is discharged, it is difficult to discharge water accumulated in the electrolyte membrane 1a and the like of the fuel cell 1. Further, since the scavenging process is maintained at a high pressure state, the energy required for the scavenging process increases correspondingly, and it cannot be said that the energy consumed during the scavenging process is efficiently utilized.

  On the other hand, in the above-described embodiment, as shown in FIG. 5, at the initial stage of scavenging, since the scavenging gas pressure is maintained at a low pressure, the flow rate of the scavenging gas can be increased and the residual gas can be quickly retained. Water can be discharged. Moreover, the energy required for scavenging can be reduced by maintaining the pressure of the scavenging gas at a low pressure. In the later stage of scavenging, since the pressure of the scavenging gas is changed to a high pressure, the volumetric flow rate of the scavenging gas can be reduced by that amount, and the residual moisture in the fuel cell 1 can also be efficiently removed.

  Of course, the contents of the present invention are not limited to the above-described embodiments. For example, in the above-described embodiment, the case where the scavenging process is performed when power generation is stopped has been described, but the scavenging process of the present invention is not limited to when power generation is stopped.

1 is a block diagram showing a fuel cell system according to a first embodiment of the present invention. It is a flowchart which shows the processing content of the scavenging control of the fuel cell system shown in FIG. It is a block diagram which shows the fuel cell system in the 2nd Embodiment of this invention. It is a flowchart which shows the processing content of the scavenging control of the fuel cell system shown in FIG. It is a graph which shows the time change of the scavenging gas pressure in the 1st and 2nd embodiment of this invention. It is a graph which shows the time change of the scavenging gas pressure in the comparative example corresponded to a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Fuel cell 3 ... Hydrogen supply flow path (fuel gas supply flow path)
5. Air compressor (scavenging means)
6. Air supply channel (oxidant gas supply channel)
12 ... ECU (scavenging judgment means, scavenging gas supply control means)
17 ... Anode pressure regulating valve (scavenging gas supply control means)
18 ... Cathode pressure regulating valve (scavenging gas supply control means)

Claims (2)

A fuel cell that generates power by supplying fuel gas and oxidant gas;
A fuel gas supply channel for supplying the fuel gas;
An oxidant gas supply channel for supplying the oxidant gas;
Scavenging means for scavenging at least one of the fuel gas flow path and the oxidant gas flow path by a scavenging gas supply;
Scavenging judgment means for judging whether or not scavenging by the scavenging means is necessary,
When the scavenging determination means determines that scavenging is necessary, scavenging that performs a low pressure scavenging process for supplying the scavenging gas supplied by the scavenging means at a low pressure and a high pressure scavenging process for supplying the scavenging gas at a pressure higher than the low pressure. A fuel cell system comprising gas supply control means. A control method of a fuel cell system for performing scavenging by flowing a scavenging gas through at least one of a fuel gas supply channel for supplying fuel gas to a fuel cell and an oxidant gas supply channel for supplying oxidant gas,
When it is determined that scavenging is necessary, the scavenging gas is supplied at a low pressure, and then the scavenging gas is supplied at a pressure higher than the low pressure.

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