JP2019079720A - Fuel cell system and operation method thereof - Google Patents

Abstract

To improve reliability of a fuel cell system where unreacted fuel gas is supplied again to a fuel cell as fuel gas, while realizing high efficiency of the fuel cell system.SOLUTION: A buffer tank 8 capable of changing capacity is provided in an unreacted fuel gas circulation passage 4 for supplying the unreacted fuel gas, as fuel gas, to a fuel cell 1. A controller 101 controls the capacity of the buffer tank 8 to a first capacity during stoppage of a fuel cell system 100, and controls the capacity of the buffer tank 8 to a second capacity larger than the first capacity during power generation. Before the impurity gas concentration of the unreacted fuel gas flowing through the unreacted fuel gas circulation passage 4 reaches a preset upper limit of impurity gas concentration, an unreacted fuel gas purge valve 6 is opened, and the impurity gas in the unreacted fuel gas circulation passage 4 is purged from an unreacted fuel gas purge passage 5 to the outside.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a fuel cell system provided with an unreacted fuel gas circulation path for supplying again, as fuel gas, unreacted fuel gas discharged from the anode of the fuel cell, and a method of operating the fuel cell system.

  In the fuel cell system, for example, in order to effectively utilize the fuel gas containing hydrogen supplied to the anode of the fuel cell to enhance the power generation efficiency of the fuel cell system, the fuel cell is discharged from the anode without being used for power generation. The unreacted fuel gas circulation path is provided such that the unreacted fuel gas is supplied again to the anode of the fuel cell.

  When a fuel cell using an electrolyte membrane is provided with an unreacted fuel gas circulation path, an impurity gas such as nitrogen contained in the oxidant gas (air) supplied to the cathode permeates from the cathode side to the anode side to cause unreacted gas The fuel gas circulating in the fuel gas circulation path is concentrated to inhibit the power generation of the fuel cell, the power generation voltage of the fuel cell is reduced, and the power generation efficiency of the fuel cell is greatly reduced.

  Therefore, the unreacted fuel gas circulation path includes an unreacted fuel gas atmosphere opening path for releasing the unreacted fuel gas to the atmosphere, and an atmosphere opening valve (purge valve) for opening and closing the unreacted fuel gas atmosphere opening path. When the predetermined condition is satisfied periodically, the atmosphere open valve (purge valve) is opened to purge the impurity gas in the unreacted fuel gas circulation path with the unreacted fuel gas to the atmosphere (purge).

  Here, when the cell voltage of the fuel cell falls below a predetermined state due to the impurity gas concentrated to the fuel gas with the passage of time from the start of power generation of the fuel cell, the air release valve (purge valve) is opened. A fuel cell system has been proposed in which the decrease in the power generation voltage of the fuel cell is suppressed by purging the impurity gas together with the unreacted fuel gas for a time only (see, for example, Patent Document 1).

Patent No. 4427833

  In the above-described conventional configuration, during power generation, in order to suppress the voltage drop due to the impurity gas, the drop of the cell voltage of the fuel cell is detected, the purge valve is opened, and the impurity gas purge is performed. The amount of impurity gas permeating from the oxidant gas side to the fuel gas side is the same regardless of the volume of the unreacted fuel gas circulation path.

  In order to improve the durability of the purge valve, there is a method of increasing the volume of the unreacted fuel gas circulation path as a method of suppressing the increase of the impurity gas concentration by reducing the number of times of operation of the purge valve during power generation.

  Further, since the purge valve is closed during the stop, the amount of impurity gas in the unreacted fuel gas circulation path increases, and the impurity gas is purged at the time of start-up. In order to improve the power generation efficiency, there is a method of reducing the volume of the unreacted fuel gas circulation path only during the stop so as not to perform the impurity gas purge at the start.

  In the above-mentioned prior art, since the volume of the unreacted fuel gas circulation path is constant, there is a problem that it is impossible to simultaneously improve the durability of the purge valve and the power generation efficiency.

  An object of the present invention is to provide a fuel cell system capable of achieving both the improvement of the durability of the purge valve and the improvement of the power generation efficiency.

  In order to solve the above-mentioned conventional problems, a fuel cell system according to the present invention comprises a fuel cell that generates electric power by reacting a fuel gas supplied to an anode with an oxidant gas supplied to a cathode. Fuel gas supply path for supplying fuel gas to the anode, unreacted fuel gas circulation path for supplying unreacted fuel gas discharged from the anode of the fuel cell to the fuel gas supply path as fuel gas, and unreacted fuel gas A transport means provided in the circulation path for supplying unreacted fuel gas to the fuel gas supply path, an unreacted fuel gas purge path branched from the unreacted fuel gas circulation path, and an unreacted fuel gas purge valve for opening and closing the unreacted fuel gas purge path And a buffer tank provided in the unreacted fuel gas circulation path and capable of changing the volume, volume changing means for changing the volume of the buffer tank, and a controller And the controller controls the volume changing means so that the volume of the buffer tank is at the first volume during stoppage, and at the time of power generation, the volume of the buffer tank is at the second volume larger than the first volume. Control the volume changing means so that the unreacted fuel gas purge valve passes the unreacted fuel gas purge valve before the impurity gas concentration of the unreacted fuel gas reaches the preset upper limit value of the impurity gas concentration. It is configured to control to open purge.

  As a result, at the time of power generation, the increase in the impurity gas concentration can be suppressed by increasing the volume of the buffer tank in the unreacted fuel gas circulation path, so the number of times of operation of the unreacted fuel gas purge valve can be reduced.

  Furthermore, at the time of stop, the volume of the buffer tank in the unreacted fuel gas circulation path is reduced, and at the time of activation to generate power, the volume of the buffer tank in the unreacted fuel gas circulation path is increased. This can be lowered, and it is not necessary to purge the impurity gas conventionally performed at the time of startup, and it becomes possible to achieve both the improvement of the durability of the unreacted fuel gas purge valve and the improvement of the power generation efficiency.

  According to the fuel cell system of the present invention, at the time of power generation, by increasing the volume of the unreacted fuel gas circulation path, the number of times of operation of the unreacted fuel gas purge valve is reduced and the durability of the unreacted fuel gas purge valve is improved. The reliability of the fuel cell system is improved.

  Further, at the time of stop, the volume of the unreacted fuel gas circulation path is reduced, and at the time of power generation by start-up, the volume of the unreacted fuel gas circulation path is increased. It is not necessary to perform the impurity gas purge which has been performed.

  As a result, the start-up time can be shortened, and the fuel gas used for the impurity gas purge can be reduced, so that the fuel cell system can be made more efficient.

Block diagram showing a schematic configuration of a fuel cell system according to Embodiments 1 and 3 of the present invention (A) A schematic view showing the volume in the buffer tank of part A in FIG. 1 and the water level in the buffer tank during stop of the fuel cell system (b) Inside the buffer tank of part A in FIG. 1 during power generation of the fuel cell system Diagram showing the volume of water and the water level in the buffer tank Flowchart showing operation method of fuel cell system in Embodiments 1 and 3 of the present invention Block diagram showing a schematic configuration of a fuel cell system according to Embodiment 2 of the present invention (A) A schematic view showing the volume in the buffer tank of part B in FIG. 4 and the water level in the buffer tank during stop of the fuel cell system (b) The buffer tank in part B in FIG. 4 during power generation of the fuel cell system Diagram showing the volume of water and the water level in the buffer tank Flow chart showing operation method of fuel cell system in Embodiment 2 of the present invention A characteristic diagram showing the relationship between the stop time of the fuel cell system and the first volume of the buffer tank during stop according to Embodiment 3 of the present invention

  According to a first aspect of the present invention, there is provided a fuel cell generating electricity by reacting a fuel gas supplied to an anode with an oxidant gas supplied to a cathode, and a fuel gas supply path for supplying the fuel gas to the anode of the fuel cell An unreacted fuel gas circulation path for supplying unreacted fuel gas discharged from the anode of the fuel cell as a fuel gas to the fuel gas supply path, and an unreacted fuel gas circulation path provided with unreacted fuel gas as a fuel gas Provided in the unreacted fuel gas circulation passage, transport means for supplying to the supply passage, an unreacted fuel gas purge passage branched from the unreacted fuel gas circulation passage, an unreacted fuel gas purge valve for opening and closing the unreacted fuel gas purge passage, A buffer tank capable of changing the volume, volume changing means for changing the volume of the buffer tank, and a controller, wherein the controller The volume changing means is controlled so that the volume becomes the first volume, and at the time of power generation, the volume changing means is controlled so that the volume of the buffer tank becomes the second volume larger than the first volume, and unreacted fuel gas The fuel cell system is controlled to open and purge the unreacted fuel gas purge valve before the impurity gas concentration of the unreacted fuel gas flowing through the circulation path reaches the preset upper limit value of the impurity gas concentration.

  With this configuration, the fuel cell system is provided with a buffer tank having a variable capacity in the unreacted fuel gas circulation path that supplies the unreacted fuel gas discharged from the anode of the fuel cell as the fuel gas again to the anode. At times, the volume of the buffer tank provided in the unreacted fuel gas circulation path is changed to be large.

  As a result, it is possible to suppress the concentration rate of the impurity gas in the unreacted fuel gas in the unreacted fuel gas circulation path including the buffer tank, thereby suppressing the number of times of operation of the unreacted fuel gas purge valve. The durability of the valve is improved, and the reliability of the fuel cell system is improved.

  In addition, the volume of the buffer tank in the unreacted fuel gas circulation path is changed to be smaller while the fuel cell system is stopped, and the volume of the buffer tank in the unreacted fuel gas circulation path is increased when the fuel cell system is activated to generate power. .

  As a result, at the time of start-up, the concentration of the impurity gas concentrated in the unreacted fuel gas circulation path including the buffer tank can be lowered, and it becomes unnecessary to perform the impurity gas purge conventionally performed at the time of start-up. As a result, the start-up time of the fuel cell system can be shortened, and the fuel gas used for the impurity gas purge can be reduced, so that the fuel cell system can be made more efficient.

In the second invention, particularly as the volume changing means in the first invention, the water supply device for supplying water into the buffer tank and the water discharge valve for discharging the water in the buffer tank are provided. The outlet of unreacted fuel gas to the reactive fuel gas circulation path is disposed at a position higher than the highest water level in the buffer tank, and the controller is configured to bring the volume of the buffer tank to the first volume during stoppage, The fuel cell system controls the amount of water in the buffer tank so that the volume of the buffer tank becomes a second volume larger than the first volume during power generation.

  With this configuration, readily available water can be used as a buffer tank volume changing means. Accordingly, by controlling the amount of water in the buffer tank without changing the tank configuration, it is possible to change the volume of the buffer tank to be large at the time of power generation.

  As a result, it is possible to suppress the concentration rate of the impurity gas in the unreacted fuel gas in the unreacted fuel gas circulation path including the buffer tank, thereby suppressing the number of times of operation of the unreacted fuel gas purge valve. The durability of the valve is improved, and the reliability of the fuel cell system is improved.

  Further, the volume of the buffer tank can be changed to be smaller by controlling the amount of water in the buffer tank without changing the tank configuration even during the stop. As a result, at the time of start-up, the concentration of the impurity gas concentrated in the fuel gas circulating in the unreacted fuel gas circulation path including the buffer tank can be lowered, and the impurity gas purge conventionally performed at the start-up is eliminated. .

  As a result, the start-up time of the fuel cell system can be shortened, and the fuel gas used for the impurity gas purge can be reduced, so that the fuel cell system can be made more efficient.

  In the third invention, in addition to the second invention in particular, the water level in the buffer tank when the volume of the buffer tank becomes the first volume, and the volume in the buffer tank when the volume of the buffer tank becomes the second volume The fuel cell system includes a water level detector that detects the water level, and the controller controls the water supplier and the water discharge valve based on the detected water level of the water level detector.

  With this configuration, the volume of the buffer tank can be set more accurately by detecting the volume of the buffer tank with the water level detector. Thus, the durability of the unreacted fuel gas purge valve can be improved by further suppressing the number of times of operation of the unreacted fuel gas purge valve, and the reliability of the fuel cell system can be further improved.

  A fourth invention is, in particular, a fuel cell system in which the controller in any of the first to third inventions controls the first volume of the buffer tank to change according to the stop time.

  With this configuration, it is not necessary to change the first volume of the buffer tank according to the stop time and unnecessarily increase the volume difference with the second volume of the buffer tank. Since the time required to change from the second volume to the first volume and the power consumption of the device required to change the volume can be reduced, it is possible to further improve the efficiency of the fuel cell system.

According to a fifth aspect of the present invention, there is provided a fuel cell that generates electric power by reacting a fuel gas supplied to an anode with an oxidant gas supplied to a cathode, and a fuel gas supply path for supplying the fuel gas to the anode of the fuel cell An unreacted fuel gas circulation path for supplying unreacted fuel gas discharged from the anode of the fuel cell as a fuel gas to the fuel gas supply path, and an unreacted fuel gas circulation path provided with unreacted fuel gas as a fuel gas Provided in the unreacted fuel gas circulation passage, transport means for supplying to the supply passage, an unreacted fuel gas purge passage branched from the unreacted fuel gas circulation passage, an unreacted fuel gas purge valve for opening and closing the unreacted fuel gas purge passage, A method of operating a fuel cell system comprising: a buffer tank capable of changing the volume; and volume changing means for changing the volume of the buffer tank The volume of the buffer tank is made the first volume by the volume changing means, and at the time of power generation, the volume of the buffer tank is made the second volume larger than the first volume by the volume changing means and unreacted gas flowing in the unreacted fuel gas circulation path It is characterized in that the unreacted fuel gas purge valve is opened and purged before the impurity gas concentration of the fuel gas reaches a preset upper limit value of the impurity gas concentration.

  By using this operation method, at the time of power generation, the volume of the buffer tank is changed to be large. As a result, it is possible to suppress the concentration rate of the impurity gas in the unreacted fuel gas in the unreacted fuel gas circulation path including the buffer tank, thereby suppressing the number of times of operation of the unreacted fuel gas purge valve. The durability of the valve is improved, and the reliability of the fuel cell system is improved.

  Also, during stoppage, the volume of the buffer tank is changed to be smaller, and when the fuel cell system is activated to generate power, the volume of the buffer tank is increased. As a result, at the time of start-up, the concentration of the impurity gas concentrated in the unreacted fuel gas circulation path including the buffer tank can be lowered, and it becomes unnecessary to perform the impurity gas purge conventionally performed at the time of start-up.

  As a result, the start-up time can be shortened, and the fuel gas used at the time of impurity gas purge can be reduced, so that it is possible to provide a method of operating a fuel cell system that can increase the efficiency of the fuel cell system.

  Hereinafter, embodiments of the present invention will be specifically exemplified. In all the drawings, the same or corresponding parts are denoted by the same reference numerals, and redundant description will be omitted.

  Further, in all the drawings, only components necessary to explain the present invention are extracted and shown, and the other components are not shown. Furthermore, the present invention is not limited to the following embodiments.

Embodiment 1
FIG. 1 is a block diagram showing a schematic configuration of a fuel cell system according to Embodiment 1 of the present invention. FIG. 2 is a schematic view showing the volume in the buffer tank and the water level in the buffer tank of part A in FIG. 1 during stop and generation of the fuel cell system in Embodiment 1 of the present invention. FIG. 3 is a flow chart showing a method of operating a fuel cell system according to Embodiment 1 of the present invention.

  As shown in FIG. 1, the fuel cell system 100 of Embodiment 1 includes a fuel cell 1, a fuel gas supply path 2, an oxidant gas supply path 3, an unreacted fuel gas circulation path 4, and an unreacted fuel. A gas purge path 5, an unreacted fuel gas purge valve 6, a transport unit 7, a buffer tank 8, a water supplier 9, a water discharge valve 10, and a controller 101 are provided.

  The fuel cell 1 generates electricity using a fuel gas containing hydrogen supplied to the anode and an oxidant gas containing oxygen supplied to the cathode. The fuel gas and the oxidant gas are supplied by respective supply devices (not shown).

  In the present embodiment, pure hydrogen gas is used as the fuel gas, and the fuel gas is supplied to the anode of the fuel cell 1 at a pressure higher than the pressure loss generated in the fuel cell system. In addition, air is used as the oxidant gas. For the fuel cell 1, a polymer electrolyte fuel cell is used.

The fuel gas supply path 2 is a path for supplying pure hydrogen gas to the anode of the fuel cell 1. The oxidant gas supply path 3 is a path for supplying air to the cathode of the fuel cell 1.

  The unreacted fuel gas circulation path 4 is a path for again supplying the unreacted fuel gas discharged from the anode of the fuel cell 1 to the anode of the fuel cell 1 as a fuel gas, and is discharged from the anode of the fuel cell 1 The outlet end of the unreacted fuel gas circulation passage 4 is in communication with the fuel gas supply passage 2 so that the unreacted fuel gas merges with the fuel gas flowing through the fuel gas supply passage 2.

  The unreacted fuel gas purge path 5 is a path branched from the unreacted fuel gas circulation path 4 and for purging the unreacted fuel gas in the unreacted fuel gas circulation path 4 to the outside. In the present embodiment, by diluting the purged unreacted fuel gas with air, the concentration of hydrogen contained in the unreacted fuel gas is lowered to the flammable range or lower and purged to the atmosphere.

  The unreacted fuel gas purge valve 6 is provided in the middle of the unreacted fuel gas purge path 5 and is an on-off valve for opening and closing the path for purging the unreacted fuel gas in the unreacted fuel gas circulation path 4 to the outside. . In the present embodiment, a solenoid valve is used for the unreacted fuel gas purge valve 6.

  Transport means 7 circulates unreacted fuel gas in unreacted fuel gas circulation path 4 (transfers unreacted fuel gas discharged from the anode of fuel cell 1 to unreacted fuel gas circulation path 4 to fuel gas supply path 2 And a pump provided in the unreacted fuel gas circulation passage 4 on the upstream side of the branch point with the unreacted fuel gas purge passage 5.

  The buffer tank 8 is provided in the unreacted fuel gas circulation path 4 on the upstream side of the transport means 7, and is a tank capable of changing the volume in the path of the unreacted fuel gas circulation path 4. In the present embodiment, the buffer tank 8 is a solid tank, and the volume of the buffer tank 8 is artificially changed by the amount of water in the buffer tank 8. Hereinafter, in the present embodiment, the volume of the buffer tank 8 is described as the volume changed by the amount of water in the buffer tank 8.

  The water supplier 9 is provided to be connected to the buffer tank 8 in order to supply water to the buffer tank 8.

  The water discharge valve 10 is provided to be connected to the bottom of the buffer tank 8 in order to discharge the water of the buffer tank 8.

  The controller 101 has a control function for controlling the fuel cell system 100, and includes an arithmetic processing unit (not shown) and a storage unit (not shown) for storing a control program. The arithmetic processing unit includes a CPU. The storage unit includes a memory.

  The polymer electrolyte fuel cell generally has a structure in which the MEA is sandwiched by the separators, and in the present embodiment, the MEA includes a gas diffusion layer, a cathode catalyst layer, a solid polymer electrolyte membrane, an anode catalyst layer, and It has a structure in which gas diffusion layers are stacked. The cell reaction proceeds in a cathode catalyst layer and an anode catalyst layer composed of a catalyst, a catalyst-supporting carrier, and an ionomer (ion conductive polymer).

  It is difficult for the fuel cell 1 to use all the supplied pure hydrogen gas for power generation because of the gas diffusion performance of the gas flow path in the fuel cell 1, etc., and the unreacted fuel gas is discharged from the fuel cell 1 Be done. If the discharged unreacted fuel gas is discarded as it is, pure hydrogen gas is wasted and the power generation efficiency of the fuel cell system 100 is reduced. Therefore, the unreacted fuel gas not used in the fuel cell 1 is reused as a fuel cell It circulates to 1 fuel gas supply route 2.

  At this time, since the impurity gas such as nitrogen contained in the air is permeated and concentrated from the oxidant gas side to the fuel gas side through the electrolyte membrane in the fuel cell 1, unreacted fuel gas is generated with the lapse of time from the start of power generation. Impurity gas is concentrated.

  Therefore, the amount of the impurity gas to be concentrated is grasped in advance by experiment, and the impurity gas is periodically purged together with the unreacted fuel gas at predetermined time intervals when the amount of the impurity gas is accumulated for a predetermined amount. As well as preventing the gas from being purged, it is possible to prevent the power generation efficiency of the fuel cell 1 from being greatly reduced due to a decrease in the power generation voltage of the fuel cell 1.

  The volume of the buffer tank 8 is set by the amount of water in the buffer tank 8 from the water supply time of the water supply device 9 and the water discharge time of the water discharge valve 10 set in advance by experiment. In the present embodiment, the volume of the unreacted fuel gas circulation path 4 is set to 200 cc, the first volume V1 of the buffer tank 8 being stopped is set to 50 cc, and the second volume V2 of the buffer tank 8 being generated is set to 300 cc.

  At this time, the volume in the non-reacted fuel gas circulation passage 4 during stoppage is 250 cc, and the volume in the non-reacted fuel gas circulation passage 4 during power generation is 500 cc. Since the volume of the buffer tank 8 changes with the amount of water in the buffer tank 8, the volume of the buffer tank 8 is proportional to the water level in the buffer tank 8.

  Here, it is assumed that the water level at the first volume V1 is the first water level H2, and the water level at the second volume V2 is the second water level H1. In addition, the interval between the start of power generation by the fuel cell 1 and the inclination of the nitrogen concentration according to the volume in the unreacted fuel gas circulation path 4 set in advance by experiment, with the unreacted fuel gas purge valve 6 opened and purged. Set from

  Here, in the case where the volume in the unreacted fuel gas circulation path 4 is 250 cc, the nitrogen concentration increases by 40% with respect to the time 15 minutes from the start of power generation of the fuel cell 1. Further, when the volume in the unreacted fuel gas circulation path 4 is 500 cc, the nitrogen concentration is inclined to increase by 20% with respect to the time 15 minutes from the start of power generation of the fuel cell 1.

  Further, in order to reduce the nitrogen concentration in the unreacted fuel gas in the unreacted fuel gas circulation passage 4 to a predetermined concentration or less, the unreacted fuel gas in the unreacted fuel gas circulation passage 4 is removed from the unreacted fuel gas purge passage 5 Purge from In the unreacted fuel gas purge operation, the unreacted fuel gas purge valve 6 is opened, and the unreacted fuel gas purge path 5 purges the unreacted fuel gas.

  In the present embodiment, whether or not the unreacted fuel gas purge operation is performed from the unreacted fuel gas purge path 5 is determined based on the nitrogen concentration in the unreacted fuel gas in the unreacted fuel gas circulation path 4.

  If the nitrogen concentration in the unreacted fuel gas in the unreacted fuel gas circulation path 4 is the first predetermined concentration, the voltage of the fuel cell 1 is reduced by the nitrogen gas in the pure hydrogen gas, and the power generation efficiency is lowered. Implement a reaction fuel gas purge operation.

  When the unreacted fuel gas purge operation is performed and the nitrogen concentration in the unreacted fuel gas circulation path 4 is normally lowered to the second predetermined concentration set to a concentration lower than the first predetermined concentration, the voltage of the fuel cell 1 is restored As a result, the power generation efficiency of the fuel cell 1 is increased.

  In the present embodiment, the first predetermined concentration is 50%, and the second predetermined concentration is 5%. Further, the time from the start of power generation of the fuel cell 1 is power generation time t1, the nitrogen concentration is α, and the unreacted fuel gas purge valve 6 is opened to purge the unreacted fuel gas from the unreacted fuel gas purge path 5 open time t2. I assume.

  Hereinafter, the operation and action of the fuel cell system 100 configured as described above will be described with reference to FIG. 1, FIG. 2 and FIG.

  As shown in FIG. 3, the controller 101 starts the time when the fuel cell system 100 starts power generation, and performs the following operation.

  The controller 101 starts acquiring the power generation time t1 of the fuel cell 1, opens the water discharge valve 10 for a predetermined time, and discharges the water in the buffer tank 8 to make the volume of the buffer tank 8 the second volume V2. The change is made (S101).

  Next, the nitrogen concentration α from the power generation time t1 is calculated from the relationship between the power generation time t1 of the fuel cell 1 and the inclination of the nitrogen concentration α, which is acquired in advance by experiment (S102). Then, it is determined whether the nitrogen concentration α is higher than 50% of the first predetermined concentration (S103). If the nitrogen concentration α is lower than 50% of the first predetermined concentration, the process returns to S102, and if the nitrogen concentration α is higher than 50% of the first predetermined concentration, the unreacted fuel gas purge valve 6 is opened and acquisition of the open time t2 is started (S104).

  Next, the nitrogen concentration α from the opening time t2 is calculated from the relationship between the opening time t2 of the unreacted fuel gas purge valve 6 of the fuel cell 1 and the inclination of the nitrogen concentration α, which is acquired in advance by experiment (S105). Then, it is determined whether the nitrogen concentration α is lower than 5% of the second predetermined concentration (S106).

  If the nitrogen concentration α is higher than 5% of the second predetermined concentration, the process returns to S105, and if the nitrogen concentration α is lower than 5% of the second predetermined concentration, the unreacted fuel gas purge valve 6 is closed (S107). , End obtaining the open time t2.

  If there is no instruction to stop the power generation of the fuel cell 1 (S108), the power generation time t1 and the open time t2 are reset, reacquisition of the power generation time t1 is started (S109), and then the process returns to S102. When there is an instruction to stop the power generation of the fuel cell 1 (S108), the fuel cell 1 is stopped and water is supplied from the water supply device 9 for a predetermined time, and the volume of the buffer tank 8 is set to the first volume V1. The change is made (S110), the power generation of the fuel cell system 100 is stopped, and the process ends.

  In each step, after the completion of each step, transition is made promptly without providing a waiting time.

  Thus, at the time of power generation, the volume of the buffer tank 8 is set to 300 cc and the volume of the unreacted fuel gas circulation path 4 is increased. At the time of stop, the volume of the buffer tank 8 is set to 50 cc and the volume of the unreacted fuel gas circulation path 4 is set. When the operation of reducing the value of .beta. Is made smaller, the volume in the unreacted fuel gas circulation path 4, which has conventionally been fixed, can be changed at the time of power generation and at the time of stop.

  As described above, in the present embodiment, by changing the volume of the unreacted fuel gas circulation path 4 so that the volume of the buffer tank 8 becomes the second volume V2 at the time of power generation, the unreacted fuel gas can be obtained. Dilutes the nitrogen concentrated in circulation path 4 with pure hydrogen gas, and lowers the nitrogen concentration α to 50% of the first predetermined concentration to suppress the concentration rate of the impurity gas in the unreacted fuel gas during power generation It becomes possible.

  Thus, the number of times of operation of the unreacted fuel gas purge valve 6 is suppressed, and the durability of the unreacted fuel gas purge valve 6 is ensured, whereby the reliability of the fuel cell system 100 is improved.

Furthermore, during stoppage, the volume of the buffer tank 8 is changed to be the first volume V1 and when starting to generate power, the second volume is changed to V2 to obtain the unreacted fuel gas circulation path 4 The concentration of the impurity gas to be concentrated can be reduced, the purge of the unreacted fuel gas at the start of the fuel cell 1 is not necessary, and the fuel cell system 100 can be made more efficient.

  In the present embodiment, although the buffer tank 8 is a solid tank, the present invention is not limited to this, but the tank itself can be deformed, and the volume of the buffer tank 8 can be changed by the deformation of the tank itself. I do not care.

  Further, in the present embodiment, the impurity gas is nitrogen gas contained in air permeating from the air side to the pure hydrogen gas side through the electrolyte membrane of the fuel cell 1. However, the present invention is not limited to this and is contained in pure hydrogen gas. It may be carbon dioxide, carbon monoxide, ammonia or the like.

  Furthermore, in order to circulate the fuel gas in the unreacted fuel gas circulation passage 4, a pump is not installed in the unreacted fuel gas circulation passage 4 and the fuel gas supply passage 2 and the unreacted fuel gas circulation passage 4 join together. You may install an ejector or an injector.

  In addition, the time for continuing the unreacted fuel gas purge operation may be any time as long as the impurity gas can be purged from the unreacted fuel gas circulation path 4 and can be made lower than the predetermined concentration.

  Further, in the present embodiment, the volume of the buffer tank 8 is set to 50 cc for the first volume V1 and 300 cc for the second volume V2. However, the present invention is not limited thereto. The second volume V2 may be a volume at which the concentration of the impurity gas is sufficiently diluted at startup with respect to the volume in the unreacted fuel gas circulation path 4.

  Further, in the present embodiment, the water supplier 9 and the water discharge valve 10 have been illustrated as a configuration for changing the volume of the buffer tank 8. Not limited to this, a water tank may be provided in the fuel cell system 100 to supply and drain water from the water tank.

  Furthermore, in the present embodiment, the determination as to whether or not the power generation stop of the fuel cell 1 is instructed and the stop operation are performed after closing the unreacted fuel gas purge valve 6 (S107), but the present invention is not limited thereto. It does not matter.

Second Embodiment
The configuration of the fuel cell system according to Embodiment 2 of the present invention will be described using FIGS. 4, 5 and 6. FIG.

  FIG. 4 is a block diagram showing a schematic configuration of a fuel cell system according to Embodiment 2 of the present invention. FIG. 5 is a schematic view showing the volume in the buffer tank and the water level in the buffer tank of the portion B in FIG. 4 during stop of the fuel cell system and during power generation in Embodiment 2 of the present invention. FIG. 6 is a flow chart showing a method of operating a fuel cell system according to Embodiment 2 of the present invention.

  In the fuel cell system 200 of the second embodiment, the same components as those of the fuel cell system 100 of the first embodiment shown in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted here.

  In the fuel cell system 200 shown in FIG. 4, the water level detector 11 is provided in the buffer tank 8, and the controller 201 controls the fuel cell system 200 based on the water level detected by the water level detector 11. This is different from the fuel cell system 100 of the first embodiment.

  The water level detector 11 is a detector that detects the water level in the buffer tank 8 using a float that moves up and down according to the water level in the buffer tank 8.

  The operation of each device constituting the fuel cell system 200 in the present embodiment is the same as that of the first embodiment, and therefore the description thereof is omitted. However, the controller 201 uses the water level detected by the water level detector 11. In addition, the water supply amount by the water supply device 9 and the water discharge amount by the water discharge valve 10 are changed so that the water level in the buffer tank 8 during operation becomes the volume of the buffer tank 8 set in advance. It is different.

  Hereinafter, the operation and action of the fuel cell system 200 configured as described above will be described with reference to FIG. 4, FIG. 5 and FIG.

  As shown in FIG. 6, the controller 201 starts the time when the fuel cell system 200 starts power generation, and performs the following operation.

  The controller 201 starts acquiring the power generation time t1 of the fuel cell 1, and discharges water until the volume of the buffer tank 8 detected by the water level detector 11 is changed to the second water level H1 corresponding to the second volume V2. The valve 10 is opened (S201).

  Next, the nitrogen concentration α from the power generation time t1 is calculated from the relationship between the power generation time t1 of the fuel cell 1 and the inclination of the nitrogen concentration α, which is acquired in advance by experiment (S202). Then, it is determined whether the nitrogen concentration α is higher than 50% of the first predetermined concentration (S203). If the nitrogen concentration α is lower than 50% of the first predetermined concentration, the process returns to S202, and if the nitrogen concentration α is higher than 50% of the first predetermined concentration, the unreacted fuel gas purge valve 6 is opened and acquisition of the open time t2 is started (S204).

  Next, the nitrogen concentration α from the opening time t2 is calculated from the relationship between the opening time t2 of the unreacted fuel gas purge valve 6 of the fuel cell 1 and the inclination of the nitrogen concentration α, which is acquired in advance by experiment (S205). Then, it is determined whether the nitrogen concentration α is lower than 5% of the second predetermined concentration (S206).

  If the nitrogen concentration α is higher than 5% of the second predetermined concentration, the process returns to S205, and if the nitrogen concentration α is lower than 5% of the second predetermined concentration, the unreacted fuel gas purge valve 6 is closed (S207). , End obtaining the open time t2.

  If there is no instruction to stop the power generation of the fuel cell 1 (S208), the power generation time t1 and the open time t2 are reset, reacquisition of the power generation time t1 is started (S209), and then the process returns to S202. When there is an instruction to stop the power generation of the fuel cell 1 (S208), the fuel cell 1 is stopped, and the volume of the buffer tank 8 detected by the water level detector 11 is the first water level H2 corresponding to the first volume V1. Water is supplied from the water supplier 9 until the change is made (S210), the power generation of the fuel cell system 100 is stopped, and the process ends.

  In each step, after the completion of each step, transition is made promptly without providing a waiting time.

  Thus, at the time of power generation, the volume of the buffer tank 8 is set to 300 cc and the volume of the unreacted fuel gas circulation passage 4 is increased. At the time of stop, the volume of the buffer tank 8 is set to 50 cc and the volume of the unreacted fuel gas circulation passage 4 is decreased. When the operation is performed, the volume of the unreacted fuel gas circulation path 4 which has conventionally been fixed can be changed between power generation and stop.

As described above, in the present embodiment, at the time of power generation, the second water level H corresponding to the second volume is the volume of the buffer tank 8 detected by the water level detector 11.
2, and the nitrogen concentrated in the unreacted fuel gas circulation path 4 is diluted with pure hydrogen gas, and the nitrogen concentration .alpha. Can be made lower than 50% of the first predetermined concentration, so that it is not being generated. It is possible to suppress the concentration rate of the impurity gas in the reaction fuel gas.

  As a result, by suppressing the number of times of operation of the unreacted fuel gas purge valve 6, the durability of the unreacted fuel gas purge valve 6 can be secured, and the reliability of the fuel cell system 100 is improved.

  Furthermore, while stopped, the volume of the buffer tank 8 detected by the water level detector 11 is changed to the first water level H2 corresponding to the first volume V1, and the second water volume corresponding to the second volume V2 is generated when power is generated. By changing to the water level H1, the concentration of the impurity gas concentrated in the unreacted fuel gas circulation path 4 can be lowered, and the purge of the unreacted fuel gas at the start of the fuel cell 1 becomes unnecessary. It becomes possible to realize efficiency.

Third Embodiment
FIG. 7 is a characteristic diagram showing the relationship between the stop time of the fuel cell system according to Embodiment 3 of the present invention and the first volume of the buffer tank during stop.

  The fuel cell system according to the third embodiment of the present invention changes the first volume V1 of the buffer tank 8 being stopped in the fuel cell system 100 according to the first embodiment according to the stop time of the fuel cell system 100. The block diagram of the fuel cell system according to the third embodiment is similar to that of the fuel cell system 100 according to the first embodiment shown in FIG.

  Further, the method of operating the fuel cell system according to the third embodiment except that the first volume V1 of the buffer tank 8 being stopped is changed according to the stop time of the fuel cell system 100 is the embodiment shown in FIG. The fuel cell system 100 is similar to the fuel cell system 100 of the first aspect.

  In the fuel cell system 100 of the third embodiment, the same components as those of the fuel cell system 100 of the first embodiment shown in FIG. 1 are given the same reference numerals, and the description thereof is omitted here.

  The difference between fuel cell system 100 of the third embodiment of the present invention and fuel cell system 100 of the first embodiment will be described with reference to FIG.

  As shown in FIG. 7, in the present embodiment, the first volume V1 of the buffer tank 8 during stop of the fuel cell system 100 is changed according to the stop time of the fuel cell system 100. That is, as the stop time of the fuel cell system 100 becomes longer, the first volume V1 is changed to be smaller, and as a result, the difference with the second volume is changed to be larger. Furthermore, after a certain time has elapsed, the minimum volume is fixed.

  With this configuration, the first volume V1 of the buffer tank 8 during stoppage of the fuel cell system 100 is changed according to the stop time, and the difference in volume between the buffer tank 8 and the second volume V2 is unnecessarily increased. There is no need.

  As a result, it is possible to suppress the time for changing from the second volume V2 to the first volume V1 of the buffer tank 8 during stoppage and the power consumption of the devices required to change the volume, and the fuel cell system 100 Efficiency can be achieved.

The fuel cell system according to the present invention improves the reliability of the fuel cell system having the unreacted fuel gas circulation path by changing the volume of the unreacted fuel gas circulation path according to the operating condition, and the fuel cell system It is possible to realize high efficiency of Therefore, it is useful in an application where stable power generation is desired over a long period of time, for example, in the field of fuel cell systems for home use or business use.

Reference Signs List 1 fuel cell 2 fuel gas supply path 3 oxidant gas supply path 4 unreacted fuel gas circulation path 5 unreacted fuel gas purge path 6 unreacted fuel gas purge valve 7 transportation means 8 buffer tank 9 water supplier 10 water discharge valve 11 water level detection 100, 200 Fuel cell system 101, 201 Controller

Claims (5)

A fuel cell that generates electric power by reacting a fuel gas supplied to an anode with an oxidant gas supplied to a cathode;
A fuel gas supply path for supplying the fuel gas to the anode of the fuel cell;
An unreacted fuel gas circulation path for supplying, as the fuel gas, the unreacted fuel gas discharged from the anode of the fuel cell to the fuel gas supply path;
Transport means provided in the unreacted fuel gas circulation path and supplying the unreacted fuel gas to the fuel gas supply path;
An unreacted fuel gas purge path branched from the unreacted fuel gas circulation path;
An unreacted fuel gas purge valve for opening and closing the unreacted fuel gas purge path;
A buffer tank provided in the unreacted fuel gas circulation path and having a variable volume;
Volume changing means for changing the volume of the buffer tank;
A controller,
Equipped with
The controller controls the volume changing means so that the volume of the buffer tank becomes the first volume during stop, and the second volume of the buffer tank is larger than the first volume at the time of power generation. The volume changing means is controlled to become a volume, and before the impurity gas concentration of the unreacted fuel gas flowing through the unreacted fuel gas circulation path reaches a preset upper limit value of the impurity gas concentration, The unreacted fuel gas purge valve is controlled to open and purge.
Fuel cell system. The volume changing means includes a water supplier for supplying water into the buffer tank, and a water discharge valve for discharging water in the buffer tank.
The outlet of the unreacted fuel gas to the unreacted fuel gas circulation path in the buffer tank is disposed at a position higher than the highest water level in the buffer tank,
The controller controls the buffer tank so that the volume of the buffer tank becomes the first volume during stoppage, and the volume of the buffer tank becomes the second volume larger than the first volume during power generation. The fuel cell system according to claim 1, wherein the amount of water in the fuel cell is controlled. A water level detector for detecting the water level in the buffer tank when the volume of the buffer tank becomes the first volume, and the water level in the buffer tank when the volume of the buffer tank becomes the second volume Equipped with
The fuel cell system according to claim 2, wherein the controller controls the water supplier and the water discharge valve based on a detected water level of the water level detector.   The fuel cell system according to any one of claims 1 to 3, wherein the controller controls the first volume of the buffer tank to be changed according to a stop time. A fuel cell that generates electric power by reacting a fuel gas supplied to an anode with an oxidant gas supplied to a cathode;
A fuel gas supply path for supplying the fuel gas to the anode of the fuel cell;
An unreacted fuel gas circulation path for supplying, as the fuel gas, the unreacted fuel gas discharged from the anode of the fuel cell to the fuel gas supply path;
Transport means provided in the unreacted fuel gas circulation path and supplying the unreacted fuel gas to the fuel gas supply path;
An unreacted fuel gas purge path branched from the unreacted fuel gas circulation path;
An unreacted fuel gas purge valve for opening and closing the unreacted fuel gas purge path;
A buffer tank provided in the unreacted fuel gas circulation path and having a variable volume;
Volume changing means for changing the volume of the buffer tank;
A method of operating a fuel cell system comprising
During stoppage, the volume changing means sets the volume of the buffer tank to the first volume, and at the time of power generation, the volume changing means sets the volume of the buffer tank to a second volume larger than the first volume, The unreacted fuel gas purge valve is opened and purged before the impurity gas concentration of the unreacted fuel gas flowing through the unreacted fuel gas circulation path reaches the preset upper limit value of the impurity gas concentration. Do,
How to operate a fuel cell system.