JP2018125069A - Fuel cell system and method for operating the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize power generation efficiency of a fuel cell without decreasing durability of an exhaust valve in a fuel cell system which supplies an unreacted fuel gas discharged from a fuel cell again to the fuel cell as a fuel gas.SOLUTION: A fuel cell system 100 comprises: a fuel gas supply passage 2 which supplies a fuel gas to a fuel cell 1; transporting means 7 provided in an unreacted fuel gas supply passage 4 for supplying the unreacted fuel gas discharged from the fuel cell 1 to a fuel gas supply passage 2 and supplying the unreacted fuel gas to the fuel gas supply passage 2; an unreacted fuel gas exhaust valve 6 which opens and closes the unreacted fuel gas exhaust passage 5 branching from the unreacted fuel gas supply passage 4; and a controller 101. The controller 101 fluctuates an amount of supply of the unreacted fuel gas by the transporting means 7 so that a fuel consumption rate of the operating fuel cell 1 becomes substantially constant according to impurity gas concentration contained in the unreacted fuel gas.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a fuel cell system that supplies unreacted fuel gas discharged from a fuel cell to the fuel cell again as a fuel gas, and an operation method thereof.

  In a fuel cell system, for example, in order to effectively use a fuel gas containing hydrogen and increase the power generation efficiency of the fuel cell system, unreacted fuel gas that has not been used in the fuel cell is supplied again to the fuel cell as a fuel gas. Is provided with a fuel gas circulation path.

  When configured so that the fuel gas circulates in the fuel gas circulation path, the impurity gas contained in the fuel gas or the nitrogen contained in the air from the oxidant gas side to the fuel gas side through the electrolyte membrane of the fuel cell, etc. Impurity gas permeates and concentrates, impedes fuel cell power generation, reduces the power generation voltage of the fuel cell, and greatly reduces the power generation efficiency of the fuel cell.

  Therefore, an unreacted fuel gas discharge path for discharging unreacted fuel gas is provided in the fuel gas circulation path, and the impurity gas flowing through the unreacted fuel gas circulation path is periodically discharged together with the unreacted fuel gas.

  Here, the amount of nitrogen gas in the air that is concentrated in the fuel gas with the passage of time from the start of power generation of the fuel cell is obtained in advance through experiments or the like, and a predetermined time interval during which the amount of nitrogen gas accumulates. A fuel cell system has been proposed in which nitrogen gas is periodically discharged together with unreacted fuel gas to prevent unreacted fuel gas from being discharged more than necessary (see, for example, Patent Document 1).

  FIG. 7 is a block diagram of a configuration of a conventional fuel cell system disclosed in Patent Document 1. In FIG. As shown in FIG. 7, the fuel cell system 300 includes a fuel cell 301, a fuel gas supply path 302, an oxidant gas supply path 303, an unreacted fuel gas supply path 304, and an unreacted fuel gas discharge path 305. , An unreacted fuel gas discharge valve 306, an ejector 307, and a controller 308.

  Of the fuel gas supplied to the fuel cell 301, unreacted fuel gas that has not been used for power generation is supplied again to the fuel cell 301 through the unreacted fuel gas supply path 304 and the ejector 307.

  Therefore, in order to discharge the nitrogen gas accumulated in the unreacted fuel gas supply path 304, the controller 308 opens the unreacted fuel gas discharge valve 306 at a predetermined time interval and passes through the unreacted fuel gas discharge path 305. The fuel gas containing nitrogen gas is discharged.

Japanese Patent Application Laid-Open No. 2008-300261

In the conventional configuration, the unreacted fuel gas is generally operated so as to have a constant supply amount. In such a case, during the circulation operation of the unreacted fuel gas, as the time elapsed from the start of power generation of the fuel cell, the fuel gas is changed to the fuel gas as shown in the timing chart showing the change in the fuel consumption rate of the conventional fuel cell shown in FIG. As the nitrogen gas concentrates, the fuel consumption rate Uf of the fuel cell during operation varies greatly. Here, the fuel consumption rate Uf of the fuel cell is expressed by (Equation 1).

（数１）のように燃料電池の燃料消費率Ｕｆを定義すると、高燃料消費率側では、燃料不足による燃料電池の発電電圧の低下の観点で、低燃料消費量側では、循環量を確保するための循環ポンプの消費電力増大による燃料電池システムの発電効率の低下の観点で、それぞれ課題があった。

If the fuel consumption rate Uf of the fuel cell is defined as in (Equation 1), the circulation rate is secured on the low fuel consumption side on the high fuel consumption rate side from the viewpoint of lowering the power generation voltage of the fuel cell due to fuel shortage In order to reduce the power generation efficiency of the fuel cell system due to an increase in power consumption of the circulation pump, there are problems.

  Further, as a method of reducing the fluctuation range of the fuel consumption rate Uf of the fuel cell, a method of shortening the cycle in which the impurity gas is discharged together with the unreacted fuel gas can be considered. There was a problem in terms of durability.

  An object of this invention is to provide the fuel cell system which can stabilize the power generation efficiency of a fuel cell, without reducing the durability of a discharge valve.

  In order to solve the above-described conventional problems, a fuel cell system of the present invention includes a fuel cell that generates power by reacting a fuel gas and an oxidant gas, a fuel gas supply path that supplies fuel gas to the fuel cell, and , An unreacted fuel gas supply path for supplying unreacted fuel gas discharged from the fuel cell as a fuel gas to the fuel gas supply path, and an unreacted fuel gas supplied from the unreacted fuel gas supply path to the fuel gas supply path An unreacted fuel gas discharge path that branches from the unreacted fuel gas supply path, an unreacted fuel gas discharge valve that opens and closes the unreacted fuel gas discharge path, and a controller. According to the impurity gas concentration contained in the unreacted fuel gas, the supply amount of the unreacted fuel gas by the conveying means is varied so that the fuel consumption rate of the fuel cell during the operation is substantially constant.

  With this configuration, the fuel cell can stably generate power, and the durability reliability of the unreacted fuel gas discharge valve can be ensured.

  According to the present invention, in a fuel cell system in which unreacted fuel gas discharged from a fuel cell is supplied again to the fuel cell as fuel gas, the fuel consumption rate Uf of the fuel cell during operation is kept constant, and the fuel cell As a result, it is possible to ensure stable power generation and to suppress the number of operations of the discharge valve of the unreacted fuel gas, thereby ensuring durability reliability of the discharge valve and improving the reliability of the fuel cell system.

1 is a block diagram showing a schematic configuration of a fuel cell system according to Embodiments 1 and 2 of the present invention. 1 is a flowchart showing a method for operating a fuel cell system according to Embodiment 1 of the present invention. In the fuel cell system of Embodiment 1 of the present invention, the fuel consumption rate of the fuel cell, the supply amount of the unreacted fuel gas, the nitrogen concentration in the unreacted fuel gas, and the passage of time from the start of power generation of the unreacted fuel gas discharge valve Timing chart showing the accompanying changes Flowchart showing the operation method of the fuel cell system in Embodiment 2 of the present invention. Block diagram showing a schematic configuration of a fuel cell system according to Embodiment 3 of the present invention. Flowchart showing the operation method of the fuel cell system in Embodiment 3 of the present invention. A block diagram showing a schematic configuration of a conventional fuel cell system Timing chart showing changes in fuel consumption rate, unreacted fuel gas supply amount, nitrogen concentration in unreacted fuel gas, and unreacted fuel gas discharge valve over time from the start of power generation in a conventional fuel cell system

  According to a first aspect of the present invention, there is provided a fuel cell that generates power by reacting a fuel gas and an oxidant gas, a fuel gas supply path for supplying the fuel gas to the fuel cell, and an unreacted fuel gas discharged from the fuel cell. From the unreacted fuel gas supply path for supplying the fuel gas to the fuel gas supply path, transport means for supplying the unreacted fuel gas from the unreacted fuel gas supply path to the fuel gas supply path, and from the unreacted fuel gas supply path An unreacted fuel gas discharge path that branches, an unreacted fuel gas discharge valve that opens and closes the unreacted fuel gas discharge path, and a controller, the controller depending on the impurity gas concentration contained in the unreacted fuel gas Thus, the fuel cell system is characterized in that the amount of unreacted fuel gas supplied by the conveying means is varied so that the fuel consumption rate of the fuel cell during operation is substantially constant.

  With this configuration, in the fuel cell system in which the unreacted fuel gas discharged from the fuel cell is supplied again to the fuel cell as the fuel gas, the supply amount of the unreacted fuel gas is reduced to the impurities contained in the unreacted fuel gas. By varying according to the gas concentration, the amount of fuel gas supplied to the fuel cell can be kept constant.

  As a result, the fuel consumption rate Uf of the fuel cell during operation can be kept constant, and a fuel cell system capable of stable power generation of the fuel cell can be provided.

  In particular, according to a second aspect of the present invention, in the first aspect of the invention, the controller conveys the fuel consumption rate of the fuel cell during operation so as to be substantially constant according to the nitrogen concentration contained in the unreacted fuel gas. The supply amount of the unreacted fuel gas by the means is varied.

  With this configuration, among the impurity gases contained in the unreacted fuel gas discharged from the fuel cell, the unreacted fuel particularly in accordance with the nitrogen concentration that greatly affects the fluctuation of the fuel consumption rate Uf of the fuel cell. By varying the gas supply amount, the fuel gas amount supplied to the fuel cell more effectively can be kept constant.

  As a result, the fuel consumption rate Uf of the fuel cell during operation can be kept constant, and a fuel cell system capable of more stable power generation of the fuel cell can be provided.

  According to a third invention, in particular, in the first invention, the controller controls the unreacted fuel gas discharge valve to be opened before the impurity gas concentration reaches an upper limit value of the impurity gas concentration set in advance. It is characterized by this.

  With this configuration, the unreacted fuel discharge valve can be opened before reaching the preset upper limit value of the impurity gas concentration. It becomes possible to suppress that the power generation efficiency of a fuel cell falls and falls greatly. Thereby, it is possible to provide a fuel cell system that enables more stable power generation of the fuel cell.

  According to a fourth aspect of the invention, in particular, in the second aspect of the invention, the controller controls the unreacted fuel gas discharge valve to open before the nitrogen concentration reaches a preset upper limit value of the nitrogen concentration. It is a feature.

  With this configuration, the impurity gas contained in the unreacted fuel gas discharged from the fuel cell is set in advance according to the nitrogen concentration that has a great influence on the fluctuation of the fuel consumption rate Uf of the fuel cell. Since the unreacted fuel discharge valve can be opened before the upper limit of the nitrogen concentration is reached, the power generation efficiency of the fuel cell is greatly reduced due to a decrease in the power generation voltage of the fuel cell due to the increase in the nitrogen concentration. This can be suppressed.

  Thereby, it is possible to provide a fuel cell system that enables more stable power generation of the fuel cell.

  According to a fifth aspect of the invention, in particular, in the first aspect of the invention, the controller opens the unreacted fuel gas discharge valve before the supply amount of the unreacted fuel gas by the transfer means reaches the supply amount upper limit value of the transfer means. It is characterized by controlling to.

  With this configuration, it is possible to open the unreacted fuel gas discharge valve before the supply amount of unreacted fuel gas by the transfer means reaches the supply amount upper limit value of the transfer means. It is possible to suppress an increase in the fuel consumption rate Uf of the fuel cell due to an insufficient amount.

  Thereby, it is possible to provide a fuel cell system that enables more stable power generation of the fuel cell.

  Hereinafter, embodiments of the present invention will be specifically described. In all the drawings, the same or corresponding parts are denoted by the same reference numerals, and redundant description thereof is omitted. Further, in all the drawings, only components necessary for explaining the present invention are extracted and illustrated, and other components are not illustrated. Furthermore, the present invention is not limited to the following embodiment.

(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 flowchart showing a method of operating the fuel cell system according to Embodiment 1 of the present invention.

  FIG. 3 shows the fuel consumption rate of the fuel cell, the supply amount of unreacted fuel gas, the nitrogen concentration in the unreacted fuel gas, and the power generation start of the unreacted fuel gas discharge valve in the fuel cell system of Embodiment 1 of the present invention. It is a timing chart showing the change of the change showing the passage of time.

  As shown in FIG. 1, the fuel cell system 100 of the present embodiment includes a fuel cell 1, a fuel gas supply path 2, an oxidant gas supply path 3, an unreacted fuel gas supply path 4, and an unreacted fuel. A gas discharge path 5, an unreacted fuel gas discharge valve 6, a transfer means 7, and a controller 101 are provided.

  The fuel cell 1 generates power using a fuel gas containing hydrogen and an oxidant gas containing oxygen. 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 is supplied at a pressure higher than the pressure loss generated in the fuel cell system. Air is used as the oxidant gas. As the fuel cell 1, a solid polymer fuel cell is used.

The fuel gas supply path 2 is a path for supplying pure hydrogen gas to the fuel cell 1. The oxidant gas supply path 3 is a path for supplying air to the fuel cell 1. The unreacted fuel gas supply path 4 is a path for supplying unreacted fuel gas discharged from the fuel cell 1 to the fuel cell 1 as fuel gas again.

  The unreacted fuel gas discharge path 5 is a path that branches from the unreacted fuel gas supply path 4 and discharges the unreacted fuel gas in the unreacted fuel gas supply path 4 to the outside.

  In the present embodiment, the unreacted fuel gas discharged from the unreacted fuel gas discharge path 5 is diluted with air, and the concentration of hydrogen contained in the unreacted fuel gas is lowered to the flammable range or less, and then returned to the atmosphere. Discharge.

  The unreacted fuel gas discharge valve 6 is provided in the path of the unreacted fuel gas discharge path 5, and converts the unreacted fuel gas in the unreacted fuel gas supply path 4 into the impurities in the unreacted fuel gas supply path 4. It is an on-off valve that periodically opens and closes the path for discharging to the outside together with the gas. In this embodiment, a solenoid valve is used.

  The transport means 7 is a pump provided in the unreacted fuel gas supply path 4 in order to circulate the unreacted fuel gas from the unreacted fuel gas supply path 4 through the fuel gas supply path 2 to the fuel cell 1. It is.

  The controller 101 only needs to have 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 MEA is sandwiched between separators. In this 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 sequentially stacked. The cell reaction proceeds in a cathode catalyst layer and an anode catalyst layer comprising a catalyst, a carrier supporting the catalyst, and an ionomer (ion conductive polymer).

  It is difficult for the fuel cell 1 to use all of the supplied pure hydrogen gas for power generation because of the gas diffusion performance of the gas flow path in the fuel cell 1, and unreacted fuel gas is discharged from the fuel cell 1. Is 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 that has not been used in the fuel cell 1 is again removed from the fuel cell. 1 is circulated through the fuel gas supply path 2.

  Then, the amount of the impurity gas concentrated in the unreacted fuel gas is grasped by experiments in advance with the passage of time from the start of power generation of the fuel cell 1, and periodically at a predetermined time interval, which is a time during which the amount of impurity gas accumulates. The impurity gas is discharged together with the unreacted fuel gas periodically (periodically) to prevent the unreacted fuel gas from being discharged more than necessary.

  At that time, in accordance with the impurity gas concentration in the unreacted fuel gas in the unreacted fuel gas supply path 4, the unreacted fuel gas 1 in the operation operation is unreacted by the transport means 7 so that the fuel consumption rate Uf of the fuel cell 1 becomes substantially constant. The supply amount of the reaction fuel gas is varied.

In the present embodiment, the supply amount of the unreacted fuel gas by the transport means 7 is set from the time from the start of power generation of the fuel cell 1 and the slope of the nitrogen concentration set in advance by experiments. Here, since the slope of the nitrogen concentration is increased by 40% with respect to the time of 15 minutes from the start of power generation of the fuel cell 1, the amount of unreacted fuel gas supplied by the conveying means 7 is adjusted to the fluctuation of the nitrogen concentration in accordance with the fluctuation of the nitrogen concentration. The slope is set to increase by 40% with respect to 15 minutes from the start of power generation of the battery 1.

  Thereby, the amount of pure hydrogen gas supplied to the fuel cell 1 can be kept constant. Further, in order to reduce the nitrogen concentration in the unreacted fuel gas in the unreacted fuel gas supply path 4 to a predetermined concentration or less, the unreacted fuel gas in the unreacted fuel gas supply path 4 is removed from the unreacted fuel gas discharge path 5. To discharge from.

  In the unreacted fuel gas discharge operation, the unreacted fuel gas discharge valve 6 is opened and the unreacted fuel gas is discharged from the unreacted fuel gas discharge path 5. In the present embodiment, whether or not to perform the unreacted fuel gas discharge operation from the unreacted fuel gas discharge path 5 is determined based on the nitrogen concentration in the unreacted fuel gas in the unreacted fuel gas supply path 4.

  If the nitrogen concentration is the first predetermined concentration, the fuel cell 1 performs the unreacted fuel gas discharge operation because the voltage is lowered by the nitrogen gas in the pure hydrogen gas and the power generation efficiency is lowered. When the unreacted fuel gas discharge operation is performed and the nitrogen concentration in the unreacted fuel gas supply path 4 is normally reduced to the second predetermined concentration, the power generation efficiency of the fuel cell 1 is increased by recovering the voltage of the fuel cell 1. . In the present embodiment, the first predetermined density is 50% and the second predetermined density is 5%.

  The operation and action of the fuel cell system 100 configured as described above will be described below with reference to FIGS.

  As shown in FIG. 2, the controller 101 starts from the time point when the fuel cell system 100 starts power generation, and always performs the following operations.

  The controller 101 starts acquiring the power generation time t1 when the fuel cell 1 starts generating power (S101). Next, the nitrogen concentration α1 is calculated from the power generation time t1 based on the relationship between the power generation time of the fuel cell 1 and the nitrogen concentration gradient β1 obtained in advance by experiments (S102). Then, the supply amount L1 of the conveying means 7 is changed in accordance with the inclination β1 of the nitrogen concentration (S103).

  It is determined whether the nitrogen concentration α1 is higher than the first predetermined concentration 50% (S104). If the nitrogen concentration α1 is lower than the first predetermined concentration 50%, the process returns to S102, and if the nitrogen concentration α1 is higher than the first predetermined concentration 50%, the unreacted fuel gas discharge valve 6 is opened (S105). Then, it is determined whether the nitrogen concentration α1 is lower than the second predetermined concentration 5% (S106).

  If the nitrogen concentration α1 is higher than the second predetermined concentration 5%, the process returns to S105. If the nitrogen concentration α1 is lower than the second predetermined concentration 5%, the unreacted fuel gas discharge valve 6 is closed (S107), and the process returns to S101. Each step shifts promptly after completion of each step without providing a waiting time. When such an operation is performed, the timing chart shown in FIG. 3 is obtained, and the fuel consumption rate Uf of the fuel cell 1 can be kept constant.

  As described above, in the present embodiment, the fuel consumption rate Uf of the fuel cell 1 during operation is substantially constant according to the nitrogen concentration in the unreacted fuel gas in the unreacted fuel gas supply path 4. Since the amount of pure hydrogen gas supplied to the fuel cell 1 can be kept constant by changing the amount of unreacted fuel gas supplied by the transport means 7, the fuel of the fuel cell 1 during operation It becomes possible to keep the consumption rate Uf constant.

Therefore, stable power generation of the fuel cell 1 is possible. Further, control is performed so that the unreacted fuel gas discharge valve 6 is opened before the nitrogen concentration reaches a preset upper limit value of the nitrogen concentration. Therefore, it is possible to suppress the power generation efficiency of the fuel cell 1 from greatly decreasing due to a decrease in the power generation voltage of the fuel cell 1 due to an increase in the nitrogen concentration.

  As a result, the fuel cell system 100 that enables more stable power generation of the fuel cell 1 can be provided. With these operations, the fuel cell system 100 can generate power stably.

  Further, in the present embodiment, the nitrogen concentration is calculated from the elapsed time from the start of power generation of the fuel cell 1, and the supply amount is varied in accordance with the nitrogen concentration. The supply amount may be varied with the elapsed time.

  Furthermore, in the present embodiment, the impurity gas is nitrogen gas contained in the air that permeates from the air side to the pure hydrogen gas side through the electrolyte membrane of the fuel cell 1, but is not limited thereto, and is contained in the pure hydrogen gas. It may be carbon dioxide, carbon monoxide, ammonia or the like.

  In order to circulate the fuel gas in the unreacted fuel gas supply path 4, a pump is not installed in the unreacted fuel gas supply path 4, and the fuel gas supply path 2 and the unreacted fuel gas supply path 4 are joined to each other. An ejector or an injector may be installed.

  The time for continuing the unreacted fuel gas discharge operation may be any time as long as the impurity gas is discharged from the unreacted fuel gas supply path 4 and can be made lower than a predetermined concentration.

(Embodiment 2)
The block diagram showing the schematic configuration of the fuel cell system according to the second embodiment of the present invention is the same as the fuel cell system 100 according to the first embodiment shown in FIG.

  FIG. 4 is a flowchart showing a method of operating the fuel cell system according to Embodiment 2 of the present invention. In addition, the same code | symbol is provided about the component similar to Embodiment 1, and the description is abbreviate | omitted here.

  Differences from the first embodiment in the operation of each device constituting the fuel cell system 100 in the present embodiment will be described.

  In the present embodiment, whether or not the unreacted fuel gas discharge operation is performed from the unreacted fuel gas discharge path 5 is determined based on the nitrogen concentration in the unreacted fuel gas in the unreacted fuel gas supply path 4 and the unreacted fuel gas unreacted by the transfer means 7 It is determined by the amount of reaction fuel gas supplied.

  If the nitrogen concentration is the first predetermined concentration, the fuel cell 1 performs the unreacted fuel gas discharge operation because the voltage decreases due to the nitrogen in the pure hydrogen gas and the power generation efficiency decreases. If the supply amount of the unreacted fuel gas by the transport means 7 is the first predetermined flow rate, the unreacted fuel gas discharge operation is performed before the upper limit value of the supply amount of the transport means 7 is reached.

  When the unreacted fuel gas discharge operation is performed and the concentration of nitrogen in the unreacted fuel gas in the unreacted fuel gas supply path 4 is normally reduced to the second predetermined concentration, the voltage of the fuel cell 1 is recovered, whereby the fuel cell 1 The power generation efficiency increases.

  Further, when the unreacted fuel gas discharge operation is performed and the supply amount of the unreacted fuel gas of the conveying means 7 is normally reduced to the second predetermined flow rate, the supply amount of the unloading means 7 is prevented from reaching the upper limit. It becomes possible to do.

  In the present embodiment, the first predetermined density is 50% and the second predetermined density is 5%. The first predetermined flow rate was 10 L / min, and the second predetermined flow rate was 3 L / min.

  Thereby, it becomes possible to set the operation interval of the unreacted fuel gas discharge valve 6 to the upper limit of the supply amount, it is possible to suppress the number of operations of the unreacted fuel gas discharge valve 6, and the conveyance means 7 Since the unreacted fuel gas discharge valve 6 can be opened before the supply amount of the unreacted fuel gas reaches the supply amount upper limit value of the conveying means 7, the fuel cell 1 of the fuel cell 1 due to the insufficient supply amount of the conveying means 7 can be opened. An increase in the fuel consumption rate Uf can be suppressed.

  Therefore, it is possible to provide the fuel cell system 100 that enables more stable power generation of the fuel cell 1.

  In the present embodiment, the amount of power generated from the fuel cell 1 is referred to as a power generation amount. In this embodiment, power is normally generated at 700W. The amount of pure hydrogen gas used in the fuel cell 1 when generating power at 700 W is 7 L / min.

  The operation and action of the fuel cell system 100 configured as described above will be described below with reference to FIG.

  As shown in FIG. 4, the controller 101 starts from the time point when the fuel cell system 100 starts power generation, and always performs the following operations.

  The controller 101 starts acquiring the power generation time t1 when the fuel cell 1 starts generating power (S201). Next, the nitrogen concentration α1 is calculated from the power generation time t1 based on the relationship between the power generation time of the fuel cell 1 obtained in advance by experiment and the slope β1 of the nitrogen concentration (S202).

  Then, the supply amount L1 of the conveying means 7 is changed in accordance with the inclination β1 of the nitrogen concentration (S203). It is determined whether the nitrogen concentration α1 is higher than the first predetermined concentration 50% and whether the supply amount L1 is higher than the first predetermined flow rate 10 L / min (S204). If the nitrogen concentration α1 is lower than the first predetermined concentration 50%, the process returns to S202. If the nitrogen concentration α1 is higher than the first predetermined concentration 50%, the unreacted fuel gas discharge valve 6 is opened (S205).

  If the supply amount L1 is lower than the first predetermined flow rate 10 L / min, the process returns to S203. If the supply amount L1 is higher than the first predetermined flow rate 10 L / min, the unreacted fuel gas discharge valve 6 is opened (S205). Then, it is determined whether the nitrogen concentration α1 is lower than the second predetermined concentration 5% and whether the supply amount L1 is lower than the second predetermined flow rate 3 L / min (S206).

  If the nitrogen concentration α1 is higher than the second predetermined concentration 5% or the supply amount L1 is higher than the second predetermined flow rate 3L / min, the process returns to S205, whether the nitrogen concentration α1 is lower than the second predetermined concentration 5% or the supply amount L1 is If it is lower than the second predetermined flow rate 3 L / min, the unreacted fuel gas discharge valve 6 is closed (S207), and the process returns to S201. Each step shifts promptly after completion of each step without providing a waiting time.

  As described above, in the present embodiment, conveyance is performed so that the fuel consumption rate Uf of the fuel cell 1 during operation is substantially constant according to the nitrogen concentration in the fuel gas in the unreacted fuel gas supply path 4. The amount of pure hydrogen gas supplied to the fuel cell 1 can be kept constant by changing the amount of unreacted fuel gas supplied by the means 7, so that the fuel consumption rate of the fuel cell 1 during operation Uf can be kept constant.

Therefore, stable power generation of the fuel cell 1 is possible. Further, the unreacted fuel gas discharge valve 6 is controlled to be opened before the supply amount of the conveying means 7 reaches the preset upper limit value of the supply amount.

  This makes it possible to suppress the number of operations of the unreacted fuel gas discharge valve 6 and to suppress an increase in the fuel consumption rate Uf of the fuel cell 1 due to an insufficient supply amount of the transport means 7.

  These operations enable more stable power generation of the fuel cell system 100 and ensure the durability reliability of the unreacted fuel gas discharge valve 6.

  Further, in the present embodiment, the nitrogen concentration is calculated from the elapsed time from the start of power generation of the fuel cell 1, and the supply amount is varied in accordance with the nitrogen concentration. The supply amount may be varied with the elapsed time.

  Further, in the present embodiment, the impurity gas is nitrogen gas contained in the air that permeates from the air side to the pure hydrogen gas side through the electrolyte membrane of the fuel cell 1, but is not limited to this, and is contained in the fuel gas. Carbon dioxide, carbon monoxide, ammonia, etc. may be used.

  In order to circulate the unreacted fuel gas in the unreacted fuel gas supply path 4, a pump is not installed in the unreacted fuel gas supply path 4, and the fuel gas supply path 2 and the unreacted fuel gas supply path 4 merge. An ejector or an injector may be installed at the site.

  The time for continuing the unreacted fuel gas discharge operation may be any time as long as the impurity gas is discharged from the unreacted fuel gas supply path 4 and can be made lower than a predetermined concentration.

  The supply amount of the conveying means 7 is set to 10 L / min for the first predetermined flow rate and 3 L / min for the second predetermined flow rate, but varies depending on the configuration of the fuel cell system 100, so that the fuel cell 1 is stable. Any flow rate value may be used as long as power can be generated.

  Further, the first predetermined flow rate may not be an absolute value, and may be, for example, an unreacted fuel gas flow value change amount before and after the unreacted fuel gas discharge operation.

(Embodiment 3)
The configuration of the fuel cell system according to Embodiment 3 of the present invention will be described with reference to FIG. FIG. 5 is a block diagram showing a schematic configuration of the fuel cell system according to Embodiment 3 of the present invention. FIG. 6 is a flowchart showing a method of operating the fuel cell system according to Embodiment 3 of the present invention. In addition, the same code | symbol is provided about the component similar to Embodiment 1, and the description is abbreviate | omitted here.

  The fuel cell system 200 shown in FIG. 5 is different from the first embodiment in that a gas sensor 8 is provided in the unreacted fuel gas supply path 4.

  The gas sensor 8 is a concentration meter that measures the nitrogen concentration in the unreacted fuel gas flowing through the unreacted fuel gas.

  Since the operation of each device constituting the fuel cell system 200 in the present embodiment is the same as that in the first embodiment, description thereof is omitted, but the controller 102 is based on the concentration value measured by the gas sensor 8. The difference is that the amount of unreacted fuel gas supplied by the transport means 7 is varied so that the fuel consumption rate Uf of the fuel cell 1 during operation is substantially constant.

  The operation and action of the fuel cell system 200 configured as described above will be described below with reference to FIG.

  FIG. 6 is a flowchart showing a method of operating the fuel cell system according to the third embodiment.

  As shown in FIG. 6, the controller 102 starts from the time when the fuel cell system 200 starts power generation, and always performs the following operations.

  The controller 102 starts measuring the nitrogen concentration α2 with the gas sensor 8 together with the start of power generation of the fuel cell 1 (S301). Then, the supply amount L2 of the conveying means 7 is varied in accordance with the nitrogen concentration gradient β2 (S302). It is determined whether the nitrogen concentration α2 is higher than the first predetermined concentration 50% (S303). If the nitrogen concentration α2 is lower than the first predetermined concentration 50%, the process returns to S302, and if the nitrogen concentration α2 is higher than the first predetermined concentration 50%, the unreacted fuel gas discharge valve 6 is opened (S304).

  Then, it is determined whether the nitrogen concentration α2 is lower than the second predetermined concentration 5% (S305). If the nitrogen concentration α2 is higher than the second predetermined concentration 5%, the process returns to S304. If the nitrogen concentration α2 is lower than the second predetermined concentration 5%, the unreacted fuel gas discharge valve 6 is closed (S306), and the process returns to S301. Each step shifts promptly after completion of each step without providing a waiting time.

  As described above, in the present embodiment, the fuel consumption rate Uf of the fuel cell 1 during the operation is determined according to the nitrogen concentration in the unreacted fuel gas in the unreacted fuel gas supply path 4 measured by the gas sensor 8. The amount of pure hydrogen gas supplied to the fuel cell 1 can be kept more constant by changing the amount of unreacted fuel gas supplied by the transport means 7 so as to be substantially constant. It becomes possible to keep the fuel consumption rate Uf of the fuel cell 1 inside more constant.

  Therefore, stable power generation of the fuel cell 1 is possible. By these operations, the fuel cell system 200 can generate more stable power.

  In the present embodiment, the concentration measured by the gas sensor 8 is nitrogen. However, the concentration is not limited to this, and carbon dioxide, carbon monoxide, ammonia, or the like contained in pure hydrogen gas may be used. Furthermore, the hydrogen concentration may be used as long as the impurity gas contained in the unreacted fuel gas can be indirectly measured.

  The fuel cell system of the present invention is a fuel cell system in which unreacted fuel gas discharged from the fuel cell is again supplied to the fuel cell as fuel gas. The amount of unreacted fuel gas supplied is included in the unreacted fuel gas. By changing according to the impurity gas concentration, stable power generation of the fuel cell becomes possible. Therefore, it is useful in applications where stable power generation is desired over a long period of time, for example, in the field of household or commercial fuel cell systems.

DESCRIPTION OF SYMBOLS 1 Fuel cell 2 Fuel gas supply path 3 Oxidant gas supply path 4 Unreacted fuel gas supply path 5 Unreacted fuel gas discharge path 6 Unreacted fuel gas discharge valve 7 Conveyance means 8 Gas sensor 100 Fuel cell system 101 Controller 102 Controller 200 Fuel cell system

Claims (5)

A fuel cell that generates power by reacting a fuel gas and an oxidant gas;
A fuel gas supply path for supplying fuel gas to the fuel cell;
An unreacted fuel gas supply path for supplying unreacted fuel gas discharged from the fuel cell as the fuel gas to the fuel gas supply path;
Conveying means for supplying the unreacted fuel gas from the unreacted fuel gas supply path to the fuel gas supply path;
An unreacted fuel gas discharge path branched from the unreacted fuel gas supply path;
An unreacted fuel gas discharge valve for opening and closing the unreacted fuel gas discharge path;
A controller, and
The controller supplies the unreacted fuel gas by the transfer means so that the fuel consumption rate of the fuel cell during operation is substantially constant according to the impurity gas concentration contained in the unreacted fuel gas. Characterized by varying the amount,
Fuel cell system.   The controller is configured to supply the unreacted fuel gas by the transport unit so that the fuel consumption rate of the fuel cell during operation is substantially constant according to the concentration of nitrogen contained in the unreacted fuel gas. The fuel cell system according to claim 1, wherein the fuel cell system is varied.   The controller according to claim 1, wherein the controller controls the unreacted fuel gas discharge valve to open before the impurity gas concentration reaches a preset upper limit value of the impurity gas concentration. The fuel cell system described.   3. The controller according to claim 2, wherein the controller controls the unreacted fuel gas discharge valve to open before the nitrogen concentration reaches a preset upper limit value of the nitrogen concentration. Fuel cell system.   The controller controls the unreacted fuel gas discharge valve to be opened before the supply amount of the unreacted fuel gas by the transfer means reaches a supply amount upper limit value of the transfer means. Item 4. The fuel cell system according to Item 1.

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