JP2014241260A - Fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently reduce a nitrogen concentration in a buffer tank.SOLUTION: A fuel cell system that supplies an anode gas and a cathode gas to a fuel cell to generate power includes: a buffer part for storing an anode off-gas discharged from the fuel cell; a purge valve for discharging to the outside the anode off-gas in a passage connecting the fuel cell and the buffer part; anode pressure control means for causing the pressure of the anode gas supplied to the fuel cell to pulsate between an upper limit pressure of pulsation and a lower limit pressure of pulsation depending on an operational state of the fuel cell system; purge execution means for opening the purge valve on the basis of an operational state of the fuel cell system; and purge mode anode pressure control means for reducing the pressure of the anode gas in accordance with the purge execution.

Description

  The present invention relates to a fuel cell system.

  As a conventional fuel cell system, there is one in which a normally closed solenoid valve is provided in an anode gas supply passage, and a normally open solenoid valve and a buffer tank (recycle tank) are provided in order from the upstream in an anode gas discharge passage.

  This conventional fuel cell system is an anode gas non-circulation type fuel cell system in which unused anode gas discharged into the anode gas discharge passage is not returned to the anode gas supply passage. A pulsation operation for pulsating the pressure is performed. In a fuel cell system that performs pulsation operation, the anode off gas in the buffer tank may flow backward to the fuel cell side when the anode gas pressure is reduced.

JP-T-2007-517369

  However, during operation of the fuel cell system, nitrogen in the cathode gas permeates from the cathode side to the anode side through the electrolyte membrane. Therefore, during the operation of the fuel cell system, the nitrogen concentration of the anode off gas in the buffer tank gradually increases. If such an anode off gas having a high nitrogen concentration is caused to flow backward, the power generation efficiency of the fuel cell may be reduced.

  For this reason, when the nitrogen concentration in the buffer tank becomes high to some extent, it is necessary to discharge the anode off-gas in the buffer tank to the outside of the fuel cell system to lower the nitrogen concentration in the buffer tank.

  At this time, if the anode off gas in the passage connecting the fuel cell and the buffer tank is discharged to the outside, the anode gas itself is discharged depending on the discharge timing, and the nitrogen concentration in the buffer tank is effectively reduced. There was a problem that it could not be made.

  The present invention has been made paying attention to such problems, and an object thereof is to efficiently reduce the nitrogen concentration in the buffer tank.

  According to an aspect of the present invention, a fuel cell system for generating electricity by supplying an anode gas and a cathode gas to a fuel cell is provided. The fuel cell system includes a buffer unit for storing anode off-gas discharged from the fuel cell, a purge valve for discharging anode off-gas in a passage connecting the fuel cell and the buffer unit, and a fuel cell system. The anode pressure control means for pulsating the pressure of the anode gas supplied to the fuel cell between the pulsation upper limit pressure and the pulsation lower limit pressure corresponding to the operation state of the fuel cell, and the purge valve is opened based on the operation state of the fuel cell system Purge execution means. Then, the pressure of the anode gas is reduced in accordance with the purge execution.

  According to this aspect, the anode pressure is reduced in accordance with the purge execution time. Therefore, during the purge execution, the differential pressure between the buffer unit side and the fuel cell side is increased, and the anode off gas is supplied from the buffer unit side to the fuel cell side. It can be made to flow backward. Therefore, a large amount of the anode off gas having a high nitrogen concentration in the buffer unit can be discharged outside the fuel cell system. Therefore, the nitrogen concentration in the buffer unit can be efficiently reduced.

1 is a schematic perspective view of a fuel cell according to an embodiment of the present invention. It is II-II sectional drawing of the fuel cell of FIG. 1 is a schematic configuration diagram of an anode gas non-circulating fuel cell system according to an embodiment of the present invention. It is a figure explaining the pulsation operation at the time of steady operation. It is a flowchart explaining the pulsation control by one Embodiment of this invention. It is a table which sets the upper limit pressure and the lower limit pressure of anode pressure based on target output electric power. It is a flowchart explaining the nitrogen concentration calculation process by one Embodiment of this invention. It is a map which calculates nitrogen permeation amount based on the temperature and moisture content of an electrolyte membrane. It is a time chart explaining the operation | movement of pulsation control by one Embodiment of this invention.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  A fuel cell has an electrolyte membrane sandwiched between an anode electrode (fuel electrode) and a cathode electrode (oxidant electrode), an anode gas containing hydrogen in the anode electrode (fuel gas), and a cathode gas containing oxygen in the cathode electrode (oxidant) Electricity is generated by supplying gas. The electrode reaction that proceeds in both the anode electrode and the cathode electrode is as follows.

Anode electrode: 2H ₂ → 4H ⁺ + 4e ⁻ (1)
Cathode electrode: 4H ⁺ + 4e ⁻ + O ₂ → 2H ₂ O (2)

  The fuel cell generates an electromotive force of about 1 volt by the electrode reactions (1) and (2).

  1 and 2 are diagrams illustrating the configuration of a fuel cell 10 according to an embodiment of the present invention. FIG. 1 is a schematic perspective view of the fuel cell 10. FIG. 2 is a II-II cross-sectional view of the fuel cell 10 of FIG.

  The fuel cell 10 is configured by arranging an anode separator 12 and a cathode separator 13 on both front and back surfaces of a membrane electrode assembly (hereinafter referred to as “MEA”) 11.

  The MEA 11 includes an electrolyte membrane 111, an anode electrode 112, and a cathode electrode 113. The MEA 11 has an anode electrode 112 on one surface of the electrolyte membrane 111 and a cathode electrode 113 on the other surface.

  The electrolyte membrane 111 is a proton-conductive ion exchange membrane formed of a fluorine-based resin. The electrolyte membrane 111 exhibits good electrical conductivity in a wet state.

  The anode electrode 112 includes a catalyst layer 112a and a gas diffusion layer 112b. The catalyst layer 112a is in contact with the electrolyte membrane 111. The catalyst layer 112a is formed of carbon black particles carrying platinum or platinum. The gas diffusion layer 112b is provided outside the catalyst layer 112a (on the opposite side of the electrolyte membrane 111) and is in contact with the anode separator 12. The gas diffusion layer 112b is formed of a member having sufficient gas diffusibility and conductivity, and is formed of, for example, a carbon cloth woven with yarns made of carbon fibers.

  Similarly to the anode electrode 112, the cathode electrode 113 includes a catalyst layer 113a and a gas diffusion layer 113b.

  The anode separator 12 is in contact with the gas diffusion layer 112b. The anode separator 12 has a plurality of groove-shaped anode gas passages 121 for supplying anode gas to the anode electrode 112 on the side in contact with the gas diffusion layer 112b.

  The cathode separator 13 is in contact with the gas diffusion layer 113b. The cathode separator 13 has a plurality of groove-like cathode gas flow paths 131 for supplying cathode gas to the cathode electrode 113 on the side in contact with the gas diffusion layer 113b.

  The anode gas flowing through the anode gas flow path 121 and the cathode gas flowing through the cathode gas flow path 131 flow in opposite directions in parallel to each other. You may make it flow in the same direction in parallel with each other.

  When such a fuel cell 10 is used as a power source for automobiles, a large amount of electric power is required, so that it is used as a fuel cell stack in which several hundred fuel cells 10 are stacked. Then, a fuel cell system that supplies anode gas and cathode gas to the fuel cell stack is configured, and electric power for driving the vehicle is taken out.

  FIG. 3 is a schematic configuration diagram of an anode gas non-circulating fuel cell system 1 according to an embodiment of the present invention.

  The fuel cell system 1 includes a fuel cell stack 2, an anode gas supply device 3, and a controller 4.

  The fuel cell stack 2 is formed by stacking a plurality of fuel cells 10, generates electric power by receiving supply of anode gas and cathode gas, and generates electric power necessary for driving a vehicle (for example, electric power necessary for driving a motor). ).

  The cathode gas supply / discharge device for supplying and discharging the cathode gas to / from the fuel cell stack 2 and the cooling device for cooling the fuel cell stack 2 are not the main part of the present invention, and are not shown for the sake of easy understanding. did. In this embodiment, air is used as the cathode gas.

  The anode gas supply device 3 includes a high-pressure tank 31, an anode gas supply passage 32, a pressure regulating valve 33, a pressure sensor 34, an anode gas discharge passage 35, a buffer tank 36, a purge passage 37, and a purge valve 38. .

  The high-pressure tank 31 stores the anode gas (hydrogen) supplied to the fuel cell stack 2 while maintaining the high-pressure state.

  The anode gas supply passage 32 is a passage for supplying the anode gas discharged from the high-pressure tank 31 to the fuel cell stack 2, and has one end connected to the high-pressure tank 31 and the other end of the fuel cell stack 2. Connected to the anode gas inlet hole 21.

  The pressure regulating valve 33 is provided in the anode gas supply passage 32. The pressure regulating valve 33 adjusts the anode gas discharged from the high-pressure tank 31 to a desired pressure and supplies it to the fuel cell stack 2. The pressure regulating valve 33 is an electromagnetic valve whose opening degree can be adjusted continuously or stepwise, and the opening degree is controlled by the controller 4.

  The pressure sensor 34 is provided in the anode gas supply passage 32 downstream of the pressure regulating valve 33. The pressure sensor 34 detects the pressure of the anode gas flowing through the anode gas supply passage 32 downstream of the pressure regulating valve 33. In the present embodiment, the pressure of the anode gas detected by the pressure sensor 34 is the pressure of the entire anode system including the anode gas flow paths 121 and the buffer tanks 36 inside the fuel cell stack (hereinafter referred to as “anode pressure”). As a substitute.

  The anode gas discharge passage 35 has one end connected to the anode gas outlet hole 22 of the fuel cell stack 2 and the other end connected to the buffer tank 36. The anode gas discharge passage 35 has a mixed gas (hereinafter referred to as “anode offgas”) of excess anode gas that has not been used for the electrode reaction and an impure gas such as nitrogen that has permeated from the cathode side to the anode gas passage 121. Is said to be discharged.

  The buffer tank 36 temporarily stores the anode off gas that has flowed through the anode gas discharge passage 35.

  The purge passage 37 has one end connected to the anode gas discharge passage 35 and the other end being an open end. The anode off gas stored in the buffer tank 36 once flows back through the anode gas discharge passage 35 and then is discharged from the opening end to the outside air through the purge passage 37.

  The purge valve 38 is provided in the purge passage 37. The purge valve 38 is an electromagnetic valve whose opening / closing is controlled by a controller. By opening the purge valve 38, the anode off gas stored in the buffer tank 36 passes through the purge passage 37 and is discharged from the open end to the outside air.

  The controller 4 includes a microcomputer having a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM), and an input / output interface (I / O interface).

  In addition to the pressure sensor 34 described above, the controller 4 cools the current sensor 41 that detects the output current of the fuel cell stack 2, the voltage sensor 42 that detects the output voltage of the fuel cell stack 2, and the fuel cell stack 2. The fuel cell system 1 includes a temperature sensor 43 that detects the temperature of the cooling water (hereinafter referred to as “cooling water temperature”) and an accelerator stroke sensor 44 that detects the amount of depression of the accelerator pedal (hereinafter referred to as “accelerator operation amount”). Various signals for detecting the operating state are input.

  Based on these input signals, the controller 4 performs a pulsation operation for periodically raising and lowering the anode pressure.

  FIG. 4 is a diagram for explaining pulsation operation during steady operation in which the operation state of the fuel cell system 1 is constant.

  As shown in FIG. 4A, the controller 4 calculates the target output power of the fuel cell stack 2 (the load of the fuel cell stack 2) based on the operating state of the fuel cell system 1, and according to the target output power. Set the upper and lower pressure limits of the anode pressure. Then, the anode pressure is periodically raised and lowered between the upper limit pressure and the lower limit pressure of the set anode pressure.

  Specifically, when the anode pressure reaches the lower limit pressure at time t1, as shown in FIG. 4B, the opening degree of the pressure regulating valve 33 is feedback controlled so that the anode pressure becomes the upper limit pressure. As a result, as shown in FIG. 4A, the anode pressure increases from the lower limit pressure toward the upper limit pressure. In this state, the anode gas is supplied from the high pressure tank 31 to the fuel cell stack 2, and the anode off gas is pushed into the buffer tank 36.

  When the anode pressure reaches the upper limit pressure at time t2, as shown in FIG. 4B, the opening degree of the pressure regulating valve 33 is feedback controlled so that the anode pressure becomes the lower limit pressure. As a result of this feedback control, the opening of the pressure regulating valve 33 is normally fully closed, and the supply of anode gas from the high-pressure tank 31 to the fuel cell stack 2 is stopped. Then, the anode gas left in the anode gas flow path 121 inside the fuel cell stack is consumed over time due to the electrode reaction of (1) described above, and as shown in FIG. The anode pressure decreases according to the consumption.

  Then, when the anode gas left in the anode gas flow path 121 is consumed and the anode pressure decreases and the pressure on the fuel cell stack 2 side becomes lower than the pressure on the buffer tank 36 side, the fuel cell stack 2 is transferred from the buffer tank 36 to the fuel cell stack 2. The anode off gas flows back to the side. As a result, the anode gas left in the anode gas channel 121 and the anode gas in the anode off-gas that has flowed back to the anode gas channel 121 are consumed over time, and the anode pressure further decreases.

  When the anode pressure reaches the lower limit pressure at time t3, the pressure regulating valve 33 is opened as at time t1. As a result, the anode gas is supplied from the high-pressure tank 31 to the fuel cell stack 2 and the anode off-gas that has flowed back to the fuel cell stack 2 side is pushed into the buffer tank 36 again. When the anode pressure reaches the upper limit pressure again at time t4, the pressure regulating valve 33 is fully closed in the same manner as at time t2.

  Here, during operation of the fuel cell system 1, as described above, impure gas such as nitrogen permeates from the cathode side to the anode gas flow path 121 through the electrolyte membrane 111. Therefore, in such an anode gas non-circulating fuel cell system 1, unless the purge valve 38 is opened, the nitrogen concentration in the anode off-gas in the buffer tank 36 gradually increases. When the anode off gas having a high nitrogen concentration flows back into the anode gas flow path 121, the anode gas necessary for the electrode reaction in the anode gas flow path 121 is insufficient, and power generation efficiency may be reduced. Therefore, when the nitrogen concentration in the buffer tank 36 becomes relatively high, the purge valve 38 is opened, the anode off gas in the buffer tank 36 is discharged to the outside of the fuel cell system 1, and the nitrogen concentration in the buffer tank 36 is Need to be reduced.

  Therefore, in this embodiment, in order to efficiently reduce the nitrogen concentration in the buffer tank 36, the lower limit pressure of the anode pressure is set lower than usual when the nitrogen concentration in the buffer tank 36 exceeds a predetermined concentration. Therefore, the purge valve 38 is opened. That is, the lower limit pressure of the anode pressure is made smaller than the normally set lower limit pressure in accordance with the purge execution. As a result, the purge valve 38 is opened in a state where the flow rate of the anode off-gas flowing backward from the buffer tank 36 to the fuel cell stack 2 side is larger than usual, so that the nitrogen concentration in the buffer tank 36 is efficiently reduced. Can be reduced.

  Hereinafter, the pulsation control according to this embodiment will be described.

  FIG. 5 is a flowchart illustrating pulsation control according to the present embodiment.

  In step S1, the controller 4 sets an upper limit pressure and a lower limit pressure of the anode pressure based on the target output power of the fuel cell stack 2 with reference to the table of FIG. As shown in FIG. 6, the difference (pulsation width) between the upper limit pressure and the lower limit pressure increases as the target output power increases. This takes into account the drainage of produced water from the fuel cell stack 2 and the exhaustability of permeated nitrogen.

  In step S2, the controller 4 performs a nitrogen concentration calculation process for calculating the nitrogen concentration in the anode system. Details of the nitrogen concentration calculation process will be described later with reference to FIG.

  In step S3, the controller 4 determines whether or not it is necessary to execute a purge when the anode pressure is lowered. Specifically, it is determined whether the boosting flag is set to 0 and the purge request flag is set to 1. The boosting flag is a flag that is set to 1 when the anode pressure is increased, and the initial value is set to 1. The purge request flag is a flag that is set to 1 when the nitrogen concentration in the anode system is equal to or higher than a predetermined concentration and it is necessary to perform a purge, and the initial value is set to 0. If the boost flag is set to 0 and the purge request flag is set to 1, the controller 4 performs the process of step S17, and otherwise performs the process of step S4.

  In step S4, the controller 4 determines whether or not the nitrogen concentration in the anode system is equal to or higher than a predetermined concentration. The controller 4 performs the process of step S5 if the nitrogen concentration in the anode system is less than the predetermined concentration, and performs the process of step S6 if the nitrogen concentration in the anode system is equal to or higher than the predetermined concentration.

  In step S5, the controller 4 sets the purge request flag to 0.

  In step S6, the controller 4 sets a purge request flag to 1.

  In step S <b> 7, the controller 4 calculates a lower limit pressure (hereinafter referred to as “purge lower limit pressure”) set at the time of purge execution. In the present embodiment, a value obtained by subtracting a predetermined value from the lower limit pressure set in step S1 is set as the purge lower limit pressure, and the purge lower limit pressure is set as a variable value according to the operating state of the fuel cell system 1. A predetermined value may be set as the purge lower limit pressure. Note that when the purge is performed, the anode pressure in the fuel cell stack 2 decreases, so that part of the anode off-gas may flow back into the fuel cell stack 2. Therefore, the predetermined value is set in advance by an experiment or the like according to the operation state of the fuel cell system 1 so that the flow rate of the anode off-gas that has flowed back becomes a flow rate that does not hinder the power generation in the fuel cell stack 2. It is desirable to keep it.

  The purge lower limit pressure is set to a value higher than the atmospheric pressure. This is because if the purge lower limit pressure is set to a value lower than the atmospheric pressure, the pressure on the anode gas discharge passage 35 side becomes lower than the pressure outside the fuel cell system 1 (= atmospheric pressure). This is because the anode off gas cannot be discharged outside the fuel cell system 1.

  In step S8, the controller 4 determines whether or not the boosting flag is set to 1. The controller 4 performs the process of step S9 when the boost flag is set to 1, that is, when the anode pressure is boosted. On the other hand, when the boost flag is set to 0, that is, when the anode pressure is lowered, the process of step S12 is performed.

  In step S9, the controller 4 determines whether or not the anode pressure detected by the pressure sensor 34 is lower than the upper limit pressure. The controller 4 performs the process of step S10 if the anode pressure is lower than the upper limit pressure, and performs the process of step S11 if the anode pressure is equal to or higher than the upper limit pressure.

  In step S10, the controller 4 feedback-controls the opening degree of the pressure regulating valve 33 based on the detected anode pressure so that the anode pressure becomes the upper limit pressure.

  In step S11, the controller 4 sets the boosting flag to 0.

  In step S12, the controller 4 determines whether or not the purge request flag is set to 1. The controller 4 performs the process of step S13 if the purge request flag is set to 0, and performs the process of step S17 if the purge request flag is set to 1.

  In step S13, the controller 4 determines whether or not the anode pressure detected by the pressure sensor 34 is higher than the lower limit pressure. The controller 4 performs the process of step S14 if the anode pressure is higher than the lower limit pressure, and performs the process of step S15 if the anode pressure is equal to or lower than the lower limit pressure.

  In step S14, the controller 4 feedback-controls the opening degree of the pressure regulating valve 33 based on the detected anode pressure so that the anode pressure becomes the lower limit pressure.

  In step S15, the controller 4 sets the boosting flag to 1.

  In step S16, the controller 4 feedback-controls the opening degree of the pressure regulating valve 33 based on the detected anode pressure so that the anode pressure becomes the upper limit pressure.

  In step S17, the controller 4 determines whether or not the anode pressure detected by the pressure sensor 34 is higher than the purge lower limit pressure. The controller 4 performs the process of step S18 if the anode pressure is higher than the purge lower limit pressure, and performs the process of step S20 if the anode pressure is equal to or lower than the purge lower limit pressure.

  In step S18, the controller 4 opens the purge valve 38.

  In step S19, the controller 4 feedback-controls the opening degree of the pressure regulating valve 33 based on the detected anode pressure so that the anode pressure becomes the purge lower limit pressure.

  In step S20, the controller 4 sets the boosting flag to 1.

  In step S21, the controller 4 sets the purge request flag to 0.

  In step S22, the controller 4 closes the purge valve 38.

  FIG. 7 is a flowchart for explaining the nitrogen concentration calculation process.

  In step S201, the controller 4 refers to the map of FIG. 8, and based on the temperature and moisture content of the electrolyte membrane 111, the amount of nitrogen permeating from the cathode side to the anode gas flow path 121 (hereinafter referred to as “nitrogen permeation amount”). Is calculated). In the present embodiment, the cooling water temperature is used as the temperature of the electrolyte membrane 111. The moisture content of the electrolyte membrane 111 is calculated based on the internal high frequency resistance (HFR) of the fuel cell stack 2 calculated by various known methods (for example, the AC impedance method).

  In step S202, the controller 4 determines whether or not the purge valve 38 is open. The controller 4 performs the process of step S203 if the purge valve 38 is closed, and performs the process of step S204 if the purge valve 38 is open.

  In step S203, the controller 4 calculates the total nitrogen amount in the anode system (hereinafter referred to as “total nitrogen amount”). Here, the total nitrogen amount is calculated by adding the nitrogen permeation amount to the previous value of the total nitrogen amount.

  In step S204, the controller 4 calculates the total nitrogen amount. Here, the total nitrogen amount is obtained by subtracting the purge flow rate per unit time calculated based on the anode pressure detected by the pressure sensor 34 from the previous value of the total nitrogen amount plus the nitrogen permeation amount. calculate. The purge flow rate is determined by the differential pressure across the purge valve 38, that is, the anode pressure minus the atmospheric pressure, and the opening of the purge valve 38. In this embodiment, since the opening degree of the purge valve 38 is constant, the purge flow rate can be calculated if the anode pressure is known.

  In step S205, the controller 4 calculates the nitrogen concentration of the entire anode system based on the total nitrogen amount.

  FIG. 9 is a time chart for explaining the operation of pulsation control according to the present embodiment.

  Until time t11, a pulsation operation is performed in which the anode pressure is raised and lowered within the range of the upper limit pressure and the lower limit pressure of the anode pressure calculated according to the target output power of the fuel cell stack 2 (FIG. 9A). During this time, since the purge valve 38 remains closed (FIG. 9C), the nitrogen concentration in the anode system gradually increases (FIG. 9F).

  When the nitrogen concentration in the anode system becomes equal to or higher than the predetermined concentration at time t12 (FIG. 9 (F); Yes in S4), the purge request flag is set to 1 (FIG. 9 (E); S6), and the purge lower limit pressure is set. Calculated (S7).

  When the anode pressure reaches the upper limit pressure at time t13 and the pressure increase flag is set to 0 (FIG. 9D), the purge valve 38 is opened (FIG. 9C); Yes in S3, No in S17 , S18), the degree of opening of the pressure regulating valve 33 is feedback-controlled based on the detected anode pressure so that the anode pressure becomes the purge lower limit pressure (FIG. 9A; S19).

  Then, after the anode pressure reaches the purge lower limit pressure at time t14, the anode pressure calculated according to the target output power of the fuel cell stack 2 again until the nitrogen concentration in the anode system becomes equal to or higher than the predetermined concentration next time. A pulsation operation is performed in which the anode pressure is raised and lowered within the range of the upper limit pressure and the lower limit pressure.

  According to the present embodiment described above, the anode pressure is lowered to the purge lower limit pressure that is smaller than the normally set lower limit pressure in accordance with the purge execution.

  As a result, the pressure difference between the buffer tank 36 and the fuel cell stack 2 can be made larger than usual during purging, and the flow rate of the anode off-gas flowing back from the buffer tank 36 to the fuel cell stack 2 can be reduced to normal. The anode pressure can be increased more than when the anode pressure is reduced. Therefore, the anode off gas having a high nitrogen concentration in the buffer tank 36 can be discharged from the purge passage 37 to the outside of the fuel cell system 1 in a larger amount than usual. Therefore, the nitrogen concentration in the buffer tank 36 can be efficiently reduced.

  In addition, by effectively reducing the nitrogen concentration in the buffer tank 36 in this manner, pulsation occurs in the range of the upper limit pressure and the lower limit pressure of the anode pressure calculated according to the target output power of the fuel cell stack 2. It is possible to suppress the anode off gas having a high nitrogen concentration from flowing back into the anode gas flow path 121 during the pressure reduction during the operation. Therefore, it is possible to suppress the shortage of the anode gas necessary for the electrode reaction in the anode gas flow path 121, and it is possible to suppress a decrease in power generation efficiency.

  Further, according to the present embodiment, purging is performed after determining that the nitrogen concentration in the anode system has reached a predetermined concentration or more.

  The anode off gas in the buffer tank 36 discharged from the purge passage 37 includes the anode gas pushed into the buffer tank 36 without being reacted. For this reason, it is possible to discharge the anode off-gas having a high nitrogen concentration from the buffer tank 36 by executing the purge after determining that the nitrogen concentration in the anode system has become equal to or higher than the predetermined concentration. Therefore, since the flow rate of the anode gas discharged to the outside of the fuel cell system 1 can also be reduced, the fuel consumption of the fuel cell system 1 can be improved.

  Further, according to this embodiment, the purge lower limit pressure is set to a value higher than the atmospheric pressure.

  Thereby, the anode off gas in the buffer tank 36 can be reliably discharged from the purge passage 37 to the outside of the fuel cell system 1.

  The embodiment of the present invention has been described above. However, the above embodiment only shows a part of application examples of the present invention, and the technical scope of the present invention is limited to the specific configuration of the above embodiment. Absent.

  For example, in the above embodiment, after the nitrogen concentration in the anode system has reached a predetermined concentration or more, purge is performed after the anode pressure reaches the upper limit pressure, and the anode pressure is reduced in accordance with the purge. A purge may be executed when the nitrogen concentration in the anode system becomes equal to or higher than a predetermined concentration, and the anode pressure may be reduced in accordance with the purge execution. That is, when the purge request is made, the anode pressure may be reduced more than that time.

  Further, when the purge valve 38 is opened to reduce the anode pressure to the purge lower limit pressure, the output power of the fuel cell stack 2 may be reduced by a predetermined amount. By reducing the output power of the fuel cell stack 2, the consumption amount of the anode gas in the fuel cell stack 2 is reduced, so that the rate of decrease of the anode pressure can be slowed. If the rate of decrease in the anode pressure is reduced, the time until the anode pressure is reduced to the purge lower limit pressure becomes longer, so the time during which the purge valve 38 is opened also becomes longer. Therefore, the flow rate of the anode off gas that can be discharged to the outside of the fuel cell system 1 at the time of purging can be increased, so that the nitrogen concentration in the buffer tank 36 can be efficiently reduced.

  In the above embodiment, the buffer tank 36 is intentionally provided downstream of the fuel cell stack 2, but such a component is not always necessary, and normal piping or an internal manifold of the fuel cell stack 2 are not necessarily required. May be regarded as a buffer tank.

1 Fuel cell system 2 Fuel cell stack (fuel cell)
4 Controller (Anode pressure control means, nitrogen concentration calculation means, purge execution means, purge anode pressure control means, output control means)
35 Anode gas discharge passage (passage)
36 Buffer tank (buffer part)
38 Purge valve

Claims (5)

A fuel cell system for generating electricity by supplying an anode gas and a cathode gas to a fuel cell,
A buffer unit for storing anode off-gas discharged from the fuel cell;
A purge valve for discharging anode off-gas in the passage connecting the fuel cell and the buffer unit to the outside;
Anode pressure control means for pulsating the pressure of the anode gas supplied to the fuel cell between the pulsation upper limit pressure and the pulsation lower limit pressure according to the operating state of the fuel cell system;
Purging means for opening the purge valve based on the operating state of the fuel cell system;
A purge anode pressure control means for reducing the pressure of the anode gas in accordance with the purge execution;
A fuel cell system comprising: The purge anode pressure control means includes:
The pressure of the anode gas is reduced to the purge lower limit pressure lower than the pulsation lower limit pressure in accordance with the purge execution.
The fuel cell system according to claim 1. A nitrogen concentration calculating means for calculating a nitrogen concentration in an anode system including the fuel cell and the buffer unit;
The purge execution means includes
Performing a purge when the nitrogen concentration exceeds a predetermined concentration;
The fuel cell system according to claim 1 or 2, characterized by the above. The nitrogen concentration calculating means includes
Based on the temperature and water content of the electrolyte membrane of the fuel cell, the amount of permeated nitrogen that permeates the electrolyte membrane from the cathode side to the anode side is calculated.
Based on the amount of permeated nitrogen, the nitrogen concentration of the anode system including the fuel cell and the buffer unit is calculated.
The fuel cell system according to claim 3. An output control means for reducing the output power of the fuel cell when the pressure of the anode gas is reduced in accordance with the purge execution;
The fuel cell system according to any one of claims 1 to 4, wherein the fuel cell system is provided.

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