JP2020009598A - Fuel cell system and operation method thereof - Google Patents

Abstract

To reduce a nitrogen concentration in a fuel gas containing an impurity in an anode without discharging hydrogen from the anode, and to achieve the downsizing by providing no diluter.SOLUTION: A fuel cell system comprises: a fuel cell stack (1); a fuel gas-supply path (2) for supplying a fuel gas to an anode (1a) of the fuel cell stack; an oxidant gas supplying part (3) for supplying an oxidant gas to a cathode (1b) of the fuel cell stack; an oxidant gas-supply path (4) for connecting the cathode and the oxidant gas supplying part; an oxidant gas-discharge path (5) for discharging an unreacted oxidant gas from the cathode to outside; current-supply means (6) for supplying an electric current between the anode and cathode of the fuel cell stack; and a control part (7). While power generation is stopped, the control part stops the supply of an oxidant gas to the cathode, and supplies hydrogen from the anode to the cathode by the current-supply means, thereby causing the concentration of nitrogen in a fuel gas containing an impurity in the anode to fall within a predetermined range.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a fuel cell system that generates power using a hydrogen-containing gas and a method of operating the fuel cell system.

  Conventionally, as a countermeasure against nitrogen accumulated in the anode during the shutdown period, this type of fuel cell system purges the fuel gas containing impurities in the anode with the fuel gas supplied from the fuel gas supply path when returning from the shutdown period. By discharging the fuel gas from the purge passage, the concentration of nitrogen in the fuel gas containing impurities in the anode is reduced. (For example, see Patent Document 1).

  FIG. 5 is a block diagram showing a configuration of a conventional fuel cell system described in the above publication.

  As shown in FIG. 5, the fuel cell system 500 includes a fuel cell stack 101, a fuel gas supply path 102, an oxidant gas supply unit 103, an oxidant gas supply path 104, an oxidant gas discharge path 105, and an unreacted fuel gas circulation. It comprises a path 106, a purge valve 107, and a diluter 108.

  When the fuel cell system 500 is to be returned from the stop period, nitrogen containing fuel gas accumulated in the anode of the fuel cell stack 101 and the unreacted fuel gas circulation path 106 during the stop period is opened as a purge gas by opening the purge valve 107 and the diluter 108. Introduce to. Further, the purge gas is discharged to the outside of the fuel cell system 500 after being diluted to a predetermined hydrogen concentration by the fuel cell stack 101 and the cathode off gas passing through the oxidizing gas discharge path 105.

JP 2007-26843 A

  However, in the conventional configuration, when the fuel cell system returns from the stop period, hydrogen is discharged as a purge gas until the nitrogen concentration in the fuel gas containing impurities in the anode is reduced. A diluter for diluting to less than the flammable range is required, and there is a problem that the fuel cell system becomes large.

  The present invention solves the above-mentioned conventional problem, in which hydrogen is transferred from the anode to the cathode when power generation of the fuel cell system is stopped, and nitrogen in the oxidant gas in the cathode is discharged from the oxidant gas discharge path. By reducing the nitrogen concentration in the gas in the cathode, it is possible to reduce the transfer of nitrogen from the cathode to the anode during the shutdown period of the fuel cell system, and to reduce the nitrogen concentration in the fuel gas containing impurities in the anode. Reduce. By reducing the nitrogen concentration in the fuel gas containing impurities in the anode during the stop period, the nitrogen concentration in the fuel gas containing impurities in the anode can be reduced without discharging hydrogen from the anode. It is an object of the present invention to provide a miniaturized fuel cell system and an operation method thereof without providing a fuel cell system.

  In order to solve the conventional problem, a fuel cell system of the present invention provides a fuel cell stack that generates power using a fuel gas containing hydrogen and an oxidizing gas, and supplies the fuel gas to an anode of the fuel cell stack. A fuel gas supply path, an oxidant gas supply unit that supplies an oxidant gas to the cathode of the fuel cell stack, an oxidant gas supply path that connects the cathode and the oxidant gas supply unit, and an unreacted oxidant gas from the cathode. An oxidizing gas discharge path for discharging gas to the outside, current supply means for supplying a current between the anode and the cathode of the fuel cell stack, and a control unit. The supply of the oxidizing gas is stopped, a predetermined current is supplied between the anode and the cathode by the current supply means, and hydrogen is supplied from the anode to the cathode.

  By supplying hydrogen from the anode to the cathode when power generation is stopped, the nitrogen concentration in the oxidant gas in the cathode can be reduced, and during the stop period, nitrogen can pass from the cathode to the anode through the electrolyte membrane. Can be reduced. Further, since the purge gas is not discharged from the anode to reduce the nitrogen concentration, the fuel cell system can be reduced in size without providing a diluter.

  The fuel cell system of the present invention supplies a current between the anode and the cathode when power generation is stopped, moves hydrogen from the anode to the cathode, and discharges nitrogen in the oxidant gas in the cathode from the oxidant gas discharge path. Further, the nitrogen concentration in the fuel gas containing impurities in the anode during the power generation stop period is reduced. As a result, when returning from the stop period, the nitrogen concentration in the fuel gas containing impurities in the anode can be reduced, so that there is no need to provide a diluter, and the size and cost of the fuel cell system can be reduced. be able to.

Block diagram of a fuel cell system according to Embodiment 1 of the present invention Block diagram of a fuel cell system according to Embodiment 2 of the present invention Block diagram of a fuel cell system according to Embodiment 3 of the present invention Block diagram of a fuel cell system according to Embodiment 4 of the present invention Block diagram showing the configuration of a conventional fuel cell system

  A first invention provides a fuel cell stack that generates power using a fuel gas containing hydrogen and an oxidant gas, a fuel gas supply path that supplies a fuel gas to an anode of the fuel cell stack, and a fuel gas supply path that supplies a fuel gas to a cathode of the fuel cell stack. An oxidizing gas supply section for supplying an oxidizing gas, an oxidizing gas supply path connecting the cathode and the oxidizing gas supply section, an oxidizing gas discharge path for discharging unreacted oxidizing gas from the cathode to the outside, A current supply unit for supplying a current between the anode and the cathode of the fuel cell stack; and a control unit, wherein the control unit stops the supply of the oxidizing gas to the cathode when the power generation is stopped. Supplies a predetermined current between the anode and the cathode to supply hydrogen from the anode to the cathode. This allows the electrochemical transfer of hydrogen from the anode to the cathode through the electrolyte membrane, reducing the concentration of nitrogen in the oxidant gas within the cathode, and during the shutdown period from the cathode to the anode. Nitrogen permeation through the electrolyte membrane can be reduced. Further, since the purge gas is not discharged from the anode to reduce the nitrogen concentration, the fuel cell system can be reduced in size without providing a dilutor.

  Also, by electrochemically transferring hydrogen from the anode to the cathode through the electrolyte membrane, pipes and pumps can be reduced and the size can be reduced as compared with the case where hydrogen is physically supplied from the anode to the cathode. it can.

  According to a second aspect, in the fuel cell system according to the first aspect, when the current flowing between the anode and the cathode by the current supply unit reaches a predetermined amount of current, the control unit supplies the current supplied by the current supply unit. Is to stop. As a result, a predetermined amount of hydrogen is supplied from the anode to the cathode, and the nitrogen in the oxidant gas in the cathode is reliably discharged, and the supply of excessive hydrogen can be prevented.

  In a third aspect, in the fuel cell system according to the first aspect, the control unit seals the cathode when a predetermined condition is satisfied after the current supply is stopped by the current supply unit. . Thus, it is possible to prevent nitrogen from entering the cathode from the atmosphere after nitrogen is discharged from the cathode by hydrogen.

  In a fourth aspect, in the fuel cell system according to the third aspect, the control unit seals the cathode after a predetermined time has elapsed after the current supply by the current supply unit is stopped. This prevents the cathode from being sealed during the supply of hydrogen to the cathode, and prevents the pressure of the gas in the cathode from increasing excessively and preventing the cathode from being deteriorated.

  In a fifth aspect, the fuel cell system according to the third aspect is provided, wherein the control unit includes a hydrogen gas concentration detecting means provided in the oxidizing gas discharge path, and the current supply is stopped by the current supply means. The cathode is sealed after the detection value of the gas concentration detection means becomes equal to or less than a predetermined value. This prevents the concentration of hydrogen in the gas in the cathode from being excessively reduced, and prevents the concentration of nitrogen in the gas in the cathode from increasing.

  In a sixth aspect of the invention, the fuel cell system according to any one of the first to fifth aspects is branched at a branch portion provided on the upstream side of the cathode in the oxidant gas supply path, and oxidizes around the cathode. The apparatus is provided with a bypass path that joins at a junction of the agent gas discharge paths. As a result, the oxidizing gas can be supplied to the oxidizing gas discharge path without supplying the oxidizing gas to the cathode, and the supply of nitrogen contained in the oxidizing gas to the cathode can be prevented. Can be.

  According to a seventh aspect of the present invention, in the fuel cell system according to the sixth aspect of the present invention, the control unit supplies a predetermined current between the anode and the cathode by at least a current supply unit from the anode to the cathode when power generation is stopped. During the supply of hydrogen, the oxidizing gas is supplied to the oxidizing gas discharge path via the bypass path. Thus, even if hydrogen is discharged together with nitrogen from the cathode, hydrogen can be diluted with the oxidizing gas and discharged safely.

  The eighth invention provides a fuel cell stack that generates power using a fuel gas containing hydrogen and an oxidizing gas, a fuel gas supply path that supplies a fuel gas to an anode of the fuel cell stack, and a fuel gas supply path that supplies a fuel gas to a cathode of the fuel cell stack. An oxidizing gas supply section for supplying an oxidizing gas, an oxidizing gas supply path connecting the cathode and the oxidizing gas supply section, an oxidizing gas discharge path for discharging unreacted oxidizing gas from the cathode to the outside, Current supply means for supplying a current between an anode and a cathode of a fuel cell stack, comprising: a fuel cell system operating method, wherein when power generation is stopped, the supply of oxidant gas to the cathode is stopped. A predetermined current is supplied between the anode and the cathode by the supply means to supply hydrogen from the anode to the cathode. As a result, the nitrogen concentration in the oxidant gas in the cathode can be reduced, and during the shutdown period, the permeation of nitrogen from the cathode to the anode through the electrolyte membrane can be reduced. Further, since the purge gas is not discharged from the anode to reduce the nitrogen concentration, the fuel cell system can be reduced in size without providing a dilutor.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present invention is not limited by the present embodiment.

(Embodiment 1)
FIG. 1 shows a block diagram of a fuel cell system according to Embodiment 1 of the present invention. 1, a fuel cell system 100 includes a fuel cell stack 1, a fuel gas supply path 2, an oxidizing gas supply unit 3, an oxidizing gas supply path 4, an oxidizing gas discharge path 5, a current supply unit. 6 and a control unit 7.

  The fuel cell stack 1 is of a solid polymer type, and has a structure in which a plurality of single cells each having an electrolyte membrane 1c sandwiched between an anode 1a and a cathode 1b are stacked in the thickness direction, and each single cell is electrically connected in series. have.

  A path is formed in each of the anode 1a and the cathode 1b. Hydrogen as a fuel gas flows through the path in the anode 1a, and air as an oxidizing gas flows through the path in the cathode 1b. The anode 1a and the cathode 1b are electrodes through which current flows.

  The fuel gas supply path 2 is a path for supplying hydrogen, which is a fuel gas, to the anode 1 a of the fuel cell stack 1. In the present embodiment, an unreacted fuel gas circulation path is provided in which unused hydrogen among the hydrogen supplied to the anode 1a is discharged from the anode 1a, returned to the fuel gas supply path 2, and reused.

  The oxidizing gas supply unit 3 is a pump that supplies air that is an oxidizing gas.

  The oxidizing gas supply path 4 is connected to the oxidizing gas supply unit 3, and is a path that supplies the air supplied by the oxidizing gas supply unit 3 to the cathode 1 b of the fuel cell stack 1.

  The oxidizing gas discharge path 5 is a pipe path through which unused air discharged from the cathode 1b of the fuel cell stack 1 passes. The downstream end of the oxidizing gas discharge path 5 is open to the atmosphere outside the casing of the fuel cell system 100. Is done.

  The current supply means 6 supplies electric power between the anode 1a and the cathode 1b to flow a current.

  The control unit 7 only needs to have a control function, and includes an arithmetic processing unit (not shown) and a storage unit (not shown) for storing a control program. A CPU is exemplified as the arithmetic processing unit. A memory is exemplified as the storage unit.

  The operation and operation of the fuel cell system 100 configured as described above will be described below.

  First, the operation of the fuel cell system 100 during power generation will be described. Hydrogen is supplied to the anode 1 a of the fuel cell stack 1, and air is supplied to the cathode 1 b of the fuel cell stack 1 from the oxidizing gas supply unit 3. Hydrogen supplied to the anode 1a is converted into protons and electrons by the catalyst present in the anode 1a. Protons are supplied to the cathode 1b via the electrolyte membrane 1c. Electrons are extracted from the anode 1a by an inverter (not shown) provided outside the fuel cell stack 1, passed through the inverter, supplied to the cathode 1b via the cathode 1b, and supplied to the cathode 1b. At the cathode 1b, oxygen, protons, and electrons contained in the air react to generate water. The fuel cell system 100 can generate electric power by drawing a current with the inverter. The inverter converts DC power into AC power, and AC power is supplied from the fuel cell system 100.

  Next, the operation of the fuel cell system 100 when power generation is stopped will be described. By stopping the inverter from drawing current, the fuel cell system 100 stops generating power. The supply of hydrogen and air supplied to the fuel cell stack 1 is stopped after the power generation is stopped. Here, the air remaining in the cathode 1b contains nitrogen. Nitrogen in the air in the cathode 1b is separated by the partial pressure difference between the nitrogen partial pressure in the air in the cathode 1b and the nitrogen partial pressure in the hydrogen containing impurities in the anode 1a through the electrolyte membrane 1c. To the anode 1a. Here, assuming that the concentration of nitrogen in the air inside the cathode 1b at the time of stopping is 79% and the pressure of the air inside the cathode 1b is the atmospheric pressure, the partial pressure of nitrogen in the air inside the cathode 1b is 80 kPa. Assuming that the concentration of nitrogen in the hydrogen containing impurities in the anode 1a is 20% and the pressure of the hydrogen containing impurities in the anode 1a is 50 kPa with respect to the atmospheric pressure, the partial pressure of nitrogen in the hydrogen containing impurities in the anode 1a is 30 kPa. Therefore, the partial pressure difference between the nitrogen partial pressure in air in the cathode 1b and the nitrogen partial pressure in hydrogen containing impurities in the anode 1a is 50 kPa.

  At the time of stoppage, the nitrogen moves from the cathode 1b to the anode 1a due to the partial pressure difference of nitrogen, so that the amount of nitrogen in the impurity-containing hydrogen in the anode 1a increases, and the nitrogen concentration in the impurity-containing hydrogen in the anode 1a increases. Rises. If the nitrogen concentration in the hydrogen containing impurities in the anode 1a rises and becomes equal to or higher than a predetermined concentration, power generation is hindered when the fuel cell system 100 next generates power. In the present embodiment, the predetermined density is 20%. Therefore, in order to reduce the amount of transfer of nitrogen from the cathode 1b to the anode 1a via the electrolyte membrane 1c, an operation of supplying hydrogen from the anode 1a to the cathode 1b and discharging nitrogen from the cathode 1b when power generation is stopped. carry out.

  After the power generation in the fuel cell system 100 is stopped, electric power is supplied between the anode 1a and the cathode 1b by the current supply means 6 to flow a current. By passing a current from the anode 1a to the cathode 1b, hydrogen in the hydrogen containing impurities in the anode 1a flows through the electrolyte membrane 1c as protons, and the protons and electrons are combined at the cathode 1b to become hydrogen, so that hydrogen in the anode 1a Of the hydrogen containing impurities moves into the cathode 1b. The amount of hydrogen transfer from the anode 1a to the cathode 1b can be defined by the integrated value of the current flowing from the anode 1a to the cathode 1b. Therefore, the amount of hydrogen supplied to the cathode 1b can be controlled by controlling the current value and the time for flowing the current. By stopping the supply of the oxidizing gas to the cathode 1b, the air in the cathode 1b is replaced by hydrogen, and the nitrogen present in the air in the cathode 1b is discharged to the oxidizing gas discharge path 5. You. The amount of hydrogen supplied to the cathode 1b is proportional to the integrated value of the current supplied by the current supply means 6. Therefore, it can be determined from the integrated value of the current supplied by the current supply means 6 whether the nitrogen in the air in the cathode 1b has been sufficiently replaced and the nitrogen concentration has been reduced. Therefore, when the integrated value of the current supplied by the current supply means 6 reaches the predetermined integrated value of the current, it is determined that the concentration of nitrogen in the air in the cathode 1b has been reduced to a predetermined value or less. The supply of power from the power supply 6 is stopped, and the flow of current is stopped. In the present embodiment, the integrated value of the current supplied by the current supply means 6 is determined so as to supply hydrogen in an amount corresponding to the volume of the path in the cathode 1b. The internal volume of the path in the cathode 1b was 100 cc, and the current was 0.2 A for 5 minutes.

  Note that while the current supply means 6 is supplying a current, hydrogen in the hydrogen containing impurities in the anode 1a is consumed. Therefore, hydrogen is continuously supplied from the fuel gas supply path 2.

  By reducing the nitrogen concentration in the air in the cathode 1b to a predetermined value or less, the amount of nitrogen permeating from the cathode 1b to the anode 1a via the electrolyte membrane 1c during the stop period of the fuel cell system 100 can be reduced. As a result, when the power generation of the fuel cell system 100 is started next time, the concentration of nitrogen in the hydrogen containing impurities in the anode 1a can be reduced, so that the fuel cell system 100 can immediately generate power. In the present embodiment, the nitrogen concentration in the air inside the cathode 1b is set to 30% or less so that the nitrogen concentration in the hydrogen containing impurities in the anode 1a is 20% or less. At this time, the pressure in the anode 1a was 50 kPa with respect to the atmospheric pressure, and the pressure in the cathode 1b was equal to the atmospheric pressure. In order to reduce the nitrogen concentration in the air in the cathode 1b from 79% to 20%, 75% or more of the air in the cathode 1b may be expelled by the hydrogen supplied from the anode 1a to the cathode 1b.

  As described above, in the present embodiment, the configuration of the fuel cell system 100 is configured such that the fuel cell stack 1 that generates power using the fuel gas containing hydrogen and the oxidizing gas, and the fuel cell stack 1 is provided with the anode 1 a of the fuel cell stack 1. A fuel gas supply path 2 for supplying gas, an oxidant gas supply unit 3 for supplying an oxidant gas to the cathode 1b of the fuel cell stack 1, and an oxidant gas supply for connecting the cathode 1b and the oxidant gas supply unit 3. A path 4, an oxidizing gas discharge path 5 for discharging unreacted oxidizing gas from the cathode 1 b to the outside, a current supply means 6 for supplying a current between the anode 1 a and the cathode 1 b of the fuel cell stack 1, By using the part 7, the nitrogen concentration in the air in the cathode 1b can be reduced when the power generation is stopped, and the electrolyte membrane 1 from the cathode 1b to the anode 1a can be reduced during the stop period. It is possible to reduce the transmission of nitrogen through. As a result, when power generation of the fuel cell system 100 is started, the concentration of nitrogen in hydrogen containing impurities in the anode 1a can be reduced, so that the fuel cell system 100 can immediately generate power. Further, since the purge gas is not discharged from the anode 1a in order to reduce the nitrogen concentration in the hydrogen containing impurities in the anode 1a, the fuel cell system 100 can be downsized without providing a diluter.

Although the unreacted fuel gas circulation path is provided in the present embodiment, the unreacted fuel gas circulation path is not necessarily provided, and a configuration may be adopted in which sealing is performed after the anode 1a.
(Embodiment 2)
FIG. 2 shows a block diagram of a fuel cell system according to Embodiment 2 of the present invention. 2, the fuel cell system 200 includes a fuel cell stack 1, a fuel gas supply path 2, an oxidant gas supply unit 3, an oxidant gas supply path 4, an oxidant gas discharge path 5, a current supply unit. 6, a control unit 7, a cathode upstream open / close valve 8, and a cathode downstream open / close valve 9. The description of the same components as those in the first embodiment is omitted here.

  The cathode upstream opening / closing valve 8 is provided on the oxidizing gas supply path 4 and is an electromagnetic valve that can supply and stop air from the oxidizing gas supply unit 3 to the cathode 1b. is there.

  The cathode downstream opening / closing valve 9 is provided on the oxidizing gas discharge path 5 and is an electromagnetic valve that can open the cathode 1b to the atmosphere or isolate the cathode 1b from the atmosphere.

  The downstream side of the anode 1a has a sealed configuration, and no unreacted fuel gas circulation path is provided.

  The operation and operation of the fuel cell system 200 configured as described above will be described below.

  The operation of the fuel cell system 200 when power generation is stopped will be described. After stopping the power generation in the fuel cell system 200, the supply of air to the cathode 1b is stopped. In order to stop the air, the oxidizing gas supply unit 3 is stopped, and the cathode upstream opening / closing valve 8 is closed. Next, power is supplied between the anode 1a and the cathode 1b by the current supply means 6 to flow a current. By passing a current from the anode 1a to the cathode 1b, hydrogen in the anode 1a flows through the electrolyte membrane 1c as protons, and the protons and electrons are combined at the cathode 1b to become hydrogen. Of hydrogen moves into the cathode 1b. The path in the cathode 1b is replaced by hydrogen, and the nitrogen present in the path in the cathode 1b is discharged to the oxidizing gas discharge path 5. When the integrated value of the current supplied by the current supply means 6 reaches a predetermined integrated value of the current, it is determined that the concentration of nitrogen in the air in the cathode 1b has been reduced to a predetermined value or less. The supply of power is stopped to stop the flow of current. In the present embodiment, the inner volume of the path in the cathode 1b is set to 100 cc, and the current is passed at 1 A for 1 minute. Thereby, the nitrogen concentration in the air in the cathode 1b can be reduced to 30% or less. As a result, during the shutdown period of the fuel cell system 200, the nitrogen concentration in the hydrogen containing impurities in the anode 1a can be reduced to 20% or less.

  Note that while the current supply means 6 is supplying a current, hydrogen in the anode 1a is consumed, so that water is continuously supplied from the fuel gas supply path 2.

  When the supply of power from the current supply means 6 is stopped and the flow of electric current is stopped, and time elapses, air flows into the cathode 1b via the oxidizing gas discharge path 5 due to diffusion from the atmosphere. There is a possibility that the concentration of nitrogen in the gas in the cathode 1b may increase. Therefore, in order to prevent the nitrogen concentration in the gas in the cathode 1b from rising, when a predetermined time has elapsed since the current supply by the current supply means 6 was stopped, the cathode upstream opening / closing valve 8 and the cathode downstream opening / closing valve 9 is closed to seal the cathode 1b. The predetermined time was 30 seconds.

  As described above, in the present embodiment, the configuration of the fuel cell system 200 is changed such that the cathode 1b is turned off when a predetermined condition is satisfied after the supply of power is stopped by the current supply unit 6 and the flow of current is stopped. The cathode upstream opening / closing valve 8 and the cathode downstream opening / closing valve 9 are sealed by closing. This can reduce the nitrogen concentration in the air in the cathode 1b when the power generation is stopped, and can prevent the nitrogen from entering the cathode 1b from the atmosphere during the stop period and increase the nitrogen concentration in the gas in the cathode 1b. . As a result, the nitrogen concentration in the hydrogen containing impurities in the anode 1a can be reduced to a predetermined concentration or less, and when the fuel cell system 200 starts power generation, the nitrogen concentration in the hydrogen containing impurities in the anode 1a can be reduced. Therefore, the fuel cell system 200 can immediately generate power. Further, since the purge gas is not discharged from the anode 1a in order to reduce the nitrogen concentration in the hydrogen containing impurities in the anode 1a, the fuel cell system 200 can be downsized without providing a dilutor.

The condition for sealing the cathode 1b is not limited to a predetermined time, but may be a temperature condition or a nitrogen concentration. Any method may be used as long as the nitrogen concentration in the gas in the cathode 1b can be suppressed to a predetermined concentration or less.
(Embodiment 3)
FIG. 3 shows a block diagram of a fuel cell system according to Embodiment 3 of the present invention. 3, the fuel cell system 300 includes a fuel cell stack 1, a fuel gas supply path 2, an oxidizing gas supply unit 3, an oxidizing gas supply path 4, an oxidizing gas discharge path 5, a current supply unit. 6, a control unit 7, a cathode upstream opening / closing valve 8, a cathode downstream opening / closing valve 9, and a hydrogen gas concentration detecting means 10. The description of the same components as those in the second embodiment is omitted here.

  The hydrogen gas concentration detecting means 10 is provided in the oxidizing gas discharge path 5 and detects the concentration of nitrogen in the gas existing in the oxidizing gas discharge path 5.

  The operation and operation of the fuel cell system 300 configured as described above will be described below.

  The operation of the fuel cell system 300 when power generation is stopped will be described. After stopping the power generation in the fuel cell system 300, the supply of air to the cathode 1b is stopped. In order to stop the air, the oxidizing gas supply unit 3 is stopped, and the cathode upstream opening / closing valve 8 is closed. Next, power is supplied between the anode 1a and the cathode 1b by the current supply means 6 to flow a current. When a current flows from the anode 1a to the cathode 1b, hydrogen in the anode 1a flows through the electrolyte membrane 1c as protons, and protons and electrons are combined at the cathode 1b to become hydrogen, so that hydrogen in the anode 1a is converted into hydrogen in the cathode 1b. Move to The air in the cathode 1b is replaced by hydrogen, and the nitrogen present in the cathode 1b is discharged to the oxidant gas discharge path 5. When the integrated value of the current supplied by the current supply means 6 reaches a predetermined integrated value of the current, it is determined that the concentration of nitrogen in the air in the cathode 1b has been reduced to a predetermined value or less. The supply of power is stopped to stop the flow of current. In the present embodiment, the inner volume of the path in the cathode 1b is set to 100 cc, and the current is passed at 2 A for 30 seconds. Thereby, the nitrogen concentration in the air in the cathode 1b can be reduced to 30% or less. As a result, during the shutdown period of the fuel cell system 300, the nitrogen concentration in the hydrogen containing impurities in the anode 1a can be set to 20% or less.

  Note that while the current supply means 6 is supplying a current, hydrogen in the hydrogen containing impurities in the anode 1a is consumed. Therefore, hydrogen is continuously supplied from the fuel gas supply path 2.

  If the supply of electric power from the current supply means 6 is stopped to stop the flow of electric current, and after a lapse of time, air may flow into the cathode 1b due to diffusion from the atmosphere, and the nitrogen concentration in the cathode 1b may increase. There is. Then, the hydrogen concentration in the oxidizing gas discharge path 5 is detected by the hydrogen gas concentration detecting means 10, and it is confirmed whether the hydrogen concentration in the oxidizing gas discharge path 5 is equal to or more than a predetermined value. If the hydrogen concentration in the gas in the oxidizing gas discharge path 5 is higher than a predetermined value, it is determined that there is almost no influence of the intrusion of air from the atmosphere into the cathode 1b. If the hydrogen concentration in the gas in the oxidizing gas discharge path 5 is equal to or less than a predetermined value, it is considered that if air enters the cathode 1b from the atmosphere any more, the effect of increasing the nitrogen concentration will occur. In order to prevent intrusion, the cathode 1 b is sealed by closing the cathode upstream opening / closing valve 8 and the cathode downstream opening / closing valve 9.

  In the present embodiment, the nitrogen concentration in the cathode 1b is reduced to 90% in order to assure the nitrogen concentration in the cathode 1b of 30% or less, and the hydrogen concentration detected by the hydrogen gas concentration detecting means 10 is reduced to 80%. %, The cathode upstream opening and closing valve 8 and the cathode downstream opening and closing valve 9 are closed to seal the cathode 1b.

  As described above, in the present embodiment, the configuration of the fuel cell system 300 is changed such that the detection value of the hydrogen gas concentration detection unit 10 is equal to or less than a predetermined value after the supply of power is stopped by the current supply unit 6 and the flow of current is stopped. , The cathode 1b is sealed by closing the cathode upstream opening / closing valve 8 and the cathode downstream opening / closing valve 9. This can reduce the nitrogen concentration in the air in the cathode 1b when the power generation is stopped, and can prevent the nitrogen from entering the cathode 1b from the atmosphere during the stop period and increase the nitrogen concentration in the gas in the cathode 1b. . As a result, the nitrogen concentration in the hydrogen containing impurities in the anode 1a is reduced to a predetermined concentration or less, and when the power generation of the fuel cell system 300 is started, the nitrogen concentration in the hydrogen containing impurities in the anode 1a can be reduced. Therefore, the fuel cell system 300 can immediately generate power. Further, since the purge gas is not discharged from the anode 1a in order to reduce the nitrogen concentration in the hydrogen containing impurities in the anode 1a, the fuel cell system 300 can be downsized without providing a diluter.

If the hydrogen gas concentration detecting means 10 can detect or estimate the hydrogen concentration in the gas in the cathode 1b, the installation location is not limited to the oxidizing gas discharge path 5, but may be in the cathode 1b or the oxidizing gas supply path 4. It may be installed in. Instead of detecting the hydrogen concentration, the nitrogen concentration may be detected and the hydrogen concentration may be estimated from the nitrogen concentration.
(Embodiment 4)
FIG. 4 shows a block diagram of a fuel cell system according to Embodiment 4 of the present invention. In FIG. 4, a fuel cell system 400 includes a fuel cell stack 1, a fuel gas supply path 2, an oxidizing gas supply unit 3, an oxidizing gas supply path 4, an oxidizing gas discharge path 5, a current supply unit. 6, a control unit 7, a cathode upstream on-off valve 8, a cathode downstream on-off valve 9, a hydrogen gas concentration detection unit 10, a branch unit 11, a junction 12, and a bypass path 13. The description of the same components as those in the second embodiment is omitted here.

  The branching section 11 is provided in the oxidizing gas supply path 4, and branches to supply the air supplied from the oxidizing gas supply section 3 not to the cathode 1b but to another path. The branch portion 11 is installed on the upstream side of the cathode upstream opening / closing valve 8.

  The junction 12 is provided in the oxidizing gas discharge path 5 and joins the air discharged from the cathode 1b and the air supplied from another path. The junction 12 is provided downstream of the cathode downstream opening / closing valve 9.

  The bypass path 13 is a path that connects the branch part 11 and the junction part 12, and is a path that supplies the air supplied by the oxidizing gas supply unit 3 to the oxidizing gas discharge path 5 without passing through the cathode 1b. is there.

  The bypass valve 14 is provided in the bypass passage 13 and is an electromagnetic valve for opening and closing the bypass passage 13.

  The operation and operation of the fuel cell system 400 configured as described above will be described below.

  The operation of the fuel cell system 400 when power generation is stopped will be described. After stopping the power generation in the fuel cell system 400, the cathode upstream opening / closing valve 8 is closed and the bypass valve 14 is opened in order to stop the supply of air to the cathode 1b. Here, the operation of the oxidizing gas supply unit 3 is continued. Thus, the air supplied by the oxidizing gas supply unit 3 passes through the bypass path 13 and is discharged to the outside of the fuel cell system 400 through the oxidizing gas discharge path 5.

  Next, power is supplied between the anode 1a and the cathode 1b by the current supply means 6 to flow a current. By passing a current from the anode 1a to the cathode 1b, hydrogen in the hydrogen containing impurities in the anode 1a flows through the electrolyte membrane 1c as protons, and the protons and electrons are combined at the cathode 1b to become hydrogen, so that hydrogen in the anode 1a Of hydrogen moves into the cathode 1b. The air in the cathode 1b is replaced by hydrogen, and the nitrogen in the air existing in the cathode 1b is discharged to the oxidant gas discharge path 5. The air supplied from the oxidizing gas supply unit 3 also flows through the oxidizing gas discharge path 5, and the air can dilute and exhaust the gas discharged from the cathode 1b. Here, the gas discharged to the oxidizing gas discharge path 5 may include not only nitrogen but also part of hydrogen. Since this hydrogen is also diluted and exhausted outside the fuel cell system 400, it can be safely discharged.

  When the integrated value of the current supplied by the current supply means 6 reaches a predetermined integrated value of the current, it is determined that the concentration of nitrogen in the air in the cathode 1b has been reduced to a predetermined value or less. The supply of power is stopped to stop the flow of current. In the present embodiment, the inner volume of the path in the cathode 1b is set to 100 cc, and the current is passed at 4 A for 15 seconds. Thereby, the nitrogen concentration in the air in the cathode 1b can be reduced to 30% or less. As a result, during the shutdown period of the fuel cell system 400, the nitrogen concentration in the hydrogen containing impurities in the anode 1a can be set to 20% or less. Note that while the current supply means 6 is supplying a current, hydrogen in the hydrogen containing impurities in the anode 1a is consumed. Therefore, hydrogen is continuously supplied from the fuel gas supply path 2.

Even after the supply of power from the current supply means 6 is stopped and the flow of current is stopped, if air is continuously supplied by the oxidizing gas supply unit 3, the air is diffused, via the cathode downstream opening / closing valve 9, Air may enter the cathode 1b. Therefore, the oxidizing gas supply unit 3 is stopped, and the cathode downstream opening / closing valve 9 is closed. As described above, by sealing the cathode 1b, the nitrogen concentration in the gas in the cathode 1b can be reduced, and the nitrogen concentration in the gas in the cathode 1b can be prevented from increasing again. In the present embodiment, the configuration of the fuel cell system 400 is such that a bypass path 13 for bypassing the cathode 1b and a bypass valve 14 are provided. This makes it possible to reduce the nitrogen concentration in the air in the cathode 1b when power generation is stopped, and to safely dilute and exhaust the gas discharged from the cathode 1b. Further, it is possible to prevent nitrogen from entering the cathode 1b during the stop period, thereby preventing the nitrogen concentration in the gas in the cathode 1b from increasing. As a result, the nitrogen concentration in the hydrogen containing the impurities in the anode 1a is reduced to a predetermined concentration or less, and when the power generation of the fuel cell system 400 is started, the nitrogen concentration in the hydrogen containing the impurities in the anode 1a can be reduced. Therefore, the fuel cell system 400 can immediately generate power. In the present embodiment, the nitrogen concentration in the gas in the anode 1a is set to 20% or less. Further, since the purge gas is not discharged from the anode 1a in order to reduce the nitrogen concentration in the hydrogen containing impurities in the anode 1a, the fuel cell system 400 can be downsized without providing a diluter.

  As described above, the fuel cell system and the operation method according to the present invention can reduce the nitrogen concentration in the air in the cathode during the stop period by supplying hydrogen from the anode to the cathode during the stop period. Therefore, the fuel cell system is useful as a fuel cell system for preventing an increase in the nitrogen concentration in the fuel gas containing impurities in the anode during the stop period, and can be applied to uses such as miniaturization and cost reduction of the fuel cell system.

REFERENCE SIGNS LIST 100 fuel cell system 200 fuel cell system 300 fuel cell system 400 fuel cell system 500 fuel cell system 1 fuel cell stack 1 a anode 1 b cathode 1 c electrolyte membrane 2 fuel gas supply path 3 oxidant gas supply unit 4 oxidant gas supply path 5 oxidation Agent gas discharge path 6 Current supply means 7 Control unit 8 Cathode upstream opening / closing valve 9 Cathode downstream opening / closing valve 10 Hydrogen gas concentration detecting means 11 Branch section 12 Converging section 13 Bypass path 14 Bypass valve 101 Fuel cell stack 102 Fuel gas supply path 103 Oxidation Agent gas supply section 104 Oxidizer gas supply path 105 Oxidizer gas discharge path 106 Unreacted fuel gas circulation path 107 Purge valve 108 Dilerator

Claims (8)

A fuel cell stack that generates power using a fuel gas containing hydrogen and an oxidant gas,
A fuel gas supply path for supplying fuel gas to the anode of the fuel cell stack;
An oxidizing gas supply unit that supplies an oxidizing gas to the cathode of the fuel cell stack;
An oxidizing gas supply path connecting the cathode and the oxidizing gas supply unit,
An oxidizing gas discharge path for discharging unreacted oxidizing gas from the cathode to the outside,
Current supply means for supplying a current between the anode and the cathode of the fuel cell stack;
And a control unit,
When the power generation is stopped, the control unit stops supplying the oxidizing gas to the cathode, supplies a predetermined current between the anode and the cathode by the current supply unit, and causes the current to flow from the anode to the cathode. A fuel cell system that supplies hydrogen.   2. The fuel cell system according to claim 1, wherein the control unit stops the current supply by the current supply unit when the current flowing between the anode and the cathode by the current supply unit reaches a predetermined current amount. 3.   The fuel cell system according to claim 1, wherein the control unit seals the cathode when a predetermined condition is satisfied after the current supply by the current supply unit is stopped.   4. The fuel cell system according to claim 3, wherein the control unit seals the cathode after a predetermined time has elapsed after the current supply by the current supply unit is stopped. 5. The control unit includes a hydrogen gas concentration detection unit provided in the oxidizing gas discharge path,
4. The fuel cell system according to claim 3, wherein the current supply is stopped by the current supply unit, and the cathode is sealed after the detection value of the hydrogen gas concentration detection unit becomes equal to or less than a predetermined value.   6. A bypass path that branches off at a branch section provided on the upstream side of the cathode in the oxidant gas supply path, bypasses the cathode, and joins at a junction of the oxidant gas discharge path. 7. The fuel cell system according to claim 1.   When the power generation is stopped, at least during the period when a predetermined current is supplied between the anode and the cathode by the current supply unit to supply hydrogen from the anode to the cathode, the control unit controls the bypass path. The fuel cell system according to claim 6, wherein the oxidizing gas is supplied to the oxidizing gas discharge path via an oxidizing gas. A fuel cell stack that generates power using a fuel gas containing hydrogen and an oxidant gas,
A fuel gas supply path for supplying fuel gas to the anode of the fuel cell stack;
An oxidizing gas supply unit that supplies an oxidizing gas to the cathode of the fuel cell stack;
An oxidizing gas supply path connecting the cathode and the oxidizing gas supply unit,
An oxidizing gas discharge path for discharging unreacted oxidizing gas from the cathode to the outside,
Current supply means for supplying a current between the anode and the cathode of the fuel cell stack, and a method of operating a fuel cell system comprising:
When power generation is stopped,
Stopping the supply of the oxidizing gas to the cathode, supplying a predetermined current between the anode and the cathode by the current supply means, and supplying hydrogen from the anode to the cathode. How to operate the battery system.

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