Method for starting fuel cell system and starting apparatus for fuel cell system

In a method for starting a fuel cell system, an oxidizer gas bypass passage is operated by an oxidizer gas bypass passage controller to supply oxidizer gas to a diluter from an oxidizer gas supply device under a condition where an oxidizer gas supply passage is sealed by an oxidizer gas supply passage sealing device and an oxidizer exhaust gas exhaust passage is sealed by an oxidizer exhaust gas exhaust passage sealing device. A fuel exhaust gas recirculation passage is operated by a fuel exhaust gas recirculation passage controller to supply fuel gas to the fuel cell from a fuel gas supply device.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2012-028756, filed Feb. 13, 2012, entitled “Method and Apparatus for Starting Fuel Cell System.” The contents of this application are incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present disclosure relates to a method for starting a fuel cell system and a starting apparatus for the fuel cell system.

2. Discussion of the Background

Fuel cells produce direct-current energy by an electrochemical reaction between fuel gas (gas mainly containing hydrogen, for example, hydrogen gas) supplied to an anode electrode, and oxidizer gas (gas mainly containing oxygen, for example, air) supplied to a cathode electrode.

Examples of known fuel cells include solid polymer electrolyte fuel cells. The solid polymer electrolyte fuel cells each include a membrane electrode assembly (MEA) including an anode electrode and a cathode electrode which are provided on both sides of an electrolyte membrane composed of a polymer ion-exchange membrane, the MEA being interposed between a pair of separators. A fuel gas flow passage is formed between one of the separators and the membrane electrode assembly in order to supply fuel gas to the anode electrode, and an oxidizer gas flow passage is formed between the other separator and the membrane electrode assembly in order to supply oxidizer gas to the cathode electrode.

During shutdown of a fuel cell, the fuel cell is in a state in which the supply of the fuel gas and the oxidizer gas is stopped, but the fuel gas remains in the fuel gas flow passage of the fuel cell, and the oxidizer gas remains in the oxidizer gas flow passage of the fuel cell. Therefore, in particular, when the shutdown period of the fuel cell is increased, the remaining fuel gas and oxidizer gas permeate through the electrolyte membrane and degrade an electrode catalyst and a catalyst support, and thus the life of the fuel cell may be decreased.

Accordingly, for example, a fuel cell apparatus (fuel cell system) disclosed in Japanese Patent No. 4357836 is configured to be shut down in a state in which an anode flow passage is completely filled with air by supplying air to the anode flow passage from a blower during shutdown of the fuel cell apparatus (refer to paragraph [0021] of Japanese Patent No. 4357836).

Also, the fuel cell apparatus disclosed in Japanese Patent No. 4357836 is configured to purge the air remaining in the anode flow passage during shutdown of the fuel cell apparatus by supplying hydrogen to the anode flow passage at the time of start of the fuel cell apparatus. After purging of the air in the anode flow passage is completed, air is supplied to a cathode flow passage (refer to claim 1 of Japanese Patent No. 4357836).

SUMMARY OF THE INVENTION

According to one aspect of the present invention, in a method for starting a fuel cell system, an oxidizer gas bypass passage is operated by an oxidizer gas bypass passage controller to supply oxidizer gas to a diluter from an oxidizer gas supply device under a condition where an oxidizer gas supply passage is sealed by an oxidizer gas supply passage sealing device and an oxidizer exhaust gas exhaust passage is sealed by an oxidizer exhaust gas exhaust passage sealing device. The oxidizer gas bypass passage is branched from the oxidizer gas supply passage and connected to the oxidizer exhaust gas exhaust passage to bypass a fuel cell. The fuel cell is provided to generate electric power by an electrochemical reaction between fuel gas supplied to an anode side and oxidizer gas supplied to a cathode side. The oxidizer gas supply device is provided to supply the oxidizer gas to the fuel cell through an oxidizer gas supply passage. The oxidizer gas bypass passage controller is configured to control an operating state of the oxidizer gas bypass passage. The oxidizer gas supply passage sealing device is provided to seal the oxidizer gas supply passage downstream of a branch portion where the oxidizer gas bypass passage is branched from the oxidizer gas supply passage. The oxidizer exhaust gas exhaust passage sealing device is provided to seal the oxidizer exhaust gas exhaust passage upstream of a connection portion where the oxidizer gas bypass passage is connected to the oxidizer exhaust gas exhaust passage. The diluter is provided to connect a downstream side of a fuel exhaust gas exhaust passage to a downstream side of the oxidizer exhaust gas exhaust passage. In the method, a fuel exhaust gas recirculation passage is operated by a fuel exhaust gas recirculation passage controller to supply fuel gas to the fuel cell from a fuel gas supply device. The fuel exhaust gas recirculation passage controller is configured to control an operating state of the fuel exhaust gas recirculation passage. The fuel gas supply device is provided to supply the fuel gas to the fuel cell through the fuel gas supply passage. In the method, a fuel exhaust gas exhaust passage is operated by a fuel exhaust gas exhaust passage controller to exhaust an anode residual gas remaining on the anode side of the fuel cell into the diluter and to replace anode-side gas in the fuel cell with the fuel gas. The fuel exhaust gas exhaust passage controller is configured to control an operating state of the fuel exhaust gas exhaust passage through which fuel exhaust gas is to be exhausted from the fuel cell.

According to another aspect of the present invention, a starting apparatus for a fuel cell system includes a first device, a second device, a third device, and a fourth device. The first device is configured to operate an oxidizer gas supply passage sealing device to seal an oxidizer gas supply passage through which oxidizer gas is to be supplied to a fuel cell. The first device is configured to operate an oxidizer exhaust gas exhaust passage sealing device to seal an oxidizer exhaust gas passage through which the oxidizer gas is to be exhausted from the fuel cell. The second device is configured to operate, in a sealed state, an oxidizer gas bypass passage controller to supply the oxidizer gas to a diluter from an oxidizer gas supply device through an oxidizer gas bypass passage which is branched from the oxidizer gas supply passage and which is connected to the oxidizer exhaust gas exhaust passage to bypass the fuel cell. The third device is configured to operate a fuel gas supply device to supply fuel gas to the fuel cell and configured to operate a fuel exhaust gas recirculation passage controller to supply fuel exhaust gas, which is exhausted from the fuel cell through a fuel exhaust gas exhaust passage, to the fuel cell through a fuel exhaust gas recirculation passage. The fourth device is configured to operate a fuel exhaust gas exhaust passage controller to exhaust anode residual gas, which contains the fuel gas and remains on an anode side of the fuel cell, to the diluter through the fuel exhaust gas exhaust passage and to replace anode-side gas in the fuel cell with the fuel gas.

DESCRIPTION OF THE EMBODIMENTS

In the drawings, a common portion is denoted by the same reference numeral, and duplicated description is omitted.

First, a configuration of a fuel cell system S in which a starting process according to an embodiment is performed is described with reference toFIG. 1.

The fuel cell system S shown inFIG. 1is mounted on, for example, a fuel cell vehicle (movable body) not shown in the drawing.

The fuel cell system S is provided with a fuel cell stack10(fuel cell), an anode system that supplies and discharges hydrogen (fuel gas) to and from an anode of the fuel cell stack10, a cathode system that supplies and discharges air (oxidizer gas) containing oxygen to and from a cathode of the fuel cell stack10, a dilution exhaust system that exhausts fuel exhaust gas from the anode system and oxidizer exhaust gas from the cathode to the outside of the fuel cell system S, a power supply system connected to an output terminal (not shown) of the fuel cell stack10to supply electric power generated by the fuel cell stack10to a load, and an electronic control unit (ECU)80serving as a controller that electronically controls these systems. The specified types of the fuel gas and the oxidizer gas are not limited to the above.

The fuel cell stack10includes a plurality (for example, several tens to several hundreds) of stacked solid polymer single cells (fuel cells) which are connected in series. Each of the single cells includes a membrane electrode assembly (MEA) and two conductive separators which hold the MEA therebetween. The MEA includes an electrolyte membrane (solid polymer membrane) composed of a monovalent cation exchange membrane and an anode and a cathode (electrodes) which hold the electrolyte membrane therebetween.

The anode and the cathode each include a porous material having conductivity, such as carbon paper, and a catalyst (Pt, Ru, or the like) carried on the porous material in order to produce an electrode reaction on the anode or the cathode.

Each of the separators has a groove formed for supplying hydrogen or air to the entire surface of the MEA and a through hole formed for supplying and exhausting hydrogen or air to and from all single cells, the groove and the through hole functioning as an anode flow passage10a(fuel gas flow passage) and a cathode flow passage10c(oxidizer gas flow passage). The anode flow passage10aand the cathode flow passage10chave a plurality of branches and junctions in order to supply the hydrogen and air to whole surface of the single cells, and the sectional area of the flow passages is minimized.

When hydrogen is supplied to each anode through the anode flow passage10a, an electrode reaction represented by formula (1) takes place, and when air is supplied to each cathode through the cathode flow passage10c, an electrode reaction represented by formula (2) takes place, producing a potential difference (open circuit voltage) in each single cell. Next, when the fuel cell stack10is electrically connected to a load72described below to draw out a current, electric power is generated from the fuel cell stack10.
2H2→4H++4e−(1)
O2+4H++4e−→2H2O  (2)

When electric power is generated from the fuel cell stack10as described above, water (water vapor) is produced on the cathode, and thus the oxidizer exhaust gas exhausted from the cathode flow passage10ccontains much moisture.

The anode system includes a hydrogen tank (not shown), a cutoff valve21, an ejector22, a hydrogen pump23, and an anode purge valve24.

A fuel gas supply passage is formed to be connected from the hydrogen tank (not shown) to the inlet of the anode flow passage10athrough a pipe31a, the cutoff valve21, a pipe31b, the ejector22, and a pipe31c. Consequently, hydrogen (fuel gas) in the hydrogen tank is supplied to the anode flow passage10athrough the fuel gas supply passage (the pipe31a, the cutoff valve21, the pipe31b, the ejector22, and the pipe31c).

The cutoff valve21is a normally closed-type cutoff valve which is controlled to be opened and closed by the ECU80. The ECU80opens the cutoff valve21when the fuel cell system S is operated (when electric power is generated by the fuel cell stack10).

The ejector22ejects the hydrogen (fuel gas) from the hydrogen tank (not shown) through a nozzle to generate negative pressure which causes fuel exhaust gas in a pipe33to be sucked. In addition, the ejector22is controlled to be opened and closed by the ECU80.

The outlet of the anode flow passage10ais connected to the intake port of the ejector23through a pipe32aand the pipe33. The exhaust gas exhausted from the anode flow passage10ais directed to the ejector22through the pipe32aand the pipe33so that the fuel exhaust gas (hydrogen) is circulated.

The fuel exhaust gas contains hydrogen remaining unconsumed by the electrode reaction on the anode and water vapor. In addition, the pipe33is provided with a gas-liquid separator (not shown) which separates between and recovers water (condensed water (liquid) and water vapor (gas) contained in the fuel exhaust gas.

In addition, a pipe34abranched from the pipe32aconnected to the output of the anode flow passage10ais connected to a suction port of the hydrogen pump23. A discharge port of the hydrogen pump23is connected to the pipe31cthrough a pipe34b, thereby forming a fuel exhaust gas recirculation passage connected from the outlet of the anode flow passage10ato the inlet of the anode flow passage10athrough the pipe32a, the pipe34a, the hydrogen pump23, the pipe34b, and the pipe31c.

The operation of the hydrogen pump23is controlled by the ECU80so as to compress the fuel exhaust gas from the pipe32aand pump it to the pipe31c.

The pipe32ais connected to a diluter60described below through the anode purge valve24and a pipe32bto form a fuel exhaust gas exhaust passage.

The anode purge valve24is a normally closed-type valve which is controlled to be opened and closed by the ECU80. When it is determined that power generation of the fuel cell stack10is unstable during the operation of the fuel cell system S, the ECU80opens the anode purge valve24for a predetermined valve opening time.

The cathode system includes an intake41, an air pump42, a humidifier43, an inlet sealing valve44, an outlet sealing valve45, and CPCV (Cathode Purge Control Valve)46.

An oxidizer gas supply passage is formed to be connected from the intake41, that takes in the outside air, to the inlet of the cathode flow passage10cthrough a pipe51a, the air pump42, a pipe51b, the humidifier43, a pipe51c, the inlet sealing valve44, and a pipe51d. As a result, the air (oxidizer gas) taken in from the intake41is supplied to the cathode flow passage10cthrough the oxidizer gas supply passage (the pipe51a, the air pump42, the pipe51b, the humidifier43, the pipe51c, the inlet sealing valve44, and the pipe51d).

The operation of the air pump42is controlled by the ECU80so as to compress the air from the pipe51aand pump it to the pipe51b.

The humidifier43is provided with a plurality of hollow fiber membranes (not shown) having moisture permeability. The humidifier43exchanges moisture between the air (air flowing from the pipe51cto the pipe51d) directed to the cathode flow passage10cand the humid oxidizer exhaust gas (oxidizer exhaust gas flowing from the pipe52bto the pipe52c) exhausted from the cathode flow passage10c, thereby humidifying the air flowing to the cathode flow passage10c.

The inlet sealing valve44is controlled to be opened and closed by the ECU80.

The outlet of the cathode flow passage10cis connected to the diluter60described below through the pipe52a, the outlet sealing valve45, the pipe52b, the humidifier43, the pipe52c, the CPCV46, and a pipe52d, forming an oxidizer exhaust gas exhaust passage.

The outlet sealing valve45is controlled to be opened and closed by the ECU80.

The CPCV46includes, for example, a butterfly valve whose degree of opening is controlled by the ECU80to control the pressure of air in the cathode flow passage10c. In detail, as the degree of opening of the CPCV46decreases, the pressure of air in the cathode flow passage10cincreases, and the oxygen concentration (volume concentration) per volume flow rate increases. Conversely, as the degree of opening of the CPCV46increases, the pressure of air in the cathode flow passage10cdecreases, and the oxygen concentration (volume concentration) per volume flow rate decreases.

The dilution exhaust system includes the diluter60and a bypass valve61.

The pipe51bconnected to the discharge port of the air pump42is connected to the diluter60through a pipe62a, the bypass valve61, a pipe62b, and the pipe52d, forming an oxidizer gas bypass passage. That is, the air may be sent to the diluter60from the air pump42while bypassing the cathode flow passage10cof the fuel cell stack10.

The bypass valve61is a normally closed-type cutoff valve and is controlled to be opened and closed by the ECU80.

The diluter60is capable of diluting the fuel exhaust gas from the pipe32bin the fuel exhaust gas exhaust passage with the oxidizer exhaust gas from the pipe52din the oxidizer exhaust gas exhaust passage or the air supplied from the open bypass valve61.

The power supply system is connected to an output terminal (not shown) of the fuel cell stack10and provided with a contactor71etc. to supply the generated power of the fuel cell stack10to a load72.

The contactor71is capable of cutting off connection between the output terminal (not shown) of the fuel cell stack10and the load72and is controlled by the ECU80.

The ECU80is a controller that electronically controls the fuel cell system S and includes CPU (Central Processing Unit), ROM (Read-Only Memory), RAM (Random-Access Memory), various interfaces, an electronic circuit, etc. According to a program stored in the ECU80, various functions are exhibited to control various devices such as the cutoff valve21, the ejector22, the hydrogen pump23, the anode purge valve24, the air pump42, the input sealing valve44, the outlet sealing valve45, the CPCV46, the bypass valve61, the contactor71, etc.

In addition, various sensors are provided in the fuel cell system S so that detected signals are transmitted to the ECU80.

<<Starting Process for Fuel Cell System>>

Next, the starting process for the fuel cell system S according to the embodiment is described with reference toFIGS. 2 and 3.FIG. 2is a flow chart of the starting process for the fuel cell system S according to the embodiment of the present application.FIG. 3is a time chart of the starting process for the fuel cell system according to the embodiment of the present application.

As shown inFIG. 3, the starting process for the fuel cell system S includes an anode replacement step (fuel gas replacement step) (Steps S101to S105inFIG. 2), a dilution step (Steps S106and S107inFIG. 2), and a cathode replacement step (oxidizer gas replacement step) (Steps S108to S112inFIG. 2), which are sequentially performed.

The starting process for the fuel cell system S executed by the ECU80is described usingFIG. 2with reference toFIG. 3.

During shutdown of the fuel cell system S, as shown inFIG. 3, the cutoff valve21and the anode purge valve24are closed, and the anode flow passage10aof the fuel cell stack10is sealed and is filled with anode residual gas (for example, air). In addition, the inlet sealing valve44and the outlet sealing valve45are closed, and the cathode flow passage10cof the fuel cell stack10is sealed and is filed with cathode residual gas (for example, air).

When detecting a command (IG-ON) to start the fuel cell system S, the ECU80starts the starting process shown inFIG. 2.

In Step S101, the RCU80opens the bypass valve61and operates the air pump24.

Consequently, the oxidizer gas bypass passage is formed, and the air taken in from the intake41is supplied to the diluter60through the pipe51a, the air pump42, the pipe51b, the pipe62a, the bypass valve61, the pipe62b, and the pipe52d.

The inlet sealing valve44and the outlet sealing valve45are closed so as to prevent the air pumped from the air pump42from flowing into the cathode flow passage10cof the fuel cell stack10.

In Step S102, the ECU80opens the cutoff valve21and operates the ejector22and the hydrogen pump23.

Consequently, the fuel gas supply passage and the fuel exhaust gas recirculation passage are formed, and hydrogen supplied from the hydrogen tank (not shown) is supplied to the inlet of the anode flow passage10athrough the pipe31a, the cutoff valve21, the pipe31b, the ejector22, and the pipe31c. In addition, the supplied hydrogen and the anode residual gas remaining in the anode flow passage10aare circulated from the outlet of the anode flow passage10ato the inlet of the anode flow passage10athrough the pipe32a, the pipe33, the ejector22, and the pipe31c. Also, these gases are circulated from the outlet of the anode flow passage10ato the inlet of the anode flow passage10athrough the pipe32a, the pipe34a, the hydrogen pump23, and the pipe31c.

Since the anode purge valve24is closed, the gas pressure (anode pressure) in the anode flow passage10ais increased by supplying hydrogen from the fuel gas supply passage (refer toFIG. 3).

In Step S103, the ECU80determines whether or not the pressure (anode pressure) detected by a pressure sensor (not shown), that detects the gas pressure in the anode flow passage10aof the fuel cell stack10, is equal to or higher than predetermined pressure (purging permission pressure P1).

The purging permission pressure P1is a threshold of pressure at which the fuel exhaust gas in the anode flow passage10amay be purged into the diluter60by opening the anode purge valve24, and is previously determined.

When the anode pressure is equal to or higher than the purging permission pressure P1(“Yes” in Step S103), the processing of the ECU80advances to Step S104. When the anode pressure is not equal to or higher than the purging permission pressure P1(“No” in Step S103), the processing of the ECU80in Step S103is repeated.

In Step S104, the ECU80opens the anode purge valve24. Consequently, the fuel exhaust gas exhaust passage is formed, and the anode residual gas (e.g., air) is discharged to the diluter60together with hydrogen.

In the diluter60, the hydrogen and the anode residual gas discharged from the pipe32b(fuel exhaust gas exhaust passage) are diluted with air supplied from the pipe52d(oxidizer gas bypass passage) and discharged to the outside.

In Step S105, the ECU80determines whether or not the purge amount of the fuel exhaust gas purged into the diluter60through the anode purge valve24is equal to more than a predetermined purge amount (anode replacement purge amount).

The anode replacement purge amount is a threshold value for determining that the anode residual gas is discharged from the anode flow passage10aand replaced with hydrogen, and is previously determined.

The amount of the fuel exhaust gas purged may be detected by, for example, a flow sensor (not shown) provided on the pipe32bor may be estimated from the valve opening elapsed time of the anode valve24.

When the purge amount is equal to or more than the anode replacement purge amount (“Yes” in Step S105), the processing of the ECU80advances to Step S106. When the purge amount is not equal to or more than the anode replacement purge amount (“No” in Step S105), the processing of the ECU80in Step S105is repeated.

In Step S106, the ECU80closes the anode purge valve24. Consequently, the fuel exhaust gas exhaust passage is sealed, and discharge of the fuel exhaust gas into the diluter60is stopped. As described above, air is supplied to the diluter60through the oxidizer gas bypass passage (refer to S101).

In Step S107, the ECU80determines whether or not a predetermined time (dilution time) has elapsed from closing of the anode purge valve24(S106).

The predetermined time (dilution time) is a time required for diluting the hydrogen, which is purged together with the anode residual gas during Steps S104to S106, with the air supplied through the oxidizer gas bypass passage and is previously determined.

When the predetermined time (dilution time) has elapsed (“Yes” in Step S107), the processing of the ECU80advances to Step S108. When the predetermined time (dilution time) has not elapsed (“No” in Step S107), the processing of the ECU80in Step S107is repeated.

In Step S108, the ECU80opens the inlet sealing valve44, the outlet sealing valve45, and the CPCV46. Consequently, the oxidizer gas supply passage and the oxidizer exhaust gas exhaust passage are formed, and the air taken in from the intake41is supplied to the inlet of the cathode flow passage10cthrough the pipe51a, the air pump42, the pipe51b, the humidifier43, the pipe51c, the inlet sealing valve44, and the pipe51d. Then, the supplied air and the cathode residual gas remaining in the cathode flow passage10cetc. during shutdown are supplied to the diluter60from the outlet of the cathode flow passage10cthrough the pipe52a, the outlet sealing valve45, the pipe52b, the humidifier43, the pipe52c, the CPCV46, and the pipe52d.

In Step S109, the ECU80determines whether or not a predetermined time (cathode replacement time) has elapsed from opening of the inlet sealing valve44, the outlet sealing valve45, and the CPCV46(S108).

The predetermined time (cathode replacement time) is a threshold value for determining that the cathode residual gas is discharged from the cathode flow passage10cand replaced with air, and is previously determined.

When the predetermined time (cathode replacement time) has elapsed (“Yes” in Step S109), the processing of the ECU80advances to Step S110. When the predetermined time (cathode replacement time) has not elapsed (“No” in Step S109), the processing of the ECU80in Step S109is repeated.

In Step S110, the ECU80closes the bypass valve61. Consequently, the oxidizer gas bypass passage is sealed. The hydrogen contained in the fuel exhaust gas purged from the fuel exhaust gas exhaust passage in a subsequent step is diluted with the oxidizer exhaust gas exhausted from the oxidizer exhaust gas exhaust passage.

In Step S111, the ECU80determines whether or not the total voltage (FC voltage) acquired from a voltage sensor (not shown), that detects the total voltage (FC voltage) of open-circuit voltage of the fuel cell stack10, in the anode flow passage10aof the fuel cell stack10is equal to or higher than a predetermined voltage (starting permission voltage).

The starting permission voltage is a threshold value for determining whether or not cathode replacement is sufficiently performed, and is previously determined. This is because when electric power is generated from the fuel cell stack10under a condition where oxygen is lacking due to insufficient cathode replacement, the catalyst may be degraded, thereby decreasing the life of the fuel cell stack10.

When the FC voltage is equal to or higher than the starting permission voltage (“Yes” in Step S111), the processing of the ECU80advances to Step S112. When the FC voltage is not equal to or higher than the starting permission voltage (“No” in Step S111), the processing of the ECU80in Step S111is repeated.

In Step S112, the ECU80turns on (connects) the contactor71(connection) and instructs a value of generated current. In this way, starting of the fuel cell system S is completed.

The above-described starting process for the fuel cell system S according to the embodiment is capable of suppressing deterioration of the catalyst and inhibiting a decrease in life of the fuel cell stack10as compared with a usual fuel cell system (for example, the fuel cell apparatus of Japanese Patent No. 4357836).

That is, when the fuel cell system S is started from a shutdown state of the fuel cell system S in which the anode flow passage10aand the cathode flow passage10care filled with air, the fuel cell apparatus (fuel cell system) disclosed in Japanese Patent No. 4357836 may cause a hydrogen concentration gradient in a stack plane or in the stacking direction of the fuel cell stack10in the anode replacement step of replacing air (anode residual gas) in the anode flow passage10awith hydrogen.

On the other hand, the fuel cell system S according to the embodiment is capable of decreasing a hydrogen concentration gradient in a stack plane or in the stacking direction of the fuel cell stack10because as shown in Step S102, the gas in the anode flow passage10ais circulated by the hydrogen pump23while hydrogen is supplied to the anode flow passage10aby opening the cutoff valve21. Therefore, it is possible to suppress the occurrence of a corrosion current and deterioration in the catalyst and inhibit a decrease in life of the fuel cell stack10.

In addition, the fuel cell system S according to the embodiment includes the oxidizer gas bypass passage (the pipes62aand62b) and the bypass valve61so that air is supplied to the diluter60while the cathode flow passage10cis sealed in the anode replacement step (refer to Step S101). As a result, the hydrogen discharged together with the anode residual gas may be diluted and discharged from the diluter60, thereby preventing an increase in hydrogen concentration in the exhaust gas discharged from the diluter60(fuel cell system S).

MODIFIED EXAMPLE

The fuel cell system S according to the embodiment is not limited to the configuration of the above-described embodiment, and various modifications may be made without deviating from the gist of the present application.

In the above-described embodiment, the anode residual gas which fills the anode flow passage10aand the cathode residual gas which fills the cathode flow passage10cduring shutdown of the fuel cell system S are air, but the residual gases are limited to this. For example, the anode flow passage10aand the cathode flow passage10cmay be filled with nitrogen gas (or air lacking of oxygen). The anode residual gas and the cathode residual gas may be different gases.

In a method for starting a fuel cell system according to the embodiment, the fuel cell system including a fuel cell that generates electric power by an electrochemical reaction between fuel gas supplied to the anode side and oxidizer gas supplied to the cathode side, a fuel gas supply passage and a fuel gas supply device that supply the fuel gas to the fuel cell, a fuel exhaust gas exhaust passage through which fuel exhaust gas is exhausted from the fuel cell, a fuel exhaust gas exhaust passage controller that controls an operating state of the fuel exhaust gas exhaust passage, a fuel exhaust gas recirculation passage through which the fuel exhaust gas is recirculated to the anode side of the fuel cell, a fuel exhaust gas recirculation passage controller that controls an operating state of the fuel exhaust gas recirculation passage, an oxidizer gas supply passage and an oxidizer gas supply device that supply the oxidizer gas to the fuel cell, an oxidizer exhaust gas exhaust passage through which oxidizer exhaust gas is exhausted from the fuel cell, an oxidizer gas bypass passage branched from the oxidizer gas supply passage and connected to the oxidizer exhaust gas exhaust passage while bypassing the fuel cell, an oxidizer gas bypass passage controller that controls an operating state of the oxidizer gas bypass passage, an oxidizer gas supply passage sealing device that seals the oxidizer gas supply passage downstream of the branch portion where the oxidizer gas bypass passage is branched from the oxidizer gas supply passage, an oxidizer exhaust gas passage sealing device that seals the oxidizer exhaust gas exhaust passage upstream of the connection portion where the oxidizer gas bypass passage is connected to the oxidizer exhaust gas exhaust passage, and a diluter that connects the downstream side of the fuel exhaust gas exhaust passage and the downstream side of the oxidizer exhaust gas exhaust passage, the method including a fuel gas replacement step of operating the oxidizer gas bypass passage by the oxidizer gas bypass passage controller to supply the oxidizer gas to the diluter from the oxidizer gas supply device under a condition where the oxidizer gas supply passage is sealed by the oxidizer gas supply passage sealing device and the oxidizer exhaust gas exhaust passage is sealed by the oxidizer exhaust gas exhaust passage sealing device, supplying the fuel gas to the fuel cell from the fuel gas supply device, operating the fuel exhaust gas recirculation passage by the fuel exhaust gas recirculation passage controller, and operating the fuel exhaust gas exhaust passage by the fuel exhaust gas exhaust passage controller to exhaust anode residual gas remaining on the anode side of the fuel cell into the diluter and replace the anode-side gas in the fuel cell with the fuel gas.

In this configuration of the embodiment, a concentration gradient of the fuel gas (hydrogen) may be decreased by operating the fuel exhaust gas recirculation passage by the fuel exhaust gas recirculation passage controller while supplying the fuel gas to the fuel cell from the fuel gas supply device. Therefore, it is possible to suppress deterioration in the catalyst and the catalyst support and inhibit a decrease in life of the fuel cell.

Also, the oxidizer gas may be supplied to the diluter from the oxidizer gas supply device by operating the oxidizer gas bypass passage by the oxidizer gas bypass passage controller, and thus the fuel gas exhausted together with the anode residual gas may be diluted by the diluter.

In addition, the method for starting the fuel cell system according to the embodiment preferably includes, after the fuel gas replacement step, a dilution step of sealing the fuel exhaust gas exhaust passage by the fuel exhaust gas exhaust passage controller and continuing the supply of the oxidizer gas to the diluter from the oxidizer gas supply device through the oxidizer gas bypass passage for a predetermined time.

In this configuration of the embodiment, the fuel gas exhausted together with the anode residual gas in the fuel gas replacement step may be securely diluted by the diluter.

In addition, the method for starting the fuel cell system according to the embodiment preferably includes, after the dilution step, an oxidizer gas replacement step of releasing the oxidizer gas supply passage from sealing by the oxidizer gas supply passage sealing device and releasing the oxidizer exhaust gas exhaust passage from sealing by the oxidizer exhaust gas exhaust passage sealing device to exhaust cathode residual gas remaining on the cathode side of the fuel cell and to replace the cathode-side gas in the fuel cell with the oxidizer gas.

In this configuration of the embodiment, the oxidizer gas replacement step may be performed after the fuel gas replacement step, and thus the cathode side may be sealed in the fuel gas replacement step. That is, in the fuel gas replacement step, the occurrence of a corrosion current may be suppressed by stopping the supply of the oxidizer gas to the cathode, thereby suppressing deterioration in the catalyst and the catalyst support and inhibiting a decrease in life of the fuel cell.

In addition, the method for starting the fuel cell system according to the embodiment preferably includes, after the oxidizer gas replacement step, stopping the oxidizer gas bypass passage by the oxidizer gas bypass passage controller.

In this configuration of the embodiment, the oxidizer gas bypass passage is stopped after the occurrence of a condition where the oxidizer exhaust gas is exhausted into the diluter from the oxidizer gas supply passage and the oxidizer exhaust gas exhaust passage, thereby preventing interruption of supply of the dilution medium (oxidizer gas/oxidizer exhaust gas) used for diluting the fuel gas by the diluter.

An apparatus for starting a fuel cell system according to the embodiment includes a unit that operates an oxidizer gas supply passage sealing device to seal an oxidizer gas supply passage, through which an oxidizer gas is supplied to a fuel cell, and operates an oxidizer exhaust gas exhaust passage sealing device to seal an oxidizer exhaust gas passage through which the oxidizer gas is exhausted from the fuel cell; a unit that, in the sealed state, operates an oxidizer gas bypass passage controller to supply the oxidizer gas to a diluter from an oxidizer gas supply device through an oxidizer gas bypass passage branched from the oxidizer gas supply passage and connected to the oxidizer exhaust gas exhaust passage while bypassing the fuel cell; a unit that operates a fuel gas supply device to supply a fuel gas to the fuel cell and operates a fuel exhaust gas recirculation passage controller to supply a fuel exhaust gas exhausted from the fuel cell through a fuel exhaust gas exhaust passage to the fuel cell through a fuel exhaust gas recirculation passage; and a unit that operates a fuel exhaust gas exhaust passage controller to exhaust an anode residual gas containing the fuel gas and remaining on the anode side of the fuel cell to the diluter through the fuel exhaust gas exhaust passage and to replace the anode-side gas in the fuel cell with the fuel gas.

In this configuration of the embodiment, a concentration gradient of the fuel gas (hydrogen) may be decreased by operating the fuel exhaust gas recirculation passage by the fuel exhaust gas recirculation passage controller while supplying the fuel gas to the fuel cell from the fuel gas supply device. Therefore, it is possible to suppress deterioration in the catalyst and the catalyst support and inhibit a decrease in life of the fuel cell.

Also, the oxidizer gas may be supplied to the diluter from the oxidizer gas supply device by operating the oxidizer gas bypass passage by the oxidizer gas bypass passage controller, and thus the fuel gas exhausted together with the anode residual gas may be diluted by the diluter.

According to the embodiment, a method and apparatus for starting a fuel cell system capable of suppressing deterioration in a fuel cell may be provided.