JP2004327164A

JP2004327164A - Fuel cell system

Info

Publication number: JP2004327164A
Application number: JP2003118413A
Authority: JP
Inventors: Michiyuki Sakuma; 宙之佐久間
Original assignee: Nissan Motor Co Ltd
Current assignee: Nissan Motor Co Ltd
Priority date: 2003-04-23
Filing date: 2003-04-23
Publication date: 2004-11-18

Abstract

<P>PROBLEM TO BE SOLVED: To sufficiently carry out water purge when a low-temperature environment is settled after the shutdown of a fuel cell system. <P>SOLUTION: In the fuel cell system provided with a fuel cell (2) in which electric power is generated by using a fuel gas and an oxidizer gas, and the fuel gas after use is discharged from the fuel gas exit and the oxidizer gas after use is discharged from the oxidizer gas exit, a fuel gas supply means (3), and an oxidizer gas supply means (4), this is equipped with a fuel gas supply stop means (31) to stop the supply of the fuel gas by means of the fuel gas supply means (3) when a shutdown instruction of this system is issued, fuel gas circulating means (13, 14, 15, 16, 31) in which the gas discharged from a fuel gas exit (2c) is circulated again to a fuel gas entrance (2a) after the shutdown instruction of this system is issued, and a liquid droplet separation/recovery means (21) to separate water vapor from this circulating gas and recover it as the liquid droplets are equipped. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
この発明は燃料電池システム、特に燃料電池の反応ガス流路内に残留する残留水を外部に排出する技術に関する。
【０００２】
【従来の技術】
燃料電池システムの運転停止時の残留水の処理方法として、残留水がシステム内に存在する状態において、システムの内圧を上げ、液滴の回収機能を持たせた部分から瞬間的に排気を行い、水滴の回収および放出を行うものがある（特許文献１参照）。
【０００３】
【特許文献１】
特開２００２−３０５０１７号公報
【０００４】
【発明が解決しようとする課題】
ところで、燃料電池システムの運転時は燃料電池の内部ガス温度は８０℃前後に達するのであるが、燃料電池システムの運転停止後に燃料極の内部ガス温度が下がると飽和蒸気量も減少し残留水が発生する。さらに水蒸気が水滴に変化すると、内部のガス量も減少し内圧が下がる。この圧力降下も飽和蒸気量の低下に繋がるので水蒸気の液化が促進される。こうした水蒸気の液化過程を考慮すれば、上記従来装置のように燃料電池システムの運転停止時における瞬間的な水パージだけでは十分とはいえず、燃料電池システムの運転停止後の低温環境下に落ち着いたとき液滴が残る可能性が十分考えられる。すなわち、水パージが不十分であると、残留水がガス流路を閉塞したり、低温下での凍結などでシステムの障害を起こす原因となることがある。
【０００５】
そこで本発明は、燃料電池システムの運転停止後の低温環境下に落ち着いたときに、水パージが十分に行われているようにすることを目的とする。
【０００６】
【課題を解決するための手段】
本発明は、燃料ガス入口より燃料極に供給される燃料ガスと酸化剤ガス入口より酸化剤極に供給される酸化剤ガスとを用いて発電し使用後の燃料ガスを燃料ガス出口より、使用後の酸化剤ガスを酸化剤ガス出口より排出する燃料電池と、前記燃料電池に燃料ガスを供給する燃料ガス供給手段と、前記燃料電池に酸化剤ガスを供給する酸化剤ガス供給手段とを備えた燃料電池システムにおいて、システムの運転停止指令が出たとき前記燃料ガス供給手段による燃料ガスの供給を停止し、このシステムの運転停止指令が出た後に、前記燃料ガス出口より排出されるガスを再び前記燃料ガス入口へと循環させ、液滴分離回収手段によりこの循環するガス中より水蒸気を分離し液滴として回収するように構成する。
【０００７】
【発明の効果】
本発明によれば、システムの運転停止指令後に燃料ガス出口より排出されるガスを循環路を介して循環し、液滴分離回収手段によりその循環するガス中に混在する水蒸気を回収するので、運転停止後にシステムが温度低下した環境下に落ち着いた状態において燃料電池内に液滴が残る可能性を抑制できる。
【０００８】
【発明の実施の形態】
以下、本発明の実施形態を添付図面に基づいて説明する。図１は燃料電池システムの概略構成図である。
【０００９】
図１において、燃料電池システムにはその内部に燃料極と酸化剤極とを有する燃料電池スタック２（燃料電池）と、燃料極に燃料ガスを供給する燃料ガス供給装置３（燃料ガス供給手段）と、酸化剤極に酸化剤ガスを供給する酸化剤ガス供給装置４（酸化剤ガス供給手段）とを備えている。
【００１０】
燃料ガス供給装置３は、燃料ガス、例えば水素ガスの貯蔵手段である燃料タンク、燃料の供給を選択的に遮断する遮断弁、減圧弁、流量調整弁などからなり、燃料電池の運転開始時には遮断弁が開かれ、減圧弁により設定された圧力まで減圧した水素ガスを燃料ガス供給通路１１を介して燃料電池スタック２の燃料ガス入口２ａに供給する。酸化剤ガス供給装置４は、酸化剤ガス、例えば空気を圧送するブロア等や流量調整弁からなり、空気を酸化剤ガス供給通路１２を介して燃料電池スタック２の酸化剤ガス入口２ｂに供給する。
【００１１】
コントローラ３１では、上記２つの供給装置３、４からの燃料電池スタック２への水素ガス及び空気の供給流量を、燃料電池スタック２に要求される出力に応じ各流量調整弁を介して制御する。燃料電池スタック２で使われなかった燃料ガスと酸化剤ガスとは燃料ガス出口２ｃと酸化剤ガス出口２ｄとから排出される。
【００１２】
さて、燃料電池システムの運転時には燃料極の内部ガス温度は８０℃前後に達するものの、燃料電池システムの運転を停止した後には燃料極の内部ガス温度が下がり飽和蒸気量が減少し残留水が発生する。さらに、水蒸気が水滴に変化すると、内部のガス量も減少し内圧が下がる。この圧力降下も飽和蒸気量の低下に繋がるので水蒸気の液化が促進される。この水蒸気の液化過程を考慮すれば、瞬間的な水パージだけでは十分とはいえず、燃料電池システムの運転停止後に低温環境下に落ち着いた状態では液滴が残る可能性が十分考えられる。
【００１３】
本実施形態では、燃料電池システムの運転停止より継続して水パージを十分に行うため、システムの運転停止指令が出た後に、燃料ガス出口２ｃより排出されるガスを再び燃料ガス入口２ａへと循環させるガス循環手段と、この循環するガス中より水蒸気を分離し液滴として回収する液滴分離回収装置２１（液滴分離回収手段）とを備える。
【００１４】
まず、ガス循環手段を説明すると、燃料電池スタック２をバイパスして燃料ガスの循環路を構成するため、燃料ガス出口２ｃから分岐して燃料ガス入口２ａに合流する循環路１３が設けられ、循環路１３の燃料ガス入口２ａへの合流部に三方弁１４を、また循環路１３の途中に循環ポンプ１５を備える。三方弁１４は例えばＯＦＦ状態で燃料ガス供給通路１１と燃料ガス入口２ａとを連通し循環路１３と燃料ガス入口２ａとの連通を遮断しているが、ＯＦＦ状態よりＯＮ状態に切換わると、燃料ガス供給通路１１と燃料ガス入口２ａの連通を遮断し代わって循環路１３と燃料ガス入口２ａとを連通する。このとき、循環ポンプ１５を働かせ、燃料極で発電に用いられなかった燃料ガスを燃料ガス出口２ｃ、循環路１３を介して再び燃料ガス入口２ａに供給する。
【００１５】
上記の循環ポンプ１５はモータ１６により駆動される。このモータ１６には電源切換スイッチ１８により、燃料電池スタック２で発電された電力が直接にまたは二次電池１７からの電力が供給される。すなわち、電源切換スイッチ１８はモータ電源を切換えるためのもので、システムの運転中には図示の中立位置にあってモータ１６に電源は接続されていない。システムの運転停止指令が出たとき、燃料ガス供給装置３からの燃料ガスの供給を停止し、図示の中立位置より接点１８ａを上側に倒すと、燃料極に残存する燃料ガスを用いて発電された電力がモータ１６に直接に供給される。ただし、燃料極に残存する燃料ガスを用いて発電されるのはしばらくの間であり、燃料極に残留する燃料ガスを用いての発電が終了したか後には接点１８ａを下側に倒し、今度は二次電池１７からの電力を供給して、循環ポンプの稼働を継続する。二次電池１７には燃料電池スタック２で発電した電力の一部が蓄えられている。
【００１６】
次に、循環路１３の上流側に液滴分離回収装置２１を備える。液滴分離回収装置２１は循環路１３中の水蒸気を分離して液化するもので、液滴分離回収装置２１のガス入口２１ａとガス出口２１ｂにはそれぞれ常閉の遮断弁２２、２３を備えており、システムの運転停止指令が出たときにはこの遮断弁２２、２３を開いてガスを導入する。また、液化した水を外部に排出するためのドレン通路２４が液滴分離回収装置２１に設けられており、このドレン通路２４にも常閉の遮断弁２５を備えている。
【００１７】
また、循環路１３には温度センサ３２と湿度センサ３３とが設けられ、これらセンサ３２、３３からの温度信号、湿度信号が入力されるコントローラ３１では、これらに基づいて二次電池１７からのモータ１６への電力供給を停止するか否かを判定する。
【００１８】
コントローラ３１で行われるこの制御内容を図２のフローチャートにより説明する。
【００１９】
図２はシステム停止からの処理を時系列的に示したものである。
【００２０】
Ｓ１でシステムの停止指示があったか否かをみる。例えばイグニッションスイッチがＯＦＦにされていれば、システムの停止指令があったと判断し、遮断弁を閉じて燃料ガス供給装置３からの燃料ガスの供給を停止する。また、液滴分離回収装置２１のガス入口２１ａ、ガス出口２１ｂにある遮断弁２２、２３を開く。
【００２１】
Ｓ２では三方弁１４をＯＦＦ状態よりＯＮ状態へと切換えると共に電源切換スイッチ１８の接点１８ａを図１に示す中立位置より上側に倒す。この時点では燃料極に燃料ガスが残留して発電が行える状態にあるので、燃料電池スタック２の発電電力によりモータ１６が駆動され循環ポンプ１５が働く。これにより、燃料ガス出口２ｃより排出された廃燃料ガスが液滴分離回収装置２１を通って燃料ガス入口２ａに戻る循環路を形成し、燃料電池スタック２内や循環路１３中の水蒸気を液滴分離回収装置２１により水にして回収する。
【００２２】
Ｓ３では第１段階の循環終了であるか否かをみる。前述のように燃料極に残留する燃料ガスにより発電が可能である間はその発電電力によりモータ１６を駆動することが可能である。そして、燃料極に残留する燃料ガスがなくなって発電が不可能になると、二次電池１７からの電力に切換えてモータ１６を継続駆動する。つまり、燃料極に残留する燃料ガスでの発電電力によるモータ１６駆動の終了が第１段階の循環終了である。
【００２３】
この第１段階の循環終了であるか否かの判定については図３、図４（いずれも図２Ｓ３のサブルーチン）のフローにより説明する。図３においてＳ１１では循環ポンプ１５の稼働時間（システムの停止指令が出たときからの時間）を計算し、この循環ポンプ１５の稼働時間と所定時間をＳ１２で比較する。ここで、所定時間は、燃料極に残留する燃料ガスで発電が行い得る時間である。この所定時間は予め設定しておく。循環ポンプ１５の稼働時間が所定時間未満であればＳ１１に戻って循環ポンプ１５の稼働時間の計算を継続し、やがて循環ポンプ１５の稼働時間が所定時間以上となればＳ１３に進み第１段階の循環終了と判断する。
【００２４】
また、図４においてＳ２１では燃料電池スタック２からの出力電流を二次電池１７に流す電線２ｅに設けた電流センサ（図示しない）等に基づいてシステムの停止指令が出たときからの燃料電池スタック２の発電量を計算し、この発電量と所定発電量とをＳ２２で比較する。ここで、所定発電量は燃料極に残留する燃料ガスで発電可能な発電量である。この所定発電量も予め設定しておく。システムの停止指令が出たときからの発電量が所定発電量未満であればＳ２１に戻って発電量の計算を継続し、システムの停止指令が出たときからの発電量が所定発電量以上となればＳ２３に進み第１段階の循環終了と判断する。
【００２５】
ここで、図３３のように循環ポンプ１５を所定時間稼働する方法では簡素な制御構成になり、これに対して図４のように循環ポンプ１５をシステムの停止指令が出たときからの発電量が所定発電量以下になるまで稼働する方法では可能な限り燃料極に残留する燃料ガスによる発電を利用することができ、効率がより向上する。
【００２６】
図２に戻り、このようにして第１段階の循環終了であることを判定したときにはＳ４に進んで電源切換スイッチ１８の接点１８ａを今度は上側より下側へと倒し、今度は二次電池１７からの電力をモータ１６に供給し続けて循環ポンプ１５を働かせる。このように、本実施形態では、二次電池１７を備えているため、燃料極に残留する燃料ガスを消費した後も廃燃料ガスを循環させて燃料電池スタック２内部の水滴を液滴分離回収装置２１に回収することができる。
【００２７】
Ｓ５では第２段階の循環終了であるか否かをみる。二次電池１７の蓄電電力によるモータ１６駆動の終了が第２段階の循環終了である。この第２段階の循環終了であるか否かの判定については図５、図６、図７（いずれも図２Ｓ５のサブルーチン）のフローにより説明する。図５においてＳ３１では湿度センサ３３により検出される循環路１３内の湿度（つまり燃料電池スタック２内湿度）を読み込み、この燃料電池スタック２内湿度と所定湿度をＳ３２で比較する。ここで、所定湿度は基準とする気温（例えば０℃）までの循環路１３内のガス温度の低下により発生する凝縮水が循環路１３を閉塞させない量になるときの湿度である。この湿度のうち十分低い値を所定湿度して予め設定しておく。燃料電池スタック内湿度が所定湿度を超えているときにはＳ３１に戻って燃料電池スタック２内湿度の読み込みを続け、燃料電池スタック２内湿度が所定湿度以下になると、基準とする気温まで循環路１３内のガス温度が低下しても凝縮水により循環路１３が閉塞することないと判断し、Ｓ３３に進んで第２段階の循環終了と判断する。
【００２８】
また、図６においてＳ４１ではセンサ３２、３２により検出される循環路１３内の温度および湿度を読み込み、Ｓ４２でシステム停止指令が出たときの内部水蒸気量を次式により算出する。
【００２９】
循環路内水蒸気量＝循環路温度での飽和水蒸気量×湿度×循環路容積…（１）
Ｓ４３では基準とする気温まで低下したときに循環路１３内に存在する水蒸気量を低温下水蒸気量として次式により算出する。
【００３０】
低温下水蒸気量＝低温時の飽和水蒸気量×循環路容積…（２）
（２）式の低温時の飽和水蒸気量は基準とする気温における飽和水蒸気量である。
【００３１】
Ｓ４４では基準とする気温まで低下したときに循環路１３内で液化する水蒸気量を液化水蒸気量として、次式により算出する。
【００３２】
液化水蒸気量＝循環路内水蒸気量−低温下水蒸気量…（３）
Ｓ４５ではこのようにして求めた液化水蒸気量と所定水蒸気量を比較する。ここで、所定水蒸気量は基準とする気温まで低下したときに循環路１３を閉塞させることのない水蒸気量である。この所定水蒸気量は予め設定しておく。液化水蒸気量が所定水蒸気量を超えているときにはＳ４１からＳ４４の操作を繰り返し、やがて液化水蒸気量が所定水蒸気量以下になると、基準とする気温まで循環路１３内のガス温度が低下しても凝縮水により循環路１３が閉塞することないと判断し、Ｓ４６に進んで第２段階の循環終了と判断する。
【００３３】
また、図７においてＳ５１では温度センサ３２により検出される循環路１３内温度を読み込み、Ｓ５２でこの循環路１３内温度から次式によりシステム停止指令が出たときにおける飽和水蒸気量を算出する。
【００３４】
循環路内水蒸気量＝循環路温度での飽和水蒸気量×循環路容積…（４）
Ｓ５３〜Ｓ５６は図６のＳ４３〜Ｓ４６と同じであるため、説明は省略する。
【００３５】
ここで、循環ポンプ１５を、図５のように燃料電池内湿度が所定湿度以下になるまで稼動させる方法では簡素な制御とすることができ、図６のように液化水蒸気量が所定水蒸気量になるまで稼働させる方法では循環させる時間を必要最小限とすることができ、効率を向上させることができる。図７の方法では湿度センサを用いずに実現でき、コスト上昇を抑制できる。
【００３６】
図２に戻り、このようにして第２段階の循環終了であると判定したらＳ６に進んで電源切換スイッチ１８を下側より中立位置に戻してモータ１６への電源接続を断ち循環ポンプ１５の稼働を停止する。Ｓ７では液滴分離回収装置２１のガス入口２１ａ、ガス出口２１ｂにある遮断弁２２、２３を閉じて循環路１３と液滴分離回収装置２１との連通を遮断しＳ８ではドレン通路２４の遮断弁２５を開き、液滴分離回収装置２１により回収された水を外部へと排出する。Ｓ９ではシステムを停止させる。
【００３７】
ここで、本実施形態の作用を説明する。
【００３８】
本実施形態（請求項１に記載の発明）によればシステムの運転停止指令後に、燃料ガス出口２ｃより排出されるガスを循環路１３を介して循環し、液滴分離回収装置２１によりその循環するガス中に混在する水蒸気を回収するようにしたので、運転停止後にシステムが温度低下した環境下でも燃料電池スタック内２に液滴が残る可能性を抑制できる。
【００３９】
システムの運転停止指令後に循環ポンプ用モータ１６に電力を供給するために、システムの運転停止指令後にも続けて燃料ガスを燃料電池スタック２に供給して発電させるのではそれだけ燃料消費が増えることになるのであるが、本実施形態（請求項３に記載の発明）によれば、システムの運転停止指令が出たとき、燃料ガス供給装置３からの燃料ガスの燃料供給を停止し、燃料極に残留する燃料ガスを用いて発電した電力を循環ポンプ用モータ１６に供給するようにしているので、燃料消費を抑制できる。
【００４０】
本実施形態（請求項４に記載の発明）によれば、燃料電池スタック２の余剰発電を充電可能な二次電池１７を有するので、燃料極に残留する燃料ガスを消費した後も循環路１３内に含まれる液滴水蒸気の回収が可能であり、液滴の残る可能性をより抑制できる。
【００４１】
本実施形態（請求項９に記載の発明）によれば、第２段階の循環終了後、液滴分離回収装置２１で回収した水を外部へ排出するようにしているので、低温下での水回収部の凍結を防止でき、かつ次回の水回収容積を確保できる。
【００４２】
さて、燃料電池の触媒となる電解質膜にとっては適度な湿潤状態が必要とされている。このため水蒸気を回収し過ぎて電解質膜を過度に乾燥させてしまったのでは、次回のシステム運転時に電解質膜が湿潤状態になるまで良好に発電できない。これを避けるため、第２実施形態では、電解質膜が湿潤状態を最低限保ちうる状態になったタイミングを第２段階の循環終了とし、このタイミング以降は燃料電池スタック２をバイパスさせた循環路を形成してさらに水蒸気を回収する。そして、所定の水蒸気量を回収できたタイミングを第３段階の循環終了として、システムを停止する。
【００４３】
このため、第２実施形態では、図１に重ねて示すように、循環ポンプ１５下流かつ三方弁１４上流の循環路１３より燃料電池スタック２を経ることなく液滴分離回収装置２１上流の循環路１３に合流するバイパス路４１を設け、このバイパス路４１の分岐部に第２三方弁４２を設ける。ここで、第２三方弁４２は例えばＯＦＦ状態で第２三方弁４２上流の循環路１３と第２三方弁４２下流の循環路１３とを連通し第２三方弁４２上流の循環路１３とバイパス路４１との連通を遮断しているが、ＯＦＦ状態よりＯＮ状態に切換わると、第２三方弁４２上流の循環路１３と第２三方弁４２下流の循環路１３との連通を遮断し、代わって第２三方弁４２上流の循環路１３とバイパス路４１とを連通する。
【００４４】
図８は第２実施形態のフローチャートで、第１実施形態の図２と置き換わるものである。ただし、図２と同一部分には同一のステップ番号をつけている。
【００４５】
図２とはＳ６１、Ｓ６２、Ｓ６３が相違する。すなわち、Ｓ６１では第２段階の循環終了であるか否かをみる。この第２段階の循環終了であるか否かの判定については図５、図６、図７（いずれも図２Ｓ５のサブルーチン）のフローにより実行すればよい。ただし、第１実施形態によれば、図５Ｓ３２に示す所定湿度、図６Ｓ４５に示す所定水蒸気量、図７ｓ５５に示す所定水蒸気量を、基準とする気温までの循環路１３内のガス温度の低下により発生する凝縮水が循環路１３を閉塞させないように設定したが、第２実施形態ではこれに代えて、電解質膜が湿潤状態を最低限保ちうるように図５Ｓ３２に示す所定湿度、図６Ｓ４５に示す所定水蒸気量、図７ｓ５５に示す所定水蒸気量を設定する。
【００４６】
そして、第２段階の循環終了であると判定したときにはガスをこれ以上、燃料電池スタック２を経由して循環させたのでは電解質膜が乾燥しすぎると判断し、Ｓ６１よりＳ６２に進み、二次電池１７による循環ポンプ１５の稼働を継続しつつ、第２三方弁４２をＯＦＦ状態からＯＮ状態に切換えガスをバイパス路４１へと流し燃料電池スタック２を含まない循環路を形成する。
【００４７】
Ｓ６３では第３段階の循環終了であるか否かをみる。これは、第１実施形態についての第２段階の循環終了であるか否かをみるのと同様である。すなわち、第３段階の循環終了であるか否かは図６、図７を流用すればよい。
【００４８】
このように第２実施形態（請求項１０に記載の発明）によれば、燃料電池スタック２内の湿度（水蒸気量）と、循環路１３内の水蒸気量とを分けた環境を設定することが可能となるので、燃料電池スタック２内の電解質膜が乾きしすぎないにようにして電解質膜の性能を維持しつつ、液滴の残留を抑制できる。
【００４９】
また、燃料電池スタック２を通さない経路でガスを循環させるので、循環行程において燃料電池スタック２の空気極側の圧力を燃料極側に合わせる制御が不要となる。
【００５０】
請求項１に記載の発明の燃料ガス供給停止手段の機能はコントローラ３１により、また請求項２に記載の電力供給手段の機能は燃料電池スタック２、二次電池１７、電源切換スイッチ１８により果たされている。
【図面の簡単な説明】
【図１】第１、第２実施形態の燃料電池システムの概略構成図。
【図２】システム停止時の制御を説明するためのフローチャート。
【図３】第１段階の循環終了の判定を説明するためのフローチャート。
【図４】第１段階の循環終了の判定を説明するためのフローチャート。
【図５】第２段階の循環終了の判定を説明するためのフローチャート。
【図６】第２段階の循環終了の判定を説明するためのフローチャート。
【図７】第２段階の循環終了の判定を説明するためのフローチャート。
【図８】第２実施形態のシステム停止時の制御を説明するためのフローチャート。
【符号の説明】
２燃料電池スタック（燃料電池）
２ａ燃料ガス入口
２ｃ燃料ガス出口
３燃料ガス供給装置（燃料ガス供給手段）
４酸化剤ガス供給装置（酸化剤ガス供給手段）
１１燃料ガス供給通路
１３循環路
１４三方弁（弁手段）
１５循環ポンプ
１６モータ
１７二次電池
１８電源切換スイッチ
２１液滴分離回収装置（液滴分離回収手段）
３１コントローラ
４１バイパス路
４２第２三方弁（弁手段）[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a fuel cell system, and more particularly to a technique for discharging residual water remaining in a reaction gas channel of a fuel cell to the outside.
[0002]
[Prior art]
As a method of treating residual water when the operation of the fuel cell system is stopped, in a state in which residual water is present in the system, the internal pressure of the system is increased, and instantaneous exhaust is performed from a portion having a function of collecting droplets, There is one that collects and releases water droplets (see Patent Document 1).
[0003]
[Patent Document 1]
JP, 2002-305017, A
[Problems to be solved by the invention]
By the way, during operation of the fuel cell system, the internal gas temperature of the fuel cell reaches about 80 ° C., but when the internal gas temperature of the fuel electrode drops after the operation of the fuel cell system is stopped, the amount of saturated steam also decreases and residual water is reduced. appear. Further, when the water vapor changes to water droplets, the amount of gas in the interior also decreases, and the internal pressure decreases. This pressure drop also leads to a decrease in the amount of saturated steam, so that the liquefaction of steam is promoted. In consideration of such a liquefaction process of water vapor, it is not sufficient to provide only an instantaneous water purge at the time of stopping the operation of the fuel cell system as in the above-described conventional apparatus, and the system is settled in a low-temperature environment after the operation of the fuel cell system is stopped. It is quite possible that droplets will remain when this occurs. That is, if the water purge is insufficient, the residual water may block the gas flow path or cause a failure of the system due to freezing at a low temperature.
[0005]
Accordingly, it is an object of the present invention to provide sufficient water purging when settling in a low-temperature environment after the operation of a fuel cell system is stopped.
[0006]
[Means for Solving the Problems]
The present invention uses a fuel gas supplied from the fuel gas inlet to the fuel electrode and an oxidant gas supplied to the oxidant electrode from the oxidant gas inlet to generate power and use the used fuel gas from the fuel gas outlet. A fuel cell that discharges a subsequent oxidant gas from an oxidant gas outlet; a fuel gas supply unit that supplies a fuel gas to the fuel cell; and an oxidant gas supply unit that supplies an oxidant gas to the fuel cell. In the fuel cell system, when a system operation stop command is issued, the supply of fuel gas by the fuel gas supply unit is stopped, and after the system operation stop command is issued, the gas discharged from the fuel gas outlet is discharged. The fuel gas is circulated again to the fuel gas inlet, and water vapor is separated from the circulating gas by a droplet separation and recovery means and collected as droplets.
[0007]
【The invention's effect】
According to the present invention, the gas discharged from the fuel gas outlet after the operation stop command of the system is circulated through the circulation path, and the water vapor mixed in the circulating gas is recovered by the droplet separation and recovery means. It is possible to suppress the possibility that droplets remain in the fuel cell in a state where the system is calm in an environment where the temperature has dropped after the shutdown.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a schematic configuration diagram of a fuel cell system.
[0009]
In FIG. 1, a fuel cell system includes a fuel cell stack 2 (fuel cell) having a fuel electrode and an oxidant electrode therein, and a fuel gas supply device 3 (fuel gas supply means) for supplying fuel gas to the fuel electrode. And an oxidant gas supply device 4 (oxidant gas supply means) for supplying an oxidant gas to the oxidant electrode.
[0010]
The fuel gas supply device 3 includes a fuel tank as storage means for fuel gas, for example, hydrogen gas, a shutoff valve for selectively shutting off the supply of fuel, a pressure reducing valve, a flow regulating valve, and the like. The valve is opened, and the hydrogen gas reduced to the pressure set by the pressure reducing valve is supplied to the fuel gas inlet 2a of the fuel cell stack 2 via the fuel gas supply passage 11. The oxidizing gas supply device 4 includes an oxidizing gas, for example, a blower for pumping air or a flow control valve, and supplies air to the oxidizing gas inlet 2 b of the fuel cell stack 2 through the oxidizing gas supply passage 12. .
[0011]
The controller 31 controls the supply flow rates of the hydrogen gas and the air from the two supply devices 3 and 4 to the fuel cell stack 2 via respective flow control valves according to the output required for the fuel cell stack 2. Fuel gas and oxidant gas not used in the fuel cell stack 2 are discharged from the fuel gas outlet 2c and the oxidant gas outlet 2d.
[0012]
While the fuel cell system operates, the internal gas temperature of the fuel electrode reaches about 80 ° C., but after the operation of the fuel cell system is stopped, the internal gas temperature of the fuel electrode decreases, the amount of saturated steam decreases, and residual water is generated. I do. Further, when the water vapor changes into water droplets, the amount of gas inside also decreases, and the internal pressure decreases. This pressure drop also leads to a decrease in the amount of saturated steam, so that the liquefaction of steam is promoted. In consideration of this water vapor liquefaction process, it is not enough to say that instantaneous water purging alone is sufficient, and it is conceivable that droplets may remain in a low-temperature environment after the operation of the fuel cell system is stopped.
[0013]
In the present embodiment, in order to sufficiently perform the water purging continuously from the stop of the operation of the fuel cell system, the gas discharged from the fuel gas outlet 2c is returned to the fuel gas inlet 2a again after the operation stop command of the system is issued. The apparatus includes a gas circulating means for circulating, and a liquid drop separating and collecting device (liquid drop separating and collecting means) 21 for separating water vapor from the circulating gas and collecting it as liquid drops.
[0014]
First, gas circulation means will be described. In order to constitute a fuel gas circulation path bypassing the fuel cell stack 2, a circulation path 13 branching from the fuel gas outlet 2 c and joining the fuel gas inlet 2 a is provided. A three-way valve 14 is provided at the junction of the passage 13 with the fuel gas inlet 2 a, and a circulation pump 15 is provided in the middle of the circulation passage 13. For example, the three-way valve 14 communicates the fuel gas supply passage 11 with the fuel gas inlet 2a in the OFF state and cuts off the communication between the circulation path 13 and the fuel gas inlet 2a. The communication between the fuel gas supply passage 11 and the fuel gas inlet 2a is cut off, and the circulation path 13 and the fuel gas inlet 2a are connected instead. At this time, the circulation pump 15 is operated to supply the fuel gas not used for power generation at the fuel electrode to the fuel gas inlet 2a again via the fuel gas outlet 2c and the circulation path 13.
[0015]
The circulation pump 15 is driven by a motor 16. The electric power generated by the fuel cell stack 2 is supplied to the motor 16 directly or from the secondary battery 17 by a power supply switch 18. That is, the power supply changeover switch 18 is for switching the motor power supply, and is in the neutral position shown in the figure during operation of the system, and the power supply is not connected to the motor 16. When the operation stop command of the system is issued, the supply of the fuel gas from the fuel gas supply device 3 is stopped, and when the contact 18a is tilted upward from the illustrated neutral position, power is generated using the fuel gas remaining on the fuel electrode. The electric power is supplied directly to the motor 16. However, power generation using the fuel gas remaining on the fuel electrode is performed for a while, and after the power generation using the fuel gas remaining on the fuel electrode is completed, the contact 18a is moved downward, and this time, Supplies the electric power from the secondary battery 17 and continues the operation of the circulation pump. The secondary battery 17 stores a part of the electric power generated by the fuel cell stack 2.
[0016]
Next, a droplet separation and recovery device 21 is provided upstream of the circulation path 13. The droplet separation and recovery device 21 separates and liquefies the water vapor in the circulation path 13, and has normally closed shut-off valves 22 and 23 at a gas inlet 21 a and a gas outlet 21 b of the droplet separation and recovery device 21, respectively. When a system stop command is issued, the shut-off valves 22 and 23 are opened to introduce gas. Further, a drain passage 24 for discharging the liquefied water to the outside is provided in the droplet separation and recovery device 21, and the drain passage 24 is also provided with a normally closed shutoff valve 25.
[0017]
Further, the circulation path 13 is provided with a temperature sensor 32 and a humidity sensor 33, and the controller 31 to which the temperature signal and the humidity signal from these sensors 32 and 33 are input, based on these, the motor from the secondary battery 17 is used. It is determined whether or not the power supply to the power supply 16 is stopped.
[0018]
The control performed by the controller 31 will be described with reference to the flowchart of FIG.
[0019]
FIG. 2 shows the processing after the system stoppage in chronological order.
[0020]
In S1, it is determined whether or not an instruction to stop the system has been issued. For example, if the ignition switch is turned off, it is determined that a system stop command has been issued, the shutoff valve is closed, and the supply of fuel gas from the fuel gas supply device 3 is stopped. Further, the shutoff valves 22 and 23 at the gas inlet 21a and the gas outlet 21b of the droplet separation and collection device 21 are opened.
[0021]
In S2, the three-way valve 14 is switched from the OFF state to the ON state, and the contact 18a of the power switch 18 is turned upward from the neutral position shown in FIG. At this time, since the fuel gas remains in the fuel electrode and power generation can be performed, the motor 16 is driven by the power generated by the fuel cell stack 2 and the circulation pump 15 operates. As a result, a circulation path for returning the waste fuel gas discharged from the fuel gas outlet 2c to the fuel gas inlet 2a through the droplet separation / recovery device 21 is formed, and the water vapor in the fuel cell stack 2 and the circulation path 13 is converted into a liquid. The water is collected by the droplet separation and collection device 21 and collected.
[0022]
In S3, it is determined whether or not the circulation of the first stage is completed. As described above, while power can be generated by the fuel gas remaining at the fuel electrode, the motor 16 can be driven by the generated power. Then, when the fuel gas remaining at the fuel electrode runs out and power generation becomes impossible, the power is switched to the power from the secondary battery 17 and the motor 16 is continuously driven. That is, the end of driving of the motor 16 by the generated electric power with the fuel gas remaining on the fuel electrode is the end of circulation in the first stage.
[0023]
The determination as to whether or not the circulation of the first stage is completed will be described with reference to the flow charts of FIGS. 3 and 4 (both are subroutines of FIG. 2S3). In FIG. 3, in S11, the operation time of the circulation pump 15 (the time from when the system stop command is issued) is calculated, and the operation time of the circulation pump 15 is compared with a predetermined time in S12. Here, the predetermined time is a time during which power generation can be performed using fuel gas remaining on the fuel electrode. This predetermined time is set in advance. If the operating time of the circulating pump 15 is shorter than the predetermined time, the process returns to S11 to continue the calculation of the operating time of the circulating pump 15, and if the operating time of the circulating pump 15 is longer than the predetermined time, the process proceeds to S13 and proceeds to the first stage. Judge that the circulation has ended.
[0024]
In FIG. 4, in S21, the fuel cell stack from the time when a system stop command is issued based on a current sensor (not shown) provided on the electric wire 2e for flowing the output current from the fuel cell stack 2 to the secondary battery 17 and the like. In step S22, the power generation amount is calculated and the generated power amount is compared with a predetermined power generation amount. Here, the predetermined power generation amount is a power generation amount that can be generated by the fuel gas remaining on the fuel electrode. This predetermined power generation amount is also set in advance. If the amount of power generation from when the system stop command is issued is less than the predetermined amount of power generation, the process returns to S21 to continue the calculation of the amount of power generation. If so, the process proceeds to S23, where it is determined that the first-stage circulation is completed.
[0025]
Here, in the method of operating the circulation pump 15 for a predetermined time as shown in FIG. 33, a simple control configuration is obtained. On the other hand, as shown in FIG. In this method, the power generation by the fuel gas remaining on the fuel electrode can be used as much as possible, and the efficiency is further improved.
[0026]
Returning to FIG. 2, when it is determined that the circulation of the first stage is completed, the process proceeds to S4, in which the contact 18a of the power supply changeover switch 18 is turned down from the upper side to the lower side, and the secondary battery 17 is turned down. , And the circulation pump 15 is operated. As described above, in the present embodiment, since the secondary battery 17 is provided, the waste fuel gas is circulated even after the fuel gas remaining on the fuel electrode is consumed, and the water droplets inside the fuel cell stack 2 are separated and collected. It can be collected in the device 21.
[0027]
In S5, it is determined whether or not the circulation of the second stage is completed. The end of driving of the motor 16 by the stored power of the secondary battery 17 is the end of circulation in the second stage. The determination as to whether or not the circulation of the second stage has been completed will be described with reference to the flow charts of FIGS. 5, 6, and 7 (all of which are subroutines of FIG. 2S5). In FIG. 5, in S31, the humidity in the circulation path 13 detected by the humidity sensor 33 (that is, the humidity in the fuel cell stack 2) is read, and the humidity in the fuel cell stack 2 is compared with a predetermined humidity in S32. Here, the predetermined humidity is a humidity at which condensed water generated due to a decrease in the gas temperature in the circulation path 13 up to a reference temperature (for example, 0 ° C.) does not block the circulation path 13. A sufficiently low value of this humidity is set in advance as a predetermined humidity. When the humidity inside the fuel cell stack exceeds the predetermined humidity, the process returns to S31 to continue reading the humidity inside the fuel cell stack 2, and when the humidity inside the fuel cell stack 2 becomes equal to or lower than the predetermined humidity, the circulation path 13 reaches the reference temperature. It is determined that the circulation path 13 is not blocked by the condensed water even if the gas temperature decreases, and the process proceeds to S33, where it is determined that the circulation of the second stage is completed.
[0028]
In FIG. 6, in S41, the temperature and humidity in the circulation path 13 detected by the sensors 32, 32 are read, and in S42, the amount of internal water vapor when a system stop command is issued is calculated by the following equation.
[0029]
The amount of water vapor in the circulation path = the amount of saturated water vapor at the circulation path temperature x the humidity x the volume of the circulation path ... (1)
In S43, the amount of water vapor present in the circulation path 13 when the temperature has decreased to the reference temperature is calculated as the low-temperature water vapor amount by the following equation.
[0030]
Low-temperature steam amount = Saturated steam amount at low temperature x Circulation volume ... (2)
The saturated steam amount at low temperature in the equation (2) is the saturated steam amount at the reference air temperature.
[0031]
In S44, the amount of water vapor liquefied in the circulation path 13 when the temperature falls to the reference temperature is calculated as the amount of liquefied water vapor by the following equation.
[0032]
Liquefied steam amount = amount of steam in the circulation path-amount of steam under low temperature ... (3)
At S45, the liquefied steam amount thus obtained is compared with a predetermined steam amount. Here, the predetermined amount of water vapor is an amount of water vapor that does not block the circulation path 13 when the temperature drops to the reference temperature. This predetermined water vapor amount is set in advance. When the liquefied steam amount exceeds the predetermined steam amount, the operations from S41 to S44 are repeated. When the liquefied steam amount eventually becomes equal to or less than the predetermined steam amount, the condensation is performed even if the gas temperature in the circulation path 13 decreases to the reference temperature. It is determined that the circulation path 13 will not be blocked by the water, and the flow proceeds to S46, where it is determined that the circulation of the second stage is completed.
[0033]
In FIG. 7, in S51, the temperature in the circulation path 13 detected by the temperature sensor 32 is read, and in S52, the amount of saturated steam at the time of issuing a system stop command from the temperature in the circulation path 13 is calculated by the following equation.
[0034]
The amount of water vapor in the circulation path = the amount of saturated water vapor at the circulation path temperature x the volume of the circulation path ... (4)
Steps S53 to S56 are the same as steps S43 to S46 in FIG.
[0035]
Here, in the method in which the circulation pump 15 is operated until the humidity in the fuel cell becomes equal to or lower than the predetermined humidity as shown in FIG. 5, simple control can be performed, and as shown in FIG. In the method operated to the extent possible, the circulating time can be minimized and efficiency can be improved. The method of FIG. 7 can be realized without using a humidity sensor, and can suppress an increase in cost.
[0036]
Returning to FIG. 2, when it is determined that the circulation of the second stage is completed, the process proceeds to S6, in which the power switch 18 is returned from the lower side to the neutral position, the power supply to the motor 16 is disconnected, and the operation of the circulation pump 15 is started. To stop. In S7, the shutoff valves 22 and 23 at the gas inlet 21a and the gas outlet 21b of the droplet separation / collection device 21 are closed to shut off the communication between the circulation path 13 and the droplet separation / collection device 21. In S8, the shutoff valve for the drain passage 24 is shut off. 25 is opened, and the water collected by the droplet separation and collection device 21 is discharged to the outside. In S9, the system is stopped.
[0037]
Here, the operation of the present embodiment will be described.
[0038]
According to the present embodiment (invention of claim 1), after the system operation stop command, the gas discharged from the fuel gas outlet 2c is circulated through the circulation path 13 and circulated by the droplet separation / collection device 21. Since the water vapor mixed in the generated gas is recovered, it is possible to suppress the possibility that droplets remain in the fuel cell stack 2 even in an environment in which the temperature of the system is lowered after the operation is stopped.
[0039]
In order to supply electric power to the circulation pump motor 16 after the system operation stop command, if the fuel gas is continuously supplied to the fuel cell stack 2 after the system operation stop command to generate power, the fuel consumption increases accordingly. However, according to the present embodiment (the invention according to claim 3), when the system operation stop command is issued, the fuel gas supply from the fuel gas supply device 3 is stopped, and the fuel electrode is stopped. Since electric power generated using the remaining fuel gas is supplied to the circulation pump motor 16, fuel consumption can be suppressed.
[0040]
According to the present embodiment (the invention described in claim 4), since the secondary battery 17 capable of charging the surplus power generation of the fuel cell stack 2 is provided, the circulation path 13 is maintained even after the fuel gas remaining on the fuel electrode is consumed. It is possible to collect the droplet water vapor contained in the inside, and it is possible to further suppress the possibility that the droplet remains.
[0041]
According to the present embodiment (the invention according to claim 9), after the end of the circulation in the second stage, the water collected by the droplet separation and collection device 21 is discharged to the outside. Freezing of the recovery section can be prevented, and the next water recovery volume can be secured.
[0042]
Now, an appropriate wet state is required for an electrolyte membrane serving as a catalyst for a fuel cell. For this reason, if the electrolyte membrane is excessively dried due to excessive collection of water vapor, power cannot be satisfactorily generated until the electrolyte membrane becomes wet during the next system operation. In order to avoid this, in the second embodiment, the timing at which the electrolyte membrane can be kept in the minimum wet state is defined as the end of circulation in the second stage, and after this timing, the circulation path that bypasses the fuel cell stack 2 is used. Form and recover more steam. Then, the system is stopped with the timing at which the predetermined amount of water vapor can be recovered as the end of the circulation in the third stage.
[0043]
For this reason, in the second embodiment, as shown in FIG. 1, a circulation path upstream of the droplet separation and collection device 21 without passing through the fuel cell stack 2 from the circulation path 13 downstream of the circulation pump 15 and upstream of the three-way valve 14. A bypass path 41 that joins the bypass path 13 is provided, and a second three-way valve 42 is provided at a branch portion of the bypass path 41. Here, the second three-way valve 42 communicates with the circulation path 13 upstream of the second three-way valve 42 and the circulation path 13 downstream of the second three-way valve 42 in an OFF state, for example, and bypasses the circulation path 13 upstream of the second three-way valve 42. Although the communication with the path 41 is interrupted, when switching from the OFF state to the ON state, the communication between the circulation path 13 upstream of the second three-way valve 42 and the circulation path 13 downstream of the second three-way valve 42 is interrupted, Instead, the circulation path 13 upstream of the second three-way valve 42 communicates with the bypass path 41.
[0044]
FIG. 8 is a flowchart of the second embodiment, which replaces FIG. 2 of the first embodiment. However, the same steps as those in FIG. 2 are denoted by the same step numbers.
[0045]
S61, S62, and S63 are different from FIG. That is, in S61, it is determined whether or not the circulation of the second stage is completed. The determination as to whether or not the circulation of the second stage is completed may be performed according to the flow of FIGS. 5, 6, and 7 (all of which are subroutines of S5 in FIG. 2). However, according to the first embodiment, the predetermined humidity shown in FIG. 5S32, the predetermined steam amount shown in FIG. 6S45, and the predetermined steam amount shown in FIG. 7S55 are reduced by lowering the gas temperature in the circulation path 13 to the reference air temperature. Although the generated condensed water is set so as not to block the circulation path 13, in the second embodiment, instead of this, the predetermined humidity shown in FIG. 5S32 and the predetermined humidity shown in FIG. A predetermined water vapor amount, a predetermined water vapor amount shown in FIG. 7s55 is set.
[0046]
When it is determined that the circulation of the second stage is completed, it is determined that the electrolyte membrane is excessively dried if the gas is circulated through the fuel cell stack 2 any more. While the operation of the circulation pump 15 by the battery 17 is continued, the second three-way valve 42 is switched from the OFF state to the ON state, and the gas flows to the bypass path 41 to form a circulation path not including the fuel cell stack 2.
[0047]
In S63, it is determined whether or not the circulation of the third stage is completed. This is the same as checking whether or not the circulation of the second stage in the first embodiment is completed. That is, whether or not the circulation of the third stage is completed may be determined by using FIGS. 6 and 7.
[0048]
As described above, according to the second embodiment (the invention according to claim 10), it is possible to set an environment in which the humidity (water vapor amount) in the fuel cell stack 2 and the water vapor amount in the circulation path 13 are separated. As a result, it is possible to prevent the electrolyte membrane in the fuel cell stack 2 from drying too much, maintain the performance of the electrolyte membrane, and suppress the droplets from remaining.
[0049]
Further, since the gas is circulated in a path that does not pass through the fuel cell stack 2, it is not necessary to control the pressure on the air electrode side of the fuel cell stack 2 to the fuel electrode side in the circulation process.
[0050]
The function of the fuel gas supply stopping means according to the first aspect of the invention is performed by the controller 31, and the function of the power supply means according to the second aspect is performed by the fuel cell stack 2, the secondary battery 17, and the power supply switch 18. Have been.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a fuel cell system according to first and second embodiments.
FIG. 2 is a flowchart for explaining control when the system is stopped.
FIG. 3 is a flowchart illustrating a first-stage determination of the end of circulation.
FIG. 4 is a flowchart for explaining the determination of the end of circulation in the first stage.
FIG. 5 is a flowchart for explaining the determination of the end of circulation in the second stage.
FIG. 6 is a flowchart for explaining the determination of the end of circulation in the second stage.
FIG. 7 is a flowchart for explaining the determination of the end of circulation in the second stage.
FIG. 8 is a flowchart illustrating control when the system is stopped according to the second embodiment.
[Explanation of symbols]
2 Fuel cell stack (fuel cell)
2a fuel gas inlet 2c fuel gas outlet 3 fuel gas supply device (fuel gas supply means)
4 Oxidant gas supply device (oxidant gas supply means)
11 fuel gas supply passage 13 circulation passage 14 three-way valve (valve means)
15 Circulating pump 16 Motor 17 Secondary battery 18 Power switch 21 Droplet separation and recovery device (droplet separation and recovery means)
31 controller 41 bypass passage 42 second three-way valve (valve means)

Claims

Using the fuel gas supplied to the fuel electrode from the fuel gas inlet and the oxidant gas supplied to the oxidant electrode from the oxidant gas inlet, generates electricity and uses the used fuel gas from the fuel gas outlet to the used oxidant. A fuel cell that discharges gas from an oxidant gas outlet,
Fuel gas supply means for supplying fuel gas to the fuel cell;
Oxidizing gas supply means for supplying an oxidizing gas to the fuel cell,
In a fuel cell system comprising
Fuel gas supply stop means for stopping supply of fuel gas by the fuel gas supply means when a system stop command is issued;
Gas circulation means for circulating the gas discharged from the fuel gas outlet to the fuel gas inlet again after the operation stop command of the system is issued;
A fuel cell system comprising: a liquid droplet separation and recovery unit that separates water vapor from the circulating gas and recovers the water vapor as liquid droplets.

The gas circulation means,
A circulation path that branches off from the fuel gas outlet and joins the fuel gas inlet via the droplet separation and collection unit;
Valve means for selectively switching a gas flow from the circulation path to the fuel gas inlet and a gas flow from the fuel gas supply path to the fuel gas inlet;
A circulation pump that circulates the gas in the circulation path from the fuel gas outlet side to the fuel gas inlet side only when receiving power supply,
When a system operation stop command is issued, the gas flow is switched from the circulation path to the fuel gas inlet using the valve means, and power supply means for supplying power to the circulation pump is provided. The fuel cell system according to claim 1.

The fuel cell system according to claim 2, wherein the power supplied by the power supply unit is power generated by using fuel gas remaining on the fuel electrode after the supply of the fuel gas is stopped.

Having a secondary battery capable of charging surplus power generated by the fuel cell, supplying power from the secondary battery to the circulation pump when power generation using fuel gas remaining in the fuel electrode is completed. The fuel cell system according to claim 3, wherein:

The fuel cell system according to claim 4, wherein it is determined whether or not power generation using fuel gas remaining on the fuel electrode has been completed based on an operation time of the circulation pump.

The method according to claim 4, wherein after the supply of the fuel gas is stopped, it is determined whether or not the power generation using the fuel gas remaining on the fuel electrode has been completed based on the amount of power generated by the fuel cell. Fuel cell system.

It has a detection means for detecting the temperature and humidity in the circulation path, whether or not to stop the power supply from the secondary battery, based on the temperature and humidity in the circulation path detected by these detection means The fuel cell system according to claim 4, wherein the determination is performed.

It has a detecting means for detecting the humidity in the circulation path, it is determined whether to stop the power supply from the secondary battery, based on the humidity in the circulation path detected by the detection means. The fuel cell system according to claim 4, wherein:

9. The fuel cell system according to claim 7, wherein after stopping the power supply from the secondary battery, the communication between the droplet separation and collection unit and the circulation path is closed to perform drainage to the outside. 10.

A bypass path that bypasses the fuel cell from the circulation path downstream of the droplet separation and collection means and joins the circulation path upstream of the droplet separation and collection means,
A valve means capable of selectively switching a gas flow from the circulation path upstream of the branch of the bypass path to the bypass path and a gas flow from the circulation path upstream of the branch section of the bypass path to the fuel gas inlet. Have
The method according to claim 4, wherein when the amount of water vapor in the circulation path decreases to a predetermined value, the valve means is used to switch the gas flow from the circulation path upstream of the branch portion of the bypass path to the bypass path. Fuel cell system.