JP4539040B2 - Fuel cell system - Google Patents

Description

【００５２】
本発明は、安定した燃焼と高い改質効率が得られることがわかる。これは、水結露手段により液滴を除去された水素系燃料ガスが導入されることと、酸素センサにより最適な空気過剰率に保持されることで、燃料改質装置１０が効果的に水蒸気改質反応を行う６３７℃に保持されたためである。一方、比較１は、酸素センサにより最適な空気過剰率に保持されるけれども、液滴を多く含む水素系燃料ガスが導入されるため燃焼が不安定となるため、燃料改質装置１０は６２７℃に保持され効果的に水蒸気改質反応が行われなかった。また、比較２は、酸素センサを使用せずに空気過剰率を成り行きの１．５にしたうえに、液滴を多く含む水素系燃料ガスが導入されるため、失火し易い燃焼となるうえに燃料改質装置１０は６１２℃に保持されあまり効果的に水蒸気改質反応が行われなかった。
【００５３】
さて、燃焼部１３に供給される水素系燃料ガス量は、燃料改質装置１０での変換効率と、燃料電池１１での使用効率に、大きく依存する。そのため、供給される水素系燃料ガス量はこれらの効率に依存して変動し易いが、酸素センサ１０を用いて空気過剰率を最適に制御すると、一酸化炭素を生成することがなく安定燃焼させることができ、安全性に優れた燃焼システムを提供することができる利点も有る。また、燃料改質装置１０を燃焼部１３で加熱しているため、水蒸気改質反応に必要な熱が回収でき、燃焼システムの効率が高まる利点も生じる。なお、この燃焼システムに用いる燃料は、都市ガス以外に、プロパンガスや灯油さらにアルコール・石炭などにも使用でき、その燃料を限定するものでない。
【００５４】
また、酸素センサ１５は、限界電流式酸素センサ以外に濃淡電池式酸素センサを用いてもよく、特にその方式や構造・材料を限定するものでない。水結露手段１７は、自動的に水が排水される、いわゆるオートドレンを用いてもよい。
【００５５】
水結露手段１７は、その内部空間中に集められ貯留する結露水が燃焼部１３まで到達することを防止するために設けた遮蔽板（記載せず）と、この貯留結露水を外部に排出する排出手段（記載せず）を備えている。また、必要によっては、水結露手段１７で集められた結露水は、排出手段の先端に設けられたイオン交換樹脂充填装置や中和装置などの浄化装置（記載せず）で浄化されて、再利用もしくは排出される。
【００５６】
酸素センサ１５は、限界電流式の酸素センサが最適であるが、特に下記２種類のいずれか材料組成の電極膜を用いた酸素センサは、水素系燃料ガスを燃焼させた燃焼排ガス中で使用する酸素センサとして優れた耐久性を有し、最適であった。第１の電極膜は、貴金属または酸素イオン伝導性金属酸化物からなる電気伝導性材料を主成分として酸化ビスマスを少なくとも少量含有した組成である。第２の電極膜は、チタンもしくはクロムもしくはジルコニウムの少なくとも１種からなる補助材料と、貴金属もしくは酸素イオン伝導性金属酸化物を主成分とした主材料からなり、少なくとも補助材料は下層に主材料は上層に配置され気相析出法で形成される組成である。これら材料組成の電極膜が優れた耐久性を有する理由は、水素系燃料ガスを燃焼させた場合に時折発生する極微量の未然水素系燃料ガスに対して、これら材料が優れた耐久信頼性を有するためと思われる。
【００５７】
（実施例２）
実施例２は、燃焼部１３で燃焼させるための炭化水素系燃料の供給方法について検討した。本発明は、燃料改質装置１０に供給される炭化水素系燃料の供給管を分岐して、燃焼部１３にも供給する様にしている。そして、燃焼初期は燃焼部１３だけに炭化水素系燃料を供給して燃焼させ、燃料改質装置１０を加熱して水蒸気改質反応が起こる温度まで昇温する様にした。その後、燃料改質装置１０が所定温度まで昇温されると、燃料改質装置１０にも炭化水素系燃料を供給して水蒸気改質反応を起こさせて水素リッチな燃料ガスを生成され、燃料電池１１の燃料極１２から排出される未使用の水素系燃料ガスを燃焼させる様にした。このことで、使用エネルギーを低減するとともに効果的に水蒸気改質反応が行われるようにした。なお、燃料改質装置１０が所定温度まで昇温された後の燃料は、必要に応じて、未使用の水素系燃料ガスと炭化水素系燃料とを混合してもよい。
【００５８】
（実施例３）
実施例３は、燃料改質装置１０の温度を制御するために、燃焼部１３にさらに混合する炭化水素系燃料およびその対応空気の供給方法について検討した。
【００５９】
本発明は、燃料改質装置１０もしくはその内部に充填された触媒２６の温度を、その近辺に配置した温度センサ２７が検知し、予め記憶させた温度になるように、制御部２５が、燃焼部１３にさらに供給される炭化水素系燃料量およびその対応空気量を増減させて温度制御する様にしている。つまり、水蒸気改質反応が最適温度で起こる様に、制御部２５が、炭化水素系燃料量をさらに混合してその量を増減させ、対応する空気量も最適な空気過剰率となる様に増減する訳である。このことで、使用エネルギーを低減するとともに効果的に水蒸気改質反応が行われるようにした。
【００６０】
（実施例４）
実施例４は、燃焼部１３で燃焼させるための空気の供給方法について検討した。本発明は、燃焼部１３に供給される燃料の概略値に従って、空気供給手段２４によって燃焼部に供給される空気は、予め想定された概略量が最初は供給され、その後、酸素センサ１５による酸素濃度信号によりその細部補正量が供給される様にした。つまり、例えばまず、制御部２５が、燃料電池１１の発電量から燃焼部１３に供給される水素系燃料の概略値を、予め設定した発電量と水素系燃料の相関特性に従って算出する。そして、この燃料概略値に対応する空気概略値を、予め設定した水素系燃料量と供給空気量の相関特性に従い、空気供給手段２４が最初は供給する。その後暫くしてから、制御部２５は、酸素センサ１５による酸素濃度信号により補正された空気量を、空気供給手段２４の送風量補正によって供給する次第である。燃料電池の発電電力の変化に伴い、燃料使用量が変化してもそれに対応する空気量が瞬時に供給されるため、良好な燃焼状態が維持でき、効果的に水蒸気改質反応が行われる。また、応答性の遅い酸素センサ１５でも使用できる利点も有る。
【００６１】
（実施例５）
実施例５は、酸素センサ１５による空気供給手段２４の補正修整方法について検討した。酸素センサ１５は、その動作駆動と燃焼排ガス中酸素濃度の制御を間欠的に行い、そのたびごとに燃焼部に空気を供給する空気供給手段２４を制御部２５が補正修整する様にした。このことにより、酸素センサ１５の寿命が向上するとともに、良好な燃焼状態維持と効果的な水蒸気改質反応が長期間にわたって行われる様にした。
【００６２】
（実施例６）
実施例５は、酸素センサ１５を排ガス流路１４中に配置する場所について検討した。酸素センサ１５は、排ガス中水分が結露してセンサのリード線を短絡させることを防止する目的で、排ガス温度が１１０℃以上の場所に配置するとした。また、配置温度の上限は、排ガスでセンサが劣化することを防止する目的で、センサ動作温度以下である排ガス温度の場所とした。このことにより、酸素センサ１５が常に正常に動作するとともに、良好な燃焼状態維持と効果的な水蒸気改質反応が長期間にわたって行われる様にした。
【００６３】
（実施例７）
実施例７は、酸素センサ１５の誤動作を防止する制御システムについて検討した。
【００６４】
この燃焼システムは、システム全体の動作状態を制御する制御手段２５に、燃焼部１３の燃焼運転動作の有無を判断する燃焼運転判断手段２８と、酸素センサ１５で検出されたセンサ出力が正常か異常かを判断するセンサ出力異常判断手段２９が接続されている。さらにセンサ出力異常判断手段２９には、センサ出力が異常と判断された場合に作動して警報を発する警報発生手段３０とが接続されている。
【００６５】
図２は、本発明の実施例である燃焼システムの動作を示す制御流れ図である。
スタートのボタンが押されると燃焼システムが起動して、炭化水素系燃料が供給管から供給されるとともに、空気供給手段２４が始動して燃焼部１３が燃焼を始め、酸素センサ１５の駆動が始まる。そして、所定時間（ｔ）が経過すると燃焼状態およびセンサ出力が安定するので、燃焼運転判断手段２８は、燃焼部１３に設置された火炎検出装置などの検出手段（記載せず）の燃焼信号による燃焼動作状態などを確認しにゆき、燃焼運転動作の有無の判断を行う。
【００６６】
燃焼運転中と判断されると、燃焼排ガスに晒された際のセンサ出力（Ａ）が読み取られ、このセンサ出力（Ａ）と、予め記憶されたセンサ出力（I）および（II）の比較がなされる。一方、燃焼運転動作が停止と判断された場合、燃焼システムの再起動が始まる。
【００６７】
そして、I≦Ａ≦IIならセンサ出力（Ａ）は正常と判断され、燃焼運転判断手段２８が燃焼停止信号を受けて燃焼停止と判断を行うまで、この作業は繰り替える。一方、II＜ＡもしくはI＞Ａならセンサ出力（Ａ）は異常と判断され、警報発生手段３０が警報を発する。予め記憶されたセンサ出力（I）および（II）は、良好な燃焼状態の燃焼排ガス中に晒された際のセンサ出力の下限値と上限値である。そのため、センサ出力（Ａ）が、この範囲中に有ることは一酸化炭素生成量が少ない良好な燃焼状態であると同時に、酸素センサが正常動作していることを意味する。一方、センサ出力（Ａ）がこの範囲外に有ることは、燃焼部は一酸化炭素生成量が多い異常燃焼状態もしくは、酸素センサの劣化を意味する。センサ出力（Ａ）が正常と判断されると、空燃比制御もしくは酸素濃度監視が行われる。空燃比制御を行う場合、予め設定した目標センサ出力値となる様に、空気供給手段２４の制御を行う。
【００６８】
さて、燃焼運転停止のボタンが押されると、制御部２５は燃焼停止と判断するので、燃料供給が停止して燃焼部１３は燃焼停止となるが、空気供給手段２４はさらに運転を継続して、酸素センサ１５に大気を供給する。そして、所定時間（Ｔ）が経過するとセンサ出力が安定するので、大気に晒された際のセンサ出力（Ｂ）が読み取られ、このセンサ出力（Ｂ）と、予め記憶されたセンサ出力（Ｘ）および（Ｙ）の比較がなされる。そして、Ｘ≦Ｂ≦Ｙならセンサ出力（Ｂ）は正常と判断され、燃焼システムは停止して空気供給手段２４と酸素センサ１５はその駆動を停止する。一方、Ｙ＜ＢもしくはＸ＞Ｂセンサ出力（Ｂ）は異常と判断され、警報発生手段３０が警報を発すると同時に前述の燃焼システムの停止を命じる。なお、予め記憶されたセンサ出力（Ｘ）および（Ｙ）は、酸素約２０％の大気に晒された際のセンサ出力の下限値と上限値である。そのため、センサ出力（Ａ）が、この範囲中に有ることは酸素センサが正常動作していることを意味し、この範囲外に有ることは酸素センサが劣化していることを意味する。
【００６９】
警報発生手段３０は、警報を１回発しても、燃焼システムは次回の駆動が正常に行える様にしているが、警報を複数回発するとその旨が燃焼システムの運転状態表示板に表示され、その点検修理を行うことを勧告して、安全性を高める様にした。
【００７０】
（実施例８）
図３は、本発明の燃焼システムで用いる酸素センサとその駆動検出回路の実施例の断面図であり、酸素センサ１５と、これを駆動させそのセンサ出力を検出する制御部２５からなる。
【００７１】
酸素センサ１５は、酸素イオン伝導性固体電解質板３１と、酸素イオン伝導性固体電解質板３１の表面に形成した一対の電極膜３２、３３と、片側の電極膜３２を囲む硝子膜３４を介して接合させた酸素拡散制限体３５とから少なくとも構成される限界電流式酸素センサである。
【００７２】
酸素センサ１５は、酸素イオン伝導性固体電解質板３１の両面に、一対の電極膜３２、３３が厚膜印刷される工程から製造が始まる。この一対の電極膜３２、３３は、貴金属または酸素イオン伝導性金属酸化物からなる電気伝導性材料３６を主成分として、酸化ビスマス３７を少なくとも少量含有した組成であり、厚膜印刷したのち乾燥したまま、または必要によりさらに溶融焼成することで形成される。その後、酸素イオン伝導性固体電解質板３１の片面に硝子膜３４を厚膜印刷したのち、酸素拡散制限体３５の構成部材をその上部に積層し、溶融焼成する。さらに後工程において、貴金属または電気伝導性材料を主成分とし硝子を少量含有した組成のリード線固定部３８、３９を溶融焼成して、一対のリード線４０、４１と一対の電極膜３２、３３を接続して、基本構造が完成する。
【００７３】
本発明の酸素センサ１５を試作して、その効果の確認を行った。
【００７４】
酸素イオン伝導性固体電解質板３１は、イットリウム（Ｙ_２Ｏ_３）の８モル％とジルコニア（ＺｒＯ_２）の９２モル％を固溶化させた安定化ジルコニアの焼成板である。
【００７５】
一対の電極膜３２、３３は、９０ｖｏｌ％の白金からなる電気伝導性材料３６に、１０ｖｏｌ％の酸化ビスマス３７を混合した組成であり、前述の酸素イオン伝導性固体電解質板３１の両面に厚膜印刷される。
【００７６】
酸素拡散制限体３５は、螺旋型形状の硝子膜３４とその上部に積層した焼成フォルステライト製のシ−ル板４２で構成させる。製法について説明する。まず、螺旋型形状の硝子膜３４を、前述の予め酸素イオン伝導性固体電解質板３１に厚膜印刷された電極膜３２の、周囲を囲む様に厚膜印刷する。そして、この厚膜印刷膜の上部にシ−ル板４２を積層して溶融焼成する。すると、酸素イオン伝導性固体電解質板３１とシ−ル板４２が接合され、これらの板および螺旋型形状の硝子膜４２の間に、微小寸法の拡散制限孔（記載せず）が形成される。また同時に、電極膜３２、３３の焼成も行なわれる。
【００７７】
リード線固定部３８、３９は、白金の９０ｖｏｌ％に硝子の１０ｖｏｌ％を混合した組成である。この組成品を７００℃で溶融焼成して、白金からなる一対のリード線４０、４１と、前述の一対の電極膜３２、３３を接続する。そして、この組成品の上に無機接着材を積層して５００℃で硬化させ、リード線の接続を強固にした。
【００７８】
この７００℃焼成は、電極膜３２、３３に混合されている酸化ビスマス３７の融点が８２０℃であり、リード線固定部３８、３９の焼成によって、電極膜３２、３３の物性が影響されないとの観点より、酸化ビスマスの融点８２０℃より１００℃低い温度とした理由に基づく。
【００７９】
なお、シ−ル板には、予め白金のヒータ４３を形成されている。そして、このヒータ４３と、白金からなる一対のヒータ用リード線４４、４５を、ヒータ用リード線固定部４６、４７の７００℃溶融焼成を介して接続した。このヒータ用リード線固定部４６、４７は、白金の９０ｖｏｌ％に硝子の１０ｖｏｌ％を混合した組成品であり、この７００℃溶融焼成は、リード線固定部３８、３９の７００℃溶融焼成と同時に行っている。そして、この組成品の上に無機接着材を積層して５００℃で硬化させ、リード線の接続を強固にした。
【００８０】
制御部２５は、その中に素子駆動用直流電源４８と電流検出部４９とヒータ加熱用直流電源５０を少なくとも備えている。素子駆動用直流電源４８および電流検出部４９は、一対のリード線４０、４１および、一対の電極膜３２、３３と閉回路を構成している。電流検出部４９は、素子駆動用直流電源４８で印加される電圧によって発生する電流値をセンサ出力として検出するものである。一方、ヒータ加熱用直流電源５０は、ヒータ４３および一対のヒータ用リード線４４、４５と閉回路を構成している。
【００８１】
酸素センサ１５の動作原理を説明する。ヒータ加熱用直流電源５０によって電圧が印加させるとヒータ４３が発熱し、酸素イオン伝導性固体電解質板３１が５００℃に加熱される。すると、酸素イオン伝導性固体電解質板３１を酸素イオンが伝導し易くなり、素子駆動用直流電源４８で印加される電圧により下記の酸素ポンピング作用が生じる。つまり、空気中の酸素分子は、酸素拡散制限体３５に設けられた微小寸法の拡散制限孔（記載せず）を経由して電極膜３２に到達した後、電圧印加による電子を授受して酸素イオンとなって酸素イオン伝導性固体電解質板３１を通過し、電極膜３３で電子が奪われて再び酸素分子となって空気中に戻る。この酸素分子の移動によって電流が流れるが、微小寸法の拡散制限孔によって酸素分子の流入が制限され、酸素濃度に対応した酸素量しか流入移動しないため、流れる電流は酸素濃度に比例した関係が得られる。この関係を利用し、電流値から酸素濃度が判別できる訳である。
【００８２】
この酸素センサ１５の排気中における耐久信頼性評価を行なった。耐久信頼性は、ヒータ加熱用直流電源５０による電圧印加によってヒータ４３を加熱して、酸素イオン伝導性固体電解質板３１を５００℃に加熱した状態で行なった。そして、素子駆動用直流電源４８によって電極膜３２、３３に０．５Ｖを印加して、流れる電流の過渡変化を測定した。この印加電圧０．５Ｖは、電流値の電圧依存性が無くなる限界電流特性が得られ始める臨界電圧値であり、電極膜３２、３３の耐久信頼性の良否に起因する電流値の低下度合いが顕著に観察できる電圧値である。
【００８３】
図４（ａ）は、白金からなる電気伝導性材料の９０ｖｏｌ％に酸化ビスマスの１０ｖｏｌ％を混合した組成の電極膜において、初期電流値と電圧印加３００時間後電流を、硝子膜の焼成温度ごとにプロットした図である。図４（ａ）から判る様に、硝子膜３４を８５０〜１０５０℃で焼成した限界電流式の酸素センサは、高い電流値と優れた耐久信頼性を有した。この理由は、硝子膜３４を焼成することで電極膜３２、３３も同時に焼成される訳であるが、電極膜３２、３３は、その中に混合されている酸化ビスマスの融点８２０℃より３０〜２３０℃高い温度で焼成されることで、酸素イオン伝導性固体電解質板３１に強固に密着してその接合抵抗が小さく、電圧印加しても接合抵抗が変化しないため、電流値が変化しないためと思われる。特に、硝子膜３４を８５０〜９７０℃で焼成した酸素センサは、極めて高い電流値と優れた耐久信頼性を示し、最も最適であった。
【００８４】
一方、１０５０℃を超えて焼成した硝子膜３４は、所期電流値が非常に小さいため、限界電流式の酸素センサを構成するに必要な大電流値が確保できず、不適格であった。この理由は、電極膜３２、３３を１１００℃等の高温で焼成したため、その中に混合されている酸化ビスマスと白金が反応して酸素非吸着性の電極膜が得られ、酸素の移動に起因する電流が得られないためである。また、硝子膜３４が流動し過ぎて、電極膜３２を覆ってしまいその面積が低下して電流が小さくなる弊害も生じていた。
【００８５】
また、８５０℃未満で焼成した硝子膜３４も、耐久信頼性が悪く不適格であった。この理由は、電極膜３２、３３を、その中に混合されている酸化ビスマスの融点８２０℃とほぼ同温度もしくはそれ以下で焼成しているため、酸素イオン伝導性固体電解質板３１に電極膜３２、３３が充分に密着できず、電圧印加すると次第に接合抵抗が大きくなるためと思われる。また特に、７５０℃以下で焼成した硝子膜３４は、初期電流値が極端に小さく、一層不適格であった。これは、電極膜の中に混合されている酸化ビスマスの焼成が不充分であるため、酸素イオン伝導性固体電解質板３１に電極膜３２、３３が全く密着せず、その接合抵抗が非常に大きいためである。
【００８６】
図４（ｂ）は、化学組成Ｌａ_１−ｘＳｒｘＣｏＯ_３の酸素イオン伝導性金属酸化物からなる電気伝導性材料の９０ｖｏｌ％に酸化ビスマスの１０ｖｏｌ％を混合した組成の電極膜において、初期電流値と電圧印加３００時間後電流を、硝子膜の焼成温度ごとにプロットした図である。図４（ｂ）から判る様に、硝子膜３４を８５０〜１０５０℃で焼成した限界電流式酸素センサは、高い電流値と優れた耐久信頼性を有した。
【００８７】
以上のことより、限界電流式の酸素センサを構成するに必要な大電流値が確保できしかもその耐久信頼性が優れた硝子膜３４の焼成温度は、８５０〜１０５０℃であり、特に８５０〜９７０℃は極めて高い電流値と優れた耐久信頼性を示して最も最適であった。
【００８８】
酸素イオン伝導性固体電解質板３１は、ジルコニア（ＺｒＯ_２）に少量のイットリウム（Ｙ_２Ｏ_３）を固溶化させたジルコニア系イオン伝導性体、（ＣｅＯ_２）_０．８（ＳｍＯ_１．５）_０．２や（ＣｅＯ_２）_０．８（ＧｄＯ_１．５）_０．２などのイットリウム系イオン伝導性体が使用可能である。これら材料は、その表面粗さＲａが、０．０５〜０．３μｍとなる様に研磨して、電極膜３２、３３が強固に密着する様にした。
【００８９】
電極膜３２、３３に混合される電気伝導性材料は、白金や金さらに銀などの貴金属、化学組成Ｌａ_１−ｘＳｒｘＣｏＯ_３やＬａＣｏＯ_３さらにＬａＭｎＯ_３などの酸素イオン伝導性金属酸化物が使用される。また、電極膜３２、３３に混合される酸化ビスマスは、３〜１５ｖｏｌ％が最適であり、この組成を重量比で表現すると例えば白金の電気伝導性材料の場合、白金の９４〜９９ｗｔ％と酸化ビスマスの１〜６ｗｔ％である。この組成は、結合材である酸化ビスマスが微少だと電極膜が酸素イオン伝導性固体電解質板に密着しないため電流が確保できないこと、半導体である酸化ビスマスが多量だと電極膜が電子不伝導性となり電流が確保できないこと、の観点から実験的に得られる組成である。さらに、電極膜３２、３３には、上記の電気伝導性材料と酸化ビスマス以外に、酸化銅や酸化カドミニウム、ジルコニア（ＺｒＯ_２、もしくは含水Ｚｒ（ＯＨ）_２）を主成分とするゾルゲル液の混合が有効であり、これら金属酸化物系材料は酸化ビスマスとの合計総量において最大２５ｖｏｌ％まで混合可能である。これは、半導体であるこれら金属酸化物系材料と酸化ビスマスが多量だと、電極膜が電子不伝導性となり電流が確保できないこと、の観点から実験的に得られる組成である。
【００９０】
酸素拡散制限体３５は、下記の３構成が使用可能である。第１構成は、拡散制限孔を形成した螺旋型形状の硝子膜３４と、その上部に積層したシ−ル板４２の構成。第２構成は、角状または円状からなる内部中空形状の硝子膜３４と、その上部に積層した微小寸法の拡散制限孔を有する多孔質なシール板４２の構成。第３構成は、角状または円状からなる内部中空形状の硝子膜３４と、その上部に積層した拡散制限孔を形成した複数積層板からなるシール板４２（微小寸法の穴を有するシール板Ａと、拡散制限孔を形成するための螺旋型形状の硝子膜と、シ−ル板Ｂを順々に積層した積層板）の構成。
【００９１】
硝子膜３４は、酸素イオン伝導性固体電解質板３１とその上部に積層したシ−ル板４２と熱膨張係数が±１０％以内で同じであり、その溶融温度が８５０〜１０５０℃特に８５０〜９７０℃が最適であり、この材料だと耐久信頼性に問題が生じなかった。例えば、酸化アルミナが３〜７ｗｔ％、酸化ホウ素が３〜７ｗｔ％、酸化カルシウムが１〜２ｗｔ％、酸化ストロンチウムが４〜６ｗｔ％、酸化バリウムが０．２〜１．５ｗｔ％、酸化ナトリウムが１０〜１３ｗｔ％、酸化カリウムが４〜８ｗｔ％、酸化チタンが６〜９ｗｔ％、残部が酸化珪素の組成品は、特に最適であり本検討実験で使用した。
【００９２】
リード線固定部３８、３９の主成分は、白金や金さらに銀などの貴金属、化学組成ＹＢａＣｕ_３Ｏ_７などが使用される。そして、この貴金属または電気伝導性金属酸化物の８５〜９７ｖｏｌ％に、硝子の３〜１５ｖｏｌ％が混合される。
【００９３】
（実施例９）
電極膜３２、３３と硝子膜３４を同時焼成した酸素センサ１５は、得られる初期電流値がばらつく課題がある。そこで、実施例９は、電極膜３２、３３を予め焼成した後に硝子膜３４を焼成する製法を採用し、初期電流値のばらつき低減が図れる電極膜３２、３３の焼成温度について検討した。検討は、下記記載の２点以外は、実施例８の場合と同じである。実施例８と異なる１点目は、安定化ジルコニアの酸素イオン伝導性固体電解質板３１に、焼成温度を異ならせて予め電極膜３２、３３を焼成した後、硝子膜３４をその最適焼成温度９２０℃で焼成したことである。異なる２点目は、同一製法の限界電流式の酸素センサ１５を５個試作し、その初期値のバラツキを測定したことである。
【００９４】
図５は、電極膜の焼成温度と初期電流値の関係を測定した特性図であり、５個試作における最大値と平均値と最低値をパラメータにして整理している。図５（ａ）は、白金からなる電気伝導性材料の９０ｖｏｌ％に酸化ビスマスの１０ｖｏｌ％を混合した組成の電極膜である。図５（ｂ）は、化学組成Ｌａ_１−ｘＳｒｘＣｏＯ_３の酸素イオン伝導性金属酸化物からなる電気伝導性材料の９０ｖｏｌ％に酸化ビスマスの１０ｖｏｌ％を混合した組成の電極膜である。
【００９５】
図５から判る様に、電極膜を７７０〜９５０℃で予め焼成した酸素センサは、全体的に高い電流値を維持することがわかる。一方、９５０℃を超えた焼成は、全体的に電流値が低下しており不適格であった。これは、電極膜が、後工程の硝子膜９２０℃焼成により再焼成されるため、その中に混合されている酸化ビスマスと白金が反応して酸素非吸着性の電極膜が得られ、酸素の移動に起因する電流が得られにくくなるためである。また、７７０℃未満の焼成は、得られる初期電流値がばらつき、不適格であった。これは、電極膜は、最初の焼成においてはその中に混合されている酸化ビスマスの焼成が不充分であるため酸素イオン伝導性固体電解質板に密着しない状態となっており、後工程の硝子膜９２０℃焼成により再焼成されるため、その密着性にばらつきが生じるためと思われる。
【００９６】
以上のことより、電流値のばらつきが小さい限界電流式酸素センサを製造するために、電極膜を予め７７０〜９５０℃で焼成した後に硝子膜を焼成する製法とした。また、この限界電流式酸素センサは、耐久信頼性が優れる利点も有る。
【００９７】
この結果は、電気伝導性材料として、白金や金さらに銀などの貴金属、化学組成Ｌａ_１−ｘＳｒｘＣｏＯ_３やＬａＣｏＯ_３さらにＬａＭｎＯ_３などの酸素イオン伝導性金属酸化物が使用され、酸化ビスマスが３〜１５ｖｏｌ％混合された電極膜３２、３３でも、同様であった。
【００９８】
（実施例１０）
硫黄酸化物が多量含まれる燃焼排ガスに長期間晒されると、酸素センサ１５の電極膜３２、３３は、その値が徐々に小さくなって耐久信頼性が低下する課題がある。そこで、実施例１０は、ジルコニアを主成分とするゾルゲル液に予め浸漬された酸化ビスマス３７を含有する電極膜３２、３３を使用し、硫黄酸化物が多量含まれる燃焼排ガスに長期間晒されても、電流低下の少ない酸素センサ１５の実現を試みた。検討は、下記記載の２点以外は、実施例８および実施例９の場合と同じである。実施例８および実施例９と異なる１点目は、安定化ジルコニアの酸素イオン伝導性固体電解質板３１に、ジルコニア（ＺｒＯ_２）を主成分とするゾルゲル液に予め浸漬された酸化ビスマス３７を含有する電極膜３２、３３を予め８２０℃で焼成した後、硝子膜３４をその最適焼成温度９２０℃で焼成したことである。実施例８および実施例９と異なる２点目は、この酸素センサ１５の耐久信頼性評価を、硫黄酸化物が２０ｐｐｍ含まれる排気中で行って流れる電流の過渡変化を測定したことである。
【００９９】
発明１は、白金からなる電気伝導性材料の９０ｖｏｌ％に、ジルコニアを主成分とするゾルゲル液に予め浸漬された酸化ビスマスの１０ｖｏｌ％を混合した組成の電極膜である。発明２は、化学組成Ｌａ_１−ｘＳｒｘＣｏＯ_３の酸素イオン伝導性金属酸化物からなる電気伝導性材料の９０ｖｏｌ％に、ジルコニアを主成分とするゾルゲル液に予め浸漬された酸化ビスマスの１０ｖｏｌ％を混合した組成の電極膜である。一方、比較１は、白金からなる電気伝導性材料の９０ｖｏｌ％に、酸化ビスマスの１０ｖｏｌ％を混合した組成の電極膜である。発明２は、化学組成Ｌａ_１−ｘＳｒｘＣｏＯ_３の酸素イオン伝導性金属酸化物からなる電気伝導性材料の９０ｖｏｌ％に、酸化ビスマスの１０ｖｏｌ％を混合した組成の電極膜である。（表２）にその検討結果を示す。
【０１００】
【表２】

【０１０１】
本発明品は、優れた耐久特性を有することがわかる。この理由は、ジルコニアを主成分とするゾルゲル液に予め浸漬された酸化ビスマスが、硫黄酸化物を吸収除去し、主成分の電気伝導性材料の劣化を抑制するためと思われる。
【０１０２】
ジルコニアを主成分とするゾルゲル液は、ジルコニア（ＺｒＯ_２）の単独ゾルゲル溶液、ジルコニアが６０部以上含有されておりシリカ（ＳｉＯ_２）などの他酸化物が残部で存在するゾルゲル溶液、が有効であった。また、含水Ｚｒ（ＯＨ）_２と表示される溶液もジルコニアゾルゲル溶液と呼ばれていて有効であり、前述組成のゾルゲル溶液が効果有った。ゾルゲル液に予め浸漬された酸化ビスマスを電極膜に混合する方法は、次の２方法が有る。第１方法は、このゾルゲル液を、白金など電気伝導性材料と酸化ビスマスを混合して電極膜の印刷ペーストを調合する際に、印刷ペーストに混合して酸化ビスマスに浸漬する方法である。第２方法は、予めゾルゲル液に浸漬した酸化ビスマスを使用して、電極膜の印刷ペーストを調合する方法である。
【０１０３】
（実施例１１）
酸素センサ１５の酸素拡散制限体３５は、高度な気密シールを必要とするため、その製法に厳密な管理を必要とする。そのため厳密な管理を必要とする酸素拡散制限体３５の形成と、複雑な製法を必要とするリード線の固定を同一工程で実施することは、複雑な製法と厳密な管理と必要とし、実用的でない。そこで、実施例１１は、酸素拡散制限体３５を形成した後に、リード線を固定する製法を採用した際の、リード線を固定するための焼成温度について検討した。
【０１０４】
図４および図５より判る様に、電極膜は、７５０℃未満で焼成すると焼成不充分となり、発生電流値が非常に小さくなる。そこで、リード線の焼成上限は７５０℃として、その焼成によって、電極膜が再溶解してその電流値に影響を与えられない様にした。一方、電極膜に混合されている酸化ビスマスは、６５０℃で結晶構造が大きく変化し始める挙動を示すので、電極膜の耐久信頼性確保の観点から、動作温度は６５０℃を超えない様にする必要が有る。そこで、リード線の焼成は、結晶構造が変化し始める６５０℃以上とし、電極膜の動作温度を６５０℃以下とすることで、耐久信頼性に影響を与えられない様にした。
【０１０５】
以上のことより、その電流値および耐久信頼性が優れた限界電流式酸素センサを製造するために、硝子膜を溶融焼成した後、リード線を最大６５０〜７５０℃で焼成して電極膜に固定する製法とした。
【０１０６】
（実施例１２）
実施例１２は、リード線固定部３８、３９の材質について検討した。
【０１０７】
貴金属または電子伝導性金属酸化物を主成分として硝子を少なくとも少量含有した組成品だけでは、接着強度が不充分であり、センサ素子の取り扱い作業中にリード線を強く引っ張ったりするとリード線外れが生じるためである。そのため、慎重な取り扱いが必要とされ、作業性や生産性が悪い課題があった。
【０１０８】
その点、リード線固定部３８、３９は、貴金属または電子伝導性金属酸化物を主成分として硝子を少なくとも少量含有した組成品と、この組成品の上部に積層した硝子もしくは無機接着材とすると、接着強度の優れたリード線固定部となり、リード線を強く引っ張ったりしてもリード線外れが生じなかった。そのため、通常の取り扱いで充分であり、作業性や生産性が大幅に向上した。
【０１０９】
（実施例１３）
気相析出法で形成される貴金属もしくは酸素イオン伝導性金属酸化物の電極膜は、酸素イオン伝導性固体電解質板に初期は良好に密着するため、良好な電流特性を示すが、電流印加に起因する耐久信頼特性に乏しい課題が有る。そこで、実施例１３は、耐久信頼性に優れた酸素センサを得るためのこの種の電極膜の材料について構成した。
【０１１０】
図６は本発明の他実施例である製造を用いた酸素センサとその駆動検出回路の断面図である。この酸素センサ１５に関し、図３との相違点のみ説明する。電極膜５１、５２は、チタンもしくはクロムもしくはジルコニウムの少なくとも１種からなる補助材料５３と、貴金属もしくは酸素イオン伝導性金属酸化物を主成分とした主材料５４からなる。そして、少なくとも補助材料５３は下層に、主材料５４は上層に配置され、気相析出法で形成される。
【０１１１】
本発明の酸素センサを試作して、その効果の確認を行った。実施例８との相違点と材料に関する重要事項のみ記載する。酸素イオン伝導性固体電解質板３１は、イットリウム（Ｙ_２Ｏ_３）の８モル％とジルコニア（ＺｒＯ_２）の９２モル％を固溶化させた安定化ジルコニアの焼成板である。この酸素イオン伝導性固体電解質板３１に、スパッタ法を用いて、チタンもしくはクロムもしくはジルコニウムの少なくとも１種からなる補助材料５３の０．０１μｍ膜厚を下層に、貴金属もしくは酸素イオン伝導性金属酸化物を主成分とした主材料５４の０．５μｍを上層にした構成の電極膜５１、５２を形成した。
【０１１２】
その耐久信頼性決果を（表３）に示す。
【０１１３】
【表３】

【０１１４】
チタンもしくはクロムもしくはジルコニウムの少なくとも１種からなる補助材料５３を下層に、貴金属もしくは酸素イオン伝導性金属酸化物を主成分とした主材料５４を上層にした電極膜５１、５２は、優れた耐久特性を有することが分かる。なお、補助材料５３の膜厚は０．００３〜０．０４μｍ、主材料５４の膜厚は０．３〜１．０μｍが最適であり、スパッタ法やＥＢ法などの気相析出法で形成される。また、補助材料５３と主材料５４は混合物として良い。
【０１１５】
貴金属もしくは酸素イオン導電性金属酸化物を主成分とした主材料５４は、白金や金さらに銀などの貴金属、化学組成Ｌａ_１−ｘＳｒｘＣｏＯ_３やＬａＣｏＯ_３さらにＬａＭｎＯ_３などの酸素イオン伝導性金属酸化物が使用される。
【０１１６】
酸素イオン伝導性固体電解質板３１は、ジルコニア（ＺｒＯ_２）に少量のイットリウム（Ｙ_２Ｏ_３）を固溶化させたジルコニア系イオン伝導性体、（ＣｅＯ_２）_０．８（ＳｍＯ_１．５）_０．２や（ＣｅＯ_２）_０．８（ＧｄＯ_１．５）_０．２などのイットリウム系イオン伝導性体が使用可能である。これら材料は、その表面粗さＲａが、０．０５〜０．３μｍとなる様に研磨して、電極膜５１、５２が強固に密着する様にした。
【０１１７】
（実施例１４）
実施例１４は、一層耐久信頼性に優れた限界電流式酸素センサを得るため、実施例１３で使用する電極膜５１、５２の結晶構造について検討した。
【０１１８】
本発明の酸素センサ１５を試作して、その効果の確認を行った。実施例１３との相違点は、スパッタ条件を異ならせて、貴金属もしくは酸素イオン伝導性金属酸化物を主成分とした主材料５４の結晶構造を変化させ、Ｘ線回折機器で解析した際に主ピークに配向した結晶構造が得られる様に、電極膜５１、５２をしたことである。その耐久信頼性決果を（表４）に示す。
【０１１９】
【表４】

【０１２０】
主材料５４が主ピークに配向した結晶構造の電極膜５１、５２は、優れた耐久性を有することが分かる。
【０１２１】
（実施例１５）
実施例１５は、一層耐久信頼性に優れた酸素センサを得るため、暖気ウオーミング時の加熱駆動方法について検討した。
【０１２２】
本発明の酸素センサとこのセンサを加熱駆動する駆動検出回路を試作して、その効果の確認を行った。検討は、下記記載の２点以外は、実施例８〜１５の場合と同じである。異なる１点目は、酸素センサ１５の酸素拡散制限体３５に併設したヒータ４３を、印加電圧値を階段状に印加させるヒータ加熱用直流電源５０により、暖気ウオーミング時は温度を階段状に上昇されたことである。異なる２点目は、この駆動検出回路の耐久信頼性評価を、５分間加熱通電と５分間非加熱通電の間欠駆動で行い、流れる電流の過渡変化を測定したことである。
【０１２３】
発明品は、５００℃加熱に必要な所定電圧をヒータ加熱用直流電源５０によりヒータ４３に５分間印加するに際し、１分間はその５０％値印加し残り４分間はその１００％値を印加する加熱通電モードであり、約３分で５００℃に到達した。そして、この５分間加熱通電（電源ＯＮ）と５分間非加熱通電（電源ＯＦＦ）の間欠駆動を行った。一方、比較品は、５００℃加熱に必要な所定電圧をヒータ４３に５分間印加するに際し、５分間その１００％値を印加する加熱通電モードであり、約２分で５００℃に到達した。そして、この５分間加熱通電（電源ＯＮ）と５分間非加熱通電（電源ＯＦＦ）の間欠駆動を行った。
【０１２４】
発明１および比較１は、白金からなる電気伝導性材料の９０ｖｏｌ％に、ジルコニウムを主成分とするゾルゲル液に予め浸漬された酸化ビスマスの１０ｖｏｌ％を混合した組成の電極膜３２、３３である。発明２および比較２は、化学組成Ｌａ_１−ｘＳｒｘＣｏＯ_３の酸素イオン伝導性金属酸化物からなる電気伝導性材料の９０ｖｏｌ％に、ジルコニウムを主成分とするゾルゲル液に予め浸漬された酸化ビスマスの１０ｖｏｌ％を混合した組成の電極膜３２、３３である。発明３および比較３は、クロムの補助材料５３の０．０１μｍ膜厚を下層に、白金の主材料５４の０．５μｍを上層にした構成の電極膜５１、５２である。発明４および比較４は、チタンの補助材料５３の０．０１μｍ膜厚を下層に、化学組成Ｌａ_１−ｘＳｒｘＣｏＯ_３の酸素イオン伝導性金属酸化物５４の０．５μｍを上層にした構成の電極膜５１、５２である。発明５および比較５は、ジルコニウムの補助材料５３の０．０１μｍ膜厚を下層に、配向したＬａ_１−ｘＳｒｘＣｏＯ_３の酸素イオン伝導性金属酸化物５４の０．５μｍを上層にした構成の電極膜５１、５２である。
【０１２５】
その耐久信頼性決果を（表５）に示す。
【０１２６】
【表５】

【０１２７】
ヒータはその温度を階段状に上昇させて加熱駆動されるので、電極膜は、緩やかに温度上昇して熱衝撃が低減し、剥離して電流が低下することが防止される。
そのため、耐久信頼性を向上させた限界電流式酸素センサが得られる。
【０１２８】
【発明の効果】
以上のように、請求項１記載の燃料電池システムは、水結露手段により液滴を除去された水素系燃料ガスが燃焼部に導入され、酸素センサにより最適な空気過剰率に保持された状態で、燃焼部が燃料改質装置を加熱する様にしている。
さらに、燃焼部の一酸化炭素生成量が多い異常燃焼状態もしくは、酸素センサの劣化を検知することができる。
【図面の簡単な説明】
【図１】 本発明の実施例１における燃料改質装置と燃料電池を備えた燃焼システムの構成図
【図２】 本発明の実施例７における燃料改質装置と燃料電池を備えた燃焼システムの動作を示す制御フローチャート
【図３】 本発明の実施例８における製造方法を用いた酸素センサとその駆動検出回路の構成図
【図４】 本発明の実施例８における製造方法を用いた酸素センサの効果特性図（硝子膜の焼成温度と電流の関係）
（ａ）白金と酸化ビスマスからなる電極膜の効果特性図
（ｂ）Ｌａ_１−ｘＳｒｘＣｏＯ_３と酸化ビスマスからなる電極膜の効果特性図
【図５】 本発明の実施例８である製造方法を用いた酸素センサの効果特性図（電極膜の焼成温度と電流の関係）
（ａ）白金と酸化ビスマスからなる電極膜の効果特性図
（ｂ）Ｌａ_１−ｘＳｒｘＣｏＯ_３と酸化ビスマスからなる電極膜の効果特性図
【図６】 本発明の実施例１３における製造方法を用いた酸素センサとその駆動検出回路の構成図
【図７】 従来の燃料改質装置と燃料電池を備えた燃焼システムの構成図
【符号の説明】
１０ 燃料改質装置
１１ 燃料電池
１２ 燃料極
１３ 燃焼部
１４ 排ガス流路
１５ 酸素センサ
１６ 燃料極排ガス流路
１７ 水結露手段
２４ 空気供給手段
２５ 制御部
２６ 触媒
２８ 燃焼運転判断手段
２９ センサ出力異常判断手段
３０ 警報発生手段
３１ 酸素イオン伝導性固体電解質板
３２、３３ 電極膜
３４ 硝子膜
３５ 酸素拡散制限体
３６ 電気伝導性材料
３７ 酸化ビスマス
３８、３９ リード線固定部
４０、４１ リード線
４２ シール板
４３ ヒータ
５０ ヒータ加熱用直流電源
５１、５２ 電極膜
５３ 補助材料
５４ 主材料[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to a fuel cell system including a fuel reformer and a fuel cell, and in particular, improves the energy efficiency of the system by efficiently reforming a hydrocarbon-based fuel into a hydrogen-rich fuel following load fluctuations. To letObjective.
[0002]
[Prior art]
A fuel cell system including a fuel reformer and a fuel cell has been proposed, and its configuration is shown in FIG. This combustion system includes a reforming unit 1 that generates a reformed gas containing hydrogen from a hydrocarbon-based fuel by using a steam reforming reaction and a partial oxidation reaction, and a fuel that generates electricity by receiving supply of hydrogen and oxygen. Battery 2, reformed gas flow path 3 that guides reformed gas from reformer 1 to fuel cell 2, and oxygen electrode that guides gas discharged from oxygen electrode 4 side of fuel cell 2 to reformer 1 Exhaust gas flow path 5, fuel electrode exhaust gas flow path 8 for guiding the gas discharged from the fuel electrode 6 side of the fuel cell 2 to the fuel section 7, and the reforming section 1 using the combustion gas generated in the fuel section 7 as a medium It is comprised from the heat-transfer part 9 which conveys heat to (for example, refer patent document 1).
[0003]
On the other hand, a limiting current type oxygen sensor is used as an oxygen sensor, and a combustion system using this oxygen sensor has been proposed. In this combustion system, a limiting current type oxygen sensor is disposed in a combustion exhaust gas passage for discharging combustion exhaust gas, and the oxygen concentration in the combustion exhaust gas is controlled to a predetermined concentration (see, for example, Patent Document 2).
[0004]
Next, the oxygen sensor will be described. The electrode used in the limiting current type oxygen sensor is obtained by baking a composition in which 1.5 to 5 wt% of bismuth oxide and a minute amount of cadmium oxide are mixed with platinum as a main component at 700 to 1100 ° C. (for example, And Patent Document 3).
[0005]
Further, there is a titanium thin film as a material for bonding the platinum thin film heater to the ceramic plate, and a technique for bonding the platinum thin film heater to the ceramic plate through the titanium thin film is known (for example, Non-Patent Document 1). reference).
[0006]
[Patent Document 1]
JP 2002-289245 A
[Patent Document 2]
JP 05-164322 A
[Patent Document 3]
JP-A-10-170476 (first page, FIG. 1, FIG. 10)
[Non-Patent Document 1]
Noriko Hanzawa “Pt / Ti / SiO heat-treated in various atmospheres₂/ AL₂O₃"Multilayer structure and temperature coefficient of resistance" Surface Technology, Vol. 53, no. 5, 2002, P346-353
[0007]
[Problems to be solved by the invention]
Heating the reforming unit 1 described in the prior art, which burns unused hydrogen-rich fuel gas discharged from the fuel electrode 6 side of the fuel cell 2 in the combustion unit 7 and generates hydrogen-rich fuel gas from the combustion gas Can be efficiently reformed into a hydrogen-rich fuel by simply combining the method to control the oxygen concentration in the flue gas from the combustion section and controlling the oxygen concentration to a predetermined level. Therefore, there was a problem that the energy efficiency of the combustion system was not improved. The reason for this is that steam residue (droplets) when the steam reforming reaction is performed in the reforming unit 1 is mixed in unused hydrogen-rich fuel gas discharged from the fuel electrode 6 side of the fuel cell 2. Therefore, the combustion section 7 is not good in combustion characteristics, and the reaction temperature in the reforming section 1 is lowered, so that the hydrocarbon-based fuel cannot be efficiently reformed into a hydrogen-rich fuel.
[0010]
  The present invention solves the above-described conventional problems and improves both the combustion characteristics of the combustion section and the steam reforming reaction characteristics of the fuel reformer.As well as excellent safetyFuel cell systemPurpose to provideAnd
[0011]
  The present inventionFuel cell system according toIs,In order to solve the above problems, a fuel reformer that reforms a hydrocarbon-based fuel into a hydrogen-rich fuel gas by a steam reforming reaction;
Generated by the fuel reformerSaid burnedA fuel cell using a feed gas as a raw material gas,
Discharged from the fuel electrode side of the fuel cell.The fuelBurning the gas,Its burningofA combustion section for heating the fuel reformer with exhaust gas heat;
Arranged in the exhaust gas flow path of the combustion sectionAnd in the exhaust gas flow pathIn exhaust gasofOxygen concentrationAn oxygen sensor for detecting
The amount of supplied air is controlled based on the signal from the oxygen sensorcontrolAnd
in frontDischarged from the fuel electrode side of the fuel cellThe fuelThe fuel electrode exhaust gas flow path for supplying the gas to the combustion sectionAs well as,In the fuel electrode exhaust gas flow pathWater condensation means to condense water vapor in fuel gas into waterWhen,
Theat leastPreparation,
The controller is connected to combustion operation determining means for determining whether or not the combustion operation of the combustion section is present, and sensor output abnormality determining means for determining whether the sensor output detected by the oxygen sensor is normal or abnormal. And
The sensor output abnormality determining means is connected to an alarm generating means that operates when a sensor output of the oxygen sensor is determined to be abnormal and issues an alarm,
The sensor output abnormality determining means includes a sensor output (A) of the oxygen sensor when the combustion operation determining means determines that combustion is being performed in the combustion section, and the combustion operation determining means is the combustion section. Read the sensor output (B) of the oxygen sensor when it is determined that combustion is not performed,
When the sensor output abnormality determining means determines that at least one of the sensor output (A) or the sensor output (B) indicates an abnormal value, the alarm generating means issues an alarm..
[0012]
  The fuel reformer effectively performs the steam reforming reaction by introducing the hydrogen-based fuel gas from which droplets have been removed by the water condensation means and maintaining the optimum excess air ratio by the oxygen sensor. The temperature is maintained, and stable combustion and high reforming efficiency are obtained. further,It is possible to detect an abnormal combustion state in which the amount of carbon monoxide produced in the combustion section is large or the deterioration of the oxygen sensor.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
The present invention can be implemented in the form of the invention described in each claim.
[0014]
  That is, the invention according to claim 1 is a fuel reformer that reforms a hydrocarbon-based fuel into a hydrogen-rich fuel gas by a steam reforming reaction;
Generated by the fuel reformerSaid burnedA fuel cell using a feed gas as a raw material gas,
Discharged from the fuel electrode side of the fuel cell.The fuelBurning the gas,Its burningofA combustion section for heating the fuel reformer with exhaust gas heat;
Arranged in the exhaust gas flow path of the combustion sectionAnd in the exhaust gas flow pathIn exhaust gasofOxygen concentrationAn oxygen sensor for detecting
The amount of supplied air is controlled based on the signal from the oxygen sensorcontrolAnd
in frontDischarged from the fuel electrode side of the fuel cellThe fuelThe fuel electrode exhaust gas flow path for supplying the gas to the combustion sectionAs well as,In the fuel electrode exhaust gas flow pathWater condensation means to condense water vapor in fuel gas into waterWhen,
Theat leastPreparation,
The controller is connected to combustion operation determining means for determining whether or not the combustion operation of the combustion section is present, and sensor output abnormality determining means for determining whether the sensor output detected by the oxygen sensor is normal or abnormal. And
The sensor output abnormality determining means is connected to an alarm generating means that operates when a sensor output of the oxygen sensor is determined to be abnormal and issues an alarm,
The sensor output abnormality determining means is configured such that the combustion operation determining means performs combustion in the combustion section. A sensor output (A) of the oxygen sensor when it is determined to be, and a sensor output (B) of the oxygen sensor when the combustion operation determining means determines that combustion is not being performed in the combustion section, reading,
When the sensor output abnormality determining means determines that at least one of the sensor output (A) or the sensor output (B) indicates an abnormal value, the alarm generating means issues an alarm.Fuel cell systemIt is.
[0015]
  The fuel reformer effectively performs the steam reforming reaction by introducing the hydrogen-based fuel gas from which droplets have been removed by the water condensation means and maintaining the optimum excess air ratio by the oxygen sensor. The temperature is maintained, and stable combustion and high reforming efficiency are obtained.Furthermore, it is possible to detect an abnormal combustion state in which the amount of carbon monoxide produced in the combustion section is large or the deterioration of the oxygen sensor.
[0018]
  Claim2In the fuel cell system according to claim 1, the control unit detects the temperature of the fuel reformer or the catalyst charged therein, and sets the temperature of the combustion unit so that the temperature is stored in advance. It is assumed that the temperature is controlled by arbitrarily mixing hydrocarbon fuel and increasing or decreasing the amount and the corresponding air amount.
[0019]
In order for the steam reforming reaction to occur at the optimum temperature, the control unit further mixes the hydrocarbon fuel amount to increase or decrease the amount, and the corresponding air amount also increases or decreases to achieve the optimal excess air ratio. The steam reforming reaction is effectively performed while reducing the energy used.
[0020]
  ClaimTo 3In the fuel cell system according to claim 1, the control unit is preliminarily assumed in advance according to the approximate value of the fuel supplied to the combustion unit, the air supplied to the combustion unit by the air supply means An approximate amount was supplied, and after a while, the detailed correction amount was supplied by an oxygen concentration signal from an oxygen sensor.
[0021]
An approximate air value corresponding to the approximate fuel value is initially supplied in accordance with a predetermined correlation characteristic between the hydrogen fuel amount and the supply air amount, and after a while, the air amount corrected by the oxygen concentration signal from the oxygen sensor is calculated. I am trying to supply. For this reason, even if the amount of fuel used changes with the change in the power generated by the fuel cell, the corresponding amount of air is instantaneously supplied, so that a good combustion state can be maintained and the steam reforming reaction can be carried out effectively. Is called. There is also an advantage that an oxygen sensor having a slow response can be used.
[0022]
  Claim4In the fuel cell system according to claim 1, the oxygen sensor intermittently performs the operation drive and the control of the oxygen concentration in the combustion exhaust gas by the operation of the oxygen sensor. The air supply means for supplying air was corrected and modified.
[0023]
The oxygen sensor intermittently controls its operation drive and oxygen concentration in the combustion exhaust gas, and corrects and corrects the air supply means for supplying air to the combustion section each time. Maintenance of the combustion state and effective steam reforming reaction are performed over a long period of time.
[0024]
  ClaimTo 5According to the present invention, in the fuel cell system according to the first aspect, the oxygen sensor is disposed at a location where the exhaust gas temperature in the exhaust gas flow path is 110 ° C. or more and the sensor operating temperature or less.
[0025]
The oxygen sensor is placed in a place where the exhaust gas temperature is 110 ° C. or higher for the purpose of preventing moisture in the exhaust gas from condensing and short-circuiting the sensor lead wire, and the upper limit of the placement temperature is deteriorated by the exhaust gas. In order to prevent this, the exhaust gas temperature is lower than the sensor operating temperature. As a result, the oxygen sensor operates normally over a long period of time, while maintaining a good combustion state and an effective steam reforming reaction over a long period of time.
[0026]
  Claim6The described invention is the fuel cell system according to claim 1,Air supply means for supplying air to the combustion section;
The air supply means continues to operate even after combustion in the combustion section stops,
The sensor output abnormality determination means reads the sensor output (B) of the oxygen sensor after a predetermined time has elapsed from the stop of combustion in the combustion section, and the alarm is generated when the sensor output (A) indicates an abnormal value. When the means issues an alarm and the sensor output (B) indicates an abnormal value, the alarm generating means issues an alarm.
[0027]
  The sensor output (A) when exposed to combustion exhaust gas with an oxygen concentration of 5 to 10% is read, and if it is within a predetermined range, it can be determined that the combustion operation is a normal combustion operation that burns in the correct oxygen concentration range. Therefore, the combustion operation can be determined as an abnormal combustion operation in which combustion is performed in different oxygen concentration regions, so that it is possible to easily check the combustion state. Further, the sensor output (B) when exposed to the atmosphere having an oxygen concentration of about 20% is read, and the oxygen sensor can be determined to be in a normal operation if it is within the predetermined region, and the oxygen sensor can be determined to be in an abnormal operation if it is outside the predetermined region. Oxygen sensor inspection can be done easily. From the above, it is possible to provide a fuel cell system excellent in safety.It is possible to detect an abnormal combustion state in which the amount of carbon monoxide produced in the combustion section is large or deterioration of the oxygen sensor even more reliably.
[0043]
【Example】
  Embodiments of the present invention will be described below with reference to the accompanying drawings.ZI will explain.
[0044]
Example 1
FIG. 1 is a configuration diagram of a combustion system including a fuel reformer and a fuel cell according to a first embodiment of the present invention. The combustion system includes a fuel reformer 10 that reforms a hydrocarbon-based fuel into a hydrogen-rich fuel gas by a steam reforming reaction, and a fuel cell that uses the hydrogen-rich fuel gas generated by the fuel reformer 10 as a raw material gas. 11, a combustion unit 13 that burns unused hydrogen fuel gas discharged from the fuel electrode 12 side of the fuel cell 11 and heats the fuel reformer 10 from the outside with the heat of the combustion exhaust gas, and an exhaust gas of the combustion unit 13 It is the structure which has at least the oxygen sensor 15 which is arrange | positioned in the flow path 14 and controls the oxygen concentration in combustion exhaust gas to predetermined concentration. Then, water vapor in the hydrogen fuel gas is condensed into the fuel electrode exhaust gas flow path 16 for supplying the unused hydrogen fuel gas discharged from the fuel electrode 12 side of the fuel cell 11 to the combustion unit 13 to form water. Water condensation means 17 is provided.
[0045]
This combustion system was prototyped and its effect was confirmed.
[0046]
First, fuel reforming will be described. The hydrocarbon-based fuel is a city gas mainly composed of methane gas. After removing sulfur compounds by the desulfurization device 18, the pressure is increased by the pressure increase device 19 and sprayed on the fuel reformer 10. The fuel reformer 10 is filled with a ruthenium catalyst, and the water added by the water addition device 20 reacts with a hydrocarbon fuel mainly composed of methane gas at around 640 ° C. to cause a steam reforming reaction. Thus, a reformed gas composed of more than 80% hydrogen, less than 20% carbon dioxide, and a small amount of carbon monoxide is obtained. The downstream of the fuel reformer 10 is a shift section 21 that oxidizes and reduces carbon monoxide at around 180 ° C. by a filled platinum catalyst system, and a platinum-ruthenium catalyst that is filled with carbon monoxide. A purifying section 22 that is selectively oxidized at around 100 ° C. and further reduced is disposed. As a result, a hydrogen-rich fuel gas in which carbon monoxide is reduced to 50 ppm or less is generated. In addition, the water | moisture-content addition apparatus 20 performs a water | moisture content addition also to the transformation part 21 as needed.
[0047]
Next, a battery that generates power using fuel will be described. The fuel cell 11 has a structure in which platinum electrodes are formed on both surfaces of a solid polymer-based hydrogen ion conductive membrane mainly composed of a fluororesin-based ion exchange membrane. Hydrogen fuel is supplied to the fuel electrode 12, and the air electrode 23. It is a battery that generates electricity by supplying oxygen gas. The hydrogen-rich fuel gas generated by the fuel reformer 10 is supplied to the fuel electrode 12 of the fuel cell 11 and is used for power generation by the air containing 20% oxygen supplied to the air electrode 23 on one side thereof.
[0048]
Further, combustion will be described. The hydrogen-based fuel gas remaining without being used in the fuel electrode 12 of the fuel cell 11 has, for example, approximately the same composition of hydrogen, carbon dioxide, and water vapor. These hydrogen-based fuel gases pass through the fuel electrode exhaust gas flow path 16 and are disposed in the middle of the water condensation means 17 such as a water retention tank (also referred to as a drain water treatment device), a condenser, or a heat exchanger for condensation. As a result, a part of the water vapor in the gas is condensed to form water, which is removed and introduced into the combustion section 13. On the other hand, the hydrocarbon-based fuel supply pipe supplied to the fuel reformer 10 is branched so as to be supplied also to the combustion section 13.
The combustor 13 includes air from the air supply means 24 mixed with a hydrogen-based fuel gas supplied via the fuel electrode exhaust gas flow path 16 and a mixed fuel obtained by mixing a hydrocarbon-based fuel composed mainly of methane gas as necessary. Are mixed and burned.
[0049]
Finally, treatment of combustion exhaust gas will be described. The combustion exhaust gas generated in the combustion unit 13 is controlled to have a predetermined oxygen concentration by controlling the amount of air supplied from the air supply means 24 by the oxygen sensor 15 disposed in the exhaust gas flow path 14 and its control unit 25. Has been. In addition, the fuel reformer 10 is heated from the outside with the combustion exhaust gas heat, and is maintained at around 640 ° C. where the steam reforming reaction occurs effectively.
[0050]
The effects of the combustion system of the present invention are shown in (Table 1). The effect was judged by the combustion state of the combustion section 13 and the reforming efficiency expressing whether the fuel reformer 10 efficiently reforms the hydrocarbon-based fuel into a hydrogen-rich fuel gas by the steam reforming reaction. In the present invention, hydrogen-based fuel gas remaining without being used in the fuel electrode 12 of the fuel cell 11 is condensed into water by condensing a part of water vapor in the gas by the water condensation means 17 using a water retention tank. Then, the droplets are removed and introduced into the combustion section 13, and a limiting current oxygen sensor is used as the oxygen sensor 15 to control the oxygen concentration in the combustion exhaust gas, and the excess air ratio is maintained at the optimum value of 1.2. ing. For comparison, a hydrogen-based fuel gas with many droplets is introduced without providing water condensation means, and comparison 1 in which the excess air ratio is maintained at 1.2 by an oxygen sensor, and droplets without water condensation means are provided. Table 2 also shows the results of Comparative 2 in which a large amount of hydrogen-based fuel gas was introduced and the oxygen excess rate was adjusted to 1.5 without using an oxygen sensor (Table 1).
[0051]
[Table 1]

[0052]
It can be seen that the present invention provides stable combustion and high reforming efficiency. This is because the hydrogen-based fuel gas from which droplets have been removed by the water dew condensation means is introduced and the optimal excess air ratio is maintained by the oxygen sensor, so that the fuel reformer 10 can effectively This is because the temperature was maintained at 637 ° C. where the quality reaction was performed. On the other hand, in comparison 1, although the optimal excess air ratio is maintained by the oxygen sensor, since the hydrogen-based fuel gas containing a large amount of droplets is introduced, combustion becomes unstable. The steam reforming reaction was not performed effectively. In comparison 2, the excess air ratio is set to 1.5 without using an oxygen sensor, and a hydrogen-based fuel gas containing a large amount of liquid droplets is introduced. The fuel reformer 10 was maintained at 612 ° C., and the steam reforming reaction was not performed very effectively.
[0053]
The amount of hydrogen-based fuel gas supplied to the combustion unit 13 depends greatly on the conversion efficiency in the fuel reformer 10 and the usage efficiency in the fuel cell 11. Therefore, the amount of hydrogen-based fuel gas to be supplied is likely to vary depending on these efficiencies, but when the excess air ratio is optimally controlled using the oxygen sensor 10, stable combustion is achieved without generating carbon monoxide. There is also an advantage that a combustion system having excellent safety can be provided. Further, since the fuel reformer 10 is heated by the combustion unit 13, heat necessary for the steam reforming reaction can be recovered, and there is an advantage that the efficiency of the combustion system is increased. The fuel used in this combustion system can be used not only for city gas but also for propane gas, kerosene, alcohol, coal, etc., and the fuel is not limited.
[0054]
The oxygen sensor 15 may use a concentration cell type oxygen sensor in addition to the limiting current type oxygen sensor, and the method, structure and material are not particularly limited. The water condensation means 17 may use a so-called auto drain from which water is automatically drained.
[0055]
The water condensation means 17 is provided with a shielding plate (not shown) provided to prevent the condensed water collected and stored in the internal space from reaching the combustion unit 13, and discharges the stored condensed water to the outside. Discharge means (not shown) is provided. If necessary, the condensed water collected by the water condensation means 17 is purified by a purification device (not shown) such as an ion exchange resin filling device or a neutralization device provided at the front end of the discharge means, and then recycled. Used or discharged.
[0056]
The oxygen sensor 15 is optimally a limit current type oxygen sensor. In particular, an oxygen sensor using an electrode film having any one of the following two material compositions is used in a combustion exhaust gas obtained by burning a hydrogen-based fuel gas. It had excellent durability as an oxygen sensor and was optimal. The first electrode film has a composition containing at least a small amount of bismuth oxide mainly composed of an electrically conductive material made of a noble metal or an oxygen ion conductive metal oxide. The second electrode film is composed of an auxiliary material composed of at least one of titanium, chromium, or zirconium and a main material mainly composed of a noble metal or an oxygen ion conductive metal oxide. It is a composition formed in the upper layer and formed by vapor deposition. The reason why the electrode films of these material compositions have excellent durability is that these materials have excellent durability and reliability against extremely small amounts of hydrogen-based fuel gas that occasionally occurs when hydrogen-based fuel gas is burned. It seems to have.
[0057]
(Example 2)
In Example 2, a method for supplying a hydrocarbon-based fuel for combustion in the combustion unit 13 was examined. In the present invention, a hydrocarbon-based fuel supply pipe supplied to the fuel reformer 10 is branched and supplied to the combustion unit 13. In the initial stage of combustion, hydrocarbon fuel is supplied only to the combustion section 13 and burned, and the fuel reformer 10 is heated to raise the temperature to a temperature at which the steam reforming reaction occurs. Thereafter, when the temperature of the fuel reformer 10 is raised to a predetermined temperature, a hydrocarbon-based fuel is also supplied to the fuel reformer 10 to cause a steam reforming reaction to generate a hydrogen-rich fuel gas. The unused hydrogen fuel gas discharged from the fuel electrode 12 of the battery 11 is burned. As a result, the energy used is reduced and the steam reforming reaction is effectively performed. The fuel after the temperature of the fuel reformer 10 is raised to a predetermined temperature may be mixed with unused hydrogen-based fuel gas and hydrocarbon-based fuel as necessary.
[0058]
(Example 3)
In Example 3, in order to control the temperature of the fuel reformer 10, a hydrocarbon-based fuel further mixed into the combustion unit 13 and a method for supplying the corresponding air were studied.
[0059]
In the present invention, the temperature of the fuel reformer 10 or the catalyst 26 filled therein is detected by a temperature sensor 27 disposed in the vicinity thereof, and the control unit 25 performs combustion so that the temperature is stored in advance. The temperature is controlled by increasing or decreasing the amount of hydrocarbon fuel and the corresponding amount of air further supplied to the section 13. In other words, the control unit 25 further increases and decreases the amount of the hydrocarbon-based fuel so that the steam reforming reaction occurs at the optimal temperature, and the corresponding air amount increases or decreases so that the optimal excess air ratio is obtained. That is why. As a result, the energy used is reduced and the steam reforming reaction is effectively performed.
[0060]
Example 4
Example 4 examined the supply method of the air for making it burn in the combustion part 13. FIG. According to the present invention, according to the approximate value of the fuel supplied to the combustion unit 13, the air supplied to the combustion unit by the air supply unit 24 is initially supplied with an approximate amount assumed in advance, and then the oxygen supplied by the oxygen sensor 15 is supplied. The detail correction amount is supplied by the density signal. That is, for example, first, the control unit 25 calculates an approximate value of the hydrogen-based fuel supplied to the combustion unit 13 from the power generation amount of the fuel cell 11 according to a preset correlation characteristic between the power generation amount and the hydrogen-based fuel. Then, the air supply means 24 initially supplies an approximate air value corresponding to the approximate fuel value according to a preset correlation characteristic between the hydrogen fuel amount and the supply air amount. After a while, the control unit 25 supplies the air amount corrected by the oxygen concentration signal from the oxygen sensor 15 by the air supply amount correction of the air supply unit 24. Even if the amount of fuel used changes as the amount of power generated by the fuel cell changes, a corresponding amount of air is instantaneously supplied, so that a good combustion state can be maintained and a steam reforming reaction is effectively performed. There is also an advantage that the oxygen sensor 15 having a slow response can be used.
[0061]
(Example 5)
Example 5 examined the correction | amendment correction method of the air supply means 24 by the oxygen sensor 15. FIG. The oxygen sensor 15 intermittently controls its operation drive and oxygen concentration in the combustion exhaust gas, and the control unit 25 corrects and corrects the air supply means 24 for supplying air to the combustion unit each time. As a result, the lifetime of the oxygen sensor 15 is improved, and good combustion state maintenance and effective steam reforming reaction are performed over a long period of time.
[0062]
(Example 6)
In Example 5, the location where the oxygen sensor 15 was disposed in the exhaust gas flow channel 14 was examined. The oxygen sensor 15 is arranged at a location where the exhaust gas temperature is 110 ° C. or higher in order to prevent moisture in the exhaust gas from condensing and shorting the sensor lead wires. In addition, the upper limit of the arrangement temperature was set to a place of the exhaust gas temperature that is lower than the sensor operating temperature in order to prevent the sensor from being deteriorated by the exhaust gas. As a result, the oxygen sensor 15 always operates normally, while maintaining a good combustion state and an effective steam reforming reaction over a long period of time.
[0063]
(Example 7)
Example 7 examined the control system which prevents the malfunction of the oxygen sensor 15.
[0064]
In this combustion system, the control means 25 that controls the operation state of the entire system, the combustion operation determination means 28 that determines whether or not the combustion operation of the combustion section 13 is present, and the sensor output detected by the oxygen sensor 15 are normal or abnormal. A sensor output abnormality determination means 29 for determining whether or not is connected. Further, the sensor output abnormality determination means 29 is connected to an alarm generation means 30 that operates when a sensor output is determined to be abnormal and issues an alarm.
[0065]
FIG. 2 is a control flowchart showing the operation of the combustion system according to the embodiment of the present invention.
When the start button is pressed, the combustion system is activated, and hydrocarbon-based fuel is supplied from the supply pipe. At the same time, the air supply means 24 is started, the combustion section 13 starts to burn, and the oxygen sensor 15 starts to be driven. . When the predetermined time (t) elapses, the combustion state and the sensor output are stabilized, so that the combustion operation determination means 28 is based on a combustion signal from a detection means (not shown) such as a flame detection device installed in the combustion section 13. After checking the combustion operation state, etc., it is judged whether or not the combustion operation is performed.
[0066]
When it is determined that the combustion operation is being performed, the sensor output (A) when exposed to the combustion exhaust gas is read, and the sensor output (A) is compared with the sensor outputs (I) and (II) stored in advance. Made. On the other hand, when it is determined that the combustion operation is stopped, the restart of the combustion system is started.
[0067]
If I ≦ A ≦ II, it is determined that the sensor output (A) is normal, and this operation is repeated until the combustion operation determining means 28 receives the combustion stop signal and determines that the combustion is stopped. On the other hand, if II <A or I> A, the sensor output (A) is determined to be abnormal, and the alarm generation means 30 issues an alarm. The sensor outputs (I) and (II) stored in advance are the lower limit value and the upper limit value of the sensor output when exposed to the combustion exhaust gas in a good combustion state. Therefore, the sensor output (A) being in this range means that the oxygen sensor is operating normally at the same time as a good combustion state with a small amount of carbon monoxide production. On the other hand, the fact that the sensor output (A) is outside this range means that the combustion section is in an abnormal combustion state where the amount of carbon monoxide produced is large, or the oxygen sensor has deteriorated. When it is determined that the sensor output (A) is normal, air-fuel ratio control or oxygen concentration monitoring is performed. When air-fuel ratio control is performed, the air supply means 24 is controlled so as to obtain a preset target sensor output value.
[0068]
When the combustion operation stop button is pressed, the control unit 25 determines that the combustion is stopped. Therefore, the fuel supply is stopped and the combustion unit 13 is stopped. However, the air supply unit 24 continues to operate. The atmosphere is supplied to the oxygen sensor 15. And since sensor output will be stabilized when predetermined time (T) passes, sensor output (B) at the time of exposure to the atmosphere will be read, this sensor output (B), and sensor output (X) memorized beforehand. And (Y) are compared. If X ≦ B ≦ Y, it is determined that the sensor output (B) is normal, the combustion system is stopped, and the air supply means 24 and the oxygen sensor 15 stop driving. On the other hand, the Y <B or X> B sensor output (B) is determined to be abnormal, and the alarm generation means 30 issues an alarm and at the same time orders the above-mentioned combustion system to stop. The sensor outputs (X) and (Y) stored in advance are a lower limit value and an upper limit value of the sensor output when exposed to the atmosphere of about 20% oxygen. Therefore, if the sensor output (A) is within this range, it means that the oxygen sensor is operating normally, and if it is outside this range, it means that the oxygen sensor has deteriorated.
[0069]
The alarm generating means 30 is configured so that the next drive can be normally performed even if the alarm is issued once. However, if the alarm is issued a plurality of times, the fact is displayed on the operation state display board of the combustion system. It was recommended to carry out the inspection and repair to improve safety.
[0070]
(Example 8)
FIG. 3 is a cross-sectional view of an embodiment of an oxygen sensor used in the combustion system of the present invention and its drive detection circuit, and comprises an oxygen sensor 15 and a control unit 25 that drives this sensor and detects its sensor output.
[0071]
The oxygen sensor 15 includes an oxygen ion conductive solid electrolyte plate 31, a pair of electrode films 32 and 33 formed on the surface of the oxygen ion conductive solid electrolyte plate 31, and a glass film 34 surrounding the electrode film 32 on one side. This is a limiting current type oxygen sensor composed of at least a bonded oxygen diffusion limiting body 35.
[0072]
The oxygen sensor 15 starts to be manufactured from a process in which a pair of electrode films 32 and 33 are printed on both surfaces of the oxygen ion conductive solid electrolyte plate 31 by thick film printing. The pair of electrode films 32 and 33 has a composition containing an electrically conductive material 36 made of a noble metal or an oxygen ion conductive metal oxide as a main component and at least a small amount of bismuth oxide 37, and is dried after thick film printing. As it is, or if necessary, it is formed by further melting and firing. After that, after a glass film 34 is printed on one surface of the oxygen ion conductive solid electrolyte plate 31, a constituent member of the oxygen diffusion limiter 35 is laminated on the upper part and melt-fired. Further, in a subsequent process, the lead wire fixing portions 38 and 39 having a composition containing a precious metal or an electrically conductive material as a main component and a small amount of glass are melted and fired to form a pair of lead wires 40 and 41 and a pair of electrode films 32 and 33. To complete the basic structure.
[0073]
The oxygen sensor 15 of the present invention was prototyped and its effect was confirmed.
[0074]
The oxygen ion conductive solid electrolyte plate 31 is made of yttrium (Y₂O₃) 8 mol% and zirconia (ZrO)₂) Is a stabilized zirconia fired plate in which 92 mol% of the solid solution is dissolved.
[0075]
The pair of electrode films 32 and 33 is a composition in which 10 vol% bismuth oxide 37 is mixed with 90 vol% platinum electroconductive material 36, and thick films are formed on both surfaces of the aforementioned oxygen ion conductive solid electrolyte plate 31. Printed.
[0076]
The oxygen diffusion limiting body 35 is composed of a helical glass film 34 and a fired forsterite seal plate 42 laminated thereon. A manufacturing method is demonstrated. First, the spiral glass film 34 is thickly printed so as to surround the periphery of the electrode film 32 previously thickly printed on the oxygen ion conductive solid electrolyte plate 31 described above. Then, a seal plate 42 is laminated on the thick printed film and melted and fired. Then, the oxygen ion conductive solid electrolyte plate 31 and the seal plate 42 are joined, and a diffusion limiting hole (not shown) having a minute dimension is formed between the plate and the helical glass film 42. . At the same time, the electrode films 32 and 33 are fired.
[0077]
The lead wire fixing portions 38 and 39 have a composition in which 90 vol% of platinum is mixed with 10 vol% of glass. This composition is melted and fired at 700 ° C. to connect the pair of lead wires 40 and 41 made of platinum and the pair of electrode films 32 and 33 described above. And the inorganic adhesive material was laminated | stacked on this composition, and it was made to harden | cure at 500 degreeC, and the connection of the lead wire was strengthened.
[0078]
In this 700 ° C. firing, the melting point of bismuth oxide 37 mixed with the electrode films 32 and 33 is 820 ° C., and the physical properties of the electrode films 32 and 33 are not affected by the firing of the lead wire fixing portions 38 and 39. From the viewpoint, it is based on the reason that the temperature is lower by 100 ° C. than the melting point of bismuth oxide 820 ° C.
[0079]
A platinum heater 43 is formed in advance on the seal plate. The heater 43 and a pair of heater lead wires 44 and 45 made of platinum were connected via 700 ° C. melting and firing of the heater lead wire fixing portions 46 and 47. The heater lead wire fixing portions 46 and 47 are compositions in which 90 vol% of platinum is mixed with 10 vol% of glass, and the 700 ° C. melting and baking are performed simultaneously with the 700 ° C. melting and baking of the lead wire fixing portions 38 and 39. Is going. And the inorganic adhesive material was laminated | stacked on this composition, and it was made to harden | cure at 500 degreeC, and the connection of the lead wire was strengthened.
[0080]
The control unit 25 includes at least an element driving DC power supply 48, a current detection unit 49, and a heater heating DC power supply 50 therein. The element driving DC power supply 48 and the current detection unit 49 constitute a closed circuit with the pair of lead wires 40 and 41 and the pair of electrode films 32 and 33. The current detector 49 detects a current value generated by a voltage applied by the element driving DC power supply 48 as a sensor output. On the other hand, the heater heating DC power supply 50 forms a closed circuit with the heater 43 and the pair of heater lead wires 44 and 45.
[0081]
The operation principle of the oxygen sensor 15 will be described. When a voltage is applied by the heater heating DC power source 50, the heater 43 generates heat, and the oxygen ion conductive solid electrolyte plate 31 is heated to 500 ° C. Then, oxygen ions are easily conducted through the oxygen ion conductive solid electrolyte plate 31, and the following oxygen pumping action is generated by the voltage applied by the element driving DC power supply 48. In other words, oxygen molecules in the air reach the electrode film 32 via a diffusion restriction hole (not shown) having a small size provided in the oxygen diffusion restriction body 35, and then give and receive electrons by applying a voltage. The ions pass through the oxygen ion conductive solid electrolyte plate 31, electrons are taken away by the electrode film 33, and then return to the air as oxygen molecules. Current flows due to the movement of oxygen molecules, but since the inflow of oxygen molecules is limited by the small-sized diffusion restriction holes and only the amount of oxygen corresponding to the oxygen concentration flows in and moves, the flowing current has a relationship proportional to the oxygen concentration. It is done. Using this relationship, the oxygen concentration can be determined from the current value.
[0082]
The durability reliability of the oxygen sensor 15 in the exhaust was evaluated. The durability reliability was performed in a state where the heater 43 was heated by applying a voltage from the heater heating DC power source 50 and the oxygen ion conductive solid electrolyte plate 31 was heated to 500 ° C. Then, 0.5 V was applied to the electrode films 32 and 33 by the element driving DC power supply 48, and the transient change of the flowing current was measured. This applied voltage of 0.5 V is a critical voltage value at which a limit current characteristic in which the voltage dependence of the current value is eliminated is obtained, and the degree of decrease in the current value due to the durability reliability of the electrode films 32 and 33 is remarkable. This is a voltage value that can be observed.
[0083]
FIG. 4 (a) shows an initial current value and a current after 300 hours of voltage application for each glass film firing temperature in an electrode film having a composition in which 90 vol% of an electrically conductive material made of platinum is mixed with 10 vol% of bismuth oxide. FIG. As can be seen from FIG. 4A, the limiting current type oxygen sensor obtained by firing the glass film 34 at 850 to 1050 ° C. had a high current value and excellent durability reliability. This is because the electrode films 32 and 33 are simultaneously fired by firing the glass film 34, but the electrode films 32 and 33 are 30 to 30 ° C. from the melting point 820 ° C. of bismuth oxide mixed therein. By firing at a high temperature of 230 ° C., it tightly adheres to the oxygen ion conductive solid electrolyte plate 31 and its junction resistance is small. Since the junction resistance does not change even when a voltage is applied, the current value does not change. Seem. In particular, an oxygen sensor obtained by baking the glass film 34 at 850 to 970 ° C. was the most optimal because it showed an extremely high current value and excellent durability reliability.
[0084]
On the other hand, the glass film 34 baked at a temperature exceeding 1050 ° C. was not suitable because the desired current value was very small, and a large current value necessary for constituting a limiting current type oxygen sensor could not be secured. This is because the electrode films 32 and 33 are baked at a high temperature such as 1100 ° C., so that bismuth oxide mixed with platinum reacts with platinum to obtain an oxygen non-adsorbing electrode film. This is because the current to be obtained cannot be obtained. In addition, the glass film 34 has flowed too much to cover the electrode film 32, and the area of the glass film 34 is reduced to reduce the current.
[0085]
Further, the glass film 34 baked at a temperature lower than 850 ° C. was also unsuitable due to poor durability reliability. This is because the electrode films 32 and 33 are fired at a temperature substantially equal to or lower than the melting point 820 ° C. of the bismuth oxide mixed therein, so that the electrode film 32 is formed on the oxygen ion conductive solid electrolyte plate 31. 33 cannot be sufficiently adhered to each other, and the junction resistance gradually increases when a voltage is applied. In particular, the glass film 34 baked at 750 ° C. or less has an extremely small initial current value and is further unsuitable. This is because the firing of bismuth oxide mixed in the electrode film is insufficient, so that the electrode films 32 and 33 do not adhere to the oxygen ion conductive solid electrolyte plate 31 at all, and the junction resistance is very large. Because.
[0086]
FIG. 4B shows the chemical composition La._1-xSrxCoO₃In an electrode film having a composition in which 90 vol% of an electrically conductive material composed of oxygen ion conductive metal oxide is mixed with 10 vol% of bismuth oxide, an initial current value and a current after 300 hours of voltage application are determined for each firing temperature of the glass film. FIG. As can be seen from FIG. 4B, the limiting current oxygen sensor obtained by firing the glass film 34 at 850 to 1050 ° C. had a high current value and excellent durability reliability.
[0087]
From the above, the firing temperature of the glass film 34 that can secure a large current value necessary for constituting a limiting current type oxygen sensor and has excellent durability and reliability is 850 to 1050 ° C., particularly 850 to 970. ° C was the most optimal with extremely high current values and excellent durability reliability.
[0088]
The oxygen ion conductive solid electrolyte plate 31 is made of zirconia (ZrO₂) A small amount of yttrium (Y₂O₃), A zirconia-based ionic conductor obtained by solidifying (CeO)₂)_0.8(SmO_1.5)_0.2Ya (CeO₂)_0.8(GdO_1.5)_0.2It is possible to use yttrium-based ion conductors such as These materials were polished so that the surface roughness Ra was 0.05 to 0.3 μm so that the electrode films 32 and 33 were firmly adhered.
[0089]
The electrically conductive material mixed with the electrode films 32 and 33 is platinum, gold, a noble metal such as silver, or a chemical composition La._1-xSrxCoO₃And LaCoO₃LaMnO₃Oxygen ion conductive metal oxides such as are used. Further, the optimal amount of bismuth oxide mixed with the electrode films 32 and 33 is 3 to 15 vol%. When this composition is expressed by weight ratio, for example, in the case of an electroconductive material of platinum, it is oxidized to 94 to 99 wt% of platinum. It is 1 to 6 wt% of bismuth. With this composition, if the amount of bismuth oxide as a binder is very small, the electrode film does not adhere to the oxygen ion conductive solid electrolyte plate, so that no current can be secured, and if the amount of bismuth oxide as a semiconductor is large, the electrode film is not electrically conductive. Thus, the composition is obtained experimentally from the viewpoint that current cannot be secured. Further, the electrode films 32 and 33 are made of copper oxide, cadmium oxide, zirconia (ZrO) in addition to the above-described electrically conductive material and bismuth oxide.₂Or hydrous Zr (OH)₂It is effective to mix a sol-gel solution mainly composed of), and these metal oxide materials can be mixed up to a maximum of 25 vol% in the total total amount with bismuth oxide. This is a composition obtained experimentally from the viewpoint that when these metal oxide-based materials, which are semiconductors, and bismuth oxide are large, the electrode film becomes electron non-conductive and current cannot be secured.
[0090]
The oxygen diffusion limiter 35 can use the following three configurations. The first configuration is a configuration of a spiral-shaped glass film 34 in which a diffusion limiting hole is formed, and a seal plate 42 laminated thereon. The second configuration is a configuration of a porous seal plate 42 having a hollow or glass inner hollow glass film 34 and a microscopic diffusion limiting hole laminated on the glass film 34. The third configuration is a sealing plate 42 (a sealing plate A having a micro-sized hole) formed of a plurality of laminated plates formed with a hollow or glass inner hollow-shaped glass film 34 and diffusion limiting holes laminated thereon. And a laminated plate obtained by sequentially laminating a spiral-shaped glass film for forming a diffusion limiting hole and a seal plate B).
[0091]
The glass film 34 has the same thermal expansion coefficient within ± 10% as the oxygen ion conductive solid electrolyte plate 31 and the seal plate 42 laminated thereon, and has a melting temperature of 850 to 1050 ° C., particularly 850 to 970. ℃ was the optimum, and this material did not cause any problems in durability reliability. For example, alumina oxide is 3-7 wt%, boron oxide is 3-7 wt%, calcium oxide is 1-2 wt%, strontium oxide is 4-6 wt%, barium oxide is 0.2-1.5 wt%, and sodium oxide is 10 A composition comprising ˜13 wt%, potassium oxide 4-8 wt%, titanium oxide 6-9 wt%, and the balance silicon oxide was particularly optimal and used in this study experiment.
[0092]
The main components of the lead wire fixing portions 38 and 39 are precious metals such as platinum, gold and silver, and a chemical composition YBaCu.₃O₇Etc. are used. And 3-15 vol% of glass is mixed with 85-97 vol% of this noble metal or electrically conductive metal oxide.
[0093]
Example 9
The oxygen sensor 15 in which the electrode films 32 and 33 and the glass film 34 are simultaneously fired has a problem that the initial current value obtained varies. Thus, in Example 9, a method of firing the glass film 34 after firing the electrode films 32 and 33 in advance was employed, and the firing temperature of the electrode films 32 and 33 capable of reducing variation in the initial current value was examined. The examination is the same as in Example 8 except for the following two points. The first difference from Example 8 is that the electrode films 32 and 33 are fired in advance on the oxygen ion conductive solid electrolyte plate 31 of stabilized zirconia at different firing temperatures, and then the glass film 34 has its optimum firing temperature 920. It is that it was baked at ° C. The second difference is that five limit current type oxygen sensors 15 of the same manufacturing method were made on a trial basis, and the variations in the initial values were measured.
[0094]
FIG. 5 is a characteristic diagram in which the relationship between the firing temperature of the electrode film and the initial current value is measured. The maximum value, the average value, and the minimum value in the five prototypes are arranged as parameters. FIG. 5A shows an electrode film having a composition in which 90 vol% of an electrically conductive material made of platinum is mixed with 10 vol% of bismuth oxide. FIG. 5B shows the chemical composition La._1-xSrxCoO₃This is an electrode film having a composition in which 10 vol% of bismuth oxide is mixed with 90 vol% of an electrically conductive material made of oxygen ion conductive metal oxide.
[0095]
As can be seen from FIG. 5, it can be seen that the oxygen sensor obtained by pre-baking the electrode film at 770 to 950 ° C. maintains a high current value as a whole. On the other hand, the firing exceeding 950 ° C. was unqualified because the current value decreased as a whole. This is because the electrode film is re-baked by baking the glass film at 920 ° C. in the subsequent process, so that bismuth oxide mixed with platinum reacts to obtain an oxygen non-adsorbing electrode film. This is because it is difficult to obtain current due to movement. In addition, firing at less than 770 ° C. was unqualified because the initial current value obtained varied. This is because the electrode film is not in close contact with the oxygen ion conductive solid electrolyte plate because the firing of bismuth oxide mixed therein is insufficient in the first firing, and the glass film in the subsequent process Since it is refired by firing at 920 ° C., it seems that the adhesiveness varies.
[0096]
From the above, in order to manufacture a limiting current type oxygen sensor with a small variation in current value, the electrode film was previously fired at 770 to 950 ° C. and then the glass film was fired. In addition, this limiting current type oxygen sensor has an advantage of excellent durability reliability.
[0097]
As a result, as an electrically conductive material, noble metals such as platinum, gold and silver, chemical composition La_1-xSrxCoO₃And LaCoO₃LaMnO₃The same applies to the electrode films 32 and 33 in which oxygen ion conductive metal oxide such as bismuth oxide is mixed and 3 to 15 vol% is mixed.
[0098]
(Example 10)
When exposed to combustion exhaust gas containing a large amount of sulfur oxide for a long period of time, the electrode films 32 and 33 of the oxygen sensor 15 have a problem that their values gradually decrease and durability reliability decreases. Therefore, Example 10 uses electrode films 32 and 33 containing bismuth oxide 37 pre-immersed in a sol-gel solution containing zirconia as a main component, and is exposed to combustion exhaust gas containing a large amount of sulfur oxide for a long time. In addition, an attempt was made to realize an oxygen sensor 15 with little current drop. The examination is the same as in Examples 8 and 9 except for the following two points. The first difference from Example 8 and Example 9 is that the stabilized zirconia oxygen ion conductive solid electrolyte plate 31 has zirconia (ZrO).₂The electrode films 32 and 33 containing the bismuth oxide 37 previously immersed in the sol-gel solution mainly containing) are baked at 820 ° C. and the glass film 34 is baked at the optimum baking temperature 920 ° C. The second difference from Example 8 and Example 9 is that the durability reliability of the oxygen sensor 15 was evaluated in an exhaust gas containing 20 ppm of sulfur oxide, and the transient change of the flowing current was measured.
[0099]
Invention 1 is an electrode film having a composition in which 90 vol% of an electrically conductive material made of platinum is mixed with 10 vol% of bismuth oxide previously immersed in a sol-gel solution mainly composed of zirconia. Invention 2 has chemical composition La_1-xSrxCoO₃This is an electrode film having a composition in which 90 vol% of an electrically conductive material made of oxygen ion conductive metal oxide is mixed with 10 vol% of bismuth oxide previously immersed in a sol-gel solution mainly composed of zirconia. On the other hand, Comparative 1 is an electrode film having a composition in which 90 vol% of an electroconductive material made of platinum is mixed with 10 vol% of bismuth oxide. Invention 2 has chemical composition La_1-xSrxCoO₃This is an electrode film having a composition in which 10 vol% of bismuth oxide is mixed with 90 vol% of an electrically conductive material made of oxygen ion conductive metal oxide. (Table 2) shows the results of the study.
[0100]
[Table 2]

[0101]
It can be seen that the product of the present invention has excellent durability characteristics. The reason for this seems to be that bismuth oxide previously immersed in a sol-gel solution containing zirconia as a main component absorbs and removes sulfur oxides and suppresses deterioration of the main conductive material.
[0102]
A sol-gel solution mainly composed of zirconia is zirconia (ZrO).₂), A single sol-gel solution, containing 60 parts or more of zirconia and silica (SiO₂A sol-gel solution in which other oxides such as) exist in the balance was effective. Also, hydrous Zr (OH)₂Is also effective because it is called a zirconia sol-gel solution, and the sol-gel solution having the above composition was effective. There are the following two methods for mixing bismuth oxide previously immersed in the sol-gel solution into the electrode film. The first method is a method in which this sol-gel solution is mixed with a printing paste and immersed in bismuth oxide when an electroconductive material such as platinum and bismuth oxide are mixed to prepare a printing paste for an electrode film. The second method is a method of preparing a printing paste for an electrode film using bismuth oxide previously immersed in a sol-gel solution.
[0103]
(Example 11)
Since the oxygen diffusion limiting body 35 of the oxygen sensor 15 requires a high degree of hermetic seal, strict management is required for its manufacturing method. Therefore, the formation of the oxygen diffusion restrictor 35 that requires strict management and the fixing of the lead wire that requires a complicated manufacturing method in the same process require a complicated manufacturing method and strict management, and are practical. Not. Therefore, Example 11 examined the firing temperature for fixing the lead wire when the manufacturing method for fixing the lead wire was adopted after the oxygen diffusion restrictor 35 was formed.
[0104]
As can be seen from FIGS. 4 and 5, when the electrode film is fired at less than 750 ° C., the firing becomes insufficient and the generated current value becomes very small. Therefore, the upper limit of firing of the lead wire was set to 750 ° C. so that the electrode film was re-dissolved by firing and the current value was not affected. On the other hand, bismuth oxide mixed in the electrode film shows a behavior in which the crystal structure starts to change greatly at 650 ° C. Therefore, from the viewpoint of ensuring the durability reliability of the electrode film, the operating temperature should not exceed 650 ° C. There is a need. Therefore, the firing of the lead wire is set to 650 ° C. or higher at which the crystal structure starts to change, and the operating temperature of the electrode film is set to 650 ° C. or lower so that the durability reliability is not affected.
[0105]
From the above, in order to manufacture a limiting current type oxygen sensor with excellent current value and durability reliability, after the glass film is melted and fired, the lead wire is fired at a maximum of 650 to 750 ° C. and fixed to the electrode film. The manufacturing method was
[0106]
Example 12
In Example 12, the material of the lead wire fixing portions 38 and 39 was examined.
[0107]
A composition containing at least a small amount of glass containing a precious metal or an electron conductive metal oxide as a main component has insufficient adhesive strength, and if the lead wire is pulled strongly during the handling operation of the sensor element, the lead wire is detached. Because. Therefore, careful handling is required, and there is a problem that workability and productivity are poor.
[0108]
In that respect, when the lead wire fixing portions 38 and 39 are a composition containing at least a small amount of glass containing a noble metal or an electron conductive metal oxide as a main component, and a glass or an inorganic adhesive laminated on the composition, The lead wire fixing portion had excellent adhesive strength, and the lead wire did not come off even when the lead wire was pulled strongly. Therefore, normal handling is sufficient, and workability and productivity are greatly improved.
[0109]
(Example 13)
The electrode film of noble metal or oxygen ion conductive metal oxide formed by vapor deposition method has good current characteristics because it adheres well to the oxygen ion conductive solid electrolyte plate at the beginning. There are problems with poor durability and reliability characteristics. Therefore, Example 13 is configured with this type of electrode film material for obtaining an oxygen sensor having excellent durability and reliability.
[0110]
FIG. 6 is a cross-sectional view of an oxygen sensor using manufacture which is another embodiment of the present invention and a drive detection circuit thereof. With respect to the oxygen sensor 15, only differences from FIG. 3 will be described. The electrode films 51 and 52 are made of an auxiliary material 53 made of at least one of titanium, chromium or zirconium and a main material 54 mainly composed of a noble metal or oxygen ion conductive metal oxide. At least the auxiliary material 53 is disposed in the lower layer and the main material 54 is disposed in the upper layer, and is formed by a vapor deposition method.
[0111]
The oxygen sensor of the present invention was prototyped and its effect was confirmed. Only differences from Example 8 and important matters regarding the material are described. The oxygen ion conductive solid electrolyte plate 31 is made of yttrium (Y₂O₃) 8 mol% and zirconia (ZrO)₂) Is a stabilized zirconia fired plate in which 92 mol% of the solid solution is dissolved. The oxygen ion conductive solid electrolyte plate 31 is coated with a noble metal or oxygen ion conductive metal oxide with a 0.01 μm film thickness of an auxiliary material 53 made of at least one of titanium, chromium, or zirconium as a lower layer by sputtering. Electrode films 51 and 52 having a structure in which 0.5 μm of the main material 54 having the main component in the upper layer was formed.
[0112]
The results of the durability reliability are shown in (Table 3).
[0113]
[Table 3]

[0114]
Electrode films 51 and 52 having an auxiliary material 53 made of at least one of titanium, chromium or zirconium as a lower layer and a main material 54 mainly composed of a noble metal or oxygen ion conductive metal oxide as an upper layer have excellent durability characteristics. It can be seen that The auxiliary material 53 has a film thickness of 0.003 to 0.04 μm, and the main material 54 has a film thickness of 0.3 to 1.0 μm, and is formed by vapor deposition such as sputtering or EB. The The auxiliary material 53 and the main material 54 may be a mixture.
[0115]
The main material 54 mainly composed of a noble metal or an oxygen ion conductive metal oxide is a noble metal such as platinum, gold or silver, a chemical composition La_1-xSrxCoO₃And LaCoO₃LaMnO₃Oxygen ion conductive metal oxides such as are used.
[0116]
The oxygen ion conductive solid electrolyte plate 31 is made of zirconia (ZrO₂) A small amount of yttrium (Y₂O₃), A zirconia-based ionic conductor obtained by solidifying (CeO)₂)_0.8(SmO_1.5)_0.2Ya (CeO₂)_0.8(GdO_1.5)_0.2It is possible to use yttrium-based ion conductors such as These materials were polished so that the surface roughness Ra was 0.05 to 0.3 μm so that the electrode films 51 and 52 were firmly adhered.
[0117]
(Example 14)
In Example 14, the crystal structure of the electrode films 51 and 52 used in Example 13 was examined in order to obtain a limiting current oxygen sensor with further excellent durability and reliability.
[0118]
The oxygen sensor 15 of the present invention was prototyped and its effect was confirmed. The difference from Example 13 is that when the sputtering conditions are changed, the crystal structure of the main material 54 mainly composed of a noble metal or oxygen ion conductive metal oxide is changed, and the main structure 54 is analyzed by an X-ray diffractometer. This is because the electrode films 51 and 52 are formed so that a crystal structure oriented in the peak is obtained. The durability reliability determination results are shown in (Table 4).
[0119]
[Table 4]

[0120]
It can be seen that the electrode films 51 and 52 having a crystal structure in which the main material 54 is oriented in the main peak have excellent durability.
[0121]
(Example 15)
In Example 15, a heating driving method during warm-up warming was examined in order to obtain an oxygen sensor with even higher durability and reliability.
[0122]
The oxygen sensor of the present invention and a drive detection circuit for heating and driving the sensor were prototyped, and the effects were confirmed. The examination is the same as in Examples 8 to 15 except for the following two points. The first difference is that the heater 43 provided in the oxygen diffusion limiter 35 of the oxygen sensor 15 is heated in a stepped manner during warming-up by a heater heating DC power supply 50 that applies an applied voltage value in a stepped manner. That is. The second difference is that the reliability evaluation of the drive detection circuit was performed by intermittent driving of heating energization for 5 minutes and non-heating energization for 5 minutes, and the transient change of the flowing current was measured.
[0123]
In the invention, when a predetermined voltage required for heating at 500 ° C. is applied to the heater 43 by the heater heating DC power source 50 for 5 minutes, the heating is applied for 50% value for 1 minute and the 100% value for the remaining 4 minutes. It was an energization mode and reached 500 ° C. in about 3 minutes. Then, intermittent driving was performed with heating energization (power ON) for 5 minutes and non-heating energization (power OFF) for 5 minutes. On the other hand, the comparative product is a heating energization mode in which a predetermined voltage necessary for heating at 500 ° C. is applied to the heater 43 for 5 minutes, and the 100% value is applied for 5 minutes, and reaches 500 ° C. in about 2 minutes. Then, intermittent driving was performed with heating energization (power ON) for 5 minutes and non-heating energization (power OFF) for 5 minutes.
[0124]
Invention 1 and Comparative Example 1 are electrode films 32 and 33 having a composition in which 90 vol% of an electrically conductive material made of platinum is mixed with 10 vol% of bismuth oxide previously immersed in a sol-gel solution containing zirconium as a main component. Invention 2 and Comparative Example 2 show the chemical composition La_1-xSrxCoO₃Electrode films 32 and 33 having a composition in which 90 vol% of an electrically conductive material made of oxygen ion conductive metal oxide is mixed with 10 vol% of bismuth oxide previously immersed in a sol-gel solution containing zirconium as a main component. Invention 3 and Comparative Example 3 are electrode films 51 and 52 having a structure in which a 0.01 μm film thickness of the auxiliary material 53 of chromium is a lower layer and a 0.5 μm thickness of the main material 54 of platinum is an upper layer. Invention 4 and Comparative Example 4 show that the titanium auxiliary material 53 has a 0.01 μm film thickness as a lower layer and a chemical composition La._1-xSrxCoO₃The electrode films 51 and 52 have a structure in which 0.5 μm of the oxygen ion conductive metal oxide 54 is formed as an upper layer. Invention 5 and Comparative Example 5 show that the auxiliary material 53 of zirconium is oriented to a lower layer with a 0.01 μm film thickness._1-xSrxCoO₃The electrode films 51 and 52 have a structure in which 0.5 μm of the oxygen ion conductive metal oxide 54 is formed as an upper layer.
[0125]
The results of the durability reliability are shown in (Table 5).
[0126]
[Table 5]

[0127]
Since the heater is heated by raising its temperature stepwise, the temperature of the electrode film gradually rises to reduce thermal shock, and it is prevented that the current is reduced due to peeling.
Therefore, a limiting current type oxygen sensor with improved durability reliability can be obtained.
[0128]
【The invention's effect】
  As described above, the claims1In the fuel cell system described above, the hydrogen fuel gas from which droplets have been removed by the water dew condensation means is introduced into the combustion section, and the combustion section is a fuel reformer while being maintained at an optimum excess air ratio by the oxygen sensor. Is heated.
Furthermore, it is possible to detect an abnormal combustion state in which the amount of carbon monoxide produced in the combustion section is large or the deterioration of the oxygen sensor.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a combustion system including a fuel reformer and a fuel cell in Embodiment 1 of the present invention.
FIG. 2 is a control flowchart showing the operation of a combustion system including a fuel reformer and a fuel cell in Embodiment 7 of the present invention.
FIG. 3 is a configuration diagram of an oxygen sensor using the manufacturing method according to Embodiment 8 of the present invention and a drive detection circuit thereof.
FIG. 4 is an effect characteristic diagram of an oxygen sensor using the manufacturing method according to Example 8 of the present invention (relationship between the firing temperature of the glass film and the current).
  (A) Effect characteristic diagram of electrode film made of platinum and bismuth oxide
  (B) La_1-xSrxCoO₃Of effect of electrode film made of bismuth oxide
FIG. 5 is an effect characteristic diagram of the oxygen sensor using the manufacturing method according to Example 8 of the present invention (relationship between the firing temperature of the electrode film and the current).
  (A) Effect characteristic diagram of electrode film made of platinum and bismuth oxide
  (B) La_1-xSrxCoO₃Of effect of electrode film made of bismuth oxide
FIG. 6 is a configuration diagram of an oxygen sensor using the manufacturing method according to Embodiment 13 of the present invention and its drive detection circuit.
FIG. 7 is a configuration diagram of a combustion system including a conventional fuel reformer and a fuel cell.
[Explanation of symbols]
  10 Fuel reformer
  11 Fuel cell
  12 Fuel electrode
  13 Combustion section
  14 Exhaust gas flow path
  15 Oxygen sensor
  16 Fuel electrode exhaust gas flow path
  17 Water condensation
  24 Air supply means
  25 Control unit
  26 Catalyst
  28 Combustion operation judgment means
  29 Sensor output abnormality judgment means
  30 Alarm generation means
  31 Oxygen ion conductive solid electrolyte plate
  32, 33 Electrode film
  34 Glass membrane
  35 Oxygen diffusion limiter
  36 Electrically conductive materials
  37 Bismuth oxide
  38, 39 Lead wire fixing part
  40, 41 Lead wire
  42 Seal plate
  43 Heater
  50 DC power supply for heater heating
  51, 52 Electrode film
  53 Auxiliary materials
  54 Main materials

Claims (6)

A fuel reformer that reforms a hydrocarbon-based fuel into a hydrogen-rich fuel gas by a steam reforming reaction;
A fuel cell using the fuel gas generated in the fuel reformer as a raw material gas,
The fuel the fuel gas that will be discharged from the fuel electrode side is burned batteries, a combustion section for heating the fuel reformer in the combustion gas heat,
An oxygen sensor that is disposed in the exhaust gas flow path of the combustion section and detects the oxygen concentration in the exhaust gas in the exhaust gas flow path ;
A control unit for controlling the amount of supplied air based on the signal of the oxygen sensor ;
Together with the fuel gas that will be discharged from the fuel electrode side of the front Symbol fuel cell provided in the fuel electrode exhaust gas flow path for supplying to the combustion section, by condensation of water vapor in the fuel gas of the fuel electrode exhaust gas flow path Water condensation means to make water ,
With at least,
The controller is connected to combustion operation determining means for determining whether or not the combustion operation of the combustion section is present, and sensor output abnormality determining means for determining whether the sensor output detected by the oxygen sensor is normal or abnormal. And
The sensor output abnormality determining means is connected to an alarm generating means that operates when a sensor output of the oxygen sensor is determined to be abnormal and issues an alarm,
The sensor output abnormality determining means includes a sensor output (A) of the oxygen sensor when the combustion operation determining means determines that combustion is being performed in the combustion section, and the combustion operation determining means is the combustion section. Read the sensor output (B) of the oxygen sensor when it is determined that combustion is not performed,
The fuel cell system in which the alarm generation unit issues an alarm when the sensor output abnormality determination unit determines that at least one of the sensor output (A) and the sensor output (B) indicates an abnormal value . Wherein the control unit, the fuel reformer or detects a temperature of the catalyst filled therein, so that the temperature is previously stored, the amount arbitrarily mixing the hydrocarbon fuel to the combustion unit The fuel cell system according to claim 1, wherein the temperature is controlled by increasing or decreasing the corresponding air amount. Wherein the control unit, the air supplied to the combustion section by the air supply means initially supplies only previously supposed schematic amounts in accordance with the approximate value of the fuel supplied to the combustion section, from then After a while, the oxygen 2. The fuel cell system according to claim 1, wherein the fine correction amount is supplied by an oxygen concentration signal from the sensor. Wherein said oxygen sensor, a control of its operation driving same according to the flue gas oxygen concentration to each occasion intermittently performed, said control unit corrects retouching said air supply means supplying air to the combustion unit Item 4. The fuel cell system according to Item 1.   2. The fuel cell system according to claim 1, wherein the oxygen sensor is disposed at a location where the exhaust gas temperature in the exhaust gas flow path is 110 ° C. or higher and lower than the sensor operating temperature. Air supply means for supplying air to the combustion section;
The air supply means continues to operate even after combustion in the combustion section stops,
The sensor output abnormality determination means reads the sensor output (B) of the oxygen sensor after a predetermined time has elapsed from the stop of combustion in the combustion section, and the alarm is generated when the sensor output (A) indicates an abnormal value. 2. The fuel cell system according to claim 1, wherein the means issues an alarm, and the alarm generating means issues an alarm when the sensor output (B) indicates an abnormal value.

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