JP2004296102A

JP2004296102A - Fuel cell system and fuel cell system stopping method

Info

Publication number: JP2004296102A
Application number: JP2003082893A
Authority: JP
Inventors: Masataka Kadowaki; 正天門脇; Masatoshi Ueda; 雅敏上田; Koji Shindo; 浩二進藤; Yukinori Akiyama; 幸徳秋山
Original assignee: Sanyo Electric Co Ltd
Current assignee: Sanyo Electric Co Ltd
Priority date: 2003-03-25
Filing date: 2003-03-25
Publication date: 2004-10-21

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system capable of repeating start and stop of a reformer without decreasing the life of the reformer even in a place where an infrastructure of nitrogen is not present, on the contrary, enhancing the life of the reformer, and tremendously enhancing the life of a fuel cell system. <P>SOLUTION: The fuel cell system 1 is equipped with a fuel supply stopping means 12 stopping the supply of fuel to a heating means 9 of a steam reformer 4 when a reforming device 8 is stopped; a temperature detecting means 16 detecting the outlet catalyst temperature of the reformer 4; a water supply stopping means 15 stopping the supply of water necessary for reforming reaction; a combustion means 17 stopping the supply of process gas from the reforming device 8 to a fuel cell 5 and burning it; and a raw fuel supply stopping means 10 stopping the supply of the raw fuel to the reforming device 8. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、燃料電池システムおよび燃料電池システム停止方法に関するものであり、さらに詳しくは、都市ガスなどの原燃料ガスの水蒸気改質により水素リッチガスを生成して燃料電池などに供給して発電する燃料電池システムおよび燃料電池システム停止方法に関するものである。
【０００２】
【従来の技術】
従来、都市ガスなどの原料炭化水素系燃料ガスを水蒸気改質して水素リッチガスを生成し、得られた水素リッチガスの化学エネルギーを燃料電池によって直接電気エネルギーに変換する燃料電池システムが知られている。
【０００３】
燃料電池は、水素を燃料とするものであり、この水素の生成には、天然ガスなどの炭化水素成分、メタノールなどのアルコール、あるいはナフサなどの分子中に水素原子を有する有機化合物を原料とし、水蒸気で改質する方法が広く用いられている。このような水蒸気を用いた改質反応は吸熱反応である。このため、水蒸気改質を行う水蒸気改質器は、原料および水蒸気、改質反応を行う改質触媒を加熱して高温にする必要がある。
【０００４】
ナフサなどの有機化合物を原料とし、これを水蒸気で改質する反応は水素や二酸化炭素の生成の他に一酸化炭素を副生成する。例えば固体高分子型燃料電池は１００℃以下で作動するため電池電極として使用する白金系触媒が一酸化炭素により被毒するため、十分な発電特性が得られなくなる。そこで改質後のプロセスガス中に含まれる一酸化炭素と、水を反応させるためのＣＯ変成器を設ける。また、発電特性を落とさないために、さらに、一酸化炭素を選択的に酸化させ一酸化炭素を低減するＣＯ除去器を設ける（例えば、特許文献１参照）。
【０００５】
図４に、従来の燃料電池システムを示す（例えば、特許文献２参照）。従来の燃料電池用改質装置３０は、脱硫した原料炭化水素系燃料ガスと水を反応させて水素リッチなガスに改質するニッケル系、ルテニウム系、ロジウム系などの改質触媒３１を具備した改質器３２と、燃料ガスを改質器３２に供給する燃料供給部３３と、水を改質器３２に供給する水供給部３４と、燃焼管３５での燃焼用燃料の燃焼により改質反応に必要な熱量を与える加熱手段３６と、改質器３２から流出する改質ガス中に含まれる一酸化炭素を水と反応させて二酸化炭素に変成する銅−亜鉛系変成触媒などを備えたＣＯ変成器３７と、ＣＯ変成器３７から流出する変成ガス中に含まれる一酸化炭素を空気または酸素と反応させて二酸化炭素にする白金、ルテニウムなどの選択酸化触媒を具備した図示しないＣＯ除去器とを備えている。
【０００６】
脱硫した原料炭化水素系燃料ガスは、水蒸気が添加された後に燃料供給部３３から改質器３２に送られる。水蒸気は、水蒸気発生器３８によりシステム内を流れる冷却水などの水が、例えば加熱手段３６で予熱され燃料電池装置の排熱と熱交換されることによって生成される。水蒸気が添加された燃料ガスは改質器３２の改質用触媒３１と接触して触媒反応（およそ７００℃、吸熱反応）により水素に富むガス（水素リッチガス）に水蒸気改質する。生成された水素リッチガスは一酸化炭素を含んでいるため、ＣＯ変成器３７にて余剰の水蒸気との反応（およそ２００〜３００℃、発熱反応）により一酸化炭素を二酸化炭素に変成する。ＣＯ変成器３７から流出する変成ガス中に含まれる一酸化炭素を図示しないＣＯ除去器の選択酸化触媒と接触させて空気または酸素と反応（およそ１００〜２００℃、発熱反応）させて二酸化炭素にして、一酸化炭素濃度の低い水素リッチガスに改質する。
上記のようにして得られた水素リッチガスは、燃料電池３９の水素極３９ａに連続的に供給されて、空気極３９ｂに供給される空気との間で電池反応を起こして発電する。
【０００７】
従来、上記の燃料電池システムの停止時には、改質装置のプロセス中に滞留している水分を排出するために、改質装置のプロセスに必ず窒素を流通させ、システムを停止させていた。改質装置の降温、停止時に、窒素を流通させず、原燃料供給および水供給を停止すると、十数サイクルで改質率が低下し、燃料電池の寿命性能が急激に低減する問題がある。そのため、燃料電池システムの設置場所には、窒素のインフラが必要であり、燃料電池の設置に制限があった。
そこで改質装置内、特にＣＯ変成器の変成触媒が酸素や水分との接触により劣化するので、ＣＯ変成器内に滞留している水分を排出するなどの考案がなされている（特許文献３参照）。それによると、改質反応部の温度が所定の温度（原燃料の熱分解温度）以下になったことを判断して、水供給を停止し、改質反応部へ原燃料を供給するというものである。
【０００８】
しかし、改質器への水供給を停止する場合、水供給停止温度が低すぎると、滞留した水が完全に置換されないまま触媒の温度が低下し、改質触媒や選択酸化触媒などの金属酸化物担体触媒表面への水分子の吸着が強固になり、改質触媒や選択酸化触媒の劣化が促進されるという問題が発生する（金属酸化物の表面は、水存在下において、水を化学吸着し、解離して生じたＯＨ基が存在する。このＯＨ基は安定で、γ−アルミナの場合は、このＯＨ基に水和した水は、２００℃程度まで蒸発しない）（非特許文献１参照）。
【０００９】
【特許文献１】
特開平７−１２６００１号公報
【特許文献２】
特開２０００−２８１３１号公報
【特許文献３】
特開２０００−９５５０４号公報
【非特許文献１】
化学工学便覧改訂第５版、ｐ２４５
【００１０】
【発明が解決しようとする課題】
さらに、改質器の温度が下がると、改質器を出てＣＯ変成器、ＣＯ除去器に達するプロセスガス温度も低下するため、それらの触媒温度が下がり過ぎ、滞留した水を十分に置換できないことがあるか、または、それを置換するために原燃料のみを大量に消費することになるという問題がある。
【００１１】
本発明の第１の目的は、窒素のインフラのない場所でも、改質器の寿命を低下させることなく、改質器の起動、停止を繰り返すことができ、逆に改質器の寿命を向上させることができ、燃料電池システムの寿命を飛躍的に向上させることができる、燃料電池システムを提供することであり、
本発明の第２の目的は、燃料電池システム停止方法であって、改質器の起動、停止を繰り返しても、変成触媒に対する水の影響や原燃料の熱分解による改質触媒上への炭素析出を抑えるとともに、改質装置すべてに使用される触媒に対して影響が少なく、燃料電池システムの寿命を飛躍的に向上させることができる、かつ、燃料電池システム停止の際に使用される原燃料を燃焼させることによって、有効に利用して熱効率を向上できる燃料電池システム停止方法を提供することである。
【００１２】
【課題を解決するための手段】
本発明者等は前記課題を解決するために鋭意研究した結果、留意すべき点は、改質器への水供給停止温度であり、水供給停止温度が、原燃料の熱分解温度以上であると、改質器内で熱分解を生じ、炭素を析出すると考えられ、また、原燃料の熱分解温度以下であれば、触媒の温度が下がり過ぎ、逆に触媒に対して悪影響を与えるが、水供給停止温度が、原燃料の熱分解温度以上であっても、改質器内に残存する水蒸気と原燃料が改質反応を継続し、その吸熱反応によって改質器の温度が急激に低下し、改質器内の水が完全に置換される前に、一気に熱分解温度以下に降温できることを見いだした。
すなわち、燃料電池システム停止時、改質器の降温する過程において、改質器の加熱手段への燃料供給を停止してエネルギー供給を停止し、原燃料および水を供給し続けて、水蒸気改質反応による吸熱によって、速やかに改質器の温度を降下させ、改質用原燃料の熱分解による炭素の析出が生じない条件まで降温させた後、改質反応に必要な水の供給を停止し、その間に燃料電池システムに供給し続ける原燃料によって、改質装置のプロセス中に存在する水分を排出することによって、窒素のインフラのない場所においても、燃料電池システムの起動停止に伴う寿命を低下を抑制し、燃料電池システムの寿命を飛躍的に向上することができることを見いだし、本発明を成すに到った。
【００１３】
本発明の請求項１記載の燃料電池システムは、改質装置において脱硫した改質用原燃料を水素リッチなガスに改質し、改質したプロセスガスを燃料電池に供給して発電する燃料電池システムであって、
前記改質装置は、改質用原燃料中の硫黄分を脱硫する脱硫手段と水蒸気改質反応を進行させるのに必要な熱量を与える加熱手段を備え、かつ改質用原燃料および水蒸気改質反応に必要な水から水蒸気改質反応によって水素リッチなガスに改質する水蒸気改質器と、水蒸気改質器において改質された水素リッチなガス中のＣＯ濃度を低減させるＣＯ変成器と、ＣＯ変成器においてＣＯ濃度を低減されたガス中のＣＯ濃度をさらに低減させるＣＯ除去器とを備えるとともに、
前記水蒸気改質器の加熱手段への燃料供給を停止する燃料供給停止手段と、前記水蒸気改質器の出口触媒温度を検出する温度検出手段と、改質反応に必要な水の供給を停止する水供給停止手段と、前記改質装置からのプロセスガスの燃料電池への供給を停止し燃焼する燃焼手段と、前記改質装置への原燃料供給停止を行う原燃料供給停止手段とを備え、
前記改質装置停止時に、前記燃料供給停止手段により前記加熱手段への燃料供給を停止して前記温度検出手段により検出された温度が所定の温度になるまで降温させ、前記加熱手段への燃料供給停止と略同時に前記改質装置からのプロセスガスの燃料電池への供給を停止し前記燃焼手段により燃焼し、前記水供給停止手段により水の供給を停止し、原燃料により前記改質装置内を置換した後、前記原燃料供給停止手段により原燃料の供給を停止することを特徴とする。
【００１４】
改質装置停止時には、先ず燃料供給停止手段により改質器の加熱手段への燃料供給を停止し、原燃料および水を供給し続けて水蒸気改質反応による吸熱によって、速やかに改質器の温度を降下させ、改質用原燃料の熱分解による炭素の析出が生じない条件まで降温させた後（水蒸気改質器の出口触媒温度を検出する温度検出手段により検出された温度が所定の温度、例えば７００℃以下２００℃の範囲内となった時）、水供給停止手段により改質反応に必要な水の供給を停止し、その間に燃料電池システムに供給し続ける原燃料によって、改質装置のプロセス中を置換して改質装置のプロセス中に存在する水分を排出し、そして原燃料供給停止手段により原燃料の供給を停止することにより、窒素のインフラのない場所でも、改質器の寿命を低下させることなく、改質器の起動、停止を繰り返すことができ、逆に改質器の寿命を向上させることができ、燃料電池システムの寿命を飛躍的に向上できる。
そして加熱手段への燃料供給停止と略同時に改質装置からのプロセスガスの燃料電池への供給を停止し、このプロセスガスを燃焼手段で燃焼することによって有効に利用して燃料電池システムの熱効率を向上できる。
【００１５】
本発明の請求項２記載の燃料電池システムは、請求項１記載の燃料電池システムにおいて、前記脱硫手段が、常温でも硫黄分を吸着脱硫可能な脱硫手段であることを特徴とする。
【００１６】
常温でも硫黄分を吸着脱硫可能な脱硫手段を用いると、改質装置運転中は勿論のこと停止操作時においても原燃料中の硫黄分を水蒸気改質反応に悪影響を与えないレベルまで脱硫することができる。
【００１７】
本発明の請求項３記載の燃料電池システムは、請求項１あるいは請求項２記載の燃料電池システムにおいて、前記燃焼手段により燃焼して得られた熱を熱交換器を介して貯蔵する蓄熱手段を備えたことを特徴とする。
【００１８】
燃焼手段により燃焼して得られた熱を熱交換器を介して貯蔵する蓄熱手段を備えれば、燃焼して得られた熱を有効に利用して燃料電池システムの熱効率をより向上できる。
【００１９】
本発明の請求項４記載の燃料電池システムは、請求項３記載の燃料電池システムにおいて、前記蓄熱手段が貯湯タンクであることを特徴とする。
【００２０】
燃焼手段により燃焼して得られた熱を貯湯タンクの湯温上昇に有効に利用して燃料電池システムの熱効率をより向上できる。
【００２１】
本発明の請求項５記載の燃料電池システムは、請求項１から請求項４のいずれかに記載の燃料電池システムにおいて、前記改質装置の出口にガス開閉弁を設け、前記原燃料供給停止手段により改質装置への改質用原燃料の供給を停止した際、前記ガス開閉弁を閉じることを特徴とする。
【００２２】
原燃料供給停止手段により改質装置への改質用原燃料の供給を停止した際、前記ガス開閉弁を閉じることによりＣＯ低減部触媒が酸素や水分との接触により劣化するのを防止できる。
【００２３】
本発明の請求項６記載の燃料電池システムは請求項５記載の燃料電池システムにおいて、前記原燃料供給停止手段により改質装置への改質用原燃料の供給を停止し、ＣＯ低減部の温度が５０℃以下になった時、一旦、前記原燃料供給停止手段により改質装置への改質用原燃料の供給を行った後、再度、前記原燃料供給停止手段により改質装置への改質用原燃料の供給を停止することを特徴とする。
【００２４】
ＣＯ低減部の温度が５０℃以下になった時、一旦、前記原燃料供給停止手段により改質装置への改質用原燃料の供給を行い改質装置の内部の圧力を常圧に維持することにより、改質装置の内部が負圧になるのを防止できる。
【００２５】
本発明の請求項７記載の燃料電池システムは、請求項１から請求項６のいずれかに記載の燃料電池システムにおいて、前記燃焼手段により燃焼して得られた熱をＣＯ変成器および／またはＣＯ除去器の温度維持に使用する手段を備えたことを特徴とする。
【００２６】
水の供給停止と略同時に改質装置からのプロセスガスの燃料電池への供給を停止し、このプロセスガスを燃焼手段で燃焼して得られた熱をＣＯ変成器および／またはＣＯ除去器の温度維持に使用することによって有効に利用して燃料電池システムの熱効率をより向上できる。
【００２７】
本発明の請求項８は、改質装置において脱硫した改質用原燃料を水素リッチなガスに改質し、改質したプロセスガスを燃料電池に供給して発電する請求項１から請求項７のいずれかに記載の燃料電池システムの停止方法であって、
前記改質装置停止時に、先ず前記燃料供給停止手段により前記水蒸気改質器の加熱手段への燃料供給を停止し、前記加熱手段への燃料供給停止と略同時に前記改質装置からのプロセスガスの燃料電池への供給を停止して、このプロセスガスを前記燃焼手段で燃焼し、前記水蒸気改質器の出口触媒温度を検出する温度検出手段により検出された温度が７００℃以下２００℃の範囲内となった時、前記水供給停止手段により改質反応に必要な水の供給を停止し、そして前記温度検出手段により検出された温度が１００℃以上４００℃以下の範囲内となった時、前記原燃料供給停止手段により改質装置への改質用原燃料の供給を停止することを特徴とする燃料電池システム停止方法である。
【００２８】
改質装置停止時には、先ず燃料供給停止手段により改質器の加熱手段への燃料供給を停止し、原燃料および水を供給し続けて水蒸気改質反応による吸熱によって、速やかに改質器の温度を降下させ、温度検出手段により検出された温度が７００℃以下２００℃の範囲内となった時、水供給停止手段により改質反応に必要な水の供給を停止し、その間に燃料電池システムに供給し続ける原燃料によって、改質装置のプロセス中に存在する水分を排出し、そして温度検出手段により検出された温度が１００℃以上４００℃以下の範囲内となった時に、原燃料供給停止手段により原燃料を供給を停止することにより、原燃料の熱分解による炭素の析出を防止でき、窒素のインフラのない場所でも、改質器の寿命を低下させることなく、改質器の起動、停止を繰り返すことができ、逆に改質器の寿命を向上させることができ、燃料電池システムの寿命を飛躍的に向上できる。
そして加熱手段への燃料供給停止と略同時に改質装置からのプロセスガスの燃料電池への供給を停止し、このプロセスガスを燃焼手段で燃焼する燃焼させることによって有効に利用して燃料電池システムの熱効率を向上できる。
【００２９】
本発明の請求項９は、請求項８記載の燃料電池システム停止方法において、前記水蒸気改質器の出口触媒温度が改質用原燃料の熱分解温度＋１５０℃〜−５０℃の範囲内となった時、前記水供給停止手段により改質反応に必要な水の供給を停止することを特徴とする。
【００３０】
改質器の出口触媒温度が原燃料の熱分解温度＋１５０℃〜−５０℃の範囲内となった時、前記水供給停止手段により水の供給を停止すれば原燃料の熱分解による炭素の析出が生じない。−５０℃より低すぎると、水蒸気改質反応が進行せず、滞留水蒸気の排出が遅くなる。
【００３１】
本発明の請求項１０は、請求項９記載の燃料電池システム停止方法において、前記水供給停止手段により改質反応に必要な水の供給を停止してから前記改質装置容量の１〜５倍の容積の原燃料を置換のために供給するか、あるいは前記水供給停止手段により改質反応に必要な水の供給を停止してから前記原燃料供給停止手段により改質装置への改質用原燃料の供給を停止するまでの時間が５分以上６０分以下となるようにすることを特徴とする。
【００３２】
前記水供給停止手段により改質反応に必要な水の供給を停止してから、水の供給を停止し改質装置容量の１〜５倍の容積の原燃料を置換のために供給するか、あるいは原燃料供給停止手段により改質装置への原燃料の供給を停止するまでの時間が５分以上６０分以下であると、原燃料の消費量を低減でき燃料電池システムの効率を向上できる。
【００３３】
本発明の請求項１１は、請求項８から請求項１０のいずれかに記載の燃料電池システム停止方法において、前記燃焼手段により燃焼して得られた熱を熱交換器を介して蓄熱手段に貯蔵することを特徴とする。
【００３４】
燃焼手段により燃焼して得られた熱を熱交換器を介して貯蔵する蓄熱手段を備えれば、燃焼して得られた熱を有効に利用して燃料電池システムの熱効率をより向上できる。
【００３５】
本発明の請求項１２は、請求項１１記載の燃料電池システム停止方法において、前記蓄熱手段が貯湯タンクであることを特徴とする。
【００３６】
燃焼手段により燃焼して得られた熱を貯湯タンクの湯温上昇に有効に利用して燃料電池システムの熱効率をより向上できる。
【００３７】
本発明の請求項１３は請求項８から請求項１２のいずれかに記載の燃料電池システム停止方法において、前記改質装置の出口にガス開閉弁を設け、前記原燃料供給停止手段により改質装置への改質用原燃料の供給を停止した際、前記ガス開閉弁を閉じることを特徴とする。
【００３８】
原燃料供給停止手段により改質装置への改質用原燃料の供給を停止した際、前記ガス開閉弁を閉じることによりＣＯ低減部触媒が酸素や水分との接触により劣化するのを防止できる。
【００３９】
本発明の請求項１４は、請求項１３記載の燃料電池システム停止方法において、前記原燃料供給停止手段により改質装置への改質用原燃料の供給を停止し、ＣＯ低減部の温度が５０℃以下になった時、一旦、前記原燃料供給停止手段により改質装置への改質用原燃料の供給を行った後、再度、前記原燃料供給停止手段により改質装置への改質用原燃料の供給を停止することを特徴とする。
【００４０】
ＣＯ低減部の温度が５０℃以下になった時、一旦、前記原燃料供給停止手段により改質装置への改質用原燃料の供給を行い、原燃料を前記改質器などに導入して改質装置の内部の圧力を常圧に維持することにより、改質装置の内部が負圧になるのを防止できる。
【００４１】
本発明の請求項１５は、請求項８から請求項１４のいずれかに記載の燃料電池システム停止方法において、前記燃焼手段により燃焼して得られた熱をＣＯ変成器および／またはＣＯ除去器の温度維持に使用することを特徴とする。
【００４２】
燃焼手段で燃焼して得られた熱をＣＯ変成器および／またはＣＯ除去器の温度維持に使用することによって有効に利用して燃料電池システムの熱効率をより向上できる。
【００４３】
【発明の実施の形態】
以下、図面により本発明の実施の形態を詳細に説明する。
図１は本発明の燃料電池システムの１実施の形態を説明する説明図である。
本発明の燃料電池システム１は、メタン、プロパン、ブタン等の炭化水素系の原燃料ガス中の硫黄分を常温でも吸着脱硫可能な脱硫器２と、脱硫した原燃料ガスと気化器３で水を気化して得られる水蒸気とから水蒸気改質反応により水素リッチな改質ガスを生成する水蒸気改質器４と、改質ガス中に含まれ、燃料電池５の白金系又は合金系電極触媒を被毒して電極特性を低下させるＣＯガスの大部分を変成してＣＯ_２にするＣＯ変成器６と、ＣＯ変成器６にてＣＯ濃度が低減された改質ガス中に未だ残存するＣＯガスをＣＯ選択酸化反応によりＣＯ_２に酸化するＣＯ除去器７とを備える改質装置８を備えている。
【００４４】
ここで水蒸気改質反応にはニッケル系、ルテニウム系、ロジウム系等の改質触媒を、変成反応には銅−亜鉛系の変成触媒を、ＣＯ選択酸化反応には白金、ルテニウム等のＣＯ酸化触媒をそれぞれ用いるものであり、これらの触媒を各反応器に充填して用いる。
【００４５】
９は改質器４に備えられたバーナなどの加熱手段であり、例えば、燃料電池システムのスタート時には原燃料ガスなどの燃料を供給して燃焼して水蒸気改質反応を進行させるのに必要な熱量を改質触媒に与え、そして燃料電池システムのスタート後に燃料電池５において発電が安定して行われるようになったら原燃料ガスなどの燃料を燃料電池５で消費されなかった未反応ガスに切り替えて供給して燃焼して水蒸気改質反応を進行させるのに必要な熱量を改質触媒に与える。
【００４６】
１０は、原燃料供給ラインに設けた開閉弁などの原燃料供給停止手段、１１は水供給ラインに設けた開閉弁などの水供給停止手段、１２は加熱手段９への燃料供給ラインに設けた開閉弁などの燃料供給停止手段、１３、１４はそれぞれＣＯ変成器６とＣＯ除去器７とからなるＣＯ低減部１５の入口および出口に設けたガス開閉弁を示す。１６は、改質器４の出口触媒温度を検出する温度検出手段を示す。
【００４７】
１０、１１、１２、１３、１４、１６は図示しない制御装置に接続されており、１０、１１、１２、１３、１４の開閉動作の制御はこの制御装置を含む制御手段により行われる。
【００４８】
１７は改質装置８からのプロセスガスの燃料電池５への供給を停止した際にそれを燃焼する燃焼手段であり、１８は燃焼手段１７で燃焼して得られた熱を熱交換する熱交換器であり、１９は熱交換器１８で回収した熱を湯として貯蔵する蓄熱手段としての貯湯タンクである。２０は前記燃焼手段１７で燃焼して得られた熱をＣＯ変成器６およびＣＯ除去器７の温度維持に使用するための手段であり、この手段２０はＣＯ変成器６およびＣＯ除去器７を収容する収容装置、ダクトや断熱材などを含む。
【００４９】
前記改質装置８の停止時には、先ず燃料供給停止手段１２の開閉弁を閉めて改質器４の加熱手段９への燃料供給を停止する。そして、改質器４へ原燃料および水を供給し続けると水蒸気改質反応による吸熱によって、速やかに改質器４の温度が降下する。原燃料の熱分解による炭素の析出が生じない条件まで改質器４を降温させた後（改質器４の出口触媒温度を検出する温度検出手段１６により検出された温度が所定の温度、例えば７００℃以下２００℃の範囲内となった時）、水供給停止手段１１の開閉弁を閉めて改質反応に必要な水の供給を停止する。その間に原燃料によって改質装置８のプロセス中を置換しプロセス中に存在する水分を排出した後、原燃料供給停止手段１０の開閉弁を閉めて原燃料の供給を停止する。好ましくは温度検出手段１６により検出された温度が１００℃以上４００℃以下の範囲内となった時、原燃料供給停止手段１０の開閉弁を閉めて原燃料の供給を停止する。このようにすることにより原燃料の熱分解による炭素の析出を防止でき、窒素のインフラのない場所でも、改質器４の寿命を低下させることなく、改質器４の起動、停止を繰り返すことができ、逆に改質器４、ＣＯ変成器６およびＣＯ除去器７の寿命を向上させることができ、燃料電池システム１の寿命を飛躍的に向上できる。
上記のように、改質用水の供給を停止する温度の例として７００℃以下２００℃、原燃料の供給を停止する温度の例として１００℃以上４００℃℃以下を挙げ両者はオーバーラップする範囲があるが、改質用水の供給を停止する温度は、原燃料の供給を停止する温度と同じかあるいは高い温度である。
【００５０】
改質器４の出口触媒温度を検出する温度検出手段１６により検出された温度が原燃料の熱分解温度＋１５０℃〜−５０℃の範囲内となった時、水供給停止手段１５の開閉弁を閉めて改質反応に必要な水の供給を停止するようにすれば、原燃料の熱分解による炭素の析出が生じない。原燃料の熱分解温度−５０℃より低すぎると、水蒸気改質反応が進行せず、滞留水蒸気の排出が遅くなる。
【００５１】
そして水の供給停止と略同時にガス開閉弁１４を閉めて改質装置８からのプロセスガスの燃料電池５への供給を停止し、このプロセスガスを燃焼手段１７で燃焼し、熱交換器１８で回収した熱を湯として貯湯タンク１９で貯蔵したり、燃焼手段１７で燃焼して得られた熱を手段２０へ送りＣＯ変成器６およびＣＯ除去器７の温度維持に使用するなどして有効に利用すれば燃料電池システム１の熱効率を向上できる。
【００５２】
原燃料供給停止手段１０により改質装置８への原燃料の供給を停止した際、ガス開閉弁１３、１４を閉じることによりＣＯ低減部１５の触媒が酸素や水分との接触により劣化するのを防止できる。
【００５３】
原燃料供給停止手段１０により改質装置８への原燃料の供給を停止した後、ＣＯ低減部１５の温度が５０℃以下になった時、一旦、原燃料供給停止手段１０の開閉弁を開けて改質装置８への原燃料の供給を行い、原燃料を改質器４などに導入し、改質装置８内を原燃料で置換した後、再度、原燃料供給停止手段１０の開閉弁を閉めて改質装置８への原燃料の供給を停止することにより、改質装置８の内部の圧力を常圧に維持し、改質装置８の内部が負圧になるのを防止できる。改質装置８の内部が負圧になると電磁弁などのシール部などから空気が混入して低減部１５の触媒などが劣化する。
【００５４】
水供給停止手段１１により改質反応に必要な水の供給を停止した後に、改質器４の出口触媒温度を検出する温度検出手段１６により検出された温度が１００℃以上４００℃以下の範囲内となった時、原燃料供給停止手段１０の開閉弁を閉めて改質装置８への原燃料の供給を停止すれば原燃料の熱分解による炭素の析出が生じない。
【００５５】
水供給停止手段１１により改質反応に必要な水の供給を停止した後に、改質装置８の容量の１〜５倍の容積の原燃料を置換のために供給するかあるいは原燃料供給停止手段１０により改質装置８への原燃料の供給を停止するまでの時間を図示しないタイマーなどの時間判定手段により５分以上６０分以下となるように制御すると、原燃料の消費量を低減でき燃料電池システムの効率を向上できる。
【００５６】
上記実施の形態の説明は、本発明を説明するためのものであって、特許請求の範囲に記載の発明を限定し、或は範囲を減縮するものではない。又、本発明の各部構成は上記実施の形態に限らず、特許請求の範囲に記載の技術的範囲内で種々の変形が可能である。
例えば上記実施の形態の説明においては、原燃料供給停止手段１０を脱硫器２の原燃料入口側の管路に設けた例を示したが、脱硫剤として常温のみで硫黄分吸着脱硫する脱硫剤を使用した場合は、原燃料供給停止手段１０を脱硫器２の出口側の管路に設けることが好ましい。
【００５７】
【実施例】
以下、本発明の内容を実施例および比較例によってさらに具体的に説明するが、本発明は実施例になんら限定されるものではない。
（実施例１）
［改質器運転条件］
Ｓ／Ｃ＝３．０
ＧＨＳＶ＝１０００ｈｒ^−１
改質触媒：市販ルテニウムアルミナ触媒
改質触媒制御温度：出口７００℃
改質器昇温５時間
［改質器停止条件Ａ］
加熱手段への燃料供給停止から水供給停止までの時間：２分間
（水供給停止時の改質器の出口触媒温度：５８０℃）
水供給停止から原燃料停止までの時間：１０分間
原燃料供給量は、ＧＨＳＶ＝１０００ｈｒ^−１運転条件の流量と同じ。
（原燃料供給停止時の改質器の出口触媒温度：３００℃）
改質装置入口開閉弁１０を５０℃にて一旦開、１０秒後、再度閉じた。
置換に使用した原燃料は、貯湯タンク１９の湯の昇温に使用した。
上記の改質器停止条件Ａで５０サイクルの起動停止試験を行った。
そして、サイクル数と、下記式で計算した改質率の関係および改質装置８の出口ＣＯ濃度を測定した結果の関係を図２に示す。
【００５８】
式：
改質率＝［（ＣＯ_２，ＣＯ）／（ＣＯ_２，ＣＯ，ＣＨ_４）］×１００
【００５９】
（実施例２）
［改質器運転条件］
実施例１と同じ。
［改質器停止条件Ｂ］
加熱手段への燃料供給停止から水供給停止までの時間：５分間
（水供給停止時の改質器の出口触媒温度：４００℃）
水供給停止から原燃料停止までの時間：６０分間
原燃料供給量は、ＧＨＳＶ＝１０００ｈｒ^−１運転条件の流量と同じ。
（原燃料供給停止時の改質器の出口触媒温度：５０℃）
改質装置入口開閉弁１０を５０℃にて一旦開、１０秒後、再度閉じた。
置換に使用した原燃料は、貯湯タンク１９の湯の昇温に使用した。
上記の改質器停止条件Ｂで５０サイクルの起動停止試験を行った。
そして、サイクル数と、上記式で計算した改質率の関係および改質装置８の出口ＣＯ濃度を測定した結果の関係を図２に示す。
【００６０】
（実施例３）
［改質器運転条件］
実施例１と同じ。
［改質器停止条件Ｃ］
加熱手段への燃料供給停止から水供給停止までの時間：０分間
（水供給停止時の改質器の出口触媒温度：７００℃）
水供給停止から原燃料停止までの時間：１０分間
原燃料供給量は、ＧＨＳＶ＝１０００ｈｒ^−１運転条件の流量と同じ。
（原燃料供給停止時の改質器の出口触媒温度：３００℃）
改質装置入口開閉弁１０を５０℃にて一旦開、１０秒後、再度閉じた。
置換に使用した原燃料は、貯湯タンク１９の湯の昇温に使用した。
上記の改質器停止条件Ｃで５０サイクルの起動停止試験を行った。
そして、サイクル数と、上記式で計算した改質率の関係および改質装置８の出口ＣＯ濃度を測定した結果の関係を図２に示す。
【００６１】
（実施例４）
［改質器運転条件］
実施例１と同じ。
［改質器停止条件Ｄ］
加熱手段への燃料供給停止から水供給停止までの時間：３０分間
（水供給停止時の改質器の出口触媒温度：３００℃）
水供給停止から原燃料停止までの時間：４分間
原燃料供給量は、ＧＨＳＶ＝１０００ｈｒ^−１運転条件の流量と同じ。
（原燃料供給停止時の改質器の出口触媒温度：２４０℃）
上記の改質器停止条件Ｄで５０サイクルの起動停止試験を行った。
そして、サイクル数と、上記式で計算した改質率の関係および改質装置８の出口ＣＯ濃度を測定した結果の関係を図２に示す。
【００６２】
（比較例１）
［改質器運転条件］
実施例１と同じ。
［改質器停止条件Ｘ］
加熱手段への燃料供給停止から水供給停止までの時間：０分間
（水供給停止時の改質器の出口触媒温度：７００℃）
水供給停止から原燃料停止までの時間：０分間
原燃料供給量は、ＧＨＳＶ＝１０００ｈｒ^−１運転条件の流量と同じ。
（原燃料供給停止時の改質器の出口触媒温度：７００℃）
上記の改質器停止条件Ｘで５０サイクルの起動停止試験を行った。
そして、サイクル数と、上記式で計算した改質率の関係および改質装置８の出口ＣＯ濃度を測定した結果の関係を図２に示す。
【００６３】
（比較例２）
［改質器運転条件］
実施例１と同じ。
［改質器停止条件Ｙ］
加熱手段への燃料供給停止から水供給停止までの時間：３０分間
（水供給停止時の改質器の出口触媒温度：１００℃）
水供給停止から原燃料停止までの時間：４分間
原燃料供給量は、ＧＨＳＶ＝１０００ｈｒ^−１運転条件の流量と同じ。
（原燃料供給停止時の改質器の出口触媒温度：８５℃）
上記の改質器停止条件Ｙで５０サイクルの起動停止試験を行った。
そして、サイクル数と、上記式で計算した改質率の関係および改質装置８の出口ＣＯ濃度を測定した結果の関係を図２に示す。
【００６４】
（改質器への水供給停止してからの経過時間と改質器の出口触媒温度の関係）
実施例１、２、３および比較例１の場合について、改質器への水供給停止してからの経過時間と改質器の出口触媒温度の関係を図３に示す。
【００６５】
（５０サイクルの起動停止試験の結果）
（実施例１、２、３、４）
実施例１、２、３においては、５０サイクルの起動停止試験を行っても改質率の大きな変化および低下も見られなかった。
実施例１、２、３においては、改質器４への水供給を停止してからも、改質器４内に滞留している水によって、改質反応が進行するため、図３に示すように改質器４の温度の低下速度は急激であった。このため、水供給停止時の改質器４の出口温度が、当初は原燃料の熱分解温度以上であっても、すぐに熱分解温度以下に降温するために、原燃料の熱分解による炭素析出の影響はなかったものと考えられる。さらに、改質反応が進行するため、改質器４内の水蒸気量が低減し、改質反応によってガス量が増えるために相対湿度も低減し、改質器４内の滞留水蒸気の排出速度が速くなったために、良い効果がもたらされものと考えられる。
ＣＯ除去器７の出口（改質装置８の出口）ＣＯ濃度に関しても、多少のふれはあるものの９ｐｐｍ以下を維持した。
【００６６】
実施例３については、性能に関する劣化は見られず、改質器４を解体したところ、触媒には炭素が析出している様子は確認されなかった。今回の５０サイクル程度では、改質率やＣＯ濃度のような性能には、全く影響がなかった。
【００６７】
よって、改質器４の出口触媒温度が７００℃にて水供給を停止してもよいが、望ましくは、原燃料の熱分解温度＋１５０℃以下が良い。低すぎると、改質反応が進行せず、滞留水蒸気の排出が遅くなる。
凡そ、原燃料の熱分解温度＋１５０℃の温度で水の供給を停止すれば、改質器４は数十秒で熱分解温度以下に達する。また、このときの水蒸気置換量は定常運転時の約３０％であり、原燃料の熱分解温度においても、水蒸気が存在していることが確認され、改質触媒上での原燃料の熱分解は起こらない。
【００６８】
実施例４は、改質器４への水供給停止時の改質器４の出口触媒温度が３００℃程度であり、燃料の熱分解の影響はないと考えられる。ＣＯ変成器６の温度分布が初期に比較して反応部位が後方にずれていた。しかし今回の５０サイクル程度では、改質率やＣＯ濃度のような性能には、あまり影響がなかった。
【００６９】
また、水の排出に使用した原燃料は、改質装置８の出口から、燃料電池５には供給されず、ＣＯ低減部１５の温度維持、および貯熱タンク１９の湯温上昇に使用された。
実施例２においては、ＣＯ低減部１５の温度維持によって、ＣＯ低減部１５内の水蒸気を早急に排出することができた。
また、貯湯タンク１９の湯温上昇にも有効に使用され、６４℃〜６７℃の湯が貯湯タンク１９内に蓄えられた。
【００７０】
（比較例１、２）
比較例１は原燃料による水蒸気パージをしていないために、改質装置８内に凝結水が滞留していると考えられる。起動時にも、この凝結水の存在のためか、各反応器の昇温に時間を要し、昇温しても、特にＣＯ低減部１５（ＣＯ変成器６、ＣＯ除去器７）においての触媒に対する影響は大きく、３サイクル目には、改質装置８の出口ＣＯ濃度は２０ｐｐｍ近くに達していた。
改質器４においては加熱手段９（加熱用バーナー）によって加熱するために、ＣＯ低減部１５程の影響は受けなかったようであるが、１０サイクルを超えたあたりから、触媒層内温度分布に変化が見られ、サイクルを追う毎に、いわゆるバンドエージング現象が起こり、２９サイクル目では改質率が約４８％にまで低下した。
【００７１】
比較例２は、改質装置８内に滞留している水分量が多かったと考えられ、よって、触媒の失活が急速に進行し、改質装置８の出口ＣＯ濃度が上昇したものと考えられる。
【００７２】
水供給停止時の改質器４の出口触媒温度は、高すぎると原燃料の熱分解による炭素析出が生じるが、加熱手段９への燃料供給を停止すれば、改質器４へ供給される原燃料が、改質器４内に滞留している水蒸気と改質反応を起こし、急激に改質器４の温度が低下し、すぐに熱分解温度以下に達する。
改質器４の熱容量にも依存するが、水供給停止時の改質器４の出口触媒温度は厳密に「原燃料の熱分解温度以下でなければならない」とはいえないことが見いだされた。
【００７３】
凡そ、原燃料の熱分解温度＋１５０℃の温度で水の供給を停止すれば、改質器４の出口触媒温度は数十秒で熱分解温度以下に達する。また、この時の水蒸気置換量は定常運転時の約３０％であり、原燃料の熱分解温度においても、水蒸気が存在していることが確認され、改質触媒上での熱分解は起こらないと考えられる。
水供給停止時の改質器４の出口触媒温度が、原燃料の熱分解温度より低くなると、供給されている原燃料と、改質器４内に滞留している水蒸気との改質反応速度が遅くなり、また、改質反応による水蒸気の消費量も多くなく、改質ガスの体積もあまり増えないため、水蒸気の相対湿度が下がらず、水蒸気の排出に時間を要することになる。
よって、水供給停止時の改質器４の出口触媒温度の下限は、せいぜい、原燃料の熱分解温度−５０℃程度低い温度である。
【００７４】
改質器４への水供給停止後の燃料供給量について、通常、流量は燃料電池システム発電時の定格時の燃料流量にすることがシステム上簡単である。
その場合、最低でも改質装置８内の置換に５分は必要である。
【００７５】
一方、貯湯タンク１９の湯の温度が上がりきると、その後は燃料（プロセスガス）を無駄に流すだけになる。水温が数℃から２０℃程度であれば、条件にもよるが、ほぼ貯湯タンク１９内のお湯のすべてがほぼ所定の温度（６４から６７℃）に達するまでには、約６０分程度かかるため、これ以上燃料（プロセスガス）を流すことは燃料の無駄になるため、最大でも６０分である。
燃料（プロセスガス）供給時間が短いと、改質装置８内の温度が高い状態で、改質装置８の入口と出口の開閉弁１０、１３、１４を閉じることになり、内部が負圧になるため、改質装置８内の触媒温度が５０℃に低減したところで、一度、原燃料を供給し、内部の圧力を常圧に維持することが好ましい。
これらの操作によって、改質装置８内部の水蒸気を効率的に排出し、窒素のインフラがなくても、燃料電池システム１の寿命を飛躍的に向上させることができる。
【００７６】
（実施例５）
天然ガスを原燃料として用いた燃料電池システムの停止例を示す。
（通常運転時）
脱硫器（常温でも硫黄分を吸着脱硫可能な脱硫手段）：１５０〜２００℃
改質器：７００℃、原燃料および改質用水を供給する。
改質器の加熱手段のバーナで燃焼させる燃料：燃料電池オフガス
ＣＯ変成器：２００〜３００℃
ＣＯ除去器：１００〜１５０℃
燃料電池：改質ガスを用いて発電する。
【００７７】
（下記停止１〜停止５の順に燃料電池システムを停止する）
（停止１）
脱硫器：１５０〜２００℃
改質器：７００℃、原燃料および改質用水を供給する。
改質器の加熱手段のバーナでの燃焼を停止する。
ＣＯ変成器：２００〜３００℃
ＣＯ除去器：１００〜１５０℃
燃料電池：発電を停止し改質ガスを燃焼手段で燃焼して熱回収する。
【００７８】
（停止２）
脱硫器：１５０〜２００℃
改質器：４５０〜５００℃、原燃料供給するが熱分解回避のために改質用水を約５分間程度１／２〜１／３程度に減少する（改質器の形状、触媒量、ガス量などにより水がなくなるまでの時間は異なる）。
改質器の加熱手段のバーナでの燃焼停止
ＣＯ変成器：２００〜３００℃
ＣＯ除去器：１００〜１５０℃
燃料電池：発電を停止し改質ガスを燃焼手段で燃焼して熱回収する。
【００７９】
（停止３）
脱硫器：１００〜１５０℃
改質器：２００〜３００℃、原燃料供給するが改質用水を停止する。
改質器の加熱手段のバーナでの燃焼停止
ＣＯ変成器：１５０〜２００℃
ＣＯ除去器：７０〜１１０℃（７０℃以下にならないようにすることが肝要である。これはＳ／Ｃ＝３の時、７０℃弱程度の露点のガスがＣＯ変成器からでる可能性があるためである。ＣＯ除去器前にドレントラップを設けて水分を除去すれば、ＣＯ除去器の最低温度は特に決めなくてもよい。）
燃料電池：発電を停止し改質ガスを燃焼手段で燃焼して熱回収する。
【００８０】
（停止４）
脱硫器：１００〜１５０℃
改質器：２００〜３００℃、原燃料を停止する。
改質器の加熱手段のバーナでの燃焼停止
ＣＯ変成器：１５０〜２００℃
ＣＯ除去器：７０〜１１０℃
改質装置：原燃料にてガス封止。
【００８１】
停止３と停止４の間で、改質用水の供給を停止してから、改質装置容量の１〜５倍の容積の原燃料を置換のために供給するか、あるいは原燃料供給停止手段により改質装置への原燃料の供給を停止するまでの時間を５分以上６０分以下となるようにする。
【００８２】
（停止５）
脱硫器：停止
改質器：停止
改質器の加熱手段のバーナでの燃焼停止
ＣＯ変成器：５０℃以下
ＣＯ除去器：５０℃以下
改質装置：ガス開閉弁を開閉して改質装置内圧を保持する。
【００８３】
（実施例６）
ＬＰＧを原燃料として用いた燃料電池システムの停止例を示す。
（通常運転時）
脱硫器（常温でも硫黄分を吸着脱硫可能な脱硫手段）：１５０〜２００℃
改質器：７００℃、原燃料および改質用水を供給する。
改質器の加熱手段のバーナで燃焼させる燃料：燃料電池オフガス
ＣＯ変成器：２００〜３００℃
ＣＯ除去器：１００〜１５０℃
燃料電池：改質ガスを用いて発電する。
【００８４】
（下記停止１〜停止５の順に燃料電池システムを停止する）
（停止１）
脱硫器：１５０〜２００℃
改質器：７００℃、原燃料および改質用水を供給する。
改質器の加熱手段のバーナでの燃焼を停止する。
ＣＯ変成器：２００〜３００℃
ＣＯ除去器：１００〜１５０℃
燃料電池：発電を停止し改質ガスを燃焼手段で燃焼して熱回収する。
【００８５】
（停止２）
脱硫器：１５０〜２００℃
改質器：３５０〜４００℃、原燃料供給するが熱分解回避のために改質用水を約５分間程度１／２〜１／３程度に減少する（改質器の形状、触媒量、ガス量などにより水がなくなるまでの時間は異なる）。
改質器の加熱手段のバーナでの燃焼停止
ＣＯ変成器：２００〜３００℃
ＣＯ除去器：１００〜１５０℃
燃料電池：発電を停止し改質ガスを燃焼手段で燃焼して熱回収する。
【００８６】
（停止３）
脱硫器：１００〜１５０℃
改質器：２００〜３００℃、原燃料供給するが改質用水を停止する。
改質器の加熱手段のバーナでの燃焼停止
ＣＯ変成器：１５０〜２００℃
ＣＯ除去器：７０〜１１０℃（７０℃以下にならないようにすることが肝要である。これはＳ／Ｃ＝３の時、７０℃弱程度の露点のガスがＣＯ変成器からでる可能性があるためである。ＣＯ除去器前にドレントラップを設けて水分を除去すれば、ＣＯ除去器の最低温度は特に決めなくてもよい。）
燃料電池：発電を停止し改質ガスを燃焼手段で燃焼して熱回収する。
【００８７】
（停止４）
脱硫器：１００〜１５０℃
改質器：２００〜３００℃、原燃料を停止する。
改質器の加熱手段のバーナでの燃焼停止
ＣＯ変成器：１５０〜２００℃
ＣＯ除去器：７０〜１１０℃
改質装置：原燃料にてガス封止。
【００８８】
停止３と停止４の間で、改質用水の供給を停止してから、改質装置容量の１〜５倍の容積の原燃料を置換のために供給するか、あるいは原燃料供給停止手段により改質装置への原燃料の供給を停止するまでの時間を５分以上６０分以下となるようにする。
【００８９】
（停止５）
脱硫器：停止
改質器：停止
改質器の加熱手段のバーナでの燃焼停止
ＣＯ変成器：５０℃以下
ＣＯ除去器：５０℃以下
改質装置：ガス開閉弁を開閉して改質装置内圧を保持する。
【００９０】
【発明の効果】
本発明の請求項１記載の燃料電池システムは、改質装置において脱硫した改質用原燃料を水素リッチなガスに改質し、改質したプロセスガスを燃料電池に供給して発電する燃料電池システムであって、
前記改質装置は、改質用原燃料中の硫黄分を脱硫する脱硫手段と水蒸気改質反応を進行させるのに必要な熱量を与える加熱手段を備え、かつ改質用原燃料および水蒸気改質反応に必要な水から水蒸気改質反応によって水素リッチなガスに改質する水蒸気改質器と、水蒸気改質器において改質された水素リッチなガス中のＣＯ濃度を低減させるＣＯ変成器と、ＣＯ変成器においてＣＯ濃度を低減されたガス中のＣＯ濃度をさらに低減させるＣＯ除去器とを備えるとともに、
前記水蒸気改質器の加熱手段への燃料供給を停止する燃料供給停止手段と、前記水蒸気改質器の出口触媒温度を検出する温度検出手段と、改質反応に必要な水の供給を停止する水供給停止手段と、前記改質装置からのプロセスガスの燃料電池への供給を停止し燃焼する燃焼手段と、前記改質装置への原燃料供給停止を行う原燃料供給停止手段とを備え、
前記改質装置停止時に、前記燃料供給停止手段により前記加熱手段への燃料供給を停止して前記温度検出手段により検出された温度が所定の温度になるまで降温させ、前記加熱手段への燃料供給停止と略同時に前記改質装置からのプロセスガスの燃料電池への供給を停止し前記燃焼手段により燃焼し、前記水供給停止手段により水の供給を停止し、原燃料により前記改質装置内を置換した後、前記原燃料供給停止手段により原燃料の供給を停止することを特徴とするものであり、
改質装置停止時には、先ず燃料供給停止手段により改質器の加熱手段への燃料供給を停止し、原燃料および水を供給し続けて水蒸気改質反応による吸熱によって、速やかに改質器の温度を降下させ、改質用原燃料の熱分解による炭素の析出が生じない条件まで降温させた後（水蒸気改質器の出口触媒温度を検出する温度検出手段により検出された温度が所定の温度、例えば７００℃以下２００℃の範囲内となった時）、水供給停止手段により改質反応に必要な水の供給を停止し、その間に燃料電池システムに供給し続ける原燃料によって、改質装置のプロセス中を置換して改質装置のプロセス中に存在する水分を排出し、そして原燃料供給停止手段により原燃料の供給を停止することにより、窒素のインフラのない場所でも、改質器の寿命を低下させることなく、改質器の起動、停止を繰り返すことができ、逆に改質器の寿命を向上させることができ、燃料電池システムの寿命を飛躍的に向上できるという顕著な効果を奏する。
そして加熱手段への燃料供給停止と略同時に改質装置からのプロセスガスの燃料電池への供給を停止し、このプロセスガスを燃焼手段で燃焼することによって有効に利用して燃料電池システムの熱効率を向上できるという顕著な効果を奏する。
【００９１】
本発明の請求項２記載の燃料電池システムは、請求項１記載の燃料電池システムにおいて、前記脱硫手段が、常温でも硫黄分を吸着脱硫可能な脱硫手段であることを特徴とするものであり、常温でも硫黄分を吸着脱硫可能な脱硫手段を用いると、改質装置運転中は勿論のこと停止操作時においても原燃料中の硫黄分を水蒸気改質反応に悪影響を与えないレベルまで脱硫することができるというさらなる顕著な効果を奏する。
【００９２】
本発明の請求項３記載の燃料電池システムは、請求項１あるいは請求項２記載の燃料電池システムにおいて、前記燃焼手段により燃焼して得られた熱を熱交換器を介して貯蔵する蓄熱手段を備えたことを特徴とするものであり、燃焼手段により燃焼して得られた熱を熱交換器を介して貯蔵する蓄熱手段を備えれば、燃焼して得られた熱を有効に利用して燃料電池システムの熱効率をより向上できるというさらなる顕著な効果を奏する。
【００９３】
本発明の請求項４記載の燃料電池システムは、請求項３記載の燃料電池システムにおいて、前記蓄熱手段が貯湯タンクであることを特徴とするものであり、燃焼手段により燃焼して得られた熱を貯湯タンクの湯温上昇に有効に利用して燃料電池システムの熱効率をより向上できるというさらなる顕著な効果を奏する。
【００９４】
本発明の請求項５記載の燃料電池システムは、請求項１から請求項４のいずれかに記載の燃料電池システムにおいて、前記改質装置の出口にガス開閉弁を設け、前記原燃料供給停止手段により改質装置への改質用原燃料の供給を停止した際、前記ガス開閉弁を閉じることを特徴とするものであり、原燃料供給停止手段により改質装置への改質用原燃料の供給を停止した際、前記ガス開閉弁を閉じることによりＣＯ低減部触媒が酸素や水分との接触により劣化するのを防止できるというさらなる顕著な効果を奏する。
【００９５】
本発明の請求項６記載の燃料電池システムは請求項５記載の燃料電池システムにおいて、前記原燃料供給停止手段により改質装置への改質用原燃料の供給を停止し、ＣＯ低減部の温度が５０℃以下になった時、一旦、前記原燃料供給停止手段により改質装置への改質用原燃料の供給を行った後、再度、前記原燃料供給停止手段により改質装置への改質用原燃料の供給を停止することを特徴とするものであり、ＣＯ低減部の温度が５０℃以下になった時、一旦、前記原燃料供給停止手段により改質装置への改質用原燃料の供給を行い改質装置の内部の圧力を常圧に維持することにより、改質装置の内部が負圧になるのを防止できるというさらなる顕著な効果を奏する。
【００９６】
本発明の請求項７記載の燃料電池システムは、請求項１から請求項６のいずれかに記載の燃料電池システムにおいて、前記燃焼手段により燃焼して得られた熱をＣＯ変成器および／またはＣＯ除去器の温度維持に使用する手段を備えたことを特徴とするものであり、水の供給停止と略同時に改質装置からのプロセスガスの燃料電池への供給を停止し、このプロセスガスを燃焼手段で燃焼して得られた熱をＣＯ変成器および／またはＣＯ除去器の温度維持に使用することによって有効に利用して燃料電池システムの熱効率をより向上できるというさらなる顕著な効果を奏する。
【００９７】
本発明の請求項８は、改質装置において脱硫した改質用原燃料を水素リッチなガスに改質し、改質したプロセスガスを燃料電池に供給して発電する請求項１から請求項７のいずれかに記載の燃料電池システムの停止方法であって、
前記改質装置停止時に、先ず前記燃料供給停止手段により前記水蒸気改質器の加熱手段への燃料供給を停止し、前記加熱手段への燃料供給停止と略同時に前記改質装置からのプロセスガスの燃料電池への供給を停止して、このプロセスガスを前記燃焼手段で燃焼し、前記水蒸気改質器の出口触媒温度を検出する温度検出手段により検出された温度が７００℃以下２００℃の範囲内となった時、前記水供給停止手段により改質反応に必要な水の供給を停止し、そして前記温度検出手段により検出された温度が１００℃以上４００℃以下の範囲内となった時、前記原燃料供給停止手段により改質装置への改質用原燃料の供給を停止することを特徴とする燃料電池システム停止方法であり、
改質装置停止時には、先ず燃料供給停止手段により改質器の加熱手段への燃料供給を停止し、原燃料および水を供給し続けて水蒸気改質反応による吸熱によって、速やかに改質器の温度を降下させ、温度検出手段により検出された温度が７００℃以下２００℃の範囲内となった時、水供給停止手段により改質反応に必要な水の供給を停止し、その間に燃料電池システムに供給し続ける原燃料によって、改質装置のプロセス中に存在する水分を排出し、そして温度検出手段により検出された温度が１００℃以上４００℃以下の範囲内となった時に、原燃料供給停止手段により原燃料を供給を停止することにより、原燃料の熱分解による炭素の析出を防止でき、窒素のインフラのない場所でも、改質器の寿命を低下させることなく、改質器の起動、停止を繰り返すことができ、逆に改質器の寿命を向上させることができ、燃料電池システムの寿命を飛躍的に向上できるという顕著な効果を奏する。
そして加熱手段への燃料供給停止と略同時に改質装置からのプロセスガスの燃料電池への供給を停止し、このプロセスガスを燃焼手段で燃焼する燃焼させることによって有効に利用して燃料電池システムの熱効率を向上できるという顕著な効果を奏する。
【００９８】
本発明の請求項９は、請求項８記載の燃料電池システム停止方法において、前記水蒸気改質器の出口触媒温度が改質用原燃料の熱分解温度＋１５０℃〜−５０℃の範囲内となった時、前記水供給停止手段により改質反応に必要な水の供給を停止することを特徴とするものであり、改質器の出口触媒温度が原燃料の熱分解温度＋１５０℃〜−５０℃の範囲内となった時、前記水供給停止手段により水の供給を停止すれば原燃料の熱分解による炭素の析出が生じない。−５０℃より低すぎると、水蒸気改質反応が進行せず、滞留水蒸気の排出が遅くなるというさらなる顕著な効果を奏する。
【００９９】
本発明の請求項１０は、請求項９記載の燃料電池システム停止方法において、前記水供給停止手段により改質反応に必要な水の供給を停止してから前記改質装置容量の１〜５倍の容積の原燃料を置換のために供給するか、あるいは前記水供給停止手段により改質反応に必要な水の供給を停止してから前記原燃料供給停止手段により改質装置への改質用原燃料の供給を停止するまでの時間が５分以上６０分以下となるようにすることを特徴とするものであり、前記水供給停止手段により改質反応に必要な水の供給を停止してから、水の供給を停止し改質装置容量の１〜５倍の容積の原燃料を置換のために供給するか、あるいは原燃料供給停止手段により改質装置への原燃料の供給を停止するまでの時間が５分以上６０分以下であると、原燃料の消費量を低減でき燃料電池システムの効率を向上できるというさらなる顕著な効果を奏する。
【０１００】
本発明の請求項１１は、請求項８から請求項１０のいずれかに記載の燃料電池システム停止方法において、前記燃焼手段により燃焼して得られた熱を熱交換器を介して蓄熱手段に貯蔵することを特徴とするものであり、燃焼手段により燃焼して得られた熱を熱交換器を介して貯蔵する蓄熱手段を備えれば、燃焼して得られた熱を有効に利用して燃料電池システムの熱効率をより向上できるというさらなる顕著な効果を奏する。
【０１０１】
本発明の請求項１２は、請求項１１記載の燃料電池システム停止方法において、前記蓄熱手段が貯湯タンクであることを特徴とするものであり、燃焼手段により燃焼して得られた熱を貯湯タンクの湯温上昇に有効に利用して燃料電池システムの熱効率をより向上できるというさらなる顕著な効果を奏する。
【０１０２】
本発明の請求項１３は請求項８から請求項１２のいずれかに記載の燃料電池システム停止方法において、前記改質装置の出口にガス開閉弁を設け、前記原燃料供給停止手段により改質装置への改質用原燃料の供給を停止した際、前記ガス開閉弁を閉じることを特徴とするものであり、原燃料供給停止手段により改質装置への改質用原燃料の供給を停止した際、前記ガス開閉弁を閉じることによりＣＯ低減部触媒が酸素や水分との接触により劣化するのを防止できるというさらなる顕著な効果を奏する。
【０１０３】
本発明の請求項１４は、請求項１３記載の燃料電池システム停止方法において、前記原燃料供給停止手段により改質装置への改質用原燃料の供給を停止し、ＣＯ低減部の温度が５０℃以下になった時、一旦、前記原燃料供給停止手段により改質装置への改質用原燃料の供給を行った後、再度、前記原燃料供給停止手段により改質装置への改質用原燃料の供給を停止することを特徴とするものであり、ＣＯ低減部の温度が５０℃以下になった時、一旦、前記原燃料供給停止手段により改質装置への改質用原燃料の供給を行い、原燃料を前記改質器などに導入して改質装置の内部の圧力を常圧に維持することにより、改質装置の内部が負圧になるのを防止できるというさらなる顕著な効果を奏する。
【０１０４】
本発明の請求項１５は、請求項８から請求項１４のいずれかに記載の燃料電池システム停止方法において、前記燃焼手段により燃焼して得られた熱をＣＯ変成器および／またはＣＯ除去器の温度維持に使用することを特徴とするものであり、燃焼手段で燃焼して得られた熱をＣＯ変成器および／またはＣＯ除去器の温度維持に使用することによって有効に利用して燃料電池システムの熱効率をより向上できるというさらなる顕著な効果を奏する。
【図面の簡単な説明】
【図１】本発明の燃料電池システムの１実施の形態を説明する説明図である。
【図２】サイクル数と、改質率の関係および改質装置の出口ＣＯ濃度を測定した結果の関係を示すグラフである。
【図３】改質器への水供給停止してからの経過時間と改質器の出口触媒温度の関係を示すグラフである。
【図４】従来の燃料電池システムの説明図である。
【符号の説明】
１燃料電池システム
２脱硫器
３気化器
４水蒸気改質器
５燃料電池
６ＣＯ変成器
７ＣＯ除去器
８改質装置
９加熱手段
１０原燃料供給停止手段
１１水供給停止手段
１２燃料供給停止手段
１３、１４ガス開閉弁
１５ＣＯ低減部
１６温度検出手段
１７燃焼手段
１８熱交換器
１９蓄熱手段としての貯湯タンク
２０ＣＯ変成器およびＣＯ除去器の温度維持に使用する手段[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a fuel cell system and a method for shutting down a fuel cell system, and more particularly, to a fuel that generates hydrogen-rich gas by steam reforming of raw fuel gas such as city gas and supplies it to a fuel cell or the like to generate power. The present invention relates to a battery system and a fuel cell system stopping method.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, there is known a fuel cell system in which a raw hydrocarbon fuel gas such as city gas is reformed by steam to generate a hydrogen-rich gas, and the chemical energy of the obtained hydrogen-rich gas is directly converted into electric energy by a fuel cell. .
[0003]
Fuel cells use hydrogen as a fuel, and the generation of hydrogen is performed using hydrocarbon compounds such as natural gas, alcohols such as methanol, or organic compounds having a hydrogen atom in a molecule such as naphtha as a raw material. A method of reforming with steam is widely used. Such a reforming reaction using steam is an endothermic reaction. For this reason, the steam reformer that performs steam reforming needs to heat the raw material, steam, and the reforming catalyst that performs the reforming reaction to a high temperature.
[0004]
The reaction of using an organic compound such as naphtha as a raw material and reforming it with steam produces not only hydrogen and carbon dioxide but also carbon monoxide as a by-product. For example, since a polymer electrolyte fuel cell operates at 100 ° C. or lower, a platinum-based catalyst used as a battery electrode is poisoned by carbon monoxide, so that sufficient power generation characteristics cannot be obtained. Therefore, a CO converter for reacting water with carbon monoxide contained in the reformed process gas is provided. In addition, a CO remover for selectively oxidizing carbon monoxide to reduce carbon monoxide is provided so as not to deteriorate power generation characteristics (for example, see Patent Document 1).
[0005]
FIG. 4 shows a conventional fuel cell system (for example, see Patent Document 2). The conventional fuel cell reforming apparatus 30 includes a nickel-based, ruthenium-based, and rhodium-based reforming catalyst 31 that reacts desulfurized raw hydrocarbon fuel gas with water to reform the gas into a hydrogen-rich gas. A reformer 32, a fuel supply unit 33 for supplying fuel gas to the reformer 32, a water supply unit 34 for supplying water to the reformer 32, and reforming by burning combustion fuel in a combustion pipe 35. A heating means 36 for giving a calorie necessary for the reaction, a copper-zinc-based conversion catalyst for converting carbon monoxide contained in the reformed gas flowing out of the reformer 32 with water and converting it to carbon dioxide, and the like are provided. A CO remover (not shown) equipped with a CO converter 37 and a selective oxidation catalyst such as platinum or ruthenium that converts carbon monoxide contained in the conversion gas flowing out of the CO converter 37 with air or oxygen to form carbon dioxide. And
[0006]
The desulfurized raw hydrocarbon fuel gas is sent from the fuel supply unit 33 to the reformer 32 after steam is added. The steam is generated by water such as cooling water flowing through the system by the steam generator 38, for example, being preheated by the heating means 36 and exchanged with the exhaust heat of the fuel cell device. The fuel gas to which steam has been added contacts the reforming catalyst 31 of the reformer 32 and undergoes steam reforming into a hydrogen-rich gas (hydrogen-rich gas) by a catalytic reaction (about 700 ° C., endothermic reaction). Since the generated hydrogen-rich gas contains carbon monoxide, the CO converter 37 converts carbon monoxide into carbon dioxide by a reaction with excess water vapor (about 200 to 300 ° C., exothermic reaction). The carbon monoxide contained in the shift gas flowing out of the CO shift converter 37 is brought into contact with a selective oxidation catalyst of a CO remover (not shown) to react with air or oxygen (about 100 to 200 ° C., exothermic reaction) to form carbon dioxide. To reform into a hydrogen-rich gas having a low carbon monoxide concentration.
The hydrogen-rich gas obtained as described above is continuously supplied to the hydrogen electrode 39a of the fuel cell 39, and generates a battery reaction with the air supplied to the air electrode 39b to generate power.
[0007]
Conventionally, when the above-mentioned fuel cell system is stopped, in order to discharge the water remaining in the process of the reformer, nitrogen is always circulated in the process of the reformer to stop the system. If the supply of raw fuel and water is stopped without flowing nitrogen when the temperature of the reformer is lowered or stopped, there is a problem that the reforming rate is reduced in more than ten cycles, and the life performance of the fuel cell is rapidly reduced. Therefore, the installation location of the fuel cell system requires a nitrogen infrastructure, and the installation of the fuel cell is limited.
Then, since the reforming catalyst in the reformer, particularly the shift converter catalyst of the CO converter is deteriorated by contact with oxygen or moisture, a method of discharging the water staying in the CO shift converter has been devised (see Patent Document 3). ). According to the method, it is determined that the temperature of the reforming reaction section has fallen below a predetermined temperature (the thermal decomposition temperature of the raw fuel), the water supply is stopped, and the raw fuel is supplied to the reforming reaction section. It is.
[0008]
However, when the water supply to the reformer is stopped, if the water supply stop temperature is too low, the temperature of the catalyst drops without completely replacing the retained water, and metal oxidation such as a reforming catalyst or a selective oxidation catalyst occurs. The adsorption of water molecules on the surface of the product carrier catalyst becomes strong, and the deterioration of the reforming catalyst and the selective oxidation catalyst is accelerated (the surface of the metal oxide is chemically adsorbed in the presence of water. The OH group is stable, and in the case of γ-alumina, water hydrated by the OH group does not evaporate to about 200 ° C. (see Non-Patent Document 1). ).
[0009]
[Patent Document 1]
JP-A-7-126001
[Patent Document 2]
JP-A-2000-28131
[Patent Document 3]
JP-A-2000-95504
[Non-patent document 1]
Chemical Engineering Handbook Revised 5th Edition, p245
[0010]
[Problems to be solved by the invention]
Furthermore, when the temperature of the reformer decreases, the temperature of the process gas that exits the reformer and reaches the CO shift converter and the CO remover also decreases, so that the catalyst temperature of the reformer becomes too low and the accumulated water cannot be sufficiently replaced. The problem is that there are times when only raw fuel is consumed to replace it.
[0011]
A first object of the present invention is to enable the starting and stopping of the reformer to be repeated without reducing the life of the reformer even in a place where there is no infrastructure for nitrogen, and conversely to improve the life of the reformer. To provide a fuel cell system that can dramatically improve the life of the fuel cell system.
A second object of the present invention is a method for shutting down a fuel cell system, in which even if the reformer is repeatedly started and stopped, the effect of water on the shift catalyst and the carbon on the reforming catalyst due to the thermal decomposition of the raw fuel are obtained. In addition to suppressing precipitation, it has little effect on the catalyst used in all reformers, and can dramatically improve the life of the fuel cell system. It is an object of the present invention to provide a fuel cell system shutdown method that can effectively utilize and improve thermal efficiency by combusting fuel.
[0012]
[Means for Solving the Problems]
The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, it should be noted that the water supply stop temperature to the reformer is higher than the raw fuel thermal decomposition temperature. It is considered that thermal decomposition occurs in the reformer and carbon is precipitated, and if the temperature is lower than the thermal decomposition temperature of the raw fuel, the temperature of the catalyst is too low, and adversely affects the catalyst. Even if the water supply stop temperature is equal to or higher than the thermal decomposition temperature of the raw fuel, the steam remaining in the reformer and the raw fuel continue the reforming reaction, and the endothermic reaction causes the temperature of the reformer to drop rapidly. However, before the water in the reformer was completely replaced, it was found that the temperature could be reduced to a temperature below the thermal decomposition temperature at a stretch.
That is, when the fuel cell system is stopped, in the process of lowering the temperature of the reformer, the fuel supply to the heating means of the reformer is stopped to stop the energy supply, the raw fuel and water are continuously supplied, and the steam reforming is performed. Due to the endothermic reaction, the temperature of the reformer is immediately lowered, and after the temperature is reduced to a condition that does not cause carbon deposition due to the thermal decomposition of the raw fuel for reforming, the supply of water required for the reforming reaction is stopped. In the meantime, the raw fuel that continues to be supplied to the fuel cell system drains the water present during the reformer process, thereby shortening the service life of the fuel cell system even when there is no nitrogen infrastructure. And found that the life of the fuel cell system can be drastically improved, leading to the present invention.
[0013]
The fuel cell system according to claim 1 of the present invention reforms a reforming raw fuel desulfurized in a reformer into a hydrogen-rich gas and supplies the reformed process gas to the fuel cell to generate power. The system
The reforming apparatus includes a desulfurization unit for desulfurizing sulfur in the raw fuel for reforming, and a heating unit for providing a heat quantity necessary for advancing the steam reforming reaction. A steam reformer that reforms water required for the reaction into a hydrogen-rich gas by a steam reforming reaction, and a CO converter that reduces the CO concentration in the hydrogen-rich gas reformed in the steam reformer, A CO remover that further reduces the CO concentration in the gas whose CO concentration has been reduced in the CO converter,
Fuel supply stopping means for stopping fuel supply to the heating means of the steam reformer, temperature detecting means for detecting an outlet catalyst temperature of the steam reformer, and stopping supply of water necessary for the reforming reaction. Water supply stop means, a combustion means for stopping the supply of process gas from the reformer to the fuel cell and burning, and a raw fuel supply stop means for stopping the supply of raw fuel to the reformer,
When the reformer is stopped, the fuel supply to the heating means is stopped by the fuel supply stopping means, the temperature is lowered until the temperature detected by the temperature detecting means reaches a predetermined temperature, and the fuel supply to the heating means is stopped. Almost simultaneously with the stop, the supply of the process gas from the reformer to the fuel cell is stopped, the fuel is burned by the combustion means, the supply of water is stopped by the water supply stop means, and the inside of the reformer is fed by the raw fuel. After the replacement, the supply of the raw fuel is stopped by the raw fuel supply stopping means.
[0014]
When the reforming apparatus is stopped, first, the fuel supply to the heating means of the reformer is stopped by the fuel supply stopping means, and the raw fuel and water are continuously supplied. After the temperature is reduced to a condition under which carbon deposition due to the thermal decomposition of the reforming raw fuel does not occur (the temperature detected by the temperature detecting means for detecting the outlet catalyst temperature of the steam reformer is a predetermined temperature, For example, when the temperature falls within the range of 700 ° C. or less and 200 ° C.), the supply of water necessary for the reforming reaction is stopped by the water supply stopping means, and the raw fuel which is continuously supplied to the fuel cell system during that time is used for the reforming apparatus. By displacing during the process to discharge water present during the reformer process, and by stopping the supply of raw fuel by the raw fuel supply stopping means, the life of the reformer can be maintained even in a place without nitrogen infrastructure. To Without made, activation of the reformer, it is possible to repeat stop and reverse the reformer life can be improved to be dramatically improved the life of the fuel cell system.
At about the same time as the fuel supply to the heating means is stopped, the supply of the process gas from the reformer to the fuel cell is stopped, and the process gas is burned by the combustion means to effectively utilize the thermal efficiency of the fuel cell system. Can be improved.
[0015]
A fuel cell system according to a second aspect of the present invention is the fuel cell system according to the first aspect, wherein the desulfurization unit is a desulfurization unit capable of adsorbing and desulfurizing sulfur even at normal temperature.
[0016]
By using desulfurization means that can adsorb and desulfurize sulfur even at normal temperature, it is possible to desulfurize the sulfur in the raw fuel to a level that does not adversely affect the steam reforming reaction, not only during the operation of the reformer but also during the shutdown operation. Can be.
[0017]
According to a third aspect of the present invention, in the fuel cell system according to the first or second aspect, the heat storage means for storing heat obtained by burning by the combustion means via a heat exchanger. It is characterized by having.
[0018]
If the heat storage means for storing the heat obtained by combustion by the combustion means via the heat exchanger is provided, the heat efficiency of the fuel cell system can be further improved by effectively utilizing the heat obtained by combustion.
[0019]
A fuel cell system according to a fourth aspect of the present invention is the fuel cell system according to the third aspect, wherein the heat storage means is a hot water storage tank.
[0020]
The heat obtained by burning by the combustion means is effectively used for increasing the temperature of hot water in the hot water storage tank, so that the thermal efficiency of the fuel cell system can be further improved.
[0021]
According to a fifth aspect of the present invention, in the fuel cell system according to any one of the first to fourth aspects, a gas switching valve is provided at an outlet of the reformer, and the raw fuel supply stopping means is provided. When the supply of the raw fuel for reforming to the reformer is stopped, the gas on-off valve is closed.
[0022]
When the supply of the raw fuel for reforming to the reformer is stopped by the raw fuel supply stopping means, the gas reducing valve can be closed to prevent the CO reduction unit catalyst from being deteriorated due to contact with oxygen or moisture.
[0023]
A fuel cell system according to a sixth aspect of the present invention is the fuel cell system according to the fifth aspect, wherein the supply of the raw fuel for reforming to the reformer is stopped by the raw fuel supply stopping means, and the temperature of the CO reduction unit is reduced. When the temperature becomes 50 ° C. or less, once the raw fuel for reforming is supplied to the reforming device by the raw fuel supply stopping device, the reforming to the reforming device is performed again by the raw fuel supply stopping device. The supply of quality fuel is stopped.
[0024]
When the temperature of the CO reduction unit becomes 50 ° C. or lower, the raw fuel for supply to the reformer is once supplied by the raw fuel supply stopping means, and the pressure inside the reformer is maintained at normal pressure. This can prevent the inside of the reformer from becoming negative pressure.
[0025]
A fuel cell system according to a seventh aspect of the present invention is the fuel cell system according to any one of the first to sixth aspects, wherein heat obtained by burning by the combustion means is converted into a CO converter and / or a CO converter. It is characterized by comprising means for maintaining the temperature of the remover.
[0026]
At about the same time as the supply of water is stopped, the supply of the process gas from the reformer to the fuel cell is stopped, and the heat obtained by burning this process gas by the combustion means is used as the temperature of the CO converter and / or the CO remover. When used for maintenance, the fuel cell system can be effectively used to further improve the thermal efficiency of the fuel cell system.
[0027]
According to claim 8 of the present invention, the reforming raw fuel desulfurized in the reformer is reformed into a hydrogen-rich gas, and the reformed process gas is supplied to a fuel cell to generate power. A method for stopping a fuel cell system according to any one of the above,
At the time of the stop of the reforming device, first, the fuel supply to the heating means of the steam reformer is stopped by the fuel supply stopping means, and the supply of the process gas from the reforming apparatus is substantially simultaneously with the stop of the fuel supply to the heating means. The supply to the fuel cell is stopped, the process gas is burned by the combustion means, and the temperature detected by the temperature detection means for detecting the outlet catalyst temperature of the steam reformer is in the range of 700 ° C to 200 ° C. When, the supply of water necessary for the reforming reaction is stopped by the water supply stopping means, and when the temperature detected by the temperature detecting means falls within the range of 100 ° C. or more and 400 ° C. or less, A method for stopping a fuel cell system, wherein the supply of raw fuel for reforming to a reformer is stopped by raw fuel supply stopping means.
[0028]
When the reforming apparatus is stopped, first, the fuel supply to the heating means of the reformer is stopped by the fuel supply stopping means, and the raw fuel and water are continuously supplied. When the temperature detected by the temperature detecting means falls within the range of 700 ° C. or less and 200 ° C., the supply of water required for the reforming reaction is stopped by the water supply stopping means. The raw fuel which continues to be supplied is used to discharge water present during the process of the reformer, and when the temperature detected by the temperature detecting means falls within the range of 100 ° C. or more and 400 ° C. or less, the raw fuel supply stopping means By stopping the supply of raw fuel, it is possible to prevent carbon deposition due to thermal decomposition of the raw fuel, and to start the reformer without reducing the life of the reformer even in a place without nitrogen infrastructure. It can be repeated stop, reverse reformer life can be improved to be dramatically improved the life of the fuel cell system.
At about the same time as the supply of fuel to the heating means is stopped, the supply of the process gas from the reformer to the fuel cell is stopped, and the process gas is effectively used by being burned by the combustion means. Thermal efficiency can be improved.
[0029]
According to a ninth aspect of the present invention, in the method for shutting down the fuel cell system according to the eighth aspect, the catalyst temperature at the outlet of the steam reformer is in the range of the thermal decomposition temperature of the raw fuel for reforming + 150 ° C to -50 ° C. In this case, the supply of water required for the reforming reaction is stopped by the water supply stopping means.
[0030]
When the outlet catalyst temperature of the reformer falls within the range of + 150 ° C. to −50 ° C. of the raw fuel, if the supply of water is stopped by the water supply stopping means, carbon is deposited by the thermal decomposition of the raw fuel. Does not occur. If the temperature is lower than −50 ° C., the steam reforming reaction does not proceed, and the discharge of the retained steam is delayed.
[0031]
According to a tenth aspect of the present invention, in the method for stopping the fuel cell system according to the ninth aspect, the supply of water required for the reforming reaction is stopped by the water supply stopping means, and then 1 to 5 times the reformer capacity. Of raw fuel for replacement, or the supply of water necessary for the reforming reaction is stopped by the water supply stopping means, and then the raw fuel is stopped by the raw fuel supply stopping means. It is characterized in that the time until the supply of the raw fuel is stopped is 5 minutes or more and 60 minutes or less.
[0032]
After the supply of water required for the reforming reaction is stopped by the water supply stopping means, the supply of water is stopped and a raw fuel having a volume of 1 to 5 times the reformer capacity is supplied for replacement, Alternatively, if the time until the supply of the raw fuel to the reformer is stopped by the raw fuel supply stopping means is 5 minutes or more and 60 minutes or less, the consumption of the raw fuel can be reduced and the efficiency of the fuel cell system can be improved.
[0033]
According to an eleventh aspect of the present invention, in the fuel cell system shutdown method according to any one of the eighth to tenth aspects, heat obtained by burning by the combustion means is stored in a heat storage means via a heat exchanger. It is characterized by doing.
[0034]
If the heat storage means for storing the heat obtained by combustion by the combustion means via the heat exchanger is provided, the heat efficiency of the fuel cell system can be further improved by effectively utilizing the heat obtained by combustion.
[0035]
According to a twelfth aspect of the present invention, in the fuel cell system shutdown method according to the eleventh aspect, the heat storage means is a hot water storage tank.
[0036]
The heat obtained by burning by the combustion means is effectively used for increasing the temperature of hot water in the hot water storage tank, so that the thermal efficiency of the fuel cell system can be further improved.
[0037]
According to a thirteenth aspect of the present invention, in the method for stopping a fuel cell system according to any one of the eighth to twelfth aspects, a gas on-off valve is provided at an outlet of the reformer, and the reformer is stopped by the raw fuel supply stopping means. When the supply of the raw fuel for reforming to the gas is stopped, the gas on-off valve is closed.
[0038]
When the supply of the raw fuel for reforming to the reformer is stopped by the raw fuel supply stopping means, the gas reducing valve can be closed to prevent the CO reduction unit catalyst from being deteriorated due to contact with oxygen or moisture.
[0039]
According to a fourteenth aspect of the present invention, in the fuel cell system shutdown method according to the thirteenth aspect, the supply of the raw fuel for reforming to the reformer is stopped by the raw fuel supply stop means, and the temperature of the CO reduction unit is reduced to 50%. When the temperature of the reforming device becomes lower than or equal to ℃, once the raw fuel supply stopping means supplies the reforming raw fuel to the reforming apparatus, the raw fuel supply stopping means again supplies the reforming raw fuel to the reforming apparatus. The supply of raw fuel is stopped.
[0040]
When the temperature of the CO reduction unit becomes 50 ° C. or lower, once, the raw fuel supply stopping means supplies the raw fuel for reforming to the reformer, and the raw fuel is introduced into the reformer or the like. By maintaining the pressure inside the reformer at normal pressure, it is possible to prevent the inside of the reformer from becoming negative pressure.
[0041]
According to a fifteenth aspect of the present invention, in the method for stopping a fuel cell system according to any one of the eighth to fourteenth aspects, heat obtained by burning by the combustion means is supplied to a CO converter and / or a CO remover. It is used for maintaining temperature.
[0042]
By using the heat obtained by combustion by the combustion means for maintaining the temperature of the CO converter and / or the CO remover, the heat efficiency can be effectively utilized and the thermal efficiency of the fuel cell system can be further improved.
[0043]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is an explanatory diagram illustrating one embodiment of the fuel cell system of the present invention.
The fuel cell system 1 of the present invention includes a desulfurizer 2 capable of adsorbing and desulfurizing a sulfur component in a hydrocarbon-based raw fuel gas such as methane, propane, and butane at room temperature, and a desulfurized raw fuel gas and water in a vaporizer 3. A steam reformer 4 that generates a hydrogen-rich reformed gas by a steam reforming reaction from steam obtained by vaporizing the gas, and a platinum-based or alloy-based electrode catalyst contained in the reformed gas and included in the fuel cell 5. Most of the CO gas that poisons and degrades the electrode characteristics is converted to CO₂And a CO gas still remaining in the reformed gas whose CO concentration has been reduced by the CO₂And a CO remover 7 that oxidizes the CO.
[0044]
Here, a reforming catalyst such as a nickel-based, ruthenium-based or rhodium-based reforming catalyst is used for the steam reforming reaction, a copper-zinc-based reforming catalyst is used for the metamorphosis reaction, and a CO oxidation catalyst such as platinum or ruthenium is used for the CO selective oxidation reaction. These catalysts are used by filling each reactor with these catalysts.
[0045]
Reference numeral 9 denotes a heating means such as a burner provided in the reformer 4. For example, at the start of the fuel cell system, a fuel such as a raw fuel gas is supplied and burned to advance a steam reforming reaction. The calorific value is given to the reforming catalyst, and when the power generation in the fuel cell 5 becomes stable after the start of the fuel cell system, the fuel such as the raw fuel gas is switched to the unreacted gas not consumed in the fuel cell 5. To provide the reforming catalyst with the amount of heat necessary for the steam reforming reaction to proceed.
[0046]
Reference numeral 10 denotes raw fuel supply stopping means such as an on-off valve provided on the raw fuel supply line, 11 denotes water supply stopping means such as an on-off valve provided on the water supply line, and 12 denotes a fuel supply line to the heating means 9. Fuel supply stopping means such as on-off valves 13 and 14 are gas on-off valves provided at an inlet and an outlet of a CO reduction unit 15 including a CO converter 6 and a CO remover 7, respectively. Reference numeral 16 denotes temperature detecting means for detecting the temperature of the catalyst at the outlet of the reformer 4.
[0047]
10, 11, 12, 13, 14, and 16 are connected to a control device (not shown), and the opening and closing operations of 10, 11, 12, 13, and 14 are controlled by control means including the control device.
[0048]
Reference numeral 17 denotes a combustion unit that burns when the supply of the process gas from the reformer 8 to the fuel cell 5 is stopped, and 18 denotes a heat exchange unit that exchanges heat obtained by burning the combustion unit 17. Reference numeral 19 denotes a hot water storage tank as heat storage means for storing heat recovered by the heat exchanger 18 as hot water. Reference numeral 20 denotes means for using the heat obtained by the combustion by the combustion means 17 to maintain the temperature of the CO converter 6 and the CO remover 7. Includes accommodation devices, ducts, and heat insulating materials.
[0049]
When the reforming device 8 is stopped, first, the on-off valve of the fuel supply stopping means 12 is closed to stop the fuel supply to the heating means 9 of the reformer 4. Then, when the raw fuel and water are continuously supplied to the reformer 4, the temperature of the reformer 4 rapidly drops due to heat absorption by the steam reforming reaction. After the temperature of the reformer 4 is lowered to a condition under which carbon deposition due to the thermal decomposition of the raw fuel does not occur (the temperature detected by the temperature detecting means 16 for detecting the outlet catalyst temperature of the reformer 4 becomes a predetermined temperature, for example, When the temperature falls within the range of 700 ° C. to 200 ° C.), the on-off valve of the water supply stopping means 11 is closed to stop the supply of water required for the reforming reaction. During that time, the raw fuel is replaced in the process of the reformer 8 to discharge the water present in the process, and then the on / off valve of the raw fuel supply stopping means 10 is closed to stop the supply of the raw fuel. Preferably, when the temperature detected by the temperature detecting means 16 falls within the range of 100 ° C. or more and 400 ° C. or less, the supply of the raw fuel is stopped by closing the open / close valve of the raw fuel supply stopping means 10. By doing so, it is possible to prevent carbon deposition due to thermal decomposition of the raw fuel, and to repeatedly start and stop the reformer 4 without reducing the life of the reformer 4 even in a place where there is no infrastructure for nitrogen. The life of the reformer 4, the CO shift converter 6, and the CO remover 7 can be improved, and the life of the fuel cell system 1 can be dramatically improved.
As described above, an example of the temperature at which the supply of the reforming water is stopped is 700 ° C. or less and 200 ° C., and an example of the temperature at which the supply of the raw fuel is stopped is 100 ° C. or more and 400 ° C. or less. However, the temperature at which the supply of the reforming water is stopped is equal to or higher than the temperature at which the supply of the raw fuel is stopped.
[0050]
When the temperature detected by the temperature detecting means 16 for detecting the catalyst temperature at the outlet of the reformer 4 becomes within the range of the thermal decomposition temperature of the raw fuel + 150 ° C. to −50 ° C., the open / close valve of the water supply stopping means 15 is opened. If the supply of water necessary for the reforming reaction is stopped by closing, the deposition of carbon due to the thermal decomposition of the raw fuel does not occur. If the thermal decomposition temperature of the raw fuel is lower than −50 ° C., the steam reforming reaction does not proceed, and the discharge of the retained steam is delayed.
[0051]
At about the same time as the supply of water is stopped, the gas on-off valve 14 is closed to stop the supply of the process gas from the reformer 8 to the fuel cell 5, and the process gas is burned by the combustion means 17 and the heat exchanger 18 The recovered heat is stored as hot water in a hot water storage tank 19, and the heat obtained by burning by the combustion means 17 is sent to the means 20 to be used for maintaining the temperatures of the CO shift converter 6 and the CO remover 7. If used, the thermal efficiency of the fuel cell system 1 can be improved.
[0052]
When the supply of the raw fuel to the reformer 8 is stopped by the raw fuel supply stopping means 10, the gas on / off valves 13 and 14 are closed to prevent the catalyst of the CO reduction unit 15 from being deteriorated by contact with oxygen or moisture. Can be prevented.
[0053]
After the supply of the raw fuel to the reformer 8 is stopped by the raw fuel supply stopping means 10, when the temperature of the CO reduction unit 15 becomes 50 ° C. or less, the open / close valve of the raw fuel supply stopping means 10 is opened once. After the raw fuel is supplied to the reformer 8, the raw fuel is introduced into the reformer 4, etc., and the inside of the reformer 8 is replaced with the raw fuel. By shutting off the supply of the raw fuel to the reforming device 8 by closing the pressure, the pressure inside the reforming device 8 can be maintained at the normal pressure, and the inside of the reforming device 8 can be prevented from becoming negative. When the inside of the reforming device 8 becomes a negative pressure, air is mixed in from a seal portion such as an electromagnetic valve and the like, and the catalyst and the like of the reduction unit 15 are deteriorated.
[0054]
After the supply of water required for the reforming reaction is stopped by the water supply stopping means 11, the temperature detected by the temperature detecting means 16 for detecting the outlet catalyst temperature of the reformer 4 is in the range of 100 ° C or more and 400 ° C or less. At this time, if the supply of the raw fuel to the reformer 8 is stopped by closing the on-off valve of the raw fuel supply stopping means 10, carbon deposition due to the thermal decomposition of the raw fuel does not occur.
[0055]
After the supply of water necessary for the reforming reaction is stopped by the water supply stopping means 11, the raw fuel having a volume of 1 to 5 times the capacity of the reformer 8 is supplied for replacement, or the raw fuel supply stopping means is stopped. When the time until the supply of the raw fuel to the reformer 8 is stopped is controlled by the time determination means such as a timer (not shown) to be not less than 5 minutes and not more than 60 minutes, the raw fuel consumption can be reduced. The efficiency of the battery system can be improved.
[0056]
The description of the above embodiments is for describing the present invention, and does not limit the invention described in the claims or reduce the scope thereof. Further, the configuration of each part of the present invention is not limited to the above embodiment, and various modifications can be made within the technical scope described in the claims.
For example, in the description of the above-described embodiment, the example in which the raw fuel supply stopping means 10 is provided in the pipeline on the raw fuel inlet side of the desulfurizer 2 has been described. In the case where is used, it is preferable to provide the raw fuel supply stopping means 10 in a pipe on the outlet side of the desulfurizer 2.
[0057]
【Example】
Hereinafter, the content of the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to the examples.
(Example 1)
[Reformer operating conditions]
S / C = 3.0
GHSV = 1000hr^-1
Reforming catalyst: Commercial ruthenium alumina catalyst
Reforming catalyst control temperature: outlet 700 ° C
Reformer temperature rise 5 hours
[Reformer stop condition A]
Time from stopping fuel supply to heating means to stopping water supply: 2 minutes
(Temperature of outlet catalyst of reformer when water supply is stopped: 580 ° C)
Time from water supply stop to raw fuel stop: 10 minutes
The raw fuel supply amount is GHSV = 1000 hr.^-1Same as the flow rate under operating conditions.
(Temperature of outlet catalyst of reformer when supply of raw fuel is stopped: 300 ° C)
The reformer inlet opening / closing valve 10 was once opened at 50 ° C., and was closed again after 10 seconds.
The raw fuel used for the replacement was used for raising the temperature of the hot water in the hot water storage tank 19.
A start-stop test of 50 cycles was performed under the above-mentioned reformer stop condition A.
FIG. 2 shows the relationship between the number of cycles, the reforming rate calculated by the following equation, and the result of measuring the outlet CO concentration of the reformer 8.
[0058]
formula:
Reforming rate = [(CO₂ , CO) / (CO₂ , CO, CH₄ )] × 100
[0059]
(Example 2)
[Reformer operating conditions]
Same as Example 1.
[Reformer stop condition B]
Time from stopping fuel supply to heating means to stopping water supply: 5 minutes
(Temperature of outlet catalyst of reformer when water supply is stopped: 400 ° C)
Time from water supply stop to raw fuel stop: 60 minutes
The raw fuel supply amount is GHSV = 1000 hr.^-1Same as the flow rate under operating conditions.
(Temperature of outlet catalyst of reformer when raw fuel supply is stopped: 50 ° C)
The reformer inlet opening / closing valve 10 was once opened at 50 ° C., and was closed again after 10 seconds.
The raw fuel used for the replacement was used for raising the temperature of the hot water in the hot water storage tank 19.
A start-stop test of 50 cycles was performed under the reformer stop condition B described above.
FIG. 2 shows the relationship between the number of cycles, the reforming rate calculated by the above equation, and the result of measuring the outlet CO concentration of the reformer 8.
[0060]
(Example 3)
[Reformer operating conditions]
Same as Example 1.
[Reformer stop condition C]
Time from stop of fuel supply to heating means to stop of water supply: 0 minutes
(Temperature of outlet catalyst of reformer when water supply is stopped: 700 ° C)
Time from water supply stop to raw fuel stop: 10 minutes
The raw fuel supply amount is GHSV = 1000 hr.^-1Same as the flow rate under operating conditions.
(Temperature of outlet catalyst of reformer when supply of raw fuel is stopped: 300 ° C)
The reformer inlet opening / closing valve 10 was once opened at 50 ° C., and was closed again after 10 seconds.
The raw fuel used for the replacement was used for raising the temperature of the hot water in the hot water storage tank 19.
Under the above reformer stop condition C, a 50-cycle start / stop test was performed.
FIG. 2 shows the relationship between the number of cycles, the reforming rate calculated by the above equation, and the result of measuring the outlet CO concentration of the reformer 8.
[0061]
(Example 4)
[Reformer operating conditions]
Same as Example 1.
[Reformer stop condition D]
Time from stopping fuel supply to heating means to stopping water supply: 30 minutes
(Temperature of outlet catalyst of reformer when water supply is stopped: 300 ° C)
Time from water supply stop to raw fuel stop: 4 minutes
The raw fuel supply amount is GHSV = 1000 hr.^-1Same as the flow rate under operating conditions.
(Catalyst outlet catalyst temperature when raw fuel supply is stopped: 240 ° C)
Under the above reformer stop condition D, a 50-cycle start / stop test was performed.
FIG. 2 shows the relationship between the number of cycles, the reforming rate calculated by the above equation, and the result of measuring the outlet CO concentration of the reformer 8.
[0062]
(Comparative Example 1)
[Reformer operating conditions]
Same as Example 1.
[Reformer stop condition X]
Time from stop of fuel supply to heating means to stop of water supply: 0 minutes
(Temperature of outlet catalyst of reformer when water supply is stopped: 700 ° C)
Time from water supply stop to raw fuel stop: 0 minutes
The raw fuel supply amount is GHSV = 1000 hr.^-1Same as the flow rate under operating conditions.
(Temperature of outlet catalyst of reformer when supply of raw fuel is stopped: 700 ° C)
Under the above reformer stop condition X, a 50-cycle start / stop test was performed.
FIG. 2 shows the relationship between the number of cycles, the reforming rate calculated by the above equation, and the result of measuring the outlet CO concentration of the reformer 8.
[0063]
(Comparative Example 2)
[Reformer operating conditions]
Same as Example 1.
[Reformer stop condition Y]
Time from stopping fuel supply to heating means to stopping water supply: 30 minutes
(Temperature of outlet catalyst of reformer when water supply is stopped: 100 ° C)
Time from water supply stop to raw fuel stop: 4 minutes
The raw fuel supply amount is GHSV = 1000 hr.^-1Same as the flow rate under operating conditions.
(Temperature of outlet catalyst of reformer when raw fuel supply is stopped: 85 ° C)
A start-stop test of 50 cycles was performed under the above-mentioned reformer stop condition Y.
FIG. 2 shows the relationship between the number of cycles, the reforming rate calculated by the above equation, and the result of measuring the outlet CO concentration of the reformer 8.
[0064]
(Relationship between the time elapsed since the water supply to the reformer was stopped and the catalyst temperature at the outlet of the reformer)
FIG. 3 shows the relationship between the elapsed time after stopping the water supply to the reformer and the temperature of the outlet catalyst of the reformer in Examples 1, 2, 3 and Comparative Example 1.
[0065]
(Results of a 50-cycle start / stop test)
(Examples 1, 2, 3, 4)
In Examples 1, 2, and 3, even after a 50-cycle start / stop test, no significant change or decrease in the reforming rate was observed.
In Examples 1, 2, and 3, even after the supply of water to the reformer 4 is stopped, the water remaining in the reformer 4 causes the reforming reaction to proceed. Thus, the rate of decrease in the temperature of the reformer 4 was rapid. For this reason, even if the outlet temperature of the reformer 4 when the water supply is stopped is initially higher than the thermal decomposition temperature of the raw fuel, the outlet temperature immediately drops to the thermal decomposition temperature or lower. It is considered that there was no influence of the precipitation. Further, since the reforming reaction proceeds, the amount of steam in the reformer 4 is reduced, and the amount of gas is increased by the reforming reaction, so that the relative humidity is also reduced. It is thought that a good effect was brought about because it became faster.
The CO concentration at the outlet of the CO remover 7 (outlet of the reformer 8) was maintained at 9 ppm or less, although there was some fluctuation.
[0066]
In Example 3, no deterioration in performance was observed, and when the reformer 4 was disassembled, no appearance of carbon deposited on the catalyst was confirmed. The performances such as the reforming rate and the CO concentration had no effect at all about 50 cycles this time.
[0067]
Therefore, the supply of water may be stopped when the outlet catalyst temperature of the reformer 4 is 700 ° C., but desirably, the temperature is equal to or lower than the thermal decomposition temperature of the raw fuel + 150 ° C. If the temperature is too low, the reforming reaction does not proceed, and the discharge of the retained steam is delayed.
If the supply of water is stopped at a temperature of approximately 150 ° C., which is the thermal decomposition temperature of the raw fuel, the reformer 4 reaches the thermal decomposition temperature or less in several tens of seconds. In addition, the amount of steam replacement at this time was about 30% of that in the steady operation, and it was confirmed that steam was present even at the thermal decomposition temperature of the raw fuel. Does not happen.
[0068]
In Example 4, the temperature of the catalyst at the outlet of the reformer 4 when the water supply to the reformer 4 was stopped was about 300 ° C., and it is considered that there is no influence of the thermal decomposition of the fuel. In the temperature distribution of the CO converter 6, the reaction site was shifted rearward as compared with the initial stage. However, the performances such as the reforming rate and the CO concentration were not significantly affected by about 50 cycles this time.
[0069]
The raw fuel used for discharging water was not supplied from the outlet of the reformer 8 to the fuel cell 5, but was used for maintaining the temperature of the CO reduction unit 15 and increasing the temperature of the hot water in the heat storage tank 19. .
In the second embodiment, by maintaining the temperature of the CO reduction unit 15, the water vapor in the CO reduction unit 15 could be quickly discharged.
In addition, it was effectively used to raise the temperature of the hot water storage tank 19, and hot water of 64 ° C. to 67 ° C. was stored in the hot water storage tank 19.
[0070]
(Comparative Examples 1 and 2)
In Comparative Example 1, it is considered that the condensed water stayed in the reformer 8 because the steam purging with the raw fuel was not performed. At the time of startup, either because of the presence of the condensed water, it takes time to raise the temperature of each reactor. Has a large effect on the third cycle, the outlet CO concentration of the reformer 8 has reached nearly 20 ppm.
In the reformer 4, since the heating was performed by the heating means 9 (heating burner), it did not seem to be affected by the CO reduction unit 15. A change was observed, and a so-called band aging phenomenon occurred every time the cycle was followed, and at the 29th cycle, the reforming rate was reduced to about 48%.
[0071]
In Comparative Example 2, it is considered that the amount of water staying in the reformer 8 was large, and therefore, the deactivation of the catalyst progressed rapidly, and the CO concentration at the outlet of the reformer 8 was considered to have increased. .
[0072]
If the outlet catalyst temperature of the reformer 4 when the water supply is stopped is too high, carbon deposition occurs due to the thermal decomposition of the raw fuel. However, if the fuel supply to the heating means 9 is stopped, the catalyst is supplied to the reformer 4. The raw fuel undergoes a reforming reaction with steam retained in the reformer 4, and the temperature of the reformer 4 rapidly drops, and immediately reaches the pyrolysis temperature or lower.
Although it depends on the heat capacity of the reformer 4, it has been found that the outlet catalyst temperature of the reformer 4 when the water supply is stopped cannot be strictly said to be "below the raw fuel thermal decomposition temperature". .
[0073]
If the supply of water is stopped at a temperature of approximately 150 ° C. of the thermal decomposition temperature of the raw fuel, the outlet catalyst temperature of the reformer 4 reaches the thermal decomposition temperature or less in several tens of seconds. In addition, the amount of steam replacement at this time is about 30% of that in the normal operation, and it is confirmed that steam is present even at the thermal decomposition temperature of the raw fuel, and no thermal decomposition occurs on the reforming catalyst. it is conceivable that.
When the outlet catalyst temperature of the reformer 4 when the water supply is stopped becomes lower than the thermal decomposition temperature of the raw fuel, the reforming reaction rate between the supplied raw fuel and the steam retained in the reformer 4 In addition, since the amount of steam consumed by the reforming reaction is not large and the volume of the reformed gas does not increase so much, the relative humidity of the steam does not decrease and it takes time to discharge the steam.
Therefore, the lower limit of the outlet catalyst temperature of the reformer 4 when the water supply is stopped is, at most, a temperature lower than the thermal decomposition temperature of the raw fuel by −50 ° C.
[0074]
Regarding the fuel supply amount after the water supply to the reformer 4 is stopped, it is generally systematic to set the flow rate to the rated fuel flow rate during power generation of the fuel cell system.
In that case, at least 5 minutes are required for replacement in the reformer 8.
[0075]
On the other hand, when the temperature of the hot water in the hot water storage tank 19 rises, the fuel (process gas) is simply flown uselessly thereafter. If the water temperature is about several degrees Celsius to about 20 degrees Celsius, it takes about 60 minutes for all of the hot water in the hot water storage tank 19 to reach almost the predetermined temperature (64 to 67 degrees Celsius), depending on the conditions. Flowing the fuel (process gas) longer than this wastes the fuel, so that it takes at most 60 minutes.
If the fuel (process gas) supply time is short, the on-off valves 10, 13, and 14 at the inlet and the outlet of the reformer 8 are closed in a state where the temperature inside the reformer 8 is high, and the inside becomes negative pressure. Therefore, when the temperature of the catalyst in the reformer 8 is reduced to 50 ° C., it is preferable to supply the raw fuel once and maintain the internal pressure at normal pressure.
Through these operations, the steam inside the reformer 8 can be efficiently discharged, and the life of the fuel cell system 1 can be drastically improved without a nitrogen infrastructure.
[0076]
(Example 5)
An example of stopping a fuel cell system using natural gas as a raw fuel will be described.
(During normal operation)
Desulfurizer (desulfurization means capable of adsorbing and desulfurizing sulfur even at normal temperature): 150 to 200 ° C
Reformer: 700 ° C, supplying raw fuel and reforming water.
Fuel burned by burner of heating means of reformer: Fuel cell off-gas
CO transformer: 200-300 ° C
CO remover: 100-150 ° C
Fuel cell: Generates power using reformed gas.
[0077]
(Stop the fuel cell system in the order of Stop 1 to Stop 5 below)
(Stop 1)
Desulfurizer: 150-200 ° C
Reformer: 700 ° C, supplying raw fuel and reforming water.
The combustion in the burner of the heating means of the reformer is stopped.
CO transformer: 200-300 ° C
CO remover: 100-150 ° C
Fuel cell: Stops power generation and burns reformed gas by combustion means to recover heat.
[0078]
(Stop 2)
Desulfurizer: 150-200 ° C
Reformer: 450-500 ° C, feeds raw fuel, but reduces reforming water to about 1/2 to 1/3 for about 5 minutes to avoid thermal decomposition (shape of reformer, amount of catalyst, gas The time until the water runs out depends on the amount etc.).
Combustion stop at the burner of the heating means of the reformer
CO transformer: 200-300 ° C
CO remover: 100-150 ° C
Fuel cell: Stops power generation and burns reformed gas by combustion means to recover heat.
[0079]
(Stop 3)
Desulfurizer: 100-150 ° C
Reformer: 200-300 ° C, supply of raw fuel, but stop the reforming water.
Combustion stop at the burner of the heating means of the reformer
CO transformer: 150-200 ° C
CO remover: 70-110 ° C (It is important to keep the temperature below 70 ° C. When S / C = 3, gas with a dew point of less than 70 ° C may come out of the CO converter. If a drain trap is provided before the CO remover to remove moisture, the minimum temperature of the CO remover does not need to be particularly determined.)
Fuel cell: Stops power generation and burns reformed gas by combustion means to recover heat.
[0080]
(Stop 4)
Desulfurizer: 100-150 ° C
Reformer: 200-300 ° C, shut off raw fuel.
Combustion stop at the burner of the heating means of the reformer
CO transformer: 150-200 ° C
CO remover: 70-110 ° C
Reformer: Gas sealed with raw fuel.
[0081]
After the supply of the reforming water is stopped between the stop 3 and the stop 4, the raw fuel having a volume of 1 to 5 times the reformer capacity is supplied for replacement, or the raw fuel supply stopping means is used. The time until the supply of the raw fuel to the reformer is stopped is set to 5 minutes to 60 minutes.
[0082]
(Stop 5)
Desulfurizer: stop
Reformer: Stop
Combustion stop at the burner of the heating means of the reformer
CO transformer: 50 ° C or less
CO remover: 50 ° C or less
Reformer: The gas on-off valve is opened and closed to maintain the reformer internal pressure.
[0083]
(Example 6)
An example of stopping a fuel cell system using LPG as a raw fuel will be described.
(During normal operation)
Desulfurizer (desulfurization means capable of adsorbing and desulfurizing sulfur even at normal temperature): 150 to 200 ° C
Reformer: 700 ° C, supplying raw fuel and reforming water.
Fuel burned by burner of heating means of reformer: Fuel cell off-gas
CO transformer: 200-300 ° C
CO remover: 100-150 ° C
Fuel cell: Generates power using reformed gas.
[0084]
(Stop the fuel cell system in the order of Stop 1 to Stop 5 below)
(Stop 1)
Desulfurizer: 150-200 ° C
Reformer: 700 ° C, supplying raw fuel and reforming water.
The combustion in the burner of the heating means of the reformer is stopped.
CO transformer: 200-300 ° C
CO remover: 100-150 ° C
Fuel cell: Stops power generation and burns reformed gas by combustion means to recover heat.
[0085]
(Stop 2)
Desulfurizer: 150-200 ° C
Reformer: 350-400 ° C, feeds raw fuel, but reduces reforming water to about 1/2 to 1/3 for about 5 minutes to avoid thermal decomposition (shape of reformer, amount of catalyst, gas The time until the water runs out depends on the amount etc.).
Combustion stop at the burner of the heating means of the reformer
CO transformer: 200-300 ° C
CO remover: 100-150 ° C
Fuel cell: Stops power generation and burns reformed gas by combustion means to recover heat.
[0086]
(Stop 3)
Desulfurizer: 100-150 ° C
Reformer: 200-300 ° C, supply of raw fuel, but stop the reforming water.
Combustion stop at the burner of the heating means of the reformer
CO transformer: 150-200 ° C
CO remover: 70-110 ° C (It is important to keep the temperature below 70 ° C. When S / C = 3, gas with a dew point of less than 70 ° C may come out of the CO converter. If a drain trap is provided before the CO remover to remove moisture, the minimum temperature of the CO remover does not need to be particularly determined.)
Fuel cell: Stops power generation and burns reformed gas by combustion means to recover heat.
[0087]
(Stop 4)
Desulfurizer: 100-150 ° C
Reformer: 200-300 ° C, shut off raw fuel.
Combustion stop at the burner of the heating means of the reformer
CO transformer: 150-200 ° C
CO remover: 70-110 ° C
Reformer: Gas sealed with raw fuel.
[0088]
After the supply of the reforming water is stopped between the stop 3 and the stop 4, the raw fuel having a volume of 1 to 5 times the reformer capacity is supplied for replacement, or the raw fuel supply stopping means is used. The time until the supply of the raw fuel to the reformer is stopped is set to 5 minutes to 60 minutes.
[0089]
(Stop 5)
Desulfurizer: stop
Reformer: Stop
Combustion stop at the burner of the heating means of the reformer
CO transformer: 50 ° C or less
CO remover: 50 ° C or less
Reformer: The gas on-off valve is opened and closed to maintain the reformer internal pressure.
[0090]
【The invention's effect】
The fuel cell system according to claim 1 of the present invention reforms a reforming raw fuel desulfurized in a reformer into a hydrogen-rich gas and supplies the reformed process gas to the fuel cell to generate power. The system
The reforming apparatus includes a desulfurization unit for desulfurizing sulfur in the raw fuel for reforming, and a heating unit for providing a heat quantity necessary for advancing the steam reforming reaction. A steam reformer that reforms water required for the reaction into a hydrogen-rich gas by a steam reforming reaction, and a CO converter that reduces the CO concentration in the hydrogen-rich gas reformed in the steam reformer, A CO remover that further reduces the CO concentration in the gas whose CO concentration has been reduced in the CO converter,
Fuel supply stopping means for stopping fuel supply to the heating means of the steam reformer, temperature detecting means for detecting an outlet catalyst temperature of the steam reformer, and stopping supply of water necessary for the reforming reaction. Water supply stop means, a combustion means for stopping the supply of process gas from the reformer to the fuel cell and burning, and a raw fuel supply stop means for stopping the supply of raw fuel to the reformer,
When the reformer is stopped, the fuel supply to the heating means is stopped by the fuel supply stopping means, and the temperature is lowered until the temperature detected by the temperature detecting means reaches a predetermined temperature, and the fuel supply to the heating means is stopped. Almost simultaneously with the stop, the supply of the process gas from the reformer to the fuel cell is stopped, the fuel is burned by the combustion means, the supply of water is stopped by the water supply stop means, and the inside of the reformer is fed by the raw fuel. After the replacement, the supply of the raw fuel is stopped by the raw fuel supply stopping means,
When the reforming apparatus is stopped, first, the fuel supply to the heating means of the reformer is stopped by the fuel supply stopping means, and the raw fuel and water are continuously supplied. After the temperature is reduced to a condition under which carbon deposition due to the thermal decomposition of the reforming raw fuel does not occur (the temperature detected by the temperature detecting means for detecting the outlet catalyst temperature of the steam reformer is a predetermined temperature, For example, when the temperature falls within the range of 700 ° C. or less and 200 ° C.), the supply of water necessary for the reforming reaction is stopped by the water supply stopping means, and the raw fuel which is continuously supplied to the fuel cell system during that time is used for the reforming apparatus. By displacing during the process to discharge water present during the reformer process, and by stopping the supply of raw fuel by the raw fuel supply stopping means, the life of the reformer can be maintained even in a place without nitrogen infrastructure. To Without made, activation of the reformer, it is possible to repeat stop and reverse the reformer life can be improved to, a marked effect that the life of the fuel cell system can be drastically improved.
At about the same time as the fuel supply to the heating means is stopped, the supply of the process gas from the reformer to the fuel cell is stopped, and the process gas is burned by the combustion means to effectively utilize the thermal efficiency of the fuel cell system. It has a remarkable effect that it can be improved.
[0091]
A fuel cell system according to a second aspect of the present invention is the fuel cell system according to the first aspect, wherein the desulfurization unit is a desulfurization unit capable of adsorbing and desulfurizing a sulfur component even at normal temperature. By using desulfurization means that can adsorb and desulfurize sulfur even at normal temperature, it is possible to desulfurize the sulfur in the raw fuel to a level that does not adversely affect the steam reforming reaction, not only during the operation of the reformer but also during the shutdown operation. It has a further remarkable effect that it can be performed.
[0092]
According to a third aspect of the present invention, in the fuel cell system according to the first or second aspect, the heat storage means for storing heat obtained by burning by the combustion means via a heat exchanger. If heat storage means is provided for storing the heat obtained by combustion by the combustion means through a heat exchanger, the heat obtained by combustion is effectively utilized. There is a further remarkable effect that the thermal efficiency of the fuel cell system can be further improved.
[0093]
A fuel cell system according to a fourth aspect of the present invention is the fuel cell system according to the third aspect, wherein the heat storage means is a hot water storage tank. Is effectively used to raise the temperature of the hot water in the hot water storage tank, and the thermal efficiency of the fuel cell system can be further improved.
[0094]
According to a fifth aspect of the present invention, in the fuel cell system according to any one of the first to fourth aspects, a gas switching valve is provided at an outlet of the reformer, and the raw fuel supply stopping means is provided. When the supply of the raw fuel for reforming to the reforming apparatus is stopped, the gas on-off valve is closed, and the raw fuel supply stopping means supplies the raw fuel for reforming to the reforming apparatus. When the supply is stopped, there is an even more remarkable effect that by closing the gas on-off valve, the CO reduction unit catalyst can be prevented from being deteriorated due to contact with oxygen or moisture.
[0095]
A fuel cell system according to a sixth aspect of the present invention is the fuel cell system according to the fifth aspect, wherein the supply of the raw fuel for reforming to the reformer is stopped by the raw fuel supply stopping means, and the temperature of the CO reduction unit is reduced. When the temperature becomes 50 ° C. or less, once the raw fuel for reforming is supplied to the reforming device by the raw fuel supply stopping device, the reforming to the reforming device is performed again by the raw fuel supply stopping device. When the temperature of the CO reduction unit becomes 50 ° C. or less, the raw fuel supply stop means temporarily stops the supply of the raw fuel for reforming to the reforming apparatus. By supplying the fuel and maintaining the pressure inside the reformer at normal pressure, a further remarkable effect that the inside of the reformer can be prevented from being negative pressure can be obtained.
[0096]
A fuel cell system according to a seventh aspect of the present invention is the fuel cell system according to any one of the first to sixth aspects, wherein heat obtained by burning by the combustion means is converted into a CO converter and / or a CO converter. A means for maintaining the temperature of the remover is provided.At substantially the same time as the supply of water is stopped, the supply of the process gas from the reformer to the fuel cell is stopped, and the process gas is burned. By using the heat obtained by the combustion in the means for maintaining the temperature of the CO converter and / or the CO remover, there is an even more remarkable effect that the thermal efficiency of the fuel cell system can be further improved by effectively utilizing the heat.
[0097]
According to claim 8 of the present invention, the reforming raw fuel desulfurized in the reformer is reformed into a hydrogen-rich gas, and the reformed process gas is supplied to a fuel cell to generate power. A method for stopping a fuel cell system according to any one of the above,
At the time of the stop of the reforming device, first, the fuel supply to the heating means of the steam reformer is stopped by the fuel supply stopping means, and the supply of the process gas from the reforming apparatus is substantially simultaneously with the stop of the fuel supply to the heating means. The supply to the fuel cell is stopped, the process gas is burned by the combustion means, and the temperature detected by the temperature detection means for detecting the outlet catalyst temperature of the steam reformer is in the range of 700 ° C to 200 ° C. When, the supply of water necessary for the reforming reaction is stopped by the water supply stopping means, and when the temperature detected by the temperature detecting means falls within the range of 100 ° C. or more and 400 ° C. or less, A method for stopping a fuel cell system, comprising stopping supply of reforming raw fuel to a reforming device by raw fuel supply stopping means.
When the reforming apparatus is stopped, first, the fuel supply to the heating means of the reformer is stopped by the fuel supply stopping means, and the raw fuel and water are continuously supplied. When the temperature detected by the temperature detecting means falls within the range of 700 ° C. or less and 200 ° C., the supply of water required for the reforming reaction is stopped by the water supply stopping means. The raw fuel which continues to be supplied is used to discharge water present during the process of the reformer, and when the temperature detected by the temperature detecting means falls within the range of 100 ° C. or more and 400 ° C. or less, the raw fuel supply stopping means By stopping the supply of raw fuel, it is possible to prevent carbon deposition due to thermal decomposition of the raw fuel, and to start the reformer without reducing the life of the reformer even in a place without nitrogen infrastructure. It can be repeated stop, reverse reformer life can be improved to, a marked effect that the life of the fuel cell system can be drastically improved.
At about the same time as the supply of fuel to the heating means is stopped, the supply of the process gas from the reformer to the fuel cell is stopped, and the process gas is effectively used by being burned by the combustion means. This has a remarkable effect that the thermal efficiency can be improved.
[0098]
According to a ninth aspect of the present invention, in the method for shutting down the fuel cell system according to the eighth aspect, the catalyst temperature at the outlet of the steam reformer is in the range of the thermal decomposition temperature of the raw fuel for reforming + 150 ° C to -50 ° C. The supply of water necessary for the reforming reaction is stopped by the water supply stopping means when the outlet catalyst temperature of the reformer is equal to the thermal decomposition temperature of the raw fuel + 150 ° C. to −50 ° C. If the water supply is stopped by the water supply stopping means when the value falls within the range, carbon deposition due to thermal decomposition of the raw fuel does not occur. If the temperature is lower than −50 ° C., the steam reforming reaction does not proceed, and a further remarkable effect that discharge of the retained steam is delayed is exerted.
[0099]
According to a tenth aspect of the present invention, in the method for stopping the fuel cell system according to the ninth aspect, the supply of water required for the reforming reaction is stopped by the water supply stopping means, and then 1 to 5 times the reformer capacity. Of raw fuel for replacement, or the supply of water necessary for the reforming reaction is stopped by the water supply stopping means, and then the raw fuel is stopped by the raw fuel supply stopping means. The time until the supply of the raw fuel is stopped is set to be not less than 5 minutes and not more than 60 minutes, and the supply of water necessary for the reforming reaction is stopped by the water supply stopping means. , The supply of water is stopped and raw fuel having a volume of 1 to 5 times the reformer capacity is supplied for replacement, or the supply of raw fuel to the reformer is stopped by raw fuel supply stopping means. If the time is less than 5 minutes and less than 60 minutes, It provides the further remarkable effect that costs amount can improve the efficiency of the reduction can fuel cell system.
[0100]
According to an eleventh aspect of the present invention, in the fuel cell system shutdown method according to any one of the eighth to tenth aspects, heat obtained by burning by the combustion means is stored in a heat storage means via a heat exchanger. If heat storage means for storing the heat obtained by combustion by the combustion means through a heat exchanger is provided, the heat obtained by combustion is effectively utilized to provide a fuel. This has a further remarkable effect that the thermal efficiency of the battery system can be further improved.
[0101]
According to a twelfth aspect of the present invention, in the fuel cell system shutdown method according to the eleventh aspect, the heat storage means is a hot water storage tank, and the heat obtained by burning by the combustion means is stored in the hot water storage tank. This has a further remarkable effect that the thermal efficiency of the fuel cell system can be further improved by effectively utilizing the hot water temperature.
[0102]
According to a thirteenth aspect of the present invention, in the method for stopping a fuel cell system according to any one of the eighth to twelfth aspects, a gas on-off valve is provided at an outlet of the reformer, and the reformer is stopped by the raw fuel supply stopping means. When the supply of the raw fuel for reforming to the fuel cell is stopped, the gas on-off valve is closed, and the supply of the raw fuel for reforming to the reforming device is stopped by the raw fuel supply stopping means. In this case, by closing the gas on-off valve, there is an even more remarkable effect that the CO reduction unit catalyst can be prevented from being deteriorated due to contact with oxygen or moisture.
[0103]
According to a fourteenth aspect of the present invention, in the fuel cell system shutdown method according to the thirteenth aspect, the supply of the raw fuel for reforming to the reformer is stopped by the raw fuel supply stop means, and the temperature of the CO reduction unit is reduced to 50%. When the temperature of the reforming device becomes lower than or equal to ℃, once the raw fuel supply stopping means supplies the reforming raw fuel to the reforming apparatus, the raw fuel supply stopping means again supplies the reforming raw fuel to the reforming apparatus. The feed of the raw fuel is stopped, and when the temperature of the CO reduction unit becomes 50 ° C. or lower, the raw fuel supply stop means temporarily supplies the raw fuel for reforming to the reforming apparatus. By supplying the raw fuel and introducing the raw fuel into the reformer or the like to maintain the pressure inside the reformer at normal pressure, it is possible to prevent the inside of the reformer from becoming negative pressure. It works.
[0104]
According to a fifteenth aspect of the present invention, in the method for stopping a fuel cell system according to any one of the eighth to fourteenth aspects, heat obtained by burning by the combustion means is supplied to a CO converter and / or a CO remover. A fuel cell system characterized by being used for maintaining a temperature, wherein heat obtained by burning by a combustion means is effectively used by maintaining the temperature of a CO converter and / or a CO remover. This has a further remarkable effect that the thermal efficiency can be further improved.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram illustrating one embodiment of a fuel cell system of the present invention.
FIG. 2 is a graph showing the relationship between the number of cycles, the reforming rate, and the result of measuring the outlet CO concentration of the reformer.
FIG. 3 is a graph showing a relationship between an elapsed time after water supply to a reformer is stopped and a catalyst temperature at an outlet of the reformer.
FIG. 4 is an explanatory diagram of a conventional fuel cell system.
[Explanation of symbols]
1 fuel cell system
2 desulfurizer
3 vaporizer
4 Steam reformer
5 Fuel cell
6 CO transformer
7 CO remover
8 Reformer
9 heating means
10 Raw fuel supply stopping means
11 Water supply stopping means
12 means for stopping fuel supply
13, 14 Gas on-off valve
15 CO reduction part
16 Temperature detection means
17 Combustion means
18 Heat exchanger
19 Hot water storage tank as heat storage means
20 Means used for maintaining the temperature of a CO converter and a CO remover

Claims

A fuel cell system that reforms a reforming raw fuel desulfurized in a reformer into a hydrogen-rich gas and supplies the reformed process gas to a fuel cell to generate power,
The reforming apparatus includes a desulfurization unit for desulfurizing sulfur in the raw fuel for reforming, and a heating unit for providing a heat quantity necessary for advancing the steam reforming reaction. A steam reformer that reforms water required for the reaction into a hydrogen-rich gas by a steam reforming reaction, and a CO converter that reduces the CO concentration in the hydrogen-rich gas reformed in the steam reformer, A CO remover that further reduces the CO concentration in the gas whose CO concentration has been reduced in the CO converter,
Fuel supply stopping means for stopping fuel supply to the heating means of the steam reformer, temperature detecting means for detecting an outlet catalyst temperature of the steam reformer, and stopping supply of water necessary for the reforming reaction. Water supply stop means, a combustion means for stopping the supply of process gas from the reformer to the fuel cell and burning, and a raw fuel supply stop means for stopping the supply of raw fuel to the reformer,
When the reformer is stopped, the fuel supply to the heating means is stopped by the fuel supply stopping means, the temperature is lowered until the temperature detected by the temperature detecting means reaches a predetermined temperature, and the fuel supply to the heating means is stopped. Almost simultaneously with the stop, the supply of the process gas from the reformer to the fuel cell is stopped, the fuel is burned by the combustion means, the supply of water is stopped by the water supply stop means, and the inside of the reformer is fed by the raw fuel. After the replacement, the supply of the raw fuel is stopped by the raw fuel supply stopping means.

2. The fuel cell system according to claim 1, wherein the desulfurization unit is a desulfurization unit capable of adsorbing and desulfurizing sulfur even at normal temperature.

3. The fuel cell system according to claim 1, further comprising a heat storage means for storing heat obtained by burning by the combustion means via a heat exchanger.

The fuel cell system according to claim 3, wherein the heat storage means is a hot water storage tank.

A gas on-off valve is provided at an outlet of the reforming device, and when the supply of the raw fuel for reforming to the reforming device is stopped by the raw fuel supply stopping means, the gas on-off valve is closed. The fuel cell system according to any one of claims 1 to 4.

The supply of the raw fuel for reforming to the reforming apparatus is stopped by the raw fuel supply stopping means, and when the temperature of the CO reduction unit becomes 50 ° C. or less, the raw fuel supply stopping means temporarily stops the supply to the reforming apparatus. The supply of the raw fuel for reforming to the reforming apparatus is stopped by the raw fuel supply stopping means again after the supply of the raw fuel for reforming is performed. The fuel cell system according to any one of the above.

The fuel according to any one of claims 1 to 6, further comprising means for using heat obtained by combustion by the combustion means for maintaining the temperature of the CO converter and / or the CO remover. Battery system.

The fuel cell according to any one of claims 1 to 7, wherein the reforming raw fuel desulfurized in the reformer is reformed into a hydrogen-rich gas, and the reformed process gas is supplied to the fuel cell to generate power. A method of stopping the system,
At the time of the stop of the reforming device, first, the fuel supply to the heating means of the steam reformer is stopped by the fuel supply stopping means, and the supply of the process gas from the reforming apparatus is substantially simultaneously with the stop of the fuel supply to the heating means. The supply to the fuel cell is stopped, the process gas is burned by the combustion means, and the temperature detected by the temperature detection means for detecting the outlet catalyst temperature of the steam reformer is in the range of 700 ° C to 200 ° C. When, the supply of water necessary for the reforming reaction is stopped by the water supply stopping means, and when the temperature detected by the temperature detecting means falls within the range of 100 ° C. or more and 400 ° C. or less, A method for stopping a fuel cell system, wherein the supply of raw fuel for reforming to a reformer is stopped by raw fuel supply stopping means.

When the outlet catalyst temperature of the steam reformer falls within the range of the thermal decomposition temperature of the raw fuel for reforming + 150 ° C to -50 ° C, the supply of water required for the reforming reaction is stopped by the water supply stopping means. 9. The method for stopping a fuel cell system according to claim 8, wherein:

The supply of water necessary for the reforming reaction is stopped by the water supply stopping means, and then the raw fuel having a volume of 1 to 5 times the reformer capacity is supplied for replacement, or the water supply stopping means is provided. Thus, the time from when the supply of water necessary for the reforming reaction is stopped to when the supply of the raw fuel for reforming to the reformer is stopped by the raw fuel supply stopping means is 5 minutes or more and 60 minutes or less. The method according to claim 9, wherein:

The method according to any one of claims 8 to 10, wherein heat obtained by burning the combustion means is stored in a heat storage means via a heat exchanger.

The method according to claim 11, wherein the heat storage means is a hot water storage tank.

A gas on-off valve is provided at an outlet of the reforming device, and when the supply of the raw fuel for reforming to the reforming device is stopped by the raw fuel supply stopping means, the gas on-off valve is closed. The method for stopping a fuel cell system according to any one of claims 8 to 12.

The supply of the raw fuel for reforming to the reforming apparatus is stopped by the raw fuel supply stopping means, and when the temperature of the CO reduction unit becomes 50 ° C. or less, the raw fuel supply stopping means temporarily stops the supply to the reforming apparatus. 14. The fuel cell system according to claim 13, wherein the supply of the raw fuel for reforming is stopped by the raw fuel supply stop means again after the supply of the raw fuel for reforming is performed. How to stop.

The method according to any one of claims 8 to 14, wherein heat obtained by burning by the combustion means is used for maintaining a temperature of a CO converter and / or a CO remover. .