JP2004278992A - Fluidized bed incinerator and its operating method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fluidized bed incinerator wherein a medium is circulated without increasing the amount of exhaust gas to be released to the air while suppressing the amount of chlorine in a solid phase to be moved to a heat recovery chamber together with the medium. <P>SOLUTION: In the fluidized bed incinerator, the amount of fluid air to be supplied to a combustion chamber during circulating the medium is a value or larger enough to keep the combustion chamber in an oxidizing atmosphere and the total amount of air to be supplied to the fluidized bed incinerator is not greater than the total supply amount of air during uniform fluidization, and part of combustion gas exhausted from the fluidized bed incinerator is circulated in addition to the fluid air supplied to the heat recovery chamber or the combustion chamber. Thus, the amount of fluid gas is increased and a superficial velocity in the chamber is increased. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

均一流動時の層内ガス中ＨＣｌ濃度は、熱回収室で５５０ｐｐｍ，燃焼室で６３０ｐｐｍであり、両室とも空気比が高いため燃焼が活発で、ＲＤＦ中の塩素が速やかに気化していることがわかる。これに対応して媒体砂（以下、媒体という）中Ｃｌ濃度は、燃焼室で１７０ｐｐｍ、熱回収室で２７０ｐｐｍと低い。
【００１６】
一方、媒体循環時の層内ガス中ＨＣｌ濃度は、熱回収室で１８０ｐｐｍ、燃焼室で１５０ｐｐｍと、均一流動時の１／２〜１／３に低下しているものの、媒体中Ｃｌ濃度は、熱回収室で２２６０ｐｐｍ、燃焼室で１９７０ｐｐｍと、両室ともに高い。
【００１７】
これは、燃焼室側に供給される流動化空気量を絞ったため、燃焼室が還元状態となり、塩素の気化率が下がってＨＣｌ濃度が低下し（古角：環境管理，ｖｏｌ．３４，Ｎｏ．９，１９９８）、Ｃｌ分を含んだ未燃チャーが媒体中に存在しているためと考えられる。また、熱力学平衡的には８００℃以上になると、ほとんどのＣｌは気相に移行するが、燃料がＲＤＦの場合、添加されているＣａによって８００℃以上の高温でも、かなりのＣｌがＣａＣｌ_２として固相に存在する（岡本：第７回日本エネルギー学会講演要旨集、１９９８）ことから、層中の灰にもＣｌが含まれており、媒体中Ｃｌ濃度が高くなっていると考えられる。また、熱回収室においては、燃焼室から仕切板下を通ってＣｌを含む未燃チャーが移動してきて燃焼しＨＣｌが発生するが、空気が大量に供給されているために希釈され、層内ガス中ＨＣｌ濃度としては下がったと考えられる。なお、層内には媒体の循環流があるため、生成したチャーや灰が媒体砂に同伴されて層内に滞留しやすく、媒体循環の過程で、Ｃｌ濃度は流動層全体で均一に近くなっている。
【００１８】
このように、媒体循環時には層内ガス中ＨＣｌ濃度は低下するものの、媒体中に多量の塩素が含まれており、この媒体中塩素や同時に存在するアルカリ金属類（Ｎａ，Ｋ）も、過熱器の腐食に影響する。また、アルカリ金属塩が管に付着すると磨耗も加速される。
【００１９】
したがって、従来方式による媒体循環では、熱回収室の空塔速度を高めることは、塩素を多量に含む媒体を過熱器に接触させる頻度を増して腐食速度を増大させることを意味するから、高価な過熱器材料を使用したり、頻繁に過熱器を交換したりする必要があり、コストの上昇を招く。つまり、従来方式による媒体循環では、熱回収室の空塔速度を高めることによる過熱器の高温高圧化には、塩素による腐食が障害となっている。腐食の問題以外に、従来技術では、燃焼室が還元雰囲気となることからＣＯが発生し、同時に毒性の高いダイオキシン類も発生しやすくなる。
【００２０】
そこで、燃焼室側の空気量を減らすことなく熱回収室側の空気量を増やすことにより媒体循環を行えば、燃焼室を酸化雰囲気に保つことができ、燃焼室において塩素やアルカリ金属が気化され、塩素の少ない媒体砂を熱回収室に移動させ、過熱器と接触させて熱回収することができる。また、ＣＯやダイオキシン類の発生も抑制される。しかしこの方法では、トータルの空気供給量が増加するため、総排ガス量（煙突から大気に放出されるガス量）が増え、その顕熱損失により、ボイラ効率が低下してしまう。
【００２１】
本発明の目的は、大気に放出される排ガス量を増加させることなく媒体循環を行い、かつ、媒体循環時に、媒体とともに固相で熱回収室に移動する塩素の量を抑制するにある。
【００２２】
【課題を解決するための手段】
本発明は、上記の目的を達成するため、熱回収室または燃焼室へ供給される流動化空気に、当該流動層炉から排出される燃焼ガスの一部を循環させて加えることにより、流動化ガス量を増加させ、その室の空塔速度を高める構成を設けたものである。
【００２３】
上記構成を設けることにより、媒体循環時にも、燃焼室の空気比を均一流動時よりも低下させることなく、また、供給される全空気量を均一流動時よりも増やすことなく、熱回収室または燃焼室の空塔速度を高めることが可能となる。燃焼室の空気比を均一流動時よりも低下させないということは、均一流動時の供給空気量が、燃焼室を酸化雰囲気に維持できる最低限の空気量に設定されていることが前提であり、均一流動時の供給空気量がそれ以上である場合には、前記最低限の空気量よりも低下させないということである。燃焼室に供給される空気の空気比が低下しないので燃焼が活発に行われ、燃焼室において投入されたごみ中の大部分の塩素が気化し、塩素濃度の低い媒体砂が熱回収室に移動する。この結果、空塔速度を高めても低塩素雰囲気での熱回収が可能となり、かつプラントから排出される排ガス量（煙突から大気に放出される燃焼ガス量）が増加することもないため、顕熱損失によるボイラ効率の低下も避けられる。また、燃焼室におけるＣＯ，ダイオキシン類の発生も抑制される。
【００２４】
熱回収室または燃焼室へ供給される流動化空気に加えられる燃焼ガス（以下、単に排ガスともいう）は、流動層炉から排出されたのち、温度を下げて除塵装置により除塵されたものを循環させて用いるのが望ましく、流動化空気に混入する前に、温度を低下させる前のもっと高温の燃焼ガスと熱交換させて昇温させるのがよい。これにより、全体としての熱効率が低下するのを防止する。
【００２５】
実際の運転に当っては、流動層が所定の温度に到達するまでは排ガスは供給せず、空気のみを供給して熱回収室、燃焼室ともに流動層が均一流動する同等の空塔速度で運転する。このとき、燃焼室に供給される空気量は、流動層が形成されるだけでなく、投入される燃料（ごみ）を燃焼させるに十分な空気量（空気比）、すなわち酸化雰囲気を維持できる空気量とする。また、熱回収室、燃焼室に供給される空気量の差（空塔速度の差）は、両室間で流動媒体の循環移動が生じない程度にしておく。
【００２６】
流動層が所定の温度になったら、燃焼室に供給される空気量を低下させることなく、熱回収室、燃焼室のいずれか一方に排ガスを供給して該一方側の室の空塔速度を他方の室の空塔速度よりも大きくして媒体の循環移動を行わせる。このとき、熱回収室、燃焼室に供給される空気量は、双方ともに均一流動時の値を維持する（この場合は熱回収室、燃焼室のいずれの空塔速度を大きくしてもよい）、燃焼室に供給される空気量を増加しその分だけ熱回収室に供給される空気量を減らす（この場合は排ガスを熱回収室に供給して熱回収室の空塔速度を大きくする）、燃焼室に供給される空気量はそのままあるいは熱回収室に供給されていた量の範囲内で増加し、熱回収室には排ガスだけを供給する（この場合は排ガスを熱回収室に供給して熱回収室の空塔速度を燃焼室の空塔速度より大きくする）、などの運転方法が採用できる。
【００２７】
【発明の実施の形態】
以下、本発明の実施の形態を図面を参照して説明する。
（実施の形態Ａ）
図１に実施の形態Ａである流動層焼却炉を用いた発電プラントの要部の系統図を示す。図示のプラントは、燃料であるごみが投入される供給シュート７を備えた流動層焼却炉（以下、流動層炉という）１と、この流動層炉１から排出される燃焼ガス８を熱源として蒸気を生成する蒸発器９と、蒸発器９を通過した燃焼ガスを用いて給水を加熱する節炭器１０と、節炭器１０に管路３４で接続され節炭器１０を通過した燃焼ガスを用いて空気を加熱する空気予熱器１１と、空気予熱器１１に管路３５で接続され空気予熱器１１を通過した燃焼ガスを水噴霧により減温する減温塔１２と、減温塔１２で水噴霧された燃焼ガスに消石灰を吹きこむ搬送ライン１３と、消石灰を吹きこまれた燃焼ガスが導入される除塵装置であるバグフィルタ１４と、バグフィルタ１４出側に吸込み側を接続された誘引送風機１５と、バグフィルタ１４底部に接続された抜き出しライン１７と、誘引送風機１５出側に煙道３８を介して接続された煙突１６と、前記空気予熱器１１の空気入り側に吐出側を接続して配置された押込送風機２０と、前記空気予熱器１１の空気出側に上流端を接続した予熱空気ライン２１と、予熱空気ライン２１の下流端に分岐して互いに並列に接続されそれぞれダンパ２４，２５を介装した予熱空気供給配管２２，２３と、流動層炉１の底部に均一に分布するように配置され前記予熱空気供給配管２２，２３に接続されて流動化空気を炉内に吹き込む複数の散気管６と、流動層炉１に内装された過熱器４の蒸気出側に接続された蒸気タービン１８と、蒸気タービン１８で駆動される発電機１９と、前記管路３４に分岐して設けられた管路３６に加熱流体入り側を接続して配置されたガス加熱器３１と、ガス加熱器３１の加熱流体出側と前記管路３５を接続する管路３７と、前記煙道３８に排ガス循環管路３２Ａを介して吸込み側を接続した排ガス循環ファン３０と、排ガス循環ファン３０の吐出側と前記ガス加熱器３１の被加熱流体入り側を接続する排ガス循環管路３２Ｂと、前記ガス加熱器３１の被加熱流体出側を前記ダンパ２５下流側の予熱空気供給配管２３に接続する排ガス循環管路３２Ｃと、排ガス循環管路３２Ｃに介装されたダンパ３３とを含んで構成されている。
【００２８】
前記散気管６の上方の炉内部分（流動層炉１の上下方向の中央部分）は、上下方向に配置された仕切板２によって、ごみが投入される燃焼室３と、前記過熱器４が設置された熱回収室５に分割されている。仕切板２の下端と散気管６の上端開口部の間には所定の間隔が設けられており、燃焼室３と熱回収室５の媒体砂（流動層を形成する媒体）が互いに行き来できるようになっている。
【００２９】
また、前記蒸発器９の蒸気出口は、前記過熱器４の蒸気入り口に蒸気管を介して接続されている。前記散気管６のうち燃焼室に配置されたものは前記予熱空気供給配管２２に接続され、残りは前記予熱空気供給配管２３に接続されている。
【００３０】
流動層を流動化させるために、押込送風機２０により、空気予熱器１１で２００〜３００℃に予熱された空気を予熱空気ライン２１に送り、予熱空気供給配管２２，２３を経て散気管６から炉内に供給するが、燃焼室３側の散気管６は予熱空気供給配管２２に、熱回収室５側の散気管６には予熱空気供給配管２３がそれぞれ接続されており、各々、ダンパ２４，２５によって、空気流量を変化させることができる。散気管６と予熱空気供給配管２２，２３が空気供給手段を構成している。また、前記過熱器４は、熱回収用の流体、すなわち蒸発器９で生成された蒸気が流れる伝熱管で構成されている。
【００３１】
上記構成のプラントにおいて、ごみは供給シュート７から流動層炉１の燃焼室３に投入され、燃焼する。流動層炉１で生成された燃焼ガス８は、蒸発器９で給水を加熱して蒸発させ、節炭器１０で前記蒸発器９に導入される前の給水を予熱したのち、空気予熱器１１で押込送風機２０で加圧された空気を予熱する。蒸発器９、節炭器１０、空気予熱器１１で前述のように熱回収された燃焼ガス８は、減温塔１２へ導入され、水噴霧により、温度を２００℃程度に降下させたのち、バグフィルタ１４に導入される。バグフィルタ１４に導入される前の燃焼ガスに、搬送ライン１３から中和剤として消石灰が吹きこまれ、バグフィルタ１４で脱塩されるとともに飛灰が除去される。飛灰が除去された燃焼ガスは誘引送風機１５によって吸引され、煙突１６から大気に放出される。
【００３２】
バグフィルタ１４で回収された飛灰は抜き出しライン１７で抜き出され、無害化処理される。蒸発器４で生成された蒸気は過熱器４に供給され、過熱されたのち蒸気タービン１８に送られて発電を行う。
【００３３】
燃焼室３で発生する燃焼熱を用いて熱回収室５に配置された過熱器４を加熱するために、燃焼室３と熱回収室５の間で流動媒体、つまり流動層を構成する砂（媒体砂）を循環させ、この媒体砂で、熱を燃焼室３から熱回収室５に移動させて過熱器４を加熱する。
【００３４】
また、節炭器１０を出た燃焼ガスの一部は、管路３６を経てガス加熱器３１に導かれ、煙道３８から取出されて排ガス循環ファン３０によりガス加熱器３１に送りこまれる排ガスを、２００〜３００℃に加熱したのち、管路３５に戻され、残りの燃焼ガスとともに減温塔１２に導かれるように構成されている。ガス加熱器３１で加熱された排ガスは、排ガス循環管路３２Ｃ，ダンパ３３を経て、予熱空気供給配管２３に導かれ、予熱空気ライン２１を経て予熱空気供給配管２３に送りこまれる流動化空気と混合されて熱回収室５側の散気管６から噴出するようになっている。
【００３５】
図２を参照して本実施の形態における媒体循環方法の概念を説明する。図中の白抜きの矢印は空気予熱器１１を経て流動層に送りこまれる供給空気を、灰色の矢印は排ガス循環管路３２Ｃを経て流動層に送りこまれる排ガスを、それぞれ示しており、矢印の数が供給量の多少を表している。なお、本実施の形態では、燃焼室と熱回収室の流れに直交する平面での断面積比は１：２としてある。
【００３６】
流動層炉１の立ち上げ時は、排ガス循環ファン３０は運転せず、排ガス循環管路３２Ｃのダンパ３３は閉じられ、すべての散気管６から同量の予熱空気が噴出される。散気管６は、燃焼室３、熱回収室５の双方に均等に分散配置されているから、燃焼室３も熱回収室５も同じ空塔速度となり、流動層は均一流動を行いながら昇温される。
【００３７】
このとき、燃焼室３に供給される空気量は、流動媒体（以下、媒体ともいう）を流動化するとともに、投入される燃料（ごみ）を燃焼させるに十分な量、すなわち燃料焼却中も酸化雰囲気を維持できる空気量に設定される。
【００３８】
流動層温度が所定の燃焼温度（８５０℃程度）に達したら、予熱空気供給配管２２，２３のダンパ２４，２５の開度は変化させず、排ガス循環ファン３０を起動し、排ガス循環管路３２Ｃのダンパ３３を開いて熱回収室５に供給される流動化空気に排ガスを加える。すると、熱回収室５側に供給される気体量が燃焼室３側に供給される気体量よりも多くなり、熱回収室５側の空塔速度が燃焼室３側の空塔速度よりも大きくなる。このため、空塔速度の差により、燃焼室３から熱回収室５への前記仕切板２の下を通っての媒体の移動及び熱回収室５から燃焼室３への前記仕切板２の上を通っての媒体の移動、すなわち媒体の循環が始まる。
【００３９】
このとき、燃焼室３への供給空気量は、立ち上げ時（均一流動時）と同じであるから、空気比は変化せず酸化雰囲気が保たれ、ごみ中のＣｌの気化が促進されて媒体中Ｃｌ濃度は低下する。同時に、Ｎａ，Ｋ等のアルカリ金属類も気化し、それらの媒体中濃度が低下する。このＣｌ濃度や、Ｎａ，Ｋ等のアルカリ金属類濃度が低下した媒体が仕切板２の下を通って熱回収室５へ移動し、この媒体から過熱器４で熱回収される。
【００４０】
一方、熱回収室５側では、空塔速度が均一流動時より大きくなるため、過熱器の熱伝達係数が増大し、均一流動時よりも過熱器出口における蒸気温度が高くなる。また、雰囲気や過熱器と接触する媒体中のＣｌ濃度や、Ｎａ，Ｋ等のアルカリ金属類濃度が低いので、過熱器の腐食が低減され、蒸気の高温高圧化が可能となる。加えて、熱回収室側に追加されたのは煙道３８から循環された排ガスであるから、総排ガス量（煙突１６から大気に放出される排ガス量）が増加することもなく、したがってボイラ効率の低下もない。さらに、使用する排ガスは、バグフィルタ１４で脱塩、除塵後のものであるから、余分なＣｌや灰を流動層に加える恐れもない。熱回収室５に供給される排ガスは、ガス加熱器３１で燃焼ガスにより加熱されているから、熱回収室５の温度を低下させる割合も少ない。
【００４１】
また、熱回収室５に供給される空気量も均一流動時と同じであるから、熱回収室５が還元雰囲気となることはない。したがって、媒体循環時に、燃焼室３に投入された燃料（ごみ）が仕切板２の上を越えて熱回収室５側に入っても、入りこんだ燃料（ごみ）はその場で燃焼して含有されていたＣｌは気化するから、層内Ｃｌ濃度が高まることはない。燃焼室３に供給される空気量が低減されず、燃焼室での燃焼が良好な状態に維持されるので、ＣＯやダイオキシン類の発生も抑制される。
（実施の形態Ｂ）
上記実施の形態Ａにおいて、媒体循環を行う際、熱回収室への空気供給を止め、熱回収室へは排ガスのみを供給して、（熱回収室の空塔速度）＞（燃焼室の空塔速度）としてもよい。排ガスには、通常数％の酸素が残っているから、熱回収室に未燃分があっても、この排ガス中の酸素で燃焼させることができる。
（実施の形態Ｃ）
上記実施の形態Ａにおいて、媒体循環を行う際、燃焼室への空気供給量を均一流動時よりも増やし、同時に熱回収室への空気供給量を前記燃焼室への空気供給量増加分だけあるいはそれ以上減らすとともに排ガスを熱回収室へ供給して（熱回収室の空塔速度）＞（燃焼室の空塔速度）としてもよい。この方法では、燃料（ごみ）が投入される燃焼室側の空気比が均一流動時よりも高くなるので、Ｃｌの気化率が実施の形態Ａの場合よりも高くなり、熱回収室へ循環される媒体に含まれるＣｌの濃度は実施の形態Ａの場合よりも低下し、燃料（ごみ）の燃焼状態もよくなる。
（実施の形態Ｄ）
図３に示す実施の形態Ｄは、流動層内の過熱器の媒体との接触による磨耗防止などのために、排ガス循環管路３２Ｃを予熱空気供給配管２３に接続する代わりに予熱空気供給配管２２に接続して、媒体循環時に、（熱回収室の空塔速度）＜（燃焼室の空塔速度）となるようにしたものである。本実施の形態は、（熱回収室の空塔速度）＜（燃焼室の空塔速度）とすることで、流動層内の過熱器と媒体との接触による磨耗を防止し、かつ燃焼室の媒体を仕切板２の上を通って熱回収室に移動させ、熱回収室の媒体を仕切板２の下を通って燃焼室に移動させることで、熱回収室と燃焼室間の媒体の循環を維持する。この方向で媒体循環を行うと、燃料（ごみ）が投入される燃焼室３から仕切板２の上を越えて燃料の一部が熱回収室５に移動してくる。このため、従来どおり、流動層炉に供給される全空気量を変えずに（熱回収室の空塔速度）＜（燃焼室の空塔速度）とすると、熱回収室側が空気不足の還元雰囲気となり、Ｃｌの気化が抑制され、媒体中Ｃｌ濃度が高くなる。
【００４２】
本実施の形態では、図３に示すように、燃焼室３に予熱空気を供給する予熱空気供給配管２２のダンパ２４の下流側に、ダンパ３３を介装した排ガス循環管路３２Ｃを接続してある。本実施の形態は、この構成により、煙道３８から取出した排ガスを燃焼室３に予熱空気とともに供給し、熱回収室５側に供給される予熱空気の量を減らすことなく、燃焼室側の空塔速度を高めて媒体循環を行わせる。この方法によれば、媒体循環時も熱回収室５が酸化雰囲気に維持され、媒体中Ｃｌ濃度を低くすることができる。
【００４３】
なお、図１に示す実施の形態において、ダンパ３３の上流側の排ガス循環管路３２Ｃを、ダンパ３３Ａを介装した排ガス循環管路３２Ｄにより予熱空気供給配管２２のダンパ２４の下流側に接続し、必要に応じてダンパ３３，３３Ａのいずれか一方を開いて熱回収室５もしくは燃焼室３の空塔速度を高めるように構成してもよい。
（実施の形態Ｅ）
流動化空気の供給を、散気管ではなく、炉の底部に配置された多孔板（分散板）とこの多孔板の下側に形成された風箱を用いている流動層炉では、熱回収室５と燃焼室３に供給される流動化空気は、それぞれ別の風箱から供給されるようになっているから、空塔速度を大きくしたい側の室の風箱に排ガス循環管路３２Ｃを接続した構成とすればよい。
【００４４】
上記各実施の形態はいずれも流動層焼却炉で蒸気を生成し、この蒸気を発電に使用するものであるが、発電プラントに限らず、高温高圧の蒸気として熱回収する流動層焼却炉を使用するシステムであれば、本発明を適用可能であることは云うまでもない。
【００４５】
【発明の効果】
本発明によれば、排ガス量を増加させることなく、熱回収室の媒体中塩素濃度を低下させることができるので、過熱器の腐食を増加させることなく過熱器と熱交換する燃焼ガスの流速を高めることが可能となり、ボイラ効率の低下を抑制できる。また、熱回収室の媒体中塩素濃度を低下させることができるので、高価な材料を使用することなく過熱器の寿命が延長され、運転コストが低減される。
【図面の簡単な説明】
【図１】本発明の実施の形態Ａを示す系統図である。
【図２】実施の形態Ａにおける流動化気体の状態を示す概念図である。
【図３】本発明の実施の形態Ｄを示す系統図である。
【図４】従来技術の流動層焼却炉の例を示す系統図である。
【図５】図４における均一流動時の流動化気体の状態を示す概念図である。
【図６】図４における媒体循環時の流動化気体の状態を示す概念図である。
【符号の説明】
１ 流動層炉
２ 仕切板
３ 燃焼室
４ 過熱器
５ 熱回収室
６ 散気管
７ 供給シュート
８ 燃焼ガス
９ 蒸発器
１０ 節炭器
１１ 空気予熱器
１２ 減温塔
１３ 搬送ライン
１４ バグフィルタ
１５ 誘引送風機
１６ 煙突
１７ 抜き出しライン
１８ 蒸気タービン
１９ 発電機
２０ 押込送風機
２１ 予熱空気ライン
２２，２３ 予熱空気供給配管
２４，２５ ダンパ
３２Ａ，３２Ｂ，３２Ｃ 排ガス循環管路
３３ ダンパ
３４，３５，３６，３７ 管路
３８ 煙道[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a fluidized bed incinerator that burns municipal solid waste, solid waste fuel (Refuse Derived Fuel, hereinafter referred to as RDF), industrial waste, and the like, and recovers and uses generated heat, and an operating method thereof.
[0002]
[Prior art]
In recent years, the amount of heat generated from municipal solid waste has increased, and in order to effectively use energy, steam generated by heat generated by incineration is used to generate garbage using this steam. In order to efficiently generate power using steam, it is necessary to provide a superheater and supply high-temperature, high-pressure steam to the turbine.
[0003]
FIG. 4 shows a system diagram of a conventional power generation plant using steam generated in a fluidized bed incinerator. The plant shown in the figure has a fluidized bed incinerator (hereinafter, referred to as a fluidized bed furnace) 1 having a supply chute 7 into which refuse as fuel is charged, and steam using a combustion gas 8 discharged from the fluidized bed furnace 1 as a heat source. , An economizer 10 that heats the feedwater using the combustion gas that has passed through the evaporator 9, an air preheater 11 that heats the air using the combustion gas that has passed through the economizer 10, A cooling tower 12 for reducing the temperature of the combustion gas passing through the air preheater 11 by spraying water, a transport line 13 for blowing slaked lime to the combustion gas sprayed with water in the cooling tower 12, and slaked lime. A bag filter 14 into which the combustion gas is introduced, an induction blower 15 having a suction side connected to the bag filter 14, an extraction line 17 connected to the bottom of the bag filter 14, and a flue to the exit side of the induction blower 15. Connected chimney 6, a push-in blower 20 arranged with the discharge side connected to the air inlet side of the air preheater 11, a preheated air line 21 connected to the air outlet side of the air preheater 11 at the upstream end, It is branched to the downstream end of the line 21 and is connected in parallel to each other and connected to preheated air supply pipes 22 and 23 having dampers 24 and 25 interposed therebetween, and to the steam outlet side of the superheater 4 installed in the fluidized bed furnace 1. A steam turbine 18 and a generator 19 driven by the steam turbine 18 are configured.
[0004]
At the bottom of the fluidized-bed furnace 1, a plurality of diffuser tubes 6 for blowing fluidized air into the furnace are arranged so as to be evenly distributed, and a portion inside the furnace above the diffuser tubes 6 (in the vertical direction of the fluidized-bed furnace 1). The central portion) is divided by a partition plate 2 arranged in a vertical direction into a combustion chamber 3 into which refuse is charged and a heat recovery chamber 5 in which the superheater 4 is installed. A predetermined space is provided between the lower end of the partition plate 2 and the upper end opening of the air diffuser 6 so that the medium sand (medium forming a fluidized bed) in the combustion chamber 3 and the heat recovery chamber 5 can flow to each other. It has become.
[0005]
The steam outlet of the evaporator 9 is connected to the steam inlet of the superheater 4 via a steam pipe. One of the diffuser tubes 6 arranged in the combustion chamber is connected to the preheated air supply pipe 22, and the rest is connected to the preheated air supply pipe 23.
[0006]
In order to fluidize the fluidized bed, the air preheated to 200 to 300 ° C. by the air preheater 11 is sent to the preheating air line 21 by the forced air blower 20 and supplied to the furnace from the diffuser pipe 6 via the preheating air supply pipe. However, on the combustion chamber 3 side and the heat recovery chamber 5 side, the system of the preheating air supply pipe is separate, and the air flow rate can be changed by the dampers 24 and 25, respectively.
[0007]
In the plant having the above configuration, refuse is charged from the supply chute 7 into the combustion chamber 3 of the fluidized bed furnace 1 and burns. The combustion gas 8 generated in the fluidized bed furnace 1 evaporates the feed water by heating the feed water in the evaporator 9 and preheats the feed water before being introduced into the evaporator 9 in the economizer 10. Preheats the air pressurized by the blower 20. The combustion gas 8 whose heat has been recovered by the evaporator 9, the economizer 10, and the air preheater 11 as described above is introduced into the cooling tower 12, and the temperature is reduced to about 200 ° C. by water spray. It is introduced into the bag filter 14. Before the combustion gas 8 is introduced into the bag filter 14, slaked lime is blown from the transfer line 13 as a neutralizing agent, and fly ash is removed by the bag filter 14. The combustion gas from which fly ash has been removed is sucked by the induction blower 15 and is discharged from the chimney 16 to the atmosphere.
[0008]
Fly ash collected by the bag filter 14 is extracted in an extraction line 17 and is rendered harmless.
[0009]
The steam generated in the evaporator 4 is supplied to the superheater 4, and after being superheated, sent to the steam turbine 18 to generate power.
[0010]
In order to heat the superheater 4 disposed in the heat recovery chamber 5 using the combustion heat generated in the combustion chamber 3, a fluid medium between the combustion chamber 3 and the heat recovery chamber 5, that is, sand forming a fluidized bed is provided. The heat is transferred from the combustion chamber 3 to the heat recovery chamber 5 to heat the superheater 4 with the medium sand.
[0011]
Hereinafter, the concept of the medium sand circulation method in the related art will be described with reference to FIGS. The white arrows in the figure indicate supply air, and the number of arrows indicates the amount of supply. The sectional area ratio between the combustion chamber and the heat recovery chamber is set to 1: 2.
[0012]
When the furnace is started up, as shown in FIG. 5, the same amount of air is supplied from all the air diffusers 6, and the temperature is raised while the fluidized bed is uniformly flown. At this time, the amount of air supplied to the combustion chamber 3 is set to an amount of air (air ratio) sufficient to fluidize the medium sand and burn the injected fuel (refuse). When the temperature of the fluidized bed (bed temperature) reaches a predetermined combustion temperature (about 850 ° C.), as shown in FIG. Is increased, and conversely, the opening of the damper 24 of the preheating air supply pipe 22 to the combustion chamber 3 is decreased. By operating the opening degrees of the dampers 24 and 25 as described above, the amount of air supplied to the heat recovery chamber 5 is made larger than the amount of air supplied to the combustion chamber 3, and the superficial velocity of the heat recovery chamber 5 is increased. The superficial velocity of the chamber 3 is set higher.
[0013]
As a result, the medium sand at the bottom of the combustion chamber 3 having a relatively high particle density flows under the partition plate 2 into the heat recovery chamber 5 having a low particle density, and the same amount of medium sand as that of the partition plate 2 The medium circulates, moving from the heat recovery chamber 5 to the combustion chamber 3 over the upper part 2. Then, the refuse is mainly burned in the combustion chamber 3, and the medium sand in the combustion chamber 3, which has become high in temperature, passes under the partition plate 2 and moves to the heat recovery chamber 5, where the medium sand in the superheater 4 converts Heat recovery is performed. Such medium circulation occurs because the superficial velocity of the heat recovery chamber 5 increases, and as the superficial velocity of the heat recovery chamber 5 increases, the heat transfer coefficient of the superheater 4 increases, and the uniform flow rate increases. The steam temperature at the outlet of the superheater 4 can be higher than at the time, and the power generation efficiency increases.
[0014]
[Problems to be solved by the invention]
In the medium circulation system described above, the following phenomenon occurs. That is, the refuse introduced into the combustion chamber contains chlorine, which is vaporized as the refuse is burned and contained in the gas in the form of HCl in the form of HCl, and a part of the chlorine is vaporized. It moves from the combustion chamber to the heat recovery chamber together with the medium sand without performing. The medium sand moved to the heat recovery chamber contacts the superheater and transfers heat. At that time, the accompanying chlorine causes corrosion of the superheater. The concentration of this chlorine in the fluidized bed when RDF was burned was measured, and the results shown in Table 1 were obtained.
[0015]
[Table 1]

The HCl concentration in the gas in the bed during uniform flow is 550 ppm in the heat recovery chamber and 630 ppm in the combustion chamber. Both chambers have a high air ratio, so combustion is active and chlorine in the RDF is quickly vaporized. I understand. Correspondingly, the Cl concentration in the medium sand (hereinafter referred to as medium) is as low as 170 ppm in the combustion chamber and 270 ppm in the heat recovery chamber.
[0016]
On the other hand, the concentration of HCl in the gas in the layer during circulation of the medium is 180 ppm in the heat recovery chamber and 150 ppm in the combustion chamber, which is reduced to ２〜 to の of that during uniform flow. Both are high, 2260 ppm in the heat recovery chamber and 1970 ppm in the combustion chamber.
[0017]
This is because the amount of fluidized air supplied to the combustion chamber is reduced, so that the combustion chamber is in a reduced state, the vaporization rate of chlorine is reduced, and the HCl concentration is reduced (Korugaku: Environmental Management, vol. 34, No. 9). It is considered that unburned char containing Cl is present in the medium. Further, when the temperature becomes 800 ° C. or higher in terms of thermodynamic equilibrium, most of the Cl shifts to the gaseous phase. ₂ (Okamoto: Abstracts of the 7th Annual Meeting of the Japan Institute of Energy, 1998), it is considered that the ash in the layer also contains Cl, and the Cl concentration in the medium is high. In the heat recovery chamber, unburned char containing Cl moves from the combustion chamber below the partition plate and burns to generate HCl. However, since a large amount of air is supplied, it is diluted, and It is considered that the concentration of HCl in the gas decreased. In addition, since there is a circulating flow of the medium in the bed, the generated char and ash are easily entrained in the bed with the medium sand, and during the medium circulation, the Cl concentration becomes nearly uniform throughout the fluidized bed. ing.
[0018]
As described above, while the medium circulates, although the HCl concentration in the gas in the bed decreases, a large amount of chlorine is contained in the medium, and the chlorine in the medium and the alkali metals (Na, K) present at the same time are also reduced by the superheater. Affects corrosion. Further, when the alkali metal salt adheres to the tube, the wear is accelerated.
[0019]
Therefore, in the medium circulation according to the conventional method, increasing the superficial velocity of the heat recovery chamber means increasing the frequency of contacting the medium containing a large amount of chlorine with the superheater to increase the corrosion rate, which is expensive. Superheater material must be used or the superheater must be replaced frequently, resulting in increased costs. That is, in the medium circulation according to the conventional method, corrosion by chlorine is an obstacle to the high temperature and high pressure of the superheater by increasing the superficial velocity of the heat recovery chamber. In addition to the problem of corrosion, in the related art, CO is generated because the combustion chamber is in a reducing atmosphere, and at the same time, highly toxic dioxins are easily generated.
[0020]
Therefore, by circulating the medium by increasing the amount of air in the heat recovery chamber without reducing the amount of air in the combustion chamber, the combustion chamber can be maintained in an oxidizing atmosphere, and chlorine and alkali metals are vaporized in the combustion chamber. The medium sand containing less chlorine can be moved to the heat recovery chamber and brought into contact with the superheater to recover the heat. Further, generation of CO and dioxins is also suppressed. However, in this method, since the total air supply amount increases, the total amount of exhaust gas (the amount of gas released from the chimney to the atmosphere) increases, and the boiler efficiency decreases due to the loss of sensible heat.
[0021]
An object of the present invention is to circulate the medium without increasing the amount of exhaust gas discharged to the atmosphere, and to suppress the amount of chlorine that moves to the heat recovery chamber in a solid phase together with the medium during circulation of the medium.
[0022]
[Means for Solving the Problems]
In order to achieve the above object, the present invention circulates a part of the combustion gas discharged from the fluidized bed furnace to fluidized air supplied to a heat recovery chamber or a combustion chamber, thereby achieving fluidization. A configuration is provided in which the gas amount is increased to increase the superficial velocity of the chamber.
[0023]
By providing the above configuration, even during the circulation of the medium, the air ratio of the combustion chamber is not reduced below that during the uniform flow, and the total amount of air supplied is not increased more than during the uniform flow, and the heat recovery chamber or It is possible to increase the superficial velocity of the combustion chamber. The fact that the air ratio in the combustion chamber is not reduced below that during uniform flow is based on the premise that the supply air amount during uniform flow is set to the minimum air amount that can maintain the combustion chamber in an oxidizing atmosphere. If the supply air amount during the uniform flow is more than that, the air amount is not reduced below the minimum air amount. Since the air ratio of the air supplied to the combustion chamber does not decrease, combustion is actively performed, most of the chlorine in the refuse input in the combustion chamber evaporates, and medium sand with a low chlorine concentration moves to the heat recovery chamber I do. As a result, even if the superficial velocity is increased, heat can be recovered in a low chlorine atmosphere, and the amount of exhaust gas discharged from the plant (the amount of combustion gas discharged from the chimney to the atmosphere) does not increase. A decrease in boiler efficiency due to heat loss can be avoided. Further, generation of CO and dioxins in the combustion chamber is also suppressed.
[0024]
The combustion gas added to the fluidized air supplied to the heat recovery chamber or the combustion chamber (hereinafter, also simply referred to as exhaust gas) is discharged from the fluidized bed furnace, and then circulated through the temperature-reduced dust removed by the dust removal device. It is preferable that the temperature is increased by exchanging heat with a higher temperature combustion gas before the temperature is lowered before mixing with the fluidizing air. This prevents the overall thermal efficiency from lowering.
[0025]
In actual operation, exhaust gas is not supplied until the fluidized bed reaches a predetermined temperature, but only air is supplied to the heat recovery chamber and combustion chamber at the same superficial velocity where the fluidized bed flows uniformly. drive. At this time, the amount of air supplied to the combustion chamber is such that not only a fluidized bed is formed but also an air amount (air ratio) sufficient to burn the injected fuel (refuse), that is, air capable of maintaining an oxidizing atmosphere. Amount. The difference in the amount of air supplied to the heat recovery chamber and the combustion chamber (difference in superficial velocity) is set to such an extent that the circulation of the fluid medium does not occur between the two chambers.
[0026]
When the fluidized bed reaches a predetermined temperature, the exhaust gas is supplied to one of the heat recovery chamber and the combustion chamber without reducing the amount of air supplied to the combustion chamber, and the superficial velocity of the one chamber is reduced. The medium is circulated and moved at a speed higher than the superficial velocity of the other chamber. At this time, the amount of air supplied to the heat recovery chamber and the combustion chamber both maintain a value at the time of uniform flow (in this case, the superficial velocity of either the heat recovery chamber or the combustion chamber may be increased). The amount of air supplied to the combustion chamber is increased and the amount of air supplied to the heat recovery chamber is reduced accordingly (in this case, exhaust gas is supplied to the heat recovery chamber to increase the superficial velocity of the heat recovery chamber). The amount of air supplied to the combustion chamber is increased as it is or within the range of the amount supplied to the heat recovery chamber, and only exhaust gas is supplied to the heat recovery chamber (in this case, exhaust gas is supplied to the heat recovery chamber. (To make the superficial velocity of the heat recovery chamber higher than the superficial velocity of the combustion chamber).
[0027]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(Embodiment A)
FIG. 1 shows a system diagram of a main part of a power plant using a fluidized bed incinerator according to Embodiment A. The plant shown in the figure has a fluidized bed incinerator (hereinafter, referred to as a fluidized bed furnace) 1 having a supply chute 7 into which refuse as fuel is charged, and steam using a combustion gas 8 discharged from the fluidized bed furnace 1 as a heat source. Evaporator 9 for generating water, a economizer 10 for heating feed water by using the combustion gas passing through the evaporator 9, and a combustion gas connected to the economizer 10 via a pipe 34 and passing through the economizer 10. An air preheater 11 for heating the air by using the air preheater 11, a cooling tower 12 connected to the air preheater 11 by a pipe line 35 for reducing the temperature of the combustion gas passing through the air preheater 11 by water spray, A transport line 13 for blowing slaked lime into the water-sprayed combustion gas, a bag filter 14 as a dust remover into which the slaked lime-blown combustion gas is introduced, and an attraction connected to the suction side of the bag filter 14 at its outlet. Blower 15 and bag filter 14 bottom , A chimney 16 connected to the outlet side of the induction blower 15 via a flue 38, and a push-in blower 20 connected to the discharge side of the air preheater 11 on the air inlet side. A preheated air line 21 having an upstream end connected to the air outlet side of the air preheater 11; and a preheated air branched to a downstream end of the preheated air line 21 and connected in parallel to each other with dampers 24 and 25 interposed therebetween. Supply pipes 22, 23, a plurality of diffuser pipes 6, which are arranged so as to be uniformly distributed at the bottom of the fluidized-bed furnace 1 and are connected to the preheating air supply pipes 22, 23 and blow fluidized air into the furnace; The steam turbine 18 connected to the steam outlet side of the superheater 4 installed in the bed furnace 1, the generator 19 driven by the steam turbine 18, and the pipe 36 branched from the pipe 34 are provided. Connect the heating fluid inlet side A gas heater 31 arranged in a vertical direction, a pipe 37 connecting the heating fluid outlet side of the gas heater 31 to the pipe 35, and a suction side connected to the flue 38 via an exhaust gas circulation pipe 32A. An exhaust gas circulating fan 30; an exhaust gas circulating pipe 32B connecting the discharge side of the exhaust gas circulating fan 30 to the heated fluid inlet side of the gas heater 31; and the heated fluid outlet side of the gas heater 31 through the damper 25. The exhaust gas circulation pipe 32C is connected to the preheated air supply pipe 23 on the downstream side, and the damper 33 is interposed in the exhaust gas circulation pipe 32C.
[0028]
A part inside the furnace above the diffuser pipe 6 (a central part in the vertical direction of the fluidized-bed furnace 1) is divided into a combustion chamber 3 into which refuse is injected by a partition plate 2 arranged in a vertical direction, and the superheater 4. It is divided into the installed heat recovery chamber 5. A predetermined space is provided between the lower end of the partition plate 2 and the upper end opening of the air diffuser 6 so that the medium sand (medium forming a fluidized bed) in the combustion chamber 3 and the heat recovery chamber 5 can flow to each other. It has become.
[0029]
The steam outlet of the evaporator 9 is connected to the steam inlet of the superheater 4 via a steam pipe. One of the diffuser tubes 6 arranged in the combustion chamber is connected to the preheated air supply pipe 22, and the rest is connected to the preheated air supply pipe 23.
[0030]
In order to fluidize the fluidized bed, the air preheated to 200 to 300 ° C. by the air preheater 11 is sent to the preheating air line 21 by the forced air blower 20, and the air is blown from the diffuser 6 through the preheating air supply pipes 22 and 23 to the furnace. The diffuser 6 on the combustion chamber 3 side is connected to a preheated air supply pipe 22, and the diffuser 6 on the heat recovery chamber 5 side is connected to a preheated air supply pipe 23. 25 allows the air flow to be varied. The air diffuser 6 and the preheated air supply pipes 22 and 23 constitute air supply means. Further, the superheater 4 is constituted by a heat transfer tube through which a heat recovery fluid, that is, steam generated by the evaporator 9 flows.
[0031]
In the plant having the above configuration, refuse is charged from the supply chute 7 into the combustion chamber 3 of the fluidized bed furnace 1 and burns. The combustion gas 8 generated in the fluidized bed furnace 1 evaporates the feed water by heating the feed water in the evaporator 9 and preheats the feed water before being introduced into the evaporator 9 in the economizer 10. Preheats the air pressurized by the blower 20. The combustion gas 8 whose heat has been recovered by the evaporator 9, the economizer 10, and the air preheater 11 as described above is introduced into the cooling tower 12, and the temperature is reduced to about 200 ° C. by water spray. It is introduced into the bag filter 14. Slaked lime is blown into the combustion gas before being introduced into the bag filter 14 from the transport line 13 as a neutralizing agent, and is desalted by the bag filter 14 and fly ash is removed. The combustion gas from which fly ash has been removed is sucked by the induction blower 15 and is discharged from the chimney 16 to the atmosphere.
[0032]
Fly ash collected by the bag filter 14 is extracted in an extraction line 17 and is rendered harmless. The steam generated in the evaporator 4 is supplied to the superheater 4, and after being superheated, sent to the steam turbine 18 to generate power.
[0033]
In order to heat the superheater 4 arranged in the heat recovery chamber 5 using the heat of combustion generated in the combustion chamber 3, a fluid medium between the combustion chamber 3 and the heat recovery chamber 5, that is, sand forming a fluidized bed ( The medium sand) is circulated, and heat is transferred from the combustion chamber 3 to the heat recovery chamber 5 to heat the superheater 4 with the medium sand.
[0034]
A part of the combustion gas exiting the economizer 10 is led to a gas heater 31 via a pipe 36, extracted from a flue 38 and sent to the gas heater 31 by an exhaust gas circulation fan 30. After being heated to 200 to 300 ° C., it is returned to the pipe line 35 and guided to the temperature reducing tower 12 together with the remaining combustion gas. The exhaust gas heated by the gas heater 31 is guided to the preheating air supply pipe 23 through the exhaust gas circulation pipe 32C and the damper 33, and is mixed with the fluidized air sent to the preheating air supply pipe 23 through the preheating air line 21. Then, the air is blown out from the air diffuser 6 on the heat recovery chamber 5 side.
[0035]
The concept of the medium circulation method according to the present embodiment will be described with reference to FIG. The white arrows in the figure indicate the supply air sent to the fluidized bed through the air preheater 11, and the gray arrows indicate the exhaust gas sent to the fluidized bed through the exhaust gas circulation line 32C. Indicates the amount of supply. In the present embodiment, the sectional area ratio on a plane orthogonal to the flow between the combustion chamber and the heat recovery chamber is set to 1: 2.
[0036]
When the fluidized bed furnace 1 is started, the exhaust gas circulation fan 30 is not operated, the damper 33 of the exhaust gas circulation pipe 32C is closed, and the same amount of preheated air is blown out of all the air diffusers 6. Since the diffuser tubes 6 are uniformly distributed in both the combustion chamber 3 and the heat recovery chamber 5, the combustion chamber 3 and the heat recovery chamber 5 have the same superficial velocity, and the fluidized bed heats up while performing uniform flow. Is done.
[0037]
At this time, the amount of air supplied to the combustion chamber 3 is an amount sufficient to fluidize a flowing medium (hereinafter, also referred to as a medium) and to burn injected fuel (refuse), that is, oxidize during fuel incineration. The air volume is set to maintain the atmosphere.
[0038]
When the fluidized bed temperature reaches a predetermined combustion temperature (about 850 ° C.), the opening degree of the dampers 24 and 25 of the preheating air supply pipes 22 and 23 is not changed, the exhaust gas circulation fan 30 is started, and the exhaust gas circulation pipe 32C And the exhaust gas is added to the fluidized air supplied to the heat recovery chamber 5. Then, the amount of gas supplied to the heat recovery chamber 5 becomes larger than the amount of gas supplied to the combustion chamber 3, and the superficial velocity of the heat recovery chamber 5 is higher than the superficial velocity of the combustion chamber 3. Become. Therefore, due to the difference in the superficial velocity, the movement of the medium under the partition plate 2 from the combustion chamber 3 to the heat recovery chamber 5 and the movement of the medium above the partition plate 2 from the heat recovery chamber 5 to the combustion chamber 3 The movement of the medium through it, ie the circulation of the medium, begins.
[0039]
At this time, since the amount of air supplied to the combustion chamber 3 is the same as that at the time of startup (at the time of uniform flow), the air ratio does not change, the oxidizing atmosphere is maintained, and the vaporization of Cl in dust is promoted. The medium Cl concentration decreases. At the same time, alkali metals such as Na and K are vaporized, and their concentration in the medium decreases. The medium in which the concentration of Cl or the concentration of alkali metals such as Na and K is reduced moves to the heat recovery chamber 5 under the partition plate 2, and heat is recovered from the medium by the superheater 4.
[0040]
On the other hand, on the heat recovery chamber 5 side, since the superficial velocity is higher than during the uniform flow, the heat transfer coefficient of the superheater increases, and the steam temperature at the superheater outlet becomes higher than during the uniform flow. Further, since the Cl concentration in the atmosphere or the medium in contact with the superheater and the concentration of alkali metals such as Na and K are low, the corrosion of the superheater is reduced, and the steam can be heated to high temperature and pressure. In addition, since the exhaust gas circulated from the flue 38 is added to the heat recovery chamber side, the total exhaust gas amount (the amount of exhaust gas discharged from the chimney 16 to the atmosphere) does not increase, and therefore, the boiler efficiency There is no decrease. Furthermore, since the exhaust gas used is the one after desalination and dust removal by the bag filter 14, there is no danger of adding extra Cl or ash to the fluidized bed. Since the exhaust gas supplied to the heat recovery chamber 5 is heated by the combustion gas in the gas heater 31, the rate of lowering the temperature of the heat recovery chamber 5 is small.
[0041]
Further, since the amount of air supplied to the heat recovery chamber 5 is the same as that during the uniform flow, the heat recovery chamber 5 does not become a reducing atmosphere. Therefore, even if the fuel (garbage) charged into the combustion chamber 3 passes over the partition plate 2 and enters the heat recovery chamber 5 side during the circulation of the medium, the fuel (garbage) that has entered therein is burned and contained on the spot. The Cl that has been vaporized evaporates, so that the Cl concentration in the layer does not increase. Since the amount of air supplied to the combustion chamber 3 is not reduced and the combustion in the combustion chamber is maintained in a favorable state, the generation of CO and dioxins is also suppressed.
(Embodiment B)
In the above-described Embodiment A, when the medium is circulated, the air supply to the heat recovery chamber is stopped, and only the exhaust gas is supplied to the heat recovery chamber. Tower speed). Since several percent of oxygen usually remains in the exhaust gas, even if there is an unburned portion in the heat recovery chamber, it can be burned with the oxygen in the exhaust gas.
(Embodiment C)
In the above-described Embodiment A, when circulating the medium, the air supply amount to the combustion chamber is increased from that at the time of uniform flow, and the air supply amount to the heat recovery chamber is simultaneously increased by the air supply amount increase to the combustion chamber or Further, the exhaust gas may be further reduced and the exhaust gas may be supplied to the heat recovery chamber (the superficial velocity of the heat recovery chamber)> (the superficial velocity of the combustion chamber). In this method, the air ratio of the combustion chamber side into which fuel (refuse) is charged is higher than that during the uniform flow, so that the Cl vaporization rate is higher than in the case of Embodiment A, and the Cl is circulated to the heat recovery chamber. The concentration of Cl contained in the medium is lower than in the case of Embodiment A, and the combustion state of fuel (refuse) is improved.
(Embodiment D)
The embodiment D shown in FIG. 3 uses a preheating air supply pipe 22 instead of connecting the exhaust gas circulation pipe 32C to the preheating air supply pipe 23 in order to prevent wear of the superheater in the fluidized bed due to contact with the medium. To circulate the medium so that (superficial velocity of the heat recovery chamber) <(superficial velocity of the combustion chamber). In the present embodiment, by setting (superficial velocity of the heat recovery chamber) <(superficial velocity of the combustion chamber), abrasion due to contact between the superheater in the fluidized bed and the medium is prevented, and the superficial velocity of the combustion chamber is reduced. By moving the medium over the partition plate 2 to the heat recovery chamber and moving the medium in the heat recovery chamber under the partition plate 2 to the combustion chamber, circulation of the medium between the heat recovery chamber and the combustion chamber To maintain. When the medium is circulated in this direction, a part of the fuel moves from the combustion chamber 3 into which the fuel (garbage) is charged, over the partition plate 2 to the heat recovery chamber 5. For this reason, as in the past, if the total amount of air supplied to the fluidized bed furnace is not changed and (the superficial velocity of the heat recovery chamber) <(the superficial velocity of the combustion chamber), the heat recovery chamber side has an air-deficient reducing atmosphere. And the Cl vaporization is suppressed, and the Cl concentration in the medium increases.
[0042]
In the present embodiment, as shown in FIG. 3, an exhaust gas circulation pipe 32C with a damper 33 interposed is connected downstream of the damper 24 of the preheating air supply pipe 22 for supplying preheating air to the combustion chamber 3. is there. In the present embodiment, with this configuration, the exhaust gas extracted from the flue 38 is supplied to the combustion chamber 3 together with the preheated air, and the amount of the preheated air supplied to the heat recovery chamber 5 is reduced without reducing the amount of the preheated air. The medium is circulated by increasing the superficial velocity. According to this method, the heat recovery chamber 5 is maintained in an oxidizing atmosphere even during circulation of the medium, and the Cl concentration in the medium can be reduced.
[0043]
In the embodiment shown in FIG. 1, the exhaust gas circulation pipe 32C upstream of the damper 33 is connected to the downstream side of the damper 24 of the preheating air supply pipe 22 by an exhaust gas circulation pipe 32D with a damper 33A interposed. If necessary, one of the dampers 33 and 33A may be opened to increase the superficial velocity of the heat recovery chamber 5 or the combustion chamber 3.
(Embodiment E)
In a fluidized bed furnace using a perforated plate (dispersion plate) placed at the bottom of the furnace and a wind box formed below the perforated plate, instead of a diffuser pipe, the fluidized air is supplied by a heat recovery chamber. 5 and the fluidized air supplied to the combustion chamber 3 are supplied from separate wind boxes, respectively, so that the exhaust gas circulation line 32C is connected to the wind box in the chamber on which the superficial velocity is to be increased. What is necessary is just to set it as the structure.
[0044]
In each of the above embodiments, steam is generated in a fluidized bed incinerator and this steam is used for power generation.However, the present invention is not limited to a power plant, but uses a fluidized bed incinerator that recovers heat as high-temperature and high-pressure steam. It goes without saying that the present invention can be applied to any system that performs this operation.
[0045]
【The invention's effect】
According to the present invention, the chlorine concentration in the medium in the heat recovery chamber can be reduced without increasing the amount of exhaust gas, so that the flow rate of the combustion gas that exchanges heat with the superheater without increasing the corrosion of the superheater is reduced. And it is possible to suppress a decrease in boiler efficiency. Further, since the chlorine concentration in the medium in the heat recovery chamber can be reduced, the life of the superheater is extended without using expensive materials, and the operating cost is reduced.
[Brief description of the drawings]
FIG. 1 is a system diagram showing Embodiment A of the present invention.
FIG. 2 is a conceptual diagram showing a state of a fluidizing gas according to Embodiment A.
FIG. 3 is a system diagram showing Embodiment D of the present invention.
FIG. 4 is a system diagram showing an example of a conventional fluidized bed incinerator.
FIG. 5 is a conceptual diagram showing a state of a fluidized gas during uniform flow in FIG.
FIG. 6 is a conceptual diagram showing a state of fluidized gas during circulation of the medium in FIG.
[Explanation of symbols]
1 Fluidized bed furnace
2 Partition plate
3 Combustion chamber
4 Superheater
5 heat recovery room
6 diffuser
7 Supply chute
8 Combustion gas
9 Evaporator
10 Economizer
11 Air preheater
12 Cooling tower
13 Transport line
14 Bag Filter
15 Induction blower
16 chimney
17 Extraction line
18 Steam turbine
19 generator
20 push blower
21 Preheating air line
22, 23 Preheating air supply piping
24, 25 damper
32A, 32B, 32C Exhaust gas circulation pipeline
33 Damper
34, 35, 36, 37 pipe
38 Flue

Claims (6)

A combustion chamber into which fuel is injected, a heat recovery chamber containing a heat transfer tube through which a heat recovery fluid flows, a fluid medium disposed in the combustion chamber and the heat recovery chamber, and a lower part of the combustion chamber and the heat recovery chamber. Air supply means for fluidizing the fluid medium and supplying air for burning the fuel, wherein the combustion chamber and the heat recovery chamber are configured such that the fluid medium is formed by a difference in superficial velocity between the two chambers. In a fluidized bed incinerator configured to circulate between the two chambers,
A fluidized bed incineration system provided with an exhaust gas circulation pipe for guiding a part of the combustion gas discharged from the fluidized bed incinerator to one of the combustion chamber and the heat recovery chamber via the air supply means. Furnace. 2. The fluidized bed incinerator according to claim 1, wherein the exhaust gas circulating conduit has exhaust gas flowing through the exhaust gas circulating conduit as a fluid to be heated, and heats a combustion gas upstream of an inlet side of the exhaust gas circulating conduit. 3. A fluidized bed incinerator comprising a gas heater as a fluid. A combustion chamber into which fuel is injected, a heat recovery chamber containing a heat transfer tube through which a heat recovery fluid flows, a fluid medium disposed in the combustion chamber and the heat recovery chamber, and a lower part of the combustion chamber and the heat recovery chamber. Air supply means for fluidizing the fluid medium and supplying air for burning the fuel, wherein the combustion chamber and the heat recovery chamber are configured such that the fluid medium is formed by a difference in superficial velocity between the two chambers. In a method of operating a fluidized bed incinerator configured to circulate between two chambers,
Until the fluidized bed reaches a predetermined temperature, the amount of air supplied from the air supply means to the combustion chamber and the heat recovery chamber, the difference in superficial velocity between the two chambers does not cause circulation movement of the fluidized medium After the fluidized bed reaches a predetermined temperature, the amount of air supplied from the air supply means to the combustion chamber and the heat recovery chamber is maintained as it is, and the fluidized bed incineration is performed. A part of the combustion gas discharged from the furnace is guided to one of the combustion chamber and the heat recovery chamber through the air supply means, and the superficial velocity of one of the combustion chamber and the heat recovery chamber is set to the other. A method for operating a fluidized-bed incinerator, wherein the fluidized medium is circulated and moved between the combustion chamber and the heat recovery chamber at a larger size. A combustion chamber into which fuel is injected, a heat recovery chamber containing a heat transfer tube through which a heat recovery fluid flows, a fluid medium disposed in the combustion chamber and the heat recovery chamber, and a lower part of the combustion chamber and the heat recovery chamber. Air supply means for fluidizing the fluid medium and supplying air for burning the fuel, wherein the combustion chamber and the heat recovery chamber are configured such that the fluid medium is formed by a difference in superficial velocity between the two chambers. In a method of operating a fluidized bed incinerator configured to circulate between two chambers,
Until the fluidized bed reaches a predetermined temperature, the amount of air supplied from the air supply means to the combustion chamber and the heat recovery chamber, the difference in superficial velocity between the two chambers does not cause circulation movement of the fluidized medium After the fluidized bed reaches a predetermined temperature, the amount of air supplied from the air supply means to the combustion chamber is maintained as it is, and the heat recovery chamber is maintained from the air supply means. To reduce the amount of air supplied to the fluidized bed incinerator, and guide a part of the combustion gas discharged from the fluidized bed incinerator to the heat recovery chamber through the air supply means, thereby reducing the superficial velocity of the heat recovery chamber. A method for operating a fluidized bed incinerator, wherein a fluid medium is circulated between the combustion chamber and the heat recovery chamber at a speed higher than the superficial velocity of the combustion chamber. A combustion chamber into which fuel is injected, a heat recovery chamber containing a heat transfer tube through which a heat recovery fluid flows, a fluid medium disposed in the combustion chamber and the heat recovery chamber, and a lower part of the combustion chamber and the heat recovery chamber. Air supply means for fluidizing the fluid medium and supplying air for burning the fuel, wherein the combustion chamber and the heat recovery chamber are configured such that the fluid medium is formed by a difference in superficial velocity between the two chambers. In a method of operating a fluidized bed incinerator configured to circulate between two chambers,
Until the fluidized bed reaches a predetermined temperature, the amount of air supplied from the air supply means to the combustion chamber and the heat recovery chamber, the difference in superficial velocity between the two chambers does not cause circulation movement of the fluidized medium After the fluidized bed reaches a predetermined temperature, the amount of air supplied from the air supply unit to the combustion chamber is increased and the amount of air supplied from the air supply unit to the heat recovery chamber is maintained. The supply of air is reduced by the increase, and a part of the combustion gas discharged from the fluidized bed incinerator is led to the heat recovery chamber through the air supply means, and the superficial velocity of the heat recovery chamber is reduced. The fluidized medium is circulated between the combustion chamber and the heat recovery chamber by increasing the velocity of the fluidized bed to a value higher than the superficial velocity of the combustion chamber. The method for operating a fluidized bed incinerator according to any one of claims 3 to 5, wherein exhaust gas supplied to the heat recovery chamber or the combustion chamber via the air supply means is subjected to dust removal by a dust remover and then upstream. A method of operating the fluidized bed incinerator, wherein the temperature is increased by the combustion gas on the side and then introduced into the air supply means.

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