JP3986831B2 - Boiler combustion method and apparatus - Google Patents

Description

表１に示す石炭のうち、無煙炭（Ｃ炭）を１００μｍ以下に粉砕して、石炭供給器１０３により２４０ｇ／ｈの一定速度で、バーナ１１１を通して管型反応器１１０に供給した。燃焼用空気１０２は９６０リットル／ｈ、ジメチルエーテル１０１は２０リットル／ｈの一定速度でそれぞれ供給し、混合して微粉炭を搬送する形で管型反応器１１０に供給した。管型反応器内は管壁温度が１４００℃となるように調整した。
【００２３】
各石炭について試験開始から２時間後の時点から４時間まで、集塵器１１３に捕集された灰分を採取し、灰中の未燃分の量を分析したところ、表２に示す本発明の結果が得られた。
【表２】

次に第二の実験例を示す。第一の実験例と同じく、図２に示す小型試験装置により、石炭の燃焼率に及ぼす含酸素有機化合物の影響を評価した。
【００２４】
表１に示す石炭のうち、無煙炭（Ｃ炭）を１００μｍ以下に粉砕して、石炭供給器１０３により２４０ｇ／ｈの一定速度で、バーナ１１１を通して管型反応器１１０に供給した。燃焼用空気１０２は９６０リットル／ｈの一定速度で供給し、微粉炭を搬送する形で管型反応器１１０に供給した。管型反応器内は管壁温度が１４００℃となるように調整した。第二の実験例では第一の実験例とは異なりジメチルエーテルを使用していない。
【００２５】
各石炭について試験開始から２時間後の時点から４時間まで、集塵器１１３に捕集された灰分を採取し、灰中の未燃分の量を分析したところ、表２に示す従来例の結果が得られた。
【００２６】
表２の結果から明らかなように、本発明よれば、ジメチルエーテルを添加することで、灰中の未燃分の量を従来例に比べておよそ１／３に低減することができ、本発明の微粉炭は従来例に比べて完全燃焼し、灰中の未燃分が少なくなり、燃焼効率を改善することができた。
【００２７】
以上で示した二つの実験結果から、以下に示す機構が明らかになった。即ち、ヒドロペルオキシラジカル（ＨＯＯ・）は酸化力を持つラジカル種であり、通常は酸素（Ｏ₂）が活性化され、有機化合物から水素を引抜いて生成する。例えば、メタン（ＣＨ₄）は（１）式によりヒドロペルオキシラジカル（ＨＯＯ・）とメチルラジカル（ＣＨ₃）を生成する。
【００２８】
ＣＨ₄＋Ｏ₂→ＣＨ₃＋ＨＯＯ・ （１）
（１）式により生成したヒドロペルオキシラジカル（ＨＯＯ・）は、連鎖的に水素引き抜き「（２）式」或いは酸素付加「（３）式」を経て酸化反応が進行する。
【００２９】
ＲＨ＋ＨＯＯ・→Ｒ・＋２・ＯＨ （２）
ＲＨ＋ＨＯＯ・→ＲＯＨ＋・ＯＨ （３）
（１）式の反応において、酸素（Ｏ₂）を活性化するには通常高温条件を出現させる必要がある。アルコール、エーテル、ケトン等の含酸素有機化合物は、メタン等の脂肪族炭化水素に比べてより低温で、（１）式の反応によりヒドロペルオキシラジカル（ＨＯＯ・）を生成する。即ち、これら含酸素有機化合物を微粉炭の搬送空気中に混合すると、微粉炭搬送時の温度条件ではラジカル生成に至らず、燃焼場に投入され輻射による加熱を受けると、炭化水素類に比べてより早く分解してラジカルを生成し、燃焼反応を開始するので、着火促進剤として適した性状を持つ。
【００３０】
石炭と共に含酸素有機化合物は燃焼過程において分解し、ヒドロペルオキシラジカル（ＨＯＯ・）等の酸化力を持つ中間生成物つまり活性中間体を生成する。例えば、ジメチルエーテル（ＣＨ₃ＯＣＨ₃）は（４）式によりヒドロペルオキシラジカル（ＨＯＯ・）とアルキルラジカル（ＣＨ₃ＯＣＨ₂・）を生成する。
【００３１】
ＣＨ₃ＯＣＨ₃＋Ｏ₂→ＣＨ₃ＯＣＨ₂・＋ＨＯＯ・ （４）
この両者のラジカルは炭化の進んだ石炭中の構造を酸化し、燃焼が開始される。
【００３２】
本発明によれば、含酸素有機化合物の添加により、より早い時間で燃焼が開始され、燃焼の完結までに要する時間が短縮されるため、燃焼装置の大幅な改造を伴うことなく、炭化の進んだ石炭の燃焼が可能となる。
【００３３】
また炭化の進行度、具体的には燃料比に応じて含酸素有機化合物の添加量を調整して、燃焼率、具体的には灰中未燃分の量を所定の値に制御することができる。即ち、燃料比の高い石炭では、燃料比の低い石炭に比べて含酸素有機化合物の添加量を増やす。尚、最適な含酸素有機化合物の添加量は、灰中未燃分の量は燃料比だけでなく、空気比、或いは燃焼装置の構造によっても変動するため、含酸素有機化合物の添加量は、各装置ごとに設定する。
【００３４】
(第二の課題を解決するための手段)
次に、本発明の第二の課題であるＮＯｘ低減の手段を示す。燃料中にＮ分を含まない他の燃料を利用する燃焼手段では、ＮＯｘの生成は基本的にはサーマル(Ｔｈｅｒｍａｌ) ＮＯｘと呼ばれる、空気中のＮ分の高温での酸化に起因する部分が主体である。これに比べて、石炭を燃料とする燃焼手段では、燃料中に含まれるＮ分の分解によるＮＯｘの生成の寄与があり、排出されるＮＯｘの量は多くなる。このため、石炭を燃料とする燃焼手段においては、排ガス中のＮＯｘ低減に関しては特別の工夫が必要となる。
【００３５】
石炭を燃料とする燃焼手段としては、コークス製造設備、高炉等の製鉄関連設備、及び石炭ガス化を含めた発電設備が主なものである。このうち製鉄関連設備では、基本的に還元的条件下で石炭の燃焼が進むため、ＮＯｘの排出に対するポテンシャルは小さい。石炭をガス化して合成ガス（ＣＯとＨ₂を含む）を得る方法でも、基本的に還元的条件下で石炭の燃焼が進むため、ＮＯｘの排出に対するポテンシャルは小さい。
【００３６】
これに対して、石炭を燃焼させる発電設備では完全燃焼が必須であり、空気を石炭に対して過剰に供給して燃焼させるためＮＯｘ生成のポテンシャルは大きい。石炭を燃焼させる方式としては、固体である石炭の供給方式として、微粉砕した石炭を気流搬送により燃焼装置に供給する石炭ボイラ装置が主流となっている。
【００３７】
微粉炭ボイラでは火炎内脱硝法により、排出される排ガス中のＮＯｘの濃度を低減する方法が採用されている。図３を例にとり、火炎内脱硝法の概要について述べる。図３における燃焼用空気は３段に分割してバーナに供給される。第一段は石炭を気流搬送するための搬送空気７１として、微粉炭管７６を通ってバーナの中心軸に沿って中央部から微粉炭とともに供給される。その量は石炭の理論空気量よりも少なく設定する。残りの空気は二次空気７２、三次空気７３として火炎の外周に旋回流発生器７５を通して旋回をかけて供給する。
【００３８】
火炉７７内に吹き込まれた石炭は、火炎からの輻射を受けて加熱され、揮発分を放出しながら粒子温度が上昇する。放出された揮発分は酸化を受け、更に粒子温度が上昇して石炭粒子に着火し、中心軸上に火炎が形成される。石炭とともに供給された一次空気は理論空気量よりも少ないため、火炎内は還元条件となり還元雰囲気８２が形成される。還元雰囲気内では燃焼ガス中には未燃分が残存することになる。二次空気及び三次空気は旋回をかけることにより、石炭を搬送する空気（一次空気）との混合は抑制されるため、火炎内に生成した還元雰囲気の消失は抑制される。
【００３９】
還元雰囲気８２では酸素が不足するため、還元力を持つＨＣＮ，Ｏ等が生成する。同時に窒素化合物における熱分解及び空気中の窒素の酸化により生成したＮＯｘは、還元域において還元力を持つＨＣＮ，Ｏ等により窒素（Ｎ₂）へと還元される。これにより火炉７７内で生成するＮＯｘの量は低減される。
【００４０】
二次空気及び三次空気が供給される還元雰囲気の外周には酸化雰囲気８３が形成され、還元雰囲気を通過したガス中の未燃分はこの領域で二次空気及び三次空気により完全酸化され、燃焼反応は完結する。更に必要があれば、アフタエアを供給する。
【００４１】
一方、燃焼排ガス中に含まれて火炉から排出されるＮＯｘの除去に関しては、接触分解法、湿式吸収法、吸着法、接触還元法、等の方法が利用されている。接触分解法は触媒を用いてＮＯｘをＮ₂に分解する方式であるが、触媒活性が不充分であり実用化には至っていない。湿式吸収法及び吸着法は、ＮＯｘをアルカリ等の吸収液に吸収させるか、活性炭等に吸着させて排ガス中から除去しようとするものであり、或いは吸収液及び吸着剤の再生あるいは処理に大きなコストがかかる。
【００４２】
接触還元法には、排ガス中における共存の有無によるＮＯｘ還元能力の違いにより、非選択的接触還元法（ＮＳＣＲ法：Ｎｏｎ−Ｓｅｌｅｃｔｉｖｅ Ｃａｔａｌｙｔｉｃ Ｒｅｄｕｃｔｉｏｎ）、選択的接触還元法（ＳＣＲ法：Ｓｅｌｅｃｔｉｖｅ Ｃａｔａｌｙｔｉｃ Ｒｅｄｕｃｔｉｏｎ法）に分けられる。非選択的接触還元法では、還元剤として水素、一酸化炭素、或いは炭化水素類が使用されるが、酸素が共存する場合にＮＯｘの還元は阻害されるため、広範な利用には至っていない。
【００４３】
これに対して、選択的接触還元法は還元剤としてはアンモニアを利用し、酸素が共存してもＮＯｘの還元は阻害されないため広く普及し、標準的な排ガス脱硝法としての地位を確立している。触媒としては、二酸化チタン（ＴｉＯ₂）を担体とし、これに例えば、モリブデン、バナジウム、タングステン等の酸化物を担持したものが利用される。
【００４４】
一方、排ガス中の未燃分を還元剤として利用する選択的接触還元法の開発も進められている。例えばゼオライト系の触媒により酸素共存化で炭化水素によりＮＯｘを還元できる。炭化水素系還元剤の中でも、含酸素有機化合物は酸素共存下でのＮＯｘの還元に対して、オレフィン類あるいはパラフィン類に比べて高活性である。
【００４５】
発明者らは、選択的接触還元法における含酸素有機化合物の特異性に着目し、燃焼過程における含酸素有機化合物の挙動を詳細に調べ、ＮＯとの特異的な反応を見出し、本発明に至った。以下に発明に至った二つの実験結果を詳細に示す。
【００４６】
第一の実験例は図２に示す小型試験装置により、ＮＯｘ排出挙動に及ぼす含酸素有機化合物の影響を評価したものである。この試験装置の構成は、既に述べたとおりである。
【００４７】
上記表１に示す石炭のうち、Ａ炭，Ｂ炭の２種の瀝青炭を１００μｍ以下に粉砕して、石炭供給器１０３により２４０ｇ／ｈの一定速度で、バーナを通して管型反応器に供給した。燃料用空気１０２は９６０リットル／ｈ、ジメチルエーテル１０１は２０リットル／ｈの一定速度でそれぞれ供給し、混合して微粉炭を搬送する形で管型反応器に供給した。管型反応器内の温度は１２００℃となるように調整した。
【００４８】
各石炭について試験開始から２時間後の時点で燃焼排ガスをガス分析計１１４に分岐してガス分析したところ、ガス中のＮＯ及びＮＯ₂の濃度として表３に示す本発明の結果が得られた。
【表３】

第二の実験例は、実験例一と同じく、図２に示す小型試験装置により、ＮＯｘ排出挙動に及ぼす含酸素有機化合物の影響を評価したものである。
【００４９】
表１に示す石炭のうち、Ａ，Ｂの２種の瀝青炭を１００μｍ以下に粉砕して、石炭供給器１０３により２４０ｇ／ｈの一定速度で、バーナ１１１を通して管型反応器１１０に供給した。燃焼用空気１０２は９６０リットル／ｈの一定速度で供給し、微粉炭を搬送する形で管型反応器に供給した。管型反応器内は管壁温度が１２００℃となるように調整した。第二の実験例では第一の実験例とは異なりジメチルエーテルを使用していない。
【００５０】
各石炭について試験開始から２時間後の時点で燃焼排ガスをガス分析計１１４に分岐してガス分析したところ、ガス中のＮＯ及びＮＯ₂の濃度として表３に示す従来例の結果が得られた。
【００５１】
表３の結果によれば、本発明ではジメチルエーテルを添加することで、ＮＯ及びＮＯ₂を従来例に比べて約１・７倍及び３〜２倍に減少することができた。
【００５２】
以上で示した二つの実験結果から、ＮＯｘ低減には、石炭ボイラにおいて気流搬送用空気のラインに含酸素有機化合物の一定量を添加し、バーナにて燃焼させる方式が有効であることがわかった。含酸素有機化合物の供給量は、微粉炭の供給量に対して５〜５０ｗｔ％、より好ましくは１０〜２５ｗｔ％の割合で添加するのが良い。含酸素有機化合物の供給量が５ｗｔ％よりも少ない場合には、下に記すようなＮＯの酸化に必要な量のラジカルを発生させることができない。逆に含酸素有機化合物の添加量が５０ｗｔ％より多い場合は未燃分としてのカルボン酸類、あるいはアルデヒド類の排出濃度が高まる恐れがある。
【００５３】
（４）式で生成したヒドロペルオキシラジカル（ＨＯＯ・）は、ＮＯをＮＯ₂へ酸化する（（５）式）。
【００５４】
ＨＯＯ・＋ＮＯ→ＨＯ・＋ＮＯ₂ （５）
ＮＯｘと総称されるＮＯとＮＯ₂であるが、両者の反応性は大きく異なる。酸素分子に比べてオゾン分子は酸化のポテンシャルが高いが、ＮＯを酸素分子に、ＮＯ₂をオゾン分子に置き換えてもアナロジーが成り立つ。即ち、ＮＯに比べてＮＯ₂は反応性が高く、容易に他の物質を酸化して自らはＮ₂へと還元される。他の物質としては、未燃の燃料、不完全燃焼生成物であるＣＯ等、或いは（４）式で生成したアルキルラジカル（ＣＨ₃ＯＣＨ₂・）等がある。
【００５５】
ＮＯがＮＯのままで存在していたのでは、触媒等の作用がないと還元反応は進行しない。またＯ₂の方が酸化活性は高く、上述の未燃の燃料、不完全燃焼生成物であるＣＯ等、あるいは（４）式で生成したアルキルラジカル（ＣＨ₃ＯＣＨ₂・）等は先にＯ₂と反応する。
【００５６】
含酸素有機化合物としては、メタノール、エタノール、プロパノール等のアルコール類、ジメチルエーテル、ジエチルエーテル、メチル−ｔ−ブチルエーテル等のエーテル類、アセトン、メチルエチルケトン等のケトン類、ホルムアルデヒド、アセトアルデヒド、プロピオンアルデヒド等のアルデヒド類、ギ酸、酢酸、プロピオン酸等のカルボン酸類、ギ酸メチル、酢酸エチル等のエステル類の少なくとも１種を使用することができる。
【００５７】
アルコール、エーテル等の含酸素有機化合物を燃焼させる場合には、酸化過程の中間生成物としてアルデヒド類が生成する。特開平１０−５７７５５号公報及び特開平１０−２１１４１７号公報に記載されているように、燃焼域の後段の煙道に含酸素有機化合物を供給する方法においては、上述したアルデヒド等の中間生成物が生成しても、これに対する除去策が不充分である。
【００５８】
これに対して、本発明の方法では含酸素有機化合物をバーナに供給するために、供給された含酸素有機化合物は必然的に燃焼ゾーンを通過することになる。１５００〜２０００℃の高温域を通過することにより、アルデヒド類はＣＯ₂にまで完全酸化され、排ガス中の濃度は極限まで低減される。
【００５９】
即ち、微粉炭中に多く含まれる縮合芳香族化合物は、ブタン、ペンタン等の脂肪族化合物、或いはベンゼン、トルエン等の単環の芳香族化合物に比較して安定であり、酸化されにくい。従って、縮合芳香族化合物を多く含む、炭化の進んだ瀝青炭あるいは無煙炭等は着火しづらい。通常の石炭バーナで無煙炭等の燃えにくい石炭を燃焼させる場合、着火に要する時間が長く、燃焼が不充分になり、燃焼効率が低下し、灰中未燃分が増加する恐れがある。微粉砕した石炭とともに含酸素有機化合物をバーナに供給することで、石炭の着火、燃焼による温度上昇に従って、ヒドロペルオキシラジカル（ＨＯＯ・）、アルキルラジカル（ＣＨ₃ＯＣＨ₂・）、メトキシラジカル（ＣＨ₃Ｏ・）及びその他のラジカル類が生成する。これらラジカルは活性が高く、微粉炭に含まれる縮合芳香族化合物と反応することができる。これにより、石炭の着火を促進することができる。
【００６０】
また、ヒドロペルオキシラジカル（ＨＯＯ・）、アルキルラジカル（ＣＨ₃ＯＣＨ₂・）、メトキシラジカル（ＣＨ₃Ｏ・）は燃焼により生成した一酸化窒素（ＮＯ）を、二酸化窒素（ＮＯ₂）に酸化する。ＮＯ₂はＮＯに比べて活性であり、ガス中に共存する炭化水素類、一酸化炭素、水素、シアン（ＨＣＮ）、アンモニア（ＮＨ₃）及びこれらに関連する化合物或いはラジカル類によりＮ₂に還元される。これにより、排ガス中のＮＯｘ濃度を低減することができる。
【００６１】
以下、本発明の具体的な実施例を下記により説明する。
【００６２】
(実施例１)
以下、本発明の概要を図１により説明する。
【００６３】
粗粉砕した石炭２は石炭貯蔵ホッパ１２に貯蔵し、ロータリーバルブ１３により石炭粉砕装置１４に供給する。供給量はロータリーバルブ１３の回転数により制御する。石炭は石炭粉砕装置１４で１００μｍ以下に粉砕する。微粉砕した石炭は、押込み通風装置６１からの空気４により石炭ボイラ装置３０の石炭バーナ３１へ搬送する。この搬送空気量は石炭重量の約１０％である。
【００６４】
含酸素有機化合物５は貯蔵タンク２１に貯蔵し、ポンプ６３により押し出す。この供給量は流量調整弁２２によって制御する。含酸素有機化合物の添加量は、実施例３，４，５に示した方法で決めるが、ほぼ石炭供給量に対する質量比で５〜５０％の範囲である。添加された含酸素有機化合物は、微粉炭とともに石炭バーナ３１に供給される。含酸素有機化合物の添加方法には、供給する含酸素有機化合物の形態に応じてガス供給方式、液噴霧方式、或いは固体供給方式等の方式が採用される。これらの含酸素有機化合物を添加する方式の詳細は、実施例２に示す。
【００６５】
石炭バーナ３１では、石炭と搬送空気、及び押込み通風装置６１からの空気３を接触させ、石炭２を燃焼させる。微粉炭とともに石炭バーナ３１に供給された含酸素有機化合物５例えばジメチルエーテルは、微粉炭の着火、燃焼に応じてガス温度が上昇するに従って分解し、ヒドロペルオキシラジカル（ＨＯＯ・）を生成する。
【００６６】
ヒドロペルオキシラジカル（ＨＯＯ・）は燃焼により生成した一酸化窒素（ＮＯ）を、二酸化窒素（ＮＯ₂）に酸化する。ＮＯ₂はＮＯに比べて活性であり、ガス中に共存する炭化水素類、一酸化炭素、水素、シアン（ＨＣＮ）、アンモニア（ＮＨ₃）及びこれらに関連する化合物或いはラジカル類によりＮ₂に還元される。含酸素有機化合物としてジメチルエーテルを添加した場合は、生成したアルキルラジカル（ＣＨ₃ＯＣＨ₂・）がＮＯ₂の還元に寄与することができる。また含酸素有機化合物としてメタノールを添加した場合は、メトキシラジカル（ＣＨ₃Ｏ・）が生成し、ＮＯ₂の還元剤として作用することができる。
【００６７】
上述のヒドロペルオキシラジカル（ＨＯＯ・）、アルキルラジカル（ＣＨ₃ＯＣＨ₂・）、メトキシラジカル（ＣＨ₃Ｏ・）及びその他のラジカル類は、ラジカル内に酸素原子を含み、この酸素原子を供与することで酸化剤として作用することができる。
【００６８】
微粉炭中に多く含まれる縮合芳香族化合物は、ブタン、ペンタン等の脂肪族化合物或いはベンゼン、トルエン等の単環の芳香族化合物に比較して安定であり、酸化されにくい。従って、縮合芳香族化合物を多く含む、炭化の進んだ瀝青炭或いは無煙炭等では着火しづらい。
【００６９】
通常の微粉炭バーナで無煙炭等の燃えにくい石炭を燃焼させる場合、着火に要する時間が長く、燃焼が不充分になり、燃焼効率が低下し、灰中未燃分が増加する恐れがある。これを解決するためにも、含酸素有機化合物を利用することができる。
【００７０】
添加された含酸素有機化合物は容易に分解して、ヒドロペルオキシラジカル（ＨＯＯ・）、アルキルラジカル（ＣＨ₃ＯＣＨ₂・）、メトキシラジカル（ＣＨ₃Ｏ・）及びその他のラジカル類を生成する。これらラジカルは活性が高く、微粉炭に含まれる縮合芳香族化合物と反応することができる。つまりラジカル類の活性により縮合芳香族化合物の結合を切り離し燃焼するので、微粉炭への着火を促進することができる。
【００７１】
石炭燃焼室の側壁は水冷管で構成された水冷壁構造となっており、石炭燃焼熱はこの伝熱管内部を流れる水、或いは蒸気により吸収される。水冷壁での熱吸収は主に輻射によるものであり、石炭燃焼時の発熱をすべて吸収することはできない。そこで、石炭燃焼室下流の煙風道に伝熱管３３を設置し、この伝熱管内を流れる水、或いは蒸気６により更に石炭燃焼時の発熱を吸収する。
【００７２】
石炭ボイラ装置３０から出る排ガスは、ダストや硫黄化合物などを含む。そこで、ダストは集塵装置５１により除去し、硫黄化合物は脱硫装置で除去する。本実施例では、石灰石（炭酸カルシウム）スラリーを用いる湿式脱硫法を示している。この方式では、脱硫塔５３で石灰石スラリー５６を噴霧し、排ガスと石灰石スラリーを接触させ、二酸化硫黄を石膏（硫酸カルシウム）として固定し、遠心分離装置５４で石灰石スラリーから石膏を分離・回収する方式である。煙突５５から排ガスを大気へ放出する際には、水蒸気が凝縮することを防止するため、排ガス温度はガス・ガス熱交換器５２により約１００℃まで上昇させる。
【００７３】
(実施例２)
ここでは含酸素有機化合物５を石炭の搬送空気に供給する方法を示す。石炭を搬送するための空気量は、石炭に対する質量比で約１０〜１５％である。これに対し、本発明による含酸素有機物の供給量は、石炭に対する質量比で最大２５〜３０％である。含酸素有機化合物の分子量は、空気の分子量よりも大きいので、加える含酸素有機化合物の種類にもよるが、搬送空気と含酸素有機化合物の体積割合は、ほぼ同じか、搬送空気の方が若干多くなる。
【００７４】
含酸素有機化合物が常温で気体の場合、図４（Ａ）のように分岐配管から供給することで、混合することが可能となる。また含酸素有機化合物５の供給量は、石炭性状、出口のＮＯｘ濃度などに応じて変化させるので、図４（Ｂ）のように配管中に供給ノズルを出す方法であれば、搬送空気の流れを乱すことがなく、更に望ましい。
【００７５】
含酸素有機化合物５が常温で液体の場合、図４（Ｃ）に示すように、気化装置６７により気体として供給することが可能である。但し、石炭搬送窒素の温度は、安全のため２００℃以下で運用するのが望ましい。従って、この方法が利用できるのは、気体温度が２００℃以下の含酸素有機化合物に限られる。気化温度が２００℃以上の含酸素有機化合物の場合、図４（Ｄ）に示すようにポンプ６３を用いて加圧し、液体を微粒化して噴霧するためのノズル６８を搬送空気配管内に設置する方式にして、搬送空気と混合することができる。
【００７６】
含酸素有機化合物が固体の場合、石炭とともにホッパに供給し、ミルで粉砕する段階で混合することができる。
【００７７】
（実施例３）
本実施例では、含酸素有機化合物５の石炭搬送空気への添加量の決め方について、図１および図５（Ａ）を用いて示す。
【００７８】
まず、図１を用いて含酸素有機化合物の石炭搬送空気への添加系統を示す。含酸素有機化合物５は含酸素有機化合物貯蔵タンク２１に貯蔵する。含酸素有機化合物５は、ポンプ６３により加圧し、実施例２に示したような方法で石炭の搬送管から添加する。含酸素有機化合物の添加量は、ポンプの下流に設置された流量調整弁２２で調整する。流量調整弁２２の開度は、含酸素有機化合物添加流量制御装置４２で制御する。含酸素有機化合物流量制御装置には、実施例３で示した石炭性状４３、ボイラ運転状態４４、ＮＯｘ排出目標値４５に応じて添加する最適な含酸素有機化合物５の添加量を算出するアルゴリズムが組み込まれており、含酸素有機化合物の流量調節弁２２は、この流量が得られるように動作する。
【００７９】
次に、含酸素有機化合物５の添加量を求めるアルゴリズムを示す。石炭の性状は、固定炭素、揮発分、水分、灰分の工業分析結果、及び炭素、水素、窒素の元素分析結果を含むものである。石炭中の固定炭素と揮発分の重量の比で定義される燃料比は、石炭の着火性の指標として用いることができる。例えば燃料比が高いということは揮発分に対して固定炭素の量が多いことを表し、脱水素が進行して芳香族環の縮合数が大きくなり、炭化が進んでいることを表し、それだけ着火が困難になる。
【００８０】
現状の一般的な仕様の微粉炭ボイラは、燃料比が０．５〜２程度の比較的揮発分の多い瀝青炭クラスの石炭を標準炭として設計されている。従って、ボイラに供給される石炭の燃料比が設計に用いた標準炭より多い場合には、含酸素有機化合物供給量を増加する。また、現在の石炭ボイラ装置排ガス中のＮＯｘは、ほぼ石炭中の窒素に起因するものであり、石炭燃焼時の排ガス中に含まれるＮＯｘ濃度は、ほぼ石炭中の窒素含有量に比例する。従って、ボイラに供給される石炭の窒素含有量が設計に用いた標準炭より多い場合には、含酸素有機化合物の量を増加する。
【００８１】
以上の方式を具体化した一例が、図５のアルゴリズムである。このアルゴリズムでは、設計炭での含酸素有機化合物添加量（設計含酸素有機化合物添加量）を補正し、基本含酸素有機化合物添加量を求める。補正に用いるのは、設計炭固定炭素を設計炭揮発分で割った設計炭の燃料比と、現在ボイラに供給されている石炭の固定炭素を揮発分で割った燃料比との差を関数器ＦＸ１に入力し、補正量１を算出する。続いて設計炭の窒素含有量と、現在ボイラに供給されている石炭の窒素含有量との差および、設計炭ＮＯｘ設定値と現在のＮＯｘ目標値との差を関数器ＦＸ２に入力し、補正量２を算出する。これら補正量１と補正量２を設計含酸素有機化合物添加量に加算し、基本含酸素有機化合物添加量を算出する。
【００８２】
(実施例４)
ＮＯｘの排出量は石炭の性状の変動、ボイラの負荷などの運用条件によって変動する。そこで、ボイラ出口の排ガス中のＮＯｘを連続分析し、この値がＮＯｘの許容レベル以下となるように、必要な含酸素有機化合物の供給量を算出し、最適な供給量を維持するように制御する。この実施例を図１および図５により示す。
【００８３】
まず図１により、含酸素有機化合物５を添加する系統を示す。含酸素有機化合物は含酸素有機化合物貯蔵タンク２１に貯蔵する。含酸素有機化合物５は、ポンプ６３により加圧し、実施例２に示したような方法で石炭の搬送菅から添加する。含酸素有機化合物５の添加量は、ポンプの下流に設置された流量調整弁２２で調整する。流量調整弁２２の開度は、含酸素有機化合物を添加する流量制御装置４２で制御する。含酸素有機化合物の流量制御装置４２は、実施例３で示した石炭性状４３、ボイラ運転状態４４、ＮＯｘ排出目標値４５に応じて添加する最適な含酸素有機化合物の添加量を算出するアルゴリズムが組み込まれており、含酸素有機化合物の流量調整弁２２は、この流量が得られるように動作する。このアルゴリズムの詳細は実施例３において、図５（Ａ）を用いて示した通りである。
【００８４】
一方、石炭ボイラ装置の出口からのＮＯｘ濃度を左右する要因は多く、前記アルゴリズムで求めた含酸素有機化合物の添加量が供給されている場合でも、石炭ボイラ装置の出口からのＮＯｘ濃度には目標値からの偏差が存在する。そこで、石炭ボイラ装置の出口からのＮＯｘを連続的にガス分析計４１により計測し、この値を含酸素有機化合物の流量制御装置４２へ入力し、ＮＯｘの計測値が目標値よりも多い場合は、含酸素有機化合物の流量調節弁２２を開き、ＮＯｘの計測値が目標値よりも小さい場合は流量調節弁を閉じる。
【００８５】
この方式を具体化したアルゴリズムの一例が図５（Ｂ）である。このアルゴリズムでは、基本含酸素有機化合物添加量を補正して、修正含酸素有機化合物添加量を算出する。補正量は、現在のＮＯｘ目標値と現在のＮＯｘ排出量の差がゼロになるように比例・積分制御方式により求めている。
【００８６】
(実施例５)
本実施例では、図６を用いて天然ガスから含酸素有機化合物を製造する実施例を示す。天然ガス２０１は脱硫装置２１１で硫化水素を除去し、加圧して水蒸気２０２とともに水蒸気改質装置２１２に供給し、水素と一酸化炭素に改質する。この反応にはニッケル系の触媒を用い、９００℃、４ＭＰａの条件で進める。反応器内部を高温に維持するために、天然ガスの一部、或いは蒸留装置２２２で分離される未反応ガス２０８を燃焼させ、この燃焼排ガスにより外部から加熱する。
【００８７】
このため、水蒸気改質装置２１２は一般的には複数の反応管を束ねた多管構造のものが反応装置に用いられる。触媒を用いる方法以外では、天然ガスと水蒸気に加えて酸素を水蒸気改質装置に供給し、天然ガスを一部、部分酸化させ、この燃焼熱により反応管内部を高温に維持して水蒸気改質反応を進める方法も実用化されている。
【００８８】
水素、一酸化炭素を主成分とする改質ガスは圧縮機２３１で加圧して含酸素有機化合物の合成反応装置２２１に供給する。含酸素有機化合物としては例えばメタノールやジメチルエーテルがある。メタノール合成は次式で示されるものである。
【００８９】
２Ｈ₂＋ＣＯ→ＣＨ₃ＯＨ （６）
この反応には銅−亜鉛系の触媒が用いられ、２５０〜３００℃、５〜１０ＭＰａの条件で進められる。ジメチルエーテルは次式で示されるメタノールの脱水反応により得られる。
【００９０】
ＣＨ₃ＯＨ＋ＣＨ₃ＯＨ→ＣＨ₃ＯＣＨ₃＋Ｈ₂Ｏ （７）
この反応には例えばγ−アルミナ触媒が用いられ、メタノール合成と同様の条件、即ち、２５０〜３００℃、５〜１０ＭＰａで進められる。従来、一酸化炭素と水素からのジメチルエーテル合成は２つの反応器が必要であったが、現在は式１の反応と式２の反応を１つの反応器内で実現する方法が開発されており、メタノール合成と同様のシステム構成とすることが可能となっている。
【００９１】
これらの含酸素有機化合物の合成は平衡反応であり、必ず未反応の水素、一酸化炭素が存在する。そこで、合成反応装置２２１を出たガスは蒸留装置２２２に導き、含酸素有機化合物２０７と未反応ガス２０８を分離する。未反応ガス２０８は圧縮機２３２で加圧して合成反応装置２２１にリサイクルするか、水蒸気改質装置２１２を加熱するための燃料として利用する。
【００９２】
(実施例６)
本実施例では、石炭、酸素から含酸素有機化合物を得るための方法について図７を用いて示す。
【００９３】
微粉砕した石炭２０４は、ガス化炉２１３で酸素２０６と反応させてガス化する。この場合、石炭ガス化ガスの組成は体積比で一酸化炭素が約６０％、水素が約３０％である。即ち、水素／一酸化炭素のモル比は０．５である。一方、下流の含酸素有機化合物の合成反応装置２２１でジメチルエーテルを合成しようとした場合、ジメチルエーテル合成に適した水素／一酸化炭素のモル比は１であり、石炭ガスの組成は水素が不足している。
【００９４】
この水素を補う方法としては、水蒸気を供給してシフト反応による方法の他、炭層ガス２０５をガス化炉に供給する方法がある。炭層ガスは石炭に随伴するガスであり、主成分は水素の割合の高い有機化合物のメタンである。従って、炭田にこのプロセスを立地する場合、燃料の石炭に加えて炭層ガスを供給することで、精製ガス中の水素／一酸化炭素比を高めることが可能である。炭層ガスは、有効利用されずに廃棄されることが多いため、炭層ガスの利用の効果は大きい。
【００９５】
ガス化炉を出た石炭ガスは約１３００℃の高温なので、熱回収装置２１４により蒸気２０８として熱を回収する。生成ガスを構成する成分のうち、含酸素有機化合物の合成触媒を被毒する成分、即ち、硫化水素などの硫黄化合物や灰分はガス精製装置２１５で除去する。また、ガス化炉は通常、２〜３ＭＰａで運用するが、含酸素燃料の合成には５〜１０ＭＰａが適しているので、コンプレッサ２３１により精製ガスを加圧する。
【００９６】
精製ガスは合成反応装置２２１に供給し、メタノール、ジメチルエーテルなどの含酸素有機化合物を合成する。この合成反応は平衡反応であり、合成反応装置の出口からのガス中には必ず未反応の一酸化炭素と水素が含まれる。そこで、蒸留装置２２２で合成された含酸素有機化合物と未反応ガスは分離する。含酸素有機化合物２０７は貯蔵タンクに供給して保管する。
【００９７】
含酸素有機化合物の収率を向上させるためには、未反応ガスはリサイクルコンプレッサ２３２により加圧して合成反応装置２２１に戻し、含酸素有機化合物合成に再利用する。未反応ガスはガスタービン発電装置に供給して発電に利用することもできる。
【００９８】
(実施例７)
本実施例では、石炭ボイラ装置、石炭ガス化装置、含酸素有機化合物合成反応装置、ガスタービン発電装置を組合わせた電力・含酸素有機化合物併産プラントへの本発明の適用事例を示す。含酸素有機化合物は、発電プラントや自動車の燃料として販売可能である。
【００９９】
この電力・含酸素有機化合物併産プラントの概要を図８により示す。微粉砕した石炭２０４は、ガス化炉２１３で酸素２０６と反応させてガス化する。この時、石炭ガス化ガスの組成は約６０％が一酸化炭素、約３０％が水素である。残りの大部分は二酸化炭素、水蒸気、窒素であり、その他に硫化水素などを含む。ガス化炉下段の温度は約１５００℃であり、石炭灰は溶融してスラグになる。スラグはガス化炉下部から排出される。ガス化炉出口のガス温度は約１３００℃であり、この熱は熱回収部２１４で蒸気２０８として回収し、蒸気タービン系に供給し、発電に利用する。
【０１００】
生成ガスを構成する成分のうち、含酸素有機化合物の合成触媒を被毒する成分、即ち硫化水素などの硫黄化合物や灰分はガス精製装置２１５で除去する。精製ガスは合成反応装置２２１に供給し、メタノール、ジメチルエーテルなどの含酸素有機化合物２０７を合成する。この合成反応は平衡反応であり、合成反応装置の出口からのガス中には必ず未反応の一酸化炭素と水素が含まれる。そこで、蒸留装置２２２で合成された含酸素有機化合物と未反応ガスは分離する。含酸素有機化合物は貯蔵タンク２１に供給して保管し、販売する。
【０１０１】
未反応ガスはガスタービン発電装置に供給して発電に利用する。具体的には空気１を圧縮機２４１で圧縮し、この圧縮空気で未反応ガスを燃焼器２４２で燃焼する。この高温・高圧の燃焼ガスにより、ガスタービン２４３を駆動し、発電機２４４を回転させ、発電する。ガスタービン排ガス２４５は酸素を含むので、ボイラ燃焼用の空気として利用することが可能である。そこで、燃焼排ガスは石炭ボイラ装置３０に供給する。
【０１０２】
石炭ボイラ装置への石炭搬送には、押込み通風装置６１により加圧された空気４を用いる。この搬送管へ、前記プロセスで合成された含酸素有機化合物５をポンプ６３で加圧して供給する。含酸素有機化合物の搬送ガスへの添加方法は、実施例２に示した方法が適用可能である。
【０１０３】
本実施例は、石炭ボイラ装置を用いた発電装置の発電出力を、ガスタービン発電により増加させるリパワリングに適するものである。本実施例では含酸素有機化合物を併産するので、これを販売することが可能である。含酸素有機化合物はクリーンな燃料であり、付加価値が高く、プラントの運用上、望ましいものである。また、含酸素有機化合物の一部を既設石炭ボイラ装置に供給することが可能であり、炭種拡大や低ＮＯｘ化などの要求に応えることが可能である。
【０１０４】
【発明の効果】
以上のように、本発明によれば、添加した含酸素有機化合物から石炭の着火、燃焼による温度上昇に従ってヒドロペルオキシラジカル（ＨＯＯ・）、アルキルラジカル（ＣＨ₃ＯＣＨ₂・）、メトキシラジカル（ＣＨ₃Ｏ・）及びその他のラジカル類が生成する。これらラジカルは活性が高く、微粉炭に含まれる縮合芳香族化合物と反応することができる。これにより、微粉炭への着火を促進することができる。従って、従来は燃料とすることが困難であった燃料比の高い無煙炭クラスの石炭が利用可能となり、エネルギーの安定供給に寄与する。
【０１０５】
また、ヒドロペルオキシラジカル（ＨＯＯ・）は燃焼により生成した一酸化窒素（ＮＯ）を、二酸化窒素（ＮＯ₂）に酸化する。ＮＯ₂はＮＯに比べて活性であり、ガス中に共存する炭化水素類、一酸化炭素、水素、シアン（ＨＣＮ）、アンモニア（ＮＨ₃）及びこれらに関連する化合物あるいはラジカル類によりＮ₂に還元され、ボイラ出口でのＮＯｘ濃度は低下する。従って、ボイラの環境適合性を高めることが可能である。
【図面の簡単な説明】
【図１】本発明の実施例として示した石炭ボイラ装置の系統構成図。
【図２】本発明の実施例として示した石炭の燃焼試験装置の概略構成図。
【図３】石炭の燃焼装置におけるＮＯｘ低減の原理を説明する説明図。
【図４】本発明における含酸素有機化合物の供給方式の一例を示す構成図。
【図５】本発明の含酸素有機化合物添加量を求めるアルゴリズムの一例を示すブロック図。
【図６】本発明における含酸素有機化合物の製造方式の一例を示す構成図。
【図７】本発明における含酸素有機化合物の製造方式の一例を示す構成図。
【図８】本発明における石炭ボイラ発電装置と含酸素燃料合成反応装置とを組合わせた一例を示す構成図。
【図９】従来例の一例として示した石炭ボイラ装置の構成図。
【図１０】従来例の一例として示した石炭ボイラ装置の構成図。
【符号の説明】
１…空気、２…石炭、３…石炭燃焼空気、４…石炭搬送空気、５…含酸素有機化合物、６…水または水蒸気、７…石炭ボイラ装置排ガス、８…アンモニア、９…ペルオキシル開始物質、１０…石膏、１２…石炭貯蔵ホッパ、１３…ロータリーバルブ、１４…石炭粉砕装置、２１…含酸素有機化合物貯蔵タンク、２２…含酸素有機化合物流量調整弁、２３…含酸素有機化合物添加部、３０…石炭ボイラ装置、３１…バーナ、３２…空気供給部、３３…伝熱管、３４…帯域Ａ、３５…帯域Ｂ、４１…ガス分析計、４２…流量制御装置、４３…石炭性状、４４…ボイラ運転条件、４５…ＮＯｘ目標値、５７…脱硝装置、５２…ガス熱交換器、５３…脱硫塔、５４…遠心分離機、５５…煙突、５６…石灰石スラリー、６１〜６３…通風装置（ファン）あるいはポンプ、６４…石炭搬送管、６５…含酸素有機化合物供給管、６７…気化装置、６８…噴霧ノズル、７１…石炭及び搬送空気、７２…二次空気、７３…三次空気、７５…バーナ、８２…還元雰囲気、８３…酸化雰囲気、１０１…含酸素有機化合物ボンベ、１０２…空気ボンベ、１０３…石炭供給器、１０４…燃焼ガス、１１０…管型反応器、１１１…バーナ、１１２…冷却器、１１３…集塵器、１１４…ガス分析計、１１５…排気口、１１６…電気炉、２０１…天然ガス、２０２…水蒸気、２０３…空気、２０４…石炭、２０５…炭層ガス、２０６…酸素、２０７…含酸素有機化合物、２０８…未反応ガス、２１１…脱硫装置、２１２…水蒸気改質装置、２１３…ガス化装置、２１４…熱回収装置、２１５…ガス精製装置、２２１…合成反応装置、２２２…蒸留装置、２３１〜２３２…圧縮機。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for reducing harmful components, particularly nitrogen oxides (NOx), in exhaust gas discharged from coal combustion in a coal boiler apparatus using coal as fuel, and further improves the ignition characteristics of coal. The present invention relates to a method for reducing the size of a boiler and reducing the unburned content contained in the recovered ash.
[0002]
[Prior art]
A method of recovering combustion heat of coal as steam according to the prior art is shown in FIGS. Figure 9 shows NOx N ₂ 10 is a system using a dedicated denitration device for reduction to NO. ₂ It is a method to reduce to.
[0003]
The coarsely pulverized coal 2 is stored in a coal storage hopper 12 and supplied to a coal pulverizer 14 by a rotary valve 13. The supply amount is controlled by the rotational speed of the rotary valve 13. Coal is pulverized to 100 μm or less by a coal pulverizer to become pulverized coal.
[0004]
The finely pulverized coal 2 is conveyed to the coal burner 31 of the coal boiler device 30 by the air 3 from the forced-in ventilation device 61. This amount of carrier air is about 10% of the coal weight. In the coal burner 31, coal is brought into contact with the carrier air and the air 3 from the forced-air ventilation device 61 to burn the coal.
[0005]
Currently, bituminous coal with good ignitability is used as fuel, but if the supply and demand of coal becomes tight in the future, carbonization will progress and it is desired to use coal with a wide range of properties, including anthracite with poor ignitability. In the conventional method, when anthracite coal is burned, it is necessary to ensure a sufficient combustion time as compared with the combustion equipment for bituminous coal.
[0006]
When NOx produced in the combustion device is accumulated in the atmosphere by being discharged, it dissolves in rainwater and causes acid rain, and further causes photochemical smog, and its reduction is an urgent issue. It has become. Since the power generation boiler generates a large amount of gas and the total amount of NOx discharged increases, reduction of the emission level is an important issue.
[0007]
Measures for reducing NOx are roughly classified into a treatment method for suppressing generation in the combustion zone and a method for removal from the combustion exhaust gas. As a method for removing from combustion exhaust gas, there is a catalytic reduction method. In FIG. 9, ammonia 8 is added to the combustion exhaust gas as a reducing agent, and NOx is converted into nitrogen (N ₂ ) Shows how to reduce. In this method, NH _Three Storage and storage facilities and catalytic reactors increase costs.
[0008]
On the other hand, there is a method that does not use a catalytic reactor. This method is shown in FIG. This method is called a non-catalytic method, in which a reducing agent such as peroxyl starting material 9 is injected into high-temperature combustion exhaust gas, and NOx is reduced under high-temperature conditions. For example, in Japanese Patent Application Laid-Open Nos. 10-57755 and 10-212417, in order to reduce NOx generated by combustion, a nitrogen-containing compound (NHi precursor) as a reducing agent is placed at a specific temperature range in the flue. Body) and an oxygen-containing organic compound (peroxyl initiator substance) that is an oxidizing agent of NO.
[0009]
This method supplies NOx to N by supplying peroxyl starting material to zone A34, which is the region above 760 ° C, and zone B35, which is the region below 760 ° C. ₂ This is a method for reducing NOx in exhaust gas. In this method, since the reducing material is supplied after the coal is burned and the amount of gas is increased, in order to obtain a large effect of reducing NOx, there is a problem that the amount of reducing material supplied becomes large and the operation cost increases. there were.
[0010]
[Problems to be solved by the invention]
Coal has a longer life than oil and is expected to remain the main energy source in Japan. At present, high-grade bituminous coal imported from overseas is mainly used in Japan. However, when the supply and demand of coal becomes tight in the future, it is desired to use coal with a wide range of properties from low-grade coal such as lignite to anthracite with advanced carbonization.
[0011]
The first problem of the present invention is to promote the ignition of coal in the burner section, improve the combustion characteristics of the coal, and efficiently burn the coal with advanced carbonization without implementing a major modification of the combustion facility. That is.
[0012]
The second object of the present invention is to provide a method and an apparatus for reducing nitrogen oxide (NOx) contained in exhaust gas discharged from a combustion process at a low cost.
[0013]
[Means for Solving the Problems]
As a means for solving the first problem, a condensed aromatic compound of pulverized coal is obtained by adding an oxygen-containing organic compound to the air that conveys the pulverized coal to a burner, and by generating an active intermediate by decomposition of the oxygen-containing organic compound. It is to oxidize.
[0014]
As a means for solving the second problem, an oxygen-containing organic compound is added to the air that conveys pulverized coal to the burner, and NO in the boiler is reduced by an active intermediate produced by the decomposition of the oxygen-containing organic compound. ₂ It is to oxidize.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
(Means for solving the first problem)
That is, the means for improving the combustion characteristic which is the first subject of the present invention will be shown. Coal is a material such as trees buried in the ground from the Paleozoic to Cenozoic, which undergoes metamorphism under conditions of high temperature and high pressure, condenses and carbonizes with dehydrogenation, deoxygenation, and the like. The longer the time of metamorphic action, the more severe the metamorphic conditions, the more carbonization proceeds and the graphite-like structure grows. Therefore, the more carbonized the coal, the less the structure is disturbed, and the reactivity to oxidation, i.e., combustion, decreases.
[0016]
The progress of carbonization can be generally evaluated by the fuel ratio. The fuel ratio is defined as the ratio of the fixed carbon in coal to the weight of volatiles. A high fuel ratio indicates that the amount of fixed carbon is large relative to the volatile matter, and that dehydrogenation proceeds to increase the number of condensed aromatic rings and carbonization proceeds. The current general specification pulverized coal boilers are designed with bituminous coal, which has a relatively high volatile content and a fuel ratio of about 0.5 to 2, as standard coal.
[0017]
However, there is a risk that the supply and demand of such bituminous coal will be tight in the future. Need to be used as fuel.
[0018]
Since coal having advanced carbonization has developed a condensed aromatic ring, the activity for oxidation reaction is low, and in order to burn pulverized coal, it is necessary to lengthen the residence time of the pulverized coal particles in the combustion zone. Specifically, for example, it is necessary to increase the size of the combustion apparatus for the same coal throughput. As one measure for avoiding such a large remodeling, there is a method in which an auxiliary for promoting ignition of coal with advanced carbonization is mixed with the coal and burned. Therefore, the mechanism of the ignition process was examined.
[0019]
Basically, in the ignition process, a sufficient amount of reactant or temperature condition is achieved for the radical chain reaction to proceed. As for the temperature condition, it is strongly affected by the structure of the combustion apparatus, so the apparatus must be modified. On the other hand, regarding the point of increasing the amount of the reactant, if the supply from the carbonized coal as the fuel is insufficient, a substance having a high oxidation activity is supplied separately. That is, addition of an ignition accelerator.
[0020]
However, supplying a mixture of oxidizers, which are well known as oxidizing agents, with fuel, may cause explosion and is dangerous. Desirably, a substance capable of appearing oxidation activity under an appropriate high temperature condition may be used.
[0021]
The present inventors have investigated in detail the thermal decomposition behavior in the combustion process of various organic compounds, found that the radical species generation process active in the oxygen-containing organic compound causes an ignition promoting action, and have led to the present invention. . Two experimental results leading to the invention are shown in detail below.
[0022]
First, a first experimental example is shown. In this experiment, the influence of an oxygen-containing organic compound on the combustion rate of coal was evaluated by a small test apparatus shown in FIG. In this test apparatus, a burner 111 is inserted into a tubular reactor 110 having an inner diameter of 50 mm and a length of 1200 mm, and the tubular reactor 110 is heated from the outside by an electric furnace 116. After the combustion gas is cooled by the cooler 112, the ash is collected by the dust collector 113, and the gas composition is analyzed by the gas analyzer 114.
[Table 1]

Of the coals shown in Table 1, anthracite coal (C charcoal) was pulverized to 100 μm or less and supplied to the tubular reactor 110 through the burner 111 at a constant rate of 240 g / h by the coal feeder 103. Combustion air 102 was supplied at a constant rate of 960 liters / h, and dimethyl ether 101 was supplied at a constant rate of 20 liters / h, mixed, and supplied to the tubular reactor 110 in a form of conveying pulverized coal. The inside of the tubular reactor was adjusted so that the tube wall temperature was 1400 ° C.
[0023]
For each coal, the ash collected in the dust collector 113 was collected from the time 2 hours after the start of the test to 4 hours, and the amount of unburned content in the ash was analyzed. Results were obtained.
[Table 2]

Next, a second experimental example is shown. Similar to the first experimental example, the influence of the oxygen-containing organic compound on the combustion rate of coal was evaluated by the small test apparatus shown in FIG.
[0024]
Of the coals shown in Table 1, anthracite coal (C charcoal) was pulverized to 100 μm or less and supplied to the tubular reactor 110 through the burner 111 at a constant rate of 240 g / h by the coal feeder 103. Combustion air 102 was supplied at a constant speed of 960 liters / h, and was supplied to the tubular reactor 110 in the form of conveying pulverized coal. The inside of the tubular reactor was adjusted so that the tube wall temperature was 1400 ° C. Unlike the first experimental example, dimethyl ether is not used in the second experimental example.
[0025]
For each coal, the ash collected in the dust collector 113 was collected from the time 2 hours after the start of the test to 4 hours, and the amount of unburned ash in the ash was analyzed. Results were obtained.
[0026]
As is apparent from the results in Table 2, according to the present invention, by adding dimethyl ether, the amount of unburned content in the ash can be reduced to about 1/3 compared to the conventional example. The pulverized coal burned completely compared to the conventional example, and the unburned content in the ash was reduced, and the combustion efficiency could be improved.
[0027]
From the two experimental results shown above, the following mechanism became clear. That is, the hydroperoxy radical (HOO.) Is a radical species having an oxidizing power, and usually oxygen (O ₂ ) Is activated and formed by extracting hydrogen from the organic compound. For example, methane (CH _Four ) Is a hydroperoxy radical (HOO.) And a methyl radical (CH _Three ) Is generated.
[0028]
CH _Four + O ₂ → CH _Three + HOO (1)
The hydroperoxy radical (HOO.) Generated by the formula (1) undergoes an oxidation reaction via chain hydrogen abstraction “formula (2)” or oxygen addition “formula (3)”.
[0029]
RH + HOO · → R · + 2 · OH (2)
RH + HOO · → ROH + · OH (3)
In the reaction of formula (1), oxygen (O ₂ ) Usually needs to be exposed to high temperature conditions. Oxygenated organic compounds such as alcohols, ethers, and ketones generate hydroperoxy radicals (HOO.) By the reaction of formula (1) at a lower temperature than aliphatic hydrocarbons such as methane. That is, when these oxygen-containing organic compounds are mixed in the pulverized coal transportation air, radicals are not generated under the temperature conditions during pulverized coal transportation, and when they are put into the combustion field and heated by radiation, compared to hydrocarbons It decomposes faster and generates radicals and starts a combustion reaction, so it has properties suitable as an ignition accelerator.
[0030]
Oxygen-containing organic compounds together with coal are decomposed in the combustion process to produce intermediate products having an oxidizing power such as hydroperoxy radicals (HOO.), That is, active intermediates. For example, dimethyl ether (CH _Three OCH _Three ) Is a hydroperoxy radical (HOO.) And an alkyl radical (CH _Three OCH ₂ ・) Is generated.
[0031]
CH _Three OCH _Three + O ₂ → CH _Three OCH ₂ ・ + HOO ・ (4)
Both radicals oxidize the structure in the carbonized coal and combustion begins.
[0032]
According to the present invention, the addition of the oxygen-containing organic compound starts the combustion at an earlier time and reduces the time required to complete the combustion. Therefore, the carbonization proceeds without significant modification of the combustion apparatus. Coal combustion is possible.
[0033]
In addition, the amount of oxygen-containing organic compound added can be adjusted according to the degree of carbonization, specifically the fuel ratio, and the combustion rate, specifically the amount of unburned ash can be controlled to a predetermined value. it can. That is, in coal with a high fuel ratio, the amount of oxygen-containing organic compound added is increased compared to coal with a low fuel ratio. The optimum amount of oxygen-containing organic compound added is that the amount of unburned ash in the ash varies not only with the fuel ratio but also with the air ratio or the structure of the combustion device. Set for each device.
[0034]
(Means for solving the second problem)
Next, means for reducing NOx, which is the second problem of the present invention, will be described. In combustion means using other fuels that do not contain N in the fuel, NOx generation is basically called thermal NOx, which is mainly caused by oxidation at a high temperature of N in air. It is. Compared to this, combustion means using coal as fuel contributes to the generation of NOx by decomposition of N contained in the fuel, and the amount of NOx discharged increases. For this reason, in the combustion means using coal as a fuel, a special device is required for reducing NOx in the exhaust gas.
[0035]
The main combustion means using coal as fuel are coke production facilities, iron-related facilities such as blast furnaces, and power generation facilities including coal gasification. Among them, iron-related facilities basically have low potential for NOx emissions because coal combustion proceeds under reducing conditions. Coal is gasified to produce synthesis gas (CO and H ₂ In this method, the combustion of coal basically proceeds under reducing conditions, and therefore the potential for NOx emission is small.
[0036]
On the other hand, complete combustion is indispensable in the power generation facility for burning coal, and the potential for NOx generation is great because air is supplied excessively to the coal and burned. As a method for burning coal, a coal boiler device that supplies finely pulverized coal to a combustion device by airflow conveyance is the mainstream as a method for supplying solid coal.
[0037]
In the pulverized coal boiler, a method of reducing the concentration of NOx in the exhaust gas discharged by the denitration method in the flame is adopted. Taking FIG. 3 as an example, an outline of the flame denitration method will be described. The combustion air in FIG. 3 is divided into three stages and supplied to the burner. The first stage is supplied with the pulverized coal from the central portion along the central axis of the burner through the pulverized coal pipe 76 as the conveying air 71 for air-conveying the coal. The amount is set smaller than the theoretical air amount of coal. The remaining air is supplied as a secondary air 72 and a tertiary air 73 by swirling around the flame periphery through a swirl flow generator 75.
[0038]
The coal blown into the furnace 77 is heated by receiving radiation from the flame, and the particle temperature rises while releasing volatile components. The released volatiles are oxidized, and the particle temperature rises to ignite the coal particles, forming a flame on the central axis. Since the primary air supplied together with the coal is less than the theoretical air amount, the reducing atmosphere is formed in the flame and a reducing atmosphere 82 is formed. In the reducing atmosphere, unburned components remain in the combustion gas. Since the secondary air and the tertiary air are swirled, mixing with the air carrying the coal (primary air) is suppressed, so that the disappearance of the reducing atmosphere generated in the flame is suppressed.
[0039]
Since oxygen is insufficient in the reducing atmosphere 82, HCN, O, etc. having reducing power are generated. At the same time, NOx produced by thermal decomposition of nitrogen compounds and oxidation of nitrogen in the air is converted into nitrogen (N ₂ ). Thereby, the amount of NOx generated in the furnace 77 is reduced.
[0040]
An oxidizing atmosphere 83 is formed on the outer periphery of the reducing atmosphere to which the secondary air and the tertiary air are supplied. Unburned gas in the gas that has passed through the reducing atmosphere is completely oxidized by the secondary air and the tertiary air in this region and burned. The reaction is complete. If necessary, supply after-air.
[0041]
On the other hand, for removal of NOx contained in combustion exhaust gas and discharged from the furnace, methods such as a catalytic cracking method, a wet absorption method, an adsorption method, and a catalytic reduction method are used. The catalytic cracking method uses a catalyst to convert NOx to N ₂ However, the catalytic activity is insufficient and it has not been put into practical use. In the wet absorption method and the adsorption method, NOx is absorbed in an absorbing solution such as alkali or adsorbed on activated carbon or the like to be removed from the exhaust gas, or a large cost is required for regeneration or treatment of the absorbing solution and the adsorbent. It takes.
[0042]
The catalytic reduction method includes a non-selective catalytic reduction method (NSCR method: Non-Selective Catalytic Reduction) and a selective catalytic reduction method (SCR method: Selective Catalytic Reduction method) depending on the difference in NOx reduction ability depending on the presence or absence of coexistence in exhaust gas. ). In the non-selective catalytic reduction method, hydrogen, carbon monoxide, or hydrocarbons are used as a reducing agent. However, since reduction of NOx is inhibited when oxygen coexists, it has not been widely used.
[0043]
On the other hand, the selective catalytic reduction method uses ammonia as a reducing agent and is widely spread because it does not inhibit the reduction of NOx even in the presence of oxygen, and has established itself as a standard exhaust gas denitration method. Yes. As the catalyst, titanium dioxide (TiO ₂ ) Is used as a carrier and, for example, a carrier carrying an oxide such as molybdenum, vanadium, or tungsten is used.
[0044]
On the other hand, development of a selective catalytic reduction method using unburned components in exhaust gas as a reducing agent is also underway. For example, NOx can be reduced by hydrocarbons in the presence of oxygen using a zeolite-based catalyst. Among hydrocarbon-based reducing agents, oxygen-containing organic compounds are more active than olefins or paraffins in reducing NOx in the presence of oxygen.
[0045]
The inventors focused on the specificity of the oxygenated organic compound in the selective catalytic reduction method, investigated in detail the behavior of the oxygenated organic compound in the combustion process, found a specific reaction with NO, and led to the present invention. It was. Two experimental results leading to the invention are shown in detail below.
[0046]
In the first experimental example, the influence of the oxygen-containing organic compound on the NOx emission behavior is evaluated by the small test apparatus shown in FIG. The configuration of this test apparatus has already been described.
[0047]
Among the coals shown in Table 1 above, two types of bituminous coals, Coal A and Coal B, were pulverized to 100 μm or less and supplied to the tubular reactor through the burner at a constant rate of 240 g / h by the coal feeder 103. Fuel air 102 was supplied at a constant rate of 960 liters / h and dimethyl ether 101 was supplied at a constant rate of 20 liters / h, mixed, and supplied to the tubular reactor in a form of conveying pulverized coal. The temperature in the tubular reactor was adjusted to 1200 ° C.
[0048]
For each coal, the combustion exhaust gas was branched to the gas analyzer 114 at 2 hours after the start of the test and analyzed for gas. ₂ The results of the present invention shown in Table 3 were obtained as the concentrations of
[Table 3]

In the second experimental example, the effect of the oxygen-containing organic compound on the NOx emission behavior was evaluated by the small test apparatus shown in FIG.
[0049]
Among the coals shown in Table 1, two kinds of bituminous coals A and B were pulverized to 100 μm or less and supplied to the tubular reactor 110 through the burner 111 at a constant rate of 240 g / h by the coal feeder 103. Combustion air 102 was supplied at a constant speed of 960 liters / h, and was supplied to the tubular reactor in the form of conveying pulverized coal. The inside of the tubular reactor was adjusted so that the tube wall temperature was 1200 ° C. Unlike the first experimental example, dimethyl ether is not used in the second experimental example.
[0050]
For each coal, the combustion exhaust gas was branched to the gas analyzer 114 at 2 hours after the start of the test and analyzed for gas. ₂ The result of the conventional example shown in Table 3 as the density | concentration of was obtained.
[0051]
According to the results in Table 3, in the present invention, NO and NO are added by adding dimethyl ether. ₂ Can be reduced to approximately 1.7 times and 3 to 2 times that of the conventional example.
[0052]
From the two experimental results shown above, it was found that a method of adding a certain amount of oxygen-containing organic compound to the air flow air line in a coal boiler and burning it with a burner is effective for reducing NOx. . The supply amount of the oxygen-containing organic compound is preferably 5 to 50 wt%, more preferably 10 to 25 wt% with respect to the supply amount of pulverized coal. When the supply amount of the oxygen-containing organic compound is less than 5 wt%, the amount of radicals necessary for NO oxidation as described below cannot be generated. On the contrary, when the amount of the oxygen-containing organic compound added is more than 50 wt%, the discharge concentration of carboxylic acids or aldehydes as unburned components may increase.
[0053]
(4) The hydroperoxy radical (HOO.) Generated by the formula ₂ To oxidize (formula (5)).
[0054]
HOO ・ + NO → HO ・ + NO ₂ (5)
NO and NO collectively called NOx ₂ However, the reactivity of both is very different. Ozone molecules have a higher oxidation potential than oxygen molecules, but NO is converted to oxygen molecules, NO ₂ The analogy holds even if ozone is replaced with ozone molecules. That is, NO compared to NO ₂ Is highly reactive and easily oxidizes other substances to itself N ₂ Reduced to Other substances include unburned fuel, incomplete combustion products such as CO, or alkyl radicals (CH _Three OCH ₂ ・) Etc.
[0055]
If NO was present as NO, the reduction reaction would not proceed without the action of a catalyst or the like. Also O ₂ The higher the oxidation activity, the above-mentioned unburned fuel, incomplete combustion products such as CO, etc., or the alkyl radical (CH) generated by the formula (4) _Three OCH ₂ ・) Etc. O first ₂ React with.
[0056]
Examples of oxygen-containing organic compounds include alcohols such as methanol, ethanol and propanol, ethers such as dimethyl ether, diethyl ether and methyl-t-butyl ether, ketones such as acetone and methyl ethyl ketone, and aldehydes such as formaldehyde, acetaldehyde and propionaldehyde. At least one of carboxylic acids such as formic acid, acetic acid and propionic acid, and esters such as methyl formate and ethyl acetate can be used.
[0057]
When oxygen-containing organic compounds such as alcohol and ether are burned, aldehydes are produced as intermediate products in the oxidation process. As described in JP-A-10-57755 and JP-A-10-212417, in the method of supplying an oxygen-containing organic compound to the flue downstream of the combustion zone, an intermediate product such as aldehyde described above is used. However, there are insufficient removal measures for this.
[0058]
On the other hand, in the method of the present invention, since the oxygenated organic compound is supplied to the burner, the supplied oxygenated organic compound necessarily passes through the combustion zone. By passing through a high temperature range of 1500 to 2000 ° C., aldehydes are converted to CO. ₂ It is completely oxidized and the concentration in the exhaust gas is reduced to the limit.
[0059]
That is, the condensed aromatic compound contained in a large amount in pulverized coal is more stable and less oxidized than an aliphatic compound such as butane and pentane, or a monocyclic aromatic compound such as benzene and toluene. Therefore, it is difficult to ignite bituminous coal or anthracite coal, which contains a large amount of condensed aromatic compounds, and has advanced carbonization. When incombustible coal such as anthracite is burned with a normal coal burner, the time required for ignition is long, combustion is insufficient, combustion efficiency is reduced, and unburned ash content may increase. By supplying oxygen-containing organic compounds to the burner together with finely pulverized coal, hydroperoxy radical (HOO), alkyl radical (CH _Three OCH ₂ ・), Methoxy radical (CH _Three O.) and other radicals are formed. These radicals are highly active and can react with the condensed aromatic compound contained in the pulverized coal. Thereby, the ignition of coal can be promoted.
[0060]
Hydroperoxy radicals (HOO), alkyl radicals (CH _Three OCH ₂ ・), Methoxy radical (CH _Three O.) represents nitrogen monoxide (NO) produced by combustion, nitrogen dioxide (NO) ₂ ). NO ₂ Is more active than NO and is coexisting with hydrocarbons, carbon monoxide, hydrogen, cyanide (HCN), ammonia (NH _Three ) And related compounds or radicals. ₂ Reduced to Thereby, the NOx concentration in the exhaust gas can be reduced.
[0061]
Specific examples of the present invention will be described below.
[0062]
(Example 1)
The outline of the present invention will be described below with reference to FIG.
[0063]
The coarsely pulverized coal 2 is stored in a coal storage hopper 12 and supplied to a coal pulverizer 14 by a rotary valve 13. The supply amount is controlled by the rotational speed of the rotary valve 13. Coal is pulverized to 100 μm or less by a coal pulverizer 14. The finely pulverized coal is conveyed to the coal burner 31 of the coal boiler device 30 by the air 4 from the forced-air ventilation device 61. This amount of carrier air is about 10% of the coal weight.
[0064]
The oxygen-containing organic compound 5 is stored in the storage tank 21 and pushed out by the pump 63. This supply amount is controlled by the flow rate adjustment valve 22. The addition amount of the oxygen-containing organic compound is determined by the method shown in Examples 3, 4 and 5, but is in the range of 5 to 50% in mass ratio with respect to the coal supply amount. The added oxygen-containing organic compound is supplied to the coal burner 31 together with the pulverized coal. As a method for adding the oxygen-containing organic compound, a gas supply method, a liquid spray method, a solid supply method, or the like is employed depending on the form of the oxygen-containing organic compound to be supplied. Details of the method of adding these oxygen-containing organic compounds are shown in Example 2.
[0065]
In the coal burner 31, the coal 2 is brought into contact with the air, the carrier air, and the air 3 from the forced draft device 61 to burn the coal 2. The oxygen-containing organic compound 5 such as dimethyl ether supplied to the coal burner 31 together with the pulverized coal is decomposed as the gas temperature rises according to the ignition and combustion of the pulverized coal, and generates hydroperoxy radicals (HOO).
[0066]
Hydroperoxy radical (HOO) converts nitrogen monoxide (NO) produced by combustion into nitrogen dioxide (NOO). ₂ ). NO ₂ Is more active than NO and is coexisting with hydrocarbons, carbon monoxide, hydrogen, cyanide (HCN), ammonia (NH _Three ) And related compounds or radicals. ₂ Reduced to When dimethyl ether is added as the oxygen-containing organic compound, the generated alkyl radical (CH _Three OCH ₂ ・) NO ₂ Can contribute to the reduction of. When methanol is added as the oxygen-containing organic compound, a methoxy radical (CH _Three O.) is generated and NO ₂ It can act as a reducing agent.
[0067]
Hydroperoxy radical (HOO), alkyl radical (CH _Three OCH ₂ ・), Methoxy radical (CH _Three O.) and other radicals contain an oxygen atom in the radical, and can act as an oxidizing agent by donating the oxygen atom.
[0068]
A condensed aromatic compound contained in a large amount in pulverized coal is more stable and less oxidized than an aliphatic compound such as butane and pentane, or a monocyclic aromatic compound such as benzene and toluene. Accordingly, it is difficult to ignite with bituminous coal or anthracite coal which contains a large amount of condensed aromatic compounds and which has been carbonized.
[0069]
When incombustible coal such as anthracite is burned with an ordinary pulverized coal burner, the time required for ignition is long, combustion is insufficient, combustion efficiency is reduced, and unburned ash content may increase. In order to solve this, an oxygen-containing organic compound can be used.
[0070]
The added oxygen-containing organic compound is easily decomposed into a hydroperoxy radical (HOO) and an alkyl radical (CH _Three OCH ₂ ・), Methoxy radical (CH _Three O.) and other radicals. These radicals are highly active and can react with the condensed aromatic compound contained in the pulverized coal. That is, since the bond of the condensed aromatic compound is cut off and burned by the activity of the radicals, ignition of the pulverized coal can be promoted.
[0071]
The side wall of the coal combustion chamber has a water-cooled wall structure composed of water-cooled tubes, and the coal combustion heat is absorbed by water or steam flowing inside the heat transfer tubes. Heat absorption at the water-cooled wall is mainly due to radiation and cannot absorb all the heat generated during coal combustion. Therefore, a heat transfer tube 33 is installed in the smoke air duct downstream of the coal combustion chamber, and heat generated during coal combustion is further absorbed by water or steam 6 flowing through the heat transfer tube.
[0072]
The exhaust gas emitted from the coal boiler device 30 includes dust, sulfur compounds, and the like. Therefore, dust is removed by the dust collector 51, and sulfur compounds are removed by the desulfurizer. In this example, a wet desulfurization method using limestone (calcium carbonate) slurry is shown. In this system, the limestone slurry 56 is sprayed in the desulfurization tower 53, the exhaust gas and the limestone slurry are brought into contact, the sulfur dioxide is fixed as gypsum (calcium sulfate), and the gypsum is separated and recovered from the limestone slurry by the centrifugal separator 54. It is. When exhaust gas is discharged from the chimney 55 to the atmosphere, the exhaust gas temperature is raised to about 100 ° C. by the gas / gas heat exchanger 52 in order to prevent water vapor from condensing.
[0073]
(Example 2)
Here, a method of supplying the oxygen-containing organic compound 5 to coal carrier air is shown. The amount of air for conveying coal is about 10 to 15% by mass ratio to coal. On the other hand, the supply amount of the oxygen-containing organic substance according to the present invention is a maximum of 25 to 30% by mass ratio with respect to coal. Since the molecular weight of the oxygen-containing organic compound is larger than the molecular weight of air, depending on the type of oxygen-containing organic compound to be added, the volume ratio of the carrier air and the oxygen-containing organic compound is almost the same or slightly more in the carrier air Become more.
[0074]
When the oxygen-containing organic compound is a gas at room temperature, FIG. A It becomes possible to mix by supplying from a branch piping like this. Further, the supply amount of the oxygen-containing organic compound 5 is changed according to the coal properties, the NOx concentration at the outlet, etc. B If it is the method of taking out a supply nozzle in piping like this, it does not disturb the flow of conveyance air, but is more desirable.
[0075]
When the oxygen-containing organic compound 5 is liquid at room temperature, FIG. C ), It can be supplied as gas by the vaporizer 67. However, it is desirable to operate the coal transport nitrogen at 200 ° C. or less for safety. Therefore, this method can be used only for oxygen-containing organic compounds having a gas temperature of 200 ° C. or lower. In the case of an oxygen-containing organic compound having a vaporization temperature of 200 ° C. or higher, FIG. D As shown in FIG. 6, the system can be mixed with the carrier air by using a method in which a nozzle 68 for atomizing and spraying the liquid is installed in the carrier air pipe by pressurizing using the pump 63.
[0076]
When the oxygen-containing organic compound is solid, it can be mixed with coal in a stage where it is supplied to the hopper and pulverized by a mill.
[0077]
(Example 3)
In this example, the method for determining the amount of oxygen-containing organic compound 5 added to the coal carrier air is shown in FIGS. A ).
[0078]
First, FIG. 1 shows a system for adding an oxygen-containing organic compound to coal transportation air. The oxygen-containing organic compound 5 is stored in the oxygen-containing organic compound storage tank 21. The oxygen-containing organic compound 5 is pressurized by the pump 63 and added from the coal conveyance pipe by the method shown in the second embodiment. The amount of oxygen-containing organic compound added is adjusted by a flow rate adjusting valve 22 installed downstream of the pump. The opening degree of the flow rate adjusting valve 22 is controlled by the oxygen-containing organic compound addition flow rate control device 42. In the oxygen-containing organic compound flow rate control device, there is an algorithm for calculating the optimum addition amount of the oxygen-containing organic compound 5 to be added according to the coal properties 43, the boiler operating state 44, and the NOx emission target value 45 shown in the third embodiment. The flow rate adjusting valve 22 of the oxygen-containing organic compound is incorporated so as to obtain this flow rate.
[0079]
Next, an algorithm for obtaining the addition amount of the oxygen-containing organic compound 5 is shown. The properties of coal include industrial analysis results of fixed carbon, volatile matter, moisture and ash, and elemental analysis results of carbon, hydrogen and nitrogen. The fuel ratio defined by the ratio of fixed carbon in coal and the weight of volatile matter can be used as an indicator of coal ignitability. For example, a high fuel ratio means that there is a large amount of fixed carbon relative to the volatile matter, which means that dehydrogenation has progressed and the condensation number of the aromatic ring has increased, and that carbonization has progressed. Becomes difficult.
[0080]
The current general specification pulverized coal boilers are designed with bituminous coal, which has a relatively high volatile content and a fuel ratio of about 0.5 to 2, as standard coal. Therefore, when the fuel ratio of the coal supplied to the boiler is larger than the standard coal used in the design, the oxygen-containing organic compound supply amount is increased. Moreover, the NOx in the current coal boiler apparatus exhaust gas is almost attributable to nitrogen in the coal, and the concentration of NOx contained in the exhaust gas during coal combustion is substantially proportional to the nitrogen content in the coal. Therefore, when the nitrogen content of the coal supplied to the boiler is higher than the standard coal used in the design, the amount of oxygen-containing organic compound is increased.
[0081]
An example embodying the above method is the algorithm of FIG. In this algorithm, the oxygen-containing organic compound addition amount (design oxygen-containing organic compound addition amount) in the design coal is corrected to obtain the basic oxygen-containing organic compound addition amount. For the correction, a function unit is used to calculate the difference between the fuel ratio of the design coal fixed carbon divided by the design coal volatile content and the fuel ratio obtained by dividing the coal fixed carbon currently supplied to the boiler by the volatile content. Input to FX1 and calculate the correction amount 1. Subsequently, the difference between the nitrogen content of the designed coal and the nitrogen content of the coal currently supplied to the boiler and the difference between the set value of the designed coal NOx and the current NOx target value are input to the function unit FX2 and corrected. The quantity 2 is calculated. The correction amount 1 and the correction amount 2 are added to the design oxygen-containing organic compound addition amount to calculate the basic oxygen-containing organic compound addition amount.
[0082]
Example 4
NOx emissions vary depending on operational conditions such as changes in coal properties and boiler load. Therefore, continuous analysis of NOx in the exhaust gas from the boiler outlet is performed, and the supply amount of the required oxygen-containing organic compound is calculated so that this value is below the allowable level of NOx, and control is performed to maintain the optimum supply amount. To do. This embodiment is shown in FIG. 1 and FIG.
[0083]
First, FIG. 1 shows a system to which the oxygen-containing organic compound 5 is added. The oxygen-containing organic compound is stored in the oxygen-containing organic compound storage tank 21. The oxygen-containing organic compound 5 is pressurized by the pump 63 and added from the coal feed by the method shown in the second embodiment. The addition amount of the oxygen-containing organic compound 5 is adjusted by a flow rate adjusting valve 22 installed downstream of the pump. The opening degree of the flow control valve 22 is controlled by a flow control device 42 that adds an oxygen-containing organic compound. The oxygen-containing organic compound flow rate control device 42 is an algorithm that calculates the optimum amount of oxygen-containing organic compound to be added according to the coal properties 43, the boiler operation state 44, and the NOx emission target value 45 shown in the third embodiment. Built-in oxygen-containing organic compound flow rate Adjustment The valve 22 operates to obtain this flow rate. Details of this algorithm are shown in FIG. A ).
[0084]
On the other hand, there are many factors that influence the NOx concentration from the outlet of the coal boiler device. Even when the amount of oxygen-containing organic compound added determined by the algorithm is supplied, the NOx concentration from the outlet of the coal boiler device is the target. There is a deviation from the value. Therefore, when NOx from the outlet of the coal boiler device is continuously measured by the gas analyzer 41 and this value is input to the flow rate control device 42 for the oxygen-containing organic compound, the measured value of NOx is larger than the target value. Then, the flow rate control valve 22 of the oxygen-containing organic compound is opened, and when the measured value of NOx is smaller than the target value, the flow rate control valve is closed.
[0085]
An example of an algorithm embodying this method is shown in FIG. B ). In this algorithm, the basic oxygen-containing organic compound addition amount is corrected, and the corrected oxygen-containing organic compound addition amount is calculated. The correction amount is obtained by the proportional / integral control method so that the difference between the current NOx target value and the current NOx emission amount becomes zero.
[0086]
(Example 5)
In this example, an example in which an oxygen-containing organic compound is produced from natural gas will be described with reference to FIG. The natural gas 201 removes hydrogen sulfide by the desulfurization device 211, pressurizes it, supplies it to the steam reformer 212 together with the steam 202, and reforms it into hydrogen and carbon monoxide. This reaction uses a nickel-based catalyst and proceeds at 900 ° C. and 4 MPa. In order to maintain the inside of the reactor at a high temperature, a part of natural gas or the unreacted gas 208 separated by the distillation apparatus 222 is burned and heated from the outside by this combustion exhaust gas.
[0087]
For this reason, the steam reformer 212 generally has a multi-tube structure in which a plurality of reaction tubes are bundled. In addition to the method using a catalyst, in addition to natural gas and steam, oxygen is supplied to the steam reformer to partially oxidize the natural gas, and this combustion heat maintains the interior of the reaction tube at a high temperature for steam reforming. A method for advancing the reaction has also been put into practical use.
[0088]
The reformed gas mainly composed of hydrogen and carbon monoxide is pressurized by the compressor 231 and supplied to the oxygen-containing organic compound synthesis reactor 221. Examples of the oxygen-containing organic compound include methanol and dimethyl ether. Methanol synthesis is represented by the following formula.
[0089]
2H ₂ + CO → CH _Three OH (6)
A copper-zinc catalyst is used for this reaction, and the reaction proceeds under conditions of 250 to 300 ° C. and 5 to 10 MPa. Dimethyl ether is obtained by dehydration reaction of methanol represented by the following formula.
[0090]
CH _Three OH + CH _Three OH → CH _Three OCH _Three + H ₂ O (7)
For example, a γ-alumina catalyst is used in this reaction, and the reaction proceeds under the same conditions as in methanol synthesis, that is, at 250 to 300 ° C. and 5 to 10 MPa. Conventionally, synthesis of dimethyl ether from carbon monoxide and hydrogen has required two reactors. Currently, a method for realizing the reaction of Formula 1 and the reaction of Formula 2 in one reactor has been developed. It is possible to have a system configuration similar to methanol synthesis.
[0091]
The synthesis of these oxygen-containing organic compounds is an equilibrium reaction, and unreacted hydrogen and carbon monoxide always exist. Therefore, the gas exiting the synthesis reaction apparatus 221 is guided to the distillation apparatus 222, and the oxygen-containing organic compound 207 and the unreacted gas 208 are separated. The unreacted gas 208 is pressurized by the compressor 232 and recycled to the synthesis reactor 221 or used as fuel for heating the steam reformer 212.
[0092]
Example 6
In this embodiment, a method for obtaining an oxygen-containing organic compound from coal and oxygen will be described with reference to FIG.
[0093]
The finely pulverized coal 204 is gasified by reacting with oxygen 206 in a gasification furnace 213. In this case, the composition of the coal gasification gas is about 60% carbon monoxide and about 30% hydrogen by volume. That is, the hydrogen / carbon monoxide molar ratio is 0.5. On the other hand, when an attempt is made to synthesize dimethyl ether in the downstream oxygen-containing organic compound synthesis reactor 221, the hydrogen / carbon monoxide molar ratio suitable for dimethyl ether synthesis is 1, and the composition of coal gas lacks hydrogen. Yes.
[0094]
As a method of supplementing this hydrogen, there is a method of supplying the coal bed gas 205 to the gasification furnace in addition to a method of supplying water vapor and a shift reaction. Coal bed gas is a gas associated with coal, and the main component is methane, which is an organic compound with a high proportion of hydrogen. Therefore, when this process is located in a coal field, it is possible to increase the hydrogen / carbon monoxide ratio in the refined gas by supplying coal bed gas in addition to fuel coal. Since coal bed gas is often discarded without being effectively used, the effect of using coal bed gas is great.
[0095]
Since the coal gas leaving the gasification furnace has a high temperature of about 1300 ° C., heat is recovered as steam 208 by the heat recovery device 214. Among the components constituting the product gas, components that poison the synthesis catalyst for oxygen-containing organic compounds, that is, sulfur compounds such as hydrogen sulfide and ash are removed by the gas purifier 215. The gasification furnace is usually operated at 2 to 3 MPa, but 5 to 10 MPa is suitable for the synthesis of the oxygen-containing fuel, so the purified gas is pressurized by the compressor 231.
[0096]
The purified gas is supplied to the synthesis reactor 221 to synthesize oxygen-containing organic compounds such as methanol and dimethyl ether. This synthesis reaction is an equilibrium reaction, and the gas from the outlet of the synthesis reactor always contains unreacted carbon monoxide and hydrogen. Therefore, the oxygen-containing organic compound synthesized by the distillation apparatus 222 and the unreacted gas are separated. The oxygen-containing organic compound 207 is supplied to the storage tank and stored.
[0097]
In order to improve the yield of the oxygen-containing organic compound, the unreacted gas is pressurized by the recycle compressor 232, returned to the synthesis reactor 221 and reused for oxygen-containing organic compound synthesis. Unreacted gas can be supplied to a gas turbine power generator and used for power generation.
[0098]
(Example 7)
In this embodiment, an application example of the present invention to an electric power / oxygen-containing organic compound co-production plant combining a coal boiler device, a coal gasifier, an oxygen-containing organic compound synthesis reaction device, and a gas turbine power generation device is shown. Oxygenated organic compounds can be sold as fuel for power plants and automobiles.
[0099]
An outline of this power / oxygen-containing organic compound production plant is shown in FIG. The finely pulverized coal 204 is gasified by reacting with oxygen 206 in a gasification furnace 213. At this time, the composition of the coal gasification gas is about 60% carbon monoxide and about 30% hydrogen. Most of the remainder is carbon dioxide, water vapor, nitrogen, and also contains hydrogen sulfide and the like. The temperature of the lower stage of the gasifier is about 1500 ° C., and the coal ash melts into slag. Slag is discharged from the lower part of the gasifier. The gas temperature at the gasifier outlet is about 1300 ° C., and this heat is recovered as steam 208 by the heat recovery unit 214, supplied to the steam turbine system, and used for power generation.
[0100]
Among the components constituting the product gas, components that poison the synthesis catalyst for oxygen-containing organic compounds, that is, sulfur compounds such as hydrogen sulfide and ash are removed by the gas purifier 215. The purified gas is supplied to the synthesis reactor 221 to synthesize an oxygen-containing organic compound 207 such as methanol or dimethyl ether. This synthesis reaction is an equilibrium reaction, and the gas from the outlet of the synthesis reactor always contains unreacted carbon monoxide and hydrogen. Therefore, the oxygen-containing organic compound synthesized by the distillation apparatus 222 and the unreacted gas are separated. The oxygen-containing organic compound is supplied to the storage tank 21 for storage and sale.
[0101]
Unreacted gas is supplied to a gas turbine power generator and used for power generation. Specifically, the air 1 is compressed by the compressor 241, and unreacted gas is combusted by the combustor 242 with this compressed air. The gas turbine 243 is driven by the high-temperature and high-pressure combustion gas, and the generator 244 is rotated to generate power. Since the gas turbine exhaust gas 245 contains oxygen, it can be used as boiler combustion air. Therefore, the combustion exhaust gas is supplied to the coal boiler device 30.
[0102]
Air 4 pressurized by the forced draft device 61 is used for transporting the coal to the coal boiler device. The oxygen-containing organic compound 5 synthesized in the above process is pressurized by a pump 63 and supplied to the transport pipe. The method shown in Example 2 can be applied to the method of adding the oxygen-containing organic compound to the carrier gas.
[0103]
The present embodiment is suitable for repowering in which the power generation output of a power generation device using a coal boiler device is increased by gas turbine power generation. In this embodiment, the oxygen-containing organic compound is co-produced and can be sold. Oxygenated organic compounds are clean fuels, have high added value, and are desirable for plant operation. In addition, a part of the oxygen-containing organic compound can be supplied to the existing coal boiler device, and it is possible to meet demands such as expansion of coal types and reduction of NOx.
[0104]
【The invention's effect】
As described above, according to the present invention, hydroperoxy radicals (HOO.), Alkyl radicals (CH _Three OCH ₂ ・), Methoxy radical (CH _Three O.) and other radicals are formed. These radicals are highly active and can react with the condensed aromatic compound contained in the pulverized coal. Thereby, the ignition to pulverized coal can be promoted. Therefore, anthracite-class coal having a high fuel ratio, which has been difficult to use as fuel in the past, can be used, contributing to a stable energy supply.
[0105]
Hydroperoxy radicals (HOO.) Convert nitric oxide (NO) produced by combustion into nitrogen dioxide (NOO). ₂ ). NO ₂ Is more active than NO and is coexisting with hydrocarbons, carbon monoxide, hydrogen, cyanide (HCN), ammonia (NH _Three ) And related compounds or radicals. ₂ The NOx concentration at the boiler outlet is reduced. Therefore, it is possible to improve the environmental compatibility of the boiler.
[Brief description of the drawings]
FIG. 1 is a system configuration diagram of a coal boiler apparatus shown as an embodiment of the present invention.
FIG. 2 is a schematic configuration diagram of a coal combustion test apparatus shown as an embodiment of the present invention.
FIG. 3 is an explanatory diagram for explaining the principle of NOx reduction in a coal combustion apparatus.
FIG. 4 is a configuration diagram showing an example of a method for supplying an oxygen-containing organic compound in the present invention.
FIG. 5 is a block diagram showing an example of an algorithm for obtaining the oxygen-containing organic compound addition amount of the present invention.
FIG. 6 is a configuration diagram showing an example of a method for producing an oxygen-containing organic compound in the present invention.
FIG. 7 is a configuration diagram showing an example of a method for producing an oxygen-containing organic compound in the present invention.
FIG. 8 is a configuration diagram showing an example in which a coal boiler power generation device and an oxygen-containing fuel synthesis reaction device according to the present invention are combined.
FIG. 9 is a configuration diagram of a coal boiler apparatus shown as an example of a conventional example.
FIG. 10 is a configuration diagram of a coal boiler apparatus shown as an example of a conventional example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Air, 2 ... Coal, 3 ... Coal combustion air, 4 ... Coal conveyance air, 5 ... Oxygen-containing organic compound, 6 ... Water or water vapor, 7 ... Coal boiler apparatus exhaust gas, 8 ... Ammonia, 9 ... Peroxyl starting material, DESCRIPTION OF SYMBOLS 10 ... Gypsum, 12 ... Coal storage hopper, 13 ... Rotary valve, 14 ... Coal grinder, 21 ... Oxygenated organic compound storage tank, 22 ... Oxygenated organic compound flow control valve, 23 ... Oxygenated organic compound addition part, 30 DESCRIPTION OF SYMBOLS ... Coal boiler apparatus, 31 ... Burner, 32 ... Air supply part, 33 ... Heat transfer tube, 34 ... Zone A, 35 ... Zone B, 41 ... Gas analyzer, 42 ... Flow control device, 43 ... Coal property, 44 ... Boiler Operating conditions, 45 ... NOx target value, 57 ... Denitration device, 52 ... Gas heat exchanger, 53 ... Desulfurization tower, 54 ... Centrifugal separator, 55 ... Chimney, 56 ... Limestone slurry, 61-63 ... Ventilation device (fan) Or pump, 64 ... coal transport pipe, 65 ... oxygen-containing organic compound supply pipe, 67 ... vaporizer, 68 ... spray nozzle, 71 ... coal and transport air, 72 ... secondary air, 73 ... tertiary air, 75 ... burner , 82 ... reducing atmosphere, 83 ... oxidizing atmosphere, 101 ... oxygen-containing organic compound cylinder, 102 ... air cylinder, 103 ... coal feeder, 104 ... combustion gas, 110 ... tube reactor, 111 ... burner, 112 ... cooler , 113 ... Dust collector, 114 ... Gas analyzer, 115 ... Exhaust port, 116 ... Electric furnace, 201 ... Natural gas, 202 ... Water vapor, 203 ... Air, 204 ... Coal, 205 ... Coal bed gas, 206 ... Oxygen, 207 DESCRIPTION OF SYMBOLS ... Oxygen-containing organic compound, 208 ... Unreacted gas, 211 ... Desulfurization device, 212 ... Steam reforming device, 213 ... Gasification device, 214 ... Heat recovery device, 215 ... Gas purification device, 221 ... Forming reactor, 222 ... distillation apparatus, 231-232 ... compressor.

Claims (7)

  The pulverized coal obtained by pulverizing coal is conveyed to the burner by air, and further, combustion air is supplied to the burner, and the combustion gas generated by burning the pulverized coal with the air by the burner is brought into contact with the heat transfer tube. In the combustion method of the boiler that heats water or steam passing through the inside of the heat transfer tube and collects heat generated during combustion of the pulverized coal, dimethyl ether is added to the air that conveys the pulverized coal to the burner, and the dimethyl ether A combustion method for a boiler, characterized in that the condensed aromatic compound of the pulverized coal is oxidized by an active intermediate produced by the decomposition of.   The pulverized coal obtained by pulverizing coal is conveyed to the burner by air, and further, combustion air is supplied to the burner, and the combustion gas generated by burning the pulverized coal with the air by the burner is brought into contact with the heat transfer tube. In the combustion method of the boiler that heats water or steam passing through the inside of the heat transfer tube and collects heat generated during combustion of the pulverized coal, dimethyl ether is added to the air that conveys the pulverized coal to the burner, and the dimethyl ether A combustion method for a boiler, characterized in that NO in the pulverized coal is oxidized to NO2 by an active intermediate produced by decomposition of NO.   The pulverized coal obtained by finely pulverizing the coal is conveyed to the burner by air, the combustion air is supplied to the burner, and the combustion gas generated by burning the pulverized coal with the air by the burner is brought into contact with the heat transfer tube. And heating the water or steam passing through the inside of the heat transfer tube, and recovering heat generated during combustion of the pulverized coal, in the boiler combustion method, the pulverized coal is supplied to the burner according to the fuel ratio of the pulverized coal. A combustion method for a boiler, characterized in that the amount of dimethyl ether added to the air to be conveyed is controlled.   Pulverized coal pulverized coal is supplied to the burner by air, the combustion gas generated by burning the pulverized coal by air from the burner is brought into contact with the heat transfer tube, and water or steam passing through the heat transfer tube is heated. In the boiler combustion method for recovering heat generated during combustion of the pulverized coal, the NOx concentration in the exhaust gas from the boiler is measured and conveyed to the burner during the combustion of the pulverized coal according to the NOx concentration. A combustion method for a boiler, characterized in that the amount of dimethyl ether added to the air to be controlled is controlled.   A pulverizer for crushing coal into pulverized coal, a ventilation device for supplying air to a boiler, a coal supply device for supplying the pulverized coal to a burner using a part of the air from the ventilation device, and the pulverized powder In a boiler apparatus having a burner that burns charcoal and the air, and a heat transfer tube that indirectly contacts water or steam with combustion gas generated when the pulverized coal is burned by the burner, added to the air conveyed to the burner A boiler combustion apparatus having a storage facility for storing dimethyl ether and a mixer for mixing the dimethyl ether with coal conveying air.   A pulverizer for crushing coal into pulverized coal, a ventilation device for supplying air to a boiler, a coal supply device for supplying the pulverized coal to a burner using a part of the air from the ventilation device, and the pulverized powder In a boiler apparatus having a burner that burns charcoal and air, and a heat transfer tube that indirectly contacts water or steam with combustion gas generated when the pulverized coal is burned by the burner, the pulverized coal is conveyed to the burner A storage facility for storing dimethyl ether to be added to air, a mixer for mixing the dimethyl ether with coal conveying air, and a control valve for increasing or decreasing the supply amount of the dimethyl ether provided in a pipe from the storage facility to the mixer. And a control device for controlling the control valve according to the properties of the pulverized coal and the operating state of the boiler. A pulverizing device for pulverizing coal into pulverized coal, a ventilation device for supplying air to a boiler, a coal supply device for supplying the pulverized coal to a burner using a part of the air from the ventilation device, and the pulverized powder In a boiler apparatus having a burner that burns charcoal and air, and a heat transfer tube that indirectly contacts water or steam with combustion gas generated when the pulverized coal is burned by the burner, added to the air conveyed to the burner A storage facility for storing dimethyl ether, a mixer for mixing the dimethyl ether with coal conveying air, a control valve for increasing or decreasing the supply amount of the dimethyl ether provided in a pipe from the storage facility to the mixer, and the boiler Provided with a measuring instrument for measuring the NOx concentration in the exhaust gas, the measured value of the NOx concentration, the limit value of the NOx concentration, the properties of the pulverized coal and the boiler Boiler, characterized in that the amount of dimethyl ether to be added to the air for conveying the pulverized coal to the burner calculated in accordance with the operating state and in which the controllable device for controlling the control valve to a predetermined amount Combustion equipment.

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