JP2004243228A

JP2004243228A - Flue gas denitrification apparatus with function of injecting and controlling reducing agent, and method for flue gas denitration

Info

Publication number: JP2004243228A
Application number: JP2003036020A
Authority: JP
Inventors: Toshimichi Wada; 敏通和田
Original assignee: Babcock Hitachi KK
Current assignee: Mitsubishi Power Ltd
Priority date: 2003-02-14
Filing date: 2003-02-14
Publication date: 2004-09-02

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flue gas denitrification apparatus having a function of injecting and controlling a reducing agent, and a method for flue gas denitrification by which the injection and distribution state of the reducing agent can be controlled to a more proper state on the basis of the currently operated state of injection and distribution. <P>SOLUTION: In the flue gas denitrification apparatus equipped with a reactor, a reactor entrance duct, a reactor exit duct, and an injection device of the reducing agent, the cross section of the entrance duct is divided into a plurality of sections and each section is provided with an injection controlling means for the reducing agent to control the amount of the reducing agent. The cross section of the exit duct is divided into a plurality of sections corresponding to the sections of the entrance duct and the flow lines of the exhaust gas. The apparatus is also provided with detecting means for NOx concentrations in exit sections of the exit duct, detecting means for the average NOx concentration of respective specified points, and a computing unit to calculate the amount of the reducing agent to be supplied to the each section of the entrance duct to keep the NOx concentration in the each section to the average value. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は還元剤注入調整機能付排煙脱硝装置に関し、特に石炭焚きボイラ排ガスなどのように排ガス中に窒素酸化物（ＮＯｘ）、ダスト、硫黄酸化物などを含むダーティ排ガスの処理に好適な還元剤注入調整機能付排煙脱硝装置および排煙脱硝方法に関する。
【０００２】
【従来の技術】
図７は、排煙脱硝装置が設置されたプラントの一般的な系統図である。
図７において、ボイラ等の排ガス発生源１から排出された排ガスは、反応器入口ダクト４から触媒６を備えた反応器５に導入される。ここで、排ガス中のＮＯｘ濃度に見合った還元剤（ここではＮＨ_３ガスを使用）がＮＨ_３注入管２およびＮＨ_３注入ノズル３を経て反応器入口ダクト４内に注入される。排ガス中のＮＯｘは反応器５内の触媒６の働きにより無害な窒素（Ｎ_２）ガスと水蒸気（Ｈ_２Ｏ）に分解され、反応器出口ダクト７を介して必要に応じて空気予熱器８で熱回収され、さらに必要に応じて脱硫装置９を経て煙突１０より大気に排出される。
前記ＮＨ_３注入ノズル３から注入されるＮＨ_３ガス量は、試運転時に、反応器入口ダクト４内のＮＯｘ濃度分布またはガス流速分布（すなわち触媒層に流入するＮＯｘ量分布）に見合うＮＨ_３注入分布となるように調整される。このＮＨ_３注入分布の調整をより容易に行うため、またはよりＮＯｘ流入量の分布に見合うＮＨ_３量の調整が可能な設備とすべく、各種のＮＨ_３注入装置が提案されている（例えば、特許文献１参照）。
【０００３】
図８には、従来のＮＨ_３注入装置の概略図を示した。この装置では、反応器入口ダクト４内のＮＨ_３注入量分布を、該反応器入口ダクト４内のＮＯｘ流入量分布に応じて、外部に設置されたＮＨ_３調整弁１７、２１の操作により自在に調整できる構造としている。すなわち、図８において、ＮＨ_３配管１５から供給されたＮＨ_３ガスは、希釈空気ファン１３により供給された空気と混合器１６で混合された後、各調整弁１７、２１に送り出される。ＮＨ_３調整弁１７は６つの系統１７−１、１７−２、１７−３、１７−４、１７−５および１７−６に区画され、それぞれオリフィル１８、ＮＨ_３注入管１９および多数の吹出しノズル２０と連設され、またＮＨ_３調整弁２１は２つの系統２１−１および２１−２に区画され、それぞれオリフィス２２、ＮＨ_３注入管２３および多数の吹出しノズル２４で連設され、各吹出しノズル２０、２４からＮＨ_３ガス量が調整されて反応器入口ダクト４内に供給される。
【０００４】
しかしながら、上記従来の装置では、プラントの連続運用において経時的に各ＮＨ_３吹出しノズルから吹き出されるＮＨ_３ガス量が変化したり、ボイラの燃焼状態変化によりＮＯｘ濃度の分布が変化した場合に対応するＮＨ_３注入量の制御は考慮されていなかった。
従って、このように経時的に反応器入口ダクト４内のＮＨ_３分散状態にアンバランスが生じた場合は、反応器入口および出口のＮＯｘ濃度を仮設計器にてトラバース測定し、必要に応じてＮＨ_３調整弁１７、２１を試行錯誤的に開閉操作することによりＮＨ_３の分散調整を行う必要があった。
しかし、プラントの運用条件は長期間一定に保って運転する必要があるのに対して、このＮＨ_３分散調整作業には反応器出入口での排ガス分析、バルブ操作等に人手、費用、時間が必要であるため、プラントの運転を止めてこれらの作業を行うことが容易でなく、やむを得ず、ＮＨ_３の分散状態の悪い状態で継続運用されているのが実態であった。
【０００５】
また、従来技術では、反応器入口ダクトに注入するＮＨ_３の分散調整は、ボイラから排出されるＮＯｘ量分布に基づいて調整されているが、調整されるプラントの条件は、プラント建設直後のＮＨ_３注入装置がクリーンな状態で調整されている。
しかし、その後、ボイラ燃焼調整または燃焼状態が経時変化する等により反応器入口ダクト内のＮＯｘ分布に変化が生じる場合がある。また、ＮＨ_３注入ノズルへの灰付着や注入管内部への錆び等の発生による各注入ノズルの吹き出し特性が経時的に変化するため、経時的にみた場合、必ずしも最適なＮＨ_３注入分布が保持されず、ＮＨ_３注入分布のアンバランスが生じていた。
また、最近は規制緩和の一環として、火力プラントの定期検査から次の定期検査までの期間が長くなってきていることから、上記した経時的なＮＨ_３注入分布のアンバランス傾向がより顕著となり、装置運用上、大きな問題となる場合があった。
【０００６】
【特許文献１】
特許第１２７０５８４号明細書（特開昭５３−６７１６２号公報）
【０００７】
【発明が解決しようとする課題】
本発明の課題は、上記従来技術の問題点を解決し、還元剤の注入分布状態を、実際に運用されている注入分布状態をベースにした、より適切な還元剤の注入分散状態に調整することができる還元剤注入調整機能付排煙脱硝装置および排煙脱硝方法を提供することにある。
【０００８】
【課題を解決するための手段】
本発明者は、上記課題について鋭意検討した結果、▲１▼反応器の入口および出口ダクトの断面に複数に分割した断面を想定し、その出口ダクトの各断面部分にＮＯｘ検出器を設けて各々のＮＯｘ濃度およびその平均ＮＯｘ濃度を検出し、▲２▼上記入口および出口ダクトの断面は、排ガス流れの流線に対応させて分割し、▲３▼かつ分割された入口ダクトの各断面に還元剤注入量調整機能を有するＮＨ_３注入管系統をブロック化して設け、上記検出したＮＯｘ濃度から算出される適切な還元剤量を各ブロック毎に調整して注入することにより、上記課題を達成できることを見出し、本発明に到達した。
すなわち、本願で特許請求される発明は以下の通りである。
【０００９】
（１）還元剤の存在下に排ガス中の窒素酸化物（ＮＯｘ）を除去する反応器と、該反応器に排ガスおよび還元剤を供給する入口ダクトと、該反応器で処理された排ガスを系外に排出する出口ダクトと、前記入口ダクトに還元剤を供給する還元剤注入装置とを備えた排煙脱硝装置において、前記入口ダクトの断面を複数に区画し、該入口ダクトに注入する還元剤量を各区画毎に調整する還元剤注入調整手段を設けるとともに、前記出口ダクトの断面を該入口ダクトの断面の各区画と排ガスの流線に沿って対応するように複数に区画し、該出口ダクトの各区画の代表点の出口ＮＯｘ濃度を検出する手段と、該各代表点のＮＯｘ濃度の平均値を検出する手段と、該検出された各区画のＮＯｘ濃度が該検出されたＮＯｘ濃度平均値となるように前記入口ダクトの各区画に供給する還元剤量を算出する演算器とを設け、該演算器により算出された各区画毎の還元剤量を前記還元剤注入調整手段によりそれぞれ調整して前記入口ダクトに供給するようにしたことを特徴とする還元剤注入調整機能付排煙脱硝装置。
（２）前記還元剤注入調整手段が、開度ロック機能を備えた制御弁であることを特徴とする（１）記載の還元剤注入調整機能付排煙脱硝装置。
【００１０】
（３）脱硝触媒を備えた反応器の入口ダクトに還元剤を注入し、排ガスとともに該反応器に導いて該排ガス中の窒素酸化物（ＮＯｘ）を除去する排煙脱硝方法において、該入口ダクトの断面を複数に区画するとともに、該反応器の出口ダクトの断面を該入口ダクトの断面の各区画と排ガスの流線に沿って対応するように複数に区画し、該出口ダクトの各区画の代表点の出口ＮＯｘ濃度および各代表点のＮＯｘ濃度の平均値を検出し、該検出された各区画のＮＯｘ濃度が該検出された平均値となるように、前記入口ダクトの各区画に供給する還元剤量を自動的または手動操作により調整することを特徴とする排煙脱硝方法。
【００１１】
【発明の実施の形態】
以下、本発明を図面により説明する。
図１は、本発明の一実施例を示すＮＨ_３注入調整機能付排煙脱硝装置の概略説明図である。
図１において、排煙脱硝装置は、ＮＨ_３の存在下に排ガス中のＮＯｘを除去する触媒６を備えた反応器５と、反応器５に排ガスおよびＮＨ_３を供給する反応器入口ダクト４と、反応器５で処理された排ガスを系外に排出する反応器出口ダクト７と、前記反応器入口ダクト４の断面をＡゾーン、Ｂゾーン、Ｃゾーンの３つの入口ゾーンに分割し、各入口ゾーンの入口ＮＯｘ検出点２５（２５−１、２５−２、２５−３）から採取した排ガスのＮＯｘ濃度を検出する入口ＮＯｘ計２９と、各入口ゾーンに注入するＮＨ_３量を後述の演算器３７からの信号に基づいて調整するＮＨ_３制御弁３６（３６−１、３６−２および３６−３）および各入口ゾーンに設置されたＮＨ_３注入管３１（３１−１、３１−２および３１−３）と、反応器出口ダクト７の断面を前記入口ゾーンと排ガスの流線３０（３０−１、３０−２、３０−３）に対応させたＡゾーン、Ｂゾーン、Ｃゾーンの３つのゾーンを想定し、該出口ゾーンの各出口ＮＯｘ検出点３２（３２−１、３２−２、３２−３）から排ガスを採取して各出口ＮＯｘ濃度およびその平均値を検出する出口ＮＯｘ計３５と、各出口ゾーンのＮＯｘ濃度が出口ＮＯｘ濃度の平均値となるように各入口ゾーンに供給するＮＨ_３量をそれぞれ算出する演算器３７とを有する。
【００１２】
ダクト内を複数の区画に分割する方法は、ボイラ（図示せず）の燃焼調整またはアンモニア注入管３１内の錆の発生や注入ノズル部への灰付着等の複合的な要因により経時的にアンモニアの吹出し分布が変化する特性を考慮して行われ、ダクト内断面の分割数（望ましくは３分割以上）や分割形状が決定される。決定された各入口ゾーンの代表的な各位置に入口ＮＯｘ検出点２５−１、２５−２、２５−３が設置される。また前記ＮＨ_３制御弁３６−１、３６−２、３６−３にはそれぞれ開度ロック機能が設けられている。
図２には、図１のＮＨ_３注入部の詳細系統説明図を示した。図２において、図８の従来のＮＨ_３注入装置と異なる点は、６系統に分割されたＮＨ_３調整弁１７の代わりに開度ロック機能を備えた３系統のＮＨ_３制御弁３６−１、３６−２、３６−３を設け、それぞれＡゾーン、ＢゾーンおよびＣゾーンに設置されたＮＨ_３注入管３１−１、３１−２、３１−３を介して各ゾーンに供給するＮＨ_３量の調整を可能にした点である。
上記装置において、まず、反応器入口ダクト４に供給される初期のＮＨ_３の分散調整は、ボイラ排ガスのＮＯｘ流入分布（反応器入口ダクトのＮＯｘ濃度分布）に基づいて行われる。図３は、図１の入口ＮＯｘ濃度の検出系統説明図である。図３において、Ａ、Ｂ、Ｃの各入口ゾーンに設けられた入口ＮＯｘ検出点２５−１、２５−２、２５−３から採取した排ガスをミキサー２７で混合した後、これを入口ＮＯｘ計２９にバルブ２８を介して供給し、排ガスのＮＯｘ濃度が計測され、このＮＯｘ濃度に見合ったＮＨ_３が各入口ゾーンのダクト内に供給されるように各ＮＨ_３制御弁３６−１、３６−２、３６−３の開度が調整され、該開度がロックされて継続した運転が行われる。
【００１３】
装置の継続運転により経時的にＮＨ_３注入分布のアンバランスが崩れ、ＮＯｘ流入分布に対して入口ダクト内に注入されるＮＨ_３注入分布がマッチしない状態となった場合には、下記の操作が行われ、反応器出口ダクト７内の３つの出口ゾーンにおける各出口ＮＯｘ濃度が、出口ＮＯｘ濃度の平均値となるように、対応する各入口ゾーンから注入するＮＨ_３量が算出され、該ＮＨ_３量が各ＮＨ_３注入管３１−１、３１−２、３１−３から供給されるため、経時変化に対して実運用上問題ない、より適切な範囲のＮＨ_３分散調整を行うことが可能となる。
【００１４】
基本的には、反応器入口ダクトに注入するＮＨ_３の分散調整は、反応器出口ＮＯｘ濃度分布がより均一になるように調整される。この理由は仮に反応器出口ＮＯｘ分布にばらつきがある場合、反応器出口ＮＯｘ計の測定値が若干の位置ずれにより大きく影響を受けること、一般的に入口ＮＯｘ濃度のばらつきはその平均濃度に対してばらつき割合が小さいこと等から出口ＮＯｘ濃度を均一に調整することにより、ＮＨ_３注入モル比（ＮＨ_３／ＮＯｘのモル比）も脱硝性能上問題とならない範囲内のばらつきとなるためである。
このように出口ＮＯｘ濃度をより均一になるよう調整すべく、ＮＨ_３注入装置に対して次のような方法でＮＨ_３の分散状態を較正する。
【００１５】
（ｉ）反応器出口ダクトの排ガス中のＮＯｘ濃度の平均値を測定する。
具体的には、切替えバルブ３３−１、３３−２、３３−３を閉にし、切替えバルブ３３−４を開にして各出口ＮＯｘ検出点３２−１、３２−２、３２−３から採取した排ガスをミキサー３４で混合した後、これを出口ＮＯｘ計３５に供給して反応器出口ダクト７の平均ＮＯｘ濃度を測定する。
（ｉｉ）その後、Ａゾーンの出口ＮＯｘの検出点３２−１の排ガスのみを出口ＮＯｘ計３５に供給してＡゾーンの反応器出口ＮＯｘ濃度を測定する。そのためには切替えバルブ３３−１のみを開にし、他のバルブ３３−２、３３−３および３２−４を閉にする。
【００１６】
（ｉｉｉ）（ｉ）で測定された出口ダクトの排ガスのＮＯｘ濃度の平均値（設定値）と、（ｉｉ）で測定されたＡゾーンの出口ＮＯｘ濃度の信号を演算器３７に導き、該Ａゾーンの出口ＮＯｘ濃度が平均値となるために必要なＮＨ_３量が算出され、算出されたＮＨ_３量が反応器入口ダクト４のＡゾーンに注入されるようにＮＨ_３制御弁３６−１の開度を調整し、この状態が維持されるように制御弁３６−１の開度をロックする。
（ｉｖ）同様の操作をＢゾーンおよびＣゾーンについて行い、それぞれのＮＨ_３制御弁３６−２、３６−３の開度を調整し、その状態が維持されるようにこれらの制御弁の開度をロックする。
（ｖ）その後、通常運用でＡゾーン、Ｂゾーン、Ｃゾーンの平均ＮＯｘ濃度（平均値）を用いた運用モードに戻る。
【００１７】
図４は、上記一連の調整を行った前後の出口ＮＯｘ濃度分布を示した。図４から、調整前では、出口ＮＯｘ濃度分布（実線）のばらつきが大きくなっているが、調整後には出口ＮＯｘ濃度分布は破線で示したようになり、ＮＯｘ濃度分布のばらつきが小さくなり、より適切な出口ＮＯｘ濃度分布に調整されたことがわかる。
また、例えば、図５に示すような中央部分の出口ＮＯｘ濃度が高い分布となっている場合には、Ｂゾーンに対してはＢゾーン内の出口ＮＯｘ濃度が平均ＮＯｘ濃度（平均値）となるように調整される。なお、中央部のＮＯｘ濃度分布が低い場合も同様である。
【００１８】
このような調整を行うことにより、調整前の出口ＮＯｘ濃度の局部的に高い箇所または低い個所の出口ＮＯｘ濃度が大幅に改善され、これにより、前記したＮＨ_３分散のばらつき（標準偏差）が大幅に改善されることになる。
図６には、出口ＮＯｘ濃度（または入口ＮＨ_３量）ばらつき（モル比ばらつき）と脱硝性能低下ファクタ（脱硝性能低下割合を触媒量の低下割合で表したもの）の関係図を示したが、ＮＨ_３分散ばらつきがある程度以上となると、急激に脱硝性能低下を生じる。換言すれば、本発明のようにある程度のラフなＮＨ_３分散調整を行うことによって経時的な脱硝性能低下を実質的に問題ない範囲に抑制することができる。
【００１９】
上記の実施例ではＮＨ_３調整弁３６−１、３６−２、３６−３を自動的に調整する方法を採用したが、各ゾーンの出口ＮＯｘ濃度を確認しながら手動によりＮＨ_３調整弁の調整するようにしてもよい。
また、入口ＮＯｘ検出点２５は、必ずしも各区画に対応した数を設置する必要はなく、反応器入口ダクトの排ガス中のＮＯｘ濃度の代表点を検出すればよい。従って、ボイラ出口ＮＯｘ濃度のばらつきが小さいプラントに対しては入口ＮＯｘ検出点は１点であってもよい。
【００２０】
【発明の効果】
本発明の還元剤注入調整機能付排煙脱硝装置および排煙脱硝方法によれば、反応器入口ダクトに注入するアンモニアの分散調整が容易となり、反応器出口ダクトの出口ＮＯｘ濃度分布をより均一にすることが可能となり、これにより、脱硝性能の向上および同一脱硝性能を得るために必要なアンモニア使用量を節減することができる。また反応器出口ダクト内の局部的に高いリークアンモニア濃度を低減することができ、後流機器への影響を軽減できる。さらに局部的に高い出口ＮＯｘ濃度を軽減できることから脱硝装置の運転管理が容易となる。さらにまたアンモニア分散調整が容易となるため、例えば部分負荷または燃料種の変更による反応器に流入するＮＯｘ量に見合った最適なアンモニア分散状態で装置の運用を行うことができる。
【図面の簡単な説明】
【図１】本発明の一実施例を示すＮＨ_３注入調整機能付排煙脱硝装置の概略説明図。
【図２】図１のＮＨ_３注入部の詳細系統説明図。
【図３】図１の入口ＮＯｘ濃度の検出系統説明図。
【図４】ＮＨ_３分布調整前後の出口ＮＯｘ濃度のばらつきを示す図。
【図５】ＮＨ_３分布調整前後の他の出口ＮＯｘ濃度のばらつきを示す図。
【図６】モル比ばらつきと脱硝性能低下ファクタの関係図。
【図７】従来技術の排煙脱硝装置を組込んだプラントの系統図。
【図８】従来技術による流体注入混合装置（ＮＨ_３注入装置）の概略図。
【符号の説明】
１…排ガス発生源、２…ＮＨ_３注入管、３…ＮＨ_３注入ノズル、４…反応器入口ダクト、５…反応器、６…触媒、７…反応器出口ダクト、２５（２５−１、２５−２、２５−３）…入口ＮＯｘ検出点、２９…入口ＮＯｘ計、３０（３０−１、３０−２、３０−３）…排ガス流れ流線、３２（３２−１、３２−２、３２−３）…出口ＮＯｘ検出点、３３（３３−１、３３−２、３３−３、３３−４）…切替えバルブ、３５…出口ＮＯｘ計、３６（３６−１、３６−２、３６−３）…ＮＨ_３制御弁、３７…演算器。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a flue gas denitration apparatus having a reducing agent injection adjusting function, and more particularly to a reduction method suitable for treating dirty exhaust gas containing nitrogen oxides (NOx), dust, sulfur oxide, etc. in the exhaust gas such as a coal-fired boiler exhaust gas. TECHNICAL FIELD The present invention relates to a flue gas denitration apparatus and a flue gas denitration method with an agent injection adjustment function.
[0002]
[Prior art]
FIG. 7 is a general system diagram of a plant in which a flue gas denitration apparatus is installed.
In FIG. 7, exhaust gas discharged from an exhaust gas generation source 1 such as a boiler is introduced from a reactor inlet duct 4 to a reactor 5 having a catalyst 6. Here, a reducing agent (here, NH ₃ gas is used) corresponding to the NOx concentration in the exhaust gas is injected into the reactor inlet duct 4 via the NH ₃ injection pipe 2 and the NH ₃ injection nozzle 3. The NOx in the exhaust gas is decomposed into harmless nitrogen (N ₂ ) gas and water vapor (H ₂ O) by the action of the catalyst 6 in the reactor 5, and is passed through the reactor outlet duct 7 as required, to the air preheater 8. , And is discharged to the atmosphere from a chimney 10 via a desulfurization device 9 as necessary.
NH ₃ amount of gas injected from the NH ₃ injection nozzles 3, at the time of commissioning the reactor NOx concentration distribution or gas flow velocity distribution in the inlet duct 4 (i.e. NOx weight distribution flowing into the catalyst layer) NH ₃ injection distribution commensurate with It is adjusted so that Various NH ₃ injection devices have been proposed in order to more easily adjust the NH ₃ injection distribution, or to provide a facility capable of adjusting the NH ₃ amount in accordance with the distribution of the NOx inflow amount (for example, see, for example, Japanese Patent Application Laid-Open No. H11-157572). Patent Document 1).
[0003]
FIG. 8 shows a schematic diagram of a conventional NH ₃ injection apparatus. In this apparatus, the distribution of the NH ₃ injection amount in the reactor inlet duct 4 can be freely adjusted by operating the NH ₃ regulating valves 17 and 21 installed outside according to the distribution of the NOx inflow amount in the reactor inlet duct 4. Adjustable structure. That is, in FIG. 8, the NH ₃ gas supplied from the NH ₃ pipe 15 is mixed with the air supplied by the dilution air fan 13 in the mixer 16 and then sent out to the respective regulating valves 17 and 21. The NH ₃ regulating valve 17 is divided into six systems 17-1, 17-2, 17-3, 17-4, 17-5, and 17-6, each having an orifice 18, an NH ₃ injection pipe 19, and a number of outlet nozzles. The NH ₃ regulating valve 21 is divided into two systems 21-1 and 21-2, each of which is connected to an orifice 22, an NH ₃ injection pipe 23, and a number of outlet nozzles 24. The NH ₃ gas amount is adjusted from 20 and 24 and supplied into the reactor inlet duct 4.
[0004]
However, the above-described conventional apparatus copes with a case where the amount of NH ₃ gas blown out from each NH ₃ blow nozzle changes over time in a continuous operation of the plant or a change in the NOx concentration distribution due to a change in the combustion state of the boiler. The control of the NH ₃ injection amount to be performed was not considered.
Therefore, when the NH ₃ dispersion state in the reactor inlet duct 4 is imbalanced with time as described above, the NOx concentrations at the reactor inlet and outlet are traversely measured by a temporary design device, and NH 3 _It was necessary to adjust the dispersion of NH ₃ by opening and closing the _three adjusting valves 17 and 21 by trial and error.
However, while it is necessary to operate the plant while keeping the operating conditions constant for a long period of time, this NH ₃ dispersion adjustment work requires manpower, cost, and time for exhaust gas analysis and valve operation at the inlet and outlet of the reactor. Therefore, it is not easy to stop the operation of the plant to perform these operations, and it is unavoidable that the plant is continuously operated in a state where the dispersion state of NH ₃ is poor.
[0005]
Further, in the related art, the dispersion of NH ₃ injected into the reactor inlet duct is adjusted based on the distribution of the amount of NOx discharged from the boiler. _{3. The} injection device is adjusted in a clean state.
However, thereafter, there is a case where the NOx distribution in the reactor inlet duct changes due to boiler combustion adjustment or a change in combustion state over time. In addition, since the blowing characteristics of each injection nozzle change with time due to ash adhered to the NH ₃ injection nozzle or rust inside the injection pipe, an optimum NH ₃ injection distribution is not necessarily maintained when viewed with time. However, there was an imbalance in the NH ₃ injection distribution.
As part of recent deregulation, since the period from the periodic inspection of the thermal power plant to the next periodic inspection is becoming longer, unbalanced trends over time NH ₃ injection distribution mentioned above becomes more remarkable, There was a case where a serious problem occurred in the operation of the device.
[0006]
[Patent Document 1]
Patent No. 1270584 (JP-A-53-67162)
[0007]
[Problems to be solved by the invention]
An object of the present invention is to solve the above-mentioned problems of the prior art and adjust the injection distribution state of the reducing agent to a more appropriate injection dispersion state of the reduction agent based on the injection distribution state actually operated. It is an object of the present invention to provide a flue gas denitration apparatus and a flue gas denitration method with a reducing agent injection adjusting function which can be performed.
[0008]
[Means for Solving the Problems]
As a result of diligent studies on the above problems, the present inventor has assumed that (1) a cross section obtained by dividing the inlet and outlet ducts of the reactor into a plurality of sections, and a NOx detector is provided at each cross section of the outlet duct. (2) The cross section of the inlet and outlet ducts is divided in accordance with the flow line of the exhaust gas flow, and (3) is reduced to each cross section of the divided inlet duct. The above object can be attained by providing an NH ₃ injection pipe system having a function of adjusting the amount of injected agent in a block manner, and adjusting and injecting an appropriate amount of reducing agent calculated from the detected NOx concentration for each block. And arrived at the present invention.
That is, the invention claimed in the present application is as follows.
[0009]
(1) A reactor for removing nitrogen oxides (NOx) in exhaust gas in the presence of a reducing agent, an inlet duct for supplying the exhaust gas and the reducing agent to the reactor, and an exhaust gas treated in the reactor In a flue gas denitration apparatus comprising an outlet duct for discharging to the outside and a reducing agent injection device for supplying a reducing agent to the inlet duct, a reducing agent for dividing the cross section of the inlet duct into a plurality of parts and injecting the inlet duct Providing a reducing agent injection adjusting means for adjusting the amount for each section, dividing the outlet duct into a plurality of sections so as to correspond to each section of the section of the inlet duct along the flow line of the exhaust gas, and Means for detecting the outlet NOx concentration at the representative point of each section of the duct; means for detecting the average value of the NOx concentration at each of the representative points; Value so that An arithmetic unit for calculating an amount of reducing agent supplied to each section of the duct; adjusting the amount of reducing agent for each section calculated by the arithmetic unit by the reducing agent injection adjusting means and supplying the adjusted amount of reducing agent to the inlet duct; A flue gas denitration device with a reducing agent injection adjustment function, characterized in that:
(2) The flue gas denitration apparatus with a reducing agent injection adjusting function according to (1), wherein the reducing agent injection adjusting means is a control valve having an opening lock function.
[0010]
(3) In a flue gas denitration method for injecting a reducing agent into an inlet duct of a reactor equipped with a denitration catalyst and guiding the reducing agent together with the exhaust gas to the reactor to remove nitrogen oxides (NOx) in the exhaust gas, the inlet duct Is sectioned into a plurality of sections, and the section of the outlet duct of the reactor is divided into a plurality of sections so as to correspond to the sections of the section of the inlet duct along the streamlines of the exhaust gas. An average value of the outlet NOx concentration at the representative point and the average value of the NOx concentration at each representative point are detected, and the detected NOx concentration of each section is supplied to each section of the inlet duct so as to become the detected average value. A flue gas denitration method comprising automatically or manually adjusting the amount of a reducing agent.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described with reference to the drawings.
FIG. 1 is a schematic explanatory view of a flue gas denitration apparatus with an NH ₃ injection adjusting function showing one embodiment of the present invention.
In Figure 1, flue gas denitration apparatus, a reactor 5 equipped with a catalyst 6 for removing NOx in the exhaust gas in the presence of NH _3, and the reactor 5 the reactor inlet duct 4 which supplies the exhaust gas and NH ₃ in The reactor outlet duct 7 for discharging the exhaust gas treated in the reactor 5 out of the system, and the cross section of the reactor inlet duct 4 are divided into three inlet zones A zone, B zone and C zone. An inlet NOx meter 29 for detecting the NOx concentration of exhaust gas collected from the inlet NOx detection points 25 (25-1, 25-2, 25-3) of the zone, and an arithmetic unit to be described later which calculates the amount of NH ₃ injected into each inlet zone The NH ₃ control valves 36 (36-1, 36-2 and 36-3) which are adjusted based on the signal from the 37, and the NH ₃ injection pipes 31 (31-1, 31-2 and 31) installed in each inlet zone. -3) and reactor outlet duct 7 are assumed to correspond to the inlet zone and the exhaust gas streamline 30 (30-1, 30-2, 30-3), and three zones A, B, and C are assumed. An outlet NOx meter 35 that collects exhaust gas from each outlet NOx detection point 32 (32-1, 32-2, 32-3) and detects each outlet NOx concentration and its average value, and the outlet NOx concentration in each outlet zone A calculator 37 for calculating the amount of NH ₃ supplied to each of the inlet zones so as to obtain an average value of the NOx concentration.
[0012]
The method of dividing the inside of the duct into a plurality of sections is based on the following factors: combustion adjustment of a boiler (not shown), rust generation in the ammonia injection pipe 31 and ash adhesion to the injection nozzle, and the like. The number of divisions (preferably three or more) and the division shape of the inner cross section of the duct are determined in consideration of the characteristics of the change of the blowout distribution. Inlet NOx detection points 25-1, 25-2, and 25-3 are set at representative positions of each of the determined entrance zones. Also, the respective opening lock function in NH ₃ control valve 36-1,36-2,36-3 are provided.
FIG. 2 shows a detailed system explanatory diagram of the NH ₃ injection section of FIG. In FIG. 2, the difference from the conventional NH ₃ injection device of FIG. 8 is that instead of the NH ₃ adjusting valve 17 divided into six systems, three systems of NH ₃ control valves 36-1 having an opening degree lock function, 36-2 and 36-3 are provided, and the amount of NH ₃ supplied to each zone via NH ₃ injection pipes 31-1, 31-2 and 31-3 installed in the A zone, the B zone and the C zone, respectively. The point is that adjustment is possible.
In the above apparatus, first, the initial dispersion adjustment of NH ₃ supplied to the reactor inlet duct 4 is performed based on the NOx inflow distribution of the boiler exhaust gas (NOx concentration distribution of the reactor inlet duct). FIG. 3 is an explanatory diagram of the detection system of the inlet NOx concentration in FIG. In FIG. 3, exhaust gas collected from inlet NOx detection points 25-1, 25-2, and 25-3 provided in each of the inlet zones A, B, and C is mixed by a mixer 27 and then mixed with an inlet NOx meter 29. supplied via a valve 28, the measured NOx concentration in the exhaust gas, the NH ₃ control valve so that the NH ₃ commensurate with the NOx concentration is fed into the duct of each inlet zone 36-1 and 36-2 , 36-3 are adjusted, the openings are locked, and continuous operation is performed.
[0013]
Over time collapsing unbalance of NH ₃ injection distribution by continuous operation of the device, when the NH ₃ injection distribution injected into the inlet duct against NOx flux distribution in a state that does not match, the following operations is performed, each outlet NOx concentration at the three exit zone in the reactor outlet duct 7, to an average value of the outlet NOx concentration, the amount of NH ₃ to be injected from the corresponding inlet zone is calculated, the NH ₃ Since the amount is supplied from each of the NH ₃ injection pipes 31-1, 31-2 and 31-3, it is possible to perform the NH ₃ dispersion adjustment in a more appropriate range that does not cause a problem in practical operation with respect to aging. Become.
[0014]
Basically, the dispersion of NH ₃ injected into the reactor inlet duct is adjusted so that the reactor outlet NOx concentration distribution becomes more uniform. The reason for this is that if there is a variation in the NOx distribution at the reactor outlet, the measured value of the NOx meter at the reactor outlet is greatly affected by a slight displacement. This is because, by adjusting the outlet NOx concentration to be uniform because the variation ratio is small, the NH ₃ injection molar ratio (the molar ratio of NH ₃ / NOx) is also within a range that does not cause a problem in denitration performance.
In order to adjust the outlet NOx concentration to be more uniform as described above, the dispersion state of NH ₃ is calibrated to the NH ₃ injection device by the following method.
[0015]
(I) The average value of the NOx concentration in the exhaust gas from the reactor outlet duct is measured.
Specifically, the switching valves 33-1, 33-2, and 33-3 were closed, and the switching valve 33-4 was opened to collect from the outlet NOx detection points 32-1, 32-2, and 32-3. After mixing the exhaust gas with a mixer 34, the mixed gas is supplied to an outlet NOx meter 35, and the average NOx concentration in the reactor outlet duct 7 is measured.
(Ii) Thereafter, only the exhaust gas at the detection point 32-1 of the NOx at the outlet of the A zone is supplied to the outlet NOx meter 35, and the NOx concentration at the reactor at the A zone is measured. For this purpose, only the switching valve 33-1 is opened, and the other valves 33-2, 33-3, and 32-4 are closed.
[0016]
(Iii) The average value (set value) of the NOx concentration of the exhaust gas of the outlet duct measured in (i) and the signal of the NOx concentration in the A zone measured in (ii) are guided to the arithmetic unit 37, The amount of NH ₃ required for the outlet NOx concentration of the zone to be an average value is calculated, and the NH ₃ control valve 36-1 is set so that the calculated NH ₃ amount is injected into the A zone of the reactor inlet duct 4. The opening is adjusted, and the opening of the control valve 36-1 is locked so that this state is maintained.
(Iv) The same operation is performed for the B zone and the C zone to adjust the opening degrees of the respective NH ₃ control valves 36-2 and 36-3, and to maintain the state thereof, the opening degrees of these control valves. To lock.
(V) Thereafter, the operation mode returns to the operation mode using the average NOx concentration (average value) of the A zone, the B zone, and the C zone in the normal operation.
[0017]
FIG. 4 shows the outlet NOx concentration distribution before and after the above series of adjustments. From FIG. 4, before the adjustment, the dispersion of the outlet NOx concentration distribution (solid line) is large, but after the adjustment, the outlet NOx concentration distribution becomes as shown by the broken line, and the dispersion of the NOx concentration distribution becomes small. It can be seen that the outlet NOx concentration distribution was adjusted appropriately.
Further, for example, when the outlet NOx concentration in the central portion has a high distribution as shown in FIG. 5, the outlet NOx concentration in the B zone becomes the average NOx concentration (average value) for the B zone. Is adjusted as follows. The same applies to the case where the NOx concentration distribution at the center is low.
[0018]
By performing such an adjustment, the outlet NOx concentration at a locally high or low outlet NOx concentration before the adjustment is greatly improved, whereby the above-described variation (standard deviation) of the NH ₃ dispersion is significantly increased. Will be improved.
Figure 6 is shows the relationship view of the outlet NOx concentration (or inlet NH ₃ amount) variation (mole ratio variation) and denitration performance degradation factor (a denitration performance reduction ratio a representation at a reduced rate of catalytic amount), When the dispersion in NH ₃ dispersion exceeds a certain level, the denitration performance is rapidly lowered. In other words, by performing a certain degree of rough NH ₃ dispersion adjustment as in the present invention, it is possible to suppress a temporal decrease in the denitration performance to a range in which there is substantially no problem.
[0019]
In the above embodiment, the method of automatically adjusting the NH ₃ adjusting valves 36-1, 36-2, and 36-3 is adopted, but the NH ₃ adjusting valve is manually adjusted while checking the outlet NOx concentration of each zone. You may make it.
In addition, the number of inlet NOx detection points 25 does not necessarily need to be set corresponding to each section, and a representative point of NOx concentration in exhaust gas of the reactor inlet duct may be detected. Therefore, for a plant in which the variation in the NOx concentration at the boiler outlet is small, the number of inlet NOx detection points may be one.
[0020]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to the flue gas denitration apparatus with a reducing agent injection adjusting function and the flue gas denitration method of the present invention, the dispersion adjustment of the ammonia injected into the reactor inlet duct becomes easy, and the outlet NOx concentration distribution of the reactor outlet duct is made more uniform. This makes it possible to improve the denitration performance and reduce the amount of ammonia used to obtain the same denitration performance. In addition, locally high leakage ammonia concentration in the reactor outlet duct can be reduced, and the influence on downstream equipment can be reduced. Further, since the locally high outlet NOx concentration can be reduced, the operation management of the denitration device becomes easy. Furthermore, since the ammonia dispersion adjustment is facilitated, the apparatus can be operated in an optimal ammonia dispersion state corresponding to the amount of NOx flowing into the reactor due to, for example, a change in the partial load or fuel type.
[Brief description of the drawings]
FIG. 1 is a schematic explanatory diagram of a flue gas denitration apparatus with an NH ₃ injection adjusting function showing one embodiment of the present invention.
FIG. 2 is a detailed system explanatory diagram of an NH ₃ injection unit in FIG. 1;
FIG. 3 is an explanatory diagram of a detection system of an inlet NOx concentration in FIG. 1;
FIG. 4 is a diagram showing variations in outlet NOx concentration before and after adjusting NH ₃ distribution.
FIG. 5 is a diagram showing variations in other outlet NOx concentrations before and after adjusting NH ₃ distribution.
FIG. 6 is a graph showing a relationship between a molar ratio variation and a denitration performance reduction factor.
FIG. 7 is a system diagram of a plant incorporating a conventional flue gas denitration apparatus.
FIG. 8 is a schematic view of a fluid injection mixing device (NH ₃ injection device) according to the prior art.
[Explanation of symbols]
1 ... an exhaust gas generating source, 2 ... NH ₃ inlet tube, 3 ... NH ₃ injection nozzles, 4 ... reactor inlet duct, 5 ... reactor, 6 ... catalyst, 7 ... reactor outlet duct, 25 (25-1,25 -2, 25-3): Inlet NOx detection point, 29: Inlet NOx meter, 30 (30-1, 30-2, 30-3) ... Exhaust gas flow line, 32 (32-1, 32-2, 32) -3) Exit NOx detection point, 33 (33-1, 33-2, 33-3, 33-4) Switching valve, 35 Exit NOx meter, 36 (36-1, 36-2, 36-3) ) ... NH ₃ control valve 37 ... calculator.

Claims

A reactor for removing nitrogen oxides (NOx) in the exhaust gas in the presence of the reducing agent, an inlet duct for supplying the exhaust gas and the reducing agent to the reactor, and discharging the exhaust gas treated in the reactor to the outside of the system In a flue gas denitration apparatus provided with an outlet duct for supplying a reducing agent to the inlet duct, a cross section of the inlet duct is divided into a plurality of sections, and an amount of the reducing agent to be injected into the inlet duct is set to each of the sections. Along with a reducing agent injection adjusting means for adjusting each section, the section of the outlet duct is divided into a plurality of sections corresponding to each section of the section of the inlet duct and the streamline of exhaust gas, and each section of the outlet duct is provided. Means for detecting the exit NOx concentration at the representative point of the section, means for detecting the average value of the NOx concentration at each representative point, and the detected NOx concentration of each section becomes the detected NOx concentration average value. So that the entrance duck And a calculator for calculating the amount of reducing agent to be supplied to each section. The amount of reducing agent for each section calculated by the calculator is adjusted by the reducing agent injection adjusting means and supplied to the inlet duct. A flue gas denitration apparatus with a reducing agent injection adjustment function, characterized in that:

2. The flue gas denitration apparatus with a reducing agent injection adjusting function according to claim 1, wherein the reducing agent injection adjusting means is a control valve having an opening lock function.

In a flue gas denitration method in which a reducing agent is injected into an inlet duct of a reactor equipped with a denitration catalyst and is introduced to the reactor together with exhaust gas to remove nitrogen oxides (NOx) in the exhaust gas, a cross section of the inlet duct is formed. Along with dividing into a plurality of sections, the section of the outlet duct of the reactor is sectioned into a plurality of sections corresponding to the sections of the section of the inlet duct along the streamline of the exhaust gas, and the representative point of each section of the outlet duct is The average value of the outlet NOx concentration and the NOx concentration of each representative point is detected, and the amount of the reducing agent supplied to each section of the inlet duct so that the detected NOx concentration of each section becomes the detected average value. The flue gas denitration method, wherein the method is adjusted automatically or manually.