JP3578327B2

JP3578327B2 - Smoke exhaust treatment method for high sulfur oil fired boiler

Info

Publication number: JP3578327B2
Application number: JP2000051725A
Authority: JP
Inventors: 忠大浦; 貞夫榊原; 誠小椋
Original assignee: 日立プラント建設株式会社
Priority date: 2000-02-28
Filing date: 2000-02-28
Publication date: 2004-10-20
Anticipated expiration: 2020-02-28
Also published as: JP2001232147A

Description

【０００１】
【発明の属する技術分野】
本発明は、高イオウ油焚きボイラの排煙処理方法に係わり、特に、イオウ分の含有率の高い高イオウ燃料（以下「高Ｓ油燃料」と称す）を燃料とする高イオウ油焚きボイラ（以下「高Ｓ油焚きボイラ」と称す）の排煙処理方法に関する。
【０００２】
【従来の技術】
従来、油炊きボイラ用の電気集塵器では、取り扱う排ガス及び排ガス中のダストに含有する水分や三酸化イオウ（ＳＯ_３）のために排ガスの露点が高く、機器腐食や灰詰まりを起こしたり、酸性の強いスマットを生成するという問題があった。さらに、排ガス中のダストが非常に細かく、電気固有抵抗率が低いため、電気集塵器の電極板に捕集したダストが再飛散し易いという問題もあった。
【０００３】
そこで、電気集塵器の入口側にアンモニアガスを注入してＳＯ_３を中和することによって上記問題点の解決を図ってきた。前記アンモニアの注入量は、ボイラでのＳＯ_３の生成量に応じて行われることが好ましいが、ＳＯ_３の生成量を求めるのに必要な排ガス中のＳＯ_３濃度は、連続して測定することができない。そこで、アンモニア注入量は、手動又は試運転時等の排ガス中のＳＯ_３濃度の測定結果に基づき、燃料消費量に比例した比例注入制御を行なっていた。また、ＳＯ_３濃度の変化に対しては、燃料に含まれるイオウ分の大小によって注入比率を設定変更することによって対応していた。そして、アンモニアの注入・停止のタイミングは、燃料バーナの点火に合わせて注入が開始され、燃料バーナの消火に合わせて注入を停止していた。
【０００４】
ところで、最近のボイラ設備では、運転コストの低減のために高Ｓ油燃料、例えばオリノコタールと呼ばれる超重質油を乳化した油（燃料中のイオウ分が通常３％程度）を使用することが多くなってきている。この高Ｓ油燃料を燃料とした高Ｓ油焚きボイラの場合、通常、ボイラの起動時（ボイラ負荷上昇時）、停止時（ボイラ負荷下降時）には、高Ｓ油燃料よりもイオウ分の低い重油燃料（燃料中のイオウ分が通常１％程度）を使用する。そして、この場合にも上記したと同様に、アンモニア注入量は、燃料消費量に比例した比例注入制御を行なうと共に、燃料バーナの消火に合わせて注入を停止していた。
【０００５】
【発明が解決しようとする課題】
しかしながら、高Ｓ油焚きボイラからの排ガスの場合には、排ガス中のＳＯ_３発生濃度の変化は、ボイラ負荷（ボイラ出力）とは必ずしも一致せず不安定になり易い。特に、ボイラの負荷下降時の高Ｓ油燃料から重油燃料への燃料切換時、更に、重油バーナを消火する高Ｓ油焚きボイラの全消火時には、従来の比例注入制御や、燃料バーナの消火に合わせた注入停止タイミングでは、アンモニア注入不足になり酸性イオウが発生し、電気集塵器内での機器腐食や灰詰まりが生じ易いという欠点がある。この結果、電気集塵器を停止せざるを得ないような問題が生じる。これを防ぐには、アンモニアを予め過剰に注入すればよいが、何の目安もなくアンモニアの注入量を増加すれば、アンモニアの注入量が過剰となり、経済的に不利益となるだけでなく、電気集塵器から未反応のアンモニアが多量に排出されて新たな公害原因となる。
【０００６】
本発明はこのような事情に鑑みて成されたもので、高Ｓ油焚きボイラの負荷下降時の高Ｓ油燃料から重油燃料への切り換え時、或いは全消火時における排ガスへのアンモニア注入量を適切に制御できるので、電気集塵器内での機器腐食や灰詰まりが生じにくい高イオウ油焚きボイラの排煙処理方法を提供することを目的とする。
【０００７】
【課題を解決するための手段】
本発明の請求項１は前記目的を達成するために、イオウ分の高い高イオウ油を燃料とする高イオウ油焚きボイラから排出された排ガスにアンモニアを注入してから電気集塵器に送気して前記排ガス中のダストを除去すると共に、前記高イオウ油焚きボイラの負荷下降時には、前記高イオウ油燃料から該高イオウ油燃料よりも低イオウ分の重油燃料に切り換える高イオウ油焚きボイラの排煙処理方法において、イオウ分の高い前記高イオウ油燃料からイオウ分の低い前記重油燃料に切り換えた後も一定時間の間は、前記重油燃料消費量に比例した比例アンモニア注入量に、前記重油燃料のイオウ分に対する前記高イオウ油燃料のイオウ分の比を乗算して求められた乗算アンモニア注入量を前記排ガス中に注入することを特徴とする。
【０００８】
本発明の請求項１は、高イオウ油焚きボイラからの排ガスの場合には、特に、ボイラ負荷下降時にイオウ分の高い高イオウ油からイオウ分の低い重油への燃料切換を行うにもかかわらず、切り換え後も一定時間の間は、電気集塵器に送気される排ガス中のＳＯ_３濃度が重油燃料のみを燃焼させる重油専燃時のＳＯ_３濃度まで下がらないという知見に基づいてなされたもので、適切なアンモニア注入制御を行なえるようにしたものである。
【０００９】
即ち、本発明の請求項１によれば、前記切り換え時から一定時間の間は、重油燃料消費量に比例した比例アンモニア注入量に、重油燃料のイオウ分の比に対する高イオウ油のイオウ分の比（高イオウ油燃料イオウ分／重油燃料イオウ分）を乗算して求められた乗算アンモニア注入量を排ガスに注入するようにしたので、高イオウ油焚きボイラからの排ガスの場合にも排ガスへのアンモニア注入量が不足することがない。これにより、電気集塵器内での機器腐食や灰詰まりが生じにくくできる。
【００１０】
本発明の請求項２は前記目的を達成するために、イオウ分の高い高イオウ油を燃料とする高イオウ油焚きボイラから排出された排ガスにアンモニアを注入してから電気集塵器に送気して前記排ガス中のダストを除去すると共に、前記高イオウ油焚きボイラの負荷下降時には、前記高イオウ油燃料から該高イオウ油燃料よりも低イオウ分の重油燃料に切り換える高イオウ油焚きボイラの排煙処理方法において、前記排ガスを送気する通風系を稼働したままで前記重油燃料用の重油バーナを消火する前記高イオウ油焚きボイラの全消火時には、前記重油バーナを消火した後も一定時間の間は、前記重油バーナを消火した時点における重油燃料消費量に対応するアンモニア注入量を前記排ガス中に定量注入し続けることを特徴とする。
【００１１】
本発明の請求項２は、排ガスを送気する通風系を稼働したままで、前記重油燃料用の重油バーナを消火する前記高イオウ油焚きボイラの全消火時には、前記重油バーナを消火した後も一定時間の間は、電気集塵器に送気される排ガス中のＳＯ_３濃度がゼロにならないという知見に基づいてなされたもので、適切なアンモニア注入制御を行なえるようにしたものである。
【００１２】
即ち、本発明の請求項２によれば、高イオウ油焚きボイラの全消火時には、重油バーナを消火した後も一定時間の間は、アンモニアを排ガス中に定量注入し続けるようにしたので、高イオウ油焚きボイラの全消火時の場合にも排ガスへのアンモニア注入量が不足することがない。これにより、電気集塵器内での機器腐食や灰詰まりが生じにくくできる。
【００１３】
【発明の実施の形態】
以下添付図面に従って、本発明に係る高イオウ油焚きボイラの排煙処理方法の好ましい実施の形態について説明する。
【００１４】
図１は、本発明の高イオウ油焚きボイラの排煙処理方法を適用する排煙処理システム１０の概略構成を示す構成図である。
【００１５】
同図に示すように、排煙処理システム１０は主として、高Ｓ油焚きボイラ１２、空気予熱器１４、電気集塵器１６、煙突１８から構成され、高Ｓ油焚きボイラ１２から排出された排ガスが、空気予熱器１４を経た後、電気集塵器１６で脱塵され、煙突１８から大気に放出されるようになっている。
【００１６】
電気集塵器１６の入口側には、アンモニアの注入手段２２が設けられ、この注入手段２２によってガス状のアンモニアが排ガス中に注入される。これにより、排ガスに含まれるＳＯ_３は、アンモニアによって中和されて硫酸アンモニウムを生成し、この硫酸アンモニウムが電気集塵器１６によって捕集される。
【００１７】
注入手段２２から排ガスに注入するアンモニアの注入量は制御装置２６によって制御される。制御装置２６には、高Ｓ油焚きボイラ１２からの信号として、高Ｓ油燃料よりもイオウ分の低い重油の重油燃料消費量信号１００、高Ｓ油燃料消費量信号１０１、重油バーナ開閉信号１０２、高Ｓ油バーナ開閉信号１０３がそれぞれ入力される。そして、制御装置２６は、これらの入力された信号からの情報に基づいて演算したアンモニア注入量を、注入制御信号３６として注入手段２２に出力する。
【００１８】
また、電気集塵器１６の入口側には、温度測定手段２０が配設され、この温度測定手段２０によって電気集塵器１６に供給される排ガスの温度が測定され、排ガス温度信号３３として制御装置２６に入力される。更に、電気集塵器１６の出口側には、アンモニアの残留濃度測定手段２４が設けられ、この残留濃度測定手段２４によって電気集塵器１６から排出された未反応の残留アンモニア濃度が測定される。残留濃度測定手段２４で測定された未反応アンモニア濃度信号３４も、制御装置２６に出力される。
【００１９】
図２は、制御装置２６の制御系統を示した系統図である。
【００２０】
制御系統は、重油制御系統４０と高Ｓ油制御系統４２の２系統から構成される。
【００２１】
各制御系統４０、４２にはそれぞれ、重油専焼時或いは高Ｓ油専焼時に、高Ｓ油焚きボイラ１２からの燃料消費量信号１００、１０１による燃料消費量に対してどの程度のアンモニア注入量を排ガス中に注入すればよいかの演算式ＦＸ_１、ＦＸ_２が設定されている。そして、この演算式に従って乗算演算器のＰ_１１、Ｐ_２１及び加算演算器Ｐ_１２、Ｐ_２２が演算する。また、重油燃料と高Ｓ油燃料との混焼時には、高Ｓ油焚きボイラ１２から重油燃料消費量信号１００と高Ｓ油燃料消費量信号１０１の両方が制御装置２６に出力され、ＦＸ_１とＦＸ_２の各々の演算式によって、重油燃料のアンモニア注入量と高Ｓ油燃料のアンモニア注入量が演算され、得られた２つのアンモニア注入量が加算される。
【００２２】
図３は、ＦＸ_１或いはＦＸ_２の演算式を図で表したもので、重油燃料或いは高Ｓ油燃料におけるそれぞれの燃料消費量に対するアンモニア注入量の注入特性を示したものである。図３に示すように、アンモニア注入量は、乗算演算器Ｐ_１１、Ｐ_２１により調整される比例注入制御と、加算演算器Ｐ_１２、Ｐ_２２により調整されるバイアス注入制御とで構成される。
【００２３】
比例注入制御は、燃料消費量が一定以上、即ち排ガス中のＳＯ_３濃度が高Ｓ油焚きボイラ１２の負荷（ボイラ出力）に比例し易い安定状態での注入制御で、燃料消費量に比例した図３の比例線Ａから得られた比例アンモニア注入量に基づいた注入制御される。
【００２４】
一般にアンモニアとＳＯ_３との反応は、ＳＯ_３＋２ＮＨ_３＋Ｈ_２Ｏ→（ＮＨ_４）_２ＳＯ_４で表される。従って、排ガス中のＳＯ_３の中和するために最低限必要な基本アンモニア注入量は次式（１）で求められ、図３の線Ａの比例注入制御は、この（１）式に基づいて構成したものである。
【００２５】
【数１】
アンモニア注入量（ｋｇ／ｈ）＝〔２モル×ＳＯ_３濃度（ｐｐｍ）〕×排ガス量（ｍ^３Ｎ／ｈｄｒｙ）×〔アンモニア分子量（＝１７）／１モルの標準体積（＝２２．４）〕×１０^−６ …式（１）
式（１）において、排気ガス量は、燃料消費信号１００、１０１から換算してもよく、実際に測定してもよい。
【００２６】
また、図３の線Ａで示された比例注入制御は、排ガス中のＳＯ_３を中和するための最低限必要な比例アンモニア注入量であり、生成されたＳＯ_３を再分解させないための必要過剰アンモニア注入量は、温度測定手段２０によって測定された排ガス温度に基づいて必要過剰アンモニア濃度を求め、図３の線Ａに加算制御される。
【００２７】
また、ＳＯ_３濃度の変化に対しては、燃料に含まれるイオウ分の大小によって注入比率を設定変更できるように、比例線Ａの傾きを図３の矢印（Ｃ、Ｄ）方向に可変できるように構成される。即ち、燃料の含有イオウ分やＳＯ_３発生量が増加すると、比例線Ａの傾きが大きくなる方向（矢印Ｃ方向）に移動し、燃料の含有イオウ分やＳＯ_３発生量が減少すると、比例線Ａの傾きが小さくなる方向（矢印Ｄ方向）に移動する。
【００２８】
一方、バイアス注入制御は、燃料消費量が一定以下（例えば、ボイラ負荷が１／４以下付近に低下した場合）即ち、排ガス中のＳＯ_３発生濃度がボイラ負荷（ボイラ出力）と一致しにくい不安定状態の場合の制御で、図３のバイアス線Ｂに基づいたアンモニア注入量が燃料消費量に関係なく一定量注入される。また、生成されたＳＯ_３を再分解させないための必要過剰アンモニア注入量は、比例注入制御の場合と同様に、排ガス温度に基づいて必要過剰アンモニア濃度を求め、図３の線Ｂに加算制御される。
【００２９】
このバイアス線Ｂのアンモニア注入量としては、高Ｓ油焚きボイラの試運転により不安定状態になる燃料消費量を把握して固定値として設定することもできるが、好ましくは、高Ｓ油焚きボイラの停止において重油バーナの消火時点での重油燃料消費量に対応するアンモニア注入量に設定するとよく、更に好ましくは、重油バーナの消火時点での重油燃料消費量に対応する最低限必要な基本アンモニア注入量（必要過剰アンモニア濃度を加算制御しない）に設定するとよい。これにより、一定負荷以下の不安定状態におけるＳＯ_３発生量の不安定さに対する対処と過剰アンモニアの不足状態が発生するのを防止することができると共に、未反応の残留アンモニアが電気集塵器１６から多量に排出されるのを防止できる。
【００３０】
また、図２に示すように、制御装置２６の重油制御系統４０には、前述した乗算演算器のＰ_１１と加算演算器Ｐ_１２との間に乗算演算器Ｐ_１３が設けられる。この乗算演算器Ｐ_１３には、重油燃料のイオウ分に対する高Ｓ油燃料のイオウ分の比（以下「Ｓ比」と称す）が設定されており、高Ｓ油バーナ開閉信号１０３により「高Ｓ油バーナが全数閉」情報と「一定時間タイマー」情報が乗算演算器Ｐ_１３に入力した時のみ、前記ＦＸ_１の演算式で得られる比例アンモニア注入量に一定時間だけＳ比が乗算される。これにより、重油専焼時の比例アンモニア注入量が一定時間だけ増加する。また、加算演算器Ｐ_１２は、ＦＸ_１の演算式に従った演算とは別に、高Ｓ油焚きボイラ１２の全消火時には、重油消費量信号１００と重油用バーナ開閉信号１０２とからの信号により制御される。即ち、重油消費量信号１００により重油バーナの消火時点の「重油燃料消費量」情報、重油バーナ開閉信号１０２により「重油バーナ全閉」情報と「一定時間タイマー」情報が加算演算器Ｐ_１２に入力されると、図３のバイアス線Ｂに基づくバイアス注入制御が一定時間だけ行なわれる。
【００３１】
そして、上記したそれぞれの条件において制御装置２６で求められたアンモニア注入量は、図２に示す調節計（ＰＩ動作）４４により、注入制御信号３６として信号変換器４６に出力されてエア信号に変換され、注入手段２２の注入弁３１の開度を調整する。これにより、排気ガス中へのアンモニア注入量が制御される。この場合、高Ｓ油焚きボイラ１２の負荷変動等を考慮して、アンモニア注入量が流量計３２により検出され、検出信号３５として制御装置２６に出力され、カスケード制御が可能なように構成されている。
【００３２】
次に、上記の如く構成された排煙処理システム１０を使用した排煙処理方法を図４に従って説明する。
【００３３】
図４は、高Ｓ油焚きボイラの運転パターンとアンモニアの注入パターンを示した図である。
【００３４】
高Ｓ油焚きボイラ１２を起動する場合は、通風系を起動させておいてから重油バーナに点火する。この重油バーナ点火の段階で排ガス中へのアンモニア注入が開始される。次に、高Ｓ油焚きボイラ１２に負荷をかけていく併入段階の一定負荷状態で高Ｓ油バーナに点火し、重油燃料と高Ｓ油燃料との混焼段階を経た後、重油バーナを消火する。この混焼時間は重油燃料から高Ｓ油燃料への燃料切替時間（Ｔ_１）に相当する。そして、高Ｓ油焚きボイラ１２本来の高Ｓ油のみの運転である高Ｓ油専焼状態で負荷を上昇させていき所望の負荷状態で定常運転に入る。
【００３５】
高Ｓ油焚きボイラ１２を停止する場合は、定常運転時の負荷状態から次第に負荷を下降させていき、一定の負荷状態のところで重油用バーナを点火し、高Ｓ油燃料と重油燃料との混焼段階を経た後、高Ｓ油用バーナを消火する。この混焼時間は高Ｓ油燃料から重油燃料への燃料切替時間（Ｔ_２）に相当する。そして、重油のみの重油専焼段階を経てから高Ｓ油焚きボイラ１２と負荷装置（例えば発電機）とを切り離す解列を経て重油バーナを消火する全消火を行なう。最後に通風系を停止する。
【００３６】
図４のアンモニア注入量とボイラ出力との関係から分かるように、起動から定常運転を経て高Ｓ油バーナを消火するまでの間、制御装置２６は、ボイラ負荷、即ち燃料消費量に比例した比例注入制御を行なう。換言すると、高Ｓ油焚きボイラからの燃料消費量信号１００、１０１により、重油専焼、高Ｓ油専焼、混焼に応じて図３の比例線Ａを使用した比例注入制御を行なう。
【００３７】
次に、高Ｓ油焚きボイラ１２の負荷下降時に高Ｓ油燃料から重油燃料に切り替わると、高Ｓ油バーナ開閉信号１０３により「高Ｓ油バーナが全数閉」情報と「一定時間タイマー」情報が乗算演算器Ｐ_１３に入力され、重油制御系統４０の比例注入制御で得られた比例アンモニア注入量に、重油燃料のイオウ分に対する高Ｓ油燃料のイオウ分のＳ比を乗算して求めれた乗算アンモニア注入量が排ガス中に一定時間（Ｔ_３）注入される。一定時間（Ｔ_３）後は、再び、重油制御系統４０の比例注入制御で得られる比例アンモニア注入量が排ガス中に注入される。例えば、重油燃料のイオウ分を１％、高Ｓ油燃料のイオウ分を３％とし、一定時間（Ｔ_３）を１時間とした場合には、比例アンモニア注入量の３倍の乗算アンモニア注入量が排ガス中に１時間注入される。これにより、電気集塵器１６の入口及び出口におけるＳＯ_３発生濃度を抑制することができる。従って、高Ｓ油焚きボイラ１２からの排ガスの場合には、ボイラ負荷下降時にイオウ分の高い高Ｓ油燃料からイオウ分の低い重油への燃料切換を行うにもかかわらず、切換後も一定時間の間は、電気集塵器に送気される排ガス中のＳＯ_３濃度が重油専燃時のＳＯ_３濃度まで下がらないという従来の問題を解決することができる。その結果、電気集塵器１６内での機器腐食や灰詰まりを生じにくくできる。
【００３８】
また、高Ｓ油焚きボイラ１２の全消火時には、重油バーナを消火すると、高Ｓ油焚きボイラ１２からは重油消費量信号１００により重油バーナを消火した時点における「重油燃料消費量」情報と、重油バーナ開閉信号１０２により「重油バーナ全閉」情報と「一定時間タイマー」情報が加算演算器Ｐ_１２に出力される。これにより、制御装置２６は、図３のバイアス線Ｂに基づいたバイアス注入制御を一定時間（Ｔ_４）、例えば１時間程度行なう。これにより、高Ｓ油焚きボイラ１２の全消火後の電気集塵器１６入口におけるＳＯ_３濃度をほぼゼロにすることができる。従って、高Ｓ油焚きボイラ１２の全消火時において、重油バーナを消火したにもかかわらず一定時間の間は、電気集塵器１６に送気される排気ガス中のＳＯ_３濃度がゼロにならないという従来の問題を解決することができる。その結果、電気集塵器１６内での機器腐食や灰詰まりを生じにくくできる。
【００３９】
また、高Ｓ油焚きボイラ１２の負荷下降時に高Ｓ油燃料から重油燃料に切り替わる場合や、全消火時の「一定時間」の長さをどの程度にするかは、高Ｓ油焚きボイラ１２の試運転等により固定時間に設定してもよいが、電気集塵器１６出口のＳＯ_３濃度を測定して測定結果に基づいて制御するとよい。又、「一定時間」を可変的に制御する場合には、電気集塵器１６出口の残留アンモニア濃度を残留濃度測定手段２４で測定し、注入濃度（アンモニア注入量／排ガス流量）より換算ＳＯ_３濃度〔（注入アンモニア濃度−残留アンモニア濃度）／２〕を求め、求めた換算ＳＯ_３濃度に基づいて制御するとよい。
【００４０】
【発明の効果】
以上説明したように、本発明の高イオウ油焚きボイラの排煙処理方法によれば、高Ｓ油焚きボイラの負荷下降時の高Ｓ油燃料から重油燃料への切り換え時、或いは全消火時における排ガスへのアンモニア注入量を適切に制御できるので、電気集塵器内での機器腐食や灰詰まりが生じにくくできる。
【図面の簡単な説明】
【図１】本発明の高イオウ油焚きボイラの排煙処理方法を適用する排煙処理システム
【図２】制御装置の制御系統を説明する説明図
【図３】制御装置により制御されるアンモニア注入量の特性を説明する説明図
【図４】高Ｓ油焚きボイラの運転パターンとアンモニア注入パターンを示した説明図
【符号の説明】
１０…排煙処理システム、１２…高Ｓ油焚きボイラ、１６…電気集塵器、１８…煙突、２０…温度測定手段、２２…注入手段、２４…残留濃度測定手段、２６制御装置、１００…重油燃料消費量信号、１０１…高Ｓ油燃料消費量信号、１０２…重油バーナ開閉信号、１０３…高Ｓ油バーナ開閉信号、４０…重油制御系統、４２…高Ｓ油制御系統、Ｐ_１１、Ｐ_２１…乗算演算器、Ｐ_１２、Ｐ_２２…加算演算器、Ｐ_１３…乗算演算器[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a high-sulfur oil-fired boiler, and more particularly to a high-sulfur oil-fired boiler using a high-sulfur fuel having a high sulfur content (hereinafter referred to as “high-S oil fuel”). Hereinafter, referred to as a “high-S oil-fired boiler”).
[0002]
[Prior art]
2. Description of the Related Art Conventionally, in an electric dust collector for an oil-fired boiler, the dew point of the exhaust gas is high due to the moisture and sulfur trioxide (SO ₃ ) contained in the exhaust gas to be handled and the dust in the exhaust gas, causing corrosion of equipment and ash clogging. There is a problem that a strongly acidic smut is generated. Furthermore, since the dust in the exhaust gas is very fine and has a low electric resistivity, there is a problem that the dust collected on the electrode plate of the electrostatic precipitator is easily scattered again.
[0003]
Therefore, the above problem has been solved by injecting ammonia gas into the inlet side of the electrostatic precipitator to neutralize SO ₃ . The injection amount of ammonia is preferably determined according to the amount of SO ₃ generated in the boiler. However, the concentration of SO ₃ in the exhaust gas required to determine the amount of SO ₃ generated should be continuously measured. Can not. In view of this, the ammonia injection amount is controlled by proportional injection in proportion to the fuel consumption based on the measurement result of the SO ₃ concentration in the exhaust gas during manual operation or test operation. Also, the change in the SO ₃ concentration has been dealt with by changing the setting of the injection ratio depending on the amount of sulfur contained in the fuel. Then, the injection and stop timing of the ammonia was started in accordance with the ignition of the fuel burner, and was stopped in accordance with the extinguishing of the fuel burner.
[0004]
By the way, in recent boiler facilities, in order to reduce the operating cost, a high-S oil fuel, for example, an oil obtained by emulsifying a super heavy oil called orinoco tar (the sulfur content in the fuel is usually about 3%) is often used. It has become to. In the case of a high-S oil-fired boiler using this high-S oil fuel as a fuel, usually, when the boiler is started (when the boiler load rises) and stopped (when the boiler load falls), the sulfur content is higher than that of the high-S oil fuel. Use low fuel oil fuel (sulfur content in fuel is usually about 1%). Also in this case, as described above, the injection amount of ammonia is controlled in proportion to the fuel consumption, and the injection is stopped when the fuel burner is extinguished.
[0005]
[Problems to be solved by the invention]
However, in the case of exhaust gas from a high-S oil-fired boiler, the change in the concentration of SO ₃ generated in the exhaust gas does not always match the boiler load (boiler output) and tends to be unstable. In particular, when switching the fuel from high S oil fuel to heavy oil fuel when the load of the boiler drops, and when completely extinguishing the high S oil fired boiler that extinguishes the heavy oil burner, the conventional proportional injection control and fire extinguishing of the fuel burner At the combined injection stop timing, there is a drawback that ammonia injection is insufficient, acid sulfur is generated, and equipment corrosion and ash clogging easily occur in the electric precipitator. As a result, there arises a problem that the electric precipitator must be stopped. In order to prevent this, it is sufficient to inject ammonia excessively in advance, but if the injection amount of ammonia is increased without any guide, the injection amount of ammonia becomes excessive, not only disadvantageous economically, A large amount of unreacted ammonia is discharged from the electrostatic precipitator, causing new pollution.
[0006]
The present invention has been made in view of the above circumstances, and the amount of ammonia injected into exhaust gas at the time of switching from high S oil fuel to heavy oil fuel when the load of a high S oil fired boiler falls or at the time of complete fire extinguishing. An object of the present invention is to provide a method for treating flue gas of a high-sulfur oil-fired boiler, which can be appropriately controlled and is less likely to cause equipment corrosion and ash clogging in an electrostatic precipitator.
[0007]
[Means for Solving the Problems]
According to a first aspect of the present invention, in order to achieve the above object, ammonia is injected into exhaust gas discharged from a high-sulfur oil-fired boiler using high-sulfur oil having a high sulfur content as fuel, and then supplied to an electric precipitator. A high sulfur oil fired boiler that switches from the high sulfur oil fuel to a heavy oil fuel having a lower sulfur content than the high sulfur oil fuel when the load of the high sulfur oil fired boiler is reduced. In the flue gas treatment method, for a certain period of time even after switching from the high-sulfur oil fuel having a high sulfur content to the heavy oil fuel having a low sulfur content, the fuel oil is added to the proportional ammonia injection amount in proportion to the fuel oil consumption. A multiplied ammonia injection amount obtained by multiplying a ratio of the sulfur content of the high sulfur oil fuel to the sulfur content of the fuel is injected into the exhaust gas.
[0008]
In the case of exhaust gas from a high-sulfur oil-fired boiler, the first aspect of the present invention is particularly advantageous in that fuel is switched from high-sulfur high-sulfur oil to low-sulfur heavy oil when the boiler load drops. during a predetermined time after switching is, SO ₃ concentration in the exhaust gas to be air in the electrostatic precipitator is made based on the finding that not reduced to SO ₃ concentration at the time of heavy oil専燃to burn only heavy fuel oil Thus, appropriate ammonia injection control can be performed.
[0009]
That is, according to the first aspect of the present invention, during a certain period of time from the time of the switching, the proportional ammonia injection amount proportional to the heavy oil fuel consumption is added to the sulfur content of the high sulfur oil with respect to the sulfur content ratio of the heavy oil fuel. The multiplied ammonia injection amount obtained by multiplying the ratio (high sulfur oil fuel sulfur content / heavy oil fuel sulfur content) is injected into the exhaust gas, so that even in the case of exhaust gas from a high sulfur oil fired boiler, There is no shortage of ammonia injection. As a result, corrosion of equipment and ash clogging in the electric precipitator can be suppressed.
[0010]
According to a second aspect of the present invention, in order to achieve the above object, ammonia is injected into exhaust gas discharged from a high-sulfur oil-fired boiler using high-sulfur oil having a high sulfur content as fuel, and then supplied to an electrostatic precipitator. A high sulfur oil fired boiler that switches from the high sulfur oil fuel to a heavy oil fuel having a lower sulfur content than the high sulfur oil fuel when the load of the high sulfur oil fired boiler is reduced. In the flue gas treatment method, when extinguishing the heavy oil burner for the heavy oil fuel while operating the ventilation system for feeding the exhaust gas, when the fire of the high sulfur oil fired boiler is completely extinguished, a fixed time after the heavy oil burner is extinguished. During this period, the ammonia injection amount corresponding to the fuel oil consumption at the time when the fuel oil burner is extinguished is continuously injected into the exhaust gas.
[0011]
Claim 2 of the present invention, with the ventilation system for sending exhaust gas in operation, while extinguishing the high-sulfur oil-fired boiler to extinguish the heavy oil burner for the heavy oil fuel, even after extinguishing the heavy oil burner This is based on the knowledge that the SO ₃ concentration in the exhaust gas sent to the electric precipitator does not become zero for a certain period of time, so that appropriate ammonia injection control can be performed.
[0012]
That is, according to the second aspect of the present invention, when the high sulfur oil-fired boiler is completely extinguished, ammonia is continuously injected into the exhaust gas for a certain period of time even after the heavy oil burner is extinguished. Even when the sulfur oil fired boiler is completely extinguished, the amount of ammonia injected into the exhaust gas is not insufficient. As a result, corrosion of equipment and ash clogging in the electric precipitator can be suppressed.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a preferred embodiment of a method for treating smoke from a high-sulfur oil-fired boiler according to the present invention will be described with reference to the accompanying drawings.
[0014]
FIG. 1 is a configuration diagram showing a schematic configuration of a flue gas treatment system 10 to which a method for treating flue gas of a high sulfur oil-fired boiler of the present invention is applied.
[0015]
As shown in FIG. 1, the flue gas treatment system 10 mainly includes a high-S oil-fired boiler 12, an air preheater 14, an electric dust collector 16, and a chimney 18, and the exhaust gas discharged from the high-S oil-fired boiler 12. After passing through the air preheater 14, the dust is removed by the electric precipitator 16 and is discharged from the chimney 18 to the atmosphere.
[0016]
An ammonia injection means 22 is provided on the inlet side of the electrostatic precipitator 16, and gaseous ammonia is injected into the exhaust gas by the injection means 22. As a result, SO ₃ contained in the exhaust gas is neutralized by ammonia to produce ammonium sulfate, and the ammonium sulfate is collected by the electrostatic precipitator 16.
[0017]
The amount of ammonia injected into the exhaust gas from the injection means 22 is controlled by the control device 26. The control device 26 includes, as signals from the high-S oil-fired boiler 12, a heavy-oil fuel consumption signal 100, a high-S oil fuel consumption signal 101, and a heavy-oil burner opening / closing signal 102 of heavy oil whose sulfur content is lower than that of the high-S oil fuel. , A high S oil burner opening / closing signal 103 is input. Then, the control device 26 outputs the ammonia injection amount calculated based on the information from these input signals to the injection means 22 as the injection control signal 36.
[0018]
A temperature measuring means 20 is disposed on the inlet side of the electric precipitator 16, and the temperature of the exhaust gas supplied to the electric precipitator 16 is measured by the temperature measuring means 20, and the temperature is controlled as an exhaust gas temperature signal 33. Input to the device 26. Further, on the outlet side of the electrostatic precipitator 16, a residual ammonia concentration measuring means 24 is provided, and the residual unreacted ammonia concentration discharged from the electric precipitator 16 is measured by the residual concentration measuring means 24. . The unreacted ammonia concentration signal 34 measured by the residual concentration measuring means 24 is also output to the control device 26.
[0019]
FIG. 2 is a system diagram showing a control system of the control device 26.
[0020]
The control system includes two systems, a heavy oil control system 40 and a high S oil control system 42.
[0021]
Each of the control systems 40 and 42 supplies the amount of ammonia injection to the fuel consumption by the fuel consumption signals 100 and 101 from the high S oil-fired boiler 12 when the heavy oil or the high S oil is used. Formulas FX ₁ and FX ₂ are set as to whether the injection should be performed. Then, the multiplication operation units P ₁₁ and P ₂₁ and the addition operation units P ₁₂ and P ₂₂ operate according to this operation expression. In addition, during the co-firing of the heavy oil fuel and the high S oil fuel, both the heavy oil fuel consumption signal 100 and the high S oil fuel consumption signal 101 are output from the high S oil firing boiler 12 to the control device 26, and the FX ₁ and FX ₁ _With the respective arithmetic expressions ₂ , the ammonia injection amount of the heavy oil fuel and the ammonia injection amount of the high S oil fuel are calculated, and the obtained two ammonia injection amounts are added.
[0022]
Figure 3 is a representation of the arithmetic expression of FX ₁ or FX ₂ in FIG shows the injection characteristics of the ammonia injection amount for each fuel consumption in heavy fuel oil or a high S fuels. As shown in FIG. 3, the ammonia injection amount is constituted by proportional injection control adjusted by multiplication operators P ₁₁ and P ₂₁ and bias injection control adjusted by addition operators P ₁₂ and P ₂₂ .
[0023]
The proportional injection control is an injection control in a stable state where the fuel consumption is equal to or more than a certain value, that is, the SO ₃ concentration in the exhaust gas is easily proportional to the load (boiler output) of the high-S oil-fired boiler 12, and is proportional to the fuel consumption. The injection control is performed based on the proportional ammonia injection amount obtained from the proportional line A in FIG.
[0024]
In general, the reaction between ammonia and SO ₃ is represented by SO ₃ + 2NH ₃ + H ₂ O → (NH ₄ ) ₂ SO ₄ . Therefore, the basic ammonia injection amount necessary for neutralizing SO _{3 in} the exhaust gas is obtained by the following equation (1), and the proportional injection control of line A in FIG. 3 is based on this equation (1). It is composed.
[0025]
(Equation 1)
Ammonia injection amount (kg / h) = [2 mol × SO ₃ concentration (ppm)] × exhaust gas amount (m ³ N / h dry) × [ammonia molecular weight (= 17) / 1 standard volume of 1 mol (= 22.4) )] × 10 ⁻⁶ Expression (1)
In the equation (1), the exhaust gas amount may be converted from the fuel consumption signals 100 and 101 or may be actually measured.
[0026]
The proportional injection control shown by the line A in FIG. 3 is a minimum necessary proportional ammonia injection amount for neutralizing SO ₃ in the exhaust gas, and is a necessary amount for preventing the generated SO ₃ from being re-decomposed. The excess ammonia injection amount is determined based on the required excess ammonia concentration based on the exhaust gas temperature measured by the temperature measuring means 20, and is controlled to be added to the line A in FIG.
[0027]
Also, with respect to the change in the SO ₃ concentration, the slope of the proportional line A can be changed in the directions of arrows (C, D) in FIG. 3 so that the injection ratio can be changed according to the amount of sulfur contained in the fuel. Is configured. That is, if the content sulfur and SO ₃ generation amount of the fuel is increased, moves in a direction inclination becomes large proportional line A (arrow C), when the content sulfur and SO ₃ generation amount of the fuel is reduced, the proportional line It moves in the direction in which the inclination of A becomes smaller (direction of arrow D).
[0028]
On the other hand, in the bias injection control, the fuel consumption is not more than a certain value (for example, when the boiler load is reduced to about ４ or less), that is, the SO ₃ generation concentration in the exhaust gas does not easily match the boiler load (boiler output). In the control in the stable state, the ammonia injection amount based on the bias line B in FIG. 3 is injected at a fixed amount regardless of the fuel consumption. Further, the necessary excess ammonia injection amount for preventing the generated SO ₃ from being re-decomposed is determined by calculating the required excess ammonia concentration based on the exhaust gas temperature and adding it to the line B in FIG. 3, as in the case of the proportional injection control. You.
[0029]
The amount of ammonia injected into the bias line B may be set as a fixed value based on the amount of fuel consumption that becomes unstable due to the trial operation of the high-S oil-fired boiler. It is preferable to set the injection amount of ammonia corresponding to the fuel oil consumption at the time of extinguishing of the fuel oil burner at the stop, and more preferably, the minimum required basic ammonia injection amount corresponding to the fuel oil consumption of the fuel oil at the time of extinguishing the fuel oil burner. (The necessary excess ammonia concentration is not controlled to be added.) Thereby, it is possible to cope with the instability of the SO ₃ generation amount in the unstable state under a certain load and to prevent the shortage of excess ammonia from occurring, and to remove the unreacted residual ammonia from the electric precipitator 16. Can be prevented from being discharged in large quantities.
[0030]
Further, as shown in FIG. 2, the fuel oil control system 40 of the control unit 26, the multiplication operation unit P ₁₃ is provided between the P ₁₁ of the multiplication operation unit described above and adders P _12. The multiplication operation unit P _13, sulfur ratio of high S fuels heavy oil fuel to sulfur (hereinafter referred to as "S ratio") is set, "high S by the high S oil burner off signal 103 oil burner only when the total number closed "information and" predetermined time timer "information is input to the multiplication operation unit P _13, S ratio for a certain time in a proportional ammonia injection amount obtained by the arithmetic expression of the FX ₁ is multiplied. Thereby, the proportional ammonia injection amount at the time of heavy oil burning is increased for a certain period of time. Furthermore, adders P _12, apart from the calculation in accordance with the arithmetic expression of the FX _1, at the time of full extinguishing high S oil-fired boiler 12, a signal from the oil consumption amount signal 100 and the heavy oil burner off signal 102. Controlled. That is, "heavy fuel oil consumption amount" of extinguishing time of heavy oil burner by fuel oil consumption signal 100 information, "heavy oil burner fully closed" by the oil burner opening and closing signal 102 information and "predetermined time Timer" information input to the adders P ₁₂ Then, the bias injection control based on the bias line B in FIG. 3 is performed for a fixed time.
[0031]
Then, the ammonia injection amount obtained by the controller 26 under each of the above conditions is output to the signal converter 46 as an injection control signal 36 by the controller (PI operation) 44 shown in FIG. Then, the opening of the injection valve 31 of the injection means 22 is adjusted. This controls the amount of ammonia injected into the exhaust gas. In this case, the ammonia injection amount is detected by the flow meter 32 in consideration of the load fluctuation of the high-S oil-fired boiler 12 and the like, output to the control device 26 as a detection signal 35, and cascade control is possible. I have.
[0032]
Next, a smoke exhaust treatment method using the smoke exhaust treatment system 10 configured as described above will be described with reference to FIG.
[0033]
FIG. 4 is a diagram showing an operation pattern of a high-S oil-fired boiler and an injection pattern of ammonia.
[0034]
When starting the high-S oil-fired boiler 12, the ventilation system is started before the heavy oil burner is ignited. At the stage of heavy oil burner ignition, injection of ammonia into exhaust gas is started. Next, the high-S oil burner is ignited at a constant load state in the entrainment stage in which a load is applied to the high-S oil-fired boiler 12, and after the co-firing stage of the heavy oil fuel and the high S oil fuel, the heavy oil burner is extinguished. I do. This co-firing time corresponds to the fuel switching time (T ₁ ) from heavy oil fuel to high S oil fuel. Then, the load is increased in the high-S oil-only firing state, which is the operation of only the high-S oil, which is the original high-S oil-fired boiler 12, and the steady-state operation is started with the desired load state.
[0035]
When the high-S oil-fired boiler 12 is stopped, the load is gradually lowered from the load state at the time of steady operation, the heavy oil burner is ignited at a constant load state, and the co-firing of the high-S oil fuel and the heavy oil fuel is performed. After the step, extinguish the high S oil burner. This co-firing time corresponds to the fuel switching time (T ₂ ) from high S oil fuel to heavy oil fuel. Then, after a heavy oil only burning stage of heavy oil only, the entire fire extinguishing is performed by extinguishing the heavy oil burner through a parallel disconnection for separating the high S oil-fired boiler 12 and a load device (for example, a generator). Finally, stop the ventilation system.
[0036]
As can be seen from the relationship between the ammonia injection amount and the boiler output in FIG. 4, during the period from start-up to steady-state operation to extinguishing the high-S oil burner, the control device 26 controls the boiler load, that is, the proportionality to the fuel consumption. Perform injection control. In other words, based on the fuel consumption signals 100 and 101 from the high S oil-fired boiler, proportional injection control using the proportional line A in FIG. 3 is performed according to heavy oil combustion, high S oil combustion, and co-firing.
[0037]
Next, when the high-S oil-fired boiler 12 is switched from the high-S oil fuel to the heavy-oil fuel when the load of the high-S oil-fired boiler 12 is lowered, the “high-S oil burner is completely closed” information and the “constant time timer” information are output by the high-S oil burner open / close signal 103. is inputted to the multiplication unit P _13, multiplication proportional ammonia injection amount obtained by the proportional injection control of the fuel oil control system 40 was determined by multiplying the sulfur S ratio of the high S fuels heavy oil fuel to sulfur content Ammonia injection amount is injected into the exhaust gas for a predetermined time (T ₃ ). After a certain time (T ₃ ), the proportional ammonia injection amount obtained by the proportional injection control of the heavy oil control system 40 is injected into the exhaust gas again. For example, when the sulfur content of heavy oil fuel is 1%, the sulfur content of high S oil fuel is 3%, and the fixed time (T ₃ ) is 1 hour, the multiplied ammonia injection amount is three times the proportional ammonia injection amount. Is injected into the exhaust gas for one hour. Thereby, the SO ₃ generation concentration at the inlet and the outlet of the electrostatic precipitator 16 can be suppressed. Therefore, in the case of the exhaust gas from the high-S oil-fired boiler 12, although the fuel is switched from the high-S oil fuel having a high sulfur content to the heavy oil having a low sulfur content when the load of the boiler is lowered, a certain period of time is maintained after the switching. During this period, the conventional problem that the SO ₃ concentration in the exhaust gas sent to the electric precipitator does not decrease to the SO ₃ concentration when fuel oil is exclusively used can be solved. As a result, corrosion of equipment and ash clogging in the electrostatic precipitator 16 can be suppressed.
[0038]
When the heavy oil burner is extinguished when the high-S oil-fired boiler 12 is completely extinguished, the “high-oil fuel consumption” information at the time when the heavy oil burner is extinguished by the heavy-oil consumption signal 100 from the high-S oil-fired boiler 12, "heavy oil burner fully closed" information and "predetermined time timer" information is output to the adders P ₁₂ by burner opening and closing signal 102. Thus, the control device 26 performs the bias injection control based on the bias line B in FIG. 3 for a certain time (T ₄ ), for example, about one hour. As a result, the SO ₃ concentration at the entrance of the electric precipitator 16 after the high-S oil-fired boiler 12 has completely extinguished the fire can be reduced to almost zero. Therefore, when the high-S oil-fired boiler 12 is completely extinguished, the SO ₃ concentration in the exhaust gas sent to the electric precipitator 16 does not become zero for a certain period of time even though the heavy oil burner is extinguished. Can be solved. As a result, corrosion of equipment and ash clogging in the electrostatic precipitator 16 can be suppressed.
[0039]
In addition, when the load of the high-S oil-fired boiler 12 is switched from the high-S oil fuel to the heavy oil fuel when the load is lowered, and the length of the “constant time” when all the fires are extinguished, The fixed time may be set by trial run or the like, but it is preferable to measure the SO ₃ concentration at the outlet of the electrostatic precipitator 16 and control based on the measurement result. When the “constant time” is variably controlled, the residual ammonia concentration at the outlet of the electrostatic precipitator 16 is measured by the residual concentration measuring means 24, and the converted SO ₃ is calculated from the injection concentration (ammonia injection amount / exhaust gas flow rate). The concentration [(injected ammonia concentration−residual ammonia concentration) / 2] may be determined, and control may be performed based on the calculated converted SO ₃ concentration.
[0040]
【The invention's effect】
As described above, according to the smoke emission treatment method for the high sulfur oil-fired boiler of the present invention, when the load is switched from the high S oil fuel to the heavy oil fuel when the load of the high S oil fired boiler is lowered, or when the fire is completely extinguished. Since the amount of ammonia injected into the exhaust gas can be appropriately controlled, device corrosion and ash clogging in the electrostatic precipitator can be suppressed.
[Brief description of the drawings]
FIG. 1 is a flue gas treatment system to which a method for treating flue gas of a high sulfur oil-fired boiler of the present invention is applied. FIG. 2 is an explanatory view illustrating a control system of a control device. FIG. 3 is an ammonia injection controlled by the control device. FIG. 4 is an explanatory diagram illustrating characteristics of the amount. FIG. 4 is an explanatory diagram illustrating an operation pattern and an ammonia injection pattern of a high-S oil-fired boiler.
DESCRIPTION OF SYMBOLS 10 ... Smoke exhaust treatment system, 12 ... High S oil fired boiler, 16 ... Electric precipitator, 18 ... Chimney, 20 ... Temperature measuring means, 22 ... Injecting means, 24 ... Residual concentration measuring means, 26 control device, 100 ... Heavy oil fuel consumption signal, 101 high S oil fuel consumption signal, 102 heavy oil burner open / close signal, 103 high S oil burner open / close signal, 40 heavy oil control system, 42 high S oil control system, P ₁₁ , P _{21 ...} multiplier _{calculator, P 12, P} _{22 ...} adders, P _{13 ...} multiplier calculator

Claims

イオウ分の高い高イオウ油を燃料とする高イオウ油焚きボイラから排出された排ガスにアンモニアを注入してから電気集塵器に送気して前記排ガス中のダストを除去すると共に、前記高イオウ油焚きボイラの負荷下降時には、前記高イオウ油燃料から該高イオウ油燃料よりも低イオウ分の重油燃料に切り換える高イオウ油焚きボイラの排煙処理方法において、
イオウ分の高い前記高イオウ油燃料からイオウ分の低い前記重油燃料に切り換えた後も一定時間の間は、前記重油燃料消費量に比例した比例アンモニア注入量に、前記重油燃料のイオウ分に対する前記高イオウ油燃料のイオウ分の比を乗算して求められた乗算アンモニア注入量を前記排ガス中に注入することを特徴とする高イオウ油焚きボイラの排煙処理方法。Ammonia is injected into exhaust gas discharged from a high-sulfur oil-fired boiler using high-sulfur oil having a high sulfur content as fuel, and then sent to an electrostatic precipitator to remove dust in the exhaust gas and remove the high-sulfur oil. When the load of the oil-fired boiler is lowered, in the method of treating exhaust gas of a high-sulfur oil-fired boiler that switches from the high-sulfur oil fuel to a heavy oil fuel having a lower sulfur than the high-sulfur oil fuel,
After switching from the high sulfur oil fuel having a high sulfur content to the heavy oil fuel having a low sulfur content, for a certain period of time, the proportional ammonia injection amount in proportion to the fuel oil consumption is changed to the sulfur injection amount of the heavy oil fuel. A method for treating flue gas in a high-sulfur oil-fired boiler, wherein a multiplied ammonia injection amount obtained by multiplying a ratio of a sulfur component of a high-sulfur oil fuel is injected into the exhaust gas.

イオウ分の高い高イオウ油を燃料とする高イオウ油焚きボイラから排出された排ガスにアンモニアを注入してから電気集塵器に送気して前記排ガス中のダストを除去すると共に、前記高イオウ油焚きボイラの負荷下降時には、前記高イオウ油燃料から該高イオウ油燃料よりも低イオウ分の重油燃料に切り換える高イオウ油焚きボイラの排煙処理方法において、
前記排ガスを送気する通風系を稼働したままで前記重油燃料用の重油バーナを消火する前記高イオウ油焚きボイラの全消火時には、前記重油バーナを消火した後も一定時間の間は、前記重油バーナを消火した時点における重油燃料消費量に対応するアンモニア注入量を前記排ガス中に定量注入し続けることを特徴とする高イオウ油焚きボイラの排煙処理方法。Ammonia is injected into exhaust gas discharged from a high-sulfur oil-fired boiler using high-sulfur oil having a high sulfur content as fuel, and then sent to an electrostatic precipitator to remove dust in the exhaust gas and remove the high-sulfur oil. When the load of the oil-fired boiler is lowered, in the method of treating exhaust gas of a high-sulfur oil-fired boiler that switches from the high-sulfur oil fuel to a heavy oil fuel having a lower sulfur than the high-sulfur oil fuel,
When the high-sulfur oil-fired boiler extinguishes the heavy oil burner for extinguishing the heavy oil burner while keeping the ventilation system for supplying the exhaust gas running, for a certain period of time after extinguishing the heavy oil burner, the heavy oil A method for treating flue gas in a high-sulfur oil-fired boiler, comprising continuously injecting a fixed amount of ammonia into the exhaust gas corresponding to the amount of fuel oil consumed when the burner is extinguished.