JP3693778B2

JP3693778B2 - Method and apparatus for controlling carbonate concentration in slurry

Info

Publication number: JP3693778B2
Application number: JP02919097A
Authority: JP
Inventors: 博文吉川; 浩石坂; 成仁高本; 滋野沢
Original assignee: Babcock Hitachi KK
Current assignee: Mitsubishi Power Ltd
Priority date: 1997-02-13
Filing date: 1997-02-13
Publication date: 2005-09-07
Anticipated expiration: 2017-02-13
Also published as: JPH10216474A

Description

【０００１】
【発明の属する技術分野】
本発明は炭酸塩を含むスラリ中の炭酸塩濃度を制御する方法と装置に関するものである。
【０００２】
【従来の技術】
排煙脱硫装置は、火力発電所で化石燃料を燃焼した際に発生する排煙中の硫黄酸化物、中でも特に二酸化硫黄（ＳＯ₂）を吸収除去する装置である。排煙中の硫黄酸化物を吸収除去する方法にはさまざまな方法があるが、脱硫性能や経済性の点から石灰石−石膏法が主に用いられている。石灰石−石膏法では、石灰石（ＣａＣＯ₃が主成分）を含む吸収液スラリでＳＯ₂を吸収するが、ボイラ負荷や使用燃料の性状の変化に応じてＣａＣＯ₃の供給量を調整し、吸収液スラリ中のＣａＣＯ₃濃度を最適な値（例えば、排ガス量や排ガス中のＳＯ₂濃度が増加すると吸収液スラリ中のＣａＣＯ₃濃度も高める）に制御することにより、経済的かつ高い脱硫性能を維持する必要がある。
【０００３】
吸収液スラリ中のＣａＣＯ₃濃度を制御する方法の１つに、吸収液スラリのｐＨを測定し、所定のｐＨとなるようにＣａＣＯ₃供給量を調整する方法がある。図８に従来技術の吸収液スラリのｐＨを測定し、ＣａＣＯ₃供給量を調整する方法による脱硫装置の一例を示す。脱硫塔は、主に塔本体１、入口ダクト２、出口ダクト３、スプレーノズル４、吸収液ポンプ５、循環タンク６、撹拌機７、空気吹き込み装置８、ミストエリミネータ９、吸収液抜き出し管１０、石膏抜き出し管１１、石灰石供給管１２、脱水機１３及びｐＨ計１４等から構成される。
【０００４】
スプレーノズル４は水平方向に複数個、更に高さ方向に複数段設置されている。また、撹拌機７および空気吹き込み装置８は脱硫塔下部の吸収液が滞留する循環タンク６に設置され、ミストエリミネータ９は吸収塔内最上部あるいは出口ダクト３内に設置される。
【０００５】
ボイラから排出される排ガスＡは、入口ダクト２より脱硫塔本体１に導入され、出口ダクトより排出される。この間、脱硫塔には吸収液抜き出し管１０を通じてポンプ５から送られる吸収液Ｂが複数のスプレーノズル４から噴霧され、吸収液と排ガスＡの気液接触が行われる。このとき吸収液は排ガスＡ中のＳＯ₂を選択的に吸収し、亜硫酸カルシウムを生成する。亜硫酸カルシウムを生成した吸収液は循環タンク６に溜まり、撹拌機７によって撹拌されながら、空気吹き込み装置８から供給される空気Ｃにより吸収液中の亜硫酸カルシウムが酸化されて石膏Ｄを生成する。石灰石Ｅなどの脱硫剤は石灰石供給管１２より循環タンク６内の吸収液に添加されるが、その供給量はｐＨ計１４の測定値により制御される。
【０００６】
すなわち、ｐＨ計の測定値が所定の値より低い場合は石灰石の供給量を増加し、逆に高い場合は石灰石Ｅの供給量を減少させる。石灰石Ｅ及び石膏Ｄが共存するタンク６内の吸収液の一部は、吸収液ポンプ５によって吸収液抜き出し管１０から再びスプレーノズル４に送られ、一部は石膏抜き出し管１１より脱水機１３に送られ、石膏Ｄが回収される。また、スプレーノズル４から噴霧されて微粒化された吸収液の内、液滴径の小さいものは排ガスＡに同伴されるが、脱硫塔上部に設けられたミストエリミネータ９によって回収される。
【０００７】
【発明が解決しようとする課題】
しかし、図８に示した従来技術ではｐＨ計１４の測定値によって石灰石の供給量を調整し、吸収液中のＣａＣＯ₃濃度を制御しているが、次のような問題点がある。すなわち、ｐＨ計１４ではＣａＣＯ₃濃度と相関のあるｐＨを測定するが、ＣａＣＯ₃濃度を直接測定しないので正確なＣａＣＯ₃濃度は把握できない。このため、吸収液スラリ中のＣａＣＯ₃濃度が高くなると脱硫性能も高くなるが、石灰石の消費量が増加し、また回収した石膏中のＣａＣＯ₃濃度が高くなると石膏の品質が低下し、石膏を他の用途に利用できなくなる。
【０００８】
これに対して、吸収液中のＣａＣＯ₃などの炭酸塩濃度を直接測定する方法として、いくつかの方法が提案されている（例えば特公平３−５２８２６号、特開平２−１９５２５３号）。特公平３−５２８２６号及び特開平２−１９５２５３号に開示されている方法では、ＣａＣＯ₃を含む吸収液に酸を添加した後、加熱し、気相中にＣＯ₂を放出させてガス中のＣＯ₂濃度を測定することによりＣａＣＯ₃濃度を算出する方法である。これらの特許出願発明に基づくＣａＣＯ₃濃度測定装置を図８に示した脱硫装置中のｐＨ計１４の代わりに使用することは可能である。これらの方法は連続測定が可能であるが、気相中にＣＯ₂を完全に放出させるのに時間がかかり、結果として測定時間が長くなるという解決すべき課題を残している。
【０００９】
一般に、ＣａＣＯ₃は吸収塔下部の循環タンク６に供給されるが、吸収液スラリの循環タンク６内の滞留時間は２〜６分程度であるのに対して、公知のＣａＣＯ₃濃度連続測定法での測定時間は１０〜２０分程度と長いため、これらの方法を用いて吸収液中のＣａＣＯ₃濃度を測定し、ＣａＣＯ₃供給量を調整して吸収液中のＣａＣＯ₃濃度を所定の値に制御することは実質的に困難である。
このような背景から、本発明者らは短時間に吸収液Ｂ中のＣａＣＯ₃濃度を連続測定する方法を提案した（特願平７−１９３８９１号）。
【００１０】
図９に特願平７−１９３８９１号の発明における一実施例のフローを示す。吸収液Ｂはライン２１からクーラ２２に送られた後、酸化槽２４に送られる。酸化槽２４では、吸収液中の溶存酸素濃度が溶存酸素計２５により測定され、溶存酸素濃度が所定の値以下の場合は過酸化水素水添加ライン２６から過酸化水素水Ｆが添加される。さらに吸収液Ｂはライン２７から酸添加槽２８に送られる。酸添加槽２８では、酸添加ライン２９から塩酸Ｇが添加され、吸収液Ｂはライン３０の途中に設置されたラインミキサー３１により撹拌された後、測定槽３２内に送られ、そこで溶存ＣＯ₂計３３及びｐＨ計３４により、それぞれ溶存ＣＯ₂濃度及びｐＨが測定される。測定が終了した吸収液Ｂはライン３５から排出される。吸収液Ｂに酸Ｇを添加すると吸収液Ｂ中のＣａＣＯ₃と等モルのＣＯ₂が発生し、溶解度以下であればＣＯ₂は水に溶解する。このため、吸収液Ｂ中の溶存ＣＯ₂濃度を測定すれば、酸Ｇを添加する前には同モルのＣａＣＯ₃が存在していたことになり、容易にＣａＣＯ₃濃度を求めることができる。
【００１１】
この方法により排煙脱硫装置で用いる脱硫スラリ（吸収液）中のＣａＣＯ₃濃度を測定した結果、測定時間１〜３分程度でＪＩＳＲ９１０１に定められている方法と測定誤差の範囲内で同じ値が得られた。しかし、吸収液Ｂに酸Ｇを添加して吸収液Ｂ中のＣａＣＯ₃と反応させる時間や溶存ＣＯ₂計３３の応答時間が必要なため、ｐＨ計３４での測定のように数〜数十秒で応答させることはできない。
【００１２】
以上のように、従来技術ではｐＨ計３４は数〜数十秒で応答してＣａＣＯ₃濃度と相関のあるｐＨを測定するが、ＣａＣＯ₃濃度を直接測定しないので、正確なＣａＣＯ₃濃度は把握できなかったり、ＣａＣＯ₃濃度測定装置では吸収液スラリ中のＣａＣＯ₃の測定に長い時間を要し、急なボイラ負荷や使用燃料の性状の変化に対応したＣａＣＯ₃供給量の調整が不可能であった。
【００１３】
本発明の課題は、上記問題点を解決し、排煙中の硫黄酸化物を吸収する吸収液などのスラリ液中の炭酸塩濃度を正確に制御する方法と装置を提案することにある。
【００１４】
【課題を解決するための手段】
本発明の上記課題は次の構成によって解決される。
すなわち、炭酸塩を含むスラリ中のｐＨの測定時からｐＨ測定結果が得られるまでの経過時間（ｐＨ測定時間（Δｔ１））に比べて前記炭酸塩濃度の測定時から炭酸塩濃度の測定結果が得られるまでの経過時間（炭酸塩濃度の測定時間（Δｔ２））が遅れることを考慮して、予め炭酸塩を含むスラリ中のｐＨと該ｐＨ測定時の前記スラリ中の炭酸塩濃度の関係を求めておき、該予め求めたスラリ中のｐＨとｐＨ測定時の炭酸塩濃度の関係から、新たにスラリのｐＨを測定した場合に得られるｐＨ測定値から該スラリ中の炭酸塩濃度を推定値として求め、前記推定した炭酸塩濃度に基づき、スラリのｐＨが求める所定のｐＨとなるように前記予め求めたスラリ中のｐＨとｐＨ測定時の炭酸塩濃度の関係から炭酸塩の供給量を調整することによりスラリ中の炭酸塩濃度を制御するスラリ中の炭酸塩濃度制御方法、または、
【００１５】
炭酸塩を含むスラリ中のｐＨ測定手段と、前記スラリ中の炭酸塩濃度測定手段と、炭酸塩を含むスラリ中のｐＨの測定時からｐＨ測定結果が得られるまでの経過時間（ｐＨ測定時間（Δｔ１））に比べて前記炭酸塩濃度の測定手段による測定時から炭酸塩濃度の測定結果が得られるまでの経過時間（炭酸塩濃度の測定時間（Δｔ２））が遅れることを考慮して、予め炭酸塩を含むスラリ中のｐＨと該ｐＨ測定手段によるｐＨ測定時のスラリ中の炭酸塩濃度の関係を求めておき、該予め求めたスラリ中のｐＨとｐＨ測定時の炭酸塩濃度の関係から、新たにｐＨ測定手段により測定した場合に得られるスラリ中のｐＨ測定値からｐＨ測定時のスラリ中の炭酸塩濃度を推定値として求め、前記推定した炭酸塩濃度に基づき、スラリのｐＨが求める所定のｐＨとなるように前記予め求めたスラリ中のｐＨとｐＨ測定時の炭酸塩濃度の関係から炭酸塩の供給量を演算する演算手段と、該演算手段により算出された炭酸塩を供給する炭酸塩供給手段とを備えたスラリ中の炭酸塩濃度制御装置である。
また、本発明は燃焼排ガスの排煙脱硫に用いる炭酸塩を含む吸収液スラリに適用できる。この場合は、本発明は次の構成からなるものである。
【００１６】
脱硫塔内でボイラを含む燃焼装置からの排ガスと炭酸塩を含む吸収液スラリを接触させて吸収液スラリ中に硫黄酸化物を吸収させた後、吸収液スラリを循環タンクに貯留し、さらにこの循環タンクに貯留した吸収液スラリを脱硫塔に循環供給して排ガスと再度接触させる排煙脱硫方法において、循環タンク内でのスラリの滞留時間及び／又はスラリ単位容積当たりの吸収硫黄酸化物量を考慮して、かつ炭酸塩を含むスラリ中のｐＨの測定時からｐＨ測定結果が得られるまでの経過時間（ｐＨ測定時間（Δｔ１））に比べて前記炭酸塩濃度の測定時から炭酸塩濃度の測定結果が得られるまでの経過時間（炭酸塩濃度の測定時間（Δｔ２））が遅れることを考慮して、予め炭酸塩を含むスラリ中のｐＨと該ｐＨ測定時の前記スラリ中の炭酸塩濃度の関係を求めておき、該予め求めたスラリ中のｐＨと該ｐＨ測定時の炭酸塩濃度との関係から、新たにｐＨを測定した場合に得られるスラリのｐＨ測定値から該スラリ中の炭酸塩濃度を推定値として求め、前記推定した炭酸塩濃度に基づき、スラリのｐＨが求める所定のｐＨとなるように前記予め求めたスラリ中のｐＨとｐＨ測定時の炭酸塩濃度の関係から炭酸塩の供給量を調整することによりスラリ中の炭酸塩濃度を制御するスラリ中の炭酸塩濃度制御方法、または、
【００１７】
ボイラを含む燃焼装置からの排ガスと炭酸塩を含む吸収液スラリを接触させて吸収液スラリ中に硫黄酸化物を吸収させる吸収塔と、排ガス中の硫黄酸化物を吸収した吸収液スラリを貯留する循環タンクと、さらにこの循環タンクに貯留した吸収液スラリを脱硫塔に循環供給するスラリ循環路を備えた排煙脱硫装置において、炭酸塩を含むスラリ中のｐＨ測定手段と、前記スラリ中の炭酸塩濃度測定手段と、循環タンク内での吸収液スラリの滞留時間及び／または吸収液スラリの単位容積当たりの吸収硫黄酸化物量を考慮し、かつ炭酸塩を含むスラリ中のｐＨの測定時からｐＨ測定結果が得られるまでの経過時間（ｐＨ測定時間（Δｔ１））に比べて前記炭酸塩濃度測定手段による測定時から炭酸塩濃度の測定結果が得られるまでの経過時間（炭酸塩濃度の測定時間（Δｔ２））が遅れることを考慮して、予め炭酸塩を含むスラリ中のｐＨと該ｐＨ測定手段によるｐＨ測定時のスラリ中の炭酸塩濃度の関係を求めておき、該予め求めたスラリ中のｐＨとｐＨ測定時の炭酸塩濃度の関係から、新たにｐＨ測定手段により測定した場合に得られるスラリ中のｐＨ測定値からスラリ中の炭酸塩濃度を推定値として求め、前記推定した炭酸塩濃度に基づき、スラリのｐＨが求める所定のｐＨとなるように前記予め求めたスラリ中のｐＨとｐＨ測定時の炭酸塩濃度の関係から炭酸塩の供給量を演算する演算手段と、該演算手段により算出された炭酸塩を供給する炭酸塩供給手段とを備えたスラリ中の炭酸塩濃度制御装置である。
【００１８】
このとき、循環タンク内での吸収液スラリの滞留時間は吸収液循環流量及び循環タンク内の吸収液量から求め、また吸収液スラリ単位容積当たりの吸収硫黄酸化物量は脱硫装置入口ガス及び出口ガス中の硫黄酸化物量濃度、ガス流量及び吸収液循環量から求めることができる。
【００１９】
【作用】
脱硫装置内で吸収液に吸収されたＳＯ₂は下記（１）または（２）式に示す反応により水素イオン（Ｈ⁺）を放出し、吸収液のｐＨを低下させる。循環タンク内でＨ⁺と石灰石の主成分であるＣａＣＯ₃が反応し、下記（３）式に示すようにＨ⁺が消費されることにより吸収液のｐＨが回復する（高くなる）。
【００２０】
Ｈ₂Ｏ＋ＳＯ₂＝Ｈ₂ＳＯ₃＝Ｈ⁺＋ＨＳＯ₃ ^-＝２Ｈ⁺＋ＳＯ₃ ^2- （１）
Ｈ₂Ｏ＋ＳＯ₂＋１／２Ｏ₂＝Ｈ₂ＳＯ₄＝２Ｈ⁺＋ＳＯ₄ ^2- （２）
２Ｈ⁺＋ＣａＣＯ₃＝Ｃａ²⁺＋Ｈ₂Ｏ＋ＣＯ₂ （３）
（３）式の反応でｐＨが回復した吸収液は吸収液ポンプによって再びスプレーノズルに送られ、排ガス中のＳＯ₂を吸収するが、その際の脱硫性能（ＳＯ₂を吸収する量）は吸収液中のＣａＣＯ₃濃度やｐＨに依存する。この吸収液中のＣａＣＯ₃濃度を測定するには、吸収液に酸を添加し、発生したＣＯ₂濃度を溶存ＣＯ₂計で測定する。
【００２１】
ＣａＣＯ₃に塩酸を添加した時の反応を下記（４）式に示す。ＣａＣＯ₃と等モルのＣＯ₂が発生する。ＣＯ₂は水に溶解するので、溶解度以下であれば溶存したＣＯ₂濃度を測定することにより吸収液中のＣａＣＯ₃濃度を求めることができる。
【００２２】
ＣａＣＯ₃＋２ＨＣｌ＝ＣａＣｌ₂＋ＣＯ₂＋Ｈ₂Ｏ（４）
しかし、吸収液中のＣａＣＯ₃濃度が変動した場合、吸収液に酸を添加して（４）式の反応を生じさせ、溶存ＣＯ₂濃度が検出されるには、用いる溶存ＣＯ₂計によっても異なるが１〜５分程度は必要となる。
【００２３】
一方、他の条件が同じであれば吸収液中のＣａＣＯ₃濃度が高くなるほど吸収液のｐＨ（ｌｏｇ（１／Ｈ⁺））も高く（Ｈ⁺濃度は低く）なる。これは、（３）式に示した反応でＨ⁺濃度が減少するためである。しかし、吸収液のｐＨは吸収液中のＣａＣＯ₃濃度だけでなく、吸収液単位体積当たりに吸収されたＳＯ₂量や循環タンク内の吸収液の滞留時間などにも影響され、さらに、吸収液に溶解している成分（Ｎａ、Ｍｇ）の種類や濃度にも影響される。このため、吸収液のｐＨの測定値だけからＣａＣＯ₃濃度を決定できない。入口ＳＯ₂濃度及び循環液量が変化した時のｐＨとＣａＣＯ₃濃度の関係の一例をそれぞれ図５および図６に示す。
【００２４】
図５および図６から明らかなように入口ＳＯ₂濃度が高い（吸収液単位容積当たりの吸収ＳＯ₂量が多い）ほど、また吸収液スラリの循環量が多い（循環タンクの滞留時間が短い）ほど同一ＣａＣＯ₃濃度でのｐＨが低くなる。これは、（３）式において入口ＳＯ₂濃度が高いほどＨ⁺濃度が高く、また吸収液スラリの循環液量が多いほど反応時間が短くなるためである。
【００２５】
このように、ｐＨとＣａＣＯ₃濃度の関係はさまざまな因子によって影響されるが、脱硫装置を運転しながら常にｐＨとＣａＣＯ₃濃度の関係を把握すればｐＨ測定値からＣａＣＯ₃濃度を容易かつ正確に推定できる。ただし、図９にＣａＣＯ₃濃度分析装置のフローの一例を示したように、ＣａＣＯ₃濃度分析装置の酸添加槽２８や測定槽３２の容積並びにＣａＣＯ₃濃度分析装置に送られる吸収液Ｂの流量などによって決まる測定時間の遅れがあるので、ｐＨとＣａＣＯ₃濃度関係を把握するには、この遅れを考慮する必要がある。
【００２６】
さらに本発明者らが鋭意研究したところ、ｐＨとＣａＣＯ₃濃度の関係は循環タンクの滞留時間（分）や吸収液単位容積当たりの吸収ＳＯ₂量（ｍｍｏｌ／Ｌ）によって整理できることが明らかになった。一例として、下記の表１に示した条件で脱硫装置を運転した時の吸収液のｐＨ測定値とＣａＣＯ₃濃度の関係を図７に示す。ただし、Ｎｏ．１〜３の各条件では吸収液のｐＨやＣａＣＯ₃濃度が異なるので、出口ＳＯ₂濃度や吸収液単位容積当たりの吸収ＳＯ₂量にやや幅がある。図７に示すように、循環タンクの滞留時間が短いほど、吸収液単位容積当たりの吸収ＳＯ₂量（ｍｍｏｌ／Ｌ）が多いほど同一ＣａＣＯ₃濃度でのｐＨが低くなる。また、図７中のＮｏ．２および３では循環タンクの滞留時間および吸収液単位容積当たりの吸収ＳＯ₂量がほぼ等しいため、吸収液のｐＨ測定値とＣａＣＯ₃濃度の関係はほぼ同じである。
【表１】

【００２７】
このように、循環タンクの滞留時間や吸収液単位容積当たりの吸収ＳＯ₂量をパラメータとしてｐＨとＣａＣＯ₃濃度の関係を整理することにより、ボイラ負荷などが急激に変化し、ＣａＣＯ₃濃度が短時間に変動しても、ｐＨの測定値並びに循環タンクの滞留時間及び吸収液単位容積当たりの吸収ＳＯ₂量からＣａＣＯ₃濃度を正確に推定可能となった。循環タンクの滞留時間及び吸収液単位容積当たりの吸収ＳＯ₂量は下記の式で計算できる。
【００２８】
循環タンクの滞留時間＝循環タンク内の吸収液量／吸収液循環流量（５）
吸収液単位容積当たりの吸収ＳＯ₂量
＝（入口ＳＯ₂濃度−出口ＳＯ₂濃度）×ガス流量／吸収液循環量（６）
【００２９】
なお、吸収液中のＮａ、Ｍｇその他の溶解成分もｐＨとＣａＣＯ₃濃度の関係に影響するが、これらの成分は排ガス中や石灰石中に不純物として含まれているもので、吸収液中でのＮａ、Ｍｇその他の溶解成分濃度が急激に変化することはなく、連続的または頻繁にｐＨとＣａＣＯ₃濃度を計測し、両者の関係を把握することで吸収液中のＮａやＭｇ他の溶解成分の影響は回避できる。
【００３０】
【発明の実施の形態】
本発明は下記の実施例によってさらに詳細に説明されるが、下記の例で制限されるものではない。
実施例１
本発明による実施例を図１に示す。図８に示した従来技術に基づく脱硫塔と同様に塔本体１、入口ダクト２、出口ダクト３、スプレーノズル４、吸収液ポンプ５、循環タンク６、撹拌機７、空気吹き込み装置８及びミストエリミネータ９等から構成されるが、本実施例では、ｐＨ計１４とＣａＣＯ₃濃度分析装置１５の両方を有し、さらにｐＨ計１４とＣａＣＯ₃濃度分析装置１５の測定結果を演算処理する演算装置１６も有する。
【００３１】
ボイラから排出される排ガスＡは、入口ダクト２より脱硫塔本体１に導入され、出口ダクト３より排出される。この間、脱硫塔には吸収液抜き出し管１０を通じて吸収液ポンプ５から送られる吸収液Ｂが複数のスプレーノズル４から噴霧され、吸収液Ｂと排ガスＡの気液接触が行われる。このとき吸収液Ｂは排ガスＡ中のＳＯ₂を選択的に吸収し、亜硫酸カルシウムを生成する。亜硫酸カルシウムを生成した吸収液は循環タンク６に溜まり、撹拌機７によって撹拌されながら、空気吹き込み装置８から供給される空気Ｃにより吸収液中の亜硫酸カルシウム酸化され石膏Ｄを生成する。
【００３２】
吸収液ポンプ５からスプレーノズル４に送られる吸収液Ｂの一部がｐＨ計１４とＣａＣＯ₃濃度分析装置１５に送られ、吸収液ＢのｐＨ及びＣａＣＯ₃濃度が測定される。ＣａＣＯ₃濃度分析装置１５での測定時間の遅れを考慮し、演算装置１６でｐＨとＣａＣＯ₃濃度の関係が求められる。例えば、図７に示したようなｐＨとＣａＣＯ₃濃度の関係が求められ、そのｐＨとＣａＣＯ₃濃度の関係を示すグラフとある時間のｐＨ測定値から、その時のＣａＣＯ₃濃度を推定する。さらに、このｐＨとＣａＣＯ₃濃度の関係を示すグラフ（曲線）から、新たに設定されるＣａＣＯ₃設定濃度でのｐＨが求まるので、そのｐＨとなるように石灰石供給管１２より循環タンク６内の吸収液に添加される石灰石Ｅの供給量を調整する。すなわち、現在のｐＨが設定ＣａＣＯ₃濃度でのｐＨより低くければ石灰石Ｅの供給量を増加し、逆に高ければ供給量を減少させる。
【００３３】
石灰石及び石膏が共存するタンク内の吸収液の一部は、吸収液ポンプ５によって吸収液抜き出し管１０から再びスプレーノズル４に送られ、一部は石膏抜き出し管１１より脱水機１３に送られ、石膏Ｃが回収される。また、スプレーノズル４から噴霧され微粒化された吸収液の内、液滴径の小さいものは排ガスＡに同伴されるが、脱硫塔上部に設けられたミストエリミネータ９によって回収される。図２に脱硫装置入口のＳＯ₂濃度が変化した時の脱硫率及び吸収液中のＣａＣＯ₃濃度の変化を示す。本発明法により、脱硫装置入口のＳＯ₂濃度が変化しても吸収液中のＣａＣＯ₃濃度を適正な値に調整することにより脱硫率を一定に維持できる。これにより、経済的に高い脱硫性能を維持できるだけでなく、高品質の石膏を回収することが可能となる。
【００３４】
比較例１
実施例１と同じ条件で脱硫装置を運転した。ただし、ｐＨ計１４のみによりＣａＣＯ₃の供給量を制御し、ＣａＣＯ₃濃度分析装置１５は使用しなかった。図３に脱硫装置入口のＳＯ₂濃度が変化した時の脱硫率及び吸収液中のＣａＣＯ₃濃度の変化を示す。実施例１に比較して、脱硫率及び吸収液中のＣａＣＯ₃濃度の変動が大きい。
【００３５】
比較例２
実施例１と同じ条件で脱硫装置を運転した。ただし、ＣａＣＯ₃濃度分析装置１５の測定値のみによりＣａＣＯ₃の供給量を制御し、ｐＨ計１４及び演算装置１６は使用しなかった。図４に脱硫装置入口のＳＯ₂濃度が変化した時の脱硫率及び吸収液中のＣａＣＯ₃濃度の変化を示す。
【００３６】
実施例１に比較して、脱硫率及び吸収液中のＣａＣＯ₃濃度の変動が大きい。上記実施例１では、ＣａＣＯ₃濃度分析装置１５として図９に示した構造のもの（特願平７−１９３８９１号に基づく装置）を用いているが、液中のＣａＣＯ₃濃度を連続して測定できる方法であれば、他の方法を用いることも可能である。また、上記実施例１は脱硫塔の下部から排ガスを導入し、上部から排出する構造でかつスプレで吸収液を排ガス中に噴霧する脱硫塔についての実施例であるが、本発明法は排ガスの流れ方向や排ガスと吸収液の接触方式（濡れ壁式吸収装置等）に関係なく有効である。
【００３７】
【発明の効果】
本発明によれば、吸収液スラリ中のＣａＣＯ₃濃度を正確に制御でき、経済的に高い脱硫性能を維持すること及び高品質の石膏を回収することが可能である。
【図面の簡単な説明】
【図１】本発明になる一実施例の脱硫装置のフロー図である。
【図２】図１の実施例における実験データを示す図である。
【図３】本発明の比較例の実験データを示す図である。
【図４】本発明の比較例の実験データを示す図である。
【図５】本発明の脱硫装置における脱硫塔流入口ＳＯ₂濃度及び循環液量が変化した時のｐＨとＣａＣＯ₃濃度の関係を示す図である。
【図６】本発明の脱硫装置における脱硫塔流入口ＳＯ₂濃度及び循環液量が変化した時のｐＨとＣａＣＯ₃濃度の関係を示す図である。
【図７】本発明の脱硫装置における脱硫塔入口ＳＯ₂、出口ＳＯ₂、循環液量、循環タンク容積が変化した時のｐＨとＣａＣＯ₃濃度の関係を示す図である。
【図８】従来技術の脱硫装置のフロー図である。
【図９】本発明者の先願発明の脱硫装置のフロー図である。
【符号の説明】
１塔本体２入口ダクト
３出口ダクト４スプレーノズル
５吸収液ポンプ６循環タンク
７撹拌機８空気吹き込み装置
９ミストエリミネータ１０吸収液抜き出し管
１１石膏抜き出し管１２石灰石供給管
１３脱水機１４ｐＨ計
１５ＣａＣＯ₃濃度分析装置
１６演算装置２１ライン
２２クーラ２３ライン
２４酸化槽２５溶存酸素計
２６過酸化水素水添加ライン
２７ライン２８酸添加槽
２９酸添加ライン３０ライン
３１ラインミキサー３２測定槽
３３溶存ＳＯ₂計３４ｐＨ計
３５ライン[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for controlling the carbonate concentration in a slurry containing carbonate.
[0002]
[Prior art]
The flue gas desulfurization apparatus is an apparatus that absorbs and removes sulfur oxides, particularly sulfur dioxide (SO ₂ ) in the flue gas generated when fossil fuel is burned in a thermal power plant. There are various methods for absorbing and removing sulfur oxides in flue gas, but the limestone-gypsum method is mainly used from the viewpoint of desulfurization performance and economy. Limestone - The gypsum method, limestone but (CaCO ₃ is the main component) absorbs SO ₂ in the absorbing solution slurry containing, by adjusting the supply amount of CaCO ₃ in response to changes in properties of the boiler load and fuel used, the absorbing liquid by controlling the CaCO ₃ concentration the optimal value of the slurry (e.g., also enhance CaCO ₃ concentration of the absorbing solution slurry and the SO ₂ concentration in the exhaust gas amount and the exhaust gas increases), maintaining the economic and high desulfurization performance There is a need to.
[0003]
One method of controlling the CaCO ₃ concentration in the absorbent slurry is a method of measuring the pH of the absorbent slurry and adjusting the CaCO ₃ supply amount so as to obtain a predetermined pH. FIG. 8 shows an example of a desulfurization apparatus using a method of measuring the pH of a prior art absorbent slurry and adjusting the CaCO ₃ supply amount. The desulfurization tower mainly comprises a tower body 1, an inlet duct 2, an outlet duct 3, a spray nozzle 4, an absorption liquid pump 5, a circulation tank 6, a stirrer 7, an air blowing device 8, a mist eliminator 9, an absorption liquid discharge pipe 10, It comprises a gypsum extraction pipe 11, a limestone supply pipe 12, a dehydrator 13, a pH meter 14, and the like.
[0004]
A plurality of spray nozzles 4 are installed in the horizontal direction and a plurality of stages in the height direction. Further, the stirrer 7 and the air blowing device 8 are installed in the circulation tank 6 where the absorption liquid stays in the lower part of the desulfurization tower, and the mist eliminator 9 is installed in the uppermost part of the absorption tower or in the outlet duct 3.
[0005]
The exhaust gas A discharged from the boiler is introduced into the desulfurization tower body 1 from the inlet duct 2 and discharged from the outlet duct. During this time, the absorption liquid B sent from the pump 5 through the absorption liquid extraction pipe 10 is sprayed from the plurality of spray nozzles 4 to the desulfurization tower, and the gas-liquid contact between the absorption liquid and the exhaust gas A is performed. At this time, the absorbing solution selectively absorbs SO ₂ in the exhaust gas A and generates calcium sulfite. The absorption liquid that has produced calcium sulfite accumulates in the circulation tank 6, and while being stirred by the stirrer 7, the calcium sulfite in the absorption liquid is oxidized by the air C supplied from the air blowing device 8 to generate gypsum D. A desulfurizing agent such as limestone E is added to the absorption liquid in the circulation tank 6 from the limestone supply pipe 12, but the supply amount is controlled by the measured value of the pH meter 14.
[0006]
That is, when the measured value of the pH meter is lower than a predetermined value, the supply amount of limestone is increased, and when it is higher, the supply amount of limestone E is decreased. A part of the absorbing liquid in the tank 6 in which limestone E and gypsum D coexist is sent again from the absorbing liquid extraction pipe 10 to the spray nozzle 4 by the absorbing liquid pump 5, and a part thereof is sent to the dehydrator 13 from the gypsum extracting pipe 11. It is sent and gypsum D is collected. Further, among the absorption liquid sprayed from the spray nozzle 4 and atomized, those having a small droplet diameter are accompanied by the exhaust gas A, but are recovered by a mist eliminator 9 provided at the upper part of the desulfurization tower.
[0007]
[Problems to be solved by the invention]
However, in the conventional technique shown in FIG. 8, the supply amount of limestone is adjusted by the measured value of the pH meter 14 to control the CaCO ₃ concentration in the absorbent, but there are the following problems. That is, measuring the pH of a correlation with the pH meter 14 in the CaCO ₃ concentration, accurate CaCO ₃ concentration does not measure the CaCO ₃ concentration directly can not be grasped. For this reason, desulfurization performance increases as the concentration of CaCO ₃ in the absorbent slurry increases, but the consumption of limestone increases, and when the concentration of CaCO ₃ in the recovered gypsum increases, the quality of gypsum decreases, It cannot be used for other purposes.
[0008]
On the other hand, several methods have been proposed as methods for directly measuring the concentration of carbonate such as CaCO ₃ in the absorbing solution (for example, Japanese Patent Publication No. 3-52826, Japanese Patent Application Laid-Open No. 2-195253). In the method disclosed in JP-B-3-52826 and JP-A-2-195253, an acid is added to an absorbing solution containing CaCO ₃ , and then heated to release CO ₂ into the gas phase to release the CO ₂ in the gas. This is a method of calculating the CaCO ₃ concentration by measuring the CO ₂ concentration. It is possible to use the CaCO ₃ concentration measuring apparatus based on these patent application inventions in place of the pH meter 14 in the desulfurization apparatus shown in FIG. Although these methods enable continuous measurement, it takes time to completely release CO ₂ into the gas phase, and as a result, the problem to be solved remains that measurement time becomes long.
[0009]
In general, CaCO ₃ is supplied to the circulation tank 6 at the lower part of the absorption tower. The residence time of the absorbent slurry in the circulation tank 6 is about 2 to 6 minutes, whereas the known continuous measurement method of CaCO ₃ concentration. Since the measurement time in this is as long as about 10 to 20 minutes, the CaCO ₃ concentration in the absorbing solution is measured using these methods, the CaCO ₃ supply amount is adjusted, and the CaCO ₃ concentration in the absorbing solution is set to a predetermined value. It is practically difficult to control.
Against this background, the present inventors have proposed a method for continuously measuring the CaCO ₃ concentration in the absorbing solution B in a short time (Japanese Patent Application No. 7-193891).
[0010]
FIG. 9 shows a flow of one embodiment in the invention of Japanese Patent Application No. 7-193891. The absorbent B is sent from the line 21 to the cooler 22 and then sent to the oxidation tank 24. In the oxidation tank 24, the dissolved oxygen concentration in the absorbing solution is measured by the dissolved oxygen meter 25, and the hydrogen peroxide solution F is added from the hydrogen peroxide solution addition line 26 when the dissolved oxygen concentration is a predetermined value or less. Further, the absorbent B is sent from the line 27 to the acid addition tank 28. In the acid addition tank 28, hydrochloric acid G is added from an acid addition line 29, and the absorbent B is stirred by a line mixer 31 installed in the middle of the line 30 and then sent into a measurement tank 32 where dissolved CO _{2 is} dissolved. The dissolved CO ₂ concentration and pH are measured by the meter 33 and the pH meter 34, respectively. Absorbing liquid B for which measurement has been completed is discharged from line 35. When the acid G is added to the absorbing liquid B, an equimolar amount of CO ₂ with CaCO ₃ in the absorbing liquid B is generated, and CO ₂ is dissolved in water if it is below the solubility. Therefore, if the dissolved CO ₂ concentration in the absorbent B is measured, the same mole of CaCO ₃ was present before the acid G was added, and the CaCO ₃ concentration can be easily determined.
[0011]
As a result of measuring the CaCO ₃ concentration in the desulfurization slurry (absorption liquid) used in the flue gas desulfurization apparatus by this method, the same value is obtained within the measurement error range within the measurement time range of 1 to 3 minutes and the method defined in JIS R9101. Obtained. However, a time for adding the acid G to the absorbing solution B to react with CaCO ₃ in the absorbing solution B and a response time of the dissolved CO ₂ meter 33 are required. Cannot respond in seconds.
[0012]
As described above, in the prior art, the pH meter 34 responds in several to several tens of seconds and measures the pH correlated with the CaCO ₃ concentration, but does not directly measure the CaCO ₃ concentration, so the accurate CaCO ₃ concentration is grasped. or not be, CaCO ₃ concentration measuring apparatus takes a long time to measure the CaCO ₃ of the absorbing liquid in the slurry, it is impossible to adjust the CaCO ₃ feed amount corresponding to a change in the nature of sudden boiler load and fuel used there were.
[0013]
An object of the present invention is to solve the above problems and propose a method and apparatus for accurately controlling the carbonate concentration in a slurry liquid such as an absorbing liquid that absorbs sulfur oxides in flue gas.
[0014]
[Means for Solving the Problems]
The above-described problem of the present invention is solved by the following configuration.
That is, the measurement result of the carbonate concentration from the measurement time of the carbonate concentration compared to the elapsed time (pH measurement time (Δt1)) from the measurement of the pH in the slurry containing carbonate to the pH measurement result is obtained. Considering that the elapsed time (measurement time of carbonate concentration (Δt2)) is delayed , the relationship between the pH in the slurry containing carbonate in advance and the carbonate concentration in the slurry at the time of pH measurement determined advance, the previously obtained from the relation between pH and carbonate concentration during pH measurements in the slurry, newly estimated carbonate concentration in said slurry from pH measurements obtained when the pH was measured in the slurry value as determined, based on said carbonate concentration estimated, adjusting the supply amount of the previously determined pH and carbonate on the relationship carbonate concentration during pH measurements in the slurry so as to have a predetermined pH at which the pH of the slurry is determined By doing A method for controlling the carbonate concentration in the slurry to control the carbonate concentration in the slurry, or
[0015]
PH measurement means in slurry containing carbonate, carbonate concentration measurement means in the slurry, and elapsed time from when pH is measured in slurry containing carbonate until pH measurement result is obtained (pH measurement time ( .DELTA.t1)) in comparison with the time elapsed from the measurement by the measuring means of carbonate concentration to the measurement results of the carbonate concentration is obtained (carbonate concentration measurement time (.DELTA.t2)) in consideration that you are delayed, to previously obtain a relation carbonate concentration in the slurry at pH measurement by the pH and the pH measuring means in the slurry including the pre Me carbonate, the pH and carbonate concentration during pH measurements in the slurry obtained Me該予From the relationship, the carbonate concentration in the slurry at the time of pH measurement is obtained as an estimated value from the pH measurement value in the slurry obtained when newly measured by the pH measuring means , and based on the estimated carbonate concentration, the pH of the slurry given that seek Calculating means for calculating the supply amount of carbonate from the relationship between the pH in the slurry obtained in advance and the carbonate concentration at the time of pH measurement so that the pH of the carbonate is supplied, and carbonate for supplying the carbonate calculated by the calculating means A carbonate concentration control device in a slurry provided with a salt supply means.
Further, the present invention can be applied to an absorbent slurry containing carbonate used for flue gas desulfurization of combustion exhaust gas. In this case, the present invention has the following configuration.
[0016]
In the desulfurization tower, the exhaust gas from the combustion device including the boiler and the absorbent slurry containing carbonate are brought into contact with each other to absorb sulfur oxide in the absorbent slurry, and then the absorbent slurry is stored in a circulation tank. In the flue gas desulfurization method in which the absorbent slurry stored in the circulation tank is circulated and supplied to the desulfurization tower and brought into contact with the exhaust gas again, the residence time of the slurry in the circulation tank and / or the amount of absorbed sulfur oxide per unit volume of the slurry is taken into consideration to, and measuring the elapsed time (pH measurement time (.DELTA.t1)) carbonate concentration from the measurement of the carbonate concentration as compared with from the measurement of pH in the slurry until the pH measurements are obtained containing carbonate Considering that the elapsed time until the result is obtained (measurement time of carbonate concentration (Δt2)) is delayed , the pH in the slurry containing carbonate in advance and the carbonate concentration in the slurry at the time of pH measurement are determined . Determined Meteor-out the relationship, the pre-determined from the relationship between the pH and carbonate concentration during the pH measurement of the slurry were, from pH measurements of the slurry obtained when newly measured pH of the slurry carbonate calculated salt concentration as an estimate, based on said carbonate concentration estimated, the previously determined pH and carbonate on the relationship carbonate concentration during pH measurements in the slurry so as to have a predetermined pH at which the pH of the slurry is determined The method for controlling the carbonate concentration in the slurry by controlling the carbonate concentration in the slurry by adjusting the supply amount of
[0017]
An absorption tower for absorbing sulfur oxide in the absorption liquid slurry by contacting the exhaust gas from the combustion apparatus including the boiler with the absorption liquid slurry containing carbonate, and storing the absorption liquid slurry that has absorbed the sulfur oxide in the exhaust gas In a flue gas desulfurization apparatus comprising a circulation tank and a slurry circulation path for supplying an absorption liquid slurry stored in the circulation tank to a desulfurization tower, pH measuring means in the slurry containing carbonate, carbonic acid in the slurry Taking into account the salt concentration measuring means, the residence time of the absorbent slurry in the circulation tank and / or the amount of absorbed sulfur oxide per unit volume of the absorbent slurry, and the pH from the time of measuring the pH in the slurry containing carbonate Compared to the elapsed time until the measurement result is obtained (pH measurement time (Δt1)), the elapsed time from the measurement by the carbonate concentration measurement means until the measurement result of the carbonate concentration is obtained ( Considering that salt concentration of the measurement time (.DELTA.t2)) is delayed, seeking relationship carbonate concentration in the slurry at pH measurement by the pH and the pH measuring device in the scan slurry including the pre Me carbonate put, the previously determined pH and p H relationship to these carbonate concentration during measurement in the slurry, the carbonate concentration in the slurry from the measured pH in the resulting slurry when measured by newly pH measuring means Obtained as an estimated value, and based on the estimated carbonate concentration, the supply amount of carbonate from the relationship between the previously determined pH in the slurry and the carbonate concentration at the time of pH measurement so that the pH of the slurry becomes the predetermined pH to be determined And a carbonate concentration control device in the slurry, comprising a calculation means for calculating the above and a carbonate supply means for supplying a carbonate calculated by the calculation means.
[0018]
At this time, the residence time of the absorbent slurry in the circulation tank is determined from the absorbent circulation flow rate and the amount of absorbent in the circulation tank, and the amount of absorbed sulfur oxide per unit volume of the absorbent slurry is the desulfurizer inlet gas and outlet gas. It can be determined from the sulfur oxide content concentration, gas flow rate, and absorption liquid circulation amount.
[0019]
[Action]
The SO ₂ absorbed in the absorbing solution in the desulfurization apparatus releases hydrogen ions (H ⁺ ) by the reaction shown in the following formula (1) or (2), thereby lowering the pH of the absorbing solution. In the circulation tank, H ⁺ reacts with CaCO _3, which is the main component of limestone, and the pH of the absorbing solution is recovered (increased) by consuming H ⁺ as shown in the following formula (3).
[0020]
H ₂ O + SO ₂ = H ₂ SO ₃ = H ⁺ + HSO ₃ ⁻ = 2H ⁺ + SO ₃ ²⁻ (1)
H ₂ O + SO ₂ + 1 / 2O ₂ = H ₂ SO ₄ = 2H ⁺ + SO ₄ ²⁻ (2)
2H ⁺ + CaCO ₃ = Ca ²⁺ + H ₂ O + CO ₂ (3)
The absorption liquid whose pH has been recovered by the reaction of formula (3) is sent again to the spray nozzle by the absorption liquid pump and absorbs SO ₂ in the exhaust gas, but the desulfurization performance (amount of absorbing SO ₂ ) at that time is absorbed. It depends on the CaCO ₃ concentration and pH in the liquid. In order to measure the CaCO ₃ concentration in the absorbing solution, an acid is added to the absorbing solution, and the generated CO ₂ concentration is measured with a dissolved CO ₂ meter.
[0021]
The reaction when hydrochloric acid is added to CaCO ₃ is shown in the following formula (4). Equimolar amount of CO ₂ is generated with CaCO ₃ . Since CO ₂ dissolves in water, the CaCO ₃ concentration in the absorbing solution can be determined by measuring the dissolved CO ₂ concentration if it is below the solubility.
[0022]
CaCO ₃ + 2HCl = CaCl ₂ + CO ₂ + H ₂ O (4)
However, when the concentration of CaCO ₃ in the absorbing solution fluctuates, an acid is added to the absorbing solution to cause the reaction of the formula (4), and the dissolved CO ₂ concentration can be detected by the dissolved CO ₂ meter used. Although it is different, about 1 to 5 minutes are required.
[0023]
On the other hand, if other conditions are the same, the higher the CaCO ₃ concentration in the absorbing solution, the higher the pH (log (1 / H ⁺ )) of the absorbing solution (the lower the H ⁺ concentration). This is because the H ⁺ concentration decreases in the reaction shown in the equation (3). However, the pH of the absorbent is affected not only by the concentration of CaCO ₃ in the absorbent, but also by the amount of SO ₂ absorbed per unit volume of the absorbent and the residence time of the absorbent in the circulation tank. It is also affected by the type and concentration of components (Na, Mg) dissolved in the. Thus, unable to determine the CaCO ₃ concentration of only the measurement values of pH of the absorption liquid. Examples of the relationship between pH and CaCO ₃ concentration when the inlet SO ₂ concentration and the circulating fluid amount change are shown in FIGS. 5 and 6, respectively.
[0024]
As apparent from FIGS. 5 and 6, the higher the inlet SO ₂ concentration (the larger the amount of absorbed SO ₂ per unit volume of absorbent), the greater the amount of absorbent slurry circulated (the residence time of the circulation tank is shorter). The lower the pH at the same CaCO ₃ concentration. This is because in Formula (3), the higher the inlet SO ₂ concentration, the higher the H ⁺ concentration, and the longer the amount of circulating fluid in the absorbent slurry, the shorter the reaction time.
[0025]
Thus, although the relationship between pH and CaCO ₃ concentration is affected by various factors, if the relationship between pH and CaCO ₃ concentration is always grasped while operating the desulfurization apparatus, the CaCO ₃ concentration can be easily and accurately determined from the measured pH value. Can be estimated. However, as shown in an example of the flow of CaCO ₃ concentration analyzer 9, the flow rate of the absorption solution B to be sent to the volume as well as CaCO ₃ concentration analyzer of CaCO ₃ acid addition tank 28 of the concentration analyzer and the measuring tank 32 Since there is a delay in measurement time determined by the above, it is necessary to consider this delay in order to grasp the relationship between pH and CaCO ₃ concentration.
[0026]
Furthermore, as a result of intensive studies by the present inventors, it has been clarified that the relationship between pH and CaCO ₃ concentration can be arranged by the residence time (minutes) of the circulation tank and the amount of absorbed SO ₂ (mmol / L) per unit volume of the absorbent. It was. As an example, FIG. 7 shows the relationship between the measured pH value of the absorbent and the CaCO ₃ concentration when the desulfurization apparatus is operated under the conditions shown in Table 1 below. However, no. Since each of the conditions 1 to ₃ has different pH and CaCO ₃ concentration of the absorbing solution, there is a slight range in the outlet SO ₂ concentration and the amount of absorbed SO ₂ per unit volume of the absorbing solution. As shown in FIG. 7, the shorter the residence time of the circulation tank, the lower the pH at the same CaCO ₃ concentration as the absorbed SO ₂ amount (mmol / L) per unit volume of the absorbing solution increases. Further, in FIG. In 2 and 3, since the residence time of the circulation tank and the amount of absorbed SO ₂ per unit volume of the absorbing liquid are substantially equal, the relationship between the measured pH value of the absorbing liquid and the CaCO ₃ concentration is almost the same.
[Table 1]

[0027]
In this way, by arranging the relationship between pH and CaCO ₃ concentration using the residence time of the circulation tank and the amount of absorbed SO ₂ per unit volume of the absorbing liquid as parameters, the boiler load and the like change rapidly, and the CaCO ₃ concentration becomes short. Even if it fluctuates over time, the CaCO ₃ concentration can be accurately estimated from the measured pH value, the residence time of the circulation tank, and the amount of absorbed SO ₂ per unit volume of the absorbent. The residence time of the circulation tank and the amount of absorbed SO ₂ per unit volume of absorbing liquid can be calculated by the following formula.
[0028]
Residence time of the circulation tank = Absorbed liquid amount in the circulation tank / Absorbed liquid circulation flow rate (5)
Absorbed SO ₂ amount per unit volume of absorbing liquid = (inlet SO ₂ concentration−outlet SO ₂ concentration) × gas flow rate / absorbing liquid circulation amount (6)
[0029]
In addition, Na, Mg and other dissolved components in the absorbent also affect the relationship between pH and CaCO ₃ concentration, but these components are contained as impurities in the exhaust gas and limestone. Concentrations of dissolved components such as Na, Mg, etc. do not change abruptly. Measure pH and CaCO ₃ concentration continuously or frequently and grasp the relationship between them to dissolve dissolved components of Na, Mg, etc. Can be avoided.
[0030]
DETAILED DESCRIPTION OF THE INVENTION
The present invention is further illustrated by the following examples, but is not limited by the following examples.
Example 1
An embodiment according to the present invention is shown in FIG. Similar to the desulfurization tower based on the prior art shown in FIG. 8, the tower body 1, the inlet duct 2, the outlet duct 3, the spray nozzle 4, the absorption liquid pump 5, the circulation tank 6, the stirrer 7, the air blowing device 8 and the mist eliminator consists of 9, etc., in this embodiment, it has both pH meter 14 and CaCO ₃ concentration analyzer 15, the arithmetic unit further processing the measurement results of the pH meter 14 and CaCO ₃ concentration analyzer 15 16 Also have.
[0031]
The exhaust gas A discharged from the boiler is introduced into the desulfurization tower body 1 from the inlet duct 2 and discharged from the outlet duct 3. During this time, the absorption liquid B sent from the absorption liquid pump 5 through the absorption liquid extraction pipe 10 is sprayed from the plurality of spray nozzles 4 to the desulfurization tower, and gas-liquid contact between the absorption liquid B and the exhaust gas A is performed. At this time, the absorbing liquid B selectively absorbs SO ₂ in the exhaust gas A to generate calcium sulfite. The absorption liquid that has produced calcium sulfite is accumulated in the circulation tank 6 and is agitated by the stirrer 7 while being oxidized by the air C supplied from the air blowing device 8 to be oxidized with calcium sulfite in the absorption liquid to produce gypsum D.
[0032]
A part of the absorption liquid B sent from the absorption liquid pump 5 to the spray nozzle 4 is sent to the pH meter 14 and the CaCO ₃ concentration analyzer 15, and the pH and CaCO ₃ concentration of the absorption liquid B are measured. Considering the delay of the measurement time in the CaCO ₃ concentration analyzer 15, the calculation device 16 obtains the relationship between pH and CaCO ₃ concentration. For example, it prompts the relationship between pH and CaCO ₃ concentration as shown in FIG. 7, the pH measured value of the pH and CaCO ₃ with a time graph showing the concentration of relevant estimates the CaCO ₃ concentration at that time. Furthermore, since the pH at the newly set CaCO ₃ set concentration is obtained from the graph ( curve ) showing the relationship between the pH and the CaCO ₃ concentration, the inside of the circulation tank 6 is set from the limestone supply pipe 12 so as to be the pH. The supply amount of limestone E added to the absorbent is adjusted. That is, if the current pH is lower than the pH at the set CaCO ₃ concentration, the supply amount of limestone E is increased, and conversely if it is higher, the supply amount is decreased.
[0033]
A part of the absorption liquid in the tank in which limestone and gypsum coexist is sent again from the absorption liquid extraction pipe 10 to the spray nozzle 4 by the absorption liquid pump 5, and a part is sent to the dehydrator 13 from the gypsum extraction pipe 11. Gypsum C is recovered. Of the absorption liquid sprayed from the spray nozzle 4 and atomized, those having a small droplet diameter are accompanied by the exhaust gas A, but are recovered by a mist eliminator 9 provided at the upper part of the desulfurization tower. FIG. 2 shows changes in the desulfurization rate and the CaCO ₃ concentration in the absorbing solution when the SO ₂ concentration at the inlet of the desulfurizer changes. According to the method of the present invention, even if the SO ₂ concentration at the inlet of the desulfurization apparatus changes, the desulfurization rate can be kept constant by adjusting the CaCO ₃ concentration in the absorbent to an appropriate value. Thereby, not only can economically high desulfurization performance be maintained, but also high-quality gypsum can be recovered.
[0034]
Comparative Example 1
The desulfurization apparatus was operated under the same conditions as in Example 1. However, the supply amount of CaCO ₃ was controlled only by the pH meter 14, and the CaCO ₃ concentration analyzer 15 was not used. FIG. 3 shows changes in the desulfurization rate and the CaCO ₃ concentration in the absorbing solution when the SO ₂ concentration at the inlet of the desulfurization apparatus changes. Compared to Example 1, a large variation in the CaCO ₃ concentration of the desulfurization rate and the absorption liquid.
[0035]
Comparative Example 2
The desulfurization apparatus was operated under the same conditions as in Example 1. However, the supply amount of CaCO ₃ was controlled only by the measured value of the CaCO ₃ concentration analyzer 15, and the pH meter 14 and the arithmetic unit 16 were not used. FIG. 4 shows changes in the desulfurization rate and the CaCO ₃ concentration in the absorption liquid when the SO ₂ concentration at the inlet of the desulfurizer changes.
[0036]
Compared to Example 1, a large variation in the CaCO ₃ concentration of the desulfurization rate and the absorption liquid. In Example 1 above, the CaCO ₃ concentration analyzer 15 having the structure shown in FIG. 9 (apparatus based on Japanese Patent Application No. 7-193891) is used, but the CaCO ₃ concentration in the liquid is continuously measured. Other methods can be used as long as they can be used. In addition, Example 1 is an example of a desulfurization tower in which exhaust gas is introduced from the lower part of the desulfurization tower and discharged from the upper part, and the absorbing liquid is sprayed into the exhaust gas by spray. It is effective regardless of the flow direction and the contact method of the exhaust gas and the absorbing liquid (wet wall type absorber).
[0037]
【The invention's effect】
According to the present invention, it is possible to accurately control the CaCO ₃ concentration in the absorbent slurry, to maintain economically high desulfurization performance, and to collect high-quality gypsum.
[Brief description of the drawings]
FIG. 1 is a flow diagram of a desulfurization apparatus according to an embodiment of the present invention.
FIG. 2 is a diagram showing experimental data in the embodiment of FIG.
FIG. 3 is a diagram showing experimental data of a comparative example of the present invention.
FIG. 4 is a diagram showing experimental data of a comparative example of the present invention.
FIG. 5 is a graph showing the relationship between pH and CaCO ₃ concentration when the desulfurization tower inlet SO ₂ concentration and the amount of circulating fluid in the desulfurization apparatus of the present invention change.
FIG. 6 is a graph showing the relationship between pH and CaCO ₃ concentration when the desulfurization tower inlet SO ₂ concentration and the amount of circulating liquid in the desulfurization apparatus of the present invention change.
FIG. 7 is a diagram showing the relationship between pH and CaCO ₃ concentration when the desulfurization tower inlet SO ₂ , outlet SO ₂ , circulating liquid amount, and circulating tank volume are changed in the desulfurization apparatus of the present invention.
FIG. 8 is a flow diagram of a conventional desulfurization apparatus.
FIG. 9 is a flow diagram of a desulfurization apparatus according to the inventor's prior invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Tower body 2 Inlet duct 3 Outlet duct 4 Spray nozzle 5 Absorption liquid pump 6 Circulation tank 7 Stirrer 8 Air blowing device 9 Mist eliminator 10 Absorption liquid extraction pipe 11 Gypsum extraction pipe 12 Limestone supply pipe 13 Dehydrator 14 pH meter 15 CaCO ₃ Concentration analyzer 16 Arithmetic unit 21 Line 22 Cooler 23 Line 24 Oxidation tank 25 Dissolved oxygen meter 26 Hydrogen peroxide solution addition line 27 Line 28 Acid addition tank 29 Acid addition line 30 Line 31 Line mixer 32 Measurement tank 33 Dissolved SO ₂ meter 34 pH meter 35 lines

Claims

Compared to the elapsed time (pH measurement time (Δt1)) from when the pH in the slurry containing carbonate is measured to when the pH measurement result is obtained, the measurement result of the carbonate concentration is obtained from the measurement of the carbonate concentration. In view of the delay in the elapsed time (measurement time of carbonate concentration (Δt2)) , the relationship between the pH in the slurry containing carbonate and the carbonate concentration in the slurry at the time of pH measurement is obtained in advance. Place, from the previously obtained relation between the pH and carbonate concentration during pH measurements in the slurry, newly obtained the carbonate concentration in said slurry from pH measurements obtained when the pH was measured in the slurry as an estimate , that the basis of the carbonate concentration was estimated to adjust the supply amount of the previously determined pH and carbonate on the relationship carbonate concentration during pH measurements in the slurry so as to have a predetermined pH at which the pH of the slurry is determined Due to the charcoal in the slurry A method for controlling carbonate concentration in a slurry, characterized by controlling the acid salt concentration.

In the desulfurization tower, the exhaust gas from the combustion device including the boiler and the absorbent slurry containing carbonate are brought into contact with each other to absorb sulfur oxide in the absorbent slurry, and then the absorbent slurry is stored in a circulation tank. In the flue gas desulfurization method in which the absorbent slurry stored in the circulation tank is circulated to the desulfurization tower and brought into contact again with the exhaust gas, the residence time of the slurry in the circulation tank and / or the amount of absorbed sulfur oxide per unit volume of the slurry is taken into consideration to, and measuring the elapsed time (pH measurement time (.DELTA.t1)) carbonate concentration from the measurement of the carbonate concentration as compared with from the measurement of pH in the slurry until the pH measurements are obtained containing carbonate Considering that the elapsed time until the result is obtained (measurement time of carbonate concentration (Δt2)) is delayed , the pH in the slurry containing carbonate in advance and the carbonate concentration in the slurry at the time of pH measurement are determined . Determined Meteor-out the relationship, the pre-determined from the relationship between the pH and carbonate concentration during the pH measurement of the slurry were, from pH measurements of the slurry obtained when newly measured pH of the slurry carbonate calculated salt concentration as an estimate, based on said carbonate concentration estimated, the previously determined pH and carbonate on the relationship carbonate concentration during pH measurements in the slurry so as to have a predetermined pH at which the pH of the slurry is determined A method for controlling the carbonate concentration in a slurry, wherein the carbonate concentration in the slurry is controlled by adjusting the supply amount of the slurry.

Find the residence time of the slurry in the circulation tank from the absorption liquid slurry circulation flow rate and the absorption slurry liquid amount in the circulation tank, and also from the sulfur oxide concentration, gas flow rate, and absorption liquid slurry circulation amount in the desulfurizer inlet gas and outlet gas. The method for controlling carbonate concentration in a slurry according to claim 2, wherein the amount of absorbed sulfur oxide per unit volume of the absorbent slurry is determined.

PH measurement means in slurry containing carbonate, carbonate concentration measurement means in the slurry, and elapsed time from when pH is measured in slurry containing carbonate until pH measurement result is obtained (pH measurement time ( .DELTA.t1)) in comparison with the time elapsed from the measurement by the measuring means of carbonate concentration to the measurement results of the carbonate concentration is obtained (carbonate concentration measurement time (.DELTA.t2)) in consideration that you are delayed, to previously obtain a relation carbonate concentration in the slurry at pH measurement by the pH and the pH measuring means in the slurry including the pre Me carbonate, the pH and carbonate concentration during pH measurements in the slurry obtained Me該予From the relationship, the carbonate concentration in the slurry at the time of pH measurement is obtained as an estimated value from the pH measurement value in the slurry obtained when newly measured by the pH measuring means , and based on the estimated carbonate concentration, the pH of the slurry given that seek Calculating means for calculating the supply amount of carbonate from the relationship between the pH in the slurry obtained in advance and the carbonate concentration at the time of pH measurement so that the pH of the carbonate is supplied, and carbonate for supplying the carbonate calculated by the calculating means A carbonate concentration control device in a slurry, comprising: a salt supply means.

An absorption tower that absorbs sulfur oxide in the absorption liquid slurry by contacting the exhaust gas from the combustion device including the boiler and the absorption liquid slurry containing carbonate, and stores the absorption liquid slurry that has absorbed the sulfur oxide in the exhaust gas In a flue gas desulfurization apparatus comprising a circulation tank and a slurry circulation path for supplying an absorbent slurry stored in the circulation tank to a desulfurization tower, pH measurement means in the slurry containing carbonate, and carbon dioxide in the slurry Taking into account the salt concentration measuring means, the residence time of the absorbent slurry in the circulation tank and / or the amount of absorbed sulfur oxide per unit volume of the absorbent slurry, and the pH from the time of measurement of the pH in the slurry containing carbonate Compared to the elapsed time until the measurement result is obtained (pH measurement time (Δt1)), the elapsed time from the measurement by the carbonate concentration measurement means until the measurement result of the carbonate concentration is obtained ( Considering that salt concentration of the measurement time (.DELTA.t2)) is delayed, seeking relationship carbonate concentration in the slurry at pH measurement by the pH and the pH measuring device in the scan slurry including the pre Me carbonate put, the previously determined pH and p H relationship to these carbonate concentration during measurement in the slurry, the carbonate concentration in the slurry from the measured pH in the resulting slurry when measured by newly pH measuring means Obtained as an estimated value, and based on the estimated carbonate concentration, the supply amount of carbonate from the relationship between the previously determined pH in the slurry and the carbonate concentration at the time of pH measurement so that the pH of the slurry becomes the predetermined pH to be determined An apparatus for controlling the concentration of carbonate in a slurry, comprising: an arithmetic means for calculating