JP4506085B2 - Cleaning method of activated carbon catalyst for white liquor oxidation and white liquor oxidation apparatus equipped with the washing mechanism - Google Patents
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Description
【０００１】
【発明の属する技術分野】
本発明の属する技術分野は、クラフトパルプ製造工程における白液酸化用の活性炭触媒の洗浄方法であって、触媒能が低下した活性炭の活性を回復できる洗浄方法および白液酸化装置の起用時の洗浄方法に関するものであり、更には該洗浄を実施できる洗浄機構を備えた白液酸化装置に関するものである。
【０００２】
【従来の技術】
クラフトパルプの蒸解・漂白工程では、硫化ナトリウムを含有する蒸解液(以下、白液と記述する)を空気酸化して、硫化ナトリウムをポリサルファイドまたはチオ硫酸ナトリウムへ変換する装置として、反応触媒である活性炭を充填した酸化反応塔が用いられている。ポリサルファイド含有の白液は、クラフト蒸解時の薬液として使用されている。また、更に白液の酸化を進めると、ポリサルファイドは酸化されチオ硫酸ナトリウムへ変換される。このチオ硫酸ナトリウム含有の白液は、クラフト蒸解後のアルカリ酸素脱リグニンの薬液(酸化白液)として使用されている。
【０００３】
硫化ナトリウムを含有する白液からポリサルファイドを生成する方法については、活性炭触媒の存在下に空気酸化する方法(特許文献１参照)、石灰泥と触媒の存在下に空気酸化する方法(特許文献２、特許文献３参照)、酸化還元樹脂により直接酸化する方法(特許文献４参照)、硫黄を溶解する方法(特許文献５、特許文献６参照)、電気分解により直接生成する方法(特許文献７参照)など種々知られているが、現在、パルプを製造する目的で工業的に実用化されているのは活性炭触媒を用いる空気酸化法のみである(特許文献８、特許文献９参照)。
【０００４】
漂白クラフトパルプ製造工程におけるアルカリ酸素脱リグニン反応に使用するアルカリ源としては、白液中のイオウを含む原子団を、触媒の存在下、チオ硫酸ナトリウムまで空気酸化した酸化白液が用いられている。ここで系外から持ち込んだ水酸化ナトリウムを使用しても酸素脱リグニンは可能ではあるが、これは水酸化ナトリウムを系外から持ち込むことになるので、クラフトパルプ製造工程のクローズド化を進める上で問題となる。また酸素脱リグニン工程からの白水は、通常、回収ボイラへ回収されるため、系外からの水酸化ナトリウムの持ち込みは薬品回収系のバランスを崩すことになる。薬品回収系のバランスを崩さないために、酸化白液のような白液由来のアルカリ源が主に使用されているのが現状である。
【０００５】
従来から用いられている白液酸化装置(以下、白液酸化塔装置と記述する)は、酸化塔本体、空気供給配管、白液供給配管、オレンジリカー出口配管(蒸解用白液の場合)または酸化白液出口配管(アルカリ酸素脱リグニン用の酸化白液の場合)などから構成され、酸化塔内部には活性炭が反応触媒として充填されている。この活性炭としては、例えば、粉末状カーボンブラックが報告されている(非特許文献１参照。)。また、ポリテトラフルオロエチレン、ポリエチレン等の非水溶性物質により活性炭を疎水化し、その疎水化活性炭を用いることにより、活性炭の分離回収が容易になるとともに、その触媒活性が向上することが記載されている(非特許文献２参照。)。また、炭素あるいは活性炭をポリテトラフルオロエチレン、ポリエチレン、ポリスチレン、弗化炭素樹脂などの疎水性物質で部分的に疎水化処理することが記載されている(特許文献１０参照。)。
【０００６】
【特許文献１】
特開昭47-10217号公報
【特許文献２】
特開平8-209573号公報
【特許文献３】
特開平9-87987号公報
【特許文献４】
特開昭56-149304号公報
【特許文献５】
特開平8-311790号公報
【特許文献６】
特開昭54-151602号公報
【特許文献７】
特表平8-512099号公報、国際公開WO95/0071号パンフレット
【特許文献８】
特開昭47-10212号公報
【特許文献９】
特開昭53-92981号公報
【非特許文献１】
吉田ら著、（Netsusokutei8(1)1981,2-5）
【非特許文献２】
触媒23巻第4号 1981年4月 P293〜295
【特許文献１０】
特公昭50-40395号公報
【０００７】
活性炭は大きな表面積を有し、耐蝕性であり、かつ電気伝導性であることから、硫化物の酸化触媒として優れている。この特性から、漂白クラフトパルプ製造工程では、白液中の硫化ナトリウムを酸化してポリサルファイドを含有する白液（この液はオレンジ色に着色しているのでオレンジリカーと称している。以下、オレンジリカーと記述する）を製造する際、また、白液中の硫化ナトリウムをチオ硫酸ナトリウムまで酸化した酸化白液を製造する際に、活性炭が触媒として使用されている。
【０００８】
しかし、白液中にはナトリウムやイオウ以外にも雑多な無機化合物が存在しており、白液の酸化を酸化塔で連続的に行うと、ポリサルファイドまたはチオ硫酸ナトリウムの生成反応の場である活性炭表面上に白液中の無機化合物が蓄積し、活性炭表面積が減少することによって活性炭の活性が低下し、十分なポリサルファイドまたはチオ硫酸ナトリウムの生成ができなくなるという問題がある。また、活性炭の活性が低下した場合、その対策として、空気の吹き込み量を上げ、酸化塔に供給する酸素量を増加させポリサルファイドまたはチオ硫酸ナトリウムの生成をコントロールすることもある。しかし、オレンジリカー調成の場合は、反応の場における酸素量が増えるため、一旦生成したポリサルファイドが蒸解に効果がないチオ硫酸イオンまで更に酸化されてしまい、蒸解時のポリサルファイドによる収率向上効果が十分に得られなくなるという問題が生ずる。
【０００９】
更に、白液酸化塔装置を停機した後に再起用する場合、白液と空気を酸化塔に供給するが、再起用直後は酸化塔および酸化塔内の活性炭が常温近くまで低下しているため、工程を流れる通常70℃以上の白液を酸化塔に供給した場合、白液と酸化塔および酸化塔内活性炭の温度の違いから、白液が急激に冷却され、白液中に溶解していた無機化合物が活性炭表面に析出し、活性炭の活性が急速に低下し、活性炭の寿命が短くなるという問題がある。
【００１０】
前記の原因で活性が低下した活性炭では白液の酸化レベルが低下して、ポリサルファイドの生成またはチオ硫酸ナトリウムの生成が不十分となる。ポリサルファイド生成量の低下はパルプ収率低下の事態を引き起こす。また、チオ硫酸ナトリウム生成量の低下はアルカリ酸素脱リグニン工程での脱リグニン率低下の原因となり、後続の漂白工程の負荷を増大させる。一方、活性炭交換のために酸化塔を運転できない時間帯では、パルプ収率の低下や脱リグニン率の低下といった事態となり、これによる経済的損失は大きい。
【００１１】
従って、漂白クラフトパルプ製造工程において、白液酸化塔装置の酸化塔に充填している活性炭の寿命をのばすと同時に、ほぼ一定のレベルで白液を酸化でき、漂白パルプ製造工程の操業の安定化を達成できる技術の確立が望まれている。
【００１２】
【発明が解決しようとする課題】
本発明が解決しようとする課題は、漂白クラフトパルプ製造工程における活性炭触媒を充填した白液酸化塔装置の連続運転過程時、または停機後の再起用時、に起きる活性炭の触媒能低下および寿命の低下という問題を解決できる活性炭洗浄方法の提供にあり、更にこれを可能とした洗浄機構を備えた白液酸化装置の提供にある。
【００１３】
【課題を解決するための手段】
酸化塔内に充填されている触媒能が低下した時、または白液酸化塔装置の再起用時に、活性炭を、６０〜９５℃の加熱水で１５〜１２０分間洗浄するか、あるいは、酸性水溶液で洗浄した後に６０〜９５℃の加熱水で１５〜１２０分間洗浄する。既存の白液酸化塔装置にこの洗浄機構を組み込む。
【００１４】
【発明の実施の形態】
本発明の対象は、漂白クラフトパルプ製造工程で白液を空気酸化法により、ポリサルファイドを含有する蒸解用白液、またはチオ硫酸ナトリウム含有のアルカリ酸素脱リグニン用の酸化白液を調成する白液酸化工程であり、本発明が提供する技術は、白液酸化塔内部に充填されている触媒能が低下した活性炭の洗浄方法と、白液酸化塔装置の再起用時の活性炭の洗浄方法、及び、これが可能な白液酸化装置である。
【００１５】
本発明の活性炭の洗浄処理を施すタイミングは、以下の通りである。
（１）白液酸化塔装置の停機後の再起用時前。
これは２つのケースがある。１番目のケースは、白液由来の炭酸ナトリウムなどの化合物が活性炭触媒の表面に析出しており、活性炭の活性が低下している場合である。２番目のケースは、再起用時の時点で活性炭の触媒能は問題ないが、低温の装置内に高温の白液を通す時に、温度差が原因で、白液由来の炭酸ナトリウムなどの化合物が活性炭触媒の表面に析出する恐れがある場合であり、このケースでは本発明の加熱水による洗浄のみが行われ、活性炭を含む装置全体の加温を目的に行われる。
（２）オレンジリカー調成用の白液酸化装置の場合は、ポリサルファイド生成に係わる酸化効率が所定値以下になった時である。白液酸化塔を連続運転していると、白液中の前記主成分とは別の無機物質が活性炭に強く吸着し、蒸解用オレンジリカーを調成するための白液酸化塔ではポリサルファイド生成量が徐々に低下してくる。
（３）アルカリ酸素脱リグニン用の酸化白液を調成する白液酸化装置の場合は、白液中の硫化ナトリウムの酸化率が所定値以下になった時である。白液酸化塔を連続運転していると、白液中の前記主成分とは別の無機物質が活性炭に強く吸着し、酸化白液中の硫化ナトリウムが所定値以上になり、チオ硫酸ナトリウム生成量が低下してくる。
【００１６】
ポリサルファイド蒸解では、オレンジリカー中の水酸化ナトリウム濃度、硫化ナトリウム濃度、ポリサルファイド濃度、硫化度などをほぼ一定の水準に維持して木材チップをパルプ化している。ポリサルファイドの添加目的は、公知のようにパルプ収率を向上させることにあるが、下記の式で示されるポリサルファイド生成に係わる酸化効率が45%以下となると、オレンジリカー中のポリサルファイド濃度が低下し、パルプ収率に優位差が認められるようになる。従って、本発明では、酸化効率が45%以下に低下した時点で活性炭触媒の洗浄処理を行う。
ポリサルファイド生成に係わる酸化効率(%)
＝(生成したポリサルファイド濃度／消費されたNa2S濃度)×100…式（１）
ポリサルファイド濃度およびNa2S濃度：Sとしてのg/L
ポリサルファイド濃度およびNa2S濃度の測定法：Tappi T694 pm-82
【００１７】
アルカリ酸素脱リグニン処理は、蒸解後の未晒パルプをアルカリ性条件下で酸素で処理し、カッパーを大幅に低下させ、後続の漂白工程における漂白付加を低減することを目的としている。このアルカリ酸素脱リグニン処理では、従来の技術で述べたようにアルカリ性薬液として酸化白液が主に使用されている。この酸化白液においては、下記の式で計算される硫化ナトリウムの酸化率が90%以下になると、脱リグニン率が有意に低下し、漂白工程へ悪影響を及ぼす。従って、この時点で活性炭触媒の洗浄・再生処理を施す。
Na2Sの酸化率(%)
＝(1−酸化白液中のNa2S濃度／酸化前白液中のNa2S濃度)×100…式（２）
酸化白液中および酸化前白液中のNa2S濃度：Na2Oとしてのg/L
Na2S濃度の測定法：Tappi T694 pm-82
【００１８】
本発明の活性炭の洗浄には２通りの方法がある。第１の方法は、活性炭の活性を低下させている原因物質が比較的容易に溶解できる場合の処理方法であり、加熱水が洗浄液として使用される。水は通常の工業用水でも良いし、工業用水を公知の精密濾過機で処理した濾過水、ボイラー凝縮水、イオン交換樹脂で処理した純水などを使用しても良い。加熱水の温度は60〜95℃の範囲であり、70〜95℃が好ましく、80〜95℃が更に好ましい。加熱水が60℃未満では、溶解が不十分となる。高温ほど好ましいが、95℃を超えると沸騰の恐れもあり、熱エネルギーを多く要する分、コストが高くなるので好ましくない。加熱水による処理時間は、15〜120分間、好ましくは30〜120分間、更に好ましくは30〜60分間である。15分間未満では洗浄不十分であり、120分間を超えて洗浄しても洗浄効果はこれ以上向上しない。
【００１９】
第２の方法は、活性炭の活性を低下させている原因物質が活性炭に強く吸着・固着しているため、単なる加熱水による洗浄では、なかなか溶解できない場合の処理方法である。この場合、まず酸性水溶液で活性炭を処理した後、続いて前記の加熱水による洗浄を施すことにより活性炭の触媒能を回復できる。酸性水溶液の具体的なpHは2.0〜6.5、好ましくは3.0〜6.5である。pHが2.0未満では、酸化塔本体の金属腐食の恐れがあるので好ましくない。また、6.5を超えると洗浄効果が低下する。この酸性水溶液は無機酸の希釈水溶液であり、塩酸、硫酸、硝酸などが挙げられるが、取り扱い易さと価格の面から硫酸が好適である。また、活性炭に吸着または固着して活性炭の活性を低下させている物質中には多くの金属が含まれているので、pH=2.0〜6.5の範囲、好ましくは3.0〜6.5の範囲で金属を封鎖できるキレート剤を酸性水溶液に添加して使用すると金属除去効果が更に高まる。このキレート剤としてはエチレンジアミン四酢酸(EDTA)、トランス-1,2-シクロヘキサンジアミン四酢酸(CyDTA)、グリコールエーテルジアミン四酢酸(GEDTAまたはEGTA)、ジエチレントリアミン五酢酸(DTPA)等が挙げられる。キレート剤の濃度は0.0001〜0.1固形分重量%である。また、酸性水溶液の温度は常温で良く、5〜40℃の範囲であり、10〜40℃が好ましく、10〜30℃が更に好ましい。5℃未満では、溶解が不十分となる。40℃を超えると酸化塔の金属が酸により腐食される恐れがあるので好ましくない。処理時間は15〜120分間、好ましくは30〜120分間、更に好ましくは30〜60分間である。15分間未満では洗浄不十分であり、120分間を超えて洗浄しても洗浄効果はこれ以上向上しない。以上の酸性水溶液による処理の後、前記の第１の方法で述べた加熱水による洗浄を行う。
【００２０】
従来から用いられている白液酸化塔装置は、図１に示すように、酸化塔本体(１)、空気供給配管(２)、白液供給配管(３)、オレンジリカー出口配管(蒸解用白液の場合)または酸化白液出口配管(アルカリ酸素脱リグニン用酸化白液の場合)(４)とから構成されている。酸化本体内部には反応の触媒である活性炭が充填されている。白液は活性炭の存在下、空気と混合されることにより酸化反応が進行し、白液中の硫化ナトリウムはポリサルファイドまたはチオ硫酸ナトリウムへ酸化される。
【００２１】
本発明の白液酸化装置の構成図を図２〜図５に示す。図２と図３は、活性炭の洗浄処理用の水または水溶液が酸化塔上部から下降するダウンフローの場合である。図４と図５は、活性炭の洗浄処理用の水または水溶液が酸化塔底部から上昇するアップフローの場合である。
【００２２】
図２に示す白液酸化装置と活性炭の洗浄方法について説明する。この装置は、従来から用いられている白液酸化塔装置(酸化塔本体(１)、空気供給配管(２)、白液供給配管(３)、オレンジリカー出口配管または酸化白液出口配管(４))に、加熱水貯蔵タンク(５)、加熱水供給配管(６)、排水配管(７)を付加したものである。加熱水供給配管は酸化塔本体頂部に直接接続する。排水配管は酸化塔本体底部に直接配管する。
【００２３】
活性炭の洗浄処理を施すタイミングは、前記のように、白液酸化塔装置停機後の再起用時前と、オレンジリカーではポリサルファイド生成に係わる酸化効率が45%以下になった時、アルカリ酸素脱リグニン用の酸化白液では硫化ナトリウムの酸化率が90%以下になった時である(以下の図３、４、５でも同様である)。これらの場合には、空気供給配管中にあるバルブ(V1)、白液供給配管中にあるバルブ(V2)、オレンジリカー出口配管または酸化白液出口配管中のバルブ(V3)をそれぞれ閉め、加熱水供給配管中のバルブ(V4)、排水配管中のバルブ(V5)を開く。加熱水供給ポンプ(P1)を起動し、所定の時間だけ加熱水を酸化塔本体へ供給し、酸化塔内部の活性炭触媒を洗浄する。洗浄水は排水配管を通して排水される。この洗浄により、活性炭触媒の表面に析出している白液の主成分を主体とする無機化合物が溶解し、活性炭の触媒能が回復する。洗浄が終了した時点で、洗浄開始時とは逆の順で操作を行い、白液の酸化を開始する。
【００２４】
図３に示す白液酸化装置と活性炭の洗浄方法について説明する。この装置は、図２で示した白液酸化装置に、洗浄用の酸性水溶液貯蔵タンク(８)と該水溶液の供給配管を付加したものである。酸性水溶液貯蔵タンクは前述の加熱水タンクと併設し、両タンク底部から配管を取り出し、これを一本の配管(洗浄水供給配管(９))にまとめ、１台のポンプ(洗浄水供給ポンプ、P2)で酸化塔本体底部から各液を供給することが設備費を少なくする観点から好ましい。勿論、別々に配管を施し、別々のポンプで酸化塔本体へ供給することも可能である。
【００２５】
図３に示す方法では、空気供給配管中にあるバルブ(V1)、白液供給配管中にあるバルブ(V2)、オレンジリカー出口配管または酸化白液出口配管中のバルブ(V3)をそれぞれ閉め、白液の酸化を停止する。停止後、酸性水溶液供給配管中のバルブ(V6)、排水配管中のバルブ(V7)を開く。洗浄水供給ポンプ(P2)を起動させ、所定の時間だけ酸性水溶液を酸化塔本体へ供給する。次いで、加熱水供給配管中のバルブ(V4)を開け、酸性水溶液供給配管中のバルブ(V6)を閉める。所定の時間だけ加熱水を酸化塔本体へ供給する。洗浄水は排水配管を通して排水される。酸性水溶液による洗浄により、活性炭触媒の表面に強く吸着している物質を溶解させる。次いで、この酸性水溶液は加熱水で洗浄され活性炭の洗浄が終了する。洗浄が終了した時点で、洗浄開始時とは逆の順で操作を行い、白液の酸化を開始する。
【００２６】
図４に示す白液酸化装置と活性炭の洗浄方法について説明する。この装置は、従来から用いられている白液酸化塔装置(酸化塔本体(１)、空気供給配管(２)、白液供給配管(３)、オレンジリカー出口配管または酸化白液出口配管(４))に、加熱水貯蔵タンク(５)、加熱水供給配管(６)、排水配管(７)を付加したものである。加熱水供給配管は酸化塔本体底部に直接接続する。加熱水タンク底部から加熱水をポンプで移送し、加熱水配管を通して酸化塔本体へ加熱水を供給する。排水配管は酸化塔本体頂部に直接配管する。図４に示す装置の操作は、図２と同様である。
【００２７】
図５に示す白液酸化装置と活性炭の洗浄方法について説明する。この装置は、図４で示した白液酸化装置に、酸性水溶液貯蔵タンク(８)と該水溶液の供給配管を付加したものである。酸性水溶液貯蔵タンクは前述の加熱水タンクと併設し、各タンク底部から配管を取り出し、これを一本の配管(９)にまとめ、１台のポンプ(P2)で酸化塔本体底部から各液を供給することが設備費を少なくする観点から好ましい。勿論、別々に配管を施し、別々のポンプで酸化塔本体へ供給することも可能である。図５に示す装置の操作は、図３と同様である。
【００２８】
白液酸化塔装置停機後の再起用時は、当然、予め解っているから、このタイミングで、図２〜図５で示した白液酸化装置のいずれか一つの装置で活性炭触媒の洗浄を開始するが、前記の各バルブ開閉やポンプ起動・停止などの一連の操作を手作業で行っても良いし、自動的に行えるシーケンスを組んで実施しても良い。
【００２９】
白液の酸化効率が45%以下の判断は、オレンジリカーまたは酸化白液中の硫化ナトリウム濃度、ポリサルファイド濃度を人手で分析し、酸化効率を計算することによる。計算値が45%を下回る時点で、各バルブ開閉やポンプ起動・停止などの一連の操作を手作業で行っても良いし、自動的に行えるシーケンスを組んで実施しても良い。図２〜図５に示した白液酸化塔装置のオレンジリカー出口配管中に、またはポリサルファイド濃度計を設置して、その分析値の出力信号から酸化効率を自動的に計算することが望ましいが、現状、ポリサルファイド濃度の自動分析計は存在しない。
【００３０】
酸化白液中の硫化ナトリウムの酸化率が90%以下の判断は、酸化前後の白液中の硫化ナトリウムを人手で分析した結果に基づいても良いし、図２〜図５に示した白液酸化塔装置の酸化白液出口配管中と、酸化前白液を採取可能な箇所との２箇所に、それぞれ硫化ナトリウム濃度計(例えば、PROCHCK社の苛性化自動滴定分析装置など)を設置して、その測定値に基づいても良い。計算値が90%を下回る時点で、各バルブ開閉やポンプ起動・停止などの一連の操作を手作業で行っても良いし、自動的に行えるシーケンスを組んで実施しても良い。
【００３１】
【実施例】
次に実施例に基づき、本発明を更に詳細に説明するが、本発明はこれらに限定されるものではない。
【００３２】
【実施例１】
白液酸化塔にクラフトパルプ工場の白液(活性アルカリ濃度：100g/L、硫化度：30%)を通じ、オレンジリカーを連続して調成した。白液の硫化ナトリウム濃度とオレンジリカーの硫化ナトリウム濃度ならびにポリサルファイド濃度の測定結果から前記の式(１)で酸化効率を計算し、酸化効率が45％を下回った時点で、停機し、図２に示す方法で加熱水により白液酸化塔内の活性炭を洗浄し、装置を再起用した。酸化効率の変化を図６に示す。
【００３３】
【比較例１】
加熱水を使用した活性炭の洗浄をしないこと以外は実施例１と同様の操作を行った。酸化効率の変化を図６に示す。
【００３４】
図６に示した結果から、比較例１では、活性炭を連続使用して約６ヶ月後には酸化効率が45%以下となり、活性炭を交換しなければならなかった。実施例１では酸化効率が45%以下になった時点で加熱水による洗浄をしたことにより、活性炭の寿命を約12ヶ月まで延ばすことができた。
【００３５】
【実施例２】
白液酸化塔にクラフトパルプ工場の白液(活性アルカリ濃度：100g/L、硫化度：30%)を通じ、アルカリ酸素脱リグニン用の酸化白液を連続して調成した。白液酸化前後の硫化ナトリウム濃度の測定結果から硫化ナトリウムの酸化率を前記の式(２)で計算し、酸化率が90%以下に時点で、停機し、図２に示す方法で加熱水により白液酸化塔内の活性炭を洗浄し、再起用した。酸化率の変化を図７に示す。
【００３６】
【比較例２】
加熱水を使用した活性炭の洗浄をしないこと以外は実施例２と同様の操作を行った。酸化率の変化を図７に示す。
【００３７】
図７に示した結果から、比較例２では、活性炭を連続使用して約8ヶ月後には酸化率が90以下となり、活性炭を交換しなければならなかった。実施例２では酸化率が90%以下になった時点で加熱水による洗浄をしたことにより、活性炭の寿命を約20ヶ月以上とすることができる。
【００３８】
【実施例３】
白液酸化塔にクラフトパルプ工場の白液(活性アルカリ濃度：100g/L、硫化度：30%)を通じ、オレンジリカーを連続して調成した。白液の硫化ナトリウム濃度とオレンジリカーの硫化ナトリウム濃度ならびにポリサルファイド濃度の測定結果から前記の式(１)で酸化効率を計算し、酸化効率が45％を下回った時点で、停機し、図５に示す方法で酸性水溶液(硫酸水溶液、ｐH＝4.0、温度：30℃)により白液酸化塔内の活性炭を洗浄後、加熱水により更に洗浄し、再起用した。酸化効率の変化を図８に示す。
【００３９】
【比較例３】
酸性水溶液、加熱水を用いて酸化塔を洗浄しないこと以外は実施例３と同様の操作を行った。酸化効率の変化を図８に示す。
【００４０】
図８に示した結果から、比較例３では、活性炭を連続使用して約5ヶ月後には酸化効率が45%以下となり、活性炭を交換しなければならなかった。実施例３では酸化効率が45%以下になった時点で加熱水による洗浄をしたことにより、活性炭の寿命を約30ヶ月までは確実に延ばすことができた。
【００４１】
【実施例４】
白液酸化塔にクラフトパルプ工場の白液(活性アルカリ濃度：100g/L、硫化度：30%)を通じ、アルカリ酸素脱リグニン用の酸化白液を連続して調成した。白液酸化前後の硫化ナトリウム濃度の測定結果から硫化ナトリウムの酸化率を前記の式(２)で計算し、酸化率が90%以下に時点で、停機し、図５に示す方法で酸性水溶液(硫酸水溶液、ｐH＝4.0、温度：30℃)により白液酸化塔内の活性炭を洗浄後、加熱水により更に洗浄し、再起用した。酸化率の変化を図９に示す。
【００４２】
【比較例４】
酸性水溶液、加熱水を用いて酸化塔内に活性炭を洗浄しないこと以外は実施例４と同様の操作を行った。酸化率の変化を図９に示す。
【００４３】
図９に示した結果から、比較例４では、活性炭を連続使用して約5ヶ月後には酸化率が90以下となり、活性炭を交換しなければならなかった。実施例５では酸化率が90%以下になった時点で加熱水による洗浄をしたことにより、活性炭の寿命を約30ヶ月以上とすることができる。
【００４４】
【発明の効果】
漂白クラフトパルプ製造工程におけるポリサルファイド蒸解液またはアルカリ酸素脱リグニン用の酸化白液を調成する酸化塔装置において、該装置の連続運転過程時や停機後の再起用時に起きる活性炭の触媒能の低下および寿命の低下という問題を、加熱水による洗浄、あるいは酸性水溶液の洗浄と加熱水による洗浄の組み合わせにより解決できる。更にこの活性炭の触媒能の回復により、パルプ収率の向上や漂白薬品の低減の効果が得られる。
【図面の簡単な説明】
【図１】従来から用いられている白液酸化塔装置の構成図である。
【図２】本発明のダウンフロー型白液酸化装置の構成図である。
【図３】本発明のダウンフロー型白液酸化装置の構成図である。
【図４】本発明のアップフロー型白液酸化装置の構成図である。
【図５】本発明のアップフロー型白液酸化装置の構成図である。
【図６】実施例１と比較例１を比較した図である。
【図７】実施例２と比較例２を比較した図である。
【図８】実施例３と比較例３を比較した図である。
【図９】実施例４と比較例４を比較した図である。
【符号の説明】
１．酸化塔本体
２．空気供給配管
３．白液供給配管
４．オレンジリカー出口配管または酸化白液出口配管
５．加熱水貯蔵タンク
６．加熱水供給配管
７．排水配管
８．酸性水溶液貯蔵タンク
９．洗浄水供給配管
V1〜V6．各配管中のバルブ
P1,P2．ポンプ[0001]
BACKGROUND OF THE INVENTION
The technical field to which the present invention relates is a method for cleaning an activated carbon catalyst for white liquor oxidation in a kraft pulp manufacturing process, which can recover the activity of activated carbon having reduced catalytic ability, and cleaning when a white liquor oxidation apparatus is used The present invention relates to a method, and further relates to a white liquor oxidation apparatus having a cleaning mechanism capable of performing the cleaning.
[0002]
[Prior art]
In the kraft pulp cooking and bleaching process, activated carbon, which is a reaction catalyst, is used as a device to convert the sodium sulfide into polysulfide or sodium thiosulfate by air oxidation of the cooking liquor containing sodium sulfide (hereinafter referred to as white liquor). An oxidation reaction tower packed with is used. Polysulfide-containing white liquor is used as a chemical for kraft cooking. Further, when the white liquor is further oxidized, polysulfide is oxidized and converted to sodium thiosulfate. This white liquor containing sodium thiosulfate is used as a chemical solution (oxidized white liquor) for alkaline oxygen delignification after kraft cooking.
[0003]
Methods for producing polysulfide from white liquor containing sodium sulfide include air oxidation in the presence of activated carbon catalyst (see Patent Document 1), air oxidation in the presence of lime mud and catalyst (
[0004]
As an alkali source used for the alkaline oxygen delignification reaction in the bleached kraft pulp manufacturing process, an oxidized white liquor obtained by oxidizing a sulfur-containing atomic group to sodium thiosulfate in the presence of a catalyst is used. . Here, oxygen delignification is possible even if sodium hydroxide brought in from outside the system is used, but this means that sodium hydroxide is brought in from outside the system. It becomes a problem. Further, since white water from the oxygen delignification step is usually recovered to a recovery boiler, bringing sodium hydroxide from outside the system will break the balance of the chemical recovery system. In order to keep the balance of the chemical recovery system, an alkaline source derived from white liquor such as oxidized white liquor is mainly used.
[0005]
Conventionally used white liquor oxidation equipment (hereinafter referred to as white liquor oxidation tower equipment) is an oxidation tower body, air supply piping, white liquor supply piping, orange liquor outlet piping (in the case of cooking white liquor) or It comprises an oxidized white liquor outlet pipe (in the case of an oxidized white liquor for alkaline oxygen delignification) and the like, and activated carbon is packed as a reaction catalyst inside the oxidation tower. As this activated carbon, for example, powdered carbon black has been reported (see Non-Patent Document 1). Further, it is described that activated carbon is hydrophobized with a water-insoluble substance such as polytetrafluoroethylene and polyethylene, and the use of the hydrophobized activated carbon facilitates separation and recovery of activated carbon and improves its catalytic activity. (See Non-Patent Document 2). Further, it is described that carbon or activated carbon is partially hydrophobized with a hydrophobic substance such as polytetrafluoroethylene, polyethylene, polystyrene, or fluorocarbon resin (see Patent Document 10).
[0006]
[Patent Document 1]
JP 47-10217 A
[Patent Document 2]
JP-A-8-209573
[Patent Document 3]
JP-A-9-87987
[Patent Document 4]
JP 56-149304 A
[Patent Document 5]
JP-A-8-311790
[Patent Document 6]
Japanese Patent Laid-Open No. 54-151602
[Patent Document 7]
JP-T-8-512099, International Publication WO95 / 0071 Pamphlet
[Patent Document 8]
Japanese Unexamined Patent Publication No. 47-10212
[Patent Document 9]
JP-A-53-92981
[Non-Patent Document 1]
Yoshida et al. (Netsusokutei 8 (1) 1981, 2-5)
[Non-Patent Document 2]
Catalyst Vol.23, No.4, April 1981, P293-295
[Patent Document 10]
Japanese Patent Publication No. 50-40395
[0007]
Activated carbon is excellent as a sulfide oxidation catalyst because it has a large surface area, is corrosion resistant, and is electrically conductive. Due to this characteristic, in the bleached kraft pulp manufacturing process, white liquor containing polysulfide by oxidizing sodium sulfide in white liquor (this liquor is colored orange, so called orange liquor. Activated carbon is used as a catalyst in the production of oxidized white liquor obtained by oxidizing sodium sulfide in white liquor to sodium thiosulfate.
[0008]
However, in addition to sodium and sulfur, other inorganic compounds are present in the white liquor. When the white liquor is continuously oxidized in an oxidation tower, activated carbon, which is a reaction site for the production of polysulfide or sodium thiosulfate, is used. There is a problem that the inorganic compound in the white liquor accumulates on the surface and the activated carbon surface area decreases, so that the activity of the activated carbon is reduced and sufficient polysulfide or sodium thiosulfate cannot be produced. Moreover, when the activity of activated carbon falls, the countermeasure may be to increase the amount of air blown and increase the amount of oxygen supplied to the oxidation tower to control the production of polysulfide or sodium thiosulfate. However, in the case of orange liquor preparation, since the amount of oxygen in the reaction field increases, the polysulfide once produced is further oxidized to thiosulfate ions that are not effective in cooking, and the yield improvement effect by polysulfide during cooking is increased. There arises a problem that it cannot be obtained sufficiently.
[0009]
Furthermore, when restarting after stopping the white liquor oxidation tower device, white liquor and air are supplied to the oxidation tower, but immediately after reactivation, the activated carbon in the oxidation tower and the oxidation tower has dropped to near room temperature, When supplying white liquor, usually 70 ° C or higher, flowing through the process to the oxidation tower, the white liquor was cooled rapidly and dissolved in the white liquor due to the temperature difference between the white liquor and the oxidation tower and activated carbon in the oxidation tower. There is a problem that the inorganic compound is deposited on the activated carbon surface, the activity of the activated carbon is rapidly reduced, and the life of the activated carbon is shortened.
[0010]
In the activated carbon whose activity is reduced due to the above-mentioned causes, the oxidation level of the white liquor is lowered and the production of polysulfide or sodium thiosulfate is insufficient. A decrease in the amount of polysulfide produced causes a decrease in pulp yield. In addition, a decrease in the amount of sodium thiosulfate produced causes a decrease in the delignification rate in the alkaline oxygen delignification step, increasing the load on the subsequent bleaching step. On the other hand, in the time zone when the oxidation tower cannot be operated due to the exchange of activated carbon, a situation such as a decrease in pulp yield and a decrease in delignification rate occurs, resulting in a large economic loss.
[0011]
Therefore, in the bleaching kraft pulp manufacturing process, the life of the activated carbon packed in the oxidation tower of the white liquor oxidation tower equipment can be extended, and at the same time the white liquor can be oxidized at an almost constant level, which stabilizes the operation of the bleaching pulp manufacturing process. Establishment of technology that can achieve this is desired.
[0012]
[Problems to be solved by the invention]
The problem to be solved by the present invention is that the activated carbon catalyst packed with activated carbon catalyst in the bleaching kraft pulp manufacturing process is activated during the continuous operation process, or when it is restarted after stopping, the decrease in the catalytic activity and the life of activated carbon. The object is to provide an activated carbon cleaning method capable of solving the problem of reduction, and further to provide a white liquor oxidation apparatus equipped with a cleaning mechanism that enables this.
[0013]
[Means for Solving the Problems]
When the catalytic capacity packed in the oxidation tower is reduced, or when the white liquor oxidation tower device is restarted, activated carbon is used. 60-95 ° C With heated water 15-120 minutes After washing or with an acidic aqueous solution 60-95 ° C With heated water 15-120 minutes Wash. This cleaning mechanism is incorporated into an existing white liquor oxidation tower apparatus.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
The object of the present invention is to prepare white liquor for cooking white liquor containing polysulfide or oxidized white liquor for alkaline oxygen delignification containing sodium thiosulfate by air oxidation in bleached kraft pulp manufacturing process It is an oxidation process, and the technology provided by the present invention includes a cleaning method for activated carbon having a reduced catalytic ability filled in the white liquor oxidation tower, a cleaning method for activated carbon when the white liquor oxidation tower apparatus is restarted, and This is a white liquor oxidation device capable of this.
[0015]
The timing for performing the cleaning treatment of the activated carbon of the present invention is as follows.
(1) Before restarting after stopping the white liquor oxidation tower device.
There are two cases. The first case is a case where a compound such as sodium carbonate derived from white liquor is deposited on the surface of the activated carbon catalyst and the activity of the activated carbon is reduced. In the second case, there is no problem with the catalytic ability of the activated carbon at the time of re-use, but when a hot white liquor is passed through a low temperature apparatus, a compound such as sodium carbonate derived from the white liquor is caused by the temperature difference. This is a case where there is a risk of precipitation on the surface of the activated carbon catalyst. In this case, only cleaning with the heated water of the present invention is performed, and the entire apparatus including activated carbon is heated for the purpose of heating.
(2) In the case of a white liquor oxidizer for preparing orange liquor, it is when the oxidation efficiency related to polysulfide formation is below a predetermined value. When the white liquor oxidation tower is continuously operated, inorganic substances other than the main components in the white liquor are strongly adsorbed on the activated carbon, and the amount of polysulfide produced in the white liquor oxidation tower for preparing orange liquor for cooking Gradually decreases.
(3) In the case of a white liquor oxidizer for preparing an oxidized white liquor for alkaline oxygen delignification, it is when the oxidation rate of sodium sulfide in the white liquor is below a predetermined value. When the white liquor oxidation tower is operated continuously, inorganic substances other than the main components in the white liquor are strongly adsorbed on the activated carbon, and sodium sulfide in the oxidized white liquor exceeds the specified value, producing sodium thiosulfate. The amount will decrease.
[0016]
In polysulfide cooking, wood chips are pulped while maintaining sodium hydroxide concentration, sodium sulfide concentration, polysulfide concentration, sulfidity, etc. in orange liquor at a substantially constant level. The purpose of adding polysulfide is to improve the pulp yield as is known, but when the oxidation efficiency related to polysulfide production represented by the following formula is 45% or less, the polysulfide concentration in orange liquor is reduced, A difference in the pulp yield is recognized. Therefore, in the present invention, the activated carbon catalyst is washed when the oxidation efficiency drops to 45% or less.
Oxidation efficiency for polysulfide production (%)
= (Polysulfide concentration produced / Na consumed 2 S concentration) x 100 ... Formula (1)
Polysulfide concentration and Na 2 S concentration: g / L as S
Polysulfide concentration and Na 2 S concentration measurement method: Tappi T694 pm-82
[0017]
The purpose of the alkaline oxygen delignification treatment is to treat the unbleached pulp after cooking with oxygen under alkaline conditions, greatly reducing the copper, and reducing the bleach addition in the subsequent bleaching step. In this alkaline oxygen delignification treatment, as described in the prior art, oxidized white liquor is mainly used as an alkaline chemical. In this oxidized white liquor, when the oxidation rate of sodium sulfide calculated by the following formula is 90% or less, the delignification rate is significantly reduced, which adversely affects the bleaching process. Therefore, at this time, the activated carbon catalyst is washed and regenerated.
Na 2 S oxidation rate (%)
= (1-Na in oxidized white liquor 2 S concentration / Na in white liquor before oxidation 2 S concentration) x 100 ... Formula (2)
Na in oxidized white liquor and white liquor before oxidation 2 S concentration: Na 2 G / L as O
Na 2 S concentration measurement method: Tappi T694 pm-82
[0018]
There are two methods for cleaning the activated carbon of the present invention. The first method is a treatment method in which a causative substance that decreases the activity of activated carbon can be dissolved relatively easily, and heated water is used as a cleaning liquid. The water may be ordinary industrial water, or filtered water obtained by treating industrial water with a known precision filter, boiler condensate, or pure water treated with an ion exchange resin. The temperature of the heated water is in the range of 60 to 95 ° C, preferably 70 to 95 ° C, and more preferably 80 to 95 ° C. When heated water is less than 60 ° C., dissolution is insufficient. A higher temperature is preferable, but if it exceeds 95 ° C., there is a fear of boiling, and the amount of heat energy required is increased, resulting in an increase in cost. The treatment time with heated water is 15 to 120 minutes, preferably 30 to 120 minutes, more preferably 30 to 60 minutes. If the cleaning time is less than 15 minutes, the cleaning is insufficient. Even if the cleaning time is longer than 120 minutes, the cleaning effect is not further improved.
[0019]
The second method is a treatment method in which the causative substance that decreases the activity of the activated carbon is strongly adsorbed and adhered to the activated carbon, so that it cannot be easily dissolved by simple washing with heated water. In this case, after the activated carbon is first treated with an acidic aqueous solution, the catalytic ability of the activated carbon can be recovered by washing with the heated water. The specific pH of the acidic aqueous solution is 2.0 to 6.5, preferably 3.0 to 6.5. A pH of less than 2.0 is not preferable because there is a risk of metal corrosion of the oxidation tower body. On the other hand, if it exceeds 6.5, the cleaning effect decreases. This acidic aqueous solution is a dilute aqueous solution of inorganic acid, and examples thereof include hydrochloric acid, sulfuric acid, nitric acid, etc., but sulfuric acid is preferred from the viewpoint of ease of handling and cost. In addition, since many metals are contained in the substance that is adsorbed or fixed to the activated carbon to reduce the activity of the activated carbon, the metal is blocked in the range of pH = 2.0 to 6.5, preferably in the range of 3.0 to 6.5. When a chelating agent that can be added to an acidic aqueous solution is used, the metal removal effect is further enhanced. Examples of the chelating agent include ethylenediaminetetraacetic acid (EDTA), trans-1,2-cyclohexanediaminetetraacetic acid (CyDTA), glycol etherdiaminetetraacetic acid (GEDTA or EGTA), diethylenetriaminepentaacetic acid (DTPA), and the like. The concentration of the chelating agent is 0.0001-0.1% solids by weight. Moreover, the temperature of acidic aqueous solution may be normal temperature, is the range of 5-40 degreeC, 10-40 degreeC is preferable and 10-30 degreeC is still more preferable. Below 5 ° C, dissolution is insufficient. If it exceeds 40 ° C, the metal in the oxidation tower may be corroded by acid, which is not preferable. The treatment time is 15 to 120 minutes, preferably 30 to 120 minutes, more preferably 30 to 60 minutes. If the cleaning time is less than 15 minutes, the cleaning is insufficient. Even if the cleaning time is longer than 120 minutes, the cleaning effect is not further improved. After the treatment with the above acidic aqueous solution, washing with heated water described in the first method is performed.
[0020]
As shown in FIG. 1, the white liquor oxidation tower apparatus conventionally used includes an oxidation tower body (1), an air supply pipe (2), a white liquor supply pipe (3), an orange liquor outlet pipe (white for cooking) (In the case of liquid) or oxidized white liquor outlet pipe (in the case of oxidized white liquor for alkaline oxygen delignification) (4). The inside of the oxidation body is filled with activated carbon which is a reaction catalyst. When white liquor is mixed with air in the presence of activated carbon, the oxidation reaction proceeds, and sodium sulfide in the white liquor is oxidized to polysulfide or sodium thiosulfate.
[0021]
The block diagram of the white liquor oxidation apparatus of this invention is shown in FIGS. FIG. 2 and FIG. 3 show the case of a down flow in which water or an aqueous solution for cleaning the activated carbon descends from the upper part of the oxidation tower. 4 and 5 show the case of upflow in which water or an aqueous solution for the activated carbon cleaning treatment rises from the bottom of the oxidation tower.
[0022]
The white liquor oxidation apparatus and activated carbon cleaning method shown in FIG. 2 will be described. This apparatus is a white liquor oxidation tower apparatus (an oxidation tower body (1), an air supply pipe (2), a white liquor supply pipe (3), an orange liquor outlet pipe or an oxidized white liquor outlet pipe (4 )), A heated water storage tank (5), a heated water supply pipe (6), and a drain pipe (7) are added. The heated water supply pipe is directly connected to the top of the oxidation tower main body. The drainage pipe is connected directly to the bottom of the oxidation tower body.
[0023]
As described above, the timing for performing the cleaning treatment of the activated carbon is prior to the restart after the white liquor oxidation tower is stopped, and when the oxidation efficiency related to polysulfide formation in Orange Liquor is 45% or less, the alkaline oxygen delignification is performed. This is when the oxidation rate of sodium sulfide is 90% or less in the white oxide liquid for use (the same applies to FIGS. 3, 4 and 5 below). In these cases, the valve (V1) in the air supply pipe, the valve (V2) in the white liquor supply pipe, the valve in the orange liquor outlet pipe or the oxidized white liquor outlet pipe (V3) are closed and heated. Open the valve (V4) in the water supply pipe and the valve (V5) in the drain pipe. The heated water supply pump (P1) is started, heated water is supplied to the oxidation tower body for a predetermined time, and the activated carbon catalyst inside the oxidation tower is washed. Wash water is drained through drain pipes. By this washing, the inorganic compound mainly composed of the main component of the white liquor deposited on the surface of the activated carbon catalyst is dissolved, and the catalytic ability of the activated carbon is recovered. When the washing is completed, the operation is performed in the reverse order of the washing start, and the oxidation of the white liquor is started.
[0024]
The white liquor oxidation apparatus and activated carbon cleaning method shown in FIG. 3 will be described. This apparatus is obtained by adding an acidic aqueous solution storage tank (8) for cleaning and a supply pipe for the aqueous solution to the white liquor oxidation apparatus shown in FIG. The acidic aqueous solution storage tank is provided with the above-mentioned heated water tank, and the pipes are taken out from the bottom of both tanks, and are combined into one pipe (washing water supply pipe (9)). One pump (washing water supply pump, In P2), it is preferable to supply each liquid from the bottom of the oxidation tower body from the viewpoint of reducing the equipment cost. Of course, it is also possible to provide piping separately and supply it to the oxidation tower body with separate pumps.
[0025]
In the method shown in FIG. 3, the valve (V1) in the air supply pipe, the valve (V2) in the white liquor supply pipe, the valve (V3) in the orange liquor outlet pipe or the oxidized white liquor outlet pipe are closed. Stop oxidation of white liquor. After stopping, open the valve (V6) in the acidic aqueous solution supply pipe and the valve (V7) in the drain pipe. The washing water supply pump (P2) is activated to supply the acidic aqueous solution to the oxidation tower main body for a predetermined time. Next, the valve (V4) in the heated water supply pipe is opened, and the valve (V6) in the acidic aqueous solution supply pipe is closed. Heating water is supplied to the oxidation tower body for a predetermined time. Wash water is drained through drain pipes. The substance strongly adsorbed on the surface of the activated carbon catalyst is dissolved by washing with an acidic aqueous solution. Next, this acidic aqueous solution is washed with heated water, and the washing of the activated carbon is completed. When the washing is completed, the operation is performed in the reverse order of the washing start, and the oxidation of the white liquor is started.
[0026]
The white liquor oxidation apparatus and activated carbon cleaning method shown in FIG. 4 will be described. This apparatus is a white liquor oxidation tower apparatus (an oxidation tower body (1), an air supply pipe (2), a white liquor supply pipe (3), an orange liquor outlet pipe or an oxidized white liquor outlet pipe (4 )), A heated water storage tank (5), a heated water supply pipe (6), and a drain pipe (7) are added. The heated water supply pipe is directly connected to the bottom of the oxidation tower main body. The heated water is pumped from the bottom of the heated water tank, and the heated water is supplied to the oxidation tower body through the heated water pipe. The drainage pipe is connected directly to the top of the oxidation tower body. The operation of the apparatus shown in FIG. 4 is the same as that of FIG.
[0027]
The white liquor oxidation apparatus and activated carbon cleaning method shown in FIG. 5 will be described. This apparatus is obtained by adding an acidic aqueous solution storage tank (8) and a supply pipe for the aqueous solution to the white liquor oxidation apparatus shown in FIG. The acidic aqueous solution storage tank is attached to the above-mentioned heated water tank, and the piping is taken out from the bottom of each tank, and this is combined into a single pipe (9), and each solution is discharged from the bottom of the oxidation tower body with one pump (P2). Supply is preferable from the viewpoint of reducing facility costs. Of course, it is also possible to provide piping separately and supply it to the oxidation tower body with separate pumps. The operation of the apparatus shown in FIG. 5 is the same as that of FIG.
[0028]
When restarting after the white liquor oxidation tower is stopped, it is naturally understood in advance, so at this timing, cleaning of the activated carbon catalyst is started in any one of the white liquor oxidizers shown in FIGS. However, a series of operations such as opening / closing of each valve and starting / stopping of the pump may be performed manually, or a sequence that can be automatically performed may be set.
[0029]
The determination that the white liquor oxidation efficiency is 45% or less is based on manually analyzing the sodium sulfide concentration and polysulfide concentration in orange liquor or oxidized white liquor and calculating the oxidation efficiency. When the calculated value falls below 45%, a series of operations such as opening / closing of each valve and starting / stopping of the pump may be performed manually, or an automatically performed sequence may be set. Although it is desirable to install the polysulfide concentration meter in the orange liquor outlet pipe of the white liquor oxidation tower apparatus shown in FIGS. 2 to 5 or to calculate the oxidation efficiency automatically from the output signal of the analysis value, At present, there is no automatic analyzer for polysulfide concentration.
[0030]
The determination that the oxidation rate of sodium sulfide in the oxidized white liquor is 90% or less may be based on the result of manual analysis of the sodium sulfide in the white liquor before and after oxidation, or the white liquor shown in FIGS. Install sodium sulfide concentration meters (such as PROCHCK's causticizing automatic titration analyzer) in two places, the oxidation white liquor outlet pipe of the oxidation tower and the place where the white liquor can be collected. , Based on the measured value. When the calculated value falls below 90%, a series of operations such as opening / closing of each valve and starting / stopping of the pump may be performed manually, or a sequence that can be automatically performed may be set.
[0031]
【Example】
EXAMPLES Next, although this invention is demonstrated in detail based on an Example, this invention is not limited to these.
[0032]
[Example 1]
Orange liquor was continuously prepared through white liquor from the kraft pulp mill (active alkali concentration: 100 g / L, sulfidity: 30%) in the white liquor oxidation tower. From the measurement results of sodium sulfide concentration of white liquor, sodium sulfide concentration of orange liquor and polysulfide concentration, the oxidation efficiency was calculated by the above formula (1). The activated carbon in the white liquor oxidation tower was washed with heated water by the method shown, and the apparatus was reused. The change in oxidation efficiency is shown in FIG.
[0033]
[Comparative Example 1]
The same operation as in Example 1 was performed except that the activated carbon was not washed with heated water. The change in oxidation efficiency is shown in FIG.
[0034]
From the results shown in FIG. 6, in Comparative Example 1, the activated carbon was continuously used, and after about 6 months, the oxidation efficiency became 45% or less, and the activated carbon had to be replaced. In Example 1, the lifetime of the activated carbon could be extended to about 12 months by washing with heated water when the oxidation efficiency reached 45% or less.
[0035]
[Example 2]
Through the white liquor oxidation tower, white liquor from the kraft pulp mill (active alkali concentration: 100 g / L, sulfidity: 30%) was used to continuously prepare an oxidized white liquor for alkaline oxygen delignification. From the measurement result of sodium sulfide concentration before and after white liquor oxidation, the oxidation rate of sodium sulfide is calculated by the above formula (2). When the oxidation rate is less than 90%, it is stopped and heated water is used as shown in FIG. The activated carbon in the white liquor oxidation tower was washed and reused. The change in the oxidation rate is shown in FIG.
[0036]
[Comparative Example 2]
The same operation as in Example 2 was performed except that the activated carbon was not washed with heated water. The change in the oxidation rate is shown in FIG.
[0037]
From the results shown in FIG. 7, in Comparative Example 2, the activated carbon was continuously used, and after about 8 months, the oxidation rate became 90 or less, and the activated carbon had to be replaced. In Example 2, the lifetime of the activated carbon can be increased to about 20 months or more by washing with heated water when the oxidation rate becomes 90% or less.
[0038]
[Example 3]
Orange liquor was continuously prepared through white liquor from the kraft pulp mill (active alkali concentration: 100 g / L, sulfidity: 30%) in the white liquor oxidation tower. From the measurement results of sodium sulfide concentration of white liquor, sodium sulfide concentration of orange liquor and polysulfide concentration, the oxidation efficiency was calculated by the above formula (1), and when the oxidation efficiency fell below 45%, it was stopped and shown in FIG. The activated carbon in the white liquor oxidation tower was washed with an acidic aqueous solution (sulfuric acid aqueous solution, pH = 4.0, temperature: 30 ° C.) by the method shown, then further washed with heated water and reused. The change in oxidation efficiency is shown in FIG.
[0039]
[Comparative Example 3]
The same operation as in Example 3 was performed except that the oxidation tower was not washed with an acidic aqueous solution and heated water. The change in oxidation efficiency is shown in FIG.
[0040]
From the results shown in FIG. 8, in Comparative Example 3, the activated carbon was continuously used, and after about 5 months, the oxidation efficiency became 45% or less, and the activated carbon had to be replaced. In Example 3, when the oxidation efficiency became 45% or less, the activated carbon was washed with heated water, so that the life of the activated carbon could be reliably extended to about 30 months.
[0041]
[Example 4]
Through the white liquor oxidation tower, white liquor from the kraft pulp mill (active alkali concentration: 100 g / L, sulfidity: 30%) was used to continuously prepare an oxidized white liquor for alkaline oxygen delignification. From the measurement result of sodium sulfide concentration before and after white liquor oxidation, the oxidation rate of sodium sulfide was calculated by the above formula (2), and when the oxidation rate was 90% or less, it was stopped and the acidic aqueous solution ( The activated carbon in the white liquor oxidation tower was washed with an aqueous sulfuric acid solution (pH = 4.0, temperature: 30 ° C.), then further washed with heated water and reused. The change in the oxidation rate is shown in FIG.
[0042]
[Comparative Example 4]
The same operation as in Example 4 was performed except that the activated carbon was not washed in the oxidation tower using an acidic aqueous solution and heated water. The change in the oxidation rate is shown in FIG.
[0043]
From the results shown in FIG. 9, in Comparative Example 4, after about 5 months of continuous use of activated carbon, the oxidation rate became 90 or less, and the activated carbon had to be replaced. In Example 5, the lifetime of the activated carbon can be increased to about 30 months or more by washing with heated water when the oxidation rate becomes 90% or less.
[0044]
【The invention's effect】
In an oxidation tower apparatus for preparing a polysulfide cooking liquor or an oxidized white liquor for alkaline oxygen delignification in the bleached kraft pulp manufacturing process, a reduction in the catalytic activity of activated carbon that occurs during the continuous operation process of the apparatus or when it is restarted after stopping The problem of reduced life can be solved by washing with heated water or a combination of washing with an acidic aqueous solution and washing with heated water. Further, the recovery of the catalytic ability of the activated carbon can improve the pulp yield and reduce bleaching chemicals.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a white liquor oxidation tower apparatus conventionally used.
FIG. 2 is a configuration diagram of a downflow type white liquor oxidation apparatus of the present invention.
FIG. 3 is a configuration diagram of a downflow type white liquor oxidation apparatus of the present invention.
FIG. 4 is a configuration diagram of an upflow type white liquor oxidation apparatus according to the present invention.
FIG. 5 is a configuration diagram of an upflow type white liquor oxidation apparatus of the present invention.
6 is a diagram comparing Example 1 and Comparative Example 1. FIG.
7 is a diagram comparing Example 2 and Comparative Example 2. FIG.
8 is a diagram comparing Example 3 and Comparative Example 3. FIG.
9 is a diagram comparing Example 4 and Comparative Example 4. FIG.
[Explanation of symbols]
1. Oxidation tower body
2. Air supply piping
3. White liquid supply piping
4). Orange liquor outlet piping or oxidized white liquor outlet piping
5). Heated water storage tank
6). Heated water supply piping
7). Drain pipe
8). Acidic aqueous solution storage tank
9. Wash water supply piping
V1 to V6. Valve in each pipe
P1, P2. pump
Claims (4)
Ａ：白液酸化塔装置の停機後の再起用時前
Ｂ：オレンジリカー調成においてポリサルファイド生成に係わる酸化効率が４５％以下になったとき
Ｃ：アルカリ酸素脱リグニン用の酸化白液調成において硫化ナトリウムの酸化率が９０％以下になったとき A method for cleaning an activated carbon catalyst for white liquor oxidation in a kraft pulp manufacturing process, wherein activated carbon having a reduced catalytic ability at any of the following timings A to C is washed with heated water at 60 to 95 ° C. for 15 to 120 minutes . A method for cleaning an activated carbon catalyst, characterized in that:
A: Before restarting after stopping the white liquor oxidation tower
B: When the oxidation efficiency related to polysulfide formation becomes 45% or less in orange liquor preparation
C: When the oxidation rate of sodium sulfide is 90% or less in the preparation of oxidized white liquor for alkaline oxygen delignification
Ａ：白液酸化塔装置停機後の再起用時前
Ｂ：オレンジリカー調成においてポリサルファイド生成に係わる酸化効率が４５％以下になったとき
Ｃ：アルカリ酸素脱リグニン用の酸化白液調成において硫化ナトリウムの酸化率が９０％以下になったとき A method for cleaning an activated carbon catalyst for white liquor oxidation in a kraft pulp manufacturing process, wherein activated carbon having a reduced catalytic ability at any of the following timings A to C is washed with an acidic aqueous solution, and further heated at 60 to 95 ° C. cleaning method of the activated carbon catalyst, characterized in that for cleaning by Ri 15 to 120 minutes in water.
A: Before restarting after stopping the white liquor oxidation tower
B: When the oxidation efficiency related to polysulfide formation becomes 45% or less in orange liquor preparation
C: When the oxidation rate of sodium sulfide is 90% or less in the preparation of oxidized white liquor for alkaline oxygen delignification
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| JPS61259754A (en) * | 1985-05-11 | 1986-11-18 | Mitsubishi Paper Mills Ltd | Method and apparatus for treating sulfide-containing aqueous solution |
| JPH07114959B2 (en) * | 1987-08-31 | 1995-12-13 | 千代田化工建設株式会社 | Activated carbon catalyst regeneration method |
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