JP2004081969A

JP2004081969A - Adsorbent for harmful substance in exhaust gas and method of removing the same

Info

Publication number: JP2004081969A
Application number: JP2002245767A
Authority: JP
Inventors: Atsushi Hirayama; 平山　敦; Toru Shiomitsu; 塩満　徹; Toshiaki Tsuji; 辻　俊昭; Takeji Meguro; 目黒　竹司; Hitoshi Kuwagaki; 桑垣　整
Original assignee: KANKYO GIJUTSU SERVICE KK; JFE Engineering Corp; Yokohama TLO Co Ltd
Current assignee: KANKYO GIJUTSU SERVICE KK; JFE Engineering Corp; Yokohama TLO Co Ltd
Priority date: 2002-08-26
Filing date: 2002-08-26
Publication date: 2004-03-18
Anticipated expiration: 2022-08-26
Also published as: JP3888950B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a safe operation means by preventing the combustion of active carbon, in a method of adsorbing and removing harmful substances in an exhaust gas by blowing the active carbon thereinto. <P>SOLUTION: An adsorbent for harmful substances in an exhaust gas comprises a mixture of the active carbon and high temperature conductor. The active carbon has an average particle diameter of 5-150 μm and a particle density of 0.5-1.7 g/ml and the high temperature conductor has a heat conductivity higher than that of the active carbon, an average particle diameter of 5-5,000 μm and a particle density of 0.1-9 g/ml. The method of removing the harmful substances in the exhaust gas using the adsorbent is also disclosed. The problem to be solved is solved by the adsorbent for harmful substances and the method of removing the harmful substances. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、ごみ焼却炉やガス化溶融炉などから排出される排ガス中に含まれるダイオキシン類、重金属類等の有害物質を吸着する吸着剤、およびそれを用いた有害物質の除去方法に関するものである。
【０００２】
【従来の技術】
ごみ焼却炉やガス化溶融炉から排出される排ガスに含まれるダイオキシン類、重金属類等の有害物質の除去方法として、活性炭を用いた吸着除去法等が用いられている。この活性炭を用いる方法は、粉末活性炭を排ガス中に吹き込む方法と粒状活性炭を充填した塔を排ガスを通過させる方法がある。活性炭はもとより炭素であるから発火の危険性をはらんでいるが燃焼排ガスは燃焼の際に酸素が消費されて低酸素濃度になっていることもあって特に対策はとられていない。
【０００３】
一方、粒状活性炭を用いる方法は、充填された活性炭層の一部が局所的に高温になることが問題となり、その対策として活性炭に熱伝導性向上材を添加して造粒し、全体として熱伝導率を高めてこの局所的発熱を放散させる技術が開発されている（特開２０００−２７２９１４号公報）、熱伝導性向上材は金属材、セラミック材、炭素材等であり、実施例で採用されているものはグラファイトである。
【０００４】
【発明が解決しようとする課題】
本発明者らは粉末活性炭を吹き込む方法においても発火に対する対策が必要であることを見出した。すなわち、粉末活性炭の吹き込みによる有害ガス除去を行う場合、吹き込み前の粉末活性炭を貯留する貯留槽、集塵装置で集塵されその後払い落とされ集塵装置底部に堆積した使用後活性炭を含む飛灰堆積層、および集塵装置底部より搬出された使用後活性炭の混入した飛灰を貯留する貯留槽等において、大量の活性炭あるいは活性炭混入飛灰が堆積するケースが存在する。また、活性炭は外部から熱を与えられない場合にも、活性炭への被吸着物質の吸着がおこる際の吸着熱、活性炭中に本質的に存在する揮発性あるいは低沸点有機化合物の自然酸化による反応熱、活性炭に吸着した有機化合物の自然酸化による反応熱等を発生する。このような発熱が、前述した活性炭あるいは活性炭混入飛灰の堆積層において発生すると、活性炭および飛灰の熱伝導性の低さのために、熱が外部に放散されずに層内に蓄熱され層温度の上昇を招き、層温度が活性炭の炭材自体の発火温度まで上昇すると層全体が炎上してしまう危険性をはらんでいる。
【０００５】
このような現象は活性炭の原料、製造法等によってはより加速される場合がある。例えば、リサイクル法の施行に伴い、建設廃材等の再利用が社会的に急務となっているが、廃材を分別し木材として新築建材として利用することは実際には困難であり、廃材の炭化、活性化による吸着剤としての利用が検討されている。とりわけごみ焼却炉におけるダイオキシン吸着への利用が実施されつつある。こうした利用は廃棄物の適正管理をすすめるため好ましいといえるが、廃木材を原料に用い活性炭を製造した場合、活性炭中にセメント等の付着物が混入するため、製品の発火点が低下し、利用条件によっては発火の危険が増す。また、従来の石炭等を原料とする活性炭に比べ、低密度のため、いったん発熱、発火した場合の類焼が早く、事故につながる危険性がより高まると考えられる。
【０００６】
【課題を解決するための手段】
本発明者らは、このような課題を解決する手段として、特定の粒径と粒子密度を有する活性炭と高熱伝導体を組み合わせて混合し、この混合物を排ガス中に吹き込むことによって有害物質の除去性を損なうことなく発火の問題を解決できることを見出した。すなわち、粉末活性炭に高熱伝導体を混合することにより、熱伝導率を向上させることが可能となり、吹き込み前の粉末活性炭を貯留する貯留槽、集塵装置で集塵され、その後払い落とされ集塵装置底部に堆積した使用後活性炭を含む飛灰堆積層、および集塵装置底部より搬出された使用後活性炭の混入した飛灰を貯留する貯留槽等の、堆積層内における発熱を速やかに外部へと放熱させ層の温度上昇を防ぎ発火を防止できる。また、市販の活性炭と高熱伝導体を物理混合するだけで得られるため、その製造に特別な工程を必要とせず、安価に製造することができる。
【０００７】
本発明は、かかる知見に基づいてなされたものであり、平均粒子径５〜１５０μｍ、粒子密度０．５〜１．７ｇ／ｍｌである活性炭と、該活性炭より高い熱伝導率を有し、かつ平均粒子径５〜５０００μｍ、粒子密度０．１〜９ｇ／ｍｌである高熱伝導体の混合物よりなる、排ガス中の有害物質吸着剤、およびそれを用いた排ガスからの有害物質の除去方法に関するものである。
【０００８】
【発明の実施の形態】
活性炭は、平均粒子径が５〜１５０μｍ程度、好ましくは１０〜１００μｍ程度、特に好ましくは１０〜５０μｍ程度、粒子密度が０．５〜１．７ｇ／ｍｌ程度、好ましくは０．６〜１．５ｇ／ｍｌ程度、特に好ましくは０．８〜１．３ｇ／ｍｌ程度のものを用いる。ここでいうところの平均粒子径とは、ふるい分け法あるいはレーザー回析法等で測定した粒度分布の累積５０％粒子径を指す。また、ここでいうところの粒子密度ρ_ｐとは、プロパノール、ブタノール、ケロシン等に浸漬し液中での重量を測定するいわゆるアルキメデス法により測定した真密度ρ_Ｔ（ｇ／ｃｃ）と、水銀圧入法あるいは窒素吸着法等によって求めた細孔容積Ｖ_ｐｏｒｅ（ｃｃ／ｇ）より求めたものであり、
ρ_ｐ＝ρ_Ｔ／（１＋ρ_Ｔ×Ｖ_ｐｏｒｅ）　…………　式（１）
で表される。
【０００９】
上記平均粒子径と粒子密度は、吸着剤を例えばろ過式集塵機前に吹き込んで用いる場合、吹き込まれた粉末が排ガス気流に乗ってろ布に付着する必要があるためであり、これより大きいとろ布に付着する前に煙道に落下してしまい、またこれより小さいと粉体としてのハンドリング性の困難さ、あるいはろ布で集塵されずにろ布を通過してしまう等の不具合を生ずる。
【００１０】
活性炭のその他の物性値としては、有害物質吸着能の点で比表面積が１００ｍ^２／ｇ以上、望ましくは３００ｍ^２／ｇ以上のものがよい。比表面積の上限は特に限定されないが実用上１２００ｍ^２／ｇ程度までのものが用いられる。また、発火現象を防止するため、用いる活性炭の発火温度は４００℃以上であることが好ましい。また望ましくは４５０℃以上、さらに望ましくは５００℃以上であることが好ましい。一方、発火温度は高い程よいが、実用的観点から最高でも６００℃程度である。活性炭は一般的に熱伝導率が低く、０．１〜０．４Ｗ／ｍＫ程度、通常０．１〜０．３Ｗ／ｍＫ程度である。ここでいうところの発火温度とは、示差熱分析計で測定した発熱ピークの立ち上がり変曲点の値である。これより発火温度が低いと、いくら熱伝導率を向上させても、発火に至る可能性が高くなる。
【００１１】
活性炭の原料は、やしがら等の植物系原料でも良いが、より望ましくは石炭系原料が好ましい。なお、ここでいうところの活性炭には、当然のことながら活性コークスも含まれる。
【００１２】
活性炭に物理混合する高熱伝導体は、用いる活性炭より熱伝導率が高いものを用いる。具体的値では０．２Ｗ／ｍＫ以上、好ましくは２〜１０００Ｗ／ｍＫ程度、特に好ましくは２０〜１０００Ｗ／ｍＫ程度のものがよい。活性炭の熱伝導率に対する比率では１０倍以上、好ましくは１００倍以上のものが望ましい。
【００１３】
高熱伝導体の具体例としては、セラミック、金属、黒鉛等が用いられるが、特に黒鉛はその熱伝導率が活性炭の数倍〜１００倍程度高く、通常入手される材料において要求される平均粒子径や粒子密度を満たすものが存在し、また主構成元素が炭素であり活性炭と同じであることから、活性炭との混合性、使用後の処理条件の面において特に好ましい。また、同様にコークスの一種であるピッチコークスやニードルコークスを用いても良い。
【００１４】
また、高熱伝導体の平均粒子径と粒子密度は、活性炭と同じ理由で、平均粒子径が５〜５０００μｍ程度、好ましくは５〜５００μｍ程度、特に好ましくは５〜２００μｍ程度、粒子密度が０．１〜９ｇ／ｍｌ程度、好ましくは０．５〜５ｇ／ｍｌ程度、特に好ましくは１〜３ｇ／ｍｌ程度のものを用いる。平均粒子径と粒子密度の意義は活性炭のところで説明した通りである。また、高熱伝導体が黒鉛である場合、黒鉛の平均粒子径は活性炭の平均粒子径の０．４〜１倍、好ましくは０．５〜１倍であることが望ましい。
【００１５】
活性炭と高熱伝導体の混合割合は、用いる高熱伝導体の熱伝導率によって異なるが、混合比率が高い程、発火防止の効果があり、また有害物質除去率の観点から高熱伝導体の重量％で１０〜８０％、特に２０〜５０％が好ましい。
【００１６】
本発明の吸着剤には第３成分を含有させることができる。例えば消石灰を混合して吹き込むことにより、酸性ガスの除去と有害物質の吸着除去との同時達成が可能となるとともに、消石灰の混合により活性炭が希釈されるため、発火防止の観点において好ましい。消石灰を添加する場合、好ましい添加量は、混合物１〜４０重量％、消石灰が９９〜６０重量％程度、好ましくは混合物２〜２０重量％、消石灰が９８〜８０重量％程度である。
【００１７】
本発明の吸着剤はそのまま排ガス中に吹き込めばよい。その際、排ガスの温度は活性炭が充分に吸着能力を発揮する温度、具体的には２５０℃以下、好ましくは２００℃以下、特に好ましくは１８０℃以下とする。ごみ焼却炉等から排出される燃焼排ガスは通常７５０〜９５０℃、ガス化溶融炉から排出される排ガスは８００〜９５０℃と高いのでこれらはまず上記温度以下まで冷却してから排ガスに吹き込む。温度の下限は酸露点による腐食の問題から概ね１６０℃程度までである。吸着剤の吹込量は除去しようとする有害物質の種類と含有量および必要とする除去の程度等に応じて定められ、これは予め試験をして定めるのがよい。吹き込む位置はガス冷却設備等で冷却後集塵装置で、集塵されるまでの間がよい。集塵装置は本発明の吸着剤を捕集できるものであればよいが、バグフィルタが特に好ましい。この集塵装置は排ガス中の飛灰等も合わせて捕集させてもよい。
【００１８】
【実施例】
［実施例１］
やしがらまたは石炭を原料とする市販の活性炭と数種類の市販の高熱伝導体との各混合物の熱伝導率、発火温度および発火に至るまでの投入電力量を測定した。
【００１９】
用いたやしがら原料活性炭は比表面積１０００ｍ^２／ｇ、平均粒子径２０μｍ、粒子密度０．９６ｇ／ｍｌ、石炭原料活性炭は比表面積９００ｍ^２／ｇ、平均粒子径２５μｍ、粒子密度１．２ｇ／ｍｌのものである。また高熱伝導体には粉末黒鉛、フレーク状黒鉛、アルミニウム粉末およびニッケル粉末の４種類を用いた。粉末黒鉛は平均粒子径１８μｍ、粒子密度１．５ｇ／ｍｌ、フレーク状黒鉛は平均粒子径１２０μｍ、粒子密度１．４ｇ／ｍｌ、アルミニウム粉末は平均粒子径１９μｍ、粒子密度１．５ｇ／ｍｌ、そして、ニッケル粉末は平均粒子径２０μｍ、粒子密度２．５ｇ／ｍｌであった。
【００２０】
発火温度は図１に示す装置を用いて発火試験を行って求めた。この装置にマッフル炉１の内部に金属製メッシュでできた円筒形容器２が設けられ、その中心に加熱用ヒータ３が設置されている。また、内部には温度計４が設置されている。各混合物５を金属製メッシュ２に充填してマッフル炉１に入れ、単位時間当り一定量の電力をヒーターに投入し、中心温度を測定した。この温度が急激に上昇する温度を発火温度とし、この時点までに投入した電力量を比較した。
得られた結果を表１に示す。
【００２１】
【表１】

【００２２】
［実施例２］
原料および製造工程の異なる活性炭（１６種類）および黒鉛（１６種類）について、イソプロパノールを浸漬液として用いアルキメデス法により真密度を求め、また窒素吸着法により細孔容積を求めた。
得られた結果を表２に示す。
【００２３】
【表２】

【００２４】
ここで、気孔率Ｒ_Ｐは真密度ρ_Ｔおよび細孔容積Ｖ_ｐｏｒｅより計算され、
Ｒ_Ｐ＝（ρ_Ｔ×Ｖ_ｐｏｒｅ）／（１＋ρ_Ｔ×Ｖ_ｐｏｒｅ）　…………　式（２）
で表される。
【００２５】
この材料について、表２数値を基に、これらの活性炭および黒鉛を吹込材料として用いた時に重要となる終末速度Ｕ_Ｔについて検討した。
終末速度Ｕ_Ｔは下式
Ｕ_Ｔ＝｛ｇ×ｄ_ｐ ^２×（ρ_ｐ−ρ_ｆ）｝／１８／μ　…………　式（３）
で表される。
ここで、ｇ：重力加速度、ｄ_ｐ：平均粒子径、ρ_ｐ：粒子密度、ρ_ｆ：空気密度、μ：空気粘度である。
【００２６】
式（３）を変形すると、ρ_ｐ＞＞ρ_ｆなので、
ｄ_ｐ＝｛（１８×μ×Ｕ_Ｔ）／（ｇ×ρ_ｐ）｝^０．５　…………　式（４）
となる。この式より異なる粒子密度の粉末について等しい終末速度を得るためには、粒子密度の比に応じた異なる平均粒子径の粉末である必要がある。ここで、Ａ粒子の粒子密度をρ_ｐＡ、Ｂ粒子の粒子密度をρ_ｐＢとすると、等しい終末速度Ｕ_Ｔが得られる平均粒子径ｄ_ｐＡおよびｄ_ｐＢは
ｄ_ｐＡ／ｄ_ｐＢ＝（ρ_ｐＡ／ρ_ｐＢ）^−０．５　…………　式（５）
の関係を満たすものである。
【００２７】
表２結果より、式（１）および式（２）を用いて計算すると、活性炭の粒子密度は０．５６ｇ／ｃｃ〜１．６ｇ／ｃｃ、黒鉛の粒子密度は１．５２〜２．２６である。よってこの値を式（５）にあてはめることにより、活性炭の平均粒子径が、黒鉛の平均粒子径の約０．４倍〜１倍、好ましくは０．４９倍〜０．９８倍にして混合し、吹込材料とすることにより、等しい終末速度が得られることがわかった。このような等しい終末速度が得られるように両材料の混合時の平均粒子径を決めることで、ごみ焼却炉の煙道に吹き込んだ際のガス流れへの同伴性、ろ過式集塵機におけるろ布への到達性、ろ布への付着性、ろ布からの払い落とし性、ろ過式集塵機において払い落とされた飛灰中における活性炭と黒鉛の混合性の均一性等が向上する。
【００２８】
また、表２記載した活性炭１６種、黒鉛１６種について、それぞれ平均粒子径と終末速度の関係を計算した。その結果を図２〜図９に示す。その際に簡単のために、活性炭においては気孔率を２０％、３５％、５０％、６０％に大きく分類して表記した。また、黒鉛の場合は、気孔率を１％、５％、１０％、２０％に大きく分類して表記した。
【００２９】
ここで、ごみ焼却炉におけるろ過式集塵機において、ろ過速度は通常０．６ｍ／ｍｉｎ〜１．２ｍ／ｍｉｎ（０．０１ｍ／ｓｅｃ〜０．０２ｍ／ｓｅｃ）で設計されている。したがって、ごみ焼却炉の煙道に吹き込んだ際のガス流れへの同伴性ばかりでなく、ろ過式集塵機におけるろ布への到達性、ろ布への付着性、ろ布からの払い落とし性、ろ過式集塵機において払い落とされた飛灰中における活性炭と黒鉛の混合性の均一性を達成するには、０．０１ｍ／ｓｅｃ〜０．０２ｍ／ｓｅｃ以下の流速を終末速度とする粒子を吹き込む必要がある。よって図２〜図９よりこの条件を満たす粒子径をもとめ、表３にまとめた。このような平均粒子径の活性炭および黒鉛を混合し吹込剤とすることで、優れた性能が発揮される。
【００３０】
【表３】

【００３１】
［実施例３］
ごみ焼却炉実機においてろ過式集塵機上流煙道中に活性炭と黒鉛の混合剤を吹き込み、ろ過式集塵機のろ布表面に形成される、飛灰、活性炭および黒鉛の付着層を採取し、付着層内における活性炭と黒鉛の存在比率を測定した。その結果を表４に示す。吹込剤には、表２および表３に記載した活性炭１６種および黒鉛１６種の中から、それぞれ５種を選び、表４に示すような条件で活性炭と黒鉛を混合し吹き込んだ。また、この試験実施時のろ過式集塵機におけるろ過速度は０．０１４ｍ／ｓｅｃであった。
【００３２】
【表４】

【００３３】
［実施例４］
ごみ焼却炉実機において、ろ過式集塵機上流煙道中に活性炭と黒鉛の混合剤を吹き込み、排ガス中ダイオキシン類の除去性能を測定した結果を表５に示す。
【００３４】
＜試験条件＞
集塵機運転温度：１７０℃
活　　性　　炭：粉末状石炭原料活性炭
高　熱　伝　導　体：黒鉛
吹　　込　　量：０．１ｇ／ｍ^３Ｎ
【００３５】
【表５】

【００３６】
【発明の効果】
本発明により、活性炭の発火を防止して排ガス中のダイオキシン等の有害物質を安定して除去することができる。
【図面の簡単な説明】
【図１】本発明で発火温度の測定に用いた発火試験機の概略構造を示す縦断面図である。
【図２】本発明で得られた黒鉛の粒子径と終末速度との関係を示すグラフである。
【図３】本発明で得られた黒鉛の粒子径と終末速度との関係を示すグラフである。
【図４】本発明で得られた黒鉛の粒子径と終末速度との関係を示すグラフである。
【図５】本発明で得られた黒鉛の粒子径と終末速度との関係を示すグラフである。
【図６】本発明で得られた黒鉛の粒子径と終末速度との関係を示すグラフである。
【図７】本発明で得られた活性炭の粒子径と終末速度との関係を示すグラフである。
【図８】本発明で得られた活性炭の粒子径と終末速度との関係を示すグラフである。
【図９】本発明で得られた活性炭の粒子径と終末速度との関係を示すグラフである。
【符号の説明】
１…マッフル炉
２…金属製メッシュ
３…ヒータ
４…熱電対（温度計）
５…吸着剤[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an adsorbent for adsorbing harmful substances such as dioxins and heavy metals contained in exhaust gas discharged from a refuse incinerator or a gasification and melting furnace, and a method for removing harmful substances using the same. is there.
[0002]
[Prior art]
As a method for removing harmful substances such as dioxins and heavy metals contained in exhaust gas discharged from a refuse incinerator or a gasification and melting furnace, an adsorption removal method using activated carbon or the like is used. As a method using this activated carbon, there are a method of blowing powdered activated carbon into exhaust gas and a method of passing exhaust gas through a column filled with granular activated carbon. Since activated carbon is naturally carbon, it has a risk of ignition. However, no particular measures have been taken for the combustion exhaust gas because oxygen is consumed during combustion and the oxygen concentration is low.
[0003]
On the other hand, in the method using granular activated carbon, there is a problem that a part of the filled activated carbon layer is locally heated to a high temperature. A technique for increasing the conductivity to dissipate this local heat has been developed (Japanese Patent Laid-Open No. 2000-272914). The thermal conductivity improving material is a metal material, a ceramic material, a carbon material, and the like, and is employed in Examples. What is being done is graphite.
[0004]
[Problems to be solved by the invention]
The present inventors have found that measures must be taken against ignition in the method of blowing powdered activated carbon. That is, when harmful gas is removed by blowing powdered activated carbon, fly ash containing used activated carbon collected in a storage tank for storing the powdered activated carbon before being blown, collected by a dust collector and then washed off and deposited on the bottom of the dust collector. There are cases where a large amount of activated carbon or fly ash mixed with activated carbon accumulates in a storage layer or the like for storing fly ash mixed with activated carbon after use, which is carried out from the sedimentary layer and the bottom of the dust collector. Activated carbon also has a heat of adsorption when the substance to be adsorbed is adsorbed on the activated carbon even when heat is not applied from the outside, and a reaction due to natural oxidation of volatile or low-boiling organic compounds essentially present in the activated carbon. Generates heat and reaction heat due to natural oxidation of organic compounds adsorbed on activated carbon. When such heat generation occurs in the above-described layer of activated carbon or fly ash mixed with activated carbon, heat is not dissipated to the outside and stored in the bed due to the low thermal conductivity of the activated carbon and fly ash. If the bed temperature rises to the ignition temperature of the activated carbon material itself due to an increase in temperature, there is a danger that the entire bed will burn.
[0005]
Such a phenomenon may be further accelerated depending on the raw material of the activated carbon, the production method, and the like. For example, with the enforcement of the Recycling Law, the recycling of construction waste materials has become an urgent social task.However, it is actually difficult to separate waste materials and use them as timber as new construction materials. Utilization as an adsorbent by activation is being studied. In particular, utilization for dioxin adsorption in refuse incinerators is being implemented. Such use is preferable because it promotes appropriate management of waste.However, when activated carbon is manufactured using waste wood as a raw material, the ignition point of the product is lowered because adhering substances such as cement are mixed in the activated carbon, and Depending on the conditions, the risk of ignition increases. In addition, compared to conventional activated carbon made from coal or the like, since the density is low, it is considered that once fired and fired, fire spread quickly and the risk of an accident was further increased.
[0006]
[Means for Solving the Problems]
As a means to solve such problems, the present inventors combine activated carbon having a specific particle size and particle density with a high thermal conductor, mix the mixture, and blow the mixture into exhaust gas to remove harmful substances. It was found that the problem of ignition could be solved without damaging the fire. That is, by mixing the powdered activated carbon with a high thermal conductor, the thermal conductivity can be improved, and the dust is collected in a storage tank for storing the powdered activated carbon before being blown, in a dust collecting device, and then dusted off. Heat generated in the sedimentary layer, such as the fly ash layer containing activated carbon deposited on the bottom of the device and the storage tank for the fly ash mixed with activated carbon discharged from the bottom of the dust collector, is quickly discharged to the outside. The heat can be radiated to prevent a rise in the temperature of the layer and prevent ignition. In addition, since it can be obtained only by physically mixing commercially available activated carbon and a high thermal conductor, it can be manufactured at low cost without requiring a special step for its manufacture.
[0007]
The present invention has been made based on such findings, has activated carbon having an average particle diameter of 5 to 150 μm, and a particle density of 0.5 to 1.7 g / ml, has a higher thermal conductivity than the activated carbon, and The present invention relates to a harmful substance adsorbent in an exhaust gas comprising a mixture of high thermal conductors having an average particle diameter of 5 to 5000 μm and a particle density of 0.1 to 9 g / ml, and a method for removing harmful substances from an exhaust gas using the same. is there.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
The activated carbon has an average particle size of about 5 to 150 μm, preferably about 10 to 100 μm, particularly preferably about 10 to 50 μm, and a particle density of about 0.5 to 1.7 g / ml, preferably 0.6 to 1.5 g. / Ml, particularly preferably about 0.8 to 1.3 g / ml. Here, the average particle size refers to a 50% cumulative particle size of the particle size distribution measured by a sieving method or a laser diffraction method. The particle density ρ _p referred to here is the true density ρ _T (g / cc) measured by the so-called Archimedes method of immersing in propanol, butanol, kerosene or the like and measuring the weight in the liquid, and mercury intrusion. _Is obtained from the pore volume V _pore (cc / g) obtained by the method or nitrogen adsorption method, etc.
ρ _p = ρ _T / (1 + ρ _T × V _pore ) Equation (1)
Is represented by
[0009]
The average particle diameter and the particle density are because, for example, when the adsorbent is used by blowing it in front of a filter-type dust collector, the blown powder needs to adhere to the filter cloth in the exhaust gas stream. The particles fall into the flue before they adhere, and if smaller than this, problems such as difficulty in handling as powder or passing through the filter cloth without being collected by the filter cloth occur.
[0010]
As other physical property values of the activated carbon, those having a specific surface area of 100 m ² / g or more, desirably 300 m ² / g or more are preferable in terms of harmful substance adsorption ability. The upper limit of the specific surface area is not particularly limited, but a practical surface area of up to about 1200 m ² / g is used. In order to prevent the ignition phenomenon, the ignition temperature of the activated carbon used is preferably 400 ° C. or higher. Preferably, the temperature is 450 ° C. or higher, more preferably 500 ° C. or higher. On the other hand, the higher the ignition temperature is, the better, but it is at most about 600 ° C. from a practical viewpoint. Activated carbon generally has a low thermal conductivity, about 0.1 to 0.4 W / mK, usually about 0.1 to 0.3 W / mK. Here, the ignition temperature is a value of a rising inflection point of an exothermic peak measured by a differential thermal analyzer. If the ignition temperature is lower than this, there is a high possibility of ignition even if the thermal conductivity is improved.
[0011]
The raw material of the activated carbon may be a plant raw material such as coconut, but more preferably a coal raw material. In addition, the activated carbon mentioned here naturally includes activated coke.
[0012]
The high thermal conductor physically mixed with the activated carbon has a higher thermal conductivity than the activated carbon used. Specific values are 0.2 W / mK or more, preferably about 2 to 1000 W / mK, and particularly preferably about 20 to 1000 W / mK. The ratio of the activated carbon to the thermal conductivity is desirably 10 times or more, preferably 100 times or more.
[0013]
As specific examples of the high thermal conductor, ceramics, metals, graphite and the like are used. In particular, graphite has a thermal conductivity several times to 100 times higher than that of activated carbon, and the average particle size required for commonly available materials And those having a particle density satisfying the above conditions, and the main constituent element is carbon, which is the same as activated carbon. Therefore, it is particularly preferable in view of the mixing property with activated carbon and the processing conditions after use. Similarly, pitch coke or needle coke which is a kind of coke may be used.
[0014]
In addition, the average particle diameter and the particle density of the high thermal conductor are, for the same reason as the activated carbon, the average particle diameter is about 5 to 5000 μm, preferably about 5 to 500 μm, particularly preferably about 5 to 200 μm, and the particle density is 0.1.のもの 9 g / ml, preferably about 0.5-5 g / ml, particularly preferably about 1-3 g / ml. The meanings of the average particle diameter and the particle density are as described for the activated carbon. When the high thermal conductor is graphite, the average particle size of the graphite is 0.4 to 1 times, preferably 0.5 to 1 times the average particle size of the activated carbon.
[0015]
The mixing ratio of the activated carbon and the high thermal conductor varies depending on the thermal conductivity of the high thermal conductor used. The higher the mixing ratio, the more effective the ignition prevention is, and from the viewpoint of the harmful substance removal rate, the higher the thermal conductor weight%. It is preferably from 10 to 80%, particularly preferably from 20 to 50%.
[0016]
The adsorbent of the present invention can contain a third component. For example, by mixing and blowing slaked lime, simultaneous removal of acidic gas and adsorption and removal of harmful substances can be achieved at the same time, and activated carbon is diluted by mixing slaked lime, which is preferable from the viewpoint of preventing ignition. When slaked lime is added, the preferable addition amount is 1 to 40% by weight of the mixture, about 99 to 60% by weight of the slaked lime, preferably 2 to 20% by weight of the mixture, and about 98 to 80% by weight of the slaked lime.
[0017]
The adsorbent of the present invention may be blown into exhaust gas as it is. At that time, the temperature of the exhaust gas is set to a temperature at which the activated carbon exerts sufficient adsorption capacity, specifically, 250 ° C. or less, preferably 200 ° C. or less, particularly preferably 180 ° C. or less. Since the combustion exhaust gas discharged from a refuse incinerator or the like is usually as high as 750 to 950 ° C. and the exhaust gas discharged from the gasification and melting furnace is as high as 800 to 950 ° C., these are first cooled to the temperature or lower and then blown into the exhaust gas. The lower limit of the temperature is about 160 ° C. due to the problem of corrosion due to the acid dew point. The amount of the adsorbent to be blown is determined according to the type and content of the harmful substance to be removed, the required degree of removal, and the like. It is preferable that the position to be blown be in a dust collecting device after being cooled by a gas cooling facility or the like, before the dust is collected. The dust collector may be any as long as it can collect the adsorbent of the present invention, and a bag filter is particularly preferable. This dust collector may collect fly ash and the like in the exhaust gas together.
[0018]
【Example】
[Example 1]
The thermal conductivity, the ignition temperature, and the amount of power input to the ignition of each mixture of commercially available activated carbon made from coconut or coal and several types of commercially available high thermal conductors were measured.
[0019]
The used coconut raw material activated carbon has a specific surface area of 1000 m ² / g, an average particle diameter of 20 μm, a particle density of 0.96 g / ml, and the coal raw material activated carbon has a specific surface area of 900 m ² / g, an average particle diameter of 25 μm, and a particle density of 1.2 g / g. ml. As the high thermal conductor, powdered graphite, flake graphite, aluminum powder and nickel powder were used. Powdered graphite has an average particle diameter of 18 μm, particle density of 1.5 g / ml, flake graphite has an average particle diameter of 120 μm, particle density of 1.4 g / ml, aluminum powder has an average particle diameter of 19 μm, particle density of 1.5 g / ml, and The nickel powder had an average particle diameter of 20 μm and a particle density of 2.5 g / ml.
[0020]
The ignition temperature was determined by performing an ignition test using the apparatus shown in FIG. In this apparatus, a cylindrical container 2 made of a metal mesh is provided inside a muffle furnace 1, and a heater 3 for heating is provided at the center of the cylindrical container 2. A thermometer 4 is installed inside. Each mixture 5 was filled in a metal mesh 2 and put in the muffle furnace 1, a constant amount of electric power was supplied to the heater per unit time, and the center temperature was measured. The temperature at which this temperature rises sharply was defined as the ignition temperature, and the amounts of power input up to this point were compared.
Table 1 shows the obtained results.
[0021]
[Table 1]

[0022]
[Example 2]
With respect to activated carbon (16 types) and graphite (16 types) having different raw materials and manufacturing steps, the true density was determined by Archimedes method using isopropanol as an immersion liquid, and the pore volume was determined by nitrogen adsorption method.
Table 2 shows the obtained results.
[0023]
[Table 2]

[0024]
Here, the porosity R _P is calculated from the true density ρ _T and the pore volume V _pore ,
R _P = (ρ _T × V _pore ) / (1 + ρ _T × V _pore ) Equation (2)
Is represented by
[0025]
This material, based on Table 2 Numerical was studied terminal velocity U _T which is important when using these activated carbon and graphite as blowing material.
Terminal velocity _{U T} is the formula _{_{^{U T = {g × d p}}} 2 × (ρ p -ρ f)} / 18 / μ ............ formula (3)
Is represented by
Here, g: gravity acceleration, d _p : average particle diameter, ρ _p : particle density, ρ _f : air density, μ: air viscosity.
[0026]
By transforming equation (3), since ρ _p >> ρ _f ,
d _p = {(18 × μ × U _T ) / (g × ρ _p )} ^0.5 ... Equation (4)
It becomes. According to this formula, in order to obtain the same terminal velocity for powders having different particle densities, powders having different average particle diameters according to the ratio of the particle densities are required. Here, when the particle density of the particle density A particle [rho _p A, B particles and [rho _p B, the average particle diameter _{d p} A and _{d p} B equal terminal velocity _{U T} is obtained _d p A / _{d p} B = (ρ _p A / ρ _p B) ^−0.5 Equation (5)
It satisfies the relationship.
[0027]
From the results in Table 2, when calculated using the formulas (1) and (2), the particle density of activated carbon is 0.56 g / cc to 1.6 g / cc, and the particle density of graphite is 1.52 to 2.26. is there. Therefore, by applying this value to the expression (5), the average particle size of the activated carbon is about 0.4 to 1 times, preferably 0.49 to 0.98 times the average particle size of graphite and mixed. It has been found that the same terminal speed can be obtained by using a blown material. By determining the average particle size when mixing both materials so that such an equal terminal velocity can be obtained, entrainment into the gas flow when blown into the flue of a refuse incinerator and filter cloth in a filter-type dust collector And the adhering property to the filter cloth, the property of removing from the filter cloth, the uniformity of mixing of activated carbon and graphite in fly ash removed by the filter-type dust collector, and the like are improved.
[0028]
The relationship between the average particle diameter and the terminal velocity was calculated for each of 16 types of activated carbon and 16 types of graphite described in Table 2. The results are shown in FIGS. At that time, for simplicity, the porosity of activated carbon is broadly classified into 20%, 35%, 50%, and 60%. In the case of graphite, the porosity is roughly classified into 1%, 5%, 10%, and 20%.
[0029]
Here, in a filtration type dust collector in a refuse incinerator, a filtration speed is usually designed at 0.6 m / min to 1.2 m / min (0.01 m / sec to 0.02 m / sec). Therefore, not only the entrainment to the gas flow when it is blown into the flue of a refuse incinerator, but also the accessibility to the filter cloth, the adhesion to the filter cloth, the ability to remove from the filter cloth, In order to achieve a uniform mixing property between activated carbon and graphite in the fly ash removed in the dust collector, it is necessary to blow particles having a flow velocity of 0.01 m / sec to 0.02 m / sec or less as a terminal velocity. is there. Accordingly, the particle diameters satisfying these conditions are determined from FIGS. 2 to 9 and summarized in Table 3. By mixing activated carbon and graphite having such an average particle diameter as a blowing agent, excellent performance is exhibited.
[0030]
[Table 3]

[0031]
[Example 3]
In a real garbage incinerator, a mixture of activated carbon and graphite is blown into the flue upstream of the filtration type dust collector, and the adhesion layer of fly ash, activated carbon and graphite formed on the filter cloth surface of the filtration type dust collector is collected. The existence ratio of activated carbon and graphite was measured. Table 4 shows the results. Five types of blowing agents were selected from 16 types of activated carbon and 16 types of graphite shown in Tables 2 and 3, respectively, and activated carbon and graphite were mixed and blown under the conditions shown in Table 4. The filtration speed of the filtration type dust collector at the time of performing this test was 0.014 m / sec.
[0032]
[Table 4]

[0033]
[Example 4]
Table 5 shows the results of measuring the performance of removing dioxins in exhaust gas by blowing a mixture of activated carbon and graphite into the flue upstream of the filter-type dust collector in the actual incinerator.
[0034]
<Test conditions>
Dust collector operating temperature: 170 ° C
Activated carbon: powdered coal raw material activated carbon high heat conductor: graphite injection amount: 0.1 g / m ³ N
[0035]
[Table 5]

[0036]
【The invention's effect】
According to the present invention, ignition of activated carbon can be prevented and harmful substances such as dioxin in exhaust gas can be stably removed.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view showing a schematic structure of an ignition tester used for measuring an ignition temperature in the present invention.
FIG. 2 is a graph showing the relationship between the particle diameter of graphite obtained in the present invention and the terminal velocity.
FIG. 3 is a graph showing the relationship between the particle diameter of graphite obtained by the present invention and the terminal velocity.
FIG. 4 is a graph showing the relationship between the particle diameter of the graphite obtained in the present invention and the terminal velocity.
FIG. 5 is a graph showing the relationship between the particle diameter of graphite obtained by the present invention and the terminal velocity.
FIG. 6 is a graph showing the relationship between the particle diameter of graphite obtained by the present invention and the terminal velocity.
FIG. 7 is a graph showing the relationship between the particle diameter of the activated carbon obtained in the present invention and the terminal velocity.
FIG. 8 is a graph showing the relationship between the particle diameter of the activated carbon obtained in the present invention and the terminal velocity.
FIG. 9 is a graph showing the relationship between the particle diameter of the activated carbon obtained in the present invention and the terminal velocity.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Muffle furnace 2 ... Metal mesh 3 ... Heater 4 ... Thermocouple (thermometer)
5 Adsorbent

Claims

Activated carbon having an average particle size of 5 to 150 μm and a particle density of 0.5 to 1.7 g / ml, having a higher thermal conductivity than the activated carbon, and having an average particle size of 5 to 5000 μm and a particle density of 0.1 to 9 g / ml. Adsorbent for harmful substances in exhaust gas, consisting of a mixture of high thermal conductors

The harmful substance adsorbent according to claim 1, wherein the high thermal conductor has a thermal conductivity of 0.2 W / mK or more.

The harmful substance adsorbent according to claim 1 or 2, wherein the high thermal conductor is graphite.

The harmful substance adsorbent according to claim 3, wherein the average particle diameter of graphite is 0.4 to 1 times the average particle diameter of activated carbon.

A harmful substance adsorbent obtained by mixing slaked lime with 1 to 40% by weight of the adsorbent according to any one of claims 1, 2, 3 and 4.

This is a method to remove harmful substances contained in exhaust gas discharged from refuse incinerators or melting furnaces. A method for removing harmful substances, comprising blowing the powder adsorbent according to any one of claims 1, 2, 3, 4, and 5 into an upstream portion of the dust collector when removing.