JP4794070B2 - Method for removing mercury contained in exhaust gas - Google Patents

Method for removing mercury contained in exhaust gas Download PDF

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JP4794070B2
JP4794070B2 JP2001192309A JP2001192309A JP4794070B2 JP 4794070 B2 JP4794070 B2 JP 4794070B2 JP 2001192309 A JP2001192309 A JP 2001192309A JP 2001192309 A JP2001192309 A JP 2001192309A JP 4794070 B2 JP4794070 B2 JP 4794070B2
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wastewater
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伸一 伊藤
正路 小川
裕二 中川
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小名浜製錬株式会社
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    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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Description

【０００１】
【発明の属する技術分野】
本発明は、シュレッダーダストを含む燃料を用いて硫黄を含む鉱石の製錬を行う製錬炉から排出される排ガスに含まれる水銀成分を簡便かつ効果的に除去する方法に関する。
【０００２】
【従来の技術】
従来、金属製錬や石油、石炭を燃料とするボイラーの排ガス中には、水銀等の有害な重金属が含まれるため、厳格な排出基準が定められており、製錬所や発電所等の排煙や排水は、この排出基準を越えないように完全にコントロールされて排出されている。
例えば銅の製錬における排ガスの処理方法としては、図５に示すように、製錬炉１で硫黄を含む鉱石を石炭や重油を主として含む燃料を用いて製錬する。製錬により製錬炉１からはＳＯ2ガス、ＳＯ3、ＭＳＯ4（Ｍは重金属類）等を含む硫黄成分、水銀成分等が含まれた排ガスが発生する。この排ガスはガス洗浄工程２に送られ、そこで水の存在下で吸着剤や気液接触させることにより、ＳＯ2ガスを主成分とするガスとＳＯ2ガス以外のＳＯ3、ＭＳＯ4等を含む硫黄成分及び水銀成分等を含む排水とに分離する。即ち、ガス洗浄工程２では洗浄水にＳＯ2ガス以外のＳＯ3、ＭＳＯ4等を含む硫黄成分及び水銀成分等を吸収させる。このうちＳＯ3は洗浄水と反応して硫酸（Ｈ2ＳＯ4）となる。ガス洗浄工程２で分離されたＳＯ2ガスを主成分とするガスは、ＳＯ2ガスを硫酸や石膏として除去回収して、全ての有害物が排出基準以下に規制された状態で系外へ排出される。また、ガス洗浄工程２で分離された排水には、水銀成分が多く存在するが、水銀成分は排水（ｐＨ１以下）に含まれる固形分に多く含まれるため、固液分離工程４で固形分と排水とに分離する。具体的には、排水をシックナー等で濃縮し、この濃縮してスラリー状とした原水スラリーを固液分離することにより、固形分を排水より分離する。分離した固形分は原水スラッジであり、この原水スラッジは製錬炉１に再供給したり、原水スラッジの一部を後述する排水二次処理工程７に原水スラリーのまま供給したり、或いは系外に排出（ブリードオフ）したりする。
【０００３】
固液分離工程４で固形分を分離した排水は、排水一次処理工程５において、炭酸カルシウム（ＣａＣＯ3）を添加することにより、排水のｐＨを２〜４に調整して硫黄成分のうち硫酸成分のみを固定化し、固液分離することにより硫酸成分を石膏（ＣａＳＯ4）として分離回収する。このとき、排水中に溶解している水銀は硫酸成分とともに分離され、石膏に移行する。排水一次処理工程５で石膏を分離した排水は、排水二次処理工程７において、前述した固液分離工程４で分離した原水スラッジの一部（原水スラリー状態）とともに水酸化カルシウム（Ｃａ(ＯＨ)2）を添加することにより、排水のｐＨを１１〜１２に調整して原水スラッジ（原水スラリー）に含まれる水銀とともに排水に主として含まれる重金属を固定化し、固液分離することにより重金属を含まない排水を得る。全ての有害物が排出基準以下に規制された状態で排水は系外へ放流される。排水二次処理工程７で固定化した固形分は二次スラッジとして製錬炉１に再供給される。
【０００４】
上記方法のように、これら排ガスに含まれる有害物除去技術はほぼ確立しているが、更に種々の改良技術が提案されている（特開平７−３０８５４２、特開平９−３０８８１７、特開平１０−２１６４７６）。
特開平７−３０８５４２号公報には、鉛精鉱又は人工的に合成した硫化鉛（ＰｂＳ）と、天然に産する黄鉄鉱（ＦｅＳ2）等の硫化鉄鉱又は合成した硫化鉄との混合物を多孔性物質担体上に担持させたものからなる吸収剤に気体状又はミスト状の水銀を随伴する排ガスを通過させることにより、水銀を吸着除去する排ガス中の水銀の除去方法が示されている。この方法では、硫化鉛に硫化鉄を混在させて多孔質物質担体に担持された吸収剤は長時間安定的に使用できる上、水銀の吸着効率もよく、吸収剤単位重量当たりの水銀除去能力が高いため、吸収剤を充填する充填層を小型化できる効果がある。また特開平９−３０８８１７号公報には、粉粒体を供給して形成されるバグフィルタによりバグフィルタ濾布表面の粉粒層で有害物を吸収、濾過又は捕捉して除去する方法の改良技術が示され、このバグフィルタ出口の排ガス中の有害物の濃度のうちの１つ以上を測定し、その濃度の増減に基づいてバグフィルタ表面の粉粒層形成に使用される粉粒体の供給量を増減することにより、排ガス中の有害物を除去するために供給する粉体の吹込み量を必要最低限にすることが可能になる。特開平１０−２１６４７６号公報には、脱硫装置に使用される循環液、吸収液、湿式電気集塵機に使用される供給水、循環水、集塵機本体内の水、及び集塵機入口の排ガスの少なくともいずれかに水銀除去剤を添加する方法が示され、この方法により、排出源から多量に排出される、水銀濃度が１０μｇ／Ｎｍ3以下のオーダーの超低濃度の排ガス中の水銀、特に金属水銀蒸気を除去できる。
【０００５】
【発明が解決しようとする課題】
一方近年では、膨大に排出される産業廃棄物の処理が重大な社会問題となっており、この産業廃棄物を有効に処理するため、廃家電や自動車等の粗大ゴミから再利用できる部分を取外し、残余の部分を小さい破片に破砕してシュレッダーダストとし、更に有価物を回収した後、残余のダストを燃料資源として利用するリサイクル技術の開発が実用段階に達し、金属の製錬においても燃料資源として活用され始めている。
しかしながら、このシュレッダーダスト中には、塩化ビニル等の含塩素プラスチックが多量に含まれているため、シュレッダーダストを燃料として使用すると燃焼排ガス中の塩素濃度が上昇し、それに伴って次のような問題が生じる結果、排ガス処理や排水処理にも新たな対策が必要になってきた。
【０００６】
即ち、前述したような排ガスの処理方法では、ガス洗浄工程で排ガスからＳＯ2ガスを主成分とするガスと排水とに分離し、排水をシックナー等の固液分離装置に通すことにより、固形分と排水とに分離する。従来の石炭や重油を主として含む燃料を用いて製錬した場合、固液分離工程で水銀成分のほとんどが固形分として沈降分離され、固液分離した後の排水に含まれる水銀含有量は極めて微量であったのに対し、シュレッダーダストを含む燃料を用いて製錬した場合、水銀と塩素が化合して形成される塩化水銀(II)（ＨｇＣｌ2）は水溶性であるため、固液分離工程で分離された固形分に含まれる水銀含有量よりも、排水に含まれる水銀含有量の方が多くなる。従って、従来の処理方法では、固液分離工程後の固形分を系外へ排出することにより水銀成分を系外へ排出していたが、固形分を系外へ排出しても水銀成分の大部分は除去されず、更に、固液分離工程後の排水に水銀成分が含まれるため、排水一次処理工程で回収される石膏に含まれる水銀含有量が増して再利用に支障を来すという問題が生じ、その解決を求められていた。
【０００７】
本発明の目的は、シュレッダーダストを含む燃料を用いて硫黄を含む鉱石の製錬を行う製錬炉から排出される排ガスに含まれる水銀成分を簡便な方法かつ効果的に除去し得る排ガスに含まれる水銀の除去方法を提供することにある。
【０００８】
【課題を解決するための手段】
請求項１に係る発明は、シュレッダーダストを含む燃料を用いて硫黄を含む鉱石の製錬を行う製錬炉から排出される排ガスに含まれる水銀を除去する方法の改良である。
その特徴ある構成は、図１に示すように、製錬炉１１から排出された排ガスを水で洗浄してＳＯ2ガスを主成分とするガスと排水とに分離するガス洗浄工程１２と、排水に含まれる固形分を原水スラッジとして分離する固液分離工程１４と、固形分を分離した排水を水銀除去剤に接触させて排水に含まれる水銀成分を除去する水銀成分除去工程１７と、水銀成分を除去した排水に炭酸カルシウムを加えて排水中に含まれる硫黄成分のうち硫酸成分を石膏として分離する排水一次処理工程１８と、硫酸成分を分離した排水に固液分離工程１４で分離した原水スラッジの一部と水酸化カルシウムとを加えて排水に主として含まれる重金属を二次スラッジとして分離する排水二次処理工程２１とを含むことにある。
【０００９】
請求項１に係る発明では、シュレッダーダストを含む燃料を用いて製錬を行うことにより発生する排ガスをガス洗浄工程１２でＳＯ2ガスを主成分とするガスと排水とに分離し、この排水を固液分離工程１４により固形分と排水とに分離しても水銀成分は固形分へと移行せず、排水に水銀成分が多量に含まれてしまう。そこで固液分離工程１４と排水一次処理工程１８の間に水銀成分除去工程１７を設けることにより、この水銀成分除去工程１７において排水を水銀除去剤に接触させて排水に含まれる水銀成分を簡便にかつ効率的に除去するため、排水一次処理工程１８において石膏として固定化される硫酸成分に水銀成分が含まれることがなく、この硫酸成分を用いて製造される石膏の品質が向上する。
【００１０】
請求項２に係る発明は、請求項１に係る発明であって、水銀成分除去工程１７で水銀除去剤により水銀成分を除去した排水の一部をガス洗浄工程１２におけるＳＯ2ガスの洗浄水に再利用する水銀の除去方法である。
請求項２に係る発明では、水銀成分除去工程１７で水銀成分を除去した排水の一部をガス洗浄工程１２におけるＳＯ2ガスの洗浄水として再利用することにより、洗浄水に含まれる水銀濃度を下げて、ガス洗浄工程１２における水銀負荷を低減する。また、ＳＯ2ガスを主成分とするガスに含まれる水銀成分濃度も低減することができる。
【００１１】
請求項３に係る発明は、請求項１に係る発明であって、水銀成分除去工程１７で水銀成分を除去する前に砂による層に排水を通過させて排水に含まれる固形分の残部を濾過する砂濾過工程１６を更に含む水銀の除去方法である。
請求項３に係る発明では、砂濾過工程１６において砂による層に排水を通過させることにより、後に続く水銀成分除去工程１７において、排水に含まれる固形分の残部による目詰まりを防止する。
【００１２】
請求項４に係る発明は、請求項１に係る発明であって、水銀除去剤が活性炭であって、活性炭が活性炭１００重量％に対して５〜２０重量％の水銀成分を吸着させる能力を有する水銀の除去方法である。
請求項５に係る発明は、請求項１に係る発明であって、精錬炉１１が反射炉である水銀の除去方法である。
【００１３】
【発明の実施の形態】
従来の石炭や重油を主として含む燃料を用いて製錬した場合は、製錬により排出される排ガスに含まれる水銀は、排ガス中に含まれるセレンと化合して水に不溶なセレン化水銀(II)（ＨｇＳｅ）を形成しており、この水に不溶な性質を有するセレン化水銀(II)は、排水を固液分離して分離される固形分中に含まれるため、固形分を系外へ排出することで、系内の水銀成分濃度を低減することができた。
しかし、産業廃棄物であるシュレッダーダストを含む燃料を用いて製錬した場合、シュレッダーダストには塩素成分が多量に含まれているため、この塩素が水銀と化合して水に可溶な性質を有する塩化水銀(II)（ＨｇＣｌ2）を形成してしまう。そのため、従来の処理方法のように排水を固液分離して固形分と排水とに分離しても水銀成分は固形分へと移行せず、排水中に水銀成分が多量に含まれてしまう。
【００１４】
このような問題を解決するため、発明者らはガス洗浄工程で固形分を分離した、水銀含有量が多く、且つｐＨが１以下という排水を排水一次処理工程で処理する前に、水銀成分除去工程を組入れ、その水銀成分の除去効果を発揮するプロセスを開発し、本発明の方法を完成するに至った。この水銀成分除去工程に適応し得るような種々の吸着剤を試験した結果、活性炭やフライアッシュ等がｐＨの低い排水に対して高い耐久性を示し、特に、活性炭が排水に含まれる水銀以外の重金属を吸着することなく水銀を選択的に吸着し、液相水銀の吸着剤として簡便且つ有効に使用できることが判った。
【００１５】
次に本発明の実施の形態について排ガスに含まれる水銀の除去方法を銅の製錬により発生する排ガスを一例として、図面を用いて説明する。
図１に示すように、硫黄を含む鉱石をシュレッダーダストを含む燃料を用いて製錬すると製錬炉１１から発生する排ガスには、ＳＯ2ガス、ＳＯ3、ＭＳＯ4（Ｍは重金属類）等を含む硫黄成分、水銀成分等が含まれる。この排ガスはガス洗浄工程１２に送られ、そこで洗浄水と気液接触させることにより、ＳＯ2ガスを主成分とするガスとＳＯ2ガス以外のＳＯ3、ＭＳＯ4等を含む硫黄成分及び水銀成分等を含む排水とに分離する。即ち、ガス洗浄工程１２では洗浄水にＳＯ2ガス以外のＳＯ3、ＭＳＯ4等を含む硫黄成分及び水銀成分等を吸収させる。このうちＳＯ3は洗浄水と反応して硫酸（Ｈ2ＳＯ4）となる。ガス洗浄工程１２では、ノズル等によって洗浄水を多数の微小液滴に細分し、これらを空塔内を通過する排ガスに分散させて排ガス中に浮遊する水銀以外の重金属や塵等の固体や液体水銀の微粒子を捕捉するスプレータイプのスクラバーにより行われる。ガス洗浄工程１２で分離されたＳＯ2ガスを主成分とするガスは、ＳＯ2ガスを硫酸や石膏として除去回収して、全ての有害物が排出基準以下に規制された状態で系外へ排出される。
【００１６】
ガス洗浄工程１２で分離されたＳＯ2ガス以外のＳＯ3、ＭＳＯ4等を含む硫黄成分及び水銀成分等が含まれる酸性の強い（フッ酸、塩酸、硫酸を含む）排水には、固形分が含まれるため、固液分離工程１４において固形分と排水とに分離する。具体的には、排水をシックナー等で濃縮し、この濃縮してスラリー状とした原水スラリーを固液分離することにより、固形分を排水より分離する。分離した固形分は原水スラッジであり、この原水スラッジは製錬炉１１に再供給したり、原水スラッジの一部を後述する排水二次処理工程２１に原水スラリーのまま供給したりする。固液分離工程１２で固形分を分離した排水は、砂濾過工程１６に送られ、砂による層に排水を通過させて排水に含まれる固形分の残部を濾過する。この砂濾過工程１６を施すことにより、次に続く水銀成分除去工程１７において、排水に含まれる固形分の残部による目詰まりを防止する。
【００１７】
固形分を分離した排水は、水銀成分除去工程１７において、排水を水銀除去剤に接触させて排水に含まれる水銀成分を除去する。この水銀成分除去工程１７により排水に含まれる水銀成分の大部分が水銀除去剤により吸着される。排水はｐＨが１以下の酸性を示す液であるため、水銀除去剤には活性炭やフライアッシュ等が用いられる。特に、活性炭が吸着能が高いため好ましい。水銀除去剤の粒径は６〜１００メッシュ、好ましくは１０〜３０メッシュである。活性炭を水銀除去剤として用いた場合、活性炭の品質にも左右されるが、活性炭は、活性炭１００重量％に対して５〜２０重量％の水銀成分を吸着させる能力を有する。
水銀成分を除去した排水を排水一次処理工程１８に送る前に水銀成分を除去した排水の一部をガス洗浄工程１２のＳＯ2ガスを洗浄する水に供給して再利用する。排水をＳＯ2ガスを洗浄する水に供給することにより、洗浄水に含まれる水銀成分濃度を下げることになり、ＳＯ2ガスを主成分とするガスに含まれる水銀成分濃度も低減することができ、続くＳＯ2の回収における、例えば、排脱石膏プラントの水銀負荷をも下げることができる。また、後に続く排水処理に回される排水の水銀成分濃度も下がるので、排水中の硫酸分を中和することによって得られる石膏の水銀成分濃度も下げることができる。
【００１８】
水銀成分を除去した排水は、排水一次処理工程１８において、炭酸カルシウム（ＣａＣＯ3）を添加することにより、排水のｐＨを２〜４に調整して硫黄成分のうち硫酸成分のみを固定化し、固液分離することにより硫酸成分を石膏（ＣａＳＯ4）として分離する。
【００１９】
排水一次処理工程１８で硫酸成分を分離した排水は、排水二次処理工程２１において、前述した固液分離工程１４で分離した原水スラッジの一部（原水スラリー状態）とともに水酸化カルシウム（Ｃａ(ＯＨ)2）を添加することにより、排水のｐＨを１１〜１２に調整して原水スラッジ（原水スラリー）に含まれる水銀とともに排水に主として含まれる重金属を固定化し、固液分離することにより重金属を固形分として分離する。全ての有害物が排出基準以下に規制された状態で排水は系外へ放流される。排水二次処理工程２１で固定化した固形分は二次スラッジとして製錬炉１１に再供給される。
【００２０】
次に排ガスに含まれる水銀の分配率を本発明の水銀除去方法と従来の方法とを用いて説明する。
シュレッダーダストを含まない石炭や重油を主として含む燃料を用いて製錬することにより発生した排ガスを従来の水銀の除去方法により処理する場合を説明する。図３に示すように、先ず、製錬炉から最初に発生する排ガスに含まれる水銀成分の割合を１００％とすると、排ガスに含まれる水銀成分の一部は排ガス中に含まれるセレンと化合して水に不溶なセレン化水銀(II)を形成しており、ガス洗浄を行ってもガス中に残ってしまうため、全ての水銀成分が排水には移行せず、ガス洗浄工程により分離されたＳＯ2ガスを主成分とするガスには水銀成分が１０％の割合で分配され、排水には９０％の割合で分配される。固液分離工程において、排水に含まれる水銀成分は、原水スラッジに９０％、排水に１０％の割合でそれぞれ移行する。従って、排水に含まれる水銀成分は９０％のうち、原水スラッジ側に８１％、排水側に９％の割合でそれぞれ移行することになる。排水側に移行した水銀成分は排水一次処理工程において、９％ほぼ全ての水銀成分が硫酸成分とともに石膏中に含まれる。原水スラッジに移行した水銀成分８１％のうち、原水スラッジの一部の割合を仮にａ、その残部を１−ａとすると、排水二次処理工程に供給される水銀成分の分配率は(１−ａ)×８１％となり、残部はａ×８１％となる。排水二次処理工程に供給された水銀成分は固形分として二次スラッジに移行し、原水スラッジの残部と二次スラッジは製錬炉に再供給されるため、製錬炉に戻る水銀成分の分配率は８１％となる。
【００２１】
次に、連続して発生する排ガスに含まれる水銀成分の分配率を[＋α]とすると、ガス洗浄工程に送られる水銀成分の割合は[８１％＋α]となる。このガス洗浄工程では前述した通りＳＯ2ガスを主成分とするガスには１０％、排水には９０％の割合で移行するので、ＳＯ2ガスを主成分とするガス側には[８１％＋α]×０．１、排水側には[８１％＋α]×０．９の割合でそれぞれ移行することになる。固液分離工程において、排水に含まれる水銀成分は、原水スラッジに８１％、排水に９％の割合でそれぞれ移行するので、排水に含まれる水銀成分[８１％＋α]×０．９のうち、原水スラッジ側には[８１％＋α]×０．８１、排水側には[８１％＋α]×０．０９の割合でそれぞれ移行する。排水側に移行した水銀成分は排水一次処理工程において、[８１％＋α]×０．０９ほぼ全ての水銀成分が硫酸成分とともに固形分として分離されて石膏中に含まれる。原水スラッジに移行した水銀成分[８１％＋α]×０．８１のうち、原水スラッジの一部の割合を仮にａ、その残部を１−ａとすると、排水二次処理工程に供給される水銀成分の分配率は(１−ａ)×[８１％＋α]×０．８１となり、残部はａ×[８１％＋α]×０．８１となる。排水二次処理工程に供給された水銀成分は固形分として二次スラッジに移行し、原水スラッジの残部と二次スラッジは製錬炉に再供給されるため、再び製錬炉に戻る水銀成分の分配率は[８１％＋α]×０．８１となる。
仮に連続して発生する排ガスの水銀分配率[＋α]が、最初に発生する排ガスの水銀分配率と同様の割合である１００％とすると、再び製錬炉に戻る水銀成分は１００％を越えてしまい、製錬炉に水銀成分を再供給するたびに水銀成分濃度が大きくなる問題が発生する。
【００２２】
シュレッダーダストを含む燃料を用いて製錬することにより発生した排ガスを従来の水銀の除去方法により処理する場合を説明する。図４に示すように、先ず、製錬炉から最初に発生する排ガスに含まれる水銀成分の割合を１００％とすると、ガス洗浄工程により分離されたＳＯ2ガスを主成分とするガスには水銀成分が５％の割合で分配され、排水には９５％の割合で分配される。ここで上述したシュレッダーダストを含まない燃料を用いた場合に比べてガス洗浄工程で分離したガスと排水との水銀の分配率が異なるのはシュレッダーダストには塩素が含まれており、この塩素が水銀と水に可溶な塩化水銀(II)を形成したため、排水側に水銀成分が多く移行したと考えられる。固液分離工程において、排水に含まれる水銀成分は、原水スラッジに１０％、排水に９０％の割合でそれぞれ移行する。従って、排水に含まれる水銀成分は９５％のうち、原水スラッジ側に９．５％、排水側に８５．５％の割合でそれぞれ移行することになる。排水側に移行した水銀成分は排水一次処理工程において、８５．５％ほぼ全ての水銀成分が硫酸成分とともに固形分として分離されて、石膏中に含まれる。原水スラッジに移行した水銀成分９．５％のうち、原水スラッジの一部の割合を仮にａ、その残部を１−ａとすると、排水二次処理工程に供給される水銀成分の分配率は(１−ａ)×９．５％となり、残部はａ×９．５％となる。排水二次処理工程に供給された水銀成分は固形分として二次スラッジに移行し、原水スラッジの残部と二次スラッジは製錬炉に再供給されるため、製錬炉に戻る水銀成分の分配率は９．５％となる。
【００２３】
次に、連続して発生する排ガスに含まれる水銀の分配率を[＋α]とすると、ガス洗浄工程に送られる水銀成分の割合は[９．５％＋α]となる。このガス洗浄工程では前述した通りＳＯ2ガスを主成分とするガス側には５％、排水側には９５％の割合で移行するので、ＳＯ2ガスを主成分とするガス側には[９．５％＋α]×０．０５、排水側には[９．５％＋α]×０．９５の割合でそれぞれ移行することになる。固液分離工程において、排水に含まれる水銀成分は、原水スラッジに１０％、排水に９０％の割合でそれぞれ移行するので、排水に含まれる水銀成分[９．５％＋α]×０．９５のうち、原水スラッジ側には[９．５％＋α]×０．０９５、排水側には[９．５％＋α]×０．８５５の割合でそれぞれ移行する。排水側に移行した水銀成分は排水一次処理工程において、[９．５％＋α]×０．８５５ほぼ全ての水銀成分が硫酸成分とともに固形分として分離されて、石膏中に含まれる。原水スラッジに移行した水銀成分[９．５％＋α]×０．０９５のうち、原水スラッジの一部の割合を仮にａ、その残部を１−ａとすると、排水二次処理工程に供給される水銀成分の分配率は(１−ａ)×[９．５％＋α]×０．０９５となり、残部はａ×[９．５％＋α]×０．０９５となる。排水二次処理工程に供給された水銀成分は固形分として二次スラッジに移行し、原水スラッジの残部と二次スラッジは製錬炉に再供給されるため、再び製錬炉に戻る水銀成分の分配率は[９．５％＋α]×０．０９５となる。
仮に連続して発生する排ガスの水銀分配率[＋α]が、最初に発生する排ガスの水銀分配率と同様の割合である１００％とすると、上述したシュレッダーダストを含まない燃料を用いた場合に比べて再び製錬炉に戻る水銀成分の分配率は小さくなるが、排水一次処理工程において、再利用する石膏に大量に水銀成分が含まれてしまい、石膏の品質が低下する。
【００２４】
シュレッダーダストを含む燃料を用いて製錬することにより発生した排ガスを本発明の水銀の除去方法により処理する場合を説明する。図２に示すように、先ず、製錬炉から最初に発生する排ガスに含まれる水銀成分の割合を１００％とすると、ガス洗浄工程で分離されたＳＯ2ガスを主成分とするガスには水銀成分が５％の割合で分配され、排水には９５％の割合で分配される。固液分離工程において、排水に含まれる水銀成分は、原水スラッジに１０％、排水に９０％の割合でそれぞれ移行する。従って、排水に含まれる水銀成分は９５％のうち、原水スラッジ側に９．５％、排水側に８５．５％の割合でそれぞれ移行することになる。排水側に移行した水銀成分は水銀成分除去工程で８５．５％ほぼ全ての水銀成分が水銀除去剤によって除去される。原水スラッジに移行した水銀成分９．５％のうち、原水スラッジの一部の割合を仮にａ、その残部を１−ａとすると、排水二次処理工程に供給される水銀成分の分配率は(１−ａ)×９．５％となり、残部はａ×９．５％となる。排水二次処理工程に供給された水銀成分は固形分として二次スラッジに移行し、原水スラッジの残部と二次スラッジは製錬炉に再供給されるため、製錬炉に戻る水銀成分の分配率は９．５％となる。
【００２５】
次に、連続して発生する排ガスに含まれる水銀成分の分配率を[＋α]とすると、ガス洗浄工程に送られる水銀成分の割合は[９．５％＋α]となる。このガス洗浄工程では前述した通りＳＯ2ガスを主成分とするガス側には５％、排水側には９５％の割合で移行するので、ＳＯ2ガスを主成分とするガス側には[９．５％＋α]×０．０５、排水側には[９．５％＋α]×０．９５の割合でそれぞれ移行することになる。固液分離工程において、排水に含まれる水銀成分は、原水スラッジに１０％、排水に９０％の割合でそれぞれ移行するので、排水に含まれる水銀成分[９．５％＋α]×０．９５のうち、原水スラッジ側には[９．５％＋α]×０．０９５、排水側には[９．５％＋α]×０．８５５の割合でそれぞれ移行する。排水側に移行した水銀成分は水銀成分除去工程において、[９．５％＋α]×０．８５５ほぼ全ての水銀成分が水銀除去剤によって除去される。原水スラッジに移行した水銀成分[９．５％＋α]×０．０９５のうち、原水スラッジの一部の割合を仮にａ、その残部を１−ａとすると、排水二次処理工程に供給される水銀成分の分配率は(１−ａ)×[９．５％＋α]×０．０９５となり、残部はａ×[９．５％＋α]×０．０９５となる。排水二次処理工程に供給された水銀成分は固形分として二次スラッジに移行し、原水スラッジの残部と二次スラッジは製錬炉に再供給されるため、再び製錬炉に戻る水銀成分の分配率は[９．５％＋α]×０．０９５となる。
【００２６】
このように、製錬炉に戻る水銀成分の分配率は再供給されるたびにその水銀成分量が減少するため、ガス洗浄工程で分離したＳＯ2、排水一次処理工程で分離した石膏のそれぞれに含まれる水銀成分濃度も低減される。なお、図２中には記載していないが、水銀成分除去工程において水銀成分を除去した排水の一部をガス洗浄工程のＳＯ2を洗浄する水に再利用するため、ガス洗浄工程により分離した排水に含まれる水銀の分配率は図２中に記載した数値より小さい数値となる。
【００２７】
【発明の効果】
以上述べたように、本発明はシュレッダーダストを含む燃料を用いて製錬を行うことにより発生する排ガスに含まれる水銀の除去方法において、固液分離工程と排水一次処理工程の間に水銀成分除去工程を設けることにより、この水銀成分除去工程において排水を水銀除去剤に接触させて排水に含まれる水銀成分を除去できるようになったため、後に続く排水一次処理工程において分離される石膏には水銀成分がほとんど含まれず、この石膏中の水銀含有量が再利用に必要十分な程度に激減し、シュレッダーダストを燃料資源として活用する際の問題点が解消する。
【図面の簡単な説明】
【図１】本発明の排ガスに含まれる水銀の除去方法を示す図。
【図２】シュレッダーダストを含む燃料を用いて製錬を行うことにより発生した排ガスを本発明の水銀の除去方法を用いて処理した際の水銀の分配率を示す図。
【図３】シュレッダーダストを含まない燃料を用いて製錬を行うことにより発生した排ガスを従来の水銀の除去方法を用いて処理した際の水銀の分配率を示す図。
【図４】シュレッダーダストを含む燃料を用いて製錬を行うことにより発生した排ガスを従来の水銀の除去方法を用いて処理した際の水銀の分配率を示す図。
【図５】従来の排ガスに含まれる水銀の除去方法を示す図。
【符号の説明】
１１ 製錬炉
１２ ガス洗浄工程
１４ 固液分離工程
１７ 水銀成分除去工程
１８ 排水一次処理工程
２１ 排水二次処理工程[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for easily and effectively removing a mercury component contained in an exhaust gas discharged from a smelting furnace for smelting ore containing sulfur using a fuel containing shredder dust.
[0002]
[Prior art]
Conventionally, exhaust gas from boilers fueled with metal smelting and oil and coal contains harmful heavy metals such as mercury, so strict emission standards have been established, and emissions from smelters and power plants have been established. Smoke and wastewater are discharged in a completely controlled manner so as not to exceed this emission standard.
For example, as a method for treating exhaust gas in copper smelting, as shown in FIG. 5, ore containing sulfur is smelted in a smelting furnace 1 using a fuel mainly containing coal or heavy oil. The smelting furnace 1 generates exhaust gas containing a sulfur component, a mercury component, and the like including SO 2 gas, SO 3 , MSO 4 (M is a heavy metal), and the like. This exhaust gas is sent to the gas cleaning step 2 where it is brought into contact with an adsorbent or gas-liquid in the presence of water, thereby containing SO 2 gas as a main component, SO 3 other than SO 2 gas, MSO 4 and the like. Separated into wastewater containing sulfur and mercury components. That is, in the gas cleaning step 2, the cleaning water absorbs a sulfur component and a mercury component containing SO 3 , MSO 4 and the like other than the SO 2 gas. Of these, SO 3 reacts with the washing water to become sulfuric acid (H 2 SO 4 ). Gas mainly composed of SO 2 gas separated by the gas washing step 2, the discharge was removed recovering SO 2 gas as sulfuric acid or gypsum, out of the system in a state in which all of the hazardous materials is regulated to below the emission standard Is done. In addition, the wastewater separated in the gas cleaning step 2 contains a large amount of mercury components, but since the mercury component is contained in a large amount in the solids contained in the wastewater (pH 1 or less), the solids in the solid-liquid separation step 4 Separated into drainage. Specifically, the solid content is separated from the waste water by concentrating the waste water with a thickener or the like, and solid-liquid separation of the concentrated raw water slurry. The separated solid content is raw water sludge, and this raw water sludge is re-supplied to the smelting furnace 1, or a part of the raw water sludge is supplied as a raw water slurry to the waste water secondary treatment step 7 described later, or outside the system. Or bleed off.
[0003]
The waste water from which the solid content has been separated in the solid-liquid separation step 4 is adjusted to a pH of 2 to 4 by adding calcium carbonate (CaCO 3 ) in the waste water primary treatment step 5 to adjust the sulfuric acid component of the sulfur component. The sulfuric acid component is separated and recovered as gypsum (CaSO 4 ) by immobilizing only and solid-liquid separation. At this time, mercury dissolved in the waste water is separated together with the sulfuric acid component and transferred to gypsum. The wastewater from which gypsum was separated in the wastewater primary treatment step 5 was separated from the raw water sludge separated in the solid-liquid separation step 4 in the wastewater secondary treatment step 7 (raw water slurry state) with calcium hydroxide (Ca (OH)). 2 ) By adjusting the pH of the wastewater to 11-12 by adding, the heavy metals mainly contained in the wastewater together with the mercury contained in the raw water sludge (raw water slurry) is fixed, and heavy metals are not contained by solid-liquid separation Get drained. Wastewater is discharged outside the system with all harmful substances regulated below the emission standard. The solid content fixed in the wastewater secondary treatment step 7 is supplied again to the smelting furnace 1 as secondary sludge.
[0004]
As described above, the technology for removing harmful substances contained in the exhaust gas is almost established, but various improved technologies have been proposed (Japanese Patent Laid-Open Nos. 7-308542, 9-308817, and 10- 10). 216476).
JP-A-7-308542 discloses a mixture of lead concentrate or artificially synthesized lead sulfide (PbS) and naturally occurring pyrite (FeS 2 ) or other sulfide ores or synthesized iron sulfide. A method for removing mercury in exhaust gas by adsorbing and removing mercury by passing an exhaust gas accompanied by gaseous or mist-like mercury through an absorbent made of a material carrier is shown. In this method, the absorbent that is mixed with lead sulfide and iron sulfide and is supported on the porous material carrier can be used stably for a long time, has good mercury adsorption efficiency, and has the ability to remove mercury per unit weight of the absorbent. Since it is high, there is an effect that the filling layer filled with the absorbent can be downsized. Japanese Patent Laid-Open No. 9-308817 discloses an improved technique for removing harmful substances by absorbing, filtering or trapping them with a granular layer on the surface of the bag filter by a bag filter formed by supplying the granular material. Measures one or more of the concentrations of harmful substances in the exhaust gas at the bag filter outlet, and supplies the granular material used to form the granular layer on the bag filter surface based on the increase or decrease of the concentration By increasing or decreasing the amount, it becomes possible to minimize the amount of powder to be supplied to remove harmful substances in the exhaust gas. Japanese Patent Application Laid-Open No. 10-216476 discloses at least one of circulating liquid, absorption liquid used in a desulfurization apparatus, supply water used in a wet electric dust collector, circulating water, water in the dust collector main body, and exhaust gas at the dust collector inlet. A method of adding a mercury removing agent is shown in this figure, and this method is used to remove mercury, especially metallic mercury vapor, in exhaust gas with an extremely low concentration of the order of 10 μg / Nm 3 or less, which is discharged in large quantities from the emission source. Can be removed.
[0005]
[Problems to be solved by the invention]
On the other hand, in recent years, the disposal of huge amounts of industrial waste has become a serious social problem, and in order to effectively treat this industrial waste, parts that can be reused from oversized garbage such as waste home appliances and automobiles have been removed. The remaining parts are shredded into small pieces to produce shredder dust, and after recovering valuable materials, the development of recycling technology that uses the remaining dust as fuel resources has reached the practical stage. Has begun to be utilized as.
However, since this shredder dust contains a large amount of chlorine-containing plastics such as vinyl chloride, the use of shredder dust as a fuel will increase the chlorine concentration in the combustion exhaust gas, resulting in the following problems. As a result, new measures have become necessary for exhaust gas treatment and wastewater treatment.
[0006]
That is, in the exhaust gas treatment method as described above, in the gas cleaning step, the exhaust gas is separated into gas mainly containing SO 2 gas and waste water, and the waste water is passed through a solid-liquid separation device such as a thickener to obtain a solid content. And wastewater. When smelting using conventional fuels mainly containing coal and heavy oil, most of the mercury components are settled and separated as solids in the solid-liquid separation process, and the mercury content in the wastewater after solid-liquid separation is extremely small. On the other hand, when smelting using fuel containing shredder dust, mercury (II) chloride (HgCl 2 ) formed by combining mercury and chlorine is water-soluble, so the solid-liquid separation process The mercury content contained in the wastewater is greater than the mercury content contained in the solid content separated in step (b). Therefore, in the conventional treatment method, the mercury component is discharged out of the system by discharging the solid content after the solid-liquid separation step out of the system, but even if the solid component is discharged out of the system, the mercury component remains large. The part is not removed, and the wastewater after the solid-liquid separation process contains mercury components, which increases the mercury content in the gypsum recovered in the wastewater primary treatment process and hinders reuse. Was sought and a solution was sought.
[0007]
An object of the present invention is included in an exhaust gas that can easily and effectively remove mercury components contained in an exhaust gas discharged from a smelting furnace that performs smelting of ore containing sulfur using fuel containing shredder dust. It is to provide a method for removing mercury.
[0008]
[Means for Solving the Problems]
The invention according to claim 1 is an improvement of a method for removing mercury contained in exhaust gas discharged from a smelting furnace for smelting ore containing sulfur using fuel containing shredder dust.
As shown in FIG. 1, the characteristic configuration includes a gas cleaning step 12 for cleaning exhaust gas discharged from the smelting furnace 11 with water and separating it into a gas mainly composed of SO 2 gas and waste water, The solid-liquid separation step 14 for separating the solid content contained in the raw water sludge, the mercury component removal step 17 for removing the mercury component contained in the waste water by bringing the waste water from which the solid content has been separated into contact with the mercury removing agent, and the mercury component Waste water primary treatment process 18 in which calcium carbonate is added to the waste water from which the sulfuric acid is removed to separate the sulfuric acid component as gypsum from the sulfur component contained in the waste water, and the raw water sludge separated in the solid-liquid separation process 14 into the waste water from which the sulfuric acid component has been separated And a waste water secondary treatment step 21 for separating heavy metals mainly contained in the waste water as secondary sludge by adding a part of the waste water and calcium hydroxide.
[0009]
In the invention according to claim 1, the exhaust gas generated by smelting using fuel containing shredder dust is separated into gas mainly containing SO 2 gas and waste water in the gas cleaning step 12, Even if it isolate | separates into solid content and waste_water | drain by the solid-liquid separation process 14, a mercury component will not transfer to solid content, but a mercury component will be contained in a large amount in waste_water | drain. Therefore, by providing a mercury component removal step 17 between the solid-liquid separation step 14 and the waste water primary treatment step 18, the mercury component contained in the waste water can be easily brought into contact with the mercury removing agent in the mercury component removal step 17. And since it removes efficiently, a mercury component is not contained in the sulfuric acid component fixed as gypsum in the waste water primary treatment process 18, and the quality of the gypsum manufactured using this sulfuric acid component improves.
[0010]
The invention according to claim 2 is the invention according to claim 1, wherein a part of the waste water from which the mercury component is removed by the mercury removing agent in the mercury component removing step 17 is used as cleaning water for SO 2 gas in the gas cleaning step 12. This is a method of removing mercury to be reused.
In the invention according to claim 2, by reusing a part of the waste water from which the mercury component has been removed in the mercury component removing step 17 as the cleaning water for SO 2 gas in the gas cleaning step 12, the concentration of mercury contained in the cleaning water is reduced. The mercury load in the gas cleaning step 12 is reduced. Further, the mercury component concentration contained in the gas containing SO 2 gas as a main component can also be reduced.
[0011]
The invention according to claim 3 is the invention according to claim 1, wherein before the mercury component is removed in the mercury component removal step 17, the wastewater is passed through the sand layer to filter the remaining solids contained in the wastewater. The method for removing mercury further includes a sand filtration step 16.
In the invention which concerns on Claim 3, clogging by the remainder of the solid content contained in waste_water | drain is prevented in the mercury component removal process 17 which follows by allowing waste_water | drain to pass through the layer by sand in the sand filtration process 16. FIG.
[0012]
The invention according to claim 4 is the invention according to claim 1, wherein the mercury removing agent is activated carbon, and the activated carbon has an ability to adsorb 5 to 20% by weight of a mercury component with respect to 100% by weight of the activated carbon. This is a method for removing mercury.
The invention according to claim 5 is the method according to claim 1, wherein the smelting furnace 11 is a reflection furnace.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
When smelting using conventional fuels mainly containing coal and heavy oil, mercury contained in the exhaust gas discharged by smelting combines with selenium contained in the exhaust gas to form insoluble mercury selenide (II ) (HgSe) and mercury (II) selenide, which is insoluble in water, is contained in the solids separated by solid-liquid separation of the waste water. By discharging, the concentration of mercury components in the system could be reduced.
However, when smelting with fuel containing shredder dust, which is industrial waste, the shredder dust contains a large amount of chlorine component, so this chlorine combines with mercury and has the property of being soluble in water. The resulting mercury (II) chloride (HgCl 2 ) is formed. Therefore, even if the wastewater is separated into solid and wastewater as in the conventional treatment method and separated into solid and wastewater, the mercury component does not migrate to the solid content, and the wastewater contains a large amount of mercury component.
[0014]
In order to solve such problems, the inventors removed the mercury component before treating the wastewater having a high mercury content and a pH of 1 or less separated in the gas washing step, in the primary wastewater treatment step. The process of incorporating the process and developing the effect of removing the mercury component was developed, and the method of the present invention was completed. As a result of testing various adsorbents that can be applied to this mercury component removal process, activated carbon, fly ash, etc. show high durability against wastewater with a low pH, especially activated carbon other than mercury contained in wastewater. It was found that mercury can be selectively adsorbed without adsorbing heavy metals and can be used simply and effectively as an adsorbent for liquid phase mercury.
[0015]
Next, an embodiment of the present invention will be described with reference to the drawings, using as an example an exhaust gas generated by copper smelting, as a method for removing mercury contained in the exhaust gas.
As shown in FIG. 1, when an ore containing sulfur is smelted using fuel containing shredder dust, exhaust gas generated from the smelting furnace 11 includes SO 2 gas, SO 3 , MSO 4 (M is heavy metal), etc. Contains sulfur components, mercury components, and the like. This exhaust gas is sent to the gas cleaning step 12, where it is brought into gas-liquid contact with cleaning water, so that a sulfur component and a mercury component containing SO 2 gas as a main component, SO 3 other than SO 2 gas, MSO 4 and the like. Separated into wastewater containing etc. That is, in the gas cleaning step 12, the cleaning component absorbs a sulfur component and a mercury component containing SO 3 and MSO 4 other than the SO 2 gas. Of these, SO 3 reacts with the washing water to become sulfuric acid (H 2 SO 4 ). In the gas cleaning step 12, the cleaning water is subdivided into a large number of fine droplets by a nozzle or the like, and these are dispersed in the exhaust gas passing through the empty tower, and solid or liquid such as heavy metals or dust other than mercury floating in the exhaust gas. This is done with a spray-type scrubber that traps mercury particles. Gas mainly composed of SO 2 gas separated by the gas washing step 12, the discharge was removed recovering SO 2 gas as sulfuric acid or gypsum, out of the system in a state in which all of the hazardous materials is regulated to below the emission standard Is done.
[0016]
Solid wastewater containing sulfur components and mercury components including SO 3 and MSO 4 other than the SO 2 gas separated in the gas cleaning step 12 (including hydrofluoric acid, hydrochloric acid and sulfuric acid) has a solid content. Since it is contained, it separates into solid content and waste water in the solid-liquid separation step 14. Specifically, the solid content is separated from the waste water by concentrating the waste water with a thickener or the like, and solid-liquid separation of the concentrated raw water slurry. The separated solid is raw water sludge, and this raw water sludge is resupplied to the smelting furnace 11 or a part of the raw water sludge is supplied as a raw water slurry to the drainage secondary treatment step 21 described later. The wastewater from which the solid content has been separated in the solid-liquid separation step 12 is sent to the sand filtration step 16 where the wastewater is passed through a layer of sand to filter the remainder of the solid content contained in the wastewater. By applying this sand filtration step 16, in the subsequent mercury component removal step 17, clogging due to the remaining solids contained in the waste water is prevented.
[0017]
In the mercury component removal step 17, the wastewater from which the solid content has been separated is brought into contact with the mercury removing agent to remove the mercury component contained in the wastewater. In the mercury component removing step 17, most of the mercury components contained in the waste water are adsorbed by the mercury removing agent. Since the waste water is an acid solution having a pH of 1 or less, activated carbon or fly ash is used as the mercury removing agent. In particular, activated carbon is preferable because of its high adsorption ability. The particle size of the mercury removing agent is 6 to 100 mesh, preferably 10 to 30 mesh. When activated carbon is used as the mercury removing agent, the activated carbon has an ability to adsorb 5 to 20% by weight of a mercury component with respect to 100% by weight of the activated carbon, although it depends on the quality of the activated carbon.
Before sending the wastewater from which the mercury component has been removed to the wastewater primary treatment step 18, a part of the wastewater from which the mercury component has been removed is supplied to the water for washing the SO 2 gas in the gas washing step 12 and reused. By supplying the wastewater to the water for cleaning the SO 2 gas, the concentration of the mercury component contained in the washing water is lowered, and the concentration of the mercury component contained in the gas containing the SO 2 gas as a main component can also be reduced. In the subsequent SO 2 recovery, for example, the mercury load of the waste gypsum plant can also be reduced. Moreover, since the mercury component density | concentration of the waste_water | drain sent for subsequent waste water treatment also falls, the mercury component density | concentration of the gypsum obtained by neutralizing the sulfuric acid content in waste_water | drain can also be lowered | hung.
[0018]
In the wastewater from which the mercury component has been removed, in the wastewater primary treatment step 18, by adding calcium carbonate (CaCO 3 ), the pH of the wastewater is adjusted to 2 to 4 to fix only the sulfuric acid component of the sulfur component, The sulfuric acid component is separated as gypsum (CaSO 4 ) by liquid separation.
[0019]
The wastewater from which the sulfuric acid component has been separated in the wastewater primary treatment step 18 is combined with a portion of the raw water sludge (raw water slurry state) separated in the solid-liquid separation step 14 in the wastewater secondary treatment step 21 together with calcium hydroxide (Ca (OH ) Add 2 ) to adjust the pH of the wastewater to 11-12, immobilize heavy metals mainly contained in the wastewater together with mercury contained in the raw water sludge (raw water slurry), and solidify the heavy metal by solid-liquid separation. Separate as minutes. Wastewater is discharged outside the system with all harmful substances regulated below the emission standard. The solid content fixed in the wastewater secondary treatment step 21 is supplied again to the smelting furnace 11 as secondary sludge.
[0020]
Next, the distribution ratio of mercury contained in the exhaust gas will be described using the mercury removal method of the present invention and the conventional method.
A case will be described in which exhaust gas generated by smelting using fuel mainly containing coal and heavy oil not containing shredder dust is treated by a conventional mercury removal method. As shown in FIG. 3, first, assuming that the ratio of the mercury component contained in the exhaust gas first generated from the smelting furnace is 100%, a part of the mercury component contained in the exhaust gas is combined with selenium contained in the exhaust gas. Formed mercury (II) selenide that is insoluble in water and remains in the gas even after gas cleaning, so all the mercury components were not transferred to the wastewater and were separated by the gas cleaning process. Mercury components are distributed at a rate of 10% in the gas containing SO 2 as the main component, and at a rate of 90% in the waste water. In the solid-liquid separation process, the mercury component contained in the wastewater is transferred to the raw water sludge at a rate of 90% and to the wastewater at a rate of 10%. Accordingly, the mercury component contained in the wastewater is transferred at a rate of 81% on the raw water sludge side and 9% on the wastewater side, out of 90%. The mercury component transferred to the drainage side is almost 9% of the mercury component together with the sulfuric acid component in the gypsum in the primary wastewater treatment process. Of the 81% of the mercury component transferred to the raw water sludge, if a part of the raw water sludge is a and the remainder is 1-a, the distribution ratio of the mercury component supplied to the wastewater secondary treatment process is (1- a) × 81%, and the balance is a × 81%. Mercury components supplied to the wastewater secondary treatment process are transferred to the secondary sludge as solids, and the remainder of the raw water sludge and the secondary sludge are resupplied to the smelting furnace. The rate is 81%.
[0021]
Next, when the distribution ratio of the mercury component contained in the continuously generated exhaust gas is [+ α], the ratio of the mercury component sent to the gas cleaning step is [81% + α]. In this gas cleaning step, as described above, the transition is performed at a rate of 10% for the gas mainly composed of SO 2 gas and 90% for the waste water, and therefore [81% + α on the gas side mainly composed of SO 2 gas. ] × 0.1, and [81% + α] × 0.9 at the drainage side. In the solid-liquid separation process, the mercury component contained in the wastewater is transferred to the raw water sludge at a rate of 81% and 9% to the wastewater, respectively, so out of the mercury component [81% + α] × 0.9 contained in the wastewater, It moves at a rate of [81% + α] × 0.81 on the raw water sludge side and [81% + α] × 0.09 on the drainage side. In the primary wastewater treatment process, the mercury component that has moved to the wastewater side is [81% + α] × 0.09, and almost all of the mercury component is separated as a solid content together with the sulfuric acid component and contained in the gypsum. Of the mercury component [81% + α] × 0.81 transferred to the raw water sludge, assuming that a part of the raw water sludge is a and the remainder is 1-a, the mercury component supplied to the wastewater secondary treatment process The distribution ratio is (1−a) × [81% + α] × 0.81, and the remainder is a × [81% + α] × 0.81. The mercury component supplied to the wastewater secondary treatment process is transferred to the secondary sludge as a solid content, and the remainder of the raw water sludge and the secondary sludge are re-supplied to the smelting furnace. The distribution rate is [81% + α] × 0.81.
If the mercury distribution ratio [+ α] of the exhaust gas generated continuously is 100%, which is the same ratio as the mercury distribution ratio of the first exhaust gas generated, the mercury component returning to the smelting furnace again exceeds 100%. Therefore, every time the mercury component is resupplied to the smelting furnace, there arises a problem that the concentration of the mercury component increases.
[0022]
A case where exhaust gas generated by smelting using fuel containing shredder dust is treated by a conventional mercury removal method will be described. As shown in FIG. 4, first, assuming that the ratio of mercury component contained in the exhaust gas first generated from the smelting furnace is 100%, the gas mainly composed of SO 2 gas separated by the gas cleaning step is mercury. Ingredients are distributed at a rate of 5% and distributed to the wastewater at a rate of 95%. Here, compared with the case where the fuel not containing shredder dust is used, the distribution ratio of mercury between the gas separated in the gas cleaning step and the waste water is different. Shredder dust contains chlorine. Since mercury (II), which is soluble in mercury and water, was formed, it is thought that a large amount of mercury component was transferred to the drainage side. In the solid-liquid separation process, the mercury component contained in the wastewater is transferred to the raw water sludge at a rate of 10% and to the wastewater at a rate of 90%. Accordingly, the mercury component contained in the wastewater moves out of 95% at a ratio of 9.5% to the raw water sludge side and 85.5% to the wastewater side. The mercury component transferred to the waste water side is contained in the gypsum in the waste water primary treatment process, in which almost all of the mercury component is separated by 85.5% as a solid content together with the sulfuric acid component. Assuming that 9.5% of the mercury component transferred to the raw water sludge is a part of the raw water sludge and that the remainder is 1-a, the distribution ratio of the mercury component supplied to the wastewater secondary treatment process is ( 1-a) × 9.5%, and the balance is a × 9.5%. Mercury components supplied to the wastewater secondary treatment process are transferred to the secondary sludge as solids, and the remainder of the raw water sludge and the secondary sludge are resupplied to the smelting furnace. The rate is 9.5%.
[0023]
Next, assuming that the distribution ratio of mercury contained in the continuously generated exhaust gas is [+ α], the ratio of the mercury component sent to the gas cleaning step is [9.5% + α]. 5% to the gas side of the main component as SO 2 gas described above in the gas washing step, the process proceeds at a rate of 95% in the waste water side, the gas side composed mainly of SO 2 gas [9 .5% + α] × 0.05, and on the drain side, [9.5% + α] × 0.95. In the solid-liquid separation process, the mercury component contained in the wastewater is transferred to the raw water sludge at a rate of 10% and 90% to the wastewater, respectively. Therefore, the mercury component contained in the wastewater [9.5% + α] × 0.95 Of these, [9.5% + α] × 0.095 is transferred to the raw water sludge side, and [9.5% + α] × 0.855 is transferred to the drainage side. The mercury component transferred to the drainage side is contained in the gypsum in the primary wastewater treatment process, with [9.5% + α] × 0.855 almost all mercury components separated as solids together with the sulfuric acid component. Of the mercury component [9.5% + α] × 0.095 transferred to the raw water sludge, assuming that a part of the raw water sludge is a and the remainder is 1-a, it is supplied to the secondary wastewater treatment process. The distribution ratio of the mercury component is (1−a) × [9.5% + α] × 0.095, and the balance is a × [9.5% + α] × 0.095. The mercury component supplied to the wastewater secondary treatment process is transferred to the secondary sludge as a solid content, and the remainder of the raw water sludge and the secondary sludge are re-supplied to the smelting furnace. The distribution rate is [9.5% + α] × 0.095.
Assuming that the mercury distribution rate [+ α] of the exhaust gas generated continuously is 100%, which is the same ratio as the mercury distribution rate of the first generated exhaust gas, compared to the case where the fuel containing no shredder dust is used. Although the distribution ratio of the mercury component returning to the smelting furnace again becomes small, in the primary wastewater treatment process, a large amount of mercury component is contained in the recycled gypsum, and the quality of the gypsum is lowered.
[0024]
The case where the exhaust gas generated by smelting using fuel containing shredder dust is treated by the mercury removal method of the present invention will be described. As shown in FIG. 2, first, assuming that the ratio of the mercury component contained in the exhaust gas first generated from the smelting furnace is 100%, the gas mainly composed of SO 2 gas separated in the gas cleaning step is mercury. Ingredients are distributed at a rate of 5% and distributed to the wastewater at a rate of 95%. In the solid-liquid separation process, the mercury component contained in the wastewater is transferred to the raw water sludge at a rate of 10% and to the wastewater at a rate of 90%. Accordingly, the mercury component contained in the wastewater moves out of 95% at a ratio of 9.5% to the raw water sludge side and 85.5% to the wastewater side. The mercury component transferred to the drainage side is 85.5% in the mercury component removal process, and almost all the mercury component is removed by the mercury removing agent. Assuming that 9.5% of the mercury component transferred to the raw water sludge is a part of the raw water sludge and that the remainder is 1-a, the distribution ratio of the mercury component supplied to the wastewater secondary treatment process is ( 1-a) × 9.5%, and the balance is a × 9.5%. Mercury components supplied to the wastewater secondary treatment process are transferred to the secondary sludge as solids, and the remainder of the raw water sludge and the secondary sludge are resupplied to the smelting furnace. The rate is 9.5%.
[0025]
Next, when the distribution ratio of the mercury component contained in the continuously generated exhaust gas is [+ α], the ratio of the mercury component sent to the gas cleaning step is [9.5% + α]. 5% to the gas side of the main component as SO 2 gas described above in the gas washing step, the process proceeds at a rate of 95% in the waste water side, the gas side composed mainly of SO 2 gas [9 .5% + α] × 0.05, and on the drain side, [9.5% + α] × 0.95. In the solid-liquid separation process, the mercury component contained in the wastewater is transferred to the raw water sludge at a rate of 10% and 90% to the wastewater, respectively. Therefore, the mercury component contained in the wastewater [9.5% + α] × 0.95 Of these, [9.5% + α] × 0.095 is transferred to the raw water sludge side, and [9.5% + α] × 0.855 is transferred to the drainage side. In the mercury component removal process, almost all mercury components [9.5% + α] × 0.855 are removed by the mercury removing agent. Of the mercury component [9.5% + α] × 0.095 transferred to the raw water sludge, assuming that a part of the raw water sludge is a and the remainder is 1-a, it is supplied to the secondary wastewater treatment process. The distribution ratio of the mercury component is (1−a) × [9.5% + α] × 0.095, and the balance is a × [9.5% + α] × 0.095. The mercury component supplied to the wastewater secondary treatment process is transferred to the secondary sludge as a solid content, and the remainder of the raw water sludge and the secondary sludge are re-supplied to the smelting furnace. The distribution rate is [9.5% + α] × 0.095.
[0026]
In this way, the distribution ratio of the mercury component that returns to the smelting furnace decreases in the amount of mercury component each time it is re-supplied, so it is included in SO 2 separated in the gas cleaning process and gypsum separated in the wastewater primary treatment process. Mercury component concentration is also reduced. Although not shown in FIG. 2, a part of the waste water from which the mercury component was removed in the mercury component removal step is reused as water for washing SO 2 in the gas washing step, and thus separated in the gas washing step. The distribution rate of mercury contained in the wastewater is smaller than the value described in FIG.
[0027]
【The invention's effect】
As described above, the present invention provides a method for removing mercury components between a solid-liquid separation step and a waste water primary treatment step in a method for removing mercury contained in exhaust gas generated by smelting using fuel containing shredder dust. By providing a process, the mercury component contained in the waste water can be removed by bringing the waste water into contact with the mercury removing agent in this mercury component removing step. The mercury content in this gypsum is drastically reduced to a level necessary and sufficient for reuse, eliminating the problems associated with using shredder dust as a fuel resource.
[Brief description of the drawings]
FIG. 1 is a diagram showing a method for removing mercury contained in exhaust gas of the present invention.
FIG. 2 is a graph showing the distribution ratio of mercury when exhaust gas generated by smelting using fuel containing shredder dust is treated using the mercury removal method of the present invention.
FIG. 3 is a diagram showing a distribution ratio of mercury when exhaust gas generated by smelting using a fuel not containing shredder dust is treated using a conventional mercury removal method.
FIG. 4 is a diagram showing a distribution ratio of mercury when exhaust gas generated by smelting using fuel containing shredder dust is treated using a conventional mercury removal method.
FIG. 5 is a view showing a conventional method for removing mercury contained in exhaust gas.
[Explanation of symbols]
11 Smelting furnace 12 Gas cleaning process 14 Solid-liquid separation process 17 Mercury component removal process 18 Wastewater primary treatment process 21 Wastewater secondary treatment process

Claims (5)

シュレッダーダストを含む燃料を用いて硫黄を含む鉱石の製錬を行う製錬炉(11)から排出される排ガスに含まれる水銀を除去する方法において、
前記製錬炉(11)から排出された排ガスを水で洗浄してＳＯ2ガスを主成分とするガスと排水とに分離するガス洗浄工程(12)と、
前記排水に含まれる固形分を原水スラッジとして分離する固液分離工程(14)と、
前記固形分を分離した排水を水銀除去剤に接触させて前記排水に含まれる水銀成分を除去する水銀成分除去工程(17)と、
前記水銀成分を除去した排水に炭酸カルシウムを加えて前記排水中に含まれる硫黄成分のうち硫酸成分を石膏として分離する排水一次処理工程(18)と、
前記硫酸成分を分離した排水に前記固液分離工程(14)で分離した原水スラッジの一部と水酸化カルシウムとを加えて前記排水に主として含まれる重金属を二次スラッジとして分離する排水二次処理工程(21)と
を含むことを特徴とする排ガスに含まれる水銀の除去方法。In a method for removing mercury contained in exhaust gas discharged from a smelting furnace (11) for smelting ore containing sulfur using fuel containing shredder dust,
The gas cleaning process of the exhaust gas discharged from the smelting furnace (11) is separated into a waste water and gas mainly composed of SO 2 gas was washed with water (12),
A solid-liquid separation step (14) for separating solids contained in the wastewater as raw water sludge;
A mercury component removing step (17) for removing the mercury component contained in the waste water by contacting the waste water from which the solid content has been separated with a mercury removing agent,
Waste water primary treatment step (18) for separating the sulfuric acid component as gypsum from the sulfur component contained in the waste water by adding calcium carbonate to the waste water from which the mercury component has been removed,
Waste water secondary treatment for separating heavy metals mainly contained in the waste water as secondary sludge by adding a part of the raw water sludge separated in the solid-liquid separation step (14) and calcium hydroxide to the waste water from which the sulfuric acid component has been separated. And a step (21) of removing mercury contained in the exhaust gas. 水銀成分除去工程(17)で水銀除去剤により水銀成分を除去した排水の一部をガス洗浄工程(12)におけるＳＯ2ガスの洗浄水に再利用する請求項１記載の水銀の除去方法。The method for removing mercury according to claim 1, wherein a part of the waste water from which the mercury component has been removed by the mercury removing agent in the mercury component removing step (17) is reused as the SO 2 gas washing water in the gas washing step (12). 水銀成分除去工程(17)で水銀成分を除去する前に砂による層に排水を通過させて前記排水に含まれる固形分の残部を濾過する砂濾過工程(16)を更に含む請求項１記載の水銀の除去方法。The sand filtration step (16) according to claim 1, further comprising a sand filtration step (16) for filtering the remainder of the solids contained in the wastewater by passing the wastewater through a layer of sand before removing the mercury component in the mercury component removal step (17). How to remove mercury. 水銀除去剤が活性炭であって、前記活性炭が前記活性炭１００重量％に対して５〜２０重量％の水銀成分を吸着させる能力を有する請求項１記載の水銀の除去方法。The mercury removal method according to claim 1, wherein the mercury removing agent is activated carbon, and the activated carbon has an ability to adsorb 5 to 20% by weight of a mercury component with respect to 100% by weight of the activated carbon. 製錬炉(11)が反射炉である請求項１記載の水銀の除去方法。The method for removing mercury according to claim 1, wherein the smelting furnace (11) is a reflection furnace.
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