JP2004076152A

JP2004076152A - Method for producing stainless steel reusing waste material in stainless steel producing process

Info

Publication number: JP2004076152A
Application number: JP2003159817A
Authority: JP
Inventors: Hiroshi Sugidachi; 杉立　宏志; Itsuo Miyahara; 宮原　逸雄
Original assignee: Kobe Steel Ltd
Current assignee: Kobe Steel Ltd
Priority date: 2002-06-18
Filing date: 2003-06-04
Publication date: 2004-03-11
Anticipated expiration: 2023-06-04
Also published as: JP4295557B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a stainless steel with which the decrease of Cr reducing energy and the increase of Cr yield into molten steel can be obtained when waste of dust etc., developed in a stainless steel producing process is reused. <P>SOLUTION: In the producing method for stainless steel having a stainless steel producing process 1, in which after making molten steel G by melting raw material with an electric furnace 11, this molten steel G is refined with a refining furnace 12, such as AOD, to make the stainless steel H, a bulky material C including carbonaceous material is formed with a briquette press 2 by adding carbonaceous reducing agent B into the zinc-containing waste A, such as electric furnace dust developed in the stainless steel producing process and the zinc is reduced, evaporated and removed by heating this bulky material C in a rotary hearth furnace 3 to make the dezincing bulky material D, and this dezincing bulky material D is charged in the oxidizing period of the refining furnace 12 as a coolant. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、ステンレス鋼製造工程で発生するダストやスケール等の廃棄物を再利用してステンレス鋼を製造する方法に関する。
【０００２】
【従来の技術】
ステンレス鋼は、一般に、スクラップやＦｅ−Ｃｒ、Ｆｅ−Ｎｉ、金属Ｎｉなどの原料を電気炉で溶解したのち、この溶鋼を精錬炉で精錬を行うことにより製造される（ステンレス鋼製造工程）。通常、電気炉は原料を単に溶解する溶解期を担当するが、場合により酸素吹き込みにより溶鋼からに脱炭を行う酸化期（「予備脱炭期」ともいう。）を設けることもある。精錬炉では酸素吹き込みにより溶鋼の脱炭を行う酸化期と、酸化期において酸化されてスラグ中に移行したＣｒを再度還元して金属に戻し溶鋼中へ回収する還元期と、溶鋼の脱酸・成分調整・温度調整を行う仕上精錬期を担当する。電気炉や精錬炉（ＶＯＤ、ＲＨ，ＡＯＤ、ＭＲＰなど）からは排ガスに随伴してダストが発生する。このダストはＦｅ、Ｎｉ、Ｃｒなどの成分を含んでいるため原料として再利用することが好ましい。また、ダストはＣｒ^６＋を含むため外部処理をするには多大なコストを要することから、経済的な観点からもリサイクルすることが望まれている。しかし、ダスト中には主にスクラップ由来のＺｎが含まれる。そのためダストをそのまま電気炉や精錬炉に戻すとＺｎが還元揮発してふたたび排ガス中に飛散するためダスト中にＺｎが濃縮される。ダスト中にＺｎが濃縮すると炉口や排ガス配管内にダストが付着してコーティングなどの問題が発生するうえ、ダストをリサイクルするたびごとにＺｎの酸化・還元を繰り返すことになるためエネルギー効率が悪い問題がある（ダスト中のＺｎの還元は吸熱反応であり炉内で行われるため熱エネルギーが消費される。一方、Ｚｎの酸化は発熱反応であるが排ガス系で行われるためその熱エネルギーのほとんどは無駄に放出される）。
【０００３】
そこで、ダストをステンレス鋼製造工程とは別の工程で還元処理したのちステンレス鋼製造工程に戻して再利用する方法の提案がなされている。
【０００４】
（従来技術１）
特許文献１には、ミルスケール、ダスト、スラッジなどに炭素質還元剤を添加してペレットに造粒し、このペレットを回転炉床炉などで加熱・還元して金属含有ペレットとなし、この金属含有ペレットを銑鉄製造用の電気アーク炉などで溶融して金属有価物（Ｆｅ、Ｎｉ、Ｃｒ、Ｍｏなど）を分離・回収する方法が開示されている。回収された金属有価物は溶融金属中に含まれ、この溶融金属は電気アーク炉から連続鋳銑機の成形型に注がれ金属塊とされる。そして実施例（例ＩＩＩ）には、２．９５質量％の炭素を含有する金属塊をステンレス鋼製造用の電気アーク炉に追加的に添加することが示されている。
【０００５】
（従来技術２）
特許文献２には、ステンレス鋼製造工程で生じた含クロム廃棄物に適当量のクロム鉱石を配合した含クロム配合物とコークスとを造粒してペレットを製造する造粒工程と、そのペレットをロータリハース炉の炉床に静置して、燃焼ガスにより加熱し、ペレットの崩壊・粉化を最小限にして、含クロム鉄ペレットを製造する還元工程と、その還元工程の排ガスの持つ顕熱を水蒸気として回収する廃熱回収工程と、還元工程で発生し、廃熱回収工程の排ガスに同伴された含亜鉛ダストを分離捕集し、回収する含亜鉛ダスト回収工程とからなるステンレス鋼製造工程廃棄物の再利用方法が開示されている。そして、実施例には、この含クロム鉄ペレットは電気炉で主原料の一部として溶解され含クロム銑鉄を製造することが示されている。
【０００６】
【特許文献１】
特開昭５６−９３８３４号公報
【特許文献２】
特開平９−２０９０４７号公報
【０００７】
【発明が解決しようとする課題】
上記従来技術１および２によれば、ペレットが回転炉床炉（ロータリハース炉）内で加熱されると、ペレット中のＺｎは炭素質還元剤により還元されて揮発しペレットから除去される。したがって、この還元後のペレットを電気炉に供給してもダスト中にＺｎが濃縮されることがなく、排ガス系でのコーティングの問題等は回避される。
【０００８】
ところが、上記従来技術１および２においては、還元後のペレットを溶解用電気炉に装入し、炭素濃度の高い含クロム銑鉄を製造するのに用いている。そのため、還元後のペレット（金属塊、含クロム鉄ペレット）中に残存させる炭素含有量は比較的高い。すなわち、上述したように、従来技術１の実施例では金属塊中の炭素含有量は２．９５質量％である。また、従来技術２の実施例２では、含クロム鉄ペレット中の炭素含有量は明示されていないが、含クロム銑鉄１２５質量部中に炭素分が４．７質量％存在し、これが含クロム鉄ペレット２１１質量部から製造されていることから、電気炉内でのクロムの還元に消費された炭素分を考慮して推算すると含クロム鉄ペレット中には２．８質量％以上の炭素分が含まれていることになる。そして、この含クロム銑鉄を次の酸化期で目標の炭素レベルまで脱炭し、ついで還元、仕上精錬を行ってステンレス鋼としている。脱炭は溶鋼中への酸素の吹き込みにより行うため、脱炭進行とともにＣｒが酸化しスラグ中へ移行する。脱炭完了後、還元期において還元剤としてＦｅ−Ｓｉなどを添加してこのＣｒ酸化物を還元することにより金属Ｃｒに戻して溶鋼中へ回収する。
【０００９】
ここで、含クロム鉄ペレット中のＣｒは回転炉床炉内での加熱によっては十分に還元されず（通常、金属化率は４０％程度以下）、大部分は酸化物の形態で残存する。この未還元のＣｒ酸化物は電気炉での溶解期において、ペレット中の残留炭素分や溶鋼中の炭素分により還元されて金属化され溶鋼中に回収されるが、その一部はスラグ中に残存してスラグ（電気炉スラグ）とともに廃棄される。そして溶鋼中に回収されたＣｒは、その後の酸化期（または予備脱炭期）においてその一部が酸化されてスラグ中に移行する。このスラグ中のＣｒはその後の還元期で再度還元され溶鋼中に回収されるが、一部はスラグ中に残存してスラグ（精錬炉スラグ）とともに廃棄される。このように、含クロム鉄ペレット中の未還元のＣｒ酸化物は、溶解期で還元後、酸化期（または予備脱炭期）で酸化され、さらに還元期で還元されるため吸熱反応である還元エネルギーが余分に必要となりエネルギーロスとなる。また、電気炉スラグと精錬炉スラグの両方にＣｒが残存するため、溶鋼へのＣｒ歩留（収率）が低い問題がある。
【００１０】
そこで本発明の目的は、ステンレス鋼製造工程で発生するダスト等の廃棄物を再利用するに際し、Ｃｒの還元エネルギーの減少とＣｒの溶鋼への収率の上昇を可能とするステンレス鋼の製造方法を提供することにある。
【００１１】
【課題を解決するための手段】
請求項１の発明は、原料を溶解して溶鋼としたのち、この溶鋼を精錬してステンレス鋼とするステンレス鋼製造工程と、前記ステンレス鋼製造工程で発生する亜鉛含有廃棄物に炭素質還元剤を添加して混合物とする還元剤添加工程と、この混合物を加熱することにより亜鉛を揮発除去して脱亜鉛混合物となす熱処理工程と、この脱亜鉛混合物を、前記ステンレス製造工程に冷却材として炉に装入する装入工程とを設けたことを特徴とするステンレス鋼の製造方法である。
【００１２】
請求項２の発明は、原料を溶解して溶鋼としたのち、この溶鋼を精錬してステンレス鋼とするステンレス鋼製造工程と、前記ステンレス鋼製造工程で発生する亜鉛含有廃棄物に炭素質還元剤を添加して混合物とする還元剤添加工程と、この混合物を加熱することにより亜鉛を揮発除去して脱亜鉛混合物となす熱処理工程と、この脱亜鉛混合物を塊成化して脱亜鉛塊成物とする脱亜鉛塊成物塊成化工程と、この脱亜鉛塊成物を、前記ステンレス製造工程に冷却材として炉に装入する装入工程とを設けたことを特徴とするステンレス鋼の製造方法である。
【００１３】
請求項３の発明は、原料を溶解して溶鋼としたのち、この溶鋼を精錬してステンレス鋼とするステンレス鋼製造工程と、前記ステンレス鋼製造工程で発生する亜鉛含有廃棄物に炭素質還元剤を添加して混合物とする還元剤添加工程と、この混合物を塊成化して炭材内装塊成物を形成する炭材内装塊成物塊成化工程と、この炭材内装塊成物を加熱することにより亜鉛を揮発除去して脱亜鉛塊成物となす熱処理工程と、この脱亜鉛塊成物を、前記ステンレス製造工程に冷却材として炉に装入する装入工程とを設けたことを特徴とするステンレス鋼の製造方法である。
【００１４】
請求項４の発明は、前記炭素質還元剤の添加量により前記混合物中の余剰炭素量を調整することによって前記冷却材中の残留炭素量を２質量％以下とする請求項１〜３のいずれか１項に記載のステンレス鋼の製造方法である。ここに、余剰炭素量（質量％）＝〔前記混合物中の炭素量（質量％）〕−〔前記混合物中に含まれるＦｅ、ＮｉおよびＺｎと結合している酸素量（質量％）〕×１２／１６である。
【００１５】
請求項５の発明は、前記冷却材を装入した後に溶鋼を強撹拌することにより有価金属の収率を高める請求項１〜４のいずれか１項に記載のステンレス鋼の製造方法である。
【００１６】
請求項６の発明は、前記冷却材の装入を前記ステンレス製造工程における酸化期および／または還元期に行う請求項１〜５のいずれか１項に記載のステンレス鋼の製造方法である。
【００１７】
請求項７の発明は、前記冷却材の装入を前記ステンレス製造工程における酸化期の末期および／または還元期の初期に行う請求項１〜５のいずれか１項に記載のステンレス鋼の製造方法である。
【００１８】
請求項８の発明は、ステンレス鋼製造工程で発生する亜鉛含有廃棄物に炭素質還元剤を添加して混合物となし、この混合物を加熱することにより亜鉛を揮発除去して脱亜鉛混合物となし、この脱亜鉛混合物を塊成化して残留炭素量を２質量％以下とした脱亜鉛塊成物である。
【００１９】
請求項９の発明は、ステンレス鋼製造工程で発生する亜鉛含有廃棄物に炭素質還元剤を添加して混合物となし、この混合物を塊成化して炭材内装塊成物を形成し、この炭材内装塊成物を加熱することにより亜鉛を揮発除去して残留炭素量を２質量％以下とした脱亜鉛塊成物である。
【００２０】
【発明の実施の形態】
以下、本発明の詳細について図を参照しつつさらに詳細に説明する。
【００２１】
実施形態の一例として、図１に示すように、原料（主原料Ｅ、造滓剤Ｆ）を溶解して溶鋼Ｇとする電気炉１１と、この溶鋼Ｇを精錬してステンレス鋼Ｈとする精錬炉であるＡＯＤ１２とからなるステンレス鋼製造工程１についての適用例を説明する。
【００２２】
ステンレス鋼製造工程１で発生する電気炉ダストなどの亜鉛含有廃棄物Ａを石炭などの炭素質還元剤Ｂと混合して図示しない混合物とする（還元剤添加工程）。この混合物をブリケットプレスなどの成形機２で塊成化し、炭材内装塊成物Ｃとする（炭材内装塊成物塊成化工程）。亜鉛含有廃棄物Ａとしては、電気炉ダストのほかにミルスケール、ミルスラッジ、ＡＯＤダストその他の精錬炉ダストを用いてもよく、これらを適宜混合して用いてもよい。炭素質還元剤Ｂとしては石炭のほかにコークス粉、木炭、廃トナーその他の炭化物が使用でき、これらを適宜混合して用いてもよい。また、必要により副原料やバインダーを添加してもよい。成形機２としてはブリケットプレスなどによる圧縮成形機のほかに転動造粒機や押出成形機などを用いてもよい。炭素質還元剤Ｂの添加と塊成化は同一の機械で行ってもよく、例えば皿型の造粒機や混合機などで混合しつつ塊成化してもよい。
【００２３】
得られた炭材内装塊成化物Ｃを還元炉である回転炉床炉３に装入する。還元炉３としては回転炉床炉のほか多段炉、ロータリキルンなどを用いることもできる。炭材内装塊成化物Ｃの水分含有量が高い場合には還元炉３への装入前に図示しないドライヤなどを用いて乾燥を行ってもよい。
【００２４】
還元炉３内で１１００〜１４００℃に加熱された炭材内装塊成物ＣからはＺｎのほかＰｂなどの重金属が還元揮発により除去され、Ｆｅ、Ｎｉ、Ｃｒ、Ｍｏなどの金属化合物が固体のまま還元され金属化された、脱亜鉛塊成物Ｄが得られる（熱処理工程）。ただし、Ｃｒの金属化率はそれほど高くなく、炭材内装塊成化物Ｃ中の炭素質還元剤Ｂ量や還元炉３内の加熱温度を調整しても４０％程度である。一方、ＦｅやＮｉの金属化率は炭材内装塊成化物Ｃ中の炭素質還元剤Ｂ量と還元炉３内の加熱温度を調整することにより９０％以上とすることができる。
【００２５】
ここで、ステンレス鋼製造工程１においては、電気炉１１にスクラップ、Ｆｅ−Ｃｒ、Ｆｅ−Ｎｉ、金属Ｎｉなどからなる主原料Ｅと生石灰などの造滓剤Ｆを装入しアーク加熱等により溶解して溶鋼Ｇを製造する。後工程にＡＯＤ１２を用いる場合には、電気炉１１は原料を単に溶解する溶解期のみを担当する。ついで、この溶鋼ＧをＡＯＤ１２に移しかえて精錬を行う。ＡＯＤ１２においては、溶鋼中にＡｒとともに酸素を吹き込んで溶鋼の脱炭を行う酸化期と、この酸化期において酸化されスラグ中に移行したＣｒをＡｒのみ吹き込んで溶鋼を攪拌することにより溶鋼中のＣで還元して金属に戻し溶鋼中に回収する還元期と、Ｆｅ−Ｓｉなどの脱酸剤（還元剤）や合金元素などを添加してＡｒのみを吹き込んで溶鋼を撹拌し、溶鋼の脱酸・成分調整・温度調整を行う仕上精錬期を担当する。ＡＯＤ１２で精錬された溶鋼はステンレス鋼Ｈとなり次工程の鋳造工程４へ送られる。
【００２６】
回転炉床炉３で加熱して得られた脱亜鉛塊成物Ｄは、ＡＯＤ１２の酸化期および／または還元期に冷却材として装入される。脱亜鉛塊成物ＤはＡＯＤ１２に装入する前に亜鉛が十分除去されているため、前述の従来技術１および２と同様、ダスト中にＺｎが濃縮されることがなく、排ガス系でのコーティングの問題等は発生しない。
【００２７】
さらに、脱亜鉛塊成物Ｄを電気炉１１の溶解期でなく直接ＡＯＤ１２の酸化期および／または還元期に装入するため、電気炉スラグ中に脱亜鉛塊成物Ｄ由来のＣｒが残存することがなく、従来技術１および２に比べＣｒ歩留が上昇する効果がある。また、脱亜鉛塊成物Ｄ中のＣｒ酸化物に関し、一旦還元されたのち再度酸化されるという無駄な経路が省略されるため、余分な還元エネルギーを必要とせずエネルギー効率が改善される効果もある。なお、還元期の末期（脱炭のための酸素吹き込み終了のころ）および／または還元期の初期（脱酸剤の添加のころ）に装入すれば、Ｃｒを再度酸化させることをいっそう確実に防げるため、より好ましい。
【００２８】
なお、回転炉床炉３における加熱後の塊成化物（脱亜鉛塊成物）Ｄの脱亜鉛率が過度に低下しない程度に炭材内装塊成物Ｃ中（すなわち前記混合物中）の炭素質還元剤Ｂ量（すなわち、余剰炭素量）は少なくしておくことが好ましい。炭材内装塊成物Ｃ中の炭素質還元剤Ｂ量を多くすると脱亜鉛塊成化物Ｄ中の残留炭素量が多くなることにより、これをＡＯＤ１２の酸化期に冷却材として使用すると脱炭のための酸素使用量が多くなることに加え、酸化期が延長され生産性が低下するためである。酸化期が延長される理由としては、溶鋼中の炭素濃度が低い領域（例えば０．４質量％以下）では脱炭反応の律速過程は溶鋼中Ｃの拡散過程と考えられるが、脱亜鉛塊成物Ｄからの炭素はもともと溶鋼中に存在したＣに比べて溶鋼への溶け落ちに時間がかかること、溶け落ち時点でまわりの溶鋼に比べて炭素分が高い領域になっていることにより拡散が遅いためと考えられる。
【００２９】
このように炭材内装塊成物Ｃ中の炭素質還元剤Ｂ量を制限すると脱亜鉛塊成物Ｄ中の鉄の金属化率は低下するものの、脱亜鉛塊成物Ｄ中の酸化鉄の増加により冷却材としての効果は却って増大し、その冷却効果は通常のスクラップによる冷却効果の２倍程度となる。
【００３０】
ＡＯＤ１２で酸化期の冷却材として装入された脱亜鉛塊成物Ｄは溶鋼中に溶け落ちるが、脱亜鉛塊成物Ｄ中に含まれていた未還元のＣｒは、後工程である還元期にＦｅ−Ｓｉなどの還元剤を装入しＡｒガスで強力に撹拌することにより収率良く回収できる。
【００３１】
また、残留炭素量が少ないほど脱亜鉛塊成物Ｄの強度は高くなり、輸送時や保管時あるいは精錬炉１２への装入時における粉化が少なくなり歩留が向上する利点もある。
【００３２】
精錬炉１２としてはＡＯＤのほかＶＯＤ、ＭＲＰなどを用いることができる。精錬炉１２としてＶＯＤを用いる場合には、電気炉１１では溶解期のあとに酸化期（予備脱炭期）と還元期を設け、ＶＯＤでは仕上精錬期のみを担当する。したがって、電気炉１１での酸化期（予備脱炭期）および／または還元期に脱亜鉛塊成物Ｄを冷却材として装入する。電気炉１１の次工程の還元期で脱亜鉛塊成物中の未還元Ｃｒが還元されて溶鋼中に回収されたのち、溶鋼はＶＯＤに移しかえられる。ＶＯＤの仕上精錬期ではＣｒの酸化を抑制するため冷却材の使用量が少ないことと、ＡＯＤに比べてＣｒの収率が低めであるため、本発明の効果はＡＯＤを用いる場合に比べて小さい。
【００３３】
なお、上記実施形態では、亜鉛含有廃棄物Ａに炭素質還元剤Ｂを加えて塊成化したのち還元炉３で加熱処理して脱亜鉛塊成物Ｄを得る方法について例示したが、亜鉛含有廃棄物Ａに炭素質還元剤Ｂを混合したまま塊成化せず混合物として還元炉３に装入して加熱処理してもよい。そして、この加熱処理によって得られる脱亜鉛混合物をそのまま冷却材として装入してもよい。また、加熱処理後の脱亜鉛混合物を塊成化して脱亜鉛塊成物Ｄとしてもよい（脱亜鉛塊成物塊成化工程）。
【００３４】
なお、脱亜鉛塊成物Ｄ（または脱亜鉛混合物）は酸化期（または予備脱炭期）および／または還元期において冷却材として使用するほか、電気炉１１や精錬炉１２の主原料および／または追加原料として使用することも可能である。
【００３５】
【実施例】
〔実施例１〕
ステンレス鋼製造工程から発生した電気炉ダストとミルスケールの混合物に石炭を添加して混合物とし、この混合物をブリケットプレスにより２１ｍｍ×３７ｍｍ×９ｍｍの枕形に塊成化し、表１に示す組成の炭材内装塊成物を作製した。
【００３６】
【表１】

【００３７】
ここに、余剰炭素量の定義は、余剰炭素量（質量％）＝〔混合物中の炭素量（質量％）〕−〔混合物中に含まれるＦｅ、ＮｉおよびＺｎと結合している酸素量（質量％）〕×１２／１６である。
【００３８】
この炭材内装塊成物を小型加熱炉内で加熱温度を１１５０〜１３５０℃の範囲内で種々変化させて加熱し、加熱後の炭材内装塊成物（脱亜鉛塊成物）の組成を化学分析により測定し、各種金属の金属化率および脱亜鉛率を求めた。なお、加熱時の雰囲気は窒素雰囲気、加熱時間は５〜８ｍｉｎとした。加熱後の炭材内装塊成物（脱亜鉛塊成物）の組成を表２に、金属化率および脱亜鉛率を表３に示す。
【００３９】
【表２】

【００４０】
【表３】

【００４１】
表２および表３より、加熱温度により脱亜鉛塊成物中の残留炭素量および脱亜鉛率、ならびに脱亜鉛塊成物の圧潰強度が変化することがわかる。１２００℃以上の加熱温度とすると脱亜鉛率が８０％以上になり好ましい。また、加熱温度が高いほど残留炭素量が少なくなり圧潰強度が上昇することがわかる。残留炭素量の評価としては、脱亜鉛塊成物中に残留する酸化鉄、酸化ニッケル、酸化クロムの還元に必要な量以下とすることが好ましい。これを超える量の炭素はステンレス鋼製造工程において溶鋼中から除去（脱炭）するために余分の酸素が必要になることに加え、脱亜鉛塊成物の圧潰強度を低下させるからである。
【００４２】
ここで、上記実施例のＳＭ−４の脱亜鉛塊成物を用いて電気炉とＡＯＤとからなる製造工程でステンレス鋼を製造する場合を想定し、実機におけるＣｒ歩留などの操業データを参考にして脱亜鉛塊成物中のＣｒの挙動を検討した。その検討結果によると、脱亜鉛塊成物を主原料の一部として電気炉に使用した場合の脱亜鉛塊成化物中のＣｒ歩留（脱亜鉛塊成物中のＣｒのうちステンレス鋼中に残るＣｒの割合）を１００とすると、ＡＯＤで酸化期に冷却材として使用した場合の塊成化物中のＣｒ歩留は１０５となりＣｒ収率が上昇することがわかった。また脱亜鉛塊成化物中のＣｒのうちステンレス鋼中に残るＣｒを還元するのに必要なエネルギーは、主原料の一部として電気炉に使用した場合を１００とすると、ＡＯＤで酸化期に冷却材として使用した場合は９５となり、エネルギー消費量が低減できることがわかった。これは、主原料の一部として脱亜鉛塊成物を電気炉に装入した場合、一旦電気炉で還元されたクロムの一部がＡＯＤの酸化期で再酸化され、酸化期の後に再度還元が必要になるためであるのに対し、ＡＯＤの酸化期（および／または還元期）に冷却材として使用した場合には電気炉での還元が不要となるためである。
【００４３】
〔実施例２〕
次に、炭材内装塊成物中の余剰炭素量と加熱処理後の炭材内装塊成物（脱亜鉛塊成物）中の残留炭素量の関係を調査した。炭材内装塊成物への石炭の添加量を変化させて表４に示すように、余剰炭素量の異なる３種類のサンプルを作製した。
【００４４】
【表４】

【００４５】
上記各サンプルを実施例１と同じ小型加熱炉内で実施例１と同じ雰囲気・加熱時間で加熱温度を１３００℃（一定）の条件下で加熱処理した。加熱後の各サンプル（脱亜鉛塊成物）の組成を表５に、各金属元素の金属化率および脱亜鉛率を表６に示す。
【００４６】
【表５】

【００４７】
【表６】

【００４８】
炭材内装塊成物中の残留炭素量は、前述したように未還元の酸化金属を還元するのに必要な量以下にすることが望ましいが、表５の分析結果より適正なものを選択できる。また、表４および表５より明らかなように、炭材内装塊成物中の余剰炭素量を調整することにより加熱後の炭材内装塊成物（脱亜鉛塊成物）中の残留炭素量を調整することができる。ただし、炭材内装塊成物の原料となる亜鉛含有廃棄物の発生源が異なる場合や添加する炭素質還元剤の種類が異なる場合には、酸化金属の被還元性や炭素分の存在形態が異なるため、適正な余剰炭素量の数値範囲は亜鉛含有廃棄物および炭素質還元剤の種類や組み合わせにより変化する。また、上記実施例１で明らかにしたように、加熱温度によっても脱亜鉛塊成物中の残留炭素量が変化する。したがってこれらの点を考慮し、用いようとする亜鉛含有廃棄物および炭素質還元剤の種類や組み合わせごとに、例えば事前に本実施例１および２と同様の試験を行って適正な余剰炭素量の数値範囲を求めておくことが必要である。
【００４９】
【発明の効果】
本発明は以上のように構成されているので、ステンレス鋼製造工程で発生するダスト等の廃棄物を再利用するに際し、Ｃｒの還元エネルギーの減少とＣｒの溶鋼への収率の上昇を可能とするステンレス鋼の製造方法を提供できることとなった。
【図面の簡単な説明】
【図１】本発明の実施に係るステンレス鋼の製造プロセスの一例を説明する設備フロー図である。
【符号の説明】
１…ステンレス鋼製造工程
１１…電気炉
１２…精錬炉（ＡＯＤ）
２…成形機（ブリケットプレス）
３…還元炉（回転炉床炉）
Ａ…亜鉛含有廃棄物（電気炉ダスト）
Ｂ…炭素質還元剤（石炭）
Ｃ…炭材内装塊成化物
Ｄ…脱亜鉛塊成物
Ｅ…主原料
Ｆ…造滓剤
Ｇ…溶鋼
Ｈ…ステンレス鋼[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for manufacturing stainless steel by reusing waste such as dust and scale generated in a stainless steel manufacturing process.
[0002]
[Prior art]
In general, stainless steel is produced by melting raw materials such as scrap, Fe—Cr, Fe—Ni, and metal Ni in an electric furnace, and then refining the molten steel in a refining furnace (stainless steel manufacturing process). Usually, an electric furnace is in charge of a melting period in which a raw material is simply melted, but in some cases, an oxidation period (also referred to as a "preliminary decarburization period") in which oxygen is blown from a molten steel to decarburize the steel is sometimes provided. In the smelting furnace, an oxidation period in which molten steel is decarburized by oxygen injection, a reduction period in which Cr that has been oxidized in the oxidation period and transferred into the slag is reduced again to be returned to the metal, and is recovered in the molten steel; Responsible for finishing and refining period for component adjustment and temperature adjustment. From an electric furnace or a smelting furnace (VOD, RH, AOD, MRP, etc.), dust is generated along with the exhaust gas. Since this dust contains components such as Fe, Ni, and Cr, it is preferable to reuse the dust as a raw material. In addition, since dust contains Cr ⁶⁺ , a large cost is required for external processing, and therefore, it is desired to recycle it from an economic viewpoint. However, dust mainly contains scrap-derived Zn. Therefore, when the dust is returned to the electric furnace or the refining furnace as it is, the Zn is reduced and volatilized and scattered again in the exhaust gas, so that the Zn is concentrated in the dust. If Zn is concentrated in the dust, the dust will adhere to the furnace port and exhaust gas piping and cause problems such as coating, and the oxidation and reduction of Zn will be repeated every time the dust is recycled, resulting in poor energy efficiency. There is a problem (the reduction of Zn in dust is an endothermic reaction and is performed in a furnace, so heat energy is consumed. On the other hand, the oxidation of Zn is an exothermic reaction, but almost all of the heat energy is performed in an exhaust gas system. Is wasted.)
[0003]
Therefore, a method has been proposed in which dust is reduced in a process different from the stainless steel manufacturing process, and then returned to the stainless steel manufacturing process and reused.
[0004]
(Prior art 1)
Patent Document 1 discloses that a carbonaceous reducing agent is added to a mill scale, dust, sludge, or the like, granulated into pellets, and the pellets are heated and reduced in a rotary hearth furnace or the like to form metal-containing pellets. A method is disclosed in which a pellet containing is melted in an electric arc furnace or the like for producing pig iron to separate and recover metal valuables (Fe, Ni, Cr, Mo, etc.). The recovered metal valuables are contained in the molten metal, and the molten metal is poured from an electric arc furnace into a forming die of a continuous cast iron machine to form a metal lump. The example (Example III) shows that a metal lump containing 2.95% by mass of carbon is additionally added to an electric arc furnace for producing stainless steel.
[0005]
(Prior art 2)
Patent Document 2 discloses a granulating step of granulating a chromium-containing composition obtained by blending an appropriate amount of chromium ore with a chromium-containing waste generated in a stainless steel production process and coke to produce pellets, The reduction process of producing chromium-containing iron pellets by standing on the hearth of a rotary hearth furnace and heating with combustion gas to minimize the collapse and powdering of the pellets, and the sensible heat of the exhaust gas in the reduction process Stainless steel production process consisting of a waste heat recovery process of recovering water as steam and a zinc-containing dust recovery process of separating and collecting zinc-containing dust generated in the reduction process and entrained in the exhaust gas of the waste heat recovery process A method for recycling waste is disclosed. Examples show that the chromium-containing iron pellets are melted as a part of the main raw material in an electric furnace to produce chromium-containing pig iron.
[0006]
[Patent Document 1]
JP-A-56-93834 [Patent Document 2]
Japanese Patent Application Laid-Open No. 9-209047
[Problems to be solved by the invention]
According to the above prior arts 1 and 2, when the pellets are heated in a rotary hearth furnace (a rotary hearth furnace), Zn in the pellets is reduced by a carbonaceous reducing agent, volatilized, and removed from the pellets. Therefore, even if the reduced pellets are supplied to an electric furnace, Zn is not concentrated in the dust, and the problem of coating in an exhaust gas system is avoided.
[0008]
However, in the above-mentioned prior arts 1 and 2, the pellets after reduction are charged into an electric furnace for melting and used to produce chromium-containing pig iron having a high carbon concentration. Therefore, the carbon content remaining in the reduced pellets (metal lumps, chromium-containing iron pellets) is relatively high. That is, as described above, in the example of the related art 1, the carbon content in the metal lump is 2.95% by mass. Further, in Example 2 of the prior art 2, although the carbon content in the chromium-containing iron pellet is not specified, the carbon content is 4.7 mass% in 125 parts by mass of the chromium-containing pig iron, and this is the chromium-containing iron. Since it is manufactured from 211 parts by mass of the pellets, when the carbon content consumed in the reduction of chromium in the electric furnace is estimated in consideration of the carbon content in the chromium-containing iron pellet, 2.8% by mass or more is contained. Will have been. Then, the chromium-containing pig iron is decarburized to a target carbon level in the next oxidation stage, and then reduced and finish refined to form stainless steel. Since decarburization is performed by blowing oxygen into molten steel, Cr is oxidized and moves into slag as decarburization proceeds. After the completion of decarburization, Fe-Si or the like is added as a reducing agent in the reduction period to reduce this Cr oxide, thereby returning it to metallic Cr and recovering it in molten steel.
[0009]
Here, Cr in the chromium-containing iron pellets is not sufficiently reduced by heating in a rotary hearth furnace (normally, the metallization ratio is about 40% or less), and most of them remain in the form of oxides. In the melting period in an electric furnace, the unreduced Cr oxide is reduced by the residual carbon content in the pellets and the carbon content in the molten steel to be metallized and recovered in the molten steel. It remains and is discarded together with the slag (electric furnace slag). The Cr recovered in the molten steel is partially oxidized in the subsequent oxidation stage (or the preliminary decarburization stage) and moves into the slag. The Cr in the slag is reduced again in the subsequent reduction period and is recovered in the molten steel, but a part thereof remains in the slag and is discarded together with the slag (refining furnace slag). As described above, the unreduced Cr oxide in the chromium-containing iron pellets is reduced in the melting period, then oxidized in the oxidizing period (or preliminary decarburization period), and further reduced in the reducing period. Extra energy is required, resulting in energy loss. Further, since Cr remains in both the electric furnace slag and the refining furnace slag, there is a problem that the Cr yield (yield) to molten steel is low.
[0010]
Accordingly, an object of the present invention is to provide a method for producing stainless steel, which can reduce the reduction energy of Cr and increase the yield of Cr to molten steel when reusing waste such as dust generated in the stainless steel production process. Is to provide.
[0011]
[Means for Solving the Problems]
The invention according to claim 1 provides a stainless steel manufacturing process in which a raw material is melted to form molten steel, and then the molten steel is refined into stainless steel; and a carbonaceous reducing agent is added to the zinc-containing waste generated in the stainless steel manufacturing process. Adding a reducing agent to form a mixture, a heat treatment step of volatilizing and removing zinc by heating the mixture to form a dezincified mixture, and a furnace using the dezincified mixture as a coolant in the stainless steel manufacturing process. And a charging step of charging the stainless steel.
[0012]
The invention of claim 2 provides a stainless steel manufacturing process in which a raw material is melted to form molten steel, and the molten steel is refined to stainless steel; and a carbonaceous reducing agent is added to the zinc-containing waste generated in the stainless steel manufacturing process. Adding a reducing agent to form a mixture, heating the mixture to volatilize and remove zinc by heating to form a dezincified mixture, and agglomerating the dezincified mixture to form a dezincified agglomerate. A process for agglomerating dezincified agglomerates, and a charging step for charging the dezincified agglomerates into a furnace as a coolant in the stainless steel manufacturing process. It is.
[0013]
The invention according to claim 3 provides a stainless steel manufacturing process in which a raw material is melted to form molten steel, and the molten steel is refined into stainless steel; and a carbonaceous reducing agent is added to the zinc-containing waste generated in the stainless steel manufacturing process. Adding a reducing agent to form a mixture by adding a mixture, agglomerating the mixture to form a carbonaceous interior agglomerate by forming the carbonaceous interior agglomerate, and heating the carbonaceous interior agglomerate A heat treatment step of volatilizing and removing zinc to form a dezincified agglomerate, and a charging step of charging the dezincified agglomerate into a furnace as a coolant in the stainless steel manufacturing step. This is a method for producing stainless steel.
[0014]
The invention according to claim 4 is characterized in that the amount of residual carbon in the coolant is adjusted to 2% by mass or less by adjusting the amount of surplus carbon in the mixture by the amount of the carbonaceous reducing agent added. Or a method for producing stainless steel according to item 1. Here, the surplus carbon amount (% by mass) = [the amount of carbon (% by mass) in the mixture] − [the amount of oxygen (% by mass) combined with Fe, Ni and Zn contained in the mixture] × 12 / 16.
[0015]
The invention according to claim 5 is the method for producing stainless steel according to any one of claims 1 to 4, wherein the molten steel is stirred vigorously after the coolant is charged to increase the yield of valuable metals.
[0016]
The invention according to claim 6 is the method for producing stainless steel according to any one of claims 1 to 5, wherein the charging of the coolant is performed during an oxidation stage and / or a reduction stage in the stainless steel production process.
[0017]
The invention of claim 7 is the method for producing stainless steel according to any one of claims 1 to 5, wherein the charging of the coolant is performed at the end of the oxidation stage and / or at the beginning of the reduction period in the stainless steel production process. It is.
[0018]
The invention according to claim 8 is to form a mixture by adding a carbonaceous reducing agent to a zinc-containing waste generated in a stainless steel production process, and by heating the mixture to volatilize and remove zinc to form a dezincified mixture. This dezincified mixture is agglomerated to reduce the residual carbon content to 2% by mass or less.
[0019]
According to a ninth aspect of the present invention, a carbonaceous reducing agent is added to a zinc-containing waste generated in a stainless steel manufacturing process to form a mixture, and the mixture is agglomerated to form a carbonaceous interior agglomerate. This is a dezincified agglomerate in which zinc is volatilized and removed by heating the material interior agglomerate to reduce the residual carbon content to 2% by mass or less.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in more detail with reference to the drawings.
[0021]
As an example of the embodiment, as shown in FIG. 1, an electric furnace 11 that melts raw materials (main raw material E and slag-making agent F) to form molten steel G, and refines the molten steel G to form stainless steel H An application example of the stainless steel manufacturing process 1 including the AOD 12 which is a furnace will be described.
[0022]
A zinc-containing waste A such as electric furnace dust generated in the stainless steel manufacturing process 1 is mixed with a carbonaceous reducing agent B such as coal to form a mixture (not shown) (a reducing agent adding step). This mixture is agglomerated by a molding machine 2 such as a briquette press to obtain a carbonaceous material interior agglomerate C (carbonaceous material interior agglomeration agglomeration step). As the zinc-containing waste A, mill scale, mill sludge, AOD dust, or other refining furnace dust may be used in addition to the electric furnace dust, or a mixture of these may be used as appropriate. As the carbonaceous reducing agent B, besides coal, coke powder, charcoal, waste toner and other carbides can be used, and these may be used as appropriate. Moreover, you may add an auxiliary raw material and a binder as needed. As the molding machine 2, a rolling granulator, an extrusion molding machine, or the like may be used in addition to a compression molding machine using a briquette press or the like. The addition and agglomeration of the carbonaceous reducing agent B may be performed by the same machine, for example, the agglomeration may be performed while mixing with a dish-type granulator or a mixer.
[0023]
The obtained carbonaceous material interior agglomerate C is charged into the rotary hearth furnace 3 which is a reduction furnace. As the reduction furnace 3, a multi-stage furnace, a rotary kiln, or the like can be used in addition to a rotary hearth furnace. When the moisture content of the carbonaceous material interior agglomerate C is high, drying may be performed using a drier or the like (not shown) before charging into the reduction furnace 3.
[0024]
From the carbonaceous interior agglomerate C heated to 1100 to 1400 ° C. in the reduction furnace 3, heavy metals such as Pb in addition to Zn are removed by reduction and volatilization, and metal compounds such as Fe, Ni, Cr and Mo are solid. The dezincified agglomerate D which is reduced and metallized as it is is obtained (heat treatment step). However, the metallization ratio of Cr is not so high, and is about 40% even if the amount of the carbonaceous reducing agent B in the carbonaceous material agglomerate C and the heating temperature in the reduction furnace 3 are adjusted. On the other hand, the metallization ratio of Fe or Ni can be made 90% or more by adjusting the amount of the carbonaceous reducing agent B in the carbonaceous material agglomerate C and the heating temperature in the reduction furnace 3.
[0025]
Here, in the stainless steel manufacturing process 1, a main raw material E made of scrap, Fe-Cr, Fe-Ni, metallic Ni and the like and a slag-making agent F such as quicklime are charged into the electric furnace 11 and melted by arc heating or the like. To produce molten steel G. When the AOD 12 is used in the post-process, the electric furnace 11 takes charge of only the melting period in which the raw material is simply melted. Next, the molten steel G is transferred to the AOD 12 for refining. In the AOD 12, the oxygen in the molten steel is blown with Ar together with oxygen to decarburize the molten steel, and the Cr that has been oxidized during the oxidation and transferred into the slag is injected into the slag by Ar alone to stir the molten steel. And a deoxidizing agent (reducing agent) such as Fe-Si, an alloying element, etc. are added and only Ar is blown into the molten steel to stir the molten steel to deoxidize the molten steel.・ Responsible for finishing and refining period for component adjustment and temperature adjustment. The molten steel refined by AOD12 becomes stainless steel H and is sent to the next casting step 4.
[0026]
The dezincified agglomerate D obtained by heating in the rotary hearth furnace 3 is charged as a coolant during the oxidation and / or reduction phases of the AOD 12. Since zinc is sufficiently removed from the dezincified agglomerate D before being charged into the AOD 12, the Zn is not concentrated in the dust as in the above-mentioned prior arts 1 and 2, and the coating in the exhaust gas system is not performed. The problem described above does not occur.
[0027]
Furthermore, since the dezincified agglomerate D is directly charged not in the melting period of the electric furnace 11 but in the oxidation stage and / or the reduction stage of the AOD 12, Cr derived from the dezincified agglomerate D remains in the electric furnace slag. Therefore, there is an effect that the Cr yield is increased as compared with the prior arts 1 and 2. Further, the use of the Cr oxide in the dezincified agglomerate D, which is once reduced and then oxidized again, eliminates a useless route, so that an extra reduction energy is not required and the energy efficiency is improved. is there. It is to be noted that if the catalyst is charged at the end of the reduction period (at the end of oxygen blowing for decarburization) and / or at the beginning of the reduction period (at the time of addition of a deoxidizing agent), it is possible to more reliably oxidize Cr again. It is more preferable because it can be prevented.
[0028]
In addition, the carbonaceous material in the carbonaceous material interior agglomerate C (that is, in the mixture) is such that the dezincing rate of the agglomerate (dezincified agglomerate) D after heating in the rotary hearth furnace 3 is not excessively reduced. It is preferable to reduce the amount of the reducing agent B (that is, the amount of excess carbon). When the amount of the carbonaceous reducing agent B in the carbonaceous material agglomerate C is increased, the amount of residual carbon in the dezincified agglomerate D is increased. In addition to the increased amount of oxygen used, the oxidation period is prolonged and the productivity is reduced. The reason why the oxidation period is extended is that in a region where the carbon concentration in the molten steel is low (for example, 0.4% by mass or less), the rate-limiting process of the decarburization reaction is considered to be the diffusion process of C in the molten steel. Carbon from the material D takes longer to melt into the molten steel than C originally existing in the molten steel, and diffusion at the time of the meltdown is due to the region where the carbon content is higher than the surrounding molten steel. Probably because it is late.
[0029]
When the amount of the carbonaceous reducing agent B in the carbonaceous material-containing agglomerate C is limited as described above, the metallization ratio of iron in the dezincified agglomerate D is reduced, but the iron oxide in the dezincified agglomerate D is reduced. With the increase, the effect as a coolant is rather increased, and the cooling effect is about twice as much as the cooling effect by ordinary scrap.
[0030]
The dezincified agglomerate D charged as a coolant in the oxidation phase in the AOD 12 melts down in the molten steel, but the unreduced Cr contained in the dezincified agglomerate D is reduced in the subsequent step of the reduction phase. Can be recovered in good yield by charging a reducing agent such as Fe-Si into the mixture and stirring vigorously with Ar gas.
[0031]
Further, the smaller the amount of residual carbon, the higher the strength of the dezincified agglomerate D, and there is also an advantage that the powdering during transportation, storage or charging into the smelting furnace 12 is reduced and the yield is improved.
[0032]
As the refining furnace 12, VOD, MRP, or the like can be used in addition to AOD. When VOD is used as the refining furnace 12, the electric furnace 11 is provided with an oxidation period (preliminary decarburization period) and a reduction period after the melting period, and the VOD is in charge of only the finishing refining period. Therefore, during the oxidation stage (preliminary decarburization stage) and / or the reduction stage in the electric furnace 11, the dezincified agglomerate D is charged as a coolant. After the unreduced Cr in the dezincified agglomerate is reduced and recovered in the molten steel in the reduction period of the next step of the electric furnace 11, the molten steel is transferred to VOD. In the VOD finish refining period, the effect of the present invention is smaller than in the case of using AOD because the amount of coolant used is small to suppress the oxidation of Cr and the yield of Cr is lower than that of AOD. .
[0033]
In the above embodiment, the method of adding the carbonaceous reducing agent B to the zinc-containing waste A to agglomerate and then performing the heat treatment in the reduction furnace 3 to obtain the dezincified agglomerate D has been described. The waste A may be charged to the reduction furnace 3 as a mixture without being agglomerated while the carbonaceous reducing agent B is mixed with the waste A, and then heat-treated. Then, the dezincified mixture obtained by this heat treatment may be directly charged as a coolant. Alternatively, the dezincified mixture after the heat treatment may be agglomerated to obtain a dezincified agglomerate D (a dezincified agglomerate agglomeration step).
[0034]
The dezincified agglomerate D (or dezincified mixture) is used as a coolant during the oxidation stage (or the pre-decarburization stage) and / or the reduction stage, and is also used as the main raw material of the electric furnace 11 and the refining furnace 12 and / or It can be used as an additional raw material.
[0035]
【Example】
[Example 1]
Coal is added to a mixture of electric furnace dust and mill scale generated from the stainless steel manufacturing process to form a mixture, and this mixture is agglomerated into a 21 mm × 37 mm × 9 mm pillow shape by a briquette press. A wood interior agglomerate was produced.
[0036]
[Table 1]

[0037]
Here, the definition of the amount of surplus carbon is the amount of surplus carbon (% by mass) = [the amount of carbon in the mixture (% by mass)] − [the amount of oxygen (mass) combined with Fe, Ni, and Zn contained in the mixture. %)] X 12/16.
[0038]
This carbonaceous interior agglomerate is heated in a small heating furnace by changing the heating temperature in a range of 1150 to 1350 ° C., and the composition of the heated carbonaceous interior agglomerate (dezinced agglomerate) is determined. It was measured by chemical analysis to determine the metallization ratio and dezincification ratio of various metals. The atmosphere during the heating was a nitrogen atmosphere, and the heating time was 5 to 8 minutes. Table 2 shows the composition of the carbonaceous interior agglomerate (dezinced agglomerate) after heating, and Table 3 shows the metallization ratio and dezincification ratio.
[0039]
[Table 2]

[0040]
[Table 3]

[0041]
Tables 2 and 3 show that the heating temperature changes the residual carbon content and the dezincing ratio in the dezincified agglomerate, and the crushing strength of the dezincified agglomerate. When the heating temperature is 1200 ° C. or higher, the dezincing rate is preferably 80% or higher. Also, it can be seen that the higher the heating temperature, the smaller the residual carbon content and the higher the crushing strength. The evaluation of the residual carbon amount is preferably not more than the amount required for reduction of iron oxide, nickel oxide, and chromium oxide remaining in the dezincified agglomerate. This is because an amount of carbon exceeding this amount requires extra oxygen to remove (decarburize) from the molten steel in the stainless steel manufacturing process, and also lowers the crushing strength of the dezincified agglomerate.
[0042]
Here, assuming a case where stainless steel is manufactured in a manufacturing process consisting of an electric furnace and an AOD using the dezincified agglomerate of SM-4 of the above embodiment, reference is made to operation data such as Cr yield in an actual machine. The behavior of Cr in the dezincified agglomerate was examined. According to the examination results, the Cr yield in the dezincified agglomerate when using the dezincified agglomerate as a part of the main raw material in the electric furnace (the Cr in the Assuming that the ratio of the remaining Cr is 100, the Cr yield in the agglomerate when the AOD is used as a coolant during the oxidation stage is 105, indicating that the Cr yield increases. The energy required to reduce the Cr remaining in stainless steel among the Cr in the dezincified agglomerate is 100% when the electric furnace is used as a part of the main raw material in the oxidation stage by AOD. When it was used as a material, it was 95, indicating that energy consumption could be reduced. This is because when dezincified agglomerates are charged into an electric furnace as part of the main raw material, part of the chromium once reduced in the electric furnace is reoxidized during the oxidation period of the AOD, and then reduced again after the oxidation period. On the other hand, when the AOD is used as a coolant during the oxidation period (and / or the reduction period) of the AOD, reduction in an electric furnace becomes unnecessary.
[0043]
[Example 2]
Next, the relationship between the amount of surplus carbon in the carbonaceous material inner agglomerate and the amount of residual carbon in the carbonaceous material inner agglomerate (dezinced agglomerate) after the heat treatment was investigated. As shown in Table 4, three types of samples having different amounts of surplus carbon were produced by changing the amount of coal added to the carbonaceous material interior agglomerate.
[0044]
[Table 4]

[0045]
Each of the samples was heat-treated in the same small heating furnace as in Example 1 under the same atmosphere and heating time as in Example 1 at a heating temperature of 1300 ° C. (constant). Table 5 shows the composition of each sample (dezinced agglomerate) after heating, and Table 6 shows the metallization ratio and dezincification ratio of each metal element.
[0046]
[Table 5]

[0047]
[Table 6]

[0048]
As described above, it is desirable that the amount of residual carbon in the carbonaceous material interior agglomerate be equal to or less than the amount required to reduce unreduced metal oxide, but an appropriate one can be selected from the analysis results in Table 5. . Further, as is clear from Tables 4 and 5, the amount of residual carbon in the carbonaceous interior agglomerate (dezinced agglomerate) after heating is adjusted by adjusting the amount of surplus carbon in the carbonaceous interior agglomerate. Can be adjusted. However, if the source of zinc-containing waste, which is the raw material of the carbonaceous interior agglomerate, is different or if the type of carbonaceous reducing agent added is different, the reducibility of the metal oxide and the form of carbon content Because of the difference, the appropriate numerical range of the surplus carbon amount varies depending on the type and combination of the zinc-containing waste and the carbonaceous reducing agent. Further, as clarified in Example 1 above, the amount of residual carbon in the dezincified agglomerates also changes depending on the heating temperature. Therefore, in consideration of these points, for each kind or combination of the zinc-containing waste and the carbonaceous reducing agent to be used, for example, the same test as in Examples 1 and 2 is performed in advance to determine the appropriate amount of excess carbon. It is necessary to determine the numerical range.
[0049]
【The invention's effect】
Since the present invention is configured as described above, it is possible to reduce the reduction energy of Cr and increase the yield of Cr to molten steel when recycling waste such as dust generated in a stainless steel manufacturing process. It is possible to provide a method for producing stainless steel.
[Brief description of the drawings]
FIG. 1 is a facility flow diagram illustrating an example of a process for producing stainless steel according to an embodiment of the present invention.
[Explanation of symbols]
1: Stainless steel manufacturing process 11: Electric furnace 12: Refining furnace (AOD)
2. Molding machine (bricket press)
3. Reduction furnace (rotary hearth furnace)
A: Zinc-containing waste (electric furnace dust)
B: Carbonaceous reducing agent (coal)
C: agglomerate of carbon material interior D: dezincified agglomerate E: main raw material F: slagging agent G: molten steel H: stainless steel

Claims

After the raw material is melted into molten steel, a stainless steel manufacturing process of refining this molten steel into stainless steel,
A reducing agent adding step of adding a carbonaceous reducing agent to the zinc-containing waste generated in the stainless steel manufacturing step to form a mixture,
A heat treatment step of volatilizing and removing zinc by heating the mixture to form a dezincified mixture;
Charging the dezincified mixture into a furnace as a coolant in the stainless steel manufacturing process;
And a method for producing stainless steel.

After the raw material is melted into molten steel, a stainless steel manufacturing process of refining this molten steel into stainless steel,
A reducing agent adding step of adding a carbonaceous reducing agent to the zinc-containing waste generated in the stainless steel manufacturing step to form a mixture,
A heat treatment step of volatilizing and removing zinc by heating the mixture to form a dezincified mixture;
Dezincified agglomerate agglomeration step of agglomerating the dezincified mixture into dezincified agglomerate, and charging the dezincified agglomerate into a furnace as a coolant in the stainless steel manufacturing step Process;
And a method for producing stainless steel.

After the raw material is melted into molten steel, a stainless steel manufacturing process of refining this molten steel into stainless steel,
A reducing agent adding step of adding a carbonaceous reducing agent to the zinc-containing waste generated in the stainless steel manufacturing step to form a mixture,
Agglomerating the mixture to form a carbonaceous interior agglomerate, a carbonaceous interior agglomerate agglomeration step;
A heat treatment step of volatilizing and removing zinc by heating the carbonaceous interior agglomerate to form a dezincified agglomerate;
Charging the dezincified agglomerate into a furnace as a coolant in the stainless steel manufacturing process;
And a method for producing stainless steel.

The stainless steel according to any one of claims 1 to 3, wherein the amount of residual carbon in the coolant is adjusted to 2% by mass or less by adjusting the amount of surplus carbon in the mixture according to the amount of the carbonaceous reducing agent added. Steel production method.
Here, the surplus carbon amount (% by mass) = [the amount of carbon in the mixture (% by mass)] − [the amount of oxygen (% by mass) combined with Fe, Ni and Zn contained in the mixture] × 12 / 16.

The method for producing stainless steel according to any one of claims 1 to 4, wherein the molten steel is stirred vigorously after charging the coolant to increase the yield of valuable metals.

The method for producing stainless steel according to any one of claims 1 to 5, wherein the charging of the coolant is performed during an oxidation stage and / or a reduction stage in the stainless steel production process.

The method for producing stainless steel according to any one of claims 1 to 5, wherein the charging of the coolant is performed at an end of an oxidation stage and / or at an early stage of a reduction stage in the stainless steel production process.

A carbonaceous reducing agent is added to the zinc-containing waste generated in the stainless steel production process to form a mixture, and the mixture is heated to volatilize and remove zinc to form a dezincified mixture. Dezincified agglomerates that have been converted to a residual carbon content of 2% by mass or less.

A carbonaceous reducing agent is added to the zinc-containing waste generated in the stainless steel manufacturing process to form a mixture, and the mixture is agglomerated to form a carbonaceous interior agglomerate, which is then heated. Dezincified agglomerates by removing zinc by volatilization to reduce the residual carbon content to 2% by mass or less.