JP4112989B2

JP4112989B2 - Operation method of heating storage furnace

Info

Publication number: JP4112989B2
Application number: JP2003009363A
Authority: JP
Inventors: 安弘岡田; 直樹平嶋; 幸一切敷
Original assignee: Nippon Steel Corp
Current assignee: Nippon Steel Corp
Priority date: 2003-01-17
Filing date: 2003-01-17
Publication date: 2008-07-02
Anticipated expiration: 2023-01-17
Also published as: JP2004218039A

Description

【０００１】
【発明の属する技術分野】
本発明は、予備処理された溶銑を受銑し、精錬炉（例えば転炉等）に供給する加熱式貯銑炉の操業方法に関する。
【０００２】
【従来の技術】
従来、高炉から出銑した溶銑をトピードカー（混銑車）や溶銑鍋等に一旦受けて搬送し、脱硫や脱燐等の予備処理が施された溶銑を更に装入鍋に移してクレーン等で搬送し、屑鉄や酸化鉄等の冷材が装入された転炉（精錬炉）内に装入している。そして、上吹きランスから酸素を吹付けて、脱炭精錬を行うことにより溶鋼が製造されている。この転炉の脱炭精錬では、吹錬を終了する吹き止め時の温度及び炭素濃度が目標値となるように、過去の吹酸実績等を参照しながら、溶銑や屑鉄、酸化鉄等の配合量を決定している。
しかし、高炉から出銑される溶銑量や転炉での溶鋼生産量の変動により、溶銑の転炉への供給条件（例えば、配合量）が変動するため、吹錬の不安定化や炭材の使用量増加による溶製コストの上昇等が生じている。また、溶銑に施される予備処理は、トピードカーや溶銑鍋の処理単位ごとに、溶銑中の燐及び硫黄の各量が目標値以下となるように過剰実施されているため、処理コストの上昇や溶銑温度の低下を招いている。そして、トピードカーや溶銑鍋の容量と転炉の容量とが釣り合わないため、待機中のトピードカーや溶銑鍋の溶銑、あるいはトピードカーや溶銑鍋に残った溶銑（残銑）等には、急激な温度低下が生じている。ここで、トピードカーや溶銑鍋からの溶銑の供給量が不足する場合、転炉を安定に操業させることができない問題も発生する。
【０００３】
この対策として、以下の方法が提案されている。
まず、特許文献１には、鋳鋼などを誘導炉により溶解する際に、造滓剤としてＳｉＯ₂ を６５〜７５質量％、Ａｌ₂ Ｏ₃ を０．５〜４質量％、及びソーダ石灰ガラスを配合したものを溶銑に添加して、スラグの低融点化とスラグによるカバー効果を作用させ、排滓を容易にする方法が記載されている。これにより、無駄な熱拡散を防止し、溶銑の温度低下を抑制することができる。
また、特許文献２には、バケットコンベアから供給される水分が付着した屑鉄（スクラップ）を、誘導加熱式の貯銑炉の雰囲気熱により乾燥して水分を低減し、この乾燥させた屑鉄を貯銑炉に装入して溶解する方法が記載されている。これにより、屑鉄を溶解した擬似溶銑を多量に製造し、後工程の転炉への安定供給が可能になり、転炉を安定して操業できる。
そして、特許文献３には、アーク炉に屑鉄と造滓剤を装入して溶解し、溶湯とスラグを分離してから溶湯を誘導加熱炉に装入し、精錬剤を添加して鋼を製造する方法が記載されている。これにより、屑鉄から溶銑を製造でき、転炉への溶銑の供給量を増加できる。
【０００４】
【特許文献１】
特開昭６２−２８４０２２号公報
【特許文献２】
特開平１１−２４８３６８号公報
【特許文献３】
特公昭６１−２８９１３号公報
【０００５】
【発明が解決しようとする課題】
しかしながら、上記した方法には、以下の問題がある。
まず、特許文献１に記載された方法では、造滓剤としてソーダ石灰系のものを用いるため、誘導炉に配置された耐火物の損耗が大きくなる。また、脱燐、脱硫などの予備処理を施した溶銑の温度や成分量を調整する方法ではないため、未調整の溶銑が転炉に装入されることで、転炉の操業が不安定になる。なお、造滓剤の粘性はＣａＯ−ＣａＦ₂ 系の造滓剤に比較してはるかに大きいため、誘導炉に屑鉄を投入した際、屑鉄の表面に造滓剤が付着し、溶銑中の炭素の屑鉄への浸炭作用が阻害されるので、屑鉄を積極的に溶解して擬似溶銑を製造できない問題もある。
そして、特許文献２に記載された方法は、擬似溶銑を多量に製造できるので、この擬似溶銑を後工程の転炉に安定供給できるが、屑鉄を溶解させる溶銑が、高炉からトピードカーや溶銑鍋で搬送された普通の溶銑であるため、予備処理が施された溶銑の場合のように、燐や硫黄などの成分量の相違、あるいは溶銑の成分や温度の変動、転炉への溶銑の配合量の変動に起因するアンマッチや、混入したスラグに起因する屑鉄の溶解不良等の問題が考慮されていない。
【０００６】
更に、特許文献３に記載された方法は、屑鉄をアーク炉に供給して溶解し溶鋼を製造する方法であり、脱燐、脱硫などの予備処理を施した溶銑の温度や成分量を調整する方法ではないため、未調整の溶銑が転炉に装入されることで、転炉の操業が不安定になる。また、屑鉄を溶解するため、屑鉄を高い温度（屑鉄溶解温度）に加熱する必要があり、しかも溶解能力に限界があるため、熱量コストも上昇し経済的でない。
本発明はかかる事情に鑑みてなされたもので、予備処理が施された溶銑の成分量の調整を行い、精錬炉への溶銑供給量の不釣り合いによる溶銑温度の低下を抑制し、かつ屑鉄の溶解を良好にしてその絶対量を増加させることにより、精錬炉への溶銑の供給量を確保して精錬炉を安定操業させることが可能な加熱式貯銑炉の操業方法を提供することを目的とする。
【０００７】
【課題を解決するための手段】
前記目的に沿う本発明に係る加熱式貯銑炉の操業方法は、脱燐及び脱硫のいずれか一方又は双方の予備処理を施した溶銑を、加熱手段を備えた貯銑炉に装入し、貯銑炉内で溶銑の温度及び成分量をそれぞれ調整し、かつ屑鉄を添加して溶解させた擬似溶銑を製造して、この擬似溶銑を精錬炉に供給する。これにより、例えば、トピードカーや溶銑鍋の処理単位ごとに過剰な予備処理が施された溶銑を、一旦貯銑炉に装入できるので、貯銑炉内の溶銑の成分量、特にＰ、Ｓの成分や炭素濃度を均一な状態に調整できる。また、貯銑炉には加熱手段が設けられているので、精錬炉への溶銑供給量の不釣り合いが生じても、貯銑炉内の溶銑温度を均一な温度に調整し維持できる。そして、貯銑炉内の溶銑に屑鉄を添加して溶解させ、多量の擬似溶銑を製造できるので、擬似溶銑を精錬炉へ安定供給できる。
これにより、温度と成分量が調整された擬似溶銑を精錬炉の必要量に応じて供給することができ、精錬炉で安定した操業を実現できる。また、吹錬の安定化、溶鋼歩留まり、製鋼時間の短縮、連鋳とのマッチングなど歩留まりの向上と生産の整流化が容易になる。
【０００８】
ここで、本発明に係る加熱式貯銑炉の操業方法において、貯銑炉内に混入したスラグの塩基度を調整して低融点スラグに改質した後、屑鉄を貯銑炉内の溶銑に添加して溶解させることが好ましい。予備処理を施した溶銑を貯銑炉に装入した際、溶銑と共に塩基度が３〜５程度の高塩基度のスラグも貯銑炉内に流入する。この高塩基度のスラグは、貯銑炉に装入された溶銑の上方に位置し、しかも粘性が高いため、貯銑炉内に屑鉄を投入した際、鉄屑の表面に付着する。これにより、溶銑中の炭素の屑鉄への浸炭作用が阻害されるので、溶銑への屑鉄の溶解効率が悪くなる。そこで、高塩基度のスラグを低塩基度にすることにより、低融点スラグに改質して粘性を低下させ、溶銑と屑鉄との接触を促進し、溶銑中の炭素による浸炭作用により低温度での屑鉄の多量溶解が可能になり、擬似溶銑を多量に製造することができる。
【０００９】
本発明に係る加熱式貯銑炉の操業方法において、低融点スラグの塩基度は０．８〜２．０であることが好ましい。ここで、塩基度はＣａＯ／ＳｉＯ₂ で表わされる。これにより、貯銑炉内の低融点スラグの流動性が改善され、高塩基度スラグの悪影響を抑制することができる。ここで、低融点スラグの塩基度が０．８未満になると、低融点スラグの流動性が良くなり過ぎて耐火物の損耗を招く。一方、低融点スラグの塩基度が２．０を超えると、低融点スラグの流動性が悪く、屑鉄の溶解効率が低下する。このため、耐火物の損耗を招くことなく、屑鉄の溶解効率を向上させるためには、低融点スラグの塩基度を０．８〜１．５とすることが好ましく、更には０．８〜１．２とすることが好ましい。
本発明に係る加熱式貯銑炉の操業方法において、低融点スラグに含まれるＡｌ₂ Ｏ₃ 濃度を５〜１５質量％とすることが好ましい。このように、低融点スラグに含まれるＡｌ₂ Ｏ₃ 濃度を調整することで、滓化し易い組成にできる。ここで、低融点スラグに含まれるＡｌ₂ Ｏ₃ 濃度が５質量％未満になると、低融点スラグの滓化不良を招く。一方、低融点スラグに含まれるＡｌ₂ Ｏ₃ 濃度が１５質量％を超えても、低融点スラグの滓化不良を招く。このため、低融点スラグを滓化し易い組成にするためには、低融点スラグに含まれるＡｌ₂ Ｏ₃ 濃度を７〜１３質量％とすることが好ましく、更には８〜１２質量％とすることが好ましい。
本発明に係る加熱式貯銑炉の操業方法において、加熱手段による加熱は誘導加熱であることが好ましい。このように、誘導加熱を行うことで、擬似溶銑中の炭素の酸化を抑制できるので、溶銑中の炭素量の低減を抑制でき、後工程での炭材の添加量を低減できる。
【００１０】
【発明の実施の形態】
続いて、添付した図面を参照しつつ、本発明を具体化した実施の形態につき説明し、本発明の理解に供する。
ここに、図１は本発明の一実施の形態に係る加熱式貯銑炉の操業方法に使用される加熱式貯銑炉の平面図、図２は図１のＡ−Ａ矢視断面図である。
【００１１】
図１、図２に示すように、本発明の一実施の形態に係る加熱式貯銑炉の操業方法に使用される加熱式貯銑炉（貯銑炉の一例）１０は、円筒状の鉄皮１１に耐火物１２が内張りされ、支持台１３に対して回動可能な貯銑炉本体１４と、この貯銑炉本体１４の下側に長手方向に渡ってそれぞれ均等に配置された６基の誘導加熱を行うインダクションヒータ（加熱手段の一例）１５とを有している。貯銑炉本体１４の上方には、クレーン等の搬送手段（図示しない）により予備処理後の溶銑１６を貯銑炉本体１４内に装入するための開閉蓋１７が配置された受銑口１８と、屑鉄の一例であるスクラップを装入するための開閉蓋１９がそれぞれ配置された６個の装入口２０と、内部の溶銑１６を溶銑鍋等に出銑するための出銑口２１とが設けられている。なお、溶銑１６の上方には、溶銑１６と共に貯銑炉本体１４内に混入したスラグ２２がある。
【００１２】
次に、本発明の一実施の形態に係る加熱式貯銑炉の操業方法について、上記した加熱式貯銑炉１０を参照しながら説明する。
まず、高炉から出銑した溶銑をトピードカー（例えば、容量が３００トン）に受銑し、予備処理場（脱燐及び脱硫処理場、ＯＲＰ処理場）に搬送する。そして、トピードカー内の溶銑に、生石灰を主成分にした脱燐脱硫用フラックスをランスを介して吹き込むことで、溶銑に予備処理を施す。この予備処理は、溶銑中の燐及び硫黄を除去して溶銑の燐量及び硫黄量の各成分量が必ず目標値（例えば、数ｐｐｍ〜数十ｐｐｍレベル）以下になるように施されるため、目標値に対して過剰な処理（低燐、低硫黄化）となる。なお、各成分量は、目標値以下になればよいため、溶銑を受銑したトピードカー毎にバラツキが生じている。
【００１３】
予備処理後の溶銑を、トピードカーで更に加熱式貯銑炉１０まで搬送した後、クレーン（図示しない）で開閉蓋１７を吊上げ、トピードカー内の溶銑を溶銑鍋を介して受銑口１８から貯銑炉本体１４（例えば、容量が２０００トン）内に装入する。なお、貯銑炉本体１４内が空の状態の場合、これを複数回繰返して貯銑炉本体１４内に溶銑１６を貯銑する。このように、貯銑炉本体１４内に貯留可能な溶銑量は、トピードカーから貯銑炉本体１４内に装入される１回分の溶銑量の数倍であり、しかも各溶銑に含まれている燐量及び硫黄量は微量であるため、複数台のトピードカーから貯銑炉本体１４内に溶銑を装入することで、トピードカー毎の燐量及び硫黄量のバラツキが平準化され、調整される。
【００１４】
ここで、貯銑炉本体１４内の溶銑の燐量及び硫黄量が、予め設定した設定値になるように、トピードカー毎の溶銑の燐量及び硫黄量に基づき、貯銑炉本体１４に供給する溶銑を選択して供給し、貯銑炉本体１４内で溶銑の成分量を調整することも可能である。
なお、貯銑炉本体１４内の溶銑の温度は、貯銑炉本体１４に設けられたインダクションヒータ１５によって均一な温度、即ち転炉（精錬炉の一例）に供給可能な温度に調整されている。
このように、貯銑炉本体１４内の溶銑１６の温度及び成分量が均一化され、しかも、転炉に供給する溶銑の配合量に見合う量の溶銑（ＯＲＰ銑）を、常時転炉へ供給できるので、転炉での炭材の節減や操業の安定化（整流化も含む）が可能になる。
【００１５】
予備処理後のトピードカー内に形成されるスラグは、その塩基度が３〜５程度と極めて高く、トピードカーから貯銑炉本体１４内に溶銑を供給する際、この高塩基度のスラグも共に貯銑炉本体１４内に混入する。この状態では、貯銑炉本体１４内の高塩基度のスラグ２２の滓化ができないので、Ａｌ₂ Ｏ₃ 濃度が５〜１５質量％となるように、Ａｌ灰（アルミドロス）などのＡｌあるいはＡｌ₂ Ｏ₃ 含有物を添加し、低融点化を図った低融点スラグを生成させる。ここで、アルミドロスを添加すると、Ａｌのテルミット反応による発熱とスラグの低融点化を図ることができるので、経済的でしかも好ましい結果を得ることができる。
また、貯銑炉本体１４内に、例えば電磁鋼板や珪素鋼板等の珪素の含有量が高い鉄屑や珪石を添加して、塩基度が０．８〜２．０となるようにし、スラグ２２の融点の低下と流動性を良好にすることも可能である。
【００１６】
このように、貯銑炉本体１４内に混入したスラグ２２の塩基度を調整して低融点スラグに改質した後、開閉蓋１９を開けて装入口２０から例えば市中の回収屑であるスクラップ（屑鉄の一例）を添加すると、スクラップが溶銑１６と速やかに接触する。これにより、溶銑中の炭素がスクラップの表面から浸炭してスクラップの溶解温度が低下し、溶銑温度が１２５０〜１４００℃の低温域でスクラップは溶銑１６に容易に溶解するので、低電力でこの浸炭と溶解を繰り返しながら多量のスクラップを溶解した擬似溶銑を増産することができる。
なお、スクラップの溶解により、溶銑１６の炭素濃度が低下するので、溶銑１６の炭素濃度が例えば４．０質量％を切った時点で、新しい溶銑を開閉蓋１７を開けて受銑口１８から装入する。これにより、予め貯銑炉本体１４内に貯留されていた溶銑１６と混合されるため、溶銑の燐及び硫黄の各成分量は、貯銑炉本体１４内に貯留されていた溶銑の燐量及び硫黄に平準化され調整される。
このように、スクラップの添加と新しい溶銑の添加を繰返し行うことで、スクラップの多量溶解による擬似溶銑の増産ができ、転炉への擬似溶銑の配合量を転炉の必要量に見合う量だけ供給することができるので、配合条件の安定化、吹錬の安定化による吹き止め成分や温度の的中率を高め、効率良く、品質の高い溶鋼を製造することができる。
そして、この製造した擬似溶銑を、転炉が必要とする量だけ、出銑口２１から供給する。
【００１７】
【実施例】
本発明に係る加熱式貯銑炉の操業方法を適用し、試験を行った結果について説明する。
まず、トピードカーが高炉から３００トンの溶銑を受銑し、このトピードカーを予備処理場に搬送して、この溶銑に生石灰や酸化鉄を吹き込み溶銑の〔Ｓ〕を０．０１０％以下、〔Ｐ〕を０．０２０％以下になるように処理した。
この予備処理後のスラグの組成は、ＣａＯが６０質量％、ＳｉＯ₂ が１５質量％であり、塩基度が４．０となっており、溶銑処理後の温度が１３００℃であった。
この溶銑を、２０００トンの容量を備えた貯銑炉本体１４内に受銑口１８から溶銑鍋を介して装入した。
【００１８】
ここで、貯銑炉本体１４内の溶銑１６に、スラグ中のＡｌ₂ Ｏ₃ 濃度が５〜１５質量％になるようＡｌ灰（アルミドロス）を添加し、テルミット反応による発熱と、Ａｌ₂ Ｏ₃ の生成によるスラグ２２の低融点化を行った。同時に、珪石や珪素鋼板屑を添加してスラグ２２の塩基度が０．８〜２．０以内になるように調整してスラグ２２の低融点化と流動性を改善した。
そして、１基当りの出力が４．５ＭＷのインダクションヒータ１５に通電して、溶銑を加熱しながら２０トン／３０分間隔でスクラップを添加して溶解した。
溶銑の貯銑炉本体１４への装入は、スクラップ添加の間の時間帯で行われ、貯銑炉本体１４内の擬似溶銑の炭素濃度が低下するのを抑制しながら、前記動作を繰り返し行った。
その結果、擬似溶銑の温度が１３３０〜１３５０℃、炭素濃度が３．９〜４．１％の擬似溶銑を溶製することができた。なお、この擬似溶銑中の硫黄は０．０１０％以下、燐は０．０２０％以下で、いずれもそのバラツキを±０．００２％以内にすることができた。
【００１９】
ここで、比較例について説明する。
まず、前記した予備処理を行った溶銑を貯銑炉本体に入れ、スラグの改質を行うことなく、スクラップを前記と同様に添加して誘導加熱を行うインダクションヒータで加熱溶解した。この場合、予備処理後の溶銑に微量に混入する高い塩基度のスラグ（塩基度４．０を超える）が、貯銑炉本体内で徐々に蓄積され、固化する。このように、高塩基度のスラグの蓄積量が増加すると、スクラップがスラグ面上に堆積したまま溶銑中に入らず、徐々に酸化してスラグと化すだけで溶解し難くなる。これにより、スラグ中の酸化鉄成分が１０％〜２０％となるので、鉄分ロスが生じて経済的でない。
【００２０】
そこで、予備処理場において、脱燐及び脱硫用の生石灰の使用量を減じることで、生成するスラグの塩基度を低くし、この溶銑を適当に混合することで貯銑炉本体内のスラグの塩基度上昇を抑えた。この結果、貯銑炉本体内のスラグ中の酸化鉄成分は５％以下となりスラグの鉄分ロスを抑えることができた。しかし、生石灰使用量を減じると予備処理後の溶銑の成分（Ｓ、Ｐ）が低位に安定し難いため、炉内の擬似溶銑の不純物成分（Ｓ、Ｐ）も増加し、前記した目標値以下の条件を満足できなくなる。このように、予備処理しない溶銑と比較すると、転炉での処理負荷は多少軽減するものの、擬似溶銑の不純物成分が上昇しバラツキが生じる（Ｓ＝０．０１０〜０．０１５％、Ｐ＝０．０２０〜０．０６０％）。このため、特に低燐、低硫黄を要求される鋼を生産する場合に使用が制限され、生産の整流化の面で問題がある。
【００２１】
以上、本発明を、一実施の形態を参照して説明してきたが、本発明は何ら上記した実施の形態に記載の構成に限定されるものではなく、特許請求の範囲に記載されている事項の範囲内で考えられるその他の実施の形態や変形例も含むものである。例えば、前記したそれぞれの実施の形態や変形例の一部又は全部を組合せて本発明の加熱式貯銑炉の操業方法を構成する場合も本発明の権利範囲に含まれる。
前記実施の形態においては、予備処理として脱燐及び脱硫の双方を行った場合について説明したが、溶銑中の燐及び硫黄の各成分量に応じて、予備処理として脱燐のみ又は脱硫のみを行うことも可能である。
【００２２】
また、前記実施の形態においては、溶銑炉内に混入したスラグの塩基度を低下させるため、溶銑にアルミドロスを添加し、Ａｌ₂ Ｏ₃ を含む低融点スラグを生成させた場合について説明した。しかし、溶銑炉内に混入したスラグの塩基度を低下させることが可能であれば、例えば溶銑にＦｅＯ等を添加し低融点スラグを生成させることも勿論可能である。
そして、前記実施の形態においては、屑鉄として鉄のスクラップを使用した場合について説明したが、例えばダスト、スラジ、型銑等の炭素含有量の多い鉄を溶銑に溶解させることも可能である。
更に、前記実施の形態においては、精錬炉として転炉を使用した場合について説明したが、例えば上吹き転炉、電気炉等を使用することも可能である。
【００２３】
【発明の効果】
請求項１〜５記載の加熱式貯銑炉の操業方法においては、温度と成分量が調整された擬似溶銑を精錬炉の必要量に応じて供給することができ、精錬炉で安定した操業を実現できる。また、吹錬の安定化、溶鋼歩留まり、製鋼時間の短縮、連鋳とのマッチングなど歩留まりの向上と生産の整流化が容易になり、溶鋼を効率良く製造できる。
そして、例えば、過剰予備処理された溶銑の精錬炉への払い出しに伴うアンマッチ、残銑の発生に起因する成分量のバラツキ、溶銑の温度低下等を防止できるので、精錬炉での例えば炭材などを用いた熱保障が解消され、より安定した吹錬が可能となり、製造コストを低減することができる。
更に、多量の擬似溶銑の溶製が可能となり、且つ均一な温度及び炭素濃度を備えた擬似溶銑を精錬炉に供給でき、特に、溶銑の配合量が少ない操業の場合に、低硫黄炭材を使用する量を低減でき、炭材などの昇熱コストを低減することができる。
特に、請求項２記載の加熱式貯銑炉の操業方法においては、高塩基度のスラグを低塩基度にすることにより、低融点スラグに改質して粘性を低下させ、溶銑と屑鉄との接触を促進し、溶銑中の炭素による浸炭作用により低温度での屑鉄の多量溶解が可能になり、擬似溶銑を多量に製造することができ経済的である。
【００２４】
請求項３記載の加熱式貯銑炉の操業方法においては、貯銑炉内の低融点スラグの流動性が改善され、高塩基度スラグの悪影響を抑制することができる。これにより、貯銑炉内に滞留した低融点スラグの排出が容易になり、貯銑炉内での過剰な低融点スラグの生成を防止できるので、溶銑の昇熱効率を向上させることができる。
請求項４記載の加熱式貯銑炉の操業方法においては、低融点スラグに含まれるＡｌ₂ Ｏ₃ 濃度を調整することで、滓化し易い組成にできるので、貯銑炉内に滞留した低融点スラグの排出が容易になる。
請求項５記載の加熱式貯銑炉の操業方法においては、誘導加熱を行うことで、擬似溶銑中の炭素の酸化を抑制できるので、溶銑中の炭素量の低減を抑制でき、後工程での炭材の添加量を低減できる。このため、精錬炉で屑鉄を多量配合した場合のように、炭材の添加量が増加することなく、また吹錬時間の延長や吹酸に伴うダストの発生などの問題も解消できる。
【図面の簡単な説明】
【図１】本発明の一実施の形態に係る加熱式貯銑炉の操業方法に使用される加熱式貯銑炉の平面図である。
【図２】図１のＡ−Ａ矢視断面図である。
【符号の説明】
１０：加熱式貯銑炉（貯銑炉）、１１：鉄皮、１２：耐火物、１３：支持台、１４：貯銑炉本体、１５：インダクションヒータ（加熱手段）、１６：溶銑、１７：開閉蓋、１８：受銑口、１９：開閉蓋、２０：装入口、２１：出銑口、２２：スラグ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for operating a heating storage furnace that receives pre-treated hot metal and supplies it to a refining furnace (for example, a converter).
[0002]
[Prior art]
Conventionally, the hot metal discharged from the blast furnace is once received by a topped car (molten car) or hot metal ladle, etc., and the hot metal that has undergone pretreatment such as desulfurization or dephosphorization is further transferred to the charging pan and conveyed by a crane or the like. However, it is charged in a converter (smelting furnace) in which a cooling material such as scrap iron or iron oxide is charged. And molten steel is manufactured by spraying oxygen from an upper blowing lance and performing decarburization refining. In the decarburization refining of this converter, blending of hot metal, scrap iron, iron oxide, etc. with reference to past blowing acid results, etc., so that the temperature and carbon concentration at the time of blowing stop when finishing blowing will be the target values. The amount is determined.
However, supply conditions (for example, blending amount) of hot metal to the converter fluctuate due to fluctuations in the amount of hot metal discharged from the blast furnace and the amount of molten steel produced in the converter. Increases in melting costs due to an increase in the amount of use of selenium. In addition, the pretreatment applied to the hot metal is carried out excessively so that the amount of phosphorus and sulfur in the hot metal is less than the target value for each processing unit of the topped car and hot metal ladle. The hot metal temperature is lowered. And since the capacity of the topped car or hot metal ladle and the capacity of the converter do not balance, the temperature of the hot metal in the waiting tope car or hot metal pan, or the hot metal remaining in the topped car or hot metal pan (residue) is drastically reduced. Has occurred. Here, when the amount of hot metal supplied from the topped car or hot metal ladle is insufficient, there is a problem that the converter cannot be operated stably.
[0003]
As a countermeasure, the following method has been proposed.
First, Patent Document 1, when dissolved by induction furnace and cast steel, the SiO ₂ 65 to 75 wt% as a slag agent, the Al ₂ O ₃ 0.5 to 4 wt%, and a soda lime glass A method is described in which the blended material is added to the hot metal so that the melting point of the slag is lowered and the cover effect of the slag is made to act, thereby facilitating the discharge. Thereby, useless heat diffusion can be prevented and temperature drop of the hot metal can be suppressed.
In Patent Document 2, scrap iron (scrap) to which moisture supplied from a bucket conveyor adheres is dried by the atmospheric heat of an induction heating type storage furnace to reduce moisture, and the dried scrap iron is stored. It describes a method of melting in a furnace. As a result, a large amount of pseudo hot metal in which scrap iron is dissolved can be manufactured, and stable supply to the converter in the subsequent process becomes possible, and the converter can be operated stably.
In Patent Document 3, scrap iron and a slagging agent are charged and melted in an arc furnace, and after the molten metal and slag are separated, the molten metal is charged into an induction heating furnace, and a refining agent is added to the steel. A method of manufacturing is described. Thereby, hot metal can be manufactured from scrap iron and the supply amount of hot metal to a converter can be increased.
[0004]
[Patent Document 1]
JP-A-62-284022 [Patent Document 2]
Japanese Patent Laid-Open No. 11-248368 [Patent Document 3]
Japanese Patent Publication No. 61-28913 [0005]
[Problems to be solved by the invention]
However, the above method has the following problems.
First, in the method described in Patent Document 1, since a soda lime-based material is used as a slagging agent, the wear of the refractory disposed in the induction furnace increases. In addition, since it is not a method of adjusting the temperature and the amount of components of hot metal that has undergone pretreatment such as dephosphorization and desulfurization, the operation of the converter becomes unstable due to the introduction of unadjusted hot metal into the converter. Become. Since the viscosity of the forming agent is much larger than the slag agent CaO-CaF ₂ based, when charged with scrap iron to the induction furnace, Zokasu agent adheres to the surface of the scrap iron, carbon in molten iron Since the carburizing action on the scrap iron is hindered, there is also a problem that the scrap iron cannot be actively dissolved to produce pseudo hot metal.
And since the method described in patent document 2 can manufacture a lot of pseudo hot metal, this pseudo hot metal can be stably supplied to the converter in the post-process, but the hot metal for melting scrap iron is transferred from the blast furnace to a topped car or hot metal ladle. Since it is a normal hot metal that has been transported, as in the case of hot metal that has undergone pretreatment, differences in the amount of components such as phosphorus and sulfur, fluctuations in hot metal components and temperature, and the amount of hot metal in the converter Problems such as unmatching due to fluctuations in the steel and poor melting of scrap iron due to mixed slag are not considered.
[0006]
Furthermore, the method described in Patent Document 3 is a method of manufacturing molten steel by supplying scrap iron to an arc furnace and adjusting the temperature and the amount of components of the hot metal subjected to pretreatment such as dephosphorization and desulfurization. Since this is not a method, the operation of the converter becomes unstable when unadjusted hot metal is charged into the converter. Moreover, in order to melt | dissolve scrap iron, it is necessary to heat scrap iron to high temperature (scrap iron melting temperature), and also since there is a limit in melt | dissolution capability, calorie | heat amount cost rises and it is not economical.
The present invention has been made in view of such circumstances, adjusting the component amount of the hot metal that has been subjected to pretreatment, suppressing a decrease in hot metal temperature due to unbalance of the hot metal supply amount to the refining furnace, and the scrap iron The objective is to provide a method for operating a heated storage furnace that can ensure stable operation of the refining furnace by ensuring the amount of hot metal supplied to the refining furnace by increasing the absolute amount by improving melting And
[0007]
[Means for Solving the Problems]
The operation method of the heating type storage furnace according to the present invention in accordance with the above object is to charge the hot metal subjected to either or both of dephosphorization and desulfurization into a storage furnace equipped with heating means, The temperature and component amount of the hot metal are adjusted in the storage furnace, and the pseudo hot metal is manufactured by adding scrap iron to be melted, and this pseudo hot metal is supplied to the refining furnace. Thereby, for example, since the hot metal that has been subjected to excessive pretreatment for each processing unit of the topped car or hot metal ladle can be once charged into the storage furnace, the amount of hot metal in the storage furnace, in particular, P, S The components and carbon concentration can be adjusted to a uniform state. In addition, since the storage furnace is provided with heating means, the hot metal temperature in the storage furnace can be adjusted to be maintained at a uniform temperature even if the supply amount of the hot metal to the refining furnace is unbalanced. And since scrap iron can be added and melted to the hot metal in a storage furnace and a lot of pseudo hot metal can be manufactured, pseudo hot metal can be stably supplied to a refining furnace.
Thereby, the pseudo hot metal in which the temperature and the component amount are adjusted can be supplied according to the required amount of the refining furnace, and a stable operation can be realized in the refining furnace. In addition, it becomes easier to improve yield and rectify production, such as stabilization of blowing, molten steel yield, shortening of steelmaking time, and matching with continuous casting.
[0008]
Here, in the operation method of the heating type storage furnace according to the present invention, after adjusting the basicity of the slag mixed in the storage furnace and reforming it to a low melting point slag, the scrap iron is turned into the hot metal in the storage furnace. It is preferable to add and dissolve it. When the hot metal subjected to the pretreatment is charged into the storage furnace, slag having a high basicity of about 3 to 5 flows into the storage furnace together with the hot metal. This high basicity slag is located above the hot metal charged in the storage furnace and has a high viscosity. Therefore, when scrap iron is put into the storage furnace, it adheres to the surface of the iron scrap. Thereby, since the carburizing action of the carbon in the hot metal to the scrap iron is inhibited, the dissolution efficiency of the scrap iron in the hot metal is deteriorated. Therefore, by changing the slag of high basicity to low basicity, it is modified to low melting point slag to reduce the viscosity, promote contact between hot metal and scrap iron, and at low temperature by carburizing action of carbon in hot metal. As a result, a large amount of scrap iron can be dissolved, and a large amount of pseudo molten iron can be produced.
[0009]
In the method for operating a heated storage furnace according to the present invention, the basicity of the low melting point slag is preferably 0.8 to 2.0. Here, the basicity is represented by CaO / SiO ₂ . Thereby, the fluidity | liquidity of the low melting-point slag in a storage furnace is improved, and the bad influence of high basicity slag can be suppressed. Here, when the basicity of the low melting point slag is less than 0.8, the fluidity of the low melting point slag becomes too good and the refractory is worn. On the other hand, when the basicity of the low melting point slag exceeds 2.0, the fluidity of the low melting point slag is poor and the dissolution efficiency of scrap iron is lowered. For this reason, in order to improve the dissolution efficiency of scrap iron without incurring refractory wear, the basicity of the low melting point slag is preferably 0.8 to 1.5, and more preferably 0.8 to 1. .2 is preferable.
In the operation method of the heating type storage furnace according to the present invention, the Al ₂ O ₃ concentration contained in the low melting point slag is preferably 5 to 15% by mass. Thus, by adjusting the Al ₂ O ₃ concentration contained in the low melting point slag, it is possible to make the composition easy to hatch. Here, if the concentration of Al ₂ O ₃ contained in the low melting point slag is less than 5% by mass, the low melting point slag will be poorly hatched. On the other hand, even if the Al ₂ O ₃ concentration contained in the low-melting slag exceeds 15% by mass, the low-melting slag is poorly hatched. For this reason, in order to make the low melting point slag easy to hatch, the Al ₂ O ₃ concentration contained in the low melting point slag is preferably 7 to 13% by mass, and more preferably 8 to 12% by mass. Is preferred.
In the operating method of the heating type storage furnace according to the present invention, the heating by the heating means is preferably induction heating. Thus, by performing induction heating, since the oxidation of carbon in the pseudo molten iron can be suppressed, the reduction of the amount of carbon in the molten iron can be suppressed, and the amount of carbonaceous material added in the subsequent process can be reduced.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described with reference to the accompanying drawings for understanding of the present invention.
FIG. 1 is a plan view of a heating type storage furnace used in the method for operating a heating type storage furnace according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view taken along the line AA in FIG. is there.
[0011]
As shown in FIGS. 1 and 2, a heating storage furnace (an example of a storage furnace) 10 used in a method for operating a heating storage furnace according to an embodiment of the present invention is a cylindrical iron. A refractory 12 is lined on the skin 11, and a storage furnace main body 14 that can be rotated with respect to the support base 13, and six units that are equally arranged in the longitudinal direction below the storage furnace main body 14 respectively. And an induction heater (an example of a heating means) 15 for performing induction heating. Above the storage furnace main body 14, a receiving port 18 is provided with an open / close lid 17 for charging the hot metal 16 after the preliminary treatment into the storage furnace main body 14 by a conveying means (not shown) such as a crane. And six loading / unloading ports 20 each provided with an open / close lid 19 for loading scrap, which is an example of scrap iron, and a spout 21 for serving the hot metal 16 inside the hot metal pan or the like. Is provided. Above the molten iron 16, there is a slag 22 mixed in the storage furnace main body 14 together with the molten iron 16.
[0012]
Next, a method for operating a heating storage furnace according to an embodiment of the present invention will be described with reference to the heating storage furnace 10 described above.
First, the hot metal discharged from the blast furnace is received by a topped car (for example, with a capacity of 300 tons) and transferred to a preliminary treatment plant (dephosphorization and desulfurization treatment plant, ORP treatment plant). Then, a dephosphorization desulfurization flux mainly composed of quick lime is blown into the hot metal in the topped car through a lance, so that the hot metal is preliminarily treated. This pretreatment is performed so that phosphorus and sulfur in hot metal are removed so that the amounts of phosphorus and sulfur in the hot metal are always below target values (for example, several ppm to several tens of ppm level). , Excessive treatment (low phosphorus, low sulfur) with respect to the target value. In addition, since each component amount should just become below a target value, the variation has arisen for every topped car which received hot metal.
[0013]
After the hot metal after the preliminary treatment is further transported to the heating storage furnace 10 by a topped car, the open / close lid 17 is lifted by a crane (not shown), and the hot metal in the topped car is stored from the receiving port 18 through the hot metal pan. It charges in the furnace main body 14 (for example, capacity is 2000 tons). When the storage furnace body 14 is empty, this is repeated a plurality of times to store the hot metal 16 in the storage furnace body 14. Thus, the amount of hot metal that can be stored in the storage furnace main body 14 is several times the amount of hot metal charged in the storage furnace main body 14 from the topped car, and is included in each hot metal. Since the amount of phosphorus and the amount of sulfur are very small, the variation of the amount of phosphorus and the amount of sulfur for each topped car is leveled and adjusted by inserting hot metal into the storage furnace main body 14 from a plurality of topped cars.
[0014]
Here, the amount of phosphorus and sulfur in the hot metal in the storage furnace main body 14 are supplied to the storage furnace main body 14 based on the amount of phosphorus and sulfur in the hot metal for each topped car so that the preset values are set. It is also possible to select and supply hot metal and adjust the amount of hot metal component in the storage furnace main body 14.
The temperature of the hot metal in the storage furnace body 14 is adjusted to a uniform temperature, that is, a temperature that can be supplied to the converter (an example of a refining furnace) by an induction heater 15 provided in the storage furnace body 14. .
As described above, the temperature and the component amount of the hot metal 16 in the storage furnace main body 14 are made uniform, and an amount of hot metal (ORP iron) corresponding to the amount of hot metal supplied to the converter is constantly supplied to the converter. As a result, it is possible to save carbon in the converter and stabilize operation (including rectification).
[0015]
The slag formed in the torpedo car after the preliminary treatment has an extremely high basicity of about 3 to 5. When supplying hot metal from the topped car into the storage furnace main body 14, this slag having a high basicity is also stored. It mixes in the furnace body 14. In this state, since the high basicity slag 22 in the storage furnace body 14 cannot be hatched, Al such as Al ash (aluminum dross) or the like so that the Al ₂ O ₃ concentration is 5 to 15% by mass. A material containing Al ₂ O ₃ is added to produce a low melting point slag with a low melting point. Here, when aluminum dross is added, heat generation due to the thermite reaction of Al and a lower melting point of the slag can be achieved, so that an economical and preferable result can be obtained.
In addition, iron scrap or silica having a high silicon content such as an electromagnetic steel plate or a silicon steel plate is added into the storage furnace main body 14 so that the basicity becomes 0.8 to 2.0, and the slag 22 It is also possible to improve the lowering of the melting point and the fluidity.
[0016]
Thus, after adjusting the basicity of the slag 22 mixed in the storage furnace main body 14 to reform the slag 22 into a low melting point slag, the opening / closing lid 19 is opened and the scrap which is, for example, collected scrap in the city from the loading port 20 is opened. When (an example of scrap iron) is added, the scrap quickly comes into contact with the hot metal 16. As a result, the carbon in the hot metal is carburized from the surface of the scrap, so that the melting temperature of the scrap is lowered, and the scrap easily dissolves in the hot metal 16 in the low temperature range of 1250 to 1400 ° C. As a result, it is possible to increase the production of pseudo hot metal in which a large amount of scrap is melted.
Since the carbon concentration of the hot metal 16 decreases due to melting of the scrap, when the carbon concentration of the hot metal 16 falls below 4.0% by mass, for example, a new hot metal is opened from the receiving port 18 by opening the opening / closing lid 17. Enter. Thereby, since it mixes with the hot metal 16 previously stored in the storage furnace main body 14, the amount of each component of hot metal phosphorus and sulfur is the amount of phosphorus in the hot metal stored in the storage furnace main body 14 and Leveled and adjusted to sulfur.
In this way, by repeatedly adding scrap and adding new hot metal, it is possible to increase production of simulated hot metal by melting large amounts of scrap, and supply the amount of simulated hot metal to the converter in an amount that matches the required amount of the converter. As a result, it is possible to increase the hit ratio of blowing components and temperature by stabilizing the blending conditions and stabilizing the blowing, and to efficiently produce high quality molten steel.
Then, the produced simulated hot metal is supplied from the outlet 21 in an amount required by the converter.
[0017]
【Example】
The result of having applied the operating method of the heating type storage furnace which concerns on this invention, and performing the test is demonstrated.
First, the topped car receives 300 tons of hot metal from the blast furnace, transports this topped car to a preliminary treatment plant, blows quicklime and iron oxide into this hot metal, and reduces the hot metal [S] to 0.010% or less, [P]. Was processed to 0.020% or less.
The composition of the slag after this pretreatment was CaO 60 mass%, SiO ₂ 15 mass%, the basicity was 4.0, and the temperature after the hot metal treatment was 1300 ° C.
This hot metal was charged into the storage furnace main body 14 having a capacity of 2000 tons from the receiving port 18 through a hot metal pan.
[0018]
Here, Al ash (aluminum dross) is added to the hot metal 16 in the storage furnace main body 14 so that the Al ₂ O ₃ concentration in the slag becomes 5 to 15% by mass, the heat generated by the thermite reaction, and Al ₂ O. _The melting point of the slag 22 was lowered by the generation of ₃ . At the same time, siliceous stone and silicon steel plate scraps were added to adjust the basicity of the slag 22 to be within 0.8 to 2.0 to improve the low melting point and fluidity of the slag 22.
Then, electricity was passed through the induction heater 15 having an output per unit of 4.5 MW, and scrap was added and melted at intervals of 20 tons / 30 minutes while heating the hot metal.
The hot metal is charged into the storage furnace main body 14 in the time zone during the addition of scrap, and the above operation is repeated while suppressing the carbon concentration of the simulated hot metal in the storage furnace main body 14 from decreasing. It was.
As a result, it was possible to produce a simulated hot metal having a simulated hot metal temperature of 1330 to 1350 ° C. and a carbon concentration of 3.9 to 4.1%. In this simulated hot metal, sulfur was 0.010% or less and phosphorus was 0.020% or less, and in both cases, the variation was within ± 0.002%.
[0019]
Here, a comparative example will be described.
First, the hot metal subjected to the above-described pretreatment was put into a storage furnace main body, and without melting the slag, the scrap was added in the same manner as described above and heated and melted with an induction heater that performs induction heating. In this case, high basicity slag (basicity exceeding 4.0) mixed in a small amount in the hot metal after the pretreatment is gradually accumulated and solidified in the storage furnace body. Thus, when the accumulation amount of slag having a high basicity increases, scrap does not enter the hot metal while being deposited on the slag surface, and it becomes difficult to dissolve only by gradually oxidizing to slag. Thereby, since the iron oxide component in slag will be 10%-20%, iron loss will arise and it is not economical.
[0020]
Therefore, by reducing the amount of quick lime used for dephosphorization and desulfurization at the pretreatment plant, the basicity of the slag to be produced is lowered, and the base of the slag in the storage furnace body is appropriately mixed with this hot metal. Suppressed the rise. As a result, the iron oxide component in the slag in the storage furnace body became 5% or less, and iron loss of the slag could be suppressed. However, since the hot metal components (S, P) after the pretreatment are difficult to stabilize at a low level when the amount of quick lime is reduced, the impurity components (S, P) of the simulated hot metal in the furnace also increase, and are below the above target values. It becomes impossible to satisfy the condition. As described above, compared with hot metal that is not pretreated, the processing load in the converter is somewhat reduced, but the impurity component of the pseudo hot metal is increased to cause variation (S = 0.0.10 to 0.015%, P = 0). 0.020-0.060%). For this reason, use is restricted especially when producing steels that require low phosphorus and low sulfur, and there is a problem in terms of rectification of production.
[0021]
As described above, the present invention has been described with reference to one embodiment. However, the present invention is not limited to the configuration described in the above embodiment, and is described in the claims. Other embodiments and modifications conceivable within the scope of the above are also included. For example, a case where the operation method of the heating type storage furnace of the present invention is configured by combining a part or all of the above-described embodiments and modifications is also included in the scope of the right of the present invention.
In the above embodiment, the case where both dephosphorization and desulfurization are performed as the pretreatment has been described. However, depending on the amount of each component of phosphorus and sulfur in the hot metal, only dephosphorization or only desulfurization is performed as the pretreatment. It is also possible.
[0022]
Further, in the above embodiment, to reduce the basicity of the slag mixed into hot metal furnace, the aluminum dross is added to the molten iron, a case was described in which to produce a low melting point slag comprises Al ₂ O _3. However, if it is possible to reduce the basicity of the slag mixed in the hot metal furnace, for example, FeO or the like can be added to the hot metal to produce a low melting point slag.
In the embodiment described above, the case where iron scrap is used as scrap iron has been described. However, for example, iron having a high carbon content such as dust, sludge, and mold iron can be dissolved in hot metal.
Furthermore, although the case where the converter was used as a refining furnace was demonstrated in the said embodiment, it is also possible to use a top blow converter, an electric furnace, etc., for example.
[0023]
【The invention's effect】
In the operation method of the heating type storage furnace of Claims 1-5, the pseudo hot metal in which temperature and the amount of components were adjusted can be supplied according to the required amount of a refining furnace, and the stable operation in a refining furnace is possible. realizable. In addition, it is easy to improve yield and streamline production, such as stabilization of blowing, molten steel yield, shortening of steelmaking time, matching with continuous casting, and the molten steel can be manufactured efficiently.
And, for example, it is possible to prevent unmatching due to the discharge of the hot metal that has been preliminarily treated to the refining furnace, variation in the amount of components due to the occurrence of residue, temperature drop of the hot metal, etc. The heat security using is eliminated, more stable blowing is possible, and the manufacturing cost can be reduced.
Furthermore, it is possible to produce a large amount of simulated hot metal, and to supply simulated hot metal having a uniform temperature and carbon concentration to the smelting furnace. The amount to be used can be reduced, and the heating cost of charcoal materials can be reduced.
In particular, in the operation method of the heating type storage furnace according to claim 2, by changing the high basicity slag to the low basicity, the low melting point slag is reformed to reduce the viscosity, The contact is promoted, and the carburizing action of carbon in the hot metal makes it possible to dissolve a large amount of scrap iron at a low temperature, which makes it possible to produce a large amount of simulated hot metal and is economical.
[0024]
In the operation method of the heating type storage furnace according to claim 3, the fluidity of the low melting point slag in the storage furnace is improved, and the adverse effect of the high basicity slag can be suppressed. Thereby, discharge of the low melting point slag staying in the storage furnace is facilitated, and generation of excessive low melting point slag in the storage furnace can be prevented, so that the heating efficiency of the hot metal can be improved.
In the operating method of the heating type storage furnace according to claim 4, since the composition can be easily hatched by adjusting the concentration of Al ₂ O ₃ contained in the low melting point slag, the low melting point retained in the storage furnace Easily discharge slag.
In the operation method of the heating type storage furnace according to claim 5, by performing induction heating, the oxidation of carbon in the pseudo molten iron can be suppressed, so that the reduction of the amount of carbon in the molten iron can be suppressed, and in the subsequent process The amount of carbon material added can be reduced. Therefore, as in the case where a large amount of scrap iron is blended in the smelting furnace, the amount of added carbonaceous material does not increase, and problems such as the extension of the blowing time and generation of dust associated with blowing acid can be solved.
[Brief description of the drawings]
FIG. 1 is a plan view of a heating type storage furnace used in a method for operating a heating type storage furnace according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view taken along the line AA in FIG.
[Explanation of symbols]
10: Heated storage furnace (storage furnace), 11: Iron skin, 12: Refractory, 13: Support base, 14: Storage furnace body, 15: Induction heater (heating means), 16: Hot metal, 17: Opening / closing lid, 18: receiving port, 19: opening / closing lid, 20: loading port, 21: outlet, 22: slag

Claims

The hot metal that has been subjected to pretreatment of either or both of dephosphorization and desulfurization is charged into a storage furnace equipped with heating means, and the temperature and component amount of the hot metal are adjusted in the storage furnace, and A method for operating a heating storage furnace, characterized in that a pseudo hot metal in which scrap iron is added and melted is manufactured, and the pseudo hot metal is supplied to a refining furnace.

2. The method of operating a heated storage furnace according to claim 1, wherein after the basicity of the slag mixed in the storage furnace is adjusted and reformed to a low melting point slag, the scrap iron is converted into the molten iron in the storage furnace. A method for operating a heating type storage furnace characterized by being added to and dissolved in the water.

The operating method of a heating type storage furnace according to claim 2, wherein the basicity of the low melting point slag is 0.8 to 2.0.

The heating type storage furnace operating method according to any one of claims 2 and 3, wherein the Al ₂ O ₃ concentration contained in the low melting point slag is 5 to 15% by mass. How to operate the storage furnace.

The operating method of the heating type storage furnace of any one of Claims 1-4 WHEREIN: The heating by the said heating means is induction heating, The operating method of the heating type storage furnace characterized by the above-mentioned.