JP3790414B2

JP3790414B2 - Hot metal refining method

Info

Publication number: JP3790414B2
Application number: JP2000330268A
Authority: JP
Inventors: 進務川; 達也佐渡; 拓男三戸; 智晶田崎
Original assignee: Nippon Steel Corp
Current assignee: Nippon Steel Corp
Priority date: 2000-10-30
Filing date: 2000-10-30
Publication date: 2006-06-28
Anticipated expiration: 2020-10-30
Also published as: JP2002129221A

Description

【０００１】
【発明に属する技術分野】
本発明は主として高炉溶銑を原料とする鉄鋼の効率的な精錬方法にかかわる。特に、転炉を使った溶銑段階での脱珪、脱りん、脱硫、スクラップ溶解法を提供し、転炉脱炭工程とあわせて効率的な精錬方法を提供するものである。
【０００２】
【従来の技術】
鋼材使用環境の厳格化、多様化に伴い、鋼材中に含まれる不純物濃度の低減、およびその制御に対するニーズは留まることがない。こうした要求にこたえるため、溶銑段階での脱珪、脱りん、脱硫処理技術が発展しており様々な形態の処理方法が検討されている。一方、溶銑予備処理は単に不純物を除去するだけでは無く、CaO 使用量の削減、転炉でのマンガン鉱石還元、転炉の生産性、寿命向上などのコスト削減の上でも有効であることが明らかとなり、現在では大量生産鋼にも適用されているに至っている。更に、近年、環境負荷の面で、製鉄副産物の処理方法についても関心が高まっている。製鉄副産物の代表的なものは製銑、製鋼工程におけるスラグであるが、これらの排出量抑制も求められている。この点では精錬効率を極限まで高め、精錬剤使用量を低減することが最重要課題であり、環境面からも溶銑予備処理技術の重要性が高まっている。スラグの再利用時には有害元素の環境中への溶出が問題とされており、その中でフッ素については具体的な法的規制が実施されている。従来、反応効率を高めるためにはスラグの流動性を高める目的で融点降下剤として蛍石（CaF₂）が多用されて来たが、これを使わない精錬プロセスの確立も課題である。
【０００３】
転炉形式の炉を利用した処理方法という側面で見た場合、特開平2-200715号公報として公開された技術がある。脱りん処理後のスラグ中酸化鉄濃度を2.5 〜５％に制御し、引き続き溶銑に脱硫剤を吹込んで脱りん・脱硫連続処理を行う方法が提示されているが、この方法では、脱りん処理後のスラグ量のばらつき、生石灰の滓化状況等の不確定要素によって、脱硫処理中の復りん、即ちスラグからのりんの戻り、および、脱硫剤の効率が大きくばらつくという問題があった。そのため、脱硫処理においては過剰な脱硫剤吹込みを行ってスラグ量を増やす、あるいはりんが目標以下に下がらない場合には次工程の転炉脱炭時に生石灰を多量添加して更にスラグ発生量を増す、という結果を招いていた。また、特開平1-147011号公報には二基の上下吹き転炉を用い、片方を脱りん炉、片方を脱炭炉として用い、脱炭炉で生成したスラグを脱りん炉で再利用する方法が述べられている。しかし、これらの方法では、脱珪処理、脱硫処理をどのように行うかの記載は無く、精錬工程トータルでの最適化については記載が無い。
【０００４】
更に、底吹きを主とする転炉を用いた例として、例えば特開昭56-90914号公報、特開昭56-90913号公報には底吹き転炉を用いた溶銑の処理方法が記載されている。しかし、多量の酸素ガスを底吹きする型の転炉の場合、炉底羽口の寿命が短く、設備の休止時間が長く、生産性が低いので量産鋼の多量処理には向かない。また、遊休設備が既にある場合は良いが新設の場合は、大量の酸素ガスと精錬剤を底吹きするための設備費用が高く、またそれらのランニングコストも高く、コストダウンを目的として行う溶銑予備処理の本来目的を逸脱する。従って、炉寿命も考慮し、高生産性を維持する目的では、上吹きを主として攪拌のためにある程度の不活性ガス、精錬剤を吹込む型の転炉を利用するのが望ましい。
【０００５】
次に、脱珪や脱硫処理といった要素機能で見てみると、溶銑の脱硫処理に関しては従来より、トーピードカーでの粉体吹込み精錬や機械攪拌法であるＫＲ処理が行われて来た。トーピードカーでの吹込み処理では溶銑上の空間容積、所謂フリーボードが小さいため、吹込み速度が制限され、処理時間が長くなり１基あたりの生産性が低いという問題がある。更にＫＲ法ではトップスラグの巻き込みによる脱硫処理になるので、スラグにある程度の液相率を保って流動性を高める必要が生じる。従って、溶融促進剤である蛍石の利用が必須となるが、スラグからのフッ素溶出規制があり好ましい方法とは言えない。
【０００６】
例えば特開平11−100608号公報にはCaF₂使用量を最小限に抑えて[%S]<0.005％に効率良く溶銑の脱珪・脱硫処理を行う方法が提案されている。しかし、一般には酸化精錬である脱珪反応と脱硫反応を同一炉内で行うのは効率的ではない。即ち、脱珪処理を先、脱硫処理を後に行うにしても、脱珪処理で生じるスラグは低塩基度で高い酸化鉄濃度をもつため、脱硫処理時には還元が生じ、酸化鉄濃度が低下した後でないと脱硫反応が効果的に進まないという結果をもたらす。また、公報中にはスラグの流動性を上げるためにCaF₂を使用するが、その使用量を少なくするために融点が低い酸化鉄を加える、という記述があり、あくまでトップスラグの流動性を確保する、という思想に基づくものである。酸化鉄を使用すると分解吸熱反応により溶銑の温度が低下して熱的余裕が低下するので、全ての場合について完全にCaF₂を使用しなくても良い方法を提供するものではない。従って、この方法も脱珪・脱硫を１つの精錬容器で行えるという、工程集約の上では望ましいが、フッ素源を使用せず、かつ熱的余裕を含めたトータルプロセスの効率として見た場合には課題がある。
【０００７】
更に、脱珪や脱硫、脱りんという精錬機能の組み合わせ、という視点で見た場合、従来、多くの研究開発は脱珪と脱りんの組み合わせの最適化についてなされている。一般に、熱力学的には溶銑中の珪素濃度が高いと、珪素がりんに対して優先酸化を起こすので、脱りん反応が生じ難い。従って、脱りん前に如何に効率的に脱珪処理を行うか、ということに工夫や開発が行われて来た。
【０００８】
例えば、CAMP−ISIJ、vol.13、p.52には脱りん処理前に溶銑鍋におけるインジェクション処理によって珪素濃度を0.1%以下に低減した後、脱りん処理を行う旨の記述がある。しかし、脱珪に伴って脱炭反応も不可避的に生じ、さらにまた、脱炭反応は珪素濃度が低下する程顕著となり、次の脱炭プロセスでスクラップを溶解する熱が不足する、という問題がある。また、スラグフォーミングによる生産障害を回避しようとすると、CaO 源を添加してスラグの塩基度を１前後確保して泡立ちし難いスラグとするのが一般的であるが、低濃度まで脱珪を行えば行う程これに要するCaO は増える。更にまた、上記の様に脱炭速度が大きくなるので、更に塩基度を上げるためにCaO 添加量を増す必要が生じ、精錬プロセストータルでのCaO 源使用量は減らせず、スラグ発生量も減らせないという結果に終る。また、脱珪処理を鍋やトーピードカーのようなフリーボードの小さな反応容器を用いると、上記のスラグフォーミングによる制約が厳しく、益々塩基度を高めてフォーミングを抑制するため、スラグ発生量がかえって増えたり、酸素供給速度を落とした操業をとらざるをえないので、処理時間がかかり、生産性を落として全量処理には適用出来ない、という問題がある。
【０００９】
【発明が解決しようとする課題】
量産鋼の溶銑予備処理−転炉プロセスに求められる機能としては脱珪、脱りん、脱硫、脱炭およびマンガン鉱石還元といった精錬機能だけでは無く、スクラップの溶解も重要な機能である。即ち、定常的な生産において製鉄所内で発生するスクラップを溶解する能力は担保する必要があるし、更に、鋼材需要が増えた場合、あるいは高炉の炉況が不安定となり、溶銑が不足する様な状況下では生産量確保の点でスクラップの多量溶解を行う必要が生じる。しかし、溶銑の脱珪、脱りん、転炉脱炭といった酸化精錬における酸素源として分解・吸熱を伴う酸化鉄源を利用したのでは、スクラップ溶解熱が不足するので、全酸素使用量に対する気体酸素比率、所謂気酸比率は高い方が望ましい。
【００１０】
一方で、脱珪、脱硫、脱りんという、不純物の除去のみの視点からはこれらの処理を全て分割して行い、その間にスラグを完全に分離することが理想であることは明白であるが現実の工業プロセスの中でこうした分割精錬を求めて行くことは、まず第一に、それら、精錬設備を建設する費用が膨大となり、現実的ではないことと、溶銑の移し替え回数が増える、あるいは長時間を要するといった理由から放熱ロスが大きくなり、熱的な余裕が無くなり、スクラップ利用の観点から好ましくない、という問題がある。更にスラグと溶銑あるいは溶鋼の分離を効率的に完全に行う技術が無い現状では排滓に長時間を要し、またスラグへの粒鉄、有価成分のロスも大きくなる、という問題もある。排滓を完全に行わなければ、前処理にて発生したスラグが次工程に持ち越されて復反応を生じるために単一機能だけを効率的に行ってもトータルプロセスで見た場合に最適かどうかは別問題となる。従って、前後工程を含め、ある程度の機能集約にも配慮した一貫精錬プロセスでの最適化が重要である。
【００１１】
溶銑予備処理、転炉脱炭および二次精錬からなるトータルの精錬プロセス効率化を考慮すると、転炉脱炭時には脱りん負荷を残さず、可能な限り少ないスラグ量で脱炭精錬を行うことが最重要課題である。これにより、転炉耐火物寿命の伸長、生産性向上がはかられるとともに、マンガン鉱石を添加することによるマンガンの溶融還元が容易となり、二次精錬での高価なマンガン合金使用量が削減できる。これを量産規模で行う時には、溶銑脱りん処理後のりん濃度のばらつきが問題となる。即ち、りん濃度が目標値以上にはずれた場合、転炉脱炭時に生石灰を多量投入して更に脱りんを行うことになるが、この時生成するスラグは転炉内に付着して次チャージのりん汚染源となる。また二次精錬に持ち越すと復りんし、更にばらつきを助長する。また、りんが高目にはずれることを懸念して過剰な生石灰添加と酸素供給を行うので精錬コストを高め、また、生成するスラグ量を増す結果となる。従って、溶銑の脱りん工程ではばらつき無く目標のりん濃度に低減することも量産プロセスの上で課題となる。
【００１２】
【課題を解決するための手段】
本発明の要旨は、
（１）出鋼孔を有する転炉型の反応容器を用い、酸素源として酸素ガス上吹きを主として行い、脱りん工程で最大の脱りん効率が得られる最適珪素濃度に脱珪処理を行う第一工程と、該精錬炉から出湯・排滓を行って出鋼孔を有する転炉型の反応容器にて該溶銑を酸素ガスを上吹きして脱りん処理する第２工程からなり、前記第一工程において、脱珪処理後の塩基度を 1.2 以上とし、スラグ中の酸化鉄濃度を４％以下とした後、脱硫剤を溶銑中に底吹きして脱硫処理を行うことを特徴とするものである。
（２）また、第一工程の脱珪処理において、使用する酸素の気酸比率を 80% 以上とすることを特徴とするものである。
【００１３】
【発明の実施の形態】
本願発明者らは、酸素ガスを大量に上吹きして溶銑の脱珪、脱りん処理を行うプロセスにおける脱りん効率のばらつきの特徴について詳細な検討を行い、第２図に示す結果を得るとともに、次の様な結論を得た。
イ）酸素ガスを上吹きする脱りん処理時の効率は処理前珪素濃度の影響を受けて変化するが、従来、冶金反応の常識であった、低珪素濃度程効率が高い訳ではなく、最適珪素濃度が存在する。
ロ）最適処理前珪素濃度より珪素濃度が高い場合に脱りんが悪化するが、これは従来の冶金反応上の常識の範疇である。即ち、りんの酸化に対して珪素の優先酸化が進むためである。
ハ）上吹き酸素により所謂スピッティングが発生し、そのスピッティングがスラグ中に叩き込まれた場合、スピッティング中の炭素、および珪素はスラグ中の酸化鉄を還元する。珪素濃度が低い場合には、生成するスラグ量が少なく、還元されるFeO 量が同じでも、FeO の濃度の低下は大きい。その結果、脱りん処理前の珪素濃度が低すぎると脱りんが悪化する。
【００１４】
従って、酸素ガス上吹きを主たる酸素源とする溶銑脱りん処理においては最適な珪素濃度（0.15〜0.35％）が存在する。更に、
ニ）蛍石等の融点降下剤を使わない場合には、スラグが固−液共存状態となり、見掛け上粘性が増すので、スピッティング粒鉄がスラグ中を沈降、分離する速度が遅くなり、益々スピッティング粒鉄によるスラグ中酸化鉄の還元反応速度が増加する。
【００１５】
要約すると、酸素ガスを多量に上吹きする溶銑脱りん法では、スピッティング粒鉄によるスラグの還元が起きるので、最適な珪素濃度とする必要がある。そこで、工程を脱珪処理を主とする第一工程と、脱りん処理を主とする第二工程に分割する、という着想を得た。また、分割工程をこれ以上増やさないために脱硫処理をこの中で行う上では、蛍石などのハロゲン化物を使用せず、脱珪処理を行うと、脱珪処理時に生成するスラグの固相率が高いので、引き続き脱硫剤を吹込んで脱硫処理を行ってもそれ程脱硫効率は低下せず、更に塩基度を1.2 以上とした後で脱硫剤を底吹きすると、効率的な脱硫処理が行えることを明らかとした。
【００１６】
即ち、蛍石等のハロゲン化物を使用せず、酸素源として主として酸素ガスを上吹きにて与え、脱珪処理を終えると、上記ハ）ニ）のメカニズムにより脱珪処理後のスラグ中の酸化鉄濃度は4%以下と低く抑えられ、なおかつフッ素を含まないので固相率が高く、極めて流動性に乏しい反応性の乏しいスラグとなるため、脱硫剤を底吹きしても、そのトップスラグによる影響、即ち、トップスラグからの復硫現象は無視し得る程小さく抑制できる。その場合にも脱珪後のスラグ塩基度を1.2 以上に保てば、固相率が更に高まり、更に望ましい。また、脱硫剤を底吹きにて吹込むと、溶銑中を浮上する間に脱硫剤粒子と溶銑間で脱硫反応が十分生じるため、総じて効率的な脱硫処理が可能となるのである。この場合、脱硫剤粒子の溶銑中の滞留時間を確保するためには吹込み深さは深い程良く、反応の比表面積を確保する上では脱硫剤粒子は細かい程良い。
【００１７】
このように、本法を適用すると、従来高炉鋳床や鍋、あるいはトーピードカーといった別処理工程を要していた脱珪処理が脱硫処理工程と機能集約され、放熱ロス、設備費用の点で有利となり、更に又脱珪を気体酸素中心に行うことができるので、発熱反応となり、熱的余裕も生まれる。
【００１８】
第一工程の脱珪処理時には、気体酸素を使用する場合でも、上吹きするのがスラグの酸化鉄濃度抑制の点で有利である。これは上記メカニズムによってスラグ中の酸化鉄の還元速度が大きくなるためであるが、スラグ中の酸化鉄濃度を４％以下に抑えるには気酸比率を80％以上とするのが望ましい。またこのようにすると、スクラップ溶解の点からも有利である。即ち、固体酸素による脱珪反応が吸熱反応であるのに対し、気体酸素による脱珪反応は発熱反応であり、発生する反応熱はスクラップ溶解に有効に利用できる。その利用形態としては、脱珪処理時に同時にスクラップを添加して溶解しても良いし、溶銑への顕熱として、次工程での熱源として利用しても良い。要は、脱珪反応に気体酸素をなるべく利用することが熱的余裕度を増す上で望ましい。ただし、転炉以外の反応容器、即ち、鍋、あるいはトーピードカーにて気体酸素による脱珪処理を行うとスラグフォーミングが激しく、容器からスラグや地金が溢れ出すので、処理が出来なくなる、という問題がある。またフォーミングを抑制しようとするとスラグの融点を高めるためにCaO 源を添加することが良く行われるが、その使用量が増えて処理コストが高くなる、という問題がある。
【００１９】
さらに、酸素源を酸素ガスとして上吹きして供給することを基本とする本法では、底吹き、あるいはランスインジェクションにて酸素ガスを供給する方法に比べて、設備的に簡便であり、ランス等のコストが掛からずに済む。また多量に底吹きする方法では、羽口まわりの耐火物の溶損が進行し易く、炉寿命が低下して結果として溶銑予備処理比率が低下する結果を招くが、そうした問題も軽減できる。
【００２０】
一方、出鋼孔を有する転炉を反応容器として利用すると、ドラッガーやバキュームクリーナー等の排滓方法に比べて出湯、排滓によってスラグと溶銑の分離を迅速に行うことができる。また、フリーボードの大きな転炉を用いることによって酸素ガス使用量を増やすことができるので、発熱反応となり、移し替えによる放熱ロス分を補うことができる。
【００２１】
本願発明の実施形態を図１により説明する。転炉型の反応容器１に溶銑２を装入する。この前後で必要に応じ、スクラップ３、または脱炭滓や二次精錬スラグの様なリサイクルスラグを装入しても良い。次に、脱珪処理を行うため、生石灰源を添加するが、この場合、炉上ホッパー４から塊状剤を上方添加、ないし上吹きランス５から供給する酸素ガス６をキャリアーガスとして粉状の生石灰を吹き付けにより供給しても良い。炉底に設けた底吹き羽口７より石灰石粉をキャリアーガス８とともにブロータンク９から供給して吹込みつつ、熱的余裕のある場合には、炉上のホッパーより鉄鉱石等の固体状酸素源も添加し、酸素ガス６を吹き付けつつ脱珪処理を行う。次に、脱珪処理後、必要に応じて、酸素ガスの上吹きを止めて、脱硫剤を底吹き羽口７より吹込み、脱硫処理を行う。
【００２２】
次に、転炉型の反応容器１を倒し、出鋼孔10より溶銑２を取鍋11に出湯し、スラグ12と分離する。出湯した溶銑２は、更に転炉型の反応容器１に装入する。その後、必要に応じ、炉上ホッパー４より生石灰等のCaO 源、鉄鉱石等の固体酸素源を添加し、酸素ガス６をランス５より吹き付けつつ、必要に応じ、微粉CaO を酸素ガス６とともに溶銑に吹き付け、溶銑の脱りん処理を行う。脱りん処理後の溶銑２は出鋼孔10より取鍋11に出湯し、脱りんスラグ13と分離され、次工程である転炉脱炭に送られる。
【００２３】
図２に本発明による効果として従来法である下記比較例１の方法における脱りん処理前珪素濃度と脱りん処理後のりん濃度の範囲を示す。また、●にて本願発明者らが本願発明に至る過程で行った試験結果を示す。即ち、酸素上吹きを主たる酸素源とした溶銑の脱りん処理においては最適な珪素濃度が存在することを明らかとしたデータである。また、図３は本願発明による効果として、従来法である比較例１の方法による、処理後のりん濃度のばらつきと、本願発明によるばらつきを比較したデータである。
【００２４】
〔実施例１〕
転炉型の反応容器に高炉溶銑275.8tをスクラップ9.1tとともに装入した。生石灰を炉上ホッパーより添加し、酸素ガスを上吹きランスより供給しつつ脱珪処理を３分間行った。脱珪後のスラグ塩基度は0.5 、酸化鉄濃度は1.8%であった。更に、出鋼孔より出湯し、スラグと分離した溶銑を、転炉型の反応容器にスクラップ16ｔとともに装入し、生石灰源を添加し、固体酸素源と酸素ガスを供給して脱りん処理を行った。脱りん処理後の溶銑は出湯、排滓後、転炉にて脱炭精錬を施した。この例では、処理後のりん濃度は目標値の0.020%より十分下げることができ、スクラップも溶解することができた。この時の処理条件、および溶銑組成、温度の経過を表１に示す。
【００２５】
〔実施例２〕
転炉型の処理容器に高炉溶銑を装入し、酸素ガスを吹き付けつつ、脱珪処理を行った。次に、酸素ガスを止め、底吹き羽口より窒素ガスをキャリアーガスとして脱硫剤を底吹きし、脱硫処理を行った。脱硫剤は微粉生石灰と金属Al分を30％含むAl灰を１：１重量比で混合した粉体である。次に、溶銑を出鋼孔から出湯し、スラグと分離した後、該溶銑を更に転炉型の精錬炉にスクラップとともに装入し、脱りん処理を施した。更に、出鋼孔より出湯し、スラグと分離した。この例では、スクラップを溶解しつつ、硫黄、りん濃度とも目標値より十分下げることができた。
【００２６】
〔実施例３〕
転炉型の反応容器に高炉溶銑をスクラップとともに装入し、生石灰と酸素源を添加して脱珪処理を行った。処理前溶銑の珪素濃度は2.0%と極めて高かった。脱珪処理後の塩基度を0.6 とした。次に、脱硫剤を底吹きして脱硫処理を施した。脱硫剤は微粉生石灰と金属Al分を30％含むAl灰を１：１重量比で混合した粉体である。更に出湯・排滓後、転炉型の反応容器に装入して脱りん処理を行った。この例では、脱珪、脱硫後に高温が維持でき、大量のスクラップを溶解できた。第２工程では最適珪素濃度の効果と合せて極めて高い効率の脱りん処理が可能となった。この例では、従来、スラグボリュームが増えすぎて処理不可能な高珪素濃度の溶銑でも、通常の溶銑同様に脱珪、脱硫、脱りん可能となり、珪素の酸化反応熱をスクラップ溶解に有効利用することができた。
【００２７】
〔比較例１〕
転炉型の処理容器に高炉溶銑とともにスクラップを装入し、酸素源と生石灰を添加して脱珪・脱りん処理を施した。つぎに、酸素ガスを止めて底吹き羽口より生石灰とソーダ灰の混合脱硫剤（生石灰：ソーダ灰＝85:15 重量比）を吹込み、脱硫処理を行った後、出湯・排滓を行った。この例では、脱硫時の復りんが大きく、結果として目標のりん濃度0.02％以下を満足しなかったので、次の転炉脱炭工程で多量の生石灰添加を要した。また、ソーダ灰を使用したため、脱硫処理時の温度低下が大きかった。
【００２８】
〔比較例２〕
トーピードカー内の高炉溶銑に酸素源として酸素ガスとミルスケールを併用し、塩基度調整用の生石灰とともに溶銑中に吹込んで脱珪処理を行った。フォーミング抑制の為、塩基度を1.2 と高めにし、ミルスケールを使用したため溶銑温度は1403℃から1340℃まで低下した。次に該溶銑を転炉型の反応容器に移し、脱りん処理、および脱硫処理を行った。この例では熱的余裕が無く、スクラップ溶解ができなかった。
【００２９】
〔比較例３〕
転炉型の反応容器に高炉溶銑を装入し、生石灰と酸素源を添加して脱珪処理を行った。脱珪後の珪素濃度は0.1%と適正濃度範囲からはずれていた。更に脱珪後の溶銑中に脱硫剤を底吹きして脱硫処理を行った。この場合、脱りんが悪く、0.03％までしか低減せず、目標であった0.02% 以下に到達できなかった。
【００３０】
【表１】

【００３１】
【発明の効果】
本発明により、量産鋼の脱珪、脱硫、脱りん処理方法として、蛍石等ハロゲン化物を使用すること無く、スクラップ溶解量を十分確保し、かつ脱珪と脱硫、脱りんとスクラップ溶解を各々機能集約した、高効率な溶銑予備処理プロセスを確立することができる。
【図面の簡単な説明】
【図１】本発明を実施するに好適な転炉型反応炉の横断面図である。
【図２】本発明による効果を示す試験データの一つであり、溶銑の脱りん処理前の珪素濃度と処理後のりん濃度の関係を示すグラフである。
【図３】本発明による効果を示す実績データの一つであり、溶銑の脱りん処理後のりん濃度のばらつきを示すグラフである。
【符号の説明】
１転炉型の反応容器
２溶銑
３スクラップ
４炉上ホッパー
５上吹きランス
６酸素ガスホルダー
７底吹き羽口
８窒素ガスホルダー
９ブロータンク
10 出鋼孔
11 取鍋
12 脱珪・脱硫スラグ
13 脱りんスラグ[0001]
[Technical field belonging to the invention]
The present invention mainly relates to a method for efficiently refining steel using blast furnace hot metal as a raw material. In particular, the present invention provides desiliconization, dephosphorization, desulfurization, and scrap melting methods at the hot metal stage using a converter, and provides an efficient refining method together with the converter decarburization process.
[0002]
[Prior art]
With the tightening and diversification of the steel material usage environment, the need for reducing the concentration of impurities contained in the steel material and its control does not remain. In order to meet these requirements, desiliconization, dephosphorization, and desulfurization treatment technologies in the hot metal stage have been developed, and various types of treatment methods have been studied. On the other hand, it is clear that hot metal pretreatment is effective not only for removing impurities but also for reducing costs such as reducing the amount of CaO used, reducing manganese ore in the converter, productivity of the converter, and improving the service life. Now, it has also been applied to mass-produced steel. Furthermore, in recent years, in terms of environmental load, there is an increasing interest in methods for treating iron manufacturing byproducts. A typical iron by-product is slag in the steelmaking and steelmaking processes, but it is also required to suppress these emissions. In this respect, increasing the refining efficiency to the limit and reducing the amount of refining agent used are the most important issues, and the importance of hot metal pretreatment technology is increasing from the environmental aspect. When slag is reused, leaching of harmful elements into the environment is a problem, and among them, specific legal regulations are implemented for fluorine. Conventionally, in order to increase the reaction efficiency, fluorite (CaF ₂ ) has been frequently used as a melting point depressant for the purpose of increasing the fluidity of slag, but the establishment of a refining process that does not use this is also an issue.
[0003]
When viewed from the aspect of a processing method using a converter type furnace, there is a technique disclosed in Japanese Patent Laid-Open No. 2-200715. A method has been proposed in which the concentration of iron oxide in the slag after dephosphorization is controlled to 2.5-5%, and then desulfurization agent is blown into the hot metal to perform dephosphorization and desulfurization continuous treatment. Due to uncertain factors such as variations in the amount of slag and hatching of quick lime later, there has been a problem that the recovery of dephosphorization during desulfurization, that is, the return of phosphorus from the slag, and the efficiency of the desulfurization agent vary greatly. Therefore, in the desulfurization treatment, excessive desulfurization agent is blown to increase the amount of slag, or if phosphorus does not fall below the target, a large amount of quick lime is added during the decarburization of the next process to further reduce the amount of slag generated. The result was to increase. In JP-A 1-147011, two vertical blow converters are used, one is used as a dephosphorization furnace and the other is used as a decarburization furnace, and the slag generated in the decarburization furnace is reused in the dephosphorization furnace. A method is described. However, in these methods, there is no description on how to perform desiliconization treatment and desulfurization treatment, and there is no description on optimization in the total refining process.
[0004]
Further, as an example using a converter mainly for bottom blowing, for example, Japanese Patent Laid-Open No. 56-90914 and Japanese Patent Laid-Open No. 56-90913 describe a hot metal processing method using a bottom blow converter. ing. However, in the case of a converter that blows a large amount of oxygen gas, the bottom of the tuyere is short, the downtime of the equipment is long, and the productivity is low, so it is not suitable for mass processing of mass-produced steel. In addition, if there is an idle facility already, it is good, but in the case of a new facility, the equipment cost for blowing a large amount of oxygen gas and smelting agent is high, and the running cost is also high, so Deviates from the original purpose of processing. Therefore, considering the furnace life, in order to maintain high productivity, it is desirable to use a converter of a type in which a certain amount of inert gas and a refining agent are blown mainly for stirring.
[0005]
Next, in terms of elemental functions such as desiliconization and desulfurization, hot metal desulfurization has been conventionally performed by powder blowing refining with a torpedo car and KR, which is a mechanical stirring method. In the blowing process with a torpedo car, since the space volume on the hot metal, so-called free board, is small, there is a problem that the blowing speed is limited, the processing time becomes long, and the productivity per unit is low. Furthermore, in the KR method, since desulfurization is performed by entraining top slag, it is necessary to increase fluidity while maintaining a certain liquid phase ratio in the slag. Therefore, the use of fluorite, which is a melting accelerator, is essential.
[0006]
For example, Japanese Patent Application Laid-Open No. 11-100608 proposes a method of efficiently performing desiliconization / desulfurization treatment of hot metal at [% S] <0.005% while minimizing the amount of CaF ₂ used. However, it is not efficient to perform desiliconization reaction and desulfurization reaction which are generally oxidative refining in the same furnace. That is, even if the desiliconization process is performed first and the desulfurization process is performed later, the slag produced by the desiliconization process has a low basicity and a high iron oxide concentration. Therefore, reduction occurs during the desulfurization process, and the iron oxide concentration decreases. Otherwise, the desulfurization reaction will not proceed effectively. The publication also mentions that CaF ₂ is used to increase the fluidity of slag, but iron oxide with a low melting point is added to reduce the amount used, ensuring the fluidity of the top slag. It is based on the idea of doing. When iron oxide is used, the temperature of the hot metal is lowered due to decomposition endothermic reaction and the thermal margin is lowered, so that it does not provide a method in which CaF ₂ may not be used completely in all cases. Therefore, this method is also desirable in terms of process integration, in which desiliconization and desulfurization can be performed in one refining vessel, but when viewed as the total process efficiency without using a fluorine source and including thermal margin. There are challenges.
[0007]
Furthermore, when viewed from the viewpoint of a combination of refining functions such as desiliconization, desulfurization, and dephosphorization, many researches and developments have so far been made on optimizing the combination of desiliconization and dephosphorization. In general, when the silicon concentration in the molten iron is high in terms of thermodynamics, silicon causes preferential oxidation with respect to phosphorus, and therefore, dephosphorization reaction hardly occurs. Accordingly, contrivances and developments have been made on how to efficiently perform the desiliconization treatment before dephosphorization.
[0008]
For example, CAMP-ISIJ, vol.13, p.52 has a description that the dephosphorization treatment is performed after the silicon concentration is reduced to 0.1% or less by the injection treatment in the hot metal ladle before the dephosphorization treatment. However, the decarburization reaction inevitably occurs with the desiliconization, and the decarburization reaction becomes more remarkable as the silicon concentration decreases, and there is a problem that the heat for melting the scrap is insufficient in the next decarburization process. is there. In order to avoid production failures due to slag forming, it is common to add a CaO source to secure a basicity of slag of about 1 to make it difficult to foam, but desiliconization is performed to a low concentration. For example, the more CaO required, the more CaO will be required. Furthermore, since the decarburization speed increases as described above, it is necessary to increase the amount of CaO added to further increase the basicity, and the total amount of CaO source used in the refining process cannot be reduced, and the amount of slag generated cannot be reduced. The result is In addition, if a reaction vessel with a small free board such as a pan or a torpedo car is used for desiliconization treatment, the restrictions imposed by the above slag forming are severe, and the amount of slag generated may increase because the basicity is increased and the formation is suppressed. However, since it is necessary to operate at a reduced oxygen supply rate, there is a problem that it takes a long time to process and cannot be applied to the total amount processing due to a decrease in productivity.
[0009]
[Problems to be solved by the invention]
In addition to the refining functions such as desiliconization, dephosphorization, desulfurization, decarburization, and manganese ore reduction, the melting of scrap is an important function as a function required for hot metal pretreatment-converter process of mass-produced steel. In other words, it is necessary to ensure the ability to melt scrap generated in steelworks in regular production, and further, when the demand for steel materials increases, or the furnace conditions of the blast furnace become unstable, and hot metal is insufficient. Under certain circumstances, it is necessary to dissolve a large amount of scrap in order to secure the production amount. However, if an iron oxide source with decomposition and endotherm is used as an oxygen source in oxidative refining such as hot metal desiliconization, dephosphorization, and converter decarburization, the heat of scrap melting is insufficient. A higher ratio, the so-called gas-acid ratio, is desirable.
[0010]
On the other hand, from the standpoint of removing impurities, such as desiliconization, desulfurization, and dephosphorization, it is clear that it is ideal to perform all of these treatments in a divided manner and completely separate the slag between them. In the first place, the demand for such refining in the industrial process is, first of all, the cost of constructing the refining equipment is enormous, which is not practical, and the number of times of hot metal transfer increases or is long. There is a problem that the heat dissipation loss increases due to the time required, the thermal margin is lost, and this is not preferable from the viewpoint of scrap utilization. In addition, there is a problem in that there is no technique for efficiently and completely separating the slag from the molten iron or molten steel, and it takes a long time to eliminate the waste, and the loss of granular iron and valuable components to the slag increases. If the waste is not completely removed, the slag generated in the pretreatment will be carried over to the next process, and a reverse reaction will occur. Is another issue. Therefore, it is important to optimize the integrated refining process, including pre- and post-processes, taking into account a certain degree of function integration.
[0011]
Considering the total refining process efficiency consisting of hot metal pretreatment, converter decarburization, and secondary refining, decarburization refining can be performed with as little slag as possible without dephosphorization load during converter decarburization. It is the most important issue. As a result, the life of the converter refractory can be extended and productivity can be improved, and manganese can be easily melted and reduced by adding manganese ore, and the amount of expensive manganese alloy used in secondary refining can be reduced. When this is performed on a mass production scale, the dispersion of phosphorus concentration after hot metal dephosphorization becomes a problem. In other words, if the phosphorus concentration deviates beyond the target value, a large amount of quicklime is added at the time of decarburization of the converter, and further dephosphorization is performed, but the slag produced at this time adheres to the converter and becomes the next charge. It becomes a source of phosphorus contamination. Moreover, if it carries over to secondary refining, it will recover and further foster variation. Moreover, since the excess quicklime addition and oxygen supply are performed because of fear that phosphorus will be exaggerated, the refining cost is increased, and the amount of slag to be generated is increased. Therefore, in the hot metal dephosphorization process, it is also a problem in the mass production process to reduce it to the target phosphorus concentration without variation.
[0012]
[Means for Solving the Problems]
The gist of the present invention is as follows.
(1) Using a converter-type reaction vessel having a steel outlet hole, oxygen gas is mainly blown as an oxygen source, and desiliconization treatment is performed to an optimum silicon concentration at which maximum dephosphorization efficiency is obtained in the dephosphorization process. One step and a second step in which the hot metal is discharged and discharged from the refining furnace, and the hot metal is blown up with oxygen gas in a converter type reaction vessel having a steel outlet hole, and the dephosphorization treatment is performed. In one step, the basicity after desiliconization treatment is 1.2 or more, the iron oxide concentration in slag is 4% or less, and then desulfurization treatment is performed by blowing the desulfurizing agent into the hot metal. It is.
(2) Further, in the desiliconization treatment in the first step, the gas-acid ratio of oxygen to be used is 80% or more.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
The inventors of the present application conducted a detailed study on the characteristics of variation in dephosphorization efficiency in the process of desiliconization and dephosphorization of hot metal by blowing a large amount of oxygen gas, and obtained the results shown in FIG. I got the following conclusion.
B) The efficiency of dephosphorization treatment with oxygen gas blowing up varies depending on the silicon concentration before treatment, but the efficiency is not as high as the low silicon concentration, which was the common sense of metallurgical reactions. There is a silicon concentration.
B) Dephosphorization worsens when the silicon concentration is higher than the optimum pre-treatment silicon concentration, which is a common sense in conventional metallurgical reactions. That is, silicon is preferentially oxidized with respect to phosphorus.
C) When the so-called spitting is generated by the top blowing oxygen and the spitting is struck into the slag, the carbon and silicon in the spitting reduce iron oxide in the slag. When the silicon concentration is low, the amount of slag produced is small, and even if the amount of FeO to be reduced is the same, the decrease in the concentration of FeO is large. As a result, if the silicon concentration before the dephosphorization process is too low, the dephosphorization is worsened.
[0014]
Therefore, there is an optimum silicon concentration (0.15 to 0.35%) in the hot metal dephosphorization process using oxygen gas blowing up as the main oxygen source. Furthermore,
D) When a melting point depressant such as fluorite is not used, the slag is in a solid-liquid coexistence state and apparently increases in viscosity, so that the speed at which spitting granulated iron settles and separates in the slag becomes slower and more and more. Reduction rate of iron oxide in slag by spitting granular iron increases.
[0015]
In summary, in the hot metal dephosphorization method in which a large amount of oxygen gas is blown up, slag is reduced by spitting granular iron, so that an optimum silicon concentration is required. Therefore, the idea of dividing the process into a first process mainly including desiliconization and a second process mainly including dephosphorization was obtained. In addition, when performing desulfurization treatment in order not to increase the number of division steps any further, if a desiliconization treatment is performed without using a halide such as fluorite, the solid phase ratio of slag generated during the desiliconization treatment Therefore, even if the desulfurization treatment is continued by blowing in the desulfurization agent, the desulfurization efficiency does not decrease that much, and if the desulfurization agent is blown to the bottom after setting the basicity to 1.2 or more, it can be said that efficient desulfurization treatment can be performed. It was clear.
[0016]
That is, without using halides such as fluorite, oxygen gas is mainly supplied as an oxygen source by top blowing, and after the desiliconization treatment is completed, the oxidation in the slag after the desiliconization treatment is performed by the mechanism of c) d). The iron concentration is kept at a low level of 4% or less, and since it does not contain fluorine, the solid phase ratio is high, resulting in a poorly reactive slag with very low fluidity. The influence, that is, the resulfurization phenomenon from the top slag can be suppressed to a negligible level. Even in this case, if the slag basicity after desiliconization is kept at 1.2 or more, the solid phase ratio is further increased, which is more desirable. In addition, when the desulfurizing agent is blown by bottom blowing, a sufficient desulfurization reaction occurs between the desulfurizing agent particles and the hot metal while floating in the hot metal, so that an efficient desulfurization treatment is generally possible. In this case, in order to secure the residence time of the desulfurizing agent particles in the hot metal, the deeper the blowing depth, the better. In order to secure the specific surface area of the reaction, the finer the desulfurizing agent particles, the better.
[0017]
In this way, when this method is applied, the desiliconization treatment, which conventionally required a separate treatment process such as a blast furnace cast floor, a pan, or a torpedo car, is integrated with the function of the desulfurization treatment process, which is advantageous in terms of heat dissipation loss and equipment costs. Furthermore, since desiliconization can be performed in the center of gaseous oxygen, an exothermic reaction occurs and a thermal margin is created.
[0018]
At the time of desiliconization treatment in the first step, even when gaseous oxygen is used, it is advantageous in terms of suppressing the iron oxide concentration in the slag to blow up. This is because the reduction rate of iron oxide in the slag is increased by the above mechanism, but it is desirable that the gas-acid ratio be 80% or more in order to keep the iron oxide concentration in the slag to 4% or less. This is also advantageous from the viewpoint of scrap melting. That is, while the desiliconization reaction with solid oxygen is an endothermic reaction, the desiliconization reaction with gaseous oxygen is an exothermic reaction, and the generated reaction heat can be effectively used for scrap melting. As its utilization form, scrap may be added and melted at the same time during the desiliconization process, or it may be utilized as a heat source in the next process as sensible heat to the hot metal. In short, it is desirable to use gaseous oxygen as much as possible for the desiliconization reaction in order to increase the thermal margin. However, there is a problem that if desiliconization treatment with gaseous oxygen is performed in a reaction vessel other than the converter, that is, a pan or a torpedo car, slag forming is intense and slag and metal overflow from the vessel, making it impossible to process. is there. In order to suppress the forming, a CaO source is often added to increase the melting point of the slag, but there is a problem that the amount of use increases and the processing cost increases.
[0019]
Furthermore, this method, which is based on supplying an oxygen source by blowing it up as oxygen gas, is simpler in terms of equipment than a method in which oxygen gas is supplied by bottom blowing or lance injection. Cost. Further, in the method of blowing a large amount, the refractory around the tuyere tends to be melted and the furnace life is shortened, resulting in a decrease in the hot metal pretreatment ratio. However, such a problem can be reduced.
[0020]
On the other hand, when a converter having a steel outlet hole is used as a reaction vessel, slag and hot metal can be quickly separated by hot water and waste as compared with waste methods such as draggers and vacuum cleaners. Moreover, since the amount of oxygen gas used can be increased by using a converter with a large freeboard, an exothermic reaction occurs, and a heat dissipation loss due to transfer can be compensated.
[0021]
An embodiment of the present invention will be described with reference to FIG. The hot metal 2 is charged into the converter type reaction vessel 1. Before and after this, if necessary, scrap 3 or recycled slag such as decarburized dredger or secondary refining slag may be charged. Next, in order to perform the desiliconization process, a quick lime source is added. In this case, the bulking agent is added upward from the furnace hopper 4 or the oxygen gas 6 supplied from the top blowing lance 5 is used as carrier gas to powdery quick lime. May be supplied by spraying. If limestone powder is supplied from a blow tank 9 together with a carrier gas 8 and blown from a bottom blowing tuyer 7 provided at the bottom of the furnace, and there is a thermal margin, solid oxygen such as iron ore from a hopper on the furnace A source is also added, and desiliconization is performed while blowing oxygen gas 6. Next, after desiliconization treatment, if necessary, the top blowing of oxygen gas is stopped, and a desulfurization agent is blown from the bottom blowing tuyere 7 to perform desulfurization treatment.
[0022]
Next, the converter-type reaction vessel 1 is turned down, the hot metal 2 is taken out from the steel hole 10 into the ladle 11 and separated from the slag 12. The hot metal 2 discharged is further charged into a converter type reaction vessel 1. Thereafter, a CaO source such as quick lime and a solid oxygen source such as iron ore are added from the furnace hopper 4 as necessary, and oxygen gas 6 is blown from the lance 5 and, if necessary, fine powder CaO together with the oxygen gas 6 is molten. Sprayed on to remove the hot metal dephosphorization. The hot metal 2 after the dephosphorization process is poured out into the ladle 11 through the tapping hole 10, separated from the dephosphorization slag 13, and sent to the converter decarburization as the next step.
[0023]
FIG. 2 shows the range of the silicon concentration before dephosphorization treatment and the phosphorus concentration after dephosphorization treatment in the method of Comparative Example 1 which is a conventional method as an effect of the present invention. In addition, the results of tests conducted by the inventors of the present invention in the process of reaching the present invention are indicated by ●. In other words, the data reveals that an optimum silicon concentration exists in the dephosphorization of hot metal using oxygen top blowing as the main oxygen source. FIG. 3 shows data comparing the variation in phosphorus concentration after the treatment according to the method of Comparative Example 1 as a conventional method and the variation according to the present invention as an effect of the present invention.
[0024]
[Example 1]
275.8t of blast furnace hot metal and 9.1t of scrap were charged into a converter reactor. Quick lime was added from the furnace hopper, and desiliconization was performed for 3 minutes while supplying oxygen gas from the top blowing lance. The slag basicity after desiliconization was 0.5 and the iron oxide concentration was 1.8%. Furthermore, the hot metal discharged from the steel hole and separated from the slag is charged together with 16t of scrap into a converter reactor, added with a quicklime source, and supplied with a solid oxygen source and oxygen gas for dephosphorization. went. The hot metal after dephosphorization was decarburized and refined in a converter after tapping and discharging. In this example, the phosphorus concentration after the treatment was sufficiently lower than the target value of 0.020%, and the scrap could be melted. Table 1 shows the treatment conditions, the hot metal composition, and the temperature.
[0025]
[Example 2]
Blast furnace hot metal was charged into a converter type processing vessel, and desiliconization treatment was performed while blowing oxygen gas. Next, the oxygen gas was stopped, and a desulfurization agent was blown from the bottom blowing tuyere using nitrogen gas as a carrier gas to perform a desulfurization treatment. The desulfurizing agent is a powder in which fine lime and Al ash containing 30% of metal Al are mixed at a weight ratio of 1: 1. Next, after the hot metal was discharged from the steel hole and separated from the slag, the hot metal was further charged into a converter-type refining furnace together with scrap and subjected to dephosphorization treatment. Furthermore, the hot water was discharged from the steel hole and separated from the slag. In this example, it was possible to sufficiently reduce the sulfur and phosphorus concentrations from the target values while melting the scrap.
[0026]
Example 3
Blast furnace hot metal was charged together with scrap into a converter-type reaction vessel, and quick lime and an oxygen source were added for desiliconization treatment. The silicon concentration in the hot metal before treatment was extremely high at 2.0%. The basicity after the desiliconization treatment was 0.6. Next, a desulfurization agent was applied by bottom blowing. The desulfurizing agent is a powder in which fine lime and Al ash containing 30% of metal Al are mixed at a weight ratio of 1: 1. Furthermore, after the hot water was discharged and discharged, it was charged into a converter type reaction vessel and subjected to dephosphorization treatment. In this example, a high temperature could be maintained after desiliconization and desulfurization, and a large amount of scrap could be melted. In the second step, the dephosphorization treatment with extremely high efficiency was possible together with the effect of the optimum silicon concentration. In this example, even with high silicon concentration hot metal that cannot be processed due to excessive slag volume, desiliconization, desulfurization, and dephosphorization can be performed in the same manner as normal hot metal, and the oxidation heat of silicon is effectively utilized for scrap melting. I was able to.
[0027]
[Comparative Example 1]
Scrap was charged together with blast furnace hot metal into a converter-type treatment vessel, and an oxygen source and quicklime were added for desiliconization and dephosphorization. Next, after stopping the oxygen gas and blowing in the desulfurization agent of quick lime and soda ash (quick lime: soda ash = 85: 15 weight ratio) from the bottom blowing tuyere, desulfurization treatment was performed, and then tapping and draining were performed. It was. In this example, the amount of recovered phosphorus during desulfurization was large, and as a result, the target phosphorus concentration of 0.02% or less was not satisfied. Therefore, a large amount of quicklime was added in the next converter decarburization process. Moreover, since soda ash was used, the temperature drop during the desulfurization treatment was large.
[0028]
[Comparative Example 2]
The blast furnace hot metal in the torpedo car was combined with oxygen gas and a mill scale as an oxygen source, and was blown into the hot metal along with quick lime for adjusting the basicity for desiliconization. In order to suppress forming, the basicity was increased to 1.2 and the mill scale was used, so the hot metal temperature decreased from 1403 ° C to 1340 ° C. Next, the hot metal was transferred to a converter type reaction vessel and subjected to dephosphorization treatment and desulfurization treatment. In this example, there was no thermal margin and the scrap could not be melted.
[0029]
[Comparative Example 3]
Blast furnace hot metal was charged into a converter-type reaction vessel, and quick lime and an oxygen source were added for desiliconization treatment. The silicon concentration after desiliconization was 0.1%, which was out of the appropriate concentration range. Further, desulfurization treatment was performed by blowing a desulfurizing agent into the hot metal after desiliconization. In this case, dephosphorization was bad, and it was reduced only to 0.03%, and the target of 0.02% or less could not be reached.
[0030]
[Table 1]

[0031]
【The invention's effect】
According to the present invention, as a method of desiliconization, desulfurization, and dephosphorization of mass-produced steel, a sufficient amount of scrap dissolution is ensured without using halides such as fluorite, and desiliconization and desulfurization, dephosphorization and scrap melting are each functioned. A centralized and highly efficient hot metal pretreatment process can be established.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a converter reactor suitable for carrying out the present invention.
FIG. 2 is one of test data showing the effect of the present invention, and is a graph showing the relationship between the silicon concentration before dephosphorization of hot metal and the phosphorus concentration after treatment.
FIG. 3 is a graph showing variation in phosphorus concentration after dephosphorization of hot metal, which is one of the actual data showing the effect of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Converter type reaction vessel 2 Hot metal 3 Scrap 4 Furnace hopper 5 Top blowing lance 6 Oxygen gas holder 7 Bottom blowing tuyere 8 Nitrogen gas holder 9 Blow tank
10 Steel hole
11 Ladle
12 Desiliconization / desulfurization slag
13 Dephosphorization slag

Claims

A first process that uses a converter-type reaction vessel having a steel outlet hole, mainly performs oxygen gas blowing as an oxygen source, and performs desiliconization treatment to an optimum silicon concentration that provides the maximum dephosphorization efficiency in the dephosphorization process; The second step of removing phosphorus from the refining furnace and dephosphorizing the hot metal with oxygen gas in a converter type reaction vessel having a steel hole , The method for refining hot metal, wherein the basicity after the desiliconization treatment is 1.2 or more, the iron oxide concentration in the slag is 4% or less, and the desulfurization treatment is performed by blowing the desulfurizing agent into the hot metal. .

In the desiliconization process of the first step, the gas-acid ratio of oxygen to be used 80 The hot metal refining method according to claim 1, wherein the hot metal refining method is at least%.