JP4248731B2 - AOD furnace tuyere cooling method - Google Patents
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【０００１】
【発明の属する技術分野】
本発明はＡＯＤ炉を用いたステンレス鋼などの精錬において羽口冷却条件を適正化することで、羽口溶損速度を低減させることを可能とする方法に関する。
【０００２】
【従来の技術】
二重管羽口の内管から酸素と不活性ガスを供給するＡＯＤプロセスはステンレス鋼精錬などにおいて広く用いられている（例えば、日本鉄鋼協会編「第３版 鉄鋼便覧 第II巻 製銑・製鋼」、昭和５４年発行、第７１８ページ以降）。この方法は、脱炭の進行に応じて、次第に内管の酸素を不活性へ置換することで、クロムの酸化を抑制しつつ脱炭させるものであるが、内管のガス種や流量が精錬中に大きく変わるため、羽口の冷却バランスが不安定となり羽口寿命が短いという問題があった。他方、外管ガスとしては窒素やＡｒなどが用いられるが、内管のガス種や流量が変わっても、外管ガスについては一定で操業することが一般的であった。
【０００３】
これに対して、例えば、特開昭５８−７７５１９号公報では、二重管羽口内管から酸素のみを吹き込む時期を設けることを特徴とする方法が開示されているが、この場合でも外管ガスの制御については記載されていない。すなわち、以上のような従来技術では、吹錬の条件に応じて羽口を適正な冷却条件に制御するという思想がなかった。
【０００４】
【発明が解決しようとする課題】
上記のように、従来の吹錬方法では、羽口寿命が極めて短いという問題点があった。本発明は、従来技術における、羽口寿命が極めて短いという問題を解決し、羽口寿命を向上させることを可能とする方法を提供するものである。
【０００５】
【課題を解決するための手段】
本発明者らは、上記のような従来技術では、吹錬の条件に応じて羽口を適正な冷却条件に制御するという思想が無いことが、羽口寿命を極めて短くしてしまう一因となっているという見地から鋭意研究を進め、底吹き羽口の冷却能を一定に保つ事により、大きさをできるだけ変化させず安定したマッシュルームを生成させ、羽口の寿命を向上させることができることを見出し、本発明を完成させた。本発明の要旨は以下の各方法にある。
▲１▼ 内管と外管とを備えた二重管羽口を通じて溶融金属容器内の溶融金属へガスを吹き込み、前記溶融金属を攪拌して吹錬する際に、前記内管のガス流量及び／又はガス組成に応じて、前記外管のガス流量及び／又はガス組成を制御することを特徴とするＡＯＤ炉の羽口冷却方法。
▲２▼ 前記溶融金属が溶鉄であり、溶鉄の組成と温度に応じて、前記外管のガス流量及び／又はガス組成を制御することを特徴とする、前記▲１▼に記載のＡＯＤ炉の羽口冷却方法。
▲３▼ 前記内管の酸素ガス流量ＱO2（Nm3/Hr/本）、不活性ガス流量Ｑ（Nm3/Hr/本）に対して、外管の不活性ガス流量Ｆ（Nm3/Hr/本）を（１）式のαが２０〜８０になるように制御することを特徴とする、前記▲１▼に記載のＡＯＤ炉の羽口冷却方法。
【０００６】
α＝(Ｆ＋0.3×Ｑ)／(Ｑ＋2×ＱO2)0.25 ・・・（１）
▲４▼ 吹錬中のαの変化を±１０％以下に制御することを特徴とする、前記▲３▼に記載のＡＯＤ炉の羽口冷却方法。
▲５▼ 前記溶鉄の炭素濃度Ｃ（％）と温度Ｔ（℃）に応じて、外管の不活性ガス流量Ｆ（Nm3/Hr/本）を調整して（２）式で計算されるβを１００〜４００に制御することを特徴とする、前記▲２▼に記載のＡＯＤ炉の羽口冷却方法。
【０００７】
β＝(Ｔs−200)×(Ｆ＋0.3×Ｑ)／｛(Ｔ−Ｔs)×(Ｑ＋2×ＱO2)0.25｝ ・・・(２)
Ｔs＝1468.6−81.18×Ｃ＋15.1×Ｃ2 ・・・（３）
▲６▼ 吹錬中のβの変化を±１０％以下に制御することを特徴とする、前記▲５▼に記載のＡＯＤ炉の羽口冷却方法。
【０００８】
【発明の実施の形態】
本発明はＡＯＤ炉の羽口における冷却バランスを適正に制御するためには、内管と外管とを備えた二重管羽口において、内管ガス流量や内管ガス組成に応じて外管冷却能を制御する必要があるという新しい知見に基づくものである。
【０００９】
つまり、本発明者らは、羽口寿命に対しては、羽口前面に生成するマッシュルームと呼ばれる凝固鉄のサイズ変化が重要であり、吹錬中にサイズが大きく変化した場合に、激しい溶損が引き起こされるという新しい知見を見出した。
【００１０】
請求項１に記載の発明ように、内管のガス流量及び／又はガス組成に応じて、外管のガス流量及び／又はガス組成を制御することでマッシュルーム形状を制御すれば、羽口溶損速度の低下を図ることができる。ここで、内管のガスとしては例えば、酸素、Ａｒ、窒素、ＣＯ、ＣＯ2などが挙げられ、外管のガスとしてはＡｒ、窒素、酸素、ＬＰＧ、ＣＯ、ＣＯ2などが挙げられる。
【００１１】
さらに、マッシュルームサイズは溶鉄の炭素濃度や温度にも影響を受けるため、請求項３に記載の発明のように、内管のガス流量及び／又はガス組成と、溶鋼の組成と温度に応じて、外管のガス流量及び／又はガス組成を制御することでマッシュルーム形状を制御し、一層の羽口溶損速度の低減効果が得られる。
【００１２】
ここで、炭素濃度は装入溶鉄の炭素濃度を基準に、送酸量と経験的に知られる脱炭酸素効率から計算する方法や、排ガス分析や溶鉄の直接サンプリングから推定する方法のいずれか、又は、それらの組み合わせで推定できる。また、温度も直接的な連続、又は、半連続の測温で知る方法や、装入溶鉄の温度を基準に、経験的に知られる昇熱効率から計算する方法のいずれか、又は、それらの組み合わせで推定できる。
【００１３】
また、請求項１では、各ガスについて制御するための具体的な制御パラメータを示している。
【００１４】
つまり、内管の酸素ガス流量（ＱO2；Nm3/Hr/本）、内管の不活性ガス流量（Ｑ；Nm3/Hr/本）に対して、外管の不活性ガス流量（Ｆ；Nm3/Hr/本）を調整して（１）式で計算されるαを２０〜８０に制御するものである。
【００１５】
α＝(Ｆ＋0.3×Ｑ)／(Ｑ＋２×ＱO2)0.25 ・・・（１）
この（１）式で表されるαは、マッシュルームサイズ即ち羽口冷却能を示す指標であり、本発明者らが詳細なる実験により求めたものである。本式は内管ガスを酸素ガス、不活性ガスとし、外管を不活性ガスとした場合の計算式であるが、不活性ガスの種類に応じて、また、他のガスを単独あるいは混合させて使用する場合、以下に示すように各ガスの影響を考慮すれば（１）式を用いてマッシュルームサイズを制御できる。
【００１６】
１）（１）式の分母は、攪拌による実効ガス流量であるため、反応性のある酸素ガスの場合は２倍とし、反応性のないＡｒガス（内管Ａｒガス流量ＱAr；Nm3/Hr/本）や窒素ガス（内管窒素ガス流量ＱN2；Nm3/Hr/本）の場合は１倍とする。即ち、Ｑ＝ＱAr＋ＱN2であり、実効ガス流量＝ＱAr＋ＱN2＋２×ＱO2である。
【００１７】
２）外管、内管の不活性ガスをＡｒガスとする場合、又は、Ａｒガスを混合する場合、（１）式の分子において、Ｆ＝ＦAr、Ｑ＝ＱArとする（内管Ａｒガス流量ＱAr；Nm3/Hr/本、外管Ａｒガス流量ＦAr；Nm3/Hr/本）。
【００１８】
３）外管、内管の不活性ガスを窒素ガスとする場合、又は、窒素ガスを混合する場合、ガス顕熱量を考慮するため、ＡｒとＮ2との比熱の比を換算係数とし、（１）式の分子において、Ｆ＝1.4×ＦN2、Ｑ＝1.4×ＱN2とする（外管窒素ガス流量ＦN2；Nm3/Hr/本）。
【００１９】
４）外管、内管を酸素ガスとする場合、又は、酸素ガスを混合する場合、酸素ガスの顕熱量と酸化発熱量を考慮し、外管ガスの場合、Ａｒガスの−１５倍、内管ガスの場合、顕熱量と発熱量が相殺するため、ゼロとする。即ち、（１）式の分子において、Ｆ＝−１５×ＦO2、Ｑ＝０×ＱO2として換算する（外管酸素ガス流量ＦO2；Nm3/Hr/本）。
【００２０】
５）外管をＬＰＧガスとする場合、又は、ＬＰＧガスを混合する場合、ＬＰＧガスの顕熱量と分解吸熱量を考慮し、Ａｒガスの９倍とし、（１）式の分子において、Ｆ＝９×ＦLPGとして換算する（外管ＬＰＧガス流量ＦLPG；Nm3/Hr/本）。
【００２１】
これらの係数は本発明者らの実験により初めて明らかとなったものである。この指標αを２０〜８０に制御した場合、図１に示すように羽口寿命は向上し、羽口冷却能の向上が図られている。αが２０よりも小さい場合にはマッシュルームが小さすぎるため羽口に対する熱負荷が大きく羽口寿命が短い。αが８０よりも大きい場合にはマッシュルームが大きすぎるため羽口閉塞が起こりやすく、設定のガス流量が出なくなるという問題が生じる。
【００２２】
請求項２に記載の発明は前記請求項１の発明において、最も良い制御方法を示したものであり、吹錬中にαの変化を±１０％以下になるように各ガスの条件を制御するというものである。つまり、αが２０〜８０にあっても、ＡＯＤの場合は吹錬中に内管ガス流量や組成が大きく変化することによりマッシュルームサイズが吹錬中に大きく変化した場合には、羽口周囲の耐火物に熱負荷や機械的損耗を与える。したがって、内管ガスの組成や流量に応じて、外管ガスの組成や流量を制御し、図２のようにαの変化を±１０％以下とすることで耐火物寿命を最も向上させることができる。αの変化が±１０％よりも大きい場合には羽口周囲の耐火物に熱負荷や機械的損耗を与えるため寿命が低下する。通常、内管ガスの流量／組成は吹錬の段階に応じて設定されているため、αを±１０％以下に制御するには、吹錬中の外管ガスの流量／組成制御して行うが、吹錬制御装置に各内管ガス条件に応じた外管ガス条件を設定しておき、自動制御することもできる。
【００２３】
また、請求項３に記載の発明では、溶鉄組成や温度に対応させるための具体的な制御パラメータを示している。
【００２４】
つまり、溶鋼の炭素濃度Ｃ（％）と温度Ｔ（℃）に応じて、外管の不活性ガス流量Ｆ（Nm3/Hr/本）を調整して（２）式で計算されるβを１００〜４００に制御することにある。
【００２５】
β＝(Ｔs−200)×(Ｆ＋0.3×Ｑ)／｛(Ｔ−Ｔs)×(Ｑ＋2×ＱO2)0.25｝ ・・・(２)
Ｔs＝1468.6−81.18×Ｃ＋15.1×Ｃ2 ・・・（３）
この（２）式は、マッシュルームサイズ即ち羽口冷却能を示し、マッシュルームサイズを溶鉄組成、温度の変化に応じて計算する式であり、本発明者らが詳細なる実験により求めたものである。本式も（１）式と同様に内管ガスを酸素ガス、不活性ガスとし、外管ガスを不活性ガスとした場合の計算式であるが、不活性ガスの種類に応じて、また、他のガスを単独あるいは混合させて使用する場合、以下に示すように（１）の場合と同様に各ガスの影響を考慮すれば（２）式を用いてマッシュルームサイズを制御できる。
【００２６】
１）（２）式の分母は、攪拌による実効ガス流量であるため、反応性のある酸素ガスの場合は２倍とし、反応性のないＡｒガス（内管Ａｒガス流量ＱAr；Nm3/Hr/本）や窒素ガス（内管窒素ガス流量ＱN2；Nm3/Hr/本）の場合は１倍とする。即ち、Ｑ＝ＱAr＋ＱN2であり、実効ガス流量＝ＱAr＋ＱN2＋２×ＱO2である。
【００２７】
２）外管、内管の不活性ガスをＡｒガスとする場合、又は、Ａｒガスを混合する場合、（１）式の分子において、Ｆ＝ＦAr、Ｑ＝ＱArとする（内管Ａｒガス流量ＱAr；Nm3/Hr/本、外管Ａｒガス流量ＦAr；Nm3/Hr/本）。
【００２８】
３）外管、内管の不活性ガスを窒素ガスとする場合、又は、窒素ガスを混合する場合、ガス顕熱量を考慮するため、比熱の比を換算係数とし、（２）式の分子において、Ｆ＝1.4×ＦN2、Ｑ＝1.4×ＱN2とする（外管窒素ガス流量ＦN2；Nm3/Hr/本）。
【００２９】
４）外管、内管を酸素ガスとする場合、又は、酸素ガスを混合する場合、酸素ガスの顕熱量と酸化発熱量を考慮し、外管ガスの場合、Ａｒガスの−１５倍、内管ガスの場合、顕熱量と発熱量が相殺するため、ゼロとする。即ち、（２）式の分子において、Ｆ＝−１５×ＦO2、Ｑ＝０×ＱO2として換算する（外管酸素ガス流量ＦO2；Nm3/Hr/本）。
【００３０】
５）外管をＬＰＧガスとする場合、又は、ＬＰＧガスを混合する場合、ＬＰＧガスの顕熱量と分解吸熱量を考慮し、Ａｒガスの９倍とし、（２）式の分子において、Ｆ＝９×ＦLPGとして換算する（外管ＬＰＧガス流量ＦLPG；Nm3/Hr/本）。
【００３１】
これらの係数は本発明者らの実験により始めて明らかとなったものである。この指標βを１００〜４００に制御した場合に、図３に示すように羽口寿命としてはさらに良い値となる。βが１００よりも小さい場合にはマッシュルームが小さすぎるため羽口に対する熱負荷が大きく羽口寿命が短い。βが４００よりも大きい場合にはマッシュルームが大きすぎるため羽口閉塞が起こりやすくなる。
【００３２】
請求項４に記載の発明は請求項３の発明において、最も良い制御方法を示したものであり、吹錬中にβの変化が±１０％以下になるように外管の不活性ガスＦを調整するというものである。つまり、βが１００〜４００にあっても、ＡＯＤの場合は吹錬中に内管ガス流量や組成だけでなく、溶鉄中炭素濃度や温度が極めて大きく変化することによりマッシュルームサイズが吹錬中に大きく変化した場合には、羽口周囲の耐火物に熱負荷や機械的損耗を与える。したがって、溶鋼の組成や温度、内管ガスの組成や流量条件に応じて、外管ガスの組成や流量を制御し、図４のようにβの変化を±１０％以下とすることで耐火物寿命を最も向上させることができる。βの変化が±１０％よりも大きい場合には羽口周囲の耐火物に熱負荷や機械的損耗を与えるため寿命が低下する。通常、内管ガスの流量／組成は吹錬の段階に応じて設定されているため、βの変化を±１０％以下に制御するには、吹錬中の外管ガスの流量／組成制御で行うが、先に述べた計算／直接測定によって得られる炭素濃度／温度条件に応じて、外管ガス条件を吹錬制御装置で自動制御することもできる。
【００３３】
【実施例】
実施例は６０トン規模のＡＯＤを用いて実施した。羽口は内管直径が１３.５mm、内管と外管の間隙が１mmのものを５本用いた。炭素濃度が１.５〜１.７％、クロム濃度が１６〜１８％、ニッケル濃度が６〜８％の溶鉄を電気炉で溶製し、ＡＯＤに装入した。吹酸開始時の溶鉄温度は１３７０〜１４７０℃であった。ＡＯＤの吹錬は０〜IV期に分け、各期間での内管ガスパターンと上吹き酸素を表１のように変化させた。尚、IV期は真空精錬である。各期間において、適宜、生石灰、スクラップを投入し、温度を制御した。
【００３４】
【表１】
(実施例−１）
実施例１は表２に示す条件で、各期間でαの値が４０〜５０の範囲にあり、またαの値の変化が±１０％以下となるように外管窒素流量を制御した。その結果、羽口寿命は３００chであった。
【００３６】
【表２】
（比較例１）
比較例１は表３に示すように、各期間で外管窒素流量は一定とした場合であるが、αが２０以下の時期があり、変化も±１０％を超えており、その結果、羽口寿命は２００chでしかなかった。
【００３８】
【表３】
（実施例−２）
実施例２は表４に示す条件で、各期間内でも炭素濃度と温度に応じてβの値が２００〜３００の範囲になるように外管窒素流量を制御した。その結果、羽口寿命は３６０chであった。
【００４０】
【表４】
（実施例−３）
実施例３は表５に示す条件で、各期間内でも炭素濃度と温度に応じてβの値の変化が±１０％以下となるように外管ガス種類と流量を制御した。その結果、羽口寿命は４００chであった。
【００４２】
【表５】
【発明の効果】
本発明により、底吹き羽口の冷却能を一定に保つ事により、安定したマッシュルームが生成し、ＡＯＤの羽口寿命を向上させることが可能となった。
【図面の簡単な説明】
【図１】パラメータαと羽口寿命の関係を示す実験結果。
【図２】パラメータαの吹錬中の変動量と羽口寿命の関係を示す実験結果。
【図３】パラメータβと羽口寿命の関係を示す実験結果。
【図４】パラメータβの吹錬中の変動量と羽口寿命の関係を示す実験結果。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method capable of reducing a tuyere melting rate by optimizing tuyere cooling conditions in refining stainless steel or the like using an AOD furnace.
[0002]
[Prior art]
The AOD process for supplying oxygen and inert gas from the inner pipe of a double pipe tuyere is widely used in stainless steel refining etc. (for example, the Japan Iron and Steel Institute edition, 3rd edition, Steel Handbook, Volume II, Steelmaking and Steelmaking) "Published in 1979, page 718 and later). This method gradually decarburizes while suppressing oxidation of chromium by gradually replacing the oxygen in the inner pipe with inert gas as the decarburization progresses, but the gas type and flow rate in the inner pipe are refined. Because of the large change in the inside, there was a problem that the cooling balance of the tuyere became unstable and the tuyere life was short. On the other hand, nitrogen, Ar, or the like is used as the outer tube gas. However, even if the gas type or flow rate of the inner tube is changed, the outer tube gas is generally operated at a constant rate.
[0003]
On the other hand, for example, Japanese Patent Application Laid-Open No. 58-77519 discloses a method characterized by providing a time when only oxygen is blown from a double pipe tuyere inner pipe. There is no description of the control. That is, in the conventional technology as described above, there is no idea of controlling the tuyere to an appropriate cooling condition according to the blowing conditions.
[0004]
[Problems to be solved by the invention]
As described above, the conventional blowing method has a problem that the tuyere life is extremely short. The present invention solves the problem that the tuyere life is extremely short in the prior art, and provides a method capable of improving the tuyere life.
[0005]
[Means for Solving the Problems]
In the conventional technology as described above, the lack of the idea of controlling the tuyere to an appropriate cooling condition in accordance with the blowing conditions is a cause of extremely shortening the tuyere life. From the point of view that it has become, by keeping the cooling capacity of the bottom blowing tuyere constant, it is possible to generate a stable mushroom without changing the size as much as possible, and to improve the life of the tuyere The headline and the present invention were completed. The gist of the present invention resides in the following methods.
(1) When a gas is blown into a molten metal in a molten metal container through a double tube tuyere having an inner tube and an outer tube, and the molten metal is stirred and blown, the gas flow rate of the inner tube and A tuyere cooling method for an AOD furnace, wherein the gas flow rate and / or gas composition of the outer tube is controlled according to the gas composition.
(2) The molten metal is molten iron, and the gas flow rate and / or gas composition of the outer tube is controlled in accordance with the composition and temperature of the molten iron. The AOD furnace according to (1), The tuyere cooling method.
( 3 ) The inner pipe oxygen gas flow rate Q O2 (Nm 3 / Hr / line) and the inert gas flow rate Q (Nm 3 / Hr / line) and the outer pipe inert gas flow rate F (Nm 3 / line) The method of cooling down tuyere of AOD furnace as described in (1) above, wherein α in (1) is controlled so as to be 20-80.
[0006]
α = (F + 0.3 × Q) / (Q + 2 × Q O2 ) 0.25 (1)
(4) The tuyere cooling method for an AOD furnace as described in (3) above, wherein the change in α during blowing is controlled to ± 10% or less.
(5) The inert gas flow rate F (Nm 3 / Hr / line) of the outer pipe is adjusted according to the carbon concentration C (%) and temperature T (° C.) of the molten iron, and is calculated by the equation (2). The tuyere cooling method for an AOD furnace as described in (2) above, wherein β is controlled to 100 to 400.
[0007]
β = (Ts−200) × (F + 0.3 × Q) / {(T−Ts) × (Q + 2 × Q O2 ) 0.25 } (2)
Ts = 1468.6−81.18 × C + 15.1 × C 2 (3)
(6) The tuyere cooling method for an AOD furnace as described in (5) above, wherein the change in β during blowing is controlled to ± 10% or less.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
In order to properly control the cooling balance at the tuyere of the AOD furnace, the present invention provides a double pipe tuyere having an inner pipe and an outer pipe, and the outer pipe according to the inner pipe gas flow rate and the inner pipe gas composition. This is based on a new finding that the cooling capacity needs to be controlled.
[0009]
That is, for the tuyere life, the present inventors are important to change the size of the solidified iron called mushrooms formed on the front surface of the tuyere, and if the size changes greatly during blowing, Discovered a new finding that
[0010]
If the mushroom shape is controlled by controlling the gas flow rate and / or gas composition of the outer tube according to the gas flow rate and / or gas composition of the inner tube, The speed can be reduced. Here, examples of the gas in the inner pipe include oxygen, Ar, nitrogen, CO, and CO 2, and examples of the gas in the outer pipe include Ar, nitrogen, oxygen, LPG, CO, and CO 2 .
[0011]
Furthermore, since the mushroom size is also affected by the carbon concentration and temperature of the molten iron, as in the invention according to claim 3, according to the gas flow rate and / or gas composition of the inner tube, and the composition and temperature of the molten steel, The mushroom shape is controlled by controlling the gas flow rate and / or gas composition of the outer tube, and a further effect of reducing the tuyere melting rate can be obtained.
[0012]
Here, the carbon concentration is based on the carbon concentration of the charged molten iron, either from the method of calculating from the amount of acid delivered and empirically known decarbonation efficiency, or from the exhaust gas analysis or from the direct sampling of molten iron, Or it can estimate by those combination. In addition, either the method of knowing the temperature by direct continuous or semi-continuous temperature measurement, the method of calculating from the temperature increase efficiency empirically known based on the temperature of the charged molten iron, or a combination thereof Can be estimated.
[0013]
Moreover, in Claim 1, the specific control parameter for controlling about each gas is shown .
[0014]
That is, the flow rate of the inert gas in the outer tube (F; Fm) for the oxygen gas flow rate in the inner tube (Q O2 ; Nm 3 / Hr / line) and the inert gas flow rate in the inner tube (Q; Nm 3 / Hr / line) Nm 3 / Hr / line) is adjusted to control α calculated by the equation (1) to 20-80.
[0015]
α = (F + 0.3 × Q) / (Q + 2 × Q O2 ) 0.25 (1)
Α represented by the equation (1) is an index indicating the mushroom size, that is, the tuyere cooling ability, and is determined by the present inventors through detailed experiments. This equation is a calculation formula when the inner tube gas is oxygen gas, inert gas, and the outer tube is inert gas. Depending on the type of inert gas, other gases may be used alone or in combination. If the effect of each gas is taken into consideration as shown below, the mushroom size can be controlled using equation (1).
[0016]
1) Since the denominator of the equation (1) is an effective gas flow rate by stirring, it is doubled in the case of reactive oxygen gas, and non-reactive Ar gas (inner Ar gas flow rate Q Ar ; Nm 3 / Hr / line) and nitrogen gas (inner pipe nitrogen gas flow rate Q N2 ; Nm 3 / Hr / line), it should be 1 time. That is, Q = Q Ar + Q N2 and effective gas flow rate = Q Ar + Q N2 + 2 × Q O2 .
[0017]
2) When the inert gas of the outer tube and the inner tube is Ar gas, or when Ar gas is mixed, in the numerator of (1), F = F Ar and Q = Q Ar (inner tube Ar Gas flow rate Q Ar ; Nm 3 / Hr / line, outer pipe Ar gas flow rate F Ar ; Nm 3 / Hr / line).
[0018]
3) When the inert gas of the outer tube and the inner tube is nitrogen gas, or when nitrogen gas is mixed, in order to consider the amount of sensible heat of gas, the ratio of the specific heat of Ar and N 2 is used as a conversion factor, 1) In the numerator of the formula, F = 1.4 × F N2 and Q = 1.4 × Q N2 (outer tube nitrogen gas flow rate F N2 ; Nm 3 / Hr / line).
[0019]
4) When the outer tube and the inner tube are made of oxygen gas, or when oxygen gas is mixed, the amount of sensible heat and oxidation calorific value of the oxygen gas is taken into consideration, and in the case of the outer tube gas, the inner gas is -15 times larger than the inner gas. In the case of tube gas, the sensible heat amount and the calorific value cancel each other, so it is set to zero. That is, in the numerator of the formula (1), F = −15 × F O2 and Q = 0 × Q O2 are converted (outer tube oxygen gas flow rate F O2 ; Nm 3 / Hr / line).
[0020]
5) When the outer tube is made of LPG gas, or when LPG gas is mixed, considering the sensible heat amount and decomposition endothermic amount of LPG gas, it is set to 9 times that of Ar gas. In the molecule of formula (1), F = Converted as 9 × F LPG (outer tube LPG gas flow rate F LPG ; Nm 3 / Hr / tube).
[0021]
These coefficients have been clarified for the first time by experiments by the present inventors. When the index α is controlled to 20 to 80, the tuyere life is improved and the tuyere cooling ability is improved as shown in FIG. When α is smaller than 20, the mushroom is too small and the heat load on the tuyere is large and the tuyere life is short. When α is larger than 80, the mushroom is too large and the tuyere is likely to be blocked, resulting in a problem that the set gas flow rate cannot be obtained.
[0022]
The invention of claim 2 shows the best control method in the invention of claim 1 and controls the conditions of each gas so that the change of α is ± 10% or less during blowing. That's it. That is, even if α is 20 to 80, in the case of AOD, if the mushroom size changes greatly during blowing due to large changes in the flow rate and composition of the inner pipe during blowing, Gives refractory a heat load and mechanical wear. Therefore, by controlling the composition and flow rate of the outer tube gas in accordance with the composition and flow rate of the inner tube gas, the change in α can be made ± 10% or less as shown in FIG. it can. When the change of α is larger than ± 10%, the refractory around the tuyere is subjected to a heat load and mechanical wear, resulting in a decrease in life. Usually, since the flow rate / composition of the inner pipe gas is set according to the stage of blowing, the flow rate / composition of the outer pipe gas during blowing is controlled in order to control α to ± 10% or less. However, the outer pipe gas conditions corresponding to the inner pipe gas conditions are set in the blowing control device, and automatic control can be performed.
[0023]
Further, in the invention described in claim 3 , specific control parameters for corresponding to the molten iron composition and temperature are shown.
[0024]
In other words, according to the carbon concentration C (%) and temperature T (° C) of the molten steel, the inert gas flow rate F (Nm 3 / Hr / bar) of the outer pipe is adjusted to calculate β calculated by the equation (2). There is to control to 100-400.
[0025]
β = (Ts−200) × (F + 0.3 × Q) / {(T−Ts) × (Q + 2 × Q O2 ) 0.25 } (2)
Ts = 1468.6−81.18 × C + 15.1 × C 2 (3)
This equation (2) indicates the mushroom size, that is, tuyere cooling ability, is an equation for calculating the mushroom size according to the change in the molten iron composition and temperature, and is obtained by the present inventors through detailed experiments. This equation is also a calculation formula when the inner tube gas is oxygen gas and inert gas and the outer tube gas is inert gas as in the equation (1), but depending on the type of the inert gas, When other gases are used alone or in combination, the mushroom size can be controlled using equation (2) if the influence of each gas is taken into consideration as in the case of (1) as shown below.
[0026]
1) Since the denominator of the equation (2) is an effective gas flow rate by stirring, it is doubled in the case of reactive oxygen gas, and there is an unreactive Ar gas (inner tube Ar gas flow rate Q Ar ; Nm 3 / Hr / line) and nitrogen gas (inner pipe nitrogen gas flow rate Q N2 ; Nm 3 / Hr / line), it should be 1 time. That is, Q = Q Ar + Q N2 and effective gas flow rate = Q Ar + Q N2 + 2 × Q O2 .
[0027]
2) When the inert gas of the outer tube and the inner tube is Ar gas, or when Ar gas is mixed, in the numerator of (1), F = F Ar and Q = Q Ar (inner tube Ar Gas flow rate Q Ar ; Nm 3 / Hr / line, outer pipe Ar gas flow rate F Ar ; Nm 3 / Hr / line).
[0028]
3) When the inert gas of the outer tube and inner tube is nitrogen gas, or when nitrogen gas is mixed, in order to consider the amount of sensible heat of gas, the ratio of specific heat is used as a conversion factor, and in the numerator of equation (2) F = 1.4 × F N2 and Q = 1.4 × Q N2 (outer tube nitrogen gas flow rate F N2 ; Nm 3 / Hr / line).
[0029]
4) When the outer tube and the inner tube are made of oxygen gas, or when oxygen gas is mixed, the amount of sensible heat and oxidation calorific value of the oxygen gas is taken into consideration, and in the case of the outer tube gas, the inner gas is -15 times larger than the inner gas. In the case of tube gas, the sensible heat amount and the calorific value cancel each other, so it is set to zero. That is, in the numerator of the formula (2), F = −15 × F O2 and Q = 0 × Q O2 are converted (outer tube oxygen gas flow rate F O2 ; Nm 3 / Hr / line).
[0030]
5) When the outer tube is made of LPG gas, or when LPG gas is mixed, considering the sensible heat amount and decomposition endothermic amount of LPG gas, it is set to 9 times that of Ar gas, and in the molecule of formula (2), F = Converted as 9 × F LPG (outer tube LPG gas flow rate F LPG ; Nm 3 / Hr / tube).
[0031]
These coefficients have been clarified for the first time by the inventors' experiments. When this index β is controlled to 100 to 400, the tuyere life is further improved as shown in FIG. When β is smaller than 100, the mushroom is too small and the heat load on the tuyere is large and the tuyere life is short. When β is larger than 400, the mushroom is too large, and the tuyere is likely to be blocked.
[0032]
The invention according to claim 4 shows the best control method in the invention of claim 3 , and the inert gas F in the outer tube is set so that the change of β becomes ± 10% or less during blowing. It is to adjust. In other words, even when β is 100 to 400, in the case of AOD, not only the inner pipe gas flow rate and composition but also the mushroom size during blowing is changed due to extremely large changes in carbon concentration and temperature in molten iron. In the case of large changes, heat load and mechanical wear are given to the refractory around the tuyere. Therefore, the composition and flow rate of the outer tube gas is controlled according to the composition and temperature of the molten steel, the composition and flow rate condition of the inner tube gas, and the change in β is made ± 10% or less as shown in FIG. The longest life can be improved. When the change in β is larger than ± 10%, the life of the refractory around the tuyere is reduced due to heat load and mechanical wear. Normally, the flow rate / composition of the inner pipe gas is set according to the stage of blowing, so to control the change in β to ± 10% or less, control the flow rate / composition of the outer pipe gas during blowing. However, depending on the carbon concentration / temperature condition obtained by the calculation / direct measurement described above, the outer tube gas condition can be automatically controlled by the blowing control device.
[0033]
【Example】
The examples were performed using a 60-ton scale AOD. The tuyere used 5 tubes with an inner tube diameter of 13.5 mm and a gap between the inner tube and the outer tube of 1 mm. Molten iron having a carbon concentration of 1.5 to 1.7%, a chromium concentration of 16 to 18%, and a nickel concentration of 6 to 8% was melted in an electric furnace and charged into the AOD. The molten iron temperature at the start of the blowing acid was 1370 to 1470 ° C. The AOD blowing was divided into 0 to IV periods, and the inner tube gas pattern and top blowing oxygen in each period were changed as shown in Table 1. The IV stage is vacuum refining. In each period, quick lime and scrap were appropriately added to control the temperature.
[0034]
[Table 1]
(Example-1)
In Example 1, the outer tube nitrogen flow rate was controlled so that the value of α was in the range of 40 to 50 in each period and the change in the value of α was ± 10% or less under the conditions shown in Table 2. As a result, the tuyere life was 300 ch.
[0036]
[Table 2]
(Comparative Example 1)
As shown in Table 3, Comparative Example 1 is a case where the outer tube nitrogen flow rate is constant in each period. However, there is a period when α is 20 or less, and the change exceeds ± 10%. Mouth life was only 200 ch.
[0038]
[Table 3]
(Example-2)
In Example 2, under the conditions shown in Table 4, the outer tube nitrogen flow rate was controlled so that the value of β was in the range of 200 to 300 depending on the carbon concentration and temperature even within each period. As a result, the tuyere life was 360 ch.
[0040]
[Table 4]
(Example-3)
In Example 3, under the conditions shown in Table 5, the type and flow rate of the outer tube gas were controlled so that the change in the value of β was ± 10% or less depending on the carbon concentration and temperature even within each period. As a result, the tuyere life was 400 ch.
[0042]
[Table 5]
【The invention's effect】
According to the present invention, by keeping the cooling ability of the bottom blown tuyere constant, a stable mushroom can be generated and the tuyere life of AOD can be improved.
[Brief description of the drawings]
FIG. 1 shows experimental results showing the relationship between parameter α and tuyere life.
FIG. 2 is an experimental result showing the relationship between the amount of fluctuation during blowing of the parameter α and the tuyere life.
FIG. 3 is an experimental result showing a relationship between a parameter β and a tuyere lifetime.
FIG. 4 is an experimental result showing a relationship between a fluctuation amount of the parameter β during blowing and a tuyere lifetime.
Claims (4)
前記内管の酸素ガス流量Ｑ O2 （ Nm 3 /Hr/ 本）、不活性ガス流量Ｑ（ Nm 3 /Hr/ 本）に対して、外管の不活性ガス流量Ｆ（ Nm 3 /Hr/ 本）を（１）式のαが２０〜８０になるように制御することを特徴とするＡＯＤ炉の羽口冷却方法。
α＝ ( Ｆ＋ 0.3 ×Ｑ ) ／ ( Ｑ＋ 2 ×Ｑ O2 ) 0.25 ・・・（１） When a gas is blown into a molten metal in a molten metal container through a double tube tuyere having an inner tube and an outer tube, and the molten metal is stirred and blown, the gas flow rate and / or gas of the inner tube An AOD furnace tuyere cooling method for controlling the gas flow rate and / or gas composition of the outer tube according to the composition ,
The inner pipe oxygen gas flow rate Q O2 ( Nm 3 / Hr / line) and the inert gas flow rate Q ( Nm 3 / Hr / line), the outer tube inert gas flow rate F ( Nm 3 / Hr / line) ) Is controlled so that α in the equation (1) is 20 to 80. A tuyere cooling method for an AOD furnace.
α = ( F + 0.3 × Q ) / ( Q + 2 × QO2 ) 0.25 ... (1)
前記溶融金属が溶鉄であり、The molten metal is molten iron;
前記溶鉄の炭素濃度Ｃ（％）と温度Ｔ（℃）に応じて、外管の不活性ガス流量Ｆ（Depending on the carbon concentration C (%) of the molten iron and the temperature T (° C.), the inert gas flow rate F ( NmNm 3Three /Hr// Hr / 本）を調整して（２）式で計算されるβを１００〜４００に制御することを特徴とするＡＯＤ炉の羽口冷却方法。The AOD furnace tuyere cooling method is characterized in that β calculated by the equation (2) is adjusted to 100 to 400 by adjusting (the present).
β＝β = (( ＴT ss −− 200)200) ×× (( Ｆ＋F + 0.30.3 ×Ｑ× Q )) ／｛/ { (( Ｔ−ＴTT s)s) ×× (( Ｑ＋Q + 22 ×Ｑ× Q O2O2 )) 0.250.25 ｝} ・・・... (( ２2 ) )
ＴT ss ＝= 1468.61468.6 −− 81.1881.18 ×Ｃ＋× C + 15.115.1 ×Ｃ× C 22 ・・・（３）... (3)
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