JP4244546B2 - Top blowing lance for converter smelting - Google Patents

Description

【００１４】
第２発明は、第１発明において、前記上吹きランスは複数個のラバールノズルを有し、その内の一部のラバールノズルが前記（１）式および（２）式により定まるスロート径Ｄｔおよび出口径Ｄｅを有していることを特徴とする転炉吹錬用上吹きランスを提供する。
【００１７】
第３発明は、第１発明または第２発明において、転炉内のスラグ量が溶鋼トン当たり５０ｋｇ未満の吹錬に用いられることを特徴とする転炉吹錬用上吹きランスを提供する。
【００１８】
【発明の実施の形態】
以下、本発明について具体的に説明する。
まず、本発明に至った検討結果について説明する。
酸素吹錬中の転炉内挙動は、その反応挙動の違いから高炭素域（Ｃ＞０．６ｍａｓｓ％）と低炭素域（Ｃ≦０．６ｍａｓｓ％）とに大別される。高炭素域では、供給される酸素はほぼ全量脱炭に費やされ、反応は酸素の供給律速であり、高い送酸速度で吹錬が行われる。一方、低炭素域では、酸素の供給律速から炭素の移動律速に変わり、酸素の一部が鉄の酸化にも費やされるので、鉄の酸化を抑制して脱炭酸素効率を高めるために送酸速度を低減させている。
【００１９】
このとき、高炭素域での吹錬では、鉄飛散やダスト発生を低減させるために、高い送酸速度を維持したまま、溶湯湯面での酸素ジェットの動圧は低くする必要がある。ただし、不必要な２次燃焼の回避、並びに、脱炭酸素効率の高位維持のため、幾何学的な酸素ジェットの形状及び軌跡はできるだけ同条件に保持する必要がある。一方、低炭素域では、脱炭酸素効率を高めるために送酸速度を低減させるが、これに伴って酸素ジェットの動圧も大幅に低下するため、そのままでは脱炭酸素効率の低下、すなわち鉄の酸化増大をもたらす。また、その悪化度合いは送酸速度を低くするほど大きくなる。そのため、浴面での酸素ジェットの動圧を可能な限り高く維持したいが、ランス高さを低下させて酸素ジェットの動圧を増大させることは、浴面からの輻射による上吹きランス先端の損耗や浴面からの鉄飛散に起因する上吹きランスへの地金付きを著しく増大させるために限界がある。このように高炭素域と低炭素域とでは相反する要求があり、しかも、ランス高さ等の操業条件の変更は可能な限り避けて対処する必要がある。
【００２０】
そこで、形状の異なる種々のラバールノズルについて、酸素ジェットの噴出流速とノズル背圧Ｐとの関係を調査した。その結果、理論的に求められる最適なノズル背圧Ｐにおいて、理論値に近い噴出流速が得られることがわかった。酸素ジェットの噴出流速とノズル背圧Ｐとの関係を調査した結果の一例を図１に示す。図１において、破線は理論値を示し、●印は、ノズル背圧Ｐが３８２ｋＰａ（３．９ｋｇ／ｃｍ²）の時に吹き付けられる酸素が最も適正に膨張して超音速化されるように設計された、すなわち、設計ノズル背圧Ｐｏが３８２ｋＰａであるラバールノズルＡでの測定値であり、また、○印は、設計ノズル背圧Ｐｏが５９８ｋＰａ（６．１ｋｇｆ／ｃｍ²）であるラバールノズルＢでの測定値である。
【００２１】
なお、ラバールノズルにおいて、ノズル背圧Ｐ（ｋＰａ）と、ラバールノズル１孔当たりの送酸速度Ｆｈ（Ｎｍ³／ｈｒ）およびラバールのスロート径Ｄｔ（ｍｍ）とは下記の（３）式に示す関係があり、（３）式に示すようにノズル背圧Ｐは送酸速度に比例する。ここで、本発明におけるノズル背圧Ｐ，Ｐｏは絶対圧（真空の状態を圧力０とし、それを基準として表示される圧力）で表示した圧力である。
【数５】

【００２２】
図１に示すように、ラバールノズルの形状に拘わらず、噴出流速は、ノズル背圧Ｐの増加に伴って増大するが、ラバールノズルＢで例示するように、設計ノズル背圧Ｐｏに達するまでは理論値と比較して減衰しており、この減衰量はノズル背圧Ｐと設計ノズル背圧Ｐｏとの差が大きいほど大きくなる。そして、ノズル背圧Ｐが設計ノズル背圧Ｐｏに近づくにつれて理論値からの減衰は低減し、設計ノズル背圧Ｐｏではほぼ理論値どおりの超音速が得られる。設計ノズル背圧Ｐｏを越えてノズル背圧Ｐをさらに増大していくと、噴出流速は増大するが、ラバールノズルＡで例示するように、理論値に対する減衰量がノズル背圧Ｐの増加とともに大きくなり、噴出流速は緩やかに増加する。この現象、すなわち設計ノズル背圧Ｐｏを越えた領域での噴出流速の減衰度合いが大きくなる現象は、設計ノズル背圧Ｐｏが低いラバールノズルほど大きく、特に、設計ノズル背圧Ｐｏが４９０ｋＰａ（５ｋｇｆ／ｃｍ²）近傍以下のラバールノズルで大きくなることがわかった。
【００２３】
さらに、ラバールノズルＡで観察されるように、設計ノズル背圧Ｐｏが低いラバールノズルでは、設計ノズル背圧Ｐｏ（この場合３８２ｋＰａ）以下のノズル背圧Ｐにおいては噴出流速の理論値との差が小さいことがわかった。この傾向は設計ノズル背圧Ｐｏが低いほど顕著であり、設計ノズル背圧Ｐｏを４９０ｋＰａ以下とすれば、理論値からの減衰が抑制されることが判明した。つまり、設計ノズル背圧Ｐｏを４９０ｋＰａ以下としてラバールノズルを設計することにより、設計ノズル背圧Ｐｏ以下のノズル背圧Ｐにおける噴出流速の理論値からの減衰を抑えることが可能であることがわかった。
【００２４】
すなわち、吹錬末期における酸素ジェットの動圧を増大させるためには、吹錬末期の低炭素域での送酸速度を前提とする低いノズル背圧Ｐ、すなわち４９０ｋＰａ以下のノズル背圧Ｐに基づいて設計すれば、理論値に近い、高い酸素ジェット動圧が吹錬末期に得られるとの知見を得た。
【００２５】
また、４９０ｋＰａ以下の低いノズル背圧Ｐに基づいて設計したラバールノズルを用いて高炭素域を高送酸速度で吹錬する場合には、前述した図１に示すラバールノズルＡに例示するように、噴出流速の増加が抑えられ、高送酸速度に基づいて設計されたラバールノズルに比べて噴出流速が低下し、酸素ジェットのエネルギーが低位に維持される。そして、高送酸速度域における噴出流速の理論値からの低減度合いは、図１に示すラバールノズルＡに例示するように、操業時のノズル背圧Ｐを４９０ｋＰａ以下と低くして設計したラバールノズルを用いた場合に大きいとの知見が得られた。さらに、このラバールノズルにおいては、ノズル背圧Ｐが設計ノズル背圧Ｐｏよりも極めて高い領域（高送酸速度域）に至っても減衰効果を持続しつつ送酸することができるので、送酸速度の上限を設定する必要はなく、したがって、幅広い送酸速度での吹錬が可能であるとの知見も得られた。
【００２６】
これらの調査結果から、吹錬の初期から中期の高炭素域における溶湯湯面での酸素ジェットの動圧を低減し、かつ、吹錬末期の低炭素域における酸素ジェットの動圧を増大させるためには、高炭素域の送酸速度に基づいてラバールノズルを設計するのではなく、吹錬末期の低炭素域の送酸速度を前提とする、４９０ｋＰａ以下の低いノズル背圧Ｐに基づいて設計すれば、吹錬の初期から中期においてはダスト発生が抑制され、吹錬末期においては理論値に近い、高い酸素ジェット動圧が得られるとの知見を得た。
【００２７】
ここで、転炉吹錬用ランスのラバールノズルにおいては、設計上、設計ノズル背圧Ｐｏ（ｋＰａ）と、雰囲気圧Ｐｅ（ｋＰａ）と、ラバールノズルのスロート径Ｄｔ（ｍｍ）と、ラバールノズルの出口径Ｄｅ（ｍｍ）とは、以下の（４）式の関係を満足している。ここで、雰囲気圧Ｐｅとは、ラバールノズルの外部の雰囲気圧、換言すれば、転炉内のガス雰囲気圧力である。
【数６】

【００２８】
したがって、設計ノズル背圧Ｐｏを４９０ｋＰａ以下としたラバールノズルにおいては、設計ノズル背圧Ｐｏ＝４９０ｋＰａ、雰囲気圧Ｐｅ＝１０１ｋＰａ （大気圧）を上記の（４）式に代入することにより、ラバールノズルの出口径Ｄｅとスロート径Ｄｔとの比（Ｄｅ／Ｄｔ）は、一義的に下記の（２）式により定まることになる。
【数７】

【００２９】
ここで、通常の転炉脱炭吹錬、すなわち溶鋼量が５０トン以上の商業用転炉吹錬においては、高炭素域におけるノズル背圧Ｐは９８０ｋＰａ近傍以上であることが多く、吹錬末期の低炭素域においても４９０ｋＰａを越えるノズル背圧Ｐで操業している。これは、従来のようなスラグ量が多い場合（およそ溶鋼トン当たり５０ｋｇ以上）においては、酸素ジェットがスラグを貫通するに十分なノズル背圧Ｐが必要であったためである。換言すれば、設計ノズル背圧Ｐｏが４９０ｋＰａ以下のラバールノズルは、スラグ量が溶鋼トン当たり５０ｋｇ未満の転炉吹錬において、その効果を如何なく発揮させることができる。
【００３０】
図２は、設計ノズル背圧Ｐｏと、高炭素域における同一送酸速度での１吹錬当たりのダスト発生量との関係を示す図である。図２からも明らかなように、設計ノズル背圧Ｐｏを４９０ｋＰａ以下としたラバールノズルを用いることにより、高送酸速度域における噴出流速の増加が抑制され、ダスト発生量は低位安定していることがわかった。一方、設計ノズル背圧Ｐｏが４９０ｋＰａを越えるラバールノズルを用いた吹錬では、ダスト発生の抑制が不十分であることがわかった。なお、図２は後述する実施例に示す転炉を用い、設計ノズル背圧Ｐｏが２８５〜７６５ｋＰａである種々のラバールノズルを用い、送酸速度等の操業条件を同一条件として高炭素域で溶銑を吹錬した試験から得られた結果である。
【００３１】
ところで、吹錬末期の低炭素域では脱炭酸素効率を高めるために送酸速度を低減させており、通常、この領域では転炉容量に拘わらず、脱炭酸素効率の高い範囲である、溶湯１トン当たり９０〜１８０Ｎｍ³ ／ｈｒ（１．５〜３．０Ｎｍ³ ／ｍｉｎに相当）の送酸量で吹錬されている。転炉容量をＷ（ｔｏｎ）として当該送酸量から吹錬末期の送酸速度Ｆ（Ｎｍ³／ｈｒ）を換算すると、送酸速度Ｆ（Ｎｍ³／ｈｒ）の範囲として下記の（５）式が得られる。
【数８】

送酸速度Ｆ（Ｎｍ³／ｈｒ）と、ラバールノズル１孔当たりの送酸速度Ｆｈ（Ｎｍ³／ｈｒ）とは、ラバールノズルの設置個数ｎにより下記の（６）式で表される。
【数９】

また、ラバールノズル１孔当たりの送酸速度Ｆｈ（Ｎｍ³／ｈｒ）と、ラバールノズルのスロート径Ｄｔ（ｍｍ）と、ノズル背圧Ｐ（ｋＰａ）とは、前述した（３）式の関係があるので、（３）式と（６）式とにより送酸速度Ｆ（Ｎｍ³／ｈｒ）は下記の（７）式で表される。
【数１０】

（７）式による送酸速度Ｆ（Ｎｍ³／ｈｒ）を（５）式に代入することにより、転炉容量Ｗ（ｔｏｎ）と、ラバールノズルの設置個数ｎと、ノズル背圧Ｐ（ｋＰａ）と、ラバールノズルのスロート径Ｄｔ（ｍｍ）との関係を表す式として下記の（１）式が得られる。
【数１１】

【００３２】
すなわち、転炉容量Ｗ（ｔｏｎ）、ラバールノズルの設置個数ｎ、および吹錬末期でのノズル背圧Ｐ（ｋＰａ）が決まれば、（１）式によりスロート径Ｄｔ（ｍｍ）が定まることになる。転炉容量Ｗは装置仕様により定まり、ラバールノズルの設置個数ｎは任意であるが、酸素配管の仕様および転炉容量Ｗ等により自ずと最適な個数に定まる。
【００３３】
なお、吹錬末期の低炭素域においてより脱炭酸素効率を高めるためには、送酸量は溶湯１トン当たり９０〜１２０Ｎｍ³／ｈｒ（１．５〜２．０Ｎｍ³／ｍｉｎに相当）がより好ましく、その場合には、ラバールノズルのスロート径Ｄｔ（ｍｍ）のより好ましい範囲として以下の（８）式が得られる。
【数１２】

【００３４】
ここで、本発明によるラバールノズルは、設計ノズル背圧Ｐｏを４９０ｋＰａ以下として設計したノズルであるので、吹錬末期に酸素ジェットの高い動圧を確保するためには、当然のことながら吹錬末期のノズル背圧Ｐを設計ノズル背圧Ｐｏの近傍にすることが好ましい。本発明者等はノズル背圧Ｐを種々変更して酸素ジェットの動圧に及ぼす試験を実施した結果、ノズル背圧Ｐが３９２ｋＰａ（４ｋｇｆ／ｃｍ²）から５８８ｋＰａ（６ｋｇｆ／ｃｍ²）の範囲であれば、設計ノズル背圧Ｐｏを４９０ｋＰａ以下として設計したラバールノズルにおいて、十分に吹錬末期の酸素ジェットの動圧を高く保持することができることを確認した。
【００３５】
この場合、ノズル背圧Ｐを４９０ｋＰａの一定値に設定しても、酸素ジェットの動圧を十分に高く保持できることも確認した。ノズル背圧Ｐを４９０ｋＰａ の一定値に設定した場合には、転炉容量Ｗ（ｔｏｎ）と、ラバールノズルの設置個数ｎと、ラバールノズルのスロート径Ｄｔ（ｍｍ）との関係を表す式として上記（１）式のＰに４９０を代入した下記の（１）′式が得られる。すなわち、転炉容量Ｗ（ｔｏｎ）およびラバールノズルの設置個数ｎが決まれば、（１）′式によりスロート径Ｄｔ（ｍｍ）が定まることになる。なお、ノズル背圧Ｐが３９２ｋＰａ未満になると、スロート径Ｄｔが大きくなり、孔径の大きなラバールノズルを複数個設置するために、上吹きランスの直径も大きくならざるを得ないという問題点が生じることもわかった。
【数１３】

【００３６】
以上のような検討結果に基き、本発明の転炉吹錬用上吹きランスは、ラバールノズルのスロート径Ｄｔ（ｍｍ）が、ノズル背圧が３９２ｋＰａから５８８ｋＰａの範囲内において上記（１）式を満たすか、または上記（１）式のＰに４９０を代入した（１）′式を満たし、出口径Ｄｅとスロート径Ｄｔとの比（Ｄｅ／Ｄｔ）が上記の（２）式を満たす構造を有するものとした。この場合に、複数個のラバールノズルの内の一部のラバールノズルがこのような条件を満たしていてもよい。
【００３７】
本発明の転炉吹錬用上吹きランスでは、その先端に設置されるラバールノズルが、吹錬末期の低い送酸速度により定まるスロート径Ｄｔと、吹錬末期の低い送酸速度を前提とする４９０ｋＰａ以下の設計ノズル背圧Ｐｏにより定まる、出口径Ｄｅとスロート径Ｄｔとの比を有しているので、吹錬の初期から中期の高炭素域における溶湯湯面での酸素ジェットの動圧が低減されてダスト発生が抑制され、かつ、吹錬末期の低炭素域においては高い酸素ジェット動圧が得られ、脱炭酸素効率の低下を防止すること、すなわち鉄の酸化を防止することができる。
【００３８】
以下、添付図面を参照して本発明の一実施形態に係る転炉吹錬用上吹きランスについて説明する。図３は本発明の一実施形態に係る転炉吹錬用上吹きランスを示す概略断面図、図４は図３に示す転炉吹錬用上吹きランスに装着されたラバールノズルの概略拡大断面図である。
【００３９】
図３に示すように、上吹きランス１は、円筒状のランス本体２と、このランス本体２の下端に溶接等により接続されたランスノズル３とで構成されており、そして、ランス本体２は、外管８、中管９、内管１０の同心円状の３種の鋼管、すなわち三重管で構成され、銅製のランスノズル３には、鉛直下向き方向または鉛直斜め下向き方向にラバールノズル４が設置されている。
【００４０】
外管８と中管９との間隙、および、中管９と内管１０との間隙は、上吹きランス１を冷却するための冷却水の流路となっており、上吹きランス１の上部に設けられた給水継手（図示せず）から供給された冷却水は中管９と内管１０との間隙を通ってランスノズル３の部位まで至り、ランスノズル３の部位で反転して外管８と中管９との間隙を通って上吹きランス１の上部に設けられた排水継手（図示せず）から排出される。この場合に給排水の経路を逆としても良い。また、内管１０の内部はラバールノズル４への酸素の供給流路となっており、上吹きランス１の上端部から内管１０内に供給された酸素は、内管１０を通り、ラバールノズル４から転炉（図示せず）内に噴出される。
【００４１】
ラバールノズル４は、図４に示すように、その断面が縮小する部分と拡大する部分の２つの円錐体で構成され、縮小部分を絞り部５、拡大部分をスカート部７、絞り部５からスカート部７に遷移する部位である、最も狭くなった部位をスロート６と呼び、１個ないし複数個のラバールノズル４がランスノズル３に設けられている。ランス本体２の内部を通ってきた酸素は、絞り部５、スロート６、スカート部７を順に通って、超音速又は亜音速のジェットとして転炉内に供給される。図４中のＤｔはスロート径、Ｄｅは出口径であり、スカート部７の広がり角度θは通常１０度以下である。
【００４２】
なお、絞り部５およびスカート部７は円錐体である必要はなく、内径が曲線的に変化する曲面で構成してもよく、また、絞り部５はスロート６と同一の内径であるストレート状の円筒形であってもよい。絞り部５およびスカート部７を、内径が曲線的に変化する曲面で構成する場合には、ラバールノズルとして理想的な流速分布が得られるが、ラバールノズルの加工が極めて困難であり、一方、絞り部５をストレート状の円筒形とした場合には、理想的な流速分布とは若干解離するが、転炉吹錬で使用には全く問題とならず、かつ、ラバールノズルの加工が極めて容易となる。本発明においては、このような種々の形態ものを全てラバールノズルと称する。
【００４３】
このような構成を有するラバールノズル４について、吹錬に先立ち、その具体的な形状を以下に示す手順によって決定する。
まず、ラバールノズル４のスロート径Ｄｔを前述した（１）式により決定する。（１）式において、転炉容量Ｗ（ｔｏｎ）は転炉の設備仕様により決まり、具体的には転炉で製造される溶鋼量に相当する。ラバールノズル４の設置個数ｎは任意に決めることが可能であるが、送酸速度Ｆは転炉容量Ｗと比例関係があり、転炉容量Ｗが大きくなるほど送酸速度Ｆも大きくなるので、ラバールノズル４の１孔当たりの送酸速度Ｆｈが極端に大きくなったり、小さくなったりしないように、経験上から定まる最適範囲内になるように決めれば良い。ノズル背圧Ｐ（ｋＰａ）は３９２ｋＰａから５８８ｋＰａの範囲内の任意の値を選択できるが、計画する実操業でのノズル背圧Ｐに近い値を採用することが好ましい。
【００４４】
これらの数値を（１）式に代入してスロート径Ｄｔ（ｍｍ）の範囲を定め、（１）式を満たす任意の値をスロート径Ｄｔとする。この場合、ノズル背圧Ｐ（ｋＰａ）を４９０ｋＰａの一定値として、前述した（１）′式によりスロート径Ｄｔの範囲を定めてもよい。
【００４５】
次いで、出口径Ｄｅを前述した（２）式により定める。具体的には、出口径Ｄｅとスロート径Ｄｔとの比（Ｄｅ／Ｄｔ）を（２）式の範囲内の任意の値に設定し、予め設定したスロート径Ｄｔから出口径Ｄｅを定める。
【００４６】
このようにして形状を決定したラバールノズル４を有するランスノズル３を製作し、ランス本体２の下端に接続して上吹きランス１を構成する。ランスノズル３が複数個のラバールノズル４を有している場合には、その内の一部のラバールノズル４のみを上記のようにして決定した形状としても良い。但し、この場合には、目的とする効果は若干低下する。
【００４７】
そして、この上吹きランス１を用いて、高炉等で製造された溶銑を転炉内で吹錬する。この吹錬において、吹錬末期の低炭素域では、酸素ジェットの動圧低下を抑えるために、ノズル背圧Ｐを３９２ｋＰａから５８８ｋＰａの範囲内とし、好ましくは３９２ｋＰａから４９０ｋＰａ以下として吹錬する。ラバールノズル４の１孔当たりの送酸速度Ｆｈは、ノズル背圧Ｐ及びスロート径Ｄｔと前述した（３）式の関係があるので、ノズル背圧Ｐ及びスロート径Ｄｔを決めることにより、自ずと送酸速度Ｆｈが定まることになる。この場合、溶湯の炭素濃度が０．６ｍａｓｓ％になったならば、直ちにノズル背圧Ｐを上記の範囲にする必要はなく、送酸速度を変更する時期に合わせて実施すればよい。
【００４８】
一方、吹錬の初期から中期における高炭素域（Ｃ＞０．６ｍａｓｓ％）では、送酸速度およびノズル背圧Ｐに拘わることなく、この上吹きランス１を用い、高送酸速度及び高ノズル背圧Ｐ等の精錬反応に見合った任意の条件で吹錬することが可能である。この場合、酸素ジェットの噴出流速を効率良く減衰させるために、高炭素域での送酸速度を、低炭素域での送酸速度の１．８倍以上とすることが好ましい。
【００４９】
転炉吹錬の際の炉内スラグ量は、スラグ量が少ない場合にはスラグに覆われる溶湯の比率が低下し、高炭素域におけるダストや鉄飛散の発生量が増大する。本発明によるラバールノズル４は高炭素域でのダストや鉄飛散の発生を抑制する効果が強く、したがって、炉内スラグ量が溶鋼トン当たり５０ｋｇ未満、望ましくは３０ｋｇ以下の吹錬に本発明を適用することにより、その効果をより一層発揮させることができる。
【００５０】
本発明による上吹きランス１を用いて転炉内の溶銑を吹錬することにより、吹錬末期における酸素ジェットの噴出流速を最適化すること、すなわち、吹錬末期の酸素ジェットの動圧を理論値に近い値まで増大させることが可能となり、鉄の酸化を抑制することができるとともに、高炭素域の高送酸速度領域での噴出流速を低下することができ、酸素ジェットエネルギーの低位維持がもたらされ、鉄飛散やダスト発生を軽減することができる。そのため、吹錬全体での鉄歩留まりを向上することができ、操業の安定化が達成される。
【００５１】
また、本発明の上吹きランス１では、低炭素域での送酸速度に対して高炭素域での送酸速度を任意に設定すること、すなわち、幅広い送酸速度の調整幅で吹錬することが可能であり、そのため、炉内状況に応じて送酸速度を自由に変更することができるという利点も有している。
【００５２】
【実施例】
以下、本発明の実施例を比較例とともに示す。
［実施例］
容量が２５０トンで、酸素を上吹きし、攪拌用ガスを底吹きする上底吹き複合吹錬用転炉の上吹きランスに本発明を適用した。ラバールノズルの設置個数ｎは５個と決定し、転炉容量Ｗが２５０トン、ラバールノズルの設置個数ｎが５個の条件を（１）′式に代入し、スロート径Ｄｔの範囲として４４．４ｍｍ〜６２．８ｍｍを得た。そして、この範囲のほぼ中央値である５４ｍｍをスロート径Ｄｔとして選択した。また、これに基づき出口径Ｄｅを（２）式の範囲内である６２ｍｍとした。
【００５３】
５孔のラバールノズルを全てこの形状とし、転炉内に約２５０トンの溶銑を装入して脱炭吹錬を行った。用いた溶銑は、転炉前工程である溶銑予備処理設備にて脱硫処理及び脱燐処理が施された溶銑である。転炉内には石灰系フラックスを添加し、少量のスラグ（溶鋼トン当たり３０ｋｇ未満）を生成させている。転炉々底に設置した羽口からは、溶湯攪拌を目的としてアルゴン又は窒素を毎分１０Ｎｍ³ 程度吹き込んだ。
【００５４】
吹錬初期から中期にわたっては、ノズル背圧Ｐが８８３ｋＰａ（９．０ｋｇｆ／ｃｍ²）、送酸速度Ｆが６００００Ｎｍ³／ｈｒの条件で送酸し、溶湯の炭素濃度が０．６ｍａｓｓ％以下となった吹錬末期には、ノズル背圧Ｐを４９０ｋＰａ（５．０ｋｇｆ／ｃｍ²）とした。ノズル背圧Ｐを４９０ｋＰａとすることにより、ラバールノズル１孔当たりの送酸速度Ｆｈは（３）式に基づいて低下し、送酸速度Ｆは３３２００Ｎｍ³／ｈｒとなった。
【００５５】
吹錬中は乾式のダスト測定装置を用いて排ガス中のダスト量を測定した。また、吹錬終了時には転炉内のスラグを採取して、スラグ中のＴ．Ｆｅ濃度を調査した。１００ヒートを越える吹錬結果から、このランスを用いた吹錬におけるダスト発生量は溶鋼トン当たり８ｋｇであり、また、吹錬を炭素量が０．０５ｍａｓｓ％で吹き止めた際のスラグ中のＴ．Ｆｅ濃度は１２ｍａｓｓ％であった。
【００５６】
［比較例］
実施例と同一の転炉を用い、溶銑予備処理を施した溶銑を５孔ノズルタイプの上吹きランスにより実施例と同一条件で吹錬した。ただし、ラバールノズルの形状は、吹錬の初期から中期にわたる送酸条件によりその形状を決定した。すなわち、送酸速度Ｆｈが１２０００Ｎｍ³／ｈｒ、ノズル背圧Ｐが８８３ｋＰａ（９．０ｋｇｆ／ｃｍ²）の条件から、（３）式によりスロート径Ｄｔを５４ｍｍとし、また、設計ノズル背圧Ｐｏを８８３ｋＰａとして、設計ノズル背圧Ｐｏが８８３ｋＰａ、雰囲気圧Ｐｅが１０１ｋＰａ（大気圧）、スロート径Ｄｔが５４ｍｍの条件から、（４）式により出口径Ｄｅを７２ｍｍとした。このように、スロート径Ｄｔは実施例と同一であったが、出口径Ｄｅは実施例と大幅に異なっていた。
【００５７】
５孔のラバールノズルを全てこの形状として吹錬し、吹錬中は乾式のダスト測定装置を用いて排ガス中のダスト量を測定した。また、吹錬終了時には転炉内のスラグを採取して、スラグ中のＴ．Ｆｅ濃度を調査した。１００ヒートを越える吹錬結果から、このランスを用いた吹錬におけるダスト発生量は溶鋼トン当たり１３ｋｇであり、また、吹錬を炭素量が０．０５ｍａｓｓ％で吹き止めた際のスラグ中のＴ．Ｆｅ濃度は１９ｍａｓｓ％であり、ダスト量およびＴ．Ｆｅ量ともに実施例よりも多かった。
【００５８】
【発明の効果】
以上説明したように、本発明によれば、広い送酸速度の調整幅を確保することが可能であり、かつ、転炉吹錬の末期における送酸が最適化され、鉄の酸化を抑制することが可能になるとともに、高炭素域の高送酸速度領域での噴出流速を低下することができるので、高炭素域でのダスト発生も抑制することが可能となり、その結果、吹錬全体での鉄歩留まりを大幅に向上することができかつ操業の安定化が達成され、工業上極めて有益な効果がもたらされる。
【図面の簡単な説明】
【図１】酸素ジェットの噴出流速とノズル背圧Ｐとの関係を示す図。
【図２】設計ノズル背圧Ｐｏと１吹錬当たりのダスト発生量との関係を示す図。
【図３】本発明を適用した転炉吹錬用上吹きランスの概略断面図。
【図４】本発明を適用したラバールノズルの概略拡大断面図。
【符号の説明】
１ 上吹きランス
２ ランス本体
３ ランスノズル
４ ラバールノズル
５ 絞り部
６ スロート
７ スカート部[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an upper blowing lance used when oxidizing and refining hot metal in a converter.
[0002]
[Prior art]
In converter blowing using hot metal, oxidative refining mainly for the purpose of decarburization is performed by top blowing oxygen or bottom blowing oxygen. In recent years, the need for refining a large amount of hot metal in a shorter time and obtaining high productivity has increased more than ever, and direct reduction in the furnace with a large amount of iron ore and Mn ore added. In addition, more oxygen sources are required for melting large amounts of iron scrap in the furnace, and technology that enables high-precision component control while stably blowing large amounts of oxygen in a short time is required. It has become. Also, due to the development of hot metal pretreatment process for the purpose of dephosphorization and desulfurization of hot metal, the amount of slag generated in converter blowing is greatly reduced, and there are many factors that are different from conventional processes. There is an urgent need to quickly optimize the converter blowing method to deal with the situation.
[0003]
In oxidation refining using an upper blowing lance, oxygen is blown into the converter as a supersonic or subsonic jet from a divergent nozzle called a Laval nozzle installed at the tip of the upper blowing lance. In this case, in order not to lower the reaction efficiency such as the decarburization reaction, usually, the oxygen supply amount (hereinafter referred to as “acid feed rate”) is relatively high and the high carbon region from the initial stage to the middle stage of blowing ( The shape of the Laval nozzle is designed based on the refining conditions at approximately C> 0.6 mass%). In other words, when the oxygen delivery rate is high, the oxygen to be blown is appropriately expanded by the Laval nozzle to be supersonic, and conversely, the low carbon region (approximately C ≦ 0. When the oxygen delivery rate corresponding to 6 mass%) is small, oxygen is excessively expanded in the Laval nozzle so that supersonic speed is inhibited.
[0004]
For the purpose of high productivity, when a Laval nozzle based on such a design philosophy is used for converter blowing with a further increase in the acid feed rate, the jet velocity of the oxygen jet supplied from the top blowing lance is further increased. The jet flow velocity reaching the molten metal surface in the converter increases, and the molten metal surface becomes more turbulent. In conventional blowing with a large amount of slag (approximately 50 kg or more per ton of molten steel), this design concept is essential to ensure penetration of the slag layer of the oxygen jet.
[0005]
However, the necessity of such a design philosophy has been reduced in recent years with low slag amount blowing. On the other hand, the turbulence of the molten metal surface due to the increase in the jet flow velocity is reduced with low slag amount. Below, spattering and splashing will cause severe molten metal splashing, increasing the amount of bullion on parts such as furnace hoods, hoods, top lances, and exhaust gas equipment, adversely affecting operations and lowering iron yield. Productivity will be degraded. In addition, the generation of iron dust due to scattering is remarkably increased, and the yield of iron is reduced from the viewpoint of dust generation.
[0006]
In order to suppress such deterioration of operating conditions, the distance between the tip of the upper blowing lance and the bath surface (hereinafter referred to as “lance height”) is optimized while optimizing the hard surface of the upper blowing lance shape such as the hole diameter and inclination angle of the Laval nozzle. ) And many measures that control the operating conditions such as the acid delivery rate have been proposed. For example, JP-A-6-228624 discloses a blowing method in which the shape of the top blowing lance is optimized and the acid feed rate and the lance height are controlled within an appropriate range according to the shape of the Laval nozzle. . However, when the structure of the Laval nozzle and the lance height are changed for the purpose of suppressing iron scattering and dust when the flow rate is increased as in the same publication, the trajectory of the oxygen jet ejected from the top blowing lance and Since the geometric shape changes greatly, unnecessary secondary combustion occurs, and a secondary adverse effect that reaction efficiency deteriorates due to fluctuations in the reaction interfacial area occurs. Further, when it is difficult to change the lance height physically or operationally, this method cannot be used.
[0007]
On the other hand, in the low-carbon region at the end of blowing, the supplied oxygen is consumed not only for decarburization but also for iron oxidation. Is reduced. In this case, since the acid delivery rate is greatly deviated from the appropriate flow rate value of the Laval nozzle, the maximum effect of the Laval nozzle is not obtained, and the oxygen jet is unnecessarily attenuated. Fe (all iron oxides in slag (FeO and Fe ₂ O _Three The decarburization reaction efficiency is reduced, as seen in the increase in the iron content). Further, the unsteady disturbance of the oxygen jet is increased, the refining reaction is not stabilized and stabilized, and the component variation at the end of blowing is increased.
[0008]
In order to suppress these phenomena, a blowing method was adopted in which the lance height was further reduced to increase and stabilize the reaction efficiency at the end of the blowing process, and the dynamic pressure of the oxygen jet on the molten metal surface was increased. However, in this case, since the acid delivery rate has greatly decreased at the end of blowing, it is necessary to maintain the lance height at a considerably low level, and iron adheres to the top blowing lance due to iron scattering. The negative effects of the system cannot be ignored, resulting in a decrease in yield and operability. Further, since the collision area of the oxygen jet to the bath surface is reduced due to the decrease in the lance height, the reaction interface area is reduced. It is difficult to obtain a great effect on the reduction of Fe.
[0009]
In order to remedy this problem, Japanese Patent Application Laid-Open No. 10-30110 discloses 0.85D to 0 in the high carbon region as compared to the proper expansion outlet diameter D of the Laval nozzle determined by the throat diameter of the Laval nozzle and the acid feed rate. A converter blowing method using an upper blowing lance having an outlet diameter of 0.94D and an upper blowing lance having an outlet diameter of 0.96D to 1.15D in a low carbon region is disclosed. Moreover, even if the same Laval nozzle is used, the outlet diameter can be changed to the above range with respect to the appropriate expansion outlet diameter D by changing the acid feed rate and the nozzle back pressure P of the Laval nozzle.
[0010]
However, in this blowing method, two or more types of top blowing lances having different shapes must be used in order to surely control the refining, and the complexity of equipment and operation cannot be ignored. In addition, when the same top blowing lance is used, it is necessary to keep it within the optimum range in both the high carbon range and low carbon range, which complicates the design of the Laval nozzle. In the high carbon range, if you want to secure a high acid feed rate for the purpose of shortening the blowing time and high productivity, and keep the acid feed rate low at the end of the blowing process, you must deviate from the above range. I don't get it. That is, the adjustment range of the acid delivery rate is limited, and there arises a problem that the acid delivery rate cannot be freely changed according to the in-furnace situation.
[0011]
[Problems to be solved by the invention]
The present invention has been made in view of such circumstances, the purpose of which is wide adjustment range of the acid feed rate, it is possible to freely change the acid feed rate according to the in-furnace situation, In addition, it reduces iron scattering and dust generation at high acid feed rates in the high carbon range, and further suppresses iron oxidation at low acid feed rates at the end of blowing and improves reaction stabilization. It is to provide a top blowing lance for converter blowing.
[0012]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present inventors have conducted intensive research focusing on the design conditions of the Laval nozzle. As a result, a Laval nozzle is designed based on a low acid feed rate at the end of blowing and a low nozzle back pressure P based on this low feed rate, that is, a low acid feed rate and a low nozzle at the end of blowing. The present inventors have found that the above problem can be solved by optimizing the Laval nozzle under the condition of the back pressure P.
[0013]
The present invention has been completed based on such knowledge, and the first invention is an upper blowing lance for converter blowing with a Laval nozzle installed at the tip thereof, and a throat diameter Dt (mm) of the Laval nozzle. ) Satisfies the following formula (1) determined from the nozzle back pressure P (kPa) under the conditions in the range of 392 kPa to 588 kPa, the converter capacity W (ton), and the number n of installed Laval nozzles, and An upper blow lance for converter blowing is provided in which the ratio (De / Dt) between the outlet diameter De and the throat diameter Dt of the Laval nozzle satisfies the following expression (2).
[Equation 3]

[0014]
According to a second aspect of the present invention, in the first aspect, the upper blow lance has a plurality of Laval nozzles, and a portion of the Laval nozzles is determined by the formulas (1) and (2). An upper blowing lance for converter blowing is provided.
[0017]
First 3 The invention is the first invention Or the second invention In the present invention, an upper blow lance for converter blowing is provided, wherein the amount of slag in the converter is used for blowing less than 50 kg per ton of molten steel.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be specifically described.
First, the examination results that led to the present invention will be described.
The behavior in the converter during oxygen blowing is roughly classified into a high carbon region (C> 0.6 mass%) and a low carbon region (C ≦ 0.6 mass%) from the difference in reaction behavior. In the high carbon region, almost all of the supplied oxygen is consumed for decarburization, and the reaction is rate-controlled to supply oxygen, and blowing is performed at a high acid feed rate. On the other hand, in the low-carbon region, the rate of oxygen supply changes to the rate of carbon transfer, and part of the oxygen is also consumed for iron oxidation. The speed is reduced.
[0019]
At this time, in the blowing in the high carbon region, it is necessary to reduce the dynamic pressure of the oxygen jet on the surface of the molten metal while maintaining a high acid feeding rate in order to reduce iron scattering and dust generation. However, in order to avoid unnecessary secondary combustion and maintain a high level of decarbonation efficiency, it is necessary to keep the geometric oxygen jet shape and locus as similar as possible. On the other hand, in the low carbon region, the acid feed rate is reduced in order to increase the decarbonation efficiency, but the dynamic pressure of the oxygen jet is also greatly reduced accordingly. Leads to increased oxidation. Moreover, the worsening degree becomes larger as the acid feeding rate is lowered. Therefore, we want to keep the dynamic pressure of the oxygen jet at the bath surface as high as possible. However, reducing the lance height and increasing the dynamic pressure of the oxygen jet can cause wear of the tip of the top blowing lance due to radiation from the bath surface. There is a limit to significantly increase the adhesion of metal to the top lance due to iron scattering from the bath surface. Thus, there is a conflicting demand between the high carbon region and the low carbon region, and it is necessary to deal with avoiding changes in operating conditions such as lance height as much as possible.
[0020]
Therefore, the relationship between the jet velocity of the oxygen jet and the nozzle back pressure P was investigated for various Laval nozzles having different shapes. As a result, it was found that the jet flow velocity close to the theoretical value can be obtained at the optimum nozzle back pressure P that is theoretically required. An example of the result of investigating the relationship between the jet velocity of the oxygen jet and the nozzle back pressure P is shown in FIG. In FIG. 1, a broken line indicates a theoretical value, and a black circle indicates that the nozzle back pressure P is 382 kPa (3.9 kg / cm ² ) Was measured so that the oxygen blown at the time of expansion was most appropriately expanded and supersonic, that is, a measurement value with a Laval nozzle A having a design nozzle back pressure Po of 382 kPa, Design nozzle back pressure Po is 598 kPa (6.1 kgf / cm ² ) Measured with a Laval nozzle B.
[0021]
In the Laval nozzle, the nozzle back pressure P (kPa) and the acid feed rate Fh (Nm) per hole in the Laval nozzle ^Three / Hr) and the Laval throat diameter Dt (mm) have the relationship shown in the following formula (3), and the nozzle back pressure P is proportional to the acid feed rate as shown in the formula (3). Here, the nozzle back pressures P and Po in the present invention are pressures expressed as absolute pressures (pressures that are displayed with reference to a vacuum state where the pressure is 0).
[Equation 5]

[0022]
As shown in FIG. 1, the ejection flow velocity increases with the increase of the nozzle back pressure P regardless of the shape of the Laval nozzle, but as shown by the Laval nozzle B, the theoretical value is reached until the design nozzle back pressure Po is reached. The amount of attenuation increases as the difference between the nozzle back pressure P and the design nozzle back pressure Po increases. As the nozzle back pressure P approaches the design nozzle back pressure Po, the attenuation from the theoretical value is reduced, and at the design nozzle back pressure Po, a supersonic speed almost equal to the theoretical value is obtained. As the nozzle back pressure P is further increased beyond the designed nozzle back pressure Po, the jet flow velocity increases, but as exemplified by the Laval nozzle A, the attenuation with respect to the theoretical value increases as the nozzle back pressure P increases. The jet flow rate increases slowly. This phenomenon, that is, the phenomenon in which the degree of attenuation of the jet flow velocity in the region exceeding the design nozzle back pressure Po increases, is greater for a Laval nozzle with a lower design nozzle back pressure Po. In particular, the design nozzle back pressure Po is 490 kPa (5 kgf / cm ² ) It became clear that it became large with the Laval nozzle below the vicinity.
[0023]
Further, as observed with the Laval nozzle A, the Laval nozzle with a low design nozzle back pressure Po has a small difference from the theoretical value of the jet flow velocity at the nozzle back pressure P of the design nozzle back pressure Po (in this case, 382 kPa) or less. I understood. This tendency becomes more prominent as the design nozzle back pressure Po is lower, and it has been found that if the design nozzle back pressure Po is 490 kPa or less, attenuation from the theoretical value is suppressed. That is, it was found that by designing the Laval nozzle with the design nozzle back pressure Po of 490 kPa or less, it is possible to suppress the attenuation from the theoretical value of the ejection flow velocity at the nozzle back pressure P of the design nozzle back pressure Po or less.
[0024]
That is, in order to increase the dynamic pressure of the oxygen jet at the end of blowing, it is based on a low nozzle back pressure P on the premise of the acid feed rate in the low carbon region at the end of blowing, that is, a nozzle back pressure P of 490 kPa or less. In other words, it was found that a high oxygen jet dynamic pressure close to the theoretical value could be obtained at the end of blowing.
[0025]
Further, when a high-carbon region is blown at a high acid feed rate using a Laval nozzle designed based on a low nozzle back pressure P of 490 kPa or less, as shown in the above-described Laval nozzle A shown in FIG. The increase in the flow rate is suppressed, and the jet flow rate is lowered as compared with a Laval nozzle designed based on a high acid feed rate, and the energy of the oxygen jet is maintained at a low level. Then, the degree of reduction from the theoretical value of the jet flow velocity in the high acid feed rate region is as shown in the Laval nozzle A shown in FIG. 1 using a Laval nozzle designed with the nozzle back pressure P during operation as low as 490 kPa or less. The knowledge that it was big was obtained. Furthermore, in this Laval nozzle, even if the nozzle back pressure P reaches a region (high acid feed rate region) that is extremely higher than the design nozzle back pressure Po, it is possible to feed the oxygen while maintaining the damping effect. It was not necessary to set an upper limit, and therefore it was found that blowing with a wide range of acid feed rates is possible.
[0026]
From these survey results, in order to reduce the dynamic pressure of the oxygen jet at the molten metal surface in the high carbon region from the beginning to the middle of blowing, and to increase the dynamic pressure of the oxygen jet in the low carbon region at the end of blowing. Therefore, instead of designing a Laval nozzle based on the high carbon feed rate, it should be designed based on a low nozzle back pressure P of 490 kPa or less, assuming a low carbon feed rate at the end of blowing. For example, it was found that the generation of dust was suppressed from the beginning to the middle of blowing and that a high oxygen jet dynamic pressure close to the theoretical value was obtained at the end of blowing.
[0027]
Here, in the Laval nozzle of the converter blowing lance, by design, the design nozzle back pressure Po (kPa), the atmospheric pressure Pe (kPa), the Laval nozzle throat diameter Dt (mm), and the Laval nozzle outlet diameter De. (Mm) satisfies the relationship of the following expression (4). Here, the atmospheric pressure Pe is an atmospheric pressure outside the Laval nozzle, in other words, a gas atmospheric pressure in the converter.
[Formula 6]

[0028]
Therefore, in a Laval nozzle in which the design nozzle back pressure Po is 490 kPa or less, the design nozzle back pressure Po = 490 kPa and the atmospheric pressure Pe = 101 kPa (atmospheric pressure) are substituted into the above equation (4), whereby the outlet diameter of the Laval nozzle is determined. The ratio (De / Dt) between De and the throat diameter Dt is uniquely determined by the following equation (2).
[Expression 7]

[0029]
Here, in normal converter decarburization blowing, that is, commercial converter blowing with a molten steel amount of 50 tons or more, the nozzle back pressure P in the high carbon region is often more than about 980 kPa, and the final stage of blowing Even in the low carbon region, the nozzle back pressure P exceeds 490 kPa. This is because when the amount of slag as in the prior art is large (approximately 50 kg or more per ton of molten steel), a sufficient nozzle back pressure P is required for the oxygen jet to penetrate the slag. In other words, a Laval nozzle having a design nozzle back pressure Po of 490 kPa or less can exert its effect in converter blowing with a slag amount of less than 50 kg per ton of molten steel.
[0030]
FIG. 2 is a diagram showing the relationship between the design nozzle back pressure Po and the amount of dust generated per blowing at the same acid feed rate in the high carbon region. As is clear from FIG. 2, by using a Laval nozzle with a design nozzle back pressure Po of 490 kPa or less, an increase in the jet flow velocity in the high acid feed rate region is suppressed, and the amount of dust generated is stable at a low level. all right. On the other hand, it was found that the dust generation was not sufficiently suppressed in the blowing using the Laval nozzle with the design nozzle back pressure Po exceeding 490 kPa. In addition, FIG. 2 uses the converter shown in the Example mentioned later, uses various Laval nozzles whose design nozzle back pressure Po is 285 to 765 kPa, and operates hot metal in the high carbon region under the same operating conditions such as the acid feed rate. It is the result obtained from the blown test.
[0031]
By the way, in the low carbon region at the end of blowing, the acid feed rate is reduced in order to increase the decarbonation efficiency. Normally, in this region, the molten metal is in a high decarbonation efficiency range regardless of the converter capacity. 90 to 180 Nm per ton ^Three / Hr (1.5-3.0Nm ^Three (Corresponding to / min). The converter capacity is W (ton), and the acid feed rate F (Nm ^Three / Hr), the acid feed rate F (Nm ^Three The following formula (5) is obtained as the range of / hr).
[Equation 8]

Acid delivery rate F (Nm ^Three / Hr) and the acid feed rate Fh (Nm per hole of Laval nozzle) ^Three / Hr) is expressed by the following equation (6) depending on the number n of the installed Laval nozzles.
[Equation 9]

Also, the acid feed rate Fh (Nm per Laval nozzle) ^Three / Hr), the throat diameter Dt (mm) of the Laval nozzle, and the nozzle back pressure P (kPa) have the relationship of the above-described equation (3). Speed F (Nm ^Three / Hr) is expressed by the following equation (7).
[Expression 10]

Acid feed rate F (Nm) according to equation (7) ^Three / Hr) by substituting into equation (5), the relationship between the converter capacity W (ton), the number n of installed Laval nozzles, the nozzle back pressure P (kPa), and the throat diameter Dt (mm) of the Laval nozzle The following formula (1) is obtained as a formula representing:
[Expression 11]

[0032]
That is, if the converter capacity W (ton), the number n of installed Laval nozzles, and the nozzle back pressure P (kPa) at the end of blowing are determined, the throat diameter Dt (mm) is determined by the equation (1). The converter capacity W is determined by the apparatus specifications, and the number n of installed Laval nozzles is arbitrary, but is automatically determined to be the optimum number by the specifications of the oxygen piping and the converter capacity W.
[0033]
In addition, in order to increase the decarbonation efficiency in the low carbon region at the end of blowing, the amount of acid sent is 90 to 120 Nm per ton of molten metal. ^Three / Hr (1.5-2.0 Nm ^Three (Corresponding to / min) is more preferable. In this case, the following equation (8) is obtained as a more preferable range of the throat diameter Dt (mm) of the Laval nozzle.
[Expression 12]

[0034]
Here, since the Laval nozzle according to the present invention is a nozzle designed with a design nozzle back pressure Po of 490 kPa or less, in order to ensure a high dynamic pressure of the oxygen jet at the end of blowing, it is natural that The nozzle back pressure P is preferably set in the vicinity of the design nozzle back pressure Po. The inventors of the present invention conducted various tests on the nozzle back pressure P to influence the dynamic pressure of the oxygen jet. As a result, the nozzle back pressure P was 392 kPa (4 kgf / cm ² ) To 588 kPa (6 kgf / cm ² In the Laval nozzle designed with the design nozzle back pressure Po of 490 kPa or less, it was confirmed that the dynamic pressure of the oxygen jet at the final stage of blowing was sufficiently high.
[0035]
In this case, it was also confirmed that the dynamic pressure of the oxygen jet can be maintained sufficiently high even when the nozzle back pressure P is set to a constant value of 490 kPa. When the nozzle back pressure P is set to a constant value of 490 kPa, the above equation (1) is expressed as the relationship between the converter capacity W (ton), the number n of installed Laval nozzles, and the Laval nozzle throat diameter Dt (mm). The following equation (1) ′ is obtained by substituting 490 for P in the equation). That is, if the converter capacity W (ton) and the number n of installed Laval nozzles are determined, the throat diameter Dt (mm) is determined by the equation (1) ′. When the nozzle back pressure P is less than 392 kPa, the throat diameter Dt increases, and a plurality of Laval nozzles having a large hole diameter are installed, so that the diameter of the top blowing lance must be increased. all right.
[Formula 13]

[0036]
Based on the above examination results, the top blowing lance for converter blowing of the present invention satisfies the above formula (1) when the throat diameter Dt (mm) of the Laval nozzle is within the range of the nozzle back pressure from 392 kPa to 588 kPa. Or satisfying the formula (1) ′ obtained by substituting 490 for P in the formula (1), and the ratio of the outlet diameter De and the throat diameter Dt (De / Dt) satisfies the formula (2). It was supposed to be. In this case, some of the plurality of Laval nozzles may satisfy such a condition.
[0037]
In the top blowing lance for converter blowing according to the present invention, the Laval nozzle installed at the tip of the blast nozzle assumes a throat diameter Dt determined by a low acid feed rate at the end of blowing and a low acid feed rate at the end of blowing. Since the ratio of the outlet diameter De and the throat diameter Dt is determined by the following design nozzle back pressure Po, the dynamic pressure of the oxygen jet on the molten metal surface in the high carbon region from the initial stage to the middle stage of blowing is reduced. As a result, dust generation is suppressed, and a high oxygen jet dynamic pressure is obtained in the low carbon region at the end of blowing, preventing a decrease in decarbonation efficiency, that is, iron oxidation.
[0038]
Hereinafter, an upper blowing lance for converter blowing according to an embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 3 is a schematic sectional view showing an upper blowing lance for converter blowing according to an embodiment of the present invention, and FIG. 4 is an enlarged schematic sectional view of a Laval nozzle attached to the upper blowing lance for converter blowing shown in FIG. It is.
[0039]
As shown in FIG. 3, the upper blowing lance 1 is composed of a cylindrical lance body 2 and a lance nozzle 3 connected to the lower end of the lance body 2 by welding or the like. The outer tube 8, the middle tube 9 and the inner tube 10 are made of three concentric steel tubes, that is, a triple tube, and a copper lance nozzle 3 is provided with a Laval nozzle 4 in a vertically downward direction or a vertically obliquely downward direction. ing.
[0040]
The gap between the outer pipe 8 and the middle pipe 9 and the gap between the middle pipe 9 and the inner pipe 10 serve as a cooling water flow path for cooling the upper blowing lance 1. Cooling water supplied from a water supply joint (not shown) provided in the pipe passes through the gap between the middle pipe 9 and the inner pipe 10 to reach the lance nozzle 3, and reverses at the lance nozzle 3 to reverse the outer pipe. The water is discharged from a drainage joint (not shown) provided on the upper portion of the upper blowing lance 1 through a gap between the intermediate pipe 8 and the middle pipe 9. In this case, the water supply / drainage path may be reversed. Further, the inside of the inner tube 10 serves as an oxygen supply channel to the Laval nozzle 4, and oxygen supplied from the upper end of the upper blow lance 1 into the inner tube 10 passes through the inner tube 10 and passes through the Laval nozzle 4. It is ejected into a converter (not shown).
[0041]
As shown in FIG. 4, the Laval nozzle 4 is composed of two cones, a portion whose cross section is reduced and a portion where the cross section is enlarged. The reduced portion is the throttle portion 5, the enlarged portion is the skirt portion 7, and the throttle portion 5 to the skirt portion. The narrowest part, which is a part transitioning to 7, is called a throat 6, and one or a plurality of Laval nozzles 4 are provided in the lance nozzle 3. Oxygen that has passed through the inside of the lance body 2 passes through the throttle portion 5, the throat 6, and the skirt portion 7 in this order, and is supplied into the converter as a supersonic or subsonic jet. In FIG. 4, Dt is the throat diameter, De is the exit diameter, and the spread angle θ of the skirt portion 7 is usually 10 degrees or less.
[0042]
The throttle portion 5 and the skirt portion 7 do not need to be conical, and may be configured by a curved surface whose inner diameter changes in a curved manner. The throttle portion 5 is a straight shape having the same inner diameter as the throat 6. It may be cylindrical. When the throttle portion 5 and the skirt portion 7 are configured with curved surfaces whose inner diameter changes in a curved manner, an ideal flow velocity distribution as a Laval nozzle can be obtained, but the processing of the Laval nozzle is extremely difficult. In the case of a straight cylindrical shape, it is slightly dissociated from the ideal flow velocity distribution, but there is no problem for use in converter blowing, and the processing of the Laval nozzle is extremely easy. In the present invention, such various forms are all referred to as Laval nozzles.
[0043]
About the Laval nozzle 4 which has such a structure, the specific shape is determined by the procedure shown below prior to blowing.
First, the throat diameter Dt of the Laval nozzle 4 is determined by the aforementioned equation (1). In the equation (1), the converter capacity W (ton) is determined by the equipment specifications of the converter, and specifically corresponds to the amount of molten steel produced in the converter. The installed number n of the Laval nozzles 4 can be arbitrarily determined. However, the acid feed rate F is proportional to the converter capacity W, and the acid feed rate F increases as the converter capacity W increases. The acid feed rate Fh per hole may be determined to be within an optimum range determined from experience so that it does not become extremely large or small. The nozzle back pressure P (kPa) can be selected from any value within the range of 392 kPa to 588 kPa, but it is preferable to adopt a value close to the nozzle back pressure P in the planned actual operation.
[0044]
By substituting these numerical values into the equation (1), the range of the throat diameter Dt (mm) is determined, and an arbitrary value satisfying the equation (1) is defined as the throat diameter Dt. In this case, the nozzle back pressure P (kPa) may be set to a constant value of 490 kPa, and the range of the throat diameter Dt may be determined by the above-described equation (1) ′.
[0045]
Next, the outlet diameter De is determined by the above-described equation (2). Specifically, the ratio (De / Dt) between the outlet diameter De and the throat diameter Dt is set to an arbitrary value within the range of the expression (2), and the outlet diameter De is determined from the preset throat diameter Dt.
[0046]
The lance nozzle 3 having the Laval nozzle 4 whose shape has been determined in this way is manufactured and connected to the lower end of the lance body 2 to constitute the upper blowing lance 1. When the lance nozzle 3 has a plurality of Laval nozzles 4, only some of the Laval nozzles 4 may have a shape determined as described above. However, in this case, the intended effect is slightly reduced.
[0047]
And using this top blowing lance 1, the hot metal manufactured in the blast furnace etc. is blown in a converter. In this blowing, in the low carbon region at the end of blowing, the nozzle back pressure P is set within the range of 392 kPa to 588 kPa, preferably 392 kPa to 490 kPa, in order to suppress the decrease in the dynamic pressure of the oxygen jet. The acid feed rate Fh per hole of the Laval nozzle 4 has the relationship of the nozzle back pressure P and the throat diameter Dt and the above-mentioned equation (3). Therefore, by determining the nozzle back pressure P and the throat diameter Dt, The speed Fh is determined. In this case, if the carbon concentration of the molten metal becomes 0.6 mass%, the nozzle back pressure P does not need to be immediately within the above range, and may be carried out in accordance with the timing of changing the acid feed rate.
[0048]
On the other hand, in the high carbon range (C> 0.6 mass%) from the initial stage to the middle stage of blowing, this high blowing speed and high nozzle are used regardless of the acid feeding speed and the nozzle back pressure P. Blowing can be performed under any conditions suitable for the refining reaction such as back pressure P. In this case, in order to efficiently attenuate the jet velocity of the oxygen jet, it is preferable that the acid feed rate in the high carbon region be 1.8 times or more the acid feed rate in the low carbon region.
[0049]
When the amount of slag in the furnace at the time of converter blowing is small, when the amount of slag is small, the ratio of the molten metal covered with the slag decreases, and the amount of dust and iron scattering in the high carbon region increases. The Laval nozzle 4 according to the present invention has a strong effect of suppressing the occurrence of dust and iron scattering in a high carbon region, and therefore the present invention is applied to blowing where the amount of slag in the furnace is less than 50 kg, preferably 30 kg or less per ton of molten steel. As a result, the effect can be further exhibited.
[0050]
By optimizing the molten metal in the converter using the top blowing lance 1 according to the present invention, the flow velocity of the oxygen jet at the end of blowing is optimized, that is, the dynamic pressure of the oxygen jet at the end of blowing. It is possible to increase to a value close to the value, it is possible to suppress the oxidation of iron, it is possible to reduce the jet flow velocity in the high acid feed rate region of the high carbon region, it is possible to keep the oxygen jet energy low It is possible to reduce iron scattering and dust generation. Therefore, the iron yield in the entire blowing can be improved and the operation can be stabilized.
[0051]
Further, in the top blowing lance 1 of the present invention, the acid feeding rate in the high carbon region is arbitrarily set with respect to the acid feeding rate in the low carbon region, that is, the blowing is performed with a wide adjustment range of the acid feeding rate. Therefore, there is also an advantage that the acid feed rate can be freely changed according to the in-furnace situation.
[0052]
【Example】
Examples of the present invention are shown below together with comparative examples.
[Example]
The present invention was applied to an upper blowing lance having a capacity of 250 tons, top blowing oxygen, and bottom blowing a stirring gas. The number n of installed Laval nozzles is determined to be 5, and the condition that the converter capacity W is 250 tons and the number n of installed Laval nozzles is 5 is substituted into Equation (1) ′, and the range of the throat diameter Dt is 44.4 mm 62.8 mm was obtained. Then, 54 mm, which is approximately the center value of this range, was selected as the throat diameter Dt. Based on this, the outlet diameter De was set to 62 mm which is within the range of the formula (2).
[0053]
All of the five-hole Laval nozzles had this shape, and about 250 tons of hot metal was charged into the converter and decarburized and blown. The hot metal used is hot metal that has been subjected to desulfurization treatment and dephosphorization treatment in a hot metal pretreatment facility that is a pre-converter process. In the converter, lime-based flux is added to generate a small amount of slag (less than 30 kg per ton of molten steel). From the tuyere installed at the bottom of the converter, argon or nitrogen was supplied at 10 Nm / min for the purpose of stirring the molten metal. ^Three Blowed about.
[0054]
The nozzle back pressure P is 883 kPa (9.0 kgf / cm) from the initial stage to the middle stage of blowing. ² ), Acid feed rate F is 60000Nm ^Three At the end of blowing, when the carbon concentration of the molten metal was 0.6 mass% or less, the nozzle back pressure P was 490 kPa (5.0 kgf / cm ² ). By setting the nozzle back pressure P to 490 kPa, the acid feed rate Fh per hole in the Laval nozzle is reduced based on the formula (3), and the acid feed rate F is 33200 Nm. ^Three / Hr.
[0055]
During blowing, the amount of dust in the exhaust gas was measured using a dry dust measuring device. At the end of blowing, slag in the converter is collected and T. The Fe concentration was investigated. From the result of blowing over 100 heat, the amount of dust generated in the blowing using this lance is 8 kg per ton of molten steel, and the T in the slag when the blowing is stopped at 0.05 mass% of carbon. . The Fe concentration was 12 mass%.
[0056]
[Comparative example]
Using the same converter as in the example, the hot metal subjected to the hot metal pretreatment was blown under the same conditions as in the example with a 5-hole nozzle type top blowing lance. However, the shape of the Laval nozzle was determined according to the acid feeding conditions from the initial stage to the middle stage of blowing. That is, the acid feed rate Fh is 12000 Nm ^Three / Hr, nozzle back pressure P is 883 kPa (9.0 kgf / cm ² ), The throat diameter Dt is 54 mm according to the expression (3), the design nozzle back pressure Po is 883 kPa, the design nozzle back pressure Po is 883 kPa, the ambient pressure Pe is 101 kPa (atmospheric pressure), and the throat diameter Dt is From the condition of 54 mm, the outlet diameter De was set to 72 mm according to the equation (4). Thus, the throat diameter Dt was the same as in the example, but the outlet diameter De was significantly different from the example.
[0057]
All five-hole Laval nozzles were blown into this shape, and the amount of dust in the exhaust gas was measured using a dry dust measuring device during blowing. At the end of blowing, slag in the converter is collected and T. The Fe concentration was investigated. From the result of blowing over 100 heat, the amount of dust generated in the blowing using this lance is 13 kg per ton of molten steel, and the T in the slag when blowing is stopped at a carbon content of 0.05 mass%. . The Fe concentration is 19 mass%, the amount of dust and T.I. The amount of Fe was larger than that of the example.
[0058]
【The invention's effect】
As described above, according to the present invention, it is possible to ensure a wide adjustment range of the acid feed rate, and the acid feed at the final stage of the converter blowing is optimized to suppress iron oxidation. As a result, it is possible to reduce the jet flow velocity in the high acid feed rate region in the high carbon region, so it is possible to suppress the generation of dust in the high carbon region. As a result, the iron yield of the steel can be greatly improved and the operation can be stabilized.
[Brief description of the drawings]
FIG. 1 is a diagram showing a relationship between an ejection speed of an oxygen jet and a nozzle back pressure P. FIG.
FIG. 2 is a diagram showing the relationship between the design nozzle back pressure Po and the amount of dust generated per blowing.
FIG. 3 is a schematic cross-sectional view of an upper blowing lance for converter blowing to which the present invention is applied.
FIG. 4 is a schematic enlarged sectional view of a Laval nozzle to which the present invention is applied.
[Explanation of symbols]
1 Top blowing lance
2 Lance body
3 Lance nozzle
4 Laval nozzle
5 Aperture part
6 Throat
7 Skirt

Claims (3)

A top blowing lance for converter blowing with a Laval nozzle installed at the tip thereof, a nozzle back pressure P (kPa) under a condition in which the throat diameter Dt (mm) of the Laval nozzle is in a range of 392 kPa to 588 kPa, The following equation (1) determined from the converter capacity W (ton) and the number n of installed Laval nozzles is satisfied, and the ratio (De / Dt) between the outlet diameter De and the throat diameter Dt of the Laval nozzle is (2 ) An upper blowing lance for converter blowing.

  The upper blowing lance has a plurality of Laval nozzles, and some of the Laval nozzles have a throat diameter Dt and an outlet diameter De determined by the expressions (1) and (2). The top blowing lance for converter blowing according to claim 1. The top blowing lance for converter blowing according to claim 1 or 2 , wherein the amount of slag in the converter is used for blowing less than 50 kg per ton of molten steel.

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