JP6468084B2 - Converter discharge method - Google Patents
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本発明は転炉の排滓方法に関する。 The present invention relates to a converter discharge method.
鉄鋼材料において不純物のＰは加工性や靭性を低下させる有害元素である。鉄鋼製造プロセスにおいて高炉などで製造された溶銑には精錬プロセスにおいて脱燐処理が行われ、鋼材品質を満たすのに必要なレベルまでＰ濃度を低減している。鋼材に要求される品質レベルの厳格化に対応するため、脱燐効率向上の技術開発がこれまで盛んに行われてきた。 In steel materials, the impurity P is a harmful element that reduces workability and toughness. The hot metal produced in a blast furnace or the like in the steel production process is dephosphorized in the refining process, and the P concentration is reduced to a level necessary to satisfy the steel quality. In order to cope with the stricter quality level required for steel materials, technological development for improving the dephosphorization efficiency has been actively conducted so far.
溶鉄中Ｐの脱燐反応は例えば下記の式（１）で表わされる。下線は溶鉄中の成分であることを示す。すなわち、ＦｅＯを含むスラグを形成し溶鉄中のＰをスラグへ酸化除去する。Ｐ2Ｏ5は分解しやすいためスラグにはＣａＯを投入してＰ2Ｏ5を安定化し、溶鉄中へＰが戻ること（復燐）を抑制している。
２Ｐ＋５ＦｅＯ＋３ＣａＯ＝３ＣａＯ・Ｐ2Ｏ5＋５Ｆｅ （１）
The dephosphorization reaction of P in molten iron is represented by, for example, the following formula (1). The underline indicates that it is a component in molten iron. That is, slag containing FeO is formed, and P in the molten iron is oxidized and removed to slag. Since P 2 O 5 is easily decomposed, CaO is added to the slag to stabilize P 2 O 5 and to prevent P from returning to the molten iron (rebound).
2 P + 5FeO + 3CaO = 3CaO · P 2
精錬プロセスにおいては、脱燐反応効率を向上させるため脱炭前に溶銑を脱燐する予備脱燐が広く行われており、混銑車（トーピードカー）や溶銑鍋などの溶銑輸送容器を使用する方式と、転炉を使用する方式に大別される。後者の転炉方式は前者の混銑車・溶銑鍋方式よりも高速で酸素を供給できるため精錬用生石灰を少なくできること、容器の内容積が大きいため溶銑およびスラグの強撹拌が可能であること、熱裕度が高くスクラップ比率の向上が可能であること、などの利点があり、近年は転炉方式が主流である。 In the refining process, preliminary dephosphorization for dephosphorizing the hot metal before decarburization is widely performed to improve the dephosphorization reaction efficiency, and a method using a hot metal transport container such as a torpedo car or hot metal ladle. The system is roughly divided into methods that use converters. The latter converter system can supply oxygen at a higher speed than the former kneading car / hot metal ladle method, so that quick lime for refining can be reduced, and the internal volume of the container is large, so that hot metal and slag can be vigorously stirred. There are advantages such as high margin and the ability to improve the scrap ratio. In recent years, converter systems have become the mainstream.
転炉方式の溶銑脱燐方法としては、非特許文献１において２基の転炉をそれぞれ脱燐、脱炭の専用炉として用いる方法（以降、脱燐−脱炭分離方式と表記）が開示されている。また、非特許文献２においては脱燐吹錬後に転炉を傾動させて脱燐スラグのみを炉口から排出し（以降、中間排滓と表記）、転炉を垂直に戻した後に引き続いて脱炭吹錬を行う方法（以降、脱燐−脱炭連続方式と表記）が開示されている。この方法は脱燐吹錬後に溶銑を排出および装入する工程がないため転炉の非稼動時間が短く且つ溶銑の移し替えに伴う放熱ロスがないこと、脱燐−脱炭分離方式よりも熱裕度が高いためスクラップ比率を向上してさらに高い生産性を実現できること、脱炭吹錬後のスラグを炉内に残して次の脱燐吹錬の造滓剤として再利用できること、などの利点がある。 As a converter-type hot metal dephosphorization method, Non-Patent Document 1 discloses a method of using two converters as dedicated furnaces for dephosphorization and decarburization (hereinafter referred to as dephosphorization-decarburization separation system). ing. In Non-Patent Document 2, after dephosphorization blowing, the converter is tilted to discharge only dephosphorization slag from the furnace port (hereinafter referred to as intermediate waste), and after the converter is returned to the vertical position, it is continuously removed. A method for performing charcoal blowing (hereinafter referred to as a dephosphorization-decarburization continuous method) is disclosed. In this method, there is no process for discharging and charging the hot metal after dephosphorization, so that the converter non-operation time is short and there is no heat loss due to the transfer of hot metal. Benefits include higher scrap ratio and higher productivity due to its high margin, and the ability to recycle slag after decarburization blown into the furnace and reuse it as the next dephosphorization blow smelting agent. There is.
脱燐−脱炭連続方式の中間排滓で排出されず炉内に残留した脱燐スラグは次の脱炭吹錬に持ち越され、脱炭反応に伴う温度上昇によりスラグから溶銑へ復燐が生じる。このため脱炭吹錬ではＣａＯを追加投入するが、残留脱燐スラグが多いほど復燐量も多くなるため、ＣａＯも多量に投入しなければならなくなる。したがって中間排滓では効率的にスラグを排出して残留スラグを可能な限り低減することが望ましく、そのための排滓方法が開示されている。 The dephosphorization slag that has not been discharged by the intermediate desulfurization of the dephosphorization-decarburization process and remained in the furnace is carried over to the next decarburization blowing, and the temperature rise accompanying the decarburization reaction causes rephosphorization from the slag to the hot metal. . For this reason, in decarburization blowing, additional CaO is added. However, since the amount of recovered phosphorus increases as the residual dephosphorization slag increases, it is necessary to add a large amount of CaO. Therefore, in the intermediate waste, it is desirable to efficiently discharge the slag and reduce the residual slag as much as possible, and a waste disposal method for that purpose is disclosed.
例えば特許文献１ではトーピードカーや溶銑鍋の排滓方法として利用されているドラッガーによりスラグを掻き出す方法、特許文献２では炉腹に設けた複数個の羽口からガスを吹き込んでスラグを波立たせて排出する方法、特許文献３では電磁力を利用してスラグを選択的に排出する方法が開示されている。また特許文献４では排滓前に鉄鉱石やミルスケールを添加してスラグの泡立ち（フォーミング）を促進する方法、特許文献５ではスラグの塩基度（ＣａＯ／ＳｉＯ2）およびＡｌ2Ｏ3濃度を所定の範囲に調整し、フォーミングしやすいスラグ性状にして排滓する方法が開示されている。このように、脱燐‐脱炭連続方式の中間排滓方法としては、何らかの外力を加えてスラグを強制的に排出する方法と、排滓前に炉内でスラグをフォーミングさせて体積を増やす方法の２つに大別される。
For example, in Patent Document 1, a method of scraping slag with a dragger used as a method for discharging a torpedo car or a hot metal ladle, and in Patent Document 2, a gas is blown from a plurality of tuyere provided on the furnace belly to discharge the slag. Patent Document 3 discloses a method for selectively discharging slag using electromagnetic force. In Patent Document 4, iron ore or a mill scale is added before evacuation to promote foaming of slag. In
しかしながら、特許文献１の方法では転炉の容量を考えると設備が大きくなりすぎるため現実的とは言えない。特許文献２の方法では炉腹に羽口を設置するため転炉の改造が必要であり、さらに吹錬中の羽口閉塞防止用にガスを常時吹き込むためコストが増大する等の問題がある。特許文献３の方法では設備投資コストがかかり、さらに高温かつ振動の激しい環境下であるため長期的な使用が難しい等の問題がある。 However, the method of Patent Document 1 is not practical because the facility becomes too large considering the capacity of the converter. In the method of Patent Document 2, the tuyeres are installed on the furnace bell, so that the converter needs to be remodeled, and further, gas is constantly blown to prevent the tuyere clogging during blowing, resulting in increased costs. In the method of Patent Document 3, there is a problem that capital investment costs are incurred, and that it is difficult to use for a long time because it is in an environment of high temperature and vibration.
また、特許文献４、５のようにスラグをフォーミングさせる方法においては、一旦フォーミングしたスラグが排滓中に鎮静して排滓効率が低下してしまうため、多量のスラグを安定的に排出することは容易ではなかった。
Moreover, in the method of forming slag as in
本発明はかかる事情を鑑みてなされたもので、転炉において溶銑の脱燐吹錬を行った後、転炉を傾動させて炉口からスラグを排滓する際に、高い排滓率が得られる排滓方法を提供することを目的とする。 The present invention has been made in view of such circumstances, and after performing dephosphorization blowing of hot metal in a converter, when the converter is tilted and slag is discharged from the furnace port, a high discharge rate is obtained. It is an object to provide a method of exclusion.
前記目的に沿う本発明に係る転炉の排滓方法は、脱燐処理後に溶銑を転炉内に残したまま、上吹きランスからの送酸により炉内のスラグをフォーミングさせ、送酸を止めた後に転炉を傾動して炉口から排出する転炉排滓方法において、ＣａＯ／ＳｉＯ2が０．８〜１．５であり、ＣａＯ／ＳｉＯ2が０．８以上１．２未満ではスラグ中Ａｌ2Ｏ3濃度：２〜１４質量％の組成を有し、ＣａＯ／ＳｉＯ2が１．２以上１．５以下のときは炉内にＡｌ2Ｏ3源を投入してＡｌ2Ｏ3濃度を４〜１４質量％とし、且つ温度が１３００〜１４００℃であるスラグを炉口より排出し、排滓途中で一旦転炉の傾動角を排滓時より小さくし、続いて式（２）を満たす量の銑鉄と、式（３）を満たす量の酸化鉄を炉内のスラグへ投入し、スラグを再びフォーミングさせた後に転炉を傾動して排滓を行うことを特徴とする、転炉排滓方法である。
換算ＦｅＯ濃度＝ＦｅＯ濃度＋Ｆｅ2Ｏ3濃度×１１２／１６０ （４）
The converter discharge method according to the present invention, which meets the above-mentioned object, forms the slag in the furnace by feeding the acid from the top blowing lance while leaving the molten iron in the converter after the dephosphorization treatment, and stops the feeding of oxygen. In the converter discharge method in which the converter is tilted and discharged from the furnace port after that, when CaO / SiO 2 is 0.8 to 1.5 and CaO / SiO 2 is 0.8 or more and less than 1.2, slag medium concentration of Al 2 O 3: 2 to 14 has the composition by weight%, when CaO / SiO 2 is 1.2 to 1.5 by introducing the Al 2 O 3 source in the furnace Al 2 O 3 The slag having a concentration of 4 to 14% by mass and a temperature of 1300 to 1400 ° C. is discharged from the furnace port. During the discharge, the tilt angle of the converter is once made smaller than that during the discharge, and then the formula (2) The amount of pig iron that satisfies the above condition and the amount of iron oxide that satisfies equation (3) are charged into the slag in the furnace, and the slag is formed again. Characterized in that to discharge slag by tilting the converter to after a converter Haikasu method.
Equivalent FeO concentration = FeO concentration + Fe 2 O 3 concentration × 112/160 (4)
本発明によれば、転炉の排滓方法において、一旦鎮静したスラグを再びフォーミングさせることができ、排滓率を従来技術よりも増加させることができる。これにより脱炭吹錬へ持ち越すスラグ中のＰを低減することができ、ＣａＯの追加投入量を削減できる。 According to the present invention, in the converter evacuation method, slag once sedated can be formed again, and the evacuation rate can be increased as compared with the prior art. Thereby, P in the slag carried over to decarburization blowing can be reduced, and the additional input amount of CaO can be reduced.
以下に、本発明の実施の形態について詳細に説明する。転炉における脱燐吹錬では、高速で酸素ジェットを溶銑表面に吹き付けることで溶銑中のＰを酸化し、スラグへＰ2Ｏ5として除去している。溶銑にはＦｅ以外にＣ、Ｓｉ、Ｍｎも含まれることから、これらの元素も酸化され、ＣＯは排ガスとなり、ＳｉＯ2、ＭｎＯ、ＦｅＯはスラグ相を形成する。また、Ｐ2Ｏ5を安定化させるためにＣａＯが投入される。さらに、転炉内壁には通常ＭｇＯ系の耐火物が張られている。したがってスラグ組成はＣａＯ−ＳｉＯ2−ＦｅＯ−ＭｇＯ−ＭｎＯ−Ｐ2Ｏ5の多成分系となる。 Hereinafter, embodiments of the present invention will be described in detail. In dephosphorization blowing in a converter, oxygen in the hot metal is oxidized by blowing an oxygen jet onto the hot metal surface at a high speed and removed to the slag as P 2 O 5 . Since the hot metal contains C, Si, and Mn in addition to Fe, these elements are also oxidized, CO becomes exhaust gas, and SiO 2 , MnO, and FeO form a slag phase. In addition, CaO is added to stabilize P 2 O 5 . Further, an MgO-based refractory is usually stretched on the converter inner wall. Therefore, the slag composition is a multicomponent system of CaO—SiO 2 —FeO—MgO—MnO—P 2 O 5 .
一般に、スラグは不純物を吸収する能力が高く、液相率が高い方が好ましい。ＣａＯ／ＳｉＯ2が高い方がＰ吸収能は良好となるが、高すぎると２ＣａＯ・ＳｉＯ2や未溶解ＣａＯのような固相が増加し、反応速度が低下しやすくなる。この観点から、低Ｐ鋼を溶製する場合は溶銑脱燐スラグのＣａＯ／ＳｉＯ2を１．２〜１．５とするのが好ましい。一方、低Ｐ鋼ではない普通鋼を溶製する場合は、ＣａＯ／ＳｉＯ2の下限値が０．８程度であっても、目標値までＰを低減することが可能である。 In general, it is preferable that slag has a high ability to absorb impurities and has a high liquid phase ratio. The higher the CaO / SiO 2 , the better the P absorption capacity. However, when the CaO / SiO 2 is too high, the solid phase such as 2CaO · SiO 2 and undissolved CaO increases and the reaction rate tends to decrease. From this viewpoint, when melting low P steel, it is preferable to set CaO / SiO 2 of the hot metal dephosphorization slag to 1.2 to 1.5. On the other hand, when melting ordinary steel that is not low P steel, even if the lower limit value of CaO / SiO 2 is about 0.8, P can be reduced to the target value.
スラグのＣａＯ／ＳｉＯ2が高いと、ＦｅＯ濃度は低くなりやすい。これは、ＣａＯ／ＳｉＯ2が高い方が粘度は低く、流動性が良好となってＦｅＯが溶銑のＣにより還元される速度が向上するためである。この反応は式（５）で表され、溶銑とスラグの界面からはＣＯガス（気泡）が発生する。
Ｃ＋ＦｅＯ＝ＣＯ（ｇ）＋Ｆｅ （５）
When CaO / SiO 2 of slag is high, the FeO concentration tends to be low. This, CaO / SiO 2 is higher viscosity is low, FeO becomes good fluidity in order to improve the speed to be reduced by C in the molten iron. This reaction is expressed by equation (5), and CO gas (bubbles) is generated from the interface between the hot metal and the slag.
C + FeO = CO (g) + Fe (5)
また、溶銑の一部は吹き付けられた酸素ジェットにより引きちぎられて粒鉄となるが、この粒鉄はＣを含んでいるため、粒鉄とスラグの界面からもＣＯ気泡が発生する。一方、スラグの表面では気泡の合体・破裂が起こってガスが散逸する。スラグの粘度が低いほど気泡がスラグ内に滞留する時間が短くなり、ガスの散逸速度が高くなる。ＣＯ気泡の発生速度が散逸速度よりも高いと気泡がスラグ内に滞留し、フォーミングが起こってスラグが膨張する。 A part of the hot metal is torn off by the sprayed oxygen jet to become granular iron. Since this granular iron contains C, CO bubbles are also generated from the interface between the granular iron and the slag. On the other hand, bubbles are coalesced and burst on the surface of the slag, causing gas to dissipate. The lower the viscosity of the slag, the shorter the time for the bubbles to stay in the slag, and the higher the gas dissipation rate. If the generation rate of CO bubbles is higher than the dissipation rate, bubbles stay in the slag, forming occurs, and the slag expands.
ＣＯ気泡の発生速度、散逸速度ともにスラグの粘度が大きく影響する。すなわち、スラグの粘度が低い場合はＣＯ気泡の発生速度が高く、かつスラグ滞留時間も短くなる。粘度が高い場合はこの逆であり、両者のバランスでフォーミング性が決まる。 The viscosity of slag greatly affects both the generation rate and dissipation rate of CO bubbles. That is, when the viscosity of the slag is low, the generation rate of CO bubbles is high and the slag residence time is also shortened. When the viscosity is high, the opposite is true, and the formability is determined by the balance between the two.
スラグの組成、温度とフォーミング性の関係を明らかにするため、本発明者らは小型炉において実験を行った。すなわち、鉄坩堝内で溶解したスラグへ２〜３ｍｍの粒状の銑鉄を投入し、フォーミングしたスラグへ鉄棒を浸漬させ、その付着高さからスラグ高さの経時変化を測定し、銑鉄投入前のスラグ高さと、銑鉄投入後の最大スラグ高さの差をフォーミング高さとした。その結果、スラグの塩基度（ＣａＯ／ＳｉＯ2）は０．８〜１．２が最も良好であり、低Ｐ鋼の溶製に好適な１．２〜１．５のフォーミング性はそれより低いことが分かった。これは、スラグの粘度が低いためＣＯ気泡の発生速度よりも気泡の滞留時間が短いことの影響が大きいことに起因すると推定される。 In order to clarify the relationship between slag composition, temperature and forming property, the present inventors conducted experiments in a small furnace. That is, put 2 to 3 mm of granular pig iron into the slag melted in the iron crucible, immerse the iron rod in the formed slag, measure the change over time of the slag height from the adhesion height, and slag before throwing the pig iron The difference between the height and the maximum slag height after the introduction of pig iron was taken as the forming height. As a result, the basicity of slag (CaO / SiO 2 ) is best from 0.8 to 1.2, and the formability of 1.2 to 1.5 suitable for melting low P steel is lower than that. I understood that. This is presumed to be due to the fact that the influence of the short bubble residence time is greater than the CO bubble generation rate due to the low viscosity of the slag.
転炉の脱燐吹錬では酸素が高速で供給されてＣＯガスが多量に発生するため、送酸中はスラグのＣａＯ／ＳｉＯ2が１．２〜１．５でもスラグのフォーミングが起こる。この状態で転炉を傾動すれば炉口よりスラグを排出することができる。しかし、転炉を傾動するには送酸を停止してランスを引き上げる必要があり、溶銑とスラグの界面へのＦｅＯの供給や粒鉄の生成が停止することになる。このため、排滓初期にはＣＯ気泡発生が継続していても、次第に溶銑−スラグ界面近傍のＦｅＯ濃度の低下、粒鉄中のＣ濃度の低下、粒鉄の沈降が起こり、ＣＯ気泡の発生は弱くなってフォーミングが次第に鎮静してしまう。スラグのＣａＯ／ＳｉＯ2が高いほど鎮静が速く、排滓中期以降の排滓速度を維持することが難しくなる。 In the dephosphorization blowing of the converter, oxygen is supplied at a high speed and a large amount of CO gas is generated. Therefore, slag forming occurs even during CaO / SiO 2 in the slag during oxygenation. If the converter is tilted in this state, slag can be discharged from the furnace port. However, in order to tilt the converter, it is necessary to stop the acid supply and raise the lance, which stops the supply of FeO to the interface between the hot metal and the slag and the generation of granular iron. For this reason, even if CO bubble generation continues in the initial stage of evacuation, the FeO concentration in the vicinity of the hot metal-slag interface gradually decreases, the C concentration in the granular iron decreases, and the precipitation of the granular iron occurs. Becomes weak and the forming gradually subsides. The higher the CaO / SiO 2 of the slag, the faster the sedation, and it becomes difficult to maintain the elimination speed after the middle stage of elimination.
一旦排滓開始した後の排滓途中に転炉を垂直に戻し、再び吹錬を行えばスラグをフォーミングさせて排滓することはできるが、時間がかかるため生産性は大幅に低下し、脱燐−脱炭連続方式の利点が失われてしまう。 Once the slag is started, the converter is returned to the vertical position during evacuation and blown again to form the slag for evacuation. However, it takes time, and the productivity is greatly reduced. The advantage of the continuous phosphorus-decarburization method is lost.
そこで本発明者らはＣａＯ／ＳｉＯ2が１．２〜１．５の条件でもフォーミング性を良好とすることができ、かつ炉口から一旦排滓した後に生産性を大幅に低下させることなくスラグを再びフォーミングさせる手段を鋭意研究した。その結果、粘度を高める作用のあるＡｌ2Ｏ3に着目し、前記した小型炉の実験から、図１に示すように、Ａｌ2Ｏ3濃度は４〜１４質量％においてフォーミング高さが高く、フォーミングが好適であることを見出した。Ａｌ2Ｏ3濃度が４質量％以上において粘度が高くなるためガス発生速度は低下するものの、気泡の滞留時間が長くなる効果が上回り、フォーミング性が向上する。ただし、Ａｌ2Ｏ3濃度が１４質量％超になるとスラグの流動性が大幅に低下してフォーミングが起こりにくくなる。 Therefore, the present inventors can improve the forming property even under the condition of CaO / SiO 2 of 1.2 to 1.5, and slag without drastically reducing the productivity after being discharged from the furnace port once. We studied earnestly on the means to form again. As a result, paying attention to Al 2 O 3 having the effect of increasing the viscosity, as shown in FIG. 1, the Al 2 O 3 concentration is 4 to 14% by mass and the forming height is high as shown in FIG. We have found that forming is suitable. When the Al 2 O 3 concentration is 4% by mass or more, the viscosity increases and the gas generation rate decreases. However, the effect of increasing the bubble residence time is improved, and the forming property is improved. However, when the Al 2 O 3 concentration exceeds 14% by mass, the fluidity of the slag is significantly lowered and forming is difficult to occur.
Ａｌ2Ｏ3源は脱燐吹錬中に投入すれば良く、例えば二次精錬スラグを用いればよい。転炉に装入する溶銑のＳｉ濃度と、脱燐吹錬中に投入する精錬材の量および組成から脱燐スラグの量と組成を推定し、予め分析しておいたＡｌ2Ｏ3源のＡｌ2Ｏ3濃度を用いれば、脱燐スラグのＡｌ2Ｏ3濃度を４〜１４質量％とするＡｌ2Ｏ3源の投入量を決定することができる。 The Al 2 O 3 source may be input during dephosphorization blowing, for example, secondary refining slag may be used. And Si concentration of the molten iron to be charged into the converter, the amount and composition of the refining material to be introduced into the dephosphorization blowing estimate the composition and amount of dephosphorization slag, of Al 2 O 3 source previously analyzed with the concentration of Al 2 O 3, it is possible to determine the input amount of Al 2 O 3 source for the concentration of Al 2 O 3 dephosphorization slag 4 to 14 wt%.
同じく前記した小型炉の実験から、図２に示すように、温度は１３００〜１４００℃においてフォーミング高さが高く、フォーミングが好適である。１３００℃以下ではスラグの粘度が高くなってガス発生速度が低くなる。一方、１４００℃超ではスラグの粘度が過剰に低くなって気泡の滞留時間が短くなる。 Similarly, from the experiment of the small furnace described above, as shown in FIG. 2, the forming height is high when the temperature is 1300 to 1400 ° C., and the forming is suitable. If it is 1300 degrees C or less, the viscosity of slag will become high and a gas generation rate will become low. On the other hand, if it exceeds 1400 ° C., the viscosity of the slag becomes excessively low and the residence time of the bubbles is shortened.
中間排滓でスラグ排出を開始した後、排滓の途中で転炉の傾動角を一旦小さくして排滓を中断し、炉内のスラグへ銑鉄と酸化鉄を投入する。これにより再びフォーミングが発生し、再度スラグを排出して排滓率を増加させることができる。 After the slag discharge is started in the intermediate slag, the tilt angle of the converter is once reduced in the middle of the slag, the slag is interrupted, and pig iron and iron oxide are put into the slag in the furnace. Thereby, forming occurs again, and the slag can be discharged again to increase the rejection rate.
ここで言う「銑鉄」とは、例えば高炉粒銑が挙げられる。溶銑温度（１２５０〜１４５０℃）で完全溶融するために、融点の観点から銑鉄のＣ濃度は３〜４．５質量％であることが好ましい。また、銑鉄の粒度は２〜２０ｍｍが好適である。２ｍｍ未満の銑鉄はスラグ内部に侵入しにくく、内部からＣＯ気泡を発生させることが難しい。一方、２０ｍｍ超の銑鉄はスラグ内部へ速く沈降し、溶融前に湯溜まりに到達してしまってＣＯ気泡の発生に寄与しにくくなる。２〜２０ｍｍの比率は８０質量％以上であれば、本発明の効果を十分に発揮することができる。 As used herein, “pig iron” includes, for example, blast furnace granule. In order to achieve complete melting at the hot metal temperature (1250 to 1450 ° C.), the C concentration of pig iron is preferably 3 to 4.5% by mass from the viewpoint of the melting point. Moreover, 2-20 mm is suitable for the particle size of pig iron. Pig iron of less than 2 mm does not easily enter the slag, and it is difficult to generate CO bubbles from the inside. On the other hand, pig iron exceeding 20 mm quickly settles into the slag and reaches the hot water pool before melting, making it difficult to contribute to the generation of CO bubbles. When the ratio of 2 to 20 mm is 80% by mass or more, the effect of the present invention can be sufficiently exhibited.
次に「酸化鉄」とは、例えばミルスケールや転炉ダストが挙げられる。炉内のスラグへ速やかに溶解させるために、粒度は１ｍｍ未満であることが好ましい。このような細粒の酸化鉄をそのまま投入しても良いし、ブリケットのような固形物に成形して投入しても良い。前記したように、スラグのＣａＯ／ＳｉＯ2が高いとＦｅＯ濃度は低くなりやすいが、酸化鉄を投入することでスラグのＦｅＯ濃度を高めることができ、再びフォーミングを発生させやすくなる。 Next, “iron oxide” includes, for example, mill scale and converter dust. In order to dissolve quickly in the slag in the furnace, the particle size is preferably less than 1 mm. Such fine iron oxide may be added as it is, or it may be molded into a solid material such as briquette. As described above, when the CaO / SiO 2 of the slag is high, the FeO concentration tends to be low, but by adding iron oxide, the FeO concentration of the slag can be increased, and it becomes easy to form again.
前記のＣ濃度および粒度を有する銑鉄を排滓中にスラグ上方より投入すれば、スラグ内部で速やかに溶融し、銑鉄に含まれるＣがスラグ中のＦｅＯと反応して式（５）の反応によりＣＯ気泡を発生し、スラグをフォーミングさせることができる。 If pig iron having the above-mentioned C concentration and particle size is thrown into the slag from above the slag, it melts rapidly inside the slag, and the C contained in the pig iron reacts with FeO in the slag by the reaction of formula (5). CO bubbles can be generated and slag can be formed.
投入方法としては、例えばスクラップシュートを使用すれば良いが、炉口からの排滓が終了した後に炉体を一旦垂直に戻し、炉上のホッパーから銑鉄を投入しても良い。この場合も銑鉄は速やかに溶融してＣＯ気泡を発生してスラグは再びフォーミングするため、炉体を傾動すればスラグを排出することができる。この方法でも再吹錬を行う必要はなく、生産性の大幅な低下は回避できる。 As a charging method, for example, a scrap chute may be used, but after the discharge from the furnace port is completed, the furnace body may be once returned to a vertical position, and pig iron may be charged from a hopper on the furnace. In this case as well, pig iron quickly melts to generate CO bubbles and the slag forms again. Therefore, if the furnace body is tilted, the slag can be discharged. This method also does not require re-blowing, and a significant reduction in productivity can be avoided.
なお、排滓中にスラグ上方から銑鉄を投入する方法も考えられるが、投入した銑鉄が流されてしまい、ＣＯ気泡を発生する前に炉外へ排出される恐れが非常に高い。したがって投入した銑鉄が再フォーミングに寄与することは難しい。むしろ、排出されたスラグを受ける排滓鍋内において銑鉄がＣＯ気泡を発生し、スラグをフォーミングさせて排滓鍋からスラグが溢出し、周辺機器を損傷する原因になる恐れがある。したがって、排滓中に銑鉄を投入する方法は好ましくない。 Although a method of throwing pig iron from above the slag can be considered during the dredging, the thrown pig iron is washed away, and there is a very high possibility that it will be discharged out of the furnace before generating CO bubbles. Therefore, it is difficult for the injected pig iron to contribute to reforming. Rather, pig iron may generate CO bubbles in the waste pan that receives the discharged slag, forming slag and overflowing the slag from the waste pan, which may cause damage to peripheral equipment. Therefore, the method of throwing pig iron into the waste is not preferable.
次に、排滓に適したフォーミング高さの観点から、銑鉄の投入量を検討した。効率的に排滓するために、溶銑の静止浴面から炉口までの距離（フリーボード）の半分以上にスラグをフォーミングさせられる分の銑鉄量が必要である。ただし、銑鉄を過剰に投入すると必要以上にガスが急速に発生してスラグが周囲に激しく飛散し、非常に危険な状態となる。このような過剰フォーミングが発生した場合は、ガス発生が落ち着くまで追加の排滓を開始できないため、排滓時間が長くなり生産性が低下してしまう。したがって銑鉄投入量には適正範囲が存在する。 Next, the amount of pig iron input was examined from the viewpoint of forming height suitable for slagging. In order to discharge efficiently, the amount of pig iron is required to form slag to more than half of the distance (free board) from the hot bath stationary bath surface to the furnace port. However, if pig iron is added excessively, gas will be generated more rapidly than necessary, and the slag will be scattered violently, making it extremely dangerous. When such excessive forming occurs, additional waste cannot be started until the gas generation has settled, so the waste time becomes longer and productivity is lowered. Therefore, there is an appropriate range for pig iron input.
ＣＯ気泡の発生量が同じ場合、転炉の断面積が大きい方がフォーミング高さは小さくなる。したがって、銑鉄投入量は転炉のフリーボードや断面積に依存する。このような観点で銑鉄の投入量を検討し、式（２）の範囲を見出した。
酸化鉄は、銑鉄中のＣ分に見合った量を投入する必要がある。式（５）の反応においてＣとＦｅＯは１２：７２の質量比で反応するため、必要な酸化鉄の量は式（６）で表わされる。
なお、換算ＦｅＯ濃度は酸化鉄に含まれるＦｅＯ濃度と、Ｆｅ2Ｏ3濃度を分子量によりＦｅＯに換算した値の和であり、式（４）で表される。
換算ＦｅＯ濃度＝ＦｅＯ濃度＋Ｆｅ2Ｏ3濃度×１１２／１６０ （４）
The converted FeO concentration is the sum of the FeO concentration contained in the iron oxide and the value obtained by converting the Fe 2 O 3 concentration into FeO by the molecular weight, and is represented by the formula (4).
Equivalent FeO concentration = FeO concentration + Fe 2 O 3 concentration × 112/160 (4)
酸化鉄は式（６）で計算される量より多く投入しても良いが、あまり過剰に投入すると式（５）の反応に寄与しないＦｅＯ分がスラグ内に残留し、スラグの粘度を低下させてＡｌ2Ｏ3により粘度を高めた効果を小さくしてしまう。このような観点から酸化鉄の投入量を検討し、式（３）の範囲を見出した。すなわち、酸化鉄の投入量は銑鉄中のＣ分に見合った量を下限値、その２倍を上限値とする。
このように、炉内のスラグへ外部から適切な量の銑鉄と酸化鉄を投入することにより、一旦鎮静したスラグを再びフォーミングさせることができ、排滓量を増加させることができる。 In this way, by introducing appropriate amounts of pig iron and iron oxide from the outside to the slag in the furnace, the slag once calmed can be formed again, and the amount of slag can be increased.
本発明では、スラグがフォーミングしにくいＣａＯ／ＳｉＯ2が１．２〜１．５であっても、スラグのＡｌ2Ｏ3含有量の調整を行うとともに、スラグ排出の途中で銑鉄及び酸化鉄をスラグに添加することにより、良好なフォーミングを実現することができた。
そして、スラグ排出の途中で銑鉄及び酸化鉄をスラグに添加することにより、良好なフォーミングを実現する効果は、スラグがフォーミングしやすいＣａＯ／ＳｉＯ2が０．８〜１．２の範囲において、スラグのＡｌ2Ｏ3含有量調整を行わない場合においても同じく享受することができることがわかった。
In the present invention, even if CaO / SiO 2 in which slag is difficult to form is 1.2 to 1.5, the content of Al 2 O 3 in the slag is adjusted, and pig iron and iron oxide are added during the slag discharge. By adding it to the slag, it was possible to realize good forming.
The effect of realizing good forming by adding pig iron and iron oxide to the slag in the middle of slag discharge is that the slag is easy to form CaO / SiO 2 in the range of 0.8 to 1.2. It was also found that the same Al 2 O 3 content can be enjoyed even when the content is not adjusted.
そこで本発明は、スラグのＣａＯ／ＳｉＯ2の範囲を０．８〜１．５とすることとした。そして、スラグのＣａＯ／ＳｉＯ2が０．８以上１．２未満ではスラグ中Ａｌ2Ｏ3濃度：２〜１４質量％の組成を有し、ＣａＯ／ＳｉＯ2が１．２以上１．５以下のときは炉内にＡｌ2Ｏ3源を投入してＡｌ2Ｏ3濃度を４〜１４質量％とすることとした。スラグのＣａＯ／ＳｉＯ2が０．８以上１．２未満であっても、炉内にＡｌ2Ｏ3源を投入してＡｌ2Ｏ3濃度を４〜１４質量％とすれば、より優れた排滓能力を得ることができる。 Therefore, in the present invention, the CaO / SiO 2 range of the slag is set to 0.8 to 1.5. The slag in the concentration of Al 2 O 3 in the CaO / SiO 2 is 0.8 or more and less than 1.2 of the slag: 2 to 14 has the composition by weight%, CaO / SiO 2 is 1.2 to 1.5 In this case, an Al 2 O 3 source was introduced into the furnace so that the Al 2 O 3 concentration was 4 to 14% by mass. Even if the CaO / SiO 2 of the slag is 0.8 or more and less than 1.2, it is more excellent if an Al 2 O 3 source is introduced into the furnace so that the Al 2 O 3 concentration is 4 to 14% by mass. Exclusion ability can be obtained.
以上説明したように、本発明に係る転炉の排滓方法は、脱燐処理後に溶銑を転炉内に残したまま、上吹きランスからの送酸により炉内のスラグをフォーミングさせ、送酸を止めた後に転炉を傾動して炉口から排出する転炉排滓方法において、ＣａＯ／ＳｉＯ2が０．８〜１．５であり、スラグのＣａＯ／ＳｉＯ2が０．８以上１．２未満ではスラグ中Ａｌ2Ｏ3濃度：２〜１４質量％の組成を有し、ＣａＯ／ＳｉＯ2が１．２以上１．５以下のときは炉内にＡｌ2Ｏ3源を投入してＡｌ2Ｏ3濃度を４〜１４質量％とし、且つ温度が１３００〜１４００℃であるスラグを炉口より排出し、排滓途中で一旦転炉の傾動角を排滓時より小さくし、続いて式（２）を満たす量の銑鉄と、式（３）を満たす量の酸化鉄を炉内のスラグへ投入し、スラグを再びフォーミングさせた後に転炉を傾動して排滓を行うことを特徴とする。 As described above, in the converter discharge method according to the present invention, after the dephosphorization process, the molten iron is left in the converter, the slag in the furnace is formed by the supply of oxygen from the top blowing lance, and the acid supply In the converter discharge method in which the converter is tilted after being stopped and discharged from the furnace port, CaO / SiO 2 is 0.8 to 1.5, and CaO / SiO 2 of the slag is 0.8 or more. If it is less than 2, it has a composition of Al 2 O 3 concentration in the slag: 2 to 14% by mass. When CaO / SiO 2 is 1.2 or more and 1.5 or less, an Al 2 O 3 source is introduced into the furnace. The slag having an Al 2 O 3 concentration of 4 to 14% by mass and a temperature of 1300 to 1400 ° C. is discharged from the furnace port, and during the discharge, the tilt angle of the converter is once made smaller than that at the time of discharge. An amount of pig iron that satisfies Equation (2) and an amount of iron oxide that satisfies Equation (3) are charged into the slag in the furnace, and the slag is recycled. It tilts the converter in After forming, characterized in that to discharge slag.
ここで、上記上吹きランスからの送酸による炉内のスラグのフォーミングについては、通常に行われる脱燐吹錬で用いられる送酸を行うことにより、実現することができる。また、脱燐吹錬終了時のスラグ組成としてＣａＯ／ＳｉＯ2＝０．８〜１．５となるように精錬材を添加して精錬を行えばよい。溶製する鋼が低燐鋼であれば、脱燐吹錬の上からはＣａＯ／ＳｉＯ2＝１．２〜１．５が最も好適なスラグ組成である。低燐鋼ではない普通鋼の溶製においては、ＣａＯ／ＳｉＯ2＝０．８〜１．２とすることができる。排滓時のスラグ温度を１３００〜１４００℃とする点についても、脱燐吹錬終了時の溶鉄温度を当該温度範囲とすることにより実現することができる。スラグ中Ａｌ2Ｏ3濃度調整方法は前述のとおりである。 Here, the formation of slag in the furnace by the acid sent from the upper blowing lance can be realized by carrying out the acid feeding used in the dephosphorization blowing performed normally. Further, refining may be performed by adding a refining material so that the slag composition at the end of dephosphorization blowing is CaO / SiO 2 = 0.8 to 1.5. If the steel to be melted is low phosphorus steel, CaO / SiO 2 = 1.2 to 1.5 is the most suitable slag composition from the top of dephosphorization blowing. In the melting of ordinary steel that is not low phosphorus steel, CaO / SiO 2 can be set to 0.8 to 1.2. Also about the point which makes the slag temperature at the time of discharge 1300-1400 degreeC, it can implement | achieve by making the molten iron temperature at the time of completion | finish of dephosphorization blowing into the said temperature range. The method for adjusting the Al 2 O 3 concentration in the slag is as described above.
以下に表１を基にして本発明の実施例を具体的に説明する。精錬に用いた転炉の形状は、溶銑表面と炉口の距離は８ｍ、転炉の炉底から溶銑の静止面までの高さは２．３ｍ、転炉の水平方向の最大断面積は３３．２ｍ2であった。 Examples of the present invention will be specifically described below based on Table 1. The shape of the converter used for refining is that the distance between the hot metal surface and the furnace port is 8 m, the height from the bottom of the converter to the hot metal stationary surface is 2.3 m, and the maximum horizontal cross-sectional area of the converter is 33 .2 m 2 .
転炉へ溶銑を装入して脱燐吹錬を行い、スラグをフォーミングさせた。脱燐吹錬時に転炉に装入する生石灰などの精錬材添加量を調整して、脱燐吹錬終了時の転炉内スラグが表１に示す値となるように調整した。また脱燐吹錬中に二次精錬スラグを添加し、スラグ中Ａｌ2Ｏ3含有量を調整した。脱燐吹錬終了時の溶銑温度を表１に示す温度となるように調整した。 Hot metal was charged into the converter and dephosphorized and blown to form slag. The amount of refining material such as quick lime charged into the converter during dephosphorization blowing was adjusted to adjust the slag in the converter at the end of dephosphorization blowing to the value shown in Table 1. Further, secondary refining slag was added during dephosphorization blowing to adjust the Al 2 O 3 content in the slag. The hot metal temperature at the end of dephosphorization was adjusted to the temperature shown in Table 1.
脱燐吹錬終了後に、送酸を停止して転炉を傾動し、スラグを炉口から炉下の排滓鍋に排出開始した。その後排滓の途中で、転炉の傾動角を排滓時より小さくして排滓を中断し、スクラップシュートから銑鉄（Ｃ濃度：４．３質量％）と転炉ダスト（換算ＦｅＯ濃度：７５％）を炉内に投入した。銑鉄の粒度は２〜２０ｍｍの比率が１００質量％であった。そして再び転炉を傾動して追加の排滓を行った。 After completion of dephosphorization, the acid feeding was stopped, the converter was tilted, and slag was started to be discharged from the furnace port to the discharge pan under the furnace. Then, in the middle of evacuation, the tilt angle of the converter was made smaller than that at the time of evacuation, and evacuation was interrupted, and pig iron (C concentration: 4.3% by mass) and converter dust (converted FeO concentration: 75) from the scrap chute. %) Was put into the furnace. The ratio of 2-20 mm of pig iron particle size was 100% by mass. Then, the converter was tilted again and additional evacuation was performed.
排出したスラグは冷却後に重量を測定し、式（８）により排滓率を評価した。
本発明は、低燐鋼の溶製を主な対象としており、脱燐性能を優先し、排滓率の目標を６５％以上とした。 The main object of the present invention is the melting of low-phosphorus steel, giving priority to dephosphorization performance, and the target of the rejection rate is set to 65% or more.
表１に処理の結果を示す。表中の下線は、本発明の範囲外となる部分を表す。 Table 1 shows the results of the processing. The underline in the table represents a part that is outside the scope of the present invention.
実施例１〜１１は発明例であり、いずれも処理条件が本発明の範囲内であったため、排滓率は６５％以上となった。 Examples 1 to 11 are invention examples, and all of the treatment conditions were within the scope of the present invention, so the rejection rate was 65% or more.
一方、実施例１２〜２２は比較例であり、実施例１２では銑鉄投入による再フォーミングを行わなかった結果、排滓率は５０％に止まった。実施例１３〜１４はスラグのＣａＯ／ＳｉＯ2、実施例１５〜１６はスラグのＡｌ2Ｏ3濃度、実施例１７〜１８はスラグの温度が本発明の範囲外であったため排滓率は６５％未満となった。実施例１９では銑鉄量が本発明の下限を下回ったため再フォーミングが弱く、排滓率は６５％未満となった。実施例２０では銑鉄量が本発明の上限を超過したため再フォーミングが激しく、転炉を傾動するまで待ち時間が発生した。その結果、サイクルタイムは大幅に伸び、生産性が低下した。 On the other hand, Examples 12 to 22 are comparative examples. In Example 12, as a result of not performing re-forming by introducing pig iron, the rejection rate was only 50%. Examples 13 to 14 were CaO / SiO 2 of slag, Examples 15 to 16 were Al 2 O 3 concentration of slag, and Examples 17 to 18 were slag temperature outside the range of the present invention, so the rejection rate was 65 %. In Example 19, since the amount of pig iron was below the lower limit of the present invention, reforming was weak, and the rejection rate was less than 65%. In Example 20, since the amount of pig iron exceeded the upper limit of the present invention, reforming was intense and a waiting time occurred until the converter was tilted. As a result, cycle time increased significantly and productivity decreased.
実施例２１では本発明の範囲よりも酸化鉄の投入量が本発明の下限を下回ったため再フォーミングが弱く、排滓率は６５％未満となった。実施例２２では本発明の範囲よりも酸化鉄の投入量が多かったためスラグのＦｅＯ濃度が過剰となり、スラグの粘度が低下して再フォーミングが弱くなり排滓率は６５％未満となった。
In Example 21, since the input amount of iron oxide was less than the lower limit of the present invention, the reforming was weak and the rejection rate was less than 65%. In Example 22, since the input amount of iron oxide was larger than the range of the present invention, the FeO concentration of the slag was excessive, the viscosity of the slag was lowered, the reforming was weakened, and the rejection rate was less than 65%.
Claims (1)
換算ＦｅＯ濃度＝ＦｅＯ濃度＋Ｆｅ2Ｏ3濃度×１１２／１６０ （４） After the dephosphorization process, the molten iron remains in the converter, the slag in the furnace is formed by sending acid from the top blowing lance, and after stopping the feeding, the converter is tilted and discharged from the furnace port. In the dredging method, the slag is CaO / SiO 2 = 0.8 to 1.5, and when CaO / SiO 2 is 0.8 or more and less than 1.2, the composition of Al 2 O 3 concentration in the slag: 2 to 14% by mass When CaO / SiO 2 is 1.2 or more and 1.5 or less, an Al 2 O 3 source is introduced into the furnace so that the Al 2 O 3 concentration is 4 to 14% by mass, and the temperature is 1300 The slag at 1400 ° C. is discharged from the furnace port, and the tilt angle of the converter is once reduced in the middle of evacuation, and then the amount of pig iron satisfying equation (2) and equation (3) A sufficient amount of iron oxide is charged into the slag in the furnace, and after the slag is formed again, the converter is tilted and discharged. A converter discharge method characterized by the above.
Equivalent FeO concentration = FeO concentration + Fe 2 O 3 concentration × 112/160 (4)
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