JP6825550B2 - How to operate the upper bottom blown converter - Google Patents
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- 239000002184 metal Substances 0.000 claims description 51
- 229910052751 metal Inorganic materials 0.000 claims description 51
- 239000007789 gas Substances 0.000 claims description 42
- 239000002893 slag Substances 0.000 claims description 39
- 238000007664 blowing Methods 0.000 claims description 31
- 238000000034 method Methods 0.000 claims description 30
- 235000008733 Citrus aurantifolia Nutrition 0.000 claims description 18
- 235000011941 Tilia x europaea Nutrition 0.000 claims description 18
- 239000004571 lime Substances 0.000 claims description 18
- 239000002904 solvent Substances 0.000 claims description 15
- 230000001590 oxidative effect Effects 0.000 claims description 12
- 238000007670 refining Methods 0.000 claims description 8
- 239000011261 inert gas Substances 0.000 claims description 6
- 238000003756 stirring Methods 0.000 claims description 6
- 229910004298 SiO 2 Inorganic materials 0.000 claims description 5
- 230000037237 body shape Effects 0.000 claims description 5
- 238000005507 spraying Methods 0.000 claims description 4
- 238000010079 rubber tapping Methods 0.000 claims description 2
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 54
- 229910052698 phosphorus Inorganic materials 0.000 description 42
- 238000005261 decarburization Methods 0.000 description 28
- 229910052742 iron Inorganic materials 0.000 description 27
- ODINCKMPIJJUCX-UHFFFAOYSA-N Calcium oxide Chemical compound [Ca]=O ODINCKMPIJJUCX-UHFFFAOYSA-N 0.000 description 22
- MYMOFIZGZYHOMD-UHFFFAOYSA-N Dioxygen Chemical compound O=O MYMOFIZGZYHOMD-UHFFFAOYSA-N 0.000 description 21
- 229910001882 dioxygen Inorganic materials 0.000 description 21
- 239000011574 phosphorus Substances 0.000 description 21
- 229910000831 Steel Inorganic materials 0.000 description 18
- 239000010959 steel Substances 0.000 description 18
- 235000012255 calcium oxide Nutrition 0.000 description 11
- 239000000292 calcium oxide Substances 0.000 description 11
- 238000012360 testing method Methods 0.000 description 9
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 description 8
- 230000000052 comparative effect Effects 0.000 description 8
- 238000002347 injection Methods 0.000 description 8
- 239000007924 injection Substances 0.000 description 8
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 7
- 230000007423 decrease Effects 0.000 description 7
- 230000000694 effects Effects 0.000 description 7
- 239000001301 oxygen Substances 0.000 description 7
- 229910052760 oxygen Inorganic materials 0.000 description 7
- 238000006243 chemical reaction Methods 0.000 description 6
- 229910018072 Al 2 O 3 Inorganic materials 0.000 description 4
- 238000004519 manufacturing process Methods 0.000 description 4
- 230000015572 biosynthetic process Effects 0.000 description 3
- 230000008859 change Effects 0.000 description 3
- 230000003247 decreasing effect Effects 0.000 description 3
- 239000000463 material Substances 0.000 description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 3
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 2
- 238000003723 Smelting Methods 0.000 description 2
- 229910052799 carbon Inorganic materials 0.000 description 2
- 239000003795 chemical substances by application Substances 0.000 description 2
- 238000002844 melting Methods 0.000 description 2
- 230000008018 melting Effects 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 230000003647 oxidation Effects 0.000 description 2
- 238000007254 oxidation reaction Methods 0.000 description 2
- 230000008569 process Effects 0.000 description 2
- 229920006395 saturated elastomer Polymers 0.000 description 2
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 1
- 239000003570 air Substances 0.000 description 1
- 230000008901 benefit Effects 0.000 description 1
- 238000006114 decarboxylation reaction Methods 0.000 description 1
- 230000030609 dephosphorylation Effects 0.000 description 1
- 238000006209 dephosphorylation reaction Methods 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 238000007865 diluting Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 238000002156 mixing Methods 0.000 description 1
- 238000006722 reduction reaction Methods 0.000 description 1
- 238000004904 shortening Methods 0.000 description 1
- 229910052710 silicon Inorganic materials 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
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Description
本発明は、高炉から出銑した高燐溶銑あるいは高炉から出銑した後に予め脱燐処理を施した低燐溶銑を転炉にて脱炭処理する際に、スラグ−メタル間反応を効率よく行うことができるようにした形状の転炉を用いて上底吹き転炉の操業を行なう方法について提案する。 INDUSTRIAL APPLICABILITY The present invention efficiently performs a slag-metal reaction when a high-phosphorus hot metal ejected from a blast furnace or a low-phosphorus hot metal that has been dephosphorized in advance after being ejected from a blast furnace is decarburized in a converter. We propose a method for operating a top-bottom blown converter using a converter with a shape that enables it.
近年の転炉の操業は、低燐鋼への需要の高まりとともに、脱炭吹錬の前に、予め溶銑の脱珪および脱燐処理を行う手法が広く普及している。予め脱燐処理を施した溶銑を用いる脱炭吹錬では、転炉での脱燐負荷が軽減され、必要最小限の石灰系媒溶剤の使用で済むため、スラグの多量発生による環境負荷も軽減できるという利点がある。 In recent years, with the increasing demand for low-phosphorus steel, the method of desiliconizing and dephosphorizing hot metal in advance before decarburization has become widespread in the operation of converters. In decarburization using hot metal that has been dephosphorized in advance, the dephosphorization load in the converter is reduced and the minimum required lime-based solvent is used, so the environmental load due to the large amount of slag is also reduced. There is an advantage that it can be done.
しかしながら、少量スラグ下での溶銑の脱炭吹錬というのは、溶鉄浴面のうち、酸化性ガス流ともスラグとも接しない自由表面の割合が増加するため、炉内雰囲気中の酸素によって溶鉄の酸化が起こる。その結果、スラグ中のＦｅＯ濃度が上昇し、鉄歩留まりの低下や炉内耐火物の損耗につながるという問題がある。これを解決するために、石灰系媒溶剤を必要以上に添加する場合があるが、これは結果的にしてスラグ量の増加を招くという問題がある。 However, decarburization of hot metal under a small amount of slag increases the proportion of the free surface of the molten iron bath surface that does not come into contact with the oxidizing gas flow or slag, so oxygen in the furnace atmosphere causes the molten iron to be removed. Oxidation occurs. As a result, there is a problem that the FeO concentration in the slag increases, leading to a decrease in iron yield and wear of the refractory in the furnace. In order to solve this, a lime-based solvent may be added more than necessary, but this has a problem that the amount of slag is increased as a result.
一方で、脱燐処理工程の短縮による転炉生産性の向上や、熱的余裕を活かしたスクラップ使用量の増加による溶鋼製造コストの低減という観点からは、高炉から出銑した溶銑を転炉に直接搬送し、脱炭処理する場合も依然として多いのが実情である。 On the other hand, from the viewpoint of improving converter productivity by shortening the dephosphorization process and reducing molten steel production costs by increasing the amount of scrap used by utilizing the thermal margin, hot metal from the blast furnace is used as the converter. In reality, there are still many cases where the products are directly transported and decarburized.
また、予め脱燐処理をしていない溶銑を用いた脱炭吹錬では、溶銑の脱炭酸素効率が低下する吹錬末期において、脱燐処理を効率よく行う目的で操業条件の変更が不可欠である。具体的には、スラグ中ＦｅＯが石灰系媒溶剤の溶融を促進する効果を利用するべく、酸素供給速度を低下させて溶鉄浴面を意図的に過酸化状態にし、スラグ中にＦｅＯを生成させる操業である。この場合、酸素供給速度の低下による転炉の生産性低下やＦｅＯの過剰な生成による鉄歩留まりの低下を招くといった問題が生じる。 In addition, in decarburization using hot metal that has not been dephosphorized in advance, it is essential to change the operating conditions for the purpose of efficient dephosphorization at the end of the smelting when the decarboxylation efficiency of the hot metal decreases. is there. Specifically, in order to utilize the effect of FeO in the slag to promote the melting of the lime-based medium solvent, the oxygen supply rate is lowered to intentionally put the molten iron bath surface in a peroxidized state to generate FeO in the slag. It is an operation. In this case, there arises a problem that the productivity of the converter is lowered due to the decrease in the oxygen supply rate and the iron yield is lowered due to the excessive production of FeO.
上記課題を解決するために、従来、石灰系媒溶剤に代わる脱燐剤や滓化促進剤を添加する方法、生成したスラグを次チャージで再利用する方法、炉体形状を最適化する方法、スラグ中へのＦｅＯの過剰な生成を抑制しつつ脱炭吹錬における脱燐処理を効率よく行う方法等が提案されている。 In order to solve the above problems, conventionally, a method of adding a dephosphorizing agent or a slag-promoting agent instead of a lime-based medium solvent, a method of reusing the generated slag in the next charge, a method of optimizing the furnace body shape, A method of efficiently performing dephosphorization treatment in decarburization blowing while suppressing excessive formation of FeO in slag has been proposed.
特許文献１には、予め脱燐処理を施した溶銑を脱炭処理する際に、石灰系媒溶剤に加えてＡｌ２Ｏ３源を添加する方法が開示されている。この方法によれば、スラグ中のＡｌ２Ｏ３濃度を増加させて、未溶解のＣａＯを減少させることでＣａＯの滓化を促進し、石灰原単位を低減させつつ高いスラグ塩基度を得ることができる。 Patent Document 1 discloses a method of adding an Al 2 O 3 source in addition to a lime-based solvent when decarburizing a hot metal that has been previously dephosphorized. According to this method, it increases the concentration of Al 2 O 3 in the slag and promote the slag formation of the CaO by reducing the CaO undissolved obtain high slag basicity while reducing the lime consumption rate Can be done.
特許文献２には、予め脱燐処理を施した溶銑を脱炭処理する際に、当該脱炭処理中に発生したスラグに対し固化材を添加して、転炉内に残留させて、次チャージの脱炭処理を行う方法が提案されている。この方法によれば、残留スラグ中のＦｅＯやＣａＯが次チャージの脱燐反応に利用されやすいため、鉄歩留まりの低下防止や石灰原単位の低減が可能としている。 In Patent Document 2, when the hot metal that has been dephosphorized in advance is decarburized, a solidifying material is added to the slag generated during the decarburization treatment and left in the converter to be charged next. A method of decarburizing the above has been proposed. According to this method, FeO and CaO in the residual slag are easily used for the dephosphorization reaction of the next charge, so that it is possible to prevent a decrease in the iron yield and reduce the lime basic unit.
特許文献３では、炉体の形状が溶鋼量にかかわらず吹錬終了時の鋼浴形状が逆円錐台形状とし、その上下面の半径および鋼浴高さが一定の関係を満たすような形状の上底吹き転炉の炉体を提案している。このような炉体形状を有する転炉を用いて精錬することにより、十分な撹拌効果による鋼浴の混合と、湯溜り部の耐火物原単位の極小化が達成できると説明している。 In Patent Document 3, the shape of the furnace body is an inverted truncated cone shape at the end of smelting regardless of the amount of molten steel, and the radius of the upper and lower surfaces thereof and the height of the steel bath satisfy a certain relationship. We are proposing a top-bottom blown converter. It is explained that by refining using a converter having such a furnace body shape, it is possible to achieve mixing of steel baths with a sufficient stirring effect and minimization of the refractory basic unit of the hot water pool.
特許文献４では、上吹き酸素ガスをＡｒガスで希釈してハードブローを行う方法を提案している。この方法によれば、炉内のＣＯ分圧を低下させながら溶鉄の強撹拌ができるため、スラグ中へのＦｅＯの過剰な生成を抑制することが可能であるとしている。 Patent Document 4 proposes a method of diluting top-blown oxygen gas with Ar gas to perform hard blowing. According to this method, since the molten iron can be strongly agitated while lowering the partial pressure of CO in the furnace, it is possible to suppress the excessive formation of FeO in the slag.
特許文献１の方法では、Ａｌ２Ｏ３源の多量添加により、熱ロスの増加、スラグ量の増加や溶鋼中のＡｌ２Ｏ３系介在物の増加を招くおそれがあった。 In the method of Patent Document 1, the addition of a large amount of Al 2 O 3 source may cause an increase in heat loss, an increase in the amount of slag, and an increase in Al 2 O 3 system inclusions in molten steel.
特許文献２の方法では、残留スラグの塩基度および成分の調整、スラグ固化材の調整および添加工程が必要であり、固化材の使用によるコスト増加、溶鋼製造時間の延長による生産性低下のおそれがあった。 The method of Patent Document 2 requires adjustment of the basicity and composition of residual slag, adjustment of the slag solidifying material, and addition steps, which may increase the cost due to the use of the solidifying material and decrease the productivity due to the extension of the molten steel production time. there were.
特許文献３は、溶湯量の変動による逆円錐台形状の上面径と下面径との比に基づく耐火物寿命の向上に着目したものであって、溶銑の脱炭精錬を最適化する方法についての言及はなく、上底吹きガス吹き込み条件および鋼浴形状が鉄歩留まりに与える影響にまでは考慮されていない。 Patent Document 3 focuses on the improvement of the refractory life based on the ratio of the upper surface diameter to the lower surface diameter of the inverted truncated cone shape due to the fluctuation of the amount of molten metal, and describes a method for optimizing the decarburization and refining of hot metal. No mention is made, and the effects of top-bottom blowing gas blowing conditions and steel bath shape on iron yield are not taken into consideration.
特許文献４の方法は、Ａｒガスの吹き付けにより溶鉄浴面が冷却されるため溶鉄への着熱の点で不利であり、また、高価なＡｒガスが多量に必要となるため溶鋼製造コストの増加を招く。 The method of Patent Document 4 is disadvantageous in terms of heat transfer to molten iron because the molten iron bath surface is cooled by spraying Ar gas, and also increases the cost of manufacturing molten steel because a large amount of expensive Ar gas is required. Invite.
上述したように、従来技術については、高炉から出銑した高燐溶銑あるいは高炉から出銑した後に予め脱燐処理を施した溶銑を脱炭処理する際の、スラグ−メタル間反応を効率よく行うための上底吹き転炉の操業技術の確立という点でなお、解決すべき課題を残していた。 As described above, in the prior art, the slag-metal reaction is efficiently performed when the high-phosphorus hot metal from the blast furnace or the hot metal that has been dephosphorized in advance after the hot metal from the blast furnace is decarburized. There was still a problem to be solved in terms of establishing the operation technology of the upper bottom blow furnace for this purpose.
そこで、本発明の目的は、高炉から出銑した高燐溶銑あるいは脱燐溶銑の脱炭精錬に際し、脱燐効率、脱炭効率の低下を招くことなく、低コストで高い生産性を確保できる転炉の操業方法を提案することにある。 Therefore, an object of the present invention is a converter that can secure high productivity at low cost without causing deterioration of dephosphorization efficiency and decarburization efficiency in decarburization refining of high-phosphorus hot metal or dephosphorized hot metal ejected from a blast furnace. The purpose is to propose a method of operating the furnace.
発明者らは、従来技術が抱えている前述の課題について検討する中で、上底吹き転炉の炉体形状と脱炭処理中のガス流量とを最適化することにより、高炉から出銑した高燐溶銑あるいは脱燐溶銑の脱炭吹錬において、スラグ中のＦｅＯの還元反応を促進できることを突き止めた。 While examining the above-mentioned problems of the prior art, the inventors set out from the blast furnace by optimizing the shape of the upper bottom blown converter and the gas flow rate during the decarburization process. It was found that the reduction reaction of FeO in slag can be promoted in the decarburization of high-phosphorus hot metal or dephosphorized hot metal.
本発明は、このような知見に基いて開発した方法である。即ち、本発明は、静置直立した状態において略円柱および逆円錐台を組合せた炉体形状をもつ転炉を用いて、高炉から出銑した溶銑あるいは高炉から出銑した後に予め脱燐処理を施した溶銑を脱炭精錬する上底吹き転炉の操業方法であって、
前記転炉は、前記略円柱の下面と前記逆円錐台の上面との共通する炉内径Ｄ１（ｍ）と、前記逆円錐台の下面である転炉の炉底径Ｄ２（ｍ）との比Ｄ１／Ｄ２が１．５〜２．５の範囲である炉体形状の転炉とし、
該転炉による上底吹きの操業条件が、溶銑に供給される酸化性ガスの総流量ＱＯ２（Ｎｍ３／ｍｉｎ／ｔ）と、上吹きガス流量Ｑｔ（Ｎｍ３／ｍｉｎ／ｔ）と、底吹きガス流量Ｑｂ（Ｎｍ３／ｍｉｎ／ｔ）とが下記数式１の関係を満たすことを特徴とする上底吹き転炉の操業方法である。
The present invention is a method developed based on such findings. That is, in the present invention, using a converter having a furnace body shape that is a combination of a substantially cylindrical column and an inverted conical table in a stationary and upright state, hot metal from the blast furnace or hot metal from the blast furnace is dephosphorized in advance. It is an operation method of an upper bottom blown converter that decarburizes and refines the applied hot metal.
The converter has a common inner diameter D 1 (m) of the lower surface of the substantially cylindrical cylinder and the upper surface of the inverted truncated cone, and a furnace bottom diameter D 2 (m) of the converter which is the lower surface of the inverted truncated cone. The ratio of D 1 / D 2 is in the range of 1.5 to 2.5.
The operating conditions for top-bottom blowing by the converter are the total flow rate Q O2 (Nm 3 / min / t) of the oxidizing gas supplied to the hot metal and the top-blowing gas flow rate Q t (Nm 3 / min / t). , A method of operating an upper bottom blown converter, characterized in that the bottom blown gas flow rate Q b (Nm 3 / min / t) satisfies the relationship of the following formula 1.
［式１］
[Equation 1]
なお、前記のように構成される本発明に係る上底吹き転炉の操業方法は、また、
（１）上吹きランスから酸化性ガスを吹き付けるとともに、炉底部に設けた底吹き羽口から撹拌用不活性ガスを吹き込むこと、
（２）上吹きランスから石灰系媒溶剤を吹き付けることにより、スラグ塩基度（ｍａｓｓ％ＣａＯ／ｍａｓｓ％ＳｉＯ２）（以下、「ｍａｓｓ％」は「％」として表記する）を２．４〜３．６に調整すること、
がより好ましい実施形態になりうるものと考えられる。
In addition, the operation method of the upper bottom blown converter according to the present invention configured as described above is also described.
(1) Blowing oxidizing gas from the top blowing lance and blowing inert gas for stirring from the bottom blowing tuyere provided at the bottom of the furnace.
(2) By spraying a lime-based solvent from the top-blown lance, the slag basicity (mass% CaO / mass% SiO 2 ) (hereinafter, "mass%" is expressed as "%") is 2.4 to 3. Adjust to .6,
Is considered to be a more preferred embodiment.
前述した構成にかかる本発明方法の上底吹き転炉の操業方法によれば、スラグ中にＦｅＯを過剰に生成させることなく、溶銑の脱炭処理を効率よく行うことができると共に、鉄歩留まりを向上させることができる。したがって、本発明方法の採用により、コストの上昇を招くことなく低燐鋼の生産性の向上を図ることができる。 According to the method of operating the top-bottom blown converter of the method of the present invention according to the above-described configuration, the decarburization treatment of hot metal can be efficiently performed without excessively generating FeO in the slag, and the iron yield can be increased. Can be improved. Therefore, by adopting the method of the present invention, it is possible to improve the productivity of low-phosphorus steel without causing an increase in cost.
また、本発明によれば、脱燐効率を低下させることなく上底吹き転炉の効率的な操業ができる。 Further, according to the present invention, the upper bottom blown converter can be efficiently operated without lowering the dephosphorization efficiency.
以下、本発明を具体的に説明する。まず、本発明を開発するに至った経緯について説明する。 Hereinafter, the present invention will be specifically described. First, the background leading to the development of the present invention will be described.
発明者らは、転炉精錬の冶金的特性に及ぼす転炉内溶鉄浴形状すなわち炉体形状の影響を調査するため、円柱形状の直胴部をもち、その下に逆円錐台形状の炉底部を設けた上底吹き転炉を用い、直胴部の炉内径Ｄ１と炉底径Ｄ２との比Ｄ１／Ｄ２を種々変えて試験を行った。 In order to investigate the effect of the molten iron bath shape in the converter, that is, the shape of the furnace body, on the metallurgical properties of converter refining, the inventors have a columnar straight body and an inverted conical trapezoidal bottom under it. the upper base with a blown converter provided, were variously changed by testing the ratio D 1 / D 2 of the furnace inside diameter D 1 and Rosoko径D 2 of the cylindrical body portion.
図１、図２は、この試験で使用した５ｔ規模の転炉設備１の概略図である。図示の２は上吹きランス、３は転炉炉体、４は鉄皮、５は炉壁耐火物、６は出湯口、７はガス導入管、８は底吹き羽口、９は溶鉄、１０はスラグ、１１は上吹き酸素ガス、１２は底吹きガス気泡、１３は石灰系媒溶剤である。 1 and 2 are schematic views of a 5t scale converter facility 1 used in this test. In the figure, 2 is a top-blown slag, 3 is a converter body, 4 is an iron skin, 5 is a refractory on the furnace wall, 6 is a hot water outlet, 7 is a gas inlet pipe, 8 is a bottom-blown tuyere, 9 is molten iron, and 10 Is a slag, 11 is a top-blown oxygen gas, 12 is a bottom-blown gas bubble, and 13 is a lime-based medium solvent.
この試験では、上吹きランス２から精錬用の上吹き酸素ガス（酸化性ガス）１１および石灰系媒溶剤１３を吹き付けると同時に炉底部に設けた底吹き羽口８からは撹拌用不活性ガスを吹き込んで、所定の初期燐濃度［％Ｐ］ｉの溶銑を脱炭処理をし、処理後のスラグ中ＦｅＯ濃度（％ＦｅＯ）および溶鋼中燐濃度［％Ｐ］ｆを測定した。ここで、上吹きランス２から吹き付ける精錬用酸化性ガスとしては、工業用純酸素ガスを使用し、底吹き羽口８から吹き込む撹拌用不活性ガスとしては、Ａｒガスを用いた。 In this test, the top-blown oxygen gas (oxidizing gas) 11 for refining and the lime-based medium solvent 13 were sprayed from the top-blown lance 2, and at the same time, the bottom-blown tuyere 8 provided at the bottom of the furnace sprayed an inert gas for stirring. By blowing in, the hot metal having a predetermined initial phosphorus concentration [% P] i was decarburized, and the FeO concentration (% FeO) in the slag and the phosphorus concentration [% P] f in the molten steel after the treatment were measured. Here, an industrial pure oxygen gas was used as the refining oxidizing gas blown from the top blowing lance 2, and an Ar gas was used as the stirring inert gas blown from the bottom blowing tuyere 8.
上記構成の転炉において、転炉炉体内に溶銑を装入した場合、転炉を静置直立した状態では、図２に示すように、全装入量（溶銑とスクラップ等の装入量合計）Ｗ、直胴部下部と逆円錐台形状の上部との共通する炉内径Ｄ１、逆円錐台形状の下部にあたる炉底径Ｄ２、直胴部での浴高さＨ１および逆円錐台形状の浴高さＨ２となる溶鉄浴が形成される。この試験において、発明者らは、転炉内溶鉄浴形状を表す指標として炉内径比Ｄ１／Ｄ２を用いて、全装入量Ｗ，逆円錐台形状の浴高さＨ２および直胴部の炉内径Ｄ１を一定とし、炉底径Ｄ２を変化させることで溶鉄浴形状を種々に調節した。 In the converter with the above configuration, when hot metal is charged into the converter furnace, the total charge (total charge of hot metal and scrap, etc.) is shown in FIG. 2 when the converter is standing upright. ) W, common furnace inside diameter D 1, the lower falls furnace bottom diameter D 2 of the inverted truncated cone shape, the bath height H 1 and inverted truncated cone in the straight body portion of the upper portion of the cylindrical body portion to bottom inverted truncated cone shape A molten iron bath having a shape bath height H 2 is formed. In this test, the inventors used the furnace inner diameter ratio D 1 / D 2 as an index showing the shape of the molten iron bath in the converter, and used the total charge W, the inverted truncated cone-shaped bath height H 2, and the straight cylinder. the furnace inside diameter D 1 of the section is constant, to adjust the molten iron bath shapes variously changing the Rosoko径D 2.
上記試験で使用した上吹きランス２は、先端部に同一形状の４個のラバールノズル型の噴射ノズル（酸素ガス吹き付け用）を、ノズル傾角１７°として上吹きランス２中心軸に対し同一円周上に等間隔で配置したものであり、先端中心部に１個のストレートノズル型の噴射ノズル（石灰系媒溶剤吹き付け用）を、ノズル傾角０°で配置したものである。なお、このラバールノズル型の噴射ノズルのスロート径は１０．０ｍｍ、出口径は１３．０ｍｍであり、ストレートノズル型の噴射ノズルの口径は１０．０ｍｍである。また、底吹き羽口８は、内径２．０ｍｍの管を６本均等配置して炉底に埋め込み、溶鉄内に底吹きガスを吹き込んだ。 The top blown lance 2 used in the above test has four Laval nozzle type injection nozzles (for blowing oxygen gas) of the same shape at the tip, and the nozzle tilt angle is 17 °, and the top blown lance 2 is on the same circumference with respect to the central axis. One straight nozzle type injection nozzle (for spraying a lime-based medium solvent) is arranged at a nozzle tilt angle of 0 ° at the center of the tip. The throat diameter of this Laval nozzle type injection nozzle is 10.0 mm, the outlet diameter is 13.0 mm, and the diameter of the straight nozzle type injection nozzle is 10.0 mm. Further, in the bottom blowing tuyere 8, six pipes having an inner diameter of 2.0 mm were evenly arranged and embedded in the furnace bottom, and the bottom blowing gas was blown into the molten iron.
この試験において、総酸素流量ＱＯ２を２．５Ｎｍ３／ｍｉｎ／ｔ、上吹き酸素ガス流量Ｑｔを２．５Ｎｍ３／ｍｉｎ／ｔ、ランス高さを６００ｍｍ、底吹きＡｒガス流量Ｑｂを０．０３Ｎｍ３／ｍｉn／tとし、炉内径比Ｄ１／Ｄ２を１．０〜３．０の範囲で種々に変更して、溶鉄中炭素濃度が０．０５ｍａｓｓ％以下になるまで脱炭処理を行い、冶金反応特性を調査した。なお、生石灰は、炉内に生成されるスラグの塩基度（％ＣａＯ／％ＳｉＯ２）が３．０となるように、その添加量を調整した。 In this test, the total oxygen flow rate Q O2 was 2.5 Nm 3 / min / t, the top-blown oxygen gas flow rate Q t was 2.5 Nm 3 / min / t, the lance height was 600 mm, and the bottom-blown Ar gas flow rate Q b . Set to 0.03 Nm 3 / min / t, change the furnace inner diameter ratio D 1 / D 2 in various ways in the range of 1.0 to 3.0, and decarburize until the carbon concentration in molten iron becomes 0.05 mass% or less. The treatment was performed and the metallurgical reaction characteristics were investigated. The amount of quicklime added was adjusted so that the basicity (% CaO /% SiO 2 ) of the slag produced in the furnace was 3.0.
次に、ランス高さを６００ ｍｍとして一定とし、酸素ガス流量比ＱＯ２／(Ｑｔ＋Ｑｂ)を０．９３〜０．９９の範囲で種々に変更した条件で、上記試験と同様に、炉内径比Ｄ１／Ｄ２を１．０〜３．０の範囲で種々に変更して、冶金反応特性を調査した。 Next, the lance height was kept constant at 600 mm, and the oxygen gas flow rate ratio Q O2 / (Q t + Q b ) was variously changed in the range of 0.93 to 0.99, as in the above test. The metallurgical reaction characteristics were investigated by variously changing the furnace inner diameter ratio D 1 / D 2 in the range of 1.0 to 3.0.
上記試験条件および結果を表１−１、１−２、また図３、図４、図５に示す。 The test conditions and results are shown in Tables 1-1 and 1-2, as well as in FIGS. 3, 4, and 5.
上掲の表１−１、表１−２、図３から明らかなように、炉内径比Ｄ１／Ｄ２の増加に伴い脱炭処理後のスラグ中ＦｅＯ濃度（ＦｅＯ）が減少することがわかった。また、酸素ガス流量比ＱＯ２／(Ｑｔ＋Ｑｂ)が０．９３〜０．９９の範囲では、酸素ガス流量比ＱＯ２／(Ｑｔ＋Ｑｂ)の値によらず、炉内径比Ｄ１／Ｄ２の増加に伴いスラグ中ＦｅＯ濃度（ＦｅＯ）は減少した。 As is clear from Tables 1-1, 1-2, and FIG. 3 above, the FeO concentration (FeO) in the slag after the decarburization treatment may decrease as the furnace inner diameter ratio D 1 / D 2 increases. all right. Further, when the oxygen gas flow rate ratio Q O2 / (Q t + Q b ) is in the range of 0.93 to 0.99, the furnace inner diameter ratio D is irrespective of the value of the oxygen gas flow rate ratio Q O 2 / (Q t + Q b ). The FeO concentration (FeO) in the slag decreased with the increase of 1 / D 2 .
また、図４から明らかなように、酸素ガス流量比ＱＯ２／(Ｑｔ＋Ｑｂ)が０．９４〜０．９８の場合は、炉内径比Ｄ１／Ｄ２が１．０〜３．０の範囲において、脱炭処理後の溶鋼中燐濃度［％Ｐ］ｆが極小となる炉内径比Ｄ１／Ｄ２が存在することがわかった。一方、ＱＯ２／(Ｑｔ＋Ｑｂ)が０．９３および０．９９の場合は、炉内径比Ｄ１／Ｄ２が１．０〜３．０の範囲において、溶鋼中燐濃度［％Ｐ］ｆが極小となる炉内径比Ｄ１／Ｄ２は存在せず、単純増加または単純減少することがわかった。 Further, as is clear from FIG. 4, when the oxygen gas flow rate ratio Q O2 / (Q t + Q b ) is 0.94 to 0.98, the furnace inner diameter ratio D 1 / D 2 is 1.0 to 3. It was found that in the range of 0, there is a furnace inner diameter ratio D 1 / D 2 in which the phosphorus concentration [% P] f in the molten steel after the decarburization treatment is minimized. On the other hand, when Q O2 / (Q t + Q b ) is 0.93 and 0.99, the phosphorus concentration in molten steel [% P] is in the range of the furnace inner diameter ratio D 1 / D 2 of 1.0 to 3.0. ] It was found that there was no furnace inner diameter ratio D 1 / D 2 in which f was minimized, and that it simply increased or decreased.
ここで、溶銑中燐濃度［％Ｐ］ｉにばらつきがあることから、脱燐率（[％Ｐ]ｉ-[％Ｐ]ｆ）／ [％Ｐ]ｉを計算して比較することとした。表1および図５から、炉内径比Ｄ１／Ｄ２が１．５以上で脱燐率が向上し、２．５を超えると脱燐率が低下することが判った。炉内径比Ｄ１／Ｄ２が１．５〜２．５の範囲で酸素ガス流量比ＱＯ２／(Ｑｔ＋Ｑｂ)が０．９９の場合には脱燐しないものがあり、０．９３〜０．９４では脱燐率が変わらない結果が得られた。 Here, since the phosphorus concentration in hot metal [% P] i varies, it was decided to calculate and compare the dephosphorization rate ([% P] i -[% P] f ) / [% P] i . .. From Table 1 and FIG. 5, it was found that when the furnace inner diameter ratio D 1 / D 2 was 1.5 or more, the dephosphorization rate was improved, and when it exceeded 2.5, the dephosphorization rate was decreased. When the furnace inner diameter ratio D 1 / D 2 is in the range of 1.5 to 2.5 and the oxygen gas flow rate ratio Q O 2 / (Q t + Q b ) is 0.99, some do not dephosphorize, 0.93. The result that the dephosphorization rate did not change was obtained at ~ 0.94.
つまり、炉内径比Ｄ１／Ｄ２が１．５以上では脱炭処理後のスラグ中ＦｅＯ濃度（ＦｅＯ）の低減効果が見られ、脱燐率も向上している。一方、炉内径比Ｄ１／Ｄ２が２．５を超えても、脱炭処理後のスラグ中ＦｅＯ濃度（ＦｅＯ）の低減効果は飽和しているうえ、脱燐率が低下し、炉底面積あたりの底吹きガス流量が増大して炉底寿命の低下につながり好ましくない。したがって、炉内径比Ｄ１／Ｄ２は１．５〜２．５の範囲とする。 That is, when the furnace inner diameter ratio D 1 / D 2 is 1.5 or more, the effect of reducing the FeO concentration (FeO) in the slag after the decarburization treatment is observed, and the dephosphorization rate is also improved. On the other hand, even if the furnace inner diameter ratio D 1 / D 2 exceeds 2.5, the effect of reducing the FeO concentration (FeO) in the slag after the decarburization treatment is saturated, and the dephosphorization rate is lowered, so that the furnace bottom It is not preferable because the bottom blowing gas flow rate per area increases and the life of the bottom of the furnace is shortened. Therefore, the furnace inner diameter ratio D 1 / D 2 is in the range of 1.5 to 2.5.
なお、酸素ガス流量比ＱＯ２／(Ｑｔ＋Ｑｂ)は、０．９８を超えるとほとんど脱燐できない場合があり、０．９４未満では、脱燐率の向上効果が飽和するうえ、非酸化性ガスの原単位が増加してコスト増となり、また、非酸化性ガスを底吹きガスとして供給する場合には、底吹きガス量が増えすぎて炉底寿命の低下につながるので好ましくない。したがって、酸素ガス流量比ＱＯ２／(Ｑｔ＋Ｑｂ)は、０．９４〜０．９８の範囲とする。 If the oxygen gas flow rate ratio Q O2 / (Q t + Q b ) exceeds 0.98, it may be almost impossible to dephosphorize, and if it is less than 0.94, the effect of improving the dephosphorization rate is saturated and non-oxidation is performed. It is not preferable to supply the non-oxidizing gas as the bottom-blown gas because the basic unit of the sex gas increases and the cost increases, and the amount of the bottom-blown gas increases too much, which leads to a decrease in the life of the bottom of the furnace. Therefore, the oxygen gas flow rate ratio Q O2 / (Q t + Q b ) is in the range of 0.94 to 0.98.
即ち、転炉の炉体形状および転炉内溶鉄浴形状を制御することで、所定の上底吹き条件におけるスラグ‐メタル間反応効率を最大化することが可能であることがわかった。 That is, it was found that it is possible to maximize the slag-metal reaction efficiency under predetermined top-bottom blowing conditions by controlling the shape of the furnace body and the shape of the molten iron bath in the converter.
なお、本発明は、上記知見に基づいてなされたものであり、本発明に係る転炉の炉体は、溶銑を収容し、静置・直立した際の溶鉄浴の縦断面形状が円柱と逆円錐台形とを組合わせた形状となる転炉であることが前提となる。 The present invention has been made based on the above findings, and the furnace body of the converter according to the present invention accommodates hot metal, and the vertical cross-sectional shape of the molten iron bath when standing or standing upright is opposite to that of a cylinder. It is premised that the converter has a shape that is a combination of a conical trapezoid.
また、上記試験では、酸化性ガスの上吹きおよび不活性ガスの底吹きを行うことが可能な上底吹き転炉を用いたが、精錬用酸化性ガスの底吹きを行うことが可能な上底吹き転炉を用いてもよい。 Further, in the above test, an upper bottom blowing converter capable of top blowing an oxidizing gas and bottom blowing of an inert gas was used, but it is possible to perform bottom blowing of an oxidizing gas for refining. A bottom blown converter may be used.
本発明において使用する溶銑は、高炉から出銑した高燐溶銑（［％Ｐ］：０．０７０〜０．１４０）あるいは高炉から出銑した後に予め脱燐処理を施した低燐溶銑（［％Ｐ］：０．０１０〜０．０４０）を用いることが前提である。その低燐溶銑としては、高炉から出銑した溶銑を溶銑鍋やトピードカー等の溶銑搬送容器で受銑した後、搬送容器内または脱炭処理用の転炉まで搬送して、予め脱燐処理を施したものを使用することがとりわけ好ましい。また、前記脱燐処理を行う際に、少ない石灰系媒溶剤の添加量で効率的に脱燐処理するために、該脱燐処理前に予め溶銑を脱珪処理し、溶銑中珪素濃度を０．２０％以下、望ましくは０．１０％以下とすることが好ましい。 The hot metal used in the present invention is high-phosphorus hot metal ([% P]: 0.070 to 0.140) from the blast furnace or low-phosphorus hot metal ([% P]) that has been dephosphorized in advance after being out of the blast furnace. P]: It is premised that 0.010 to 0.040) is used. As the low-phosphorus hot metal, the hot metal from the blast furnace is received in a hot metal transport container such as a hot metal pot or a topedo car, and then transported into the transport container or to a converter for decarburization treatment to be dephosphorized in advance. It is especially preferable to use the given one. Further, when performing the dephosphorization treatment, in order to efficiently dephosphorize with a small amount of a lime-based medium solvent added, the hot metal is desiliconized in advance before the dephosphorization treatment to reduce the silicon concentration in the hot metal to 0. It is preferably 20% or less, preferably 0.10% or less.
上吹きランスから吹き込む酸化性ガスとしては、酸素ガスが一般的であるが、酸素ガスと希ガスの混合ガス、空気および酸素富化空気などを用いることができる。本発明で使用する酸化性ガスとは、酸素濃度が空気と同等またはそれ以上である酸素含有ガスの全てである。上吹きランスから吹き込む石灰系媒溶剤として、生石灰を用いることができ、炉内に生成されるスラグの塩基度（％ＣａＯ／％ＳｉＯ２）は２．４〜３．６になるように調整することが好ましい。スラグ塩基度が２．４未満では、スラグ塩基度が低すぎて、脱燐能が低くなりすぎ、３．６を超えて添加すると石灰原単位が多くなりすぎて、コスト高になるので好ましくない。 Oxygen gas is generally used as the oxidizing gas blown from the top-blown lance, but a mixed gas of oxygen gas and a rare gas, air, oxygen-enriched air, or the like can be used. The oxidizing gas used in the present invention is all oxygen-containing gases having an oxygen concentration equal to or higher than that of air. Quick lime can be used as the lime-based medium solvent blown from the top-blown lance, and the basicity (% CaO /% SiO 2 ) of the slag produced in the furnace is adjusted to 2.4 to 3.6. Is preferable. If the slag basicity is less than 2.4, the slag basicity is too low and the dephosphorylation ability is too low, and if it is added in excess of 3.6, the lime basic unit becomes too large and the cost is high, which is not preferable. ..
底吹き羽口から吹き込まれる不活性ガスとしては、ＡｒガスやＨｅガスなどの希ガスまたはＮ２ガスを用いることができる。 As the inert gas blown from the bottom blowing tuyere, a rare gas such as Ar gas or He gas or N 2 gas can be used.
以上説明したように、本発明によれば、スラグ中ＦｅＯ濃度を低減し、鉄歩留を向上することができるため、転炉での生産性が向上する。併せて、低燐溶鋼を安定して生産できる。 As described above, according to the present invention, the FeO concentration in the slag can be reduced and the iron yield can be improved, so that the productivity in the converter is improved. At the same time, low-phosphorus molten steel can be produced stably.
この実施例では、図１に示す転炉設備と同様の構成のものを用いた。即ち、容量が３００ｔの上底吹き転炉（酸素ガス上吹きおよびＡｒガス底吹き）において、高炉から出銑した高燐溶銑あるいは高炉から出銑した後に予め脱燐処理を施した溶銑を用いて脱炭処理した。使用した上吹きランスは、先端部に同一形状の４個のラバールノズル型の噴射ノズル（酸素ガス吹き付け用）を、ノズル傾角１７°として上吹きランスの中心軸に対して同一円周上に等間隔で配置してあり、中心に1個のストレートノズル型の噴射ノズル（石灰系媒溶剤投射用）を、ノズル傾角０°で配置したものである。ラバールノズル型の噴射ノズルのスロート径は５０．０ｍｍ、出口径は５３．０ｍｍであり、ストレートノズル型の噴射ノズルの口径は５０．０ｍｍである。 In this example, the equipment having the same configuration as the converter equipment shown in FIG. 1 was used. That is, in a top-bottom blown converter having a capacity of 300 tons (oxygen gas top-blown and Ar gas bottom-blown), a high-phosphorus hot metal tapped from the blast furnace or a hot metal that has been dephosphorized in advance after tapping from the blast furnace is used. Decarburized. The top-blowing lance used was four Laval nozzle-type injection nozzles (for blowing oxygen gas) with the same shape at the tip, with a nozzle tilt angle of 17 ° and even intervals on the same circumference with respect to the central axis of the top-blowing lance. A straight nozzle type injection nozzle (for projecting a lime-based medium solvent) is arranged at a nozzle tilt angle of 0 ° in the center. The throat diameter of the Laval nozzle type injection nozzle is 50.0 mm, the outlet diameter is 53.0 mm, and the diameter of the straight nozzle type injection nozzle is 50.0 mm.
前記上底吹き転炉内に、温度が１２８０〜１３１０℃の溶銑を装入した。次いで、底吹き羽口からＡｒガスを撹拌用ガスとして溶銑中に吹き込みながら、上吹きランスから酸素ガスを溶銑浴面に向けて吹き付けて、脱炭処理を開始した。使用した溶銑の化学成分を表２に示す。 Hot metal having a temperature of 1280 to 1310 ° C. was charged into the upper bottom blown converter. Next, while Ar gas was blown into the hot metal as a stirring gas from the bottom blowing tuyere, oxygen gas was blown from the top blowing lance toward the hot metal bath surface to start the decarburization treatment. Table 2 shows the chemical composition of the hot metal used.
脱炭処理中に、上吹きランスから石灰系媒溶剤として生石灰を投射し、溶鉄中炭素濃度が０．０５ｍａｓｓ％以下になるまで脱炭処理を行った。生石灰は、炉内に生成されるスラグの塩基度（％ＣａＯ／％ＳｉＯ２）が３．０となるように、その添加量を調整した。 During the decarburization treatment, quick lime was projected from the top-blown lance as a lime-based medium solvent, and the decarburization treatment was performed until the carbon concentration in the molten iron became 0.05 mass% or less. The amount of quicklime added was adjusted so that the basicity (% CaO /% SiO 2 ) of the slag produced in the furnace was 3.0.
前記脱炭処理において、溶銑装入後かつ脱炭処理開始前の炉内径比Ｄ１／Ｄ２を２．０、脱炭処理中の酸素ガス流量比ＱＯ２／(Ｑｔ＋Ｑｂ)を０．９６とした（発明例１、発明例２）。 In the decarburization treatment, the furnace inner diameter ratio D 1 / D 2 after the hot metal charging and before the start of the decarburization treatment is 2.0, and the oxygen gas flow rate ratio Q O 2 / (Q t + Q b ) during the decarburization treatment is 0. It was set to .96 (Invention Example 1, Invention Example 2).
また、比較のために、炉内径比Ｄ１／Ｄ２のみを１．２に変更した条件（比較例１、比較例４）、酸素ガス流量比ＱＯ２／(Ｑｔ＋Ｑｂ)のみを０．９９に変更した条件（比較例２、比較例５）、Ｄ１／Ｄ２を１．２かつＱＯ２／(Ｑｔ＋Ｑｂ)を０．９９に変更した条件（比較例３、比較例６）でも脱炭処理を行った。 For comparison, only the condition in which only the furnace inner diameter ratio D 1 / D 2 was changed to 1.2 (Comparative Example 1 and Comparative Example 4) and the oxygen gas flow rate ratio Q O 2 / (Q t + Q b ) were 0. Conditions changed to .99 (Comparative Example 2, Comparative Example 5), conditions in which D 1 / D 2 was changed to 1.2 and Q O 2 / (Q t + Q b ) was changed to 0.99 (Comparative Example 3, Comparative Example) 6) was also decarburized.
前述の条件で転炉の操業を行ない、その結果を表３−１、表３−２としてまとめた。 The converter was operated under the above conditions, and the results are summarized in Table 3-1 and Table 3-2.
表３−１、表３−２から明らかなように、比較例１〜３に比べて、発明例１では、脱炭処理後のスラグ中ＦｅＯ濃度（ＦｅＯ）および溶鋼中燐濃度［％Ｐ］ｆが最も低減し、脱燐率（[％Ｐ]ｉ-[％Ｐ]ｆ）／ [％Ｐ]ｉが最も高かった。同様に、比較例４〜６に比べて、発明例２では、脱炭処理後のスラグ中ＦｅＯ濃度（ＦｅＯ）および溶鋼中燐濃度［％Ｐ］ｆが最も低減し、脱燐率（[％Ｐ]ｉ-[％Ｐ]ｆ）／[％Ｐ]ｉが最も高かった。このように、本発明方法を適用することで、鉄歩留を向上させながら低燐鋼の溶製に適した転炉操業が可能となることが確認できた As is clear from Tables 3-1 and 3-2, in Invention Example 1, the FeO concentration (FeO) in the slag and the phosphorus concentration [% P] in the molten steel after the decarburization treatment were compared with those of Comparative Examples 1 to 3. f was the lowest, and the dephosphorization rate ([% P] i -[% P] f ) / [% P] i was the highest. Similarly, as compared with Comparative Examples 4 to 6, in Invention Example 2, the FeO concentration (FeO) in the slag and the phosphorus concentration [% P] f in the molten steel after the decarburization treatment were most reduced, and the dephosphorization rate ([%]. P] i -[% P] f ) / [% P] i was the highest. As described above, it was confirmed that by applying the method of the present invention, it is possible to operate a converter suitable for melting low-phosphorus steel while improving the iron yield.
１ 転炉設備
２ 上吹きランス
３ 転炉炉体
４ 鉄皮
５ 炉壁耐火物
６ 出湯口
７ ガス導入管
８ 底吹き羽口
９ 溶鉄
１０ スラグ
１１ 上吹き酸素ガス
１２ 底吹きガス気泡
１３ 石灰系媒溶剤
1 converter equipment 2 top blown lance 3 converter furnace body 4 iron skin 5 refractory on the furnace wall 6 hot water outlet 7 gas introduction pipe 8 bottom blown tuyere 9 molten iron 10 slag 11 top blown oxygen gas 12 bottom blown gas bubbles 13 lime Medium solvent
Claims (3)
前記転炉は、前記略円柱の下面と前記逆円錐台の上面との共通する炉内径Ｄ１（ｍ）と、前記逆円錐台の下面である転炉の炉底径Ｄ２（ｍ）との比Ｄ１／Ｄ２が１．５〜２．５の範囲である炉体形状の転炉とし、
該転炉による上底吹きの操業条件が、溶銑に供給される酸化性ガスの総流量ＱＯ２（Ｎｍ３／ｍｉｎ／ｔ）と、上吹きガス流量Ｑｔ（Ｎｍ３／ｍｉｎ／ｔ）と、底吹きガス流量Ｑｂ（Ｎｍ３／ｍｉｎ／ｔ）とが下記数式１の関係を満たすことを特徴とする上底吹き転炉の操業方法。
［式１］
Using a converter with a furnace body shape that is a combination of a substantially cylindrical column and an inverted conical table in a stationary and upright state, decarburize the hot metal that has been tapped from the blast furnace or the hot metal that has been dephosphorized in advance after tapping from the blast furnace. It is the operation method of the upper bottom blown furnace for refining.
The converter has a common inner diameter D 1 (m) of the lower surface of the substantially cylindrical cylinder and the upper surface of the inverted truncated cone, and a furnace bottom diameter D 2 (m) of the converter which is the lower surface of the inverted truncated cone. A converter with a furnace body shape in which the ratio D 1 / D 2 is in the range of 1.5 to 2.5.
The operating conditions for top-bottom blowing by the converter are the total flow rate Q O2 (Nm 3 / min / t) of the oxidizing gas supplied to the hot metal and the top-blowing gas flow rate Q t (Nm 3 / min / t). , A method of operating an upper bottom blown converter, characterized in that the bottom blown gas flow rate Q b (Nm 3 / min / t) satisfies the relationship of the following formula 1.
[Equation 1]
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