A steelmaking furnace that refines molten pig iron from a blast furnace into molten steel. The word "furnace" refers to a furnace that converts pig iron into steel. The pear-shaped furnace body is supported on both sides and can rotate back and forth, which also corresponds to the name "converter." Converters began with the acid bottom-blown converter invented by Bessemer in England in 1856, followed by the basic bottom-blown converter invented by Thomas in England in 1879, the pure oxygen top-blown converter and oxygen bottom-blown converter after World War II, and finally the combined top- and bottom-blown converter. [Iguchi Yasutaka] Bessemer ConverterThe furnace body is lined with silica bricks, and has a top opening for charging, slag removal, and tapping that is eccentric to the center line of the furnace body. The bottom of the furnace has an air-blowing tuyere and is replaceable. The capacity of the furnace is indicated by the tons of molten steel that can be refined at one time, and some are close to 30 tons. Molten pig iron is charged, and the silicon, manganese, and carbon in the molten pig iron are burned by the oxygen in the blown-in air, raising the temperature. It is a very efficient steelmaking furnace that does not require fuel, and steel is produced in about 20 minutes. The heating surface of the furnace is lined with an acidic material, so it is refined with acidic slag. Therefore, the phosphorus and sulfur in the molten pig iron cannot be removed, so low-phosphorus, low-sulfur hematite pig iron is required. This method developed in the United States, the Soviet Union, and Northern Europe, which produce high-grade ores, but is not used today. [Iguchi Yasutaka] Thomas ConverterThe shape is the same as a Bessemer converter, but it uses basic dolomite as the refractory material and is refined with basic slag, making it possible to dephosphorize and desulfurize. However, because it is basic, it requires molten pig iron with a low silicon content, and since the heat generated by the oxidation of silicon cannot be used, it requires the heat of oxidation of 2 to 2.5% phosphorus. It developed in Western Europe, which produces high-phosphorus iron ore, and was once the mainstream steelmaking method in France, Belgium, and Luxembourg. The slag with a high phosphorus content produced by this method can be used as fertilizer, known as Thomas-phosphorus fertilizer. These bottom-air-blown converters had limitations on the molten iron composition depending on the type of refractory and heat source, and air-blown converters caused heat loss due to nitrogen, and at the same time, nitrogen was absorbed into the molten steel, adversely affecting the properties of the steel. This was the main reason why converters were overwhelmed by open hearth furnaces, despite being highly productive and energy-saving steelmaking furnaces. For this reason, oxygen enrichment was implemented, which improved the nitrogen problem, but the drawback of high oxygen levels in the molten steel due to dephosphorization remained. There was also a limit to how much oxygen enrichment could be achieved due to the risk of tuyere erosion caused by oxygen enrichment. [Iguchi Yasutaka] Pure oxygen top blowing converterAlso called LD converter. A lance is lowered directly above the molten iron from the throat on the center line of the furnace body, and pure oxygen gas is blown into the furnace. The hearth has no tuyere and is integrated with the belly, with a tap hole at the top of the belly. The refractories are basic, and magnesia, tar dolomite, and magnesium-carbon bricks are used. Oxygen top-blowing is also seen in the Bessemer patent, but oxygen was expensive at the time and was not realized. Later, high-purity oxygen became cheap through the Linde-Frenkel process, making it possible to use it in steelmaking. The pure oxygen top-blowing converter process was semi-industrialized in Switzerland by the German R. Durrer in 1946, and was later industrialized in Linz and Donabitz, Austria (1953). The name LD process is said to be derived from the initials of these place names. This process has many great features, including the ease with which low-nitrogen steel can be obtained, high thermal efficiency with little heat loss to waste gas, no particular restrictions on the composition of the molten iron, and the possibility of mixing scrap iron at about 30%. For these reasons, it developed rapidly in Japan and Europe during the post-World War II reconstruction period. In Europe, which produces high-phosphorus pig iron, other methods were developed, such as the LD-AC process (OLP-OCP), which sprays powdered quicklime along with oxygen to promote the production of slag effective for dephosphorization, the Kaldor process, which rotates the furnace body in an inclined or horizontal position to promote the reaction between the slag and the metal, and the rotor process. [Iguchi Yasutaka] Pure oxygen bottom blowing converterThe bottom blowing process, in which the molten steel is very well stirred and the refining reaction is promoted, has problems with wear and tear on the tuyere and hearth refractory, making it difficult to introduce pure oxygen, but in 1965 Canada developed a double-tube tuyere that simultaneously blows in a hydrocarbon gas and utilizes the endothermic cooling of the decomposition. By using this tuyere, West Germany succeeded in commercializing the oxygen bottom blowing converter process (OBM) in 1968. In the United States, US Steel developed it and named it Q-BOP. In France, the LWS process, which uses liquid fuel as a coolant, was developed. Bottom blowing has the advantages of less iron oxide in the slag, improved steel yield, and reduced oxygen in the molten steel, but it also has the disadvantage of increased hydrogen. [Iguchi Yasutaka] Top and bottom combined blowing converterIt is also called a pure oxygen top-and-bottom blown converter or a top-and-bottom blown converter. It was developed to take advantage of the advantages of both bottom and top blowing, and some types use argon or carbon dioxide gas to cool the bottom blowing tuyere. The above steelmaking processes that use pure oxygen are collectively known as the Basic Oxygen Process (BOP). Some converters have a capacity of nearly 400 tons, and are equipped with waste gas recovery equipment and various sensing devices and are computer-controlled to produce much of the crude steel we produce today. In addition, extra-furnace refining has become more common, and the role of converters is changing. Extra-furnace refining involves desiliconization, dephosphorization, desulfurization, etc. in ladles or torpedo cars before the molten iron is charged into the converter, and further decarburization, deoxidization, and denitrification of the molten steel under vacuum after it is tapped from the converter. [Iguchi Yasutaka] ©Shogakukan "> Structure of Thomas Converter and Pure Oxygen Top-Blown Converter Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend |
高炉からの溶銑(ようせん)を溶鋼に精錬する製鋼炉。銑鉄を鋼に転化convertする炉という意味。また洋ナシ形の炉体は両側で支持されて前後に回転でき、これも転炉という名称と呼応する。 転炉は1856年イギリスのベッセマーにより発明された酸性底吹転炉に始まり、1879年イギリスのトーマスによる塩基性底吹転炉、第二次世界大戦後の純酸素上吹転炉、酸素底吹転炉、さらに上下吹複合吹錬転炉へと発展を続けている。 [井口泰孝] ベッセマー転炉炉体は珪石(けいせき)れんがで内張りされ、上部に炉体中心線より偏心した装入、排滓(はいさい)、出鋼用の炉口をもつ。炉底は空気吹き用羽口(はぐち)をもち交換可能である。炉の容量は1回で精錬できる溶鋼のトン数で示し、30トンに近いものもある。溶銑を装入し、吹き込んだ空気中の酸素により溶銑中のシリコン、マンガン、さらに炭素が燃焼し温度が上昇する。約20分間で鋼になるという、燃料を要しない非常に効率のよい製鋼炉である。炉の加熱面が酸性材料で裏張りされているため酸性スラグで精錬する。したがって、溶銑中のリン、硫黄(いおう)を除去できないので、低リン、低硫黄のヘマタイト銑が必要であり、高品位鉱を産するアメリカ、ソ連、北欧で発展したが、現在は用いられていない。 [井口泰孝] トーマス転炉形状はベッセマー転炉と変わらないが、耐火物に塩基性ドロマイトを用い、塩基性スラグで精錬するため、脱リン、脱硫が可能である。ただし塩基性であるからシリコンの低い溶銑を必要とし、シリコンの酸化発熱を利用できないため2~2.5%のリンの酸化熱を必要とする。高リン鉄鉱石を産する西欧で発展し、かつてフランス、ベルギー、ルクセンブルクでは製鋼法の主流を占めていた。本法によるリン含有量の高いスラグはトーマスリン肥として肥料になる。 これら空気底吹転炉では耐火物の種類と発熱源に対応して溶銑成分に制限があり、空気吹きのため窒素による熱損失と同時に、窒素が溶鋼に吸収され、鋼の性質に悪影響を及ぼす。これが、転炉が生産性が高く、省エネルギーの製鋼炉でありながら平炉に圧倒された大きな原因である。このため酸素富化が行われ、窒素の問題は改善されたが、脱リンによる溶鋼中の酸素が高くなる欠点は残った。また酸素富化による羽口溶損の点で富化に限界があった。 [井口泰孝] 純酸素上吹転炉LD転炉ともいう。炉体の中心線上の炉口よりランスを溶銑直上に降ろし、純酸素ガスを吹き付け吹錬する。炉底は羽口がなく炉腹と一体で、炉腹上部に出鋼孔がある。耐火物は塩基性で、マグネシア、タールドロマイト、マグカーボンれんがが用いられている。酸素上吹きはベッセマーの特許にもみられるが、当時は酸素が高価で実現しなかった。その後リンデ‐フレンケル法により高純度の酸素が安価になり製鋼への利用も可能になった。純酸素上吹転炉法はドイツのデューラーR. Durrerにより1946年スイスで半工業化に成功、その後オーストリアのリンツとドナビッツで工業化された(1953)。LD法という名称はこれらの地名の頭文字によるともいわれている。本法は低窒素鋼が容易に得られ、廃ガスへの熱損失が少なく熱効率が高く、溶銑成分にとくに制約がなく、また30%程度のくず鉄の配合も可能である、など非常に大きな特徴をもつ。そのため第二次世界大戦後の復興期の日本、ヨーロッパで急速に発展した。高リン銑を産するヨーロッパでは、酸素とともに粉状の生石灰を吹き付け脱リンに有効なスラグの生成を促進させるLD‐AC法(OLP‐OCP)、またスラグと金属間の反応を促進させるため炉体を傾斜あるいは横型として回転させるカルドー法、ローター法なども開発された。 [井口泰孝] 純酸素底吹転炉溶鋼の攪拌(かくはん)が非常によく精錬反応が促進される底吹法では、羽口、炉底耐火物の損耗という問題点があり、純酸素の導入が困難であったが、1965年カナダで炭化水素系ガスを同時に吹き込み、この分解の吸熱冷却を利用する二重管羽口が開発された。この羽口を利用することにより西ドイツで純酸素底吹転炉法(OBM)の工業化に成功した(1968)。アメリカではUSスチール社が開発し、Q‐BOPと名づけた。フランスでは冷却剤に液体燃料を使うLWS法が開発された。底吹きでは、スラグ中の酸化鉄が少なく、鋼の歩留り向上、溶鋼中の酸素の低減という利点があるが、水素の増加という欠点もある。 [井口泰孝] 上下吹複合吹錬転炉純酸素上底吹転炉、上底吹転炉ともいう。底吹きと上吹きの利点の両方を生かすため開発された転炉で、底吹き羽口の冷却にアルゴンや炭酸ガスを用いる形式のものもある。 以上の純酸素を用いる製鋼法は塩基性酸素製鋼法(Basic Oxygen Process=BOP)と総称される。転炉の容量で400トンに近いものもあり、廃ガスの回収装置や種々の感知装置を取り付けコンピュータ制御を行うなどし、現在の粗鋼の多くを生産する。また、炉外精錬が盛んになり、転炉の役割が変わりつつある。炉外精錬とは、溶銑を転炉へ装入前に、取鍋(とりべ)やトーピードカーtorpedo car(混銑車)で脱ケイ、脱リン、脱硫などを行ったり、転炉より出鋼後、溶鋼を真空下でさらに脱炭、脱酸、脱窒を行うことである。 [井口泰孝] ©Shogakukan"> トーマス転炉と純酸素上吹転炉の構造 出典 小学館 日本大百科全書(ニッポニカ)日本大百科全書(ニッポニカ)について 情報 | 凡例 |
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