JP2004292837A

JP2004292837A - Method for manufacturing raw material for sintering

Info

Publication number: JP2004292837A
Application number: JP2003082981A
Authority: JP
Inventors: Tetsuya Jinno; 哲也神野
Original assignee: JFE Steel Corp
Current assignee: JFE Steel Corp
Priority date: 2003-03-25
Filing date: 2003-03-25
Publication date: 2004-10-21
Anticipated expiration: 2023-03-25
Also published as: JP4175158B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing raw materials for sintering by which sintered ore with superior strength can be stably obtained. <P>SOLUTION: The raw materials for sintering can be manufactured by mixing iron ore with an SiO<SB>2</SB>-containing raw material using a drum mixer 5 to form an SiO<SB>2</SB>-containing layer composed of the SiO<SB>2</SB>-containing raw material around core ore composed of the coarse-grained iron ore, feeding pulverized iron oxide to the drum mixer 5 to form a pulverized iron oxide layer composed of the pulverized iron oxide on the surface of the SiO<SB>2</SB>-containing layer and then feeding a limestone type powdered raw material and a solid fuel type powdered raw material to the drum mixer 5. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、製鉄所の高炉用原料として用いられる焼結鉱の焼結用原料を製造する方法に関する。
【０００２】
【従来の技術】
製鉄所の高炉用原料として用いられる焼結鉱は、一般に、次のような方法で製造される。すなわち、図７に示すように、粒径１０ｍｍ以下の鉄鉱石１と珪石、蛇紋岩、ニッケルスラグ等のＳｉＯ_２含有原料２、石灰石などのＣａＯを含有する石灰石系粉原料３および粉コークス、無煙炭等の固体燃料系粉原料４を製造用の水分と共にドラムミキサー５に入れ、これらをドラムミキサー５で混合して擬似粒子と称される粒状物を得る。そして、混合工程で得られた擬似粒子をドワイトロイド式焼結機のパレット上に適当な厚さ（例えば５００〜７００ｍｍ）で置いて表層部の固体燃料を燃焼させ、その燃焼熱によって擬似粒子を焼結させて焼結ケーキとする。この焼結ケーキは破砕、整粒され、一定の粒径以上の焼結鉱を得る。一方、それ未満の粒径を有するものは返鉱となり、焼結用原料として再利用される。
【０００３】
このような方法で製造される焼結鉱のＪＩＳＭ８７１３で規定される被還元性（以下、単に被還元性またはＪＩＳ−Ｒ１と記す）と高炉でのガス利用率η_ＣＯとの関係を図８に、またガス利用率η_ＣＯと燃料比との関係を図９に示す。これらの図から明らかなように、焼結鉱の被還元性とガス利用率との間には正の相関があり、またガス利用率と燃料比との間には負の相関がある。このことから、焼結鉱の被還元性は高炉での燃料比と負の相関があることが分かり（図１０参照）、焼結鉱の被還元性を向上させると高炉での燃料比が低下する。従って、被還元性の高い焼結鉱は高炉用原料として好適な焼結鉱であると言えるが、焼結鉱の冷間強度も高炉での通気性を確保するうえで重要な因子であり、焼結鉱の冷間強度に下限基準を設定して高炉を操業している場合がほとんどである。
【０００４】
なお、高炉でのガス利用率η_ＣＯおよび燃料比は、
η_ＣＯ＝ＣＯ_２（％）／〔ＣＯ（％）＋ＣＯ_２（％）〕
燃料比＝（石炭＋コークス）の使用量（ｋｇ）／銑鉄（１ｔｏｎ）
で定義され、ＣＯ_２（％）及びＣＯ（％）はいずれも高炉の炉頂ガス中の体積％である。
表１に、焼結鉱を形成する主要鉱物組織であるカルシウムフェライト：ｎＣａＯ・Ｆｅ_２Ｏ_３、ヘマタイト（赤鉄鉱）：Ｆｅ_２Ｏ_３、カルシウムシリケート：ＣａＯ・ＳｉＯ_２、マグネタイト（磁鉄鉱）：Ｆｅ_３０_４の４つの被還元性と引張強度を示す。
【０００５】
【表１】

【０００６】
表１に示すように、焼結鉱を形成する４つの主要鉱物組織のうち、被還元性の高いものはヘマタイトであり、引張強度の高いものはカルシウムフェライトである。従って、高炉用原料として好適な焼結鉱とは、図１１に示すような構造の焼結鉱、すなわち表層部が引張強度の高いカルシウムフェライトＣＦで形成され、かつ内部が被還元性の高いヘマタイトＨｅで形成された焼結鉱であると言える。
【０００７】
しかし、従来は、前述したように、鉄鉱石１、ＳｉＯ_２含有原料２、石灰石系粉原料３および固体燃料系粉原料４をドラムミキサー５で同時に混合して得られた擬似粒子を焼結用原料として焼結鉱を製造しているため、混合工程で得られる擬似粒子が図１２に示すような構造、すなわち核となる粗粒の鉄鉱石１の表面に石灰石系粉原料３や固体燃料系粉原料４、粉鉱石などが付着した構造となる。このため、図１２に示すような構造の擬似粒子をドワイトロイド式焼結機で焼結すると、焼結鉱の構造が図１３に示すような構造、すなわちヘマタイトＨｅ、カルシウムフェライトＣＦ、カルシウムシリケートＣＳ、マグネタイトＭｇの４つの鉱物組織が混在する構造となってしまい、被還元性に優れ且つ冷間強度の高い焼結鉱を安定して製造することが困難であった。
【０００８】
そこで、本出願人は特許文献１にて、焼結鉱の焼結用原料として、平均粒径が２ｍｍ以上の粗粒の鉄鉱石を核とする第一層を有し、その第一層の外表面を石灰石系粉原料や固体燃料系粉原料以外の平均粒径が２ｍｍ以下の粉鉱石およびＳｉＯ_２含有原料からなる第二層を有するとともに、さらに石灰石系粉原料および固体燃料系粉原料からなる第三層を有する焼結用擬似粒子を得ることが最適であることを見出した。この擬似粒子は、焼結過程でＣａＯとＳｉＯ_２の反応が遅れ、冷間強度の低いカルシウムシリケートの生成が抑制されることで、焼結鉱の表層部には冷間強度の高いカルシウムフェライトが生成され、また焼結鉱の内部には被還元性の高いヘマタイトが生成されるため、微細気孔が多くて被還元性に優れ且つ冷間強度の高い焼結鉱を安定して製造することが可能になる。
【０００９】
【特許文献１】
国際公開番号ＷＯ０１／９２５８８号公報
【００１０】
【発明が解決しようとする課題】
しかしながら、特許文献１に開示された擬似粒子で焼結鉱を製造した場合には、焼結工程での溶融体（スラグ）量が減少し、この溶融体量減少と溶融体量が偏析することにより、焼結鉱の強度低下や歩留まり低下などを生じることがあった。
本発明は、このような問題点に着目してなされたものであり、強度の良好な焼結鉱を安定して得ることのできる焼結用原料の製造方法を提供することを目的とするものである。
【００１１】
【課題を解決するための手段】
上記の目的を達成するために、請求項１の発明に係る焼結用原料の製造方法は、直径１０ｍｍ以下の鉄鉱石とＳｉＯ_２含有原料、石灰石系粉原料および固体燃料系粉原料を製造用水分と共にドラムミキサーで混合して焼結鉱の焼結用原料を製造する際に、前記鉄鉱石および前記ＳｉＯ_２含有原料を前記ドラムミキサーで混合して粗粒の鉄鉱石からなる核鉱石の周りに前記ＳｉＯ_２含有原料からなるＳｉＯ_２含有層を形成し、次いで前記ドラムミキサーに微粉酸化鉄を供給して前記ＳｉＯ_２含有層の表面に前記微粉酸化鉄からなる微粉酸化鉄層を形成した後、前記ドラムミキサーに前記石灰石系粉原料および前記固体燃料系粉原料を供給して前記焼結用原料を製造することを特徴とする。
【００１２】
請求項２の発明に係る焼結用原料の製造方法は、請求項１記載の焼結用原料の製造方法において、前記ドラムミキサーに前記鉄鉱石および前記ＳｉＯ_２含有原料を供給してから前記鉄鉱石が前記ドラムミキサーの排出口に到達するまでの滞留時間を１０〜１２０秒の範囲内に設定して、前記焼結用原料を製造することを特徴とする。
【００１３】
請求項３の発明に係る焼結用原料の製造方法は、請求項１記載の焼結用原料の製造方法において、前記ドラムミキサーに前記鉄鉱石および前記ＳｉＯ_２含有原料を供給してから前記鉄鉱石が前記ドラムミキサーの排出口に到達するまでの滞留時間を１０〜９０秒の範囲内に設定して、前記焼結用原料を製造することを特徴とする。
【００１４】
請求項４の発明に係る焼結用原料の製造方法は、請求項１乃至３のいずれか１項記載の焼結用原料の製造方法において、前記ドラムミキサーに前記石灰石系粉原料および前記固体燃料系粉原料を供給する際に、前記ドラムミキサーへの前記固体燃料系粉原料の供給量を減らして前記焼結用原料を製造することを特徴とする。
【００１５】
【作用】
本発明者らは、種々の検討を重ねた結果、焼結鉱の焼結用原料（擬似粒子）を製造する際に、ＳｉＯ_２を多く含有する鉄鉱石やＳｉＯ_２含有原料を石灰石系粉原料および固体燃料系粉原料から分離して製造し、さらに石灰石系粉原料および固体燃料系粉原料を製造の後半の過程で添加して製造することで、石灰石系粉原料と固体燃料系粉原料を焼結用原料の外装部に付着させてＣａＯとＳｉＯ_２の反応を遅らせ、被還元性が悪く且つ冷間強度も低いカルシウムシリケートの生成を抑制することによって、焼結鉱表面には強度の高いカルシウムフェライトが生成され、また焼結鉱内部には被還元性の高いヘマタイトが生成されることを見出した。
【００１６】
しかし、焼結過程の溶融体は外装部のＣａＯとの反応によるカルシウムフェライトが主体となり、ＳｉＯ_２との反応による溶融体（スラグ）形成は限られる。すなわち、溶融体形成は、石灰石系粉原料の存在する外装部分に限られる。このため、溶融体量が少なく、この少量の溶融体結合による焼結鉱強度は弱くなりやすいことから、溶融体量減少と溶融体が偏析することによって、得られる焼結鉱の強度低下や歩留まり低下などを生じることがあった。
【００１７】
本発明では、この外装部分に生じる溶融体量を増加させると共にカルシウムフェライトの融液粘性を低下させ、かつ溶融体の偏析を防止すると共に浸透深さ向上を図ることにより、この問題解決を図ったものである。すなわち、ＳｉＯ_２系融液にＦｅＯを加えると融液粘性が低下すると共に溶融体量の微増が図れることに注目し、ＦｅＯ源としてミルスケール等の微粉酸化鉄の添加利用に着目したものである。
ここで、ミルスケールとは製鉄所の圧延工程で発生する微粉酸化鉄（高温下で鋼板表面に生成した酸化鉄が圧延時に剥離したもので、圧延環水スラッジとして回収できる）を指し、例えば表２に示す成分を有する。
【００１８】
【表２】

【００１９】
本発明においては、核鉱石の表面に付着するＳｉＯ_２含有原料や粉鉱石等の細粒原料とその外装部分に付着する石灰石系粉原料との間にミルスケール等の微粉酸化鉄を介在せしめることにより、焼結工程で生成されるカルシウムフェライトの融液粘性を低下させ、細粒原料粒子間にカルシウムフェライト融液を浸透させ、強度の向上を図るものである。
【００２０】
また、微粉酸化鉄の酸化熱（式（１）及び（２）参照）を利用することによって、ドラムミキサーに供給される固体燃料系粉原料の供給量を減少させることができると共にＳＯｘ、ＮＯｘの発生量を低減できるという付随的効果もある。
Ｆｅ＋０．５Ｏ_２→２ＦｅＯ：１１５０ｋｃａｌ／ｋｇ−Ｆｅ ‥‥（１）
２Ｆｅ＋０．５Ｏ_２→２Ｆｅ_２Ｏ_３：４４０ｋｃａｌ／ｋｇ−ＦｅＯ ‥‥（２）
なお、核鉱石の表面に付着したＳｉＯ_２含有原料や微粉鉱石等の細粒原料とその外装部分に付着する石灰石系粉原料との間にミルスケール等の微粉酸化鉄を介在せしめるには、石灰石系粉原料と固体燃料系粉原料を焼結用原料の外装部に付着させる前の段階で添加する必要があり、その添加時期は下記の通りである。
【００２１】
まず、石灰石系粉原料と固体燃料系粉原料を焼結用原料の外装部に付着させるための時間の設定、すなわち、製造されつつある焼結用原料に対し石灰石系粉原料と固体燃料系粉原料を添加した後、該焼結用原料がドラムミキサーの排出口に到達するまでの添加後の滞留時間、いわゆる石灰石系粉原料と固体燃料系粉原料を焼結用原料の外装部に付着させるための添加後の製造時間（以降、単に外装時間と記す）の設定によって、外装部付着・形成効果が異なることを見出した。
【００２２】
本発明者らは、図４に示すように、石灰石系粉原料および固体燃料系粉原料を除く焼結用原料の製造時間を一定として、石灰石系粉原料および固体燃料系粉原料の外装時間を６０秒から３６０秒で変化させた実験を実施した。
その結果、図５に示すように、石灰石系粉原料および固体燃料系粉原料の外装時間を長く設定すると、焼結鉱の被還元性向上に有効な０．５ｍｍ以下の微細孔が減少することが判明した。このことから、焼結鉱の被還元性を向上させるためには、石灰石系粉原料および固体燃料系粉原料の外装時間を９０秒以下に設定することが望ましいことが分かった。
【００２３】
また、別の実験により、石灰石系粉原料および固体燃料系粉原料の外装時間が１０秒を下回ると、添加した石灰石系粉原料および固体燃料系粉原料が原料中の一部分に偏析を起こし、均一な焼結状態が得られず、効果が発揮されないことが判明した。ここで、外装時間が１０秒から９０秒と言う外装時間は、ドラムミキサーの回転数で言うと２ｍｉｎ^−１から３６ｍｉｎ^−１に相当する。
【００２４】
図６に、電子線マイクロアナライザー（以下、ＥＰＭＡと記す）を用いて焼結用原料の擬似粒子中のＣａとＦｅの分布状況を分析した結果を示す。同図に示すように、石灰石系粉原料および固体燃料系粉原料の外装時間を適切な時間（例えば６０秒）に設定するとＣａの分布が外輪状となり、外装化が達成されていることを確認できるが、石灰石系粉原料および固体燃料系粉原料の外装時間を長く設定するとドラムミキサー内で粒子が壊れ、その結果、石灰石系粉原料が擬似粒子内に取り込まれることによって、Ｃａが全体に分布して従来法と変化が無くなっていることを確認できた。つまり、ドラムミキサー内では製造だけでなく、擬似粒子の破壊も同時に進行していることから、外装時間を長くとりすぎると、外装のために添加した石灰石系粉原料および固体燃料系粉原料が擬似粒子の破壊により内部に取り込まれて内外装の両方に存在することになる。これにより、焼結鉱表面には強度の高いカルシウムフェライトを、また焼結鉱内部には被還元性の高いヘマタイトを選択的に生成することが困難となり、図５の条件が重要であることが分かった。
【００２５】
また、前述したように、外装時間を短くし過ぎては、添加した石灰石系粉原料および固体燃料系粉原料が焼結用原料の中で偏析してしまい、焼結機上でのムラ焼けの原因となる。そこで、本発明者らが調査した結果、偏析しないためには、外装時間を１０秒以上に設定することが必要であることが分かった。すなわち、外装時間は厳密な条件下にあり、単に後半部分においての添加では内装化されてしまう。
【００２６】
本発明での前記外装時間の条件を満たすことにより、石灰石系粉原料および固体燃料系粉原料が内部に取り込まれることなく、初めて外装化されることになり、ＳｉＯ_２含有原料を石灰石系粉原料から分離した石灰石のない状態で焼結用原料を製造することが達成されるのである。これにより、ＣａＯとＳｉＯ_２の反応を遅らせ、被還元性が悪く、冷間強度も低いカルシウムシリケートの生成を抑制することができる。この条件のもと、まず、ミルスケール等の微粉酸化鉄を添加し、次いで石灰石系粉原料および固体燃料系粉原料を添加することにより、焼結用原料の外装部に石灰石系粉原料と固体燃料系粉原料が付着するのである。微粉酸化鉄の添加に際しては、９０秒以下の滞留領域で添加し、続いて６０秒以下の滞留領域で石灰石系粉原料と固体燃料系粉原料を添加すれば、石灰石系粉原料および固体燃料系粉原料を除く細粒原料から製造された擬似粒子表面に内装されることなくミルスケール等の微粉酸化鉄を付着させ、更にその表面に石灰石系粉原料と固体燃料系粉原料を付着させることができる。
【００２７】
そして、本発明では、外装化された石灰石系粉原料と鉄鉱石の界面焼結過程で生成される融液生成の際にＦｅＯの存在により融液粘性の低下を図って、鉄鉱石の表面に付着した細粒原料の粒子間に浸透させ、細粒原料の周囲を覆うことにより、十分な冷間強度を発揮させるのである。これにより、強度の良好な焼結鉱を安定して得ることができる。
【００２８】
なお、石灰石系粉原料の外装化は重要であるが、微粉酸化鉄の細粒原料中への若干の混入は許容でき、この場合の微粉酸化鉄の添加時期は、石灰石系粉原料が９０秒以下に対し、１２０秒以下に許容できる。したがって、微粉酸化鉄を１２０秒以下の滞留領域で添加し、９０秒以下の領域で石灰石系粉原料および固体燃料系粉原料を添加することで、核鉄鉱石の表面に付着したＳｉＯ_２含有原料や粉鉱石等の細粒原料とその外装部分に付着する石灰石系粉原料との間にミルスケール等の微粉酸化鉄を介在させることができる。
【００２９】
さらに、ミルスケール等の微粉酸化鉄を添加することで、微粉酸化鉄の酸化反応熱を利用できるため、ドラムミキサー内に供給される固体燃料系粉原料の供給量を減少させてコストの低減を図ることができる。なお、ドラムミキサー内への微粉酸化鉄の供給量としては、１．０質量％〜３５．０質量％程度までの範囲が好ましい。融液粘性低下効果を安定させるためには、ドラムミキサー内への微粉酸化鉄の供給量を２．０質量％以上とすることが好ましい。
【００３０】
【発明の実施の形態】
以下、本発明の実施の形態を図面に基づいて説明する。
図１乃至図３は本発明の一実施形態を示す図であり、高炉用原料として使用される焼結鉱を製造する場合には、先ず、図１の（ａ）に示すように、直径１０ｍｍ以下の鉄鉱石とニッケルスラグ等のＳｉＯ_２含有原料を製造用水分と共にドラムミキサー５内にドラムミキサー５の装入口５ａから供給する。そして、ドラムミキサー５を所定速度で回転させ、図２の（ａ）に示すような構造の粒状物８、すなわち粗粒の鉄鉱石からなる核鉱石６の周りにＳｉＯ_２含有層７が形成された二層構造の粒状物８を造る。
【００３１】
次に、図１の（ｂ）に示すように、ドラムミキサー５内にミルスケール等の微粉酸化鉄を供給し、ドラムミキサー５内で製造された二層構造の粒状物８と微粉酸化鉄とを混合して、図２の（ｂ）に示すような構造の粒状物１０、すなわちＳｉＯ_２含有層７の表面に微粉酸化鉄層９が形成された三層構造の粒状物１０を造る。
【００３２】
次に、図１の（ｃ）に示すように、石灰石系粉原料および粉コークス等の固体燃料系粉原料を製造用水分と共にドラムミキサー５内に供給する。そして、ドラムミキサー５内で製造された三層構造の粒状物１０と石灰石系粉原料および固体燃料系粉原料とを混合して、図２の（ｃ）に示すような構造の擬似粒子（焼結用原料）１２、すなわち微粉酸化鉄層９の表面に石灰石系粉原料及び固体燃料系粉原料からなるＣａＯ含有層１１が形成された四層構造の擬似粒子１２を造る。なお、四層構造の擬似粒子１２を製造した後は、従来と同様に、擬似粒子１２の燃料成分である固体燃料系粉原料をドワイトロイド式焼結機で燃焼させて焼結鉱を製造する。
【００３３】
このように、直径１０ｍｍ以下の鉄鉱石とＳｉＯ_２含有原料、石灰石系粉原料および固体燃料系粉原料を製造用水分と共にドラムミキサー５で混合して焼結鉱の焼結用原料を製造する際に、鉄鉱石およびＳｉＯ_２含有原料をドラムミキサー５で混合して粗粒の鉄鉱石からなる核鉱石６の周りにＳｉＯ_２含有層７を形成し、次いでドラムミキサー５に微粉酸化鉄を供給してＳｉＯ_２含有層７の表面に微粉酸化鉄層９を形成した後、ドラムミキサー５に石灰石系粉原料および固体燃料系粉原料を供給して混合すると、混合工程で得られる擬似粒子１２の構造がＳｉＯ_２含有層７とＣａＯ含有層１１との間に微粉酸化鉄層９を有する四層構造となる。したがって、このような構造の擬似粒子を焼結用原料としてドワイトロイド式焼結機で焼結処理すると、焼結工程で得られる焼結鉱の構造が図３に示すような構造、すなわち表層部が引張強度の高いカルシウムフェライトＣＦで形成され、内部が被還元性の高いヘマタイトＨｅで形成された構造となるので、焼結鉱の表層部にカルシウムシリケートが生成されることを抑制することができ、これにより、被還元性に優れ且つ冷間強度の高い焼結鉱を安定して得ることができる。
【００３４】
また、ミルスケール等の微粉酸化鉄を添加することにより、焼結工程で微粉酸化鉄の酸化発熱を利用できるため、ドラムミキサー内への固体燃料系粉原料４の供給量を減少させてコストの低減も図ることができる。
【００３５】
【発明の効果】
以上説明したように、本発明に係る焼結用原料の製造方法によれば、混合工程で得られる擬似粒子の構造がＳｉＯ_２含有層とＣａＯ含有層との間に微粉酸化鉄層を有する四層構造となる。これにより、擬似粒子のＳｉＯ_２とＣａＯが焼結工程で反応することが微粉酸化鉄層によって抑制されるため、被還元性に優れ且つ冷間強度の高い焼結鉱を安定して得ることができる。また、ミルスケール等の微粉酸化鉄を添加することにより、焼結工程で微粉酸化鉄の酸化発熱を利用できるため、ドラムミキサー内への固体燃料系粉原料の供給量を減少させてコストの低減も図ることができる。
【図面の簡単な説明】
【図１】本発明の一実施形態に係る焼結用原料の製造方法を説明するための図である。
【図２】図１の各工程で得られる擬似粒子の構造を模式的に示す図である。
【図３】本発明の一実施形態に係る焼結用原料の製造方法で得られる焼結鉱の構造を模式的に示す図である。
【図４】石灰石系粉原料と固体燃料系粉原料の外装実験方法を説明するための図である。
【図５】外装時間と焼結鉱の被還元性との関係を示す図である。
【図６】外装時間を変化させた場合の擬似粒子中のＣａとＦｅの分布状況を示す図である。
【図７】従来の焼結鉱の製造方法を説明するための図である。
【図８】焼結鉱の被還元性と高炉でのガス利用率との関係を示す図である。
【図９】高炉でのガス利用率と燃料比との関係を示す図
【図１０】焼結鉱の被還元性と高炉での燃料比との関係を示す図である。
【図１１】高炉用原料として好適な焼結鉱の構造を模式的に示す図である。
【図１２】従来の焼結鉱の製造方法で得られる擬似粒子の構造を模式的に示す図である。
【図１３】従来の焼結鉱の製造方法で得られる焼結鉱の構造を模式的に示す図である。
【符号の説明】
１鉄鉱石
２ＳｉＯ_２含有原料
３石灰石系粉原料
４固体燃料系粉原料
５ドラムミキサー
６核鉱石
７ＳｉＯ_２含有層
９微粉酸化鉄層
１１ＣａＯ含有層
１２擬似粒子
Ｈｅヘマタイト
ＣＦカルシウムフェライト
ＣＳカルシウムシリケート
Ｍｇマグネタイト[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a raw material for sintering sinter used as a raw material for a blast furnace in an ironworks.
[0002]
[Prior art]
In general, sintered ore used as a raw material for a blast furnace in an ironworks is manufactured by the following method. That is, as shown in FIG. 7, iron ore 1 having a particle size of 10 mm or less, SiO ₂ -containing raw material 2 such as silica, serpentine, nickel slag, limestone powder raw material 3 containing CaO such as limestone, and coke, anthracite The solid fuel system powder raw material 4 such as the above is put in a drum mixer 5 together with water for production, and these are mixed by the drum mixer 5 to obtain a granular material called pseudo particles. Then, the pseudo particles obtained in the mixing process are placed on a pallet of a dwy-toroid type sintering machine with an appropriate thickness (for example, 500 to 700 mm) to burn the solid fuel in the surface layer portion, and the pseudo heat is generated by the combustion heat. Sinter to make a sintered cake. This sintered cake is crushed and sized to obtain a sintered ore having a certain particle size or more. On the other hand, one having a particle size smaller than that is returned to ore and reused as a raw material for sintering.
[0003]
FIG. 8 shows the relationship between the reducibility defined in JIS M8713 (hereinafter simply referred to as reducibility or JIS-R1) of the sintered ore produced by such a method and the gas utilization rate η _CO in the blast furnace. FIG. 9 shows the relationship between the gas utilization rate η _CO and the fuel ratio. As is clear from these figures, there is a positive correlation between the reducibility of the sintered ore and the gas utilization ratio, and there is a negative correlation between the gas utilization ratio and the fuel ratio. This shows that the reducibility of the sinter has a negative correlation with the fuel ratio in the blast furnace (see Fig. 10). When the reducibility of the sinter is improved, the fuel ratio in the blast furnace decreases. To do. Therefore, it can be said that the highly reducible sintered ore is a suitable sintered ore as a raw material for blast furnace, but the cold strength of the sintered ore is also an important factor in ensuring air permeability in the blast furnace, In most cases, the blast furnace is operated with a lower limit set for the cold strength of the sintered ore.
[0004]
The gas utilization rate η _CO and fuel ratio in the blast furnace are
η _CO = CO ₂ (%) / [CO (%) + CO ₂ (%)]
Fuel ratio = (coal + coke) consumption (kg) / pig iron (1 ton)
CO ₂ (%) and CO (%) are both volume% in the blast furnace top gas.
In Table 1, calcium ferrite: nCaO · Fe ₂ O ₃ , hematite (hematite): Fe ₂ O ₃ , calcium silicate: CaO · SiO ₂ , magnetite (magnetite): Fe, which are main mineral structures forming sintered ore _The _four reducibility and tensile strength of ₃ 0 ₄ are shown.
[0005]
[Table 1]

[0006]
As shown in Table 1, among the four main mineral structures forming the sintered ore, the one having high reducibility is hematite, and the one having high tensile strength is calcium ferrite. Therefore, the sintered ore suitable as a blast furnace raw material is a sintered ore having a structure as shown in FIG. 11, that is, a hematite whose surface layer portion is formed of calcium ferrite CF having high tensile strength and whose inside is highly reducible. It can be said that it is a sintered ore formed of He.
[0007]
However, conventionally, as described above, the pseudo ore obtained by simultaneously mixing the iron ore 1, the SiO ₂ containing raw material 2, the limestone powder raw material 3 and the solid fuel powder raw material 4 with the drum mixer 5 is used for sintering. Since the sintered ore is manufactured as a raw material, the quasi-particles obtained in the mixing step have a structure as shown in FIG. 12, that is, the surface of the coarse iron ore 1 serving as the core, the limestone powder raw material 3 and the solid fuel system It becomes the structure where the powder raw material 4, powder ore, etc. adhered. For this reason, when the pseudo particles having the structure shown in FIG. 12 are sintered by the Dwytroid type sintering machine, the structure of the sintered ore is shown in FIG. 13, that is, hematite He, calcium ferrite CF, calcium silicate CS. Therefore, it becomes difficult to stably produce a sintered ore having excellent reducibility and high cold strength.
[0008]
Therefore, the present applicant has, in Patent Document 1, as a raw material for sintering ore sintering, a first layer having a core of coarse iron ore having an average particle diameter of 2 mm or more, The outer surface has a second layer composed of a fine ore having a mean particle size of 2 mm or less other than the limestone powder raw material and the solid fuel powder raw material and a SiO ₂ -containing raw material, and further from the limestone powder raw material and the solid fuel powder raw material. It has been found that it is optimal to obtain a sintering pseudoparticle having a third layer. This pseudo particle has a slow reaction between CaO and SiO ₂ during the sintering process, and the formation of calcium silicate with low cold strength is suppressed, so that calcium ferrite with high cold strength is formed on the surface layer of the sintered ore. Because hematite with high reducibility is produced inside the sintered ore, it is possible to stably produce a sintered ore with many fine pores, excellent reducibility and high cold strength. It becomes possible.
[0009]
[Patent Document 1]
International Publication No. WO01 / 92588
[Problems to be solved by the invention]
However, when the sintered ore is manufactured with the pseudo-particles disclosed in Patent Document 1, the amount of melt (slag) in the sintering process decreases, and this decrease in melt amount and the amount of melt segregate. As a result, the strength or yield of the sintered ore may be reduced.
This invention is made paying attention to such a problem, and it aims at providing the manufacturing method of the raw material for sintering which can obtain stably the sintered ore with favorable intensity | strength. It is.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, a method for producing a sintering raw material according to the invention of claim 1 is a method for producing iron ore having a diameter of 10 mm or less, a SiO ₂ containing raw material, a limestone powder raw material, and a solid fuel powder raw material. When the raw material for sintering sintered ore is produced by mixing with a drum mixer together with the minute, the iron ore and the SiO ₂ -containing raw material are mixed with the drum mixer to surround the core ore composed of coarse iron ore. After forming a SiO ₂ -containing layer made of the SiO ₂ -containing raw material, and then supplying finely divided iron oxide to the drum mixer to form a finely divided iron oxide layer made of the finely divided iron oxide on the surface of the SiO ₂ -containing layer The limestone powder raw material and the solid fuel powder raw material are supplied to the drum mixer to produce the sintering raw material.
[0012]
The method for producing a raw material for sintering according to the invention of claim 2 is the method for producing a raw material for sintering according to claim 1, wherein the iron ore and the SiO ₂ -containing raw material are supplied to the drum mixer, and then the iron ore is supplied. The residence time until the stone reaches the discharge port of the drum mixer is set in a range of 10 to 120 seconds, and the raw material for sintering is manufactured.
[0013]
The method for producing a raw material for sintering according to the invention of claim 3 is the method for producing a raw material for sintering according to claim 1, wherein the iron ore and the SiO ₂ -containing raw material are supplied to the drum mixer, and then the iron ore is supplied. The sintering raw material is manufactured by setting a residence time until the stone reaches the discharge port of the drum mixer within a range of 10 to 90 seconds.
[0014]
The method for producing a raw material for sintering according to the invention of claim 4 is the method for producing a raw material for sintering according to any one of claims 1 to 3, wherein the limestone powder raw material and the solid fuel are added to the drum mixer. When supplying the system powder material, the amount of the solid fuel system powder material supplied to the drum mixer is reduced to produce the sintering material.
[0015]
[Action]
The present inventors have, as a result of various investigations, when manufacturing raw material for sintering of sinter (pseudoparticles), limestone-based powder material iron ore and SiO ₂ containing raw material containing a large amount of SiO ₂ The limestone powder raw material and the solid fuel powder raw material are produced by adding the limestone powder raw material and the solid fuel powder raw material in the latter half of the manufacturing process. The surface of the sintered ore has high strength by adhering to the exterior of the sintering raw material and delaying the reaction between CaO and SiO ₂ and suppressing the formation of calcium silicate with poor reducibility and low cold strength. It has been found that calcium ferrite is produced and that hematite with high reducibility is produced inside the sintered ore.
[0016]
However, the melt in the sintering process is mainly composed of calcium ferrite due to the reaction with CaO in the exterior, and the formation of the melt (slag) due to the reaction with SiO ₂ is limited. That is, the melt formation is limited to the exterior portion where the limestone powder raw material is present. For this reason, the amount of melt is small, and the strength of sintered ore due to this small amount of melt bonding tends to be weak, so the decrease in melt amount and the segregation of the melt result in a decrease in strength and yield of the obtained ore. Decrease may occur.
[0017]
In the present invention, this problem is solved by increasing the amount of the melt generated in the exterior portion and lowering the melt viscosity of calcium ferrite, preventing segregation of the melt and improving the penetration depth. Is. That is, when FeO is added to the SiO ₂ -based melt, the melt viscosity is lowered and the amount of melt can be slightly increased, and the addition of fine iron oxide such as mill scale as the FeO source is focused on. .
Here, the mill scale refers to fine iron oxide generated in the rolling process of a steel mill (iron oxide generated on the surface of a steel plate at high temperature is peeled off during rolling and can be recovered as rolling water sludge). It has the component shown in 2.
[0018]
[Table 2]

[0019]
In the present invention, finely divided iron oxide such as mill scale is interposed between a fine-grained raw material such as SiO ₂ -containing raw material or fine ore that adheres to the surface of the nuclear ore and a limestone-based powder raw material that adheres to the exterior portion thereof. Thus, the melt viscosity of calcium ferrite produced in the sintering process is lowered, the calcium ferrite melt is infiltrated between the fine-grain raw material particles, and the strength is improved.
[0020]
In addition, by using the heat of oxidation of finely divided iron oxide (see equations (1) and (2)), the amount of solid fuel-based powder raw material supplied to the drum mixer can be reduced, and SOx and NOx can be reduced. There is also an accompanying effect that the generation amount can be reduced.
Fe + 0.5O ₂ → 2FeO: 1150 kcal / kg-Fe (1)
2Fe + 0.5O ₂ → 2Fe ₂ O ₃ : 440 kcal / kg-FeO (2)
In order to interpose fine iron oxide such as mill scale between the fine-grained raw material such as SiO ₂ containing raw material or fine ore attached to the surface of the nuclear ore and the limestone-based powder raw material attached to the exterior part thereof, limestone It is necessary to add the system powder raw material and the solid fuel system powder raw material at the stage before adhering them to the exterior of the sintering raw material, and the addition time is as follows.
[0021]
First, setting the time for attaching the limestone powder raw material and the solid fuel powder raw material to the exterior of the sintering raw material, that is, the limestone powder raw material and the solid fuel powder for the sintering raw material being manufactured. After adding the raw material, the residence time after the addition until the sintering raw material reaches the discharge port of the drum mixer, the so-called limestone powder raw material and the solid fuel powder raw material are adhered to the exterior of the sintering raw material For this reason, it has been found that the effect of adhesion / formation of the exterior part varies depending on the setting of the production time after the addition (hereinafter simply referred to as exterior time).
[0022]
As shown in FIG. 4, the present inventors set the production time of the sintering raw material excluding the limestone powder raw material and the solid fuel powder raw material to be constant, and set the exterior time of the limestone powder raw material and the solid fuel powder raw material. Experiments were performed with a change from 60 seconds to 360 seconds.
As a result, as shown in FIG. 5, when the exterior time of the limestone powder raw material and the solid fuel powder raw material is set long, the fine pores of 0.5 mm or less effective for improving the reducibility of the sintered ore are reduced. There was found. From this, it was found that in order to improve the reducibility of the sintered ore, it is desirable to set the exterior time of the limestone powder raw material and the solid fuel powder raw material to 90 seconds or less.
[0023]
Further, according to another experiment, when the exterior time of the limestone powder raw material and the solid fuel powder raw material is less than 10 seconds, the added limestone powder raw material and the solid fuel powder raw material are segregated in a part of the raw material, and are uniform. As a result, it was found that no effective sintered state was obtained and the effect was not exhibited. Here, the outer time exterior time say 10 seconds and 90 seconds, corresponding from 2min ^-1 in terms of the number of revolutions of the drum mixer to 36min ^-1.
[0024]
FIG. 6 shows the result of analyzing the distribution of Ca and Fe in the pseudo particles of the raw material for sintering using an electron beam microanalyzer (hereinafter referred to as EPMA). As shown in the figure, when the exterior time of the limestone powder raw material and the solid fuel powder raw material is set to an appropriate time (for example, 60 seconds), the distribution of Ca becomes an outer ring shape, and it is confirmed that the exteriorization is achieved. However, if the exterior time of the limestone powder raw material and the solid fuel powder raw material is set long, the particles break in the drum mixer, and as a result, the limestone powder raw material is taken into the pseudo particles, so that Ca is distributed throughout. As a result, it was confirmed that there was no change from the conventional method. In other words, not only manufacturing but also the destruction of the pseudo-particles is proceeding at the same time in the drum mixer, so if the exterior time is too long, the limestone powder material and the solid fuel-based powder material added for the exterior are simulated. It is taken in by the destruction of the particles and exists in both the interior and exterior. This makes it difficult to selectively generate high-strength calcium ferrite on the surface of the sintered ore and selectively generate highly reducible hematite inside the sintered ore, and the condition of FIG. 5 is important. I understood.
[0025]
In addition, as described above, if the exterior time is too short, the added limestone powder raw material and solid fuel powder raw material are segregated in the raw material for sintering, and uneven burning on the sintering machine may occur. Cause. Therefore, as a result of investigations by the present inventors, it has been found that it is necessary to set the exterior time to 10 seconds or more in order to prevent segregation. In other words, the exterior time is under strict conditions, and if it is simply added in the latter half, it will be interiorized.
[0026]
By satisfying the condition of the exterior time in the present invention, the limestone powder raw material and the solid fuel powder raw material are not externally incorporated for the first time, and the SiO ₂ -containing raw material is converted into the limestone powder raw material. It is achieved that the raw material for sintering is produced without limestone separated from the material. Thus, delaying the reaction of CaO and SiO _2, it can be reducible poor, to suppress the formation of cold strength low calcium silicate. Under this condition, first, fine iron oxide such as mill scale is added, and then limestone powder raw material and solid fuel powder raw material are added, so that the limestone powder raw material and solid are added to the exterior of the sintering raw material. Fuel system powder raw material adheres. When adding fine powdered iron oxide, if it is added in a residence region of 90 seconds or less, and then a limestone powder material and a solid fuel powder material are added in a residence region of 60 seconds or less, the limestone powder material and the solid fuel system are added. A fine powdered iron oxide such as a mill scale can be attached to the surface of a pseudo particle manufactured from a fine particle raw material excluding the powder raw material, and a limestone powder raw material and a solid fuel powder raw material can be attached to the surface. it can.
[0027]
In the present invention, the melt viscosity is reduced due to the presence of FeO when the melt is generated during the interfacial sintering process between the exteriorized limestone powder raw material and iron ore, and the surface of the iron ore is reduced. By infiltrating between the particles of the adhering fine raw material and covering the periphery of the fine raw material, sufficient cold strength is exhibited. Thereby, a sintered ore with good strength can be obtained stably.
[0028]
It is important to make the exterior of the limestone powder raw material, but slight mixing of fine iron oxide into the fine particle raw material is acceptable. In this case, the addition time of fine iron oxide is 90 seconds for the limestone powder raw material. The following is acceptable for 120 seconds or less. Therefore, by adding fine iron oxide in a residence region of 120 seconds or less and adding a limestone powder material and a solid fuel powder material in a region of 90 seconds or less, the SiO ₂ -containing material attached to the surface of the nuclear iron ore Fine iron oxides such as mill scale can be interposed between fine-grained raw materials such as powder ore and limestone-based powder raw materials adhering to the exterior portion.
[0029]
Furthermore, by adding fine iron oxide such as mill scale, the heat of oxidation reaction of fine iron oxide can be used, so the supply amount of solid fuel powder raw material supplied into the drum mixer can be reduced to reduce costs. Can be planned. In addition, as supply_amount | feed_rate of fine powder iron oxide in a drum mixer, the range to about 1.0 mass%-about 35.0 mass% is preferable. In order to stabilize the effect of lowering the melt viscosity, it is preferable that the supply amount of finely divided iron oxide into the drum mixer is 2.0% by mass or more.
[0030]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 to FIG. 3 are diagrams showing an embodiment of the present invention. When producing a sintered ore used as a raw material for a blast furnace, first, as shown in FIG. The following iron ore and raw materials containing SiO ₂ such as nickel slag are supplied into the drum mixer 5 together with moisture for production from the inlet 5a of the drum mixer 5. Then, the drum mixer 5 is rotated at a predetermined speed, and the SiO ₂ containing layer 7 is formed around the granular material 8 having the structure as shown in FIG. 2A, that is, the core ore 6 made of coarse iron ore. A two-layered granular material 8 is produced.
[0031]
Next, as shown in FIG. 1B, fine iron oxide such as a mill scale is supplied into the drum mixer 5, and the two-layered granular material 8 and fine iron oxide produced in the drum mixer 5 To form a granular material 10 having a structure as shown in FIG. 2B, that is, a granular material 10 having a three-layer structure in which a fine iron oxide layer 9 is formed on the surface of the SiO ₂ -containing layer 7.
[0032]
Next, as shown in FIG. 1 (c), a solid fuel-based powder material such as limestone-based powder material and powdered coke is supplied into the drum mixer 5 together with manufacturing moisture. Then, the three-layered granular material 10 produced in the drum mixer 5 is mixed with the limestone-based powder raw material and the solid fuel-based powder raw material, and the pseudo particles (fired) having the structure as shown in FIG. The quasi-particles 12 having a four-layer structure in which a CaO-containing layer 11 made of a limestone-based powder material and a solid fuel-based powder material is formed on the surface of the fine pulverized iron oxide layer 9. In addition, after manufacturing the pseudo-particles 12 having the four-layer structure, a sintered ore is manufactured by burning the solid fuel-based powder raw material, which is a fuel component of the pseudo-particles 12, with a Dwytroid-type sintering machine, as in the past. .
[0033]
Thus, when the iron ore having a diameter of 10 mm or less, the SiO ₂ -containing raw material, the limestone powder raw material, and the solid fuel powder raw material are mixed together with the manufacturing moisture by the drum mixer 5 to produce the sintering raw material for the sintered ore. Then, the iron ore and the SiO ₂ -containing raw material are mixed by the drum mixer 5 to form the SiO ₂ -containing layer 7 around the core ore 6 made of coarse iron ore, and then the finely mixed iron oxide is supplied to the drum mixer 5. After the fine iron oxide layer 9 is formed on the surface of the SiO ₂ -containing layer 7, when the limestone powder raw material and the solid fuel powder raw material are supplied to the drum mixer 5 and mixed, the structure of the pseudo particles 12 obtained in the mixing step Becomes a four-layer structure having a fine iron oxide layer 9 between the SiO ₂ -containing layer 7 and the CaO-containing layer 11. Therefore, when the pseudo particles having such a structure are subjected to sintering treatment as a raw material for sintering by a Dwytroid type sintering machine, the structure of the sintered ore obtained in the sintering step is a structure as shown in FIG. Is made of calcium ferrite CF with high tensile strength and the inside is made of hematite He with high reducibility, so that it is possible to suppress the formation of calcium silicate in the surface layer portion of the sintered ore. Thus, it is possible to stably obtain a sintered ore having excellent reducibility and high cold strength.
[0034]
Also, by adding fine iron oxide such as mill scale, the oxidation heat of fine iron oxide can be used in the sintering process, so the amount of solid fuel-based powder raw material 4 supplied to the drum mixer can be reduced and the cost can be reduced. Reduction can also be achieved.
[0035]
【The invention's effect】
As described above, according to the method for manufacturing a raw material for sintering according to the present invention, the structure of the pseudo particles obtained in the mixing step includes a fine iron oxide layer between the SiO ₂ -containing layer and the CaO-containing layer. It becomes a layer structure. As a result, since the fine powdered iron oxide layer suppresses the reaction between the pseudo-particles SiO ₂ and CaO in the sintering process, it is possible to stably obtain a sintered ore with excellent reducibility and high cold strength. it can. In addition, by adding fine iron oxide such as mill scale, the oxidation heat of fine iron oxide can be used in the sintering process, so the supply amount of solid fuel powder raw material into the drum mixer can be reduced to reduce cost Can also be planned.
[Brief description of the drawings]
FIG. 1 is a diagram for explaining a method for producing a raw material for sintering according to an embodiment of the present invention.
2 is a diagram schematically showing the structure of pseudo particles obtained in each step of FIG. 1. FIG.
FIG. 3 is a diagram schematically showing a structure of a sintered ore obtained by the method for producing a raw material for sintering according to one embodiment of the present invention.
FIG. 4 is a view for explaining an exterior experiment method for a limestone powder raw material and a solid fuel powder raw material.
FIG. 5 is a diagram showing the relationship between exterior time and reducibility of sintered ore.
FIG. 6 is a diagram showing a distribution state of Ca and Fe in pseudo particles when the exterior time is changed.
FIG. 7 is a diagram for explaining a conventional method for producing sintered ore.
FIG. 8 is a diagram showing the relationship between the reducibility of sintered ore and the gas utilization rate in a blast furnace.
FIG. 9 is a diagram showing the relationship between the gas utilization rate in the blast furnace and the fuel ratio. FIG. 10 is a diagram showing the relationship between the reducibility of the sintered ore and the fuel ratio in the blast furnace.
FIG. 11 is a diagram schematically showing a structure of a sintered ore suitable as a blast furnace raw material.
FIG. 12 is a diagram schematically showing the structure of pseudo particles obtained by a conventional method for producing sintered ore.
FIG. 13 is a diagram schematically showing a structure of a sintered ore obtained by a conventional method for producing a sintered ore.
[Explanation of symbols]
1 ore 2 SiO ₂ containing feedstock 3 limestone based flour feedstock 4 solid fuel-based powder material 5 drum mixer 6 nuclear Ore 7 SiO ₂ containing layer 9 micronized iron oxide layer 11 CaO-containing layer 12 pseudoparticles He hematite CF calcium ferrite CS calcium silicate Mg magnetite

Claims

When the iron ore having a diameter of 10 mm or less, the SiO ₂ -containing raw material, the limestone powder raw material, and the solid fuel powder raw material are mixed together with moisture for production with a drum mixer, the iron ore is produced when the raw material for sintering the sintered ore is produced. And the SiO ₂ -containing raw material are mixed with the drum mixer to form a SiO ₂ -containing layer made of the SiO ₂ -containing raw material around the core ore made of coarse iron ore, and then the fine powder iron oxide is added to the drum mixer After supplying and forming the fine iron oxide layer made of fine iron oxide on the surface of the SiO ₂ -containing layer, the limestone powder raw material and the solid fuel powder raw material are supplied to the drum mixer for the sintering. A method for producing a raw material for sintering, characterized by producing the raw material.

The residence time from when the iron ore and the SiO ₂ -containing raw material are supplied to the drum mixer until the iron ore reaches the discharge port of the drum mixer is set within a range of 10 to 120 seconds, and the firing is performed. The method for producing a sintering raw material according to claim 1, wherein the raw material for sintering is produced.

The residence time from when the iron ore and the SiO ₂ -containing raw material are supplied to the drum mixer until the iron ore reaches the discharge port of the drum mixer is set within a range of 10 to 90 seconds, and the firing is performed. The method for producing a sintering raw material according to claim 1, wherein the raw material for sintering is produced.

When the limestone powder raw material and the solid fuel powder raw material are supplied to the drum mixer, the amount of the solid fuel powder raw material supplied to the drum mixer is reduced to produce the sintering raw material. The method for manufacturing a raw material for sintering according to any one of claims 1 to 3.