JP5608144B2 - Method for producing reduced iron - Google Patents
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本発明は、鉄鉱石や製鉄所ダスト（例えば、製銑工程や製鋼工程で発生するダスト）等の酸化鉄含有物質と、石炭やコークス等の炭素質還元剤とを含む塊成物を加熱炉に装入して加熱し、該塊成物中の酸化鉄を還元して還元鉄を製造する方法に関するものである。 The present invention relates to an agglomerate containing an iron oxide-containing material such as iron ore or ironworks dust (for example, dust generated in a steelmaking process or a steelmaking process) and a carbonaceous reducing agent such as coal or coke. And reducing iron oxide in the agglomerate to produce reduced iron.
酸化鉄を還元して還元鉄を製造する方法としては、酸化鉄含有物質と炭素質還元剤に、必要に応じて水分やバインダーを混合し、得られた混合物をペレットやブリケットなどの形状の塊成物に成形し、この塊成物を乾燥させた後、回転炉床炉などの加熱炉に装入して加熱し、該塊成物中の酸化鉄を還元して還元鉄を製造する技術が知られている（例えば、特許文献１、２）。 As a method for producing reduced iron by reducing iron oxide, if necessary, water and a binder are mixed with an iron oxide-containing substance and a carbonaceous reducing agent, and the resulting mixture is formed into pellets, briquettes, etc. A technology for producing reduced iron by forming into a product, drying the agglomerate, and then charging and heating in a heating furnace such as a rotary hearth furnace to reduce iron oxide in the agglomerate Is known (for example, Patent Documents 1 and 2).
これらのうち特許文献１には、酸化鉄物質、炭素質物質、およびバインダー物質（結合剤）を含む混合物を成形した塊成物を回転炉床炉へ装入し、１３１６〜１４２７℃で４〜１０分間加熱することによって、酸化鉄を還元し、還元鉄を製造する方法が記載されている。 Among these, Patent Document 1 discloses that an agglomerate formed from a mixture containing an iron oxide substance, a carbonaceous substance, and a binder substance (binder) is charged into a rotary hearth furnace, and is heated at 1316-1427 ° C for 4 to 4 minutes. A method for producing reduced iron by reducing iron oxide by heating for 10 minutes is described.
また、特許文献２には、炭材内装ペレットまたはブリケットの還元を促進し、かつ還元帯での還元鉄の再酸化を防止した還元鉄の製造方法が記載されている。具体的には、還元期の最終段階で燃焼ガスの酸化度を低めに変更するか、または燃焼ガスの流速を小さくしてペレットまたはブリケット内部から発生するＣＯガスを有効に活用することによって、炭材内装ペレットまたはブリケットの表層部まで還元を促進し、かつ還元帯での還元鉄の再酸化を防止する技術が開示されている。この文献には、回転炉床炉による炭材内装ペレットの還元は、温度の上昇とともにペレットの表面から内部に進行し、バーナー燃焼ガスの輻射熱により最高１３００℃程度に加熱され、８〜１０分間で還元が終わることが記載されている。 Patent Document 2 describes a method for producing reduced iron that promotes the reduction of carbonaceous material-containing pellets or briquettes and prevents reoxidation of reduced iron in the reduction zone. Specifically, by changing the oxidation degree of the combustion gas to a low level in the final stage of the reduction phase, or by reducing the flow rate of the combustion gas and effectively utilizing the CO gas generated from the inside of the pellet or briquette, A technique for promoting reduction to the surface layer portion of a material-incorporated pellet or briquette and preventing reoxidation of reduced iron in the reduction zone is disclosed. According to this document, the reduction of the pellets in the carbonaceous material by the rotary hearth furnace proceeds from the surface of the pellets to the inside as the temperature rises, and is heated to about 1300 ° C. by the radiant heat of the burner combustion gas. It is described that the reduction ends.
ところで、還元鉄は、高炉や電気炉等の溶解炉において鉄源として用いられる。そのため還元鉄を製造するにあたっては、塊成物に含まれる酸化鉄を還元鉄とすることによる鉄の金属化率、および還元鉄の強度等が重要となる。これらのうち、鉄の金属化率については、上記溶解炉で鉄源として用いるため、７５％以上であることが望まれる。還元鉄の強度としては、加熱炉からの排出時や、次工程に供されるまでに壊れて粉化しないことが要求される。また、加熱炉で得られた還元鉄を高炉へ装入して鉄源として用いる場合には、還元鉄が高炉内で粉化しないことも要求され、具体的には、７３５Ｎ／個（７５ｋｇｆ／個）以上の圧潰強度が求められる。しかし、上記特許文献１、２には、還元鉄の強度（圧潰強度）については特に記載されていない。 By the way, reduced iron is used as an iron source in melting furnaces such as a blast furnace and an electric furnace. Therefore, when manufacturing reduced iron, the metalization rate of iron by making the iron oxide contained in an agglomerate into reduced iron, the intensity | strength of reduced iron, etc. become important. Among these, the metallization rate of iron is desirably 75% or more because it is used as an iron source in the melting furnace. The strength of the reduced iron is required not to be broken and pulverized before being discharged from the heating furnace or used in the next process. Further, when the reduced iron obtained in the heating furnace is charged into the blast furnace and used as an iron source, it is also required that the reduced iron is not pulverized in the blast furnace. Specifically, 735 N / piece (75 kgf / The above-mentioned crushing strength is required. However, Patent Documents 1 and 2 do not particularly describe the strength (crush strength) of reduced iron.
還元鉄の強度について考慮した技術として特許文献３が知られている。この特許文献３には、製鉄工場などで発生する鉄やニッケル、クロムなどの金属成分を含むダスト［特にＣａを多量（ＣａＯ換算の乾量基準で１５質量％以上のＣａ成分）に含有するダスト］から、上記金属成分を有価成分として効率よく回収できるように改善された処理法が開示されている。そしてこの文献には、有価金属成分を還元するために配合する炭素質還元剤量を、還元に寄与するフリーＣ換算で、当該ダスト中に含まれる還元性金属酸化物（鉄、ニッケル、クロム、鉛、亜鉛などの酸化物）の還元に要する理論量のＣに対し−２％以上、＋１％以下とすることにより、有価金属成分の加熱還元を無駄なく効率よく進めることができ、しかも生成する金属成分の圧潰強度を高めることができると記載されている。 Patent Document 3 is known as a technique considering the strength of reduced iron. In this Patent Document 3, dust containing metal components such as iron, nickel, and chromium generated in an iron factory or the like [particularly, dust containing a large amount of Ca (a Ca component of 15 mass% or more on a dry basis in terms of CaO)). ], An improved treatment method is disclosed so that the metal component can be efficiently recovered as a valuable component. And in this document, the amount of carbonaceous reducing agent blended for reducing valuable metal components is reduced metal oxides (iron, nickel, chromium, (2) Oxidation of lead, zinc, etc.) -2% or more and + 1% or less with respect to the theoretical amount of C required for reduction, valuable metal components can be efficiently heated and reduced without waste. It is described that the crushing strength of the metal component can be increased.
本発明の目的は、上記特許文献３に開示されている方法とは異なる方法で圧潰強度の高い還元鉄を製造する方法を提供することにある。 An object of the present invention is to provide a method for producing reduced iron having a high crushing strength by a method different from the method disclosed in Patent Document 3.
上記課題を解決することのできた本発明に係る還元鉄の製造方法とは、酸化鉄含有物質と炭素質還元剤とを含む塊成物を加熱炉に装入して加熱し、該塊成物中の酸化鉄を還元して還元鉄を製造する方法であって、塩基度（ＣａＯ／ＳｉＯ2比）が０．５〜０．９の塊成物を前記加熱炉に装入し、鉄の金属化率が５０％以上（１００％を含まない）で、全炭素量が５．５質量％以下で、且つ１１００〜１２００℃に加熱されている中間還元鉄を得る工程と、得られた中間還元鉄を１２５０〜１３５０℃の温度域内で設定される到達温度Ｔまで平均昇温速度Ｖを３０〜７０℃／分として加熱する工程とを含む点に要旨を有している。 The method for producing reduced iron according to the present invention that has solved the above-mentioned problem is that an agglomerate containing an iron oxide-containing substance and a carbonaceous reducing agent is charged in a heating furnace and heated, and the agglomerate is obtained. A method for producing reduced iron by reducing iron oxide therein, wherein an agglomerate having a basicity (CaO / SiO 2 ratio) of 0.5 to 0.9 is charged into the heating furnace, A step of obtaining intermediate reduced iron having a metallization rate of 50% or more (not including 100%), a total carbon amount of 5.5% by mass or less and being heated to 1100 to 1200 ° C., and the intermediate obtained It has a gist in that it includes a step of heating the reduced iron to an ultimate temperature T set within a temperature range of 1250 to 1350 ° C. with an average heating rate V of 30 to 70 ° C./min.
前記中間還元鉄を得る工程において、前記塊成物を前記加熱炉に装入してからの昇温時間は、例えば、３００秒以上とすることが好ましい。前記中間還元鉄を得る工程において、前記塊成物を前記加熱炉に装入して加熱し、昇温した後、恒温保持を行ってもよい。前記中間還元鉄を得る工程において、前記塊成物を前記加熱炉に装入して加熱して昇温するときの平均昇温速度ｖを前記平均昇温速度Ｖよりも大きくして加熱することが好ましく、前記平均昇温速度ｖは、例えば、７０℃／分超、２００℃／分以下に制御して加熱することが推奨される。 In the step of obtaining the intermediate reduced iron, the temperature raising time after the agglomerate is charged into the heating furnace is preferably, for example, 300 seconds or more. In the step of obtaining the intermediate reduced iron, the agglomerate may be charged into the heating furnace, heated, heated, and then kept at a constant temperature. In the step of obtaining the intermediate reduced iron, heating the agglomerate into the heating furnace and heating it to raise the temperature to an average temperature increase rate v higher than the average temperature increase rate V. It is recommended that the average heating rate v is controlled to be, for example, more than 70 ° C./minute and 200 ° C./minute or less.
本発明によれば、塩基度を所定の範囲に調整した塊成物を加熱炉で加熱し、鉄の金属化率、全炭素量、および温度を所定の範囲に制御してから、更に所定の平均昇温速度Ｖで１２５０〜１３５０℃の温度域に加熱しているため、上記特許文献３のように、塊成物に配合する炭素質還元剤の配合量を調整しなくても還元鉄の圧潰強度を７３５Ｎ／個以上に高めることができる。 According to the present invention, an agglomerate whose basicity is adjusted to a predetermined range is heated in a heating furnace, the iron metallization rate, the total carbon content, and the temperature are controlled to a predetermined range, and then, Since it is heated to a temperature range of 1250 to 1350 ° C. at an average temperature increase rate V, the reduced iron content can be reduced without adjusting the amount of the carbonaceous reducing agent to be blended into the agglomerate as in Patent Document 3 above. The crushing strength can be increased to 735 N / piece or more.
本発明者は、塊成物を加熱炉で加熱し、該塊成物中の酸化鉄を還元して得られる還元鉄の圧潰強度を７３５Ｎ／個以上に高めるために、鋭意検討を重ねてきた。その結果、還元鉄の圧潰強度が低くなる原因は、還元鉄内に生成する空隙にあり、この空隙が増大するに連れて還元鉄の圧潰強度が低くなること、この空隙を低減するには、塩基度を所定の範囲に調整した塊成物を用意し、この塊成物を加熱炉で、鉄の金属化率、全炭素量、および温度が所定の範囲を満足するように加熱して中間還元鉄を製造し、得られた中間還元鉄を更に所定の平均昇温速度Ｖで１２５０〜１３５０℃の温度域に加熱すれば、還元鉄の圧潰強度を７３５Ｎ／個以上に高められることを見出し、本発明を完成した。 The present inventor has intensively studied to increase the crushing strength of reduced iron obtained by heating the agglomerate in a heating furnace and reducing iron oxide in the agglomerate to 735 N / piece or more. . As a result, the cause of the reduced crushing strength of the reduced iron lies in the voids generated in the reduced iron, the reduced crushing strength of the reduced iron as this void increases, to reduce this void, Prepare an agglomerate with basicity adjusted to a predetermined range, and heat this agglomerate in a heating furnace so that the iron metallization rate, total carbon content, and temperature satisfy the predetermined range. It has been found that if reduced iron is produced and the obtained intermediate reduced iron is further heated to a temperature range of 1250 to 1350 ° C. at a predetermined average heating rate V, the crushing strength of reduced iron can be increased to 735 N / piece or more. The present invention has been completed.
即ち、本発明では、塊成物を加熱炉に装入して加熱し、還元鉄を製造するにあたり、鉄の金属化率、全炭素量、および温度が所定の範囲を満足している中間還元鉄を得る工程と、得られた中間還元鉄を更に加熱する工程に分け、中間還元鉄を得る工程では、塊成物の表面のみならず内部においても酸化鉄の還元を促進して塊成物に含まれる炭素を消費すると共に、鉄の金属化率を高め、更に塊成物内に溶融スラグを生成させて塊成物の体積を収縮させている。こうした中間還元鉄を更に加熱することによって圧潰強度が高い還元鉄を製造できる。以下、本発明について詳細に説明する。 That is, in the present invention, when the agglomerate is charged into a heating furnace and heated to produce reduced iron, intermediate reduction in which the metallization rate of iron, the total carbon content, and the temperature satisfy predetermined ranges. The process of obtaining iron and the process of further heating the obtained intermediate reduced iron, the process of obtaining intermediate reduced iron, promotes the reduction of iron oxide not only on the surface of the agglomerate but also inside the agglomerate. Is consumed, and the metallization rate of iron is increased, and molten slag is generated in the agglomerate to reduce the volume of the agglomerate. By further heating such intermediate reduced iron, reduced iron with high crushing strength can be produced. Hereinafter, the present invention will be described in detail.
本発明では、酸化鉄含有物質と炭素質還元剤とを含む塊成物を加熱炉に装入して加熱し、該塊成物中の酸化鉄を還元して還元鉄を製造する。 In the present invention, an agglomerate containing an iron oxide-containing substance and a carbonaceous reducing agent is charged into a heating furnace and heated, and iron oxide in the agglomerate is reduced to produce reduced iron.
上記酸化鉄含有物質としては、例えば、鉄鉱石、砂鉄、製鉄ダスト、非鉄製錬残渣、製鉄廃棄物などを用いることができる。上記炭素質還元剤としては、炭素含有物質を用いることができ、例えば、石炭やコークスなどを用いることができる。 As the iron oxide-containing substance, for example, iron ore, iron sand, iron-making dust, non-ferrous smelting residue, iron-making waste, and the like can be used. As said carbonaceous reducing agent, a carbon containing substance can be used, for example, coal, coke, etc. can be used.
上記塊成物は、その他の成分として、例えば、バインダー（結合剤）やＭｇＯ含有物質、ＣａＯ含有物質、合成スラグなどを配合してもよい。上記バインダーとしては、例えば、多糖類（例えば、小麦粉やコーンスターチ等の澱粉）などを用いることができる。上記ＭｇＯ含有物質としては、例えば、ＭｇＯ粉末、天然鉱石や海水などから抽出されるＭｇＯ含有物質、或いはドロマイトや炭酸マグネシウム（ＭｇＣＯ3）などを用いることができる。上記ＣａＯ含有物質としては、例えば、生石灰（ＣａＯ）や石灰石（主成分はＣａＣＯ3）などを用いることができる。上記合成スラグとしては、例えば、プリメルトスラグを用いることができる。プリメルトスラグとは、それ自体が既にスラグ化されており、溶融温度が低く、短時間で液相が生成して金属鉄の焼結をより促進する作用を有しているスラグを意味する。プリメルトスラグとしては、例えば、Ａｌ2Ｏ3、ＣａＯおよびＳｉＯ2含有量から定まるＡｌ2Ｏ3−ＣａＯ−ＳｉＯ2３元系スラグの固相線温度（以下、「プリメルトスラグ固相線温度」ということがある。）ＴS・Pが１３００℃以下のスラグを意味する。上記プリメルトスラグとしては、例えば、高炉スラグおよび／または製鋼スラグを用いることができる。製鋼スラグには、例えば、転炉スラグ、溶銑予備処理スラグ、電気炉スラグなどが含まれる。 The agglomerate may contain, as other components, for example, a binder (binder), an MgO-containing material, a CaO-containing material, or synthetic slag. As said binder, polysaccharides (for example, starches, such as wheat flour and corn starch), etc. can be used, for example. As the MgO-containing substance, e.g., MgO powder, MgO-containing substance to be extracted such as from natural ore or seawater, or dolomite and magnesium carbonate (MgCO 3) or the like can be used. As the CaO-containing material, e.g., quicklime (CaO) or limestone (main component CaCO 3) or the like can be used. As the synthetic slag, for example, premelt slag can be used. Pre-melt slag means slag that has already been converted into slag, has a low melting temperature, and has a function of further promoting the sintering of metallic iron by generating a liquid phase in a short time. As the premelt slag, for example, the solidus temperature of Al 2 O 3 —CaO—SiO 2 ternary slag determined from the contents of Al 2 O 3 , CaO and SiO 2 (hereinafter referred to as “premelt slag solidus temperature”). ) Ss · P means slag of 1300 ° C or less. As the premelt slag, for example, blast furnace slag and / or steelmaking slag can be used. Steelmaking slag includes, for example, converter slag, hot metal pretreatment slag, electric furnace slag, and the like.
上記塊成物は常法に従って形成すればよく、その形状は特に限定されず、例えば、ペレット状やブリケット状などであればよい。上記塊成物の大きさも特に限定されないが、例えば、塊成物の体積に相当する真球を模擬したときに、この真球の直径が９〜３０ｍｍ程度となる塊成物を用いることが好ましい。 The said agglomerate should just be formed in accordance with a conventional method, The shape is not specifically limited, For example, what is necessary is just a pellet form, a briquette form, etc. The size of the agglomerate is not particularly limited. For example, when a true sphere corresponding to the volume of the agglomerate is simulated, it is preferable to use an agglomerate having a true sphere diameter of about 9 to 30 mm. .
本発明の製造方法では、上記塊成物として、塩基度（ＣａＯ／ＳｉＯ2比）が０．５〜０．９のものを用意する。上記塊成物の塩基度が０．５を下回るか、０．９を超えると、スラグの融点が高くなり過ぎてスラグ液相を充分に確保できず、還元鉄内に空隙が生成し易くなり、圧潰強度が低下する。従って上記塊成物の塩基度は、０．５以上とし、好ましくは０．６５以上、より好ましくは０．７以上とする。また、上記塊成物の塩基度は、０．９以下とし、好ましくは０．８５以下、より好ましくは０．８以下とする。 In the production method of the present invention, as the agglomerate, one having a basicity (CaO / SiO 2 ratio) of 0.5 to 0.9 is prepared. If the basicity of the agglomerate is less than 0.5 or exceeds 0.9, the melting point of the slag becomes too high to sufficiently secure the slag liquid phase, and voids are likely to be generated in the reduced iron. , Crushing strength decreases. Therefore, the basicity of the agglomerate is 0.5 or more, preferably 0.65 or more, more preferably 0.7 or more. The basicity of the agglomerate is 0.9 or less, preferably 0.85 or less, more preferably 0.8 or less.
上記塊成物の塩基度は、該塊成物を製造する際に用いた原料混合物に含まれるＣａＯ量とＳｉＯ2量の質量比（ＣａＯ／ＳｉＯ2）に基づいて算出する。なお、塊成物の塩基度は、塊成物に含まれているＣａＯ量とＳｉＯ2量から直接算出してもよい。 The basicity of the agglomerate is calculated based on the mass ratio (CaO / SiO 2 ) between the CaO amount and the SiO 2 amount contained in the raw material mixture used in producing the agglomerate. The basicity of the agglomerate may be directly calculated from the amount of CaO and the amount of SiO 2 contained in the agglomerate.
次に、用意した塩基度が０．５〜０．９の上記塊成物を加熱炉に装入し、加熱することによって、鉄の金属化率が５０％以上（１００％を含まない）で、全炭素量が５．５質量％以下で、且つ１１００〜１２００℃に加熱されている中間還元鉄を製造する。鉄の金属化率、全炭素量、および塊成物の温度が所定の範囲になるように加熱して中間還元鉄とした後、得られた中間還元鉄を後述するように所定の平均昇温速度Ｖで１２５０〜１３５０℃の温度域まで加熱することによって、還元鉄の内部に生成する空隙を減らすことができ、還元鉄の圧潰強度を高めることができる。 Next, the prepared agglomerates having a basicity of 0.5 to 0.9 are charged into a heating furnace and heated, so that the iron metallization rate is 50% or more (not including 100%). The intermediate reduced iron having a total carbon amount of 5.5% by mass or less and heated to 1100 to 1200 ° C. is produced. After heating the iron metalization rate, the total carbon content, and the temperature of the agglomerate to a predetermined range to obtain intermediate reduced iron, the intermediate reduced iron obtained was heated at a predetermined average temperature as described later. By heating at a speed V to a temperature range of 1250 to 1350 ° C., voids generated inside the reduced iron can be reduced, and the crushing strength of the reduced iron can be increased.
上記鉄の金属化率が５０％を下回ると、未還元部分が多過ぎるため、これを後述するように所定の平均昇温速度Ｖで１２５０〜１３５０℃の温度域に加熱しても酸化鉄の還元が充分に進まず、還元鉄内部に空隙が生成し、還元鉄の圧潰強度が低下する。従って上記鉄の金属化率は５０％以上とし、好ましくは６０％以上、より好ましくは７０％以上とする。上記鉄の金属化率は高い方が好ましいが、後述するように後段で更なる加熱を行うため、ここでは鉄の金属化率を１００％にする必要はない。鉄の金属化率は、好ましくは９５％以下であり、より好ましくは９０％以下、更に好ましくは８５％以下である。 When the iron metallization rate is less than 50%, there are too many unreduced parts, so that even if this is heated to a temperature range of 1250 to 1350 ° C. at a predetermined average heating rate V as described later, Reduction does not proceed sufficiently, voids are generated inside the reduced iron, and the crushing strength of the reduced iron decreases. Therefore, the metallization rate of the iron is 50% or more, preferably 60% or more, more preferably 70% or more. Although it is preferable that the iron metallization rate is higher, it is not necessary to set the iron metallization rate to 100% because further heating is performed later as described later. The metallization rate of iron is preferably 95% or less, more preferably 90% or less, and still more preferably 85% or less.
上記鉄の金属化率は、化学分析値により下記式（１）から算出できる。
鉄の金属化率（％）＝［金属鉄量(質量％)／塊成物に含まれる全鉄量（質量％）］×１００ ・・・（１）
The metallization rate of iron can be calculated from the following formula (1) based on chemical analysis values.
Iron metalization rate (%) = [Amount of metal iron (% by mass) / Total amount of iron contained in agglomerate (% by mass)] × 100 (1)
上記全炭素量が５．５質量％を超えると、上記中間還元鉄に含まれる炭素が後述する加熱工程で還元鉄中へ拡散し、浸炭して鉄の融点が降下するため、鉄の溶融が促進され、還元鉄の内部に空隙が生成して還元鉄の圧潰強度が低下する。従って上記全炭素量は５．５質量％以下、好ましくは５．０質量％以下、より好ましくは４．５質量％以下である。 If the total carbon content exceeds 5.5% by mass, the carbon contained in the intermediate reduced iron diffuses into the reduced iron in the heating step described later, and carburizes to lower the melting point of the iron. As a result, voids are generated inside the reduced iron, and the crushing strength of the reduced iron is reduced. Therefore, the total carbon content is 5.5% by mass or less, preferably 5.0% by mass or less, more preferably 4.5% by mass or less.
上記中間還元鉄の温度が１１００℃を下回ると、鉄の金属化率が５０％以上に到達するのに長時間を要するため、生産性が低下する。また、上記中間還元鉄の温度が１１００℃を下回ると、温度が低過ぎるため、塊成物に含まれる酸化鉄の還元が促進されず、中間還元鉄に含まれる残留炭素量が増大する。そのためこの残留炭素が、後述する加熱工程で塊成物に含まれる還元鉄へ拡散し、浸炭して鉄の融点が降下するため、鉄の溶融が促進され、還元鉄の内部に空隙が生成して還元鉄の圧潰強度が低下する。従って上記中間還元鉄の温度は、１１００℃以上、好ましくは１１２０℃以上、より好ましくは１１３０℃以上である。しかし上記中間還元鉄の温度が１２００℃を超えて高過ぎると、塊成物内に生成するスラグの融液量が増加し、溶融スラグが塊成物の外へ染み出し、塊成物内に空隙が生成して還元鉄の圧潰強度が低下する。従って上記中間還元鉄の温度は、１２００℃以下、好ましくは１１８０℃以下、より好ましくは１１７０℃以下である。なお、上記温度は、塊成物の最表面から２０ｍｍ以内の領域における温度を制御すればよい（以下、温度について同じ）。 When the temperature of the intermediate reduced iron is lower than 1100 ° C., it takes a long time for the iron metallization rate to reach 50% or more, and thus productivity is lowered. Moreover, since the temperature is too low when the temperature of the intermediate reduced iron is lower than 1100 ° C., the reduction of iron oxide contained in the agglomerate is not promoted, and the amount of residual carbon contained in the intermediate reduced iron increases. Therefore, this residual carbon diffuses into the reduced iron contained in the agglomerate in the heating step described later, and carburizes to lower the melting point of the iron, so that the melting of the iron is promoted and voids are generated inside the reduced iron. This reduces the crushing strength of reduced iron. Therefore, the temperature of the intermediate reduced iron is 1100 ° C. or higher, preferably 1120 ° C. or higher, more preferably 1130 ° C. or higher. However, if the temperature of the intermediate reduced iron exceeds 1200 ° C. and is too high, the amount of slag melt generated in the agglomerate increases, and the molten slag oozes out of the agglomerate and enters the agglomerate. A space | gap produces | generates and the crushing strength of reduced iron falls. Therefore, the temperature of the intermediate reduced iron is 1200 ° C. or lower, preferably 1180 ° C. or lower, more preferably 1170 ° C. or lower. In addition, the said temperature should just control the temperature in the area | region within 20 mm from the outermost surface of an agglomerate (it is the same about temperature below).
上記鉄の金属化率および上記全炭素量を上記範囲に制御するには、１１００〜１２００℃での加熱時間を調整すればよい。即ち、上記加熱炉に装入した塊成物は、炉内で加熱し、１１００〜１２００℃の温度域内で設定される到達温度ｔまで平均昇温速度ｖで加熱する。このとき到達温度ｔまで昇温した時点において、上記鉄の金属化率および上記中間還元鉄に含まれる全炭素量が所定の範囲を満足している場合には、後述するように、１２５０〜１３５０℃の温度域内で設定される到達温度Ｔまで平均昇温速度Ｖで加熱すればよい。 In order to control the metallization rate of iron and the total amount of carbon within the above ranges, the heating time at 1100 to 1200 ° C. may be adjusted. That is, the agglomerate charged in the heating furnace is heated in the furnace and is heated at an average temperature increase rate v up to an ultimate temperature t set in a temperature range of 1100 to 1200 ° C. At this time, when the temperature is raised to the ultimate temperature t, if the iron metallization rate and the total carbon content in the intermediate reduced iron satisfy a predetermined range, as described later, 1250 to 1350, respectively. What is necessary is just to heat with the average temperature increase rate V to the ultimate temperature T set within the temperature range of ° C.
一方、上記到達温度ｔまで昇温した時点において、上記鉄の金属化率および上記全炭素量が所定の範囲を満足していない場合には、上記鉄の金属化率と上記全炭素量が所定の範囲を満足するまで該到達温度ｔで恒温保持を行えばよい。 On the other hand, if the iron metallization rate and the total carbon amount do not satisfy the predetermined range at the time when the temperature is raised to the ultimate temperature t, the iron metallization rate and the total carbon amount are predetermined. The constant temperature may be maintained at the ultimate temperature t until the above range is satisfied.
上記到達温度ｔで恒温保持を行うには、炉内に設けた燃焼バーナーの燃焼条件を制御して炉内の温度を調整すればよい。 In order to maintain the constant temperature at the reached temperature t, the temperature in the furnace may be adjusted by controlling the combustion conditions of the combustion burner provided in the furnace.
このように本発明の中間還元鉄は、１１００〜１２００℃の温度域内で任意に設定される到達温度ｔに加熱されており、このときの鉄の金属化率が５０％以上で、全炭素量が５．５質量％以下である。例えば、１１００℃に加熱されたときの鉄の金属化率と全炭素量が上記範囲を満足していればよい。 As described above, the intermediate reduced iron of the present invention is heated to an ultimate temperature t arbitrarily set within a temperature range of 1100 to 1200 ° C., and the metallization rate of iron at this time is 50% or more, and the total carbon amount Is 5.5% by mass or less. For example, the metallization rate of iron and the total carbon amount when heated to 1100 ° C. should satisfy the above range.
本発明の製造方法では、上記塊成物を上記加熱炉に装入してからの昇温時間（即ち、上記塊成物を上記加熱炉に装入してから上記到達温度ｔに到達するまでの時間）は、３００秒（５分）以上とすることが好ましい。上記昇温時間が３００秒未満では、急激な温度上昇により塊成物表面のみの酸化鉄の還元が進み、塊成物内部の酸化鉄の還元は進まず、塊成物内部に炭素が多く残留する。その結果、後述する加熱工程において塊成物中に残留した炭素が還元鉄に拡散し、浸炭により鉄の融点が降下し、塊成物内部の還元鉄が溶融して空隙が生成し、還元鉄の圧潰強度が低下することがある。従って上記昇温時間は、３００秒以上とすることが好ましく、より好ましくは３５０秒以上、更に好ましくは４００秒以上である。しかし上記昇温時間が長過ぎると、生産性が悪くなる。従って上記昇温時間は、５００秒以下とすることが好ましく、より好ましくは４８０秒以下、更に好ましくは４６０秒以下である。 In the production method of the present invention, the temperature rise time after charging the agglomerate into the heating furnace (that is, from when the agglomerate is charged into the heating furnace until reaching the ultimate temperature t). Is preferably 300 seconds (5 minutes) or longer. When the temperature rise time is less than 300 seconds, reduction of iron oxide only on the agglomerate surface proceeds due to rapid temperature rise, and reduction of iron oxide inside the agglomerate does not proceed, and much carbon remains inside the agglomerate. To do. As a result, carbon remaining in the agglomerate in the heating process described later diffuses into the reduced iron, the melting point of the iron is lowered by carburization, the reduced iron inside the agglomerate melts and voids are generated, and the reduced iron The crushing strength may decrease. Accordingly, the temperature raising time is preferably 300 seconds or more, more preferably 350 seconds or more, and still more preferably 400 seconds or more. However, if the temperature raising time is too long, productivity is deteriorated. Therefore, the temperature raising time is preferably 500 seconds or less, more preferably 480 seconds or less, and still more preferably 460 seconds or less.
上記塊成物を上記加熱炉に装入してからの昇温時間を上記範囲に制御するには、例えば、炉床の回転速度を調整する方法や、炉内に設けた燃焼バーナーの燃焼条件を制御して炉内の温度を調整する方法等が採用できる。 In order to control the temperature rising time after charging the agglomerate into the heating furnace within the above range, for example, a method of adjusting the rotation speed of the hearth or the combustion conditions of the combustion burner provided in the furnace A method of adjusting the temperature in the furnace by controlling the temperature can be adopted.
また、上記全炭素量を上記範囲に制御するには、上記加熱炉内における加熱条件（加熱温度や加熱時間など）を考慮して上記塊成物の成分組成を調整し、塊成物に含有させる全炭素量を調整してもよい。 In order to control the total carbon content within the above range, the composition of the agglomerate is adjusted in consideration of the heating conditions (heating temperature, heating time, etc.) in the heating furnace, and contained in the agglomerate. You may adjust the total carbon amount to make.
本発明の製造方法では、上記塊成物を前記加熱炉に装入して加熱して昇温するときの平均昇温速度ｖが、後述する平均昇温速度Ｖよりも大きくなるように加熱すればよい。即ち、上記昇温速度ｖよりも後述する平均昇温速度Ｖを小さくすることによって、還元鉄内に空隙が生成し難くなるため、圧潰強度が向上する。従って上記平均昇温速度ｖは、７０℃／分超として加熱することが好ましく、より好ましくは１００℃／分以上、更に好ましくは１３０℃／分以上である。上記平均昇温速度ｖは、２００℃／分以下として加熱することが好ましく、より好ましくは１８０℃／分以下である。 In the production method of the present invention, the above-mentioned agglomerate is charged in the heating furnace and heated so as to increase the temperature so that the average temperature increase rate v is higher than the average temperature increase rate V described later. That's fine. That is, by making an average temperature rising rate V, which will be described later, smaller than the temperature rising rate v, it becomes difficult for voids to be generated in the reduced iron, so that the crushing strength is improved. Therefore, it is preferable to heat the average temperature rising rate v exceeding 70 ° C./min, more preferably 100 ° C./min or more, and further preferably 130 ° C./min or more. The average heating rate v is preferably 200 ° C./min or less, and more preferably 180 ° C./min or less.
次に、鉄の金属化率、全炭素量、および温度が所定の範囲を満足する中間還元鉄は、１２５０〜１３５０℃の温度域内で設定される到達温度Ｔまで平均昇温速度Ｖを３０〜７０℃／分として加熱する。例えば、到達温度Ｔを１３００℃とし、１３００℃に到達するまでの平均昇温速度Ｖが３０〜７０℃／分となるように制御すればよい。 Next, the intermediate reduced iron whose iron metalization rate, total carbon amount, and temperature satisfy the predetermined ranges has an average temperature increase rate V of 30 to the ultimate temperature T set within a temperature range of 1250 to 1350 ° C. Heat at 70 ° C./min. For example, the ultimate temperature T may be set to 1300 ° C., and the average temperature increase rate V until reaching 1300 ° C. may be controlled to be 30 to 70 ° C./min.
上記到達温度Ｔが１２５０℃を下回ると、還元が不充分となり、鉄の金属化率、還元鉄の純度、還元鉄の強度などが低下する。従って上記到達温度Ｔは、１２５０℃以上とし、好ましくは１２６０℃以上、より好ましくは１２７０℃以上とする。一方、１３５０℃を超えて加熱しても還元効率は殆ど変化せず、エネルギーの無駄になる。従って上記到達温度Ｔは１３５０℃以下とし、好ましくは１３４０℃以下、より好ましくは１３３０℃以下とする。 When the temperature T is less than 1250 ° C., the reduction is insufficient, and the metallization rate of iron, the purity of reduced iron, the strength of reduced iron, and the like are reduced. Accordingly, the ultimate temperature T is 1250 ° C. or higher, preferably 1260 ° C. or higher, more preferably 1270 ° C. or higher. On the other hand, even if heating exceeds 1350 ° C., the reduction efficiency hardly changes, and energy is wasted. Accordingly, the ultimate temperature T is 1350 ° C. or lower, preferably 1340 ° C. or lower, more preferably 1330 ° C. or lower.
上記平均昇温速度Ｖが小さ過ぎると、加熱時間が長くなり過ぎるため、生産性が劣化する。従って上記平均昇温速度は３０℃／分以上とし、好ましくは４０℃／分以上、より好ましくは５０℃／分以上とする。しかし上記平均昇温速度Ｖが大き過ぎると、空隙の発生を抑制するために必要なスラグ液相を充分に確保できないため、圧潰強度が低下する。従って上記平均昇温速度Ｖは７０℃／分以下とし、好ましくは６５℃／分以下、より好ましくは６０℃／分以下とする。 If the average temperature increase rate V is too small, the heating time becomes too long, so that productivity is deteriorated. Therefore, the average temperature rising rate is 30 ° C./min or more, preferably 40 ° C./min or more, more preferably 50 ° C./min or more. However, if the average temperature increase rate V is too large, a sufficient slag liquid phase for suppressing the generation of voids cannot be ensured, so that the crushing strength decreases. Therefore, the average temperature rising rate V is set to 70 ° C./min or less, preferably 65 ° C./min or less, more preferably 60 ° C./min or less.
本発明の製造方法では、得られた還元鉄を溶解炉で溶解して鉄を製造するときの生産性を高めるために、上記到達温度Ｔにおける鉄の金属化率は、７５％以上とすることが好ましく、より好ましくは９０％以上である。 In the production method of the present invention, in order to increase productivity when the obtained reduced iron is melted in a melting furnace to produce iron, the metallization rate of iron at the ultimate temperature T is 75% or more. Is more preferable, and 90% or more is more preferable.
本発明の製造方法で得られる還元鉄は、還元鉄１個あたりの圧潰荷重が７３５Ｎ以上（７５ｋｇｆ以上）となるため、電気加熱炉のみならず、高炉へ装入して鉄源として利用できる。 The reduced iron obtained by the production method of the present invention has a crushing load per reduced iron of 735 N or more (75 kgf or more), so that it can be used not only in an electric heating furnace but also in a blast furnace and used as an iron source.
以下、実施例を挙げて本発明をより具体的に説明するが、本発明はもとより下記実施例によって制限を受けるものではなく、前・後記の趣旨に適合し得る範囲で適当に変更を加えて実施することも勿論可能であり、それらはいずれも本発明の技術的範囲に包含される。 EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention.
酸化鉄含有物質と炭素質還元剤とを含む塊成物（ペレット）を小型高周波急速加熱炉で加熱し、ペレット中の酸化鉄を還元して還元鉄を製造した。具体的には、酸化鉄含有物質として下記表１に示す成分組成の鉄鉱石、炭素質還元剤として下記表２に示す成分組成の炭材、添加剤として下記表３に示す合成スラグ（プリメルトスラグ）および消石灰、結合剤として小麦粉を用い、これらを下記表４に示す配合割合で混合し、更に適量の水分を添加してタイヤ型造粒機を用いて生ペレットを製造した。生ペレットの直径（即ち、生ペレットの体積に相当する真球の直径）は１７ｍｍとした。 An agglomerate (pellet) containing an iron oxide-containing substance and a carbonaceous reducing agent was heated in a small high-frequency rapid heating furnace to reduce the iron oxide in the pellet to produce reduced iron. Specifically, iron ore having the component composition shown in Table 1 below as the iron oxide-containing substance, carbonaceous material having the component composition shown in Table 2 as the carbonaceous reducing agent, and synthetic slag (premelt as shown in Table 3 below) as the additive Slag), slaked lime, and wheat flour as a binder were mixed at a blending ratio shown in Table 4 below, and an appropriate amount of water was added to produce a raw pellet using a tire type granulator. The diameter of the raw pellet (that is, the diameter of the true sphere corresponding to the volume of the raw pellet) was 17 mm.
得られた生ペレットを乾燥機で１０５℃、２０時間かけて乾燥し、付着水を完全に除去して乾燥ペレットを製造した。乾燥ペレットの成分組成を下記表５に示す。得られた乾燥ペレットの見掛密度は１８００〜２０００ｋｇ／ｍ3であり、乾燥ペレットのスラグの塩基度（ＣａＯ／ＳｉＯ2）は０．７５であった。 The obtained raw pellets were dried with a dryer at 105 ° C. for 20 hours, and the adhered water was completely removed to produce dry pellets. The component composition of the dried pellet is shown in Table 5 below. The apparent density of the obtained dried pellet was 1800 to 2000 kg / m 3 , and the basicity (CaO / SiO 2 ) of the slag of the dried pellet was 0.75.
得られた乾燥ペレットを小型高周波急速加熱炉で加熱した。小型高周波急速加熱炉としては、ＳＫメディカル電子製の「発振器の型式：ＭＵ−１７００、炉の型式：ＵＤ−２５０」を用いた。小型高周波急速加熱炉の概略説明図を図１に示す。なお、乾燥ペレットを加熱した際に発生するＣＯ2含有ガスによる黒鉛製チューブの消耗を防止するために、加熱スリーブ（加熱用の筒）としては、黒鉛製チューブをアルミナ製チューブで被覆したものを用いた。 The obtained dried pellet was heated in a small high-frequency rapid heating furnace. As a small high-frequency rapid heating furnace, “oscillator model: MU-1700, furnace model: UD-250” manufactured by SK Medical Electronics was used. A schematic illustration of a small high-frequency rapid heating furnace is shown in FIG. In order to prevent the graphite tube from being consumed by the CO 2 -containing gas generated when the dried pellets are heated, the heating sleeve (heating cylinder) is made of a graphite tube covered with an alumina tube. Using.
上記小型高周波急速加熱炉（炉内温度は室温）に乾燥ペレットを装入し、下記表６に示す到達温度ｔまで平均昇温速度ｖを１５０〜６００℃／分として加熱した後、この温度で下記表６に示す時間保持して中間還元鉄を得た。加熱時の雰囲気は、流速３ＮＬ／分のＮ2ガス雰囲気とした。下記表６には、室温から到達温度ｔに達するまでに要した時間（到達時間）を示す。なお、中間還元鉄を得るまでの工程を以下、一段階目加熱ということがある。 The small high-frequency rapid heating furnace (furnace temperature is room temperature) was charged with dry pellets and heated to an average temperature increase rate v of 150 to 600 ° C./min up to the ultimate temperature t shown in Table 6 below. Intermediate reduced iron was obtained by maintaining the time shown in Table 6 below. The atmosphere during heating was an N 2 gas atmosphere with a flow rate of 3 NL / min. Table 6 below shows the time (arrival time) required to reach the ultimate temperature t from room temperature. Hereinafter, the process until obtaining the intermediate reduced iron may be referred to as first stage heating.
得られた中間還元鉄に含まれる鉄の金属化率、全炭素量、および体積収縮率を測定するために、下記表６に示す到達温度ｔに達し、所定時間恒温保持した後、直ちに加熱を中止して室温まで急速冷却した。室温まで急速冷却するときの雰囲気は、流速３ＮＬ／分のＨｅガス雰囲気とした。 In order to measure the metallization rate, total carbon content, and volume shrinkage rate of iron contained in the obtained intermediate reduced iron, the temperature reached an attainable temperature t shown in Table 6 below, and after maintaining a constant temperature for a predetermined time, heating was performed immediately. Stopped and cooled rapidly to room temperature. The atmosphere for rapid cooling to room temperature was a He gas atmosphere with a flow rate of 3 NL / min.
上記鉄の金属化率は、上記式（１）から算出した。上記全炭素量は、化学分析によって求めた。 The metallization rate of the iron was calculated from the above formula (1). The total carbon amount was determined by chemical analysis.
上記体積収縮率は、加熱前後におけるペレットの体積を測定し、下記式（２）で算出した。体積収縮率が正の値の場合は、体積が収縮していることを意味し、負の値の場合は、体積が膨張していることを意味している。
体積収縮率（体積％）＝［（加熱前のペレットの体積−加熱後のペレットの体積）／加熱前のペレットの体積］×１００ ・・・（２）
The volume shrinkage ratio was calculated by the following formula (2) by measuring the volume of the pellet before and after heating. When the volume shrinkage rate is a positive value, it means that the volume is contracted, and when it is a negative value, it means that the volume is expanded.
Volume shrinkage (volume%) = [(volume of pellet before heating−volume of pellet after heating) / volume of pellet before heating] × 100 (2)
下記表６に、一段階目加熱終了時点における鉄の金属化率、全炭素量、体積収縮率を示す。 Table 6 below shows the iron metallization rate, total carbon content, and volume shrinkage rate at the end of the first stage heating.
一方、上記一段階目加熱で得られた中間還元鉄を室温まで急速冷却せず、更に加熱して還元鉄を製造する実験も行った。即ち、上記で得られた中間還元鉄を、引き続き下記表６に示す平均昇温速度Ｖで到達温度Ｔ（１３００℃）まで加熱した後、直ちに加熱を中止して室温まで急速冷却して還元鉄を製造した。加熱時の雰囲気は、流速３ＮＬ／分のＮ2ガス雰囲気とし、二段階目加熱終了時点（１３００℃に到達した時点）から室温まで冷却するときの雰囲気は、流速３ＮＬ／分のＨｅガス雰囲気とした。なお、中間還元鉄を加熱して昇温する工程を以下、二段階目加熱ということがある。 On the other hand, an experiment was also conducted in which reduced iron obtained by the first stage heating was not rapidly cooled to room temperature but heated to produce reduced iron. That is, the intermediate reduced iron obtained above was continuously heated to the ultimate temperature T (1300 ° C.) at the average temperature increase rate V shown in Table 6 below, and then immediately stopped and rapidly cooled to room temperature. Manufactured. The atmosphere during heating is a N 2 gas atmosphere with a flow rate of 3 NL / min, and the atmosphere when cooling from the end of the second stage heating (when reaching 1300 ° C.) to room temperature is a He gas atmosphere with a flow rate of 3 NL / min. did. Hereinafter, the process of heating the intermediate reduced iron to raise the temperature may be referred to as second stage heating.
また、二段階目加熱を行って得られた還元鉄について、鉄の金属化率および全炭素量を上述した方法で測定した。測定結果を下記表６に示す。 Moreover, about the reduced iron obtained by performing a 2nd step heating, the metallization rate of iron and the total carbon amount were measured by the method mentioned above. The measurement results are shown in Table 6 below.
また、得られた還元鉄の圧潰強度を測定した。還元鉄の圧潰強度は、２枚の平板間に還元鉄を設置し、還元鉄が圧縮されるように平板に荷重して還元鉄の破壊時における荷重（圧潰荷重）を強度試験機で測定した。なお、圧潰荷重の測定は、１個の還元鉄について行った。測定結果を下記表６に示す。 Moreover, the crushing strength of the obtained reduced iron was measured. The crushing strength of reduced iron was measured by measuring the load (crushing load) at the time of fracture of reduced iron by placing reduced iron between two flat plates, loading reduced plate so that reduced iron was compressed. . Note that the crush load was measured for one reduced iron. The measurement results are shown in Table 6 below.
下記表６から次のように考察できる。Ｎｏ．１〜１８で得られた還元鉄は、いずれも鉄の金属化率が９０％以上となり、また全炭素量が１質量％未満となったが、Ｎｏ．１、４、１８は、一段階目加熱で得られた中間還元鉄の、鉄の金属化率および／または全炭素量が本発明で規定する要件を満足していないため、この中間還元鉄を更に加熱して還元しても得られる還元鉄の圧潰強度は７３５Ｎ／個を下回り、強度不足となった。 From Table 6 below, it can be considered as follows. No. Each of the reduced irons obtained in Nos. 1 to 18 had an iron metallization rate of 90% or more and a total carbon amount of less than 1% by mass. Nos. 1, 4, and 18 indicate that the intermediate reduced iron obtained by the first stage heating does not satisfy the requirements defined in the present invention in terms of the metallization ratio and / or the total carbon amount of the intermediate reduced iron. Further, the crushing strength of the reduced iron obtained by heating and reduction was less than 735 N / piece, and the strength was insufficient.
詳細には、Ｎｏ．１は、一段階目加熱において、到達温度ｔにおける恒温保持時間が短かったため、鉄の金属化率が所定の範囲を下回り、また全炭素量が過剰であったため、還元鉄の圧潰強度を高めることができなかった。Ｎｏ．４は、一段階目加熱において、到達温度ｔにおける恒温保持時間が短かったため、鉄の金属化率は５０％以上となったが、全炭素量が過剰であったため、還元鉄の圧潰強度を高めることができなかった。Ｎｏ．１８は、一段階目加熱において、到達温度ｔまでの到達時間が短く、平均昇温時間ｖが大きいため、塊成物の表面のみの還元が促進され、内部の還元が不充分となった。その結果、鉄の金属化率は所定の範囲を下回り、また全炭素量が過剰であったため、還元鉄の圧潰強度を高めることができなかった。またＮｏ．１８は、到達温度ｔから到達温度Ｔまでの平均昇温速度Ｖが小さ過ぎたため、全加熱時間が長くなり、生産性も低下していた。 Specifically, no. In 1st stage heating, since the constant temperature holding time at the ultimate temperature t was short in the first stage heating, the metallization rate of iron was below a predetermined range, and the total carbon amount was excessive, so the crushing strength of reduced iron was increased. I could not. No. In No. 4, since the constant temperature holding time at the ultimate temperature t was short in the first stage heating, the metallization rate of iron was 50% or more, but the total carbon amount was excessive, so the crushing strength of reduced iron was increased. I couldn't. No. No. 18 had a short reaching time to the reaching temperature t and a large average temperature rising time v in the first stage heating, so that the reduction of only the surface of the agglomerate was promoted and the internal reduction became insufficient. As a result, the metallization rate of iron was below a predetermined range, and the total carbon amount was excessive, so that the crushing strength of reduced iron could not be increased. No. In No. 18, since the average temperature increase rate V from the ultimate temperature t to the ultimate temperature T was too small, the total heating time became longer and the productivity also decreased.
一方、Ｎｏ．２、３、５〜１７は、いずれも本発明で規定する要件を満足する製造条件で還元鉄を製造した例であり、一段階目加熱において、鉄の金属化率、全炭素量、および温度が所定の範囲を満足している中間還元鉄が得られているため、得られた中間還元鉄を更に加熱して還元することによって、圧壊強度が７３５Ｎ／個以上の還元鉄を製造できた。 On the other hand, no. 2, 3, 5 to 17 are examples in which reduced iron was produced under production conditions satisfying the requirements specified in the present invention. In the first stage heating, the metallization rate of iron, the total carbon content, and the temperature Since intermediate reduced iron satisfying the predetermined range was obtained, reduced iron having a crushing strength of 735 N / piece or more could be produced by further heating and reducing the obtained intermediate reduced iron.
Claims (5)
塩基度（ＣａＯ／ＳｉＯ2比）が０．５〜０．９の塊成物を前記加熱炉に装入し、鉄の金属化率が５０％以上（１００％を含まない）で、全炭素量が５．５質量％以下で、且つ１１００〜１２００℃に加熱されている中間還元鉄を得る工程と、
得られた中間還元鉄を１２５０〜１３５０℃の温度域内で設定される到達温度Ｔまで平均昇温速度Ｖを３０〜７０℃／分として加熱する工程とを含むことを特徴とする還元鉄の製造方法。 A method for producing reduced iron by charging an agglomerate containing an iron oxide-containing substance and a carbonaceous reducing agent into a heating furnace and heating the agglomerate, and reducing the iron oxide in the agglomerate,
An agglomerate having a basicity (CaO / SiO 2 ratio) of 0.5 to 0.9 is charged into the heating furnace, and the iron metallization rate is 50% or more (not including 100%), and the total carbon Obtaining intermediate reduced iron having an amount of 5.5% by mass or less and being heated to 1100 to 1200 ° C .;
A step of heating the obtained intermediate reduced iron to an ultimate temperature T set within a temperature range of 1250 to 1350 ° C. at an average temperature increase rate V of 30 to 70 ° C./min. Method.
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