JP2004083849A - Method for producing high strength coke - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing high strength cokes having a strength over the conventional strength limit without changing brands, properties or blending mass ratios of the constituting coals and without changing the charging coal density. <P>SOLUTION: This method for producing a high strength coke is provided by crushing each brand of coals by predetermined particle sizes corresponding to the accumulated volume ratios of coarse inert organizations presenting in each of the cokes obtained by dry distillation of each brand of coals, and also blending the crushed each brand of coals so that the particle size of the blended coal in total becomes a prescribed particle size. <P>COPYRIGHT: (C)2004,JPO

Description

【００２５】
但し、Ｚは基準値（％）、Ｘは粉砕した後の石炭における３ｍｍ以下または６．７ｍｍ以上の質量比（％）、Ｙは石炭装入密度（乾炭ベース、ｔ／ｍ^３）、ａ，ｂ，ｃはそれぞれ定数を示す。
【００２６】
（７）　前記基準値以上の粗大イナート組織の累積体積比を有する銘柄の石炭を粉砕した後の３ｍｍ以下の質量比が、配合炭全体の３ｍｍ以下の質量比より２〜１４％多くなるように粉砕し、かつ、前記基準値未満の粗大イナート組織の累積体積比を有する銘柄の石炭を粉砕した後の３ｍｍ以下の質量比が配合炭全体の３ｍｍ以下の質量比より２〜１４％少なくなるように粉砕することを特徴とする上記（５）または（６）に記載の高強度コークスの製造方法。
【００２７】
（８）　前記基準値以上の粗大イナート組織の累積体積比を有する銘柄の石炭を、粉砕した後の６．７ｍｍ以上の質量比が配合炭全体の６．７ｍｍ以上の質量比より１〜１０％少なくなるように粉砕し、かつ、前記基準値未満の粗大イナート組織の累積体積比を有する銘柄の石炭を、粉砕した後の６．７ｍｍ以上の質量比が、配合炭全体の６．７ｍｍ以上の質量比より１〜１０％多くなるように粉砕することを特徴とする上記（５）または（６）に記載の高強度コークスの製造方法。
【００２８】
（９）　前記基準値以上の粗大イナート組織の累積体積比を有し、かつ全膨張率が３５体積％以上である銘柄の石炭を、粉砕した後の３ｍｍ以下の質量比が配合炭全体の３ｍｍ以下の質量比より２〜４％多くなるように粉砕することを特徴とする上記（７）に記載の高強度コークスの製造方法。
【００２９】
（１０）　前記基準値以上の粗大イナート組織の累積体積比を有し、かつ、全膨張率が３５体積％以上である銘柄の石炭を、粉砕した後の６．７ｍｍ以上の質量比が配合炭全体の６．７ｍｍ以上の質量比より１〜４％少なくなるように粉砕することを特徴とする上記（８）に記載の高強度コークスの製造方法。
【００３０】
【発明の実施の形態】
石炭中に存在するイナート組織は、コークス炉での乾留過程で軟化溶融する組織（ビトリニット、およびエグジニット）に比べて揮発分が低く、乾留後のコークス中にほぼそのままの形態で残留する。そのため、石炭中に存在するイナート組織と軟化溶融する組織とでは、コークス炉での乾留時において収縮率が異なり、この収縮率の差によって両組織の界面に応力が発生し、コークス中に残留したイナート組織の内部あるいは周辺にクラックが発生する。
【００３１】
図１に、コークス中に残留したイナート組織とその周辺の組織の一例を示す。
【００３２】
コークス中に残留したイナート組織のサイズは、０．１μｍから１０ｍｍ程度の幅広い範囲で存在し、石炭中のイナート組織がほぼ同じ形態で残存したものである。ここで、イナート組織のサイズとは、イナートの絶対最大長のことである（以下、同様とする）。
【００３３】
図１に示すように、コークス中に残留したｍｍオーダー（１．０ｍｍ以上）サイズの粗大イナート組織には、イナート組織の内部または周辺に、ｍｍオーダー（１．０ｍｍ以上）サイズの大きなクラックが生成し得る。
【００３４】
グリフィスの破壊条件式（例えば、「Ｊ．Ｆ．Ｋｎｏｔｔ（宮本博訳）、破壊力学の基礎、ｐ．１０７、培風館（１９７７）」、参照）によると、大きなサイズのクラックは、小さなサイズのクラックよりも低い応力で進展・拡大するため、粗大イナート組織の内部あるいは周辺に生成したｍｍオーダーの大きなクラックは、コークスが衝撃を受けた際の脆性破壊の起点（欠陥）となりやすい。そのため、このようなｍｍオーダーの大きなクラックが多数存在するコークスは、著しく強度が低下し、容易に粉化する。
【００３５】
そこで、本発明者は、コークスの強度低下の原因となるコークス中に生じる大きなクラックを低減させるためには、コークス炉に装入する前に石炭を粉砕処理して石炭中の粗大イナート組織のサイズを低減すれば良いことに着目し、各種銘柄の石炭を粉砕した後、コークス炉で乾留して得られたコークスの強度を測定し、石炭中に存在するイナート組織のサイズ（特定サイズのイナート組織の累積体積比）がコークスの強度（ＤＩ）に与える影響について調査した。
【００３６】
図２に、種々の条件で石炭を粉砕してコークス炉で乾留した場合での、コークス中に残留したサイズが＋１．５ｍｍの粗大イナート組織の累積体積比とコークス強度（ＤＩ）との関係を示す。なお、この際、粉砕した石炭の炉装入密度を０．８５ｔ／ｍ^３一定とし、乾留して得られたコークス中に残留した全サイズのイナート組織の累積体積比を４２％一定とした。前記全サイズのイナート組織の累積体積比（以下、総イナート比率という場合もある）は、ＪＩＳ　Ｍ８８１６（１９９２）に示される方法に準じて測定されるイナーチニットグループの容量百分率である。
【００３７】
図２から、＋１．５ｍｍの粗大イナート組織の累積体積比が小さくなると、コークス強度（ＤＩ）が、著しく向上していることが解かる。
【００３８】
また、同様に、図３には、種々の条件で石炭を粉砕してコークス炉で乾留した場合での、コークス中に残留した総イナート比率（全サイズのイナート組織の累積体積比）とコークス強度（ＤＩ）との関係を示す。なお、この際、粉砕した石炭の炉装入密度を０．８５ｔ／ｍ^３一定とし、乾留して得られたコークス中に残留した＋１．５ｍｍの粗大イナート組織の累積体積比は１０％一定とした。
【００３９】
図３から、コークス強度（ＤＩ）は、コークス中に残留した総イナート比率によらず、ほぼ一定（ＤＩ：８５）であることが解かる。
【００４０】
図２および３の結果は、コークス強度（ＤＩ）を支配する因子が、コークス中に残留した総イナート比率ではなく、＋１．５ｍｍの粗大イナート組織の累積体積比であることを意味している。
【００４１】
さらに、図４には、コークス炉に装入する石炭の粉砕により、コークス中に残留した＋１．５ｍｍの粗大イナート組織の累積体積比を低減した場合としない場合とでの、コークス中におけるイナート組織の形態とコークス強度（ＤＩ）との対応関係を示す。なお、写真でマーキングされた部分が＋１．５ｍｍの粗大イナート組織である。
【００４２】
この図からも、＋１．５ｍｍの粗大イナート組織の存在量（比）の低減が、コークス強度を著しく高めることが解かる。
【００４３】
なお、図２〜４においては、コークス中に残留した＋１．５ｍｍの粗大イナート組織の累積体積比について調査したが、本発明者は、粗大イナート組織のサイズを＋１．０ｍｍとしても実験的に同様な結果を確認した。
【００４４】
以上の本発明者の調査結果から、コークス中に残留したイナート組織において、＋１．０ｍｍの粗大イナート組織の存在量（累積体積比）の低減が、コークス強度を著しく高めることが判明した。この知見を基に、コークス炉装入前の石炭を粗大イナート組織の累積体積比に応じて粉砕制御することが、本発明における第１の特徴である。
【００４５】
さらに、コークス炉に装入する石炭中のイナート組織の存在形態は、石炭の銘柄によって様々であり、石炭の銘柄に関わらず一様に粉砕するのが、必ずしも粗大イナート組織の粉砕、低減に有効に結びつかない恐れがある。
【００４６】
そこで、本発明者は、実際の石炭の粉砕工程において、＋１．０ｍｍの粗大イナート組織をより効果的に粉砕し、その累積体積比を低減するため、各種銘柄の石炭におけるイナート組織の存在形態を調査した。
【００４７】
図５は、粉砕前の石炭粒度（原炭粒度）と、コークス中に残留した総イナート比率、及び、＋１．５ｍｍのイナート組織の累積体積比との関係を示すものである。
【００４８】
この図から、＋６．７ｍｍの石炭（原炭）中に、＋１．５ｍｍの粗大イナートが濃縮されていることが解かる。
【００４９】
さらに、表１に、３つの銘柄について、総イナート比率と＋１．５ｍｍのイナート組織の累積体積比を調査した結果を示す。
【００５０】
この表から、石炭の銘柄の違いにより、原炭中の＋１．５ｍｍの粗大イナート組織の累積体積比が大きく異なることが解かる。
【００５１】
図５及び表１から、＋１．５ｍｍの粗大イナート組織の累積体積比は、石炭の銘柄又は石炭（原炭）の粒度によって、大きく異なることが判明した。なお、図５及び表１においては、＋１．５ｍｍの粗大イナート組織の累積体積比について調査したが、本発明者は、粗大イナート組織のサイズを＋１．０ｍｍとしても、その累積体積比は、＋１．５ｍｍの粗大イナート組織の累積体積比と同じく、石炭の銘柄又は石炭粒度によって、大きく異なることを、実験的に確認した。
【００５２】
そこで、本発明においては、上記実験結果及び確認を踏まえ、各種銘柄の石炭の中でも、特に、＋１．０ｍｍの粗大イナート組織が濃縮されている石炭を粉砕の対象とし、通常、石炭（原炭）は、ＪＩＳ規格に従って作製された篩によって篩い分けられるので、ＪＩＳ規格（ＪＩＳ　Ｚ８８０１、網ふるい）における篩目６．７ｍｍ（呼び寸法）を、粉砕対象石炭の好ましい臨界粒径として採用した。また、石炭の銘柄としては、特に限定されず、本発明が実施可能な範囲であれば、公知のものを適宜選択して用いればよい。
【００５３】
このように、ＪＩＳ規格で規定する篩目で則り、石炭（原炭）を粉砕するための好ましい石炭粒径を＋６．７ｍｍと規定した点が、本発明における第２の特徴である。
【００５４】
なお、発明者らは、＋６．７ｍｍよりも大きな呼び寸法の篩い、例えば＋８．０ｍｍや＋９．５ｍｍの石炭（原炭）粒子中にも粗大イナート組織が濃縮されていることを確認しているが、篩い目が大きくなるほど、前記石炭（原炭）粒子の存在割合は小さくなり、また、測定誤差も大きくなる。一方、＋６．７ｍｍよりも小さな呼び寸法の篩い、すなわち、＋５．６ｍｍや＋４．７５ｍｍの石炭（原炭）粒子中にも粗大イナート組織がある程度は濃縮されているが、＋６．７ｍｍの石炭（原炭）粒子に比べると粗大イナート組織の濃縮度は低い。このような理由で、本発明においては、粉砕の対象とする石炭（原炭）粒度は、＋６．７ｍｍとするのが好ましい。
【００５５】
本発明において、粗大イナート組織とは、そのサイズが絶対最大長さで１．０ｍｍ以上、好ましくは、１．５ｍｍ以上のイナート組織とする。これは、このようなサイズの粗大イナート組織を有するコークスは強度が低下する、つまり、ドラム試験での落下衝撃の際に、粗大イナート組織の内部又は周辺において大きなクラックが発生し、より早く進展、拡大するためである。
【００５６】
また、本発明において、単一銘柄の石炭中またはコークス中に存在するイナート組織の量を表す指標として、イナート組織の累積体積比を用いる。
【００５７】
通常、２次元断面における面積比は、３次元空間における体積比として扱うことができるので、顕微鏡による断面観察写真の画像解析などによりイナート組織の累積面積比を求め、これをイナート組織の累積体積比として扱うことができる。
【００５８】
これは、ＪＩＳ　Ｍ８８１６（１９９２）の石炭の微細組織成分及び反射率測定方法において、研磨試料の２次元断面における各微細組織成分の含有率を容量百分率として扱うのと同様の考え方である。
【００５９】
各銘柄の石炭を乾留して得られたコークス中に存在する粗大イナート組織の累積面積比を具体的に求める場合、例えば、以下のような方法によって求められる。
【００６０】
（１）石炭を原炭のまま、あるいは所定粒度に粉砕した後、乾留しコークスを製造する。ここで乾留は、好ましくは、炉温を１０００℃〜１３００℃とし、炭中温度が７００℃〜１２００℃に到達するまで乾留することが好ましい。
【００６１】
（２）コークスを採取し、その切断面を樹脂埋めして顕微鏡により写真撮影をする。
【００６２】
（３）コークスの切断面写真において、絶対最大長が１ｍｍ以上の粗大イナート組織をマーキングし、画像解析ソフトを用いて、マーキングした領域（累積面積）が、切断面写真の全領域（面積）に占める割合Ｓｉ（％）を計測する。
【００６３】
（４）切断面写真において、コークス壁と気孔を２値化し、気孔の領域（累積面積）が切断面写真の全領域（面積）に占める割合Ｓｐ（％）を計測する。
【００６４】
（５）切断面写真における粗大イナートの累積面積比：Ｘ（％）＝Ｓｉ／（１００−Ｓｐ）×１００を求める。
【００６５】
なお、上記の方法は、石炭の乾留後にコークス中に存在する粗大イナート組織の累積体積比を測定する方法であるが、石炭中のイナート組織は、乾留によりコークス化してもほとんど変化せず、ほぼ同じ形態で残存するので、上記と同様な方法で、石炭中に存在する粗大イナート量を測定することもできる。
【００６６】
石炭中に存在する粗大イナート量を上記の方法により測定する場合は、上記（３）において、「切断面写真の全領域（面積）」の代わりに、「観察領域内における石炭粒子の面積和」を用い、石炭粒子中の気孔は無視し得るほど少ない（Ｓｐはほぼ０％）ため上記（４）の工程は不要となる。この方法は、前者の方法よりもイナート組織の判別が容易であり、測定時間が短いという長所がある。しかし、発明者らの検討によると、石炭中のイナート組織は、コークス化してもほとんど同じ形態で残存するものの、厳密には、その一部は乾留過程において分離したり、あるいは溶融したりして、イナート組織のサイズが多少変わる場合がある。したがって、測定の容易性または測定精度・信頼性などの要求に応じて、どちらの方法を用いるかは、適宜選択すればよい。
【００６７】
各銘柄の石炭の粉砕条件を決定するための指標となる、粗大イナート組織に関する基準値（所定のコークス強度向上効果を得るためのイナート組織累積体積比の臨界値。なお、この定義については後述する。）は、例えば、上記の方法などで測定された各銘柄の石炭中、または、当該石炭をコークス炉で乾留して得られたコークス中に存在する粗大イナート組織の累積体積比の測定値とコークス強度との関係に基づいて設定できる。
【００６８】
本発明では、コークス炉装入前の配合炭を構成する各銘柄の石炭（原炭）を基準値に基づいて所定の粉砕条件で粉砕する、例えば、粗大イナート組織の累積体積比が基準値以上の銘柄の石炭（原炭）については、他の銘柄の石炭（原炭）に比べて微粉砕を相対的に強めに実施するなどにより、コークス強度を所定強度まで向上することができる。ちなみに本願明細書において、配合炭とは、配合前の石炭を粉砕し、配合した石炭のことを意味する。
【００６９】
しかし、上述した通り、コークス強度は、配合炭のコークス炉での装入密度によっても影響を受け、通常、嵩密度の低下にともない粒子間接着が悪化するため、コークス強度は低下する。
【００７０】
したがって、このような問題をなくすため、各銘柄の石炭の配合割合に基づいて各銘柄の石炭の粉砕条件を調整するか、または、各銘柄の石炭の粉砕条件に基づいて各銘柄の石炭の配合割合を調整することにより、特定銘柄の石炭を粉砕後に配合炭全体のコークス炉での装入密度を所定値以上とすることが好ましい。例えば、粗大イナート組織の累積体積比が上記基準値以上の銘柄の石炭を微粉砕することにより配合炭全体のコークス炉での装入密度が低下するが、他の上記基準値未満の銘柄の石炭を粉砕しないか、または、粗粉砕することにより、配合炭全体の装入密度または粒度を所定範囲内に確保することができる。
【００７１】
なお、コークス炉での配合炭全体の装入密度（または粉砕後の配合炭粒度）の基準値は、従来から知られているコークス強度と装入密度（または粉砕後の配合炭粒度）との関係から設定できる。
【００７２】
なお、粗大イナート組織の累積体積比が上記基準値以上の銘柄の石炭を微粉砕した後、上記基準値未満の粗粉砕した銘柄の石炭と配合せずに単味で乾留しても高強度コークスを得ることができる場合は、微粉砕した石炭のみを乾留しても良い。
【００７３】
微粉砕は、装入密度低下を招き、コークス強度低下の要因として作用するため、微粉砕による強度向上効果と装入密度低下効果の両方を考慮して、微粉砕した石炭のみを装入して乾留するか、粗粉砕した銘柄の石炭と組み合わせて配合して乾留するかを適宜選択するのが好ましい。
【００７４】
次に、石炭（原炭）の粉砕条件を決定するための具体的な方法について説明する。
【００７５】
本発明において、石炭（原炭）の粉砕により、石炭中またはコークス中の＋１．０ｍｍの粗大イナート組織の累積体積比を基準値未満に低減するが、この基準値は、石炭の銘柄や性状によって異なるので、あらかじめ、銘柄別又はグループ別に、粗大イナート組織の累積体積比とコークス強度との関係を求めておき、これに基づき上記基準値を設定する。
【００７６】
通常、上記関係は、図６に模式的に示すように、コークス強度は、粗大イナート組織の累積体積比（Ｚ）の増大に伴い、ほぼ直線的に減少するから、基準値は、例えば、粗大イナート組織の累積体積比の低減幅（Ｘ１−Ｘ２＝ΔＺ）とコークス強度（ＤＩ）の向上幅（ＤＩ２−ＤＩ１＝ΔＤＩ）に基づいて、以下のように設定することができる。
【００７７】
図７に、粗大イナート組織の累積体積比（横軸）が異なる複数銘柄の石炭を用いて、これらを粉砕した後の３ｍｍ以下の石炭の質量比を、例えば、８０％から９０％に変化させた場合（この変化（増加）で、粗大イナート組織の低減程度がわかる。）のコークス冷間強度（ＤＩ）の変化（すなわち、３ｍｍ以下が９０％の石炭を乾留して得られたコークスのＤＩと、３ｍｍ以下が８０％の石炭を乾留して得られたコークスのＤＩの差：ΔＤＩ１５０／１５、縦軸）を調査した結果を示す。
【００７８】
この図から、ある銘柄の石炭における粗大イナート組織の累積体積比を境に、粉砕による強度ＤＩ変化（ΔＤＩ１５０／１５）が急激に大きくなることが解かる。このような粗大イナート組織の累積体積比の境を、所定のコークス強度向上効果が得られるための基準値（臨界値）とする。
【００７９】
すなわち、粗大イナート組織の累積体積比が基準値以上の銘柄の石炭においては、石炭の粉砕による粗大イナート組織の累積体積比の低減によるコークス強度の増大量（向上幅）が大きく、一方、粗大イナート組織の累積体積比が基準値未満の銘柄の石炭においては、粗大イナート組織の累積体積比の低減によるコークス強度の増大量（向上幅）は小さい。
【００８０】
このように、粗大イナート組織の累積体積比と石炭中３ｍｍ以下の質量比の所定範囲内におけるコークス強度の変化量との関係から、石炭の粗大イナート組織の累積体積比の低減（石炭の微粉砕強化）によりコークス強度の増大量が大きく変化するような粗大イナート組織の累積体積比の臨界値を上記基準値として採用することができる。
【００８１】
なお、上記図７においては、粉砕による石炭中の粗大イナート組織の累積体積比低減に対するコークス強度向上量を評価するに当たって、その石炭粉砕粒度として３ｍｍ以下の質量比を用いたが、これに代えて６．７ｍｍ以上の質量比を採用し、同様な関係グラフを作成し基準値を決めることもできる。なお、石炭粉砕粒度として３ｍｍ以下の質量比は、通常のコークス製造操業において、原料の均一化または装入密度とコークス強度との関係から所定コークス強度を維持するための管理指標として用いられている。
【００８２】
一方、上述のように＋１．０ｍｍの粗大イナート組織は、ＪＩＳ規格（ＪＩＳＺ８８０１、網ふるい）における篩目で６．７ｍｍ以上の粒径の石炭（原炭）に濃縮されているため、粉砕による石炭中の粗大イナート組織低減に対するコークス強度向上量をより高い精度および信頼性をもって評価するために、粉砕石炭中の６．７ｍｍ以上の質量比を採用する方が好ましい。
【００８３】
石炭粉砕粒度として６．７ｍｍ以上の質量比を採用して上記図７の関係グラフを作成する場合には、石炭中粗大イナート組織の累積体積比（横軸）が異なる複数銘柄の石炭を用いて、石炭粉砕後の６．７ｍｍ以上の質量比を１０％から３％に変化させた場合（この変化（減少）で、石炭中粗大イナート組織の低減程度がわかる。）のコークス冷間強度（ＤＩ）の変化（すなわち、６．７ｍｍ以上が３％の石炭を乾留して得られたコークスのＤＩと、６．７ｍｍ以上が１０％の石炭を乾留して得られたコークスのＤＩの差：ΔＤＩ１５０／１５、縦軸）から作成できる。
【００８４】
本発明の実施形態において、例えば、以下のようにして各銘柄の石炭粉砕条件を決定するための指標として、粗大イナート組織の累積体積比に関する基準値を設定することができる。
【００８５】
先ず、石炭中粗大イナート組織の累積体積比が異なる複数銘柄の石炭を用いて、粉砕後の石炭における３ｍｍ以下の質量比の所定範囲（Ｘ±α［％］）および石炭装入密度（Ｙ［乾炭ベース、ｔ／ｍ^３］）が一定の条件で、図７に示すような粗大イナート組織の累積体積比と粉砕後の石炭における３ｍｍ以下の質量比の所定範囲（Ｘ±α［％］）内におけるコークス強度の変化量（ΔＤＩ１５０／１５）との関係グラフを作成し、ΔＤＩ１５０／１５が急激に変化した粗大イナート組織の累積体積比の臨界値を基準値とする。
【００８６】
ΔＤＩ１５０／１５は、石炭装入密度Ｙ［乾炭ベース、ｔ／ｍ^３］を一定条件とし、粉砕した後の石炭における３ｍｍ以下の質量比がＸ−α％の場合およびＸ＋α％の場合において、それぞれ乾留して得られたコークスの冷間強度（ＤＩ）を測定し、これらの差（ΔＤＩ１５０／１５）をとることにより求められる。なお、上記αは、粉砕した後の石炭における３ｍｍ以下の質量比の中心値（Ｘ）に対する偏差を示すが、コークスの冷間強度（ＤＩ）の変化量（ΔＤＩ）が求まる範囲であれば、特に規定するものではない。
【００８７】
なお、上記の実施形態は、石炭粉砕粒度として、３ｍｍ以下の質量比の所定範囲（Ｘ±α［％］）を採用した例であるが、これに代えて６．７ｍｍ以上の質量比の所定範囲（Ｘ’±β［％］）を用いても良く、この場合、上述の通り、粉砕による石炭中粗大イナート組織低減に対して、コークス強度向上量をより高い精度および信頼性をもって評価できる。
【００８８】
この様に、各銘柄の石炭粉砕条件を決定するための指標となる、粗大イナート組織に関する基準値は、図７に示すような関係グラフでコークスの冷間強度（ＤＩ）の変化量（ΔＤＩ）が大きいところ、つまり、微粉砕（粗大イナート組織の低減）によるコークス強度の向上効果が小さい領域において粗大イナート組織の累積体積比が設定されるため、この基準値の設定に多少のばらつきがあっても、コークス強度の向上効果に与える影響は無視できる。
【００８９】
上記の通り、各銘柄の石炭粉砕条件を決定するための指標となる、粗大イナート組織の累積体積比に関する基準値は、粉砕した後の石炭粒度（３ｍｍ以下または６．７ｍｍ以上の質量比（ＸまたはＸ’））および石炭装入密度（Ｙ）［乾炭ベース、ｔ／ｍ^３］によって変化するが、予め、少なくとも３条件以上の粉砕後の石炭粒度（３ｍｍ以下または６．７ｍｍ以上の質量比（ＸまたはＸ’））および石炭装入密度（Ｙ）［乾炭ベース、ｔ／ｍ^３］における基準値との関係、すなわち図７に示すような関係グラフを求めておけば、上記基準値を前記ＸおよびＹを変数とする計算式を基に設定することが可能となる。
【００９０】
本発明者らの検討結果によれば、上記粗大イナート組織の累積体積比に関する基準値は以下のような式で表すことができる。
【００９１】
【数３】

【００９２】
ここで、Ｘは粉砕後の石炭における３ｍｍ以下または６．７ｍｍ以上の質量比（％）、Ｙは石炭装入密度（乾炭ベース、ｔ／ｍ^３）、ａ，ｂ，ｃはそれぞれ定数を示す。
【００９３】
上記ＸおよびＹにおいて、少なくとも３水準以上の条件でそれぞれ図７に示すような関係グラフを作成し、それぞれの粗大イナート量の基準値Ｚ（％）を予め求めておくことにより上記（１）式は決められる。
【００９４】
例えば、Ｘを３ｍｍ以下の質量比とし、その変化量（α）を５とし、水準１：Ｘ＝８０％、Ｙ＝０．８０、水準２：Ｘ＝８５％、Ｙ＝０．８５、水準３：Ｘ＝８２％、Ｙ＝０．８１の３水準における図７に示すような関係グラフから、発明者らが求めた上記（１）式の各定数は、ａ＝−０．４、ｂ＝２０、ｃ＝２７であった。
【００９５】
また、Ｘを６．７ｍｍ以上の質量比とし、その変化量（α）を２とし、水準１：Ｘ＝１０％、Ｙ＝０．８０、水準２：Ｘ＝６％、Ｙ＝０．８５、水準３：Ｘ＝８％、Ｙ＝０．８１の３水準における図７に示すような関係グラフから、発明者らが求めた上記（１）式の各定数は、ａ＝０．６、ｂ＝２０、ｃ＝−１１であった。
【００９６】
次に、上記基準値に基づいて各銘柄の石炭を所定粒度に粉砕する場合の実施形態として、その粉砕粒度範囲について説明する。
【００９７】
前記粉砕の第１の実施形態としては、前記基準値以上の粗大イナート組織の累積体積比を有する銘柄の石炭を粉砕した後の３ｍｍ以下の質量比をＡ（％）、前記基準値未満の粗大イナート組織の累積体積比を有する銘柄の石炭を粉砕した後の３ｍｍ以下の質量比をＢ（％）、粉砕した後の配合炭全体の３ｍｍ以下の質量比をＬ（％）とする場合に、以下の関係を満足するように粉砕を行なう。
【００９８】
【数４】

【００９９】
前記粉砕の第２の実施形態としては、前記基準値以上の粗大イナート組織の累積体積比を有する銘柄の石炭を粉砕した後の６．７ｍｍ以上の質量比をＡ’（％）、前記基準値未満の粗大イナート組織の累積体積比を有する銘柄の石炭を粉砕した後の６．７ｍｍ以上の質量比をＢ’（％）、粉砕した後の配合炭全体の６．７ｍｍ以上の質量比をＬ’（％）とする場合に、以下の関係を満足するように粉砕を行なう。
【０１００】
【数５】

【０１０１】
上記（２）または（３）式により、様々な配合炭粒度、装入密度に応じて、粗大イナート組織の累積体積比に関する基準値を規定することが可能であり、微粉砕を強化すべき石炭と微粉砕しない又は粗粉砕すべき石炭を様々な操業条件に応じて容易に判別することが可能となる。
【０１０２】
Ａ＜Ｌ＋２、または、Ａ’＞Ｌ’−１の場合は、粗大イナート組織の累積体積比が基準値以上の銘柄の石炭中、ひいては配合炭全体中の粗大イナート組織の累積体積比を十分に減らすことができないので、強度の高いコークスを得ることができにくくなり得る。一方、Ａ＞Ｌ＋１４、または、Ａ’＜Ｌ’−１０の場合は、著しく微粉砕する必要があり、粉砕によるコークス強度向上効果に比べて、微粉の発生に起因する発塵量増大、炉壁へのカーボン付着などの操業上の問題発生、電力コストの増加、時間あたりの処理量の低下などを考慮すると工業的に得策でないため、好ましくない。
【０１０３】
したがって、本発明では、上記（２）式において、Ｌ＋２≦Ａ≦Ｌ＋１４を満足するように、つまり、粗大イナート組織の累積体積比が基準値以上の銘柄の石炭を粉砕した後の３ｍｍ以下の質量比（Ａ）が配合炭全体の３ｍｍ以下の質量比（Ｌ）より２〜１４％多くなるように粉砕することを必要条件とする。
【０１０４】
または、上記（３）式において、Ｌ’−１０≦Ａ’≦Ｌ’−１を満足するように、つまり、粗大イナート組織の累積体積比が基準値以上の銘柄の石炭を粉砕後、６．７ｍｍ以上の質量比（Ａ’）が配合炭全体の６．７ｍｍ以上の質量比（Ｌ’）より１〜１０％少なくなるように粉砕することを必要条件とする。
【０１０５】
また、Ｂ＞Ｌ−２、または、Ｂ’＜Ｌ’＋１の場合は、粗い石炭粒子が少ないため、配合炭の装入密度が大きく低下する可能性があるため、好ましくない。一方、Ｂ＜Ｌ−１４、または、Ｂ’＞Ｌ’＋１０の場合は、著しく粗い石炭粒子が多くなってしまい、コークス強度が低下し得るため好ましくない。
【０１０６】
したがって、本発明では、上記（２）式において、Ｌ−１４≦Ｂ≦Ｌ−２を満足するように、つまり、粗大イナート組織の累積体積比が基準値未満の銘柄の石炭を粉砕した後の３ｍｍ以下の質量比（Ｂ）が配合炭全体の３ｍｍ以下の質量比（Ｌ）より２〜１４％少なくなるように粉砕することを必要条件とする。
【０１０７】
または、上記（３）式において、Ｌ’＋１≦Ｂ’≦Ｌ’＋１０を満足するように、つまり、粗大イナート組織の累積体積比が基準値以上の銘柄の石炭を粉砕した後の６．７ｍｍ以上の質量比（Ｂ’）が配合炭全体の６．７ｍｍ以上の質量比（Ｌ’）より１〜１０％多くなるように粉砕することを必要条件とする。
【０１０８】
また、配合炭全体の３ｍｍ以下の質量比が７０％未満、または、配合炭全体の６．７ｍｍ以上の質量比が１５％超になると、粗粒が多すぎて著しくコークス強度が低下する場合があるので、配合炭の目標とする所望の粉砕粒度は、配合炭全体の３ｍｍ以下の質量比が７０％以上、または、配合炭全体の６．７ｍｍ以上の質量比が１５％以下であることが好ましい。また、上限は特に規定するものではない。
【０１０９】
本発明においては、上記のように各銘柄の石炭毎に上記基準値に応じて粉砕する他、上記基準値以上の銘柄の石炭からなるグループと基準値未満の銘柄の石炭からなるグループの２つのグループに分け、グループ毎に上記基準値に応じて粉砕してもよい。
【０１１０】
また、石炭の銘柄によって石炭化度が異なり、これにより粉砕後の配合炭の粒度分布に少なからず影響を与える可能性が考えられる。この問題をなくすために、特に石炭化度が大きく異なる複数銘柄の石炭を、イナート組織の累積体積比によりグループ分けして粉砕する場合は、石炭化度も考慮してグループ化するのが好ましい。
【０１１１】
なお、一般に石炭化度を表す指標として、ビトリニットの最大反射率（Ｒ０、ＪＩＳ　Ｍ８８１６）、揮発分（ＪＩＳ　Ｍ８８１４）等が知られており、本発明においても石炭の石炭化度を測定する場合にこれらの方法を用いてもよいが、特に、ビトリニットの最大反射率または平均反射率を用いるのが好ましい。　次に、石炭の全膨張率を考慮した場合の粉砕方法について説明する。一般的に、石炭を細粒化すると膨張性が低下する。膨張性の高い石炭と低い石炭とを配合する実際のコークス製造プロセスにおいて、膨張性の高い石炭を極端に微粉砕すると配合炭全体の膨張性の低下を招き、著しくコークス強度を低下させる恐れがある。
【０１１２】
そこで、本発明者らが各銘柄の石炭の粗大イナート組織と、全膨張率（ＪＩＳＭ８８０１（１９９３））、３ｍｍ以下の質量比およびコークス強度の関係について検討した結果、粗大イナート組織の累積体積比が基準値以上の銘柄の石炭のうちで、石炭の全膨張率が３５体積％以上の銘柄の石炭を粉砕した後の３ｍｍ以下の質量比Ｃ（％）または６．７ｍｍ以上の質量比Ｃ’（％）、粉砕した後の配合炭全体の３ｍｍ以下の質量比をＬ（％）または６．７ｍｍ以上の質量比Ｌ’（％）とする場合に、以下の（４）式または（５）式を満足するように粉砕を行なうとコークス強度がより向上することを見出した。
【０１１３】
【数６】

【０１１４】
【数７】

【０１１５】
Ｃ＜Ｌ＋２、または、Ｃ’＞Ｌ−１の場合は、上記コークス強度の向上効果を充分発揮することができなくなるため好ましくない。一方、Ｃ＞Ｌ＋４、または、Ｃ’＜Ｌ’−４の場合は、膨張性が大きく低下しコークス強度が低下するため好ましくない。
【０１１６】
よって、本発明において粗大イナート組織の累積体積比が基準値以上の銘柄の石炭のうちで、全膨張率が３５％以上の銘柄の石炭を粉砕する際に、上記（４）式において、Ｌ＋２≦Ｃ≦Ｌ＋１４を満足するように、つまり、当該銘柄の石炭を粉砕した後の３ｍｍ以下の質量比（Ｃ）が配合炭全体の３ｍｍ以下の質量比（Ｌ）より２〜４％多くなるように粉砕することが好ましい。
【０１１７】
または、上記（５）式において、Ｌ’−４≦Ｃ’≦Ｌ−１を満足するように、つまり、当該銘柄の石炭を粉砕した後の６．７ｍｍ以上の質量比（Ｃ’）が配合炭全体の６．７ｍｍ以上の質量比（Ｌ’）より１〜４％少なくなるように粉砕することが好ましい。
【０１１８】
【実施例】
（実施例１）
石炭中の粗大イナート組織に起因するコークス中の粗大イナート量の測定を目的として、あらかじめ配合前の各銘柄の石炭を３ｍｍ以下の質量比は８５％、装入密度（乾炭）は０．８５（ｔ／ｍ^３）の一定条件で乾留炉に装入し乾留することによりコークスを製造した。その結果から、図７と同様な粗大イナート量（１．０ｍｍ以上の粗大イナート組織の体積比）とコークス強度の変化量ΔＤＩ１５０／１５の関係グラフを作成し、ΔＤＩの大きい点（粗大イナート組織の体積比）を粗大イナート量の基準値として確認したところ、その基準値は１０％であった。
【０１１９】
コークス中の１ｍｍ以上の粗大イナート組織の累積体積比（粗大イナート量）が基準値（１０％）以上かつ全膨張率が３５体積％以上の石炭Ａ、粗大イナート量が基準値（１０％）以上かつ全膨張率が３５体積％未満の石炭Ｂ、粗大イナート量が基準値（１０％）未満の石炭Ｃを、所定の粒度に粉砕した後、質量ベースでＡ：Ｂ：Ｃ＝１：１：１となるように配合して、配合炭全体の３ｍｍ以下の質量比が７７％になるようにした。その後、配合炭を実炉をシミュレートできる乾留炉に装入しコークスを製造し、乾留後のコークスのドラム強度ＤＩ１５０／１５（ドラム１５０回転後に残った粒径１５ｍｍ以上の粒子の割合；ＪＩＳ　Ｋ２１５１（１９９３））を測定した。Ａ、Ｂ、Ｃの石炭性状（粗大イナート量（１．０ｍｍ以上の粗大イナート組織の累積体積比）、全膨張率、トータルイナート（全てのイナート組織の累積体積比））を表１に、石炭Ａ，石炭Ｂ，石炭Ｃ、およびこれらの石炭からなる配合炭における粉砕後の３ｍｍ以下の質量比を表２に示す。
【０１２０】
また、本発明範囲内または範囲外の各条件でおこなった実施例および比較例により得られたコークスのドラム強度ＤＩ１５０／１５を図８に示す。
【０１２１】
【表１】

【０１２２】
【表２】

【０１２３】
実施例１は、粗大イナート量が基準値（１０％）以上の石炭Ａ、Ｂを配合炭全体の３ｍｍ以下の質量比よりも６％大きな８３質量％になるように微粉砕し、粗大イナート量が基準値（１０％）未満の石炭Ｃを配合炭全体の３ｍｍ以下の質量比よりも１２％小さな６５質量％になるように粗粉砕した例である。
【０１２４】
実施例２は、実施例１の粗大イナート量が基準値（１０％）以上の石炭のうち、全膨張率が３５％以上の石炭Ａを配合炭全体の３ｍｍ以下の質量比よりも２％大きな７９質量％になるように微粉砕し、全膨張率が３５％未満の石炭Ｂを配合炭全体の３ｍｍ以下の質量比よりも１０％大きな８７質量％になるように微粉砕し、粗大イナート量が基準値（１０％）未満の石炭Ｃを配合炭全体の３ｍｍ以下の質量比よりも１２％小さな６５質量％になるように粗粉砕した例である。
【０１２５】
比較例１は、石炭Ａ、Ｂ、Ｃともに３ｍｍ以下の質量比を７７％に粉砕した例である。
【０１２６】
比較例２では、トータルイナートを粉砕条件決定の基準に用い、トータルイナートの大きな石炭Ｃの３ｍｍ以下の質量比が配合炭全体の３ｍｍ以下の質量比よりも１０％大きな８７質量％になるように微粉砕し、トータルイナートの小さな石炭Ａ、Ｂの３ｍｍ以下の質量比が配合炭全体の３ｍｍ以下の質量比よりも５％小さな７２質量％になるように粗粉砕した例である。
【０１２７】
図８に示すように、実施例のコークスはいずれも、比較例のコークスよりも明らかに高いＤＩ１５０／１５を示す。そして、実施例１のコークスよりも実施例２のコークスの方がより高いＤＩ１５０／１５を示す。以上より本発明の明確な効果を確認した。
【０１２８】
また比較例２では比較例１に比べて強度が低下しており、トータルイナートを粉砕条件決定の基準に用いると強度が低下する恐れがあることを確認した。
【０１２９】
（実施例３）
石炭中の粗大イナート組織に起因するコークス中の粗大イナート量の測定を目的として、あらかじめ配合前の各銘柄の石炭を６．７ｍｍ以上の質量比は７％、装入密度（乾炭）は０．７９（ｔ／ｍ^３）の一定条件で乾留炉に装入し乾留することによりコークスを製造した。その結果から、石炭粉砕粒度として６．７ｍｍ以上の質量比を採用し、図７と同様な粗大イナート量（１．０ｍｍ以上の粗大イナート組織の体積比）とコークス強度の変化量ΔＤＩ１５０／１５の関係グラフを作成し、ΔＤＩの大きい点（粗大イナート組織の体積比）を粗大イナート量の基準値として確認したところ、その基準値は９％であった。
【０１３０】
コークス中の１ｍｍ以上の粗大イナート組織の累積体積比（粗大イナート量）が基準値（９％）以上かつ全膨張率が３５体積％以上の石炭Ｄ、粗大イナート量が基準値（９％）以上かつ全膨張率が３５体積％未満の石炭Ｅ、粗大イナート量が基準値（９％）未満の石炭Ｆを所定の粒度に粉砕した後、質量ベースでＤ：Ｅ：Ｆ＝１：１：１となるように配合して、配合炭全体の６．７ｍｍ以上質量比が７％になるようにした。その後、配合炭を実炉をシミュレートできる乾留炉に装入しコークスを製造し、乾留後のコークスのドラム強度ＤＩ１５０／１５（ＪＩＳ　Ｋ２１５１（１９９３））を測定した。Ｄ、Ｅ、Ｆの石炭性状（粗大イナート量（１．０ｍｍ以上の粗大イナート組織の累積体積比）、全膨張率、トータルイナート（全てのイナート組織の累積体積比））を表３に、石炭Ｄ，石炭Ｅ，石炭Ｆ、およびこれらの石炭からなる配合炭における粉砕後の６．７ｍｍ以上の質量比を表４に示す。また、本発明範囲内または範囲外の各条件でおこなった実施例および比較例で得られたコークスのドラム強度ＤＩ１５０／１５を表４に示す。
【０１３１】
【表３】

【０１３２】
【表４】

【０１３３】
実施例３は、粗大イナート量が基準値（９％）以上の石炭Ｄ、Ｅを配合炭全体の６．７ｍｍ以上の質量比よりも２％小さな５質量％になるように微粉砕し、粗大イナート量が基準値（９％）未満の石炭Ｆを配合炭全体の６．７ｍｍ以上の質量比よりも４％大きな１１質量％になるように粗粉砕した例である。
【０１３４】
実施例４は、粗大イナート量が基準値（９％）以上の石炭のうち全膨張率が３５％以上の石炭Ｄを配合炭全体の６．７ｍｍ以上の質量比よりも１％小さな６質量％になるように微粉砕し、全膨張率が３５％未満の石炭Ｅを配合炭全体の６．７ｍｍ以上の質量比よりも３％小さな４質量％になるように微粉砕し、粗大イナート量が基準値（１０％）未満の石炭Ｆを配合炭全体の６．７ｍｍ以上の質量比よりも４％大きな１１質量％になるように粗粉砕した例である。
【０１３５】
比較例３は、石炭Ｄ、Ｅ、Ｆともに６．７ｍｍ以上の質量比を７％に粉砕した例である。
【０１３６】
表４に示すように、実施例のコークスはいずれも、比較例のコークスよりも明らかに高いコークスのドラム強度ＤＩ１５０／１５を示す。そして、実施例３のコークスよりも実施例４のコークスの方がより高いＤＩ１５０／１５を示す。以上より本発明の明確な効果を確認した。
【０１３７】
【発明の効果】
本発明によれば、コークス強度の低下をもたらす粗大なイナート組織の累積体積比を低減して、使用する石炭銘柄および配合比率を変えることなく、また、石炭装入密度を低下させることなく、強度の高いコークスを得ることが可能な高強度コークスの製造方法を提供することができる。
【０１３８】
したがって、本発明を用いれば、安価かつ低品位である非微粘結炭の使用比率を上昇させても、良好なコークス強度が維持できるため、コークスの製造費を低減できるという顕著な効果をもたらす
【図面の簡単な説明】
【図１】コークス中に存在するイナート組織とその周辺の組織を示す図である。
【図２】＋１．５ｍｍの粗大イナート組織の累積体積比とコークス強度（ＤＩ）との関係を示す図である。
【図３】＋１．５ｍｍの粗大イナート組織の累積体積比は一定とし、コークス中の総イナート比率を変えた場合の、コークス強度（ＤＩ）を示す図である。
【図４】コークス中の＋１．５ｍｍの粗大イナート組織の存在量（比）の低減前後の対比で、イナート組織の存在態様とコークス強度（ＤＩ）との対応関係を示す図である。
【図５】粉砕前の石炭粒度（原炭粒度）と、総イナート比率、及び、＋１．５ｍｍのイナート組織の累積体積比との関係を示す図である。
【図６】粗大イナート組織の累積体積比とコークス強度との関係を模式的に示す図である。
【図７】粗大イナート組織の累積体積比（横軸）が異なる複数銘柄の石炭を用い、粉砕後の石炭粒度において、３ｍｍ以下の微粉の質量比を８０％から９０％に変化させた場合における変化を示す図である。
【図８】本発明の実施例および比較例におけるコークスのドラム強度の測定結果を示した図である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing coke, and more particularly, to a method for pulverizing and adjusting mixed coal for charging in a coke oven to improve the strength and yield of coke obtained by dry distillation in a coke oven.
[0002]
[Prior art]
The blast furnace coke is manufactured by blending and pulverizing many brands of coal, or pulverizing and blending many brands of coal, respectively, and then charging the coke oven and carbonizing. At this time, the particle size of the blended coal charged into the coke oven is adjusted so that the mass ratio of 3 mm or less is 70 to 90%.
[0003]
Generally, the fine pulverization of coal charged into a coke oven is performed in order to make the properties of a blended coal composed of a plurality of brands of coal uniform, and within a predetermined condition range, the finer the pulverized coal, the higher the coke strength. It is known to improve.
[0004]
However, if the coal is finely pulverized, the bulk density is reduced when the coal is charged into a coke oven, which causes a reduction in coke strength. The reason is that the gap between the coal particles increases due to the decrease in the bulk density in the coke oven, the adhesion between the coal particles deteriorates during the carbonization process, and a brittle portion is formed in the coke. In addition, due to the decrease in bulk density, there is also a problem that the amount of coal charged into the coke oven decreases and the productivity of coke decreases.
[0005]
Therefore, several methods for pulverizing coal and adjusting the particle size of blended coal that greatly affect coke strength have been proposed from the viewpoint of improving coke strength (for example, see Patent Documents 1 to 5).
[0006]
For example, Patent Literature 1 describes a method for producing metallurgical coke in which two or more types of coal are separately pulverized according to coal properties and the particle size distribution is adjusted according to properties.
[0007]
However, the production method described in Patent Document 1 aims to improve the porosity while suppressing a decrease in strength. In this production method, there is a possibility that the coke strength does not reach a desired level. is there.
[0008]
Further, Patent Document 2 discloses a method of producing a high-strength coke by adjusting the pulverized particle size according to the reflectance (Ro) for the purpose of blending a large amount of inexpensive coal. Specifically, coal having a reflectivity of less than 0.8 is finely pulverized so that the sieve under 5 mm sieve is substantially 100% and the sieve under 3 mm sieve is 80% or more. Describes a pulverization method of coarsely pulverizing so as to be coarser than coal having a reflectance of less than 0.8%.
[0009]
In this patent document 2, the maximum flowability (MF) in the ghee cellar fluidity test is 3 or more among coals having a mass ratio of 3 mm or less of 80 ± 5% and a reflectivity of 0.8 or more in the entire coal blend. Moreover, it is indicated that it is preferable to coarsely pulverize a coal having a total inertness (percentage of the inertinite component described in JIS M8816 “Method of measuring fine structure component and reflectance of coal”) of less than 20%, most.
[0010]
However, even with the pulverization method described in Patent Document 2, the strength of coke is about 83 in DI, and there is a possibility that coke with a desired strength cannot be obtained.
[0011]
Patent Literature 3 discloses, as a coal for charging a coke oven capable of obtaining high-strength coke, coal containing non-sintered coal particles in an amount of 20 to 80% by mass and having a particle size in a predetermined range. Has been described. Further, Patent Documents 4 and 5 describe a method of obtaining coal for charging a coke oven by dividing a plurality of brands of coal into a plurality of groups according to properties (degree of coking) and pulverizing the coal to a predetermined particle size. Have been.
[0012]
However, even with the coal or the method described in Patent Documents 3, 4, and 5, there is a possibility that coke having a desired strength cannot be obtained.
[0013]
As described above, in the production of coke, the particle size of the blended coal is adjusted to be a predetermined particle size by pulverizing various brands of coal to improve the coke characteristics. In view of the point, there is a possibility that the intensity level does not reach an expected level in any of the methods described in the above patent documents.
[0014]
[Patent Document 1]
JP-A-11-181441
[Patent Document 2]
JP 2000-336373 A
[Patent Document 3]
JP 2001-181644 A
[Patent Document 4]
JP 2001-181650 A
[Patent Document 5]
JP 2001-279254 A
[0015]
[Problems to be solved by the invention]
As described above, there is a limit in the improvement of coke strength only by the conventional particle size adjustment of coal, and the inert (texture of an inert substance that does not soften and melt) in the texture of coal as described in Patent Document 2 described above. However, there is also a problem that a sufficient coke strength cannot be obtained with respect to a method of pulverizing coal based on the total content (hereinafter, sometimes referred to as a total inert). However, further improvement in the strength of blast furnace coke has been demanded due to demands for more efficient and stable operation of the blast furnace.
[0016]
Therefore, in view of the above-described circumstances, the present invention focuses on the relationship between the form of the inert structure of coal and the coke strength in the blended coal charged into the coke oven, and according to the size of the inert structure of the coal, By controlling pulverization and blending, it is possible to produce coke that has a strength exceeding the conventional strength limit without changing the coal brand or properties that make up the blended coal and the blending mass ratio, and without reducing the coal charge density. An object of the present invention is to provide a method for producing high-strength coke to be produced.
[0017]
[Means for Solving the Problems]
The gist of the present invention is as follows.
[0018]
(1) In a method for producing coke by charging a blended coal composed of one or more kinds of different brands of coal into a coke oven, followed by carbonization.
The coal of each brand is pulverized to a predetermined particle size in accordance with the cumulative volume ratio of the coarse inert structure present in the coal of each brand or coke obtained by carbonizing the coal, and the coal of each brand after the pulverization. A method for producing high-strength coke, characterized in that the blended coal obtained by blending is blended so that the particle size of the whole blended coal becomes a predetermined particle size.
[0019]
(2) The method for producing high-strength coke according to the above (1) or (2), wherein the coal of each brand in which the coarse inert structure is concentrated is selectively pulverized to a predetermined particle size.
[0020]
(3) The method for producing high-strength coke according to (2), wherein the coal of each brand in which the coarse inert structure is concentrated is coal having a particle diameter of 6.7 mm or more.
[0021]
(4) The method for producing high-strength coke according to any one of the above (1) to (3), wherein the coarse inert structure is an inert structure of 1.0 mm or more.
[0022]
(5) Setting the pulverized particle size of each brand of coal based on a mass ratio of 3 mm or less or 6.7 mm or more after pulverizing each brand of coal and a reference value obtained from the coal charging density. The method for producing high-strength coke according to any one of the above (1) to (4), which is characterized by the following.
[0023]
(6) The method for producing high-strength coke according to (5), wherein the reference value is represented by the following equation (1).
[0024]
(Equation 2)

[0025]
Here, Z is a reference value (%), X is a mass ratio (%) of 3 mm or less or 6.7 mm or more in the pulverized coal, and Y is a coal charge density (dry coal base, t / m ³ ), A, b, and c indicate constants, respectively.
[0026]
(7) The mass ratio of 3 mm or less after pulverizing a brand of coal having a cumulative volume ratio of the coarse inert structure equal to or greater than the reference value is 2 to 14% larger than the mass ratio of 3 mm or less of the entire blended coal. The mass ratio of 3 mm or less after pulverizing and pulverizing the brand coal having the cumulative volume ratio of the coarse inert structure less than the reference value is 2 to 14% less than the mass ratio of 3 mm or less of the whole blended coal. (5) or (6), wherein the high-strength coke is produced.
[0027]
(8) The mass ratio of 6.7 mm or more after pulverizing the brand coal having the cumulative volume ratio of the coarse inert structure equal to or more than the reference value is 1 to 10% more than the mass ratio of 6.7 mm or more of the entire blended coal. Pulverized so as to reduce, and a brand of coal having a cumulative volume ratio of the coarse inert structure less than the reference value, the mass ratio of 6.7 mm or more after pulverization, the mass ratio of 6.7 mm or more of the whole blended coal The method for producing high-strength coke according to the above (5) or (6), wherein the pulverization is carried out so as to increase the mass ratio by 1 to 10%.
[0028]
(9) A coal having a cumulative volume ratio of a coarse inert structure equal to or greater than the reference value and a brand having a total expansion rate of 35% by volume or more has a mass ratio of 3 mm or less after pulverization. The method for producing high-strength coke according to the above (7), wherein the pulverization is carried out so as to increase the mass ratio by 2 to 4% from the following mass ratio.
[0029]
(10) The mass ratio of 6.7 mm or more after pulverizing a brand of coal having a cumulative volume ratio of a coarse inert structure equal to or more than the reference value and a total expansion rate of 35% by volume or more is a blended coal. The method for producing a high-strength coke according to the above (8), wherein the pulverization is performed so that the mass ratio is 1 to 4% less than the mass ratio of 6.7 mm or more.
[0030]
BEST MODE FOR CARRYING OUT THE INVENTION
The inert structure present in the coal has a lower volatile content than the structure (vitrinit and extrinite) that softens and melts during the carbonization process in a coke oven, and remains in the coke after carbonization in almost the same form. Therefore, the shrinkage rate differs between the inert structure and the softening and melting structure present in the coal during the dry distillation in the coke oven, and the difference in the shrinkage ratio causes stress at the interface between the two structures and remains in the coke. Cracks occur inside or around the inert tissue.
[0031]
FIG. 1 shows an example of the inert structure remaining in the coke and the surrounding structure.
[0032]
The size of the inert structure remaining in the coke exists in a wide range from about 0.1 μm to about 10 mm, and the inert structure in the coal remains in almost the same form. Here, the size of the inert tissue means the absolute maximum length of the inert (the same applies hereinafter).
[0033]
As shown in FIG. 1, in the coarse inert structure of the order of mm (1.0 mm or more) remaining in the coke, a large crack of the order of mm (1.0 mm or more) is generated inside or around the inert structure. I can do it.
[0034]
According to Griffith's fracture condition formula (see, for example, “JF Knott (Translated by Hiroshi Miyamoto), Fundamentals of Fracture Mechanics, p. 107, Baifukan (1977)”), a crack of a large size becomes a crack of a small size. Since the crack develops and expands with a lower stress than that, a large crack of the order of mm generated inside or around the coarse inert structure tends to be a starting point (defect) of brittle fracture when the coke is impacted. For this reason, coke in which a large number of such cracks having a size on the order of mm are significantly reduced in strength and easily powdered.
[0035]
Therefore, the present inventor, in order to reduce the large cracks generated in the coke causing a decrease in the strength of the coke, pulverizing the coal before charging the coke oven, the size of the coarse inert structure in the coal Focusing on reducing the size of coal, pulverizing various brands of coal, measuring the strength of coke obtained by carbonization in a coke oven, and measuring the size of the inert structure present in the coal (an inert structure of a specific size) Of the coke strength (DI) was investigated.
[0036]
FIG. 2 shows the relationship between the cumulative volume ratio of the coarse inert structure having a size of +1.5 mm remaining in the coke and the coke strength (DI) when the coal was pulverized under various conditions and carbonized in a coke oven. Show. At this time, the furnace charging density of the pulverized coal was 0.85 t / m ³ The cumulative volume ratio of the inert structure of all sizes remaining in the coke obtained by carbonization was kept constant at 42%. The cumulative volume ratio of the inert structures of all sizes (hereinafter, sometimes referred to as a total inert ratio) is a capacity percentage of the inertinite group measured according to the method described in JIS M8816 (1992).
[0037]
FIG. 2 shows that the coke strength (DI) is significantly improved when the cumulative volume ratio of the coarse inert structure of +1.5 mm is reduced.
[0038]
Similarly, FIG. 3 shows the total inert ratio (cumulative volume ratio of the inert structure of all sizes) and the coke strength when the coal was pulverized under various conditions and carbonized in a coke oven. (DI). At this time, the furnace charging density of the pulverized coal was 0.85 t / m ³ The cumulative volume ratio of the +1.5 mm coarse inert structure remaining in the coke obtained by carbonization was kept constant at 10%.
[0039]
FIG. 3 shows that the coke strength (DI) is almost constant (DI: 85) regardless of the total inert ratio remaining in the coke.
[0040]
The results in FIGS. 2 and 3 indicate that the factor governing coke strength (DI) is not the total inert ratio remaining in the coke, but the cumulative volume ratio of the coarse inert structure of +1.5 mm.
[0041]
Further, FIG. 4 shows the inert structure in the coke with and without reducing the cumulative volume ratio of the +1.5 mm coarse inert structure remaining in the coke by pulverizing the coal charged into the coke oven. And the coke strength (DI) are shown. The part marked in the photograph is a coarse inert structure of +1.5 mm.
[0042]
From this figure, it can be seen that the reduction of the abundance (ratio) of the coarse inert structure of +1.5 mm significantly increases the coke strength.
[0043]
In FIGS. 2 to 4, the cumulative volume ratio of the +1.5 mm coarse inert structure remaining in the coke was investigated. Results were confirmed.
[0044]
From the results of the above-described investigation by the present inventors, it was found that, in the inert structure remaining in the coke, the reduction of the abundance (cumulative volume ratio) of the coarse inert structure of +1.0 mm significantly increased the coke strength. The first feature of the present invention is to control the pulverization of coal before charging in a coke oven in accordance with the cumulative volume ratio of the coarse inert structure based on this finding.
[0045]
Furthermore, the existence form of the inert structure in the coal charged into the coke oven varies depending on the brand of coal, and it is always effective to grind uniformly regardless of the brand of coal, which is effective for grinding and reducing the coarse inert structure. May not be linked to
[0046]
Therefore, in the actual pulverization step of the coal, the present inventor has determined the existence form of the inert structure in various brands of coal in order to more effectively pulverize the coarse inert structure of +1.0 mm and reduce the cumulative volume ratio. investigated.
[0047]
FIG. 5 shows the relationship between the coal particle size (raw coal particle size) before pulverization, the total inert ratio remaining in the coke, and the cumulative volume ratio of the +1.5 mm inert structure.
[0048]
From this figure, it can be seen that +1.5 mm of coarse inert is concentrated in +6.7 mm of coal (raw coal).
[0049]
Further, Table 1 shows the results of an investigation on the total inert ratio and the cumulative volume ratio of the inert structure of +1.5 mm for the three brands.
[0050]
From this table, it is understood that the cumulative volume ratio of the coarse inert structure of +1.5 mm in the raw coal greatly differs depending on the brand of coal.
[0051]
From FIG. 5 and Table 1, it was found that the cumulative volume ratio of the coarse inert structure of +1.5 mm greatly differs depending on the brand of coal or the particle size of coal (raw coal). In addition, in FIG. 5 and Table 1, the cumulative volume ratio of the coarse inert structure of +1.5 mm was investigated. It was experimentally confirmed that, as in the case of the cumulative volume ratio of the coarse inert structure of 0.5 mm, it greatly differs depending on the brand or coal particle size of the coal.
[0052]
Therefore, in the present invention, based on the above experimental results and confirmation, among coals of various brands, in particular, coal in which a coarse inert structure of +1.0 mm is concentrated is targeted for pulverization, and usually coal (raw coal) is used. Is sieved by a sieve manufactured according to the JIS standard. Therefore, a 6.7 mm (nominal size) mesh in the JIS standard (JIS Z8801, a mesh sieve) was adopted as a preferable critical particle size of the coal to be pulverized. Further, the brand of coal is not particularly limited, and any known coal may be appropriately selected and used as long as the present invention can be implemented.
[0053]
As described above, the second feature of the present invention is that the preferred coal particle size for pulverizing coal (raw coal) is defined as +6.7 mm in accordance with the sieves defined by the JIS standard.
[0054]
The inventors have confirmed that the coarse inert structure is also concentrated in a sieve having a nominal size larger than +6.7 mm, for example, in coal (raw coal) particles of +8.0 mm and +9.5 mm. However, as the sieve size increases, the proportion of the coal (raw coal) particles present decreases, and the measurement error also increases. On the other hand, a coarse inert structure is concentrated to some extent in a sieve having a nominal size smaller than +6.7 mm, that is, coal (raw coal) particles of +5.6 mm and +4.75 mm, but a coal of +6.7 mm ( The concentration of coarse inert microstructure is lower than that of raw coal) particles. For this reason, in the present invention, the particle size of coal (raw coal) to be pulverized is preferably set to +6.7 mm.
[0055]
In the present invention, the coarse inert structure is an inert structure having a size of 1.0 mm or more, preferably 1.5 mm or more in absolute maximum length. This is because coke having a coarse inert structure of such a size has a reduced strength, that is, a large crack is generated inside or around the coarse inert structure at the time of a drop impact in a drum test, and the coke has a faster progress, It is to enlarge.
[0056]
In the present invention, the cumulative volume ratio of the inert structure is used as an index indicating the amount of the inert structure present in a single brand of coal or coke.
[0057]
Usually, the area ratio in a two-dimensional cross section can be treated as a volume ratio in a three-dimensional space. Therefore, the cumulative area ratio of the inert tissue is obtained by image analysis of a cross-sectional observation photograph with a microscope, and this is calculated as the cumulative volume ratio of the inert tissue. Can be treated as
[0058]
This is the same idea as treating the content of each microstructure component in a two-dimensional cross section of a polishing sample as a percentage by volume in the method for measuring the microstructure component and reflectance of coal according to JIS M8816 (1992).
[0059]
When the cumulative area ratio of the coarse inert structure present in the coke obtained by carbonizing each type of coal is specifically determined, for example, the cumulative area ratio is determined by the following method.
[0060]
(1) Coal is produced as it is as raw coal or after pulverized to a predetermined particle size, followed by dry distillation. Here, the carbonization is preferably carried out at a furnace temperature of 1000 ° C. to 1300 ° C. and carbonization until the temperature in the coal reaches 700 ° C. to 1200 ° C.
[0061]
(2) Collect coke, fill the cut surface with resin, and take a photograph with a microscope.
[0062]
(3) In the photograph of the cut surface of coke, the coarse inert structure having an absolute maximum length of 1 mm or more is marked, and the area (cumulative area) marked using image analysis software becomes the entire region (area) of the cut surface photograph. The occupying ratio Si (%) is measured.
[0063]
(4) In the photograph of the cut surface, the coke wall and the pores are binarized, and the ratio Sp (%) of the region of the pores (accumulated area) to the entire region (area) of the photograph of the cut surface is measured.
[0064]
(5) The cumulative area ratio of the coarse inert in the photograph of the cut surface: X (%) = Si / (100−Sp) × 100 is determined.
[0065]
The above method is a method of measuring the cumulative volume ratio of the coarse inert structure present in coke after carbonization of coal, but the inert structure in coal hardly changes even when coking by carbonization, and is substantially unchanged. Since it remains in the same form, the amount of coarse inert present in the coal can be measured in the same manner as described above.
[0066]
When the amount of coarse inert present in the coal is measured by the above-described method, in the above (3), instead of “the entire area (area) of the cut surface photograph”, “the area sum of the coal particles in the observation area” is used. And the number of pores in the coal particles is negligibly small (Sp is almost 0%), so that the step (4) is unnecessary. This method has an advantage that the inert tissue can be easily identified and the measurement time is shorter than the former method. However, according to studies by the inventors, although the inert structure in coal remains almost in the same form even after coking, strictly speaking, a part thereof is separated or melted during the carbonization process. However, the size of the inert tissue may vary slightly. Therefore, which method should be used may be appropriately selected according to requirements such as ease of measurement or measurement accuracy and reliability.
[0067]
Reference value for coarse inert structure (critical value of cumulative volume ratio of inert structure to obtain a predetermined coke strength improving effect, which is an index for determining the grinding conditions of coal of each brand. The definition will be described later. ) Is, for example, the measured value of the cumulative volume ratio of the coarse inert structure present in the coal of each brand measured in the above method or in the coke obtained by carbonizing the coal in a coke oven. It can be set based on the relationship with coke strength.
[0068]
In the present invention, coal (raw coal) of each brand constituting the blended coal before charging in a coke oven is pulverized under predetermined pulverization conditions based on a reference value. For example, the cumulative volume ratio of a coarse inert structure is equal to or more than a reference value. With regard to the coal (raw coal) of the brand (1), the coke strength can be improved to a predetermined strength by performing fine grinding relatively relatively as compared with the coal (raw coal) of the other brands. Incidentally, in the specification of the present application, blended coal means coal which is obtained by pulverizing coal before blending and blending.
[0069]
However, as described above, the coke strength is also affected by the charging density of the blended coal in the coke oven, and the coke strength is usually lowered because the interparticle adhesion is deteriorated as the bulk density is lowered.
[0070]
Therefore, in order to eliminate such problems, adjust the grinding conditions of each brand of coal based on the blending ratio of each brand of coal, or mix each brand of coal based on the grinding conditions of each brand of coal. By adjusting the ratio, it is preferable that the charge density of the entire blended coal in the coke oven be equal to or higher than a predetermined value after pulverizing the coal of a specific brand. For example, the charging density in a coke oven of the entire blended coal is reduced by finely pulverizing coal of a brand whose coarse volume inert structure has a cumulative volume ratio equal to or higher than the above reference value, but other brands of coal having a brand of less than the above reference value. By not pulverizing or coarsely pulverizing, the charged density or the particle size of the entire blended coal can be ensured within a predetermined range.
[0071]
In addition, the reference value of the charging density (or the blended coal particle size after pulverization) of the entire blended coal in the coke oven is determined by the conventionally known coke strength and the charging density (or the blended coal particle size after pulverization). Can be set from the relationship.
[0072]
In addition, after finely pulverizing the coal of the brand whose cumulative volume ratio of the coarse inert structure is equal to or more than the above-mentioned reference value, even if it is dry-distilled simply without blending with the coal of the coarsely-ground brand of less than the above-mentioned reference value, the high strength coke can be obtained. If it is possible to obtain carbon dioxide, only finely pulverized coal may be carbonized.
[0073]
Since the fine pulverization causes a decrease in the charging density and acts as a factor of a decrease in the coke strength, only the finely pulverized coal is charged in consideration of both the strength improving effect and the charging density lowering effect by the fine pulverization. It is preferable to appropriately select whether to dry-distill or dry-distill in combination with coarsely ground brand coal.
[0074]
Next, a specific method for determining the grinding conditions of coal (raw coal) will be described.
[0075]
In the present invention, by pulverizing coal (raw coal), the cumulative volume ratio of the coarse inert structure of +1.0 mm in coal or coke is reduced to less than a reference value, but this reference value depends on the brand and properties of the coal. Therefore, the relationship between the cumulative volume ratio of the coarse inert structure and the coke strength is determined in advance for each brand or group, and the reference value is set based on the relationship.
[0076]
Normally, as the relationship is schematically shown in FIG. 6, the coke strength decreases almost linearly with an increase in the cumulative volume ratio (Z) of the coarse inert structure. Based on the reduction width of the cumulative volume ratio of the inert structure (X1-X2 = ΔZ) and the improvement width of the coke strength (DI) (DI2-DI1 = ΔDI), it can be set as follows.
[0077]
In FIG. 7, using a plurality of brands of coal having different cumulative volume ratios (horizontal axis) of the coarse inert structure, the mass ratio of the coal of 3 mm or less after pulverizing them is changed from 80% to 90%, for example. (The change (increase) indicates the degree of reduction of the coarse inert microstructure). The change in the coke cold strength (DI) (that is, the DI of the coke obtained by carbonizing 90% of coal of 3 mm or less). And DI of coke obtained by carbonizing 80% of coal of 3 mm or less: ΔDI150 / 15 (vertical axis).
[0078]
From this figure, it can be seen that the change in strength DI (ΔDI150 / 15) due to pulverization sharply increases at the boundary of the cumulative volume ratio of the coarse inert structure in a certain brand of coal. The boundary of the cumulative volume ratio of the coarse inert structure is defined as a reference value (critical value) for obtaining a predetermined coke strength improving effect.
[0079]
That is, in the case of coal whose cumulative volume ratio of the coarse inert structure is equal to or more than the reference value, the amount of increase in coke strength (improvement width) due to reduction of the cumulative volume ratio of the coarse inert structure due to pulverization of the coal is large, while In the coal whose brand cumulative volume ratio is less than the reference value, the amount of increase (improvement range) in the coke strength due to the reduction in the cumulative volume ratio of the coarse inert structure is small.
[0080]
Thus, from the relationship between the cumulative volume ratio of the coarse inert structure and the amount of change in coke strength within a predetermined range of the mass ratio of 3 mm or less in the coal, the reduction of the cumulative volume ratio of the coarse inert structure of the coal (fine pulverization of coal) The critical value of the cumulative volume ratio of the coarse inert structure in which the amount of increase in coke strength greatly changes due to the strengthening) can be used as the reference value.
[0081]
In FIG. 7, in evaluating the amount of improvement in coke strength with respect to the reduction of the cumulative volume ratio of the coarse inert structure in the coal by pulverization, a mass ratio of 3 mm or less was used as the particle size of the pulverized coal. By adopting a mass ratio of 6.7 mm or more, a similar relationship graph can be created to determine a reference value. In addition, the mass ratio of 3 mm or less as the coal pulverization particle size is used as a control index for maintaining a predetermined coke strength from the relationship between the uniformity of the raw materials or the charging density and the coke strength in a normal coke production operation. .
[0082]
On the other hand, as described above, the coarse inert structure of +1.0 mm is concentrated into coal (raw coal) having a particle size of 6.7 mm or more by a sieve according to JIS (JIS Z8801, a mesh sieve). In order to evaluate the amount of improvement in coke strength with respect to the reduction of the coarse inert structure in the medium with higher accuracy and reliability, it is preferable to employ a mass ratio of 6.7 mm or more in the pulverized coal.
[0083]
In the case where the relationship graph of FIG. 7 is created by employing the mass ratio of 6.7 mm or more as the coal pulverized particle size, a plurality of brands of coal having different cumulative volume ratios (horizontal axis) of the coarse inert structure in the coal are used. The coke cold strength (DI) when the mass ratio of 6.7 mm or more after coal pulverization was changed from 10% to 3% (this change (decrease) indicates the degree of reduction of the coarse inert structure in the coal.) (Ie, the difference between the DI of coke obtained by carbonizing 3% or more of coal at 6.7 mm or more and the DI of coke obtained by carbonizing 10% of coal at 6.7 mm or more: ΔDI150) / 15, vertical axis).
[0084]
In the embodiment of the present invention, for example, a reference value relating to the cumulative volume ratio of the coarse inert structure can be set as an index for determining the coal grinding conditions of each brand as follows.
[0085]
First, using a plurality of brands of coal having different cumulative volume ratios of the coarse inert structure in the coal, a predetermined range (X ± α [%]) of a mass ratio of 3 mm or less in the pulverized coal and a density of charged coal (Y [ Dry coal base, t / m ³ ]), The amount of change in the coke strength within a predetermined range (X ± α [%]) of the cumulative volume ratio of the coarse inert structure and the mass ratio of 3 mm or less in the pulverized coal as shown in FIG. A relationship graph with (ΔDI150 / 15) is created, and the critical value of the cumulative volume ratio of the coarse inert structure in which ΔDI150 / 15 has rapidly changed is set as a reference value.
[0086]
ΔDI150 / 15 is the coal charge density Y [dry coal base, t / m ³ ], The cold strength (DI) of the coke obtained by carbonization was measured when the mass ratio of 3 mm or less in the pulverized coal was X-α% and X + α%, It is determined by taking the difference (ΔDI150 / 15). The above α indicates the deviation of the mass ratio of 3 mm or less of the pulverized coal with respect to the center value (X), but as long as the variation (ΔDI) of the cold strength (DI) of coke is determined. It is not specified.
[0087]
The above embodiment is an example in which a predetermined range (X ± α [%]) of a mass ratio of 3 mm or less is adopted as the coal pulverized particle size, but a predetermined range of a mass ratio of 6.7 mm or more is used instead. The range (X ′ ± β [%]) may be used. In this case, as described above, the improvement in coke strength can be evaluated with higher accuracy and reliability with respect to the reduction of the coarse inert structure in coal by pulverization.
[0088]
As described above, the reference value for the coarse inert structure, which is an index for determining the coal crushing conditions of each brand, is obtained by calculating the change amount (ΔDI) of the cold strength (DI) of coke in a relation graph as shown in FIG. Is large, that is, in a region where the effect of improving the coke strength by the fine pulverization (reduction of the coarse inert structure) is small, the cumulative volume ratio of the coarse inert structure is set. However, the effect on the effect of improving the coke strength can be ignored.
[0089]
As described above, the reference value for the cumulative volume ratio of the coarse inert structure, which is an index for determining the coal grinding conditions of each brand, is the coal particle size after grinding (3 mm or less or mass ratio of 6.7 mm or more (X Or X ')) and coal charge density (Y) [dry coal base, t / m ³ The particle size of the coal after pulverization under at least three conditions (mass ratio (X or X ′) of 3 mm or less or 6.7 mm or more (X or X ′)) and the density of charged coal (Y) [dry coal base, t / M ³ , Ie, a relation graph as shown in FIG. 7, the reference value can be set based on a calculation formula using X and Y as variables.
[0090]
According to the study results of the present inventors, the reference value relating to the cumulative volume ratio of the coarse inert structure can be expressed by the following equation.
[0091]
[Equation 3]

[0092]
Here, X is the mass ratio (%) of 3 mm or less or 6.7 mm or more in the pulverized coal, and Y is the coal charge density (dry coal base, t / m ³ ), A, b, and c indicate constants, respectively.
[0093]
In the above X and Y, a relation graph as shown in FIG. 7 is created under at least three or more levels of conditions, and the reference value Z (%) of each coarse inert amount is obtained in advance to obtain the above equation (1). Is determined.
[0094]
For example, X is a mass ratio of 3 mm or less, the change amount (α) is 5, level 1: X = 80%, Y = 0.80, level 2: X = 85%, Y = 0.85, level 3: From the relation graph as shown in FIG. 7 at three levels of X = 82% and Y = 0.81, the respective constants of the above equation (1) obtained by the inventors are a = −0.4, b = 20, c = 27.
[0095]
Further, X is a mass ratio of 6.7 mm or more, and the variation (α) is 2. Level 1: X = 10%, Y = 0.80, Level 2: X = 6%, Y = 0.85 Level 3: X = 8%, Y = 0.81 From the relationship graph as shown in FIG. 7 at three levels, the constants of the above equation (1) obtained by the inventors are a = 0.6, b = 20 and c = -11.
[0096]
Next, a description will be given of a pulverized particle size range as an embodiment in which each brand of coal is pulverized to a predetermined particle size based on the above reference values.
[0097]
As a first embodiment of the pulverization, a mass ratio of 3 mm or less after pulverizing a brand of coal having a cumulative volume ratio of a coarse inert structure equal to or more than the reference value is defined as A (%), When the mass ratio of 3 mm or less after pulverizing a brand of coal having the cumulative volume ratio of the inert structure is B (%), and the mass ratio of 3 mm or less of the entire blended coal after pulverization is L (%), Grinding is performed so as to satisfy the following relationship.
[0098]
(Equation 4)

[0099]
As a second embodiment of the pulverization, a mass ratio of 6.7 mm or more after pulverizing a brand of coal having a cumulative volume ratio of a coarse inert structure equal to or more than the reference value is defined as A ′ (%). B ′ (%) is the mass ratio of 6.7 mm or more after pulverizing a brand of coal having a cumulative volume ratio of a coarse inert structure of less than B, and L is the mass ratio of 6.7 mm or more of the entire blended coal after pulverization. In the case of '(%), pulverization is performed so as to satisfy the following relationship.
[0100]
(Equation 5)

[0101]
According to the above formula (2) or (3), it is possible to define a reference value relating to the cumulative volume ratio of the coarse inert structure according to various blended coal particle sizes and charged densities, and the coal to be pulverized should be strengthened. It is possible to easily discriminate the coal which is not pulverized or which should be coarsely pulverized according to various operating conditions.
[0102]
In the case of A <L + 2 or A ′> L′−1, the cumulative volume ratio of the coarse inert structure in the coal whose brand volume is larger than the reference value, that is, in the entire blended coal, is sufficiently increased. Since it cannot be reduced, it may be difficult to obtain high-strength coke. On the other hand, in the case of A> L + 14 or A ′ <L′−10, it is necessary to remarkably pulverize, and compared to the effect of improving the coke strength by pulverization, the amount of dust generated due to the generation of fine powder increases, Considering the occurrence of operational problems such as carbon deposition on the surface, an increase in electric power costs, and a decrease in the throughput per unit time, it is not industrially feasible and is not preferred.
[0103]
Therefore, in the present invention, in the above equation (2), L + 2 ≦ A ≦ L + 14 is satisfied, that is, a mass of 3 mm or less after pulverizing coal of a brand whose cumulative volume ratio of the coarse inert structure is equal to or more than the reference value. It is a necessary condition that pulverization is performed so that the ratio (A) is 2 to 14% larger than the mass ratio (L) of 3 mm or less of the whole blended coal.
[0104]
Alternatively, in the above formula (3), after pulverizing a brand of coal that satisfies L′−10 ≦ A ′ ≦ L′−1, that is, after pulverizing a brand of coal whose cumulative volume ratio of the coarse inert structure is equal to or more than a reference value. It is a necessary condition that the pulverization is performed so that the mass ratio (A ′) of 7 mm or more is 1 to 10% less than the mass ratio (L ′) of 6.7 mm or more of the entire blended coal.
[0105]
Further, when B> L−2 or B ′ <L ′ + 1, the amount of coarse coal particles is small, so that the charging density of the blended coal may be significantly reduced, which is not preferable. On the other hand, when B <L−14 or B ′> L ′ + 10, the number of extremely coarse coal particles increases, and the coke strength may decrease.
[0106]
Therefore, in the present invention, in the above formula (2), L-14 ≦ B ≦ L−2 is satisfied, that is, after the coal of the brand having the cumulative volume ratio of the coarse inert structure less than the reference value is pulverized. It is a necessary condition that pulverization is performed so that the mass ratio (B) of 3 mm or less is 2 to 14% less than the mass ratio (L) of 3 mm or less of the whole coal blend.
[0107]
Alternatively, in the above formula (3), 6.7 mm after pulverizing a brand of coal in which L ′ + 1 ≦ B ′ ≦ L ′ + 10 is satisfied, that is, the cumulative volume ratio of the coarse inert structure is equal to or more than the reference value. It is a necessary condition that pulverization is performed so that the above mass ratio (B ′) is 1 to 10% larger than the mass ratio (L ′) of 6.7 mm or more of the whole blended coal.
[0108]
Also, when the mass ratio of 3 mm or less of the whole coal blend is less than 70%, or the mass ratio of 6.7 mm or more of the whole coal blend exceeds 15%, the coke strength may be significantly reduced due to too much coarse particles. Therefore, the desired desired crushed particle size of the coal blend is that the mass ratio of 3 mm or less of the whole coal blend is 70% or more, or the mass ratio of 6.7 mm or more of the whole coal blend is 15% or less. preferable. The upper limit is not particularly specified.
[0109]
In the present invention, in addition to pulverizing according to the reference value for each brand of coal as described above, there are two groups, a group consisting of coal having a brand not less than the reference value and a group consisting of coal having a brand less than the reference value. You may divide into groups and grind each group according to the said reference value.
[0110]
Further, the degree of coalification varies depending on the brand of coal, which may have a considerable effect on the particle size distribution of the blended coal after pulverization. In order to eliminate this problem, in particular, when a plurality of brands of coal having greatly different degrees of coalification are pulverized by being divided into groups based on the cumulative volume ratio of the inert structure, it is preferable to group the coals in consideration of the degree of coalification.
[0111]
In general, the maximum reflectance (R0, JIS M8816), volatile matter (JIS M8814) and the like of vitrinite are known as indices indicating the degree of coalification. Although these methods may be used, it is particularly preferable to use the maximum reflectance or the average reflectance of vitrinite. Next, a pulverization method in consideration of the total expansion coefficient of coal will be described. Generally, when coal is refined, its expandability is reduced. In the actual coke production process of blending high expansive coal and low expansive coal, if the highly expansive coal is extremely finely pulverized, the overall expansibility of the blended coal may be reduced and the coke strength may be significantly reduced. .
[0112]
Then, the present inventors examined the relationship between the coarse inert structure of each brand of coal, the total expansion coefficient (JIS M8801 (1993)), the mass ratio of 3 mm or less, and the coke strength. As a result, the cumulative volume ratio of the coarse inert structure was Among the coals of the brands equal to or higher than the reference value, the mass ratio C (%) of 3 mm or less or the mass ratio C ′ of 6.7 mm or more after pulverizing the coal of the brand whose total expansion rate of the coal is 35% by volume or more is pulverized. %), When the mass ratio of 3 mm or less of the whole blended coal after pulverization is L (%) or the mass ratio L ′ (%) of 6.7 mm or more, the following formula (4) or (5) It has been found that when pulverization is performed so as to satisfy the above, coke strength is further improved.
[0113]
(Equation 6)

[0114]
(Equation 7)

[0115]
C <L + 2 or C ′> L−1 is not preferable because the effect of improving the coke strength cannot be sufficiently exhibited. On the other hand, when C> L + 4 or C ′ <L′−4, the expandability is greatly reduced and the coke strength is reduced, which is not preferable.
[0116]
Therefore, in the present invention, when pulverizing coal having a total expansion rate of 35% or more among the coals having a cumulative inertia structure having a cumulative volume ratio of not less than a reference value, in the above formula (4), L + 2 ≦ In such a manner that C ≦ L + 14 is satisfied, that is, the mass ratio (C) of 3 mm or less after pulverizing the coal of the brand is 2 to 4% larger than the mass ratio (L) of 3 mm or less of the entire blended coal. Pulverization is preferred.
[0117]
Alternatively, in the above formula (5), a mass ratio (C ′) of 6.7 mm or more after pulverizing the coal of the brand such that L′−4 ≦ C ′ ≦ L−1 is satisfied. It is preferable to pulverize so that the mass ratio (L ') of 6.7 mm or more of the whole coal is reduced by 1 to 4%.
[0118]
【Example】
(Example 1)
For the purpose of measuring the amount of coarse inert in the coke caused by the coarse inert structure in the coal, the weight ratio of coal of each brand before blending of 3 mm or less is 85% and the charging density (dry coal) is 0.85 in advance. (T / m ³ The coke was produced by charging the mixture in a carbonization furnace under the constant conditions described in (1) and carbonizing. From the results, a graph similar to that shown in FIG. 7 was made between the amount of coarse inert (volume ratio of the coarse inert structure of 1.0 mm or more) and the amount of change in coke intensity ΔDI150 / 15, and a point where ΔDI was large (the coarse inert structure (Volume ratio) was confirmed as a reference value of the coarse inert amount, and the reference value was 10%.
[0119]
Coal A with a cumulative volume ratio (coarse inert amount) of coarse inert structure of 1 mm or more in coke (coarse inert amount) or more and a total expansion coefficient of 35 vol% or more, and a coarse inert amount of not less than standard value (10%). Further, coal B having a total expansion coefficient of less than 35% by volume and coal C having a coarse inert amount of less than a reference value (10%) are pulverized to a predetermined particle size, and then A: B: C = 1: 1: 1 on a mass basis. 1 so that the mass ratio of 3 mm or less of the entire coal blend was 77%. Thereafter, the coking coal is charged into a carbonization furnace capable of simulating a real furnace to produce coke, and the drum strength DI150 / 15 of the coke after carbonization (the ratio of particles having a particle diameter of 15 mm or more remaining after rotation of the drum 150; JIS K2151) (1993)). Table 1 shows the coal properties of A, B, and C (coarse inert amount (cumulative volume ratio of coarse inert structure of 1.0 mm or more), total expansion coefficient, and total inert (cumulative volume ratio of all inert structure)). Table 2 shows the mass ratio of 3 mm or less after pulverization of A, Coal B, Coal C, and a blended coal composed of these coals.
[0120]
FIG. 8 shows the drum strength DI150 / 15 of coke obtained by the examples and the comparative examples performed under the conditions within or outside the range of the present invention.
[0121]
[Table 1]

[0122]
[Table 2]

[0123]
In Example 1, coals A and B having a coarse inert amount equal to or more than a reference value (10%) are finely pulverized so as to be 83% by mass, which is 6% larger than a mass ratio of 3 mm or less of the entire blended coal. This is an example of coarsely pulverizing coal C having a value of less than the reference value (10%) to 65% by mass, which is 12% smaller than the mass ratio of 3 mm or less of the entire blended coal.
[0124]
In Example 2, the coal A having a total expansion rate of 35% or more among the coals having a coarse inert amount of the reference value (10%) or more of Example 1 which is 2% larger than the mass ratio of 3 mm or less of the entire blended coal. Finely pulverized to 79% by mass, and finely pulverized coal B having a total expansion rate of less than 35% to 87% by mass, which is 10% larger than the mass ratio of 3 mm or less of the entire blended coal. This is an example of coarsely pulverizing coal C having a value of less than the reference value (10%) to 65% by mass, which is 12% smaller than the mass ratio of 3 mm or less of the entire blended coal.
[0125]
Comparative Example 1 is an example in which the mass ratio of 3 mm or less for each of coals A, B, and C was pulverized to 77%.
[0126]
In Comparative Example 2, the total inert was used as a criterion for determining the crushing conditions, and the mass ratio of coal C having a large total inert of 3 mm or less was 87% by mass which was 10% larger than the mass ratio of 3 mm or less of the whole blended coal. This is an example in which finely pulverized and coarsely pulverized so that the mass ratio of 3 mm or less of coals A and B having a small total inertia is 5% smaller than the mass ratio of 3 mm or less of the whole blended coal.
[0127]
As shown in FIG. 8, all of the cokes of the example show a significantly higher DI 150/15 than the coke of the comparative example. And the coke of Example 2 shows higher DI150 / 15 than the coke of Example 1. From the above, a clear effect of the present invention was confirmed.
[0128]
Further, in Comparative Example 2, the strength was lower than that in Comparative Example 1, and it was confirmed that the strength might be reduced when the total inert was used as a criterion for determining the grinding conditions.
[0129]
(Example 3)
For the purpose of measuring the amount of coarse inert in the coke caused by the coarse inert structure in the coal, the weight ratio of coal of each brand before blending of 6.7 mm or more is 7% and the charging density (dry coal) is 0 in advance. .79 (t / m ³ The coke was produced by charging the mixture in a carbonization furnace under the constant conditions described in (1) and carbonizing. From the results, a mass ratio of 6.7 mm or more was adopted as the coal pulverized particle size, and the coarse inert amount (volume ratio of the coarse inert structure of 1.0 mm or more) and the change in coke strength ΔDI150 / 15 similar to FIG. A relation graph was created, and a point where ΔDI was large (volume ratio of the coarse inert structure) was confirmed as a reference value of the coarse inert amount. The reference value was 9%.
[0130]
Coal D with a cumulative volume ratio (coarse inert amount) of coarse inert structure of 1 mm or more in coke (coarse inert amount) or more and a total expansion rate of 35 vol% or more, and a coarse inert amount of not less than standard value (9%). In addition, coal E having a total expansion rate of less than 35% by volume and coal F having a coarse inert amount of less than a reference value (9%) are pulverized to a predetermined particle size, and then D: E: F = 1: 1: 1 on a mass basis. So that the mass ratio of 6.7 mm or more of the entire blended coal was 7%. Thereafter, the coal blend was charged into a carbonization furnace capable of simulating a real furnace to produce coke, and the drum strength DI150 / 15 (JIS K2151 (1993)) of the coke after carbonization was measured. Table 3 shows the coal properties of D, E, and F (coarse inert amount (cumulative volume ratio of coarse inert structure of 1.0 mm or more), total expansion coefficient, and total inert (cumulative volume ratio of all inert structure)). Table 4 shows the mass ratio of 6.7 mm or more after pulverization of D, Coal E, Coal F, and the blended coal composed of these coals. Table 4 shows the drum strength DI150 / 15 of the coke obtained in Examples and Comparative Examples performed under the conditions within or outside the range of the present invention.
[0131]
[Table 3]

[0132]
[Table 4]

[0133]
In Example 3, coals D and E having a coarse inert amount equal to or more than a reference value (9%) are finely pulverized so as to be 5% by mass, which is 2% smaller than a mass ratio of 6.7 mm or more of the entire blended coal. This is an example in which coal F having an inert amount of less than a reference value (9%) is coarsely pulverized to 11% by mass, which is 4% larger than the mass ratio of 6.7 mm or more of the entire blended coal.
[0134]
In Example 4, coal D having a total expansion rate of 35% or more among coals having a coarse inert amount equal to or more than a reference value (9%) is 6% by mass, which is 1% smaller than the mass ratio of the entire blended coal of 6.7 mm or more. And the coal E having a total expansion of less than 35% is finely pulverized to 4% by mass, which is 3% smaller than the mass ratio of the entire blended coal of 6.7 mm or more, and the coarse inert amount is This is an example in which coal F of less than the reference value (10%) is coarsely pulverized to 11% by mass, which is 4% larger than the mass ratio of 6.7 mm or more of the entire coal blend.
[0135]
Comparative Example 3 is an example in which the mass ratio of 6.7 mm or more for each of coals D, E, and F was pulverized to 7%.
[0136]
As shown in Table 4, all of the cokes of the examples show significantly higher coke drum strength DI150 / 15 than the coke of the comparative example. And the coke of Example 4 shows a higher DI150 / 15 than the coke of Example 3. From the above, a clear effect of the present invention was confirmed.
[0137]
【The invention's effect】
According to the present invention, the cumulative volume ratio of a coarse inert structure that causes a decrease in coke strength is reduced, without changing the coal brand and blending ratio used, and without lowering the coal charge density, And a method for producing high-strength coke capable of obtaining high-strength coke.
[0138]
Therefore, when the present invention is used, even if the use ratio of non-fine caking coal which is inexpensive and low in quality is increased, good coke strength can be maintained, so that a significant effect that the cost of producing coke can be reduced is obtained.
[Brief description of the drawings]
FIG. 1 is a diagram showing an inert structure existing in coke and a structure around the inert structure.
FIG. 2 is a diagram showing a relationship between a cumulative volume ratio of a coarse inert structure of +1.5 mm and coke strength (DI).
FIG. 3 is a diagram showing coke strength (DI) when the cumulative volume ratio of a coarse inert structure of +1.5 mm is fixed and the total inert ratio in coke is changed.
FIG. 4 is a diagram showing a correspondence relationship between the presence state of an inert structure and coke strength (DI) in comparison with before and after a reduction in the abundance (ratio) of a +1.5 mm coarse inert structure in coke.
FIG. 5 is a diagram showing the relationship between the coal particle size (raw coal particle size) before pulverization, the total inert ratio, and the cumulative volume ratio of an inert structure of +1.5 mm.
FIG. 6 is a diagram schematically showing a relationship between a cumulative volume ratio of a coarse inert structure and coke strength.
FIG. 7 shows a case where a plurality of brands of coal having different cumulative volume ratios (horizontal axis) of a coarse inert structure are used and the mass ratio of fine powder of 3 mm or less is changed from 80% to 90% in the coal particle size after pulverization. It is a figure showing a change.
FIG. 8 is a view showing measurement results of drum strength of coke in Examples and Comparative Examples of the present invention.

Claims (10)

A method for producing coke by charging a blended coal comprising one or more kinds of different brands of coal into a coke oven and then carbonizing the mixture.
The coal of each brand is pulverized to a predetermined particle size in accordance with the cumulative volume ratio of the coarse inert structure present in the coal of each brand or coke obtained by carbonizing the coal, and the coal of each brand after the pulverization. A method for producing high-strength coke, characterized in that the blended coal obtained by blending is blended so that the particle size of the whole blended coal becomes a predetermined particle size. The method for producing high-strength coke according to claim 1, wherein coal of each brand in which the coarse inert structure is concentrated is selectively pulverized to a predetermined particle size. 3. The method for producing high-strength coke according to claim 1, wherein the coal of each brand in which the coarse inert structure is concentrated is coal having a particle size of 6.7 mm or more. 4. The method for producing high-strength coke according to any one of claims 1 to 3, wherein the coarse inert structure is an inert structure of 1.0 mm or more. Based on the mass ratio of 3 mm or less or 6.7 mm or more after pulverizing the coal of each brand and the reference value obtained from the coal charging density, the pulverized particle size of the coal of each brand is set. A method for producing a high-strength coke according to claim 1. The method according to claim 5, wherein the reference value is represented by the following equation (1).

Here, Z is a reference value (%), X is a mass ratio (%) of 3 mm or less or 6.7 mm or more in the pulverized coal, Y is a coal charging density (dry coal base, t / m ³ ), a , B, and c indicate constants, respectively. A brand of coal having a cumulative volume ratio of the coarse inert structure equal to or greater than the reference value, pulverized so that the mass ratio of 3 mm or less after pulverization is 2 to 14% larger than the mass ratio of 3 mm or less of the entire blended coal, In addition, a brand of coal having a cumulative volume ratio of a coarse inert structure less than the reference value is pulverized so that the mass ratio of 3 mm or less after pulverization is 2 to 14% less than the mass ratio of 3 mm or less of the entire blended coal. The method for producing high-strength coke according to claim 5 or 6, wherein The mass ratio of 6.7 mm or more after pulverizing the brand coal having the cumulative volume ratio of the coarse inert structure equal to or more than the reference value is 1 to 10% less than the mass ratio of 6.7 mm or more of the entire coal blend. Pulverized, and the mass ratio of 6.7 mm or more after pulverizing a brand of coal having a cumulative volume ratio of a coarse inert structure less than the reference value is 1% more than the mass ratio of 6.7 mm or more of the entire blended coal. The method for producing high-strength coke according to claim 5 or 6, wherein the pulverization is performed so that the amount increases by 10%. A brand coal having a cumulative volume ratio of the coarse inert structure equal to or greater than the reference value, and having a total expansion rate of 35% by volume or more, a mass ratio of 3 mm or less after pulverization is 3 mm or less of the entire coal blend. The method for producing a high-strength coke according to claim 7, wherein the pulverization is performed so as to increase the mass ratio by 2 to 4%. The mass ratio of 6.7 mm or more after pulverizing a brand of coal having a cumulative volume ratio of a coarse inert structure equal to or more than the reference value and a total expansion rate of 35% by volume or more is 6% of the total blended coal. The method for producing a high-strength coke according to claim 8, wherein the pulverization is performed so that the mass ratio is 1 to 4% smaller than the mass ratio of 0.7 mm or more.

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