JP3672632B2

JP3672632B2 - Consumable probe for simultaneous measurement of molten slag temperature and electrical conductivity, and method for simultaneous measurement of molten slag temperature and electrical conductivity

Info

Publication number: JP3672632B2
Application number: JP22858595A
Authority: JP
Inventors: 賢一片山; 隆山内
Original assignee: Nisshin Steel Co Ltd
Current assignee: Nippon Steel Nisshin Co Ltd
Priority date: 1995-08-14
Filing date: 1995-08-14
Publication date: 2005-07-20
Anticipated expiration: 2015-08-14
Also published as: JPH0954057A

Description

【０００１】
【産業上の利用分野】
本発明は、電気炉，転炉等の炉内溶融スラグの電気伝導度からスラグ組成を推定するときに使用される溶融スラグの温度，電気伝導度同時測定用消耗型プローブ及び溶融スラグの温度，電気伝導度同時測定方法に関する。
【０００２】
【従来の技術】
鉄，非鉄等の金属精錬では、千数百度の高温溶融金属や溶融スラグが処理されている。このような高温雰囲気における精錬反応の進行を知るための情報を溶融金属から得るため、直接的には温度測定や固体電池による酸素濃度測定等が採用されている。また、最近では、特開平４−３４６６１１号公報で紹介されているように、精錬反応の際に放出される発光スペクトルを光ファイバーを介して分光器に取り込み解析する方法も開発されている。
他方、溶融スラグの情報を得る手段としては、スラグをサンプリングし、前処理後、蛍光Ｘ線分析，ＩＣＰ分析等の機器分析によって成分分析することが一般的である。しかし、サンプリングから分析結果を得るまでに長時間を要するため、このサンプル分析法が適用される対象が限られていた。
【０００３】
そこで、迅速性を必要とする場合、たとえば特開昭５５−１２８５２０号で開示されているように、スラグの電気抵抗を測定し、抵抗値からスラグの滓化率を判定している。特開平２−５４１２５号公報では、高さ方向に関して複数の回路を形成した電極を外周に埋め込んだプローブを使用し、転炉のスラグレベルを高精度で測定している。
電気炉においても、電極から取り出されたレジスタンス，リアクタンス等の電気抵抗指標に基づき炉内の状況を推定し、間接的に安定操業の維持に利用している。
【０００４】
【発明が解決しようとする課題】
電極から取り出された電気抵抗指標は、スラグの性状を推定する上で有望視されているものの、実際に現場で測定する際には種々の障害によって信頼性が低下する。たとえば、溶融スラグの電気伝導度を測定する場合、操業状態が常に一定でないため、測定時の温度条件が種々変動する。そのため、高精度の電気抵抗指標を得るためには、電気伝導度を測定した位置にある溶融スラグの温度も測定し、測定された温度に応じて電気抵抗指標を補正する必要がある。
また、転炉，取鍋等の製錬容器のように、炉内状況が観察し難い箇所に存在する溶融スラグを測定する場合、操業条件の変化によってスラグの正確な位置を常に把握することができない。そのため、センサーを容器内に挿入する際、適切な挿入位置が不明確になる。すなわち、測定ごとに測定位置が変り、正確な電気伝導度を測定することが困難になる。
【０００５】
更に、溶融金属及び溶融スラグは、一般的に比重が大きく異なることから、それぞれ下層及び上層に分離した状態で存在している。しかし、メタル層とスラグ層との界面近傍では、粒状の金属がスラグ中に細かく懸濁した部分が存在し、また溶融金属の対流等によってメタル／スラグ界面の乱れによって、メタル層とスラグ層とが明確な境界で区分されていない。そのため、間違って溶融金属の位置を測定する場合もあった。
このように従来法では、測定条件として測定位置を最適にするための調整時間が必要であったり、測温も別途行うことが必要なことから、迅速な対応が困難であった。また、コスト的にも、負担の大きな測定方法であった。
本発明は、このような問題を解消すべく案出されたものであり、溶融スラグの電気伝導度と温度を同時に測定し、その測定値から最適なスラグ組成に調整するための迅速な判定が可能な温度，電気伝導度同時測定用消耗型プローブを提供し、精度の高い測定値を低コストで迅速に得ることを目的とする。
【０００６】
【課題を解決するための手段】
本発明の溶融スラグの温度，電気伝導度同時測定用消耗型プローブは、その目的を達成するため、プローブ先端に配置され、被測定溶融スラグに対し半耐食性の保護管で保護された熱電対素線と、該熱電対素線の近傍に配置された電気伝導度測定用の電極と、前記熱電対素線及び前記電極対の基部を絶縁状態で固定する耐火物と、前記保護管及び前記電極対を保護する保護キャップとを備え、かつ前記熱電対素線の先端測温部と前記電極の先端を前記耐火物から略同じ高さ位置としており、保護管が溶融スラグによって溶損したとき、熱電対素線と電気伝導度測定用電極との間に電気伝導度測定用回路が形成されることを特徴とする。
また、電極対のうちの１本の先端位置と片方の電極の先端位置との差を、両電極間の間隙以下になるようにプローブ先端に配置してもよい。この差の調整によって、メタルのレベルを検出する機能を付与することができる。
【０００７】
溶融酸化物の電気伝導度は、メタルプールに浮遊しているスラグ等の溶融酸化物にプローブを浸漬し、温度測定用熱電対による溶融酸化物の測温と同時に、電極対間に形成された電気伝導度測定用回路により測定される。電気伝導度の測定値は、同時に測定された温度情報を取り込んで、スラグ組成の推定に使用される。また、電極対のうちの１本の先端位置と片方の電極の先端位置との差を両電極間の間隙以下になるようにプローブ先端に配置したプローブを使用するとき、溶融金属と共存する状態の溶融酸化物に向けてプローブを下降させ、電極間に電流が流れることから溶融酸化物に電極が到達したことを推定し、電気伝導度の測定値の急激な変化から溶融金属に電極が到達したことを推定する。次いで、溶融酸化物層中の測定位置までプローブを上昇させ、溶融酸化物の温度及び電気伝導度を測定する。
【０００８】
【作用】
電気伝導度は、スラグ組成によって変わるが、温度の影響も大きく受ける。そのため、正確なスラグ組成を求める場合、温度の測定が重要である。温度の測定値に応じて検出された電気伝導度を補正し、得られた補正値からスラグ組成を推定するとき、操業条件に応じて変動する温度の影響を相殺し、高精度の推定が可能になる。本発明は、このような前提に立って、電気伝導度の測定と同時にスラグ温度を測定できるプローブを開発し、且つこの測定プローブで得られた情報に基づきスラグ組成を高精度で判定するものである。
本発明に従った電気伝導度測定プローブは、上底吹き転炉，ＡＯＤ炉，電気アーク炉，電気抵抗炉等の炉内や、ＲＨ法，ＶＯＤ法等で精錬する際の取鍋内等、構造的，設備的にスラグを観察し難い箇所で測定するときに特に有効である。
このプローブは、たとえば図１に示すように、プローブ１の先端にＵ字型のガラス管２で保護された熱電対素線３を挿入している。また、熱電対による測温位置の先端部に、先端位置を揃えた電極対４を固定用の耐火物５に絶縁状態で組み込んでいる。電極対４は、この構成により耐火物の電気抵抗の影響を受けることなく、高精度でスラグの電気伝導度を測定できる。電極対４は、コストを下げるため鋼，ステンレス鋼等で作製することも可能である。
【０００９】
また、容器内溶鋼の湯面に向けて測定プローブを下降させる際、操業条件によってはスラグ温度の低い表面層近傍が固化していることもある。このような状況下で測定プローブを下降させると、プローブ浸漬時に物理的な力によって保護管が破損する虞れがある。下降時の破損は、たとえばアルミ，銅等でできた保護キャップ６をプローブ先端に装着することにより防止できる。
電極対４の材質としては、より厳密な測定を必要とする場合には耐食性に優れた貴金属又は高融点金属等が使用される。他方、高価な材質に替えて測温用の熱電対素線３を伝導度測定用電極対の片方の電極として使用するとき、コストダウンが図られる。電極対４は、図３に示すように絶縁材７を介して固定用耐火物５に挿通される。固定用耐火物５は、耐火性円筒８の先端加工部を塞ぐように取り付けられ、耐火性円筒８と共に外紙管９に挿入される。
【００１０】
熱電対素線３を伝導度測定用電極対の片方の電極に兼用する場合、図２に示すように、溶融スラグに対して半耐食性の物質でできた保護管２で熱電対素線３を被覆する。半耐食性物質は、温度測定に必要な数秒〜数十秒間だけ素線３をスラグから保護する。それ以上時間が経過すると、溶融又はスラグとの反応により保護管２が完全に侵食され、熱電対素線４が露出する。半耐食性保護管２の材質には、被測定スラグの組成及び温度に応じて最適な材質を使用することが望ましい。たとえば、石英ガラス質の保護管であれば、ＮａＯ₂ ，ＰｂＯ，ＢａＯ等の微量添加によって、融点を被測定物の温度近くに調整したものが使用される。
測温後、半耐食性保護管２の溶損により熱電対素線３が露出すると、測温が不可能になるが、露出した熱電対素線３は、電気伝導度測定用電極の片方に利用できる。この熱電対素線３は、片方の電極４との間に電気伝導度測定用の回路を構成する。このとき、片方の電極４は、熱電対と同様にスラグに対して優れた耐食性を示す白金，モリブデン，タングステン等の貴金属又は高融点金属を線状又は棒状に加工したものが使用される。
【００１１】
最適な測定位置が不明なときは、図４に示すように、測温用熱電対３を中心として、片方の電気伝導度測定電極１０と対称位置に露出状態の溶融金属検知用電極１１を備えたプローブを使用することが好ましい。溶融金属検知用電極１１は、長い鋼製又はステンレス鋼製のワイヤ又はロッドでできており、その長さはスラグ／メタルの界面状態に応じて調整されている。すなわち、電気伝導度測定電極１０と溶融金属検知用電極１１との長さの差は、スラグ／メタルの厚みｄ以上に設定される。これにより、電気伝導度測定用電極対３，１０がメタルプールに接することなく、溶融金属検知用電極１１のみをメタルプールに浸漬し、メタルの湯面レベルを検出することができる。
スラグ／メタルの界面厚みｄは、測定しようとする工程や炉の特性によって異なるが、検知棒，電磁気的センサー等を使用して予め求めておくことが好ましい。また、スラグ／メタル界面が大きく波打っていたり、界面近くのスラグ中に多量の流鉄が懸濁する可能性がある場合には、それに応じて電気伝導度測定電極１０と溶融金属検知用電極１１との長さの差を十分大きくしておくことがよい。
【００１２】
プローブ下降中の電極対長さの差Ｌと電極対間の距離Ｄとの関係が電気伝導度の測定に及ぼす影響を、図５を参照しながら説明する。長さ差Ｌ≦距離Ｄでは、メタルに電気伝導度測定用電極（短電極）１０が接近し長さ差Ｌに等しくなった時点で、図６（ａ）に示すように電気伝導度が急上昇する。そこで、溶融金属検知用電極（長電極）１１がメタルに接触したことが推定される。このとき、長さ差Ｌ≧スラグ／メタル界面の厚みｄとしているので、短電極１０がメタルに接触する確率が低くなる。
これに対し、長さ差Ｌ＞距離Ｄでは、メタルと短電極１０との間の距離が長さ差Ｌに等しくなっても図６（ｂ）に示すように電気伝導度の明確な上昇が検出されず、更にプローブが下降してメタルまでの距離が距離Ｄに等しくなった時点で初めて電気伝導度の上昇が明らかになる。このとき、短電極１０の先端がメタルから長さ差Ｌより更に短い位置に達しているので、短電極１０がメタルに接触する確率が高くなる。その結果、電気伝導度測定用電極１０に溶融金属が付着し、その後に実施されるスラグ層での電気伝導度の測定に誤差が生じ易くなる。
【００１３】
このようなことから、電極対長さの差Ｌと電極対間の距離Ｄとの間に、長さ差Ｌ≦距離Ｄの関係を維持しておくことが重要である。そして、溶融金属検知用（長）電極先端がメタルプールに完全に到達したと判定されると、プローブ１の下降を停止する。そして、目標位置にプローブ１を再度上昇させ、スラグの測温及び電気伝導度の測定を行う。このとき、電気伝導度の測定には、溶融金属検知用の電極１１を使用せず、前述したように片方の電気伝導度測定用電極１０と測温用熱電対３との間に回路を形成し、スラグの電気伝導度を測定する。
このように、電気伝導度測定用の電極をメタルまで浸漬させることなく、スラグの厚みやメタルレベルが把握でき、結果として目標位置で電気伝導度及び温度を同時に、すなわち１回のプローブ挿入動作で測定できる。このような場合でも、溶融金属検知用電極１１には、安価な鋼又はステンレス鋼が使用でき、著しいコストアップを防がれる。また、本発明に従ったプローブは、スラグ／メタル界面を検出できることから、たとえばメタル湯面のレベルセンサーとしても使用される。更に、熱電対の保護管２，外紙管９，電極１０，１１の材質を耐食性のある材質に替えるとき、繰返し使用可能な耐久性プローブとなる。
【００１４】
【実施例】
実施例１：
ステンレス鋼溶銑を製造している電気アーク炉において、スクラップを主とする装入原料が溶け落ちた時点で、炉内に生成したスラグの組成を調整することに適用した実施例を説明する。プローブとしては、Ｒ型熱電対を石英ガラス質の保護管に挿入し、径８ｍｍ，長さ３５ｍｍのＳＵＳ３０４製円柱電極を２５ｍｍの間隔で配置して電極対を構成した図１のプローブを使用した。
電気炉で１０チャージ分について測定した結果、スラグの比電気伝導度は１５００℃における値に補正して０．９３〜１．４６Ω^-1／ｃｍの範囲にあった。予め求めておいた１５００℃におけるスラグ中ＣａＯ濃度と比電気伝導度との関係から、各チャージでのＣａＯ濃度を推定し、出銑時のＣａＯ濃度が目標値の４０％になるように不足分のＣａＯを炉内に供給した。取鍋に出銑した後、取鍋からスラグをサンプリングし、サンプル分析によって実際のＣａＯ濃度を測定した。その結果を、表１に示す。
【００１５】
実施例２：
次に、プローブ先端に径１．５ｍｍ及び長さ３５ｍｍの白金製電気伝導度測定用電極の１本を設け、融点１５００℃に調整したシリカガラス質の保護管にＲ型熱電対を挿入した図３のプローブを使用し、スラグの温度及び電気伝導度を測定した。この場合、測定用熱電対による測温開始後、測温不能となった時点で測温用熱電対と露出電極との間に回路が形成され、この回路を介して電気伝導度が測定される。
この場合の測定手順を、図７のフローに示す。先ず、昇降装置によってプローブを測定位置まで下降させ、スラグ層に浸漬する。この瞬間から、プローブ先端位置、正確には熱電対先端の感温部スラグの温度測定が開始される。熱電対素線の被覆材及びスラグの成分，温度等にもよるが、数秒から数十秒で被覆材が溶損し素線が露出するまで、測温データが得られる。素線が露出すると、短絡によって測温エラーが発生するので、測温データの取込みを中止する。同時に、電気伝導度測定用回路が形成され、電気伝導度が測定される。ここで、電気伝導度測定用電極の１本が露出した白金製の電極であり、片方が露出したＲ型熱電対素線となる。この両電極間に電源部からある電圧下で電流が供給され、そのときの抵抗値から電気伝導度が算出される。
【００１６】
この消耗型電気伝導度測定プローブを使用して、実施例１と同様に電気アーク炉で５チャージ分について温度及び電気伝導度を測定した。測定に要する時間は、操業条件によって各チャージで２０〜８０秒の範囲で異なっていた。測定結果に基づいて調整用のＣａＯを供給し、取鍋出銑後のスラグからサンプル分析によって実際のＣａＯ濃度を測定した。出銑時のスラグ中ＣａＯ濃度の目標値４５％に対する実際の分析値を、表１に比較して示した。
表１から明らかなように、実施例１及び２共に目標ＣａＯ濃度にほぼ調整できており、高精度でＣａＯ濃度が推定されていることが判る。その結果、電気炉溶銑のＳ濃度は０．０１〜０．０２％の低位に安定しており、良好な脱硫反応が行われたことが確認された。
【００１７】
実施例３：
真空精錬装置内の取鍋に浮遊しているスラグの電気伝導度測定に適用した実施例を説明する。脱ガス中の真空精錬装置は、容器にカバーが設置されて内部が真空状態にある。そのため、内部にある取鍋内のスラグ面を正確に把握することは困難である。そこで、電気電導度測定用電極対の１本を、溶融金属検知用の電極としたプローブ（図４参照）を使用した。プローブの先端に径１ｍｍのタングステン製電極を測温用熱電対の先端位置までの長さで設置し、それより２０ｍｍ長い長さで径８ｍｍの鋼製電極を設置した。なお、タングステン製電極と鋼製電極との間は４０ｍｍの間隔に保ち、その間隔に石英質保護管に挿入したＲ型熱電対を配置した。
真空精錬装置では、酸素吹込みにより脱炭処理するが、吹き込まれた酸素によって溶鋼中のＳｉが酸化してＳｉＯ₂ を生成したり、昇熱作用で耐火物が溶損すること等によってスラグ中のＣａＯ濃度が変化する。そこで、酸素吹込み後に高真空下の撹拌処理に移行する時点で、取鍋内にプローブを挿入しスラグの温度及び電気電導度を測定した。
【００１８】
本実施例の測定手順を、図８のフローに示す。先ず、電源部から所定の電圧を長電極１１と短電極１０間にかけた状態で、昇降装置によりプローブを測定位置に下降させ、スラグ層に浸漬した。このとき、最適な測定位置を決定するため、所定の速度でプローブを下降させた。プローブの先端がスラグ面に達ないうちは、長電極１１と短電極１０との間に電流が流れない。プローブ先端の電極１０，１１がスラグ層に浸漬されると急激に電流が流れ始めるので、そのときのプローブ位置を記憶しておく。更にプローブを下降させると、長電極１１がメタルプールに到達し、電流値が急激に上昇する。そこで、この時点をプローブ先端がメタルプールに到達した時点と判断し、プローブの下降を停止させる。下降停止したときのプローブ位置と、最初にプローブ先端がスラグ面に到達した位置から、スラグ厚みが算出される。そして、測定しようとする位置、たとえばスラグ層の中間位置まで、プローブを再度上昇させて測温を開始する。測温が開始されると、実施例２と同様に熱電対素線の被覆材溶損→電気伝導度測定用回路の形成の順で電気伝導度が測定される。
【００１９】
このようにして、測定位置を把握することが困難な状況においても、最適な測定位置でスラグの温度及び電気伝導度を測定することが可能になった。その結果、電気伝導度空推定されるスラグ中のＣａＯ濃度に応じて真空フィーダによりＣａＯを補給し、スラグ中のＣａＯ濃度の目標値４０％に調整した。
真空容器を開放した後、溶鋼及びスラグをサンプリングし、分析によって実際のＣａＯ濃度及びメタル中Ｓ濃度を測定した。分析値を、電気伝導度から推定されたＣａＯ濃度と比較して表１に示す。また、測定結果の一例を図９に示す。
一連の測定，適正位置の決定，測温及び補正には、図１０及び図１１に示す回路構成をもつ制御系を使用した。これにより、各種手順が瞬時に行われ、目的とするスラグ組成の推定に利用可能になった。このようにして、本発明によるとき、従来法のように諸条件の影響を受けることなく、現場操業に迅速に対処することが可能になる。
【００２０】

【００２１】
比較例１：
実施例１と同じ電気アーク炉において５チャージにわたり、比電気伝導度のみを測定し、測定値に基づいてＣａＯの供給量を制御した。この場合には、表２の結果にみられるように、温度補正を行っていないため精度良くＣａＯ濃度を調整することが困難であった。
【００２２】
比較例２：
実施例３と同じ真空精錬装置内の取鍋内に浮遊するスラグの電気伝導度を、５チャージにわたって測定した。この場合、実施例１と同じプローブを使用し、装置内に設置したカメラによる上方からの映像に基づきオペレータが測定位置を判断し、プローブを適当な位置まで挿入した。このようにして挿入されたプローブから得られた電気伝導度に基づいてＣａＯ供給量を制御した。しかし、電気伝導度から推定されたＣａＯ濃度は、表２に示されるように、真空容器開放後の実際のスラグサンプル分析値とはかなり異なっていた。このように、比較例２では、実施例に比較してスラグ中のＣａＯ濃度のバラツキが大きく、結果として脱硫能が安定化しなかったことが判る。
【００２３】

【００２４】
【発明の効果】
以上に説明したように、本発明のプローブは、溶融スラグの電気伝導度を測定すると同時に、その測定位置にあるスラグの温度をも測定し、測温結果に基づき電気伝導度から推定されるスラグ組成を補正している。そのため、操業中に１回の測定作業で、溶融スラグの電気伝導度が正確に測定され、種々の操業条件の変化に拘らず、スラグ組成を高精度で推定することが可能になる。また、目視等によって被測定位置を判断する作業も不必要で、測定ミスによる再測定の必要もなくなり、作業の簡略化も図られる。しかも、同時に溶融スラグやメタルのレベルも把握されるため、電気伝導度の測定以外にも、たとえばスラグ量の推定から各種精錬剤，還元剤等の最適添加量の把握を始めとして精錬上で重要な情報を得ることに利用される。
【図面の簡単な説明】
【図１】実施例１で使用したプローブ
【図２】実施例２で使用したプローブ
【図３】実施例２で使用したプローブの断面
【図４】実施例３で使用したプローブ
【図５】実施例３で使用したプローブの機能を説明する図
【図６】Ｌ≦Ｄのプローブ（ａ）及びＬ＞Ｄのプローブ（ｂ）で得られた電気伝導度（電流値）の変化を示したグラフ
【図７】実施例２の測定手順を示すフロー
【図８】実施例３の測定手順を示すフロー
【図９】実施例３で得られた測定値の経時変化を示すグラフ
【図１０】電気伝導度の測定に使用される制御系の回路構成
【図１１】電気伝導度の測定に使用される制御系の回路構成
【符号の説明】
１：プローブ２：保護管（ガラス管）３：熱電対素線４：電極対
５：固定用耐火物６：保護キャップ７：絶縁材８：耐火物製円筒
９：外紙管１０：電気伝導度測定用電極（短電極）１１：溶融金属検知用電極（長電極）[0001]
[Industrial application fields]
The present invention relates to the temperature of molten slag used when estimating the slag composition from the electric conductivity of molten slag in the furnace such as an electric furnace or converter, the temperature of the consumable probe for simultaneous measurement of electric conductivity, and the temperature of the molten slag, The present invention relates to a method for simultaneously measuring electrical conductivity.
[0002]
[Prior art]
In metal refining such as iron and non-ferrous metals, high-temperature molten metal and molten slag of a few hundred degrees are processed. In order to obtain information for knowing the progress of the refining reaction in such a high-temperature atmosphere from the molten metal, temperature measurement, oxygen concentration measurement using a solid battery, or the like is directly employed. Recently, as introduced in JP-A-4-346611, a method has been developed in which an emission spectrum emitted during a refining reaction is taken into a spectroscope via an optical fiber and analyzed.
On the other hand, as a means for obtaining information on molten slag, it is common to sample the slag and analyze the components by instrumental analysis such as fluorescent X-ray analysis and ICP analysis after pretreatment. However, since it takes a long time to obtain an analysis result from sampling, the target to which this sample analysis method is applied is limited.
[0003]
Therefore, when quickness is required, for example, as disclosed in JP-A-55-128520, the electrical resistance of the slag is measured, and the hatching rate of the slag is determined from the resistance value. In JP-A-2-54125, a slag level of a converter is measured with high accuracy by using a probe in which electrodes having a plurality of circuits formed in the height direction are embedded in the outer periphery.
Even in an electric furnace, the state in the furnace is estimated based on electrical resistance indices such as resistance and reactance extracted from the electrodes, and is indirectly used for maintaining stable operation.
[0004]
[Problems to be solved by the invention]
Although the electrical resistance index taken out from the electrode is considered promising for estimating the properties of the slag, the reliability decreases due to various obstacles when actually measured in the field. For example, when measuring the electrical conductivity of molten slag, the operating conditions are not always constant, and thus the temperature conditions during measurement vary in various ways. Therefore, in order to obtain a highly accurate electrical resistance index, it is necessary to measure the temperature of the molten slag at the position where the electrical conductivity is measured, and to correct the electrical resistance index according to the measured temperature.
In addition, when measuring molten slag in places where it is difficult to observe furnace conditions, such as smelting vessels such as converters and ladles, it is always possible to grasp the exact position of slag by changing operating conditions. Can not. Therefore, when inserting a sensor in a container, an appropriate insertion position becomes unclear. That is, the measurement position changes for each measurement, and it becomes difficult to measure the accurate electrical conductivity.
[0005]
Furthermore, the molten metal and the molten slag are generally separated into a lower layer and an upper layer, respectively, because their specific gravity is greatly different. However, in the vicinity of the interface between the metal layer and the slag layer, there is a portion where the granular metal is finely suspended in the slag, and due to turbulence of the metal / slag interface due to convection of the molten metal, the metal layer and the slag layer Are not separated by clear boundaries. Therefore, the position of the molten metal was sometimes measured by mistake.
As described above, the conventional method requires adjustment time for optimizing the measurement position as a measurement condition, and it is also necessary to perform temperature measurement separately. Moreover, it was a measuring method with a heavy burden also in terms of cost.
The present invention has been devised to solve such problems, and it is possible to measure the electrical conductivity and temperature of molten slag at the same time, and to make a quick determination to adjust the measured slag composition to the optimum slag composition. An object of the present invention is to provide a consumable probe for simultaneous measurement of possible temperature and electrical conductivity, and to obtain a highly accurate measurement value quickly at low cost.
[0006]
[Means for Solving the Problems]
The consumable probe for simultaneous measurement of the temperature and electrical conductivity of the molten slag according to the present invention is provided with a thermocouple element disposed at the tip of the probe and protected by a semi-corrosion-resistant protective tube against the measured molten slag. A wire, an electrode for electrical conductivity measurement arranged in the vicinity of the thermocouple wire, a refractory for fixing the thermocouple wire and the base of the electrode pair in an insulated state, the protective tube, and the electrode A protective cap that protects the pair, and the tip of the thermocouple wire and the tip of the electrode are positioned at substantially the same height from the refractory, and when the protective tube is melted by molten slag, An electrical conductivity measurement circuit is formed between the thermocouple wire and the electrical conductivity measurement electrode.
Further, the probe tip may be arranged so that the difference between the tip position of one of the electrode pairs and the tip position of one of the electrodes is equal to or smaller than the gap between the two electrodes. By adjusting this difference, a function of detecting the metal level can be provided.
[0007]
The electrical conductivity of the molten oxide was formed between the electrode pair at the same time as the temperature of the molten oxide was measured by a thermocouple for temperature measurement by immersing the probe in molten oxide such as slag floating in the metal pool. It is measured by a circuit for measuring electrical conductivity. The measured value of electrical conductivity takes in the temperature information measured at the same time and is used to estimate the slag composition. In addition, when using a probe arranged at the probe tip so that the difference between the tip position of one of the electrode pairs and the tip position of one of the electrodes is less than the gap between the two electrodes, the coexistence with the molten metal The probe is lowered toward the molten oxide, and it is estimated that the electrode has reached the molten oxide because current flows between the electrodes, and the electrode reaches the molten metal from a sudden change in the measured conductivity. I guess it was. Next, the probe is raised to the measurement position in the molten oxide layer, and the temperature and electrical conductivity of the molten oxide are measured.
[0008]
[Action]
The electric conductivity varies depending on the slag composition, but is greatly affected by the temperature. Therefore, temperature measurement is important when obtaining an accurate slag composition. When the detected electrical conductivity is corrected according to the measured value of the temperature and the slag composition is estimated from the obtained correction value, the influence of the temperature that varies depending on the operating conditions is offset and high-precision estimation is possible. become. Based on this assumption, the present invention has developed a probe that can measure the slag temperature simultaneously with the measurement of electrical conductivity, and determines the slag composition with high accuracy based on the information obtained by this measurement probe. is there.
The electric conductivity measurement probe according to the present invention is used in furnaces such as top-bottom blowing converters, AOD furnaces, electric arc furnaces, electric resistance furnaces, ladles when refining by the RH method, VOD method, etc. This is particularly effective when measuring slag where it is difficult to observe structurally or equipment.
In this probe, for example, as shown in FIG. 1, a thermocouple wire 3 protected by a U-shaped glass tube 2 is inserted at the tip of the probe 1. In addition, an electrode pair 4 having the same tip position is incorporated in the fixed refractory 5 in an insulated state at the tip of the temperature measurement position by the thermocouple. With this configuration, the electrode pair 4 can measure the electric conductivity of the slag with high accuracy without being affected by the electric resistance of the refractory. The electrode pair 4 can be made of steel, stainless steel or the like in order to reduce the cost.
[0009]
Further, when the measurement probe is lowered toward the molten steel surface of the molten steel in the container, the vicinity of the surface layer having a low slag temperature may be solidified depending on the operating conditions. If the measurement probe is lowered under such circumstances, the protective tube may be damaged by physical force when the probe is immersed. Damage when descending can be prevented by attaching a protective cap 6 made of, for example, aluminum or copper to the tip of the probe.
As a material of the electrode pair 4, a noble metal or a high melting point metal having excellent corrosion resistance is used when more strict measurement is required. On the other hand, when the thermocouple wire 3 for temperature measurement is used as one electrode of the electrode pair for conductivity measurement instead of an expensive material, the cost can be reduced. The electrode pair 4 is inserted through the fixing refractory 5 via an insulating material 7 as shown in FIG. The fixing refractory 5 is attached so as to close the tip processed portion of the refractory cylinder 8 and is inserted into the outer paper tube 9 together with the refractory cylinder 8.
[0010]
When the thermocouple wire 3 is also used as one electrode of the conductivity measuring electrode pair, as shown in FIG. 2, the thermocouple wire 3 is attached by a protective tube 2 made of a material that is semi-corrosive to molten slag. Cover. The semi-corrosion resistant material protects the wire 3 from the slag for only several seconds to several tens of seconds necessary for temperature measurement. When more time elapses, the protective tube 2 is completely eroded by the reaction with melting or slag, and the thermocouple wire 4 is exposed. As the material of the semi-corrosion resistant protective tube 2, it is desirable to use an optimum material according to the composition and temperature of the slag to be measured. For example, in the case of a quartz glass protective tube, a tube whose melting point is adjusted close to the temperature of the object to be measured by adding a trace amount of NaO ₂ , PbO, BaO or the like is used.
After the temperature measurement, if the thermocouple wire 3 is exposed due to melting of the semi-corrosion-resistant protective tube 2, the temperature measurement becomes impossible, but the exposed thermocouple wire 3 is used for one of the electrodes for measuring the electrical conductivity. it can. This thermocouple wire 3 constitutes a circuit for measuring electrical conductivity with one electrode 4. At this time, the one electrode 4 is formed by processing a noble metal such as platinum, molybdenum, tungsten or the like having a high corrosion resistance against slag or a high melting point metal like a thermocouple into a linear or rod shape.
[0011]
When the optimum measurement position is unknown, as shown in FIG. 4, a molten metal detection electrode 11 is provided in an exposed state at a symmetrical position with respect to one of the electric conductivity measurement electrodes 10 around the thermocouple 3 for temperature measurement. It is preferable to use a probe. The molten metal detection electrode 11 is made of a long steel or stainless steel wire or rod, and its length is adjusted in accordance with the slag / metal interface state. That is, the difference in length between the electrical conductivity measurement electrode 10 and the molten metal detection electrode 11 is set to be equal to or greater than the slag / metal thickness d. As a result, only the molten metal detection electrode 11 can be immersed in the metal pool without the electrical conductivity measurement electrode pairs 3 and 10 coming into contact with the metal pool, and the level of the molten metal surface can be detected.
The slag / metal interface thickness d varies depending on the process to be measured and the characteristics of the furnace, but is preferably obtained in advance using a detection rod, an electromagnetic sensor, or the like. In addition, when there is a possibility that the slag / metal interface is greatly undulated or a large amount of liquid iron is suspended in the slag near the interface, the electrical conductivity measurement electrode 10 and the molten metal detection electrode are accordingly provided. It is preferable to make the difference in length from 11 sufficiently large.
[0012]
The influence of the relationship between the electrode pair length difference L while the probe is lowered and the distance D between the electrode pairs on the measurement of electrical conductivity will be described with reference to FIG. When the length difference L ≦ distance D, the electrical conductivity rapidly increases as shown in FIG. 6A when the electrical conductivity measurement electrode (short electrode) 10 approaches the metal and becomes equal to the length difference L. To do. Therefore, it is estimated that the molten metal detection electrode (long electrode) 11 is in contact with the metal. At this time, since the length difference L ≧ slag / metal interface thickness d, the probability that the short electrode 10 contacts the metal is reduced.
On the other hand, when the length difference L> distance D, even if the distance between the metal and the short electrode 10 is equal to the length difference L, the electrical conductivity is clearly increased as shown in FIG. Only when the probe is further lowered and the distance to the metal is equal to the distance D is not detected, the increase in electrical conductivity becomes apparent. At this time, since the tip of the short electrode 10 has reached a position shorter than the length difference L from the metal, the probability that the short electrode 10 contacts the metal is increased. As a result, molten metal adheres to the electrode 10 for measuring electrical conductivity, and an error is likely to occur in the measurement of electrical conductivity in the slag layer performed thereafter.
[0013]
For this reason, it is important to maintain the relationship of length difference L ≦ distance D between the difference L between the electrode pairs and the distance D between the electrode pairs. When it is determined that the tip of the molten metal detection (long) electrode has completely reached the metal pool, the descent of the probe 1 is stopped. Then, the probe 1 is raised again to the target position, and slag temperature measurement and electrical conductivity measurement are performed. At this time, the electrode 11 for detecting the molten metal is not used for measuring the electric conductivity, and a circuit is formed between the one electrode 10 for measuring electric conductivity and the thermocouple 3 for temperature measurement as described above. And measuring the electrical conductivity of the slag.
In this way, the thickness and metal level of the slag can be grasped without immersing the electrode for measuring the electric conductivity up to the metal, and as a result, the electric conductivity and temperature can be simultaneously measured at the target position, that is, by one probe insertion operation. It can be measured. Even in such a case, inexpensive steel or stainless steel can be used for the molten metal detection electrode 11, and a significant increase in cost can be prevented. Further, since the probe according to the present invention can detect the slag / metal interface, it is also used, for example, as a level sensor for a molten metal surface. Furthermore, when the materials of the thermocouple protective tube 2, the outer paper tube 9, and the

electrodes

10 and 11 are changed to materials having corrosion resistance, a durable probe that can be used repeatedly is obtained.
[0014]
【Example】
Example 1:
An embodiment applied to adjusting the composition of the slag generated in the furnace at the time when the charging raw material mainly composed of scrap melts in the electric arc furnace producing stainless steel hot metal will be described. The probe shown in FIG. 1 was used in which an R-type thermocouple was inserted into a quartz glass protective tube, and a cylindrical electrode made of SUS304 having a diameter of 8 mm and a length of 35 mm was arranged at an interval of 25 mm. .
As a result of measuring for 10 charges in an electric furnace, the specific electric conductivity of the slag was corrected to a value at 1500 ° C. and was in the range of 0.93 to 1.46 Ω ⁻¹ / cm. Estimate the CaO concentration at each charge from the relationship between the CaO concentration in the slag and the specific electrical conductivity at 1500 ° C. obtained in advance, so that the CaO concentration at the output is 40% of the target value. Of CaO was fed into the furnace. After tapping into the ladle, slag was sampled from the ladle and the actual CaO concentration was measured by sample analysis. The results are shown in Table 1.
[0015]
Example 2:
Next, a diagram showing a probe having a diameter of 1.5 mm and a length of 35 mm made of platinum electrical conductivity measuring electrode provided at the probe tip, and an R-type thermocouple inserted in a silica glass protective tube adjusted to a melting point of 1500 ° C. The slag temperature and electrical conductivity were measured using 3 probes. In this case, a circuit is formed between the thermocouple for temperature measurement and the exposed electrode when temperature measurement becomes impossible after the temperature measurement by the measurement thermocouple is started, and the electrical conductivity is measured through this circuit. .
The measurement procedure in this case is shown in the flow of FIG. First, the probe is lowered to the measurement position by the lifting device and immersed in the slag layer. From this moment, measurement of the temperature of the probe tip position, more precisely, the temperature sensing portion slag at the tip of the thermocouple is started. Although it depends on the thermocouple element covering material, slag component, temperature, etc., temperature measurement data is obtained until the covering material melts and the element wire is exposed in several seconds to several tens of seconds. If the bare wire is exposed, a temperature measurement error occurs due to a short circuit, so the reading of temperature measurement data is stopped. At the same time, an electric conductivity measuring circuit is formed and the electric conductivity is measured. Here, one of the electrodes for measuring electric conductivity is an exposed platinum electrode, and one of the electrodes is an R-type thermocouple wire exposed. A current is supplied between the electrodes under a certain voltage from the power supply unit, and the electrical conductivity is calculated from the resistance value at that time.
[0016]
Using this expendable electrical conductivity measurement probe, the temperature and electrical conductivity were measured for 5 charges in the electric arc furnace in the same manner as in Example 1. The time required for the measurement varied in the range of 20 to 80 seconds for each charge depending on the operating conditions. Based on the measurement results, CaO for adjustment was supplied, and the actual CaO concentration was measured by sample analysis from the slag after the ladle. The actual analysis value for the target value of 45% of the CaO concentration in the slag at the time of tapping is shown in Table 1.
As is apparent from Table 1, it can be seen that both Examples 1 and 2 can be substantially adjusted to the target CaO concentration, and the CaO concentration is estimated with high accuracy. As a result, the S concentration of the electric furnace hot metal was stable at a low level of 0.01 to 0.02%, and it was confirmed that a good desulfurization reaction was performed.
[0017]
Example 3:
The example applied to the electrical conductivity measurement of the slag floating in the ladle in the vacuum refining apparatus will be described. The vacuum smelting apparatus during degassing has a cover in the container and the inside is in a vacuum state. Therefore, it is difficult to accurately grasp the slag surface in the ladle inside. Therefore, a probe (see FIG. 4) was used in which one of the electrode pairs for measuring electrical conductivity was an electrode for detecting molten metal. A tungsten electrode having a diameter of 1 mm was installed at the tip of the probe in a length up to the position of the thermocouple for temperature measurement, and a steel electrode having a diameter of 8 mm and a length 20 mm longer than that was installed. Note that an interval of 40 mm was maintained between the tungsten electrode and the steel electrode, and an R-type thermocouple inserted into the quartz protective tube was disposed at the interval.
In the vacuum refining equipment, decarburization is performed by blowing oxygen, but Si in the molten steel is oxidized by the blown oxygen to generate SiO ₂ , or the refractory is melted by the heating effect, etc. CaO concentration changes. Therefore, at the time of shifting to a stirring process under high vacuum after blowing oxygen, a probe was inserted into the ladle, and the temperature and electrical conductivity of the slag were measured.
[0018]
The measurement procedure of this example is shown in the flow of FIG. First, in a state where a predetermined voltage was applied between the long electrode 11 and the short electrode 10 from the power supply unit, the probe was lowered to the measurement position by the lifting device and immersed in the slag layer. At this time, in order to determine the optimum measurement position, the probe was lowered at a predetermined speed. As long as the tip of the probe does not reach the slag surface, no current flows between the long electrode 11 and the short electrode 10. When the

electrodes

10 and 11 at the tip of the probe are immersed in the slag layer, current starts to flow rapidly, and the probe position at that time is stored. When the probe is further lowered, the long electrode 11 reaches the metal pool, and the current value increases rapidly. Therefore, this time is determined as the time when the probe tip reaches the metal pool, and the descent of the probe is stopped. The slag thickness is calculated from the probe position when the descent is stopped and the position where the probe tip first reaches the slag surface. Then, the probe is raised again to a position to be measured, for example, an intermediate position of the slag layer, and temperature measurement is started. When temperature measurement is started, the electrical conductivity is measured in the order of coating member melting damage of the thermocouple wire → formation of the electrical conductivity measurement circuit in the same manner as in Example 2.
[0019]
In this way, it is possible to measure the temperature and electrical conductivity of the slag at the optimum measurement position even in a situation where it is difficult to grasp the measurement position. As a result, CaO was replenished by a vacuum feeder in accordance with the CaO concentration in the slag, which was estimated to be empty in electrical conductivity, and adjusted to a target value of 40% for the CaO concentration in the slag.
After opening the vacuum vessel, the molten steel and slag were sampled, and the actual CaO concentration and S concentration in the metal were measured by analysis. The analytical values are shown in Table 1 in comparison with the CaO concentration estimated from the electrical conductivity. An example of the measurement result is shown in FIG.
A control system having the circuit configuration shown in FIGS. 10 and 11 was used for a series of measurements, determination of appropriate positions, temperature measurement, and correction. As a result, various procedures were performed instantaneously and became available for estimation of the target slag composition. Thus, according to the present invention, it is possible to quickly cope with on-site operation without being affected by various conditions as in the conventional method.
[0020]

[0021]
Comparative Example 1:
In the same electric arc furnace as in Example 1, only the specific electrical conductivity was measured over 5 charges, and the supply amount of CaO was controlled based on the measured value. In this case, as seen in the results in Table 2, it was difficult to adjust the CaO concentration with high accuracy because the temperature was not corrected.
[0022]
Comparative Example 2:
The electrical conductivity of the slag floating in the ladle in the same vacuum refining apparatus as in Example 3 was measured over 5 charges. In this case, the same probe as in Example 1 was used, the operator judged the measurement position based on the image from above by the camera installed in the apparatus, and the probe was inserted to an appropriate position. The CaO supply amount was controlled based on the electrical conductivity obtained from the probe inserted in this manner. However, as shown in Table 2, the CaO concentration estimated from the electrical conductivity was quite different from the actual slag sample analysis value after the vacuum vessel was opened. Thus, in Comparative Example 2, it can be seen that the variation in the CaO concentration in the slag was larger than that in the Example, and as a result, the desulfurization ability was not stabilized.
[0023]

[0024]
【The invention's effect】
As described above, the probe of the present invention measures the electrical conductivity of the molten slag and simultaneously measures the temperature of the slag at the measurement position, and estimates the slag from the electrical conductivity based on the temperature measurement result. The composition is corrected. Therefore, the electrical conductivity of the molten slag is accurately measured by a single measurement operation during operation, and the slag composition can be estimated with high accuracy regardless of changes in various operation conditions. Further, it is unnecessary to determine the position to be measured by visual observation or the like, eliminating the need for re-measurement due to a measurement error, and simplifying the operation. In addition, since the level of molten slag and metal is also grasped at the same time, in addition to the measurement of electrical conductivity, it is important for refining, for example, from estimating the amount of slag to grasping the optimum amount of various refining agents and reducing agents. It is used to obtain useful information.
[Brief description of the drawings]
FIG. 1 Probe used in Example 1 FIG. 2 Probe used in Example 2 FIG. 3 Cross section of probe used in Example 2 FIG. 4 Probe used in Example 3 FIG. FIG. 6 is a diagram for explaining the function of the probe used in Example 3. FIG. 6 shows changes in electrical conductivity (current value) obtained with the probe (a) with L ≦ D and the probe (b) with L> D. Graph [FIG. 7] Flow showing the measurement procedure of Example 2 [FIG. 8] Flow showing the measurement procedure of Example 3 [FIG. 9] Graph showing the change over time of the measurement values obtained in Example 3 [FIG. 10]. Circuit configuration of control system used for measuring electrical conductivity [Fig. 11] Circuit configuration of control system used for measuring electrical conductivity [Explanation of symbols]
1: Probe 2: Protective tube (glass tube) 3: Thermocouple wire 4: Electrode pair 5: Refractory for fixing 6: Protective cap 7: Insulating material 8: Cylinder made of refractory 9: Outer paper tube 10: Electric conduction Measurement electrode (short electrode) 11: Molten metal detection electrode (long electrode)

Claims

A thermocouple element disposed at the probe tip and protected by a semi-corrosion-resistant protective tube against the molten slag to be measured; an electrode for measuring electrical conductivity disposed in the vicinity of the thermocouple element; and the thermocouple A refractory that fixes the base of the wire and the electrode pair in an insulated state; a protective cap that protects the protective tube and the electrode pair; and a temperature measuring portion of the thermocouple wire and a tip of the electrode For the electrical conductivity measurement between the thermocouple element and the electrical conductivity measuring electrode when the protective tube is melted by the measured molten slag. Consumable probe for simultaneous measurement of temperature and electrical conductivity of molten slag where a circuit is formed.

An electrode pair for electrical conductivity measurement arranged at the tip of the probe so that the difference between the tip position of one of the electrode pairs and the tip position of one of the electrodes is equal to or less than the gap between both electrodes, and the vicinity of the electrode pair A thermocouple element disposed at the probe tip position and protected by a semi-corrosion-resistant protective tube against the molten slag to be measured, and a refractory for fixing the thermocouple element and the base of the electrode pair in an insulated state, A protective cap for protecting the protective tube and the electrode pair, and a tip temperature measuring portion of the thermocouple wire and a short tip of the electrode are set at substantially the same height from the refractory, When the metal level is detected by a single electrode and the protective tube is melted by the molten slag to be measured, an electric conductivity measuring circuit is formed between the thermocouple element and the electric conductivity measuring electrode. Measurement of temperature and electrical conductivity of molten slag Use consumable probe.

The probe according to claim 1 is immersed in molten slag coexisting with the molten metal, temperature measurement of the molten slag is started by a thermocouple for temperature measurement, and the semi-corrosion resistant protective tube becomes impossible to measure temperature due to melting. A temperature of the molten slag characterized by measuring the electric conductivity of the molten slag by an electric conductivity measuring circuit formed between the exposed thermocouple for measuring temperature and the electrode for measuring electric conductivity; Simultaneous measurement method of electrical conductivity.

The probe according to claim 2 is lowered toward the molten slag in a state of coexisting with the molten metal in a state in which a circuit is formed between the electrode pair for electrical conductivity measurement, and a current flows between the electrodes. Estimate that the electrode has arrived, estimate that the electrode has reached the molten metal from the sudden change in the measured value of electrical conductivity, then raise the probe to the measurement position in the molten slag layer, and the temperature of the molten slag And a method for simultaneously measuring the temperature and electrical conductivity of molten slag, characterized by measuring electrical conductivity.