201037082 六、發明說明： 【發明所屬之技術領域】 本發明是關於在熔鐵（hot metal )中添加脫硫劑並進 行攪拌，藉此將熔鐵施以脫硫處理的技術。 【先前技術】 以往，關於在熔鐵中添加脫硫劑並藉由攪拌翼（旋轉 0 翼）進行攪拌以對熔鐵實施脫硫處理的方法，例如專利文 獻1所記載的技術是已知的。專利文獻1所揭示的技術， 是從開始進行脫硫處理經過既定時間爲止讓攪拌翼以既定 轉數旋轉（前期步驟），然後將攪拌翼的轉數相對降低或 讓旋轉停止（中期步驟），之後將攪拌翼的轉數相對提高 或讓旋轉再度開始（後期步驟）。該技術之目的，是在中 期步驟促進脫硫劑的上浮（段落〔0015〕），在後期步驟 ，藉由讓上浮後的脫硫劑撞擊攪拌翼而在脫硫劑產生新的 Q 反應界面（段落〔〇〇18〕、〔 0019〕），藉此提昇脫硫效 率。依據其揭示的內容，脫硫劑較佳爲分成2〜3次來投入 (段落〔〇〇 1 4〕），又在前期步驟及後期步驟都添加脫硫 劑。 根據專利文獻1的記載可知’在將含有脫硫劑之助熔 劑（flux )分成複數次來添加於熔鐵的情況，當所添加的 脫硫劑成爲能分散於熔鐵內之攪拌狀態時，實施新的脫硫 劑的添加。此外，在專利文獻1，如上述般雖揭示將攪拌 翼的轉數暫時降低，但在攪拌翼的轉數降低時（中期步驟 -5- 201037082 )並未實施脫硫劑的添加。亦即，依據專利文獻1的技術 ，將攪拌翼的轉數暫時降低是爲了提昇已經添加的脫硫劑 之脫硫效率。 〔專利文獻1〕日本特開2008-101262號公報 【發明內容】 本發明人等，發現習知技術存在著以下的問題點。亦 即，在以能讓已經添加的脫硫劑分散於熔鐵內的攪拌力進 行攪拌的狀態下，新添加的脫硫劑與熔鐵表面直接接觸的 可能性很高。這時，由於脫硫劑和熔鐵的濕潤性不佳，如 第8圖所示，新添加的脫硫劑8接觸熔鐵表面時會產生凝 集，而有導致脫硫反應效率降低之虞。本發明是著眼於上 述問題點而開發完成的，其目的是爲了提供一種可提昇所 添加的脫硫劑的反應效率之熔鐵之脫硫處理方法。 爲了解決上述課題，本發明具備以下的特徵。 (1 ) 一種熔鐵之脫硫處理方法，是將添加脫硫劑後 的溶鐵施以攪拌，使該脫硫劑分散以進行熔鐵的脫硫處理 ;該熔鐵之脫硫處理方法的特徵在於：將脫硫劑分成複數 次添加於熔鐵中，在第2次以後的脫硫劑的添加當中，至 少一次是暫時將上述攪拌停止或將攪拌力減弱以讓熔渣上 浮至熔鐵表面，並在該上浮後的熔渣上添加脫硫劑。 (2 )在上述（1 )的技術中，上述攪拌，是讓浸漬在 熔鐵中的攪拌翼旋轉而實施，藉由將上述攪拌翼的轉數暫 時降低（減少），以讓用來添加脫硫劑的熔渣上浮。 -6- 201037082 (3) 在上述（2)的技術中，上述熔渣上之脫硫劑的 添加，是在位於攪拌翼的旋轉軸附近的熔渣上進行。 (4) 在上述（2)或（3)的技術中，經由將上述攪 拌翼的轉數暫時降低而上浮後的熔渣，是藉由將上述攪拌 翼的轉數增加而捲入熔鐵內，在將上浮後的熔渣捲入熔鐵 內時，讓上述攪拌翼往下方移動。 (5 )在上述（2 )〜（4 )的技術中，藉由將上述攪拌 0 翼的轉數暫時降低而使熔渣上浮時，是減少攪拌翼的浸漬 深度。 依據本發明，藉由在熔渣上添加新的脫硫劑，可防止 新添加的脫硫劑發生凝集。然後，藉由將攬拌力回復成能 使脫硫劑分散的強度，可將上浮的熔渣中的新脫硫劑和熔 渣一起導入熔鐵內。結果，可謀求脫硫反應效率的提昇。 關於脫硫反應，反應界面面積（脫硫劑和熔鐵的接觸面積 )越大越能促進脫硫反應。此外，依據上述（2)的發明 Q ，可利用攪拌翼的轉數來控制熔渣的上浮。 依據上述（3 )的發明，藉由攪拌翼的旋轉，熔鐵的 表面會朝向攪拌翼的旋轉軸傾斜，上浮熔渣層的厚度是越 接近旋轉軸附近越厚。以該上浮熔渣層較厚的部分爲目標 (target )來添加脫硫劑，可更確實地防止新添加的脫硫 劑發生凝集。此外，在讓攪拌翼的轉數上昇時將上浮的熔 渣捲入熔鐵內的舉動，是從旋轉軸附近的熔渣層開始進行 。因此’藉由在旋轉軸附近添加脫硫劑，有助於在短時間 內進行將新添加的脫硫劑捲入熔鐵內的舉動。 201037082 此外，依據上述（4)的發明，在讓一旦降低後的攪 拌翼的轉數上昇而將上浮的熔渣捲入時，藉由使攪拌翼往 下方移動，可促進新添加的脫硫劑的捲入舉動，並能增加 熔渣對攪拌翼的撞擊。藉此可進一步提昇脫硫反應效率。 此外，依據上述（5 )的發明，藉由減少攪拌翼的浸 漬深度，能使上浮的熔渣撞擊攪拌翼而增加新的反應界面 ，藉此可提昇脫硫反應效率。再者，在上述（4)技術中 讓攪拌翼往下方移動時，可增加上浮後的熔渣和攪拌翼的 撞擊次數，且藉由在先前的步驟讓攪拌翼往上方移動，能 使往下方移動後的攪拌翼的高度成爲最佳高度。或者是能 使上述攪拌翼有更多的下降量。 【實施方式】 (第1實施形態） 接著參照圖式來說明本發明的第1實施形態。但本發 明並不限定於以下所揭示的例子。第1圖係顯示本實施形 態的熔鐵之脫硫處理設備之槪念圖。又第3圖係第1圖所 示的脫硫處理設備的利用狀態的一例。 (構造） 首先說明設備的構造。第1圖中，符號1代表熔鐵鍋 (hot-metal ladle )。在該熔鐵鍋1內收容熔鐵2。對於收 容有熔鐵2之熔鐵鍋1內，從上側插入攪拌翼3，而成爲 將攪拌翼3浸漬在熔鐵2內的狀態。上述攪拌翼3，例如 -8- 201037082 是 4 片葉片（f 〇 u r - b 1 a d e d，c r 〇 s s - s h a p e d )的 成。該攪拌翼3的旋轉軸4是朝向上下方向 動馬達5而能進行旋轉。驅動馬達5，是按 7的指令來實施轉數的控制。而且，藉由以 拌翼3進行旋轉驅動，以機械性地攪拌熔鐵 2，而讓添加於熔鐵2中的脫硫劑8 (參照第 溶鐵2中以進行脫硫。此外，符號6代表脫 。脫硫劑添加裝置6，可按照來自控制器7 定量的脫硫劑8添加於熔鐵2中。 將攪拌翼3的旋轉模式和脫硫劑8的添 (schedule)資訊輸入控制器7。第2圖係 態的旋轉模式和脫硫劑8的添加模式之時序 圖中，縱軸表示攪拌翼的轉數，橫軸表示脫 時間，箭頭表示脫硫劑的投入。依據第2圖 硫處理開始時是讓攪拌翼3的轉數成爲目的 Q 的轉數N1’而以該轉數N1爲目標進行轉數 定的次數（本例爲2次），每經過既定時間 3的轉數降低至熔渣上浮用轉數N2。此外， 的添加’在開始進行脫硫處理而使攬拌翼3 的之脫硫處理用的轉數N1之時點，作爲第 理是添加既定量（本例爲全體的約1/2)的 外，當攪拌翼3的轉數降低至熔渣上浮用轉 渣上浮後，再添加既定量（本例分別爲全體 脫硫劑8。 攪拌翼3所構 配置，藉由驅 照來自控制器 既定轉數將攪 鍋1中的熔鐵 3圖）分散於 硫劑添加裝置 的指令而將既 加模式之時序 顯示本實施形 的例子。第2 硫處理的經過 的時序，在脫 之脫硫處理用 控制。但以既 暫時讓攪拌翼 關於脫硫劑8 的轉數成爲目 1次的添加處 脫硫劑8。此 數N2而使熔 的約1 / 4 )的 -9 - 201037082 在此’上述脫硫處理用的轉數N 1，是能讓比重低的 脫硫劑8分散於熔鐵2中的轉數。依據發明人等的調查， 只要將攪拌翼3的轉數設定在8 Orpin以上，即可讓添加於 熔鐵2中的脫硫劑8 (或是含有脫硫劑8的助熔劑）分散 而能進行脫硫。但是，隨著攪拌翼的磨耗等會使攪拌效率 變差。對應於此攪拌效率降低，必須增加上述脫硫處理用 的轉數N1。因此’爲了確保目的之攪拌狀態，只要能按 照攪拌翼3的使用狀況來設定變更成適當的轉數即可。亦 即，上述脫硫處理用的轉數N 1的範圍，可考慮設備規格 、設備負擔等而在事前求出，再按照使用狀況，適當地設 定及變更該脫硫處理用的轉數N1即可。 此外’熔渣上浮用轉數N 2，是將攪拌效率降低至能 讓熔渣9上浮至熔鐵2的表面2 a (參照第3圖）的轉數。 通常，只要將攪拌翼3的轉數降低至上述脫硫處理用的轉 數N1之60 %左右，即可使熔渣9上浮至熔鐵2的表面2a 。因此，熔渣上浮用轉數N 2，例如只要是將上述脫硫處 理用的轉數N 1降低40 %以上的轉數即可。但是，若同時 考慮到避免增加脫硫處理的時間，讓熔渣上浮之攪拌翼3 的轉數宜設定成上述脫硫處理用的轉數N1之50〜60%。 N2也能按照上述熔渣的上浮、所需時間等的狀況來進行 適當的設定及變更，這是理所當然的。 (動作、作用） 接著說明使用上述設備及上述脫硫時序之熔鐵2的脫 -10- 201037082 硫處理方法的例子。控制器7，若判定開始進行脫硫處理 ，就對馬達5輸出：爲了形成上述脫硫處理用的轉數N1 之轉數指令。亦即，控制器7是對馬達5輸出指令，以脫 硫處理用的轉數N 1爲目標値而使停止中的攪拌翼3以既 定的轉數增加率將轉數上昇。藉此，攪拌翼3會朝向上述 脫硫處理用的轉數N1而以既定上昇率將轉數上昇。而且 ，若成爲脫硫處理用的轉數N1的話，就以維持該轉數的 0 方式進行轉數控制。 此外，控制器7，以與上述攪拌翼3的轉數上昇同步 的方式，將第1次的脫硫劑添加指令輸出給脫硫劑添加裝 置6。脫硫劑8的添加時期設定成：攪拌翼3的轉數成爲 脫硫處理用的轉數N 1的時點或其附近的時刻。第i次的 脫硫劑8的添加量，是全體脫硫劑8的1 / 2。所添加的脫 硫劑8’是依序藉由攪拌翼3的旋轉而被捲入熔鐵2中， 藉由攪拌翼3旋轉所產生的攪拌而分散於該熔鐵2中。分 Q 散於熔鐵2中的脫硫劑8，會和熔鐵2中的硫（S )產生 脫硫反應。 若攪拌翼3的轉數成爲脫硫處理用的轉數N1，進行 轉數控制而使攪拌翼3的轉數維持脫硫處理用的轉數N1 既定時間。在此期間進行脫硫反應。所謂既定時間，只要 讓上述脫硫反應進行既定程度以上，例如進行到可推定 脫硫反應已達飽和爲止的時間即可。若經過既定時間的話 ’控制器7對馬達5輸出：成爲溶澄上浮用轉數N2的指 令。藉此’攪拌翼3的轉數以既定的轉數減少率逐漸減少 -11 - 201037082 至熔渣上浮用轉數N2。 若攪拌翼3的轉數成爲熔渣上浮用轉數N2的話，以 可推定讓既定量以上的熔渣上浮到熔鐵2表面的時間，將 攪拌翼3的轉數保持在熔渣上浮用轉數N2。是否有既定 量以上的熔渣上浮到熔鐵2表面如後述般由於能利用目視 確認，因此很容易估計上述推定時間。將攪拌翼3的轉數 保持在熔渣上浮用轉數N2的時間例如爲30秒。然後，將 攪拌翼3的轉數以既定的轉數增加率往脫硫處理用的轉數 N1上昇，而回復該脫硫處理用的轉數N1。 以與該攪拌翼3轉數上昇同步的方式，在熔渣上浮過 程中將第2次的脫硫劑添加指令輸出給脫硫劑添加裝置6 。添加位置宜在攪拌翼3的旋轉軸4附近。旋轉軸4附近 是指，例如相對於旋轉軸4和熔鐵鍋1內壁之間的距離， 靠旋轉軸4側之1 /3的範圍內。 針對添加在旋轉軸附近的理由，使用第3圖（顯示利 用第1圖的設備而在轉數N2附近進行作業中之熔渣和脫 硫劑的關係）作說明。熔鐵2的表面2 a，如第3圖之示意 圖所示，是朝向攪拌翼3的旋轉軸4傾斜，藉由攪拌翼3 的旋轉而將上浮的熔渣9拉向該攪拌翼3的旋轉軸4側。 因此，上浮之熔渣9層，是在攪拌翼3的旋轉軸4側變厚 。藉由朝向該熔渣層變厚之熔渣9部分添加脫硫劑8，可 確實地將脫硫劑8投入熔渣9內。 此外，上浮的熔渣9，也可能存在於攪拌翼3的旋轉 軸4附近以外，因此朝向攪拌翼3的旋轉軸4附近以外的 -12- 201037082 熔渣上投入脫硫劑8亦可。但藉由使添加位置靠近攪拌翼 3的旋轉軸4側，在上浮的熔渣覆蓋熔鐵2的表面全面之 前，就能將攪拌翼3的轉數往脫硫處理用的轉數N1開始 上昇，如此有助於攪拌翼3的轉數之暫時減少期間的縮短 。此外，若攪拌翼3的轉數上昇，上浮的熔渣9當中位於 旋轉軸4附近的熔渣會被捲入熔鐵2內。因此，藉由將脫 硫劑8的添加位置設定在旋轉軸4附近，有助於上述添加 0 用之轉數暫時減少時間之縮短。 如以上所說明’藉由將脫硫劑8和上浮的熔渣9 一起 捲入熔鐵2內而進行分散，可抑制脫硫劑8的凝集，並讓 脫硫劑8分散在熔鐵2內。結果，可增加脫硫劑8和熔鐵 2的接觸面積而能促進脫硫反應。 接著，若將攪拌翼3的轉數回復成脫硫處理用的轉數 N 1 ’以既定時間對攪拌翼3進行脫硫處理用的轉數n 1之 轉數控制。而且’在此期間進行脫硫反應。所謂既定時間 Q ，是讓上述脫硫反應進行既定程度以上，例如可推定脫硫 反應已達飽和爲止的時間。若經過既定時間的話，控制器 7對馬達5輸出：讓轉數降低至第2次的熔渣上浮用轉數 N2的控制指令。藉此，攪拌翼3的轉數以既定的轉數減 少率減少至熔渣上浮用轉數N2。 若攪拌翼3的轉數成爲熔渣上浮用轉數N2的話，以 可推定讓既定量以上的溶渣上浮到溶鐵2表面的時間，將 攪拌翼3的轉數保持在熔渣上浮用轉數N2。然後，將攪 拌翼3的轉數以既定的轉數增加率往脫硫處理用的轉數 -13- 201037082 N1上昇，而回復該脫硫處理用的轉數N1。以與該攪拌翼 3的轉數上昇同步的方式’將第3次的脫硫劑添加指令輸 出至脫硫劑添加裝置6。添加位置較佳爲在攪拌翼3的旋 轉軸4附近。接著，若攪拌翼3的轉數成爲脫硫處理用的 轉數N1 ’以既定時間對攪拌翼3實施脫硫處理用的轉數 N1之轉數控制，然後減少攪拌翼3的轉數而結束脫硫處 理。 (本實施形態的效果） 第8圖係顯示習知技術的脫硫劑添加方法（上半部） ，亦即添加於熔鐵上的示意圖；以及這時在熔鐵上的凝集 舉動（下半部）。脫硫劑8，特別是C a Ο系的脫硫劑8， 由於容易在熔鐵2上凝集，若一次全部投入，脫硫劑8會 如第8圖下半部所示般凝集成塊狀而使未反應的CaO變多 ，藉由分次添加可減少凝集。再者，依據本實施形態，第 2次以後的脫硫劑8之添加是朝上浮的熔渣9進行，藉此 可進一步抑制熔鐵2上之脫硫劑8的凝集，結果可進一步 促進脫硫反應效率。 此外，上浮的熔渣9 (脫硫劑），藉由攪拌翼3的轉 數之再度上昇，會被捲入攪拌翼3側。因此，上浮之脫硫 反應呈飽和狀態之熔渣9 (脫硫劑），藉由撞擊攪拌翼3 而產生龜裂或分裂。因此，構成熔渣9之脫硫劑會隨著該 龜裂和分裂等而出現新的反應界面，藉由該反應界面會進 行新的脫硫反應。如此，除了新添加的脫硫劑8以外，構 -14- 201037082 成熔渣9之脫硫劑也會和熔鐵2中的硫產生脫硫反應。 此外，藉由將第2次以後之脫硫劑8的添加位置設定 在攪拌翼3的旋轉軸4附近，即使上浮的熔渣9未覆蓋熔 鐵2的表面（熔融液面）全體，仍可進行第2次以後的脫 硫劑8之添加。此外，藉由攪拌翼3的旋轉，上浮的熔渣 9會被拉向攪拌翼3的旋轉軸4側，在攪拌翼3的旋轉軸 4附近’上浮熔渣9的厚度變得最厚。藉由在該熔渣9變 0 厚的部分添加脫硫劑8，可確實地將脫硫劑8添加於熔渣 9層內。再者，在讓攪拌翼3的轉數上昇時，是從位於旋 轉軸4側的熔渣9開始捲入熔鐵2中，而有助於加速進行 脫硫反應。 在此，上浮的熔渣9 (脫硫劑），會使熔鐵2的表面 變黑，因此可利用目視或監視器來進行確認。因此，取代 自動控制（自動添加新的脫硫劑8 )，一邊確認上浮熔渣 9的狀況一邊調整第2次以後的脫硫劑8之添加時點亦可 〇 此外，在上述實施形態所例示的，是暫時降低攪拌翼 3的轉數而添加脫硫劑8的情況，但暫時停止攪拌翼3而 添加脫硫劑8亦可。但在停止攪拌翼3的情況，脫硫處理 時間會變長。 此外，在上述實施形態所例示的，是暫時降低攪拌翼 3的轉數而使熔渣9上浮，接著一邊將攪拌翼3的轉數提 高一邊添加脫硫劑8的情況。但取代此情況，在將攪拌翼 3的轉數保持於熔渣上浮用轉數N2時實施脫硫劑8的添 -15- 201037082 加亦可。但一邊將攪拌翼3的轉數提高一邊添加脫硫劑8 的情況，可縮短脫硫處理時間。其理由如下所述。 相對於攪拌翼3的轉數變化，熔渣9的上浮會有遲延 的情況。因此，在攪拌翼3的轉數從熔渣上浮用轉數N2 開始上昇的初期狀態，熔渣9的上浮還在發生中。接著， 隨著攪拌翼3之轉數的上昇，上浮的熔渣9被拉向攪拌翼 3的旋轉軸4側，依序被捲入熔鐵2內。以與該熔渣9捲 入同步的方式，進行脫硫劑8的添加，藉此可將所添加之 脫硫劑8捲入熔鐵2的舉動加速。如以上所說明，在一邊 使攪拌翼3的轉數上昇一邊添加脫硫劑8的情況，可縮短 將攪拌翼3的轉數保持在熔渣上浮用轉數N2的時間，且 能縮短脫硫劑8從添加至捲入熔鐵2內的時間。 此外，熔鐵2的攪拌不是使用攪拌翼3亦可。也能適 用於藉由其他手段來攪拌熔鐵2之脫硫處理設備。又關於 首次的脫硫劑添加，可使用與習知技術同樣的添加方法， 也能使用上述例之第2次以後的添加方法。例如能在維持 高攬拌力下添加脫硫劑，在有充分量的熔渣存在的情況， 在能確保熔渣上浮的攪拌力下添加脫硫劑亦可。 (第2實施形態） 接著參照圖式來說明第2實施形態。關於與上述第1 實施形態同樣的裝置等是賦予相同的符號來作說明。又同 樣地並不限定於以下的例子。 本實施形態之基本構造是與上述第1實施形態相同。 -16- 201037082 但關於脫硫處理中的攪拌翼3之昇降控制是不同的。在第 1實施形態雖未說明，第1圖的脫硫處理設備是具備：用 來讓攪拌翼3昇降之攪拌翼昇降裝置（未圖示）。通常的 攪拌翼3之昇降控制，在脫硫處理前是將攪拌翼3下降至 熔鐵鍋1內而將攪拌翼3浸漬在溶鐵2中，接著在脫硫處 理中，是讓攪拌翼3在高度保持一定的狀態下旋轉而進行 攪拌，然後當脫硫處理結束的話，讓攪拌翼3上昇而將該 0 攪拌翼3從溶鐵鍋1取出。相對於此，本實施形態的不同 點在於：在脫硫處理中適當地實施攪拌翼3的昇降。 在此，本實施形態之攪拌翼3的旋轉模式及脫硫劑8 的添加模式的時序是與上述第1實施形態相同。例如，在 以下的說明，作爲攪拌翼3的旋轉模式及脫硫劑8的添加 模式，是例示採用第2圖的時序的情況。亦即，如第2圖 的時序所示，隨著脫硫處理開始，讓攪拌翼3的轉數成爲 目的之脫硫處理用的轉數N 1，而以該轉數N 1爲目標進行 Q 轉數控制。但在脫硫處理中有2次，每經過既定時間暫時 讓攪拌翼3的轉數降低至熔渣上浮用轉數N2。此外，關 於脫硫劑8的添加，在開始進行脫硫處理而使攪拌翼3的 轉數成爲目的之脫硫處理用的轉數N 1之時點，作爲第1 次的添加處理是添加例如全體的約1 /2量的脫硫劑8。再 者，當攪拌翼3的轉數降低至熔渣上浮用轉數N 2時，分 別添加1 /4量的脫硫劑8。但攪拌翼3的旋轉模式及脫硫 劑8的添加模式並不限定於此。 再者，在本實施形態，如上述般，在脫硫處理中可適 -17- 201037082 當地實施攪拌翼3的昇降。在本實施形態’控制器7是以 與攪拌翼3的旋轉速度的變化同步的方式，對上述攪拌翼 昇降裝置輸出：讓攪拌翼3昇降’亦即改變攪拌翼3在熔 鐵2中的浸漬深度之指令（未圖示）。 第4圖係顯示：與攪拌翼3的旋轉速度同步之浸漬深 度（攪拌翼3的高度位置）之變更模式的時序。第4(a) 圖是和第2圖同樣的，顯示隨著脫硫處理的經過時間（橫 軸）之攪拌翼轉數（縱軸）的變化。第4 ( b )圖係顯示隨 著脫硫處理的經過時間（橫軸）之攪拌翼3的浸漬深度（ 以攪拌翼3的高度位置表示，縱軸）的變化。在此，第4 (b )圖的虛線是表示攪拌翼3的轉數之變更模式的時序 。攪拌翼3的高度位置，例如爲攪拌翼3的重心位置。此 外，縱軸上的D〇，是非攪拌狀態下之熔鐵2的表面2a ( 熔融液面）的高度。 上述與攪拌翼3的旋轉速度同步之浸漬深度之變更模 式中，在讓攪拌翼3的轉數暫時降低而使熔渣8上浮時’ 暫時減少攪拌翼3的浸漬深度。例如上昇至讓攪拌翼23 的一部分從熔鐵2露出的狀態。再者，隨著攪拌翼3的轉 數暫時降低而上浮之熔渣9，在藉由增加攪拌翼3的轉數 而被捲入熔鐵2內時，讓攪拌翼3往下方移動。 (動作、作用） 第5圖~第7圖，是以攪拌翼3的昇降動作爲中心而 示意地顯示本實施形態。第5圖係顯示攪拌翼上昇的狀態 -18- 201037082 ，第6圖係顯示朝向上浮熔渣添加脫硫劑的狀態，第7圖 係顯示攪拌翼下降的狀態。在第4圖所示的例子，配合一 旦降低轉數而使熔渣9上浮的舉動，讓攪拌翼3往上方移 動（第5圖）。接著，對於隨著攪拌翼3之旋轉上昇而遲 延上浮的熔渣9，添加脫硫劑8 (第6圖）。然後，上浮 後的熔渣9和所添加的脫硫劑8 —起再度被捲入熔鐵2內 時，讓上昇的攪拌翼3往下方移動而返回原先的位置（第[Technical Field] The present invention relates to a technique in which a desulfurizing agent is added to a hot metal and stirred, whereby the molten iron is subjected to a desulfurization treatment. [Prior Art] A method in which a desulfurizing agent is added to a molten iron and the molten iron is subjected to a desulfurization treatment by stirring with a stirring blade (rotating a wing), for example, a technique described in Patent Document 1 is known. . According to the technique disclosed in Patent Document 1, the stirring blade is rotated at a predetermined number of revolutions from the start of the desulfurization process for a predetermined period of time (previous step), and then the number of rotations of the stirring blade is relatively lowered or the rotation is stopped (interim step). The number of revolutions of the agitating wing is then increased relatively or the rotation is started again (late step). The purpose of this technique is to promote the lifting of the desulfurizing agent in the intermediate step (paragraph [0015]). In the later stage, a new Q reaction interface is generated in the desulfurizing agent by causing the desulfurizing agent after the floating to hit the stirring wing ( Paragraphs [〇〇18], [0019]), thereby improving the desulfurization efficiency. According to the disclosure, the desulfurizing agent is preferably divided into 2 to 3 times (paragraph [〇〇 14]), and a desulfurizing agent is added in both the preliminary step and the later step. According to the description of Patent Document 1, when a flux containing a desulfurizing agent is added to a molten iron in a plurality of times, when the added desulfurizing agent is in a stirred state in which it can be dispersed in the molten iron, The addition of a new desulfurizing agent is implemented. Further, in Patent Document 1, as described above, the number of revolutions of the agitating blades is temporarily lowered. However, when the number of revolutions of the agitating blades is lowered (intermediate step -5 - 201037082), the addition of the desulfurizing agent is not performed. That is, according to the technique of Patent Document 1, the number of revolutions of the stirring blade is temporarily lowered in order to increase the desulfurization efficiency of the desulfurizing agent which has been added. [Patent Document 1] JP-A-2008-101262 SUMMARY OF THE INVENTION The present inventors have found that the prior art has the following problems. That is, in a state where the stirring force capable of dispersing the added desulfurizing agent in the molten iron is stirred, there is a high possibility that the newly added desulfurizing agent is in direct contact with the surface of the molten iron. At this time, since the wettability of the desulfurizing agent and the molten iron is not good, as shown in Fig. 8, the newly added desulfurizing agent 8 is agglomerated upon contact with the surface of the molten iron, and there is a possibility that the efficiency of the desulfurization reaction is lowered. The present invention has been developed in view of the above problems, and an object thereof is to provide a method for desulfurization of molten iron which can improve the reaction efficiency of the added desulfurizing agent. In order to solve the above problems, the present invention has the following features. (1) A method for desulfurizing molten iron by subjecting molten iron after adding a desulfurizing agent to agitation, dispersing the desulfurizing agent to perform desulfurization treatment of molten iron; and the method for desulfurizing the molten iron The method is characterized in that the desulfurizing agent is added to the molten iron in plural times, and at least one of the addition of the desulfurizing agent after the second time is to temporarily stop the stirring or weaken the stirring force to allow the slag to float to the molten iron. a surface, and a desulfurizing agent is added to the slag after the floating. (2) In the technique of the above (1), the stirring is performed by rotating a stirring blade immersed in the molten iron, and the number of rotations of the stirring blade is temporarily lowered (reduced) to be used for adding The slag of the sulfur agent floats. -6- 201037082 (3) In the technique of the above (2), the addition of the desulfurizing agent on the slag is performed on the slag located in the vicinity of the rotating shaft of the stirring blade. (4) In the technique of the above (2) or (3), the slag which has been floated by temporarily lowering the number of revolutions of the agitating blades is rolled into the molten iron by increasing the number of revolutions of the agitating blades When the slag after the floating is caught in the molten iron, the stirring blade is moved downward. (5) In the techniques of the above (2) to (4), the immersion depth of the stirring blade is reduced when the slag is floated by temporarily lowering the number of revolutions of the stirring 0 wing. According to the present invention, by adding a new desulfurizing agent to the slag, aggregation of the newly added desulfurizing agent can be prevented. Then, by returning the stirring force to the strength at which the desulfurizing agent can be dispersed, the new desulfurizing agent and the molten slag in the floating slag can be introduced into the molten iron together. As a result, the efficiency of the desulfurization reaction can be improved. Regarding the desulfurization reaction, the larger the reaction interface area (the contact area of the desulfurizing agent and the molten iron), the more the desulfurization reaction can be promoted. Further, according to the invention Q of the above (2), the number of revolutions of the stirring blade can be utilized to control the floating of the slag. According to the invention of the above (3), the surface of the molten iron is inclined toward the rotation axis of the stirring blade by the rotation of the stirring blade, and the thickness of the floating slag layer is thicker toward the vicinity of the rotating shaft. By adding a desulfurizing agent to the thicker portion of the floating slag layer, it is possible to more reliably prevent agglomeration of the newly added desulfurizing agent. Further, the action of entraining the floating slag into the molten iron when the number of revolutions of the stirring blade is increased is started from the slag layer in the vicinity of the rotating shaft. Therefore, by adding a desulfurizing agent in the vicinity of the rotating shaft, it is possible to carry out the action of entraining the newly added desulfurizing agent into the molten iron in a short time. 201037082 Further, according to the invention of the above (4), when the floating slag is taken up by increasing the number of revolutions of the stirring blade once lowered, the newly added desulfurizing agent can be promoted by moving the stirring blade downward. The action of getting involved and increasing the impact of the slag on the agitating wing. Thereby, the efficiency of the desulfurization reaction can be further improved. Further, according to the invention of the above (5), by reducing the depth of the immersion of the stirring blade, the floating slag can be caused to hit the stirring wing to increase the new reaction interface, thereby improving the efficiency of the desulfurization reaction. Furthermore, in the technique of the above (4), when the stirring blade is moved downward, the number of impacts of the slag and the stirring blade after the floating can be increased, and the stirring wing can be moved upward by the previous step. The height of the moving agitating wing becomes the optimum height. Or it is possible to increase the amount of the above-mentioned stirring wings. [Embodiment] (First embodiment) A first embodiment of the present invention will be described below with reference to the drawings. However, the present invention is not limited to the examples disclosed below. Fig. 1 is a view showing a concept of a desulfurization treatment apparatus for molten iron in the present embodiment. Further, Fig. 3 is an example of the utilization state of the desulfurization treatment equipment shown in Fig. 1. (Structure) First, the configuration of the device will be explained. In Fig. 1, the symbol 1 represents a hot-metal ladle. The molten iron 2 is housed in the molten iron pot 1. In the molten iron pan 1 in which the molten iron 2 is accommodated, the stirring blade 3 is inserted from the upper side, and the stirring blade 3 is immersed in the molten iron 2. The agitating blades 3 described above, for example, -8-201037082, are the formation of four blades (f 〇 u r - b 1 a d e d, c r 〇 s s - s h a p e d ). The rotating shaft 4 of the stirring blade 3 is rotatable by moving the motor 5 in the vertical direction. The drive motor 5 is controlled by the command of 7 to implement the number of revolutions. Further, the molten iron 2 is mechanically stirred by the rotation of the mixing blade 3, and the desulfurizing agent 8 added to the molten iron 2 is referred to (refer to the molten iron 2 for desulfurization. Further, symbol 6 The desulfurizer addition device 6 can be added to the molten iron 2 in accordance with the desulfurizing agent 8 quantified from the controller 7. The rotation mode of the stirring blade 3 and the schedule information of the desulfurizing agent 8 are input to the controller. 7. In the timing chart of the rotation mode of the second embodiment and the addition mode of the desulfurizing agent 8, the vertical axis represents the number of revolutions of the stirring blade, the horizontal axis represents the off time, and the arrow represents the input of the desulfurizing agent. At the start of the sulfur treatment, the number of revolutions of the stirring blade 3 is the number of revolutions N1' of the destination Q, and the number of revolutions is determined by the number of revolutions N1 (two times in this example), and the number of revolutions per predetermined time is three. It is reduced to the number of revolutions N2 of the slag floating. In addition, the addition of 'the number of revolutions N1 for the desulfurization treatment of the bellows 3 is started as the first reason. For about 1/2 of the total, when the number of revolutions of the stirring wing 3 is lowered until the slag is floated up, the slag is floated up, Adding a predetermined amount (in this example, the entire desulfurizing agent 8 is configured by the stirring blade 3, and the molten iron 3 in the stirring pot 1 is driven by a predetermined number of rotations from the controller) is dispersed in the sulfur additive adding device. In the timing of the addition mode, the example of the present embodiment is shown. The timing of the second sulfur treatment is controlled by the desulfurization treatment, but the number of revolutions of the stirring blade with respect to the desulfurizing agent 8 is temporarily made. The addition of the desulfurizing agent 8 is the same. This number N2 is about 1/4 of the melting of -9 - 201037082. Here, the number of revolutions N 1 for the above-mentioned desulfurization treatment is a desulfurizing agent 8 which can make the specific gravity low. The number of revolutions dispersed in the molten iron 2. According to the investigation by the inventors, the desulfurizing agent 8 (or the flux containing the desulfurizing agent 8) added to the molten iron 2 can be dispersed by setting the number of revolutions of the stirring blade 3 to 8 Orpin or more. Desulfurization is carried out. However, the agitation efficiency is deteriorated as the agitating blades are worn or the like. In response to the decrease in the stirring efficiency, it is necessary to increase the number of revolutions N1 for the above-described desulfurization treatment. Therefore, in order to ensure the stirring state of the object, it is only necessary to change the setting to an appropriate number of revolutions in accordance with the use state of the stirring blade 3. In other words, the range of the number of revolutions N 1 for the desulfurization treatment can be obtained beforehand in consideration of equipment specifications and equipment burden, and the number of revolutions N1 for the desulfurization treatment can be appropriately set and changed according to the use condition. can. Further, the number of revolutions N 2 of the slag floating is to reduce the stirring efficiency to the number of revolutions at which the slag 9 can be floated up to the surface 2 a of the molten iron 2 (see Fig. 3). Usually, the slag 9 is floated up to the surface 2a of the molten iron 2 as long as the number of revolutions of the stirring blade 3 is reduced to about 60% of the number N1 of the above-described desulfurization treatment. Therefore, the number of revolutions N 2 of the slag floating may be, for example, a number of revolutions in which the number of revolutions N 1 for the desulfurization treatment is reduced by 40% or more. However, if it is considered at the same time to avoid an increase in the time of the desulfurization treatment, the number of revolutions of the stirring blade 3 for allowing the slag to float is set to 50 to 60% of the number N1 of the above-described desulfurization treatment. It is a matter of course that N2 can be appropriately set and changed in accordance with the state of the slag floating up, the required time, and the like. (Operation and Action) Next, an example of the desulfurization treatment method using the above-described equipment and the above-described desulfurization timing of the molten iron 2 will be described. When it is determined that the desulfurization process is started, the controller 7 outputs to the motor 5 a number of revolutions command for forming the number of revolutions N1 for the desulfurization process. In other words, the controller 7 outputs a command to the motor 5 to increase the number of revolutions at a predetermined number of revolutions by the number of revolutions N 1 for desulfurization processing. Thereby, the stirring blade 3 raises the number of revolutions at a predetermined rate of increase toward the number of revolutions N1 for the above-described desulfurization treatment. Further, when the number of revolutions N1 for the desulfurization treatment is obtained, the number of revolutions is controlled by the number 0 in which the number of revolutions is maintained. Further, the controller 7 outputs the first desulfurizing agent addition command to the desulfurizing agent adding device 6 in synchronization with the increase in the number of revolutions of the agitating blades 3. The addition timing of the desulfurizing agent 8 is set such that the number of revolutions of the stirring blade 3 becomes the time point of the number of revolutions N 1 for the desulfurization treatment or the vicinity thereof. The amount of the desulfurizing agent 8 added in the i-th time is 1/2 of the total desulfurizing agent 8. The desulfurizing agent 8' to be added is sequentially wound into the molten iron 2 by the rotation of the stirring blade 3, and is dispersed in the molten iron 2 by the agitation generated by the rotation of the stirring blade 3. The desulfurizing agent 8 dispersed in the molten iron 2 will react with the sulfur (S) in the molten iron 2 to cause desulfurization. When the number of revolutions of the stirring blade 3 becomes the number of revolutions N1 for the desulfurization treatment, the number of revolutions is controlled to maintain the number of revolutions of the stirring blade 3 for the predetermined number of revolutions N1 for the desulfurization treatment. The desulfurization reaction is carried out during this period. In the predetermined period of time, the desulfurization reaction may be carried out at a predetermined level or more, for example, to a time until the desulfurization reaction can be estimated to have reached saturation. When the predetermined time elapses, the controller 7 outputs to the motor 5: an instruction to dissolve the number of revolutions N2. Thereby, the number of revolutions of the agitating wing 3 is gradually reduced by a predetermined number of revolutions -11 - 201037082 to the number of revolutions N2 of the slag floating. When the number of revolutions of the agitation blade 3 is the number N2 of the slag floating, it is estimated that the slag of a predetermined amount or more is floated up to the surface of the molten iron 2, and the number of revolutions of the agitation blade 3 is maintained at the slag floating. Number N2. Whether or not a predetermined amount of slag is floated up to the surface of the molten iron 2 can be visually confirmed as will be described later, so that the estimated time can be easily estimated. The time during which the number of revolutions of the stirring blade 3 is maintained at the number of revolutions N2 of the slag is, for example, 30 seconds. Then, the number of revolutions of the stirring blade 3 is increased to the number of revolutions N1 for the desulfurization treatment at a predetermined rate of increase in rotation, and the number of revolutions N1 for the desulfurization treatment is returned. The second desulfurizing agent addition command is output to the desulfurizing agent adding device 6 during the slag floating process so as to be synchronized with the increase in the number of revolutions of the stirring blade 3. The addition position is preferably in the vicinity of the rotating shaft 4 of the stirring blade 3. The vicinity of the rotating shaft 4 means, for example, a distance between the rotating shaft 4 and the inner wall of the molten iron 1 in the range of 1/3 of the side of the rotating shaft 4. For the reason of addition in the vicinity of the rotating shaft, the relationship between the slag and the desulfurizing agent in the operation in the vicinity of the number of revolutions N2 using the apparatus of Fig. 1 will be described. The surface 2a of the molten iron 2, as shown in the schematic view of Fig. 3, is inclined toward the rotating shaft 4 of the stirring blade 3, and the floating slag 9 is pulled toward the rotating wing 3 by the rotation of the stirring blade 3. Shaft 4 side. Therefore, the 9 layers of the slag floating upward are thickened on the side of the rotating shaft 4 of the stirring blade 3. By adding the desulfurizing agent 8 to the slag portion 9 which is thickened toward the slag layer, the desulfurizing agent 8 can be surely put into the slag 9. Further, the slag 9 that has been floated may be present in the vicinity of the rotating shaft 4 of the stirring blade 3, and therefore the desulfurizing agent 8 may be supplied to the slag of -12-201037082 other than the vicinity of the rotating shaft 4 of the stirring blade 3. However, by bringing the addition position closer to the side of the rotating shaft 4 of the stirring blade 3, the number of revolutions of the stirring blade 3 can be increased to the number N1 of the desulfurization treatment before the floating slag covers the entire surface of the molten iron 2. This contributes to the shortening of the temporary reduction period of the number of revolutions of the stirring wing 3. Further, if the number of revolutions of the agitating blades 3 rises, the slag located in the vicinity of the rotating shaft 4 among the floating slags 9 is drawn into the molten iron 2. Therefore, by setting the addition position of the desulfurizing agent 8 in the vicinity of the rotating shaft 4, it is possible to contribute to the shortening of the temporary decrease in the number of revolutions for the above-mentioned addition. As described above, by dispersing the desulfurizing agent 8 and the floating slag 9 together in the molten iron 2, aggregation of the desulfurizing agent 8 can be suppressed, and the desulfurizing agent 8 can be dispersed in the molten iron 2 . As a result, the contact area of the desulfurizing agent 8 and the molten iron 2 can be increased to promote the desulfurization reaction. Then, when the number of revolutions of the stirring blade 3 is returned to the number of revolutions N 1 ' for the desulfurization treatment, the number of revolutions n 1 of the desulfurization treatment of the stirring blade 3 is controlled for a predetermined period of time. Moreover, the desulfurization reaction is carried out during this period. The predetermined time Q is such that the desulfurization reaction is carried out to a predetermined level or more, and for example, it is estimated that the desulfurization reaction has reached saturation. When the predetermined time has elapsed, the controller 7 outputs to the motor 5 a control command for lowering the number of revolutions to the second slag floating number N2. Thereby, the number of revolutions of the stirring blade 3 is reduced to the slag floating number N2 at a predetermined number of revolutions. When the number of revolutions of the agitation blade 3 is the number N2 of the slag floating, it is estimated that the slag of a predetermined amount or more is floated up to the surface of the molten iron 2, and the number of revolutions of the agitation blade 3 is maintained at the slag. Number N2. Then, the number of revolutions of the stirring blade 3 is increased to the number of revolutions -13 - 201037082 N1 for the desulfurization treatment at a predetermined rate of increase of the number of revolutions, and the number of revolutions N1 for the desulfurization treatment is returned. The third desulfurizing agent addition command is outputted to the desulfurizing agent adding device 6 in a manner synchronized with the increase in the number of revolutions of the stirring blade 3. The addition position is preferably in the vicinity of the rotating shaft 4 of the stirring blade 3. Then, when the number of revolutions of the stirring blade 3 becomes the number of revolutions N1' for the desulfurization treatment, the number of revolutions of the number of revolutions N1 for performing the desulfurization treatment on the stirring blade 3 is controlled for a predetermined period of time, and then the number of revolutions of the stirring blade 3 is reduced to end. Desulfurization treatment. (Effect of the present embodiment) Fig. 8 is a view showing a conventional method of adding a desulfurizing agent (top half), that is, a schematic diagram added to a molten iron; and agglomeration action on the molten iron at this time (lower half) ). The desulfurizing agent 8, particularly the C a lanthanide desulfurizing agent 8, is easily aggregated on the molten iron 2, and if it is all charged at once, the desulfurizing agent 8 will be agglomerated as shown in the lower half of Fig. 8. In addition, the amount of unreacted CaO is increased, and aggregation can be reduced by fractional addition. Further, according to the present embodiment, the addition of the desulfurizing agent 8 after the second time is performed by the slag 9 which is floated upward, whereby the aggregation of the desulfurizing agent 8 on the molten iron 2 can be further suppressed, and as a result, the desorption can be further promoted. Sulfur reaction efficiency. Further, the floating slag 9 (desulfurizing agent) is caught in the side of the stirring blade 3 by the increase in the number of revolutions of the stirring blade 3. Therefore, the slag 9 (desulfurizing agent) in which the floating desulfurization reaction is in a saturated state causes cracking or splitting by hitting the stirring blade 3. Therefore, the desulfurizing agent constituting the slag 9 exhibits a new reaction interface with the cracking, splitting, etc., and a new desulfurization reaction is carried out by the reaction interface. Thus, in addition to the newly added desulfurizing agent 8, the desulfurizing agent of the slag 9 is also desulfurized by the sulfur in the molten iron 2. Further, by setting the addition position of the desulfurizing agent 8 after the second time or later to the vicinity of the rotating shaft 4 of the stirring blade 3, even if the floating slag 9 does not cover the entire surface (melt surface) of the molten iron 2, The addition of the desulfurizing agent 8 after the second time is performed. Further, by the rotation of the stirring blade 3, the floating slag 9 is pulled toward the rotating shaft 4 side of the stirring blade 3, and the thickness of the floating slag 9 becomes the thickest in the vicinity of the rotating shaft 4 of the stirring blade 3. By adding the desulfurizing agent 8 to the portion where the slag 9 is made thick, the desulfurizing agent 8 can be surely added to the slag 9 layer. Further, when the number of revolutions of the agitation blade 3 is increased, the slag 9 located on the side of the rotary shaft 4 is wound into the molten iron 2, which contributes to accelerate the desulfurization reaction. Here, the floating slag 9 (desulfurizing agent) causes the surface of the molten iron 2 to be blackened, so that it can be confirmed by visual observation or a monitor. Therefore, in place of the automatic control (automatic addition of a new desulfurizing agent 8), it is possible to adjust the addition of the desulfurizing agent 8 after the second time while confirming the state of the floating slag 9, and the exemplified in the above embodiment In the case where the number of revolutions of the stirring blade 3 is temporarily lowered and the desulfurizing agent 8 is added, the stirring blade 3 may be temporarily stopped and the desulfurizing agent 8 may be added. However, in the case where the stirring blade 3 is stopped, the desulfurization treatment time becomes long. Further, in the above-described embodiment, the number of revolutions of the stirring blade 3 is temporarily lowered to cause the slag 9 to float, and the desulfurizing agent 8 is added while the number of revolutions of the stirring blade 3 is increased. However, in place of this, it is also possible to carry out the addition of the desulfurizing agent 8 when the number of revolutions of the stirring blade 3 is maintained at the number of revolutions N2 of the slag. However, when the desulfurizing agent 8 is added while increasing the number of revolutions of the stirring blade 3, the desulfurization treatment time can be shortened. The reason is as follows. The slag 9 may have a delay in the floating of the slag 9 with respect to the change in the number of revolutions of the stirring blade 3. Therefore, the floating state of the slag 9 is still occurring in the initial state in which the number of revolutions of the agitation blade 3 rises from the slag floating rotation number N2. Then, as the number of revolutions of the stirring blade 3 rises, the floating slag 9 is pulled toward the rotating shaft 4 side of the stirring blade 3, and is sequentially wound into the molten iron 2. The addition of the desulfurizing agent 8 is carried out in synchronization with the entrainment of the slag 9, whereby the action of the added desulfurizing agent 8 to be entangled in the molten iron 2 can be accelerated. As described above, when the desulfurizing agent 8 is added while the number of revolutions of the stirring blade 3 is increased, the number of revolutions of the stirring blade 3 can be shortened while maintaining the number of revolutions of the slag floating N2, and the desulfurization can be shortened. The time from the addition of the agent 8 to the entrainment into the molten iron 2. Further, the stirring of the molten iron 2 may not be performed by using the stirring blade 3. It is also applicable to a desulfurization treatment apparatus which stirs the molten iron 2 by other means. Further, as for the first desulfurizing agent addition, the same addition method as the conventional technique can be used, and the second and subsequent addition methods of the above examples can also be used. For example, a desulfurizing agent can be added while maintaining a high mixing power, and when a sufficient amount of slag is present, a desulfurizing agent may be added under a stirring force capable of ensuring the slag floating. (Second Embodiment) Next, a second embodiment will be described with reference to the drawings. The same components and the like as those of the above-described first embodiment are denoted by the same reference numerals. The same is not limited to the following examples. The basic structure of this embodiment is the same as that of the first embodiment described above. -16- 201037082 However, the lifting control of the stirring blade 3 in the desulfurization treatment is different. In the first embodiment, the desulfurization treatment apparatus of Fig. 1 includes a stirring blade lifting device (not shown) for raising and lowering the agitating blades 3. In the conventional lifting control of the stirring blade 3, before the desulfurization treatment, the stirring blade 3 is lowered into the molten iron pot 1 and the stirring wing 3 is immersed in the molten iron 2, and then in the desulfurization treatment, the stirring wing 3 is allowed. When the height is kept constant, the mixture is rotated and stirred. Then, when the desulfurization treatment is completed, the stirring blade 3 is raised to take the 0 stirring blade 3 out of the molten iron pan 1. On the other hand, this embodiment differs in that the lifting and lowering of the stirring blade 3 is appropriately performed in the desulfurization treatment. Here, the rotation mode of the stirring blade 3 and the timing of the addition mode of the desulfurizing agent 8 of the present embodiment are the same as those of the above-described first embodiment. For example, in the following description, the rotation mode of the stirring blade 3 and the addition mode of the desulfurizing agent 8 are exemplified by the timing of the second drawing. In other words, as shown in the timing of Fig. 2, as the desulfurization process is started, the number of revolutions of the stirring blade 3 is set to the number of revolutions N1 for the purpose of the desulfurization treatment, and Q is performed with the number of revolutions N1 as the target. The number of revolutions control. However, in the desulfurization treatment, there are two times, and the number of revolutions of the stirring blade 3 is temporarily lowered to the number of revolutions N2 of the slag floating per predetermined time. In addition, when the desulfurization treatment is started, the number of revolutions of the stirring blade 3 is changed to the number of revolutions N 1 for the purpose of the desulfurization treatment, and the first addition treatment is added, for example, Approximately 1 / 2 of the amount of desulfurizer 8 . Further, when the number of revolutions of the stirring blade 3 is lowered to the number of revolutions N 2 of the slag floating, a 1/4 amount of the desulfurizing agent 8 is separately added. However, the rotation mode of the stirring blade 3 and the addition mode of the desulfurizing agent 8 are not limited thereto. Further, in the present embodiment, as described above, in the desulfurization treatment, the lifting and lowering of the stirring blade 3 can be performed locally in the range of -17 to 201037082. In the present embodiment, the controller 7 outputs the stirring blade lifting device so that the agitating blade 3 is lifted and lowered, that is, the impregnation of the agitating blade 3 in the molten iron 2 is changed in synchronization with the change in the rotational speed of the agitating blade 3. Depth instruction (not shown). Fig. 4 shows the timing of the change mode of the immersion depth (the height position of the stirring blade 3) in synchronization with the rotation speed of the stirring blade 3. Fig. 4(a) is the same as Fig. 2, showing the change in the number of rotations of the stirring blade (vertical axis) with the elapsed time (horizontal axis) of the desulfurization treatment. The fourth (b) diagram shows the change in the immersion depth (indicated by the height position of the stirring blade 3, the vertical axis) of the stirring blade 3 with the elapsed time (horizontal axis) of the desulfurization treatment. Here, the broken line in Fig. 4(b) is a timing chart showing a change mode of the number of revolutions of the stirring blade 3. The height position of the stirring wing 3 is, for example, the position of the center of gravity of the stirring wing 3. Further, D〇 on the vertical axis is the height of the surface 2a (melt surface) of the molten iron 2 in the non-stirred state. In the above-described changing mode of the immersion depth in synchronization with the rotation speed of the stirring blade 3, when the number of revolutions of the stirring blade 3 is temporarily lowered to cause the slag 8 to float, the immersion depth of the stirring blade 3 is temporarily reduced. For example, it is raised to a state where a part of the stirring blade 23 is exposed from the molten iron 2. Further, as the slag 9 which is temporarily lowered as the number of revolutions of the stirring blade 3 is lowered, when the number of revolutions of the stirring blade 3 is increased, the stirring blade 3 is moved downward. (Operation and Action) Figs. 5 to 7 are schematic views showing the present embodiment centering on the lifting operation of the stirring blade 3. Fig. 5 shows the state in which the stirring blade is raised -18-201037082, the sixth figure shows the state in which the desulfurizing agent is added to the floating slag, and the seventh figure shows the state in which the stirring blade is lowered. In the example shown in Fig. 4, the stirring blade 3 is moved upward by the action of lowering the number of revolutions to cause the slag 9 to float upward (Fig. 5). Next, the desulfurizing agent 8 is added to the slag 9 which is delayed in as the rotation of the stirring blade 3 rises (Fig. 6). Then, when the slag 9 after the floating and the added desulfurizing agent 8 are once again caught in the molten iron 2, the rising stirring blade 3 is moved downward to return to the original position (the first)
亦即，在要讓熔渣9上浮時，如第5圖的空白箭頭所 示讓攪拌翼3上昇，以減少攪拌翼3在熔鐵2中的浸漬深 度。這時，旋轉的攪拌翼3會撞擊上浮的熔渣9。不隨著 轉數降低而減少攪拌翼3的浸漬深度的理由在於：在此時 期熔渣尙未充分的上浮。而且，配合被推定爲熔渣9已上 浮的時期，進行攪拌翼3的上昇。 在此狀態下，如第6圖所示，在上浮的熔渣9上投入 Q 脫硫劑8。若脫硫劑8的添加結束的話，如第7圖的空白 箭頭所示讓攪拌翼3往下方移動。藉由攪拌翼3之往下方 移動，上浮的熔渣9被捲入熔鐵2內（如第7圖的箭頭所 示），且讓其與攪拌翼3的撞擊增加，而謀求促進脫硫反 應。這時，由於事先讓攪拌翼3上昇移動，能使攪拌翼3 有更多的下降量，而能使其與上浮熔渣9的撞擊量變得更 多。 此外已確認出，藉由在脫硫處理時進行攪拌翼3的昇 降，熔渣的平均粒徑會變小。 -19 201037082 此外，在將上浮熔渣9捲入時’讓攪拌翼3進行複數 次的昇降亦可。在本實施形態的例子，是配合上浮熔渣開 始捲入的時期來投入脫硫劑8的情況’但即使要提早投入 脫硫劑8的情況，仍宜在與上浮熔渣的接觸變多的時期讓 攪拌翼3下降。此外，在第5圖所示的攪拌翼上昇和第7 圖所示的攪拌翼下降當中，僅進行任—方亦可’但藉由組 合昇降可獲得更大的脫硫效率改善效果。 再者，爲了讓熔鐵浴內的流動從穩定狀態急劇改變成 非穩定狀態以增加熔鐵中的S和脫硫劑（助熔劑）的接觸 機會，不須添加脫硫劑而適當地追加攪拌翼之昇降控制亦 可，亦即，一邊將攪拌翼的轉數暫時降低而讓熔渣上昇一 邊將攪拌翼上昇，一邊將攪拌翼的轉數增加一邊將攪拌翼 降低。此外，在首次添加脫硫劑時也是’按照以上所述的 目的等而適當地進行攪拌翼的昇降控制亦可。 (本實施形態的效果） 藉由將攪拌翼3的轉數暫時降低而使熔渣9上浮時’ 減少攪拌翼3的浸漬深度。藉由減少攪拌翼3的浸漬深度 ，上浮的溶渣9會撞擊攪拌翼3而使新的反應界面增多’ 藉此可提昇脫硫的反應效率。此外，隨著攪拌翼3的轉數 暫時降低而上浮的熔渣9，藉由增加攪拌翼3的轉數而被 捲入熔鐵2內時，將攪拌翼3往下方移動。結果，將上浮 的熔渣9和所添加的脫硫劑8 —起捲入時，藉由增加攪拌 翼3的浸漬深度，可促進新添加的脫硫劑8之捲入舉動並 -20 - 201037082 增加熔渣9對攪拌翼3的撞擊。藉此可進一步提昇脫硫的 反應效率。這時由於事先減少攪拌翼3的浸漬深度，能使 往下方移動的攪拌翼3高度成爲最適當的高度（例如回復 原先的高度）。 〔實施例〕 依據以下條件，進行第1實施形態（第2圖）、第2 0 實施形態（第4圖）及比較例（以第2圖的模式投入脫硫 劑，攪拌翼轉數固定在N1)之熔鐵的脫硫處理。通常攪 拌之攪拌翼上端面高度，是靜止熔融液面下100cm。 •熔鐵 處理前組成：C : 4.3質量％，S : 0.023質量％(S〇) 處理量：3 0 0順 •脫硫劑 種類：石灰 Q 使用量：1 5 00kg •處理時間 轉數N1的處理每1次：約8分鐘 轉數N2的處理每1次：約2分鐘 所得結果整理如下。Sf代表脫硫處理後的熔鐵的S濃 度。 •第1實施形態 ：脫S率 In ( SQ/Sf) =2. 1 •第2實施形態 ：脫S率In ( SQ/Sf) =3.0 .比較例 ：脫 S 率 In ( SQ/Sf) =1.8 -21 - 201037082 依據本發明，不需要特別的設備負擔，可防止所添加 的脫硫劑凝集而導致之反應效率降低，能以優異的脫硫效 率進行熔鐵的脫硫處理。 【圖式簡單說明】 第1圖係顯示本發明的第1實施形態之脫硫處理設備 的槪略圖。 第2圖係本發明的第1實施形態之脫硫時序圖。 第3圖係顯示本發明的第1實施形態之熔渣和脫硫劑 的關係。 第4 ( a )( b )圖係本發明的第2實施形態之攪拌翼 的昇降時序圖。 第5圖係顯示攪拌翼上昇的狀態。 第6圖係顯示對上浮熔渣添加脫硫劑的狀態。 第7圖係顯示攪拌翼下降的狀態。 第8圖係顯示脫硫劑的凝集。 【主要元件符號說明】 1 :熔鐵鍋 2 :溶鐵 2a :表面 3 :攪拌翼 4 :旋轉軸 5 :馬達 -22- 201037082 6 :脫硫劑添加裝置 7 :控制器 8 :脫硫劑 9 :熔渣 N 1 :脫硫處理用的轉數 N2 :熔渣上浮用轉數That is, when the slag 9 is to be floated, the stirring blade 3 is raised as indicated by a blank arrow in Fig. 5 to reduce the immersion depth of the stirring blade 3 in the molten iron 2. At this time, the rotating stirring blade 3 hits the floating slag 9. The reason why the impregnation depth of the stirring blade 3 is not reduced as the number of revolutions is lowered is that the molten slag is not sufficiently floated at this time. Further, the fitting is estimated to be a period in which the slag 9 has been raised, and the stirring of the stirring blade 3 is performed. In this state, as shown in Fig. 6, the Q desulfurizing agent 8 is placed on the floating slag 9. When the addition of the desulfurizing agent 8 is completed, the stirring blade 3 is moved downward as indicated by a blank arrow in Fig. 7 . By the downward movement of the stirring wing 3, the floating slag 9 is taken up into the molten iron 2 (as indicated by the arrow in Fig. 7), and the collision with the stirring wing 3 is increased to promote the desulfurization reaction. . At this time, since the agitating blade 3 is moved upward in advance, the agitating blade 3 can be more lowered, and the amount of collision with the floating slag 9 can be increased. Further, it has been confirmed that the average particle diameter of the slag becomes small by performing the rise and fall of the stirring blade 3 at the time of the desulfurization treatment. -19 201037082 In addition, when the floating slag 9 is wound up, the stirring blade 3 may be lifted and lowered several times. In the example of the present embodiment, the desulfurizing agent 8 is supplied in a period in which the floating slag starts to be entrained. However, even if the desulfurizing agent 8 is to be introduced early, it is preferable to increase the contact with the floating slag. The stirring wing 3 is lowered during the period. Further, in the case where the agitating blade as shown in Fig. 5 is raised and the agitating blade is lowered as shown in Fig. 7, only one of them may be performed, but a larger desulfurization efficiency improving effect can be obtained by the combination of lifting and lowering. Further, in order to change the flow in the molten iron bath from a stable state to an unstable state to increase the contact chance between the S in the molten iron and the desulfurizing agent (flux), it is necessary to appropriately add the stirring without adding a desulfurizing agent. The lifting control of the wing may be such that the number of revolutions of the stirring blade is temporarily lowered, the slag is raised, and the stirring blade is raised, and the stirring blade is lowered while increasing the number of rotations of the stirring blade. In addition, when the desulfurizing agent is added for the first time, the lifting and lowering control of the stirring blade may be appropriately performed in accordance with the above-described purpose and the like. (Effects of the present embodiment) When the slag 9 is floated by temporarily lowering the number of revolutions of the stirring blade 3, the immersion depth of the stirring blade 3 is reduced. By reducing the impregnation depth of the agitating blades 3, the floating slag 9 will hit the agitating blades 3 to increase the new reaction interface', thereby increasing the reaction efficiency of desulfurization. Further, as the slag 9 which is temporarily lowered as the number of revolutions of the stirring blade 3 is temporarily lowered, and the number of revolutions of the stirring blade 3 is increased, the stirring blade 3 is moved downward. As a result, when the floating slag 9 and the added desulfurizing agent 8 are entangled, the newly added desulfurizing agent 8 can be promoted by increasing the impregnation depth of the stirring blade 3 and -20 - 201037082 The impact of the slag 9 on the agitating blades 3 is increased. Thereby, the reaction efficiency of desulfurization can be further improved. At this time, since the impregnation depth of the agitation blade 3 is reduced in advance, the height of the agitation blade 3 which is moved downward can be made the most appropriate height (e.g., the original height is restored). [Examples] According to the following conditions, the first embodiment (second drawing), the second embodiment (fourth drawing), and the comparative example were carried out (the desulfurizing agent was introduced in the mode of Fig. 2, and the number of stirring blades was fixed at Desulfurization treatment of molten iron of N1). The height of the upper end face of the stirring blade which is usually stirred is 100 cm below the surface of the static melt. • Composition before molten iron treatment: C: 4.3 mass%, S: 0.023 mass% (S〇) Treatment capacity: 3 0 0 cis • Desulfurizer type: lime Q Usage: 1 5 00 kg • Processing time revolution N1 Treatment 1 time: About 8 minutes The number of revolutions N2 is processed once every 1 minute: about 2 minutes. The results are as follows. Sf represents the S concentration of the molten iron after the desulfurization treatment. • First embodiment: De-S ratio In (SQ/Sf) = 2. 1 • Second embodiment: De-S ratio In (SQ/Sf) = 3.0. Comparative example: De-S rate In (SQ/Sf) = 1.8 - 21 - 201037082 According to the present invention, a special equipment load is not required, the reaction efficiency of the added desulfurizing agent is prevented from being lowered, and the molten iron desulfurization treatment can be performed with excellent desulfurization efficiency. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic view showing a desulfurization treatment apparatus according to a first embodiment of the present invention. Fig. 2 is a desulfurization timing chart of the first embodiment of the present invention. Fig. 3 is a view showing the relationship between the slag and the desulfurizing agent in the first embodiment of the present invention. The fourth (a) and (b) drawings are diagrams showing the raising and lowering timing of the stirring blade according to the second embodiment of the present invention. Fig. 5 shows the state in which the stirring blade is raised. Fig. 6 is a view showing a state in which a desulfurizing agent is added to the floating slag. Fig. 7 shows the state in which the stirring wing is lowered. Figure 8 shows the agglutination of the desulfurizing agent. [Explanation of main component symbols] 1 : Melting iron pot 2 : Iron melting 2a : Surface 3 : Stirring wing 4 : Rotary shaft 5 : Motor-22- 201037082 6 : Desulfurizer addition device 7 : Controller 8 : Desulfurizer 9 : slag N 1 : number of revolutions N2 for desulfurization treatment: number of revolutions for slag floating
-23--twenty three-