Simulation Analysis on Fluid Mechanics around Skimmer and Separation Efficiency of Iron Dam in the Blast Furnace Main Trough

鋼鐵產業是經濟發展的根本，現今除了提升產能外，如何在具有競爭力的價格中生產出高品質的鋼材相當重要。然而，高爐主流道會受到鐵水與爐渣的侵蝕，其具有高額的修繕成本，因此對於高爐主流道中的流力與鐵渣分離的探討是必須的。本文使用計算流體力學模擬高爐主流道內空氣、鐵水與爐渣瞬態的流動變化，探討不同流道底部形狀、檔板開口、總質量流率及鐵渣比對於流場變化以及鐵水出口(Iron Dam)的鐵渣分離的影響。本研究沒有考慮熱傳現象及流動為紊流，並使用有限體積法與多相流模型體積分率法(Volume of Fluid Model, VOF)模擬空氣、爐渣及鐵水三相流體於高爐主流道內速度分佈，以獲得剪切應力分佈及藉由相間界面形態以估算鐵水出口處之鐵渣分離效率。分別經由兩相(鐵水與空氣)系統及三相系統(鐵水、爐渣及空氣)之數值模擬分析，本研究獲得重要結果如下： (1)兩相系統 主流道緩衝區的最大壁面剪切應力發生在鐵水出口前端，並發現流道為鈍角底部的流場會產生較大迴流現象，故其最大壁面剪切應力比弧形底部的流道大25.58 %。 (2)三相系統 a.當有爐渣從鐵水出口流出時，會造成檔板後方的壁面剪切應力增加，且爐渣損失越多，則剪切應力越大，當爐渣損失率上升3.06%，檔板後方的壁面剪切應力則增加1.79%。 b.在鐵渣比為1：9及出鐵口的總質量流率為15 ton/min情況下，檔板開口從0.3 m增加至0.4 m，於鐵水出口前端最大壁面剪切應力上升65.89%，此為檔板後的流量增加所導致。 c.固定鐵渣比為1：6及檔板開口為0.4m時，出鐵口的總質量流率從5.5 ton/min增加至15 ton/min，於鐵水出口前端壁面剪切應力最大值增加45.74%，此因滯留時間短而使得於相同流道內的流速變快所致。 d.當檔板開口由0.4 m降到0.3 m，在出鐵口總質量流率15 ton/min鐵渣比為1：9時，本文發現爐渣損失率從3.06%變為0%，此結果是由於檔板開口降低，鐵水與爐渣的界面高於檔板底部，而造成爐渣無法從鐵水出口流出。 e.高爐出鐵時總質量流率從5.5 ton/min增加至15 ton/min，在檔板開口為0.4 m及爐渣比為1：6情況下，爐渣損失率上升1.63%，此因總質量流率增加使得鐵水與爐渣於高爐主流道內的滯留時間縮短所致。 f.當鐵渣比由1：1增加到1：9且檔板開口為0.4m及出鐵口總質量流率5.5 ton/min時，則爐渣損失率上升1.53%，此因進入高爐主流道內的爐渣比例增加時，使得鐵水上層的爐渣變厚及鐵水與爐渣的界面降低，導致爐渣容易從檔板底部流向鐵水出口。Iron and steel industry is the fundamentals of economic development. Aside from pursuing higher productivity, it is also important know how to produce higher quality steel at the competitive price. However, the blast furnace main trough is worn by molten iron and slag, which has expensive repairs. It’s essential to investigate fluid mechanics and separation in blast furnace main trough. Therefore, in the present work a computational fluid dynamics model has been developed to study the transient flow behavior of air, liquid iron and slag in the blast furnace main trough. We investigate the effects of bottom shape of the blast furnace runner, the height of the opening under the skimmer, the total mass flow rate and the ratio of iron to slag on the flow patterns and separation efficiency at iron dam. In addition, the mathematical model is isothermal and turbulent flow to simulate velocity distribution by utilizing the finite volume method and multiple-phase fluid model (VOF method), respectively, followed by calculating shear stress on the wall of trough and mass flow rate to estimate the separation efficiency of iron and slag at the iron dam. The significant results of this study were summary as follows: (1)Two phase system(iron and air) In the buffer zone of blast furnace trough, the maximum shear stress is occurred in the front of iron dam, which the maximum shear stress of obtuse runner is over that of arc-shaped runner for 25.58% because the recirculation in obtuse runner is more than arc-shaped runner. (2)Three phase system(iron, air and slag) a.The shear stress around skimmer of blast furnace trough will raise due to slag loss (slags fall into the iron dam through the bottom of skimmer). The more slag loss in iron dam will cause the higher velocity and the greater shear stress. As slag loss percentage was increased from 0% to 3.06%, the shear stress behind skimmer would be raised by 1.79%. b.When the ratio of iron to slag was set by 1:9, the total mass flow rate was fixed as 15 ton/min from taphole, and the height of the opening under the skimmer was increased from 0.3m to 0.4m, the maximum shear stress in the front of iron dam was raised by 65.89%. c.As the total mass flow rate was changed from 5.5 ton/min to 15 ton/min, the maximum shear stress in the front of iron dam was increased by 45.74%, resulting from that higher velocity owing to reducing the residence time. d.When the height of the opening under the skimmer was changed from 0.4m to 0.3m, the slag loss percentage was decreased from 3.06% to 0% due to the fact that the interface between iron and slag is lower than the bottom of skimmer. e.The slag loss percentage would be raised by 1.63% when the total mass flow rate was changed from 5.5 ton/min to 15 ton/min for reducing the residence time. f.With adding the amount of slag in trough, the interface between iron and slag is lower than the bottom of skimmer. As the ratio of iron to slag at taphole was enhanced, the slag loss percentage will be increased from 0% to 1.58%.摘要 i Abstract iii 目錄 v 圖目錄 viii 表目錄 xii 符號說明 xiii 第一章 緒論 1 1-1 前言 1 1-2 研究目的 3 1-3 研究方法 4 1-4 本文架構 5 第二章 文獻回顧 6 2-1 流體力學 6 2-1-1 流體的連續介質模型 6 2-1-2 流體的慣性 6 2-1-3 流體的壓縮性 7 2-1-4 流體的膨脹性 7 2-1-5 流體的黏性 7 2-1-6 層流與紊流 8 2-1-7 有旋流動與無旋流動 9 2-1-8 質量守恆方程式 9 2-1-9 動量守恆方程式 10 2-2 紊流模型 12 2-3 離散方法概論 13 2-3-1 離散化的目的 13 2-3-2 離散時所使用的網格 14 2-3-3 有限體積法 14 2-3-3-1 有限體積法基本思想 14 2-3-3-2 有限體積法使用的網格 15 2-3-3-3 有限體積法離散格式 17 2-4 壓力修正法 17 2-4-1 SIMPLE法 17 2-4-2 SIMPLER法 18 2-4-3 SIMPLEC法 18 2-4-4 PISO法 18 2-5 多相流系統-VOF模型 19 2-6 高爐主流道 21 2-6-1 鐵渣分離效果 21 2-6-2 流力 23 2-6-3 高爐出鐵口 27 第三章 研究方法 30 3-1 物理模型 30 3-2 數學模式 32 3-2-1 基本假設 32 3-2-2 守恆方程式 33 3-3 邊界條件 36 3-4 初始條件 36 3-5 數值方法 38 3-6 數值計算 41 3-7 敏感度分析 43 第四章 結果與討論 45 4-1 計算模式驗證 45 4-1-1 網格敏感度測試 45 4-1-2 理論與現場數據驗證 46 4-2 兩相系統變因討論 51 4-3 三相系統變因討論 62 4-3-1 鐵渣分離效果之敏感度分析 62 4-3-1-1 檔板開口 62 4-3-1-2 總質量流率 65 4-3-1-3 鐵渣比 67 4-3-2 流力之敏感度分析 70 4-3-2-1 檔板開口 70 4-3-2-2 總質量流率 80 4-3-2-3 鐵渣比 86 第五章 結論與未來方向 92 5-1 結論 92 5-2 未來工作 93 參考文獻 9