在許多高溫鋼鐵冶煉製程中都運用底吹氣體攪拌，以增進反應速率與提高產能，但是氣體底吹會伴隨氣體回擊侵蝕底部耐火材以及底吹元件，造成成本增加及冶煉效率降低。由於底吹的常溫氣體對於鐵水冶煉溫度來說為相對低溫，因此在吹入爐中時有機會在爐底噴吹管處形成鐵相固凝物。此固凝物可保護爐底底吹管及其周圍之耐火材，因此經由製程操作條件來預知固凝物的型態及尺寸對於耐火材料的保護極為重要。

由於實際鋼鐵冶煉過程所形成之固凝物不易觀察，因此本實驗建立具低溫氣體調控之水模及蠟模來研究高溫冶煉爐內固凝物生成型態，探討相同底吹管直徑6.25mm下，不同的液相性質、底吹氣體流量及液相過熱度對於固凝物的生成、型態及尺寸之影響，同時針對固凝物成長達穩態所需時間及成長速度作記錄。本研究之水模實驗過熱度設定為12-18℃，底吹氣體流量為60-150 Nl/min，底吹氣體溫度則為-150℃，利用熱傳及流動相似性進行換算可得，蠟模實驗之對應過熱度為67-87℃，底吹氣體之對應流量為30-90 Nl/min，底吹氣體溫度則為-110℃。

由實驗結果可以觀察到水模及蠟模之固凝物皆是以單孔圓錐狀為主，氣體由中央之空心圓柱吹出。此外，由於固態蠟之熱傳導係數較差，造成蠟模之圓錐狀固凝物比較細長。本研究亦觀察到在固凝物可降低氣泡回擊之效應。在水模及蠟模固凝物達穩態尺寸觀察方面，隨著液相過熱度降低及底吹氣體流量上升，固凝物的尺寸會增加。在成長時間方面，實驗中也觀察到隨著液相過熱度降低及底吹氣體流量上升，固凝物成長速率與達穩態時間也上升。因此在探討固凝物成長速率、達穩態時間與固凝物的尺寸之關連可發現，固凝物達穩態時間與其成長速率成正比，達穩態後之高度則與其達穩態時間平方成正比。

In pyrometallurgical processes, gas bottom-blown technique has been widely applied to agitate the liquid bath inside the vessel to enhance metallurgical efficiency via high mixing intensity. In general, the erosion of refractory lining near gas bottom-blown tuyere is severer than other area inside the vessel due to back attack of blown gas bubbles. One of the countermeasures to alleviate the erosion is to generate an iron accretion sitting on the refractory lining via appropriate bottom-blown conditions. The covering of the accretion can protect the refractory lining from being eroded by the back attack of gas bubbles. Therefore, how to generate accretion with proper size and shape is one important issue for high performance gas bottom- blown process.

Due to high temperature operation, it is extremely difficult to visualize what is happening inside the pyrometallurgical vessels. Therefore, water and wax model were adopted to investigate the effects of gas bottom-blown condition on the shape and dimensions of solid accretion. In the water model, experiments were conducted with the flow rate of the bottom-blowing gas set in the range of 60~150 Nl/min, and the superheat set in the range of 12~18℃. The air temperature was controlled at -150±2℃ by flowing air through the pipe immersed in the liquid nitrogen bath. A similarity conversion was used for correlating the conditions of a water model and a wax model. After the conversion, the flow rate of the bottom-blowing gas was set in the range of 30~90 Nl/min, the superheat was set in the range of 20~40℃, and the air temperature was set at -110±2℃ in the wax model.

In the water and wax model, the accretions were in cone shape of with a hollow channel for gas flowing through. It also shows that the shapes of wax accretions were taller and thinner than ice accretion. The back-attack of bottom-blowing gas can also be observed in the experiment. The final size of accretions of water model and wax model were proportional to the gas flow rate and inversely proportional to the liquid temperature. In addition, the growth time which is the duration from the wax accretion just formed until it reached a steady state, increases with gas flow rate and decreases with liquid temperature. It also shows the accretion growth rate increases with gas flow rate and decreases with liquid temperature. Therefore, the accretion growth rate and the growth time are both proportional to the final of sizes accretions. The results show that the final heights of accretions were direct proportional to growing velocity and square of growth time.

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