一貫作業鋼鐵冶煉製程中會產生一些集塵灰及礦泥，統稱為固雜料。固雜料內含有高比例之鐵氧化物與碳，可經由碳熱還原反應生成直接還原鐵(DRI, Direct Reduced Iron)，作為高爐原料來回收。為了避免儲存、搬運和高爐加料過程中產生碎裂，而影響高爐透氣性，故DRI壓碎強度須足夠(大於0.60 kg/mm2)。
本研究針對固雜料渣組成對軟熔性質之影響進行評估。藉由實驗結果與相圖之曲線走向，以了解並建立渣相軟熔性資料庫，作為調整之參考。鹽基度(B2)和FeO都會影響渣之軟熔溫度，固雜料渣相之B2需要低於1.43以下，變形溫度才能低於1250℃，DRI內部才有熔渣固結現象，DRI強度也會跟著提高。接下來探討添加劑(Fe2O3、SiO2、石墨)與還原溫度對固雜料經由碳熱還原反應生成直接還原鐵(DRI)壓碎強度之影響。當固雜料配比不適當或還原溫度降低時所生成DRI的壓碎強度會低於規格要求的0.60 kg/mm2，藉由適當添加劑的加入，可以確保DRI強度合乎高爐進料要求。
本研究配置兩組不同組成配比的固雜料。第ㄧ種固雜料(樣品A)的主要組成是28.82%含油脫水礦泥(Oily DW Sludge)、19.15%高爐礦泥(BF Sludge)、17.05%轉爐礦泥(BOF Slurry)、13.55%含油銹皮(Oily Mill Scale)。固雜料(樣品A)用於小規模(Laboratory Scale)試驗，分別添加10、15、20% Fe2O3，5、10、15% SiO2與2、4、6%石墨，均勻混拌後壓錠成Pellet，經不同反應溫度(1150~1250℃)，探討添加劑與反應溫度對DRI壓碎強度之影響。研究發現樣品A在1250℃，15分鐘進行碳熱還原後，所得DRI壓碎強度為1.66 kg/mm2。添加10與15% Fe2O3，可提高其DRI壓碎強度，但是添加20% Fe2O3，DRI壓碎強度反而會減弱。添加5% SiO2，DRI壓碎強度增加，添加10與15% SiO2，DRI壓碎強度變差。添加2、4、6%石墨，DRI壓碎強度明顯減弱。反應溫度降低，DRI壓碎強度會變差。當反應溫度降為1200℃時，添加15% Fe2O3，DRI壓碎強度仍高於0.60 kg/mm2。
中鋼RHF (Rotary Hearth Furnace)製程，係將調漿，脫水後，經混練擠型成小圓柱狀顆粒再進爐反應，經由實驗發現其成型最佳水份介於17~21區間。另外，針對樣品A以950℃，5分鐘下測試其驟熱爆裂阻抗發現，避免驟熱爆裂之最佳水分區間為15~19%。综合考量擠型性能和驟熱爆裂阻抗，當固雜料進行模擬製程試驗時，其進料最適水分區間為17~19%。另ㄧ種固雜料樣品B與樣品A有類似的組成，唯轉爐礦泥減為10.10%、而高爐煙塵(BF Flue Dust)從原來的2.66%增為9.20%，此組成預期會使DRI的強度變差。樣品B藉由先導型規模(Pilot Scale)試驗，控制水分於18%，擠出成型的樣品，於1200℃，15分鐘反應後，其DRI壓碎強度為0.48 kg/mm2。再分別添加2、4、6、8%廢氧化鐵粉，於1200℃，15分鐘反應後進行壓碎強度試驗，結果發現添加6與8%廢氧化鐵粉，DRI壓碎強度可提高至0.61、0.71 kg/mm2。
根據碳熱反應原理和DRI壓碎強度形成機構，固雜料化學組成中(C/Ored)mol是影響DRI壓碎強度之主要因素。固雜料適度添加Fe2O3，使(C/Ored)mol小於1.20，可以確保DRI壓碎強度在0.60 kg/mm2以上。

In integrated steel plants, dusts and sludges, commonly referred to as “residual materials”, are inevitably generated during steel production. Due to high iron oxides and carbon contents, these residual materials can be converted into direct reduced iron (DRI) through the carbothermic reduction. DRI can be recycled as the feedstock of blast furnace for liquid iron production. It is known that the permeability of blast furnace would be deteriorated in case of the severe breakage of burden materials. Therefore, it is strictly required that the crushing strength of DRI has to be higher than 0.60 kg/mm2 to avoid its breakage during storage, transportation, and charging into blast furnace.
The study focuses on the effect of the softening and melting temperature of slag composition based on residual materials in China Steel Company. The results compared with data of phase diagram can estimate how to adjust recipe of residual materials in order to meet the feed demand of blast furnace. The results show both basicity (B2) and FeO content can affect the softening and melting temperature of slag. When B2 is lower than 1.13, the deformation temperature is probably less than 1250℃. The solidified softened slag could intensify DRI crushing strength. At next stage, the study investigates the effect of additives to residual materials on the crushing strength of DRI. By adding proper agents, it can assure DRI crushing strength to meet the feed demand of blast furnace. The mixture (Case A) which was made of nine kinds of residual materials was composed of 28.82% oily dewater sludge, 19.15% blast furnace sludge, 17.05% basic oxygen furnace slurry, and 13.55% oily mill scale. The rest of the residual materials were basic oxygen furnace dust, blast furnace flue dust, wastes incinerator fly-ash, blast furnace high-zinc sludge, and cold-rolling sludge. Additives included powdery reagents of Fe2O3, SiO2, and graphite. Experimental conditions of the lab-scale carbothermic reaction included reaction time ranging from 10 to 20 minutes and reaction temperature between 1150 and 1250℃. Results shows adding proper amount of Fe2O3 will decrease the value of (C/Ored)mol and increase the iron content of DRI. It would raise the crushing strength of DRI. It also was found that adding a little SiO2 would induce the partially softening and melting slag phase under 1250℃ due to the lower B2 value (down to 0.89) of the residual materials specimens. The higher crushing strength of DRI was obtained due to sintering. Furthermore, the addition of graphite resulted in the value of (C/Ored)mol above 1.20. It declined the DRI strength. On the other hand, increasing reduction time or reaction temperature could enlarge effect of additives on the crushing strength of DRI. When reaction temperature decreased to 1200℃, adding 15% Fe2O3 made crushing strength of DRI higher than 0.60 kg/mm2.
In in-situ process of RHF, the intact green pellet of residual materials is essential. Blending water content with residual materials affects discharge.of extruder. The appropriate water content was between 17~21%. Besides, the condition of heat fragment was conducted at 950℃ for 5 minutes. The optimal water content was 15~19% for resistance of heat fragment. Synthesizing both results, 17~19% water content is the best condition for pilot scale. The mixture (Case B) had similar composition to Case A, but BOF slurry decreased from 17.05 to 10.10% and BF flue dust increased from 2.66 to 9.20%. This recipe expected to produce worse strength of DRI due to excess carbon content. The pellets via an extruder with water content (18%) were reduced at 1200℃ for 15 minutes. The result shows the crushing strength for Case B was 0.48 kg/mm2. Adding 2, 4, 6, 8% Fe2O3 from acid regenerate plant (ARP) to Case B was reduced at 1200℃ for 15 minutes. It shows 6 and 8% Fe2O3 can increase crushing strength of DRI to 0.61 and 0.71 kg/mm2.
According above results shows that high value (＞1.20) of (C/Ored)mol in residual materials would cause the crushing strength of DRI under 0.60 kg/mm2. So adding appropriate Fe2O3 which consumes carbon and introduces softened slag within DRI assures the crushing strength of DRI above 0.60 kg/mm2.

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