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造粒超细三氧化二铁粉的流态化及直接还原实验的研究
Alternative TitleExperimental Study on Direct Reduction of Ultrafine and Granulated Hematite Powder in a Fluidized Bed
吴荣方
Subtype博士
Thesis Advisor朱庆山
2013-05-01
Degree Grantor中国科学院研究生院
Degree Discipline化学工程
Keyword超细粉   直接还原   造粒   流态化   失流   烧结活性
Abstract超细铁粉作为粉末冶金工业的基础原料之一,已被广泛应用在化工、机械、电子、医药、农业等国民经济的诸多领域中。由于目前制备超细铁粉的各种生产工艺(如等离子体法、溅射法、蒸发法、羰基法等)存在着原料价格高、设备复杂、生产能力小、反应条件苛刻和单位耗能高等缺点而难以实现工业化生产,因此低成本大规模生产超细铁粉的技术亟待开发研究。 流化床是一种气固接触充分、传热传质效率高且可直接处理铁粉的直接还原反应器。采用流化床直接还原超细氧化铁粉可望实现连续、高效、大规模地生产超细铁粉,具有良好的应用前景。然而,在流态化还原超细氧化铁的过程中存在着超细氧化铁粉的非均匀流态化和还原过程中的粘结失流等技术难题,目前关于超细氧化铁粉流态化直接还原的研究鲜有报道。 针对上述问题,本文以平均粒径为239 nm的超细三氧化二铁(Fe2O3)粉为原料,在实验室自制的流化床中对超细Fe2O3粉进行了冷态流态化实验,热态氢气直接还原实验和由此制取的超细还原铁粉的烧结实验研究,提出通过造粒延缓还原过程中粘结失流的方法。取得的创新性结果如下: (1)采用高纯氩气作为流化介质,在直径为35 mm的流化床中研究了超细Fe2O3粉造粒前后的冷态流化行为。结果表明,超细Fe2O3粉的流化过程与C类物料类似,随操作气速增加经历节涌、沟流后实现了聚团流态化,最小流化速度为0.09 m/s,床层膨胀比为1.37。根据力平衡原理计算得到的最小聚团尺寸为158 μm。采用了烧结造粒工艺将超细Fe2O3粉团聚为150-180 μm的颗粒,XRD分析表明造粒-烧结过程Fe2O3未发生物相改变。对900?C烧结6h(900?C -6h)的Fe2O3颗粒,实验测定最小流化速度为0.11 m/s,床层膨胀比为1.90。造粒改善了超细Fe2O3粉流化质量,达到稳定的散式流态化。 (2)以50%H2+50%Ar为还原气体,分别在450?C、500?C、550?C下研究了超细Fe2O3粉造粒前后的流态化还原过程,考察了温度对流化时间和金属化率的影响。结果表明,在450 ?C,超细Fe2O3可被还原至金属铁,会发生粘结失流,远低于文献报道的最低失流温度。无论造粒与否,超细Fe2O3粉流态化还原时间随温度升高而缩短,失流产物的金属化率随温度升高而降低。相同的反应温度下,造粒不仅延长了Fe2O3粉的流态化时间,而且还提高了失流时产物的金属化率。 (3)对还原产物的XRD分析表明,无论造粒与否,还原顺序均为Fe2O3→Fe3O4→Fe。还原产物的SEM微观形貌表明在颗粒表面和颗粒接触面之间均存在烧结现象。新鲜金属铁的粘结是造成超细Fe2O3流化还原过程中失流的主要原因。 (4)考察了烧结温度对造粒超细Fe2O3的流态化还原行为的影响。结果表明,降低烧结温度,导致造粒Fe2O的流态化还原时间延长。300?C造粒-烧结的Fe2O3在550?C下还原120 min未出现失流,且还原产物的金属化率达到98%,表明造粒-低温烧结工艺有助于超细Fe2O3粉实现持续温度的流态化还原以制备超细铁粉。 (5)考察了造粒前后超细Fe2O3在450-500?C间的等温还原行为,采用收缩未反应核模型分析了其动力学行为。结果表明,反应温度升高,造粒前后超细Fe2O3的还原反应速率均增加。Fe2O3→Fe3O4反应快,Fe3O4→Fe是反应控制步骤,在控制步骤中,造粒前后超细Fe2O3粉的表观活化能分别为44.80 kJ/mol和47.66 kJ/mol,表明造粒对超细Fe2O3的还原速率影响不大,但可降低其还原失流趋势,改善流态化还原的质量。 (6)研究了造粒前后的超细Fe2O3还原制取的还原铁粉和商用还原铁粉的烧结行为。结果表明,制备的超细还原铁粉具有非常好的烧结活性,以10 K/min升至900?C时,烧结体已达理论密度的91%以上,而相同条件下,商用铁粉尚未发生烧结,与此对比,文献中纳米级铁粉经900?C烧结30min后仅达到理论密度的90%。因此,流态化制备的超细铁粉性能良好,且造粒并未影响超细还原铁粉的烧结性能。
Other AbstractUltrafine iron powder, which is one of the basic raw materials in the powder metallurgy industry, has been widely used in many fields such as chemical industry, machinery, electronics, medicine, agriculture and so on. Ultrafine iron powder can be produced by various methods like the plasma method, the sputtering method, the vacuum evaporation method and the carbonyl process. These methods have however many disadvantages such as using high cost, small production capacity, complex devices and extreme reaction conditions and high energy consumption, and are not suitable to produce the ultrafine iron powder in industrial scale. It is therefore of urgent demands to develop a process that can produce ultrafine iron powders in large scale with low cost. Fluidized bed reactors, which have the advantages of high mass and heat transfer efficiency, are considered to have great potential to produce ultrafine iron powder at large scale. However, channeling, slugging and defluidization caused by sticking of iron particles always happen during the reduction process of ultrafine hematite powders. Up to now, to the best of my knowledge, the reduction of ultrafine hematite powders using fluidized bed reactors to produce ultrafine iron powder has not yet been reported. In the present thesis, the fluidization behaviors of an ultrafine hematite powder with average diameter of 239 nm have been investigated at room temperature under argon and at 450-550 ?C under hydrogen as well. Granulation was employed to improve the fluidization quality of the ultrafine powder and to tackle the defluidization problem during the reduction process. Main conclusions obtained are as following: (1) The fluidization behavior of the ultrafine hematite powder was investigated in a fluidized bed with I.D 35 mm by using the high purity argon as the fluidized medium. It was found that the fluidization behavior of the ultrafine hematite is similar to that of group C powders, where with increasing the superficial gas velocity, the bed experiences slugging, channeling, disrupting and finally a stable agglomerating fluidization. The minimum fluidized velocity was measured to be 0.09 m/s with a bed expansion ratio of 1.7. The agglomeration size was estimated to be 158 μm using a force balance model. The ultrafine hematite powder was granulated, sintered and sieved to obtain granulates of 150-180 μm, where new phases were not detected after the granulation and sintering as characterized by XRD.
Pages124
Language中文
Document Type学位论文
Identifierhttp://ir.ipe.ac.cn/handle/122111/8243
Collection研究所(批量导入)
Recommended Citation
GB/T 7714
吴荣方. 造粒超细三氧化二铁粉的流态化及直接还原实验的研究[D]. 中国科学院研究生院,2013.
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