抑制铁矿粉多级流化还原粘结失流研究

发布时间：2018-07-06 16:23

本文选题：流化床 + 铁矿粉　；参考：《中国科学院大学(中国科学院过程工程研究所)》2017年博士论文

【摘要】：流态化气基还原炼铁直接以粉矿为原料,省去了球团、烧结和炼焦等工序,是一种很有发展前景的直接还原炼铁技术。随着优质铁矿资源的减少,选矿后得到的矿粉中细粉(粒度在100 μm左右)含量越来越高。这些细粉具有较高的还原速率,可以充分发挥流态化炼铁技术的优势,然而其在高温气基流化还原过程中,由于颗粒表面粘性增大或者铁晶须的生成较易发生粘结并形成大聚团,继而导致整个床层的失流,会对稳定生产造成严重影响。针对这一问题,本文以铁矿粉在不同多级流化还原工艺中出现的中间产物(如低金属化率颗粒、Fe3O4、FeO和富碳颗粒等)为研究对象,通过模拟工业上的多级流化还原系统,提出了一系列高效的抑制粘结失流方法,并对其作用机制进行了深入研究。本文所取得的主要研究成果如下:揭示了还原条件对多级流化还原预还原段低金属化率颗粒表面铁析出形貌及其粘结行为的影响规律,提出了调控铁析出形貌抑制铁矿粉多级流化还原粘结失流的操控方法。研究表明在CO中混入H2可以加快铁晶粒的生长速率,同时增加还原初期矿粉表面的铁形核数量,导致矿粉表面新生成的金属铁由晶须状转变为致密状。随着CO-CO2中CO2含量的升高,矿粉表面新生成的金属铁会由"锋利"的晶须状转变为"仙人掌状",并且表面铁的分布密度会变小。随着还原温度的降低,矿粉表面铁晶须的强度会变弱。这些均可以显著减少低金属化率颗粒流化还原过程中形成的聚团量。此外,在预还原段将低金属化率颗粒表面的铁析出形貌由晶须状转变为致密状,可以有效降低防止深还原段高金属化率颗粒失流的MgO加入量。揭示了 MgO对多级流化还原过程中不同价态铁氧化物矿粉粘结失流的抑制机制,提出了添加MgO抑制铁矿粉多级流化还原粘结失流的较优加入时段。MgO与不同价态铁氧化物间的界面反应行为表明,在中低温(700和800 ℃)下MgO对Fe2O3、Fe3O4和FeO矿粉粘结失流的抑制作用主要是物理阻隔效应。在高温(900 ℃)下对于主要成分为Fe2O3的矿粉来说,物理阻隔效应依然是主要抑制作用;对于主要成分为Fe3O4和FeO的矿粉来说,化学反应形成的阻隔层是抑制粘结失流的主要原因,并且MgO在FeO矿粉表面形成的化学阻隔层厚度大于其在Fe3O4矿粉表面形成的。化学阻隔层比物理粘附引起的抑制作用更加有效。因此在Fe3O4和FeO稳定存在的多级流化还原工艺中,加入MgO对高温下粘结失流的抑制效果由强到弱可按如下顺序排列:FeOFe3O4Fe2O3。还原实验结果表明加入MgO抑制粘结失流对铁矿粉还原速率的影响较小。制备新型添加剂CaO/Fe2O3强化了钙组分对铁矿粉流化还原过程中粘结失流的抑制效果,并揭示了其抑制机制。研究表明分析纯CaO粉末和Ca(NO3)2·4H20分解产生的CaO对粘结失流的抑制作用较弱,而Fe(NO3)3·9H20和Ca(NO3)2·4H20混合物分解产生的CaO/Fe2O3具有较好的抑制效果。CaO/Fe2O3的还原结果表明Ca组分主要通过物理阻隔效应抑制粘结失流。微观组织结构观察表明CaO/Fe2O3不仅可以抑制"锋利"尖状铁的生成,还可以使Ca组分紧密地包覆在粘性铁表面,从而降低其表面粘性。此外,研究表明引入Fe2O3强化性能较差添加剂对粘结失流的抑制效果具有普适性。揭示了铁矿粉多级流化还原过程中的碳沉积和演变行为,发现沉积碳不仅是还原过程中矿粉颗粒粘结的抑制剂,还是性能优越的固相还原剂。高还原势、低温及H2的引入可以加速多级流化还原预还原段碳的沉积,尤其是石墨型游离碳的沉积。石墨型游离碳可以抑制铁晶须生成,降低颗粒表面粘性,从而防止矿粉颗粒在高温深还原中发生粘结。高温深还原中石墨型游离碳和碳化铁均会通过气化反应和固相还原反应被消耗,并且石墨型游离碳的反应活性高于碳化铁。为了强化流态化技术在直接还原炼铁中的应用,提出了利用高活性沉积碳通过固固反应将铁矿粉还原至较高金属化率的方法,并且证明了它的可行性。综上所述,本文围绕抑制铁矿粉多级流化还原粘结失流展开,基于铁矿粉在不同工艺中的演变特性,提出了一系列高效的操控方法,如调控铁析出形貌抑制多级流化还原预还原段低金属化率颗粒的粘结,同时减少防止深还原段高金属化率颗粒失流的MgO加入量;在多级流化还原的FeO段加入MgO,利用高温下固固反应形成的化学阻隔层高效地抑制粘结失流;制备新型抑制粘结失流添加剂CaO/Fe2O3,强化Ca组分对粘结失流的抑制效果。此外,在深入分析铁矿粉多级流化还原中碳沉积和演变行为的基础上,提出了直接利用沉积碳进行高温深还原的方法。与前人研究相比,本文所提出的抑制方法更加贴近实际工业过程,更具针对性和高效性,可操作性强。
[Abstract]:The fluidized gas based reduction ironmaking directly takes powder ore as the raw material, and saves the pelletizing, sintering and coking processes. It is a very promising direct reduction iron smelting technology. With the reduction of high quality iron ore resources, the fine powder in the ore powder (the grain size is about 100 m) is getting higher and higher after the mineral resources. These fine powders have high reduction rate. It can give full play to the advantages of fluidized iron smelting technology. However, in the process of high temperature gas based fluidized reduction, it can cause the loss of the whole bed because of the increase of the viscosity of the particle surface or the formation of the ferric whisker, which will lead to the severe effect on the stable production. In this paper, the iron ore powder is used in this paper. The intermediate products (such as low metal rate particles, Fe3O4, FeO and carbon rich particles) in different multistage fluidized reduction processes are studied. A series of efficient methods for inhibiting bond loss are proposed by simulating the multistage fluidized reduction system in the industry, and the mechanism of its action is deeply studied. The main research obtained in this paper The results are as follows: the influence of reduction conditions on the iron precipitation morphology and bond behavior of the low metallized particles on the reduction rate of the reduced stage is revealed. The control method of controlling the iron precipitation morphology to restrain the multistage flow reduction of iron ore is proposed. The study shows that the mixing of H2 in CO can accelerate the growth rate of iron grain. At the same time, the number of iron nucleation on the surface of the ore powder at the initial stage of reduction is increased, which leads to the change of the newly formed metal iron on the surface of the mineral powder from the whisker to the dense shape. With the increase of the content of the CO-CO2, the newly formed metal iron on the surface of the mineral powder will change from the sharp whisker to the "fairy palm", and the distribution density of the surface iron will be smaller. With the reduction temperature, the distribution density of the surface iron will be smaller. The strength of the iron whisker on the surface of the mineral powder will be weakened. These can significantly reduce the mass of the particles in the low metallization grain flow reduction process. In addition, the iron precipitation morphology of the low metallized particle surface is changed from the whisker shape to the dense shape in the pre reduction section, which can effectively reduce the high metallizing rate particles in the deep reduction section. The MgO addition of the loss of flow reveals the inhibition mechanism of MgO on the bond loss of the different valence iron oxide ore powders during the multistage reduction process. It is suggested that the interfacial reverse behavior between.MgO and the different valence iron oxides with the addition of MgO to inhibit the multilevel flow reduction of the iron ore is shown to be under the medium and low temperature (700 and 800 degrees C). The inhibition effect of MgO on the loss of Fe2O3, Fe3O4 and FeO is mainly the physical barrier effect. At high temperature (900 C), the physical barrier effect is still the main inhibitory effect for the mineral powder with the main composition of Fe2O3; for the mineral powder with the main composition of Fe3O4 and FeO, the barrier layer formed by the chemical reaction is the main inhibition of the bond loss. For reasons, the thickness of the chemical barrier layer formed by the MgO on the surface of the FeO ore powder is greater than that formed on the surface of the Fe3O4 ore powder. The chemical barrier layer is more effective than the inhibitory effect caused by physical adhesion. Therefore, in the multistage fluidized reduction process of Fe3O4 and FeO, the inhibition effect of adding MgO on the bond loss at high temperature is strong to weak. The results of FeOFe3O4Fe2O3. reduction experiments show that the effect of adding MgO to inhibit the reduction of iron ore is less. The preparation of new additive CaO/Fe2O3 strengthens the inhibition effect of calcium component on the loss of bond in the flow reduction process of iron ore, and reveals its inhibition mechanism. The study shows that pure CaO powder and Ca (NO) are analyzed. 3) the suppression of CaO produced by the decomposition of 2. 4H20 is weak, while Fe (NO3) 3. 9H20 and Ca (NO3) 2. 4H20 have a good inhibition effect. The reduction of.CaO/Fe2O3 shows that Ca components mainly inhibit the bond loss by physical barrier effect. Microstructural observation shows that CaO/Fe2O3 is not only possible. The inhibition of the formation of sharp sharp iron can also make the Ca components tightly coated on the surface of the viscous iron and reduce the surface viscosity. In addition, the study shows that the inhibition effect of the additive on the poor performance of Fe2O3 is universally suitable. The carbon deposition and evolution behavior of the iron ore powder in the multistage fluidized reduction process is revealed. The deposition of carbon is not only an inhibitor for the bonding of mineral particles in the reduction process, but also a solid state reducing agent. High reduction potential, low temperature and H2 can accelerate the deposition of carbon in the pre reduction stage, especially the deposition of graphite free carbon. Graphite free carbon can inhibit the formation of iron crystal and reduce the viscosity of the particles. In order to prevent the mineral particles from bonding in high temperature and deep reduction, both graphite free carbon and iron carbide will be consumed by gasification and solid state reduction in high temperature deep reduction, and the reactive activity of graphite free carbon is higher than that of iron carbide. In order to strengthen the application of fluidized technology in direct reduction of iron smelting, the use of high activity is put forward. The feasibility of the reduction of iron ore to higher metallization by the solid solid reaction is demonstrated by the solid solid reaction. In summary, this paper presents a series of efficient manipulation methods based on the evolution characteristics of iron ore in different processes, such as the regulation of iron precipitation. The appearance inhibits the bonding of low metallized particles in the pre reduction section of the multistage fluidized bed, and reduces the amount of MgO added to prevent the loss of the high metallized particles in the deep reduction section. In the FeO section of the multistage fluidized reduction, MgO is added to the chemical barrier layer formed by the solid solid reaction at high temperature. In addition, on the basis of deep analysis of the carbon deposition and evolution behavior in the multistage reduction of iron ore powder, the method of direct use of deposited carbon for high temperature and deep reduction is put forward on the basis of further analysis of the behavior of carbon deposition and evolution in the multistage reduction of iron ore powder. Compared with previous studies, the suppression method proposed in this paper is more close to the actual industrial process and is more useful than the previous research. It is pertinent and efficient, and has strong maneuverability.
【学位授予单位】：中国科学院大学(中国科学院过程工程研究所)
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TF552

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