【作者】 尹国亮；

【导师】 温良英；

【作者基本信息】 重庆大学 ， 冶金工程， 2014， 博士

【摘要】 流态化技术因其具有传热传质条件好、温度均匀、物料运输方便等优势，已广泛应用于石油化工、能源环保、冶金、材料、生化制药等工业领域。在非高炉炼铁气基还原法中，流态化预还原铁矿粉越来越受到广大科技工作者的重视，但铁矿粉在流化预还原过程中往往会相互粘结或粘结反应器壁，甚至引起失流破坏正常生产过程。因此，粘结是限制流态化气体还原发展的关键问题之一，引起了国内外学者的广泛关注。关于粘结失流的原因及防止方法已提出很多，大多数学者认为是因为金属铁晶须的生成及其烧结，在防止方法上着重在研究添加物或铁矿粉预处理的作用效果，但对铁晶须的形成及其控制尚看不出简单的规律，相关基础理论尚待深入。本论文针对典型铁矿粉颗粒，采用激光粒度分析、矿粉物性分析、颗粒聚团与破碎分析、化学反应过程的模拟等系列现代分析方法，揭示铁矿粉流态化过程中颗粒的粘结与破碎机理，并讨论影响流态化过程中颗粒粘结与破碎的因素，从而为铁矿粉流态化还原过程中的粘结失流提供依据；分析还原条件对矿粉金属化率、金属铁的分布形态、铁矿粉间粘结方式的影响及其相互关系，探索铁矿粉颗粒间的粘结机理，为解决流态化预还原过程中铁矿粉粘结失流、改善流化质量和还原反应进程奠定理论基础。采用自主开发设计的粉体综合特性测试仪，测定了四种铁矿粉的休止角、崩溃角、分散度、松装密度、振实密度、流动性等物性参数。研究发现，矿粉的休止角与崩溃角随粒度的变化具有相同的变化趋势，休止角与崩溃角越大，矿粉的流动性越差，矿粉颗粒之间越容易团聚；铁矿粉的分散度随粒度的减小而减小；通过霍尔流量计可以直接测量矿粉的流动性的趋势与休止角和崩溃角所反映的情况一致，同样的流动性差的细颗粒容易发生团聚；利用松装密度和振实密度确定的压缩度、Hausner比判别法、计点法三种评价手段对四种铁矿粉的流动状况进行评价，得出四种矿粉中澳矿最适合流态化操作；钒钛矿不适合流态化操作，巴西矿和北方矿在粒度小于150目时流动性较差，150目以上时流动性不稳定，有团聚粘结的趋向。采用物理实验与数值模拟结合的方法研究了突破力随粒径的增大而减小的规律，得到了单一均匀粒度颗粒突破力的计算关系式：通过实验表明，该公式能较好的表征气体流过B类颗粒散料填充床的突破力。对于不同粒度分布的矿粉，在平均粒度相等的情况下，按照二项/泊松离散分布函数进行设计，并引入一个表征粒度分布对流态化特性影响的判别因子Fa。得出突破力与Fa值之间的对应关系，即两种离散分布函数下颗粒的Fa值相近且均小于原矿的Fa值，基于两种分布为基础建立的流态化实验模型的突破力也相近且小于原矿的突破力。为典型铁矿粉流态化特性中的突破力提供了基础判断依据。通过实验测定稳定气速下床层压降随时间的变化规律，间接考察流态化过程中铁矿粉的粘结现象。结果表明：在流态化过程中四种矿粉都存在不同程度的破碎现象，其中，澳矿在较低气速下（0.21m/s）存在破碎，而钒钛矿随气速的增大一直存在破碎，巴西矿和北方矿的破碎规律相似，在0.32m/s气速后，破碎现象已不明显。在流态化过程反映的矿粉的破碎现象与物性参数测定的矿粉的流动状况相似。利用COMSOL的化学反应工程模块对铁矿粉的还原反应过程进行了数值模拟，研究了颗粒粒度、形状、还原温度、还原气氛等因素对还原过程的影响。结果表明：3mm及以上粒径颗粒的反应速率随着反应时间的增加先升高后降低，3mm以下粒径的颗粒反应速率随着反应时间的增加不断降低；并更容易产生铁瘤或铁晶须；颗粒的凸起与不规则处会优先反应，同时得到顶角角度为60°、70°、80°的颗粒的反应过程向底面扩散的趋势明显，固体产物不易在顶角处聚集，相对于其他的角度不易产生铁瘤及铁晶须；而50°及以下的角度质量分数随时间变化较小，固体产物容易在顶角处聚集，从而增加了产生铁瘤及铁晶须的可能性；反应过程中颗粒受热不均，则未反应物核心会向局部受热的反方向不断偏移，最终消失，而局部受热的部位，固体产物不断增加，使产物层增厚，产物层在局部聚集容易产生液相并与附近的颗粒发生粘结；H2还原时颗粒产物层界面规则，而CO还原时反应界面不规则。通过分析Fe、O原子间的距离发现H2还原时易产生铁瘤，而CO还原时易产生铁晶须；铁瘤与铁晶须在颗粒表面产生后，铁瘤对颗粒的后续反应影响较小，而铁晶须对颗粒的后续反应影响较大。是促使铁矿粉颗粒粘结的主要原因。更多还原

【Abstract】 Because of its good heat and mass transfer condition, temperature uniformity, andthe advantages of the material transportation is convenient, Fluidization technology arewidely used in petrochemical, energy, environmental protection, metallurgy, materials,biochemical, pharmaceutical and other industrial fields. In the non-blast furnace gasbase reduction method, the fluidization prereduced iron ore powder more and more getthe attention of the general scientific and technical workers, but the iron ore powder inthe process of fluidization prereduction tend to bond or bond to each other the reactorwall, even cause of defluidization and destroy the normal production process. Therefore,the bond is one of the key problem of confining the development of fluidization gasreduction, which caused the wide attention of scholars both at home and abroad. Thecause of defluidization and prevent method has put forward a lot of, Most scholarsbelieve that because of the formation of metallic iron whisker and its sintering, on theprevent way to, emphasize the research additives or iron pretreatment effect.But on ironwhisker formation and its control is still don’t see a simple rule, the relevant basictheories remain to be further.For typical iron ore powder particles, this paper uses the image ore particle sizeanalysis, physical property analysis, granular poly group and fracture analysis, chemicalreaction process of simulation, etc. Series of modern analysis methods, revealing thegathering and binding mechanism of iron ore powder particles in the process offluidization. And discuss the influence factor of gathering and binding in the process offluidization, providing the basis to fluidization in the process ofiron ore powderfluidized reduction. Analysis of the effect of reduction conditions on metallization ratethe breeze, the distribution of metallic iron form, the influence of the bonding way ofthe iron ore powder and their mutual relationship, and explore the bonding mechanismof iron ore powder particles between, to solve the defluidization in the process ofironore powder fluidized reduction and improves the quality of fluidization and reductionreaction process to lay the theoretical foundation.The self-designed powder comprehensive characteristics tester is used to measurethe angle of repose, collapse angle, the angle of dispersion, apparent density, tap density,fluidity and other physical parameters. The study found that the angle of repose andcollapse angle have the same change tendency with the change of particle size. The angle of repose and collapse angle increase with decreasingliquidity, then the particlesare prone to agglomerate. The dispersiondegree decreases with decreasing particle size.Hall flow meter can directly measure the fluidity trend, and the fluidity trend isconsistent with the case reflected by the angle of repose and collapse angle. In the sameway, particles of decreasing liquidity are prone to agglomerate. The compressiondegree, Hausner ratio criterion and scoring method determined by apparent density andtap density are used to evaluate the fluidity of the four kinds of iron ore. The resultshows that the Austrian ore is the most suitable for fluidization operation; Vanadiumtitanium ore is not suitable for fluidization operation. When the particle sizeof Brazilianore and northern ore is below150mesh, the fluidity become worse; when the particlesize is above150mesh, the fluidity is not steady, and is prone to agglomerate.Using the combined method of physical experiment and numerical simulation toget the rule of breakup force with particles size, desity, bed height. Through theoreticalderivation method got a uniform particle size particles break force calculation formula:After verification, the mathematical model can better characterize the breakupforce of B type particle through bulk packed bed. For the different particle sizedistribution ore powder, in the case of the average particle size is equal, according to theproportion of the binomial distribution and poisson distribution allocation granularity ofraw material, and introduce a discriminant factor Fa. Study found there is acorresponding relationship between the Fa values and breakup force, under two kinds ofdiscrete distribution of Fa values are similar and less than the Fa value of raw material,in the same time, under two kinds of discrete distribution of breakup force are similarand less than the Fa value of raw material.The change law of the bed pressure drop over time is tested through the experimentin the stable gas velocity, and the agglomeration is indirectly examined in thefluidization process. The result shows that there is varying degree breakage in the fourkinds of iron ore in the fluidization process. There is the breakage phenomenon in theAustralianore under lower gas velocity（0.21m/s）. There is breakage phenomenon invanadium titanium ore with increasing gas velocity The breakage law of Brazilian ore issimilar to the breakage law of northern ore. The breakage is not obvious after0.32m/sgas velocity. The breakage phenomenon reflected in the fluidization process is similarto the flow condition measured by physical parameters. Using chemical reaction engineering module of COMSOL, simulates the reductionreaction process of iron ore powder, the effect of particle sizes, particle shapes,reduction temperature, and reaction atmosphere on reduction process. The results show,The reaction rate of particles with grain size3mm or more than3mm increasesfirst and then decreases with the time increasing; the reaction rate of the particles withgarain size below3mm decreases with time increasing; particles with grain size below3mm tend to produce iron tumor or iron whisker. Particle projections and irregularitiesgive priority to reaction, at the same time particles of the vertex angle60°,70°,80°tend to diffuse to the bottom obviously. Solid product dose not tend to gather at apexangle, and compare with particles of other angles, particles of the vertex angle60°,70°,80°do not tend to produce iron tumor or iron whisker.The mass fraction of particleswith angle below50°change a little over time, and solid products tend to gather at apexangle, which increasing the possibility of producing iron tumor or iron whisker.Particlesare heated unevenly in the processs of reaction, the unreacted core will shift towards theopposite direction of partial heating, eventually disappear.as to partial heating parts, thesolid products continue to increase, and make the product layer thicken, which tend toproduce liquid phase andadhension. When H2is reduced, the product layer interface isregular, but when Co is reduced, the reaction interface is irregular. After the sufaces ofparticles produce iron tumor and iron whiskey, the iron tumor has little impact on thesubsequent reaction; while the iron whisker has a greater influence on the subsequentreaction.更多还原