【作者】 冯志力；

【导师】 余永富； 刘根凡；

【作者基本信息】 华中科技大学 ， 化工过程机械， 2011， 博士

【摘要】 近10年来,中国钢铁工业所需的铁矿石连续自给率不足50%,铁矿资源短缺已成为制约中国钢铁工业发展的“瓶颈”,开发新的铁矿资源已成为当务之急。目前国内尚不能有效利用的菱铁矿、褐铁矿,鲕状赤铁矿等复杂难选铁矿石储量多达100亿吨,若采用行之有效的磁化焙烧-磁选工艺加以处理,则可望转化为现实的战略资源。不过,常规的磁化焙烧,如竖炉、回转窑等工艺存在流程复杂、成本较高等诸多缺陷,难以实现大规模的工业应用。针对这一问题,本文利用气-固流态化高效传热传质的优点,通过热重实验、悬浮态实验、计算机数值模拟和半工业试验相结合的方法,对菱铁矿的热解和磁化焙烧新工艺开展了系统深入的研究。选用了国内两种典型的菱铁矿,即陕西大西沟菱铁矿和云南王家滩菱铁矿,采用热重分析技术对菱铁矿在惰性气氛中的热解动力学进行了实验研究。实验应用等升温速率多重扫描法,热分析动力学的数据采用Kissinger法、FWO法和Friedman法相结合的方法处理,确定菱铁矿的热解机理并求取动力学参数。研究结果表明：大西沟菱铁矿的热解机理为收缩圆柱体模型R2,而王家滩菱铁矿的热解机理为一级化学反应F1,两者的热分解均属化学反应控制。王家滩菱铁矿的热解实验数据还表明,当粒径大于某一尺寸时,菱铁矿颗粒的热解动力学参数会受其影响。本文进一步将这种影响引入到指前因子,建立了吻合度较高的数学关联式。论文还采用X衍射分析法和光学显微分析法研究了菱铁矿在惰性气氛中热解的物相学,以验证焙烧矿磁性转化的效果。菱铁矿热解残留物的X衍射及磨片的光学显微分析结果表明,FeCO3热解后绝大部分转化为棕灰白的Fe3O4,偶见颗粒外表或邻近裂缝边缘的热解产物呈现白色的Fe2O3,此乃中间产物FeO被气氛中微量O2氧化所致。另外,热解残留物中裂隙发育充分,焙烧矿的可磨性非常好。为分析温度和气氛对菱铁矿热解过程的影响,本文首次在稀相悬浮状态下进行了菱铁矿的等温热解实验,在获取菱铁矿热解动力学模式及参数的同时,为后期的数值模拟提供有效的实验支撑。实验结果表明：王家滩菱铁矿在悬浮态下热解的机理为球体收缩模型R3,仍然属化学反应控制；尾气中CO的最高峰值比CO2的最高峰值滞后约5-10s不等,温度越高,滞后时间越长；FeO的磁化速率在温度段600℃～650℃增速较快,于700℃附近出现最大值；随着气氛中CO2的含量的增加,FeCO3热解的速度单调下降,而FeO的磁化速率单调上升,不过两者的变化幅度逐步趋缓至16%CO2时几近饱和。本文还采用了颗粒随机轨道模型和颗粒表面反应模型相结合的方法,对王家滩菱铁矿在多级循环流态化磁化焙烧装置中的热解进行了数值模拟。模拟结果表明,管式反应器中的烟气呈现活塞流,不利于反应器内组分的扩散和颗粒物的滞留；平齐式料管入口处存在的狭长涡旋迟滞颗粒流的下滑并可能诱发料管的堵塞,改进后的插入式料管则完全消除了上述缺陷和隐患；温度和滞留时间对菱铁矿的热解率的影响非常显著,管式反应器对菱铁矿的热解贡献率不足50%。为了验证数值模拟计算的结果,针对王家滩菱铁矿的流态化磁化焙烧进行了半工业试验,试验表明：在弱还原气氛(1.5%C0)、1028℃温度下菱铁矿样中碳酸铁的热解率为90.3%-94.5%,与其热解模拟计算值86.49%基本一致；接近中性的热解气氛适宜菱铁矿的热解和磁性转化,即CO气氛浓度不宜超过1.5%或O2浓度不大于1.85%。更多还原

【Abstract】 During the past ten years, the self-sufficient rate of iron ore for steel industry in China is continuously less than 50%. Heavy shortage of domestic iron ore is limiting the development of iron and steel industry of China, and the exploiture of new iron ore reserves is an emergent task for China. More than 10 billion tons of iron ore reserves, such as siderite, limonite and oolitic hematite, cannot be utilized effectively. Magnetizing roasting followed by magnetic separation is an effective technique to convert iron ore, however, such a kind of new technology isn’t well developed in China up till now for its very complexity. Traditional magnetizing roasting technology of shaft-type and rotary furnace also has the problems of high-cost and process-complication. To take the advantage of fast heat and mass transferring of fluidization of gas-solid, a kind of new technology named Multi-grade Circulating and Fluidizing Magnetizing Roasting (MCFMR) was developed to convert siderite to high magnetic oxidized iron ore. Therefore, current work is indulged to make a systematic and deep research on the kinetics of siderite decomposition and the new technology of MCFMR furnace through theoretical analysis, simulated experiments, CFD simulation and experiment in full-scale plant.Thermal decomposition of two kinds of siderites were investigated under pure N2 atmosphere, one is from Daxigou and the other is from Wangjiatan. The non-isothermal method with thermo-gravimeter (TG) by multi-scanning is used in the experiment research and the data processing method includes Kissinger, FWO and Friedman methods. Reactive mechanisms and kinetic parameters of thermal decomposition of siderites were obtained. The results indicates that the shrinking cylinder model is the best model fitting the experiment data of Daxigou siderite, while the first-order reaction model is the best model fitting that of Wanjiatan’s. However thermal decomposition mechanisms of the two siderites are both controlled by the same reaction rate. The value of pre-exponential factors exhibited a strong dependence on the Wanjiatan siderite particles with a certain size, and a new equation of first-order reaction model with the effect of particle size was developed which matches great with the data of TG experiments.To verify the magnetizing effectiveness of roasting ore, the chemical phase of the siderites in inert atmosphere was researched by using X-ray diffraction method and the optical microscopy method. The X-ray diffraction patterns and the optical microscopy patterns of the solid residue show that magnetite of the siderite ore is mainly consists of brown gray Fe3O4 and small amount of white Fe2O3 sometimes can be found at the surface or at the crack edge of siderite particle, which was converted from middle product, FeO, by the trace oxygen in the atmosphere. The roasted siderite ore was well grindable for the rich cracks in the solid residue.To analysis the influence of temperature and atmosphere to the siderite ore, an isothermal decomposition experiment of siderite ore in the dilute phase suspension condition was executed in current work. The pyrolysis kinetic mode and parameters are obtained from the experiment, and the results are helpful to construct the simulation model which was solved next. It was found that the shrinking sphere model with surface reaction rate controlling mechanism is the best model fitting the experiment data. The experiment results showed that the peak concentration of CO in the off-gas came out 5～10 seconds later than that of CO2. The magnetization rate of FeO was speeding-up obviously between 600℃and 650℃and a maximum speed appeared at around 700℃. With the increase of concentration of CO2 in the atmosphere, the decomposition rate of siderite ore was reducing and the magnetization rate of FeO was rising first, and then both showing a tendency to a limit at the concentration of 16% CO2.A numerical simulation for the decomposition of Wangjiatan siderite in MCFMR furnace was done by using particle stochastic trajectory model coupled with partical surface reaction model. The results indicated that the gas flow in the tubular reactor is plug flow, and it was adverse for the diffusion of the species and the detention of the particles in the reactor. Furthermore, a long and narrow eddy flow in the feed inlet of flat nozzle would stagnate the siderite particles and it may induce a block in feed nozzle. However such a hidden trouble can be greatly improved by using a insert feed nozzle. It also shows that the flue gas temperature and the particle delay-time in the fourth grade has great influence on the decomposition rate of siderite, while the tubular reaction has a much smaller influence on the ratio of decomposition which is no more than 50%.To verify the numerical simulation results, a half-industry test was executed for Wangjiatan siderite. Experiment results shows that the decomposition ration of siderite is between 90.3% and 94.5% in a weak reduction atmosphere (the content of CO is less than 1.5%) with a temperature of 1028℃. This value is roughly consistent to the result of numerical simulation which is 86.49%. It can also be concluded that the neutral atmosphere is more benefit of the decomposition and magnetic convert of siderite and the content of CO should be kept no more than 1.5% or the content of O2 no more than 1.85%.更多还原