基于磁化焙烧的多孔介质褐铁矿还原度的特性研究

发布时间：2018-05-01 18:45

本文选题：褐铁矿 + 磁化焙烧　；参考：《内蒙古科技大学》2015年硕士论文

【摘要】：钢铁材料是目前及将来长时间内国家经济发展的重要基础之一。然而，，目前我国高品位铁矿资源已日渐匮乏。以褐铁矿为代表的低品位难选铁矿的高效检选已经成为实现我国经济、社会可持续发展过程中必须解决的问题。传统的褐铁矿焙烧还原主要是在竖炉、沸腾炉和回转窑等中进行，但是这些设备存在能耗高、还原时间长等缺点，造成设备整体结构及相关技术不过关，不仅还原焙烧质量较差，而且操作管理难度大，结构复杂，投资高，收尘系统复杂。基于内蒙古固阳褐铁矿循环流化床磁化焙烧的开发项目，为了深入了解微细褐铁矿粉的还原机理及动力学行为，本文针对褐铁矿粉在中、低温下气体还原的过程建立数学模型，对褐铁矿磁化焙烧进行数值模拟，为低品位褐铁矿的应用提供理论依据。本文运用同步热分析仪研究CO还原褐铁矿粉的动力学过程。应用扫描电镜分析了脱水后褐铁矿的结构，利用比表面和孔隙度分析仪测定了比表面积和孔隙度的变化。结果表明，褐铁矿的磁化焙烧是一个很容易进行的反应，在给定的条件范围内，同时受到环境温度、反应气体浓度和颗粒自身大小的影响。由同步热分析仪的结果可确定褐铁矿的反应活化能，细颗粒的矿粉具有较低的活化能。根据褐铁矿脱水后的SEM图和吸附等温线BET分类分析得出脱水后的褐铁矿具有高气孔率，其曲线更符合第Ⅲ类吸附等温线。根据褐铁矿粉磁化焙烧情况，建立的气固还原反应的动力学模型包括颗粒内非稳态的传热方程、孔隙内气体传输方程和基于描述孔径分布的改进随机孔模型的非均相化学反应动力学方程，采用全隐式有限体积法对控制方程进行数值求解。利用MATLAB，模拟了在不同温度、不同初始气体浓度、不同矿粉粒径及不同初始孔隙率的条件下反应速率和磁化还原所需时间的关系，研究了一氧化碳浓度分布随孔隙率的变化和不同粒径、不同温度下CO浓度沿褐铁矿颗粒径向方向分布的情况。结果表明，模型预测结果与实验结果吻合较好。提高反应温度可明显缩短反应完成的时间，褐铁矿焙烧反应速率与还原气体CO浓度近似成正比，温度升高时CO的有效渗入深度减小，当颗粒的粒径变大时，会影响反应气体向颗粒内部的传输，具有大孔隙率的褐铁矿将更有利于反应的进行。
[Abstract]:Iron and steel material is one of the important foundations of national economic development at present and in the future. However, high-grade iron ore resources in China are increasingly scarce. The efficient detection and separation of low grade refractory iron ore represented by limonite has become a problem that must be solved in the process of realizing the sustainable development of economy and society in our country. The traditional limonite roasting reduction is mainly carried out in shaft furnace, fluidized bed furnace and rotary kiln, but these equipments have the disadvantages of high energy consumption, long reduction time and so on, resulting in the whole structure of the equipment and related technology being not up to standard. Not only the quality of reduction roasting is poor, but also the operation management is difficult, the structure is complex, the investment is high, and the dust collecting system is complex. Based on the development project of magnetization roasting in circulating fluidized bed of Guyang limonite in Inner Mongolia, in order to deeply understand the reduction mechanism and kinetic behavior of limonite powder, a mathematical model for the reduction process of limonite powder at medium and low temperatures is established in this paper. Numerical simulation of magnetization roasting of limonite provides theoretical basis for the application of low grade limonite. The kinetic process of CO reduction of limonite powder was studied by means of synchronous thermal analyzer. The structure of limonite after dehydration was analyzed by SEM, and the changes of specific surface area and porosity were measured by using specific surface area and porosity analyzer. The results show that the magnetization roasting of limonite is a very easy reaction, which is affected by the ambient temperature, reaction gas concentration and particle size under given conditions. The reaction activation energy of limonite can be determined from the results of simultaneous thermal analyzer. According to the SEM diagram of limonite after dehydration and the BET classification analysis of adsorption isotherm, it is concluded that the dehydrated limonite has high porosity, and its curve is more in line with the third type adsorption isotherm. According to the magnetization roasting of limonite powder, the kinetic model of gas-solid reduction reaction is established, which includes the unsteady heat transfer equation in particles. The gas transfer equation in pores and the heterogeneous chemical reaction kinetics equation based on the improved stochastic pore model describing pore size distribution are numerically solved by the fully implicit finite volume method. The relationship between the reaction rate and the time required for magnetization reduction under different temperatures, different initial gas concentrations, different particle sizes and different initial porosity was simulated by MATLAB. The distribution of carbon monoxide concentration along the radial direction of limonite particles under different particle sizes and temperatures was studied. The results show that the predicted results are in good agreement with the experimental results. Increasing the reaction temperature can obviously shorten the reaction completion time. The roasting rate of limonite is approximately proportional to the CO concentration of the reductive gas, and the effective penetration depth of CO decreases when the temperature increases, and when the particle size becomes larger, the effective penetration depth of CO decreases with the increase of temperature. Limonite with large porosity will affect the transport of reaction gas to the particle, and limonite with large porosity will be more favorable to the reaction.
【学位授予单位】：内蒙古科技大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TD951

【参考文献】