基于还原焙烧的鼓泡流化床内颗粒停留时间研究

发布时间：2018-11-06 08:44

【摘要】：流化床作为效能最高的磁化焙烧反应器，在磁化焙烧技术中发挥重要作，促进复杂难选铁矿资源的高效利用，提高低品位铁矿资源的利用效率。而在流化床焙烧工艺中，焙烧时间(停留时间)是决定低品位铁矿石还原程度的重要因素，过长会发生过度焙烧现象，过短会产生欠还原反应。因此了解颗粒在流化床内的停留时间分布规律对认识和控制磁化焙烧反应工艺很有必要。本研究以内置竖直隔板的流化床流动颗粒为对象，并对其在流化床内的停留时间进行了试验研究，探讨了停留时间与磁化焙烧流化工艺的关系。在流化床内使用竖直隔板将流化床分成不同流化区域，能够促使新旧物料更换，停留时间分布均匀，在不同的流化区域逐级升温，在出口段区域达到最佳焙烧温度，这样能有效地改善气固间的传质和传热，提高反应转化率及产品的产率。在颗粒停留时间的试验研究中，以石英玻璃珠为床料，采用平均停留时间的方法和脉冲法研究。在冷态试验台基础上研究了进料速率、表观流化气速、颗粒粒径、内置竖直隔板等因素对颗粒停留时间的影响。平均停留时间的方法研究表明，进料速率、表观流化气速为影响平均停留时间的主要因素，，平均停留时间随进料速率和表观流化气速的增大而减小，在一定范围内，进料速率达到临界值后，不随进料速率的增大而发生改变，颗粒在床内的停留时间主要取决于表观流化气速的改变，且在一定的范围内三者之间有固定线性的关系；颗粒料径和中间的隔板高度的影响较大，两侧通流高度达到一定高度后对平均停留时间几乎没有影响。利用脉冲法研究得到，依据流化床内褐铁矿粉实际磁化焙烧情况，采用床内设置竖直隔板，改进颗粒在流化床反应器的流化情况，可解决单流化床的单位容积混合强度不高和减少单床的死区和短路的问题，颗粒在床内的停留时间分布(RTD)更加均匀。表观流化气速的增大，RTD分布更加集中，但增大表观流化气速停留时间偏离平均停留时间加大；而进料速率和粒径的增大，RTD分布分散。上述的试验研究结果能够为磁化焙烧鼓泡流化床物料停留时间和工业上采用竖直隔板提供理论依据。
[Abstract]:As the most effective magnetization roasting reactor, fluidized bed plays an important role in magnetization roasting technology, which promotes the efficient utilization of complex refractory iron ore resources and improves the utilization efficiency of low-grade iron ore resources. In the fluidized bed roasting process, the roasting time (residence time) is an important factor to determine the reduction degree of low-grade iron ore. Therefore, it is necessary to understand the residence time distribution of particles in the fluidized bed and to control the magnetization roasting reaction process. In this study, fluidized bed particles with built-in vertical separator were taken as the object, and their residence time in the fluidized bed was studied experimentally, and the relationship between the residence time and magnetization roasting fluidization process was discussed. In the fluidized bed, the fluidized bed is divided into different fluidized areas by vertical separator, which can promote the replacement of old and new materials, the uniform distribution of residence time, the temperature rise step by step in different fluidized areas, and the optimum roasting temperature in the outlet region. In this way, the mass transfer and heat transfer between the gas and solid can be improved effectively, and the conversion rate and the yield of the product can be increased. In the experimental study of particle residence time, the average residence time method and pulse method were used to study quartz glass beads as bed material. The effects of feed rate, apparent fluidized gas velocity, particle size and built-in vertical partition on particle residence time were studied on the basis of cold test rig. The study on the method of average residence time shows that the feed rate and apparent fluidized gas velocity are the main factors affecting the mean residence time, and the mean residence time decreases with the increase of the feed rate and the apparent fluidized gas velocity, and the average residence time decreases with the increase of the feed rate and the apparent fluidized gas velocity in a certain range. When the feed rate reaches the critical value, it does not change with the increase of the feed rate. The residence time of particles in the bed mainly depends on the change of the apparent fluidized gas velocity, and there is a fixed linear relationship between the three in a certain range. The diameter of particle material and the height of the partition board in the middle have a great influence on the average residence time (RTD) when the height of both sides reaches a certain height. According to the actual magnetization and roasting of limonite powder in fluidized bed, the vertical separator was installed in the bed to improve the fluidization of particles in the fluidized bed reactor. It can solve the problem that the unit volume mixing strength of single fluidized bed is not high and the dead zone and short circuit of single bed are reduced. The (RTD) distribution of particles in the bed is more uniform. With the increase of the apparent fluidized gas velocity, the RTD distribution is more concentrated, but the residence time of the apparent fluidized gas velocity deviates from the average residence time, and the RTD distribution is dispersed with the increase of the feed rate and particle size. The experimental results can provide a theoretical basis for the residence time of magnetized roasted bubbling fluidized bed material and the adoption of vertical separator in industry.
【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】：TQ051.13

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