褐煤流化床热风干燥特性与传质传热数值模拟

发布时间：2017-12-28 18:41

本文关键词：褐煤流化床热风干燥特性与传质传热数值模拟　出处：《中国矿业大学》2016年硕士论文　论文类型：学位论文

【摘要】：蒙东地区褐煤由于高水分、低发热量、易风化和自燃的缺点,应用受到很大限制,因此对褐煤的脱水提质尤为紧迫。目前流化床干燥技术已被应用到褐煤干燥中,但大多数研究还仅限于传统的实验阶段,另外床体内气固两相强烈的非线性、以及传质传热的复杂性使实验研究过程受阻。CFD技术的出现,可用它获得实验过程中不易测得的数据,而且通过与实验相结合,为流化床干燥研究提供更准确、更深入的理论基础。本文在前人已开展的流化床热风干燥的实验基础上,利用Fluent软件,选用欧拉双流体模型对褐煤在流化床内的干燥过程进行二维数值模拟,研究干燥条件对褐煤流动特性、干燥特性及传热传质过程的影响。流动特性模拟结果表明:气泡的生长、聚并、破裂过程是影响流化过程的主要因素;通过压降曲线可以确定临界流化速度,粒径越大,临界流化速度越大,初始床层高度对其没有影响,模拟结果与实验值相吻合。模拟计算得到的褐煤干燥特性与实验结果相一致,粒度的减小、入口风温的增加都能使干燥速率增加,传热传质增强,其中风温对干燥速率的影响最大;随着颗粒内水分的减少,干燥速率减慢,传热系数减小。干燥过程中颗粒温度不断升高,最终温度趋于热风温度;气体湿度分布可以很好的展现颗粒水分在床内的脱除情况。通过用户自定义函数将微波加入到流化床干燥过程中,发现微波强化后的干燥效果优于单纯热风干燥。微波功率对干燥特性的影响非常显著,随功率的增加,脱水速率加快,传热传质增强,而干燥后期随水分的减少微波作用减弱。在微波作用下褐煤颗粒温度升高、速率加快,干燥后期颗粒的温度远高于热风温度。
[Abstract]:The application of lignite in the east of Mongolia is limited because of its high moisture, low heat, easy weathering and spontaneous combustion, so the dehydration of lignite is very urgent. At present, fluidized bed drying technology has been applied to lignite drying, but most of the researches are limited to traditional experimental stage. Besides, the strong nonlinearity of gas solid two phase in the bed and the complexity of mass transfer and heat transfer impede the experimental research process. The emergence of CFD technology can be used to get data that is not easy to be measured in the experimental process, and it will provide a more accurate and deeper theoretical basis for fluidized bed drying research by combining with experiment. This paper has carried out the experimental basis of fluidized bed hot blast in the previous drying, using Fluent software, two-dimensional numerical simulation using Euler two fluid model of drying process of lignite in fluidized bed. The effect of drying conditions on the flow characteristics and process characteristics of lignite drying and heat and mass transfer. The simulation results show that the flow characteristic of bubble growth, coalescence and rupture process are the main factors affecting the flow process; pressure drop curve can be determined by the critical fluidization velocity, particle size increasing, the critical fluidization velocity increasing, the initial bed height on the no effect, simulation results and experimental values are in good agreement. Consistent with the experimental results to simulate the drying characteristics of lignite are calculated, and the reduction of particle size increased entrance wind temperature can increase the drying rate, heat transfer enhancement, the effect of air temperature on the drying rate; with the decrease in particle moisture, slows the drying rate, heat transfer coefficient decreases. In the process of drying, the temperature of the particles rises continuously, and the final temperature tends to hot air temperature, and the distribution of gas humidity can well show the removal of grain moisture in the bed. Microwave is added to the fluidized bed drying process by user defined function. It is found that the drying effect of microwave intensification is better than that of simple hot air drying. The influence of microwave power on drying characteristics is very significant. With the increase of power, the rate of dehydration is accelerated, heat and mass transfer is enhanced, and the microwave action decreases with the decrease of moisture at the later stage of drying. Under the effect of microwave, the temperature of lignite particles is higher and the rate is quicker, and the temperature of the grain is much higher than the hot air temperature in the later period of drying.
【学位授予单位】：中国矿业大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TQ051.13;TQ536

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