油页岩流化床流化特性及传热传质的研究

发布时间：2018-06-09 03:50

本文选题：油页岩 + CFD　；参考：《大连理工大学》2015年硕士论文

【摘要】：能源是一个社会和国家发展壮大的基石和支柱,伴随着石油使用量的增加,石油资源仅能维持70年左右就会枯竭。应对石油枯竭危机、寻找新生能源,成为各个国家面临的重大议题。油页岩富含有机质,可以通过干馏等方式产生油和可燃气体,也可以用来燃烧发电。随着技术的进步,油页岩干馏生产页岩油生产成本的降低,而且其己探明总储量要比石油还要大,油页岩资源正渐渐成为石油的替代品。大部分油页岩含水率较高,造成能耗增大、油质下降等不利影响。干馏之前,要使用高温气体将油页岩的水分蒸发掉。流化床干燥器以其高效的传热、传质特点正越来越多的应用到油页岩的干燥过程。对油页岩在流化床中行为和机理研究对于更加高效地进行油页岩的干燥,提供了良好的理论基础,将来可以更好地利用油页岩资源。受实验条件的限制,油页岩颗粒在流化床干燥中的行为和机理不能进行有效地监测和测量。本文以双流体模型和颗粒动力学理论为基础建立流化床模型,使用流体力学软件耦合用户自定义函数(UDF)的方法,对颗粒在流化床中最小流化速度、床层膨胀高度、初始气泡尺寸、床层压降、气固传热等进行了研究,并得到了以下结论：小颗粒的完全流化速度和最小鼓泡速度的差要比大颗粒的要大；计算了不同速度下的床层膨胀高度并且与经验关联式进行了比较,发现随着气速的增大,床层的膨胀高度近乎呈线性增加；增加气速,气泡的初始尺寸也增大,振动有着抑制气泡增大的作用,提高振动频率气泡尺寸减小,提高振幅气泡尺寸略有增加；床层压降随着气速的增大呈现先下降后上升的趋势；在加入振动后,发现随振动强度的增大压降变化不大,压降标准差曲线随压降的增大逐渐变大；床层高度的增加,床层压降也逐渐增大,而且在床层完全流化后床层高度对压降的影响最大。气固传热系数在近布风板区域主要受气固两相的温差控制,在远离布风板区域主要受颗粒浓度的控制；在床层所有区域,颗粒浓度对气固两相的热交换系数都起着重要作用；在近布风板区域,烟气的温度受壁面温度的影响呈现两侧低中间高的趋势,而在远离布风板的区域温度沿径向分布比较均匀。进气温度越高流化床的干燥能力越强。干燥在初始阶段主要受外部烟气温度控制,干燥在后半段主要受内部毛细空隙水分扩散控制。本文研究了油页岩颗粒在流化床中流动特征参数和气固传热传质的规律,为流化床的设计和油页岩干燥机理进一步深入研究奠定了基础。
[Abstract]:Energy is the cornerstone and pillar of the development and expansion of a society and country. With the increase of oil use, oil resources can only be exhausted for about 70 years. To deal with the crisis of oil exhaustion and to find new energy sources, it has become a major issue for all countries. Oil shale is rich in machinery and can produce oil and flammable by dry distillation. Gas can also be used to burn electricity. With the progress of technology, the production cost of shale oil production in oil shale dry distillation is reduced, and its proven total reserves are larger than oil. Oil shale resources are becoming a substitute for oil. Most oil shale has high water cut, resulting in higher energy consumption, lower oil quality and other adverse effects. A fluidized bed dryer has been applied to the drying process of oil shale with its high heat transfer and mass transfer characteristics. The study on the behavior and mechanism of oil shale in the fluidized bed provides a good theoretical basis for the more efficient drying of oil shale, which will be possible in the future. Better use of oil shale resources. Limited by the experimental conditions, the behavior and mechanism of oil shale particles in fluidized bed drying can not be effectively monitored and measured. In this paper, a fluidized bed model is built on the basis of two fluid model and particle dynamics theory, and the method of coupling user custom function (UDF) with fluid mechanics software is used. The minimum fluidization velocity in the fluidized bed, the height of the bed expansion, the initial bubble size, the bed pressure drop and the gas solid heat transfer have been studied. The following conclusions are obtained: the difference between the complete fluidization velocity of the small particles and the minimum bubble velocity is larger than that of the large particles; the height of the bed expansion at different speeds is calculated and the correlation with the empirical formula is calculated. It is found that the expansion height of the bed is almost linearly increased with the increase of gas velocity, and the initial size of the bubble increases with the increase of gas velocity. The vibration has the effect of inhibiting the increase of bubbles, increasing the bubble size of the vibration frequency and increasing the size of the amplitude bubble, and the pressure drop of the bed layer decreases first with the increase of gas velocity. After the vibration, it is found that the pressure drop varies little with the increase of the vibration intensity, the standard deviation curve of the pressure drop increases gradually with the increase of the pressure drop; the bed height increases, the bed pressure drop increases gradually, and the height of the bed layer has the greatest influence on the pressure drop after the bed layer is completely fluidizing. The heat transfer coefficient of the gas solid is in the near distribution wind plate area. The temperature difference control of the main gas-solid two phases is mainly controlled by the particle concentration in the area far away from the distribution wind plate. In all areas of the bed, the concentration of particles plays an important role in the heat exchange coefficient of the gas-solid two phases; in the near distribution wind plate area, the temperature of the flue gas is under the influence of the wall temperature at the lower middle height, but is far from the air distribution. The region temperature of the plate is more uniform along the radial distribution. The higher the air inlet temperature is, the stronger the drying capacity of the fluidized bed. The drying is mainly controlled by the external flue gas temperature in the initial stage, and the drying is mainly controlled by the internal capillary void diffusion in the second half. This paper studies the characteristics of the flow characteristics and the heat and mass transfer in the fluidized bed. The rule laid a foundation for further study of fluidized bed design and oil shale drying mechanism.
【学位授予单位】：大连理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TE662

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