Homogeneous Fluidization Characteristics of Vibrating Fluidized Beds
Homogeneous Fluidization Characteristics of Vibrating Fluidized Beds
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DOI：
10.1002/cjce.5450820521
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发表时间：
2008-05
影响因子：
2.1
通讯作者：
Haibo Jin;Z. Tong;Ji-yu Zhang;Bijiang Zhang
中科院分区：
文献类型：
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作者：
Haibo Jin;Z. Tong;Ji-yu Zhang;Bijiang Zhang
近年来，利用机械振动来改善流化床在处理较大颗粒时的性能已引起人们越来越多的兴趣。振动流化床（VFB）相对于传统流化床的优点包括降低最小流化速度和流化压降、提高气固接触效率以及改善流化床层的均匀性和稳定性。这些优点可用于干燥、冷却、加热、分离、混合等过程。在常规流化床中，均相或非均相流化的可能性与所谓的流化系统的稳定性直接相关。此外，处理稳定性的理论往往考察其密度微涨落的行为.床层密度的稳定性是颗粒状固体分离的一个焦点问题。床层密度的任何大的波动将导致某些区域的分离失败，这导致总分离效率的降低。在开发更好的分离技术时，将需要床层的更大稳定性。已经提出了一种对振动流化床中的粒状材料进行分类的方法（Zhang等人，1996; Chen等人，1993年），其可用于细粒煤的分离和废焦渣混合物的分离。所有这些技术都使用振动能量来改善床的均匀性。振动对流化质量的影响是流化床分选的重要环节。然而，在文献中只有少数研究振动对结晶均匀性的影响。通过分析电容图，莫尔斯（1955）提出，均匀性和稳定性只存在于较小颗粒（1 - 70 µm）和高频振动（10 - 50 Hz）的床层中。Mushtaev（1979）用电容探针测量空隙率在空间和时间上的波动，指出当振动加速度超过4g，即aω时，床层均匀性开始下降，颗粒床层的喷泉作用严重
n recent years, there has been growing interest in utilizing mechani-cal vibration to improve the performance of a fl uidized bed in the processing of relatively large particles. The advantages of vibrating fl uidized beds (VFB) over conventional fl uidized beds include reduced minimal fl uidization velocity and fl uidization pressure drops, increased effi ciency of gas-solid contact and improved homogeneity and stability of the fl uidized bed layers. These advantages can be used in drying, cooling, heating, separating, mixing process, etc. In conventional fl uidized beds, the possibility for arising of homo- or heterogeneous fl uidization is connected directly with the so-called stability of the fl uidized system. Moreover, the theories dealing the stability often examine the behavior of their density micro-fl uctuation. The stability of the bed density is a subject of focus in the segregation of granular solids. Any large fl uctuation in the bed density will result in a failure of separation in some regions and this leads to a decrease in the total separation effi ciency. In developing better separation technology, a greater stability of bed layers will be required. A method for the classifi cation of granular materials in vibrating fl uidized beds has already been suggested (Zhang et al., 1996; Chen et al., 1993), which is useful in the separation of fi ne coal and the segregation of waste coke-slag mixture. All these technologies use vibration energy to improve bed homogeneity. The effects of vibration on fl uidization quality are important for separation in fl uidized beds. However, there have been only few studies of the effect of vibration on fl uidization homogeneity in the literature. By analyzing capacitance charts, Morse (1955) suggests that homogeneity and stability exist only for beds of smaller particles (1 –70 µm) and high frequencies of vibration (l0 – 50 Hz). By measuring the fl uctuations of voidage in space and in time using a capacitance probe, Mushtaev (1979) showed that the bed homogeneity begins to deterio-rate with severe fountain action of the particle beds when the vibration acceleration exceeds 4 g, namely aω