Homogeneous fluidization characteristics of vibrating fluidized beds

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