The study of the formation mechanism and stable operation of suspension beds on dual flow distributors

• Main Authors: Sheau-Pyng Ju, 朱曉萍
• Other Authors: Wei-Min Lu
• Format: Others
• Language: zh-TW
• Published: 2003
• Online Access: http://ndltd.ncl.edu.tw/handle/85451592618704073516

博士 === 國立臺灣大學 === 化學工程學研究所 === 91 === Galdart D group particles with mono size (dp=2 mm) were used to study the mechanism of formation, stable operation range and characteristics of suspension beds on dual flow distributors. During the formation of a stable bubbling bed, it will experience five stages: the induced, the first growing, the oscillating shallow bed transient, the second growing and the final stable stage. The corresponding discharge mechanism of particle for each stage is raining, weeping, dumping (O), weeping and dumping (B). If the particle feeding rate or gas velocity is not large enough, the suspension bed will only experience three stage. That is, the suspension bed has reach its stable status at oscillating stage. On the other hands, if the particle feeding rate or gas velocity is large, the suspension bed will keep growing after it forms a bubbling bed until it comes to a slugging bed or flooding phase. Moreover, when the opening ratio of the plate is too large, or the particle feeding rate is too small, only a dilute phase can be observed. The influences of the operation variables on the formation of single stage suspension beds were discussed separately in the study. The discussed operation variables included the particle feeding rate (Fv’), the normalized air velocity through the hole (Uo/Ut), the opening ratio of the plate (m), the ratio of the diameter of the hole to the diameter of the particle (do/dp) , the density of particles and design of perforated plate. The mappings of the stable operation ranges for Galdart D group particles at various opening ratio were also obtained. A model was developed to predict the formation course of the stable suspension bed. The predicted result agrees qualitatively well with the experimental data. Furthermore, the pressure signals of suspension bed were analyzed with Fast Fourier Transform and chaotic time series analysis. It found that the correlation dimension (system complexities) will decrease abruptly when the type of suspension bed started to transform. This may made it possible to judge the type of suspension bed with chaotic time series analysis. At last, a dual flow multi-stage suspension bed system was studied experimentally. It was found that the type of the bed above each stage of the multi-stage system is different from it of the single-stage system for given operating conditions. Two typical types of beds were formed in a triple-stage system and they are the equal hold-up beds (O.O.O) and the non-equal hold-up beds (B.B.B). The formation of dual and triple stage system were studied at opening ratio is 0.42. The sequence of the formation of the suspension beds above the plate changed with the velocities of the air through the hole or the particle feeding rates. The stability and stable operation range for equi-holdup bubbling bed were discussed.