Dispersion of Floating Solid Particles in Aerated Stirred Tank Reactors: Minimum Impeller Speeds for Off-Surface and Ultimately Homogeneous Solid Suspension and Solids Concentration Profiles

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• 作者：Atsushi Tagawa ; Naoki Dohi ; and Yoshinori Kawase
• 刊名：Industrial & Engineering Chemistry Research
• 出版年：2006
• 出版时间：January 18, 2006
• 年：2006
• 卷：45
• 期：2
• 页码：818 - 829
• 全文大小：248K
• 年卷期：v.45,no.2(January 18, 2006)
• ISSN：1520-5045

文摘

Effects of impeller design, baffle, and gas flow rate on distributions of floating solid particles were examinedin a stirred tank of 0.2 m i.d. for solid concentrations up to 50 vol %. Dual small cross-section impellersystems, i.e., dual four-flat blade disk turbines and dual four-pitched blade downflow disk turbines, and largecross-section impellers, i.e., Maxblend impeller and Fullzone impeller, were used. The minimum impellerspeeds for off-surface floating-particle suspension decreased with aeration because bubbles rising near thetank wall enhanced the breakup of the floating-particle stagnant layer formed on the liquid surface and thenthe dispersion of floating particles into the liquid. The minimum impeller speeds for ultimately homogeneousfloating-particle suspension also decreased with aeration. These results are contrary to those for the settlingparticles. The local solid particle concentrations at different heights in the stirred tank were measured. Theaxial solid particles concentration profiles were examined using the proposed one-dimensional floating-particledispersion model. The Peclet numbers for floating-particle dispersion in the model were reasonably correlatedin terms of impeller speed, power consumption, and forces exerted on floating particles. It was found that thelarge cross-section impellers could disperse completely floating particles into the liquid with less agitatedspeed and power consumption as compared with the dual small cross-section impeller systems used in thiswork.