Agitation impellers

Commercial-scale operations are conducted in batch, fed-batch, or continuous culture systems. Fermentation vessels include the conventional baffled aerated tank, with or without impeller agitation, and the ak-lift tower fermentors in which ak is sparged into an annular space between the... 

Impeller-agitated tanks These can be operated as continuous leaching tanks, singly or in a series. If the sohds feed is a mixture of particles of different setthng velocities and if it is desirable that all particles reside in the leaching tank the same lengths of time, design of a continuous stirred leach tank is difficult and uncertain. 

Figure 5-5H. A typical radial Impeller agitator. Operates as agitating turbine or a conventional propeller, wide range of applications. Courtesy of Struthers-Wells Corp., Warren, Pa.

The catalyst impregnation on the dispersed CNFs must be carefully optimized to obtain a sufficient dispersion of noble metals. Dispersion ofthe CNF in the particular solvent is desirable for uniform impregnation ofthe catalyst. CNFs with very small diameter are very important for effective dispersion. Sophisticated procedures for dispersion must be applied. In the present study, nanodispersion at an impeller agitation of 16 500 rpm was applied to disperse the thin CNFs better. 

Nagata, et al. (Nl, N2), Kawamura et al. (K4), and Yagi and Miyauchi (Y2) have studied the characteristics of various impeller agitated multistaged vessels. Such vessels were assumed to be a succession of plug-flow and backmix units, whose relative sizes were a function of the impeller speed. The parameter of the model, the fraction of total volume in a plug-flow, could also be related to a dispersion coefficient. Verification of the model was then obtained with kinetic experiments. 

The impeller is the part of the agitator that impacts force to the material being mixed. Propellers, turbines, gates, anchors, and paddles are all types of impellers. Typically, the impeller is a single propeller or turbine blade connected to a shaft that is driven by an electric motor at a fixed speed. There are two classes of impeller agitators axial-flow and radial-flow, and the mixing characteristics are shown in Figure 3.14. 

A revolving propeller traces out a helix in the fluid. One full revolution moves the liquid a fixed distance. The ratio of this distance to the propeller diameter is known as the pitch. In the case of turbines, pitch is the angle the blades make with the horizontal plane. Propellers are members of the axial class of impeller agitators. The propeller is turned so that it produces a flow toward the bottom of the vessel. Propellers are more frequently used for liquid blending operations than for mass transfer pmposes (Treybal, 1980). 

Toluene and olefinic stock from storage are pumped (at 80°F) separately through individual driers and filters into the alkylation reactor. The streams combine just before they enter the reactor. The reactor is batch operated 4 hr/cycle it is equipped with a single impeller agitator and a feed hopper for solid aluminum chloride which is charged manually from small drams. The alkylation... 

High Asptct-Ratio Bubble Columns and Multiple-Impeller Agitated Tanks... 

Figure 7. Stream lines in impeller agitated reactor which result from the superposition of rotational and overturn motion...

M. Bouaifi, M. Roustan, Bubble size and mass transfer coefficients in dual-impeller agitated reactors, Can. J. Chem. Eng. 76 (1998) 390-397. 

The single-impeller agitator consists of one vertical shaft containing horizontal arms. The shaft may be placed off center in order to create rapid circulation past, or local turbulence at, the point of contact between the nitrating acid and the organic compound. 

The double-impeller agitator consists of two vertical shafts rotating in opposite directions, and each shaft has a series of horizontal arms attached. The lower blades have an upward thrust, whereas the upper ones repel the liquid downward. This conformation provides a reaction mix that is essentially homogeneous. 

Typically, oxygen transfer can be modified acting through the rate of impeller agitation or through the aeration or micro-aeration flow rate, which change the ki a term of Equation 1. The dissolved oxygen controller... 

Modern reactors are made of stainless steel and have capacities up to as much as 180 m (50,000 U.S. gal.). Designs vary, and include top and bottom entry stirrers and multiple impellers. Agitation of the reaction mixture must be given serious attention since many monomers are less dense than water while their polymers are more dense. The mixing systems must then pull monomer down from the surface of the charge and lift polymer olT the floor of the reaction vessel. 

Figure 10.22. Mean particle diameter as a function of tip speed for various impellers (agitation time of 20 min). (From Fondy and Bates [1963]).

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