Tanks and agitation

For systems handling slurries, special consideration has to be given to tank design to maintain the slurry in suspension. Usually an agitator is employed for this purpose. Quite often the tank is not just a holding 

Where possible it is highly desirable to develop basic design parameters from similar existing and performing applications, and use these as specified minimum design parameters (or at least as evaluations of the adequacy of equipment offered by vendors), together with the mechanical features offered. The most significant performance aspects are  

The impeller design, dimensions, and speed should be compared for consistency with the claimed pumping rate. 

As regards the mechanical features, the most significant are the following. 

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In flue gas desulphurization systems, equipment such as absorber towers, demister supports, gas outlets, recycle and process pipings, process tanks, and agitators are highly exposed to corrosive and abrasive environments. Chlorobutyl rubber of 60 Shore A... 

Fig. 7a. Mixing tank and agitator (courtesy of Mixing Equipment Co.)...

Degumming. Crude coconut oil is continuously heated to 80-90°C, and 85% phosphoric acid at a range of 0.05-0.10% by volume of feedstock is dispersed in the oil via an in-line static mixer. The mixture is conveyed into a coagulation tank and agitated for 20-30 min. 

These conditions are readily achieved in small-scale agitated reactors. However, in large industrial reactors, it is not easy to achieve good mixing, and special care should be given to the design of the tank and agitator. Furthermore, even when... 

About 200 gallons of cream, milk, and condensed milk were placed in the 500 gallon tank and agitated for 15 minutes ... 

Since a well-designed turbine impeller provides very thorough mixing of the liquid, it can reasonably be assumed that the concentration throughout the liquid phase in such devices is quite uniform. Therefore the benefits of counter-current flow for continuous operation cannot be had with a single tank and agitator. 

In many types of contactors, such as stirred tanks, rotary agitated columns, and pulsed columns, mechanical energy is appHed externally in order to reduce the drop si2e far below the values estimated from equations 36 and 37 and thereby increase the rate of mass transfer. The theory of local isotropic turbulence can be appHed to the breakup of a large drop into smaller ones (66), resulting in an expression of the form... 

Topics that acquire special importance on the industrial scale are the quality of mixing in tanks and the residence time distribution in vessels where plug flow may be the goal. The information about agitation in tanks described for gas/liquid and slurry reactions is largely apphcable here. The relation between heat transfer and agitation also is discussed elsewhere in this Handbook. Residence time distribution is covered at length under Reactor Efficiency. A special case is that of laminar and related flow distributions characteristic of non-Newtonian fluids, which often occiu s in polymerization reactors. 

The eonstant K and the exponents b and d must be determined for the partieular type of agitator, its size and loeation in the tank, the dimensions of the tank, and the depth of the liquid. 

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