Agitators, types

An Excel spreadsheet program (Example 7-l.xls) was developed to determine the theoretical power of any agitator type with given fluid physical properties and tank geometry. 

The values of eonstant C and the exponents a, b, and e depend on the type of agitator, whether baffles are used and their type, and whether the transfer is via the vessel wall or to eoils. Baffles are normally used in most applieations, and the values of a, b and e in the literamre are 2/3, 1/3, and 0.14 respeetively. Tables 7-14 and 7-15 give typieal eorrelations for various agitator types. 

Agitator type Baffled Reynolds number (Np ) Nusselt number Remarks... 

No restrietion is plaeed on agitator type, whereas if a eoil is installed it restriets agitator dimensions. 

For agitator types of propellers, turbines with flat blades and paddles, 4 and a are 1.5 and 1.4, respeetively. The eriterion for Equation 7-92 is the absenee of any immobile solid on the bottom of the tank. 

Table I provides an overview of general reactor designs used with PS and HIPS processes on the basis of reactor function. The polymer concentrations characterizing the mass polymerizations are approximate there could be some overlapping of agitator types with solids level beyond that shown in the tcd>le. Polymer concentration limits on HIPS will be lower because of increased viscosity. There are also additional applications. Tubular reactors, for example, in effect, often exist as the transfer lines between reactors and in external circulating loops associated with continuous reactors.

The selection chart given in Figure 10.57, which has been adapted from a similar chart given by Penney (1970), can be used to make a preliminary selection of the agitator type, based on the liquid viscosity and tank volume. 

Agitator Type Surface Number Range L a m b c Terms Additional Comments Ref. 

Figure 10.2 Illustration of an agitation type flotation cell. From Nguyen and Schulze [53], Copyright 2004, Dekker.

Descriptions of the continuous processes have been reported in some recent reviews [1,17,18]. After elimination of butadiene, the C4 stream (raffinate-1) is desulfurized with aqueous caustic soda, washed, and thoroughly dried over alumina or silica gel, and then cooled before entering a reactor which is generally of the agitated type. The activator (protogen or initiator in the Kennedy s terminology [1]) is added with the hydrocarbon feed at a concentration that is a few percent of the Lewis acid concentration. When water is used, the process does not necessarily need a specific addition, because the control of drying process can afford the required trace amounts of water for a catalytic initiation. 

The work of Fox and Gex [Eqs. (17) and (24)] does represent a systematic approach to the problem, and their definition of mixedness (time when the last wisp of red color disappeared) is probably a conservative one. If the rash assumption is made that the results of different workers can be compared, the data of van de Vusse indicate that the results of Fox and Gex with propeller mixers would probably predict results for other agitator types within about a fourfold factor. While they are far from precise in a general way, these relations should be useful for rough estimates of mixing time. 

K = sl constant, dependent on the agitator type, size, and the agitator-tank geometry,... 

---