Stirred tank design baffles

A basic stirred tank design is shown in Fig. 23-30. Height to diameter ratio is H/D = 2 to 3. Heat transfer may be provided through a jacket or internal coils. Baffles prevent movement of the mass as a whole. A draft tube enhances vertical circulation. The vapor space is about 20 percent of the total volume. A hollow shaft and impeller increase gas circulation (as in Fig. 23-31). A splasher can be attached to the shaft at the hquid surface to improve entrainment of gas. A variety of impellers is in use. The pitched propeller moves the liquid axially, the flat blade moves it radially, and inclined blades move it both axially and radially. The anchor and some other designs are suited to viscous hquids. 

FIG. 23-30a A basic stirred tank design, not to scale, showing a lower radial impeller and an upper axial impeller boused in a draft tube. Four equally spaced baffles are standard. H = beigbt of liquid level, Dj = tank diameter, d = impeller diameter. For radial impellers, 0.3 < d/Dt < 0.6. 

Stirred tank design, 287,288 baffles, 287 draft tubes, 287... 

Figure 5-12. Typical proportion of stirred tank design with radial and axial impellers and baffles. The upper axial impeller is housed in a draft tube. For radial impellers,. 3 < d/Dt <. 6...

Chapter 7, Reactor Design, discusses continuous and batch stirred-tank reactors and die packed-bed catalytic reactor, which are frequently used. Heat exchangers for stirred-tank reactors described are the simple jacket, simple jacket with a spiral baffle, simple jacket with agitation nozzles, partial pipe-coil jacket, dimple jacket, and the internal pipe coil. The amount of heat removed or added determines what jacket is selected. Other topics discussed are jacket pressure drop and mechanical considerations. Chapter 7 also describes methods for removing or adding heat in packed-bed catalytic reactors. Also considered are flow distribution methods to approach plug flow in packed beds. 

Stirred-tank reactors equipped with high-speed impellers are normally equipped with two or four baffles designed to prevent the formation of a vortex and rotation of the reaction mixture with the stirrer, as illustrated in Figure 4. Each baffle has a width of between 0.08 and 0,12 times the tank diameter. In normal practice, there is a space between the tank wall and the baffle equal to about one-third the baffle width. It is also desirable to keep the baffles off the bottom of the tank to keep solids from depositing. 

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