Double mixing blades

Many other blade designs have been developed for specific applications. The double-naben blade (Fig. 18-41 is a good blade for mixes which ride, that is, form a lump which bridges across the sigma blade. 

Figure 3.3 Mixing blades for double-armed batch mixer [18]. (a) Sigma, (b) 180° single curve, (c) multiwing overlap, and (d) double naben.

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. 

Neutralization. The intermediate product from the reactor must be neutralized immediately, as hydrolysis may occur and badly affect the process and the product quality. This is achieved in a double-step continuous neutralization unit. The multi-bladed mixer gives exceptionally homogeneous mixing (30). 

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