Page 85 - Adsorption, Ion Exchange & Catalysis- 2007, Elsevier - Copy

Else_AIEC-INGLE_cH003.qxd 7/13/2006 1:45 PM Page 81
3.3 T Reactors o-Phase Agitated w 81

Figure 3.16 Pitched-blade turbine.

Figure 3.17 Left: Straight-blade open turbine. Right: Curved-blade open turbine.

heel in solid suspension applications. Moreover, they are ef fective in laminar flow applica-
tions, especially when impeller Reynolds numbers drop below 50.

Disc-type turbines In this type of turbines, blades can be straight or curved. In the
related literature, the term “straight” is some times replaced by the term “flat. The most ”
popular turbine of this type is the straight-blade disc turbine, which is better kno wn as the
“Rushton turbine” (Figure 3.18). v The same turbine is also called “flat-blade turbine, aned
disc” or simply “flat-blade turbine. ”
This type is a good cost-efe impeller for low concentrations of immiscible liquid v fecti
w
or gas. To very strong trailing vortices are shed from each blade. These areas of high
shear are responsible for breaking the larger droplets to smaller droplets. Maximum aera-
tion numbers should be limited to 0.1. Like all radial-flow impellers, the Rushton turbine
is designed to provide the high shear conditions required for breaking bubbles and thus
increasing the oxygen transfer rate.