Extraction - Principles of Chemical Separations with Environmental Applications - page 125

Interface
can be at
top or
bottom

Light-
phase
outlet

Heavy-
phase
inlet

Central shaft

Flat disk

Stator

Light-
phase
inlet

Heavy-phase
outlet

Figure 5.4 Agitated-tower extraction.

and the y -axis is the group σ
ρ c

0 . 2

a v
ε

1 . 5

µ c
ρ

,

V s , d =

where V s , c , superficial velocities of continuous and dispersed

phases, respectively, ft / h

µ c = viscosity of continuous phase, lb / ft · h

σ = interfacial tension between phases, dyn / cm

ft 3

ρ c = density of continuous phase, lb /

ft 3

ρ = density difference between phases, lb /

specific surface area of packing, ft 2 ft 3 a v = /

ε = fraction voids or porosity of packed section.

It is important to note that neither group is dimensionless, so proper units must be used.
The y -axis can be estimated from physical properties and the corresponding x -axis
found. Then, the required dispersed or continuous solvent phase velocity can be found
as a function of a specified diluent flowrate. If the diluent is the dispersed phase, the
continuous solvent flowrate is found and likewise if the diluent is the continuous phase,
the dispersed solvent flowrate is determined. Obviously, there will be some variation
with column diameter and the best design is most easily determined with a spreadsheet