GrasasYaceites 1-57. pdf

6. SOLID-LIQUID PHASES SEPARATION 
The olive, and then its paste, is formed by three
basic components: oil, water and dry matter. The
aim of this step is to separate the oil from the
others. At present, the press system coexists with
centrifugation systems although press plants can
be found on a marginal level. Therefore, we are
going to describe the horizontal centrifuges.
Fundamentals of Centrifugation
The system widely used is the continuous
extraction system (the paste is loaded and the
phases separation are performed continuously)
based on the centrifugal force applied to the olive
paste. The mathematic expression for centrifugal
force is:
Fc = 
␳␻
2
r
Where, 
␳ = mass of the centrifuged element
␻ = angular speed
r = turning radius
Each horizontal centrifuge has specific values
for 
␻ and r, considering mass as a density function
(d), it can be established that centrifugal force
depends on the density of centrifuged elements Fc
= k d. When applied to olive paste, formed by
components (pomace, vegetation water and oil)
with different density (1.2, 1.082 and 0.916 g/cm
3
respectively) three concentric rings will be
separated whose radius are related to the element
density with the highest for pomace and the
smallest for the oil (Figure 1).There are outlets at
different distances from the rotation radius allowing
the liquid phases to be separated (oil and
vegetation water).
In a decanter the solid phase is separated as
follows, the centrifuge is formed by a cylindrical-
conical bowl inside where there is a hollow space,
with a similar shape, with helical blades. They rotate
in the same direction at 3000-5000 rpm although
there is a slight difference between the speeds of
both parts (10-20 rpm). For this reason a relative
movement is produced in the contact point between
these centrifuge parts, and pomace is thrown in the
opposite direction of the liquid outlets and the
movement of the hollow space