GrasasYaceites 1-57. pdf

7. CENTRIFUGATION SYSTEMS
Nowadays, two centrifugation systems can be
found working the so-called two phases and three
phases. These names are incorrect since for both
types three phases are produced and therefore
they should be called two way or three way
systems. In the seventies the three way system
appeared commercially: one way for pomace and
the others for the liquid phases (oil and vegetation
water). In this system the olive paste is loaded
with water (around 50% of the fruit dry weight) to
increase the vegetation water phase thickness.
The main problem is the large amount of waste
water (alpechín) produced (1.2 L/kg olives) and its
strong contaminant capacity (COD = 80000 ppm),
its elimination shows some technical difficulties
and is expensive. Environmental regulations have
more restrictions, and then a new system had to
be developed. During the crop year 1991/92 the
system ‘two phases’ or ‘two way’ appeared. The
name is explained because there is one outlet for
oil and another for vegetation water + pomace.
For normal olive pastes the addition of water to
the decanter is not needed. Longitudinal and
cross sections for both two and three way
systems, are shown in Figures 2 and 3. In the
cross section two ways for liquid phases can be
observed in the three way system, while there is
only one for oil in the two way system. Operation
schemes for both centrifugation systems are
shown in Figure 4, where the most important
differences between both extraction designs can
be distinguished. The main advantages for the two
way system are:
• Water saving
• Energy saving
• Lower capital investment
• Very low by-product production, only waste
water from oil washing (0.25 L/ kg olives) and
its contaminant capacity is smaller (COD =
10000 ppm).
28
GRASAS Y ACEITES
, 57 (1), 
ENERO
-
MARZO
, 25-31, 2006, 
ISSN
: 0017-3495
MARINO UCEDA, ANTONIO JIMÉNEZ AND GABRIEL BELTRÁN
Figure 1
Distribution of centrifugal forces in a decanter for two and three
way systems.

---

The disadvantages are:
• Management and exploitation of pomace. It is
produced by 60% higher, its moisture is
around 60%, has high sugar content and
dissolved solids from alpechín.
• Few visual control points for oil mill
management since alpechín disappeared and
thus, pomace has to be monitored more often.
• Matching the decanter performance to olives
with different characteristics since water
addition to the paste injection is eliminated.
In addition to a centrifugation system
description, its effect on oil quality and process yield
should be discussed. The process yield can be
evaluated by the oil content on the dry weight of
pomace since most of the oil loss will be in the
pomace. The pomace oil content for ‘Picual’ should
range between 5.6 and 7.1% to have similar yields
to the three way system. During the crop year
1993/94, 25 oil mills in Jaén were monitored
obtaining as mean oil content of pomace 6.69%,
which was within the range for optimal working. For
oil characteristics, the most important differences
with the three way system are explained by the
absence of water addition in the decanter. Oils from
two way systems have higher phenol content and
oxidative stability. For this reason oils are more
fragrant with higher bitterness and pungent
characteristics (Hermoso et al., 1991b).