(408a) Design of a Centrifugal Separator for Olive Oil Extraction Via Multiphase Flow CFD Simulation

Computational Fluid Dynamics (CFD) is a mature field comprising methodologies suitable not just for simulating complex fluid flows towards efficient food product design (forward problem), but also for deriving geometric and operational specifications towards robust process design (inverse problem).

Olive oil is the oil obtained solely from the fruit of the olive tree (Olea Europaea), a dominant tree crop of the Mediterranean Basin. Constituting a key Mediterranean diet component with outstanding nutritional quality, it contains a very high level of monounsaturated fats (most notably oleic acid) which epidemiological studies suggest it is strongly linked to a reduction in coronary heart disease risk. It is consumed raw or cooked and used in cosmetics, pharmaceuticals, soaps and traditional oil lamps. Quality assurance is a consideration of extreme importance in olive oil production, thereby excluding any oils obtained via solvents or re-esterification processes and of any mixture with oils of other kinds. Virgin olive oils’ low acidity and supreme quality is ensured by exclusive use of mechanical/physical means under mild (particularly thermal) conditions, thereby avoiding any chemical alterations in the oil, and forbidding any treatment other than washing, decantation, centrifugation and filtration.

Modern, continuous industrial olive oil extraction relies on 4 processing stages: olive fruit cleaning and crushing towards a fine paste, malaxation towards olive droplet agglomeration and aroma generation,  water-assisted olive paste decanting via centrifugation, and final wet olive oil purification via filtration. The centrifugal force induces rapid phase separation, due to density differences (solids > water > oil). A moving coil inside the decanter's rotating conical drum pushes the solid material out of the system. Oxygen and light adversely affect olive oil quality at all stages, resulting in severe quality deterioration. Oxidation begins immediately upon harvesting as active enzymes rapidly degrade the endogenous oil. If additional oxygen interaction with olive paste is allowed during extraction, acidity increases further.

Two-phase oil decanting centrifuges avoid excessive water use and oil polyphenol solubilization losses at the expense of a lower extraction capability; the olive paste is separated in 2 phases: oil and pomace. This type of decanter, instead of three separate exits (oil, water and solids), has only two outlet streams (water is discharged by the decanter coil together with the pomace, yielding a wetter residue stream).

The present paper focuses on the design problem for a continuous two-phase olive oil centrifugal separator. Addressing it by means of elaborate CFD simulations, we examine the effect of key geometric and operational parameters on efficiency and olive oil quality. Accurate thermodynamic and rheological property models have been employed and combined with a multiphase k-ε turbulent flow model to calculate phase, velocity and pressure distributions for various inlet flows and compositions, and in order to derive geometric specifications for optimal unit design.