Use of a mixing-coil heat exchanger combined with microwave and ultrasound technology in an olive oil extraction process

Abstract

Abstract This study addressed the possibility to improve the conditioning process of olive paste in order to make the extra-virgin olive oil (EVOO) extraction process in a continuous and rapid manner than the traditional one. An innovative heat exchanger, the mixing-coil heat exchanger (MCHE), having a mixing-coil inside was employed. Also, a continuous microwave machine (MW) and ultrasonic machine (US) prototypes were joined to it. These three prototypes were installed in a commercial olive oil extraction plant. Four conditioning processes (ML; MCHE; MCHE + ML, MCHE + MW and MCHE + US + MW) employing the prototypes were compared to the traditional one (ML) in which only one malaxer machine was employed to condition the olive paste. Olive oil extractability index (E) and olive paste rheological parameters were determined. The use of MCHE alone showed the worst results in terms of extractability (E = 74.03), having processing time of 3.84 min. Moreover, the not sufficient paste treatment didn't permit the optimal working of the three-phase decanter. Consequently, the highest solids amount in waste water was registered, compared with the other conditioning processes considered. Using the MW coupled to MCHE permitted the reduction of the conditioning time to 4.19 min instead of 40 min of ML condition, and made the process continuous, cause the employment of MW and MCHE (continuous machines) instead of ML (discontinuous machine). The E registered (85.76) resulted statistically equal to those of the traditional conditioning (E = 85.91) and MCHE − ML (E = 85.78). Conditioning time of the latter was 23.84 min. Using the three prototypes together, the investigators confirmed a process continuity and conditioning time of 5.80 min and found a value of E equal to 87.16%, not statistically different form the E value of ML conditioning process. The specific energies employed were 15.75 and 25.71 kJ kg−1 for MCHE + MW and MCHE + US + MW, respectively. Industrial relevance text The present study addressed the use of an innovative heat exchanger, provided by an inner mixing spring, to fast condition the olive paste. It was used also in combination with an ultrasound machine and a microwave machine. The microwave machine leads to the extraction efficiency increasing and the ultrasound machine improves slightly the extraction efficiency. The results demonstrated these new technologies are able to substitute the classical malaxation operation discontinuous and time costly. Moreover, the layout of the plant resulted simplest and smallest than the traditional one.