3D computational fluid dynamics simulation and experimental validation for prediction of heat transfer in a new malaxer machine

Modelling the Rheology of Olive Paste for Oil Extraction Plant Automation: Effects of the Crushing Process on the Rheology of Olive Pastes

In extra virgin olive oil production, it is essential to obtain a well-prepared olive paste which allows not only the extraction of the oil drops from the olives, but also the achievement of a high-quality oil while maintaining high yields. This work addresses the problem of determining the effect of three crushing machines on the viscosity of the olive paste: a hammer crusher, a disk crusher and a de-stoner were tested. The tests were repeated on both the paste leaving each machine and the paste to which water was added; this was done with the main aim of considering the different dilutions of the paste while entering the decanter. A power law and the Zhang and Evans model were used to analyse the rheological behaviour of the paste. The experimental results allow validation of the two models with a high (more than 0.9) coefficient of determination between experimental and numerical data. The results also show that the pastes obtained with the two classic crushing methods (hammers and disks) are almost identical, with a packing factor of about 17.9% and 18.6%, respectively. Conversely, the paste obtained with the de-stoner entails higher viscosity values and a smaller solid packing factor, of about 2.8%. At 30% dilution with water, the volume of the solid concentration dropped to about 11.6% for the hammer and disc crushers, while for the de-stoner it only reached 1.8%. This behaviour is also reflected in the evaluation of yields, which were 6% lower with the de-stoner. No significant differences regarding the legal parameters of oil quality were found using the three different crushing systems. Finally, this paper establishes some fundamental pillars in the research for an optimal model for identifying the rheological behaviour of the paste as a function of the crusher used. Indeed, since there is an increasing need for automation in the oil extraction process, these models can be of great help in optimizing this process.

Investigation on the Effects of a Pulsed Electric Field (PEF) Continuous System Implemented in an Industrial Olive Oil Plant

The aim of this study was to investigate how the treatment of olive paste of the Picholine variety with pulsed electric fields (PEF) under real operating conditions in a large-scale olive oil extraction plant affects the extractability, chemical composition and sensory profile of the oils. The application of pulsed electric fields (PEF) as a non-thermal food processing technology is interesting for many food extraction processes. The results of this study show that pulsed electric fields can be used as a pretreatment before oil separation to increase the extractability of the process and improve the content of functional components. The application of pulsed electric field (PEF) treatment (2.4 kV/cm, 4 kJ/kg, 6 µs pulse width) to olive paste through a continuous system significantly increased the extractability and total concentration of phenols (especially oleuropein derivatives) compared to the control. In addition, the volatile compounds, α-tocopherol, the fatty acid profile and the main legal quality parameters of extra virgin olive oil (EVOO), including free acidity, peroxide values, extinction indices and sensory analysis, were evaluated. The pulsed electric fields (PEF) treatment did not modify these EVOO quality parameters, neither the α-tocopherol content nor the volatile profile. The sensory properties of EVOO were not affected as well as the PEF treatment showed a similar intensity of fruity and pungent attributes without any off-flavor according to the European Union legal standards. An increase in the bitter taste attribute was observed in the PEF oils. Consequently, this study demonstrates that pulsed electric fields (PEF) processing could be implemented in olive oil processing as pretreatment for improving the efficiency of the process.

Experimental Evaluation of Functional and Energy Performance of Pneumatic Oenological Presses for High Quality White Wines

In this article, experimental tests on two different kinds of pneumatic presses have been carried out in two Apulian wineries to evaluate energy consumption related to yield performance. The presses are employed to process Bombino Nero variety grapes, crushed and transformed in rosé wine though a pomace less process. The pneumatic pressured press realized a 2 h:48 min long process, with a maximum pressure on the product of 1.4 bar and a must moulding of 69% of extracted must. In regard to the vacuum press, the process duration is 3 h:18 min, with a maximum pressure of 0.9 bar and a must moulding of 58%. During the pressing operation, mean values of must flow rate are comparable: 2.1 L min−1 m−2 for the pressured press and 2.9 L min−1 m−2 for the vacuum press. However, a more detailed analysis gives more insight on the behaviour of the two presses. In regard to the pressured press, a compression phase characterized by few steps and at lowest pressure values has proven particularly effective, especially in the first phase (must moulding of 41% with a must flow rate of 4.6 L min−1 m−2), at the lowest pressure values. On the other hand, by analysing vacuum press process, the phases sequence is much more gradual, must moulding decreases as the extraction proceeds (from 28% to 6%), and in the last three phases a very low amount of must is extracted, with must moulding smaller than 10%. The energy consumption of the pressured press during compression is mainly related to the engine power absorption (one of the two in operation), and it is below 4 kW except during start-up, due to the starting currents. The highest power is reached in the last phase in which the maximum pressure is applied and a great amount of must is extracted. On the other hand, energy consumption in the vacuum press gradually decreases. A similar trend was not observed for the specific energy for either press: while it increases along the whole process for the vacuum press, it reaches a maximum value in the second phase of the pressured one. Results show the need to pursue new studies on single component design and on pressing cycles, especially in high-capacity pneumatic vacuum presses. Several advantages on wine production costs could be achieved, even retaining high quality wines.

A Real Case Study of a Full-Scale Anaerobic Digestion Plant Powered by Olive By-Products

The anaerobic digestion plant studied in this paper is one of the first full-scale plants using olive oil by-products. This is a two-stage plant with a power of 100 kWe. Two tests were performed: the first on olive pulp and pitted pomace and the second on biomass consisting of 10% crushed cereal. In both cycles, the retention time was 40 days. The production of biogas was between 51 and 52 m³/h, with limited fluctuations. The specific production values of biogas indicate that a volume of biogas greater than 1 m³/kg was produced in both tests. The produced biogas had a methane percentage of about 60% and the specific production (over total volatile solids, TVS) of methane was of the order of 0.70 m³methane/kg_TVS. FOS/Alk (ratio between volatile organic acids and alkalinity) was always lower than 1 and tended to decrease in the second digester, indicating a stable methanogenic phase and the proper working of the methanogenic bacteria in the second reactor. The concentration of incoming biomass TPC (total polyphenols content) can vary significantly, due to the seasonality of production or inadequate storage conditions, but all measured values of TPC, between 1840 and 3040 mg gallic acid kg⁻¹, are considered toxic both for acidogenic and methanogenic bacteria. By contrast, during the process the polyphenols decreased to the minimum value at the end of the acidogenic phase, biogas production did not stop, and the methane percentage was high.

Modified Rotating Reel for Malaxer Machines: Assessment of Rheological Characteristics, Energy Consumption, Temperature Profile, and Virgin Olive Oil Quality

The properties of food products are the result of changes produced in raw materials as a result of process treatments. In the olive oil extraction process, these changes can be observed as differences in quality, nutritional characteristics, taste, and flavor, and are especially due to the time and temperature of the malaxation phase. These parameters are closely related to the mechanical design of malaxer machines. In this study, a new reel model for malaxer machines was designed. The new model was incorporated into an industrial malaxer machine and experimental tests were carried out to study the effects of two different reel designs (modified and unmodified profile) on the rheological characteristics of olive paste, the energy consumption of the plant, and the temperature profile inside the machine. The main commercial parameters of the produced olive oil were studied, as well as the extraction yield and the extraction efficiency of the plant. The malaxer machine equipped with the modified reel showed better homogenization of the paste, which led to improved heat exchange and rheological properties. The results of this study showed that a specific modification of the rotating reel can improve the performance of the malaxer in terms of improving the viscosity of the paste, 127,157.67 (mPa sⁿ) for the malaxer with the modified reel at the beginning of malaxation, reaching a final value of 64,626.00 (mPa sⁿ) at the end. The unmodified malaxer showed an initial viscosity coefficient of 133,754.00 (mPa sⁿ) and a final value of 111,990.67 (mPa sⁿ). This led to a reduction in malaxing times, an increase in the work capacity of the plant, and a reduction in total energy consumption and slowed down the oxidative phenomena responsible for the decrease in the quality of olive oil.

Low-frequency, high-power ultrasound treatment at different pressures for olive paste: Effects on olive oil yield and quality

Ultrasound technology was employed to test its action on the extraction of olive oil at the industrial scale. Because of its mechanical effects, ultrasound waves were applied to the olive paste, between the crushing and malaxing operations. Comparative experiments were performed between traditional extraction processes and the innovative extraction process, with the addition of the ultrasound treatment. Different levels of pressure were tested on olive paste, using four different olive cultivars. Pressure level played an important role in olive oil extractability. When ultrasound was subjected to olive paste with a pressure of about 3.5 bar, there was a significant increase of extractability compared to the traditional process. On the other hand, there was no significant effect between ultrasound treatment and traditional technology on extractability when ultrasound at a pressure level of 1.7 bar was used.

Modelling Energy Consumption and Energy-Saving in High-Quality Olive Oil Decanter Centrifuge: Numerical Study and Experimental Validation

In this study, an energy consumption model of a decanter centrifuge was proposed, in particular for a technologically evolved machine equipped with an electromechanical recovery system. This model should be suitably coupled with an auto-adaptive controlling technique used to accurately manage the olive oil process. To achieve this goal, a solid physical and theoretical basis that simple to implement is required. To date there have only been limited scientific studies modelling energy consumption applied to the machines used in olive oil extraction processes. Therefore, the model was developed using fluid dynamic analysis and physical constraints to give it a solid basis. It was then simplified sufficiently for future implementation in automatic machine systems. The empirical model was validated through power measurements conducted in two harvesting seasons under varying operating conditions. The model estimates the power absorbed by the bowl and that produced and recovered by the screw, with high accuracy in each harvesting season. When considering the two harvesting seasons as a single season, the prediction accuracy remains considerable, despite a marginal increase in errors (correlation coefficient greater than 0.90). Finally, the model indicates that the screw conveyor speed is the most important parameter to achieve the desired energy recovery level, while the differential speed, which is a process parameter, has only a negligible impact on energy saving.

Influence of the feed pipe position of an industrial scale two-phase decanter on extraction efficiency and chemical-sensory characteristics of virgin olive oil

BACKGROUND

Nowadays, olive oil extraction is basically achieved by means of two-phase decanters, which allow a reduction of water consumption and the leaching of phenolic compounds. Despite this, most of the working settings derive from studies carried out on three-phase decanters. Hence, the aim of the present study was to assess the influence of two-phase decanter feed pipe position (FP) on the extraction efficiency and chemical-sensory characteristics of virgin olive oil. Three different positions were considered: at 825 mm (FP1), 610 mm (FP2) and 520 mm (FP3) from the outlet of the oily phase.

RESULTS

Position FP3 allowed the highest oil recovery (up to 10%), the lowest percentage of oil in the olive pomace and, in general, a regular trend in terms of oil extraction efficiency. However, the oily must that came out of the decanter was not completely clean in terms of residual content of solid sediment and water. The feeding position partially affected the profile of antioxidant compounds.

CONCLUSION

In two-phase decanters, loading the olive paste close to the outlet of the oily phase is recommended to increase the extraction efficiency without jeopardizing the chemical-sensory characteristics of virgin olive oil. © 2018 Society of Chemical Industry.

Specification of a new de-stoner machine: evaluation of machining effects on olive paste's rheology and olive oil yield and quality

BACKGROUND

An industrial prototype of a partial de-stoner machine was specified, built and implemented in an industrial olive oil extraction plant. The partial de-stoner machine was compared to the traditional mechanical crusher to assess its quantitative and qualitative performance. The extraction efficiency of the olive oil extraction plant, olive oil quality, sensory evaluation and rheological aspects were investigated.

RESULTS

The results indicate that by using the partial de-stoner machine the extraction plant did not show statistical differences with respect to the traditional mechanical crushing. Moreover, the partial de-stoner machine allowed recovery of 60% of olive pits and the oils obtained were characterised by more marked green fruitiness, flavour and aroma than the oils produced using the traditional processing systems.

CONCLUSION

The partial de-stoner machine removes the limitations of the traditional total de-stoner machine, opening new frontiers for the recovery of pits to be used as biomass. Moreover, the partial de-stoner machine permitted a significant reduction in the viscosity of the olive paste. © 2016 Society of Chemical Industry.