DOI: 10.3303/CET24109005 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Paper Received: 8 January 2024; Revised: 6 March 2024; Accepted: 2 May 2024 
Please cite this article as: Romaniello R., Perone C., Berardi A., Leone A., Tamborrino A., 2024, Biomass Recovery from Olive Oil Extraction 
Line: Opportunities for Reuse of By-products and Energy Saving, Chemical Engineering Transactions, 109, 25-30  DOI:10.3303/CET24109005 
  

 CHEMICAL ENGINEERING TRANSACTIONS  
 

VOL. 109, 2024 

A publication of 

 
The Italian Association 

of Chemical Engineering 
Online at www.cetjournal.it 

Guest Editors: Leonardo Tognotti, Rubens Maciel Filho, Viatcheslav Kafarov 
Copyright © 2024, AIDIC Servizi S.r.l. 
ISBN 979-12-81206-09-0; ISSN 2283-9216 

Biomass Recovery from Olive Oil Extraction Line: 
Opportunities for Reuse of By-Products and Energy Saving 

Roberto Romanielloa,*, Claudio Peronea, Antonio Berardib, Alessandro Leoneb, 
Antonia Tamborrinob 
aDepartment of Agriculture, Food, Natural Resources and Engineering (DAFNE), University of Foggia, Via Napoli 25, 71122 
Foggia, Italy 
bDepartment of Soil, Plant and Food Science (DiSSPA), University of Bari Aldo Moro, Via Amendola 165/A, Bari, 70126 
Bari, Italy 
roberto.romaniello@unifg.it 

There is an increasing need to produce more energy from renewable sources and improve the energy efficiency 
of the processes to reduce the environmental impact. At the same time, it would also be desirable to enhance 
the reuse of by-products from the perspective of a circular economy. 
With this purpose in mind it is of great interest considering the recovery of the olive pits along the extraction 
process for energy reuses. From this perspective, it is of great interest to consider the recovery of olive stones 
along the extraction process for energy reuse, in particular for the reduction of energy consumption linked to 
heat treatments for the conditioning of olive pastes. 
Mainly there are two ways to recover pits during the process: 1) by using a pomace destoner machine at the 
end of the process; 2) by using a combined crusher-destoner machine at the beginning of the process. 
In this work, the quality as biofuel of olive stones recovered with both methods was considered to evaluate the 
possible energy savings compared to the reference case (process line without stone recovery). In addition, the 
sustainability of the processes was evaluated by considering the increase in electrical energy required by the 
addition of the new pitting machines. 
The results show how an adequate organization and management of the process can lead to benefits both in 
terms of energy savings and plant operating costs. 

1. Introduction 
In recent decades, numerous innovations have been introduced in the olive oil extraction process, in order to 
make the process more efficient with a consequent more rational use of energy. These novel technologies 
mainly focused on the conditioning of the olive paste by using heat exchangers and by mild physical 
technologies, such as microwave-assisted systems, low-frequency ultrasound, high-frequency ultrasound, and 
pulsed electric field (Tamborrino et al., 2021).  
However, huge amounts of by-products and waste are produced during the extraction process and they should 
be properly handled to avoid serious environmental impact on land and water bodies. The solid biomass 
residues from olive oil extraction process have become an important source of renewable energy and an 
economical alternative to traditional fossil fuels used for home heating, especially in rural areas (Khdair and 
Abu-Rumman, 2020). Since agri-food industry consume a high amount of energy, solid biomass by-product as 
olive stone can be used to reduce the environmental impact of the mill (Cini et al., 2008). 
The olive stones represent a significative source of energy, therefore its recovery from the pomace has become 
common in many oil mills, since this is a low-cost operation made with a mechanical-pneumatic machine (Peri, 
2014).  
However, olive pits can be recovered also at the initial stage o f the extraction process, in particular at crushing 
stage by using a total destoner machine. Nevertheless, the total removing of the stones from the olive paste 
lead to a decrease of oil yield (Amirante et al., 1987). Other studies support this thesis, as reported in Tamborrino 

25



et al. (2020), where was presented a new partial de-stoner machine which allows to recover a variable fraction 
of the stone from the olive paste (at least 60 %), to avoid yield losses. In the same study (Tamborrino et al., 
2020), the authors compared the main combustion parameters of the olive stone obtained both from partial 
destoner machine (Pa-DM) and pomace destoner machine (Po-DM). As already stated above, the practice of 
pits recovery could represent a valuable aid, especially for small and medium-sized mills, in the direction of 
reducing their environmental impact. This is even more so if the stone is used mainly within the company for 
conditioning olive paste. Preheating the olive paste with a tube in tube heat exchanger before malaxation is now 
common practice both to make the process more efficient and because the malaxer is a poor heat exchanger 
(Perone et al, 2021). This therefore led to an increase in the thermal energy requirement within the mill, making 
the use of self-produced olive stone even more attractive. 
In this study, the possible energy savings by using olive stones as biofuel, recovered with both methods, was 
carried out by comparing the main energy parameters to the reference case (process line without stone 
recovery). Since the use of additional technologies for stone recovery introduces an increase in energy 
expenditure, it was also evaluated the sustainability of the processes from the point of view of operating costs. 

2. Materials and Methods 
The experimental analysis was carried out in a medium-size olive oil industrial mill equipped with two machines 
able to recover the stone at two different stages, i.e. at crushing and solid-liquid separation stage, respectively. 
The quality of the olive stone, from the point of view of the combustion parameters, varies depending on the 
phase in which recovery takes place (Tamborrino et al., 2020).  
The energy consumption of the extraction line with the addition of the machines to recover the stone was 
performed and the main energy indices were evaluated.   

2.1 Experimental plan layout 

Figure 1 represents a schematic configuration of the mill layout in which the experimental tests were carried out. 
The extraction process can be divided into different stages: olive cleaning, olive crushing, olive paste 
conditioning, solid-liquid separation and liquid-liquid separation. In the cleaning stage a batch of olives of about 
700 kg are fed into the hopper to be cleaned by a first defoliation and a subsequent cleaning in the washing 
machine. Then a cavity pump moves the olives into the crushing stage where the olive paste is prepared by 
means of a hammer crusher or a partial destoner machine (Pa-DM). The three-way valve in Figure 1 exemplifies 
the possibility of diverting the flow of olives onto one or the other crushing machine. Pa-DM consist of a hammer 
crusher and a de-stoner section with a rotating perforated cylinder (holes diameter of 2 mm) which rotate at 200 
rpm. Inside the cylinder there is a counter rotating shaft (900 rpm) which force the olive paste to rub the inner 
surface, so that the olive pulp is ejected outside the cylinder with a percentage of stone of about 40% of total, 
in order to avoid yield losses.  

 

Figure 1: Layout of industrial olive mill. C, crusher; CB, conveyor belt; CP, cavity pump; D, defoliator; DC, 3-
phase decanter centrifuge; E, elevator; HE, heat exchanger; H, hopper; M, malaxer; Pa-DM, partial de-stoner 
machine; Po-DM, pomace de-stoner machine; SC, screw conveyor; T, three-way valve; VC, vertical centrifuge; 
W, washing machine. EM1, EM2, EM3, energy meters. 

26



The paste obtained by one of two milling methods undergoes a pre-conditioning in a tube-in-tube heat exchanger 
to raise the temperature at 27 °C, and then is supplied in one of six malaxer, with a nominal capacity of 700 l. 
After 40 minutes of malaxation, the paste is sent to the solid-liquid separation stage, where a 3-phase decanter 
centrifuge produces three fractions: olive oil, wastewater and olive pomace. The latter can be treated with a 
pomace destoner machine (Po-DM) to recover the stone. The pomace pitting is carried by compressing the 
product against a grid with suitable openings so that fine soft particles pass through the grid, while olive stones 
are retained inside and then discharged. 
The olive oil separated by means of decanter centrifuge proceeds in the vertical centrifuges for the final 
separation of dispersed solids and water droplets. 

2.2 Electric and thermal energy 

As depicted in Figure 1, the industrial mill can be operated in two different ways: by using a Pa-DM to recover 
the stone from olive paste at the crushing stage; by using a Po-DM to recover the stone from pomace at solid-
liquid separation stage. In the first case the olives are diverted into the Pa-DM and the Po-DM is deactivated, 
while in the second the olives are diverted into the crusher and the Po-DM is put into operation. A third way 
(reference case) is also possible by deactivating both Pa-DM and Po-DM. 
The electrical energy of the olive oil extraction process in each configuration was measured by means of three 
energy meters (EM). As shown in Figure 1, the EM1 measured the energy consumption of the cleaning and 
crushing stage (olive paste preparation), EM2 the energy absorption of the olive paste conditioning, and EM3 
the energy related to the separation process (both solid-liquid and liquid-liquid separation). In particular the 
energy meters were used to measure active power (P) and active energy (E). The reactive components were 
neglected since the electrical cabinets were equipped with power factor correction devices. 
As for the thermal energy supplied to olive paste in the conditioning stage, it was computed by installing a mass 
flow rate of the olive paste at the inlet of the heat exchanger and two thermocouples at its inlet and outlet. In the 
same way, a flow meter of the hot water and its temperature at the inlet and outlet of the external jacket of 
malaxers were used to evaluate the heat requirement during malaxation. 
The energy efficiency of the process was evaluated, as reported in Perone et al. (2022), by evaluating the 
following indices and referring them to the single processing cycle (cyc subscript): 

𝑁𝑁𝑁𝑁𝑁𝑁 𝐸𝐸𝐸𝐸𝑁𝑁𝐸𝐸𝐸𝐸𝐸𝐸 (𝑁𝑁𝐸𝐸) = 𝐸𝐸𝐸𝐸𝑁𝑁𝐸𝐸𝐸𝐸𝐸𝐸 𝑜𝑜𝑜𝑜𝑁𝑁𝑜𝑜𝑜𝑜𝑁𝑁 �
𝑀𝑀𝑀𝑀
𝑐𝑐𝐸𝐸𝑐𝑐� − 𝐸𝐸𝐸𝐸𝑁𝑁𝐸𝐸𝐸𝐸𝐸𝐸 𝑖𝑖𝐸𝐸𝑜𝑜𝑜𝑜𝑁𝑁 �

𝑀𝑀𝑀𝑀
𝑐𝑐𝐸𝐸𝑐𝑐� (6) 

𝐸𝐸𝐸𝐸𝑁𝑁𝐸𝐸𝐸𝐸𝐸𝐸 𝑃𝑃𝐸𝐸𝑜𝑜𝑃𝑃𝑜𝑜𝑐𝑐𝑁𝑁𝑖𝑖𝑃𝑃𝑖𝑖𝑁𝑁𝐸𝐸 (𝐸𝐸𝑃𝑃) =
𝑌𝑌𝑖𝑖𝑁𝑁𝑌𝑌𝑃𝑃 𝑜𝑜𝑜𝑜𝑁𝑁𝑜𝑜𝑜𝑜𝑁𝑁 �𝑘𝑘𝐸𝐸𝑜𝑜𝑜𝑜𝑜𝑜𝑐𝑐𝐸𝐸𝑐𝑐 �

𝐸𝐸𝐸𝐸𝑁𝑁𝐸𝐸𝐸𝐸𝐸𝐸 𝑖𝑖𝐸𝐸𝑜𝑜𝑜𝑜𝑁𝑁 �𝑀𝑀𝑀𝑀𝑐𝑐𝐸𝐸𝑐𝑐�
 (7) 

𝑆𝑆𝑜𝑜𝑁𝑁𝑐𝑐𝑖𝑖𝑆𝑆𝑖𝑖𝑐𝑐 𝐸𝐸𝐸𝐸𝑁𝑁𝐸𝐸𝐸𝐸𝐸𝐸 (𝑆𝑆𝐸𝐸) =
𝐸𝐸𝐸𝐸𝑁𝑁𝐸𝐸𝐸𝐸𝐸𝐸 𝑖𝑖𝐸𝐸𝑜𝑜𝑜𝑜𝑁𝑁 �𝑀𝑀𝑀𝑀𝑐𝑐𝐸𝐸𝑐𝑐�

𝑌𝑌𝑖𝑖𝑁𝑁𝑌𝑌𝑃𝑃 𝑜𝑜𝑜𝑜𝑁𝑁𝑜𝑜𝑜𝑜𝑁𝑁 �𝑘𝑘𝐸𝐸𝑜𝑜𝑜𝑜𝑜𝑜𝑐𝑐𝐸𝐸𝑐𝑐 �
 (8) 

𝐸𝐸𝐸𝐸𝑁𝑁𝐸𝐸𝐸𝐸𝐸𝐸 𝑈𝑈𝑈𝑈𝑁𝑁 𝐸𝐸𝑆𝑆𝑆𝑆𝑖𝑖𝑐𝑐𝑖𝑖𝑁𝑁𝐸𝐸𝑐𝑐𝐸𝐸 (𝐸𝐸𝑈𝑈𝐸𝐸) =
𝐸𝐸𝐸𝐸𝑁𝑁𝐸𝐸𝐸𝐸𝐸𝐸 𝑜𝑜𝑜𝑜𝑁𝑁𝑜𝑜𝑜𝑜𝑁𝑁 �𝑀𝑀𝑀𝑀𝑐𝑐𝐸𝐸𝑐𝑐�

𝐸𝐸𝐸𝐸𝑁𝑁𝐸𝐸𝐸𝐸𝐸𝐸 𝑖𝑖𝐸𝐸𝑜𝑜𝑜𝑜𝑁𝑁 �𝑀𝑀𝑀𝑀𝑐𝑐𝐸𝐸𝑐𝑐�
 (9) 

In order to obtain the primary energy, it was used the national energy efficiency (GSE) for electricity and an 
overall efficiency for thermal energy by considering generation, distribution regulation and emission losses. 

3. Results and discussions 
Table 1 shows the power and electric active energy consumption for each extraction process configuration over 
one working day (12 hours of operation), which means 24 processing cycles at 3000 kg/h capacity. It could be 
noted that the electric energy consumption increases with the introduction of technologies to recover the stone 
from the olive paste. However, the consumption is higher when the stone are recovered by Po-DM. This is 
mainly due to the fact that Pa-DM is operated for about 15 minutes every processing cycle, while Po-DM works 
almost continuously, being connected to the outlet of the decanter centrifuge. In fact, the separation stage as 
an almost constant power request, due to the common practice of the operator to withholds the olive paste of 
the following batch in the malaxer until the decanter centrifuge is completely drained from the previous batch 
(Perone et al., 2022). This can be also seen by analysing the mean value and standard deviation of electric 

27



power requested by the crushing stage of the extraction process with Pa-Dm. Although the pitting phase 
introduces approximately 15 kW of additional power, the average value was 12.67 kW (Pcsh), with a standard 
deviation of 11.22 kW, which indicates the cyclical nature of the operation. Instead, taking into consideration the 
separation phase with Po-DM, it can be seen that this constantly requires an additional power of around 8 kW 
(Psep equal to 18.21 ± 0.47 kW) respect to that with Pa-DM (Psep equal to 8.21 ± 0.47 kW), and that of the 
reference case (Psep equal to 8.71 ± 0.54 kW). 
Definitely, the energy consumption was 352.13 kWh (23.09 % crushing stage, 47.11 % conditioning stage and 
29.80 % separation stage) for the reference case, 411.32 kWh (37.11 % crushing stage, 38.83 % conditioning 
stage and 24.06 % separation stage) for Pa-DM case, and 464.32 kWh (18.41 % crushing stage, 37.25 % 
conditioning stage and 44.35 % separation stage) for Po-DM case. As expected, the Pa-DM line introduces an 
increase in energy consumption in the crushing stage and the Po-DM line in the separation stage, if compared 
to the reference case. 

Table 1: Power and active energy over two hours of working. Ea, active energy; P, electric power. Subscripts – 
tot, total; csh, crushing stage; cond, conditioning stage; sep, separation stage 

  Ea,tot 
(kWh) 

Pgen 

(kW) 
Ea,csh 

(kWh) 
Pcsh 

(kW) 
Ea,cond 

(kWh) 
Pcond 

(kW) 
Ea,sep 

(kWh) 
Psep 

(kW) 

Reference 
µ 352.13 29.22 81.29 6.75 165.89 13.77 104.95 8.71 
σ - 3.36 - 2.99 - 2.54 - 0.54 
% 100.00 23.09 47.11 29.80 

          

Pa-DM 
µ 411.32 34.13 152.65 12.67 159.72 13.25 98.95 8.21 
σ - 11.22 - 11.22 - 2.52 - 0.47 
% 100.00 37.11 38.83 24.06 

          

Po-DM 
µ 440.52 36.56 81.09 6.73 164.08 13.62 195.35 16.21 
σ - 3.32 - 2.98 - 2.52 - 0.47 
% 100.00 18.41 37.25 44.35 

 
However, the conditioning stage introduces also a thermal energy requirement. Table 2 shows the energy 
consumption, both electrical and thermal, consumed for each processing cycle. The conditioning stage is exactly 
the same in each configuration. Heat requirement to preheat the olive paste in the heat exchanger and to warm 
the service fluid in the external jacket of the malaxers was estimated using the calorimetric formula and the 
measurements carried out as reported in section 2.2. The influence of thermal energy was 37.53 % in the 
reference case, while it decreased in the case of Pa-DM (33.97 %) and Po-DM (31.29 %), since the electric 
energy increased due to the additional absorption for stone recovery. The output energy due to the energy value 
of the olive oil (34.5 MJ/kg), by considering an average yield of 17 % was 4398.75 MJ in each configuration.  

Table 2: Energy balance for each extraction process configuration. 

Input 
Reference Pa-DM Po-DM 

Energy 
(MJ/cyc)  

Ratio 
(%) 

Energy 
(MJ/cyc)  

Ratio 
(%) 

Energy 
(MJ/cyc)  

Ratio 
(%) 

Electricity 52.82 62.47% 61.70 66.03% 66.08 67.55% 
Heat 
Total 

31.74 37.53% 31.74 33.97% 31.74 32.45% 
84.56 100.00% 93.44 100.00% 97.82 100.00% 

       

Output 
Reference Pa-DM Po-DM 

Energy 
(MJ/cyc)  

Ratio 
(%) 

Energy 
(MJ/cyc)  

Ratio 
(%) 

Energy 
(MJ/cyc)  

Ratio 
(%) 

Total(*) 4398.75 100.00% 4398.75 100.00% 4398.75 100.00% 
* calculated with an average yield of 17 % and an energy value of 34.5 MJ/kg  
 
Tables 3 reports the energy indices estimated on the basis of primary energy consumption. The primary energy 
was obtained by considering the national energy efficiency (GSE) of 46 % for electricity and an overall efficiency 
for thermal energy of about 81 % in the reference case, with condensing boiler, and of about 77 % in the case 
of Pa-DM and Po-DM, with biomass (stone) boiler. In the estimation of primary energy, the conversion factors 
of the energy carriers into primary energy were also taken into account (provided by GSE). The primary energy 

28



conversion factor of the individual energy carrier is the sum of the non-renewable and renewable contribution. 
It was 1.05 (non-renewable) and zero (renewable) for natural gas, and 0.2 (non-renewable) and 0.8 (renewable) 
for stone biofuel. Therefore, it is important to note that a significant portion of the energy produced by the 
combustion of the olive stone is renewable, contributing to the reduction of the environmental impact of the 
extraction process. 
The specific energy (ES) on the basis of primary energy was 1.22 MJ/kg in the reference case and it increases 
to 1.37 MJ/kg in Pa-DM configuration process and to 1.45 MJ/kg in Po-DM one. The energy productivity was 
calculated as the inverse of SE, thus it was 0.82, 0.73 and 0.69 for reference, Pa-DM and Po-DM case, 
respectively. The net energy (NE) is almost the same in each case, since the energy of the output product (olive 
oil) is an order of magnitude higher. The energy use efficiency (EUE) was 28.16 in the reference case and 25.10 
and 23.81 for Pa-DM and Po-DM configuration, respectively. However, these values do not consider the self-
produced heat in the case of stone recovery. When taking this contribution into account, the thermal energy 
requirement must be deducted, both in Pa-DM and Po-DM cases, since it is obtained from the combustion of a 
process by-product. As a result, SE become 1.05 MJ/kg for Pa-DM processing line and 1.13 MJ/kg in the case 
of Po-DM. This means that the SE required outside the system boundaries is reduced by about 13.9 % and 7.3 
%, respectively. Regarding EUE it increased to 32.80 (14.1 %) for Pa-DM and to 30.62 (8.0 %) for Po-DM.   

Table 3: Energy indices for each extraction process configuration with and without (total) self- produced heat. 

 
Reference Pa-DM Po-DM 

Total Self-produced 
heat Total Self-produced 

heat Total Self-produced 
heat 

ES (MJ/kg) 1.22 - 1.37 1.05 1.45 1.13 
NE (Mj/cyc) 

EUE (-) 
4,242.57 - 4,223.52 4,264.62 4214.00 4255.10 

28.16 - 25.10 32.80 23.81 30.62 
EP (kg/MJ) 0.82 - 0.73 0.95 0.69 0.89 

 
In terms of operating costs, the extra electricity costs must be considered in the case of Pa-DM and Po-DM, but 
at the same time the costs due to the production of heat for conditioning the olive paste must be eliminated. 
Table 4 summarize the energy costs by considering only the net costs of the energy carrier. The working day is 
12 hours, while one year of processing was assumed to be 60 days.  
As reported in Tamborrino et al. (2020) the lower heating value (LHV) of stone is about 16.61 MJ/kg when 
recovered with Pa-DM, and 16.11 MJ/kg when recovered by Po-DM. Therefore 2.47 kg/cyc of olive stone are 
used in the case of Pa-DM and 2.55 kg/cyc in the Po-DM configuration. This biofuel is completely self-produced 
in the mill, therefore it does not introduce any additional cost, other than the indirect one due to the introduction 
of the Pa-DM and Po-DM machines and already computed in electricity costs. In fact, the extraction line with 
Pa-DM introduces an additional electricity cost of 1,235.30 €/year, while the one with Po-DM is 1,844.59 €/year. 
In these two configurations, however, an economic saving of 2,067.89 €/year is due to the self-produced heat. 
Consequently, the net saving amounts to 832.59 €/year and 223.30 €/year for Pa-DM and Po-DM, respectively.   

Table 4: Energy costs and savings for each energy source and in each configuration. 

  Energy 
(MJ/cyc) 

U.M. 
(unit) 

LHV 

(MJ/unit) 
Fuel/energy 

(unit/cyc) 
Cost 

(€/unit) 
Cost/cyc 

(€/cyc) 
Cost/day 

(€/day) 
Cost/year 

(€/year) 
Saving 
(€/year) 

Reference 
Electricity 114.83 MJ - 114.83 0.04 € 5.10 € 122.48 € 7,348.86 € 0.00 € 

Heat 41.36 Sm3 34.56 1.20 1.20 € 1.44 € 34.46 € 2,067.89 € 0.00 € 
Total 156.18 MJ - 156.18 - 6.54 € 156.95 € 9,416.75 € 0.00 € 

           

Pa-DM 
Electricity 134.13 MJ - 134.13 0.04 € 5.96 € 143.07 € 8,584.16 € -1,235.30 € 

Heat 41.10 kg 16.61 2.47 0.40 € 0.00 € 0.00 € 0.00 € 2,067.89 € 
Total 175.23 MJ - 175.23 - 5.96 € 143.07 € 8,584.16 € 832.59 € 

           

Po-DM 
Electricity 143.65 MJ - 143.65 0.04 € 6.38 € 153.22 € 9,193.45 € -1,844.59 € 

Heat 41.10 kg 16.11 2.55 0.40 € 0.00 € 0.00 € 0.00 € 2,067.89 € 
Total 184.75 MJ - 184.75 - 6.38 € 153.22 € 9,193.45 € 223.30 € 

 
Since both Pa-DM and Po-DM can recover on average about 50 % of olive stone (which represent about 26 % 
in the olive mass balance), the annual production can be estimated to be about 131 t/year. Of these, 
approximately 3.5 t/year must be used to produce heat during the olive paste conditioning stage. Approximately 

29



127.5 kg of olive pits remain available to the mill which can potentially be sold at around €0.4/kg generating an 
additional income of around 51,000.00 €/year.  

4. Conclusions 
In this study, the possibility of improving the energy efficiency of a medium-sized oil mill was evaluated by 
evaluating the use of one of its by-products, i.e. olive stone, with a view to the circular economy. In order to 
recover the olive stone during the extraction process the introduction of two different technologies was taken 
into consideration. A solution involves the introduction of a pomace destoner machine (Po-DM) at the exit of the 
three-phase decanter centrifuge, the other the introduction of a new partial destoning machine (Pa-DM) as an 
alternative to the classic crusher. Hence, when the stone are recovered from pomace a new machine was added 
to the extraction process, while to recover the stone in the crushing stage a new machine completely replace 
the crusher. Pa-DM consists of two main units: hammer crusher and destoner machine. 
The energy consumption of the extraction lines configured with both Pa-DM and Po-D were evaluated and 
compared with the reference case (with hammer crusher and Po-DM deactivated). To evaluate the energy 
performance in each configuration four energy indices were evaluated: specific energy (SE in MJ/kg); energy 
productivity EP in kg/MJ), net energy (NE in MJ) and energy use efficiency (EUE as the ratio on energy output 
to the input). Among these, SE and EUE better explain the efficiency of the system. It was found that SE was 
1.22 MJ/kg in the reference case and increased to 1.37 MJ/kg and 1.45 MJ/kg for Pa-DM and Po-DM, 
respectively. As for the EUE it was calculated 28.16, 25.10 and 2.81 for reference, Pa-DM and Po-DM 
configuration. This apparent worsening of the use of energy resources is due to the fact that Pa-DM and Po-DM 
introduce an increase in electricity consumption. However, Pa-DM and Po-DM make it possible to completely 
reduce the heat requirement for conditioning the olive paste. Taking this contribution into account, the SE values 
become 1.05 MJ/kg and 1.13 MJ/kg, while EUE become 32.80 and 30.62 for Pa-DM and Po-DM, respectively. 
It is worth noting that the use of olive stone as biofuel introduces a share of production from renewable sources 
equal to 80 % (GSE source). Regarding operating costs, it was observed that Pa-DM introduces an increase in 
electricity expenditure of 1,235.30 €/year, while Po-DM involves an increase of 1,844.59 €/year. However, the 
cost savings for heat production amount to 2,067,89 €/year in both cases. Therefore, using Pa-DM leads to a 
cost reduction of 832.59 €/year, while Po-DM produces a reduction of 223.30 €/year. Since both technologies 
can recover on average around 50 % of the stone existing in the starting product, a further income of around 
51,000.00 €/year could originate from the sale of the portion of stone not used for combustion in the mill.  
The analysis conducted suggests that an adequate management of the process, mainly with an early recovery 
of the stone in the crushing stage could guarantee both energy and plant operating costs savings. 

References 

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Cini, E., Recchia, L., Daou, M., & Boncinelli, P. (2008, September). Human health benefits and energy saving 
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Peri, C. (Ed.). (2014). The extra virgin olive oil handbook. New York, NY, USA:: John Wiley & Sons. 
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exchanger for the conditioning of olive paste. Applied Sciences, 11(4), 1858. 
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in the olive oil extraction industry: Comparative assessment of energy consumption in two management 
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Tamborrino, A., Servili, M., Leone, A., Romaniello, R., Perone, C., & Veneziani, G. (2020). Partial De‐Stoning 
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Tamborrino, A., Taticchi, A., Romaniello, R., Perone, C., Esposto, S., Leone, A., & Servili, M. (2021). 
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