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A tri-generation plant fuelled with olive tree pruning residues in
Apulia: An energetic and economic analysis
Riccardo Amirante
, Maria Lisa Clodoveo
, Elia Distaso
, Francesco Ruggiero
Paolo Tamburrano
Department of Mechanics, Mathematics and Management (DMMM), Polytechnic of Bari, Via Re David 200, 70126, Bari, Italy
Department of Agro-Environmental and Territorial Sciences (DISAAT), University of Bari, Via Amendola 165/A, 70126, Bari, Italy
Department of Civil Engineering and Architecture (DICAR), Polytechnic of Bari, Via Orabona, 70126, Bari, Italy
article info
Article history:
Received 12 March 2015
Received in revised form
30 September 2015
Accepted 30 November 2015
Available online 22 December 2015
Agricultural residues
Organic Rankine Cycle
Economic analysis
This paper presents the energetic and economic analysis of a virtuous example consisting of a tri-
generation system fuelled only with olive tree pruning residues and planned to be located next to
Bari Airport (Apulia, Italy). The main goal is to demonstrate the feasibility and convenience of producing
cooling, heating and electrical power from olive tree pruning residues in those regions characterized by a
high availability of this kind of biomass, such as Apulia. A strategic location was selected, namely Bari
Airport (Apulia), and this paper demonstrates the economic convenience of installing a commercially
available Organic Rankine Cycle (ORC) unit of 280 kW
that is capable of satisfying the thermal demands
of the airport, with the addition of an absorption chiller for air conditioning in the airport buildings. First
it is veried that the quantity of oil tree pruning residues available in the area surrounding the airport
fully can satisfy the plant demand of feedstock. Then a detailed description of the components of the
plant is provided. The performance of the plant is therefore evaluated in order to assess the thermo-
dynamic competitiveness of a tri-generative system fuelled with this type of biomass. Finally, a detailed
economic analysis is carried out with the aim of demonstrating the advantages that the plant can assure
in terms of payback period (PBP), net present value (NPV) and internal rate of return (IRR). Two different
typologies of government incentives are considered. In both of which, the PBP is 6 years with an IRR of
about 21% and this points out the great economic attractiveness of the project. From an ecological point
of view, the plant can ensure a remarkable reduction in CO
©2015 Elsevier Ltd. All rights reserved.
1. Introduction
For over twenty years, governments have taken a number of
actions to solve the environmental problem concerning greenhouse
gas emissions and global warming caused by the excessive con-
sumption of fossil fuels. Energy policies implemented to date have
been promoting renewable energy exploitation, providing full
support by means of a number of incentives [1]. Such policies have
already led to a signicant change in the energy mix, which is
continuously replacing conventional fuels with renewable energy
sources. European countries planned to meet the 2020 targets on
renewable energies thanks to such a relevant paradigm shift in
renewable energy exploitation [2]. Biomass is a form of renewable
energy that can effectively be utilized to reduce the impact of the
energy production from fossil fuels on the global environment and
can be converted into useful forms of energy by using different
processes. Several techniques, plants and devices for extracting
energy from waste biomass are available. The techniques for energy
extraction from waste biomass can be grouped in the following
families: Combustion, Pyrolysis/Gasication, Bio-processing.
Biomass energy systems can generally provide several advantages
such as a low carbon footprint and a lower delivered energy cost
compared to fossil fuels. In biomass-fuelled power plants the
electricity generation is usually coupled with the production of
heating and/or cooling with the aim of increasing the overall ef-
ciency, since the electrical efciency is low in the plants fuelled
with biomass.
Despite the energetic use of agricultural wastes can play an
important role in reducing the consumption of fossil fuels, such a
practice is not so widespread as expected in those regions having
*Corresponding author.
E-mail address: (P. Tamburrano).
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Renewable Energy 89 (2016) 411e421
large availability of agricultural residues [3]. This paper is focused
on a particular type of agricultural residues largely diffused in farms
of the Mediterranean region, namely olive tree pruning residues,
and aims to demonstrate that their energetic use can be very
protable in a tri-generation system, also thanks to the recent ad-
vances both in the tri-generation technology and in mechanical and
management systems for harvesting, packaging and transportation
[4]. It is planned to realize the tri-generative power plant in a region
having a large quantity of oil olive crops, namely Apulia (south of
Italy). The plant will be capable of satisfying the entire thermal and
cooling demands of the buildings of Bari Airport as well as part of
the electrical energy required by the Airport.
This paper aims to assess the feasibility and protability of this
system for tri-generation from the direct combustion of olive tree
pruning residues. As starting point the availability of biomass in
Apulia, particularly in the zone nearby the plant location, is quan-
tied and compared with the needed amount of feedstock for the
plant operation. Then the components of the proposed tri-
generative plant are described in details. A thorough economic
analysis is nally exposed in order to evaluate the economic con-
venience of the project. In conclusion an estimation of the annual
quantity of CO
that can be saved by the proposed plant is also
2. The agro-energetic Apulian model
2.1. Potential of olive tree pruning residues for energy generation in
the Mediterranean region
The simultaneous generation of electricity, heating and cooling
from olive tree pruning residues in tri-generative plants can be
instrumental in increasing energy production from renewable
sources. The Apulian context best ts this objective, by virtue of the
high percentage of cultivated elds of olive trees and the conse-
quential great quantity of pruning residues that are usually un-
employed and burned on elds.
In the European Community, olive groves are mostly present in
the Mediterranean region. In fact, Mediterranean countries, led by
Spain, produce 10 million tons of olives per year, which is 75% of the
world production [5]. The Italian cultivation of olive trees is
diffused above all in southern and insular regions where about 80%
of the Italian production of olives and oil olive is obtained. As a
matter of fact, the Italian region having the greatest extension of
olive cultivated land is Apulia with 377550 ha, followed by Calabria
(194887 ha) and Sicily (161967 ha). Ever-increasing advances and
research studies on the olive oil production technology demon-
strate the importance of olive oil production upon Italian economy
Every year, in these zones, farmers have the problem of
disposing, at their own expenses, of tons of pruning residues. In Ref.
[7], the management of pruning residues is considered: the authors
argue that pruning residues, despite having generally represented a
disposal problem, can become a real opportunity for additional
revenue if an energy recovery of such wastes is performed, using
them as fuels for energy production; thus, in addition to elimi-
nating the problem of disposal, the future commercialization of
such agricultural wastes can be a source of income rather than a
cost for farmers.
In the past, the inefciency and low availability as well as the
high costs of harvesting machines were all limiting factors in
exploiting tree pruning residues. A large part of such residues was
usually burned on elds, while only the thickest branches were
recovered by farmers and used as fuel-wood [8,9]. A change in
farmers' mentality is now possible by virtue of recent advances in
designing harvesting machines, which are more reliable and ef-
cient than in the past, thus allowing farmers to be able to perform
collection and harvesting processes effectively in terms of cost and
time. In this regard, new industrial pruning harvesters capable of
overcoming the limits of common small units were tested in Ref.
[7], showing that the introduction of the industrial technology can
be instrumental in increasing the energetic use of pruning residues.
More effective strategies in managing such residues can help
farmers better exploit older and smaller size machines, especially in
small farms and in those groves where steep terrain and/or irreg-
ular spacing do not allow the protable use of large industrial
harvesting units [7].
2.2. Availability of feedstock and plant demand
This section aims to assess whether the availability of raw ma-
terial meets the requirements of the plant presented here, which is
going to be realized at Bari Airport.
It should be noted that the by-product present on a eld cannot
entirely be used for energetic valorisation because of the
apotential availability of residues
chipping cost [V/t]
fuel cost required for the transportation [V/t]
overall cost for feedstock procurement [V/year]
harvesting cost [V/t]
cost for loading and unloading the feedstock [V/t]
transportation cost [V/t]
fpruning frequency per year
lower heating value of dry biomass [kcal/kg]
lower heating value of wet biomass [kcal/kg]
henthalpy [kJ/kg]
Ppressure [bar]
total electrical power [kW]
weight of the feedstock transported [t]
total useful cooling power [kW]
mass of olives per year [t/year/hectare]
mass of wet by-product (pruning residues) [t/year/
total useful thermal power [kW]
Ttemperature [
Upercentage of humidity
Yratio of the by-product to the olive yield
mass ow rate of fuel [t/year]
overall electrical efciency
total efciency
CCP combined cooling and power
CHP combined heating and power
CCHP combined cooling, heating and power
IRR internal rate of return
NPV net present value
PBP payback period
R. Amirante et al. / Renewable Energy 89 (2016) 411e421412
permanence time on the eld and weather conditions during the
harvesting as well as the plot of the land (dimension and form). In
order to evaluate the net potential availability of olive tree pruning
residues in Apulia accounting for all of these factors, a valid
calculation method was recently proposed in Refs. [10,11]. This
method quanties the quantity of olive tree pruning residues per
hectare per year by means of the following equation:
100 (1)
where Q
is the mass of wet by-product (pruning residues) per
hectare that is yearly obtainable, Q
is the mass of olives per year
obtained in the eld, Yis the ratio of the overall by-product to the
overall olive yield, fis equal to the pruning frequency per year and a
is the potential availability that takes into account the character-
istics of harvesting techniques and eld as well as climatic
Once coefcients aand fare known, equation (1) allows calcu-
lating the precise value of Q
achievable from a specic zone,
provided that factor Yis properly estimated. To accomplish this
task, two equations have been retrieved in Ref. [10], specically one
for the provinces of Bari and Foggia and the other one for the
provinces of Lecce, Brindisi and Taranto. These formulations
calculate the by product/product ratio, Y, as a function of the yield
of olives, Q
Y¼0:566 þ1:496
for Bari and Foggia (2)
Y¼0:305 þ1:401
for Taranto;Lecce and Brindisi (3)
Using Equations (1)e(3), it is possible to depict the regional map
of the net pruning residues available per year, as shown in Fig. 1.In
addition, Fig. 1 shows their energetic potential, which was obtained
by multiplying Q
and the lower heating value (H
) calculated
through equation (4):
where H
is the lower heating value of dry biomass and averages
4200 kcal/kg for pruning residues, Uis the average humidity per-
centage present in the residuals collected on the eld. This
approach has general validity and can be applied to other zones of
Italy as well as other European countries, provided that coefcients
a,Uand f, along with the relation between Yand Q
, are tuned in
relation to the specic zone.
The plant has been designed to ensure an electrical power (P
of about 280 kW. Using the expression of the electrical efciency
) and knowing the lower heating value of the fuel, the quantity
of biomass needed for the plant operation covering a period of a
year can be retrieved from the analytical expression of
where _
denotes the fuel mass ow rate. Considering that the
plant is expected to operate 8000 h per year and that its electrical
efciency is equal to 11.2% (as reported in the following section),
and assuming the lower heating value of pruning residues present
on elds equal to 2540 kcal/kg (according to equation (4) and
assuming 40% humidity remained in residuals on elds), it results
that _
is equal to 6800 t/year.
Such a feedstock demand must fully be satised by the farms
surrounding the airport. In this regard, Table 1 reports the pro-
duction of tree pruning residues in the municipalities nearest the
plant location (average distance <20 km), along with their average
distances from the plant. The quantities of pruning residues in each
municipality were calculated by multiplying the hectares of land
covered by olive trees and the value of Q
resulting from equation
(1). The total production of pruning residues resulting from Table 1
is 12656.02 t/year, which is well above the plant demand, thus
demonstrating that a very small area is sufcient to fully satisfy the
plant demand. In particular, the complete production of tree
pruning residues in Modugno (569.47 t/year), Bari (771.18 t/year)
and Bitonto (4986.49 t/year) together with a small part of the
production in Giovinazzo (472.86 t/year) are capable of satisfying
the annual demand of the plant. Only taking into account these four
municipalities, the average distance from the plant can be calcu-
lated as a weighted mean (in which the weights are the quantity of
tree pruning residues) and results to be equal to 10.1 km.
3. Description of the plant
3.1. Electrical and thermal demands of the airport
The designed plant is a tri-generative system employing a
commercially available ORC for simultaneous production of
Fig. 1. Plant location along with the distribution of olive pruning residues (t/year) and their energetic potential (tep/year) in Apulia.
R. Amirante et al. / Renewable Energy 89 (2016) 411e421 413
electricity and useful heat combined with an absorption chiller
used to generate chilled water for air conditioning. Fig. 2 depicts the
thermal power required by the airport buildings during the year: it
is concentrated in months comprised between November and April
with a maximum demand of 410000 kW h in January. The electrical
demand of the airport, as depicted in Fig. 3, is always present
during the year and is subjected to an increase in the summer
season, due to the air conditioning, with a peak of 1000000 kW h in
July and August.
In the hot seasons (May, June, July, August, September, October),
chilled water is needed to cool the buildings of the airport, whilst
the thermal power required by the thermal users of the buildings is
null. Contrarily, in the cold seasons (November, December, January,
February, March, and April) the demand for cooling power is zero,
while the buildings need useful thermal power. Because of such a
thermal and cooling demand of the buildings during the year, it is
not possible to perform a complete tri-generation, with the power
plant assuming a combined cooling and power (CCP) conguration
in the hot season and a combined heating and power (CHP)
conguration in the cold season.
The power plant has been designed in order to satisfy the
maximum thermal demand, which occurs in January. Considering
the overall number of hours over which this thermal demand is
distributed, the maximum thermal power provided by the plant
must be equal to about 1500 kW. In a similar way, the maximum
cooling power achievable by the plant has been set equal to the
maximum cooling power demanded by the buildings in July,
namely 500 kW. As a result, the absorption chiller of the plant has
been chosen so as to provide a maximum cooling power of 500 kW.
3.2. Plant layout and components
Fig. 4 shows the layout of the plant along with the state point
information. The main sub-systems of the plant, namely the
biomass combustor, the ORC unit, the thermal users and the ab-
sorption chiller are analysed in the following sub-sections.
3.2.1. Biomass combustor
On the left of Fig. 4, the schematic representation of the biomass
combustor (dashed red box) is reported, where the top black box
indicates the combustion chamber. This is fed with pre-dried
pruning residues by means of a pneumatic system, which allows
burning bigger size pieces of wood as well as leaves and tree barks.
The biomass combustor is equipped with radiative and
convective heat exchangers at its top for transferring heat from the
ue gases generated from the combustion to the diathermic oil
(denoted by the green line), thus increasing its temperature. After
exiting the heat exchanger, the ue gases are subjected to partic-
ulate and ash elimination. To accomplish this task, a cyclone and an
electrostatic lter, which is at present the best method of separa-
tion for the smallest particles, are placed downstream of the heat
Before being discharged into the atmosphere, the ue gases ow
through a nal heat exchanger (referred to as the exhaust regen-
erator) which allows increasing the overall efciency of the plant by
recovering most of the residual thermal energy of the exhaust
In order to reduce the NO
emission (the limit value established
by the normative is 200 mg/Nm
), the strategy consists in the
introduction of a certain quantity of urea in the combustion
chamber, so that NO
can react with the injected urea to form
molecular nitrogen. To optimize the chemical reaction between
urea and NO
, the temperature and reaction time must properly be
controlled. The best range of temperature is between 800 and
110 0
C, with the optimum being equal to 1000
C, while the best
residence time ranges from 0.2 to 0.5 s.
3.2.2. ORC
The choice of an ORC system results from its peculiar charac-
teristics, specically: the turbine isentropic efciency can be as
Table 1
Tree pruning residues production in the nearest municipalities and their distances from the plant.
Town Tree pruning residues production (t/year) Average distance (km)
Modugno 569.47 9
Bari 771.18 10
Bitonto 4986.49 10
Giovinazzo 1937.61 13
Bitetto 1292.99 15
Bitritto 423.23 15
Binetto 337.58 18
Palo 2337.47 15
Tot 12656.02 e
Fig. 2. Airport thermal demand.
Fig. 3. Airport electrical demand.
R. Amirante et al. / Renewable Energy 89 (2016) 411e421414
high as 90%, the turbine can rotate at very low rotational speed and,
as a result, can directly be connected to the electric generator
without the need for a gear reducer. Furthermore, the turbine
blades are subjected to low usury thanks to humidity absence
during the steam expansion, and the system ensures short time for
maintenance and long life of the components because this tech-
nology is nowadays mature and reliable. All these advantages have
contributed to make ORC systems the most widespread technology
for small-scale combined heating and power generation from
biomass [12,13]. However, thanks to recent technological advances
in designing gas to gas heat exchanger [14e16] and micro water-
steam expanders, it was demonstrated in Ref. [17] that the
employment of small combined cycles as a valid alternative to ORC
systems for CHP from biomass will be feasible in the near future
and will be able to guarantee competitive thermodynamic
A CAD representation of the selected ORC unit is shown in Fig. 5.
This unit is commercially available [18] and has been selected
among commercially available units in order to satisfy the
maximum thermal demand of the airport while ensuring the
maximum possible electrical efciency. In fact, the unit is capable of
generating an electrical power of about 281 kW with an efciency
of 16.4%, which is very high level of performance despite the small-
scale application and despite the very high condensation temper-
ature required by the thermal users. The thermodynamic cycle of
the ORC is reported in Fig. 6 along with all the values of pressure,
temperature and enthalpy; Fig. 7 shows the heat exchange both in
the boiler (which is made up of an economizer and an evaporator)
and in the condenser (which also comprises a de-superheater).
Both graphs have been retrieved by the authors using the data
provided by the manufacturer. More details regarding the perfor-
mance parameters of the ORC unit are provided in Table 2.
The proposed application is a high temperature conguration, as
the heat source comes from the biomass combustion. As occurs in
most of the commercially available ORC units to be used in high
temperature applications (i.e. biomass combustion), the working
uid is not directly coupled to the ue gas, but a thermal oil is used
as a thermal vector between the combustor and the ORC, in order to
privilege safety and economic aspects. Indeed, the use of the
thermal oil allows avoiding local overheating and allows the heat
exchanger to operate at atmospheric pressure, as also discussed in
Ref. [19]. Moreover, the adopted temperature (about 310
C) for the
hot side of the thermal oil (therminol 66) ensures a very long oil
life. The utilization of the thermal oil also allows operation without
requiring the presence of licensed operators.
The working uid is a siloxane, namely MDM
87 °C
70 °C
Diathermic oil
Sat. Steam 260 °C
water 19.2 kg/sec
87 °C
70 °C
70 °C
87 °C
87 °C
70 °C
12 °C
7 °C
MDM=5.063 k g/sec
Water 2.11 kg/sec
POWER =1516 kW
87 °C
70 °C
310 °C
225 °C
9 bar
0.20 bar
260 °C
149 °C
Dry Steam
215 °C
Flue gas 5544 kg/h
Fig. 4. Plant layout with state point information.
Fig. 5. CAD representation of the ORC unit [18].
R. Amirante et al. / Renewable Energy 89 (2016) 411e421 415
(octamethyltrisiloxane, molecular formula ¼C
temperature ¼290
C, critical pressure ¼14.20 bar, molecular
weight ¼236.5 kg/kmol). The siloxanes are the most used molecules
in high temperature CHP applications, because they have the desired
characteristics that best full the high working temperatures [20].
The use of MDM as the working uid results from the fact that MDM is
the most suitablein cycles having high condensation temperatures. In
fact, in the proposed plant the condensation temperature must be of
the order of 100
C to satisfy the needs of the heating network (hot
water at 87
C is needed in the plant). Despite the very high conden-
sation temperature, the use of MDM allows the back-pressure of the
turbine to be kept as low as possible, by virtue of its very low
condensationpressure at 100
C (20 kPa).As a result,the working uid
can be expandedin the turbine to 20kPa, and, at thisexit pressure, the
temperature of the steam is still very high (215
C). This temperature
level makes the employment of the regenerator mandatory in order to
maximize the efciency of the cycle.
3.2.3. Thermal users and absorption chiller
In the condenser of the ORC system, the working uid disposes
of the remaining heat to the cooling water (azure line) which is
used either in an additional heat exchanger for thermal uses or in
the absorption chiller (purple dashed box) using a solution of
lithium bromide salt and water for cold generation. When the
thermal power produced by the plant exceeds the demand for
Fig. 6. Thermodynamic cycle of the ORC.
Fig. 7. Temperature vs thermal power in the boiler (top) and condenser (bottom).
Table 2
Specications of the biomass combustor, exhaust regeneratorand ORCvalid both for the combined cooling and power conguration and for the combined heating
and power conguration.
Plan component Description Value
Biomass combustor Input power 2500 kW
Thermal power transferred to the Diathermic-oil 2141 kW
Heat exchanger efciency 85.6%
Mass ow rate of the ue gases 5544 kg/h
Exhaust regenerator Flue gas temperature at the exhaust regenerator inlet 220
Flue gas temperature at the exhaust regenerator outlet 100
Maximum mass ow rate of water entering the exhaust regenerator 2.11 kg/s
Water temperature at the inlet of the exhaust regenerator 70
Water temperature at the outlet of the exhaust regenerator 87
Maximum thermal power transferred to the water 150 kW
Efciency of the exhaust regenerator 81%
ORC Thermal power transferred to the working uid 1713 kW
Gross electrical power of the steam turbine 300 kW
Net electrical power 281 kW
Turbine isentropic efciency 85%
ORC overall electrical efciency 16.4%
Mass ow rate of cooling water (condenser) 19.2 kg/s
Temperature of the water at the condenser inlet 70
Temperature of the water at the condenser outlet 87
Thermal power achievable in the condenser 1366 kW
ORC thermal efciency 80%
ORC efciency (thermal þelectrical) 96%
R. Amirante et al. / Renewable Energy 89 (2016) 411e421416
chilled water or useful thermal power, the excess thermal power is
dissipated through a heat dissipator.
In the conguration proposed, two insulated water tanks are
used to regulate the ow of the hot water used as thermal vector for
the absorption chiller and for the thermal user: a large part of the
hot water (at 70
C) is sent from the bottom tank to the condenser
of the ORC cycle, while the remaining part is sent to the exhaust
regenerator. The hot water exits these two devices at higher tem-
perature (87
C) and is conveyed into the top tank, which is used to
distribute the hot water either to the thermal user or to the
generator of the absorption chiller. Finally, the hot water at lower
temperature (70
C) exiting either the generator or the thermal
user is delivered back to the bottom tank in order to have a
continuous operation mode. In Fig. 4, the heat dissipator system is
depicted below the heat exchanger indicating the thermal users;
the heat dissipator is activated by acting on a three-way valve,
which is also capable of regulating the thermal power to be dissi-
pated according to the demand of either the thermal users or the
absorption chiller.
On the right hand side of Fig. 4, it is possible to observe the
components of the absorption chiller, specically the absorber
coupled with the generator, the condenser, the lamination valve
and the evaporator. In the conguration proposed for the absorp-
tion chiller, a cooling tower is used to dispose of the heat trans-
ferred to the condenser coolant. The choice of an absorption
refrigerator instead of a compressor refrigerator results from the
fact that the former allows the recovery of the surplus heat;
furthermore, an absorption refrigerator does not need a
compressor to realize the refrigeration cycle, which results in a
substantial reduction in the electric power compared to a standard
compressor refrigerator. It should be noted that novel and effective
studies have been conducted in order to recognise the optimum hot
water temperature for absorption chillers [21,22].
The selected unit is a commercially available lithium bromide
absorber that is capable of providing the maximum efciency (72%)
with a hot water temperature of 87
C. This choice was made in
order to maintain the same condensation temperature of the ORC
both in Summer and in Winter. This choice allows the ORC unit to
operate constantly at its design conditions and allows the
complexity of the regulation system to be reduced.
3.3. Efciency analysis
All the components of the power plant shown in Fig. 4 are
commercially available, and their performance parameters are
clearly indicated by the manufacturer. Table 2 reports the speci-
cations along with the setting chosen for the biomass combustor,
the exhaust regenerator and the ORC system. As indicated in this
table, a great part (2141 kW) of the input power (2500 kW) is
transferred to the diathermic oil according to the efciency of the
heat exchanger (85.6%), while the residual thermal energy of the
exhaust gases is partly recovered through the exhaust regenerator
and is transferred to the hot water (maximum thermal power
recovered ¼150 kW). Not all the thermal energy transported by the
diathermic oil (2141 kW) can be transferred to the ORC, because of
the efciency of the heat exchanger of the ORC system (80%); as a
result, the thermal power in input to the ORC results to be equal to
1710 kW. For this value of input power, the chosen ORC system is
capable of producing 281 kW
, while a thermal power of 1366 kW
is still available in form of hot water exiting the condenser. The
overall efciency (including both the electrical and the thermal
power produced) of the ORC system, excluding the heat exchangers
and the other components of the plant, is equal to 0.96.
The setting shown in Table 2 is valid both for the summer sea-
son, when only air conditioning is needed (combined cooling and
power conguration), and for the rest of the year, when the ab-
sorption chiller is unnecessary and the thermal energy transferred
to the water in the condenser can be recovered only for thermal use
(combined heating and power conguration).
Table 3 reports the setting regarding only the former case
(combined cooling and power conguration). In this case, it is
noteworthy that cold water at 7
C is available for the cooling
system with a maximum cooling power of 500 kW. The electrical
efciency (
)isdened by equation (5) and is equal to 11.2%, while
the overall efciency (
) is 31.2% according to equation (6):
where Q
denotes the cooling power. In contrast, Table 4 reports
the setting regarding the latter case (combined heating and power
conguration), when chilled water is not needed. In this case, a
maximum useful thermal power of 1516 kW can be produced
(35.5 kg/s of hot water at 87
C) in January. The maximum overall
, results to be equal to 71.8%, according to equation (7):
where Q
denotes the useful thermal power.
The maximum potential of the proposed plant in the two
different congurations is also illustrated by the bar charts of Fig. 8
for completeness.
Fig. 9 shows how the overall efciency of the plant changes with
the months. The partial load strategy consists in producing the
same electrical power (281 kWe), while dissipating the excess
thermal and cooling power through proper dissipation systems. In
this manner the ORC operates at its design conditions so that the
efciency of the ORC is not reduced at partial loads; as a result, the
electrical energy obtained from biomass is always the maximum
possible. This strategy is also justied by the large availability of
feedstock in the zone surrounding the airport (see Section 2).
4. Economic analysis
In this section the economic advantages that the plant can ensure
are analysed. In particular, the payback period (PBP), the net present
value (NPV) and the internal rate of return (IRR) are evaluated. To
accomplish this task, it is necessary to quantify the periodic cash
ow of the investment, in terms of annual costs and incomings.
4.1. Cost estimation
The main costs to be sustained are the overall cost for the
realization of the plant and the annual cost required for the pro-
curement of the necessary feedstock.
The cost of the plant, given by the sum of the costs of the
components and the installation costs, amounts to 2900000 V.
The yearly cost due to the procurement of the necessary feed-
stock (C
), expressed in V/year, can be calculated as follows:
where _
is the fuel mass ow rate, C
is the harvesting cost, C
the transportation cost and C
is the chipping cost.
The cost of harvesting depends on the machines used for this
purpose. In this analysis, a machine (referred to as the baler)
capable of both collecting tree pruning residues and grouping them
into cylindrical bales, as with the forage waste, is considered. This
R. Amirante et al. / Renewable Energy 89 (2016) 411e421 417
machine was constructed for forage and in a second time modied
for olive tree pruning residues. A bale has a diameter of 1.50 m and a
width of 1.20m, the medium weight varies between 400 and 450 kg,
and the time necessary to produce a bale is about 15 min. According
to the specication provided by the manufacturer, the operation
costs for the harvesting operation can be estimated to be C
¼26 V/t.
The overall transportation cost per tons of feedstock (C
) is given
by the sum of the cost of the fuel required for the round trip (C
) and
the cost for loading and unloading the feedstock (C
), divided by the
weight of the feedstock transported (P
According to typical vehicles for transportation of feedstock, the
maximum weight of feedstock that can be loaded on the vehicle
amounts to P
¼18 t.
To calculate C
, the average speed of the vehicle during the round
trip can be assumed equal to 30 km/h with a fuel consumption
equal to about 40 V/h in the case of transporting 18 t of feedstock,
which results in a fuel cost per km equal to 1.33 V/km. The distance
of a round trip can be taken equal to the average distance of the
farmers from the plant, namely 10.1 km (see Section 2.2). With
these assumptions, C
amounts to about 26.9 V(multiplying 1.33 V/
km by 20.2 km, considering the round trip). With regard to C
, the
time to load and unload 18 t of feedstock can be assumed equal to
1 h (45 min necessary to load and 15 min to unload); if these op-
erations are performed manually, C
averages 25 V, according to the
average salary of a worker [23].
Hence, substituting C
¼26.9 V,C
¼25 Vand P
¼18 t in
equation (9) results in a total transportation cost (C
) equal to 2.9 V/t.
The chipping stage allows obtaining a solid biofuel in the form of
chips with dimensions suitable for the biomass combustor. The cost
of the chipping phase can be estimated to be equal to C
In conclusion, it has been demonstrated that C
¼26 V/t,
Table 3
Specications of the absorption chiller and efciency parameters valid for the summer conguration (combined cooling and power conguration).
Summer conguration (electricity þcooling)
Absorption chiller Maximum mass ow rate of hot water through the generator 9.77 kg/s
Temperature of hot water entering the generator 87
Temperature of hot water exiting the generator 70
Maximum thermal power transferred to the generator 695 kW
Maximum mass ow rate of cold water through the evaporator 23.89 kg/s
Temperature of cold water at the evaporator inlet 12
Temperature of cold water at the evaporator outlet 7
COP 72%
Plant efciency Net electrical power 281 kW
Useful thermal power e
Maximum cooling power 500 kW
Electrical efciency 11.2%
Maximum overall efciency 31.2%
Table 4
Specications of the thermal users and efciency parameters valid for the combined heating and power conguration.
Winter conguration (electricity þheating)
Thermal user Maximum mass ow rate of hot water available for thermal users 21.31 kg/s
Temperature of hot water available for thermal users 87
Temperature of hot water returning to the bottom tank 70
Plant efciency Net electrical power 281 kW
Maximum thermal power available for thermal use 1516 kW
Cooling power e
Electrical efciency 11.2%
Maximum overall efciency 71.8%
Fig. 8. Maximum potentiality of the plant in the summer season (cooling and power)
and in the winter season (heating and power).
Fig. 9. Overall effciency vs months.
R. Amirante et al. / Renewable Energy 89 (2016) 411e421418
¼2.9 V/t and C
¼5V/t. Substituting these values in Equation (8)
and considering that _
¼6800 t/year, the cost required for the
procurement of the necessary feedstock amounts to
¼230500 V/year.
4.2. Incomings estimation
The main incomings are represented by the avoided costs of hot
water and electricity generation.
The rst contribution can be calculated from the examination of
the annual thermal demand of the airport shown in Fig. 2, which
amounts to 1680000 kWh
. Considering that 1 Nm
of methane
averagely costs 0.30 Vand that the quantity of methane required to
produce 1680000 kWh
is about 159200 Nm
according to the
current technology, it results that the cost avoided for thermal
power production is equal to 47760.00 V/year.
The avoided cost of electricity results from the fact that the
overall electrical energy required by the airport is partly provided
by the power plant. The plant produces an electrical power of
281 kW over 80 00 h, so the overall electrical energy provided to the
airport buildings results to be equal to 2248000 kW h/year. In
addition, the plant allows saving an electrical energy of
610000 kW h necessary for the cooling of the buildings (see Fig. 3).
Summing up these two contributions and considering that the
current price of electricity in that area is 0.12 V/kWh, the overall
avoided cost of electricity is 342960.00 V/year.
Further incomings are given by government incentives, which
can be grouped into two categories independent from each other.
The rst one is equal to 75% of the overall capital cost of the plant
and regards CCHP biomass efuelled plants built in the south re-
gions of Italy with a capital cost comprised between 2 and 25 mil-
lions of Euros. With this incentive, the initial plant cost of
2900000.00 Vis lowered to 725000.00 V.
The other one regards all CCHP biomass efuelled plants and
ensures a bonus per every KWh
produced during the initial 15
years. The bonus is equal to 0.227 V/kWh
in the rst year and then
is reduced by 2% per year.
4.3. Analysis of the investments
The estimation of costs and incomings achieved in Sections 4.2
and 4.3 allows evaluating the annual cash ow of the investments.
Fig. 10 shows the annual cash ow during a period of 15 years: the
situation regarding the rst kind of incentive is depicted in red,
while the other case is plotted in blue.
The rst type of incentives leads to having an initial outlay lower
than the second type, but also a lower annual cash ow in all the
subsequent years. This results from the fact that the rst type of in-
centivesonly ensures a reduction in theinitial cost of the plant,whilst
the second type gives a bonus for eachelectrical kWh produced, thus
ensuring additional annual incomings for the subsequent 15 years.
The calculation of the payback period and net present value can
be instrumental both in evaluating the protability of the invest-
ment and in recognizing which of the two typologies of govern-
ment incentives is more suitable. These indicators are plotted in
Fig. 11 for both categories of incentives, with the assumption that
the discount rate is equal to 8%. It can immediately be noticed that
the investment has a PBP value of 6 years for both cases; further-
more, we can state that the second typology of government in-
centives (a bonus for each electrical kWh produced) ensures more
gains than the rst one. In fact, at the end of the 15th year the NPV is
646399.00 Vin the rst case and 2386248.00 Vin the second one.
These results can be generalized considering what happens at
the changing of the discount rate. For both types of government
incentives, Fig. 12 shows the NPV of the investment after the 15-th
year as a function of the discount rate. It is clear that this graph
conrms that the second type of incentives is more convenient
than the other one, regardless of the discount rate chosen.
From the examination of Fig. 12, we can also appreciate the in-
ternal rate of return (IRR) of the investment. It is almost constant
regardless of the typology of the incentive, being equal toabout 21%
in both cases. This value points out the protability of the invest-
ment once again.
5. Ecological considerations
This nal section evaluates the quantity of CO
that will not be
released into the atmosphere after the proposed power plant is built
at Bari Airport. To perform this evaluation,it must be considered that
of methane weighs 0.7 kg, and 2.75 kg of CO
are normally
produced per kg of methane in a stoichiometric reaction.
With regard to the heat generation, the quantity of methane
Fig. 10. Annual cash ows of the investment vs number of years, considering the two typologies of government incentives separately.
R. Amirante et al. / Renewable Energy 89 (2016) 411e421 419
required to produce 1680000 kW h is 159200 Nm
, thus the annual
quantity not released into the atmosphere will be 306460 kg.
With regard to the electricity production, supposing a reference
electrical efciency of 0.60, it results that the methane necessary
for the electrical generation is 316050 kg. Thereby, the avoided
release of CO
for electricity generation will be equal to 869140 kg.
Overall, the mass of CO
avoided per year will be 1175600 kg.
In conclusion, it results that the proposed tri-generative plant
can be very important in the Apulia context from an ecological
point of view. Furthermore, the plant can lead to a double ecological
gain, because in addition to avoiding the combustion of fossil fuels
for energy production, it can also avoid that a lot of olive pruning
residues are burned on elds with considerable quantities of CO
released into the atmosphere. Such a practise is prohibited by the
Italian law and produces a great quantity of dioxin because of the
low temperature combustion, while the produced pollutants are
almost completely eliminated in the biomass combustor of the
proposed tri-generative plant.
6. Conclusions
For over twenty years ever increasing attention has been given
to the ecological problem in national politics. One of the most
effective ways to reduce CO
emissions is the use of biomass as fuel
for energy production. This research is focused on the energetic use
of agricultural wastes in Apulia, in particular olive tree pruning
residues. At present, such agricultural residues are burned on
Apulian elds (despite being prohibited by the Italian law) with a
consequential loss of possible energy exploitation.
In the real case considered, pre-dried olive tree pruning residues
are directly used as solid fuel in a tri-generative power plant of
about 280 kW
planned to be located near Bari Airport.
The Apulia context was analysed with respect to the availability
of feedstock, nding that the resource of biomass present in a very
small area surrounding the plant location is sufcient to satisfy the
energetic needs of the plant. Afterwards, the plant was described in
detail. It is composed of a biomass combustor, a co-generative ORC
Fig. 11. Net present value of the investment vs number of years for the two typologies of government incentives.
Fig. 12. Net present value of the investment after the 15-th year, as a function of the discount rate for the two typologies of government incentives.
R. Amirante et al. / Renewable Energy 89 (2016) 411e421420
system and an absorption chiller, which ensures chilled water in
the summer. Moreover, to reduce the quantity of pollutant com-
ponents like NO
and CO, an electrostatic lter will be positioned
downstream of the exhaust regenerator.
In the winter season, when the production of chilled water is
unnecessary, the plant will be able to produce a maximum thermal
power of 1516 kW in the form of hot water at 87
C along with a net
electrical power of 281 kW. In contrast, part of the thermal power
can be transferred to the generator of the absorption chiller with
the aim of producing chilled water (maximum cooling power of
500 kW) in the summer season. In the former case (combined
heating and power conguration), the overall efciency of the plant
is 71.8%, while, in the latter case (combined cooling and power
conguration) the plant is able to produce electricity and cooling
power with a maximum overall efciency of 31.2%.
The main economic advantages come from the avoided costs of
electricity and methane necessary for generating the thermal po-
wer. Two typologies of government incentives have been consid-
ered: according to the rst one, the government nances a
percentage of the plant cost, contrarily, according to the other one,
the government provides a bonus for every electrical kWh pro-
duced. In both cases, the payback period is 6 years and the internal
rate of return is about 21%, highlighting that the proposed project is
highly convenient from an economic point of view. From an
ecological point of view, the plant is remarkably eco-efcient,
ensuring a reduction of 1175600 kg/year in CO
Although this research activity is concerned with a specic zone,
namely the area surrounding Bari Airport, the results can be
applied to other zones of the Mediterranean region, which has
continuous availability of residues from olive tree pruning
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... Generally, the obtained product is either liquid (bio-oil), gaseous (biogas) biofuel, or solid soil amendment, called biochar. The biofuels are generally used to produce heat and electricity within the co/tri generation plants (Amirante et al. 2016;Borello et al. 2017;Colantoni et al. 2019;Alonso-Fariñas et al. 2020;Aguado et al. 2021) while reducing the fossil fuels' environmental impact. ...
... In addition, the use of olive oil wastes and OTP residues as fuels for combined cooling, heating, and power (CCHP) plants was also investigated in few recent papers. For instance, Amirante et al. (2016) conducted a feasibility study of a trigeneration plant fueled by OTP residues by performing an energetic and economic study of the system. Results showed that the electric efficiency of the plant was up to 11.2%. ...
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The olive oil production is a key economic sector for the producing countries, mainly in the Mediterranean region. However, the worldwide increasing oil production led to the generation of huge amounts of wastes detrimental for the environment. Therefore, efficient and sustainable management of olive industry wastes has recently acquired significant interest in the scientific research community. In the actual world energy context, various studies dealt with the valorization of the solid/liquid waste streams obtained from the discontinuous/continuous extraction of olive oil for energy purposes. The application of waste-to-energy treatments to these effluents can turn them out into an important energy resource. This review article presents the main used oil extraction techniques and their related research developments. The characterization of the generated wastes and the factors behind their bad environmental impacts are highlighted. Relevant research works related to biochemical and thermochemical conversion of olive mill wastes are extensively reviewed and discussed in terms of product yields and composition. A recent update of the studies addressing olive industry waste applications for energy production is also given. This investigation revealed a lack of studies in relation to the hydrothermal processing of olive mill wastes. Despite their suitability for this process (e.g., high moisture content), few papers have investigated the hydrothermal conversion of these waste streams. This scientific gap opens a very interesting research direction, which has to be further investigated.
... While the aforementioned studies examined several biomass types, numerous works can be found in the literature focusing specifically on the exploitation of olive oil industry residues (i.e., pomace, kernel and husk) for power generation or fuel production [52e58] through pyrolysis [59e61] and/or gasification [53,55,58,62,63]. In particular and to the best of our knowledge, exploitation of olive-based residues in combined pyrolysis/gasification processes is almost always complemented with a downstream process for syngas exploitation such as thermal engines and turbines [52,53,55,58,64], while only one of them examines the integration of a SOFC system [60]. Moreover, there exists a literature gap concerning the integration of biomass pyrolysis with bio-char gasification and downstream electricity production by syngas-fed SOFC, irrespective of the biomass type [13,20]. ...
The present work elaborates on the simulation and techno-economic analysis of a pro- posed MW-scale hybrid scheme that enables the production of different marketable products (i.e., electric energy and bio-oil) from the thermochemical exploitation of olive kernel residual biomass. In this regard, detailed calculations for mass and energy balances, process simulation in Aspen Plus and economic analysis with complementary sensitivity scenarios were conducted, with the aim to model and assses the feasibility of an integrated process for electricity and crude bio-oil co-generation via subsequent stages of biomass pyrolysis, bio-char gasification, syngas-fed SOFC and steam turbine. Notably, it was demonstrated that the provision of 20 tn/day of raw olive kernel resulted in a net electricity generation of 1685 kWel as well as production of 3.4 tn/day of bio-oil, without the need for external heating. Equally importantly, the overall electric efficiency and the combined bio- oil/power co-generation efficiency of the integrated process were equal to 46.8% and 77.0%, respectively, being amongst the highest values reported in relevant works. Moreover, economic analysis revealed that syngas clean-up and SOFC units account for 75% of the total fixed capital investment as well as for 62% of the annual operation costs. Nonetheless, increased unit cost is largely counterbalanced by the fact that electricity generation ac- counts for ~85% of total profits. Also, it was found that the proposed venture is not profitable considering current market values for electricity and bio-oil. However, sensitivity analysis revealed that a main equipment cost reduction of 70% is a prerequisite for the break-even electricity price to attain the current market values. Moreover, profitability can be marginally improved further by accounting for a state subsidization of more than half of the initial investment and by the increase of the crude bio-oil price at 700 €/tn.
... However, to comply with the newly emerging air pollution criteria, combustion and power generation technologies were further developed and reported by many researchers. Amirante et al. (2016) discussed a high technology Combined Cooling, Heating and Power (CCHP) plant of 281 kW capacity in Italy. These authors recorded that this plant fired with olive tree pruning residues have advantages both in economic terms as well as for reduction in CO 2 emissions. ...
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The valorization of different organic residues like municipal solid wastes, sewage sludge, and olive tree by-products, specifically pruning products; pomace and olive mill wastewater, more commonly known as the vegetation water of olives or margins is becoming more and more required in the different modern communities and relevant and crucial in terms of environmental preservation. The treatment of these wastes should be associated and viewed under two simultaneous approaches: good disposal of these cumbersome and problematic residues and righteous valorization by considering economic profitability. Thus, pruning products and pomace could be an important and valuable source of food for animals, a second-grade oil source for cosmetic soap making, production of biogas, and electrical energy from all these problematic residues. Besides, the removal of polyphenols from olive mill wastewater would have a double interest: to solve a major environmental problem and to recover and valorize the olive mill wastewater for later applications in food animal processing and soil amendments and fertilization. Using margins as process watering during composting or co-composting, stages of pre-fermentation-fermentation, and maturation are well recommended to obtain a compost of high soil fertilizing quality. The advantage of compost made from margins is the absence of pathogenic microorganisms and high levels of phosphorus and potassium content, unlike urban solid waste. About municipal solid wastes, it is recommended and interesting to associate two kinds of wastes by co-composting for example, vegetable gardens-pruning products, pomace-municipal solid waste, and green wastes-olive mill wastewater…, to get a mixed compost of good physical–chemical and biological qualities, safe and useful for agricultural soil fertilization.
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... The first and main application for olive tree wood is biomass as a source of energy. Olive tree wood has been burned for years as a source of cooling or heating and electric energy, with important advantages in economic terms and with a considerable reduction in CO 2 emissions [38,39]. In fact, many authors have based their research on the evaluation of the best pyrolysis conditions to optimize the energy and products obtained [40]. ...
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In the European Union (EU), a total of 11,301,345 hectares are dedicated to the cultivation of fruit trees, mainly olive orchards, grapevines, nut trees (almond, walnut, chestnut, hazelnut, and pistachio), apple and pear trees, stone fruit trees (peach, nectarine, apricot, cherry, and plum), and citrus fruit trees (orange, clementine, satsuma, mandarin, lemon, grapefruit, and pomelo). Pruning these trees, together with plantation removal to a lesser extent, produces a huge amount of wood waste. A theoretical calculation of the wood waste in the European Union estimates approximately 2 and 25 million tons from wood plantation removal and pruning, respectively, per year. This wood waste is usually destroyed by in-field burning or crushing into the soil, which result in no direct economic benefits. However, wood from tree pruning, which is enriched in high added-value molecules, offers a wide spectrum of possibilities for its valorization. This review focuses on the contribution of wood waste to both sustainability and the circular economy, considering its use not only as biomass but also as a potential source of bioactive compounds. The main bioactive compounds found in wood are polyphenols, terpenes, polysaccharides, organic compounds, fatty acids, and alkaloids. Polyphenols are the most ubiquitous compounds in wood. Large amounts of hydroxytyrosol (up to 25 g/kg dw), resveratrol (up to 66 g/kg dw), protocatechuic acid (up to 16.4 g/kg), and proanthocyanins (8.5 g/kg dw) have been found in the wood from olive trees, grapevines, almond trees and plum trees, respectively. The bioactivity of these compounds has been demonstrated at lower concentrations, mainly in vitro studies. Bioactive compounds present antioxidant, antimicrobial, antifungal, biostimulant, anti-inflammatory, cardioprotective, and anticarcinogenic properties, among others. Therefore, wood extracts might have several applications in agriculture, medicine, and the food, pharmaceutical, nutraceutical, and cosmetics industries. For example, olive tree wood extract reduced thrombin-induced platelet aggregation in vitro; grapevine tree wood extract acts a preservative in wine, replacing SO2; chestnut tree wood extract has antifungal properties on postharvest pathogens in vitro; and stone tree wood extracts are used for aging both wines and brandies. Moreover, the use of wood waste contributes to the move towards both a more sustainable development and a circular economy.
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The use of biomass can be a strategic way to realize a carbon-neutral energy plan, ensuring a fuel feedstock. Residual biomass arising from pruning is demonstrated to be an important energy resource in terms of quantity and quality. In the Salento peninsula, Apulia Region, in the south of Italy, a dramatic outbreak of Xylella fastidiosa has decimated olive trees since 2013, gaining a considerable amount of wood biomass. This paper, starting from the need to find a way to optimize the use of this available stock, reviews the main technologies on the utilization of olive wood for energy purposes. In particular, processes and products are here described, and an energy analysis compares lower heating value (LHV), higher heating value (HHV), mass yield, process operating conditions, and energy generated and spent by the process in order to find the most effective technology in order to optimize the energy use of olive biomass. The conclusions show the advantages and disadvantages of each technology. Pyrolysis performs well, showing the best results for both char HHV and syngas yield under different operating conditions. Gasification seems to be the most appropriate among conversion technologies to optimize olive tree pruning for energy purposes, as it can be used to produce both electrical and thermal energy. In terms of economic valorization, char is the most promising material representing a value-added product, the quality and versatility of which ranges from fuel to soil improvers and additives for the construction of supercapacitors. Conversely, its disadvantages are mainly represented by high ash content, which can slightly decrease the boiler efficiency. Finally, the amount of alkali metals can produce several problems, such as fouling, slagging, corrosion, etc., posing a challenge for combustion control and pollutant minimization.
Combined cooling, heating, and power systems (CCHP) are considered one of the most efficient energy systems since they have a less detrimental environmental impact, and therefore sustainable energy savings, and eventually less CO2 emissions. An even higher advantage is possible when a renewable energy fuel source (e.g., Biomass) is used. The proposed study presents the energy modeling of a 169 kWe capacity, biomass-based CCHP system retrofitted to a historical building, located in Perugia, Italy. Two well-known simulation software’s, ASPEN Plus and TRNSYS, are purposely integrated. In the first phase of the study, a wood biomass combustion-based externally fired gas turbine (EFGT) along with an Organic Rankine Cycle (ORC) system is modeled in Aspen Plus. In the later phase, a historical building “Sant’ Apollinare” model, and the remaining CCHP system are developed in TRNSYS. The transient system is modeled such that it fulfills the peak thermal energy demands of the retrofitted building. The main components of the system are a heat exchanger (HE), storage tanks (TK), a single-stage LiBr-H2O absorption chiller (ACH), and balance of plant (BOP) components. A heat exchanger recovers heat from the gas cycle, which is then utilized for running an ORC, heating and cooling of the end-user building, biomass drying, and domestic hot water (DHW) supply. A storage tank supplies direct heat to the end-user in winter and drives the ACH in summer. The results of the model provide data on the performance parameters of different components of the CCHP system such as temperature, power consumption, and energy profiles that allow evaluating the overall energy performance of the CCHP system. Finally, a feasibility analysis of the system is carried out on the basis of economic indexes such as simple pay back (SPB) period, net present value (NPV) and profitability index (PI), for two different case scenarios assumed for fuel (e.g., biomass) supply cost. The SPB is 2.93 years, when biomass is obtained for free. Whereas, if biomass is purchased from the market the SPB becomes 7.15 years. From an environmental perspective, the plant ensures a decrease of 632 tons of CO2 emissions annually.
Olive oil is one of the major features of the Mediterranean diet signifying healthy nutritional practices of both ancient and modern times. It is an exceptional food and contains several components beneficial for wellbeing and well-being. Olive oil, as well as the olive tree leaves are rich in oleuropein. During maturation of the fruit and the leaves, oleuropein is broken down to hydroxytyrosol and elenolic acid that are valuable components. These are antioxidants that strengthen the immune system. Oil mills use different technologies and consume a lot of water and energy. Depending on the technology, along with the main product line, side-streams such as cakes, pomace, kernel, and different types of olive mill wastewaters are generated. Wastes are also generated from subsequent treatment facilities for pomace oil and soap production. Captured oils are reclaimed and refined if possible. Only part of the beneficial chemicals such as polyphenols in the olive fruit is retained in the olive oil phase and a substantial part goes into the waste streams. More than fifty different valuable phenolics and other organic compounds have been identified in olive mill wastewaters. Pomace contains another good portion of polyphenols depending on the extraction technology. These chemicals need to be processed or removed from wastewaters by pretreatment for easier environmental management as the wastes are not acceptable to the receiving environmental media, and moreover they inhibit waste treatment. Integrated with this treatment, biotechnological conversions, or recovery of pure ingredients from the wastes are advisable to produce valuable raw materials for food, energy, agriculture, and pharmaceutical sectors. With the rising of 3R (reduce, reuse, recycle) trends, conservation of water and energy has become an issue in the olive industry. This strategy extends from preservation of these resources to enrichment of the beneficial ingredients in the product oil and reclamation of chemicals from olive by-products and wastes. Another option is adding wastes into adjusted cultures as substrates for biomass production and use the products in food, energy, and fertilizer industries. Innovative, and revised conversion technologies are needed for treatment, reuse, and reclamation of these chemicals from by-product and waste streams. There is a high number of scientific publications to address these more challenging goals. In this article new trends for stand-alone or integrated methods of waste treatment/pretreatment in management schemes for olive agro-industry with waste minimization, bioconversion and recovery/purification of beneficial chemicals are evaluated. Among the options, biotechnology of producing fuel, food, animal feed, pharmaceuticals, and fertilizers is especially important. These are being discussed for development of a profile leading to future research interests in view of the big number of published scientific research related to olive agro-industry.
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In the context of the circular economy, the recovery of wood waste from fruit trees as well as fruit residues contribute greatly to sustainable development. The main bioactive products from fruits and fruit trees have multiple properties including antioxidant, antimicrobial, antifungal, biostimulant, anti-inflammatory, cardioprotective anticarcinogenic. From an economic and ecological point of view, the implementation of the concept of biological recovery of waste and its incorporation into a sustainable and renewable cycle is possible, but this requires integrated technology and systematic management. This work highlights various applications, methods and effective solutions for the recovery of waste from fruit trees in the agro-food, pharmaceutical and cosmetic industries.
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Agricultural pruning residues represent an emerging type of by-products very poorly attended so far, usually incinerated in the open fields where they are produced, this way provoking negative environmental effects and facilitating the loss of valuable resources. The present study examines the potential exploitation of Hippophae rhamnoeides (sea buckthorn) pruning, a poorly exploited substrate, the fruits of which have been widely used for dietary supplement production, and thus its cultivation has significantly grown. The study conducted dilute acid pretreatment followed by anaerobic digestion towards the production of biogas (methane). Initially, a parametric analysis was carried out to establish the optimum pretreatment conditions, enabling partially hemicellulose depolymerization from the original feedstock. It was found that the parameters of solids loading, and duration of pretreatment had a positive impact on hydrolysis, leading to maximum overall sugars yield of 19.00 ± 2.14% (per g of biomass) under 30% loading (w/v), 121 °C, 2% H3PO4, and 120-min hydrolysis conditions. However, higher temperature and acid concentration were not equally effective in enhancing hydrolysis yields under the conditions tested. Next, study of acid pretreatment with response surface methodology (RSM) and biochemical methane potential (BMP) assays were employed to evaluate the potential of the treated feedstock for biogas production. As a result of the high lignin content of the substrate, as well as possible toxicity and inhibition phenomena due to the acid hydrolysis conditions, the maximum BMP yield obtained from the tests was equal to the yield of the untreated substrate (225.30 mL CH4/g VSadded). Concerning the tested factors, even if none of them alone exhibited statistically significant differences in the results, the combination of acid concentration and time seems to have considerably affected the obtained yields. Graphical abstract
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Designing and manufacturing high-efficiency heat exchangers is usually considered a limiting factor in the development of gas turbines employing either heat recovery Joule-Brayton cycles or external combustion. In this work, an innovative heat exchanger is proposed, modeled, and partially tested to validate the developed numerical model employed for its design. The heat exchanger is based on an intermediate medium (aluminum oxide Al(2)O(3)) flowing in countercurrent through an hot stream of gas. In this process, heat can be absorbed from the hot gas, temporarily stored, and then similarly released in a second pipe, where a cold stream is warmed up. A flow of alumina particles with very small diameter (of the order of hundreds of microns) can be employed to enhance the heat transfer. Experimental tests demonstrate that simple one-dimensional steady equations, also neglecting conduction in the particles, can be effectively employed to simulate the flow in the vertical part of the pipe, namely, to compute the pipe length required to achieve a prescribed heat exchange. On the other side, full three-dimensional computational fluid dynamics simulations have been performed to demonstrate that a more thorough gas flow and particle displacement analysis is needed to avoid a bad distribution of alumina particles and, thus, to achieve high thermal efficiency. [DOI: 10.1115/1.4002157]
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The main objective of the proposed research is to estimate the energy potentials of the olive trees pruning residues and olive husk residues in the Apulia region (Southern Italy) and to compare the possible bioenergy conversion routes for heat and power generation. 46 006_Pantaleo(537)_37 27-07-2009 11:20 Pagina 46 The part I of the research proposes a preliminary review of the olive oil chain residues in the Apulia region and an assessment of technical potentials and biomass supply costs. The investigation is carried out through a review of existing literature, structured interviews with operators, elaboration of available statistical data, assessment of the typology and current use of the by-products, analysis of olive trees pruning techniques and olive milling processes. The results show a high potential of pruning residues (about 177 kt/year at 15% moisture content) and crude olive husk (about 915 kt/year at 50% average moisture content). The supply costs are, in most cases, compatible with the energy conversion routes, and in particular they result in the range of 45-55 €/t (35% moisture content) for rotobales and chips from PR.
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This paper proposes the design of an innovative high temperature gas-to-gas heat exchanger based on solid particles as intermediate medium, with application in medium and large scale externally fired combined power plants fed by alternative and dirty fuels, such as biomass and coal. An optimization procedure, performed by means of a genetic algorithm combined with computational fluid dynamics (CFD) analysis, is employed for the design of the heat exchanger: the goal is the minimization of its size for an assigned heat exchanger efficiency. Two cases, corresponding to efficiencies equal to 80% and 90%, are considered.The scientific and technical difficulties for the realization of the heat exchanger are also faced up; in particular, this work focuses on the development both of a pressurization device, which is needed to move the solid particles within the heat exchanger, and of a pneumatic conveyor, which is required to deliver back the particles from the bottom to the top of the plant in order to realize a continuous operation mode. An analytical approach and a thorough experimental campaign are proposed to analyze the proposed systems and to evaluate the associated energy losses.
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In the field of biomass and bio-energy production, an analysis was performed of the whole production process from biomass supply to bio-energy production. The available biomass, harvesting and transportation costs and the distribution of supply area were quantified. The assessment of volumes was based on forest type and its relative increment. The transportation costs, influenced by different species-specific and site-specific factors, were calculated by integrating data in a geographic information system (GIS). The economic values calculated were the main economic indicators (net present value (NPV), internal rate of return (IRR) and Payback Period). The results show that: (a) there is a good supply of forest biomass across most of the territory of Basilicata region, Italy; (b) the harvesting and transportation costs are dependent on biomass density and distances; (c) there are strong margins for economic profits at the level of each single supply basin; and (d) the endogenous value added was estimated to about 150 seasonal workers.
Conference Paper
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Designing and manufacturing high-efficiency heat exchangers is usually considered a limiting factor in the development of both heat recovery Joule-Brayton cycles and closed-cycle (external combustion) gas turbine plants. In this work, an innovative heat exchanger is proposed, modeled and partially tested to validate the developed numerical model employed for its design. The heat exchanger is based on an intermediate medium (aluminum oxide Al 2O3) flowing in counter-current through an hot stream of gas. In this process, heat can be absorbed from the hot gas, temporarily stored and then similarly released in a second pipe, where a cold stream is warmed up. A flow of alumina particles with very small diameter (of the order of hundreds of micron) can be employed to enhance the heat transfer. Experimental tests demonstrate that simple one-dimensional steady equations, also neglecting conduction in the particles, can be effectively employed to simulate the flow in the vertical part of the pipe, namely to compute the pipe length required to achieve a prescribed heat exchange. On the other side, full three-dimensional Computational Fluid Dynamics (CFD) simulations have been performed to demonstrate that a more thorough gas flow and particle displacement analysis is needed to avoid some geometrical details that may cause a bad distribution of alumina particles, and thus to achieve high thermal efficiency.
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In this article, treatment and disposal alternatives of olive oil mill wastes and technical requirements for their management are covered. Waste characteristics, treatment options with regard to the economic feasibility, and challenges of existing waste disposal practices in olive growing countries are mentioned. Attention is drawn to present-day techniques of waste management. The search concerning the environmentally acceptable, economically feasible, and practically applicable methods of disposal of olive oil mill wastes is referred. In the management schemes, compliance with environmental regulations and economic and social benefits of the olive oil production are the goals that must be simultaneously achieved.
The renewable energy policies in the European Union have already led to a significant progress; the energy mix should further change until 2020. Italy is planning to meet the 2020 targets on renewable energies also thanks to a relevant paradigm shift in renewable energy exploitation. Indeed, in 2005 the sector where RES were more present in Italy was electricity production with 203 PJ of renewable origin, while in the heating and cooling sector renewable energy penetration was limited to 80 PJ. On the contrary, in 2020 heating and cooling is expected to absorb the highest amount of renewable energy (438 PJ) with renewable electricity expected to count for 356 PJ. Bioenergy, a renewable energy resource particularly suitable for electricity, heating & cooling and in transport, will be at the core of this sectorial shift in renewable energy production and use and is expected to become the dominant form of RES before 2020. The paper makes a detailed analysis of the recent developments and expected evolution of the Italian energy mix in next decade. It provides an overview of the Italian bioenergy sector in comparison with other Renewable Energy Sources (RES) and with leading countries in the European Union with a special focus on the production, exploitation and potentials on the basis of the analysis of the Italian National Renewable Action Plan.
Evaluation of a typical integrated solar absorption cooling system has been carried out to determine its overall performance. Analysis of the results revealed an operational efficiency of 61% for the solar collectors at a mean differential temperature (ΔT) of 51 °C as compared with the manufacturer’s rating of 70% at a ΔT of 60 °C. The absorption chiller did however perform quite satisfactorily and achieved a coefficient of performance (COP) of 0.69 as compared with the manufacturer’s rating of 0.7 despite the slight deviation at the collectors end. The installation strategy for the hot water storage tanks also appears to have achieved its objective of maintaining controlled temperature stratification in the tanks. It could therefore be concluded that the system has proved its potential as a viable cooling technology for application in buildings. However, in order to maintain appropriate hot water supply temperature during low solar radiation levels, supplementary heat source such as gas or biomass fired system would have to be considered and incorporated into solar absorption cooling systems.
A recent novel adjustment of the Span–Wagner equation of state for siloxanes, used as working fluids in high-temperature organic Rankine cycles, is applied in a mathematical model to solve cycles under several working conditions. The proposed scheme includes a thermo-oil intermediate heat circuit between the heat source and the organic Rankine cycle. Linear and cyclic siloxanes are assayed in saturated, superheated and supercritical cycles. The cycle includes an internal heat exchanger (regenerative cycle), although a non-regenerative scheme is also solved. In the first part of the study, a current of combustion gases cooled to close to their dew point temperature is taken as the reference heat source. In the second part, the outlet temperature of the heat source is varied over a wide range, determining appropriate fluids and schemes for each thermal level. Simple linear (MM, MDM) siloxanes in saturated regenerative schemes show good efficiencies and ensure thermal stability of the working fluid.