Market of Olive Residues for Energy

1. Market of Olive Residues for Energy
Regional Energy Agency of
Central Macedonia
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2. Work Package 3: Analysis of Local Situations + SWOT analyses + Possible
Trends
One joint report for the 5 Regional “state of the art” reports from each
Deliverable 3.1: involved area describing the current olive-milling residues market (with a
focus on energy uses.
Regional Energy Agency of Central Macedonia (REACM) -
Leader of WP3:
ANATOLIKI S.A.
Partners Involved: ARE Liguria-Italy, UC Liguria-Italy, AGENER-Spain, IPTPO-Croatia, UP ZRS-
Slovenia
Date: July 2008
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3. 1. Olive Oil Extraction Process and By-Products (solid olive oil residues)................................... 5
2. Pomace Oil Extraction Process and By-Products (pomace oil solid residues).......................... 9
3. Olive oil and solid residues production in Spain, Italy, Greece, Slovenia & Croatia ................ 18
4. Energy Exploitation Methods .............................................................................................. 23
6. The current supply chains and the end-uses of solid residues in each region. ....................... 29
7. National and Regional policy aspects .................................................................................. 42
8. Technological Equipment & Costs ....................................................................................... 48
9. Annex ................................................................................................................................ 64
10. References ....................................................................................................................... 65
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4. With more than 4.5 million hectares under cultivation, it is the second-most
important agro-food sector in Europe. The production residues of olive and
olive oil production are utilised as solid biomass fuel. The estimated
amount of residues is about 1.5 million tons, including stones/pits and
exhausted olive pomace.
The raw material is the so-called olive pomace. The olive pomace is a by-
product of the olive oil production process and constitutes a mixture of
olive pits, olive pulp and the water added in the olive mills. The moisture
content is approximately 40-70-% depending on the olive oil extraction
process. The amount of raw material depends on climate conditions, which
determine the annual production period (8 to 9 months/year).
The production of olive oil begins with the picking of olives, continues with their transport and ends
up with their processing in olive mills. After harvesting, any remaining leaves are removed; the olives
are washed, and are ground into a pulp using a revolving mill, usually constructed with stainless steel
or granite. The entire olive, including the pit, is pressed until it becomes a paste, which is then
whipped, adding water. Next comes the phase to separate solid from liquid, either by the traditional
process, or by a continuous system (centrifuge): 3-phase process or 2-phase process.
Olive mill technology generates a variety of wastes both solid and liquid. Solid wastes are generated
also in the olive groves during pruning of olive trees. In this category of wastes are also included:
leaves and small branches, the olives pits and the remained pomace resultant from olive oil
extraction. Leaves can be used as animal feed, as fertilizer or in the production of compost, while
small branches, pits and dried olive pomace also can be used for energy production. Liquid wastes
are known as Olive Mill Waste Water (OMWW) and are used in some cases as additives for the
manufacture of cosmetics and also for biogas, since substantial amounts of unrecoverable oil and
fine residues of pomace remain in the particles of OMWW.
Figure 1:Olive pomace (virgin) Figure 2: Olive Pits
The scope of this report is to study the energy exploitation potential of solid wastes produced
during olive oil extraction, as well as to analyse the regional situation in the five regions below:
1. The region of Liguria in Italy.
2. The region of Jaen in Spain.
3. The region of Chania in the island of Crete, Greece.
4. The region of Istria in Croatia.
5. The region of Istria in Slovenia.
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5. 1. Olive Oil Extraction Process and By-Products (solid olive oil
residues).
Four to ten kilos of olives are needed to produce just 1 litre of
olive oil. The olive tree begins to produce olives between the ages
of 5 to 10 years, reaching maturity at about 20 years. After 100 to
150 years, its production begins to decline. The age of the tree
influences only the quantity produced, not the quality. The
harvesting can be done by hand hitting the tree with a flexible pole so that the olives fall into canvas
covers placed on the ground or by means of mechanical vibrations.
Some olive varieties may be picked in October when they are still green, while other varieties may be
left until February when they are at the peak of ripeness and bursting with oil. Olives are usually
pressed within 24 hours if the weather is hot. If the weather is cooler, the pressing may occur within
72 hours of harvesting.
Until about 30 years ago, almost all olive oil was obtained through pressing. In the 70s, the mills
gradually abandoned the traditional olive pressing process for economical reasons. Nowadays the
traditional method is only used for processing small quantities of ecological olive oil. The alternative
method is the continuous system works by means of the centrifugation of the beaten olive paste,
producing three products: oil, pomace and residual water, just like the pressing system. During the
90s, there was a major change in the raw material arriving at the olive pomace oil extractors. This
was due to the fact that a large number of Spanish mills changed the olive oil continuous extraction
equipment, converting from the three phase to the two phase system in order to optimize extraction
costs and prevent the production of a highly polluting residual wastewater.
At present, three types of olive pomace can be considered, depending on the extraction system used
on the olives (shown in Figure 3):
Figure 3: Flow scheme of the 3 different olive oil production processes, a) traditional process, b) 3-phase
decanter process, c) 2-phase decanter process.
Source: TDC OLIVE “By product Reusing”
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6. • The Traditional process”, also known as traditional method. The ground paste is placed
between pressing mats and is subject to pressure, to expel the oil mix (mixture of oil and
water). The mixture is then poured into a vat or holding tank. This is allowed to rest so that
gravity and different densities come into play, separating the oil from the water.
• The “3-phase process”. The process based on a 3-phase decanter: 1 litre of water is added
per kilo of paste; it is then added to a horizontal centrifugal machine, where the solid is
separated from the oil must. The must is then passed on to a vertical centrifugal machine,
where the oil is separated from the vegetable water.
• The “2-phase process”. The process based on a 2-phase decanter: Same process as above,
but instead of adding water for the horizontal centrifugation, the vegetable water is recycled.
The main differences between the extracted raw materials are due to water content. Two-phase
pomace has moisture approximately 50-70% and contains a certain amount of sugars as a result of
the presence of vegetation water, while traditional pomace has a moisture content of between 25-
30% in the pressing system, and 45-60% in 3-phase centrifugal systems.
Figure 4: Example of an olive oil processing line
In Spain the most widely used process is the “2-phase”. In Italy both “3-phase” and traditional
methods are used, while in Greece “3-phase” is more common. In Slovenia the only method not used
is the “3-phase” and finally in Croatia all methods are used.
Comparing the three processes:
• The main disadvantage of the “3-phase process” is the huge amount of water needed and
consequently the production of vegetable water.
• The stream of the milled olives in “2-phase process” is separated in a 2-phase decanter. This
system enables reduced fresh water consumption and the elimination of wastewater
streams. Unfortunately, pomace which is produced comprises both, solids and water
(OMWW) from the olives and poses again difficulties for disposal, as it is very difficult to
handle, dries out very slowly and it is again very polluting.
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7. • As a method of pressing, the traditional process entails high labour costs and has certain
disadvantages due to the fact that the pressing devices used cannot prevent small pieces of
paste from one batch remaining in the press to the next batch, thus contributing to an
increase in acidity.
More specifically three-phase centrifugation has the following advantages:
• It enhances the subsequent drying process, since at least 25% of the residual water
contained in the “2-phase process” is removed from the paste. This moisture decrease allows
for the use of lower drying temperatures, which is favourable for obtaining an oil of better
quality in the further chemical extraction.
• Major energy and financial savings are derived because the evaporation of the residual water
in the evaporators/concentrators of the power plants takes place with zero net energy
consumption. In fact, the process uses the residual energy of the exhaust steam from the
turbine.
• It enables a residual water concentrate to be obtained, which is rich in mineral salts, sugars
and polyphenols. This concentrate is of high commercial value due to its use as animal feed
and organic-mineral fertilizer.
• The resulting residual water is the departure point for obtaining compounds of high added
value because they are beneficial to human health
The main olive solid residues which are generated during the olive oil production are the following:
Pits: The olive stones.
Pomace or virgin pomace or olive pomace or crude olive cake: The residual paste after the
olive oil extraction. It is constituted from a mixture of olive pit/stone, olive pulp & skin, as
well as pomace olive oil plus the water added in the olive mills. The moisture content is
about 35-70% depending on the olive oil production process.
Table 1: Solid olive oil by-products glossary
English pits or stones
Spanish huesco
Italian nocciolino
Greek κουκούτσι
Croatian koštice maslina
Slovenian koščice
English pomace or virgin pomace or olive pomace or crude olive cake
(The residual paste after the olive oil extraction)
Spanish orujo
Italian sansa vergine
Greek ελαιοπυρήνας
Croatian komina maslina
Slovenian oljčne tropine (Ostanek oljčne drozge po ekstrakciji oljčnega olja)
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8. English “traditional system” pomace
(contains:pomace oil, pulp, pits, approx.25 % humidity)
Spanish orujo
Italian sansa vergine
Greek ελαιοπυρήνας παραδοσιακού συστήματος
Croatian sirova komina maslina
Slovenian oljčne tropine tradicionalne predelave
(vsebnost: ostanek olja v oljčnih tropinah, meso ali pulpa
(mezokarp), koščice (endokarp), približno 25 % vlage)
English “2-phase” pomace
(contains:pomace oil, pulp, pits, approx.60 % humidity)
Spanish alperujo
Italian sansa vergine
Greek Διφασικός ελαιοπυρήνας
Croatian komina maslina – produkt 2-faznog centrifugalnog sustava
Slovenian oljčne torpine 2-faznega sistema
(vsebnost: ostanek olja v oljčnih tropinah, meso ali pulpa
(mezokarp), koščice (endokarp), približno 55 % vlage)
English “3-phase” pomace
(contains:pomace oil, pulp, pits, approx.50 % humidity)
Spanish orujo
Italian sansa vergine
Greek Τριφασικός ελαιοπυρήνας
Croatian komina maslina – produkt 3-faznog centrifugalnog sustava
Slovenian oljčne torpine 3-faznega sistema
(vsebnost: ostanek olja v oljčnih tropinah, meso ali pulpa
(mezokarp), koščice (endokarp), približno 48 % vlage
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9. 2. Pomace Oil Extraction Process and By-Products (pomace oil solid
residues).
Olive pomace is the solid by-product obtained from the extraction of olive oil. It is made up of skin,
pulp and stone (pit, kernel). Olive pomace after the extraction of olive oil still contains some oil,
called pomace oil, which can be subtracted with further procedures from the olive pomace. The
stone can be separated from the olive pomace in order to be sold as a biofuel, but the extraction
may become complicated. Only a minimum quantity of stone is separated to allow drying and
extraction in optimal conditions.
The pomace oil can be separated in two ways: i) using solvents (traditional method), and ii) through
physical extraction or centrifugation (second centrifugation). The first process is based on a solid-
liquid extraction where the fats are separated (extracted) with a solvent (hexane). Once this
operation has been carried out, the oil from the mixture with hexane is separated through
distillation.
According to the traditional method, pomace oil is extracted from the dried pomace (8% moisture
approximately) with solvent (hexane). Then the hexane, which is dangerous for the public health, is
separated from the pomace oil. The product obtained is called crude pomace oil or pomace oil.
The extraction of the pomace oil begins with the delivery of fatty olive pomace from oil mills. The
trucks from the oil mills unload the raw material in a storage yard. The two components of the olive
pomace (the pulp and the stone) are separated. This is because the pulp contains a major part of oil
while the stone, which presents an important percentage of the solid, contains so little oil that its
recovery is not interesting.
The system used for the drying process is a rotating cylinder ,as shown in figure 5, heated internally
by hot gases fed from a combustor or burner situated in the front part of the cylinder. The
temperature inside the dryer, which is usually made from steel, may exceed 427oC. The rotary dryer
has a slight inclination (about two degrees) and except from drying the pomace, acts as a conveying
device and stirrer. The flow of the air inside has the same direction with the dried material. To
facilitate fast drying, metallic fins are used inside the rotating cylinder so as to blend the pomace. The
outgoing dry pomace is carried from the dryer for additional processing. The goal of the drying
process is to reduce the moisture of pomace to approximately 8%. Values of final moisture above
10% are highly associated with hexane retention (and the associated potential health effects) in the
final product. On the other hand, low (below 8%) moisture levels increase the chance of fire inside
the rotary dryer.
Furthermore, if the fresh or stored two-phase pomace is subjected to a second centrifugation, it is
possible to extract between 40-60% of the retained residual oil. The process is carried out using
horizontal centrifugal machines or decanters. The oil obtained is known as “second centrifugation
oil” and is commercially classified for its properties as “crude pomace oil”.
The pomace enters the rotor through an immobile input pipe and is driven ahead by an inner rotor.
The centrifugal forces cause the solids to sediment on the rotor walls. The worm screw turns in the
same direction as the rotor, but at a different speed, making the solids move towards the conical end
of the rotor. Separation takes place along the cylindrical part of the rotor, and the oil leaves the rotor
through adjustable plates on the casing. The extraction of this residual oil by centrifugation can be
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10. carried out in two or three phase systems depending on the capacity of the extractors for eliminating
the residual water produced in three-phase centrifugation.
Figure 5: Material and air flow in the structural parts of a rotary dryer
Source: Rotary Drying of Olive Stones: Fuzzy Modeling and Control, N. C. TSOURVELOUDIS, L. KIRALAKIS,
Department of Production Engineering and Management, Technical University of Crete, University Campus,
Chania, GREECE
Pomace from the traditional extraction system and those from the three phase extraction require
different preconditioning procedures than those coming from two phase pomace prior to their
extraction with solvent. Figure 6 shows the block diagram of the treatment for pressed pomace or
pomace from the three-phase process, where the pneumatically removal of the stone is done just
after drying. The stone is separated, in the majority of cases, using separating machines where the
air which flows against the pomace current pulls off the lighter pulp particles, leaving behind the
heavier and larger stone pieces. To separate the pulp from the air flow which carries it, cyclones are
used, which enable the air to be cleaned and emitted into the atmosphere. The pressed pomace and
pomace from the three-phase process must be directly subjected to a drying process immediately
after leaving the mills in order to prevent the rapid deterioration of the oil, particularly free acidity.
Figure 6: Block diagram of the oil production from pressed pomace or 3-phase pomace
Source: Production of pomace olive oil, By Pedro Sánchez Moral and M Victoria Ruiz Méndez
The other main difference between 3- phase pomace and pomace from the two-phase process lies in
the method of removing the stone. Figure 7 shows the block diagram corresponding to the
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11. treatment of two-phase pomace in order to obtain oil from this residue by using solvents. Stone
removal, as can be seen, is prior to drying and is carried out using mills with filters with
approximately 3mm spaces, which allow solids smaller than this size to pass through, expelling the
larger stone directly to the drying phase. This provides greater yield in the physical extraction,
reduced waste due to the metal parts which rub directly against the paste to be extracted and better
exploitation of the resulting by-products.
Figure 7: Block diagram of the oil production from 2-phase pomace
Figure 8: 2-phase production chain of olives to produce olive oil and fuel.
Source: Andalusian Energy Agency/VTT, EUBIONET2 IEE Project
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12. This phase is compulsory for the process of extraction of pomace oil with hexane process. This stage
consumes a great amount of energy and is under continuous research with the objective of
minimizing storage, residence times, energy costs, and to improving the quality of the obtained oil.
Normally, drying takes place in rotary heat dryers in which both the product (pomace) to be dried
and the hot drying gases are introduced at high temperatures (400 to 800°C). When the pomace
leaves the “trommel”, it should have the appropriate moisture content of approximately 8%.
The hot drying gases may come from a number of sources:
a) From the combustion of the residual exhausted olive pomace which is obtained after the
extraction with solvents of the dry fatty pomace. This is a more widely-used fuel, but it is also
the most polluting due to the emission of fine particles produced in the combustion. These
fine particles are swept away by the drying gases.
b) From the combustion of stones. This material may come either from the pomace paste itself
after the drying phase, or from the previous centrifugation before the physical extraction
phase. Due to the low ash content of these stones and the type of combustion, this material
is very efficient, in terms of heat, cost and environmental impact. These pieces of stones
have found important markets outside, with their exportation being very active. This demand
has increased its price, which is nowadays rather high. It should be noted that the olive
stones have several important advantages as a fuel:
• It is an annually renewable fuel with zero net contribution to the greenhouse effect.
• It is not subjected to market fluctuations because the material is produced in the
same plants where it is consumed. Thus, its price does not depend on the
international market for fossil fuels.
• Its combustion produces hot gases in a stable range of temperatures, which may
reach up to 800°C.
• With careful control of the combustion, the drying gases broadly comply with
European Legislation for gaseous pollutants.
c) The drying gases can also come from the exhausted gases from a turbine or gas engine in a
cogeneration process of electricity using natural gas. Obviously, this installation must be
close to the drying installation. In recent years, in order to increase profitability, some of
such cogeneration plants have made agreements with drying plants for selling them the
exhausted gases from their turbines or engines. Alternatively, they have created joint
enterprises for this business. From an environmental point of view, the use of these gases is
the cleanest system for drying pomace. However, they have two main disadvantages:
• Natural gas is a non-renewable fossil fuel, which is subject to huge market
fluctuations. Unexpected high prices for the gas can seriously affect the economic
viability of the plants.
• The hot gases produced never exceed 500°C. This circumstance makes the
enlargement of the drying facilities necessary. On the other hand, the low
temperature of the hot gases produces better quality chemically extracted oil.
The most important element of the drying process is the drying drum, a “trommel”, which consists of
a rotary cylinder supported on rolling strips. A toothed sprocket and two rollers control its rotation.
The rotation speed depends on the size of the cylinder. The cylinder may be a single or a double
passage drier. In the double passage driers, there are two concentric cylinders where the exterior
cylinder is supported by the interior one which, in turn, is supported on the rolling strips. There are a
series of blades in the interior of the inner cylinder which ensure that the pomace comes into contact
with the hot gas flow. They also impulse the pomace to move forward. Inside the drum, the hot
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13. gasses transfer their heat to the water contained in the olive pomace, which is evaporated. The
gasses and the steam are then put in contact with fresh material until them al cooled to below 100°C.
The gasses are evacuated from the drum, together with the produced steam, through cyclones, by an
induced draught fan. In addition, this device produces a light vacuum in the drum. Before being
emitted to the atmosphere these gases are passed through highly efficient cyclonic decanters which
remove the fine particle in suspension and make them suitable for emission.
The oil reflects the thermal aggression to which it is submitted by developing brown colours, due to
the alteration of the double bonds of the hydrocarbonate chains, and the formation of triglyceride
dimers and polymers. Drying also produces an increase in the concentration of oxidized compounds,
significantly higher K232 values, and oxidized triglycerides, which increase by 35%.
The strong drying process which was applied after the first appearance of the of two-phase pomace
caused the formation of an unusually high quantity of Polycyclic Aromatic Hydrocarbons (PAHs),
possibly due to the polymerization of the sugars at temperatures above 400°C and the direct effect
of combustion fumes on the material to be dried.
Depending on the degree of humidity at the entrance to the dryer, different drying processes can be
chosen. At present there are basically three types of drying:
Single stage direct drying.
This type of single stage dryer is ideal for pomace cake, 3-phase pomace and two-phase pomace
when this has previously passed through the dehydrated physical extraction stage in three phases.
This drying system can also be used for 2- phase pomace which does not need to be totally dried, as
required for chemical extraction, but will be used as fuel in cogeneration plants with biomass for
producing electricity.
Two stage direct drying.
This system is ideal for pomace from the three phase process which is to be dried at low
temperatures in order to improve the quality of the oils obtained in the chemical extraction step. It is
also highly suited to drying 2-phase olive pomace where the first drying stage reduces the humidity
to below 50% and the second further reduces it to around 10%, as required for a good chemical
extraction.
Direct drying in one stage with recirculation of dried pomace and prior mixing.
This system is highly advisable for two-phase pomace, when humidity, after stone removal and
physical extraction, is above 70%. The advantage of the procedure lies in the recirculation of part of
the dried pomace which leaves the dryer. This material is then mixed with damp olive pomace. The
mixture is, therefore assimilated to a pomace from the three-phase process with moisture content
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14. below 50% at the entrance to the dryer. The mixture then follows a similar process to that of pomace
coming from the 3-phase process, permitting an increase in dryer yield and production.
Chemical extraction with solvents is achieved in three phases: preparation of the fatty pulp,
extraction with hexane, desolventization of the extracted pulp and distillation of the fatty miscella.
However, after the drying process, the pomace requires certain preparation in order to maximize the
extraction efficiency. This is due to the fact that the dried pulp is not appropriate for direct
extraction. The main problem is related to the extremely low percolation. Therefore, the treatments
have the objective of preparing the pulp so that an increase in solvent penetration into the solid
layer could be obtained. This preparation will, therefore, facilitate oil extraction and the subsequent
desolventization and extractors’ unloading.
This preparation is made by granulating the pulp with machinery which is used, among other uses, in
the granulation of compound animal feeding stuffs. However, the fatty "pulp" is not easily granulated
due to its high oil content. To improve the conditions of the process, a suitably -sized mesh, (6 x 60
m/m) should be selected, and steam should be used in small quantities as compacting agent.
However, the use of large quantities of steam is detrimental because, then, the humidity content of
the granule will increase, and this will negatively affect the subsequent extraction.
In the former discontinuous extractors stones are still used to increase percolation. In general, if the
“granulated pulp” fractions and the stone fragments are going to be remixed for extraction, the
degree of compaction is less important than when only the granulated pulp fraction is extracted. In
this case, a certain level of compromise is required, enabling good percolation, desolventization and
discharging together with good drainage.
The advantage of submitting only the correctly granulated pulp to extraction is that the material
submitted to extraction is richer in fat. This, in turn, leads to solvent and energy savings as well as an
increase in distillation and extraction capacity because the granulated pulp contains, at least, 15%
less inert material than if it also contained stones. To achieve this, the pulp must be correctly
separated from the stone fragments, which should be sufficiently clean to ensure that the oil content
in stones is below 2 %.
The extraction with solvent (chemical extraction) process may be achieved in three different types of
extractors:
Discontinuous
These are extractors with simple contact equipment, where both the extraction and the distillation
of the resultant miscella are carried out in a discontinuous or batch format. They are no longer used
for economic, technical or safety reasons.
Semi-continuous
This is the most generalized system in the pomace oil sector. In this case, extraction is made through
the gradual enrichment of the miscella, using a system of multiple contacts with fixed layers. In other
words,, the fresh solvent is introduced into the tank where the solid is most drained in fat, flowing
through the different tanks and leaving the system through the most recently filled tank. This takes
place in discontinuous extractors but the distillation process is continuous. The system is made up of
a series of cylindrical extractors consisting of loading and discharging nozzles, hexane or miscella
inputs and steam input for the desolventization. There is also an air output. The extractor itself
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15. operates as an extractor and desolventizer. The extractors are loaded with fatty pomace in pellet
form from an upper hopper. The exhausted olive cake is discharged under pressure after
desolventization. As there are several extractors in the system, the unit is similar to a continuous
extractor in that, while one is filling up, others are at the washing with hexane or enriched miscella
stage and another is at the desolventization and discharge stage. There are a number of
manufacturers of semi continuous extractors differing only in size, in the number of extractors
installed and the continuous or semi-continuous distillation system installed. Other differences are
insignificant.
Continuous
In this system, the basic operation of solid-liquid extraction is carried out through multiple contacts
in counter current. The input and the solvent enter the extraction stage system at opposite ends.
With the system of multiple contacts against the flow, the solid is gradually impoverished in fats from
the first to the final stage, while the hexane miscella is gradually enriched from the last to the first
stage. The separation efficiency in this type of operation is greater than in the other forms of contact.
Most frequently used in the industry are continuous moving solid layer and percolation extractors.
The most notable differences between the different suppliers are in the system unit or the extraction
unit, which is made up of three basic sections: a) Extraction of oil, and b) Desolventization of pulp –
cooling, and, c) Distillation and recovery of solvent.
The efficiency of the best-known extractors (DE SMET, ROTOCEL, LURGI, CROWN, EX – TECHNIK) is
similar. The differences lie in other aspects, such as: construction quality, knowledge of the raw
material, technical service, operating and safety system facilities. The authorized solvent for the
extraction of fats is n-hexane. Its main advantages are selectivity, extraction power, almost zero
influence on the oil quality, physical properties, (latent heat of vaporization, boiling temperature
(60°C), steam tension) and chemical properties (low corrosive action).
Certainly, the extraction stages that have suffered major evolution and have been subjected to more
conceptual changes with respect to their basic design in recent years have been desolventization and
cooling. The reasons behind this pressure for new developments are demands for a decrease in
energy and hexane consumption, in addition to questions of safety in storage and transportation.
To remove the hexane retained in the solid, a desolventizer is used: it consists of a vertical column
made up of various cylindrical trays, each of which has a double base heated by steam. The solvent
simply evaporates in the heat into a dry atmosphere in the upper trays. A direct jet of steam is used
on the lower trays to remove the majority of the residual solvent from the exhausted olive cake. The
exhausted olive cake is usually dried and cooled on additional trays located below those used in the
desolventization process.
Distillation is the process which separates the components of the dissolution, exploiting the different
boiling points of the micelle components through the addition of sufficient heat for the component
with the lowest boiling point to distil.
Moreover, the addition of heat is combined with the action of a vacuum unit, allowing the
temperatures reached to be lower than would be necessary under atmospheric conditions, thus at
the same time managing to increase the energy performance of the process and its efficiency.
The purpose of the distillation of the miscella is to separate, by evaporation, the solvent from the oil
which remains liquid throughout the operation. The following points should be observed during the
process: a) the hexane should be recovered in order to reincorporate it into the process. b) The oil
should be free of hexane in order to prevent risk in the subsequent processing (storage and refining).
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16. The oil should be in the distillation unit for as short a time as possible, only as long as necessary for
the finished product to be lower than 150 ppm of hexane in oil.
Finally, hexane leaks should be avoided, not only for safety reasons due to the formation of explosive
atmospheres, but also because the concentration of hexane saturation in the air is high and increases
with temperature. Taking into consideration the fact that in Andalusia there is a large extraction
industry, every possible effort is made to ensure that measures are taken to reduce levels of Organic
Solvent consumption which currently stand at 6000 t/year compared to 1500 t/year under the
National Plan for the Reduction of Annual Emissions of VOCs.
The exploitation of pomace from an environmental point of view may be approached in a number of
ways, such as composting gasification, steam explosion treatment for obtaining hydroxytyrosol (or
the extraction of oils as presented above. The by-products generated are the stone, the fat-free solid
(or exhausted olive cake) and the residual wastewater.
The stone has very good properties as a fuel for heating, even for domestic installations. In addition
to the use as fuel, with the properties discussed above, stones are also used as abrasive material for
cleaning walls, for example, in the manufacturing of furfural, and for the manufacturing of active
carbon for the treatment of gases, water or other special applications.
The traditional use of exhausted olive pomace is as fuel in drying ovens or steam boilers because of
its thermal capacity. As mentioned above, the pomace oil extraction industry is a high energy
consumer, particularly at the pomace drying stage and during extraction with solvent. This fact,
together with the imbalance currently existing in Spain between the generation of and increasing
demand for electrical energy has led the sector to propose electrical cogeneration projects, such
that, by exploiting the calorific potential of the exhausted olive cake or the pomace (biomass), it is
possible to generate electrical energy and exploit the residual thermal energy for the stages of drying
and extraction with solvent. Similarly, the ashes produced in combustion are used to manufacture
manures, given their high soluble potassium content.
And finally, what is perhaps the newest use of olive mill wastewater, complex agro industries are
integrally exploiting the pomace with evaporators/concentrators capable of removing the olive mill
wastewater and exploiting the residual energy of the exhaust steam from electricity generating
turbines. The liquid generated in this process is used as cooling water in the capacitors and the
resulting concentrate is excellent for use in the manufacturing of manures and fertilizers, and for its
use as animal feed.
Table 2: Solid pomace oil by-products glossary
English pomace oil or olive kernel oil or olive pomace oil or crude pomace oil
Spanish orujo
Italian Olio di sansa
16

17. Greek πυρηνέλαιο
Croatian ulje komine maslina
Slovenian ostanek olja v oljčnih tropinah
dried pomace
English
(contains:pomace oil, pulp, pits, approx.10% humidity)
Spanish orujo deshidrato
Italian Sansa essiccata
Greek ξηρή ελαιοπυρήνα
Croatian suha komina maslina
Slovenian suhe oljčne tropine
(vsebnost: ostanek olja v oljčnih tropinah, meso ali pulpa (mezokarp),
koščice (endokarp), približno 8 % vlage)
exhausted pomace or depleted olive pomace or extracted olive
English pomace or exhausted (deoiled) olive cake
(contains: pulp, with or without pits, approx.10 % humidity)
Spanish orujillo
Italian Sansa esausta
Greek πυρηνόξυλο
Croatian iscrpljena komina masline
Slovenian Suhe tropine brez ostankov olja
(vsebnost: meso ali pulpa (mezokarp) z koščicami ali brez, približno 8
% vlage)
Harvesting of olive tree prunings takes place twice a year, once after harvesting of olives and a
second time at the end of spring. It is 100% manual operation and there is not any specific field trial
for cost estimation. Most of the amount of that type of biomass is burned at the roadside after
harvesting. Only high diameter branches are collected and used by inhabitants for domestic heating.
A little percentage of these quantities is provided to the wood market, but there is no specific
inventory in the area. Proximate analysis and energy content are shown in the following table. The
conversion of olive pellets for subsequent heating is being recently considered.
Table 3: Proximate analysis and energy content
17

18. 3. Olive oil and solid residues production in Spain, Italy, Greece,
Slovenia & Croatia
Most countries along the Mediterranean Sea produce olive oil in varying quantities. Spain, Italy, and
Greece represent more than three-fourths of the total olive oil output in the world. The largest
producer, Spain, supplies about one-third of the olive oil globally. The olive oil produced in Spain is
exported to nearly 100 countries. Italy is the second largest producer, with one-fourth of the world's
total production. Greece is the third largest producer, representing about one-fifth of the global total
production. With a consumption of about 20 quarts (19 litres) per person per year, Greeks are the
largest consumers of olive oil per capita in the world.
Figure 9: Olive figures by producing country
Source: TDC-Olive network
Spain has 2.5 million hectares of olive tress under cultivation, where the Andalusia region (No 1 in
the graph below) occupies the southern third of the peninsula and represents the most important
region, with about 1,158,959 ha area under production, it produces approximately 75% of the total
olive oil produced in Spain. The Andalusia Community is composed of eight provinces, from east to
west: Almería, Granada, Jaén, Córdoba, Málaga, Seville, Cádiz, and Huelva. The production of olive oil
is extended throughout the region, although it is concentrated primarily in the provinces of Jaén and
Córdoba. The province of Jaén, with approximately a quarter of the Spanish olive growing surface
area, represents about 40-45% of the Spanish olive oil production and nearly 15-20% of the world
production. It is interesting to note that the province of Jaén produces more olive oil than all of
Greece.
A high number of olive mills exist in Spain. The majority of the olive mills uses two-phase extraction
systems. Moreover, there are about 50 pomace oil extracting industries, only 20% of which are
Cooperative Societies. They are characterised by the absence of public undertakings and foreign
18

19. capital. These companies frequently work as extractors of pomace oil, thus prolonging the plants’
utilization period.
Figure 10: Spanish and Andalusia regions for olive growing
The Italian olive production covers approximately an area of 1.2 million ha, 80% of which is located
in southern Italy, where Puglia represents the most important region, with about 370.000 ha,
followed by Calabria (about 186.000 ha) and Sicily (about 60.000 ha). These three regions account for
more than 60 percent of Italian olive production. In the centre-north of Italy, the most important
regions for olive-tree production are Tuscany (about 108.000 ha), Lazio (about 87.000 ha), Campania
(about 81.000 ha), and Abruzzo (about 44.000 ha). The other Italian regions, except Piedmont and
Valle d’Aosta which have lesser olive production, cover a relatively small area: Sardinia (about 39.000
ha), Basilicata (about 31.000 ha), Umbria (about 28.000 ha), and Liguria (about 14.000 ha).
Figure 11: Distribution of olive cultivation areas in Italy with reference to climate
The main extraction systems in Italy are classic press, continuous centrifugation (two-phase and
three-phase options) and various mixed systems plus the percolation system, which is statistically
19

20. insignificant. Mixed systems can be defined as a whole group of possible combinations between the
first two types. For example, a roller crusher, typical of a traditional extraction, can substitute a disc
crusher or a hammer crusher in a continuous processing line. On the contrary, a disc crusher can be
placed before a press, normally after the mixer. Mixed systems can be sometimes a solution to
specific problems and should represent about 9% of all extraction systems, though they are often
identified with the continuous group. On national basis, the press and the continuous systems
seemed to equal each other (44.8% the first and 45.6% the second) until the end of the ’90 but today
things have changed and the centrifugal technology prevails on the traditional. Giving a close look to
the different regions, the continuous prevails remarkably in the south while the press system still
plays a major role in the centre-north of the country. No data are available on the percentage
incidence of two-phase and three-phase options within the continuous centrifugation category.
Greece devotes 60% of its cultivated land to olive growing. Greece holds the third place in world
olive production with more than 132 million trees, 3000 mills and 220 bottling companies which
produce approximately 350,000 tons of olive oil annually, out of which 82% is extra-virgin. About
30% per cent of Greek oil is produced in island Crete, 26% in Peloponissos (southern peninsula), 10%
in the Aegean island of Lesvos, 10% in the Ionian Islands (Adriatic Sea) and the remaining 24% is
scattered around the rest of the country. Olive groves represent 20.5% of total farmland and olive oil
production 14% of total plant production. In total approximately 1,200,000 hectares of land grow,
over 140,000,000 trees. Only one sixth of those trees are intended for table olive production.
Consumption of olive oil in Greece is the highest in the world, 23 kilos per capita, compared to the
E.U. average of 4.65 kilos, Spain’s 13.68 and Italy’s 12.41 (Source: International Olive Oil Council).
Figure 12: Distribution of olive cultivation in Greece
Figure 13: Olive Oil production in Greece
20

21. There are about 2,700 registered olive mills in Greece. The vast majority of the producers are small
scale land owners with 3.2-4.8 ha or less. The percentage of the olive mills depending on the
extraction method used is: 80% olive mills using the three-phase method, 18% use the classical
extraction method and a very small percentage use the two-phase or “ecological” two-phase
method. These percentages are not related to the production volumes.
There are near 520,000 olive growers, 50.5% of which are professional farmers. The large number of
olive growers in relation to the cultivated land reveals that there is no large scale industrialised olive
farming. This means that olive cultivation although systematic and much improved by the application
of recent technological developments and scientific progress still remains a “family” affair.20% of the
mills are cooperative ones while the rest belong to the private sector. Private mills are usually small
family operations. The average mill employs specialized personnel (1-2) and some 3-4 non specialized
labourers.
There are 35 olive pomace extraction plants in Greece with the largest number concentrated in Crete
(11) and the Peloponnese oil (10). Crude Olive Pomace Oil production comes to an average of 40,000
tons per year.
The average production of olive groves is particularly high, 360 kilos/ hectare when the
corresponding world average is 160Kg/ hectare. In certain areas such as Crete average production is
even higher going up to 500Kg/ hectare.
Table 4: Type of Olive solid residues
Type of solid residues Number Olive
Country Data virgin dried of olive- cultivation
leaves pruning pits
pomace pomace mills area (in ha)
National × × × × × 1722 2.509.677
Spain Regional
× × × × × 327 n.a
-Jaen-
National × × × × × 6000 1.200.000
Italy Regional
× × × × 180 13.500
-Liguria
National × × × × × 2500 1.125.000
Greece Regional
× × × × × 124 41.759
-Crete-
National × × × × 125 30.000
Croatia Regional
× × × × 18 3.600
-Istria -
National × × × 12 1470
Slovenia Regional
× × × 11 1420
-Istrian -
21

22. Table 5 Type of Olive oil production methods
Production methods used
Country Data 2 phase 3 phase
Traditional centrifugal centrifugal Other
system system
National 100%
Spain
-Jaen- 100%
National 37.5% 0.7% 47.5% Mixed (2.5) - 9,6 %. Other- 4,2 %
Italy
-Liguria- 52% 0,005% 30% Mixed (2.5) - 13 %. Other- 0,02%
National 5% 7% 88%
Greece
-Crete- 1% 5% 94%
National 43% 57% (2-phase and 3-phase)
Croatia
-Istria - 6% 63% 31%
National 33,3% 33,3% 33,3%
Slovenia
-Istrian - 36% 27% 36%
Table 6: Olive by-products
Quantity of (tn/year)
Country Data dry
produced virgin pit/stone
pomace
olive oil pomace
(with pits)
National 1.230.000 4.920.000 4.222.000 2.500.000
Spain
-Jaen- 544.555 2.058.221 1.770.378 1.050.000
National 721.418 n.a n.a n.a
Italy Not 3.240 potentially
-Liguria- 5.500 12.000
existing (27% of virgin pomace)
National 352.000 598.000 53.800-161.500
Greece
-Crete- 33.300 n.a 56.500 5.100-15.400
National 5.000 18.200 n.a 3.640
Croatia
-Istria - 810 3.509 n.a 710
National 275 1100 n.a 281
Slovenia
-Istrian - 255 1000 n.a 258
22

23. 4. Energy Exploitation Methods
Thermochemical processes are quite flexible in their current application and it can be stated that no
installation is similar to another. On the other hand, it is also true that installations are less bulky,
simpler and smaller compared to biochemical ones, whereas they have to use heat and/or gas
immediately. A customised exhaust filtering system must be used in order to avoid environmentally
harmful gases.
These thermochemical processes are: combustion, gasification, pyrolysis. These processes are the
simplest to apply and they are based upon the thermal transformation of the biomass when
subjected to high temperatures (300-1500 oC).
Figure 14: Overview of thermochemical processes.
Source: CRES – Centre for Renewable Energy Sources
The simplest way to exploit olive solid residues for energy production is by direct combustion. This
can take place however, only after olive pomace is dried. Combustion type of boilers gives off their
heat to radiators in exactly the same way as e.g. an oil-fired one. These boilers are mainly automatic;
since they are equipped with a silo containing olive dried pomace or exhausted pomace. A screw
feeder feeds the fuel simultaneously with the output demand of the dwelling. A typical example of
dried or exhausted pomace boilers is shown in figure 15
Advantageous features of these kinds of boilers are the high thermal efficiency, the low operation
cost and the need of non frequent cleaning. Despite an often simple construction, most of the
automatically fired boilers can achieve an efficiency of 80-90% and a CO emission of approximately
100 ppm. For some boilers, the figures are 92% and 20 ppm, respectively. An important condition for
achieving these good results is that the boiler efficiency during day-to-day operation is close to full
23

24. load. For automatic boilers, it is of great importance that the boiler nominal output (at full load) does
not exceed the maximum output demand in winter periods.
Figure 15: Mile Boiler P, Samaras, Greece
Figure 16:Energía de la Loma, S.A, Spain.
In terms of large scale plants utilizing olive husk, fluidized bed combustors proved to be a reliable
solution. In a fluidized-bed boiler, the fuel is fed into a solid bed, which has been fluidized, i.e., lifted
off a distribution plate by blowing air or gas through the plate. The amount of bed material is very
large in comparison to that of the fuel. Fluidized bed combustors have a variety of advantages,
including their simplicity of construction, their flexibility in accepting solid, liquid or gaseous fuels (in
combination and with variable characteristics), and their high combustion efficiency at a remarkably
24

25. low temperature 750-950 °C which minimizes thermal NOx generation and enhance the efficiency of
SO2 absorption from the products of combustion. Fluidized bed units are eminently suitable for
intermittent operation. The fluidized bed (FB) boilers provide good possibility to burn several
different fuels in the same boiler: coal, peat together with biomass, waste, recycled/recovered fuel
(REF) or refuse derived fuel (RDF). The combustion may take place under atmospheric or high
pressure either in bubbling (BFB) or circulating fluidized bed (CFB) boiler. FB boilers are well
controllable because of the fluid like bed and are reliable in operation. Furthermore, the ashes
produced after combustion can be used as additives in manufacture.
The gasification process can be broken down into three phases. The first phase is a process of
pyrolysis during which the biomass is converted by heat into char and volatile matter, such as steam,
methanol, acetic acids and tars. The second phase is an exothermic reaction in which part of the
carbon is oxidized to carbon dioxide. In the third phase, part of the carbon dioxide, the volatile
compounds and the steam are reduced to carbon monoxide, hydrogen and methane. This mixture of
gases diluted with nitrogen from the air and unreduced carbon dioxide is known as producer gas. If
the original feedstock is charcoal, then the gasification process becomes two-phased, and the
amount of tar produced is cut down. A composition of olive kernel gasification with air mixture is
shown in table 7.
Syngas (from “synthesis gas”) is the name given to a gas mixture that contains varying amounts of
carbon monoxide and hydrogen generated by the gasification of a carbon containing fuel to a
gaseous product with a heating value. Syngas consists primarily of carbon monoxide, carbon dioxide
and hydrogen and has less than half the energy density of natural gas. Syngas is combustible and
often used as a fuel source or as an intermediate for the production of other chemicals. Syngas for
use as a fuel is most often produced by gasification of coal or municipal waste. Four types of gasifier
are currently available for commercial use: countercurrent fixed bed, co-current fixed bed, fluidized
bed and entrained flow. Concerning olive dried pomace the fluidized bed reactors have already been
tested in terms of gasification.
Table 7: Gas mixture from olive kernel gasification with air
Component %
vv
CO 8.6
CO2 21.7
H2 5.4
CH 4 3
C2H4 1.6
C2H6 0.3
N2 59.46
Tar production in this case seems to be the major problem which this procedure faces, since it is
formed at a temperature of ≈800°C and disturbs the fluidization. Another problem to solve during
this process is the gas cleaning from tar and other suspended solids that come from fluidized bed or
chars. Ash-related problems including sintering, agglomeration, deposition, erosion and corrosion,
due to the low melting point ash of agroresidues consist a main obstacle for economical and viable
application of this conversion method for energy exploitation of the specific residues
25

26. Pyrolysis is the transformation of a compound or material into one or more substances by heat alone
(without oxidation); in other words thermal decomposition. Pyrolysis is somewhat similar to
vaporization, however, it is a relatively slow chemical process compared to the vaporization. The
temperature at which pyrolysis occurs depends on the fuel type and the heating rate. Coal for
example pyrolises at about 420oC. This temperature is below the spontaneous ignition temperature
of coal. Pyrolysis products consist of volatile gases, liquids (tar), and char generally. Products range
from lighter volatiles to heavier tars. The composition of the volatile matter (gases), products of
pyrolisis, depends also on the fuel. Pyrolysis of biomass is the thermal degradation of the material in
the absence of reacting gases, and occurs prior to or simultaneously with gasification reactions in a
gasifier. The liquid fraction of pyrolisised biomass consists of an insoluble viscous tar, and
pyroligneous acids (acetic acid, methanol, acetone, esters, aldehydes, and furfural). The distribution
of pyrolysis products varies depending on the feedstock composition, heating rate, temperature, and
pressure.
BIOCHEMICAL PROCESSES
This biochemical process consists in the treatment of the biomass introduced in a digester without
oxygen. After the biomass is introduced in the digester, a bacterial culture which is responsible for
the biogas production is added.
The anaerobic digestion is not the only option in the biological treatment of vegetable water, but is
the most widespread application of waste management for energy exploitation.
In this process, and after having homogenised the biomass that is going to be used, a mixture of
gases is obtained; the most important one is methane.
This process depends on the operation temperature. This operation parameter is fundamental in
order to obtain a good yield during the process. Dependence of this process on temperature is due to
the bacteria charged for the digestion, which acts at certain temperatures. The biogas produced is
responsible for the biomass agitation that takes place in the digester.
The obtained biogas in anaerobic digestion is obtained at the rate of 300 l/kg of dry material, with an
approximate calorific value of 5,500 Kcal/m3. The biogas composition is variable, but it is
predominantly formed of methane (55-65%) and carbon dioxide (35-45%) and in less proportion,
nitrogen (0-3%), hydrogen (0-1%), oxygen (0-1%) and hydrogen sulphide (tracks).
Anaerobic digestion is appropriate for high humidity biomass treatment, since a watery mean helps
the process. The fuel used will be the one which could be digested, depending on the fat material,
humidity, etc. Degasified two-phase pomace or “alperujo” can be energy used in a biomass direct
combustion thermoelectric power station.
Biogas can be used to generate heat and/or power, as well as treated as a transport fuel. The
digested residual, on the other hand, can be applied to the land-farm, instead of inorganic fertilizers
to improve soil fertility.
26

27. Hundreds of biogas applications have been established during the last two decades in Europe. The
biogas schemes applied include several technological solutions characterised by different digester
design, mixing process, filtering and various end uses.
Recent studies report the use of fermentation processes, as a way to obtain some interesting
industrial bio products (bio alcohols). During many years of applied research, attention has been paid
to the use of acid and enzymatic hydrolysis processes, in order to convert the lingo-cellulosic
residues into fermentable sugars to obtain ethanol, unicellular protein and several chemical
products.
Generally, most of the ligno-cellulosic residues, before being submitted to fermentation, have to be
submitted to a series of treatments, in order to optimise conditions. The complete sequence would
be:
• Pre-treatment by mechanical, physical or biological ways.
• Chemical or enzymatic hydrolysis.
• Hydrolysed conditioning.
• Fermentative processes: in co-culture and in a sequential way, throughout a
sacharification and simultaneous fermentation, by direct microbial conversion.
Currently many technologies are been developed in order to obtain liquid bio fuels (ethanol) from
lingo-cellulosic materials. Two main lingo-cellulosic materials sources exist in the olive oil sector: the
two-phase or “alperujo”, the three-phase pomace, and the olive grove pruning.
Research in three-phase pomace (which could be also extended to two-phase pomace or “alperujo”),
is done by separating the extracted pulp from the pit fragments, using temperatures between 190-
236 ºC and time periods between 120-240 seconds, has achieved a selective solvolysis of their main
compounds (lignin, hemi cellulose and cellulose). After a fast auto hydrolysis process (steam
explosion) the result is one soluble and another insoluble fragment.
The average heating value of dry pomace (with stones, low moisture content) is 3500-4000 kcal/kg
while for pits is 4000-4500 kcal/kg.
Table 8: Comparison of Heating Values of Olive by-products
Kcal/kg Spain Italy Greece Slovenia Croatia
Average heating value of dry pomace 3.500 –
3800 n.a. 4.216 n.a.
(with stones, low moisture) 4.000
Average heating value of virgin pomace 4.604 –
1800 1.800 n.a. 4219
( with pomace oil & pits, high moisture) 4.974
Average Heating value of pit/stone 4100 4.750 4.500 4.805 4.500
27

28. As we can see from the table 8 dry pomace and pits have a little less heating value as compared to
coal and a little more than wood. The energy potential than can be produced in each country is
depicted in table 9 below.
Table 9: Energy Potential from Olive by-products
Regional data
Spain Italy Greece Slovenia Croatia
MWh/year
~Jaen~ ~Liguria~ ~Crete~ ~Istria~ ~Istrian~
Energy potential of dry
231.700-
pomace(with stones, low 3.183.064 n.a. n.a. n.a.
267.400
moisture)
Energy potential of virgin
pomace ( with pomace oil & 4.307.906 25.000 4.587 17.206
pits, high moisture)
Energy potential of 26.780-
5.005.814 17.898,57 1.570 4.930
pit/stone 80.330
Table 10: Heating value of fossil fuels.
Fuel kcal/kg
1 Propane 11060
2 Butane 10940
3 LPG Mixture 10960
4 Diesel 10200
5 Fuel Oil 9600
6 Town Gas 9100
7 Coal 4498
8 Wood 3890
9 Natural Gas 8300 – 9700 kcal/m3
28

29. 6. The current supply chains and the end-uses of solid residues in each
region.
Province of Jaen
Jaén is the region with the main production of olive oil in Spain. Therefore the elimination of the
waste is very important in this process. To eliminate the residues, the olive-mills use a 2-phase
process: Olive pomace results from the extraction of olive oil through physical processes. With a
variable composition, it is mainly used as a raw material to extract the residual oil that remains in the
solid cake, prior to drying. A by-product designated as virgin pomace is obtained (humidity 62-70%)
that goes through a pitted machine, while the pit is mainly used as fuel to produce heat for thermal
use. Afterward, the virgin pomace goes through a process of drying and extraction and new by-
product results, designated dry pomace (humidity 10%). This by-product is mainly used as fuel to
produce electricity.
Figure 17: Supply chain chart
Both of the following two types of energetic applications of the olive grove solid residues are used in
Spain:
1. Thermal application: The biomass (olive solid residues) is used for the domestic sector, for
heating and sanitary hot water (SHW); also at industrial level for steam
process that comes from reused residues.
2. Electrical application: The technology used for obtaining electricity is the Rankine vapour cycle,
with generation or co-generation (heat + electricity) electrical plants
(steam conventional cycles). Another alternative is the electricity
generation through gasification processes.
The optimal electrical energy plant size is between 10 to 25 MW, the normal size is 25 MW so that it
is the most profitable.
Since some years ago, the Spanish Government began to promote thermal installations, but at the
beginning problems or barriers in energy exploitation were existed. In Spain the development of the
sector (of biomass installation) depended on two factors: Logistics & Distribution. Nowadays, a lot of
29

30. companies related to this sector create new distribution companies that supply biomass to all the
thermal installations.
Figure 18: Energy Production Potential from Biomass in Andalusia, Spain
The biomass industry remains underdeveloped in most industrialized countries. It supplies just three
per cent of Spain’s total electricity consumption, while in most industrialized countries the figure is
only one per cent. This is mainly due to lack of government support. Spanish biomass electricity
producers receive a premium on top of the normal price for electricity; however this premium is not
high enough to make biomass attractive to most investors so it is necessary to increase the
premiums for the biomass sector.
The implementation of the biomass electricity installations mainly depends on government policy. In
the years 2004-2007, the price of which was established by government, were not profitable for
implementation of olive-pomace installations. Finally in May 2007 the prices changed and
investments in the biomass sector helped to develop old projects and start new ones.
Potential facilitating factors, opportunities or barriers concerning the energy exploitation of olive
residues:
Biomass energy is increasingly popular as an alternative energy source for a variety of reasons:
• It is widely available in the region (Jaen).
• It can provide solutions to the climate change issue. The use of biomass does not increase
atmospheric levels of carbon dioxide, a primary greenhouse gas, because of the life-cycles of
plants and trees. The use of biomass can also decrease the amount of methane, another
greenhouse gas, which is emitted from decaying organic matter. Biomass is a renewable,
CO2 –neutral, fuel making it a valuable technology in efforts to reduce CO2 emissions in order
to curb global warning and climate change.
Spain’s olive-mills use a process of two phases to eliminate olive grove residues. This process is the
most appropriate for the extraction of olive oil: Olive residues can be composted, burned, use for
heating, for animal feed supplement or returned to the olive trees as mulch. The biomass or wastes
represent a cheap and technically feasible option to contribute to the reduction of the CO2
emissions.
30

31. • When utilizing the 2-phase system the fresh water consumption is reduced and also the
wastewater streams are eliminated.
• When the refined oil is extracted, the leftover fibrous material is primary lignin and cellulose.
This residue has still a high calorific value, and it can be composted, burned, use for heating,
for animal feed supplement or returned to the olive trees as mulch.
• The remaining leaves and stone can be pyrolysed under non-oxidative atmosphere or
gasification can take place with energy or alternative fuel production. It can be a solution to
the environmental problems that their land filling or combustion could create.
Liguria Region
Ligurian millers are craftsmen who work third party’s olives (imported olives) or their own’s (local
olives). The quantity of residues therefore depends on imports but it is not easily figured. Most
millers (over 60%) deliver pomace to pomace refineries: there are 2 small refineries in Liguria, but
most pomace is sent to Tuscany or Latium (where there are big refineries) that pays very little money
(more or less as much as the transport cost). Therefore, in Liguria there is only virgin pomace
potentially available. The other millers use pomace for agronomic use (10%) and the rest dispose of it
in another way. Liguria has a few pilot projects for alternative disposal of pomace (calcium addiction
to 2-phase pomace and then delivery to a biomass plant located in another region) but there are
environmental, procedural, legal or technical difficulties.
Olive pit separation from virgin pomace (pit recovery range amounts to 18-30%) seems to have the
highest potential in terms of heating value and price. At the moment pits are not purchasable in
shops, only some mills sell them directly. There is a small district heating system in Arnasco fuelled
with pit.
The following energy applications can use olive solid residues.
Anaerobic digestion: widely applied 40-50% of organic material is transformed into biogas which can
be used to generate electricity or thermal energy. The main drawback is the production of small
quantities of mud.
Gasification or combustion: to produce thermal energy or for cogeneration. Gasification allows using
virgin pomace which is transformed into syngas made of CO and H. In Italy syngas is used to generate
electricity in Calabria in a plant owned by Guascor. It produces 23MWt and 4.2 MWe. This kind of
plants has the advantages that pomace does not need to be dried and high performances, but they
need big quantities of pomace. The small quantities of pomace available in Liguria make it not
economically viable the use for this kind of plant application.
Direct combustion is motivated by the high heating value of the pomace which is 4.65 kWh/kg (the
pit has a heating value of 5.4 kWh/Kg and can be used as it is or to produce pellets). Unfortunately
for direct combustion it is needed to have dry pomace (according to law) but in Liguria there is only
virgin pomace. In Italy there exist biomass plants burning dry pomace together with wood chips and
other biomass.
• In Liguria there are cases of pit separation and consequent use it as domestic fuel. It is
also sold for the same aim.
31

32. • There is a case of use of calcium for pomace drying (UNIECO) at Lucchi & Guastalli mill
with subsequent use as fuel in biomass boilers (in Tuscany and Lombardy)
• There is a small (70 kW – 64 mt length) district heating plant running with olive nut in the
municipality of Arnasco. It heats up the church and the annexed building.
Figure 19: Pomace production in the region of Liguria divided in province areas below
Potential facilitating factors, opportunities or barriers concerning the energy exploitation of olive
residues:
• Green certificates for electrical energy
• Possibility to use heat for the many greenhouses in Liguria (flowers and farming)
• Funding opportunities for <1MW plants, coming from the Rural Development Plan 2007-
2013
• Mills have a low energy demand (for electricity in the range 16-70 kW and for heat around
40.000 kcal) therefore there is a need for different potential users.
• Presence of virgin pomace only and absence of regional pomace refineries therefore, need to
find a way to dry pomace in order to increase its heating value. Pelletising could be a
solution?
• Presence of many scattered small mills, therefore the transport factor becomes crucial in the
feasibility study. And transport in Liguria is particularly difficult due to orography
• Presence of different milling systems, which generate different kinds of pomace.
• Seasonality of residues.
• Different crop yield each year.
32

33. Chania Region
In Greece oil refineries buy virgin pomace from olive millers, extract pomace oil from virgin pomace
and they use the exhausted pomace either for their own energy needs or they sell it to the millers as
a heating fuel.
Dried or exhausted pomace is mainly used for heating purposes today on Crete for:
a) Houses
b) Greenhouses
c) Various small-sized industries
Today, exhausted pomace is used extensively in Crete for heat production; in the future, it has very
good prospects in power generation and/or heat and power cogeneration. Since a large proportion
of power in Crete is generated today from wind energy, it is likely that, in the future, biomass will
also contribute to the generation of green electricity
Figure 20: Supply chain chart
Its heating value is 3500-4000 Kcal/ kg (with a moisture content of 12%) and its price is
approximately 0,05 Euros/ kg; thus, it is a very attractive option as a fuel in comparison to oil. Dried
or exhausted pomace, however, has not yet found applications in power generation or cogeneration
of heat and power in Greece. Because it can be easily burnt and the combustion technology is well
known widely, it can be used as a solid fuel for power generation in the future. Presently, it is used in
houses and in greenhouses for space heating and hot water. Also, it is used in various industries for
drying purposes and/or for hot water heating. Greece exports small quantities to other European
countries each year, where dried or exhausted pomace is used as fuel. The required machinery for
the dried or exhausted pomace combustion is the boiler (including the burner), which is quite simple
to use and not expensive. These boilers are reliable and made locally.
Potential facilitating factors, opportunities or barriers concerning the energy exploitation of olive
residues:
33

34. Dried or exhausted pomace can be used for power generation or cogeneration of heat and power in
Crete, since it presents many advantages, such as:
• There is no need for harvesting of raw materials and transportation because it is produced in
the dried or exhausted pomace processing plants.
• Its moisture content is very low and its heating value is high.
• Its price is rather low in comparison with its heating value.
• The combustion technology is well known. Since it is granular, either fixed bed reactors or
fluidized bed reactors can be used.
• The generated power can be consumed either inside the plant or can be sent to the grid.
• The Greek Government offers good subsidies for investments in the field of Renewable
Energy Sources and, of course, in Biomass.
• The use of Biomass for power generation in Crete will reduce the CO2 emissions on the
island.
• In the case that such a plant should be created, various other solid agricultural residues can
be used together with the Olive Kernel Wood as raw materials.
• The creation of such a plant will help in power generation to and from small-decentralized
plants instead of larger centralized power plants that exist today in Crete.
• The sulphur content of dried or exhausted pomace is minimal.
• The efficiency of small-sized combustion plants is very low. The dried or exhausted pomace
processing plants operate seasonally. The produced heat from dried or exhausted pomace
should be used at the time that cogeneration of the heat and power is obtained (during its
operational period which is from November – April), or outside the plant for nearby heat-
requiring operations.
• Initially, the price of the dried or exhausted pomace may rise, due to an initial local deficit of
this Biomass source.
• Nowadays, fewer people work in agriculture. There are no incentives or opportunities to the
farmers to exploit olive residues in order to produce energy from them.
• People should be informed about the environmental and energy benefits of the olive
residues exploitation.
• Cretan’s admitted that they would like to exploit olive residues only if they had a financial
incentive.
• Most millers are at a senior age and lack knowledge about new possibilities and procedures
for olive residues exploitation.
Table 11: Relationship between Energy production & Energy consumption in ABEA olive industry
Total Energy
Total Energy
consumption (Biomass Energy production/
Year production (Biomass)
+Electric) Energy consumption
(1010 kcal)
(1010 kcal)
2001 4.7 2.72 1.73
2002 7.1 4.54 1.56
2003 5.7 3.84 1.48
34

35. Figure 21: The island of Crete
Figure 22: The region of Chania in the island of Crete
Table 12: Olive residues production in Crete.
Average heating Thermal Energy
olive residues Production (tn) 2003 Yearly change value production
(kcal/kg) (109kcal)
pits 103695 +8.553 4437 460
olive prunings 1550723 +57.670 3990 6187
Istria Region
35

36. In Slovene Istria, olive residues are usually (95.4 % of residues) composted and returned to the olive
groves as fertilizer. The composting of olive residues is integrated in the processing cycle of each oil
mill. After the 3-6 month composting period, the olive residues are spared on the surface as fertilizer,
returning nutrients to the soil. Only 4.6 % of olive residues are used for energy purposes, to generate
heat. This amount of residues produces enough green energy for heating two households. Until now
there is no any supply chain in Slovene Istria region. The end users of olive residues are now mainly
olive millers which use olive residues for composting. Two of them use olive residues for their private
energy purposes (heating). Both of them have around 60 tons of residues per year. If they would use
all of residues, it would be enough energy for heating at least 5 more households. Presently they are
heating only their own two households.
In figure 23 we can see the current supply chain & end-uses of residues in the region of Istrian.
Figure 23: Supply chain chart
In figure 24 are shown new capacities for local generation of electricity from Renewables. Planned
development of electricity generation from renewables does not include the energy exploitation of
olive residue, because of their small quantities.
Figure 24: RES production and planned new capacities
600 120
Small hydroelectric Small hydroelectric
station 110 station
500 Wind 100 Wind
90
Landfil gass Landfil gass
400 80
New capacities (MWh)
C apacities (M W h)
70 Purification plants
Purification plants
60
300 Biogass
Biogass 50
40 Wood
200 Wood
30
Solar
Solar 20
100
10 Olive residues
Olive residues
0
0 2010 2020
2006 year
36

37. In Slovenia olive residue is treated as waste and not as secondary product. They don’t use olive
residue for energy most of them are thrown away or use like fertilizer in olive fields.
Two best practices are identified in SLO Istria region, where olive miller uses olive residues mostly as
fuel for house heating and water heating.
A description of the above two mills follows:
1. The first is a 3-phase mill. After olive oil extraction, olive residues are too wet to burn
immediately and therefore disposed to the field/meadow behind the mill. Olive residues are left
to dry on the open space. Olive residues are mixed up/turned upside down several times to
speed up the drying process. After certain time they are collected and loaded into big wooden
containers and stored in the shed next to boiler room. Dried olive residues are used directly for
burning/combustion in the stove.
2. The second mill is a traditional one which in past they used to dispose olive residues back at
olive fields. Today they put them directly into a wooden container in order to dry them on open
air (but under roof) and use them only for energy purposes; production of heat for heating
private house and olive mill (ca. 250 m²).
Figure 25: Slovenia
Table 13: Olive mill data
Št. Mill name Name Surname Address ZC Town Technology
1 Oljarna TORKLA Beno Bajda Obrtna ulica 11 6310 Izola 2
2 Kocijančič Ido Kocjančič Frenkova 5 6276 Pobegi 2
3 Oljarna Torkla Šalara Franko Lisjak Obrtniška ulica 26a, Šalara 6000 Koper 2
4 Oljarna Torkla Krkavče Patricij Ternav Krkavče 97 6274 Šmarje 2,5
5 Oljarna Prinčič Prinčič Sv. Peter 18 6333 Sečovlje 2
6 Oljarna Krožera Fulvio Marzi Srgaši 40 6274 Šmarje 2,5
7 Oljarna Peroša Viktor Peroša Nova vas nad Dragonjo 8 6333 Sečovlje 3
8 Oljarna Čok Erika Čok Plavje 10 6281 Škofije traditional
9 Oljarna Oljka Evelin Toškan Vanganel 40 6000 Koper traditional
10 Oljarna Hrvatin Marinko Hrvatin Ul. 15 maja 10b 6000 Koper 2
37

38. Dobrovo v
11 Oljarna v Brdih Zadružna cesta 9 5212 2
Brdih
12 Oljarna Agapito Ivan Agapito Spodnje Škofije 15 6281 Škofije traditional
Waste water
Technology Olives processed (t) Olive oil production (t) Olive residues (t)
(t)
Traditional 305,8 61,2 122,3 183,45
2 phase 612,7 122,5 536,1 122,54
2,5 /3 phase 304,5 60,9 167,5 334,98
SUM 1223,0 244,6 825,9 640,97
Potential facilitating factors, opportunities or barriers concerning the energy exploitation of olive
residues:
• Based on upward trend of petrol prices on global markets and breakthrough of new
technologies, which use alternative / renewable sources of energy (for instance wood
biomass in Slovenia), the use of olive residues could be an alternative source of energy, in
first place for heating / production of heat and later for production of electricity.
• Since the quantity of olive residues in Slovenia is very small, the exploitation of these is not
suitable for larger energy plants, such as large heating stations or power plants. Their use is
most suitable for heating individual olive mills and private households, which are in direct
proximity of olive mills. These conclusions are based on calculation of ratio between yearly
energetic potential of olive residues, comparing to yearly energetic needs for energy in
Slovenia, which is very low.
• Usage of olive residues has very important impact on the environment. Figure 26 below
shows emission comparison between extra-light heating oil and olive residues (if they would
use all olive residues in Slovenia for heating).
Figure 26: emission comparison between extra-light heating oil and olive residues
ELKO Olive residues
2.500
2.000
1.500
kg
1.000
500
0
CO2 * 1000 SO2 NOx CxHy CO * 100 dust
In calculation of emissions, CO2 is not considered as the result of burning olive residues. Although
biomass releases carbon dioxide (CO2) into the atmosphere when combusted, the amount of CO2
released is equal to or less than the amount that the crop absorbs while growing (net emissions of
CO2 are zero).
38

39. Istrian region
The Istrian region (Croatia) has a long olive growing and oil producing tradition. According to the
latest official statistical data, a total of 600,000 olive trees are cultivated in Istria. Lately, traditional
extensive olive cultivation methods were replaced with intensive modern growing technology, and
olive growing has become attractive trend in agriculture. Moreover, the olive oil is one of the most
important typical food products in Istria. The olive oil market has recently improved especially since
the consumers pay more attention to both health and nutritional aspects of food.
Olive sector in Istrian Region (Croatia) is organized as follows: Olive producers use services of 18 olive
mills, mostly SME’s (Table 14, Figure 28). Olive mills produce olive oil and they are responsible for
olive mill waste management. The treatment of olive milling residues in the region encompasses
different treatments.
Table 14: Olive mill data
Št. Mill name Name Surname Address Zip code Town Technology
1 Agro Millo Valter Smilović Baredine 16 52460 Buje 2
2 Agrofin Boris Vekić Zambratija bb 52475 Savudrija 3
3 Al Torcio Tranquilio Beletić Ulica Torci 18 52466 Novigrad 2
4 Baiocco Andrej Đurić Galižana 8a 52216 Galižana 3
5 Brist d.o.o. Silvano Puhar Ušićevi dvori bb 52203 Medulin -
6 Kraljević – CUI Danijel Kraljević Farnežine 52470 Umag 2
7 Olea d’ oro Germano Kraicer Partizanski put bb 52100 Pula 3
8 Pastorvicchio Antonio Pastorvicchio Istarska 28 52215 Vodnjan 2
9 Pavlović Alojzije Pavlović Crveni vrh bb 52475 Savudrija -
Pilar – Stella
10 Maris Pilar family Stella Maris 52470 Umag 2
11 Torač Franko Vladišković Žbandaj bb 52440 Poreč 2
12 Babić Ante Babić Stancija Vineri bb 52466 Novigrad 3
13 Bronzi Sergio Černeka Bronzi 51 52420 Buzet 2
14 Brtonigla Šišot family Ronko bb 52474 Brtonigla Traditional
15 Pašutići Miljenko Prodan Pašutići bb 52420 Buzet 2
Agrolaguna
16 Agrolaguna d.o.o. M. Vlašića 34 52440 Poreč 2
17 Rovinjsko selo Miro Pokrajac Rovinjsko selo 50 52210 Rovinj 2
Agroprodukt Agroprodukt
18 d.o.o. d.o.o. Trgovačka 135 52215 Vodnjan 3
Olive mill owners manage waste waters mostly using physical treatment processes in their own
organization or by means of waste management companies. There are also some cases of OMWW
releasing in the environment. In Croatia, olive residues are treated as a waste and not as secondary
products. But, there are some cases of crude pomace treating as an organic fertilizer, usually placed
back to the olive fields (with or without composting). Some mills deposit pomace in the mill vicinity
39

40. or release it in the environment. There are a very few cases of using pomace for energy purposes (as
furnace fuel).
At the moment in Croatia there is a lack of successful energy exploitation of olive residues. Quantities
of residues are relatively low in Croatia but in the following period significant increasing could be
foreseen.
Figure 27: Supply chain chart
Potential facilitating factors, opportunities or barriers concerning the energy exploitation of olive
residues:
One of the main goals of Croatian energy development sector is to increase the use of renewable
energy sources.
The advantages of energy end-uses of these residues are:
• The improvement of olive waste management
• Not increase atmospheric levels of carbon dioxide, a primary greenhouse gas and at the
same time it can also decrease the amount of methane, another greenhouse gas, which is
emitted from decaying organic matter. Biomass is a renewable, CO2 –neutral, fuel making it
a valuable technology in efforts to reduce CO2 emissions in order to curb global warning and
climate change.
Figure 28: Location of olive mills in Istrian Region
40