Kolios N., Dalabakis P. & Arvanitis A. (2011), “Agricultural Applications in the Neo Erasmio Geothermal Field (Thrace, Northeastern Greece)”, Presentation at the GEOFAR European Conference “Innovative Solutions for Geothermal Energy Financing”, Athens, 17 - 18 March 2011

1. AGRICULTURAL APPLICATIONS
IN THE NEO ERASMIO
GEOTHERMAL FIELD
(THRACE, NORTHEASTERN
GREECE)
• Dr. Nikolaos Kolios
I.G.M.E., Regional Branch of Central Macedonia, Thessaloniki, Greece
• Dr. Paschalis Dalabakis
National Agricultural Research Foundation (N.AG.RE.F.), Sindos, Thessaloniki, Greece
• Dr. Apostolos Arvanitis
Division of Geothermal Energy, I.G.M.E., Olympic Village, Acharnae, Attica, Greece
GEOFAR EUROPEAN CONFERENCE
“INNOVATIVE SOLUTIONS FOR GEOTHERMAL ENERGY FINANCING”
Athens, March 17th-18th 2011

2. The area of Neo Erasmio lies at the
eastern edge of the Delta Nestos basin
(Thrace, Northeastern Greece).
At present 22 exploration boreholes
and 6 production wells have been drilled
by I.G.M.E. These resulted in defining a
low enthalpy geothermal field.
The proven low enthalpy geothermal field
of Neo Erasmio - Magana has an area of
16 km2. The probable field covers an area
of 24 km2.

3. Map of isothermal curves at the top of the geothermal reservoir
in the Neo Erasmio geothermal field
with the location of dehydration & asparagus treatment plant
The Neo Erasmio geothermal field is a
characteristic example of low enthalpy field
where the stratified aquifers are supplied by
an active fault system that affects the
substratum of the migmatic gneisses.
The geothermal reservoir is located at depths
between 200 and 440 m.
The vales of the geothermal gradient are very
high (up to 25oC/100 m).
The water temperatures range from 30 to
68oC.
The waters with T.D.S. values 0.57-10.1 g/l
are classified into 2 main categories:
Na-Cl & Na-HCO3CI waters
Location of dehydration &
asparagus treatment plant

4. EARLY SEASONEARLY SEASON ASPARAGUSASPARAGUS
PRODUCTION USING LOWPRODUCTION USING LOW
ENTHALPY GEOTHERMAL ENERGYENTHALPY GEOTHERMAL ENERGY
(February(February -- April)April)
USE OF GEOTHERMAL ENERGYUSE OF GEOTHERMAL ENERGY
FOR TOMATO DRYINGFOR TOMATO DRYING
(July(July -- September)September)
Company: GEOTHERMICA HELLAS LTD
MAIN ACTIVITIES:

5. PRODUCTION WELL
Depth: 350 m
Artesian Flow Rate : 40-45 m3/h
Optimum Flow Rate : 100 m3/h
T=60.2°C
Fluids are of very good quality
(Cond=1,080 μS/cm)
Thermal Energy Output: 3.5 MWth
Pumping Station
Pumping and
distribution of
geothermal waters
are driven by two
centrifugal pumps
(20 KW)

6. The use of geothermal water
for soil heating was developed
in Neo Erasmio for early season
asparagus production.
April 1997: First application of
heating asparagus plantations
with geothermal energy.
Soil heating usually starts in
mid January and early season
asparaguses are produced
between February and April,
having much higher market
prices than the in-season
produced asparaguses.
Schematic diagram of the soil heating system
Conveyance and distribution of geothermal waters is made through subsoil
networks of plastic (PVC) pipes of various diameters (3-5΄΄).
Following completion of their thermal cycle under the asparagus rows,
geothermal waters are rejected into a second subsoil pipe network.

7. This project was the first
geothermal application
worldwide for non-covered
intensive cultivations.
The soil heating is accomplished
by the direct flow of the geothermal
water through corrugated
polypropylene (PP) pipes with an
outside diameter of 28 mm, located
30-40 cm below the ground level.
The inlet water temperature in the
PP pipe system is 60oC and the
used water is rejected at a
temperature of 25-35oC.
Cross-section of a covered asparagus bed
Distribution network: 4,500 m of non insulated buried PVC and PE pipes
(diameter 3-5΄΄).
100,000 m of PP spiral pipes (1΄΄) buried under the asparagus crowns.

8. Depending on the heat energy
requirements, the selected period for
heating process initiation and the
expected period of starting harvest
process, a one, two or three-pipes
arrangement can be selected.
Soil heating can raise the soil
temperature by 5-15oC, depending
upon the ambient conditions
(temperature, moisture, winds and
precipitation), the water flow rate and
temperature, the presence of plastic foil
etc.
The base growth temperature is found to
be 10°C, while optimum production yields
have been reported to vary between 24.5°C
and 33°C.
The upper soil temperature limit for
productive response of the root storage
system shouldn’t exceed 35°C.
Two pipes (bidirectional) subsoil heating system
Bidirectional subsoil heating system with measurement instruments

9. Two types of early season asparagus
are produced in Neo Erasmio:
white and green asparaguses.
Without covering, asparagus spears
are frequently exposed to severe
frost conditions.
Low covering with plastic film is
indispensable in order to face such
unfavorable situations.
Green asparagus spears in Neo Erasmio
White asparagus spears in Neo Erasmio

10. Preparatory Works and Harvest of White Asparagus
in the Early Season
Covering ridges with black
plastic film ensures:
1) reduction of heat losses
2) protection of ridges from snow
and raindrops.
3) white color of asparagus spears
Asparagus spears are collected daily
by cutting them within the ridges at
23-25 cm length.
White asparagus plantation under black plastic film
covering
White asparagus plantation under black plastic film
covering

11. Preparatory Works and Harvest of Green Asparagus
in the Early Season
Protection of asparagus rows with
transparent plastic film ensures:
Photosynthesis process to be held in an
optimum level.
Serious reduction of heat losses from
radiation.
Optimum spears growth rates (15-
20cm/day) especially during sunny days.
Serious reduction of spears fibrous part
(quality improvement).
Green asparagus plantation under transparent
plastic film covering

12. Green asparagus plantations ready for winter production
Green asparagus emerges in
shorter times due to the absence
of earth ridges.
When spears grow in the open air,
they are more vulnerable against
bad weather conditions (frost,
cold rains, wind etc).
Emerged spears must be
protected by low height
transparent film laid on
metallic arches.
Harvest process is made daily
and regards spears longer
than 22 cm from surface.

13. Temperature Monitoring
T°C of soil, air and G-W outlet are measured
hourly using data loggers (thermistors).
Monitoring commences once the ridges are
prepared and covered by the black plastic film.
A very useful tool for modeling and control of
root storage system activation and for planning
production behavior of the plantation.
T°C (+12cm)
T°C (0cm)
T°C (-30cm)
To
C (air)
To
C (outlet)

14. The total cultivation area in N. Erasmio
is currently 10 ha (100 stremmas).
With 13,000-13,500 plants per hectare,
winter productions are maintained
high in the range of 6,000-8,000 kg/ha
(600-800 kg/stremma).
The heat energy requirements may vary
between 110 and 150 KWt/ha depending
on the desirable period to start harvest.
Early season asparaguses are produced
between February and April, having
much higher market prices that the in-
season produced asparaguses.

15. A tomato dehydration unit
has been operating since
2001 in Neo Erasmio.
The unit uses low salinity
geothermal water (which
during winter and spring is used
asparagus cultivation) to heat
atmospheric air to 55-58oC
through finned-tube air
heater coils.
The geothermal wellhead is
located about 1,400 m from
the drier and the geothermal
water is transmitted in non-
insulated PVC pipes having
diameter 110 mm.
Overview of dehydration plant in Neo Erasmio
Drying tunnel
With geothermal dehydration and
due to mild temperatures (55-60oC),
the product retains its nutrients
(including vitamins and lycopene, the
nutrient responsible for the deep-red
color of tomatoes) and flavors resulting
in high-quality dried tomatoes.

16. The complete tomato dehydration process can be divided into 3 stages:
(i) a pre-drying preparation step (pretreatment)
(ii) the drying step and
(iii) the post-drying treatment
General
schematic
diagram of
the geothermal
tomato drying
process

17. The pre-drying treatment
prepares the raw tomatoes
(Roma variety) for the
dehydration process.
This step involves initially
the selection of the tomatoes,
regarding their maturity and
soundness (40-70% of the
tomatoes are selected to
proceed for drying).
The sorting of the tomatoes
into two sizes is followed:
tomatoes > 90 g and
tomatoes of lower weight.
Pre-drying preparation
Sorting and halving

18. Pre-drying preparation
The raw tomatoes are then
- placed in crates,
- washed to remove dust, dirt,
plant parts etc,
- cut into two halves and
- placed into stainless steel
trays (mesh type, 100×50 cm2).
It is noted that blanching of
the raw tomatoes is not required
because of the richness of
tomatoes in antioxidants
substances.
Initial washing of tomatoes

19. Pre-drying preparation
Final washing of tomatoes
Tomatoes arranged on trays
Quality control of tomatoes
Tomatoes placed on trays ready to be dried

20. Drying
step
The drying step is carried out in a tunnel drier.
This drying system consists of the following main components:
(a) Finned-tube coil air-water heat exchanger (INTERKLIMA) for
heating the drying air
(b) Fan units
(c) Drying tunnel
(d) Measuring instruments

21. Drying step
Finned-tube coil air-water heat exchanger (INTERKLIMA) for heating the
drying air.
The ‘cold’ air enters the heat
exchanger at atmospheric
conditions (20-35oC) and leaves
the exchanger at an almost
constant temperature of 58oC.
The incoming geothermal water
has a temperature of 59oC,
while the temperature of the
water at the outlet is 51-53oC.
The mean water flow rate is
about 25 m3/h.
Air - geothermal water heat exchanger system
(red pipes: geothermal water inlet, blue pipes: geothermal water outlet)

22. Drying step
Fan units
The air flow rate in the tunnel is 20,000-25,000 m3/h and the superficial
air velocity in the tunnel (without the trays loaded with product) is 1.7 m/sec.
In the presence of the loaded trays that block partially the cross-section of
the tunnel the air velocity increases by 20-50%, depending on the location
inside the tunnel. The hot air, which is not recycled, is introduced into the
ovens in a continuous flow with a renewal rate of 700 times per hour.
Two fan units were installed
in the system, totaling a rated
power of 7 kW.

23. Drying step
Drying tunnel
The long rectangular
tunnel (width 1 m
and height 2 m)
is constructed of
polyurethane
aluminum panels.
The heated air flows
counter-currently
with regards to the
trays in the tunnel.
Heat exchanger system beside the drying tunnel
(red pipes: geothermal water inlet
blue pipes: geothermal water outlet)

24. Drying stepDrying tunnel
The tomato-loaded
trays are placed at
the entry of the
tunnel and they are
conveyed towards
the end (where the
hot air enters the
tunnel) in a semi-
continuous manner:
approximately every
45 min a series of
25 trays with dried
product are removed
and 25 trays loaded
with raw tomatoes
are inserted at the
entry and push the
upstream trays
toward the end.

25. Drying step
Drying tunnel
About 7 kg of raw
tomatoes are placed
on each tray.
The profile of
temperature with the
height of the tunnel
seems to be uniform,
as deduced for
temperature
measurements at
various heights and
from the uniformity
of the product drying
regardless of the
tray position.

26. Drying step
Measuring instruments
The inlet and outlet temperatures
of both air stream and geothermal
water are continuously monitored
using thermocouples.
The moisture content is
measured by weighing certain
marked trays at various locations
in the tunnel.

27. Effect of temperature on dehydration of tomato under constant air velocity of 1.0 m/sec
Rate of dehydration increases with increasing air temperature.
Rate of dehydration increases with increasing air velocity.

28. Effect of temperature and air velocity on dehydration time
The effect of air velocity on dehydration time decreases with increasing
air temperature.

29. Post-drying treatment
The post-dehydration step involves:
inspection and screening (the
removal of dehydrated pieces
of unwanted size, of foreign
materials etc) and
packaging in glass jars with olive
or sunflower oil, wine vinegar,
salt, garlic and various
herbs.
Picture of the packaged product in glass jars

30. Packaging
Vacuum packaging
Cold rooms for refrigeration of final packaged
products

31. Packaging
Products are packaged observing
the strictest hygiene conditions.
Throughout the production and
standardization procedures no salt
and no preservatives are added.

32. The solids contents of
the Roma tomatoes range
between 8 to 10% w/w
and the moisture content
of the final product is
estimated to be around
20%. Accordingly, the
weight of the processed
product reduced about
10-12 times after drying
(moisture content was
about 90% before drying
process). Final dried tomato product
The removal of the moisture content appears to be faster at the first half part
of the tunnel. The residence time of the product in the drier was 30-35 hours,
adjusted by trial-and-error to achieve the best quality product.

33. Advantages of dehydration of tomatoes at mild temperatures
Apart of the color preservation, mild drying conditions are supposed to
reduce the isomerization of lycopene.
Lycopene is the tomato nutrient responsible for the deep-red color of the
tomatoes and it has been suggested that lycopene’s antioxidant properties -
the highest among those of all the dietary carotenoids - may explain its
apparent ability to reduce an individual’s risk of prostate and certain other
cancers. It is reported that high drying temperatures lead to partial
degradation of the nutrient through isomerization and oxidation reactions.
Lycopene in fresh tomatoes is found as trans-isomer and isomerization
converts all trans-isomers to cisisomers, which are less effective antioxidants.
Dehydration at 50-57oC, i.e. at mild temperature
conditions and for relatively long times, appears
to retain the color and the aroma of the
tomatoes, in contrast to the tomatoes dried in
industrial driers (employing conventional fuels)
using air temperatures higher than temperature
80oC, shorter drying times and air recycling.

34. During
2001-2009
more
almost
85 tn
of high
quality
dried
tomatoes
have
been
produced.
Yearly production of dried tomatoes since 2001

35. The unit has been modified 5 years ago to double the drying capacity.
The unit can be easily modified to dehydrate many other vegetable products
(e.g. peppers, onions, mushrooms, olives and asparaguses) or fruits (figs,
apricots, apples etc.).
More than 1 ton of peppers, olives, figs, apples and apricots have been dried
so far during 2008-2009.
Recently, the curing of fresh olives (a process to render the olives edible by
removing its pungent taste) by drying has been investigated in the plant in
order to substitute the classic method of brine curing, which leaves residual
quantities of salt in the olives. The preliminary tests proved quite optimistic.
OlivesPeppersApples Asparaguses

36. Soil warming in connection with an arch-type
plastic cover of rows supported by frames
(low tunnel technology) can be also used for
protected vegetable cultivation aiming at
intensive growth and at shorter cultivation
periods.
One vegetable that can be grown economically
in this way is lettuce, especially in areas that
are cold at night.
Lettuce is generally grown at low light
intensities and at rather cool temperatures.
Lettuce plants prefer a daylight temperature
of 16-20ºC, whereas high temperatures often
results in spindly growth.
Arch-type plastic covered rows (low tunnels)
for intensive lettuce cultivation in N. Erasmio

37. The total geothermally
heated cultivation area
growing lettuce (different
varieties of lettuce) was
about 30 stremmas (3 ha).
The lettuce cultivation took
place during 2009-2010 in
two periods:
1st production (November-
December)
2nd production (March-April)
During the last two winters
> 2,000 kg of lettuce
were grown in Neo Erasmio
at reduced heating cost.
Subsoil heating in combination with low tunnel technology
for intensive lettuce cultivation in Neo Erasmio

38. Surface
heating in
combination
with low
tunnel
technology
for intensive
lettuce
cultivation
in Neo
Erasmio
Using low tunnel technology in combination with soil warming (subsoil or
surface heating) accomplished by circulating geothermal water through
PE or PP pipes at temperature of 40-60oC, early-season, intensive and
quality cultivation for growing various vegetables (lettuce, basil, rocket,
parsley, watermelons, beans, strawberries, etc) can be done.

39. Neo Erasmio: Panoramic view of (a) the dehydration plant and
(b) a geothermal heating system (surface heating) in combination
with low tunnel technology for intensive lettuce cultivation