INTERNATIONAL SUMMER SCHOOL on Direct Application of Geothermal

Under the auspice of the Division of Earth Sciences

GEOTHERMAL APPLICATIONS IN GREECE WITH EMPHASIS ON THE AEGEAN ISLANDS

N. Andritsos1, and M. Fytikas2

1Chemical Process Engineering Research Institute, P.O. Box 361, 57001, Thermi, Greece 2 Department of Geology, Aristotle University of Thessaloniki, GR 54006, Thessaloniki, Greece

Abstract land, Larderello-Italy and in the active vol- canic arc in the Aegean). On the other is a clean and hand, low-temperature regions are more reliable energy resource, capable of widespread and can be found in most partially contributing to the energy needs countries. There is an abundance of appli- of the world. Geothermal energy is cations of low- and moderate temperature available in most parts of Greece and, geothermal energy as listed in the Lindal especially, in many Aegean Islands, table (Lindal, 1970). In some cases, the although this potential has not so far geothermal water cannot be used directly, exploited adequately. This paper reviews because of the problems of scaling and/or the current status of utilisation activities in corrosion and a heat exchanger is used to Greece, with special emphasis placed on convey the heat to a working fluid. Low- the current and potential applications in temperature geothermal waters (typically the Aegean region. The possibilities of less than 40¼C) or geothermal effluents geothermal development in the Aegean from cascade use can be also exploited include, apart from the classical uses of using heat pumps. The utilisation of geo- and balneology, water thermal energy in principle employs known , fruit and vegetable dehy- technology, borrowed mainly from the oil dration and fish farming. Geothermal de- (e.g. drilling technology, scale and corro- salination appears to be an attractive way sion control), domestic and power sectors. to tackle part of the pressing problem of However, in some cases high contents of water shortage in several Aegean islands. dissolved solids and/or gases in the geo- 1. INTRODUCTION thermal fluid may cause additional tech- nical and environmental problems. Geothermal energy is known from Geothermal energy is considered a antiquity and has been used for centuries sustainable energy resource, capable of for bathing, cooking or even heating. How- providing a small, but significant, part of ever, large-scale geothermal utilisation world energy needs, especially on a local started almost 100 years ago. The geo- basis. The geothermal resources are enor- thermal uses are usually divided into two mous and improving technology will allow categories: in electrical uses, i.e. the pro- geothermal energy to be more active in duction of electrical power, and in direct the near future. Provided that it is pro-perly uses. The electrical uses are limited to implemented, geothermal energy is a sus- fluid temperatures above 100¼C; the utili- tainable resource and benign to the en- sation of fluids with temperatures lower vironment. In general, the use of geother- than 150ºC is only possible with a ‘binary” mal energy reduces emission of green- power plant. The high-temperature fluids house gases, since the emission of these for conventional electricity generation are gases from geothermal plants is an order confined in certain areas on earth asso- of magnitude lower than that from burning ciated with seismic and magmatic activity fossil fuels. The efficient removal of hydro- and young volcanism (e.g. California, Ice- gen sulphide from high-temperature steam

- 172 - and the reinjection of spent geothermal The pumping and heating methods of waters reduce significantly any potential the geothermal greenhouse and soil heat- negative environmental impact of geother- ing installations in Greece are illustrated in mal energy. Figures 1 and 2. Almost 80% of the heat- Greece is rich in geothermal energy. ing systems are of direct heat use by em- In particular, in the Aegean islands and ploying finned metallic tubes, plastic coastal areas there are abundant easily polyethylene ‘bags’ having diameter of accessible geothermal resources reaching ~0.2 m, placed on the ground and used almost 100¼C. Despite all these geo- only in one cultivating period, and corru- thermal resources, the degree of geother- gated polypropylene (PP) pipes of o.d. 28 mal energy utilisation in Greece is rather mm (buried, on ground or aerial). The PP poor. A review of the geothermal potential pipes last between 3 and 7 cultivating peri- of Greece can be found in Fytikas (1987) ods. Fan heaters are used when the water and Fytikas et al (2000). Fytikas (2002) temperature exceeds 60¼C; in all cases discusses in particular the origin and the this heating method is combined with characteristics of the geothermal resour- direct heating with PP pipes in a cas- ces in the Aegean region. Islands with low cading use. The use of plate heat ex- and moderate temperature geothermal re- changers is limited to about 11% of the sources include Milos, Santorini, Kimolos, total greenhouse area. Most geothermal Kos, Nisyros, Evia, Chios, Lesvos and waters for greenhouse heating are trans- Samothraki. ported over distances less than 500 m, The scope of this paper is two-fold: although a distance of 2500 m is reported first, to present the developments in in Geras, Lesvos. Almost 80% of trans- geothermal activities during the past three portation pipes are of PVC and are un- hears (a review of geothermal applications insulated. The vast majority (>70%) of the in 1999 in Greece can be found in Fytikas geothermal waters used in greenhouse et al., 2000), and, second, to examine the and soil heating has a temperature less potential uses of geothermal energy in the than 50¼C. The main reason for this is the Aegean islands. easiest handling and the better quality of the low temperature waters. Finally, 2. GEOTHERMAL APPLICATIONS IN reinjection of the geothermal waters is GREECE practiced only in 20% of the installations, but this percentage is increasing over the Greenhouse and soil heating are the last few years. major applications of geothermal energy in 2) Space heating. There are not any new Greece, although the last three years a developments in this sector. The use noteworthy diversification has been taken of geothermal energy for space heating is place. The developments in geothermal practiced only in a spa complex in application with emphasis on the Aegean Traianoupoli, Thrace and in several area and in comparison with those houses. presented in Fytikas et al (2000) can be 3) Aquaculture. Last winter the first use summarized as follows: of geothermal water in aquaculture 1) Greenhouse and soil heating. The de- was practiced in Porto Lagos for anti-frost velopments include the construction of protection/heating of artificial ponds. The 4.6 ha of new geothermal greenhouses in water came from two new production wells Polichnitos (Lesvos Island), Nea Apollonia in the South-East of Nea Kessani geo- and Nigrita. In addition, the greenhouse thermal field with a water temperature of unit in Nea Kessani started again ope- 38¼C. The installed thermal capacity of the ration last year after being dormant for installation is 2 MWt. The use of geo- several years. No major developments oc- thermal energy in this fish farm averted the curred in the area of soil heating aiming severe damage of the fish stock occurred (currently 12 ha) exclusively in the out-of- in other farms of the region during the season asparagus cultivation, although se- heavy frosts of last winter. veral small-scale projects are in the stage 4) Bathing and balneology. There is no of implementation. The combined area of any systematic study of the use of greenhouse and soil geothermal heating in geothermal energy in spas and bathing. A Greece is about 35 ha. conservative estimate (assuming the water leaving the bathing centers has a tem-

- 173 - perature of 30¼C) of the total thermal ca- in Kimolos, Samothraki, Sousaki, Methana pacity of the Greek spa resorts is 35 MWt, and Aedipsos and dissolved H2S in with a load factor of 0.15 (Fytikas et al, Sousaki and Methana) and, finally, the 2000). mild weather conditions of most islands 5) Agricultural drying. A tomato dehydra- rich with geothermal energy. tion unit has been established in N. The new uses or the expansion of Erasmio, 25 km south of Xanthi, and pro- current geothermal applications in the is- duced “sun-dried” tomatoes (Andritsos et land areas of Greece can be summarised al, 2002). The unit uses low cost geo- as follows: thermal water to heat atmospheric air to 1) Greenhouse and soil heating. There 55¡C in finned tube air heater coils. During are 7.5 ha of geothermal greenhouses its first year of operation 4 tn of high in Lesvos (Polychnitos and Geras), Milos quality dried tomatoes were produced. and Nisyros Islands with an installed 6) Water desalination. A geothermal de- capacity of ~8 MWt. Table 2 presents the salination plant has been completed greenhouse installations in the Aegean is- last year and tested in Kimolos Island. lands and in some coastal areas. Other in- More details can be found in the following formation presented in the table includes: chapter. greenhouse area, covering material (glass 7) Other direct uses. Another geothermal or plastic), heating method and percen- application practiced in Greece the tage of heating needs covered by geother- last 5 years involves the cultivation of spi- mal energy. Some problems encountered rulina (green-blue algae) in temperature- during operation and comments on the in- controlled ponds in Therma-Nigrita utilizing stallation are also included. The potential both the geothermal heat and the dis- of expanding greenhouse geothermal solved CO2 in the geothermal water. The heating is rather greater in the colder is- plant has a capacity of producing about lands of Northern Aegean (Lesvos, Chios 2000 kg of dried spiroulina. and Samothraki) as well as in Evia Island. 8) Geothermal Heat Pumps. Apart from In Lesvos Island, apart from the Poli- the three small heat pump systems chnitos geothermal field, other locations reported in Fytikas et al (2000) a new pro- for possible greenhouse and soil heating ject has been recently completed dealing are Argennos, Stipsi-Kalloni and Lisvori, with the heating and cooling of the Mining where a geothermal greenhouse was in and Electrical Engineering Building of the operation several years ago. National Technical University in Athens. 2. Space heating including DHE. District Table 1 presents the thermal capacity heating is rather difficult to be imple- of direct use systems in operation in mented in because of the way the houses Greece. The total installed thermal capaci- are built in Greece and of cultural reasons. ty in 2002 reached 69 MWt, up about 20% It has been suggested the use of geo- of the capacity reported for 1999 (Fytikas thermal energy for heating the district of et al, 2000). Sousaki, but the high content of the fluids in dissolved solids and gases (and espe- 3. POTENTIAL GEOTHERMAL cially H2S, Andritsos et al, 1994) makes APPLICATIONS IN THE the project rather costly. Individual houses AEGEAN ISLANDS and residential buildings can be heated by geothermal energy, especially in Northern The prospects of using geothermal Aegean. In an interesting example, the energy in a variety of applications in the heating needs of a house in Milos are wider region of Aegean Sea appears to be provided by the recirculation (by natural large due to the enormous geothermal convection) of ‘clean’ water through a potential of the region. Some drawbacks in “downhole heat exchanger” (DHE). The this development is the large discrepancy system consists of a metallic U-tube sub- in energy demand between summer (due merged in a swallow (20 m) geothermal to tourism) and winter, the relative isolati- well with 60¼C water, which is directly on of some islands that makes almost connected to house radiators. The DHE impossible the electricity transmission and eliminates the need of the geothermal fluid increases the transportation cost of green- disposal, which may be costly in small house products, the aggressiveness of so- systems. The method uses a system of me geothermal fluids (very saline waters pipes placed inside a well and a working

- 174 - fluid (usually ‘clean’ water) is pumped required. Cherry-tomato is almost the only through the pipes or allowed to circulate agricultural products that can be dehy- by natural convection to extract heat from drated in Cyclades islands (Santorini, the well water. The warm fluid then passes Milos). On the other hand, in the islands of through the house heating system. A Northern Aegean with richer crop pro- schematic of a simple DHE system is duction several crops can be dried: pep- presented in Figure 3. In general it can be pers, onions, apricots, figs and prunes. applied in cases where shallow wells (10- 6) Water desalination. Desalination tech- 50 m) contain hot water. These areas are nology has been available for deca- not many (e.g. Klamath Falls - USA, New des. Two are the most important techno- Zealand), but some Greek islands satisfy logies: thermal desalination and membra- this criterion (Milos, Kimolos, Santorini and ne desalination (mainly ). even Lesvos). The former is employed for large seawater 3) Aquaculture. The potential of using desalination, especially in countries and geothermal energy for fish farming industries with low fuel cost. Two refineries appears to be significant especially in the in Greece, in Aspropyrgos and Thessa- islands and the coastal areas of Northern loniki, apply this technology for brine water Aegean Sea and especially in Lesvos, desalination. In general, the thermal tech- where several fish farms are in operation. nologies for seawater desalination sys- 4) Bathing and balneology. Thermal spas tems are the multistage flash distillation and bathing centres operate at 56 (MSF) process and the multiple effect locations in Greece, almost half of which distillation (MED). Membrane technology are located in coastal or island areas. has been used widely during the recent Twelve spas are in operation in the years for small or large systems. In the Aegean islands. In the 90’s new bathing Aegean Sea there are numerous islands complexes were constructed or (e.g. in facing severe problems of water supply. Kyllini, Polichnitos, Kythnos), while others Water needs are partially covered by were expanded or renovated (e.g. Aedip- wells, small dams, collection of rain and sos, Sidirokastro). Certain swimming pools ship transportation. There are reverse os- are also heated by geothermal fluid mosis membrane desalination plants in (Aedipsos-Evia island, Aridea). There is several islands (e.g. Syros and Myconos), large potential in expanding the number of but several hotel businesses have also spa facilities in the Aegean region and in installed desalination units. The major using geothermal water to heat swimming drawback of both desalination technolo- pools. gies is the large energy requirements in 5) Agricultural drying. Drying or dehydra- the form of oil or electricity. The large tion of fruits and vegetable under the amounts of energy required for the de- sun is a traditional method for food pre- salination process is opening the way to servation in Greek islands. Low- and mo- the use of other energy resources, among derate temperature geothermal energy them geothermal energy, in the Greek can be efficiently used in fruit and Islands. vegetable dehydration and can be partially Two desalination projects have recent- substitute the traditional ‘sun-drying’ pro- ly commenced in the islands of Kimolos cess. Recently, it has been demonstrated and Milos. The Kimolos project has been in Thrace that geothermal energy can be completed last year and a detailed des- successfully used in drying tomatoes (An- cription can be found in Karytsas et al dritsos et al, 2002). Geothermal drying can (2002). The Milos project is implemented reduce some of the quality problems of the through a THERMIE programme and it is dried products associated sun-drying, like in the stage of well drilling. Both plants use dust and insect contamination and a MED process and utilise (or will utilise) enzymic activities. Geothermal water, with low enthalpy water (60-100oC) from shal- temperature as low as 55¼C, can be used low bores (50-200 m). In a MED geo- to heat atmospheric air in finned tube air thermal plant, a stream of geothermally heater coils. In case that the geothermal heated seawater flows through a low-pres- water is corrosive, as is usually the case sure vessel containing several chambers with the saline geothermal waters encoun- or stages, each operating at a slightly tered in the Aegean region, a second lower pressure than the previous one. As water-water heat exchanger may be the seawater enters each stage, a portion

- 175 - of it “flashes” into steam and is then installation of a binary ORC unit in the condensed to produce a pure distillate island of Lesvos. The construction of a product, which is pumped into the fresh- small binary unit is also scheduled for water tank. The concentrated brine construction to supply electricity for the remaining at the end of the process is Milos desalination plant. In a binary sys- rejected to the sea. A schematic of the tem the geothermal water is passed process is shown in Figure 1. through a heat exchanger, as shown in 7) Geothermal Heat Pumps. Recently a Figure 7, where its heat is transferred into geothermal heat pump (GHP) system a second (binary) liquid, such as iso- was installed in a municipal building in pentane, freon, ammonia or pentane, that Rhodes city (140 kW rated power), used boils at a lower temperature than water. for both heating and cooling. In addition, a When heated, the binary liquid flashes to heat pump (coupled with ground heat vapour, which, like steam, expands across storage uniformly distributed below the and spins the turbine blades. The vapour building basement) is in operation for is then recondensed to a liquid and is heating and cooling an office building of reused repeatedly. In this closed loop 6000 m2 by utilising the warm water (36¼C) cycle, there are no emissions to the air. of a nearby well. The heat pump rating is The potential for electrical generation 220 kW. The GHP are similar to ordinary using ORC units in several Aegean islands air-conditioners and heat pumps, but it (Milos, Nisyros, Lesvos and possibly utilises the ground instead of the outside Chios) is large and a preliminary estimate air to provide air-conditioning, heating and is ~20 MWe. The substitution of fossil fuel hot water. There are several types of GHP derived electric power by a “green” power systems. The most common type is the from ORC units, which may be located earth-coupled GHP (Figure 5), which uses away from the coast, will undoubtedly sealed vertical or horizontal pipes as heat have a positive impact on the environment exchanger through which water is circu- (reduction of CO2, NOx and CO emission), lated to transfer heat from the ground to will reduce the noise associated with con- the house. In the second type, the ventional power plants and avert possible groundwater type (Figure 6), the heat oil spill during oil shipment. pump extracts heat from the water pro- duced in a shallow well. The mild climatic 4. CONCLUDING REMARKS conditions prevailing in most island and coastal areas in Greece seem to make In conclusion, the geothermal potential rather uneconomical at a first glance the of Greece and especially of the Aegean investment in such units, although the Islands is big and the prospects are good, combination of the system with air-condi- although due to technical and economic tioning using seawater may turn out to be constraints the degree of exploitation is so attractive. far very limited. Most of these highly tou- 8) Electric Power generation. It is well ristic islands face a significant water shor- known that a double-flash 2 MWe tage, especially during summer time,with power plant was installed in 1985 in Milos possible negative impact on tourism. Geo- and operated intermittently till 1989, when thermal desalination appears to be an it was shut down due to technical attractive way to tackle part of the pressing problems and environmental protests due problem of water shortage in several Aegean islands (mainly in Milos, Nisyros, to H2S emission to the atmosphere. It is noted that by using common technology, Santorini, but also in Lesvos and Chios). the hydrogen sulphide could be efficiently Greenhouse and soil heating can be ex- abated from the geothermal gases. panded in Lesvos, the island with the most Because of the unfortunate fate of the geothermal greenhouses, and new geo- Milos electrical plant, a renewal of interest thermal greenhouses can be established for power generation in Milos and Nisiros in Nenita (Chios) and in Therma (Samo- in flash cycle units is not probable. On the thraki). Another interesting geothermal other hand, the installation of small binary application seems to be the geothermal Organic Rankine Cycle (ORC) units dehydration of some traditionally sun-dried cannot be excluded. During the past three vegetables and fruits, such as cherry- years the Public Power Corporation has tomatoes, apricots, figs and prunes. started exploratory work towards the “Green” electric power from modular

- 176 - binary ORC units can be produced not bilities of Geothermal Energy Development only for the needs of the desalination in the Aegean Islands Region, September plants, but also for the needs of the 5-7, 2002, Milos Island, Greece. Fytikas, M. Origin and characteristics of the islands in a environmentally benign way geothermal energy resources of the with the reduction of noise and the Aegean Island. To be presented at the Int. elimination of greenhouse gases and of Workshop on Possibilities of Geothermal the risk of oil spills. In all touristic places Energy Development in the Aegean there is also the possibility of using Islands Region, September 5-7, 2002, geothermal heat pumps (or in favourable Milos Island, Greece. areas downhole heat exchangers) for Fytikas, M, Andritsos, N, Karydakis, G, Kolios, heating in the winter, coupled with the N, Mendrinos, D, Papachristou, M. Geo- possibility of using seawater for air- thermal exploration and development acti- vities in Greece during 1995-1999. Proc. _f conditioning in the summer. Finally, the ‘World Geothermal Congress 2000’, (ed. extension of bathing period in almost all S. Rybach et al.), Kyushu-Tohoku, Japan, spa resorts is possible by using May 28 - June 10, 2000. geothermal fluids directly or indirectly for Fytikas, M. Geothermal situation in Greece. space heating and heating of open or Geothermics, 17, pp. 549-556, 1988. closed swimming pools. Karytsas, C., Alexandrou, V. and Boukis, I. The Kimolos geothermal desalination project. 6. REFERENCES To be presented at the Int. Workshop on Possibilities of Geothermal Energy Deve- Andritsos, N., A.J. Karabelas, Ch. Emannouel lopment in the Aegean Islands Region, and G. Karydakis. Characterization of September 5-7, 2002, Milos Island, fluids from low-enthalpy geothermal fields Greece. in Greece. Communications of Internatio- Lindal, B. Industrial and other applications of nal Symposium GEOTHERMICS 94 IN geothermal energy. In Geothermal EUROPE, Orléans, Febr.8-9, 1994. Éditi- Energy, UNESCO, Paris, 135-148, 1973. ons BRGM, Orléans, pp. 173-180, 1994. Lund, J.W., and Freeston, D.H. World-wide Andritsos, N. Dalampakis, P and Kolios, N. Use direct uses of geothermal energy 2000, of geothermal energy for tomato drying Ð Geothermics, 30, 29-68, 2001. possibilities in the Aegean islands. To be presented at the Int. Workshop on Possi-

Table 1. Summary of the geothermal direct uses in Greece in 2002.

Installed Annual Energy Use Capacity Use Capacity (TJ/yr = 1012 J/yr) Factor (MWt) Space Heating 1.15 13.3 0.37 Greenhouse Heating 27.8 265 0.32 Fish and Animal Farming 2.0 9.2 0.15 Agricultural Drying 0.15 1.0 0.20 Bathing and Swimming 35* 164* 0.15* Water Desalination 1.8 Other Uses 1 0.4 4.1 0.32 Geothermal Heat Pumps 1.0 7.2 0.25 TOTAL 69.3 464 0.23 * conservative estimate, 1 spirulina production

- 177 - Table 2. Geothermal greenhouses (and soil heating units) in the Aegean islands and coastal areas in 2002.

Covere Inlet/outlet Flow % cover of d area, Heating Location temper. rate Cultivation heating Problems-comments ha method (¡C) (L/s) needs (type) N. Erasmio, 7.7 (P) 60/30 17 Asparagus Soil heating 100 - no corrosion/scaling Xanthi with PP - small heat pump and house & pool heating Polichnitos, 6.0 (P) 80/35 17 Vegetables Fan coils+ 100 - corrosion problems Lesvos PP Geras, 0.4 (P) 38/25 6 Vegetables PP 100 - water transportation Lesvos 2500 m Milos 0.55 (P) 46/24 3 Vegetables PP 100 - limited water

N. Kessani, 0.2 (P), 72/40 15 Vegetables Fan coils + 100 - CaCO3 scale Xanthi 0.4 (G) PP problems, needs scale inhibitors Lisvori, 0.45 (P) 70/- - - Fan coils + - -out of operation, Lesvos PP corrosion problems Nisyros 0.05 (P) 50/- - - Plastic bags - -out of operation

heaters/PP;fan 11

Artesianflow; 10 (G) Glass covered, (P) plastic coveredh.e./PP;plate 11 , plastic bags, PP: direct heating using plastic bags

Submerg.;37 finned PP pipes;

Centrifugal;35 pipes; 9 55

plasticbags; 14 Line18 shaft; and polypropylene corrugated pipes, respectively.

Figure 2. Percentage distribution of the Figure 1. Percentage distribution of the heating systems of geothermal greenhouses pumping methods of geothermal fluids (total (including soil heating, total covered area 35 flow rate 250 kg/s). ha).

Re circ ulat i on p u mp

Hea t con vec t o rs

W ell

Pe r fo r a ti ons

Figure 3. Schematic of a simple DHE system.

- 178 - Figure 4. Schematic of a multiple effect distillation process. A: Vacuum chamber. B and C: inlet and outlet of cooling seawater. D: distillate product. E: feed seawater. F: brine outlet. G: heat recovery from the brine. H: condensate steam. J: dry steam.

Heat pumps

Boiler Floor heating

Heat pump Recirculation pump Heat exchanger

Downhole heat Submergible Reinjection exchanger pump Production well well

Figure 5. Schematic of a GHP system using a downhole heat exchanger Figure 6. Schematic of a GHP system (coaxial double plastic pipe). using underground water.

Geothermal 'binary fluid' fluid

Turbine Heat Generator exchanger

Reinjection Regenerator Figure 6. Schematic of the organic cycle power production process.

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