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INTERNATIONAL SUMMER SCHOOLon Direct Application of Geothermal Energy

Under the auspice of theDivision of Earth Sciences

THE KIMOLOS GEOTHERMAL DESALINATION PROJECT

C. Karytsas, V. Alexandrou and I. Boukis

Centre for Renewable Energy Sources (CRES), 19th km Marathonos Ave, 190.09, Pikermi

ABSTRACT

The Kimolos Geothermal DesalinationProject is concerned with the exploitationof the low enthalpy geothermal potential ofKimolos island for the production of freshwater through geothermal water desalina-tion, with the intent of achieving watersufficiency for the island.

Funding for the project was providedby the THERMIE EU-DGXVII programthrough contract No. GE-438-94-HE.

The island of Kimolos, faces pronoun-ced water scarcity problems, as otherAegean Sea islands also do. Never-theless, Kimolos Isl. is fortunate enough topossess a very significant source ofenvironmentally friendly energy which isrenewable and of low cost, that is the lowenthalpy geothermal energy potential.

The desalination method applied isthat of Multiple-Effect Distillation (MED)with distillation under vacuum in verticaltubes. The unit will use low enthalpy geo-thermal energy (with a wellhead tem-perature of approximately 61oC) as theheating and feed-water medium.

The unit, built during the period of1998-1999 produced, in average, 3.24m3/h of fresh water, when a geothermalwater flow-rate of 50 m3/h at a wellheadtemperature of 61oC was utilized. Thefresh water produced had a TotalDissolved Solid (TDS) content of less than10 ppm, according to the plant’s built-insalinity meter.

Several tests to measure and quantifythe differential production of the unit took-place during the monitoring period.Different geothermal water yields weretested against the fresh-water productionrate of the unit.

According to the results of this projectthe exploitation of low enthalpy geothermalenergy in the unit results in the substitutionof at least 500 TOE/year [1 TOE (TonnesOil Equivalent) = 8,000,000 kcal/h].

Our intention in this demonstrativeproject is to demonstrate the technology ofproducing clear fresh desalinated waterfrom low enthalpy geothermal resourceson Kimolos Isl. Further-on, we investigatethe technical and financial feasibility forapplying and disseminating such innova-tive desalination schemes in other regionsof Greece and the EU with similarrenewable energy sources potential.

1. OBJECTIVES

The main objective of this project is toexploit part of the low enthalpy geothermalpotential of Kimolos island for theproduction of fresh water through sea-water or geothermal water desalination,with the intent of achieving watersufficiency for Kimolos Island inducingfurther agricultural, industrial and touristdevelopment on the island.

The desalination method applied is theMultiple-effect Distillation (MED) methodwith distillation under vacuum in verticaltubes. The unit will use low enthalpygeothermal energy as the heating andfeed-water medium.

Renewable Energy Source driven seawater desalination units, such as thosedriven by low enthalpy geothermal energy,guarantee friendly to the environment, costeffective and energy efficient production ofdesalinated water in regions with severewater supply problems (such as several ofthe Aegean Islands), which neverthelessare fortunate enough to have renewable

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energy resources at first hand forimmediate exploitation.

The island of Kimolos, similarily tonumerous other Aegean Sea islands,faces pronounced water scarcity prob-lems. On Kimolos Isl. drinking water isavailable through transportation by watertankers from Peireus, which lies somesixty nautical miles away and costs morethan 5,28 € per cubic meter or in the formof bottled water at 0,44 € per 1.5 litres.Water for sanitary purposes originatesfrom rain collector tanks gathered from thewater rained down on the roof of thehouses. Rain in the Western Cyclades isvery scarce (with a rainfall less than 450mm rain annually).

Nevertheless, Kimolos Isl., like otherislands or regions facing similar waterscarcity problems, is fortunate enough topossess a very significant source ofenvironmentally friendly energy which isrenewable and of low cost, that is the lowenthalpy geothermal energy potential.With this desalination unit we intend notonly to minimize this water scarcityproblem but also to induce developmenton the island through water sufficiency.

Our intention in this demonstrativeproject is to demonstrate the technology ofprodu-cing clear fresh desalinated waterfrom geothermal water on Kimolos Isl. Inparal-lel we investigate the technical andfinan-cial feasibility for further applying anddisseminating such innovative desalinationschemes in other regions of Greece andthe EU.

2. GEOLOGICAL AND GEOTHERMAL

BACKGROUND

The Island of Kimolos belongs to theMilos Island Volcanic Complex, which ispart of the Active Aegean Volcanic Arc.High, Medium and Low Enthalpy geother-mal resources have been detected in theMilos Island Volcanic Complex with tem-peratures rising on Milos Island as high as330oC at a depth of 1100m and withnumerous thermal springs of up to 90oCon Milos and Kimolos Isl (see Map 1).

The island of Kimolos, with a surfacearea of 36 km2 is located in the northernpart of the previously mentioned MilosIsland Volcanic Complex (Fytikas et al.,1984). The volcanic activity of the islandwas manifested before the lower Pleisto-

cene being presently exhausted, the lastvolcanic eruptive cycle taking place, on theeast side of the island, just 900,000 yearsago.

On the Northern part of Kimolos islandthe geological, geophysical, geothermaland hydrogeological data all lead to theassumption that a significant reservoir liesat depths of 100 to 300 m within volcano-clastic and volcanic (lavas) rocks, beingsupplied from a system of deep faults.

A NE-SW tectonic lineament withnumerous thermal springs aligned on itwith temperatures of up to 65oC seems tocontinue to be active. Most of the volcaniceruptive activity has been affected by this,still active, lineament (Fytikas and Vougi-oukalakis, 1992). The existence of thistectonic lineament together with an olderone, with a NW-SE direction, allow theflow of sea-water parallel to these sys-tems, cold-water descending and hotwa-ter ascending. According to geological,geochemical, geophysical, volcanologicaland geothermal data (Fytikas, 1995) it isdetermined that the geothermal resourceson Kimolos Isl. are formed by the entrap-ment of ascending hot sea-water in porousvolcanoclastic aquifers. The main hydro-geological characteristic is the existence ofat least 6 aquifers isolated by imperme-able pyroclastic material. These aquifersare characterized by very low resistivityvalues when geoelectrical surveying isperformed (Tsokas, 1985 and Thanas-oulas and Tsokas, 1985). The aquifers atthe depth of 20-30 m have been found tohave temperatures of 40 to 45oC, atdepths of 50m temperatures of over 59oCand at depths of 200m bottom-holetemperatures of at least 61oC.

At greater depths (deeper than 800m),especially in the southeastern side of theisland, temperatures may rise over 100oCor even higher.

The island is covered with a plentitudeof rocks, products of extensive hydro-thermal alterations, in fact one of thelargest and of finest quality bentonite inthe world lies just 2 Km from the region ofPrassa (NNE region of the island).

Shallow exploratory boreholes (atleast 10) drilled to depths of 40m havegiven temperatures of up to 35oC.

Two boreholes were drilled in the regi-on of Prassa . The boreholes were named

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PRASSA-1 and PRASSA-2. The technicalspecifications of the two boreholes are

given in the following Table 2.1.

Table 2.1: Technical specifications of the Prassa-1 and Prassa-2 boreholes

PRASSA-1 PRASSA-2

Total Depth 188 m 238 m

Diameter of Piping 8 5/8 ” 8 5/8 ”

Piezometer 100 m 115 m

Total Thickness of Aquifers 60 m 54 m

Hydraulic Conductivity (k) 2.2 10-6 m/sec 0.9 10-6 m/sec

Transmissivity (T) from therecovery pumping test

0.640 m2/h 0.289 m2/h

Number of Aquifers 6 3

Well head Temperature 61.5 oC 49.2 oC

Optimal Flow-rate 80 m3/h 30 m3/h

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The chemical composition of the geo-thermal water of PRASSA-1 and PRAS-SA-2 boreholes based on analyses per-formed by IGMR on Oct. 1995 (537/13-10-95) is provided in the following Table 2.2.

A remarkable point of these analysesis the similarity of the geothermal watercomposition among the thermal springs,CRES-1 exploratory borehole, PRASSA-1and PRASSA-2 and sea-water, the onlydifference being a slightly higher CO2, Caand SO4 content of the geothermal water.This is probably due to dissolution of car-bonate rocks in the subsurface, provingthat the previously mentioned mechanismis responsible for the formation of thegeothermal resources on this island.

From all chemical analyses performedon the low enthalpy geothermal watersamples from Kimolos Isl. we obtain reser-voir temperature of approx. 64 - 78oC fromthe SiO2 geothermometer, 108-114oC fromthe Na/K geothermometer and 169 to228oC from the Na-K-Ca geothermometer.

Two very important facts concerningthe chemical composition of the geother-mal water of PRASSA-1 are pointed out:

a) The geothermal water has acomposition very similar to that of sea-water, with a slightly increased content ofCO2, Ca and SO4 and a decreased contentof Na and Cl.

b) Harmful elements such as As, Pb, Znetc. are almost not detectable andtherefore, since the chemical compositionof the geothermal water permits its use fordesalination.

Based on the previously mentioned re-sults it was further decided to proceed andcarry-on with our project by utilizing thegeothermal energy provided from thePRASSA-1 borehole, due to it’s suitablewell-head temperature, hydraulic charac-teristics and chemical composition.

The second borehole PRASSA-2 al-though perfect in chemical compositionhas been abandoned due to its poor hyd-raulic characteristics and rather low tem-perature. On April 1996, Geotech Ltd.proceeded with further pump tests on thePRASSA-2 borehole which lead to similarconclusions as previously.

Table 2.2: The chemical composition (in ppm [mg/l]) of the liquid phase of the geothermalwaters of boreholes PRASSA-1 and PRASSA-2 (Samples 1c and 2c analysed by IGMR1995)

Element PRASSA-1c PRASSA-2c

Ca 1,066.1 1,042.1

Mg 1,240.3 1,230.6

K 391.0 391.0

Fe 1.3 0.9

Na 10,345.5 10,115.6

Mn 0.19 0.18

Zn 1.9 1.9

Pb <0.05 <0.05

Cd <0.005 <0.005

Ba 0.05 0.03

Ni 0.02 0.12

As <0.010 <0.010

Hg <0.001 <0.001

Cr <0.05 <0.05

Al 0.275 0.080

Li 0.40 0.40

Sr 14.0 14.0

SiO2 35.0 28.0

CO2 128.0 110.0

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HCO3- 108.6 109.8

Cl- 19,217.2 18,578.9

SO42- 3,563.8 3,568.6

NO3- <0.5 <0.5

NH4+ <0.1 <0.1

F 0.75 0.60

B 2.75 2.75

pH 6.80 6.80

Conductivity (_S/cm) 47,986 45,965

Another scenario examined the use ofPRASSA-2 as a reinjection borehole if thehydraulic properties permit it, which ishowever doubtful due to high bento-nitization rate of this particular borehole.

The final design of the GeothermalEnergy Desalination Plant, the sizing andorder of equipment, the manufacturing,assembly/installation have all been basedon the following characteristics andfeatures:

• The well-head temperature level of thegeothermal water

• The chemical composition and, hence,the possibility to desalinate the verysame geothermal water

• The geothermal water quantity andhydraulic parameters of the aquifers

• The water needs of the island

• The technical and financial feasibility

• The possibility of future extension ofthe unit’s production capability.

A very important factor that had adirect effect on the size and productivity ofour unit water, and consequently on theoptimal and final design of the unit, wasthe level of the well-head temperature ofthe geothermal water.

Nevertheless, since the well-headtemperatures from PRASSA-1 finally isbetween

58 and 62oC the direct consequencehas been an inevitable drop in the ex-pected water production rate. As a result,the utilization of desalination systemslarger than 2-effect were strictly prohibiteddue to the limits in the temperature gradi-ent between effects. Hence, a smaller 2-effect desalination unit (namely D-TU-2-1200 – ALFA LAVAL DESALT) wasconsidered, manufactured and contributed

to the Kimolos project, instead of the origi-nally planned 3-effect desalination unit.

Another significant point concerningthe design of the unit is the slight differ-ence among the geothermal water com-position and that of the seawater, espe-cially Ca and SO4 content. This, accordingto the desalination unit provider ALFALAVAL, can be easily overcome by incre-asing the anti-scalant dosage versus thetypical figures or even through the blen-ding of two suitable anti-scalants insteadof one.

Moreover, since no corrosive substan-ces or gases, such as H2S, have beendetected in the geothermal water, it isobvious that it can be freely desalinated.

Another important parameter that af-fected the optimal-final design of the plantand assisted us to proceed with the D-TU-2-1200 ALFA LAVAL unit, is that in case ofan increase of the well-head temperatureduring the development of the geothermalfield (which is according to the world-wideaccepted geothermal field usual practice)we may expect a 3-4% rise of fresh-waterproductivity per 1oC increase of well-headtemperature.

Furthermore, it may be possible in thenear future to proceed with the drilling of athird borehole, PRASSA-3, in the closevicinity of PRASSA-1 to deeper aquiferswithin the Lavas (depths larger than 160m)and to depths of 250-300m whichaccording to the geological-geothermalfacts, may be able to give over 68oC withflow-rates of over 100 m3/h, resulting to anincrease of the D-TU-2-1200 fresh-waterproduction over 5 m3/h. Moreover,according to a probable future scenario, ifwell-head temperatures are over 70oC, itwould be feasible (and this has actuallybeen taken into account) to increase the

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size of the unit to a 3-effect by just addingand properly adjusting a third effect to theexisting 2-effect D-TU-2-1200 unit,increasing the production capacity offresh-water of the plant to over 9 m3/h.

Another important issue, taken intoconsideration during the design phase ofthe desalination unit are the actual waterneeds of the island. It should be noted thatduring winter time the permanentpopulation of the island is approximately800 inhabitants, with water needs ofapproximately 40 to 50 m3/day, whereasduring the summer time the populationand water needs doubles to 1,600inhabitants and 100 to 120 m3/day. Thisresults to a total water demand, for bothdrinking and sanitary purposes, of 22,000m3/y. From this quantity 6,500 m3/y or29,5% are covered by rain-water manage-ment practices and from bottled-water,leaving a water deficit of approximately15,500 m3/y or 42.6 m3 per day whichequals to a production rate of 3.55 m3/h in12 hours per day.

The desalination unit has beendesigned to operate at this time stage insuch a manner to produce with an averagerate of approximately 75 m3/day of freshwater through the pumping of 60 m3/h ofgeothermal water with a well headtemperature of approximately 60 oC, seealso Table 4.1.

Nevertheless, as already explained,this production capacity may be easilychanged by simply decreasing or increa-sing the borehole pumping capacity from50 m3/h to 100 m3/h.

With this planning we achieve wholeavailability of the fresh-water productionand provide for future modest increase ofthe water needs or giving solution todraught problems. The cost of the produ-ced fresh-water, since there is provisionfor subsidy of up to 50% (or even higher),according to the Greek Law for theoperational costs of desalination unitsoperated by municipalities, is estimated tobe 1,03 €/m3 for the case of a 90 m3/dayunit, when subsidy to the initial investmentof 80% is achieved then the price of thewater produced falls down to 0,94 €/m3).

3. DISTILLATION OPERATION PRINCIPLE

The proposed MED-Vertical Tubedistillation method is based on the multi-effect distillation rising film principle at lowevaporation temperatures (less than 70°C-ALFA LAVAL, 1993), due to the reducedpressure (almost vacuum). The rising filmprinciple takes advantage of the fact thatthe inner tube surfaces are alwayscovered with a thin film of feed water thatprevents scale formation. The workingprinciple is as follows:

The vapor forms a column around thetube center which presses the feed wateragainst the tube surface ensuring acontinuous thin film of water on the tubesurfaces hereby eliminating dry spotswhere scale may deposit.

A controlled amount of sea feed wateris led into the bottom of each effect andinto the tubes in the heat exchanger,where the low enthalpy geothermal energyin the form of hot water of less than 70 °C,as the heating medium, heats it up (seeFigure 1).

Part of the sea-water is evaporatedunder vacuum, which is created by meansof water ejectors connected to each effect.The vacuum makes it possible to lower theboiling temperature and thereby minimi-zing the amount of energy necessary forevaporating the feed water, andfurthermore the low boiling temperatureprevents deposits of scale inside thetubes.

The vapour generated in the first ef-fect passes a separation compartmentwhere the remaining feed water dropletsare separated from the vapour and areextracted with the brine. The separatedvapour leaves the first effect and flowsthrough the vapour connection pipe to theheat exchanger in the second effect, andthe vapour is now used as the heatingmedium for the second effect. Brineextracted from the first effect is mixed withsea feed water and is brought toevaporation by means of the heat from thevapour generated in the first effect. Thisprocess is repeated in the second, third,fourth etc., when these occur.

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The vapor used for heating of the second,third, fourth etc. effects condenses on theoutside of the heat exchanger tubes, andflows through the flash pipe in the bottomof the heat exchanger into the flash tank.Separated vapour from the third effect isled into the condenser where it iscondensed on the outside of the con-denser tubes in which sea cooling water isflowing. The condensate flow down intothe flash tank at the bottom of thecondenser. The condensate is extractedfrom the flash tank by the freshwater pumpand is pumped into the fresh-water tank.

According to the GE/438/94/HE contractthe desalination unit can be designed insuch an innovative way so that in the casethat the geothermal water chemical com-position allows it, it will be feasible todesalinate the low enthalpy geothermalwater itself, instead of the sea-water. Thiswill result in an increase of the energyefficiency of the unit simultaneously dec-reasing the required capital investmentsand operational costs (no heat exchan-gers, no sea-water preheating etc.).

4. THE DESALINATION PLANT

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The desalination plant has been ins-talled at the Prassa site in an engine-roomerected for the purposes of the projectduring the winter 1999 and the spring2000. The dimensions of the engine-roomare 8.15m in length by 5.00 m in width by4.20 m in height. Within the engine-roomis included the well-head, the D-TU-2-1200 distillation unit and the electrical-automation panel.

A geothermal water flow of an esti-mated well-head temperature of 60-620Cwith a flow rate of about 80 m3/h is broughtas the heating medium to the heatexchange stage of the first effect. Thegeothermal water after providing itsthermal energy from 60-620C to 530C isdivided into two streams, the first of whichenters to the desalination unit as the feedwater (with a flow rate of 50 m3/h at 530C).The remainder of the geothermal water,which is not fed into the unit as the feedwater, is discarded to the sea or may bereinjected. Following the desalination ofthe feed water there is a stream of brinewater equal to approximately 46 m3/h atapproximately 320C which is also dis-carded to the sea.

A second sea-water pump room existsjust by the sea. This sea-water pump roomhas been erected to enclose the sea-watercooling system sea-water pump, the sea-water filter, electrical panel and the headof the sea-water cooling system piping.

For details see Photos 1-5.

4.1. The D-TU-2-1200 Desalination Unit

The D-TU-2-1200 desalination unit wasmanufactured in Denmark by ALFALAVAL DESALT A/S.

The productivity of the DTU-2-1200desalination unit was tested, at thefacilities of KYNDBY Power station in Den-mark, before the unit was transported toGreece.

The basic parameters taken into con-sideration were the rate of the productionof fresh-water versus changing parame-ters such geothermal (hot) water flow-rate,temperature, feed-water flow-rate andtemperature.

Table 4.1 below, shows the change ofproductivity of the DTU-2-1200 unit basedon variations of the geothermal water flow-rate (from 50 m3/h to 80 m3/h) and well-head temperatures (from 60 to 62oC).

The calculations are based on thefollowing assumptions:

a) Feed-water flow-rate 50 m3/h

b) Feed-water temperature 53oC

c) Seawater cooling temperature 20oC

d) Evaporation Temperature in second effect 40oC

4.2. The geothermal water system

The Geothermal water system of theunit consists of the PRASSA 1 borehole(which has been detailed in Chapter 2), ofthe Geothermal Water Pump (GWP) andof the piping which connects the boreholewell-head, through the GWP, with the hot-water entrance of the Desalination Unit.

Table 4.1: The change of productivity of the DTU-2-1200 unit based on changes of thegeothermal water flow-rate

Geothermal water

Well-head Temperature 60oC

Geothermal water

Well-head Temperature62 oC

Geothermal water flow-rate

(m3/h)

Fresh water production

(m3/h)

50 2.89 3.09

60 3.55 3.80

70 3.98 4.25

80 4.33 4.62

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4.2.1. The geothermal water pump

The geothermal water pump installedat PRASSA-1 is a multi-stage down-holevertical shaft pump.

The technical specifications of thegeothermal water pump are given in thefollowing Table 4.2.

4.2.2. The sea-water cooling systemand the sea-water and brine rejectionsystem

Sea-water is used for the unit’s cool-ing system, which is necessary to producethe vacuum in the distillation effects. Thesea-water is pumped from a site near thePrassa geothermal springs, where apumping station has been built just on thesea-side (see Map 2). The distance of thissite from the plant site is approximately200 m. This sea-water pump room hasbeen erected to enclose the sea-watercooling system, the sea-water pump, thesea-water filter, electrical panel and thehead of the sea-water cooling systempiping.

The sea-water cooling systemconsists of the following components:

• Sea-water pump

• Sea-water filters

• The supply system pipeline to thedesalination plant

The seawater pump has a yield of 250m3/h and pressure of 5 bar.

The supply system pipeline is furtherdivided to three pipes which have beenburied within a trench 0.5 m wide and 0.6m deep, and covered by the excavationproducts. The pipes are plastic HighDensity Polyethylene (HDPE) 125 mm indiameter. The total pipe length from thesea pumping unit to the plant is 522 m(3x171m).

According to the final design the brinetogether with the remaining geothermalwater are discarded into the sea. This ispermitted due to the chemical composition(very close to sea water) of both fluids andtheir temperatures. This has been basedon the Environmental Impact Assessmentthat has been carried out for the plant.

Table 4.2: Technical specifications of the geothermal water pump

Type of pump rotor 8 KHM

Number of stages 20

Nominal Power Consumption of Motor 60 HP

Nominal Head Pressure 90 m

Capacity - Speed 100 m3/h - 1450 rpm

Water Pump Performance Rate 78-79%

Diameter of water outlet 5”

Impeller Material Seawater resistant bronze

Material of Shaft Stainless steel

Inverter 45 kW ABB

The sea-water and brine rejectionsystem consists of 5 pipes, each with adiameter of 125 mm, which discards thesea-water and brine to the sea 50m to

80m south-east of the site of springs and150m to the south-southeast of the plantsite. The pipes have been placed within atrench 0.5 m wide and 0.6 m deep, and

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covered by the excavation products. Theyare also HDPE pipes with a diameter of

125 mm and the total length of the pipes is456m (5x91m).

5. THE UNIT OPERATION

The operation of the unit has proventhat the Kimolos geothermal desalinationunit operates in a very efficient wayproducing a considerable quantity of cleardesalinated water with a noteworthyrational use of energy.

The unit, in average, produced 3.24m3/h fresh water when geothermal waterof 50 m3/h at 61oC was used. Theproduced fresh water was crystal clearwith a Total Dissolved Solid content of lessthan 10 ppm, as directly measured by theplant’s built-in salinity meter.

Several tests to measure and quantifythe differential production of the unit took-place during the monitoring period.Different geothermal water yields weretested against the fresh-water productionrate of the unit.

For example in one instance that thegeothermal production flow-rate increasedto the level of 70 m3/h the fresh-waterproduction of the unit exceeded 4.12 m3/h.When the geothermal water yield fell downto 60 m3/h the fresh-water productiondecreased to approximately 3.63 m3/h.

The tests were performed in order toprove that the geothermal desalination unitfresh-water production depends largely onthe geothermal water production rate, afact that was proven during the initialmonitoring stages of the unit operation.

A remarkable point was that even witha water yield of only 30 m3/h the unit wasable to produce 1.18 m3/h of fresh-water.

Another significant parameter whichseems to have contributed to the successof the project and the unit operation wasthat the well-head temperature of thePRASSA-1 borehole was measured at 61

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– 61.5oC, two degrees higher than theanticipated well-head temperature of 59oC,which was employed during the optimaldesign of the unit. This improvedtemperature level difference, a factorcrucial for thermal distillation units workingunder vacuum, has led to a significantincrease of the finally measuredproduction rate of the unit.

6. CONCLUSIONS

The final success of this geothermalapplication project is very crucial for thelocal population since this island encoun-ters serious freshwater (drinking and irri-gation) scarcity problems, not only duringthe summer Tourist period (which is verypronounced) but all around the year. Itshould be noted that during the winter timethe permanent population of the island isapproximately 800 inhabitants, with waterneeds of approximately 40 to 50 m3/day,whereas during the summer time thepopulation and water needs rise to at least1600 inhabitants and 100 to 120 m3/day.

The Geothermal Energy DesalinationPlant designed, manufactured, installed,commissioned and operated through theGE/438/94/HE innovative-demonstrativeproject is virtually just the core unit onwhich the Municipality of Kimolos mayproceed for further development de-pending on the needs and financialfeasibility, having a pronounced impact tothe local population.

The exploitation scheme under investi-gation concerns sea water or geothermalwater desalination by the method of multieffect distillation under vacuum [MED unit]with the low enthalpy geothermal wateracting as the heating medium (with tem-peratures of over 55oC and up to 65oC).Several cases are investigated, dependingon the final wellhead temperature of thegeothermal water, and the actualfreshwater demands of the island. Thepossibility of desalinating the geothermalwater itself is also examined. All of theseparameters are correlated with the actualcost effectiveness of the desalinationplant.

According to the results of this projectthe exploitation of low enthalpy geothermalenergy in the unit results in the substitutionof at least 500 TOE/year [1 TOE (TonnesOil Equivalent) = 8,000,000 kcal/h].

The actual dissemination of the resultsof this project will provide fresh water todeveloping regions of Greece, which facesignificant water scarcity problems, suchas Milos, Santorini, Nisyros, Kos, Chiosetc. The proposed utilization schemes willexploit a friendly to the environmentenergy source, which is at the same timeof low energy production cost, beingcapable for further application in othergeothermal rich EU regions which alsoface similar fresh water supply problems.

REFERENCES

ALFA LAVAL (1993) “The Desalt D.TUConcept”, pp.12

Fytikas M., et al. (1984) “Tertiary to Quaternaryevolution of the volcanism in the AegeanRegion”, In: Dixon, G.E., and Robertson,A.H.F. (eds), The Geological evolution ofthe Eastern Mediterranean, SpecialPublication of the Geological Society No.17, Blackwell Scientific Publications,Oxford, pp. 687-699.

Fytikas, M., (1995) “Geological-Geothermalsurvey of the region of Prassa Kimolos Isl.-Selection of the geothermal productiveborehole drilling sites”, Report for CRES,THERMIE GE.438.94.HE, 25 p. [inGreek].

Fytikas, M., and Vougioukalakis, G., (1992)“Volcanic Structure and evolution ofKimolos and Polyaigos Isl., (Milos Island

Complex)”, 6th Congress of the GreekGeologic Society, pp. 221-237, Athens, [inGreek].

GEOTECH, (1996) “Pumping tests at PRASSA2 borehole”, Report for CRES, THERMIEGE.438.94.HE, 8 p. and Diagrams [inGreek].

I.G.M.R. (1995) “Drilling of Geothermal Bore-holes at Prassa Kimolos – Execution andestimation of results”, Internal Report, 38p. [in Greek].

Karytsas, C., (1998) “Geothermal Energy DrivenDesalination Plants”, Geothermal Resour-ces Council Bulletin, Vol. 27., No 4. pp.111-115.

Louis, J., (1995) “Technical report of the geo-physical survey at Prassa Kimolos”, Univ.Athens Report for CRES, THERMIEGE.438 94.HE, 14 p. [in Greek].

Thanassoulas, C., and Tsokas, G., (1985)“Geo-electrical Study of Kimolos Isl”.,

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IGMR Internal Report, 9 p. andAppendices, [in Greek].

Tsokas, G., (1985) “Geophysical survey of theislands of Milos and Kimolos”, unpublishedDoctorate Thesis, The University ofThessaloniki.

PHOTOGRAPHS

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