INTERNATIONAL SUMMER SCHOOL on Direct Application of Geothermal Energy Under the auspice of the Division 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 According to the results of this project the exploitation of low enthalpy geothermal The Kimolos Geothermal Desalination energy in the unit results in the substitution Project is concerned with the exploitation of at least 500 TOE/year [1 TOE (Tonnes of the low enthalpy geothermal potential of Oil Equivalent) = 8,000,000 kcal/h]. Kimolos island for the production of fresh Our intention in this demonstrative water through geothermal water desalina- project is to demonstrate the technology of tion, with the intent of achieving water producing clear fresh desalinated water sufficiency for the island. from low enthalpy geothermal resources Funding for the project was provided on Kimolos Isl. Further-on, we investigate by the THERMIE EU-DGXVII program the technical and financial feasibility for through contract No. GE-438-94-HE. applying and disseminating such innova- The island of Kimolos, faces pronoun- tive desalination schemes in other regions ced water scarcity problems, as other of Greece and the EU with similar Aegean Sea islands also do. Never- renewable energy sources potential. theless, Kimolos Isl. is fortunate enough to possess a very significant source of 1. OBJECTIVES environmentally friendly energy which is renewable and of low cost, that is the low The main objective of this project is to enthalpy geothermal energy potential. exploit part of the low enthalpy geothermal potential of Kimolos island for the The desalination method applied is production of fresh water through sea- that of Multiple-Effect Distillation (MED) water or geothermal water desalination, with distillation under vacuum in vertical with the intent of achieving water tubes. The unit will use low enthalpy geo- sufficiency for Kimolos Island inducing thermal energy (with a wellhead tem- further agricultural, industrial and tourist o perature of approximately 61 C) as the development on the island. heating and feed-water medium. The desalination method applied is the The unit, built during the period of Multiple-effect Distillation (MED) method 1998-1999 produced, in average, 3.24 with distillation under vacuum in vertical 3 m /h of fresh water, when a geothermal tubes. The unit will use low enthalpy 3 water flow-rate of 50 m /h at a wellhead geothermal energy as the heating and o temperature of 61 C was utilized. The feed-water medium. fresh water produced had a Total Dissolved Solid (TDS) content of less than Renewable Energy Source driven sea 10 ppm, according to the plant’s built-in water desalination units, such as those salinity meter. driven by low enthalpy geothermal energy, guarantee friendly to the environment, cost Several tests to measure and quantify effective and energy efficient production of the differential production of the unit took- desalinated water in regions with severe place during the monitoring period. water supply problems (such as several of Different geothermal water yields were the Aegean Islands), which nevertheless tested against the fresh-water production are fortunate enough to have renewable rate of the unit. - 206 - energy resources at first hand for cene being presently exhausted, the last immediate exploitation. volcanic eruptive cycle taking place, on the The island of Kimolos, similarily to east side of the island, just 900,000 years numerous other Aegean Sea islands, ago. faces pronounced water scarcity prob- On the Northern part of Kimolos island lems. On Kimolos Isl. drinking water is the geological, geophysical, geothermal available through transportation by water and hydrogeological data all lead to the tankers from Peireus, which lies some assumption that a significant reservoir lies sixty nautical miles away and costs more at depths of 100 to 300 m within volcano- than 5,28 per cubic meter or in the form clastic and volcanic (lavas) rocks, being of bottled water at 0,44 per 1.5 litres. supplied from a system of deep faults. Water for sanitary purposes originates A NE-SW tectonic lineament with from rain collector tanks gathered from the numerous thermal springs aligned on it water rained down on the roof of the with temperatures of up to 65oC seems to houses. Rain in the Western Cyclades is continue to be active. Most of the volcanic very scarce (with a rainfall less than 450 eruptive activity has been affected by this, mm rain annually). still active, lineament (Fytikas and Vougi- Nevertheless, Kimolos Isl., like other oukalakis, 1992). The existence of this islands or regions facing similar water tectonic lineament together with an older scarcity problems, is fortunate enough to one, with a NW-SE direction, allow the possess a very significant source of flow of sea-water parallel to these sys- environmentally friendly energy which is tems, cold-water descending and hotwa- renewable and of low cost, that is the low ter ascending. According to geological, enthalpy geothermal energy potential. geochemical, geophysical, volcanological With this desalination unit we intend not and geothermal data (Fytikas, 1995) it is only to minimize this water scarcity determined that the geothermal resources problem but also to induce development on Kimolos Isl. are formed by the entrap- on the island through water sufficiency. ment of ascending hot sea-water in porous Our intention in this demonstrative volcanoclastic aquifers. The main hydro- project is to demonstrate the technology of geological characteristic is the existence of produ-cing clear fresh desalinated water at least 6 aquifers isolated by imperme- from geothermal water on Kimolos Isl. In able pyroclastic material. These aquifers paral-lel we investigate the technical and are characterized by very low resistivity finan-cial feasibility for further applying and values when geoelectrical surveying is disseminating such innovative desalination performed (Tsokas, 1985 and Thanas- schemes in other regions of Greece and oulas and Tsokas, 1985). The aquifers at the EU. the depth of 20-30 m have been found to have temperatures of 40 to 45oC, at depths of 50m temperatures of over 59oC 2. GEOLOGICAL AND GEOTHERMAL and at depths of 200m bottom-hole BACKGROUND temperatures of at least 61oC. The Island of Kimolos belongs to the At greater depths (deeper than 800m), Milos Island Volcanic Complex, which is especially in the southeastern side of the part of the Active Aegean Volcanic Arc. island, temperatures may rise over 100oC High, Medium and Low Enthalpy geother- or even higher. mal resources have been detected in the The island is covered with a plentitude Milos Island Volcanic Complex with tem- of rocks, products of extensive hydro- peratures rising on Milos Island as high as thermal alterations, in fact one of the 330oC at a depth of 1100m and with o largest and of finest quality bentonite in numerous thermal springs of up to 90 C the world lies just 2 Km from the region of on Milos and Kimolos Isl (see Map 1). Prassa (NNE region of the island). The island of Kimolos, with a surface 2 Shallow exploratory boreholes (at area of 36 km is located in the northern least 10) drilled to depths of 40m have part of the previously mentioned Milos given temperatures of up to 35oC. Island Volcanic Complex (Fytikas et al., 1984). The volcanic activity of the island Two boreholes were drilled in the regi- was manifested before the lower Pleisto- on of Prassa . The boreholes were named 207 PRASSA-1 and PRASSA-2. The technical given in the following Table 2.1. specifications of the two boreholes are 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 the 0.640 m2/h 0.289 m2/h recovery pumping test Number of Aquifers 6 3 Well head Temperature 61.5 oC 49.2 oC Optimal Flow-rate 80 m3/h 30 m3/h 208 The chemical composition of the geo- a) The geothermal water has a thermal water of PRASSA-1 and PRAS- composition very similar to that of sea- SA-2 boreholes based on analyses per- water, with a slightly increased content of formed by IGMR on Oct. 1995 (537/13-10- CO2, Ca and SO4 and a decreased content 95) is provided in the following Table 2.2. of Na and Cl. A remarkable point of these analyses b) Harmful elements such as As, Pb, Zn is the similarity of the geothermal water etc. are almost not detectable and composition among the thermal springs, therefore, since the chemical composition CRES-1 exploratory borehole, PRASSA-1 of the geothermal water permits its use for and PRASSA-2 and sea-water, the only desalination. difference being a slightly higher CO2, Ca Based on the previously mentioned re- and SO4 content of the geothermal water. sults it was further decided to proceed and This is probably due to dissolution of car- carry-on with our project by utilizing the bonate rocks in the subsurface, proving geothermal energy provided from the that the previously mentioned mechanism PRASSA-1 borehole, due to it’s suitable is responsible for the formation of the well-head temperature, hydraulic charac- geothermal resources on this island. teristics and chemical composition. From all chemical analyses performed The second borehole PRASSA-2 al- on the low enthalpy geothermal water though perfect in chemical composition samples from Kimolos Isl. we obtain reser- has been abandoned due to its poor hyd- o voir temperature of approx.