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Possibilities of electric power generation in the Republic of Croatia from medium temperature geothermal sources

As early as 1998, the Energy Institute “Hrvoje Požar” prepared a Program of Geothermal Energy Usage in the Republic of Croatia, which shows that in the Republic of Croatia there are several medium temperature geothermal sources with relatively lower temperature of geothermal water in the range from 90 – 140 C, by means of which it is possible to produce electric power, e.g. Lunjkovec-Kutnjak (140 C), Ferdinandovac (125 C), Babina Greda (125 C) and Rečica (120 C). However, concrete initiatives for the construction of geothermal power plants have only recently been started. For the generation of electric power from medium temperature geothermal sources, binary plants come to the fore, either with the Organic Rankine Cycle (ORC) or with the Kalina Cycle. In literature, the Kalina cycle is cited as thermodynamically more favorable than ORC, i.e. reaching higher thermodynamic efficiency and giving more power. On the other hand, conclusions of the authors of this paper published in previous papers, obtained on the basis of calculations for a medium temperature geothermal source in Croatia (Velika Ciglena) with relatively high temperature of geothermal water (175 C) are opposite - the ORC cycle is thermodynamically better than the Kalina cycle! This was explained by relatively high temperature of geothermal water and relatively high average annual temperature of cooling air in condenser (15 C), which has more unfavorable influence in the Kalina cycle than in the ORC. In this paper the comparison of the ORC and Kalina cycles will be performed for a medium geothermal field with relatively lower temperature of geothermal fluid (140 C) and again relatively high average annual temperature of cooling air in condenser (15 C): concretely for the geothermal field Lunjkovec-Kutnjak, probably one of the first geothermal power stations to be built in Croatia. The comparison of ORC and Kalina cycles will be performed on the basis of results of energy analysis. Aim of the comparison is to propose the most suitable binary plant either with the Organic Rankine Cycle (ORC) or with the Kalina Cycle for medium temperature geothermal sources in the Republic of Croatia with relatively lower temperatures of geothermal water. For both cycles the optimization of main cycle parameters will be performed: ORC - the upper cycle pressure and Kalina cycle - concentration of ammonia.

electric power generation; Republic of Croatia; medium temperature; geothermal sources; Organic Rankine cycle; Kalina Cycle

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