Influence of working fluid on ORC with low temperature geothermal source – Case study geothermal power plant “Babina Greda”

Abstract

Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.

In 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 some low/medium temperature geothermal sources (geothermal water) in the range from 100 to 170 ºC, by means of which it is possible to produce electricity in binary plants, either with the Organic Rankine Cycle (ORC) or with the Kalina cycle. However concrete initiatives for the construction of geothermal power plants have only recently been started. In accordance with this authors in previous papers have presented result of an energy-exergy analysis of geothermal resources Velika Ciglena (175 ºC), Lunjkovec-Kutnjak (140 ºC), Babina Greda (125 ºC) and Rečica (120 ºC), in order to determine which cycle is better for the conditions in Croatia. The analysis results have shown that the ORC with isopentane as working fluid is thermodynamically better from the Kalina cycle for temperatures of all cited geothermal sources and cooling air, and considering the problems that all the new technologies as Kalina cycle encounter in their early phase of application, authors propose the application of binary plants using ORC cycle for all low/medium temperature geothermal sources in the Republic of Croatia. Researches related to the application of the ORC generally deals with the selection of the working fluid, optimization of the ORC unit and the whole plant and analysis of possible modifications with aim to increase its thermodynamic efficiency or net mechanical power output. Although in the available literature, there are a large number of published research results on the selection of the working fluid, however, every geothermal source is a case for itself with respect to the temperature of geothermal water and the cooling fluid on location (water or air). Therefore, in this paper will be presented the results of analysis of the working fluid influence on both thermodynamic efficiency and useful work and others plant characteristics for the case of Geothermal Power Plant “Babina Greda” with lower temperature of geothermal water - 125 ºC. As the working fluid the next refrigerants and hydrocarbons will be analyzed: R236fa, toluene, R365mfc, R236ea, C5F12, hexane, R123, R245ca, R245fa, R21, R114, R113, R12, R11, R152a, R142b, R141b, R600a, R600, R601a and R601.