Different design aspects of an Organic Rankine Cycle turbine for electricity production using a geothermal binary power plant

Highlights: • The European Union trends create an opportunity for geothermal power plants. • The combine analysis of heat source, Organic Rankine Cycle and turbine were done. • The binary geothermal power plant can obtain approximately 2 MW of power output. • The parameters of a low-temperature heat source for Polish conditions are determined. • Designed the two-stage axial turbine reached the internal efficiency of 79%. In recent years, pressure has been growing to increase the share of renewable energy sources in electricity generation, which may offer opportunities for the development of geothermal energy in regions that have been so far considered unprofitable in this respect. One such country currently undergoing an energy transition is Poland in which low-temperature geothermal resources are currently used for district heating and recreation purposes. Nevertheless, research on the possibilities of using geothermal energy for electricity production is ongoing. The objective of this paper was to perform a comprehensive analysis of a binary power plant construction in relation to low-temperature petro-geothermal resources. The potential binary power plant is located in the area characterized by temperature of 120 °C at depths of 5000 m. About half of Poland's area, especially the regions of western and central Poland, has these characteristics. It was assumed that brine at volume flow rate of 400 m³/h is a heat source for the Organic Rankine Cycle with isobutane as a working medium. The thermal efficiency based on the First Law of Thermodynamics and the power output were estimated at 10.5% and 1.79 MW_e, respectively. In addition, the thermal efficiency based on the Second Law of Thermodynamics was calculated at 29.0%. For the calculated cycle parameters, a preliminary design of a two-stage axial turbine was constructed. All results were compared to the other binary power plants and they confirm that establishing the binary power plant in Poland would be thermodynamically justified. The main novelty of the present work is the combination of three issues, namely the selection of the low- temperature heat source, the design and analysis of the cycle together with a turbine adapted to these conditions.