| Title | Thermodynamic Evaluations for Efficient Energy Conversion of Geothermal Heat |
|---|---|
| Authors | G. Herbst, B. Bartenstein, H.-J. Wiemer, D. Kuhn |
| Year | 2010 |
| Conference | World Geothermal Congress |
| Keywords | power plants, Organic Rankine Cycle. |
| Abstract | Power generation from geothermal energy in Germany is a rather new sector. Typically, drilling holes are at a depth of ca. 4 km with geothermal water temperature of ca. 150 °C (ca. 420 K). With these boundary conditions an Organic Rankine Cycle (ORC) is used for power generation. This paper describes the numerical calculation of such OR-cycles by means of the commercial code IPSEpro. With the resulting thermodynamic values for pressure or temperature respectively, an overall efficiency is determined. In addition, the calculations have been carried out for the working fluids isopentane and R-245fa. The thermodynamic fluid properties from IPSEpro have been validated with data from the database Refprop of the National Institute of Standards and Technology (NIST). The deviations of IPSEpro are discussed within this paper. An alternative application for geothermal energy are hybrid power stations. There the geothermal heat can be used for the preheating of the water steam cycle (WSC) of conventional power stations. This paper compares from a technical point of view the net power output of single power generation from geothermal energy within an ORC respectively an WSC with the combined power generation within a hybrid power station. The calculations show that the increase of efficiency of the WSC is mainly limited by the steam quality at the same boundary conditions. The advantage of preheating the WSC of a big power plant with geothermal energy depends on the ratio of power output of the WSC and the ORC. |