Investigating the application range of ORC power plants for the exploitation of two-phase geothermal resources

Abstract

The design of a geothermal power plant exploiting a two-phase geothermal resource is a demanding task, due to the fact that different technologies and plant configurations must be considered, as well as the lack of flexible and reliable models for computing the thermophysical properties of geofluids, whose composition and chemistry is highly site-specific. This study presents a novel thermophysical property modelling framework aimed at modelling any arbitrary single- or two-phase geothermal brine. Recognising the potential synergy of two historically separate fields of research, fluid partition and property modelling, existing partitioning simulators, like Reaktoro, are coupled with high-accuracy thermophysical fluid property computation engines, like CoolProp and ThermoFun. The resultant Python-based framework, GeoProp, is validated against a range of primary and secondary data and will be made available to the public. Considering a two-phase geothermal resource, the design of direct steam cycles with flash as well as binary geothermal power plants is investigated from a thermodynamic perspective. A parametric study on geofluid composition, i.e. mineral and non-condensable gases (NCG) content, and inlet conditions, i.e. temperature and steam quality, is used to compare the performance and define the application envelope of these two technologies.