Working fluid selection for organic Rankine cycle power generation using hot produced supercritical CO2 from a geothermal reservoir

Highlights: • Geothermal heat mining simulations using CO₂ as heat extraction fluid were performed. • Working fluid selection criteria for organic Rankine cycle using hot supercritical CO₂ were proposed. • Thermal performance of the organic Rankine cycle using hot supercritical CO₂ was evaluated. • The suitable working fluids for organic Rankine cycle using hot supercritical CO₂ were selected. -- Abstract: Geothermal heat mining simulations using supercritical CO₂ (sCO₂) were performed in this research. Working fluid selection criteria for power generation using sCO₂ from a geothermal reservoir are then presented for subcritical, superheated and supercritical organic Rankine cycles (ORCs). Meanwhile, method of working fluid classification for ORC is proposed. To get the most feasible ORC design, this study introduces the concept of "turning point" for isentropic and dry working fluids, as well as minimum turbine inlet temperature for wet working fluids. A thermodynamic model was developed with capabilities to obtain the optimal working fluid mass flow rate, evaporation temperature, superheated temperature, and supercritical pressure, to evaluate the thermal performance of the three ORC approaches using hot produced sCO₂. With this model, thirty potential working fluids with critical temperatures in the range from 50 to 225 °C were screened for utilizing hot produced sCO₂ considering physical properties, environmental and safety impacts, and thermodynamic performances. Finally, the thermodynamic results were compared for all possible working fluids.