Thermodynamic analysis of a transcritical CO₂ geothermal power plant

In this chapter, the thermodynamic performance assessment of a geothermal power plant based on the transcritical CO2-Rankine cycle (tCO2-RC) is presented. At first, the description of the system, its operating principles, its major differences from the subcritical cycle, and the significance of using CO2 as the working fluid are discussed in detail. The governing equations originating from the First and Second Laws of Thermodynamics are then defined for each component of the system. As a case study, the geothermal brine conditions of an existing plant in Aydın, Turkey, are taken to assess the feasibility of using tCO2-RC. A comparison between adapting a tCO2-RC and an ORC operating with R134a is done in order to investigate the system improvement potential. Parametric studies are also conducted to assess the effect of various system parameters such as the geothermal water inlet temperature, the turbine inlet pressure, and the pump inlet pressure on the energy and exergy efficiencies of the system. For the ORC operating with R134a at the baseline conditions, the energy and exergy efficiencies are obtained as 6.64% and 26.86%, respectively. In addition, for the tCO2-RC plant, the energy and exergy efficiencies are evaluated as 8.20% and 35.03%, respectively. The comparative study shows that adopting tCO2-RC is a feasible option to be used in a geothermal power plant.