Use of CO2 as working fluid in geothermal systems

This thesis has focused on the thermodynamic modelling of geothermal wells focusing on the behaviour of such systems using different working fluid. A specific attention has been given to CO2-based geothermal system, a configuration that has received increasingly more attention in recent years. In the scope of this thesis two different models have been developed: a simplified model based on simple cubic real-gas Equation of State (EoS) has been used to perform a theoretical analysis in order to gain a better understanding of the system behaviour. The results of this analysis are presented in Chapter 2. A more detailed model, developed to allow more exact estimation of the system performances, is presented in Chapter 3. Together with the detailed model, a tool capable of performing exergo-economic analyses has been developed to speed up surface equipment modelling and is presented in Appendix A. Finally, in Chapter 4, a possible application, a geothermal-based High Temperature Heat Pumps (HTHP) for industrial steam production, has been presented.