Dry-Cooled Rankine Cycle Operated With Binary Carbon Dioxide Based Working Fluids

Abstract

The dry-cooled Rankine cycle working with a zeotropic mixture of CO2+C6F6 is influenced by the ambient temperature as air is used as the heat sink. Varying heat sink temperatures allow for operating the cycle under sliding condensation pressure which may benefit a hybrid PV-CSP plant. The study demonstrates the effect of this operation mode on composition shift and condensation pressure and investigates the cycle performance. The results show that defining the turbine design conditions significantly impact whether the system´s thermodynamic performance behaves acceptably in off-design conditions. Operating the turbine which was designed for a big pressure ratio in part-load especially if both, inlet and outlet pressure are at off-design conditions, is not favorable and leads to deteriorated efficiencies. Under some constraints for turbine and heat exchanger design, the proposed cycle enhances the hybrid PV-CSP system.

Keywords

• Rankine Cycle
• Transcritical Cycle
• CO2-Based Mixtures