Theoretical Analysis of a Self-Condensing CO2 Transcritical Power Cycle With Regeneration Involving Dense Particle Suspensions in a Solar Thermal Power Plant

Abstract

The choice of heat transfer fluids (HTFs) significantly dictates the thermal efficiency of the solar power plant. Presently, molten salt is widely used choice owing to its phase, low cost, and non-toxic nature. Along with other alternatives like liquid metals and multiphase fluids, these HTFs are limited to peak operating temperatures ranging from 300 to 550 °C. With the introduction of dense particle suspensions as an HTF, the highest operating temperatures in a solar thermal power plant can reach up to 700 °C, offering considerable scope for improving thermal efficiency. Due to the higher average specific heat as compared to the alternatives, CO2 is a promising working fluid in the considered range of moderately high operating temperatures. The cost of the components and size of the power block make the transcritical CO2 cycle an attractive alternative. The present work analyzes the theoretical efficiency of the proposed cycle, with the peak operating temperature ranging from 550 °C to 700 °C. The effects of the variation in the lower operating pressure and the condensation temperature have also been analyzed. It is observed that thermodynamic efficiencies as high as 40% can be reached at the maximum operating temperature. The optimum combination of the lower operating pressure and the condensation temperature is also noted.