Preliminary investigation on the adoption of CO2-SO2 working mixtures in a transcritical Recompression cycle

Abstract

This paper investigates the interest and potential of using working fluids based on Carbon and Sulphur Dioxide mixtures (CO 2 -SO 2 ) in a transcritical Recompression cycle. In order to assess the actual thermodynamic potential of the concept proposed, the influence of dopant (SO 2 ) content is assessed for two different turbine inlet temperatures (550 °C and 700 °C). The results obtained are compared with other CO 2 mixtures already proposed in literature (CO 2 -C 6 F 6 and CO 2 -TiCl 4 )) and for two alternative cycle layouts ( Recuperated Rankine and Precompression ). The results pf the analysis reveal that, at high ambient temperature, the Recompression cycle operating on CO 2 -SO 2 , with Sulphur Dioxide content between 20% and 30%(v), is a very interesting option for Concentrated Solar Power plants, able to achieve thermal efficiencies ≈ 45% and ¿51% at 550 °C and 700 °C respectively. At a minimum cycle temperature of 50 °C, the proposed configuration leads to thermal efficiency gains of 6% and 2% with respect to the Brayton and Recompression cycles working on pure CO 2 . This performance enhancement of the Recompression cycle with CO 2 -SO 2 is comparable to or higher than that enabled by other CO 2 mixtures proposed in literature, but with significantly higher specific work (smaller footprint) and temperature rise across the solar receiver (lower installation costs). • CO 2 mixtures enable thermal efficiencies higher than 50% at high ambient temperatures. • Recompression is the most interesting layout to exploit CO 2 -SO 2 mixtures. • CO 2 -SO 2 mixtures enable a good compromise between thermal efficiency and specific work.