Sensitivity analysis of supercritical CO2 power cycle energy and exergy efficiencies regarding cycle component efficiencies for concentrating solar power

Abstract

Supercritical CO2 cycles have been said to be a good alternative to the Rankine Cycles for Concentrating Solar Power plants of the future. The next generation molten salts will be able to achieve 700 °C, which is a suitable temperature for Supercritical CO2 cycles. However, there is a big uncertainty about the efficiencies of the cycle components, which could make these cycles unviable. A sensitivity analysis of the energy efficiency of the Recompression Cycle and Partial Cooling Cycle, regarding turbomachinery isentropic efficiencies and Recuperator effectiveness variations, has been carried out to show that the Recompression Cycle’s energy efficiency is considerably more sensitive than the Partial Cooling Cycle’s. From the sensitivity analysis, it can also be concluded that the Recompression Cycle is the best performing cycle for most of the studied cases, with energy efficiencies in the range between 32.97% and 51.91%. Exergetically, the Recompression Cycle is also more suitable in most situations, and the exergy analysis on cycle components shows that irreversibilities occur mainly in the Recuperators, which means that future research should focus on methods to reduce irreversibilities in these components.The state-of-the-art of Supercritical Rankine Cycle plant net energy efficiencies currently reach 45.60% for fossil fuel plants. Although Supercritical CO2 cycles are a simpler and more compact alternative, this work concludes that only the optimized Recompression Cycle with turbomachinery isentropic efficiencies over 92% and Recuperator effectiveness over 95% are able to obtain similar or higher efficiencies than actual Supercritical Rankine Cycles. Furthermore, the sensitivity analysis plots permit the areas to be mapped where each of the optimized two-cycle efficiencies can compete with the Supercritical Rankine Cycles regarding the turbomachinery isentropic efficiencies and Recuperator effectiveness.