Thermo-economic optimization and part-load analysis of the combined supercritical CO2 and Kalina cycle

Abstract The supercritical CO2 (sCO2) power cycle has emerged as a promising technology for the use of nuclear energy. However, a large amount of cooling heat is wasted in the sCO2 gas cooler. In this paper, two typical sCO2 Brayton cycles including simple sCO2 cycle (SSC) and recompression sCO2 cycle (RSC) are integrated with Kalina power cycles to provide a higher energy conversion efficiency for nuclear power plants. A comparison study of the SSC-Kalina cycle and the RSC-Kalina cycle is conducted from the viewpoints of thermodynamics and economics, and multi-objective optimization using genetic algorithms is carried out to gain maximum exergetic efficiency (ηex) and minimum levelized cost of electricity (LCOE) at the design stage. To meet the requirement of wide-range load adjustment, the valve control strategy and variable-speed compressor control strategy are proposed for the topping sCO2 cycle, while the sliding pressure control strategy is adopted for the bottoming Kalina cycle. The part-load performance of the combined cycle under different control strategies is analyzed and compared based on the preliminary design parameters for the main system components. Results show that the RSC-Kalina cycle always has better performance than the SSC-Kalina cycle, and they can gain an improvement by 6.37% and 7.53% for the ηex, and 3.51% and 5.84% for the LCOE compared with the stand-alone RSC and SSC, respectively. Compared with the valve control strategy, the variable-speed compressor control strategy enables the RSC-Kalina cycle to obtain higher efficiency under partial plant loads, and the ηex ranges from 29.67% to 58.24% under 10–100% relative plant load. The bottoming Kalina cycle can be well adapted to the parameter variations of the topping cycle by using the sliding pressure control strategy no matter which sCO2 control strategy is adopted.