Preliminary design and part-load performance analysis of a recompression supercritical carbon dioxide cycle combined with a transcritical carbon dioxide cycle

Nuclear energy can be efficiently converted to electrical energy in the supercritical carbon dioxide (sCO₂) power system. In this paper, a combined cycle comprising a topping sCO₂ cycle and a bottoming transcritical CO₂ cycle (tCO₂) is investigated. Multi-objective optimization by means of a genetic algorithm is carried out to obtain better thermodynamic and economic performance in the design stage. The methodology for part-load operation of the combined sCO₂-tCO₂ cycle is proposed and the quantitative performance analysis is conducted for the utilization of nuclear energy. The results indicate that there exists optimal values for the maximum system exergetic efficiency and the minimum total product unit cost. A composite control strategy by adjusting the rotational speed of compressors and the opening of bypass valve is proposed for the topping sCO₂ cycle operation from the point of view of both efficiency and operation range. The bottoming tCO₂ cycle is well adapt to the changes of parameters in the topping sCO₂ cycle and heat sink temperature by using the sliding pressure control strategy. The combined sCO₂-tCO₂ cycle can operate under 10–100% normalized generator load when the variation scope of heat sink temperature is 5–25 ℃.The corresponding exergetic efficiency of combined sCO₂-tCO₂ cycle ranges from 24.5% to 65.7%.