To improve the flexibility of coal-fired power units and support renewable energy integration, molten salt thermal storage has been widely considered a promising retrofit option. However, under unified operating conditions, the comparative effects of different heat-release pathways and steam extraction ratios on flexibility, full-cycle thermodynamic performance, and economic performance have not been sufficiently clarified. In this study, a thermodynamic model of a 600 MW subcritical coal-fired power unit coupled with a two-tank molten salt thermal storage system was established in Ebsilon and validated against the design heat-balance data under typical load conditions, with maximum relative deviations of 0.06% for power output, 0.95% for main steam flow rate, and 1.24% for heat consumption rate. Three representative heat-release pathways were comparatively investigated under identical heat-storage conditions, with steam extraction ratios ranging from 2% to 18%. The results show that increasing the extraction ratio raises the thermal storage capacity from 9.762 to 84.636 MWh and enhances the downward peak-shaving capability, but weakens the full-cycle thermodynamic performance. Among the three schemes, Scheme 2 exhibits the strongest upward peak-shaving performance, with upward peak-shaving energy increasing from 2.893 to 24.395 MWh, and also yields the highest annual net profit (0.546–4.342 million CNY). Scheme 3 exhibits the best full-cycle thermal and exergy efficiencies, with full-cycle thermal efficiency of 42.76–41.56% and full-cycle exergy efficiency of 38.34–37.27%. In addition, Schemes 1 and 2 show significantly higher round-trip efficiencies than Scheme 3, with Scheme 2 becoming more advantageous at higher extraction ratios. Scheme 1 exhibits the shortest static payback period (7.12–7.63 years) and the highest internal rate of return (12.77–11.65%). These results indicate that the three schemes have distinct advantages in peak-shaving performance, full-cycle thermodynamic performance, and economic performance, and provide a comparative basis for engineering selection and parameter optimization of molten-salt-based flexibility retrofits in coal-fired power units.

To evaluate the techno-economic performance of supercritical carbon dioxide (sCO2) power cycles in particle-based solar tower systems, thermodynamic and techno-economic models were established for four configurations: RC-ORC, RC, RE-ORC, and RE. A one-dimensional design method was used for key printed circuit heat exchangers, and multiple cost correlations with a trimmed-mean treatment were adopted to reduce the influence of extreme cost estimates. The results show that the primary heat exchanger (PHX) dominates system investment, accounting for more than 50% of total cost in all configurations. After screening 48 pure ORC working fluids, Cyclopropane and Trans-butene were identified as the economically preferable fluids for RC-ORC and RE-ORC, respectively. ORC working-fluid selection should therefore consider not only net power output, but also the effect of heat transfer and flow characteristics on intermediate heat exchanger cost. Scale analysis shows that the specific investment cost decreases rapidly over 50–300 MW, while the reduction becomes much smaller above 300 MW. At large scales, RC-ORC and RE-ORC gradually approach 1756.64 $/kW. These results highlight the importance of PHX cost reduction, heat-exchanger-oriented ORC fluid selection, and appropriate system scaling.