Single-peaked convex efficiency curve in S-CO2 brayton cycle under wide load conditions: Distinctive features compared to the S-H2O rankine cycle

Abstract

Under part-load conditions, the supercritical carbon dioxide (S-CO₂) Brayton cycle’s thermal efficiency follows a single-peaked convex curve trend, unlike the supercritical water (S-H₂O) Rankine cycle, with no complete explanation yet for this phenomenon. Analysis identifies a key difference in regeneration: as load decreases from 100% to 30%, the S-CO₂ cycle experiences a significant 22.1% increase in unit regeneration capacity, while the S-H₂O cycle shows a decrease. Meanwhile, the isentropic efficiency of the S-CO₂ turbine drops from 90% (full load) to 55% (30% load). The interplay between these positive and negative impacts accounts for the single-peaked convex curve variation in thermal efficiency of S-CO₂ cycle (48.41% at full load, 48.58% at 90% load, and 39.54% at 30% load). This pattern reflects the balance between regeneration benefits and turbine work limitations under part-load conditions. The study clarifies the single-peaked convex curve trend in S-CO₂ cycle’s part-load efficiency, creates a solid theoretical framework to grasp its high-efficiency traits across a wide load range, and highlights its possible uses in fluctuating load situations like renewable energy integration. The analysis of the cycle’s positive and negative effects reveals universally applicable insights, offering inspiration for research in other related fields.