Transient Thermodynamic Modeling of Air Cooler in Supercritical CO₂ Brayton Cycle for Solar Molten Salt Application

Supercritical CO₂ Brayton power cycle is getting commercially attractive for power generation due to its numerous advantages like zero water discharge, compactness, low environmental emission and potential to reach high thermal efficiency at lower costs. A typical recuperated sCO₂ closed cycle consists of three heat exchangers (main heat exchanger, cooler and recuperator) and two turbomachinery (sCO₂ turbine and sCO₂ compressor). The cooler which can use air or water as heat sink is the focus of this study. The purpose of the paper is investigation of behavior of thermodynamic parameters of cooler during transient operations. In this study, dynamic simulation is performed to analyze the transient behavior of air cooler in sCO₂ cycle using molten salt as heat source from solar energy. Transient study is critical to understand the thermodynamic behavior of each system with time. Rapid changes in ambient temperature, operating loads, start-ups and shutdowns affect the performance of the turbomachinery and heat exchangers. The change in the thermal performance of air cooler with the change in boundary conditions is demonstrated here. The simulation is setup by having a steady state design of 100MWe sCO₂ cycle with operating temperature of 700°C and pressure of 250 barA. Dynamic calculations are done using LMS AMESim. Transients studied in this paper include (i) step variation (ii) standard variation (iii) linear variation of air temperature. This work thus serves as a framework to develop a design basis for sCO₂ cycle components as a function of transient operating conditions.