Session: 30-09 Systems 1 and Components

Submission Number: 177551

Design and Off-Design Performance Analysis of Split-Reheat Supercritical Carbon Dioxide Power Cycle 

Abstract 

supercritical carbon dioxide (sCO₂) power cycles are attractive for compact, high-efficiency power conversion across concentrated solar power, nuclear power, and waste-heat recovery applications. Among various cycle layouts, the split-reheat power cycle has been shown to demonstrate significant thermodynamic performance improvement compared to other cycle layouts used for indirect thermal energy input [1]. However, its off-design performance is yet to be thoroughly investigated. This paper aims to develop and validate a steady-state design point and off-design model of a split-reheat sCO₂ cycles to enable their full characterisation and pave the way for future research on developing control strategies for this cycle. A 50 MWe case study is used to illustrate the methodology where the heat input is provided by a small modular nuclear reactor (SMR). For accurate modelling, the heat exchangers (high temperature heat recovery heat exchanger, low temperature heat recovery heat exchanger, recuperator, cooler) are discretised and solutions to the heat transfer equations are obtained using an LMTD-based 1-D formulation. Turbomachinery maps from Sandia National Laboratories (SNL) [2] are scaled to match the components design point using the Dyreby method, whereas compressor-turbine matching is maintained via nozzle-area constraint. The system is constrained by the compressor inlet temperature (CIT), compressor inlet pressure (CIP), turbine inlet temperature (TIT), maximum cycle pressure, and minimum approach temperatures to prevent flow crossover in the heat exchangers. The findings indicate that the operating envelope is characterized by the recuperator pinch and pressure-drop limitations at high flow rates, whereas compressor surge margin becomes the limiting factor at low flow rates. To simulate load-following operation, the sCO₂ mass flow rate, split ratio, and SMR coolant mass flow rate are changed to match changes in the power demand on the grid. The results of this study provide a reliable baseline for the off-design evaluation of split-reheat sCO₂ cycles under dynamic load conditions.

Keywords

supercritical carbon dioxide, split-reheat power cycle, off-design, small modular reactor, turbomachinery maps, numerical analysis, small modular reactor.

References 

[1]          H. A. Chibli, M. Read, and A. Sayma, “Evaluation of the performance of multiple supercritical CO2 power cycles in Waste Heat Recovery applications,” in International Seminar on ORC Power Systems, 

[2]          J. Pasch, T. Conboy, D. Fleming, and G. Rochau, “SANDIA REPORT Supercritical CO 2 Recompression Brayton Cycle: Completed Assembly Description.” [Online]. Available: http://www.ntis.gov/help/ordermethods.asp?loc=7-4-0#online

 

Presenting Author: Reem Ahmed Brunel University of London

Presenting Author Biography: Reem Ahmed is a Marie Skłodowska-Curie doctoral researcher (PhD student) at Brunel University London. Her research focuses on control strategies and optimisation of supercritical CO₂ (sCO₂) power generation systems for both direct and indirect heating configurations.

Authors:

Reem Ahmed Brunel University of London
Abdulnaser Sayma Brunel University of London