Systematic evaluation of efficiency improvement options for sCO2 Brayton cycles

Abstract

Supercritical CO2 (sCO2) based power cycles have gained an increased attention because of their potential to offer a higher cycle efficiency combined with improved process economics and operational flexibility. The potential for further development and commercialization is determined by the right balance between cycle efficiency, design complexity, and economics. The present study analyzes different pathways to improve the design of generic sCO2 Brayton cycles for power generation based on a structured pattern known from conventional water-steam cycles. Starting from a simple cycle design, different options such as preheating, intercooled compression, reheating, and split-compression are investigated. The application of an exergy analysis for each design provides the possibility to identify the location and magnitude of thermodynamic inefficiencies for each design option. With the use of a complexity metric, the offset between efficiency improvement and increase in system size and complexity can be quantified in the absence of appropriate economic data. The results show the inherent trade-off between the increase in efficiency and complexity with the best cycle improvement options being preheating by recuperation, split-compression, and intercooled compression. In principle, the suggested complexity metric approach is useful when evaluating similar systems and provides tangible results for subsequent, more detailed studies.