Systematic Evaluation of Efficiency Improvement Options for sCO2 Brayton Cycles

orc2019 Tracking Number 77

Nonconventional working fluids have the potential to improve conventional, high-temperature thermal power generation processes and to enable the efficient exploitation of low-temperature heat resources. In particular, supercritical CO2 (sCO2) based power cycles have gained increased attention because of their potential to offer increased cycle efficiency, improved process economics, and operational flexibility. Various simple and more complex cycle layouts have been suggested and analyzed with the objective of improving cycle efficiency. However, with respect to potential further development and commercialization, the right balance between cycle efficiency, design complexity, and economics is required. The present study analyzes possible pathways to improve the design of generic sCO2 Brayton cycles for power generation based on a structured pattern known from conventional water­steam cycles. Starting from a simple cycle design, different options such as preheating by internal recuperation, intercooled compression, reheating, and split­recompression are investigated and their impacts on cycle efficiency and complexity are evaluated. 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 measure, the offset between efficiency improvement and the increase in system size and complexity can be quantified in the absence of economic data. The combined results thus provide a possibility to identify and evaluate promising options in system design for sCO2 cycles.