Thermodynamic and turbomachinery design analysis of supercritical Brayton cycles for exhaust gas heat recovery

Abstract

Significant amount of energy is wasted in engine systems as waste heat. In this study, the use of supercritical Brayton cycles for recovering exhaust gas heat of large-scale engines is investigated. The aim of the study is to investigate the electricity production potential with different operational conditions and working fluids, and to identify the main design parameters affecting the cycle power production. The studied process configurations are the simple recuperated cycle and intercooled recuperated cycle. As the performance of the studied cycle is sensitive on the turbomachinery design and efficiencies, the design of the process turbine and compressor were included in the analysis. Cycles operating with CO2 and ethane resulted in the highest performances in both the simple and intercooled cycle configurations, while the lowest cycle performances were simulated with ethylene and R116. 18.3 MW engine was selected as the case engine and maximum electric power output of 1.76 MW was simulated by using a low compressor inlet temperature, intercooling, and high turbine inlet pressure. It was concluded that working fluid and the cycle operational parameters have significant influence not only on the thermodynamic cycle design, but also highly affects the optimal rotational speed and geometry of the turbomachines.