Thermodynamic, Exergy and Environmental Impact Assessment of S-CO2 Brayton Cycle Coupled with ORC as Bottoming Cycle

Abstract

In this article, a thermodynamic, exergy, and environmental impact assessment was carried out on a Brayton S-CO2 cycle coupled with an organic Rankine cycle (ORC) as a bottoming cycle to evaluate performance parameters and potential environmental impacts of the combined system. The performance variables studied were the net power, thermal and exergetic efficiency, and the brake-specific fuel consumption (BSFC) as a function of the variation in turbine inlet temperature (TIT) and high pressure (PHIGH), which are relevant operation parameters from the Brayton S-CO2 cycle. The results showed that the main turbine (T1) and secondary turbine (T2) of the Brayton S-CO2 cycle presented higher exergetic efficiencies (97%), and a better thermal and exergetic behavior compared to the other components of the System. Concerning exergy destruction, it was found that the heat exchangers of the system presented the highest exergy destruction as a consequence of the large mean temperature difference between the carbon dioxide, thermal oil, and organic fluid, and thus this equipment presents the greatest heat transfer irreversibilities of the system. Also, through the Life Cycle Analysis, the potential environmental impact of the system was evaluated to propose a thermal design according to the sustainable development goals. Therefore, it was obtained that T1 was the component with a more significant environmental impact, with a maximum value of 4416 Pts when copper is selected as the equipment material.