Supercritical CO2 cycle and applications – Potential use in ships

Abstract

With climate change being the defining issue of our generation, decarbonization of the shipping industry has become the top priority of the maritime community. In an effort to reduce emissions from shipping, numerous technological and design solutions are being investigated. This thesis focuses on the recovery of the heat wasted by marine engines using a supercritical carbon dioxide Brayton cycle. The supercritical carbon dioxide Brayton cycle is an innovative technology that promises power generation with unprecedented performance and a small form factor, due to the properties of supercritical fluids. The objective of this thesis is to provide important insight on this new technology as well as the current stage of research. Furthermore, a thermodynamic model will be developed in MATLAB with the use of the COOLPROP library, aiming to analyze and optimize the performance of a recuperated supercritical carbon dioxide Brayton cycle used for waste heat recovery of a MAN 6G70ME-C10.5-GA-EGRBP marine engine. The performance analysis was conducted at the engine’s specified maximum continuous rating as well as at partial loads. The results showed that with the use of this technology, the combined system’s thermal efficiency can be increased by 2.9% and its specific fuel oil consumption can be reduced by 2.8%, while there are also significant performance benefits even at lower loads. Moreover, the effect of the main engine’s power on the supercritical Brayton cycle’s performance was studied, where 7 marine engines of the same injection technology and different power outputs were compared, and the results revealed a possible relationship between the optimal pressure ratio and the engine’s exhaust gas temperature. Finally, our model was compared to a similar organic Rankine cycle model, an already field proven technology in the waste heat recovery sector. The results showed that both systems have similar performance.