Original scientific paper
Exergy Analysis of Supercritical CO2 System for Marine Diesel Engine Waste Heat Recovery Application
Vedran Mrzljak
orcid.org/0000-0003-0323-2600
; University of Rijeka, Faculty of Engineering, Vukovarska 58, 51000 Rijeka, Croatia
Maro Jelić
; University of Dubrovnik, Maritime Department, Ćira Carića 4, 20000 Dubrovnik, Croatia
Igor Poljak
; University of Zadar, Department of Maritime Sciences, Mihovila Pavlinovića 1, 23000 Zadar, Croatia
Vedran Medica-Viola
; University of Rijeka, Faculty of Engineering, Vukovarska 58, 51000 Rijeka, Croatia
Abstract
In this research is performed an exergy analysis of supercritical CO2 system which uses various
waste heat flows from marine diesel engine to produce additional mechanical power. The performed
exergy analysis contains whole system as well as each system component individually. The observed
system produces useful mechanical power equal to 2299.47 kW which is transferred to the main
propulsion propeller shaft. Additionally produced mechanical power by using waste heat only will
reduce marine diesel engine fuel consumption and exhaust gas emissions. Main cooler has the highest
exergy destruction of all system components and simultaneously the lowest exergy efficiency in the
observed system, equal to 32.10% only. One of the possibilities how main cooler exergy efficiency
can be increased is by decreasing water mass flow rate through the main cooler and simultaneously by
increasing water temperature at the main cooler outlet. Observed system has five heat exchangers which
are involved in the CO2 heating process, and it is interesting that the last CO2 heater (exhaust gas waste
heat exchanger) increases the CO2 temperature more than all previous four heat exchangers. Whole
analyzed waste heat recovery supercritical CO2 system has exergy destruction equal to 2161.68 kW
and exergy efficiency of 51.54%. In comparison to a similar CO2 system which uses waste heat from
marine gas turbine, system analyzed in this paper has approximately 12% lower exergy efficiency due
to much lower waste heat temperature levels (from marine diesel engine) in comparison to temperature
levels which occur at the marine gas turbine exhaust.
Keywords
Exergy analysis, Supercritical CO2 system, Waste heat recovery, Marine diesel engine
Hrčak ID:
306236
URI
Publication date:
18.7.2023.
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