Auxiliary power through marine waste heat recovery using a CO₂-organic cascading cycle

An appreciable part of primary energy input to a marine diesel engine is rejected as waste heat. Thus, through marine diesel engine waste heat recovery significant amount of secondary energy can be produced to satisfy the auxiliary power requirement of the marine ship. In present study, a CO₂-organic fluid cascading cycle is considered for the utilization of the waste heat released by the marine diesel engine. R290, R600 and R1233zd (E) are considered as the working fluids of the bottoming cycle for their lower global warming potentials. The analysis revealed that power output of the cascading cycle is comparable to that of the baseline transcritical CO₂ power cycle. However, for similar power output, operating pressure in the flue gas-CO₂ heat recovery unit of the transcritical CO₂ power cycle is significantly higher compared to that of the cascading cycle. Thus, possible leakage due to very high operating pressure of a conventional CO₂ power cycle can be addressed by using the cascading system. Bare module costs per unit power output of cascading cycles are also significantly smaller. It is also apparent from the study that the marine diesel engine waste heat recovery through the CO₂-organic cascading cycle would lead to 8–9.5% annual fuel saving. Reduced fuel consumption will also result in lesser CO₂ emission from the marine ship.