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The maritime industry will continue to see increasing regulatory requirements to reduce carbon emissions from ships' operations. Improving the energy efficiency of ships with waste heat recovery systems based on the organic Rankine cycle (ORC) is an attractive way to meet these tightening requirements. The operational profile of a ship has a huge influence on the feasibility of installing ORC onboard as it affects the waste heat source profile from the diesel engines. However, to date, scant attention has been paid to examining the effects that the operational profile has on the marine application of ORC as it is both difficult and expensive to obtain. The present paper aims to describe a methodology that can overcome this problem by developing a generic ship speed profile that defines the ship's operational profile. This speed profile works together with a fit-for-purpose diesel engine waste heat model to derive a waste heat source profile that is used as the input to a thermoeconomic analysis that can justify the installation of ORC. The proposed methodology allows for an objective comparison of the feasibility of ORC subjected to variations in the operational profile. Furthermore, the optimum ORC design can be identified to meet payback time expectations of different shipowners. [ABSTRACT FROM AUTHOR]

A review of the literature indicates that current tri-generation cycles show low thermal performance, even when optimised for maximum useful output. This paper presents a Finite Time analysis of a tri-generation cycle that is based upon coupled power and refrigeration Carnot cycles. The analysis applies equally well to Stirling cycles or any cycle that exhibits isothermal heat transfer with the environment and is internally reversible. It is shown that it is possible to obtain a significantly higher energy utilisation factor with this type of cycle by considering the energy transferred during the isothermal compression and expansion processes as useful products thus making the energy utilisation larger than the enthalpy drop of the working fluid of the power cycle. The cycle is shown to have the highest energy utilisation factor when energy is supplied from a low temperature heat source and in this case the output is biased towards heating and cooling. [ABSTRACT FROM AUTHOR]