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When considering waste heat recovery systems for marine applications, which are estimated to be suitable to reduce the carbon dioxide emissions up to 20%, the use of organic Rankine cycle power systems has been proven to lead to higher savings compared to the traditional steam Rankine cycle. However, current methods to estimate the techno-economic feasibility of such a system are complex, computationally expensive and require significant specialized knowledge. This is the first article that presents a simplified method to carry out feasibility analyses for the implementation of organic Rankine cycle waste heat recovery units on board vessels using low-sulfur fuels. The method consists of a set of regression curves derived from a synthetic dataset obtained by evaluating the performance of organic Rankine cycle systems over a wide range of design and operating conditions. The accuracy of the proposed method is validated by comparing its estimations with the ones attained using thermodynamic models. The results of the validation procedure indicate that the proposed approach is capable of predicting the organic Rankine cycle annual energy production and levelized cost of electricity with an average accuracy within 4.5% and 2.5%, respectively. In addition, the results suggest that units optimized to minimize the levelized cost of electricity are designed for lower engine loads, compared to units optimized to maximize the overall energy production. The reliability and low computational time that characterize the proposed method, make it suitable to be used in the context of complex optimizations of the whole ship's machinery system.

The selection of a proper machinery system is one of the primary decisions to be taken during the ship-design phase. Nonetheless, this selection is made challenging by the presence of a variety of alternatives, and by the limited data availability at the early stages of the design phase. An optimization framework is presented in this paper, supporting decision making at the earliest stages of the ship-design process. The framework is suitable to perform the screening and the selection of optimal machinery configurations for a predefined ship operational profile, and it includes both linear and non-linear optimization routines. The results of the linear and the non-linear approaches are compared, and indications on what conditions are the most suitable for the application of one or the other approach are provided. Both approaches are tested for two case studies, a bulk carrier and a small cruise ship. The results indicate that both optimization approaches lead to the same layout of the machinery system, but to slightly different unit scheduling. This suggests that the use of the linear approach is suitable for design purposes, but less appropriate for operational optimization. In addition, the findings of the work suggest that the trade-off between fuel consumption and volume of the engines should be considered when selecting the machinery system for a ship.

A well-verified heat transfer correlation to predict the thermal performance of flow condensation is essential for optimal condenser design in organic Rankine cycle systems. This paper aims at evaluating the prediction accuracy of existing correlations for the flow condensation in plate heat exchangers, and studying the impact of using different correlations for the design and performance estimation of organic Rankine cycle units. In order to achieve these goals, an experimental test campaign was conducted with the working conditions that commonly prevail in condensers of organic Rankine cycle units, and the test data were subsequently utilized for comparison with the predicted values calculated using existing correlations. Moreover, a simulation framework was applied for a case study of waste heat recovery. The results indicate that the correlations from Yan et al. (1999) show best predictive performance to the test data, resulting in a mean absolute percentage deviations below 20 %. With respect to the case study, the required heat transfer area for the plate condenser ranged from 75.8 m2 to 132 m2, and the estimated power output of the unit, for a given condenser design, varied in the range -7.2 % to +8 % compared to the target value. The results hence indicate the need for more accurate prediction methods and generally applicable heat transfer correlations

The selection of a proper machinery system is one of the primary decisions to be taken during the ship design phase. Several machinery system configurations are possible, including the use of mechanical and diesel electric propulsion. Nonetheless, little data is available at the early stages of the design phase, making it challenging to define the optimal configuration to be installed on board. Moreover, the screening of different alternatives is a lengthy process, which is mostly carried out manually by the ship designers. As a way to support decision making at the earliest stages of the ship design process, an optimization framework was developed. The framework is suitable to perform the screening and the selection of optimal machinery configurations for a predefined ship operational profile, and it includes both linear and nonlinear optimization routines. The linear approach has faster, and more reliable solvers, but requires a relatively high simplification of the behaviour of the machinery system. The nonlinear approach, while more accurately representing the system performance, requires longer computational times. In addition, the latter can be expanded to multi-objective optimizations, where the solver not only tries to reach the minimum fuel consumption for a ship, but also takes into account the required space on board. The aim of this paper is to compare the results of the linear and the nonlinear approaches, and to provide indications on what conditions are the most suitable for the application of one, or the other approach. Both approaches are tested for two case studies, a bulk carrier and a small cruise ship. The results show that both the optimization approaches led to the same layout of the machinery system, with the linear optimizer converging in a much shorter time. However, the attained solutions feature slightly different unit scheduling. This suggests that, while the linear approach might be the most suitable for design purposes, it

Gas-fuelled shipping is expected to increase significantly in the coming years. Similarly, much effort is devoted to the study of waste heat recovery systems to be implemented on board ships. In this context, the organic Rankine cycle (ORC) technology is considered one of the most promising solutions. The ORC favorably compares to the steam Rankine cycle because of its simple layout and high efficiency, achievable by selecting a working fluid with desirable properties. This paper aims at assessing the fuel savings attainable by implementing ORC units on board vessels powered by liquefied natural gas (LNG). The study compares the performance of six different ORC configurations both in design and off-design operation, and provides guidelines with respect to the most promising heat sources and sinks to be utilized by an ORC unit in order to maximize the annual fuel savings. In addition, this paper describes a novel ORC layout rejecting heat to two heat sinks. The results indicate equivalent fuel savings up to 8.9 % when harvesting heat from the exhaust gases, and that the novel configuration ensures an increment of the ORC design power output up to 41 % when utilizing the jacket cooling water as heat source.