Modelling and simulation of organic Rankine cycle waste heat recovery system with the operational profile of a ship

Abstract

Organic Rankine cycle (ORC) is a promising new technology to improve the energy efficiency of ships by recovering energy from the diesel engine’s waste heat. Unlike land-based applications of ORC in geothermal or biomass power plants, the temperature and flow of the waste heat source onboard a ship vary with its operational profile and environmental conditions as it sails around the world. In addition, the design of the ORC also involves multiple design options starting from the selection of cycle configuration, working fluid, components and control strategy that are peculiar to ship operations. All these make it difficult to compare different options objectively and efficiently. A system modelling and simulation approach that requires minimal data input to assess the feasibility of ORC onboard ships is proposed using a commercial-off-the-shelf software tool, Amesim. A novel waste heat source model is developed based on the generic operational profile for a ship and a fit-for-purpose diesel engine waste heat model. This is followed by a detailed analysis of the various ORC design options for marine applications that will provide a foundation on which advanced thermoeconomic optimisation can be performed to find the optimum solution. The results from the models are verified with other studies and also validated with experiments where available. The case study on the offshore service vessel demonstrated how the feasibility of different ORC can be affected by changing the generic operational profile. The proposed methodology has contributed to the research field by providing a holistic and systematic way for the shipowners to justify their investment decision on adopting ORC on their ships based on its thermal, economic and environmental performance taking into account the ship’s operational profile. Waste heat recovery improves the overall energy efficiency of their shipboard energy systems and will help in the overall strategy of decarbonising the maritime industry.