Investigation on thermo-economic performance of shipboard waste heat recovery system integrated with cascade latent thermal energy storage

Abstract

Waste heat recovery (WHR) from engine exhaust gas is a viable solution to improve energy utilization and reduce greenhouse gas emissions for marine power plants. However, the WHR system will operate inefficiently and even be shut down due to the variations of waste heat availability. In this study, a CO2-based WHR system integrated with cascade latent thermal energy storage (CLTES) is presented to ensure the efficient and continuous operation throughout the ship's voyage. The objective of the current work is to assess the thermo-economic performance of the proposed WHR system in a case cruise through theoretical analysis. The thermodynamic models under both design and off-design conditions are developed, and the strategy of exhaust gas assignment for WHR system is identified. Also the effects of main design parameters on the system performance are discussed. In addition, the performance comparison between the proposed WHR system and the conventional one is carried out. The results show that there is a trade-off between pump efficiency and turbine efficiency for the desired power capacity, and turbine efficiency has greater impact on the thermo-economic performance enhancement of the proposed system than pump efficiency. The total net power output and heating capacity from the proposed system during a daily voyage are respectively 5356 kWh and 6958 kWh, which are 19.1 % and 7.9 % higher than those of the traditional WHR system. And the levelized exergy cost of the proposed system decreases by 17.9 % compared with the reference cycle.