Dynamic modelling of ORC system for vessel waste heat recovery

Abstract

The present study presents the dynamic modelling in Dymola software of a vessel waste heat recovery Organic Rankine Cycle-ORC operating with R1233zd(E) that functions as a topping cycle of a cascade prototype also involving an Ejector Vapor Compression Cycle-EVCC as a bottoming cycle developed in the framework of the ZHENIT project. The ORC is designed to have a nominal thermal input of about 95 kWth and is driven by Therminol VP1 oil at inlet and outlet temperatures of 150 ℃ and 130 ℃ while it includes two operating modes: 1) electricity-only, in which a recuperator is used and the condensation temperature is low and 2) combined heat and power (CHP), in which the recuperator is bypassed and the condensation temperature is raised to produce hot water. At the system design point, the evaporation temperature is 120 ℃, the condensation temperature 30℃ and 50℃ for electricity-only mode and CHP mode respectively, the superheating degree at expander inlet 10 K and the subcooling degree at condenser outlet 5 K. The system dynamic behavior is investigated considering a pump and expander reduction speed from 100% to 80% of the nominal. According to the results, the system has a fast response to the aforementioned disturbances.