Novel marine ejector-compression waste heat-driven refrigeration system: Technical possibilities and environmental advantages

Abstract

A novel combined ejector-compression refrigeration system for provision rooms of merchant ships was conceptualized and analyzed. The principle possibility of recovery of onboard low-grade heat (85–95 °С) of jacket cooling water was confirmed. Two ejectors of different geometries to ensure the ejector stage operation when the seawater temperature varies in a wide range were designed and proposed to install in parallel. The performance of the combined system was compared to a vapor-compression one and the choice of the rational temperatures in the condenser-evaporator tC/Ev was performed. The combined system COPtotal is considerably higher than the vapor-compression system, and it weakly depends on heat source temperature. At condensing temperature tC = 34 °С the decreasing in tC/Ev from 20/15 to 10/5 °С results in increasing of COPtotal up to 13.5 % at generation temperature tG = 80 °С and up to 15.6 % at tG = 90 °С. Utilizing the combined system for the onboard cold production will contribute to fuel savings of 25 to 33 % per voyage (operation and transport) vs. vapor-compression system. The combined system inherent the lower specific CO2 emission per 1 kW h of cooling energy emrefr than the standard system for all considered operation modes. The value of emrefr for combined system at tC/Ev = 10/5 °C, tG = 80 °C and tC = 36 °C or tC = 42 °C is 23.1% or 18.3%, respectively, less than for the vapor-compression one. The approach to analysis proposed can be used for assessment of the feasibility of utilization of low-grade heat and the retrofit of ship refrigeration systems.