A feasibility study of Organic Rankine Cycle (ORC) power generation using thermal and cryogenic waste energy on board an LNG passenger vessel

This study develops a novel approach to reutilize cryogenic and thermal waste energy on a liquefied natural gas (LNG)-powered passenger vessel. The waste energy is identified through a series of field tests of the LNG evaporation system and other important machinery systems, including the main engines, on a case ship. An Organic Rankine Cycle (ORC) power generation system is proposed to work between the LNG boiling temperature of -138 degrees C (at 5bar) and the waste heat temperature level of 400 degrees C from the main engines' exhaust gas. The proposed ORC system is designed in terms of the field testing data and analyzed through simulation using Siemens LMS Imagine.Lab AMESim. Two different arrangements (single stage and 2 stages) of ORC are energetically, exergically, and economically analyzed. Three optimal working fluids are examined in high vacuum and above atmospheric condensing pressures in the temperature range of -110 degrees C to 300 degrees C. The proposed ORC systems are characterized by a significant improvement in thermal efficiency and power production in high vacuum condensing pressures. The 2-stage ORC presents higher power output and fuel cost saving per year than the single-stage ORC with almost the same payback time. The higher percentage of exergy destruction occurs at the evaporator of the ORC system. The increase in the exergy destruction on the condenser at higher condensing pressures contributes to the decrease of the exergy efficiency of the ORC systems.