Cryogenic energy assisted power generation utilizing low flammability refrigerants

Abstract

Cryogenic carbon-neutral fuels are potential alternatives as future marine fuels, releasing waste cryogenic energy during regasification and waste thermal energy during combustion. Organic Rankine Cycles (ORCs), using flammable hydrocarbon working fluids, are the preferred waste energy reutilization technology, prioritized over Brayton and Kaline cycles due to their compact system configuration. However, hydrocarbon flammability and explosiveness poses a huge safety risk. Therein lies the novelty of this study which presents an advanced dynamic model of a cryogenic enhanced ORC utilizing low flammability hydrofluorocarbons as working fluids for simultaneous reutilization of waste thermal and cryogenic energy from carbon-neutral cryogenic fuels. The evaporation temperature exhibits a direct correlation with energy and an inverse correlation with the exergy performance. System overcharging leads to a drastic performance decline, while undercharging can be tolerated to a certain liquid-to-volume ratio until critical failure. Marine classification societies’ recommendations-based scenarios were employed to gauge the emission reduction potential of low flammability working fluids for cryogenic ORCs, pitted against traditional combustion technologies. A maximum specific net-work, thermal efficiency, exergy efficiency, and cryogenic energy efficiency of 45.64 kJ/kg, 10.43 %, 12.75 %, and 11.8 % was achieved, respectively, with 85 % reduction in GHG emissions, using R452B as the working fluid.