A feasibility study of HFO refrigerants for onboard BOG liquefaction processes

Abstract

As the global demand for natural gas continues to increase, the production of liquefied natural gas (LNG) and the demand for LNG carriers are also on the rise. Following the advent of LNG propulsion engines, there has been widespread adoption of systems that use LNG or boil-off gas (BOG) as fuel, and subsequently re-liquefy remaining gas thorough the re-liquefaction system. In this study, we investigated the feasibility of hydrofluro-olefins (HFO) refrigerants, the newly developed refrigerants having low flammability and low global warming potential (GWP), in BOG re-liquefaction systems for liquefied natural gas carriers. Simulations of BOG re-liquefaction process were conducted and optimized to minimize energy consumption. Then, the explosion risk and global warming potential during the lifespan of the re-liquefaction processes are also analyzed. The optimization results indicate that using HFO refrigerants in the re-liquefaction process yields comparable energy consumption to the conventional hydrocarbon refrigerants. Additionally, the use of HFO refrigerants can contribute to reducing explosion risk of liquefaction process. However, despite HFO refrigerants being considered an environmentally friendly refrigerant, it is important to note that global warming impact has not decreased as significantly as expected. This is primarily due to the fact that the GWP of the system is heavily influenced by energy consumption. © 2023 The Authors. Published by Elsevier Ltd.