Review on the design and optimization of BOG re-liquefaction process in LNG ship

In recent years, liquefied natural gas (LNG) boil-off gas (BOG) re-liquefaction technologies in LNG ships have been developing rapidly as LNG trade across the sea has become a hot spot in global energy trade. However, there are lots of restrictions on board and BOG re-liquefaction is an energy-intensive industrial process. Reducing energy consumption, improving efficiency and reducing costs play an important role in the BOG re-liquefaction processes. In this paper, the detailed progress of design and optimization for the BOG re-liquefaction processes in recent years are summarized. Two categories of the re-liquefaction processes, indirect re-liquefaction processes and direct re-liquefaction processes, are specifically discussed. The indirect re-liquefaction process includes the nitrogen refrigeration cycle re-liquefaction process, the mixed refrigerant cycle re-liquefaction process and the oxygen refrigeration cycle re-liquefaction process. Finally, the challenges and the future directions to address these challenges for the BOG re-liquefaction process in LNG ships are proposed.