Dual precooling enhanced nitrogen-expanded BOG reliquefaction process for LNG-fueled ships

By re-liquefying the evaporated gas in the BOG reliquefaction process, operational expenses are minimized, simultaneously advancing environmental sustainability and improving resource usage. Most current reliquefaction processes untilize a single precooling cycle, with limited research on multi-stage precooling configurations. This paper proposes a dual precooling cycle that utilizes propane and BOG itself as precooling agents, and reliquefies BOG using a nitrogen inverse Brayton cycle. The design focuses minimizing specific energy consumption (SEC) through simulation and optimization. Optimization results indicate that the BOG reliquefaction process achieves an SEC of 1.017 kWh/kg_LNG and an exergy efficiency of 27.29 % respectively. More than 20 % improvement in SEC compared to other single precooling processes. Cost analyses show that the dual precooled BOG liquefaction process is economically sound. Ultimately, through an analysis of the system based on BOG components and temperature variations, the system was able to operate stably.