Performance enhancement of marine LNG BOG reliquefaction systems via passive diffuser integration: a thermodynamic and economic assessment

Abstract This article presents a novel thermodynamic approach to improve energy efficiency and cost-effectiveness of boil-off gas (BOG) reliquefaction systems on marine carriers. The study investigates the impact of installing six stationary diffusers upstream of each compressor within both the BOG and mixed refrigerant (MR) cycles. Simulation using Aspen HYSYS revealed substantial performance improvements: the coefficient of performance (COP) increased by 16.42% (from 0.14 to 0.163), exergetic efficiency (FOM) improved by 16.07% (from 22.4% to 26%), specific power consumption decreased by 14.12% (from 3638 to 3124 kW/[kg/s]), and specific energy consumption declined by 14.85% (from 1.01 to 0.86 kWh/[kg/s]). Additionally, the total heat rejected to seawater increased by 18.19% (from 191.9 to 226.81 kW), and the energy cost for a 10-day voyage dropped by 14.85% (from $9892 to $8423). These gains were accompanied by a 68.48% rise in total plant irreversibility due to increased compressor discharge temperatures. The results confirm that integrating passive diffusers can significantly enhance the thermodynamic and economic performance of marine LNG reliquefaction systems.