EXERGY ANALYSIS OF LIQUEFIED NATURAL GAS (LNG) BOIL-OFF GAS (BOG) RE-LIQUEFACTION CYCLES FOR ON-BOARD APPLICATION

摘要

This research paper presents boil-off gas (BOG) of liquefied natural gas (LNG) re-liquefaction cycles for onboard system. Several BOG reliquefaction cycles are investigated to maintain the proper pressure of BOG in the LNG storage tank. A thermodynamically simple cycle such as single mixed refrigerant (SMR), the improved SMR cycles with one phase separator (SMR-P, SMR-P’), and a combination cycle (HYBRID) of SMR and expander are proposed and analyzed. From the analysis results, the work consumption per unit LNG of each cycle is 0.712, 0.899, 0.832, and 0.656 kWh/kg?BOG, respectively. For the onboard system, compactness is also one of the important factors. Size of the cycles are proportional to the mass flow rate and the total heat transfer amount. The HYBRID cycle has the proper mass flow rate and amount of heat transfer for onboard system. The analysis result reveals that the HYBRID cycle is the most appropriate BOG re-liquefaction cycle in the respect of specific work consumption per unit BOG and compactness.