Performance analysis of a boil-off gas re-liquefaction process for LNG carriers

Abstract

With the growth of LNG demand and rapid rise in natural gas prices, it is of great significance to develop an efficient boil-off gas (BOG) re-liquefaction process for LNG carriers. This paper proposes a BOG re-liquefaction process using the single mixed refrigerant (SMR) cycle, and comprehensively compares it with the typical Mark III process. The processes were rigorously simulated with Aspen HYSYS, and performed process optimization in terms of specific energy consumption (SEC) as the objective function using the genetic algorithm method. Sensitivity and exergy analysis were also conducted to assess process variables and irreversibility. Furthermore, the processes were performed economic analysis including the total capital cost (TCC), total operating cost and total annualized cost (TAC). The results show that the SEC and major equipment exergy loss of the proposed process have 529.4 kWh/ton and 465 kW, which are 50.34% and 40.88% lower than the Mark III process. Additionally, the TAC for proposed process presents 4.07 million USD/year, compared to 6.62 million USD/year for the Mark III, resulting in a 38.55% annual savings.