A re-liquefaction process of LNG boil-off gas using an improved Kapitsa cycle: Eliminating the BOG compressor

Chenghong Wang, Daming Sun, Qie Shen, Yuanyuan Duan and Xiaoxue Huang

Energy, 2024, vol. 304, issue C

Abstract: Re-liquefication of boil-off gas (BOG) from liquefied natural gas is essential for maintaining LNG tank safety and facilitating methane recovery. This study aims to reduce the energy consumption of the BOG re-liquefaction process based on the reverse Brayton cycle (RBC) and eliminates the need for a BOG compressor. The classical Kapitsa cycle is improved by making the expander backpressure lower than the pressure of liquid nitrogen after throttling and employed in the BOG re-liquefaction process without a BOG compressor. A comprehensive analysis is conducted, including the sensitivity of independent operating parameters, global optimization using a genetic algorithm, and subsequent thermodynamic, economic, and environmental assessments based on the optimization results. Furthermore, the impact of BOG flowrate and temperature variations on system performance is investigated. Results showed that the proposed process is more efficient than the conventional BOG indirect processes employing the classical Kapitsa cycle or RBC. A minimum specific energy consumption (SEC) of 0.82 kWh·kg−1 is achieved, and the figure of merit is up to 30.9 %. The payback period of total capital investment is estimated to be merely one month. Carbon dioxide emissions are decreased by 137462 kg·h−1 compared to direct BOG emissions. SEC could reach 0.82 kWh·kg−1 across varying BOG flowrates by adjusting the refrigerant flowrate.

Keywords: Liquefied natural gas; Boil-off gas; Re-liquefication; Kapitsa cycle; Optimization; Liquid nitrogen (search for similar items in EconPapers)
Date: 2024
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Persistent link: https://EconPapers.repec.org/RePEc:eee:energy:v:304:y:2024:i:c:s0360544224017523

DOI: 10.1016/j.energy.2024.131979

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