Optimal design of boil-off gas reliquefaction process in LNG regasification terminals

• Published in: Computers & chemical engineering Vol. 117; pp. 171 - 190
• Main Authors: Nagesh Rao, Harsha, Karimi, Iftekhar A
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 02.09.2018
• Subjects: Boil-off gas; LNG; Regasification terminal; Reliquefaction; Boil-off gas; LNG; Regasification terminal; Reliquefaction
• ISSN: 0098-1354; 1873-4375
• DOI: 10.1016/j.compchemeng.2018.06.003

•Minimum-cost design of the BOG reliquefaction process in LNG Regasification Terminals.•Superstructure allows two-stage recondensation and direct/indirect BOG cooling by LNG.•Developed custom simulation modules for the process units to eliminate explicit constraints.•Two-stage recondensation is optimal for all the BOG rates and conditions considered.•2-recondenser scheme with BOG cooling by HP-LNG before the first recondenser is robust. Boil-off gas (BOG) generation in liquefied natural gas (LNG) regasification terminals is substantial and unavoidable. Most terminals employ a cost-intensive BOG reliquefaction process using the send-out LNG. In this work, we study the preliminary design of this process with the objective of minimizing its total annualized cost (TAC). We present a comprehensive superstructure for the reliquefaction process that incorporates several process options for cooling BOG using LNG at different pressures, and allows recondensation in multiple stages. Then, we develop custom simulation/sizing modules for the process units in our superstructure, and implement a procedure to reduce explicit constraints during optimization. Considering realistic design specifications and operational constraints, we optimize a case study terminal for various BOG rates and conditions. While the TAC increases substantially with BOG rate, two-stage recondensation is always optimal. A 2-recondenser scheme with BOG cooling by the high-pressure LNG before the first recondenser is optimal for most cases.