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.

液化天然气（LNG）再气化终端中产生大量的蒸发气体（BOG），这是不可避免的。大多数终端使用送出的LNG进行成本高昂的BOG再液化过程。在这项工作中，我们研究了此过程的初步设计，目的是将其总年度成本（TAC）降至最低。我们为再液化过程提供了一个全面的上部结构，其中包括了几种工艺选项，用于在不同压力下使用LNG冷却BOG，并允许在多个阶段进行再冷凝。然后，我们为上层建筑中的工艺单元开发定制的仿真/尺寸确定模块，并实施减少优化过程中显式约束的过程。考虑到现实的设计规范和操作限制，我们针对各种BOG费率和条件优化了案例研究终端。尽管TAC随着BOG速率的增加而大大增加，但两步再冷凝始终是最佳的。在大多数情况下，在第一个再冷凝器之前采用高压液化天然气进行BOG冷却的2再冷凝器方案是最佳的。