LNG接收站BOG多阶压缩再液化工艺优化分析

Simulation-based optimization and analysis of BOG multi-stage compression and recondensation process at LNG receiving terminal

LNG接收站蒸发气体(BOG)处理量和液化天然气(LNG)外输量的波动对BOG再冷凝工艺提出低能耗、大弹性、易操作的要求。以系统总能耗最小为目标函数,对建立的BOG多阶压缩再液化工艺模型中压缩阶数和阶压比等参数进行了优化,并分析了该工艺模型在工况波动影响系统能耗时的各阶压比的抗干扰性及系统的操作弹性。结果表明:多阶压缩工艺系统阶数越多,系统的总压比、总能耗越小,BOG处理能力也越大;但随着系统阶数的增加,节能效果降低。多阶再液化工艺中二阶系统比现有一阶系统的操作弹性增大12%,且在LNG与BOG质量比≤10时,二阶系统的BOG压缩功耗可节约33%以上。针对一般气源型接收站工况,二阶系统是节能且操作弹性大的BOG处理工艺。

As BOG （boil-off gas） production and LNG downstream load fluctuate frequently and sharply at LNG receiving terminal, BOG recondensation process operates with high energy consumption and instability. Through thermodynamics-based analysis of BOG processing system, a BOG multi-stage compression and recondensation process model was established, aiming at lowing energy-consumption as well as improving flexibility and operability of the BOG recondensation process. The model parameters of number of stages and single stage compression ratio were optimized by minimizing the objective function of total energy. The result showed that for a specific BOG and LNG load, the more the stages of the multi- stage compression and recondensation process system, the less the energy consumed （correspondingly, a smaller total compression ratio and a larger processing capacity of BOG）; however, the energy-saving effect became more and more insignificant as the system number of system stages increased. Compared with the current one-stage system, operating flexibility of the two-stage system was improved by 12%, and compression energy was saved by more than 33% when the mass ratio of LNG and BOG was less than 10. Two-stage system was recommended for processing BOG at LNG receiving terminal.