混合制冷级联天然气液化工艺优化及分析

Optimization and analysis of natural gas liquefaction process in mixed fluid cascade

混合制冷级联(MFC)工艺是大型基地负荷型天然气液化过程最具竞争力的工艺之一,其工艺由天然气预冷、液化和过冷三个混合制冷循环构成,涉及冷剂配比、制冷温度及压力等关键参数,使其过程复杂和敏感。针对MFC液化工艺,建立了以比功耗为目标的优化函数,借助Aspen HYSYS流程模拟与物性计算,采用序列二次规划法(SQP)优化算法对MFC工艺进行全局优化,并对工艺过程进行有效能分析。优化结果表明,全局优化后,MFC液化过程的比功耗为899.36 kJ/kg,降低了7.38%;多股流换热器冷热复合曲线匹配得更好。通过有效能分析发现,制冷压缩机机组的有效能损失占比最大,优化后多股流换热器的有效能损失显著降低,液化过程的有效能效率由38.17%提高到41.21%,能量利用效率提高明显。

The mixed fluid cascade(MFC)process is one of the most competitive processes for large-scale base-loaded natural gas liquefaction process,which consists of three mixed refrigeration cycles of natural gas pre-cooling,liquefaction,and subcooling,which involves key parameters such as refrigerant ratios,refrigeration temperatures,and pressures,which makes the process complex and sensitive.For the MFC liquefaction process,an optimization function with specific power consumption as the objective is established,and with the help of Aspen HYSYS process simulation and physical property calculation,the sequential quadratic programming(SQP)optimization algorithm is used to globally optimize the MFC process and conduct energy efficient analysis of the process.The optimization results show that after the global optimization,the specific power consumption of the MFC liquefaction process is 899.36 kJ/kg,which is 7.38%lower.The cold-heat composite curve of the multi-strand flow heat exchanger is better matched.Through the effective energy analysis,it is found that the effective energy loss of the refrigeration compressor unit accounts for the largest proportion,and the effective energy loss of the multi-strand flow heat exchanger is significantly reduced after the optimization,and the effective energy efficiency of the liquefaction process is increased from 38.17%to 41.21%,and the energy utilization efficiency is improved obviously.