乙烯深冷分离工艺中LNG冷能利用的可行性

充分利用液化天然气（LNG）携带的冷量,不仅可降低下游天然气供气成本,还可减少LNG汽化带来的环境污染;传统乙烯深冷分离工艺需压缩制冷系统提供不同温位的冷量分离裂解气,消耗大量压缩功耗.将LNG冷量用于30万吨/年乙烯装置的深冷分离工艺,取代部分压缩制冷负荷的集成利用研究结果表明:LNG冷量在乙烯分离工艺中的利用率达76.5％,可替代原工艺中的冷量负荷约22472 kW,节省丙烯、乙烯、甲烷冷剂三机压缩制冷的功耗约11968 kW,大大降低乙烯装置的能耗成本.但LNG冷量仅与乙烯分离工艺集成,传热过程火用效率较低,建议将LNG冷量集成利用于两种或以上冷量利用工艺中,从而减少利用过程的冷火用损失,提高LNG冷量的利用效率.

Utilization of Cryogenic Energy of LNG in Ethylene Cryogenic Separation Process

Liquefied natural gas (LNG) has a large amount of cold energy. If LNG’s cryogenic energy can be used effectively, its gasification would cost fewer and make environmental pollution less. The conventional ethylene cryogenic separation process needs different degrees of cryogenic energy, which comes from compressing refrigeration system, to separate cracking gas for ethylene and propylene. In this paper, the LNG’s cryogenic energy is used into ethylene cryogenic separation process to reduce the electrical power consumption of its compressing refrigeration system. The research in an unit of annual producing 300 kT ethylene shows that LNG can provide 22472 kW cryogenic energy, resulting a direct save of 11968 kW of compressing power and making the applied rate of LNG’s cryogenic energy as high as 76.5%. However, the corresponding exergy efficiency is too low, when LNG’s cryogenic energy only used in ethylene separation process, for the high heat transfer temperature difference. So two or more processes, which need cold energy, should be integrated with LNG’s cold energy, to lower heat transfer temperature difference, reduce exergy loss and improve the applied rate of LNG’s cold energy.