Abstract: The simulation model of LNG cold energy Rankine cycle power generation system is introduced, and its economy is analyzed. Using the ratio of system heat exchange area to net electric generation as the objective function to evaluate the investment efficiency, the cycle characteristics and process parameters of propane, propylene, ethane and trifluoromethane under different operating conditions are studied. The results show that the exergy efficiency of propylene system is higher than that of the other three, and the exergy efficiency of propane, ethane and trifluoromethane decreases in turn; the choice of medium has obvious influence on the value of objective function, and even in some cases, the difference of objective function caused by different circulating working medium can reach 1.3 times; taking the minimum objective function as the objective, the minimum temperature difference of condenser is 5 ℃, while the minimum temperature difference of superheater should be greater than 6 ℃; taking the objective function as the main evaluation index, ethane and trifluoromethane are more suitable as working medium of LNG cold energy Rankine cycle power generation system.    

Key words: LNG cold energy, Rankine cycle, objective function, the minimum temperature difference, optimization

摘要： 介绍了液化天然气(LNG)冷能朗肯循环发电系统模拟模型,并对其经济性进行了分析。采用系统换热面积与净发电量之比为目标函数评价投资效率,对丙烷、丙烯、乙烷和三氟甲烷4种循环工质在不同运行条件下进行了循环特性研究和工艺参数优化。结果表明:丙烯系统火用效率高于其他3种工质,丙烷、乙烷和三氟甲烷火用效率依次降低;工质的选择对目标函数值有明显影响,某些情况下,不同循环工质导致目标函数差距可达1.3倍;以最低目标函数为目标,冷凝器最小温差为5 ℃,而过热器最小温差宜大于6 ℃;以目标函数作为主要评价指标,乙烷和三氟甲烷更适合作为LNG冷能朗肯循环发电系统工质。

关键词: LNG冷能, 朗肯循环, 目标函数, 最小温差, 优化