中文摘要：

针对低压天然气特点，设计了3套天然气闭式膨胀液化流程，选择PR（Peng—Robinson）方程进行混合物的相平衡计算，采用化工模拟软件PRO／Ⅱ进行了模拟计算；分析比较了不同液化流程的关键热力学参数，并进行了关键设备的可行性分析。结果表明：丙烷预冷双级天然气膨胀液化流程的比功耗比无预冷单级天然气膨胀液化流程、无预冷双级天然气膨胀液化流程低，液化率高，而且设备均可实现。综合分析结果，选用了丙烷预冷双级天然气膨胀液化流程。并指出天然气节流前温度越低，其液化率越高，比功耗越小。天然气膨胀比越高，液化率越高。

英文摘要：

According to the characteristics of low - pressure natural gas, three closed expander liquefaction systems for natural gas were designed. The PR （ Peng - Robinson） equation was selected to calculate phase equilibrium of the mixture, the chemical process simulation software PRO/II was used to simulate the difference liquefaction systems and the effects of some key thermodynamics parameters on liquefaction systems were analyzed in detail. The results shown that the liquefaction power with propane pre - cooling was less than one of single - stage liquefaction system without pre - cooling and the two - stage liquefaction system without pre - cooling, and had higher liquefaction rate. According to analysis results, the liquefaction system with propane pre -cooling is a better choice. At last,we notice that the lower the throttling temperature is, the higher the liquefaction rate is, the smaller the liquefaction power is. The higher the expansion ratio is, the higher the liquefaction rate is.