膨胀机液化流程中的冷剂配比及性能优化

Seletction of refrigerant composition for energy efficient expansion liquefaction process

小型天然气液化装置具有结构紧凑、投资少、操作简单等优点。采用化工软件HYSYS对氮气膨胀流程、丙烷预冷氮气膨胀流程和丙烷预冷N2-CH4膨胀流程进行模拟,以比功耗为目标函数,对液化流程的关键参数以及制冷剂组分进行优化,发现由于N2和CH4的比热容Cp、绝热指数k不同,使得N2与CH4之间存在最优配比。结果表明,优化后的丙烷预冷膨胀液化流程比功耗要比传统氮气膨胀液化流程要少22.7%。制冷剂在循环过程中均处于气相,受外部环境影响较小,因此优化后的N2-CH4膨胀流程在我国小型零散天然气市场具有良好的前景。

Small - scale LNG（ Liquefied Natural Gas） plants has many advantanges, including compact structure, low initial equipment cost, simple operation and so on. In this paper, expansion process, nitrogen expansion cycle with propane pre -cooling and N2 - CH4 expansion process with propane pre - cooling were simulated and designed by the software Aspen Hysys and optimized with unit power consumption as the index. Due to the different specific heat capacity and isentropic exponent, the optimal value of refrigerant composition was obtained. The optimization results indicate that the process with propane pre - cooling demands less unit power consumption by 22.7% than the conventional nitrogen expansion process. The refrigerants exist in vapour phase, which owns better adaptability to the changing surroundings, therefore the optimized N2 - CH4 expansion process plus propane pre - cooling shows great prospects in small - scale LNG plants.