Design and Optimization of an Improved Small-Scale Liquefaction Process for the Natural Gas Pressure-Reducing Station in Pipelines

A small-scale liquefaction process without any extra energy consumption was proposed to liquefy a part of natural gas in the pressure-reducing station. A heat exchanger network was integrated with two turboexpander-driven compressors to achieve higher performance of the natural gas liquefaction process in a pressure-reducing station. On the basis of the process simulation, the effects of the feed gas pressure (p1) and the final and intermediate expansion pressures (p10 and p7) on system performance have been investigated to determine the optimal design conditions for the proposed system. The results showed that the liquefaction rate (LR) and the exergy utilization rate (EUR) can reach their maximal values of 17.8 and 28.2%, respectively, at the optimal condition, where p1=6,241 kPa, p7=5,000 kPa, and p10=1,600 kPa. The optimized LR and EUR have been increased by 41.2 and 43.8% compared with the corresponding values from the literature.