Performance analysis on a novel small-scale autocascade natural gas liquefaction system utilizing a rectifying column.

Small-scale natural gas liquefaction systems have gained extensive attentions due to the increasing demands of scattered natural gas field explorations. This paper proposed a novel small-scale auto-cascade natural gas liquefaction system operating with a common oil-lubricating compressor, in which a rectifying column was utilized to serve as a plurality of gas-liquid separators to separate the more volatile and less volatile components in the mixed refrigerant. At the same time, the lubricating oil entrained in the refrigerant was better removed to avoid block in the low temperature section. Nitrogen (R728), methane (R50), ethylene (R1150)， propane (R290) and iso-butane (R600a) were selected as the components of the mixed refrigerants. Simulations by ASPEN HYSYS showed that the concentration of each component and system pressures both have obvious impacts on the performance of the system. Especially, the specific liquefaction work was 0.641 kW•h/kg, where the optimum suction pressure was 300 kPa with the concentration of 0.14/0.27/0.16/0.16/0.27 (R728/R50/R1150/R290/R600a).