A small-scale natural gas liquefaction process utilizing the pressure energy of the high-pressure pipelines.

In this paper, the authors proposed and investigated a novel approach for small-scale Liquefied Natural Gas (LNG) production, based on the recovered pressure energy in pipelines without any other energy consumption. Thermodynamic analysis is firstly conducted with the software HYSYS 7.2, after which the effects of the pressure of the feed gas, the outlet pressures of the first-stage and the second-stage expanders on the liquefaction rate and exergy utilizing rate of the novel process were subsequently discussed in details. The results showed that, (1) the maximum liquefaction rate and exergy utilizing rate of the new process can be 24.3% and 29.6% respectively; (2) the liquefaction rate and the exergy utilizing rate are predominantly dependent upon the pressure of feed gas and the final expansion pressure; (3) the optimal pressure of the feed gas is 6.5 MPa considering the pressure durability of the equipment; (4) the exergy losses of the boosters, expanders and HX1 account for more than three-fourths of the total exergy loss. Due to its simplicity and relatively high liquefaction rate, the proposed cycle may be a promising scheme for efficient utilization of recovered pressure energy in small- or medium- scale citygates.