Process synthesis of natural gas liquefaction through exergy loss recovery at the pressure reduction station via enhancement strategy method

Abstract

Using natural gas (NG), as a low-carbon energy source, has been highly prevalent in order to address the growing energy demand, leading to its increased global consumption. NG is commonly transported through pipeline, where high-pressure gas is transferred to the desired location through pipes and subsequently reduced at pressure reduction station (PRS) so as to reach the proper distribution pressure. The conventional form of this process leads to energy loss. To tackle this issue, NG liquefaction methods, particularly self-cooling, are widely used due to their low power consumption, simplicity, low investment costs, and the ability to recover wasted energy. In the present study, an innovative bifunctional process has been developed to liquefy natural gas and reduce the pipeline pressure with zero or near-zero power consumption. Two schemes were devised based on the storage method. These include the Low-pressure Liquefaction Pressure Reduction System (L-LPRS) for storage in atmospheric flat-bottom tanks, and the High-pressure Liquefaction Pressure Reduction System (H-LPRS) for storage in high-pressure vacuum bullet tanks. Comparing these configurations with similar studies, it shows notable improvement in performance criteria. Thanks to the configuration of this cycle, the energy consumption for the liquification process was brought to zero. This is while the feed pressure is 50 bar, which is a common number for many PRSs, and the designed equipment are conventional, making it feasible to implement the findings of this study. The results indicated that the liquefaction rate (LR) reached 25.03 % in the L-LPRS and 28.3 % in the H-LPRS. At the maximum LR condition, the specific power consumption and exergy efficiency for the L-LPRS were 14.75 kWh/ton LNG and 63.3 %, respectively. The exergy efficiency of the H-LPRS was 63.9 %, with no significant power consumption required. Thus, H-LPRS achieved a higher liquefaction rate without compromising exergy efficiency or consuming excess power. According to the obtained results, replacing conventional systems with LPRS might recover 60 % of the exergy typically wasted in PRS.