Thermodynamic, environmental and economic analysis of liquefied natural gas cold energy polygeneration system under fluctuating regasification rates.

Fluctuations in regasification rates at liquefied natural gas (LNG) receiving terminals, driven by spatiotemporal variability of downstream demand, hinder the effective recovery of LNG cold energy. To address this issue, an integrated cold and power cogeneration system incorporating cold energy storage (CES) units is proposed. The system combines an organic Rankine cycle (ORC), two CES units, and a cold energy recovery module. This study systematically analyzes the operating characteristics of the proposed system under both steady-state and unsteady conditions. Under steady-state conditions, the influence of key operating parameters on system efficiency is investigated, and a multi-objective optimization approach is introduced to coordinate these parameters. Under unsteady conditions, the impact of regasification rate fluctuations on system performance is examined, and, based on real case studies, the instantaneous performance, single-day operation, and multi-day behavior of the system are evaluated. In addition, environmental and economic analyses are conducted. The results demonstrate that the proposed CES units significantly enhance system performance, increasing the cold energy recovery rate from 10.30% to 86.04% and improving the exergy efficiency to 44.81%. The system achieves an average equivalent power output of 616 MW⋅h/d and CO2 emission reductions of 282 t/d. Although the initial investment cost increases slightly, the net present value rises by 184%, the annual profit increases by 187%, and the payback period is shortened to 1.1 years. These results demonstrate that the proposed configuration provides a practical and flexible solution for enhancing LNG cold energy utilization, with strong potential for large-scale deployment across diverse terminal types.