Thermodynamic analysis of cold energy recovery from LNG regasification

The LNG market connects numerous export and import markets, and the global LNG trade has been growing steadily. Despite the availability of multiple alternatives, only a small fraction of this global cryogenic potential is currently utilized, and a negligible number of regasification terminals are equipped with cold energy recovery systems. This paper explores various options for recovering cold energy from LNG regasification processes including electricity production, refrigeration, cryogenic separation processes, CO 2 capture and liquefaction. The present study examines the industrial recovery options, proposing both conventional and innovative process schemes and analysing them in terms of their thermodynamic modelling and feasibility. Nine case studies were selected and simulated using Aspen Hysys software, considering material and energy balances. Specific energy consumptions are calculated, and an exergetic comparison methodology is adopted to provide a unified approach capable to embrace heterogeneous systems utilizing mechanical/electrical energy, thermal energy, and chemical energy. The temperature profiles are examined, and sensitivity analyses are performed on key parameters. The integration of direct cooling and condensation brings high exergy efficiency of above 40% and economic advantages due to the absence of an external refrigeration cycle. Coupling regasification with CO2 liquefaction reduces specific energy consumption by 53% compared to the conventional process. Similarly, in the case of an ethylene production plant, energy consumption is reduced by 95%. Simulations for electricity generation using an ORC cycle with LNG as the cold source achieve around 25% exergy efficiency, but the LCOE (Levelized Cost of Electricity) is attractive, ranging from 0.07 to 0.09 euro/kWh. Integration with an Air Separation Unit (ASU) for cryogenic distillation leads to a 41% decrease in specific energy consumption. Further integration with Allam and cascade ORC cycles has been simulated. Globally, air separation shows exergy efficiencies of 37-38%, which is higher than the average 25% obtained from conventional thermodynamic cycles with low-temperature hot sources. Regarding cryogenic CO2 capture, it exhibits lower specific energy consumption compared to traditional processes. The exergy efficiency is high at 22%, and the LCOP (Levelized Cost of CO2 Production) of 55 euro/ton is attractive for carbon capture processes that can be coupled with regasification units and NG utilization (a.e. for hydrogen and electricity production).

Automated summary

This paper explores various options for recovering cold energy from LNG regasification processes, such as electricity production, refrigeration, cryogenic separation processes, CO2 capture, and liquefaction. The study proposes conventional and innovative process schemes and examines their feasibility and thermodynamic modelling. Results show significant energy consumption reduction and economic advantages through integration of different processes, such as coupling regasification with CO2 liquefaction and integrating with an Air Separation Unit (ASU) for cryogenic distillation. Cryogenic CO2 capture also exhibits lower energy consumption and attractive cost for carbon capture processes.