Waste cold energy recovery from liquefied natural gas (LNG) regasification including pressure and thermal energy

• Published in: Energy (Oxford) 2018-06, Vol.152, p.770-787
• Main Authors: Le, Si, Lee, Jui-Yuan, Chen, Cheng-Liang
• Format: Article
• Language: English
• Subjects: Cold energy recovery; Cold pressing; Computational fluid dynamics; Configurations; Energy recovery; Energy shortages; Equations of state; Expansion; Flow rates; Fossil fuels; Heat recovery; Liquefied natural gas; Liquefied natural gas (LNG); Mass flow rate; Mathematical models; Methane; Natural gas; Organic Rankine cycle; Phase transitions; Pressure; Pressure energy recovery; Rankine cycle; Regasification; Residual energy; Thermal energy; Thermodynamic properties; Waste heat recovery; Working fluids
• ISSN: 0360-5442; 1873-6785
• DOI: 10.1016/j.energy.2018.03.076

The world has been concentrating on waste heat recovery for several decades. The attention has recently been turned to waste energy in cold streams. This work focuses on the recovery of waste cold energy released from the Liquefied Natural Gas (LNG) regasification process, including pressure energy and thermal energy. A direct expansion configuration involving different steps of expansion and mass flow rate extraction at intermediate pressure levels is adopted in the mathematical models for pressure energy recovery. A direct-configuration organic Rankine cycle (ORC) is employed subsequently to recover residual cold energy. An equation of state for methane (the main component of LNG) is used to estimate the thermodynamic properties of LNG in a long-range phase transition of the regasification process. The modified Peng-Robinson (PR) and the Soave-Redlich-Kwong (SRK) equations of state are used to calculate thermodynamic properties of the ORC working fluids. All the models are developed and solved using MATLAB. By adopting propane as the ORC working fluid, the multistage expansion and thermal energy extraction can recover 215 kJ per kilogram of flowing LNG, which can generate 1.7 GWh annually for 1 kg/s LNG, with a payback period less than seven years. •Recover waste cold energy released from Liquefied Natural Gas regasification process.•A direct expansion configuration involving different expansion steps is investigated to recovery pressure energy.•A direct-configuration organic Rankine cycle is employed subsequently to recover residual cold energy.•The total energy recovered from 1 kg/s of LNG regasification can generate 1.7 GWh electricity annually.