LNG cold and cryogenic recovery: Science and thermodynamics

Why ultra-cold is high-grade energy, yet mostly wasted

What this tab covers The thermodynamics: the grade (temperature or pressure) of the energy being recovered, energy versus exergy efficiency, and how harsh the waste stream is on equipment.

LNG arrives at about minus 162 C and is normally warmed with seawater, throwing away a large store of cold. Capturing it can generate power, run air separation or cold chains, and boost liquid-air storage.

Grade of energy

Favourable

This is recovery in reverse: the valuable stream is very cold rather than hot. Because the gap from ambient is about 180 to 190 degrees, the cold is high grade in thermodynamic terms, even though the energy per kilogram is modest. A 2019 review puts the cold released on regasification at about 830 kJ per kg of LNG. Exergy estimates vary with send-out pressure and method: a 2022 IIT Bombay paper cites 800 to 900 kJ/kg in its abstract but its own calculations give about 1,020 to 1,080 kJ/kg, so treat the figure as a range of roughly 800 to 1,100 kJ/kg (about 220 to 300 kWh per tonne, calculated).¹²³

Cold released on regasification about 830 kJ/kg LNG¹ Cold exergy (range across one paper's figures) about 800-1,100 kJ/kg (about 220-300 kWh/t, calculated)² Volume change on regasification about 600 times³

Exergy versus energy efficiency

Mixed

Seawater vaporisers destroy almost all of this exergy; a 2022 thermodynamic analysis found the vaporiser heat exchanger accounts for most of the exergy destroyed in a terminal. A textbook ceiling of about 0.24 kWh of electricity per kg regasified is often quoted, but that equals roughly the whole cold exergy, so real power cycles recover well under it. Using the cold directly, for example to cool inlet air in an air separation unit, keeps more of its value: Osaka Gas has reported that its LNG-assisted air separation needs about half the electricity of a conventional unit. A 2016 trade report said Japan, the leader, captured not much more than a quarter of the available cold across its terminals.²³

Theoretical power ceiling (textbook value cited) about 0.24 kWh per kg LNG² Air separation electricity saving about 50%³ Share of cold captured in Japan (2016 report) not much more than 25%³

Media compatibility and corrosiveness

Favourable

LNG itself is clean and non-corrosive, so fouling is minor on the cold side; the challenge is cryogenic materials and freezing. Heat exchangers use stainless steel or aluminium rather than carbon steel, and intermediate fluids such as propane are used so that water-based streams do not freeze onto LNG-cooled surfaces. Osaka Gas's first cryogenic power system used a propane Rankine cycle with seawater as the heat source.³

First LNG cold power plant Senboku 1, Osaka Gas, 1979³ First LNG-assisted air separation Senboku 1, 1977³

Variants compared²³⁴⁷

Variant	How cold is used	Key figure	Main limit
Cold power generation	Rankine or direct expansion cycle with LNG as heat sink	Theoretical ceiling about 0.24 kWh/kg LNG; practical output lower	Needs steady send-out; low output per tonne
Air separation and industrial cold	Precooling air for oxygen and nitrogen; cold stores; dry ice	About 50% less electricity for air gases (Osaka Gas)	Needs an industrial buyer beside the terminal
Liquid air energy storage (LAES)	LNG cold helps liquefy air for storage	Standalone round trip about 50-60%; LNG cold modelled to add 15-35%	Few commercial plants; site must be near a terminal

Sources

LNG cold energy utilization: Prospects and challenges (He, Chong, Zheng, Ju, Linga), Energy 170: 557-568 Elsevier (via RePEc IDEAS), 2019
Thermodynamic Analysis of LNG Regasification Process (Yadav, Banerjee, Seethamraju), Chemical Engineering Transactions 94 [note: internal figures inconsistent; abstract values used with caution] AIDIC, 2022
Cold energy extracts value from the LNG supply chain (trade report, 2016) Riviera Maritime Media, 2016
Liquid air energy storage: A critical review (She et al.), Renewable and Sustainable Energy Reviews 208 Elsevier (via RePEc IDEAS), 2025
Liquid Air Energy Storage with LNG cold recovery for air liquefaction improvement (Peng et al.), Energy Procedia 158 University of Birmingham, 2019