The work systematically evaluates working-fluid choices and advanced cycle architectures for extracting power from LNG’s cold-temperature range up to ambient conditions. Using modeling and optimization, the researchers pinpoint a standout configuration: a two-stage Rankine cycle with reheating, designed to better match temperature levels during heat addition and expansion.

To explore the design space, the team screened 30 single-working-fluid options and 49 binary mixtures, then compared four enhanced configurations incorporating reheating, regeneration, and Kalina-cycle integration. The calculations were performed in Aspen HYSYS, while a Python genetic algorithm searched across pressures, temperatures, and fluid compositions to maximize net output.

Because LNG storage centers around roughly −162 °C, each kilogram retains about 830 kJ of cold energy available for conversion. The central challenge is that regasification heat transfer is often too limited or poorly aligned with conventional cycle temperature profiles, leaving much of the potential unexploited.

Among single-fluid systems, hexafluoroethane (R116) performed best in the upper cycle, while ethane (R170) was strongest in the lower cycle. Together, these selections delivered 7.5 MW of net power with a thermal efficiency of 24.1%.

Binary mixtures improved performance stability and nudged output higher. The best conventional two-stage baseline combined R116 in the upper cycle with an optimized R1150/R23 mixture in the lower cycle, achieving about 7.7 MW—roughly 2.6% above the top single-fluid design.

The largest gains emerged from reheating. In the optimal scheme, R116 drives the upper-cycle expansion, while an R1150/R170 mixture operates in the lower cycle. Expansion is split into two turbine stages, separated by additional heating, which raises effective operating pressure and preserves usable heat for the downstream stage.

This reheated architecture produced 9.2 MW of net power at an LNG capacity of 216 tonnes per hour. The improvement corresponds to roughly 22% over the best single-fluid case and 19% over the best mixed-fluid baseline, while regeneration and Kalina integration offered little net advantage due to reduced effective heat transfer between stages.

Overall, the findings emphasize that maximizing cold-energy recovery requires optimizing the entire thermodynamic system, not just individual components. For real LNG terminals, the authors highlight reheating as the clearest pathway toward additional low-carbon electricity generation.

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Subject of Research: Cold energy recovery from LNG using advanced binary working fluid power cycles

Article Title: Enhancements and optimization of LNG cold energy recovery via advanced binary working fluid power cycle systems

News Publication Date: 11-May-2026

Web References: https://doi.org/10.48130/een-0026-0007

References: Wong SH, Xiao G, Zhang D. 2026. Enhancements and optimization of LNG cold energy recovery via advanced binary working fluid power cycle systems. Energy & Environment Nexus 2: e014. doi: 10.48130/een-0026-0007

Image Credits: Credit: Shing-hon Wong, Gongkui Xiao & Dongke Zhang

Keywords

LNG cold energy, regasification, binary working fluids, two-stage Rankine cycle, reheating, cryogenic power generation, Aspen HYSYS, thermal efficiency, optimization

LNG is transported globally at cryogenic temperatures near -162 °C, enabling efficient long-distance shipment and storage. However, the regasification process, which warms LNG back to piping and consumer-ready conditions, typically wastes much of this substantial cooling potential. Conventional terminal practices often vent this cold energy to ambient surroundings or seawater, resulting in a considerable loss of exergy—the maximum usable work obtainable from a system. This inefficiency presents an untapped opportunity for energy recovery, one that the new research systematically addresses through advanced thermodynamic cycle engineering.

Rankine cycles, long established in power generation, convert thermal gradients into mechanical work via phase changes of working fluids. The research team innovatively applied a two-stage variant of this cycle, wherein separate working fluids operate in tandem through upper and lower cycles bridged by an intermediate heat exchanger. This design effectively narrows the temperature difference between the cold LNG and warmer seawater, mitigating thermodynamic irreversibilities caused by temperature mismatches and boosting overall cycle efficiency.

Crucially, the selection of optimal working fluids is paramount to maximizing system performance. The researchers conducted a rigorous screening of 30 single fluids and 49 binary mixtures, leveraging a sophisticated optimization framework that couples genetic algorithms with Aspen HYSYS simulations. Parameters such as evaporation and condensation pressures, intermediate heat exchanger temperatures, and mixture compositions were meticulously tuned to identify fluid combinations that harmonize with the LNG temperature profiles.

The results reveal that hexafluoroethane (R116) excels as the upper cycle fluid due to its dry-fluid properties that promote superior heat rejection characteristics, while ethane (R170) and pentafluoroethane (R1150) emerged as leading candidates for the lower cycle. Notably, the pairing of R116 in the upper cycle with R170 in the lower cycle achieved a net power output of 7.5 MW with a thermal efficiency of 24.1%, underscoring the potential of single-fluid systems for LNG cold recovery with efficient heat transfer dynamics.

Further enhancement was realized through the use of binary mixtures, which exhibit temperature glide during phase transitions, better aligning the working fluid heat exchange processes with the non-isothermal warming curve of LNG. These mixtures demonstrated notable reductions in exergy losses by minimizing temperature mismatches throughout evaporation and condensation, offering more consistent thermal performance. While mixed fluids modestly outperformed single fluids—yielding up to 7.7 MW—the marginal gains emphasize the importance of fluid selection alongside system architecture.

The most remarkable advance, however, stems from the integration of reheating in the two-stage Rankine cycle. By incorporating reheating between turbine expansion stages, the system sustains higher upper-cycle pressures and retains exhaust temperatures favorable for driving the lower cycle. This configuration yielded a substantial power increase to 9.2 MW, marking a 22 percent improvement over the best single-fluid baseline. The reheating process simultaneously enhances work extraction and ensures optimal thermal synergies between cycle stages, establishing it as the preferred approach over regeneration or Kalina cycle variations that were also evaluated but found less effective.

Underpinning these findings is a robust simulation methodology designed to emulate realistic LNG terminal conditions, including a representative receiving capacity of 216 tonnes per hour. This holistic assessment enabled the evaluation of cycle thermodynamics, fluid properties, and optimization constraints, guiding the design toward configurations that can seamlessly integrate with existing regasification infrastructure while maximizing cold energy utilization.

The implications of this research stretch beyond theoretical thermodynamics; they offer practical pathways for LNG terminals worldwide to significantly reduce energy wastage and carbon footprints by converting previously squandered refrigeration potential into clean electricity. Capturing LNG’s cold energy through reheated two-stage Rankine cycles not only improves terminal efficiency but also supports broader energy transition goals by facilitating cleaner power generation from fossil fuel supply chains.

Moreover, the study underscores the transformative power of combining advanced working fluid science with innovative cycle architectures, demonstrating that the interplay between fluid thermophysical properties and system design profoundly influences overall energy recovery potential. This nuanced approach to thermodynamic matching paves the way for future exploration of mixed-fluid cycles and multi-stage power systems optimized via data-driven computational techniques.

Looking ahead, integrating such cycles at operational LNG terminals will require meticulous engineering to ensure economic feasibility, material compatibility under cryogenic and high-pressure conditions, and adherence to safety standards. However, the clearly demonstrated performance gains offer compelling motivation for industry adoption and further research into scalable, reliable LNG cold energy recovery technologies.

In summary, this pioneering work by Shing-hon Wong and colleagues from The University of Western Australia provides a vital technical breakthrough in LNG cold energy recovery. By systematically blending thermodynamic insights, advanced simulations, and optimized fluid pairings, they have charted a viable and impactful route toward capturing wasted cryogenic energy and converting it into valuable power. The reheated two-stage Rankine cycle, with its superior efficiency and net power output, stands out as a transformative innovation poised to reshape energy efficiency strategies at LNG terminals internationally.

Subject of Research: Not applicable

Article Title: Enhancements and optimization of LNG cold energy recovery via advanced binary working fluid power cycle systems

News Publication Date: 11 May 2026

References:
DOI: 10.48130/een-0026-0007

Keywords: LNG cold energy recovery, two-stage Rankine cycle, reheating, working fluid optimization, cryogenic energy, thermal efficiency, hexafluoroethane, ethane, binary mixtures, power generation, thermodynamic optimization, LNG terminal energy utilization