5 Effective Methods to Improve LNG Recovery Rate

Improving LNG recovery rates have become a critical factor for operational efficiency and economic performance because of the global energy shift and the rapid expansion of the LNG market. Improved recovery rates lead to decreased energy loss and consumption, which increases profit margins. Additionally, increased recovery rates reduce carbon emissions and improve the stability of the supply chain.

KAITIAN GAS, the industry’s best in gas recovery and LNG solutions, states that for both LNG import/regasification and export/liquefaction stages, a significant portion of the cold energy, boil-off gas (BOG), and low temperature by products herein remain and can be recovered. This is a loss to a company. It has been shown in industry advancements that realizing cold energy recovery potential in process optimization and effective BOG controlling will improve the liquefaction yield/ratio performance.

Optimize Mixed Refrigerant and Precooling Processes to Reduce Energy Consumption

In LNG liquefaction systems, Mixed Refrigerant Cycles (MRC) and precooling processes are among the highest energy-consuming steps and have the largest impact on liquefaction yield. With LNG plants increasing in scale and efficiency requirements tightening, optimizing refrigerant composition, heat exchanger efficiency, and precool temperature distribution has become a key engineering measure.

Key Benefits of Optimization

Reduces compressor load and overall energy consumption

Improves heat exchanger efficiency and unit LNG energy value

Prevents mismatches between refrigerant and natural gas cooling curves

Typical Optimization Steps

Step	Key Actions	Expected Outcome	Tools / Monitoring
MR Composition Optimization	Adjust N₂/CH₄ for low temp, C₂H₆/C₃H₈ for high/precool, smooth intermediate components	Match NG cooling curve, reduce compressor power, improve heat transfer	HYSYS, Aspen Plus, RTO, APC
Precool Zone Flow Adjustment	Modify propane evaporation temp, adjust PP stage load, optimize flow & exchanger ratio	Reduce NG enthalpy before main cryo, improve ΔTmin, lower shaft power	DCS temp monitoring, flow & energy efficiency control
Compressor Load & Recycle Optimization	Adjust recycle ratio, control inlet & discharge temp, enhance interstage cooling	Avoid overload, reduce loop energy, stabilize refrigerant flow	Compressor load curves, vibration & performance monitoring
Cryo ΔTmin Optimization	Adjust refrigerant flow, bypass control, optimize exchanger zones	Approach design ΔT, minimize overcooling/overheating, lower SEC	Temperature profile & heat transfer efficiency data
Online Monitoring & APC Loop	Auto-adjust composition, evaporation pressure, recycle ratio; real-time temp & load control	Maintain peak yield, reduce energy, avoid manual errors	APC, RTO, historical trend analysis

Important Considerations:

Refrigerant drift can increase SEC; perform weekly MR sampling and monthly calibration
Rapid temperature adjustments can stress plate-fin exchangers; keep ΔT ≤1–2°C/min
Compressor discharge temperature must be monitored; implement interlocks
Avoid overcooling; match precool to NG cooldown curve
All operations should go through APC/DCS for consistency

Strengthen BOG Management and Re-liquefaction to Reduce Losses

Boil-off Gas (BOG) is generated during LNG storage, transport, and loading due to temperature rise and heat conduction. Uncontrolled BOG leads to LNG losses, reduced quality, and greenhouse gas emissions.

KAITIAN GAS recommends a systematic BOG management strategy:

Strategy	Core Actions	Benefits
Monitor Loading & Storage	Temperature and pressure sensors in high-temp/high-pressure zones	Identify high BOG generation points, reduce losses
Optimize Subcool & Re-liquefaction	Use compression re-liquefaction, fuel recovery, or subcooling	Reduce BOG, increase liquefaction yield, minimize cargo loss
Small-Scale Energy Utilization	Generate power from BOG or combine with PV systems	Increase energy efficiency, reduce carbon emissions
Establish Monitoring System	Track BOG generation, recovery, and utilization	Enable real-time optimization, ensure stable recovery

Studies show BOG management can significantly increase annual LNG production and generate millions in additional revenue, while also reducing CO₂ emissions and improving energy utilization efficiency.

Recover LNG Cold Energy to Enhance Overall System Efficiency

Cold energy from LNG, often at –162°C, is a valuable resource. If unused, it is wasted through flash gas or temperature rise. KAITIAN GAS advises recovering LNG cold energy across multiple stages:

Cold Energy Recovery Principles

LNG cold energy recovery primarily relies on heat exchangers and gas-liquid heat exchange devices. Before liquefaction, natural gas is pre-cooled to the required cryogenic refrigeration level via heat exchangers, thereby reducing the load on the main refrigeration system. After liquefaction, the recovered cryogenic energy can be used in secondary refrigeration or compression-reliquefaction systems, reducing BOG (boiling-off gas) losses. Simultaneously, the cold energy can also be used to provide cryogenic energy for refrigerant compressors, generator sets, or plant thermal processes, maximizing overall plant energy efficiency.

By rationally utilizing LNG cold energy, the specific energy consumption (SEC) of the liquefaction unit can be reduced by approximately 5–10%, and compressor power consumption can be decreased, significantly improving overall system efficiency.

Cold Energy Recovery Methods

Stage	Measures	Goals
NG Precooling	Use LNG cold energy, optimize heat exchanger layout	Reduce main refrigeration load, increase heat transfer efficiency
BOG Re-liquefaction	Condense BOG using recovered cold	Lower BOG losses, improve LNG recovery, reduce flash gas
Cold-Driven Power	Drive low-temp cycles or industrial cooling	Increase energy efficiency, reduce external power demand, improve sustainability

Cautions

Several operational details must be considered during LNG cold energy recovery to ensure system stability and efficiency.

First, freeze protection for heat exchangers is crucial. Cryogenic liquids easily cause frost to form on pipes or heat exchangers; therefore, freeze protection or bypass devices should be installed to ensure safe operation.

Second, the system temperature difference must be precisely controlled. Excessive temperature differences reduce heat exchange efficiency and affect energy recovery; therefore, the temperature difference between LNG and process gases needs to be strictly monitored.

Third, the recovery rate must match the downstream load. Cold energy recovery must be coordinated with process requirements to avoid excessive cryogenic temperatures leading to flash evaporation or energy waste.

Finally, monitoring and closed-loop optimization are key to maintaining optimal system performance. Real-time control of LNG flow, temperature, and reliquefaction load using an APC (Advanced Process Control) system ensures the cold energy recovery process operates continuously within its optimal range.

In liquefaction plants or refueling stations, recovering LNG cold energy can save approximately 5–10% of refrigeration energy consumption, effectively reducing the load on the main refrigeration system. Furthermore, combining cold energy recovery with BOG (Boil-off Gas) recovery can further reduce tank flash evaporation by 0.5–1%, thereby improving LNG recovery rates.

In terms of economic benefits, this method can reduce the production cost per ton of LNG, increase annual operating profits, and reduce carbon emissions while decreasing energy consumption, achieving a win-win situation for both economic and environmental benefits.

Apply Turbo Expanders in Low-Temperature / LNG Recovery Sections

Turbo expanders convert high-pressure gas into work, generating self-cooling effects. Their application in low-temperature and LNG recovery sections improves liquefaction yield and reduces energy consumption.

The Role of the Turbine Expander in the Cryogenic Stage

The turbine expander utilizes the expansion of high-pressure gas to drive a generator or directly propel the process fluid, achieving a self-cooling effect.

Its application in the cryogenic stage can lower the gas temperature to the extremely low temperature range required for liquefaction, increasing LNG liquid phase yield; or it can replace part of the compression refrigeration load, reducing energy consumption and specific energy consumption (SEC); finally, it can improve the condensation efficiency of LNG components, increasing the amount of liquid phase recovered.

LNG Recovery Section Optimization

In the LNG recovery section, the turboexpander expands the natural gas or fractionated components, effectively reducing the temperature and thus achieving efficient liquefaction of LNG components such as propane and ethane. This reduces flash evaporation and the generation of escape gases, improves the total LNG recovery rate, and can be coordinated with cold energy recovery and BOG recovery to further optimize the energy efficiency of the entire liquefaction process.

Operational Advantages

Content	Function
Higher Liquid Recovery	Converts cold energy into LNG yield, reducing losses
Lower Energy Consumption	Reduces compressor load and MRC cycles
System Stability	Maintains consistent low-temperature operation
Environmental Gains	Reduces BOG emissions and energy waste

Operational Notes

Control expander inlet pressure and flow to match design
Prevent freezing in pipelines/exchangers
Schedule regular maintenance for high-speed rotors
Coordinate with main refrigeration, LNG separation, and BOG recovery systems

Turbo expanders can increase LNG liquid recovery by 1–3% and lower SEC by ~5%, saving millions in large-scale LNG plants annually.

Optimize Feed Gas Pretreatment, LNG Recovery, and Digital Control

In the LNG liquefaction process, feed pretreatment, LNG recovery, and digital control are key components for improving liquid phase recovery rate and overall system efficiency.

Feed Pretreatment Optimization

Natural gas feedstocks typically contain moisture, carbon dioxide, sulfides, and heavy hydrocarbons. Insufficient pretreatment can lead to cryogenic freezing, heat exchanger frosting, or corrosion, reducing liquefaction efficiency. Optimizing pretreatment processes (such as dehydration, CO₂/H₂S removal, and heavy hydrocarbon separation) not only protects cryogenic equipment but also reduces flash evaporation and escape gas generation, improving LNG recovery rates from the source.

LNG Recovery Strategy

Natural gas liquids (LNGs) contain components such as ethane, propane, and butane. Insufficient recovery of these cryogenically liquefiable components can result in liquid phase loss. Optimizing the LNG recovery process, such as using turbine expanders in the cryogenic stage, precisely controlling fractionation pressure and temperature, and combining subcooling and reliquefaction systems, can achieve efficient LNG liquefaction and maximize recovery, significantly increasing total liquid LNG production.

Digital Control and Closed-Loop Optimization

Digital control systems (such as DCS, APC, or RTO) can monitor and optimize feed flow rate, composition, cryogenic temperature, LNG recovery pressure, and BOG recovery load in real time. Through closed-loop control, refrigerant ratio, evaporation temperature, and recirculation ratio can be automatically adjusted to maintain the entire liquefaction process at its optimal operating point, reducing energy consumption, improving liquid phase recovery rate, and ensuring safe and stable plant operation.

Comprehensive Effects

Integrating feed pretreatment optimization, LNG recovery strategies, and digital control organically improves LNG recovery efficiency across the entire chain from source to cryogenic stage. Studies show that optimized processes can additionally increase liquid phase recovery rate by 1–3%, reduce flash evaporation and BOG losses, and reduce specific energy consumption (SEC) by approximately 5%, achieving a win-win situation in terms of both economic and environmental benefits.

Conclusion

Across the LNG value chain—from feed gas, liquefaction, transport, storage, to regasification—every stage offers opportunities to increase recovery rate. By implementing these five technical strategies, companies can improve liquefaction yield per unit of feed, reduce energy consumption, minimize losses, and enhance environmental compliance.

For KAITIAN GAS, these solutions align perfectly with high-efficiency, reliable, and sustainable LNG operations, demonstrating how advanced equipment and process optimization can drive measurable performance improvements across the entire LNG system.

References

Air Products. “LNG Process Technology and Design Optimization for Mixed Refrigerant Cycles (AP-C3MR / AP-X).” Air Products Technical Paper, 2020.
GIIGNL – International Group of Liquefied Natural Gas Importers. “LNG Custody Transfer Handbook – BOG Generation and Management.” 2022 Edition.
Shell Global Solutions. “Energy Efficiency Improvements in LNG Liquefaction through Cold Energy Utilization.” Shell Technical Report, 2019.
Kawasaki Heavy Industries. “LNG Boil-off Gas Re-liquefaction Technology and Flash Gas Reduction Methods.” KHI Cryogenic Systems White Paper, 2021.
U.S. Department of Energy (DOE). “Turboexpander-Based Natural Gas Liquefaction and NGL Recovery Performance Analysis.” DOE NETL Report, 2018.
Energy Reports Journal. “Process Optimization and Digital Control Strategies to Improve LNG Recovery Rates.” Energy Reports, Vol. 8, 2022.