LNG Plants
LNG plant compressor lubricants are selected for the specific compressor duty, gas composition and lubrication system. LNG facilities contain natural-gas booster compressors, refrigerant compressors, boil-off gas compressors and flash-gas compressors, each with different operating requirements.
Propane and mixed-refrigerant circuits expose lubricants to hydrocarbon dilution, which reduces operating viscosity. Boil-off gas and flash-gas compressors handle methane-rich vapour under low-temperature conditions, but the lubricant temperature depends on the compressor design and its separation from the process gas.
NEXT Lubricants supplies PAO and PAG formulations for lubricated compressors across LNG liquefaction plants, export terminals, storage facilities and import terminals.
Key takeaways
- LNG facilities use compressors for feed-gas boosting, refrigerant circulation, boil-off gas recovery and flash-gas handling.
- Each compressor position requires a separate lubricant assessment based on the gas, refrigerant, pressure, temperature and lubrication system.
- Propane and mixed hydrocarbon refrigerants dissolve into conventional lubricants and reduce operating viscosity.
- PAG formulations resist hydrocarbon dilution and help maintain operating viscosity in LNG refrigerant and process-gas compressors.
- PAO formulations provide low-temperature fluidity, oxidation stability and low volatility for methane-rich gas and separately lubricated compressor duties.
- Some LNG boil-off gas compressors use oil-free cylinders while the crankcase and running gear use a separate lubricant isolated from the process gas.
- Final lubricant chemistry and viscosity grade depend on the current lubricant, compressor requirements and complete operating envelope.
Compression process
LNG Plants: Process, Applications & Compressor Role
LNG plants remove water, CO₂, heavier hydrocarbons and other contaminants from natural gas before cooling it to approximately −162°C. Liquefaction reduces the gas volume for storage and transportation.
Compression supports several stages of this process. Natural-gas booster compressors raise the feed-gas pressure, refrigerant compressors circulate the fluids that produce the cooling, and boil-off and flash-gas compressors recover methane-rich vapour from storage and process operations.
LNG facilities use centrifugal, reciprocating and rotary screw compressors. Some compressors allow direct contact between the lubricant and gas, while others isolate the lubricant from the process stream or use oil-free compression chambers.
Natural Gas Booster Compression
Compression of treated natural gas where additional pressure is required before or within the liquefaction process.
Propane Refrigerant Compression
Propane pre-cooling cycles reduce the temperature of the natural gas and other refrigerant streams before final liquefaction. Large LNG plants use centrifugal compressors, while smaller and modular plants also use oil-injected rotary screw compressors.
Mixed-Refrigerant Compression
Mixed-refrigerant compressors circulate combinations of methane, ethane, ethylene, propane, nitrogen and other components through the liquefaction cycle. The refrigerant composition and direct gas–oil contact determine the dilution effect on the lubricant.
Boil-Off Gas Compression
BOG compressors recover methane-rich vapor generated during LNG storage and transfer for reuse, fuel gas or reliquefaction.
Flash Gas Compression
Compressors recover vapor generated during pressure reduction or LNG handling and return it to the process or fuel-gas system.
LNG Import & Regasification Terminals
Compression is primarily associated with boil-off and vapor management at receiving, storage and regasification terminals rather than the LNG vaporisation step itself. Burckhardt specifically supplies BOG compressors for LNG import terminals.
Selection
Factors Affecting Lubricant Selection
LNG compressor lubricant selection is influenced by the compressor position, gas or refrigerant characteristics and the overall operating envelope.
- Gas Composition Methane and heavier hydrocarbons have different solubility characteristics in compressor lubricants. Increasing concentrations of ethane, propane, butane, pentane and heavier components generally increase dilution and reduce in-service viscosity.
- Suction and Discharge Conditions Pressure, compression ratio and the number of compression stages influence gas solubility, mechanical loading, discharge temperature and the viscosity required to maintain an effective lubricant film.
- Oil and Gas Temperature Temperature affects gas solubility, lubricant viscosity and oxidation rate. Lower oil temperatures can increase the amount of hydrocarbon dissolved in the lubricant, while elevated temperatures increase thermal and oxidative stress.
- Gas and Load Variability Changes in well conditions, gas composition, flow rate and compressor load can alter dilution, discharge temperature and lubricant-film requirements throughout the operating cycle.
Process
What NEXT needs to recommend a lubricant
A lubricant recommendation is based on the information below. Provide whatever information is available; NEXT will identify whether any additional details are required.
- Compressor Details Manufacturer, model, serial number and compressor type, such as reciprocating, rotary screw or centrifugal.
- Current Lubricant and Performance Current oil, oil volume, operating hours and any problems with viscosity, deposits, consumption, carryover or lubricant life.
- Gas Composition Main hydrocarbon components and any water, CO₂, H₂S, nitrogen, oxygen or other substances present. An existing gas-composition report can also be provided.
- Operating Conditions Suction and discharge pressures and temperatures, oil temperature and relevant operating limits for each compression stage.
- Application and Specific Requirements How the compressor is used and any purity, catalyst, material-compatibility, minimum-viscosity or other application-specific requirements.
- Final Recommendation NEXT evaluates the available information and confirms the recommended product, lubricant chemistry and ISO viscosity grade, with compatibility and changeover guidance where required.
Benefits
Operational Benefits of Correct Lubricant Selection
Selecting the lubricant for the specific LNG compressor duty provides several operational benefits.
- Stable Operating Viscosity Helps maintain sufficient film strength after hydrocarbons dissolve into and dilute the lubricant.
- Reduced Unplanned Downtime Helps prevent lubrication-related wear, overheating, valve problems, deposits and unexpected compressor shutdowns.
- Extended Component Life Supports the protection of cylinders, piston rings, packing, bearings, rotors and other lubricated components.
- Lower Lubricant Consumption Supports appropriate cylinder lubrication and helps reduce excessive oil use, carryover and unnecessary top-ups.
- Clean Running and Deposit Control Helps minimise varnish, carbon and deposit formation for cleaner valves, cylinders and oil-system components.
- More Consistent Compressor Efficiency Supports effective sealing and lubrication without creating unnecessary viscous resistance or friction.
- Longer and More Predictable Service Intervals Improves resistance to oxidation, viscosity loss and contamination for more controlled maintenance planning.
- Reliable Performance Across Changing Conditions Provides greater operating confidence as well pressure, flow rate and gas composition change over time.
products
Recommended NEXT LNG Compressor Lubricants
NEXT GPL PAG
Hydrocarbon Refrigeration & LNG Process Compressor Lubricant
Base Oil: PAG
ISO Range: 32 – 680
NEXT PAO
Cryogenic LNG & Process Gas Compressor Lubricant
Base Oil: PAO
ISO Range: 15 – 320
Cross reference tool
Our technical team can help identify the right product.
TECHNICAL SUPPORT
Lubricant Selection, Technical Support and Compatibility Documentation
NEXT combines application knowledge, laboratory data and an extensive internal cross-reference database to support lubricant selection, conversions and compressor troubleshooting.
Depending on the application, we can provide:
- Application-Specific Product Recommendations Lubricant recommendations based on gas or refrigerant composition, compressor design, operating conditions and current performance issues.
- Lubricant Cross-Referencing Identifies suitable NEXT alternatives by comparing base-oil chemistry, viscosity, application, specifications and operating requirements.
- Compatibility and Conversion Documentation Provides chemistry comparisons, mixture-test data, material compatibility, flushing requirements and top-off or changeover guidance.
- Dilution Data and PVT Graphs Shows how gas or refrigerant concentration, pressure and temperature affect lubricant dilution, density and operating viscosity.
- Troubleshooting and Root-Cause Support Supports investigations into foaming, oil carryover, dilution, deposits, corrosion, high lubricant consumption and reduced oil life.
Frequently Asked question
What type of oil is used in LNG compressors?
LNG compressors can use PAG or PAO lubricants depending on compressor position, gas composition, gas/oil contact and operating conditions. NEXT’s current LNG range includes GPL PAG, GPL PAO and NEXT PAO.
Why is PAG used in LNG compressors?
PAG is particularly useful where hydrocarbon refrigerants or process gas dissolve into conventional lubricants and reduce operating viscosity. NEXT GPL PAG is specifically formulated for hydrocarbon dilution resistance and LNG boil-off/flash-gas compression.
Why is PAO used in LNG compression?
PAO provides low volatility, low carryover, thermal stability and excellent low-temperature fluidity. NEXT GPL PAO is specifically positioned for LNG boil-off and cryogenic gas compression.
Does an LNG BOG compressor lubricant operate at −160°C?
Not necessarily. BOG gas can approach LNG storage temperature, but some compressors use oil-free cylinders specifically to keep lubricant out of the gas path. The lubricant temperature therefore has to be established separately from the gas suction temperature.
Can one lubricant be used for every compressor in an LNG plant?
Not automatically. Feed-gas, refrigerant, BOG and flash-gas compressors can differ significantly in gas composition, temperature, pressure and lubrication architecture. Each position should be evaluated separately.
What is the difference between LNG refrigerant and BOG compression?
Refrigerant compressors drive the cooling cycles that liquefy natural gas, while BOG compressors recover methane vapor generated from stored or transferred LNG. The gases and operating conditions are different, so their lubricant requirements can also differ.
Related Applications
Explore Other Gas Compression Applications
Natural Gas Processing & NGL
Industrial & Specialty Gas
Compression and liquefaction of nitrogen, hydrogen, helium and other industrial gases.
Petrochemical Gas Compression
Lubricants for hydrocarbon, cracked, recycle and reactive gas streams in petrochemical processing.
Natural Gas Transmission & Storage
Compression of treated natural gas in pipeline and storage infrastructure.