Vapor Recovery Units
Vapor recovery unit compressor lubricants are selected for compressors that recover low-pressure, hydrocarbon-rich vapors from storage tanks, production facilities, loading operations and other vented gas sources.
Recovered vapors contain methane, ethane, propane, butane, pentane and heavier condensable hydrocarbons, along with water vapor, carbon dioxide (CO2), hydrogen sulfide (H2S) and other components. Where the process gas contacts the lubricant, hydrocarbons dissolve into it or condense into it and reduce its operating viscosity substantially.
NEXT Lubricants supplies mineral, polyalphaolefin (PAO), polyalkylene glycol (PAG) and polyethylene glycol (PEG) lubricants for vapor recovery units. Mineral and PAO lubricants suit lighter, less dilution-prone vapors; PAG, water-soluble PAG (PAG-WS) and PEG formulations resist viscosity reduction in richer, more condensable hydrocarbon streams.
- Vapor recovery units compress low-pressure vapor streams whose flow, composition and condensate content shift with tank pressure, liquid composition and operating activity.
- Heavier hydrocarbons — propane, butane, pentane and heavier — dissolve into the lubricant more readily than lighter methane and ethane, and reduce in-service viscosity.
- Low suction pressure alone does not cause dilution. Vapor composition, pressure and temperature together determine how much hydrocarbon the lubricant retains.
- Recovered tank and loading vapors carry condensable heavy hydrocarbons, which makes vapor recovery one of the most dilution-aggressive duties in gas compression.
- Five NEXT lubricants cover the vapor-recovery dilution range: NEXT GPL MIN and NEXT GPL PAO for lighter, less dilution-prone vapors; NEXT GPL PAG for light-to-medium hydrocarbon streams; NEXT GPL PAG-WS for heavy and sour vapors; and NEXT GPL PAG-EO (PEG, hydrocarbon solubility below 3 wt%) for the most severe dilution.
- Suction separation and condensate control remain essential. Lubricant selection does not compensate for continuous liquid carryover.
How Vapor Recovery Units work and the compressor's role
Vapor recovery units collect low-pressure hydrocarbon vapors that would otherwise be vented, flared or routed to another emissions-control system. The recovered vapor is compressed and directed to a sales-gas line, fuel-gas system, processing facility or other recovery destination.
A typical system contains a vapor-collection network, a suction scrubber or separator, the compressor, controls and downstream cooling or separation equipment. The suction scrubber removes free liquids before the vapor enters the compressor; the control system maintains the required tank or collection-system pressure.
VRU compressors operate under low and changing suction pressures as tank levels, production rates, loading activity and ambient conditions vary. Reciprocating, oil-injected rotary screw, rotary vane and other compressor designs serve different combinations of capacity, pressure ratio, vapor composition and package design.
The lubricant protects bearings, cylinders, piston rings, packing, rotors, vanes and other moving components. In oil-injected compressors and process-exposed lubrication points, maintaining viscosity after hydrocarbon dilution determines component protection.
Crude Oil & Condensate Tank Vapor Recovery
Vapor recovery units recover flash, working and breathing vapors from crude-oil and condensate storage tanks operating at or near atmospheric pressure. Crude-oil and condensate tanks rank among the largest sources of recoverable vapor.
Tank Battery & Wellsite VRUs
Upstream production facilities capture vapors from tank batteries and other low-pressure production sources for recovery instead of venting or flaring.
Loading & Terminal Vapor Recovery
Truck, rail and terminal loading generates displacement vapors as liquid hydrocarbons enter storage or transport vessels. Vapor-recovery systems collect these streams for processing or recovery.
Flash Gas Recovery
Pressure reduction of hydrocarbon liquids releases dissolved gases as flash vapor. VRU compressors recover these streams and return them to a process, fuel-gas or sales-gas system.
Process & Low-Pressure Vent Recovery
Vapor recovery units also recover vapors from compressors, dehydrators and other low-pressure sources within oil-and-gas and process facilities.
Factors affecting lubricant selection
Vapor recovery combines hydrocarbon-rich vapor, low suction pressure, variable flow and the possibility of condensation. The following factors determine the lubricant chemistry and viscosity required.
- Vapor composition and molecular weight Indicates the concentration of methane, ethane, propane, butane, pentane and heavier components that interact with the lubricant.
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Hydrocarbon dilution and operating viscosity
Determines whether the formulation maintains sufficient film thickness after hydrocarbons dissolve into the lubricant. -
Condensability and dew-point conditions
Determines whether heavier hydrocarbons remain as vapor or condense into the suction system, compressor or lubricant. -
Suction and discharge conditions
Set the pressure ratio, compressor loading, discharge temperature, gas density and the amount of hydrocarbon the lubricant retains. -
Lubricant and gas temperature
Govern hydrocarbon solubility, in-service viscosity, oxidation rate and the likelihood of condensation. -
Condensate and liquid carryover
Disturbs the lubricating film and dilutes the lubricant, which makes effective suction separation and drainage essential. -
Variable flow and cycling duty
Create changing thermal and lubrication demands as tank pressure, production rate and vapor generation fluctuate. -
Water, CO₂ and H₂S
Determine corrosion risk, lubricant stability, material compatibility and whether sour-gas requirements apply.
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 also serves.
- 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.
Operational Benefits of Correct Lubricant Selection
Selecting the lubricant according to the compressor, gas composition and operating conditions can provide several operational benefits.
- Stable Operating Viscosity Maintains sufficient film strength after hydrocarbons dissolve into and dilute the lubricant.
- Reliable Variable-Load Performance Sustains lubrication across changing suction pressure, vapor flow, compressor load and cycling.
- Reduced Unplanned Downtime Prevents lubrication-related wear, overheating, valve problems, deposits and unexpected compressor shutdowns.
- Extended Component Life Protects cylinders, piston rings, packing, bearings, rotors and other lubricated components.
- Clean Running and Deposit Control Minimizes varnish, carbon and deposit formation for cleaner valves, cylinders and lubricant-system components.
- Longer and More Predictable Service Intervals Resists oxidation, viscosity loss and contamination for controlled maintenance planning.
Recommended NEXT Vapor Recovery Unit Compressor Lubricants
NEXT GPL PAG-EO
Very Heavy / Severe-Dilution Vapor Recovery
Base Oil: PEG
ISO Range: 32 – 220
NEXT GPL MIN
Wet / Light Hydrocarbon Vapor Recovery
Base Oil: Mineral
ISO Range: 32 – 680
Our technical team can help identify the right product.
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.
What type of oil is used in a vapor recovery unit compressor?
VRU compressors can use mineral, PAO or PAG lubricants depending on vapor composition, compressor design and operating conditions. Lighter vapor streams may suit mineral or PAO lubricants, while hydrocarbon-rich or heavily diluting streams can require PAG or water-soluble PAG chemistry to maintain sufficient operating viscosity.
Why can VRU vapors reduce compressor oil viscosity?
Recovered vapors can contain propane, butane and heavier hydrocarbons that dissolve into the lubricant or condense into it. This reduces the viscosity of the oil-hydrocarbon mixture. Corken specifically warns that condensation of hydrocarbons such as butane can result in crankcase-oil dilution.
Is oil dilution always worse in a VRU than in other gas compressors?
Not necessarily. VRUs can be highly dilution-prone, particularly when handling condensable or heavier hydrocarbon vapors, but severity depends on the actual vapor composition, temperature, pressure and lubricant chemistry. It is better to evaluate the specific VRU stream than assume every VRU is more severe than every other gas-compression application.
When should PAG be used instead of PAO in a VRU?
PAG becomes particularly useful where hydrocarbon dilution causes PAO or mineral oil to lose too much operating viscosity. Standard GPL PAG is suited to lighter and medium hydrocarbon streams, while GPL PAG-WS provides greater dilution resistance for heavier or more demanding vapor compositions.
What is the difference between NEXT GPL PAG and NEXT GPL PAG-WS for vapor recovery?
NEXT GPL PAG is primarily suited to light-to-medium hydrocarbon vapor service. GPL PAG-WS uses EO/PO PAG chemistry and is positioned for heavier and sour vapor streams where greater resistance to hydrocarbon dilution is required. Your current VRU category explicitly distinguishes the two this way.
Does low suction pressure cause oil dilution in a VRU?
No. Low suction pressure is characteristic of many VRU applications, but hydrocarbon dilution is primarily caused by the composition of the vapor and the amount of refrigerant/hydrocarbon dissolved or condensed into the lubricant. Pressure and temperature influence that behavior, but low suction pressure by itself is not the reason the oil becomes diluted.
Does sub-atmospheric suction matter for lubricant selection?
Yes, but mainly because it changes the compressor operating envelope, pressure ratio and sealing requirements. Its significance depends on compressor design, so actual suction and discharge conditions should be provided rather than using sub-atmospheric operation as a lubricant-chemistry rule.
Does variable flow change the lubricant choice?
It can. Many VRUs operate under changing loads as tank pressure, production rates or loading activity vary. The selected lubricant should therefore maintain suitable viscosity and stability across the expected operating range rather than one design point.
Can one lubricant be used for several VRUs on the same site?
Possibly, but only after comparing their vapor compositions, compressor designs and operating conditions. A crude-oil tank VRU and a condensate or loading-vapor compressor can experience substantially different dilution conditions, so one lubricant should not be applied across all units solely because they are all called VRUs.
When should NEXT GPL PAG-EO be used in a vapor recovery unit?
NEXT GPL PAG-EO is intended for VRU applications where heavy or highly condensable hydrocarbons cause severe lubricant dilution. Its PEG chemistry has very low hydrocarbon solubility, helping maintain operating viscosity in streams containing heavier hydrocarbons such as butane, pentane and condensate-rich vapors. For lighter vapor streams, GPL PAG or GPL PAG-WS may provide a better fit, so selection should be based on the actual vapor composition, pressure and temperature.
Explore Other Gas Compression Applications
Natural Gas Processing & NGL
Natural Gas Gathering
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Petrochemical Gas Compression
Lubricants for hydrocarbon, cracked, recycle and reactive gas streams in petrochemical processing.