How Vapour Recovery Units Work: A Technical Overview for Oil and Gas Operators
July 2, 2026In the oil and gas sector, managing hydrocarbon vapours during storage, transfer, and production is both a regulatory requirement and an environmental responsibility. vapour recovery units (VRUs) have become a cornerstone technology for operators who need to capture these emissions, recover valuable hydrocarbons, and maintain compliance with increasingly stringent environmental standards.
What Is a Vapour Recovery Unit?
A vapour recovery unit is a mechanical system designed to collect hydrocarbon vapours that would otherwise be vented or flared from storage tanks, processing equipment, and other pressure vessels. These vapours — primarily composed of volatile organic compounds (VOCs) and methane — represent both an economic loss and a significant environmental hazard if released uncontrolled into the atmosphere.
VRUs typically consist of a suction unit, a compression stage, a scrubber or knockout drum, and a control panel. The system creates a low-pressure draw on the storage vessel or collection header, pulling vapours into the inlet where they are compressed and sent downstream for recovery, reuse, or further processing.
How the Vapour Recovery Process Works
The process begins at the vapour source — typically a tank battery, crude oil storage tank, or produced water tank. As liquid hydrocarbon levels fluctuate due to filling, temperature changes, and barometric pressure shifts, gas vapours accumulate in the headspace above the liquid. Without a recovery system, these vapours would either be vented to atmosphere or combusted in a flare.
When a VRU is in place, those vapours are drawn through a dedicated vapour collection line to the recovery unit inlet. A suction regulator maintains a slight negative pressure on the tank, preventing over-pressurization while continuously drawing vapours into the system. The incoming stream then passes through a scrubber to remove entrained liquids before entering the compressor.
The compressor — the heart of any VRU — increases the pressure of the vapour stream, making it suitable for injection into a sales gas pipeline, a fuel gas system, or a vapour recovery tower. Depending on the configuration and the composition of the vapour stream, operators may also recover heavier hydrocarbon liquids that condense out during compression.
Types of Compressors Used in Vapour Recovery
Several compressor technologies are used in VRU applications. Rotary vane compressors are popular for low-flow, low-pressure applications because of their simplicity and low maintenance requirements. Reciprocating compressors offer greater flexibility across a wider range of pressures and flow rates. Screw compressors are preferred in high-volume applications where continuous duty and low maintenance are priorities.
Selecting the right compressor type depends on the expected vapour volume, composition, inlet pressure, and discharge pressure requirements. A well-engineered vapor recovery system will account for all of these variables to ensure reliable, efficient operation under actual field conditions.
Regulatory Drivers and Environmental Benefits
Regulatory pressure from agencies such as the Environmental Protection Agency (EPA) and provincial equivalents in Canada has significantly accelerated the adoption of vapour recovery technology. Regulations targeting methane emissions and VOC releases from oil and gas facilities have made uncontrolled venting increasingly costly, both in terms of penalties and reputational risk.
Beyond compliance, VRUs offer measurable economic benefits. Methane recovered from tank vapours can be sold or used as fuel gas, offsetting operating costs. Heavier liquids recovered during compression add to the operator hydrocarbon inventory. In many cases, VRU installations pay for themselves within months through recovered product value and avoided regulatory fees.
Sizing and Installation Considerations
Proper sizing is critical to VRU performance. An undersized unit will allow vapours to escape through pressure relief valves; an oversized unit will short-cycle and wear prematurely. Key inputs for sizing include tank working volumes, throughput rates, liquid temperatures, vapour pressure of the stored hydrocarbon, and expected ambient temperature range.
Installation considerations include the location of the unit relative to the tank battery, available utilities such as power and fuel gas, drainage provisions for recovered liquids, and access requirements for maintenance. Many VRU installations also require a programmable logic controller (PLC) or SCADA integration to monitor tank pressures and compressor operation remotely.
Maintenance and Operational Reliability
Like any rotating equipment, VRUs require routine maintenance to remain effective. Typical maintenance tasks include compressor oil changes, filter replacements, belt or coupling inspections, valve servicing, and periodic performance testing. Well-maintained units commonly achieve uptime rates above 95%, making them highly dependable for continuous emissions control.
Operators in remote locations or with limited maintenance resources may benefit from VRU designs that prioritize simplicity, use common spare parts, and integrate remote monitoring capabilities. The goal is to maximize the time the system operates within its design parameters while minimizing unplanned shutdowns.
Conclusion
Vapour recovery units represent a proven, cost-effective solution for reducing hydrocarbon emissions from oil and gas storage and production facilities. By capturing vapours that would otherwise be lost to the atmosphere, these systems help operators meet regulatory requirements, recover valuable product, and demonstrate environmental stewardship. As emissions regulations continue to tighten globally, the role of VRUs in responsible oil and gas operations will only grow more important.
Patricia Duarte was born in Sacramento, California Studied at University of San Francisco. Currently working as Author at Myfitv, Patricia Duarte helps readers learn the field of Marketing, Health, Education, Construction, Business etc hone their skills, and find their unique voice so they can stand out from the crowd.