Vapor Recovery versus Flaring
October 23, 2015

Regulatory requirements to control vent gas from oil and gas (O&G) storage tanks tend to have the choice of vapor recovery or flaring. The federal NSPS OOOO and state air permitting rule are the major drivers for storage tank emission controls. Storage tank vent gas is natural gas that will contain methane (CH4), volatile organic compounds (VOCs) and possibly hydrogen sulfide (H2S) for sour gas wells.  



Operators are aware of the nationwide push to further reduce emissions from production facilities. This is especially true for flaring of natural gas since flaring results in combustion emissions (e.g., NOx, CO2) with the natural gas product wasted. Regulators want to maximize the amount of gas that is sent to sales, used as an on-site fuel source or used for other useful purposes. There is indication that royalty payments on vented and flared gas will be expanded for federal and state lands.  

It may be expedient to use a flare or enclosed combustor to control storage tank emissions, but operators should consider recovering the gas and sending it to a sales line or use it as a fuel for onsite operations.  Of course, to use a vapor recovery unit (VRU) the facility will need to have a destination (pipeline, fuel gas system) for the recovered gas. Flaring may be the only alternative for remote facilities that do not have a pipeline to send the recovered gas. Enclosed combustors and flares are very good back up emission control devices that are used with vapor recovery systems.

Some ideas to consider that may make vapor recovery more attractive:

  • Determine the value of the natural gas that could be recovered by a VRU. The value of the recovered natural will offset and often more than exceed the cost of the VRU’s initial cost and ongoing operational costs. Flaring will not increase gas production for the facility; a VRU can increase profits.
  • Route multiple wells to a central facility/battery for separation and storage. With a greater oil production at a central facility the amount of vent gas will be larger than the individual wells. This will enhance the economic justification for installing a vapor recovery system to limit flaring. 
  • Compare the facility air emissions based flaring storage tank vent gas to recovery with a VRU.  For some locations, using a VRU will lower emissions enough for the facility to quality for a “General Permit” (e.g., TCEQ Standard Permit, PBRs). Also a VRU may ensure that facility potential to emit (PTE) emissions are below major source permitting thresholds and so avoid Title 5 (Part 70) air permitting.

Some benefits of VRUs over flaring of vent gas are listed below.


  • VRUs recover natural gas product and send the gas to a pipeline or uses it for useful purpose (e.g., fuel gas)
  • Value of the recovered gas offsets vapor recovery costs
  • Conservation of natural resources
  • Reduce risk for air pollution enforcement penalties
  • Lower risk for greenhouse gas emissions liabilities


  • Lower air pollution from methane, VOC and CO2 emissions
  • Lower regulatory risk and liability
  • Treated as process equipment according to NSPS OOOO.
  • No EPA performance testing required
  • Fewer testing and monitoring requirements under NSPS OOOO


  •  No open combustion of natural gas
  •  No open flame that could ignite facility vented natural gas streams


  • No open flame visible to neighbors (although a properly designed and operating enclosed combustors would not have visible flame from a side angle view)
  • No flame detection by satellite imagery

For reference, below are some of the benefits and limitations of VRUs and flaring systems.

VRU Benefits

  • Recovers storage tank vented natural gas and sends gas to the system and/or gas pipeline
  • 100% recovery of vent gas with properly designed and operating closed vent piping and sealed thief hatches
  • Reduces VOC and methane gases
  • Results in lower emissions than combustors and candle stick flares
  • Treated as process equipment according to NSPS OOOO.
  • Electric motor driven VRUs do not have combustion emissions (e.g., CO2)
  • No visible flame from operation
  • No EPA testing required
  • Can recover vent gas streams from 5,000 standard cubic feet (SCF) per day to greater than 1,000,000 SCF per day

VRU Limitations

  • Electric VRUs require a power source
  • VRUs using gas powered engines result in combustion emissions
  • Requires a pipeline or system to receive the recovered gas

Flaring Benefits

  • Enclosed combustors may have a destruction efficiency of 95 to 99.99%+. NSPS OOOO enclosed combustors can be stack tested to verify the design meets EPA minimum destruction efficiency of 95%. Meeting the NSPS OOOO test requirements results in a 99.99% destruction efficiency.
  • Open flame (candlestick) flares can reduce methane and VOC emissions by 95 to 98%
  • Enclosed combustors are designed to operate with no visible flame
  • Can be designed to burn gas streams of less than 50 standard cubic feet (SCF) per day to greater than 1,000,000 SCF per day

Flaring Limitations

  • Flaring results in emissions of CO2 (a greenhouse gas), NOx, CO, VOCs and particulate matter
  • Considered an emission control device by regulators and has certain standards that must be met
  • NSPS OOOO has testing and monitoring requirements applicable to enclosed combustors and flares
  • Open flame (candlestick) flares have an open, visible flame visible to neighbors
  • Open flame has potential to ignite vented natural gas streams
  • Smoking flares and combustors are a regulatory violation 

HY-BON’s Complete Solution

HY-BON has engineered solutions for your vapor recovery and flaring needs. With our IQR and Leak Detection and Repair (LDAR) services we offer a complete package for operators to comply with the storage vessel emission control requirements. We can help you determine if a vapor recovery unit or an enclosed combustor is the best choice for your operation to stay in compliance. Our designs meet all applicable air quality regulatory requirements for oil and gas operations.