Caution When Using 99% DRE or Greater on Combustors

Enclosed combustion devices (ECDs) are frequently used by oil and gas (O&G) operators to reduce methane (CH4) and VOC emissions from natural gas venting. The efficiency of an enclosed combustor is often referred to as the control efficiency or destruction and removal efficiency (DRE).

Federal (NSPS OOOOa) and many State environmental regulations require control devices used to control venting sources to have a minimum DRE of 95%. For air permitting and annual emission inventory reporting, operators often use a DRE of 98% for ECDs controlling venting sources. Most State air permitting agencies will accept a default DRE of 98% for ECDs controlling venting sources. State agencies often require design, testing and/or monitoring data for ECDs claiming a DRE greater than 98%

ECDs tested using manufacturer testing procedures in NSPS OOOOa (§60.5413a(d)) often demonstrate a DRE much greater than 99%. Cimarron’s ECDs all tested well above 99.9% DRE. Note that this testing does not use natural gas as the fuel and is conducted under controlled conditions.

Some ECD suppliers claim a DRE much greater than 99% for their ECDs. The basis for this may be the NSPS OOOOa manufacturer testing results.

Caution Using 99% DRE or Greater for Permits

Operators should use much caution when using a 99% DRE or greater for permits because ECDs operating at a typical oil and gas production facility may not achieve this DRE. Many base the DRE on the NSPS OOOOa manufacturer testing results. Below are some reasons for not achieving DREs greater than 99%.

NSPS OOOOa manufacturer DRE test results greater than 99% may not be consistently achieved at production facilities because OOOOa test conditions would vary from actual field operations. This could be caused by:

  • Propene fuel used by OOOOa test instead of field natural gas or storage tank vent gas.
  • ECDs can install an extension on the combustion tube during OOOOa testing to meet the sample port location requirements. For these test-modified units the actual field model would have a shorter combustion zone.
  • Wind speed variations at field locations.
  • Ambient air temperature variations at field operation location.
  • Minimum and maximum gas flow rates at field locations.
  • Ambient pressure variation due to site elevation


Reasons For Defensible DRE

Some reasons to use a defensible DRE are:

  1. Permit violations due to underestimation of air emissions (e.g., VOCs).
  2. Underestimation of emissions reported to annual State environmental agency emission inventories and the EPA mandatory greenhouse gas emission inventories. A company would be required to resubmit their inventory to correct any errors. For State emission inventories, fees would be owed for the difference in emissions.
  3. State environmental permitting agencies may require onsite field testing to demonstrate DREs greater than 98%.
  • The Colorado Air Pollution Control Division’s Regulation 7 requires periodic stack testing of certain ECD applications to demonstrate DRE is above 95%. Testing DRE results is required to be used for annual emission inventory calculations and reporting.


Ways to Ensure DRE

To ensure combustion DRE greater than 99%, we suggest the following monitoring parameters:

  1. Inlet pressure
  2. Flue gas temperature
  3. Flue gas temperature-controlled louvers to adjust excess air
  4. Conduct DRE field stack testing of the ECD if want to use a DRE greater than 99%. Cimmaron conducted a site-specific DRE testing of an enclosed combustor burning field natural gas at an oil and gas facility located in Colorado. The results yielded a DRE of 99.5% or above.

For more information, review the Cimarron blog at: Quad O Enclosed Combustors – Should You Claim 95% DRE OR 99%+ DRE?


Cimarron’s NSPS Quad O performance tested enclosed combustors have achieved a 99.9%+ DRE burning propylene, but we do not claim 99.9% DRE for a simple, natural draft enclosed combustor.

For the typical ECD using in oil and gas operations, it may not be accurate to claim DREs greater than 99%.

Enclosed combustors operating at a typical oil and gas production location may not achieve a DRE greater than 99% due to the following:

  • Field gas composition variation
  • Flow rate variation
  • Wind speed interacting with the air inlets
  • Ambient temperature variation
  • Ambient pressure variation due to site elevation

Cimarron conducted site-specific DRE testing of an enclosed combustor burning field natural gas at an oil and gas facility located in Colorado. The results yielded a DRE of 99.5%.

Achieving combustion DRE greater than 99% would require monitoring the following parameters:

  • Inlet pressure
  • Flue gas temperature
  • Flue gas temperature-controlled louvers to adjust excess air


Cimarron – Who We Are

Cimarron’s overall goal is to reduce GHG emissions for all industries as we work with our clients to create a cleaner environment.

The company engineers and manufactures environmental, production and process equipment for the upstream, midstream and downstream energy industries, as well as environmental control solutions for biogas at wastewater facilities, digester tanks and landfills.

Our flares and ECDs meet all federal and state environmental regulatory requirements for control efficiency and destruction efficiency.

Cimarron offers our customers the know-how and environmental expertise to meet the environmental standards of today and tomorrow. Cimarron is committed to bring value to the Energy industry and their shareholders based on our financial strength, experienced personnel, and engineering capabilities.

As a company, we strive every day to make a difference through innovation (e.g. ESG), customer focus, and operational efficiency. In addition to being present in all major regions in the US, Cimarron serves more than 45 countries around the world, ranging from offshore to desert. From key operational centers in the United States, Italy and the United Arab Emirates, Cimarron offers ongoing service and support through its own field service personnel and strategic third-party partners, creating a cleaner environment for our customers and their shareholders.

Since its founding in the mid-1970’s in Oklahoma, the company’s product offering has expanded from production equipment to include the largest line of environmental solutions that capture or incinerate fugitive vapors. With the acquisitions of HY-BON/EDI in 2019 and AEREON (including Jordan Technologies) in 2020, Cimarron has added strong brands, products, and services to its portfolio.

Please contact us to learn more about our products and services and about all our ESG solutions at or visit our website

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