OIL & GAS EQUIPMENT | Updated May 2026 | 8 min read
What You’ll Learn in This Guide
- What an enclosed combustor device is and how it differs from a flare
- What Quad O Certified Enclosed Combustor designs deliver under EPA OOOOb
- How an enclosed combustor reaches 98% Destruction and Removal Efficiency without auxiliary air
- When to choose an enclosed combustor vs an open flare for storage tank vent gas service
- What continuous monitoring instrumentation OOOOb requires on enclosed combustors
- How the Tri-Point acquisition expanded Hero’s enclosed combustor product line
- Common enclosed combustor selection mistakes and how to avoid them
An enclosed combustor device is one of the two standard answers to controlling storage tank vent gas, flash gas, and process emissions on oil and gas affected facilities under EPA OOOOb. Where an open flare burns waste gas in an exposed flame visible against the sky, an enclosed combustor burns the same gas inside a refractory-lined chamber that hides the flame, controls combustion conditions tightly, and meets the same 98% Destruction and Removal Efficiency without auxiliary air or visible emissions. For operators selecting equipment for OOOOb storage vessel control, the enclosed combustor device is increasingly the default choice because it satisfies regulators, neighbors, and OPEX budgets simultaneously.
Hero Process Solutions, founded in 2011 and headquartered in Kellyville, Oklahoma with operations in Midland, Texas, manufactures enclosed combustor and vapor combustor systems for upstream production, midstream gas processing, and refining customers. The product line was significantly expanded through the 2020 acquisition of Tri-Point Oil & Gas Production Systems assets, which brought certified enclosed combustor designs and engineering depth into the company’s portfolio.
DIRECT ANSWER: An enclosed combustor device is a refractory-lined combustion chamber that burns oil and gas vent stream waste gas at 1,800 to 2,000°F inside an insulated enclosure rather than at an open flare tip. EPA Quad O Certified Enclosed Combustor designs are tested and certified under EPA 40 CFR 60 Subpart OOOO and OOOOb to deliver 98% or greater Destruction and Removal Efficiency on tank vent gas, flash gas, and similar low-pressure vapor streams. The enclosed configuration hides the flame, controls combustion temperature and residence time tightly, eliminates visible flame and smoke concerns, and reduces noise compared to an open flare in continuous service.
1. What an Enclosed Combustor Device Is
An enclosed combustor device is built around a vertical refractory-lined combustion chamber, typically 8 to 30 feet tall. Waste gas enters at the base through a burner assembly with integral pilot and ignition system. Combustion air is supplied by natural draft or by a forced-draft blower depending on the design. The burner fires upward into the refractory chamber where the combustion zone is held at 1,800 to 2,000°F. Exhaust gases vent from the top of the chamber after sufficient residence time to complete destruction of hydrocarbons.
The refractory lining serves three purposes: it insulates the chamber so combustion temperature can be held high enough for complete destruction without external utility heat input, it shields surrounding equipment from the radiant heat of the combustion zone, and it physically encloses the flame so visible flame is not seen from neighboring properties.
Continuous monitoring instrumentation tracks pilot flame presence, combustion zone temperature, and exhaust composition through a sample port near the stack outlet. The control system maintains stable combustion across the full operating range of waste-gas flow and composition.
2. What “Quad O Certified” Actually Means
“Quad O” is the industry shorthand for EPA 40 CFR Part 60 Subpart OOOO (the original NSPS for oil and gas facilities). “Quad O Certified Enclosed Combustor” designs are specific enclosed combustor models that have been tested at independent laboratories and certified to meet the destruction efficiency requirements of Subpart OOOO at specified operating conditions.
The certification matters because it eliminates the need for operators to perform full destruction efficiency testing on every installation. A Quad O Certified Enclosed Combustor design delivers the certified destruction efficiency by design when installed and operated per the specification, and the operator’s compliance documentation references the certification rather than a site-specific destruction test.
Hero’s enclosed combustor product line, including the Tri-Point/Leed Fabrication and Edge Manufacturing & Technology designs acquired in 2020, includes multiple Quad O Certified models sized for storage tank vent gas applications across the upstream and midstream landscape.
KEY INSIGHT: A Quad O Certified Enclosed Combustor saves the operator the cost and risk of conducting destruction efficiency testing on each individual installation. The certified design carries forward the destruction efficiency claim as long as the unit is installed and operated within the certified envelope. That single advantage is what makes certified designs the default choice for most affected facilities.
3. How Enclosed Combustors Reach 98% DRE Without Auxiliary Air
An open flare typically requires steam, air, or fuel gas injection to achieve 98% Destruction and Removal Efficiency on heavy hydrocarbon vent streams, because turbulent mixing of waste gas with combustion air at the open flame is not naturally complete. An enclosed combustor reaches 98% DRE by controlling three combustion parameters tightly inside the chamber.
Combustion temperature is held at 1,800 to 2,000°F by the refractory enclosure and burner design. This is well above the temperature at which hydrocarbon destruction is essentially complete.
Residence time at combustion temperature is set by the chamber volume relative to gas flow rate, typically 0.5 to 1.5 seconds. This is long enough for full destruction of even heavier hydrocarbons and aromatics.
Turbulence is provided by the burner design — typically a swirl or radial-injection burner that mixes waste gas with combustion air before flame stabilization. The enclosed chamber forces complete mixing rather than allowing entrainment shortcuts that open flames sometimes permit.
Together, these three controls eliminate the need for steam, air, or fuel gas auxiliaries. The enclosed combustor uses ambient air drawn into the chamber by natural draft, or by a small low-pressure blower for higher-flow units.
4. Enclosed Combustor vs Open Flare for Tank Vent Gas Service
| Aspect | Enclosed Combustor | Open Flare |
|---|---|---|
| Visible flame | None (enclosed in refractory chamber) | Visible above tip |
| Typical DRE | 98%+ certified (Quad O) | 98%+ with auxiliary air or steam (OOOOb) |
| Auxiliary air or steam required | Not required | Air-assist or steam-assist often required for heavy gas |
| Noise | Lower (enclosure dampens) | Higher (especially air-assisted) |
| Visible smoke risk | None (enclosed, controlled combustion) | Possible during turndown or composition shift |
| Footprint | Compact (vertical chamber) | Stack plus radiation zone |
| Best application | Continuous tank vent, flash gas, low-pressure vapor | Continuous and emergency relief, higher pressure inlet |
The enclosed combustor is the default choice for continuous control of storage tank vent gas, flash gas from production separators, and similar low-pressure vapor streams. The open flare is the default choice for higher-pressure relief streams and emergency relief duty. Many facilities use both — enclosed combustor for routine vent gas control, open flare for emergency relief.
5. EPA OOOOb Continuous Parametric Monitoring Requirements
For enclosed combustors used as control devices on OOOOb-affected facilities, the continuous parametric monitoring requirements include pilot flame presence (typically redundant thermocouple and ionization rod), combustion zone temperature (thermocouple in the refractory chamber at the certified measurement location), and vent-gas flow rate at the inlet.
Data must be logged at intervals frequent enough to detect deviations — typically 15 seconds to 1 minute — and retained for five years with reporting through EPA’s CEDRI portal. Visit our EPA OOOOb compliance resource for the full monitoring and recordkeeping requirements.
For Quad O Certified Enclosed Combustor designs, the certified operating envelope defines the temperature and flow parameters that constitute compliance. Operating within the envelope satisfies OOOOb; operating outside it triggers a deviation event that must be documented and resolved.
6. The Tri-Point Acquisition and Hero’s Combustor Product Line
Hero Process Solutions acquired select assets from Tri-Point Oil & Gas Production Systems in 2020, including the Leed Fabrication, Superior Fabrication Inc. (SFI), and Edge Manufacturing & Technology brands. The acquisition brought engineered Quad O Certified Enclosed Combustor designs into the product line, expanding what was originally a flare-focused business into the full vapor combustor category.
The acquired designs include enclosed combustor models sized for typical upstream tank battery applications (50 to 500 SCFM continuous vent gas), midstream gas processing applications (500 SCFM and above), and refinery vent gas control. Each design carries the original Quad O certification and is offered through Hero’s broader vapor combustor portfolio.
For context on the brand transition that brought these designs under the Hero Process Solutions name, see our companion article on the 2024 rebrand from Hero Flare to Hero Process Solutions.
7. Sizing and Integration with Tank Battery Vent Header
Enclosed combustor sizing for storage tank vent gas service starts with the working loss, breathing loss, and flash gas inventory from the tank battery, calculated using EPA AP-42 emission factors and a flash equation on the separator outlet liquid composition. The unit must handle the combined peak from all three sources at the worst-case fill event.
Integration with the tank battery vent header requires four design elements. First, vent header sizing that delivers combined peak flow at acceptable pressure drop. Second, a knockout drum upstream of the combustor to remove any liquid carryover. Third, vacuum breakers and pressure-vacuum relief valves on individual tanks to prevent backpressure from creating tank issues. Fourth, a flame arrestor between the tank battery and the combustor to prevent flame propagation back into the tank vapor space.
Hero’s liquid knockout systems are commonly specified upstream of enclosed combustor installations to handle liquid carryover from the tank battery.
8. Common Enclosed Combustor Selection Mistakes
| Mistake | Why It Hurts | Fix |
|---|---|---|
| Specifying non-certified enclosed combustor for OOOOb-affected facility | Operator must perform destruction efficiency testing at installation | Specify Quad O Certified design from approved catalog |
| Undersizing for peak fill event flow | Combustor operates outside certified envelope during peak, triggers deviation | Size for combined peak working + flash + breathing loss |
| Missing knockout drum upstream | Liquid carryover damages refractory and burner | Specify properly sized knockout drum for the tank battery |
| Skipping flame arrestor on vent header | Risk of flame propagation back into tank vapor space | Install flame arrestor between battery manifold and combustor |
| Treating enclosed combustor as drop-in for open flare without thermal analysis | Different radiation and dispersion profile may affect site layout | Run site-specific thermal and dispersion check during integration |
| Ignoring certified operating envelope at commissioning | Operating outside envelope voids the certification’s compliance value | Document operating conditions match certified envelope at commissioning |
Frequently Asked Questions
What is an enclosed combustor device?
An enclosed combustor device is a refractory-lined combustion chamber that burns oil and gas vent stream waste gas at 1,800 to 2,000°F inside an insulated enclosure rather than at an open flame. The enclosed design hides the flame, controls combustion temperature and residence time tightly, and reaches 98% Destruction and Removal Efficiency on hydrocarbon vent gas without steam, air, or fuel gas auxiliaries.
What does “Quad O Certified” mean for an enclosed combustor?
“Quad O” is industry shorthand for EPA 40 CFR Part 60 Subpart OOOO. A Quad O Certified Enclosed Combustor is a specific design that has been independently tested and certified to deliver the destruction efficiency required by Subpart OOOO at specified operating conditions. Operators using a certified design reference the certification in their compliance documentation rather than conducting site-specific destruction testing on each unit.
How does an enclosed combustor reach 98% DRE without auxiliary air or steam?
Three combustion controls inside the refractory chamber deliver 98% DRE without external auxiliaries. Combustion temperature is held at 1,800 to 2,000°F by the refractory enclosure. Residence time at temperature (0.5 to 1.5 seconds) is set by chamber volume relative to gas flow. Turbulence is provided by burner design (swirl or radial injection) that mixes waste gas with ambient combustion air. Together these eliminate the need for steam, air, or fuel gas auxiliaries.
When should I choose an enclosed combustor over an open flare?
Choose an enclosed combustor for continuous control of storage tank vent gas, flash gas, and other low-pressure vapor streams where hidden flame, low noise, and OOOOb 98% DRE compliance are priorities. Choose an open flare for emergency relief duty, higher-pressure inlet streams, and larger volumes. Many facilities use both — enclosed combustor for routine vent control, open flare for emergency events.
What monitoring does OOOOb require on an enclosed combustor?
OOOOb requires continuous monitoring of pilot flame presence (redundant thermocouple and ionization rod), combustion zone temperature (thermocouple in the refractory chamber at the certified measurement location), and vent-gas flow rate at the inlet. Data is logged at 15-second to 1-minute intervals, retained for five years, and reported through CEDRI. Operating within the Quad O Certified envelope constitutes ongoing compliance.
Where did Hero Process Solutions’ enclosed combustor designs come from?
The current enclosed combustor product line came primarily through the 2020 acquisition of Tri-Point Oil & Gas Production Systems assets, including the Leed Fabrication, Superior Fabrication Inc., and Edge Manufacturing & Technology brands. The acquisition brought Quad O Certified Enclosed Combustor designs and engineering depth into the company portfolio. The designs are now supplied under the Hero Process Solutions brand following the 2024 rebrand from Hero Flare.
