The Case for Moving Beyond Open Flaring
Open flaring has long been the default method for disposing of waste gases at oil and gas facilities, chemical plants, and refineries. While flaring converts methane into CO2 — a less potent greenhouse gas — it remains a significant source of incomplete combustion byproducts, black carbon, and various air pollutants. Regulatory bodies across North America and globally are increasingly restricting routine flaring, pushing operators to evaluate alternative combustion and emission control technologies.
Thermal oxidizers have emerged as one of the most effective alternatives, offering higher destruction efficiency, lower visible emissions, and greater flexibility across a range of vapor stream compositions. But choosing between a thermal oxidizer and a flare isn’t a straightforward decision — each technology has distinct advantages depending on the operational context. This guide breaks down both solutions to help engineers and facility managers make an informed choice.
How Open Flares Work
A flare combusts waste gases at the tip of a flare stack, using a combination of the gas’s own combustion energy and assist gases (steam, air, or fuel) to maintain stable ignition and efficient combustion. Ground flares use enclosed combustion chambers to reduce visible flame and noise. Flares are robust, relatively low-maintenance, and capable of handling very high flow rates and surging conditions. They’re often the first choice for safety relief applications because they can rapidly dispose of large volumes of gas during upset conditions.
However, open flares have limitations: combustion efficiency can vary significantly depending on wind, flow rate, and gas composition; they produce visible emissions; and they are subject to stringent opacity and destruction efficiency requirements under regulations like 40 CFR Part 60.
How Thermal Oxidizers Work
Thermal oxidizers (TOs) destroy volatile organic compounds (VOCs), hazardous air pollutants (HAPs), and odorous gases through high-temperature combustion, typically at temperatures between 1,400°F and 1,800°F with residence times of 0.5 to 2 seconds. At these conditions, destruction and removal efficiencies (DRE) of 99% or greater are achievable across a wide range of contaminants.
Modern thermal oxidizers for industrial applications come in several configurations including direct-fired thermal oxidizers (DFTOs), recuperative thermal oxidizers (RTOs) with heat recovery, and catalytic oxidizers for lower-temperature operation. Each design balances capital cost, operating cost, energy efficiency, and applicable contaminant types.
Key Differences: Thermal Oxidizer vs Flare
The most important differences between thermal oxidizers and flares relate to combustion efficiency, applicable regulatory requirements, cost, and operational flexibility. Thermal oxidizers consistently achieve higher destruction efficiencies (99%+) compared to well-designed flares (98%+) and poorly performing flares (as low as 80%). Thermal oxidizers produce no visible flame, no smoke, and significantly lower particulate emissions. They are ideal for facilities where opacity limits, community relations, or permit conditions make visible emissions unacceptable.
However, flares generally have lower capital costs and are more tolerant of variable flow rates and emergency relief scenarios. A flare’s flow capacity can be sized for maximum emergency events while operating continuously at much lower turndown rates, something thermal oxidizers handle less gracefully without sophisticated control systems.
Regulatory Considerations
Regulatory requirements are a major driver in the thermal oxidizer vs flare decision. Under EPA NSPS rules and various state air quality regulations, facilities must demonstrate that their emission control equipment achieves minimum destruction efficiencies and maintains continuous compliance. For facilities subject to Maximum Achievable Control Technology (MACT) standards, thermal oxidizers often provide more straightforward compliance paths due to their consistent, measurable performance.
Choosing the appropriate high-temperature emission control systems requires a thorough review of applicable federal, state, and local regulations, permit conditions, and the specific compounds present in the waste gas stream.
When to Choose Each Technology
Choose a thermal oxidizer when you need consistently high DRE for HAPs or VOCs, when visible emissions must be minimized, when the waste gas composition is relatively consistent and continuous, or when heat recovery can offset operating fuel costs. Choose a flare when you need emergency relief capacity for large upset volumes, when the waste gas composition or flow varies dramatically, when capital budget is constrained, or when the application is primarily a safety relief device rather than a continuous emission control tool.
Conclusion
The choice between a thermal oxidizer and a flare is rarely black and white. Many facilities operate both: a thermal oxidizer for continuous emission control under normal operations and a flare for emergency relief scenarios. Working with experienced combustion engineers who understand both technologies — and the regulatory landscape governing your operation — is the best way to ensure you select and design the right combination of emission control solutions for your facility.
Charles Perkins was born in California, Studied at California State University. Currently working as Manager at Hoonskate, Charles Perkins helps readers learn the Health, Marketing, Insurance, Lawyer etc hone their skills, and find their unique voice so they can stand out from the crowd.