Regenerative Thermal Oxidizers (RTO)

What is a regenerative thermal oxidizer?

A regenerative thermal oxidizer (RTO) is a type of air pollution control equipment that destroys hazardous air pollutants (HAP), volatile organic compounds (VOC) and odorous emissions created during industrial processes. RTOs are the most common air pollution control technology in use today.

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Regenerative Thermal Oxidizer
RTO systems destroy VOCs in industrial exhaust air to reduce air pollution.

RTO technology uses combustion at high temperatures to oxidize air pollutants from industrial exhaust streams, which turns them into CO2 and H2O before they’re released into the atmosphere. The term “regenerative” in regenerative thermal oxidizer comes from the ceramic media heat exchanger, which retains heat from the prior combustion cycle to preheat (and partially oxidize) the pollutant-filled airstream for the next cycle.

Because RTOs have heat recovery of 95% as an industry standard, they have the lowest operating cost of all thermal oxidizer systems – not to mention the longest service life and highest reliability. Regenerative thermal oxidizers are ideal for process streams with high air flow and low VOC content, achieving VOC destruction of 99%+. It’s even possible for an RTO to operate with no auxiliary fuel use whatsoever if process VOC concentration levels are >/3-4% lower explosive limit (LEL).

Not sure which technology is best? Call us or request a quote. Our cost-benefit analysis for your specific application will compare multiple options, recommend the most cost-effective technology and clearly explain the trade-offs of each.

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How does a regenerative thermal oxidizer work?

Diagram illustrating how a regenerative thermal oxidizer works

(1) A regenerative thermal oxidizer (RTO) works by pushing a pollutant-filled airstream through the oxidizer, usually with a system fan.

(2) The flow of air through the RTO is controlled by valves that direct the airstream into one of two heat exchangers (chambers containing ceramic media beds).

(3) RTOs have a minimum of two beds of ceramic media (saddles and/or structured media block) used as heat exchangers. As dirty air passes through the first media bed, it absorbs heat from the hot ceramic media, then enters the combustion chamber.

(4) In the combustion chamber, dirty air is held at temperature (>1500°F) for a specific dwell time (>.5 seconds). This oxidizes VOCs and HAPs into carbon dioxide and water vapor.

(5) Hot, clean air exits the combustion chamber and moves into the second ceramic media bed which absorbs the heat for reuse.

(6) Cooled, clean air is then exhausted into the atmosphere.

The valves (2) change direction every few minutes which reverses the flow direction, so the heat transfer alternates between the two ceramic media beds. This is what gives RTOs their high fuel efficiency and low operating costs, making them highly desirable VOC abatement systems.

Time, Temperature & Turbulence

Time, temperature and turbulence – aka “The Three T’s”- are critical and co-dependent factors that determine regenerative thermal oxidizer performance.

Time: When airflow is constant, larger combustion chambers provide longer dwell times. For most applications the dwell time is between .5 and 1 second.

Temperature: The RTO combustion chamber maintains a temperature over 1500°F, which is essential for efficient VOC destruction.

Turbulence: VOCs must mix with sufficient heat and oxygen to trigger the chemical reaction (oxidation) that breaks them down into carbon dioxide and water. RTO designs facilitate turbulence to ensure thorough mixing of the polluted process air, increasing VOC destruction efficiency.

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regenerative thermal oxidizer system used for industrial air pollution control
Regenerative thermal oxidizers oxidize organic solvents and other pollutants.

Types of Oxidizers

There are several different oxidizer technologies. If you’re unsure which system is best for your application, we can help.

Direct Fired Thermal Oxidizers (DFTO)

Direct fired thermal oxidizers (aka afterburners) represent the most basic thermal oxidizer technology. DFTOs have the lowest capital/maintenance costs compared to other systems, and are very effective in treating process air with high VOC concentrations.

Regenerative Thermal Oxidizers (RTO)

Regenerative Thermal Oxidizers are the most widely used air pollution control technology today. They have the lowest operating cost compared to other thermal oxidizer systems, with high reliability and long service life. Learn more about regenerative thermal oxidizers or check out our used RTO inventory.

Recuperative Thermal Oxidizers

Recuperative thermal oxidizers have an integrated air to air heat exchanger that uses hot treated air from the combustion chamber to pre-heat inbound process air. Because of this heat recovery, less fuel is consumed by the burner.

Catalytic Recuperative Oxidizers

Catalytic recuperative oxidizers (aka catalytic oxidizers) use less fuel because they operate at a lower temperature compared to other thermal oxidizer systems (typically 600°F – 650°F). They’re best for clean applications without halogens, sulfurs, silicone or particulates. Learn more about catalytic recuperative oxidizers or check out our current used catalytic oxidizer inventory.

Regenerative Catalytic Oxidizers (RCO)

Regenerative Catalytic Oxidizers operate similar to RTOs (see above) but include a layer of catalyst impregnated ceramic media, making them even more fuel efficient than RTOs. RCOs work well for low-VOC process airstreams (below 16%) and have a long service life.

VOC Rotary Concentrators

VOC Rotary Concentrators are air pollution control systems that pre-condition pre-condition the airstream before it goes to a paired oxidizer for VOC destruction. VOC concentrators work by absorbing VOCs from high-volume, low-VOC process air, then releasing the concentrated VOCs into a smaller vapor stream that is treated in a thermal oxidizer. Learn more about VOC rotary concentrators.

Who Uses Regenerative Thermal Oxidizers?

Regenerative Thermal Oxidizers are used by manufacturers in a wide range of industries and applications. The Kono Kogs team has experience with practically every possible oxidizer application across many industries around the globe.

Some of the Processes Regenerative Thermal Oxidizers are Used to Treat Include:

An RTO for VOC control can be even more efficient when integrated with a VOC rotary concentrator.

The Kono Kogs Inc. (KKI) team has in-depth understanding of every process airstream our RTO systems are used to treat. Explore RTO case studies or contact us with your questions about your specific application.

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How much does a regenerative thermal oxidizer cost?

The cost of a regenerative thermal oxidizer depends on its size, features and installation site. In general, RTO systems can cost anywhere from $100k to over $2M.

The Total Cost of Ownership (TCO) is the initial capital investment in the equipment plus installation and operating costs like fuel, electricity, and compressed air. RTOs have the lowest operating cost compared to other types of thermal oxidizers. Used, fully refurbished RTO systems from Kono Kogs can save you 40% or more in capital costs compared to buying new – with comparable guarantees and warranties.

Step one is choosing the optimal equipment for your application. Though manufacturers looking for RTOs may be experts in their industry, they’re often not an expert when it comes to air pollution control technologies. The KKI team has over 150 years’ combined experience designing, reconditioning, and installing thermal oxidizer systems. We’re happy to perform a cost-benefit analysis for your project, explain your options including the trade-offs of each, and provide a professional recommendation.

A regenerative thermal oxidizer is a significant investment, but it doesn’t have to be a major long-term expense. Contact the KKI team for help selecting the most cost-effective system for your application.

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RTO design configured for low VOC process air stream
RTOs come in different designs, sizes & configurations.

Regenerative Thermal Oxidizer Design

Certain RTO design factors can make a significant difference in both capital and operating costs:

Process air volume flowrate affects the size of the RTO unit, dampers and ductwork you’ll need.

Process air exhaust temperature determines the need for ductwork insulation, fan sizing, and affects expected operating costs.

Type & concentration of pollutants affects material of construction, heat exchanger efficiency, and greatly determines operating costs of electricity and fuel.

Complexity of RTO design affects how much RTO maintenance will be required. RTOs come in different designs, sizes and configurations.

Projected growth could make it smarter to install a higher-capacity system right away, rather than adding a second RTO in the future.

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Questions to consider before purchasing a regenerative thermal oxidizer:

  • Is the RTO optimized for my exhaust airstream?
    • RTO’s typically treat airstreams with a 0-10% Lower Explosive Limit (LEL)
    • RTO systems can handle 25% LEL airstreams, though hot gas bypass systems and other features may be needed
  • Is the ceramic media in the RTO optimized for my exhaust airstream?
    • Maximum thermal efficiency
    • Lowest pressure drop
    • Ability to handle organic/inorganic particulates
  • Does the RTO need to handle potentially corrosive emissions/halogens?
    • Special materials of construction may be required
  • Is the process sensitive to pressure pulses that can occur with poppet valve technology?
  • Rotary valve technology may be a better option
  • Does the RTO main fan use a variable frequency drive (VFD)?
    • VFDs are important for efficient operation, volume turn-down and idle operation
  • Would an induced draft fan be a better choice than a forced draft fan?
    • Solvents with a high boiling point can build up on fan wheel
  • Is the RTO skid mounted with little welding required in the field?
    • Ease of installation results in lower turnkey cost
  • Are the RTO PLC controls configured with remote access for troubleshooting?
    • Remote access can ease troubleshooting and reduce the frequency of service visits
  • Are process emissions visible to the naked eye?
    • A puff capture feature may be required to eliminate visible emissions
  • Would a fuel gas injection system be a wise choice for this application?
    • Fuel injection can provide significant fuel savings
  • Is there a risk of ceramic media plugging due to condensing VOCs?
    • A bake-out feature can address organic compound build-up
  • Is there enough heat in the RTO exhaust (>250°F) to consider the benefits of secondary heat recovery?
  • Do the local government codes require low NOX operation?
  • Is there a used RTO system available with the features needed?
    • Quality-built used regenerative thermal oxidizer (RTO) systems have a long life, can save 40-60% vs. new units, and have performance and parts warranties comparable to new systems.

For examples of our work, check out these RTO units before & after refurbishment by Kono Kogs.

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regenerative thermal oxidizers (RTO)
An inlet mixing box was added to this RTO system to handle two airstream temperatures.

Regenerative Thermal Oxidizer vs Thermal Oxidizer

Compared to other thermal oxidizer systems, regenerative thermal oxidizers are more efficient and reliable, and have a longer service life. However RTOs have a more complex build and are heavier, which can affect shipping, installation and commissioning costs.

In thermal oxidizers, air flows only one way through the system. RTOs create airflow reversals using dampers and control logic, which makes them much more thermally efficient. RTOs are the best option for most industrial processes, however when 99.99% destruction of VOCs is a requirement, a thermal recuperative oxidizer may be the better solution.

Regenerative Thermal Oxidizer vs Recuperative Thermal Oxidizer

The main difference between regenerative and recuperative thermal oxidizers is how each one recovers heat while operating. Recuperative thermal oxidizers use metal as the heat exchange material, while regenerative thermal oxidizers use ceramic media.

Regenerative Thermal Oxidizer Components

In many cases, KKI can help businesses comply with environmental regulations and reduce operating costs by repairing, rebuilding, or upgrading their existing regenerative thermal oxidizer. We have an extensive inventory of RTO parts including ceramic media, fans, burners, and much more, plus an in-house fabrication shop.

When the cost of regenerative thermal oxidizer repair outweighs the benefit, KKI can facilitate RTO replacement. We offer used “as-is” regenerative thermal oxidizers as well as fully refurbished systems with parts and performance warranties.

Available RTO components from Kono Kogs include:

  • Exhaust stacks
  • Combustion chambers
  • Media chambers
  • Media cold face support
  • Gas trains
  • Process ductwork/supports
  • Process T dampers
  • Hot bypass valves
  • Access platforms
  • PLC cabinets
  • Actuators
  • Insulation & cladding
  • Pneumatic controls

Examples of regenerative thermal oxidizer upgrades/services we offer:

The components and services above are by no means comprehensive. KKI can handle any RTO rebuild or replacement project you’re facing. We invite you to send us your trickiest projects and look forward to the challenge!

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Regenerative Thermal Oxidizer Manufacturers

The best-built RTOs make the best used RTOs. KKI selects only the best pre-owned regenerative thermal oxidizers and stands behind them with warranties that match new equipment Original Equipment Manufacturer (OEM) warranties.

regenerative thermal oxidizer manufacturers
Refurbished TANN RTO with a small footprint

Check out our used RTO inventory from manufacturers including:

Save Money on Quality RTO Systems from Kono Kogs, Inc.

KKI is the leading global supplier of high-quality used air pollution control equipment. Our team has a 100% success rate meeting our performance guarantees and has earned repeat business from multiple customers. Whether you’re looking to get more efficient service out of your existing RTO or learn about your replacement options, KKI can help.


Request a quote online or call 920.432.2699 for more information.