Thermal Oxidizers (TOX): Understanding the 6 types of TOX systems

Refurbished Thermal Oxidizers

A thermal oxidizer combusts hazardous air pollutants (HAPs) at high temperature for air pollution control.

A thermal oxidizer is a combustion system used to control air pollution by destroying hazardous air pollutants (HAP), volatile organic compounds (VOC), and odorous emissions discharged from industrial processes. Also referred to as TOX or thermal incinerator, a thermal oxidizer is designed to oxidize hydrocarbon-based pollutants into CO2 and H2O before exhausting them to the atmosphere.

Thermal Oxidizer vs. RTO

Though both can technically be called thermal oxidizers, a true thermal oxidizer is slightly different from a regenerative thermal oxidizer (RTO). Specifically, a thermal oxidizer uses an air-to-air heat exchange system to heat intake air before combustion, while an RTO incorporates two heat exchange beds, one before and one after the combustion chamber. Air flow in a thermal oxidizer goes uni-directionally. Airflow in an RTO reverses direction periodically as the two beds of the RTO are heated and cooled in each cycle. The air flow is reversed using switching valves.

The 3 T’s of Thermal Oxidizers: Time, Temperature & Turbulence

What is the dwell time of a thermal oxidizer?

Typically 0.5 seconds to greater than 1.0 seconds depending upon the VOC characteristics and the local codes. Given a constant rate of flow, the larger the combustion chamber, the longer the dwell time. More time typically equates to greater VOC destruction efficiency. In most applications the dwell time requirement is between .5 – 1 second.

What is the operating temperature of a thermal oxidizer?

Typically 1400 F minimum up to 1600+F depending upon the VOC characteristics. Thermocouples inside the chamber monitor temperature and adjust gas burner firing as needed. Adequate temperature is essential to ensure VOC destruction efficiency. In most cases a data log of chamber temperature is required for air quality compliance.

What is the role of turbulence in a thermal oxidizer?

VOCs must combine with oxygen and heat to trigger the chemical reaction that breaks them down into CO2 and H2O. There are many successful thermal oxidizer designs that ensure sufficient turbulence, such as introducing the process air at an angle to induce spin or creating internal choke points. The better the mixing and heat distribution, the higher the VOC destruction.

How Does a Thermal Oxidizer Work?

diagram showing how a thermal oxidizer works
  1. A pollutant-filled airstream is pushed through the oxidizer, usually with a system fan. If the process airstream doesn’t have enough oxygen for combustion, ambient air is added.
  2. The flow of air passes through an air-to-air heat exchanger (if equipped) to preheat the air before entering the burner/combustion chamber. Thermal oxidizers can operate with an integral heat exchanger for fuel savings, or without one for capital cost savings.
  3. In the combustion chamber the air is heated to a sufficiently high temperature and held at high temperature with turbulence, to ensure VOC destruction. Typical operating temperatures are >1400°F, with dwell times of .5 – 1.0 second. This combusts the VOCs into CO2 and H2O.
  4. The hot, clean air continues through the hot pass of the heat exchanger (if equipped).
  5. Cooled, clean air is then exhausted to the atmosphere.

VOC thermal oxidizer
Thermal oxidizers designed with heat recovery require less fuel to operate.

The 6 Types of Thermal Oxidizers

The different types of thermal oxidizers include direct-fired oxidizers, recuperative oxidizers, and regenerative thermal oxidizers (RTOs). Catalytic recuperative oxidizers and regenerative catalytic oxidizers (RCOs) sometimes get grouped in as well. If you’re unsure which system is best for your application, we can help.

  1. 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.
  2. 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.
  3. 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.
  4. 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.
  5. 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.
  6. VOC Rotary Concentrators—While not truly an oxidizer, VOC Rotary Concentrators are air pollution control systems that pre-condition an airstream before it is sent to a paired oxidizer for VOC destruction. VOC concentrators work by absorbing VOCs from high-volume, low-VOC concentration process air, then releasing the concentrated VOCs into a smaller vapor stream that is treated in a thermal or catalytic oxidizer. Learn more about VOC rotary concentrators.

Who Uses Thermal Oxidizers?

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.

We have an in-depth understanding of every process airstream our systems are used to treat. Explore our thermal oxidizer case studies or contact us with questions about the different technologies available for your specific application.

direct fired thermal oxidizer
The cost of a thermal oxidizer varies by size, type, and location of the installation.

How Much does a Thermal Oxidizer Cost?

The cost of a thermal oxidizer addition includes the initial capital investment in the equipment as well as the operating and installation costs. Buying a pre-owned, fully refurbished thermal oxidizer from Kono Kogs can save you 40% or more in capital costs compared to the cost of new, with comparable guarantees and warranties.

Kono Kogs recommends carefully thinking through the Total Cost of Ownership (TCO) before making a purchase. A thermal oxidizer system with a low capital cost might not represent your lowest TCO in operation over time. As a rule of thumb, consider a two-year period when calculating the total cost.

Capital Costs Include:

Operating Costs Include:

Both capital and operating costs can vary widely between different thermal oxidizers. Some TOX technologies have fuel costs 5-10x higher than other systems. A Thermal Oxidizer with a low initial cost could have a higher TCO over two years compared to that of a Catalytic Oxidizer or Regenerative Thermal Oxidizer.

Kono Kogs is happy to provide a cost-benefit analysis for your project. We’ll compare multiple technologies, explain the trade-offs of each option, and give you our professional recommendation on the most cost-effective system.

Questions to Ask when Considering a Thermal Oxidizer (TOX)

  • Is a thermal oxidizer the most cost-effective oxidizer solution for my airstream? (See: Selecting an Oxidizer)
  • Would a heat exchanger be cost effective?
  • Is a plate heat exchanger or shell and tube style heat exchanger a better choice?
  • Shell and tube heat exchangers are more robust than plate style heat exchangers.
  • Is there a potential for particulates that could plug the heat exchanger?
  • Shell and tube heat exchangers are better than plate designs for particulate applications.
  • Silicone: Clean-able heat exchangers are sometimes the best solution for silicone applications.
  • Tube size is an important consideration when particulates are expected.

Other Considerations:

  • Is there a need for heat or steam in your plant?
  • Secondary heat recovery has good payback with thermal oxidizers.
  • Do local codes require low NOX operation?
  • Low NOX burners can be retrofit for these applications.

Thermal Oxidizer Manufacturers

The best-built Thermal Oxidizers make the best used Thermal Oxidizers. Kono Kogs selects only the best pre-owned Thermal Oxidizers and stands behind them.

Check out our inventory of oxidizer systems from OEMs such as:

  • CECO ADWEST Technologies
  • Dürr MEGTEC Systems
  • CMM Group
  • REECO (Dürr)
  • TANN Corp.

Kono Kogs Knows Everything About Thermal Oxidizers

Kono Kogs is the world’s leading supplier of used Thermal Oxidizers. We also offer thermal oxidizer services including turnkey installation, repair, preventive maintenance, and upgrades. Our team has over 150 years of combined experience, and a 100% success rate in meeting performance guarantees. Whether we can help you get more years out of your existing system or find a replacement, we look forward to the challenge!

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Emergency DFTO Thermal Oxidizer Fabrication for Recycling Emissions

An oil recycling company in the Southwest needed a new thermal oxidizer shell ASAP. This case study shows how KKI came through despite supply chain challenges.

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Emergency DFTO Thermal Oxidizer Fabrication for Recycling Emissions

Kono Kogs is the world’s leading supplier of used thermal oxidizers.

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