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Thermal Oxidizer

What is a thermal oxidizer?

A thermal oxidizer is a type of air pollution control equipment used in industrial processes to reduce emissions of volatile organic compounds (VOCs), harmful air pollutants (HAPs), and other greenhouse gases (GHG). Using extreme high temperatures (1500°F) to trigger a combustion reaction, the VOCs & air pollutants undergo thermal oxidization, transforming the organic solvents into CO2 and H2O.

Similar to an incinerator, a thermal oxidizer is an EPA-approved device to treat VOCs, HAPs, contaminated gases, and aerosolized solvents.

Thermal Oxidizers (TOs) are available in a few different varieties:

  1. Direct-fired Thermal Oxidizer (DFTO): The simplest type of thermal oxidizer, it's just a burner in a box with a fan. The direct-fired TO does not have any heat recovery system. This is the least expensive type of equipment, but has the highest energy costs.
  2. Thermal Recuperative Oxidizer (TRO): The recuperative type features an air-to-air heat exchanger (HEX), and uses the waste heat to pre-heat the incoming air to the burner. The TRO offers 60-70% thermal efficiency. It's more expensive than the DFTO, but offers lower energy costs.
  3. Regenerative Thermal Oxidizer (RTO): The most common type of thermal oxidizer, the RTO uses ceramic media to capture and recycle waste heat, offering 95% thermal efficiency. The RTO is the most expensive thermal oxidizer, but offers the lowest energy costs.
  4. Gas Flare (Vapor Combustor): While not technically a type of thermal oxidizer, the flare is similar to the direct-fired thermal oxidizer but it does not require supplemental natural gas. Flares are used on very high concentration VOC gas streams (over 3-5% of LEL).
  5. Catalytic Thermal Oxidizer (CATOX): This type uses a metal catalyst to speed along the VOC's decomposition reaction. The main advantage of catalytic thermal oxidizers is that they can operate at much lower temperatures of 800°F-900°F instead of 1400°F-1500°F.
  6. Regenerative Catalytic Thermal Oxidizer (RCO): Similar to the catalytic oxidizer above, the RCO adds the same ceramic media from the RTO for waste heat recovery. The RCO is the most expensive type of oxidizer, but it offers by far the lowest operating costs.

Thermal Oxidizer effectiveness on:

Volatile Organic Compounds (VOCs)95
Organic Hazardous Air Pollutants (HAPs)90
Odors* (Organic-based)80

*A thermal oxidizer may not be effective at removing inorganic odor compounds.

*A Rotary RTO or Three-chamber RTO will be the most effective at removing odor compounds.

Particulate matter50

*Note: only direct-fired and recuperative oxidizers are effective at treating particulates.

Acids, Chlorinated, and Fluorinated compounds35
Corrosive fumes, vapors, gases15
Heavy Metals5

Main components of a Thermal Oxidizer

Ductwork and Process Fan

A thermal oxidizer will typically use a forced-draft fan setup instead of an induced-draft fan system, because the process air temperature is usually cooler on the inlet side. Installing the fan on the coolest side offers the best fan performance due to increased air density at lower temperatures.

Combustion Chamber (Firing box)

The primary component of the thermal oxidizer system is the combustion chamber, or firing box, which houses the burner. Contaminated air passes through the combustion chamber, designed to provide enough time at temperature (residence time) to achieve the desired destruction efficiency (DRE).

Burner, Gas Train, Combustion Blower

The heat-generating system of the thermal oxidizer is comprised of the burner, gas train, and combustion blower. The gas train provides natural gas and the combustion blower provides ambient air with oxygen for combustion. Most burners come equipped with an ultra low NOX controller to tweak the air and fuel mixture to increase flame size and reduce peak flame temperatures, thereby reducing NOX production.

Primary Heat Exchanger

In a recuperative or regenerative thermal oxidizer design, there is a primary heat exchanger to use the hot, clean air exiting the combustion chamber to pre-heat the incoming dirty air. In the recuperative oxidizer design, the heat exchange is via an air-to-air heat exchanger (HEX). In the regenerative oxidizer design, the heat exchange using multiple ceramic media chambers.

Secondary Heat Recovery and Stack

After passing through the primary heat exchanger, the air is still quite warm (200-600°F, and can be used to heat other process liquids or gases via an optional secondary heat exchanger. After passing through the heat exchanger(s), the clean air is exhaust to atmosphere via a stack.

A 3-D CAD rendering of a direct-fired thermal oxidizer (DFTO).

a drawing sketch of a recuperative thermal oxidizer design

A drawing of a basic thermal recuperative oxidizer (TRO),
with primary heat exchanger mounted on top.

A two-chamber regenerative thermal oxidizer (RTO) from Epcon LP.

A thermal oxidizer (TO) from CECO Adwest, known for their distinctive long oxidizer systems.

A smaller 10,000 CFM regenerative thermal oxidizer (RTO) being craned into place.

Thermal Oxidizer Design Considerations

Air Volume Flowrate (CFM)

The volume of process air to be treated is a key consideration. A single thermal oxidizer (TO) system can be designed to handle any amount from 100 CFM (DFTO) to over 80,000 CFM (RTO). Multiple thermal oxidizers can be combined to treat any volume of air.

Each type of thermal oxidizer has a range of air volume flowrates that it can feasibly handle without getting too large or too small (too costly).

Destruction or Removal Efficiency (DRE)

Each type of thermal oxidizer can offer a slightly different destruction or removal efficiency. A one-direction flow unit like a direct-fired thermal oxidizer (DFTO) or thermal recuperative oxidizer (TRO) with simple air-to-air heat exchanger will offer the highest DRE of 99%. Most 3-chamber RTOs can also offer 99% DRE. A 2-chamber RTO will be limited to 95-98% DRE due to dirty air that escapes during the periodic switching of air flow direction.

Factors that impact DRE:

  1. Temperature
  2. Residence time
  3. Air mixing
  4. Purge cycles (2-can RTOs only)

Retention time, or residence time, is the length of time that a VOC/organic is at the appropriate oxidation temperature. Typically, if a 95% destruction/removal efficiency (DRE) is required, then a residence time of a half a second is adequate. Meaning if the organic is brought up to a temperature of about 1400°F, and maintained at 1400°F for half a second, then 95% of the VOCs will decompose. Both retention time and residence time refer to time inside the thermal oxidizer's combustion chamber. Sufficient air mixing, also known as turbulence, must also be achieved. If the turbulence occurs and if the 1400°F for a half a second is achieved, with adequate oxygen, then 95% of the volatile organics will be destroyed. In some cases, particularly in the chemical industry, oxygen must be added to a process stream. For each organic, a specific temperature and a specific retention time is required to achieve the desired level of destruction. The table above illustrates these points for several VOCs.

Temperatures and Residence Times to Achieve Target DRE   (in °F)
95% DRE 99% DRE
0.5sec 1.0sec 0.5sec 1.0sec
Toluene 1351 1317 1372 1338
Benzene 1489 1415 1640 1640
Styrene 1445 1391 1480 1424

Type of Thermal Oxidizer

Key considerations include:

  1. Upfront Cost: Each type of thermal oxidizer has a typical cost that varies based on the size of the equipment. Do you want to: compare rough costs for each type or get a budget cost for your project?
  2. Operating cost: annual operating costs include electricity, natural gas, compressed air (if needed), maintenance costs, and personnel.
  3. Break-even point: Upfront investment cost vs Annual operating cost: Each type of thermal oxidizer offers a trade-off between initial cost and operating cost. The lower your upfront cost, the higher your operating cost will be, and vice-versa. Understanding the break-even timing will help you decide which type of TO is the best long-term solution for your company.
  4. Energy usage increases with the required airflow and size of equipment, but varies inversely with the upfront investment cost & themal efficiency of the system. The more expensive your initial cost, the higher your thermal efficiency, and the lower your energy usage, operating costs, and GHG production will be.
  5. Destruction efficiency: See above discussion.
  6. Footprint, Weight, Size: Some types of thermal oxidizer aren't feasible at certain sizes. The size, weight, and footprint of the equipment varies inversely with energy cost.

Different types of thermal oxidizer designs:

  1. Direct-fired thermal oxidizer (DFTO)
  2. Thermal recuperative oxidizer (TRO) - a DFTO plus heat exchanger.
  3. Regenerative thermal oxidizer (RTO) - uses ceramic media for thermal energy storage (TES).
  4. Catalytic oxidizer - uses a metal catalyst to lower the required destruction temperature.
  5. Recuperative and Regenerative catalytic oxidizers - same as above plus a heat recovery system.
Click here to compare all types of thermal oxidizer designs.

Industries, Applications, & Case Studies

Thermal Oxidizers are used in many industries and applications, including:

Automotive Paint Spray Booth
  • Thermal oxidizers are used to control VOC emissions from manufacturing plants in the automotive, marine, and vehicle manufacturing industries. Specific applications include treating VOCs from paint booths, controlling HAPs from paint curing ovens, engine test and quality control, rubber/tire manufacturing, and component painting.

Chemical Processing
  • Processing or production of chemicals generates exhaust air contaminated with harmful air pollutants and VOCs. These vapors should be captured and treated prior to release to atmosphere. A thermal oxidizer is typically the most robust solution for these applications which have a high concentration of VOCs.

  • Printing operations require VOC abatement, use of Permanent Total Enclosures (PTEs) for fugitive emissions capture, odor elimination, and toxic fumes destruction. A thermal oxidizer is an effective control device for Flexographic, Web Offset, Rotogravure, and Converting processes to treat water- or solvent-based inks and exhausts from dryers/ovens.

Ethanol & Biodiesel
  • The production of ethanol and biodiesel fuels from dried, distilled grains like corn or cellulose plants creates airborne VOCs, NOX, odors, particulate matter (PM), aerosols, and other Hazardous Air Pollutants (HAPs). A large recuperative thermal oxidizer is an ideal solution for kiln and dryer emissions with high levels of particulate matter (PM).

Composites & FRP
  • A thermal oxidizer is often used to control the air pollutants from the manufacturing of Carbon Fiber, FRP, Fiberglass, and other composites. Composite resins containing styrene need to be thermally treated before emitting to atmosphere. Other pollutants from ovens and furnaces include Hydrogen Cyanide, Ammonia (NH3), and Nitrous Oxide (NOX).

Food, Meat, Bakery
  • Food production generates particulate matter, grease mists, and odors which need to be controlled prior to emission. A recuperative thermal oxidizer can be the ideal solution to control exhaust streams with high amounts of airborne particulates, aerosols, or smoke. Large air volumes would use a 3‑chamber regenerative thermal oxidizer which offers 99% control.

Industrial Ovens
  • Industrial ovens for curing parts, resins, paints, and coatings will generates hazardous air pollutants and contaminants that need to be captured and destroyed prior to emitting to atmosphere. A thermal oxidizer is often used to control exhausts from ovens when they flash off VOCs and other HAPs.

Oil & Gas Processing
  • Thermal oxidizers are the primary air pollution control device for off-gas treatment from Oil & Gas processing, including VOCs and HAPs from petrochemical processing, natural gas processing, refineries, and more mid-stream and down-stream processes. An RTO can be used when levels of PM are low and air flow rates are high.

Packaging & Labeling
  • Applying graphics and adhesive labels to flexible packaging or metal containers releases volatile organics (VOCs) that need to be oxidized and decomposed prior to emission. A thermal oxidizer can be a robust solution to treat both the application and drying air streams. Large air volumes will require a regenerative thermal oxidizer (RTO).

Paint Booth
Paint Booths & Hangars
  • Paint Booths in the Aerospace, Automotive, Heavy Machinery, Bus, Train, and vehicle OEM industries produce a high-volume exhaust stream of low-concentration VOCs which is well suited to thermal recuperative oxidizers and RTOs. The downdraft or cross-draft paint booths often use a dry-filter and or wet scrubber to catch the paint overspray and particulate prior to the final VOC destruction device.

  • Tablet coating, fluid-bed processing, and tray drying in the Pharmaceutical industry offers unique air pollution control challenges as the ethanol, isopropyl alcohol (IPA), and other VOCs often release all-at-once with concentrations exceeding 100% of LEL. This poses a fire and explosion risk, so dilution air is required for plant safety. A thermal oxidizer is often used as the final control device.

  • In the semiconductor and microchip fab industries, thermal oxidizers are used for control of VOC emissions from chip manufacturing, LCDs, printed circuit boards (PCBs), and more. Thermal oxidizers are highly robust, designed to operate 24/7 for 50+ weeks per year with minimal downtime. They can be designed to withstand corrosive acids or other destructive solvents in the exhaust.

The Best Thermal Oxidizer Manufacturers

Epcon Industrial Systems

Epcon Industrial Systems L.P. based in The Woodlands, Texas offers a complete line of thermal oxidizer technologies for use in nearly every industry: Aerospace and Defense, Aluminum, Asphalt and Roofing manufacturing, Automotive, Chemical, Coffee Roasting, Coil Coating, Composites, Electronics, Food and Beverage, Metal Finishing, Metal Packaging, Oil & Gas, Pharmaceutical, Printing, Packaging, Pulp & Paper, Wastewater Treatment, Web Processing, and Wood Products.

Epcon differentiators:

  • 250,000 sqft facility with state-of-the-art fabrication machinery
  • High-quality materials and welding
  • Pre-assembled and tested prior to shipment
  • 4,000 completed systems world wide
  • Product offerings limited to oxidizers
  • No scrubber, concentrator, or dust collectors

Catalytic Products

Catalytic Product International (CPI) is based just northwest of Chicago. CPI is one of the few female-led companies in the industry. CPI specializes in smaller RTOs, thermal oxidizers, and catalytic oxidizers. CPI offers thermal oxidizers to the following industries: Chemical Processing, Coffee Roasting, Coil Coating, Drum & Container Manufacturing, Flavors & Fragrances, Flexographic Printing, Foam Production, Food & Bakery, Metal Decorating, Renewable Fuels, Rubber, Semiconductor, and Wastewater Treatment.

Catalytic Products differentiators:

  • Specialize in Catalytic Thermal Oxidizers
  • Competitive Pricing for thermal oxidizers and smaller RTOs
  • Unique technology for siloxanes & SiO2
  • No scrubber product offering
  • CPI's larger RTOs are more expensive than industry average

Ship and Shore

Ship and Shore Environmental provides thermal oxidizers and RTOs globally, including the U.S., Canada, Dubai, UAE, China, Singapore, Asia, and more. Headquartered in Southern California, just south of L.A., S&SE is a provider of thermal oxidizer equipment to the printing, plastics, composites, oil & gas, semiconductor, pharmaceutical, wood, and pulp & paper industries. Ship and Shore is a minority- and woman-owned business, which can help customers fulfill their supplier diversity targets.

Ship and Shore differentiators:

  • Experienced in many industries
  • Large SoCal Fabrication Shop
  • Offers many technologies
  • Initial bids can be lower cost
  • Reports of up-charges during project
  • Some negative customer reviews
  • No scrubber product line

Pollution Systems

Pollution Systems is based in Houston, Texas and offers regenerative and recuperative thermal oxidizer technologies and designs. They supply primarily to Texas and the Southern US region, with a focus on oil & gas, tank degassing, animal feed, food processing, metal finishing, and chemical processing. Pollution Systems is an industry leader in temporary thermal oxidizers for pipeline and tank degassing.

Pollution Systems differentiators:

  • Custom engineered solutions
  • Industry-focused expertise
  • High quality construction
  • Dedicated technical support group
  • Limited to only a few industries/applications
  • Can be higher cost

John Zink Hamworthy

John Zink Hamworthy offers a full line of thermal oxidizer technologies and equipment. JZH is based in Tulsa, Oklahoma with offices around the country and North America. With a focus on the Oil and Gas, Powerplant, and Landfill & Biogas applications, JZH is a leading oxidizer supplier for those industries. John Zink Hamworthy is a conglomorate of smaller companies, wholly owned by Koch Industries.

John Zink Hamworthy differentiators:

  • High quality construction
  • Highest reliability
  • Focused on a few specific industries
  • Offers turn-key solutions, integrated systems
  • Limited to only a few industries/applications
  • Can be higher cost

TANN Corporation

TANN builds thermal oxidizers for the Automotive, Paint, Coatings, Pharmaceutical, Printing, and Animal Rendering industries. TANN has provided a majority of the thermal oxidizers to General Motors' plants and many of their suppliers. TANN's oxidizers have the best thermal efficiencies in the industry. TANN has locations in the United States and Germany, and works with partner groups in Mexico and China.

TANN differentiators:

  • Custom and standard thermal oxidizer designs with in-house fabrication
  • Thermal efficiencies up to 97%
  • High reliability and easy maintenance
  • Custom designs to fit available footprint
  • Usually higher cost vs peers

Gulf Coast Environmental

Gulf Coast Environmental Systems (GCES) offers a full line of thermal oxidizers worldwide. GCES' often offers a competitive price for thermal oxidizers and RTOs. With custom engineered solutions and quality in-house construction, GCES' products are a great value. Perfect for the cost-conscious industrial buyer who wants a quality system at a fair price. GCES supplies the Paint, Coating, Composites, Ethanol, Pharmaceutical, Landfill, and Semiconductor industries.

Gulf Coast differentiators:

  • Often best price
  • Custom engineered systems
  • Quality in-house construction
  • Often fastest delivery time
  • RTO units can be tall & heavy
  • Extended warranty is expensive

Intellishare Environmental

Intellishare Environmental is a small company based in Wisconsin and offers direct-fired, recuperative, and regenerative thermal oxidizers. Intellishare's thermal oxidizers were developed on a modular platform and can be configured to fit nearly any space requirement. Their recuperative heat exchanger offers 50-75% thermal efficiency. Intellishare has provided thermal recuperative oxidizers for Honda, Toyota, Nissan, and more Fortune 500 customers.

Intellishare differentiators:

  • Excellent customer service
  • Competitive Pricing on DFTOs and TROs
  • Standard models from 200-5,000 SCFM
  • Not competitive on RTOs
  • Smaller company, only a few employees
  • Some issues with burner reliability

Anguil Environmental

Anguil Environmental is based in Wisconsin and builds all types of thermal oxidizer equipment in their large fabrication facility. Anguil offers fair pricing and has a very technically capable team. Anguil has experience in many industries, focused on thermal oxidiation technologies and products. They are one of the leading suppliers of TOs and build oxidizers for almost every major industry in the United States. Anguil was voted "one of the best managed companies in America".

Anguil differentiators:

  • Offers all types of thermal oxidizers
  • Large in-house fabrication facility
  • Competitive pricing
  • Good technology, solid equipment
  • Can be difficult to work with
  • Reports of up-charges during project

thermal oxidizer optional equipment

Thermal Oxidizer: Optional Equipment

Ultra Low NOx Emission Burners

Ultra low NOx burners are required by many customers and are legally required in many areas of California as well as several other states. The key to achieving an ultra-low level of NOx is uniform heating and operating at minimum combustion temperature which is achieved by operating lean (lower fuel-to-air ratio). More NOx is produced at higher flame temperatures. NOx emissions do not form in significant amounts until flame temperatures reach 2800°F. Ultra low NOx burners are expensive and typically cost $10,000 - $30,000 USD depending on size.

Flame Arrestor

A flame arrestor (arrester) is a safety device that stops combustion by extinguishing the open flame. The flame arrestor can be mounted to the inlet of the oxidizer and utilized to prevent flame propagation in the case the high temp limit or 50% of LEL limit is exceeded, or in the case of a thermal event. Cost is typically in the $10,000 - $15,000 USD range based on size.

Natural Gas Flow Meter

A digital gas flow meter with by-pass look can be installed on the inlet of the gas train. Cost is typically in the $8,000 - $11,000 USD range based on size.

Secondary Heat Exchanger

For sufficiently large thermal oxidizers, the waste heat from the primary heat exchanger (~500°F) may be used to heat process air or liquids. For example, TO waste heat can be used to heat drying ovens, generate hot water, heat the plant in the winter, or many other industrial applications.

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