Regenerative Thermal Oxidizer

What is a regenerative thermal oxidizer?

A Regenerative Thermal Oxidizer (RTO) is an industrial-grade air pollution control device that use high temperatures to combust and decompose volatile organic compounds (VOCs) into CO2 and water vapor.

Also known as an RTO, a regenerative thermal oxidizer heats the VOC-laden process exhaust gas to temperatures in the range of 1400-1500°F.

RTOs are available in many different shapes and sizes. The two main designs are the 2-tower and 3-tower RTO (may also be called a 2-can or 3-can RTO). The 2-tower design will suit most cases, while the 3-tower design will be used when the highest destruction efficiency is required (in cases of odor complaints, for example).

Regenerative Thermal Oxidizers (RTOs) are used to destroy VOCs and other organic hazardous air pollutants. They are not good for treating particulates, inorganic gases, heavy metals, acids, nor other corrosive gases. If these other contaminants are present, an RTO maybe used in combination with a dust collector or wet scrubber, depending on the situation.

Regenerative Thermal Oxidizer effectiveness on:

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

*Note: an RTO may not be effective at removing inorganic odor compounds.

Acids, Chlorinated, and Fluorinated compounds35
Particulate matter25
Corrosive fumes, vapors, gases15
Heavy Metals5

Main components of an RTO

Ductwork and Fan/Blower

RTOs will use either a forced draft or induced draft fan system, depending on the process air temperature. Installing the fan on the coolest side offers the best performance.

Combustion Chamber and Burner

At the top of the towers sits the combustion chamber which connects all the towers together. Air passes up through one tower then passes horizontally through the upper combustion chamber and across the burner then finally passes down through another tower.

Ceramic media towers

RTOs achieve 95% thermal efficiency by absorbing and storing the waste heat from combustion in large towers of ceramic media. By periodically switching the airflow direction, the waste heat stored in the media may be released to heat incoming air.

Switching Air Valves

RTOs periodically cycle each tower between (Cycle 1) admitting dirty process air and releasing heat from ceramic media, (Cycle 2) purging and cleaning, or (Cycle 3) exhausting and absorbing heat from post-combustion air into the ceramic media.

Heat Exchanger and Stack

After passing through the combustion chamber, the air can be extracted and used to heat other process liquids or gases via a heat exchanger. Otherwise the clean air passes down through a ceramic bed, releasing its heat, then is exhaust via a stack.

Operation: How does an RTO work?

The left tower's exhaust air valve is in the open position. The left tower (C3) is warming up by absorbing heat from the outgoing air. It will be hot by the end of this cycle.

The center tower's purge air valve is in the open position. The center tower (C2) was previously filled with dirty inlet air so it's now purging that air back to the inlet fan.

The right tower's inlet air valve is in the open position. The right tower (C1) is hot from the last cycle and is now releasing heat to warm the incoming dirty air.

A flow schematic for a 3-tower regenerative thermal oxidizer (RTO).

A three-tower regenerative thermal oxidizer (RTO).
Used for applications with odors or high DRE requirements.

RTO Design Considerations

Air Volume Flowrate (CFM)

The volume of process air to be treated is a key consideration. A single RTO system can be designed to handle any amount from 1,000 CFM to over 50,000 CFM. Multiple RTOs can be combined to treat any volume of air.

Destruction or Removal Efficiency (DRE)

Factors that impact DRE:

  1. Temperature
  2. Residence time
  3. Purge cycle
    • Two-cycle no purge (2-tower RTO)
    • Three-cycle with purge (3-tower)

Materials of Construction

Material options include:

  1. Stainless steel
  2. Carbon steel, painted
  3. Aluminized steel
  4. Galvanized steel
  5. Insulation and cladding
  6. Dampers

Equipment Configuration & Layout

Key questions include:

  1. Are multiple control devices needed?
    • Due to high air volume -> 2 RTOs in parallel
    • Due to multiple contaminants -> equipment in series
      • Is a scrubber required?   (Scrubber + RTO combo)
  2. Fan location: induced draft or forced draft?
  3. Type of valves: compressed air (pneumatic), hydraulic, poppet, or rotary
  4. Inlet ductwork, outlet ductwork and exhaust stack
  5. Test ports & access platforms
Industries, Applications, & Case Studies
Automotive Paint Spray Booth
  • RTOs are used in automotive, marine, and other vehicle manufacturing for treating VOCs from paint booths, controlling HAPs from paint curing ovens, engine test and quality control, tire manufacturing, and component painting. The high volume, low concentration conditions are ideal for a regenerative thermal oxidizer.

Chemical Processing
  • Manufacturing or processing chemicals generates exhaust air contaminated with toxic gases and VOCs. These vapors need to be captured and treated prior to release to atmosphere. An RTO is the most robust solution for these applications: tank vents, separators, acid gases, chemical production, and ceramic kilns.

  • Printing operations require VOC abatement, use of Permanent Total Enclosures (PTEs) for fugitive emissions capture, odor elimination, and toxic fumes destruction. An RTO 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). An RTO is a reliable solution for your kiln and dryer emissions.

Composites & FRP
  • An RTO is an appropriate solution for abating the air pollutants from Carbon Fiber, FRP, FIberglass, and other composite manufacturing. Composite resins contain styrene that needs 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 creates odors which often need to be controlled prior to emission. A three-tower RTO is the ideal solution for to controls odors in large-volume exhausts. The 3-chamber regenerative thermal oxidizer offers 99+% control. Smaller exhaust volumes can use a thermal recuperative oxidizer (TRO) with heat exchanger (HEX).

Industrial Ovens
  • Industrial ovens for curing parts, paints, and coatings generates air pollution and contaminants that need to be captured and controlled. The oven will flash off VOCs and other HAPs that need to be destroyed by an RTO or other thermal treatment device.

Natural Gas Processing
  • RTOs are a popular air pollution control device for off-gas treatment from Natural Gas processing, including VOCs and HAPs from amine tail-gas treatment systems, sulfur recovery units, nitrogen rejection units (NRU), glycol regenerators, liquefied natural gas (LNG) processes, and storage tank venting.

Packaging & Labeling
  • Applying coatings, graphics, and adhesive labels to flexible packaging or metal containers releases VOCs that need to be captured and destroyed. An RTO is the most robust solution to treat both the application and drying air streams.

Paint Booth
Paint Booths & Hangars
  • Paint Booths in the Automotive, Industrial, Aerospace, or vehicle OEM industries require high-volume, low-concentration VOC abatement that is well suited to RTOs. The high-flow downdraft or cross-draft paint booths often use a dry-filter and or wet scrubber system to catch the paint overspray and dried 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 releases into concentrations in excess of 100% LEL. This poses a fire and explosion risk, so dilution air is required for plant safety. An RTO is often used as the final control device.

  • In the semiconductor industry, RTOs are used for control of VOC emissions from chip manufacturing, LCDs, printed circuit boards (PCBs), and more. RTOs are highly robust, operating 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 RTO Manufacturers

CECO Adwest

CECO offers their Adwest brand of RETOX RTOs to control VOCs, odors, and more. CECO RTO systems come standard with flameless natural gas injection for NOx-free operation, which utilizes a fraction of the gas of traditional combustion burners. CECO builds RTOs for the paint, print, packaging, food processing, landfill, ethanol, composites, chemical, wood products, wastewater, and semiconductor industries.

CECO differentiators:

  • Custom engineered, special metallurgy available for acid/corrosive gases
  • Large flow capacity, up to 100k CFM
  • Compact low profile: Short, light-weight units
  • Many technologies come standard: such as flameless natural gas injection
  • Good technical field support
  • RTOs are factory pre-wired and tested
  • More expensive compared to peers
  • Large footprint (long units)

Gulf Coast Environmental

Gulf Coast Environmental Systems (GCES) offers RTOs worldwide. GCES' often offers the best price for RTOs, and with custom engineered solutions and quality in-house construction, GCES' RTOs are the best value in the industry. Perfect for the cost-conscious industrial buyer who wants a quality system at a fair price. GCES builds RTOs for the Paint Booth, Coating, Composites, Ethanol, Pharmaceutical, and Automotive industries.

Gulf Coast differentiators:

  • Often best price
  • Custom engineered systems
  • Quality in-house construction
  • Often fastest delivery time
  • Small footprint required
  • Experienced with Three-Can RTOs
  • Proficient technical field support
  • RTO units can be tall & heavy, sometimes limited to ground floor / concrete pad install
  • Extended warranty is expensive

TANN Corporation

TANN builds RTOs for the Automotive, Paint, Coatings, Pharmaceutical, Printing, and Animal Rendering industries. TANN has provided a majority of the RTOs to General Motors' plants and many of their suppliers. TANN RTOs 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 RTO designs with in-house fabrication
  • Thermal efficiencies up to 97%
  • Available with structured (honeycomb) media or random packed media
  • Poppet values use a metal-to-metal machined surface, come with a 5-year warranty
  • Custom Designs to fit existing space
  • Higher Cost RTOs

Epcon Industrial Systems

Epcon Industrial Systems L.P. based in The Woodlands, Texas offers a full line of 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 collector

Catalytic Products

Catalytic Product International (CPI) is one of the leading manufacturers of Catalytic Oxidizers. CPI offers their VECTOR brand of catalytic oxidizer in five types: Recuperative, Electric, Regenerative, Ammonia, and CO/NOX. CPI also offers standard RTOs 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 RTOs
  • Unique technology for SiO2
  • Only offers oxidizer products
  • Pricing can be inconsistent

Ship and Shore Environmental

Ship and Shore provides oxidizers globally, including the U.S., Dubai, UAE, China, Asia, and more. Headquartered in Southern California, just south of L.A., S&SE is a provider of RTOs, and Catalytic 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
  • Offer many technologies
  • Initial bids can be lower cost
  • Reports of up-charges during project
  • Some negative customer reviews

Anguil Environmental

Anguil Environmental is based in Wisconsin and builds RTOs, Thermal Oxidizers, and Catalytic Oxidizer equipment in their large fabrication facility. Anguil offers fair pricing and has a very capable team. They have a lot of experience in many industries, especially with RTOs and RCOs. They build oxidizers for almost every major industry in the United States.

Anguil differentiators:

  • Many equipment options
  • Large in-house fabrication facility
  • Competitive Pricing
  • Good technology, solid equipment
  • Can be difficult to work with
  • Reports of up-charges during project
  • Issues with hot spots in RTOs

Durr Megtec Systems

Megtec Systems is a manufacturer of RTOs and other pollution control equipment based in Wisconsin. Megtec also manufactures electrostatic precipitators, filtration, and solvent recovery equipment. They supply primarily to the domestic U.S. and are focused on the wood products, printing, web forming, textiles, battery manufacturing, and more. Megtec was recently sold from Babcock and Wilcox (B&W) to Durr Cleantech.

Megtec Systems differentiators:

  • In-house fabrication facility
  • RTOs have high reliability
  • Experienced in niche industries
  • Historically competitive, but
  • Recently bought by Durr
  • Recent quotes have been high cost

John Zink Hamworthy

John Zink Hamworthy offers a diverse selection of RTOs, oxidizers, flares, burners, and more. 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 RTO supplier for those industries. John Zink Hamworthy is a conglomorate of smaller companies, 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

regenerative thermal oxidizer optional equipment

RTO: Optional Equipment

Natural Gas Injection

Natural Gas Injection, a.k.a. Supplemental Fuel Injection or Flameless Operation, is a method of RTO operation where the combustion chamber is operating without an open flame. At the inlet to the RTO tower, natural gas is injected into the incoming dirty air stream to increase the VOC concentration to ~3-5% of LEL. At this concentration, as long as the combustion chamber is operating at temperature set point (~1500°F), the VOCs will combust fully without an open flame, generating heat to maintain the set point, and the reaction will continue.

The main advantages of natural gas injection are:

  • Minimizing silica (SiO2) formation
  • Reducing natural gas consumption
  • Lowering NOX emission levels.

Specialized Ceramic Media Bed

  1. Random packing
  2. Saddles
  3. Monolith
  4. Structured media
  5. SiO2-Resistant (silica-resistant) structured ceramic media
  6. Corrosion resistant coating

Waste Heat Recovery

For sufficiently large RTOs, the waste heat from the RTO (~200°F) may be captured and used to heat process air or liquids. For example, RTO waste heat can be used to heat drying ovens, generate hot water, heat the plant in the winter, or another 100-200°F application.

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