EPA-452/F-03-022

Air Pollution Control Technology 

Fact Sheet

EPA-CICA Fact Sheet Thermal Incinerator 1

Name of Technology: Thermal Incinerator

This type of incinerator is also referred to as a direct flame incinerator, thermal oxidizer, or afterburner.

However, the term afterburner is generally appropriate only to describe a thermal oxidizer used to control

gases coming from a process where combustion is incomplete.

Type of Technology: Destruction by thermal oxidation

Applicable Pollutants: Primarily volatile organic compounds (VOC). Some particulate matter (PM),

commonly composed as soot (particles formed as a result of incomplete combustion of hydrocarbons (HC),

coke, or carbon residue) will also be destroyed in various degrees.

Achievable Emission Limits/Reductions:

VOC destruction efficiency depends upon design criteria (i.e., chamber temperature, residence time, inlet VOC

concentration, compound type, and degree of mixing) (EPA, 1992). Typical thermal incinerator design

efficiencies range from 98 to 99.99% and above, depending on system requirements and characteristics of

the contaminated stream (EPA, 1992; EPA, 1996a). The typical design conditions needed to meet 98% or

greater control or a 20 parts per million by volume (ppmv) compound exit concentration are: 870°C (1600°F)

combustion temperature, 0.75 second residence time, and proper mixing. For halogenated VOC streams,

1100°C (2000°F) combustion temperature, 1.0 second residence time, and use of an acid gas scrubber on

the outlet is recommended (EPA, 1992).

For vent streams with VOC concentration below approximately 2000 ppmv, reaction rates decrease, maximum

VOC destruction efficiency decreases, and an incinerator outlet VOC concentration of 20 ppmv, or lower may

be achieved (EPA, 1992).

Controlled emissions and/or efficiency test data for PM in incinerators are not generally available in the

literature. Emission factors for PM in phthalic anhydride processes with incinerators are available, however.

The PM control efficiencies for these processes were found to vary from 79 to 96% (EPA, 1998). In EPA’s

1990 National Inventory, incinerators used as control devices for PM were reported as achieving 25 to 99%

control efficiency of particulate matter 10 microns or less in aerodynamic diameter (PM10) at point source

facilities (EPA, 1998). Table 1 presents a breakdown of the PM10 control efficiency ranges by industry for

recuperative incinerators (EPA, 1996b). The VOC control efficiency reported for these devices ranged from

0 to 99.9%. These ranges of control efficiencies are large because they include facilities that do not have

VOC emissions and control only PM, as well as facilities which have low PM emissions and are primarily

concerned with controlling VOC (EPA, 1998).
EPA-CICA Fact Sheet Thermal Incinerator 2

Table 1. Thermal Incinerator PM10 Destruction Efficiencies by Industry (EPA, 1996b)

Industry/Types of Sources 

PM10 Control

Efficiency (%)

Petroleum and Coal Products

asphalt roofing processes (blowing, felt saturation); mineral

calcining; petroleum refinery processes (asphalt blowing,

catalytic cracking, coke calcining, sludge converter); sulfur

manufacturing

25 - 99.9

Chemical and Allied Products

carbon black manufacturing (mfg); charcoal mfg; liquid waste

disposal; miscellaneous chemical mfg processes; pesticide mfg;

phthalic anhydride mfg (xylene oxidation); plastics/synthetic

organic fiber mfg; solid waste incineration (industrial)

50 - 99.9

Primary Metals Industries

by-product coke processes (coal unloading, oven charging and

pushing, quenching); gray iron cupola and other miscellaneous

processes; secondary aluminum processes (burning/drying,

smelting furnace); secondary copper processes (scrap drying,

scrap cupola, and miscellaneous processes); steel foundry

miscellaneous processes; surface coating oven

70 - 99.9

Electronic and Other Electric Equipment

chemical mfg miscellaneous processes; electrical equipment

bake furnace; fixed roof tank; mineral production miscellaneous

processes; secondary aluminum roll/draw extruding; solid waste

incineration (industrial)

70 - 99.9

Electric, Gas, and Sanitary Services

internal combustion engines; solid waste incineration (industrial,

commercial/ institutional)

90 - 98

Stone, Clay, and Glass Products

barium processing kiln; coal cleaning thermal dryer; fabricated

plastics machinery; wool fiberglass mfg

50 - 95

Food and Kindred Products

charcoal processing, miscellaneous; 

corn processing, miscellaneous, 

fugitive processing, miscellaneous; 

soybean processing, miscellaneous

70 - 98

Mining

asphalt concrete rotary dryer; organic chemical air oxidation

units, sulfur production

70 - 99.6

National Security and International Affairs

solid waste incineration (commercial/institutional and

municipal)

70

Textile Mill Products

plastics/synthetic organic fiber (miscellaneous processes)

88 - 95

Industrial Machinery and Equipment

secondary aluminum processes (burning/drying, smelt furnace)

88 -98

Lumber and Wood Products

solid waste incineration (industrial)

70

Transportation Equipment

solid waste incineration (industrial)

70 - 95
EPA-CICA Fact Sheet Thermal Incinerator 3

Applicable Source Type: Point

Typical Industrial Applications:

Thermal incinerators can be used to reduce emissions from almost all VOC sources, including reactor vents,

distillation vents, solvent operations, and operations performed in ovens, dryers, and kilns. They can handle

minor fluctuations in flow, however, excess fluctuations require the use of a flare (EPA, 1992). Their fuel

consumption is high, so thermal units are best suited for smaller process applications with moderate-to-high

VOC loadings.

Incinerators are used to control VOC from a wide variety of industrial processes, including, but not limited to

the following (EPA, 1992):

• Storing and loading/unloading of petroleum products and other volatile organic liquids;

• Vessel cleaning (rail tank cars and tank trucks, barges);

• Process vents in the synthetic organic chemical manufacturing industry (SOCMI);

• Paint manufacturing;

• Rubber products and polymer manufacturing;

• Plywood manufacturing;

• Surface coating operations:

Appliances, magnetic wire, automobiles, cans, metal coils, paper, film and foil, pressure

sensitive tapes and labels, magnetic tape, fabric coating and printing, metal furniture, wood

furniture, flatwood paneling, aircraft, miscellaneous metal products;

• Flexible vinyl and urethane coating; 

• Graphic arts industry; and

• Hazardous waste treatment storage, and disposal facilities (TSDFs). 

Emission Stream Characteristics:

a. Air Flow: Typical gas flow rates for thermal incinerators are 0.24 to 24 standard cubic meters per

second (sm3

/sec) (500 to 50,000 standard cubic feet per minute (scfm)) (EPA, 1996a).

b. Temperature: Most incinerators operate at higher temperatures than the ignition temperature,

which is a minimum temperature. Thermal destruction of most organic compounds occurs between

590°C and 650°C (1100°F and 1200°F). Most hazardous waste incinerators are operated at 980°C

to 1200°C (1800°F to 2200°F) to ensure nearly complete destruction of the organics in the waste

(AWMA, 1992).

a. Pollutant Loading: Thermal incinerators can be used over a fairly wide range of organic vapor

concentrations. For safety considerations, the concentration of the organics in the waste gas must

be substantially below the lower flammable level (lower explosive limit, or LEL) of the specific

compound being controlled. As a rule, a safety factor of four (i.e., 25% of the LEL) is used (EPA,

1991, AWMA, 1992). The waste gas may be diluted with ambient air, if necessary, to lower the

concentration. Considering economic factors, thermal incinerators perform best at inlet

concentrations of around 1500 to 3000 ppmv, because the heat of combustion of hydrocarbon

gases is sufficient to sustain the high temperatures required without addition of expensive auxiliary

fuel (EPA, 1995).

d. Other Considerations: Incinerators are not generally recommended for controlling gases

containing halogen- or sulfur-containing compounds, because of the formation of hydrogen chloride,

hydrogen fluoride gas, sulfur dioxide, and other highly corrosive acid gases. It may be necessary

to install a post-oxidation acid gas treatment system in such cases, depending on the outlet

concentration. This would likely make incineration an uneconomical option. (EPA, 1996a). Thermal
EPA-CICA Fact Sheet Thermal Incinerator 4

incinerators are also not generally cost-effective for low-concentration, high-flow organic vapor

streams (EPA, 1995).

Emission Stream Pretreatment Requirements:

Typically, no pretreatment is required, however, in some cases, a concentrator (e.g., carbon or zeolite

adsorption) may be used to reduce the total gas volume to be treated by the more expensive incinerator. 

Cost Information:

The following are cost ranges (expressed in 2002 dollars) for packaged thermal incinerators of conventional

design under typical operating conditions, developed using EPA cost-estimating spreadsheets (EPA, 1996a)

and referenced to the volumetric flow rate of the waste stream treated. The costs do not include costs for a

post-oxidation acid gas treatment system. Costs can be substantially higher than in the ranges shown when

used for low to moderate VOC concentration streams (less than around 1000 to 1500 ppmv). As a rule,

smaller units controlling a low concentration waste stream will be much more expensive (per unit volumetric

flow rate) than a large unit cleaning a high pollutant load flow. Operating and Maintenance (O & M) Costs,

Annualized Cost, and Cost Effectiveness are dominated by the cost of supplemental fuel required.

a. Capital Cost: $53,000 to $190,000 per sm3

/sec ($25 to $90 per scfm)

b. O & M Cost: $11,000 to $160,000 per sm3

/sec ($5 to $75 per scfm), annually

c. Annualized Cost: $17,000 to $208,000 per sm3

/sec ($8 to $98 per scfm), annually

d. Cost Effectiveness: $440 to $3,600 per metric ton ($400 to $3,300 per short ton), annualized

cost per ton per year of pollutant controlled

Theory of Operation:

Incineration, or thermal oxidation is the process of oxidizing combustible materials by raising the temperature

of the material above its auto-ignition point in the presence of oxygen, and maintaining it at high temperature

for sufficient time to complete combustion to carbon dioxide and water. Time, temperature, turbulence (for

mixing), and the availability of oxygen all affect the rate and efficiency of the combustion process. These

factors provide the basic design parameters for VOC oxidation systems (ICAC, 1999).

A straight thermal incinerator is comprised of a combustion chamber and does not include any heat recovery

of exhaust air by a heat exchanger (this type of incinerator is referred to as a recuperative incinerator).

The heart of the thermal incinerator is a nozzle-stabilized flame maintained by a combination of auxiliary fuel,

waste gas compounds, and supplemental air added when necessary. Upon passing through the flame, the

waste gas is heated from its preheated inlet temperature to its ignition temperature. The ignition temperature

varies for different compounds and is usually determined empirically. It is the temperature at which the

combustion reaction rate exceeds the rate of heat losses, thereby raising the temperature of the gases to

some higher value. Thus, any organic/air mixture will ignite if its temperature is raised to a sufficiently high

level (EPA, 1996a).

The required level of VOC control of the waste gas that must be achieved within the time that it spends in the

thermal combustion chamber dictates the reactor temperature. The shorter the residence time, the higher the

reactor temperature must be. The nominal residence time of the reacting waste gas in the combustion

chamber is defined as the combustion chamber volume divided by the volumetric flow rate of the gas. Most

thermal units are designed to provide no more than 1 second of residence time to the waste gas with typical

temperatures of 650 to 1100°C (1200 to 2000°F). Once the unit is designed and built, the residence time is
EPA-CICA Fact Sheet Thermal Incinerator 5

not easily changed, so that the required reaction temperature becomes a function of the particular gaseous

species and the desired level of control (EPA, 1996a).

Studies based on actual field test data, show that commercial incinerators should generally be run at 870°C

(1600°F) with a nominal residence time of 0.75 seconds to ensure 98% destruction of non-halogenated

organics (EPA, 1992).

Advantages:

Incinerators are one of the most positive and proven methods for destroying VOC, with efficiencies up to

99.9999% possible. Thermal incinerators are often the best choice when high efficiencies are needed and

the waste gas is above 20% of the LEL. 

Disadvantages:

Thermal incinerator operating costs are relatively high due to supplemental fuel costs.

Thermal incinerators are not well suited to streams with highly variable flow because of the reduced residence

time and poor mixing during increased flow conditions which decreases the completeness of combustion. This

causes the combustion chamber temperature to fall, thus decreasing the destruction efficiency (EPA, 1991).

Incinerators, in general, are not recommended for controlling gases containing halogen- or sulfur-containing

compounds because of the formation of highly corrosive acid gases. It may be necessary to install a postoxidation acid gas treatment system in such cases, depending on the outlet concentration (EPA, 1996a).

Thermal incinerators are also not generally cost-effective for low-concentration, high-flow organic vapor

streams (EPA, 1995).

Other Considerations:

Thermal incinerators are not usually as economical, on an annualized basis, as recuperative or regenerative

incinerators because they do not recover waste heat energy from the exhaust gases. This heat can be used

to preheat incoming air, thus reducing the amount of supplemental fuel required. If there is additional heat

energy available, it can be used for other process heating needs. 

References:

AWMA, 1992. Air & Waste Management Association, Air Pollution Engineering Manual. Van Nostrand

Reinhold, New York. 

EPA, 1991. U.S. EPA, Office of Research and Development, “Control Technologies for Hazardous Air

Pollutants,” EPA/625/6-91/014, Washington, D.C., June. 

EPA, 1992. U.S. EPA, Office of Air Quality Planning and Standards, “Control Techniques for Volatile

Organic Emissions from Stationary Sources,” EPA-453/R-92-018, Research Triangle Park, NC.,

December.

EPA, 1995. U.S. EPA, Office of Air Quality Planning and Standards, “Survey of Control Technologies for

Low Concentration Organic Vapor Gas Streams,” EPA-456/R-95-003, Research Triangle Park, NC., May.

EPA, 1996a. U.S. EPA, Office of Air Quality Planning and Standards, “OAQPS Control Cost Manual,”

Fifth Edition, EPA 453/B-96-001, Research Triangle Park, NC. February. 

EPA, 1996b. U.S. EPA, “1990 National Inventory,” Research Triangle Park, NC, January. 
EPA-CICA Fact Sheet Thermal Incinerator 6

EPA, 1998. U.S. EPA, Office of Air Quality Planning and Standards, “Stationary Source Control

Techniques Document for Fine Particulate Matter,” EPA-452/R-97-001, Research Triangle Park, NC.,

October.

ICAC, 1999. Institute of Clean Air Companies internet web page www.icac.com, Control Technology

Information - Thermal Oxidation, page accessed March 1999.