Air Pollution Control Technology Fact Sheet EPA-452/F-03-022 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., chambertemperature, 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). Forvent 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 1 Thermal Incinerator ------- Table 1. Thermal Incinerator PM10 Destruction Efficiencies by Industry (EPA, 1996b) PM10 Control Industry/Types of Sources Efficiency (%) Petroleum and Coal Products 25 - 99.9 asphalt roofing processes (blowing, felt saturation); mineral calcining; petroleum refinery processes (asphalt blowing, catalytic cracking, coke calcining, sludge converter); sulfur manufacturing Chemical and Allied Products 50 - 99.9 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) Primary Metals Industries 70 - 99.9 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 Electronic and Other Electric Equipment 70 - 99.9 chemical mfg miscellaneous processes; electrical equipment bake furnace; fixed roof tank; mineral production miscellaneous processes; secondary aluminum roll/draw extruding; solid waste incineration (industrial) Electric, Gas, and Sanitary Services 90-98 internal combustion engines; solid waste incineration (industrial, commercial/ institutional) Stone, Clay, and Glass Products 50-95 barium processing kiln; coal cleaning thermal dryer; fabricated plastics machinery; wool fiberglass mfg Food and Kindred Products 70-98 charcoal processing, miscellaneous; corn processing, miscellaneous, fugitive processing, miscellaneous; soybean processing, miscellaneous Mining 70 - 99.6 asphalt concrete rotary dryer; organic chemical air oxidation units, sulfur production National Security and International Affairs 70 solid waste incineration (commercial/institutional and municipal) Textile Mill Products 88-95 plastics/synthetic organic fiber (miscellaneous processes) Industrial Machinery and Equipment 88 -98 secondary aluminum processes (burning/drying, smelt furnace) Lumber and Wood Products 70 solid waste incineration (industrial) Transportation Equipment 70-95 solid waste incineration (industrial) EPA-CICA Fact Sheet 2 Thermal Incinerator ------- 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 mode rate-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- orsulfur-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 3 Thermal Incinerator ------- 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 undertypical 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, orthermal 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. Theshorterthe 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 4 Thermal Incinerator ------- 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 post- oxidation 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 5 Thermal Incinerator ------- 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. EPA-CICA Fact Sheet 6 Thermal Incinerator ------- |