EPA-452/F-03-018
Air Pollution Control Technology
Fact Sheet
Name of Technology: Catalytic Incinerator
This type of incinerator is also referred to as a catalytic oxidizer, or catalytic reactor.
Type of Technology: Destruction by oxidation.
Applicable Pollutants:
Volatile organic compounds (VOC) and many types of particulate matter (PM). In the past, catalytic
incinerators were not recommended as a control device for PM, since the PM, unless removed prior to
incineration, often coated (or "blinded") the catalyst so that the catalyst's active sites were prevented from
aiding in the oxidation of pollutants in the gas stream (EPA, 1 998). Examples are gases containing chlorine,
sulfur, and other atoms, such as phosphorous, bismuth, lead, arsenic, antimony, mercury, iron oxide, tin, and
zinc that may deactivate the supported noble metal catalysts (EPA, 1 991).
However, catalysts have been recently developed that can tolerate almost any compound. Most of these
catalysts are single or mixed metal oxides, often supported by a mechanically strong carrier such as various
types of alumina. Catalysts such as chromia/alumina, cobalt oxide, and cop per oxide/manganese oxide have
been used for oxidation of gases containing chbrinated compounds. Platinum-based catalysts are active for
oxidation of sulfurcontaining VOC, although they are rapidly deactivated by the presence of chlorine (EPA,
1996a).
Achievable Emission Limits/Reductions:
VOC destructbn efficiency is dependent upon VOC composition and concentration, operating temperature,
oxygen concentration, catalyst characteristics, and space velocity. Space velocity is commonly defined as
the volumetric flow of gas entering the catalyst bed chamber divided by the volume of the catalyst bed. The
relatio nsh ip between space velocity and VOC destruction efficiency is stronglyinfluenced by catalyst operating
temperature. As space velocity increases, VOC destruction efficiency decreases, and as temperature
increases, VOC destruction efficiency increases. As an example, a catalytic unit operating at about 450"C
(840T) with a catalyst bed volume of 0.014 to 0.057 cubic meter (m3) (0.5 to 2 cubic feet (ft3)) per 0.47
standard cubic meters per second (sm3/sec) (1,000 standard cubic feet per minute (scfm)) of offgas passing
through the device can achieve 95 percent VOC destruction efficiency (EPA, 1992). Higher destruction
efficiencies of (98 - 99 percent) are achievable, but require larger catalyst volumes and/or higher
temperatures, and are usually designed on a site-specific basis (EPA, 1991).
In EPA's 1990 National Inventory, incinerators as a group, including catalytic incinerators, were reported as
being used as control devices for PM and were reported as achieving 25 - 99% control efficiency of PM10 at
point source facilities (EPA, 1998). Table 1 presents a breakdown of the PM10 control efficiency ranges by
industry where catalytic incinerators have been reported (EPA, 1996b). The VOC control efficiency reported
for these devices ranged from 0 to 99.9%, however, it is assumed that reports of higher efficiencies (greater
than 99%) are attributable to thermal incinerators. These ranges of control efficiencies are large because they
includefacilities that do nothave VOC emissions and control only PM, as well as facilities which have low PM
emissions and are primarily concerned with controlling VOC (EPA, 1998).
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Table 1. PM10 Destruction Efficiencies for Catalytic Incinerators and Catalytic
Incinerators with HeatExchangerby Industry (EPA, 1996b)
Industry/Types of Sources
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
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)
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
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)
Electric, Gas, and Sanitary Services
internal combustion engines; solid waste incineration (industrial,
commercial/ institutional)
Stone, Clay, and Glass Products
barium processing kiln; coal cleaning thermal dryer; fabricated
plastics machinery; wool fiberglass mfg
Mining
asphalt concrete rotary dryer; organic chemical air oxidation units,
sulfur production
Educational Services
solid waste incineration (commercial/ institutional)
Paper and Allied Products
boiler
Printing and Publishing
surface coating dryer; fugitives
PM10 Control
Efficiency(%)
25-99.9
50-99.9
70-99.9
70 - 99.9
90-98
50-95
70 - 99.6
80
95
95
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Catalytic Incinerator
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Applicable Source Type: Point
Typical Industrial Applications:
Catalytic incinerators can be used to reduce emissions from a variety of statbnary sources. Solvent
evaporation processes associated with surface coating and printing operations are a major source of VOC
emissions, and catalytic incineration is widely used by many industries in this category. Catalytic incinerators
are also used to control emissions from the following (EPA, 1992):
Varnish cookers;
Foundry core ovens;
Filter paper processing ovens;
Plywood veneer dryers;
Gasoline bulk loading stations;
Process vents in the synthetic organic chem ical manufacturing industry (SOCM I);
Rubber products and polymer manufacturing; and
Polyethylene, polystyrene, and polyester resin manufacturing.
Catalytic oxidation is most suited to systems with lower exhaust volumes, when there is little variation in
the type and concentration of VOC, and where catalyst poisons or other fouling contaminants such as
silicone, sulfur, heavy hydrocarbons and particulates are not present.
Emission Stream Characteristics:
a. Air Flow: Typical gas flow rates for packaged catalytic incinerators are 0.33 to 24 sm3/sec (700
to 50,000 scfm) (EPA, 1996a).
b. Temperature: Catalysts in catalytic incinerators cause the oxidizing reaction to occurat a lower
temperature than is required for thermal ignition. Waste gas is heated by auxiliary burners to
approximately 320°C to 430°C (600°F to SOOT) before entering the catalyst bed (AW MA, 1992).
The maximum design exhaust temperature of the catalyst is typically 540" - 675"C (1000°- 1250T).
c. Pollutant Loading: Catalytic incinerators can and have been used effectively at very low inlet
loadings; down to 1 part per million by volume (ppmv) or less (EPA, 1995). As with thermal and
recuperative incinerators, for safety consideratbns, the maximum 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.
d. Other Considerations: Characteristics of theinletstream should be evaluated in detail, because
of the sensitivity of catalytic incinerators to VOC inlet stream flow conditions, which may cause
catalyst deactivation (EPA, 1992).
Emission Stream Pretreatment Requirements:
Typically, if design conditions are satisfied no pretreatment is required, however, in some cases, PM removal
may be necessary before the waste gas enters the incinerator.
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Cost Information:
The following are cost ranges (expressed in 2002 dollars) forpackaged catalytic incinerators of conventional
design with fixed beds undertypical operating conditions,developed using EPA cost-estimating spreadsheets
(EPA, 1996 a) 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 the ranges
shown when used for low-VOC concentration streams (less than around 100 ppmv). As a rule, smaller units
controlling a low concentration waste stream will be much more expensive (per unitvolumetricflow rate) than
a large unit cleaning a high pollutant load flow. Ope ration and Maintenance (O & M) Costs, An nualized Cost,
and Cost Effectiveness are dominated by the cost of supplemental fuel required.
a. Capital Cost: $47,000 to $191,000 per sm3/sec ($22 to $90 per scfm)
b. O & M Cost: $8,500 to $53,000 per sm3/sec ($4 to $25 per scfm), annually
c. Annualized Cost: $17,000 to $106,000 per sm3/sec ($8 to $50 per scfm), annually
d. Cost Effectiveness: $105 to $5,500 per metric ton ($100 to $5,000 per short ton), annualized
cost per ton per year of pollutant controlled. However, when used to treat very low
concentratbns of toxic air pollutants (less than 100 ppmv), the cost per ton removed may be
many thousands of dollars, because only a small amount of pollutant is being destroyed.
Theory of Operation:
Catalytic incinerators operate very similar to thermal/recuperative incinerators, with the primarydifference that
the gas, after passing through the flame area, passes through a catalyst bed. The catalyst has the effect of
increasing the oxidation reactbn rate, enabling conversion at lower reaction temperatures than in thermal
incineratorunits. Catalysts, therefore, alsoallowforsmallerincineratorsize. Catalysts typically used for VOC
incineration include platinum and palladium. Other formulatbns include metal oxides, which are used for gas
streams containing chlorinated compounds (EPA, 1998).
In a catalytic incinerator, the gas stream is introduced into a mixing chamber where it is also heated. The
waste gas usually passes through a recuperative heat exchanger where it is preheated by post combustion
gas. The heated gas then passes through the catalyst bed. Oxygen and VOC migrate to the catalystsurface
by gas diffusion and are adsorbed onto the catalyst active sites on the surface of the catalyst where oxidation
then occurs. The oxidation reactbn products are then desorbed from the active sites by the gas and
transferred by diffusion back into the gas stream (EPA, 1998).
Particulate matter can rapidly coat the catalyst so that the catalyst active sites are prevented from aiding in
the oxidation of pollutants in the gas stream. This effect of PM on the catalyst is called blinding, and will
deactivate the catalyst overtime. Because essentially all the active surface of the catalyst is contained in
relatively small pores, the PM need not be large to blind the catalyst. No general guidelines exist as to the
PM concentratbn and size that can be tolerated bycatalysts, because the pore size and volume of catalysts
vary widely. This information is likely to be available from the catalyst manufacturers (EPA, 1996a).
The method of contacting the VOC-containing stream with the catalyst serves to distinguish catalystic
incineration systems. Both fixed-bed and fluid-bed systems are used.
Fixed-bed catalytic incinerators may use a monolith catalyst or a packed-bed catalyst (EPA, 1996a):
Mono Nth Catalyst Incinerators - The most widespread method of contacting the VOC-containing stream
with the catalyst is the catalyst monolith. In this scheme the catalyst is a porous solid block containing
parallel, non-intersecting channels aligned in the direction of the gas flow. Monoliths offer the
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advantages of minimal attrition due to thermal expansion/contraction during startup/shutdown and low
overall pressure drop.
Packed-Bed Catalytic Incinerators - A second contacting scheme is a simple packed-bed in which
catalyst particles are supported either in a tube or in shallow trays through which the gases pass. This
scheme is not in widespread use due to its inherentlyhigh pressuredrop, compared to a monolith, and
the breaking of catalyst particles due to thermal expansion when the confined catalyst bed is
heated/cooled during startup/shutdown. However, the tray type arrangement of a packed-bed scheme,
where the catalyst is pelletized, is used by several industries (e.g., heat-set web-offset printing).
Pelletized catalyst is advantageous where large amounts of such contaminants as phosphorous orsilicon
compounds are present.
Fluid-bed catalytic incinerators have the advantage of very high mass transfer rates, although the overall
pressure drop is somewhat higherthan for a monolith. An additional advantage of fluid-beds is a high bed-
side heat transfer as compared to a normal gas heat transfer coefficient. This higher heat transfer rate to heat
transfertubes immersed in the bed allows higher heat release rates per unit volume of gas processed and,
therefore, may allow waste gas with higher heating values to be processed without exceeding maximum
perm issible temperatures in the catalyst bed. In these reactors the gas phase temperature rise from gas inlet
to gas outlet is low, depending on the extent of heat transfer through imbedded heat transfer surfaces. The
catalyst temperatures depend on the rate of reaction occurring at the catalyst surface and the rate of heat
exchange between the catalyst and imbedded heat transfer surfaces.
As a general rule, fluid-bed systems are more tolerant of PM in the gas stream than either fixed-bed or
monolithic catalysts. This is due to the constant abrasion of the fluidized catalystpellets, which helps remove
PM from the exterbrof the catalysts in a continuous manner. A disadvantage of a fluid-bed is the gradual loss
of catalyst by attrition. However, attrition-resistant catalysts have been developed to overcome this
disadvantage.
Advantages:
Advantages of catalytic incinerators over other types of incinerators include (AWM A, 1992; Cooper and
Alley, 1994):
b. Lower fuel requirements;
c. Lower operating temperatures;
d. Little or no insulation requirements;
e. Reduced fire hazards;
f. Reduced flashback problems; and
g. Less volume/size required.
Disadvantages:
Disadvantages of catalytic incinerators include (AWMA, 1992):
a. High initial cost;
b. Catalyst poisoning is possible;
c. Particulate often must first be removed; and
d. Spent catalyst that cannot be regenerated may need to be disposed.
Other Considerations:
Catalytic incinerators offer many advantages for the appropriate application. However, selection of a
catalytic incineratorshould be considered carefully, as the sensitivity of catalytic incinerators to VOC inlet
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stream flow conditions and catalyst deactivation limit their applicability for many industrial processes (EPA,
1992).
References:
AWMA, 1992. Air & Waste Management Association, Air Pollution Engineering Manual. Van Nostrand
Reinhold, New York.
Cooper & Alley, 1994. C. D. Cooper and F. C. Alley, Air Pollution Control: A Design Approach, Second
Edition, Waveland Press, Inc. IL.
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, 1 996a. 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, 1 996b. U.S. EPA, "1990 National Inventory," Research Triangle Park, NC, January.
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.
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