United States Solid Waste and
Environmental Protection Emergency Response
Agency (5305)
EPA530-S-94-014
May 1994
vvEPA
Combustion Emissions
Technical Resource
Document (CETRED)
Executive Summary
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EXECUTIVE SUMMARY
The Draft Combustion Emissions Technical Resource Document
(CETRED) contains the initial technical .analysis by the U.S.
Environmental Protection Agency (EPA), concerning emissions -of
dioxins/furans and particulate matter from certain types of
devices that burn hazardous waste: 'cement kilns, light-weight
aggregate kilns, incinerators, and industrial boilers. CETRED
represents the first, preliminary step in the development of
regulations under the Resource Conservation and Recovery Act
(RCRA) and the Clean Air Act (CAA) to•impose upgraded standards
on hazardous waste combustors (HWCs). CETRED also represents a
major effort towards implementing the commitment made by EPA
Administrator Carol M. Browner in the Draft Hazardous Waste
Minimization and Combustion Strategy, released on May 18, 1993,
to upgrade the technical standards governing emissions from HWCs.
EPA's intention in releasing CETRED at this time is to give
the regulated community and other interested persons the earliest
possible opportunity to understand the nature of the technical
analysis that EPA is pursuing. CETRED can appropriately be
regarded as a preliminary technical analysis of certain HWCs and
their emissions of PM and dioxins/furans. CETRED represents the
current state of analysis of EPA's technical staff in the Office
of Solid Waste as regards the emission levels of PM and
dioxins/furans achievable by the best controlled sources,.
At this time, CETRED does not contain a characterization of
emissions for toxic metals and other hazardous air pollutants
from the HWCs studied. EPA will initiate a technical analysis to
characterize these emissions in the near future. EPA expects to
make the results of that analysis available to the public for
review prior to the time that any regulatory proposal would be
developed.
Process Descriptions
Cement Kilns. Many cement facilities burning hazardous
wastes use "wet" process kilns where the raw materials are
slurried before introduction to the kiln. Hazardous waste is ..
burned in other types of cement kilns, however, including long
dry kilns, preheater kilns, and preheater/precalciner kilns.
Liquid hazardous waste fuels are fired into the hot, lower
end of the kiln as a supplement to fossil fuels. Solid hazardous
waste fuels are also fired using several methods, including: (1)
in long wet or dry kilns, containerized waste can be charged
through a hatch on the rotating kiln wall in the calcining zone
of the kiln; '(2) in. preheater or precalciner kilns, solid waste
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fuels can be injected directly into the precalciner vessel .
preheater inlet; (3) in long wet or dry kilns, containerized
waste can be.injected at the.hot end of. the kiln using an "air
cannon" .at a; high enough velocity to project the Containers in
the calcining zone; and (4) powdered hazardous waste.can be
pneumatically fired into the hot end pf'.the kiln.
Cement kilns are normally equipped with either an
electrostatic precipitator (ESP) or fabric filter (FF) to control
emissions of particulate matter (PM).
Light-weight Aggregate Kilns. Light-weight aggregate kilns
slowly heat raw materials such as clay, shale, or slate to expand
the particles to form light-weight materials generally for use in
concrete products. The light-weight aggregate concrete is
produced either for structural or thermal insulation purposes.
When burning hazardous waste, these kilns generally burn the
liquid waste as their sole fuel.
Most light-weight aggregate kilns burning hazardous waste •
are equipped with FFs to control PM emissions.
Hazardous Waste Incinerators. Hazardous waste incineration
technology has been developed over a number of years as a means
of treating various types of waste to destroy toxic organics in
the waste and reduce the volume of the waste. There are many
types of incinerators in use including rotary kilns, fluidized
bed units, liquid injection units, and fixed hearth units.
Incinerators use many, types of air pollution control devices
to control emissions of particulate matzter, metals,'' and acid"
gases. In general, the control systems can be 'grouped into th'e
following three. categories: (1) wet, systems, where a wet . .,
scrubber is used for both particulate and acid gas control; (2)
dry-systems where a FF or ESP is used for PM control, sometimes* •
in. combination with dry scrubbing for acid gas control; and (3)
hybrid wet/dry systems where a dry technique .(ESP or FF) is used
for PM (and possibly acid gas control with use of dry scrubbing)
followed by a wet technique (venturi or packed bed scrubber) for
acid gas control. ' ' •
Boilers. The three common boiler design categories that
burn hazardous waste are firetube, watertube, and stoker-fired.
Although most boilers-burn liquid hazardous waste, some burn
solid hazardous waste. The hazardous waste firing rate
(percentage df heat input contributed by the hazardous-waste)
'ranges from less than 10:, per cent to 100 percent. . , .
PM Emission Levels .'"•='
EPAY is evaluating PM emission levels because controlling PM
will control emissions of most toxic-.meteals and toxic organic
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compounds adsorbed .onto- the PM. PM levels are evaluated for
several different source categories (or subsets thereof), as well
as various degrees of" aggregation of these source categories.
For example, commercial incinerators are evaluated separately
from on-site incinerators as a crude attempt to determine if the
best controlled of the generally smaller.on-site incinerators -are
achieving PM emissions levels substantially different from the
best controlled commercial incinerators. Further, PM emissions
from the best controlled incinerators, boilers, and industrial
furnaces are evaluated as an aggregated group representing the
hazardous waste combustor source category. While the Agency - is
interested in examining the appropriateness and implementability
of establishing standards that apply across all types of
hazardous waste combustors, EPA recognizes that in doing so there
may be technical and policy determinations that have not yet been
fully illuminated or explored. The Agency emphasizes that, at
this time, it has not decided if and which source categories will
be grouped in determining PM emission limits.
• For this study, EPA is evaluating PM emission data that
facilities had submitted to the EPA Regional Offices and the
States as part of Certification's of Compliance under the Agency's
Boiler and Industrial Furnace (BIF) Rule, and from incinerator
trial burns used to consider, issuance of operating permits. To
identify the best controlled sources, the sources are ranked in
order of ascending PM emission levels considering
the average emission level for the source and the variability of
the emissions data. The best 12 percent (or best five sources,
which ever is greater) of the sources are then selected as
(potentially) the best controlled sources. Each of the sources
in the selected pool is then evaluated to determine if they
achieve low PM emissions because they use advanced control
techniques or because they simple burn wastes or other materials
with low levels of ash. Sources with low PM levels because of
low ash feed rates are screened out of the pool as being
unrepresentative of best controlled sources, and the next best
controlled sources are brought into the pool as replacements.
Once the pool of the best controlled sources is established,
their emissions data are analyzed statistically to predict a PM
emission level that could be achieved under two alternative
approaches. Under Option 1, a PM emission level is identified
that all of the sources in the best controlled source pool could
be expected to meet 99 percent of the time, with 95 percent
confidence. Under Option 2, a PM emission level is identified
that a source with emissions equivalent to the average for the
sources in the pool, and displaying emissions variability similar
to sources in the pool', courld be expected to meet 99 percent of
the time, with 95 percent -confidence. Under Option 1, all of the
sources in the best controlled source pool should be able,to
achieve the- PM level without modifications, while under Option 2,
some of the sources in the pool may not be able to achieve the.PM
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level without modifications to the facility design or operation
while a- i
T~ i-^t table below presents the PM emission levels achievable
by the best controlled sources for the source categories and
groups of source categories, and for the alternative analytical
approaches:
PM EMISSION LEVELS ACHIEVABLE BY THE BEST CONTROLLED SOURCES
(gr/dscf @ 7% 02)
Source Category
Option 1*
Option 2+
Cement Kilns
0.033
0.010
Lightweight Agg. Kilns
0.022
0.0077
Commercial Incinerators
0.010
0.0049
On-Site Incinerators
0.015
0.0075
All HW Incinerators
0.0057
0.004
Boilers
0.021
All Hazardous Waste Combustors
s identified tha
. . ._
P°01 could be expected to meet 99 percent of
the time, with 95 percent .confidence
Under_Option 2, a PM emission level is" identified that a source with
emissions equivalent to the average for the sources in the pool and
displaying emissions variability similar to sources in the pool could be
expected to meet 99 percent of the time, with 95 percent confidence.
Dioxin/Furan Emission Levels
Dioxin/furan emission levels are evaluated for hazardous
waste burning incinerators, cement kilns, lightweight aggregate
kilns, and boilers in the ,aggregate (i.e., as a hazardous waste
-combustor (HWC) source category). EPA is not currently aware of
any overriding technical reason why all HWCs should not be able
to meet the emission level achievable by the best controlled
sources.
_The dioxin/furan emissions data used for the analysis are
obtained from BIF Certifications of Compliance and incinerator
Trial Burn results. The Agency,is using the same methodology
used for PM to identify the. best controlled sources, except that
the sources in the (potentially) best -controlled source pool are
screened for three criteria. First, the pool sources are
screened to determine if they have low dioxin/furan emissions
because their feedstreams contain insignificant levels of
chlorine.
Then, two additional screening criteria are used because of.
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concern about the potential conflict between minimizing
dioxin/furan and PM emissions at the same time. Given that
dioxins/furans may be formed in HWCs operating under good
combustion practices by surface-catalyzed reactions, dioxin/furan
emissions can be affected by PM emissions. Thus, these screening
criteria ensure that the dioxin/furan emissions from the pool
sources are representative of emissions from sources that use
best operating practices to control both PM and dioxin/furans.
The first of these criteria screened out of the pool sources that
had low PM emissions because they are feeding materials with low
ash content. These sources may have low dioxin emissions simply
because there was little PM to promote surface-catalyzed
formation. The second criterion screened out sources that have
high PM emissions. These sources may have low dioxin emissions
simply because they are not removing PM and thereby providing an
attenuated residence time (e.g., in an ESP or FF) for surface-
catalyzed reactions to take place.
After the pool of best controlled and representative sources
is identified, the same statistical approaches used to analyze PM
emissions are used to analyze dioxin/furan emissions. The table
below presents the dioxin/furan emission levels achievable by the
best controlled HWC sources under the alternative analytical
approaches:
DIOXIN/FURAN EMISSION LEVELS ACHIEVABLE
BY THE BEST CONTROLLED SOURCES
(ng/dscm @ 7% O2)
Basis
TEQ
Total Tetra-Octa Congeners
Option 1*
0.17
9.4
Option 2+
0.12
5.4
Under Option 1, a PM emission level is identified tnat all or tne sources
in the best controlled source pool could be expected to meet 99 percent of
the time, with 95 percent confidence.
Under Option 2, a PM emission level is identified that a source with
emissions equivalent to the average for the sources in the pool, and
displaying emissions variability similar to sources in the pool, could be
expected to meet 99 percent of the time, with 95 percent confidence.
Note that EPA believes that it is appropriate to control
dioxin/furan emissions for HWCs based on toxicity equivalents
(TEQs). Under this approach, weighting functions knows as
toxicity equivalence factors are assigned to the various dioxin
and furan congeners to account for their toxicity relative to
2,3,7,8 TCDD. EPA is considering whether it is also appropriate
to control emissions based on total tetra-octa congeners. If so,
emission limits would be established on the basis of total
congeners as well as TEQ.
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European Emission Regulations
On March 23, 1992, the EEC issued a proposal for a Council
Directive on the Incineration of Hazardous Waste. The Directive
requires all its Member States to establish laws, regulations,
and administrative procedures to comply with the directive by
June 30, 1994. The directive'stipulates that any new incinerator
must comply immediately and existing facilities by June 30, 1997.
The regulatory approach adopted in the 1992 EEC Directive
establishes a wide array of continuous emission monitoring
requirements, including continuous monitors for carbon monoxide
and total dust emission levels, and monthly measurements for
metals, dioxins, and furans. A summary of European guidelines
and limits for PM and dioxins/furans is presented below:
EMISSION GUIDELINES/LIMITS FOR WASTE INCINERATION IN EUROPE
Pollutant
(Daily Averages)
Total Dust (mg/m3)
' Dioxin/furan (ngTEQ/m3 ) 1
EEC Guideline
5
0.1
Netherlands
Limit
5
0.1
Germany
Limit
5
, 0.1
Waste incineration has been in use in Europe longer than in
North America. The air pollution control device (APCD) systems
are similar. However, because the majority of the European
facilities have undergone retrofits and have faced'more stringent
emission standards, design differences exist. Incinerators in
Europe currently incorporate some sort of dust control device,
such as wet and dry electrostatic precipitators (ESP) or fabric
filters (FF). Most facilities have added multi-stage wet and dry
scrubbers or spray drying and dry absorption processes for
controlling acid gas and heavy metal emissions. The future trend
is expected to be toward wet scrubbers, even though all APCD
1 It is important to note that the European guideline or
limit of 0.1 TEQ is corrected to 11% oxygen, and compliance is
based on daily averaging. EPA requires that dioxin/furan
emissions be corrected to a stack gas oxygen level of 7%. A 0.1
limit at a 11% oxygen correction factor is equivalent to a 0.14
limit at a 7% correction factor. Further, EPA requires hazardous
waste burning devices operating under RCRA regulations to comply
with emissions standards generally on a hourly rolling averaging
period. The European guidelines/limits are based on daily
averaging, a less stringent approach in terms of operational
variability. Finally, RCRA .regulations require a facility to
comply with the emissions standard for each of three triplicate
runs during a Trial Burn or compliance test. Compliance with the
European guidelines/limits is based on the average of test runs.
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systems must be a zero liquid discharge systems. Some new
technologies that are emerging include adding Selective Catalytic
Reduction-DeNOx reactors, activated carbon filters, and gas
suspension absorbers. As new options arise, it appears to_be the
general practice in Europe to continue to retrofit facilities
with new APCDs in series with existing equipment.
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