United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/6007S8-89/063 May 1990
f/EPA Project Summary
Municipal Waste Combustion
Assessment: Technical Basis for
Good Combustion Practice
P.J. Schindler and L.P. Nelson
The EPA's Office of Air Quality
Planning and Standards (OAQPS) Is
developing emission standards and
guidelines for, respectively, new and
existing municipal waste combustors
(MWCs) under the authority of
Sections 111 (b) and 111 (d) of the
Clean Air Act (CAA). The EPA's Office
of Research and Development (ORD)
is providing support in developing
the technical basis for good com-
bustion practice (QCP), which Is
Included In the regulatory alterna-
tives considered In selecting the
proposed standards and guidelines.
This report defines GCP and sum-
marizes the approach used to
Implement GCP Into the proposed
MWC standards and guidelines. The
report Identifies the minimum subset
of GCP operating parameters that can
be monitored continuously to ensure
that the GCP goals are achieved.
Finally, the report provides a detailed
description of the data and rationale
used to establish quantitative operat-
ing limits for each of the continuous
operating parameters.
This Pro/ect Summary was
developed by EPA's Air and Energy
Engineering Research Laboratory, Re-
search Triangle Park, NC, to announce
key findings of the research pro/ect
that Is fully documented In a separate
report of the same title (see Project
Report ordering Information at back).
Introduction
On July 7, 1987, the U.S EPA
announced its intent to develop air
emission standards for new municipal
waste combustors (MWCs) and emission
guidelines for existing MWCs, under the
authority of Section 111 of the Clean Air
Act (CAA). The New Source Performance
Standards (NSPS) will apply to all MWCs
that commence construction after the
proposal date, and the guidelines will
apply to all MWCs not covered by the
NSPS.
Concurrent with the announcement
that it intended to further regulate MWCs,
EPA published interim operational
guidance for use by EPA Regions and
States in making best available control
technology (BACT) determinations under
the Prevention of Significant Deterioration
(PSD) provisions of the Clean Air Act.
The operational guidance specified that
combustion controls are a demonstrated
technology for controlling emissions of
carbon monoxide (CO) and organics from
MWCs. The technical basis for the
operational guidance came from EPA's
1987 Report to Congress on MWCs. The
Report to Congress examined two
emission control strategies: combustion
controls and add-on flue gas cleaning
controls.
Performance Data/Rationale
The combustion control strategy
defined in the Report to Congress,
termed good combustion practices
(GCP), identified three elements: design,
operation/control, and verification. The
strategy required that: (1) MWCs be
designed to minimize organic emissions,
(2) the systems be operated within
established design limits and that com-
bustion control measures be in place to
prevent operating outside of these limits,
and (3) verification measures be in place
(e.g., continuous monitors) to ensure that
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combustors continuously maintain good
operations. It was judged that these
conditions would minimize trace organic
emissions. A group of components was
identified for each of the three GCP
elements, each of which makes a
necessary contribution to the GCP
control strategy.
Following the July 7, 1987, announce-
ment, data gathering was continued to
provide additional technical support for
the proposed regulation. Consistent with
the approach laid out in the operational
guidance, data gathering addressed both
combustion and add-on controls. The
new data and information gathered on
destruction, formation, and control of
trace organic compounds resulted in
revisions to the GCP control strategy.
The need to develop a practical
implementation strategy to incorporate
GCP into the standards and guidelines
also forced revisions to the format of the
recommendations. The revised GCP
include seven components, each related
to MWC design and operating conditions
needed to control emissions of organic
pollutants. These components include
conditions related to: waste feeding,
combustion temperature, amount and
distribution of combustion air, mixing,
paniculate matter (PM) carryover.
downstream temperature control, and
combustion monitoring and control.
This report summarizes the rationale
used to identify each component as a
necessary requirement of the GCP
control strategy. Some of the conditions
(e.g., mixing) cannot be measured
directly. Therefore, combustion paramet-
ers are specified as surrogates for
verifying the degree to which each
condition is satisfied. For example, CO
concentrations in flue gases are indica-
tors of the degree of mixing. Because
mixing cannot be quantified by itself, it is
necessary to use CO in flue gases as a
surrogate to verify mixing performance.
Some combustor design and operating
conditions (e.g., downstream flue gas
temperature) can be measured directly.
Thus, no need exists to specify
surrogates for this condition. This report
describes the approach used to identify
surrogates and numeric operating ranges
and limits for each.
Implementing
Recommendations
The final step in GCP development
was to implement the GCP recom-
mendations into the proposed standards
and guidelines by identifying a minimum
set of operating parameters that could be
monitored continuously to ensure that the
GCP goals are achieved. Three operating
parameters were selected which meet
this criterion: CO in flue gases, maximum
operating load, and PM control device
inlet temperature. This report describes
the rationale for selecting each parameter
for inclusion in the standards and
guidelines, and provides a detailed
discussion of the data used to establish
quantitative operating limits. The CO
emission levels are established on a
technology specific basis because inher-
ent design and operating characteristics
of various combustor technologies enable
some design types to achieve lower CO
emission levels than other technologies.
Thus, the CO emission levels that
correspond to the use of GCP vary based
on the combustor technology employed.
The population of existing MWCs was
categorized based on: conventional mass
burn waterwall, mass burn refractory wall,
mass burn rotary waterwall, modular
starved air, modular excess air, refuse-
derived-fuel (RDF) combustors, and
fluidized bed combustors (FBC).
CO in Flue Gases
Long term continuous CO data were
gathered from existing MWCs for use in
establishing an achievable emission limit.
Data were acquired from two mass burn
waterwall MWCs, one modular starved air
MWC, and two RDF-fired MWCs. The
data were statistically analyzed to deter-
mine exceedance frequencies for various
averaging times, and recommended
emission limits were established based
on a 1-in-10-year exceedance of a 4-hour
block average. Where no longterm data
were available to characterize the per-
formance of an MWC technology, long-
term emissions were extrapolated from a
review of shortterm data. Sometimes,
when longterm data appeared not to
adequately represent emission levels that
correspond to the use of GCP, shortterm
parametric test data were used to
establish the achievable emission levels.
The CO emission levels were established
ranging from 50 to 150 ppm, corrected to
7% 02, 4-hour block average. The
emission levels selected were judged to
reflect the use of GCP for each MWC
technology.
Maximum Operating Load
The maximum operating load level
was selected as a continuous operating
parameter to serve as a surrogate for PM
carryover. The rationale for selecting this
parameter was that high load operation
results in increased flue gas flow rates,
which can lead to increased PM
entrainment and carryover. Data are
presented showing a relationship be-
tween PM carryover and polychlorinateq
dibenzo-p-dioxin (CDD) and dibenzofurar
(CDF) emissions. The GCP recommenda-
tion is for each MWC that produces
steam not to exceed a maximurr
operating load of 100% steam flow, 4
hour average. This recommendatior
cannot be implemented for MWCs tha
do not generate steam.
PM Control Device Inlet
Temperature
The third continuous operatin;
requirement addresses the potential fo
CDD/CDF formation to occur in lov
temperature portions of the MW(
system. Low temperature CDD/CDI
formation has been observed am
quantified in several full scale MWCs
and bench scale laboratory experiment
have examined the parameters control
ling these reactions. The recommendei
control strategy in full scale MWCs is t
minimize the flue gas residence time i
the temperature window where the rate <
the formation reactions is highest (25C
400 °C). Data are presented showing th
relationship between electrostati
precipitator (ESP) operating temperatur
and CDD/CDF removal. These data ar
used to establish the GCP recorr
mendation that all MWCs maintain PI
control device temperatures belo
232 "C. The data indicate that thes
conditions will minimize CDD/CD
concentrations in stack flue gases t
preventing formation and, in some case
enhancing removal of CDD/CDF in th
flue gas cleaning device.
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P.J. Schindler and LP. Nelson are with Energy and Environmental Research
Corp.. Durham, NC 27707.
James D. Kilgroe is the EPA Project Officer (see below).
The complete report, entitled "Municipal Waste Combustion Assessment:
Technical Basis for Good Combustion Practice," (Order No. PB 90-154
949IAS; Cost: $23.00, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield. VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Air and Energy Engineering Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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