PB91-162552
Combustion Control of PCDD/PCDF Emissions from
Municipal Waste Incinerators in North America
(U.S.) Environmental Protection Agency, Research Triangle Park, NC
1990
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EI'A/600/D-90/241
COMBUSTION CONTROL OF PCDD/PCDF EMISSIONS
FROM MUNICIPAL WASTE INCINERATORS IN NORTH AMERICA
James D. Kilgroe
U.S. Environmental Protection Agency
Office of Research and Development
Air and Energy Engineering Research Laboratory
Research Triangle Park, NC 27711
ABSTRACT
New regulations to control air pollution emissions from municipal waste incineration
have been enacted in Canada and are being developed in the United States.
Regulations in both countries will require the use of good combustion practice
(GCP). The U.S. Environmental Protection Agency defines three goals for their GCP
strategy: to maximize furnace destruction of organics, to limit the relative amount
of flyash carried from combustor3 with flue gases, and to operate flyash collection
devices at temperatures which minimize the de novo synthesis of polychlorinated
dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/PCDF). This paper
describes the rationale for this GCP strategy, presents data showing the effects of
electrostatic precipitator operating temperature on PCDD/PCDF formation rates, and
briefly describes current North American incinerator design and operating practices
which must be changed to reduce formation and emission of PCDD/PCDF.
INTRODUCTION
New U.S. and Canadian air pollution emission regulations for municipal waste
incinerators will require the use of good combustion practice (GCP) and the
application of flue ga3 cleaning technology to control emissions.1,2 The Canadian
guidelines specify that all incinerators use GCP and flue gas cleaning technology to
limit emissions to the levels achievable by a lime spray dryer absorber (SDA) and
fabric filter (FF). The proposed U.S. guidelines which apply to existing facilities
would require GCP for all facilities. The level of flue gas cleaning required would
depend on the facility capacity.
The proposed EPA emission rules apply to municipal waste combustors (MWCs), a term
used for municipal waste incinerators, refuse derived fuel (RDF) combustors, or any
other combu3tor burning municipal solid waste. There are many MWC facilities in the
U.S. which do not use flue gas cleaning equipment (small MWCs) or which use only
electrostatic precipitators (ESPs). While some of these facilities will be required
to use various techniques for acid gas control, all will be required to use GCP and
control particulate, trace metal, and organic (PCDD/PCDF) emissions. This paper
will discuss the use of good combustion techniques as abetted by the proper
operation of particulate control devices for controlling PCDD/PCDF emissions.
CONTROL STRATEGY
Organic compounds such as PCDD/PCDF may originate in the waste and pass through the
incinerator or combustor undestroyed. They may also originate in the high
temperature regions of the furnace from thermal decomposition products which are not
completely oxidized due to insufficient combustion air, mixing, temperature, or
residence time. Or, they may originate from reactions downstream of the combustion
chamber.
EPA has proposed the use of good combustion practice (GCP) to limit the formation
and emission of PCDD/PCDF and other organics.1 The GCP strategy is to maximize
furnace destruction of organics and limit PCDD/PCDF formation downstream of the
c.ombustor. Implicit in the strategy is the proper design and operation of flue gas
cleaning devices used to collect flya3h. Downstream formation is to be limited by
avoiding excessive transport of flyash from the furnace with flue gases and by

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control devices operate at
ensuring that ESPs and other particulate matter (PM)
temperatures which minimize the formation of PCDD/PCDF.
EPA's proposed emission guidelines for existing incinerators are predicated on the
use of ESPs at all but very large regional facilities (>2200 Mg/d capacity). These
regional facilities would probably use GCP and SDA+FF to control emissions. Large
facilities (>225 Mg/d <2200 Mg/d) would probably use GCP and ESPs in combination
with furnace or duct injection of calcium based compounds for acid gas control (dry
sorbent injection). Small facilities (<225 mg/d) would probably use GCP and ESPs.1
The proposed FPA emission guidelines for existing MWCs are:
	Facility Capacity	
Pollutant
Small
Large
Regional
MWC Metals, mg/dscm (as PM)
MWC Organics, ng/Nm3 (as PCDD/PCDF)
MWC Acid Gases
HC1, % Red.c
S02, % Red.d
	NOx, ppmv	
69a
500
(1000)b
none
none
none
69
125
(250)
50
50
hone
34
5-30
95
85
none
a All emissions corrected to 7% oxygen, dry basis,
b Values in ( ) are for RDF facilities.
c Indicated percent reduction or less than 25 ppmv.
d Indicated percent reduction or less than 30 ppmv.
These proposed guidelines are to be finalized in December 1990. Some modifications
are expected, including selection of a specific PCDD/PCDF emission limit for
regional facilities.
CO Emission Limits
Low combustion gas concentrations of organics and CO are associated with good
combustion conditions. Poor combustion conditions generally lead to increased
concentration of CO and organics in flue gases.
Test results from a mass burn incinerator in Quebec City, Quebec, and a RDF
combustor in Hartford, Connecticut(United States), have shown a moderately strong
correlation between CO and flue gas concentrations of PCDD/PCDF. (See Figure l.)^'4
Te3t3 at these two facilities were performed while the incinerators were operating
over a range of good and poor combuction conditions. Examination of data from these
tests shows that combustion efficiency deteriorates gradually with changing
conditions and that there is no readily discernible CO concentration at which
combustion efficiency changes from good to bad. Also, many factors affect PCDD/PCDF
emission, and it is impossible to define a CO concentration which results in any
specified limitation of PCDD/PCDF emissions. Since different types of incinerators
exhibit inherently different CO emission characteristics, the EPA has proposed as a
limit the lowest continuous CO emission that has been demonstrated for each
technology. The proposed rules, which are based on a 4-hour averaging time, would
limit modular incinerators to 50 ppm, mass burn incinerators to 100 ppm, fluidized
bed combustors to 100 ppm, RDF combustors to 150 ppm, rotary waterwall combustors to
150 ppm, and coal-RDF co-fired combustors to 150 ppm (all concentrations corrected
to 7% 02 in dry gas).
2

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MID-CONNECTICUT - RDP COMBUSTOR
QUEBEC CITY - MASS BURN INCINERATOR
R'-OJOl
700	<400	600	eoo	1000
CARBON MONOXIDE fonuv)
Biuret. CofrcUttoc\o/00«vjrCDD/?QDP.
•a
R1 - Q.t7<
fl	10	17	M
UNCONTROLLED ASU / REFUSE FED (k*/«x)
R^urr 2. ContUlkvio/ PU anyDve uvl PQDD/TCDP.
Operating Load Limit
PCDD/PCDF can be formed downstream of the furnace by rif» novo synthesis reactions on
the surface of flyash. The amount formed is believed to be proportional to the
amount of flyash and the time individual particles reside at temperatures ranging
from about 150 to 400°C. A limit on maximum operating load as measured by steam
flowrate has been proposed by EPA to avoid excessive flyash entrainment and
subsequent flyash carryover to downstream locations where rie novo synthesis
reactions occur.
The results of tests at the Quebec incinerator-and other facilities have shown that
PCDD/PCDF concentrations in flue gases are strongly correlated to the amount of
entrained flyash in flue gases (see Figure 2).s Incinerators should therefore
minimize, within practical considerations, the amounts of PM entrained in flue gases
to limit PCDD/PCDF formation downstream of the furnace/combustor.
The relative amount of flyash in flue gases depends on the type of combustion
technology and the specific combustion parameters such as under-to-overfire air
ratio. However, excessive amounts of flyash, relative to normal conditions, are
entrained in flue gases if the rate of waste burned exceeds the design capacity of
the combustor. Higher volumetric flue gas flowrates and increased particle
entrainment result from operation above the design load. Since there are no
commercially available systems in the U.S. for measuring the amounts of entrained
flyash or validated techniques for continuously measuring flue gas flowrates, EPA
has proposed a maximum limit on operating load as measured by steam flowrate.
Facilities which do not produce steam are not subject to this requirement.
Maximum PM Control Device Inlet Temperature
Maximum rates of PCDD/PCDF formation by novo reactions are believed to occur at
temperatures near 300°C.®'^ Net formation results from competing reactions
involving PCDD/PCDF formation, dechlorination, and destruction (transformation to
other compounds) . Below 300°C, net formation rates diminish with decreasing
reaction temperatures.
Dry flue gas cleaning devices for collecting PM, such as ESPs, retain large amounts
of flyash which can serve as a source of rte novn reactions. EPA has proposed that
3

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PM control devices be limited to operation at inlot temperatures below 230°C to
avoid excessive formation of PCDD/PCDF.
ESPs can simultaneously collect PM associated PCDD/PCDF and function as chemical
reactors that generate and emit PCDD/PCDF. A large fraction of the PCDD/PCDF
entering an ESP is probably associated with flya3h which can be collected. However,
accumulated flyash within the ESP can serve as a source for do novo synthesis of
PCDD/PCDF. Newly formed PCDD/PCDF can remain with the collected flyash: it can be
re-entra±ned along with associated flyash, or it can be desorbed into the flue gas
stream as a vapor. The amount formed within an ESP will depend primarily on the
rate at which flyash and organic precursors enter the ESP, the composition of flue
gases (02 and water vapor) , the length of time flyash i3 retained (amount
accumulated), and the temperature. If other factors are relatively constant, then
the temperature at which the PM control device is operated will play a dominant role
in determining the PCDD/PCDF collection, formation, and stack emission rate. At
inlet temperatures near 300°C, formation will dominate and outlet concentrations of
PCDD/PCDF will generally exceed inlet concentrations. At some lower inlet
temperatures, the inlet and outlet concentrations will approach a balance, and as
inlet temperature is further reduced, formation rates will become negligible or
cease.
In tests conducted by EPA to investigate the effects of ESP inlet temperature on
PCDD/PCDF collection, formation, and emission rates, it was found that the
measurable rates of formation occur at temperatures as low as 150°C.S These tests
were conducted at a Montgomery County, Ohio, mass burn refractory incinerator
equipped with an ESP. Temperatures at the inlet to the ESP were controlled by the
amount of water sprayed into a quench chamber upstream of the ESP. PCDD/PCDF
measurements were made in triplicate at each of six test conditions (see Table 1).
Test variables included: combustion conditions (normal and poor), ESP inlet
temperature (300 to 150°C), and method of acid gas control [none, injection of CaC03
into the furnace, or injection of Ca(OH)2 into the duct upstream of the ESP].
PCDD/PCDF concentrations at the ESP inlet were observed to decrease with decreasing
ESP inlet temperature because of the scrubbing effect of water sprays in the quench
chamber. PCDD/PCDF concentrations at ESP outlet were higher than the corresponding
PCDD/PCDF concentrations at the inlet for all test conditions. For tests without
sorbent addition, the reduction of the average ESP inlet temperature from 299 to
202°C reduced the average stack concentration of PCDD/PCDF from 17,100 to 870
ng/Nm^, respectively.
Although no tests were conducted at 150°C without sorbent injection, the tests with
furnace injection of CaC03 indicated that further reductions of inlet temperature
will lead to lower PCDD/PCDF formation rates.
Injection of sorbents into the furnace or duct has been advocated as a method for
controlling PCDD/PCDF. It is believed that the reduction of HC1 concentrations will
reduce the overall number of reactions leading to the formation of chlorinated
organics. Results of the Montgomery tests show that, on a weight basis, furnace
injection at 200°C inlet temperature produced higher concentrations of PCDD/PCDF
(1480 ng/Nm^) than tests at this temperature without sorbent injection (870 ng/Nm^).
However, on a 2378 toxic equivalent basis, the sorbent injection tests had lower
PCDD/PCDF concentration (5.0 ng/Nm^) than comparable tests without sorbent injection
(6.2 ng/Nm3). It is possible that furnace sorbent injection retards dechlorination
of octa- and hepta-isomers to penta- and tetra-isomers. Duct injection of Ca(OH2)
produced lower stack concentrations of PCDD/PCDF, both on a weight basis and a toxic
equivalent basis, than furnace injection of CaC03- However, the furnace injection
system was not optimized and it did not remove HC1 as efficiently as the duct
injection system. Poor combustion conditions resulted in marginally higher stack
emissions of PCDD/PCDF on a toxic equivalency basis.
4

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Table 1. Montgomery County Incinerator Test Re3ult3a
Test Conditions
PCDD/PCDF Test Results*3
Combustion
Sorbent Injection ESP Inlet
Temp., °C
Weight Basis (2378 Toxic Eouiv.lc
ESP Inlet
ESP Outlet
Normal
Normal
Normal
Normal
Normal
Poor
None
None
None
Furnace
Furnace
Duct
299
279
202
201
148
152
250 (1.3)
210 (1.3)
34	(0.2)
35	(0.2)
14 (0.0S)
5 (0.08)
17,100 (103)
14,800 (118)
870 (6.2)
1480 (5.0)
670 (2.9)
57 (0.1)
a Mean temperature and PCDD/PCDF concentrations for 3 tests at each of 6 3ets of
conditions.
b PCDD/PCDF concentrations adjusted to 7% O2, dry basis.
c Based on U.S. EPA toxic equivalency factors.
Additional tests are needed to evaluate the effects of dry sorbent injection either
into the furnace or flue gas duct, on PCDD/PCDF emission control.
Many existing facilities in the U.S. will require equipment and operating procedure
modifications to comply with combustion and emission requirements specified in new
rules proposed by EPA. Furnace destruction of organic compounds (low CO) and
minimization of flyash entrained in combustion gases will be important means of
controlling downstream "formation of PCDD/PCDF in small and large facilities.
However, ESPs and FFs can function as reactors in which PCDD/PCDF forms, and in many
cases the operating temperature of the PM control device will be the dominant factor
in determining the rate at which PCDD/PCDF is emitted to the atmosphere or
discharged as solid waste with collected flyash. In systems which do not use wet
scrubbers or spray dryers, the PM control device should be operated at the lowest
possible temperature to minimize formation of organic pollutants.
Many mass burn facilities in the U.S. do not control acid gas emissions, and it is
the practice of these facilities to operate with ESP inlet temperatures ranging from
approximately 200 to 350°C. Of 19 mass burn facilities for which data are
available, 14 operate with ESP inlet temperatures which exceed EPA's proposed limit
of 230°C. Tests at two mass burn facilities with ESP inlet temperatures exceeding
230°C had PCDD/PCDF concentrations at the ESP outlet which normally exceeded
PCDD/PCDF concentrations at the inlet by 5 to more than 100 percent. At another
facility, tests at ESP inlet temperatures ranging from 225 to 247°C indicated outlet
concentrations which were lower than inlet concentrations by 10 to 80 percent.
Several RDF spreader stokers have combustion gas air preheaters downstream of the
ESP and operate with ESP inlet temperatures close to 300°C. A 2200 Mg/day RDF
facility in Detroit, Michigan, which began operation in 1988 has exhibited stack
emissions of PCDD/PCDF which range from approximately 3000 to 5000 ng/Nm^.
Modular starved air incinerators equipped with LSPs also indicate PCDD/PCDF
formation when the control devices are operated at temperatures near 300°C.
There is now ample evidence that PM control devices can function as chemical
reactors which form PCDD/PCDF and other organics. In incinerator systems which do
not employ wet or dry (both duct sorbent injection and SDA) scrubbers, the PM
control device should be operated at the lowest possible temperature to minimize
formation of organic pollutants.
RETROFIT OF EXISTING FACILITIES
5

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REFERENCES
1.	Federal Register, 40 CFR Parts 60, 51, and 52, December 20, 1989.
2.	Operating and Emission Guidelines for Municipal Solid Waste Incinerators,
CCMF.-TS-TRE003, June 1989.
3.	Kilgroe, J.D. et al., Control of PCDD/PCDF Emissions from Refuse-derived Fuel
Combustors, Presented at Ninth International Symposium on Chlorinated Dioxins
and Related Compounds (Dioxin '89), Toronto, Ontario, Canada, September 1989.
4.	Environment Canada, NITEP. Environmental Characterization of Mass Burning
Incinerator Technology at Quebec City, Summary Report, EPS 3/UP/5, June 1988.
5.	Brna, T.G. and J.D. Kilgroe, Control of PCDD/PCDF Emissions from Municipal
Waste Combustion Systems, Presented at Ninth International Symposium on
Chlorinated Dioxins and Related Compounds (Dioxin '89), Toronto, Ontario,
Canada, September 1989.
6.	Stieglitz, L. and H. Vogg, Formation and Decomposition of Polychlorodi-
benzodioxins and -furans in Municipal Waste Report kfK4379, Laboratorium fur
Isotopentechnik, Institut fur Heize Chemie, Kernforschungszentrum Karlsruhe,
February 1988.
7.	Hagenmaier, H. et al., Envir. Sci. and Tech., 21 (11), 1987, p 1085.
6

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A r.' i.M? I - D-717 TECHNICAL REPORT DATA
H illv 1-. 1 ill (J'lejse rccJ intlfticdons on the reverse bejo/e eontfleti
i. ncrom no.
EPA/600/D-90/241
p
' PB91-162 552
•3. TITLE ANO SUBTITLE
Combustion Control of PCDD/PCDF Emissions from
•j. HCI'OUT DATE
Municipal Waste Incinerators in North America
C. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
James D. Kilgroe
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS

10. PROGRAM ELEMENT NO.
See Block 12


11. CONTRACT/GRANT NO.
NA (Inhouse)
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development

13. TYPE OF REPORT AND PERIOD COVERED
Published paper; 3-8/90
Air and Energy Engineering Researcli Laboratory
Research Triangle Park, North Carolina 27711
14. SPONSORING AGENCY CODE
EPA/600/13
is.supplementary notesproject officer is James D. Kilgroe, Mail Drop 65, 919/
541-2854. Presented at International Conference on Organohalogen Compounds, 10th
International Meetine, Bavreuth. FRG, 9/10-14/90.
i6. abstract paper diSCUSSes combustion control of emissions of polychlorinated
dibenzo-p-dioxins (PCDD) and polychlorinated dibenzofurans (PCDF) from municipal
waste incinerators in North America. New regulations to control air pollution emis-
sions from municipal waste incineration have been enacted in Canada and are being
developed in the U. S. Regulations in both countries will require the use of good
combustion practice (GCP). The U.S. EPA defines three goals for their GCP stra-
tegy: to maximize furnace destruction of organics, to limit the relative amount of
flyash carried from combustors with flue gases, and to operate flyash collection de-
vices at temperatures which minimize the de novo synthesis of PCDD/PCDF. The
paper describes the rationale for this GCP strategy, presents data showing the
effects of electrostatic precipitator operating temperature on PCDD/PCDF formation
rates, and briefly describes current North American incinerator design and opera-
ting practices which must be changed to reduce formation and emission of PCDD/
PCDF.
17.
KEY WORDS AND DOCUMENT ANALYSIS

a. DESCRIPTORS
b. IDENTIFIERS/OPEN ENDED TERMS
c. cosati Field/Group
Pollution
Combustion
Incinerators
Wastes
Halohydrocarbons
Furans
Pollution Control
Stationary Sources
Municipal Waste Incin-
erators
Dioxins
13	B
21B
14	G
07 C
18. DISTRIBUTION STATEMENT
Release to Public

19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
7


20. SECURITY CLASS (This page)
Unclassified
22. PRICE
EPA Form 2220-1 (9«73)

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