Control of Air  Pollution Emissions
               From Municipal Waste Incinerators in the U. S. A,*

                                  James D. Kilgroe
                        U. S. Environmental Protection Agency
                     National Risk Management Research Laboratory
                 Research Triangle Park, North Carolina 27711, U. S. A.

                                   Anthony Licata
                   Licata Energy and Environmental Consultants, Inc.
                                 345 Concord Road
                         Yonkers, New York 10710, U.S.A.

       The U.S. Environmental Protection Agency (EPA) is currently developing air pollution
regulations for three types of solid waste incinerators:  municipal waste combustors (MWCs),
medical waste incinerators (MWIs), and hazardous waste combustors (HWCs). The MWC
regulations were proposed in September 1994, the MWI regulations were proposed in February
1995, and the HWC regulations are scheduled for proposal before the end of 1995.  This paper
will summarize the MWC regulations, identify the technologies on which they are based, and
discuss accumulated knowledge on the control of polychlorinated dibenzo-/?-dioxins (PCDDs),
polychlorinated dibenzofurans (PCDFs), and mercury (Hg).

       In June 1987, EPA announced its intention to develop new air pollution rules for
MWCs. 1 This decision was based, in part, on a study of the potential environmental risk
associated  with MWCs.2  Pollutants posing the highest risks included PCDDs/PCDFs and
hazardous trace metals.  On December 20, 1989, EPA proposed New Source Performance
Standards (NSPS) for new MWCs and Emission Guidelines (EGs) for existing MWCs.3
NSPS and EGs for MWCs larger than 225 Mg/day in capacity were promulgated in February
 This paper has been reviewed in accordance with the U.S. Environmental Protection Agency's peer and
administrative policies and has been approved for publication.

       The November  1990 Clear Air Act Amendments directed EPA to establish MWC
emission limits for participate matter (PM), hydrogen chloride (HC1), sulfur dioxide (SC^),
nitrogen oxides (NOX), carbon monoxide (CO), PCDDs/PCDFs, cadmium (Cd), Hg, and lead
(Pb). These emission limits were to be based on the application of maximum achievable control
technology (MACT).5 Revised MWC air pollution regulations were subsequently proposed by
EPA on September 20,1994,6
       This  paper  provides a brief overview of MWC technologies, a summary of EPA's
revised air pollution rules for MWCs, a review of current knowledge concerning formation and
control of PCDDs/PCDFs, a review of knowledge on the control of Hg, and information on the
performance of commercial  technologies  for continuously controlling  emissions of
PCDDs/PCDFs and Hg. The focus of the paper is the control of air pollution emissions as
needed to reduce risks from long-term exposures to PCDDs/PCDFs and Hg. The paper does
not address the requirements for complying with short-term (short averaging time) emission

MWC Technologies
       Three major types of MWCs are commonly used in the U.S.: mass burn, refuse-derived
fuel (RDF), and modular. 7 The best combustion technologies ensure adequate waste burnout
and produce minimal products of incomplete combustion (PICs) in the flue gas.  In the U.S.,
dry flue gas cleaning technologies are generally used to control air pollution emissions.^ Wet
scrubbing systems  are seldom used.  PM is typically collected in electrostatic precipitators
(ESPs) or fabric filters (FFs).  Most trace metals such as Cd  and Pb are solids at flue gas
cleaning temperatures and are efficiently collected in ESPs or FFs. Hg is normally a vapor at
flue gas cleaning temperatures, and special methods must be used for its control.^ 10
       Acid gases  are controlled by dry or semi-dry scrubbers by injecting calcium-based
reagents, quicklime (CaO) or hydrated lime [Ca(OH)2], into the flue gas to convert HC1 and
SC"2 into solid compounds that can be collected in a PM control device. ,l1  Several methods
may be used to inject and mix the sorbent with the flue gas:  lime spray dryers (SD), dry
sorbent injection of limestone or lime into the furnace (FSI), or dry sorbent injection into the
flue gas duct (DSI). Selective non-catalytic reduction (SNCR), the most advanced NOX control
technology  being  applied  in the U.S.  on MWCs, uses either ammonia (NHj) or urea
[CO(NH2)2l as a reagent to reduce NOX to nitrogen. 12
       The chemistry involved in acid gas and NOx control and the mechanisms involved in
PM control are generally well understood.  The major problem associated with control of these
pollutants (PM, acid gases, and NOX) is  the engineering optimization of flue gas cleaning
processes that are also effective in the control of trace metals and trace organics.

      The most difficult to control MWC pollutants of concern are PCDDs/PCDFs and Hg.
PCDDs/PCDFs can be formed in MWCs as a high temperature PIC or they can be formed
downstream of the combustor by low temperature synthesis reactions involving fly ash J.I 3
Hg, typically a vapor at flue gas cleaning temperatures, is difficult to collect in flue gas cleaning

Revised Federal Emission Control Requirements
      On September 20,  1994, EPA proposed revised NSPS for new MWCs and EGs for
existing MWCs. 6 These revised rules require the use of good combustion practice (GCP) and
MACT flue gas cleaning techniques to continuously limit emission of PCDDs/PCDFs, CO,
PM, Cd, Hg, Pb, HC1, SO2, and NOX-5'6 The control technologies on which the performance
requirements are based are summarized  in Table 1. These technologies or technology
combinations which give equivalent or better performance with the proposed requirements may
be used.
      The method of achieving PCDDs/PCDFs control is to use GCP in  combination with
appropriate flue gas cleaning techniques.  The objectives of GCP are  to maximize furnace
destruction of organics and  minimize  low  temperature  PCDD/PCDF  formation
reactions. 13i 14,15 Furnace destruction of organics is controlled by establishing technology-
based emission limits for CO (see Table 2).  Downstream formation and stack emissions are
controlled by a limit on steam load in waste-to-energy plants and a limit on PM control device
operating temperature. The load is a surrogate parameter used to limit the relative amount of
PM carried out of the combustor with flue  gas (PM carryover).  The purpose of the inlet
temperature limit is to control PCDD/PCDF synthesis reaction rates, and solid- and vapor-phase
partitioning of PCDDs/PCDFs in the PM control device. Solid-phase PCDD/PCDF emissions
are limited by the use of efficient PM control equipment such as high performance ESPs or
      The Hg emission limit is based on the injection of powdered activated carbon or a lime-
enhanced activated carbon sorbent in conjunction with dry scrubbing. The activated carbon
adsorbs gas-phase Hg and is collected in the PM control device.
      Acid gases  (HC1 and SO2) and metal (Cd,  Hg,  and  Pb) emission limits require
equipment and operating conditions that complement PCDD/PCDF control.  Acid gas sorbents
may reduce PCDD/PCDF formation rates, and the use of activated carbon for  Hg control
improves PCDD/PCDF control.
      The proposed 1994 EPA emission requirements for new and existing sources are
summarized in Table 3.  The proposed rules have different requirements for new and existing
plants, and for small (>  35 to <  225 Mg/day) and large (> 225 Mg/day)  plants.  The

PCDD/PCDF emission requirements can be met by complying with emission limits for total
tetra- through octa-PCDDs/PCDFs or International Toxic Equivalency (TEQ) factors for
PCDDs/PCDFs relative to 2,3,7,8-tetrachlorodibenzo-p-dioxin.  The proposed limits are: 60
ng/dscm (or 1.0 ng TEQ/dscm) for small existing plants, 30 ng/dscm (or 0.5 ng TEQ/dscm) for
large existing plants, and  13 ng/dscm (or 0.20 ng TEQ/dscm) for large and small new plants,
EPA emission concentrations are expressed in dry standard cubic meters (dscin) corrected to 7
percent $2 and standard conditions at 20 C (68 F) and 101.3 kPa (14.7psi). In comparison,
the 7 percent correction factor is 1.4 times more restrictive than the 11 percent 02 factor used in
European standards. The comparison between dioxin TEQs and dioxin mass emission rate is
provided for reference only. The ratio of mass concentration to TEQ concentration varies from
test to test and typically ranges between 30 and 100:1.
       Although PCDD/PCDF emissions cannot be continuously monitored,  operating and
emission  parameters which correlate with PCDD/PCDF emissions will be continuously
monitored and controlled.  These continuous compliance parameters include CO emission
limits, boiler steam load, and PM control device inlet temperatures. Opacity and SO2 are to be
continuously monitored to guarantee proper operation of the flue gas cleaning equipment. Each
MWC will also be subject to annual PCDD/PCDF compliance  tests.  The use  of these
continuous monitoring and compliance parameters will ensure that each MWC operates at
conditions necessary to control formation and emission of PCDDs/PCDFs.

Dioxin and Mercury Control Technologies
       Control technologies in the U.S. for PM and acid gas control also provide a degree of
control for PCDDs/PCDFs and Hg. Both PCDDs/PCDFs and Hg may be in a vapor-phase at
flue gas temperatures, and collection of trace quantities of these compounds is dependent on the
adsorption on fly ash and flue gas  cleaning sorbents with subsequent collection in a PM control
device. The capture efficiency of PCDDs/PCDFs and Hg in conventional MWC air pollution
control equipment used in the U. S. depends primarily on the amount of carbon in the fly ash,
the properties of sorbents injected into the flue gas, and the operating temperature of the PM
control device.
             Field tests have also shown that in semi-dry scrubbing systems, PCDDs/PCDFs
and Hg emissions decrease with increasing fly  ash carbon content.  Variations  in combustion
conditions affect the amounts of carbon in fly ash and its capacity for adsorbing semi-volatile
trace organics and Hg.  Increased combustion efficiencies needed to maximize destruction of
organics  reduce  the absorption  capacity of fly ash and its ability to capture semi-volatile
pollutants in PM control devices.  The formation and emission of PCDDs/PCDFs and emission

of Hg are affected by the PM control device operating temperature as the adsorption of semi-
volatile pollutants is reduced with increasing operating temperatures.
       Methods which can be used to enhance control of PCDDs/PCDFs and Hg in MWCs
equipped with conventional dry and semi-dry flue gas cleaning systems include:
       Enhanced PCDDs/PCDFs Control
              *      Good Combustion Practices,
                    Injection of Activated Carbon, and
                    Injection of Enhanced Lime Sorbents,
       Enhanced Control of Mercury
              *      Injection of Sodium Sulfide,
                    Injection of Activated Carbon, and
                    Injection of Enhanced Lime Sorbents.

PCDD/PCDF Formation Mechanisms
       There are probably three primary routes for PCDD/PCDF formation:  (1) gas-phase
reactions involving chlorinated precursors such as chlorobenzenes (CBs), chlorophenols (CPs),
or polychlorinated  biphenyls  (PCBs); (2) condensation  reactions involving gas-phase
precursors and fly ash; and (3) solid-phase reactions on the surface of fly ash involving metal
chlorides and fly ash carbon. 16-21  j^g tnir(j route of formation, which involves the reaction of
unburned carbon in fly ash to form  PCDDs/PCDFs, is called de novo synthesis. 17,18
       Gas-phase precursors can originate as waste thermal decomposition products or as high
temperature PICs.  Low temperature oxidation reactions involving fly ash carbon can also
produce CPs or other precursor compounds that in turn react to form PCDDs/PCDFs by surface
mediated reactions (condensation, absorption-desorption, etc.),22
       De novo  synthesis consists of low temperature carbon oxidation reactions which
provide the biaryl ring structures for PCDD/PCDF formation and metal ion catalyzed reactions
which  provide the necessary chlorine (Cl) for PCDD/PCDF formation. Low  temperature
carbon oxidation reactions may be catalyzed by metal ions or carbon structures similar to
activated carbon.23,24 j^  Q for (oxy)-chlorination reactions can be provided from either
metal chlorides in the fly ash or HC1 in the flue gas. 24,25
       De novo synthesis reactions generate a variety of chloro-organic compounds including
CPs,  chloro-benzonitriles, -thiophenes,  -benzofurans,  -benzothiophenes,  PCDDs,
-naphthalenes, PCDFs, and -benzenes (see Figure 1).2  Laboratory experiments (see Figure 2)
show that de novo reactions occur at temperatures ranging from approximately 250 to 600 C
with peak tetra- to octa-PCDD/PCDF formation rates near 300 and 470 C, respectively.20
Maximum formation rates are typically reported to occur near 300 C.1^-20  ^ temperatures

above 600 C, chloro-organics are rapidly destroyed, and at temperatures below 250 C reaction
rates result in minimal formation.

PCDD/PCDF Control at MWCs
       Stack emission of PCDDs/PCDFs from MWCs has been found to range from <0.01 to
> 400 ng TEQ/dscm (<1,0 to >20,000 ng/dscm),  depending on combustion and flue gas
cleaning conditions (see Figure 3).26,27,28 Although the stack emissions are dependent on
combustion conditions, the highest emissions are generally obtained with MWCs equipped with
only ESPs followed in order of decreasing emissions by DSI/ESP, SD/ESP, DSI/FF, and
       Factors affecting the formation and subsequent emission of PCDDs/PCDFs from
MWCs include the:
                  Composition and properties of waste,
                  Combustion  conditions,
                  Composition of flue gas,
                  Amount of entrained PM,
                  Hue gas time/temperature profile,
                  PM control device operating temperature, and
             *     Methods of acid gas and PM control.

Composition and Properties of Waste: Rapid changes in waste composition or properties may
cause combustion upsets and lead  to PCDD/PCDF formation. Although PCDDs/PCDFs are
formed during steady state combustion conditions, the amounts formed are believed to increase
substantially during combustion  upsets associated with improper feed conditions.  It is
important to blend or mix waste prior to combustion to reduce variations in heating content,
volatility, and moisture content. 13,14,15
      While waste composition probably affects the amounts of specific organics formed
during combustion, there is no conclusive scientific  evidence that  specific solid waste
components, such as polyvinyl chloride (PVC), are primarily responsible for the formation and
emission of PCDDs/PCDFs.29 Sufficient Cl is available from other waste components to
account for observed levels of PCDDs/PCDFs in MWCs.

Combustion Conditions: Any PCDDs/PCDFs contained  in the waste are believed to be
destroyed in active flame zones or  the high temperature regions of MWCs.''^  However, the
fuel composition and combustion  conditions determine the specific PICs that are necessary
precursors for PCDD/PCDF formation. These precursor compounds are formed by the thermal

destruction, oxidation, and synthesis reactions which occur in the burning waste bed, the active
flame region above the bed, and the high temperature regions of the furnace. Combustion
conditions and the time/temperature profile in the cooling zones downstream of the combustor
determine the amounts of PCDDs/PCDFs processor material entering flue gas cleaning devices
and the potential for formation within the devices.  PICs which have been  implicated in
PCDD/PCDF formation include: CBs, CPs, PCBs, and the carbon in fly ash.22,23,24,25
       GCP can be used to maximize the furnace destruction of organics and minimize the
downstream formation of PCDDs/PCDFs by controlling the amounts of PM carried out of the
furnace with flue gas. Furnace destruction of organics must include destruction of both gas-
and condensed-phase organics.  Field  test experiments have shown that  formation  of
PCDD/PCDF and other trace organics correlates with the CO and the amounts of PM carried out
of the combustor with flue gases (see Figures 4 and 5). 13,14,30,31,32  in extensive tests at a
RDF combustor, CO and THC were found to be the two best parameters for predicting PCDDs,
PCDFs, CBs, CPs, and PAHs at the SD inlet.32
       Waste and its associated thermal decomposition products must be exposed to elevated
temperatures for a sufficient time to completely destroy their organic components. Time scales
required for destruction are typically measured in milliseconds for gaseous compounds in active
flame zones. Combustion reaction times in the order of seconds to minutes may be required for
the complete destruction of small solid particles.  Combustion temperatures and residence times
of 980 C (1800 F) and 1 to  2 seconds, respectively, are generally believed sufficient to
thermally destroy gas-phase compounds J  However, even at temperatures of 980 C or higher,
residence times needed for the complete combustion of entrained solid  particles may  be
insufficient, and residual unbumed carbon in fly ash may lead to heterogeneous reactions which
form PCDDs/PCDFs.13
       The amount of excess air used for combustion must be high enough to minimize the
existence of fuel-rich pockets and low enough to avoid quenching of combustion reactions.7,13
The distribution of combustion air is also important. Burning refuse beds contain drying,
devolatization,  combustion, and burnout zones.  Each zone  requires a different  amount of
combustion air.  State-of-the-art MWCs often use zoned underfire air supplies to provide proper
air distribution to the refuse bed and overfire air to complete combustion of pyrolysis products
leaving the bed.'
       Poor mixing increases the amount of organic material available for the formation of
PCDDs/PCDFs. It may result  in local stoichiometries that are insufficient for the complete
oxidization of gas- and solid-phase organics. Poor mixing may also lead to the formation of
difficult-to-destroy soot particles. Methods of achieving good mixing include the use of furnace
configuration and overfire air jets.7,13

Composition of Flue Gas:  The effects of flue gas composition  on PCDDs/PCDFs are
complex.^' <22 Oxygen is required for the low temperature carbon oxidation reactions that are
associated with de nova synthesis. Oxygen and H^O are also required for the Deacon process
reaction  which provides Cl  for the chlorination of PCDDs/PCDFs or their precursor
compounds.  The Cl for the Deacon process reaction may come from either the inorganic
chlorides in fly ash or the HC1 in flue gas. PCDD/PCDF formation increases with increasing
levels of HC1 or Cl2 in combustion gases.25,33  Although the flue gas concentrations of C>2
and H2O may affect the rate of PCDD/PCDF formation, the waste moisture content and excess
air levels determine the concentrations of these two constituents.  It is generally not practical to
control the moisture content of wastes, and the amount of excess air must be fixed  at levels
needed to obtain good combustion.

Entrained Paniculate Matter: The entrainment and carryover of fly ash into the cooler regions of
MWCs may lead to the formation of PCDDs/PCDFs and other trace organics. Metal ions or fly
ash carbon can catalyze condensation formation reactions, and fly ash carbon can serve as the
source of organics for the de nova synthesis of PCDDs/PCDFs.  PM  carryover is determined
by the aerodynamic properties of particles, the method of waste combustion, and combustor gas
flow characteristics. Methods of limiting PM carryover include proper furnace design, control
of the underfire to overfire air ratio, the amount of excess air, and load  (refuse burn rate). ^3,15
        The correlation between PM carryover and PCDD/PCDF emission rates from tests at
the  Quebec City, Canada, Mass Burn Combustor is shown in Figure  5.30 These data, which
are  measured in the stack downstream of an ESP, show the effects of  changing combustion
conditions on emission of PCDDs/PCDFs. Changes in the PM carryover rate can be attributed
primarily to changes in the flue gas flow rate and the ratio of underfire to  overfire air. At higher
loads, increased gas flow rates increase entrainment and carryover of PM. Higher underfire air
flow rates also increase PM entrainment.  During the low combustion temperature tests at
Quebec City, Canada, excess air rates were increased to lower the combustion temperature.
This had the effect of increasing volumetric flow rates and particle entrainment. During the
poor combustion air distribution tests, the underfire to overfire air ratio was increased, thereby
increasing PM carryover.  Increasing emission rates  of PCDDs/PCDFs with increasing
amounts of fly ash is consistent with heterogeneous formation theories.

Time/Temperature  Profile:   Pilot scale  combustor experiments have  shown  that the
concentration of PCDDs/PCDFs in downstream flue gas depends on the  time/temperature
profile in the cooling sections of combustion systems.33,34,35 The time/temperature profile is

determined by the time required by flue gas and suspended PM to pass through the heat
extraction regions of  boilers, superheaters, and economizers. High flue gas temperature
quench rates reduce the time that entrained particles spend in the temperature range associated
with high PCDD/PCDF formation rates.

PM Control Device Operating Temperature:  ESPs and FFs can function as chemical reactors
that generate and emit PCDDs/PCDFs.36 A large fraction of the PCDDs/PCDFs entering PM
control devices is commonly associated with collectible fly ash. However, the large mass of
particles within the device can serve as a source for the synthesis of PCDDs/PCDFs.  Limiting
the temperature at which PM control  devices are operated is important in controlling  the
formation and emission of PCDDs/PCDFs.13,14,1536,37
      The ESP operating temperature is perhaps the most important variable affecting  the
formation and emission of chloro-organics in ESP systems. At PM control device operating
temperatures above 250 C, de novo  synthesis  reaction  rates become significant and  the
partitioning of PCDDs/PCDFs into a vapor-phase increases with increasing temperature.
      The results of tests to evaluate the effects of ESP operating temperature on the formation
and emission of PCDDs/PCDFs are depicted in Figure 6. These tests were conducted on a
mass burn refractory MWC  with a water spray flue gas quench chamber and an ESP located in
Montgomery County, Ohio.36  Quench water flow rates were adjusted to obtain nominal ESP
inlet temperatures of 300 , 200 , and 150 C. The test conditions included:  normal and poor
combustion (low temperature) tests at 300 C inlet temperature; normal combustion with and
without furnace injection of CaCOj at 200 C inlet temperature; and normal combustion with
furnace injection of CaCOj and duct injection of Ca(OH)2 at 150 C ESP inlet temperature.
      The flue gas concentrations of PCDDs/PCDFs were higher at the ESP outlet than at the
inlet for all tests, indicating  PCDD/PCDF formation within the ESP.    Under normal
combustion conditions  at the high ESP inlet temperature (300 C), ESP inlet concentrations of
PCDDs/PCDFs averaged 200  ng/dscm (mass) while stack concentrations averaged  17,000
ng/dscm. Reducing the ESP inlet temperature to 200 C without sorbent injection reduced
average stack emissions to 870 ng/dscm. For tests with furnace injection of CaCOj, stack
emissions of PCDDs/PCDFs averaged 1480 ng/dscm at an ESP inlet temperature of 200 C and
670 ng/dscm at 150 C inlet temperature. The lowest emissions (57 ng/dscm) were obtained
using duct injection of Ca(OH)2- Operating at the lowest practical ESP operating temperature is
critically important in minimizing PCDD/PCDF emissions.

Methods of Acid Gas  and PM Control: The methods of acid gas  and PM control are major
determinants of PCDD/PCDF emissions.  Acid  gas  controls modify the chemistry of

PCDD/PCDF formation, affect flue gas quench rates, and allow operation of PM control
devices at low operating temperatures. Low operating temperatures are necessary to control de
novo synthesis rates and partitioning of trace organics between vapor  and solid phases.
Efficient collection of PM is necessary to collect solid-phase organics. Vapor-phase organics
can be absorbed onto the surface of PM as it passes through the fly ash filter cake in FFs.
      FSI, DSI, and SD can be used to reduce acid gases, modify PCDD/PCDF formation
chemistry, and allow for  lower PM control device operating temperatures. Pilot scale
experiments have shown that injection of Ca(OH)2 into the flue gas at temperatures greater than
800 C significantly  reduces the formation  of PCDDs/PCDFs.33   The reduction in
PCDD/PCDF yield appears to result from both a reduction in the HC1 content of flue  gas and an
inhibitory effect on fly ash surface reactions. DSI can also be used to remove HC1 and reduce
heterogeneous  formation  rates  in  the PM control device,  but  substantial amounts of
PCDDs/PCDFs may be formed  upstream of the sorbent injection  point.   Most of these
PCDDs/PCDFs will be retained in the PM control device if the PM control device operating
temperatures are low enough.  SD systems combine the advantages inherent in high flue gas
quench rates, sorbents which probably modify PCDD/PCDF synthesis reactions, and low PM
control device operating temperatures.
      Flue gas concentrations of PCDDs/PCDFs can either decrease or increase across an
ESP.27  Increases are associated with high rates of PCDD/PCDF synthesis within a PM control
device.  PM control devices containing collected fly ash can serve as reactors for formation of
PCDDs/PCDFs.36 The amount formed will depend on the temperature, the mass of PM within
the control device, the composition of the fly ash, the composition of the flue gas, and the
residence time of PM within the device.  Maximum de novo synthesis reaction rates occur at
temperatures  ranging from 300  to 470 C.20    Lowering PM control device operating
temperatures to less than 250 C results in a major reduction in PCDD/PCDF formation rates
and alters the partitioning of vapor- and solid-phase PCDDs/PCDFs.  In  ESPs operating
temperature is critical, and it may be necessary to scrub  acid gases for the flue gas to permit
lowering the PM control device temperature to levels where acid gas corrosion is not  a problem.
      PM control device collection efficiencies >99  percent are  probably necessary to
adequately control PCDD/PCDF emissions. At the lower PM control inlet device temperatures
typically employed by  dry scrubbing  systems, formation  rates are greatly reduced  and
PCDDs/PCDFs are predominantly retained on captured fly ash. Although substantial quantities
of trace organics may be formed during the combustion process, most of the semi-volatile
organics are effectively collected in dry  scrubbing systems.  This is especially true of SD/FF

       MWCs equipped with SD/ESP systems are less efficient in controlling PCDD/PCDF
emissions than similar MWCs equipped with SD/FF, 27,38 j^g iatter devices have better PM
control efficiencies, and the flue gas is passed through a filler cake where PCDDs/PCDFs can
be adsorbed on fly ash and sorbent particles. A review of data from eight different combustion
units equipped with SD/ESPs indicated PCDD/PCDF emissions ranging from 9 to 173 ng/dscm
(mass).  All but one of these units had emissions of less than 75 ng/dscm, and the average for
the range of typical emissions was 38.1 ng/dscm.38
       The performance  of SD/ESP systems in controlling PCDDs/PCDFs can also be
improved by the injection of activated  carbon into the flue gas at the entrance to the SD system
or by use of a carbon-enhanced lime-based sorbent in place of iirne.39,40,41  Durjng three
EPA-sponsored tests at the Camden County, New  Jersey, MWC, stack concentrations of
PCDDs/PCDFs without activated carbon averaged 46.8 ng/dscm.  During three tests in which
360 mg/dscm of dry activated carbon  was injected into the flue gas upstream of the SD/ESP,
stack concentration of PCDD/PCDF averaged 5.6 ng/dscm.40,41  Jests in Europe on  MWCs
equipped with SD/FF and SD/ESP systems have also shown the effectiveness  of  carbon
injection for reducing PCDD/PCDF emissions.-^^
       An EPA review of data from 20  different combustion units equipped with  SD/FF
systems indicated PCDD/PCDF emissions ranging from 1 to 22 ng/dscm. Nineteen units had
emissions less than 12 ng/dscm and the average for these units was 6.6 ng/dscm. Two large
MWCs with DSI/FF systems had PCDD/PCDF emissions of 5 and 18 ng/dscm.38

Continuous Control of PCDDs/PCDFs
      .There is currently no  feasible method for  continuously measuring  PCDD/PCDF
emissions.  Continuous control of PCDDs/PCDFs is of concern from regulatory and risk
assessment perspectives.  EPA's strategy to ensure continuous compliance with PCDD/PCDF
emission limits is to place limits on CO concentrations, steam load, PM control device operating
temperature, and opacity.  The first three parameters are used to limit formation and partitioning
of PCDDs/PCDFs, and the final parameter (opacity) will ensure proper operation  of the PM
control device which is needed for effective collection of solid-phase PCDDs/PCDFs.  The
effectiveness of these parameters for continuously controlling PCDD/PCDF emissions is
verified by periodic compliance tests on each MWC that is subject to regulation.

Control of Other Organics
       Field test measurements show that a wide variety  of trace organics are formed during
combustion of municipal solid waste. Trace organics formed include PCDDs/PCDFs, CBs,
CPs, PCBs, PAHs, and a variety of volatile organics.  Analysis of data from the Quebec City

MWC mass burn tests and the Mid-Connecticut RDF combustor tests show that flue gas
concentrations of PCDDs/PCDFs, CBs, CPs, and PAHs all correlate with each other and with
flue gas concentrations of CO and THC.30,32  Measures taken to  control emission of
PCDDs/PCDFs are also effective in controlling CBs, CPs, and PAHs,  (It is expected that these
measures will also control PCBs, but the concentrations of PCBs in MWC flue gases are
generally so low that strong statistical correlations with other pollutants are not found.)

       Combustion controls are effective in controlling all trace organics. Dry and semi-dry
scrubbers with FFs are effective in controlling semi-volatile organics but the degree of control is
probably related  to the amounts of carbon in the fly ash.   Activated carbon or lime enhanced
sorbents should also enhance capture of all semi-volatile organics in MWCs equipped with dry
and semi-dry scrubbing systems. Dry and semi-dry scrubbing systems  are not effective for
controlling volatile organics, and the best method for controlling these pollutants is the use of
GCP as a preventive measure.

Mercury Control in MWCs
       The capture of Hg in flue gas cleaning devices depends on the :
                 Waste composition,
                 Flue gas properties (temperature, gas composition, moisture, etc.),
                 Hg form [speciation and phase (vapor or solid)],
                 Fly ash and sorbent properties, and
                 Type of control devices.

       The waste composition and the relative amounts of Hg in each component determine the
concentration of Hg in MWC flue gas. Hg mass balances from Environment Canada's Quebec
City mass burn test project indicated that more than  96  percent  of Hg in the MWC output
streams was in either  the collected ESP ash or the flue gas, indicating the  volatile nature of Hg
in MSW.30 Thermal-chemical calculations indicate that Hg is converted to elemental mercury
(Hg) in the high temperature regions of the combustor. As the flue gas cools, Hg is converted
to other Hg species.42,43

Mercury Speciation and Control Mechanisms
       The form of Hg  in flue gas depends on the flue gas composition and temperature.  For
combustion systems  containing substantial amounts of Cl in the waste (or fuel), the two
predominant forms of Hg at flue gas cleaning temperatures (< 300 C) are believed to be ionic

mercury (Hg2+) and Hg.42-45 Thermochemical equilibrium calculations indicate that the
Hg2+ win be predominantly mercuric chloride (HgC^j).^
       Most metals condense to form solid particles as flue gas is cooled so that they can be
collected as PM. However, both Hg and HgCl2 are vapors [Hg(v)] at typical flue gas cleaning
control device operating temperatures (300 to 140 C), and special methods must be devised for
their capture.-** 10
       Hg in MWC flue gases can be captured if it is in the solid-phase [Hg(s)J or is adsorbed
on fly ash or special sorbents such as activated carbon or enhanced lime-based sorbents
containing activated carbon. Hg(v) capture without the use of special sorbents depends on the
amount of carbon in the fly ash. Well-designed and well-operated mass burn combustors have
little carbon in their fly ash and, even when equipped with SD/FFs or SD/ESPs, they exhibit
Hg control levels below 50 percent.  Conversely, RDF combustors  contain relatively high
amounts of carbon in the fly ash (> 2 percent). And, they commonly exhibit control efficiencies
above 80 and 90 percent when equipped with SD/ESPs and SD/FFs, respectively.  Figure 7
shows the  distribution of Hg stack concentrations for RDF and non-RDF MWCs equipped with
SD/FF and SD/ESP systems.38
       Two  techniques employed for Hg capture in dry flue gas cleaning systems are the use of
activated carbon and sodium sulfide (Na2S).9*10 js^S, a crystalline solid, is dissolved in
water and injected upstream of the flue gas cleaning equipment.  Hg(v) and Hg2+(v) are
converted  to a solid form of Hg [mercury sulfide (HgS)] that can be collected in a PM control
device. Na2S has been used at MWC facilities in Europe and Canada for Hg control.  Na2S
test results from European facilities show Hg emissions ranging from 40 to 70 jig/dscrn and
removal efficiencies from 65 to 90 percent JO Na2S is not currently being used in the U.S.
       Activated carbon can be used in three ways to control Hg(v) emissions: (1) it can be
injected as a powder in dry or semi-dry scrubbers to absorb Hg(v) for subsequent collection in
an ESP or FF,9>10 (2) it can be used in a lime-enhanced  sorbent system, combining both lime
and carbon in a single multi-pollutant sorbent,46 and (3) flue  gas can be filtered through a
carbon bed polishing filter downstream of other air pollution control devices to enhance removal
of Hg(v) and other pollutants.^  Carbon bed filters are currently being applied to European
MWCs where they are primarily used to improve emission control of PCDDs/PCDFs, Hg, and
other trace metals.  '

Carbon Capture Mechanism
       The adsorption of Hg and organics by activated  carbon and coke is controlled by the
properties of both the carbon and the adsorbate, and by the conditions under which  they are
contacted. This phenomenon is generally believed to result from the diffusion of vapor -phase

molecules into the pore structure of carbon particles. These molecules are retained at the surface
in the liquid stale because of intermolecular or Van der Waals forces.
       As the temperature falls, or as the partial pressure of the vapor above the carbon rises,
the average time that a molecule resides on the surface increases.  So does the fraction of the
available surface covered by the adsorbate.  However, the carbon surface is not uniform and
consists of sites whose activities vary. More active sites will become occupied first and, as the
activity of the remaining  available sites decreases, the adsorption energy will change.
       The physical structure of activated carbon and coke is not known in detail, but it is
believed to contain  randomly distributed pores in the carbon, between which lies a complex
network of irregular interconnected passages.  Pores range in diameter down  to a few
angstroms, and provide an internal surface area from 300 to 1,000 m^/g of carbon.  The
volume of pores at each diameter is  an important variable that directly affects carbon
       Since adsoiption  lakes place at the carbon/gas interface, the surface area of the carbon is
one of the mosi important factors lo consider. The second factor is  the pore radius. Laboratory
bench scale tests have shown lhat both  increasing the surface area and  the addition of sulfur
compounds result in higher adsorption rates of Hg .  Most of the  laboratory work on carbon
adsorption has been done on Hg, not with the Hg compounds normally found  in MWC flue
       The actual adsorption capacity of carbon is affected by:
              *       Gas temperature,
              *       Inlel concentrations of Hg,
              *       Species of Hg,
              *       Type of carbon and surface area,
                     Contact time,
              *       Flue gas moisture,
                     Acid content of flue gas, and
                     Concentration of organics such as dioxin.

Performance of Activated Carbon Systems
       The performance of activated carbon systems depends primarily on the carbon injection
rate, carbon injection method, carbon properties, flue gas temperature, and PM control method.
Performance tests in the U.S. and Europe have primarily been limited to the application  of
carbon injection to mass burn MWCs equipped with SD/FF or SD/ESP systems. 10,39,40,48
       EPA has sponsored two major field tests on the injection of powdered activated carbon
for Hg control and has selected this  technology  as the  basis for Hg emission  control

requirements on MWCs.^0,41,48-50 Both tests were conducted at facilities with conventional
mass-burn  waterwall combustors. The first was conducted on an MWC in Stanislaus County,
California, equipped with a SD/FF system.  The second was conducted on two MWCs in
Camden County, New Jersey, equipped with SD/ESP systems. These tests show that stack
concentrations of Hg depend on the Hg concentration in the flue gas (SD inlet concentration),
the carbon content of fly ash, and the operating conditions of the carbon injection system.
       Mercury concentrations in MWC flue gas are highly variable with time. In MWCs the
total solid-phase flue gas carbon (carbon in fly ash plus the carbon injection rate) appears to be
the key determinant of Hg capture.  In the absence of carbon injection, the amount of Hg
captured depends on the amount of carbon in the fly ash.  When the fly ash carbon content is
low or when Hg concentrations are high, poor removal efficiencies are obtained.  When the fly
ash carbon content is high and the Hg concentrations are low, high removal efficiencies are
       Injection of powdered activated carbon into the flue gas can be used to increase solid-
phase carbon concentration. Increasing the carbon injection rate reduces both the average and
variability of emissions.  At high carbon injection rates, there is generally sufficient carbon to
capture low or high  levels of Hg.  The amount of excess carbon needed for continuously high
levels  of capture will depend on the  variation of Hg concentration  in the flue gas.  Highly
variable Hg inlet concentrations will require high excess carbon injection rates to ensure
continuous Hg capture.
        In SD/FF tests at the Stanislaus County MWC, Hg capture without carbon injection
ranged from 16 to 46 percent.  Outlet Hg concentrations for these tests ranged from 311 to 538
[ig/dscm.   Hg capture increased with increasing carbon injection rates and, at the highest
injection rates of approximately 70 to 100 mg/dscm, Hg outlet concentrations ranged from 17 to
77 [ig/dscm (see Figure 8).4&"50 5> outlet temperatures at Stanislaus County normally ranged
between 136 and 145 C.
              During the Camden County  SD/ESP carbon injection test project, Hg capture
without carbon injection ranged from  18 to 92  percent. ^0,41  When dry carbon injection rates
exceeded 150 mg/dscm and the ESP inlet temperature was 132 C, stack emissions of Hg were
generally less than 80 |ig/dscm (see Figure 9).  The dependency of Hg reduction efficiency on
the total solid carbon concentration in  the flue gas during the Camden County tests is shown in
Figure 10.
       The performance of activated carbon in absorbing Hg is dependent on temperature. The
temperature at the inlet to the PM control device is normally used as a parameter in evaluating
the performance of the device in collecting condensed or absorbed pollutants. The PM control
device inlet temperature tor SD/FF and SD/ESP systems on MWCs is normally between 135

and 145 C. Tests on the Camden County SD/ESP system at 177 C indicated only moderate
reduction in Hg capture relative to similar tests at 132 C (see Figure lOJ.^Q'^l  Temperature
variations over the normal operating range of SD/FFs and SD/ESPs can be expected to have
only minor effects on Hg capture. Similar tests on European MWCs have shown that carbon
injection can be used to reduce Hg emissions in SD/FF and SD/ESP systems to less than 80
       ESPs and  wet scrubbers  are commonly used to control emissions from European
MWCs. Some European plants have installed activated carbon beds downstream of the primary
air pollution control devices to act as polishing filters for the control of metals, dioxins, and acid
gases.  The use of activated carbon filter beds in combination with conventional control
equipment has demonstrated Hg reductions exceeding 99 percent and Hg outlet concentrations
of less than 1 {J.g/dscm.47

Enhanced Lime-Based Sorbents
       Several enhanced lime-based sorbents are commercially available for use in  MWCs.
One enhanced sorbent (Scansorb) is designed for improved  HC1 and  S(>2 control in dry
injection systems.-'1 Another sorbent (Sorbalit) is a multipollutant sorbent designed for control
of acid gases, Hg,  and trace organics/ Sorbalit is produced by mixing lime, surface-activated
carbon, a sulfur-based compound, and other additives. The  carbon content can range from 4 to
65 percent depending  on die technical and economic requirements of each project.

       Comparative performance tests between Sorbalit and a typical activated carbon on a
mass-burn MWC equipped with an SD/FF system has indicated equivalent or slightly higher
capture of Hg  by the  enhanced lime-based sorbent.^6 The lime-based sorbent captured 87.7
percent of the total Hg, while the conventional  activated carbon captured 84.2 percent.  Analysis
of the sampling train  data indicated that it captured 83.2 percent of the vapor-phase Hg, while
the conventional carbon captured 77.6 percent. Additional performance testing is being planned
to evaluate the effectiveness of Sorbalit in controlling emissions from MWCs with other flue
gas cleaning equipment configurations.

Form of Mercury Emissions
       In conducting risk assessments, it is important to estimate the form and speciation of
Hg stack emissions. The transport, deposition, and environmental uptake of Hg are dependent
on the form and speciation of Hg. Several studies estimate the speciation of Hg in MWC flue
gases.   Metzger  and Braun  estimate that nearly all  Hg in  MWCs at flue  gas cleaning
temperatures is in the form of mercury chlorides,^"  Lindqvist and  Schager estimate that the

speciation of Hg in raw flue gases is approximately 20 percent Hg , 60 percent Hg2+, and 20
percent Hg(s).^ Pacyna estimates that Hg emissions from European waste incinerators consist
of 10 percent Hg , 85 percent Hg2+, and 5 percent Hg(s).^2
       There is currently no validated U.S. method for determining the speciation of Hg in
stack gas. However, information on the chemical behavior of Hg and the distribution of Hg in
EPA's multimetal sampling train (Method 29) can be used to estimate the form and speciation of
Hg in the MWC stack gas. These estimations are valid only for measurements downstream of
the air pollution control devices. The phase and speciation of Hg at inlet sample locations can
be significantly affected by PM collected in the Method 29 probe and filter.  For outlet samples,
Hg found in the probe and filter can be assumed to have been either vapor-phase Hg absorbed
onto PM or a solid-phase Hg compound.  Both are associated with PM as designated by
Hg(PM).  HgCl2 is soluble in water and should be removed in the HNOg/^C^ impingers.
Hg found  in the  downstream  KMnC^/^SC^  impingers was probably  Hg(v).   The
distribution of multimetal train samples collected during the activated carbon injection tests at
the Camden County MWC and Stanislaus County tests is shown in Figure 11.40,41
       For the Camden and Stanislaus County tests, the fraction of Hg(PM) was generally
below 5 percent and exceeded 10 percent for only one test Tests with stack concentrations of
Hg >100 p,g/dscm represent tests without carbon injection or low carbon injection feed rates.
For these tests, Hg ranges from 2 to 26 percent of total Hg.  As carbon injection rates and Hg
capture increase, the percentage of Hg  as a fraction of total Hg increases. This implies that
Hg2+ is more easily captured by activated carbon than Hg.  For stack concentrations of Hg
<50 |ig/dscm, the fraction of Hg ranges from approximately  14 to 72 percent.
       From the results of these tests it can generally be concluded that, for MWCs equipped
with SD/ESPs and SD/FFs, the stack  emission of Hg(PM) is negligible unless further Hg is
absorbed on the surface of PM between the stack sampling location and the stack exit.
       At low levels of control, the stack concentration of Hg is probably  15 to 30 percent
Hg(v) and the rest is Hg2+(v) and Hg(PM). In MWCs with SD/FF or SD/ESP systems, stack
concentrations of Hg(PM) are probably less than 5 percent. At high levels of control, Hg2+(v)
is  selectively removed, increasing the relative concentration of Hg  (v).  The relative
concentration of Hg (v) may be 50 percent or higher.

       Dioxin formation is predominantly associated with heterogeneous  reactions involving
fly ash.  These low-temperature synthesis reactions can occur downstream  of the combustor at
temperatures ranging from approximately 250 to 600 C.

       The flue gas cleaning systems most commonly employed on MWCs in the U.S. include:
ESPs, DSI/FFs, SD/ESPs, and SD/FFs.
       Spray dryers and FFs can be used to continuously reduce PCDD/PCDF emissions to
less than 20 ng/dscm. Activated carbon, which is needed for Hg control in many MWCs, will
provide additional PCDD/PCDF control.
       Spray dryers and ESPs can be used to reduce typical PCDD/PCDF emissions from
mass burn cornbustors to less than 75 ng/dscm. Injection of activated carbon, to control Hg
emissions,  can be used to  further reduce PCDD/PCDF emissions to less than 30 ng/dscm
(about 0.5 ng TEQ/dscm).
       The Hg in MSW is volatilized during combustion and converted to elemental and ionic
Hg. Hg in MWC flue gas is believed to be predominantly HgCl2 and Hg. Both are predicted
to be in a vapor phase at stack gas temperatures.
       In dry flue gas cleaning systems, Hg(v) can be adsorbed onto the surface of particles for
collection in PM control devices.  Hg(v) can be adsorbed either on the residual carbon in fly
ash, on activated carbon, or on enhanced lime-based sorbents which have been injected into the
flue gas.
       RDF cornbustors have relatively high amounts of carbon in their fly ash (>2 percent)
and those equipped with SD/FFs may attain Hg removal efficiencies of >90 percent  due to
adsorption of Hg(v) onto the fly ash carbon.  Other  types of MWCs, such as water-wall mass-
burn cornbustors, may require the injection of activated carbon or enhanced lime-based sorbents
to obtain efficient Hg(v) control.
       Nearly all of the uncontrolled Hg in MWC stack gas  is in a vapor form. Method 29
sampling train data suggest that carbon absorption  methods collect Hg2+(v) more efficiently
than Hg(v).  As Hg removal efficiencies increase, HgCl2 (v) is selectively removed and the
proportion of Hg that is Hg(v) increases. In MWCs equipped with SD/FFs and SD/ESPs, the
relative amount of Hg(PM) in stack gas will generally be less than 5 percent

       The major portion of the work covered in this paper was supported  by  the U. S.
Enviornmental Protection Agency's, Municipal Waste Combustion Research Program. Testing
of the enhanced lime-based sorbent (Sorbalit) was partially supported by the Dravo Lime

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                    Table 1. Basis for Proposed MACT Performance Requirements
                                      (September 20, 1994)
Proposed Requirements

Emissions Guidelines (EG) - Existing Plants
Small (>35 to 225 Mg/day)
Large (>225 Mg/day)

New Source Performance Standards (NSPS) - New Plants
Small (>35 to 225 Mg/day)
Large (>225 Mg/day)
                                            Basis for Emission Limits
                                            GCP + DSI + ESP + CI
                                            GCP + SD/ESP (or SD/FF)
   CI + SNCR
                                            GCP + SD/FF + CI
                                            GCP + SD/FF + CI + SNCR
a Technologies which provide equivalent or better performance may also be used.
b GCP     =   Good Combustion Practice
  ESP     =   Electrostatic Precipitator
  DI       =   Dry Injection of Sorbent (FSI = Furnace Sorbent Injection and DSI = Duct Sorbent Injection)
  CI       =   Carbon Injection
  SD/ESP  =   Lime Spray Dryer Absorber and ESP
  SD/FF   =   Lime Spray Dryer Absorber and Fabric Filter Baghouse
  SNCR   =   Selective Non-catalytic Reduction
                 Table 2. Proposed Good Combustion Practice Requirements for MWCs
                                      (September 20, 1994)
CO Requirements
Tvne of Combustor
                                                CO Emission Limits
                                       EG Limit,  ppmv      NSPS Limit, ppmv
                                        (Avg. Time, h)         (Avg. Time, h)
Mass Bum Water Wall (MBWW)
Mass Bum Refractory Wall (MBRW)
Mass Burn Rotary Water Wall (RWW)
Mass Burn Rotary Wall Refractory (RWR)
Refuse-Derived Fuel Stokers (RDF)
Huidized Bed Combustors (FBC)
Modular Combustion Units (MCU)
Coal/RDF Mixed Fuel-Fired (Coal/RDF)
                                             100  (4)
                                             100  (4)
                                             250 (24)
                                             100 (24)
                                             200 (24)
                                             100  (4)
                                              50  (4)
                                             150  (4)
100  (4)
100  (4)
100 (24)
100  (4)
150 (24)
100  (4)
 50  (4)
150  (4)
2,     Load not to exceed maximum load demonstrated during most recent PCDD/PCDF compliance tests.
3.     PM control device inlet temperature not to exceed level demonstrated during most recent PCDD/PCDF
compliance tests.
4.     Chief facility operator,  shift  supervisors, and control room  operators must meet training and
certification requirements.

                             Table 3.  Proposed Emission Limits for MWCsa
                                         (September 20,1994)

Guideline Limits
- Existing Plants
(or % Reduction)

ng/dscm [ng TEQ/dscm}b
Opacityc, %
Cd, mg/dscm
Pb, mg/dscm
Hg, mg/dscm
HC1, ppmv
SO2 ppmv
NOX, ppmv
a All emissions corrected
" Aw*fan/a f\f tHrv/ cto/l
>35 to 225 Mg/Day
60 [1.0]
0.08 (85)
250 (50)
80 (50)
to 7 percent 0^
r lv*c tc 11 cf rn"t K"OA \/T/fli/^H
>225 Mg/Day
30 [0.5]
0.08 (85)
35 (95)
35 (75)

1 O *2 T"i"v t/^ >nn ttrolp'r*!
NSPS Limits - New Plants
(or % Reduction)
Large and Small
^35 Mg/day
13 [0.2]
0.08 (85)
25 (95)
30 (80)

fc V*oc/i"l f\r\ I ntf*m<^t i /^n nl T*/
Equivalency factors.  Values are weight of total tetra- through octa- cogeners.  Values in brackets for [toxic
equivalents based on 1989 International Toxic Equivalency (TEQ) factors].
c   EPA Method 9. Limit for 6-minute averages.
    24-hour averaging time.
e   Applies to large plants only. 24-hour averaging time.










Di- to Octa-
 Fiy Ash
 Heated in
 Moist Air
                   5000  10000 15000 20000 25000 30000
                 Organics Formed, ng/g
          Figure  1.    Chloro-organies Formed
                       During De Nova Synthesis

i ROO-
1 nnn~
n J






Fly Ash Heated
in Moist Air
Tetra- to octa-
                250  300   350   400   470   550
                        Temperature, C
         Figure 2.  Effect of Temperature on
                   De Nova Formation Rates
                   of Tetra- to Octa-PCDD/PCDF






1 000 j
1 , i , , . . , !

j ^ x v* y^y
1 00 J orfT^S ^ 'K V
:  * v V

10 !


1 -

0.1 7.

0,01 i
0.001 !

0,0001 -

(x:'': ^
;'. "'- : r4
x x-
'"': -~; . N/^ ' ^

/V' "j" ,.| .r-, ,, ' >
AI, jit ^.pV-1'-!'-' '
+ ^!- 'to 'J
-i- ^%q> ^
jjpT 4j-
fj)Q (|
i ~i* I
o + ''"



i i !
200 300 400 500
Temperature, F







150           200

   Temperature, C
                Figure 3.   Dependency of PCDD/PCDF Emissions on Technology and
                          PM Control Device Operating Temperature [36].


R2 = 0.70

o Good o
 Poor o

pcmtion !

                                  CO  at 12% COz, ppm
           Figure  4.    Relationship Between CO  and PCOO/PCDF
                       Concentrations at SD inlet, Mid-Connecticut WIWC



                        Uncontrolled  Asb/Refuse  Fed,  kg/Mg
            Figure 5.    Relationship of PM Carryover  to  PCOO/PCDF
                        Emissions, Quebec City MWC







n 1

	 	 	 	 .-. 	 	 -^-v 	 	 	

4 T^

w n

/" A


{ ' ' I - fl IQ LJ U L L \~f 3 1 U I 1 1 7
- LJ 	

1 i ' 1 ' 1 r I ' 1
0 150 200 250 300 35C
                   ESP InjLet Temperature, C

  Figure 6.   Effect of ESP inlet Temperature on PCDD/PCDF

            Formation, Montgomery County MWC




                  m Non-RDF  p. RDF
                  aid        L..-.1
               Figure 7.  Hg Capture in MWCs with. SD/FFs and SD/ESPs
                         Large Plants (>225 Mg/d)

















 40 -

 20 -

- 0

                       500                  900

                      Inlet Hg Concentration, ug/dscm at 7% 02
                   LFR = Low Feed Rate (approximately 6.6 kg/h)
             	*  MFR = Medium Feed Rate (approximately 13.2 kg/h)

                            Feed Rate (approximately 26.4 kg/h)
      Figure 8.    Performance of Activated Carbon in  SD/FF

                   System, Stanislaus County MWC

 rs     *



o   200

                  300           400

Injected Carbon, mg/dscm @ 7 % 62
                   Dry Carbon @ 1 32 C A Wet Carbon @ 1 32 C *  Dry Carbon @ 1 77 C
               Figure 9.   Effect of Injected Carbon on Mercury Control in

                          SD/ESP, Camden County MWC

2    60-

                               200         300         400

                                 Total Carbon, mg/dscm @ 7% 02
                  Dry Carbon @ 132 C 'A Wei Carbon (g 132 C -  Dry Carbon @ 177 C
            Figure  10. Effect of Total Carbon on Mercury Control in
                          SD/ESP, Camden County MWC
700 "
60 0-
40 0 "
300 '
20 0 "

 A Al


* m



1 ^,
i * L


^, 	 ^~,~....


            0   100 200  300 400 500  600  700 800
                 Stack Concentration of Hg, ^g/dscm
        Figure 11. Distribution of Hg in EPA Method 29
                Sampling Train, Camden County and
                Stanislaus County Carbon Injection
                                                           Elemental Hg
                                                           Solid Phase Hg

      (Please read Instructions on the /reverse before completing,
                                                       3. RE
 Control of Air Pollution Emissions from Municipal
 Waste Incinerators in the U. S. A.
                                                       5. REPORT DATE
                                    6. PERFORMING ORGANIZATION CODE
 James D. Kilgroe (EPA) and Anthony Licata
                                    8. PERFORMING ORGANIZATION REPORT NO.
 Licata Energy and Environmental Consultants,  Inc.
 345 Concord Road
 Yonkers,  New York 10710
                                    10, PROGRAM ELEMENT NO.
                                    11. CONTRACT/GRANT NO.
                                      NA (inhouse/cooperative)
 EPA, Office of Research and Development
 Air Pollution Prevention and Control Division
 Research Triangle Park, NC  27711
                                                       13.TYPE.OF REPORT AND PE
                                                        Published paper; 1
                                    14. SPONSORING AGENCY CODE
is.SUPPLEMENTARY NOTES  EPA project officer is James D.  Kilgroe,  Mail Drop 65, 919/541-
 2854. Presented at Seoul International Waste Treatment Technology Conference and
 Exhibition, Seoul, Korea, 8/23-27/95.
i  BSTRACT Tne paper summarizes EPA's municipal waste combustor (MWC) regula-
 tions, proposed in  September 1994. The paper identifies the technologies on which
 they are based and discusses accumulated knowledge on the control of polychlorinated
 dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and mercury
 (Hg), In addition to the MWC regulations,  EPA is also currently developing regula-
 tions for  two other types of solid waste incinerators:  medical waste incinerators,
 proposed in February 1995; and hazardous waste combustors,  scheduled for proposal
 before the end of 1995.
                              KEY WORDS AND DOCUMENT ANALYSIS
                                           b.lDENTIFIERS/OPEN ENDED TERMS
                                                 c. COSATI Field/Group
Pollution Control
Stationary Sources
Municipal Waste
Medical Waste
Hazardous Waste
13 B

 Release to Public
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