United States
Environmental Protection
Agency
Hazardous Waste Engineering
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-86/011 July 1986
Project Summary
Control of Air Emissions from
Hazardous Waste Combustion
Sources: Field Evaluations of
Pilot-Scale Air Pollution Control
Devices
C. W. Westbrook, C. E. Tatsch, and Lawrence Cottone
Pilot-scale air pollution control devices
supplied by Hydro-Sonics Systems, ETS,
Inc., and Vulcan Engineering Company
were installed at the ENSCO, Inc. In-
cinerator in El Dorado, Arkansas in the
spring of 1984. Each of these units
treated an uncontrolled slipstream of
the incinerator exhaust gas. Simulta-
neous measurements of the total par-
ticulate and HCI in the gas streams were
made at the inlet to and exit from the
units using an EPA Method 5 sampling
train. Particle sizing at both locations
using Andersen impactors was also
done. The units supplied by Hydro-
Sonics Systems and ETS, Inc. exhibited
a high degree of HCI and paniculate
matter control. The Hydro-Sonic Tandem
Nozzle SuperSub Model 100 gave the
best overall performance for HCI and
particulate control and ability to ac-
commodate the variable composition of
the exhaust gas.
This Protect Summary was developed
by EPA's Hazardous Waste Engineering
Research Laboratory, Cincinnati, OH, to
announce key findings of the research
project that Is fully documented In a
separate report of the same title (see
Project Report ordering Information at
back).
Introduction
Much hazardous waste generated has
characteristics that make incineration the
disposal method of choice. Incineration
of these wastes must be performed ac-
cording to the applicable regulations of
the Resource Conservation and Recovery
Act (RCRA) and State and local regula-
tions. The RCRA regulations specify the
destruction and removal efficiency (ORE)
that must be achieved for principal waste
components and set limits for the emis-
sion rates of particulate matter and
hydrogen chloride (HCI).
Purpose
The purpose of this project was to
evaluate innovative air pollution control
devices and to test their performances on
commercial-scale facilities. The specific
goals were to examine the cleaning
capabilities of each device under specified
operating conditions. The pollutants to be
monitored were particulates; total mass,
and as a function of particle size; and
hydrogen chloride (HCI).
The data developed in the project will
be useful to EPA and others in the waste
management community to assist in
optimizing the control of air emissions
from hazardous waste combustion.
Approach
Three vendors with pilot units meeting
the project criteria agreed to participate.
They are Hydro-Sonics®* System, Inc.;
ETS, Inc.; and Vulcan Engineering. The
Hydro-Sonic® pilot unit is a wet scrubber
that operates by fine atomization of water
"Mention of trade marks or commercial products
does not constitute endorsement or recommenda-
tion for use.
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into the gas stream resulting in HCI
capture and particle growth with final
removal by cyclonic action. The ETS, Inc.
unit uses dry lime injection for paniculate
capture. The unit provided by Vulcan
Engineering is a high temperature
(>550°C, 1000°F) metallic weave filtra-
tion system. It is not currently designed
for acid gas control.
A commercial hazardous waste incin-
erator owned by ENSCO, Inc. in El Dorado,
Arkansas was selected for the study.
A pilot unit was installed to permit a
slipstream of particulate-laden gas from
the emergency bypass stack to be drawn
through the unit. Inlet and outlet gas
streams were sampled simultaneously
by EPA Method 5 for the concentration
and total mass of the particulate matter
and HCI. Particle size distributions were
also determined at both locations.
Each APCD vendor operated his own
equipment and was allowed to vary
conditions to test the performance of the
unit. ENSCO operated their facility in a
routine manner during these tests. No
special fuel blends or operating proce-
dures were used to accommodate the
units.
Test Source Description
The host plant for these tests was
ENSCO, Inc.'s incineration complex in El
Dorado, Arkansas. This permitted facility
primarily incinerates polychlorinated
biphenyl (PCB) contaminated oils and
capacitors.
The plant is designed to receive and
incinerate whole capacitors. The shredded
parts are transported with a screw con-
veyor into a rotary kiln. The kiln exit gas
passes through a cyclone that removes
much of the large suspended particulate
matter. The gases then pass into a two-
chambered afterburner referred to as the
thermal oxidation unit (TOU). The up-
stream side of the afterburner can be
fired with PCB-containing oils or other
high Btu liquids.
Gases leaving the TOU are drawn into
a custom-designed wet scrubber. This
unit consists of two circulating water
loops. The first, prequench, loop removes
the bulk of the particulate and HCI. Lime
slurry is added for pH control. Slowdown
is routed to a pond for solids settling. The
clarified water is recycled. The second
loop is comprised of a jet eductor, knock-
out vessel, and demister. Fresh makeup
water is added to maintain inventory. All
blowdown from this loop is used as a
makeup to the first loop. No water is
discharged from this system except for
that evaporated and carried out with the
stack gas.
The incinerator typically operates 24
hours per day, 7 days per week. In general,
wastes of a specific class are accumulated
onsite until sufficient quantity is available
for burns of at least one day. This permits
achieving and maintaining steady-state
incineration conditions.
During these tests, accumulated wastes
were incinerated on the schedule deter-
mined by plant management. No special
wastes were burned or excluded. Close
contact was maintained with plant per-
sonnel so that the APCD testing spanned
only one operating condition, insofar as
possible.
Description of APCD Connection
to Plant
Connection was made to the emergency
bypass stack. The stack, located between
the TOU and the scrubber, is refractory
lined. Openings around the stack cap
were plugged to prevent air infiltration
into the stack. A stainless steel duct was
connected to a flanged opening in the
stack. The duct connected to a vertical
section leading to a Hastalloy cooling
section. Gas cooling was by direct water
spray. A temperature control device
mounted at the exit of the cooling section
modulated the water flow. The cooled
gas was then ducted to the APCD con-
nection via a 12-inch ID 17-foot horizontal
run of insulated carbon steel pipe. The
APCD gas inlet sample ports were located
near the midpoint of this duct. The two
ports were on the vertical and horizontal
axes perpendicular to the gas flow.
Test Method Description
The test program was designed to
withdraw a slipstream of incinerator ex-
haust gas and to test the APCD's per-
formance in removing particulate and
HCI.
Both the concentration of total par-
ticulate in the gas stream and particulate
mass per unit time were determined using
EPA Method 5. The impinger solutions in
the back half of the train provided
equivalent information for HCI. The par-
ticle size distribution at both the inlet and
outlet test locations was determined using
Andersen cascade impactors.
Due to the large difference in particle
loadings between the inlet and outlet
sites, it was not possible to obtain simul-
taneous impactor runs spanning the same
time interval. Typically, 5 to 7 minutes
operation at the inlet site produced
optimum stage loadings. Operation for
60 to 90 minutes was required at the
outlet location to collect an adequate
sample. Impactor runs were arranged to
coincide with one or more Method 5
runs.
An onsite laboratory was set up to
reduce as much of the test data as pos-
sible. Facilities were available to properly
clean all of the test equipment, recover
samples, and to desiccate the particulate
catches. A certified accurate balance was
used to weigh all of the samples. A
chloride ion-specific electrode and sup-
porting electronics were available to
measure chloride concentrations in the
Method 5 train back-half impingers.
Chloride audit solutions were onsite to
audit this procedure.
The impactor data were processed at
the conclusion of the test using the
Particulate Data Reduction (PADRE)
program.1
Hydro-Sonics Air Pollution
Control Device
General Description
Lone Star Steel Co. originally developed
this wet scrubber to control particulate
emissions from various iron and steel-
making operations. It has been used on
electric arc furnaces, coke oven emis-
sions, open hearth steel furnaces, and
sintering plants. The scrubbers have also
been used on exhaust streams containing
uranium hexafluoride and its hydrolysis
products with particulate removal ef-
ficiency consistently exceeding 99
percent.
There are three versions of the scrub-
ber: The Steam-Hydro, the Tandem Nozzle,
and the SuperSub. All versions have the
same basic concept. Water is atomized
into the waste gas stream forming water
droplets of about the same size as the
particulate. The gas stream then enters a
turbulent contact zone in which the
particles are wetted and vapors are
absorbed. Particle growth then takes place
in an agglomeration zone. Because of the
design, a single waste droplet may contain
hundreds of micronic and submicronic
dust particles. As a result of the growth
of droplets containing particulate into in-
creasingly large size, the initial size of the
particulate has only a small effect on its
removal. Actual removal of the agglomer-
ated particle is accomplished in a specially
designed low-pressure-drop cyclone.
Water and particulate are gravity drained
from the cyclone bottom, and the cleaned
gases exit through the top. Demisters are
not required.
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The Steam-Hydro employs a supersonic
ejector drive to provide the energy for
pumping and cleaning the polluted gas.
Steam or compressed air is commonly
employed as the working fluid. The gas is
drawn into the unit by the ejector nozzle
which is fitted with a water injection ring
at the exit of the nozzle. The expanding
jet causes violent shattering of the water
droplets and turbulent mixing of gas and
water. The steam version is most attrac-
tive when there is a source of waste heat
available to generate the high-pressure
steam.
The Tandem Nozzle scrubber uses a
fan drive to pump the polluted gas and to
provide the energy to generate the fine
water droplets. The system uses two
subsonic nozzles and agglomeration sec-
tions in series. Both nozzles are equipped
with water spray rings. The first section
serves to condense vapors, remove the
larger particulates, and initiate growth of
the fine particulate. Additional water is
atomized at the exit of the second nozzle
and is turbulently mixed to continue the
agglomeration of the particles.
The SuperSub version of the system is
a combination of the above two system
concepts. A small supersonic ejector
(steam or air) is located upstream of the
subsonic nozzle. The system's main driv-
ing force is fan power as in the Tandem
Nozzle version. This arrangement provides
good water atomization for fine particle
control coupled with the lower energy
requirements of the fan drive. Water
consumption is about the same as a
venturi scrubber.
Test Results
Test data for these units were collected
between March 15,1984, and March 23,
1984. Table 1 shows the removal ef-
ficiency data for total particulate and
chloride organized by the APCD operating
version. With the exception of the Tandem
Nozzle runs, chloride removal for all
combinations was greater than 98 per-
cent. Runs using recycle water from the
ENSCO scrubber show higher removal of
chloride than those using freshwater.
Since the recycle water contained some
alkalinity, this is not surprising. In a
commercial application, alkalinity would
be added to the scrubbing water. Thus,
chloride removals of 99 percent or better
should be expected for any version of this
unit.
Particulate removal efficiency ranges
from about 82 to 88 percent for the
Steam-Hydro and Tandem Nozzle ver-
sions. The SuperSub version achieved a
particulate removal efficiency of about 95
percent. It should be noted that these
removal efficiencies refer only to the gas
stream brought into the APCD and not
the efficiency that might be obtained on
the entire gas stream from the ENSCO
incinerator. Since the APCD connection
to the main gas duct resulted in a bias
toward the smaller particles, we would
expect that substantially higher removal
efficiencies would have been obtained if
the APCD had been treating the unbiased
gas stream.
Shown in Table 2 are the percent mass
less than 1 micron at the inlet and outlet
of the unit. Much of the particulate matter
exists below 1 micron, whether at the
inlet or outlet of the control device. It
must be noted that the design philosophy
of the unit is to agglomerate fine particles.
Thus, it is to be expected that some
submicron particles entering the device
exit as particles greater than 1 micron in
size. These data indicate that the
SuperSub configuration is the most ef-
fective of the versions tested for control
of the submicron particulate matter from
this source.
ETS, Inc. Dry Scrubber
General Description
The unit has two major components:
the dry reactor and a particulate collection
device. The patented dry reaction has a
number of unique components. The basic
operating principles are as follows. Flue
gas is directed cyclonically into the reactor.
The rotating slinger unit (driven by a
hydraulic motor) delivers the dry reactant
(usually 200 mesh hydrated lime) per-
pendicular to the flue gas flow. This
creates maximum mixing and intimate
contact of the reactant and pollutants. An
internal recirculator, with no moving
parts, is located above the slinger. This
device increases the contact time and
enhances removal of the acid gases. The
slinger then directs the dry reaction pro-
ducts down and into an expansion section
where the larger particles are removed.
The finer particulate matter is carried
into the particulate collection device.
The particulate collector can be a con-
ventional baghouse, an electrostatic fabric
filter (ESFF) baghouse, or a Reduced En-
trainment Precipitator (REP) developed by
ETS. The lime dust entrained in the flue
gas continues to react with acid gas
components throughout the transport
ductwork. In addition, the lime dust aids
in building a reactive filter cake on the
fabric filters. This serves two purposes.
First, reaction with acid gas components
continues until final particulate removal
occurs. Secondly, the precoat assists in
removing the fine particulate without ex-
cessive pressure drops across the filters.
This system is totally dry. The reactants
are delivered as dry powder, not as a
slurry required for the spray dryer type
scrubbers. The reacted product is also a
dry powder and can be handled as one
handles dust collected in a baghouse.
Since no water is used at any point in the
Table 1. Particulate and Chloride Removal Efficiencies: Hydro-Sonic Scrubber
Configuration'
SH/Lo/R
SH/Lo/F
SH/Hi/R
TN/-/R
TN/-/F
SS/-/F
Paniculate
efficiency
(Percent)
81.6
87.4
88.2
92. J
86.3
95.4
Chloride
efficiency
(Percent)
99.1
98.7
98.8
99.8
96.0
98.3
' Configuration codes are: SH = Steam-Hydro; TN = Tandem Nozzle; S = SuperSub; Hi = High
energy input; Lo - Low energy input; - = not applicable to this version; Fresh = Freshwater used
in APCD: R = Recycle water from ENSCO scrubber used in APCD.
Table 2. Comparison of Fine Particle (<1 Micron) Enrichment Factors (Out/In) for
Various Operating Conditions
Operating
Condition
SH/Lo/F
SH/Lo/F
TN/-/F
SS/-/F
SS/-/F
Inlet
Impactor
Run No.
2
3
4
5
6
Percent
of Mass
<1 Micron
43
57
38
64
70
Outlet
Impactor
Run No.
3
4
5
6
7
Percent
of Mass
<1 Micron
69
67
60
36
26
Out/In
1.6
1.2
1.6
0.6
0.4
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system, there is no mist carryover prob-
lem, little or no corrosion in the exhaust
stack which remains dry, and minimum
loss of stack gas buoyancy since this
energy is not used to evaporate water.
Test Results
The ETS system was installed during
the last week of March 1984. The system
was operated and tested during April 1-
10 and April 23-26, 1984. Two reactant
materials, hydrated lime and nahcolite
were evaluated for HCI removal ef-
fectiveness.
The unit tested has a rated capacity of
2000 ACFM. The dry scrubber was con-
nected to a pulse jet baghouse which
used Nomex® fabric cartridges. An in-
duced draft fan was located at the outlet
of the baghouse forcing the cleaned gas
into the 12-inch I.D. vertical exhaust
stack.
Given in Table 3 are the paniculate and
HCI removal efficiency data for the two
reactants at the various stoichiometries.
Six of the nine tests using lime as the
reactant indicate an HCI removal effi-
ciency of over 98 percent. Only one of the
tests using nahcolite achieved over 90
percent HCI removal. The stoichiometric
ratio (SR) ranges from 2 to 9 for the tests
in which lime was the reactant. The data
suggest that the SR for lime must be
nearly 3:1 to ensure scrubbing efficiencies
of 99 percent.
Due to limitation in the feed equipment,
nahcolite was injected at much lower
stoichiometric ratios. The HCI removal
efficiency does not appear to correlate
with the nahcolite/HCI stoichiometric
ratio up to a ratio of 1.7. Therefore, from
these tests, it is not possible to determine
the nahcolite/HCI ratio required to
achieve 99 percent HCI removal.
The paniculate removal efficiencies are
calculated strictly from the Method 5
data. No allowance has been made for
the reactant materials added in the dry
reactor. For most of the runs, the weight
of reactant added ranged from about 40
percent to over 100 percent of the weight
of paniculate entering the system from
the incinerator. The reactants added were
100 percent less than 200 mesh (74
microns). Obviously some of the material
was much smaller and may have passed
through the baghouse.
The calculated paniculate removal effi-
ciencies for the first 10 runs were all
greater than 90 percent with most in the
95 to 98 percent range. It should be
noted that, due to the bias toward smaller
particles caused by the slipstream sample
withdrawal, this is the removal efficiency
TaWe 3. Summary Results: ETS Unit
Reactant
used
Lime
Lime
Lime
Lime
Lime
Lime
Lime
Lime
Lime
Nahcolite
Nahcolite
Nahcolite
Nahcolite
Nahcolite
Nahcolite
Nahcolite
Stoichiometric
ratio
2.80
4.53
4.50
6.61
8.71
8.07
5.29
1.94
2.42
0.70
0.53
0.87
-
0.56
1.73
0.98
HCI
Efficiency
percent
98.7
89.0
98.0
99.2
98.9
99.6
99.8
56.3
79.1
93.2
82.0
54.7
(2)
53.8
68.1
33.1
Particulates
efficiency
percent
91
97
96
95
95
98
90
98
98
96
(1)
76
75
85
83
38
(1) Torn baghouse cartridge.
(2) Sample lost.
for the finer particles in the ENSCO in-
cinerator exhaust gas. Since the unit
would be expected to remove the larger
particles more easily, the removal effi-
ciency for the total gas stream would be
expected to be even higher.
It is suspected that the low efficiencies
measured for the last six nahcolite runs
were due to persistent difficulties in
sealing the cartridges in the baghouse. In
addition, a tear was discovered in one
cartridge after the second nahcolite run.
The paniculate removal efficiencies re-
ported for the last six nahcolite runs do
not accurately reflect the paniculate re-
moval capabilities of the unit.
The paniculate control capability of the
ETS unit as a function of particle size was
also determined. Table 4 shows the per-
centages of paniculate matter less than
1 micron in size in the inlet and outlet
samples. In our opinion, these data imply
that a significant fraction of the paniculate
matter in the unit exhaust originated
with the lime injected for HCI control.
Vulcan Engineering Company
Hi-Tac Filter
General Description
The high temperature air cleaning (Hi-
Tac) device was developed by Vulcan
Engineering Company for the removal of
paniculate matter from gas streams at
higher collector inlet temperatures than
previously possible. The unit is not de-
signed nor equipped to control HCI
emissions. Although the Hi-Tac unit looks
much like a conventional baghouse, there
are substantial differences.
The filter media is entirely metallic.
This results in greater resistance to mois-
Table 4. Comparison of Fine Particle
(
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movable cartridge elements. Each ele-
ment consists of a metallic reinforcing
framework covered with stainless steel
mesh. The weave may be varied to deter-
mine the appropriate design for a par-
ticular source.
During this test program, the following
three types of weaves were in the unit:
Module I - 150 x 105 plain weave
Module II - 325 x 325 twilled weave
Module III and IV - 50 x 250 dutch
weave.
The total removal efficiencies for par-
ticulate matter are shown in Table 5.
Removal efficiency for particulate matter
was quite erratic, varying from 34 percent
to 98 percent. Excluding run number 1,
the average removal efficiency was 89.7
percent. Inspections of the cartridges
before and after test runs indicated that
cake formation on the filter fabric was
not reliable. During several inspections
following cartridge cleaning, it was ob-
served that a very large portion (about 70
percent) of the fabric surface was still
covered by the filter cake, with about 20
percent of the surface clean down to the
fabric. The sticky particulate from the
incinerator interferred with proper cake
formation and filter cleaning. It is possible
that fabric weave changes or precoating
of the fabric might correct this difficulty.
The test program was not designed to
explore these options.
Particulate removal versus gas flow
rate through the APCD, and particulate
removal versus air-to-cloth ratio showed
no clear trends. It is suspected that the
peculiar cake formation properties and
resultant filter cleaning problems made
these standard plots of little value.
Recognizing the difficulties cited above
for particulate control, an attempt was
made to assess the removal efficiency at
various particulate size ranges. These
data indicated 90 percent or better control
of particles of less than 1 micron but
Table 5.
Vulcan High
Baghouse
Run
number
1
2
3
4
5
6
7
8
9
10
Temperature
Particulate
removal
(Percent)
34.2
93.1
90.4
92.5
94.2
84.3
89.3
74.8
90.0
98.4
decreasing efficiency as the particle size
increases.
These apparently strange results may
be due to the method used, determining
small differences between highly variable
numbers, or to agglomeration of fine,
sticky particles passing through the filters.
In summary, the test results indicate
that effective control of the fine par-
ticulates generated by hazardous waste
combustion may be achievable by the Hi-
Tac unit. Additional development work to
address the problem of sticky particulate
will be required.
Conclusions
1. All versions of the Hydro-Sonic units
tested achieved excellent HCI control,
considering that no alkalinity was
added to the scrubber water for pH
control. Ninety-nine percent removal
of HCI was obtained without adding
additional alkalinity to the ENSCO
scrubber recycle water. With additional
alkalinity, any of these units should be
capable of well over 99 percent HCI
removal.
2. The Tandem Nozzle SuperSub Model
100 achieved the best particulate re-
moval of the three Hydro-Sonic units
tested.
3. The ETS dry scrubber achieved both
high removal efficiencies for HCI and
particulate.
4. The ETS scrubber reagent hydrated
lime consumption appears to be high
(3 moles lime per mole HCI) but can-
not be stated with confidence since
no attempts were made to improve
utilization through reagent recycle.
5. The ETS unit does not presently have
capability to adjust reagent feed rate
to accommodate rapidly varying HCI
content in the gas to be treated.
6. The Vulcan Hi-Tac unit is not designed
to, and cannot presently, remove acid
gases from the exhaust gas being-
treated. Therefore, it is not applicable
to incinerators burning significant
amounts of halogenated hazardous
wastes.
7. Further development work and/or
emissions testing will be required be-
fore the Hi-Tac unit demonstrates the
capability to reliably control sources
which might produce sticky particulate
as encountered in the exhaust of the
ENSCO incinerator.
8. Considerable variability was encoun-
tered in the ENSCO exhaust gas for
particulate concentration, particulate
size distribution, HCI concentration,
flue gas moisture content, and exhaust
gas temperature. It is necessary that
any air pollution control device in-
stalled on a hazardous waste incinera-
tor have design features that allow
compensation for this variability.
9. Of the APCDs tested in this project,
the Hydro-Sonic Tandem Nozzle
SuperSub gave the best overall per-
formance in terms of HCI and
particulate removal and ability to ac-
commodate variability in the gas
stream being treated.
Reference
1. Tatsch, C.W., W.M. Yeager, and G.L
Johnson, 1984. PADRE: A comput-
erized data reduction system for cas-
cade impactor measurements. Journal
of the Air Pollution Control Association,
Volume 34, No. 6, pp. 655-660.
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C. W. Westbrook and C. E. Tatsch are with Research Triangle Institute, Research
Triangle Park, NC 27709; and Lawrence Cottone is with Engineering-Science,
Inc., Fairfax, Virginia 22030.
Harry M. Freeman is the EPA Project Officer (see below).
The complete report, entitled "Control of Air Emissions from Hazardous Waste
Combustion Sources: Field Evaluations of Pilot-Scale Air Pollution Control
Devices," (Order No. PB86-151 677/AS; Cost: $16.95, subject to change) will
be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA2216J
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Hazardous Waste Engineering Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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