United States
Environmental Protection
Agency
Hazardous Waste Engineering
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-85/097 Dec. 1985
&EPA Project Summary
Destruction of Hazardous
Wastes Cofired in Industrial
Boilers: Pilot-Scale Parametrics
Testing
C. D. Wolbach and A. R. Carman
The full report presents the results of
pilot-scale testing of the destruction of
hazardous wastes. A combustion unit
burning no. 2 distillate oil cofired with
various materials found in the Resource
Conservation and Recovery Act (RCR A)
Appendix 8 list was tested for its
destruction and removal efficiency
(ORE) with respect to the Appendix 8
compounds. The pilot-scale unit was
configured to simulate the thermal
history of a 40 million Btu/hrwatertube
boiler. The operating parameters of the
combustor were varied over a range of
values representative of the normal
operating envelope of an industrial-
sized packaged watertube boiler. Com-
pounds employed in the testing included
carbon tetrachloride, chloroform, 1,2-
dichloroethane, and chlorobenzene. Var-
iables studied included firing rate (two
values), flame shape or swirl (three
values), excess air rate orstoichiometry
(three values), waste to fuel ratio (three
values), and waterwall effects. In addi-
tion to direct measurements of DRE,
efforts were made to model the thermal
and DRE histories of the combustor
unit.
A total of 44 runs were conducted
generating 99 individual DRE data
points. It was found that under most
operating conditions most compounds
could be destroyed to greater than
99.99 percent efficiency. However,
under selected conditions certain com-
pounds exhibited less than 99.99 per-
cent DRE. Parameters most affecting
DRE were waterwalls (by heat extrac-
tion), and excess air rate. Excess air rate
effects were found to be non-linear.
That is, there was found to be an
optimum excess air rate for DRE. The
simulation effort cumulated in a math-
ematical model. The model runs on a
personal computer, predicts tempera-
ture profiles within 50 degrees Celsius,
and predicts destruction efficiency con-
servatively.
This Project 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
Thermal destruction of wastes by direct
incineration or by cofiring with conven-
tional fuels in boilers, furnaces, or kilns is
one of the most effective methods cur-
rently available for disposal of hazardous
organic material. While direct incinera-
tion of hazardous wastes is regulated by
Part 264 of the Resource Conservation
and Recovery Act (RCRA) as adopted in
January 1981, boiler cofiring is currently
exempt from RCRA provisions. However,
the potential for boiler cofiring regula-
tions has been evaluated by the U.S.
Environmental Protection Agency (EPA)
and they are, at the time of writing, in the
process of preparing regulatory positions
and drafting regulationsfor promulgation.
To support this effort, EPA's Incineration
Research Branch (IRB) in conjunction
with the Office of Solid Waste is con-
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ducting research and development pro-
grams on incineration effectiveness and
regulatory impacts.
The global purpose of this study was to
gather data to aid the EPA in selecting a
strategy or set of strategies for regulating
the combustion of hazardous wastes in
boilers. The specific objectives were two-
fold: to identify which of several boiler
operational parameters has a major im-
pact, positive or negative, on boiler ORE;
and, to evaluate and if practical, establish
a mathematical model for predicting a
maximum amount of cofired waste that a
particular boiler configuration might emit.
In particular, those parameters that could
be easily changed by an operator or might
represent major differences between
boiler types were studied. A secondary
objective of the study was to gain suf-
ficient information to allow judgements
of what particular parameters to monitor
closely during full-scale testing. Within
that objective was the intent to establish
some common basis for comparing full-
scale boilers. A final objective was to
obtain information that would give insight
on how regulations might be cast so that
trial burns would not be needed.
Procedures
The facility used to achieve the purpose
and objectives of the study is the Acurex
pilot-scale furnace whose thermal char-
acteristics closely approximated a 12-
megawatt (40 million Btu/hr) packaged
D-type watertube boiler.
The furnace has a single burner, front-
wall-fired, into a horizontally oriented
firebox. The premixed fuel oil/waste
mixture is pumped out of drums through a
pressure-atomizing nozzle and stabilized
at the front wall. The fuel flow is moni-
tored by rotameter. Combustion air is
preheated and injected in the annular
region around the fuel delivery tube. The
IFRF/Acurex burner design allows swirl
adjustments by rotating swirl blocks. Air
flow is monitored by hot wire anemom-
eter.
The postflame gases travel down the
4.55m (15 ft) by 83.5 cm (33 in.) diameter
radiant section tunnel. The walls are
refractory lined with optionally mounted
waterwalls. Ports along the top and sides
of the furnace accommodate ceramic type
R thermocouple probes for gas temper-
ature profiles. Type K probes are embedded
in the refractory for wall temperature
determinations. Thermocouples are also
placed at the manifold inlet to and from
the outlet of each cooling panel, and to
and from the burner quarl. Cooling fluid
flow measurements are made by rotam-
eter.
After traversing the radiant section, the
hot gases make a 90-degree turn and
pass upward through the convective
section. The U-tube cooling drawer as-
semblies extract heat from the gas stream
as necessary to bring the temperature
down to levels that can be handled by the
bag house. Downstream of the last tube
bank, a stainless steel probe extracts gas
samples for continuous emissions anal-
ysis. Electro-optical analyses are used to
define levels of CO, CO2, O2, NO*, and
total unburnt hydrocarbon (THC) (Appen-
dix A.5). Samples for the Volatile Organics
Sampling Train (VOST) are extracted with
a stainless steel probe from the end of an
8-in. diameter 15-ft long duct. The gases
are then exhausted to a 45-ft high stack.
The test plan divided the tests into
three subsets: a baseline study burning
only distillate oil, a single compound study
of one hazardous waste compound cofired
with distillate oil, and a multiple com-
pound study burning more than one
compound simultaneously. Parameters
studied included excess air rate, fuel
firing rate, amount of waterwall surface
area, burner swirl setting, and waste
type. The selection of waste types for the
composite "soup" encompassed a large
range of predicted destructibility. The
baseline study was designed to define the
thermal environment within the facility
under the various operating conditions of
choice, to define the magnitude of the
effects of changes in variables on the
thermal environment, and to demonstrate
the ability of a simulation to predict the
thermal environment resulting from a
specific set of variable settings. The single
compound studies had two goals: to
define the magnitude of variable effects
on destruction efficiency; and to define
the effects of cofiring wastes on the
expected thermal environment. The final,
multiple compound studies were to de-
termine the destruction efficiencies of
several compounds with known thermal
environments.
Results and Discussion
A summary of the results of this
program is presented in Table 1. The
values are penetration values or C/C0 ( =
(100-DRE)/100). The penentration value
is the mass rate of waste flowing into the
combustor (C0) divided by the mass rate of
waste leaving (C). A semiquantitative
summary of the effects of the operating
variables on ORE is presented in Table 2.
These values are rough estimates of the
difference between either temperature or
ORE for two runs where only the specified
parameter was varied. For example, a
change in firing rate between 0.8 million
Btu/hr and 1.2 million Btu/hr changed
the temperature profile by about 110°C
(200°F). The corresponding change in
DRE was about a factor of three.
For each firing condition, radial temper-
ature profiles were measured at five cross
sections. During the first several runs,
about 120 individual temperature points
were measured. After establishing the
reproducibility of the individual location
temperatures, the number of points
measured per run was reduced to 40. The
reproducibility of the thermal distribution
is shown in Table 3.
Having a thermally well-characterized
and accessible combustor allowed a
detailed simulation effort based upon the
simple, conservative, destruction-predic-
tion model forwarded by one author in
1981. The si mutation is comprised of two
modules—one that predicts the bulk gas
thermal history and the second that
estimates the corresonding amount of
destruction. The model does not consider
the 90 to 99 percent destruction that
occurs in the flame. Yet it conservatively
predicts within about two orders of magni-
tude the destruction efficiency of this
combustor. The set of data for carbon
tetrachloride is presented in Figure 1.
Conclusions and
Recommendations
The primary purpose of this study was
to determine which boiler operational
variables play the most significant part in
boiler DREs. The study determined that
within the pilot-scale unit the use of
waterwalls and the variation of excess air
were significant, and that there appeared
to be an optimal excess air rate. The study
also demonstrated that operational var-
iables could change DREs by two to three
orders of magnitude. Further experi-
mental work should be carried out to
verify some of the findings. The modeling
results should be applied to full-scale
units to estimate the model's ability to aid
permitting. Specific conclusions are that:
• Of the variables studied, the order of
influence on DRE is: waterwalls >
compound > excess air > firing rate >
flame shape. The order of influence on
temperature profiles is: waterwall >
excess air >firing rate >compound—
flame shape.
• Except for waste composition, the
influence of operational variables on
DRE corresponds to the influence on
bulk temperature profiles.
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Table 1. A verage Fractional Breakthrough C/C0 for Each Waste and Firing Condition
/c
/a"
lla
III
Ilia
IV
IVa
V
Va
VI
Via
VII
IX
Condition
(0.8, 10, 7.5, 8)
(0.8, 10, 7.5, 0)
(0.8, 25, 7.5, 8)
(0.8, 25, 7.5, 0)
(0.8, 50, 7.5, 8)
(0.8. 50, 7.5. 0)
(1.2, 10. 7.5. 8)
(1.2, 10, 7.5, 0)
(1.2, 25, 7.5, 8)
(1.2, 25. 7.5, 0)
(1.2, 50. 7.5, 8)
(1.2, 50. 7.5. 0)
(0.8, 25. 5.0, 8)
(1.2. 25. 5.0, 8)
Chlorobenzene**
1. 4 ±0.1 x JO'* (4)
4.2 x 10~*(1)
1.4 ±0.3x 10~*(4)
4±3x 10~7{6)
8.9 ±6x10'* (5)
2.5 ±2 x 10'7(3)
6±8x 10's(5)
2.2±0.5x10'7(3)
4.5 ±2x1 0^(5)
0.5±0.3x10'7(3)
5.5 ±2 x 10'* (4)
3.4 ±0.7 x 10'7(3)
2.0 ±0.5 x 10~* (3)
Carbon
Tetrachloride Chloroform
1.6 ±0.2x10'* (2) 1.6 ±0.2x10'* (3)
e
5 ±3x10'* (5) 2.6±2x10's(5)
2. 1 x 10'* (1) 2.0 ± 0.8 x 10's (3)
1.2 ±0.3x10'* (2) 3.2 ± 0.5 x 10'* (3)
..
2.5 ±1 x 10'* (2) 8.8 ±2x1 0's (3)
..
7.9 ±6 x W* (3) 1.1 ± 0.02 x 10'* (2)
__
6.3 ±3x10'* (3)
1.5 ±0.3x10'* (3)
1,2 Dichloroethane
5 ±2x10'° (3)
1 ±0.5 x 10~*(2)
1 ±0.2x 10'" (3)
-
-
-
8 ±4x 10'e(2)
__
--
--
°± represents 1 standard deviation from average.
"(I indicates number of valid data points.
^(Firing Rate in Million Btu/hr, percent Excess Air, Swirl, percent Waterwall).
aftun conditions suffixed with an "a" are without waterwalls. All other conditions are with waterwalls in place.
'Not tested under that condition.
'C0 = mass rate of compound in; C - mass rate of compound out.
• From comparison of ORE with high
heat extraction and low heat extrac-
tion in the combustor, it is concluded
that in-flame destruction accounts for
only about 90 to 99 percent of the DRE.
The remaining destruction must be
achieved from postflame thermal oxi-
dation and decomposition.
• Residence time within the flame is
insufficient to destroy both POHCs and
PICs. Without sufficient postflame time
and temperature, the quantity of PICs
passing out of the boiler will be
significant.
• Significant volatile PICs emitted dur-
ing combustion of chlorinated organ-
ics include methylene chloride, ethyl-
ene trichloride, perchloroethylene, and
the ethylene dichlorides. Suspected
PICs—but not positively identified—
include chloromethane, chloroethane,
chloroethylene, and propylene chlor-
ide.
• A model capable of predicting within a
few degrees the temperature profile
within a furnace has been validated.
The model can be used to predict
within an order of magnitude the
destruction efficiency of the modeled
furnace.
• Conclusions on CO versus DRE versus
excess air cannot be drawn from this
data. Carbon monoxide levels showed
minimal variation over the range of
DRE observed.
Table 2. Semiquantitative Estimation of the Effects of the Independent Variables on
Temperature Profile and DRE
Range of
Variable
Waterwalls
Excess air rate
Firing rate
Burner swirl
Compound
Temperature Changes
°C (± °F/
275 (500)
165 (300)
110 (200)
30 (50)
30 (50)
Range of DRE Changes
(Factor)*
100
10
3
1
20
°C/C0 is mass rate of waste out divided by mass rate of waste in.
Table 3.
Reproducibility of Temperature Measurements at Four Selected Points Within the
Pilot-Scale Furnace"
Within run (with waterwalls)
Within run (without waterwalls)
Between all runs
Number
of Points
40
48
40
Average
Difference0
°C (°F)
10 (18)
7 (13)
29 (53)
Standard
Deviation
°C(°F)
6 (10)
4 (7)
17 (30)
"The points are at 8 and 12 in. from the wall and at cross sections C-3 andE-2.
''Difference between two measurements at the same location.
This study showed that certain var-
iables play a major role in determining
DRE and gave insight on underlying
physical and chemical mechanisms. Re-
sults of the program suggest the following
areas of research which need to be
addressed:
• The study strongly reinforced the
concept that only a fraction of the
destruction of a compound is achieved
in the flame zone. Verification and
quantification of the breakthrough
phenomenon is necessary with flames
closely approximating full-scale boiler
flames.
• In close conjunction with the study of
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breakthrough of compounds from the
flame zone, there should be studies on
the formation and destruction of PICs
in both the flame and postf lame zones.
• This program clearly demonstrated the
effect of compound structure on ORE.
Thisfact should be applied to testing of
potential surrogates (such as sulfur
hexafloride) for establishing boiler and
incinerator capabilities.
• The observation of optimum ORE in
the excess air region of 20 to 50
percent should be studied in detail,
and verified on a full-scale unit.
• A key operating criterion that should
be considered when using boilers for
waste destruction is the placing of
upper and lower limits on excess air
rates.
• The current thermal destruction model
should be applied to full-scale boiler
data to calibrate empirical approxima-
tions and evaluate the level of con-
servatism.
• The weakest point in the model ap-
pears to be the availability of reliable
pseudo-first-order empirical global ki-
netic data for the thermal destruction
of a wide range of compounds. Further
work in this area would be a definite
asset.
• Material following aerodynamic paths
outside of the bulk gas flow pattern is
the chief contributor to insufficient
ORE. Studies of breakthrough mechan-
isms and their relative significance
should be undertaken.
• Thermal NOX appears to show a strong
upper bound correlation. That is, for a
given NOX level the ORE will be at least
a certain amount. Qualitatively this
correlation was expected, but it needs
to be verified in other units.
70-1 _
I
S
I
CO
I
.§
u.
CU
8
10'
w~
J0.8 million Btu/hr model
0.8 million Btu/hr experimental
Q 1.2 million Btu/hr model
1.2 million Btu/hr experimental
Model
Test Data
o
10
20
30
40
50
60
70
Excess Air (percent)
Figure 1.
Comparison of weighted average model prediction and pilot-scale carbon
tetrachloride destruction data at variable excess air.
•tr U. S. GOVERNMENT PRINTING OFFICE: 1986/646-116/20731
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C. D. Wolbach and A. R. Carman are withAcurex Corporation, Mountain View, CA
94039.
Robert A. Olexsey is the EPA Project Officer (see below).
The complete report, entitled "Destruction of Hazardous Wastes Cofired in
Industrial Boilers: Pilot-Scale Parametrics Testing," (Order No. PB 85-242
139/AS; Cost: $16.95, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
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
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No G-35
Official Business
Penalty for Private Use $300
EPA/600/S2-85/097
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