United States
Environmental Protection
Agency
Hazardous Waste Engineering
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-85/082 Dec. 1985
ŁEPA Project Summary
Interim Report on PIC
Minimization in a Research
Combustor
Laurel J. Staley
A series of five organic compounds
(1,1,2,2-tetrachloroethane, trichloro-
ethylene, Freon-113, carbon tetrachlo-
ride and chlorobenzene) were burned in
heptane in a 100,000 Btu/hour water-
jacketed research combustor in order
to determine what, if any, PICs (Prod-
ucts of Incomplete Combustion)
formed under conditions of extreme
flame quenching. For each test, excess
air levels were varied from 120% of the-
oretical air to 240% of theoretical air
which, for the combustor used, repre-
sented the limits of flame stability. Re-
sults show that PICs do not always
occur predictably, but are very much in-
fluenced by the POHC (Principal Or-
ganic Hazardous Constituent) being
burned. Where they do occur, however,
the emission levels of PICs increase
with increasing levels of excess air,
over the range of air levels investigated.
This report covers the period of
January-March 1985, and the work
was completed as of March 31, 1985.
This Project Summary was devel-
oped by EPA's Hazardous Waste Engi-
neering Research Laboratory, Cincin-
nati, OH, to announce key findings of
the research project that is fully docu-
mented in a separate report of the same
title (see Project Report ordering infor-
mation at back).
Introduction
Although the Resource Conservation
and Recovery Act regulations require
99.99% Destruction and Removal Effi-
ciency (ORE) with respect to Principal
Organic Hazardous Constituents
(POHCs), those chemical contami-
nants within a hazardous waste
stream that are burned by an incinera-
tor, there is also a concern about Prod-
ucts of Incomplete Combustion (PICs).
These latter compounds are formed
even as the POHCs in the incinerator
are destroyed. They can be more toxic
than the original feed chemicals.
Thus, under those unwanted combus-
tion conditions that favor the forma-
tion of PICs, hazardous waste inciner-
ation may give rise to a potentially
serious air pollution problem.
The purpose of the work described in
the full report is to identify certain sets
of conditions under which PICs form or
are more prevalent so that future work
can focus on how and why they form
and how to minimize their formation.
Contained within the full report is a de-
scription of the combustor and auxiliary
equipment used in the study, a descrip-
tion of the experiments conducted, and
discussions of the results and the impli-
cations of the work. The work described
is preliminary and rather limited; all
conclusions are tentative and subject to
verification.
Experimental Design
Figure 1 is a sketch of the Turbulent
Flame Reactor (TFR) which was used to
conduct the experimentation.
The purpose of the experiment was to
determine those operating regimes
which allowed (1) incomplete burning of
POHCs, and (2) formation of significant
levels of PIC. A further objective was to
compare the POHC and PIC levels thus
produced with concentrations that result
from flameout.
The above objectives were accom-
plished by burning five compounds
(trichloroethylene (TCE), carbon tetra-
chloride, tetrachloroethane, chloroben-
zene and Freon-113) in a series of five
separate combustion tests. For each of
the five tests, the compound of interest
was present as a 2.0 mole percent solu-
tion in heptane in the combustor feed.
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To CO CO2 + 0
Monitors
To TENAX
(Heated Line)
To THC Monitor
-Ov
N. X
\ ^x
- T.C. for Exhaust
Gas Temp
' H20
Air
(From
Compressor)
Swirl Vane
Adjustment
IT
a
Heptane &
Waste Compound
Figure 1. Turbulent flame reactor.
In a sixth test, Freon-113 and chloro-
benzene were burned together to deter-
mine if there were any mixture effects
which influenced POHC destruction
and/or PIC formation. For this test, both
Freon-113 and chlorobenzene were
present at the same concentrations (two
mole percent each) as when they were
burned separately. This resulted in a
total POHC concentration of four mole
percent for this test.
In each test, the firing rate of heptane/
POHC was held constant while the com-
bustion air flow rate was varied to pro-
duce (CO) levels which spanned the
range of observable values. At five or
sometimes six different sets of operat-
ing conditions corresponding to five or
six different CO levels, Tenax trap sam-
ples were taken for purposes of deter-
mining POHC destruction and PIC for-
mation.
At one point during each test, the
flame was purposely extinguished dur-
ing a sampling run. Sampling contin-
ued. Theoretically, when the flame goes
out, there should be a discharge of soot
and PIC-laden exhaust gas from the re-
actor. The objective was to sample this
emission and measure the unburned
POHCs as well as to determine the types
and levels of PICs produced during this
"upset" condition. (It should be noted
that all discharges from the TFR were
scrubbed and filtered through an acti-
vated carbon filter to remove pollutants
prior to discharge to the atmosphere.)
Results and Conclusions
The DREs achieved throughout this
test series exceeded 99.99% in 62.5% of
the tests. For the remaining tests, ORE
exceeded 99.9% except for the three
times (two of which were flameouts) in
which the ORE was slightly less than
99.9%.
Fuel-lean combustion resulted in the
highest levels of PICs and unburned
POHCs. Emission levels of PICs and
POHCs increased with increasing ex-
cess air levels. One explanation for this
trend is that the temperature drop
brought about by flooding the TFR with
excess cold combustion air quenched
the combustion reactions before they
could reach completion. Stable com-
bustion intermediates present when the
reaction was quenched (either POHCs
or PICs) were emitted in the discharge.
POHC and PIC levels produced under
relatively fuel-rich combustion condi-
tions were consistently low even
though elevated carbon monoxide lev-
els indicated that combustion condi-
tions were poor. Even though the
POHCs were apparently destroyed, it is
conceivable that PICs may still be form-
ing under these conditions. The PICs
produced under relatively fuel-rich con-
ditions could possibly be different from
those produced under fuel-lean condi-
tions and perhaps were not detectable
using the methods and equipment used
to analyze the samples generated dur-
ing this study.
Types and amounts of PICs produced
during flameouts were not appreciably
different from those produced during
fuel-lean operation. This is significant.
Flameouts are momentary upsets
which result in the production of a finite
amount of POHC- and PIC-laden ex-
haust gas. Excessively fuel-lean com-
bustion, however, often results in a
stable though inefficient flame which
can emit POHC- and PIC-laden gases for
hours.
In two cases, these experiments have
identified hard-to-burn POHCs that con-
tradict previous expectations of inciner-
ability based on heats of combustion
and degree of halogenation. On the
basis of the limited data gathered in
these tests, no conclusions can be
drawn regarding the setting of poten-
tially new criteria for choosing POHCs
and predicting which PICs can form
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under a particular set of combustion
conditions. Yet these results and those
of other researchers in the field may be
the basis for developing a more accu-
rate way of identifying "hard-to-burn"
POHCs and predicting PIC formation.
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The EPA author, LaurelJ. Staleyfalso the EPA Project Officer, see below), is with
Hazardous Waste Engineering Research Laboratory, Cincinnati, OH 45268.
The complete report, entitled "Interim Report on PIC Minimization in a Research
Combustor," (Order No. PB 85-233 336/AS; Cost: $7.00, subject to change)
will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
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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EPA/600/S2-85/082
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