United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S2-89/021 Aug. 1989
Project Summary
Continuous Performance
Monitoring Techniques for
Hazardous Waste Incinerators
Rachel K. Nihart, John C. Kramlich, Gary S. Samuelsen, and
W. Randall Seeker
The report gives results of a study
to determine the feasibility of an in-
cinerator performance measuring
methodology based on real-time
continuous exhaust measurements of
combustion intermediates; i.e.,
carbon monoxide, total hydro-
carbons, and methane. The key issue
was the correlation that exists
between destruction and removal
efficiency (ORE) and these inter-
mediates. The study consisted of five
steps:
1. A review of methods for moni-
toring intermediate species in the
exhaust gases.
2. Selection of instruments for eval-
uation.
3. Evaluation of the instruments for
response and potential interfer-
ences.
4. An experiment in which test
organic compounds were incin-
erated in a laboratory-scale turbu-
lent diffusion spray flame.
5. An analysis of the exhaust gas for
both destruction efficiency (DE)
of the waste compounds and the
emission of intermediate species
over a range of operating condi-
tions from high- to low-efficiency
operation.
This Project Summary was devel-
oped by EPA's Air and Energy
Engineering Research Laboratory, Re-
search Triangle Park, NC, 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
A number of programs sponsored by
the U.S. Environmental Protection
Agency (EPA) have shown that thermal
destruction is an effective technique for
eliminating organic hazardous waste.
Both field tests of operating incinerators
and bench scale tests on turbulent
diffusion spray flames have indicated that
properly operated incinerators are very
efficient. They have been found to
destroy compounds to typically
> 99.99% destruction and removal effi-
ciency (ORE) when operated correctly.
However, there is currently no way to
continuously monitor the ORE perform-
ance of the hazardous waste incinerator.
More than 300 organic wastes have
been identified by the EPA as being
hazardous. A particular waste stream
may consist of a number of these com-
pounds, and assurance must be given
that the incinerator is not releasing any of
them during normal operation. Because
of the wide range of compounds and the
low concentration levels that need to be
measured, direct real-time continuous
monitoring is beyond the state-of-the-art
of measuring techniques. EPA's licensing
procedure requires that high efficiency
operation (ORE >99.99%) be demon-
strated prior to operation for a selected
set of constituents in the waste stream.
After licensing, the incinerator is main-
tained within the range of operating
conditions stipulated in the permit. During
-------
routine operation, it is desirable to
monitor the destruction efficiency (DE) of
the unit and thereby allow corrective
action to be initiated at the onset of
unsafe performance. Methods available to
measure specific hazardous waste com-
pounds that are used during licensing
trial burns (e.g., organic trapping and gas
chromatography separation and analysis)
are suitable for routine performance
monitoring. They are both skill- and
labor-intensive, noncontinuous, and the
results are not immediately available after
sampling.
Thus, there is a need for the devel-
opment of an indirect real-time con-
tinuous monitoring methodology for haz-
ardous waste incinerator performance. A
number of indirect methodologies have
been proposed. For this discussion, the
potential methodologies can be cate-
gorized as:
• Tracer measurements (within waste
stream composition or added).
• System parameter measurements
(pressure, temperature, flow rate).
• Combustion intermediate species
measurements (e.g., CO, hydro-
carbons).
• Combustion product measurements
(C02, 02, NOX).
Methodologies which rely on these
measurements are largely untested and
not completely developed. This study will
concentrate on the use of intermediate
species as a measure of incinerator
performance since they appear most
feasible at this time. Field tested and
relatively low cost instrumentation is
commercially available for several of the
stable species.
Combustion of Organics
The combustion of organic molecules
is a complex series of elementary
reaction steps involving a myriad of
intermediate species. For example, to
completely describe the oxidation of the
simplest organic (methane) requires more
than 100 reactions and involves 25 inter-
mediate species. For more complex
organics, the numbers increase geo-
metrically with the molecular weight.
However, only a few of the species are
stable; e.g., lower molecular weight
hydrocarbons, methane (CH4), carbon
monoxide (CO), and formaldehyde. Also,
these stable intermediates are common
to the combustion of most organic
compounds including hazardous waste
and auxiliary fuels.
Organics burn in a complex series of
fundamental reaction steps that even-
tually lead through CO as the principal
intermediate before the completely oxi-
dized state (C02) is reached. CO is a
thermally stable compound, compared to
hazardous waste organics. Since it is a
intermediate, large amounts of CO are
produced in the flame zone that will be
eventually destroyed if mixing is good. If
mixing is poor, CO can escape the flame
by mechanisms of thermal quenching.
Excessive CO emissions usually reflect
poor mixing or incorrectly set combustion
air. The CO level measured in the stack
depends on many factors; e.g., waste
properties, spray nozzle design and
operation, combustion air mixing pattern,
and incinerator chamber design. CO can
be measured continuously, using nondis-
persive infrared analyzers, to concen-
trations of a few parts per million (ppm).
Exhaust emissions of hydrocarbons
have three sources: (1) the unburned
hazardous organic constituents due to a
low DE, (2) unburned hydrocarbons from
the auxiliary fuel, and (3) intermediate
hydrocarbons generated during the com-
bustion of the hazardous waste and
auxiliary fuel. Which of these is dominant
depends on the operating condition of the
incinerator. However, the dominant
source is likely the intermediate and, in
particular, the light intermediates such as
methane that are typically more thermally
stable than the hazardous and fuel
constituents. Total hydrocarbons can be
measured with a flame ionization detector
(FID) down to a few ppm, while CH4 can
be measured with similar sensitivity using
a nondispersive infrared analyzer (NDIR).
Formaldehyde, another hydrocarbon
intermediate, is somewhat less stable
than CO or CH4 and no suitable instru-
mentation is currently available for
routine continuous monitoring.
Study Objective
The objective of this study is to
determine the feasibility of an incinerator
performance monitoring methodology
based on real-time continuous exhaust
measurements of combustion intermedi-
ates, specifically: CO, total hydrocarbons,
and CH4. The key issue is the correlation
between destruction and removal effi-
ciency (ORE) and these intermediates.
The study involved five steps:
1. A review of methods for monitoring
intermediate species in exhaust
gases.
2. Selection of instruments for evalua-
tion.
3. An evaluation of the instrument
response and potential interfere™
4. An experiment in which a set of
organic compounds are incineratt
a laboratory-scale turbulent diffu
spray flame.
5. Analysis of the exhaust gas for
DE of the waste compounds and
emission of intermediate species i
a range of operating conditions I
high- to low-efficiency operation.
Study Approach
This approach was designed
determine if correlation exists betw
the level of combustion intermediates
the DE in the turbulent spray flame.
turbulent flame reactor (TFR) can
operated under conditions where D
are very high (>99.999%). The 1
conditions investigated covered a rai
of low-efficiency conditions and f
failure modes: fuel rich, excessively i
lean, poor atomization quality, and fla
quench. These failure modes were c
sidered to be representative of pi
operation conditions that might exist
liquid injection incinerators.
The exhaust concentrations of the t
hazardous waste compounds were me
ured along with the concentrations of tc
hydrocarbons, CH4, and CO for each
the conditions delineated above in on
to assess the correlation between DE a
the concentration of intermediate specii
The test compounds were mixed to <.
by mass with diesel fuel and introduc
to the reactor. The compounds usec
acrylonitrile, benzene, chloroform, a
chlorobenzene—were selected becau
they are EPA-listed hazardous orgar
compounds and because they are e
pected to represent a broad range
incinerability behavior.
The purpose of this study was
determine the feasibility of utilizing re.
time continuous exhaust measuremen
of combustion intermediates as a way
monitor incinerator performance. The k<
issue was to determine if a dire
correlation exists between DE ar
intermediate species concentration mea
urements. DE was based on exhau
measurements for specific input was
compounds using a Tenax cartridge fi
capture and gas chromatography, flair
This report distinguishes between wastt
destruction efficiency (DE) and waste destructior
and removal efficiency (ORE). DE is based or
measurement of input and output concentrations
of a species across a thermal treatment reactoi
but upstream of any control device which
removes that species form the flow exhaust.
-------
ionizatio.T detection for sample analysis.
The intermediate species measurements
were selected to be continuous and real-
time. A comparison of the potential
intermediate measurements with the
availability of commercial instruments
resulted in the selection of a Beckman
402 Total Hydrocarbon Analyzer (THC), a
Beckman 864 NDIR methane analyzer,
and an Anarad AR-500 NDIR CO
analyzer. The response of each instru-
ment was compared to DE measure-
ments from a turbulent spray flame in
order to experimentally determine if
flame zone correlation exists.
The TFR was designed so that the
processes controlling DE in the flame
(e.g , atomization quality, ballistic trans-
port, turbulent mixing, flame quench, and
flame-surface impingement) simulate
those that control DE in the flame zone of
a liquid injection incinerator The cold
walls of the TFR were designed to
emphasize flame zone performance by
quenching post-flame reactions. As such,
the TFR data do not directly address how
post-flame processes such as after-
burners and gas cleaning equipment
affect the flame-zone correlations.
The data presented are cross-plotted to
produce the DE/continuous monitoring
correlations shown in Figure 1 These
represent a broad range of operating
conditions form high flame efficiency to
low DE failure conditions. Two general
correlations were observed between DE
and the intermediate species measure-
ments:
1. THC and CH4: The correlation be-
tween DE, THC, and CH4 is nearly
proportional; i.e., a linear increase in
the intermediate concentration cor-
responds to a proportional increase in
the hazardous component concentra-
tion.
2. CO: The CO correlation indicates
that a significant increase in CO
emissions is necessary before the
exhaust concentration of waste com-
pounds increases substantially.
Fundamental combustion kinetic studies
(e.g., laminar flat-flames) indicate that
hydrocarbon flames can be divided into
two partially overlapping regions. In the
first,, hydrocarbon fuel is rapidly con-
sumed by reaction with flame radicals
(0,H,OH) to produce CO and water. In
the second region, the CO is oxidized to
CO2 at a relatively slow rate. The flame
can be made to operate inefficiently by,
for example, a reduction in temperature
or the addition of flame inhibiting
compounds. The first manifestation of
this inefficiency is tho release of CO
because the hydrocarbon destruction
reactions remain sufficiently fast to
quantitatively remove organic molecules.
It is only after the flame has become
extremely inefficient that hydrocarbons
are released, by which time the CO
emissions are substantial.
Although £ direct comparison between
laminar flat-flame and turbulent flame
results is difficult due to the fundamental
difference between the processes, the
reactions occurring in each are the same.
These reactions are simply super-
imposed on different fluid dynamic back-
grounds. Thus, a qualitative explanation
for the flame zone correlations observed
here would include:
• Since the hydrocarbon intermediates
and the model waste compounds are
made up of organic molecules, the
flame destruction rate of each is
similar, at least relative to the slower
CO destruction rate.
• Decreased flame efficiency is evi-
denced by CO release while hydro-
carbon intermediates and the waste
compounds are still quantitatively
destroyed.
• Further decreases in flame efficiency
bring about a concurrent release of
hydrocarbon intermediate and organic
wastes due to the (relative to CO)
similarity in their flame destruction
rates.
Conclusions
These data support the following
conclusions:
• A turbulent spray flame operating
without afterburners or postflame gas
cleaning can achieve a DE of 99.99%
This implies that careful design of
efficient burners can cause the flame
zone of a liquid injection incinerator to
perform most, if not all, of the legally
required waste destruction.
• The data indicate that flame conditions
which minimize CO, THC, and CH4
emissions result in optimum waste DE.
This indicates that maximum flame
efficiency, defined by the release of
fuel and fuel fragments, also results in
maximum waste destruction.
• Less than optimum DE performance
was accompanied by an increased
release of intermediate species. This
means that, for all conditions
examined in this study, a change in
DE toward lower efficiency was always
accompanied by an increase in CO,
THC, and CH4.
• The range of conditions for optimum
flame performance, as defined by CO,
THC, and CH4, was found to be less
than or equal to the range for high DE.
This means that, under some condi-
tions, the flame performance could
decrease withoc a significant de-
crease in DE.
• CO was found to increase signiricantly
under some conditions in which the DE
remained high.
Application of these results to the
continuous monitoring behavior of a full-
scale incinerator requires seme assess-
ment of how the postflame zone process,
such as afterburners or scrubbers, affect
the flame zon3 correlations. Due to the
very low solubility of hydrocarbons and
CO in aqueous solutions, incinerator
scrubbing systems would not be
expected to alter the continuous moni-
toring correlations for organic wastes.
However, the afterburner may be
expected to impact the postf'ame zone
correlations. The aliphatic hydrocarbons
that make up the bulk of THC, in
particular CH4, are generally equally or
more resistant to nonflame thermal
destruction than the waste corr pounds
upon which thermal testing has been
performed. This indicates that monitoring
THC and CH4 approach is potentially
more conservative than indicate* by the
flame measurements. Thermal testing
has not been performed on CO. However,
detailed chemical kinetic predictions indi-
cate that the nonflame thermal destruc-
tion rate of CO is approximately II .e same
as that for hydrocarbons (as opposed to
the flame destruction rates in which the
hydrocarbons predomine e). Thus, no
large alteration of the f! tie zone corre-
lation would be expected.
The correlations shown in Figure 1
suggest that CO is possibly an overly
conservative indicator of flame perform-
ance. That is, a,i incinerator shutdown
procedure based on response of a CO
monitor may be environmentally safe but
economically impractica1 The results of
this study suggest the following approach
to incinerator monitoring and control:
• Use CO as an indicator of flame per-
formance, but not as an incinerator
shutdown criterion. This should pro-
vide a way to tune the flame
operating parameters.
• Use THC as a shutdown alarm to
indicate potential waste compound
release.
Use of these two instruments in tandem
provides, through CO, a way to tune for
flame efficiency and, through THC, a way
-------
to indicate incipient waste emission and
direct shutdown.
Quality Assurance/Quality Control
requirements are applicable to this
project. The data contained in this report
are NOT supported by QA/QC docu-
mentation as required by the U.S.
Environmental Protection Agency's
Quality Assurance Policy.
99.0
Excess Air, 3.8 Iph
O Excess Air, 5.7 Iph
Excess Air, 2.8 Iph
Poor Atomization
Quench Coils
1000 3000 5000
10,000
CO (ppm)
15,000
Excess Air, 3.8 Iph .
O Excess Air, 5.7 Iph
D Excess Air, 2.8 Iph
Poor Atomization
O Quench Coils
99.0
15,000
Excess Air, 3.8 Iph
O Excess Air, 5.7 Iph
D Excess Air, 2.8 Iph
Poor Atomization
Quench Coils
o.oov
99.5
99.9
100.0
99.0
150 250
350 450 550
CH4 (ppm)
650
99.5
99.9
100.0
U.
U.
W
Figure 1. Fraction of hazardous compound remaining m the exhaust as a function ol
intermediate species concentrations.
-------
R. Nihart, J. Kramtich, G. Samuelsen, and W. Seeker are with Energy and Environ-
mental Research Corp., Irvine, CA 92714-4190.
W. Steven Lanier is the EPA Project Officer (see below).
The complete report, entitled "Continuous Performance Monitoring Techniques for
Hazardous Waste Incinerators," (Order No. PB 89-195 192IAS; Cost: $15.95,
subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield. VA22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Air and Energy Engineering Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC27711
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
EPA/600/S2-89/021
CHICAGO
------- |