United States
 Environmental Protection
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

1. A  review of methods for moni-
   toring intermediate species in the
   exhaust gases.
2. Selection of instruments for eval-
3. Evaluation  of the instruments for
   response and potential interfer-
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

  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).

  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
  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-
•   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
2.  Selection of instruments for evalua-
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-
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-
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
•  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

   These data  support the  following
•  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
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.
   Excess  Air, 3.8 Iph

O Excess  Air, 5.7 Iph

   Excess  Air, 2.8 Iph

   Poor Atomization

   Quench  Coils
                                                      1000   3000   5000
                    CO  (ppm)
                                                                                      Excess  Air, 3.8 Iph .

                                                                                   O Excess  Air, 5.7 Iph

                                                                                   D Excess  Air, 2.8 Iph

                                                                                      Poor Atomization

                                                                                   O Quench  Coils
                                                                                   Excess Air,  3.8 Iph

                                                                                O Excess Air,  5.7 Iph

                                                                                D Excess Air,  2.8 Iph
                                                                                   Poor Atomization
                                                                                   Quench Coils


                                                            150   250
                 350   450   550
                   CH4 (ppm)

                                            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
Center for Environmental Research
Cincinnati OH 45268
Official Business
Penalty for Private Use $300