United States
                    Environmental Protection
                    Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
                    Research and Development
EPA/600/S7-90/001 Apr. 1990
&EPA         Project  Summary
                    Design  Report:  Low-NOx  Burners
                    for  Package  Boilers

                    R.A. Brown, H. Dehne, S. Eaton, H. B. Mason, and S. Torbov
                      A low-NOx burner was designed for
                   residual  oil-fired  industrial boilers
                   including boilers cofiring nitrated
                   wastes. The design  employs deep
                   staging to achieve NOX levels lower
                   than  conventional  low-NOx  ap-
                   proaches while maintaining an envi-
                   ronment  favorable  to  high waste
                   destruction efficiency. A cylindrical
                   shell  precombustor  chamber fired
                   substoichiometrically is  to  be
                   retrofitted to the burner opening of
                   the boiler. Remaining combustion air
                   would be  added  through retrofit
                   sidefire wall air ports. The design is
                   based on fabrication from lightweight
                   refractory block modules  covered
                   with  a Saffil™ fiber veneer. This
                   design  allows  quick thermal
                   response necessary for industrial
                   boiler applications  which is  not
                   possible with heavy castable or brick
                   refractory. Design  dimensions  and
                   materials specifications are made for
                   the thermal  input capacity range of
                   15-59 MWa.  Annular spool section
                   modules  are installed to fire higher
                   loads in the range of 15-29 MW, and a
                   geometric scale-up is used for larger
                   capacities. Construction and field
                   evaluation of the burner has not been
                   performed.
                       This   Project  Summary  was
                   developed by EPA's Air and  Energy
                   Engineering Research Laboratory,
                   Research  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 Readers more familiar with nonmetric units
                     may use the conversion factors at the back.
Introduction

  The Iow-N0x burner design reported
here  was  motivated by two regulatory
needs for more effective NOX  emission
reduction.  The primary  need is for
additional  emission reduction  for new
industrial  boilers firing high  nitrogen
residual oil. This  requirement  derives
from  Section  III of  the Clean  Air Act,
which  directs  that New  Source
Performance Standards  (NSPS) be
periodically reviewed and  tightened as
new  technology is developed-.  The
current standard for  residual-oil-fired
industrial package boilers  constructed
after July 6, 1984, was set at 172 ng/J on
an NO2 basis that corresponds to about
330  ppm. This emission  standard
requires a fairly low degree of  emission
reduction  from  uncontrolled levels
because of a lack  of demonstrated
technology applicable to package boilers
without introducing operational problems.
The current burner design effort was
initiated in part to support EPA in the next
series of revisions of the NSPS so that
additional emission reduction technology
would be available.
  The second need addressed by the
burner arises from the requirements of
the Resource Conservation and Recovery
Act  (RCRA) for disposal  technologies
such  as  thermal  destruction as
alternatives to land disposal. Where the
waste has high heat content, cofiring of
the  waste  in  industrial boilers  is a
practical means  of destruction while
recovering fuel credits from the heating
value. If the  waste has high  nitrogen
content,  however, the NOX emissions
from  cofiring may be unacceptably high
unless additional steps are taken for NOX
reduction.  Approximately  114 RCRA
Appendix VIII compounds and 30 F and K

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category listings  contain significant
nitrogen  in the form of nitriles, amines,
nitrobenzene, and  cyanides. Thermal
destruction  of these  wastes currently
presents a challenge to simultaneously
satisfy the intent of both the Clean Air Act
and RCRA. The current burner design is
intended to  offer waste  generators a
thermal  destruction  option which is  high
in destruction efficiency but low in  NOX
emissions  in order  to treat  nitrated
wastes.

Approach
   The design goals set for the low-NOx
burner were:
•  Fuels:
   - High nitrogen residual oil
   - Nitrated waste cofired with residual
     oil
   - Natural gas or distillate oil for light-
     off
•  NOX emissions:
   - 100-125 ppm with residual oil
   - 200-300 ppm with nitrated waste
     cofiring
*  Carbon monoxide: < 35  ppm
•  Smoke emissions: < 4 Bacharach
•  Capacity: 15-59 MW thermal input
•  Turndown: >5:1
•  Destruction efficiency with  waste
   cofiring: > 99.99%
   The  concept  for the  burner  was
derived  from an earlier EPA-sponsored
program in  which  a  deep-staging
prototype burner  was designed  and
tested for an  enhanced   oil  recovery
(EOR) steam generator firing crude oil.
With this concept, low conversion of fuel
nitrogen compounds to  NOX is achieved
by creating a hot, fuel-rich first stage with
relatively long residence time. The  high
temperatures and long residence time
serve to drive the kinetics of fuel nitrogen
intermediary species toward recombina-
tion to Ng rather than oxidation to NO.
   The  earlier EOR  burner  used  a
regenerative design  for the precombustor
in which the refractory was cooled by the
incoming  combustion air.  The
precombustor was fabricated from heavy
refractory bricks. The  NOX performance
for this prototype burner was 65 ppm.
   Although  the  earlier   design  was
appropriate for the EOR steamer, several
changes were needed for  the  more
demanding industrial  boiler application.
The  high density refractory in the EOR
burner required a long thermal response
time to  keep thermal stresses  within
acceptable limits. A faster  response was
needed  for the industrial boiler for rapid
start-up,  shut down, and load following.
For the boiler burner  design, this  was
approached by using a nonregenerative
design  with a  lightweight  insulating
refractory. This design also gave a better
capacity turndown potential  than  the
regenerable design.
   An additional  change was required  in
the size of the unit. The EOR NOX design
goal  was 65 ppm which necessitated a
precombustor nearly  as  long as  the
radiant section  of the steamer. In  the
current design, the goal of 100-125 ppm
allows  a shorter combustor  to be  built,
since the combustor  length is needed
primarily to provide  residence time  for
the  fuel  nitrogen  compounds  to
recombine  to N2 prior to introduction  of
stage air. The necessary length was also
reduced by introducing stage air from the
side  of the  boiler rather  than  at  the
interface of the  precombustor and  the
boiler.  This allows additional residence
time  in the boiler prior to  staging  for
nitrogen reactions to occur.
   Changes in the prior design  were also
needed in  the  sophistication  of  the
control  system  as well  as  safety
measures for rapid shutdown.

Burner Design
   The general burner design is shown in
Figure  1 for a nominal 15 MW heat input
capacity. For higher capacities, up to 29
MW, additional spools can be inserted  to
give  added  combustor volume. The
burner  diameter of 2.1 m was selected  to
adapt  to  the firing  wall  of  package
industrial  boilers,  and to  give gas
velocities in the  precombustor  typical  of
commercial operation with  lightweight
refractory.
   The combustor length was selected  to
give  a  predicted boiler exit  NOX level  of
85 ppm (corrected to 3% oxygen). This
target  gives  a  margin of  safety   in
achieving the design  goal of 100 ppm.
NOX  as a function of precombustor length
was  predicted using  test data from the
prior EPA  burner development for the
EOR steamer, and fuel nitrogen kinetic
calculations.
   For the precombustor stoichiometry  of
0.7 and  temperature  of 1540°C, inter-
polations and extrapolations  of the EOR
burner  test  data snowed a reduction  in
total  fixed nitrogen concentrations at the
exit of the precombustor to a level of 112
ppm, (at 0% oxygen) for a precombustor
residence time  of 400 msec.  A further
reduction in  total fixed  nitrogen  to  85
ppm  is predicted for the  cooling zone
between the exit  of the precombustor and
the injection  of second  stage air at the
stage  air  ports.  The  completion  of
combustion  in  the   second  stage  is
predicted to yield 60 ppm NOX (corrected
to 3%  oxygen)  from  the  fuel nitrogen
species, and 25  ppm thermal NOX for
total flue gas concentration of 85 ppm <
3%  oxygen.  For these  NOX  designl
predictions, the internal  combustor length)
needed was   2.7  m  for  the  15 M\
capacity.
   The throat  diameter at the transitionl
from the precombustor  to the boiler wasl
set at  0.9 m  for the 15  MW design tol
maintain exit  velocities below  35 m/s.l
This is the desired velocity at full load tol
allow  flame  shaping and capacity!
turndown similar to conventional  register)
burners.
   The location of  the stage air ports tol
be retrofitted to the boiler  sidewalls wasl
selected as the farthest  upstream point atl
which the fuel nitrogen kinetics are effec-l
tively frozen and no additional reduction!
would accrue from longer  exposure. For!
the nominal 15 MW design, this length!
was 2.1 m from the front:wall. This gives!
a second stage residence  time  of about!
620 msec. Calculations  of CO and smoke!
burnout show that, for this residence time!
and the design temperatures, the CO  is I
effectively  burned  out,  and  the  soot  is I
burned to below  the particulate emission!
standards.
   The burner to be fired at the front end I
of the precombustor is  a standard com-1
mercial  register  burner with  adjustable!
louver  blades.  This burner offers capa-l
bilities  for flame shaping  and provides I
high turndown  ratios. Fuel atomizers and!
jets are specified for residual oil, waste I
fuel, natural gas,  and (if needed) distillate I
oil for  light-off. Steam atomization  is I
specified for both the waste and residual [
oil.
   The insulating refractory configuration I
for the precombustor is shown in Figure
2. Section  I  is  Pyro-Bloc® H  with  a I
maximum design limit of 1340°C. Section
II is  Unifelt® XT, a Saffil veneer with  a
maximum design temperature of  1650°C
and  a recommended  continuous use
temperature of 1570°C. Section  III is  a
Unikote™ S coating  with a  use  limit of
1650°C. This  coating  is  partly  to give
structural  rigidity  prior to  curing and [
hardening of the insulating blocks.
   The front and rear end plates of the I
precombustor  use  a  more  complex
structure to accommodate  the burner |
throats and the need for greater  thermal
conduction away from the wall. The throat I
is fabricated from castable  refractory that
has  sufficient strength  to be  self-
supported.  The  castable will  also be
anchored by studs welded  to the front
plate and to the boiler front wall  tubes.  A
lightweight  castable refractory is placed
behind the  castable plastic refractory in
the front plate assembly.  This  provides

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                   Burner End
                    Section
                                             Boiler and End
                                             Throat Section
          Oil  X*
         Burner
        Location

                                                                                                      Boiler
                                                                                                      Location
                                                                                      Secondary
                                                                                         Air
 Figure 1.    The combustor section.

thermal  insulation while the  castable
refractory  and the studs conduct heat
away from the localized hot spots on the
front face.

Conclusions
   The initial objective of this project was
to design, fabricate, install,  and evaluate
the EPA low-NOx heavy oil  burner for an
industrial package boiler in the 59-74 MW
thermal  input range. Early in the project,
this objective was  revised  in two ways.
The capacity range for  the burner was
lowered and  broadened because  (1)
almost no industrial boilers  in  the 59-74
MW range were firing residual oil to  serve
as  a  demonstration,  and  (2)   most
operators who could  use the burner  for
low-NOx firing of nitrated  waste had
boilers in  the  15-29  MW thermal  input
range. The design range was accordingly
changed to 15-59 MW.
   The second revision of  the objective
was to adapt the design to  the industrial
boiler application with  the more stringent
requirements for faster thermal response.
   In addressing these  objectives, the
design  development effort in the current
project led to selection of the lightweight
refractory precombustor/burner design
with boiler  sidefire  air. Although  this
burner  was not fabricated and evaluated
in  the field, the following conclusions on
the design are based on  the process
engineering analyses done as part of the
design  development.

Emissions Performance
   The  estimated  performance of the
design  based on previous test results and
kinetic  estimates  is 85 ppm  at 3%
oxygen. The  emission goal selected for
this program  was 100-125  ppm, so the
final design should give  sufficient margin
to  meet  the  emission performance
demands of the intended market.


Burner Performance
   The use of the lightweight refractory
should  allow thermal response during
start-up, shutdown,  and load  swings
comparable to conventional burners and
should  not  constrain  industrial  boiler
applications. The burner is smaller, much
lighter; and cheaper than the earlier EPA
oil  burner design. The  control  logic
during start-up is more complex due to
the two-stage  operation,  but  not  out of
line with new boilers with advanced  low-
NOx systems.


Market Niche
   The burner addresses a need for both
high  nitrogen residual oil  firing  and
cofiring of nitrated wastes. Conventional
low-NOx burners for high-capacity pack-
age boilers firing high nitrogen residual
oil cannot lower emissions below the 250-
350 ppm  range without  causing flame
impingement, combustible emissions, or
instabilities. With  waste  cofiring, the
unique hot first stage used in the  burner
design  offers  simultaneous  high  waste
destruction efficiency  and  low-NOx
emissions. This burner avoids the  prob-
lem with other burners where measures

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                                                                                Pyro-Bloc Plus
                                                                                Module
                         III
 Figure 2.     Combustor cross section, Pyro-Bloc Plus module arrangement.
taken to lower NOX are counterproductive
for high waste thermal destruction.

Reliability
  The present  design uses lightweight
refractory to improve  thermal response
and  reduce failure risk  from thermal
shock.  The design increases the  risk,
however,  of  mechanical failure  and
overtemperature.

Scale-Up
  Burner design data are given over a
4:1   capacity  range.  The general
configuration,  stoichiometric  ratios,
residence times, and  temperatures all
remain nearly  identical across that range,
however. Therefore, there is not expected
to be significant performance variations
with scale-up.

Developmental Status
   Although the burner concept is derived
from the earlier  EPA oil  burner, many
differences in materials and configuration
were  made to  address  the  industrial
boiler market. Thus,  the  first prototype
field  evaluation  will  have  a  larger
component  of  shakedown  and
confirmatory testing than that for a simple
hardware scale-up..

Nonmetric Equivalents
   Readers  more familiar with  nonmetric
units may use the following  conversion
factors:
Yields
Metric
°C
cm
m
MW
ng/J
Pa
tonne
Multiplied by
9/5°C + 32
0.391
3.281
3.414
0.0023
0.0040
1.102
Nonmetric
°F
in.
ft.
1Q6Btu/hr
lb/106 Btu
in. H2O
ton

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   R.A. Brown, H. Define, S. Eaton,  H. B. Mason, and S. Torbov are with Acurex
        Corporation, Mountain View, California, 94039
   William P. Llnak is the EPA Project Officer (see below).
   The complete report, entitled "Design Report: Low-NOx Burners for Package
        Boilers," (Order No. PB 90-159 898/AS; Cost: $23.00, subject to change)
        will be available only from:
            National Technical Information Service
            5285 Port Royal Road
            Springfield, VA 22161
            Telephone: 703-487-4850
   The EPA Project Officer can be contacted at:
            Air and Energy Engineering Research Laboratory
            U.S. Environmental Protection Agency
            Research Triangle Park, NC 27711
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300

EPA/600/S7-90/001

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