United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S7-86/044 Apr. 1 987
Project Summary
The Establishment of Design
Criteria for Optimum Burners for
Application to Heavy Fuel Fired
Package Boilers
G. C. England, D. W. Pershing, and M. P. Heap
This report describes results of a re-
search program to develop low-NOx
heavy oil burners for application to in-
dustrial package boilers. Bench scale
studies have been conducted which
define the mechanisms of NOX forma-
tion and control during staged com-
bustion. These studies showed that
>80% of total NO, emissions can be
due to conversion of fuel-bound nitrogen
to NO,. Conceptual design criteria were
established based on these bench scale
studies for an optimized two-stage
combustion system which minimizes
NOX emissions from conversion of both
fuel-bound nitrogen and molecular
nitrogen in the combustion air.
Volume I of the report documents
Phase 1 of this program, bench scale
studies which defined optimum condi-
tions for two-stage combustion. This
information led to a conceptual two-
stage low-NOx burner design. Volume
II gives results of pilot scale experiments
conducted in two test facilities with
nominal capacities of 0.9 and 2.9 MWt,
including tests of commercial burners
for both firetube and watertube boilers.
A wide range of petroleum-, coal-, and
shale-derived fuels were investigated.
Tests were also conducted with proto-
type advanced low-NOx burners which
demonstrated that NOX emissions <
100 ppm (corrected to 0% O2) could be
achieved almost independently of the
bound nitrogen content in the fuel. The
conceptual design was successfully
scaled from 21 kWt to 0.9 MW, to 2.9
MW, with similar NOX emissions
performance.
This Project Summary was developed
by EPA's Air and Energy Engineering Re-
search Laboratory, Research Triangle
Park, NC, to announce key findings of
the research project that Is fully docu-
mented in two separate volumes (see
Project Report ordering information at
back).
Introduction
NOX emissions from stationary combus-
tors can be reduced by combustion modi-
fication techniques which involve staging
the heat release process. However, the
application of these techniques to re-
sidual-fuel-oil-fired combustors has been
only partially successful because of a
tradeoff in pollutant emissions. The de-
crease in NOX emissions is often ac-
companied by an increase in paniculate
emissions. The optimization of combustion
modification techniques to control NOX
emissions from liquid-fuel-fired combus-
tors has also proved difficult because of
the limited knowledge of the controlling
phenomena.
The conversion of the nitrogen con-
tained in liquid fuels to NOX can contribute
significantly to the total NOX emissions
when such fuels are burned in stationary
combustors. The amount of fuel NO (NO
produced from fuel nitrogen) increases
with increasing fuel nitrogen content.
The other contribution to NOX emissions,
thermal NO (produced from molecular
nitrogen), depends primarily on tempera-
ture and oxygen availability and is rela-
tively insensitive to fuel properties. Thus,
as fuel nitrogen content increases, fuel
-------
NO constitutes an increasing fraction of
the total emissions. The formation of
thermal NO depends strongly on tempera-
ture; therefore, combustion firing density
and heat extraction control the amount of
thermal NO produced. Fuel NO formation
is strongly affected by fuel/air mixing
conditions and depends on burner design.
Many studies have dealt with the
mechanism of fuel nitrogen oxidation,
resulting in the following simplified ex-
planation. Initially the nitrogen in the fuel
is released during thermal decomposition.
The nitrogen-containing hydrocarbons are
pyrolized, and the dominant nitrogen
compound evolved is probably HCN. The
fate of this HCN is then almost totally
determined by the local reactant stoichio-
metry:
• Fuel-Lean. The presence of oxygen
favors the formation of NO. For
homogeneous premixed condition,
>75% of the fuel nitrogen could be
converted to NO. The heterogeneous
nature of liquid fuel combustion
usually limits the conversion to <50%
(unless the fuel nitrogen content is
low), and this depends on atomizer
and air delivery system design.
• Fuel-Rich. The absence of oxygen
favors the formation of N2. Under
fuel-rich conditions, fixed nitrogen
species exist in the gas phase mainly
as NO, NH3, or HCN, and their relative
concentrations depend on stoichio-
metry and temperature.
For typical fuels and combustion condi-
tions, equilibrium total fixed nitrogen
(TFN) concentrations (the sum of NO,
HCN, and NH3 concentrations) are <1.0
ppm for mixtures containing between 60
and 70% of the theoretical air require-
ments. Thus, if a combustor could be
operated to achieve these near-equilib-
rium TFN levels, fuel nitrogen conversion
would be minimized.
Staged combustion is the modification
of the combustion process to minimize
fuel NO formation and, provided heat
removal occurs in the second stage,
thermal NO formation is also restricted.
In staged combustion, fuel is mixed with
less than the stoichiometric air require-
ment. These conditions maximize con-
version of fuel nitrogen to N2 prior to the
addition of the remaining air to complete
combustion. Staged combustion can be
achieved through burner design by re-
ducing the rate of fuel/air mixing pro-
ducing a fuel-rich zone in the core of the
flame, or by physically dividing the total
airstream, thus giving a well-defined
fuel-rich zone. Under most practical con-
ditions the limit of NOX control for liquid
fuels by staged combustion has tradi-
tionally been dictated by the onset of
smoke emissions.
The objective of the beginning of this
program was to extend the studies con-
ducted under an earlier EPA contract.
The specific goals were to:
• Document conceptual designs for
low-emission heavy fuel oil burners
suitable for firetube and watertube
package boilers.
• Determine the optimum time/tem-
perature/stoichiometry history dur-
ing staged liquid fuel combustion in
order to minimize NOX and particulate
emissions in advanced low-emission
burners and combustors.
• Develop optimum atomizers for ad-
vanced low-NOx combustors.
• Extend a prior study of fuel effects to
include a wide range of synthetic
liquid fuels.
Bench Scale Studies
Volume I of the report documents the
bench scale studies conducted in a 21
kW, down-fired refractory tunnel furnace.
The total range of fuels included in the
fuel effects studies included 3 distillate
petroleum oils, 13 petroleum-derived
residual fuel oils, a heavy petroleum crude
oil, and 9 coal-and shale-derived liquid
fuels. An analysis of each of these fuels
is presented in the full report.
Fuel NOX emission was determined
directly in the tunnel furnace by sub-
stituting (for combustion air) a nitrogen-
free oxidant consisting of argon, oxygen,
and carbon dioxide (the furnace is dubbed
the "Argon" furnace for this reason).
Total and fuel NOX emissions for all of the
fuels tested under excess air conditions
are given in the full report. These data
were taken at 5% excess O2, 132°C air
preheat, and 0.53 cmVsec firing rate. An
ultrasonic fuel atomizer was used with
an air atomization pressure of 103 kPa
(gauge). Fuel viscosity was maintained at
12 cSt (0.000012 m2s) by appropriate
selection of fuel temperature. Total NOX
refers to emissions produced with air as
the oxidant. Fuel NOX is defined as the
emissions measured when burning the
fuel in the argon/oxygen/carbon dioxide
mixture. Both total and fuel NOK emissions
increase with increasing fuel nitrogen
content. The difference between total and
fuel NOX is defined to be thermal NOX
which is approximately constant for all of
the heavy residual oils. In general, alter-
native fuels have higher nitrogen contents
than petroleum-derived fuels and there-
fore produce higher fuel NOX emissions.
With few exceptions, fuel NOX emissions
from both alternative and petroleum-
derived fuels appear to correlate well on
the basis of fuel-nitrogen content. The
total NOX emissions from some alternative
fuels are higher than from pure petro-
leum-derived fuels of similar nitrogen
content which suggests a greater pro-
duction of thermal NOX. Distillation results
indicate that both total mass and nitrogen
are evolved for these alternative fuels at
significantly lower temperatures than for
the petroleum-derived residual fuel oils.
Thermal NO formation may be increased
for these fuels because of higher peak
flame temperatures in the early portion
of the flame since more fuel is burned
prior to vitiation of the combustor air with
recirculated combustion products, or
because the relatively high vaporization
rates produce higher local combustion
intensities.
TFN levels were measured at the exit
of the fuel-rich first zone as a function of
first-stage stoichiometric ratio (SR,) for
the Alaskan diesel oil, three petroleum-
derived liquid fuels, three alternate liquid
fuels, and methane doped with 0.79%
nitrogen (by weight) as ammonia. All
fuels investigated showed similar trends.
TFN concentration decreased with de-
creasing SR, and minimized at about SR,
= 0.8. TFN increased significantly as the
primary zone stoichiometry was further
reduced. TFN for both the ammonia-doped
methane and the fuel oil with similar
nitrogen content showed similar char-
acteristics under fuel-lean conditions.
However, below SRi = 0,7 the heavy oil
produced significantly less TFN than the
gaseous fuel. These results suggest that,
although the impact of fuel composition
is reduced under staged conditions, there
can still be a significant impact on NOX
emissions.
The ultimate level of exhaust NOX
produced during staged combustion re-
sults from conversion of TFN existing the
first stage and any thermal NOX produc-
tion which occurs during burnout.
Second-stage thermal NOX production
was not considered to be significant in
this study because changes in heat ex-
traction during burnout had almost no
effect on final emissions. Minimum ex-
haust NOX and TFN concentration at the
exit of the first stage were measured as a
function of total fuel-nitrogen content for
seven liquid fuels and the methane/
ammonia mixture. In general, the mini-
mum exhaust NOX concentration occurred
at SRi = 0.78 ± 0.02. NOX emissions and
TFN under staged conditions correlate
well with total fuel-nitrogen content, but
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the slope is significantly less than under
excess air conditions. Only the SRC-II
heavy distillate exhibited unusually high
exhaust NOX emissions, and this was the
direct result of high first-stage TFN yield.
NO, NH3, and HCN were substantially
higher at the optimum stoichiometry for
this fuel than for fuels with comparable
nitrogen content. The increased TFN may
be the result of basic chemical bonding
differences between the parent coal from
which the SRC-II was derived and petro-
leum liquids. Since this fuel was not
tested at pilot scale, this anomalous be-
havior could not be confirmed; however it
is well outside the limits of normal ex-
perimental errors. The results do indicate
that high exhaust NOX levels can be
directly associated with high first-stage
TFN levels.
TFN concentrations were found in
excess of equilibrium levels. It has been
suggested that increasing the tempera-
ture of the primary zone would prove
beneficial. The impact of first-stage heat
extraction was investigated in the bench
scale tunnel furnace by inserting or re-
moving cooling coils to extract heat along
the walls of the furnace, and by inserting
or removing choke sections in the furnace
which reduce radiative heat loss. The
results presented in the full report, ob-
tained with crude shale oil, demonstrate
the impact of first-stage heat loss on the
fate of fuel nitrogen. The hot conditions
refer to the furnace without primary zone
cooling and with a choke section installed
at the exit of the first stage to minimize
radiative heat loss from the first stage.
Cooling coils were added to the first
stage, and the radiation choke was re-
moved for the cool furnace conditions. Ex-
haust NOX and primary zone gas tem-
perature are reported as a function of
stoichiometric ratio for these two furnace
conditions. Minimum NOX emissions were
reduced for the hot furnace case, and the
optimum stoichiometry was shifted
toward more fuel-rich conditions.
Axial profiles in the report explain this
shift in the minimum emission levels.
Heat extraction from the first stage im-
pacts the rate of decay of TFN species.
Under cold conditions, both NO and HCN
essentially freeze; whereas, without heat
extraction, the initial rate of decay for all
three species is much faster, leading to
low TFN concentrations at the exit of the
fuel-rich first stage. Heat extraction also
affects the rate of CO oxidation.
The bench scale results demonstrate
that a two-stage combustion system can
be driven toward equilibrium levels by
increasing the temperature in the fuel-
rich first stage. Since the ultimate level of
TFN at the exit of the first stage is
kinetically limited, the minimum NOX level
is controlled by a tradeoff between
temperature in the rich stage and the
time required for TFN decay at that
temperature. This suggests that an
optimum staged combustion system
should minimize heat loss from the first
stage to maintain gas temperatures as
close to adiabatic as possible. Conditions
in the second stage should also be
optimized. The oxidation of TFN to NO is
much lower in diffusion flames than in
premixed flames; therefore, mixing should
be controlled to provide an attached dif-
fusion flame in the second stage. This
suggests that relatively slow mixing
should take place between second-stage
air and first-stage combustion products.
Mixing should also be controlled to mini-
mize peak second-stage flame tempera-
tures, thereby minimizing thermal NOX
formation. Studies undertaken in the
tunnel furnace under an earlier EPA study
showed that two methods of secondary
air injection (radial versus axial injection)
providing different mixing rates in the
second stage produced similar NOX emis-
sions, suggesting that NOX emissions
were insensitive to second-stage mixing
in that experiment. The scale of the bench
scale tunnel furnace is so small that
mixing was probably rapid in both cases.
However, results obtained at pilot scale
showed that mixing can have a significant
effect on NOX emissions. Since mixing is
a scale-dependent phenomenon, its
significance can be expected to increase
as scale increases. Second-stage mixing
effects were investigated in this study in
the pilot scale experiments.
In practice there are many possible
approaches to controlling mixing, includ-
ing variation in air injection velocity,
injection angle, number of injectors, and
swirl intensity. The approach taken for a
specific application must provide mixing
which most closely achieves the mixing
goals of the conceptual design while
maintaining a flame shape which is
commensurate with furnace geometry.
Pilot Scale Studies
The pilot scale studies described in
Volume II were aimed at identifying the
impact of fuel type and operating condi-
tions on NOX emissions using conven-
tional package boiler burner equipment,
and developing advanced Iow-N0x burner
concepts based on the optimization of
two-stage combustion. Experiments were
conducted in two test facilities: a 0.9 MW
test furnace which simulates the thermal
environment and geometry of a firetube
package boiler furnace (Firetube Simula-
tor), and a 2.9 MW test furnace which
simulates the thermal environment of a
watertube package boiler (Small Water-
tube Simulator — SWS).
The control of NOX emissions from
practical boiler/burner systems is usually
limited by a tradeoff between decreased
NOX emissions and increased smoke
emissions. The report shows NOX vs.
smoke emissions produced in the SWS
firing a California No. 6 oil with two
different burners. Results were obtained
with a commercially available burner
which is widely applied on packaged
watertube boilers. The combustion air is
divided into two coaxial streams with
variable swirl and flow through each
passage. Air and fuel are mixed in the
refractory throat of the burner and the
flame is stabilized by recirculation of hot
partial products of combustion. The data
show that, as the minimum NOX level
decreases through adjustments to the
burner and excess 02 level, smoke emis-
sions increase. The tests indicate that
minimum NOX emissions are similar for
similar smoke levels regardless of burner
settings. Data are shown with increased
furnace insulation to raise gas tempera-
ture at the exit of the furnace. This
resulted in slightly lower achievable
minimum NOX levels for equivalent smoke
emissions, suggesting that the burnout
of soot which is formed in the flame is
enhanced by the increased furnace
temperature.
Data were also obtained with a dis-
tributed mixing coal burner (designed
under a prior EPA contract ) which was
modified for oil firing. The burner is similar
to the commercial burner except for two
major differences: (1) throat diameter is
larger to decrease air velocity at the throat,
and (2) a portion of the combustion air is
added through four ports around the
burner throat. This permits the burner to
be operated with less than the stoichio-
metric air requirements at the burner
throat. The results is a fuel-rich zone
within the core of the flame with pro-
gressive air addition farther downstream.
Minimum NOX was again limited by the
onset of smoke emissions regardless of
burner settings. Comparison of results
obtained with the two burners shows
that about the same minimum level of
NOX emissions (150 ppm) was achieved
at a Bacharach smoke number of 6 in
spite of the substantial difference in
fuel/air mixing. This suggests that there
is a limit to the level of NO, control
-------
possible with conventional burner
systems
The bench scale studies indicated that
staged combustion can be further op-
timized by providing a physically separate
first stage. This permits the optimization
of conditions in the first stage without
affecting the second stage, or vice versa.
The bench scale studies suggested that
an optimum two-stage combustion system
should be designed according to the
criteria shown in Tahie 1 The combustion
process is divided into three zones: a fuel
injection zone, a fuel-rich holdup zone,
and a second stage burnout zone.
The table shows the desired optimum
conditions for each zone. Fuel injection
should provide rapid mixing of small fuel
droplets with the primary air and mini-
mum heat extraction in order to drive the
liquid fuel into the gas phase as quickly
as possible. The fuel-rich holdup zone
should provide a plug flow residence time
of >200 ms with minimum heat extraction
in order to maximize TFN decay Condi-
tions in the second-stage burnout zone
should provide slow mixing of the second-
stage air with the primary combustion
products in order to minimize oxidation of
TFN to NOX, and peak flame temperatures
should not exceed 1500°C in order to
minimize thermal NOX formation.
Two prototype Iow-N0x burners, shown
in Figure 1, were constructed with
nominal design firing rates of 0.6 and 2.9
MW. The first stage was constructed
from high-temperature refractories and
insulation to minimize heat loss through
the walls of the first stage, permitting
near-adiabatic temperatures. Fuel and
primary air were injected at the entry of a
divergent quarl which forms the initial
section of the fuel-rich holdup zone.
Calculated plug flow residence time in
the fuel-rich zone for a first-stage
stoichiometric ratio of 0.7 was about 0.56
sec for the small prototype burner, and
0.43 sec for the intermediate prototype
burner. The primary combustion products
were directed through a convergent sec-
tion which serves to minimize radiative
heat loss, ensure complete mixing of the
primary products, and minimize back-
mixing of the secondary air into the pri-
mary zone. Secondary air was injected
parallel to the burner axis annularly
around the primary exit. Two different
commercial atomizers were used, an
ultrasonic air-assist atomizer and an in-
ternal mixing steam-assist atomizer.
Also shown in Figure 1 are the Firetube
Simulator and Small Watertube Simulator
furnaces. The combustion chamber of
Table 1. Design Criteria for Scaleup of Low-NO* Concept
A. Fuel Vaporization Zone
1) Fuel/Air Mixing
2) Fuel Injection
31 Heat Extraction
4) Geometry
B. Fuel-Rich Holdup Zone
1} Residence Time
2) Heat Extraction
3) Geometry
4) Stoichiometry
C. Second-Stage Burnout
1} Secondary Fuel/Air
Mixing
2) Heat Extraction
Rapid mixing of fuel and air for maximum utilization of residence
time.
Finely atomized droplets to allow rapid vaporization of fuel. 98% of
droplets < 50 nm.
Minimum heat loss to maximize droplet vaporization.
Not defined.
Mean residence time >200 msec at high temperature.
Minimize heat extraction to maximize rate of decay of XN species
to N2. Preferably exit temperature >1400K
Designed to maximize true residence time/volume ratio.
Variable from 0.4 to J.I 6. Optimum at 0.65-0.85.
Slow to minimize peak flame temperature, thus minimizing second
stage thermal NOX formation.
Optimize to limit peak flame temperature <1811K.
the Firetube Simulator is 3.2 m long with
an internal diameter of 0.6 m. The furnace
is comprised of calonmetric sections
cooled by heat transfer fluid, and the wall
temperature is nominally 230°C. The
furnace of the Small Watertube Simulator
is 5.2 m long with an internal diameter of
1 8 m. The furnace is externally spray-
cooled and has a partial refractory lining
to control total heat extraction
The report shows the influence of first-
stage stoichiometric ratio (SR, on exhaust
emissions from the bench scale studies
carried out in the tunnel furnace and
from the prototype tests with residual oils
containing about 0.6% nitrogen. The
dependence of NOX emissions on SR,
was similar in all three experiments.
Smoke and CO emissions from the small
prototype burner were low for SR!>0.7,
but increased sharply as SR, was de-
creased further. CO emissions were <100
ppm, and smoke number was generally
<5 at the point where the minimum NOX
level occurred. CO and smoke emissions
performance for the intermediate proto-
type was similar. The minimum NOX level
ranged from about 89 ppm in the tunnel
furnace to 84 ppm m the small prototype
burner and 74 ppm in the intermediate
prototype burner. The optimum SR,,
appears to shift downward as scale in-
creases, going from 0.8 for the tunnel
furnace to 0.7 in the small prototype
burner and to 0.56 in the intermediate
prototype burner. This shift in the opti-
mum SR, and minimum NOX level is most
likely due to reduced first-stage heat loss
associated with the increase in scale
which leads to higher temperatures in
the first stage. Equilibrium calculations
(free energy minimization) confirmed that
the optimum SR, should move more fuel-
rich with increased temperature; how-
ever, the TFN concentrations which were
measured in the tunnel furnace and small
prototype burner are greatly (about 2
orders of magnitude) in excess of equilib-
rium values Hence, even with first-stage
exit temperatures of 1600°C at SR, = 0.7
and a first-stage residence time of 500
ms, kinetic limitations are significant.
Decreasing SR, reduced first-stage NO;
but, below about SR, = 0.8, significant
amounts of NH3 and HCN were formed.
Thus, as in the bench scale studies, there
exists a minimum in the exhaust NOX
because of competition between de-
creased first-stage NO and increased
oxidizable nitrogen species. Other than
shifting the optimum SR,, concept scale-
up did little to alter this competition or
the TFN species distribution.
The residence time in the fuel-rich
zone to achieve the desired TFN con-
centration is an important practical design
parameter since it largely determines the
size of the precombustor. Figure 2 sum-
-------
Second Stage
Air
Recycled
Flue Products
First Stage
Air
(a) Small Prototype Burner (0.6 MW1425°C. Further, the rate of NO
decay decreases significantly when the
NH3 concentration falls to zero, indicating
that TFN speciation is important in first-
stage processing. These calculations sup-
port the concept that reactions in the
form: NO + NH, — N2 are controlling the
fuel-rich TFN reduction, and that it is
essential to have both high temperatures
(>1425°C) and a proper TFN species
distribution in order to achieve very low
exhaust NOX levels. The calculations also
indicate the need for a long residence
time in the primary zone, but that the
required time to achieve a given level of
TFN decreases with increasing first-stage
temperatures.
Figure 3- summarizes NOX emissions
from each of the pilot- and bench-scale
experiments as a function of fuel nitrogen
content. Figure 3a shows NOX from the
commercial burners tested in the Firetube
Simulator and the Small Watertube
Simulator, the 3 MW distributed mixing
-------
200
l/oo
S
<0
-C
Uj
I
I
c
5 „
O IP Burner/SWS (2.3. 2.9 &
3.5 MWJ
O SP Burner/SWS (0.59 MWJ
D SP Burner/ FS (0.59 & 0.88
A Tunnel Furnace (21 kWJ
0 400
as
o
^
•6
O
-C
ki
3
.5
«J
u.
200
0.2 0.4 0.6 0.8 0 0.2
Primary Zone Residence Time, sec
0.4 0.6 0.8
Figure 2.
Effect of first-stage residence time on exhaust NO, emissions and TFN decay
for bench-scale, small pilot-scale (SP). and intermediate pilot-scale (IP) staged
combustors.
program to systems of different scale in
order to achieve NOX emissions <100
ppm even when firing high-nitrogen fuels.
Successful scaling criteria for advanced
low-NOx burners were developed and
verified over a range in scale of 750 to 1.
burner, the bench scale tunnel furnace,
and the two pilot-scale prototype burners.
Data from the tunnel furnace showed
that NOX emissions were > 1000 ppm for
fuels with nitrogen content X).6%. How-
ever, the application and optimization of
staged combustion dramatically reduced
NOX emissions to 190 ppm at this same
level of fuel-bound nitrogen. NOX emis-
sions from the Firetube Simulator with
commercial burner A were also high,
reaching 1060 ppm when burning the
high nitrogen (2.08 wt % nitrogen) crude
Paraho shale oil. In contrast, NO,; from
commercial burner B in the same furnace
were only 550 ppm when firing the same
fuel. This illustrates the strong depen-
dence of NOX emissions on burner design
for conventional burner systems. The
application of staged combustion to com-
mercial burner A further decreased NOX
emissions to 490 ppm when burning the
shale oil, but at the expense of increased
smoke emissions
NOX emissions from a 3 MW com-
mercial watertube burner in the Small
Watertube Simulator were much lower
than either of the commercial firetube
burners for fuels with equivalent bound
nitrogen content. NOX emissions were
very strongly dependent on fuel nitrogen
content with all of the conventional burner
systems which were tested. The NOX
emissions from the optimized tunnel
furnace and the prototype pilot scale
burners were influenced by fuel nitrogen
to a much lesser extent and were only a
fraction of the emission level from the
commercial burners.
Figure 3b shows the fuel nitrogen
dependence more clearly for the tunnel
furnace and for the pilot-scale prototype
burners. Data are shown for various fuels
including a distillate oil (with and without
pyridine), residual oils, a coal-derived
liquid, and a propane/NH3 mixture. The
data indicate that NOX is only weakly
dependent on nitrogen content with the
small and intermediate prototype burners.
Comparison of results obtained with the
NH3-doped gas, pyridine-doped distillate
oil, and actual residual oils shows that
differences in NOX due to fuel volatility
are small in absolute terms, especially for
systems with short residence time in the
first stage where the characteristic time
for the vaporization of fuel approaches
the time available for TFN decay. Scale-
up of the concept resulted in dependence
of NOX emissions on fuel nitrogen level.
This is probably due to the increased
temperature in the fuel-rich zone because
of the increase in scale.
In conclusion, these results indicate
that it should be possible to apply the
Iow-N0x burner concept developed in this
-------
woo
800
I
O
600
400
200
3.0% Excess 02
21 kW j
Tunnel /
Furnace' (Unstaged)
3.2
Commercial
Watertube Burner
MW Commercial
Firetube Burner B
MW Commercial
Firetube Burner A
Unstaged
•— Staged
21 kW tunnel
Furnace
(Optimum Staged) —
\
Prototype Burners
(0.6 & 2.9 MWJ
200
1.0 2.0
Fuel Nitrogen (by Wt), Percent
(a)
3.0
I
O 100 -
O
1,0
Wt % Fuel Nitrogen
Legend:
Intermediate
Prototype
2.3 MW,
Small
Prototype
0.59 MWt
O
O
a
O
(b)
2.0
Argon
Furnace
21 kW,
€
n
O
Propane + NH3
Distillate
(+ Pyridine)
Residual Oil
Coal Liquids
Shale Liquids
Figure 3.
Effect of fuel nitrogen content on NO* emissions from: fa) all bench- and pilot-scale burners tested, and (b) low-NO, prototype
burners.
-------
G. England. D. Pershing, and M. Heap are with Energy and Environmental
Research Corp., Irvine, CA 92718.
Joseph A. McSorley is the EPA Project Officer (see below).
The complete report consists of two volumes, entitled "The Establishment of
Design Criteria for Optimum Burners for Application to Heavy Fuel Fired
Package Boilers:"
"Volume I. Laboratory Scale Tests,"(Order No. PB 87-145 637/AS; Cost:
$18.95, subject to change).
"Volume II. Pilot Scale Tests," (Order No. PB 87-145 645/AS; Cost $18.95,
subject to change).
The above reports 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:
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/S7-86/044
0000329 PS
*GENCT
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