United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S7-85/013 July 1985
Project Summary
Evaluation and Demonstration of
Low-NOx Systems for TEOR
Steam Generators: Final Report—
Field Evaluation of Commercial
Prototype Burner
G. England, Y. Kwan, and R. Payne
The goals of this program were to
develop, demonstrate, and evaluate a
low-NQ burner for crude-oil-fired
steam generators used forthermally
enhanced oil recovery (TEOR). The
burner designed and demonstrated
under this program was developed
from design criteria established in
bench- and pilot-scale experiments.
This report describes the results of the
final phase of the program in which the
full-scale (16 MW() commercial proto-
type burner was successfully installed
and tested in the Kern County, CA, oil
fields on a conventional TEOR steam
generator. A 30-day continuous moni-
toring test demonstrated the capability
of the burner to continuously maintain
NOL emissions of 70 ppm with CO
emissions below 50 ppm and particu-
late emissions below 0.23 g/dscm.
Detailed emission measurements also
showed negligible emissions of organic
species, including EPA priority pollut-
ants. Thermal efficiency of the steam
generator was similar to that prior to
the low-NOg burner retrofit and was
within the normal range for conven-
tional steam generators. The mechani-
cal performance of all major burner
components was satisfactory-
This Project Summary was deve-
loped by EPA's Air and Energy Engi-
neering 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 order-
ing information at back).
Introduction
Enhanced oil recovery processes are
applied to oilfield production in order to
extract heavy, viscous crude oil and tar
sands which cannot otherwise be pro-
duced. A significant fraction of total U.S. oil
reserves require application of enhanced
oil recovery in order to be realized. Ther-
mally enhanced oil recovery (TEOR)
involves injecting wet steam which is typi-
cally produced by combusting crude oil in
oilfield steam generators ranging in size
from 7 to 15 MW capacity. More than
90 percent of all oilfield steam generators
in the U.S. are in California, about one-
third of which are in Kern County. About
one-third of the produced crude oil is con-
sumed by the steam generator, amount-
ing to over 200,000 barrels (nearly 32
million liters) of crude oil consumed per
day at full capacity.
The crude oilsfired in these steam gen-
erators are typically high in nitrogen (0.8
to 1.0 percent) and sulfur content. Com-
bustion of these fuels leads to high levels
of N0xand SOxemissions unless preven-
tative measures are taken. The contribu-
tion of fuel-bound nitrogen to NOX emis-
sions from fuel oil combustion is well
documented. A survey of conventional
TEOR steam generators in Kern County
showed that uncontrolled NOX emissions
-------
ranged from 160to 825 ppm (corrected to
3 percent 02), depending on operating
conditions and design variables, with an
average emission level of about 325 ppm
at an average excess oxygen level of 4.5
percent. These high emission levels and
deteriorating air quality have prompted
state and local legislation regulating NOX
emissions from TEOR generators, which
threatens to limit oil production unless
NOX control methods are applied. For
certain new or modified stationary sour-
ces (including TEOR steam generators)
these regulations require application of
the Best Available Control Technology
(BACT) or the Lowest Achievable Emis-
sion Rate (LAER) to control the emissions
of any air contaminant or precursor for
which there is a national ambient air
quality standard (including NO,). Addi-
tionally, NOX emissions from alt steam
generators are currently limited to 130
mg/MJ (about 225 ppm, corrected to 3
percent oxygen). Further reductions to
108 and 60 mg/MJ (about 190 and 105
ppm) may be required if ambient NO2
concentrations exceed certain trigger
levels. NOX control techniques including
Iow-N0x burners, postflame NH3 injec-
tion, or other postflame treatment
methods (e.g., selective catalytic reduc-
tion) have been considered in order to
comply with regulations. Enhanced oil
recovery operations are projected to
expand in Kern County through 1995.
The level of N0xcontrol required to meet
both growth and air quality goals has typ-
ically been difficult to achieve with avail-
able technology while maintaining
acceptable CO and particulate emissions
as well as practical flame conditions in
the steamer.
This report describes the final phase of
a program which addresses the need for
advanced NC^ control technology for oil-
field steam generators. A full-scale (15.7
MW,) burner system has been developed
and tested, the concept for which was
based on fundamental studies. The
design development phase of this pro-
gram has been extensively documented.
The full-scale burner was constructed
and tested in an experimental test fur-
nace prior to being retrofitted to a field-
operating steam generator. This report
describes the retrofit and testing of the
burner on a conventional steam genera-
tor firing heavy crude oil in Kern County,
CA. The emission goals of the program
were: (l)todevelop to commercial scale a
low-NC^ heavy fuel oil burner;(2)to dem-
onstrate a full-scale burner system for
use either as a retrofit or in new units; (3)
to evaluate the system in the field over a
prolonged period of time; (4) to achieve
NOX emissions less than 85 ppm and CO
less than 45 ppm with low smoke/partic-
ulate emissions and acceptable flame
shape; and (5) to ensure acceptance of
the technology by the industry. All of
these goals were achieved.
Concept Background and
Development
Combustion-generated NOX emissions
can be reduced by combustion modifica-
tion techniques which involve staging
the heat release process. Techniques
such as flue gas recirculation strive to
control NO formed from molecular nitro-
gen (thermal NO) by suppressing peak
flame temperature, and are only partially
effective with nitrogen-containing fuels.
NO formation from nitrogen in the fuel
(fuel NO) is very sensitive to reactant stoi-
chiometry, and can be significantly
reduced by initially burning the fuel
under fuel-rich conditions. Staged com-
bustion, therefore involves creating a
fuel-rich zone to promote formation of
molecular nitrogen from the nitrogen
species (HCN, NH3, NO) evolved as the
liquid fuel decomposes, followed by a
fuel-lean zone optimized for minimum
NO formation.
The mechanisms controlling NOX for-
mation during staged combustion were
identified in a previous study for liquid
fuels ranging from distillate and residual
oils to alternative coal- and shale-derived
oils. The key parameters were first-stage
stoichiometry, thermal environment, and
residence time. NOX was relatively
insensitive to second (burnout) stage
parameters. These bench-scale studies
showed that under optimum staged con-
ditions, NOX emissions below 100 ppm
were possible and were independent of
fuel nitrogen content.
Refractory
Lining
Based on the results of the bench-scale
studies, prototype combustors were
designed and tested at 2 x 106 and 10 x
106 Btu/hr to further develop scaling
criteria for the design of a full-scale (60 *
106 Btu/hr) burner. These pilot/scale
tests confirmed that a staged combustion
system could be designed and scaled
over a 150:1 range which is capable of
achieving less than 85 ppm NO (at 3 per-
cent O2) firing high-nitrogen residual oil,
with low CO and smoke emissions.
Burner Design
'• Figure 1 shows the full-scale burner.
Optimizing both the fuel-rich and fuel-
lean stages is achieved utilizing a physi-
cally separate first-stage chamber,
formed by a 2.1 m I.D. horizontal cylinder
which is refractory lined and recupera-
tively cooled to maintain first-stage
temperature; the exterior of the chamber
is also insulated to prevent heat loss. The
recuperative design reduces thermal
inertia and thermal stresses developed
during transient (start-up and shutdown)
operation by employing a relatively thin
layer of refractory. Substantial primary
air preheat is developed, which enhances
full vaporization near the fuel injector.
A commercial air register, ignitor, and
fuel gun are used in the primary ignition
zone. The atomizer is a twin-fluid
internal-mixing atomizer using steam for
atomization. Primary throat diameter
was scaled up from the pilot-scale
burners on the basis of constant velocity.
The exit diameter of the chamber is
reduced to provide a first-stage exit
velocity of about 50 ft/sec (15 m/sec)
while reducing radiative heat losses from
the first stage.
Secondary air is admitted at the
chamber exit through discrete ports
oriented parallel to and normal to the
Secondary
Air Inlet
I i \ II T~I
Figure 1. Full-scale commercial prototype burner design.
Steam
Generator
Radiant
Section
-------
burner axis. The distribution of secondary
air can be varied to provide some degree
of control over second-stage mixing.
Testing on the bench and small pilot-
scale systems had shown that emissions
were insensitive to second-stage mixing
and excess oxygen level; however, at 2.9
MWt, results suggested that these par-
ameters may have greater influence on
emissions and flame shape in larger
systems.
The burner is equipped with a hybrid
electropneumatic control system for nor-
mal ignition sequences and load modula-
tion. A programmable controller controls
first-stage stoichiometric ratio and
second-stage excess oxygen level for
minimum NOX emissions. The hybrid ap-
proach was selected for the reliability and
easy field maintenance of a pneumatic
system, plus the flexibility and more pre-
cise control possible with a programma-
ble electronic controller.
Field Retrofit
After the preliminary burner eval-
uation was completed in the test furnace,
the burner was transported to the host
steam generator site in Kern County. The
burner had undergone about 131 hours
of operation during the preliminary eval-
uation, and first-stage parameters had
been optimized.
The retrofit task of the demonstration
program involved selecting an existing
steam generator typical of those cur-
rently in operation to host the demonstra-
tion, transporting the burner to the host
site, removing the existing burner hard-
ware, and installing the prototype burner
hardware and controls. TEOR steam gen-
erators are relatively simple in construc-
tion compared with boilers, and utilize a
single-pass drumless design. The radiant
section is formed by a horizontal,
refractory-lined steel cylinder, with the
burner at one end and an exhaust tran-
sistion leading to a convective econom-
izer section at the other end. Steaming
tubes extend axially and are supported
near the refractory on tube hangers
around the generator circumference. The
entire unit, with feedwater pump and
controls, is normally skid-mounted and
shop-assembled and is shipped by rail car
or truck to the installation site.
Retrofit installation of the Iow-N0x
burner onto the host steamer required
replacing the refractory-faced front wall
of the radiant section, lengthening the
foundation and skid to accommodate the
length of the burner, extending plumbing
and electrical wiring, and installing sup-
plementary controls (e.g., programmable
controls, additional limit switches and
relays, and oxygen probe). Revised oper-
ating procedures to accommodate heat-
up and cooldown of the refractory lining
were also developed. Following comple-
tion and shakedown of the retrofit, test-
ing was initiated.
Field Test Results
The steam generator was field tested in
three phases: (1) optimization, (2)
detailed characterization, and (3) 30-day
evaluation.
The purpose of the initial test series
was to optimize the burner operating
parameters to achieve safe start-up and
shutdown, acceptable flame characteris-
tics in the steam generator radiant sec-
tion, and low NO, CO, and smoke
emissions. The steam generator was
gradually brought to full load on crude oil.
Initial emission measurements were
consistent with results obtained in the
test furnace. However, at full load, flame
impingement on the walls of the radiant
section near the burner was encountered
(Figure 2). The flame shape was much
wider and shorter compared to that
obtained in the test furnace, most likely a
result of smaller furnace diameter in the
steam generator.
The initial degree of control over
secondary air injection was not sufficient
to produce an acceptable flame, so other
modifications were considered. Although
a considerable body of literature des-
cribes the behavior of confined double-
concentric jets in both nonreacting and
flame environments, there is little infor-
mation for highly confined systems sim-
ilar to the present burner/furnace
combination. The multijet method of
secondary air addition also added
another degree of uncertainty in attempt-
ing to design the optimum modification
by classical methods. A very brief series
of 1/5-scale, cold isothermal modeling
tests were therefore conducted using an
existing flow modeling facility in order to
evaluate the potential effectiveness of
the proposed modifications.
The hardware for the 1/5-scale model
was geometrically scaled. Secondary air
jet velocity was held constant while pri-
mary flowrate exit velocity was reduced
to maintain the same momentum ratio as
at full scale. The flow pattern was visual-
ized with plane illumination and injection
of soap bubbles using a commercial
neutral-buoyancy bubble generator. Mix-
ing patterns were determined by tracer
concentration measurements.
The baseline configuration was evalu-
ated first to determine whether the
approach to scaling would produce
results similar to field observations. The
flow patterns in the model and full-scale
steamer appeared to be similar, charac-
terized by a strong external recirculation
zone near the burner exit, rapid expan-
sion of the primary jet toward the wall,
and a lazy central recirculation zone. The
point where the boundary of the primary
streams reached the wall in the model
correspond approximately to the point
where flame impingement had occurred
in the actual steam generator. The appar-
ent spreading angle of the primary jet
boundary was about 20 degrees (half-
angle). The model also indicated that pri-
mary fluid was rapidly entrained into the
secondary jets and external recirculation
zone, very near the burner exit. Overall,
the results obtained with the model in the
baseline configuration appeared to
represent conditions observed in the
steam generator.
Figure 3 shows model results for base-
line conditions and for two modifications
considered for the full-scale burner. The
first modification (3b) involved decreas-
ing the first-stage exit diameter. The pro-
posed diameter reduction increased the
primary to secondary jet momentum ratio
from 0.35 to 0.56. The resulting flow
pattern showed that the point where the
primary jet reached the wall was moved
50 percent farther downstream, with an
apparent spreading angle of 15 degrees.
Velocity in the external recirculation zone
was somewhat reduced, and the central
recirculation zone disappeared entirely.
Tube Hangers
Impingement
Region
iT^Jf
™ ^^
^^^(LjEi^
^•7 ""
V|
-------
(a) Initial Configuration
Tube
Hangers
(b) Modification 1: Reduced (c) Modification 2: Same as
Exit Diameter Modification J Plus
Increased Secondary
Nozzle Diameter
Figure 3. Effect of changing primary and secondary jet momentum on mixing and flow
patterns in cold isothermal model.
The mixing profiles indicated that the
entrainment of primary fluid toward the
walls near the burner was significantly
reduced. Downstream of the region near
the exit, both streams appeared to be well
mixed, although downstream conditions
in the model may not accurately repres-
ent full-scale conditions.
A second field modification considered
was to remove inserts from the axial
secondary air ports, thereby enlarging
the port area and reducing the momen-
tum of the secondary jets. Figure 3c
shows the flow and mixing patterns
obtained with both modifications simu-
lated in the model. This combination
resulted in a primary to secondary jet
momentum ratio of 0.99. Reduction of
the secondary jet momentum further
reduced the apparent spreading angle of
the primary fluid boundary to about 13
degrees, and significantly reduced the
primary fluid concentration at the walls
of the model near the burner exit. In spite
of the delayed mixing between the
streams near the burner, good mixing
was still achieved at a distance about
equivalent to the midpoint of the steam
generator, as shown by the region of 0.7
primary fluid concentration.
The results of the isothermal model
tests indicated that entrainment of pri-
mary combustion products toward the
furnace walls near the burners could be
reduced or delayed by modifying the exit
geometry. The rationale for selecting one
of the modifications over the others was
based on interpretation of the isothermal
model results as well as engineering
judgement based on experience. Reduc-
ing the primary zone exit diameter
appeared to offer reasonable potential for
reducing entrainment without adversely
affecting downstream mixing. Addition-
ally, if the result of this modification was
not satisfactory, the secondary air ports
could be enlarged afterward. Since this
appeared to be a reasonable and cost-
effective approach, a temporary sleeve of
low-grade refractory bricks was installed
in the primary exit to increase the velocity
of gases at the first-stage exit by 47 per-
cent. The secondary air ports were not
changed.
Burner Optimization
The second series of burner shake-
down tests showed that the modification
had been successful in eliminating the
flame impingement problem completely
with all 16 secondary air ports wide open.
The visible flame was significantly nar-
rower and slightly longer than the origi-
nal flame. The center of the flame
appeared clear with no signs of smoke or
central recirculation zones. Flame shape
was similar to the region in Figure 3b
bounded by the isopleths of 0.6 to 0.7
primary fluid concentration. Overall
flame length was about 5.5 to 6.1 m
(between the third and fourth rows of
tube hangers). The "tail" of the flame
occasionally licked the steam tubes;
however, this was considered minor and
did not raise concern over tube or refrac-
tory life. Since the flame shape produced
by the first modification was considered
adequate, no attempts were necessary to
further improve flame shape, and burner
optimization tests were initiated.
Figure 4 shows NO, CO, and smoke
emissions from the steam generator fir-
ing at 54 x 1Q6 Btu/hr after optimization
of second-stage flame shape. Data are
shown versus first-stage stoichiometric
ratio for two excess oxygen levels. The
fuel was Kern Front crude oil (Table 1).
Minimum NO levels were between 55
and 65 ppm (corrected to 3 percent oxy-
gen). CO and smoke emissions were also
low at the optimum stoichiometry; how-
ever, below the optimum stoichiometry,
smoke was slightly higher for 2 percent
excess oxygen than at 3 percent. This
behavior was attributed to second-stage
mixing; however, since conditions below
the optimum stoichiometry do not repres-
ent normal operation, no further optimi-
zation was required. NO and CO
emissions were insensitive to excess
oxygen. It should also be mentioned that
the measured CO emissions were near
the detection limit of the continuous
(non-dispersive infrared) analyzer and
Table 1. Properties of Kern Front Crude
Oil Used in Full-Scale Burner
Field Evaluation
Kern Front
Crude
Oil
Ultimate Analysis, wt %
Carbon 85.42
Hydrogen 1088
Nitrogen 0.83
Sulfur 1.05
Ash 0.03
Oxygen {by difference) 1.79
100.00
Specific Gravity (@ 15°C) 0 978
Viscosity
SSU @ 140°F 2,450
cp @ 60°C 518
SSU@210°F 274
cp @ 99°C 58
Heat of Combustion
Btu/lb, Gross 18.310
Net —
kJ/g, Gross 42.6
Net —
-------
150
I
•7$
o
100
50
Excess Oi(Dry)
A 2.0 Percent
O 3.0 Percent
15
O
^
00
100
8 BO
0
10
8
0.5 0.6 0.7 0.5
First-Stage Stoichiometric Ratio
Figure 4. Field test results: NO, CO, and smoke emissions
optimized burner configuration (54 x /0B Btu/hr).
may represent interference by C02. Mea-
surements of COby gaschromatography
indicated that true levels were below 1
ppm.
Long Term Evaluation
Particulates
Based on the results of the optimiza-
tion tests, ideal operating conditions
were programmed into the burner control
system. A more detailed emission char-
acterization was performed at the opti-
mum full-load operation point, including
paniculate mass loading and size distri-
bution, organic compounds, and manual
(reference method) gas analyses, in addi-
tion to the normal continuous gas anal-
yses. Total paniculate mass loading was
determined three ways (EPA method 5,
cascade impactors, and modified EPA
Source Assessment Sampling System).
Results from five measurements ranged
from 23 x 1Q3 to 46 * 103 /L/g/m3 (0.010
to 0.020 gr/dscf) of flue gas. This is the
level expected for quantitative conver-
sion of ash in the fuel. Visual inspection
of paniculate catches indicated that no
carbonaceous paniculate was present.
Figure 5 shows paniculate size distribu-
tion, for the optimum full-load operating
condition. Most of the paniculate is very
fine, with approximately 65 percent
.below 1 um.
0.6
0.7
from steam generator with
Organic Emissions
Emission of organic compounds was
also determined. Total (volatile, semi-
volatile, and non-volatile) organic com-
pound emissions were below 0.3
mg/dscm). Emission of priority pollu-
tants was between 6 and 14 pg/dscm.
Although no Federal standard has been
established for emission of organic spe-
cies, these levels are considered low for
oil-fired sources. Emissions of NH3and
HCN were also low, below 1 ppm.
30-Day Test
NOX C0?, CO, S02, and O2were moni-
tored continuously in the steam genera-
tor exhaust during 30-day test under
another EPA contract. Complete results
are not yet available. Flue-gas oxygen
concentration averaged about 2.8 per-
cent (dry-basis) during this period, in
agreement with the control system set
point.
NOXemissions averaged about 69 ppm
during the 9-day period for which
detailed data were available, and CO
emissions remained below 50 ppm. N
emissions typically ranged between 5
and 75 ppm (corrected to 3 percent 02).
SO x emissions were measured during
• this period. SO2 concentration ranged
8
Q
.a
00
1
0.8
0.6
0.4
0.2
0.1
Total Mass Loading:
34 x rO3 ijg/m3 f0.015 gr/dscf)
i
0.01
Figure 5.
10 50 90
Cumulative Percent Undersize
99
99.99
Field test results: paniculate size distribution (by cascade impactors) under optimum
conditions.
-------
between about 520 and 650 ppm (cor-
rected to 3 percent OJ and averaged
about 580 ppm. These levels are in the
range expected based on 100 percent
conversion of the sulfur in the fuel.
Preliminary evaluation of results
obtained over the entire 30-day period
indicates that these results are typical of
the entire period.
Efficiency
Thermal efficiency of the host steam
generator was determined before and
after the commercial prototype burner
was retrofitted. Table 2 shows thermal
efficiency determined by input/output
measurements and by heat loss. In gen-
eral, the heat loss method is considered
to be more accurate because of the
smaller errors involved with each mea-
surement. Unrealistically high efficiency
determined by the input/output method
is most likely due to errors in the mea-
surement of steam quality. Data obtained
by the host operators prior to the burner
retrofit showed heat loss efficiency rang-
ing from 83.6 to 87.8 percent (neglecting
unmeasured and radiation losses). Aver-
age heat loss efficiency was 85.5 per-
cent. Data obtained during the burner
tests prior to the 30-day test showed
average heat-loss efficiency of 86.1 per-
cent. Thus it can be seen that thermal
efficiency was similar before and after
the burner retrofit.
Mechanical Performance
After the 30-day test, the burner was
inspected to determine the mechanical
condition of each major component. The
burner had undergone over 1600 hours
of testing and was cycled 20 times, 7 of
which were unforeseen shutdowns,
including three power outages. Addition-
ally the burner had survived the rigors of
being transported 480 km from the EER
test site in El Toro, CA, to the host steam
generator site.
The overall mechanical condition of the
burner was very good after the 30-day
test. A key area of concern was how well
the refractory lining had survived the 30-
day test, especially the numerous ther-
mal cycles. Inspection of the refractory
lining showed that all refractory, includ-
ing the primary burner throat, was in
excellent shape, except for a small sec-
tion of brick on the front wall and the
temporary sleeve in the first stage exit.
These relatively minor problems have
been corrected. The burner control sys-
tem successfully maintained emissions
of criteria pollutants within the program
goals for the duration of the 30-day test
without operator supervision. This
proves the practicality of maintaining
minimum NOxemissions through control
of first stage stoichiometry. Minor excur-
sions in NOxoccurred due to drift in the
fuel-flow meter output as a result of
changes in ambient temperature. The
output of the fuel flow meter is utilized by
the programmable controller to maintain
constant first stage stoichiometry. The
drift problem has also been corrected.
Performance of all other control ele-
ments was satisfactory.
The mechanical condition and opera-
bility of the burner were generally satis-
factory at the end of the 30-day test.
Scaling and Applicability
Criteria developed in bench- and pilot-
scale tests were applied to the design of
the full-scale prototype Iow-N0x burner.
These criteria: (1) optimized of "the fuel-
rich first stage conditions for maximum
conversion of fuel-bound nitrogen to N^
and (2) optimized second-stage condi-
tions for minimum thermal NO and
smoke formation. The key design criteria
are:
1. Fuel Injection
- High quality atomization.
- Premixed fuel/air.
- Minimal heat extraction to maxi-
mize fuel vaporization rate.
2. First-Stage Fuel-Rich Zone
- Stoichiometric ratio approxi-
Table 2. Thermal Efficiency of Host Steam Generator
A. Prior to Burner Retrofit
Date
9/2/82
1 1/22/82
12/6/82
1 1/4/83
8/16/83
5/19/83
Heat
Release (a)
MWt
15.7
18.4
16.6
15.7
12.1
16.7
Excess O2
wet basis
3.7
3.1
2.8
2.8
2.3
2.9
Steam (b)
Quality
66
82
68
75
81
73
Thermal (c)
Efficiency
80
82
80
86
91
93
Flue Gas
Exhaust
Temperature
°C
177
259
160
232
215
232
Thermal (c)
Efficiency
87.1
83.6
87.8
84.8
85.1
84.8
avg
15.9
2.9
74
85.3
213
(a) per barrel of crude oil
(b) by electrical conductivity
(c) input/output - determined by host
(d) heat loss - determined by EER according to ASME method. Estimates were used where measurements were not taken.
85.5
B. After Burner Retrofit
Date
1/5/84
1/7/84
1/7/84
1/9/84
avg
Time
1225
—
0725
0750
—
Heat (a)
Release
MWt
15.7
15.7
15.7
15.7
15.7
Excess
o.
%. dry
2.9
2.9
2.9
3.0
2.9
Steam
Quality (b)
%
83
73
83
84
81
Thermal
Efficiency (c)
%
103
87
97
95
95.5
Flue Gas
Exhaust
Temperature
°C
196
204
210
234
211
Thermal
Efficiency (d)
%
86.4
86.4
86.2
85.4
86.1
-------
mately 0.7 to minimize total fixed
nitrogen (TFN) concentration.
- Residence time in excess of 400
msec to allow sufficient TFN
decay.
- Control of heat loss to produce a
first-stage temperature in excess
of 1427°C to promote rapid con-
version of fuel nitrogen fragments
to molecular nitrogen.
3. Second-Stage Air Injection
- Partial quenching to minimize
thermal NO formation in the
second stage.
- Refractory choke to prevent back-
mixing and reduce heat loss.
- Intermediate to rapid second-
stage mixing to minimize smoke
formation and control flame
shape.
Full-scale burner tests, firing high-
nitrogen heavy oils in the experimental
furnace and in the oilfield steam genera-
tor, confirmed that the design criteria
could be applied to full-scale hardware to
produce the expected emission results.
Figure 6 compares NOX emissions from
bench-, pilot-, and full-scale tests versus
first-stage residence time. The results
represent a 750:1 range in scale. Below
approximately 0.6 seconds, NOX emis-
sions from the tunnel furnace are slightly
higher than from the pilot-scale systems
due to higher heat losses from the first
stage associated with the smaller scale.
Data from the full-scale system indi-
cate that increasing residence time
above 0.6 seconds is less beneficial. This
asymptotic behavior may indicate a shift
in the controlling mechanisms from first
to second stage processes at very low
NOX levels. Earlier pilot-scale tests firing
nitrogen-free fuels (distillate oil, pro-
pane) produced minimum NOX levels of
about 40 to 50 ppm from the optimized
burner configuration, which was attrib-
uted to second-stage thermal NOxforma-
tion. Although full-scale burner perfor-
mance indicated that emissions exhi-
bited some sensitivity to second-stage
parameters (mixing, confinement), this
sensitivity is much less severe than typi-
cally encountered in conventional sys-
tems: the greatest impact is on flame
shape.
Figure 7 compares NOX emissions
from the prototype burner to field test
data for conventional 50 x 106 Btu/hr
steam generator burners and for other
current N0xcontrol technology. Average
NOxemissions from conventional bur-
ners range from about 230 to 280 ppm
over the range of excess air investigated.
, By comparison, emissions from the pro-
o.
0.
-3
O
9.
x
O
1
5
5
§
140
120
100
80
60
40
20
A
O
O
Tunnel Furnace 70 x 103 Btu/hr (21 kW)
Small Prototype 3x10* Btu/hr (1 MW)
Intermediate Prototype 10 x 10* Btu/hr (3 MW)
Commercial Prototype 55 x 10e Btu/hr (16 MW)—Test Furnace
Commercial Prototype 54 x /O6 Btu/hr—Field Test
0.2 0.4 0.6 0.8 1.0
First-Stage Residence Time, seconds
1.2
Figure 6.
Comparison of A/0X emissions from bench-, pilot-, and full-scale prototype burner
designs.
totype low NOX burner are about 65 ppm
and insensitive to excess oxygen. This
represents a 77 percent reduction over
average NOX emissions at 3 percent ex-
cess oxygen, without adverse impact on
other pollutant emissions. Other low-
NOX burner data indicated that the main
benefit of the burners tested was
improved operability at lowexcessair
levels. Recent low-NOxburnertechnol-
ogy has shown that significantly reduced
NOX emissions can be achieved by de-
layed fuel/air mixing within the steam
generator in combination with flue gas
recirculation; however, the impact of the
result ing flame conditions on furnace
integrity has not been fully evaluated:
some low excess oxygen conditions can
result in high CO and smoke emissions.
NOX reduction by postflame NH3 injection
into the steam generator radiant section
has produced N0xemission levelscom-
parable to those achieved in this pro-
gram. Test results indicated that it was
difficult to maintain optimum NH3 inject-
ion conditions over extended periods
because of changes in furnace heat
transfer caused by tube fouling in the con-
vective section. This could lead to NH3
breakthrough or higher N0xemissions. If
the practical problems can be resolved,
these developing technologies may prove
to be key to NOX reduction.
Conclusions
The prototype Iow-N0xburner which
was developed in this program demon-
strates the applicability of the general
design criteria developed in bench- and
pilot-scale studies. Results of the 30-day
test demonstrated that all program emis-
sion goals were met for an extended
period of time with no adverse impact on
steam generator performance. Following
the test program, the host management
requested that the burner remain
installed on the steam generator. Burner
performance will be monitored to deter-
mine long-term performance and estab-
lish operating and maintenance costs.
-------
500
400
§; 300
0
200
;oo
\ \
50 x 10* Btu/hr Steam Generators
Conventional Burners
A verage of 64 Tests
± Std. Dev.
Low-N0« Burners
Low-NOi Burner
NH3 Injection •
This Work
I
0 12345
Excess O2 (Dry), percent
Figure 7. Comparison of prototype burner performance to conventional technology and
current low-NOi burner technology.
G. England, Y. Kwan, andR. Payne are with Energy and Environmental Research
Corp.. Irvine, CA 92714.
Michael C. Osborne is the EPA Project Officer (see below).
The complete report, entitled "Evaluation and Demonstration ofLow-NOi Burner
Systems for TEOR Steam Generators: Final Report—Field Evaluation of
Commercial Prototype Burner," (Order No. PB 85-185 874/AS; Cost: $ 17.50,
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:
Air and Energy Engineering Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park. NC27711
U. S. GOVERNMENT PRINTING OFFICE: 1985/559-111/20612
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