United States
Environmental Protection
Agency
Industrial Environmental
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S7-84-076 Sept. 1984
Project Summary
Evaluation and Demonstration of
Low-NOx Burner Systems for
TEOR Steam Generators -
Design Phase Report
G.C. England, M.P. Heap, Y. Kwan, and R. Payne
A program to translate design criteria
developed in bench- and pilot-scale
combustors to a 16 MW commercial
grade prototype burner that can be
retrofitted to existing thermally en-
hanced oil recovery (TEOR) steam
generators is currently in progress.
Laboratory- and pilot-scale data have
been used to develop a low-NOx burner.
capable of operating with high-nitrogen
liquid fuels such as crude oils and
synthetic fuels. Emissions of NO« can
be minimized by application of a staged
combustion process in which the first
stage is thermally isolated and provides
long residence time under high temper-
ature, optimally fuel-rich conditions.
The design criteria for this process were
developed in a previous EPA-sponsored
study, carried out in a 21 kW (70,000
Btu/hr) tunnel furnace and applied to
two pilot-scale prototype burners at 0.6
MW (2 x 106 Btu/hr) and 3 MW (10 x 106
Btu/hr).
The report summarized here describes
results of the design development tests
and compares results of all three scales of
experiment. Firing a heavy fuel oil con-
taining above 0.6 percent bound nitro-
gen, test results indicate that NO« emis-
sions below 85 ppm (at 3 percent O2)
are possible while CO and smoke are
low. Translation of the design require-
ments to practical burner designs, and
additional requirements for initial
fuel/air contacting and second-stage
air addition are presented and dis-
cussed. Data obtained over a scale
range of 30:1 show that residence time
and temperature in the first stage are
the most important scaling parameters
for this low-NOx burner design and that
aerodynamic effects are second order
parameters. Detailed design of the 16
MW prototype burner is also discussed,
which was selected to meet the design
criteria as well as requirements for com-
mercial-grade oil field equipment. Key
aspects of the hardware design are the
use of commercial primary burner
equipment a refractory-lined first stage
chamber which is regeneratrvely air-
cooled, and variable second-stage air in-
jection to optimize emissions and flame
shape. Discussion of the detailed
design includes retrofit requirements
and specifications for primary throat/
atomizer design, first-stage residence
time and temperature, refractory lining
design, and preliminary requirements
for second-stage air injection. The bur-
ner will be briefly evaluated in a test fur-
nace prior to retrofit and performance
testing in a field-operating steam gener-
ator in Kem County, California.
This Project Summary was developed
by EPA's Industrial Environmental
Research Laboratory. Research Triangle
Park, NC, to announce key findings of
the research project that is fully docu-
mented in a separate report of the same
title (see Project Report ordering infor-
mation at back).
Introduction
Enhanced oil recovery processes are
applied to oil field 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.
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oil reserves require application of enhanced
oil recovery in order to be realized.
Thermally enhanced oil recovery (TEOR)
involves injection of wet steam which is
produced by combusting crude oil in oil
field steam generators, typically ranging
in size from 7 to 15 MW capacity. More
than 90 percent of all oil field steam
generators in the United States are
located in California, one-third (approxi-
mately 1000 units) of which are located in
Kern County. Approximately one-third of
the produced crude oil is consumed by
the steam generator, amounting to over
200,000 barrels of crude oil consumed
per day at full capacity. The crude oils
which are fired in these steam generators
are typically high in nitrogen (—0.8 to 1.0
percent) and sulfur content. Uncontrolled
emissions of NOX and SOX can therefore
reach high levels and potentially worsen
ambient air quality.
Local legislation regulating emissions
of NO, from oil field steam generators
threatens to limit oil production unless
NOX control methods are applied. A
ceiling on total NOX emissions from all
steam generators in Kern County has
been established which limits total
emissions to 1979 levels; thus new
generators cannot be brought on line
without reducing emissions from existing
ones. New generators are required to
have "best available control technology"
(BACT) which may include Iow-N0x
burners, postflame NH3 injection, or other
postflame treatment methods. In addi-
tion, if ambient N02 level in Bakersfield
exceeds a specified level, the total NO*
ceiling is lowered to the equivalent of
0.14 Ib NO,/10s Btu (60 mg/MJ) or 105
ppm NO, corrected to 3 percent oxygen, if
all steamers are in operation. Enhanced
oil recovery operations are projected to
expand through 1995. The level of NOX
control required to meet both growth and
air quality goals has typically been
difficult to achieve with available technol-
ogy while maintaining acceptable CO and
particulate emissions and practical flame
conditions within the steamer.
This program addresses the need for
advanced NO* control technology for oil-
field steam generators, and concerns the
development of a full-scale burner
system, for which the concept is based on
fundamental studies. The burner will be
retrofittable to existing steam generators
and will produce acceptable emissions of
CO and particulate while maintaining a
flame form compatible with the steamer
design. The emission goals for NOx are to
achieve less than 85 ppm NOx at 3
percent excess oxygen.
The major elements of this program
are:
1. Conceptual design development—to
verify and refine design scaling
criteria developed under previous
EPA contracts in order to develop
hardware designs.
2. Detailed burner design and construc-
tion—to produce a commercial-
grade full-scale burner suitable for
retrofit on an existing steam genera-
tor.
3. Burner optimization and evaluation—
to minimize pollutant emissions in a
field-operating TEOR steam genera-
tor firing high-nitrogen crude oil and
evaluate performance over an ex-
tended period of time.
The report discusses the first two
elements of the project, through comple-
tion of the detailed engineering design of
the full-scale (16 MW) commercial
prototype burner.
/VOX Formation and Control
NOX emissions from stationary com-
bustors can be reduced by combustion
modification techniques which involve
staging the heat release process. How-
ever, optimization of these techniques to
control NOx emissions from liquid-fuel-
fired combustors has proven difficult
because of the limited knowledge of the
controlling phenomena and the problems
associated with the scaling of combustion
systems.
Many studies have been carried out to
determine the mechanism of NO forma-
tion in flames, both from molecular
nitrogen (thermal NO) and from nitrogen
contained in the fuel (fuel NO). Field test
data and laboratory studies have estab-
lished the importance of fuel NO to the
total emission of NOX from residual fuel
oil flames. Thermal NO formation is strong-
ly dependent upon temperature, and its
formation can be reduced by decreasing
flame temperatures by techniques such
as the addition of cooled combustion
products to the combustion air (flue gas
recirculation). However, since most NO
formed in residual fuel oil flames is fuel
NO and its formation is not strongly
dependent upon temperature, flue gas
recirculation is not an effective NOX
control technique. Fuel NO formation is
very sensitive to reactant stoichiometry.
Fuel-rich conditions promote the forma-
tion of molecular nitrogen from fixed
nitrogen species (NO + NH3 + HCN) which
are formed as the liquid fuel decomposes.
Consequently, staged combustion (in-
volving the formation of a fuel-rich zone
either by delaying fuel/air mixing or by
dividing the combustion air sup_ply into
two and injecting one portion downstream
from the burner) is the most effective
NOx control technique for residual fuels.
In a previous study, parameters control-
ling the effectiveness of staged combus-
tion for a wide range of liquid fuels
containing bound nitrogen were defined
in a series of bench-scale studies which
were carried out in a refractory tunnel
furnace. Exhaust NO levels from a staged
combustion system depend on:
1. First-Stage Processing. Total fixed
nitrogen (TFN) is minimized if the
residence time of the fuel-rich
reactants is maximized at high
temperatures and at an optimum
stoichiometry which is temperature
dependent.
2. Mixedness. Since stoichiometry
must be controlled, it is important
that the reactants are well mixed.
3. Second-Stage Processing. Exhaust
NO levels are the sum of thermal NO
formation and conversion (or reten-
tion) of TFN species to NO during
heat release in the second stage, and
the second stage must be designed to
minimize these effects.
4. Fuel Properties. The rate of evolution
of nitrogen species from the liquid
fuel droplets has an impact because
it dictates the time available for N2
formation in the first zone. This can
be overcome by minimizing droplet
size.
This information has been used to
construct bench- and pilot-scale combus-
tors having NOX emissions below 100
ppm (corrected to 0 percent oxygen) and
acceptable emission levels for CO and
smoke when firing fuels containing
greater than 0.5 percent fuel-bound
nitrogen.
The bench-scale tests indicated that
TFN concentration is minimized most
effectively by increasing the temperature
of the fuel-rich zone. The combination of
high first-stage temperature, optimum
stoichiometry, and long first-stage resi-
dence time resulted in exhaust NOX levels
below 100 ppm regardless of the nitrogen
content of the liquid fuel. To translate this
information into a full-scale (i.e., 18 MW)
burner design requires information on
how the controlling parameters scale.
The approach used.was to obtain experi-
mental data with 2 x 106 Btu/hr (0.6 MW)
and 10 x 106 Btu/hr (3 MW) prototype
combustors, and thereby confirm the
appropriate criteria for the design and
fabrication of the full-scale combustor. In
addition, isothermal (cold flow) spray/flow^B
field tests were conducted to assessM
mixing and atomization characteristics
-------
produced by full-scale hardware in the
region near the burner throat.
Pilot-Scale Development
Prototype Combustors
Two prototype low-NOx burners, shown
in Figure 1, were constructed with
nominal design firing rates of 2 x 106
Btu/hr (0.6 MW) (small pilot-scale or SP)
and 10x 106Btu/hr(3 MW)(intermediate
pilot-scale or IP). Each test burner
contains three major elements
1 An air/fuel injection system
2 A fuel-rich holdup zone.
3 A secondary air injectiqn section
The primary zone is constructed from
high temperature refractories and insula-
tion to minimize heat loss through the
walls and permit near-adiabatic condi-
tions in the primary zone Fuel and
primary air are injected at the entry of a
divergent which forms the initial section
of the fuel-rich holdup zone. The residence
time in the fuel-rich zone, calculated at a
first-stage stoichiometric ratio of 0.7, is
approximately 0.50 sec for the SP burner
and 0.42 sec for the IP burner. The
primary products are directed through a
convergent section which serves to
minimize radiative heat loss, ensure
complete mixing of the primary products,
and minimize backmixmg of secondary
air into the primary zone Secondary air is
injected parallel to the burner axis
annularly around the primary exit
Fuel Injection
A number of different commercial
atomizers were used in the two combus-
tors. Most of the data were, however,
obtained with an ultrasonic, air-assist
atomizer and an internal-mixing steam-
assist atomizer. At the 0.6 MW scale, the
ultrasonic atomizer produced droplets
with a narrow size distribution about a
mean diameter of 20 um, and the
internal-mixing atomizer produced drop-
lets with a much broader size distribution
about a mean diameter of 40 //m At
larger scales the ultrasonic atomizer has
been found to produce droplets with a
mean size greater than 120/um.
Several air/fuel injection hardware
changes were investigated during the 3
MW burner testing. Table 1 summarizes
the first-stage hardware variations which
were evaluated. Most of the configura-
tions were variations on the fuel/air pre-
mixer concept with different exit geome-
tries. The premixer design is scaled up on
the basis of constant velocity and swirl
numbers from the 0.6 MW design utilized
in the small pilot-scale prototype.
Second-Stage Design
Second-stage mixing effects were
extensively evaluated in the 3-MW
studies, to determine limits of additional
NO reduction possible through variations
in the second-stage mixing and to
develop practical information on the
tradeoffs between NOx/smoke emissions
and flame shape. In addition to the first-
stage exit sleeve shown in .Table 1,
Recycled
Flue Products
Atomization
Air
Second
Stage Air
Burner
First Stage
Air
(bl Firetube Simulator
(a) Small Prototype Burner (0 6 MW)
Fuel & Air
Injection
Fuel-Rich
Holdup
Sections
Oil and
Atomizing
Fluid
. First-stage
Secondary
Air Injection
Second-stage Air
Fuel/Air
Premixer
(c) Intermediate Prototype Burner (3 MW)
Id) Small Watertube Simulator
Figure 1. Prototype burners and experimental test furnace
-------
several air injection port configurations
were tested to vary second-stage mixing.
The number of ports, diameter (yielding
two velocity levels), and distance from the
centerline were varied. Figure 2 illustrates
the different hardware configurations
used.
Test Facilities
The pilot-scale burner tests were
conducted at two test facilities:
• Firetube Simulator (FS) (Previous
Study). The combustion chamber is
3.2 m long with an internal diameter
of 0.6 m. The chamber is composed
of calorimetric sections cooled by
heat transfer fluid and has a nominal
wall temperature of 230°C. Only the
SP burner was tested in this facility.
• SmaH Watertube Simulator ISWS)
(This Study). The furnace is 5.2 m in
length and 1.8 m inside diameter, is
externally spray-cooled, and has a
partial refractory lining. The total
heat extraction is controlled by
varying the percentage of internal
surface which is covered by refrac-
tory. Both the SP and IP burners were
tested in this facility.
Pilot-Scale Results
First-Stage Parameters
Figure 3 shows the influence of the
first-stage stoichiometric ratio (SRi) on
exhaust emissions from the bench-scale
studies carried out in the tunnel furnace
and the prototype tests with different
residual oils containing approximately
0.6 percent nitrogen. The curves are
generally lower but similar in shape to
those obtained in other staged combus-
tion studies. As SRi decreased, NOx
emissions decreased rapidly until a
minimum was reached and then increased.
Smoke and CO emissions from the SP
burner were low for SRi > 0.7, but under
more fuel-rich conditions emissions
increased sharply. CO was less than 100
ppm and smoke number was generally
less than 5 at the point where the
minimum NOx level occurred. CO and
smoke emissions from the IP burner
were also low for SRi greater than the
point where minimum NOx occurred. CO
and smoke emissions from the IP burner
were also low for SRi greater than the
point where minimum NOx occurred;
however, for many of the configurations
tested, the sharp increase in emissions
below this point was less severe. Differ-
ences in second-stage thermal environ-
ment between the 2 x 106 Btu/hr (0.6
MW) firetube simulator and the 10 x 106
Btu/hr (3 MW) small watertube simulator
may contribute to the observed difference
in burnout of CO and smoke. Comparison
Table 1. First-Stage Hardware Configurations in 3 MW Tests
Configuration
. ...-LJ
jJ / sws
T~\
v 1 1
^ // x sws
I S 1 1
• • - n
... V1_J
i| /// ^"^ sws
——*\ . s . 1
n
First-Stage
— Premixer
— Swirl(S=O.4)
— Parallel Exit
— Premixer
— Swirl (S=0.4)
— Set Back Parallel Exit
tt
— No Swirl
— Parallel Exit
Second-Stage
— Axial Air Injection
— Annulus Injector
— 51 CM First-Stage Exit Diameter
— Axial Air Injection
— Annulus Injector
— 5 1 CM First-Stage Exit Diameter
— Annulus Injector
— 51 CM First-Stage Exit Diameter
sws
sws
— Premixer
— Swirl(S=O.4)
— Divergent Exit (L/D=2.6)
— 2 Channel (Low Velocity)
— Swirl
— Divergent Exit (L/D=t.1)
Axial Air Injection
Annulus Injector
51 CM First-Stage Exit Diameter
Axial Air Injection
Annulus Injector
36 CM First-Stage Exit Diameter
v,
sws
— Premixer
— Swirl(S=0.4)
— Divergent Exit (L/D=2.6)
Axial Air Injection
Annulus Injector
36 CM First-Stage Exit Diameter
L-T
sws
— Premixer
— Swirl(S=O.4)
— Parallel Exit
Axial Air Injection
Annulus Injector
36 CM First-Stage Exit Diameter
-------
(al
Secondary Air
Primary
Spriman
Zone
SWS
Annular
Furnace
Injector
Secondary Air
Primery
SWS
Inboard Ports
Zone
Furnace
(c)
Secondary Air <—*^JT
Primary
\ Primary
j Zone
SWS
Outboard Ports
Furnace
Figure 2. Secondary air injection configurations investigated with 3 MW pilot scale burner
(ports shown in axial orientation).
of the three sets of results indicates that
concept scaleup shifted the optimum SRi
from 0.8 to 0.7 in going from 70,000
Btu/hr (0.02 MW) to 2 x 106 Btu/hr (0.6
MW), and to 0.56 in going to 8 x 106
Btu/hr (2.5 MW). This shift can be
attributed to reduced heat losses and
therefore higher temperatures, and to
changes in fuel/air mixing characteris-
tics, associated with the increase in
scale.
The influence of burner load with the
IP burner is shown in Figure 4 with and
without air preheat. Fuel flowrate was
varied above and below the baseline load
from 2.3 MW to 3.5 MW throughput.
Minimum NOx emissions increased with
load, ranging from 95 ppm to 77 ppm at
3.5 to 2.3 MW load, respectively, without
first-stage air preheat. With first-stage air
preheat, minimum NOx ranged from 88 to
63 ppm at the same loads, respectively.
The optimum stoichiometry in the first
stage was not shifted significantly.
Optimum SRi varied from 0.54 to 0.56
with preheat and from 0.55 to 0.57 with-
out preheat. Smoke emissions were
insensitive to load.
The effect of atomizer and air distribu-
tion variations can be seen in Figure 5.
NOx emissions increased substantially
when the swirl vanes were removed from
the premixer assembly (Configuration III).
Optimum stoichiometry was also shifted
to the fuel-lean side. The steep depend-
ence of NO, on SRi was somewhat
reduced at high primary air preheat for
Configuration III; however, only limited
data was obtained. Observation of the
flame from the rear of the SWS indicated
that a rather bright, narrow jet flame
was formed in the first stage chamber.
Utilization of available volume for resi-
dence time is probably very poor in this
configuration, accounting for the increased
NOX emission.
The experimental narrow-angle Y-jet
atomizer and ultrasonic atomizer produced
similar NOx emissions under equivalent
conditions, although slightly higher than
baseline in both cases. Smoke numbers
from the Y-jet and internal-mixing
atomizer were 2 for all data shown in
Figure 5.
Second-Stage Effects
The method of secondary air injection
can potentially impact exhaust NOX
levels, and different modes of injection
have been examined in both prototype
burner systems. The standard annular
(parallel) air injection system provided a
relatively slow mixing rate and resulted in
long diffusion-type flames. In the small
prototype burner, rapid mixing was ob-
tained by injecting the second-stage air
radially through a water-cooled boom
inserted along the firetube axis from the
rear. NO, emissions remained essentiaHy
constant when the ratio of air between
the axial and radial injectors was varied:
however, smoke emissions were sub-
stantially decreased as secondary air was
transferred from the parallel injector to
the radial injector. Similar results were
obtained in both prototype burners when
swirl vanes were added to the annular
second-stage air injection system, sug-
gesting a relative insensitivity of NOx
emissions to changes in mixing while
providing some measure of control over
flame shape. In larger practical-scale
burner systems, however, mechanical
considerations may well preclude the use
of narrow annular passages for secon-
dary air injection. To overcome this
limitation the potential use of discrete
secondary air injection ports has been
investigated in the IP burner. Typical data
are presented in Figure 6a, and show that
with axial injection there is no difference
in minimum NOX between the annulus
and discrete ports; with radial injection to
induce rapid mixing, an increase of some
25 ppm NOx was observed. This configu-
ration produced short intense flames and,
although the level of smoke emission was
generally low, the range of operation over
which low smoke could be maintained
was extended. The reason for this
apparent increased sensitivity to mixing
at the larger scale is not immediately
apparent from the data, but is believed to
be due to increased formation of thermal
NOx in local high-intensity combustion
zones close to the air jets.
Figure 6 shows the results of doubling
the velocity of first-stage combustion
products entering the second stage. This
was accomplished by adding a sleeve to
the first-stage exit. The flame produced
by this configuration was very short with-
out a visible smoky trail. The increase
in velocity by a factor of 2 decreased
flame length by a factor of 3 to 4, and
increased NOX emissions to 95 ppm from
72 ppm. Further optimization of exit
velocity and swirl level may be possible to
improve NO, and flame shape character-
istics with the annular air injector.
All the TFN which exists in the first
stage does not result in NO in the
combustion products of the second stage.
Thus, it is important to design the second-
stage air injection system to minimize NO
formation from TFN species. In addition,
thermal NO formation must be minimized
which requires that second-stage flame
temperatures must be maintained below
some critical threshold. Heat extraction
between the fuel-rich zone and the
secondary air injection system allows
some control over temperature in the
-------
200
150
100
5
o'
so
-
i
»«
r 100
Q.
O'
0.4
0.6
0.8
1.0
0.4
0.6
S/f,
o.a
s/?,
i.o
Figure 3. Influence of scale on combustor performance.
second stage. Tests in the SP burner
showed that interstage cooling, in the
form of coils around the periphery of the
second-stage throat (approximately 6
percent of the heat input was removed),
decreased the minimum exhaust NOx by
approximately 20 ppm. Exactly analogous
results were achieved when 40 percent
flue gas recycle was introduced with the
second-stage air (ANOX = 18 ppm). In both
tests there was a minor impact on smoke
emissions; thus, it appears that at the
optimum operating conditions, second-
stage thermal NOx formation accounts for
approximately 20 percent of the total
exhaust NOx emissions. Use of interstage
cooling may become more important in
subsequent scaleup if air preheat is
added and/or rich-zone heat loss is
reduced further. Tests in the IP burner at
3.8 MW in which excess air was varied
from 0.3 to 4.5 percent produced a 16
ppm variation in NO,, suggesting about
the same order of magnitude for thermal
NOx formation as in the SP tests.
Without Preheat
o
o
o o
o o
With Preheat
o
O
•O
o o
0.4
0.5
0.6
0.7
0.4
0.5
0.6
0.7
200
ISO
I
I
i
roo
sa
Primary Air Temp = 52°C
• 3.5 MW
O 2.9 MW
O 2.3MW
t
200
150
too
50
_ 93.5 MW (Primary Air Temp •-
238 ± 5°C)
O2.9 MW (Primary Air Temp -
239 ± 5°C)
O2.3 MW (Primary Air Temp =
| 222±20°CJ
0.4
0.5
0.6
0.7
0.4
0.5
0.6
0.7
Sfl,
Sfl,
Figure 4. Influence of load on emissions from IP burner.
Scaling and Full-Scale Burner
Design
Design Criteria
The experimental work carried out on
the bench and prototype combustors has
provided an understanding of the control-
ling mechanisms of NOx formation and
control in staged liquid fuel combustion.
The data suggest that application of these
concepts can be achieved in a staged
burner which consists of three major
components with the following charac-
teristics:
• Fuel Injection System
— High quality atomization to pro-
duce a small mean droplet size.
— Rapidly mixed fuel and air.
— Minimal heat extraction and air
preheat to maximize fuel vaporiza-
tion rate.
• First-Stage Fuel-Rich Zone
— Stoichiometric ratio approximately
0.7 or lower to minimize TFN
concentration.
— Residence time in excess of 400
msec to allow sufficient TFN
decay.
— Control of heat loss to produce a
first-stage exit temperature in
excess of 2600°F (1425°C).
• 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 second-stage mixing
-------
to reduce smoke formation with-
out affecting minimum N0«.
The residence time in the fuel-rich zone
required to achieve the desired TFN
concentration i% an important practical
design parameter. Figure 7 summarizes
minimum exhaust NO, and TFN data for
the tunnel furnace and the prototype
burners firing in both the firetube
simulator and the small watertube simu-
lator as a function of the first-stage
residence time. At both bench and small
pilot scales, increasing the first-stage
residence time significantly decreased
exhaust NO, because of an associated
decrease in TFN. (Increasing first-stage
residence time allows HCN, NH3, and NO
to decay further toward equilibrium
val ues.)Both the exhaust NOX and the TFN
from the SP burner were lower than from
the tunnel furnace because of the
increased rich-zone temperature asso-
ciated with the increase in scale.
The first-stage residence time was
varied in the SP burner/firetube simula-
tor tests by altering the firing rate, and in
the SP burner/watertube simulator tests
by changing the reactor length at a fixed
firing rate. A strong correlation between
the two sets of experiments suggests that
the controlling processes are dominated
by kinetic effects (time and temperature)
and not by aerodynamics and that the
principal influence of firing rate is on
residence time. Clea/ly, increasing firing
rate also increases first-stage tempera-
ture, but this effect is small because even
at 2 x 106 Btu/hr (0.6 MW) the prototype
heat losses were low. First-stage exit
temperatures measured at SRi of 0.7
were 2950°F (1620°C) compared to
calculated adiabatic flame temperature of
3180°F(1750°C).
The key elements in these design
characteristics are the requirements for a
high-temperature, optimally fuel-rich,
primary combustion zone with a long
residence time. A number of the remaining
parameters are scale-dependent and must
be optimized at the burner scale under
consideration. The mean droplet size
produced by a given atomizer design, for
example, does not remain constant with
scale, but tends to increase as size
increases. Drop-size distributions pro-
duced by full-scale (18 MW) atomizers
under isothermal conditions showed that
the mean drop size was similar for an
ultrasonic atomizer and a Y-jet atomizer
(Figure 8); however, radial distribution of
fuel mass within the swirling flow field
was very different. While small droplets
are more favorable, combustion condi-
tions are such that droplet size alone does
200
150
roo
.
Primary Air Temp = 52°C
P Baseline - Swirl Number =i 0.4
• Zero Swirl
200
150
100
50
Primary Air Temp = 230°C
0.4 0.5 0.6 0.7
SR,
0.4 0.5
0.6 0.7
(a)
200
150
roo
i so
Primary Air Temp = 52°C
- O Baseline - Ultrasonic; Air;
69kPa
• 75 Degree Y-Jet; Steam;
483 kPa; Smoke No. = 2
2OO -
150
100
50
Primary Air Temp = 230°C
^Baseline - Ultrasonic; Air;
69kPa
^Internal Mixing; Steam;
483 kPa; Smoke No. = 2
0.4
0.5 0.6
SR,
0.7
0.4
0.5
•0.6
7
Ib)
Figure 5. Effect of (a) swirl and (b) atomizer type on NOn emissions.
not have a large impact on minimum
NOX. Rather, increased droplet size leads
to greater sensitivity to those parameters
which control fuel/air mixing and spray
penetration. For practical applications,
optimum results are obtained by selecting
and matching spray angles and air
register designs to provide for uniform
distribution and rapid mixing.
Similarly, the overall burner perform-
ance has been shown to be more
sensitive to the mode of secondary
combustion air injection at larger burner
scales. Rapid mixing is required to
suppress smoke formation, but may
impact minimum NOX performance. In
practical applications a major additional
concern is the shape of the second-stage
flame and its interaction with its heat
transfer surroundings, which can be
strongly influenced by mixing. Final-
designs of secondary air injection will
therefore represent a compromise be-
tween NOx emissions, flame shape, and
other pollutants such as particulates and
CO.
The impact of fuel type on the ability of
such burners to achieve low-NOx emis-
sions is also important. The influence of
fuel-nitrogen content on the performance
of the small-scale Iow-N0x prototype
burner was established by conducting
-------
200
ISO
^ roo
I
i so
2.9 MW
. No Preheat
o Vv»
. O Baseline (annular injector)
• 8 Axial Ports
+ 8 Radial Ports '
200
O 1BO
roo
50
2.9 MW
Primary Air Temperature
= 240°C
34m/s
17m/s £xit
Velocity
O Baseline (Configuration I)
• Configuration VII
0.4
0.4
0.7
0.5 0.6
SR,
(a)
Figure 6. Second-stage mixing effects.
i).5 0.6
SR,
(b)
0.7
O IP Burner/SWS (2.4, 3. 3.6 MW)
O SP Burner/SWS (0.6 MW)
D SP Burner/FS (0.6. 0.9 MW)
A Tunnel Furnace (21 kW)
~ 200
^
5
i
1
«
Uj
I
c
100
4OO
i
I,
| 200
0 0.2 0.4 0.6 0.8 0 0.2 0.4 0.6 0.8
Primary Zone Residence Time, sec
Figure 7. Second-stage NO, production and first-stage TFN decay for bench scale and pilot
scale.
tests with a distillate oil, residual oils, a
coal liquid, and propane + NH3. Data
obtained in these tests are shown in
Figure 9 which indicates that with the SP
burner minimum NO* emissions are only
weakly dependent upon total fuel nitrogen
content. Figure 9 also summarizes data
obtained in the small-scale tunnel
furnace, and in the larger 10 x 108 Btu/hr
(3 MW) prototype. Concept scaleup
reduced the dependence on fuel-nitrogen;
this is probably because of the increased
fuel-rich temperature. Thus this low NOX
concept should be capable of producing
NOx emissions less than 100 ppm at 0%
Oz (85 ppm at 3% Oz) even when firing the
high-nitrogen crude oils typical, for
example, of the Kern County oil fields.
Final Engineering Design
Two full-scale design concepts evolved
from the detailed engineering design
study. The first utilized a multilayer,
castable refractory lining to insulate the
first stage, similar to the pilot-scale
prototypes. Analysis of this design proved
that, although the criteria for temperature
and residence time could be achieved, the
refractory lining would be excessively
prone to failure due to thermal stresses,
especially during start-up and shutdown.
This is primarily due to the large thermal
inertia of the thick monolithic refractory
lining. An alternate design was developed
which utilizes a thin refractory lining
contained by a hallow cylindrical shell
which is cooled by the primary combus-
tion air. This "regenerative" design,
based in part on a commercial direct-fired
air heater design, was selected for
construction after consideration of sever-
al factors, including structural integrity of
the refractory lining, heat loss to sur-
roundings, temperature profile within the
first stage, space-efficiency (compact-
ness), and transient performance. Both
concepts employ commercially available
primary burner components, and secon-
dary air is injected through two sets of
discrete ports, oriented axially and radially,
to allow control over second-stage flame
shape..
Figure 10 illustrates the basic construc-
tion of the regenerative burner design.
The refractory lining is made up of 15 cm
(6-in.) thick, 90 percent-alumina brick
installed directly against the inner
stainless steel shell. Primary air enters
the hollow shell near the burner exit and
flows toward the primary burner throat,
cooling the shell and gaining preheat
(hence the term "regenerative"). Materi-
als and dimensions were selected com-
mensurate with the design operating
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conditions outlined in Table 2. A substan-
tial degree of conservatism was incorpor-
ated in the final design. The outer shell is
externally insulated to reduce heat losses
and personnel safety hazard. Second-
stage air is injected through a separate
module and can be mixed radially or
axially at the first-stage exit. After optimi-
zation of the secondary air injection, the
variable components can be fixed to
reduce complexity. Second-stage air
injection will be optimized for velocity and
radial/axial split.
Commercial-grade control equipment
has been used to accommodate the
additional control requirements of the
burner and provide simple interfacing
with the existing steam generator con-
trols. The control system is designed to
maintain first-stage stoichiometric ratio
and flue gas oxygenations through
closed-loop control. The system uses a
pneumatic primary control loop with a
feedback trim signal generated by a pro-
grammable controller and flow measure-
ment instrumentation.
Construction of the burner was com-
pleted in May 1983, with commissioning
in the field in October 1983. The burner
will be briefly evaluated in an experiment-
al test furnace prior to the field installa-
tion.
to
§
I
200
ISO
700
50
Hyvis 04
Y-Jet
O Centerline
• 16° Half Angle
1OO
200
30O
400
500
200
.8
co
§ 100
I
I
Hyvis 04
Ultrasonic
O Centerline
• 8° Half Angle
Figure 8.
100 200 300
Atomizing Pressure. kPa
Drop size from ultrasonic and Y-jet atomizers.
400
500
-------
200
T»
O
100 -
Legend:
i.o
Fuel Nitrogen, wt. %
Intermediate
Prototype
2.3 MW
•
•
Small
Prototype
0.6 MW
0
0
a
O
Argon
Furnace
21 kW
c
c
A
Propane + NH,
Distillate (+ Pyridine)
Residual Oil
Shale Liquids
Figure 9. Influence of fuel nitrogen on second-stage NO, - bench- and pilot-scale data.
10
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Igniter
Oil Gun
Flame Detector.
Control Panel
Steamer
\ Air
Skid \ Compressor
Feedwater Pump
Expansion
Combustion Joint
Air Blower
Ignitor
Oil Gun
Flame Detector
Skid
Feedwater
Pump
Steamer
Figure 10. Conceptual burner designs for TEOR steam generators.
Tattle 2. First-Stage Design Specifications and Performance
Horizontal Cylinder
Flat Wall Entrance
Configuration 30-Degree Convergent Exit Cone
Volume
Inside Diameter
Outside Diameter
Overall Length
Refractory Lining Thickness
Primary Burner Throat Diameter
First-Stage Exit Diameter
» at Design
g Point '
IPerformanc
Operatin
Load
First-Stage Stoichiometric Ratio
Gas Temperature
Hot-Face Refractory Temperature
Inner Shell Temperature
Primary Air Velocity at Primary Throat
Exit Gas Velocity
Mean Residence Time
18.3 m3 (650 ft3)
21 3 cm (7.0 ft)
262 cm (8.6 ft)
554 cm (18.0 ft)
15 cm (0.5 ft)
38 cm (1.25 ftj
130 cm (4.25 ft)
18 MW (60 x JO1 Btu/hr)
0.6O
165O°C(3000°F)
156O°C(2850°F)
335°C(650°F)
40m/s(130ft/s)
16m/s(50ft/s)
0.8s
11
"USGPO: 1984-759-102-10677
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G. C. England, M. P. Heap, Y. Kwan, and R. Payne are with Energy and
Environmental Research Corporation. Irvine, CA 92714-4190.
W. S. Laniar is the EPA Project Officer (see below).
The complete report, entitled "Evaluation and Demonstration of Low-NO* Burner
Systems for TEOR Steam Generators—Design Phase Report," (Order No. PB
84-224 393; Cost: $28.00, 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:
Industrial Environmental 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
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