United States
Environmental Protection
Agency
Air and Energy Environmental
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S7-85/045 Nov. 1985
&ER& Project Summary
Evaluation of the Riley Stoker
Corporation Distributed Mixing
Burner
R. Lisauskas, A. Abele, F. Jones, and R. Payne
The reduction of NO«. S0«, and par-
ticulate emissions from utility and in-
dustrial boilers has been a high priority
concern of the U.S. EPA and all of the
major boiler burner manufacturers for
several years. In fact, a number of
independent concurrent efforts have
been and are being conducted to devel-
op low-NOx burners. As part of EPA's
Limestone Injection into a Multistage
Burner (LIMB) program, this program
represents one portion of an effort by
the EPA to compare the results of these
individual studies and identify the most
promising approaches for further prog-
ress. Five Riley Stoker Corporation
(RSC) burners will be tested in the
EPA'sLargeWatertubeSimulator(LWS)
experimental facility at Energy and
Environmental Research Corporation
(EER) under this program. Results of
these tests will be compared with other
burners tested in the LWS and will also
be used to project the field performance
of the burners.
This report summarizes the results of
the first phase of testing that evaluated
the NOX performance and sulfur capture
potential of an RSC second-generation
low-NO. burner. These tests involved
the NOx optimization of a prototype
100 x 10" Btu/hr* RSC Distributed
Mixing Burner (DMB) followed by the
injection of dry sorbent materials for
SC-2 reduction. The DMB was deter-
mined to be sensitive to burner adjust-
ments in terms of stability, flame char-
acteristics, and emissions. It was nec-
"Metric equivalents are included, under Nomencla-
ture, at the back of this Summary for readers more
familiar with that system.
essary to iteratively modify the coal
spreader design and burner adjustments
to achieve acceptable NO, performance
with the three test coals. Following
optimization of the burner parameters,
the DMB performance was verified over
operating ranges typical of field instal-
lations. The SO: reduction potential of
the RSC DMB was studied using two
sorbents and two injection locations.
The burner was adjusted during injec-
tion of sorbent to determine the opti-
mum burner conditions for SO2 reduc-
tion and the extent of NO./SO, reduc-
tion tradeoffs.
This Project Summary was developed
by EPA's Air and Energy Engineering
Research Laboratory, Research Triangle
Park, NC, to announce key findings of
the research project that is fully docu-
mented in a separate report of the same
title (see Project Report ordering infor-
mation at back).
Introduction
The design of the prototype Ri ley Stoker
Corporation (RSC) Distributed Mixing
Burner (DMB) was based on EPA DMB
design criteria. The basic burner is shown
in Figure 1. The coal and primary air enter
the burner through a coal-head which is
connected to an axial coal nozzle. The
coal-head is equipped with adjustable
vanes to distribute coal uniformly in the
nozzle. The telescoping nozzle adjusts the
primary setback in the burner throat. The
venturi-shaped nozzle accelerates the
coal stream through the throat of the
venturi, concentrating the coal particles
in the center of the coal pipe prior to
reaching the coal spreader. An impeller-
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Adjustable
Swirl Control
Tertiary
Air Port
Venturi
Coal Nozzle
Coal
Spreader
Refractory
Throat
Tertiary Air
f Coal/Primary Air
t I Adjustable
C// Vanes
•Coal Head
Retractable
Coal Nozzle
Adjustment
Figure 1. The Riley Stoker Corporation 100x 10* Btu/hr distributed mixing burner.
type spreader, at the end of the nozzle,
imparts swirl to the coal and primary air,
providing for mixing with the secondary
air. Two concentric secondary air pas-
sages are supplied from individual wind-
boxes. Each air passage is equipped with
an adjustable register for swirl control.
The windboxes, which were incorporated
as an experimental expedient, facilitate
remote control of the air-flows from the
furnace control room. Tertiary (or staging)
air is supplied from four ports evenly
spaced around the burner exit. Tertiary
inserts (8, 10, and 12 in. in diameter)
permit evaluation of a range of tertiary
velocities.
During the optimization of the RSC
DMB, several iterative modifications were
made in the design of the coal spreader.
Previous testing at EER with RSC burners
indicated that NO, emissions could be
changed by a factor of two by modifying
the spreader design. The first design
tested with the RSC DMB was the con-
ically shaped spreader developed for the
Controlled Combustion Venturi (CCV)
burner. The spreader is shown in Figure
2(a). The remaining spreaders tested were
based on a 4-in. diameter support tube.
This large diameter body increased the
primary velocity through the venturi
nozzle thereby concentrating the coal
stream and improving the dispersion of
the coal with the impeller blades. These
designs are summarized in Figure 2(b).
Fuels and Sorbents
Three fuels and two sorbents were
utilized in the RSC DMB tests. Table 1
lists the laboratory analyses of the coals.
The Utah coal has been used at the test
facility in the development of low-emis-
sion, high-efficiency burners. Its char-
acteristics include low sulfur content
(0.74 percent, dry) and high-volatile mat-
ter (40.47 percent, dry). Indiana coal has
been used as the base fuel in the develop-
ment of LIMB technology because of its
relatively high sulfur content (2.73 per-
cent, dry). The Indiana coal has signif-
icantly less volatiles (34.26 percent, dry)
than the Utah coal. This difference would
test the applicability of the DMB to various
coals. The Illinois coal, from the Crown II
mine in Virden, IL, is the coal burned at
CILCO Duck Creek Station. The CILCO
station was the basis for previous studies
at EER of RSC burners, and the use of the
Illinois coal will permit extrapolation of
test results in EER's facilities to an
operating utility boiler. The Illinois coal
has a high sulfur content (3.97 percent,
dry) and provides the opportunity to
evaluate LIMB technology for high sulfur
fuels.
The two sorbents used for the evalua-
tion of S02 reduction potential were a
preground processed limestone (Vicron
45-3) and a preground hydrated lime
(Colton). These two materials represent
high-purity calcium-based sorbents. The
Vicron 45-3 is 98-99 percent pure CaCO3,
while the Colton hydrated lime is 90.5
percent Ca(OH)2. Mass median particle
diameters were 11 and 7 /urn, respectively.
(a) Spreader No. 1—Controlled Combustion Venturi Spreader
Coal +
Primary Air
Spreader
Design
2
3
4
5
Number
of Blades
4
4
4
4
Blade
Angle
15°
35°
35°
28°
Blade
Length
Long
Long
Short
Short
(b) Impeller Designs Based on 4-in. Support Tube
Figure 2. Coal spreaders tested in the Riley Stoker Corporation Distributed Mixing Burner.
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Table 1. Summary of Coal Composition
Utah Coal
Reporting
Basis
Proximate (% Wt)
Moisture
Ash
Volatile
Fixed C
Total
Sulfur
Btu/Lb
MMFBtu/Lb
MAP Btu/Lb
Ultimate (% wt)
Moisture
Carbon
Hydrogen
Nitrogen
Sulfur
Ash
Oxygen
Total
Elemental Ash
/O/ 14/fl
( /O VVl/
SiO?
AlzOa
TiOi
Fe^)3
CaO
MgO
/Va20
K2O
PiOs
S03
Optimization
Porf ormanco
As Rec'd
5.46
10.00
38.26
46.28
100.00
0.70
11930
5.46
67.59
5.09
1.21
0.70
10.00
9.95
100.00
of RSC
Dry
0.00
10.57
40.47
48.96
100.00
0.74
12619
14269
14111
0.00
71.50
5.38
1.28
0.74
10.57
10.53
100.00
66.17
16.49
0.68
4.95
3.72
0.87
1.27
2.11
0.30
3.07
DMB
The performance and emissions of the
RSC DMB were sensitive to its adjustable
parameters. As in previous
tests or HSU
Indiana Coal
As Rec'd
7.75
9.17
31.60
51.48
100.00
2.52
11498
7.75
66.42
4.56
1.10
2.52
9.17
8.48
100.00
Dry
0.00
9.94
34.26
55.80
100.00
2.73
12465
14048
13841
0.00
72.00
4.95
1.19
2.73
9.94
9.19
100.00
43.08
23.79
0.49
27.85
1.16
0.20
0.17
0.65
0.22
0.19
increased for
resulted
Illinois Coal
As Rec'd
10.66
9.37
34.51
45.46
100.00
3.54
11265
10.66
61.99
4.54
0.96
3.54
9.37
8.94
100.00
Dry
0.00
10.49
38.62
50.89
100.00
3.97
12609
14349
14086
0.00
69.38
5.08
1.08
3.97
10.49
10.00
100.00
49.45
17.28
0.68
18.41
4.33
0.83
1.40
2.15
0.18
4.31
Spreader No. 3, which
in a coal-head pressure over 14
in. H2O and low primary velocity. The
length of the blades was reduced for
Spreader No. 4 to attempt to decrease the
coal-head pressure. The coal-head pres-
sure remained excessively high for this
spreader. The final modification reposi-
tioned the blade angle and resulted in
acceptable performance, with stable
flames under staged conditions and flame
length between 1 9 and 20 ft.
The other adjustable burner parameters
include: (a) secondary air register vane
position, (b) secondary air bias, (c) coal
nozzle and spreader position, and (d)
tertiary air velocity. Under (a), the range of
register positions that produced stable
conditions and acceptable flame shape
was very narrow. Closing the register
vanes to less than 20° open increased
flame length. Opening the registers more
than 30° open resulted in the base of the
flame lifting off the burner exit with
resulting instability. For (b), the best
burner performance was achieved when
the secondary air flow was equally dis-
tributed to the inner and outer passages.
Bias to either passage resulted in longer
flames. For (c), the RSC DMB coal nozzle
was designed to vary primary setback, the
distance between the nozzle and the
burner exit. Retracting the nozzle venturi
increased the coal-head pressure with
little effect on flame shape. Again, the
actual effect depended on spreader de-
sign. The position of the spreader in the
venturi-shaped coal nozzle also affected
burner performance, but also depended
on the spreader design. Regarding (d).
increasing the tertiary velocity from 90 to
about 200 ft/sec with variable air inserts.
while maintaining a burner zone stoich-
iometry (SRe) of 80 to 70 percent, de-
creased flame length. The additional
mixing enhanced by jet entrainment
produced correspondingly higher NOX
emissions.
The staged performance of the RSC
DMB is summarized in Figure 3. NO*
emissions were substantially higher for
Spreader No. 5 (200 ppm*) than produced
by Spreader No. 2 (165 ppm) with Utah
coal. CO levels were comparable; but.
more important, carbon burnout improved
impeller was critical in determining flame
shape and operating characteristics. The
initial spreader design tested, the conical-
ly shaped CCV spreader, produced a long,
narrow unstaged flame that impinged on
the rear wall 22 ft from the firing face. The
results of the iterative development of the
RSC DMB coal spreader necessary to
achieve stable flames with the relatively
low-volatile Indiana coal are summarized
in Table 2. The first of these spreaders
resulted in a flame over 22 ft long that
impinged on the rear wall of the LWS. The
angle of the spreader blades was then
Table 2. Iterative Development of RSC DMB Coal Spreaders
Spreader Design
Performance Characteristics
No. 2: 4-in. pipe with four long
blades @ 15°
No. 3: 4-in. pipe with four long
blades @ 35°
No. 4: 4-in. pipe with four short
blades @ 35°
No. 5: 4-in. pipe with four short
blades @ 28°
Flame length > 22 ft.
High coal-head pressure (> 14-in. HsQ) resulting in low
primary velocity. Combustion products blow back through
open spreader support pipe.
High coal-head pressure.
Acceptable coal-head pressure (10-in. HyO). Flame length
19-20 ft under staged conditions.
-------
Load = 100x 10" Btu/hr
SR^ = 120% TA (theoretical air)
m Utah Coat 4-in. Pipe w/4 Blades @ 15°
£ Utah )
f Illinois > 4-in. Pipe w/4 Blades @ 28°
A Indiana I
5001—i , 1 i 1 1 / 00
i
400
300
200
100
80
60
40
20
70 80 90 100 110 120
Burner Zone Stoichiometry, percent TA
70 80 90 100 110 120
Burner Zone Stoichiometry, percent TA
Figure 3. Summary of the Riley Stoker Corporation Distributed Mixing Burner performance.
significantly with Spreader No. 5. Fly ash
carbon was reduced from 22 to about 10
percent at comparable conditions. NOX
emissions with Spreader No. 5 were
similar for each coal. The effect of excess
air on NO, and CO is shown in Figure 4.
The emissions from the three fuels fall
within a range of 40 ppm with an average
slope of approximately 4 ppm/percent
theoretical air (TA). The RSC DMB was
able to operate over a wide range of
excess air with transient data, indicating
that the rise of CO emissions occurs at
about 10 percent excess air.
The ability to lower the burner heat
output, or turndown capability, was eval-
uated for each coal with the final spreader
configuration. The results are shown in
Figure 5. With the Utah and Illinois coals,
it was possible to maintain stable staged
operation (SRs = 70 percent TA) down to
60 percent of full load. For the Indiana
coal, it was necessary to decrease staging
to a burner zone Stoichiometry of 90
percent TA for stable operation at 60 x 106
Btu/hr. This was probably related to the
relatively low volatile content of the
Indiana coal. For each coal, firing rate had
little effect on NOX emissions. NOX emis-
sions decreased between 10 and 16
percent when the firing rate was de-
creased from 100 x 106 to 60 x 106
Btu/hr. Combustion efficiency, as indi-
cated by CO levels, did not change
significantly.
Burner performance for the optimized
configuration is listed in Table 3 for each
coal tested.
Performance of the Riley Stoker
DMB for SO2 Control
The reduction of S02 emissions with
the injection of sorbents through burner
passages was evaluated for each coal
with three sorbent/injection location
combinations; Vicron (limestone) through
the tertiary air ports, Vicron into the
pulverizer with the coal, and hydrated
lime through the tertiary air ports. The
resu Its from the f u 11 load sorbent injection
tests for all three coals are summarized in
Figure 6. The injection of hydrated lime
material through the tertiary ports proved
to be most effective in S02 reduction,
achieving an estimated 50 percent cap-
ture at calcium-to-sulfur molar ratio
(Ca/S) = 2.0 for each coal. Injection
location did not make a significant dif-
ference in S02 reduction with the lime-
Load = 100x10* Btu/hr
SRB = 70% TA (theoretical air)
• Utah Coal 4-in. Pipe w/4 Blades @ 15°
O Utah
• Illinois 4-in. Pipe w/4 Blades @ 28°
A Indiana
500
400
300
200
i
700
100
80
I
g
w
O
O
O
60
40
20
110
120
130
140
110
120
130
140
Overall Stoichiometry, percent Tf-
Overall Stoichiometry, percent TA
•All concentrations reported are corrected to 3
percent 0:.
Figure 4. Effect of excess air on emissions from the Riley Stoker Corporation Distributed
Mixing Burner.
-------
Spreader = 4-in. Pipe w/4 Blades @ 20°
S/?T = '20% TA (theoretical air)
• Illinois
A Indiana SRB = 90%TA
500
300
200
;oo
100
c 80
S
| 60
40
20
50 60 70 80 90 100
Firing Rate, 10* Btu/hr
50 60 70 80 90 100
Firing Rate, 70° Btu/hr
Figure S. Effect of load on Riley Stoker Corporation Distributed Mixing Burner emissions with
optimized spreader (No. 5).
Table 3. Summary of RSC DMB Performance
Coal
Flame Length, ft
Stability at 60% Capacity
Carbon Utilization, %
NOi Emissions
Corrected to 3% Oa ppm
Utah
20
Acceptable at
SRB = 70% TA
98.9
210
Indiana
19-20
Acceptable at
SRB = 90% TA
98.8
235
Illinois
19-20
Acceptable at
SRB = 70% TA
99.0
218
stone material, with capture in the range
of 35 percent at Ca/S = 2.0. There was no
measurable effect of coal composition on
the degree of SOz reduction achieved
with any of the sorbent/injection location
combinations. Intuitively, an effect of
composition, in particular the sulfur con-
tent, would be expected. The sulfation
reaction would be thought to be driven in
part by the concentration of sulfur spe-
cies.
The burner variables were changed
while injecting Vicron through the tertiary
ports to evaluate the potential of tuning
the RSC DMB to enhance SOz capture.
The sensitivity of the RSC DMB perform-
ance to burner parameters limited the
range of the changes. None of the chang-
es in burner settings improved capture,
with capture reduced for most of the
changes. The interaction of the sorbent
jet with the flame and its effect on sorbent
calcination and activation are poorly
understood in large-scale systems.
Thermal environment is important in
the capture of sulfur species by sorbents.
Residence time inthetemperature regime
necessary for sulfation predicates the
degree of SOz reduction by the sorbent
material. The effect of firing rate and its
inherent effect on thermal environment
was evaluated with sorbent injection at
60 percent of the RSC DMB capacity. The
results are compared with full load tests
(shown as solid lines) in Figure 7. The
level of capture achieved at low load (27
percent at Ca/S = 2.0) with the Vicron
limestone was lower than capture at full
load (35 percent at Ca/S = 2.0). At Ca/S =
3, the capture at low load is comparable to
that achieved at full load. The feed rate
necessary for Ca/S = 1 at low load was
near the lower limit of the sorbent feeder
operating range with the result that the
feed rate was probably intermittent and
actually lower than indicated. This may
account for the very low capture at Ca/S =
1. At Ca/S = 2.0, there was no significant
difference between injection locations for
Vicron at partial load as in the case of the
full load tests. The hydrated lime again
achieved the highest capture (48 percent
at Ca/S = 2.0). At Ca/S > 1.6, the
effectiveness of the lime decreases at low
load. Gas temperatures measured at the
exit of the LWS with an aspirated thermo-
couple were in the range of 1650°F at low
load (60 x 106 Btu/hr), while at full load
(100 x 10s Btu/hr) the exit temperature
was 1850°F. The ideal temperature win-
dow for the most favorable sulfation rates
is 2200-1500°F. Because of the nature of
the LWS furnace, a reduction in load
increases mean residence time but also
reduces the mean furnace temperature.
The result isthatthetime available in the
sulfation temperature window is relatively
insensitive to load, and little effect of
firing rate on sulfur capture would be
expected.
For the tests where sorbent was in-
jected through the tertiary air ports, the
actual sorbent injection pipes were con-
centric on the axis of the tertiary air ports.
The sorbent was transported with an air
flow which was independent of the
tertiary air flow. During these tertiary air
port sorbent injection tests, constant
sorbent transport air flow was maintained
to the extent possible. High sorbent feed
rates generally resulted in increased
resistance to the air flow, thus some
variation in transport flow and velocity
was experienced. Most of the full load
tests were conducted with the injection
velocity matchi ng the tertiary air velocity.
Based on general interest, a brief series
of tests were conducted with variable
sorbent injection velocity, achieved by
varying the amount of transport air flow
through the sorbent injection pipes. For
this particular arrangement, reduced
sorbent injection velocity significantly
decreased S02 capture, probably due to
reduced penetration of the sorbent jet
into the LWS, and hence poorer disper-
sion. This effect is currently being eval-
uated by EER.
Summary of Riley Stoker DMB
Results
The performance of the RSC DMB was
verified over typical boiler operating
ranges of load and excess air. Combus-
tion efficiency was acceptable for the test
furnace, and measured NOX emissions
were well below NSPS levels. In sum-
-------
70
60
? 50
1.0
01
O 30
O
20
10
Load =100x10* Btu/hr Q Utah Coal
S/?B = 70% TA (theoretical air) • Indiana Coal
S/?T = 120% TA A Illinois Coal
oX°
.•O
*>/'
0 / 2 340
[CaJ/[S], Molar Ratio
fa) Vicron Through Tertiary
Ports
1 2 3401 2 34
[Ca]/[Sl Molar Ratio [Ca]/[Sl Molar Ratio
(b) Vicron With Coal (c) Hydrated Lime Through
Figure 6. Effect of coal composition on SOz capture.
mary, the Riley Stoker DMB burner tests
showed that:
• Optimized NOX emissions from the
three coals tested ranged from 205 to
245 ppm corrected to 3 percent 02.
• Carbon utilization exceeded 98.8 per-
cent for all coals at optimum condi-
tions.
• There was no measurable effect of
coal composition on the degree of SOa
reduction with any of the sorbent/
injection location combinations.
• Injection of hydrated lime through the
tertiary air ports provides the most
effective S02 capture, achieving an
estimated 45 to 57 percent at a Ca/S
molar ratio of 2.
• Injection location did not make a
significant difference in S02 reduction
with limestone. S02 capture was ap-
proximately 35 percent at a Ca/S
molar ratio of 2.
Nomenclature
Btu 1 Btu = 1.055 kJ.
Ca/S Calcium-to-sulfur molar ratio,
based on calcium in sorbent
and sulfur in coal.
CCV Controlled Combustion
Venturi burner.
DMB
EER
EPA
ft
°F
in.
Ib
LIMB
LWS
MAP
MMF
NOx
RSC
SOx
SRB
Tertiary Ports
Distributed Mixing Burner.
Energy and Environmental
Research Corporation.
U.S. Environmental
Protection Agency.
1 ft = 30.48 cm.
°C = 5/9(°F-32)
1 in. = 2.54 cm.
1 Ib = 0.454 kg.
Limestone injection into a
multistage burner.
EPA's Large Watertube
Simulator combustion test
facility.
Analysis of coal reported on
Moisture- and Ash-Free
basis.
Analysis of coal reported on
Moisture- and Mineral-
matter-Free basis. Mineral
matter consists of ash and
sulfur in coal.
Nitrogen oxides.
Riley Stoker Corporation
Sulfur oxides.
Burner zone stoichiometry
represents percentage of air
required for stoichiometric
combustion passing through
burner exit, including primary
and secondary air.
SRT Overall, or total,
stoichiometry represents
percentage of air required for
stoichiometric combustion
passing through primary,
secondary, and tertiary
passages.
TA Theoretical air required for
stoichiometric combustion.
-------
Load = 60 x 10eBtu/hr
SRn - 70% TA (theoretical air)
S/?T = 720% TA
70
60
50
40
a.
I
o™ 30
20
10
\ \
O Vicron Through Tertiary Ports
A Vicron With Coal
O Hydrated Lime Through Tertiary Rons
Full Load Hydrated
Lime Through
Tertiaries
Full Load
Vicron With
Coal
Full Load
Vicron
Through
Tertiaries
Figure 7.
5 / 2
(Ca]/[S\ Molar Ratio
Effect of load on SOz capture.
. S. GOVERNMENT PRINTING OFFICE:!985/646-116/20719
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R. Lisauskas is with Riley Stoker Corp., Worcester, MA 01613; A. Abele, F. Jones,
and R. Payne are with Energy and Environmental Research Corp., Irvine, CA
92718.
Charles C. Masser is the EPA Project Officer (see below).
The complete report, entitled "Evaluation of the Riley Stoker Corporation
Distributed Mixing Burner," (Order No. PB 86-117 033/AS; Cost: $11.95,
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
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
EPA/600/S7-85/045
PS
U S ENVIR PROTECTION AGENCY
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