United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S7-86/026 Sept. 1986
f/EPA Project Summary
Prototype Evaluation of
Commercial Second
Generation Low-N0x Burner
Performance and Sulfur
Capture
R. A. Lisauskas and D. C. Itse
Pilot scale combustion tests were
conducted on a Riley Stoker second
generation Iow-N0x burner combined
with dry sorbent injection for sulfur
dioxide (SO2) control. The burner de-
sign is based on the distributed mixing
concept. Combustion tests were con-
ducted at 100 x 106 Btu/hr (29 MW) in
EPA's Large Watertube Simulator
(LWS) test furnace. Results were ob-
tained for three different U.S. coals and
two sorbents.
Nitrogen oxides (NOX) were reduced
by up to 60% with this advanced burner
design. SO2 reductions of 50% at a Ca/S
ratio of 2 were obtained with hydrated
lime (Ca(OH)2). Highest reductions
were achieved when the hydroxide was
injected through tertiary air ports on
the periphery of the burner. When lime-
stone was used as the sorbent, SO2
capture was on the order of 35% at a
Ca/S of 2.
In order to aid the scale-up of the
pilot scale results to utility and indus-
trial boilers, two commercial Riley
burners were also tested at two differ-
ent scales (100 and 50 x 106 Btu/hr). A
furnace heat release parameter was
used to extrapolate pilot scale NOX
emissions to operating field boilers. In
addition, the Riley burner test results
are compared with data from other
burners also tested in the LWS test fa-
cility.
This Project Summary was devel-
oped by EPA's Air and Energy Engineer-
ing Research Laboratory, Research Tri-
angle Park, NC, to announce key
findings of the research project that is
fully documented in a separate report
of the same title (see Project Report
ordering information at back).
Introduction and Objectives
In recent years, the U.S. has turned
increasingly to coal to meet its energy
needs. Emission regulations for coal-
fired industrial and utility boilers are di-
rected toward limitations on nitrogen
oxides (NOX), sulfur dioxide (S02), and
particulate matter. NOX and S02 are
believed to be two of the major acid-
forming precursor gases of acid precipi-
tation. Although there is still consider-
able scientific debate over the
relationship between emissions and
acid deposition, the control of S02 from
power plants is the major focus of pro-
posed acid rain regulation strategies.
As part of its effort to develop emis-
sion controls for industrial and utility
steam boilers, the U.S. EPA is develop-
ing Limestone Injection into Multistage
Burners (LIMB) technology as a poten-
tial low cost control technology for both
NOX and S02. The program described
here is one of several prototype-scale
test programs sponsored by the EPA to
evaluate the sulfur capture potential of
Iow-N0x burners combined with the in-
jection of conventional sorbents. Under
this program, five Riley Stoker burners
were tested in the EPA's Large Water-
-------
tube Simulator (LWS) furnace operated
by the Energy and Environmental Re-
search Corporation (EERC) at their El
Toro, California, test facilities.
The objectives of this program were
to (1) characterize NOX emissions for
each burner, (2) evaluate each burner
for combined NOX/S02 control with sor-
bent injection under acceptable operat-
ing conditions, (3) extrapolate the per-
formance of the burners to field
conditions, and (4) compare the results
with other burner testing.
The test program was conducted in
two phases. Phase 1 was performed on
a single 100 x 106 Btu/hr Riley Stoker
Distributed Mixing Burner (DMB). The
Riley DMB is a second generation com-
mercial scale low-NOx coal burner. Low-
NOX operation was first established for
the DMB during baseline tests. All of the
adjustable burner variables were inves-
tigated to achieve Iow-N0x emissions, a
wide operating range, acceptable flame
characteristics, and combustion effi-
ciency. Following these initial tests the
S02 reduction potential of the burner
was evaluated. Calcium-based sorbents
were injected through two different
burner passages: (1)the coal nozzle,
and (2) the tertiary air ports. During the
Phase 1 testing, performance data were
obtained for three different fuels and
two sorbents.
Under Phase 2, two commercial Riley
burner designs, the Flare and Con-
trolled Combustion Venturi (CCV)*
burners, were evaluated in the LWS.
The Flare burner is a conventional high
turbulence burner, while the CCV is a
first generation Iow-N0x burner. Both
the Flare and CCV designs were tested
at scales of 50 x 106 and 100 x 106 Btu/
hr. These commercial burner tests at
different experimental scales provided
a link between the LWS results with
other pilot scale furnaces and with ac-
tual field operation. The CCV burner
was also tested under staged combus-
tion conditions in a DMB configuration.
As in the DMB design, staging air was
supplied by four tertiary air ports on the
periphery of the burner.
In addition to burner characterization
and NOX emissions tests, limited sor-
bent injection tests were conducted
with the Flare and CCV burners to evalu-
ate the effect of burner design on SO2
reduction potential. The multistage CCV
burner was evaluated on three different
sorbents.
Description of Experimental
Systems
Test Burners
Riley Stoker DMB
The Riley Stoker Distributed Mixing
burner (DMB), shown in Figure 1, is
based on design criteria developed in
previous U.S. EPA studies. It is a dual
register burner with secondary air en-
tering through separate concentric air
passages surrounding the coal nozzle.
Swirl is imparted through adjustable ra-
dial vanes at the entrance of each pas-
sage. Although these two air passages
would normally be incorporated in a
common windbox, they were fed sepa-
rately for this test program. This al-
lowed independent flow measurement
of each secondary air stream.
The burner was equipped with four
tertiary air ports around the periphery of
the burner for staged combustion.
These tertiary air ports are smaller and
somewhat nearer the burner in the Riley
Stoker design than prescribed in the
EPA's DMB criteria. These design
changes increased flame stability under
deeply staged combustion conditions.
The tertiary air ports were also
equipped with inserts to further in-
crease the tertiary air velocity and im-
prove downstream air/fuel mixing.
In addition, the burner incorporates
the venturi coal nozzle design devel-
oped for the Riley Stoker Controlled
Combustion Venturi (CCV) burner. Both
coal spreader and nozzle setback posi-
tion were adjustable in the test burner.
Tertiary
Air Port
Venturi
Coal Nozzle
Coal
Spreader
CCV Burner
The CCV burner, shown in Figure 2,
was developed for retrofit into existing
coal fired boilers. Secondary air is sup-
plied through a single annular flow pas-
sage and register for swirl control. The
burner employs a four bladed spreader
and venturi coal nozzle. NOX is con-
trolled through controlled air/fuel mix-
ing. The coal spreader imparts swirl to
the primary coal air stream and divides
the stream into fuel-rich and -lean layers
before mixing with the secondary air.
Tests were conducted on both a conical
and straight cylindrical spreader body
design.
The CCV burner was also tested in a
multistage, or distributed mixing
burner, configuration. Staging air was
supplied by four tertiary air ports on the
periphery of the burner, as in the DMB
design. The CCV burner was tested at
two different sizes: 100 x 106 and
50 x 106 Btu/hr. The objective of these
tests was to investigate the effects of
heat input on NOX emissions.
Flare Burner
The Flare burner, also illustrated in
Figure 2, is designed to produce a
rapidly mixed, intense stable flame.
This burner utilizes secondary air swirl
control and a multivane coal spreader
which promotes rapid mixing of the
coal stream with the secondary air. This
burner produces high NOX emissions,
1.0-1.2 Ib NOX/106 Btu, and low carbon
loss in the flyash. The Flare burner was
also tested at 100 x 106 and 50 x 106
Btu/hr.
Coal/Primary Air
Secondary Air
Figure 1. Riley Stoker Distributed Mixing Burner.
-------
Adjustable
Swirl Control
Flare Burner
Coal Nozzle
and Spreader
Coal/Primary Air
Secondary
Air
CCV Burner
Coal Nozzle
and Spreader
Figure 2. Riley Stoker CCV* and Flare burners (*Protected by U.S. Patent No. 4.479.442).
Test Facility
LWS
All of the testing under this contract
was conducted in the EPA Large Water-
tube Simulator (LWS) furnace, designed
to simulate furnace conditions in utility
boilers. The furnace is fired with a single
burner mounted on the front wall. The
furnace gas exit is at the top on the rear
wall. With this configuration, the gas
flow pattern is similar to that in a wall-
fired boiler. The outer surface of the fur-
nace is cooled by water sprays and is
open to the atmosphere. In order to
maintain thermal similarity with coal
fired boilers, the flame zone of the fur-
nace is refractory lined. The furnace
wall near the burner, however, is uncov-
ered to ensure that the wall temperature
near the burner will be cool as in field
operation.
Sorbent Injection System
The sorbent injection system was de-
signed to feed into two locations: (1) the
primary air/coal stream after the pulver-
izer, and (2) the tertiary air ports. Sor-
bent feed rate was controlled by a screw
feeder. The sorbent was entrained by
the compressed air and conveyed to the
injection location. Sorbent was added
to the primary air stream through a sin-
gle nozzle downstream of the pulver-
izer. For injection through tertiary air
ports, the sorbent was split into four
streams and was injected through noz-
zles located on the axis of each tertiary
air port.
Fuels and Sorbents
Three coals were used during the test
program: Utah, Indiana, and Illinois.
Utah coal was chosen as the baseline
low (0.7%) sulfur coal because it had
been used previously in Iow-N0x burner
tests supported by the EPA in the LWS.
Indiana coal has also been used as a
medium (2.5%) sulfur base coal in other
EPA funded sorbent injection tests. The
high (3.5%) sulfur Illinois coal was se-
lected in order to relate the tests to
other pilot- and full-scale burner devel-
opment tests conducted by Riley
Stoker. All three coals were used during
the DMB tests. However, only the Utah
and Illinois coals were used for the CCV
and Flare burner tests.
Three sorbents were evaluated dur-
ing the program: limestone (Vicron
45-3), hydrated lime, and dolomite. The
sorbents were purchased, pre-milled in
50 or 100 Ib (22.5 or 45 kg) sacks.
Limestone and hydrated lime were
used as sorbents during the DMB test.
Dolomite was tested during the CCV
and Flare burner tests in addition to
limestone and hydrated lime.
Test Plan
The test program was divided into
two phases: (1)the DMB tests, and
(2) the commercial burner tests. During
Phase 1, burner performance and S02
reduction potential were evaluated for
the Riley DMB. Burner performance in-
cludes NOX emissions, CO emissions,
carbon content in the flyash, and flame
length. Initially, burner performance
was evaluated based on: coal spreader
position, coal nozzle position, swirl reg-
ister position, degree of staging, tertiary
air port size, and coal spreader design.
Following these tests, the S02 reduc-
tion potential of burner sorbent injec-
tion was investigated at the optimum
burner configuration. Two burners were
evaluated in Phase 2: the Riley CCV and
Flare burners. Field test data exist for
these commercial burner designs on a
variety of furnace sizes and configura-
tions. The prime objective of these tests
was to vary furnace thermal environ-
ment with a constant burner design.
These tests along with data contributed
by Riley Stoker provided a basis for pro-
jecting NOX emissions in the LWS to
utility boilers.
Sorbent injection tests were also
conducted in Phase 2 to evaluate the
SO2 reduction potential of LIMB with
Riley's present commercial burner
products.
Test Results
A/OX Emissions
NOX emissions for the 100 x 106 Btu/
hr test burner configurations are sum-
marized in Figure 3 for Utah coal. Test
results are presented as a function of
excess air for the final DMB design con-
figuration. The lowest NOX emissions
were achieved with the DMB, ranging
from 240 ppm firing Utah coal to 290
ppm firing Indiana coal at 20% excess
air. In comparison, the Flare burner pro-
duced NOX emissions of 675 to 700 ppm
at 20% excess air. This level of emis-
sions is typical of boilers designed prior
to the New Source Performance Stand-
ards (NSPS), and is representative of
uncontrolled NOX emissions.
NOX emissions from the DMB were
less sensitive to excess air than from the
other burners. All of these data were
taken at a burner zone stoichiometry
(SRB) of 0.7. CO emissions from the
DMB were only 20 to 40 ppm. The car-
bon content of the flyash, a measure of
combustion efficiency, was 6.2 to 10.1%
based on loss on ignition (LOI). NOX
emissions from the Flare burner were
sensitive to excess air, increasing 130
ppm for a 10% increase in excess air. CO
-------
7000
800
0 600
I
of
O
.s
I
400
i
200
Burner, Spreader
Flare
CCV, Straight
CCV. Cone
CCV. Straight, S/?B = 0.7
DMB.
/./ 1.2
Overall Stoichiometric Ratio (SR-r)
1.3
1.4
Figure 3. NOt emissions from Riley Stoker burners firing Utah coal in the L WS.
emissions were less than 60 ppm while
the carbon content of the flyash was
only 3.9 to 5.5%.
The Riley CCV burner was tested in
two coal nozzle configurations while fir-
ing the Utah coal: an expanding cone
coal spreader and a straight center body
coal spreader. Testing during the origi-
nal CCV burner development program
showed that spreader design can
change NOX emissions by a factor of
two.
The cone spreader design was origi-
nally developed for the CCV burner and
has been installed on three utility fur-
naces. Testing this spreader provided
data for extrapolating NOX emissions
from the LWS to the field. The straight
spreader was developed for staged
combustion with the CCV burner.
The performance of the Riley DMB in
the LWS is compared with various com-
mercial burners in Table 1. NOX emis-
sions from Utah coal for the DMB were
over 400 ppm lower than the Flare
burner and 70 ppm lower than the CCV
burner equipped with the cone
spreader. The flame length for the DMB
was the same as the baseline CCV
burner and longer than the Flare burner
flame. The combustion efficiency for
the unstaged CCV burner can be im-
proved with the straight spreader de-
sign at the expense of NOX. Otherwise,
the combustion efficiency for each
burner design was comparable.
The DMB could also be operated over
an excess air and load range similar to
the Flare and CCV burners. Comparison
of the performance indicates that the
DMB should be retrofittable to units cur-
rently equipped with the Flare or CCV
burners.
Sulfur Capture
Sulfur capture with the DMB is shown
in Figure 4 as percent S02 capture, for
the three coals, two sorbents, and three
injection locations. At a calcium to sul-
fur molar ratio (Ca/S) equal to 2, sulfur
capture ranged from an average of 32%
with limestone to 50% capture with hy-
drated lime for each coal.
Limestone with slightly more effec-
tive as a sorbent when injected through
the coal nozzle (35% capture) than when
injected through the tertiary air ports
(32% capture). Injection of hydrated
lime through the coal nozzle was not
evaluated in detail because it performed
poorly, achieving 27% SO2 capture dur-
ing screening tests.
Coal composition, or more specifi-
cally sulfur content, was not a major
variable in sulfur capture with the DMB.
Figure 4 reveals no measurable effect of
coal composition on the degree of S02
reduction with any of the sorbent/injec-
tion combinations. Other researchers,
however, have found that coal composi-
tion can have a major effect on sulfur
capture. The sulfation reaction is
thought to be driven in part by the con-
centration of sulfur species in the flue
gas.
The most favorable window for sulfur
capture has been identified as 870 to
1230°C. At above 1230°C, sorbents tend
to dead burn, and chemical equilibrium
prohibits SO2 adsorption if SO2 is less
than 2500 ppm. At below 870°C, SO2 ad-
sorption is too slow to be significant.
Gas temperatures measured at the exit
Table 1. Performance of 100 x 106 Btu/Hr Riley Burners Firing Utah Coal in the LWS
Spreader
Minimum Excess Air, %
Minimum Load,
% Capacity
Flame Length, ft (m)
Carbon Utilization, %
Nox @ 0% O2, ppm
Flare
Flare
8
75
14-16 (4.3-4.9)
99.3
686
CCV
Unstaged
Cone
10
60
20 (6. 1)
97.9
304
Straight
10
70
15 (4.6)
99.1
465
CCV
SRg=0.7
Straight
17
20-21 (6.1-6.4)
99.1
274
DMB
SRB=0.7
Straight
10
60
20(6.1)
98.9
234
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70
60
50
40
§
r
20
JO
Coal Nozzle Injection
of Limestone
\ \ r
Coal Type
Indiana A ~ ~ ~~ ~ *
Illinois D
Tertiary Air Port Injection
of Limestone
Tertiary Air Port Injection
of Hydrated Lime
j 1 I L
50 1 2 3 4 50
Calcium to Sulfur Molar Ratio (Ca/S)
Figure 4. SOz capture with the Riley Stoker DMB.
of the LWS with the DMB were in the
range of 900°C at low load and 930 to
1010°C at full load (100 x 106 Btu/hr).
Peak temperatures as high as 1270°C
were measured within the flame at full
load. The effect of thermal environment
on S02 capture was investigated by re-
ducing the heat input to the burner to
62 x 106 Btu/hr. As shown in Figure 5,
limestone injection S02 capture at low
load decreased for low Ca/S ratios, but
was comparable to the full load results
at Ca/S equal to 3.0. The opposite was
true for injection of hydrated lime: S02
capture at low load was comparable to
the full load SO2 capture, and increased
less rapidly as Ca/S increased.
Figure 6 compares sulfur capture for
all five of the Riley Stoker burners using
limestone injected through the coal noz-
zle. At a Ca/S ratio of two, sulfur capture
ranged from 22 to 35%. The highest sul-
fur capture was with the CCV burner
staged to SRB equal to 0.7. Sulfur cap-
ture with the DMB was slightly lower at
32%. The Flare burner achieved the low-
est sulfur capture.
The effect of firing rate and burner
scale on sulfur capture for the unstaged
CCV burner with the cone spreader is
shown in Figure 7 for Illinois coal. Sulfur
capture using the 100 x 106 Btu/hr CCV
burner at full load is compared to that
for the 100 x 106 Btu/hr burner at part
load and the 50 x 106 Btu/hr CCV burner
at full load. Sulfur capture increased
50% from 28% capture to 42% capture
by firing the smaller burner in the LWS.
Sulfur capture was 38% at Ca/S equal to
2 for the 100 x 106 Btu/hr fired at
58 x 106 Btu/hr. This may be due to
higher peak temperatures in the un-
staged burners.
Application to the Field
Data gathered under this program
were used in conjunction with data from
other combustion tests of Riley Stoker
burners to extrapolate LWS NOX, emis-
sions to operating boilers. A Burner
Area Heat Release (BAHR) parameter
was used to relate NOX emissions from
furnaces of various sizes and thermal
environments. BAHR ranks the relative
combustion intensity of different fur-
naces, and is similar to parameters used
by other boiler manufacturers. The
BAHR is defined as the total gross fuel
input divided by the cooled surface in
the main flame zone.
Full load NOX emissions at 20% ex-
cess air are plotted for various burner
and furnace combinations in Figure 8.
Data for the Flare burner and the CCV
burner with the cone spreader were
available from three test facilities of in-
terest and a number of field units. In
addition to the EPA LWS, the test facili-
ties included the Riley Coal Burner Test
Facility (CBTF) and the EERC Medium
Tunnel (MT) furnace. These Flare and
CCV burner results were used as a basis
for extrapolating NOX emissions for the
other low-NOx burners. Unstaged CCV
burner data were available from several
utility boilers ranging from 360-400
MWe.
As shown in Figure 8, there is a linear
relationship between NOX and BAHR for
the Flare and CCV burners. The slope of
the line for NOX versus BAHR is nearly
identical for the two burners. Other low-
NOx burner performance has been ex-
trapolated parallel to the CCV burner
with the cone spreader correlation.
Using this thermal scaling criteria, DMB
NOX emissions would be about 400 ppm
in a large field boiler as compared to
900 ppm for the Flare burner.
During these pilot scale tests, sulfur
capture resulting from injecting lime-
stone with the coal ranged from 22 to
35%. The best results were achieved
with the DMB and CCV burner, straight
spreader. Injection of hydrated lime
through the tertiary air ports in the DMB
produced 50% S02 capture at Ca/S
equal to 2. Injection of sorbents through
-------
70
50
40
O
O
to
§ 30
0.
20
10
Full Load
Hydrated Lime
Through Tertiaries
Full Load
Vicron With
Coal
/ ^^ Full Load
* Vicron Through
Tertiaries
Data at 62 Percent of Full Load
Vicron Through Tertiary Ports
A Vicron With Coal
D Hydrated Lime Through Tertiary Ports
Figure 5.
12345
Calcium to Sulfur Molar Ratio (Ca/S)
Effect of thermal environment on SOz capture with the Ftiley DMB firing Utah coal.
the tertiary air ports of the CCV-MS
burner only produced 35 to 40% S02 re-
duction at Ca/S equal to 2.
The injection of sorbents in the flame
zone of boilers presents problems to be
addressed prior to application to the
field. The increased solids loading in
bottom ash and flyash will have to be
accommodated. A more serious prob-
lem may be the reduction of ash melting
temperatures and thus, the increased
tendency toward slagging. For the LIMB
process to become a viable control al-
ternative, there must be additional
understanding of the sorbent injection
process, particle interaction, and the
controlling mechanisms of sulfation.
-------
60
50
40
I
O 30
20
10
Burner, Spreader
Flare
CCV, Straight
CCV, Cone
CCV, Straight. SRB = 0. 7
O '
A '
O •
V '
2 3
Calcium to Sulfur Molar Ratio (Ca/SJ
Figure 6. SOi capture with Riley Stoker burners firing Utah coal.
-------
60
50
40
3°
20
10
Burner Size
A SOx10eBtu/hr
O 100xWeBtu/hr
D 100x10*Btu/hrat
. Low Load .
Figure 7.
01 2345
Calcium to Sulfur Molar Ratio (Ca/S)
Effect of thermal environment on SOz capture during coal nozzle injection of
limestone with an unstaged CCV burner firing Illinois coal.
-------
1200
1000
800
to
I
g'
.o
.§
I
d
600
400
200
O Flare
' A CCV Burner, Straight Spreader
V CCV Burner, Cone Spreader
. O CCV-MS Burner
Flare -
CCV
Straight
Open Symbols—EPA 68-02-3912
Solid Symbols—Riley Stoker
Open/Solid Symbols—EPRIRP21S4
LWS LWS MT CBTF
I . 1 I , . I,
360 MW, 400 MW,
, ,1 . . \ . ,
1.4
1.2
1.0
0.8
0.6
0.4
0.2
3
DO
.1
I
i
0 100 200 300 400
Burner Area Heat fie/ease, W3 Btu/(hr-f?) (x 3.153 x 10'* W/crrf)
Figure 8. Projected /VOX emissions from Riley Stoker burners.
R. A. Lisauskas andD. C. Itse are with Riley Stoker Corp., Worcester, MA 01606.
Charles C. Masser is the EPA Project Officer (see below).
The complete report, entitled "Prototype Evaluation of Commercial Second
Generation Low-NO* Burner Performance and Sulfur Capture," (Order No. PB
86-220 407'/AS; Cost: $22.95, 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. NC 27711
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