United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S7-85/046 Dec. 1985
oEPA Project Summary
Prototype Evaluation of
Commercial Second
Generation Low-N0x
Burner Performance and
Sulfur Dioxide Capture Potential
A. Abele, F. Jones, B. Cetegen, and R. Payne
The expanded use of coal for utility
and industrial boiler applications has
focused attention on the control of NO,
and SOzemissionsfrom pulverized coal
combustion. Various EPA programs
have demonstrated the principle of
staged combustion as a means of con-
trolling NO, emissions. Other programs
are evaluating the potential for SO2
control with the injection of calcium-
based sorbents into furnace combustion
chambers. Under this program, Stein-
muller Staged Mixing (SM) burners
were tested in EPA's Large Watertube
Simulator (LWS) test facility. The objec-
tives of the program were to provide a
comparative evaluation of the SM
burner in the LWS with field operation
and to optimize its performance for low
NO, emissions, high efficiency, and
combined NO«/SOz control with sor-
bent injection. The experimental effort
included evaluating two SM burners in
the LWS using three coals and three
sorbents. The evaluation of the two
burners, the Weiher S M burner currently
in operation in a 700 MW boiler in West
Germany and a second generation SM
burner, included characterization of
burner performance and NO, emissions
and S02 reduction with sorbent injec-
tion through burner passages. The
impact of the NO, and SO2 control
techniques on ash characteristics (in-
cluding slagging and fouling behavior,
and SO2/SO3 speciation) was also
evaluated.
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 reduction of N0«, SO,, and panicu-
late emissions from utility and industrial
boilers has been a high-priority concern
of the USEPA and all of the major boiler/
burner manufacturersfor several years. In
fact, a number of unrelated concurrent
efforts have been and are being conducted
to develop low-NO, burners. This program
represents one portion of an effort by the
EPA to compare the results of these
individual studies and identify the most
promising avenues for further success.
Under this program, Steinmuller (LCS)
staged mixing (SM) burners were tested
in EPA's Large Watertube Boiler Simu-
lator (LWS) test facility. Although LCS
does not build boilers in the United States,
they have already tested a burner with
outboard staged air ports in a 700 MW
boiler, Weiher Unit III, in Germany. Sor-
bent injection is currently being tested in
the same boiler to assess the potential for
combined N0,/S02 control. Tests of a
scaled-down Steinmuller low-NO, burner
in the LWS will provide EPA with a
relative comparison with combined low-
NOx/SO, operation in a large boiler.
-------
TwoLCSSM burners were evaluated in
ERA'S LWS for combined NOX/S02 reduc-
tion potential. A scaled-down 100 x 106
Btu/hr SM burner, matching the design
parameters of the 235 x 106 Btu/hr
burners installed at the Weiher III boiler,
was evaluated in the first phase of testing
to establish a basis for comparing burner
performance in the LWS with an oper-
ating boiler. The SM burner design was
then optimized, resulting in the SM-II
burner, by incorporating advanced LCS
design concepts in a second phase of
testing. These advanced designs included
modifications of the secondary and terti-
ary air velocity, tertiary air location, and
the coal nozzle configuration. These SM
burners were tested with three coals,
including that used at the Weiher boiler in
Germany. SC>2 reduction potential by the
injection of calcium-based sorbents
through burner passages was evaluated
with three sorbents. Detailed measure-
ments were performed at selected condi-
tions to characterize burner performance.
The basic configuration of the Weiher
SM test burner has four passages. Coal
and primary air enter the burner vertically
upward and are injected through an
annular passage to the burner exit. Coal
is distributed uniformly by accelerating
the coal and primary air mixture from a
low velocity region at the head of the
burner into the annular passage. The
basic SM configuration does not use an
impeller at the exit of the coal annulus, so
that the coal and primary air flow is purely
axial. A small portion of combustion air is
supplied through the large central core
passage. This core air cools the ignition
equipment, establishes bluff body recir-
culation to provide stability at the base of
the flame, and supplies additional oxygen
at the ignition point to improve stability
Secondary air is supplied through a single
annulus around the coal pipe. Swirl is
varied in the secondary air passage by a
block of fixed-angle vanes that are mov-
able to alter the distribution of air either
passing through or around the vanes. Air
to complete the combustion process is
provided through four tertiary ports
around the burner exit.
The optimization tests of the SM burner
utilized the same basic configuration. The
advanced concepts evaluated'during the
second phase of tests included.
• Secondary passage insert to increase
secondary air velocity.
• Tertiary air port location (radial dis-
tance from burner).
• Inserts in the tertiary ducts to increase
velocity.
• Variable annular coal splitter to vary
the coal/primary air distribution.
• Venturi insert in the annular coal
nozzle
The secondary insert, designed to in-
crease the secondary air velocity by about
30 percent, was used throughout the
second phase optimization tests in an
arrangement termed the SM-II burner.
Three fuels and three sorbents were
used during this test program. The coals
tested (all high-volatile bituminous) were
from Utah, Indiana, and the Saar region of
Germany. Both the Utah and Saar coals
are low in sulfur, 0.73-0.96 and 0.72-
0 87 percent, respectively. The Indiana
coal has a medium level of sulfur (1.35-
1.46 percent). The Indiana and Utah coals
have been used previously in burner
development and sorbent injection stud-
ies, and thus provide a link to a broad data
base Two of the sorbents were lime-
stones and the third was a hydrated lime.
The limestones (CaCOa) included Vicron
45-3 and Rheinisch-Westfaelische Kalk-
steinwerke (RWK) CaCOs, prepulverized
to a median particle size of 9.8 and 20 /urn,
respectively. The hydrated lime was also
from RWK with a mass median diameter
of 4 /jm.
Burner Performance and
NOX Emissions
Weiher III SM Burner
The Weiher SM burner is very simple,
having a single adjustable parameter, the
secondary air swirler. The position of the
swirler, and resulting degree of secondary
air swirl generated, had little effect on
emissions over most of its range; however
NO, emissions increased about 100 to
550 ppm* at the maximum swirl position.
For stable full-load operating conditions,
the flame length was about 21 ft (6.4 m)
with the ignition point at the burner exit.
General operation of the test burner was
observed to be typical of the SM burners
at Weiher.
Emissions from the Weiher SM burner
were sensitive to both the degree of
staging and excess air levels. The rate of
decrease in NO, emissions ranged from 5
to 7.5 ppm/1 percent theoretical air
change in the burner zone stoichiometry.
The effect of excess air change was
slightly greater, 9 to 15 ppm decrease in
NO, for each 1 percent theoretical air
decrease. At nominal design point condi-
'Note All emissions are reported on a dry basis and
are corrected to 0 percent 0:.
tions(SRB = 80%TA, SRT=125%TA), NO,
emissions were 415, 450, and 570 ppm
for Utah, Saar, and Indiana coal, respec-
tively.
SM-II Burner
The SM-II burner was optimized using
both the adjustable burner parameters
and hardware modifications to the burner
geometry The effect of each parameter
evaluated is summarized below.
Secondary Air Swirl. The position of the
swirl vane device, and the resulting
degree of secondary air swirl generated,
had negligible effect on emissions as long
as the flame was stable. However, de-
creasing swirl resulted in progressively
increasing flame length and flame de-
tachment.
Core Air Flow. Increasing core air flow
generally decreased NO, emissions with
no significant effect on combustion effi-
ciency as measured by CO levels. At the
highest flow through the core air passage,
flame length and detachment increased.
Secondary Air Velocity. Increasing the
secondary air velocity, by installing an
insert in the throat of the Weiher SM
burner, had no significant effect on
emissions. Flame stability was improved
to allow stable operation at lower burner
zone stoichiometry.
Tertiary Port Location. Of the two loca-
tions tested, the set of tertiary air ports
farther from the burner centerline pro-
duced lower NO, emissions, with the
difference becoming greater at lower
burner zone stoichiometry.
Tertiary Air Velocity. Tertiary velocity
was varied, using inserts in the ports that
increased the velocity by about 50 per-
cent. For both the inner and outer port
locations, the higher tertiary air velocity
(i.e., smaller port diameter) produced
lower NO, emissions. Again, the differ-
ence in emissions became greater as
staging was increased.
Coal Nozzle Design. Two inserts for the
annular coal nozzle were evaluated. A
variable blocking device, that divided the
coal stream and increased the primary
velocity, produced a narrow flame that
reduced NO, under unstaged conditions.
Staging this configuration significantly
increased CO emissions. This device also
resulted in a much higher pressure drop
across the coal nozzle, which caused
operational problems for the pulverizer
and primary air system. A venturi-shaped
insert increased NO, emissions along
-------
with flame standoff. Best overall perform-
ance was achieved with the baseline
annular coal nozzle.
The optimized configuration of the SM-
II burner included the following hardware:
• Secondary air insert.
• Baseline annular coal nozzle.
• Outer tertiary port location.
• Small-diameter, high-velocity tertiary
air ports.
This configuration produced stable full-
load flames about 21 ft (6.4 m) long. NOX
emissions at full-load design point condi-
tions (SRB = 80% TA, SRT = 125% TA) for
this optimized SM-II burner were 370,
370, and 500 ppm for Utah, Saar, and
Indiana coals, respectively. Emissions
from the SM-II burner were also sensitive
to burner zone stoichiometry and overall
excess air. The nominal rate of change in
NO, with burner zone stoichiometry was
about 10 ppm/1 percent theoretical air
change. The effect of excess air was less,
about 6.5 ppm decrease in NOX for each 1
percent change in excess air.
Comparison of We/her SM and
SM-II Burners
Overall performance of the basic
Weiher SM burner was improved with
the optimum hardware. NOX emissions
were lower at design point conditions,
and combustion efficiency was higher.
The range of operation, including excess
air and turndown, was maintained if not
improved. Range of operation could prob-
ably be further improved by design
changes in secondary swirl generation.
Increasing swirl would allow staged
operation over the entire load range with
stable attached flames.
The NO, emissions from the optimum
SM-II design were more sensitive to
burner zone stoichiometry than the
Weiher burner, while the effect of excess
air on emissions was much less for the
optimized burner. Combustion efficiency
with Saar coal was improved with the
optimized burner
Sulfur Dioxide Control
Weiher SM Burner
The SOz reduction tests with sorbent
injection for the Weiher SM burner util-
ized three sorbents, three injection loca-
tions, and three coals. The sorbents, two
limestones and a hydrated lime, were
injected with the coal at the pulverized
outlet, through nozzles on both the axis of
the inner tertiary air ports and the axis of
the outer tertiary ports For the Weiher
SM burner configuration, tertiary air
flowed through the inner set of ports only.
Most of the S02 tests were conducted
with the Saar coal to obtain data for
comparison with sorbent injection tests
planned at the Weiher III boiler.
The two limestone sorbents, the Vicron
and the RWK CaCO3, achieved similar
SOz reduction when injected with the
Saar coal, 35 and 32 percent at a Ca/S
molar ratio of 2, respectively. Sulfur
capture with RWK hydrated lime injected
with the coal was lower, particularly for
Ca/S molar ratios greater than 2. Greater
S02 reduction was achieved by injecting
the hydrated lime through either the inner
or outer tertiary ports, with 49 and 54
percent capture at a Ca/S molar ratio of
2, respectively. Capture with the Vicron
and RWK limestones was again similar
for injection through the inner tertiary air
ports, about 32 percent at a Ca/S molar
ratio of 2. However, injection through the
outer tertiary ports resulted in substan-
tially higher capture with the Vicron
limestone (40 percent at a Ca/S molar
ratio of 2) than with the RWK limestone
(29 percent).
The trends for S02 reduction were
similar for the two U.S. coals with the
Weiher burner. Highest capture was
achieved with the RWK Ca(OH)2 injected
through the inner tertiary ports, with 49
percent capture at a Ca/S molar ratio of 2
for Utah coal and 35 percent for Indiana
coal. Injecting Vicron through the tertiary
ports yielded higher SOz capture than
injection with the coal, about 35 to 30
percent, respectively, for both U.S. coals.
SM-II Burner
The potential for SOz reduction for the
SM-II burner was determined with two
sorbents, Vicron limestone and RWK
Ca(OH)2, through three injection loca-
tions: with the coal, through the inner
tertiary ports, and through the outer
tertiary ports. Sorbent was injected only
through the tertiary ports through which
the air flowed.
The trends for all three fuels with the
optimized SM burner were similar, with
the best performance in terms of SOz
capture achieved by injecting RWK
Ca(OH)2 through the outer tertiary ports
and with little difference in the effective-
ness of injection location for the Vicron
limestone. Levels of SOz capture at a
Ca/S molar ratio of 2 for the higher sulfur
content Indiana coal were 50 percent
with the RWK Ca(OH)2 through the outer
tertiary ports, 33 percent with Vicron
through the outer tertiary ports, and 30
percent with Vicron injected with the
coal. For each combination of sorbent and
injection configuration, sulfur capture is
an average of about 4 percent higher with
the higher sulfur content Indiana coal
than with the Utah coal. Intuitively, an
effect of composition (sulfur content, in
particular) would be expected. The sulfa-
tion reaction would be thought to be
driven in part by the concentration of
sulfur species.
Comparison of Weiher SM and
SM-II Burners
In general, the trends in SOz capture for
various sorbent and injection locations
for the Weiher and optimized SM burner
were similar. The most effective sorbent
with Saar and Utah coals was the RWK
hydrated lime injected through the outer
tertiary ports for both burners. For the
Weiher SM burner, limestone injection
through, the tertiary ports achieved SOz
reduction comparable to the hydrated
lime. The injection location of the lime-
stone sorbent had some effect on capture
achieved with the Weiher burner, but
essentially no effect with the optimized
burner. Tertiary air velocity, varied using
inserts during tests with the optimized
burner, did not measurably affect capture.
Coal type, or composition, had little effect
on SOz capture by sorbent injection for
the optimum and Weiher burners. Oper-
ating variables that had negligible effect
on SOz reduction with sorbent injection
for both burners included degree of
staging and firing rate.
During the Weiher SM burner tests,
NO, emissions increased when limestone
was injected into the mill with the Saar
coal. The increase in NO, appeared to be
proportional to the sorbent injection rate,
ranging from 5 to 15 percent over the
baseline NO, emissions as sorbent flow
increased. This phenomenon occurred
with the U.S. coals also but to a much
lesser degree. NO, emissions did not
change measurably during the sorbent
injection tests with the optimized SM
burner.
-------
A. Abele. F. Jones. B. Cetegen, and R. Payne are with Energy and Environmental
Research Corporation, Irvine, CA 92718.
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 Dioxide Capture Poten-
tial, " (Order No. PB 86-122 009/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
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
BULK RATE
POSTAGE & FEES I
EPA
PERMIT No. G-3
Official Business
Penalty for Private Use $300
EPA/600/S7-85/046
------- |