United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park, NC 27711
Research and Development
EPA/600/S7-89/009 Dec. 1989
&EBX Project Summary
Evaluation of Internally Staged
Coal Burners and Sorbent Jet
Aerodynamics for Combined
SO2/NOX Control in Utility
Boilers: Volume 2. Testing in a
100 Million Btu/Hr Experimental
Furnace
B. M. Cetegen, J. Clough, G. C. England, T. R. Johnson, Y. Kwan, and
R. Payne
As part of EPA's Limestone
Injection/Multistage Burner (LIMB)
program, testing was conducted on a
29 MWt (100 million Btu/hr) coal-fired
experimental furnace. The primary
objective was to explore the potential
for effectively removing SO2 using
calcium-based sorbents, through
appropriate selection of injection
location and Injector design and
operating parameters. To reduce SO2
and NOX simultaneously, the sorbent
was tested with the furnace operating
with an internally staged low-NOx
burner, which was designed to stage
fuel/air staging Internally within the
burner. Such internal staging is
intended to avoid the need for
external tertiary air ports, and thus
simplify the retrofit of such a low-NOx
burner into existing pre- NSPS utility
furnaces. The testing reported here
was a follow-on to testing on a
smaller scale (2.9 MWt, or 10 million
Btu/hr).
Because this testing emphasized
improving sorbent performance, the
testing of options for reducing NOX
emissions from the burner by internal
staging was limited. The options
tested were limited to two coal
splitters (referred to as the T-15 and
T- 30 splitters), designed to divide the
coal stream into four Initially fuel-rich
flames. The best set of conditions
(the T-30 splitter with low swirl in the
secondary air) resulted in NOX
emissions of 550 ppm (dry, 0% O2),
compared to 830-900 ppm from the
baseline unstaged burner, a
reduction of about 35 percent (less
than the 50-60 percent desired).
Flame length from the staged burner
was acceptable (6.7 m, and CO was
less than 40 ppm. Additional NOX
reductions might have been achieved
had additional staging approaches
(e.g., divided secondary air registers)
also been tested.
Variables addressed during the
SO2 sorbent testing included:
injection location (three locations on
the front wall, one on the rear wall),
injection velocity, injector diameter;
number of injectors, and injector
design (single-pipe vs. double-
concentric jets). Three sorbents were
tested. With the recirculation patterns
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created in the furnace by the burner,
reasonable SO2 could be removed
under only two conditions: Injection
from the rear wall at an optimum
velocity, to avoid the sorbent's
penetrating into the recirculation
zone while at the same time getting
adequate dispersion in the exhaust
flow; and injection high on the front
wall (5.8 m above the burner), using
large jets having sufficient
momentum to penetrate through the
recirculation zone into the furnace
exhaust flow. At a Ca/S molar ratio of
2, SO2 removals under these injection
conditions were: 30-40 % with Vicron
45-3 limestone (10 pm mass mean);
45-50% with D3002 dolomite (12 pm);
and 58-62% with Type-S pressure-
hydrated dolomitlc lime (1.4 pm).
This Project Summary was
developed by EPA's Air and Energy
Engineering Research Laboratory,
Research Triangle Park, NC, to
announce key findings of this
research project that is fully
documented in a separate report of
the same title (see Project Report
ordering information at back).
Introduction
LIMB technology is being investigated
to control S02 and NOX simultaneously
for existing coal-fired utility boilers. The
process envisions the use of calcium-
based sorbent to remove intermediate
levels of S02 (50 to 60%), and staged
burners for NOX reduction, for retrofit
applications as a potential component of
an acid rain control strategy.
The testing described in this report is
part of a larger project to explore the
potential for reducing combined S02/NOX
utilizing internally staged coal burners to
reduce NOX emissions, while selecting
sorbent injector design and operating
parameters to improve SO2 capture.
Testing on a 2.9 MWt experimental
furnace was described earlier. This report
addresses testing on a 29 MWt furnace,
intended to confirm the most promising
results from the smaller-scale testing.
Some staged burners which have
been tested in other studies involve the
use of external tertiary air ports to delay
fuel and air mixing. In some cases, it
could be difficult to retrofit such external
ports into existing boilers, due to
structural or other constraints. An
objective of this study was to confirm
certain burner design approaches which
could achieve the benefits of air staging
without external ports—i.e., with the
staging internal to the burner, in a
manner which would facilitate retrofit.
Because the emphasis of the 29 MWt
testing was to assess improved sorbent
injection alternatives, only a limited
number of burner internal staging options
were tested here; these were the options
which appeared to be the most promising
based upon the smaller-scale testing.
The sulfur capture performance of a
sorbent is dictated by the surface area it
develops upon calcination, upon its
residence time at sulfation temperature,
and upon its dispersion in the furnace.
Injection near the burner would provide
the greatest residence time and the best
dispersion, but could subject the sorbent
to high temperatures which would greatly
reduce its surface area/reactivity. Testing
in this study focussed on sorbent
injection remote from the internally
staged burner, since the smaller-scale
work had indicated that unacceptable
sorbent deactivation could probably not
be prevented during injection near the
flame zone, no matter how the injectors
were designed. The sorbent injector
design/operating parameters tested
during this study included: injector
location, injector diameter, injection
velocity, number of injectors at a given
location, and injector configuration (i.e.,
single-pipe jets versus double-concentric
jets, which provide a sheath of annular air
around the sorbent jet to protect it from
high temperatures). Three sorbents were
tested.
Experimental Equipment
The testing was conducted on a 29
MWt (100 million Btu/hr) experimental
furnace, referred to as the Large
Watertube Simulator (LWS). The LWS is
a full-scale model of a small wall-fired
utility boiler, having a firing depth of 6.7
m, and cooled by external water sprays
onto its corrugated steel walls. Insulation
inside the furnace is designed to cause
the furnace gas to drop to 1230°C (the
upper end of the "sulfation temperature
window"), just before the gas passes the
furnace nose; this is the approximate
location of that isotherm in a full-scale
boiler.
In all testing, the LWS was operated
with a single 29 MWt burner mounted in
the front wall. During the initial
optimization of the limited internal staging
options, this burner was operated with
and without two different coal splitters
which had provided good NOX reductions
during the earlier smaller-scale testing.
During the sorbent injection testing, the
burner was operated at the conditions
which gave the best NOX performance
during the initial optimization testing (T-
30 coal splitter, low swirl setting in
secondary air register). Sorbent was
injected at three locations on the front
(firing) wall of the furnace, and one on the
rear wall.
Results
The burner optimization studies
showed some potential for NOX reduction
with the internally staged burner tested
here (the IS-100 burner). The intent of the
internally staged burner is to achieve NOX
reductions without the external tertiary air
ports characteristic of commercial low-
NOX burners, and to achieve the internal
fuel/air staging with high burner velocities
(to facilitate retrofit into existing pre-
NSPS boilers without extensive
modifications to increase the size of the
burner opening in the firing wall). The
baseline unstaged burner tested here
with the annular coal nozzle (a typical
pre-NSPS burner configuration) gave NOX
emissions of 830-900 ppm (dry, 0% 02),
typical of pre-NSPS burners. Significant
reductions were achieved with the staged
IS-100 burner using axial coal nozzles
employing the T-15 or T-30 coal splitters,
which were designed to divide the coal
stream into four initially fuel-rich flames.
These splitters reduced NOX by aboul
150-200 ppm. The optimum configuration
in these tests was with the T-30 coal
nozzle and the low swirl register setting
This configuration gave 550 ppm NO,
(dry, 0% O2), with an acceptable flame
length of 6.7 m, and CO less than 4C
ppm. The NOX reductions achieved were
limited in part because--due emphasizing
the SO2 portion of this project-the ful
range of internal staging options was not
investigated (e.g., divided secondary aii
registers were not employed in the IS-
100 burner).
Sorbent injection from the front wall ol
the furnace gave unexpectedly poor SO2
capture; better sorbent performance
would have been anticipated, considering
that the gas temperatures at the injectior
points were near optimum. Cold-flow
physical modelling showed that this pooi
capture was caused by a stronc
recirculation zone above the burner whicf
extended into the upper furnace region
This zone created a downflow of furnace
gas along the front wall, which drew th<
sorbent into the flame. The bulk of th<
gas flow to the furnace exit took the forn
of a relatively thin layer of gas, about O.I
m thick, flowing up the rear wall. In viev
of this flow pattern, sorbent injection fron
the rear wall appeared to be an attractive
approach, because of the low risk of th<
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injected sorbents being carried into the
flame.
Sorbent injection from the rear wall
gave reasonable SO2 capture, reaching
35% capture at Ca/S = 2 for Vicron 45-3
limestone (10 urn mass mean). Capture
was very sensitive to sorbent injection
velocity, because it was necessary to
match the jet penetration to the thickness
of the gas flow up the rear wall. If
injection velocity was too high, sorbent
penetrated across the thin exit flow layer
into the recirculation zone, and was
carried down into the flame zone. If the
injection velocity was too low, the sorbent
was not adequately dispersed in the
upflow stream.
Reasonable 802 was a'so captured
from front wall injection in the upper
furnace region, 5.8 m above the burner.
However, good front-wall performance
could be achieved only with large-
diameter, high-velocity jets. These jets
had sufficient momentum to penetrate
across the recirculation zone and carry
most of the sorbent into the exiting flue
gas flow. With four 15-cm diameter jets at
an injection velocity of 21 m/s, the SO2
capture by Vicron at Ca/S = 2 was 30%.
Capture was improved when the jets
were configured in a double- concentric
mode, with the sorbent injected in a 2.5-
cm diameter jet along the axis of the
larger (15-cm diameter) annular air jet.
Apparently, this allowed a greater fraction
of the sorbent to reach the exit gas flow
without being drawn down into the flame
zone. The capture increased as the
sorbent jet velocity was increased,
consistent with results observed with
double-concentric jet tests in earlier,
smaller-scale testing. The reason for this
effect is not clear, but it is thought to be
related to changes in mixing conditions in
the jet. Capture during front-wall injection
was also greater with a larger number of
jets (4 vs 2), probably because, with four
jets, the two outermost jets near the sides
of the furnace were delivering sorbent to
a region where the recirculation down-
flow into the burner zone was not so
strong. The best capture achieved with
the double-concentric jets was about
40% at Ca/S = 2 for Vicron limestone.
Tests were conducted using D3002
dolomite and Type S pressure- hydrated
dolomitic lime, as well as Vicron
limestone, for the best front- and rear-wall
injection configurations. The dolomitic
sorbents gave superior capture to the
limestone. Dolomite gave SO2 captures
in the range 45 to 50% at Ca/ S = 2, and
the pressure hydrate gave captures in the
range 58 to 62%. The relative
performance of these three sorbents
(dolomitic hydrate better than raw
dolomite better than limestone) is similar
to results that have been observed in
other experimental investigations.
•&U. S. GOVERNMENT PRINTING nFFIfF. 1QRQ / 7AR-01 7 /f!71 Ql
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8. M. Cetegen, J. Clough, G. C. England, T. R. Johnson, Y. Kwan, and R. Payne
are with Energy and Environmental Research Corp., Irvine, CA 92718-
2798.
D. Bruce Henschel is the EPA Project Officer (see below).
The complete report, entitled "Evaluation of Internally Staged Coal Burners and
Sorbent Jet Aerodynamics for Combined S02/NOX Control in Utility
Boilers: Vol. 2. Testing in a 100 Million Btu/Hr Experimental Furnace,"
(Order No. PB 90-108 8461 AS; Cost: $23.00, 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:
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
Official Business
Penalty for Private Use $300
EPA/600/S7-89/009
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