United States	National Risk Management

Environmental Protection	Research Laboratory

Agency	Research Triangle Park NC 27711

Research and Development	EPA/600/SR-96/062 June 1996

«>EPA Project Summary

Prototype Scale Testing of LIMB
Technology for a Pulverized-
Coal-Fired Boiler

G.C. England, D.K, Moyeda, Q. Nguyen, and B.A. Folsom

The report summarizes results of a
project conducted to evaluate furnace
sorbent injection for control of sulfur
dioxide (SOj) emissions from coal-fired
utility boilers. The project, sponsored
by the U.S. Environmental Protection
Agency (EPA) and the Electric Power
Research Institute, is one of three sor-
bent injection projects conducted on
full-scale, coal-fired utility boilers in the
U.S. The emphasis of the project was
on evaluating a wide range of process
parameters during relatively short-term
periods of operation to enhance under-
standing of the process, as opposed to
a demonstration of sorbent injection
over an extended period of time under
optimum sorbent injection conditions.
The process parameters which were
evaluated included sorbent type, boiler
operating conditions, and injection pa-
rameters. A very flexible sorbent Injec-
tion system was installed at the host
boiler and tested over a wide range of
conditions. A flue gas humidification
system also was installed and tested
to enhance electrostatic precipitator
performance during sorbent injection.
Energy and Environmental Research
Corporation conducted the project.

This Project Summary was developed
by EPA's National Risk Management
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).

Program Goals

Primary goals of the program were to
provide information on parameters that af-
fect calcium utilization in tangentially fired

boilers and to document the impacts of
sorbent injection on the boiler, ancillary
equipment, and pollutant emissions. Sec-
ondary goals were to document humidifi-
cation system performance and to
establish an information base for future
combined sorbent injection/humidification
designs that are optimized for S02 re-
moval.

Host Boiler

The host boiler for the program was
Richmond Power and Light's Whitewater
Valley Unit 2 in Richmond, Indiana. This
unit, one of the smallest existing tangen-
tially fired utility boilers, is a Combustion
Engineering (CE) VU-40 steam generator
with a nominal rating of 61 MWe. Pendant
and spaced superheaters in combination
with a baffleless boiler bank result in a
single-pass cross-flow arrangement of heat
transfer surfaces. It has a finned tube
economizer and a rotating regenerative
air heater. At full load, 540,000 Ib/hr* of
steam at 1320 psig and 955° F is gener-
ated. Unit 2 was commissioned in 1972
and is a balanced draft design. Three
elevations of burners are located at the
furnace corners (12 burners total). The
burners were previously modified by CE
with a low nitrogen oxide (NO„ concentric
firing system. The plant fires a medium
sulfur (2.5 lb sulfur per 10® Btu) bitumi-
nous coal blend.

Unit 2 is equipped with a Lodge-Cottrell
cold-side electrostatic precipitator (ESP),
erected with the boiler. The ESP treats
227,000 acfm of flue gas at 285°F. The
design specific collection area of the ESP
is 198 ft2/1000 acfm. It has two mechani-

* Readers more familiar with metric units may use the
factors listed at the end of this Summary to convert to
that system.

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cal fields, four equal electrical fields in
series, and a design particulate removal
efficiency of 99.0%.

Baseline Tests

Baseline tests were performed on the
host boiler to establish normal performance
prior to operation of the prototype furnace
sorbent injection and flue gas humidifica-
tion system. The test results were used to
establish the impact of sorbent injection/
humidification on boiler and ESP perfor-
mance over a wide range of operating
conditions. The baseline tests included
characterization of air pollutant emissions;
boiler thermal performance, including
slagging and fouling tendencies; ESP op-
eration and performance; and furnace flow
and temperature characteristics.

Baseline Emissions

Average emissions of NOx, S02, and
particulate were determined on the host
boiler over a range of boiler loads and
coal sulfur contents. NOx emissions ranged
from 0.65 lb/106 Btu at full boiler load to
0.53 lb/10s Btu at low load. The baseline
NOx levels are significantly below the un-
controlled emissions from the host boiler
prior to the low NOx concentric firing sys-
tem retrofit. During the baseline tests, the
coal sulfur content varied from 1.7 to 3.1%
on an as-received basis. S02 emissions
were found to correlate well with coal sul-
fur content. Typical of bituminous coals,
essentially no inherent sulfur capture in
the coal ash was detected. Particulate
emissions were 0.04 to 0.13 lb/106 Btu
over the range of conditions tested.

Baseline Boiler Efficiency

An on-line boiler performance monitor-
ing system developed by Energy and En-
vironmental Research Corporation (EER)
was used to determine boiler efficiency,
which ranged from 88.1% at the nominal
low load condition (40 MWe) to approxi-
mately 87.7% at maximum boiler load (64
MWe). The measured efficiency was ap-
proximately equal to the manufacturer's
predicted design efficiency.

Baseline Gas-Side Fouling

Fouling of gas-side tube surfaces in the
superheaters and convective passes is
expected to increase during sorbent injec-
tion because the spent sorbent will result
in a large increase in the total amount of
particulate matter entrained in the gas.
Baseline fouling characteristics were de-
termined so that the impact of sorbent
injection could be quantified. A surface
"cleanliness coefficient" was defined for
each boiler section as the ratio of actual
heat absorbed to average heat absorbed

at a given boiler load. This was monitored
on-line during operation with the boiler
performance monitoring system. The stan-
dard deviation of cleanliness coefficient
was used to represent the range of
baseline gas-side fouling. Measurements
were also made using an air-cooled foul-
ing probe to quantify the rate of deposit
buildup in the upper furnace and super-
heater sections.

Baseline ESP Performance

Baseline performance of the ESP was
determined while firing the baseline and
high sulfur coals. The baseline coal had a
sulfur content of 2.0 to 3.0%, while the
high sulfur had between 3.5 and 5.3%
sulfur. The collection efficiency of the ESP
was slightly below the design value, even
when firing the high sulfur coal. However,
stack opacity remained well below regu-
lated levels. Fly ash resistivity was normal
for the coal type and flue gas conditions
occurring during the tests. No significant
difference in fly ash resistivity between
baseline and high sulfur coals was ob-
served.

Process Design Measurements

Flow and temperature fields were ex-
tensively characterized to provide infor-
mation needed to support the detailed
design of the sorbent injection system and
flue gas humidifier. Tests included mea-
surement of gas temperature, velocity, gas
species concentration, and radiative flux
at locations in the furnace and superheat-
ers. Additionally, physical measurements
were taken of ductwork and areas of in-
terference to accommodate the process
equipment that would be installed during
the sorbent injection/humidification system
retrofit.

Baseline Test Conclusions

The baseline tests indicated that the
host boiler and ESP for the sorbent injec-
tion/humidification prototype were perform-
ing essentially as designed, within normal
limits. Relatively minor problem areas (ex-
cessive air heater leakage, air heater bas-
ket corrosion, missing tube shields, ESP
plate misalignment) were corrected during
the tests to ensure that sorbent injection/
humidification was evaluated under condi-
tions representative of normal boiler ther-
mal operation. The tests provided baseline
data for air pollutant emissions, boiler ther-
mal performance, fouling trends, and per-
formance of the ESP, fans, and coal
pulverizers. Additionally, historical data pro-
vided by the plant were used to establish
baseline reliability and availability of the
unit.

Prototype System Design

The sorbent injection and humidification
systems were designed in two steps:

•	Process design studies were con-
ducted to establish design specifi-
cations expected to result in
optimum system performance on
the host boiler and to develop boiler
specific conceptual designs.

•	Engineering design studies were
conducted to translate the concep-
tual design into engineering designs
that included specification of equip-
ment, controls and instrumentation,
and process equipment arrange-
ment.

Sorbent Injection System

The approach to the design of the sor-
bent injection system was based on a
generalized methodology developed by
EER, which involves (1) the application of
various experimental and analytical meth-
ods to determine boiler locations at which
temperature levels are optimum for sor-
bent injection, and (2) to define injection
conditions that will produce uniform dis-
persion of the sorbent material. The opti-
mum injection configuration developed for
full boiler load operation consisted of eight
3-in. diameter injectors located near the
plane of the boiler nose with an injection
velocity of 140 ft/sec. Sorbent transport
air corresponded to 2.5% of total combus-
tion air. The optimum injection configura-
tion for low boiler load operation consisted
of four 2-in. diameter injectors with an
injection velocity of 326 ft/sec. Sorbent
transport air corresponded to 2.0% of to-
tal combustion air.

Sorbent Selection

Bench-scale testing of 15 candidate sor-
bent materials was conducted to establish
their relative reactivity towards S02. Four
sorbents representing a range of avail-
able materials were selected for use in
the field evaluation studies. These included
highly and moderately reactive calcific hy-
drates, a highly reactive atmospheric do-
lomitic hydrate, and a limestone of
relatively low reactivity characteristic of
this sorbent class.

Humidification System

Sorbent injection was expected to in-
crease particulate emissions due to (1) an
increase in total particulate matter enter-
ing the ESP by a factor of 2 to 3, (2) a
decrease in the mean particle size at the
inlet, and (3) an increase in dust resistivity
that would degrade ESP performance. The
methodology for designing the humidifica-
tion system included experimental and

2

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computational efforts. Twin-fluid atomiz-
ers were selected and installed as an ar-
ray of 28 atomizers in the existing flue
gas duct close to the air heater. Com-
pressed air was used as the atomizing
medium. Spacing was chosen to minimize
overlap of adjacent sprays and impaction
on the duct walls while achieving rapid
and uniform mixing of the water droplets
and flue gas. The design was capable of
achieving complete evaporation of water
down to a 75°F approach to adiabatic
saturation temperature.

Waste Management

The product of S02 removal by sorbent
injection is solid calcium compounds, pri-
marily unreacted calcium oxide and the
reaction product, calcium sulfate. These
solids are removed from the flue gas, with
the fly ash creating a solid waste stream.
Modifications to normal fly ash handling
and disposal practices necessary to ac-
commodate this additional solid waste bur-
den included

•	Removal of the ash mixture through
the dustless unloader into a 20-ton
dump truck;

•	Segregation of spent sorbent/fly ash
mixtures from conventional fly ash
and disposal at the landfill; and

•	Treatment of the ash system sluice/
Hydroveyor water with sulfuric acid
to neutralize pH.

Sorbent Injection Results

The test program was limited to para-
metric tests of short duration that focused
on establishing data quality, sorbent utili-
zation data, and the effects of injection
parameters and boiler operating conditions
on S02 removal. Three sorbents were se-
lected for evaluation during the paramet-
ric tests program: Marblehead hydrate,
Linwood hydrate, and Marblehead hydrate
containing a calcium lignosulfonate addi-
tive. Sorbent injection parameters investi-
gated included

•	Injection location (upper and lower
furnace),

•	Number of sorbent injectors,

•	Sorbent jet velocity at the injector
exit,

•	Sorbent nozzle tilt and yaw, and

•	Sorbent type.

S02 Removal

Marblehead hydrated lime was used as
the baseline sorbent during the paramet-
ric tests. S02 removal ranged from 23 to
48% at a Ca/S (molar) ratio of 2.0, de-
pending on injection configuration and
boiler load. S02 removal of 50% was
achieved at a Ca/S of 2.5 with the boiler

operating at 50 MWe (82% of maximum
continuous rating). At near full load (60
MWe), a Ca/S of 3.0 or greater was re-
quired to achieve 50% S02 removal.

In addition to load, other boiler operat-
ing parameters, (e.g., excess oxygen (02)
and burner adjustments) were varied. S02
removal generally increased with increas-
ing excess 02 especially near full load.
Increasing furnace exit gas temperature
caused S02 removal to decrease, sug-
gesting that the gas temperature at the
point of sorbent injection in the upper fur-
nace was higher than optimum, particu-
larly at full load. The capability of favorably
modifying the burner air distribution to af-
fect the upper furnace thermal environ-
ment was also evaluated. At full load, the
impact of burner adjustments on S02 re-
moval was estimated to be 2 to 4%.

In general, sorbent injection parameters
such as injection velocity and nozzle tilt/
yaw had only a second order impact on
S02 removal. Calcium utilization for the
three sorbents was evaluated at Ca/S of
1.7 and 2.3 and 60 MWe boiler load. Ironi-
cally, the highest calcium utilization was
not achieved at the design configuration,
but with sorbent injection higher up in the
furnace and with higher injection velocity.
Injection velocity was increased by increas-
ing the sorbent transport air flow with con-
stant injector diameter. Attempts to further
optimize sorbent injection were limited by
the available furnace wall penetrations.
Shifting more of the sorbent above the
nose plane of the superheater region re-
sulted in lower calcium utilization. This
was likely due to a combination of less
than optimum temperatures and reduced
residence time. Calcium utilization was
similar for all three sorbents.

ESP and Boiler Impacts

ESP performance was substantially de-
graded by sorbent injection. However, hu-
midification of the flue gases to moderate
levels (approximately 130°F approach to
adiabatic saturation temperature) restored
performance. In most tests, opacity re-
mained near baseline levels and was be-
low 20% for nearly all the tests.

Boiler performance was carefully moni-
tored throughout the tests, using the on-
line boiler performance monitoring system.
Sorbent injection resulted in significant
superheater fouling, but this was easily
controllable by operating the six retract-
able sootblowers in the superheater and
boiler banks on a 1-hour cycle. There was
no impact on furnace fouling or slagging.
The host boiler is equipped with a finned-
tube economizer and a rotary regenera-
tive air heater. There are no sootblowers

in the economizer, and decreased heat
absorption was observed in the econo-
mizer during sorbent injection, although
unacceptable buildup of deposits did not
occur. Air heater performance was also
satisfactory, and there was no evidence
of permanent fouling. Heat loss efficiency
was slightly lower with sorbent injection,
primarily due to the increase in deposits
which resulted in increased stack gas tem-
perature.

Discussion

S02 removal for the nominal design con-
ditions was considerably below the level
predicted during the design phase. A con-
tributing factor is thought to be boiler clean-
liness and its impact on the furnace gas
temperature at the injection locations. Tem-
perature and velocity probing of the test
unit disclosed a very complex flow tem-
perature and flow field. Significant gradi-
ents were observed. These factors were
considered in the design phase and were
accommodated to the extent possible in
the actual installation of injectors subject
to physical limitations and interferences.
Sorbent injection clearly tended to increase
gas temperatures at the injection plane,
which contributed to a large part of the
difference between predicted and mea-
sured results. However, it is not sufficient
to explain the entire difference. Tests were
conducted to estimate the degree of sor-
bent dispersion. The measurements re-
vealed considerable variation in the local
Ca/S ratio, indicating non-uniform sorbent
dispersion, which in turn contributes to a
decrease in S02 removal. The analysis
suggests that the complex flow and tem-
perature field can potentially contribute to
low S02 removal.

Conclusions

The efficiency of sorbent utilization in
small tangentially fired boilers may be af-
fected by complex flow and temporal char-
acteristics, requiring higher rates of sorbent
injection to achieve S02 control targets
than less complex systems. The maxi-
mum rate of sorbent practically achiev-
able on a long-term basis will be boiler
specific and most probably limited by foul-
ing tendencies. In applications of sorbent
injection to tangentially fired boilers where
substantial temperature and velocity gra-
dients may exist in the upper furnace, the
design of the sorbent injection system must
recognize the potential influence of local
conditions in order to maximize sorbent
utilization. In addition, sorbent injection it-
self may have an impact on gas tempera-
tures at the injection location, which may
affect S02 removal if the impact is large.

3

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Metric Conversions

Readers more familiar with metric units
may use the factors in Table 1 to convert
to that system.

Table 1. Metric Conversion Factors

Nonmetric	Multiplied by	Yields Metric

acfm

4.719 x 10*

m>s

Btu

1.055 x 10'

J

"F

S/S(°F-32)

°c

ft

3.048 X 10 ¦'

m

ff

9.290 x 10*

m*

fP/1000 acfm

1.968 X 10*

rrf/1000 mVs

in.

2.540X10*

m

to

4.536 X 10 ¦'

kg

psig

6895 (psig + 14.7)

Pa (absolute)

ton

9.072x 10'

kg

G.C. England, O.K. Moyeda, Q. Nguyen, and B.A. Folsom are with Energy and

Environmental Research Corp., Irvine, CA 92718.

David G. Lachapelle is the EPA Project Officer (see below).

The complete report, entitled "Prototype Scale Testing of LIMB Technology for a
Puh/erized-Coal-Fired Boiler,' (Order No. PB96-1838S0; Cost:$21.50, subject to
change) will be available only from

National Technical Information Service
5285 Port Royal Road
Springfield, VA22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at

National Risk Management Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711

United States

Environmental Protection Agency
National Risk Management
Research Laboratory (G-72)
Cincinnati, OH 45268

Official Business
Penalty for Private Use
$300

EPA/60CVSR-96/062

BULK RATE
POSTAGE & FEES PAID
EPA

PERMIT No. G-35

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