United States
Environmental Protection
Agency
Air and Energy
Engineering Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S7-88/020 Jan. 1989
Project Summary
Evaluations of Electrostatic
Precipitator Performance at
Edgewater Unit 4 LIMB
Demonstration
John P. Gooch and James L. DuBard
The EPA is sponsoring a
demonstration of Limestone
Injection Multistage Burners (LIMB)
technology at Ohio Edison's
Edgewater Station Unit 4, which
employs a wall-fired boiler of 105
MW electric generating capacity. The
boiler is equipped with large
electrostatic precipitator (nominal
SCA 600 ft2/1000 acfm* at 528,000
acfm) of modern design that was
retrofitted in 1982. This report
describes extensive laboratory- and
pilot-scale studies, as well as
preliminary on-site tests at Unit 4.
This Project Summary was devel-
oped by EPA's Air and Energy
Engineering Research Laboratory,
Research Triangle 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
Coal-fired utility boilers account for
approximately 70% of the SOX emissions
and 20% to 25% of the NOX emissions in
the U.S. These emissions are believed to
be precursors of acid precipitation. The
coal-fired electric generating capacity
east of the Mississippi River
(approximately 180,000 MW) accounts
for 16 million tons of SOX and 4 to 5
" Readers more familiar with metric units may use
the conversion factors listed near the end of this
summary
million tons of NOX discharged into the
atmosphere annually. Only about 10% of
the coal-fired utility boilers in the
eastern U.S. are subject to SOX and NOX
emission controls under the New Source
Performance Standards (NSPS). A
significant reduction of SOX and NOX
emissions may require retrofit applica-
tions of emission control technology to
the existing boiler population.
LIMB technology is a retrofit SOX and
NOX emission control technology which
may be applicable to a significant
number of existing wall-fired and
tangentially fired boilers. LIMB tech-
nology involves injecting a calcium-
based sorbent directly into a furnace that
is equipped with Iow-N0x burners.
Since 1986, the development of LIMB
technology has focused on furnace
injection of hydrated lime, at about
2200°F, with subsequent humidification
of the combustion gas downstream of the
heat exchangers. The particulate matter
suspended in the combustion gas stream
(fly ash and partially sulfated sorbent)
must be collected in an existing
electrostatic precipitator (ESP).
Candidates among existing boilers for
a retrofit application of LIMB technology
are mostly equipped with small ESPs that
were designed to collect low-resistivity
fly ash from high-sulfur coal com-
bustion. These ESPs typically have
specific collection areas (SCA) less than
300 ft2/1000 acfm. A retrofit application of
LIMB technology will result in changes in
the suspended particulate matter that
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present a difficult challenge to these
ESPs.
The EPA is sponsoring a demon-
stration of LIMB technology at Ohio
Edison's Edgewater Station Unit 4, which
employs a wall-fired boiler of 105 MW
electric generating capacity. This partic-
ular unit has a large ESP (nominal SCA
600 ft2/1000 acfm at 528,000 acfm) of
modern design that was retrofitted in
1982.
LIMB tests, with furnace injection of
pulverized limestone, began during 1984
in a 1 million Btu/hr pilot coal combustor.
The early tests focussed on calcium
utilization and SOX removal issues, but
some data were also obtained on the
changes in dust resistivity, mass loading,
and particle size distribution that impact
ESP performance. During 1985, the
emphasis in LIMB development shifted
to furnace injection of hydrated lime.
Measurements of the changes in dust
properties caused by LIMB were used to
perform preliminary estimates of the
impact of LIMB on the Edgewater Unit 4
ESP, using the mathematical model. The
data from the pilot coal combustor were
also used to estimate the impact of LIMB
on small ESPs with SCAs in the range of
200 to 300 ft2/iooO acfm. The experi-
mental data and the results of
mathematical modeling have been
reported.
The master plan for a demonstration of
LIMB technology included preliminary
tests of the impact of LIMB on the EPA
mobile pilot ESP. The pilot ESP was
refurbished and installed on a com-
bustion gas sidestream from a heating
plant boiler in Oromocto, New Brunswick,
for the purpose of evaluating operating
problems and performance upgrading
methods prior to the Edgewater demon-
stration project. However, satisfactory
boiler operation with LIMB could not be
achieved in the allotted time period
before the pilot ESP was moved to the
Edgewater demonstration site. There-
fore, the pilot coal combustor was the
only significant source of data on LIMB
dust properties prior to the preliminary
LIMB trials at Edgewater Unit 4 during
September, 1987. Following the prelim-
inary LIMB trials, which were conducted
without humidification of the combustion
gas stream, extensive tests of the impact
of humidification on ESP performance
were conducted during January and
February 1988. Results of these tests
have been reported.
Summary of Results and
Conclusions
This section summarizes the principal
findings related to the impact of LIMB on
ESP performance, both from the
preliminary LIMB trials at Edgewater Unit
4 and from tests in the pilot coal
combustion facility with a laboratory ESP
installed on the combustion gas stream.
The principal findings cover dust
resistivity, electrical and mechanical
operation, dust loading and particle size
distribution, electrode dust accumulation
and cleaning, and mass emissions and
opacity.
Dust Resistivity
Edgewater Unit 4
• During baseline operation, the dust
resistivity measured in situ at the ESP
inlet averaged 3x1010 ohm-cm at
350 °F.
• During operation with LIMB, the dust
resistivity was too high to be measured
accurately with the point-plane in situ
resistivity probe. The measured values
were in the range of 1x1012 to 5x1012
ohm-cm, at 300° to 360°F, but the
actual values are believed to have
ranged as high as 1x1014 ohm-cm.
Pilot Facility
• Laboratory measurements of LIMB
dust resistivity indicated values as high
as 1x1014 ohm-cm at the operating
temperatures experienced in the
Edgewater Unit 4 ESP.
• Cold-side combustion gas stream
humidification was found to be an
effective means of moderating LIMB
dust resistivity. The resistivity values
(measured both in situ and in the
laboratory) dropped over two orders of
magnitude at temperatures of
approximately 220°F, representing
about a 100°F approach to the
adiabatic saturation temperature.
• LIMB dust resistivity is expected to be
below 1x1012 ohm-cm within a 100"F
approach to saturation, and below
1x1010 ohm-cm within a 50°F ap-
proach to saturation.
Electrical Operation
Edgewater Unit 4
• During baseline operation, there was
no evidence in the measured trans-
former-rectifier secondary voltage-
current curves of any electrical or
mechanical malfunction. J
• During operation with LIMB, there was
severe electrical malfunction caused by
the high resistivity of the precipi-tated
LIMB dust. Electrical degradation
began in the ESP inlet field and
progressed to the fifth field within three
to four hours of operation with LIMB.
Electrical degradation resulted in the
immediate onset of back corona at the
threshold voltage for primary corona.
There was no working voltage range
which would permit useful
electrification of the ESP.
Pilot Facility
• Furnace sorbent injection caused
severe electrical degradation of the
laboratory ESP. Humidification within a
100°F approach to saturation was
necessary to permit useful electrifica-
tion of the ESP.
• At a fixed operating voltage applied to
the laboratory ESP, the operating
current increased with increasing
humidification and closer approach to
saturation.
Mechanical Operation
Edgewater Unit 4
• During an internal inspection of the
ESP after furnace sorbent injection,
there was no evidence of any serious
electrode misalignments or electrode
cleaning difficulties. The ESP appeared
to be in good mechanical operating
condition. However, problems were
encountered with the ash removal
system during the LIMB tests.
Dust Loading and Particle Size
Distribution
Edgewater Unit 4
• LIMB had an adverse impact on the
mass loading and particle size
distribution of dust entering the ESP.
The overall mass loading increased by
about a factor of two.
• During operation with LIMB, the mass
loading increased by about a factor ol
10 in the particle size range from 0.5 tc
1.0 iim. This is the particle size range
where ESPs are least efficient and the
particulate emissions contribute mosf
strongly to plume opacity.
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pilot Facility
-> Furnace injection of hydrated lime
resulted in changes in the suspended
particulate matter that were consistent
with data from the preliminary LIMB
trials at Edgewater Unit 4. At a typical
Ca/S stoichiometry of about 2, the
overall mass loading increased by a
factor of 2 to 3, and the fine particulate
mass loading increased about tenfold.
Electrode Dust Accumulation
and Cleaning
Pilot Facility
• There was a rapid accumulation of
dust deposits on the laboratory ESP
electrodes during furnace sorbent
injection and combustion gas stream
humidification. Dust deposits on the
high voltage discharge electrodes built
up very rapidly.
• There was no difficulty in cleaning the
ESP electrodes by mechanical
rapping, even at a close approach to
adiabatic saturation. LIMB dust was
removed more easily than the fly ash
from pulverized coal combustion.
Mass Emissions and Opacity
Edgewater Unit 4
• During baseline operation, the ESP
operated with a clear stack. Opacity
readings were in the range of 1% to
2%.
• During operation with LIMB, opacity
rose rapidly to the 20% limit after
electrical degradation began in the fifth
ESP field. Steady state operation of
the ESP with LIMB was not achieved
during the preliminary trials. Furnace
sorbent injection had to be stopped
after 3 to 4 hours to avoid exceeding
the opacity limit.
• Mathematical modeling of the ESP
performance during cold-side
humidification of the combustion gas
stream indicated that the performance
will be satisfactory within a 100°F
approach to saturation because of the
large size of the ESP.
Pilot Facility
• There was no catastrophic
spontaneous reentrainment from the
laboratory ESP electrodes of
humidified LIMB dust, as
humidification was increased all the
way to the point of adiabatic saturation.
• Spontaneous reentrainment of pre-
cipitated LIMB dust occurred in large
agglomerates which did not affect the
measured outlet gas opacity. In an
operating ESP, these agglom-erates
would be quickly recollected.
• The outlet gas opacity decreased
(concurrently with the increasing
operating current) with increasing
humidification and a closer approach to
saturation.
• The outlet gas opacity decreased by
several percentage points after the
laboratory ESP electrodes were
rapped. This performance improve-
ment is a result of the improved
electrical operating condition obtained
with cleaner electrodes.
Future Work
A long term demonstration of LIMB
technology with humidification is planned
at Edgewater during the last part of CY
1988. The test plan for the demonstration
includes evaluations of the performance
of the full scale ESP with humidification.
Pilot-scale studies are also planned with
the EPA pilot ESP system. These
experiments will focus on performance
enhancements which may be achieved
with electrode modifications and
humidification on ESPs with smaller SCA
values that are more typical of the
potential LIMB retrofit candidate
population than the large ESP installed at
Edgewater.
Metric Equivalents
Readers more familiar with metric units
may use the following equivalents to
convert from the nonmetric units used in
this summary:
Nonmetric
Multiplied
by
Yields
metric
Btu/hr
cfm
°F
ft2
ton
0.293
0.000472
5/9 (°F - 32)
0.0930
907.18
W
m3/s
°C
m2
kg
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John P. Gooch and James L. DuBard are with Southern Research Institute,
Birmingham, AL 35255.
The complete report entitled, "Evaluations of Electrostatic Precipitator Perform-
ance at Edgewater Unit 4 LIMB Demonstration," (Order No. PB 89-109 1771 AS;
Cost $15.95, cost 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/S7-88/020
0000329 PS
It 60604
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