United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park, NC 27711
Research and Development
EPA/600/S7-91 /004 May 1991
EPA Project Summary
Technology for the Control of
Particulates and Sulfur
Oxides by Electrostatic
Techniques
Edward B. Dismukes and John P. Gooch
Supported by the U.S. EPA, Southern
Research Institute has performed re-
search in several areas related to the
cleanup process for flue gas known as
E-SOX. These activities laid part of the
foundation for the pilot-scale demon-
stration of E-SOX at Ohio Edison's Burger
station.
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 E-SOX process for jointly controlling
paniculate matter and sulfur oxides (SOX).
mainly SO2, is based on the injection of a
spray of an aqueous slurry of slaked lime at
the inlet of an electrostatic precipftator (ESP).
The SO2 reacts with calcium hydroxide--
Ca(OH)2— to produce calcium sulfite
(CaSO3); the resulting solid reaction prod-
.jjgt-gsaociated with paifof the Ca(OH)2 that
does not react, is collected in the ESP along
with fly ash from the boiler. In the initial
concept of E-SOX, the electrical compo-
nents would be removed from the first field
of the ESP and replaced with the spray
nozzles for the slurry. Currently, however,
the common concept of E-SOX entails the
use of a separate spray chamber ahead of
the ESP.
Several tasks related to the development
of the E-SOX process were performed at
Southern Research Institute between Au-
gust 1,1985 and July 31,1990:
1. A survey of ESPs in the utility industry
where the E-SOX process may find ap-
plication.
2. Analysis of the technical and economic
aspects of the E-SOX process. (This task
was completed with the assistance of
subcontractor Gilbert/Commonwealth,
Inc.)
3. Measurement and modeling of the per-
formance of a precharger that can be in-
corporated in the E-SOX process.
4. Investigation of the E-SOXprocess using
a pilot-scale combustion facility.
5. Development of a measurement tech-
nique that is suitable for determining the
electrical resistivity of E-SOX particulate
matter and the development of a method
for predicting the resistivity of solids from
the E-SOX process and other sorbent
processes for control of SOX.
Surveys
Tasks 1 and 2 (above) were in the nature
of a survey and analysis of technological
information. First, the population of ESPs in
the utility industry that may provide sites for
application of E-SOX was surveyed. Sec-
ond, a technical and economic assessment
of the E-SOX process itself was performed.
The survey of ESPs was undertaken with
the assistance of the Electric Power Re-
search Institute, which made available a
large data base that had been compiled for
EPRI by a contractor, Burns and Roe. A
more limited data base was then compiled
by Southern Research, to achieve more
specific relevance to application of E-SOX
technology, Only ESPs associated with
power boilers burning Eastern bituminous
coals, with 1% or more sulfur, and ESPs
Printed on Recycled Paper
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having specific collecting areas between
100 and 400 ft*/(1000 acfm) were of inter-
est. Moreover, only ESPs associated with
boilers rated for more than 50 MW were
included in the revised data base. Some
275 ESPs offering potential sites for the
application of E-SOX were identified and
their relevant characteristics listed.
The technical assessment of E-SOX
technology led to a number of conclusions,
some of which were modified on the basis of
information gained elsewhere since the
technology assessment was completed.The
original conclusions were:
• The appropriate mechanical system de-
sign will mostly utilize commercially avail-
able equipment. The only hems that pose
developmental problems are the two-fluid
nozzle spray system, the ESP precharger,
and the ESP large-diameter electrodes.
* From an operating point of view, the great-
est concern is adequate spray drying in
theguttedfirstfieidoftheESPto minimize
tenacious depositsinthesubsequent ESP
fields. (Note: this analysis was made as-
suming that spraying of solid would occur
inthegutted first ESPfield, not in a separate
spray chamber.)
• ESP performance on this type of particu-
late needs to be verified. In particular, the
mass loadings and size distribution of the
particulate at the end of the spray section,
the ESP electrical properties (secondary
voltages and currents), and gas distribu-
tion device requirements need to be es-
tablished. (Noterthis requirement has been
satisfied to a considerable degree by the
pilot-scale demonstration at the Burger
station, discussed below.)
• The capability of a vacuum-type fly-ash
handling system to continuously remove
hoppormatorial needs to be demonstrated.
Additional equipment requirements (for
example, a delumperto prevent oversize
material) need to be defined.
• Retrofit capital costs will be very site spe-
cific, particularly if conventional ESP
modifications (taller plates or an outlet
field) are required.
•The largest component affecting operating
cost is the reagent consumption. There-
fore, process stoichiometry is critical to
cost. Also, pebble lime shows a distinct
economic advantage over lime hydrate.
• Future research efforts should concen-
trate on optimizing the process param-
eters - In particular, slurry droplet size,
CayS ratfo, approach temperature, and
residence time requirements.
• Because of the performance advantages
indicated by the precharger and large
diameter electrodes, these technologies
should be further demonstrated at an ap-
propriate equipment scale. (Note: as dis-
cussed below, the performance advan-
tage afforded by a precharger seems to
marginal at best.)
Experimental Research
An area of experimental investigation
concerned the use of a cold-pipe precharger
for enhancing particle charging in the E-
SOX process. (This type of precharger is
alluded to in the above discussion of the
survey of E-SOX technobgy.) Southern
Research personnel visited EPA's precipi-
tator research facility at Research Triangle
Park, NC, where a precharger had been
installed. Measurements were made of par-
ticle charge produced by the precharger,
and they were summarized by relationships
between particle diameter and charge im-
parted in the precharger at different operat-
ing voltages and current densities. The
charging performance of then cold-pipe
precharger was then compared with that of
a conventional ESP. The conclusion was
that for E-SOX solids of low resistivity, which
is to be expected as the rule, the precharger
offers no clear advantage over the conven-
tional ESP.
Another area of experimental study con-
sisted of performjing E-SOX experiments in
a pilot-scale, coal-fired combustor rated for
1 million Btu/h. These experiments yielded
samples of E-SOX solids that were charac-
terized by various techniques but used pri-
marily in the study of electrical resistivity
discussed below. Other experiments com-
pared SO2 removals by injection of slurries
prepared either by mixing commercial hy-
drated lime with water or simultaneously
slaking quicklime and preparing a slurry
therefrom. The s urry prepared from quick-
lime gave slightly better SO2 removal.
The final experimental study led to the
development of a laboratory method that
yields repeatable data on the electrical re-
sistivity of solids: from the E-SOX process
and other sorbent processes for SO2 con-
trol, such as LIMB.* The resistivities of
separate compounds of calcium that are
present in E-SO|X and LIMB solids were
determined. An effort was made to develop
a method for predicting the resistivities of
these solids, based primarily on the effects
of the distinct calcium compounds, but the
effort was not successful.
Pilot-Scale Demonstration
This demonstration is being conducted at
the Burger power station of the Ohio Edison
Company at the 5-MW scale. A key compo-
nent of the facility is a pilot-scale ESP,
which was moved to the Burger site from
the Valmont station of the Public Service
Company of Colorado. This ESP has four
electrified fields; it also has cold-pipe charg-
ing electrodes in each field, but they have
not been used in testing to date. The ESP
is preceded by a spray chamber, where a
slurry of slaked lime is injected. At the inlet
to the first field of the ESP, a droplet- im-
pingement device intercepts and removes
large slurry droplets and dry residues of
droplets. The remaining smaller particles
are then collected in the ESP.
ESP performance was tested by South-
ern Research during the spring of 1990. The
principal finding was that the efficiency of
solids collection deteriorated markedly when
operation with E-SOX began. The expla-
nation for the deterioration is that the dried
sorbent particles had very tow cohesiveness
and, as a consequence, were extensively
reentrained after precipitation.
•Limestone Injection Multistate Burner System.
•&U. S. GOVERNMENT PRINTING OFFICE: 199 1/548-028/20205
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E Dlsmukes andJ. Gooch are with Southern Research Institute, Birmingham, AL
35255-5305.
Louis S, Hovls is the EPA Project Officer (see below). '<
The complete report, entitled "Technology for the Control of Pahiculates and Sulfur
Oxides by Electrostatic Techniques," (Order No. PB91-171355/AS; Cost: $17.00,
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
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EPA/600/S7-91/004
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