United States
Environmental Protection
Agency
Industrial Environmental Research
Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S9-82-005b Aug. 1983
v>EPA Project Summary
Third Symposium on the
Transfer and Utilization of
Paniculate Control Technology:
Volume II. Electrostatic
Precipitators
F. P. Vendetti, J. A. Armstrong, and M. Durham
Summarized herein is Volume II of
the four volumes of proceedings of the
Third Symposium on the Transfer and
Utilization of Particulate Control Tech-
nology held in Orlando, Fl_ March 9-12,
1981. Volume II papers deal particularly
with electrostatic precipitators (ESPs)
as particulate control devices. The
papers discuss fundamentals of the
design and fabrication of ESPs, addi-
tions to the theory and the analysis of
the operation of ESPs, the operation
and maintenance of ESPs, advanced
designs and concepts, and the applica-
tion of ESPs fired by other than conven-
tional fuels.
Volumes I, III, and IV are described in
three separate project summaries.
This Project Summary was developed
by EPA's Industrial Environmental Re-
search 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 papers in Volume II of the four
volumes of proceedings were presented
at the Third Symposium on the Transfer
and Utilization of Particulate Control Tech-
nology in Orlando, FL, March 9-12,1981,
sponsored by the Particulate Technology
Branch of EPA's Industrial Environmental
Research Laboratory at Research Triangle
Park, NC.
The symposium brought together re-
searchers, manufacturers, users, govern-
ment agencies, educators, and students
to discuss new technology and provided
an effective means for the transfer of this
technology out of the laboratories and
into the hands of the users.
The three major categories of control
technologies—electrostatic precipitators
(ESPs), scrubbers, and fabric filters—were
the major concern of the symposium.
These technologies were discussed from
the perspectives of economics new tech-
nical advancements in science and engi-
neering, and applications. Several papers
dealt with combinations of devices and
technologies, leading to a concept of
using a systems approach to particulate
control, rather than device control. Addi-
tional topic areas included novel control
devices, high-temperature/high-pressure
applications, fugitive emissions, and
measurement techniques.
The symposium was conducted as a
series of parallel sessions, each contain-
ing four to six related papers. The sessions
were scheduled to avoid conflict due to
simultaneous sessions dealing with the
same topic. Each series of related ses-
sions represented a thread of technology.
These parallel threads, extending over
the total period of the symposium, pro-
vided a highly integrated approach to the
total subject of particulate control tech-
nology, with strands of specialized tech-
nologies. These strands of specialized
technologies, or perspectives, provided
the basis for the division of the papers
into four volumes, each volume contain-
ing a set of related session topics so as to
provide easy access to a unified technol-
ogy area.
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Volume II Papers
Volume II, summarized here, was de-
voted to ESPs, the major thread of the
symposium. One section of Volume II
consists of papers dealing with the funda-
mentals or theory of ESPs. Several papers
were devoted to mathematical modeling;
some of the modeling was devoted to
ionic conduction of flyash layers, back
corona, total system modeling, and rap-
ping reentrainment and opacity modeling.
Several papers in this section dealt with
measurement and interpretation of var-
ious parametric data. A number of papers
described attempts to measure and for-
mulate reentrainment phenomena. The
general topics of particle transport in the
electrohydrodynamics field, turbulent dif-
fusion, and the application of laser doppler
instrumentation to particle transport
measurements indicate a new depth of
theoretical studies in ESP. In the section
on operation and maintenance, the con-
cept of "intelligent" ESP controls was
introduced; it is certain that this concept
will be developed further in the near
future as it provides use of the micro-
processor in comparing and weighting
several parameters to determine opera-
ting voltages and rapping intervals with a
degree of precision heretofore not pos-
sible.
A special section of Volume II is devoted
to advance design in ESPs. Two-stage
and multi-electrode devices are explored
in depth. Prechargers are treated in
several papers, and one of the papers
deals with temperature-controlled elec-
trodes. Several papers dealt with the
physics of pulse-energization as well as
operating experiences with pulsed power
operation. Afinal small section of Volume
II deals with the use of ESPs in connection
with boilers using unusual fuels and
multiple fuels.
Section A—Fundamentals
Mathematical Modeling of
Ionic Conduct/on in
Flyash Layers
R. Mosley, Southern Research Institute
Electrical conduction *in flyash layers
placed between two metal electrodes is
discussed in terms of ionic migration.
Mathematical models are formulated
based on the solution of the current
transport equation coupled with Poisson's
equation. Thermal diffusion and field
dependent ionic mobilities are considered.
Since the electrodes are assumed to be
blocking in nature, the models account
for both cations and anions. The appro-
priate representations of the mathemat-
ical solution to the coupled transport
equations which apply in the different
regions of the flyash layer are discussed.
The electric field, the potential, and the
charge-density profiles in these different
regions are expressed in terms of hyper-
bolic functions. Airy functions, or alge-
braic functions. To the extent possible,
the models are compared with available
experimental measurements.
Measurements of Electrical
Properties of Flyash Layers
R. B. Mosley,
Southern Research Institute
The results of a series of measurements
of the electrical conduction properties of
flyash are discussed. Current-voltage
curves for flyash layers between two
metal electrodes were measured under a
variety of conditions. Measured electric
potential and resistivity profiles demon-
strate that the electric field and the
charge-carrier densities are non-uniform
within the flyash layer. Activation en-
ergies associated with the electrical
migration of alkali metal ions were meas-
ured. The net charge accumulated in the
layer as a result of steady*state conduction
of ions was measured. A thermal anneal
experiment designed to measure the
thermal diffusion coefficient of the alkali
metal ions (particularly sodium ions) in
some flyash layers is described. Some
observations of the electrical breakdown
properties of flyash layers also are de-
scribed. The dependence of the break-
down voltage on gas pressure is pre-
sented, and the breakdown process is
discussed.
Laser Doppler Anemometer
Measurements of Particle
Velocity in a Laboratory
Precipitator
P. A. Lawless, Research Triangle Institute
A laboratory ESP was constructed to
permit direct measurement of particle
velocities by means of laser Doppler
anemometry. Components of velocity in
the direction of flow and perpendicular to
the walls were measured for a range of
electrical conditions and particle sizes.
Data are presented and interpreted in
light of current theories for particle
charging and electric field configurations.
The effects of back corona on the partic!
motion are noted.
Progress in Modeling
Back Corona
P. A. Lawless, Research TriangleInstitut
Computer modeling of the electrics
conditions in the wire-duct geometry ha
been pursued, reducing the number of ai
hoc assumptions and including sucl
effects as differing negative and positivi
ion mobilities, ion-ion recombination, ant
avalanche breakdown in the dust layer
The ability of the model to reproduce th<
effects of back corona is presented.
A Computer Model for
ESP Performance
P. A. Lawless. Research Triangle Instituti
A computer model has been developec
for describing ESP performance. It incor
porates theoretical particle charging the-
ory and electric field calculations, anc
empirical estimates of turbulent diffusion
and corona wind effects. Rapping and
sneakage reentrainment losses are ac-
counted for. Using realistic estimates for
unmeasured quantities, it predicts the
performance of full scale ESPs quite well,
if back-corona conditions are avoided.
Methods of handling back corona are
discussed.
Measurement and
Interpretation of Current
Density Distribution and
Charge/Mass Data
M. Durham, Denver Research Institute
Techniques have been developed for
measuring charge-to-mass ratios (Q/M)
and current density distribution (COD) in
ESPs. Q/M is measured by an in-stack
Faraday cage device. Details of the design
of the probe are presented, and sampling
precautions are described. The role of
particle-size distribution in interpreting
Q/M data is also discussed.
Corona current density distribution is
measured by a plate consisting of 96
isolated 2-in. squares. By means of a
picoammeter and a switching box, the
current from a single square or a combi-
nation of squares can be measured. This
device has been used to analyze the
performance of several corona electrodes,
as well as the effect of pulsed excitation.
Experimental data are presented and
interpretation of results is described.
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The Relationship Between Gas
Stream Turbulence and
Collection Efficiency in a
Lab-Scaled Electrostatic
Precipitator
B. E. Pyle, Southern Research Institute
Experimental measurements of the
turbulence transport properties of micron-
sized particles have been carried out in a
laboratory scale ESP of conventional
wire/plate design. The relationships be-
tween ESP collection efficiency, particle
size, level of gas turbulence, and the
electrical operating conditions of the ESP
were investigated. The results of these
measurements are compared with the
theoretical predictions of an ESP mathe-
matical model based on a turbulent mass-
-transport principle. The agreement be-
tween the theoretical predictions and the
experimental results is shown to depend
to a large degree on the boundary condi-
tions assumed at the collector plates. One
result obtained from these investigations
was that the ESP collection efficiencies
were found to be inversely related to the
level of turbulence in the gas stream.
Particle Deposition Profiles and
Reentrainment in a Wire-Plate
Electrostatic Precipitator
E. Arce-Medina,
North Carolina State University at Raleigh
A recently devised radiotracer tech-
nique has been used to measure local
particle deposition profiles and friction
and impaction reentrainment in the EPA
pilot-scale ESP at Research Triangle Park,
NC. Reentrainment rates are shown to
vary with gas velocity and inlet dust
loading, and with the magnitude of the
dust layer thickness on the plate. The
implications of the results on ESP per-
formance and modeling are discussed.
Particle Transport in the
EHD Field
T. Yamamoto, Denver Research Institute
The study of the motion of fine particu-
lates in the EHD (electrohydrodynamic)
field has become important not only in the
design of ESPs, but also in electrostatic
painting. *
Experimental and theoretical studies
have been conducted in the case of two-
dimensional, two-wire, plate configura-
tion ESPs. In the numerical study, the
external force (which consists of the
electrostatic field and space charge den-
sity) was first obtained. The second step
was to solve the Navier-Stokes equations
in the form of vorticity-stream function
equations with appropriate boundary
conditions. The particle trajectories were
computed by integrating the equations of
motion in accordance with the electro-
static and the EHD forces.
The implications of the results to ESP
performance and design are discussed by
introducing the dimensionless EHD
charge number. The calculated numerical
results demonstrate close agreement
with the experiment.
Surface Reentrainment of
Collected Fly Ash in
Electrostatic Precipitators
M. Mitchner, Stanford University
Experiments have been performed in a
horizontal-flow wire-and-plate ESP (plate-
to-plate spacing, 0.25 m) to study the
effects of flow speed (from 3 to 22 ft/sec)
and corona-type on the reentrainment of
collected flyash. The deposited dust layer
is observed to exhibit a well-defined
structure, with regions of highly com-
pacted dust separated by regions of
loosely packed dust. At lower flow speeds,
the loosely packed areas are considerably
deeper than the surrounding regions;
whereas at higher speeds, the reverse is
the case. Surface reentrainment is ob-
served to take place pri marily from regions
corresponding to locations of loosely
packed dust. Two modes of reentrainment
are observed: a continuous erosion pro-
cess which becomes more pronounced at
higher speeds, and a relatively infrequent
large-scale fall-off process which tends
to occur at lower speeds. It is shown that
the dust layer structure results from the
variation of corona current density, J, on
the collector surface: the compacted
regions occur where J is large, and the
loosely packed areas occur where J is
zero (or small, in a time-average sense).
Electromechanics of
Precipitated Ash Layers
G. B. Moslehi. Stanford University
The electrical field distribution in a
current-carrying ash layer, modelled as a
regular array of uniform resistive spheres,
is found analytically as a function of
contact area for the cases of volume
conduction, surface conduction, and the
combined case. The electrical compres-
sive stress is then evaluated, from which
the contact area is found. Hence the field
distribution, average layer resistivity, and
average cohesive stress are determined
self-consistently in terms of fundamental
quantities.
The theory predicts that the layer resis-
tivity decreases with current (or applied
field) in agreement with experiment. It
also shows that there is a strong field
enhancement (above the average value)
around the contact points. This effect
results in a much enhanced cohesive
stress compared with that calculated from
the average field. It also appears to explain
the onset of back discharge as due to the
intermittent micro-arcs between the
spheres. Experiments are in progress to
test various aspects of the theory.
Experimental
Measurements of the Effect of
Turbulent Diffusion on
Precipitator Efficiency
G. L. Leonard. Stanford University
The Deutsch model for predicting par-
ticle collection in an ESP assumes uni-
form particle concentration profiles, and
thus infinite mixing by the turbulent flow.
Recent theories (which treat the mixing
process as finite and thus allow for the
formation of non-uniform particle concen-
tration profiles) predict efficiencies far in
excess of Deutsch predictions. This paper
presents optically determined in situ
particle concentration profiles in a parallel
plate ESP and compares them with the
predictions of these newer theories.
Experiments were designed to permit
separate control and precise measure-
ment of the degree of turbulence and of
particle mobility in the ESP. These meas-
urements, combined with the develop-
ment of a new technique to achieve
accurately controlled charging of a mono-
disperse aerosol, enable a critical assess-
ment of these new theories to be made.
Can Reentrainment be
Explained Using a New
Precipitator Formula?
S. Maartmann. Flakt Industri AB
According to ESP literature, reentrain-
ment is defined as a decrease in migration
velocity calculated according to the
Andersson-Deutsch formula when gas
velocity is increased above a certain limit.
Despite many efforts, there is as yet no
generally accepted formula which covers
the variation of efficiency within the
whole gas velocity range including that in
which reentrainment takes place.
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The paper describes how investigations
of test results, particularly from tests with
pilot ESP plants, lead to the development
of a new expression for efficiency. The
possibility of using the expression as the
base for a new ESP formula is discussed,
as well as the possible general use of the
new efficiency expression.
A Laboratory Furnace for the
Production of Synthetic
Fly ash from Small Coal Samples
K. M. Sullivan. Australian
Coal Industries Research Laboratory
A laboratory furnace was developed to
produce a synthetic flyash from a small
coal sample. Similarity was achieved by
subjecting pulverized coal particles to a
similar thermal and chemical history to
that experienced in a full-scale power
station boiler. The furnace was designed
to accommodate small coal samples,
while operating parameters were defined
to produce similarity between the syn-
thetic flyash and isokinetically sampled
flyash from power stations, in each
instance when using the same coal.
Subsequent confirmative testing has
shown the ability of the furnaces to pro-
duce synthetic flyash that is similar to
power station flyash. The furnaces are
used to investigate proposed coal mining
areas which are intended for future use
for power generation. For this to occur, a
number of bore-core coal samples are
examined and the derived synthetic flyash
is tested electrically, physically, chemi-
cally, and microscopically to rank and
ascertain the variability of flyash from the
proposed mining area. In this way, the
furnaces are used as an early means of
assisting future coal mining/power sta-
tion development.
Computer Simulation of the
Wide Plate Spacing Effect
E. A. Samuel. Buell Envirotech
A numerical simulation code has been
developed to analyze the coupled electro-
aerodynamic phenomena within an ESP,
including the perturbations to the space
charge distribution introduced by the
dust-laden gas flow. The ESP collection
efficiency calculated from the trajectories
of the charged dust particles showed
good agreement with that measured for
oil drops in model ESPs using light scat-
tering techniques. The computer model
had been used to predict the existence of
an optimal wire-to-wire spacing for a
given plate spacing. This study investi-
gated the effect of plate spacing on the
collection efficiency with a view toward
explaining the wide-plate spacing effect
presently claimed industrywide to be
advantageous. The effect on the collection
efficiency of using mixed plate spacings
in a single ESP is discussed.
Simultaneous Measurements of
Aerodynamic Size and Electric
Charge of Aerosol Particles in
Real Time on a Single
Particle Basis
M. K. Mazumder, University of Arkansas
An instrument has been developed for
measuring the aerodynamic relaxation
time (tp) and electrical migration velocity
(Vp) of aerosol particles in real time and on
individual particle basis in the range from
0.3 to 10.0 fjm in diameter. The instru-
ment uses a laser Doppler velocimeter
(LDV) to measure particle motion in an
applied electric field. It operates by elec-
trically charging the particles, subjecting
them to the oscillatory electric field, and
then measuring the amplitude (Vp) and
relative phase lag (0) of the particles with
respect to the electrical field. A micro-
computer-controlled signal processing
and data storage system-measures both
and Vp, computes da and q for individual
particles, and stores the data to generate
the size- and charge-distributions of the
aerosol particles. The distributions can be
compared with the size distribution of
both charged and uncharged particles to
examine the fraction of particles that are
charged, as well as the relative magni-
tudes of the charge.
Application of Laser Doppler
Instrumentation to Particle
Transport Measurements in an
Electrostatic Precipitator
M. K. Mazumder. University of Arkansas
Development of two-laser based instru-
ments—a two-color, frequency-biased
laser Doppler velocimeter (LDV), and a
single-particle aerodynamic relaxation
time (SPART) analyzer—and their applica-
tions to ESPs are discussed. The LDV
provides simultaneous measurements of
two orthogonal velocity components, one
along the flow direction and the other
along the electrical field, of flyash partic-
ipates at any desired point inside the ESP.
The SPART analyzer measures, in real
time, the aerodynamic size distribution of
particulates in the respirable range, 0.1 to
10.0/^m in diameter. Experimental data
on the measurement of free stream an
boundary-layer turbulence, electrical mi
gration velocity, particle flux, and codec
tion efficiency as a function of size am
electrical properties of aerosol particu
lates are presented. The results an
compared with those from the present!'
available mathematical models of th<
ESPs.
The Application of
Measurements of Aerosol
Charge Acquisition by Bipolar
Ions to the Problem of
Back Corona
R. Fjeld. Clemson University
Experiments were conducted to meas-
ure charge acquisition by aerosols ex-
posed simultaneously to positive anc
negative ions of unequal current densi-
ties. Initially uncharged, highly monodis-
perse aerosols in the submicrometei
diameter size range were subjected tc
countercurrents of positive and negative
ions in the presence of low electric fields.
The ratio of positive to negative ion
current density was varied between zero
(the unipolar negative case) and infinity
(the unipolar positive case) to determine
the effect of countercurrent ions of op-
posite polarity on unipolar charge acqui-
sition. Comparisons of experimental data
with theory are presented, and the poten-
tial implications of the measurements
with respect to the effects of back corona
are discussed.
Identification of Back
Discharge Severity
S. Masuda, University of Tokyo
As a parameter to identify qualitatively
the severity of back discharge, the charge
impairment factor is proposed. This factor
can be theoretically calculated from the
values of positive and negative ionic cur-
rent density. To measure these two
quantities, a bipolar current probe was
developed, and its test results are pre-
sented. Finally, a comparison is shown
between the measured particle charge
and its calculated value from the probe
diagnosis data. This reveals that back
discharge occurs in a very irregular distri-
bution, especially when dust resistivity is
not too high (less than 1012 ohm-cm), so
that the measured value of particle charge
provides a much higher value than that
calculated from the probe data obtained
at an active channel of back discharge.
This means that the space factor of back
-------
discharge must also be taken as an
important parameter.
Section B—Operation and
Maintenance
Modeling of Electrostatic
Precipitators with Respect to
Rapping Reentrainment and
Outlet Opacity
M. G. Faulkner.
Southern Research Institute
Revisions of the EPA mathematical
model of ESP, which allow a dynamic
time-dependent representation of rapping
reentrainment and predictions of outlet
opacity, are discussed. The new rapping
reentrainment scheme allows different
rapping schedules for the various inde-
pendent sections, reentrainment due to
rapping of a specified percentage of the
total mass collected in a given increment
of length with a specified particle size
distribution, recharging and recollection
of reentrained particles, a representation
of hopper boil-up, and a time history of
dust layer thickness. The addition of
opacity calculations based on Mie theory
allows the prediction of total and frac-
tional opacities based on predicted outlet
mass loadings and particle size distribu-
tions, a specified complex index of refrac-
tion, particle density, and stack diameter.
Simulations demonstrating the predicted
effects on outlet paniculate emissions
and opacity are presented.
New Precipitator Technology for
Particulate Control
J. R. Zarfoss, Environmental Elements
All ESP designs must accommodate
the requirement of adequately cleaning
the internal components. However, the
collection of highly resistive particulate
matter is considered to be one of the more
demanding applications. The fundamen-
tal capabilities needed to meet this chal-
lenge are the collecting surface response
to rapping and the discharge electrode
characteristics. This paper outlines a
development program on this subject
which spans 6 years, beginning with
laboratory studies and concluding with
the results from working installations.
One of the basic studies quantifies and
compares the rapping response, full size,
of three popular collection surface de-
signs. Levels of surface accelerations,
frequency, and uniformity are described.
Techniques for altering the voltage and
current characteristics of the discharge
electrodes are also presented. All of the
information relates to actual measure-
ments and is useful in all ESP designs.
Low-Frequency Sonic Cleaning
Applied to Electrostatic
Precipitators
J. A. Schwartz,
KVB. Inc., A Research Cottrell Co.
Low-frequency acoustic devices (horns)
have been demonstrated to solve many of
the dust buildup problems associated with
the operation of ESPs. Dust particles
clinging to surfaces are dislodged by
sound-wave vibrational energy. While
horns have been widely used in Europe
since 1969, they were only recently
introduced into the U.S. Horns appear to
be a significant improvement, in terms of
reliability and maintenance costs, over
cleaning methods which vibrate equip-
ment parts.
Most applications to date have been to
the inlet area of the ESP; i.e., inlet ducts,
turning vanes, and distribution plates.
The horns have proven very effective in
these applications, and the paper details
several case histories. The paper also
addresses the potential for cleaning ESP
internals (plates and wires), with a dis-
cussion of limited application results in
this area and plans for future tests.
The Impact of Intelligent
Precipitator Controls
N. 2. Shilling, Buell Envirotech Corp.
This paper describes both operational
hardward and the supporting software
required for the implementation of com-
puter control of an ESP. Specific examples
are drawn from an operating ESP with a
microcomputer control system (Intelligent
Precipitator) which is serving a utility
boiler.
Various features of the logical software
which permit feedback control of the ESP
operation are described. These include
adaptive/recursive control of ESP second-
ary voltage, and plate and wire rapping
frequency and intensity. Criteria are de-
rived for obtaining minimum ESP power
consumption for a given collection effi-
ciency. Instrumentation and potential
regimes of unstable operation with feed-
back control are defined. Finally, logical
control sequences for control of the ESP
in response to various plant operational
and emergency conditions are described.
An Energy Management
System for Electrostatic
Precipitators
R. R. Crynack, Wheelabrator Frye, Inc.
As the emphasis of air pollution control
regulation shifts toward maintaining daily
compliance with stringent standards, the
user must direct more attention to main-
taining optimum performance from this
control equipment. With rising energy
costs and the connected load of an ESP
serving a utility boiler over 1% of the total
generating capacity, the energy cost of
operating an ESP is substantial. To deal
with this situation, an energy manage-
ment system is proposed which can
monitor ESP electrical equipment and
optimize energy consumption while main-
taining continuous compliance. The
energy management system is a micro-
processor-based device which is con-
nected to the power supply controls and
auxiliaries and regulates electrical power
in response to actual on-line ESP oper-
ational needs. A prototype energy man-
agement system has been operating on
an ESP serving a utility boiler for over a
year, with a high degree of success.
Relationship Between
Electrostatic Precipitator
Performance and
Recordkeeping Practices
S. P. Schliesser,
PEDCo Environmental, Inc.
This paper discusses the sensitivity of
the performance and reliability of ESPs to
the quality of their operation and mainte-
nance (O&M). It also discusses the factors
on which O&M quality depends, includ-
ing: (1) instrumentation to monitor key
performance parameters, (2) recordkeep-
ing practices, and (3) an understanding of
the relationship between key parameters
and performance. The discussion pre-
sents evidence of this relationship be-
tween ESP performance and O&M qual-
ity, identifies key performance parameters
and associated instrumentation, and pro-
vides criteria for evaluating O&M and
performance levels. An established rela-
tionship between particulate emissions
and electrical operating conditions can
serve as a measure of the performance of
the O&M team and the ESP itself. These
same principles will prove beneficial
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when applied to other control technol-
ogies.
An Operation and Maintenance
Program for a Phosphate Rock
Electrostatic Precipitator
D. B. Rimberg.
North American PEMCO, Inc.
An extensive investigation was per-
formed on a weighted-wire ESP to im-
prove its performance on opacity. The
application was on a phosphate rock
fertilizer calciner. The program was de-
signed to upgrade ESP performance
without major investment in new pollu-
tion control equipment. Through a sam-
pling and cleaning program, it was
determined that resistivity conditioning
by moisture control was required. The
investigation resulted in achieving compli-
ance with no capital equipment invest-
ment. Sampled grain loading was reduced
by a factor of ten. A regulated preventive
maintenance program was instituted,
thereby maintaining continuous mass and
opacity compliance status. Details of the
management and technical procedures
implemented to effect such a program are
described.
Section C—Advanced Design
Electrostatic Precipitator
Performance with Pulse
Excitation
D. Rugg, Denver Research Institute
A laboratory ESP was energized by
pulsed power supplies. The voltage-
current characteristics were measured
under clean and high-resistivity dust
conditions. The results, which illustrate
the voltage limitations for pulse excita-
tion, are shown. Charge-to-mass ratios,
particle-size distributions, and mass-
efficiency were analyzed to determine the
major factors which account for the
increase in mass efficiency for pulse
excitation compared to efficiencies ob-
tained with dc excitation. The data and
the results of the analysis are presented.
Development of a Charging
Device for High Resistivity
Dust Using Heated and Cooled
Electrodes
G. Rinard. Denver Research Institute
An efficient cooled-pipe charger/col-
lector, capable of controlling back ioniza-
tion and allowing efficient charging of
particles, has been developed. It has also
been shown to be an excellent collector.
Feasibility tests were conducted, utilizing
parallel heated pipes and corona dis-
charge wires placed in a plane normal to
gas flow, to determine if the dust resistiv-
ity, and thus back ionization, could be
controlled by heating a small collector
surface area. The success of these tests
led to the development of a more practical
design utilizing cooling on the collector
pipes. Cooled pipes are more practical for
many applications since they do not
require the input of high quality heat. The
results of the testing of the heated and
cooled electrodes that led to the present
design are given.
The Evaluation of Novel
Electrostatic Precipitator
Systems Using a Transportable
Prototype
G. Rinard, Denver Research Institute
A program is presently being conducted
to advance the development of econom-
ically feasible, two-stage ESPs for collec-
tion of high resistivity dust. The objectives
of this program are to: (1) evaluate the
SoRI precharger on various sources of
high resistivity dust, (2) optimize the
downstream collector for use with a
precharger, and (3) evaluate alternative
ESP designs. These goals will be achieved
through the design, fabrication, and
testing of a transportable ESP (TEP) on
problem sources of high resistivity dust.
In order to determine alternative ESP
designs for testing in the TEP, a program
to investigate novel precharger and col-
lector technology was undertaken. The
design goals for the TEP and configuration
for the first series of testing are presented.
Results of the testi ng for the downstrea m
collector are also presented.
Analysis of the Electrical and
Charging Characteristics of a
Three Electrode Precharger
K. J. McLean, University of Wollongong
The SoRI/EPA Three Electrode Pre-
charger is analyzed by examining its
electrical characteristics and a limited set
of charge/mass measurements. It is
concluded that, for the test conditions
operating at the time, the biasing of the
grid reduces the back corona component
of the total current flowing to the dis-
charge electrodes for a restricted range of
operating conditions.
Particle Charging in an
Electrostatic Precipitator by
Pulse and DC Voltages
L E. Sparks. USEPA
Measurements of particle charge as
function of particle radius for dc and pul
energization were made at the exit o<
pilot plant ESP. The experimental app
ratus utilizes a Milliken cell which allov
measurement at three values of di
electrical resistivity—low (approximate
1010 ohm cm), moderate (approximate
1011 ohm cm), and high (greater than 1C
ohm cm). All experiments were conduct
using a resuspended flyash. To compa
the charging characteristics of dc ai
pulse supplies, the average current de
sities for both cases were kept identic!
The results are compared with theory ai
previous experimental data.
Particle Collection in a
Two-Stage Electrostatic
Precipitator with Various
Collector Stages
L E. Sparks, USEPA
Data for pilot plant studies of partic
collection in a two-stage ESP are pn
sented. The ESP consisted of the EPA
Southern Research Institute prechargi
followed by various downstream collect'
configurations. The configuration of th
collector was changed by changing th
discharge electrode geometry and methc
of energization. Discharge geometrii
studied included wires, grid, and flat pla
discharge electrodes. Pulse and dc ene
gization was also studied. The expei
ments show that significant improvi
ments in ESP performance are possible
a properly designed two-stage system.
High Intensity Ionizer
Development
M. H. Anderson,
Southern Research Institute
Results from parallel laboratory ar
field studies to characterize the perforn
ance of a "double-bellmouth" higl
intensity ionizer (HII) are presented. The;
studies include measurements after th
HII of particle charge as a function
particle diameter, charge-to-mass rati
the gas velocity distribution downstrea
from the HII, electrical effects in transitic
cavities containing highly charged pan
cles, and effects on particulate matt
collection for a 1 MW HII/ESP combim
tion. The studies show that the HII charge
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fine particles in accordance with field
charging theory; the gas velocity distribu-
tion after the HII can be adjusted by
varying the anode purge air conditions;
space charge precipitation effects can be
significant in transition cavities following
the HII; and the HII improves performance
of an ESP for small-scale HII/ESP com-
binations, depending on ESP operating
conditions.
Demonstration of Air Pollution
Systems High Intensity
Ionizer/Electrostatic
Precipitator on an Oil-Fired
Boiler
G. Raemhild and A. Prem.
Air Pollution Systems. Inc.
A study was performed to evaluate the
applicability of Air Pollution Systems High
Intensity Ionizer (HII) to the ESP of particu-
late emissions from a high-sulfur oil-fired
boiler. The study was conducted on a 350
MW boiler at Long Island Lighting
Company's Northport Station, Unit 1.
Testing was done at 360 and 125 MW
andincludedtotal mass samples, cascade
impactor tests, and ultra-fine particle
analysis. The electrical and physical
parameters for the three field ESP in the
mobile/HII/ESPpilot plant were adjusted
to simulate the south-side ESP on Unit 1
as closely as possible. Simultaneous
inlet/outlet particulate sampling was
performed using the same methods as on
the main ESP. Performance tests were
conducted with the HII both "on" and
"off" at 8400, 7000, and 3500 acfro. The
results showed a significant decrease in
particle penetration when the HII was
energized.
Primary and Secondary
lonization in an Electron Beam
Precipitator System
W. C. Finney, Florida State University
Recent investigation into the possibility
of using energetic electron beams for
generating high ion current densities for
particle charging in ESPs has shown
exceptional promise. Copius ion current
densities, at least 500 times that in a
conventional corona-driven ESP, have
been reported earlier. Experimental re-
sults, however, have indicated a second-
ary charging phenomenon in a parallel
plate system which affects the charge
density stability.
The results of a study of the onset and
extent of secondary ionization are pre-
sented here. Current vs. voltage experi-
ments were performed using the parallel
plate system used in previous ion current
density investigations. The electron beam
f I ux delivered to the system was restricted
to determine the effect of primary ioniza-
tion alone; then the transition to second-
ary ionization was explored.
The plate system's variable parameters
were analyzed to quantify the conditions
for initiation of secondary ionization. This
secondary ionization is thought to be the
result of the combined effects of space
charge and plate voltage in the ESP
section.
Influence on Particle
Charging of Electrical
Parameters at DC and Pulse
Voltages
H. J. Joergensen,
Technical University of Denmark
Enhanced particle charging is consid-
ered to be one of the reasons for the
improved performance of pulse-energized
ESPs. For a pulsed condition, the charging
levels obtained are influenced by several
electrical parameters, such as underlying
dc voltage, pulse level, and pulse repeti-
tion frequency. The reported investigation
examines these influencing factors. The
measurements are performed by a Fara-
day cage method on a conducting ball of
3-mm diameter, charged within the inter-
electrode space of two circular cylindrical
electrodes. The investigation includes dc,
as well as pulse energization. The results
of the dc situation are compared with the
saturation charges expected from the
field charging theory. In the case of pulse
energization, a simple model for the field
charging under pulsed conditions is sug-
gested and is used for a similar com-
parison.
Boxer-Charger Mark III and Its
Application in ESPs
S. Masuda. University of Tokyo
The latest model of Boxer-Charger
(denoted Mark III) uses double-helix elec-
trode units and very-fast-rising pulse
voltages with 40-300 ns duration time for
their excitation. The helical discharge
wires of a double-helix unit are insulated
not by ordinary insulators but by coils
which effectively reflect such a fast-
rising, short duration pulse voltage. This
is called "inductance-insulation." Its
charging performance and effect on the
collection performance of an ESP are
presented. The collection performance at
dust resistivity of 10"-1012 ohm-cm can
be greatly increased to a level equal to
that obtainable under no back-discharge
condition, when the precharging is made
in front of each collection field repeatedly
and the collection field energized with dc-
plus-pulse voltage.
The Performance of an
Experimental Precipitator with
an All-Plate Zone
J. Dalmon,
Central Electricity Research Laboratories
An All-Plate ESP collector zone has
been developed by the C.E.G.B. and tested
in a small research rig at atmospheric
temperatures. To provide data more
closely related to power station ESP
conditions, a program of tests has been
carried out with the permission of the
EPA on their experimental ESP facility at
Research Triangle Park (NC). This consists
of a four-zone, single-lane unit; for the
tests, the conventional discharge wires in
one zone were replaced by a single
charged plate. In all zones, the spacing
between the earthed plates was 200 mm.
The gas velocity was kept constant at 1.6
m/s and the gas temperature ranged
from 17°C to 150°C. The test dust was
flyash having a mass median diameter of
7.2 fjm and a resistivity of 2 X 10'2 ohm
cm.
The performance was evaluated as an
"Effective Migration Velocity" (EMV) en-
hancement factor, with plate-plate elec-
trodes/EMV with wire-plate electrodes.
The factor averaged 3.1 for Zone 3 ESP.
The results indicate a clear advantage
for an ESP incorporating an all-plate zone.
The Physics of Pulse
Energization of Electrostatic
Precipitators
L Menegozzi, Research-Cottrell
Analytical/numerical computations for
pulser operation are given for a simple
geometry. The model describes and calcu-
lates the negative ion density produced by
corona discharge due to a dc voltage with
superimposed pulses. The space charge
is then used to estimate wire-quenching
effects, and compute the charging and
collecting fields. The computer calcula-
tions also provide the amplitude and
duration of the resultant current pulses.
This information is needed for analytical
treatment of back-corona suppression
with pulse energization. Finally, the ESP
enhancement factors for both large and
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small particles are obtained. The results
indicate that pulser application is a con-
ceptually sound technology that would
improve ESP performance in power-
limited situations such as those arising
with high resistivity dusts. The results
also give a deeper insight into the dynam-
ics of pulse energization.
Advanced Electrode Design for
Electrostatic Precipitators
S. Bernstein, Flow Research Co.
The subject of this paper is a wavy-
electrode ESP which employs a new
collector electrode. The wavy-electrode
ESP incorporates a contoured collector
electrode geometry which produces near-
ly uniform electric field along the elec-
trode. This feature allows operation with
higher average electric field strengths
near the electrode than for conventional
designs. The wavy electrodes provide
separated flow zones within their "val-
leys" which fluid-dynamically shields
particles from the main stream. The
design also provides mechanical rigidity
to vertical bending without the sharp
flanges normal to the flow commonly
found in conventional ESPs. These fea-
tures permit increased performance for
all particle sizes, but especially help in the
ESP of fine particles, which are normally
the most difficult to collect. The paper
describes the features of this advanced
electrode design and an analysis of its
significantly improved performance over
conventional systems.
Section D—Industrial
Applications
Problems in Applying an
Electrostatic Precipitator to a
Salvage Fuel-Fired Boiler
C. R. Thompson.
Naval Facilities Engineering Command
This paper addresses the problems
encountered in applying ESP technology
to a trash-burning, salvage, fuel-fired
boiler. The ESPs were designed and
constructed between 1972 and 1976.
Stack emission tests after construction
was completed showed that the emis-
sions were 0.86 gr/dscf at 12% C02. The
Virginia Air Emission Standard was 0.14
gr/dscf at 12% CO2. Outlined are the
steps undertaken to achieve final compli-
ance. Each improvement to the ESPs
(such as correction of inlet gas flow
patterns, plate and wire alignment, wire
improvements, increasing the number of
collecting fields, and increasing power to
the fields) is described and discussed.
Also, improvements to the salvage fuel-
fired boiler operating mode (such as tra
feed, overfired and underfired air, a
excess air) are outlined. Finally, t
designed and actual operating parametc
for the ESP are presented and compart
The Application of Electrostat
Precipitators to Boilers Firing
Multiple Fuels
R. L. Bump, Research-Cottrell
Recent years have seen a swing
boiler designs which afford versatility
the fuel. This is, of course, a result of t!
economics and availability of conventior
fuels. Many process industries are usi
their own waste products as a princip
fuel source. The varying conditions ii
posed on the air pollution control devi
as a result of this practice are discuss
in this paper. Case histories are pr
sented, as well as a discussion of some
the operational considerations whi
must be recognized. Since the pulp a
paper industry has been a forerunner
this activity, the majority of data present
derive from this application.
F. P. Venditti. J. A. Armstrong, and M. Durham are with the Denver Research
Institute, Denver, CO 80208.
Dale L. Harmon is the EPA Project Officer (see below).
The complete report, entitled "Third Symposium on the Transfer and Utilization of
Particulate Control Technology: Volume II. Electrostatic Precipitators," (Order
No. PB83-149 591; Cost: $34.50. subject to change) will be a vailable 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:
Industrial Environmental 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
Postage and
Fees Paid
Environmental
Protection
Agency
EPA 335
Official Business
Penalty for Private Use $300
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