EPA-600/2-77-055
February 1977
Environmental Protection Technology Series
ELECTRIC CURTAIN DEVICE FOR CONTROL AND
REMOVAL OF FINE PARTICLES
Industrial Environmental Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into five series. These five broad
categories were established to facilitate further development and application of
environmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The five series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
This report has been assigned to the ENVIRONMENTAL PROTECTION
TECHNOLOGY series. This series describes research performed to develop and
demonstrate instrumentation, equipment, and methodology to repair or prevent
environmental degradation from point and non-point sources of.pollution. This
work provides the new or improved technology required for the control and
treatment of pollution sources to meet environmental quality standards.
EPA REVIEW NOTICE
This report has been reviewed by the U.S. Environmental
Protection Agency, and approved for publication. Approval
does not signify that the contents necessarily reflect the
views and policy of the Agency, nor does mention of trade
names or commercial products constitute endorsement or
recommendation for use.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/2-77-055
February 1977
ELECTRIC CURTAIN DEVICE
FOR CONTROL AND REMOVAL
OF FINE PARTICLES
by
A. Yen, R.J. Turnbull, andC.D. Hendricks
University of Illinois
Charged Particle Research Laboratory
Urbana, Illinois 61801
Grant No. R803047
ROAPNo. 21ADL-029
Program Element No. 1AB012
EPA Project Officer: D. C. Drehmel
Industrial Environmental Research Laboratory
Office of Energy, Minerals, and Industry
Research Triangle Park, NC 27711
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Research and Development
Washington, DC 20460
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Ill
TABLE OF CONTENTS
Page
I. INTRODUCTION 1
E. THEORY FOR PLANAR CURTAIN REPULSION FORCE ON
A CHARGED PARTICLE 2
in. THE CHARGER FOR SOLID PARTICLES 7
IV. EXPERIMENTAL PROCEDURE AND OBSERVATIONS . . 9
A. Inclined Plane Electric Curtain 9
B. Horizontal Plane Electric Curtain 11
C. Vertical Plane Electric Curtain 13
V. CHARGED WATER PARTICLES AS INTERMEDIATE
COLLECTOR FOR FINE PARTICULATE MATERIALS . . 22
VI. CONCLUSION 25
VII. REFERENCES 26
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FIGURES
Figure Page
1. Physical dimensions and the potential of a planar electro-
static curtain 3
2. Planar electrostatic curtain positioned at an angle of 45°
with respect to vertical axis 10
3. Horizontal planar electrostatic curtain . 1Z
4. Lycopodium particles suspended by a horizontal planar
curtain excited by a 6-phase AC voltage. (Film No. 1). . 14
5. A system with a vertical planar electrostatic curtain. For
the experiment of trapping particles from an air flow. . . 16
6. Flyash particles brought toward a vertical planar curtain
were confined on a plane in front of the curtain. Planar
electric curtain was excited by a 6-phase AC voltage.
(Film No. 3) 18
7. Double curtain system used to trap particles from air flow.
Rods with dark and light ends are in opposite polarities. . 20
8. Setup of the experiment on water particles 23
TABLE
Table Page
1 Density of test substances 15
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1. INTRODUCTION
The electric curtain can be considered as a device similar in con-
cept to the quadrupole mass spectrometer developed by Paul et al. [1],
Masuda has discussed the action between charged particles and an elec-
tric curtain [2], A planar curtain consists of a set of equally spaced
parallel electrodes which are excited by either single phase or six phase
ac voltages. The former is designated as the "standing-wave electric
curtain" ; the latter, the "traveling-wave electric curtain. "
The following experiments were carried out. A planar curtain
oriented at 45° with respect to the vertical axis was operated at its op-
timum single-phase ac voltage against the free-fall of charged particles,
such as corona charged lycopodium, silica and feldspar. A horizontal
planar curtain was also demonstrated to hold charged particles against
gravity when it was energized by a. six-phase ac potential. Finally, a
vertical planar curtain and corona charging section were connected and
sealed together by a wind duct. An air flow mixed with test charged
particles was introduced into the system near the corona section end and
the motion of the charged particles was examined just in front of the cur-
tain surface.
t
In all of these three experiments, the curtains were shown to be ef-
fective to a certain degree. While three variables in the first two experi-
ments, namely potential on corona wires, particle size, and potential on
the electric curtain, needed to be adjusted, in the third experiment the
* ' "
air flow, in addition, had to be controlled to a proper value.
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2.
2. THEORY FOR PLANAR CURTAIN REPULSION
FORCE ON A CHARGED PARTICLE
Some (4.8 mm) diameter (d) brass rods were placed parallel to each
other in the same plane so that the interelectrode spacing was 7. 5 mm
between nearest rod axes.
This set of brass electrodes was charged by an ac voltage of an an-
gular frequency co and peak voltage V_. This voltage generates a repulsion
force between the particles and these rods. It is the force which is res-
ponsible for suspending the incoming charged particles against other ex-
ternal forces.
- By following the method used by Masuda et al. [2], [7] which is the
linear approximation of equations of motion using two terms in the poten-
tial expansion, an expression for the repulsion force was derived. The
periodic potential shown in Figure 1 can be represented by a Fourier
expansion, i. e. , at t = 0.
00 -2rmr
V(x, z) = X(x) Z(z) = ^=1 Vm-e X Z sin(-^p x) (m = odd integers). (1)
-2ir z -6ir
V(x, z) = V e X sin(-|2_ x) + V e X Z Sin(-i2__ x)
x j x
V(x, z) = V. e T" sin(Jl x) + V, e a Z sin(JZ_ x). (2)
i a 3 a
The coefficients V and V are determined by the boundary conditions
V( 4 - r, 0) = Vn and V(4, r) = VA,
& u ^ o
/ -3TT3
' 3-rrr
I , JTrr
| cos(-^~ ) - e
V, = -
a - A
= A
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3.
-v.
a/2
-v,
-v,
o X
a
a/2 = 2r a = 4r
X= 2a
Figure 1. Physical dimensions and the potential of a planar electrostatic
curtain.
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4.
-Zirr -irr
a
-2irr
,3irr - , trr
cos( - ) - e a cos( - )
a a
Therefore,
-TTZ -3ir z
a I T3 \T g T-ri / . v\ o
E
x
V(x, z,t) = A V sin( x) . e a + B V sin( - x) e I cos cot
U cL U 9- I
(5)
V(x. z.t)
-TTZ -3lTZ
- TT IT a 3TT , 3lT a .
A V" cos( x) e - B V_. cos( x) e / cos cot
a. 0 a ' a 0 a /
(6)
E
z 5 z
-7TZ_ -3lT
3. 37T 3TT ^"
A V. sin( x) e + B V. sin( x) e I cos cot
a 0 a a 0 a /
(7)
If we represent the coordinates of the particle by
x(t) = XQ + Re[x
z(t) = ZQ + Re[z
where X , Z denote the center of oscillation and &ť z represent the os
cillation components, the equations of motion are:
d x , dx
m__=qEx - 6uua
at
d z dz
m _ = q s-i ~~ DTTiJ a .
dt2 z dt (9)
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5.
where \i is the viscosity of the medium, a is the radius of the charged
particle, and the q is the charge on the particle, normally x Ť X
z < < ZQ, so
, ZQ)
(10)
(8), (9), and (10) combine to give
' V
-mw + jco6irya
XJe
3. U
24 ,2222
m oo + Soir U a w
2 =
1E,
2 0. 2 2 2 2
-rnoj + 36iT y a oj
-IT
-3TT
(U)
-3TT
24 ,, 2222
m co + 3oiT y a to
,
(mco + j
(12)
The time-averaged repulsion force (in z-direction) is then:
3E 3E
Z
0' 0
+ (z - Z.)
'
.
0 9 z
., z,
mq (f} V0
= - 7^
rz _. 2 4
, _
_. _, 2 2 2.
2(m w + 36ir y a )
A2 e
12AB cos( - XJ e
a 0
27B2 e
(13)
-------
A and B as defined in Equations (3) and (4) are functions of the
ratio (r/a), thus, the repulsion force on a charged particle is not only
a function of peak voltage on the curtain electrodes, the frequency of
the voltage, and the charge on the particle but also a function of the
geometrical arrangement of the curtain electrodes.
With the arrangement of the brass rods in our curtain, (r/a) = ,
then A2 = 4. 25, 12AB = 1. 51 and 27B2 = 0. 1.
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7.
3. THE CHARGER FOR SOLID PARTICLES
The unipolar corona discharge technique, which has been historically
proven to be the best method of charging dust particles [5], [6], [3], is
the method used in this work. A rectangular corona (negative) section
was used to charge various particles during our experiment. It contains
ten . 28 mm piano wires. The optimum wire-to-wire space that will
produce maximum ion current was estimated to be 38 mm. The remain-
ing dimensions of the corona section are length 15. 2 cm, width 5. 1 cm,
and height 42 cm.
If a semiempirically determined value of the critical field is use'd [3],
one could find that a corona onset voltate is about 3. 3 kV for this corona
box.
An expression formulated by Cooperman [4] can be used to estimate,
to a first approximation, the corona current in the duct with the wire(s)
charged up to V = 10 kV.
i = v(v - vft) -= ( current
0' 2 ...,/. cm
b log(4b/-rra)
where k is the ion mobility, b is the distance between wire and plate,
and a is the wire radius. The total corona current of our duct-type
-4
charger is then 4. 18 x 10 A provided the 152. 4 cm corona wire has
a clean and smooth surface. It is known that the suspended and depo-
sited particles inside the duct may influence the corona. That influence
is directly related to the amount and property of the particles.
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Ideally, the maximum available corona current for particle charging
in the duct-type corona charger of the present configurations is
-4
4. 18 x 10 A. The charging mechanisms are (a) fie Id-charging process
and (b) diffusion-charging process. When particles with diameters larger
than 1 ym pass through the discharge space inside the corona charger,
mechanism (a) dominates the particle charging. The particles distort
the electric field lines such that gas ions traveling along them are
intercepted by the particles and the attractive image force will make
the gas ions adhere to the particles. For the submicron particles
(d < 0. 2 ym) mechanism (b) is dominant; particles get charged by col-
liding with ions governed by random thermal motion.
Both (a) and (b) are equally important in charging particles of
diameter in the range of 0. 2 - 1.0 ym.
The particles used in this work were sieved down to No. 400 mesh
(^ 37 y m). Because the particle size and density distributions are
unknown, further difficulties will be introduced later.
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9.
4. EXPERIMENTAL PROCEDURE AND OBSERVATIONS
A. Inclined Plane Electric Curtain
All experiments were conducted at room temperature except for
localized heating due to the"ion current in the corona wires. The setup
for the first experiment is illustrated in Figure 2. A duct-type corona
charger is in the vertical position, and a planar curtain, which is
positioned at 45° with respect to the vertical axis, is placed just under
the corona box. The test particles, after being sieved through a No. 400
mesh ( < 37 ym), were fed to the corona charger. The particles were
fairly well dispersed after sieving; some of the particles were collected
on the plate electrodes while some went through the entire "discharge
space and fell toward the curtain surface. As the particle-to-curtain-
surface distance decreased, the repulsion force on the particle increased,
and the effect of the resultant force (gravitational force and the repulsion
force) became apparent. Some of the particles were seen to move along
the 45° inclined curtain face without touching (see Figure 2), when the
electric field strength of the corona was 4 to 5 kV/cm and the curtain was
excited just below the breakdown strength. Samples that were tested are
(1) lycopodium (2) silica (3) feldspar and (4) flyash (from Detroit Edison).
A 30 kV, 5 mA dc power supply was used to energize the corona wires
(negative). When the maximum voltage, which corresponds to a field
strength of 11 kV/cm, was applied to the corona wires, the minute parti-
cle charge produced from the friction between the nylon mesh and the brush
made it impossible for these particles to pass across even the very first
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10.
CORONA BOX
CORONA WIRES
Figure 2. Planar electrostatic curtain positioned at an angle of
45° with respect to vertical axis.
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11.
corona wire. Through trial and error, the electric field strength used
in this work was then chosen to be 4 - 5 kV/cm. The test sample
particles passed the corona charger without being precipitated out on
the plate and were observed to fall toward the curtain surface. Some of
the particles fell through the curtain as if they were neutral, and some
of the particles fell on the rod electrodes. To reduce the effect from
the electric field between the corona wire closest to the curtain elec-
trode, the distance between these two highly charged conductors was
adjusted to six inches. The effect from the air motion was also elimi-
nated by enclosing the curtain-particle interaction space inside the
transparent Plexiglas plates. The accumulation of sample particles
near the lower end of the curtain was apparent (near point B in Figure 2).
B. Horizontal Plane Electric Curtain
A horizontal planar curtain was used to suspend charged particles
against gravity. Its electrodes were excited by a six-phase ac voltage
power supply. The voltage on the curtain was just below the break-
down strength in air. As shown in Figure 3, a duct-type corona charger
was also placed in the vertical position and was held above the curtain
surface. At the same electric field strength (as described above) in
8 9
the corona discharge space, the ion density should be around 10 - 10
ions per cubic centimeter. The corona box acted like an electrostatic
precipitator and collected most particles on its grounded aluminum
plates. The charging mechanism depended on the particle size of the
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12.
CORONA BOX
CORONA WIRES
e-o o o
Figure 3. Horizontal planar electrostatic curtain.
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13.
test samples (see Section 2). All four test samples were used. Charged
sample particles, which escaped the corona charger, were observed to
experience the electric force from the curtain. This force was of a
traveling wave in nature. This force not only supported the particles'
weight but also transported them in a preselected direction. Lycopodium
particles' motion, under the influence of an electric curtain, excited by
six phase ac voltage, is shown in Figure 4. While the total charge on a
particle, going through either of the two charging mechanisms described,
is related to the particle size [3], the gravitational force is directly pro-
portional to its density. The test samples with larger densities would
certainly be more difficult to suspend by the electric curtain. The den-
sities of the test samples are given in Table 1. Up to this point, the
electric curtain has been used to act on the charged particles against
gravity.
C. Vertical Plane Electric Curtain
It is of interest of conduct an experiment demonstrating the interaction
between the repulsion force from a curtain and the charged particles brought
toward it by an air drag. Figure 5 shows the system built for the experi-
ment of trapping particles from an air flow. This system was made as air-
tight as possible. The test sample particles were fed into the opening end
of the corona box by an atomizer at one end of the system, and were dragged
through the system by an air flow produced by a vacuum cleaner and con-
trolled by a butterfly valve positioned at another end of the system. After
-------
/
Figure 4. Lycopodium particles suspended by a
6-phase AC voltage. (Film No.
horizontal planar curtain excited by a
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15.
TABLE 1
Density of Test Substances
Sample density (g/cm )
-4
Lycopodium 1.1 x 10
Water 1
Silicon Monoxide 2. 1
Silicon Dioxide 2.2-2.1
Flyash 2.2-2.6
Feldspar 2. 7
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CORONA BOX
BAFFLES
o
o
o
o
EXHAUST
TO
VACUUM
CLEANER
INLET
VERTICAL
PLANAR
CURTAIN
Figure 5. A system with a vertical planar electrostatic curtain. For the experiment of
trapping particles from an air flow.
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17.
being charged by passing through the .corona box, the particles were
allowed to see only the uniform portion of the curtain surface which
was parallel to the duct cross section connecting the corona box and
the electric curtain. The same test materials were used in this
system. The flyash was found to be the most difficult one to stop with
the vertical electric curtain. The motion of the flyash particles con-
fined to a plane parallel to the surface of a vertical curtain has been
recorded, and is shown in Figure 6. These particles disappeared
from their confined plane at the instant the curtain voltage was turned
off. The highest air flow speed against which the flyash particles could
be stopped at the curtain surface was found to be 1. 08 cm/sec. Higher
air flow speeds would bring flyash particles onto the curtain electrodes.
-------
Figure 6. Flyash particles brought toward a vertical planar curtain were confined on a plane
in front of the curtain. Planar electric curtain was excited by a 6-phase AC
voltage. (Film No. 3)
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19.
The inability of the planar curtain to stop more sample particles
could be attributed to various effects. First, when the samples were
fed to the system, the particles were not very well dispersed; most of
them lumped together and formed particle clouds. The charging ef-
ficiency of the corona could be much lower than the case in which all
the particles were completely dispersed. In the case of flyash, the
results were expected to be affected by the fact, reported by Bickelhaupt
[8], that the volume conduction process is controlled by an ionic mecha-
r
nism in which lithium and sodium are the principal charge carriers.
Second, the air flow pattern inside the system could be very complicated;
the turbulence seemed to be unavoidable, even when baffles were used to
regulate the air flow inside a section of the duct connecting the corona
charger and the electric curtain. Third, the curtain field was limited
by the breakdown value of air.
One way to avoid the third disadvantage was to construct a double
curtain; its relative arrangement is shown in Figure 7. The electric
field in the space enclosed by the two parallel curtains was stronger due
to the superposition of the fields of the individual curtains. Some interest-
ing features have been observed with flyash. Particles were seen in the
region having stronger electric fields; they stayed in that region for a few
seconds. When the air flow was turned off, with the voltages on the electric
curtains left on, thin columns formed by the trapped flyash particles were
seen inside the enclosed space, the columns were vertical and parallel to
to the curtain rods, and each column was located at the center of the four
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CORONA
SECTION
ATOMIZER
DOUBLE
CURTAIN
OUTLET
DUCT
EXHAUST
(TO
VACUUM
CLEANER)
Figure 7. Double curtain system used to trap particles from air flow. Rods with dark and
light ends are in opposite polarities.
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21.
nearest neighboring rods. However, the performance of the double
curtain in stopping particles was very little better than the single cur-
tain.
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22.
5. CHARGED WATER PARTICLES AS INTERMEDIATE COLLECTOR
FOR FINE PARTICULATE MATERIALS
j.
Water drops can be made highly charged particles. It would be
useful if one could use the highly charged water droplets as intermediate
collectors for oppositely charged solid particles. If the charge-to-mass
ratio of the final compound becomes larger than that of the particle,
then the planar electric curtain together with the charged water droplets
can be considered a better dust collector. Miller [9] has developed an
electric sprayer which is used in painting and coating. This same
mechanism was used to generate a water film. The razor-blade sharp
edges formed a thin slot from which the water was compressed out. These
sharp edges also served as charging electrodes. A sprayer with a slot
width of 0. 001 in. and length of 2 in. was used, but the result was not
promising. The failure was mainly due to machining difficulties in making
the slot width smaller than 0. 001 in. Another technique has been developed
for generating charged water droplets. A glass nozzle with an orifice
diameter of 0. 0009 in. was made. It was connected to a system shown in
Figure 8. Compressed air was applied to the inlet of a steel dispensing
vessel containing distilled water; the outlet of the vessel is connected
through a millipore filter housing to the glass nozzle which has a very
small orifice. The glass nozzel neck was glued with epoxy onto a "PZT
Bimorph" crystal. This crystal was excited by a frequency generator and
was used as an electromechanical transducer, which broke a continous
water jet into a train of water droplets. After passing through a charging
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D.C. VOLTAGE
POWER SUPPLY
COMPRESSED
AIR
INLET
MILLIPORE
FILTER
HOUSING
GLASS
NOZZLE
PRESSURE
GAUGE
CRYSTAL
-------
24.
electrode (a cylinder in this case), the droplets reached a highly
charged state such that the electrical pressure overcame the sur-
face tension and split into smaller particles [10]. The size of the
final water particles was measured and found to be around 30 y m
(diameter) under the following conditions. The pressure inside
the dispersion vessel was 55 pounds per square inch. The frequency
applied to the transducer was 25 KHz and the voltage on the charging
cylinder was 730 V dc. A layer of water particles was suspended in
front of the surface of the planar electric curtain, which was positioned
either horizontally or vertically. The performance of this curtain was
very severely limited by the fact that the water drops caused electrical
breakdown between the rods.
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25.
6. CONCLUSION
All of the different materials mentioned above have been stopped
or transported by the planar curtain to a certain degree with external
forces due to either gravity or air drag. The air flow was restricted
to about 1-2 crn/sec for particle confinement. Part of the particles
passed through the curtain without being affected. The optimum con-
dition for the planar curtain was achieved by improving the insulation
between curtain electrodes. Breakdown occured first between the rods
at the upper limit of the field strength in air. Because of the wide range
of flyash particle sizes and the variation in the composition and specific
gravity of the flyash, the experimental observation on the interaction
between the planar electric curtain and the charged flyash cannot be used
to clarify the results in a general sense. The water drop experiment was
severly limited by electrical breakdown and unless some configuration
could be designed to overcome this, it does not appear to be a useful
technique for droplet collection. A similar experiment, which has been
conducted by Pilat [11], has proved that the collection of fine particles by
water droplets in a spray scrubber could be substantially increased by
electrostatically charging the droplets and particles to opposite polarities.
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26.
REFERENCES
[1] W. Paul and H. Steinevedel, "Ein neues massenspektrometer ohne
magnetfeld, " Zeitschrift fur Naturforschung, vol. 8a, pp. 448-450,
1953.
[2] S. Masuda, K, Fujibayashi, K. Ishida and H. Inaba, "Confinement
and transportation of charged aerosol clouds via electric curtain, "
Electrical Engineering in Japan, vol. 92, pp. 43-52, 1972.
[3] H. J. White, Industrial Electrostatic Precipitation. Addison-Wesley
Publishing Co. , Inc. , Reading, Mass. , 1963.
[4] P. Cooperman, "A theory for space charge limited current with
application to electrical precipitation, " Trans. AIEE, vol. 79,
p. 49, I960.
[5] O. J. Lodge, "The electrical collection of dust and smoke with
special reference to the collection of metallic fume, and to a
possible purification of the atmosphere, " J. Soc. Chem. Ind. ,
(London, England) vol. V, pp. 572-576, 1886.
[6] F. G. Cottrell, "The electrical precipitation of suspended particles, "
J. Ind. Eng. Chem. , vol. 3, p. 542, 1911.
[7] S. Masuda and Y. Matsumoto, "Theoretical characteristics of
standing wave electric curtain, " Electrical Engineering in Japan,
vol. 93, pp. 71-77, 1973.
[8] R. E. Bickelhaupt, Proceedings Symposium on Control of Fine
Particulate Emissions from Industrial Sources, San Franciso,
California, January 15-18, 1975.
[9] E. P. Miller, "Electrostatic coating, " Electrostatics and Its
Application, A. D. Morre, Ed. New York: Wiley-Interscience
Publication, John Wiley & Sons, 1973.
[10] M. A. Abbas and J. Latham, "The instability of evaporating charged
drops, " J. Fluid Mech. , vol. 30, p. 663, 1967.
[11] M. J. Pilat, "Collection of aerosol particles by electrostatic
droplet spray scrubbers, " Proceedings Symposium on Electro-
static Precipitators For The Control of Fine Particles,
September 1974.
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27.
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing}
. REPORT NO.
EPA-6QO/2-77-055
2.
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
Electric Curtain Device for Control and Removal
of Fine Particles
5. REPORT DATE
February 1977
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
A. Yen, R.J. Turnbull, andC.D. Hendricks
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
University of Illinois
Charged Particle Research Laboratory
Urbana, Illinois 61801
10. PROGRAM ELEMENT NO.
1AB012; ROAP 21ADL-029
11. CONTRACT/GRANT NO.
R803047
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Industrial Environmental Research Laboratory
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PE
Final; 5/75-10/76
RIOD COVERED
14. SPONSORING AGENCY CODE
EPA/600/13
is.SUPPLEMENTARY NOTES IERL-RTP project officer for this report is D.C. Drehmel, Mail
Drop 61, 919/549-8411 Ext 2925.
16. ABSTRACT
The report gives results of an evaluation of an electric curtain for the
purpose of particulate control and removal. If the particles are charged by corona,
the curtain will stop them only in a very slow air flow (less than 2 cm/sec). At
these slow flows, a vertical curtain would stop the particles and a 45-degree curtain
would move them along the curtain without penetrating it. A horizontal electric
curtain could be used to suspend the particles against gravity. Finally, an attempt
to use highly charged water drops as the particle collection mechanism was unsuc-
cessful because of electrical breakdown caused by the water.
17.
KEY WORDS AND DOCUMENT ANALYSIS
a.
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
COSATI Field/Group
Air Pollution
Electrostatic
Separators
Filtration
Particles
Charged Particles
Electrodes
Electric Corona
Air Pollution Control
Stationary Sources
Particulate Control
Electric Curtains
13B
07A
07D
20H
09A
20C
3. DISTRIBUTION STATEMENT
Unlimited
19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
31
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
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