Note: Descriptions are shown in the official language in which they were submitted.
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GRID TYPE ELECTROSTATIC SEPARATOR/COLLECTOR AND METHOD OF
USING SAME
REFERENCE TO RELATED APPLICATIONS
This application claims one or more inventions which were disclosed in
Provisional Application Number 60/979,206, filed October 11, 2007, entitled
"GRID
TYPE ELECTROSTATIC SEPARATOR/COLLECTOR AND METHOD OF USING
SAME" and Provisional Application Number 61/086,274, filed August 5, 2008,
entitled
"GRID TYPE ELECTROSTATIC SEPARATOR/COLLECTOR AND METHOD OF
USING SAME". The benefit under 35 USC 119(e) of the United States
provisional
applications is hereby claimed, and the aforementioned applications are hereby
incorporated herein by reference.
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The invention pertains to the field of separator apparatuses. More
particularly, the
invention pertains to an apparatus that can function as a filter unit as a
precipitator or as a
separator of materials that have different electrical properties.
DESCRIPTION OF RELATED ART
U.S. Patent No. 4,172,028 discloses an electrostatic sieve having parallel
sieve
electrodes that are either vertical or inclined. The particles are normally
introduced into
the electric sieve under the control of a feeder that is placed directly in
front of the
opposing screen electrode. The powder is attracted directly from the feeder
tray to the
opposing screen electrode by induced electric field that exists between the
tray and the
screen electrode. This system is a static air system.
Prior art precipitators have difficulty collecting highly conductive and very
poorly
conductive particulates.
SUMMARY OF THE INVENTION
The present invention includes an improved apparatus for collecting
particulates
using an aperture air flow control system and an inline series of alternating
discharge and
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grid type electrodes each with a separate electrical circuit centrally located
between either
parallel grid electrodes and/or plate electrodes.
The present invention also includes a method for improving the rate of lateral
movement and collection of particulates using the aperture air flow control
system and an
inline series of alternating discharge and grid type electrodes each with a
separate
electrical circuit centrally located between either parallel grid electrodes
and/or plate
electrodes.
In a preferred embodiment, the spacing between parallel grid and discharge
electrodes varies between 0.50 and 1.50 inches with a narrow air stream being
drawn
between the electrodes.
The present invention also includes an improved method of charging particles
using a pre-charger designed with a narrow air input channel. Using a narrow
air input
channel into the main air stream increases the probability that entrained
particles and
generated ions will come in contact, resulting in a high percentage of
particles being
charged.
In another embodiment, an external enclosed pre-discharger design and physical
arrangement improves agglomeration of sub-micron particles. The present
invention also
includes an external opposing dual channel discharger design to improve
agglomeration of
particles. In one embodiment, two or more separate electrode arrangements are
used
within the collecting chamber to improve the operation and collection
efficiency of the
apparatus. In another embodiment, multiple collection chambers are placed in
series,
preferably with a discharge chamber placed in between each of the collection
chambers to
recharge the particles. Various designs recharge the particles, to increase
collection
efficiency.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a cross sectional view of a cylindrical or rectangular multiple
grid
separator/collector of U.S. Patent No. 7,105,041, herein incorporated by
reference.
FIG. 2 shows a cross sectional view of a cylindrical or rectangular grid
separator/collector
of U.S. Patent No. 7,105,041 that has a center corona wire, multiple grids,
and
plate electrodes.
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FIG. 3 shows a cross sectional view of a rectangular multiple grid
separator/collector of
U.S. Patent No. 7,105,041 that has a normally grounded center grid electrode
located between two opposing charged electrodes.
FIG. 4 shows a cross sectional view of a modified-U-shaped electrode grid
separator/collector apparatus of U.S. Patent No. 7,105,041.
FIG. 5 shows an enlarged cross-sectional view of the radius of the U shaped
electrode grid
separator/collector and the interaction of the various forces affecting
separation.
FIG. 6 shows a cross-sectional view of a grid separator/collector of the
present invention,
with alternating discharge and grid type electrodes each with a separate
electrical
circuit centrally located between parallel grid or plate electrodes.
FIG. 7 shows a section drawing of an example of a grid used in the
electrostatic
precipitator/collector of the present invention.
FIG. 8 shows a cross sectional view of a dual channel discharger in an
embodiment of the
present invention.
FIG. 9 shows a cross sectional view of opposing external enclosed discharge
chambers in
an embodiment of the present invention.
FIG. 10 shows a cross sectional view of an electrode configuration for
collection of sub-
micron particles in an embodiment of the present invention.
FIG. 11 shows a pre-discharger and collection chamber arrangement in an
embodiment of
the present invention.
FIG. 12 shows a cross-sectional view of a corona generating electrode design
that uses a
45 degree angle chamber on each side of the main entrained airflow passage.
FIG. 13 shows a cross-sectional view of two saw tooth corona electrodes
located in a
corona chamber with each electrode facing an attracting electrode, where gases
pass through the electrical field into a control orifice and into the main
entrained
air stream.
FIG. 14 is a cross-sectional view showing two opposing corona-charging
electrodes, one
wire electrode, and another saw tooth electrode that are located in an
aperture
where gases to be charged flow around the corona charging electrodes.
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DETAILED DESCRIPTION OF THE INVENTION
A grid electrostatic precipitator (GEP) is a dynamic air system where a
gradient air
flow exists between the center air flow and collecting plate electrodes.
External discharge
electrodes are designed to charge and then agglomerate the fine particles into
larger
particles for ease of collection.
The present invention includes a grid type electrostatic
precipitator/collector with a
narrow air stream, various external pre-discharger designs with the ability to
agglomerate
sub-micron particles into larger particles and one or more collection chambers
(fields).
The pre-chargers preferably include a narrow air input channel. In one
embodiment, the
collection chamber includes both a recharging zone and a high voltage zone. In
another
embodiment, at least two collection chambers are placed in series and are
separated by
agglomerating recharging units. In yet another embodiment, one or more of the
collection
chambers placed in series includes a recharging zone and a high voltage zone.
The present
invention also addresses the differential flow pattern, illustrated in FIG. 10
and discussed
in U.S. Patent No. 6,482,253, herein incorporated by reference, that occurs
between the
central flow and the airflow at the surface that faces the discharge electrode
and the back
side surface of the grid electrodes, where a substantial drop in flow occurs
and the
collecting plate electrodes.
In the embodiments of the present invention, the main air stream is preferably
a
single column of air flowing in a vertical direction or a single row of air
flowing in a
horizontal direction.
One problem with agglomeration is that, once two or more particles agglomerate
into a larger, agglomerated particle, the agglomerated particle loses
polarity. The present
invention solves this problem by recharging these particles, permitting them
to
agglomerate further, which makes them even easier to collect. Recharging may
be
repeated over and over, to further increase the collection efficiency of the
apparatus.
FIG. 1 illustrates a cross-section of a vertical, rectangular, dual vertical
grid type
electrostatic separator/collector (GES/C). The apparatus includes a structural
frame (14)
and a center support plate electrode (9) with entrained gas entering at (17)
and exiting
at (1). It is important to have a narrow column (or row) of airflow and good
control of the
internal pressure. The air stream is preferably drawn into the apparatus. The
entrained gas
flows between a polarized charging grid (7) and the ground potential grid
electrode (6).
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Directly behind the two input grids (6) and (7) are additional grid electrodes
(8), at ground
potential, and a charged grid (5). It should be understood that the apparatus
could be
expanded laterally so that other grid electrodes can be used to move the
particles further
from the air stream. The apparatus is also a sealed unit so that the air
stream is restricted
between the input (17) and (22) (see Figures 2-3) and the gas exit conduits
(1). This unit
can be designed to operate with the input air moving either vertically or
horizontally
through the apparatus.
An electric field (24) is established between the alternating electrodes (5)
and (6),
(6) and (7), and (7) and (8). Generally the spacing between the last grid
electrodes (7)
and (8), and the plate electrode results in the absence of an electric field
because of the
distance between the plate and the grid electrodes. The charged particles move
laterally (16), and gravitationally settle (18) in the open space (25).
When processing large, high-density particles, these particles may gravitate
out of
the process before the next grid electrode or the collection plate electrode
(10). The
collecting plate electrode (10) is used when collecting fine non-conductive
particles or
when there is a mixture of conducting and non-conducting particles. Deposited
particles
are removed by a tapping apparatus (32), or by a squeegee or other removal
methods. The
spacing between parallel grid electrodes preferably varies between 3/8 and
1.50 inches.
The spacing between electrodes, the electrical potential between electrodes
and the
number of grid electrodes are each a function of the concentration of solids
in the air
stream, the size of the particles, electrical and physical characteristics of
the particles, and
flow rate, as well as other process variables.
The grid supports (2) and (11) are preferably constructed from a dielectric
material
with openings (15) in the collection area. The dislodged powder falls by
gravity or is
tapped from the plate electrodes (10) and is collected (34) at the bottom of
the
precipitating chamber (33).
FIG. 2 illustrates another vertical GES/C. A wire electrode (21) or other type
of
corona-generating electrode can be used to generate the necessary ions. The
corona
wire (21) is supported at both ends (43). This arrangement is preferred
primarily for
processing non-conductive particulates. For processing conductive particles,
the corona
wire is removed and the grid electrodes are moved closer together. This Figure
also uses a
single input (22) in contrast with the dual input (17) shown in FIG. 1. The
electric field
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lines of force (19) are generated at 90 degrees to the flow of the entrained
gas input and
illustrate the area where gas ions are produced by the corona discharge
electrode (21). The
charged particles that follow these lines of force result in the separation of
the solid
particles by passing through the grounded electrode (3) and the charged
electrode (4) from
the air stream (22) and are collected by gravity (18) or, for some materials,
deposited (37)
on the plate electrode (10). When designed as a rectangular unit, it can be
operated with
the input air moving either vertically or horizontally through the apparatus.
When
designed as a circular apparatus the grids are in a circular pattern and the
solid plate
electrode (42) is a cylinder.
FIG. 3 shows a top view of another separator/collector. This separator is
designed
to operate with a high solid to gas ratio or when a high number of particle
clusters are
found in the material. Entrained air can enter either in a vertical mode or a
horizontally
mode as shown by (22) and flows between the grounded electrodes (7) and the
charging
plate or grid electrode (46), dividing the stream into basically two
processing zones. The
concentration or spacing between wire grids of each electrode is preferably
varied to
provide more or fewer lines of force that determine the number of trails a
particle may
have before moving laterally onto the next electrode grid. When the
concentration of the
solid is high, the center electrode (46) is the charging electrode and the
electrodes (7) are
at ground potential. These units preferably operate in a vertical position
with either
horizontal or perpendicular air input.
The polarities of the electrodes change when the apparatus processes clusters
of
powder that are lightly bonded and need more resident time to break down into
smaller
particles that respond to the electrical forces available.
Figs. 4 and 5 show another design used to separate fine particles from an
entrained
air stream. As shown in the figures, the preferred shape for the electrodes is
either a
parabolic or a "modified U shape". The shape is basically that of the letter
"U", with a
bottom portion and more-or-less perpendicular side portions. However, the
"modified-U"
preferred shape has sides which are not perpendicular, but angled nearly to a
"V" shape,
and the sides meet the bottom at a radius, rather than a right angle, as
shown.
The "modified U shaped" electrode assembly is a very efficient design and
method
for separating solids from an air stream. The major forces used to separate
the particles
from the air stream are the force of gravity that exerts a vertical downward
force, the
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electrical inductive field force generated between the plate and grid
electrodes and the
angular, tangential force exerted on the particles as they traverse the
angular section and
around the radius of solid and grid electrodes.
The combination of the electrical field and the physical radius of the
modified-U
shaped electrode contribute to efficient separation by inducing turbulence and
drag
components to the air stream and particles.
The entrained air enters at (47) and is immediately subjected to the
electrical lateral
forces established between the modified U shaped plate electrode (48) and the
wire grid
electrodes (52) and (53). The entrained air (50) is drawn down the surface of
the
modified U shaped plate electrode (48) by the exhaust system located after the
exit (1). As
the air (50) flows down the angular section (56), the particulates (49) are
laterally
expelled (51) from the airflow. When the entrained air reaches the start of
the radius (54)
or tangent point, shown in FIG. 5, the particles have a natural tendency to
continue in a
straight path due to the mass of the particulates. Particles traveling along
the radius (55)
are subject to additional stresses due to the increase in the drag forces on
both the air and
particulates. These physical forces combined with the electrical repelling
forces produce a
very efficient method for removing particulates from a moving air stream. Some
of the
other factors that affect the separation are the density and conductivity of
the material, air
velocity, air volume and solids to gas ratio. The temperature of the U shaped
plate
electrode is preferably controlled. The inside surface (57) can be heated or
cooled by
electrical or other means.
FIG. 4 also shows conducting wires (58) at electrical ground level. The
conducting
wires (58) neutralize electrical charges that remain on some of the particles
after passing
through the last grid electrode. This is especially useful for processing fine
particulates.
Similar devices can be used in all of the designs herein. It is important to
neutralize the
charge on the particles, especially the fine particles that have been
separated from the air
stream.
In one embodiment, a grid type electrostatic separator/collector (GES/C)
includes
alternating discharge and grid type electrodes. Using parallel and opposing
grid electrodes
achieves early lateral transfer of particles through the grid into an area
where the airflow is
at a lower velocity or static conditions.
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The centrally located discharge corona electrode shown in FIG. 2 uses standard
wire or saw-tooth configurations. In contrast, in some embodiments of the
present
invention, a combination of alternating saw tooth or wire type discharge and
grid type
electrodes that have different circuits that operate at different levels of
current and voltage
are used. This series of electrodes is preferably centrally located between
the parallel grid
or plate electrodes.
When a discharge electrode is placed between parallel grid electrodes and a
voltage is applied, an electric field is established, generating flux lines
that charged
particles follow, ions, and an electric wind that introduces predictable
turbulence.
At the surface of the grids, the air velocity develops turbulence or a shear
factor
associated with the boundary layer, generating unstable eddy or vortex
rotation. The
combination of the above factors also improves the separation and traverse of
particles
from the main air stream and into the lower air velocity collection area.
FIG. 6 shows a grid electrostatic separator/collector (80) of the present
invention.
Entrained air input (81) enters the collector (80) and usually includes both
conductive and
nonconductive particles. A pre-charger (82) includes a discharge electrode
(62) and a plate
electrode (83) plus a filter (85) that is used to prevent contaminating
outside dust from
coating the discharge (62) and plate electrodes (83). Air flows (87) through
the pre-
charger (82) and ions are released from the pre-charger (82) and are drawn
through an
aperture (88). The ions attach (86) to the non-conductive particles.
The particles then travel through the collector aperture (65) into the main
part of
the collector (80). The collector (80) includes a series of alternating
central discharge
electrodes (68) and central grid electrodes (67) centrally located between the
parallel grid
electrodes (61). Although three central discharge electrodes (68) and five
central grid
electrodes (67) are shown in FIG. 6, any combination using both discharge
electrodes (68)
and grid electrodes (67) as the central electrodes could be used in
embodiments of a grid
electrostatic precipitator/collector (80) of the present invention.
An example of a grid that may be used in the electrostatic
precipitator/collector of
the present invention is shown in FIG. 7. A small opening (202) of the grids
alternates
with a large opening (203) of the grids. An example of the dimensions that
could be used
include 0.250 inches for the opening width (200), 0.060 inches for the
thickness (201),
(203) of the web material, 4.421 inches for the small opening (202) of the
grids,
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and 8.983 inches for the large opening (204) of the grids. These dimensions
are examples
only; the grid varies in size depending on the application.
The electric field (84), established when central discharge electrodes (68)
are
placed between parallel grid electrodes (61), generates flux lines (66).
Charged particles
laterally move (89) in a direction following the flux lines (66) and an
electric wind (63)
introduces predictable turbulence. At the surface of the grids (61) and (67),
the air velocity
develops turbulence or a shear factor associated with the boundary layer
generating
unstable eddy or vortex (60) rotation. Particles are collected (64) on the
plate
electrodes (83).
In a preferred embodiment, the spacing (69) between central grid electrodes
(67)
and the parallel opposing grid electrodes (61) varies between 0.50 and 1.50
inches. The
same distance variation preferably applies to the distance between the central
discharge
electrodes (68) and the parallel opposing grid electrodes (61).
The series of discharge and grid type electrodes preferably have different
circuits
that operate at different levels of current and voltage. As an example, FIG. 6
shows two of
those circuits (70) and (71).
The present invention replaces the corona discharge electrodes (21) of FIG. 2
with
a series of a combination of central discharge electrodes (68) and central
grid
electrodes (67). The collector of the present invention combines the
advantages of high
voltage obtained from using a central grid electrode (67) and also the
advantage of having
corona-generating electrodes to better collect non-conductive particles.
Some advantages of the embodiments employing a series of alternating discharge
electrodes and grid electrodes include improved charging of particulates,
faster removal of
entrained particles from the main air stream and onto the collecting plates,
which results in
shorter and less expensive equipment, and the ability to have improved field
effects by
having both a high voltage-high current for the discharge -grid conditions and
a higher
voltage-low current condition for grid-grid conditions, resulting in more
efficient lateral
particle removal and collection.
The combination of electrodes also achieves a stable corona discharge by
controlling both the voltage and the current. Drift velocity is not a major
concern because
the distance the particles have to travel before they are out of the main air
stream is short.
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The distance between the discharge and extracting or grid electrodes is
relatively close,
preferably 0.50 to 1.50 inches.
During the early process of charging particulates, blinding or interference
from
other particles can occur prohibiting all particles from reaching the maximum
charge and
responding to the flux lines of the electric field. By alternating single or
multiple groups of
discharge and grid electrodes along the length of the collection chamber, the
problem is
substantially reduced.
FIG. 8 is a cross sectional view of an external dual channel discharger (126)
where
the entrained air enters (100) and exits through the orifice (136) into the
collection
chamber (135). The collection chamber will be referred to as a "field" herein,
similar to
the term used by the electrostatic precipitator (ESP) industry. Particles are
polarized in
separate chambers (a negative chamber (217) and a positive chamber (218)) with
a
negative (117) and positive (118) discharge using a high voltage direct
current (HVDC).
The exterior sides and the center plate separating the two sides (103) are at
ground
potential (116). Charged particles exiting the polarizing channels (217) and
(218)
converge in a converging air zone (146) and mix to agglomerate (106) (see FIG.
9) into
larger particles. Other components include the discharge electrodes (105) and
the plate
electrodes (103). An electric field (104) is established between these
electrodes (103)
and (105) perpendicular to the air flow. Ions generated by the discharge
electrode (105)
follow the flux lines of the electric field (104) and interact with the
particles, resulting in
charged particles. Charging of particulates is also improved because of the
close distance
between the discharge and plate electrode resulting in a high gas ion to
particle ratio.
In this embodiment, the present invention has dual channels (217) and (218)
where
the particles are charged with opposite polarities using a high voltage direct
current. The
particles then flow into a converging air zone (146) where the polarized
particles mix and
agglomerate (106) into larger particles. The agglomeration (106) continues as
the particles
flow into a narrow single channel (130) before entering the collection chamber
(135). In a
preferred embodiment, the width of the single channel (130) ranges from 3/
inches
to 2%Z inches. Using narrow airflow channels (217) and (218) in the discharger
improves
the probability of agglomerating the fine particles by exposing the particles
to a high
concentration of polarized particles. In a preferred embodiment, the width of
each of the
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airflow channels (217) and (218) are the same, and ranges from 3/ inches to
1'/z inches
such that the total width of both channels ranges from 1'/Z inches to 3
inches.
In an example of the dual channel discharger (126), the dimensions include 3/8
of
an inch between the plate electrodes (103) and discharge electrodes (105) such
that each of
the polarizing channels (217) and (218) are 3/ inches wide. In this example,
the single
channel (130) is preferably 1 inch wide.
FIG. 9 shows a cross sectional view of opposing external enclosed discharge
chambers. Although two opposing discharger chambers (102) located on each side
of the
input channel are shown in this figure, additional discharge chambers (102)
are also within
the spirit of the present invention. For example, a greater number of
discharge
chambers (102) may be required for higher velocities. Each chamber includes a
corona
discharge electrode (105), two plate electrodes (103), two chamber air input
orifices (112),
two filters (111) (shown in FIG. 10 and FIG. 11), one over each side of the
input
orifices (112), and two control exit orifices (125) where the generated ions
(121) enter the
main air stream. The close up view (123) illustrates the charging of a non-
conductive
particle (122) by ion (121) attachment.
In a preferred embodiment, the width of the main air stream, which is also the
distance between the two chambers (102), is preferably in the range of 3/ to
2%z inches. In
another preferred embodiment, the width of the output orifice (125) from the
discharge
chambers (102) into the main air stream preferably ranges from 10/1000 inch
to 60/1000 inch.
Advantages of this system include the ability to adjust the ion input by
varying
either the orifice width (125) or the operating current. Another advantage is
that the
discharge electrodes are kept clean, resulting in maintaining a consistent ion
input. Fine
particle agglomeration is effective in this system because of the narrow air
channel and the
turbulent airflow created by the ions being drawn into the main air stream.
FIG. 10 is a cross sectional view of a collection chamber/field (135) showing
a
preferred electrode configuration for collection of sub-micron particles. Used
in
conjunction with a tangential blower (114) that exhausts at (119) are the
input (136) and
output (137) orifices that create a narrow air stream that flows past two
independently
controlled electrical zones (131) and (132). These zones include the discharge
zone (131)
that has a separate circuit including separate plate electrodes (133), grid
electrodes (107)
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and the discharge electrodes (105). In this zone (131), the current is the
controlling factor.
The second zone (132) has separate plate electrodes (134) and opposing and
parallel
grids (138), where a higher voltage can be applied. The plate electrodes (133)
in the first
zone (131) can operate separately from the plate electrodes (134) in the
second zone (132).
The second zone (132) has a much higher field strength, which allows it to
collect the sub-
micron particles. The second zone (132) preferably does not have discharge
electrodes (105).
The discharge zone (131) is placed first because agglomerated particles will
lose
most of their charge and need to be recharged in order to continue to
agglomerate.
Particles that are not collected in zone (131) will be subjected to a higher
voltage in
zone (132), resulting in a stronger electrical field (104) that improves
collection of sub-
micron particles.
The collection process begins with particles entering at orifice (136) and
being
polarized by the corona from the discharge electrodes (105). The charged
particles then
respond to the opposite polarity of the grid electrode (107) and the electric
field (104) and
move laterally (109) or perpendicular to the airflow by following the flux
lines of the
electric field. Because of the momentum of the particles, the particles pass
through the
grid (107) into an area where there is a sharp drop in the air velocity (151)
and decreases
to near static conditions (115) at the collection plate surface (133) and
(134). The sharp
drop in flow immediately behind the grid electrode (151) is dependent on the
porosity of
the grid and airflow operating parameters. Due to the close proximity of the
electrodes in
the first zone (131), charging of the particles is aided by the turbulence
created by the
corona wind (127), movement of ions and the eddy currents (128) generated at
the surface
of the grid electrodes (107) and (138).
Sub-micron particles are collected when charged particles (124) follow the
flux
lines of the electrical field (104) and move laterally (109) through the grid
electrode (107)
into an area where there is a sharp drop in air movement and reaching near
static
conditions at the collecting plate surface (115).
In one example, the typical dimensions for one field include a distance
between the
discharge electrodes (105) and grid electrodes (107) that is preferably
between'/h inches
and 1.0 inch. The width of the collection chamber (135) is preferably 6.0 to
12.0 inches.
The width of the grid electrodes can vary between 6 and 12 inches, depending
on the
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structural size of equipment. There are preferably 3 to 6 discharge electrodes
(105) per
grid and 3 to 4 grid electrodes (107), (138). The length of the combined
processing
zones (131) and (132) is preferably 18 to 24 inches. The input (136) and exit
(137) orifices
are preferably each 1.0 to 2.0 inches wide.
The length of the processing zones, the number of electrodes, and the height
will
vary depending on the application. Another dimension that will vary based on
the size and
operating requirements is the aspect ratio of the width of the input and
output orifice to the
width of the field or collecting chamber. In preferred embodiments, aspect
ratios of 10:1
or 3:1 may be used.
The external enclosed discharger shown in FIG. 9 is different than the one
shown
in FIG. 10 in that there is only one exit orifice (137) and one plate
electrode (103) in
FIG. 10, while in FIG. 9, there are two plate electrodes (103) one on both
sides of the
discharge electrode (105) and two exit orifices (125). Filters (111) shown
over the input
orifices (112) in FIG. 10 would normally be used with the design shown in FIG.
9. The
filters maintain consistent long-term operation by keeping the electrodes
clean.
Another method for improving the collection of fine and sub-micron particles
is to
recharge the particles more frequently. It is difficult to charge, agglomerate
and collect
ultra fine particles. The collection by the first field may be high but it is
not 100 percent.
Some of the particles will not be sufficiently charged to respond to the
electrical field. By
re-charging and then re-agglomerating these particles at frequent intervals,
the process
becomes more efficient.
FIG. 11 illustrates the concept of using two or more fields (135) in series
along
with external dischargers (126) and (102). The two chambers are preferably
fairly close
together. In a preferred embodiment, the apparatus has a short 1 to 2 inch
straight
section (140) for air flow control and then the discharge section (126) or
(102). Details of
preferred embodiments of the fields are shown in FIG. 10, while Figs. 8 and 9
give details
of the external discharger (126) and (102). Although the electrode
configuration from
FIG. 10 is shown in FIG. 11, other electrode configurations disclosed herein,
as well as
electrode configurations known in the art, or combinations of different
electrode
configurations could be used for the collection chambers in this embodiment.
Although two chambers are shown in FIG. 11, additional chambers are also
within
the spirit of the invention. In fact, more fields (135) in series may further
increase the
CA 02640907 2008-10-10
14
chances of collecting the sub-micron particles. There is preferably at least
one
discharge (102) or (126) between each of the collection chambers (135). Having
multiple
fields (135) and/or discharge chambers increases the success rate in
collecting the sub-
micron particles.
Collecting sub-micron particles is also tied into continuously collecting both
inorganic and organic particles. The particles may be recharged by an energy
source (113).
One method for recharging the particles uses an ultraviolet energy source.
FIG. 10 and
FIG. 11 indicate the position of an ultra violet energy source (113).
Alternative energy
sources for recharging the particles include plasma energy or microwave
energy. Any of
these energy sources could be used after the first field to charge and/or
destroy the organic
particles.
The pre-charger shown in FIG. 12 draws air to be charged through orifices
(112)
and (152) into the main entrained air stream (100) at a 45-degree angle. The
45-degree
angle reduces the chance of air turbulence or eddies causing particles to
accumulate at the
exit of the orifice and blocking the orifice. Controlling the amount of air
flowing through
the orifice reduces this problem. Other controlling factors are the width of
the narrow pre-
charger chamber (156), location of the discharge electrode (105) and the
thickness of the
dielectric material (108). The input orifices (112) and output orifices (152)
permit
controlled amounts of air to be drawn into the chamber to be electrically
charged and mix
in a narrow channel (154) with the main entrained air flow (100). In one
embodiment of a
grid electrostatic precipitator, the design of the corona-generating electrode
uses the 45-
degree angle chamber shown in FIG. 12.
In other embodiments, other pre-charger designs may be used. One of the
arrangements, shown in FIG. 13, shows a cross-sectional view of two saw tooth
corona
electrodes (105) in an elongated corona chamber (139) attached together and
facing in the
opposite direction. The tips of the saw tooth corona electrode (105) face the
grounded
attracting plate electrodes (103) and operate with an electrical field (104)
between the two
electrodes (105) and (103).
On the left hand side of FIG. 13, the gases (150) to be charged are filtered
and
enter through a control orifice (141) close to the charging electrodes, pass
through a
HVDC electric field (104) and exit through another controlling orifice or
aperture (125)
near the attracting plate electrode (103). The spacing between the corona
electrode (105)
CA 02640907 2008-10-10
and the dielectric material (108) are preferably in the low 1 or 2 thousandths
to 10 or more
depending on the flow conditions of the main air stream (100) and the need to
have
enough flow and velocity of air and ions to keep the corona electrodes (105)
clean. The
chamber behind the first input orifice (141) acts as a plenum chamber (142)
that provides a
uniform distribution of air to the corona-charging electrode (105). Ions (143)
are
preferably injected perpendicular and into the entrained air stream.
The right hand side shows a slight modification where the input gases (150)
are
drawn through the air filter (111), but do not pass through controlling
apertures (141). The
input gases (150) only exit through the controlling apertures (125) near the
attracting plate
electrode (103). Selection of the location of the input orifice and the exit
orifice is
important because it permits the generated ions entering the main entrained
air stream to
exit the chamber before losing their charge to the attracting electrode. Other
design and
operating features of this apparatus include the ability to increase the
distance between the
corona (105) and attracting plate electrodes (103) so that a higher voltage is
generated and
maintained, resulting in the production of more ions.
FIG. 14 shows another apparatus that improves ion generation and still
protects the
charging electrode. This design improves the penetration of the generated ions
into the
center of the main air stream (100) while still protecting the charging
electrode. The
corona electrodes (105) are located in the slotted apertures or orifices (125)
made of
dielectric material (108) that is not affected by the corona discharge and
where the gases to
be charged (150) flow close to or over the surface of the corona electrodes
(144) and (105)
and become ionized and are attracted to the plate or ribbon electrodes (145)
that are
centrally located between the corona electrodes, by the HVDC electric field.
The ribbon
attracting electrodes (145) are centrally located between the opposing corona
electrodes
and in the retained airflow.
The corona electrodes generate controlled amounts of electrically charged
gases
that are attracted to the opposing attracting electrode by the electrical
field (104). These
charged particles are preferably drawn into the main stream (100) by negative
pressure of
the precipitator, or forced into and mixed under low pressure with the main
entrained
airflow (100). Having the ability to protect the corona-generating electrode
opens the door
to extending the life of electrodes and generating higher ion counts using
less energy.
CA 02640907 2008-10-10
16
In a preferred embodiment, the width of the main air stream (100) ranges from
3/
to 2%z inches. In one example, the width is 1 inch.
The high velocity gases and particulates in the main air stream (100) keep the
attracting electrodes (145) clean. The charging corona electrodes (144) and
(105) are kept
clean by the positive constant flow of gases over the surface of the
electrodes. Clearance
between the electrode and sidewall of the orifice may vary and is based on
operating
parameters of the GEP. If the pre-charger design of Fig. 14 was used with the
precipitators
shown in Figs. 10 and 11, it would require a slightly wider input channel to
compensate
for the width of center ribbon electrodes (145).
It should be noted that, in the case of designs shown in Figs. 13 and 14, the
number
of corona electrode units, inline with the airflow, are examples only. The
number may
vary, depending upon the application and process requirements.
The pre-charger arrangements shown in FIG. 13 and FIG. 14 could be used
instead
of the pre-chargers of Figs. 8 and 9 in combination with any of the
precipitators disclosed
herein, including, but not limited to, the precipitators shown in Figs. 10 and
11 and the
precipitator embodiments including alternative grid and discharge electrodes.
Accordingly, it is to be understood that the embodiments of the invention
herein
described are merely illustrative of the application of the principles of the
invention. The
embodiments can also be used in combination with each other, within the spirit
of the
present invention. Reference herein to details of the illustrated embodiments
is not
intended to limit the scope of the claims, which themselves recite those
features regarded
as essential to the invention.
