U.S. patent number 3,740,927 [Application Number 05/194,980] was granted by the patent office on 1973-06-26 for electrostatic precipitator.
This patent grant is currently assigned to American Standard Inc.. Invention is credited to James Henry Vincent.
United States Patent |
3,740,927 |
Vincent |
June 26, 1973 |
ELECTROSTATIC PRECIPITATOR
Abstract
Covers an electrical precipitator composed of two tandem
electrostatic sections arranged to eliminate dust or dirt or any
form of particulate matter which may be conveyed with air or gas or
any other fluid medium. The first section may, for example, include
one or more pairs of positively charged vertical plates between
each pair of which are positioned a plurality of negatively charged
vertical wires, so that a Corona discharge may be developed between
the vertical wires and the two parallel plates of each pair to
electrically charge the particulate matter transmitted between the
vertical plates. The second section, which is contiguous to the end
of the first section and constitutes an add-on for the first
section, includes a plurality of metallic grids which are parallel
to each other, but perpendicular to the plates of the first
section. The first and last grids of the second section may be
connected to a source of voltage which does not create a corona
field, and the remaining grids of the second section are "floated"
between the first and last grids so as to become charged by voltage
induced in such grids so that particles of matter entering the
second section and traversing the opening of the various grids will
respond to the electric field between adjacent grids and to the
aerodynamic flow pattern developed between all of the grids, so
that the particulate matter may be collected and removed from the
fluid medium.
Inventors: |
Vincent; James Henry
(Plainfield, NY) |
Assignee: |
American Standard Inc. (New
York, NY)
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Family
ID: |
26890584 |
Appl.
No.: |
05/194,980 |
Filed: |
November 2, 1971 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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804050 |
Feb 25, 1969 |
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869195 |
Oct 24, 1969 |
3616606 |
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65843 |
Aug 21, 1970 |
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Current U.S.
Class: |
96/54 |
Current CPC
Class: |
B03C
3/09 (20130101) |
Current International
Class: |
B03C
3/09 (20060101); B03C 3/04 (20060101); B03c
003/09 () |
Field of
Search: |
;55/103,123,130,131,138,139,154,155,156,127,128,129,132,136,137 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1,334,881 |
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Jul 1963 |
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FR |
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422,619 |
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Dec 1925 |
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DD |
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Primary Examiner: Talbert, Jr.; Dennis E.
Parent Case Text
This application is a continuation in part of my earlier
application, Ser. No. 804,050, entitled "Electrostatic
Precipitator," filed Feb. 25, 1969, now abandoned my earlier
application, Ser. No. 869,195, entitled "Multi Stage Electrostatic
Precipitator," filed Oct. 24, 1969, now U.S. Pat. No. 3,616,606 and
my earlier application, Ser. No. 65,843, entitled "Multi-Grid
Electrostatic Precipitator," filed Aug. 21, 1970. All of these
applications are assigned to the assignee of the present patent
application.
Claims
What is claimed is:
1. An electrostatic precipitator for removing charged particles,
comprising a plurality of parallel apertured grids arranged in
sequential order so that the charged particles, in travelling along
a path perpendicular to said grids, will traverse the apertures of
said grids, means for applying a voltage of one polarity to the
first of said grids and a voltage of opposite polarity to the last
of said grids, so that the only voltages impressed upon the
intermediate grids will be voltages induced on the intermediate
grids, whereby all of said grids will act to divert said charged
particles and collect them on all of said grids.
2. An electrostatic precipitator according to claim 1, in which the
total area of the openings of each grid is about 60 to 70 percent
of the effective area of said grid.
3. An electrostatic precipitator according to claim 1, in which the
apertures of all of the grids are sufficiently large so as to cause
the particles to travel in vortical paths in the wake of each grid
to facilitate the collection of said particles on said grids.
4. An electrostatic precipitator for upgrading a precipitator which
is discharging electrically charged particles, comprising two
parallel grids, a source of voltage connected between said two
grids, a plurality of additional grids interposed between said
first two grids so that voltages will be induced on the surfaces of
said additional grids, all of said grids being arranged parallel to
each other and substantially perpendicular to the path of the
charged particles so that the charged particles may traverse the
apertures of said grids, each of said grids having apertures which
aggregate between 60 and 70 percent of the effective area of each
grid, the grids being spaced from each other by a predetermined
distance, whereby the particles will be vorticized in the wake of
each of the grids and slowed up so as to be attracted by said grids
and removed.
5. An electrostatic precipitator according to claim 4, in which the
source of voltage is of the alternating type.
6. An electrostatic precipitator according to claim 4, including
means for charging said particles before they traverse the paths
through the apertures of said grids.
Description
This invention relates to electrical precipitators and, more
particularly, to apparatus and equipments for the precipitation of
dust, dirt or other particulate matter which may be included with,
or suspended in, a fluid medium such as air or gas.
The prior applications, and this application, disclose arrangements
of an electrostatic precipitator for the removal of particulate
matter borne by a fluid medium such as air or gas. The
electrostatic precipitator embodies two series sections. The first
section embodies one or more pairs of parallel metallic plates and
a plurality of conductors which are parallel to each other and
aligned between the two parallel plates of each pair so that, upon
the application of a sufficient voltage between the parallel plates
and the intervening conductors, a Corona discharge may be
established between the plates of each pair and the several related
conductors so that particulate matter transmitted along the path
between the two parallel plates of each pair will be electrically
charged and deflected toward the two plates of the first section.
If the several conductors are negatively charged, the particles
traversing the path may become negatively charged and, if the
plates are positively charged, they will attract the charged
particles so that they may be deposited on the parallel plates and
then removed. Notwithstanding the intended operation, a great many
charged particles will not be removed by the first section and can
be, and often is a public nuisance. The second section, which may
be an "add-on" section, may include two or three or more parallel
grids which are parallel to each other but perpendicular to the
plates of the first section and so arranged that a non-Corona
electrostatic field may be established between the adjacent grids.
The first grid would normally be brought to substantially the same
polarity as the plates of the first section, that is, to a positive
potential (which may be grounded). The third grid, and, if fifth,
seventh, etc., grids are employed, would be charged to the same
potential as the first grid, but the second grid, and the fourth,
sixth, etc., grids would be charged to negative potential. The
openings in all of the grids are rather large, and the spacings of
the grids are sufficiently large, so that the air or gas will be
entrained in vortices and particulate matter will be entrapped in
the vortices. The electrostatic field established between the grids
of the second section will act on the particles that leave the
first section so that they may be attracted to and collected on the
grids of the second section whereupon they will be removed from the
system.
In the arrangements described in the earlier applications, the
first section may be any conventional electrostatic precipitator of
the plate-wire (Cottrell) type. In fact, the first section need not
be restricted to the type of device referred to above, but it may
consist of any precipitating device which suitably charges the dust
particles or other particulate matter electrically prior to their
entry into the second (grid) section. The second section and the
combination of the two sections provide the main areas of novelty
and operative improvement in precipitating systems.
A fundamental novel concept is involved in the basic mechanisms by
which dust or other particulate matter is collected in the second
(i.e., the grid) section and it employs interaction between the
electric field applied between successive grid pairs and the
aerodynamic forces in the wake of the structure behind each grid.
Each "grid" is in the form of a flat plate having an array of
openings or holes such that air may flow through the grid in a path
essentially at right angles to the grid. The air flow through such
a grid will be such that, notwithstanding the flatness of the grids
and the absence of circulators, recirculating flow zones or
vortices will be created in the wake of the solid areas of the
grid. Dust particles or other particulate matter passing through
the holes in a grid may be drawn into these vortices, and the
particles may reside there for a short period before continuing on
their downstream paths. During the time that such a particle is
thus trapped in a vortex, it is, to all intents and purposes,
substantially stationary and thus temporarily removed from the
downstream sweeping action of the flowing gas, and can thus be
easily acted upon by an applied electric field to sweep the
particle to a collecting boundry, the particle either moving back
to the upstream grid through which it just passed, or moving
forward to the adjacent downstream grid. By increasing the number
of grids placed in parallel and perpendicular to the path of the
main gas stream, the chances are substantially increased that a
given particle may be trapped into an eddy or vortex, and so the
chances are increased that the particle will be collected.
Therefore, any increase in the number of grid stages will increase
the overall particle collection efficiency. Theoretical and
experimental investigations have established the conclusion that,
without this vortex-enhanced electrostatic collection effect, the
efficiency of the grid-type precipitator structure would be so low
as to be of little value. In order to maximize the vortical
formations and the particle collection effect, the grids themselves
must be designed and arranged so that a maximum amount of air, and
hence dust, will be entrained into the vortices, and this requires
grids with an open area within a predetermined range. However, upon
decreasing the open area too drastically, aerodynamic instabilities
will be produced in the wake structure of the grids. It has been
found that for optimum operation, the percentage of open area in
the grid should lie in the range from about 60 percent to about 70
percent.
For effective utilization of the above-mentioned grid
vortex-enhanced collection mechanism, the grids must be properly
spaced from each other so that they do not physically interfere
with one another's wake structure. Specifically, the spacing
between adjacent grids must be at least as great as the mean extent
of the vortices downstream from each grid. It is a general rule of
thumb that, if we assign a characteristic dimension to the grid
such as the mean width of the solid portions behind which the
vortices are generated, then the spacing between adjacent grids
should preferably be at least three times as great as that
dimension. The efficiency of dust collection is not materially
affected, either adversely or otherwise, by increasing the grid
spacing to distances greater than this, provided that there is no
loss in maximum effective electric field that can be maintained
between the grids without sparkover.
One of the principal objects of the present invention is to improve
the operational characteristics of a conventional electrostatic
precipitator by including a plurality of charged grids so as to
provide more opportunities for deflecting and removing particles of
matter that enter the precipitator. Such an arrangement, if added
to a conventional precipitator, such as a Cottrell structure, for
example, will improve the overall efficiency. When such a
multi-grid structure is joined to such a conventional first
section, the first section may be reduced in length so that shorter
plates may be employed along with a smaller number of parallel
conductors between the plates of the first section. This,
therefore, reduces the cost of the overall precipitator while at
the same time achieving an increased efficiency in the removal of
particulate matter from the fluid stream.
This invention will be better understood from the following
description and explanation when read in connection with the
accompanying drawing in which
FIG. 1 discloses and illustrates a cross-section of a dual section
electrostatic precipitator embodying a plurality of pairs of
oppositely poled grids sequentially arranged in its second section,
in which the second section embodies two grids which are oppositely
poled, between which are interposed a plurality of additional
grids, sometimes called "floating" grids; and
FIG. 2 illustrates a portion of a grid structure to exemplify the
dimensional character of the structure.
Throughout the drawing the same or similar reference characters
will be employed to designate the same or similar parts.
Referring to FIG. 1 of the drawing, there is illustrated a dual
section electrostatic precipitator in which the first section
includes three (or more) vertical parallel plate conductors such as
P-1, P-2 and P-3 organized as two groups and arranged so that a
plurality of vertical conductors W-10, W-11 and W-12 are typically
interposed midway between a pair of the plates P-1 and P-2 and a
plurality of vertical conductors W-20, W-21 and W-22 are typically
interposed midway between the vertical plates P-2 and P-3, as
shown. The second section includes, for illustrative purposes, six
parallel grids G-21 to G-26. Plates P-1, P-2 and P-3 of the first
section may be supplied, for example, with substantially equal
voltages of the same polarity, for example, positive voltages as
shown, while the conductors W-10, W-11 and W-12 of one path of the
first section and the conductors W-20, W-21 and W-22 of the other
path of the first section, have applied thereto negative voltages
with respect to the several plates between which the conductors are
interposed. It will be apparent that a common source of
appropriately high voltage may be so arranged that its positive
terminal is connected to the several plates P-1 and P-2 and its
negative terminal will be connected to the conductors W-10, W-11
and W-12, as well as to conductors W-20, W-21 and W-22.
Furthermore, the plates P-1, P-2 and P-3 may be connected to
ground. The grids G-21 to G-26 of the second section are poled so
that the same positive voltage will be applied to the grid G-21
while the corresponding negative voltage will be applied to the
grid G-26. The voltages that may be employed in practice may be as
high as 40 or more kilovolts as developed by a steady DC source, a
pulsed DC source, an AC source or any other suitable voltage wave
form. It is essential that the second section be substantially free
of Corona discharge and this may require appropriate adjustment or
reduced voltages between grids G-21 and G-26.
As the stream of gas or other fluid with the accompanying entrained
dust, dirt or other particulate matter, which may be obtained from
any source of such dust, dirt or particulate matter, such as a gas
engine, or a smoke stack, or a factory, for example, and may be
impelled or pressurized by a fan or other blower (not shown), the
particulate matter will be driven between the two parallel paths of
the first section, one path being provided by plates P-1 and P-2
and the other path by plates P-2 and P-3. Any particulate matter
not removed by the first or conventional section will enter the
second section which includes the several grids G-21 to G-26 which,
as already noted, are equally spaced from each other and are
parallel to each other and are also perpendicular to the plates
P-1, P-2 and P-3 of the first section.
The electrostatic field in the first section, that is, the
electrostatic field between, for example, each of the wires W-10,
W-11 and W-12 and the adjacent plates P-1 and P-2 and the
electrostatic field between the wires W-20, W-21 and W-22 and the
adjacent plates P-2 and P-3 are substantially perpendicular to the
flow path of the particulate matter transmitted through the first
section. On the other hand, the electrostatic field between any
pair of adjacent grids such as G-21 and G-26 of the second section
is substantially parallel to the direction of movement of the
particulate matter which traverses or escapes from the first
section and enters the second section.
In the first section of FIG. 1, each conductor, such as W-10 or
W-20, serves as a discharge electrode producing a negative Corona
discharge effect so that substantially the entire space in the
region of these various conductors of the first section is
subjected to the Corona field. Dust particles will be charged
predominantly negatively. These negatively charged wires, such as
W-10 and W-20, attract any of the particles of matter which have
positive charges thereon. The positively charged plates P-1, P-2
and P-3 attract and serve as collectors of the negatively charged
particles. Hence, a good proportion of the particles, whether
negatively charged or positively charged, are attracted to and are
deposited on the surfaces of the plates P-1, P-2 and P-3, or on the
conductors W-10 to W-12 and W-20 to W-22.
Any of the particles that traverse the first section, because they
have not been sufficiently attracted by the positively charged
plates or the negatively charged conductors of the first section
and, therefore have not been deposited on the plates or conductors
of that section and removed, will enter the second section. The
particulate matter entering the second section may contain
predominantly negatively charged particles but may also contain
some positively charged particles. Both types of particles will be
treated by the second section.
Negatively charged particles entering the region of the first pair
of grids G-21 and G-26 of the second section will tend to be
attracted by the first grid G-21 and hence turned back and
collected on the first grid G-21. Those not collected there will
pass to the region between the remaining grids G-22 to G-26. The
collection processes outlined here are greatly assisted by the
vortex effects previously mentioned. Similarly, any positively
charged particles may be attracted toward and deposited on grids
G-22 to G-26, and substantially assisted by the vortex effects. The
overall probability of collection of particles increases with the
number of grids employed. Thus, as described earlier, the overall
efficiency of the system is increased.
It will be apparent that the FIG. 1 arrangement is capable of
acting and removing, and does remove, both positively and
negatively charged particles that may be passed by the first
section of the precipitator and received by its second section.
Moreover, the peak voltage in the second section need not be the
same as the voltage in the first section. The voltage applied to
the second section may be higher or lower than the voltage applied
to the first section as may be desired, but Corona discharge in the
second section should be avoided. The voltages applied to either
section may be a steady d.c., pulsed d.c., or a.c. as desired. For
example, the first section may have a steady or pulsed d.c. voltage
while the second section may have an a.c. voltage. This type of
bi-polar arrangement has been found to be quite efficient in
removing a very high percentage of particulate matter which is
transmitted through the filter.
Although the arrangement of FIG. 1 has been shown and described as
embodying mechanism to charge incoming particles predominantly in a
negative sense, reversing the voltages in the first section will
cause predominantly positively charged particles to enter the
second (grid) section. The same collection processes occur as
described above. Furthermore, the voltages applied to the grids
G-21 and G-26 may be reversed, regardless of the polarities in the
first section, without basically changing the collection properties
of the structure. Still further, the voltages applied to the grids
may be alternating, either at 60 cycles per second or at any other
frequency. In relation to the basic collection mechanism described
above involving the vortices in the wake of the grids, the range of
frequencies of applied voltage that can be used in the practice of
this invention is limited to that where the duration of one-half
cycle exceeds the mean time period that a particle is trapped in in
a given vortex, which in turn is a function of grid geometry and
dimensions and of the air flow velocity.
Because of the overall high efficiency due to the addition of the
second section of the electrostatic precipitator of FIG. 1, the
length of the plates P-1, P-2 and P-3 of the first section and the
number of vertical conductors such as W-10 and W-20 in the first
section may be reduced. The reduction in the length of the plates
and in the number of vertical conductors materially affects the
overall length of the equipment as well as the cost of the
equipment and its installation and, at the same time, there is a
significant improvement in the overall efficiency of the particle
collecting features.
The intermediate grids G-22, G-23, G-24 and G-25 of the second
section are "floating" grids in that no voltage is directly applied
thereto, but voltages are induced on the several grids G-22 to
G-25. Assuming that the grids G-21 and G-26 have respective
positive and negative applied polarities, and the voltage is, for
example, 40 KV, as shown, then the grid G-22 will have induced
thereon an 8KV voltage of a negative polarity, the grid G-23 will
have a negative 16KV induced voltage, and the grids G-24 and G-25
will have induced negative 24 and 32 KV voltages, as shown. And so
on if additional grids or different applied voltages were
employed.
In the arrangement of FIG. 1, each negative particle traversing the
grid G-21 will be deflected by the induced negative voltage on grid
G-22 to repel and turn back the negatively charged particle to grid
G-21 where it may be collected and removed. The same particle will
also be subjected to the vortical effect immediately upon entering
the opening of the grid G-21 to aid in the collection process.
Likewise, the increased induced voltages on the remaining
downstream grids G-22 to G-25 will repel negatively charged
particles that reach the regions of the respective grids and
deflect and turn back such negatively charged particles to the
various grids G-21 to G-25, which may attract and collect the
negatively charged particles and, therefore, remove them from the
air stream. Again the collection process will be aided by the
vortical formations. Naturally, the number of grids interposed
between the two outer grids G-21 and G-26 may be increased or
decreased as desired for increasing or decreasing the trend toward
reversing the path of any negatively charged particles to the first
grid G-21.
Positively charged particles will be collected by the same
mechanisms as already described. It will be apparent that similar
collection effects will be produced by reversing the polarities on
the several grids of the second section.
The several arrangements shown and illustrated in the drawing serve
to improve the efficiency of collection and elimination of
particles passing through the parallel and sequential paths of the
conventional or other precipitator in the first section. Because of
the increased efficiency due to the second section of the
arrangements of this invention, the first section may be simplified
so that smaller components may be employed and the number of
conductors reduced, thereby reducing the cost of the overall
equipment and improving the overall operation at the same time. The
equipment of this invention may be made suitable for those other
purposes for which electrostatic precipitators of the kind herein
described are conventionally employed. Naturally, any suitable
means for receiving and accumulating particles removed by the
various elements of both sections may be employed in the practice
of this invention.
One metallic grid configuration that has been successfully used in
connection with a circularly perforated plate is shown fragmentally
in FIG. 2 where adjacent holes have equally spaced centers
staggered by 60.degree., as shown. Typically, the holes were 1 inch
in diameter, with the centers spaced about 1.2 inches apart, so
that the percentage open area would be about 63 percent. The plate
had a thickness of one-quarter of an inch. In this instance, if the
characteristic grid dimension d is taken to the width of the solid
portion of grid between adjacent holes as measured along the line
of centers, the preferable minimum spacing allowable between
adjacent grids should be about 0.6 inches for a plate having 1 inch
holes. The spacing between adjacent plates should be somewhere
between 3d and 6d or between about 1.2 inches and 3.6 inches.
Although the elements of the first section are parallel to each
other and the elements of the second section are likewise parallel
to each other, their relative directions may be changed over
considerable angles within the scope and spirit of this invention.
Moreover, although the several elements are shown as linear or are
linearly arranged, the various elements may be curved to be
spherical or elliptical or of any other desired shape within the
scope and spirit of this invention.
While this invention has been shown and described in certain
particular arrangements merely for illustration and explanation, it
will be apparent that the arrangements and operating features may
be arranged in other and widely varied organizations for the
purpose of carrying out the general principles and objectives of
the present invention.
* * * * *