U.S. patent number 3,668,835 [Application Number 05/008,295] was granted by the patent office on 1972-06-13 for electrostatic dust separator.
Invention is credited to Pierre Vicard.
United States Patent |
3,668,835 |
Vicard |
June 13, 1972 |
ELECTROSTATIC DUST SEPARATOR
Abstract
In an electrostatic dust separator having a ionizing electrode
axially disposed within a Venturi, an annular nozzle produces a
spray of an auxiliary substance in the gas stream issuing from the
Venturi, around a polarizing electrode. The coarse particles of the
spray are electrified by influence and they attract and retain the
finer ionized dust particles carried by the gas. The spraying
nozzle may be disposed within an auxiliary Venturi to increase the
velocity of the gas and to improve impact effects between the dust
particles and the sprayed particles. The ionizing electrode is
preferably formed with fins to enhance the ionizing corona
discharge, while the polarizing electrode is on the contrary smooth
to avoid any noticeable discharge effect. The gas to be treated may
be fed into the inlet of the main Venturi by an injector nozzle to
produce a negative pressure whereby a portion of the gas issuing
from the main Venturi may be recycled into same through an annular
passage provided around the said main Venturi.
Inventors: |
Vicard; Pierre (Lyon,
FR) |
Family
ID: |
26214841 |
Appl.
No.: |
05/008,295 |
Filed: |
February 3, 1970 |
Foreign Application Priority Data
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Feb 13, 1969 [FR] |
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6903675 |
Mar 24, 1969 [FR] |
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6907777 |
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Current U.S.
Class: |
96/27; 55/DIG.38;
55/319; 55/338; 55/345; 55/418; 55/456; 261/DIG.54; 261/116;
261/117; 261/118; 361/229 |
Current CPC
Class: |
B03C
3/36 (20130101); Y10S 261/54 (20130101); Y10S
55/38 (20130101) |
Current International
Class: |
B03C
3/36 (20060101); B03C 3/34 (20060101); B03c
003/36 (); B03c 003/41 () |
Field of
Search: |
;55/5,10,11,7,107,117,118,119,120,122,124,127,128,130,134,135,136,137,138,139
;261/DIG.54,64,115,116,117,118 ;317/3 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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159,412 |
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Aug 1940 |
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OE |
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4,824 |
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1886 |
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GB |
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421,811 |
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Dec 1934 |
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GB |
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940,930 |
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Nov 1963 |
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GB |
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Primary Examiner: Talbert, Jr.; Dennis E.
Claims
I claim:
1. An electrostatic dust separator comprising:
a Venturi unit having an inlet and an outlet for a dust-laden
gas;
a high-voltage ionizing electrode disposed axially of said Venturi
and terminating substantially at the outlet thereof, said ionizing
electrode being in the form of a rod having thin longitudinally
extending radial fins to ionize dust particles in the gas within
said unit, and said ionizing electrode having a predetermined
polarity;
a high-voltage polarizing electrode forming an extension of said
ionizing electrode beyond the outlet of said Venturi unit, said
electrode being in the form of a smooth rod, said polarizing
electrode having the same polarity as said ionizing electrode;
spraying means to produce around said polarizing electrode a spray
of particles of an auxiliary substance;
and means to collect said sprayed particles together with the dust
particles which they have attracted and retained.
2. In a dust separator as claimed in claim 1, means to recycle into
the inlet of said Venturi unit a portion of the gas issuing from
the outlet thereof.
3. In a dust separator as claimed in claim 1:
an outer casing axially enclosing said Venturi unit while leaving
an annular gas-recycling passage around same;
an axial injector nozzle in said outer casing in front of the inlet
of said Venturi unit to receive the gas to be treated and to inject
same into said inlet together with a portion of the gas issuing
from the outlet of said Venturi unit upstream of the spraying
means, said portion thus being recycled through said passage.
4. In a dust separator as claimed in claim 3, a butterfly valve
disposed within said injector nozzle, the diameter of said valve
being such that at its position transverse to said injector nozzle
it leaves an annular gas passage through said injector nozzle.
5. In a dust separator as claimed in claim 1, an intermediate
casing axially enclosing said Venturi unit while being spaced
therefrom, said intermediate casing having a first and a second end
respectively joined to the inlet and to the outlet of said Venturi
unit so as to determine therewith a closed annular space, and said
Venturi unit and said intermediate casing being made of an
electrical conducting material;
means within said closed annular space to form a radially directed
electrical connection between said Venturi unit and said
intermediate casing;
an electrically conducting outer casing enclosing said intermediate
casing while leaving an annular gas passage between itself and said
intermediate casing;
means to form a radially directed connection between said
intermediate casing and said outer casing;
means to recycle into the inlet of said Venturi unit through said
annular gas passage a portion of the gas issuing from the outlet of
said Venturi unit;
and means to electrically connect said intermediate cas-ing with
said outer casing.
6. An electrostatic dust separator comprising:
a Venturi unit having an inlet at one end for the dust-laden gas to
be treated, and an outlet at the other end through which said gas
issues;
a high-voltage ionizing electrode axially disposed in said Venturi
unit to ionize dust particles in the gas flowing therethrough;
spraying means adjacent the outlet to produce in the gas issuing
from said Venturi unit a spray of particles of an auxiliary
substance;
electrifying means adjacent the outlet to electrify said sprayed
particles with such a polarity that they attract and retain ionized
dust particles in the gas issuing from said Venturi unit;
and means adjacent said outlet to collect said sprayed particles
together with the dust particles which they have retained;
an auxiliary Venturi unit disposed downstream of the first named
unit to receive the gas issuing from the outlet of said first-named
Venturi unit, said auxiliary Venturi unit having an inlet portion
disposed adjacent the outlet of the first named Venturi unit, and
having a neck portion and an outlet portion with said spraying
means and said electrifying means being so disposed within said
auxiliary Venturi unit that the spray of particles of said
auxiliary substance is produced in the vicinity of the neck portion
of said auxiliary Venturi unit in order that said particles of said
auxiliary substance may act on the dust particles in a zone wherein
the gas which contains said dust particles flows with a high
velocity.
7. An electrostatic dust separator comprising:
an elongated outer casing having a first end and a second end;
an injector nozzle disposed in axial alignment with the axis of
said outer casing and at the first end of said outer casing to
receive the dust-laden gas to be treated;
a main Venturi unit axially disposed within said outer casing while
leaving an annular gas-recycling passage between said main Venturi
unit and said outer casing, said main Venturi unit having an inlet
portion, a neck portion and an outlet portion, with said inlet
portion disposed in spaced relationship to said injector nozzle,
said inlet portion being disposed between said injector nozzle and
said second end, said inlet portion being disposed downstream of
said injector nozzle to receive the gas issuing therefrom, and at a
distance therefrom so as to form therewith a gas-recycling injector
device;
a high-voltage electrode axially disposed within said main Venturi
unit to ionize dust particles in the gas flowing therethrough;
insulating means to support said ionizing electrode;
an auxiliary Venturi unit axially disposed within said outer casing
downstream of said main Venturi unit to receive the gas issuing
therefrom and leaving an annular space between said outer casing
and said auxiliary Venturi unit, said auxiliary Venturi unit having
an inlet portion, a neck portion and an outlet portion, with said
inlet portion of said auxiliary Venturi unit being spaced from the
outlet portion of said main Venturi unit so as to leave an
intermediate annular zone;
means to substantially prevent gas flow through said annular
space;
a high-voltage polarizing electrode extending axially of and
adjacent to the inlet portion of said auziliary Venturi unit;
insulating means to support said polarizing electrode;
an annular spraying nozzle axially disposed in the outlet portion
of said auxiliary Venturi unit to produce an annular diverging
spray of electrically conducting liquid particles which surrounds
said polarizing electrode and passes through said intermediate
annular zone so as to collect within said annular space together
with the ionized dust particles which they have retained;
means to supply an electrically-conducting liquid to said annular
nozzle;
means to remove collected liquid and dust particles from said
annular space;
and means for exhausting gas from the second end of said outer
casing downstream of the outlet portion of said auxiliary Venturi
unit.
Description
The present invention relates to electrostatic dust separators of
the kind comprising an axial high voltage electrode disposed in a
Venturi unit so as to ionize the dust particles in suspension in
the gas which flows through the said unit, the said particles being
thereafter electrostatically separated from the gas itself.
In accordance with the present invention an electrostatic dust
separator of the kind above referred to, comprises means disposed
downstream of the Venturi unit for producing in the gas stream
which issues from the said unit a spray of particles of an
auxiliary substance, these particles being appropriately
electrified so as to attract and to retain the ionized dust
particles in suspension in the gas stream. The auxiliary substance,
which may be a divided solid or preferably a liquid such as water,
may be sprayed around a polarizing electrode disposed in the gas
stream.
The axial ionizing electrode is conveniently formed of a rod
provided with thin radially extending longitudinal fins between
which the gas stream may circulate so as to dislodge any dust
particle which could have settled on the said electrode, while the
polarizing electrode is preferably made of a mere smooth rod.
A portion of the gas issuing from the outlet of the Venturi unit is
preferably recycled into the inlet thereof in order that the
ionized dust particles entrained by the recycled gas may form
nuclei adapted to attract and to retain the dust particles in
suspension in the untreated gas.
In the annexed drawings :
FIG. 1 is a general vertical section of an electrostatic dust
separator according to the invention.
FIG. 2 reproduces to an enlarged scale the upper portion of FIG. 1,
but showing the butterfly valve at its transverse position.
FIGS. 3 and 4 are cross-sections taken along lines III--III and
IV--IV of FIG. 1.
FIG. 5 is a view similar to FIG. 1, but illustrating a modified
embodiment.
FIG. 6 is a transverse section taken along line VI--VI of FIG.
5.
FIG. 7 is a vertical section showing the lower portion of another
embodiment of the invention.
The electrostatic dust separator illustrated in FIGS. 1 to 4
comprises a vertical cylindrical casing 1 having at its upper end a
converging injector nozzle 2. This injector nozzle opens in front
of the converging inlet 3 of a conduit comprising a neck portion 4
followed by a diverging portion 5, the said conduit thus forming a
Venturi unit which is axially maintained within the outer casing 1
by radial arms such as 6.
An insulating cross-member 7 is provided in the vicinity of the
lower end or outlet of Venturi unit 3-4-5. This cross-member
carries two vertical axial electrodes 8 and 9. The first one
extends upwardly through the Venturi unit and it terminates in the
vicinity of the neck of the said unit, while the other one 9
extends downwardly well below the lower end thereof.
As shown in FIG. 3 the first electrode 8, or ionizing electrode, is
formed of a rod provided with a relatively large number of
longitudinal radial fins 10 of quite reduced thickness which
therefore have a relatively sharp outer edge. These fins may for
instance be mounted in longitudinal slots milled in the periphery
of the rod and in which they are retained by soldering or
otherwise. As to the second electrode 9, or polarizing electrode,
it is formed of a smooth rod of relatively large diameter, as
illustrated in FIG. 4.
Below the lower end of the lower electrode 9 there is provided
within the casing 1 an annular nozzle 11 carried by a tube 12 which
extends through the conical bottom 13 of the casing, its outer end
14 being adapted to be connected with an appropriate supply. The
nozzle 11 is so arranged as to produce a slightly diverging annular
spray, concentric to the lower electrode 9 without any intermediate
screen and at a relatively small distance thereof. This spray
strikes the casing wall, as indicated at 15. The spraying nozzle 11
is supplied with an appropriate liquid under pressure, as for
instance water, it being however noted that it would also be
possible to spray solid particles in suspension in a gas such as
air. The nozzle, the liquid or the pulverized solid arc
electrically conducting and the nozzle is grounded.
The bottom 13 of casing 1 has a lower outlet 16 closed by an
appropriate air-lock device, while a lateral exhaust 17 is provided
somewhat above the said bottom.
In the embodiment illustrated in FIGS. 1 and 2,the upper nozzle 2
is equipped with a valve 18 of the butterfly type, pivoted about a
transverse horizontal axis, this valve, of circular contour, being
of such diameter that at the horizontal position (see FIG. 2), it
does not fully close the nozzle but leaves an annular gas passage
19 between its periphery and the inner side of this nozzle.
Both electrodes 8 and 9 are connected by means (not illustrated)
with an appropriate high voltage source, also not shown.
In operation the dust-laden gas enters the apparatus through nozzle
2, valve 18 being fully open as illustrated in FIG. 1. This gas
flows downwardly in the form of a jet through the converging
portion 3, the neck 4 and the diverging portion 5. There is thus
obtained an injector effect whereby gas is sucked from the annular
space which surrounds the Venturi unit 3-4-5. The gaseous mass thus
realized flows downwardly at a high velocity along the ionizing
electrode 8, the water vapor contained by the gas condensing on the
dust particles in the neck portion 4, in a per se known manner.
Owing to the presence of the sharp outer edges of the fins 10, the
high voltage applied to electrode 8 results in a sparkless electric
discharge , of the type generally called "corona effect," between
this electrode and the surrounding walls of the Venturi, whereby
the suspended particles are strongly ionized.
A substantial portion of the gas issuing from the lower end of the
Venturi unit 3-4-5 is recycled upwardly between the said unit and
casing 1, together with the suspended particles, due to the
injector effect of the jet from nozzle 2. The gaseous mass which
flows through the Venturi unit is thus, so to speak, inseminated
with already ionized particles which play the role of nuclei on
which the other particles tend to agglomerate. This progressive
growth of the suspended particles facilitates their separation.
The remainder of the gas issuing from the Venturi unit 3-4-5 flows
downwardly towards outlet 17 around the polarizing electrode 9 and
through the spray 15 of relatively coarse particles issuing from
the spraying nozzle 11. Owing to the vicinity of this high voltage
polarizing electrode 9, which due to its smooth outer surface
produces no corona effect, these coarse particles become
electrified by influence as they issue from nozzle 11, in such a
manner that the gas flows through a zone which contains coarse
particles carrying an electric charge of opposed polarity with
respect to the ionization charge. These coarse particles therefore
attract and retain electrostatically the finer ionized dust
particles in suspension in the gas, which are therefore entrained
towards the bottom 13 of casing 1, wherefrom they may be
periodically evacuated through the air-lock or like valve device
16. Of course some of these coarse particles may be entrained by
the gas through the outlet 17, but owing to their dimensions they
are easily separated by means of a conventional sleeve filter,
centrifugal separator or similar apparatus, together with the finer
particles which they have retained.
Owing to the insemination of the incoming gas with already ionized
particles entrained by the recycled gas, the ionization effects
within the Venturi unit 3-4-5 are extremely rapid. The velocity of
the gas flow through the latter may therefore be quite high. The
production of filtered gas is thus important and moreover the dust
particles cannot settle on the inner walls of the Venturi, which
eliminates the frequent cleaning operations generally required in
conventional electrostatic separators. Owing to the particular
construction of the ionizing electrode 8, the gas stream may freely
circulate between the successive radial fins where dust particles
cannot therefore be retained. When the flow of the incoming
dust-laden gas is so small that the velocity of the gas jet issuing
from nozzle 2 becomes insufficient, it is possible to reduce the
effective cross-sectional area of this nozzle by closing valve 18
(or more accurately by bringing it to the horizontal position),
which of course increases the velocity of the jet.
It may furthermore be noted that the recycled gas stream is
submitted to a sudden change of direction at the outlet of the
Venturi unit 3-4-5, as shown by the arrows in FIG. 1. This entails
a quite noticeable centrifugal acceleration which tends to separate
the biggest particles from this stream. In other words the zone
immediately below the Venturi unit acts as a centrifugal separator
for the particles in the recycled gas stream, those which have
grown by collecting and retaining smaller particles within the
Venturi, being selectively projected downwardly towards the
spraying nozzle 11.
It is obvious that the butterfly valve 18 is of no use when the
flow (quantity per unit of time) of dust-laden gas to be filtered
is substantially constant. The inlet portion or the neck of the
Venturi unit could be provided with helicoidal vanes imparting to
the gas stream a rotational motion of high angular velocity in
order to separate the biggest particles. In such a case the fins 10
should also be helicoidal so as not to hinder circulation of the
gas between them : also care would have to be taken that the vanes
do not short-circuit the axial electrode (the latter could be of
reduced length or the vanes could be made of an insulating
material). The apparatus could comprise a lower settling chamber of
large volume for a better separation of the coarse particles from
the gas before the latter reaches the outlet 17. The spray of
electrified particles below the Venturi unit could be realized in
any appropriate manner. The inner side of the walls of the Venturi
unit 3-4-5 could be provided with fins or blades in order to
enhance ionization of the incoming dust particles. In some cases
the recycling could be dispensed with.
In the modification illustrated in FIG. 5 the Venturi unit 3-4-5 is
surrounded by an intermediate cylindrical casing 20 of
substantially larger diameter (about twice the diameter of the neck
portion 4 of the Venturi), this intermediate casing being spaced
from the main outer casing 1 so as to leave an annular passage for
the recycled gas stream. The upper and lower edges of this
intermediate casing 20 are joined with the upper and, respectively,
the lower end of the Venturi so as to form therewith a single
member enclosing an inner closed annular space, this member being
supported by the radial arms 6. Radial partitions such as 21 are
disposed within the said closed space between the Venturi unit
3-4-5 and the intermediate casing 20. These partitions, as well as
the intermediate casing, the Venturi unit itself and the supporting
arms 6 are made of a conducting material such as a metal. The
closed space may further be filled with a conducting substance such
as water.
With such an arrangement the Venturi unit 3-4-5 is only connected
electrically with the intermediate casing 20 which is itself
grounded through arms 6.
Under such conditions when a high-voltage is applied to the upper
electrode 8, the Venturi unit 3-4-5 becomes electrified by
influence, which means that electric charges of a polarity opposed
to that of electrode 8 appear on its inner surface, while charges
of the other polarity flow freely from the Venturi unit towards the
intermediate casing 20 through the radial partitions 21 (and also
through the conducting substance which fills the hollow space
between the Venturi and the intermediate casing when such a filling
is provided). Owing to the distance between the Venturi unit 3-4-5
and the intermediate casing, the electrostatic field which appears
between the venturi and the upper electrode 8 is much stronger.
Furthermore the ionization current which circulates between the
electrode and the Venturi may freely flow towards the intermediate
casing 20 without determining on the inner surface of the Venturi
localized electric charges which could limit the ionization
effects.
It is obvious that similar considerations would apply to the lower
spray 15, namely that in order to enhance electrostatic influence
effects the spraying nozzle 11 should be grounded through a
connection of substantial length. But in this case the said
connection is comprised of the oblique tube 12 which may be
provided relatively long without requiring any particular
arrangement for this purpose.
In the embodiment of FIG. 7 an additional Venturi unit 22-23 is
disposed below the outlet of the diverging portion 5 of the main
Venturi unit with which it is connected by a perforated
intermediate zone 24. This zone may be formed of a perforated plate
or of a grid, as shown. The spraying nozzle 11 is axially disposed
within the additional Venturi unit 22-23 and it is carefully
stream-lined, as illustrated. Its annular spray is so directed as
to flare upwardly and to pass through the perforated zone or grid
24. The lower end or outlet of the additional Venturi unit is
flanged outwardly as shown as 25, so as to close the annular space
between the said Venturi unit and the outer casing, apart from some
holes 26 of reduced cross-section.
In operation the gas stream issuing from the diverging portion 5 of
the main Venturi unit is considerably accelerated in the converging
inlet 22 of the additional Venturi unit. Under such conditions the
impact effects between the dust particles or agglomerates of dust
particles and the coarse liquid particles from the spraying nozzle
11 are greatly enhanced. The coarse particles collect between the
additional Venturi and the outer casing together with the dust
particles which they have entrained, and the liquid flows through
the holes 26 towards the bottom of casing 1, wherefrom it is
evacuated through the air-lock device 16.
The angle of the spray with respect to the axis of the apparatus in
the zone 24 is preferably below 45.degree..
It is further to be noted that the recycled gas stream passes
through the grid 24 as indicated by the arrows 27.
* * * * *