Note: Descriptions are shown in the official language in which they were submitted.
This inventlon relates to the art of dust
collection, and more particularly to a new and improved
method and apparatus of the electrostatic ~ype for
separating particulate matter Erom a gas stream.
Th~s application is a divisional application
of Canadian application serial number 276,392, filed
April 18, 1977.
Dust collection methods and apparatus of the
electrostatic type such as electrostatic precipitation
are well known and offer the advantage of handling
relatively heavy dust loads. Dust collection methods
and apparatus of the mechanical filtration type which
employ a porous filter medium, such as fabric filters
or bag houses, provide a very efficient collection Qf
small particles. It would be highly advantageous to
provide a dust collection method and apparatus which
combines the various desirable fea~ures of these two
types. Furthermore, it would be highly desirable to
provide an efficient and effective method and apparatus
for cleaning or otherwise removing collected dust from
surfaces of apparatus of the foregoing types.
SUM2~ARY OF_THE_INVENTION
It is therefore, an object of this invention
to provide a new and improved method and apparatus for
collecting dust advantageously comb$ning various
desirable features oP the electrostatic and mechanical
filtration types and to provide a method and apparatus
for cleaning collected dust from surfaces o apparatus
of the electrostatic type.
,
mb / ~
fl~
T~ic present invention provides a method and apparatus
for separating particulate matter Erom a gas stream. In one
aspect thereof, the method includes moving dirty gas through
an electrostatic precipitator to correct a portion o~ the
particulate matter from -the gas s~ream; moving gas from the
precipitator through a filter element of flexible foxaminous
material to collect the remainder of the particulate matter from
the gas stream; withdrawing clean gas from the filter 'element;
and introducing a:controlled quantity of'high pressure fluid
in the form of a jet at predetermined times at a location and
in a direction so as to induce a substantial flow of gas through
the filter element causing the filter element to be flexed
inwardly and abruptly and from the filter element to the
preclpitator to remove collected particulate matter'from the
filter element and from the precipitator.
In one aspect thereof, the apparatus includes a
housing having an inlet for receiving dirty gas and an outlet;
a hollow electrostatic precipitator within the housing~ the
precipitator having an inlet communicating with the dirty gas
inlet and an outlet, the precipitator having a hollow collecting
element be-tween the precipitator inlet and the precipit.ator
outlet and of a material which is impervious to gas, the
precipitator including corona producing means therein; means
for moving gas from the dirty gas inlet through an electrost~.tic
precipitator and to the housing outlet; and cleaning means for
introducing a controlled quantity o~' high pressure ~luid in the
form of a jet at predetermined times adjacent the precipitator
outlet and in a direc-tion toward the precipitator inlet in a
manner inducing a substantial flow of gas through the collecting
element in a direction from the precipitatox outlet toward the
precipitator inlet to remove the collected particulate matter
from the collecting elementO
~,~
-2-
., , ~ .
42
In a fuxther aspect thereoE, the apparatus includesa houslng having an inlet for receiving gas from the stream
containing the particulate matter and an outlet; an electro- .
static precipitator within the housing, the precipitator com-
prising a hollow and elongated collecting element of a material
which is impervious to gas and having an inlet a-t one end
thereof communicating wi.th the gas inlet and an outlet at
another end thereof and electrode means within -the collecting
element; a hollow, elongated filter element of fle~ible foraminous
material within the housing having an inlet at one end thereof
operatively connected to the outlet of the precipitator
collecting element, means operatively associated with the
housing for moving the gas from the gas inlet through the
precipitator collecting element and the filter element and to
the housing outlet; cleaning means for introducing a controlled
quantity of high pressure gas in the form of a iet at predeter-
mined times adjacent the precipitator inlet in a manner inducing
a substantial flow of gas from the gas stream along the collect~
ing element in a direction from the precipitator outlet toward
the precipitator inlet to remove collected particulate matter
- from the collecting element, the cleaning means including means
for directin~ the controlled quantity of high pressure gas
generally centrally and longitudinally of the collecting
element, and the directing means of the cl.eaning means being
locate~ relative to the outlet of the precipitator collectlng
element and to the
~'i"`~ '
sd/~ 3_
filter elemellt inlet such ~hat the flow of gas induced
by the c].eaning means causes the filter element to
be flexed inwardly and abruptly the.reby dislo~ging
collected particulate matter from the surface of the
filter element.
The foregoing and additional advantages and
characterizing features of the present invention will
become clearly apparent upon a reading of the ensuing
detailed description together with the included drawing
wherein:
BRIEF_DESCRIPTION OF THE DRAWING FIGURES
Fig. 1 is a side elevational view of an
installation of apparatus according to the present
invention;
Fig. 2 is an enlarged vertical sectional view
taken about on line 2-2 of Fig. 1 and showing apparatus
according to the present invention for separating
particulate matter from a gas stream;
Fig~ 3 is an enlarged vertical sectional view,
with parts broken away and some parts shown in elevation,
of the apparatus of Fig. 2;
Fig. 4 is a plan view taken about on line 4-4
of Fig. 3;
mb~ - 3a -
. . .
~3l'7'~ -
1Fig. 5 is a sectional view taken about on line 5-5 of
Fig. 3;
Fig. 6 is a sectional view taken about on line 6-6 of
Fig. 3;
Fig. 7 is a fragmentary vertical sectional view illustrating
the upper mounting arrangement for the corona wire in the
apparatus of Fig. 3;
Fig. 8 is a fragmentary vertical sectional view
illustrating the lower mounting arrangement for the corona
wire in the apparatus of Fig. 3;
Fig. 9 is a fragmentary perspective view with parts re-
moved illustrating apparatus according to another embodiment
of the present invention; and
Fig. 10 is a fragmentary vertical sectional view of the
apparatus of Fig~ 9
DETAILED DESCRIPTION OF THE ILLUSTRATED EM~ODI~ENTS
Referring now to Fig. 1, the apparatus according to the
present invention for separating particulate matter from a gas
stream includes a housing having an upper portion generally de-
signated 10, which preferably is hollow rectangular in shape,and a lower or hopper portion generally designated 12 which is
defined by tapered sidewalls leading from the lower end of
housing portion 10 to an outlet 14. The upper 10 and lower 12
housing portions are separated by a horizontally clisposed tube
sheet which will be shown in further detall presently. The
apparatus further comprises an inlet conduit 16 for receiving
dirty gas which is connected to one end of a duct 18 extending
--4--
4~
1 along the lower end of the upper housing portion 10. Duct 1~
can be hollow rectan~ular in shapP and is in fluid communication
with the lower housing region 12 whereby ~he incoming gas stream
flows first horizontally along conduit 16 and duct lSt is di-
rected downwardly into housing portion 12, and then flows up-
wardly through the remainder of the apparatus in a mlanner which
will be described in further detail presently. The apparatus
also includes an outlet conduit 20 connected to the housing
upper portion 10 and through which cleaned gas leaves the
apparatus. Gas is moved through the apparatus rom inlet 1~
to outlet 20 by a motor driven fan 21 which preferably is con-
nected to the outlet 20 in a known manner, the output of the
fan being connected to a duct or conduit through which the
cleaned gas is conveyed.
. The apparatus of the present invention further comprises
at least one dust collector unit generally designated 24 and
comprising electrostatic precipitator means 26 and ~ilter
means 2~, of foraminous ma~erial. Typically a plurali~y of
units are included in the apparatust an additional unit 24.'
including precipitator 26' and filter 28' bein~ indicated in
Fig. 1. The particular number of units is, of course, deter-
mined by the desired operating parameters of the installation.
In each dust collector unit illustrated in Fig. 1, ~or example
unit 24, the precipitator 26 is elongated and hollow having
an inlet at one end which is connected to an aperture provided
in the tube sheet separating the housing portions whereby the
interior of the precipitator is in fluid communication wi.th
the lower housing portion 12. The inlet end of the precipi-
tator is relatively rigidly secured in the tube sheet aperture,
in a manner which will be described in detail presently, thereby
--5--
7'~2
1 provlding support for the entire unit. The outlet of the pre-
cipitator is in fluid communication with an inlet or lower end
of the filter means 28, the -upper end of which is located near
the upper end of housing portion 10. There is provided stru-
tural support for the unit adjacent the upper end in a manner
which will be described in detail presently. T'ne interior of
the precipitator can be viewed as a charging zone for applying
electrostatic charge to particles in the gas stream, i.e., dust
particles, travelling through the precipitator and to the filter.
~igs. 2-~ illustrate in further detail a single dust
collector unit 24 including an electrostatic precipitator 26
and a filter means 28. As shown in ~ig. 2, the unit 24 is
disposed generally vertically within the housing 10 resting at
the lower end thereof on a tube sheet element 32 and with the
upper end thereof located slightly below a top wall 34 of the
housing portion 10. Precipitator 26 is disposed generally
ver~ically in the housing, is hollow, preferably generally
cylindrical in shape, and is of the type wherein gas flows
from the inlet at one end axially within and along the pre-
cipitator and through the outlet at the opposite end. Pre-
cipitator 26 includes a hollow collecting element in the form
of a cylinder or tube 36 of electrically conducting material,
preferably metal, and the sleeve 36 is fixed at one end thereof
in a lower end insulator element 38 as shown in further detail
in ~ig. 3. In particular, the tubular or sleeve-like element
33 is o:E a re:latively constant inner diameter along the axial
length thereof arld includes a first axial portion 4~ having an
outer cliameter substantially equal to the inner diameter of
the tubular collector element 36 and a second axial portion 42
X
74Z
laving a larger outer dia~eter, the two portions meeting a-t
an annular seat or edge surface 43 disposed in a plane generally
perpendicular -to the longi-tudinal axis of element 38 and located
approximately midway between the ends thereof. In the present
illustration, the lower end of sleeve 36 fits snugly over the
axial por-tion 40 and extends in~o an annular recess formed in
the portion 42 adjacent the seat surface 43 for added stability.
: Thus sleeve 36 fits on insulator 38 in a.manner providing a gas
tight seal between the components which can be augmented if
des1red by sealant material. The axial end face of portion 42
of element 38 rests on and contacts tube sheet 32 in a manner
~ surrounding an aperture or opening 46 provided in tube sheet 32
: for this particular dust collector unit. As shown in Fig. 3,
each aperture in the tube sheet 32 is provided with.a sealing
structure in the form of an upstanding annular element 48 fixed
to sheet 32 and surrounding the opening 46, element 48 having
an inner diameter greater than the diameter of opening 46. In
addition, the inner diameter of element 48 is slightly greater
than the outer diameter of the portion 42 of insulator element
38. A pair of axially spaced annular grooves 50 and 51 are
provided on the outer surface of portion 42 located a distance
from the end face thereof less than the axial length of element
: 48. Grooves 50 and 51 are provided with O-ring type sealing
elements 52 and 53, respectively, seated therein and of a
diameter sufficient to provide sealing contact with the inner
surface of element 48 when the end portion 42 of insulator 38
is fitted therein as shown in Fig. 3.
Precipitator 26 further .includes an upper end insulator
element 56 which also is generally sleeve like having an inner
~ .
; ~j b -7-
7~
1 diameter substantially constant along the axial length thereo~.
Element 56 has an outer diameter substantially equal to the
inner diameter of tube 36 whereby the outl.et end of tube 36
is fitted over and along the element 56 as shown in Fig. 3
The upper end o~ element 56 is formed to include a radial flange
portion 58 defining a planar axial end face 59. The end of tube
36 abuts against the opposite axial ~ace of flange portion 5~.
~ high voltage cable designated 62 is brazed or otherwise con-
nected at one end to the outer surface of tube 36 adjacent the
end abutting the radial flange of insulator element 56 and is
provided with insulation of Teflon* or similar material which
: is capable of withstanding voltages in the neighborhood of 50,000
; volts. The end insulator elements 38 and 56 are of dielectric
material such as a polyester laminate, and tube 36 preferably is
o~ stainless steel.
Precipitator 26 further comprises an elongated corona
electrode66 located centrally of the collecting structure,
preferably coincident with the longitudinal axis o~ the tube 3~!.
The corona electrode 66 is in the form of a relatively thin wire,
preferably of stainless steel, which is connected at the upper
end as viewed in Fig. 2 in a manner which will be described
in detail presently. The lower end of corona wire 66 as shown in
Fig. 3 is ~itted thro~tgh an aperture provided in a rod element
68 of dielectric material. The end o~ wire 66 can be fixed ~o
rod 68 in various ways, one of which is to provide a ~:not therein
as detailed in Fig. 8 and fill the opening wi-th body 70 of
sealant material such as silîcone sealant material co~merclally
available under the designation Dow Corning* No. 732. The oppo-
site ends of rod 68 fit in opposed longitudinal recesses 72 and
*Trademark.
X
17'~2
13 provided at diametrically opposite locations along the lower
end of the insula-tor element 38, and the axially aligned ends or
~erminations of recesses 72, 73 abu-t the ends of rod 68 to hold
or fix the rod agains-t further axial upward movement as viewed
in Fig. 3.
The filter means 28 of foraminous, dielectric material
has the shape of a tube or sleeve which preferably is thin-walled
and disposed with the longitudinal axis thereof coincident with
the longitudinal axis of sleeve 36 of precipitator 26. The inlet
or lower end of filter means 28 as shown in ~igs. 2 and 3 is in
fluid communication with the upper or outlet end of the collector
element 36 of precipitator 26. In the present illustration, pre-
cipitator 26 and filter 28 are in series flow relation. The
outer diameter of the filter el ment 28 is slightly larger than
- the outer dlameter of tube 36. Filter means 28 can comprise
various types of foraminous or porous dielectric material such
as woven, knitted or non-woven cloth or fabric, permeable
membrane materi.al, or fibrous material. The material of filter
means 28, in addition to being foraminous and preferably
dielectric, also should be relatively flexible for a reason which
will be described presently. A type of woven cloth mater:Lal
found to serve satisfactorily as filter element 28 is commercially
available from the DuPont Company under the designa~ion Nomex*
Fil~er Media and having a weight of twelve ou~ces per square
yard and a permeability of 30-50 cubic ~eet per minute per
square ~:oot at a pressure dl~erential o~ one-ha.lf inch water.
Various other Eabrics which will not support combustion and
satisfy the foregoing requirements along with certain fiberglass
materials can be employed.
Filter means 28 is supported in the apparatus in the
*Trademark
,
sd~ 6 -9-
lollowing manner. ~n end closure element 76 of dielectric
material is supported in axially spaced vertical relation with
respect to insulator 56 by a plurality of support rods 78 posi-
tioned between the elemen-ts 76 and 58. In particular, element
76 can be of the same dielectric material as elements 58 and 38,
i.e. polyester laminate, and is generally disc-shaped. The
inner axial end surface of element 76 is provided with circum~
ferential bores or recesses located radially inwardly of the
periphery of element 76 and extendin~ a relativel~ small axial
distance into the body of element 76. In the present illus-
tration there are six recesses. In a similar manner, element 58
is provided with axially aligned recesses circumferentially
spaced and located radially inwardly of the periphery of
element 58 and radially outwardly of the axial passage there-
- through. The support rods 78~ in the present instance six in
; number~ are fitted at opposite ends thereof into corresponding
recesses in the elements 76 and 58 and sealed therein with
suitable material such as epoxy cement. The filter means 28
then is fitted over and on the elements 76 and 58, the overall
length of the assembly being determined primarily by the axial
length of rods 78. The axial length of filter sleeve 28 is
such that it terminates at opposite ends flush with the outer
end face of insulator 76 and with the lower end face of the
radial flange portion of insulator 58. Each axial end of
filter 28 is fastened to the corresponding insulator element
76, 58 by a pa:Lr of clamp a.ssemblies :Lncluding bands ~0, 81
of metal such as stainless steel drawn tight around
~d/~ 10-
v
7~
1 the peripheral surface of the corresponding insulator elements
by a bolt and nut assembly 82,~3 tightening radial outward
flanges of the band as shown in Fig. 5. Alternative arrangements
for securing the filter element 28 in the assembly can of course
be employed.
The apparatus of the present invention further comprises
cleaning means for introducing a controlled quantity of high
pr~ssure fluid at predetermined times adjacent the precipitator
outlet and in a direction toward the precipitator inlet. The
1~ high pressure fluid is introduced in a manner inducing a sub-
stantial flow of gas through and along within the filter element
28 toward the inle~ thereof and then along within the collecting
element of the precipitator in a direction from the precipitator
outlet toward the precipita~or inlet. This, in turn) serves to
remove collected particulate matter from the surface of the
~ilter element and the precipitator collecting element in a
manner which will be described in further detail presently. The
cleaning means comprises conduit means ~8 for introducing the
high pressure fluid and which in the present instance is
located within the filter means 28 and disposed or positioned so
that the longitudinal axis of the conduit 88 and filter means 28
are coincident. The conduit 88 extends from the upper end o~
filter means 28 as viewed in Figs. 2 and 3 axially downwardly
along and within filter 2~ and in the present illustration
terminates a relatively small distance from the lower axial end
of filter 28 which is adjacent the out]et precipitator 26. The
diameter of conduit 88 is relatively small, and in the present
illustration the corona wire 66 extends along and within conduit
88 and is generally coincident with the longitudinal axis of
conduit 88. The end closure element 76 is provided with a
~ 4Z
1 central aperture, and the upper end of conduit 8~ is fitted
snugly and ti~htly therein in a manner thus serving to
fi~edly mount conduit 88 in the apparatus. The upper end
of conduit 88 extends axially beyond the outer end face of
closure 76 for connection to a supply of high pressure ~luid
in a manner which now will be described.
As shown in Figs. 2 and 3, the upper end of conduit 88
threads into one end of an elbow 92, the oth~r end of which is
connected to one end of a feed or supply conduit 9~. In an
installation such as that shown in Fig. 1 including a plurality
of dust collector units 24, there will be a corresponding plur-
ality of feed or supply conduits similar to conduit 9~rJ one
for each dust collector unit. Conduit 94 is connected in fluid
communication with the outlet of a valve 9~, the inlet of which
is connected by a conduit 9~ to a header or mainfold lOQ fixedly
mounted to housing 10 adjacent the upper end thereof as shown
in Fig. 1. Manifold 100 is connected by a conduit 101 to a
source or supply of high pressure such as compressed air. There
are additional valves, for example those designated 96' and 9~`'
in Fig. 1, and corresponding conduits similar to conduit 98 for
connection to mainfold 100, the particular number being deter-
mined by the number of dust collector units included withi.n a
~iven installation. In some instances, where a large number of
units are included, it may be feasible to connect two feed con-
duits 9~ through a single valve to the manifold 100 whereby
cleaning o~ two units is done simultaneously. Valve 9~ is
connected by a control line 102 to a control assembly 104 which
is ixedly molmted to the manifold 100. The control 10~ serves
-12-
7~Z
1 to provide the proper timing relationship for the valves as
will be described in detailpresently. Additional lines are
provided for the additional valves included in the installati.on
Corona wire 66 ls fixedly mounted at the upper end of the
assembly in the following manner. Wire 66 is fixedly connected
to one end of a connector element in the form o~ a metal rod
108, preferably of stainless steel, which extends through an
opening provided in elbow 92 and is disposed generally vertically
as shown in Figs. 2 and 3. One method of securing wire 66 to
rod 108 is detailed in Fig. 7. The end of wire ~6 LS provided
with a loop which is inserted into a slot provided at the end
of rod 108 and a bolt or rivet~ e element 110 is inserted
therethrough with both ends being peened over and smoothed where
upon a quantit~y 112 of sealant such as silicon sealant commercially
available under the designation Dow Corning* 732 is filled in the
slot. The exposed end of rod 108 is provided with a coil spring
114 fitted circumferentially thereon, and a washer, nut combina-
tion 116,118 is connected on the threaded end of rod 113 and
tightened up against spring 114 so that the opposite end of
spring 114 contacts elbow 92 for the purpose of adjusting the
tension in wire 66. An electrical cable 120 insulated in a
manner similar to that of cable 6~ is connected to the rod or
connector element 108 at the outer end thereof be~ween a pair
of nuts threaded thereon in a conventional manner.
By way of example, an installation was cons~ructed wherein
:Eor each dust collector unlt 24 the precipitator collector el.ement
36 had an overall length of about 40 inches, an outer diameter
of about 4 inches and a wall. thickness of about 0.35 inch.
Filter element 28 had an overall length of about ~,9 inches and
-13-
*Trademark
X
1 an inner diameter of about 6 inches. Conduit 8~ was o~ stain-
less steel having an inner diameter of about 3/~ inch and an
overall length such that it terminates about 6 inches above the
upper surface of insulator element 58 as viewed in Figs. 2 ar~d 3.
Corona wire can have a diameter of about 0.031 inch and be o~
stainless steel.
The apparatus of the present invention operates in the
following manner. The operation of a single dust collector unit
2~ will be described, it being understood that the same operation
occurs for each unit in a multiple unit installation as shown in
Fig. 1. Dirty gas is introduced to the apparatus through inlet
conduit 16 and duct 18 is moved by operation of the fan
through electrostatic precipitator means to collect a major
portion of the particulate matter ~rom the gas stream. In par-
ticular, the gas to be cleaned flows from duct 18 first down-
wardly i.nto hopper portion 12 and then upwardly through aperture
46 in tube sheet 32 into the precipitator 26 at the bottom thereof
as viewed in Figs 1-3~ The ~as flows axially within precipitator
2~ along the entire length of tube 36. The corona electrode 66
is maintained at a relatively ne~ative potential, and tube 36
is maintained at a relatively positive potential. In a dust
collector having dimensions according to the example hereinabove,
the potential dif~erence would be about 40l000 volts and the
corona current about 5 milliamperes, and ef~ective operation re-
sults when the power supply provides a filtered d.c. volta~e.
FurthermoreJ the relative polarities o~ corona electrode 66 and
collector 36 can be chan~ed. Having a corona elect~ode 66 at a
relatively negative potential is preferred because it has been
~ound to provide a more stable corona at a relatively lar~er
-14-
L7~
1 current to provide more efficient dust collection.
Dust particles and o~her particulate matter entering pre-
cipitator 26 are charged in the corona current and a major
portion of the charged particles is collected on the inner
surface of collector element 36. In particular, the particulate
laden gas passes upward parallel to corona discharge wire 66
where the particles become charged, and then the charged par-
ticles are attracted to and become deposited on the metal ~ube
36 which is charged to a polarity opposite that of corona wire
66. The gas is moved by the fan ~rough precipitator 26 50 as
to be electrically neutral. That is, there is no electric field
applied to the cylindrical filter element 28. The charged dust
particles and other particulate matter collect on the inner surface
of filter element 28 with the result that the filter removes the
remainder of the particulate matter ~rom the gas stream. Clean
gas then is wi.thdrawn from filter 28 by the fan and leaves the
apparatus through outlet 20. While gas is ~.oved through the
apparatus by a fan connected to the outlet 20 which serves to
draw gas through the apparatus in the present illustration, the
gas could be moved by a fan connected to inlet 16 which would
force or propel gas through the apparatus.
In the method and apparatus according to the present in-
vention, deposi.ting the charged dust particles on a fabric filter
element with no external electric field applied to the fabric
~ilter results in enhanced collection ef:~iciency and much in-
creased throughput. Ln particular, when no high voltage is
applied to the precipitator 26 so that the dust particles entering
~ilter 28 are uncharged, the fabric ~ilter behaves as a conven-
tional, continuous cleaniny,, pulse ~ype baghouse. This behavior
17~Z
1 remains constant as voltage is increased, until the corona
discharge onset voltage is reached. Once a corona is generated
and particles are charged, a sudden change is filtration re-
sistance, in particular a sudden pressure drop,takes place.
This decrease in resistance continues as voltage is increased
because the dust particles become more highly charged and because
more particles are deposited on the metal tube 36.
By comparing a plot of fabric pressure drop vs. air cloth
ratio- or filtration rate for electrostatic opera~ion to a plot
of the same parameters without electrostatic operation, i.e. ~Jith
the high voltage on and the voltage off, in the apparatus of the
present invention, it was determined that at an equivalent
pressure drop, the application of electrostatic charge to the
particles with no electric field applied to the fabric filter
gives rise to a four fold increase in filtration rate per unit
- fabric area. In addition, movin~ electrically charged particles
toward an uncharged fa~ric filter according to the method of the
present invention resul~s in the particles approaching the filter
relatively softly or gently sothat the par~icles are collected
on the fabric filter surface rather than 'being embedded therein
thereby facilitating subsequent cleaning of the filter. The di-
electric nature of the filter material is believed to contribute
to this result.
Periodically, the deposited particulate material is cleaned
from the lnner surfaces of tube 36 and fabric filter 28 by means
of a short burst of cornpressed air emanating :Erom the pipe 8~.
This jet oE primary air entrains and mi~es with a secondary air
flow, and this reverse flo~7 of air through the ~'abric 28 and
do~7n along precipitator tube 36 from outlet to inlet dislodges
~16-
t7~Z
1 the accumulated particulate layer on both elements. In parti-
cular, the flexible fabric filter el~ment 28 is drawn abruptly
inwardly as indicated by the broken lines in Figs. 3 and 5 and
against the support rods 78. The arrows in Fig. 5 indicate the
direction of the reverse flow of air causing the inward move-
ment of filter 28. The abrupt inward flexing of fabric filter
2~ together with the induced re~erse flow dislodges collected
dust particles from the inner surface thereof, and the dislodged
particles fall down through filter 2~, precipitator 26, housing
portion 12 and outlet 1~ to a hopper or suitable collector. The
force of the induced reverse flow of air in a downward direction
enha~ces the foregoing and also serves to dislodge particulate
matter from the inner surface of tube 36 which then also falls
down through precipitator 26, housing portion 12 and outlet 14.
Introducing the jet of air or other gas in this manner provides
a pump-like or fan-like effect cleaning the inner surfaces of
the filter and precipitator collector electrode.
In a typical installation including a plurality of dust
collector units 24, each unit is cleaned about once every four
minutes. The air pressure employed is generally in the range
from about 60 psig. to about ~0 psig. , and the jet or pulse of
air or gas from conduit ~ typically has a duration of about 0.3
second and a magnitude of about 1.5 standard cubic feet of air.
The full cleaning cycle for each dust collector unit is accom-
plished in about one second. In an installation of a number of
units or cartrîd~es 2~, for example as shown in Fig. 1, the exact
number o units and hence the size of the housing depends of
course on the flow rate of gas which must be fi.ltered. In such
an installation, only a small fraction of the total number o~
-17-
~ 4Z
1 units is cleaned at one time, and thPrefore the operation of
the installation is not interrupted or cartridge cleaning.
In other words, there is no need to provide any isolation struc-
ture for the dust collection units or groups thereo~. The outlet
or nozzle end o~ conduit 88 alternatively may be located within
precipita~or 26, pre~erably near the outlet thereof. The outlet
or nozzle of conduit 88 must be located so that the pulse or iet
of gas issuing ~herefrom induces a ~low which draws or pulls
filter 28 inwardly rather than expanding the filter 28. In the
present illustration, locating a portion of the length of corona
wire 66 within conduit 88 may cause vibration of wire ~6 when the
je~ o~ gas is introduc~d by conduit 88 which, in turn, can clean
; the wire.
- Fig. 9 illustrates apparatus according to another embodiment
of the present invention. A hollow, generally rectangular housing
designated 120 has opposed sidewalls 121, 122, a top 123 and a
base or bottom wall 124, and housing 120 is provided with a dirty
gas inlet 126 and a clean gas outlet 128. Located within housing
120 is an electrostati.c precipitator means generally designated
130 and including opposed sidewalls 132,133 joined by opposite
end walls. The precipitator sidewalls 132 and 133 have outwardly
directed extensions 134 and 135, respectively which join the
housin~ sidewalls 121 and 122, respectively. The precipi~ator
is open at the :Lower end as viewed Fig. 9 deining an inl.et which
is in fluid communication with the dirty gas inlet 126. The pre-
cipitator also includes a top wall 136 provided with at least
one aperture defining the precipitator outlet. An annular rim
138 surrounds the aperture. The sidewalls are formed to include
inwardly curved surface portions 140 and 142 which serve to pro-
-18-
X
1 vide a constriction to define a Venturi region adjacent the
outlet end of the precipitator. In the present illustration,
precipitator 130 includes a pair of corona wires 1~ 145. ~.n
electrical potential difference is maintained between electrodes
14~,145 and the precipitator walls 132,133 in a manner similar
to that of the preceding embodiment.
The apparatus further comprises filter means 150 of fora-
minous material similar to filter 28 in the apparatus of Figs.
1-8 and positioned in housing 120 with the inlet thereof in
fluid communication with the precipitator outlet. In the present
illustration, two filters designated 15Q and 150' are shown in
Fig. 9 and each of the filters 150,150' is generally hollow
cylindrical in shape, preferably being of flexible fabric material
which can be the same as that of filters 2~ in Figs. 1 8, and
is closed at the top by a closure ele~ent 152. Each ~ilter is
secured at the lower end thereof to precipitator 130 by a clamp
154 fastening it to rim 138 and is held in an upright vertical
position by connection through a brac~et 15~ to a suitable
supporting element such as a horizontally disposed rod 156
located in the upper portion of housing 120.
The apparatus further comprises cleaning means in the form
of a conduit designated 160 which extends into precipitator 130
in a direction along and adjacent the top surface 136. Conduit
160 ln the present instance is disposed generally perpendicular
to the direction of the yas stream traveling along the precipi-
tator 130. Conduit lGO is located downstream of the narrow
portion of the Venturi passage and adjacent the precipitator
outlet. One end of conduit 160 is connected to a source of
high pressure fluid such a.s compressed air in a manner similar
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1 to that of the embodiment of Figs. 1-8, with suitable flow
apparatus operatively connected between conduit 160 and the
source. ~. plurality of orifices 162 is provided in conduit
160, the nozzle-like apertures 162 being in spaced location
along conduit 160 and being located so as to be directed
toward the inlet end of the precipitator~
In operation, dirty gas is introduced to the apparatus
through inlet 126 and is moved by operation of a fan ~not shown)
which for example would be operatively connected to outlet 128
in a manner similar to the preceding embodiment. The gas is
moved through precipitator 130 as indicated by the arrows in
Fig. 9 to collect a major 2ortion of the particulate matter from
~he gas stream. The ~enturi region in precipitator 130 increases
the velocity of gas which is desirable in some situations. Pre-
cipitator 130 is operated in a manner generally similar to pre-
cipitator 26 in Figs. 1-8. The gas is moved further by the fan
through precipitator 130 and then into the filters 150 which are
electrically neutral, i.e. no electric field is applied thereto.
The charged dust particles and other particulate matter collect
on the inner surfaces of filters 150 which remove the remainder
of the particula~e matter from the gas stream in a manner similar
to filter 28 in Figs. 1-8. Clean gas then is withdrawn from
filters 150 by the fan and lea~es the apparatus through outlet
12~
Periodically, the deposited particulate material is cleaned
from the inner surfaces of precipitator 130 and fabric filters
150 by means of a short burst of compressed air emanating from
each of the nozzle-like openings 162 of conduit 160. There jets
of primary air entrain and mix with a secondary air flow and the
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4Z
1resulting reverse flow of air through the fabric filters 150
and downward along precipitator 130 as indicated by the arrows
in Fig. 10 dislodges the accumulated particulate layer on both
elements in a manner similar to the apparatus of Figs. 1-8.
The Venturi region in precipitator 130 increases the velocity
of cleaning air which is desirable in situations where the nature
of the material of filters 150 calls for high velocity flow. The
dislodged particulate material falls into the lower region of
housing 120 and can be removed in a suitable manner.
10It is therefore apparent that the pxesent invention accom-
plishes its intended objects. While embodiments of the present
invention have been described in detail this is for the purpose
of illustration, not limitation.
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